gcc

GNU project C and C++ compiler

TLDR

Compile multiple source files into executable

>_ gcc [source1.c] [source2.c] -o [executable]
copy

Allow warnings, debug symbols in output

>_ gcc [source.c] -Wall -Og -o [executable]
copy

Include libraries from a different path

>_ gcc [source.c] -o [executable] -I[header_path] -L[library_path] -l[library_name]
copy

Compile source code into Assembler instructions

>_ gcc -S [source.c]
copy

Compile source code without linking

>_ gcc -c [source.c]
copy

SYNOPSIS

Header "SYNOPSIS" gcc [ -c | -S | -E ][ -std= standard ] [ -g ][ -pg ][ -O level ] [ -W warn ...][ -Wpedantic ] [ -I dir ...][ -L dir ...] [ -D macro [= defn ]...][ -U macro ] [ -f option ...][ -m machine-option ...] [ -o outfile ][@ file ] infile ...

Only the most useful options are listed here; see below for the remainder. g++ accepts mostly the same options as gcc .

OPTIONS

Header "OPTIONS"

Option Summary

Subsection "Option Summary" Here is a summary of all the options, grouped by type. Explanations are in the following sections.

" OverallOptions "4 Item "Overall Options" -c -S -E -o file -x language -v -### --help [ = class [ ,... ]] --target -help --version -pass -exit -codes -pipe -specs= file -wrapper @ file -ffile -prefix -map= old = new -fplugin= file -fplugin -arg - name = arg -fdump -ada -spec [ -slim ] -fada -spec -parent= unit -fdump -go -spec= file

" CLanguage Options "4 Item "C Language Options" -ansi -std= standard -fgnu89 -inline -fpermitted -flt -eval -methods= standard -aux -info filename -fallow -parameterless -variadic -functions -fno -asm -fno -builtin -fno -builtin - function -fgimple -fhosted -ffreestanding -fopenacc -fopenacc -dim= geom -fopenmp -fopenmp -simd -fms -extensions -fplan9 -extensions -fsso -struct= endianness -fallow -single -precision -fcond -mismatch -flax -vector -conversions -fsigned -bitfields -fsigned -char -funsigned -bitfields -funsigned -char

" (C+ Language Options "4 Item " Language Options" -fabi -version= n -fno -access -control -faligned -new= n -fargs -in -order= n -fchar8_t -fcheck -new -fconstexpr -depth= n -fconstexpr -loop -limit= n -fconstexpr -ops -limit= n -fno -elide -constructors -fno -enforce -eh -specs -fno -gnu -keywords -fno -implicit -templates -fno -implicit -inline -templates -fno -implement -inlines -fms -extensions -fnew -inheriting -ctors -fnew -ttp -matching -fno -nonansi -builtins -fnothrow -opt -fno -operator -names -fno -optional -diags -fpermissive -fno -pretty -templates -frepo -fno -rtti -fsized -deallocation -ftemplate -backtrace -limit= n -ftemplate -depth= n -fno -threadsafe -statics -fuse -cxa -atexit -fno -weak -nostdinc++ -fvisibility -inlines -hidden -fvisibility -ms -compat -fext -numeric -literals -Wabi= n -Wabi -tag -Wconversion -null -Wctor -dtor -privacy -Wdelete -non -virtual -dtor -Wdeprecated -copy -Wdeprecated -copy -dtor -Wliteral -suffix -Wmultiple -inheritance -Wno -init -list -lifetime -Wnamespaces -Wnarrowing -Wpessimizing -move -Wredundant -move -Wnoexcept -Wnoexcept -type -Wclass -memaccess -Wnon -virtual -dtor -Wreorder -Wregister -Weffc++ -Wstrict -null -sentinel -Wtemplates -Wno -non -template -friend -Wold -style -cast -Woverloaded -virtual -Wno -pmf -conversions -Wno -class -conversion -Wno -terminate -Wsign -promo -Wvirtual -inheritance

" Objective-Cand Objective -(C+ Language Options "4 Item "Objective-C and Objective- Language Options" -fconstant -string -class= class-name -fgnu -runtime -fnext -runtime -fno -nil -receivers -fobjc -abi -version= n -fobjc -call -cxx -cdtors -fobjc -direct -dispatch -fobjc -exceptions -fobjc -gc -fobjc -nilcheck -fobjc -std=objc1 -fno -local -ivars -fivar -visibility= [ public | protected | private | package ] -freplace -objc -classes -fzero -link -gen -decls -Wassign -intercept -Wno -protocol -Wselector -Wstrict -selector -match -Wundeclared -selector

" DiagnosticMessage Formatting Options "4 Item "Diagnostic Message Formatting Options" -fmessage -length= n -fdiagnostics -show -location= [ once | every-line ] -fdiagnostics -color= [ auto | never | always ] -fdiagnostics -format= [ text | json ] -fno -diagnostics -show -option -fno -diagnostics -show -caret -fno -diagnostics -show -labels -fno -diagnostics -show -line -numbers -fdiagnostics -minimum -margin -width= width -fdiagnostics -parseable -fixits -fdiagnostics -generate -patch -fdiagnostics -show -template -tree -fno -elide -type -fno -show -column

" WarningOptions "4 Item "Warning Options" -fsyntax -only -fmax -errors= n -Wpedantic -pedantic -errors -w -Wextra -Wall -Waddress -Waddress -of -packed -member -Waggregate -return -Waligned -new -Walloc -zero -Walloc -size -larger -than= byte-size -Walloca -Walloca -larger -than= byte-size -Wno -aggressive -loop -optimizations -Warray -bounds -Warray -bounds= n -Wno -attributes -Wattribute -alias= n -Wbool -compare -Wbool -operation -Wno -builtin -declaration -mismatch -Wno -builtin -macro -redefined -Wc90 -c99 -compat -Wc99 -c11 -compat -Wc++ -compat -Wc++11 -compat -Wc++14 -compat -Wc++17 -compat -Wcast -align -Wcast -align=strict -Wcast -function -type -Wcast -qual -Wchar -subscripts -Wcatch -value -Wcatch -value= n -Wclobbered -Wcomment -Wconditionally -supported -Wconversion -Wcoverage -mismatch -Wno -cpp -Wdangling -else -Wdate -time -Wdelete -incomplete -Wno -attribute -warning -Wno -deprecated -Wno -deprecated -declarations -Wno -designated -init -Wdisabled -optimization -Wno -discarded -qualifiers -Wno -discarded -array -qualifiers -Wno -div -by -zero -Wdouble -promotion -Wduplicated -branches -Wduplicated -cond -Wempty -body -Wenum -compare -Wno -endif -labels -Wexpansion -to -defined -Werror -Werror=* -Wextra -semi -Wfatal -errors -Wfloat -equal -Wformat -Wformat=2 -Wno -format -contains -nul -Wno -format -extra -args -Wformat -nonliteral -Wformat -overflow= n -Wformat -security -Wformat -signedness -Wformat -truncation= n -Wformat -y2k -Wframe -address -Wframe -larger -than= byte-size -Wno -free -nonheap -object -Wjump -misses -init -Whsa -Wif -not -aligned -Wignored -qualifiers -Wignored -attributes -Wincompatible -pointer -types -Wimplicit -Wimplicit -fallthrough -Wimplicit -fallthrough= n -Wimplicit -function -declaration -Wimplicit -int -Winit -self -Winline -Wno -int -conversion -Wint -in -bool -context -Wno -int -to -pointer -cast -Winvalid -memory -model -Wno -invalid -offsetof -Winvalid -pch -Wlarger -than= byte-size -Wlogical -op -Wlogical -not -parentheses -Wlong -long -Wmain -Wmaybe -uninitialized -Wmemset -elt -size -Wmemset -transposed -args -Wmisleading -indentation -Wmissing -attributes -Wmissing -braces -Wmissing -field -initializers -Wmissing -format -attribute -Wmissing -include -dirs -Wmissing -noreturn -Wmissing -profile -Wno -multichar -Wmultistatement -macros -Wnonnull -Wnonnull -compare -Wnormalized= [ none | id | nfc | nfkc ] -Wnull -dereference -Wodr -Wno -overflow -Wopenmp -simd -Woverride -init -side -effects -Woverlength -strings -Wpacked -Wpacked -bitfield -compat -Wpacked -not -aligned -Wpadded -Wparentheses -Wno -pedantic -ms -format -Wplacement -new -Wplacement -new= n -Wpointer -arith -Wpointer -compare -Wno -pointer -to -int -cast -Wno -pragmas -Wno -prio -ctor -dtor -Wredundant -decls -Wrestrict -Wno -return -local -addr -Wreturn -type -Wsequence -point -Wshadow -Wno -shadow -ivar -Wshadow=global, -Wshadow=local, -Wshadow=compatible -local -Wshift -overflow -Wshift -overflow= n -Wshift -count -negative -Wshift -count -overflow -Wshift -negative -value -Wsign -compare -Wsign -conversion -Wfloat -conversion -Wno -scalar -storage -order -Wsizeof -pointer -div -Wsizeof -pointer -memaccess -Wsizeof -array -argument -Wstack -protector -Wstack -usage= byte-size -Wstrict -aliasing -Wstrict -aliasing=n -Wstrict -overflow -Wstrict -overflow= n -Wstringop -overflow= n -Wstringop -truncation -Wsubobject -linkage -Wsuggest -attribute= [ pure | const | noreturn | format | malloc ] -Wsuggest -final -types -Wsuggest -final -methods -Wsuggest -override -Wswitch -Wswitch -bool -Wswitch -default -Wswitch -enum -Wswitch -unreachable -Wsync -nand -Wsystem -headers -Wtautological -compare -Wtrampolines -Wtrigraphs -Wtype -limits -Wundef -Wuninitialized -Wunknown -pragmas -Wunsuffixed -float -constants -Wunused -Wunused -function -Wunused -label -Wunused -local -typedefs -Wunused -macros -Wunused -parameter -Wno -unused -result -Wunused -value -Wunused -variable -Wunused -const -variable -Wunused -const -variable= n -Wunused -but -set -parameter -Wunused -but -set -variable -Wuseless -cast -Wvariadic -macros -Wvector -operation -performance -Wvla -Wvla -larger -than= byte-size -Wvolatile -register -var -Wwrite -strings -Wzero -as -null -pointer -constant

" Cand Objective-C-only Warning Options "4 Item "C and Objective-C-only Warning Options" -Wbad -function -cast -Wmissing -declarations -Wmissing -parameter -type -Wmissing -prototypes -Wnested -externs -Wold -style -declaration -Wold -style -definition -Wstrict -prototypes -Wtraditional -Wtraditional -conversion -Wdeclaration -after -statement -Wpointer -sign

" DebuggingOptions "4 Item "Debugging Options" -g -g level -gdwarf -gdwarf - version -ggdb -grecord -gcc -switches -gno -record -gcc -switches -gstabs -gstabs+ -gstrict -dwarf -gno -strict -dwarf -gas -loc -support -gno -as -loc -support -gas -locview -support -gno -as -locview -support -gcolumn -info -gno -column -info -gstatement -frontiers -gno -statement -frontiers -gvariable -location -views -gno -variable -location -views -ginternal -reset -location -views -gno -internal -reset -location -views -ginline -points -gno -inline -points -gvms -gxcoff -gxcoff+ -gz [ = type ] -gsplit -dwarf -gdescribe -dies -gno -describe -dies -fdebug -prefix -map= old = new -fdebug -types -section -fno -eliminate -unused -debug -types -femit -struct -debug -baseonly -femit -struct -debug -reduced -femit -struct -debug -detailed [ = spec-list ] -feliminate -unused -debug -symbols -femit -class -debug -always -fno -merge -debug -strings -fno -dwarf2 -cfi -asm -fvar -tracking -fvar -tracking -assignments

" OptimizationOptions "4 Item "Optimization Options" -faggressive -loop -optimizations -falign -functions[= n [: m :[ n2 [: m2 ]]]] -falign -jumps[= n [: m :[ n2 [: m2 ]]]] -falign -labels[= n [: m :[ n2 [: m2 ]]]] -falign -loops[= n [: m :[ n2 [: m2 ]]]] -fassociative -math -fauto -profile -fauto -profile[= path ] -fauto -inc -dec -fbranch -probabilities -fbranch -target -load -optimize -fbranch -target -load -optimize2 -fbtr -bb -exclusive -fcaller -saves -fcombine -stack -adjustments -fconserve -stack -fcompare -elim -fcprop -registers -fcrossjumping -fcse -follow -jumps -fcse -skip -blocks -fcx -fortran -rules -fcx -limited -range -fdata -sections -fdce -fdelayed -branch -fdelete -null -pointer -checks -fdevirtualize -fdevirtualize -speculatively -fdevirtualize -at -ltrans -fdse -fearly -inlining -fipa -sra -fexpensive -optimizations -ffat -lto -objects -ffast -math -ffinite -math -only -ffloat -store -fexcess -precision= style -fforward -propagate -ffp -contract= style -ffunction -sections -fgcse -fgcse -after -reload -fgcse -las -fgcse -lm -fgraphite -identity -fgcse -sm -fhoist -adjacent -loads -fif -conversion -fif -conversion2 -findirect -inlining -finline -functions -finline -functions -called -once -finline -limit= n -finline -small -functions -fipa -cp -fipa -cp -clone -fipa -bit -cp -fipa -vrp -fipa -pta -fipa -profile -fipa -pure -const -fipa -reference -fipa -reference -addressable -fipa -stack -alignment -fipa -icf -fira -algorithm= algorithm -flive -patching= level -fira -region= region -fira -hoist -pressure -fira -loop -pressure -fno -ira -share -save -slots -fno -ira -share -spill -slots -fisolate -erroneous -paths -dereference -fisolate -erroneous -paths -attribute -fivopts -fkeep -inline -functions -fkeep -static -functions -fkeep -static -consts -flimit -function -alignment -flive -range -shrinkage -floop -block -floop -interchange -floop -strip -mine -floop -unroll -and -jam -floop -nest -optimize -floop -parallelize -all -flra -remat -flto -flto -compression -level -flto -partition= alg -fmerge -all -constants -fmerge -constants -fmodulo -sched -fmodulo -sched -allow -regmoves -fmove -loop -invariants -fno -branch -count -reg -fno -defer -pop -fno -fp -int -builtin -inexact -fno -function -cse -fno -guess -branch -probability -fno -inline -fno -math -errno -fno -peephole -fno -peephole2 -fno -printf -return -value -fno -sched -interblock -fno -sched -spec -fno -signed -zeros -fno -toplevel -reorder -fno -trapping -math -fno -zero -initialized -in -bss -fomit -frame -pointer -foptimize -sibling -calls -fpartial -inlining -fpeel -loops -fpredictive -commoning -fprefetch -loop -arrays -fprofile -correction -fprofile -use -fprofile -use= path -fprofile -values -fprofile -reorder -functions -freciprocal -math -free -frename -registers -freorder -blocks -freorder -blocks -algorithm= algorithm -freorder -blocks -and -partition -freorder -functions -frerun -cse -after -loop -freschedule -modulo -scheduled -loops -frounding -math -fsave -optimization -record -fsched2 -use -superblocks -fsched -pressure -fsched -spec -load -fsched -spec -load -dangerous -fsched -stalled -insns -dep[= n ]-fsched -stalled -insns[= n ] -fsched -group -heuristic -fsched -critical -path -heuristic -fsched -spec -insn -heuristic -fsched -rank -heuristic -fsched -last -insn -heuristic -fsched -dep -count -heuristic -fschedule -fusion -fschedule -insns -fschedule -insns2 -fsection -anchors -fselective -scheduling -fselective -scheduling2 -fsel -sched -pipelining -fsel -sched -pipelining -outer -loops -fsemantic -interposition -fshrink -wrap -fshrink -wrap -separate -fsignaling -nans -fsingle -precision -constant -fsplit -ivs -in -unroller -fsplit -loops -fsplit -paths -fsplit -wide -types -fssa -backprop -fssa -phiopt -fstdarg -opt -fstore -merging -fstrict -aliasing -fthread -jumps -ftracer -ftree -bit -ccp -ftree -builtin -call -dce -ftree -ccp -ftree -ch -ftree -coalesce -vars -ftree -copy -prop -ftree -dce -ftree -dominator -opts -ftree -dse -ftree -forwprop -ftree -fre -fcode -hoisting -ftree -loop -if -convert -ftree -loop -im -ftree -phiprop -ftree -loop -distribution -ftree -loop -distribute -patterns -ftree -loop -ivcanon -ftree -loop -linear -ftree -loop -optimize -ftree -loop -vectorize -ftree -parallelize -loops= n -ftree -pre -ftree -partial -pre -ftree -pta -ftree -reassoc -ftree -scev -cprop -ftree -sink -ftree -slsr -ftree -sra -ftree -switch -conversion -ftree -tail -merge -ftree -ter -ftree -vectorize -ftree -vrp -funconstrained -commons -funit -at -a -time -funroll -all -loops -funroll -loops -funsafe -math -optimizations -funswitch -loops -fipa -ra -fvariable -expansion -in -unroller -fvect -cost -model -fvpt -fweb -fwhole -program -fwpa -fuse -linker -plugin --param name = value -O -O0 -O1 -O2 -O3 -Os -Ofast -Og

" ProgramInstrumentation Options "4 Item "Program Instrumentation Options" -p -pg -fprofile -arcs --coverage -ftest -coverage -fprofile -abs -path -fprofile -dir= path -fprofile -generate -fprofile -generate= path -fprofile -update= method -fprofile -filter -files= regex -fprofile -exclude -files= regex -fsanitize= style -fsanitize -recover -fsanitize -recover= style -fasan -shadow -offset= number -fsanitize -sections= s1 , s2 ,... -fsanitize -undefined -trap -on -error -fbounds -check -fcf -protection= [ full | branch | return | none ] -fstack -protector -fstack -protector -all -fstack -protector -strong -fstack -protector -explicit -fstack -check -fstack -limit -register= reg -fstack -limit -symbol= sym -fno -stack -limit -fsplit -stack -fvtable -verify= [ std | preinit | none ] -fvtv -counts -fvtv -debug -finstrument -functions -finstrument -functions -exclude -function -list= sym , sym ,... -finstrument -functions -exclude -file -list= file , file ,...

" PreprocessorOptions "4 Item "Preprocessor Options" -A question = answer -A - question [ = answer ] -C -CC -D macro [ = defn ] -dD -dI -dM -dN -dU -fdebug -cpp -fdirectives -only -fdollars -in -identifiers -fexec -charset= charset -fextended -identifiers -finput -charset= charset -fmacro -prefix -map= old = new -fno -canonical -system -headers -fpch -deps -fpch -preprocess -fpreprocessed -ftabstop= width -ftrack -macro -expansion -fwide -exec -charset= charset -fworking -directory -H -imacros file -include file -M -MD -MF -MG -MM -MMD -MP -MQ -MT -no -integrated -cpp -P -pthread -remap -traditional -traditional -cpp -trigraphs -U macro -undef -Wp, option -Xpreprocessor option

" AssemblerOptions "4 Item "Assembler Options" -Wa, option -Xassembler option

" LinkerOptions "4 Item "Linker Options" object-file-name -fuse -ld= linker -l library -nostartfiles -nodefaultlibs -nolibc -nostdlib -e entry --entry= entry -pie -pthread -r -rdynamic -s -static -static -pie -static -libgcc -static -libstdc++ -static -libasan -static -libtsan -static -liblsan -static -libubsan -shared -shared -libgcc -symbolic -T script -Wl, option -Xlinker option -u symbol -z keyword

" DirectoryOptions "4 Item "Directory Options" -B prefix -I dir -I - -idirafter dir -imacros file -imultilib dir -iplugindir= dir -iprefix file -iquote dir -isysroot dir -isystem dir -iwithprefix dir -iwithprefixbefore dir -L dir -no -canonical -prefixes --no -sysroot -suffix -nostdinc -nostdinc++ --sysroot= dir

" CodeGeneration Options "4 Item "Code Generation Options" -fcall -saved - reg -fcall -used - reg -ffixed - reg -fexceptions -fnon -call -exceptions -fdelete -dead -exceptions -funwind -tables -fasynchronous -unwind -tables -fno -gnu -unique -finhibit -size -directive -fno -common -fno -ident -fpcc -struct -return -fpic -fPIC -fpie -fPIE -fno -plt -fno -jump -tables -frecord -gcc -switches -freg -struct -return -fshort -enums -fshort -wchar -fverbose -asm -fpack -struct[= n ] -fleading -underscore -ftls -model= model -fstack -reuse= reuse_level -ftrampolines -ftrapv -fwrapv -fvisibility= [ default | internal | hidden | protected ] -fstrict -volatile -bitfields -fsync -libcalls

" DeveloperOptions "4 Item "Developer Options" -d letters -dumpspecs -dumpmachine -dumpversion -dumpfullversion -fchecking -fchecking= n -fdbg -cnt -list -fdbg -cnt= counter-value-list -fdisable -ipa - pass_name -fdisable -rtl - pass_name -fdisable -rtl - pass-name = range-list -fdisable -tree - pass_name -fdisable -tree - pass-name = range-list -fdump -debug -fdump -earlydebug -fdump -noaddr -fdump -unnumbered -fdump -unnumbered -links -fdump -final -insns [ = file ] -fdump -ipa -all -fdump -ipa -cgraph -fdump -ipa -inline -fdump -lang -all -fdump -lang - switch -fdump -lang - switch - options -fdump -lang - switch - options = filename -fdump -passes -fdump -rtl - pass -fdump -rtl - pass = filename -fdump -statistics -fdump -tree -all -fdump -tree - switch -fdump -tree - switch - options -fdump -tree - switch - options = filename -fcompare -debug [ = opts ] -fcompare -debug -second -fenable - kind - pass -fenable - kind - pass = range-list -fira -verbose= n -flto -report -flto -report -wpa -fmem -report -wpa -fmem -report -fpre -ipa -mem -report -fpost -ipa -mem -report -fopt -info -fopt -info - options [ = file ] -fprofile -report -frandom -seed= string -fsched -verbose= n -fsel -sched -verbose -fsel -sched -dump -cfg -fsel -sched -pipelining -verbose -fstats -fstack -usage -ftime -report -ftime -report -details -fvar -tracking -assignments -toggle -gtoggle -print -file -name= library -print -libgcc -file -name -print -multi -directory -print -multi -lib -print -multi -os -directory -print -prog -name= program -print -search -dirs -Q -print -sysroot -print -sysroot -headers -suffix -save -temps -save -temps=cwd -save -temps=obj -time [ = file ]

" Machine-DependentOptions "4 Item "Machine-Dependent Options" AArch64Options -mabi= name -mbig -endian -mlittle -endian -mgeneral -regs -only -mcmodel=tiny -mcmodel=small -mcmodel=large -mstrict -align -mno -strict -align -momit -leaf -frame -pointer -mtls -dialect=desc -mtls -dialect=traditional -mtls -size= size -mfix -cortex -a53 -835769 -mfix -cortex -a53 -843419 -mlow -precision -recip -sqrt -mlow -precision -sqrt -mlow -precision -div -mpc -relative -literal -loads -msign -return -address= scope -mbranch -protection= none | standard | pac-ret [+ leaf ]| bti -march= name -mcpu= name -mtune= name -moverride= string -mverbose -cost -dump -mstack -protector -guard= guard -mstack -protector -guard -reg= sysreg -mstack -protector -guard -offset= offset -mtrack -speculation AdaptevaEpiphany Options -mhalf -reg -file -mprefer -short -insn -regs -mbranch -cost= num -mcmove -mnops= num -msoft -cmpsf -msplit -lohi -mpost -inc -mpost -modify -mstack -offset= num -mround -nearest -mlong -calls -mshort -calls -msmall16 -mfp -mode= mode -mvect -double -max -vect -align= num -msplit -vecmove -early -m1reg - reg AMDGCN Options -march= gpu -mtune= gpu -mstack -size= bytes ARCOptions -mbarrel -shifter -mjli -always -mcpu= cpu -mA6 -mARC600 -mA7 -mARC700 -mdpfp -mdpfp -compact -mdpfp -fast -mno -dpfp -lrsr -mea -mno -mpy -mmul32x16 -mmul64 -matomic -mnorm -mspfp -mspfp -compact -mspfp -fast -msimd -msoft -float -mswap -mcrc -mdsp -packa -mdvbf -mlock -mmac -d16 -mmac -24 -mrtsc -mswape -mtelephony -mxy -misize -mannotate -align -marclinux -marclinux_prof -mlong -calls -mmedium -calls -msdata -mirq -ctrl -saved -mrgf -banked -regs -mlpc -width= width -G num -mvolatile -cache -mtp -regno= regno -malign -call -mauto -modify -reg -mbbit -peephole -mno -brcc -mcase -vector -pcrel -mcompact -casesi -mno -cond -exec -mearly -cbranchsi -mexpand -adddi -mindexed -loads -mlra -mlra -priority -none -mlra -priority -compact mlra-priority-noncompact -mmillicode -mmixed -code -mq -class -mRcq -mRcw -msize -level= level -mtune= cpu -mmultcost= num -mcode -density -frame -munalign -prob -threshold= probability -mmpy -option= multo -mdiv -rem -mcode -density -mll64 -mfpu= fpu -mrf16 -mbranch -index ARMOptions -mapcs -frame -mno -apcs -frame -mabi= name -mapcs -stack -check -mno -apcs -stack -check -mapcs -reentrant -mno -apcs -reentrant -mgeneral -regs -only -msched -prolog -mno -sched -prolog -mlittle -endian -mbig -endian -mbe8 -mbe32 -mfloat -abi= name -mfp16 -format= name -mthumb -interwork -mno -thumb -interwork -mcpu= name -march= name -mfpu= name -mtune= name -mprint -tune -info -mstructure -size -boundary= n -mabort -on -noreturn -mlong -calls -mno -long -calls -msingle -pic -base -mno -single -pic -base -mpic -register= reg -mnop -fun -dllimport -mpoke -function -name -mthumb -marm -mflip -thumb -mtpcs -frame -mtpcs -leaf -frame -mcaller -super -interworking -mcallee -super -interworking -mtp= name -mtls -dialect= dialect -mword -relocations -mfix -cortex -m3 -ldrd -munaligned -access -mneon -for -64bits -mslow -flash -data -masm -syntax -unified -mrestrict -it -mverbose -cost -dump -mpure -code -mcmse AVROptions -mmcu= mcu -mabsdata -maccumulate -args -mbranch -cost= cost -mcall -prologues -mgas -isr -prologues -mint8 -mn_flash= size -mno -interrupts -mmain -is -OS_task -mrelax -mrmw -mstrict -X -mtiny -stack -mfract -convert -truncate -mshort -calls -nodevicelib -Waddr -space -convert -Wmisspelled -isr BlackfinOptions -mcpu= cpu [ - sirevision ] -msim -momit -leaf -frame -pointer -mno -omit -leaf -frame -pointer -mspecld -anomaly -mno -specld -anomaly -mcsync -anomaly -mno -csync -anomaly -mlow -64k -mno -low64k -mstack -check -l1 -mid -shared -library -mno -id -shared -library -mshared -library -id= n -mleaf -id -shared -library -mno -leaf -id -shared -library -msep -data -mno -sep -data -mlong -calls -mno -long -calls -mfast -fp -minline -plt -mmulticore -mcorea -mcoreb -msdram -micplb C6XOptions -mbig -endian -mlittle -endian -march= 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Options. 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-mstd -struct -return -mno -std -struct -return -munaligned -doubles -mno -unaligned -doubles -muser -mode -mno -user -mode -mv8plus -mno -v8plus -mvis -mno -vis -mvis2 -mno -vis2 -mvis3 -mno -vis3 -mvis4 -mno -vis4 -mvis4b -mno -vis4b -mcbcond -mno -cbcond -mfmaf -mno -fmaf -mfsmuld -mno -fsmuld -mpopc -mno -popc -msubxc -mno -subxc -mfix -at697f -mfix -ut699 -mfix -ut700 -mfix -gr712rc -mlra -mno -lra SPUOptions -mwarn -reloc -merror -reloc -msafe -dma -munsafe -dma -mbranch -hints -msmall -mem -mlarge -mem -mstdmain -mfixed -range= register-range -mea32 -mea64 -maddress -space -conversion -mno -address -space -conversion -mcache -size= cache-size -matomic -updates -mno -atomic -updates SystemV Options -Qy -Qn -YP, paths -Ym, dir TILE-GxOptions -mcpu=CPU -m32 -m64 -mbig -endian -mlittle -endian -mcmodel= code-model TILEProOptions -mcpu= cpu -m32 V850Options -mlong -calls -mno -long -calls -mep -mno -ep -mprolog -function -mno -prolog -function -mspace -mtda= n -msda= n -mzda= n -mapp -regs -mno -app -regs -mdisable -callt -mno -disable -callt -mv850e2v3 -mv850e2 -mv850e1 -mv850es -mv850e -mv850 -mv850e3v5 -mloop -mrelax -mlong -jumps -msoft -float -mhard -float -mgcc -abi -mrh850 -abi -mbig -switch VAXOptions -mg -mgnu -munix VisiumOptions -mdebug -msim -mfpu -mno -fpu -mhard -float -msoft -float -mcpu= cpu-type -mtune= cpu-type -msv -mode -muser -mode VMSOptions -mvms -return -codes -mdebug -main= prefix -mmalloc64 -mpointer -size= size VxWorksOptions -mrtp -non -static -Bstatic -Bdynamic -Xbind -lazy -Xbind -now x86Options -mtune= cpu-type -march= cpu-type -mtune -ctrl= feature-list -mdump -tune -features -mno -default -mfpmath= unit -masm= dialect -mno -fancy -math -387 -mno -fp -ret -in -387 -m80387 -mhard -float -msoft -float -mno -wide -multiply -mrtd -malign -double -mpreferred -stack -boundary= num -mincoming -stack -boundary= num -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip -mrecip= opt -mvzeroupper -mprefer -avx128 -mprefer -vector -width= opt -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd -mptwrite -mprefetchwt1 -mclflushopt -mclwb -mxsavec -mxsaves -msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp -mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg -mshstk -mmanual -endbr -mforce -indirect -call -mavx512vbmi2 -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq -mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid -mrdseed -msgx -mcldemote -mms -bitfields -mno -align -stringops -minline -all -stringops -minline -stringops -dynamically -mstringop -strategy= alg -mmemcpy -strategy= strategy -mmemset -strategy= strategy -mpush -args -maccumulate -outgoing -args -m128bit -long -double -m96bit -long -double -mlong -double -64 -mlong -double -80 -mlong -double -128 -mregparm= num -msseregparm -mveclibabi= type -mvect8 -ret -in -mem -mpc32 -mpc64 -mpc80 -mstackrealign -momit -leaf -frame -pointer -mno -red -zone -mno -tls -direct -seg -refs -mcmodel= code-model -mabi= name -maddress -mode= mode -m32 -m64 -mx32 -m16 -miamcu -mlarge -data -threshold= num -msse2avx -mfentry -mrecord -mcount -mnop -mcount -m8bit -idiv -minstrument -return= type -mfentry -name= name -mfentry -section= name -mavx256 -split -unaligned -load -mavx256 -split -unaligned -store -malign -data= type -mstack -protector -guard= guard -mstack -protector -guard -reg= reg -mstack -protector -guard -offset= offset -mstack -protector -guard -symbol= symbol -mgeneral -regs -only -mcall -ms2sysv -xlogues -mindirect -branch= choice -mfunction -return= choice -mindirect -branch -register x86Windows Options -mconsole -mcygwin -mno -cygwin -mdll -mnop -fun -dllimport -mthread -municode -mwin32 -mwindows -fno -set -stack -executable Xstormy16Options -msim XtensaOptions -mconst16 -mno -const16 -mfused -madd -mno -fused -madd -mforce -no -pic -mserialize -volatile -mno -serialize -volatile -mtext -section -literals -mno -text -section -literals -mauto -litpools -mno -auto -litpools -mtarget -align -mno -target -align -mlongcalls -mno -longcalls zSeriesOptions See S/390 and zSeries Options.

Options Controlling the Kind of Output

Subsection "Options Controlling the Kind of Output" Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCCis capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file.

For any given input file, the file name suffix determines what kind of compilation is done:

" file .c "4 Item "file.c" C source code that must be preprocessed.

" file .i "4 Item "file.i" C source code that should not be preprocessed.

" file .ii "4 Item "file.ii" (C+ source code that should not be preprocessed.

" file .m "4 Item "file.m" Objective-C source code. Note that you must link with the libobjc library to make an Objective-C program work.

" file .mi "4 Item "file.mi" Objective-C source code that should not be preprocessed.

" file .mm "4 Item "file.mm" 0

" file .M "4 Item "file.M" Objective -(C+ source code. Note that you must link with the libobjc library to make an Objective -(C+ program work. Note that .M refers to a literal capital M.

" file .mii "4 Item "file.mii" Objective -(C+ source code that should not be preprocessed.

" file .h "4 Item "file.h" C, (C+, Objective-C or Objective -(C+ header file to be turned into a precompiled header (default), or C, (C+ header file to be turned into an Ada spec (via the -fdump -ada -spec switch).

" file .cc "4 Item "file.cc" 0

" file .cp "4 Item "file.cp"

" file .cxx "4 Item "file.cxx"

" file .cpp "4 Item "file.cpp"

" file .CPP "4 Item "file.CPP"

" file .c++ "4 Item "file.c++"

" file .C "4 Item "file.C" (C+ source code that must be preprocessed. Note that in .cxx , the last two letters must both be literally x .Likewise, .C refers to a literal capital C.

" file .mm "4 Item "file.mm" 0

" file .M "4 Item "file.M" Objective -(C+ source code that must be preprocessed.

" file .mii "4 Item "file.mii" Objective -(C+ source code that should not be preprocessed.

" file .hh "4 Item "file.hh" 0

" file .H "4 Item "file.H"

" file .hp "4 Item "file.hp"

" file .hxx "4 Item "file.hxx"

" file .hpp "4 Item "file.hpp"

" file .HPP "4 Item "file.HPP"

" file .h++ "4 Item "file.h++"

" file .tcc "4 Item "file.tcc" (C+ header file to be turned into a precompiled header or Ada spec.

" file .f "4 Item "file.f" 0

" file .for "4 Item "file.for"

" file .ftn "4 Item "file.ftn" Fixed form Fortran source code that should not be preprocessed.

" file .F "4 Item "file.F" 0

" file .FOR "4 Item "file.FOR"

" file .fpp "4 Item "file.fpp"

" file .FPP "4 Item "file.FPP"

" file .FTN "4 Item "file.FTN" Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor).

" file .f90 "4 Item "file.f90" 0

" file .f95 "4 Item "file.f95"

" file .f03 "4 Item "file.f03"

" file .f08 "4 Item "file.f08" Free form Fortran source code that should not be preprocessed.

" file .F90 "4 Item "file.F90" 0

" file .F95 "4 Item "file.F95"

" file .F03 "4 Item "file.F03"

" file .F08 "4 Item "file.F08" Free form Fortran source code that must be preprocessed (with the traditional preprocessor).

" file .go "4 Item "file.go" Go source code.

" file .brig "4 Item "file.brig" BRIGfiles (binary representation of HSAIL).

" file .d "4 Item "file.d" D source code.

" file .di "4 Item "file.di" D interface file.

" file .dd "4 Item "file.dd" D documentation code (Ddoc).

" file .ads "4 Item "file.ads" Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called specs .

" file .adb "4 Item "file.adb" Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies .

" file .s "4 Item "file.s" Assembler code.

" file .S "4 Item "file.S" 0

" file .sx "4 Item "file.sx" Assembler code that must be preprocessed.

" other "4 Item "other" An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way.

You can specify the input language explicitly with the -x option:

" -x language "4 Item "-x language" Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next -x option. Possible values for language are: 10 c c -header cpp -output c++ c++ -header c++ -cpp -output objective -c objective -c -header objective -c -cpp -output objective -c++ objective -c++ -header objective -c++ -cpp -output assembler assembler -with -cpp ada d f77 f77 -cpp -input f95 f95 -cpp -input go brig

" -x none "4 Item "-x none" Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if -x has not been used at all).

If you only want some of the stages of compilation, you can use -x (or filename suffixes) to tell gcc where to start, and one of the options -c , -S ,or -E to say where gcc is to stop. Note that some combinations (for example, -x cpp-output -E )instruct gcc to do nothing at all.

" -c "4 Item "-c" Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. By default, the object file name for a source file is made by replacing the suffix .c , .i , .s ,etc., with .o . Unrecognized input files, not requiring compilation or assembly, are ignored.

" -S "4 Item "-S" Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. By default, the assembler file name for a source file is made by replacing the suffix .c , .i ,etc., with .s . Input files that don't require compilation are ignored.

" -E "4 Item "-E" Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. Input files that don't require preprocessing are ignored.

" -o file "4 Item "-o file" Place output in file file .This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. If -o is not specified, the default is to put an executable file in a.out ,the object file for source . suffix in source .o ,its assembler file in source .s ,a precompiled header file in source . suffix .gch ,and all preprocessed C source on standard output.

" -v "4 Item "-v" Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper.

" -### "4 Item "-###" Like -v except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or CW(C`./ -_ (C' . This is useful for shell scripts to capture the driver-generated command lines.

" --help "4 Item "--help" Print (on the standard output) a description of the command-line options understood by gcc .If the -v option is also specified then --help is also passed on to the various processes invoked by gcc ,so that they can display the command-line options they accept. If the -Wextra option has also been specified (prior to the --help option), then command-line options that have no documentation associated with them are also displayed.

" --target -help "4 Item "--target-help" Print (on the standard output) a description of target-specific command-line options for each tool. For some targets extra target-specific information may also be printed.

" --help={ class |[ ^ ] qualifier } [ ,... ]"4 Item "--help={class|[^]qualifier}[,...]" Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes:

" optimizers "4 Item "optimizers" Display all of the optimization options supported by the compiler.

" warnings "4 Item "warnings" Display all of the options controlling warning messages produced by the compiler.

" target "4 Item "target" Display target-specific options. Unlike the --target -help option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not currently support the extended --help= syntax.

" params "4 Item "params" Display the values recognized by the --param option.

" language "4 Item "language" Display the options supported for language ,where language is the name of one of the languages supported in this version of GCC.

" common "4 Item "common" Display the options that are common to all languages. These are the supported qualifiers:

" undocumented "4 Item "undocumented" Display only those options that are undocumented.

" joined "4 Item "joined" Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: --help=target .

" separate "4 Item "separate" Display options taking an argument that appears as a separate word following the original option, such as: -o output-file . Thus for example to display all the undocumented target-specific switches supported by the compiler, use: 1 --help=target,undocumented The sense of a qualifier can be inverted by prefixing it with the ^ character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take an argument) that have a description, use: 1 --help=warnings,^joined,^undocumented The argument to --help= should not consist solely of inverted qualifiers. Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes is target .For example, to display all the target-specific optimization options, use: 1 --help=target,optimizers The --help= option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. If --help is also specified anywhere on the command line then this takes precedence over any --help= option. If the -Q option appears on the command line before the --help= option, then the descriptive text displayed by --help= is changed. Instead of describing the displayed options, an indication is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the --help= option is used). Here is a truncated example from the ARMport of gcc : 5 % gcc -Q -mabi=2 --help=target -c The following options are target specific: -mabi= 2 -mabort -on -noreturn [disabled] -mapcs [disabled] The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at -O2 by using: 1 -Q -O2 --help=optimizers Alternatively you can discover which binary optimizations are enabled by -O3 by using: 3 gcc -c -Q -O3 --help=optimizers > /tmp/O3 -opts gcc -c -Q -O2 --help=optimizers > /tmp/O2 -opts diff /tmp/O2 -opts /tmp/O3 -opts | grep enabled

" --version "4 Item "--version" Display the version number and copyrights of the invoked GCC.

" -pass -exit -codes "4 Item "-pass-exit-codes" Normally the gcc program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify -pass -exit -codes ,the gcc program instead returns with the numerically highest error produced by any phase returning an error indication. The C, (C+, and Fortran front ends return 4 if an internal compiler error is encountered.

" -pipe "4 Item "-pipe" Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNUassembler has no trouble.

" -specs= file "4 Item "-specs=file" Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc driver program uses when determining what switches to pass to cc1 , cc1plus , as , ld ,etc. More than one -specs= file can be specified on the command line, and they are processed in order, from left to right.

" -wrapper "4 Item "-wrapper" Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list. 1 gcc -c t.c -wrapper gdb, --args This invokes all subprograms of gcc under gdb--args ,thus the invocation of cc1 is gdb--args cc1 ... .

" -ffile -prefix -map= old = new "4 Item "-ffile-prefix-map=old=new" When compiling files residing in directory old ,record any references to them in the result of the compilation as if the files resided in directory new instead. Specifying this option is equivalent to specifying all the individual -f* -prefix -map options. This can be used to make reproducible builds that are location independent. See also -fmacro -prefix -map and -fdebug -prefix -map .

" -fplugin= name .so "4 Item "-fplugin=name.so" Load the plugin code in file name .so,assumed to be a shared object to be dlopen'd by the compiler. The base name of the shared object file is used to identify the plugin for the purposes of argument parsing (See -fplugin -arg - name - key = value below). Each plugin should define the callback functions specified in the Plugins API.

" -fplugin -arg - name - key = value "4 Item "-fplugin-arg-name-key=value" Define an argument called key with a value of value for the plugin called name .

" -fdump -ada -spec [ -slim ]"4 Item "-fdump-ada-spec[-slim]" For C and (C+ source and include files, generate corresponding Ada specs.

" -fada -spec -parent= unit "4 Item "-fada-spec-parent=unit" In conjunction with -fdump -ada -spec [ -slim ]above, generate Ada specs as child units of parent unit .

" -fdump -go -spec= file "4 Item "-fdump-go-spec=file" For input files in any language, generate corresponding Go declarations in file .This generates Go CW(C`const (C' , CW(C`type (C' , CW(C`var (C' ,and CW(C`func (C' declarations which may be a useful way to start writing a Go interface to code written in some other language.

" @ file "4 Item "@file" Read command-line options from file .The options read are inserted in place of the original @ file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @ file options; any such options will be processed recursively.

"Compiling (C+ Programs"

Subsection "Compiling Programs" (C+ source files conventionally use one of the suffixes .C , .cc , .cpp , .CPP , .c++ , .cp ,or .cxx ;(C+ header files often use .hh , .hpp , .H ,or (for shared template code) .tcc ;and preprocessed (C+ files use the suffix .ii .GCCrecognizes files with these names and compiles them as (C+ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc ).

However, the use of gcc does not add the (C+ library. g++ is a program that calls GCCand automatically specifies linking against the (C+ library. It treats .c , .h and .i files as (C+ source files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a .h extension for use in (C+ compilations. On many systems, g++ is also installed with the name c++ .

When you compile (C+ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for (C+ programs.

Options Controlling C Dialect

Subsection "Options Controlling C Dialect" The following options control the dialect of C (or languages derived from C, such as (C+, Objective-C and Objective -(C+) that the compiler accepts:

" -ansi "4 Item "-ansi" In C mode, this is equivalent to -std=c90 .In (C+ mode, it is equivalent to -std=c++98 . This turns off certain features of GCCthat are incompatible with ISO C90 (when compiling C code), or of standard (C+ (when compiling (C+ code), such as the CW(C`asm (C' and CW(C`typeof (C' keywords, and predefined macros such as CW(C`unix (C' and CW(C`vax (C' that identify the type of system you are using. It also enables the undesirable and rarely used ISOtrigraph feature. For the C compiler, it disables recognition of (C+ style // comments as well as the CW(C`inline (C' keyword. The alternate keywords CW(C`_ _asm_ _ (C' , CW(C`_ _extension_ _ (C' , CW(C`_ _inline_ _ (C' and CW(C`_ _typeof_ _ (C' continue to work despite -ansi .You would not want to use them in an ISOC program, of course, but it is useful to put them in header files that might be included in compilations done with -ansi .Alternate predefined macros such as CW(C`_ _unix_ _ (C' and CW(C`_ _vax_ _ (C' are also available, with or without -ansi . The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -Wpedantic is required in addition to -ansi . The macro CW(C`_ _STRICT_ANSI_ _ (C' is predefined when the -ansi option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISOstandard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. Functions that are normally built in but do not have semantics defined by ISOC (such as CW(C`alloca (C' and CW(C`ffs (C' )are not built-in functions when -ansi is used.

" -std= "4 Item "-std=" Determine the language standard. This option is currently only supported when compiling C or (C+. The compiler can accept several base standards, such as c90 or c++98 ,and GNUdialects of those standards, such as gnu90 or gnu++98 .When a base standard is specified, the compiler accepts all programs following that standard plus those using GNUextensions that do not contradict it. For example, -std=c90 turns off certain features of GCCthat are incompatible with ISOC90, such as the CW(C`asm (C' and CW(C`typeof (C' keywords, but not other GNUextensions that do not have a meaning in ISOC90, such as omitting the middle term of a CW(C`?: (C' expression. On the other hand, when a GNUdialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict-conforming programs may be rejected. The particular standard is used by -Wpedantic to identify which features are GNU extensions given that version of the standard. For example -std=gnu90 -Wpedantic warns about (C+ style // comments, while -std=gnu99 -Wpedantic does not. A value for this option must be provided; possible values are

" c90 "4 Item "c90" 0

" c89 "4 Item "c89"

" iso9899:1990 "4 Item "iso9899:1990" Support all ISOC90 programs (certain GNUextensions that conflict with ISOC90 are disabled). Same as -ansi for C code.

" iso9899:199409 "4 Item "iso9899:199409" ISOC90 as modified in amendment 1.

" c99 "4 Item "c99" 0

" c9x "4 Item "c9x"

" iso9899:1999 "4 Item "iso9899:1999"

" iso9899:199x "4 Item "iso9899:199x" ISOC99. This standard is substantially completely supported, modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). See < http://gcc.gnu.org/c99status.html >for more information. The names c9x and iso9899:199x are deprecated.

" c11 "4 Item "c11" 0

" c1x "4 Item "c1x"

" iso9899:2011 "4 Item "iso9899:2011" ISOC11, the 2011 revision of the ISOC standard. This standard is substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional C11 features from Annexes F and G) and the optional Annexes K (Bounds-checking interfaces) and L (Analyzability). The name c1x is deprecated.

" c17 "4 Item "c17" 0

" c18 "4 Item "c18"

" iso9899:2017 "4 Item "iso9899:2017"

" iso9899:2018 "4 Item "iso9899:2018" ISOC17, the 2017 revision of the ISOC standard (published in 2018). This standard is same as C11 except for corrections of defects (all of which are also applied with -std=c11 )and a new value of CW(C`_ _STDC_VERSION_ _ (C' ,and so is supported to the same extent as C11.

" c2x "4 Item "c2x" The next version of the ISOC standard, still under development. The support for this version is experimental and incomplete.

" gnu90 "4 Item "gnu90" 0

" gnu89 "4 Item "gnu89" GNUdialect of ISOC90 (including some C99 features).

" gnu99 "4 Item "gnu99" 0

" gnu9x "4 Item "gnu9x" GNUdialect of ISOC99. The name gnu9x is deprecated.

" gnu11 "4 Item "gnu11" 0

" gnu1x "4 Item "gnu1x" GNUdialect of ISOC11. The name gnu1x is deprecated.

" gnu17 "4 Item "gnu17" 0

" gnu18 "4 Item "gnu18" GNUdialect of ISOC17. This is the default for C code.

" gnu2x "4 Item "gnu2x" The next version of the ISOC standard, still under development, plus GNUextensions. The support for this version is experimental and incomplete.

" c++98 "4 Item "c++98" 0

" c++03 "4 Item "c++03" The 1998 ISO(C+ standard plus the 2003 technical corrigendum and some additional defect reports. Same as -ansi for (C+ code.

" gnu++98 "4 Item "gnu++98" 0

" gnu++03 "4 Item "gnu++03" GNUdialect of -std=c++98 .

" c++11 "4 Item "c++11" 0

" c++0x "4 Item "c++0x" The 2011 ISO(C+ standard plus amendments. The name c++0x is deprecated.

" gnu++11 "4 Item "gnu++11" 0

" gnu++0x "4 Item "gnu++0x" GNUdialect of -std=c++11 . The name gnu++0x is deprecated.

" c++14 "4 Item "c++14" 0

" c++1y "4 Item "c++1y" The 2014 ISO(C+ standard plus amendments. The name c++1y is deprecated.

" gnu++14 "4 Item "gnu++14" 0

" gnu++1y "4 Item "gnu++1y" GNUdialect of -std=c++14 . This is the default for (C+ code. The name gnu++1y is deprecated.

" c++17 "4 Item "c++17" 0

" c++1z "4 Item "c++1z" The 2017 ISO(C+ standard plus amendments. The name c++1z is deprecated.

" gnu++17 "4 Item "gnu++17" 0

" gnu++1z "4 Item "gnu++1z" GNUdialect of -std=c++17 . The name gnu++1z is deprecated.

" c++2a "4 Item "c++2a" The next revision of the ISO(C+ standard, tentatively planned for 2020. Support is highly experimental, and will almost certainly change in incompatible ways in future releases.

" gnu++2a "4 Item "gnu++2a" GNUdialect of -std=c++2a .Support is highly experimental, and will almost certainly change in incompatible ways in future releases.

" -fgnu89 -inline "4 Item "-fgnu89-inline" The option -fgnu89 -inline tells GCCto use the traditional GNUsemantics for CW(C`inline (C' functions when in C99 mode. Using this option is roughly equivalent to adding the CW(C`gnu_inline (C' function attribute to all inline functions. The option -fno -gnu89 -inline explicitly tells GCCto use the C99 semantics for CW(C`inline (C' when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option is not supported in -std=c90 or -std=gnu90 mode. The preprocessor macros CW(C`_ _GNUC_GNU_INLINE_ _ (C' and CW(C`_ _GNUC_STDC_INLINE_ _ (C' may be used to check which semantics are in effect for CW(C`inline (C' functions.

" -fpermitted -flt -eval -methods= style "4 Item "-fpermitted-flt-eval-methods=style" ISO/IECTS 18661 -3 defines new permissible values for CW(C`FLT_EVAL_METHOD (C' that indicate that operations and constants with a semantic type that is an interchange or extended format should be evaluated to the precision and range of that type. These new values are a superset of those permitted under C99/C11, which does not specify the meaning of other positive values of CW(C`FLT_EVAL_METHOD (C' .As such, code conforming to C11 may not have been written expecting the possibility of the new values. -fpermitted -flt -eval -methods specifies whether the compiler should allow only the values of CW(C`FLT_EVAL_METHOD (C' specified in C99/C11, or the extended set of values specified in ISO/IECTS 18661 -3. style is either CW(C`c11 (C' or CW(C`ts -18661 -3 (C' as appropriate. The default when in a standards compliant mode ( -std=c11 or similar) is -fpermitted -flt -eval -methods=c11 .The default when in a GNU dialect ( -std=gnu11 or similar) is -fpermitted -flt -eval -methods=ts -18661 -3 .

" -aux -info filename "4 Item "-aux-info filename" Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped ( I , N for new or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition ( C or F ,respectively, in the following character). In the case of function definitions, a K&R -style list of arguments followed by their declarations is also provided, inside comments, after the declaration.

" -fallow -parameterless -variadic -functions "4 Item "-fallow-parameterless-variadic-functions" Accept variadic functions without named parameters. Although it is possible to define such a function, this is not very useful as it is not possible to read the arguments. This is only supported for C as this construct is allowed by (C+.

" -fno -asm "4 Item "-fno-asm" Do not recognize CW(C`asm (C' , CW(C`inline (C' or CW(C`typeof (C' as a keyword, so that code can use these words as identifiers. You can use the keywords CW(C`_ _asm_ _ (C' , CW(C`_ _inline_ _ (C' and CW(C`_ _typeof_ _ (C' instead. -ansi implies -fno -asm . In (C+, this switch only affects the CW(C`typeof (C' keyword, since CW(C`asm (C' and CW(C`inline (C' are standard keywords. You may want to use the -fno -gnu -keywords flag instead, which has the same effect. In C99 mode ( -std=c99 or -std=gnu99 ),this switch only affects the CW(C`asm (C' and CW(C`typeof (C' keywords, since CW(C`inline (C' is a standard keyword in ISOC99.

" -fno -builtin "4 Item "-fno-builtin" 0

" -fno -builtin - function "4 Item "-fno-builtin-function" Don't recognize built-in functions that do not begin with __builtin_ as prefix. GCCnormally generates special code to handle certain built-in functions more efficiently; for instance, calls to CW(C`alloca (C' may become single instructions which adjust the stack directly, and calls to CW(C`memcpy (C' may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCCmay use information about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with -Wformat for bad calls to CW(C`printf (C' when CW(C`printf (C' is built in and CW(C`strlen (C' is known not to modify global memory. With the -fno -builtin - function option only the built-in function function is disabled. function must not begin with __builtin_ .If a function is named that is not built-in in this version of GCC,this option is ignored. There is no corresponding -fbuiltin - function option; if you wish to enable built-in functions selectively when using -fno -builtin or -ffreestanding ,you may define macros such as: 2 #define abs(n) _ _builtin_abs ((n)) #define strcpy(d, s) _ _builtin_strcpy ((d), (s))

" -fgimple "4 Item "-fgimple" Enable parsing of function definitions marked with CW(C`_ _GIMPLE (C' . This is an experimental feature that allows unit testing of GIMPLE passes.

" -fhosted "4 Item "-fhosted" Assert that compilation targets a hosted environment. This implies -fbuiltin .A hosted environment is one in which the entire standard library is available, and in which CW(C`main (C' has a return type of CW(C`int (C' .Examples are nearly everything except a kernel. This is equivalent to -fno -freestanding .

" -ffreestanding "4 Item "-ffreestanding" Assert that compilation targets a freestanding environment. This implies -fno -builtin .A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at CW(C`main (C' .The most obvious example is an OSkernel. This is equivalent to -fno -hosted .

" -fopenacc "4 Item "-fopenacc" Enable handling of OpenACC directives CW(C`#pragma acc (C' in C/ (C+ and CW(C`!$acc (C' in Fortran. When -fopenacc is specified, the compiler generates accelerated code according to the OpenACC Application Programming Interface v2.0 < https://www.openacc.org >.This option implies -pthread ,and thus is only supported on targets that have support for -pthread .

" -fopenacc -dim= geom "4 Item "-fopenacc-dim=geom" Specify default compute dimensions for parallel offload regions that do not explicitly specify. The geom value is a triple of ':' -separated sizes, in order 'gang', 'worker' and, 'vector'. A size can be omitted, to use a target-specific default value.

" -fopenmp "4 Item "-fopenmp" Enable handling of OpenMP directives CW(C`#pragma omp (C' in C/ (C+ and CW(C`!$omp (C' in Fortran. When -fopenmp is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v4.5 < https://www.openmp.org >.This option implies -pthread ,and thus is only supported on targets that have support for -pthread . -fopenmp implies -fopenmp -simd .

" -fopenmp -simd "4 Item "-fopenmp-simd" Enable handling of OpenMP's SIMDdirectives with CW(C`#pragma omp (C' in C/ (C+ and CW(C`!$omp (C' in Fortran. Other OpenMP directives are ignored.

" -fgnu -tm "4 Item "-fgnu-tm" When the option -fgnu -tm is specified, the compiler generates code for the Linux variant of Intel's current Transactional Memory ABIspecification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of GCC,as the official specification changes. Please note that not all architectures are supported for this feature. For more information on GCC'ssupport for transactional memory, Note that the transactional memory feature is not supported with non-call exceptions ( -fnon -call -exceptions ).

" -fms -extensions "4 Item "-fms-extensions" Accept some non-standard constructs used in Microsoft header files. In (C+ code, this allows member names in structures to be similar to previous types declarations. 4 typedef int UOW; struct ABC { UOW UOW; }; Some cases of unnamed fields in structures and unions are only accepted with this option. Note that this option is off for all targets but x86 targets using ms-abi.

" -fplan9 -extensions "4 Item "-fplan9-extensions" Accept some non-standard constructs used in Plan 9 code. This enables -fms -extensions ,permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. This is only supported for C, not (C+.

" -fcond -mismatch "4 Item "-fcond-mismatch" Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for (C+.

" -flax -vector -conversions "4 Item "-flax-vector-conversions" Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code.

" -funsigned -char "4 Item "-funsigned-char" Let the type CW(C`char (C' be unsigned, like CW(C`unsigned char (C' . Each kind of machine has a default for what CW(C`char (C' should be. It is either like CW(C`unsigned char (C' by default or like CW(C`signed char (C' by default. Ideally, a portable program should always use CW(C`signed char (C' or CW(C`unsigned char (C' when it depends on the signedness of an object. But many programs have been written to use plain CW(C`char (C' and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. The type CW(C`char (C' is always a distinct type from each of CW(C`signed char (C' or CW(C`unsigned char (C' ,even though its behavior is always just like one of those two.

" -fsigned -char "4 Item "-fsigned-char" Let the type CW(C`char (C' be signed, like CW(C`signed char (C' . Note that this is equivalent to -fno -unsigned -char ,which is the negative form of -funsigned -char .Likewise, the option -fno -signed -char is equivalent to -funsigned -char .

" -fsigned -bitfields "4 Item "-fsigned-bitfields" 0

" -funsigned -bitfields "4 Item "-funsigned-bitfields"

" -fno -signed -bitfields "4 Item "-fno-signed-bitfields"

" -fno -unsigned -bitfields "4 Item "-fno-unsigned-bitfields" These options control whether a bit-field is signed or unsigned, when the declaration does not use either CW(C`signed (C' or CW(C`unsigned (C' .By default, such a bit-field is signed, because this is consistent: the basic integer types such as CW(C`int (C' are signed types.

" -fsso -struct= endianness "4 Item "-fsso-struct=endianness" Set the default scalar storage order of structures and unions to the specified endianness. The accepted values are big-endian , little-endian and native for the native endianness of the target (the default). This option is not supported for (C+. Warning: the -fsso -struct switch causes GCCto generate code that is not binary compatible with code generated without it if the specified endianness is not the native endianness of the target.

"Options Controlling (C+ Dialect"

Subsection "Options Controlling Dialect" This section describes the command-line options that are only meaningful for (C+ programs. You can also use most of the GNUcompiler options regardless of what language your program is in. For example, you might compile a file firstClass.C like this:

1 g++ -g -fstrict -enums -O -c firstClass.C

In this example, only -fstrict -enums is an option meant only for (C+ programs; you can use the other options with any language supported by GCC.

Some options for compiling C programs, such as -std ,are also relevant for (C+ programs.

Here is a list of options that are only for compiling (C+ programs:

" -fabi -version= n "4 Item "-fabi-version=n" Use version n of the (C+ ABI.The default is version 0. Version 0 refers to the version conforming most closely to the (C+ ABIspecification. Therefore, the ABIobtained using version 0 will change in different versions of G++ as ABIbugs are fixed. Version 1 is the version of the (C+ ABIthat first appeared in G++ 3.2. Version 2 is the version of the (C+ ABIthat first appeared in G++ 3.4, and was the default through G++ 4.9. Version 3 corrects an error in mangling a constant address as a template argument. Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter. Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of (C+11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and --, and a class scope function used as a template argument. Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope. Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers. Version 9, which first appeared in G++ 5.2, corrects the alignment of CW(C`nullptr_t (C' . Version 10, which first appeared in G++ 6.1, adds mangling of attributes that affect type identity, such as ia32 calling convention attributes (e.g. stdcall ). Version 11, which first appeared in G++ 7, corrects the mangling of sizeof... expressions and operator names. For multiple entities with the same name within a function, that are declared in different scopes, the mangling now changes starting with the twelfth occurrence. It also implies -fnew -inheriting -ctors . Version 12, which first appeared in G++ 8, corrects the calling conventions for empty classes on the x86_64 target and for classes with only deleted copy/move constructors. It accidentally changes the calling convention for classes with a deleted copy constructor and a trivial move constructor. Version 13, which first appeared in G++ 8.2, fixes the accidental change in version 12. See also -Wabi .

" -fabi -compat -version= n "4 Item "-fabi-compat-version=n" On targets that support strong aliases, G++ works around mangling changes by creating an alias with the correct mangled name when defining a symbol with an incorrect mangled name. This switch specifies which ABIversion to use for the alias. With -fabi -version=0 (the default), this defaults to 11 ( GCC7 compatibility). If another ABIversion is explicitly selected, this defaults to 0. For compatibility with GCCversions 3.2 through 4.9, use -fabi -compat -version=2 . If this option is not provided but -Wabi= n is, that version is used for compatibility aliases. If this option is provided along with -Wabi (without the version), the version from this option is used for the warning.

" -fno -access -control "4 Item "-fno-access-control" Turn off all access checking. This switch is mainly useful for working around bugs in the access control code.

" -faligned -new "4 Item "-faligned-new" Enable support for (C+17 CW(C`new (C' of types that require more alignment than CW(C`void* ::operator new(std::size_t) (C' provides. A numeric argument such as CW(C` -faligned -new=32 (C' can be used to specify how much alignment (in bytes) is provided by that function, but few users will need to override the default of CW(C`alignof(std::max_align_t) (C' . This flag is enabled by default for -std=c++17 .

" -fchar8_t "4 Item "-fchar8_t" 0

" -fno -char8_t "4 Item "-fno-char8_t" Enable support for CW(C`char8_t (C' as adopted for (C+2a. This includes the addition of a new CW(C`char8_t (C' fundamental type, changes to the types of UTF-8 string and character literals, new signatures for user-defined literals, associated standard library updates, and new CW(C`_ _cpp_char8_t (C' and CW(C`_ _cpp_lib_char8_t (C' feature test macros. This option enables functions to be overloaded for ordinary and UTF-8 strings: 4 int f(const char *); // #1 int f(const char8_t *); // #2 int v1 = f("text"); // Calls #1 int v2 = f(u8"text"); // Calls #2 and introduces new signatures for user-defined literals: 6 int operator""_udl1(char8_t); int v3 = u8 (Aqx (Aq_udl1; int operator""_udl2(const char8_t*, std::size_t); int v4 = u8"text"_udl2; template<typename T, T...> int operator""_udl3(); int v5 = u8"text"_udl3; The change to the types of UTF-8 string and character literals introduces incompatibilities with ISO(C+11 and later standards. For example, the following code is well-formed under ISO(C+11, but is ill-formed when -fchar8_t is specified. 10 char ca[] = u8"xx"; // error: char -array initialized from wide // string const char *cp = u8"xx";// error: invalid conversion from // const char8_t* (Aq to const char* (Aq int f(const char*); auto v = f(u8"xx"); // error: invalid conversion from // const char8_t* (Aq to const char* (Aq std::string s{u8"xx"}; // error: no matching function for call to // std::basic_string<char>::basic_string() (Aq using namespace std::literals; s = u8"xx"s; // error: conversion from // basic_string<char8_t> (Aq to non -scalar // type basic_string<char> (Aq requested

" -fcheck -new "4 Item "-fcheck-new" Check that the pointer returned by CW(C`operator new (C' is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the (C+ standard specifies that CW(C`operator new (C' only returns CW0 if it is declared CW(C`throw() (C' ,in which case the compiler always checks the return value even without this option. In all other cases, when CW(C`operator new (C' has a non-empty exception specification, memory exhaustion is signalled by throwing CW(C`std::bad_alloc (C' .See also new(nothrow) .

" -fconcepts "4 Item "-fconcepts" Enable support for the (C+ Extensions for Concepts Technical Specification, ISO19217 (2015), which allows code like 2 template <class T> concept bool Addable = requires (T t) { t + t; }; template <Addable T> T add (T a, T b) { return a + b; }

" -fconstexpr -depth= n "4 Item "-fconstexpr-depth=n" Set the maximum nested evaluation depth for (C+11 constexpr functions to n .A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512.

" -fconstexpr -loop -limit= n "4 Item "-fconstexpr-loop-limit=n" Set the maximum number of iterations for a loop in (C+14 constexpr functions to n .A limit is needed to detect infinite loops during constant expression evaluation. The default is 262144 (1<<18).

" -fconstexpr -ops -limit= n "4 Item "-fconstexpr-ops-limit=n" Set the maximum number of operations during a single constexpr evaluation. Even when number of iterations of a single loop is limited with the above limit, if there are several nested loops and each of them has many iterations but still smaller than the above limit, or if in a body of some loop or even outside of a loop too many expressions need to be evaluated, the resulting constexpr evaluation might take too long. The default is 33554432 (1<<25).

" -fdeduce -init -list "4 Item "-fdeduce-init-list" Enable deduction of a template type parameter as CW(C`std::initializer_list (C' from a brace-enclosed initializer list, i.e. 4 template <class T> auto forward(T t) -> decltype (realfn (t)) { return realfn (t); } void f() { forward({1,2}); // call forward<std::initializer_list<int>> } This deduction was implemented as a possible extension to the originally proposed semantics for the (C+11 standard, but was not part of the final standard, so it is disabled by default. This option is deprecated, and may be removed in a future version of G++.

" -fno -elide -constructors "4 Item "-fno-elide-constructors" The (C+ standard allows an implementation to omit creating a temporary that is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. This option also causes G++ to call trivial member functions which otherwise would be expanded inline. In (C+17, the compiler is required to omit these temporaries, but this option still affects trivial member functions.

" -fno -enforce -eh -specs "4 Item "-fno-enforce-eh-specs" Don't generate code to check for violation of exception specifications at run time. This option violates the (C+ standard, but may be useful for reducing code size in production builds, much like defining CW(C`NDEBUG (C' .This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the specifications, so throwing an unexpected exception results in undefined behavior at run time.

" -fextern -tls -init "4 Item "-fextern-tls-init" 0

" -fno -extern -tls -init "4 Item "-fno-extern-tls-init" The (C+11 and OpenMP standards allow CW(C`thread_local (C' and CW(C`threadprivate (C' variables to have dynamic (runtime) initialization. To support this, any use of such a variable goes through a wrapper function that performs any necessary initialization. When the use and definition of the variable are in the same translation unit, this overhead can be optimized away, but when the use is in a different translation unit there is significant overhead even if the variable doesn't actually need dynamic initialization. If the programmer can be sure that no use of the variable in a non-defining TUneeds to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining TUwill be executed before any uses in another TU),they can avoid this overhead with the -fno -extern -tls -init option. On targets that support symbol aliases, the default is -fextern -tls -init .On targets that do not support symbol aliases, the default is -fno -extern -tls -init .

" -fno -gnu -keywords "4 Item "-fno-gnu-keywords" Do not recognize CW(C`typeof (C' as a keyword, so that code can use this word as an identifier. You can use the keyword CW(C`_ _typeof_ _ (C' instead. This option is implied by the strict ISO(C+ dialects: -ansi , -std=c++98 , -std=c++11 ,etc.

" -fno -implicit -templates "4 Item "-fno-implicit-templates" Never emit code for non-inline templates that are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. If you use this option, you must take care to structure your code to include all the necessary explicit instantiations to avoid getting undefined symbols at link time.

" -fno -implicit -inline -templates "4 Item "-fno-implicit-inline-templates" Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization need the same set of explicit instantiations.

" -fno -implement -inlines "4 Item "-fno-implement-inlines" To save space, do not emit out-of-line copies of inline functions controlled by CW(C`#pragma implementation (C' .This causes linker errors if these functions are not inlined everywhere they are called.

" -fms -extensions "4 Item "-fms-extensions" Disable Wpedantic warnings about constructs used in MFC,such as implicit int and getting a pointer to member function via non-standard syntax.

" -fnew -inheriting -ctors "4 Item "-fnew-inheriting-ctors" Enable the P0136 adjustment to the semantics of (C+11 constructor inheritance. This is part of (C+17 but also considered to be a Defect Report against (C+11 and (C+14. This flag is enabled by default unless -fabi -version=10 or lower is specified.

" -fnew -ttp -matching "4 Item "-fnew-ttp-matching" Enable the P0522 resolution to Core issue 150, template template parameters and default arguments: this allows a template with default template arguments as an argument for a template template parameter with fewer template parameters. This flag is enabled by default for -std=c++17 .

" -fno -nonansi -builtins "4 Item "-fno-nonansi-builtins" Disable built-in declarations of functions that are not mandated by ANSI/ISOC. These include CW(C`ffs (C' , CW(C`alloca (C' , CW(C`_exit (C' , CW(C`index (C' , CW(C`bzero (C' , CW(C`conjf (C' ,and other related functions.

" -fnothrow -opt "4 Item "-fnothrow-opt" Treat a CW(C`throw() (C' exception specification as if it were a CW(C`noexcept (C' specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial destructors, the exception specification actually makes the function smaller because the EHcleanups for those variables can be optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification results in a call to CW(C`terminate (C' rather than CW(C`unexpected (C' .

" -fno -operator -names "4 Item "-fno-operator-names" Do not treat the operator name keywords CW(C`and (C' , CW(C`bitand (C' , CW(C`bitor (C' , CW(C`compl (C' , CW(C`not (C' , CW(C`or (C' and CW(C`xor (C' as synonyms as keywords.

" -fno -optional -diags "4 Item "-fno-optional-diags" Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class.

" -fpermissive "4 Item "-fpermissive" Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive allows some nonconforming code to compile.

" -fno -pretty -templates "4 Item "-fno-pretty-templates" When an error message refers to a specialization of a function template, the compiler normally prints the signature of the template followed by the template arguments and any typedefs or typenames in the signature (e.g. CW(C`void f(T) [with T = int] (C' rather than CW(C`void f(int) (C' )so that it's clear which template is involved. When an error message refers to a specialization of a class template, the compiler omits any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error message rather than easier, you can use -fno -pretty -templates to disable them.

" -frepo "4 Item "-frepo" Enable automatic template instantiation at link time. This option also implies -fno -implicit -templates .

" -fno -rtti "4 Item "-fno-rtti" Disable generation of information about every class with virtual functions for use by the (C+ run-time type identification features ( CW(C`dynamic_cast (C' and CW(C`typeid (C' ).If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but G++ generates it as needed. The CW(C`dynamic_cast (C' operator can still be used for casts that do not require run-time type information, i.e. casts to CW(C`void * (C' or to unambiguous base classes. Mixing code compiled with -frtti with that compiled with -fno -rtti may not work. For example, programs may fail to link if a class compiled with -fno -rtti is used as a base for a class compiled with -frtti .

" -fsized -deallocation "4 Item "-fsized-deallocation" Enable the built-in global declarations 2 void operator delete (void *, std::size_t) noexcept; void operator delete[] (void *, std::size_t) noexcept; as introduced in (C+14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default under -std=c++14 and above. The flag -Wsized -deallocation warns about places that might want to add a definition.

" -fstrict -enums "4 Item "-fstrict-enums" Allow the compiler to optimize using the assumption that a value of enumerated type can only be one of the values of the enumeration (as defined in the (C+ standard; basically, a value that can be represented in the minimum number of bits needed to represent all the enumerators). This assumption may not be valid if the program uses a cast to convert an arbitrary integer value to the enumerated type.

" -fstrong -eval -order "4 Item "-fstrong-eval-order" Evaluate member access, array subscripting, and shift expressions in left-to-right order, and evaluate assignment in right-to-left order, as adopted for (C+17. Enabled by default with -std=c++17 . -fstrong -eval -order=some enables just the ordering of member access and shift expressions, and is the default without -std=c++17 .

" -ftemplate -backtrace -limit= n "4 Item "-ftemplate-backtrace-limit=n" Set the maximum number of template instantiation notes for a single warning or error to n .The default value is 10.

" -ftemplate -depth= n "4 Item "-ftemplate-depth=n" Set the maximum instantiation depth for template classes to n . A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. ANSI/ISO(C+ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in (C+11). The default value is 900, as the compiler can run out of stack space before hitting 1024 in some situations.

" -fno -threadsafe -statics "4 Item "-fno-threadsafe-statics" Do not emit the extra code to use the routines specified in the (C+ ABIfor thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe.

" -fuse -cxa -atexit "4 Item "-fuse-cxa-atexit" Register destructors for objects with static storage duration with the CW(C`_ _cxa_atexit (C' function rather than the CW(C`atexit (C' function. This option is required for fully standards-compliant handling of static destructors, but only works if your C library supports CW(C`_ _cxa_atexit (C' .

" -fno -use -cxa -get -exception -ptr "4 Item "-fno-use-cxa-get-exception-ptr" Don't use the CW(C`_ _cxa_get_exception_ptr (C' runtime routine. This causes CW(C`std::uncaught_exception (C' to be incorrect, but is necessary if the runtime routine is not available.

" -fvisibility -inlines -hidden "4 Item "-fvisibility-inlines-hidden" This switch declares that the user does not attempt to compare pointers to inline functions or methods where the addresses of the two functions are taken in different shared objects. The effect of this is that GCCmay, effectively, mark inline methods with CW(C`_ _attribute_ _ ((visibility ("hidden"))) (C' so that they do not appear in the export table of a DSOand do not require a PLTindirection when used within the DSO.Enabling this option can have a dramatic effect on load and link times of a DSOas it massively reduces the size of the dynamic export table when the library makes heavy use of templates. The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object. You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect. Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary.

" -fvisibility -ms -compat "4 Item "-fvisibility-ms-compat" This flag attempts to use visibility settings to make GCC's(C+ linkage model compatible with that of Microsoft Visual Studio. The flag makes these changes to GCC'slinkage model:

"1." 4 Item "1." It sets the default visibility to CW(C`hidden (C' ,like -fvisibility=hidden .

"2." 4 Item "2." Types, but not their members, are not hidden by default.

"3." 4 Item "3." The One Definition Rule is relaxed for types without explicit visibility specifications that are defined in more than one shared object: those declarations are permitted if they are permitted when this option is not used. In new code it is better to use -fvisibility=hidden and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior. Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODRto define types with the same name differently.

" -fno -weak "4 Item "-fno-weak" Do not use weak symbol support, even if it is provided by the linker. By default, G++ uses weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it results in inferior code and has no benefits. This option may be removed in a future release of G++.

" -nostdinc++ "4 Item "-nostdinc++" Do not search for header files in the standard directories specific to (C+, but do still search the other standard directories. (This option is used when building the (C+ library.)

In addition, these optimization, warning, and code generation options have meanings only for (C+ programs:

" -Wabi (C, Objective-C, (C+ and Objective -(C+ only)" 4 Item "-Wabi (C, Objective-C, and Objective- only)" Warn when G++ it generates code that is probably not compatible with the vendor-neutral (C+ ABI.Since G++ now defaults to updating the ABIwith each major release, normally -Wabi will warn only if there is a check added later in a release series for an ABIissue discovered since the initial release. -Wabi will warn about more things if an older ABIversion is selected (with -fabi -version= n ). -Wabi can also be used with an explicit version number to warn about compatibility with a particular -fabi -version level, e.g. -Wabi=2 to warn about changes relative to -fabi -version=2 . If an explicit version number is provided and -fabi -compat -version is not specified, the version number from this option is used for compatibility aliases. If no explicit version number is provided with this option, but -fabi -compat -version is specified, that version number is used for ABIwarnings. Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated is compatible. You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. Known incompatibilities in -fabi -version=2 (which was the default from GCC3.4 to 4.9) include:

"*" 4 A template with a non-type template parameter of reference type was mangled incorrectly: 3 extern int N; template <int &> struct S {}; void n (S<N>) {2} This was fixed in -fabi -version=3 .

"*" 4 SIMDvector types declared using CW(C`_ _attribute ((vector_size)) (C' were mangled in a non-standard way that does not allow for overloading of functions taking vectors of different sizes. The mangling was changed in -fabi -version=4 .

"*" 4 CW(C`_ _attribute ((const)) (C' and CW(C`noreturn (C' were mangled as type qualifiers, and CW(C`decltype (C' of a plain declaration was folded away. These mangling issues were fixed in -fabi -version=5 .

"*" 4 Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing CW(C`va_arg (C' to complain. On most targets this does not actually affect the parameter passing ABI,as there is no way to pass an argument smaller than CW(C`int (C' . Also, the ABIchanged the mangling of template argument packs, CW(C`const_cast (C' , CW(C`static_cast (C' ,prefix increment/decrement, and a class scope function used as a template argument. These issues were corrected in -fabi -version=6 .

"*" 4 Lambdas in default argument scope were mangled incorrectly, and the ABIchanged the mangling of CW(C`nullptr_t (C' . These issues were corrected in -fabi -version=7 .

"*" 4 When mangling a function type with function-cv-qualifiers, the un-qualified function type was incorrectly treated as a substitution candidate. This was fixed in -fabi -version=8 ,the default for GCC5.1.

"*" 4 CW(C`decltype(nullptr) (C' incorrectly had an alignment of 1, leading to unaligned accesses. Note that this did not affect the ABIof a function with a CW(C`nullptr_t (C' parameter, as parameters have a minimum alignment. This was fixed in -fabi -version=9 ,the default for GCC5.2.

"*" 4 Target-specific attributes that affect the identity of a type, such as ia32 calling conventions on a function type (stdcall, regparm, etc.), did not affect the mangled name, leading to name collisions when function pointers were used as template arguments. This was fixed in -fabi -version=10 ,the default for GCC6.1. It also warns about psABI-related changes. The known psABI changes at this point include:

"*" 4 For SysV/x86 -64, unions with CW(C`long double (C' members are passed in memory as specified in psABI. For example: 4 union U { long double ld; int i; }; CW(C`union U (C' is always passed in memory.

" -Wabi -tag ( (C+ and Objective -(C+ only)" 4 Item "-Wabi-tag ( and Objective- only)" Warn when a type with an ABItag is used in a context that does not have that ABItag. See (C+ Attributes for more information about ABItags.

" -Wctor -dtor -privacy ( (C+ and Objective -(C+ only)" 4 Item "-Wctor-dtor-privacy ( and Objective- only)" Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions. Also warn if there are no non-private methods, and there's at least one private member function that isn't a constructor or destructor.

" -Wdelete -non -virtual -dtor ( (C+ and Objective -(C+ only)" 4 Item "-Wdelete-non-virtual-dtor ( and Objective- only)" Warn when CW(C`delete (C' is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base class if the base class does not have a virtual destructor. This warning is enabled by -Wall .

" -Wdeprecated -copy ( (C+ and Objective -(C+ only)" 4 Item "-Wdeprecated-copy ( and Objective- only)" Warn that the implicit declaration of a copy constructor or copy assignment operator is deprecated if the class has a user-provided copy constructor or copy assignment operator, in (C+11 and up. This warning is enabled by -Wextra .With -Wdeprecated -copy -dtor ,also deprecate if the class has a user-provided destructor.

" -Wno -init -list -lifetime ( (C+ and Objective -(C+ only)" 4 Item "-Wno-init-list-lifetime ( and Objective- only)" Do not warn about uses of CW(C`std::initializer_list (C' that are likely to result in dangling pointers. Since the underlying array for an CW(C`initializer_list (C' is handled like a normal (C+ temporary object, it is easy to inadvertently keep a pointer to the array past the end of the array's lifetime. For example:

"*" 4 If a function returns a temporary CW(C`initializer_list (C' ,or a local CW(C`initializer_list (C' variable, the array's lifetime ends at the end of the return statement, so the value returned has a dangling pointer.

"*" 4 If a new-expression creates an CW(C`initializer_list (C' ,the array only lives until the end of the enclosing full-expression, so the CW(C`initializer_list (C' in the heap has a dangling pointer.

"*" 4 When an CW(C`initializer_list (C' variable is assigned from a brace-enclosed initializer list, the temporary array created for the right side of the assignment only lives until the end of the full-expression, so at the next statement the CW(C`initializer_list (C' variable has a dangling pointer. 6 // li (Aqs initial underlying array lives as long as li std::initializer_list<int> li = { 1,2,3 }; // assignment changes li to point to a temporary array li = { 4, 5 }; // now the temporary is gone and li has a dangling pointer int i = li.begin()[0] // undefined behavior

"*" 4 When a list constructor stores the CW(C`begin (C' pointer from the CW(C`initializer_list (C' argument, this doesn't extend the lifetime of the array, so if a class variable is constructed from a temporary CW(C`initializer_list (C' ,the pointer is left dangling by the end of the variable declaration statement.

" -Wliteral -suffix ( (C+ and Objective -(C+ only)" 4 Item "-Wliteral-suffix ( and Objective- only)" Warn when a string or character literal is followed by a ud-suffix which does not begin with an underscore. As a conforming extension, GCCtreats such suffixes as separate preprocessing tokens in order to maintain backwards compatibility with code that uses formatting macros from CW(C`<inttypes.h> (C' . For example: 3 #define _ _STDC_FORMAT_MACROS #include <inttypes.h> #include <stdio.h> int main() { int64_t i64 = 123; printf("My int64: %" PRId64" \ n", i64); } In this case, CW(C`PRId64 (C' is treated as a separate preprocessing token. Additionally, warn when a user-defined literal operator is declared with a literal suffix identifier that doesn't begin with an underscore. Literal suffix identifiers that don't begin with an underscore are reserved for future standardization. This warning is enabled by default.

" -Wlto -type -mismatch "4 Item "-Wlto-type-mismatch" During the link-time optimization warn about type mismatches in global declarations from different compilation units. Requires -flto to be enabled. Enabled by default.

" -Wno -narrowing ( (C+ and Objective -(C+ only)" 4 Item "-Wno-narrowing ( and Objective- only)" For (C+11 and later standards, narrowing conversions are diagnosed by default, as required by the standard. A narrowing conversion from a constant produces an error, and a narrowing conversion from a non-constant produces a warning, but -Wno -narrowing suppresses the diagnostic. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in SFINAEcontexts. With -Wnarrowing in (C+98, warn when a narrowing conversion prohibited by (C+11 occurs within {} ,e.g. 1 int i = { 2.2 }; // error: narrowing from double to int This flag is included in -Wall and -Wc++11 -compat .

" -Wnoexcept ( (C+ and Objective -(C+ only)" 4 Item "-Wnoexcept ( and Objective- only)" Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. CW(C`throw() (C' or CW(C`noexcept (C' )but is known by the compiler to never throw an exception.

" -Wnoexcept -type ( (C+ and Objective -(C+ only)" 4 Item "-Wnoexcept-type ( and Objective- only)" Warn if the (C+17 feature making CW(C`noexcept (C' part of a function type changes the mangled name of a symbol relative to (C+14. Enabled by -Wabi and -Wc++17 -compat . As an example: 3 template <class T> void f(T t) { t(); }; void g() noexcept; void h() { f(g); } In (C+14, CW(C`f (C' calls CW(C`f<void(*)()> (C' ,but in (C+17 it calls CW(C`f<void(*)()noexcept> (C' .

" -Wclass -memaccess ( (C+ and Objective -(C+ only)" 4 Item "-Wclass-memaccess ( and Objective- only)" Warn when the destination of a call to a raw memory function such as CW(C`memset (C' or CW(C`memcpy (C' is an object of class type, and when writing into such an object might bypass the class non-trivial or deleted constructor or copy assignment, violate const-correctness or encapsulation, or corrupt virtual table pointers. Modifying the representation of such objects may violate invariants maintained by member functions of the class. For example, the call to CW(C`memset (C' below is undefined because it modifies a non-trivial class object and is, therefore, diagnosed. The safe way to either initialize or clear the storage of objects of such types is by using the appropriate constructor or assignment operator, if one is available. 2 std::string str = "abc"; memset (&str, 0, sizeof str); The -Wclass -memaccess option is enabled by -Wall . Explicitly casting the pointer to the class object to CW(C`void * (C' or to a type that can be safely accessed by the raw memory function suppresses the warning.

" -Wnon -virtual -dtor ( (C+ and Objective -(C+ only)" 4 Item "-Wnon-virtual-dtor ( and Objective- only)" Warn when a class has virtual functions and an accessible non-virtual destructor itself or in an accessible polymorphic base class, in which case it is possible but unsafe to delete an instance of a derived class through a pointer to the class itself or base class. This warning is automatically enabled if -Weffc++ is specified.

" -Wregister ( (C+ and Objective -(C+ only)" 4 Item "-Wregister ( and Objective- only)" Warn on uses of the CW(C`register (C' storage class specifier, except when it is part of the GNU ExplicitRegister Variables extension. The use of the CW(C`register (C' keyword as storage class specifier has been deprecated in (C+11 and removed in (C+17. Enabled by default with -std=c++17 .

" -Wreorder ( (C+ and Objective -(C+ only)" 4 Item "-Wreorder ( and Objective- only)" Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: 5 struct A { int i; int j; A(): j (0), i (1) { } }; The compiler rearranges the member initializers for CW(C`i (C' and CW(C`j (C' to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by -Wall .

" -Wno -pessimizing -move ( (C+ and Objective -(C+ only)" 4 Item "-Wno-pessimizing-move ( and Objective- only)" This warning warns when a call to CW(C`std::move (C' prevents copy elision. A typical scenario when copy elision can occur is when returning in a function with a class return type, when the expression being returned is the name of a non-volatile automatic object, and is not a function parameter, and has the same type as the function return type. 9 struct T { ... }; T fn() { T t; ... return std::move (t); } But in this example, the CW(C`std::move (C' call prevents copy elision. This warning is enabled by -Wall .

" -Wno -redundant -move ( (C+ and Objective -(C+ only)" 4 Item "-Wno-redundant-move ( and Objective- only)" This warning warns about redundant calls to CW(C`std::move (C' ;that is, when a move operation would have been performed even without the CW(C`std::move (C' call. This happens because the compiler is forced to treat the object as if it were an rvalue in certain situations such as returning a local variable, where copy elision isn't applicable. Consider: 8 struct T { ... }; T fn(T t) { ... return std::move (t); } Here, the CW(C`std::move (C' call is redundant. Because G++ implements Core Issue 1579, another example is: 12 struct T { // convertible to U ... }; struct U { ... }; U fn() { T t; ... return std::move (t); } In this example, copy elision isn't applicable because the type of the expression being returned and the function return type differ, yet G++ treats the return value as if it were designated by an rvalue. This warning is enabled by -Wextra .

" -fext -numeric -literals ( (C+ and Objective -(C+ only)" 4 Item "-fext-numeric-literals ( and Objective- only)" Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNUextensions. When this option is turned off these suffixes are treated as (C+11 user-defined literal numeric suffixes. This is on by default for all pre -(C+11 dialects and all GNUdialects: -std=c++98 , -std=gnu++98 , -std=gnu++11 , -std=gnu++14 . This option is off by default for ISO(C+11 onwards ( -std=c++11 ,...).

The following -W... options are not affected by -Wall .

" -Weffc++ ( (C+ and Objective -(C+ only)" 4 Item "-Weffc++ ( and Objective- only)" Warn about violations of the following style guidelines from Scott Meyers' Effective(C+ series of books:

"*" 4 Define a copy constructor and an assignment operator for classes with dynamically-allocated memory.

"*" 4 Prefer initialization to assignment in constructors.

"*" 4 Have CW(C`operator= (C' return a reference to CW*this .

"*" 4 Don't try to return a reference when you must return an object.

"*" 4 Distinguish between prefix and postfix forms of increment and decrement operators.

"*" 4 Never overload CW(C`&& (C' , CW(C`|| (C' ,or CW(C`, (C' . This option also enables -Wnon -virtual -dtor ,which is also one of the effective (C+ recommendations. However, the check is extended to warn about the lack of virtual destructor in accessible non-polymorphic bases classes too. When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use grep-v to filter out those warnings.

" -Wstrict -null -sentinel ( (C+ and Objective -(C+ only)" 4 Item "-Wstrict-null-sentinel ( and Objective- only)" Warn about the use of an uncasted CW(C`NULL (C' as sentinel. When compiling only with GCCthis is a valid sentinel, as CW(C`NULL (C' is defined to CW(C`_ _null (C' .Although it is a null pointer constant rather than a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers.

" -Wno -non -template -friend ( (C+ and Objective -(C+ only)" 4 Item "-Wno-non-template-friend ( and Objective- only)" Disable warnings when non-template friend functions are declared within a template. In very old versions of GCCthat predate implementation of the ISOstandard, declarations such as friendint foo(int) ,where the name of the friend is an unqualified-id, could be interpreted as a particular specialization of a template function; the warning exists to diagnose compatibility problems, and is enabled by default.

" -Wold -style -cast ( (C+ and Objective -(C+ only)" 4 Item "-Wold-style-cast ( and Objective- only)" Warn if an old-style (C -style) cast to a non-void type is used within a (C+ program. The new-style casts ( CW(C`dynamic_cast (C' , CW(C`static_cast (C' , CW(C`reinterpret_cast (C' ,and CW(C`const_cast (C' )are less vulnerable to unintended effects and much easier to search for.

" -Woverloaded -virtual ( (C+ and Objective -(C+ only)" 4 Item "-Woverloaded-virtual ( and Objective- only)" Warn when a function declaration hides virtual functions from a base class. For example, in: 3 struct A { virtual void f(); }; struct B: public A { void f(int); }; the CW(C`A (C' class version of CW(C`f (C' is hidden in CW(C`B (C' ,and code like: 2 B* b; b ->f(); fails to compile.

" -Wno -pmf -conversions ( (C+ and Objective -(C+ only)" 4 Item "-Wno-pmf-conversions ( and Objective- only)" Disable the diagnostic for converting a bound pointer to member function to a plain pointer.

" -Wsign -promo ( (C+ and Objective -(C+ only)" 4 Item "-Wsign-promo ( and Objective- only)" Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same size. Previous versions of G++ tried to preserve unsignedness, but the standard mandates the current behavior.

" -Wtemplates ( (C+ and Objective -(C+ only)" 4 Item "-Wtemplates ( and Objective- only)" Warn when a primary template declaration is encountered. Some coding rules disallow templates, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL,so one can still use the STL.One may also instantiate or specialize templates.

" -Wmultiple -inheritance ( (C+ and Objective -(C+ only)" 4 Item "-Wmultiple-inheritance ( and Objective- only)" Warn when a class is defined with multiple direct base classes. Some coding rules disallow multiple inheritance, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL,so one can still use the STL.One may also define classes that indirectly use multiple inheritance.

" -Wvirtual -inheritance "4 Item "-Wvirtual-inheritance" Warn when a class is defined with a virtual direct base class. Some coding rules disallow multiple inheritance, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL,so one can still use the STL.One may also define classes that indirectly use virtual inheritance.

" -Wnamespaces "4 Item "-Wnamespaces" Warn when a namespace definition is opened. Some coding rules disallow namespaces, and this may be used to enforce that rule. The warning is inactive inside a system header file, such as the STL,so one can still use the STL.One may also use using directives and qualified names.

" -Wno -terminate ( (C+ and Objective -(C+ only)" 4 Item "-Wno-terminate ( and Objective- only)" Disable the warning about a throw-expression that will immediately result in a call to CW(C`terminate (C' .

" -Wno -class -conversion ( (C+ and Objective -(C+ only)" 4 Item "-Wno-class-conversion ( and Objective- only)" Disable the warning about the case when a conversion function converts an object to the same type, to a base class of that type, or to void; such a conversion function will never be called.

"Options Controlling Objective-C and Objective -(C+ Dialects"

Subsection "Options Controlling Objective-C and Objective- Dialects" ( NOTE:This manual does not describe the Objective-C and Objective -(C+ languages themselves.

This section describes the command-line options that are only meaningful for Objective-C and Objective -(C+ programs. You can also use most of the language-independent GNUcompiler options. For example, you might compile a file some_class.m like this:

1 gcc -g -fgnu -runtime -O -c some_class.m

In this example, -fgnu -runtime is an option meant only for Objective-C and Objective -(C+ programs; you can use the other options with any language supported by GCC.

Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., -Wtraditional ).Similarly, Objective -(C+ compilations may use (C+ -specific options (e.g., -Wabi ).

Here is a list of options that are only for compiling Objective-C and Objective -(C+ programs:

" -fconstant -string -class= class-name "4 Item "-fconstant-string-class=class-name" Use class-name as the name of the class to instantiate for each literal string specified with the syntax CW(C`@"..." (C' .The default class name is CW(C`NXConstantString (C' if the GNUruntime is being used, and CW(C`NSConstantString (C' if the NeXT runtime is being used (see below). The -fconstant -cfstrings option, if also present, overrides the -fconstant -string -class setting and cause CW(C`@"..." (C' literals to be laid out as constant CoreFoundation strings.

" -fgnu -runtime "4 Item "-fgnu-runtime" Generate object code compatible with the standard GNUObjective-C runtime. This is the default for most types of systems.

" -fnext -runtime "4 Item "-fnext-runtime" Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OSX. The macro CW(C`_ _NEXT_RUNTIME_ _ (C' is predefined if (and only if) this option is used.

" -fno -nil -receivers "4 Item "-fno-nil-receivers" Assume that all Objective-C message dispatches ( CW(C`[receiver message:arg] (C' )in this translation unit ensure that the receiver is not CW(C`nil (C' .This allows for more efficient entry points in the runtime to be used. This option is only available in conjunction with the NeXT runtime and ABIversion 0 or 1.

" -fobjc -abi -version= n "4 Item "-fobjc-abi-version=n" Use version n of the Objective-C ABIfor the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32 -bit) ABIwithout support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32 -bit) ABIwith support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64 -bit) ABI.If nothing is specified, the default is Version 0 on 32 -bit target machines, and Version 2 on 64 -bit target machines.

" -fobjc -call -cxx -cdtors "4 Item "-fobjc-call-cxx-cdtors" For each Objective-C class, check if any of its instance variables is a (C+ object with a non-trivial default constructor. If so, synthesize a special CW(C` -(id) .cxx_construct (C' instance method which runs non-trivial default constructors on any such instance variables, in order, and then return CW(C`self (C' .Similarly, check if any instance variable is a (C+ object with a non-trivial destructor, and if so, synthesize a special CW(C` -(void) .cxx_destruct (C' method which runs all such default destructors, in reverse order. The CW(C` -(id) .cxx_construct (C' and CW(C` -(void) .cxx_destruct (C' methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The CW(C` -(id) .cxx_construct (C' methods are invoked by the runtime immediately after a new object instance is allocated; the CW(C` -(void) .cxx_destruct (C' methods are invoked immediately before the runtime deallocates an object instance. As of this writing, only the NeXT runtime on Mac OSX 10.4 and later has support for invoking the CW(C` -(id) .cxx_construct (C' and CW(C` -(void) .cxx_destruct (C' methods.

" -fobjc -direct -dispatch "4 Item "-fobjc-direct-dispatch" Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page.

" -fobjc -exceptions "4 Item "-fobjc-exceptions" Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by (C+. This option is required to use the Objective-C keywords CW@try , CW@throw , CW@catch , CW@finally and CW@synchronized .This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OSX 10.2 and earlier).

" -fobjc -gc "4 Item "-fobjc-gc" Enable garbage collection ( GC)in Objective-C and Objective -(C+ programs. This option is only available with the NeXT runtime; the GNUruntime has a different garbage collection implementation that does not require special compiler flags.

" -fobjc -nilcheck "4 Item "-fobjc-nilcheck" For the NeXT runtime with version 2 of the ABI,check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using -fno -objc -nilcheck .Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNUruntime, or an older version of the NeXT runtime ABI,is used.

" -fobjc -std=objc1 "4 Item "-fobjc-std=objc1" Conform to the language syntax of Objective-C 1.0, the language recognized by GCC4.0. This only affects the Objective-C additions to the C/ (C+ language; it does not affect conformance to C/ (C+ standards, which is controlled by the separate C/ (C+ dialect option flags. When this option is used with the Objective-C or Objective -(C+ compiler, any Objective-C syntax that is not recognized by GCC4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of GCC.

" -freplace -objc -classes "4 Item "-freplace-objc-classes" Emit a special marker instructing ld (1) not to statically link in the resulting object file, and allow dyld (1) to load it in at run time instead. This is used in conjunction with the Fix-and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OSX 10.3 and later.

" -fzero -link "4 Item "-fzero-link" When compiling for the NeXT runtime, the compiler ordinarily replaces calls to CW(C`objc_getClass("...") (C' (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the -fzero -link flag suppresses this behavior and causes calls to CW(C`objc_getClass("...") (C' to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The GNUruntime currently always retains calls to CW(C`objc_get_class("...") (C' regardless of command-line options.

" -fno -local -ivars "4 Item "-fno-local-ivars" By default instance variables in Objective-C can be accessed as if they were local variables from within the methods of the class they're declared in. This can lead to shadowing between instance variables and other variables declared either locally inside a class method or globally with the same name. Specifying the -fno -local -ivars flag disables this behavior thus avoiding variable shadowing issues.

" -fivar -visibility= [ public | protected | private | package ]"4 Item "-fivar-visibility=[public|protected|private|package]" Set the default instance variable visibility to the specified option so that instance variables declared outside the scope of any access modifier directives default to the specified visibility.

" -gen -decls "4 Item "-gen-decls" Dump interface declarations for all classes seen in the source file to a file named sourcename .decl .

" -Wassign -intercept (Objective-C and Objective -(C+ only)" 4 Item "-Wassign-intercept (Objective-C and Objective- only)" Warn whenever an Objective-C assignment is being intercepted by the garbage collector.

" -Wno -protocol (Objective-C and Objective -(C+ only)" 4 Item "-Wno-protocol (Objective-C and Objective- only)" If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the -Wno -protocol option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them.

" -Wselector (Objective-C and Objective -(C+ only)" 4 Item "-Wselector (Objective-C and Objective- only)" Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed for each selector appearing in a CW(C`@selector(...) (C' expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the -fsyntax -only option is being used.

" -Wstrict -selector -match (Objective-C and Objective -(C+ only)" 4 Item "-Wstrict-selector-match (Objective-C and Objective- only)" Warn if multiple methods with differing argument and/or return types are found for a given selector when attempting to send a message using this selector to a receiver of type CW(C`id (C' or CW(C`Class (C' .When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment.

" -Wundeclared -selector (Objective-C and Objective -(C+ only)" 4 Item "-Wundeclared-selector (Objective-C and Objective- only)" Warn if a CW(C`@selector(...) (C' expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the CW(C`@selector(...) (C' expression, either explicitly in an CW@interface or CW@protocol declaration, or implicitly in an CW@implementation section. This option always performs its checks as soon as a CW(C`@selector(...) (C' expression is found, while -Wselector only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used.

" -print -objc -runtime -info "4 Item "-print-objc-runtime-info" Generate C header describing the largest structure that is passed by value, if any.

Options to Control Diagnostic Messages Formatting

Subsection "Options to Control Diagnostic Messages Formatting" Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g. how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options.

" -fmessage -length= n "4 Item "-fmessage-length=n" Try to format error messages so that they fit on lines of about n characters. If n is zero, then no line-wrapping is done; each error message appears on a single line. This is the default for all front ends. Note -this option also affects the display of the #error and #warning pre-processor directives, and the deprecated function/type/variable attribute. It does not however affect the pragmaGCCwarning and pragmaGCCerror pragmas.

" -fdiagnostics -show -location=once "4 Item "-fdiagnostics-show-location=once" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information once ;that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior.

" -fdiagnostics -show -location=every -line "4 Item "-fdiagnostics-show-location=every-line" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line.

" -fdiagnostics -color[= WHEN ] "4 Item "-fdiagnostics-color[=WHEN]" 0

" -fno -diagnostics -color "4 Item "-fno-diagnostics-color" Use color in diagnostics. WHEN is never , always , or auto .The default depends on how the compiler has been configured, it can be any of the above WHEN options or also never if GCC_COLORS environment variable isn't present in the environment, and auto otherwise. auto means to use color only when the standard error is a terminal. The forms -fdiagnostics -color and -fno -diagnostics -color are aliases for -fdiagnostics -color=always and -fdiagnostics -color=never ,respectively. The colors are defined by the environment variable GCC_COLORS . Its value is a colon-separated list of capabilities and Select Graphic Rendition ( SGR)substrings. SGRcommands are interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include 1 for bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to 37 for foreground colors, 90 to 97 for 16 -color mode foreground colors, 38;5;0 to 38;5;255 for 88 -color and 256 -color modes foreground colors, 49 for default background color, 40 to 47 for background colors, 100 to 107 for 16 -color mode background colors, and 48;5;0 to 48;5;255 for 88 -color and 256 -color modes background colors. The default GCC_COLORS is 4 error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01: \ quote=01:fixit -insert=32:fixit -delete=31: \ diff -filename=01:diff -hunk=32:diff -delete=31:diff -insert=32: \ type -diff=01;32 where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan, 32 is green, 34 is blue, 01 is bold, and 31 is red. Setting GCC_COLORS to the empty string disables colors. Supported capabilities are as follows. Item "error=" SGRsubstring for error: markers. Item "warning=" SGRsubstring for warning: markers. Item "note=" SGRsubstring for note: markers. Item "range1=" SGRsubstring for first additional range. Item "range2=" SGRsubstring for second additional range. Item "locus=" SGRsubstring for location information, file:line or file:line:column etc. Item "quote=" SGRsubstring for information printed within quotes. Item "fixit-insert=" SGRsubstring for fix-it hints suggesting text to be inserted or replaced. Item "fixit-delete=" SGRsubstring for fix-it hints suggesting text to be deleted. Item "diff-filename=" SGRsubstring for filename headers within generated patches. Item "diff-hunk=" SGRsubstring for the starts of hunks within generated patches. Item "diff-delete=" SGRsubstring for deleted lines within generated patches. Item "diff-insert=" SGRsubstring for inserted lines within generated patches. Item "type-diff=" SGRsubstring for highlighting mismatching types within template arguments in the (C+ frontend.

" -fno -diagnostics -show -option "4 Item "-fno-diagnostics-show-option" By default, each diagnostic emitted includes text indicating the command-line option that directly controls the diagnostic (if such an option is known to the diagnostic machinery). Specifying the -fno -diagnostics -show -option flag suppresses that behavior.

" -fno -diagnostics -show -caret "4 Item "-fno-diagnostics-show-caret" By default, each diagnostic emitted includes the original source line and a caret ^ indicating the column. This option suppresses this information. The source line is truncated to n characters, if the -fmessage -length=n option is given. When the output is done to the terminal, the width is limited to the width given by the COLUMNS environment variable or, if not set, to the terminal width.

" -fno -diagnostics -show -labels "4 Item "-fno-diagnostics-show-labels" By default, when printing source code (via -fdiagnostics -show -caret ), diagnostics can label ranges of source code with pertinent information, such as the types of expressions: 4 printf ("foo %s bar", long_i + long_j); ~^ ~~~~~~~~~~~~~~~ | | char * long int This option suppresses the printing of these labels (in the example above, the vertical bars and the (L"char * (R" and (L"long int (R" text).

" -fno -diagnostics -show -line -numbers "4 Item "-fno-diagnostics-show-line-numbers" By default, when printing source code (via -fdiagnostics -show -caret ), a left margin is printed, showing line numbers. This option suppresses this left margin.

" -fdiagnostics -minimum -margin -width= width "4 Item "-fdiagnostics-minimum-margin-width=width" This option controls the minimum width of the left margin printed by -fdiagnostics -show -line -numbers .It defaults to 6.

" -fdiagnostics -parseable -fixits "4 Item "-fdiagnostics-parseable-fixits" Emit fix-it hints in a machine-parseable format, suitable for consumption by IDEs. For each fix-it, a line will be printed after the relevant diagnostic, starting with the string (L"fix-it: (R". For example: 1 fix -it:"test.c":{45:3 -45:21}:"gtk_widget_show_all" The location is expressed as a half-open range, expressed as a count of bytes, starting at byte 1 for the initial column. In the above example, bytes 3 through 20 of line 45 of (L"test.c (R" are to be replaced with the given string: 5 00000000011111111112222222222 12345678901234567890123456789 gtk_widget_showall (dlg); ^^^^^^^^^^^^^^^^^^ gtk_widget_show_all The filename and replacement string escape backslash as (L" \ \ (R", tab as (L" \ t (R", newline as (L" \ n (R", double quotes as (L" \ (R" (L", non-printable characters as octal (e.g. vertical tab as (R" \ 013"). An empty replacement string indicates that the given range is to be removed. An empty range (e.g. (L"45:3 -45:3 (R") indicates that the string is to be inserted at the given position.

" -fdiagnostics -generate -patch "4 Item "-fdiagnostics-generate-patch" Print fix-it hints to stderr in unified diff format, after any diagnostics are printed. For example: 3 ---test.c +++ test.c @ -42,5 +42,5 @ void show_cb(GtkDialog *dlg) { -gtk_widget_showall(dlg); + gtk_widget_show_all(dlg); } The diff may or may not be colorized, following the same rules as for diagnostics (see -fdiagnostics -color ).

" -fdiagnostics -show -template -tree "4 Item "-fdiagnostics-show-template-tree" In the (C+ frontend, when printing diagnostics showing mismatching template types, such as: 2 could not convert (Aqstd::map<int, std::vector<double> >() (Aq from (Aqmap<[...],vector<double>> (Aq to (Aqmap<[...],vector<float>> the -fdiagnostics -show -template -tree flag enables printing a tree-like structure showing the common and differing parts of the types, such as: 4 map< [...], vector< [double != float]>> The parts that differ are highlighted with color ( (L"double (R" and (L"float (R" in this case).

" -fno -elide -type "4 Item "-fno-elide-type" By default when the (C+ frontend prints diagnostics showing mismatching template types, common parts of the types are printed as (L"[...] (R" to simplify the error message. For example: 2 could not convert (Aqstd::map<int, std::vector<double> >() (Aq from (Aqmap<[...],vector<double>> (Aq to (Aqmap<[...],vector<float>> Specifying the -fno -elide -type flag suppresses that behavior. This flag also affects the output of the -fdiagnostics -show -template -tree flag.

" -fno -show -column "4 Item "-fno-show-column" Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column numbers, such as dejagnu .

" -fdiagnostics -format= FORMAT "4 Item "-fdiagnostics-format=FORMAT" Select a different format for printing diagnostics. FORMAT is text or json . The default is text . The json format consists of a top-level JSONarray containing JSON objects representing the diagnostics. The JSONis emitted as one line, without formatting; the examples below have been formatted for clarity. Diagnostics can have child diagnostics. For example, this error and note: 8 misleading -indentation.c:15:3: warning: this (Aqif (Aq clause does not guard... [ -Wmisleading -indentation] 15 | if (flag) | ^~ misleading -indentation.c:17:5: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the (Aqif (Aq 17 | y = 2; | ^ might be printed in JSONform (after formatting) like this: 10 [ { "kind": "warning", "locations": [ { "caret": { "column": 3, "file": "misleading -indentation.c", "line": 15 }, "finish": { "column": 4, "file": "misleading -indentation.c", "line": 15 } } ], "message": "this \ u2018if \ u2019 clause does not guard...", "option": " -Wmisleading -indentation", "children": [ { "kind": "note", "locations": [ { "caret": { "column": 5, "file": "misleading -indentation.c", "line": 17 } } ], "message": "...this statement, but the latter is ..." } ] }, ... ] where the CW(C`note (C' is a child of the CW(C`warning (C' . A diagnostic has a CW(C`kind (C' .If this is CW(C`warning (C' ,then there is an CW(C`option (C' key describing the command-line option controlling the warning. A diagnostic can contain zero or more locations. Each location has up to three positions within it: a CW(C`caret (C' position and optional CW(C`start (C' and CW(C`finish (C' positions. A location can also have an optional CW(C`label (C' string. For example, this error: 7 bad -binary -ops.c:64:23: error: invalid operands to binary + (have (AqS (Aq {aka (Aqstruct s (Aq} and (AqT (Aq {aka (Aqstruct t (Aq}) 64 | return callee_4a () + callee_4b (); | ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~ | | | | | T {aka struct t} | S {aka struct s} has three locations. Its primary location is at the (L"+ (R" token at column 23. It has two secondary locations, describing the left and right-hand sides of the expression, which have labels. It might be printed in JSONform as: 10 { "children": [], "kind": "error", "locations": [ { "caret": { "column": 23, "file": "bad -binary -ops.c", "line": 64 } }, { "caret": { "column": 10, "file": "bad -binary -ops.c", "line": 64 }, "finish": { "column": 21, "file": "bad -binary -ops.c", "line": 64 }, "label": "S {aka struct s}" }, { "caret": { "column": 25, "file": "bad -binary -ops.c", "line": 64 }, "finish": { "column": 36, "file": "bad -binary -ops.c", "line": 64 }, "label": "T {aka struct t}" } ], "message": "invalid operands to binary + ..." } If a diagnostic contains fix-it hints, it has a CW(C`fixits (C' array, consisting of half-open intervals, similar to the output of -fdiagnostics -parseable -fixits .For example, this diagnostic with a replacement fix-it hint: 5 demo.c:8:15: error: (Aqstruct s (Aq has no member named (Aqcolour (Aq; did you mean (Aqcolor (Aq? 8 | return ptr ->colour; | ^~~~~~ | color might be printed in JSONform as: 10 { "children": [], "fixits": [ { "next": { "column": 21, "file": "demo.c", "line": 8 }, "start": { "column": 15, "file": "demo.c", "line": 8 }, "string": "color" } ], "kind": "error", "locations": [ { "caret": { "column": 15, "file": "demo.c", "line": 8 }, "finish": { "column": 20, "file": "demo.c", "line": 8 } } ], "message": " \ u2018struct s \ u2019 has no member named ..." } where the fix-it hint suggests replacing the text from CW(C`start (C' up to but not including CW(C`next (C' with CW(C`string (C' 'svalue. Deletions are expressed via an empty value for CW(C`string (C' ,insertions by having CW(C`start (C' equal CW(C`next (C' .

Options to Request or Suppress Warnings

Subsection "Options to Request or Suppress Warnings" Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error.

The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by GCC.

" -fsyntax -only "4 Item "-fsyntax-only" Check the code for syntax errors, but don't do anything beyond that.

" -fmax -errors= n "4 Item "-fmax-errors=n" Limits the maximum number of error messages to n ,at which point GCCbails out rather than attempting to continue processing the source code. If n is 0 (the default), there is no limit on the number of error messages produced. If -Wfatal -errors is also specified, then -Wfatal -errors takes precedence over this option.

" -w "4 Item "-w" Inhibit all warning messages.

" -Werror "4 Item "-Werror" Make all warnings into errors.

" -Werror= "4 Item "-Werror=" Make the specified warning into an error. The specifier for a warning is appended; for example -Werror=switch turns the warnings controlled by -Wswitch into errors. This switch takes a negative form, to be used to negate -Werror for specific warnings; for example -Wno -error=switch makes -Wswitch warnings not be errors, even when -Werror is in effect. The warning message for each controllable warning includes the option that controls the warning. That option can then be used with -Werror= and -Wno -error= as described above. (Printing of the option in the warning message can be disabled using the -fno -diagnostics -show -option flag.) Note that specifying -Werror= foo automatically implies -W foo .However, -Wno -error= foo does not imply anything.

" -Wfatal -errors "4 Item "-Wfatal-errors" This option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages.

You can request many specific warnings with options beginning with -W ,for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning -Wno - to turn off warnings; for example, -Wno -implicit .This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to (C+ Dialect Options and Objective-Cand Objective -(C+ Dialect Options .

Some options, such as -Wall and -Wextra ,turn on other options, such as -Wunused ,which may turn on further options, such as -Wunused -value .The combined effect of positive and negative forms is that more specific options have priority over less specific ones, independently of their position in the command-line. For options of the same specificity, the last one takes effect. Options enabled or disabled via pragmas take effect as if they appeared at the end of the command-line.

When an unrecognized warning option is requested (e.g., -Wunknown -warning ),GCCemits a diagnostic stating that the option is not recognized. However, if the -Wno - form is used, the behavior is slightly different: no diagnostic is produced for -Wno -unknown -warning unless other diagnostics are being produced. This allows the use of new -Wno - options with old compilers, but if something goes wrong, the compiler warns that an unrecognized option is present.

" -Wpedantic "4 Item "-Wpedantic" 0

" -pedantic "4 Item "-pedantic" Issue all the warnings demanded by strict ISOC and ISO(C+ ; reject all programs that use forbidden extensions, and some other programs that do not follow ISOC and ISO(C+. For ISOC, follows the version of the ISOC standard specified by any -std option used. Valid ISOC and ISO(C+ programs should compile properly with or without this option (though a rare few require -ansi or a -std option specifying the required version of ISOC ).However, without this option, certain GNUextensions and traditional C and (C+ features are supported as well. With this option, they are rejected. -Wpedantic does not cause warning messages for use of the alternate keywords whose names begin and end with __ .Pedantic warnings are also disabled in the expression that follows CW(C`_ _extension_ _ (C' .However, only system header files should use these escape routes; application programs should avoid them. Some users try to use -Wpedantic to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all ---only those for which ISOC requires a diagnostic, and some others for which diagnostics have been added. A feature to report any failure to conform to ISOC might be useful in some instances, but would require considerable additional work and would be quite different from -Wpedantic .We don't have plans to support such a feature in the near future. Where the standard specified with -std represents a GNU extended dialect of C, such as gnu90 or gnu99 ,there is a corresponding basestandard ,the version of ISOC on which the GNU extended dialect is based. Warnings from -Wpedantic are given where they are required by the base standard. (It does not make sense for such warnings to be given only for features not in the specified GNU C dialect, since by definition the GNUdialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.)

" -pedantic -errors "4 Item "-pedantic-errors" Give an error whenever the basestandard (see -Wpedantic ) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in some other cases that do not prevent compilation of programs that are valid according to the standard. This is not equivalent to -Werror=pedantic ,since there are errors enabled by this option and not enabled by the latter and vice versa.

" -Wall "4 Item "-Wall" This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in (C+ Dialect Options and Objective-Cand Objective -(C+ Dialect Options . -Wall turns on the following warning flags: -Waddress -Warray -bounds=1 (only with -O2 ) -Wbool -compare -Wbool -operation -Wc++11 -compat -Wc++14 -compat -Wcatch -value ( (C+ and Objective -(C+ only) -Wchar -subscripts -Wcomment -Wduplicate -decl -specifier (C and Objective-C only) -Wenum -compare (in C/ObjC; this is on by default in (C+) -Wformat -Wint -in -bool -context -Wimplicit (C and Objective-C only) -Wimplicit -int (C and Objective-C only) -Wimplicit -function -declaration (C and Objective-C only) -Winit -self (only for (C+) -Wlogical -not -parentheses -Wmain (only for C/ObjC and unless -ffreestanding ) -Wmaybe -uninitialized -Wmemset -elt -size -Wmemset -transposed -args -Wmisleading -indentation (only for C/ (C+) -Wmissing -attributes -Wmissing -braces (only for C/ObjC) -Wmultistatement -macros -Wnarrowing (only for (C+) -Wnonnull -Wnonnull -compare -Wopenmp -simd -Wparentheses -Wpessimizing -move (only for (C+) -Wpointer -sign -Wreorder -Wrestrict -Wreturn -type -Wsequence -point -Wsign -compare (only in (C+) -Wsizeof -pointer -div -Wsizeof -pointer -memaccess -Wstrict -aliasing -Wstrict -overflow=1 -Wswitch -Wtautological -compare -Wtrigraphs -Wuninitialized -Wunknown -pragmas -Wunused -function -Wunused -label -Wunused -value -Wunused -variable -Wvolatile -register -var Note that some warning flags are not implied by -Wall .Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually.

" -Wextra "4 Item "-Wextra" This enables some extra warning flags that are not enabled by -Wall .(This option used to be called -W .The older name is still supported, but the newer name is more descriptive.) -Wclobbered -Wcast -function -type -Wdeprecated -copy ( (C+ only) -Wempty -body -Wignored -qualifiers -Wimplicit -fallthrough=3 -Wmissing -field -initializers -Wmissing -parameter -type (C only) -Wold -style -declaration (C only) -Woverride -init -Wsign -compare (C only) -Wredundant -move (only for (C+) -Wtype -limits -Wuninitialized -Wshift -negative -value (in (C+03 and in C99 and newer) -Wunused -parameter (only with -Wunused or -Wall ) -Wunused -but -set -parameter (only with -Wunused or -Wall ) The option -Wextra also prints warning messages for the following cases:

"*" 4 A pointer is compared against integer zero with CW(C`< (C' , CW(C`<= (C' , CW(C`> (C' ,or CW(C`>= (C' .

"*" 4 ( (C+ only) An enumerator and a non-enumerator both appear in a conditional expression.

"*" 4 ( (C+ only) Ambiguous virtual bases.

"*" 4 ( (C+ only) Subscripting an array that has been declared CW(C`register (C' .

"*" 4 ( (C+ only) Taking the address of a variable that has been declared CW(C`register (C' .

"*" 4 ( (C+ only) A base class is not initialized in the copy constructor of a derived class.

" -Wchar -subscripts "4 Item "-Wchar-subscripts" Warn if an array subscript has type CW(C`char (C' .This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by -Wall .

" -Wno -coverage -mismatch "4 Item "-Wno-coverage-mismatch" Warn if feedback profiles do not match when using the -fprofile -use option. If a source file is changed between compiling with -fprofile -generate and with -fprofile -use ,the files with the profile feedback can fail to match the source file and GCCcannot use the profile feedback information. By default, this warning is enabled and is treated as an error. -Wno -coverage -mismatch can be used to disable the warning or -Wno -error=coverage -mismatch can be used to disable the error. Disabling the error for this warning can result in poorly optimized code and is useful only in the case of very minor changes such as bug fixes to an existing code-base. Completely disabling the warning is not recommended.

" -Wno -cpp "4 Item "-Wno-cpp" (C, Objective-C, (C+, Objective -(C+ and Fortran only) Suppress warning messages emitted by CW(C`#warning (C' directives.

" -Wdouble -promotion (C, (C+, Objective-C and Objective -(C+ only)" 4 Item "-Wdouble-promotion (C, , Objective-C and Objective- only)" Give a warning when a value of type CW(C`float (C' is implicitly promoted to CW(C`double (C' .CPUs with a 32 -bit (L"single-precision (R" floating-point unit implement CW(C`float (C' in hardware, but emulate CW(C`double (C' in software. On such a machine, doing computations using CW(C`double (C' values is much more expensive because of the overhead required for software emulation. It is easy to accidentally do computations with CW(C`double (C' because floating-point literals are implicitly of type CW(C`double (C' .For example, in: 4 float area(float radius) { return 3.14159 * radius * radius; } the compiler performs the entire computation with CW(C`double (C' because the floating-point literal is a CW(C`double (C' .

" -Wduplicate -decl -specifier (C and Objective-C only)" 4 Item "-Wduplicate-decl-specifier (C and Objective-C only)" Warn if a declaration has duplicate CW(C`const (C' , CW(C`volatile (C' , CW(C`restrict (C' or CW(C`_Atomic (C' specifier. This warning is enabled by -Wall .

" -Wformat "4 Item "-Wformat" 0

" -Wformat= n "4 Item "-Wformat=n" Check calls to CW(C`printf (C' and CW(C`scanf (C' ,etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes, in the CW(C`printf (C' , CW(C`scanf (C' , CW(C`strftime (C' and CW(C`strfmon (C' (an X/Open extension, not in the C standard) families (or other target-specific families). Which functions are checked without format attributes having been specified depends on the standard version selected, and such checks of functions without the attribute specified are disabled by -ffreestanding or -fno -builtin . The formats are checked against the format features supported by GNU libc version 2.2. These include all ISOC90 and C99 features, as well as features from the Single Unix Specification and some BSDand GNU extensions. Other library implementations may not support all these features; GCCdoes not support warning about features that go beyond a particular library's limitations. However, if -Wpedantic is used with -Wformat ,warnings are given about format features not in the selected standard version (but not for CW(C`strfmon (C' formats, since those are not in any version of the C standard).

" -Wformat=1 "4 Item "-Wformat=1" 0

" -Wformat "4 Item "-Wformat" Option -Wformat is equivalent to -Wformat=1 ,and -Wno -format is equivalent to -Wformat=0 .Since -Wformat also checks for null format arguments for several functions, -Wformat also implies -Wnonnull .Some aspects of this level of format checking can be disabled by the options: -Wno -format -contains -nul , -Wno -format -extra -args ,and -Wno -format -zero -length . -Wformat is enabled by -Wall .

" -Wno -format -contains -nul "4 Item "-Wno-format-contains-nul" If -Wformat is specified, do not warn about format strings that contain NULbytes.

" -Wno -format -extra -args "4 Item "-Wno-format-extra-args" If -Wformat is specified, do not warn about excess arguments to a CW(C`printf (C' or CW(C`scanf (C' format function. The C standard specifies that such arguments are ignored. Where the unused arguments lie between used arguments that are specified with $ operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to CW(C`va_arg (C' to skip the unused arguments. However, in the case of CW(C`scanf (C' formats, this option suppresses the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed.

" -Wformat -overflow "4 Item "-Wformat-overflow" 0

" -Wformat -overflow= level "4 Item "-Wformat-overflow=level" Warn about calls to formatted input/output functions such as CW(C`sprintf (C' and CW(C`vsprintf (C' that might overflow the destination buffer. When the exact number of bytes written by a format directive cannot be determined at compile-time it is estimated based on heuristics that depend on the level argument and on optimization. While enabling optimization will in most cases improve the accuracy of the warning, it may also result in false positives.

" -Wformat -overflow "4 Item "-Wformat-overflow" 0

" -Wformat -overflow=1 "4 Item "-Wformat-overflow=1" Level 1 of -Wformat -overflow enabled by -Wformat employs a conservative approach that warns only about calls that most likely overflow the buffer. At this level, numeric arguments to format directives with unknown values are assumed to have the value of one, and strings of unknown length to be empty. Numeric arguments that are known to be bounded to a subrange of their type, or string arguments whose output is bounded either by their directive's precision or by a finite set of string literals, are assumed to take on the value within the range that results in the most bytes on output. For example, the call to CW(C`sprintf (C' below is diagnosed because even with both a and b equal to zero, the terminating NULcharacter ( CW(Aq \ 0 (Aq )appended by the function to the destination buffer will be written past its end. Increasing the size of the buffer by a single byte is sufficient to avoid the warning, though it may not be sufficient to avoid the overflow. 5 void f (int a, int b) { char buf [13]; sprintf (buf, "a = %i, b = %i \ n", a, b); }

" -Wformat -overflow=2 "4 Item "-Wformat-overflow=2" Level 2 warns also about calls that might overflow the destination buffer given an argument of sufficient length or magnitude. At level 2 ,unknown numeric arguments are assumed to have the minimum representable value for signed types with a precision greater than 1, and the maximum representable value otherwise. Unknown string arguments whose length cannot be assumed to be bounded either by the directive's precision, or by a finite set of string literals they may evaluate to, or the character array they may point to, are assumed to be 1 character long. At level 2 ,the call in the example above is again diagnosed, but this time because with a equal to a 32 -bit CW(C`INT_MIN (C' the first CW%i directive will write some of its digits beyond the end of the destination buffer. To make the call safe regardless of the values of the two variables, the size of the destination buffer must be increased to at least 34 bytes. GCCincludes the minimum size of the buffer in an informational note following the warning. An alternative to increasing the size of the destination buffer is to constrain the range of formatted values. The maximum length of string arguments can be bounded by specifying the precision in the format directive. When numeric arguments of format directives can be assumed to be bounded by less than the precision of their type, choosing an appropriate length modifier to the format specifier will reduce the required buffer size. For example, if a and b in the example above can be assumed to be within the precision of the CW(C`short int (C' type then using either the CW%hi format directive or casting the argument to CW(C`short (C' reduces the maximum required size of the buffer to 24 bytes. 5 void f (int a, int b) { char buf [23]; sprintf (buf, "a = %hi, b = %i \ n", a, (short)b); }

" -Wno -format -zero -length "4 Item "-Wno-format-zero-length" If -Wformat is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed.

" -Wformat=2 "4 Item "-Wformat=2" Enable -Wformat plus additional format checks. Currently equivalent to -Wformat -Wformat -nonliteral -Wformat -security -Wformat -y2k .

" -Wformat -nonliteral "4 Item "-Wformat-nonliteral" If -Wformat is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a CW(C`va_list (C' .

" -Wformat -security "4 Item "-Wformat-security" If -Wformat is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to CW(C`printf (C' and CW(C`scanf (C' functions where the format string is not a string literal and there are no format arguments, as in CW(C`printf (foo); (C' .This may be a security hole if the format string came from untrusted input and contains CB%n .(This is currently a subset of what -Wformat -nonliteral warns about, but in future warnings may be added to -Wformat -security that are not included in -Wformat -nonliteral .)

" -Wformat -signedness "4 Item "-Wformat-signedness" If -Wformat is specified, also warn if the format string requires an unsigned argument and the argument is signed and vice versa.

" -Wformat -truncation "4 Item "-Wformat-truncation" 0

" -Wformat -truncation= level "4 Item "-Wformat-truncation=level" Warn about calls to formatted input/output functions such as CW(C`snprintf (C' and CW(C`vsnprintf (C' that might result in output truncation. When the exact number of bytes written by a format directive cannot be determined at compile-time it is estimated based on heuristics that depend on the level argument and on optimization. While enabling optimization will in most cases improve the accuracy of the warning, it may also result in false positives. Except as noted otherwise, the option uses the same logic -Wformat -overflow .

" -Wformat -truncation "4 Item "-Wformat-truncation" 0

" -Wformat -truncation=1 "4 Item "-Wformat-truncation=1" Level 1 of -Wformat -truncation enabled by -Wformat employs a conservative approach that warns only about calls to bounded functions whose return value is unused and that will most likely result in output truncation.

" -Wformat -truncation=2 "4 Item "-Wformat-truncation=2" Level 2 warns also about calls to bounded functions whose return value is used and that might result in truncation given an argument of sufficient length or magnitude.

" -Wformat -y2k "4 Item "-Wformat-y2k" If -Wformat is specified, also warn about CW(C`strftime (C' formats that may yield only a two-digit year.

" -Wnonnull "4 Item "-Wnonnull" Warn about passing a null pointer for arguments marked as requiring a non-null value by the CW(C`nonnull (C' function attribute. -Wnonnull is included in -Wall and -Wformat .It can be disabled with the -Wno -nonnull option.

" -Wnonnull -compare "4 Item "-Wnonnull-compare" Warn when comparing an argument marked with the CW(C`nonnull (C' function attribute against null inside the function. -Wnonnull -compare is included in -Wall .It can be disabled with the -Wno -nonnull -compare option.

" -Wnull -dereference "4 Item "-Wnull-dereference" Warn if the compiler detects paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. This option is only active when -fdelete -null -pointer -checks is active, which is enabled by optimizations in most targets. The precision of the warnings depends on the optimization options used.

" -Winit -self (C, (C+, Objective-C and Objective -(C+ only)" 4 Item "-Winit-self (C, , Objective-C and Objective- only)" Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the -Wuninitialized option. For example, GCCwarns about CW(C`i (C' being uninitialized in the following snippet only when -Winit -self has been specified: 5 int f() { int i = i; return i; } This warning is enabled by -Wall in (C+.

" -Wimplicit -int (C and Objective-C only)" 4 Item "-Wimplicit-int (C and Objective-C only)" Warn when a declaration does not specify a type. This warning is enabled by -Wall .

" -Wimplicit -function -declaration (C and Objective-C only)" 4 Item "-Wimplicit-function-declaration (C and Objective-C only)" Give a warning whenever a function is used before being declared. In C99 mode ( -std=c99 or -std=gnu99 ),this warning is enabled by default and it is made into an error by -pedantic -errors .This warning is also enabled by -Wall .

" -Wimplicit (C and Objective-C only)" 4 Item "-Wimplicit (C and Objective-C only)" Same as -Wimplicit -int and -Wimplicit -function -declaration . This warning is enabled by -Wall .

" -Wimplicit -fallthrough "4 Item "-Wimplicit-fallthrough" -Wimplicit -fallthrough is the same as -Wimplicit -fallthrough=3 and -Wno -implicit -fallthrough is the same as -Wimplicit -fallthrough=0 .

" -Wimplicit -fallthrough= n "4 Item "-Wimplicit-fallthrough=n" Warn when a switch case falls through. For example: 11 switch (cond) { case 1: a = 1; break; case 2: a = 2; case 3: a = 3; break; } This warning does not warn when the last statement of a case cannot fall through, e.g. when there is a return statement or a call to function declared with the noreturn attribute. -Wimplicit -fallthrough= also takes into account control flow statements, such as ifs, and only warns when appropriate. E.g. 10 switch (cond) { case 1: if (i > 3) { bar (5); break; } else if (i < 1) { bar (0); } else return; default: ... } Since there are occasions where a switch case fall through is desirable, GCCprovides an attribute, CW(C`_ _attribute_ _ ((fallthrough)) (C' ,that is to be used along with a null statement to suppress this warning that would normally occur: 8 switch (cond) { case 1: bar (0); _ _attribute_ _ ((fallthrough)); default: ... } (C+17 provides a standard way to suppress the -Wimplicit -fallthrough warning using CW(C`[[fallthrough]]; (C' instead of the GNUattribute. In (C+11 or (C+14 users can use CW(C`[[gnu::fallthrough]]; (C' ,which is a GNUextension. Instead of these attributes, it is also possible to add a fallthrough comment to silence the warning. The whole body of the C or (C+ style comment should match the given regular expressions listed below. The option argument n specifies what kind of comments are accepted:

"*< -Wimplicit -fallthrough=0 disables the warning altogether.>" 4 Item "*<-Wimplicit-fallthrough=0 disables the warning altogether.>" 0 Item "*<-Wimplicit-fallthrough=1 matches .* regular>" expression, any comment is used as fallthrough comment.

"*< -Wimplicit -fallthrough=2 case insensitively matches>" 4 Item "*<-Wimplicit-fallthrough=2 case insensitively matches>" CW(C`.*falls?[ \ t -]*thr(ough|u).* (C' regular expression.

"*< -Wimplicit -fallthrough=3 case sensitively matches one of the>" 4 Item "*<-Wimplicit-fallthrough=3 case sensitively matches one of the>" following regular expressions: Item "*<-fallthrough>" 0 Item "*<@fallthrough@>" Item "*<lint -fallthrough[ t]*>" Item "*<[ t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S | |-)?THR(OUGH|U)[ t.!]*(-[^nr]*)?>" Item "*<[ t.!]*(Else,? |Intentional(ly)? )?Fall((s | |-)[Tt]|t)hr(ough|u)[ t.!]*(-[^nr]*)?>" Item "*<[ t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s | |-)?thr(ough|u)[ t.!]*(-[^nr]*)?>"

"*< -Wimplicit -fallthrough=4 case sensitively matches one of the>" 4 Item "*<-Wimplicit-fallthrough=4 case sensitively matches one of the>" following regular expressions: Item "*<-fallthrough>" 0 Item "*<@fallthrough@>" Item "*<lint -fallthrough[ t]*>" Item "*<[ t]*FALLTHR(OUGH|U)[ t]*>"

"*< -Wimplicit -fallthrough=5 doesn't recognize any comments as>" 4 Item "*<-Wimplicit-fallthrough=5 doesn't recognize any comments as>" fallthrough comments, only attributes disable the warning. The comment needs to be followed after optional whitespace and other comments by CW(C`case (C' or CW(C`default (C' keywords or by a user label that precedes some CW(C`case (C' or CW(C`default (C' label. 8 switch (cond) { case 1: bar (0); /* FALLTHRU */ default: ... } The -Wimplicit -fallthrough=3 warning is enabled by -Wextra .

" -Wif -not -aligned (C, (C+, Objective-C and Objective -(C+ only)" 4 Item "-Wif-not-aligned (C, , Objective-C and Objective- only)" Control if warning triggered by the CW(C`warn_if_not_aligned (C' attribute should be issued. This is enabled by default. Use -Wno -if -not -aligned to disable it.

" -Wignored -qualifiers (C and (C+ only)" 4 Item "-Wignored-qualifiers (C and only)" Warn if the return type of a function has a type qualifier such as CW(C`const (C' .For ISOC such a type qualifier has no effect, since the value returned by a function is not an lvalue. For (C+, the warning is only emitted for scalar types or CW(C`void (C' . ISOC prohibits qualified CW(C`void (C' return types on function definitions, so such return types always receive a warning even without this option. This warning is also enabled by -Wextra .

" -Wignored -attributes (C and (C+ only)" 4 Item "-Wignored-attributes (C and only)" Warn when an attribute is ignored. This is different from the -Wattributes option in that it warns whenever the compiler decides to drop an attribute, not that the attribute is either unknown, used in a wrong place, etc. This warning is enabled by default.

" -Wmain "4 Item "-Wmain" Warn if the type of CW(C`main (C' is suspicious. CW(C`main (C' should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This warning is enabled by default in (C+ and is enabled by either -Wall or -Wpedantic .

" -Wmisleading -indentation (C and (C+ only)" 4 Item "-Wmisleading-indentation (C and only)" Warn when the indentation of the code does not reflect the block structure. Specifically, a warning is issued for CW(C`if (C' , CW(C`else (C' , CW(C`while (C' ,and CW(C`for (C' clauses with a guarded statement that does not use braces, followed by an unguarded statement with the same indentation. In the following example, the call to (L"bar (R" is misleadingly indented as if it were guarded by the (L"if (R" conditional. 3 if (some_condition ()) foo (); bar (); /* Gotcha: this is not guarded by the "if". */ In the case of mixed tabs and spaces, the warning uses the -ftabstop= option to determine if the statements line up (defaulting to 8). The warning is not issued for code involving multiline preprocessor logic such as the following example. 6 if (flagA) foo (0); #if SOME_CONDITION_THAT_DOES_NOT_HOLD if (flagB) #endif foo (1); The warning is not issued after a CW(C`#line (C' directive, since this typically indicates autogenerated code, and no assumptions can be made about the layout of the file that the directive references. This warning is enabled by -Wall in C and (C+.

" -Wmissing -attributes "4 Item "-Wmissing-attributes" Warn when a declaration of a function is missing one or more attributes that a related function is declared with and whose absence may adversely affect the correctness or efficiency of generated code. For example, the warning is issued for declarations of aliases that use attributes to specify less restrictive requirements than those of their targets. This typically represents a potential optimization opportunity. By contrast, the -Wattribute -alias=2 option controls warnings issued when the alias is more restrictive than the target, which could lead to incorrect code generation. Attributes considered include CW(C`alloc_align (C' , CW(C`alloc_size (C' , CW(C`cold (C' , CW(C`const (C' , CW(C`hot (C' , CW(C`leaf (C' , CW(C`malloc (C' , CW(C`nonnull (C' , CW(C`noreturn (C' , CW(C`nothrow (C' , CW(C`pure (C' , CW(C`returns_nonnull (C' ,and CW(C`returns_twice (C' . In (C+, the warning is issued when an explicit specialization of a primary template declared with attribute CW(C`alloc_align (C' , CW(C`alloc_size (C' , CW(C`assume_aligned (C' , CW(C`format (C' , CW(C`format_arg (C' , CW(C`malloc (C' , or CW(C`nonnull (C' is declared without it. Attributes CW(C`deprecated (C' , CW(C`error (C' ,and CW(C`warning (C' suppress the warning.. You can use the CW(C`copy (C' attribute to apply the same set of attributes to a declaration as that on another declaration without explicitly enumerating the attributes. This attribute can be applied to declarations of functions, variables, or types. -Wmissing -attributes is enabled by -Wall . For example, since the declaration of the primary function template below makes use of both attribute CW(C`malloc (C' and CW(C`alloc_size (C' the declaration of the explicit specialization of the template is diagnosed because it is missing one of the attributes. 3 template <class T> T* _ _attribute_ _ ((malloc, alloc_size (1))) allocate (size_t); template <> void* _ _attribute_ _ ((malloc)) // missing alloc_size allocate<void> (size_t);

" -Wmissing -braces "4 Item "-Wmissing-braces" Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for CW(C`a (C' is not fully bracketed, but that for CW(C`b (C' is fully bracketed. This warning is enabled by -Wall in C. 2 int a[2][2] = { 0, 1, 2, 3 }; int b[2][2] = { { 0, 1 }, { 2, 3 } }; This warning is enabled by -Wall .

" -Wmissing -include -dirs (C, (C+, Objective-C and Objective -(C+ only)" 4 Item "-Wmissing-include-dirs (C, , Objective-C and Objective- only)" Warn if a user-supplied include directory does not exist.

" -Wmissing -profile "4 Item "-Wmissing-profile" Warn if feedback profiles are missing when using the -fprofile -use option. This option diagnoses those cases where a new function or a new file is added to the user code between compiling with -fprofile -generate and with -fprofile -use ,without regenerating the profiles. In these cases, the profile feedback data files do not contain any profile feedback information for the newly added function or file respectively. Also, in the case when profile count data (.gcda) files are removed, GCCcannot use any profile feedback information. In all these cases, warnings are issued to inform the user that a profile generation step is due. -Wno -missing -profile can be used to disable the warning. Ignoring the warning can result in poorly optimized code. Completely disabling the warning is not recommended and should be done only when non-existent profile data is justified.

" -Wmultistatement -macros "4 Item "-Wmultistatement-macros" Warn about unsafe multiple statement macros that appear to be guarded by a clause such as CW(C`if (C' , CW(C`else (C' , CW(C`for (C' , CW(C`switch (C' ,or CW(C`while (C' ,in which only the first statement is actually guarded after the macro is expanded. For example: 3 #define DOIT x++; y++ if (c) DOIT; will increment CW(C`y (C' unconditionally, not just when CW(C`c (C' holds. The can usually be fixed by wrapping the macro in a do-while loop: 3 #define DOIT do { x++; y++; } while (0) if (c) DOIT; This warning is enabled by -Wall in C and (C+.

" -Wparentheses "4 Item "-Wparentheses" Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. Also warn if a comparison like CW(C`x<=y<=z (C' appears; this is equivalent to CW(C`(x<=y ? 1 : 0) <= z (C' ,which is a different interpretation from that of ordinary mathematical notation. Also warn for dangerous uses of the GNUextension to CW(C`?: (C' with omitted middle operand. When the condition in the CW(C`? (C' :operator is a boolean expression, the omitted value is always 1. Often programmers expect it to be a value computed inside the conditional expression instead. For (C+ this also warns for some cases of unnecessary parentheses in declarations, which can indicate an attempt at a function call instead of a declaration: 5 { // Declares a local variable called mymutex. std::unique_lock<std::mutex> (mymutex); // User meant std::unique_lock<std::mutex> lock (mymutex); } This warning is enabled by -Wall .

" -Wsequence -point "4 Item "-Wsequence-point" Warn about code that may have undefined semantics because of violations of sequence point rules in the C and (C+ standards. The C and (C+ standards define the order in which expressions in a C/ (C+ program are evaluated in terms of sequencepoints ,which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a CW(C`&& (C' , CW(C`|| (C' , CW(C`? : (C' or CW(C`, (C' (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and (C+ standards specify that (L"Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored. (R". If a program breaks these rules, the results on any particular implementation are entirely unpredictable. Examples of code with undefined behavior are CW(C`a = a++; (C' , CW(C`a[n] = b[n++] (C' and CW(C`a[i++] = i; (C' .Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. The (C+17 standard will define the order of evaluation of operands in more cases: in particular it requires that the right-hand side of an assignment be evaluated before the left-hand side, so the above examples are no longer undefined. But this warning will still warn about them, to help people avoid writing code that is undefined in C and earlier revisions of (C+. The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the GCCreadings page, at < http://gcc.gnu.org/readings.html >. This warning is enabled by -Wall for C and (C+.

" -Wno -return -local -addr "4 Item "-Wno-return-local-addr" Do not warn about returning a pointer (or in (C+, a reference) to a variable that goes out of scope after the function returns.

" -Wreturn -type "4 Item "-Wreturn-type" Warn whenever a function is defined with a return type that defaults to CW(C`int (C' .Also warn about any CW(C`return (C' statement with no return value in a function whose return type is not CW(C`void (C' (falling off the end of the function body is considered returning without a value). For C only, warn about a CW(C`return (C' statement with an expression in a function whose return type is CW(C`void (C' ,unless the expression type is also CW(C`void (C' .As a GNUextension, the latter case is accepted without a warning unless -Wpedantic is used. Attempting to use the return value of a non - CW(C`void (C' function other than CW(C`main (C' that flows off the end by reaching the closing curly brace that terminates the function is undefined. Unlike in C, in (C+, flowing off the end of a non - CW(C`void (C' function other than CW(C`main (C' results in undefined behavior even when the value of the function is not used. This warning is enabled by default in (C+ and by -Wall otherwise.

" -Wshift -count -negative "4 Item "-Wshift-count-negative" Warn if shift count is negative. This warning is enabled by default.

" -Wshift -count -overflow "4 Item "-Wshift-count-overflow" Warn if shift count >= width of type. This warning is enabled by default.

" -Wshift -negative -value "4 Item "-Wshift-negative-value" Warn if left shifting a negative value. This warning is enabled by -Wextra in C99 and (C+11 modes (and newer).

" -Wshift -overflow "4 Item "-Wshift-overflow" 0

" -Wshift -overflow= n "4 Item "-Wshift-overflow=n" Warn about left shift overflows. This warning is enabled by default in C99 and (C+11 modes (and newer).

" -Wshift -overflow=1 "4 Item "-Wshift-overflow=1" This is the warning level of -Wshift -overflow and is enabled by default in C99 and (C+11 modes (and newer). This warning level does not warn about left-shifting 1 into the sign bit. (However, in C, such an overflow is still rejected in contexts where an integer constant expression is required.) No warning is emitted in (C+2A mode (and newer), as signed left shifts always wrap.

" -Wshift -overflow=2 "4 Item "-Wshift-overflow=2" This warning level also warns about left-shifting 1 into the sign bit, unless (C+14 mode (or newer) is active.

" -Wswitch "4 Item "-Wswitch" Warn whenever a CW(C`switch (C' statement has an index of enumerated type and lacks a CW(C`case (C' for one or more of the named codes of that enumeration. (The presence of a CW(C`default (C' label prevents this warning.) CW(C`case (C' labels outside the enumeration range also provoke warnings when this option is used (even if there is a CW(C`default (C' label). This warning is enabled by -Wall .

" -Wswitch -default "4 Item "-Wswitch-default" Warn whenever a CW(C`switch (C' statement does not have a CW(C`default (C' case.

" -Wswitch -enum "4 Item "-Wswitch-enum" Warn whenever a CW(C`switch (C' statement has an index of enumerated type and lacks a CW(C`case (C' for one or more of the named codes of that enumeration. CW(C`case (C' labels outside the enumeration range also provoke warnings when this option is used. The only difference between -Wswitch and this option is that this option gives a warning about an omitted enumeration code even if there is a CW(C`default (C' label.

" -Wswitch -bool "4 Item "-Wswitch-bool" Warn whenever a CW(C`switch (C' statement has an index of boolean type and the case values are outside the range of a boolean type. It is possible to suppress this warning by casting the controlling expression to a type other than CW(C`bool (C' .For example: 4 switch ((int) (a == 4)) { ... } This warning is enabled by default for C and (C+ programs.

" -Wswitch -unreachable "4 Item "-Wswitch-unreachable" Warn whenever a CW(C`switch (C' statement contains statements between the controlling expression and the first case label, which will never be executed. For example: 7 switch (cond) { i = 15; ... case 5: ... } -Wswitch -unreachable does not warn if the statement between the controlling expression and the first case label is just a declaration: 8 switch (cond) { int i; ... case 5: i = 5; ... } This warning is enabled by default for C and (C+ programs.

" -Wsync -nand (C and (C+ only)" 4 Item "-Wsync-nand (C and only)" Warn when CW(C`_ _sync_fetch_and_nand (C' and CW(C`_ _sync_nand_and_fetch (C' built-in functions are used. These functions changed semantics in GCC4.4.

" -Wunused -but -set -parameter "4 Item "-Wunused-but-set-parameter" Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration). To suppress this warning use the CW(C`unused (C' attribute. This warning is also enabled by -Wunused together with -Wextra .

" -Wunused -but -set -variable "4 Item "-Wunused-but-set-variable" Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by -Wall . To suppress this warning use the CW(C`unused (C' attribute. This warning is also enabled by -Wunused ,which is enabled by -Wall .

" -Wunused -function "4 Item "-Wunused-function" Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by -Wall .

" -Wunused -label "4 Item "-Wunused-label" Warn whenever a label is declared but not used. This warning is enabled by -Wall . To suppress this warning use the CW(C`unused (C' attribute.

" -Wunused -local -typedefs (C, Objective-C, (C+ and Objective -(C+ only)" 4 Item "-Wunused-local-typedefs (C, Objective-C, and Objective- only)" Warn when a typedef locally defined in a function is not used. This warning is enabled by -Wall .

" -Wunused -parameter "4 Item "-Wunused-parameter" Warn whenever a function parameter is unused aside from its declaration. To suppress this warning use the CW(C`unused (C' attribute.

" -Wno -unused -result "4 Item "-Wno-unused-result" Do not warn if a caller of a function marked with attribute CW(C`warn_unused_result (C' does not use its return value. The default is -Wunused -result .

" -Wunused -variable "4 Item "-Wunused-variable" Warn whenever a local or static variable is unused aside from its declaration. This option implies -Wunused -const -variable=1 for C, but not for (C+. This warning is enabled by -Wall . To suppress this warning use the CW(C`unused (C' attribute.

" -Wunused -const -variable "4 Item "-Wunused-const-variable" 0

" -Wunused -const -variable= n "4 Item "-Wunused-const-variable=n" Warn whenever a constant static variable is unused aside from its declaration. -Wunused -const -variable=1 is enabled by -Wunused -variable for C, but not for (C+. In C this declares variable storage, but in (C+ this is not an error since const variables take the place of CW(C`#define (C' s. To suppress this warning use the CW(C`unused (C' attribute.

" -Wunused -const -variable=1 "4 Item "-Wunused-const-variable=1" This is the warning level that is enabled by -Wunused -variable for C. It warns only about unused static const variables defined in the main compilation unit, but not about static const variables declared in any header included.

" -Wunused -const -variable=2 "4 Item "-Wunused-const-variable=2" This warning level also warns for unused constant static variables in headers (excluding system headers). This is the warning level of -Wunused -const -variable and must be explicitly requested since in (C+ this isn't an error and in C it might be harder to clean up all headers included.

" -Wunused -value "4 Item "-Wunused-value" Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to CW(C`void (C' .This includes an expression-statement or the left-hand side of a comma expression that contains no side effects. For example, an expression such as CW(C`x[i,j] (C' causes a warning, while CW(C`x[(void)i,j] (C' does not. This warning is enabled by -Wall .

" -Wunused "4 Item "-Wunused" All the above -Wunused options combined. In order to get a warning about an unused function parameter, you must either specify -Wextra -Wunused (note that -Wall implies -Wunused ),or separately specify -Wunused -parameter .

" -Wuninitialized "4 Item "-Wuninitialized" Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a CW(C`setjmp (C' call. In (C+, warn if a non-static reference or non-static CW(C`const (C' member appears in a class without constructors. If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the -Winit -self option. These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or clobbered as a whole. They do not occur for variables or elements declared CW(C`volatile (C' .Because these warnings depend on optimization, the exact variables or elements for which there are warnings depends on the precise optimization options and version of GCCused. Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed.

" -Winvalid -memory -model "4 Item "-Winvalid-memory-model" Warn for invocations of __atomic Builtins , __sync Builtins , and the C11 atomic generic functions with a memory consistency argument that is either invalid for the operation or outside the range of values of the CW(C`memory_order (C' enumeration. For example, since the CW(C`_ _atomic_store (C' and CW(C`_ _atomic_store_n (C' built-ins are only defined for the relaxed, release, and sequentially consistent memory orders the following code is diagnosed: 4 void store (int *i) { _ _atomic_store_n (i, 0, memory_order_consume); } -Winvalid -memory -model is enabled by default.

" -Wmaybe -uninitialized "4 Item "-Wmaybe-uninitialized" For an automatic (i.e. local) variable, if there exists a path from the function entry to a use of the variable that is initialized, but there exist some other paths for which the variable is not initialized, the compiler emits a warning if it cannot prove the uninitialized paths are not executed at run time. These warnings are only possible in optimizing compilation, because otherwise GCCdoes not keep track of the state of variables. These warnings are made optional because GCCmay not be able to determine when the code is correct in spite of appearing to have an error. Here is one example of how this can happen: 12 { int x; switch (y) { case 1: x = 1; break; case 2: x = 4; break; case 3: x = 5; } foo (x); } If the value of CW(C`y (C' is always 1, 2 or 3, then CW(C`x (C' is always initialized, but GCCdoesn't know this. To suppress the warning, you need to provide a default case with assert (0) or similar code. This option also warns when a non-volatile automatic variable might be changed by a call to CW(C`longjmp (C' . The compiler sees only the calls to CW(C`setjmp (C' .It cannot know where CW(C`longjmp (C' will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because CW(C`longjmp (C' cannot in fact be called at the place that would cause a problem. Some spurious warnings can be avoided if you declare all the functions you use that never return as CW(C`noreturn (C' . This warning is enabled by -Wall or -Wextra .

" -Wunknown -pragmas "4 Item "-Wunknown-pragmas" Warn when a CW(C`#pragma (C' directive is encountered that is not understood by GCC.If this command-line option is used, warnings are even issued for unknown pragmas in system header files. This is not the case if the warnings are only enabled by the -Wall command-line option.

" -Wno -pragmas "4 Item "-Wno-pragmas" Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also -Wunknown -pragmas .

" -Wno -prio -ctor -dtor "4 Item "-Wno-prio-ctor-dtor" Do not warn if a priority from 0 to 100 is used for constructor or destructor. The use of constructor and destructor attributes allow you to assign a priority to the constructor/destructor to control its order of execution before CW(C`main (C' is called or after it returns. The priority values must be greater than 100 as the compiler reserves priority values between 0 --100 for the implementation.

" -Wstrict -aliasing "4 Item "-Wstrict-aliasing" This option is only active when -fstrict -aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in -Wall . It is equivalent to -Wstrict -aliasing=3

" -Wstrict -aliasing=n "4 Item "-Wstrict-aliasing=n" This option is only active when -fstrict -aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way -O works. -Wstrict -aliasing is equivalent to -Wstrict -aliasing=3 . Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but -fstrict -aliasing still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only. Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only. Level 3 (default for -Wstrict -aliasing ): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the common pun+dereference pattern in the front end: CW(C`*(int*)&some_float (C' . If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types.

" -Wstrict -overflow "4 Item "-Wstrict-overflow" 0

" -Wstrict -overflow= n "4 Item "-Wstrict-overflow=n" This option is only active when signed overflow is undefined. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level. An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all.

" -Wstrict -overflow=1 "4 Item "-Wstrict-overflow=1" Warn about cases that are both questionable and easy to avoid. For example the compiler simplifies CW(C`x + 1 > x (C' to CW1 .This level of -Wstrict -overflow is enabled by -Wall ;higher levels are not, and must be explicitly requested.

" -Wstrict -overflow=2 "4 Item "-Wstrict-overflow=2" Also warn about other cases where a comparison is simplified to a constant. For example: CW(C`abs (x) >= 0 (C' .This can only be simplified when signed integer overflow is undefined, because CW(C`abs (INT_MIN) (C' overflows to CW(C`INT_MIN (C' ,which is less than zero. -Wstrict -overflow (with no level) is the same as -Wstrict -overflow=2 .

" -Wstrict -overflow=3 "4 Item "-Wstrict-overflow=3" Also warn about other cases where a comparison is simplified. For example: CW(C`x + 1 > 1 (C' is simplified to CW(C`x > 0 (C' .

" -Wstrict -overflow=4 "4 Item "-Wstrict-overflow=4" Also warn about other simplifications not covered by the above cases. For example: CW(C`(x * 10) / 5 (C' is simplified to CW(C`x * 2 (C' .

" -Wstrict -overflow=5 "4 Item "-Wstrict-overflow=5" Also warn about cases where the compiler reduces the magnitude of a constant involved in a comparison. For example: CW(C`x + 2 > y (C' is simplified to CW(C`x + 1 >= y (C' .This is reported only at the highest warning level because this simplification applies to many comparisons, so this warning level gives a very large number of false positives.

" -Wstringop -overflow "4 Item "-Wstringop-overflow" 0

" -Wstringop -overflow= type "4 Item "-Wstringop-overflow=type" Warn for calls to string manipulation functions such as CW(C`memcpy (C' and CW(C`strcpy (C' that are determined to overflow the destination buffer. The optional argument is one greater than the type of Object Size Checking to perform to determine the size of the destination. The argument is meaningful only for functions that operate on character arrays but not for raw memory functions like CW(C`memcpy (C' which always make use of Object Size type -0. The option also warns for calls that specify a size in excess of the largest possible object or at most CW(C`SIZE_MAX / 2 (C' bytes. The option produces the best results with optimization enabled but can detect a small subset of simple buffer overflows even without optimization in calls to the GCCbuilt-in functions like CW(C`_ _builtin_memcpy (C' that correspond to the standard functions. In any case, the option warns about just a subset of buffer overflows detected by the corresponding overflow checking built-ins. For example, the option will issue a warning for the CW(C`strcpy (C' call below because it copies at least 5 characters (the string CW"blue" including the terminating NUL)into the buffer of size 4. 11 enum Color { blue, purple, yellow }; const char* f (enum Color clr) { static char buf [4]; const char *str; switch (clr) { case blue: str = "blue"; break; case purple: str = "purple"; break; case yellow: str = "yellow"; break; } return strcpy (buf, str); // warning here } Option -Wstringop -overflow=2 is enabled by default.

" -Wstringop -overflow "4 Item "-Wstringop-overflow" 0

" -Wstringop -overflow=1 "4 Item "-Wstringop-overflow=1" The -Wstringop -overflow=1 option uses type-zero Object Size Checking to determine the sizes of destination objects. This is the default setting of the option. At this setting the option will not warn for writes past the end of subobjects of larger objects accessed by pointers unless the size of the largest surrounding object is known. When the destination may be one of several objects it is assumed to be the largest one of them. On Linux systems, when optimization is enabled at this setting the option warns for the same code as when the CW(C`_FORTIFY_SOURCE (C' macro is defined to a non-zero value.

" -Wstringop -overflow=2 "4 Item "-Wstringop-overflow=2" The -Wstringop -overflow=2 option uses type-one Object Size Checking to determine the sizes of destination objects. At this setting the option will warn about overflows when writing to members of the largest complete objects whose exact size is known. It will, however, not warn for excessive writes to the same members of unknown objects referenced by pointers since they may point to arrays containing unknown numbers of elements.

" -Wstringop -overflow=3 "4 Item "-Wstringop-overflow=3" The -Wstringop -overflow=3 option uses type-two Object Size Checking to determine the sizes of destination objects. At this setting the option warns about overflowing the smallest object or data member. This is the most restrictive setting of the option that may result in warnings for safe code.

" -Wstringop -overflow=4 "4 Item "-Wstringop-overflow=4" The -Wstringop -overflow=4 option uses type-three Object Size Checking to determine the sizes of destination objects. At this setting the option will warn about overflowing any data members, and when the destination is one of several objects it uses the size of the largest of them to decide whether to issue a warning. Similarly to -Wstringop -overflow=3 this setting of the option may result in warnings for benign code.

" -Wstringop -truncation "4 Item "-Wstringop-truncation" Warn for calls to bounded string manipulation functions such as CW(C`strncat (C' , CW(C`strncpy (C' ,and CW(C`stpncpy (C' that may either truncate the copied string or leave the destination unchanged. In the following example, the call to CW(C`strncat (C' specifies a bound that is less than the length of the source string. As a result, the copy of the source will be truncated and so the call is diagnosed. To avoid the warning use CW(C`bufsize -strlen (buf) -1) (C' as the bound. 4 void append (char *buf, size_t bufsize) { strncat (buf, ".txt", 3); } As another example, the following call to CW(C`strncpy (C' results in copying to CW(C`d (C' just the characters preceding the terminating NUL,without appending the NULto the end. Assuming the result of CW(C`strncpy (C' is necessarily a NUL-terminated string is a common mistake, and so the call is diagnosed. To avoid the warning when the result is not expected to be NUL-terminated, call CW(C`memcpy (C' instead. 4 void copy (char *d, const char *s) { strncpy (d, s, strlen (s)); } In the following example, the call to CW(C`strncpy (C' specifies the size of the destination buffer as the bound. If the length of the source string is equal to or greater than this size the result of the copy will not be NUL-terminated. Therefore, the call is also diagnosed. To avoid the warning, specify CW(C`sizeof buf -1 (C' as the bound and set the last element of the buffer to CW(C`NUL (C' . 6 void copy (const char *s) { char buf[80]; strncpy (buf, s, sizeof buf); ... } In situations where a character array is intended to store a sequence of bytes with no terminating CW(C`NUL (C' such an array may be annotated with attribute CW(C`nonstring (C' to avoid this warning. Such arrays, however, are not suitable arguments to functions that expect CW(C`NUL (C' -terminated strings. To help detect accidental misuses of such arrays GCCissues warnings unless it can prove that the use is safe.

" -Wsuggest -attribute= [ pure | const | noreturn | format | cold | malloc ]"4 Item "-Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]" Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below.

" -Wsuggest -attribute=pure "4 Item "-Wsuggest-attribute=pure" 0

" -Wsuggest -attribute=const "4 Item "-Wsuggest-attribute=const"

" -Wsuggest -attribute=noreturn "4 Item "-Wsuggest-attribute=noreturn"

" -Wmissing -noreturn "4 Item "-Wmissing-noreturn"

" -Wsuggest -attribute=malloc "4 Item "-Wsuggest-attribute=malloc" Warn about functions that might be candidates for attributes CW(C`pure (C' , CW(C`const (C' or CW(C`noreturn (C' or CW(C`malloc (C' .The compiler only warns for functions visible in other compilation units or (in the case of CW(C`pure (C' and CW(C`const (C' )if it cannot prove that the function returns normally. A function returns normally if it doesn't contain an infinite loop or return abnormally by throwing, calling CW(C`abort (C' or trapping. This analysis requires option -fipa -pure -const ,which is enabled by default at -O and higher. Higher optimization levels improve the accuracy of the analysis.

" -Wsuggest -attribute=format "4 Item "-Wsuggest-attribute=format" 0

" -Wmissing -format -attribute "4 Item "-Wmissing-format-attribute" Warn about function pointers that might be candidates for CW(C`format (C' attributes. Note these are only possible candidates, not absolute ones. GCCguesses that function pointers with CW(C`format (C' attributes that are used in assignment, initialization, parameter passing or return statements should have a corresponding CW(C`format (C' attribute in the resulting type. I.e. the left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a CW(C`format (C' attribute to avoid the warning. GCCalso warns about function definitions that might be candidates for CW(C`format (C' attributes. Again, these are only possible candidates. GCCguesses that CW(C`format (C' attributes might be appropriate for any function that calls a function like CW(C`vprintf (C' or CW(C`vscanf (C' ,but this might not always be the case, and some functions for which CW(C`format (C' attributes are appropriate may not be detected.

" -Wsuggest -attribute=cold "4 Item "-Wsuggest-attribute=cold" Warn about functions that might be candidates for CW(C`cold (C' attribute. This is based on static detection and generally will only warn about functions which always leads to a call to another CW(C`cold (C' function such as wrappers of (C+ CW(C`throw (C' or fatal error reporting functions leading to CW(C`abort (C' .

" -Wsuggest -final -types "4 Item "-Wsuggest-final-types" Warn about types with virtual methods where code quality would be improved if the type were declared with the (C+11 CW(C`final (C' specifier, or, if possible, declared in an anonymous namespace. This allows GCCto more aggressively devirtualize the polymorphic calls. This warning is more effective with link time optimization, where the information about the class hierarchy graph is more complete.

" -Wsuggest -final -methods "4 Item "-Wsuggest-final-methods" Warn about virtual methods where code quality would be improved if the method were declared with the (C+11 CW(C`final (C' specifier, or, if possible, its type were declared in an anonymous namespace or with the CW(C`final (C' specifier. This warning is more effective with link-time optimization, where the information about the class hierarchy graph is more complete. It is recommended to first consider suggestions of -Wsuggest -final -types and then rebuild with new annotations.

" -Wsuggest -override "4 Item "-Wsuggest-override" Warn about overriding virtual functions that are not marked with the override keyword.

" -Walloc -zero "4 Item "-Walloc-zero" Warn about calls to allocation functions decorated with attribute CW(C`alloc_size (C' that specify zero bytes, including those to the built-in forms of the functions CW(C`aligned_alloc (C' , CW(C`alloca (C' , CW(C`calloc (C' , CW(C`malloc (C' ,and CW(C`realloc (C' .Because the behavior of these functions when called with a zero size differs among implementations (and in the case of CW(C`realloc (C' has been deprecated) relying on it may result in subtle portability bugs and should be avoided.

" -Walloc -size -larger -than= byte-size "4 Item "-Walloc-size-larger-than=byte-size" Warn about calls to functions decorated with attribute CW(C`alloc_size (C' that attempt to allocate objects larger than the specified number of bytes, or where the result of the size computation in an integer type with infinite precision would exceed the value of PTRDIFF_MAX on the target. -Walloc -size -larger -than= PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte-size of SIZE_MAX or more or by -Wno -alloc -size -larger -than .

" -Wno -alloc -size -larger -than "4 Item "-Wno-alloc-size-larger-than" Disable -Walloc -size -larger -than= warnings. The option is equivalent to -Walloc -size -larger -than= SIZE_MAX or larger.

" -Walloca "4 Item "-Walloca" This option warns on all uses of CW(C`alloca (C' in the source.

" -Walloca -larger -than= byte-size "4 Item "-Walloca-larger-than=byte-size" This option warns on calls to CW(C`alloca (C' with an integer argument whose value is either zero, or that is not bounded by a controlling predicate that limits its value to at most byte-size .It also warns for calls to CW(C`alloca (C' where the bound value is unknown. Arguments of non-integer types are considered unbounded even if they appear to be constrained to the expected range. For example, a bounded case of CW(C`alloca (C' could be: 9 void func (size_t n) { void *p; if (n <= 1000) p = alloca (n); else p = malloc (n); f (p); } In the above example, passing CW(C` -Walloca -larger -than=1000 (C' would not issue a warning because the call to CW(C`alloca (C' is known to be at most 1000 bytes. However, if CW(C` -Walloca -larger -than=500 (C' were passed, the compiler would emit a warning. Unbounded uses, on the other hand, are uses of CW(C`alloca (C' with no controlling predicate constraining its integer argument. For example: 5 void func () { void *p = alloca (n); f (p); } If CW(C` -Walloca -larger -than=500 (C' were passed, the above would trigger a warning, but this time because of the lack of bounds checking. Note, that even seemingly correct code involving signed integers could cause a warning: 8 void func (signed int n) { if (n < 500) { p = alloca (n); f (p); } } In the above example, n could be negative, causing a larger than expected argument to be implicitly cast into the CW(C`alloca (C' call. This option also warns when CW(C`alloca (C' is used in a loop. -Walloca -larger -than= PTRDIFF_MAX is enabled by default but is usually only effective when -ftree -vrp is active (default for -O2 and above). See also -Wvla -larger -than= byte-size .

" -Wno -alloca -larger -than "4 Item "-Wno-alloca-larger-than" Disable -Walloca -larger -than= warnings. The option is equivalent to -Walloca -larger -than= SIZE_MAX or larger.

" -Warray -bounds "4 Item "-Warray-bounds" 0

" -Warray -bounds= n "4 Item "-Warray-bounds=n" This option is only active when -ftree -vrp is active (default for -O2 and above). It warns about subscripts to arrays that are always out of bounds. This warning is enabled by -Wall .

" -Warray -bounds=1 "4 Item "-Warray-bounds=1" This is the warning level of -Warray -bounds and is enabled by -Wall ;higher levels are not, and must be explicitly requested.

" -Warray -bounds=2 "4 Item "-Warray-bounds=2" This warning level also warns about out of bounds access for arrays at the end of a struct and for arrays accessed through pointers. This warning level may give a larger number of false positives and is deactivated by default.

" -Wattribute -alias= n "4 Item "-Wattribute-alias=n" 0

" -Wno -attribute -alias "4 Item "-Wno-attribute-alias" Warn about declarations using the CW(C`alias (C' and similar attributes whose target is incompatible with the type of the alias.

" -Wattribute -alias=1 "4 Item "-Wattribute-alias=1" The default warning level of the -Wattribute -alias option diagnoses incompatibilities between the type of the alias declaration and that of its target. Such incompatibilities are typically indicative of bugs.

" -Wattribute -alias=2 "4 Item "-Wattribute-alias=2" At this level -Wattribute -alias also diagnoses cases where the attributes of the alias declaration are more restrictive than the attributes applied to its target. These mismatches can potentially result in incorrect code generation. In other cases they may be benign and could be resolved simply by adding the missing attribute to the target. For comparison, see the -Wmissing -attributes option, which controls diagnostics when the alias declaration is less restrictive than the target, rather than more restrictive. Attributes considered include CW(C`alloc_align (C' , CW(C`alloc_size (C' , CW(C`cold (C' , CW(C`const (C' , CW(C`hot (C' , CW(C`leaf (C' , CW(C`malloc (C' , CW(C`nonnull (C' , CW(C`noreturn (C' , CW(C`nothrow (C' , CW(C`pure (C' , CW(C`returns_nonnull (C' ,and CW(C`returns_twice (C' . -Wattribute -alias is equivalent to -Wattribute -alias=1 . This is the default. You can disable these warnings with either -Wno -attribute -alias or -Wattribute -alias=0 .

" -Wbool -compare "4 Item "-Wbool-compare" Warn about boolean expression compared with an integer value different from CW(C`true (C' / CW(C`false (C' .For instance, the following comparison is always false: 3 int n = 5; ... if ((n > 1) == 2) { ... } This warning is enabled by -Wall .

" -Wbool -operation "4 Item "-Wbool-operation" Warn about suspicious operations on expressions of a boolean type. For instance, bitwise negation of a boolean is very likely a bug in the program. For C, this warning also warns about incrementing or decrementing a boolean, which rarely makes sense. (In (C+, decrementing a boolean is always invalid. Incrementing a boolean is invalid in (C+17, and deprecated otherwise.) This warning is enabled by -Wall .

" -Wduplicated -branches "4 Item "-Wduplicated-branches" Warn when an if-else has identical branches. This warning detects cases like 4 if (p != NULL) return 0; else return 0; It doesn't warn when both branches contain just a null statement. This warning also warn for conditional operators: 1 int i = x ? *p : *p;

" -Wduplicated -cond "4 Item "-Wduplicated-cond" Warn about duplicated conditions in an if-else-if chain. For instance, warn for the following code: 2 if (p ->q != NULL) { ... } else if (p ->q != NULL) { ... }

" -Wframe -address "4 Item "-Wframe-address" Warn when the __builtin_frame_address or __builtin_return_address is called with an argument greater than 0. Such calls may return indeterminate values or crash the program. The warning is included in -Wall .

" -Wno -discarded -qualifiers (C and Objective-C only)" 4 Item "-Wno-discarded-qualifiers (C and Objective-C only)" Do not warn if type qualifiers on pointers are being discarded. Typically, the compiler warns if a CW(C`const char * (C' variable is passed to a function that takes a CW(C`char * (C' parameter. This option can be used to suppress such a warning.

" -Wno -discarded -array -qualifiers (C and Objective-C only)" 4 Item "-Wno-discarded-array-qualifiers (C and Objective-C only)" Do not warn if type qualifiers on arrays which are pointer targets are being discarded. Typically, the compiler warns if a CW(C`const int (*)[] (C' variable is passed to a function that takes a CW(C`int (*)[] (C' parameter. This option can be used to suppress such a warning.

" -Wno -incompatible -pointer -types (C and Objective-C only)" 4 Item "-Wno-incompatible-pointer-types (C and Objective-C only)" Do not warn when there is a conversion between pointers that have incompatible types. This warning is for cases not covered by -Wno -pointer -sign , which warns for pointer argument passing or assignment with different signedness.

" -Wno -int -conversion (C and Objective-C only)" 4 Item "-Wno-int-conversion (C and Objective-C only)" Do not warn about incompatible integer to pointer and pointer to integer conversions. This warning is about implicit conversions; for explicit conversions the warnings -Wno -int -to -pointer -cast and -Wno -pointer -to -int -cast may be used.

" -Wno -div -by -zero "4 Item "-Wno-div-by-zero" Do not warn about compile-time integer division by zero. Floating-point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs.

" -Wsystem -headers "4 Item "-Wsystem-headers" Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command-line option tells GCCto emit warnings from system headers as if they occurred in user code. However, note that using -Wall in conjunction with this option does not warn about unknown pragmas in system headers ---for that, -Wunknown -pragmas must also be used.

" -Wtautological -compare "4 Item "-Wtautological-compare" Warn if a self-comparison always evaluates to true or false. This warning detects various mistakes such as: 3 int i = 1; ... if (i > i) { ... } This warning also warns about bitwise comparisons that always evaluate to true or false, for instance: 1 if ((a & 16) == 10) { ... } will always be false. This warning is enabled by -Wall .

" -Wtrampolines "4 Item "-Wtrampolines" Warn about trampolines generated for pointers to nested functions. A trampoline is a small piece of data or code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is made up of code and thus requires the stack to be made executable in order for the program to work properly.

" -Wfloat -equal "4 Item "-Wfloat-equal" Warn if floating-point values are used in equality comparisons. The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you should check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken.

" -Wtraditional (C and Objective-C only)" 4 Item "-Wtraditional (C and Objective-C only)" Warn about certain constructs that behave differently in traditional and ISOC. Also warn about ISOC constructs that have no traditional C equivalent, and/or problematic constructs that should be avoided.

"*" 4 Macro parameters that appear within string literals in the macro body. In traditional C macro replacement takes place within string literals, but in ISOC it does not.

"*" 4 In traditional C, some preprocessor directives did not exist. Traditional preprocessors only considered a line to be a directive if the # appeared in column 1 on the line. Therefore -Wtraditional warns about directives that traditional C understands but ignores because the # does not appear as the first character on the line. It also suggests you hide directives like CW(C`#pragma (C' not understood by traditional C by indenting them. Some traditional implementations do not recognize CW(C`#elif (C' ,so this option suggests avoiding it altogether.

"*" 4 A function-like macro that appears without arguments.

"*" 4 The unary plus operator.

"*" 4 The U integer constant suffix, or the F or L floating-point constant suffixes. (Traditional C does support the L suffix on integer constants.) Note, these suffixes appear in macros defined in the system headers of most modern systems, e.g. the _MIN / _MAX macros in CW(C`<limits.h> (C' . Use of these macros in user code might normally lead to spurious warnings, however GCC'sintegrated preprocessor has enough context to avoid warning in these cases.

"*" 4 A function declared external in one block and then used after the end of the block.

"*" 4 A CW(C`switch (C' statement has an operand of type CW(C`long (C' .

"*" 4 A non - CW(C`static (C' function declaration follows a CW(C`static (C' one. This construct is not accepted by some traditional C compilers.

"*" 4 The ISOtype of an integer constant has a different width or signedness from its traditional type. This warning is only issued if the base of the constant is ten. I.e. hexadecimal or octal values, which typically represent bit patterns, are not warned about.

"*" 4 Usage of ISOstring concatenation is detected.

"*" 4 Initialization of automatic aggregates.

"*" 4 Identifier conflicts with labels. Traditional C lacks a separate namespace for labels.

"*" 4 Initialization of unions. If the initializer is zero, the warning is omitted. This is done under the assumption that the zero initializer in user code appears conditioned on e.g. CW(C`_ _STDC_ _ (C' to avoid missing initializer warnings and relies on default initialization to zero in the traditional C case.

"*" 4 Conversions by prototypes between fixed/floating -point values and vice versa. The absence of these prototypes when compiling with traditional C causes serious problems. This is a subset of the possible conversion warnings; for the full set use -Wtraditional -conversion .

"*" 4 Use of ISOC style function definitions. This warning intentionally is not issued for prototype declarations or variadic functions because these ISOC features appear in your code when using libiberty's traditional C compatibility macros, CW(C`PARAMS (C' and CW(C`VPARAMS (C' .This warning is also bypassed for nested functions because that feature is already a GCCextension and thus not relevant to traditional C compatibility.

" -Wtraditional -conversion (C and Objective-C only)" 4 Item "-Wtraditional-conversion (C and Objective-C only)" Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed-point argument except when the same as the default promotion.

" -Wdeclaration -after -statement (C and Objective-C only)" 4 Item "-Wdeclaration-after-statement (C and Objective-C only)" Warn when a declaration is found after a statement in a block. This construct, known from (C+, was introduced with ISOC99 and is by default allowed in GCC.It is not supported by ISOC90.

" -Wshadow "4 Item "-Wshadow" Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in (C+), or instance variable (in Objective-C) or whenever a built-in function is shadowed. Note that in (C+, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum. Same as -Wshadow=global .

" -Wno -shadow -ivar (Objective-C only)" 4 Item "-Wno-shadow-ivar (Objective-C only)" Do not warn whenever a local variable shadows an instance variable in an Objective-C method.

" -Wshadow=global "4 Item "-Wshadow=global" The default for -Wshadow .Warns for any (global) shadowing.

" -Wshadow=local "4 Item "-Wshadow=local" Warn when a local variable shadows another local variable or parameter. This warning is enabled by -Wshadow=global .

" -Wshadow=compatible -local "4 Item "-Wshadow=compatible-local" Warn when a local variable shadows another local variable or parameter whose type is compatible with that of the shadowing variable. In (C+, type compatibility here means the type of the shadowing variable can be converted to that of the shadowed variable. The creation of this flag (in addition to -Wshadow=local )is based on the idea that when a local variable shadows another one of incompatible type, it is most likely intentional, not a bug or typo, as shown in the following example: 8 for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i) { for (int i = 0; i < N; ++i) { ... } ... } Since the two variable CW(C`i (C' in the example above have incompatible types, enabling only -Wshadow=compatible -local will not emit a warning. Because their types are incompatible, if a programmer accidentally uses one in place of the other, type checking will catch that and emit an error or warning. So not warning (about shadowing) in this case will not lead to undetected bugs. Use of this flag instead of -Wshadow=local can possibly reduce the number of warnings triggered by intentional shadowing. This warning is enabled by -Wshadow=local .

" -Wlarger -than= byte-size "4 Item "-Wlarger-than=byte-size" Warn whenever an object is defined whose size exceeds byte-size . -Wlarger -than= PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte-size of SIZE_MAX or more or by -Wno -larger -than .

" -Wno -larger -than "4 Item "-Wno-larger-than" Disable -Wlarger -than= warnings. The option is equivalent to -Wlarger -than= SIZE_MAX or larger.

" -Wframe -larger -than= byte-size "4 Item "-Wframe-larger-than=byte-size" Warn if the size of a function frame exceeds byte-size . The computation done to determine the stack frame size is approximate and not conservative. The actual requirements may be somewhat greater than byte-size even if you do not get a warning. In addition, any space allocated via CW(C`alloca (C' ,variable-length arrays, or related constructs is not included by the compiler when determining whether or not to issue a warning. -Wframe -larger -than= PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte-size of SIZE_MAX or more or by -Wno -frame -larger -than .

" -Wno -frame -larger -than "4 Item "-Wno-frame-larger-than" Disable -Wframe -larger -than= warnings. The option is equivalent to -Wframe -larger -than= SIZE_MAX or larger.

" -Wno -free -nonheap -object "4 Item "-Wno-free-nonheap-object" Do not warn when attempting to free an object that was not allocated on the heap.

" -Wstack -usage= byte-size "4 Item "-Wstack-usage=byte-size" Warn if the stack usage of a function might exceed byte-size . The computation done to determine the stack usage is conservative. Any space allocated via CW(C`alloca (C' ,variable-length arrays, or related constructs is included by the compiler when determining whether or not to issue a warning. The message is in keeping with the output of -fstack -usage .

"*" 4 If the stack usage is fully static but exceeds the specified amount, it's: 1 warning: stack usage is 1120 bytes

"*" 4 If the stack usage is (partly) dynamic but bounded, it's: 1 warning: stack usage might be 1648 bytes

"*" 4 If the stack usage is (partly) dynamic and not bounded, it's: 1 warning: stack usage might be unbounded -Wstack -usage= PTRDIFF_MAX is enabled by default. Warnings controlled by the option can be disabled either by specifying byte-size of SIZE_MAX or more or by -Wno -stack -usage .

" -Wno -stack -usage "4 Item "-Wno-stack-usage" Disable -Wstack -usage= warnings. The option is equivalent to -Wstack -usage= SIZE_MAX or larger.

" -Wunsafe -loop -optimizations "4 Item "-Wunsafe-loop-optimizations" Warn if the loop cannot be optimized because the compiler cannot assume anything on the bounds of the loop indices. With -funsafe -loop -optimizations warn if the compiler makes such assumptions.

" -Wno -pedantic -ms -format (MinGW targets only)" 4 Item "-Wno-pedantic-ms-format (MinGW targets only)" When used in combination with -Wformat and -pedantic without GNUextensions, this option disables the warnings about non-ISO CW(C`printf (C' / CW(C`scanf (C' format width specifiers CW(C`I32 (C' , CW(C`I64 (C' ,and CW(C`I (C' used on Windows targets, which depend on the MSruntime.

" -Waligned -new "4 Item "-Waligned-new" Warn about a new-expression of a type that requires greater alignment than the CW(C`alignof(std::max_align_t) (C' but uses an allocation function without an explicit alignment parameter. This option is enabled by -Wall . Normally this only warns about global allocation functions, but -Waligned -new=all also warns about class member allocation functions.

" -Wplacement -new "4 Item "-Wplacement-new" 0

" -Wplacement -new= n "4 Item "-Wplacement-new=n" Warn about placement new expressions with undefined behavior, such as constructing an object in a buffer that is smaller than the type of the object. For example, the placement new expression below is diagnosed because it attempts to construct an array of 64 integers in a buffer only 64 bytes large. 2 char buf [64]; new (buf) int[64]; This warning is enabled by default.

" -Wplacement -new=1 "4 Item "-Wplacement-new=1" This is the default warning level of -Wplacement -new .At this level the warning is not issued for some strictly undefined constructs that GCCallows as extensions for compatibility with legacy code. For example, the following CW(C`new (C' expression is not diagnosed at this level even though it has undefined behavior according to the (C+ standard because it writes past the end of the one-element array. 3 struct S { int n, a[1]; }; S *s = (S *)malloc (sizeof *s + 31 * sizeof s ->a[0]); new (s ->a)int [32]();

" -Wplacement -new=2 "4 Item "-Wplacement-new=2" At this level, in addition to diagnosing all the same constructs as at level 1, a diagnostic is also issued for placement new expressions that construct an object in the last member of structure whose type is an array of a single element and whose size is less than the size of the object being constructed. While the previous example would be diagnosed, the following construct makes use of the flexible member array extension to avoid the warning at level 2. 3 struct S { int n, a[]; }; S *s = (S *)malloc (sizeof *s + 32 * sizeof s ->a[0]); new (s ->a)int [32]();

" -Wpointer -arith "4 Item "-Wpointer-arith" Warn about anything that depends on the (L"size of (R" a function type or of CW(C`void (C' .GNUC assigns these types a size of 1, for convenience in calculations with CW(C`void * (C' pointers and pointers to functions. In (C+, warn also when an arithmetic operation involves CW(C`NULL (C' .This warning is also enabled by -Wpedantic .

" -Wpointer -compare "4 Item "-Wpointer-compare" Warn if a pointer is compared with a zero character constant. This usually means that the pointer was meant to be dereferenced. For example: 3 const char *p = foo (); if (p == (Aq \ 0 (Aq) return 42; Note that the code above is invalid in (C+11. This warning is enabled by default.

" -Wtype -limits "4 Item "-Wtype-limits" Warn if a comparison is always true or always false due to the limited range of the data type, but do not warn for constant expressions. For example, warn if an unsigned variable is compared against zero with CW(C`< (C' or CW(C`>= (C' .This warning is also enabled by -Wextra .

" -Wabsolute -value (C and Objective-C only)" 4 Item "-Wabsolute-value (C and Objective-C only)" Warn for calls to standard functions that compute the absolute value of an argument when a more appropriate standard function is available. For example, calling CW(C`abs(3.14) (C' triggers the warning because the appropriate function to call to compute the absolute value of a double argument is CW(C`fabs (C' .The option also triggers warnings when the argument in a call to such a function has an unsigned type. This warning can be suppressed with an explicit type cast and it is also enabled by -Wextra .

" -Wcomment "4 Item "-Wcomment" 0

" -Wcomments "4 Item "-Wcomments" Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline appears in a // comment. This warning is enabled by -Wall .

" -Wtrigraphs "4 Item "-Wtrigraphs" Warn if any trigraphs are encountered that might change the meaning of the program. Trigraphs within comments are not warned about, except those that would form escaped newlines. This option is implied by -Wall .If -Wall is not given, this option is still enabled unless trigraphs are enabled. To get trigraph conversion without warnings, but get the other -Wall warnings, use -trigraphs -Wall -Wno -trigraphs .

" -Wundef "4 Item "-Wundef" Warn if an undefined identifier is evaluated in an CW(C`#if (C' directive. Such identifiers are replaced with zero.

" -Wexpansion -to -defined "4 Item "-Wexpansion-to-defined" Warn whenever defined is encountered in the expansion of a macro (including the case where the macro is expanded by an #if directive). Such usage is not portable. This warning is also enabled by -Wpedantic and -Wextra .

" -Wunused -macros "4 Item "-Wunused-macros" Warn about macros defined in the main file that are unused. A macro is used if it is expanded or tested for existence at least once. The preprocessor also warns if the macro has not been used at the time it is redefined or undefined. Built-in macros, macros defined on the command line, and macros defined in include files are not warned about. Note: If a macro is actually used, but only used in skipped conditional blocks, then the preprocessor reports it as unused. To avoid the warning in such a case, you might improve the scope of the macro's definition by, for example, moving it into the first skipped block. Alternatively, you could provide a dummy use with something like: 2 #if defined the_macro_causing_the_warning #endif

" -Wno -endif -labels "4 Item "-Wno-endif-labels" Do not warn whenever an CW(C`#else (C' or an CW(C`#endif (C' are followed by text. This sometimes happens in older programs with code of the form 5 #if FOO ... #else FOO ... #endif FOO The second and third CW(C`FOO (C' should be in comments. This warning is on by default.

" -Wbad -function -cast (C and Objective-C only)" 4 Item "-Wbad-function-cast (C and Objective-C only)" Warn when a function call is cast to a non-matching type. For example, warn if a call to a function returning an integer type is cast to a pointer type.

" -Wc90 -c99 -compat (C and Objective-C only)" 4 Item "-Wc90-c99-compat (C and Objective-C only)" Warn about features not present in ISOC90, but present in ISOC99. For instance, warn about use of variable length arrays, CW(C`long long (C' type, CW(C`bool (C' type, compound literals, designated initializers, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows CW(C`_ _extension_ _ (C' .

" -Wc99 -c11 -compat (C and Objective-C only)" 4 Item "-Wc99-c11-compat (C and Objective-C only)" Warn about features not present in ISOC99, but present in ISOC11. For instance, warn about use of anonymous structures and unions, CW(C`_Atomic (C' type qualifier, CW(C`_Thread_local (C' storage-class specifier, CW(C`_Alignas (C' specifier, CW(C`Alignof (C' operator, CW(C`_Generic (C' keyword, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows CW(C`_ _extension_ _ (C' .

" -Wc++ -compat (C and Objective-C only)" 4 Item "-Wc++-compat (C and Objective-C only)" Warn about ISOC constructs that are outside of the common subset of ISOC and ISO(C+, e.g. request for implicit conversion from CW(C`void * (C' to a pointer to non - CW(C`void (C' type.

" -Wc++11 -compat ( (C+ and Objective -(C+ only)" 4 Item "-Wc++11-compat ( and Objective- only)" Warn about (C+ constructs whose meaning differs between ISO(C+ 1998 and ISO(C+ 2011, e.g., identifiers in ISO(C+ 1998 that are keywords in ISO(C+ 2011. This warning turns on -Wnarrowing and is enabled by -Wall .

" -Wc++14 -compat ( (C+ and Objective -(C+ only)" 4 Item "-Wc++14-compat ( and Objective- only)" Warn about (C+ constructs whose meaning differs between ISO(C+ 2011 and ISO(C+ 2014. This warning is enabled by -Wall .

" -Wc++17 -compat ( (C+ and Objective -(C+ only)" 4 Item "-Wc++17-compat ( and Objective- only)" Warn about (C+ constructs whose meaning differs between ISO(C+ 2014 and ISO(C+ 2017. This warning is enabled by -Wall .

" -Wcast -qual "4 Item "-Wcast-qual" Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a CW(C`const char * (C' is cast to an ordinary CW(C`char * (C' . Also warn when making a cast that introduces a type qualifier in an unsafe way. For example, casting CW(C`char ** (C' to CW(C`const char ** (C' is unsafe, as in this example: 6 /* p is char ** value. */ const char **q = (const char **) p; /* Assignment of readonly string to const char * is OK. */ *q = "string"; /* Now char** pointer points to read -only memory. */ **p = (Aqb (Aq;

" -Wcast -align "4 Item "-Wcast-align" Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a CW(C`char * (C' is cast to an CW(C`int * (C' on machines where integers can only be accessed at two -or four-byte boundaries.

" -Wcast -align=strict "4 Item "-Wcast-align=strict" Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a CW(C`char * (C' is cast to an CW(C`int * (C' regardless of the target machine.

" -Wcast -function -type "4 Item "-Wcast-function-type" Warn when a function pointer is cast to an incompatible function pointer. In a cast involving function types with a variable argument list only the types of initial arguments that are provided are considered. Any parameter of pointer-type matches any other pointer-type. Any benign differences in integral types are ignored, like CW(C`int (C' vs. CW(C`long (C' on ILP32targets. Likewise type qualifiers are ignored. The function type CW(C`void (*) (void) (C' is special and matches everything, which can be used to suppress this warning. In a cast involving pointer to member types this warning warns whenever the type cast is changing the pointer to member type. This warning is enabled by -Wextra .

" -Wwrite -strings "4 Item "-Wwrite-strings" When compiling C, give string constants the type CW(C`const char[ CIlength CW](C' so that copying the address of one into a non - CW(C`const (C' CW(C`char * (C' pointer produces a warning. These warnings help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using CW(C`const (C' in declarations and prototypes. Otherwise, it is just a nuisance. This is why we did not make -Wall request these warnings. When compiling (C+, warn about the deprecated conversion from string literals to CW(C`char * (C' .This warning is enabled by default for (C+ programs.

" -Wcatch -value "4 Item "-Wcatch-value" 0

" -Wcatch -value= n ((C+ and Objective -(C+ only)" 4 Item "-Wcatch-value=n ( and Objective- only)" Warn about catch handlers that do not catch via reference. With -Wcatch -value=1 (or -Wcatch -value for short) warn about polymorphic class types that are caught by value. With -Wcatch -value=2 warn about all class types that are caught by value. With -Wcatch -value=3 warn about all types that are not caught by reference. -Wcatch -value is enabled by -Wall .

" -Wclobbered "4 Item "-Wclobbered" Warn for variables that might be changed by CW(C`longjmp (C' or CW(C`vfork (C' .This warning is also enabled by -Wextra .

" -Wconditionally -supported ( (C+ and Objective -(C+ only)" 4 Item "-Wconditionally-supported ( and Objective- only)" Warn for conditionally-supported ( (C+11 [intro.defs]) constructs.

" -Wconversion "4 Item "-Wconversion" Warn for implicit conversions that may alter a value. This includes conversions between real and integer, like CW(C`abs (x) (C' when CW(C`x (C' is CW(C`double (C' ;conversions between signed and unsigned, like CW(C`unsigned ui = -1 (C' ;and conversions to smaller types, like CW(C`sqrtf (M_PI) (C' .Do not warn for explicit casts like CW(C`abs ((int) x) (C' and CW(C`ui = (unsigned) -1 (C' ,or if the value is not changed by the conversion like in CW(C`abs (2.0) (C' .Warnings about conversions between signed and unsigned integers can be disabled by using -Wno -sign -conversion . For (C+, also warn for confusing overload resolution for user-defined conversions; and conversions that never use a type conversion operator: conversions to CW(C`void (C' ,the same type, a base class or a reference to them. Warnings about conversions between signed and unsigned integers are disabled by default in (C+ unless -Wsign -conversion is explicitly enabled.

" -Wno -conversion -null ( (C+ and Objective -(C+ only)" 4 Item "-Wno-conversion-null ( and Objective- only)" Do not warn for conversions between CW(C`NULL (C' and non-pointer types. -Wconversion -null is enabled by default.

" -Wzero -as -null -pointer -constant ( (C+ and Objective -(C+ only)" 4 Item "-Wzero-as-null-pointer-constant ( and Objective- only)" Warn when a literal 0 is used as null pointer constant. This can be useful to facilitate the conversion to CW(C`nullptr (C' in (C+11.

" -Wsubobject -linkage ( (C+ and Objective -(C+ only)" 4 Item "-Wsubobject-linkage ( and Objective- only)" Warn if a class type has a base or a field whose type uses the anonymous namespace or depends on a type with no linkage. If a type A depends on a type B with no or internal linkage, defining it in multiple translation units would be an ODRviolation because the meaning of B is different in each translation unit. If A only appears in a single translation unit, the best way to silence the warning is to give it internal linkage by putting it in an anonymous namespace as well. The compiler doesn't give this warning for types defined in the main .C file, as those are unlikely to have multiple definitions. -Wsubobject -linkage is enabled by default.

" -Wdangling -else "4 Item "-Wdangling-else" Warn about constructions where there may be confusion to which CW(C`if (C' statement an CW(C`else (C' branch belongs. Here is an example of such a case: 7 { if (a) if (b) foo (); else bar (); } In C/ (C+, every CW(C`else (C' branch belongs to the innermost possible CW(C`if (C' statement, which in this example is CW(C`if (b) (C' .This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, GCCissues a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost CW(C`if (C' statement so there is no way the CW(C`else (C' can belong to the enclosing CW(C`if (C' .The resulting code looks like this: 9 { if (a) { if (b) foo (); else bar (); } } This warning is enabled by -Wparentheses .

" -Wdate -time "4 Item "-Wdate-time" Warn when macros CW(C`_ _TIME_ _ (C' , CW(C`_ _DATE_ _ (C' or CW(C`_ _TIMESTAMP_ _ (C' are encountered as they might prevent bit-wise-identical reproducible compilations.

" -Wdelete -incomplete ( (C+ and Objective -(C+ only)" 4 Item "-Wdelete-incomplete ( and Objective- only)" Warn when deleting a pointer to incomplete type, which may cause undefined behavior at runtime. This warning is enabled by default.

" -Wuseless -cast ( (C+ and Objective -(C+ only)" 4 Item "-Wuseless-cast ( and Objective- only)" Warn when an expression is casted to its own type.

" -Wempty -body "4 Item "-Wempty-body" Warn if an empty body occurs in an CW(C`if (C' , CW(C`else (C' or CW(C`do while (C' statement. This warning is also enabled by -Wextra .

" -Wenum -compare "4 Item "-Wenum-compare" Warn about a comparison between values of different enumerated types. In (C+ enumerated type mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C this warning is enabled by -Wall .

" -Wextra -semi ( (C+, Objective -(C+ only)" 4 Item "-Wextra-semi (, Objective- only)" Warn about redundant semicolon after in-class function definition.

" -Wjump -misses -init (C, Objective-C only)" 4 Item "-Wjump-misses-init (C, Objective-C only)" Warn if a CW(C`goto (C' statement or a CW(C`switch (C' statement jumps forward across the initialization of a variable, or jumps backward to a label after the variable has been initialized. This only warns about variables that are initialized when they are declared. This warning is only supported for C and Objective-C; in (C+ this sort of branch is an error in any case. -Wjump -misses -init is included in -Wc++ -compat .It can be disabled with the -Wno -jump -misses -init option.

" -Wsign -compare "4 Item "-Wsign-compare" Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. In (C+, this warning is also enabled by -Wall .In C, it is also enabled by -Wextra .

" -Wsign -conversion "4 Item "-Wsign-conversion" Warn for implicit conversions that may change the sign of an integer value, like assigning a signed integer expression to an unsigned integer variable. An explicit cast silences the warning. In C, this option is enabled also by -Wconversion .

" -Wfloat -conversion "4 Item "-Wfloat-conversion" Warn for implicit conversions that reduce the precision of a real value. This includes conversions from real to integer, and from higher precision real to lower precision real values. This option is also enabled by -Wconversion .

" -Wno -scalar -storage -order "4 Item "-Wno-scalar-storage-order" Do not warn on suspicious constructs involving reverse scalar storage order.

" -Wsized -deallocation ( (C+ and Objective -(C+ only)" 4 Item "-Wsized-deallocation ( and Objective- only)" Warn about a definition of an unsized deallocation function 2 void operator delete (void *) noexcept; void operator delete[] (void *) noexcept; without a definition of the corresponding sized deallocation function 2 void operator delete (void *, std::size_t) noexcept; void operator delete[] (void *, std::size_t) noexcept; or vice versa. Enabled by -Wextra along with -fsized -deallocation .

" -Wsizeof -pointer -div "4 Item "-Wsizeof-pointer-div" Warn for suspicious divisions of two sizeof expressions that divide the pointer size by the element size, which is the usual way to compute the array size but won't work out correctly with pointers. This warning warns e.g. about CW(C`sizeof (ptr) / sizeof (ptr[0]) (C' if CW(C`ptr (C' is not an array, but a pointer. This warning is enabled by -Wall .

" -Wsizeof -pointer -memaccess "4 Item "-Wsizeof-pointer-memaccess" Warn for suspicious length parameters to certain string and memory built-in functions if the argument uses CW(C`sizeof (C' .This warning triggers for example for CW(C`memset (ptr, 0, sizeof (ptr)); (C' if CW(C`ptr (C' is not an array, but a pointer, and suggests a possible fix, or about CW(C`memcpy (&foo, ptr, sizeof (&foo)); (C' . -Wsizeof -pointer -memaccess also warns about calls to bounded string copy functions like CW(C`strncat (C' or CW(C`strncpy (C' that specify as the bound a CW(C`sizeof (C' expression of the source array. For example, in the following function the call to CW(C`strncat (C' specifies the size of the source string as the bound. That is almost certainly a mistake and so the call is diagnosed. 7 void make_file (const char *name) { char path[PATH_MAX]; strncpy (path, name, sizeof path -1); strncat (path, ".text", sizeof ".text"); ... } The -Wsizeof -pointer -memaccess option is enabled by -Wall .

" -Wsizeof -array -argument "4 Item "-Wsizeof-array-argument" Warn when the CW(C`sizeof (C' operator is applied to a parameter that is declared as an array in a function definition. This warning is enabled by default for C and (C+ programs.

" -Wmemset -elt -size "4 Item "-Wmemset-elt-size" Warn for suspicious calls to the CW(C`memset (C' built-in function, if the first argument references an array, and the third argument is a number equal to the number of elements, but not equal to the size of the array in memory. This indicates that the user has omitted a multiplication by the element size. This warning is enabled by -Wall .

" -Wmemset -transposed -args "4 Item "-Wmemset-transposed-args" Warn for suspicious calls to the CW(C`memset (C' built-in function where the second argument is not zero and the third argument is zero. For example, the call CW(C`memset (buf, sizeof buf, 0) (C' is diagnosed because CW(C`memset (buf, 0, sizeof buf) (C' was meant instead. The diagnostic is only emitted if the third argument is a literal zero. Otherwise, if it is an expression that is folded to zero, or a cast of zero to some type, it is far less likely that the arguments have been mistakenly transposed and no warning is emitted. This warning is enabled by -Wall .

" -Waddress "4 Item "-Waddress" Warn about suspicious uses of memory addresses. These include using the address of a function in a conditional expression, such as CW(C`void func(void); if (func) (C' ,and comparisons against the memory address of a string literal, such as CW(C`if (x == "abc") (C' .Such uses typically indicate a programmer error: the address of a function always evaluates to true, so their use in a conditional usually indicate that the programmer forgot the parentheses in a function call; and comparisons against string literals result in unspecified behavior and are not portable in C, so they usually indicate that the programmer intended to use CW(C`strcmp (C' .This warning is enabled by -Wall .

" -Waddress -of -packed -member "4 Item "-Waddress-of-packed-member" Warn when the address of packed member of struct or union is taken, which usually results in an unaligned pointer value. This is enabled by default.

" -Wlogical -op "4 Item "-Wlogical-op" Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected. Also warns when the operands of a logical operator are the same: 2 extern int a; if (a < 0 && a < 0) { ... }

" -Wlogical -not -parentheses "4 Item "-Wlogical-not-parentheses" Warn about logical not used on the left hand side operand of a comparison. This option does not warn if the right operand is considered to be a boolean expression. Its purpose is to detect suspicious code like the following: 3 int a; ... if (!a > 1) { ... } It is possible to suppress the warning by wrapping the LHSinto parentheses: 1 if ((!a) > 1) { ... } This warning is enabled by -Wall .

" -Waggregate -return "4 Item "-Waggregate-return" Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.)

" -Wno -aggressive -loop -optimizations "4 Item "-Wno-aggressive-loop-optimizations" Warn if in a loop with constant number of iterations the compiler detects undefined behavior in some statement during one or more of the iterations.

" -Wno -attributes "4 Item "-Wno-attributes" Do not warn if an unexpected CW(C`_ _attribute_ _ (C' is used, such as unrecognized attributes, function attributes applied to variables, etc. This does not stop errors for incorrect use of supported attributes.

" -Wno -builtin -declaration -mismatch "4 Item "-Wno-builtin-declaration-mismatch" Warn if a built-in function is declared with an incompatible signature or as a non-function, or when a built-in function declared with a type that does not include a prototype is called with arguments whose promoted types do not match those expected by the function. When -Wextra is specified, also warn when a built-in function that takes arguments is declared without a prototype. The -Wno -builtin -declaration -mismatch warning is enabled by default. To avoid the warning include the appropriate header to bring the prototypes of built-in functions into scope. For example, the call to CW(C`memset (C' below is diagnosed by the warning because the function expects a value of type CW(C`size_t (C' as its argument but the type of CW32 is CW(C`int (C' .With -Wextra , the declaration of the function is diagnosed as well. 5 extern void* memset (); void f (void *d) { memset (d, (Aq \ 0 (Aq, 32); }

" -Wno -builtin -macro -redefined "4 Item "-Wno-builtin-macro-redefined" Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of CW(C`_ _TIMESTAMP_ _ (C' , CW(C`_ _TIME_ _ (C' , CW(C`_ _DATE_ _ (C' , CW(C`_ _FILE_ _ (C' ,and CW(C`_ _BASE_FILE_ _ (C' .

" -Wstrict -prototypes (C and Objective-C only)" 4 Item "-Wstrict-prototypes (C and Objective-C only)" Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies the argument types.)

" -Wold -style -declaration (C and Objective-C only)" 4 Item "-Wold-style-declaration (C and Objective-C only)" Warn for obsolescent usages, according to the C Standard, in a declaration. For example, warn if storage-class specifiers like CW(C`static (C' are not the first things in a declaration. This warning is also enabled by -Wextra .

" -Wold -style -definition (C and Objective-C only)" 4 Item "-Wold-style-definition (C and Objective-C only)" Warn if an old-style function definition is used. A warning is given even if there is a previous prototype.

" -Wmissing -parameter -type (C and Objective-C only)" 4 Item "-Wmissing-parameter-type (C and Objective-C only)" A function parameter is declared without a type specifier in K&R -style functions: 1 void foo(bar) { } This warning is also enabled by -Wextra .

" -Wmissing -prototypes (C and Objective-C only)" 4 Item "-Wmissing-prototypes (C and Objective-C only)" Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global functions that do not have a matching prototype declaration in a header file. This option is not valid for (C+ because all function declarations provide prototypes and a non-matching declaration declares an overload rather than conflict with an earlier declaration. Use -Wmissing -declarations to detect missing declarations in (C+.

" -Wmissing -declarations "4 Item "-Wmissing-declarations" Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. In C, no warnings are issued for functions with previous non-prototype declarations; use -Wmissing -prototypes to detect missing prototypes. In (C+, no warnings are issued for function templates, or for inline functions, or for functions in anonymous namespaces.

" -Wmissing -field -initializers "4 Item "-Wmissing-field-initializers" Warn if a structure's initializer has some fields missing. For example, the following code causes such a warning, because CW(C`x.h (C' is implicitly zero: 2 struct s { int f, g, h; }; struct s x = { 3, 4 }; This option does not warn about designated initializers, so the following modification does not trigger a warning: 2 struct s { int f, g, h; }; struct s x = { .f = 3, .g = 4 }; In C this option does not warn about the universal zero initializer {0 } : 2 struct s { int f, g, h; }; struct s x = { 0 }; Likewise, in (C+ this option does not warn about the empty { } initializer, for example: 2 struct s { int f, g, h; }; s x = { }; This warning is included in -Wextra .To get other -Wextra warnings without this one, use -Wextra -Wno -missing -field -initializers .

" -Wno -multichar "4 Item "-Wno-multichar" Do not warn if a multicharacter constant ( 'FOOF' )is used. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable code.

" -Wnormalized= [ none | id | nfc | nfkc ]"4 Item "-Wnormalized=[none|id|nfc|nfkc]" In ISOC and ISO(C+, two identifiers are different if they are different sequences of characters. However, sometimes when characters outside the basic ASCIIcharacter set are used, you can have two different character sequences that look the same. To avoid confusion, the ISO10646 standard sets out some normalizationrules which when applied ensure that two sequences that look the same are turned into the same sequence. GCCcan warn you if you are using identifiers that have not been normalized; this option controls that warning. There are four levels of warning supported by GCC.The default is -Wnormalized=nfc ,which warns about any identifier that is not in the ISO10646 (L"C (R" normalized form, NFC .NFCis the recommended form for most uses. It is equivalent to -Wnormalized . Unfortunately, there are some characters allowed in identifiers by ISOC and ISO(C+ that, when turned into NFC,are not allowed in identifiers. That is, there's no way to use these symbols in portable ISOC or (C+ and have all your identifiers in NFC. -Wnormalized=id suppresses the warning for these characters. It is hoped that future versions of the standards involved will correct this, which is why this option is not the default. You can switch the warning off for all characters by writing -Wnormalized=none or -Wno -normalized .You should only do this if you are using some other normalization scheme (like (L"D (R"), because otherwise you can easily create bugs that are literally impossible to see. Some characters in ISO10646 have distinct meanings but look identical in some fonts or display methodologies, especially once formatting has been applied. For instance CW(C` \ u207F (C' ,(L" SUPERSCRIPTLATIN SMALL LETTER N (R", displays just like a regular CW(C`n (C' that has been placed in a superscript. ISO10646 defines the NFKC normalization scheme to convert all these into a standard form as well, and GCCwarns if your code is not in NFKCif you use -Wnormalized=nfkc .This warning is comparable to warning about every identifier that contains the letter O because it might be confused with the digit 0, and so is not the default, but may be useful as a local coding convention if the programming environment cannot be fixed to display these characters distinctly.

" -Wno -attribute -warning "4 Item "-Wno-attribute-warning" Do not warn about usage of functions declared with CW(C`warning (C' attribute. By default, this warning is enabled. -Wno -attribute -warning can be used to disable the warning or -Wno -error=attribute -warning can be used to disable the error when compiled with -Werror flag.

" -Wno -deprecated "4 Item "-Wno-deprecated" Do not warn about usage of deprecated features.

" -Wno -deprecated -declarations "4 Item "-Wno-deprecated-declarations" Do not warn about uses of functions, variables, and types marked as deprecated by using the CW(C`deprecated (C' attribute.

" -Wno -overflow "4 Item "-Wno-overflow" Do not warn about compile-time overflow in constant expressions.

" -Wno -odr "4 Item "-Wno-odr" Warn about One Definition Rule violations during link-time optimization. Requires -flto -odr -type -merging to be enabled. Enabled by default.

" -Wopenmp -simd "4 Item "-Wopenmp-simd" Warn if the vectorizer cost model overrides the OpenMP simd directive set by user. The -fsimd -cost -model=unlimited option can be used to relax the cost model.

" -Woverride -init (C and Objective-C only)" 4 Item "-Woverride-init (C and Objective-C only)" Warn if an initialized field without side effects is overridden when using designated initializers. This warning is included in -Wextra .To get other -Wextra warnings without this one, use -Wextra -Wno -override -init .

" -Woverride -init -side -effects (C and Objective-C only)" 4 Item "-Woverride-init-side-effects (C and Objective-C only)" Warn if an initialized field with side effects is overridden when using designated initializers. This warning is enabled by default.

" -Wpacked "4 Item "-Wpacked" Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable CW(C`f.x (C' in CW(C`struct bar (C' is misaligned even though CW(C`struct bar (C' does not itself have the packed attribute: 8 struct foo { int x; char a, b, c, d; } _ _attribute_ _((packed)); struct bar { char z; struct foo f; };

" -Wpacked -bitfield -compat "4 Item "-Wpacked-bitfield-compat" The 4.1, 4.2 and 4.3 series of GCCignore the CW(C`packed (C' attribute on bit-fields of type CW(C`char (C' .This has been fixed in GCC4.4 but the change can lead to differences in the structure layout. GCC informs you when the offset of such a field has changed in GCC4.4. For example there is no longer a 4 -bit padding between field CW(C`a (C' and CW(C`b (C' in this structure: 5 struct foo { char a:4; char b:8; } _ _attribute_ _ ((packed)); This warning is enabled by default. Use -Wno -packed -bitfield -compat to disable this warning.

" -Wpacked -not -aligned (C, (C+, Objective-C and Objective -(C+ only)" 4 Item "-Wpacked-not-aligned (C, , Objective-C and Objective- only)" Warn if a structure field with explicitly specified alignment in a packed struct or union is misaligned. For example, a warning will be issued on CW(C`struct S (C' ,like, CW(C`warning: alignment 1 of (Aqstruct S (Aq is less than 8 (C' ,in this code: 4 struct _ _attribute_ _ ((aligned (8))) S8 { char a[8]; }; struct _ _attribute_ _ ((packed)) S { struct S8 s8; }; This warning is enabled by -Wall .

" -Wpadded "4 Item "-Wpadded" Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller.

" -Wredundant -decls "4 Item "-Wredundant-decls" Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing.

" -Wno -restrict "4 Item "-Wno-restrict" Warn when an object referenced by a CW(C`restrict (C' -qualified parameter (or, in (C+, a CW(C`_ _restrict (C' -qualified parameter) is aliased by another argument, or when copies between such objects overlap. For example, the call to the CW(C`strcpy (C' function below attempts to truncate the string by replacing its initial characters with the last four. However, because the call writes the terminating NULinto CW(C`a[4] (C' ,the copies overlap and the call is diagnosed. 6 void foo (void) { char a[] = "abcd1234"; strcpy (a, a + 4); ... } The -Wrestrict option detects some instances of simple overlap even without optimization but works best at -O2 and above. It is included in -Wall .

" -Wnested -externs (C and Objective-C only)" 4 Item "-Wnested-externs (C and Objective-C only)" Warn if an CW(C`extern (C' declaration is encountered within a function.

" -Wno -inherited -variadic -ctor "4 Item "-Wno-inherited-variadic-ctor" Suppress warnings about use of (C+11 inheriting constructors when the base class inherited from has a C variadic constructor; the warning is on by default because the ellipsis is not inherited.

" -Winline "4 Item "-Winline" Warn if a function that is declared as inline cannot be inlined. Even with this option, the compiler does not warn about failures to inline functions declared in system headers. The compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by -Winline to appear or disappear.

" -Wno -invalid -offsetof ( (C+ and Objective -(C+ only)" 4 Item "-Wno-invalid-offsetof ( and Objective- only)" Suppress warnings from applying the CW(C`offsetof (C' macro to a non-POD type. According to the 2014 ISO(C+ standard, applying CW(C`offsetof (C' to a non-standard-layout type is undefined. In existing (C+ implementations, however, CW(C`offsetof (C' typically gives meaningful results. This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to ignore the warning about it. The restrictions on CW(C`offsetof (C' may be relaxed in a future version of the (C+ standard.

" -Wint -in -bool -context "4 Item "-Wint-in-bool-context" Warn for suspicious use of integer values where boolean values are expected, such as conditional expressions (?:) using non-boolean integer constants in boolean context, like CW(C`if (a <= b ? 2 : 3) (C' .Or left shifting of signed integers in boolean context, like CW(C`for (a = 0; 1 << a; a++); (C' .Likewise for all kinds of multiplications regardless of the data type. This warning is enabled by -Wall .

" -Wno -int -to -pointer -cast "4 Item "-Wno-int-to-pointer-cast" Suppress warnings from casts to pointer type of an integer of a different size. In (C+, casting to a pointer type of smaller size is an error. Wint-to-pointer-cast is enabled by default.

" -Wno -pointer -to -int -cast (C and Objective-C only)" 4 Item "-Wno-pointer-to-int-cast (C and Objective-C only)" Suppress warnings from casts from a pointer to an integer type of a different size.

" -Winvalid -pch "4 Item "-Winvalid-pch" Warn if a precompiled header is found in the search path but cannot be used.

" -Wlong -long "4 Item "-Wlong-long" Warn if CW(C`long long (C' type is used. This is enabled by either -Wpedantic or -Wtraditional in ISOC90 and (C+98 modes. To inhibit the warning messages, use -Wno -long -long .

" -Wvariadic -macros "4 Item "-Wvariadic-macros" Warn if variadic macros are used in ISOC90 mode, or if the GNU alternate syntax is used in ISOC99 mode. This is enabled by either -Wpedantic or -Wtraditional .To inhibit the warning messages, use -Wno -variadic -macros .

" -Wvarargs "4 Item "-Wvarargs" Warn upon questionable usage of the macros used to handle variable arguments like CW(C`va_start (C' .This is default. To inhibit the warning messages, use -Wno -varargs .

" -Wvector -operation -performance "4 Item "-Wvector-operation-performance" Warn if vector operation is not implemented via SIMDcapabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be implemented CW(C`piecewise (C' ,which means that the scalar operation is performed on every vector element; CW(C`in parallel (C' ,which means that the vector operation is implemented using scalars of wider type, which normally is more performance efficient; and CW(C`as a single scalar (C' ,which means that vector fits into a scalar type.

" -Wno -virtual -move -assign "4 Item "-Wno-virtual-move-assign" Suppress warnings about inheriting from a virtual base with a non-trivial (C+11 move assignment operator. This is dangerous because if the virtual base is reachable along more than one path, it is moved multiple times, which can mean both objects end up in the moved-from state. If the move assignment operator is written to avoid moving from a moved-from object, this warning can be disabled.

" -Wvla "4 Item "-Wvla" Warn if a variable-length array is used in the code. -Wno -vla prevents the -Wpedantic warning of the variable-length array.

" -Wvla -larger -than= byte-size "4 Item "-Wvla-larger-than=byte-size" If this option is used, the compiler will warn for declarations of variable-length arrays whose size is either unbounded, or bounded by an argument that allows the array size to exceed byte-size bytes. This is similar to how -Walloca -larger -than= byte-size works, but with variable-length arrays. Note that GCCmay optimize small variable-length arrays of a known value into plain arrays, so this warning may not get triggered for such arrays. -Wvla -larger -than= PTRDIFF_MAX is enabled by default but is typically only effective when -ftree -vrp is active (default for -O2 and above). See also -Walloca -larger -than= byte-size .

" -Wno -vla -larger -than "4 Item "-Wno-vla-larger-than" Disable -Wvla -larger -than= warnings. The option is equivalent to -Wvla -larger -than= SIZE_MAX or larger.

" -Wvolatile -register -var "4 Item "-Wvolatile-register-var" Warn if a register variable is declared volatile. The volatile modifier does not inhibit all optimizations that may eliminate reads and/or writes to register variables. This warning is enabled by -Wall .

" -Wdisabled -optimization "4 Item "-Wdisabled-optimization" Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCC'soptimizers are unable to handle the code effectively. Often, the problem is that your code is too big or too complex; GCCrefuses to optimize programs when the optimization itself is likely to take inordinate amounts of time.

" -Wpointer -sign (C and Objective-C only)" 4 Item "-Wpointer-sign (C and Objective-C only)" Warn for pointer argument passing or assignment with different signedness. This option is only supported for C and Objective-C. It is implied by -Wall and by -Wpedantic ,which can be disabled with -Wno -pointer -sign .

" -Wstack -protector "4 Item "-Wstack-protector" This option is only active when -fstack -protector is active. It warns about functions that are not protected against stack smashing.

" -Woverlength -strings "4 Item "-Woverlength-strings" Warn about string constants that are longer than the (L"minimum maximum (R" length specified in the C standard. Modern compilers generally allow string constants that are much longer than the standard's minimum limit, but very portable programs should avoid using longer strings. The limit applies after string constant concatenation, and does not count the trailing NUL.In C90, the limit was 509 characters; in C99, it was raised to 4095. (C+98 does not specify a normative minimum maximum, so we do not diagnose overlength strings in (C+. This option is implied by -Wpedantic ,and can be disabled with -Wno -overlength -strings .

" -Wunsuffixed -float -constants (C and Objective-C only)" 4 Item "-Wunsuffixed-float-constants (C and Objective-C only)" Issue a warning for any floating constant that does not have a suffix. When used together with -Wsystem -headers it warns about such constants in system header files. This can be useful when preparing code to use with the CW(C`FLOAT_CONST_DECIMAL64 (C' pragma from the decimal floating-point extension to C99.

" -Wno -designated -init (C and Objective-C only)" 4 Item "-Wno-designated-init (C and Objective-C only)" Suppress warnings when a positional initializer is used to initialize a structure that has been marked with the CW(C`designated_init (C' attribute.

" -Whsa "4 Item "-Whsa" Issue a warning when HSAILcannot be emitted for the compiled function or OpenMP construct.

Options for Debugging Your Program

Subsection "Options for Debugging Your Program" To tell GCCto emit extra information for use by a debugger, in almost all cases you need only to add -g to your other options.

GCCallows you to use -g with -O .The shortcuts taken by optimized code may occasionally be surprising: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in different places because they have been moved out of loops. Nevertheless it is possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs.

If you are not using some other optimization option, consider using -Og with -g . With no -O option at all, some compiler passes that collect information useful for debugging do not run at all, so that -Og may result in a better debugging experience.

" -g "4 Item "-g" Produce debugging information in the operating system's native format (stabs, COFF,XCOFF, or DWARF).GDBcan work with this debugging information. On most systems that use stabs format, -g enables use of extra debugging information that only GDBcan use; this extra information makes debugging work better in GDBbut probably makes other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gstabs+ , -gstabs , -gxcoff+ , -gxcoff ,or -gvms (see below).

" -ggdb "4 Item "-ggdb" Produce debugging information for use by GDB.This means to use the most expressive format available ( DWARF,stabs, or the native format if neither of those are supported), including GDBextensions if at all possible.

" -gdwarf "4 Item "-gdwarf" 0

" -gdwarf - version "4 Item "-gdwarf-version" Produce debugging information in DWARFformat (if that is supported). The value of version may be either 2, 3, 4 or 5; the default version for most targets is 4. DWARFVersion 5 is only experimental. Note that with DWARFVersion 2, some ports require and always use some non-conflicting DWARF3 extensions in the unwind tables. Version 4 may require GDB7.0 and -fvar -tracking -assignments for maximum benefit. GCCno longer supports DWARFVersion 1, which is substantially different than Version 2 and later. For historical reasons, some other DWARF-related options such as -fno -dwarf2 -cfi -asm )retain a reference to DWARFVersion 2 in their names, but apply to all currently-supported versions of DWARF.

" -gstabs "4 Item "-gstabs" Produce debugging information in stabs format (if that is supported), without GDBextensions. This is the format used by DBXon most BSD systems. On MIPS,Alpha and System V Release 4 systems this option produces stabs debugging output that is not understood by DBX. On System V Release 4 systems this option requires the GNUassembler.

" -gstabs+ "4 Item "-gstabs+" Produce debugging information in stabs format (if that is supported), using GNUextensions understood only by the GNUdebugger ( GDB).The use of these extensions is likely to make other debuggers crash or refuse to read the program.

" -gxcoff "4 Item "-gxcoff" Produce debugging information in XCOFFformat (if that is supported). This is the format used by the DBXdebugger on IBMRS/6000 systems.

" -gxcoff+ "4 Item "-gxcoff+" Produce debugging information in XCOFFformat (if that is supported), using GNUextensions understood only by the GNUdebugger ( GDB).The use of these extensions is likely to make other debuggers crash or refuse to read the program, and may cause assemblers other than the GNU assembler ( GAS)to fail with an error.

" -gvms "4 Item "-gvms" Produce debugging information in Alpha/VMS debug format (if that is supported). This is the format used by DEBUGon Alpha/VMS systems.

" -g level "4 Item "-glevel" 0

" -ggdb level "4 Item "-ggdblevel"

" -gstabs level "4 Item "-gstabslevel"

" -gxcoff level "4 Item "-gxcofflevel"

" -gvms level "4 Item "-gvmslevel" Request debugging information and also use level to specify how much information. The default level is 2. Level 0 produces no debug information at all. Thus, -g0 negates -g . Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, and line number tables, but no information about local variables. Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3 . If you use multiple -g options, with or without level numbers, the last such option is the one that is effective. -gdwarf does not accept a concatenated debug level, to avoid confusion with -gdwarf - level . Instead use an additional -g level option to change the debug level for DWARF.

" -feliminate -unused -debug -symbols "4 Item "-feliminate-unused-debug-symbols" Produce debugging information in stabs format (if that is supported), for only symbols that are actually used.

" -femit -class -debug -always "4 Item "-femit-class-debug-always" Instead of emitting debugging information for a (C+ class in only one object file, emit it in all object files using the class. This option should be used only with debuggers that are unable to handle the way GCC normally emits debugging information for classes because using this option increases the size of debugging information by as much as a factor of two.

" -fno -merge -debug -strings "4 Item "-fno-merge-debug-strings" Direct the linker to not merge together strings in the debugging information that are identical in different object files. Merging is not supported by all assemblers or linkers. Merging decreases the size of the debug information in the output file at the cost of increasing link processing time. Merging is enabled by default.

" -fdebug -prefix -map= old = new "4 Item "-fdebug-prefix-map=old=new" When compiling files residing in directory old ,record debugging information describing them as if the files resided in directory new instead. This can be used to replace a build-time path with an install-time path in the debug info. It can also be used to change an absolute path to a relative path by using . for new .This can give more reproducible builds, which are location independent, but may require an extra command to tell GDB where to find the source files. See also -ffile -prefix -map .

" -fvar -tracking "4 Item "-fvar-tracking" Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging information format supports this information). It is enabled by default when compiling with optimization ( -Os , -O , -O2 ,...), debugging information ( -g )and the debug info format supports it.

" -fvar -tracking -assignments "4 Item "-fvar-tracking-assignments" Annotate assignments to user variables early in the compilation and attempt to carry the annotations over throughout the compilation all the way to the end, in an attempt to improve debug information while optimizing. Use of -gdwarf -4 is recommended along with it. It can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end. By default, this flag is enabled together with -fvar -tracking , except when selective scheduling is enabled.

" -gsplit -dwarf "4 Item "-gsplit-dwarf" Separate as much DWARFdebugging information as possible into a separate output file with the extension .dwo .This option allows the build system to avoid linking files with debug information. To be useful, this option requires a debugger capable of reading .dwo files.

" -gdescribe -dies "4 Item "-gdescribe-dies" Add description attributes to some DWARFDIEs that have no name attribute, such as artificial variables, external references and call site parameter DIEs.

" -gpubnames "4 Item "-gpubnames" Generate DWARF CW(C`.debug_pubnames (C' and CW(C`.debug_pubtypes (C' sections.

" -ggnu -pubnames "4 Item "-ggnu-pubnames" Generate CW(C`.debug_pubnames (C' and CW(C`.debug_pubtypes (C' sections in a format suitable for conversion into a GDBindex. This option is only useful with a linker that can produce GDBindex version 7.

" -fdebug -types -section "4 Item "-fdebug-types-section" When using DWARFVersion 4 or higher, type DIEs can be put into their own CW(C`.debug_types (C' section instead of making them part of the CW(C`.debug_info (C' section. It is more efficient to put them in a separate comdat section since the linker can then remove duplicates. But not all DWARFconsumers support CW(C`.debug_types (C' sections yet and on some objects CW(C`.debug_types (C' produces larger instead of smaller debugging information.

" -grecord -gcc -switches "4 Item "-grecord-gcc-switches" 0

" -gno -record -gcc -switches "4 Item "-gno-record-gcc-switches" This switch causes the command-line options used to invoke the compiler that may affect code generation to be appended to the DW_AT_producer attribute in DWARFdebugging information. The options are concatenated with spaces separating them from each other and from the compiler version. It is enabled by default. See also -frecord -gcc -switches for another way of storing compiler options into the object file.

" -gstrict -dwarf "4 Item "-gstrict-dwarf" Disallow using extensions of later DWARFstandard version than selected with -gdwarf - version .On most targets using non-conflicting DWARFextensions from later standard versions is allowed.

" -gno -strict -dwarf "4 Item "-gno-strict-dwarf" Allow using extensions of later DWARFstandard version than selected with -gdwarf - version .

" -gas -loc -support "4 Item "-gas-loc-support" Inform the compiler that the assembler supports CW(C`.loc (C' directives. It may then use them for the assembler to generate DWARF2+line number tables. This is generally desirable, because assembler-generated line-number tables are a lot more compact than those the compiler can generate itself. This option will be enabled by default if, at GCCconfigure time, the assembler was found to support such directives.

" -gno -as -loc -support "4 Item "-gno-as-loc-support" Force GCCto generate DWARF2+line number tables internally, if DWARF2+ line number tables are to be generated.

" gas-locview-support "4 Item "gas-locview-support" Inform the compiler that the assembler supports CW(C`view (C' assignment and reset assertion checking in CW(C`.loc (C' directives. This option will be enabled by default if, at GCCconfigure time, the assembler was found to support them.

" gno-as-locview-support "4 Item "gno-as-locview-support" Force GCCto assign view numbers internally, if -gvariable -location -views are explicitly requested.

" -gcolumn -info "4 Item "-gcolumn-info" 0

" -gno -column -info "4 Item "-gno-column-info" Emit location column information into DWARFdebugging information, rather than just file and line. This option is enabled by default.

" -gstatement -frontiers "4 Item "-gstatement-frontiers" 0

" -gno -statement -frontiers "4 Item "-gno-statement-frontiers" This option causes GCCto create markers in the internal representation at the beginning of statements, and to keep them roughly in place throughout compilation, using them to guide the output of CW(C`is_stmt (C' markers in the line number table. This is enabled by default when compiling with optimization ( -Os , -O , -O2 , ...), and outputting DWARF2 debug information at the normal level.

" -gvariable -location -views "4 Item "-gvariable-location-views" 0

" -gvariable -location -views=incompat5 "4 Item "-gvariable-location-views=incompat5"

" -gno -variable -location -views "4 Item "-gno-variable-location-views" Augment variable location lists with progressive view numbers implied from the line number table. This enables debug information consumers to inspect state at certain points of the program, even if no instructions associated with the corresponding source locations are present at that point. If the assembler lacks support for view numbers in line number tables, this will cause the compiler to emit the line number table, which generally makes them somewhat less compact. The augmented line number tables and location lists are fully backward-compatible, so they can be consumed by debug information consumers that are not aware of these augmentations, but they won't derive any benefit from them either. This is enabled by default when outputting DWARF2 debug information at the normal level, as long as there is assembler support, -fvar -tracking -assignments is enabled and -gstrict -dwarf is not. When assembler support is not available, this may still be enabled, but it will force GCCto output internal line number tables, and if -ginternal -reset -location -views is not enabled, that will most certainly lead to silently mismatching location views. There is a proposed representation for view numbers that is not backward compatible with the location list format introduced in DWARF5, that can be enabled with -gvariable -location -views=incompat5 .This option may be removed in the future, is only provided as a reference implementation of the proposed representation. Debug information consumers are not expected to support this extended format, and they would be rendered unable to decode location lists using it.

" -ginternal -reset -location -views "4 Item "-ginternal-reset-location-views" 0

" -gnointernal -reset -location -views "4 Item "-gnointernal-reset-location-views" Attempt to determine location views that can be omitted from location view lists. This requires the compiler to have very accurate insn length estimates, which isn't always the case, and it may cause incorrect view lists to be generated silently when using an assembler that does not support location view lists. The GNUassembler will flag any such error as a CW(C`view number mismatch (C' .This is only enabled on ports that define a reliable estimation function.

" -ginline -points "4 Item "-ginline-points" 0

" -gno -inline -points "4 Item "-gno-inline-points" Generate extended debug information for inlined functions. Location view tracking markers are inserted at inlined entry points, so that address and view numbers can be computed and output in debug information. This can be enabled independently of location views, in which case the view numbers won't be output, but it can only be enabled along with statement frontiers, and it is only enabled by default if location views are enabled.

" -gz [ = type ]"4 Item "-gz[=type]" Produce compressed debug sections in DWARFformat, if that is supported. If type is not given, the default type depends on the capabilities of the assembler and linker used. type may be one of none (don't compress debug sections), zlib (use zlib compression in ELFgABI format), or zlib-gnu (use zlib compression in traditional GNUformat). If the linker doesn't support writing compressed debug sections, the option is rejected. Otherwise, if the assembler does not support them, -gz is silently ignored when producing object files.

" -femit -struct -debug -baseonly "4 Item "-femit-struct-debug-baseonly" Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the struct is defined. This option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit -struct -debug -reduced for a less aggressive option. See -femit -struct -debug -detailed for more detailed control. This option works only with DWARFdebug output.

" -femit -struct -debug -reduced "4 Item "-femit-struct-debug-reduced" Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the type is defined, unless the struct is a template or defined in a system header. This option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit -struct -debug -baseonly for a more aggressive option. See -femit -struct -debug -detailed for more detailed control. This option works only with DWARFdebug output.

" -femit -struct -debug -detailed [ = spec-list ]"4 Item "-femit-struct-debug-detailed[=spec-list]" Specify the struct-like types for which the compiler generates debug information. The intent is to reduce duplicate struct debug information between different object files within the same program. This option is a detailed version of -femit -struct -debug -reduced and -femit -struct -debug -baseonly , which serves for most needs. A specification has the syntax[ dir: | ind: ][ ord: | gen: ]( any | sys | base | none ) The optional first word limits the specification to structs that are used directly ( dir: )or used indirectly ( ind: ). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is structone direct; struct two * indirect; . The optional second word limits the specification to ordinary structs ( ord: )or generic structs ( gen: ). Generic structs are a bit complicated to explain. For (C+, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit -struct -debug -detailed does not yet implement them. The third word specifies the source files for those structs for which the compiler should emit debug information. The values none and any have the normal meaning. The value base means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling foo.c ,debug information is generated for types declared in that file and foo.h , but not other header files. The value sys means those types satisfying base or declared in system or compiler headers. You may need to experiment to determine the best settings for your application. The default is -femit -struct -debug -detailed=all . This option works only with DWARFdebug output.

" -fno -dwarf2 -cfi -asm "4 Item "-fno-dwarf2-cfi-asm" Emit DWARFunwind info as compiler generated CW(C`.eh_frame (C' section instead of using GAS CW(C`.cfi_* (C' directives.

" -fno -eliminate -unused -debug -types "4 Item "-fno-eliminate-unused-debug-types" Normally, when producing DWARFoutput, GCCavoids producing debug symbol output for types that are nowhere used in the source file being compiled. Sometimes it is useful to have GCCemit debugging information for all types declared in a compilation unit, regardless of whether or not they are actually used in that compilation unit, for example if, in the debugger, you want to cast a value to a type that is not actually used in your program (but is declared). More often, however, this results in a significant amount of wasted space.

Options That Control Optimization

Subsection "Options That Control Optimization" These options control various sorts of optimizations.

Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you expect from the source code.

Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.

The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them.

Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section.

Most optimizations are completely disabled at -O0 or if an -O level is not set on the command line, even if individual optimization flags are specified. Similarly, -Og suppresses many optimization passes.

Depending on the target and how GCCwas configured, a slightly different set of optimizations may be enabled at each -O level than those listed here. You can invoke GCCwith -Q --help=optimizers to find out the exact set of optimizations that are enabled at each level.

" -O "4 Item "-O" 0

" -O1 "4 Item "-O1" Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. With -O ,the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. -O turns on the following optimization flags: -fauto -inc -dec -fbranch -count -reg -fcombine -stack -adjustments -fcompare -elim -fcprop -registers -fdce -fdefer -pop -fdelayed -branch -fdse -fforward -propagate -fguess -branch -probability -fif -conversion -fif -conversion2 -finline -functions -called -once -fipa -profile -fipa -pure -const -fipa -reference -fipa -reference -addressable -fmerge -constants -fmove -loop -invariants -fomit -frame -pointer -freorder -blocks -fshrink -wrap -fshrink -wrap -separate -fsplit -wide -types -fssa -backprop -fssa -phiopt -ftree -bit -ccp -ftree -ccp -ftree -ch -ftree -coalesce -vars -ftree -copy -prop -ftree -dce -ftree -dominator -opts -ftree -dse -ftree -forwprop -ftree -fre -ftree -phiprop -ftree -pta -ftree -scev -cprop -ftree -sink -ftree -slsr -ftree -sra -ftree -ter -funit -at -a -time

" -O2 "4 Item "-O2" Optimize even more. GCCperforms nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to -O ,this option increases both compilation time and the performance of the generated code. -O2 turns on all optimization flags specified by -O .It also turns on the following optimization flags: -falign -functions -falign -jumps -falign -labels -falign -loops -fcaller -saves -fcode -hoisting -fcrossjumping -fcse -follow -jumps -fcse -skip -blocks -fdelete -null -pointer -checks -fdevirtualize -fdevirtualize -speculatively -fexpensive -optimizations -fgcse -fgcse -lm -fhoist -adjacent -loads -finline -small -functions -findirect -inlining -fipa -bit -cp -fipa -cp -fipa -icf -fipa -ra -fipa -sra -fipa -vrp -fisolate -erroneous -paths -dereference -flra -remat -foptimize -sibling -calls -foptimize -strlen -fpartial -inlining -fpeephole2 -freorder -blocks -algorithm=stc -freorder -blocks -and -partition -freorder -functions -frerun -cse -after -loop -fschedule -insns -fschedule -insns2 -fsched -interblock -fsched -spec -fstore -merging -fstrict -aliasing -fthread -jumps -ftree -builtin -call -dce -ftree -pre -ftree -switch -conversion -ftree -tail -merge -ftree -vrp Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos.

" -O3 "4 Item "-O3" Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the following optimization flags: -fgcse -after -reload -finline -functions -fipa -cp -clone -floop -interchange -floop -unroll -and -jam -fpeel -loops -fpredictive -commoning -fsplit -paths -ftree -loop -distribute -patterns -ftree -loop -distribution -ftree -loop -vectorize -ftree -partial -pre -ftree -slp -vectorize -funswitch -loops -fvect -cost -model -fversion -loops -for -strides

" -O0 "4 Item "-O0" Reduce compilation time and make debugging produce the expected results. This is the default.

" -Os "4 Item "-Os" Optimize for size. -Os enables all -O2 optimizations except those that often increase code size: -falign -functions -falign -jumps -falign -labels -falign -loops -fprefetch -loop -arrays -freorder -blocks -algorithm=stc It also enables -finline -functions ,causes the compiler to tune for code size rather than execution speed, and performs further optimizations designed to reduce code size.

" -Ofast "4 Item "-Ofast" Disregard strict standards compliance. -Ofast enables all -O3 optimizations. It also enables optimizations that are not valid for all standard-compliant programs. It turns on -ffast -math and the Fortran-specific -fstack -arrays ,unless -fmax -stack -var -size is specified, and -fno -protect -parens .

" -Og "4 Item "-Og" Optimize debugging experience. -Og should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience. It is a better choice than -O0 for producing debuggable code because some compiler passes that collect debug information are disabled at -O0 . Like -O0 , -Og completely disables a number of optimization passes so that individual options controlling them have no effect. Otherwise -Og enables all -O1 optimization flags except for those that may interfere with debugging: -fbranch -count -reg -fdelayed -branch -fif -conversion -fif -conversion2 -finline -functions -called -once -fmove -loop -invariants -fssa -phiopt -ftree -bit -ccp -ftree -pta -ftree -sra

If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.

Options of the form -f flag specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo is -fno -foo .In the table below, only one of the forms is listed ---the one you typically use. You can figure out the other form by either removing no- or adding it.

The following options control specific optimizations. They are either activated by -O options or are related to ones that are. You can use the following flags in the rare cases when (L"fine-tuning (R" of optimizations to be performed is desired.

" -fno -defer -pop "4 Item "-fno-defer-pop" For machines that must pop arguments after a function call, always pop the arguments as soon as each function returns. At levels -O1 and higher, -fdefer -pop is the default; this allows the compiler to let arguments accumulate on the stack for several function calls and pop them all at once.

" -fforward -propagate "4 Item "-fforward-propagate" Perform a forward propagation pass on RTL.The pass tries to combine two instructions and checks if the result can be simplified. If loop unrolling is active, two passes are performed and the second is scheduled after loop unrolling. This option is enabled by default at optimization levels -O , -O2 , -O3 , -Os .

" -ffp -contract= style "4 Item "-ffp-contract=style" -ffp -contract=off disables floating-point expression contraction. -ffp -contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. -ffp -contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to -ffp -contract=off . The default is -ffp -contract=fast .

" -fomit -frame -pointer "4 Item "-fomit-frame-pointer" Omit the frame pointer in functions that don't need one. This avoids the instructions to save, set up and restore the frame pointer; on many targets it also makes an extra register available. On some targets this flag has no effect because the standard calling sequence always uses a frame pointer, so it cannot be omitted. Note that -fno -omit -frame -pointer doesn't guarantee the frame pointer is used in all functions. Several targets always omit the frame pointer in leaf functions. Enabled by default at -O and higher.

" -foptimize -sibling -calls "4 Item "-foptimize-sibling-calls" Optimize sibling and tail recursive calls. Enabled at levels -O2 , -O3 , -Os .

" -foptimize -strlen "4 Item "-foptimize-strlen" Optimize various standard C string functions (e.g. CW(C`strlen (C' , CW(C`strchr (C' or CW(C`strcpy (C' )and their CW(C`_FORTIFY_SOURCE (C' counterparts into faster alternatives. Enabled at levels -O2 , -O3 .

" -fno -inline "4 Item "-fno-inline" Do not expand any functions inline apart from those marked with the CW(C`always_inline (C' attribute. This is the default when not optimizing. Single functions can be exempted from inlining by marking them with the CW(C`noinline (C' attribute.

" -finline -small -functions "4 Item "-finline-small-functions" Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this way. This inlining applies to all functions, even those not declared inline. Enabled at levels -O2 , -O3 , -Os .

" -findirect -inlining "4 Item "-findirect-inlining" Inline also indirect calls that are discovered to be known at compile time thanks to previous inlining. This option has any effect only when inlining itself is turned on by the -finline -functions or -finline -small -functions options. Enabled at levels -O2 , -O3 , -Os .

" -finline -functions "4 Item "-finline-functions" Consider all functions for inlining, even if they are not declared inline. The compiler heuristically decides which functions are worth integrating in this way. If all calls to a given function are integrated, and the function is declared CW(C`static (C' ,then the function is normally not output as assembler code in its own right. Enabled at levels -O3 , -Os .Also enabled by -fprofile -use and -fauto -profile .

" -finline -functions -called -once "4 Item "-finline-functions-called-once" Consider all CW(C`static (C' functions called once for inlining into their caller even if they are not marked CW(C`inline (C' .If a call to a given function is integrated, then the function is not output as assembler code in its own right. Enabled at levels -O1 , -O2 , -O3 and -Os , but not -Og .

" -fearly -inlining "4 Item "-fearly-inlining" Inline functions marked by CW(C`always_inline (C' and functions whose body seems smaller than the function call overhead early before doing -fprofile -generate instrumentation and real inlining pass. Doing so makes profiling significantly cheaper and usually inlining faster on programs having large chains of nested wrapper functions. Enabled by default.

" -fipa -sra "4 Item "-fipa-sra" Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value. Enabled at levels -O2 , -O3 and -Os .

" -finline -limit= n "4 Item "-finline-limit=n" By default, GCClimits the size of functions that can be inlined. This flag allows coarse control of this limit. n is the size of functions that can be inlined in number of pseudo instructions. Inlining is actually controlled by a number of parameters, which may be specified individually by using --param name = value . The -finline -limit= n option sets some of these parameters as follows:

" max-inline-insns-single "4 Item "max-inline-insns-single" is set to n /2.

" max-inline-insns-auto "4 Item "max-inline-insns-auto" is set to n /2. See below for a documentation of the individual parameters controlling inlining and for the defaults of these parameters. Note: there may be no value to -finline -limit that results in default behavior. Note: pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way does it represent a count of assembly instructions and as such its exact meaning might change from one release to an another.

" -fno -keep -inline -dllexport "4 Item "-fno-keep-inline-dllexport" This is a more fine-grained version of -fkeep -inline -functions , which applies only to functions that are declared using the CW(C`dllexport (C' attribute or declspec.

" -fkeep -inline -functions "4 Item "-fkeep-inline-functions" In C, emit CW(C`static (C' functions that are declared CW(C`inline (C' into the object file, even if the function has been inlined into all of its callers. This switch does not affect functions using the CW(C`extern inline (C' extension in GNUC90. In (C+, emit any and all inline functions into the object file.

" -fkeep -static -functions "4 Item "-fkeep-static-functions" Emit CW(C`static (C' functions into the object file, even if the function is never used.

" -fkeep -static -consts "4 Item "-fkeep-static-consts" Emit variables declared CW(C`static const (C' when optimization isn't turned on, even if the variables aren't referenced. GCCenables this option by default. If you want to force the compiler to check if a variable is referenced, regardless of whether or not optimization is turned on, use the -fno -keep -static -consts option.

" -fmerge -constants "4 Item "-fmerge-constants" Attempt to merge identical constants (string constants and floating-point constants) across compilation units. This option is the default for optimized compilation if the assembler and linker support it. Use -fno -merge -constants to inhibit this behavior. Enabled at levels -O , -O2 , -O3 , -Os .

" -fmerge -all -constants "4 Item "-fmerge-all-constants" Attempt to merge identical constants and identical variables. This option implies -fmerge -constants .In addition to -fmerge -constants this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating-point types. Languages like C or (C+ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option results in non-conforming behavior.

" -fmodulo -sched "4 Item "-fmodulo-sched" Perform swing modulo scheduling immediately before the first scheduling pass. This pass looks at innermost loops and reorders their instructions by overlapping different iterations.

" -fmodulo -sched -allow -regmoves "4 Item "-fmodulo-sched-allow-regmoves" Perform more aggressive SMS-based modulo scheduling with register moves allowed. By setting this flag certain anti-dependences edges are deleted, which triggers the generation of reg-moves based on the life-range analysis. This option is effective only with -fmodulo -sched enabled.

" -fno -branch -count -reg "4 Item "-fno-branch-count-reg" Disable the optimization pass that scans for opportunities to use (L"decrement and branch (R" instructions on a count register instead of instruction sequences that decrement a register, compare it against zero, and then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, IA-64 and S/390. Note that the -fno -branch -count -reg option doesn't remove the decrement and branch instructions from the generated instruction stream introduced by other optimization passes. The default is -fbranch -count -reg at -O1 and higher, except for -Og .

" -fno -function -cse "4 Item "-fno-function-cse" Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. The default is -ffunction -cse

" -fno -zero -initialized -in -bss "4 Item "-fno-zero-initialized-in-bss" If the target supports a BSSsection, GCCby default puts variables that are initialized to zero into BSS.This can save space in the resulting code. This option turns off this behavior because some programs explicitly rely on variables going to the data section ---e.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that. The default is -fzero -initialized -in -bss .

" -fthread -jumps "4 Item "-fthread-jumps" Perform optimizations that check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. Enabled at levels -O2 , -O3 , -Os .

" -fsplit -wide -types "4 Item "-fsplit-wide-types" When using a type that occupies multiple registers, such as CW(C`long long (C' on a 32 -bit system, split the registers apart and allocate them independently. This normally generates better code for those types, but may make debugging more difficult. Enabled at levels -O , -O2 , -O3 , -Os .

" -fcse -follow -jumps "4 Item "-fcse-follow-jumps" In common subexpression elimination ( CSE),scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSEencounters an CW(C`if (C' statement with an CW(C`else (C' clause, CSEfollows the jump when the condition tested is false. Enabled at levels -O2 , -O3 , -Os .

" -fcse -skip -blocks "4 Item "-fcse-skip-blocks" This is similar to -fcse -follow -jumps ,but causes CSEto follow jumps that conditionally skip over blocks. When CSE encounters a simple CW(C`if (C' statement with no else clause, -fcse -skip -blocks causes CSEto follow the jump around the body of the CW(C`if (C' . Enabled at levels -O2 , -O3 , -Os .

" -frerun -cse -after -loop "4 Item "-frerun-cse-after-loop" Re-run common subexpression elimination after loop optimizations are performed. Enabled at levels -O2 , -O3 , -Os .

" -fgcse "4 Item "-fgcse" Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. Note: When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding -fno -gcse to the command line. Enabled at levels -O2 , -O3 , -Os .

" -fgcse -lm "4 Item "-fgcse-lm" When -fgcse -lm is enabled, global common subexpression elimination attempts to move loads that are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. Enabled by default when -fgcse is enabled.

" -fgcse -sm "4 Item "-fgcse-sm" When -fgcse -sm is enabled, a store motion pass is run after global common subexpression elimination. This pass attempts to move stores out of loops. When used in conjunction with -fgcse -lm , loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. Not enabled at any optimization level.

" -fgcse -las "4 Item "-fgcse-las" When -fgcse -las is enabled, the global common subexpression elimination pass eliminates redundant loads that come after stores to the same memory location (both partial and full redundancies). Not enabled at any optimization level.

" -fgcse -after -reload "4 Item "-fgcse-after-reload" When -fgcse -after -reload is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to clean up redundant spilling. Enabled by -fprofile -use and -fauto -profile .

" -faggressive -loop -optimizations "4 Item "-faggressive-loop-optimizations" This option tells the loop optimizer to use language constraints to derive bounds for the number of iterations of a loop. This assumes that loop code does not invoke undefined behavior by for example causing signed integer overflows or out-of-bound array accesses. The bounds for the number of iterations of a loop are used to guide loop unrolling and peeling and loop exit test optimizations. This option is enabled by default.

" -funconstrained -commons "4 Item "-funconstrained-commons" This option tells the compiler that variables declared in common blocks (e.g. Fortran) may later be overridden with longer trailing arrays. This prevents certain optimizations that depend on knowing the array bounds.

" -fcrossjumping "4 Item "-fcrossjumping" Perform cross-jumping transformation. This transformation unifies equivalent code and saves code size. The resulting code may or may not perform better than without cross-jumping. Enabled at levels -O2 , -O3 , -Os .

" -fauto -inc -dec "4 Item "-fauto-inc-dec" Combine increments or decrements of addresses with memory accesses. This pass is always skipped on architectures that do not have instructions to support this. Enabled by default at -O and higher on architectures that support this.

" -fdce "4 Item "-fdce" Perform dead code elimination ( DCE)on RTL. Enabled by default at -O and higher.

" -fdse "4 Item "-fdse" Perform dead store elimination ( DSE)on RTL. Enabled by default at -O and higher.

" -fif -conversion "4 Item "-fif-conversion" Attempt to transform conditional jumps into branch-less equivalents. This includes use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by -fif -conversion2 . Enabled at levels -O , -O2 , -O3 , -Os ,but not with -Og .

" -fif -conversion2 "4 Item "-fif-conversion2" Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. Enabled at levels -O , -O2 , -O3 , -Os ,but not with -Og .

" -fdeclone -ctor -dtor "4 Item "-fdeclone-ctor-dtor" The (C+ ABIrequires multiple entry points for constructors and destructors: one for a base subobject, one for a complete object, and one for a virtual destructor that calls operator delete afterwards. For a hierarchy with virtual bases, the base and complete variants are clones, which means two copies of the function. With this option, the base and complete variants are changed to be thunks that call a common implementation. Enabled by -Os .

" -fdelete -null -pointer -checks "4 Item "-fdelete-null-pointer-checks" Assume that programs cannot safely dereference null pointers, and that no code or data element resides at address zero. This option enables simple constant folding optimizations at all optimization levels. In addition, other optimization passes in GCCuse this flag to control global dataflow analyses that eliminate useless checks for null pointers; these assume that a memory access to address zero always results in a trap, so that if a pointer is checked after it has already been dereferenced, it cannot be null. Note however that in some environments this assumption is not true. Use -fno -delete -null -pointer -checks to disable this optimization for programs that depend on that behavior. This option is enabled by default on most targets. On Nios IIELF, it defaults to off. On AVR,CR16, and MSP430,this option is completely disabled. Passes that use the dataflow information are enabled independently at different optimization levels.

" -fdevirtualize "4 Item "-fdevirtualize" Attempt to convert calls to virtual functions to direct calls. This is done both within a procedure and interprocedurally as part of indirect inlining ( -findirect -inlining )and interprocedural constant propagation ( -fipa -cp ). Enabled at levels -O2 , -O3 , -Os .

" -fdevirtualize -speculatively "4 Item "-fdevirtualize-speculatively" Attempt to convert calls to virtual functions to speculative direct calls. Based on the analysis of the type inheritance graph, determine for a given call the set of likely targets. If the set is small, preferably of size 1, change the call into a conditional deciding between direct and indirect calls. The speculative calls enable more optimizations, such as inlining. When they seem useless after further optimization, they are converted back into original form.

" -fdevirtualize -at -ltrans "4 Item "-fdevirtualize-at-ltrans" Stream extra information needed for aggressive devirtualization when running the link-time optimizer in local transformation mode. This option enables more devirtualization but significantly increases the size of streamed data. For this reason it is disabled by default.

" -fexpensive -optimizations "4 Item "-fexpensive-optimizations" Perform a number of minor optimizations that are relatively expensive. Enabled at levels -O2 , -O3 , -Os .

" -free "4 Item "-free" Attempt to remove redundant extension instructions. This is especially helpful for the x86 -64 architecture, which implicitly zero-extends in 64 -bit registers after writing to their lower 32 -bit half. Enabled for Alpha, AArch64 and x86 at levels -O2 , -O3 , -Os .

" -fno -lifetime -dse "4 Item "-fno-lifetime-dse" In (C+ the value of an object is only affected by changes within its lifetime: when the constructor begins, the object has an indeterminate value, and any changes during the lifetime of the object are dead when the object is destroyed. Normally dead store elimination will take advantage of this; if your code relies on the value of the object storage persisting beyond the lifetime of the object, you can use this flag to disable this optimization. To preserve stores before the constructor starts (e.g. because your operator new clears the object storage) but still treat the object as dead after the destructor you, can use -flifetime -dse=1 .The default behavior can be explicitly selected with -flifetime -dse=2 . -flifetime -dse=0 is equivalent to -fno -lifetime -dse .

" -flive -range -shrinkage "4 Item "-flive-range-shrinkage" Attempt to decrease register pressure through register live range shrinkage. This is helpful for fast processors with small or moderate size register sets.

" -fira -algorithm= algorithm "4 Item "-fira-algorithm=algorithm" Use the specified coloring algorithm for the integrated register allocator. The algorithm argument can be priority ,which specifies Chow's priority coloring, or CB ,which specifies Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented for all architectures, but for those targets that do support it, it is the default because it generates better code.

" -fira -region= region "4 Item "-fira-region=region" Use specified regions for the integrated register allocator. The region argument should be one of the following:

" all "4 Item "all" Use all loops as register allocation regions. This can give the best results for machines with a small and/or irregular register set.

" mixed "4 Item "mixed" Use all loops except for loops with small register pressure as the regions. This value usually gives the best results in most cases and for most architectures, and is enabled by default when compiling with optimization for speed ( -O , -O2 ,...).

" one "4 Item "one" Use all functions as a single region. This typically results in the smallest code size, and is enabled by default for -Os or -O0 .

" -fira -hoist -pressure "4 Item "-fira-hoist-pressure" Use IRAto evaluate register pressure in the code hoisting pass for decisions to hoist expressions. This option usually results in smaller code, but it can slow the compiler down. This option is enabled at level -Os for all targets.

" -fira -loop -pressure "4 Item "-fira-loop-pressure" Use IRAto evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on machines with large register files (>= 32 registers), but it can slow the compiler down. This option is enabled at level -O3 for some targets.

" -fno -ira -share -save -slots "4 Item "-fno-ira-share-save-slots" Disable sharing of stack slots used for saving call-used hard registers living through a call. Each hard register gets a separate stack slot, and as a result function stack frames are larger.

" -fno -ira -share -spill -slots "4 Item "-fno-ira-share-spill-slots" Disable sharing of stack slots allocated for pseudo-registers. Each pseudo-register that does not get a hard register gets a separate stack slot, and as a result function stack frames are larger.

" -flra -remat "4 Item "-flra-remat" Enable CFG-sensitive rematerialization in LRA.Instead of loading values of spilled pseudos, LRAtries to rematerialize (recalculate) values if it is profitable. Enabled at levels -O2 , -O3 , -Os .

" -fdelayed -branch "4 Item "-fdelayed-branch" If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. Enabled at levels -O , -O2 , -O3 , -Os , but not at -Og .

" -fschedule -insns "4 Item "-fschedule-insns" If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating-point instruction is required. Enabled at levels -O2 , -O3 .

" -fschedule -insns2 "4 Item "-fschedule-insns2" Similar to -fschedule -insns ,but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. Enabled at levels -O2 , -O3 , -Os .

" -fno -sched -interblock "4 Item "-fno-sched-interblock" Disable instruction scheduling across basic blocks, which is normally enabled when scheduling before register allocation, i.e. with -fschedule -insns or at -O2 or higher.

" -fno -sched -spec "4 Item "-fno-sched-spec" Disable speculative motion of non-load instructions, which is normally enabled when scheduling before register allocation, i.e. with -fschedule -insns or at -O2 or higher.

" -fsched -pressure "4 Item "-fsched-pressure" Enable register pressure sensitive insn scheduling before register allocation. This only makes sense when scheduling before register allocation is enabled, i.e. with -fschedule -insns or at -O2 or higher. Usage of this option can improve the generated code and decrease its size by preventing register pressure increase above the number of available hard registers and subsequent spills in register allocation.

" -fsched -spec -load "4 Item "-fsched-spec-load" Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule -insns or at -O2 or higher.

" -fsched -spec -load -dangerous "4 Item "-fsched-spec-load-dangerous" Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule -insns or at -O2 or higher.

" -fsched -stalled -insns "4 Item "-fsched-stalled-insns" 0

" -fsched -stalled -insns= n "4 Item "-fsched-stalled-insns=n" Define how many insns (if any) can be moved prematurely from the queue of stalled insns into the ready list during the second scheduling pass. -fno -sched -stalled -insns means that no insns are moved prematurely, -fsched -stalled -insns=0 means there is no limit on how many queued insns can be moved prematurely. -fsched -stalled -insns without a value is equivalent to -fsched -stalled -insns=1 .

" -fsched -stalled -insns -dep "4 Item "-fsched-stalled-insns-dep" 0

" -fsched -stalled -insns -dep= n "4 Item "-fsched-stalled-insns-dep=n" Define how many insn groups (cycles) are examined for a dependency on a stalled insn that is a candidate for premature removal from the queue of stalled insns. This has an effect only during the second scheduling pass, and only if -fsched -stalled -insns is used. -fno -sched -stalled -insns -dep is equivalent to -fsched -stalled -insns -dep=0 . -fsched -stalled -insns -dep without a value is equivalent to -fsched -stalled -insns -dep=1 .

" -fsched2 -use -superblocks "4 Item "-fsched2-use-superblocks" When scheduling after register allocation, use superblock scheduling. This allows motion across basic block boundaries, resulting in faster schedules. This option is experimental, as not all machine descriptions used by GCCmodel the CPUclosely enough to avoid unreliable results from the algorithm. This only makes sense when scheduling after register allocation, i.e. with -fschedule -insns2 or at -O2 or higher.

" -fsched -group -heuristic "4 Item "-fsched-group-heuristic" Enable the group heuristic in the scheduler. This heuristic favors the instruction that belongs to a schedule group. This is enabled by default when scheduling is enabled, i.e. with -fschedule -insns or -fschedule -insns2 or at -O2 or higher.

" -fsched -critical -path -heuristic "4 Item "-fsched-critical-path-heuristic" Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is enabled, i.e. with -fschedule -insns or -fschedule -insns2 or at -O2 or higher.

" -fsched -spec -insn -heuristic "4 Item "-fsched-spec-insn-heuristic" Enable the speculative instruction heuristic in the scheduler. This heuristic favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling is enabled, i.e. with -fschedule -insns or -fschedule -insns2 or at -O2 or higher.

" -fsched -rank -heuristic "4 Item "-fsched-rank-heuristic" Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is enabled, i.e. with -fschedule -insns or -fschedule -insns2 or at -O2 or higher.

" -fsched -last -insn -heuristic "4 Item "-fsched-last-insn-heuristic" Enable the last-instruction heuristic in the scheduler. This heuristic favors the instruction that is less dependent on the last instruction scheduled. This is enabled by default when scheduling is enabled, i.e. with -fschedule -insns or -fschedule -insns2 or at -O2 or higher.

" -fsched -dep -count -heuristic "4 Item "-fsched-dep-count-heuristic" Enable the dependent-count heuristic in the scheduler. This heuristic favors the instruction that has more instructions depending on it. This is enabled by default when scheduling is enabled, i.e. with -fschedule -insns or -fschedule -insns2 or at -O2 or higher.

" -freschedule -modulo -scheduled -loops "4 Item "-freschedule-modulo-scheduled-loops" Modulo scheduling is performed before traditional scheduling. If a loop is modulo scheduled, later scheduling passes may change its schedule. Use this option to control that behavior.

" -fselective -scheduling "4 Item "-fselective-scheduling" Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the first scheduler pass.

" -fselective -scheduling2 "4 Item "-fselective-scheduling2" Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the second scheduler pass.

" -fsel -sched -pipelining "4 Item "-fsel-sched-pipelining" Enable software pipelining of innermost loops during selective scheduling. This option has no effect unless one of -fselective -scheduling or -fselective -scheduling2 is turned on.

" -fsel -sched -pipelining -outer -loops "4 Item "-fsel-sched-pipelining-outer-loops" When pipelining loops during selective scheduling, also pipeline outer loops. This option has no effect unless -fsel -sched -pipelining is turned on.

" -fsemantic -interposition "4 Item "-fsemantic-interposition" Some object formats, like ELF,allow interposing of symbols by the dynamic linker. This means that for symbols exported from the DSO,the compiler cannot perform interprocedural propagation, inlining and other optimizations in anticipation that the function or variable in question may change. While this feature is useful, for example, to rewrite memory allocation functions by a debugging implementation, it is expensive in the terms of code quality. With -fno -semantic -interposition the compiler assumes that if interposition happens for functions the overwriting function will have precisely the same semantics (and side effects). Similarly if interposition happens for variables, the constructor of the variable will be the same. The flag has no effect for functions explicitly declared inline (where it is never allowed for interposition to change semantics) and for symbols explicitly declared weak.

" -fshrink -wrap "4 Item "-fshrink-wrap" Emit function prologues only before parts of the function that need it, rather than at the top of the function. This flag is enabled by default at -O and higher.

" -fshrink -wrap -separate "4 Item "-fshrink-wrap-separate" Shrink-wrap separate parts of the prologue and epilogue separately, so that those parts are only executed when needed. This option is on by default, but has no effect unless -fshrink -wrap is also turned on and the target supports this.

" -fcaller -saves "4 Item "-fcaller-saves" Enable allocation of values to registers that are clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code. This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. Enabled at levels -O2 , -O3 , -Os .

" -fcombine -stack -adjustments "4 Item "-fcombine-stack-adjustments" Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to combine them. Enabled by default at -O1 and higher.

" -fipa -ra "4 Item "-fipa-ra" Use caller save registers for allocation if those registers are not used by any called function. In that case it is not necessary to save and restore them around calls. This is only possible if called functions are part of same compilation unit as current function and they are compiled before it. Enabled at levels -O2 , -O3 , -Os ,however the option is disabled if generated code will be instrumented for profiling ( -p ,or -pg )or if callee's register usage cannot be known exactly (this happens on targets that do not expose prologues and epilogues in RTL).

" -fconserve -stack "4 Item "-fconserve-stack" Attempt to minimize stack usage. The compiler attempts to use less stack space, even if that makes the program slower. This option implies setting the large-stack-frame parameter to 100 and the large-stack-frame-growth parameter to 400.

" -ftree -reassoc "4 Item "-ftree-reassoc" Perform reassociation on trees. This flag is enabled by default at -O and higher.

" -fcode -hoisting "4 Item "-fcode-hoisting" Perform code hoisting. Code hoisting tries to move the evaluation of expressions executed on all paths to the function exit as early as possible. This is especially useful as a code size optimization, but it often helps for code speed as well. This flag is enabled by default at -O2 and higher.

" -ftree -pre "4 Item "-ftree-pre" Perform partial redundancy elimination ( PRE)on trees. This flag is enabled by default at -O2 and -O3 .

" -ftree -partial -pre "4 Item "-ftree-partial-pre" Make partial redundancy elimination ( PRE)more aggressive. This flag is enabled by default at -O3 .

" -ftree -forwprop "4 Item "-ftree-forwprop" Perform forward propagation on trees. This flag is enabled by default at -O and higher.

" -ftree -fre "4 Item "-ftree-fre" Perform full redundancy elimination ( FRE)on trees. The difference between FREand PREis that FREonly considers expressions that are computed on all paths leading to the redundant computation. This analysis is faster than PRE,though it exposes fewer redundancies. This flag is enabled by default at -O and higher.

" -ftree -phiprop "4 Item "-ftree-phiprop" Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at -O and higher.

" -fhoist -adjacent -loads "4 Item "-fhoist-adjacent-loads" Speculatively hoist loads from both branches of an if-then-else if the loads are from adjacent locations in the same structure and the target architecture has a conditional move instruction. This flag is enabled by default at -O2 and higher.

" -ftree -copy -prop "4 Item "-ftree-copy-prop" Perform copy propagation on trees. This pass eliminates unnecessary copy operations. This flag is enabled by default at -O and higher.

" -fipa -pure -const "4 Item "-fipa-pure-const" Discover which functions are pure or constant. Enabled by default at -O and higher.

" -fipa -reference "4 Item "-fipa-reference" Discover which static variables do not escape the compilation unit. Enabled by default at -O and higher.

" -fipa -reference -addressable "4 Item "-fipa-reference-addressable" Discover read-only, write-only and non-addressable static variables. Enabled by default at -O and higher.

" -fipa -stack -alignment "4 Item "-fipa-stack-alignment" Reduce stack alignment on call sites if possible. Enabled by default.

" -fipa -pta "4 Item "-fipa-pta" Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units. It is not enabled by default at any optimization level.

" -fipa -profile "4 Item "-fipa-profile" Perform interprocedural profile propagation. The functions called only from cold functions are marked as cold. Also functions executed once (such as CW(C`cold (C' , CW(C`noreturn (C' ,static constructors or destructors) are identified. Cold functions and loop less parts of functions executed once are then optimized for size. Enabled by default at -O and higher.

" -fipa -cp "4 Item "-fipa-cp" Perform interprocedural constant propagation. This optimization analyzes the program to determine when values passed to functions are constants and then optimizes accordingly. This optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled by default at -O2 , -Os and -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -fipa -cp -clone "4 Item "-fipa-cp-clone" Perform function cloning to make interprocedural constant propagation stronger. When enabled, interprocedural constant propagation performs function cloning when externally visible function can be called with constant arguments. Because this optimization can create multiple copies of functions, it may significantly increase code size (see --param ipcp -unit -growth= value ). This flag is enabled by default at -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -fipa -bit -cp "4 Item "-fipa-bit-cp" When enabled, perform interprocedural bitwise constant propagation. This flag is enabled by default at -O2 and by -fprofile -use and -fauto -profile . It requires that -fipa -cp is enabled.

" -fipa -vrp "4 Item "-fipa-vrp" When enabled, perform interprocedural propagation of value ranges. This flag is enabled by default at -O2 .It requires that -fipa -cp is enabled.

" -fipa -icf "4 Item "-fipa-icf" Perform Identical Code Folding for functions and read-only variables. The optimization reduces code size and may disturb unwind stacks by replacing a function by equivalent one with a different name. The optimization works more effectively with link-time optimization enabled. Although the behavior is similar to the Gold Linker's ICFoptimization, GCCICF works on different levels and thus the optimizations are not same -there are equivalences that are found only by GCCand equivalences found only by Gold. This flag is enabled by default at -O2 and -Os .

" -flive -patching= level "4 Item "-flive-patching=level" Control GCC'soptimizations to produce output suitable for live-patching. If the compiler's optimization uses a function's body or information extracted from its body to optimize/change another function, the latter is called an impacted function of the former. If a function is patched, its impacted functions should be patched too. The impacted functions are determined by the compiler's interprocedural optimizations. For example, a caller is impacted when inlining a function into its caller, cloning a function and changing its caller to call this new clone, or extracting a function's pureness/constness information to optimize its direct or indirect callers, etc. Usually, the more IPAoptimizations enabled, the larger the number of impacted functions for each function. In order to control the number of impacted functions and more easily compute the list of impacted function, IPAoptimizations can be partially enabled at two different levels. The level argument should be one of the following:

" inline-clone "4 Item "inline-clone" Only enable inlining and cloning optimizations, which includes inlining, cloning, interprocedural scalar replacement of aggregates and partial inlining. As a result, when patching a function, all its callers and its clones' callers are impacted, therefore need to be patched as well. -flive -patching=inline -clone disables the following optimization flags: -fwhole -program -fipa -pta -fipa -reference -fipa -ra -fipa -icf -fipa -icf -functions -fipa -icf -variables -fipa -bit -cp -fipa -vrp -fipa -pure -const -fipa -reference -addressable -fipa -stack -alignment

" inline-only-static "4 Item "inline-only-static" Only enable inlining of static functions. As a result, when patching a static function, all its callers are impacted and so need to be patched as well. In addition to all the flags that -flive -patching=inline -clone disables, -flive -patching=inline -only -static disables the following additional optimization flags: -fipa -cp -clone -fipa -sra -fpartial -inlining -fipa -cp When -flive -patching is specified without any value, the default value is inline-clone . This flag is disabled by default. Note that -flive -patching is not supported with link-time optimization ( -flto ).

" -fisolate -erroneous -paths -dereference "4 Item "-fisolate-erroneous-paths-dereference" Detect paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This flag is enabled by default at -O2 and higher and depends on -fdelete -null -pointer -checks also being enabled.

" -fisolate -erroneous -paths -attribute "4 Item "-fisolate-erroneous-paths-attribute" Detect paths that trigger erroneous or undefined behavior due to a null value being used in a way forbidden by a CW(C`returns_nonnull (C' or CW(C`nonnull (C' attribute. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This is not currently enabled, but may be enabled by -O2 in the future.

" -ftree -sink "4 Item "-ftree-sink" Perform forward store motion on trees. This flag is enabled by default at -O and higher.

" -ftree -bit -ccp "4 Item "-ftree-bit-ccp" Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information. This pass only operates on local scalar variables and is enabled by default at -O1 and higher, except for -Og . It requires that -ftree -ccp is enabled.

" -ftree -ccp "4 Item "-ftree-ccp" Perform sparse conditional constant propagation ( CCP)on trees. This pass only operates on local scalar variables and is enabled by default at -O and higher.

" -fssa -backprop "4 Item "-fssa-backprop" Propagate information about uses of a value up the definition chain in order to simplify the definitions. For example, this pass strips sign operations if the sign of a value never matters. The flag is enabled by default at -O and higher.

" -fssa -phiopt "4 Item "-fssa-phiopt" Perform pattern matching on SSAPHI nodes to optimize conditional code. This pass is enabled by default at -O1 and higher, except for -Og .

" -ftree -switch -conversion "4 Item "-ftree-switch-conversion" Perform conversion of simple initializations in a switch to initializations from a scalar array. This flag is enabled by default at -O2 and higher.

" -ftree -tail -merge "4 Item "-ftree-tail-merge" Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping. This flag is enabled by default at -O2 and higher. The compilation time in this pass can be limited using max-tail-merge-comparisons parameter and max-tail-merge-iterations parameter.

" -ftree -dce "4 Item "-ftree-dce" Perform dead code elimination ( DCE)on trees. This flag is enabled by default at -O and higher.

" -ftree -builtin -call -dce "4 Item "-ftree-builtin-call-dce" Perform conditional dead code elimination ( DCE)for calls to built-in functions that may set CW(C`errno (C' but are otherwise free of side effects. This flag is enabled by default at -O2 and higher if -Os is not also specified.

" -ftree -dominator -opts "4 Item "-ftree-dominator-opts" Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at -O and higher.

" -ftree -dse "4 Item "-ftree-dse" Perform dead store elimination ( DSE)on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. This flag is enabled by default at -O and higher.

" -ftree -ch "4 Item "-ftree-ch" Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at -O and higher. It is not enabled for -Os ,since it usually increases code size.

" -ftree -loop -optimize "4 Item "-ftree-loop-optimize" Perform loop optimizations on trees. This flag is enabled by default at -O and higher.

" -ftree -loop -linear "4 Item "-ftree-loop-linear" 0

" -floop -strip -mine "4 Item "-floop-strip-mine"

" -floop -block "4 Item "-floop-block" Perform loop nest optimizations. Same as -floop -nest -optimize .To use this code transformation, GCChas to be configured with --with -isl to enable the Graphite loop transformation infrastructure.

" -fgraphite -identity "4 Item "-fgraphite-identity" Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using -fgraphite -identity we can check the costs or benefits of the GIMPLE-> GRAPHITE-> GIMPLEtransformation. Some minimal optimizations are also performed by the code generator isl, like index splitting and dead code elimination in loops.

" -floop -nest -optimize "4 Item "-floop-nest-optimize" Enable the isl based loop nest optimizer. This is a generic loop nest optimizer based on the Pluto optimization algorithms. It calculates a loop structure optimized for data-locality and parallelism. This option is experimental.

" -floop -parallelize -all "4 Item "-floop-parallelize-all" Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking that it is profitable to parallelize the loops.

" -ftree -coalesce -vars "4 Item "-ftree-coalesce-vars" While transforming the program out of the SSArepresentation, attempt to reduce copying by coalescing versions of different user-defined variables, instead of just compiler temporaries. This may severely limit the ability to debug an optimized program compiled with -fno -var -tracking -assignments .In the negated form, this flag prevents SSAcoalescing of user variables. This option is enabled by default if optimization is enabled, and it does very little otherwise.

" -ftree -loop -if -convert "4 Item "-ftree-loop-if-convert" Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of the vectorization pass to handle these loops. This is enabled by default if vectorization is enabled.

" -ftree -loop -distribution "4 Item "-ftree-loop-distribution" Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For example, the loop 4 DO I = 1, N A(I) = B(I) + C D(I) = E(I) * F ENDDO is transformed to 6 DO I = 1, N A(I) = B(I) + C ENDDO DO I = 1, N D(I) = E(I) * F ENDDO This flag is enabled by default at -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -ftree -loop -distribute -patterns "4 Item "-ftree-loop-distribute-patterns" Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O3 ,and by -fprofile -use and -fauto -profile . This pass distributes the initialization loops and generates a call to memset zero. For example, the loop 4 DO I = 1, N A(I) = 0 B(I) = A(I) + I ENDDO is transformed to 6 DO I = 1, N A(I) = 0 ENDDO DO I = 1, N B(I) = A(I) + I ENDDO and the initialization loop is transformed into a call to memset zero. This flag is enabled by default at -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -floop -interchange "4 Item "-floop-interchange" Perform loop interchange outside of graphite. This flag can improve cache performance on loop nest and allow further loop optimizations, like vectorization, to take place. For example, the loop 4 for (int i = 0; i < N; i++) for (int j = 0; j < N; j++) for (int k = 0; k < N; k++) c[i][j] = c[i][j] + a[i][k]*b[k][j]; is transformed to 4 for (int i = 0; i < N; i++) for (int k = 0; k < N; k++) for (int j = 0; j < N; j++) c[i][j] = c[i][j] + a[i][k]*b[k][j]; This flag is enabled by default at -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -floop -unroll -and -jam "4 Item "-floop-unroll-and-jam" Apply unroll and jam transformations on feasible loops. In a loop nest this unrolls the outer loop by some factor and fuses the resulting multiple inner loops. This flag is enabled by default at -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -ftree -loop -im "4 Item "-ftree-loop-im" Perform loop invariant motion on trees. This pass moves only invariants that are hard to handle at RTLlevel (function calls, operations that expand to nontrivial sequences of insns). With -funswitch -loops it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes store motion.

" -ftree -loop -ivcanon "4 Item "-ftree-loop-ivcanon" Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number easily. Useful especially in connection with unrolling.

" -ftree -scev -cprop "4 Item "-ftree-scev-cprop" Perform final value replacement. If a variable is modified in a loop in such a way that its value when exiting the loop can be determined using only its initial value and the number of loop iterations, replace uses of the final value by such a computation, provided it is sufficiently cheap. This reduces data dependencies and may allow further simplifications. Enabled by default at -O and higher.

" -fivopts "4 Item "-fivopts" Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees.

" -ftree -parallelize -loops=n "4 Item "-ftree-parallelize-loops=n" Parallelize loops, i.e., split their iteration space to run in n threads. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The optimization is only profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e.g. by memory bandwidth. This option implies -pthread ,and thus is only supported on targets that have support for -pthread .

" -ftree -pta "4 Item "-ftree-pta" Perform function-local points-to analysis on trees. This flag is enabled by default at -O1 and higher, except for -Og .

" -ftree -sra "4 Item "-ftree-sra" Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at -O1 and higher, except for -Og .

" -fstore -merging "4 Item "-fstore-merging" Perform merging of narrow stores to consecutive memory addresses. This pass merges contiguous stores of immediate values narrower than a word into fewer wider stores to reduce the number of instructions. This is enabled by default at -O2 and higher as well as -Os .

" -ftree -ter "4 Item "-ftree-ter" Perform temporary expression replacement during the SSA->normalphase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTLgeneration. This is enabled by default at -O and higher.

" -ftree -slsr "4 Item "-ftree-slsr" Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible. This is enabled by default at -O and higher.

" -ftree -vectorize "4 Item "-ftree-vectorize" Perform vectorization on trees. This flag enables -ftree -loop -vectorize and -ftree -slp -vectorize if not explicitly specified.

" -ftree -loop -vectorize "4 Item "-ftree-loop-vectorize" Perform loop vectorization on trees. This flag is enabled by default at -O3 and by -ftree -vectorize , -fprofile -use , and -fauto -profile .

" -ftree -slp -vectorize "4 Item "-ftree-slp-vectorize" Perform basic block vectorization on trees. This flag is enabled by default at -O3 and by -ftree -vectorize , -fprofile -use , and -fauto -profile .

" -fvect -cost -model= model "4 Item "-fvect-cost-model=model" Alter the cost model used for vectorization. The model argument should be one of unlimited , dynamic or cheap . With the unlimited model the vectorized code-path is assumed to be profitable while with the dynamic model a runtime check guards the vectorized code-path to enable it only for iteration counts that will likely execute faster than when executing the original scalar loop. The cheap model disables vectorization of loops where doing so would be cost prohibitive for example due to required runtime checks for data dependence or alignment but otherwise is equal to the dynamic model. The default cost model depends on other optimization flags and is either dynamic or cheap .

" -fsimd -cost -model= model "4 Item "-fsimd-cost-model=model" Alter the cost model used for vectorization of loops marked with the OpenMP simd directive. The model argument should be one of unlimited , dynamic , cheap .All values of model have the same meaning as described in -fvect -cost -model and by default a cost model defined with -fvect -cost -model is used.

" -ftree -vrp "4 Item "-ftree-vrp" Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if -fdelete -null -pointer -checks is enabled.

" -fsplit -paths "4 Item "-fsplit-paths" Split paths leading to loop backedges. This can improve dead code elimination and common subexpression elimination. This is enabled by default at -O3 and above.

" -fsplit -ivs -in -unroller "4 Item "-fsplit-ivs-in-unroller" Enables expression of values of induction variables in later iterations of the unrolled loop using the value in the first iteration. This breaks long dependency chains, thus improving efficiency of the scheduling passes. A combination of -fweb and CSEis often sufficient to obtain the same effect. However, that is not reliable in cases where the loop body is more complicated than a single basic block. It also does not work at all on some architectures due to restrictions in the CSEpass. This optimization is enabled by default.

" -fvariable -expansion -in -unroller "4 Item "-fvariable-expansion-in-unroller" With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code.

" -fpartial -inlining "4 Item "-fpartial-inlining" Inline parts of functions. This option has any effect only when inlining itself is turned on by the -finline -functions or -finline -small -functions options. Enabled at levels -O2 , -O3 , -Os .

" -fpredictive -commoning "4 Item "-fpredictive-commoning" Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops. This option is enabled at level -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -fprefetch -loop -arrays "4 Item "-fprefetch-loop-arrays" If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. Disabled at level -Os .

" -fno -printf -return -value "4 Item "-fno-printf-return-value" Do not substitute constants for known return value of formatted output functions such as CW(C`sprintf (C' , CW(C`snprintf (C' , CW(C`vsprintf (C' ,and CW(C`vsnprintf (C' (but not CW(C`printf (C' of CW(C`fprintf (C' ).This transformation allows GCCto optimize or even eliminate branches based on the known return value of these functions called with arguments that are either constant, or whose values are known to be in a range that makes determining the exact return value possible. For example, when -fprintf -return -value is in effect, both the branch and the body of the CW(C`if (C' statement (but not the call to CW(C`snprint (C' ) can be optimized away when CW(C`i (C' is a 32 -bit or smaller integer because the return value is guaranteed to be at most 8. 3 char buf[9]; if (snprintf (buf, "%08x", i) >= sizeof buf) ... The -fprintf -return -value option relies on other optimizations and yields best results with -O2 and above. It works in tandem with the -Wformat -overflow and -Wformat -truncation options. The -fprintf -return -value option is enabled by default.

" -fno -peephole "4 Item "-fno-peephole" 0

" -fno -peephole2 "4 Item "-fno-peephole2" Disable any machine-specific peephole optimizations. The difference between -fno -peephole and -fno -peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. -fpeephole is enabled by default. -fpeephole2 enabled at levels -O2 , -O3 , -Os .

" -fno -guess -branch -probability "4 Item "-fno-guess-branch-probability" Do not guess branch probabilities using heuristics. GCCuses heuristics to guess branch probabilities if they are not provided by profiling feedback ( -fprofile -arcs ).These heuristics are based on the control flow graph. If some branch probabilities are specified by CW(C`_ _builtin_expect (C' ,then the heuristics are used to guess branch probabilities for the rest of the control flow graph, taking the CW(C`_ _builtin_expect (C' info into account. The interactions between the heuristics and CW(C`_ _builtin_expect (C' can be complex, and in some cases, it may be useful to disable the heuristics so that the effects of CW(C`_ _builtin_expect (C' are easier to understand. It is also possible to specify expected probability of the expression with CW(C`_ _builtin_expect_with_probability (C' built-in function. The default is -fguess -branch -probability at levels -O , -O2 , -O3 , -Os .

" -freorder -blocks "4 Item "-freorder-blocks" Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. Enabled at levels -O , -O2 , -O3 , -Os .

" -freorder -blocks -algorithm= algorithm "4 Item "-freorder-blocks-algorithm=algorithm" Use the specified algorithm for basic block reordering. The algorithm argument can be simple ,which does not increase code size (except sometimes due to secondary effects like alignment), or stc ,the (L"software trace cache (R" algorithm, which tries to put all often executed code together, minimizing the number of branches executed by making extra copies of code. The default is simple at levels -O , -Os ,and stc at levels -O2 , -O3 .

" -freorder -blocks -and -partition "4 Item "-freorder-blocks-and-partition" In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and .o files, to improve paging and cache locality performance. This optimization is automatically turned off in the presence of exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections. When -fsplit -stack is used this option is not enabled by default (to avoid linker errors), but may be enabled explicitly (if using a working linker). Enabled for x86 at levels -O2 , -O3 , -Os .

" -freorder -functions "4 Item "-freorder-functions" Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections CW(C`.text.hot (C' for most frequently executed functions and CW(C`.text.unlikely (C' for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. This option isn't effective unless you either provide profile feedback (see -fprofile -arcs for details) or manually annotate functions with CW(C`hot (C' or CW(C`cold (C' attributes. Enabled at levels -O2 , -O3 , -Os .

" -fstrict -aliasing "4 Item "-fstrict-aliasing" Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and (C+), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an CW(C`unsigned int (C' can alias an CW(C`int (C' ,but not a CW(C`void* (C' or a CW(C`double (C' .A character type may alias any other type. Pay special attention to code like this: 4 union a_union { int i; double d; }; int f() { union a_union t; t.d = 3.0; return t.i; } The practice of reading from a different union member than the one most recently written to (called (L"type-punning (R") is common. Even with -fstrict -aliasing ,type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. However, this code might not: 7 int f() { union a_union t; int* ip; t.d = 3.0; ip = &t.i; return *ip; } Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.: 4 int f() { double d = 3.0; return ((union a_union *) &d) ->i; } The -fstrict -aliasing option is enabled at levels -O2 , -O3 , -Os .

" -falign -functions "4 Item "-falign-functions" 0

" -falign -functions= n "4 Item "-falign-functions=n"

" -falign -functions= n : m "4 Item "-falign-functions=n:m"

" -falign -functions= n : m : n2 "4 Item "-falign-functions=n:m:n2"

" -falign -functions= n : m : n2 : m2 "4 Item "-falign-functions=n:m:n2:m2" Align the start of functions to the next power-of-two greater than n ,skipping up to m -1 bytes. This ensures that at least the first m bytes of the function can be fetched by the CPU without crossing an n -byte alignment boundary. If m is not specified, it defaults to n . Examples: -falign -functions=32 aligns functions to the next 32 -byte boundary, -falign -functions=24 aligns to the next 32 -byte boundary only if this can be done by skipping 23 bytes or less, -falign -functions=32:7 aligns to the next 32 -byte boundary only if this can be done by skipping 6 bytes or less. The second pair of n2 : m2 values allows you to specify a secondary alignment: -falign -functions=64:7:32:3 aligns to the next 64 -byte boundary if this can be done by skipping 6 bytes or less, otherwise aligns to the next 32 -byte boundary if this can be done by skipping 2 bytes or less. If m2 is not specified, it defaults to n2 . Some assemblers only support this flag when n is a power of two; in that case, it is rounded up. -fno -align -functions and -falign -functions=1 are equivalent and mean that functions are not aligned. If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is 65536. Enabled at levels -O2 , -O3 .

" -flimit -function -alignment "4 Item "-flimit-function-alignment" If this option is enabled, the compiler tries to avoid unnecessarily overaligning functions. It attempts to instruct the assembler to align by the amount specified by -falign -functions ,but not to skip more bytes than the size of the function.

" -falign -labels "4 Item "-falign-labels" 0

" -falign -labels= n "4 Item "-falign-labels=n"

" -falign -labels= n : m "4 Item "-falign-labels=n:m"

" -falign -labels= n : m : n2 "4 Item "-falign-labels=n:m:n2"

" -falign -labels= n : m : n2 : m2 "4 Item "-falign-labels=n:m:n2:m2" Align all branch targets to a power-of-two boundary. Parameters of this option are analogous to the -falign -functions option. -fno -align -labels and -falign -labels=1 are equivalent and mean that labels are not aligned. If -falign -loops or -falign -jumps are applicable and are greater than this value, then their values are used instead. If n is not specified or is zero, use a machine-dependent default which is very likely to be 1 ,meaning no alignment. The maximum allowed n option value is 65536. Enabled at levels -O2 , -O3 .

" -falign -loops "4 Item "-falign-loops" 0

" -falign -loops= n "4 Item "-falign-loops=n"

" -falign -loops= n : m "4 Item "-falign-loops=n:m"

" -falign -loops= n : m : n2 "4 Item "-falign-loops=n:m:n2"

" -falign -loops= n : m : n2 : m2 "4 Item "-falign-loops=n:m:n2:m2" Align loops to a power-of-two boundary. If the loops are executed many times, this makes up for any execution of the dummy padding instructions. Parameters of this option are analogous to the -falign -functions option. -fno -align -loops and -falign -loops=1 are equivalent and mean that loops are not aligned. The maximum allowed n option value is 65536. If n is not specified or is zero, use a machine-dependent default. Enabled at levels -O2 , -O3 .

" -falign -jumps "4 Item "-falign-jumps" 0

" -falign -jumps= n "4 Item "-falign-jumps=n"

" -falign -jumps= n : m "4 Item "-falign-jumps=n:m"

" -falign -jumps= n : m : n2 "4 Item "-falign-jumps=n:m:n2"

" -falign -jumps= n : m : n2 : m2 "4 Item "-falign-jumps=n:m:n2:m2" Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping. In this case, no dummy operations need be executed. Parameters of this option are analogous to the -falign -functions option. -fno -align -jumps and -falign -jumps=1 are equivalent and mean that loops are not aligned. If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is 65536. Enabled at levels -O2 , -O3 .

" -funit -at -a -time "4 Item "-funit-at-a-time" This option is left for compatibility reasons. -funit -at -a -time has no effect, while -fno -unit -at -a -time implies -fno -toplevel -reorder and -fno -section -anchors . Enabled by default.

" -fno -toplevel -reorder "4 Item "-fno-toplevel-reorder" Do not reorder top-level functions, variables, and CW(C`asm (C' statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static variables are not removed. This option is intended to support existing code that relies on a particular ordering. For new code, it is better to use attributes when possible. -ftoplevel -reorder is the default at -O1 and higher, and also at -O0 if -fsection -anchors is explicitly requested. Additionally -fno -toplevel -reorder implies -fno -section -anchors .

" -fweb "4 Item "-fweb" Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as CSE,loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables no longer stay in a (L"home register (R". Enabled by default with -funroll -loops .

" -fwhole -program "4 Item "-fwhole-program" Assume that the current compilation unit represents the whole program being compiled. All public functions and variables with the exception of CW(C`main (C' and those merged by attribute CW(C`externally_visible (C' become static functions and in effect are optimized more aggressively by interprocedural optimizers. This option should not be used in combination with -flto . Instead relying on a linker plugin should provide safer and more precise information.

" -flto[= n ] "4 Item "-flto[=n]" This option runs the standard link-time optimizer. When invoked with source code, it generates GIMPLE(one of GCC'sinternal representations) and writes it to special ELFsections in the object file. When the object files are linked together, all the function bodies are read from these ELFsections and instantiated as if they had been part of the same translation unit. To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link. It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time. For example: 3 gcc -c -O2 -flto foo.c gcc -c -O2 -flto bar.c gcc -o myprog -flto -O2 foo.o bar.o The first two invocations to GCCsave a bytecode representation of GIMPLEinto special ELFsections inside foo.o and bar.o .The final invocation reads the GIMPLEbytecode from foo.o and bar.o ,merges the two files into a single internal image, and compiles the result as usual. Since both foo.o and bar.o are merged into a single image, this causes all the interprocedural analyses and optimizations in GCCto work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in bar.o into functions in foo.o and vice-versa. Another (simpler) way to enable link-time optimization is: 1 gcc -o myprog -flto -O2 foo.c bar.c The above generates bytecode for foo.c and bar.c , merges them together into a single GIMPLErepresentation and optimizes them as usual to produce myprog . The important thing to keep in mind is that to enable link-time optimizations you need to use the GCCdriver to perform the link step. GCCautomatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option. You can always override the automatic decision to do link-time optimization by passing -fno -lto to the link command. To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see -fuse -linker -plugin )passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, -fwhole -program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions. When a file is compiled with -flto without -fuse -linker -plugin ,the generated object file is larger than a regular object file because it contains GIMPLEbytecodes and the usual final code (see -ffat -lto -objects .This means that object files with LTOinformation can be linked as normal object files; if -fno -lto is passed to the linker, no interprocedural optimizations are applied. Note that when -fno -fat -lto -objects is enabled the compile stage is faster but you cannot perform a regular, non-LTO link on them. When producing the final binary, GCConly applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLEbytecodes and final object code. GCCautomatically selects which files to optimize in LTOmode and which files to link without further processing. Generally, options specified at link time override those specified at compile time, although in some cases GCCattempts to infer link-time options from the settings used to compile the input files. If you do not specify an optimization level option -O at link time, then GCCuses the highest optimization level used when compiling the object files. Note that it is generally ineffective to specify an optimization level option only at link time and not at compile time, for two reasons. First, compiling without optimization suppresses compiler passes that gather information needed for effective optimization at link time. Second, some early optimization passes can be performed only at compile time and not at link time. There are some code generation flags preserved by GCCwhen generating bytecodes, as they need to be used during the final link. Currently, the following options and their settings are taken from the first object file that explicitly specifies them: -fPIC , -fpic , -fpie , -fcommon , -fexceptions , -fnon -call -exceptions , -fgnu -tm and all the -m target flags. Certain ABI-changing flags are required to match in all compilation units, and trying to override this at link time with a conflicting value is ignored. This includes options such as -freg -struct -return and -fpcc -struct -return . Other options such as -ffp -contract , -fno -strict -overflow , -fwrapv , -fno -trapv or -fno -strict -aliasing are passed through to the link stage and merged conservatively for conflicting translation units. Specifically -fno -strict -overflow , -fwrapv and -fno -trapv take precedence; and for example -ffp -contract=off takes precedence over -ffp -contract=fast .You can override them at link time. If LTOencounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to ISOC99 6.2.7 ),a non-fatal diagnostic may be issued. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages. Another feature of LTOis that it is possible to apply interprocedural optimizations on files written in different languages: 4 gcc -c -flto foo.c g++ -c -flto bar.cc gfortran -c -flto baz.f90 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran Notice that the final link is done with g++ to get the (C+ runtime libraries and -lgfortran is added to get the Fortran runtime libraries. In general, when mixing languages in LTOmode, you should use the same link command options as when mixing languages in a regular (non-LTO) compilation. If object files containing GIMPLEbytecode are stored in a library archive, say libfoo.a ,it is possible to extract and use them in an LTOlink if you are using a linker with plugin support. To create static libraries suitable for LTO,use gcc-ar and gcc-ranlib instead of ar and ranlib ; to show the symbols of object files with GIMPLEbytecode, use gcc-nm .Those commands require that ar , ranlib and nm have been compiled with plugin support. At link time, use the flag -fuse -linker -plugin to ensure that the library participates in the LTOoptimization process: 1 gcc -o myprog -O2 -flto -fuse -linker -plugin a.o b.o -lfoo With the linker plugin enabled, the linker extracts the needed GIMPLEfiles from libfoo.a and passes them on to the running GCC to make them part of the aggregated GIMPLEimage to be optimized. If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside libfoo.a are extracted and linked as usual, but they do not participate in the LTOoptimization process. In order to make a static library suitable for both LTOoptimization and usual linkage, compile its object files with -flto -ffat -lto -objects . Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and -fwhole -program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of -fwhole -program is not needed when linker plugin is active (see -fuse -linker -plugin ). The current implementation of LTOmakes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCCdo not work with an older or newer version of GCC. Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELFand DWARF. If you specify the optional n ,the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used. The default value for n is 1. You can also specify -flto=jobserver to use GNUmake's job server mode to determine the number of parallel jobs. This is useful when the Makefile calling GCCis already executing in parallel. You must prepend a + to the command recipe in the parent Makefile for this to work. This option likely only works if MAKE is GNUmake.

" -flto -partition= alg "4 Item "-flto-partition=alg" Specify the partitioning algorithm used by the link-time optimizer. The value is either 1to1 to specify a partitioning mirroring the original source files or balanced to specify partitioning into equally sized chunks (whenever possible) or max to create new partition for every symbol where possible. Specifying none as an algorithm disables partitioning and streaming completely. The default value is balanced .While 1to1 can be used as an workaround for various code ordering issues, the max partitioning is intended for internal testing only. The value one specifies that exactly one partition should be used while the value none bypasses partitioning and executes the link-time optimization step directly from the WPAphase.

" -flto -odr -type -merging "4 Item "-flto-odr-type-merging" Enable streaming of mangled types names of (C+ types and their unification at link time. This increases size of LTOobject files, but enables diagnostics about One Definition Rule violations.

" -flto -compression -level= n "4 Item "-flto-compression-level=n" This option specifies the level of compression used for intermediate language written to LTOobject files, and is only meaningful in conjunction with LTOmode ( -flto ).Valid values are 0 (no compression) to 9 (maximum compression). Values outside this range are clamped to either 0 or 9. If the option is not given, a default balanced compression setting is used.

" -fuse -linker -plugin "4 Item "-fuse-linker-plugin" Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in GNUld 2.21 or newer. This option enables the extraction of object files with GIMPLEbytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that use hidden visibility) are similar to -fwhole -program . See -flto for a description of the effect of this flag and how to use it. This option is enabled by default when LTOsupport in GCCis enabled and GCCwas configured for use with a linker supporting plugins ( GNUld 2.21 or newer or gold).

" -ffat -lto -objects "4 Item "-ffat-lto-objects" Fat LTOobjects are object files that contain both the intermediate language and the object code. This makes them usable for both LTOlinking and normal linking. This option is effective only when compiling with -flto and is ignored at link time. -fno -fat -lto -objects improves compilation time over plain LTO,but requires the complete toolchain to be aware of LTO.It requires a linker with linker plugin support for basic functionality. Additionally, nm , ar and ranlib need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). GCCprovides the gcc-ar , gcc-nm , gcc-ranlib wrappers to pass the right options to these tools. With non fat LTOmakefiles need to be modified to use them. Note that modern binutils provide plugin auto-load mechanism. Installing the linker plugin into CI$libdir /bfd-plugins has the same effect as usage of the command wrappers ( gcc-ar , gcc-nm and gcc-ranlib ). The default is -fno -fat -lto -objects on targets with linker plugin support.

" -fcompare -elim "4 Item "-fcompare-elim" After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic. If possible, eliminate the explicit comparison operation. This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. Enabled at levels -O , -O2 , -O3 , -Os .

" -fcprop -registers "4 Item "-fcprop-registers" After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. Enabled at levels -O , -O2 , -O3 , -Os .

" -fprofile -correction "4 Item "-fprofile-correction" Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, GCCuses heuristics to correct or smooth out such inconsistencies. By default, GCCemits an error message when an inconsistent profile is detected. This option is enabled by -fauto -profile .

" -fprofile -use "4 Item "-fprofile-use" 0

" -fprofile -use= path "4 Item "-fprofile-use=path" Enable profile feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available: -fbranch -probabilities -fprofile -values -funroll -loops -fpeel -loops -ftracer -fvpt -finline -functions -fipa -cp -fipa -cp -clone -fipa -bit -cp -fpredictive -commoning -fsplit -loops -funswitch -loops -fgcse -after -reload -ftree -loop -vectorize -ftree -slp -vectorize -fvect -cost -model=dynamic -ftree -loop -distribute -patterns -fprofile -reorder -functions Before you can use this option, you must first generate profiling information. By default, GCCemits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using -Wno -error=coverage -mismatch .Note this may result in poorly optimized code. Additionally, by default, GCCalso emits a warning message if the feedback profiles do not exist (see -Wmissing -profile ). If path is specified, GCClooks at the path to find the profile feedback data files. See -fprofile -dir .

" -fauto -profile "4 Item "-fauto-profile" 0

" -fauto -profile= path "4 Item "-fauto-profile=path" Enable sampling-based feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available: -fbranch -probabilities -fprofile -values -funroll -loops -fpeel -loops -ftracer -fvpt -finline -functions -fipa -cp -fipa -cp -clone -fipa -bit -cp -fpredictive -commoning -fsplit -loops -funswitch -loops -fgcse -after -reload -ftree -loop -vectorize -ftree -slp -vectorize -fvect -cost -model=dynamic -ftree -loop -distribute -patterns -fprofile -correction path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata.afdo in the current directory. Producing an AutoFDO profile data file requires running your program with the perf utility on a supported GNU/Linux target system. For more information, see < https://perf.wiki.kernel.org/ >. E.g. 2 perf record -e br_inst_retired:near_taken -b -o perf.data \ --your_program Then use the create_gcov tool to convert the raw profile data to a format that can be used by GCC.You must also supply the unstripped binary for your program to this tool. See < https://github.com/google/autofdo >. E.g. 2 create_gcov --binary=your_program.unstripped --profile=perf.data \ --gcov=profile.afdo

The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled.

" -ffloat -store "4 Item "-ffloat-store" Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory. This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a CW(C`double (C' is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEEfloating point. Use -ffloat -store for such programs, after modifying them to store all pertinent intermediate computations into variables.

" -fexcess -precision= style "4 Item "-fexcess-precision=style" This option allows further control over excess precision on machines where floating-point operations occur in a format with more precision or range than the IEEEstandard and interchange floating-point types. By default, -fexcess -precision=fast is in effect; this means that operations may be carried out in a wider precision than the types specified in the source if that would result in faster code, and it is unpredictable when rounding to the types specified in the source code takes place. When compiling C, if -fexcess -precision=standard is specified then excess precision follows the rules specified in ISOC99 ;in particular, both casts and assignments cause values to be rounded to their semantic types (whereas -ffloat -store only affects assignments). This option is enabled by default for C if a strict conformance option such as -std=c99 is used. -ffast -math enables -fexcess -precision=fast by default regardless of whether a strict conformance option is used. -fexcess -precision=standard is not implemented for languages other than C. On the x86, it has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable.

" -ffast -math "4 Item "-ffast-math" Sets the options -fno -math -errno , -funsafe -math -optimizations , -ffinite -math -only , -fno -rounding -math , -fno -signaling -nans , -fcx -limited -range and -fexcess -precision=fast . This option causes the preprocessor macro CW(C`_ _FAST_MATH_ _ (C' to be defined. This option is not turned on by any -O option besides -Ofast since it can result in incorrect output for programs that depend on an exact implementation of IEEEor ISOrules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.

" -fno -math -errno "4 Item "-fno-math-errno" Do not set CW(C`errno (C' after calling math functions that are executed with a single instruction, e.g., CW(C`sqrt (C' .A program that relies on IEEEexceptions for math error handling may want to use this flag for speed while maintaining IEEEarithmetic compatibility. This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEEor ISOrules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. The default is -fmath -errno . On Darwin systems, the math library never sets CW(C`errno (C' .There is therefore no reason for the compiler to consider the possibility that it might, and -fno -math -errno is the default.

" -funsafe -math -optimizations "4 Item "-funsafe-math-optimizations" Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEEor ANSIstandards. When used at link time, it may include libraries or startup files that change the default FPUcontrol word or other similar optimizations. This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEEor ISOrules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables -fno -signed -zeros , -fno -trapping -math , -fassociative -math and -freciprocal -math . The default is -fno -unsafe -math -optimizations .

" -fassociative -math "4 Item "-fassociative-math" Allow re-association of operands in series of floating-point operations. This violates the ISOC and (C+ language standard by possibly changing computation result. NOTE:re-ordering may change the sign of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot be used on code that relies on rounding behavior like CW(C`(x + 2**52) -2**52 (C' .May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno -signed -zeros and -fno -trapping -math be in effect. Moreover, it doesn't make much sense with -frounding -math .For Fortran the option is automatically enabled when both -fno -signed -zeros and -fno -trapping -math are in effect. The default is -fno -associative -math .

" -freciprocal -math "4 Item "-freciprocal-math" Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. For example CW(C`x / y (C' can be replaced with CW(C`x * (1/y) (C' ,which is useful if CW(C`(1/y) (C' is subject to common subexpression elimination. Note that this loses precision and increases the number of flops operating on the value. The default is -fno -reciprocal -math .

" -ffinite -math -only "4 Item "-ffinite-math-only" Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or + -Infs. This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEEor ISOrules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. The default is -fno -finite -math -only .

" -fno -signed -zeros "4 Item "-fno-signed-zeros" Allow optimizations for floating-point arithmetic that ignore the signedness of zero. IEEEarithmetic specifies the behavior of distinct +0.0 and -0.0 values, which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even with -ffinite -math -only ). This option implies that the sign of a zero result isn't significant. The default is -fsigned -zeros .

" -fno -trapping -math "4 Item "-fno-trapping-math" Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option requires that -fno -signaling -nans be in effect. Setting this option may allow faster code if one relies on (L"non-stop (R" IEEEarithmetic, for example. This option should never be turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEEor ISOrules/specifications for math functions. The default is -ftrapping -math .

" -frounding -math "4 Item "-frounding-math" Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option should be specified for programs that change the FProunding mode dynamically, or that may be executed with a non-default rounding mode. This option disables constant folding of floating-point expressions at compile time (which may be affected by rounding mode) and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes. The default is -fno -rounding -math . This option is experimental and does not currently guarantee to disable all GCCoptimizations that are affected by rounding mode. Future versions of GCCmay provide finer control of this setting using C99's CW(C`FENV_ACCESS (C' pragma. This command-line option will be used to specify the default state for CW(C`FENV_ACCESS (C' .

" -fsignaling -nans "4 Item "-fsignaling-nans" Compile code assuming that IEEEsignaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs. This option implies -ftrapping -math . This option causes the preprocessor macro CW(C`_ _SUPPORT_SNAN_ _ (C' to be defined. The default is -fno -signaling -nans . This option is experimental and does not currently guarantee to disable all GCCoptimizations that affect signaling NaN behavior.

" -fno -fp -int -builtin -inexact "4 Item "-fno-fp-int-builtin-inexact" Do not allow the built-in functions CW(C`ceil (C' , CW(C`floor (C' , CW(C`round (C' and CW(C`trunc (C' ,and their CW(C`float (C' and CW(C`long double (C' variants, to generate code that raises the (L"inexact (R" floating-point exception for noninteger arguments. ISOC99 and C11 allow these functions to raise the (L"inexact (R" exception, but ISO/IEC TS 18661 -1:2014, the C bindings to IEEE754 -2008, does not allow these functions to do so. The default is -ffp -int -builtin -inexact ,allowing the exception to be raised. This option does nothing unless -ftrapping -math is in effect. Even if -fno -fp -int -builtin -inexact is used, if the functions generate a call to a library function then the (L"inexact (R" exception may be raised if the library implementation does not follow TS18661.

" -fsingle -precision -constant "4 Item "-fsingle-precision-constant" Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants.

" -fcx -limited -range "4 Item "-fcx-limited-range" When enabled, this option states that a range reduction step is not needed when performing complex division. Also, there is no checking whether the result of a complex multiplication or division is CW(C`NaN + I*NaN (C' ,with an attempt to rescue the situation in that case. The default is -fno -cx -limited -range ,but is enabled by -ffast -math . This option controls the default setting of the ISOC99 CW(C`CX_LIMITED_RANGE (C' pragma. Nevertheless, the option applies to all languages.

" -fcx -fortran -rules "4 Item "-fcx-fortran-rules" Complex multiplication and division follow Fortran rules. Range reduction is done as part of complex division, but there is no checking whether the result of a complex multiplication or division is CW(C`NaN + I*NaN (C' ,with an attempt to rescue the situation in that case. The default is -fno -cx -fortran -rules .

The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code.

" -fbranch -probabilities "4 Item "-fbranch-probabilities" After running a program compiled with -fprofile -arcs , you can compile it a second time using -fbranch -probabilities ,to improve optimizations based on the number of times each branch was taken. When a program compiled with -fprofile -arcs exits, it saves arc execution counts to a file called sourcename .gcda for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. With -fbranch -probabilities ,GCCputs a REG_BR_PROB note on each JUMP_INSN and CALL_INSN . These can be used to improve optimization. Currently, they are only used in one place: in reorg.c ,instead of guessing which path a branch is most likely to take, the REG_BR_PROB values are used to exactly determine which path is taken more often. Enabled by -fprofile -use and -fauto -profile .

" -fprofile -values "4 Item "-fprofile-values" If combined with -fprofile -arcs ,it adds code so that some data about values of expressions in the program is gathered. With -fbranch -probabilities ,it reads back the data gathered from profiling values of expressions for usage in optimizations. Enabled by -fprofile -generate , -fprofile -use ,and -fauto -profile .

" -fprofile -reorder -functions "4 Item "-fprofile-reorder-functions" Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. Enabled with -fprofile -use .

" -fvpt "4 Item "-fvpt" If combined with -fprofile -arcs ,this option instructs the compiler to add code to gather information about values of expressions. With -fbranch -probabilities ,it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator. Enabled with -fprofile -use and -fauto -profile .

" -frename -registers "4 Item "-frename-registers" Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization most benefits processors with lots of registers. Depending on the debug information format adopted by the target, however, it can make debugging impossible, since variables no longer stay in a (L"home register (R". Enabled by default with -funroll -loops .

" -fschedule -fusion "4 Item "-fschedule-fusion" Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow. Enabled at levels -O2 , -O3 , -Os .

" -ftracer "4 Item "-ftracer" Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job. Enabled by -fprofile -use and -fauto -profile .

" -funroll -loops "4 Item "-funroll-loops" Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll -loops implies -frerun -cse -after -loop , -fweb and -frename -registers . It also turns on complete loop peeling (i.e. complete removal of loops with a small constant number of iterations). This option makes code larger, and may or may not make it run faster. Enabled by -fprofile -use and -fauto -profile .

" -funroll -all -loops "4 Item "-funroll-all-loops" Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. -funroll -all -loops implies the same options as -funroll -loops .

" -fpeel -loops "4 Item "-fpeel-loops" Peels loops for which there is enough information that they do not roll much (from profile feedback or static analysis). It also turns on complete loop peeling (i.e. complete removal of loops with small constant number of iterations). Enabled by -O3 , -fprofile -use ,and -fauto -profile .

" -fmove -loop -invariants "4 Item "-fmove-loop-invariants" Enables the loop invariant motion pass in the RTLloop optimizer. Enabled at level -O1 and higher, except for -Og .

" -fsplit -loops "4 Item "-fsplit-loops" Split a loop into two if it contains a condition that's always true for one side of the iteration space and false for the other. Enabled by -fprofile -use and -fauto -profile .

" -funswitch -loops "4 Item "-funswitch-loops" Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition). Enabled by -fprofile -use and -fauto -profile .

" -fversion -loops -for -strides "4 Item "-fversion-loops-for-strides" If a loop iterates over an array with a variable stride, create another version of the loop that assumes the stride is always one. For example: 2 for (int i = 0; i < n; ++i) x[i * stride] = ...; becomes: 6 if (stride == 1) for (int i = 0; i < n; ++i) x[i] = ...; else for (int i = 0; i < n; ++i) x[i * stride] = ...; This is particularly useful for assumed-shape arrays in Fortran where (for example) it allows better vectorization assuming contiguous accesses. This flag is enabled by default at -O3 . It is also enabled by -fprofile -use and -fauto -profile .

" -ffunction -sections "4 Item "-ffunction-sections" 0

" -fdata -sections "4 Item "-fdata-sections" Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the section's name in the output file. Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the ELFobject format have linkers with such optimizations. On AIX,the linker rearranges sections (CSECTs) based on the call graph. The performance impact varies. Together with a linker garbage collection (linker --gc -sections option) these options may lead to smaller statically-linked executables (after stripping). On ELF/DWARFsystems these options do not degenerate the quality of the debug information. There could be issues with other object files/debug info formats. Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. These options affect code generation. They prevent optimizations by the compiler and assembler using relative locations inside a translation unit since the locations are unknown until link time. An example of such an optimization is relaxing calls to short call instructions.

" -fbranch -target -load -optimize "4 Item "-fbranch-target-load-optimize" Perform branch target register load optimization before prologue / epilogue threading. The use of target registers can typically be exposed only during reload, thus hoisting loads out of loops and doing inter-block scheduling needs a separate optimization pass.

" -fbranch -target -load -optimize2 "4 Item "-fbranch-target-load-optimize2" Perform branch target register load optimization after prologue / epilogue threading.

" -fbtr -bb -exclusive "4 Item "-fbtr-bb-exclusive" When performing branch target register load optimization, don't reuse branch target registers within any basic block.

" -fstdarg -opt "4 Item "-fstdarg-opt" Optimize the prologue of variadic argument functions with respect to usage of those arguments.

" -fsection -anchors "4 Item "-fsection-anchors" Try to reduce the number of symbolic address calculations by using shared (L"anchor (R" symbols to address nearby objects. This transformation can help to reduce the number of GOTentries and GOTaccesses on some targets. For example, the implementation of the following function CW(C`foo (C' : 2 static int a, b, c; int foo (void) { return a + b + c; } usually calculates the addresses of all three variables, but if you compile it with -fsection -anchors ,it accesses the variables from a common anchor point instead. The effect is similar to the following pseudocode (which isn't valid C): 5 int foo (void) { register int *xr = &x; return xr[&a -&x] + xr[&b -&x] + xr[&c -&x]; } Not all targets support this option.

" --param name = value "4 Item "--param name=value" In some places, GCCuses various constants to control the amount of optimization that is done. For example, GCCdoes not inline functions that contain more than a certain number of instructions. You can control some of these constants on the command line using the --param option. The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases. In order to get minimal, maximal and default value of a parameter, one can use --help=param -Q options. In each case, the value is an integer. The allowable choices for name are:

" predictable-branch-outcome "4 Item "predictable-branch-outcome" When branch is predicted to be taken with probability lower than this threshold (in percent), then it is considered well predictable.

" max-rtl-if-conversion-insns "4 Item "max-rtl-if-conversion-insns" RTLif-conversion tries to remove conditional branches around a block and replace them with conditionally executed instructions. This parameter gives the maximum number of instructions in a block which should be considered for if-conversion. The compiler will also use other heuristics to decide whether if-conversion is likely to be profitable.

" max-rtl-if-conversion-predictable-cost "4 Item "max-rtl-if-conversion-predictable-cost" 0

" max-rtl-if-conversion-unpredictable-cost "4 Item "max-rtl-if-conversion-unpredictable-cost" RTLif-conversion will try to remove conditional branches around a block and replace them with conditionally executed instructions. These parameters give the maximum permissible cost for the sequence that would be generated by if-conversion depending on whether the branch is statically determined to be predictable or not. The units for this parameter are the same as those for the GCCinternal seq_cost metric. The compiler will try to provide a reasonable default for this parameter using the BRANCH_COST target macro.

" max-crossjump-edges "4 Item "max-crossjump-edges" The maximum number of incoming edges to consider for cross-jumping. The algorithm used by -fcrossjumping is O(N^2) in the number of edges incoming to each block. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size.

" min-crossjump-insns "4 Item "min-crossjump-insns" The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched.

" max-grow-copy-bb-insns "4 Item "max-grow-copy-bb-insns" The maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction.

" max-goto-duplication-insns "4 Item "max-goto-duplication-insns" The maximum number of instructions to duplicate to a block that jumps to a computed goto. To avoid O(N^2) behavior in a number of passes, GCCfactors computed gotos early in the compilation process, and unfactors them as late as possible. Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored.

" max-delay-slot-insn-search "4 Item "max-delay-slot-insn-search" The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time.

" max-delay-slot-live-search "4 Item "max-delay-slot-live-search" When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph.

" max-gcse-memory "4 Item "max-gcse-memory" The approximate maximum amount of memory that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization is not done.

" max-gcse-insertion-ratio "4 Item "max-gcse-insertion-ratio" If the ratio of expression insertions to deletions is larger than this value for any expression, then RTLPRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream.

" max-pending-list-length "4 Item "max-pending-list-length" The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources.

" max-modulo-backtrack-attempts "4 Item "max-modulo-backtrack-attempts" The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time.

" max-inline-insns-single "4 Item "max-inline-insns-single" Several parameters control the tree inliner used in GCC. This number sets the maximum number of instructions (counted in GCC's internal representation) in a single function that the tree inliner considers for inlining. This only affects functions declared inline and methods implemented in a class declaration ( (C+).

" max-inline-insns-auto "4 Item "max-inline-insns-auto" When you use -finline -functions (included in -O3 ), a lot of functions that would otherwise not be considered for inlining by the compiler are investigated. To those functions, a different (more restrictive) limit compared to functions declared inline can be applied.

" max-inline-insns-small "4 Item "max-inline-insns-small" This is bound applied to calls which are considered relevant with -finline -small -functions .

" max-inline-insns-size "4 Item "max-inline-insns-size" This is bound applied to calls which are optimized for size. Small growth may be desirable to anticipate optimization oppurtunities exposed by inlining.

" uninlined-function-insns "4 Item "uninlined-function-insns" Number of instructions accounted by inliner for function overhead such as function prologue and epilogue.

" uninlined-function-time "4 Item "uninlined-function-time" Extra time accounted by inliner for function overhead such as time needed to execute function prologue and epilogue

" uninlined-thunk-insns "4 Item "uninlined-thunk-insns" 0

" uninlined-thunk-time "4 Item "uninlined-thunk-time" Same as --param uninlined-function-insns and --param uninlined-function-time but applied to function thunks

" inline-min-speedup "4 Item "inline-min-speedup" When estimated performance improvement of caller + callee runtime exceeds this threshold (in percent), the function can be inlined regardless of the limit on --param max-inline-insns-single and --param max-inline-insns-auto .

" large-function-insns "4 Item "large-function-insns" The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth .This parameter is useful primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end.

" large-function-growth "4 Item "large-function-growth" Specifies maximal growth of large function caused by inlining in percents. For example, parameter value 100 limits large function growth to 2.0 times the original size.

" large-unit-insns "4 Item "large-unit-insns" The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth . For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times. If B is small relative to A, the growth of unit is 300 \ % and yet such inlining is very sane. For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus for smaller units, the size is increased to --param large-unit-insns before applying --param inline-unit-growth .

" inline-unit-growth "4 Item "inline-unit-growth" Specifies maximal overall growth of the compilation unit caused by inlining. For example, parameter value 20 limits unit growth to 1.2 times the original size. Cold functions (either marked cold via an attribute or by profile feedback) are not accounted into the unit size.

" ipcp-unit-growth "4 Item "ipcp-unit-growth" Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. For example, parameter value 10 limits unit growth to 1.1 times the original size.

" large-stack-frame "4 Item "large-stack-frame" The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much.

" large-stack-frame-growth "4 Item "large-stack-frame-growth" Specifies maximal growth of large stack frames caused by inlining in percents. For example, parameter value 1000 limits large stack frame growth to 11 times the original size.

" max-inline-insns-recursive "4 Item "max-inline-insns-recursive" 0

" max-inline-insns-recursive-auto "4 Item "max-inline-insns-recursive-auto" Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining. --param max-inline-insns-recursive applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline -functions (included in -O3 )is enabled; --param max-inline-insns-recursive-auto applies instead.

" max-inline-recursive-depth "4 Item "max-inline-recursive-depth" 0

" max-inline-recursive-depth-auto "4 Item "max-inline-recursive-depth-auto" Specifies the maximum recursion depth used for recursive inlining. --param max-inline-recursive-depth applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline -functions (included in -O3 )is enabled; --param max-inline-recursive-depth-auto applies instead.

" min-inline-recursive-probability "4 Item "min-inline-recursive-probability" Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers. When profile feedback is available (see -fprofile -generate )the actual recursion depth can be guessed from the probability that function recurses via a given call expression. This parameter limits inlining only to call expressions whose probability exceeds the given threshold (in percents).

" early-inlining-insns "4 Item "early-inlining-insns" Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty.

" max-early-inliner-iterations "4 Item "max-early-inliner-iterations" Limit of iterations of the early inliner. This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining.

" comdat-sharing-probability "4 Item "comdat-sharing-probability" Probability (in percent) that (C+ inline function with comdat visibility are shared across multiple compilation units.

" profile-func-internal-id "4 Item "profile-func-internal-id" A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler uses an id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc.

" min-vect-loop-bound "4 Item "min-vect-loop-bound" The minimum number of iterations under which loops are not vectorized when -ftree -vectorize is used. The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization.

" gcse-cost-distance-ratio "4 Item "gcse-cost-distance-ratio" Scaling factor in calculation of maximum distance an expression can be moved by GCSEoptimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.e., the expressions that have cost less than gcse-unrestricted-cost .Specifying 0 disables hoisting of simple expressions.

" gcse-unrestricted-cost "4 Item "gcse-unrestricted-cost" Cost, roughly measured as the cost of a single typical machine instruction, at which GCSEoptimizations do not constrain the distance an expression can travel. This is currently supported only in the code hoisting pass. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances.

" max-hoist-depth "4 Item "max-hoist-depth" The depth of search in the dominator tree for expressions to hoist. This is used to avoid quadratic behavior in hoisting algorithm. The value of 0 does not limit on the search, but may slow down compilation of huge functions.

" max-tail-merge-comparisons "4 Item "max-tail-merge-comparisons" The maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging.

" max-tail-merge-iterations "4 Item "max-tail-merge-iterations" The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging.

" store-merging-allow-unaligned "4 Item "store-merging-allow-unaligned" Allow the store merging pass to introduce unaligned stores if it is legal to do so.

" max-stores-to-merge "4 Item "max-stores-to-merge" The maximum number of stores to attempt to merge into wider stores in the store merging pass.

" max-unrolled-insns "4 Item "max-unrolled-insns" The maximum number of instructions that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled.

" max-average-unrolled-insns "4 Item "max-average-unrolled-insns" The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled.

" max-unroll-times "4 Item "max-unroll-times" The maximum number of unrollings of a single loop.

" max-peeled-insns "4 Item "max-peeled-insns" The maximum number of instructions that a loop may have to be peeled. If a loop is peeled, this parameter also determines how many times the loop code is peeled.

" max-peel-times "4 Item "max-peel-times" The maximum number of peelings of a single loop.

" max-peel-branches "4 Item "max-peel-branches" The maximum number of branches on the hot path through the peeled sequence.

" max-completely-peeled-insns "4 Item "max-completely-peeled-insns" The maximum number of insns of a completely peeled loop.

" max-completely-peel-times "4 Item "max-completely-peel-times" The maximum number of iterations of a loop to be suitable for complete peeling.

" max-completely-peel-loop-nest-depth "4 Item "max-completely-peel-loop-nest-depth" The maximum depth of a loop nest suitable for complete peeling.

" max-unswitch-insns "4 Item "max-unswitch-insns" The maximum number of insns of an unswitched loop.

" max-unswitch-level "4 Item "max-unswitch-level" The maximum number of branches unswitched in a single loop.

" lim-expensive "4 Item "lim-expensive" The minimum cost of an expensive expression in the loop invariant motion.

" iv-consider-all-candidates-bound "4 Item "iv-consider-all-candidates-bound" Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations. If there are more candidates than this, only the most relevant ones are considered to avoid quadratic time complexity.

" iv-max-considered-uses "4 Item "iv-max-considered-uses" The induction variable optimizations give up on loops that contain more induction variable uses.

" iv-always-prune-cand-set-bound "4 Item "iv-always-prune-cand-set-bound" If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one.

" avg-loop-niter "4 Item "avg-loop-niter" Average number of iterations of a loop.

" dse-max-object-size "4 Item "dse-max-object-size" Maximum size (in bytes) of objects tracked bytewise by dead store elimination. Larger values may result in larger compilation times.

" dse-max-alias-queries-per-store "4 Item "dse-max-alias-queries-per-store" Maximum number of queries into the alias oracle per store. Larger values result in larger compilation times and may result in more removed dead stores.

" scev-max-expr-size "4 Item "scev-max-expr-size" Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer.

" scev-max-expr-complexity "4 Item "scev-max-expr-complexity" Bound on the complexity of the expressions in the scalar evolutions analyzer. Complex expressions slow the analyzer.

" max-tree-if-conversion-phi-args "4 Item "max-tree-if-conversion-phi-args" Maximum number of arguments in a PHIsupported by TREEif conversion unless the loop is marked with simd pragma.

" vect-max-version-for-alignment-checks "4 Item "vect-max-version-for-alignment-checks" The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer.

" vect-max-version-for-alias-checks "4 Item "vect-max-version-for-alias-checks" The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer.

" vect-max-peeling-for-alignment "4 Item "vect-max-peeling-for-alignment" The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means no limit.

" max-iterations-to-track "4 Item "max-iterations-to-track" The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate.

" hot-bb-count-ws-permille "4 Item "hot-bb-count-ws-permille" A basic block profile count is considered hot if it contributes to the given permillage (i.e. 0...1000) of the entire profiled execution.

" hot-bb-frequency-fraction "4 Item "hot-bb-frequency-fraction" Select fraction of the entry block frequency of executions of basic block in function given basic block needs to have to be considered hot.

" max-predicted-iterations "4 Item "max-predicted-iterations" The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound. The known number of iterations is predicted correctly, while the unknown number of iterations average to roughly 10. This means that the loop without bounds appears artificially cold relative to the other one.

" builtin-expect-probability "4 Item "builtin-expect-probability" Control the probability of the expression having the specified value. This parameter takes a percentage (i.e. 0 ... 100) as input.

" builtin-string-cmp-inline-length "4 Item "builtin-string-cmp-inline-length" The maximum length of a constant string for a builtin string cmp call eligible for inlining.

" align-threshold "4 Item "align-threshold" Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block.

" align-loop-iterations "4 Item "align-loop-iterations" A loop expected to iterate at least the selected number of iterations is aligned.

" tracer-dynamic-coverage "4 Item "tracer-dynamic-coverage" 0

" tracer-dynamic-coverage-feedback "4 Item "tracer-dynamic-coverage-feedback" This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion. The tracer-dynamic-coverage-feedback parameter is used only when profile feedback is available. The real profiles (as opposed to statically estimated ones) are much less balanced allowing the threshold to be larger value.

" tracer-max-code-growth "4 Item "tracer-max-code-growth" Stop tail duplication once code growth has reached given percentage. This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth.

" tracer-min-branch-ratio "4 Item "tracer-min-branch-ratio" Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent).

" tracer-min-branch-probability "4 Item "tracer-min-branch-probability" 0

" tracer-min-branch-probability-feedback "4 Item "tracer-min-branch-probability-feedback" Stop forward growth if the best edge has probability lower than this threshold. Similarly to tracer-dynamic-coverage two parameters are provided. tracer-min-branch-probability-feedback is used for compilation with profile feedback and tracer-min-branch-probability compilation without. The value for compilation with profile feedback needs to be more conservative (higher) in order to make tracer effective.

" stack-clash-protection-guard-size "4 Item "stack-clash-protection-guard-size" Specify the size of the operating system provided stack guard as 2 raised to num bytes. Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks.

" stack-clash-protection-probe-interval "4 Item "stack-clash-protection-probe-interval" Stack clash protection involves probing stack space as it is allocated. This param controls the maximum distance between probes into the stack as 2 raised to num bytes. Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks.

" max-cse-path-length "4 Item "max-cse-path-length" The maximum number of basic blocks on path that CSEconsiders.

" max-cse-insns "4 Item "max-cse-insns" The maximum number of instructions CSEprocesses before flushing.

" ggc-min-expand "4 Item "ggc-min-expand" GCCuses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collector's heap should be allowed to expand between collections. Tuning this may improve compilation speed; it has no effect on code generation. The default is 30% + 70% * ( RAM/1GB)with an upper bound of 100% when RAM>= 1GB. If CW(C`getrlimit (C' is available, the notion of (L" RAM(R" is the smallest of actual RAMand CW(C`RLIMIT_DATA (C' or CW(C`RLIMIT_AS (C' .If GCCis not able to calculate RAMon a particular platform, the lower bound of 30% is used. Setting this parameter and ggc-min-heapsize to zero causes a full collection to occur at every opportunity. This is extremely slow, but can be useful for debugging.

" ggc-min-heapsize "4 Item "ggc-min-heapsize" Minimum size of the garbage collector's heap before it begins bothering to collect garbage. The first collection occurs after the heap expands by ggc-min-expand %beyond ggc-min-heapsize .Again, tuning this may improve compilation speed, and has no effect on code generation. The default is the smaller of RAM/8,RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATAor RLIMIT_ASare not exceeded, but with a lower bound of 4096 (four megabytes) and an upper bound of 131072 (128 megabytes). If GCCis not able to calculate RAMon a particular platform, the lower bound is used. Setting this parameter very large effectively disables garbage collection. Setting this parameter and ggc-min-expand to zero causes a full collection to occur at every opportunity.

" max-reload-search-insns "4 Item "max-reload-search-insns" The maximum number of instruction reload should look backward for equivalent register. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance.

" max-cselib-memory-locations "4 Item "max-cselib-memory-locations" The maximum number of memory locations cselib should take into account. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance.

" max-sched-ready-insns "4 Item "max-sched-ready-insns" The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass. Increasing values mean more thorough searches, making the compilation time increase with probably little benefit.

" max-sched-region-blocks "4 Item "max-sched-region-blocks" The maximum number of blocks in a region to be considered for interblock scheduling.

" max-pipeline-region-blocks "4 Item "max-pipeline-region-blocks" The maximum number of blocks in a region to be considered for pipelining in the selective scheduler.

" max-sched-region-insns "4 Item "max-sched-region-insns" The maximum number of insns in a region to be considered for interblock scheduling.

" max-pipeline-region-insns "4 Item "max-pipeline-region-insns" The maximum number of insns in a region to be considered for pipelining in the selective scheduler.

" min-spec-prob "4 Item "min-spec-prob" The minimum probability (in percents) of reaching a source block for interblock speculative scheduling.

" max-sched-extend-regions-iters "4 Item "max-sched-extend-regions-iters" The maximum number of iterations through CFGto extend regions. A value of 0 disables region extensions.

" max-sched-insn-conflict-delay "4 Item "max-sched-insn-conflict-delay" The maximum conflict delay for an insn to be considered for speculative motion.

" sched-spec-prob-cutoff "4 Item "sched-spec-prob-cutoff" The minimal probability of speculation success (in percents), so that speculative insns are scheduled.

" sched-state-edge-prob-cutoff "4 Item "sched-state-edge-prob-cutoff" The minimum probability an edge must have for the scheduler to save its state across it.

" sched-mem-true-dep-cost "4 Item "sched-mem-true-dep-cost" Minimal distance (in CPUcycles) between store and load targeting same memory locations.

" selsched-max-lookahead "4 Item "selsched-max-lookahead" The maximum size of the lookahead window of selective scheduling. It is a depth of search for available instructions.

" selsched-max-sched-times "4 Item "selsched-max-sched-times" The maximum number of times that an instruction is scheduled during selective scheduling. This is the limit on the number of iterations through which the instruction may be pipelined.

" selsched-insns-to-rename "4 Item "selsched-insns-to-rename" The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler.

" sms-min-sc "4 Item "sms-min-sc" The minimum value of stage count that swing modulo scheduler generates.

" max-last-value-rtl "4 Item "max-last-value-rtl" The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register.

" max-combine-insns "4 Item "max-combine-insns" The maximum number of instructions the RTLcombiner tries to combine.

" integer-share-limit "4 Item "integer-share-limit" Small integer constants can use a shared data structure, reducing the compiler's memory usage and increasing its speed. This sets the maximum value of a shared integer constant.

" ssp-buffer-size "4 Item "ssp-buffer-size" The minimum size of buffers (i.e. arrays) that receive stack smashing protection when -fstack -protection is used.

" min-size-for-stack-sharing "4 Item "min-size-for-stack-sharing" The minimum size of variables taking part in stack slot sharing when not optimizing.

" max-jump-thread-duplication-stmts "4 Item "max-jump-thread-duplication-stmts" Maximum number of statements allowed in a block that needs to be duplicated when threading jumps.

" max-fields-for-field-sensitive "4 Item "max-fields-for-field-sensitive" Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis.

" prefetch-latency "4 Item "prefetch-latency" Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also lead to less streams being prefetched (see simultaneous-prefetches ).

" simultaneous-prefetches "4 Item "simultaneous-prefetches" Maximum number of prefetches that can run at the same time.

" l1-cache -line -size "4 Item "l1-cache-line-size" The size of cache line in L1 data cache, in bytes.

" l1-cache -size "4 Item "l1-cache-size" The size of L1 data cache, in kilobytes.

" l2-cache -size "4 Item "l2-cache-size" The size of L2 data cache, in kilobytes.

" prefetch-dynamic-strides "4 Item "prefetch-dynamic-strides" Whether the loop array prefetch pass should issue software prefetch hints for strides that are non-constant. In some cases this may be beneficial, though the fact the stride is non-constant may make it hard to predict when there is clear benefit to issuing these hints. Set to 1 if the prefetch hints should be issued for non-constant strides. Set to 0 if prefetch hints should be issued only for strides that are known to be constant and below prefetch-minimum-stride .

" prefetch-minimum-stride "4 Item "prefetch-minimum-stride" Minimum constant stride, in bytes, to start using prefetch hints for. If the stride is less than this threshold, prefetch hints will not be issued. This setting is useful for processors that have hardware prefetchers, in which case there may be conflicts between the hardware prefetchers and the software prefetchers. If the hardware prefetchers have a maximum stride they can handle, it should be used here to improve the use of software prefetchers. A value of -1 means we don't have a threshold and therefore prefetch hints can be issued for any constant stride. This setting is only useful for strides that are known and constant.

" loop-interchange-max-num-stmts "4 Item "loop-interchange-max-num-stmts" The maximum number of stmts in a loop to be interchanged.

" loop-interchange-stride-ratio "4 Item "loop-interchange-stride-ratio" The minimum ratio between stride of two loops for interchange to be profitable.

" min-insn-to-prefetch-ratio "4 Item "min-insn-to-prefetch-ratio" The minimum ratio between the number of instructions and the number of prefetches to enable prefetching in a loop.

" prefetch-min-insn-to-mem-ratio "4 Item "prefetch-min-insn-to-mem-ratio" The minimum ratio between the number of instructions and the number of memory references to enable prefetching in a loop.

" use-canonical-types "4 Item "use-canonical-types" Whether the compiler should use the (L"canonical (R" type system. Should always be 1, which uses a more efficient internal mechanism for comparing types in (C+ and Objective -(C+. However, if bugs in the canonical type system are causing compilation failures, set this value to 0 to disable canonical types.

" switch-conversion-max-branch-ratio "4 Item "switch-conversion-max-branch-ratio" Switch initialization conversion refuses to create arrays that are bigger than switch-conversion-max-branch-ratio times the number of branches in the switch.

" max-partial-antic-length "4 Item "max-partial-antic-length" Maximum length of the partial antic set computed during the tree partial redundancy elimination optimization ( -ftree -pre )when optimizing at -O3 and above. For some sorts of source code the enhanced partial redundancy elimination optimization can run away, consuming all of the memory available on the host machine. This parameter sets a limit on the length of the sets that are computed, which prevents the runaway behavior. Setting a value of 0 for this parameter allows an unlimited set length.

" rpo-vn-max-loop-depth "4 Item "rpo-vn-max-loop-depth" Maximum loop depth that is value-numbered optimistically. When the limit hits the innermost rpo-vn-max-loop-depth loops and the outermost loop in the loop nest are value-numbered optimistically and the remaining ones not.

" sccvn-max-alias-queries-per-access "4 Item "sccvn-max-alias-queries-per-access" Maximum number of alias-oracle queries we perform when looking for redundancies for loads and stores. If this limit is hit the search is aborted and the load or store is not considered redundant. The number of queries is algorithmically limited to the number of stores on all paths from the load to the function entry.

" ira-max-loops-num "4 Item "ira-max-loops-num" IRAuses regional register allocation by default. If a function contains more loops than the number given by this parameter, only at most the given number of the most frequently-executed loops form regions for regional register allocation.

" ira-max-conflict-table-size "4 Item "ira-max-conflict-table-size" Although IRAuses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory for huge functions. If the conflict table for a function could be more than the size in MBgiven by this parameter, the register allocator instead uses a faster, simpler, and lower-quality algorithm that does not require building a pseudo-register conflict table.

" ira-loop-reserved-regs "4 Item "ira-loop-reserved-regs" IRAcan be used to evaluate more accurate register pressure in loops for decisions to move loop invariants (see -O3 ).The number of available registers reserved for some other purposes is given by this parameter. Default of the parameter is the best found from numerous experiments.

" lra-inheritance-ebb-probability-cutoff "4 Item "lra-inheritance-ebb-probability-cutoff" LRAtries to reuse values reloaded in registers in subsequent insns. This optimization is called inheritance. EBBis used as a region to do this optimization. The parameter defines a minimal fall-through edge probability in percentage used to add BBto inheritance EBBin LRA.The default value was chosen from numerous runs of SPEC2000on x86 -64.

" loop-invariant-max-bbs-in-loop "4 Item "loop-invariant-max-bbs-in-loop" Loop invariant motion can be very expensive, both in compilation time and in amount of needed compile-time memory, with very large loops. Loops with more basic blocks than this parameter won't have loop invariant motion optimization performed on them.

" loop-max-datarefs-for-datadeps "4 Item "loop-max-datarefs-for-datadeps" Building data dependencies is expensive for very large loops. This parameter limits the number of data references in loops that are considered for data dependence analysis. These large loops are no handled by the optimizations using loop data dependencies.

" max-vartrack-size "4 Item "max-vartrack-size" Sets a maximum number of hash table slots to use during variable tracking dataflow analysis of any function. If this limit is exceeded with variable tracking at assignments enabled, analysis for that function is retried without it, after removing all debug insns from the function. If the limit is exceeded even without debug insns, var tracking analysis is completely disabled for the function. Setting the parameter to zero makes it unlimited.

" max-vartrack-expr-depth "4 Item "max-vartrack-expr-depth" Sets a maximum number of recursion levels when attempting to map variable names or debug temporaries to value expressions. This trades compilation time for more complete debug information. If this is set too low, value expressions that are available and could be represented in debug information may end up not being used; setting this higher may enable the compiler to find more complex debug expressions, but compile time and memory use may grow.

" max-debug-marker-count "4 Item "max-debug-marker-count" Sets a threshold on the number of debug markers (e.g. begin stmt markers) to avoid complexity explosion at inlining or expanding to RTL. If a function has more such gimple stmts than the set limit, such stmts will be dropped from the inlined copy of a function, and from its RTL expansion.

" min-nondebug-insn-uid "4 Item "min-nondebug-insn-uid" Use uids starting at this parameter for nondebug insns. The range below the parameter is reserved exclusively for debug insns created by -fvar -tracking -assignments ,but debug insns may get (non-overlapping) uids above it if the reserved range is exhausted.

" ipa-sra-ptr-growth-factor "4 Item "ipa-sra-ptr-growth-factor" IPA-SRA replaces a pointer to an aggregate with one or more new parameters only when their cumulative size is less or equal to ipa-sra-ptr-growth-factor times the size of the original pointer parameter.

" sra-max-scalarization-size-Ospeed "4 Item "sra-max-scalarization-size-Ospeed" 0

" sra-max-scalarization-size-Osize "4 Item "sra-max-scalarization-size-Osize" The two Scalar Reduction of Aggregates passes ( SRAand IPA-SRA) aim to replace scalar parts of aggregates with uses of independent scalar variables. These parameters control the maximum size, in storage units, of aggregate which is considered for replacement when compiling for speed ( sra-max-scalarization-size-Ospeed )or size ( sra-max-scalarization-size-Osize )respectively.

" tm-max-aggregate-size "4 Item "tm-max-aggregate-size" When making copies of thread-local variables in a transaction, this parameter specifies the size in bytes after which variables are saved with the logging functions as opposed to save/restore code sequence pairs. This option only applies when using -fgnu -tm .

" graphite-max-nb-scop-params "4 Item "graphite-max-nb-scop-params" To avoid exponential effects in the Graphite loop transforms, the number of parameters in a Static Control Part (SCoP) is bounded. A value of zero can be used to lift the bound. A variable whose value is unknown at compilation time and defined outside a SCoP is a parameter of the SCoP.

" loop-block-tile-size "4 Item "loop-block-tile-size" Loop blocking or strip mining transforms, enabled with -floop -block or -floop -strip -mine ,strip mine each loop in the loop nest by a given number of iterations. The strip length can be changed using the loop-block-tile-size parameter.

" ipa-cp-value-list-size "4 Item "ipa-cp-value-list-size" IPA-CP attempts to track all possible values and types passed to a function's parameter in order to propagate them and perform devirtualization. ipa-cp-value-list-size is the maximum number of values and types it stores per one formal parameter of a function.

" ipa-cp-eval-threshold "4 Item "ipa-cp-eval-threshold" IPA-CP calculates its own score of cloning profitability heuristics and performs those cloning opportunities with scores that exceed ipa-cp-eval-threshold .

" ipa-cp-recursion-penalty "4 Item "ipa-cp-recursion-penalty" Percentage penalty the recursive functions will receive when they are evaluated for cloning.

" ipa-cp-single-call-penalty "4 Item "ipa-cp-single-call-penalty" Percentage penalty functions containing a single call to another function will receive when they are evaluated for cloning.

" ipa-max-agg-items "4 Item "ipa-max-agg-items" IPA-CP is also capable to propagate a number of scalar values passed in an aggregate. ipa-max-agg-items controls the maximum number of such values per one parameter.

" ipa-cp-loop-hint-bonus "4 Item "ipa-cp-loop-hint-bonus" When IPA-CP determines that a cloning candidate would make the number of iterations of a loop known, it adds a bonus of ipa-cp-loop-hint-bonus to the profitability score of the candidate.

" ipa-cp-array-index-hint-bonus "4 Item "ipa-cp-array-index-hint-bonus" When IPA-CP determines that a cloning candidate would make the index of an array access known, it adds a bonus of ipa-cp-array-index-hint-bonus to the profitability score of the candidate.

" ipa-max-aa-steps "4 Item "ipa-max-aa-steps" During its analysis of function bodies, IPA-CP employs alias analysis in order to track values pointed to by function parameters. In order not spend too much time analyzing huge functions, it gives up and consider all memory clobbered after examining ipa-max-aa-steps statements modifying memory.

" lto-partitions "4 Item "lto-partitions" Specify desired number of partitions produced during WHOPRcompilation. The number of partitions should exceed the number of CPUs used for compilation.

" lto-min-partition "4 Item "lto-min-partition" Size of minimal partition for WHOPR(in estimated instructions). This prevents expenses of splitting very small programs into too many partitions.

" lto-max-partition "4 Item "lto-max-partition" Size of max partition for WHOPR(in estimated instructions). to provide an upper bound for individual size of partition. Meant to be used only with balanced partitioning.

" lto-max-streaming-parallelism "4 Item "lto-max-streaming-parallelism" Maximal number of parallel processes used for LTOstreaming.

" cxx-max-namespaces-for-diagnostic-help "4 Item "cxx-max-namespaces-for-diagnostic-help" The maximum number of namespaces to consult for suggestions when (C+ name lookup fails for an identifier.

" sink-frequency-threshold "4 Item "sink-frequency-threshold" The maximum relative execution frequency (in percents) of the target block relative to a statement's original block to allow statement sinking of a statement. Larger numbers result in more aggressive statement sinking. A small positive adjustment is applied for statements with memory operands as those are even more profitable so sink.

" max-stores-to-sink "4 Item "max-stores-to-sink" The maximum number of conditional store pairs that can be sunk. Set to 0 if either vectorization ( -ftree -vectorize )or if-conversion ( -ftree -loop -if -convert )is disabled.

" allow-store-data-races "4 Item "allow-store-data-races" Allow optimizers to introduce new data races on stores. Set to 1 to allow, otherwise to 0.

" case-values-threshold "4 Item "case-values-threshold" The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. If the value is 0, use the default for the machine.

" tree-reassoc-width "4 Item "tree-reassoc-width" Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value.

" sched-pressure-algorithm "4 Item "sched-pressure-algorithm" Choose between the two available implementations of -fsched -pressure .Algorithm 1 is the original implementation and is the more likely to prevent instructions from being reordered. Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by algorithm 1 and the rather aggressive approach taken by the default scheduler. It relies more heavily on having a regular register file and accurate register pressure classes. See haifa-sched.c in the GCCsources for more details. The default choice depends on the target.

" max-slsr-cand-scan "4 Item "max-slsr-cand-scan" Set the maximum number of existing candidates that are considered when seeking a basis for a new straight-line strength reduction candidate.

" asan-globals "4 Item "asan-globals" Enable buffer overflow detection for global objects. This kind of protection is enabled by default if you are using -fsanitize=address option. To disable global objects protection use --param asan -globals=0 .

" asan-stack "4 Item "asan-stack" Enable buffer overflow detection for stack objects. This kind of protection is enabled by default when using -fsanitize=address . To disable stack protection use --param asan -stack=0 option.

" asan-instrument-reads "4 Item "asan-instrument-reads" Enable buffer overflow detection for memory reads. This kind of protection is enabled by default when using -fsanitize=address . To disable memory reads protection use --param asan -instrument -reads=0 .

" asan-instrument-writes "4 Item "asan-instrument-writes" Enable buffer overflow detection for memory writes. This kind of protection is enabled by default when using -fsanitize=address . To disable memory writes protection use --param asan -instrument -writes=0 option.

" asan-memintrin "4 Item "asan-memintrin" Enable detection for built-in functions. This kind of protection is enabled by default when using -fsanitize=address . To disable built-in functions protection use --param asan -memintrin=0 .

" asan-use-after-return "4 Item "asan-use-after-return" Enable detection of use-after-return. This kind of protection is enabled by default when using the -fsanitize=address option. To disable it use --param asan -use -after -return=0 . Note: By default the check is disabled at run time. To enable it, add CW(C`detect_stack_use_after_return=1 (C' to the environment variable ASAN_OPTIONS .

" asan-instrumentation-with-call-threshold "4 Item "asan-instrumentation-with-call-threshold" If number of memory accesses in function being instrumented is greater or equal to this number, use callbacks instead of inline checks. E.g. to disable inline code use --param asan -instrumentation -with -call -threshold=0 .

" use-after-scope-direct-emission-threshold "4 Item "use-after-scope-direct-emission-threshold" If the size of a local variable in bytes is smaller or equal to this number, directly poison (or unpoison) shadow memory instead of using run-time callbacks.

" max-fsm-thread-path-insns "4 Item "max-fsm-thread-path-insns" Maximum number of instructions to copy when duplicating blocks on a finite state automaton jump thread path.

" max-fsm-thread-length "4 Item "max-fsm-thread-length" Maximum number of basic blocks on a finite state automaton jump thread path.

" max-fsm-thread-paths "4 Item "max-fsm-thread-paths" Maximum number of new jump thread paths to create for a finite state automaton.

" parloops-chunk-size "4 Item "parloops-chunk-size" Chunk size of omp schedule for loops parallelized by parloops.

" parloops-schedule "4 Item "parloops-schedule" Schedule type of omp schedule for loops parallelized by parloops (static, dynamic, guided, auto, runtime).

" parloops-min-per-thread "4 Item "parloops-min-per-thread" The minimum number of iterations per thread of an innermost parallelized loop for which the parallelized variant is preferred over the single threaded one. Note that for a parallelized loop nest the minimum number of iterations of the outermost loop per thread is two.

" max-ssa-name-query-depth "4 Item "max-ssa-name-query-depth" Maximum depth of recursion when querying properties of SSAnames in things like fold routines. One level of recursion corresponds to following a use-def chain.

" hsa-gen-debug-stores "4 Item "hsa-gen-debug-stores" Enable emission of special debug stores within HSAkernels which are then read and reported by libgomp plugin. Generation of these stores is disabled by default, use --param hsa -gen -debug -stores=1 to enable it.

" max-speculative-devirt-maydefs "4 Item "max-speculative-devirt-maydefs" The maximum number of may-defs we analyze when looking for a must-def specifying the dynamic type of an object that invokes a virtual call we may be able to devirtualize speculatively.

" max-vrp-switch-assertions "4 Item "max-vrp-switch-assertions" The maximum number of assertions to add along the default edge of a switch statement during VRP.

" unroll-jam-min-percent "4 Item "unroll-jam-min-percent" The minimum percentage of memory references that must be optimized away for the unroll-and-jam transformation to be considered profitable.

" unroll-jam-max-unroll "4 Item "unroll-jam-max-unroll" The maximum number of times the outer loop should be unrolled by the unroll-and-jam transformation.

" max-rtl-if-conversion-unpredictable-cost "4 Item "max-rtl-if-conversion-unpredictable-cost" Maximum permissible cost for the sequence that would be generated by the RTLif-conversion pass for a branch that is considered unpredictable.

" max-variable-expansions-in-unroller "4 Item "max-variable-expansions-in-unroller" If -fvariable -expansion -in -unroller is used, the maximum number of times that an individual variable will be expanded during loop unrolling.

" tracer-min-branch-probability-feedback "4 Item "tracer-min-branch-probability-feedback" Stop forward growth if the probability of best edge is less than this threshold (in percent). Used when profile feedback is available.

" partial-inlining-entry-probability "4 Item "partial-inlining-entry-probability" Maximum probability of the entry BBof split region (in percent relative to entry BBof the function) to make partial inlining happen.

" max-tracked-strlens "4 Item "max-tracked-strlens" Maximum number of strings for which strlen optimization pass will track string lengths.

" gcse-after-reload-partial-fraction "4 Item "gcse-after-reload-partial-fraction" The threshold ratio for performing partial redundancy elimination after reload.

" gcse-after-reload-critical-fraction "4 Item "gcse-after-reload-critical-fraction" The threshold ratio of critical edges execution count that permit performing redundancy elimination after reload.

" max-loop-header-insns "4 Item "max-loop-header-insns" The maximum number of insns in loop header duplicated by the copy loop headers pass.

" vect-epilogues-nomask "4 Item "vect-epilogues-nomask" Enable loop epilogue vectorization using smaller vector size.

" slp-max-insns-in-bb "4 Item "slp-max-insns-in-bb" Maximum number of instructions in basic block to be considered for SLPvectorization.

" avoid-fma-max-bits "4 Item "avoid-fma-max-bits" Maximum number of bits for which we avoid creating FMAs.

" sms-loop-average-count-threshold "4 Item "sms-loop-average-count-threshold" A threshold on the average loop count considered by the swing modulo scheduler.

" sms-dfa-history "4 Item "sms-dfa-history" The number of cycles the swing modulo scheduler considers when checking conflicts using DFA.

" hot-bb-count-fraction "4 Item "hot-bb-count-fraction" Select fraction of the maximal count of repetitions of basic block in program given basic block needs to have to be considered hot (used in non-LTO mode)

" max-inline-insns-recursive-auto "4 Item "max-inline-insns-recursive-auto" The maximum number of instructions non-inline function can grow to via recursive inlining.

" graphite-allow-codegen-errors "4 Item "graphite-allow-codegen-errors" Whether codegen errors should be ICEs when -fchecking .

" sms-max-ii-factor "4 Item "sms-max-ii-factor" A factor for tuning the upper bound that swing modulo scheduler uses for scheduling a loop.

" lra-max-considered-reload-pseudos "4 Item "lra-max-considered-reload-pseudos" The max number of reload pseudos which are considered during spilling a non-reload pseudo.

" max-pow-sqrt-depth "4 Item "max-pow-sqrt-depth" Maximum depth of sqrt chains to use when synthesizing exponentiation by a real constant.

" max-dse-active-local-stores "4 Item "max-dse-active-local-stores" Maximum number of active local stores in RTLdead store elimination.

" asan-instrument-allocas "4 Item "asan-instrument-allocas" Enable asan allocas/VLAs protection.

" max-iterations-computation-cost "4 Item "max-iterations-computation-cost" Bound on the cost of an expression to compute the number of iterations.

" max-isl-operations "4 Item "max-isl-operations" Maximum number of isl operations, 0 means unlimited.

" graphite-max-arrays-per-scop "4 Item "graphite-max-arrays-per-scop" Maximum number of arrays per scop.

" max-vartrack-reverse-op-size "4 Item "max-vartrack-reverse-op-size" Max. size of loc list for which reverse ops should be added.

" unlikely-bb-count-fraction "4 Item "unlikely-bb-count-fraction" The minimum fraction of profile runs a given basic block execution count must be not to be considered unlikely.

" tracer-dynamic-coverage-feedback "4 Item "tracer-dynamic-coverage-feedback" The percentage of function, weighted by execution frequency, that must be covered by trace formation. Used when profile feedback is available.

" max-inline-recursive-depth-auto "4 Item "max-inline-recursive-depth-auto" The maximum depth of recursive inlining for non-inline functions.

" fsm-scale-path-stmts "4 Item "fsm-scale-path-stmts" Scale factor to apply to the number of statements in a threading path when comparing to the number of (scaled) blocks.

" fsm-maximum-phi-arguments "4 Item "fsm-maximum-phi-arguments" Maximum number of arguments a PHImay have before the FSMthreader will not try to thread through its block.

" uninit-control-dep-attempts "4 Item "uninit-control-dep-attempts" Maximum number of nested calls to search for control dependencies during uninitialized variable analysis.

" indir-call-topn-profile "4 Item "indir-call-topn-profile" Track top N target addresses in indirect-call profile.

" max-once-peeled-insns "4 Item "max-once-peeled-insns" The maximum number of insns of a peeled loop that rolls only once.

" sra-max-scalarization-size-Osize "4 Item "sra-max-scalarization-size-Osize" Maximum size, in storage units, of an aggregate which should be considered for scalarization when compiling for size.

" fsm-scale-path-blocks "4 Item "fsm-scale-path-blocks" Scale factor to apply to the number of blocks in a threading path when comparing to the number of (scaled) statements.

" sched-autopref-queue-depth "4 Item "sched-autopref-queue-depth" Hardware autoprefetcher scheduler model control flag. Number of lookahead cycles the model looks into; at ' ' only enable instruction sorting heuristic.

" loop-versioning-max-inner-insns "4 Item "loop-versioning-max-inner-insns" The maximum number of instructions that an inner loop can have before the loop versioning pass considers it too big to copy.

" loop-versioning-max-outer-insns "4 Item "loop-versioning-max-outer-insns" The maximum number of instructions that an outer loop can have before the loop versioning pass considers it too big to copy, discounting any instructions in inner loops that directly benefit from versioning.

Program Instrumentation Options

Subsection "Program Instrumentation Options" GCCsupports a number of command-line options that control adding run-time instrumentation to the code it normally generates. For example, one purpose of instrumentation is collect profiling statistics for use in finding program hot spots, code coverage analysis, or profile-guided optimizations. Another class of program instrumentation is adding run-time checking to detect programming errors like invalid pointer dereferences or out-of-bounds array accesses, as well as deliberately hostile attacks such as stack smashing or (C+ vtable hijacking. There is also a general hook which can be used to implement other forms of tracing or function-level instrumentation for debug or program analysis purposes.

" -p "4 Item "-p" 0

" -pg "4 Item "-pg" Generate extra code to write profile information suitable for the analysis program prof (for -p )or gprof (for -pg ).You must use this option when compiling the source files you want data about, and you must also use it when linking. You can use the function attribute CW(C`no_instrument_function (C' to suppress profiling of individual functions when compiling with these options.

" -fprofile -arcs "4 Item "-fprofile-arcs" Add code so that program flow arcs are instrumented. During execution the program records how many times each branch and call is executed and how many times it is taken or returns. On targets that support constructors with priority support, profiling properly handles constructors, destructors and (C+ constructors (and destructors) of classes which are used as a type of a global variable. When the compiled program exits it saves this data to a file called auxname .gcda for each source file. The data may be used for profile-directed optimizations ( -fbranch -probabilities ),or for test coverage analysis ( -ftest -coverage ).Each object file's auxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c ,or dir/foo.gcda for output file specified as -o dir/foo.o ).

" --coverage "4 Item "--coverage" This option is used to compile and link code instrumented for coverage analysis. The option is a synonym for -fprofile -arcs -ftest -coverage (when compiling) and -lgcov (when linking). See the documentation for those options for more details.

"*" 4 Compile the source files with -fprofile -arcs plus optimization and code generation options. For test coverage analysis, use the additional -ftest -coverage option. You do not need to profile every source file in a program.

"*" 4 Compile the source files additionally with -fprofile -abs -path to create absolute path names in the .gcno files. This allows gcov to find the correct sources in projects where compilations occur with different working directories.

"*" 4 Link your object files with -lgcov or -fprofile -arcs (the latter implies the former).

"*" 4 Run the program on a representative workload to generate the arc profile information. This may be repeated any number of times. You can run concurrent instances of your program, and provided that the file system supports locking, the data files will be correctly updated. Unless a strict ISOC dialect option is in effect, CW(C`fork (C' calls are detected and correctly handled without double counting.

"*" 4 For profile-directed optimizations, compile the source files again with the same optimization and code generation options plus -fbranch -probabilities .

"*" 4 For test coverage analysis, use gcov to produce human readable information from the .gcno and .gcda files. Refer to the gcov documentation for further information. With -fprofile -arcs ,for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code.

" -ftest -coverage "4 Item "-ftest-coverage" Produce a notes file that the gcov code-coverage utility can use to show program coverage. Each source file's note file is called auxname .gcno .Refer to the -fprofile -arcs option above for a description of auxname and instructions on how to generate test coverage data. Coverage data matches the source files more closely if you do not optimize.

" -fprofile -abs -path "4 Item "-fprofile-abs-path" Automatically convert relative source file names to absolute path names in the .gcno files. This allows gcov to find the correct sources in projects where compilations occur with different working directories.

" -fprofile -dir= path "4 Item "-fprofile-dir=path" Set the directory to search for the profile data files in to path . This option affects only the profile data generated by -fprofile -generate , -ftest -coverage , -fprofile -arcs and used by -fprofile -use and -fbranch -probabilities and its related options. Both absolute and relative paths can be used. By default, GCCuses the current directory as path ,thus the profile data file appears in the same directory as the object file. In order to prevent the file name clashing, if the object file name is not an absolute path, we mangle the absolute path of the sourcename .gcda file and use it as the file name of a .gcda file. When an executable is run in a massive parallel environment, it is recommended to save profile to different folders. That can be done with variables in path that are exported during run-time:

" CB%p "4 Item "%p" process ID.

" CB%q {VAR} "4 Item "%q{VAR}" value of environment variable VAR

" -fprofile -generate "4 Item "-fprofile-generate" 0

" -fprofile -generate= path "4 Item "-fprofile-generate=path" Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use -fprofile -generate both when compiling and when linking your program. The following options are enabled: -fprofile -arcs , -fprofile -values , -finline -functions ,and -fipa -bit -cp . If path is specified, GCClooks at the path to find the profile feedback data files. See -fprofile -dir . To optimize the program based on the collected profile information, use -fprofile -use .

" -fprofile -update= method "4 Item "-fprofile-update=method" Alter the update method for an application instrumented for profile feedback based optimization. The method argument should be one of single , atomic or prefer-atomic . The first one is useful for single-threaded applications, while the second one prevents profile corruption by emitting thread-safe code. Warning: When an application does not properly join all threads (or creates an detached thread), a profile file can be still corrupted. Using prefer-atomic would be transformed either to atomic , when supported by a target, or to single otherwise. The GCCdriver automatically selects prefer-atomic when -pthread is present in the command line.

" -fprofile -filter -files= regex "4 Item "-fprofile-filter-files=regex" Instrument only functions from files where names match any regular expression (separated by a semi-colon). For example, -fprofile -filter -files=main.c;module.*.c will instrument only main.c and all C files starting with 'module'.

" -fprofile -exclude -files= regex "4 Item "-fprofile-exclude-files=regex" Instrument only functions from files where names do not match all the regular expressions (separated by a semi-colon). For example, -fprofile -exclude -files=/usr/* will prevent instrumentation of all files that are located in /usr/ folder.

" -fsanitize=address "4 Item "-fsanitize=address" Enable AddressSanitizer, a fast memory error detector. Memory access instructions are instrumented to detect out-of-bounds and use-after-free bugs. The option enables -fsanitize -address -use -after -scope . See < https://github.com/google/sanitizers/wiki/AddressSanitizer >for more details. The run-time behavior can be influenced using the ASAN_OPTIONS environment variable. When set to CW(C`help=1 (C' , the available options are shown at startup of the instrumented program. See < https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time -flags > for a list of supported options. The option cannot be combined with -fsanitize=thread .

" -fsanitize=kernel -address "4 Item "-fsanitize=kernel-address" Enable AddressSanitizer for Linux kernel. See < https://github.com/google/kasan/wiki >for more details.

" -fsanitize=pointer -compare "4 Item "-fsanitize=pointer-compare" Instrument comparison operation (<, <=, >, >=) with pointer operands. The option must be combined with either -fsanitize=kernel -address or -fsanitize=address The option cannot be combined with -fsanitize=thread . Note: By default the check is disabled at run time. To enable it, add CW(C`detect_invalid_pointer_pairs=2 (C' to the environment variable ASAN_OPTIONS .Using CW(C`detect_invalid_pointer_pairs=1 (C' detects invalid operation only when both pointers are non-null.

" -fsanitize=pointer -subtract "4 Item "-fsanitize=pointer-subtract" Instrument subtraction with pointer operands. The option must be combined with either -fsanitize=kernel -address or -fsanitize=address The option cannot be combined with -fsanitize=thread . Note: By default the check is disabled at run time. To enable it, add CW(C`detect_invalid_pointer_pairs=2 (C' to the environment variable ASAN_OPTIONS .Using CW(C`detect_invalid_pointer_pairs=1 (C' detects invalid operation only when both pointers are non-null.

" -fsanitize=thread "4 Item "-fsanitize=thread" Enable ThreadSanitizer, a fast data race detector. Memory access instructions are instrumented to detect data race bugs. See < https://github.com/google/sanitizers/wiki#threadsanitizer >for more details. The run-time behavior can be influenced using the TSAN_OPTIONS environment variable; see < https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags >for a list of supported options. The option cannot be combined with -fsanitize=address , -fsanitize=leak . Note that sanitized atomic builtins cannot throw exceptions when operating on invalid memory addresses with non-call exceptions ( -fnon -call -exceptions ).

" -fsanitize=leak "4 Item "-fsanitize=leak" Enable LeakSanitizer, a memory leak detector. This option only matters for linking of executables and the executable is linked against a library that overrides CW(C`malloc (C' and other allocator functions. See < https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer >for more details. The run-time behavior can be influenced using the LSAN_OPTIONS environment variable. The option cannot be combined with -fsanitize=thread .

" -fsanitize=undefined "4 Item "-fsanitize=undefined" Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. Various computations are instrumented to detect undefined behavior at runtime. Current suboptions are:

" -fsanitize=shift "4 Item "-fsanitize=shift" This option enables checking that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and (C+, as well as between ISOC90 and C99, etc. This option has two suboptions, -fsanitize=shift -base and -fsanitize=shift -exponent .

" -fsanitize=shift -exponent "4 Item "-fsanitize=shift-exponent" This option enables checking that the second argument of a shift operation is not negative and is smaller than the precision of the promoted first argument.

" -fsanitize=shift -base "4 Item "-fsanitize=shift-base" If the second argument of a shift operation is within range, check that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and (C+, as well as between ISOC90 and C99, etc.

" -fsanitize=integer -divide -by -zero "4 Item "-fsanitize=integer-divide-by-zero" Detect integer division by zero as well as CW(C`INT_MIN / -1 (C' division.

" -fsanitize=unreachable "4 Item "-fsanitize=unreachable" With this option, the compiler turns the CW(C`_ _builtin_unreachable (C' call into a diagnostics message call instead. When reaching the CW(C`_ _builtin_unreachable (C' call, the behavior is undefined.

" -fsanitize=vla -bound "4 Item "-fsanitize=vla-bound" This option instructs the compiler to check that the size of a variable length array is positive.

" -fsanitize=null "4 Item "-fsanitize=null" This option enables pointer checking. Particularly, the application built with this option turned on will issue an error message when it tries to dereference a NULLpointer, or if a reference (possibly an rvalue reference) is bound to a NULLpointer, or if a method is invoked on an object pointed by a NULLpointer.

" -fsanitize=return "4 Item "-fsanitize=return" This option enables return statement checking. Programs built with this option turned on will issue an error message when the end of a non-void function is reached without actually returning a value. This option works in (C+ only.

" -fsanitize=signed -integer -overflow "4 Item "-fsanitize=signed-integer-overflow" This option enables signed integer overflow checking. We check that the result of CW(C`+ (C' , CW(C`* (C' ,and both unary and binary CW(C` -(C' does not overflow in the signed arithmetics. Note, integer promotion rules must be taken into account. That is, the following is not an overflow: 2 signed char a = SCHAR_MAX; a++;

" -fsanitize=bounds "4 Item "-fsanitize=bounds" This option enables instrumentation of array bounds. Various out of bounds accesses are detected. Flexible array members, flexible array member-like arrays, and initializers of variables with static storage are not instrumented.

" -fsanitize=bounds -strict "4 Item "-fsanitize=bounds-strict" This option enables strict instrumentation of array bounds. Most out of bounds accesses are detected, including flexible array members and flexible array member-like arrays. Initializers of variables with static storage are not instrumented.

" -fsanitize=alignment "4 Item "-fsanitize=alignment" This option enables checking of alignment of pointers when they are dereferenced, or when a reference is bound to insufficiently aligned target, or when a method or constructor is invoked on insufficiently aligned object.

" -fsanitize=object -size "4 Item "-fsanitize=object-size" This option enables instrumentation of memory references using the CW(C`_ _builtin_object_size (C' function. Various out of bounds pointer accesses are detected.

" -fsanitize=float -divide -by -zero "4 Item "-fsanitize=float-divide-by-zero" Detect floating-point division by zero. Unlike other similar options, -fsanitize=float -divide -by -zero is not enabled by -fsanitize=undefined ,since floating-point division by zero can be a legitimate way of obtaining infinities and NaNs.

" -fsanitize=float -cast -overflow "4 Item "-fsanitize=float-cast-overflow" This option enables floating-point type to integer conversion checking. We check that the result of the conversion does not overflow. Unlike other similar options, -fsanitize=float -cast -overflow is not enabled by -fsanitize=undefined . This option does not work well with CW(C`FE_INVALID (C' exceptions enabled.

" -fsanitize=nonnull -attribute "4 Item "-fsanitize=nonnull-attribute" This option enables instrumentation of calls, checking whether null values are not passed to arguments marked as requiring a non-null value by the CW(C`nonnull (C' function attribute.

" -fsanitize=returns -nonnull -attribute "4 Item "-fsanitize=returns-nonnull-attribute" This option enables instrumentation of return statements in functions marked with CW(C`returns_nonnull (C' function attribute, to detect returning of null values from such functions.

" -fsanitize=bool "4 Item "-fsanitize=bool" This option enables instrumentation of loads from bool. If a value other than 0/1 is loaded, a run-time error is issued.

" -fsanitize=enum "4 Item "-fsanitize=enum" This option enables instrumentation of loads from an enum type. If a value outside the range of values for the enum type is loaded, a run-time error is issued.

" -fsanitize=vptr "4 Item "-fsanitize=vptr" This option enables instrumentation of (C+ member function calls, member accesses and some conversions between pointers to base and derived classes, to verify the referenced object has the correct dynamic type.

" -fsanitize=pointer -overflow "4 Item "-fsanitize=pointer-overflow" This option enables instrumentation of pointer arithmetics. If the pointer arithmetics overflows, a run-time error is issued.

" -fsanitize=builtin "4 Item "-fsanitize=builtin" This option enables instrumentation of arguments to selected builtin functions. If an invalid value is passed to such arguments, a run-time error is issued. E.g. passing 0 as the argument to CW(C`_ _builtin_ctz (C' or CW(C`_ _builtin_clz (C' invokes undefined behavior and is diagnosed by this option. While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined gives a diagnostic message. This currently works only for the C family of languages.

" -fno -sanitize=all "4 Item "-fno-sanitize=all" This option disables all previously enabled sanitizers. -fsanitize=all is not allowed, as some sanitizers cannot be used together.

" -fasan -shadow -offset= number "4 Item "-fasan-shadow-offset=number" This option forces GCCto use custom shadow offset in AddressSanitizer checks. It is useful for experimenting with different shadow memory layouts in Kernel AddressSanitizer.

" -fsanitize -sections= s1 , s2 ,... "4 Item "-fsanitize-sections=s1,s2,..." Sanitize global variables in selected user-defined sections. si may contain wildcards.

" -fsanitize -recover [ = opts ]"4 Item "-fsanitize-recover[=opts]" -fsanitize -recover= controls error recovery mode for sanitizers mentioned in comma-separated list of opts .Enabling this option for a sanitizer component causes it to attempt to continue running the program as if no error happened. This means multiple runtime errors can be reported in a single program run, and the exit code of the program may indicate success even when errors have been reported. The -fno -sanitize -recover= option can be used to alter this behavior: only the first detected error is reported and program then exits with a non-zero exit code. Currently this feature only works for -fsanitize=undefined (and its suboptions except for -fsanitize=unreachable and -fsanitize=return ), -fsanitize=float -cast -overflow , -fsanitize=float -divide -by -zero , -fsanitize=bounds -strict , -fsanitize=kernel -address and -fsanitize=address . For these sanitizers error recovery is turned on by default, except -fsanitize=address ,for which this feature is experimental. -fsanitize -recover=all and -fno -sanitize -recover=all is also accepted, the former enables recovery for all sanitizers that support it, the latter disables recovery for all sanitizers that support it. Even if a recovery mode is turned on the compiler side, it needs to be also enabled on the runtime library side, otherwise the failures are still fatal. The runtime library defaults to CW(C`halt_on_error=0 (C' for ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for AddressSanitizer is CW(C`halt_on_error=1 (C' .This can be overridden through setting the CW(C`halt_on_error (C' flag in the corresponding environment variable. Syntax without an explicit opts parameter is deprecated. It is equivalent to specifying an opts list of: 1 undefined,float -cast -overflow,float -divide -by -zero,bounds -strict

" -fsanitize -address -use -after -scope "4 Item "-fsanitize-address-use-after-scope" Enable sanitization of local variables to detect use-after-scope bugs. The option sets -fstack -reuse to none .

" -fsanitize -undefined -trap -on -error "4 Item "-fsanitize-undefined-trap-on-error" The -fsanitize -undefined -trap -on -error option instructs the compiler to report undefined behavior using CW(C`_ _builtin_trap (C' rather than a CW(C`libubsan (C' library routine. The advantage of this is that the CW(C`libubsan (C' library is not needed and is not linked in, so this is usable even in freestanding environments.

" -fsanitize -coverage=trace -pc "4 Item "-fsanitize-coverage=trace-pc" Enable coverage-guided fuzzing code instrumentation. Inserts a call to CW(C`_ _sanitizer_cov_trace_pc (C' into every basic block.

" -fsanitize -coverage=trace -cmp "4 Item "-fsanitize-coverage=trace-cmp" Enable dataflow guided fuzzing code instrumentation. Inserts a call to CW(C`_ _sanitizer_cov_trace_cmp1 (C' , CW(C`_ _sanitizer_cov_trace_cmp2 (C' , CW(C`_ _sanitizer_cov_trace_cmp4 (C' or CW(C`_ _sanitizer_cov_trace_cmp8 (C' for integral comparison with both operands variable or CW(C`_ _sanitizer_cov_trace_const_cmp1 (C' , CW(C`_ _sanitizer_cov_trace_const_cmp2 (C' , CW(C`_ _sanitizer_cov_trace_const_cmp4 (C' or CW(C`_ _sanitizer_cov_trace_const_cmp8 (C' for integral comparison with one operand constant, CW(C`_ _sanitizer_cov_trace_cmpf (C' or CW(C`_ _sanitizer_cov_trace_cmpd (C' for float or double comparisons and CW(C`_ _sanitizer_cov_trace_switch (C' for switch statements.

" -fcf -protection= [ full | branch | return | none ]"4 Item "-fcf-protection=[full|branch|return|none]" Enable code instrumentation of control-flow transfers to increase program security by checking that target addresses of control-flow transfer instructions (such as indirect function call, function return, indirect jump) are valid. This prevents diverting the flow of control to an unexpected target. This is intended to protect against such threats as Return-oriented Programming ( ROP),and similarly call/jmp -oriented programming ( COP/JOP). The value CW(C`branch (C' tells the compiler to implement checking of validity of control-flow transfer at the point of indirect branch instructions, i.e. call/jmp instructions. The value CW(C`return (C' implements checking of validity at the point of returning from a function. The value CW(C`full (C' is an alias for specifying both CW(C`branch (C' and CW(C`return (C' .The value CW(C`none (C' turns off instrumentation. The macro CW(C`_ _CET_ _ (C' is defined when -fcf -protection is used. The first bit of CW(C`_ _CET_ _ (C' is set to 1 for the value CW(C`branch (C' and the second bit of CW(C`_ _CET_ _ (C' is set to 1 for the CW(C`return (C' . You can also use the CW(C`nocf_check (C' attribute to identify which functions and calls should be skipped from instrumentation. Currently the x86 GNU/Linux target provides an implementation based on Intel Control-flow Enforcement Technology ( CET).

" -fstack -protector "4 Item "-fstack-protector" Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call CW(C`alloca (C' ,and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits.

" -fstack -protector -all "4 Item "-fstack-protector-all" Like -fstack -protector except that all functions are protected.

" -fstack -protector -strong "4 Item "-fstack-protector-strong" Like -fstack -protector but includes additional functions to be protected ---those that have local array definitions, or have references to local frame addresses.

" -fstack -protector -explicit "4 Item "-fstack-protector-explicit" Like -fstack -protector but only protects those functions which have the CW(C`stack_protect (C' attribute.

" -fstack -check "4 Item "-fstack-check" Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but you only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. Note that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see the stack being extended. You can additionally specify a string parameter: no means no checking, generic means force the use of old-style checking, specific means use the best checking method and is equivalent to bare -fstack -check . Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks:

"1." 4 Item "1." Modified allocation strategy for large objects: they are always allocated dynamically if their size exceeds a fixed threshold. Note this may change the semantics of some code.

"2." 4 Item "2." Fixed limit on the size of the static frame of functions: when it is topped by a particular function, stack checking is not reliable and a warning is issued by the compiler.

"3." 4 Item "3." Inefficiency: because of both the modified allocation strategy and the generic implementation, code performance is hampered. Note that old-style stack checking is also the fallback method for specific if no target support has been added in the compiler. -fstack -check= is designed for Ada's needs to detect infinite recursion and stack overflows. specific is an excellent choice when compiling Ada code. It is not generally sufficient to protect against stack-clash attacks. To protect against those you want -fstack -clash -protection .

" -fstack -clash -protection "4 Item "-fstack-clash-protection" Generate code to prevent stack clash style attacks. When this option is enabled, the compiler will only allocate one page of stack space at a time and each page is accessed immediately after allocation. Thus, it prevents allocations from jumping over any stack guard page provided by the operating system. Most targets do not fully support stack clash protection. However, on those targets -fstack -clash -protection will protect dynamic stack allocations. -fstack -clash -protection may also provide limited protection for static stack allocations if the target supports -fstack -check=specific .

" -fstack -limit -register= reg "4 Item "-fstack-limit-register=reg" 0

" -fstack -limit -symbol= sym "4 Item "-fstack-limit-symbol=sym"

" -fno -stack -limit "4 Item "-fno-stack-limit" Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If a larger stack is required, a signal is raised at run time. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the flags -fstack -limit -symbol=_ _stack_limit and -Wl, --defsym,_ _stack_limit=0x7ffe0000 to enforce a stack limit of 128KB. Note that this may only work with the GNUlinker. You can locally override stack limit checking by using the CW(C`no_stack_limit (C' function attribute.

" -fsplit -stack "4 Item "-fsplit-stack" Generate code to automatically split the stack before it overflows. The resulting program has a discontiguous stack which can only overflow if the program is unable to allocate any more memory. This is most useful when running threaded programs, as it is no longer necessary to calculate a good stack size to use for each thread. This is currently only implemented for the x86 targets running GNU/Linux. When code compiled with -fsplit -stack calls code compiled without -fsplit -stack ,there may not be much stack space available for the latter code to run. If compiling all code, including library code, with -fsplit -stack is not an option, then the linker can fix up these calls so that the code compiled without -fsplit -stack always has a large stack. Support for this is implemented in the gold linker in GNUbinutils release 2.21 and later.

" -fvtable -verify= [ std | preinit | none ]"4 Item "-fvtable-verify=[std|preinit|none]" This option is only available when compiling (C+ code. It turns on (or off, if using -fvtable -verify=none )the security feature that verifies at run time, for every virtual call, that the vtable pointer through which the call is made is valid for the type of the object, and has not been corrupted or overwritten. If an invalid vtable pointer is detected at run time, an error is reported and execution of the program is immediately halted. This option causes run-time data structures to be built at program startup, which are used for verifying the vtable pointers. The options std and preinit control the timing of when these data structures are built. In both cases the data structures are built before execution reaches CW(C`main (C' .Using -fvtable -verify=std causes the data structures to be built after shared libraries have been loaded and initialized. -fvtable -verify=preinit causes them to be built before shared libraries have been loaded and initialized. If this option appears multiple times in the command line with different values specified, none takes highest priority over both std and preinit ; preinit takes priority over std .

" -fvtv -debug "4 Item "-fvtv-debug" When used in conjunction with -fvtable -verify=std or -fvtable -verify=preinit ,causes debug versions of the runtime functions for the vtable verification feature to be called. This flag also causes the compiler to log information about which vtable pointers it finds for each class. This information is written to a file named vtv_set_ptr_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise. Note: This feature appends data to the log file. If you want a fresh log file, be sure to delete any existing one.

" -fvtv -counts "4 Item "-fvtv-counts" This is a debugging flag. When used in conjunction with -fvtable -verify=std or -fvtable -verify=preinit ,this causes the compiler to keep track of the total number of virtual calls it encounters and the number of verifications it inserts. It also counts the number of calls to certain run-time library functions that it inserts and logs this information for each compilation unit. The compiler writes this information to a file named vtv_count_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise. It also counts the size of the vtable pointer sets for each class, and writes this information to vtv_class_set_sizes.log in the same directory. Note: This feature appends data to the log files. To get fresh log files, be sure to delete any existing ones.

" -finstrument -functions "4 Item "-finstrument-functions" Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions are called with the address of the current function and its call site. (On some platforms, CW(C`_ _builtin_return_address (C' does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.) 4 void _ _cyg_profile_func_enter (void *this_fn, void *call_site); void _ _cyg_profile_func_exit (void *this_fn, void *call_site); The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. This instrumentation is also done for functions expanded inline in other functions. The profiling calls indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use CW(C`extern inline (C' in your C code, an addressable version of such functions must be provided. (This is normally the case anyway, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.) A function may be given the attribute CW(C`no_instrument_function (C' ,in which case this instrumentation is not done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory).

" -finstrument -functions -exclude -file -list= file , file ,... "4 Item "-finstrument-functions-exclude-file-list=file,file,..." Set the list of functions that are excluded from instrumentation (see the description of -finstrument -functions ).If the file that contains a function definition matches with one of file ,then that function is not instrumented. The match is done on substrings: if the file parameter is a substring of the file name, it is considered to be a match. For example: 1 -finstrument -functions -exclude -file -list=/bits/stl,include/sys excludes any inline function defined in files whose pathnames contain /bits/stl or include/sys . If, for some reason, you want to include letter , in one of sym ,write , .For example, -finstrument -functions -exclude -file -list=',,tmp' (note the single quote surrounding the option).

" -finstrument -functions -exclude -function -list= sym , sym ,... "4 Item "-finstrument-functions-exclude-function-list=sym,sym,..." This is similar to -finstrument -functions -exclude -file -list , but this option sets the list of function names to be excluded from instrumentation. The function name to be matched is its user-visible name, such as CW(C`vector<int> blah(const vector<int> &) (C' ,not the internal mangled name (e.g., CW(C`_Z4blahRSt6vectorIiSaIiEE (C' ).The match is done on substrings: if the sym parameter is a substring of the function name, it is considered to be a match. For C99 and (C+ extended identifiers, the function name must be given in UTF-8, not using universal character names.

" -fpatchable -function -entry= N [, M ] "4 Item "-fpatchable-function-entry=N[,M]" Generate N NOPs right at the beginning of each function, with the function entry point before the M thNOP. If M is omitted, it defaults to CW0 so the function entry points to the address just at the first NOP. The NOPinstructions reserve extra space which can be used to patch in any desired instrumentation at run time, provided that the code segment is writable. The amount of space is controllable indirectly via the number of NOPs; the NOPinstruction used corresponds to the instruction emitted by the internal GCCback-end interface CW(C`gen_nop (C' .This behavior is target-specific and may also depend on the architecture variant and/or other compilation options. For run-time identification, the starting addresses of these areas, which correspond to their respective function entries minus M , are additionally collected in the CW(C`_ _patchable_function_entries (C' section of the resulting binary. Note that the value of CW(C`_ _attribute_ _ ((patchable_function_entry (N,M))) (C' takes precedence over command-line option -fpatchable -function -entry=N,M .This can be used to increase the area size or to remove it completely on a single function. If CW(C`N=0 (C' ,no pad location is recorded. The NOPinstructions are inserted at ---and maybe before, depending on M ---the function entry address, even before the prologue.

Options Controlling the Preprocessor

Subsection "Options Controlling the Preprocessor" These options control the C preprocessor, which is run on each C source file before actual compilation.

If you use the -E option, nothing is done except preprocessing. Some of these options make sense only together with -E because they cause the preprocessor output to be unsuitable for actual compilation.

In addition to the options listed here, there are a number of options to control search paths for include files documented in DirectoryOptions . Options to control preprocessor diagnostics are listed in WarningOptions .

" -D name "4 Item "-D name" Predefine name as a macro, with definition CW1 .

" -D name = definition "4 Item "-D name=definition" The contents of definition are tokenized and processed as if they appeared during translation phase three in a #define directive. In particular, the definition is truncated by embedded newline characters. If you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax. If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you should quote the option. With sh and csh , -D' name ( args... )= definition ' works. -D and -U options are processed in the order they are given on the command line. All -imacros file and -include file options are processed after all -D and -U options.

" -U name "4 Item "-U name" Cancel any previous definition of name ,either built in or provided with a -D option.

" -include file "4 Item "-include file" Process file as if CW(C`#include "file" (C' appeared as the first line of the primary source file. However, the first directory searched for file is the preprocessor's working directory insteadof the directory containing the main source file. If not found there, it is searched for in the remainder of the CW(C`#include "..." (C' search chain as normal. If multiple -include options are given, the files are included in the order they appear on the command line.

" -imacros file "4 Item "-imacros file" Exactly like -include ,except that any output produced by scanning file is thrown away. Macros it defines remain defined. This allows you to acquire all the macros from a header without also processing its declarations. All files specified by -imacros are processed before all files specified by -include .

" -undef "4 Item "-undef" Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined.

" -pthread "4 Item "-pthread" Define additional macros required for using the POSIXthreads library. You should use this option consistently for both compilation and linking. This option is supported on GNU/Linux targets, most other Unix derivatives, and also on x86 Cygwin and MinGW targets.

" -M "4 Item "-M" Instead of outputting the result of preprocessing, output a rule suitable for make describing the dependencies of the main source file. The preprocessor outputs one make rule containing the object file name for that source file, a colon, and the names of all the included files, including those coming from -include or -imacros command-line options. Unless specified explicitly (with -MT or -MQ ),the object file name consists of the name of the source file with any suffix replaced with object file suffix and with any leading directory parts removed. If there are many included files then the rule is split into several lines using \ -newline. The rule has no commands. This option does not suppress the preprocessor's debug output, such as -dM .To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with -MF ,or use an environment variable like DEPENDENCIES_OUTPUT .Debug output is still sent to the regular output stream as normal. Passing -M to the driver implies -E ,and suppresses warnings with an implicit -w .

" -MM "4 Item "-MM" Like -M but do not mention header files that are found in system header directories, nor header files that are included, directly or indirectly, from such a header. This implies that the choice of angle brackets or double quotes in an #include directive does not in itself determine whether that header appears in -MM dependency output.

" -MF file "4 Item "-MF file" When used with -M or -MM ,specifies a file to write the dependencies to. If no -MF switch is given the preprocessor sends the rules to the same place it would send preprocessed output. When used with the driver options -MD or -MMD , -MF overrides the default dependency output file. If file is - ,then the dependencies are written to stdout .

" -MG "4 Item "-MG" In conjunction with an option such as -M requesting dependency generation, -MG assumes missing header files are generated files and adds them to the dependency list without raising an error. The dependency filename is taken directly from the CW(C`#include (C' directive without prepending any path. -MG also suppresses preprocessed output, as a missing header file renders this useless. This feature is used in automatic updating of makefiles.

" -MP "4 Item "-MP" This option instructs CPPto add a phony target for each dependency other than the main file, causing each to depend on nothing. These dummy rules work around errors make gives if you remove header files without updating the Makefile to match. This is typical output: 1 test.o: test.c test.h test.h:

" -MT target "4 Item "-MT target" Change the target of the rule emitted by dependency generation. By default CPPtakes the name of the main input file, deletes any directory components and any file suffix such as .c ,and appends the platform's usual object suffix. The result is the target. An -MT option sets the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to -MT ,or use multiple -MT options. For example, -MT '$(objpfx)foo.o' might give 1 $(objpfx)foo.o: foo.c

" -MQ target "4 Item "-MQ target" Same as -MT ,but it quotes any characters which are special to Make. -MQ '$(objpfx)foo.o' gives 1 $$(objpfx)foo.o: foo.c The default target is automatically quoted, as if it were given with -MQ .

" -MD "4 Item "-MD" -MD is equivalent to -M -MF file ,except that -E is not implied. The driver determines file based on whether an -o option is given. If it is, the driver uses its argument but with a suffix of .d ,otherwise it takes the name of the input file, removes any directory components and suffix, and applies a .d suffix. If -MD is used in conjunction with -E ,any -o switch is understood to specify the dependency output file, but if used without -E ,each -o is understood to specify a target object file. Since -E is not implied, -MD can be used to generate a dependency output file as a side effect of the compilation process.

" -MMD "4 Item "-MMD" Like -MD except mention only user header files, not system header files.

" -fpreprocessed "4 Item "-fpreprocessed" Indicate to the preprocessor that the input file has already been preprocessed. This suppresses things like macro expansion, trigraph conversion, escaped newline splicing, and processing of most directives. The preprocessor still recognizes and removes comments, so that you can pass a file preprocessed with -C to the compiler without problems. In this mode the integrated preprocessor is little more than a tokenizer for the front ends. -fpreprocessed is implicit if the input file has one of the extensions .i , .ii or .mi .These are the extensions that GCCuses for preprocessed files created by -save -temps .

" -fdirectives -only "4 Item "-fdirectives-only" When preprocessing, handle directives, but do not expand macros. The option's behavior depends on the -E and -fpreprocessed options. With -E ,preprocessing is limited to the handling of directives such as CW(C`#define (C' , CW(C`#ifdef (C' ,and CW(C`#error (C' .Other preprocessor operations, such as macro expansion and trigraph conversion are not performed. In addition, the -dD option is implicitly enabled. With -fpreprocessed ,predefinition of command line and most builtin macros is disabled. Macros such as CW(C`_ _LINE_ _ (C' ,which are contextually dependent, are handled normally. This enables compilation of files previously preprocessed with CW(C` -E -fdirectives -only (C' . With both -E and -fpreprocessed ,the rules for -fpreprocessed take precedence. This enables full preprocessing of files previously preprocessed with CW(C` -E -fdirectives -only (C' .

" -fdollars -in -identifiers "4 Item "-fdollars-in-identifiers" Accept $ in identifiers.

" -fextended -identifiers "4 Item "-fextended-identifiers" Accept universal character names in identifiers. This option is enabled by default for C99 (and later C standard versions) and (C+.

" -fno -canonical -system -headers "4 Item "-fno-canonical-system-headers" When preprocessing, do not shorten system header paths with canonicalization.

" -ftabstop= width "4 Item "-ftabstop=width" Set the distance between tab stops. This helps the preprocessor report correct column numbers in warnings or errors, even if tabs appear on the line. If the value is less than 1 or greater than 100, the option is ignored. The default is 8.

" -ftrack -macro -expansion [ = level ]"4 Item "-ftrack-macro-expansion[=level]" Track locations of tokens across macro expansions. This allows the compiler to emit diagnostic about the current macro expansion stack when a compilation error occurs in a macro expansion. Using this option makes the preprocessor and the compiler consume more memory. The level parameter can be used to choose the level of precision of token location tracking thus decreasing the memory consumption if necessary. Value 0 of level de-activates this option. Value 1 tracks tokens locations in a degraded mode for the sake of minimal memory overhead. In this mode all tokens resulting from the expansion of an argument of a function-like macro have the same location. Value 2 tracks tokens locations completely. This value is the most memory hungry. When this option is given no argument, the default parameter value is 2 . Note that CW(C` -ftrack -macro -expansion=2 (C' is activated by default.

" -fmacro -prefix -map= old = new "4 Item "-fmacro-prefix-map=old=new" When preprocessing files residing in directory old , expand the CW(C`_ _FILE_ _ (C' and CW(C`_ _BASE_FILE_ _ (C' macros as if the files resided in directory new instead. This can be used to change an absolute path to a relative path by using . for new which can result in more reproducible builds that are location independent. This option also affects CW(C`_ _builtin_FILE() (C' during compilation. See also -ffile -prefix -map .

" -fexec -charset= charset "4 Item "-fexec-charset=charset" Set the execution character set, used for string and character constants. The default is UTF-8. charset can be any encoding supported by the system's CW(C`iconv (C' library routine.

" -fwide -exec -charset= charset "4 Item "-fwide-exec-charset=charset" Set the wide execution character set, used for wide string and character constants. The default is UTF-32 or UTF-16, whichever corresponds to the width of CW(C`wchar_t (C' .As with -fexec -charset , charset can be any encoding supported by the system's CW(C`iconv (C' library routine; however, you will have problems with encodings that do not fit exactly in CW(C`wchar_t (C' .

" -finput -charset= charset "4 Item "-finput-charset=charset" Set the input character set, used for translation from the character set of the input file to the source character set used by GCC.If the locale does not specify, or GCCcannot get this information from the locale, the default is UTF-8. This can be overridden by either the locale or this command-line option. Currently the command-line option takes precedence if there's a conflict. charset can be any encoding supported by the system's CW(C`iconv (C' library routine.

" -fpch -deps "4 Item "-fpch-deps" When using precompiled headers, this flag causes the dependency-output flags to also list the files from the precompiled header's dependencies. If not specified, only the precompiled header are listed and not the files that were used to create it, because those files are not consulted when a precompiled header is used.

" -fpch -preprocess "4 Item "-fpch-preprocess" This option allows use of a precompiled header together with -E .It inserts a special CW(C`#pragma (C' , CW(C`#pragma GCC pch_preprocess " CIfilename CW"(C' in the output to mark the place where the precompiled header was found, and its filename . When -fpreprocessed is in use, GCCrecognizes this CW(C`#pragma (C' and loads the PCH. This option is off by default, because the resulting preprocessed output is only really suitable as input to GCC.It is switched on by -save -temps . You should not write this CW(C`#pragma (C' in your own code, but it is safe to edit the filename if the PCHfile is available in a different location. The filename may be absolute or it may be relative to GCC's current directory.

" -fworking -directory "4 Item "-fworking-directory" Enable generation of linemarkers in the preprocessor output that let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the preprocessor emits, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. GCCuses this directory, when it's present in the preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, but this can be inhibited with the negated form -fno -working -directory .If the -P flag is present in the command line, this option has no effect, since no CW(C`#line (C' directives are emitted whatsoever.

" -A predicate = answer "4 Item "-A predicate=answer" Make an assertion with the predicate predicate and answer answer .This form is preferred to the older form -A predicate ( answer ) ,which is still supported, because it does not use shell special characters.

" -A - predicate = answer "4 Item "-A -predicate=answer" Cancel an assertion with the predicate predicate and answer answer .

" -C "4 Item "-C" Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive. You should be prepared for side effects when using -C ;it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a # .

" -CC "4 Item "-CC" Do not discard comments, including during macro expansion. This is like -C ,except that comments contained within macros are also passed through to the output file where the macro is expanded. In addition to the side effects of the -C option, the -CC option causes all (C+ -style comments inside a macro to be converted to C -style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line. The -CC option is generally used to support lint comments.

" -P "4 Item "-P" Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers.

" -traditional "4 Item "-traditional" 0

" -traditional -cpp "4 Item "-traditional-cpp" Try to imitate the behavior of pre-standard C preprocessors, as opposed to ISOC preprocessors. See the GNUCPP manual for details. Note that GCCdoes not otherwise attempt to emulate a pre-standard C compiler, and these options are only supported with the -E switch, or when invoking CPPexplicitly.

" -trigraphs "4 Item "-trigraphs" Support ISOC trigraphs. These are three-character sequences, all starting with ?? ,that are defined by ISOC to stand for single characters. For example, ??/ stands for \ ,so '??/n' is a character constant for a newline. The nine trigraphs and their replacements are 2 Trigraph: ??( ??) ??< ??> ??= ??/ ?? (Aq ??! ?? - Replacement: [ ] { } # \ ^ | ~ By default, GCCignores trigraphs, but in standard-conforming modes it converts them. See the -std and -ansi options.

" -remap "4 Item "-remap" Enable special code to work around file systems which only permit very short file names, such as MS-DOS.

" -H "4 Item "-H" Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the #include stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a valid one with ...! .

" -d letters "4 Item "-dletters" Says to make debugging dumps during compilation as specified by letters .The flags documented here are those relevant to the preprocessor. Other letters are interpreted by the compiler proper, or reserved for future versions of GCC,and so are silently ignored. If you specify letters whose behavior conflicts, the result is undefined.

" -dM "4 Item "-dM" Instead of the normal output, generate a list of #define directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file foo.h ,the command 1 touch foo.h; cpp -dM foo.h shows all the predefined macros. If you use -dM without the -E option, -dM is interpreted as a synonym for -fdump -rtl -mach .

" -dD "4 Item "-dD" Like -dM except in two respects: it does not include the predefined macros, and it outputs both the #define directives and the result of preprocessing. Both kinds of output go to the standard output file.

" -dN "4 Item "-dN" Like -dD ,but emit only the macro names, not their expansions.

" -dI "4 Item "-dI" Output #include directives in addition to the result of preprocessing.

" -dU "4 Item "-dU" Like -dD except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output is delayed until the use or test of the macro; and #undef directives are also output for macros tested but undefined at the time.

" -fdebug -cpp "4 Item "-fdebug-cpp" This option is only useful for debugging GCC.When used from CPPor with -E ,it dumps debugging information about location maps. Every token in the output is preceded by the dump of the map its location belongs to. When used from GCCwithout -E ,this option has no effect.

" -Wp, option "4 Item "-Wp,option" You can use -Wp, option to bypass the compiler driver and pass option directly through to the preprocessor. If option contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and -Wp forcibly bypasses this phase. The preprocessor's direct interface is undocumented and subject to change, so whenever possible you should avoid using -Wp and let the driver handle the options instead.

" -Xpreprocessor option "4 Item "-Xpreprocessor option" Pass option as an option to the preprocessor. You can use this to supply system-specific preprocessor options that GCCdoes not recognize. If you want to pass an option that takes an argument, you must use -Xpreprocessor twice, once for the option and once for the argument.

" -no -integrated -cpp "4 Item "-no-integrated-cpp" Perform preprocessing as a separate pass before compilation. By default, GCCperforms preprocessing as an integrated part of input tokenization and parsing. If this option is provided, the appropriate language front end ( cc1 , cc1plus ,or cc1obj for C, (C+, and Objective-C, respectively) is instead invoked twice, once for preprocessing only and once for actual compilation of the preprocessed input. This option may be useful in conjunction with the -B or -wrapper options to specify an alternate preprocessor or perform additional processing of the program source between normal preprocessing and compilation.

Passing Options to the Assembler

Subsection "Passing Options to the Assembler" You can pass options to the assembler.

" -Wa, option "4 Item "-Wa,option" Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas.

" -Xassembler option "4 Item "-Xassembler option" Pass option as an option to the assembler. You can use this to supply system-specific assembler options that GCCdoes not recognize. If you want to pass an option that takes an argument, you must use -Xassembler twice, once for the option and once for the argument.

Options for Linking

Subsection "Options for Linking" These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step.

" object-file-name "4 Item "object-file-name" A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker.

" -c "4 Item "-c" 0

" -S "4 Item "-S"

" -E "4 Item "-E" If any of these options is used, then the linker is not run, and object file names should not be used as arguments.

" -flinker -output= type "4 Item "-flinker-output=type" This option controls the code generation of the link time optimizer. By default the linker output is determined by the linker plugin automatically. For debugging the compiler and in the case of incremental linking to non-lto object file is desired, it may be useful to control the type manually. If type is exec the code generation is configured to produce static binary. In this case -fpic and -fpie are both disabled. If type is dyn the code generation is configured to produce shared library. In this case -fpic or -fPIC is preserved, but not enabled automatically. This makes it possible to build shared libraries without position independent code on architectures this is possible, i.e. on x86. If type is pie the code generation is configured to produce -fpie executable. This result in similar optimizations as exec except that -fpie is not disabled if specified at compilation time. If type is rel the compiler assumes that incremental linking is done. The sections containing intermediate code for link-time optimization are merged, pre-optimized, and output to the resulting object file. In addition, if -ffat -lto -objects is specified the binary code is produced for future non-lto linking. The object file produced by incremental linking will be smaller than a static library produced from the same object files. At link-time the result of incremental linking will also load faster to compiler than a static library assuming that majority of objects in the library are used. Finally nolto-rel configure compiler to for incremental linking where code generation is forced, final binary is produced and the intermediate code for later link-time optimization is stripped. When multiple object files are linked together the resulting code will be optimized better than with link time optimizations disabled (for example, the cross-module inlining will happen), most of benefits of whole program optimizations are however lost. During the incremental link (by -r )the linker plugin will default to rel .With current interfaces to GNUBinutils it is however not possible to link incrementally LTOobjects and non-LTO objects into a single mixed object file. In the case any of object files in incremental link cannot be used for link-time optimization the linker plugin will output warning and use nolto-rel .To maintain the whole program optimization it is recommended to link such objects into static library instead. Alternatively it is possible to use H.J. Lu's binutils with support for mixed objects.

" -fuse -ld=bfd "4 Item "-fuse-ld=bfd" Use the bfd linker instead of the default linker.

" -fuse -ld=gold "4 Item "-fuse-ld=gold" Use the gold linker instead of the default linker.

" -fuse -ld=lld "4 Item "-fuse-ld=lld" Use the LLVM lld linker instead of the default linker.

" -l library "4 Item "-llibrary" 0

" -l library "4 Item "-l library" Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIXcompliance and is not recommended.) The -l option is passed directly to the linker by GCC.Refer to your linker documentation for exact details. The general description below applies to the GNUlinker. The linker searches a standard list of directories for the library. The directories searched include several standard system directories plus any that you specify with -L . Static libraries are archives of object files, and have file names like lib library .a .Some targets also support shared libraries, which typically have names like lib library .so . If both static and shared libraries are found, the linker gives preference to linking with the shared library unless the -static option is used. It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o-lz bar.o searches library z after file foo.o but before bar.o .If bar.o refers to functions in z ,those functions may not be loaded.

" -lobjc "4 Item "-lobjc" You need this special case of the -l option in order to link an Objective-C or Objective -(C+ program.

" -nostartfiles "4 Item "-nostartfiles" Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib , -nolibc ,or -nodefaultlibs is used.

" -nodefaultlibs "4 Item "-nodefaultlibs" Do not use the standard system libraries when linking. Only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static -libgcc or -shared -libgcc ,are ignored. The standard startup files are used normally, unless -nostartfiles is used. The compiler may generate calls to CW(C`memcmp (C' , CW(C`memset (C' , CW(C`memcpy (C' and CW(C`memmove (C' . These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified.

" -nolibc "4 Item "-nolibc" Do not use the C library or system libraries tightly coupled with it when linking. Still link with the startup files, libgcc or toolchain provided language support libraries such as libgnat , libgfortran or libstdc++ unless options preventing their inclusion are used as well. This typically removes -lc from the link command line, as well as system libraries that normally go with it and become meaningless when absence of a C library is assumed, for example -lpthread or -lm in some configurations. This is intended for bare-board targets when there is indeed no C library available.

" -nostdlib "4 Item "-nostdlib" Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static -libgcc or -shared -libgcc ,are ignored. The compiler may generate calls to CW(C`memcmp (C' , CW(C`memset (C' , CW(C`memcpy (C' and CW(C`memmove (C' . These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a ,a library of internal subroutines which GCCuses to overcome shortcomings of particular machines, or special needs for some languages. In most cases, you need libgcc.a even when you want to avoid other standard libraries. In other words, when you specify -nostdlib or -nodefaultlibs you should usually specify -lgcc as well. This ensures that you have no unresolved references to internal GCC library subroutines. (An example of such an internal subroutine is CW(C`_ _main (C' ,used to ensure (C+ constructors are called.)

" -e entry "4 Item "-e entry" 0

" --entry= entry "4 Item "--entry=entry" Specify that the program entry point is entry .The argument is interpreted by the linker; the GNUlinker accepts either a symbol name or an address.

" -pie "4 Item "-pie" Produce a dynamically linked position independent executable on targets that support it. For predictable results, you must also specify the same set of options used for compilation ( -fpie , -fPIE , or model suboptions) when you specify this linker option.

" -no -pie "4 Item "-no-pie" Don't produce a dynamically linked position independent executable.

" -static -pie "4 Item "-static-pie" Produce a static position independent executable on targets that support it. A static position independent executable is similar to a static executable, but can be loaded at any address without a dynamic linker. For predictable results, you must also specify the same set of options used for compilation ( -fpie , -fPIE ,or model suboptions) when you specify this linker option.

" -pthread "4 Item "-pthread" Link with the POSIXthreads library. This option is supported on GNU/Linux targets, most other Unix derivatives, and also on x86 Cygwin and MinGW targets. On some targets this option also sets flags for the preprocessor, so it should be used consistently for both compilation and linking.

" -r "4 Item "-r" Produce a relocatable object as output. This is also known as partial linking.

" -rdynamic "4 Item "-rdynamic" Pass the flag -export -dynamic to the ELFlinker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for some uses of CW(C`dlopen (C' or to allow obtaining backtraces from within a program.

" -s "4 Item "-s" Remove all symbol table and relocation information from the executable.

" -static "4 Item "-static" On systems that support dynamic linking, this overrides -pie and prevents linking with the shared libraries. On other systems, this option has no effect.

" -shared "4 Item "-shared" Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options used for compilation ( -fpic , -fPIC ,or model suboptions) when you specify this linker option.[1]

" -shared -libgcc "4 Item "-shared-libgcc" 0

" -static -libgcc "4 Item "-static-libgcc" On systems that provide libgcc as a shared library, these options force the use of either the shared or static version, respectively. If no shared version of libgcc was built when the compiler was configured, these options have no effect. There are several situations in which an application should use the shared libgcc instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared libgcc . Therefore, the G++ driver automatically adds -shared -libgcc whenever you build a shared library or a main executable, because (C+ programs typically use exceptions, so this is the right thing to do. If, instead, you use the GCCdriver to create shared libraries, you may find that they are not always linked with the shared libgcc . If GCCfinds, at its configuration time, that you have a non-GNU linker or a GNUlinker that does not support option --eh -frame -hdr , it links the shared version of libgcc into shared libraries by default. Otherwise, it takes advantage of the linker and optimizes away the linking with the shared version of libgcc ,linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time. However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ driver, or using the option -shared -libgcc ,such that it is linked with the shared libgcc .

" -static -libasan "4 Item "-static-libasan" When the -fsanitize=address option is used to link a program, the GCCdriver automatically links against libasan .If libasan is available as a shared library, and the -static option is not used, then this links against the shared version of libasan .The -static -libasan option directs the GCC driver to link libasan statically, without necessarily linking other libraries statically.

" -static -libtsan "4 Item "-static-libtsan" When the -fsanitize=thread option is used to link a program, the GCCdriver automatically links against libtsan .If libtsan is available as a shared library, and the -static option is not used, then this links against the shared version of libtsan .The -static -libtsan option directs the GCC driver to link libtsan statically, without necessarily linking other libraries statically.

" -static -liblsan "4 Item "-static-liblsan" When the -fsanitize=leak option is used to link a program, the GCCdriver automatically links against liblsan .If liblsan is available as a shared library, and the -static option is not used, then this links against the shared version of liblsan .The -static -liblsan option directs the GCC driver to link liblsan statically, without necessarily linking other libraries statically.

" -static -libubsan "4 Item "-static-libubsan" When the -fsanitize=undefined option is used to link a program, the GCCdriver automatically links against libubsan .If libubsan is available as a shared library, and the -static option is not used, then this links against the shared version of libubsan .The -static -libubsan option directs the GCC driver to link libubsan statically, without necessarily linking other libraries statically.

" -static -libstdc++ "4 Item "-static-libstdc++" When the g++ program is used to link a (C+ program, it normally automatically links against libstdc++ .If libstdc++ is available as a shared library, and the -static option is not used, then this links against the shared version of libstdc++ .That is normally fine. However, it is sometimes useful to freeze the version of libstdc++ used by the program without going all the way to a fully static link. The -static -libstdc++ option directs the g++ driver to link libstdc++ statically, without necessarily linking other libraries statically.

" -symbolic "4 Item "-symbolic" Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option -Xlinker -z -Xlinker defs ).Only a few systems support this option.

" -T script "4 Item "-T script" Use script as the linker script. This option is supported by most systems using the GNUlinker. On some targets, such as bare-board targets without an operating system, the -T option may be required when linking to avoid references to undefined symbols.

" -Xlinker option "4 Item "-Xlinker option" Pass option as an option to the linker. You can use this to supply system-specific linker options that GCCdoes not recognize. If you want to pass an option that takes a separate argument, you must use -Xlinker twice, once for the option and once for the argument. For example, to pass -assert definitions ,you must write -Xlinker -assert -Xlinker definitions .It does not work to write -Xlinker (L" -assert definitions (R" ,because this passes the entire string as a single argument, which is not what the linker expects. When using the GNUlinker, it is usually more convenient to pass arguments to linker options using the option = value syntax than as separate arguments. For example, you can specify -Xlinker -Map=output.map rather than -Xlinker -Map -Xlinker output.map .Other linkers may not support this syntax for command-line options.

" -Wl, option "4 Item "-Wl,option" Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas. You can use this syntax to pass an argument to the option. For example, -Wl, -Map,output.map passes -Map output.map to the linker. When using the GNUlinker, you can also get the same effect with -Wl, -Map=output.map .

" -u symbol "4 Item "-u symbol" Pretend the symbol symbol is undefined, to force linking of library modules to define it. You can use -u multiple times with different symbols to force loading of additional library modules.

" -z keyword "4 Item "-z keyword" -z is passed directly on to the linker along with the keyword keyword .See the section in the documentation of your linker for permitted values and their meanings.

Options for Directory Search

Subsection "Options for Directory Search" These options specify directories to search for header files, for libraries and for parts of the compiler:

" -I dir "4 Item "-I dir" 0

" -iquote dir "4 Item "-iquote dir"

" -isystem dir "4 Item "-isystem dir"

" -idirafter dir "4 Item "-idirafter dir" Add the directory dir to the list of directories to be searched for header files during preprocessing. If dir begins with = or CW$SYSROOT ,then the = or CW$SYSROOT is replaced by the sysroot prefix; see --sysroot and -isysroot . Directories specified with -iquote apply only to the quote form of the directive, CW(C`#include " CIfile CW"(C' . Directories specified with -I , -isystem , or -idirafter apply to lookup for both the CW(C`#include " CIfile CW"(C' and CW(C`#include < CIfile CW>(C' directives. You can specify any number or combination of these options on the command line to search for header files in several directories. The lookup order is as follows:

"1." 4 Item "1." For the quote form of the include directive, the directory of the current file is searched first.

"2." 4 Item "2." For the quote form of the include directive, the directories specified by -iquote options are searched in left-to-right order, as they appear on the command line.

"3." 4 Item "3." Directories specified with -I options are scanned in left-to-right order.

"4." 4 Item "4." Directories specified with -isystem options are scanned in left-to-right order.

"5." 4 Item "5." Standard system directories are scanned.

"6." 4 Item "6." Directories specified with -idirafter options are scanned in left-to-right order. You can use -I to override a system header file, substituting your own version, since these directories are searched before the standard system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files; use -isystem for that. The -isystem and -idirafter options also mark the directory as a system directory, so that it gets the same special treatment that is applied to the standard system directories. If a standard system include directory, or a directory specified with -isystem ,is also specified with -I ,the -I option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain. This is to ensure that GCC'sprocedure to fix buggy system headers and the ordering for the CW(C`#include_next (C' directive are not inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options.

" -I - "4 Item "-I-" Split the include path. This option has been deprecated. Please use -iquote instead for -I directories before the -I - and remove the -I - option. Any directories specified with -I options before -I - are searched only for headers requested with CW(C`#include " CIfile CW"(C' ;they are not searched for CW(C`#include < CIfile CW>(C' .If additional directories are specified with -I options after the -I - ,those directories are searched for all #include directives. In addition, -I - inhibits the use of the directory of the current file directory as the first search directory for CW(C`#include " CIfile CW"(C' .There is no way to override this effect of -I - .

" -iprefix prefix "4 Item "-iprefix prefix" Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final / .

" -iwithprefix dir "4 Item "-iwithprefix dir" 0

" -iwithprefixbefore dir "4 Item "-iwithprefixbefore dir" Append dir to the prefix specified previously with -iprefix ,and add the resulting directory to the include search path. -iwithprefixbefore puts it in the same place -I would; -iwithprefix puts it where -idirafter would.

" -isysroot dir "4 Item "-isysroot dir" This option is like the --sysroot option, but applies only to header files (except for Darwin targets, where it applies to both header files and libraries). See the --sysroot option for more information.

" -imultilib dir "4 Item "-imultilib dir" Use dir as a subdirectory of the directory containing target-specific (C+ headers.

" -nostdinc "4 Item "-nostdinc" Do not search the standard system directories for header files. Only the directories explicitly specified with -I , -iquote , -isystem ,and/or -idirafter options (and the directory of the current file, if appropriate) are searched.

" -nostdinc++ "4 Item "-nostdinc++" Do not search for header files in the (C+ -specific standard directories, but do still search the other standard directories. (This option is used when building the (C+ library.)

" -iplugindir= dir "4 Item "-iplugindir=dir" Set the directory to search for plugins that are passed by -fplugin= name instead of -fplugin= path / name .so .This option is not meant to be used by the user, but only passed by the driver.

" -L dir "4 Item "-Ldir" Add directory dir to the list of directories to be searched for -l .

" -B prefix "4 Item "-Bprefix" This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. The compiler driver program runs one or more of the subprograms cpp , cc1 , as and ld .It tries prefix as a prefix for each program it tries to run, both with and without machine / version / for the corresponding target machine and compiler version. For each subprogram to be run, the compiler driver first tries the -B prefix, if any. If that name is not found, or if -B is not specified, the driver tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/ .If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your PATH environment variable. The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds a directory separator character at the end of the path. -B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to include files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends include to the prefix. The runtime support file libgcc.a can also be searched for using the -B prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Another way to specify a prefix much like the -B prefix is to use the environment variable GCC_EXEC_PREFIX . As a special kludge, if the path provided by -B is [dir/]stage N / ,where N is a number in the range 0 to 9, then it is replaced by [dir/]include .This is to help with boot-strapping the compiler.

" -no -canonical -prefixes "4 Item "-no-canonical-prefixes" Do not expand any symbolic links, resolve references to /../ or /./ ,or make the path absolute when generating a relative prefix.

" --sysroot= dir "4 Item "--sysroot=dir" Use dir as the logical root directory for headers and libraries. For example, if the compiler normally searches for headers in /usr/include and libraries in /usr/lib ,it instead searches dir /usr/include and dir /usr/lib . If you use both this option and the -isysroot option, then the --sysroot option applies to libraries, but the -isysroot option applies to header files. The GNUlinker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot still works, but the library aspect does not.

" --no -sysroot -suffix "4 Item "--no-sysroot-suffix" For some targets, a suffix is added to the root directory specified with --sysroot ,depending on the other options used, so that headers may for example be found in dir / suffix /usr/include instead of dir /usr/include .This option disables the addition of such a suffix.

Options for Code Generation Conventions

Subsection "Options for Code Generation Conventions" These machine-independent options control the interface conventions used in code generation.

Most of them have both positive and negative forms; the negative form of -ffoo is -fno -foo .In the table below, only one of the forms is listed ---the one that is not the default. You can figure out the other form by either removing no- or adding it.

" -fstack -reuse= reuse-level "4 Item "-fstack-reuse=reuse-level" This option controls stack space reuse for user declared local/auto variables and compiler generated temporaries. reuse_level can be all , named_vars ,or none . all enables stack reuse for all local variables and temporaries, named_vars enables the reuse only for user defined local variables with names, and none disables stack reuse completely. The default value is all .The option is needed when the program extends the lifetime of a scoped local variable or a compiler generated temporary beyond the end point defined by the language. When a lifetime of a variable ends, and if the variable lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. Legacy code extending local lifetime is likely to break with the stack reuse optimization. For example, 3 int *p; { int local1; p = &local1; local1 = 10; .... } { int local2; local2 = 20; ... } if (*p == 10) // out of scope use of local1 { } Another example: 6 struct A { A(int k) : i(k), j(k) { } int i; int j; }; A *ap; void foo(const A& ar) { ap = &ar; } void bar() { foo(A(10)); // temp object (Aqs lifetime ends when foo returns { A a(20); .... } ap ->i+= 10; // ap references out of scope temp whose space // is reused with a. What is the value of ap ->i? } The lifetime of a compiler generated temporary is well defined by the (C+ standard. When a lifetime of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. However some of the legacy code relies on the behavior of older compilers in which temporaries' stack space is not reused, the aggressive stack reuse can lead to runtime errors. This option is used to control the temporary stack reuse optimization.

" -ftrapv "4 Item "-ftrapv" This option generates traps for signed overflow on addition, subtraction, multiplication operations. The options -ftrapv and -fwrapv override each other, so using -ftrapv -fwrapv on the command-line results in -fwrapv being effective. Note that only active options override, so using -ftrapv -fwrapv -fno -wrapv on the command-line results in -ftrapv being effective.

" -fwrapv "4 Item "-fwrapv" This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others. The options -ftrapv and -fwrapv override each other, so using -ftrapv -fwrapv on the command-line results in -fwrapv being effective. Note that only active options override, so using -ftrapv -fwrapv -fno -wrapv on the command-line results in -ftrapv being effective.

" -fwrapv -pointer "4 Item "-fwrapv-pointer" This option instructs the compiler to assume that pointer arithmetic overflow on addition and subtraction wraps around using twos-complement representation. This flag disables some optimizations which assume pointer overflow is invalid.

" -fstrict -overflow "4 Item "-fstrict-overflow" This option implies -fno -wrapv -fno -wrapv -pointer and when negated implies -fwrapv -fwrapv -pointer .

" -fexceptions "4 Item "-fexceptions" Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCCgenerates frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, GCCenables it by default for languages like (C+ that normally require exception handling, and disables it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in (C+. You may also wish to disable this option if you are compiling older (C+ programs that don't use exception handling.

" -fnon -call -exceptions "4 Item "-fnon-call-exceptions" Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows trapping instructions to throw exceptions, i.e. memory references or floating-point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as CW(C`SIGALRM (C' .

" -fdelete -dead -exceptions "4 Item "-fdelete-dead-exceptions" Consider that instructions that may throw exceptions but don't otherwise contribute to the execution of the program can be optimized away. This option is enabled by default for the Ada front end, as permitted by the Ada language specification. Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.

" -funwind -tables "4 Item "-funwind-tables" Similar to -fexceptions ,except that it just generates any needed static data, but does not affect the generated code in any other way. You normally do not need to enable this option; instead, a language processor that needs this handling enables it on your behalf.

" -fasynchronous -unwind -tables "4 Item "-fasynchronous-unwind-tables" Generate unwind table in DWARFformat, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector).

" -fno -gnu -unique "4 Item "-fno-gnu-unique" On systems with recent GNUassembler and C library, the (C+ compiler uses the CW(C`STB_GNU_UNIQUE (C' binding to make sure that definitions of template static data members and static local variables in inline functions are unique even in the presence of CW(C`RTLD_LOCAL (C' ;this is necessary to avoid problems with a library used by two different CW(C`RTLD_LOCAL (C' plugins depending on a definition in one of them and therefore disagreeing with the other one about the binding of the symbol. But this causes CW(C`dlclose (C' to be ignored for affected DSOs; if your program relies on reinitialization of a DSOvia CW(C`dlclose (C' and CW(C`dlopen (C' ,you can use -fno -gnu -unique .

" -fpcc -struct -return "4 Item "-fpcc-struct-return" Return (L"short (R" CW(C`struct (C' and CW(C`union (C' values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC-compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc). The precise convention for returning structures in memory depends on the target configuration macros. Short structures and unions are those whose size and alignment match that of some integer type. Warning: code compiled with the -fpcc -struct -return switch is not binary compatible with code compiled with the -freg -struct -return switch. Use it to conform to a non-default application binary interface.

" -freg -struct -return "4 Item "-freg-struct-return" Return CW(C`struct (C' and CW(C`union (C' values in registers when possible. This is more efficient for small structures than -fpcc -struct -return . If you specify neither -fpcc -struct -return nor -freg -struct -return ,GCCdefaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to -fpcc -struct -return ,except on targets where GCCis the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. Warning: code compiled with the -freg -struct -return switch is not binary compatible with code compiled with the -fpcc -struct -return switch. Use it to conform to a non-default application binary interface.

" -fshort -enums "4 Item "-fshort-enums" Allocate to an CW(C`enum (C' type only as many bytes as it needs for the declared range of possible values. Specifically, the CW(C`enum (C' type is equivalent to the smallest integer type that has enough room. Warning: the -fshort -enums switch causes GCCto generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.

" -fshort -wchar "4 Item "-fshort-wchar" Override the underlying type for CW(C`wchar_t (C' to be CW(C`short unsigned int (C' instead of the default for the target. This option is useful for building programs to run under WINE. Warning: the -fshort -wchar switch causes GCCto generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.

" -fno -common "4 Item "-fno-common" In C code, this option controls the placement of global variables defined without an initializer, known as tentativedefinitions in the C standard. Tentative definitions are distinct from declarations of a variable with the CW(C`extern (C' keyword, which do not allocate storage. Unix C compilers have traditionally allocated storage for uninitialized global variables in a common block. This allows the linker to resolve all tentative definitions of the same variable in different compilation units to the same object, or to a non-tentative definition. This is the behavior specified by -fcommon ,and is the default for GCCon most targets. On the other hand, this behavior is not required by ISO C, and on some targets may carry a speed or code size penalty on variable references. The -fno -common option specifies that the compiler should instead place uninitialized global variables in the BSSsection of the object file. This inhibits the merging of tentative definitions by the linker so you get a multiple-definition error if the same variable is defined in more than one compilation unit. Compiling with -fno -common is useful on targets for which it provides better performance, or if you wish to verify that the program will work on other systems that always treat uninitialized variable definitions this way.

" -fno -ident "4 Item "-fno-ident" Ignore the CW(C`#ident (C' directive.

" -finhibit -size -directive "4 Item "-finhibit-size-directive" Don't output a CW(C`.size (C' assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling crtstuff.c ;you should not need to use it for anything else.

" -fverbose -asm "4 Item "-fverbose-asm" Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). -fno -verbose -asm ,the default, causes the extra information to be omitted and is useful when comparing two assembler files. The added comments include:

"*" 4 information on the compiler version and command-line options,

"*" 4 the source code lines associated with the assembly instructions, in the form FILENAME:LINENUMBER:CONTENTOF LINE,

"*" 4 hints on which high-level expressions correspond to the various assembly instruction operands. For example, given this C source file: 4 int test (int n) { int i; int total = 0; for (i = 0; i < n; i++) total += i * i; return total; } compiling to (x86_64) assembly via -S and emitting the result direct to stdout via -o - 1 gcc -S test.c -fverbose -asm -Os -o - gives output similar to this: 5 .file "test.c" # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64 -pc -linux -gnu) [...snip...] # options passed: [...snip...] .text .globl test .type test, @function test: .LFB0: .cfi_startproc # test.c:4: int total = 0; xorl %eax, %eax # <retval> # test.c:6: for (i = 0; i < n; i++) xorl %edx, %edx # i .L2: # test.c:6: for (i = 0; i < n; i++) cmpl %edi, %edx # n, i jge .L5 #, # test.c:7: total += i * i; movl %edx, %ecx # i, tmp92 imull %edx, %ecx # i, tmp92 # test.c:6: for (i = 0; i < n; i++) incl %edx # i # test.c:7: total += i * i; addl %ecx, %eax # tmp92, <retval> jmp .L2 # .L5: # test.c:10: } ret .cfi_endproc .LFE0: .size test, . -test .ident "GCC: (GNU) 7.0.0 20160809 (experimental)" .section .note.GNU -stack,"",@progbits The comments are intended for humans rather than machines and hence the precise format of the comments is subject to change.

" -frecord -gcc -switches "4 Item "-frecord-gcc-switches" This switch causes the command line used to invoke the compiler to be recorded into the object file that is being created. This switch is only implemented on some targets and the exact format of the recording is target and binary file format dependent, but it usually takes the form of a section containing ASCIItext. This switch is related to the -fverbose -asm switch, but that switch only records information in the assembler output file as comments, so it never reaches the object file. See also -grecord -gcc -switches for another way of storing compiler options into the object file.

" -fpic "4 Item "-fpic" Generate position-independent code ( PIC)suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table ( GOT).The dynamic loader resolves the GOTentries when the program starts (the dynamic loader is not part of GCC;it is part of the operating system). If the GOTsize for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that -fpic does not work; in that case, recompile with -fPIC instead. (These maximums are 8k on the SPARC,28k on AArch64 and 32k on the m68k and RS/6000.The x86 has no such limit.) Position-independent code requires special support, and therefore works only on certain machines. For the x86, GCCsupports PICfor System V but not for the Sun 386i. Code generated for the IBMRS/6000 is always position-independent. When this flag is set, the macros CW(C`_ _pic_ _ (C' and CW(C`_ _PIC_ _ (C' are defined to 1.

" -fPIC "4 Item "-fPIC" If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on AArch64, m68k, PowerPC and SPARC. Position-independent code requires special support, and therefore works only on certain machines. When this flag is set, the macros CW(C`_ _pic_ _ (C' and CW(C`_ _PIC_ _ (C' are defined to 2.

" -fpie "4 Item "-fpie" 0

" -fPIE "4 Item "-fPIE" These options are similar to -fpic and -fPIC ,but the generated position-independent code can be only linked into executables. Usually these options are used to compile code that will be linked using the -pie GCCoption. -fpie and -fPIE both define the macros CW(C`_ _pie_ _ (C' and CW(C`_ _PIE_ _ (C' .The macros have the value 1 for -fpie and 2 for -fPIE .

" -fno -plt "4 Item "-fno-plt" Do not use the PLTfor external function calls in position-independent code. Instead, load the callee address at call sites from the GOTand branch to it. This leads to more efficient code by eliminating PLTstubs and exposing GOTloads to optimizations. On architectures such as 32 -bit x86 where PLTstubs expect the GOTpointer in a specific register, this gives more register allocation freedom to the compiler. Lazy binding requires use of the PLT; with -fno -plt all external symbols are resolved at load time. Alternatively, the function attribute CW(C`noplt (C' can be used to avoid calls through the PLTfor specific external functions. In position-dependent code, a few targets also convert calls to functions that are marked to not use the PLTto use the GOTinstead.

" -fno -jump -tables "4 Item "-fno-jump-tables" Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction with -fpic or -fPIC for building code that forms part of a dynamic linker and cannot reference the address of a jump table. On some targets, jump tables do not require a GOTand this option is not needed.

" -ffixed - reg "4 Item "-ffixed-reg" Treat the register named reg as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). reg must be the name of a register. The register names accepted are machine-specific and are defined in the CW(C`REGISTER_NAMES (C' macro in the machine description macro file. This flag does not have a negative form, because it specifies a three-way choice.

" -fcall -used - reg "4 Item "-fcall-used-reg" Treat the register named reg as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way do not save and restore the register reg . It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results. This flag does not have a negative form, because it specifies a three-way choice.

" -fcall -saved - reg "4 Item "-fcall-saved-reg" Treat the register named reg as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way save and restore the register reg if they use it. It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results. A different sort of disaster results from the use of this flag for a register in which function values may be returned. This flag does not have a negative form, because it specifies a three-way choice.

" -fpack -struct[= n ] "4 Item "-fpack-struct[=n]" Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, representing the maximum alignment (that is, objects with default alignment requirements larger than this are output potentially unaligned at the next fitting location. Warning: the -fpack -struct switch causes GCCto generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface.

" -fleading -underscore "4 Item "-fleading-underscore" This option and its counterpart, -fno -leading -underscore ,forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. Warning: the -fleading -underscore switch causes GCCto generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch.

" -ftls -model= model "4 Item "-ftls-model=model" Alter the thread-local storage model to be used. The model argument should be one of global-dynamic , local-dynamic , initial-exec or local-exec . Note that the choice is subject to optimization: the compiler may use a more efficient model for symbols not visible outside of the translation unit, or if -fpic is not given on the command line. The default without -fpic is initial-exec ;with -fpic the default is global-dynamic .

" -ftrampolines "4 Item "-ftrampolines" For targets that normally need trampolines for nested functions, always generate them instead of using descriptors. Otherwise, for targets that do not need them, like for example HP-PA or IA-64, do nothing. A trampoline is a small piece of code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. Therefore, it requires the stack to be made executable in order for the program to work properly. -fno -trampolines is enabled by default on a language by language basis to let the compiler avoid generating them, if it computes that this is safe, and replace them with descriptors. Descriptors are made up of data only, but the generated code must be prepared to deal with them. As of this writing, -fno -trampolines is enabled by default only for Ada. Moreover, code compiled with -ftrampolines and code compiled with -fno -trampolines are not binary compatible if nested functions are present. This option must therefore be used on a program-wide basis and be manipulated with extreme care.

" -fvisibility= [ default | internal | hidden | protected ]"4 Item "-fvisibility=[default|internal|hidden|protected]" Set the default ELFimage symbol visibility to the specified option ---all symbols are marked with this unless overridden within the code. Using this feature can very substantially improve linking and load times of shared object libraries, produce more optimized code, provide near-perfect APIexport and prevent symbol clashes. It is strongly recommended that you use this in any shared objects you distribute. Despite the nomenclature, default always means public; i.e., available to be linked against from outside the shared object. protected and internal are pretty useless in real-world usage so the only other commonly used option is hidden . The default if -fvisibility isn't specified is default ,i.e., make every symbol public. A good explanation of the benefits offered by ensuring ELF symbols have the correct visibility is given by (L"How To Write Shared Libraries (R" by Ulrich Drepper (which can be found at < https://www.akkadia.org/drepper/ >)---however a superior solution made possible by this option to marking things hidden when the default is public is to make the default hidden and mark things public. This is the norm with DLLs on Windows and with -fvisibility=hidden and CW(C`_ _attribute_ _ ((visibility("default"))) (C' instead of CW(C`_ _declspec(dllexport) (C' you get almost identical semantics with identical syntax. This is a great boon to those working with cross-platform projects. For those adding visibility support to existing code, you may find CW(C`#pragma GCC visibility (C' of use. This works by you enclosing the declarations you wish to set visibility for with (for example) CW(C`#pragma GCC visibility push(hidden) (C' and CW(C`#pragma GCC visibility pop (C' . Bear in mind that symbol visibility should be viewed as part of the APIinterface contract and thus all new code should always specify visibility when it is not the default; i.e., declarations only for use within the local DSOshould always be marked explicitly as hidden as so to avoid PLTindirection overheads ---making this abundantly clear also aids readability and self-documentation of the code. Note that due to ISO(C+ specification requirements, CW(C`operator new (C' and CW(C`operator delete (C' must always be of default visibility. Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be compiled with visibility other than the default. You may need to explicitly say CW(C`#pragma GCC visibility push(default) (C' before including any such headers. CW(C`extern (C' declarations are not affected by -fvisibility ,so a lot of code can be recompiled with -fvisibility=hidden with no modifications. However, this means that calls to CW(C`extern (C' functions with no explicit visibility use the PLT,so it is more effective to use CW(C`_ _attribute ((visibility)) (C' and/or CW(C`#pragma GCC visibility (C' to tell the compiler which CW(C`extern (C' declarations should be treated as hidden. Note that -fvisibility does affect (C+ vague linkage entities. This means that, for instance, an exception class that is be thrown between DSOs must be explicitly marked with default visibility so that the type_info nodes are unified between the DSOs. An overview of these techniques, their benefits and how to use them is at < http://gcc.gnu.org/wiki/Visibility >.

" -fstrict -volatile -bitfields "4 Item "-fstrict-volatile-bitfields" This option should be used if accesses to volatile bit-fields (or other structure fields, although the compiler usually honors those types anyway) should use a single access of the width of the field's type, aligned to a natural alignment if possible. For example, targets with memory-mapped peripheral registers might require all such accesses to be 16 bits wide; with this flag you can declare all peripheral bit-fields as CW(C`unsigned short (C' (assuming short is 16 bits on these targets) to force GCCto use 16 -bit accesses instead of, perhaps, a more efficient 32 -bit access. If this option is disabled, the compiler uses the most efficient instruction. In the previous example, that might be a 32 -bit load instruction, even though that accesses bytes that do not contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated. In some cases, such as when the CW(C`packed (C' attribute is applied to a structure field, it may not be possible to access the field with a single read or write that is correctly aligned for the target machine. In this case GCCfalls back to generating multiple accesses rather than code that will fault or truncate the result at run time. Note: Due to restrictions of the C/ (C+11 memory model, write accesses are not allowed to touch non bit-field members. It is therefore recommended to define all bits of the field's type as bit-field members. The default value of this option is determined by the application binary interface for the target processor.

" -fsync -libcalls "4 Item "-fsync-libcalls" This option controls whether any out-of-line instance of the CW(C`_ _sync (C' family of functions may be used to implement the (C+11 CW(C`_ _atomic (C' family of functions. The default value of this option is enabled, thus the only useful form of the option is -fno -sync -libcalls .This option is used in the implementation of the libatomic runtime library.

" GCCDeveloper Options"

Subsection "GCC Developer Options" This section describes command-line options that are primarily of interest to GCCdevelopers, including options to support compiler testing and investigation of compiler bugs and compile-time performance problems. This includes options that produce debug dumps at various points in the compilation; that print statistics such as memory use and execution time; and that print information about GCC's configuration, such as where it searches for libraries. You should rarely need to use any of these options for ordinary compilation and linking tasks.

Many developer options that cause GCCto dump output to a file take an optional = filename suffix. You can specify stdout or - to dump to standard output, and stderr for standard error.

If = filename is omitted, a default dump file name is constructed by concatenating the base dump file name, a pass number, phase letter, and pass name. The base dump file name is the name of output file produced by the compiler if explicitly specified and not an executable; otherwise it is the source file name. The pass number is determined by the order passes are registered with the compiler's pass manager. This is generally the same as the order of execution, but passes registered by plugins, target-specific passes, or passes that are otherwise registered late are numbered higher than the pass named final ,even if they are executed earlier. The phase letter is one of i (inter-procedural analysis), l (language-specific), r ( RTL),or t (tree). The files are created in the directory of the output file.

" -d letters "4 Item "-dletters" 0

" -fdump -rtl - pass "4 Item "-fdump-rtl-pass"

" -fdump -rtl - pass = filename "4 Item "-fdump-rtl-pass=filename" Says to make debugging dumps during compilation at times specified by letters .This is used for debugging the RTL-based passes of the compiler. Some -d letters switches have different meaning when -E is used for preprocessing. Debug dumps can be enabled with a -fdump -rtl switch or some -d option letters .Here are the possible letters for use in pass and letters ,and their meanings:

" -fdump -rtl -alignments "4 Item "-fdump-rtl-alignments" Dump after branch alignments have been computed.

" -fdump -rtl -asmcons "4 Item "-fdump-rtl-asmcons" Dump after fixing rtl statements that have unsatisfied in/out constraints.

" -fdump -rtl -auto_inc_dec "4 Item "-fdump-rtl-auto_inc_dec" Dump after auto-inc-dec discovery. This pass is only run on architectures that have auto inc or auto dec instructions.

" -fdump -rtl -barriers "4 Item "-fdump-rtl-barriers" Dump after cleaning up the barrier instructions.

" -fdump -rtl -bbpart "4 Item "-fdump-rtl-bbpart" Dump after partitioning hot and cold basic blocks.

" -fdump -rtl -bbro "4 Item "-fdump-rtl-bbro" Dump after block reordering.

" -fdump -rtl -btl1 "4 Item "-fdump-rtl-btl1" 0

" -fdump -rtl -btl2 "4 Item "-fdump-rtl-btl2" -fdump -rtl -btl1 and -fdump -rtl -btl2 enable dumping after the two branch target load optimization passes.

" -fdump -rtl -bypass "4 Item "-fdump-rtl-bypass" Dump after jump bypassing and control flow optimizations.

" -fdump -rtl -combine "4 Item "-fdump-rtl-combine" Dump after the RTLinstruction combination pass.

" -fdump -rtl -compgotos "4 Item "-fdump-rtl-compgotos" Dump after duplicating the computed gotos.

" -fdump -rtl -ce1 "4 Item "-fdump-rtl-ce1" 0

" -fdump -rtl -ce2 "4 Item "-fdump-rtl-ce2"

" -fdump -rtl -ce3 "4 Item "-fdump-rtl-ce3" -fdump -rtl -ce1 , -fdump -rtl -ce2 ,and -fdump -rtl -ce3 enable dumping after the three if conversion passes.

" -fdump -rtl -cprop_hardreg "4 Item "-fdump-rtl-cprop_hardreg" Dump after hard register copy propagation.

" -fdump -rtl -csa "4 Item "-fdump-rtl-csa" Dump after combining stack adjustments.

" -fdump -rtl -cse1 "4 Item "-fdump-rtl-cse1" 0

" -fdump -rtl -cse2 "4 Item "-fdump-rtl-cse2" -fdump -rtl -cse1 and -fdump -rtl -cse2 enable dumping after the two common subexpression elimination passes.

" -fdump -rtl -dce "4 Item "-fdump-rtl-dce" Dump after the standalone dead code elimination passes.

" -fdump -rtl -dbr "4 Item "-fdump-rtl-dbr" Dump after delayed branch scheduling.

" -fdump -rtl -dce1 "4 Item "-fdump-rtl-dce1" 0

" -fdump -rtl -dce2 "4 Item "-fdump-rtl-dce2" -fdump -rtl -dce1 and -fdump -rtl -dce2 enable dumping after the two dead store elimination passes.

" -fdump -rtl -eh "4 Item "-fdump-rtl-eh" Dump after finalization of EHhandling code.

" -fdump -rtl -eh_ranges "4 Item "-fdump-rtl-eh_ranges" Dump after conversion of EHhandling range regions.

" -fdump -rtl -expand "4 Item "-fdump-rtl-expand" Dump after RTLgeneration.

" -fdump -rtl -fwprop1 "4 Item "-fdump-rtl-fwprop1" 0

" -fdump -rtl -fwprop2 "4 Item "-fdump-rtl-fwprop2" -fdump -rtl -fwprop1 and -fdump -rtl -fwprop2 enable dumping after the two forward propagation passes.

" -fdump -rtl -gcse1 "4 Item "-fdump-rtl-gcse1" 0

" -fdump -rtl -gcse2 "4 Item "-fdump-rtl-gcse2" -fdump -rtl -gcse1 and -fdump -rtl -gcse2 enable dumping after global common subexpression elimination.

" -fdump -rtl -init -regs "4 Item "-fdump-rtl-init-regs" Dump after the initialization of the registers.

" -fdump -rtl -initvals "4 Item "-fdump-rtl-initvals" Dump after the computation of the initial value sets.

" -fdump -rtl -into_cfglayout "4 Item "-fdump-rtl-into_cfglayout" Dump after converting to cfglayout mode.

" -fdump -rtl -ira "4 Item "-fdump-rtl-ira" Dump after iterated register allocation.

" -fdump -rtl -jump "4 Item "-fdump-rtl-jump" Dump after the second jump optimization.

" -fdump -rtl -loop2 "4 Item "-fdump-rtl-loop2" -fdump -rtl -loop2 enables dumping after the rtl loop optimization passes.

" -fdump -rtl -mach "4 Item "-fdump-rtl-mach" Dump after performing the machine dependent reorganization pass, if that pass exists.

" -fdump -rtl -mode_sw "4 Item "-fdump-rtl-mode_sw" Dump after removing redundant mode switches.

" -fdump -rtl -rnreg "4 Item "-fdump-rtl-rnreg" Dump after register renumbering.

" -fdump -rtl -outof_cfglayout "4 Item "-fdump-rtl-outof_cfglayout" Dump after converting from cfglayout mode.

" -fdump -rtl -peephole2 "4 Item "-fdump-rtl-peephole2" Dump after the peephole pass.

" -fdump -rtl -postreload "4 Item "-fdump-rtl-postreload" Dump after post-reload optimizations.

" -fdump -rtl -pro_and_epilogue "4 Item "-fdump-rtl-pro_and_epilogue" Dump after generating the function prologues and epilogues.

" -fdump -rtl -sched1 "4 Item "-fdump-rtl-sched1" 0

" -fdump -rtl -sched2 "4 Item "-fdump-rtl-sched2" -fdump -rtl -sched1 and -fdump -rtl -sched2 enable dumping after the basic block scheduling passes.

" -fdump -rtl -ree "4 Item "-fdump-rtl-ree" Dump after sign/zero extension elimination.

" -fdump -rtl -seqabstr "4 Item "-fdump-rtl-seqabstr" Dump after common sequence discovery.

" -fdump -rtl -shorten "4 Item "-fdump-rtl-shorten" Dump after shortening branches.

" -fdump -rtl -sibling "4 Item "-fdump-rtl-sibling" Dump after sibling call optimizations.

" -fdump -rtl -split1 "4 Item "-fdump-rtl-split1" 0

" -fdump -rtl -split2 "4 Item "-fdump-rtl-split2"

" -fdump -rtl -split3 "4 Item "-fdump-rtl-split3"

" -fdump -rtl -split4 "4 Item "-fdump-rtl-split4"

" -fdump -rtl -split5 "4 Item "-fdump-rtl-split5" These options enable dumping after five rounds of instruction splitting.

" -fdump -rtl -sms "4 Item "-fdump-rtl-sms" Dump after modulo scheduling. This pass is only run on some architectures.

" -fdump -rtl -stack "4 Item "-fdump-rtl-stack" Dump after conversion from GCC's(L"flat register file (R" registers to the x87's stack-like registers. This pass is only run on x86 variants.

" -fdump -rtl -subreg1 "4 Item "-fdump-rtl-subreg1" 0

" -fdump -rtl -subreg2 "4 Item "-fdump-rtl-subreg2" -fdump -rtl -subreg1 and -fdump -rtl -subreg2 enable dumping after the two subreg expansion passes.

" -fdump -rtl -unshare "4 Item "-fdump-rtl-unshare" Dump after all rtl has been unshared.

" -fdump -rtl -vartrack "4 Item "-fdump-rtl-vartrack" Dump after variable tracking.

" -fdump -rtl -vregs "4 Item "-fdump-rtl-vregs" Dump after converting virtual registers to hard registers.

" -fdump -rtl -web "4 Item "-fdump-rtl-web" Dump after live range splitting.

" -fdump -rtl -regclass "4 Item "-fdump-rtl-regclass" 0

" -fdump -rtl -subregs_of_mode_init "4 Item "-fdump-rtl-subregs_of_mode_init"

" -fdump -rtl -subregs_of_mode_finish "4 Item "-fdump-rtl-subregs_of_mode_finish"

" -fdump -rtl -dfinit "4 Item "-fdump-rtl-dfinit"

" -fdump -rtl -dfinish "4 Item "-fdump-rtl-dfinish" These dumps are defined but always produce empty files.

" -da "4 Item "-da" 0

" -fdump -rtl -all "4 Item "-fdump-rtl-all" Produce all the dumps listed above.

" -dA "4 Item "-dA" Annotate the assembler output with miscellaneous debugging information.

" -dD "4 Item "-dD" Dump all macro definitions, at the end of preprocessing, in addition to normal output.

" -dH "4 Item "-dH" Produce a core dump whenever an error occurs.

" -dp "4 Item "-dp" Annotate the assembler output with a comment indicating which pattern and alternative is used. The length and cost of each instruction are also printed.

" -dP "4 Item "-dP" Dump the RTLin the assembler output as a comment before each instruction. Also turns on -dp annotation.

" -dx "4 Item "-dx" Just generate RTLfor a function instead of compiling it. Usually used with -fdump -rtl -expand .

" -fdump -debug "4 Item "-fdump-debug" Dump debugging information generated during the debug generation phase.

" -fdump -earlydebug "4 Item "-fdump-earlydebug" Dump debugging information generated during the early debug generation phase.

" -fdump -noaddr "4 Item "-fdump-noaddr" When doing debugging dumps, suppress address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different compiler binaries and/or different text / bss / data / heap / stack / dso start locations.

" -freport -bug "4 Item "-freport-bug" Collect and dump debug information into a temporary file if an internal compiler error ( ICE)occurs.

" -fdump -unnumbered "4 Item "-fdump-unnumbered" When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without -g .

" -fdump -unnumbered -links "4 Item "-fdump-unnumbered-links" When doing debugging dumps (see -d option above), suppress instruction numbers for the links to the previous and next instructions in a sequence.

" -fdump -ipa - switch "4 Item "-fdump-ipa-switch" 0

" -fdump -ipa - switch - options "4 Item "-fdump-ipa-switch-options" Control the dumping at various stages of inter-procedural analysis language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the file is created in the same directory as the output file. The following dumps are possible:

" all "4 Item "all" Enables all inter-procedural analysis dumps.

" cgraph "4 Item "cgraph" Dumps information about call-graph optimization, unused function removal, and inlining decisions.

" inline "4 Item "inline" Dump after function inlining. Additionally, the options -optimized , -missed , -note ,and -all can be provided, with the same meaning as for -fopt -info ,defaulting to -optimized . For example, -fdump -ipa -inline -optimized -missed will emit information on callsites that were inlined, along with callsites that were not inlined. By default, the dump will contain messages about successful optimizations (equivalent to -optimized )together with low-level details about the analysis.

" -fdump -lang -all "4 Item "-fdump-lang-all" 0

" -fdump -lang - switch "4 Item "-fdump-lang-switch"

" -fdump -lang - switch - options "4 Item "-fdump-lang-switch-options"

" -fdump -lang - switch - options = filename "4 Item "-fdump-lang-switch-options=filename" Control the dumping of language-specific information. The options and filename portions behave as described in the -fdump -tree option. The following switch values are accepted:

" all "4 Item "all" Enable all language-specific dumps.

" class "4 Item "class" Dump class hierarchy information. Virtual table information is emitted unless ' slim 'is specified. This option is applicable to (C+ only.

" raw "4 Item "raw" Dump the raw internal tree data. This option is applicable to (C+ only.

" -fdump -passes "4 Item "-fdump-passes" Print on stderr the list of optimization passes that are turned on and off by the current command-line options.

" -fdump -statistics - option "4 Item "-fdump-statistics-option" Enable and control dumping of pass statistics in a separate file. The file name is generated by appending a suffix ending in .statistics to the source file name, and the file is created in the same directory as the output file. If the - option form is used, -stats causes counters to be summed over the whole compilation unit while -details dumps every event as the passes generate them. The default with no option is to sum counters for each function compiled.

" -fdump -tree -all "4 Item "-fdump-tree-all" 0

" -fdump -tree - switch "4 Item "-fdump-tree-switch"

" -fdump -tree - switch - options "4 Item "-fdump-tree-switch-options"

" -fdump -tree - switch - options = filename "4 Item "-fdump-tree-switch-options=filename" Control the dumping at various stages of processing the intermediate language tree to a file. If the - options form is used, options is a list of - separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful are ignored. The following options are available

" address "4 Item "address" Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug environment.

" asmname "4 Item "asmname" If CW(C`DECL_ASSEMBLER_NAME (C' has been set for a given decl, use that in the dump instead of CW(C`DECL_NAME (C' .Its primary use is ease of use working backward from mangled names in the assembly file.

" slim "4 Item "slim" When dumping front-end intermediate representations, inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when they are directly reachable by some other path. When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures. When dumping RTL,print the RTLin slim (condensed) form instead of the default LISP-like representation.

" raw "4 Item "raw" Print a raw representation of the tree. By default, trees are pretty-printed into a C -like representation.

" details "4 Item "details" Enable more detailed dumps (not honored by every dump option). Also include information from the optimization passes.

" stats "4 Item "stats" Enable dumping various statistics about the pass (not honored by every dump option).

" blocks "4 Item "blocks" Enable showing basic block boundaries (disabled in raw dumps).

" graph "4 Item "graph" For each of the other indicated dump files ( -fdump -rtl - pass ), dump a representation of the control flow graph suitable for viewing with GraphViz to file . passid . pass .dot .Each function in the file is pretty-printed as a subgraph, so that GraphViz can render them all in a single plot. This option currently only works for RTLdumps, and the RTLis always dumped in slim form.

" vops "4 Item "vops" Enable showing virtual operands for every statement.

" lineno "4 Item "lineno" Enable showing line numbers for statements.

" uid "4 Item "uid" Enable showing the unique ID( CW(C`DECL_UID (C' )for each variable.

" verbose "4 Item "verbose" Enable showing the tree dump for each statement.

" eh "4 Item "eh" Enable showing the EHregion number holding each statement.

" scev "4 Item "scev" Enable showing scalar evolution analysis details.

" optimized "4 Item "optimized" Enable showing optimization information (only available in certain passes).

" missed "4 Item "missed" Enable showing missed optimization information (only available in certain passes).

" note "4 Item "note" Enable other detailed optimization information (only available in certain passes).

" all "4 Item "all" Turn on all options, except raw , slim , verbose and lineno .

" optall "4 Item "optall" Turn on all optimization options, i.e., optimized , missed ,and note . To determine what tree dumps are available or find the dump for a pass of interest follow the steps below.

"1." 4 Item "1." Invoke GCCwith -fdump -passes and in the stderr output look for a code that corresponds to the pass you are interested in. For example, the codes CW(C`tree -evrp (C' , CW(C`tree -vrp1 (C' ,and CW(C`tree -vrp2 (C' correspond to the three Value Range Propagation passes. The number at the end distinguishes distinct invocations of the same pass.

"2." 4 Item "2." To enable the creation of the dump file, append the pass code to the -fdump - option prefix and invoke GCCwith it. For example, to enable the dump from the Early Value Range Propagation pass, invoke GCCwith the -fdump -tree -evrp option. Optionally, you may specify the name of the dump file. If you don't specify one, GCC creates as described below.

"3." 4 Item "3." Find the pass dump in a file whose name is composed of three components separated by a period: the name of the source file GCCwas invoked to compile, a numeric suffix indicating the pass number followed by the letter t for tree passes (and the letter r for RTLpasses), and finally the pass code. For example, the Early VRPpass dump might be in a file named myfile.c.038t.evrp in the current working directory. Note that the numeric codes are not stable and may change from one version of GCCto another.

" -fopt -info "4 Item "-fopt-info" 0

" -fopt -info - options "4 Item "-fopt-info-options"

" -fopt -info - options = filename "4 Item "-fopt-info-options=filename" Controls optimization dumps from various optimization passes. If the - options form is used, options is a list of - separated option keywords to select the dump details and optimizations. The options can be divided into three groups:

"1." 4 Item "1." options describing what kinds of messages should be emitted,

"2." 4 Item "2." options describing the verbosity of the dump, and

"3." 4 Item "3." options describing which optimizations should be included. The options from each group can be freely mixed as they are non-overlapping. However, in case of any conflicts, the later options override the earlier options on the command line. The following options control which kinds of messages should be emitted:

" optimized "4 Item "optimized" Print information when an optimization is successfully applied. It is up to a pass to decide which information is relevant. For example, the vectorizer passes print the source location of loops which are successfully vectorized.

" missed "4 Item "missed" Print information about missed optimizations. Individual passes control which information to include in the output.

" note "4 Item "note" Print verbose information about optimizations, such as certain transformations, more detailed messages about decisions etc.

" all "4 Item "all" Print detailed optimization information. This includes optimized , missed ,and note . The following option controls the dump verbosity:

" internals "4 Item "internals" By default, only (L"high-level (R" messages are emitted. This option enables additional, more detailed, messages, which are likely to only be of interest to GCCdevelopers. One or more of the following option keywords can be used to describe a group of optimizations:

" ipa "4 Item "ipa" Enable dumps from all interprocedural optimizations.

" loop "4 Item "loop" Enable dumps from all loop optimizations.

" inline "4 Item "inline" Enable dumps from all inlining optimizations.

" omp "4 Item "omp" Enable dumps from all OMP(Offloading and Multi Processing) optimizations.

" vec "4 Item "vec" Enable dumps from all vectorization optimizations.

" optall "4 Item "optall" Enable dumps from all optimizations. This is a superset of the optimization groups listed above. If options is omitted, it defaults to optimized-optall ,which means to dump messages about successful optimizations from all the passes, omitting messages that are treated as (L"internals (R". If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename . Otherwise the dump is output onto stderr .Though multiple -fopt -info options are accepted, only one of them can include a filename .If other filenames are provided then all but the first such option are ignored. Note that the output filename is overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, stderr should be used instead. In the following example, the optimization info is output to stderr : 1 gcc -O3 -fopt -info This example: 1 gcc -O3 -fopt -info -missed=missed.all outputs missed optimization report from all the passes into missed.all ,and this one: 1 gcc -O2 -ftree -vectorize -fopt -info -vec -missed prints information about missed optimization opportunities from vectorization passes on stderr . Note that -fopt -info -vec -missed is equivalent to -fopt -info -missed -vec .The order of the optimization group names and message types listed after -fopt -info does not matter. As another example, 1 gcc -O3 -fopt -info -inline -optimized -missed=inline.txt outputs information about missed optimizations as well as optimized locations from all the inlining passes into inline.txt . Finally, consider: 1 gcc -fopt -info -vec -missed=vec.miss -fopt -info -loop -optimized=loop.opt Here the two output filenames vec.miss and loop.opt are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are ignored. Thus only vec.miss is produced which contains dumps from the vectorizer about missed opportunities.

" -fsave -optimization -record "4 Item "-fsave-optimization-record" Write a SRCFILE.opt-record.json.gz file detailing what optimizations were performed, for those optimizations that support -fopt -info . This option is experimental and the format of the data within the compressed JSONfile is subject to change. It is roughly equivalent to a machine-readable version of -fopt -info -all ,as a collection of messages with source file, line number and column number, with the following additional data for each message:

"*" 4 the execution count of the code being optimized, along with metadata about whether this was from actual profile data, or just an estimate, allowing consumers to prioritize messages by code hotness,

"*" 4 the function name of the code being optimized, where applicable,

"*" 4 the (L"inlining chain (R" for the code being optimized, so that when a function is inlined into several different places (which might themselves be inlined), the reader can distinguish between the copies,

"*" 4 objects identifying those parts of the message that refer to expressions, statements or symbol-table nodes, which of these categories they are, and, when available, their source code location,

"*" 4 the GCCpass that emitted the message, and

"*" 4 the location in GCC'sown code from which the message was emitted Additionally, some messages are logically nested within other messages, reflecting implementation details of the optimization passes.

" -fsched -verbose= n "4 Item "-fsched-verbose=n" On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints to the dump files. For n greater than zero, -fsched -verbose outputs the same information as -fdump -rtl -sched1 and -fdump -rtl -sched2 . For n greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For n greater than two, it includes RTLat abort point, control-flow and regions info. And for n over four, -fsched -verbose also includes dependence info.

" -fenable - kind - pass "4 Item "-fenable-kind-pass" 0

" -fdisable - kind - pass = range-list "4 Item "-fdisable-kind-pass=range-list" This is a set of options that are used to explicitly disable/enable optimization passes. These options are intended for use for debugging GCC. Compiler users should use regular options for enabling/disabling passes instead.

" -fdisable -ipa - pass "4 Item "-fdisable-ipa-pass" Disable IPApass pass . pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1.

" -fdisable -rtl - pass "4 Item "-fdisable-rtl-pass" 0

" -fdisable -rtl - pass = range-list "4 Item "-fdisable-rtl-pass=range-list" Disable RTLpass pass . pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. range-list is a comma-separated list of function ranges or assembler names. Each range is a number pair separated by a colon. The range is inclusive in both ends. If the range is trivial, the number pair can be simplified as a single number. If the function's call graph node's uid falls within one of the specified ranges, the pass is disabled for that function. The uid is shown in the function header of a dump file, and the pass names can be dumped by using option -fdump -passes .

" -fdisable -tree - pass "4 Item "-fdisable-tree-pass" 0

" -fdisable -tree - pass = range-list "4 Item "-fdisable-tree-pass=range-list" Disable tree pass pass .See -fdisable -rtl for the description of option arguments.

" -fenable -ipa - pass "4 Item "-fenable-ipa-pass" Enable IPApass pass . pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1.

" -fenable -rtl - pass "4 Item "-fenable-rtl-pass" 0

" -fenable -rtl - pass = range-list "4 Item "-fenable-rtl-pass=range-list" Enable RTLpass pass .See -fdisable -rtl for option argument description and examples.

" -fenable -tree - pass "4 Item "-fenable-tree-pass" 0

" -fenable -tree - pass = range-list "4 Item "-fenable-tree-pass=range-list" Enable tree pass pass .See -fdisable -rtl for the description of option arguments. Here are some examples showing uses of these options. 10 # disable ccp1 for all functions -fdisable -tree -ccp1 # disable complete unroll for function whose cgraph node uid is 1 -fenable -tree -cunroll=1 # disable gcse2 for functions at the following ranges [1,1], # [300,400], and [400,1000] # disable gcse2 for functions foo and foo2 -fdisable -rtl -gcse2=foo,foo2 # disable early inlining -fdisable -tree -einline # disable ipa inlining -fdisable -ipa -inline # enable tree full unroll -fenable -tree -unroll

" -fchecking "4 Item "-fchecking" 0

" -fchecking= n "4 Item "-fchecking=n" Enable internal consistency checking. The default depends on the compiler configuration. -fchecking=2 enables further internal consistency checking that might affect code generation.

" -frandom -seed= string "4 Item "-frandom-seed=string" This option provides a seed that GCCuses in place of random numbers in generating certain symbol names that have to be different in every compiled file. It is also used to place unique stamps in coverage data files and the object files that produce them. You can use the -frandom -seed option to produce reproducibly identical object files. The string can either be a number (decimal, octal or hex) or an arbitrary string (in which case it's converted to a number by computing CRC32). The string should be different for every file you compile.

" -save -temps "4 Item "-save-temps" 0

" -save -temps=cwd "4 Item "-save-temps=cwd" Store the usual (L"temporary (R" intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling foo.c with -c -save -temps produces files foo.i and foo.s ,as well as foo.o .This creates a preprocessed foo.i output file even though the compiler now normally uses an integrated preprocessor. When used in combination with the -x command-line option, -save -temps is sensible enough to avoid over writing an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using -save -temps . If you invoke GCCin parallel, compiling several different source files that share a common base name in different subdirectories or the same source file compiled for multiple output destinations, it is likely that the different parallel compilers will interfere with each other, and overwrite the temporary files. For instance: 2 gcc -save -temps -o outdir1/foo.o indir1/foo.c& gcc -save -temps -o outdir2/foo.o indir2/foo.c& may result in foo.i and foo.o being written to simultaneously by both compilers.

" -save -temps=obj "4 Item "-save-temps=obj" Store the usual (L"temporary (R" intermediate files permanently. If the -o option is used, the temporary files are based on the object file. If the -o option is not used, the -save -temps=obj switch behaves like -save -temps . For example: 3 gcc -save -temps=obj -c foo.c gcc -save -temps=obj -c bar.c -o dir/xbar.o gcc -save -temps=obj foobar.c -o dir2/yfoobar creates foo.i , foo.s , dir/xbar.i , dir/xbar.s , dir2/yfoobar.i , dir2/yfoobar.s ,and dir2/yfoobar.o .

" -time [ = file ]"4 Item "-time[=file]" Report the CPUtime taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). Without the specification of an output file, the output looks like this: 2 # cc1 0.12 0.01 # as 0.00 0.01 The first number on each line is the (L"user time (R", that is time spent executing the program itself. The second number is (L"system time (R", time spent executing operating system routines on behalf of the program. Both numbers are in seconds. With the specification of an output file, the output is appended to the named file, and it looks like this: 2 0.12 0.01 cc1 <options> 0.00 0.01 as <options> The (L"user time (R" and the (L"system time (R" are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options.

" -fdump -final -insns [ = file ]"4 Item "-fdump-final-insns[=file]" Dump the final internal representation ( RTL)to file .If the optional argument is omitted (or if file is CW(C`. (C' ),the name of the dump file is determined by appending CW(C`.gkd (C' to the compilation output file name.

" -fcompare -debug [ = opts ]"4 Item "-fcompare-debug[=opts]" If no error occurs during compilation, run the compiler a second time, adding opts and -fcompare -debug -second to the arguments passed to the second compilation. Dump the final internal representation in both compilations, and print an error if they differ. If the equal sign is omitted, the default -gtoggle is used. The environment variable GCC_COMPARE_DEBUG ,if defined, non-empty and nonzero, implicitly enables -fcompare -debug .If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it is used for opts ,otherwise the default -gtoggle is used. -fcompare -debug= ,with the equal sign but without opts , is equivalent to -fno -compare -debug ,which disables the dumping of the final representation and the second compilation, preventing even GCC_COMPARE_DEBUG from taking effect. To verify full coverage during -fcompare -debug testing, set GCC_COMPARE_DEBUG to say -fcompare -debug -not -overridden , which GCCrejects as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to -w%n -fcompare -debug not overridden will do.

" -fcompare -debug -second "4 Item "-fcompare-debug-second" This option is implicitly passed to the compiler for the second compilation requested by -fcompare -debug ,along with options to silence warnings, and omitting other options that would cause the compiler to produce output to files or to standard output as a side effect. Dump files and preserved temporary files are renamed so as to contain the CW(C`.gk (C' additional extension during the second compilation, to avoid overwriting those generated by the first. When this option is passed to the compiler driver, it causes the first compilation to be skipped, which makes it useful for little other than debugging the compiler proper.

" -gtoggle "4 Item "-gtoggle" Turn off generation of debug info, if leaving out this option generates it, or turn it on at level 2 otherwise. The position of this argument in the command line does not matter; it takes effect after all other options are processed, and it does so only once, no matter how many times it is given. This is mainly intended to be used with -fcompare -debug .

" -fvar -tracking -assignments -toggle "4 Item "-fvar-tracking-assignments-toggle" Toggle -fvar -tracking -assignments ,in the same way that -gtoggle toggles -g .

" -Q "4 Item "-Q" Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes.

" -ftime -report "4 Item "-ftime-report" Makes the compiler print some statistics about the time consumed by each pass when it finishes.

" -ftime -report -details "4 Item "-ftime-report-details" Record the time consumed by infrastructure parts separately for each pass.

" -fira -verbose= n "4 Item "-fira-verbose=n" Control the verbosity of the dump file for the integrated register allocator. The default value is 5. If the value n is greater or equal to 10, the dump output is sent to stderr using the same format as n minus 10.

" -flto -report "4 Item "-flto-report" Prints a report with internal details on the workings of the link-time optimizer. The contents of this report vary from version to version. It is meant to be useful to GCCdevelopers when processing object files in LTOmode (via -flto ). Disabled by default.

" -flto -report -wpa "4 Item "-flto-report-wpa" Like -flto -report ,but only print for the WPAphase of Link Time Optimization.

" -fmem -report "4 Item "-fmem-report" Makes the compiler print some statistics about permanent memory allocation when it finishes.

" -fmem -report -wpa "4 Item "-fmem-report-wpa" Makes the compiler print some statistics about permanent memory allocation for the WPAphase only.

" -fpre -ipa -mem -report "4 Item "-fpre-ipa-mem-report" 0

" -fpost -ipa -mem -report "4 Item "-fpost-ipa-mem-report" Makes the compiler print some statistics about permanent memory allocation before or after interprocedural optimization.

" -fprofile -report "4 Item "-fprofile-report" Makes the compiler print some statistics about consistency of the (estimated) profile and effect of individual passes.

" -fstack -usage "4 Item "-fstack-usage" Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending .su to the auxname . auxname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields:

"*" 4 The name of the function.

"*" 4 A number of bytes.

"*" 4 One or more qualifiers: CW(C`static (C' , CW(C`dynamic (C' , CW(C`bounded (C' . The qualifier CW(C`static (C' means that the function manipulates the stack statically: a fixed number of bytes are allocated for the frame on function entry and released on function exit; no stack adjustments are otherwise made in the function. The second field is this fixed number of bytes. The qualifier CW(C`dynamic (C' means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are made in the body of the function, for example to push/pop arguments around function calls. If the qualifier CW(C`bounded (C' is also present, the amount of these adjustments is bounded at compile time and the second field is an upper bound of the total amount of stack used by the function. If it is not present, the amount of these adjustments is not bounded at compile time and the second field only represents the bounded part.

" -fstats "4 Item "-fstats" Emit statistics about front-end processing at the end of the compilation. This option is supported only by the (C+ front end, and the information is generally only useful to the G++ development team.

" -fdbg -cnt -list "4 Item "-fdbg-cnt-list" Print the name and the counter upper bound for all debug counters.

" -fdbg -cnt= counter-value-list "4 Item "-fdbg-cnt=counter-value-list" Set the internal debug counter lower and upper bound. counter-value-list is a comma-separated list of name : lower_bound : upper_bound tuples which sets the lower and the upper bound of each debug counter name .The lower_bound is optional and is zero initialized if not set. All debug counters have the initial upper bound of CW(C`UINT_MAX (C' ; thus CW(C`dbg_cnt (C' returns true always unless the upper bound is set by this option. For example, with -fdbg -cnt=dce:2:4,tail_call:10 , CW(C`dbg_cnt(dce) (C' returns true only for third and fourth invocation. For CW(C`dbg_cnt(tail_call) (C' true is returned for first 10 invocations.

" -print -file -name= library "4 Item "-print-file-name=library" Print the full absolute name of the library file library that would be used when linking ---and don't do anything else. With this option, GCCdoes not compile or link anything; it just prints the file name.

" -print -multi -directory "4 Item "-print-multi-directory" Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in GCC_EXEC_PREFIX .

" -print -multi -lib "4 Item "-print-multi-lib" Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by ; ,and each switch starts with an @ instead of the - ,without spaces between multiple switches. This is supposed to ease shell processing.

" -print -multi -os -directory "4 Item "-print-multi-os-directory" Print the path to OSlibraries for the selected multilib, relative to some lib subdirectory. If OSlibraries are present in the lib subdirectory and no multilibs are used, this is usually just . ,if OSlibraries are present in lib suffix sibling directories this prints e.g. ../lib64 , ../lib or ../lib32 ,or if OSlibraries are present in lib/ subdir subdirectories it prints e.g. amd64 , sparcv9 or ev6 .

" -print -multiarch "4 Item "-print-multiarch" Print the path to OSlibraries for the selected multiarch, relative to some lib subdirectory.

" -print -prog -name= program "4 Item "-print-prog-name=program" Like -print -file -name ,but searches for a program such as cpp .

" -print -libgcc -file -name "4 Item "-print-libgcc-file-name" Same as -print -file -name=libgcc.a . This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a .You can do: 1 gcc -nostdlib <files>... gcc -print -libgcc -file -name

" -print -search -dirs "4 Item "-print-search-dirs" Print the name of the configured installation directory and a list of program and library directories gcc searches ---and don't do anything else. This is useful when gcc prints the error message installationproblem, cannot exec cpp0: No such file or directory . To resolve this you either need to put cpp0 and the other compiler components where gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Don't forget the trailing / .

" -print -sysroot "4 Item "-print-sysroot" Print the target sysroot directory that is used during compilation. This is the target sysroot specified either at configure time or using the --sysroot option, possibly with an extra suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing.

" -print -sysroot -headers -suffix "4 Item "-print-sysroot-headers-suffix" Print the suffix added to the target sysroot when searching for headers, or give an error if the compiler is not configured with such a suffix ---and don't do anything else.

" -dumpmachine "4 Item "-dumpmachine" Print the compiler's target machine (for example, i686-pc -linux -gnu )---and don't do anything else.

" -dumpversion "4 Item "-dumpversion" Print the compiler version (for example, CW3.0 , CW6.3.0 or CW7 )---and don't do anything else. This is the compiler version used in filesystem paths and specs. Depending on how the compiler has been configured it can be just a single number (major version), two numbers separated by a dot (major and minor version) or three numbers separated by dots (major, minor and patchlevel version).

" -dumpfullversion "4 Item "-dumpfullversion" Print the full compiler version ---and don't do anything else. The output is always three numbers separated by dots, major, minor and patchlevel version.

" -dumpspecs "4 Item "-dumpspecs" Print the compiler's built-in specs ---and don't do anything else. (This is used when GCCitself is being built.)

Machine-Dependent Options

Subsection "Machine-Dependent Options" Each target machine supported by GCCcan have its own options ---for example, to allow you to compile for a particular processor variant or ABI,or to control optimizations specific to that machine. By convention, the names of machine-specific options start with -m .

Some configurations of the compiler also support additional target-specific options, usually for compatibility with other compilers on the same platform.

AArch64Options Subsection "AArch64 Options"

These options are defined for AArch64 implementations:

" -mabi= name "4 Item "-mabi=name" Generate code for the specified data model. Permissible values are ilp32 for SysV-like data model where int, long int and pointers are 32 bits, and lp64 for SysV-like data model where int is 32 bits, but long int and pointers are 64 bits. The default depends on the specific target configuration. Note that the LP64and ILP32ABIs are not link-compatible; you must compile your entire program with the same ABI,and link with a compatible set of libraries.

" -mbig -endian "4 Item "-mbig-endian" Generate big-endian code. This is the default when GCCis configured for an aarch64_be-* -* target.

" -mgeneral -regs -only "4 Item "-mgeneral-regs-only" Generate code which uses only the general-purpose registers. This will prevent the compiler from using floating-point and Advanced SIMDregisters but will not impose any restrictions on the assembler.

" -mlittle -endian "4 Item "-mlittle-endian" Generate little-endian code. This is the default when GCCis configured for an aarch64-* -* but not an aarch64_be-* -* target.

" -mcmodel=tiny "4 Item "-mcmodel=tiny" Generate code for the tiny code model. The program and its statically defined symbols must be within 1MB of each other. Programs can be statically or dynamically linked.

" -mcmodel=small "4 Item "-mcmodel=small" Generate code for the small code model. The program and its statically defined symbols must be within 4GB of each other. Programs can be statically or dynamically linked. This is the default code model.

" -mcmodel=large "4 Item "-mcmodel=large" Generate code for the large code model. This makes no assumptions about addresses and sizes of sections. Programs can be statically linked only.

" -mstrict -align "4 Item "-mstrict-align" 0

" -mno -strict -align "4 Item "-mno-strict-align" Avoid or allow generating memory accesses that may not be aligned on a natural object boundary as described in the architecture specification.

" -momit -leaf -frame -pointer "4 Item "-momit-leaf-frame-pointer" 0

" -mno -omit -leaf -frame -pointer "4 Item "-mno-omit-leaf-frame-pointer" Omit or keep the frame pointer in leaf functions. The former behavior is the default.

" -mstack -protector -guard= guard "4 Item "-mstack-protector-guard=guard" 0

" -mstack -protector -guard -reg= reg "4 Item "-mstack-protector-guard-reg=reg"

" -mstack -protector -guard -offset= offset "4 Item "-mstack-protector-guard-offset=offset" Generate stack protection code using canary at guard .Supported locations are global for a global canary or sysreg for a canary in an appropriate system register. With the latter choice the options -mstack -protector -guard -reg= reg and -mstack -protector -guard -offset= offset furthermore specify which system register to use as base register for reading the canary, and from what offset from that base register. There is no default register or offset as this is entirely for use within the Linux kernel.

" -mstack -protector -guard= guard "4 Item "-mstack-protector-guard=guard" 0

" -mstack -protector -guard -reg= reg "4 Item "-mstack-protector-guard-reg=reg"

" -mstack -protector -guard -offset= offset "4 Item "-mstack-protector-guard-offset=offset" Generate stack protection code using canary at guard .Supported locations are global for a global canary or sysreg for a canary in an appropriate system register. With the latter choice the options -mstack -protector -guard -reg= reg and -mstack -protector -guard -offset= offset furthermore specify which system register to use as base register for reading the canary, and from what offset from that base register. There is no default register or offset as this is entirely for use within the Linux kernel.

" -mtls -dialect=desc "4 Item "-mtls-dialect=desc" Use TLSdescriptors as the thread-local storage mechanism for dynamic accesses of TLSvariables. This is the default.

" -mtls -dialect=traditional "4 Item "-mtls-dialect=traditional" Use traditional TLSas the thread-local storage mechanism for dynamic accesses of TLSvariables.

" -mtls -size= size "4 Item "-mtls-size=size" Specify bit size of immediate TLSoffsets. Valid values are 12, 24, 32, 48. This option requires binutils 2.26 or newer.

" -mfix -cortex -a53 -835769 "4 Item "-mfix-cortex-a53-835769" 0

" -mno -fix -cortex -a53 -835769 "4 Item "-mno-fix-cortex-a53-835769" Enable or disable the workaround for the ARMCortex -A53 erratum number 835769. This involves inserting a NOPinstruction between memory instructions and 64 -bit integer multiply-accumulate instructions.

" -mfix -cortex -a53 -843419 "4 Item "-mfix-cortex-a53-843419" 0

" -mno -fix -cortex -a53 -843419 "4 Item "-mno-fix-cortex-a53-843419" Enable or disable the workaround for the ARMCortex -A53 erratum number 843419. This erratum workaround is made at link time and this will only pass the corresponding flag to the linker.

" -mlow -precision -recip -sqrt "4 Item "-mlow-precision-recip-sqrt" 0

" -mno -low -precision -recip -sqrt "4 Item "-mno-low-precision-recip-sqrt" Enable or disable the reciprocal square root approximation. This option only has an effect if -ffast -math or -funsafe -math -optimizations is used as well. Enabling this reduces precision of reciprocal square root results to about 16 bits for single precision and to 32 bits for double precision.

" -mlow -precision -sqrt "4 Item "-mlow-precision-sqrt" 0

" -mno -low -precision -sqrt "4 Item "-mno-low-precision-sqrt" Enable or disable the square root approximation. This option only has an effect if -ffast -math or -funsafe -math -optimizations is used as well. Enabling this reduces precision of square root results to about 16 bits for single precision and to 32 bits for double precision. If enabled, it implies -mlow -precision -recip -sqrt .

" -mlow -precision -div "4 Item "-mlow-precision-div" 0

" -mno -low -precision -div "4 Item "-mno-low-precision-div" Enable or disable the division approximation. This option only has an effect if -ffast -math or -funsafe -math -optimizations is used as well. Enabling this reduces precision of division results to about 16 bits for single precision and to 32 bits for double precision.

" -mtrack -speculation "4 Item "-mtrack-speculation" 0

" -mno -track -speculation "4 Item "-mno-track-speculation" Enable or disable generation of additional code to track speculative execution through conditional branches. The tracking state can then be used by the compiler when expanding calls to CW(C`_ _builtin_speculation_safe_copy (C' to permit a more efficient code sequence to be generated.

" -march= name "4 Item "-march=name" Specify the name of the target architecture and, optionally, one or more feature modifiers. This option has the form -march= arch { + [ no ] feature }*. The permissible values for arch are armv8-a , armv8.1-a , armv8.2-a , armv8.3-a , armv8.4-a , armv8.5-a or native . The value armv8.5-a implies armv8.4-a and enables compiler support for the ARMv8.5 -A architecture extensions. The value armv8.4-a implies armv8.3-a and enables compiler support for the ARMv8.4 -A architecture extensions. The value armv8.3-a implies armv8.2-a and enables compiler support for the ARMv8.3 -A architecture extensions. The value armv8.2-a implies armv8.1-a and enables compiler support for the ARMv8.2 -A architecture extensions. The value armv8.1-a implies armv8-a and enables compiler support for the ARMv8.1 -A architecture extension. In particular, it enables the +crc , +lse ,and +rdma features. The value native is available on native AArch64 GNU/Linux and causes the compiler to pick the architecture of the host system. This option has no effect if the compiler is unable to recognize the architecture of the host system, The permissible values for feature are listed in the sub-section on aarch64-feature -modifiers,, -march and -mcpu FeatureModifiers .Where conflicting feature modifiers are specified, the right-most feature is used. GCCuses name to determine what kind of instructions it can emit when generating assembly code. If -march is specified without either of -mtune or -mcpu also being specified, the code is tuned to perform well across a range of target processors implementing the target architecture.

" -mtune= name "4 Item "-mtune=name" Specify the name of the target processor for which GCCshould tune the performance of the code. Permissible values for this option are: generic , cortex-a35 , cortex-a53 , cortex-a55 , cortex-a57 , cortex-a72 , cortex-a73 , cortex-a75 , cortex-a76 , ares , exynos-m1 , emag , falkor , neoverse-e1 , neoverse-n1 , qdf24xx , saphira , phecda , xgene1 , vulcan , octeontx , octeontx81 , octeontx83 , thunderx , thunderxt88 , thunderxt88p1 , thunderxt81 , tsv110 , thunderxt83 , thunderx2t99 , cortex-a57.cortex -a53 , cortex-a72.cortex -a53 , cortex-a73.cortex -a35 , cortex-a73.cortex -a53 , cortex-a75.cortex -a55 , cortex-a76.cortex -a55 native . The values cortex-a57.cortex -a53 , cortex-a72.cortex -a53 , cortex-a73.cortex -a35 , cortex-a73.cortex -a53 , cortex-a75.cortex -a55 , cortex-a76.cortex -a55 specify that GCC should tune for a big.LITTLE system. Additionally on native AArch64 GNU/Linux systems the value native tunes performance to the host system. This option has no effect if the compiler is unable to recognize the processor of the host system. Where none of -mtune= , -mcpu= or -march= are specified, the code is tuned to perform well across a range of target processors. This option cannot be suffixed by feature modifiers.

" -mcpu= name "4 Item "-mcpu=name" Specify the name of the target processor, optionally suffixed by one or more feature modifiers. This option has the form -mcpu= cpu { + [ no ] feature }*,where the permissible values for cpu are the same as those available for -mtune .The permissible values for feature are documented in the sub-section on aarch64-feature -modifiers,, -march and -mcpu FeatureModifiers .Where conflicting feature modifiers are specified, the right-most feature is used. GCCuses name to determine what kind of instructions it can emit when generating assembly code (as if by -march )and to determine the target processor for which to tune for performance (as if by -mtune ).Where this option is used in conjunction with -march or -mtune ,those options take precedence over the appropriate part of this option.

" -moverride= string "4 Item "-moverride=string" Override tuning decisions made by the back-end in response to a -mtune= switch. The syntax, semantics, and accepted values for string in this option are not guaranteed to be consistent across releases. This option is only intended to be useful when developing GCC.

" -mverbose -cost -dump "4 Item "-mverbose-cost-dump" Enable verbose cost model dumping in the debug dump files. This option is provided for use in debugging the compiler.

" -mpc -relative -literal -loads "4 Item "-mpc-relative-literal-loads" 0

" -mno -pc -relative -literal -loads "4 Item "-mno-pc-relative-literal-loads" Enable or disable PC-relative literal loads. With this option literal pools are accessed using a single instruction and emitted after each function. This limits the maximum size of functions to 1MB. This is enabled by default for -mcmodel=tiny .

" -msign -return -address= scope "4 Item "-msign-return-address=scope" Select the function scope on which return address signing will be applied. Permissible values are none ,which disables return address signing, non-leaf ,which enables pointer signing for functions which are not leaf functions, and all ,which enables pointer signing for all functions. The default value is none .This option has been deprecated by -mbranch -protection.

" -mbranch -protection= none | standard | pac-ret [+ leaf ]| bti "4 Item "-mbranch-protection=none|standard|pac-ret[+leaf]|bti" Select the branch protection features to use. none is the default and turns off all types of branch protection. standard turns on all types of branch protection features. If a feature has additional tuning options, then standard sets it to its standard level. pac-ret[+ leaf ] turns on return address signing to its standard level: signing functions that save the return address to memory (non-leaf functions will practically always do this) using the a -key. The optional argument leaf can be used to extend the signing to include leaf functions. bti turns on branch target identification mechanism.

" -msve -vector -bits= bits "4 Item "-msve-vector-bits=bits" Specify the number of bits in an SVEvector register. This option only has an effect when SVEis enabled. GCCsupports two forms of SVEcode generation: (L"vector-length agnostic (R" output that works with any size of vector register and (L"vector-length specific (R" output that allows GCCto make assumptions about the vector length when it is useful for optimization reasons. The possible values of bits are: scalable , 128 , 256 , 512 , 1024 and 2048 . Specifying scalable selects vector-length agnostic output. At present -msve -vector -bits=128 also generates vector-length agnostic output. All other values generate vector-length specific code. The behavior of these values may change in future releases and no value except scalable should be relied on for producing code that is portable across different hardware SVEvector lengths. The default is -msve -vector -bits=scalable ,which produces vector-length agnostic code.

-march and -mcpu Feature Modifiers Subsection "-march and -mcpu Feature Modifiers"

Feature modifiers used with -march and -mcpu can be any of the following and their inverses no feature :

" crc "4 Item "crc" Enable CRCextension. This is on by default for -march=armv8.1 -a .

" crypto "4 Item "crypto" Enable Crypto extension. This also enables Advanced SIMDand floating-point instructions.

" fp "4 Item "fp" Enable floating-point instructions. This is on by default for all possible values for options -march and -mcpu .

" simd "4 Item "simd" Enable Advanced SIMDinstructions. This also enables floating-point instructions. This is on by default for all possible values for options -march and -mcpu .

" sve "4 Item "sve" Enable Scalable Vector Extension instructions. This also enables Advanced SIMDand floating-point instructions.

" lse "4 Item "lse" Enable Large System Extension instructions. This is on by default for -march=armv8.1 -a .

" rdma "4 Item "rdma" Enable Round Double Multiply Accumulate instructions. This is on by default for -march=armv8.1 -a .

" fp16 "4 Item "fp16" Enable FP16extension. This also enables floating-point instructions.

" fp16fml "4 Item "fp16fml" Enable FP16fmla extension. This also enables FP16extensions and floating-point instructions. This option is enabled by default for -march=armv8.4 -a .Use of this option with architectures prior to Armv8.2 -A is not supported.

" rcpc "4 Item "rcpc" Enable the RcPc extension. This does not change code generation from GCC, but is passed on to the assembler, enabling inline asm statements to use instructions from the RcPc extension.

" dotprod "4 Item "dotprod" Enable the Dot Product extension. This also enables Advanced SIMDinstructions.

" aes "4 Item "aes" Enable the Armv8 -a aes and pmull crypto extension. This also enables Advanced SIMDinstructions.

" sha2 "4 Item "sha2" Enable the Armv8 -a sha2 crypto extension. This also enables Advanced SIMDinstructions.

" sha3 "4 Item "sha3" Enable the sha512 and sha3 crypto extension. This also enables Advanced SIMD instructions. Use of this option with architectures prior to Armv8.2 -A is not supported.

" sm4 "4 Item "sm4" Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMDinstructions. Use of this option with architectures prior to Armv8.2 -A is not supported.

" profile "4 Item "profile" Enable the Statistical Profiling extension. This option is only to enable the extension at the assembler level and does not affect code generation.

" rng "4 Item "rng" Enable the Armv8.5 -a Random Number instructions. This option is only to enable the extension at the assembler level and does not affect code generation.

" memtag "4 Item "memtag" Enable the Armv8.5 -a Memory Tagging Extensions. This option is only to enable the extension at the assembler level and does not affect code generation.

" sb "4 Item "sb" Enable the Armv8 -a Speculation Barrier instruction. This option is only to enable the extension at the assembler level and does not affect code generation. This option is enabled by default for -march=armv8.5 -a .

" ssbs "4 Item "ssbs" Enable the Armv8 -a Speculative Store Bypass Safe instruction. This option is only to enable the extension at the assembler level and does not affect code generation. This option is enabled by default for -march=armv8.5 -a .

" predres "4 Item "predres" Enable the Armv8 -a Execution and Data Prediction Restriction instructions. This option is only to enable the extension at the assembler level and does not affect code generation. This option is enabled by default for -march=armv8.5 -a .

Feature crypto implies aes , sha2 ,and simd , which implies fp . Conversely, nofp implies nosimd ,which implies nocrypto , noaes and nosha2 .

AdaptevaEpiphany Options Subsection "Adapteva Epiphany Options"

These -m options are defined for Adapteva Epiphany:

" -mhalf -reg -file "4 Item "-mhalf-reg-file" Don't allocate any register in the range CW(C`r32 (C' ... CW(C`r63 (C' . That allows code to run on hardware variants that lack these registers.

" -mprefer -short -insn -regs "4 Item "-mprefer-short-insn-regs" Preferentially allocate registers that allow short instruction generation. This can result in increased instruction count, so this may either reduce or increase overall code size.

" -mbranch -cost= num "4 Item "-mbranch-cost=num" Set the cost of branches to roughly num (L"simple (R" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases.

" -mcmove "4 Item "-mcmove" Enable the generation of conditional moves.

" -mnops= num "4 Item "-mnops=num" Emit num NOPs before every other generated instruction.

" -mno -soft -cmpsf "4 Item "-mno-soft-cmpsf" For single-precision floating-point comparisons, emit an CW(C`fsub (C' instruction and test the flags. This is faster than a software comparison, but can get incorrect results in the presence of NaNs, or when two different small numbers are compared such that their difference is calculated as zero. The default is -msoft -cmpsf ,which uses slower, but IEEE-compliant, software comparisons.

" -mstack -offset= num "4 Item "-mstack-offset=num" Set the offset between the top of the stack and the stack pointer. E.g., a value of 8 means that the eight bytes in the range CW(C`sp+0...sp+7 (C' can be used by leaf functions without stack allocation. Values other than 8 or 16 are untested and unlikely to work. Note also that this option changes the ABI;compiling a program with a different stack offset than the libraries have been compiled with generally does not work. This option can be useful if you want to evaluate if a different stack offset would give you better code, but to actually use a different stack offset to build working programs, it is recommended to configure the toolchain with the appropriate --with -stack -offset= num option.

" -mno -round -nearest "4 Item "-mno-round-nearest" Make the scheduler assume that the rounding mode has been set to truncating. The default is -mround -nearest .

" -mlong -calls "4 Item "-mlong-calls" If not otherwise specified by an attribute, assume all calls might be beyond the offset range of the CW(C`b (C' / CW(C`bl (C' instructions, and therefore load the function address into a register before performing a (otherwise direct) call. This is the default.

" -mshort -calls "4 Item "-mshort-calls" If not otherwise specified by an attribute, assume all direct calls are in the range of the CW(C`b (C' / CW(C`bl (C' instructions, so use these instructions for direct calls. The default is -mlong -calls .

" -msmall16 "4 Item "-msmall16" Assume addresses can be loaded as 16 -bit unsigned values. This does not apply to function addresses for which -mlong -calls semantics are in effect.

" -mfp -mode= mode "4 Item "-mfp-mode=mode" Set the prevailing mode of the floating-point unit. This determines the floating-point mode that is provided and expected at function call and return time. Making this mode match the mode you predominantly need at function start can make your programs smaller and faster by avoiding unnecessary mode switches. mode can be set to one the following values:

" caller "4 Item "caller" Any mode at function entry is valid, and retained or restored when the function returns, and when it calls other functions. This mode is useful for compiling libraries or other compilation units you might want to incorporate into different programs with different prevailing FPUmodes, and the convenience of being able to use a single object file outweighs the size and speed overhead for any extra mode switching that might be needed, compared with what would be needed with a more specific choice of prevailing FPUmode.

" truncate "4 Item "truncate" This is the mode used for floating-point calculations with truncating (i.e. round towards zero) rounding mode. That includes conversion from floating point to integer.

" round-nearest "4 Item "round-nearest" This is the mode used for floating-point calculations with round-to-nearest-or-even rounding mode.

" int "4 Item "int" This is the mode used to perform integer calculations in the FPU,e.g. integer multiply, or integer multiply-and-accumulate. The default is -mfp -mode=caller

" -mno -split -lohi "4 Item "-mno-split-lohi" 0

" -mno -postinc "4 Item "-mno-postinc"

" -mno -postmodify "4 Item "-mno-postmodify" Code generation tweaks that disable, respectively, splitting of 32 -bit loads, generation of post-increment addresses, and generation of post-modify addresses. The defaults are msplit-lohi , -mpost -inc ,and -mpost -modify .

" -mnovect -double "4 Item "-mnovect-double" Change the preferred SIMDmode to SImode. The default is -mvect -double ,which uses DImode as preferred SIMDmode.

" -max -vect -align= num "4 Item "-max-vect-align=num" The maximum alignment for SIMDvector mode types. num may be 4 or 8. The default is 8. Note that this is an ABIchange, even though many library function interfaces are unaffected if they don't use SIMDvector modes in places that affect size and/or alignment of relevant types.

" -msplit -vecmove -early "4 Item "-msplit-vecmove-early" Split vector moves into single word moves before reload. In theory this can give better register allocation, but so far the reverse seems to be generally the case.

" -m1reg - reg "4 Item "-m1reg-reg" Specify a register to hold the constant -1, which makes loading small negative constants and certain bitmasks faster. Allowable values for reg are r43 and r63 , which specify use of that register as a fixed register, and none ,which means that no register is used for this purpose. The default is -m1reg -none .

AMDGCN Options Subsection "AMD GCN Options"

These options are defined specifically for the AMDGCN port.

" -march= gpu "4 Item "-march=gpu" 0

" -mtune= gpu "4 Item "-mtune=gpu" Set architecture type or tuning for gpu .Supported values for gpu are

" fiji "4 Item "fiji" Compile for GCN3Fiji devices (gfx803).

" gfx900 "4 Item "gfx900" Compile for GCN5Vega 10 devices (gfx900).

" -mstack -size= bytes "4 Item "-mstack-size=bytes" Specify how many bytes of stack space will be requested for each GPU thread (wave-front). Beware that there may be many threads and limited memory available. The size of the stack allocation may also have an impact on run-time performance. The default is 32KB when using OpenACC or OpenMP, and 1MB otherwise.

ARCOptions Subsection "ARC Options"

The following options control the architecture variant for which code is being compiled:

" -mbarrel -shifter "4 Item "-mbarrel-shifter" Generate instructions supported by barrel shifter. This is the default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.

" -mjli -always "4 Item "-mjli-always" Force to call a function using jli_s instruction. This option is valid only for ARCv2 architecture.

" -mcpu= cpu "4 Item "-mcpu=cpu" Set architecture type, register usage, and instruction scheduling parameters for cpu .There are also shortcut alias options available for backward compatibility and convenience. Supported values for cpu are

" arc600 "4 Item "arc600" Compile for ARC600.Aliases: -mA6 , -mARC600 .

" arc601 "4 Item "arc601" Compile for ARC601.Alias: -mARC601 .

" arc700 "4 Item "arc700" Compile for ARC700.Aliases: -mA7 , -mARC700 . This is the default when configured with --with -cpu=arc700 .

" arcem "4 Item "arcem" Compile for ARCEM.

" archs "4 Item "archs" Compile for ARCHS.

" em "4 Item "em" Compile for ARCEM CPU with no hardware extensions.

" em4 "4 Item "em4" Compile for ARCEM4 CPU.

" em4_dmips "4 Item "em4_dmips" Compile for ARCEM4 DMIPS CPU.

" em4_fpus "4 Item "em4_fpus" Compile for ARCEM4 DMIPS CPU with the single-precision floating-point extension.

" em4_fpuda "4 Item "em4_fpuda" Compile for ARCEM4 DMIPS CPU with single-precision floating-point and double assist instructions.

" hs "4 Item "hs" Compile for ARCHS CPU with no hardware extensions except the atomic instructions.

" hs34 "4 Item "hs34" Compile for ARCHS34 CPU.

" hs38 "4 Item "hs38" Compile for ARCHS38 CPU.

" hs38_linux "4 Item "hs38_linux" Compile for ARCHS38 CPU with all hardware extensions on.

" arc600_norm "4 Item "arc600_norm" Compile for ARC600 CPU with CW(C`norm (C' instructions enabled.

" arc600_mul32x16 "4 Item "arc600_mul32x16" Compile for ARC600 CPU with CW(C`norm (C' and 32x16 -bit multiply instructions enabled.

" arc600_mul64 "4 Item "arc600_mul64" Compile for ARC600 CPU with CW(C`norm (C' and CW(C`mul64 (C' -family instructions enabled.

" arc601_norm "4 Item "arc601_norm" Compile for ARC601 CPU with CW(C`norm (C' instructions enabled.

" arc601_mul32x16 "4 Item "arc601_mul32x16" Compile for ARC601 CPU with CW(C`norm (C' and 32x16 -bit multiply instructions enabled.

" arc601_mul64 "4 Item "arc601_mul64" Compile for ARC601 CPU with CW(C`norm (C' and CW(C`mul64 (C' -family instructions enabled.

" nps400 "4 Item "nps400" Compile for ARC700 on NPS400chip.

" em_mini "4 Item "em_mini" Compile for ARCEM minimalist configuration featuring reduced register set.

" -mdpfp "4 Item "-mdpfp" 0

" -mdpfp -compact "4 Item "-mdpfp-compact" Generate double-precision FPXinstructions, tuned for the compact implementation.

" -mdpfp -fast "4 Item "-mdpfp-fast" Generate double-precision FPXinstructions, tuned for the fast implementation.

" -mno -dpfp -lrsr "4 Item "-mno-dpfp-lrsr" Disable CW(C`lr (C' and CW(C`sr (C' instructions from using FPXextension aux registers.

" -mea "4 Item "-mea" Generate extended arithmetic instructions. Currently only CW(C`divaw (C' , CW(C`adds (C' , CW(C`subs (C' ,and CW(C`sat16 (C' are supported. This is always enabled for -mcpu=ARC700 .

" -mno -mpy "4 Item "-mno-mpy" Do not generate CW(C`mpy (C' -family instructions for ARC700.This option is deprecated.

" -mmul32x16 "4 Item "-mmul32x16" Generate 32x16 -bit multiply and multiply-accumulate instructions.

" -mmul64 "4 Item "-mmul64" Generate CW(C`mul64 (C' and CW(C`mulu64 (C' instructions. Only valid for -mcpu=ARC600 .

" -mnorm "4 Item "-mnorm" Generate CW(C`norm (C' instructions. This is the default if -mcpu=ARC700 is in effect.

" -mspfp "4 Item "-mspfp" 0

" -mspfp -compact "4 Item "-mspfp-compact" Generate single-precision FPXinstructions, tuned for the compact implementation.

" -mspfp -fast "4 Item "-mspfp-fast" Generate single-precision FPXinstructions, tuned for the fast implementation.

" -msimd "4 Item "-msimd" Enable generation of ARCSIMD instructions via target-specific builtins. Only valid for -mcpu=ARC700 .

" -msoft -float "4 Item "-msoft-float" This option ignored; it is provided for compatibility purposes only. Software floating-point code is emitted by default, and this default can overridden by FPXoptions; -mspfp , -mspfp -compact ,or -mspfp -fast for single precision, and -mdpfp , -mdpfp -compact ,or -mdpfp -fast for double precision.

" -mswap "4 Item "-mswap" Generate CW(C`swap (C' instructions.

" -matomic "4 Item "-matomic" This enables use of the locked load/store conditional extension to implement atomic memory built-in functions. Not available for ARC6xx or ARC EM cores.

" -mdiv -rem "4 Item "-mdiv-rem" Enable CW(C`div (C' and CW(C`rem (C' instructions for ARCv2 cores.

" -mcode -density "4 Item "-mcode-density" Enable code density instructions for ARCEM. This option is on by default for ARCHS.

" -mll64 "4 Item "-mll64" Enable double load/store operations for ARCHS cores.

" -mtp -regno= regno "4 Item "-mtp-regno=regno" Specify thread pointer register number.

" -mmpy -option= multo "4 Item "-mmpy-option=multo" Compile ARCv2 code with a multiplier design option. You can specify the option using either a string or numeric value for multo . wlh1 is the default value. The recognized values are:

" 0 "4 Item "0" 0

" none "4 Item "none" No multiplier available.

" 1 "4 Item "1" 0

" w "4 Item "w" 16x16 multiplier, fully pipelined. The following instructions are enabled: CW(C`mpyw (C' and CW(C`mpyuw (C' .

" 2 "4 Item "2" 0

" wlh1 "4 Item "wlh1" 32x32 multiplier, fully pipelined (1 stage). The following instructions are additionally enabled: CW(C`mpy (C' , CW(C`mpyu (C' , CW(C`mpym (C' , CW(C`mpymu (C' ,and CW(C`mpy_s (C' .

" 3 "4 Item "3" 0

" wlh2 "4 Item "wlh2" 32x32 multiplier, fully pipelined (2 stages). The following instructions are additionally enabled: CW(C`mpy (C' , CW(C`mpyu (C' , CW(C`mpym (C' , CW(C`mpymu (C' ,and CW(C`mpy_s (C' .

" 4 "4 Item "4" 0

" wlh3 "4 Item "wlh3" Two 16x16 multipliers, blocking, sequential. The following instructions are additionally enabled: CW(C`mpy (C' , CW(C`mpyu (C' , CW(C`mpym (C' , CW(C`mpymu (C' ,and CW(C`mpy_s (C' .

" 5 "4 Item "5" 0

" wlh4 "4 Item "wlh4" One 16x16 multiplier, blocking, sequential. The following instructions are additionally enabled: CW(C`mpy (C' , CW(C`mpyu (C' , CW(C`mpym (C' , CW(C`mpymu (C' ,and CW(C`mpy_s (C' .

" 6 "4 Item "6" 0

" wlh5 "4 Item "wlh5" One 32x4 multiplier, blocking, sequential. The following instructions are additionally enabled: CW(C`mpy (C' , CW(C`mpyu (C' , CW(C`mpym (C' , CW(C`mpymu (C' ,and CW(C`mpy_s (C' .

" 7 "4 Item "7" 0

" plus_dmpy "4 Item "plus_dmpy" ARCHS SIMD support.

" 8 "4 Item "8" 0

" plus_macd "4 Item "plus_macd" ARCHS SIMD support.

" 9 "4 Item "9" 0

" plus_qmacw "4 Item "plus_qmacw" ARCHS SIMD support. This option is only available for ARCv2 cores.

" -mfpu= fpu "4 Item "-mfpu=fpu" Enables support for specific floating-point hardware extensions for ARCv2 cores. Supported values for fpu are:

" fpus "4 Item "fpus" Enables support for single-precision floating-point hardware extensions.

" fpud "4 Item "fpud" Enables support for double-precision floating-point hardware extensions. The single-precision floating-point extension is also enabled. Not available for ARCEM.

" fpuda "4 Item "fpuda" Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point extension is also enabled. This option is only available for ARCEM.

" fpuda_div "4 Item "fpuda_div" Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point, square-root, and divide extensions are also enabled. This option is only available for ARCEM.

" fpuda_fma "4 Item "fpuda_fma" Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. The single-precision floating-point and fused multiply and add hardware extensions are also enabled. This option is only available for ARCEM.

" fpuda_all "4 Item "fpuda_all" Enables support for double-precision floating-point hardware extensions using double-precision assist instructions. All single-precision floating-point hardware extensions are also enabled. This option is only available for ARCEM.

" fpus_div "4 Item "fpus_div" Enables support for single-precision floating-point, square-root and divide hardware extensions.

" fpud_div "4 Item "fpud_div" Enables support for double-precision floating-point, square-root and divide hardware extensions. This option includes option fpus_div .Not available for ARCEM.

" fpus_fma "4 Item "fpus_fma" Enables support for single-precision floating-point and fused multiply and add hardware extensions.

" fpud_fma "4 Item "fpud_fma" Enables support for double-precision floating-point and fused multiply and add hardware extensions. This option includes option fpus_fma .Not available for ARCEM.

" fpus_all "4 Item "fpus_all" Enables support for all single-precision floating-point hardware extensions.

" fpud_all "4 Item "fpud_all" Enables support for all single -and double-precision floating-point hardware extensions. Not available for ARCEM.

" -mirq -ctrl -saved= register-range , blink , lp_count "4 Item "-mirq-ctrl-saved=register-range, blink, lp_count" Specifies general-purposes registers that the processor automatically saves/restores on interrupt entry and exit. register-range is specified as two registers separated by a dash. The register range always starts with CW(C`r0 (C' ,the upper limit is CW(C`fp (C' register. blink and lp_count are optional. This option is only valid for ARCEM and ARCHS cores.

" -mrgf -banked -regs= number "4 Item "-mrgf-banked-regs=number" Specifies the number of registers replicated in second register bank on entry to fast interrupt. Fast interrupts are interrupts with the highest priority level P0. These interrupts save only PCand STATUS32 registers to avoid memory transactions during interrupt entry and exit sequences. Use this option when you are using fast interrupts in an ARCV2 family processor. Permitted values are 4, 8, 16, and 32.

" -mlpc -width= width "4 Item "-mlpc-width=width" Specify the width of the CW(C`lp_count (C' register. Valid values for width are 8, 16, 20, 24, 28 and 32 bits. The default width is fixed to 32 bits. If the width is less than 32, the compiler does not attempt to transform loops in your program to use the zero-delay loop mechanism unless it is known that the CW(C`lp_count (C' register can hold the required loop-counter value. Depending on the width specified, the compiler and run-time library might continue to use the loop mechanism for various needs. This option defines macro CW(C`_ _ARC_LPC_WIDTH_ _ (C' with the value of width .

" -mrf16 "4 Item "-mrf16" This option instructs the compiler to generate code for a 16 -entry register file. This option defines the CW(C`_ _ARC_RF16_ _ (C' preprocessor macro.

" -mbranch -index "4 Item "-mbranch-index" Enable use of CW(C`bi (C' or CW(C`bih (C' instructions to implement jump tables.

The following options are passed through to the assembler, and also define preprocessor macro symbols.

" -mdsp -packa "4 Item "-mdsp-packa" Passed down to the assembler to enable the DSPPack A extensions. Also sets the preprocessor symbol CW(C`_ _Xdsp_packa (C' .This option is deprecated.

" -mdvbf "4 Item "-mdvbf" Passed down to the assembler to enable the dual Viterbi butterfly extension. Also sets the preprocessor symbol CW(C`_ _Xdvbf (C' .This option is deprecated.

" -mlock "4 Item "-mlock" Passed down to the assembler to enable the locked load/store conditional extension. Also sets the preprocessor symbol CW(C`_ _Xlock (C' .

" -mmac -d16 "4 Item "-mmac-d16" Passed down to the assembler. Also sets the preprocessor symbol CW(C`_ _Xxmac_d16 (C' .This option is deprecated.

" -mmac -24 "4 Item "-mmac-24" Passed down to the assembler. Also sets the preprocessor symbol CW(C`_ _Xxmac_24 (C' .This option is deprecated.

" -mrtsc "4 Item "-mrtsc" Passed down to the assembler to enable the 64 -bit time-stamp counter extension instruction. Also sets the preprocessor symbol CW(C`_ _Xrtsc (C' .This option is deprecated.

" -mswape "4 Item "-mswape" Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol CW(C`_ _Xswape (C' .

" -mtelephony "4 Item "-mtelephony" Passed down to the assembler to enable dual -and single-operand instructions for telephony. Also sets the preprocessor symbol CW(C`_ _Xtelephony (C' .This option is deprecated.

" -mxy "4 Item "-mxy" Passed down to the assembler to enable the XYmemory extension. Also sets the preprocessor symbol CW(C`_ _Xxy (C' .

The following options control how the assembly code is annotated:

" -misize "4 Item "-misize" Annotate assembler instructions with estimated addresses.

" -mannotate -align "4 Item "-mannotate-align" Explain what alignment considerations lead to the decision to make an instruction short or long.

The following options are passed through to the linker:

" -marclinux "4 Item "-marclinux" Passed through to the linker, to specify use of the CW(C`arclinux (C' emulation. This option is enabled by default in tool chains built for CW(C`arc -linux -uclibc (C' and CW(C`arceb -linux -uclibc (C' targets when profiling is not requested.

" -marclinux_prof "4 Item "-marclinux_prof" Passed through to the linker, to specify use of the CW(C`arclinux_prof (C' emulation. This option is enabled by default in tool chains built for CW(C`arc -linux -uclibc (C' and CW(C`arceb -linux -uclibc (C' targets when profiling is requested.

The following options control the semantics of generated code:

" -mlong -calls "4 Item "-mlong-calls" Generate calls as register indirect calls, thus providing access to the full 32 -bit address range.

" -mmedium -calls "4 Item "-mmedium-calls" Don't use less than 25 -bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution of function calls is suppressed, to allow use of the 25 -bit range, rather than the 21 -bit range with conditional branch-and-link. This is the default for tool chains built for CW(C`arc -linux -uclibc (C' and CW(C`arceb -linux -uclibc (C' targets.

" -G num "4 Item "-G num" Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. The default value of num is 4 for any ARCconfiguration, or 8 when we have double load/store operations.

" -mno -sdata "4 Item "-mno-sdata" Do not generate sdata references. This is the default for tool chains built for CW(C`arc -linux -uclibc (C' and CW(C`arceb -linux -uclibc (C' targets.

" -mvolatile -cache "4 Item "-mvolatile-cache" Use ordinarily cached memory accesses for volatile references. This is the default.

" -mno -volatile -cache "4 Item "-mno-volatile-cache" Enable cache bypass for volatile references.

The following options fine tune code generation:

" -malign -call "4 Item "-malign-call" Do alignment optimizations for call instructions.

" -mauto -modify -reg "4 Item "-mauto-modify-reg" Enable the use of pre/post modify with register displacement.

" -mbbit -peephole "4 Item "-mbbit-peephole" Enable bbit peephole2.

" -mno -brcc "4 Item "-mno-brcc" This option disables a target-specific pass in arc_reorg to generate compare-and-branch ( CW(C`br CIcc CW(C' )instructions. It has no effect on generation of these instructions driven by the combiner pass.

" -mcase -vector -pcrel "4 Item "-mcase-vector-pcrel" Use PC-relative switch case tables to enable case table shortening. This is the default for -Os .

" -mcompact -casesi "4 Item "-mcompact-casesi" Enable compact CW(C`casesi (C' pattern. This is the default for -Os , and only available for ARCv1 cores. This option is deprecated.

" -mno -cond -exec "4 Item "-mno-cond-exec" Disable the ARCompact-specific pass to generate conditional execution instructions. Due to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARCport has kept a special pass around that tries to find more conditional execution generation opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable offset range because they are conditionalized, you should consider using -mmedium -calls instead.

" -mearly -cbranchsi "4 Item "-mearly-cbranchsi" Enable pre-reload use of the CW(C`cbranchsi (C' pattern.

" -mexpand -adddi "4 Item "-mexpand-adddi" Expand CW(C`adddi3 (C' and CW(C`subdi3 (C' at RTLgeneration time into CW(C`add.f (C' , CW(C`adc (C' etc. This option is deprecated.

" -mindexed -loads "4 Item "-mindexed-loads" Enable the use of indexed loads. This can be problematic because some optimizers then assume that indexed stores exist, which is not the case.

" -mlra "4 Item "-mlra" Enable Local Register Allocation. This is still experimental for ARC, so by default the compiler uses standard reload (i.e. -mno -lra ).

" -mlra -priority -none "4 Item "-mlra-priority-none" Don't indicate any priority for target registers.

" -mlra -priority -compact "4 Item "-mlra-priority-compact" Indicate target register priority for r0..r3 / r12..r15.

" -mlra -priority -noncompact "4 Item "-mlra-priority-noncompact" Reduce target register priority for r0..r3 / r12..r15.

" -mmillicode "4 Item "-mmillicode" When optimizing for size (using -Os ),prologues and epilogues that have to save or restore a large number of registers are often shortened by using call to a special function in libgcc; this is referred to as a millicode call. As these calls can pose performance issues, and/or cause linking issues when linking in a nonstandard way, this option is provided to turn on or off millicode call generation.

" -mcode -density -frame "4 Item "-mcode-density-frame" This option enable the compiler to emit CW(C`enter (C' and CW(C`leave (C' instructions. These instructions are only valid for CPUs with code-density feature.

" -mmixed -code "4 Item "-mmixed-code" Tweak register allocation to help 16 -bit instruction generation. This generally has the effect of decreasing the average instruction size while increasing the instruction count.

" -mq -class "4 Item "-mq-class" Enable q instruction alternatives. This is the default for -Os .

" -mRcq "4 Item "-mRcq" Enable Rcq constraint handling. Most short code generation depends on this. This is the default.

" -mRcw "4 Item "-mRcw" Enable Rcw constraint handling. Most ccfsm condexec mostly depends on this. This is the default.

" -msize -level= level "4 Item "-msize-level=level" Fine-tune size optimization with regards to instruction lengths and alignment. The recognized values for level are:

" 0 "4 Item "0" No size optimization. This level is deprecated and treated like 1 .

" 1 "4 Item "1" Short instructions are used opportunistically.

" 2 "4 Item "2" In addition, alignment of loops and of code after barriers are dropped.

" 3 "4 Item "3" In addition, optional data alignment is dropped, and the option Os is enabled. This defaults to 3 when -Os is in effect. Otherwise, the behavior when this is not set is equivalent to level 1 .

" -mtune= cpu "4 Item "-mtune=cpu" Set instruction scheduling parameters for cpu ,overriding any implied by -mcpu= . Supported values for cpu are

" ARC600 "4 Item "ARC600" Tune for ARC600CPU.

" ARC601 "4 Item "ARC601" Tune for ARC601CPU.

" ARC700 "4 Item "ARC700" Tune for ARC700CPU with standard multiplier block.

" ARC700-xmac "4 Item "ARC700-xmac" Tune for ARC700CPU with XMACblock.

" ARC725D "4 Item "ARC725D" Tune for ARC725DCPU.

" ARC750D "4 Item "ARC750D" Tune for ARC750DCPU.

" -mmultcost= num "4 Item "-mmultcost=num" Cost to assume for a multiply instruction, with 4 being equal to a normal instruction.

" -munalign -prob -threshold= probability "4 Item "-munalign-prob-threshold=probability" Set probability threshold for unaligning branches. When tuning for ARC700 and optimizing for speed, branches without filled delay slot are preferably emitted unaligned and long, unless profiling indicates that the probability for the branch to be taken is below probability . The default is ( REG_BR_PROB_BASE/2),i.e. 5000.

The following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release:

" -margonaut "4 Item "-margonaut" Obsolete FPX.

" -mbig -endian "4 Item "-mbig-endian" 0

" -EB "4 Item "-EB" Compile code for big-endian targets. Use of these options is now deprecated. Big-endian code is supported by configuring GCCto build CW(C`arceb -elf32 (C' and CW(C`arceb -linux -uclibc (C' targets, for which big endian is the default.

" -mlittle -endian "4 Item "-mlittle-endian" 0

" -EL "4 Item "-EL" Compile code for little-endian targets. Use of these options is now deprecated. Little-endian code is supported by configuring GCCto build CW(C`arc -elf32 (C' and CW(C`arc -linux -uclibc (C' targets, for which little endian is the default.

" -mbarrel_shifter "4 Item "-mbarrel_shifter" Replaced by -mbarrel -shifter .

" -mdpfp_compact "4 Item "-mdpfp_compact" Replaced by -mdpfp -compact .

" -mdpfp_fast "4 Item "-mdpfp_fast" Replaced by -mdpfp -fast .

" -mdsp_packa "4 Item "-mdsp_packa" Replaced by -mdsp -packa .

" -mEA "4 Item "-mEA" Replaced by -mea .

" -mmac_24 "4 Item "-mmac_24" Replaced by -mmac -24 .

" -mmac_d16 "4 Item "-mmac_d16" Replaced by -mmac -d16 .

" -mspfp_compact "4 Item "-mspfp_compact" Replaced by -mspfp -compact .

" -mspfp_fast "4 Item "-mspfp_fast" Replaced by -mspfp -fast .

" -mtune= cpu "4 Item "-mtune=cpu" Values arc600 , arc601 , arc700 and arc700-xmac for cpu are replaced by ARC600 , ARC601 , ARC700 and ARC700-xmac respectively.

" -multcost= num "4 Item "-multcost=num" Replaced by -mmultcost .

ARMOptions Subsection "ARM Options"

These -m options are defined for the ARMport:

" -mabi= name "4 Item "-mabi=name" Generate code for the specified ABI.Permissible values are: apcs-gnu , atpcs , aapcs , aapcs-linux and iwmmxt .

" -mapcs -frame "4 Item "-mapcs-frame" Generate a stack frame that is compliant with the ARMProcedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying -fomit -frame -pointer with this option causes the stack frames not to be generated for leaf functions. The default is -mno -apcs -frame . This option is deprecated.

" -mapcs "4 Item "-mapcs" This is a synonym for -mapcs -frame and is deprecated.

" -mthumb -interwork "4 Item "-mthumb-interwork" Generate code that supports calling between the ARMand Thumb instruction sets. Without this option, on pre -v5 architectures, the two instruction sets cannot be reliably used inside one program. The default is -mno -thumb -interwork ,since slightly larger code is generated when -mthumb -interwork is specified. In AAPCS configurations this option is meaningless.

" -mno -sched -prolog "4 Item "-mno-sched-prolog" Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the function's body. This means that all functions start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start of functions inside an executable piece of code. The default is -msched -prolog .

" -mfloat -abi= name "4 Item "-mfloat-abi=name" Specifies which floating-point ABIto use. Permissible values are: soft , softfp and hard . Specifying soft causes GCCto generate output containing library calls for floating-point operations. softfp allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. hard allows generation of floating-point instructions and uses FPU-specific calling conventions. The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI,and link with a compatible set of libraries.

" -mgeneral -regs -only "4 Item "-mgeneral-regs-only" Generate code which uses only the general-purpose registers. This will prevent the compiler from using floating-point and Advanced SIMDregisters but will not impose any restrictions on the assembler.

" -mlittle -endian "4 Item "-mlittle-endian" Generate code for a processor running in little-endian mode. This is the default for all standard configurations.

" -mbig -endian "4 Item "-mbig-endian" Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor.

" -mbe8 "4 Item "-mbe8" 0

" -mbe32 "4 Item "-mbe32" When linking a big-endian image select between BE8and BE32formats. The option has no effect for little-endian images and is ignored. The default is dependent on the selected target architecture. For ARMv6 and later architectures the default is BE8,for older architectures the default is BE32.BE32format has been deprecated by ARM.

" -march= name [ +extension... ]"4 Item "-march=name[+extension...]" This specifies the name of the target ARMarchitecture. GCCuses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in conjunction with or instead of the -mcpu= option. Permissible names are: armv4t , armv5t , armv5te , armv6 , armv6j , armv6k , armv6kz , armv6t2 , armv6z , armv6zk , armv7 , armv7-a , armv7ve , armv8-a , armv8.1-a , armv8.2-a , armv8.3-a , armv8.4-a , armv8.5-a , armv7-r , armv8-r , armv6-m , armv6s-m , armv7-m , armv7e-m , armv8-m.base , armv8-m.main , iwmmxt and iwmmxt2 . Additionally, the following architectures, which lack support for the Thumb execution state, are recognized but support is deprecated: armv4 . Many of the architectures support extensions. These can be added by appending + extension to the architecture name. Extension options are processed in order and capabilities accumulate. An extension will also enable any necessary base extensions upon which it depends. For example, the +crypto extension will always enable the +simd extension. The exception to the additive construction is for extensions that are prefixed with +no... :these extensions disable the specified option and any other extensions that may depend on the presence of that extension. For example, -march=armv7 -a+simd+nofp+vfpv4 is equivalent to writing -march=armv7 -a+vfpv4 since the +simd option is entirely disabled by the +nofp option that follows it. Most extension names are generically named, but have an effect that is dependent upon the architecture to which it is applied. For example, the +simd option can be applied to both armv7-a and armv8-a architectures, but will enable the original ARMv7 -A Advanced SIMD(Neon) extensions for armv7-a and the ARMv8 -A variant for armv8-a . The table below lists the supported extensions for each architecture. Architectures not mentioned do not support any extensions.

" armv5te "4 Item "armv5te" 0

" armv6 "4 Item "armv6"

" armv6j "4 Item "armv6j"

" armv6k "4 Item "armv6k"

" armv6kz "4 Item "armv6kz"

" armv6t2 "4 Item "armv6t2"

" armv6z "4 Item "armv6z"

" armv6zk "4 Item "armv6zk"

" +fp "4 Item "+fp" The VFPv2 floating-point instructions. The extension +vfpv2 can be used as an alias for this extension.

" +nofp "4 Item "+nofp" Disable the floating-point instructions.

" armv7 "4 Item "armv7" The common subset of the ARMv7 -A, ARMv7 -R and ARMv7 -M architectures.

" +fp "4 Item "+fp" The VFPv3 floating-point instructions, with 16 double-precision registers. The extension +vfpv3-d16 can be used as an alias for this extension. Note that floating-point is not supported by the base ARMv7 -M architecture, but is compatible with both the ARMv7 -A and ARMv7 -R architectures.

" +nofp "4 Item "+nofp" Disable the floating-point instructions.

" armv7-a "4 Item "armv7-a" 0

" +mp "4 Item "+mp" The multiprocessing extension.

" +sec "4 Item "+sec" The security extension.

" +fp "4 Item "+fp" The VFPv3 floating-point instructions, with 16 double-precision registers. The extension +vfpv3-d16 can be used as an alias for this extension.

" +simd "4 Item "+simd" The Advanced SIMD(Neon) v1 and the VFPv3 floating-point instructions. The extensions +neon and +neon-vfpv3 can be used as aliases for this extension.

" +vfpv3 "4 Item "+vfpv3" The VFPv3 floating-point instructions, with 32 double-precision registers.

" +vfpv3-d16 -fp16 "4 Item "+vfpv3-d16-fp16" The VFPv3 floating-point instructions, with 16 double-precision registers and the half-precision floating-point conversion operations.

" +vfpv3-fp16 "4 Item "+vfpv3-fp16" The VFPv3 floating-point instructions, with 32 double-precision registers and the half-precision floating-point conversion operations.

" +vfpv4-d16 "4 Item "+vfpv4-d16" The VFPv4 floating-point instructions, with 16 double-precision registers.

" +vfpv4 "4 Item "+vfpv4" The VFPv4 floating-point instructions, with 32 double-precision registers.

" +neon-fp16 "4 Item "+neon-fp16" The Advanced SIMD(Neon) v1 and the VFPv3 floating-point instructions, with the half-precision floating-point conversion operations.

" +neon-vfpv4 "4 Item "+neon-vfpv4" The Advanced SIMD(Neon) v2 and the VFPv4 floating-point instructions.

" +nosimd "4 Item "+nosimd" Disable the Advanced SIMDinstructions (does not disable floating point).

" +nofp "4 Item "+nofp" Disable the floating-point and Advanced SIMDinstructions.

" armv7ve "4 Item "armv7ve" The extended version of the ARMv7 -A architecture with support for virtualization.

" +fp "4 Item "+fp" The VFPv4 floating-point instructions, with 16 double-precision registers. The extension +vfpv4-d16 can be used as an alias for this extension.

" +simd "4 Item "+simd" The Advanced SIMD(Neon) v2 and the VFPv4 floating-point instructions. The extension +neon-vfpv4 can be used as an alias for this extension.

" +vfpv3-d16 "4 Item "+vfpv3-d16" The VFPv3 floating-point instructions, with 16 double-precision registers.

" +vfpv3 "4 Item "+vfpv3" The VFPv3 floating-point instructions, with 32 double-precision registers.

" +vfpv3-d16 -fp16 "4 Item "+vfpv3-d16-fp16" The VFPv3 floating-point instructions, with 16 double-precision registers and the half-precision floating-point conversion operations.

" +vfpv3-fp16 "4 Item "+vfpv3-fp16" The VFPv3 floating-point instructions, with 32 double-precision registers and the half-precision floating-point conversion operations.

" +vfpv4-d16 "4 Item "+vfpv4-d16" The VFPv4 floating-point instructions, with 16 double-precision registers.

" +vfpv4 "4 Item "+vfpv4" The VFPv4 floating-point instructions, with 32 double-precision registers.

" +neon "4 Item "+neon" The Advanced SIMD(Neon) v1 and the VFPv3 floating-point instructions. The extension +neon-vfpv3 can be used as an alias for this extension.

" +neon-fp16 "4 Item "+neon-fp16" The Advanced SIMD(Neon) v1 and the VFPv3 floating-point instructions, with the half-precision floating-point conversion operations.

" +nosimd "4 Item "+nosimd" Disable the Advanced SIMDinstructions (does not disable floating point).

" +nofp "4 Item "+nofp" Disable the floating-point and Advanced SIMDinstructions.

" armv8-a "4 Item "armv8-a" 0

" +crc "4 Item "+crc" The Cyclic Redundancy Check ( CRC)instructions.

" +simd "4 Item "+simd" The ARMv8 -A Advanced SIMDand floating-point instructions.

" +crypto "4 Item "+crypto" The cryptographic instructions.

" +nocrypto "4 Item "+nocrypto" Disable the cryptographic instructions.

" +nofp "4 Item "+nofp" Disable the floating-point, Advanced SIMDand cryptographic instructions.

" +sb "4 Item "+sb" Speculation Barrier Instruction.

" +predres "4 Item "+predres" Execution and Data Prediction Restriction Instructions.

" armv8.1-a "4 Item "armv8.1-a" 0

" +simd "4 Item "+simd" The ARMv8.1 -A Advanced SIMDand floating-point instructions.

" +crypto "4 Item "+crypto" The cryptographic instructions. This also enables the Advanced SIMDand floating-point instructions.

" +nocrypto "4 Item "+nocrypto" Disable the cryptographic instructions.

" +nofp "4 Item "+nofp" Disable the floating-point, Advanced SIMDand cryptographic instructions.

" +sb "4 Item "+sb" Speculation Barrier Instruction.

" +predres "4 Item "+predres" Execution and Data Prediction Restriction Instructions.

" armv8.2-a "4 Item "armv8.2-a" 0

" armv8.3-a "4 Item "armv8.3-a"

" +fp16 "4 Item "+fp16" The half-precision floating-point data processing instructions. This also enables the Advanced SIMDand floating-point instructions.

" +fp16fml "4 Item "+fp16fml" The half-precision floating-point fmla extension. This also enables the half-precision floating-point extension and Advanced SIMDand floating-point instructions.

" +simd "4 Item "+simd" The ARMv8.1 -A Advanced SIMDand floating-point instructions.

" +crypto "4 Item "+crypto" The cryptographic instructions. This also enables the Advanced SIMDand floating-point instructions.

" +dotprod "4 Item "+dotprod" Enable the Dot Product extension. This also enables Advanced SIMDinstructions.

" +nocrypto "4 Item "+nocrypto" Disable the cryptographic extension.

" +nofp "4 Item "+nofp" Disable the floating-point, Advanced SIMDand cryptographic instructions.

" +sb "4 Item "+sb" Speculation Barrier Instruction.

" +predres "4 Item "+predres" Execution and Data Prediction Restriction Instructions.

" armv8.4-a "4 Item "armv8.4-a" 0

" +fp16 "4 Item "+fp16" The half-precision floating-point data processing instructions. This also enables the Advanced SIMDand floating-point instructions as well as the Dot Product extension and the half-precision floating-point fmla extension.

" +simd "4 Item "+simd" The ARMv8.3 -A Advanced SIMDand floating-point instructions as well as the Dot Product extension.

" +crypto "4 Item "+crypto" The cryptographic instructions. This also enables the Advanced SIMDand floating-point instructions as well as the Dot Product extension.

" +nocrypto "4 Item "+nocrypto" Disable the cryptographic extension.

" +nofp "4 Item "+nofp" Disable the floating-point, Advanced SIMDand cryptographic instructions.

" +sb "4 Item "+sb" Speculation Barrier Instruction.

" +predres "4 Item "+predres" Execution and Data Prediction Restriction Instructions.

" armv8.5-a "4 Item "armv8.5-a" 0

" +fp16 "4 Item "+fp16" The half-precision floating-point data processing instructions. This also enables the Advanced SIMDand floating-point instructions as well as the Dot Product extension and the half-precision floating-point fmla extension.

" +simd "4 Item "+simd" The ARMv8.3 -A Advanced SIMDand floating-point instructions as well as the Dot Product extension.

" +crypto "4 Item "+crypto" The cryptographic instructions. This also enables the Advanced SIMDand floating-point instructions as well as the Dot Product extension.

" +nocrypto "4 Item "+nocrypto" Disable the cryptographic extension.

" +nofp "4 Item "+nofp" Disable the floating-point, Advanced SIMDand cryptographic instructions.

" armv7-r "4 Item "armv7-r" 0

" +fp.sp "4 Item "+fp.sp" The single-precision VFPv3 floating-point instructions. The extension +vfpv3xd can be used as an alias for this extension.

" +fp "4 Item "+fp" The VFPv3 floating-point instructions with 16 double-precision registers. The extension +vfpv3 -d16 can be used as an alias for this extension.

" +vfpv3xd-d16 -fp16 "4 Item "+vfpv3xd-d16-fp16" The single-precision VFPv3 floating-point instructions with 16 double-precision registers and the half-precision floating-point conversion operations.

" +vfpv3-d16 -fp16 "4 Item "+vfpv3-d16-fp16" The VFPv3 floating-point instructions with 16 double-precision registers and the half-precision floating-point conversion operations.

" +nofp "4 Item "+nofp" Disable the floating-point extension.

" +idiv "4 Item "+idiv" The ARM-state integer division instructions.

" +noidiv "4 Item "+noidiv" Disable the ARM-state integer division extension.

" armv7e-m "4 Item "armv7e-m" 0

" +fp "4 Item "+fp" The single-precision VFPv4 floating-point instructions.

" +fpv5 "4 Item "+fpv5" The single-precision FPv5 floating-point instructions.

" +fp.dp "4 Item "+fp.dp" The single -and double-precision FPv5 floating-point instructions.

" +nofp "4 Item "+nofp" Disable the floating-point extensions.

" armv8-m.main "4 Item "armv8-m.main" 0

" +dsp "4 Item "+dsp" The DSPinstructions.

" +nodsp "4 Item "+nodsp" Disable the DSPextension.

" +fp "4 Item "+fp" The single-precision floating-point instructions.

" +fp.dp "4 Item "+fp.dp" The single -and double-precision floating-point instructions.

" +nofp "4 Item "+nofp" Disable the floating-point extension.

" armv8-r "4 Item "armv8-r" 0

" +crc "4 Item "+crc" The Cyclic Redundancy Check ( CRC)instructions.

" +fp.sp "4 Item "+fp.sp" The single-precision FPv5 floating-point instructions.

" +simd "4 Item "+simd" The ARMv8 -A Advanced SIMDand floating-point instructions.

" +crypto "4 Item "+crypto" The cryptographic instructions.

" +nocrypto "4 Item "+nocrypto" Disable the cryptographic instructions.

" +nofp "4 Item "+nofp" Disable the floating-point, Advanced SIMDand cryptographic instructions. -march=native causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.

" -mtune= name "4 Item "-mtune=name" This option specifies the name of the target ARMprocessor for which GCCshould tune the performance of the code. For some ARMimplementations better performance can be obtained by using this option. Permissible names are: arm7tdmi , arm7tdmi-s , arm710t , arm720t , arm740t , strongarm , strongarm110 , strongarm1100 ,0 strongarm1110 , arm8 , arm810 , arm9 , arm9e , arm920 , arm920t , arm922t , arm946e-s , arm966e-s , arm968e-s , arm926ej-s , arm940t , arm9tdmi , arm10tdmi , arm1020t , arm1026ej-s , arm10e , arm1020e , arm1022e , arm1136j-s , arm1136jf-s , mpcore , mpcorenovfp , arm1156t2-s , arm1156t2f-s , arm1176jz-s , arm1176jzf-s , generic-armv7 -a , cortex-a5 , cortex-a7 , cortex-a8 , cortex-a9 , cortex-a12 , cortex-a15 , cortex-a17 , cortex-a32 , cortex-a35 , cortex-a53 , cortex-a55 , cortex-a57 , cortex-a72 , cortex-a73 , cortex-a75 , cortex-a76 , ares , cortex-r4 , cortex-r4f , cortex-r5 , cortex-r7 , cortex-r8 , cortex-r52 , cortex-m0 , cortex-m0plus , cortex-m1 , cortex-m3 , cortex-m4 , cortex-m7 , cortex-m23 , cortex-m33 , cortex-m1.small -multiply , cortex-m0.small -multiply , cortex-m0plus.small -multiply , exynos-m1 , marvell-pj4 , neoverse-n1 , xscale , iwmmxt , iwmmxt2 , ep9312 , fa526 , fa626 , fa606te , fa626te , fmp626 , fa726te , xgene1 . Additionally, this option can specify that GCCshould tune the performance of the code for a big.LITTLE system. Permissible names are: cortex-a15.cortex -a7 , cortex-a17.cortex -a7 , cortex-a57.cortex -a53 , cortex-a72.cortex -a53 , cortex-a72.cortex -a35 , cortex-a73.cortex -a53 , cortex-a75.cortex -a55 , cortex-a76.cortex -a55 . -mtune=generic - arch specifies that GCCshould tune the performance for a blend of processors within architecture arch . The aim is to generate code that run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCCversions as CPUmodels come and go. -mtune permits the same extension options as -mcpu ,but the extension options do not affect the tuning of the generated code. -mtune=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.

" -mcpu= name [ +extension... ]"4 Item "-mcpu=name[+extension...]" This specifies the name of the target ARMprocessor. GCCuses this name to derive the name of the target ARMarchitecture (as if specified by -march )and the ARMprocessor type for which to tune for performance (as if specified by -mtune ).Where this option is used in conjunction with -march or -mtune , those options take precedence over the appropriate part of this option. Many of the supported CPUs implement optional architectural extensions. Where this is so the architectural extensions are normally enabled by default. If implementations that lack the extension exist, then the extension syntax can be used to disable those extensions that have been omitted. For floating-point and Advanced SIMD(Neon) instructions, the settings of the options -mfloat -abi and -mfpu must also be considered: floating-point and Advanced SIMDinstructions will only be used if -mfloat -abi is not set to soft ;and any setting of -mfpu other than auto will override the available floating-point and SIMDextension instructions. For example, cortex-a9 can be found in three major configurations: integer only, with just a floating-point unit or with floating-point and Advanced SIMD.The default is to enable all the instructions, but the extensions +nosimd and +nofp can be used to disable just the SIMDor both the SIMDand floating-point instructions respectively. Permissible names for this option are the same as those for -mtune . The following extension options are common to the listed CPUs:

" +nodsp "4 Item "+nodsp" Disable the DSPinstructions on cortex-m33 .

" +nofp "4 Item "+nofp" Disables the floating-point instructions on arm9e , arm946e-s , arm966e-s , arm968e-s , arm10e , arm1020e , arm1022e , arm926ej-s , arm1026ej-s , cortex-r5 , cortex-r7 , cortex-r8 , cortex-m4 , cortex-m7 and cortex-m33 . Disables the floating-point and SIMDinstructions on generic-armv7 -a , cortex-a5 , cortex-a7 , cortex-a8 , cortex-a9 , cortex-a12 , cortex-a15 , cortex-a17 , cortex-a15.cortex -a7 , cortex-a17.cortex -a7 , cortex-a32 , cortex-a35 , cortex-a53 and cortex-a55 .

" +nofp.dp "4 Item "+nofp.dp" Disables the double-precision component of the floating-point instructions on cortex-r5 , cortex-r7 , cortex-r8 , cortex-r52 and cortex-m7 .

" +nosimd "4 Item "+nosimd" Disables the SIMD(but not floating-point) instructions on generic-armv7 -a , cortex-a5 , cortex-a7 and cortex-a9 .

" +crypto "4 Item "+crypto" Enables the cryptographic instructions on cortex-a32 , cortex-a35 , cortex-a53 , cortex-a55 , cortex-a57 , cortex-a72 , cortex-a73 , cortex-a75 , exynos-m1 , xgene1 , cortex-a57.cortex -a53 , cortex-a72.cortex -a53 , cortex-a73.cortex -a35 , cortex-a73.cortex -a53 and cortex-a75.cortex -a55 . Additionally the generic-armv7 -a pseudo target defaults to VFPv3 with 16 double-precision registers. It supports the following extension options: mp , sec , vfpv3-d16 , vfpv3 , vfpv3-d16 -fp16 , vfpv3-fp16 , vfpv4-d16 , vfpv4 , neon , neon-vfpv3 , neon-fp16 , neon-vfpv4 .The meanings are the same as for the extensions to -march=armv7 -a . -mcpu=generic - arch is also permissible, and is equivalent to -march= arch -mtune=generic - arch . See -mtune for more information. -mcpu=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.

" -mfpu= name "4 Item "-mfpu=name" This specifies what floating-point hardware (or hardware emulation) is available on the target. Permissible names are: auto , vfpv2 , vfpv3 , vfpv3-fp16 , vfpv3-d16 , vfpv3-d16 -fp16 , vfpv3xd , vfpv3xd-fp16 , neon-vfpv3 , neon-fp16 , vfpv4 , vfpv4-d16 , fpv4-sp -d16 , neon-vfpv4 , fpv5-d16 , fpv5-sp -d16 , fp-armv8 , neon-fp -armv8 and crypto-neon -fp -armv8 . Note that neon is an alias for neon-vfpv3 and vfp is an alias for vfpv2 . The setting auto is the default and is special. It causes the compiler to select the floating-point and Advanced SIMDinstructions based on the settings of -mcpu and -march . If the selected floating-point hardware includes the NEONextension (e.g. -mfpu=neon ),note that floating-point operations are not generated by GCC'sauto-vectorization pass unless -funsafe -math -optimizations is also specified. This is because NEONhardware does not fully implement the IEEE754 standard for floating-point arithmetic (in particular denormal values are treated as zero), so the use of NEONinstructions may lead to a loss of precision. You can also set the fpu name at function level by using the CW(C`target("fpu=") (C' function attributes or pragmas.

" -mfp16 -format= name "4 Item "-mfp16-format=name" Specify the format of the CW(C`_ _fp16 (C' half-precision floating-point type. Permissible names are none , ieee ,and alternative ; the default is none ,in which case the CW(C`_ _fp16 (C' type is not defined.

" -mstructure -size -boundary= n "4 Item "-mstructure-size-boundary=n" The sizes of all structures and unions are rounded up to a multiple of the number of bits set by this option. Permissible values are 8, 32 and 64. The default value varies for different toolchains. For the COFF targeted toolchain the default value is 8. A value of 64 is only allowed if the underlying ABIsupports it. Specifying a larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions. This option is deprecated.

" -mabort -on -noreturn "4 Item "-mabort-on-noreturn" Generate a call to the function CW(C`abort (C' at the end of a CW(C`noreturn (C' function. It is executed if the function tries to return.

" -mlong -calls "4 Item "-mlong-calls" 0

" -mno -long -calls "4 Item "-mno-long-calls" Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 64 -megabyte addressing range of the offset-based version of subroutine call instruction. Even if this switch is enabled, not all function calls are turned into long calls. The heuristic is that static functions, functions that have the CW(C`short_call (C' attribute, functions that are inside the scope of a CW(C`#pragma no_long_calls (C' directive, and functions whose definitions have already been compiled within the current compilation unit are not turned into long calls. The exceptions to this rule are that weak function definitions, functions with the CW(C`long_call (C' attribute or the CW(C`section (C' attribute, and functions that are within the scope of a CW(C`#pragma long_calls (C' directive are always turned into long calls. This feature is not enabled by default. Specifying -mno -long -calls restores the default behavior, as does placing the function calls within the scope of a CW(C`#pragma long_calls_off (C' directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.

" -msingle -pic -base "4 Item "-msingle-pic-base" Treat the register used for PICaddressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins.

" -mpic -register= reg "4 Item "-mpic-register=reg" Specify the register to be used for PICaddressing. For standard PICbase case, the default is any suitable register determined by compiler. For single PICbase case, the default is R9 if target is EABIbased or stack-checking is enabled, otherwise the default is R10 .

" -mpic -data -is -text -relative "4 Item "-mpic-data-is-text-relative" Assume that the displacement between the text and data segments is fixed at static link time. This permits using PC-relative addressing operations to access data known to be in the data segment. For non-VxWorks RTPtargets, this option is enabled by default. When disabled on such targets, it will enable -msingle -pic -base by default.

" -mpoke -function -name "4 Item "-mpoke-function-name" Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this: 9 t0 .ascii "arm_poke_function_name", 0 .align t1 .word 0xff000000 + (t1 -t0) arm_poke_function_name mov ip, sp stmfd sp!, {fp, ip, lr, pc} sub fp, ip, #4 When performing a stack backtrace, code can inspect the value of CW(C`pc (C' stored at CW(C`fp + 0 (C' .If the trace function then looks at location CW(C`pc -12 (C' and the top 8 bits are set, then we know that there is a function name embedded immediately preceding this location and has length CW(C`((pc[ -3]) & 0xff000000) (C' .

" -mthumb "4 Item "-mthumb" 0

" -marm "4 Item "-marm" Select between generating code that executes in ARMand Thumb states. The default for most configurations is to generate code that executes in ARMstate, but the default can be changed by configuring GCCwith the --with -mode= state configure option. You can also override the ARMand Thumb mode for each function by using the CW(C`target("thumb") (C' and CW(C`target("arm") (C' function attributes or pragmas.

" -mflip -thumb "4 Item "-mflip-thumb" Switch ARM/Thumb modes on alternating functions. This option is provided for regression testing of mixed Thumb/ARM code generation, and is not intended for ordinary use in compiling code.

" -mtpcs -frame "4 Item "-mtpcs-frame" Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno -tpcs -frame .

" -mtpcs -leaf -frame "4 Item "-mtpcs-leaf-frame" Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno -apcs -leaf -frame .

" -mcallee -super -interworking "4 Item "-mcallee-super-interworking" Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest of the function. This allows these functions to be called from non-interworking code. This option is not valid in AAPCSconfigurations because interworking is enabled by default.

" -mcaller -super -interworking "4 Item "-mcaller-super-interworking" Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small overhead in the cost of executing a function pointer if this option is enabled. This option is not valid in AAPCSconfigurations because interworking is enabled by default.

" -mtp= name "4 Item "-mtp=name" Specify the access model for the thread local storage pointer. The valid models are soft ,which generates calls to CW(C`_ _aeabi_read_tp (C' , cp15 ,which fetches the thread pointer from CW(C`cp15 (C' directly (supported in the arm6k architecture), and auto ,which uses the best available method for the selected processor. The default setting is auto .

" -mtls -dialect= dialect "4 Item "-mtls-dialect=dialect" Specify the dialect to use for accessing thread local storage. Two dialect sare supported --- gnu and gnu2 .The gnu dialect selects the original GNUscheme for supporting local and global dynamic TLSmodels. The gnu2 dialect selects the GNUdescriptor scheme, which provides better performance for shared libraries. The GNUdescriptor scheme is compatible with the original scheme, but does require new assembler, linker and library support. Initial and local exec TLSmodels are unaffected by this option and always use the original scheme.

" -mword -relocations "4 Item "-mword-relocations" Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). This is enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and when -fpic or -fPIC is specified. This option conflicts with -mslow -flash -data .

" -mfix -cortex -m3 -ldrd "4 Item "-mfix-cortex-m3-ldrd" Some Cortex -M3 cores can cause data corruption when CW(C`ldrd (C' instructions with overlapping destination and base registers are used. This option avoids generating these instructions. This option is enabled by default when -mcpu=cortex -m3 is specified.

" -munaligned -access "4 Item "-munaligned-access" 0

" -mno -unaligned -access "4 Item "-mno-unaligned-access" Enables (or disables) reading and writing of 16 -and 32 -bit values from addresses that are not 16 -or 32 -bit aligned. By default unaligned access is disabled for all pre -ARMv6, all ARMv6 -M and for ARMv8 -M Baseline architectures, and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures are accessed a byte at a time. The ARMattribute CW(C`Tag_CPU_unaligned_access (C' is set in the generated object file to either true or false, depending upon the setting of this option. If unaligned access is enabled then the preprocessor symbol CW(C`_ _ARM_FEATURE_UNALIGNED (C' is also defined.

" -mneon -for -64bits "4 Item "-mneon-for-64bits" Enables using Neon to handle scalar 64 -bits operations. This is disabled by default since the cost of moving data from core registers to Neon is high.

" -mslow -flash -data "4 Item "-mslow-flash-data" Assume loading data from flash is slower than fetching instruction. Therefore literal load is minimized for better performance. This option is only supported when compiling for ARMv7 M -profile and off by default. It conflicts with -mword -relocations .

" -masm -syntax -unified "4 Item "-masm-syntax-unified" Assume inline assembler is using unified asm syntax. The default is currently off which implies divided syntax. This option has no impact on Thumb2. However, this may change in future releases of GCC. Divided syntax should be considered deprecated.

" -mrestrict -it "4 Item "-mrestrict-it" Restricts generation of ITblocks to conform to the rules of ARMv8 -A. ITblocks can only contain a single 16 -bit instruction from a select set of instructions. This option is on by default for ARMv8 -A Thumb mode.

" -mprint -tune -info "4 Item "-mprint-tune-info" Print CPUtuning information as comment in assembler file. This is an option used only for regression testing of the compiler and not intended for ordinary use in compiling code. This option is disabled by default.

" -mverbose -cost -dump "4 Item "-mverbose-cost-dump" Enable verbose cost model dumping in the debug dump files. This option is provided for use in debugging the compiler.

" -mpure -code "4 Item "-mpure-code" Do not allow constant data to be placed in code sections. Additionally, when compiling for ELFobject format give all text sections the ELFprocessor-specific section attribute CW(C`SHF_ARM_PURECODE (C' .This option is only available when generating non-pic code for M -profile targets with the MOVTinstruction.

" -mcmse "4 Item "-mcmse" Generate secure code as per the (L"ARMv8 -M Security Extensions: Requirements on Development Tools Engineering Specification (R", which can be found on < http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf >.

AVROptions Subsection "AVR Options"

These options are defined for AVRimplementations:

" -mmcu= mcu "4 Item "-mmcu=mcu" Specify Atmel AVRinstruction set architectures ( ISA)or MCUtype. The default for this option is@tie{} avr2 . GCCsupports the following AVRdevices and ISAs: Item "avr2" (L"Classic (R" devices with up to 8@tie{}KiB of program memory. mcu CW@tie {}= CW(C`attiny22 (C' , CW(C`attiny26 (C' , CW(C`at90c8534 (C' , CW(C`at90s2313 (C' , CW(C`at90s2323 (C' , CW(C`at90s2333 (C' , CW(C`at90s2343 (C' , CW(C`at90s4414 (C' , CW(C`at90s4433 (C' , CW(C`at90s4434 (C' , CW(C`at90s8515 (C' , CW(C`at90s8535 (C' . Item "avr25" (L"Classic (R" devices with up to 8@tie{}KiB of program memory and with the CW(C`MOVW (C' instruction. mcu CW@tie {}= CW(C`ata5272 (C' , CW(C`ata6616c (C' , CW(C`attiny13 (C' , CW(C`attiny13a (C' , CW(C`attiny2313 (C' , CW(C`attiny2313a (C' , CW(C`attiny24 (C' , CW(C`attiny24a (C' , CW(C`attiny25 (C' , CW(C`attiny261 (C' , CW(C`attiny261a (C' , CW(C`attiny43u (C' , CW(C`attiny4313 (C' , CW(C`attiny44 (C' , CW(C`attiny44a (C' , CW(C`attiny441 (C' , CW(C`attiny45 (C' , CW(C`attiny461 (C' , CW(C`attiny461a (C' , CW(C`attiny48 (C' , CW(C`attiny828 (C' , CW(C`attiny84 (C' , CW(C`attiny84a (C' , CW(C`attiny841 (C' , CW(C`attiny85 (C' , CW(C`attiny861 (C' , CW(C`attiny861a (C' , CW(C`attiny87 (C' , CW(C`attiny88 (C' , CW(C`at86rf401 (C' . Item "avr3" (L"Classic (R" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory. mcu CW@tie {}= CW(C`at43usb355 (C' , CW(C`at76c711 (C' . Item "avr31" (L"Classic (R" devices with 128@tie{}KiB of program memory. mcu CW@tie {}= CW(C`atmega103 (C' , CW(C`at43usb320 (C' . Item "avr35" (L"Classic (R" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory and with the CW(C`MOVW (C' instruction. mcu CW@tie {}= CW(C`ata5505 (C' , CW(C`ata6617c (C' , CW(C`ata664251 (C' , CW(C`atmega16u2 (C' , CW(C`atmega32u2 (C' , CW(C`atmega8u2 (C' , CW(C`attiny1634 (C' , CW(C`attiny167 (C' , CW(C`at90usb162 (C' , CW(C`at90usb82 (C' . Item "avr4" (L"Enhanced (R" devices with up to 8@tie{}KiB of program memory. mcu CW@tie {}= CW(C`ata6285 (C' , CW(C`ata6286 (C' , CW(C`ata6289 (C' , CW(C`ata6612c (C' , CW(C`atmega48 (C' , CW(C`atmega48a (C' , CW(C`atmega48p (C' , CW(C`atmega48pa (C' , CW(C`atmega48pb (C' , CW(C`atmega8 (C' , CW(C`atmega8a (C' , CW(C`atmega8hva (C' , CW(C`atmega8515 (C' , CW(C`atmega8535 (C' , CW(C`atmega88 (C' , CW(C`atmega88a (C' , CW(C`atmega88p (C' , CW(C`atmega88pa (C' , CW(C`atmega88pb (C' , CW(C`at90pwm1 (C' , CW(C`at90pwm2 (C' , CW(C`at90pwm2b (C' , CW(C`at90pwm3 (C' , CW(C`at90pwm3b (C' , CW(C`at90pwm81 (C' . Item "avr5" (L"Enhanced (R" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory. mcu CW@tie {}= CW(C`ata5702m322 (C' , CW(C`ata5782 (C' , CW(C`ata5790 (C' , CW(C`ata5790n (C' , CW(C`ata5791 (C' , CW(C`ata5795 (C' , CW(C`ata5831 (C' , CW(C`ata6613c (C' , CW(C`ata6614q (C' , CW(C`ata8210 (C' , CW(C`ata8510 (C' , CW(C`atmega16 (C' , CW(C`atmega16a (C' , CW(C`atmega16hva (C' , CW(C`atmega16hva2 (C' , CW(C`atmega16hvb (C' , CW(C`atmega16hvbrevb (C' , CW(C`atmega16m1 (C' , CW(C`atmega16u4 (C' , CW(C`atmega161 (C' , CW(C`atmega162 (C' , CW(C`atmega163 (C' , CW(C`atmega164a (C' , CW(C`atmega164p (C' , CW(C`atmega164pa (C' , CW(C`atmega165 (C' , CW(C`atmega165a (C' , CW(C`atmega165p (C' , CW(C`atmega165pa (C' , CW(C`atmega168 (C' , CW(C`atmega168a (C' , CW(C`atmega168p (C' , CW(C`atmega168pa (C' , CW(C`atmega168pb (C' , CW(C`atmega169 (C' , CW(C`atmega169a (C' , CW(C`atmega169p (C' , CW(C`atmega169pa (C' , CW(C`atmega32 (C' , CW(C`atmega32a (C' , CW(C`atmega32c1 (C' , CW(C`atmega32hvb (C' , CW(C`atmega32hvbrevb (C' , CW(C`atmega32m1 (C' , CW(C`atmega32u4 (C' , CW(C`atmega32u6 (C' , CW(C`atmega323 (C' , CW(C`atmega324a (C' , CW(C`atmega324p (C' , CW(C`atmega324pa (C' , CW(C`atmega325 (C' , CW(C`atmega325a (C' , CW(C`atmega325p (C' , CW(C`atmega325pa (C' , CW(C`atmega3250 (C' , CW(C`atmega3250a (C' , CW(C`atmega3250p (C' , CW(C`atmega3250pa (C' , CW(C`atmega328 (C' , CW(C`atmega328p (C' , CW(C`atmega328pb (C' , CW(C`atmega329 (C' , CW(C`atmega329a (C' , CW(C`atmega329p (C' , CW(C`atmega329pa (C' , CW(C`atmega3290 (C' , CW(C`atmega3290a (C' , CW(C`atmega3290p (C' , CW(C`atmega3290pa (C' , CW(C`atmega406 (C' , CW(C`atmega64 (C' , CW(C`atmega64a (C' , CW(C`atmega64c1 (C' , CW(C`atmega64hve (C' , CW(C`atmega64hve2 (C' , CW(C`atmega64m1 (C' , CW(C`atmega64rfr2 (C' , CW(C`atmega640 (C' , CW(C`atmega644 (C' , CW(C`atmega644a (C' , CW(C`atmega644p (C' , CW(C`atmega644pa (C' , CW(C`atmega644rfr2 (C' , CW(C`atmega645 (C' , CW(C`atmega645a (C' , CW(C`atmega645p (C' , CW(C`atmega6450 (C' , CW(C`atmega6450a (C' , CW(C`atmega6450p (C' , CW(C`atmega649 (C' , CW(C`atmega649a (C' , CW(C`atmega649p (C' , CW(C`atmega6490 (C' , CW(C`atmega6490a (C' , CW(C`atmega6490p (C' , CW(C`at90can32 (C' , CW(C`at90can64 (C' , CW(C`at90pwm161 (C' , CW(C`at90pwm216 (C' , CW(C`at90pwm316 (C' , CW(C`at90scr100 (C' , CW(C`at90usb646 (C' , CW(C`at90usb647 (C' , CW(C`at94k (C' , CW(C`m3000 (C' . Item "avr51" (L"Enhanced (R" devices with 128@tie{}KiB of program memory. mcu CW@tie {}= CW(C`atmega128 (C' , CW(C`atmega128a (C' , CW(C`atmega128rfa1 (C' , CW(C`atmega128rfr2 (C' , CW(C`atmega1280 (C' , CW(C`atmega1281 (C' , CW(C`atmega1284 (C' , CW(C`atmega1284p (C' , CW(C`atmega1284rfr2 (C' , CW(C`at90can128 (C' , CW(C`at90usb1286 (C' , CW(C`at90usb1287 (C' . Item "avr6" (L"Enhanced (R" devices with 3 -byte PC,i.e. with more than 128@tie{}KiB of program memory. mcu CW@tie {}= CW(C`atmega256rfr2 (C' , CW(C`atmega2560 (C' , CW(C`atmega2561 (C' , CW(C`atmega2564rfr2 (C' . Item "avrxmega2" (L" XMEGA(R" devices with more than 8@tie{}KiB and up to 64@tie{}KiB of program memory. mcu CW@tie {}= CW(C`atxmega16a4 (C' , CW(C`atxmega16a4u (C' , CW(C`atxmega16c4 (C' , CW(C`atxmega16d4 (C' , CW(C`atxmega16e5 (C' , CW(C`atxmega32a4 (C' , CW(C`atxmega32a4u (C' , CW(C`atxmega32c3 (C' , CW(C`atxmega32c4 (C' , CW(C`atxmega32d3 (C' , CW(C`atxmega32d4 (C' , CW(C`atxmega32e5 (C' , CW(C`atxmega8e5 (C' . Item "avrxmega3" (L" XMEGA(R" devices with up to 64@tie{}KiB of combined program memory and RAM,and with program memory visible in the RAMaddress space. mcu CW@tie {}= CW(C`attiny1614 (C' , CW(C`attiny1616 (C' , CW(C`attiny1617 (C' , CW(C`attiny212 (C' , CW(C`attiny214 (C' , CW(C`attiny3214 (C' , CW(C`attiny3216 (C' , CW(C`attiny3217 (C' , CW(C`attiny412 (C' , CW(C`attiny414 (C' , CW(C`attiny416 (C' , CW(C`attiny417 (C' , CW(C`attiny814 (C' , CW(C`attiny816 (C' , CW(C`attiny817 (C' . Item "avrxmega4" (L" XMEGA(R" devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program memory. mcu CW@tie {}= CW(C`atxmega64a3 (C' , CW(C`atxmega64a3u (C' , CW(C`atxmega64a4u (C' , CW(C`atxmega64b1 (C' , CW(C`atxmega64b3 (C' , CW(C`atxmega64c3 (C' , CW(C`atxmega64d3 (C' , CW(C`atxmega64d4 (C' . Item "avrxmega5" (L" XMEGA(R" devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program memory and more than 64@tie{}KiB of RAM. mcu CW@tie {}= CW(C`atxmega64a1 (C' , CW(C`atxmega64a1u (C' . Item "avrxmega6" (L" XMEGA(R" devices with more than 128@tie{}KiB of program memory. mcu CW@tie {}= CW(C`atxmega128a3 (C' , CW(C`atxmega128a3u (C' , CW(C`atxmega128b1 (C' , CW(C`atxmega128b3 (C' , CW(C`atxmega128c3 (C' , CW(C`atxmega128d3 (C' , CW(C`atxmega128d4 (C' , CW(C`atxmega192a3 (C' , CW(C`atxmega192a3u (C' , CW(C`atxmega192c3 (C' , CW(C`atxmega192d3 (C' , CW(C`atxmega256a3 (C' , CW(C`atxmega256a3b (C' , CW(C`atxmega256a3bu (C' , CW(C`atxmega256a3u (C' , CW(C`atxmega256c3 (C' , CW(C`atxmega256d3 (C' , CW(C`atxmega384c3 (C' , CW(C`atxmega384d3 (C' . Item "avrxmega7" (L" XMEGA(R" devices with more than 128@tie{}KiB of program memory and more than 64@tie{}KiB of RAM. mcu CW@tie {}= CW(C`atxmega128a1 (C' , CW(C`atxmega128a1u (C' , CW(C`atxmega128a4u (C' . Item "avrtiny" (L" TINY(R" Tiny core devices with 512@tie{}B up to 4@tie{}KiB of program memory. mcu CW@tie {}= CW(C`attiny10 (C' , CW(C`attiny20 (C' , CW(C`attiny4 (C' , CW(C`attiny40 (C' , CW(C`attiny5 (C' , CW(C`attiny9 (C' . Item "avr1" This ISAis implemented by the minimal AVRcore and supported for assembler only. mcu CW@tie {}= CW(C`attiny11 (C' , CW(C`attiny12 (C' , CW(C`attiny15 (C' , CW(C`attiny28 (C' , CW(C`at90s1200 (C' .

" -mabsdata "4 Item "-mabsdata" Assume that all data in static storage can be accessed by LDS/ STS instructions. This option has only an effect on reduced Tiny devices like ATtiny40. See also the CW(C`absdata (C' AVRVariable Attributes,variable attribute .

" -maccumulate -args "4 Item "-maccumulate-args" Accumulate outgoing function arguments and acquire/release the needed stack space for outgoing function arguments once in function prologue/epilogue. Without this option, outgoing arguments are pushed before calling a function and popped afterwards. Popping the arguments after the function call can be expensive on AVRso that accumulating the stack space might lead to smaller executables because arguments need not be removed from the stack after such a function call. This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions.

" -mbranch -cost= cost "4 Item "-mbranch-cost=cost" Set the branch costs for conditional branch instructions to cost .Reasonable values for cost are small, non-negative integers. The default branch cost is 0.

" -mcall -prologues "4 Item "-mcall-prologues" Functions prologues/epilogues are expanded as calls to appropriate subroutines. Code size is smaller.

" -mgas -isr -prologues "4 Item "-mgas-isr-prologues" Interrupt service routines (ISRs) may use the CW(C`_ _gcc_isr (C' pseudo instruction supported by GNUBinutils. If this option is on, the feature can still be disabled for individual ISRs by means of the AVRFunction Attributes,, CB(C`no_gccisr (C' function attribute. This feature is activated per default if optimization is on (but not with -Og , CW@pxref {OptimizeOptions}), and if GNUBinutils support PR21683( CW(C`https://sourceware.org/PR21683 (C' ).

" -mint8 "4 Item "-mint8" Assume CW(C`int (C' to be 8 -bit integer. This affects the sizes of all types: a CW(C`char (C' is 1 byte, an CW(C`int (C' is 1 byte, a CW(C`long (C' is 2 bytes, and CW(C`long long (C' is 4 bytes. Please note that this option does not conform to the C standards, but it results in smaller code size.

" -mmain -is -OS_task "4 Item "-mmain-is-OS_task" Do not save registers in CW(C`main (C' .The effect is the same like attaching attribute AVRFunction Attributes,, CB(C`OS_task (C' to CW(C`main (C' .It is activated per default if optimization is on.

" -mn -flash= num "4 Item "-mn-flash=num" Assume that the flash memory has a size of num times 64@tie{}KiB.

" -mno -interrupts "4 Item "-mno-interrupts" Generated code is not compatible with hardware interrupts. Code size is smaller.

" -mrelax "4 Item "-mrelax" Try to replace CW(C`CALL (C' resp. CW(C`JMP (C' instruction by the shorter CW(C`RCALL (C' resp. CW(C`RJMP (C' instruction if applicable. Setting -mrelax just adds the --mlink -relax option to the assembler's command line and the --relax option to the linker's command line. Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code. Relaxing must be turned on if linker stubs are needed, see the section on CW(C`EIND (C' and linker stubs below.

" -mrmw "4 Item "-mrmw" Assume that the device supports the Read-Modify-Write instructions CW(C`XCH (C' , CW(C`LAC (C' , CW(C`LAS (C' and CW(C`LAT (C' .

" -mshort -calls "4 Item "-mshort-calls" Assume that CW(C`RJMP (C' and CW(C`RCALL (C' can target the whole program memory. This option is used internally for multilib selection. It is not an optimization option, and you don't need to set it by hand.

" -msp8 "4 Item "-msp8" Treat the stack pointer register as an 8 -bit register, i.e. assume the high byte of the stack pointer is zero. In general, you don't need to set this option by hand. This option is used internally by the compiler to select and build multilibs for architectures CW(C`avr2 (C' and CW(C`avr25 (C' . These architectures mix devices with and without CW(C`SPH (C' . For any setting other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or removes this option from the compiler proper's command line, because the compiler then knows if the device or architecture has an 8 -bit stack pointer and thus no CW(C`SPH (C' register or not.

" -mstrict -X "4 Item "-mstrict-X" Use address register CW(C`X (C' in a way proposed by the hardware. This means that CW(C`X (C' is only used in indirect, post-increment or pre-decrement addressing. Without this option, the CW(C`X (C' register may be used in the same way as CW(C`Y (C' or CW(C`Z (C' which then is emulated by additional instructions. For example, loading a value with CW(C`X+const (C' addressing with a small non-negative CW(C`const < 64 (C' to a register Rn is performed as 3 adiw r26, const ; X += const ld <Rn>, X ; <Rn> = *X sbiw r26, const ; X -= const

" -mtiny -stack "4 Item "-mtiny-stack" Only change the lower 8@tie{}bits of the stack pointer.

" -mfract -convert -truncate "4 Item "-mfract-convert-truncate" Allow to use truncation instead of rounding towards zero for fractional fixed-point types.

" -nodevicelib "4 Item "-nodevicelib" Don't link against AVR-LibC's device specific library CW(C`lib<mcu>.a (C' .

" -Waddr -space -convert "4 Item "-Waddr-space-convert" Warn about conversions between address spaces in the case where the resulting address space is not contained in the incoming address space.

" -Wmisspelled -isr "4 Item "-Wmisspelled-isr" Warn if the ISRis misspelled, i.e. without _ _vector prefix. Enabled by default.

CW(C`EIND (C' and Devices with More Than 128 Ki Bytes of Flash Subsection "EIND and Devices with More Than 128 Ki Bytes of Flash"

Pointers in the implementation are 16@tie{}bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range of 64@tie{}Ki words.

In order to facilitate indirect jump on devices with more than 128@tie{}Ki bytes of program memory space, there is a special function register called CW(C`EIND (C' that serves as most significant part of the target address when CW(C`EICALL (C' or CW(C`EIJMP (C' instructions are used.

Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations:

"*" 4 The compiler never sets CW(C`EIND (C' .

"*" 4 The compiler uses CW(C`EIND (C' implicitly in CW(C`EICALL (C' / CW(C`EIJMP (C' instructions or might read CW(C`EIND (C' directly in order to emulate an indirect call/jump by means of a CW(C`RET (C' instruction.

"*" 4 The compiler assumes that CW(C`EIND (C' never changes during the startup code or during the application. In particular, CW(C`EIND (C' is not saved/restored in function or interrupt service routine prologue/epilogue.

"*" 4 For indirect calls to functions and computed goto, the linker generates stubs .Stubs are jump pads sometimes also called trampolines .Thus, the indirect call/jump jumps to such a stub. The stub contains a direct jump to the desired address.

"*" 4 Linker relaxation must be turned on so that the linker generates the stubs correctly in all situations. See the compiler option -mrelax and the linker option --relax . There are corner cases where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message.

"*" 4 The default linker script is arranged for code with CW(C`EIND = 0 (C' . If code is supposed to work for a setup with CW(C`EIND != 0 (C' ,a custom linker script has to be used in order to place the sections whose name start with CW(C`.trampolines (C' into the segment where CW(C`EIND (C' points to.

"*" 4 The startup code from libgcc never sets CW(C`EIND (C' . Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on CW(C`EIND (C' ,see the AVR-LibC user manual ( CW(C`http://nongnu.org/avr -libc/user -manual/ (C' ).

"*" 4 It is legitimate for user-specific startup code to set up CW(C`EIND (C' early, for example by means of initialization code located in section CW(C`.init3 (C' .Such code runs prior to general startup code that initializes RAMand calls constructors, but after the bit of startup code from AVR-LibC that sets CW(C`EIND (C' to the segment where the vector table is located. 1 #include <avr/io.h> static void _ _attribute_ _((section(".init3"),naked,used,no_instrument_function)) init3_set_eind (void) { _ _asm volatile ("ldi r24,pm_hh8(_ _trampolines_start) \ n \ t" "out %i0,r24" :: "n" (&EIND) : "r24","memory"); } The CW(C`_ _trampolines_start (C' symbol is defined in the linker script.

"*" 4 Stubs are generated automatically by the linker if the following two conditions are met: Item "-<The address of a label is taken by means of the gs modifier>" (short for generatestubs )like so: 2 LDI r24, lo8(gs(<func>)) LDI r25, hi8(gs(<func>))

" -<The final location of that label is in a code segment>" 4 Item "-<The final location of that label is in a code segment>" outside the segment where the stubs are located.

"*" 4 The compiler emits such CW(C`gs (C' modifiers for code labels in the following situations:

" -<Taking address of a function or code label.>" 4 Item "-<Taking address of a function or code label.>" 0

" -<Computed goto.>" 4 Item "-<Computed goto.>"

" -<If prologue-save function is used, see -mcall -prologues >"4 Item "-<If prologue-save function is used, see -mcall-prologues>" command-line option.

" -<Switch/case dispatch tables. If you do not want such dispatch>" 4 Item "-<Switch/case dispatch tables. If you do not want such dispatch>" tables you can specify the -fno -jump -tables command-line option.

" -<C and (C+ constructors/destructors called during startup/shutdown.>" 4 Item "-<C and constructors/destructors called during startup/shutdown.>" 0 Item "-<If the tools hit a gs() modifier explained above.>"

"*" 4 Jumping to non-symbolic addresses like so is not supported: 5 int main (void) { /* Call function at word address 0x2 */ return ((int(*)(void)) 0x2)(); } Instead, a stub has to be set up, i.e. the function has to be called through a symbol ( CW(C`func_4 (C' in the example): 3 int main (void) { extern int func_4 (void); /* Call function at byte address 0x4 */ return func_4(); } and the application be linked with -Wl, --defsym,func_4=0x4 . Alternatively, CW(C`func_4 (C' can be defined in the linker script.

Handling of the CW(C`RAMPD (C' , CW(C`RAMPX (C' , CW(C`RAMPY (C' and CW(C`RAMPZ (C' Special Function Registers Subsection "Handling of the RAMPD, RAMPX, RAMPY and RAMPZ Special Function Registers"

Some AVRdevices support memories larger than the 64@tie{}KiB range that can be accessed with 16 -bit pointers. To access memory locations outside this 64@tie{}KiB range, the content of a CW(C`RAMP (C' register is used as high part of the address: The CW(C`X (C' , CW(C`Y (C' , CW(C`Z (C' address register is concatenated with the CW(C`RAMPX (C' , CW(C`RAMPY (C' , CW(C`RAMPZ (C' special function register, respectively, to get a wide address. Similarly, CW(C`RAMPD (C' is used together with direct addressing.

"*" 4 The startup code initializes the CW(C`RAMP (C' special function registers with zero.

"*" 4 If a AVRNamed Address Spaces,named address space other than generic or CW(C`_ _flash (C' is used, then CW(C`RAMPZ (C' is set as needed before the operation.

"*" 4 If the device supports RAMlarger than 64@tie{}KiB and the compiler needs to change CW(C`RAMPZ (C' to accomplish an operation, CW(C`RAMPZ (C' is reset to zero after the operation.

"*" 4 If the device comes with a specific CW(C`RAMP (C' register, the ISR prologue/epilogue saves/restores that SFRand initializes it with zero in case the ISRcode might (implicitly) use it.

"*" 4 RAMlarger than 64@tie{}KiB is not supported by GCCfor AVRtargets. If you use inline assembler to read from locations outside the 16 -bit address range and change one of the CW(C`RAMP (C' registers, you must reset it to zero after the access.

AVRBuilt-in Macros Subsection "AVR Built-in Macros"

GCCdefines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and thus triggered by the -mmcu= command-line option.

For even more AVR-specific built-in macros see AVRNamed Address Spaces and AVRBuilt-in Functions . Item "__AVR_ARCH__" Build-in macro that resolves to a decimal number that identifies the architecture and depends on the -mmcu= mcu option. Possible values are: CW2 , CW25 , CW3 , CW31 , CW35 , CW4 , CW5 , CW51 , CW6 for mcu = CW(C`avr2 (C' , CW(C`avr25 (C' , CW(C`avr3 (C' , CW(C`avr31 (C' , CW(C`avr35 (C' , CW(C`avr4 (C' , CW(C`avr5 (C' , CW(C`avr51 (C' , CW(C`avr6 (C' , respectively and CW100 , CW102 , CW103 , CW104 , CW105 , CW106 , CW107 for mcu = CW(C`avrtiny (C' , CW(C`avrxmega2 (C' , CW(C`avrxmega3 (C' , CW(C`avrxmega4 (C' , CW(C`avrxmega5 (C' , CW(C`avrxmega6 (C' , CW(C`avrxmega7 (C' ,respectively. If mcu specifies a device, this built-in macro is set accordingly. For example, with -mmcu=atmega8 the macro is defined to CW4 . Item "__AVR_Device__" Setting -mmcu= device defines this built-in macro which reflects the device's name. For example, -mmcu=atmega8 defines the built-in macro CW(C`_ _AVR_ATmega8_ _ (C' , -mmcu=attiny261a defines CW(C`_ _AVR_ATtiny261A_ _ (C' ,etc. The built-in macros' names follow the scheme CW(C`_ _AVR_ CIDevice CW__ (C' where Device is the device name as from the AVRuser manual. The difference between Device in the built-in macro and device in -mmcu= device is that the latter is always lowercase. If device is not a device but only a core architecture like avr51 ,this macro is not defined. Item "__AVR_DEVICE_NAME__" Setting -mmcu= device defines this built-in macro to the device's name. For example, with -mmcu=atmega8 the macro is defined to CW(C`atmega8 (C' . If device is not a device but only a core architecture like avr51 ,this macro is not defined. Item "__AVR_XMEGA__" The device / architecture belongs to the XMEGAfamily of devices. Item "__AVR_HAVE_ELPM__" The device has the CW(C`ELPM (C' instruction. Item "__AVR_HAVE_ELPMX__" The device has the CW(C`ELPM R CIn CW,Z(C' and CW(C`ELPM R CIn CW,Z+(C' instructions. Item "__AVR_HAVE_MOVW__" The device has the CW(C`MOVW (C' instruction to perform 16 -bit register-register moves. Item "__AVR_HAVE_LPMX__" The device has the CW(C`LPM R CIn CW,Z(C' and CW(C`LPM R CIn CW,Z+(C' instructions. Item "__AVR_HAVE_MUL__" The device has a hardware multiplier. Item "__AVR_HAVE_JMP_CALL__" The device has the CW(C`JMP (C' and CW(C`CALL (C' instructions. This is the case for devices with more than 8@tie{}KiB of program memory. Item "__AVR_HAVE_EIJMP_EICALL__" 0 Item "__AVR_3_BYTE_PC__" The device has the CW(C`EIJMP (C' and CW(C`EICALL (C' instructions. This is the case for devices with more than 128@tie{}KiB of program memory. This also means that the program counter ( PC)is 3@tie{}bytes wide. Item "__AVR_2_BYTE_PC__" The program counter ( PC)is 2@tie{}bytes wide. This is the case for devices with up to 128@tie{}KiB of program memory. Item "__AVR_HAVE_8BIT_SP__" 0 Item "__AVR_HAVE_16BIT_SP__" The stack pointer ( SP)register is treated as 8 -bit respectively 16 -bit register by the compiler. The definition of these macros is affected by -mtiny -stack . Item "__AVR_HAVE_SPH__" 0 Item "__AVR_SP8__" The device has the SPH(high part of stack pointer) special function register or has an 8 -bit stack pointer, respectively. The definition of these macros is affected by -mmcu= and in the cases of -mmcu=avr2 and -mmcu=avr25 also by -msp8 . Item "__AVR_HAVE_RAMPD__" 0 Item "__AVR_HAVE_RAMPX__" Item "__AVR_HAVE_RAMPY__" Item "__AVR_HAVE_RAMPZ__" The device has the CW(C`RAMPD (C' , CW(C`RAMPX (C' , CW(C`RAMPY (C' , CW(C`RAMPZ (C' special function register, respectively. Item "__NO_INTERRUPTS__" This macro reflects the -mno -interrupts command-line option. Item "__AVR_ERRATA_SKIP__" 0 Item "__AVR_ERRATA_SKIP_JMP_CALL__" Some AVRdevices ( AT90S8515,ATmega103) must not skip 32 -bit instructions because of a hardware erratum. Skip instructions are CW(C`SBRS (C' , CW(C`SBRC (C' , CW(C`SBIS (C' , CW(C`SBIC (C' and CW(C`CPSE (C' . The second macro is only defined if CW(C`_ _AVR_HAVE_JMP_CALL_ _ (C' is also set. Item "__AVR_ISA_RMW__" The device has Read-Modify-Write instructions ( XCH,LAC, LAS and LAT). Item "__AVR_SFR_OFFSET__=offset" Instructions that can address I/O special function registers directly like CW(C`IN (C' , CW(C`OUT (C' , CW(C`SBI (C' ,etc. may use a different address as if addressed by an instruction to access RAMlike CW(C`LD (C' or CW(C`STS (C' .This offset depends on the device architecture and has to be subtracted from the RAMaddress in order to get the respective I/O@tie{}address. Item "__AVR_SHORT_CALLS__" The -mshort -calls command line option is set. Item "__AVR_PM_BASE_ADDRESS__=addr" Some devices support reading from flash memory by means of CW(C`LD* (C' instructions. The flash memory is seen in the data address space at an offset of CW(C`_ _AVR_PM_BASE_ADDRESS_ _ (C' .If this macro is not defined, this feature is not available. If defined, the address space is linear and there is no need to put CW(C`.rodata (C' into RAM.This is handled by the default linker description file, and is currently available for CW(C`avrtiny (C' and CW(C`avrxmega3 (C' .Even more convenient, there is no need to use address spaces like CW(C`_ _flash (C' or features like attribute CW(C`progmem (C' and CW(C`pgm_read_* (C' . Item "__WITH_AVRLIBC__" The compiler is configured to be used together with AVR-Libc. See the --with -avrlibc configure option.

BlackfinOptions Subsection "Blackfin Options"

" -mcpu= cpu [ - sirevision ]"4 Item "-mcpu=cpu[-sirevision]" Specifies the name of the target Blackfin processor. Currently, cpu can be one of bf512 , bf514 , bf516 , bf518 , bf522 , bf523 , bf524 , bf525 , bf526 , bf527 , bf531 , bf532 , bf533 , bf534 , bf536 , bf537 , bf538 , bf539 , bf542 , bf544 , bf547 , bf548 , bf549 , bf542m , bf544m , bf547m , bf548m , bf549m , bf561 , bf592 . The optional sirevision specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision are enabled. If sirevision is none ,no workarounds are enabled. If sirevision is any ,all workarounds for the targeted processor are enabled. The CW(C`_ _SILICON_REVISION_ _ (C' macro is defined to two hexadecimal digits representing the major and minor numbers in the silicon revision. If sirevision is none ,the CW(C`_ _SILICON_REVISION_ _ (C' is not defined. If sirevision is any ,the CW(C`_ _SILICON_REVISION_ _ (C' is defined to be CW0xffff . If this optional sirevision is not used, GCCassumes the latest known silicon revision of the targeted Blackfin processor. GCCdefines a preprocessor macro for the specified cpu . For the bfin-elf toolchain, this option causes the hardware BSP provided by libgloss to be linked in if -msim is not given. Without this option, bf532 is used as the processor by default. Note that support for bf561 is incomplete. For bf561 , only the preprocessor macro is defined.

" -msim "4 Item "-msim" Specifies that the program will be run on the simulator. This causes the simulator BSPprovided by libgloss to be linked in. This option has effect only for bfin-elf toolchain. Certain other options, such as -mid -shared -library and -mfdpic ,imply -msim .

" -momit -leaf -frame -pointer "4 Item "-momit-leaf-frame-pointer" Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions.

" -mspecld -anomaly "4 Item "-mspecld-anomaly" When enabled, the compiler ensures that the generated code does not contain speculative loads after jump instructions. If this option is used, CW(C`_ _WORKAROUND_SPECULATIVE_LOADS (C' is defined.

" -mno -specld -anomaly "4 Item "-mno-specld-anomaly" Don't generate extra code to prevent speculative loads from occurring.

" -mcsync -anomaly "4 Item "-mcsync-anomaly" When enabled, the compiler ensures that the generated code does not contain CSYNCor SSYNCinstructions too soon after conditional branches. If this option is used, CW(C`_ _WORKAROUND_SPECULATIVE_SYNCS (C' is defined.

" -mno -csync -anomaly "4 Item "-mno-csync-anomaly" Don't generate extra code to prevent CSYNCor SSYNCinstructions from occurring too soon after a conditional branch.

" -mlow64k "4 Item "-mlow64k" When enabled, the compiler is free to take advantage of the knowledge that the entire program fits into the low 64k of memory.

" -mno -low64k "4 Item "-mno-low64k" Assume that the program is arbitrarily large. This is the default.

" -mstack -check -l1 "4 Item "-mstack-check-l1" Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel.

" -mid -shared -library "4 Item "-mid-shared-library" Generate code that supports shared libraries via the library IDmethod. This allows for execute in place and shared libraries in an environment without virtual memory management. This option implies -fPIC . With a bfin-elf target, this option implies -msim .

" -mno -id -shared -library "4 Item "-mno-id-shared-library" Generate code that doesn't assume ID-based shared libraries are being used. This is the default.

" -mleaf -id -shared -library "4 Item "-mleaf-id-shared-library" Generate code that supports shared libraries via the library IDmethod, but assumes that this library or executable won't link against any other IDshared libraries. That allows the compiler to use faster code for jumps and calls.

" -mno -leaf -id -shared -library "4 Item "-mno-leaf-id-shared-library" Do not assume that the code being compiled won't link against any IDshared libraries. Slower code is generated for jump and call insns.

" -mshared -library -id=n "4 Item "-mshared-library-id=n" Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library but is no more space -or time-efficient than omitting this option.

" -msep -data "4 Item "-msep-data" Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory management by eliminating relocations against the text section.

" -mno -sep -data "4 Item "-mno-sep-data" Generate code that assumes that the data segment follows the text segment. This is the default.

" -mlong -calls "4 Item "-mlong-calls" 0

" -mno -long -calls "4 Item "-mno-long-calls" Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 24 -bit addressing range of the offset-based version of subroutine call instruction. This feature is not enabled by default. Specifying -mno -long -calls restores the default behavior. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.

" -mfast -fp "4 Item "-mfast-fp" Link with the fast floating-point library. This library relaxes some of the IEEEfloating-point standard's rules for checking inputs against Not-a-Number ( NAN),in the interest of performance.

" -minline -plt "4 Item "-minline-plt" Enable inlining of PLTentries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic .

" -mmulticore "4 Item "-mmulticore" Build a standalone application for multicore Blackfin processors. This option causes proper start files and link scripts supporting multicore to be used, and defines the macro CW(C`_ _BFIN_MULTICORE (C' . It can only be used with -mcpu=bf561 [ - sirevision ]. This option can be used with -mcorea or -mcoreb ,which selects the one-application-per-core programming model. Without -mcorea or -mcoreb ,the single -application/dual -core programming model is used. In this model, the main function of Core B should be named as CW(C`coreb_main (C' . If this option is not used, the single-core application programming model is used.

" -mcorea "4 Item "-mcorea" Build a standalone application for Core A of BF561when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core A, and the macro CW(C`_ _BFIN_COREA (C' is defined. This option can only be used in conjunction with -mmulticore .

" -mcoreb "4 Item "-mcoreb" Build a standalone application for Core B of BF561when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core B, and the macro CW(C`_ _BFIN_COREB (C' is defined. When this option is used, CW(C`coreb_main (C' should be used instead of CW(C`main (C' . This option can only be used in conjunction with -mmulticore .

" -msdram "4 Item "-msdram" Build a standalone application for SDRAM.Proper start files and link scripts are used to put the application into SDRAM,and the macro CW(C`_ _BFIN_SDRAM (C' is defined. The loader should initialize SDRAMbefore loading the application.

" -micplb "4 Item "-micplb" Assume that ICPLBs are enabled at run time. This has an effect on certain anomaly workarounds. For Linux targets, the default is to assume ICPLBs are enabled; for standalone applications the default is off.

C6XOptions Subsection "C6X Options"

" -march= name "4 Item "-march=name" This specifies the name of the target architecture. GCCuses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: c62x , c64x , c64x+ , c67x , c67x+ , c674x .

" -mbig -endian "4 Item "-mbig-endian" Generate code for a big-endian target.

" -mlittle -endian "4 Item "-mlittle-endian" Generate code for a little-endian target. This is the default.

" -msim "4 Item "-msim" Choose startup files and linker script suitable for the simulator.

" -msdata=default "4 Item "-msdata=default" Put small global and static data in the CW(C`.neardata (C' section, which is pointed to by register CW(C`B14 (C' .Put small uninitialized global and static data in the CW(C`.bss (C' section, which is adjacent to the CW(C`.neardata (C' section. Put small read-only data into the CW(C`.rodata (C' section. The corresponding sections used for large pieces of data are CW(C`.fardata (C' , CW(C`.far (C' and CW(C`.const (C' .

" -msdata=all "4 Item "-msdata=all" Put all data, not just small objects, into the sections reserved for small data, and use addressing relative to the CW(C`B14 (C' register to access them.

" -msdata=none "4 Item "-msdata=none" Make no use of the sections reserved for small data, and use absolute addresses to access all data. Put all initialized global and static data in the CW(C`.fardata (C' section, and all uninitialized data in the CW(C`.far (C' section. Put all constant data into the CW(C`.const (C' section.

CRISOptions Subsection "CRIS Options"

These options are defined specifically for the CRISports.

" -march= architecture-type "4 Item "-march=architecture-type" 0

" -mcpu= architecture-type "4 Item "-mcpu=architecture-type" Generate code for the specified architecture. The choices for architecture-type are v3 , v8 and v10 for respectively ETRAX4, ETRAX100, and ETRAX100 LX. Default is v0 except for cris-axis-linux-gnu, where the default is v10 .

" -mtune= architecture-type "4 Item "-mtune=architecture-type" Tune to architecture-type everything applicable about the generated code, except for the ABIand the set of available instructions. The choices for architecture-type are the same as for -march= architecture-type .

" -mmax -stack -frame= n "4 Item "-mmax-stack-frame=n" Warn when the stack frame of a function exceeds n bytes.

" -metrax4 "4 Item "-metrax4" 0

" -metrax100 "4 Item "-metrax100" The options -metrax4 and -metrax100 are synonyms for -march=v3 and -march=v8 respectively.

" -mmul -bug -workaround "4 Item "-mmul-bug-workaround" 0

" -mno -mul -bug -workaround "4 Item "-mno-mul-bug-workaround" Work around a bug in the CW(C`muls (C' and CW(C`mulu (C' instructions for CPU models where it applies. This option is active by default.

" -mpdebug "4 Item "-mpdebug" Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect of turning off the #NO_APP formatted-code indicator to the assembler at the beginning of the assembly file.

" -mcc -init "4 Item "-mcc-init" Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes.

" -mno -side -effects "4 Item "-mno-side-effects" Do not emit instructions with side effects in addressing modes other than post-increment.

" -mstack -align "4 Item "-mstack-align" 0

" -mno -stack -align "4 Item "-mno-stack-align"

" -mdata -align "4 Item "-mdata-align"

" -mno -data -align "4 Item "-mno-data-align"

" -mconst -align "4 Item "-mconst-align"

" -mno -const -align "4 Item "-mno-const-align" These options ( no- options) arrange (eliminate arrangements) for the stack frame, individual data and constants to be aligned for the maximum single data access size for the chosen CPUmodel. The default is to arrange for 32 -bit alignment. ABIdetails such as structure layout are not affected by these options.

" -m32 -bit "4 Item "-m32-bit" 0

" -m16 -bit "4 Item "-m16-bit"

" -m8 -bit "4 Item "-m8-bit" Similar to the stack -data -and const-align options above, these options arrange for stack frame, writable data and constants to all be 32 -bit, 16 -bit or 8 -bit aligned. The default is 32 -bit alignment.

" -mno -prologue -epilogue "4 Item "-mno-prologue-epilogue" 0

" -mprologue -epilogue "4 Item "-mprologue-epilogue" With -mno -prologue -epilogue ,the normal function prologue and epilogue which set up the stack frame are omitted and no return instructions or return sequences are generated in the code. Use this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variables needs to be allocated.

" -mno -gotplt "4 Item "-mno-gotplt" 0

" -mgotplt "4 Item "-mgotplt" With -fpic and -fPIC ,don't generate (do generate) instruction sequences that load addresses for functions from the PLTpart of the GOTrather than (traditional on other architectures) calls to the PLT.The default is -mgotplt .

" -melf "4 Item "-melf" Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets.

" -mlinux "4 Item "-mlinux" Legacy no-op option only recognized with the cris-axis-linux-gnu target.

" -sim "4 Item "-sim" This option, recognized for the cris-axis-elf, arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated consecutively.

" -sim2 "4 Item "-sim2" Like -sim ,but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000.

CR16Options Subsection "CR16 Options"

These options are defined specifically for the CR16ports.

" -mmac "4 Item "-mmac" Enable the use of multiply-accumulate instructions. Disabled by default.

" -mcr16cplus "4 Item "-mcr16cplus" 0

" -mcr16c "4 Item "-mcr16c" Generate code for CR16Cor CR16C+architecture. CR16C+architecture is default.

" -msim "4 Item "-msim" Links the library libsim.a which is in compatible with simulator. Applicable to ELFcompiler only.

" -mint32 "4 Item "-mint32" Choose integer type as 32 -bit wide.

" -mbit -ops "4 Item "-mbit-ops" Generates CW(C`sbit (C' / CW(C`cbit (C' instructions for bit manipulations.

" -mdata -model= model "4 Item "-mdata-model=model" Choose a data model. The choices for model are near , far or medium . medium is default. However, far is not valid with -mcr16c ,as the CR16Carchitecture does not support the far data model.

C-SKY Options Subsection "C-SKY Options"

GCCsupports these options when compiling for C -SKY V2 processors.

" -march= arch "4 Item "-march=arch" Specify the C -SKY target architecture. Valid values for arch are: ck801 , ck802 , ck803 , ck807 ,and ck810 . The default is ck810 .

" -mcpu= cpu "4 Item "-mcpu=cpu" Specify the C -SKY target processor. Valid values for cpu are: ck801 , ck801t , ck802 , ck802t , ck802j , ck803 , ck803h , ck803t , ck803ht , ck803f , ck803fh , ck803e , ck803eh , ck803et , ck803eht , ck803ef , ck803efh , ck803ft , ck803eft , ck803efht , ck803r1 , ck803hr1 , ck803tr1 , ck803htr1 , ck803fr1 , ck803fhr1 , ck803er1 , ck803ehr1 , ck803etr1 , ck803ehtr1 , ck803efr1 , ck803efhr1 , ck803ftr1 , ck803eftr1 , ck803efhtr1 , ck803s , ck803st , ck803se , ck803sf , ck803sef , ck803seft , ck807e , ck807ef , ck807 , ck807f , ck810e , ck810et , ck810ef , ck810eft , ck810 , ck810v , ck810f , ck810t , ck810fv , ck810tv , ck810ft ,and ck810ftv .

" -mbig -endian "4 Item "-mbig-endian" 0

" -EB "4 Item "-EB"

" -mlittle -endian "4 Item "-mlittle-endian"

" -EL "4 Item "-EL" Select big -or little-endian code. The default is little-endian.

" -mhard -float "4 Item "-mhard-float" 0

" -msoft -float "4 Item "-msoft-float" Select hardware or software floating-point implementations. The default is soft float.

" -mdouble -float "4 Item "-mdouble-float" 0

" -mno -double -float "4 Item "-mno-double-float" When -mhard -float is in effect, enable generation of double-precision float instructions. This is the default except when compiling for CK803.

" -mfdivdu "4 Item "-mfdivdu" 0

" -mno -fdivdu "4 Item "-mno-fdivdu" When -mhard -float is in effect, enable generation of CW(C`frecipd (C' , CW(C`fsqrtd (C' ,and CW(C`fdivd (C' instructions. This is the default except when compiling for CK803.

" -mfpu= fpu "4 Item "-mfpu=fpu" Select the floating-point processor. This option can only be used with -mhard -float . Values for fpu are fpv2_sf (equivalent to -mno -double -float -mno -fdivdu ), fpv2 ( -mdouble -float -mno -divdu ),and fpv2_divd ( -mdouble -float -mdivdu ).

" -melrw "4 Item "-melrw" 0

" -mno -elrw "4 Item "-mno-elrw" Enable the extended CW(C`lrw (C' instruction. This option defaults to on for CK801and off otherwise.

" -mistack "4 Item "-mistack" 0

" -mno -istack "4 Item "-mno-istack" Enable interrupt stack instructions; the default is off. The -mistack option is required to handle the CW(C`interrupt (C' and CW(C`isr (C' function attributes.

" -mmp "4 Item "-mmp" Enable multiprocessor instructions; the default is off.

" -mcp "4 Item "-mcp" Enable coprocessor instructions; the default is off.

" -mcache "4 Item "-mcache" Enable coprocessor instructions; the default is off.

" -msecurity "4 Item "-msecurity" Enable C -SKY security instructions; the default is off.

" -mtrust "4 Item "-mtrust" Enable C -SKY trust instructions; the default is off.

" -mdsp "4 Item "-mdsp" 0

" -medsp "4 Item "-medsp"

" -mvdsp "4 Item "-mvdsp" Enable C -SKY DSP,Enhanced DSP,or Vector DSPinstructions, respectively. All of these options default to off.

" -mdiv "4 Item "-mdiv" 0

" -mno -div "4 Item "-mno-div" Generate divide instructions. Default is off.

" -msmart "4 Item "-msmart" 0

" -mno -smart "4 Item "-mno-smart" Generate code for Smart Mode, using only registers numbered 0 -7 to allow use of 16 -bit instructions. This option is ignored for CK801where this is the required behavior, and it defaults to on for CK802. For other targets, the default is off.

" -mhigh -registers "4 Item "-mhigh-registers" 0

" -mno -high -registers "4 Item "-mno-high-registers" Generate code using the high registers numbered 16 -31. This option is not supported on CK801,CK802, or CK803,and is enabled by default for other processors.

" -manchor "4 Item "-manchor" 0

" -mno -anchor "4 Item "-mno-anchor" Generate code using global anchor symbol addresses.

" -mpushpop "4 Item "-mpushpop" 0

" -mno -pushpop "4 Item "-mno-pushpop" Generate code using CW(C`push (C' and CW(C`pop (C' instructions. This option defaults to on.

" -mmultiple -stld "4 Item "-mmultiple-stld" 0

" -mstm "4 Item "-mstm"

" -mno -multiple -stld "4 Item "-mno-multiple-stld"

" -mno -stm "4 Item "-mno-stm" Generate code using CW(C`stm (C' and CW(C`ldm (C' instructions. This option isn't supported on CK801but is enabled by default on other processors.

" -mconstpool "4 Item "-mconstpool" 0

" -mno -constpool "4 Item "-mno-constpool" Create constant pools in the compiler instead of deferring it to the assembler. This option is the default and required for correct code generation on CK801and CK802,and is optional on other processors.

" -mstack -size "4 Item "-mstack-size" 0

" -mno -stack -size "4 Item "-mno-stack-size" Emit CW(C`.stack_size (C' directives for each function in the assembly output. This option defaults to off.

" -mccrt "4 Item "-mccrt" 0

" -mno -ccrt "4 Item "-mno-ccrt" Generate code for the C -SKY compiler runtime instead of libgcc. This option defaults to off.

" -mbranch -cost= n "4 Item "-mbranch-cost=n" Set the branch costs to roughly CW(C`n (C' instructions. The default is 1.

" -msched -prolog "4 Item "-msched-prolog" 0

" -mno -sched -prolog "4 Item "-mno-sched-prolog" Permit scheduling of function prologue and epilogue sequences. Using this option can result in code that is not compliant with the C -SKY V2 ABI prologue requirements and that cannot be debugged or backtraced. It is disabled by default.

DarwinOptions Subsection "Darwin Options"

These options are defined for all architectures running the Darwin operating system.

FSFGCC on Darwin does not create (L"fat (R" object files; it creates an object file for the single architecture that GCCwas built to target. Apple's GCCon Darwin does create (L"fat (R" files if multiple -arch options are used; it does so by running the compiler or linker multiple times and joining the results together with lipo .

The subtype of the file created (like ppc7400 or ppc970 or i686 )is determined by the flags that specify the ISA that GCCis targeting, like -mcpu or -march .The -force_cpusubtype_ALL option can be used to override this.

The Darwin tools vary in their behavior when presented with an ISA mismatch. The assembler, as ,only permits instructions to be used that are valid for the subtype of the file it is generating, so you cannot put 64 -bit instructions in a ppc750 object file. The linker for shared libraries, /usr/bin/libtool ,fails and prints an error if asked to create a shared library with a less restrictive subtype than its input files (for instance, trying to put a ppc970 object file in a ppc7400 library). The linker for executables, ld ,quietly gives the executable the most restrictive subtype of any of its input files.

" -F dir "4 Item "-Fdir" Add the framework directory dir to the head of the list of directories to be searched for header files. These directories are interleaved with those specified by -I options and are scanned in a left-to-right order. A framework directory is a directory with frameworks in it. A framework is a directory with a Headers and/or PrivateHeaders directory contained directly in it that ends in .framework .The name of a framework is the name of this directory excluding the .framework .Headers associated with the framework are found in one of those two directories, with Headers being searched first. A subframework is a framework directory that is in a framework's Frameworks directory. Includes of subframework headers can only appear in a header of a framework that contains the subframework, or in a sibling subframework header. Two subframeworks are siblings if they occur in the same framework. A subframework should not have the same name as a framework; a warning is issued if this is violated. Currently a subframework cannot have subframeworks; in the future, the mechanism may be extended to support this. The standard frameworks can be found in /System/Library/Frameworks and /Library/Frameworks .An example include looks like CW(C`#include <Framework/header.h> (C' ,where Framework denotes the name of the framework and header.h is found in the PrivateHeaders or Headers directory.

" -iframework dir "4 Item "-iframeworkdir" Like -F except the directory is a treated as a system directory. The main difference between this -iframework and -F is that with -iframework the compiler does not warn about constructs contained within header files found via dir .This option is valid only for the C family of languages.

" -gused "4 Item "-gused" Emit debugging information for symbols that are used. For stabs debugging format, this enables -feliminate -unused -debug -symbols . This is by default ON.

" -gfull "4 Item "-gfull" Emit debugging information for all symbols and types.

" -mmacosx -version -min= version "4 Item "-mmacosx-version-min=version" The earliest version of MacOS X that this executable will run on is version .Typical values of version include CW10.1 , CW10.2 ,and CW10.3.9 . If the compiler was built to use the system's headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make choices that are compatible with as many systems and code bases as possible.

" -mkernel "4 Item "-mkernel" Enable kernel development mode. The -mkernel option sets -static , -fno -common , -fno -use -cxa -atexit , -fno -exceptions , -fno -non -call -exceptions , -fapple -kext , -fno -weak and -fno -rtti where applicable. This mode also sets -mno -altivec , -msoft -float , -fno -builtin and -mlong -branch for PowerPC targets.

" -mone -byte -bool "4 Item "-mone-byte-bool" Override the defaults for CW(C`bool (C' so that CW(C`sizeof(bool)==1 (C' . By default CW(C`sizeof(bool) (C' is CW4 when compiling for Darwin/PowerPC and CW1 when compiling for Darwin/x86, so this option has no effect on x86. Warning: The -mone -byte -bool switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model.

" -mfix -and -continue "4 Item "-mfix-and-continue" 0

" -ffix -and -continue "4 Item "-ffix-and-continue"

" -findirect -data "4 Item "-findirect-data" Generate code suitable for fast turnaround development, such as to allow GDBto dynamically load .o files into already-running programs. -findirect -data and -ffix -and -continue are provided for backwards compatibility.

" -all_load "4 Item "-all_load" Loads all members of static archive libraries. See man ld (1) for more information.

" -arch_errors_fatal "4 Item "-arch_errors_fatal" Cause the errors having to do with files that have the wrong architecture to be fatal.

" -bind_at_load "4 Item "-bind_at_load" Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched.

" -bundle "4 Item "-bundle" Produce a Mach-o bundle format file. See man ld (1) for more information.

" -bundle_loader executable "4 Item "-bundle_loader executable" This option specifies the executable that will load the build output file being linked. See man ld (1) for more information.

" -dynamiclib "4 Item "-dynamiclib" When passed this option, GCCproduces a dynamic library instead of an executable when linking, using the Darwin libtool command.

" -force_cpusubtype_ALL "4 Item "-force_cpusubtype_ALL" This causes GCC'soutput file to have the ALL subtype, instead of one controlled by the -mcpu or -march option.

" -allowable_client client_name "4 Item "-allowable_client client_name" 0

" -client_name "4 Item "-client_name"

" -compatibility_version "4 Item "-compatibility_version"

" -current_version "4 Item "-current_version"

" -dead_strip "4 Item "-dead_strip"

" -dependency -file "4 Item "-dependency-file"

" -dylib_file "4 Item "-dylib_file"

" -dylinker_install_name "4 Item "-dylinker_install_name"

" -dynamic "4 Item "-dynamic"

" -exported_symbols_list "4 Item "-exported_symbols_list"

" -filelist "4 Item "-filelist"

" -flat_namespace "4 Item "-flat_namespace"

" -force_flat_namespace "4 Item "-force_flat_namespace"

" -headerpad_max_install_names "4 Item "-headerpad_max_install_names"

" -image_base "4 Item "-image_base"

" -init "4 Item "-init"

" -install_name "4 Item "-install_name"

" -keep_private_externs "4 Item "-keep_private_externs"

" -multi_module "4 Item "-multi_module"

" -multiply_defined "4 Item "-multiply_defined"

" -multiply_defined_unused "4 Item "-multiply_defined_unused"

" -noall_load "4 Item "-noall_load"

" -no_dead_strip_inits_and_terms "4 Item "-no_dead_strip_inits_and_terms"

" -nofixprebinding "4 Item "-nofixprebinding"

" -nomultidefs "4 Item "-nomultidefs"

" -noprebind "4 Item "-noprebind"

" -noseglinkedit "4 Item "-noseglinkedit"

" -pagezero_size "4 Item "-pagezero_size"

" -prebind "4 Item "-prebind"

" -prebind_all_twolevel_modules "4 Item "-prebind_all_twolevel_modules"

" -private_bundle "4 Item "-private_bundle"

" -read_only_relocs "4 Item "-read_only_relocs"

" -sectalign "4 Item "-sectalign"

" -sectobjectsymbols "4 Item "-sectobjectsymbols"

" -whyload "4 Item "-whyload"

" -seg1addr "4 Item "-seg1addr"

" -sectcreate "4 Item "-sectcreate"

" -sectobjectsymbols "4 Item "-sectobjectsymbols"

" -sectorder "4 Item "-sectorder"

" -segaddr "4 Item "-segaddr"

" -segs_read_only_addr "4 Item "-segs_read_only_addr"

" -segs_read_write_addr "4 Item "-segs_read_write_addr"

" -seg_addr_table "4 Item "-seg_addr_table"

" -seg_addr_table_filename "4 Item "-seg_addr_table_filename"

" -seglinkedit "4 Item "-seglinkedit"

" -segprot "4 Item "-segprot"

" -segs_read_only_addr "4 Item "-segs_read_only_addr"

" -segs_read_write_addr "4 Item "-segs_read_write_addr"

" -single_module "4 Item "-single_module"

" -static "4 Item "-static"

" -sub_library "4 Item "-sub_library"

" -sub_umbrella "4 Item "-sub_umbrella"

" -twolevel_namespace "4 Item "-twolevel_namespace"

" -umbrella "4 Item "-umbrella"

" -undefined "4 Item "-undefined"

" -unexported_symbols_list "4 Item "-unexported_symbols_list"

" -weak_reference_mismatches "4 Item "-weak_reference_mismatches"

" -whatsloaded "4 Item "-whatsloaded" These options are passed to the Darwin linker. The Darwin linker man page describes them in detail.

DECAlpha Options Subsection "DEC Alpha Options"

These -m options are defined for the DECAlpha implementations:

" -mno -soft -float "4 Item "-mno-soft-float" 0

" -msoft -float "4 Item "-msoft-float" Use (do not use) the hardware floating-point instructions for floating-point operations. When -msoft -float is specified, functions in libgcc.a are used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines issue floating-point operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them. Note that Alpha implementations without floating-point operations are required to have floating-point registers.

" -mfp -reg "4 Item "-mfp-reg" 0

" -mno -fp -regs "4 Item "-mno-fp-regs" Generate code that uses (does not use) the floating-point register set. -mno -fp -regs implies -msoft -float .If the floating-point register set is not used, floating-point operands are passed in integer registers as if they were integers and floating-point results are passed in CW$0 instead of CW$f0 .This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with -mno -fp -regs must also be compiled with that option. A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers.

" -mieee "4 Item "-mieee" The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEEfloating-point standard. However, for full compliance, software assistance is required. This option generates code fully IEEE-compliant code except that the inexact-flag is not maintained (see below). If this option is turned on, the preprocessor macro CW(C`_IEEE_FP (C' is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional IEEE values such as not-a-number and plus/minus infinity. Other Alpha compilers call this option -ieee_with_no_inexact .

" -mieee -with -inexact "4 Item "-mieee-with-inexact" This is like -mieee except the generated code also maintains the IEEE inexact-flag .Turning on this option causes the generated code to implement fully-compliant IEEEmath. In addition to CW(C`_IEEE_FP (C' , CW(C`_IEEE_FP_EXACT (C' is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since there is very little code that depends on the inexact-flag ,you should normally not specify this option. Other Alpha compilers call this option -ieee_with_inexact .

" -mfp -trap -mode= trap-mode "4 Item "-mfp-trap-mode=trap-mode" This option controls what floating-point related traps are enabled. Other Alpha compilers call this option -fptm trap-mode . The trap mode can be set to one of four values:

" n "4 Item "n" This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division by zero trap).

" u "4 Item "u" In addition to the traps enabled by n ,underflow traps are enabled as well.

" su "4 Item "su" Like u ,but the instructions are marked to be safe for software completion (see Alpha architecture manual for details).

" sui "4 Item "sui" Like su ,but inexact traps are enabled as well.

" -mfp -rounding -mode= rounding-mode "4 Item "-mfp-rounding-mode=rounding-mode" Selects the IEEErounding mode. Other Alpha compilers call this option -fprm rounding-mode .The rounding-mode can be one of:

" n "4 Item "n" Normal IEEErounding mode. Floating-point numbers are rounded towards the nearest machine number or towards the even machine number in case of a tie.

" m "4 Item "m" Round towards minus infinity.

" c "4 Item "c" Chopped rounding mode. Floating-point numbers are rounded towards zero.

" d "4 Item "d" Dynamic rounding mode. A field in the floating-point control register ( fpcr ,see Alpha architecture reference manual) controls the rounding mode in effect. The C library initializes this register for rounding towards plus infinity. Thus, unless your program modifies the fpcr , d corresponds to round towards plus infinity.

" -mtrap -precision= trap-precision "4 Item "-mtrap-precision=trap-precision" In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs to be terminated. GCCcan generate code that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of an application, different levels of precisions can be selected:

" p "4 Item "p" Program precision. This option is the default and means a trap handler can only identify which program caused a floating-point exception.

" f "4 Item "f" Function precision. The trap handler can determine the function that caused a floating-point exception.

" i "4 Item "i" Instruction precision. The trap handler can determine the exact instruction that caused a floating-point exception. Other Alpha compilers provide the equivalent options called -scope_safe and -resumption_safe .

" -mieee -conformant "4 Item "-mieee-conformant" This option marks the generated code as IEEEconformant. You must not use this option unless you also specify -mtrap -precision=i and either -mfp -trap -mode=su or -mfp -trap -mode=sui .Its only effect is to emit the line .eflag48 in the function prologue of the generated assembly file.

" -mbuild -constants "4 Item "-mbuild-constants" Normally GCCexamines a 32 -or 64 -bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it outputs the constant as a literal and generates code to load it from the data segment at run time. Use this option to require GCCto construct all integer constants using code, even if it takes more instructions (the maximum is six). You typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment.

" -mbwx "4 Item "-mbwx" 0

" -mno -bwx "4 Item "-mno-bwx"

" -mcix "4 Item "-mcix"

" -mno -cix "4 Item "-mno-cix"

" -mfix "4 Item "-mfix"

" -mno -fix "4 Item "-mno-fix"

" -mmax "4 Item "-mmax"

" -mno -max "4 Item "-mno-max" Indicate whether GCCshould generate code to use the optional BWX, CIX, FIX and MAXinstruction sets. The default is to use the instruction sets supported by the CPUtype specified via -mcpu= option or that of the CPUon which GCCwas built if none is specified.

" -mfloat -vax "4 Item "-mfloat-vax" 0

" -mfloat -ieee "4 Item "-mfloat-ieee" Generate code that uses (does not use) VAXF and G floating-point arithmetic instead of IEEEsingle and double precision.

" -mexplicit -relocs "4 Item "-mexplicit-relocs" 0

" -mno -explicit -relocs "4 Item "-mno-explicit-relocs" Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimal instruction scheduling. GNUbinutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as GCCdetects the capabilities of the assembler when it is built and sets the default accordingly.

" -msmall -data "4 Item "-msmall-data" 0

" -mlarge -data "4 Item "-mlarge-data" When -mexplicit -relocs is in effect, static data is accessed via gp-relative relocations. When -msmall -data is used, objects 8 bytes long or smaller are placed in a smalldata area (the CW(C`.sdata (C' and CW(C`.sbss (C' sections) and are accessed via 16 -bit relocations off of the CW$gp register. This limits the size of the small data area to 64KB, but allows the variables to be directly accessed via a single instruction. The default is -mlarge -data .With this option the data area is limited to just below 2GB. Programs that require more than 2GB of data must use CW(C`malloc (C' or CW(C`mmap (C' to allocate the data in the heap instead of in the program's data segment. When generating code for shared libraries, -fpic implies -msmall -data and -fPIC implies -mlarge -data .

" -msmall -text "4 Item "-msmall-text" 0

" -mlarge -text "4 Item "-mlarge-text" When -msmall -text is used, the compiler assumes that the code of the entire program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When -msmall -data is used, the compiler can assume that all local symbols share the same CW$gp value, and thus reduce the number of instructions required for a function call from 4 to 1. The default is -mlarge -text .

" -mcpu= cpu_type "4 Item "-mcpu=cpu_type" Set the instruction set and instruction scheduling parameters for machine type cpu_type .You can specify either the EV style name or the corresponding chip number. GCCsupports scheduling parameters for the EV4,EV5 and EV6family of processors and chooses the default values for the instruction set from the processor you specify. If you do not specify a processor type, GCCdefaults to the processor on which the compiler was built. Supported values for cpu_type are

" ev4 "4 Item "ev4" 0

" ev45 "4 Item "ev45"

" 21064 "4 Item "21064" Schedules as an EV4and has no instruction set extensions.

" ev5 "4 Item "ev5" 0

" 21164 "4 Item "21164" Schedules as an EV5and has no instruction set extensions.

" ev56 "4 Item "ev56" 0

" 21164a "4 Item "21164a" Schedules as an EV5and supports the BWXextension.

" pca56 "4 Item "pca56" 0

" 21164pc "4 Item "21164pc"

" 21164PC "4 Item "21164PC" Schedules as an EV5and supports the BWXand MAXextensions.

" ev6 "4 Item "ev6" 0

" 21264 "4 Item "21264" Schedules as an EV6and supports the BWX,FIX, and MAXextensions.

" ev67 "4 Item "ev67" 0

" 21264a "4 Item "21264a" Schedules as an EV6and supports the BWX,CIX, FIX, and MAXextensions. Native toolchains also support the value native , which selects the best architecture option for the host processor. -mcpu=native has no effect if GCCdoes not recognize the processor.

" -mtune= cpu_type "4 Item "-mtune=cpu_type" Set only the instruction scheduling parameters for machine type cpu_type .The instruction set is not changed. Native toolchains also support the value native , which selects the best architecture option for the host processor. -mtune=native has no effect if GCCdoes not recognize the processor.

" -mmemory -latency= time "4 Item "-mmemory-latency=time" Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application and the size of the external cache on the machine. Valid options for time are

" number "4 Item "number" A decimal number representing clock cycles.

" L1 "4 Item "L1" 0

" L2 "4 Item "L2"

" L3 "4 Item "L3"

" main "4 Item "main" The compiler contains estimates of the number of clock cycles for (L"typical (R" EV4& EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and Bcache), as well as to main memory. Note that L3 is only valid for EV5.

FR30Options Subsection "FR30 Options"

These options are defined specifically for the FR30port.

" -msmall -model "4 Item "-msmall-model" Use the small address space model. This can produce smaller code, but it does assume that all symbolic values and addresses fit into a 20 -bit range.

" -mno -lsim "4 Item "-mno-lsim" Assume that runtime support has been provided and so there is no need to include the simulator library ( libsim.a )on the linker command line.

FT32Options Subsection "FT32 Options"

These options are defined specifically for the FT32port.

" -msim "4 Item "-msim" Specifies that the program will be run on the simulator. This causes an alternate runtime startup and library to be linked. You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed.

" -mlra "4 Item "-mlra" Enable Local Register Allocation. This is still experimental for FT32, so by default the compiler uses standard reload.

" -mnodiv "4 Item "-mnodiv" Do not use div and mod instructions.

" -mft32b "4 Item "-mft32b" Enable use of the extended instructions of the FT32Bprocessor.

" -mcompress "4 Item "-mcompress" Compress all code using the Ft32B code compression scheme.

" -mnopm "4 Item "-mnopm" Do not generate code that reads program memory.

FRVOptions Subsection "FRV Options"

" -mgpr -32 "4 Item "-mgpr-32" Only use the first 32 general-purpose registers.

" -mgpr -64 "4 Item "-mgpr-64" Use all 64 general-purpose registers.

" -mfpr -32 "4 Item "-mfpr-32" Use only the first 32 floating-point registers.

" -mfpr -64 "4 Item "-mfpr-64" Use all 64 floating-point registers.

" -mhard -float "4 Item "-mhard-float" Use hardware instructions for floating-point operations.

" -msoft -float "4 Item "-msoft-float" Use library routines for floating-point operations.

" -malloc -cc "4 Item "-malloc-cc" Dynamically allocate condition code registers.

" -mfixed -cc "4 Item "-mfixed-cc" Do not try to dynamically allocate condition code registers, only use CW(C`icc0 (C' and CW(C`fcc0 (C' .

" -mdword "4 Item "-mdword" Change ABIto use double word insns.

" -mno -dword "4 Item "-mno-dword" Do not use double word instructions.

" -mdouble "4 Item "-mdouble" Use floating-point double instructions.

" -mno -double "4 Item "-mno-double" Do not use floating-point double instructions.

" -mmedia "4 Item "-mmedia" Use media instructions.

" -mno -media "4 Item "-mno-media" Do not use media instructions.

" -mmuladd "4 Item "-mmuladd" Use multiply and add/subtract instructions.

" -mno -muladd "4 Item "-mno-muladd" Do not use multiply and add/subtract instructions.

" -mfdpic "4 Item "-mfdpic" Select the FDPICABI, which uses function descriptors to represent pointers to functions. Without any PIC/PIE -related options, it implies -fPIE .With -fpic or -fpie ,it assumes GOTentries and small data are within a 12 -bit range from the GOTbase address; with -fPIC or -fPIE ,GOToffsets are computed with 32 bits. With a bfin-elf target, this option implies -msim .

" -minline -plt "4 Item "-minline-plt" Enable inlining of PLTentries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic . It's enabled by default if optimizing for speed and compiling for shared libraries (i.e., -fPIC or -fpic ),or when an optimization option such as -O3 or above is present in the command line.

" -mTLS "4 Item "-mTLS" Assume a large TLSsegment when generating thread-local code.

" -mtls "4 Item "-mtls" Do not assume a large TLSsegment when generating thread-local code.

" -mgprel -ro "4 Item "-mgprel-ro" Enable the use of CW(C`GPREL (C' relocations in the FDPICABI for data that is known to be in read-only sections. It's enabled by default, except for -fpic or -fpie :even though it may help make the global offset table smaller, it trades 1 instruction for 4. With -fPIC or -fPIE ,it trades 3 instructions for 4, one of which may be shared by multiple symbols, and it avoids the need for a GOTentry for the referenced symbol, so it's more likely to be a win. If it is not, -mno -gprel -ro can be used to disable it.

" -multilib -library -pic "4 Item "-multilib-library-pic" Link with the (library, not FD)pic libraries. It's implied by -mlibrary -pic ,as well as by -fPIC and -fpic without -mfdpic .You should never have to use it explicitly.

" -mlinked -fp "4 Item "-mlinked-fp" Follow the EABIrequirement of always creating a frame pointer whenever a stack frame is allocated. This option is enabled by default and can be disabled with -mno -linked -fp .

" -mlong -calls "4 Item "-mlong-calls" Use indirect addressing to call functions outside the current compilation unit. This allows the functions to be placed anywhere within the 32 -bit address space.

" -malign -labels "4 Item "-malign-labels" Try to align labels to an 8 -byte boundary by inserting NOPs into the previous packet. This option only has an effect when VLIWpacking is enabled. It doesn't create new packets; it merely adds NOPs to existing ones.

" -mlibrary -pic "4 Item "-mlibrary-pic" Generate position-independent EABIcode.

" -macc -4 "4 Item "-macc-4" Use only the first four media accumulator registers.

" -macc -8 "4 Item "-macc-8" Use all eight media accumulator registers.

" -mpack "4 Item "-mpack" Pack VLIWinstructions.

" -mno -pack "4 Item "-mno-pack" Do not pack VLIWinstructions.

" -mno -eflags "4 Item "-mno-eflags" Do not mark ABIswitches in e_flags.

" -mcond -move "4 Item "-mcond-move" Enable the use of conditional-move instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mno -cond -move "4 Item "-mno-cond-move" Disable the use of conditional-move instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mscc "4 Item "-mscc" Enable the use of conditional set instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mno -scc "4 Item "-mno-scc" Disable the use of conditional set instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mcond -exec "4 Item "-mcond-exec" Enable the use of conditional execution (default). This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mno -cond -exec "4 Item "-mno-cond-exec" Disable the use of conditional execution. This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mvliw -branch "4 Item "-mvliw-branch" Run a pass to pack branches into VLIWinstructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mno -vliw -branch "4 Item "-mno-vliw-branch" Do not run a pass to pack branches into VLIWinstructions. This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mmulti -cond -exec "4 Item "-mmulti-cond-exec" Enable optimization of CW(C`&& (C' and CW(C`|| (C' in conditional execution (default). This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mno -multi -cond -exec "4 Item "-mno-multi-cond-exec" Disable optimization of CW(C`&& (C' and CW(C`|| (C' in conditional execution. This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mnested -cond -exec "4 Item "-mnested-cond-exec" Enable nested conditional execution optimizations (default). This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -mno -nested -cond -exec "4 Item "-mno-nested-cond-exec" Disable nested conditional execution optimizations. This switch is mainly for debugging the compiler and will likely be removed in a future version.

" -moptimize -membar "4 Item "-moptimize-membar" This switch removes redundant CW(C`membar (C' instructions from the compiler-generated code. It is enabled by default.

" -mno -optimize -membar "4 Item "-mno-optimize-membar" This switch disables the automatic removal of redundant CW(C`membar (C' instructions from the generated code.

" -mtomcat -stats "4 Item "-mtomcat-stats" Cause gas to print out tomcat statistics.

" -mcpu= cpu "4 Item "-mcpu=cpu" Select the processor type for which to generate code. Possible values are frv , fr550 , tomcat , fr500 , fr450 , fr405 , fr400 , fr300 and simple .

GNU/LinuxOptions Subsection "GNU/Linux Options"

These -m options are defined for GNU/Linux targets:

" -mglibc "4 Item "-mglibc" Use the GNUC library. This is the default except on *-* -linux -*uclibc* , *-* -linux -*musl* and *-* -linux -*android* targets.

" -muclibc "4 Item "-muclibc" Use uClibc C library. This is the default on *-* -linux -*uclibc* targets.

" -mmusl "4 Item "-mmusl" Use the musl C library. This is the default on *-* -linux -*musl* targets.

" -mbionic "4 Item "-mbionic" Use Bionic C library. This is the default on *-* -linux -*android* targets.

" -mandroid "4 Item "-mandroid" Compile code compatible with Android platform. This is the default on *-* -linux -*android* targets. When compiling, this option enables -mbionic , -fPIC , -fno -exceptions and -fno -rtti by default. When linking, this option makes the GCCdriver pass Android-specific options to the linker. Finally, this option causes the preprocessor macro CW(C`_ _ANDROID_ _ (C' to be defined.

" -tno -android -cc "4 Item "-tno-android-cc" Disable compilation effects of -mandroid ,i.e., do not enable -mbionic , -fPIC , -fno -exceptions and -fno -rtti by default.

" -tno -android -ld "4 Item "-tno-android-ld" Disable linking effects of -mandroid ,i.e., pass standard Linux linking options to the linker.

H8/300Options Subsection "H8/300 Options"

These -m options are defined for the H8/300 implementations:

" -mrelax "4 Item "-mrelax" Shorten some address references at link time, when possible; uses the linker option -relax .

" -mh "4 Item "-mh" Generate code for the H8/300H.

" -ms "4 Item "-ms" Generate code for the H8S.

" -mn "4 Item "-mn" Generate code for the H8S and H8/300H in the normal mode. This switch must be used either with -mh or -ms .

" -ms2600 "4 Item "-ms2600" Generate code for the H8S/2600. This switch must be used with -ms .

" -mexr "4 Item "-mexr" Extended registers are stored on stack before execution of function with monitor attribute. Default option is -mexr . This option is valid only for H8S targets.

" -mno -exr "4 Item "-mno-exr" Extended registers are not stored on stack before execution of function with monitor attribute. Default option is -mno -exr . This option is valid only for H8S targets.

" -mint32 "4 Item "-mint32" Make CW(C`int (C' data 32 bits by default.

" -malign -300 "4 Item "-malign-300" On the H8/300H and H8S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8S is to align longs and floats on 4 -byte boundaries. -malign -300 causes them to be aligned on 2 -byte boundaries. This option has no effect on the H8/300.

HPPAOptions Subsection "HPPA Options"

These -m options are defined for the HPPAfamily of computers:

" -march= architecture-type "4 Item "-march=architecture-type" Generate code for the specified architecture. The choices for architecture-type are 1.0 for PA1.0, 1.1 for PA 1.1, and 2.0 for PA2.0 processors. Refer to /usr/lib/sched.models on an HP-UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures runs on higher numbered architectures, but not the other way around.

" -mpa -risc -1 -0 "4 Item "-mpa-risc-1-0" 0

" -mpa -risc -1 -1 "4 Item "-mpa-risc-1-1"

" -mpa -risc -2 -0 "4 Item "-mpa-risc-2-0" Synonyms for -march=1.0 , -march=1.1 ,and -march=2.0 respectively.

" -mcaller -copies "4 Item "-mcaller-copies" The caller copies function arguments passed by hidden reference. This option should be used with care as it is not compatible with the default 32 -bit runtime. However, only aggregates larger than eight bytes are passed by hidden reference and the option provides better compatibility with OpenMP.

" -mjump -in -delay "4 Item "-mjump-in-delay" This option is ignored and provided for compatibility purposes only.

" -mdisable -fpregs "4 Item "-mdisable-fpregs" Prevent floating-point registers from being used in any manner. This is necessary for compiling kernels that perform lazy context switching of floating-point registers. If you use this option and attempt to perform floating-point operations, the compiler aborts.

" -mdisable -indexing "4 Item "-mdisable-indexing" Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling MIGgenerated code under MACH.

" -mno -space -regs "4 Item "-mno-space-regs" Generate code that assumes the target has no space registers. This allows GCCto generate faster indirect calls and use unscaled index address modes. Such code is suitable for level 0 PAsystems and kernels.

" -mfast -indirect -calls "4 Item "-mfast-indirect-calls" Generate code that assumes calls never cross space boundaries. This allows GCCto emit code that performs faster indirect calls. This option does not work in the presence of shared libraries or nested functions.

" -mfixed -range= register-range "4 Item "-mfixed-range=register-range" Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma.

" -mlong -load -store "4 Item "-mlong-load-store" Generate 3 -instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the +k option to the HPcompilers.

" -mportable -runtime "4 Item "-mportable-runtime" Use the portable calling conventions proposed by HPfor ELFsystems.

" -mgas "4 Item "-mgas" Enable the use of assembler directives only GASunderstands.

" -mschedule= cpu-type "4 Item "-mschedule=cpu-type" Schedule code according to the constraints for the machine type cpu-type .The choices for cpu-type are 700 7100 , 7100LC , 7200 , 7300 and 8000 .Refer to /usr/lib/sched.models on an HP-UX system to determine the proper scheduling option for your machine. The default scheduling is 8000 .

" -mlinker -opt "4 Item "-mlinker-opt" Enable the optimization pass in the HP-UX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error messages when linking some programs.

" -msoft -float "4 Item "-msoft-float" Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all HPPA targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. -msoft -float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a ,the library that comes with GCC,with -msoft -float in order for this to work.

" -msio "4 Item "-msio" Generate the predefine, CW(C`_SIO (C' ,for server IO.The default is -mwsio .This generates the predefines, CW(C`_ _hp9000s700 (C' , CW(C`_ _hp9000s700_ _ (C' and CW(C`_WSIO (C' ,for workstation IO.These options are available under HP-UX and HI-UX.

" -mgnu -ld "4 Item "-mgnu-ld" Use options specific to GNU ld . This passes -shared to ld when building a shared library. It is the default when GCCis configured, explicitly or implicitly, with the GNUlinker. This option does not affect which ld is called; it only changes what parameters are passed to that ld . The ld that is called is determined by the --with -ld configure option, GCC'sprogram search path, and finally by the user's PATH .The linker used by GCCcan be printed using which`gcc -print -prog -name=ld` .This option is only available on the 64 -bit HP-UX GCC,i.e. configured with hppa*64*-* -hpux* .

" -mhp -ld "4 Item "-mhp-ld" Use options specific to HP ld . This passes -b to ld when building a shared library and passes +AcceptTypeMismatch to ld on all links. It is the default when GCCis configured, explicitly or implicitly, with the HPlinker. This option does not affect which ld is called; it only changes what parameters are passed to that ld . The ld that is called is determined by the --with -ld configure option, GCC'sprogram search path, and finally by the user's PATH .The linker used by GCCcan be printed using which `gcc -print -prog -name=ld` .This option is only available on the 64 -bit HP-UX GCC,i.e. configured with hppa*64*-* -hpux* .

" -mlong -calls "4 Item "-mlong-calls" Generate code that uses long call sequences. This ensures that a call is always able to reach linker generated stubs. The default is to generate long calls only when the distance from the call site to the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set by the branch type being used. The limits for normal calls are 7,600,000 and 240,000 bytes, respectively for the PA2.0 and PA1.X architectures. Sibcalls are always limited at 240,000 bytes. Distances are measured from the beginning of functions when using the -ffunction -sections option, or when using the -mgas and -mno -portable -runtime options together under HP-UX with the SOMlinker. It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is used to build the application. The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32 -bit ELFsystems in pic code and it is quite long.

" -munix= unix-std "4 Item "-munix=unix-std" Generate compiler predefines and select a startfile for the specified UNIXstandard. The choices for unix-std are 93 , 95 and 98 . 93 is supported on all HP-UX versions. 95 is available on HP-UX 10.10 and later. 98 is available on HP-UX 11.11 and later. The default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to 11.00, and 98 for HP-UX 11.11 and later. -munix=93 provides the same predefines as GCC3.3 and 3.4. -munix=95 provides additional predefines for CW(C`XOPEN_UNIX (C' and CW(C`_XOPEN_SOURCE_EXTENDED (C' ,and the startfile unix95.o . -munix=98 provides additional predefines for CW(C`_XOPEN_UNIX (C' , CW(C`_XOPEN_SOURCE_EXTENDED (C' , CW(C`_INCLUDE_ _STDC_A1_SOURCE (C' and CW(C`_INCLUDE_XOPEN_SOURCE_500 (C' ,and the startfile unix98.o . It is important to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, extreme care is needed in using this option. Library code that is intended to operate with more than one UNIX standard must test, set and restore the variable CW(C`_ _xpg4_extended_mask (C' as appropriate. Most GNUsoftware doesn't provide this capability.

" -nolibdld "4 Item "-nolibdld" Suppress the generation of link options to search libdld.sl when the -static option is specified on HP-UX 10 and later.

" -static "4 Item "-static" The HP-UX implementation of setlocale in libc has a dependency on libdld.sl. There isn't an archive version of libdld.sl. Thus, when the -static option is specified, special link options are needed to resolve this dependency. On HP-UX 10 and later, the GCCdriver adds the necessary options to link with libdld.sl when the -static option is specified. This causes the resulting binary to be dynamic. On the 64 -bit port, the linkers generate dynamic binaries by default in any case. The -nolibdld option can be used to prevent the GCCdriver from adding these link options.

" -threads "4 Item "-threads" Add support for multithreading with the dcethread library under HP-UX. This option sets flags for both the preprocessor and linker.

IA-64 Options Subsection "IA-64 Options"

These are the -m options defined for the Intel IA-64 architecture.

" -mbig -endian "4 Item "-mbig-endian" Generate code for a big-endian target. This is the default for HP-UX.

" -mlittle -endian "4 Item "-mlittle-endian" Generate code for a little-endian target. This is the default for AIX5 and GNU/Linux.

" -mgnu -as "4 Item "-mgnu-as" 0

" -mno -gnu -as "4 Item "-mno-gnu-as" Generate (or don't) code for the GNUassembler. This is the default.

" -mgnu -ld "4 Item "-mgnu-ld" 0

" -mno -gnu -ld "4 Item "-mno-gnu-ld" Generate (or don't) code for the GNUlinker. This is the default.

" -mno -pic "4 Item "-mno-pic" Generate code that does not use a global pointer register. The result is not position independent code, and violates the IA-64 ABI.

" -mvolatile -asm -stop "4 Item "-mvolatile-asm-stop" 0

" -mno -volatile -asm -stop "4 Item "-mno-volatile-asm-stop" Generate (or don't) a stop bit immediately before and after volatile asm statements.

" -mregister -names "4 Item "-mregister-names" 0

" -mno -register -names "4 Item "-mno-register-names" Generate (or don't) in , loc ,and out register names for the stacked registers. This may make assembler output more readable.

" -mno -sdata "4 Item "-mno-sdata" 0

" -msdata "4 Item "-msdata" Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs.

" -mconstant -gp "4 Item "-mconstant-gp" Generate code that uses a single constant global pointer value. This is useful when compiling kernel code.

" -mauto -pic "4 Item "-mauto-pic" Generate code that is self-relocatable. This implies -mconstant -gp . This is useful when compiling firmware code.

" -minline -float -divide -min -latency "4 Item "-minline-float-divide-min-latency" Generate code for inline divides of floating-point values using the minimum latency algorithm.

" -minline -float -divide -max -throughput "4 Item "-minline-float-divide-max-throughput" Generate code for inline divides of floating-point values using the maximum throughput algorithm.

" -mno -inline -float -divide "4 Item "-mno-inline-float-divide" Do not generate inline code for divides of floating-point values.

" -minline -int -divide -min -latency "4 Item "-minline-int-divide-min-latency" Generate code for inline divides of integer values using the minimum latency algorithm.

" -minline -int -divide -max -throughput "4 Item "-minline-int-divide-max-throughput" Generate code for inline divides of integer values using the maximum throughput algorithm.

" -mno -inline -int -divide "4 Item "-mno-inline-int-divide" Do not generate inline code for divides of integer values.

" -minline -sqrt -min -latency "4 Item "-minline-sqrt-min-latency" Generate code for inline square roots using the minimum latency algorithm.

" -minline -sqrt -max -throughput "4 Item "-minline-sqrt-max-throughput" Generate code for inline square roots using the maximum throughput algorithm.

" -mno -inline -sqrt "4 Item "-mno-inline-sqrt" Do not generate inline code for CW(C`sqrt (C' .

" -mfused -madd "4 Item "-mfused-madd" 0

" -mno -fused -madd "4 Item "-mno-fused-madd" Do (don't) generate code that uses the fused multiply/add or multiply/subtract instructions. The default is to use these instructions.

" -mno -dwarf2 -asm "4 Item "-mno-dwarf2-asm" 0

" -mdwarf2 -asm "4 Item "-mdwarf2-asm" Don't (or do) generate assembler code for the DWARFline number debugging info. This may be useful when not using the GNUassembler.

" -mearly -stop -bits "4 Item "-mearly-stop-bits" 0

" -mno -early -stop -bits "4 Item "-mno-early-stop-bits" Allow stop bits to be placed earlier than immediately preceding the instruction that triggered the stop bit. This can improve instruction scheduling, but does not always do so.

" -mfixed -range= register-range "4 Item "-mfixed-range=register-range" Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma.

" -mtls -size= tls-size "4 Item "-mtls-size=tls-size" Specify bit size of immediate TLSoffsets. Valid values are 14, 22, and 64.

" -mtune= cpu-type "4 Item "-mtune=cpu-type" Tune the instruction scheduling for a particular CPU,Valid values are itanium , itanium1 , merced , itanium2 , and mckinley .

" -milp32 "4 Item "-milp32" 0

" -mlp64 "4 Item "-mlp64" Generate code for a 32 -bit or 64 -bit environment. The 32 -bit environment sets int, long and pointer to 32 bits. The 64 -bit environment sets int to 32 bits and long and pointer to 64 bits. These are HP-UX specific flags.

" -mno -sched -br -data -spec "4 Item "-mno-sched-br-data-spec" 0

" -msched -br -data -spec "4 Item "-msched-br-data-spec" (Dis/En)able data speculative scheduling before reload. This results in generation of CW(C`ld.a (C' instructions and the corresponding check instructions ( CW(C`ld.c (C' / CW(C`chk.a (C' ). The default setting is disabled.

" -msched -ar -data -spec "4 Item "-msched-ar-data-spec" 0

" -mno -sched -ar -data -spec "4 Item "-mno-sched-ar-data-spec" (En/Dis)able data speculative scheduling after reload. This results in generation of CW(C`ld.a (C' instructions and the corresponding check instructions ( CW(C`ld.c (C' / CW(C`chk.a (C' ). The default setting is enabled.

" -mno -sched -control -spec "4 Item "-mno-sched-control-spec" 0

" -msched -control -spec "4 Item "-msched-control-spec" (Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e. before reload). This results in generation of the CW(C`ld.s (C' instructions and the corresponding check instructions CW(C`chk.s (C' . The default setting is disabled.

" -msched -br -in -data -spec "4 Item "-msched-br-in-data-spec" 0

" -mno -sched -br -in -data -spec "4 Item "-mno-sched-br-in-data-spec" (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads before reload. This is effective only with -msched -br -data -spec enabled. The default setting is enabled.

" -msched -ar -in -data -spec "4 Item "-msched-ar-in-data-spec" 0

" -mno -sched -ar -in -data -spec "4 Item "-mno-sched-ar-in-data-spec" (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads after reload. This is effective only with -msched -ar -data -spec enabled. The default setting is enabled.

" -msched -in -control -spec "4 Item "-msched-in-control-spec" 0

" -mno -sched -in -control -spec "4 Item "-mno-sched-in-control-spec" (En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads. This is effective only with -msched -control -spec enabled. The default setting is enabled.

" -mno -sched -prefer -non -data -spec -insns "4 Item "-mno-sched-prefer-non-data-spec-insns" 0

" -msched -prefer -non -data -spec -insns "4 Item "-msched-prefer-non-data-spec-insns" If enabled, data-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the data speculation much more conservative. The default setting is disabled.

" -mno -sched -prefer -non -control -spec -insns "4 Item "-mno-sched-prefer-non-control-spec-insns" 0

" -msched -prefer -non -control -spec -insns "4 Item "-msched-prefer-non-control-spec-insns" If enabled, control-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the control speculation much more conservative. The default setting is disabled.

" -mno -sched -count -spec -in -critical -path "4 Item "-mno-sched-count-spec-in-critical-path" 0

" -msched -count -spec -in -critical -path "4 Item "-msched-count-spec-in-critical-path" If enabled, speculative dependencies are considered during computation of the instructions priorities. This makes the use of the speculation a bit more conservative. The default setting is disabled.

" -msched -spec -ldc "4 Item "-msched-spec-ldc" Use a simple data speculation check. This option is on by default.

" -msched -control -spec -ldc "4 Item "-msched-control-spec-ldc" Use a simple check for control speculation. This option is on by default.

" -msched -stop -bits -after -every -cycle "4 Item "-msched-stop-bits-after-every-cycle" Place a stop bit after every cycle when scheduling. This option is on by default.

" -msched -fp -mem -deps -zero -cost "4 Item "-msched-fp-mem-deps-zero-cost" Assume that floating-point stores and loads are not likely to cause a conflict when placed into the same instruction group. This option is disabled by default.

" -msel -sched -dont -check -control -spec "4 Item "-msel-sched-dont-check-control-spec" Generate checks for control speculation in selective scheduling. This flag is disabled by default.

" -msched -max -memory -insns= max-insns "4 Item "-msched-max-memory-insns=max-insns" Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction group. Frequently useful to prevent cache bank conflicts. The default value is 1.

" -msched -max -memory -insns -hard -limit "4 Item "-msched-max-memory-insns-hard-limit" Makes the limit specified by msched-max-memory-insns a hard limit, disallowing more than that number in an instruction group. Otherwise, the limit is (L"soft (R", meaning that non-memory operations are preferred when the limit is reached, but memory operations may still be scheduled.

LM32Options Subsection "LM32 Options"

These -m options are defined for the LatticeMico32 architecture:

" -mbarrel -shift -enabled "4 Item "-mbarrel-shift-enabled" Enable barrel-shift instructions.

" -mdivide -enabled "4 Item "-mdivide-enabled" Enable divide and modulus instructions.

" -mmultiply -enabled "4 Item "-mmultiply-enabled" Enable multiply instructions.

" -msign -extend -enabled "4 Item "-msign-extend-enabled" Enable sign extend instructions.

" -muser -enabled "4 Item "-muser-enabled" Enable user-defined instructions.

M32COptions Subsection "M32C Options"

" -mcpu= name "4 Item "-mcpu=name" Select the CPUfor which code is generated. name may be one of r8c for the R8C/Tiny series, m16c for the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c for the M32C/80 series.

" -msim "4 Item "-msim" Specifies that the program will be run on the simulator. This causes an alternate runtime library to be linked in which supports, for example, file I/O. You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed.

" -memregs= number "4 Item "-memregs=number" Specifies the number of memory-based pseudo-registers GCCuses during code generation. These pseudo-registers are used like real registers, so there is a tradeoff between GCC'sability to fit the code into available registers, and the performance penalty of using memory instead of registers. Note that all modules in a program must be compiled with the same value for this option. Because of that, you must not use this option with GCC'sdefault runtime libraries.

M32R/DOptions Subsection "M32R/D Options"

These -m options are defined for Renesas M32R/D architectures:

" -m32r2 "4 Item "-m32r2" Generate code for the M32R/2.

" -m32rx "4 Item "-m32rx" Generate code for the M32R/X.

" -m32r "4 Item "-m32r" Generate code for the M32R. This is the default.

" -mmodel=small "4 Item "-mmodel=small" Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the CW(C`ld24 (C' instruction), and assume all subroutines are reachable with the CW(C`bl (C' instruction. This is the default. The addressability of a particular object can be set with the CW(C`model (C' attribute.

" -mmodel=medium "4 Item "-mmodel=medium" Assume objects may be anywhere in the 32 -bit address space (the compiler generates CW(C`seth/add3 (C' instructions to load their addresses), and assume all subroutines are reachable with the CW(C`bl (C' instruction.

" -mmodel=large "4 Item "-mmodel=large" Assume objects may be anywhere in the 32 -bit address space (the compiler generates CW(C`seth/add3 (C' instructions to load their addresses), and assume subroutines may not be reachable with the CW(C`bl (C' instruction (the compiler generates the much slower CW(C`seth/add3/jl (C' instruction sequence).

" -msdata=none "4 Item "-msdata=none" Disable use of the small data area. Variables are put into one of CW(C`.data (C' , CW(C`.bss (C' ,or CW(C`.rodata (C' (unless the CW(C`section (C' attribute has been specified). This is the default. The small data area consists of sections CW(C`.sdata (C' and CW(C`.sbss (C' . Objects may be explicitly put in the small data area with the CW(C`section (C' attribute using one of these sections.

" -msdata=sdata "4 Item "-msdata=sdata" Put small global and static data in the small data area, but do not generate special code to reference them.

" -msdata=use "4 Item "-msdata=use" Put small global and static data in the small data area, and generate special instructions to reference them.

" -G num "4 Item "-G num" Put global and static objects less than or equal to num bytes into the small data or BSSsections instead of the normal data or BSS sections. The default value of num is 8. The -msdata option must be set to one of sdata or use for this option to have any effect. All modules should be compiled with the same -G num value. Compiling with different values of num may or may not work; if it doesn't the linker gives an error message ---incorrect code is not generated.

" -mdebug "4 Item "-mdebug" Makes the M32R -specific code in the compiler display some statistics that might help in debugging programs.

" -malign -loops "4 Item "-malign-loops" Align all loops to a 32 -byte boundary.

" -mno -align -loops "4 Item "-mno-align-loops" Do not enforce a 32 -byte alignment for loops. This is the default.

" -missue -rate= number "4 Item "-missue-rate=number" Issue number instructions per cycle. number can only be 1 or 2.

" -mbranch -cost= number "4 Item "-mbranch-cost=number" number can only be 1 or 2. If it is 1 then branches are preferred over conditional code, if it is 2, then the opposite applies.

" -mflush -trap= number "4 Item "-mflush-trap=number" Specifies the trap number to use to flush the cache. The default is 12. Valid numbers are between 0 and 15 inclusive.

" -mno -flush -trap "4 Item "-mno-flush-trap" Specifies that the cache cannot be flushed by using a trap.

" -mflush -func= name "4 Item "-mflush-func=name" Specifies the name of the operating system function to call to flush the cache. The default is _flush_cache ,but a function call is only used if a trap is not available.

" -mno -flush -func "4 Item "-mno-flush-func" Indicates that there is no OSfunction for flushing the cache.

M680x0Options Subsection "M680x0 Options"

These are the -m options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most common choices are given below.

" -march= arch "4 Item "-march=arch" Generate code for a specific M680x0 or ColdFire instruction set architecture. Permissible values of arch for M680x0 architectures are: 68000 , 68010 , 68020 , 68030 , 68040 , 68060 and cpu32 .ColdFire architectures are selected according to Freescale's ISAclassification and the permissible values are: isaa , isaaplus , isab and isac . GCCdefines a macro CW(C`_ _mcf CIarch CW__ (C' whenever it is generating code for a ColdFire target. The arch in this macro is one of the -march arguments given above. When used together, -march and -mtune select code that runs on a family of similar processors but that is optimized for a particular microarchitecture.

" -mcpu= cpu "4 Item "-mcpu=cpu" Generate code for a specific M680x0 or ColdFire processor. The M680x0 cpu sare: 68000 , 68010 , 68020 , 68030 , 68040 , 68060 , 68302 , 68332 and cpu32 .The ColdFire cpu sare given by the table below, which also classifies the CPUs into families:

"Family : -mcpu arguments" 4 Item "Family : -mcpu arguments" 0

" 51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm "4 Item "51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm"

" 5206 : 5202 5204 5206 "4 Item "5206 : 5202 5204 5206"

" 5206e : 5206e "4 Item "5206e : 5206e"

" 5208 : 5207 5208 "4 Item "5208 : 5207 5208"

" 5211a : 5210a 5211a "4 Item "5211a : 5210a 5211a"

" 5213 : 5211 5212 5213 "4 Item "5213 : 5211 5212 5213"

" 5216 : 5214 5216 "4 Item "5216 : 5214 5216"

" 52235 : 52230 52231 52232 52233 52234 52235 "4 Item "52235 : 52230 52231 52232 52233 52234 52235"

" 5225 : 5224 5225 "4 Item "5225 : 5224 5225"

" 52259 : 52252 52254 52255 52256 52258 52259 "4 Item "52259 : 52252 52254 52255 52256 52258 52259"

" 5235 : 5232 5233 5234 5235 523x "4 Item "5235 : 5232 5233 5234 5235 523x"

" 5249 : 5249 "4 Item "5249 : 5249"

" 5250 : 5250 "4 Item "5250 : 5250"

" 5271 : 5270 5271 "4 Item "5271 : 5270 5271"

" 5272 : 5272 "4 Item "5272 : 5272"

" 5275 : 5274 5275 "4 Item "5275 : 5274 5275"

" 5282 : 5280 5281 5282 528x "4 Item "5282 : 5280 5281 5282 528x"

" 53017 : 53011 53012 53013 53014 53015 53016 53017 "4 Item "53017 : 53011 53012 53013 53014 53015 53016 53017"

" 5307 : 5307 "4 Item "5307 : 5307"

" 5329 : 5327 5328 5329 532x "4 Item "5329 : 5327 5328 5329 532x"

" 5373 : 5372 5373 537x "4 Item "5373 : 5372 5373 537x"

" 5407 : 5407 "4 Item "5407 : 5407"

" 5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485 "4 Item "5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485" -mcpu= cpu overrides -march= arch if arch is compatible with cpu .Other combinations of -mcpu and -march are rejected. GCCdefines the macro CW(C`_ _mcf_cpu_ CIcpu CW(C' when ColdFire target cpu is selected. It also defines CW(C`_ _mcf_family_ CIfamily CW(C' , where the value of family is given by the table above.

" -mtune= tune "4 Item "-mtune=tune" Tune the code for a particular microarchitecture within the constraints set by -march and -mcpu . The M680x0 microarchitectures are: 68000 , 68010 , 68020 , 68030 , 68040 , 68060 and cpu32 .The ColdFire microarchitectures are: cfv1 , cfv2 , cfv3 , cfv4 and cfv4e . You can also use -mtune=68020 -40 for code that needs to run relatively well on 68020, 68030 and 68040 targets. -mtune=68020 -60 is similar but includes 68060 targets as well. These two options select the same tuning decisions as -m68020 -40 and -m68020 -60 respectively. GCCdefines the macros CW(C`_ _mc CIarch CW(C' and CW(C`_ _mc CIarch CW__ (C' when tuning for 680x0 architecture arch .It also defines CW(C`mc CIarch CW(C' unless either -ansi or a non-GNU -std option is used. If GCCis tuning for a range of architectures, as selected by -mtune=68020 -40 or -mtune=68020 -60 , it defines the macros for every architecture in the range. GCCalso defines the macro CW(C`_ _m CIuarch CW__ (C' when tuning for ColdFire microarchitecture uarch ,where uarch is one of the arguments given above.

" -m68000 "4 Item "-m68000" 0

" -mc68000 "4 Item "-mc68000" Generate output for a 68000. This is the default when the compiler is configured for 68000 -based systems. It is equivalent to -march=68000 . Use this option for microcontrollers with a 68000 or EC000core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

" -m68010 "4 Item "-m68010" Generate output for a 68010. This is the default when the compiler is configured for 68010 -based systems. It is equivalent to -march=68010 .

" -m68020 "4 Item "-m68020" 0

" -mc68020 "4 Item "-mc68020" Generate output for a 68020. This is the default when the compiler is configured for 68020 -based systems. It is equivalent to -march=68020 .

" -m68030 "4 Item "-m68030" Generate output for a 68030. This is the default when the compiler is configured for 68030 -based systems. It is equivalent to -march=68030 .

" -m68040 "4 Item "-m68040" Generate output for a 68040. This is the default when the compiler is configured for 68040 -based systems. It is equivalent to -march=68040 . This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions.

" -m68060 "4 Item "-m68060" Generate output for a 68060. This is the default when the compiler is configured for 68060 -based systems. It is equivalent to -march=68060 . This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions.

" -mcpu32 "4 Item "-mcpu32" Generate output for a CPU32.This is the default when the compiler is configured for CPU32 -based systems. It is equivalent to -march=cpu32 . Use this option for microcontrollers with a CPU32or CPU32+core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360.

" -m5200 "4 Item "-m5200" Generate output for a 520X ColdFire CPU.This is the default when the compiler is configured for 520X -based systems. It is equivalent to -mcpu=5206 ,and is now deprecated in favor of that option. Use this option for microcontroller with a 5200 core, including the MCF5202,MCF5203, MCF5204 and MCF5206.

" -m5206e "4 Item "-m5206e" Generate output for a 5206e ColdFire CPU.The option is now deprecated in favor of the equivalent -mcpu=5206e .

" -m528x "4 Item "-m528x" Generate output for a member of the ColdFire 528X family. The option is now deprecated in favor of the equivalent -mcpu=528x .

" -m5307 "4 Item "-m5307" Generate output for a ColdFire 5307 CPU.The option is now deprecated in favor of the equivalent -mcpu=5307 .

" -m5407 "4 Item "-m5407" Generate output for a ColdFire 5407 CPU.The option is now deprecated in favor of the equivalent -mcpu=5407 .

" -mcfv4e "4 Item "-mcfv4e" Generate output for a ColdFire V4e family CPU(e.g. 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to -mcpu=547x ,and is now deprecated in favor of that option.

" -m68020 -40 "4 Item "-m68020-40" Generate output for a 68040, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040. The option is equivalent to -march=68020 -mtune=68020 -40 .

" -m68020 -60 "4 Item "-m68020-60" Generate output for a 68060, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68060. The option is equivalent to -march=68020 -mtune=68020 -60 .

" -mhard -float "4 Item "-mhard-float" 0

" -m68881 "4 Item "-m68881" Generate floating-point instructions. This is the default for 68020 and above, and for ColdFire devices that have an FPU.It defines the macro CW(C`_ _HAVE_68881_ _ (C' on M680x0 targets and CW(C`_ _mcffpu_ _ (C' on ColdFire targets.

" -msoft -float "4 Item "-msoft-float" Do not generate floating-point instructions; use library calls instead. This is the default for 68000, 68010, and 68832 targets. It is also the default for ColdFire devices that have no FPU.

" -mdiv "4 Item "-mdiv" 0

" -mno -div "4 Item "-mno-div" Generate (do not generate) ColdFire hardware divide and remainder instructions. If -march is used without -mcpu , the default is (L"on (R" for ColdFire architectures and (L"off (R" for M680x0 architectures. Otherwise, the default is taken from the target CPU (either the default CPU,or the one specified by -mcpu ).For example, the default is (L"off (R" for -mcpu=5206 and (L"on (R" for -mcpu=5206e . GCCdefines the macro CW(C`_ _mcfhwdiv_ _ (C' when this option is enabled.

" -mshort "4 Item "-mshort" Consider type CW(C`int (C' to be 16 bits wide, like CW(C`short int (C' . Additionally, parameters passed on the stack are also aligned to a 16 -bit boundary even on targets whose APImandates promotion to 32 -bit.

" -mno -short "4 Item "-mno-short" Do not consider type CW(C`int (C' to be 16 bits wide. This is the default.

" -mnobitfield "4 Item "-mnobitfield" 0

" -mno -bitfield "4 Item "-mno-bitfield" Do not use the bit-field instructions. The -m68000 , -mcpu32 and -m5200 options imply -mnobitfield .

" -mbitfield "4 Item "-mbitfield" Do use the bit-field instructions. The -m68020 option implies -mbitfield .This is the default if you use a configuration designed for a 68020.

" -mrtd "4 Item "-mrtd" Use a different function-calling convention, in which functions that take a fixed number of arguments return with the CW(C`rtd (C' instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including CW(C`printf (C' ); otherwise incorrect code is generated for calls to those functions. In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) The CW(C`rtd (C' instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32processors, but not by the 68000 or 5200. The default is -mno -rtd .

" -malign -int "4 Item "-malign-int" 0

" -mno -align -int "4 Item "-mno-align-int" Control whether GCCaligns CW(C`int (C' , CW(C`long (C' , CW(C`long long (C' , CW(C`float (C' , CW(C`double (C' ,and CW(C`long double (C' variables on a 32 -bit boundary ( -malign -int )or a 16 -bit boundary ( -mno -align -int ). Aligning variables on 32 -bit boundaries produces code that runs somewhat faster on processors with 32 -bit busses at the expense of more memory. Warning: if you use the -malign -int switch, GCC aligns structures containing the above types differently than most published application binary interface specifications for the m68k.

" -mpcrel "4 Item "-mpcrel" Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies -fpic , allowing at most a 16 -bit offset for pc-relative addressing. -fPIC is not presently supported with -mpcrel ,though this could be supported for 68020 and higher processors.

" -mno -strict -align "4 Item "-mno-strict-align" 0

" -mstrict -align "4 Item "-mstrict-align" Do not (do) assume that unaligned memory references are handled by the system.

" -msep -data "4 Item "-msep-data" Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute-in-place in an environment without virtual memory management. This option implies -fPIC .

" -mno -sep -data "4 Item "-mno-sep-data" Generate code that assumes that the data segment follows the text segment. This is the default.

" -mid -shared -library "4 Item "-mid-shared-library" Generate code that supports shared libraries via the library IDmethod. This allows for execute-in-place and shared libraries in an environment without virtual memory management. This option implies -fPIC .

" -mno -id -shared -library "4 Item "-mno-id-shared-library" Generate code that doesn't assume ID-based shared libraries are being used. This is the default.

" -mshared -library -id=n "4 Item "-mshared-library-id=n" Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library, but is no more space -or time-efficient than omitting this option.

" -mxgot "4 Item "-mxgot" 0

" -mno -xgot "4 Item "-mno-xgot" When generating position-independent code for ColdFire, generate code that works if the GOThas more than 8192 entries. This code is larger and slower than code generated without this option. On M680x0 processors, this option is not needed; -fPIC suffices. GCCnormally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as: 1 relocation truncated to fit: R_68K_GOT16O foobar If this happens, you should recompile your code with -mxgot . It should then work with very large GOTs. However, code generated with -mxgot is less efficient, since it takes 4 instructions to fetch the value of a global symbol. Note that some linkers, including newer versions of the GNUlinker, can create multiple GOTs and sort GOTentries. If you have such a linker, you should only need to use -mxgot when compiling a single object file that accesses more than 8192 GOTentries. Very few do. These options have no effect unless GCCis generating position-independent code.

" -mlong -jump -table -offsets "4 Item "-mlong-jump-table-offsets" Use 32 -bit offsets in CW(C`switch (C' tables. The default is to use 16 -bit offsets.

MCoreOptions Subsection "MCore Options"

These are the -m options defined for the Motorola M*Core processors.

" -mhardlit "4 Item "-mhardlit" 0

" -mno -hardlit "4 Item "-mno-hardlit" Inline constants into the code stream if it can be done in two instructions or less.

" -mdiv "4 Item "-mdiv" 0

" -mno -div "4 Item "-mno-div" Use the divide instruction. (Enabled by default).

" -mrelax -immediate "4 Item "-mrelax-immediate" 0

" -mno -relax -immediate "4 Item "-mno-relax-immediate" Allow arbitrary-sized immediates in bit operations.

" -mwide -bitfields "4 Item "-mwide-bitfields" 0

" -mno -wide -bitfields "4 Item "-mno-wide-bitfields" Always treat bit-fields as CW(C`int (C' -sized.

" -m4byte -functions "4 Item "-m4byte-functions" 0

" -mno -4byte -functions "4 Item "-mno-4byte-functions" Force all functions to be aligned to a 4 -byte boundary.

" -mcallgraph -data "4 Item "-mcallgraph-data" 0

" -mno -callgraph -data "4 Item "-mno-callgraph-data" Emit callgraph information.

" -mslow -bytes "4 Item "-mslow-bytes" 0

" -mno -slow -bytes "4 Item "-mno-slow-bytes" Prefer word access when reading byte quantities.

" -mlittle -endian "4 Item "-mlittle-endian" 0

" -mbig -endian "4 Item "-mbig-endian" Generate code for a little-endian target.

" -m210 "4 Item "-m210" 0

" -m340 "4 Item "-m340" Generate code for the 210 processor.

" -mno -lsim "4 Item "-mno-lsim" Assume that runtime support has been provided and so omit the simulator library ( libsim.a) from the linker command line.

" -mstack -increment= size "4 Item "-mstack-increment=size" Set the maximum amount for a single stack increment operation. Large values can increase the speed of programs that contain functions that need a large amount of stack space, but they can also trigger a segmentation fault if the stack is extended too much. The default value is 0x1000.

MePOptions Subsection "MeP Options"

" -mabsdiff "4 Item "-mabsdiff" Enables the CW(C`abs (C' instruction, which is the absolute difference between two registers.

" -mall -opts "4 Item "-mall-opts" Enables all the optional instructions ---average, multiply, divide, bit operations, leading zero, absolute difference, min/max, clip, and saturation.

" -maverage "4 Item "-maverage" Enables the CW(C`ave (C' instruction, which computes the average of two registers.

" -mbased= n "4 Item "-mbased=n" Variables of size n bytes or smaller are placed in the CW(C`.based (C' section by default. Based variables use the CW$tp register as a base register, and there is a 128 -byte limit to the CW(C`.based (C' section.

" -mbitops "4 Item "-mbitops" Enables the bit operation instructions ---bit test ( CW(C`btstm (C' ),set ( CW(C`bsetm (C' ),clear ( CW(C`bclrm (C' ),invert ( CW(C`bnotm (C' ),and test-and-set ( CW(C`tas (C' ).

" -mc= name "4 Item "-mc=name" Selects which section constant data is placed in. name may be tiny , near ,or far .

" -mclip "4 Item "-mclip" Enables the CW(C`clip (C' instruction. Note that -mclip is not useful unless you also provide -mminmax .

" -mconfig= name "4 Item "-mconfig=name" Selects one of the built-in core configurations. Each MeP chip has one or more modules in it; each module has a core CPUand a variety of coprocessors, optional instructions, and peripherals. The CW(C`MeP -Integrator (C' tool, not part of GCC,provides these configurations through this option; using this option is the same as using all the corresponding command-line options. The default configuration is default .

" -mcop "4 Item "-mcop" Enables the coprocessor instructions. By default, this is a 32 -bit coprocessor. Note that the coprocessor is normally enabled via the -mconfig= option.

" -mcop32 "4 Item "-mcop32" Enables the 32 -bit coprocessor's instructions.

" -mcop64 "4 Item "-mcop64" Enables the 64 -bit coprocessor's instructions.

" -mivc2 "4 Item "-mivc2" Enables IVC2scheduling. IVC2is a 64 -bit VLIWcoprocessor.

" -mdc "4 Item "-mdc" Causes constant variables to be placed in the CW(C`.near (C' section.

" -mdiv "4 Item "-mdiv" Enables the CW(C`div (C' and CW(C`divu (C' instructions.

" -meb "4 Item "-meb" Generate big-endian code.

" -mel "4 Item "-mel" Generate little-endian code.

" -mio -volatile "4 Item "-mio-volatile" Tells the compiler that any variable marked with the CW(C`io (C' attribute is to be considered volatile.

" -ml "4 Item "-ml" Causes variables to be assigned to the CW(C`.far (C' section by default.

" -mleadz "4 Item "-mleadz" Enables the CW(C`leadz (C' (leading zero) instruction.

" -mm "4 Item "-mm" Causes variables to be assigned to the CW(C`.near (C' section by default.

" -mminmax "4 Item "-mminmax" Enables the CW(C`min (C' and CW(C`max (C' instructions.

" -mmult "4 Item "-mmult" Enables the multiplication and multiply-accumulate instructions.

" -mno -opts "4 Item "-mno-opts" Disables all the optional instructions enabled by -mall -opts .

" -mrepeat "4 Item "-mrepeat" Enables the CW(C`repeat (C' and CW(C`erepeat (C' instructions, used for low-overhead looping.

" -ms "4 Item "-ms" Causes all variables to default to the CW(C`.tiny (C' section. Note that there is a 65536 -byte limit to this section. Accesses to these variables use the CW%gp base register.

" -msatur "4 Item "-msatur" Enables the saturation instructions. Note that the compiler does not currently generate these itself, but this option is included for compatibility with other tools, like CW(C`as (C' .

" -msdram "4 Item "-msdram" Link the SDRAM-based runtime instead of the default ROM-based runtime.

" -msim "4 Item "-msim" Link the simulator run-time libraries.

" -msimnovec "4 Item "-msimnovec" Link the simulator runtime libraries, excluding built-in support for reset and exception vectors and tables.

" -mtf "4 Item "-mtf" Causes all functions to default to the CW(C`.far (C' section. Without this option, functions default to the CW(C`.near (C' section.

" -mtiny= n "4 Item "-mtiny=n" Variables that are n bytes or smaller are allocated to the CW(C`.tiny (C' section. These variables use the CW$gp base register. The default for this option is 4, but note that there's a 65536 -byte limit to the CW(C`.tiny (C' section.

MicroBlazeOptions Subsection "MicroBlaze Options"

" -msoft -float "4 Item "-msoft-float" Use software emulation for floating point (default).

" -mhard -float "4 Item "-mhard-float" Use hardware floating-point instructions.

" -mmemcpy "4 Item "-mmemcpy" Do not optimize block moves, use CW(C`memcpy (C' .

" -mno -clearbss "4 Item "-mno-clearbss" This option is deprecated. Use -fno -zero -initialized -in -bss instead.

" -mcpu= cpu-type "4 Item "-mcpu=cpu-type" Use features of, and schedule code for, the given CPU. Supported values are in the format v X . YY . Z , where X is a major version, YY is the minor version, and Z is compatibility code. Example values are v3.00.a , v4.00.b , v5.00.a , v5.00.b , v6.00.a .

" -mxl -soft -mul "4 Item "-mxl-soft-mul" Use software multiply emulation (default).

" -mxl -soft -div "4 Item "-mxl-soft-div" Use software emulation for divides (default).

" -mxl -barrel -shift "4 Item "-mxl-barrel-shift" Use the hardware barrel shifter.

" -mxl -pattern -compare "4 Item "-mxl-pattern-compare" Use pattern compare instructions.

" -msmall -divides "4 Item "-msmall-divides" Use table lookup optimization for small signed integer divisions.

" -mxl -stack -check "4 Item "-mxl-stack-check" This option is deprecated. Use -fstack -check instead.

" -mxl -gp -opt "4 Item "-mxl-gp-opt" Use GP-relative CW(C`.sdata (C' / CW(C`.sbss (C' sections.

" -mxl -multiply -high "4 Item "-mxl-multiply-high" Use multiply high instructions for high part of 32x32 multiply.

" -mxl -float -convert "4 Item "-mxl-float-convert" Use hardware floating-point conversion instructions.

" -mxl -float -sqrt "4 Item "-mxl-float-sqrt" Use hardware floating-point square root instruction.

" -mbig -endian "4 Item "-mbig-endian" Generate code for a big-endian target.

" -mlittle -endian "4 Item "-mlittle-endian" Generate code for a little-endian target.

" -mxl -reorder "4 Item "-mxl-reorder" Use reorder instructions (swap and byte reversed load/store).

" -mxl -mode - app-model "4 Item "-mxl-mode-app-model" Select application model app-model .Valid models are

" executable "4 Item "executable" normal executable (default), uses startup code crt0.o .

" -mpic -data -is -text -relative "4 Item "-mpic-data-is-text-relative" Assume that the displacement between the text and data segments is fixed at static link time. This allows data to be referenced by offset from start of text address instead of GOTsince PC-relative addressing is not supported.

" xmdstub "4 Item "xmdstub" for use with Xilinx Microprocessor Debugger ( XMD)based software intrusive debug agent called xmdstub. This uses startup file crt1.o and sets the start address of the program to 0x800.

" bootstrap "4 Item "bootstrap" for applications that are loaded using a bootloader. This model uses startup file crt2.o which does not contain a processor reset vector handler. This is suitable for transferring control on a processor reset to the bootloader rather than the application.

" novectors "4 Item "novectors" for applications that do not require any of the MicroBlaze vectors. This option may be useful for applications running within a monitoring application. This model uses crt3.o as a startup file. Option -xl -mode - app-model is a deprecated alias for -mxl -mode - app-model .

MIPSOptions Subsection "MIPS Options"

" -EB "4 Item "-EB" Generate big-endian code.

" -EL "4 Item "-EL" Generate little-endian code. This is the default for mips*el-* -* configurations.

" -march= arch "4 Item "-march=arch" Generate code that runs on arch ,which can be the name of a generic MIPSISA, or the name of a particular processor. The ISAnames are: mips1 , mips2 , mips3 , mips4 , mips32 , mips32r2 , mips32r3 , mips32r5 , mips32r6 , mips64 , mips64r2 , mips64r3 , mips64r5 and mips64r6 . The processor names are: 4kc , 4km , 4kp , 4ksc , 4kec , 4kem , 4kep , 4ksd , 5kc , 5kf , 20kc , 24kc , 24kf2_1 , 24kf1_1 , 24kec , 24kef2_1 , 24kef1_1 , 34kc , 34kf2_1 , 34kf1_1 , 34kn , 74kc , 74kf2_1 , 74kf1_1 , 74kf3_2 , 1004kc , 1004kf2_1 , 1004kf1_1 , i6400 , i6500 , interaptiv , loongson2e , loongson2f , loongson3a , gs464 , gs464e , gs264e , m4k , m14k , m14kc , m14ke , m14kec , m5100 , m5101 , octeon , octeon+ , octeon2 , octeon3 , orion , p5600 , p6600 , r2000 , r3000 , r3900 , r4000 , r4400 , r4600 , r4650 , r4700 , r5900 , r6000 , r8000 , rm7000 , rm9000 , r10000 , r12000 , r14000 , r16000 , sb1 , sr71000 , vr4100 , vr4111 , vr4120 , vr4130 , vr4300 , vr5000 , vr5400 , vr5500 , xlr and xlp . The special value from-abi selects the most compatible architecture for the selected ABI(that is, mips1 for 32 -bit ABIs and mips3 for 64 -bit ABIs). The native Linux/GNU toolchain also supports the value native , which selects the best architecture option for the host processor. -march=native has no effect if GCCdoes not recognize the processor. In processor names, a final 000 can be abbreviated as k (for example, -march=r2k ).Prefixes are optional, and vr may be written r . Names of the form n f2_1 refer to processors with FPUs clocked at half the rate of the core, names of the form n f1_1 refer to processors with FPUs clocked at the same rate as the core, and names of the form n f3_2 refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, n f is accepted as a synonym for n f2_1 while n x and b fx are accepted as synonyms for n f1_1 . GCCdefines two macros based on the value of this option. The first is CW(C`_MIPS_ARCH (C' ,which gives the name of target architecture, as a string. The second has the form CW(C`_MIPS_ARCH_ CIfoo CW(C' , where foo is the capitalized value of CW(C`_MIPS_ARCH (C' . For example, -march=r2000 sets CW(C`_MIPS_ARCH (C' to CW"r2000" and defines the macro CW(C`_MIPS_ARCH_R2000 (C' . Note that the CW(C`_MIPS_ARCH (C' macro uses the processor names given above. In other words, it has the full prefix and does not abbreviate 000 as k .In the case of from-abi , the macro names the resolved architecture (either CW"mips1" or CW"mips3" ).It names the default architecture when no -march option is given.

" -mtune= arch "4 Item "-mtune=arch" Optimize for arch .Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of arch values is the same as for -march . When this option is not used, GCCoptimizes for the processor specified by -march .By using -march and -mtune together, it is possible to generate code that runs on a family of processors, but optimize the code for one particular member of that family. -mtune defines the macros CW(C`_MIPS_TUNE (C' and CW(C`_MIPS_TUNE_ CIfoo CW(C' ,which work in the same way as the -march ones described above.

" -mips1 "4 Item "-mips1" Equivalent to -march=mips1 .

" -mips2 "4 Item "-mips2" Equivalent to -march=mips2 .

" -mips3 "4 Item "-mips3" Equivalent to -march=mips3 .

" -mips4 "4 Item "-mips4" Equivalent to -march=mips4 .

" -mips32 "4 Item "-mips32" Equivalent to -march=mips32 .

" -mips32r3 "4 Item "-mips32r3" Equivalent to -march=mips32r3 .

" -mips32r5 "4 Item "-mips32r5" Equivalent to -march=mips32r5 .

" -mips32r6 "4 Item "-mips32r6" Equivalent to -march=mips32r6 .

" -mips64 "4 Item "-mips64" Equivalent to -march=mips64 .

" -mips64r2 "4 Item "-mips64r2" Equivalent to -march=mips64r2 .

" -mips64r3 "4 Item "-mips64r3" Equivalent to -march=mips64r3 .

" -mips64r5 "4 Item "-mips64r5" Equivalent to -march=mips64r5 .

" -mips64r6 "4 Item "-mips64r6" Equivalent to -march=mips64r6 .

" -mips16 "4 Item "-mips16" 0

" -mno -mips16 "4 Item "-mno-mips16" Generate (do not generate) MIPS16code. If GCCis targeting a MIPS32or MIPS64architecture, it makes use of the MIPS16e ASE. MIPS16code generation can also be controlled on a per-function basis by means of CW(C`mips16 (C' and CW(C`nomips16 (C' attributes.

" -mflip -mips16 "4 Item "-mflip-mips16" Generate MIPS16code on alternating functions. This option is provided for regression testing of mixed MIPS16/non -MIPS16 code generation, and is not intended for ordinary use in compiling user code.

" -minterlink -compressed "4 Item "-minterlink-compressed" 0

" -mno -interlink -compressed "4 Item "-mno-interlink-compressed" Require (do not require) that code using the standard (uncompressed) MIPSISA be link-compatible with MIPS16and microMIPS code, and vice versa. For example, code using the standard ISAencoding cannot jump directly to MIPS16or microMIPS code; it must either use a call or an indirect jump. -minterlink -compressed therefore disables direct jumps unless GCC knows that the target of the jump is not compressed.

" -minterlink -mips16 "4 Item "-minterlink-mips16" 0

" -mno -interlink -mips16 "4 Item "-mno-interlink-mips16" Aliases of -minterlink -compressed and -mno -interlink -compressed .These options predate the microMIPS ASE and are retained for backwards compatibility.

" -mabi=32 "4 Item "-mabi=32" 0

" -mabi=o64 "4 Item "-mabi=o64"

" -mabi=n32 "4 Item "-mabi=n32"

" -mabi=64 "4 Item "-mabi=64"

" -mabi=eabi "4 Item "-mabi=eabi" Generate code for the given ABI. Note that the EABIhas a 32 -bit and a 64 -bit variant. GCCnormally generates 64 -bit code when you select a 64 -bit architecture, but you can use -mgp32 to get 32 -bit code instead. For information about the O64 ABI,see < http://gcc.gnu.org/projects/mipso64-abi.html >. GCCsupports a variant of the o32 ABIin which floating-point registers are 64 rather than 32 bits wide. You can select this combination with -mabi=32 -mfp64 .This ABIrelies on the CW(C`mthc1 (C' and CW(C`mfhc1 (C' instructions and is therefore only supported for MIPS32R2,MIPS32R3 and MIPS32R5processors. The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64 -bit register rather than a pair of 32 -bit registers. For example, scalar floating-point values are returned in CB$f0 only, not a CB$f0 / CB$f1 pair. The set of call-saved registers also remains the same in that the even-numbered double-precision registers are saved. Two additional variants of the o32 ABIare supported to enable a transition from 32 -bit to 64 -bit registers. These are FPXX ( -mfpxx )and FP64A( -mfp64 -mno -odd -spreg ). The FPXXextension mandates that all code must execute correctly when run using 32 -bit or 64 -bit registers. The code can be interlinked with either FP32or FP64,but not both. The FP64Aextension is similar to the FP64extension but forbids the use of odd-numbered single-precision registers. This can be used in conjunction with the CW(C`FRE (C' mode of FPUs in MIPS32R5 processors and allows both FP32and FP64Acode to interlink and run in the same process without changing FPUmodes.

" -mabicalls "4 Item "-mabicalls" 0

" -mno -abicalls "4 Item "-mno-abicalls" Generate (do not generate) code that is suitable for SVR4 -style dynamic objects. -mabicalls is the default for SVR4 -based systems.

" -mshared "4 Item "-mshared" 0

" -mno -shared "4 Item "-mno-shared" Generate (do not generate) code that is fully position-independent, and that can therefore be linked into shared libraries. This option only affects -mabicalls . All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and -fpic .However, as an extension, the GNUtoolchain allows executables to use absolute accesses for locally-binding symbols. It can also use shorter GP initialization sequences and generate direct calls to locally-defined functions. This mode is selected by -mno -shared . -mno -shared depends on binutils 2.16 or higher and generates objects that can only be linked by the GNUlinker. However, the option does not affect the ABIof the final executable; it only affects the ABI of relocatable objects. Using -mno -shared generally makes executables both smaller and quicker. -mshared is the default.

" -mplt "4 Item "-mplt" 0

" -mno -plt "4 Item "-mno-plt" Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations. This option only affects -mno -shared -mabicalls .For the n64 ABI,this option has no effect without -msym32 . You can make -mplt the default by configuring GCCwith --with -mips -plt .The default is -mno -plt otherwise.

" -mxgot "4 Item "-mxgot" 0

" -mno -xgot "4 Item "-mno-xgot" Lift (do not lift) the usual restrictions on the size of the global offset table. GCCnormally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as: 1 relocation truncated to fit: R_MIPS_GOT16 foobar If this happens, you should recompile your code with -mxgot . This works with very large GOTs, although the code is also less efficient, since it takes three instructions to fetch the value of a global symbol. Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64k's worth of GOTentries. Very few do. These options have no effect unless GCCis generating position independent code.

" -mgp32 "4 Item "-mgp32" Assume that general-purpose registers are 32 bits wide.

" -mgp64 "4 Item "-mgp64" Assume that general-purpose registers are 64 bits wide.

" -mfp32 "4 Item "-mfp32" Assume that floating-point registers are 32 bits wide.

" -mfp64 "4 Item "-mfp64" Assume that floating-point registers are 64 bits wide.

" -mfpxx "4 Item "-mfpxx" Do not assume the width of floating-point registers.

" -mhard -float "4 Item "-mhard-float" Use floating-point coprocessor instructions.

" -msoft -float "4 Item "-msoft-float" Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead.

" -mno -float "4 Item "-mno-float" Equivalent to -msoft -float ,but additionally asserts that the program being compiled does not perform any floating-point operations. This option is presently supported only by some bare-metal MIPS configurations, where it may select a special set of libraries that lack all floating-point support (including, for example, the floating-point CW(C`printf (C' formats). If code compiled with -mno -float accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure.

" -msingle -float "4 Item "-msingle-float" Assume that the floating-point coprocessor only supports single-precision operations.

" -mdouble -float "4 Item "-mdouble-float" Assume that the floating-point coprocessor supports double-precision operations. This is the default.

" -modd -spreg "4 Item "-modd-spreg" 0

" -mno -odd -spreg "4 Item "-mno-odd-spreg" Enable the use of odd-numbered single-precision floating-point registers for the o32 ABI.This is the default for processors that are known to support these registers. When using the o32 FPXXABI, -mno -odd -spreg is set by default.

" -mabs=2008 "4 Item "-mabs=2008" 0

" -mabs=legacy "4 Item "-mabs=legacy" These options control the treatment of the special not-a-number (NaN) IEEE754 floating-point data with the CW(C`abs. CIfmt CW(C' and CW(C`neg. CIfmt CW(C' machine instructions. By default or when -mabs=legacy is used the legacy treatment is selected. In this case these instructions are considered arithmetic and avoided where correct operation is required and the input operand might be a NaN. A longer sequence of instructions that manipulate the sign bit of floating-point datum manually is used instead unless the -ffinite -math -only option has also been specified. The -mabs=2008 option selects the IEEE754 -2008 treatment. In this case these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in particular where the input operand is a NaN. These instructions are therefore always used for the respective operations.

" -mnan=2008 "4 Item "-mnan=2008" 0

" -mnan=legacy "4 Item "-mnan=legacy" These options control the encoding of the special not-a-number (NaN) IEEE754 floating-point data. The -mnan=legacy option selects the legacy encoding. In this case quiet NaNs (qNaNs) are denoted by the first bit of their trailing significand field being 0, whereas signaling NaNs (sNaNs) are denoted by the first bit of their trailing significand field being 1. The -mnan=2008 option selects the IEEE754 -2008 encoding. In this case qNaNs are denoted by the first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first bit of their trailing significand field being 0. The default is -mnan=legacy unless GCChas been configured with --with -nan=2008 .

" -mllsc "4 Item "-mllsc" 0

" -mno -llsc "4 Item "-mno-llsc" Use (do not use) ll , sc ,and sync instructions to implement atomic memory built-in functions. When neither option is specified, GCCuses the instructions if the target architecture supports them. -mllsc is useful if the runtime environment can emulate the instructions and -mno -llsc can be useful when compiling for nonstandard ISAs. You can make either option the default by configuring GCCwith --with -llsc and --without -llsc respectively. --with -llsc is the default for some configurations; see the installation documentation for details.

" -mdsp "4 Item "-mdsp" 0

" -mno -dsp "4 Item "-mno-dsp" Use (do not use) revision 1 of the MIPSDSP ASE. This option defines the preprocessor macro CW(C`_ _mips_dsp (C' .It also defines CW(C`_ _mips_dsp_rev (C' to 1.

" -mdspr2 "4 Item "-mdspr2" 0

" -mno -dspr2 "4 Item "-mno-dspr2" Use (do not use) revision 2 of the MIPSDSP ASE. This option defines the preprocessor macros CW(C`_ _mips_dsp (C' and CW(C`_ _mips_dspr2 (C' . It also defines CW(C`_ _mips_dsp_rev (C' to 2.

" -msmartmips "4 Item "-msmartmips" 0

" -mno -smartmips "4 Item "-mno-smartmips" Use (do not use) the MIPSSmartMIPS ASE.

" -mpaired -single "4 Item "-mpaired-single" 0

" -mno -paired -single "4 Item "-mno-paired-single" Use (do not use) paired-single floating-point instructions. This option requires hardware floating-point support to be enabled.

" -mdmx "4 Item "-mdmx" 0

" -mno -mdmx "4 Item "-mno-mdmx" Use (do not use) MIPSDigital Media Extension instructions. This option can only be used when generating 64 -bit code and requires hardware floating-point support to be enabled.

" -mips3d "4 Item "-mips3d" 0

" -mno -mips3d "4 Item "-mno-mips3d" Use (do not use) the MIPS-3D ASE. The option -mips3d implies -mpaired -single .

" -mmicromips "4 Item "-mmicromips" 0

" -mno -micromips "4 Item "-mno-micromips" Generate (do not generate) microMIPS code. MicroMIPS code generation can also be controlled on a per-function basis by means of CW(C`micromips (C' and CW(C`nomicromips (C' attributes.

" -mmt "4 Item "-mmt" 0

" -mno -mt "4 Item "-mno-mt" Use (do not use) MTMultithreading instructions.

" -mmcu "4 Item "-mmcu" 0

" -mno -mcu "4 Item "-mno-mcu" Use (do not use) the MIPSMCU ASE instructions.

" -meva "4 Item "-meva" 0

" -mno -eva "4 Item "-mno-eva" Use (do not use) the MIPSEnhanced Virtual Addressing instructions.

" -mvirt "4 Item "-mvirt" 0

" -mno -virt "4 Item "-mno-virt" Use (do not use) the MIPSVirtualization ( VZ)instructions.

" -mxpa "4 Item "-mxpa" 0

" -mno -xpa "4 Item "-mno-xpa" Use (do not use) the MIPSeXtended Physical Address ( XPA)instructions.

" -mcrc "4 Item "-mcrc" 0

" -mno -crc "4 Item "-mno-crc" Use (do not use) the MIPSCyclic Redundancy Check ( CRC)instructions.

" -mginv "4 Item "-mginv" 0

" -mno -ginv "4 Item "-mno-ginv" Use (do not use) the MIPSGlobal INValidate ( GINV)instructions.

" -mloongson -mmi "4 Item "-mloongson-mmi" 0

" -mno -loongson -mmi "4 Item "-mno-loongson-mmi" Use (do not use) the MIPSLoongson MultiMedia extensions Instructions ( MMI).

" -mloongson -ext "4 Item "-mloongson-ext" 0

" -mno -loongson -ext "4 Item "-mno-loongson-ext" Use (do not use) the MIPSLoongson EXTensions ( EXT)instructions.

" -mloongson -ext2 "4 Item "-mloongson-ext2" 0

" -mno -loongson -ext2 "4 Item "-mno-loongson-ext2" Use (do not use) the MIPSLoongson EXTensions r2 ( EXT2)instructions.

" -mlong64 "4 Item "-mlong64" Force CW(C`long (C' types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined.

" -mlong32 "4 Item "-mlong32" Force CW(C`long (C' , CW(C`int (C' ,and pointer types to be 32 bits wide. The default size of CW(C`int (C' s, CW(C`long (C' sand pointers depends on the ABI.All the supported ABIs use 32 -bit CW(C`int (C' s.The n64 ABI uses 64 -bit CW(C`long (C' s,as does the 64 -bit EABI;the others use 32 -bit CW(C`long (C' s.Pointers are the same size as CW(C`long (C' s, or the same size as integer registers, whichever is smaller.

" -msym32 "4 Item "-msym32" 0

" -mno -sym32 "4 Item "-mno-sym32" Assume (do not assume) that all symbols have 32 -bit values, regardless of the selected ABI.This option is useful in combination with -mabi=64 and -mno -abicalls because it allows GCC to generate shorter and faster references to symbolic addresses.

" -G num "4 Item "-G num" Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. GCCcan then generate more efficient accesses to the data; see -mgpopt for details. The default -G option depends on the configuration.

" -mlocal -sdata "4 Item "-mlocal-sdata" 0

" -mno -local -sdata "4 Item "-mno-local-sdata" Extend (do not extend) the -G behavior to local data too, such as to static variables in C. -mlocal -sdata is the default for all configurations. If the linker complains that an application is using too much small data, you might want to try rebuilding the less performance-critical parts with -mno -local -sdata .You might also want to build large libraries with -mno -local -sdata ,so that the libraries leave more room for the main program.

" -mextern -sdata "4 Item "-mextern-sdata" 0

" -mno -extern -sdata "4 Item "-mno-extern-sdata" Assume (do not assume) that externally-defined data is in a small data section if the size of that data is within the -G limit. -mextern -sdata is the default for all configurations. If you compile a module Mod with -mextern -sdata -G num -mgpopt ,and Mod references a variable Var that is no bigger than num bytes, you must make sure that Var is placed in a small data section. If Var is defined by another module, you must either compile that module with a high-enough -G setting or attach a CW(C`section (C' attribute to Var 's definition. If Var is common, you must link the application with a high-enough -G setting. The easiest way of satisfying these restrictions is to compile and link every module with the same -G option. However, you may wish to build a library that supports several different small data limits. You can do this by compiling the library with the highest supported -G setting and additionally using -mno -extern -sdata to stop the library from making assumptions about externally-defined data.

" -mgpopt "4 Item "-mgpopt" 0

" -mno -gpopt "4 Item "-mno-gpopt" Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see -G , -mlocal -sdata and -mextern -sdata . -mgpopt is the default for all configurations. -mno -gpopt is useful for cases where the CW$gp register might not hold the value of CW(C`_gp (C' .For example, if the code is part of a library that might be used in a boot monitor, programs that call boot monitor routines pass an unknown value in CW$gp . (In such situations, the boot monitor itself is usually compiled with -G0 .) -mno -gpopt implies -mno -local -sdata and -mno -extern -sdata .

" -membedded -data "4 Item "-membedded-data" 0

" -mno -embedded -data "4 Item "-mno-embedded-data" Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAMrequired when executing, and thus may be preferred for some embedded systems.

" -muninit -const -in -rodata "4 Item "-muninit-const-in-rodata" 0

" -mno -uninit -const -in -rodata "4 Item "-mno-uninit-const-in-rodata" Put uninitialized CW(C`const (C' variables in the read-only data section. This option is only meaningful in conjunction with -membedded -data .

" -mcode -readable= setting "4 Item "-mcode-readable=setting" Specify whether GCCmay generate code that reads from executable sections. There are three possible settings:

" -mcode -readable=yes "4 Item "-mcode-readable=yes" Instructions may freely access executable sections. This is the default setting.

" -mcode -readable=pcrel "4 Item "-mcode-readable=pcrel" MIPS16PC-relative load instructions can access executable sections, but other instructions must not do so. This option is useful on 4KSc and 4KSd processors when the code TLBs have the Read Inhibit bit set. It is also useful on processors that can be configured to have a dual instruction/data SRAMinterface and that, like the M4K, automatically redirect PC-relative loads to the instruction RAM.

" -mcode -readable=no "4 Item "-mcode-readable=no" Instructions must not access executable sections. This option can be useful on targets that are configured to have a dual instruction/data SRAMinterface but that (unlike the M4K) do not automatically redirect PC-relative loads to the instruction RAM.

" -msplit -addresses "4 Item "-msplit-addresses" 0

" -mno -split -addresses "4 Item "-mno-split-addresses" Enable (disable) use of the CW(C`%hi() (C' and CW(C`%lo() (C' assembler relocation operators. This option has been superseded by -mexplicit -relocs but is retained for backwards compatibility.

" -mexplicit -relocs "4 Item "-mexplicit-relocs" 0

" -mno -explicit -relocs "4 Item "-mno-explicit-relocs" Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by -mno -explicit -relocs , is to use assembler macros instead. -mexplicit -relocs is the default if GCCwas configured to use an assembler that supports relocation operators.

" -mcheck -zero -division "4 Item "-mcheck-zero-division" 0

" -mno -check -zero -division "4 Item "-mno-check-zero-division" Trap (do not trap) on integer division by zero. The default is -mcheck -zero -division .

" -mdivide -traps "4 Item "-mdivide-traps" 0

" -mdivide -breaks "4 Item "-mdivide-breaks" MIPSsystems check for division by zero by generating either a conditional trap or a break instruction. Using traps results in smaller code, but is only supported on MIPSII and later. Also, some versions of the Linux kernel have a bug that prevents trap from generating the proper signal ( CW(C`SIGFPE (C' ).Use -mdivide -traps to allow conditional traps on architectures that support them and -mdivide -breaks to force the use of breaks. The default is usually -mdivide -traps ,but this can be overridden at configure time using --with -divide=breaks . Divide-by-zero checks can be completely disabled using -mno -check -zero -division .

" -mload -store -pairs "4 Item "-mload-store-pairs" 0

" -mno -load -store -pairs "4 Item "-mno-load-store-pairs" Enable (disable) an optimization that pairs consecutive load or store instructions to enable load/store bonding. This option is enabled by default but only takes effect when the selected architecture is known to support bonding.

" -mmemcpy "4 Item "-mmemcpy" 0

" -mno -memcpy "4 Item "-mno-memcpy" Force (do not force) the use of CW(C`memcpy (C' for non-trivial block moves. The default is -mno -memcpy ,which allows GCCto inline most constant-sized copies.

" -mlong -calls "4 Item "-mlong-calls" 0

" -mno -long -calls "4 Item "-mno-long-calls" Disable (do not disable) use of the CW(C`jal (C' instruction. Calling functions using CW(C`jal (C' is more efficient but requires the caller and callee to be in the same 256 megabyte segment. This option has no effect on abicalls code. The default is -mno -long -calls .

" -mmad "4 Item "-mmad" 0

" -mno -mad "4 Item "-mno-mad" Enable (disable) use of the CW(C`mad (C' , CW(C`madu (C' and CW(C`mul (C' instructions, as provided by the R4650 ISA.

" -mimadd "4 Item "-mimadd" 0

" -mno -imadd "4 Item "-mno-imadd" Enable (disable) use of the CW(C`madd (C' and CW(C`msub (C' integer instructions. The default is -mimadd on architectures that support CW(C`madd (C' and CW(C`msub (C' except for the 74k architecture where it was found to generate slower code.

" -mfused -madd "4 Item "-mfused-madd" 0

" -mno -fused -madd "4 Item "-mno-fused-madd" Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available. The default is -mfused -madd . On the R8000 CPUwhen multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSRFlush to Zero bit. This may be undesirable in some circumstances. On other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions.

" -nocpp "4 Item "-nocpp" Tell the MIPSassembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them.

" -mfix -24k "4 Item "-mfix-24k" 0

" -mno -fix -24k "4 Item "-mno-fix-24k" Work around the 24K E48 (lost data on stores during refill) errata. The workarounds are implemented by the assembler rather than by GCC.

" -mfix -r4000 "4 Item "-mfix-r4000" 0

" -mno -fix -r4000 "4 Item "-mno-fix-r4000" Work around certain R4000 CPUerrata:

" -" 4 A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division.

" -" 4 A double-word or a variable shift may give an incorrect result if executed while an integer multiplication is in progress.

" -" 4 An integer division may give an incorrect result if started in a delay slot of a taken branch or a jump.

" -mfix -r4400 "4 Item "-mfix-r4400" 0

" -mno -fix -r4400 "4 Item "-mno-fix-r4400" Work around certain R4400 CPUerrata:

" -" 4 A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division.

" -mfix -r10000 "4 Item "-mfix-r10000" 0

" -mno -fix -r10000 "4 Item "-mno-fix-r10000" Work around certain R10000 errata:

" -" 4 CW(C`ll (C' / CW(C`sc (C' sequences may not behave atomically on revisions prior to 3.0. They may deadlock on revisions 2.6 and earlier. This option can only be used if the target architecture supports branch-likely instructions. -mfix -r10000 is the default when -march=r10000 is used; -mno -fix -r10000 is the default otherwise.

" -mfix -r5900 "4 Item "-mfix-r5900" 0

" -mno -fix -r5900 "4 Item "-mno-fix-r5900" Do not attempt to schedule the preceding instruction into the delay slot of a branch instruction placed at the end of a short loop of six instructions or fewer and always schedule a CW(C`nop (C' instruction there instead. The short loop bug under certain conditions causes loops to execute only once or twice, due to a hardware bug in the R5900 chip. The workaround is implemented by the assembler rather than by GCC.

" -mfix -rm7000 "4 Item "-mfix-rm7000" 0

" -mno -fix -rm7000 "4 Item "-mno-fix-rm7000" Work around the RM7000 CW(C`dmult (C' / CW(C`dmultu (C' errata. The workarounds are implemented by the assembler rather than by GCC.

" -mfix -vr4120 "4 Item "-mfix-vr4120" 0

" -mno -fix -vr4120 "4 Item "-mno-fix-vr4120" Work around certain VR4120errata:

" -" 4 CW(C`dmultu (C' does not always produce the correct result.

" -" 4 CW(C`div (C' and CW(C`ddiv (C' do not always produce the correct result if one of the operands is negative. The workarounds for the division errata rely on special functions in libgcc.a .At present, these functions are only provided by the CW(C`mips64vr* -elf (C' configurations. Other VR4120errata require a NOPto be inserted between certain pairs of instructions. These errata are handled by the assembler, not by GCCitself.

" -mfix -vr4130 "4 Item "-mfix-vr4130" Work around the VR4130 CW(C`mflo (C' / CW(C`mfhi (C' errata. The workarounds are implemented by the assembler rather than by GCC, although GCCavoids using CW(C`mflo (C' and CW(C`mfhi (C' if the VR4130 CW(C`macc (C' , CW(C`macchi (C' , CW(C`dmacc (C' and CW(C`dmacchi (C' instructions are available instead.

" -mfix -sb1 "4 Item "-mfix-sb1" 0

" -mno -fix -sb1 "4 Item "-mno-fix-sb1" Work around certain SB-1 CPU core errata. (This flag currently works around the SB-1 revision 2 (L"F1 (R" and (L"F2 (R" floating-point errata.)

" -mr10k -cache -barrier= setting "4 Item "-mr10k-cache-barrier=setting" Specify whether GCCshould insert cache barriers to avoid the side effects of speculation on R10K processors. In common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the (L"taken (R" branch. It later aborts these instructions if the predicted outcome is wrong. However, on the R10K, even aborted instructions can have side effects. This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later aborted. If a DMAoperation writes to the same area of memory before the (L"dirty (R" line is flushed, the cached data overwrites the DMA-ed data. See the R10K processor manual for a full description, including other potential problems. One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. -mr10k -cache -barrier= setting controls GCC'simplementation of this workaround. It assumes that aborted accesses to any byte in the following regions does not have side effects:

"1." 4 Item "1." the memory occupied by the current function's stack frame;

"2." 4 Item "2." the memory occupied by an incoming stack argument;

"3." 4 Item "3." the memory occupied by an object with a link-time-constant address. It is the kernel's responsibility to ensure that speculative accesses to these regions are indeed safe. If the input program contains a function declaration such as: 1 void foo (void); then the implementation of CW(C`foo (C' must allow CW(C`j foo (C' and CW(C`jal foo (C' to be executed speculatively. GCChonors this restriction for functions it compiles itself. It expects non-GCC functions (such as hand-written assembly code) to do the same. The option has three forms:

" -mr10k -cache -barrier=load -store "4 Item "-mr10k-cache-barrier=load-store" Insert a cache barrier before a load or store that might be speculatively executed and that might have side effects even if aborted.

" -mr10k -cache -barrier=store "4 Item "-mr10k-cache-barrier=store" Insert a cache barrier before a store that might be speculatively executed and that might have side effects even if aborted.

" -mr10k -cache -barrier=none "4 Item "-mr10k-cache-barrier=none" Disable the insertion of cache barriers. This is the default setting.

" -mflush -func= func "4 Item "-mflush-func=func" 0

" -mno -flush -func "4 Item "-mno-flush-func" Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common CW(C`_flush_func (C' ,that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target GCCwas configured for, but commonly is either CW(C`_flush_func (C' or CW(C`_ _cpu_flush (C' .

" mbranch-cost= num "4 Item "mbranch-cost=num" Set the cost of branches to roughly num (L"simple (R" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. A zero cost redundantly selects the default, which is based on the -mtune setting.

" -mbranch -likely "4 Item "-mbranch-likely" 0

" -mno -branch -likely "4 Item "-mno-branch-likely" Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported by the selected architecture. An exception is for the MIPS32and MIPS64architectures and processors that implement those architectures; for those, Branch Likely instructions are not be generated by default because the MIPS32 and MIPS64architectures specifically deprecate their use.

" -mcompact -branches=never "4 Item "-mcompact-branches=never" 0

" -mcompact -branches=optimal "4 Item "-mcompact-branches=optimal"

" -mcompact -branches=always "4 Item "-mcompact-branches=always" These options control which form of branches will be generated. The default is -mcompact -branches=optimal . The -mcompact -branches=never option ensures that compact branch instructions will never be generated. The -mcompact -branches=always option ensures that a compact branch instruction will be generated if available. If a compact branch instruction is not available, a delay slot form of the branch will be used instead. This option is supported from MIPSRelease 6 onwards. The -mcompact -branches=optimal option will cause a delay slot branch to be used if one is available in the current ISAand the delay slot is successfully filled. If the delay slot is not filled, a compact branch will be chosen if one is available.

" -mfp -exceptions "4 Item "-mfp-exceptions" 0

" -mno -fp -exceptions "4 Item "-mno-fp-exceptions" Specifies whether FPexceptions are enabled. This affects how FPinstructions are scheduled for some processors. The default is that FPexceptions are enabled. For instance, on the SB-1, if FPexceptions are disabled, and we are emitting 64 -bit code, then we can use both FPpipes. Otherwise, we can only use one FPpipe.

" -mvr4130 -align "4 Item "-mvr4130-align" 0

" -mno -vr4130 -align "4 Item "-mno-vr4130-align" The VR4130pipeline is two-way superscalar, but can only issue two instructions together if the first one is 8 -byte aligned. When this option is enabled, GCCaligns pairs of instructions that it thinks should execute in parallel. This option only has an effect when optimizing for the VR4130. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level -O3 .

" -msynci "4 Item "-msynci" 0

" -mno -synci "4 Item "-mno-synci" Enable (disable) generation of CW(C`synci (C' instructions on architectures that support it. The CW(C`synci (C' instructions (if enabled) are generated when CW(C`_ _builtin_ _ _clear_cache (C' is compiled. This option defaults to -mno -synci ,but the default can be overridden by configuring GCCwith --with -synci . When compiling code for single processor systems, it is generally safe to use CW(C`synci (C' .However, on many multi-core ( SMP)systems, it does not invalidate the instruction caches on all cores and may lead to undefined behavior.

" -mrelax -pic -calls "4 Item "-mrelax-pic-calls" 0

" -mno -relax -pic -calls "4 Item "-mno-relax-pic-calls" Try to turn PICcalls that are normally dispatched via register CW$25 into direct calls. This is only possible if the linker can resolve the destination at link time and if the destination is within range for a direct call. -mrelax -pic -calls is the default if GCCwas configured to use an assembler and a linker that support the CW(C`.reloc (C' assembly directive and -mexplicit -relocs is in effect. With -mno -explicit -relocs ,this optimization can be performed by the assembler and the linker alone without help from the compiler.

" -mmcount -ra -address "4 Item "-mmcount-ra-address" 0

" -mno -mcount -ra -address "4 Item "-mno-mcount-ra-address" Emit (do not emit) code that allows CW(C`_mcount (C' to modify the calling function's return address. When enabled, this option extends the usual CW(C`_mcount (C' interface with a new ra-address parameter, which has type CW(C`intptr_t * (C' and is passed in register CW$12 . CW(C`_mcount (C' can then modify the return address by doing both of the following:

"*" 4 Returning the new address in register CW$31 .

"*" 4 Storing the new address in CW(C`* CIra-address CW(C' , if ra-address is nonnull. The default is -mno -mcount -ra -address .

" -mframe -header -opt "4 Item "-mframe-header-opt" 0

" -mno -frame -header -opt "4 Item "-mno-frame-header-opt" Enable (disable) frame header optimization in the o32 ABI.When using the o32 ABI,calling functions will allocate 16 bytes on the stack for the called function to write out register arguments. When enabled, this optimization will suppress the allocation of the frame header if it can be determined that it is unused. This optimization is off by default at all optimization levels.

" -mlxc1 -sxc1 "4 Item "-mlxc1-sxc1" 0

" -mno -lxc1 -sxc1 "4 Item "-mno-lxc1-sxc1" When applicable, enable (disable) the generation of CW(C`lwxc1 (C' , CW(C`swxc1 (C' , CW(C`ldxc1 (C' , CW(C`sdxc1 (C' instructions. Enabled by default.

" -mmadd4 "4 Item "-mmadd4" 0

" -mno -madd4 "4 Item "-mno-madd4" When applicable, enable (disable) the generation of 4 -operand CW(C`madd.s (C' , CW(C`madd.d (C' and related instructions. Enabled by default.

MMIXOptions Subsection "MMIX Options"

These options are defined for the MMIX:

" -mlibfuncs "4 Item "-mlibfuncs" 0

" -mno -libfuncs "4 Item "-mno-libfuncs" Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size.

" -mepsilon "4 Item "-mepsilon" 0

" -mno -epsilon "4 Item "-mno-epsilon" Generate floating-point comparison instructions that compare with respect to the CW(C`rE (C' epsilon register.

" -mabi=mmixware "4 Item "-mabi=mmixware" 0

" -mabi=gnu "4 Item "-mabi=gnu" Generate code that passes function parameters and return values that (in the called function) are seen as registers CW$0 and up, as opposed to the GNUABI which uses global registers CW$231 and up.

" -mzero -extend "4 Item "-mzero-extend" 0

" -mno -zero -extend "4 Item "-mno-zero-extend" When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones.

" -mknuthdiv "4 Item "-mknuthdiv" 0

" -mno -knuthdiv "4 Item "-mno-knuthdiv" Make the result of a division yielding a remainder have the same sign as the divisor. With the default, -mno -knuthdiv ,the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used.

" -mtoplevel -symbols "4 Item "-mtoplevel-symbols" 0

" -mno -toplevel -symbols "4 Item "-mno-toplevel-symbols" Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the CW(C`PREFIX (C' assembly directive.

" -melf "4 Item "-melf" Generate an executable in the ELFformat, rather than the default mmo format used by the mmix simulator.

" -mbranch -predict "4 Item "-mbranch-predict" 0

" -mno -branch -predict "4 Item "-mno-branch-predict" Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch.

" -mbase -addresses "4 Item "-mbase-addresses" 0

" -mno -base -addresses "4 Item "-mno-base-addresses" Generate (do not generate) code that uses baseaddresses .Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require -mno -base -addresses .

" -msingle -exit "4 Item "-msingle-exit" 0

" -mno -single -exit "4 Item "-mno-single-exit" Force (do not force) generated code to have a single exit point in each function.

MN10300Options Subsection "MN10300 Options"

These -m options are defined for Matsushita MN10300architectures:

" -mmult -bug "4 Item "-mmult-bug" Generate code to avoid bugs in the multiply instructions for the MN10300 processors. This is the default.

" -mno -mult -bug "4 Item "-mno-mult-bug" Do not generate code to avoid bugs in the multiply instructions for the MN10300processors.

" -mam33 "4 Item "-mam33" Generate code using features specific to the AM33processor.

" -mno -am33 "4 Item "-mno-am33" Do not generate code using features specific to the AM33processor. This is the default.

" -mam33 -2 "4 Item "-mam33-2" Generate code using features specific to the AM33/2.0processor.

" -mam34 "4 Item "-mam34" Generate code using features specific to the AM34processor.

" -mtune= cpu-type "4 Item "-mtune=cpu-type" Use the timing characteristics of the indicated CPUtype when scheduling instructions. This does not change the targeted processor type. The CPUtype must be one of mn10300 , am33 , am33-2 or am34 .

" -mreturn -pointer -on -d0 "4 Item "-mreturn-pointer-on-d0" When generating a function that returns a pointer, return the pointer in both CW(C`a0 (C' and CW(C`d0 (C' .Otherwise, the pointer is returned only in CW(C`a0 (C' ,and attempts to call such functions without a prototype result in errors. Note that this option is on by default; use -mno -return -pointer -on -d0 to disable it.

" -mno -crt0 "4 Item "-mno-crt0" Do not link in the C run-time initialization object file.

" -mrelax "4 Item "-mrelax" Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step. This option makes symbolic debugging impossible.

" -mliw "4 Item "-mliw" Allow the compiler to generate LongInstruction Word instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro CW(C`_ _LIW_ _ (C' .

" -mno -liw "4 Item "-mno-liw" Do not allow the compiler to generate LongInstruction Word instructions. This option defines the preprocessor macro CW(C`_ _NO_LIW_ _ (C' .

" -msetlb "4 Item "-msetlb" Allow the compiler to generate the SETLB and Lcc instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro CW(C`_ _SETLB_ _ (C' .

" -mno -setlb "4 Item "-mno-setlb" Do not allow the compiler to generate SETLB or Lcc instructions. This option defines the preprocessor macro CW(C`_ _NO_SETLB_ _ (C' .

MoxieOptions Subsection "Moxie Options"

" -meb "4 Item "-meb" Generate big-endian code. This is the default for moxie-* -* configurations.

" -mel "4 Item "-mel" Generate little-endian code.

" -mmul.x "4 Item "-mmul.x" Generate mul.x and umul.x instructions. This is the default for moxiebox-* -* configurations.

" -mno -crt0 "4 Item "-mno-crt0" Do not link in the C run-time initialization object file.

MSP430Options Subsection "MSP430 Options"

These options are defined for the MSP430:

" -masm -hex "4 Item "-masm-hex" Force assembly output to always use hex constants. Normally such constants are signed decimals, but this option is available for testsuite and/or aesthetic purposes.

" -mmcu= "4 Item "-mmcu=" Select the MCUto target. This is used to create a C preprocessor symbol based upon the MCUname, converted to upper case and pre -and post-fixed with __ .This in turn is used by the msp430.h header file to select an MCU-specific supplementary header file. The option also sets the ISAto use. If the MCUname is one that is known to only support the 430 ISAthen that is selected, otherwise the 430X ISAis selected. A generic MCUname of msp430 can also be used to select the 430 ISA.Similarly the generic msp430x MCU name selects the 430X ISA. In addition an MCU-specific linker script is added to the linker command line. The script's name is the name of the MCUwith .ld appended. Thus specifying -mmcu=xxx on the gcc command line defines the C preprocessor symbol CW(C`_ _XXX_ _ (C' and cause the linker to search for a script called xxx.ld . This option is also passed on to the assembler.

" -mwarn -mcu "4 Item "-mwarn-mcu" 0

" -mno -warn -mcu "4 Item "-mno-warn-mcu" This option enables or disables warnings about conflicts between the MCUname specified by the -mmcu option and the ISAset by the -mcpu option and/or the hardware multiply support set by the -mhwmult option. It also toggles warnings about unrecognized MCUnames. This option is on by default.

" -mcpu= "4 Item "-mcpu=" Specifies the ISAto use. Accepted values are msp430 , msp430x and msp430xv2 .This option is deprecated. The -mmcu= option should be used to select the ISA.

" -msim "4 Item "-msim" Link to the simulator runtime libraries and linker script. Overrides any scripts that would be selected by the -mmcu= option.

" -mlarge "4 Item "-mlarge" Use large-model addressing (20 -bit pointers, 32 -bit CW(C`size_t (C' ).

" -msmall "4 Item "-msmall" Use small-model addressing (16 -bit pointers, 16 -bit CW(C`size_t (C' ).

" -mrelax "4 Item "-mrelax" This option is passed to the assembler and linker, and allows the linker to perform certain optimizations that cannot be done until the final link.

" mhwmult= "4 Item "mhwmult=" Describes the type of hardware multiply supported by the target. Accepted values are none for no hardware multiply, 16bit for the original 16 -bit -only multiply supported by early MCUs. 32bit for the 16/32 -bit multiply supported by later MCUs and f5series for the 16/32 -bit multiply supported by F5 -series MCUs. A value of auto can also be given. This tells GCCto deduce the hardware multiply support based upon the MCUname provided by the -mmcu option. If no -mmcu option is specified or if the MCUname is not recognized then no hardware multiply support is assumed. CW(C`auto (C' is the default setting. Hardware multiplies are normally performed by calling a library routine. This saves space in the generated code. When compiling at -O3 or higher however the hardware multiplier is invoked inline. This makes for bigger, but faster code. The hardware multiply routines disable interrupts whilst running and restore the previous interrupt state when they finish. This makes them safe to use inside interrupt handlers as well as in normal code.

" -minrt "4 Item "-minrt" Enable the use of a minimum runtime environment -no static initializers or constructors. This is intended for memory-constrained devices. The compiler includes special symbols in some objects that tell the linker and runtime which code fragments are required.

" -mcode -region= "4 Item "-mcode-region=" 0

" -mdata -region= "4 Item "-mdata-region=" These options tell the compiler where to place functions and data that do not have one of the CW(C`lower (C' , CW(C`upper (C' , CW(C`either (C' or CW(C`section (C' attributes. Possible values are CW(C`lower (C' , CW(C`upper (C' , CW(C`either (C' or CW(C`any (C' .The first three behave like the corresponding attribute. The fourth possible value - CW(C`any (C' -is the default. It leaves placement entirely up to the linker script and how it assigns the standard sections ( CW(C`.text (C' , CW(C`.data (C' ,etc) to the memory regions.

" -msilicon -errata= "4 Item "-msilicon-errata=" This option passes on a request to assembler to enable the fixes for the named silicon errata.

" -msilicon -errata -warn= "4 Item "-msilicon-errata-warn=" This option passes on a request to the assembler to enable warning messages when a silicon errata might need to be applied.

NDS32Options Subsection "NDS32 Options"

These options are defined for NDS32implementations:

" -mbig -endian "4 Item "-mbig-endian" Generate code in big-endian mode.

" -mlittle -endian "4 Item "-mlittle-endian" Generate code in little-endian mode.

" -mreduced -regs "4 Item "-mreduced-regs" Use reduced-set registers for register allocation.

" -mfull -regs "4 Item "-mfull-regs" Use full-set registers for register allocation.

" -mcmov "4 Item "-mcmov" Generate conditional move instructions.

" -mno -cmov "4 Item "-mno-cmov" Do not generate conditional move instructions.

" -mext -perf "4 Item "-mext-perf" Generate performance extension instructions.

" -mno -ext -perf "4 Item "-mno-ext-perf" Do not generate performance extension instructions.

" -mext -perf2 "4 Item "-mext-perf2" Generate performance extension 2 instructions.

" -mno -ext -perf2 "4 Item "-mno-ext-perf2" Do not generate performance extension 2 instructions.

" -mext -string "4 Item "-mext-string" Generate string extension instructions.

" -mno -ext -string "4 Item "-mno-ext-string" Do not generate string extension instructions.

" -mv3push "4 Item "-mv3push" Generate v3 push25/pop25 instructions.

" -mno -v3push "4 Item "-mno-v3push" Do not generate v3 push25/pop25 instructions.

" -m16 -bit "4 Item "-m16-bit" Generate 16 -bit instructions.

" -mno -16 -bit "4 Item "-mno-16-bit" Do not generate 16 -bit instructions.

" -misr -vector -size= num "4 Item "-misr-vector-size=num" Specify the size of each interrupt vector, which must be 4 or 16.

" -mcache -block -size= num "4 Item "-mcache-block-size=num" Specify the size of each cache block, which must be a power of 2 between 4 and 512.

" -march= arch "4 Item "-march=arch" Specify the name of the target architecture.

" -mcmodel= code-model "4 Item "-mcmodel=code-model" Set the code model to one of

" small "4 Item "small" All the data and read-only data segments must be within 512KB addressing space. The text segment must be within 16MB addressing space.

" medium "4 Item "medium" The data segment must be within 512KB while the read-only data segment can be within 4GB addressing space. The text segment should be still within 16MB addressing space.

" large "4 Item "large" All the text and data segments can be within 4GB addressing space.

" -mctor -dtor "4 Item "-mctor-dtor" Enable constructor/destructor feature.

" -mrelax "4 Item "-mrelax" Guide linker to relax instructions.

NiosIIOptions Subsection "Nios II Options"

These are the options defined for the Altera Nios IIprocessor.

" -G num "4 Item "-G num" Put global and static objects less than or equal to num bytes into the small data or BSSsections instead of the normal data or BSS sections. The default value of num is 8.

" -mgpopt= option "4 Item "-mgpopt=option" 0

" -mgpopt "4 Item "-mgpopt"

" -mno -gpopt "4 Item "-mno-gpopt" Generate (do not generate) GP-relative accesses. The following option names are recognized:

" none "4 Item "none" Do not generate GP-relative accesses.

" local "4 Item "local" Generate GP-relative accesses for small data objects that are not external, weak, or uninitialized common symbols. Also use GP-relative addressing for objects that have been explicitly placed in a small data section via a CW(C`section (C' attribute.

" global "4 Item "global" As for local ,but also generate GP-relative accesses for small data objects that are external, weak, or common. If you use this option, you must ensure that all parts of your program (including libraries) are compiled with the same -G setting.

" data "4 Item "data" Generate GP-relative accesses for all data objects in the program. If you use this option, the entire data and BSSsegments of your program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressable range of the global pointer.

" all "4 Item "all" Generate GP-relative addresses for function pointers as well as data pointers. If you use this option, the entire text, data, and BSSsegments of your program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressable range of the global pointer. -mgpopt is equivalent to -mgpopt=local ,and -mno -gpopt is equivalent to -mgpopt=none . The default is -mgpopt except when -fpic or -fPIC is specified to generate position-independent code. Note that the Nios IIABI does not permit GP-relative accesses from shared libraries. You may need to specify -mno -gpopt explicitly when building programs that include large amounts of small data, including large GOTdata sections. In this case, the 16 -bit offset for GP-relative addressing may not be large enough to allow access to the entire small data section.

" -mgprel -sec= regexp "4 Item "-mgprel-sec=regexp" This option specifies additional section names that can be accessed via GP-relative addressing. It is most useful in conjunction with CW(C`section (C' attributes on variable declarations and a custom linker script. The regexp is a POSIXExtended Regular Expression. This option does not affect the behavior of the -G option, and the specified sections are in addition to the standard CW(C`.sdata (C' and CW(C`.sbss (C' small-data sections that are recognized by -mgpopt .

" -mr0rel -sec= regexp "4 Item "-mr0rel-sec=regexp" This option specifies names of sections that can be accessed via a 16 -bit offset from CW(C`r0 (C' ;that is, in the low 32K or high 32K of the 32 -bit address space. It is most useful in conjunction with CW(C`section (C' attributes on variable declarations and a custom linker script. The regexp is a POSIXExtended Regular Expression. In contrast to the use of GP-relative addressing for small data, zero-based addressing is never generated by default and there are no conventional section names used in standard linker scripts for sections in the low or high areas of memory.

" -mel "4 Item "-mel" 0

" -meb "4 Item "-meb" Generate little-endian (default) or big-endian (experimental) code, respectively.

" -march= arch "4 Item "-march=arch" This specifies the name of the target Nios IIarchitecture. GCCuses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: r1 , r2 . The preprocessor macro CW(C`_ _nios2_arch_ _ (C' is available to programs, with value 1 or 2, indicating the targeted ISAlevel.

" -mbypass -cache "4 Item "-mbypass-cache" 0

" -mno -bypass -cache "4 Item "-mno-bypass-cache" Force all load and store instructions to always bypass cache by using I/O variants of the instructions. The default is not to bypass the cache.

" -mno -cache -volatile "4 Item "-mno-cache-volatile" 0

" -mcache -volatile "4 Item "-mcache-volatile" Volatile memory access bypass the cache using the I/O variants of the load and store instructions. The default is not to bypass the cache.

" -mno -fast -sw -div "4 Item "-mno-fast-sw-div" 0

" -mfast -sw -div "4 Item "-mfast-sw-div" Do not use table-based fast divide for small numbers. The default is to use the fast divide at -O3 and above.

" -mno -hw -mul "4 Item "-mno-hw-mul" 0

" -mhw -mul "4 Item "-mhw-mul"

" -mno -hw -mulx "4 Item "-mno-hw-mulx"

" -mhw -mulx "4 Item "-mhw-mulx"

" -mno -hw -div "4 Item "-mno-hw-div"

" -mhw -div "4 Item "-mhw-div" Enable or disable emitting CW(C`mul (C' , CW(C`mulx (C' and CW(C`div (C' family of instructions by the compiler. The default is to emit CW(C`mul (C' and not emit CW(C`div (C' and CW(C`mulx (C' .

" -mbmx "4 Item "-mbmx" 0

" -mno -bmx "4 Item "-mno-bmx"

" -mcdx "4 Item "-mcdx"

" -mno -cdx "4 Item "-mno-cdx" Enable or disable generation of Nios IIR2 BMX (bit manipulation) and CDX(code density) instructions. Enabling these instructions also requires -march=r2 .Since these instructions are optional extensions to the R2 architecture, the default is not to emit them.

" -mcustom - insn = N "4 Item "-mcustom-insn=N" 0

" -mno -custom - insn "4 Item "-mno-custom-insn" Each -mcustom - insn = N option enables use of a custom instruction with encoding N when generating code that uses insn .For example, -mcustom -fadds=253 generates custom instruction 253 for single-precision floating-point add operations instead of the default behavior of using a library call. The following values of insn are supported. Except as otherwise noted, floating-point operations are expected to be implemented with normal IEEE754 semantics and correspond directly to the C operators or the equivalent GCCbuilt-in functions. Single-precision floating point:

" fadds , fsubs , fdivs , fmuls "4 Item "fadds, fsubs, fdivs, fmuls" Binary arithmetic operations.

" fnegs "4 Item "fnegs" Unary negation.

" fabss "4 Item "fabss" Unary absolute value.

" fcmpeqs , fcmpges , fcmpgts , fcmples , fcmplts , fcmpnes "4 Item "fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes" Comparison operations.

" fmins , fmaxs "4 Item "fmins, fmaxs" Floating-point minimum and maximum. These instructions are only generated if -ffinite -math -only is specified.

" fsqrts "4 Item "fsqrts" Unary square root operation.

" fcoss , fsins , ftans , fatans , fexps , flogs "4 Item "fcoss, fsins, ftans, fatans, fexps, flogs" Floating-point trigonometric and exponential functions. These instructions are only generated if -funsafe -math -optimizations is also specified. Double-precision floating point:

" faddd , fsubd , fdivd , fmuld "4 Item "faddd, fsubd, fdivd, fmuld" Binary arithmetic operations.

" fnegd "4 Item "fnegd" Unary negation.

" fabsd "4 Item "fabsd" Unary absolute value.

" fcmpeqd , fcmpged , fcmpgtd , fcmpled , fcmpltd , fcmpned "4 Item "fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned" Comparison operations.

" fmind , fmaxd "4 Item "fmind, fmaxd" Double-precision minimum and maximum. These instructions are only generated if -ffinite -math -only is specified.

" fsqrtd "4 Item "fsqrtd" Unary square root operation.

" fcosd , fsind , ftand , fatand , fexpd , flogd "4 Item "fcosd, fsind, ftand, fatand, fexpd, flogd" Double-precision trigonometric and exponential functions. These instructions are only generated if -funsafe -math -optimizations is also specified. Conversions:

" fextsd "4 Item "fextsd" Conversion from single precision to double precision.

" ftruncds "4 Item "ftruncds" Conversion from double precision to single precision.

" fixsi , fixsu , fixdi , fixdu "4 Item "fixsi, fixsu, fixdi, fixdu" Conversion from floating point to signed or unsigned integer types, with truncation towards zero.

" round "4 Item "round" Conversion from single-precision floating point to signed integer, rounding to the nearest integer and ties away from zero. This corresponds to the CW(C`_ _builtin_lroundf (C' function when -fno -math -errno is used.

" floatis , floatus , floatid , floatud "4 Item "floatis, floatus, floatid, floatud" Conversion from signed or unsigned integer types to floating-point types. In addition, all of the following transfer instructions for internal registers X and Y must be provided to use any of the double-precision floating-point instructions. Custom instructions taking two double-precision source operands expect the first operand in the 64 -bit register X. The other operand (or only operand of a unary operation) is given to the custom arithmetic instruction with the least significant half in source register src1 and the most significant half in src2 .A custom instruction that returns a double-precision result returns the most significant 32 bits in the destination register and the other half in 32 -bit register Y. GCCautomatically generates the necessary code sequences to write register X and/or read register Y when double-precision floating-point instructions are used.

" fwrx "4 Item "fwrx" Write src1 into the least significant half of X and src2 into the most significant half of X.

" fwry "4 Item "fwry" Write src1 into Y.

" frdxhi , frdxlo "4 Item "frdxhi, frdxlo" Read the most or least (respectively) significant half of X and store it in dest .

" frdy "4 Item "frdy" Read the value of Y and store it into dest . Note that you can gain more local control over generation of Nios IIcustom instructions by using the CW(C`target("custom - CIinsn CW= CIN CW")(C' and CW(C`target("no -custom - CIinsn CW")(C' function attributes or pragmas.

" -mcustom -fpu -cfg= name "4 Item "-mcustom-fpu-cfg=name" This option enables a predefined, named set of custom instruction encodings (see -mcustom - insn above). Currently, the following sets are defined: -mcustom -fpu -cfg=60 -1 is equivalent to: -mcustom -fmuls=252 -mcustom -fadds=253 -mcustom -fsubs=254 -fsingle -precision -constant -mcustom -fpu -cfg=60 -2 is equivalent to: -mcustom -fmuls=252 -mcustom -fadds=253 -mcustom -fsubs=254 -mcustom -fdivs=255 -fsingle -precision -constant -mcustom -fpu -cfg=72 -3 is equivalent to: -mcustom -floatus=243 -mcustom -fixsi=244 -mcustom -floatis=245 -mcustom -fcmpgts=246 -mcustom -fcmples=249 -mcustom -fcmpeqs=250 -mcustom -fcmpnes=251 -mcustom -fmuls=252 -mcustom -fadds=253 -mcustom -fsubs=254 -mcustom -fdivs=255 -fsingle -precision -constant Custom instruction assignments given by individual -mcustom - insn = options override those given by -mcustom -fpu -cfg= ,regardless of the order of the options on the command line. Note that you can gain more local control over selection of a FPU configuration by using the CW(C`target("custom -fpu -cfg= CIname CW")(C' function attribute or pragma.

These additional -m options are available for the Altera Nios II ELF (bare-metal) target:

" -mhal "4 Item "-mhal" Link with HALBSP. This suppresses linking with the GCC-provided C runtime startup and termination code, and is typically used in conjunction with -msys -crt0= to specify the location of the alternate startup code provided by the HALBSP.

" -msmallc "4 Item "-msmallc" Link with a limited version of the C library, -lsmallc ,rather than Newlib.

" -msys -crt0= startfile "4 Item "-msys-crt0=startfile" startfile is the file name of the startfile (crt0) to use when linking. This option is only useful in conjunction with -mhal .

" -msys -lib= systemlib "4 Item "-msys-lib=systemlib" systemlib is the library name of the library that provides low-level system calls required by the C library, e.g. CW(C`read (C' and CW(C`write (C' . This option is typically used to link with a library provided by a HALBSP.

NvidiaPTXOptions Subsection "Nvidia PTX Options"

These options are defined for Nvidia PTX:

" -m32 "4 Item "-m32" 0

" -m64 "4 Item "-m64" Generate code for 32 -bit or 64 -bit ABI.

" -misa= ISA-string "4 Item "-misa=ISA-string" Generate code for given the specified PTXISA (e.g. sm_35 ).ISA strings must be lower-case. Valid ISAstrings include sm_30 and sm_35 .The default ISAis sm_30.

" -mmainkernel "4 Item "-mmainkernel" Link in code for a _ _main kernel. This is for stand-alone instead of offloading execution.

" -moptimize "4 Item "-moptimize" Apply partitioned execution optimizations. This is the default when any level of optimization is selected.

" -msoft -stack "4 Item "-msoft-stack" Generate code that does not use CW(C`.local (C' memory directly for stack storage. Instead, a per-warp stack pointer is maintained explicitly. This enables variable-length stack allocation (with variable-length arrays or CW(C`alloca (C' ),and when global memory is used for underlying storage, makes it possible to access automatic variables from other threads, or with atomic instructions. This code generation variant is used for OpenMP offloading, but the option is exposed on its own for the purpose of testing the compiler; to generate code suitable for linking into programs using OpenMP offloading, use option -mgomp .

" -muniform -simt "4 Item "-muniform-simt" Switch to code generation variant that allows to execute all threads in each warp, while maintaining memory state and side effects as if only one thread in each warp was active outside of OpenMP SIMDregions. All atomic operations and calls to runtime (malloc, free, vprintf) are conditionally executed (iff current lane index equals the master lane index), and the register being assigned is copied via a shuffle instruction from the master lane. Outside of SIMDregions lane 0 is the master; inside, each thread sees itself as the master. Shared memory array CW(C`int _ _nvptx_uni[] (C' stores all-zeros or all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD regions). Each thread can bitwise-and the bitmask at position CW(C`tid.y (C' with current lane index to compute the master lane index.

" -mgomp "4 Item "-mgomp" Generate code for use in OpenMP offloading: enables -msoft -stack and -muniform -simt options, and selects corresponding multilib variant.

OpenRISCOptions Subsection "OpenRISC Options"

These options are defined for OpenRISC:

" -mboard= name "4 Item "-mboard=name" Configure a board specific runtime. This will be passed to the linker for newlib board library linking. The default is CW(C`or1ksim (C' .

" -mnewlib "4 Item "-mnewlib" For compatibility, it's always newlib for elf now.

" -mhard -div "4 Item "-mhard-div" Generate code for hardware which supports divide instructions. This is the default.

" -mhard -mul "4 Item "-mhard-mul" Generate code for hardware which supports multiply instructions. This is the default.

" -mcmov "4 Item "-mcmov" Generate code for hardware which supports the conditional move ( CW(C`l.cmov (C' ) instruction.

" -mror "4 Item "-mror" Generate code for hardware which supports rotate right instructions.

" -msext "4 Item "-msext" Generate code for hardware which supports sign-extension instructions.

" -msfimm "4 Item "-msfimm" Generate code for hardware which supports set flag immediate ( CW(C`l.sf*i (C' ) instructions.

" -mshftimm "4 Item "-mshftimm" Generate code for hardware which supports shift immediate related instructions (i.e. CW(C`l.srai (C' , CW(C`l.srli (C' , CW(C`l.slli (C' , CW(C`1.rori (C' ).Note, to enable generation of the CW(C`l.rori (C' instruction the -mror flag must also be specified.

" -msoft -div "4 Item "-msoft-div" Generate code for hardware which requires divide instruction emulation.

" -msoft -mul "4 Item "-msoft-mul" Generate code for hardware which requires multiply instruction emulation.

PDP-11 Options Subsection "PDP-11 Options"

These options are defined for the PDP-11:

" -mfpu "4 Item "-mfpu" Use hardware FPPfloating point. This is the default. ( FISfloating point on the PDP-11/40 is not supported.) Implies -m45.

" -msoft -float "4 Item "-msoft-float" Do not use hardware floating point.

" -mac0 "4 Item "-mac0" Return floating-point results in ac0 (fr0 in Unix assembler syntax).

" -mno -ac0 "4 Item "-mno-ac0" Return floating-point results in memory. This is the default.

" -m40 "4 Item "-m40" Generate code for a PDP-11/40. Implies -msoft -float -mno -split.

" -m45 "4 Item "-m45" Generate code for a PDP-11/45. This is the default.

" -m10 "4 Item "-m10" Generate code for a PDP-11/10. Implies -msoft -float -mno -split.

" -mint16 "4 Item "-mint16" 0

" -mno -int32 "4 Item "-mno-int32" Use 16 -bit CW(C`int (C' .This is the default.

" -mint32 "4 Item "-mint32" 0

" -mno -int16 "4 Item "-mno-int16" Use 32 -bit CW(C`int (C' .

" -msplit "4 Item "-msplit" Target has split instruction and data space. Implies -m45.

" -munix -asm "4 Item "-munix-asm" Use Unix assembler syntax.

" -mdec -asm "4 Item "-mdec-asm" Use DECassembler syntax.

" -mgnu -asm "4 Item "-mgnu-asm" Use GNUassembler syntax. This is the default.

" -mlra "4 Item "-mlra" Use the new LRAregister allocator. By default, the old (L"reload (R" allocator is used.

picoChipOptions Subsection "picoChip Options"

These -m options are defined for picoChip implementations:

" -mae= ae_type "4 Item "-mae=ae_type" Set the instruction set, register set, and instruction scheduling parameters for array element type ae_type .Supported values for ae_type are ANY , MUL ,and MAC . -mae=ANY selects a completely generic AEtype. Code generated with this option runs on any of the other AEtypes. The code is not as efficient as it would be if compiled for a specific AEtype, and some types of operation (e.g., multiplication) do not work properly on all types of AE. -mae=MUL selects a MULAE type. This is the most useful AEtype for compiled code, and is the default. -mae=MAC selects a DSP-style MACAE. Code compiled with this option may suffer from poor performance of byte (char) manipulation, since the DSPAE does not provide hardware support for byte load/stores.

" -msymbol -as -address "4 Item "-msymbol-as-address" Enable the compiler to directly use a symbol name as an address in a load/store instruction, without first loading it into a register. Typically, the use of this option generates larger programs, which run faster than when the option isn't used. However, the results vary from program to program, so it is left as a user option, rather than being permanently enabled.

" -mno -inefficient -warnings "4 Item "-mno-inefficient-warnings" Disables warnings about the generation of inefficient code. These warnings can be generated, for example, when compiling code that performs byte-level memory operations on the MACAE type. The MACAE has no hardware support for byte-level memory operations, so all byte load/stores must be synthesized from word load/store operations. This is inefficient and a warning is generated to indicate that you should rewrite the code to avoid byte operations, or to target an AEtype that has the necessary hardware support. This option disables these warnings.

PowerPCOptions Subsection "PowerPC Options"

These are listed under

RISC-VOptions Subsection "RISC-V Options"

These command-line options are defined for RISC-V targets:

" -mbranch -cost= n "4 Item "-mbranch-cost=n" Set the cost of branches to roughly n instructions.

" -mplt "4 Item "-mplt" 0

" -mno -plt "4 Item "-mno-plt" When generating PICcode, do or don't allow the use of PLTs. Ignored for non-PIC. The default is -mplt .

" -mabi= ABI-string "4 Item "-mabi=ABI-string" Specify integer and floating-point calling convention. ABI-string contains two parts: the size of integer types and the registers used for floating-point types. For example -march=rv64ifd -mabi=lp64d means that long and pointers are 64 -bit (implicitly defining int to be 32 -bit), and that floating-point values up to 64 bits wide are passed in F registers. Contrast this with -march=rv64ifd -mabi=lp64f ,which still allows the compiler to generate code that uses the F and D extensions but only allows floating-point values up to 32 bits long to be passed in registers; or -march=rv64ifd -mabi=lp64 ,in which no floating-point arguments will be passed in registers. The default for this argument is system dependent, users who want a specific calling convention should specify one explicitly. The valid calling conventions are: ilp32 , ilp32f , ilp32d , lp64 , lp64f ,and lp64d .Some calling conventions are impossible to implement on some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid because the ABIrequires 64 -bit values be passed in F registers, but F registers are only 32 bits wide. There is also the ilp32e ABIthat can only be used with the rv32e architecture. This ABIis not well specified at present, and is subject to change.

" -mfdiv "4 Item "-mfdiv" 0

" -mno -fdiv "4 Item "-mno-fdiv" Do or don't use hardware floating-point divide and square root instructions. This requires the F or D extensions for floating-point registers. The default is to use them if the specified architecture has these instructions.

" -mdiv "4 Item "-mdiv" 0

" -mno -div "4 Item "-mno-div" Do or don't use hardware instructions for integer division. This requires the M extension. The default is to use them if the specified architecture has these instructions.

" -march= ISA-string "4 Item "-march=ISA-string" Generate code for given RISC-V ISA(e.g. rv64im ).ISAstrings must be lower-case. Examples include rv64i , rv32g , rv32e ,and rv32imaf .

" -mtune= processor-string "4 Item "-mtune=processor-string" Optimize the output for the given processor, specified by microarchitecture name. Permissible values for this option are: rocket , sifive-3 -series , sifive-5 -series , sifive-7 -series , and size . When -mtune= is not specified, the default is rocket . The size choice is not intended for use by end-users. This is used when -Os is specified. It overrides the instruction cost info provided by -mtune= ,but does not override the pipeline info. This helps reduce code size while still giving good performance.

" -mpreferred -stack -boundary= num "4 Item "-mpreferred-stack-boundary=num" Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred -stack -boundary is not specified, the default is 4 (16 bytes or 128 -bits). Warning: If you use this switch, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.

" -msmall -data -limit= n "4 Item "-msmall-data-limit=n" Put global and static data smaller than n bytes into a special section (on some targets).

" -msave -restore "4 Item "-msave-restore" 0

" -mno -save -restore "4 Item "-mno-save-restore" Do or don't use smaller but slower prologue and epilogue code that uses library function calls. The default is to use fast inline prologues and epilogues.

" -mstrict -align "4 Item "-mstrict-align" 0

" -mno -strict -align "4 Item "-mno-strict-align" Do not or do generate unaligned memory accesses. The default is set depending on whether the processor we are optimizing for supports fast unaligned access or not.

" -mcmodel=medlow "4 Item "-mcmodel=medlow" Generate code for the medium-low code model. The program and its statically defined symbols must lie within a single 2 GiB address range and must lie between absolute addresses -2 GiB and +2 GiB. Programs can be statically or dynamically linked. This is the default code model.

" -mcmodel=medany "4 Item "-mcmodel=medany" Generate code for the medium-any code model. The program and its statically defined symbols must be within any single 2 GiB address range. Programs can be statically or dynamically linked.

" -mexplicit -relocs "4 Item "-mexplicit-relocs" 0

" -mno -exlicit -relocs "4 Item "-mno-exlicit-relocs" Use or do not use assembler relocation operators when dealing with symbolic addresses. The alternative is to use assembler macros instead, which may limit optimization.

" -mrelax "4 Item "-mrelax" 0

" -mno -relax "4 Item "-mno-relax" Take advantage of linker relaxations to reduce the number of instructions required to materialize symbol addresses. The default is to take advantage of linker relaxations.

" -memit -attribute "4 Item "-memit-attribute" 0

" -mno -emit -attribute "4 Item "-mno-emit-attribute" Emit (do not emit) RISC-V attribute to record extra information into ELF objects. This feature requires at least binutils 2.32.

RL78Options Subsection "RL78 Options"

" -msim "4 Item "-msim" Links in additional target libraries to support operation within a simulator.

" -mmul=none "4 Item "-mmul=none" 0

" -mmul=g10 "4 Item "-mmul=g10"

" -mmul=g13 "4 Item "-mmul=g13"

" -mmul=g14 "4 Item "-mmul=g14"

" -mmul=rl78 "4 Item "-mmul=rl78" Specifies the type of hardware multiplication and division support to be used. The simplest is CW(C`none (C' ,which uses software for both multiplication and division. This is the default. The CW(C`g13 (C' value is for the hardware multiply/divide peripheral found on the RL78/G13(S2 core) targets. The CW(C`g14 (C' value selects the use of the multiplication and division instructions supported by the RL78/G14 (S3 core) parts. The value CW(C`rl78 (C' is an alias for CW(C`g14 (C' and the value CW(C`mg10 (C' is an alias for CW(C`none (C' . In addition a C preprocessor macro is defined, based upon the setting of this option. Possible values are: CW(C`_ _RL78_MUL_NONE_ _ (C' , CW(C`_ _RL78_MUL_G13_ _ (C' or CW(C`_ _RL78_MUL_G14_ _ (C' .

" -mcpu=g10 "4 Item "-mcpu=g10" 0

" -mcpu=g13 "4 Item "-mcpu=g13"

" -mcpu=g14 "4 Item "-mcpu=g14"

" -mcpu=rl78 "4 Item "-mcpu=rl78" Specifies the RL78core to target. The default is the G14 core, also known as an S3 core or just RL78.The G13 or S2 core does not have multiply or divide instructions, instead it uses a hardware peripheral for these operations. The G10 or S1 core does not have register banks, so it uses a different calling convention. If this option is set it also selects the type of hardware multiply support to use, unless this is overridden by an explicit -mmul=none option on the command line. Thus specifying -mcpu=g13 enables the use of the G13 hardware multiply peripheral and specifying -mcpu=g10 disables the use of hardware multiplications altogether. Note, although the RL78/G14core is the default target, specifying -mcpu=g14 or -mcpu=rl78 on the command line does change the behavior of the toolchain since it also enables G14 hardware multiply support. If these options are not specified on the command line then software multiplication routines will be used even though the code targets the RL78core. This is for backwards compatibility with older toolchains which did not have hardware multiply and divide support. In addition a C preprocessor macro is defined, based upon the setting of this option. Possible values are: CW(C`_ _RL78_G10_ _ (C' , CW(C`_ _RL78_G13_ _ (C' or CW(C`_ _RL78_G14_ _ (C' .

" -mg10 "4 Item "-mg10" 0

" -mg13 "4 Item "-mg13"

" -mg14 "4 Item "-mg14"

" -mrl78 "4 Item "-mrl78" These are aliases for the corresponding -mcpu= option. They are provided for backwards compatibility.

" -mallregs "4 Item "-mallregs" Allow the compiler to use all of the available registers. By default registers CW(C`r24..r31 (C' are reserved for use in interrupt handlers. With this option enabled these registers can be used in ordinary functions as well.

" -m64bit -doubles "4 Item "-m64bit-doubles" 0

" -m32bit -doubles "4 Item "-m32bit-doubles" Make the CW(C`double (C' data type be 64 bits ( -m64bit -doubles ) or 32 bits ( -m32bit -doubles )in size. The default is -m32bit -doubles .

" -msave -mduc -in -interrupts "4 Item "-msave-mduc-in-interrupts" 0

" -mno -save -mduc -in -interrupts "4 Item "-mno-save-mduc-in-interrupts" Specifies that interrupt handler functions should preserve the MDUCregisters. This is only necessary if normal code might use the MDUCregisters, for example because it performs multiplication and division operations. The default is to ignore the MDUCregisters as this makes the interrupt handlers faster. The target option -mg13 needs to be passed for this to work as this feature is only available on the G13 target (S2 core). The MDUCregisters will only be saved if the interrupt handler performs a multiplication or division operation or it calls another function.

IBMRS/6000 and PowerPC Options Subsection "IBM RS/6000 and PowerPC Options"

These -m options are defined for the IBMRS/6000 and PowerPC:

" -mpowerpc -gpopt "4 Item "-mpowerpc-gpopt" 0

" -mno -powerpc -gpopt "4 Item "-mno-powerpc-gpopt"

" -mpowerpc -gfxopt "4 Item "-mpowerpc-gfxopt"

" -mno -powerpc -gfxopt "4 Item "-mno-powerpc-gfxopt"

" -mpowerpc64 "4 Item "-mpowerpc64"

" -mno -powerpc64 "4 Item "-mno-powerpc64"

" -mmfcrf "4 Item "-mmfcrf"

" -mno -mfcrf "4 Item "-mno-mfcrf"

" -mpopcntb "4 Item "-mpopcntb"

" -mno -popcntb "4 Item "-mno-popcntb"

" -mpopcntd "4 Item "-mpopcntd"

" -mno -popcntd "4 Item "-mno-popcntd"

" -mfprnd "4 Item "-mfprnd"

" -mno -fprnd "4 Item "-mno-fprnd"

" -mcmpb "4 Item "-mcmpb"

" -mno -cmpb "4 Item "-mno-cmpb"

" -mmfpgpr "4 Item "-mmfpgpr"

" -mno -mfpgpr "4 Item "-mno-mfpgpr"

" -mhard -dfp "4 Item "-mhard-dfp"

" -mno -hard -dfp "4 Item "-mno-hard-dfp" You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC.Specifying the -mcpu= cpu_type overrides the specification of these options. We recommend you use the -mcpu= cpu_type option rather than the options listed above. Specifying -mpowerpc -gpopt allows GCCto use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying -mpowerpc -gfxopt allows GCCto use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. The -mmfcrf option allows GCCto generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture. The -mpopcntb option allows GCCto generate the popcount and double-precision FPreciprocal estimate instruction implemented on the POWER5processor and other processors that support the PowerPC V2.02 architecture. The -mpopcntd option allows GCCto generate the popcount instruction implemented on the POWER7processor and other processors that support the PowerPC V2.06 architecture. The -mfprnd option allows GCCto generate the FPround to integer instructions implemented on the POWER5+processor and other processors that support the PowerPC V2.03 architecture. The -mcmpb option allows GCCto generate the compare bytes instruction implemented on the POWER6processor and other processors that support the PowerPC V2.05 architecture. The -mmfpgpr option allows GCCto generate the FPmove to/from general-purpose register instructions implemented on the POWER6X processor and other processors that support the extended PowerPC V2.05 architecture. The -mhard -dfp option allows GCCto generate the decimal floating-point instructions implemented on some POWERprocessors. The -mpowerpc64 option allows GCCto generate the additional 64 -bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64 -bit, doubleword quantities. GCCdefaults to -mno -powerpc64 .

" -mcpu= cpu_type "4 Item "-mcpu=cpu_type" Set architecture type, register usage, and instruction scheduling parameters for machine type cpu_type . Supported values for cpu_type are 401 , 403 , 405 , 405fp , 440 , 440fp , 464 , 464fp , 476 , 476fp , 505 , 601 , 602 , 603 , 603e , 604 , 604e , 620 , 630 , 740 , 7400 , 7450 , 750 , 801 , 821 , 823 , 860 , 970 , 8540 , a2 , e300c2 , e300c3 , e500mc , e500mc64 , e5500 , e6500 , ec603e , G3 , G4 , G5 , titan , power3 , power4 , power5 , power5+ , power6 , power6x , power7 , power8 , power9 , powerpc , powerpc64 , powerpc64le , rs64 ,and native . -mcpu=powerpc , -mcpu=powerpc64 ,and -mcpu=powerpc64le specify pure 32 -bit PowerPC (either endian), 64 -bit big endian PowerPC and 64 -bit little endian PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. Specifying native as cpu type detects and selects the architecture option that corresponds to the host processor of the system performing the compilation. -mcpu=native has no effect if GCCdoes not recognize the processor. The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others. The -mcpu options automatically enable or disable the following options: -maltivec -mfprnd -mhard -float -mmfcrf -mmultiple -mpopcntb -mpopcntd -mpowerpc64 -mpowerpc -gpopt -mpowerpc -gfxopt -mmulhw -mdlmzb -mmfpgpr -mvsx -mcrypto -mhtm -mpower8 -fusion -mpower8 -vector -mquad -memory -mquad -memory -atomic -mfloat128 -mfloat128 -hardware The particular options set for any particular CPUvaries between compiler versions, depending on what setting seems to produce optimal code for that CPU;it doesn't necessarily reflect the actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like -mcpu=970 -mno -altivec . On AIX,the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at present because AIXdoes not have full support for these options. You may still enable or disable them individually if you're sure it'll work in your environment.

" -mtune= cpu_type "4 Item "-mtune=cpu_type" Set the instruction scheduling parameters for machine type cpu_type ,but do not set the architecture type or register usage, as -mcpu= cpu_type does. The same values for cpu_type are used for -mtune as for -mcpu .If both are specified, the code generated uses the architecture and registers set by -mcpu ,but the scheduling parameters set by -mtune .

" -mcmodel=small "4 Item "-mcmodel=small" Generate PowerPC64 code for the small model: The TOCis limited to 64k.

" -mcmodel=medium "4 Item "-mcmodel=medium" Generate PowerPC64 code for the medium model: The TOCand other static data may be up to a total of 4G in size. This is the default for 64 -bit Linux.

" -mcmodel=large "4 Item "-mcmodel=large" Generate PowerPC64 code for the large model: The TOCmay be up to 4G in size. Other data and code is only limited by the 64 -bit address space.

" -maltivec "4 Item "-maltivec" 0

" -mno -altivec "4 Item "-mno-altivec" Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set -mabi=altivec to adjust the current ABIwith AltiVec ABI enhancements. When -maltivec is used, the element order for AltiVec intrinsics such as CW(C`vec_splat (C' , CW(C`vec_extract (C' ,and CW(C`vec_insert (C' match array element order corresponding to the endianness of the target. That is, element zero identifies the leftmost element in a vector register when targeting a big-endian platform, and identifies the rightmost element in a vector register when targeting a little-endian platform.

" -mvrsave "4 Item "-mvrsave" 0

" -mno -vrsave "4 Item "-mno-vrsave" Generate VRSAVEinstructions when generating AltiVec code.

" -msecure -plt "4 Item "-msecure-plt" Generate code that allows ld and ld.so to build executables and shared libraries with non-executable CW(C`.plt (C' and CW(C`.got (C' sections. This is a PowerPC 32 -bit SYSVABI option.

" -mbss -plt "4 Item "-mbss-plt" Generate code that uses a BSS CW(C`.plt (C' section that ld.so fills in, and requires CW(C`.plt (C' and CW(C`.got (C' sections that are both writable and executable. This is a PowerPC 32 -bit SYSVABI option.

" -misel "4 Item "-misel" 0

" -mno -isel "4 Item "-mno-isel" This switch enables or disables the generation of ISELinstructions.

" -mvsx "4 Item "-mvsx" 0

" -mno -vsx "4 Item "-mno-vsx" Generate code that uses (does not use) vector/scalar ( VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSXinstruction set.

" -mcrypto "4 Item "-mcrypto" 0

" -mno -crypto "4 Item "-mno-crypto" Enable the use (disable) of the built-in functions that allow direct access to the cryptographic instructions that were added in version 2.07 of the PowerPC ISA.

" -mhtm "4 Item "-mhtm" 0

" -mno -htm "4 Item "-mno-htm" Enable (disable) the use of the built-in functions that allow direct access to the Hardware Transactional Memory ( HTM)instructions that were added in version 2.07 of the PowerPC ISA.

" -mpower8 -fusion "4 Item "-mpower8-fusion" 0

" -mno -power8 -fusion "4 Item "-mno-power8-fusion" Generate code that keeps (does not keeps) some integer operations adjacent so that the instructions can be fused together on power8 and later processors.

" -mpower8 -vector "4 Item "-mpower8-vector" 0

" -mno -power8 -vector "4 Item "-mno-power8-vector" Generate code that uses (does not use) the vector and scalar instructions that were added in version 2.07 of the PowerPC ISA.Also enable the use of built-in functions that allow more direct access to the vector instructions.

" -mquad -memory "4 Item "-mquad-memory" 0

" -mno -quad -memory "4 Item "-mno-quad-memory" Generate code that uses (does not use) the non-atomic quad word memory instructions. The -mquad -memory option requires use of 64 -bit mode.

" -mquad -memory -atomic "4 Item "-mquad-memory-atomic" 0

" -mno -quad -memory -atomic "4 Item "-mno-quad-memory-atomic" Generate code that uses (does not use) the atomic quad word memory instructions. The -mquad -memory -atomic option requires use of 64 -bit mode.

" -mfloat128 "4 Item "-mfloat128" 0

" -mno -float128 "4 Item "-mno-float128" Enable/disable the __float128 keyword for IEEE128 -bit floating point and use either software emulation for IEEE128 -bit floating point or hardware instructions. The VSXinstruction set ( -mvsx , -mcpu=power7 , -mcpu=power8 ),or -mcpu=power9 must be enabled to use the IEEE128 -bit floating point support. The IEEE128 -bit floating point support only works on PowerPC Linux systems. The default for -mfloat128 is enabled on PowerPC Linux systems using the VSXinstruction set, and disabled on other systems. If you use the ISA3.0 instruction set ( -mpower9 -vector or -mcpu=power9 )on a 64 -bit system, the IEEE128 -bit floating point support will also enable the generation of ISA3.0 IEEE 128 -bit floating point instructions. Otherwise, if you do not specify to generate ISA3.0 instructions or you are targeting a 32 -bit big endian system, IEEE128 -bit floating point will be done with software emulation.

" -mfloat128 -hardware "4 Item "-mfloat128-hardware" 0

" -mno -float128 -hardware "4 Item "-mno-float128-hardware" Enable/disable using ISA3.0 hardware instructions to support the __float128 data type. The default for -mfloat128 -hardware is enabled on PowerPC Linux systems using the ISA3.0 instruction set, and disabled on other systems.

" -m32 "4 Item "-m32" 0

" -m64 "4 Item "-m64" Generate code for 32 -bit or 64 -bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32 -bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64 -bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for -mpowerpc64 .

" -mfull -toc "4 Item "-mfull-toc" 0

" -mno -fp -in -toc "4 Item "-mno-fp-in-toc"

" -mno -sum -in -toc "4 Item "-mno-sum-in-toc"

" -mminimal -toc "4 Item "-mminimal-toc" Modify generation of the TOC(Table Of Contents), which is created for every executable file. The -mfull -toc option is selected by default. In that case, GCCallocates at least one TOCentry for each unique non-automatic variable reference in your program. GCC also places floating-point constants in the TOC.However, only 16,384 entries are available in the TOC. If you receive a linker error message that saying you have overflowed the available TOCspace, you can reduce the amount of TOCspace used with the -mno -fp -in -toc and -mno -sum -in -toc options. -mno -fp -in -toc prevents GCCfrom putting floating-point constants in the TOCand -mno -sum -in -toc forces GCCto generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the TOC.You may specify one or both of these options. Each causes GCCto produce very slightly slower and larger code at the expense of conserving TOCspace. If you still run out of space in the TOCeven when you specify both of these options, specify -mminimal -toc instead. This option causes GCCto make only one TOCentry for every file. When you specify this option, GCCproduces code that is slower and larger but which uses extremely little TOCspace. You may wish to use this option only on files that contain less frequently-executed code.

" -maix64 "4 Item "-maix64" 0

" -maix32 "4 Item "-maix32" Enable 64 -bit AIXABI and calling convention: 64 -bit pointers, 64 -bit CW(C`long (C' type, and the infrastructure needed to support them. Specifying -maix64 implies -mpowerpc64 , while -maix32 disables the 64 -bit ABIand implies -mno -powerpc64 .GCCdefaults to -maix32 .

" -mxl -compat "4 Item "-mxl-compat" 0

" -mno -xl -compat "4 Item "-mno-xl-compat" Produce code that conforms more closely to IBMXL compiler semantics when using AIX-compatible ABI.Pass floating-point arguments to prototyped functions beyond the register save area ( RSA)on the stack in addition to argument FPRs. Do not assume that most significant double in 128 -bit long double value is properly rounded when comparing values and converting to double. Use XLsymbol names for long double support routines. The AIXcalling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. IBMXL compilers access floating-point arguments that do not fit in the RSAfrom the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without optimization.

" -mpe "4 Item "-mpe" Support IBMRS/6000 SP ParallelEnvironment ( PE).Link an application written to use message passing with special startup code to enable the application to run. The system must have PEinstalled in the standard location ( /usr/lpp/ppe.poe/ ),or the specs file must be overridden with the -specs= option to specify the appropriate directory location. The Parallel Environment does not support threads, so the -mpe option and the -pthread option are incompatible.

" -malign -natural "4 Item "-malign-natural" 0

" -malign -power "4 Item "-malign-power" On AIX,32 -bit Darwin, and 64 -bit PowerPC GNU/Linux, the option -malign -natural overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option -malign -power instructs GCCto follow the ABI-specified alignment rules. GCCdefaults to the standard alignment defined in the ABI. On 64 -bit Darwin, natural alignment is the default, and -malign -power is not supported.

" -msoft -float "4 Item "-msoft-float" 0

" -mhard -float "4 Item "-mhard-float" Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the -msoft -float option, and pass the option to GCCwhen linking.

" -mmultiple "4 Item "-mmultiple" 0

" -mno -multiple "4 Item "-mno-multiple" Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWERsystems, and not generated on PowerPC systems. Do not use -mmultiple on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740and PPC750which permit these instructions in little-endian mode.

" -mupdate "4 Item "-mupdate" 0

" -mno -update "4 Item "-mno-update" Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use -mno -update ,there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data.

" -mavoid -indexed -addresses "4 Item "-mavoid-indexed-addresses" 0

" -mno -avoid -indexed -addresses "4 Item "-mno-avoid-indexed-addresses" Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targeting Power6 and disabled otherwise.

" -mfused -madd "4 Item "-mfused-madd" 0

" -mno -fused -madd "4 Item "-mno-fused-madd" Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent -mfused -madd option is now mapped to the machine-independent -ffp -contract=fast option, and -mno -fused -madd is mapped to -ffp -contract=off .

" -mmulhw "4 Item "-mmulhw" 0

" -mno -mulhw "4 Item "-mno-mulhw" Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors.

" -mdlmzb "4 Item "-mdlmzb" 0

" -mno -dlmzb "4 Item "-mno-dlmzb" Generate code that uses (does not use) the string-search dlmzb instruction on the IBM405, 440, 464 and 476 processors. This instruction is generated by default when targeting those processors.

" -mno -bit -align "4 Item "-mno-bit-align" 0

" -mbit -align "4 Item "-mbit-align" On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field. For example, by default a structure containing nothing but 8 CW(C`unsigned (C' bit-fields of length 1 is aligned to a 4 -byte boundary and has a size of 4 bytes. By using -mno -bit -align , the structure is aligned to a 1 -byte boundary and is 1 byte in size.

" -mno -strict -align "4 Item "-mno-strict-align" 0

" -mstrict -align "4 Item "-mstrict-align" On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system.

" -mrelocatable "4 Item "-mrelocatable" 0

" -mno -relocatable "4 Item "-mno-relocatable" Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire contents of CW(C`.got2 (C' and 4 -byte locations listed in the CW(C`.fixup (C' section, a table of 32 -bit addresses generated by this option. For this to work, all objects linked together must be compiled with -mrelocatable or -mrelocatable -lib . -mrelocatable code aligns the stack to an 8 -byte boundary.

" -mrelocatable -lib "4 Item "-mrelocatable-lib" 0

" -mno -relocatable -lib "4 Item "-mno-relocatable-lib" Like -mrelocatable , -mrelocatable -lib generates a CW(C`.fixup (C' section to allow static executables to be relocated at run time, but -mrelocatable -lib does not use the smaller stack alignment of -mrelocatable .Objects compiled with -mrelocatable -lib may be linked with objects compiled with any combination of the -mrelocatable options.

" -mno -toc "4 Item "-mno-toc" 0

" -mtoc "4 Item "-mtoc" On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program.

" -mlittle "4 Item "-mlittle" 0

" -mlittle -endian "4 Item "-mlittle-endian" On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The -mlittle -endian option is the same as -mlittle .

" -mbig "4 Item "-mbig" 0

" -mbig -endian "4 Item "-mbig-endian" On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The -mbig -endian option is the same as -mbig .

" -mdynamic -no -pic "4 Item "-mdynamic-no-pic" On Darwin and Mac OSX systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries.

" -msingle -pic -base "4 Item "-msingle-pic-base" Treat the register used for PICaddressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins.

" -mprioritize -restricted -insns= priority "4 Item "-mprioritize-restricted-insns=priority" This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value 0 , 1 , or 2 to assign no, highest, or second-highest (respectively) priority to dispatch-slot restricted instructions.

" -msched -costly -dep= dependence_type "4 Item "-msched-costly-dep=dependence_type" This option controls which dependences are considered costly by the target during instruction scheduling. The argument dependence_type takes one of the following values:

" no "4 Item "no" No dependence is costly.

" all "4 Item "all" All dependences are costly.

" true_store_to_load "4 Item "true_store_to_load" A true dependence from store to load is costly.