1GCC(1)                                GNU                               GCC(1)
2
3
4

NAME

6       gcc - GNU project C and C++ compiler
7

SYNOPSIS

9       gcc [-c|-S|-E] [-std=standard]
10           [-g] [-pg] [-Olevel]
11           [-Wwarn...] [-pedantic]
12           [-Idir...] [-Ldir...]
13           [-Dmacro[=defn]...] [-Umacro]
14           [-foption...] [-mmachine-option...]
15           [-o outfile] [@file] infile...
16
17       Only the most useful options are listed here; see below for the
18       remainder.  g++ accepts mostly the same options as gcc.
19

DESCRIPTION

21       When you invoke GCC, it normally does preprocessing, compilation,
22       assembly and linking.  The "overall options" allow you to stop this
23       process at an intermediate stage.  For example, the -c option says not
24       to run the linker.  Then the output consists of object files output by
25       the assembler.
26
27       Other options are passed on to one stage of processing.  Some options
28       control the preprocessor and others the compiler itself.  Yet other
29       options control the assembler and linker; most of these are not
30       documented here, since you rarely need to use any of them.
31
32       Most of the command line options that you can use with GCC are useful
33       for C programs; when an option is only useful with another language
34       (usually C++), the explanation says so explicitly.  If the description
35       for a particular option does not mention a source language, you can use
36       that option with all supported languages.
37
38       The gcc program accepts options and file names as operands.  Many
39       options have multi-letter names; therefore multiple single-letter
40       options may not be grouped: -dv is very different from -d -v.
41
42       You can mix options and other arguments.  For the most part, the order
43       you use doesn't matter.  Order does matter when you use several options
44       of the same kind; for example, if you specify -L more than once, the
45       directories are searched in the order specified.  Also, the placement
46       of the -l option is significant.
47
48       Many options have long names starting with -f or with -W---for example,
49       -fmove-loop-invariants, -Wformat and so on.  Most of these have both
50       positive and negative forms; the negative form of -ffoo would be
51       -fno-foo.  This manual documents only one of these two forms, whichever
52       one is not the default.
53

OPTIONS

55   Option Summary
56       Here is a summary of all the options, grouped by type.  Explanations
57       are in the following sections.
58
59       Overall Options
60           -c  -S  -E  -o file  -combine  -no-canonical-prefixes -pipe
61           -pass-exit-codes -x language  -v  -###  --help[=class[,...]]
62           --target-help --version -wrapper@file -fplugin=file
63           -fplugin-arg-name=arg
64
65       C Language Options
66           -ansi  -std=standard  -fgnu89-inline -aux-info filename -fno-asm
67           -fno-builtin  -fno-builtin-function -fhosted  -ffreestanding
68           -fopenmp -fms-extensions -trigraphs  -no-integrated-cpp
69           -traditional  -traditional-cpp -fallow-single-precision
70           -fcond-mismatch -flax-vector-conversions -fsigned-bitfields
71           -fsigned-char -funsigned-bitfields  -funsigned-char
72
73       C++ Language Options
74           -fabi-version=n  -fno-access-control  -fcheck-new -fconserve-space
75           -ffriend-injection -fno-elide-constructors -fno-enforce-eh-specs
76           -ffor-scope  -fno-for-scope  -fno-gnu-keywords
77           -fno-implicit-templates -fno-implicit-inline-templates
78           -fno-implement-inlines  -fms-extensions -fno-nonansi-builtins
79           -fno-operator-names -fno-optional-diags  -fpermissive
80           -fno-pretty-templates -frepo  -fno-rtti  -fstats
81           -ftemplate-depth=n -fno-threadsafe-statics -fuse-cxa-atexit
82           -fno-weak  -nostdinc++ -fno-default-inline
83           -fvisibility-inlines-hidden -fvisibility-ms-compat -Wabi
84           -Wconversion-null  -Wctor-dtor-privacy -Wnon-virtual-dtor
85           -Wreorder -Weffc++  -Wstrict-null-sentinel -Wno-non-template-friend
86           -Wold-style-cast -Woverloaded-virtual  -Wno-pmf-conversions
87           -Wsign-promo
88
89       Objective-C and Objective-C++ Language Options
90           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime
91           -fno-nil-receivers -fobjc-call-cxx-cdtors -fobjc-direct-dispatch
92           -fobjc-exceptions -fobjc-gc -freplace-objc-classes -fzero-link
93           -gen-decls -Wassign-intercept -Wno-protocol  -Wselector
94           -Wstrict-selector-match -Wundeclared-selector
95
96       Language Independent Options
97           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
98           -fdiagnostics-show-option
99
100       Warning Options
101           -fsyntax-only  -pedantic  -pedantic-errors -w  -Wextra  -Wall
102           -Waddress  -Waggregate-return  -Warray-bounds -Wno-attributes
103           -Wno-builtin-macro-redefined -Wc++-compat -Wc++0x-compat
104           -Wcast-align  -Wcast-qual -Wchar-subscripts -Wclobbered  -Wcomment
105           -Wconversion  -Wcoverage-mismatch  -Wno-deprecated
106           -Wno-deprecated-declarations -Wdisabled-optimization
107           -Wno-div-by-zero -Wempty-body  -Wenum-compare -Wno-endif-labels
108           -Werror  -Werror=* -Wfatal-errors  -Wfloat-equal  -Wformat
109           -Wformat=2 -Wno-format-contains-nul -Wno-format-extra-args
110           -Wformat-nonliteral -Wformat-security  -Wformat-y2k
111           -Wframe-larger-than=len -Wjump-misses-init -Wignored-qualifiers
112           -Wimplicit  -Wimplicit-function-declaration  -Wimplicit-int
113           -Winit-self  -Winline -Wno-int-to-pointer-cast
114           -Wno-invalid-offsetof -Winvalid-pch -Wlarger-than=len
115           -Wunsafe-loop-optimizations -Wlogical-op -Wlong-long -Wmain
116           -Wmissing-braces  -Wmissing-field-initializers
117           -Wmissing-format-attribute  -Wmissing-include-dirs
118           -Wmissing-noreturn  -Wno-mudflap -Wno-multichar  -Wnonnull
119           -Wno-overflow -Woverlength-strings  -Wpacked
120           -Wpacked-bitfield-compat  -Wpadded -Wparentheses
121           -Wpedantic-ms-format -Wno-pedantic-ms-format -Wpointer-arith
122           -Wno-pointer-to-int-cast -Wredundant-decls -Wreturn-type
123           -Wsequence-point  -Wshadow -Wsign-compare  -Wsign-conversion
124           -Wstack-protector -Wstrict-aliasing -Wstrict-aliasing=n
125           -Wstrict-overflow -Wstrict-overflow=n -Wswitch  -Wswitch-default
126           -Wswitch-enum -Wsync-nand -Wsystem-headers  -Wtrigraphs
127           -Wtype-limits  -Wundef  -Wuninitialized -Wunknown-pragmas
128           -Wno-pragmas -Wunsuffixed-float-constants  -Wunused
129           -Wunused-function -Wunused-label  -Wunused-parameter
130           -Wno-unused-result -Wunused-value  -Wunused-variable
131           -Wvariadic-macros -Wvla -Wvolatile-register-var  -Wwrite-strings
132
133       C and Objective-C-only Warning Options
134           -Wbad-function-cast  -Wmissing-declarations
135           -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
136           -Wold-style-declaration  -Wold-style-definition -Wstrict-prototypes
137           -Wtraditional  -Wtraditional-conversion
138           -Wdeclaration-after-statement -Wpointer-sign
139
140       Debugging Options
141           -dletters  -dumpspecs  -dumpmachine  -dumpversion -fdbg-cnt-list
142           -fdbg-cnt=counter-value-list -fdump-noaddr -fdump-unnumbered
143           -fdump-unnumbered-links -fdump-translation-unit[-n]
144           -fdump-class-hierarchy[-n] -fdump-ipa-all -fdump-ipa-cgraph
145           -fdump-ipa-inline -fdump-statistics -fdump-tree-all
146           -fdump-tree-original[-n] -fdump-tree-optimized[-n] -fdump-tree-cfg
147           -fdump-tree-vcg -fdump-tree-alias -fdump-tree-ch
148           -fdump-tree-ssa[-n] -fdump-tree-pre[-n] -fdump-tree-ccp[-n]
149           -fdump-tree-dce[-n] -fdump-tree-gimple[-raw]
150           -fdump-tree-mudflap[-n] -fdump-tree-dom[-n] -fdump-tree-dse[-n]
151           -fdump-tree-phiprop[-n] -fdump-tree-phiopt[-n]
152           -fdump-tree-forwprop[-n] -fdump-tree-copyrename[-n] -fdump-tree-nrv
153           -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-n]
154           -fdump-tree-forwprop[-n] -fdump-tree-fre[-n] -fdump-tree-vrp[-n]
155           -ftree-vectorizer-verbose=n -fdump-tree-storeccp[-n]
156           -fdump-final-insns=file -fcompare-debug[=opts]
157           -fcompare-debug-second -feliminate-dwarf2-dups
158           -feliminate-unused-debug-types -feliminate-unused-debug-symbols
159           -femit-class-debug-always -fenable-icf-debug -fmem-report
160           -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs
161           -frandom-seed=string -fsched-verbose=n -fsel-sched-verbose
162           -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose -ftest-coverage
163           -ftime-report -fvar-tracking -fvar-tracking-assignments
164           -fvar-tracking-assignments-toggle -g  -glevel  -gtoggle  -gcoff
165           -gdwarf-version -ggdb  -gstabs  -gstabs+  -gstrict-dwarf
166           -gno-strict-dwarf -gvms  -gxcoff  -gxcoff+ -fno-merge-debug-strings
167           -fno-dwarf2-cfi-asm -fdebug-prefix-map=old=new
168           -femit-struct-debug-baseonly -femit-struct-debug-reduced
169           -femit-struct-debug-detailed[=spec-list] -p  -pg
170           -print-file-name=library  -print-libgcc-file-name
171           -print-multi-directory  -print-multi-lib  -print-multi-os-directory
172           -print-prog-name=program  -print-search-dirs  -Q -print-sysroot
173           -print-sysroot-headers-suffix -save-temps -save-temps=cwd
174           -save-temps=obj -time[=file]
175
176       Optimization Options
177           -falign-functions[=n] -falign-jumps[=n] -falign-labels[=n]
178           -falign-loops[=n] -fassociative-math -fauto-inc-dec
179           -fbranch-probabilities -fbranch-target-load-optimize
180           -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves
181           -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping
182           -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules
183           -fcx-limited-range -fdata-sections -fdce -fdce -fdelayed-branch
184           -fdelete-null-pointer-checks -fdse -fdse -fearly-inlining -fipa-sra
185           -fexpensive-optimizations -ffast-math -ffinite-math-only
186           -ffloat-store -fexcess-precision=style -fforward-propagate
187           -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm
188           -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining
189           -finline-functions -finline-functions-called-once -finline-limit=n
190           -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg
191           -fipa-pta -fipa-pure-const -fipa-reference -fipa-struct-reorg
192           -fipa-type-escape -fira-algorithm=algorithm -fira-region=region
193           -fira-coalesce -fira-loop-pressure -fno-ira-share-save-slots
194           -fno-ira-share-spill-slots -fira-verbose=n -fivopts
195           -fkeep-inline-functions -fkeep-static-consts -floop-block
196           -floop-interchange -floop-strip-mine -fgraphite-identity
197           -floop-parallelize-all -flto -flto-compression-level -flto-report
198           -fltrans -fltrans-output-list -fmerge-all-constants
199           -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves
200           -fmove-loop-invariants -fmudflap -fmudflapir -fmudflapth
201           -fno-branch-count-reg -fno-default-inline -fno-defer-pop
202           -fno-function-cse -fno-guess-branch-probability -fno-inline
203           -fno-math-errno -fno-peephole -fno-peephole2 -fno-sched-interblock
204           -fno-sched-spec -fno-signed-zeros -fno-toplevel-reorder
205           -fno-trapping-math -fno-zero-initialized-in-bss
206           -fomit-frame-pointer -foptimize-register-move
207           -foptimize-sibling-calls -fpeel-loops -fpredictive-commoning
208           -fprefetch-loop-arrays -fprofile-correction -fprofile-dir=path
209           -fprofile-generate -fprofile-generate=path -fprofile-use
210           -fprofile-use=path -fprofile-values -freciprocal-math -fregmove
211           -frename-registers -freorder-blocks -freorder-blocks-and-partition
212           -freorder-functions -frerun-cse-after-loop
213           -freschedule-modulo-scheduled-loops -frounding-math
214           -fsched2-use-superblocks -fsched-pressure -fsched-spec-load
215           -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=n]
216           -fsched-stalled-insns[=n] -fsched-group-heuristic
217           -fsched-critical-path-heuristic -fsched-spec-insn-heuristic
218           -fsched-rank-heuristic -fsched-last-insn-heuristic
219           -fsched-dep-count-heuristic -fschedule-insns -fschedule-insns2
220           -fsection-anchors -fselective-scheduling -fselective-scheduling2
221           -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops
222           -fsignaling-nans -fsingle-precision-constant
223           -fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector
224           -fstack-protector-all -fstrict-aliasing -fstrict-overflow
225           -fthread-jumps -ftracer -ftree-builtin-call-dce -ftree-ccp
226           -ftree-ch -ftree-copy-prop -ftree-copyrename -ftree-dce
227           -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
228           -ftree-loop-im -ftree-phiprop -ftree-loop-distribution
229           -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize
230           -ftree-parallelize-loops=n -ftree-pre -ftree-pta -ftree-reassoc
231           -ftree-sink -ftree-sra -ftree-switch-conversion -ftree-ter
232           -ftree-vect-loop-version -ftree-vectorize -ftree-vrp
233           -funit-at-a-time -funroll-all-loops -funroll-loops
234           -funsafe-loop-optimizations -funsafe-math-optimizations
235           -funswitch-loops -fvariable-expansion-in-unroller -fvect-cost-model
236           -fvpt -fweb -fwhole-program -fwhopr -fwpa -fuse-linker-plugin
237           --param name=value -O  -O0  -O1  -O2  -O3  -Os
238
239       Preprocessor Options
240           -Aquestion=answer -A-question[=answer] -C  -dD  -dI  -dM  -dN
241           -Dmacro[=defn]  -E  -H -idirafter dir -include file  -imacros file
242           -iprefix file  -iwithprefix dir -iwithprefixbefore dir  -isystem
243           dir -imultilib dir -isysroot dir -M  -MM  -MF  -MG  -MP  -MQ  -MT
244           -nostdinc -P  -fworking-directory  -remap -trigraphs  -undef
245           -Umacro  -Wp,option -Xpreprocessor option
246
247       Assembler Option
248           -Wa,option  -Xassembler option
249
250       Linker Options
251           object-file-name  -llibrary -nostartfiles  -nodefaultlibs
252           -nostdlib -pie -rdynamic -s  -static  -static-libgcc
253           -static-libstdc++ -shared -shared-libgcc  -symbolic -T script
254           -Wl,option  -Xlinker option -u symbol
255
256       Directory Options
257           -Bprefix  -Idir  -iquotedir  -Ldir -specs=file  -I- --sysroot=dir
258
259       Target Options
260           -V version  -b machine
261
262       Machine Dependent Options
263           ARC Options -EB  -EL -mmangle-cpu  -mcpu=cpu  -mtext=text-section
264           -mdata=data-section  -mrodata=readonly-data-section
265
266           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
267           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-float
268           -mno-apcs-float -mapcs-reentrant  -mno-apcs-reentrant
269           -msched-prolog  -mno-sched-prolog -mlittle-endian  -mbig-endian
270           -mwords-little-endian -mfloat-abi=name  -msoft-float  -mhard-float
271           -mfpe -mfp16-format=name -mthumb-interwork  -mno-thumb-interwork
272           -mcpu=name  -march=name  -mfpu=name -mstructure-size-boundary=n
273           -mabort-on-noreturn -mlong-calls  -mno-long-calls -msingle-pic-base
274           -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport
275           -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns
276           -mpoke-function-name -mthumb  -marm -mtpcs-frame  -mtpcs-leaf-frame
277           -mcaller-super-interworking  -mcallee-super-interworking -mtp=name
278           -mword-relocations -mfix-cortex-m3-ldrd
279
280           AVR Options -mmcu=mcu  -mno-interrupts -mcall-prologues
281           -mtiny-stack  -mint8
282
283           Blackfin Options -mcpu=cpu[-sirevision] -msim
284           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
285           -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
286           -mno-csync-anomaly -mlow-64k -mno-low64k  -mstack-check-l1
287           -mid-shared-library -mno-id-shared-library  -mshared-library-id=n
288           -mleaf-id-shared-library  -mno-leaf-id-shared-library -msep-data
289           -mno-sep-data  -mlong-calls  -mno-long-calls -mfast-fp -minline-plt
290           -mmulticore  -mcorea  -mcoreb  -msdram -micplb
291
292           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu -mmax-stack-frame=n
293           -melinux-stacksize=n -metrax4  -metrax100  -mpdebug  -mcc-init
294           -mno-side-effects -mstack-align  -mdata-align  -mconst-align
295           -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
296           -melf  -maout  -melinux  -mlinux  -sim  -sim2 -mmul-bug-workaround
297           -mno-mul-bug-workaround
298
299           CRX Options -mmac -mpush-args
300
301           Darwin Options -all_load  -allowable_client  -arch
302           -arch_errors_fatal -arch_only  -bind_at_load  -bundle
303           -bundle_loader -client_name  -compatibility_version
304           -current_version -dead_strip -dependency-file  -dylib_file
305           -dylinker_install_name -dynamic  -dynamiclib
306           -exported_symbols_list -filelist  -flat_namespace
307           -force_cpusubtype_ALL -force_flat_namespace
308           -headerpad_max_install_names -iframework -image_base  -init
309           -install_name  -keep_private_externs -multi_module
310           -multiply_defined  -multiply_defined_unused -noall_load
311           -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs
312           -noprebind  -noseglinkedit -pagezero_size  -prebind
313           -prebind_all_twolevel_modules -private_bundle  -read_only_relocs
314           -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
315           -sectobjectsymbols  -sectorder -segaddr -segs_read_only_addr
316           -segs_read_write_addr -seg_addr_table  -seg_addr_table_filename
317           -seglinkedit -segprot  -segs_read_only_addr  -segs_read_write_addr
318           -single_module  -static  -sub_library  -sub_umbrella
319           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
320           -weak_reference_mismatches -whatsloaded -F -gused -gfull
321           -mmacosx-version-min=version -mkernel -mone-byte-bool
322
323           DEC Alpha Options -mno-fp-regs  -msoft-float  -malpha-as  -mgas
324           -mieee  -mieee-with-inexact  -mieee-conformant -mfp-trap-mode=mode
325           -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants
326           -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
327           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
328           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time
329
330           DEC Alpha/VMS Options -mvms-return-codes -mdebug-main=prefix
331           -mmalloc64
332
333           FR30 Options -msmall-model -mno-lsim
334
335           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float
336           -msoft-float -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble
337           -mno-double -mmedia  -mno-media  -mmuladd  -mno-muladd -mfdpic
338           -minline-plt -mgprel-ro  -multilib-library-pic -mlinked-fp
339           -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
340           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
341           -moptimize-membar -mno-optimize-membar -mscc  -mno-scc  -mcond-exec
342           -mno-cond-exec -mvliw-branch  -mno-vliw-branch -mmulti-cond-exec
343           -mno-multi-cond-exec  -mnested-cond-exec -mno-nested-cond-exec
344           -mtomcat-stats -mTLS -mtls -mcpu=cpu
345
346           GNU/Linux Options -muclibc
347
348           H8/300 Options -mrelax  -mh  -ms  -mn  -mint32  -malign-300
349
350           HPPA Options -march=architecture-type -mbig-switch
351           -mdisable-fpregs  -mdisable-indexing -mfast-indirect-calls  -mgas
352           -mgnu-ld   -mhp-ld -mfixed-range=register-range -mjump-in-delay
353           -mlinker-opt -mlong-calls -mlong-load-store  -mno-big-switch
354           -mno-disable-fpregs -mno-disable-indexing  -mno-fast-indirect-calls
355           -mno-gas -mno-jump-in-delay  -mno-long-load-store
356           -mno-portable-runtime  -mno-soft-float -mno-space-regs
357           -msoft-float  -mpa-risc-1-0 -mpa-risc-1-1  -mpa-risc-2-0
358           -mportable-runtime -mschedule=cpu-type  -mspace-regs  -msio  -mwsio
359           -munix=unix-std  -nolibdld  -static  -threads
360
361           i386 and x86-64 Options -mtune=cpu-type  -march=cpu-type
362           -mfpmath=unit -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387
363           -msoft-float -mno-wide-multiply  -mrtd  -malign-double
364           -mpreferred-stack-boundary=num -mincoming-stack-boundary=num -mcld
365           -mcx16 -msahf -mmovbe -mcrc32 -mrecip -mmmx  -msse  -msse2 -msse3
366           -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -maes -mpclmul -mfused-madd
367           -msse4a -m3dnow -mpopcnt -mabm -mfma4 -mxop -mlwp -mthreads
368           -mno-align-stringops  -minline-all-stringops
369           -minline-stringops-dynamically -mstringop-strategy=alg -mpush-args
370           -maccumulate-outgoing-args  -m128bit-long-double
371           -m96bit-long-double  -mregparm=num  -msseregparm -mveclibabi=type
372           -mpc32 -mpc64 -mpc80 -mstackrealign -momit-leaf-frame-pointer
373           -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=code-model
374           -mabi=name -m32  -m64 -mlarge-data-threshold=num -msse2avx
375
376           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld
377           -mno-pic -mvolatile-asm-stop  -mregister-names  -msdata -mno-sdata
378           -mconstant-gp  -mauto-pic  -mfused-madd
379           -minline-float-divide-min-latency
380           -minline-float-divide-max-throughput -mno-inline-float-divide
381           -minline-int-divide-min-latency -minline-int-divide-max-throughput
382           -mno-inline-int-divide -minline-sqrt-min-latency
383           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
384           -mearly-stop-bits -mfixed-range=register-range -mtls-size=tls-size
385           -mtune=cpu-type -milp32 -mlp64 -msched-br-data-spec
386           -msched-ar-data-spec -msched-control-spec -msched-br-in-data-spec
387           -msched-ar-in-data-spec -msched-in-control-spec -msched-spec-ldc
388           -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
389           -msched-prefer-non-control-spec-insns
390           -msched-stop-bits-after-every-cycle
391           -msched-count-spec-in-critical-path
392           -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost
393           -msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-
394           insns
395
396           IA-64/VMS Options -mvms-return-codes -mdebug-main=prefix -mmalloc64
397
398           LM32 Options -mbarrel-shift-enabled -mdivide-enabled
399           -mmultiply-enabled -msign-extend-enabled -muser-enabled
400
401           M32R/D Options -m32r2 -m32rx -m32r -mdebug -malign-loops
402           -mno-align-loops -missue-rate=number -mbranch-cost=number
403           -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func
404           -mflush-func=name -mno-flush-trap -mflush-trap=number -G num
405
406           M32C Options -mcpu=cpu -msim -memregs=number
407
408           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020
409           -m68020-40  -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200
410           -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
411           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div
412           -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
413           -malign-int  -mstrict-align  -msep-data  -mno-sep-data
414           -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
415           -mxgot -mno-xgot
416
417           M68hc1x Options -m6811  -m6812  -m68hc11  -m68hc12   -m68hcs12
418           -mauto-incdec  -minmax  -mlong-calls  -mshort
419           -msoft-reg-count=count
420
421           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div
422           -mrelax-immediates -mno-relax-immediates  -mwide-bitfields
423           -mno-wide-bitfields -m4byte-functions  -mno-4byte-functions
424           -mcallgraph-data -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes
425           -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
426           -mstack-increment
427
428           MeP Options -mabsdiff -mall-opts -maverage -mbased=n -mbitops -mc=n
429           -mclip -mconfig=name -mcop -mcop32 -mcop64 -mivc2 -mdc -mdiv -meb
430           -mel -mio-volatile -ml -mleadz -mm -mminmax -mmult -mno-opts
431           -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf -mtiny=n
432
433           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2
434           -mips3  -mips4  -mips32  -mips32r2 -mips64  -mips64r2 -mips16
435           -mno-mips16  -mflip-mips16 -minterlink-mips16
436           -mno-interlink-mips16 -mabi=abi  -mabicalls  -mno-abicalls -mshared
437           -mno-shared  -mplt  -mno-plt  -mxgot  -mno-xgot -mgp32  -mgp64
438           -mfp32  -mfp64  -mhard-float  -msoft-float -msingle-float
439           -mdouble-float  -mdsp  -mno-dsp  -mdspr2  -mno-dspr2 -mfpu=fpu-type
440           -msmartmips  -mno-smartmips -mpaired-single  -mno-paired-single
441           -mdmx  -mno-mdmx -mips3d  -mno-mips3d  -mmt  -mno-mt  -mllsc
442           -mno-llsc -mlong64  -mlong32  -msym32  -mno-sym32 -Gnum
443           -mlocal-sdata  -mno-local-sdata -mextern-sdata  -mno-extern-sdata
444           -mgpopt  -mno-gopt -membedded-data  -mno-embedded-data
445           -muninit-const-in-rodata  -mno-uninit-const-in-rodata
446           -mcode-readable=setting -msplit-addresses  -mno-split-addresses
447           -mexplicit-relocs  -mno-explicit-relocs -mcheck-zero-division
448           -mno-check-zero-division -mdivide-traps  -mdivide-breaks -mmemcpy
449           -mno-memcpy  -mlong-calls  -mno-long-calls -mmad  -mno-mad
450           -mfused-madd  -mno-fused-madd  -nocpp -mfix-r4000  -mno-fix-r4000
451           -mfix-r4400  -mno-fix-r4400 -mfix-r10000 -mno-fix-r10000
452           -mfix-vr4120  -mno-fix-vr4120 -mfix-vr4130  -mno-fix-vr4130
453           -mfix-sb1  -mno-fix-sb1 -mflush-func=func  -mno-flush-func
454           -mbranch-cost=num  -mbranch-likely  -mno-branch-likely
455           -mfp-exceptions -mno-fp-exceptions -mvr4130-align -mno-vr4130-align
456           -msynci -mno-synci -mrelax-pic-calls -mno-relax-pic-calls
457           -mmcount-ra-address
458
459           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon
460           -mabi=gnu -mabi=mmixware  -mzero-extend  -mknuthdiv
461           -mtoplevel-symbols -melf  -mbranch-predict  -mno-branch-predict
462           -mbase-addresses -mno-base-addresses  -msingle-exit
463           -mno-single-exit
464
465           MN10300 Options -mmult-bug  -mno-mult-bug -mam33  -mno-am33
466           -mam33-2  -mno-am33-2 -mreturn-pointer-on-d0 -mno-crt0  -mrelax
467
468           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
469           -m10 -mbcopy  -mbcopy-builtin  -mint32  -mno-int16 -mint16
470           -mno-int32  -mfloat32  -mno-float64 -mfloat64  -mno-float32
471           -mabshi  -mno-abshi -mbranch-expensive  -mbranch-cheap -msplit
472           -mno-split  -munix-asm  -mdec-asm
473
474           picoChip Options -mae=ae_type -mvliw-lookahead=N
475           -msymbol-as-address -mno-inefficient-warnings
476
477           PowerPC Options See RS/6000 and PowerPC Options.
478
479           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mpower
480           -mno-power  -mpower2  -mno-power2 -mpowerpc  -mpowerpc64
481           -mno-powerpc -maltivec  -mno-altivec -mpowerpc-gpopt
482           -mno-powerpc-gpopt -mpowerpc-gfxopt  -mno-powerpc-gfxopt -mmfcrf
483           -mno-mfcrf  -mpopcntb  -mno-popcntb -mpopcntd -mno-popcntd -mfprnd
484           -mno-fprnd -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp
485           -mno-hard-dfp -mnew-mnemonics  -mold-mnemonics -mfull-toc
486           -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc -m64  -m32
487           -mxl-compat  -mno-xl-compat  -mpe -malign-power  -malign-natural
488           -msoft-float  -mhard-float  -mmultiple  -mno-multiple
489           -msingle-float -mdouble-float -msimple-fpu -mstring  -mno-string
490           -mupdate  -mno-update -mavoid-indexed-addresses
491           -mno-avoid-indexed-addresses -mfused-madd  -mno-fused-madd
492           -mbit-align  -mno-bit-align -mstrict-align  -mno-strict-align
493           -mrelocatable -mno-relocatable  -mrelocatable-lib
494           -mno-relocatable-lib -mtoc  -mno-toc  -mlittle  -mlittle-endian
495           -mbig  -mbig-endian -mdynamic-no-pic  -maltivec -mswdiv
496           -mprioritize-restricted-insns=priority
497           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
498           -mcall-sysv  -mcall-netbsd -maix-struct-return
499           -msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt -misel
500           -mno-isel -misel=yes  -misel=no -mspe -mno-spe -mspe=yes  -mspe=no
501           -mpaired -mgen-cell-microcode -mwarn-cell-microcode -mvrsave
502           -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes
503           -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype
504           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
505           -msdata=opt  -mvxworks  -G num  -pthread
506
507           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu=
508           -patch= -mbig-endian-data -mlittle-endian-data -msmall-data -msim
509           -mno-sim -mas100-syntax -mno-as100-syntax -mrelax
510           -mmax-constant-size= -mint-register= -msave-acc-in-interrupts
511
512           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type
513           -mhard-float  -msoft-float  -mhard-dfp -mno-hard-dfp
514           -mlong-double-64 -mlong-double-128 -mbackchain  -mno-backchain
515           -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
516           -mmvcle -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
517           -mtpf-trace -mno-tpf-trace  -mfused-madd  -mno-fused-madd
518           -mwarn-framesize  -mwarn-dynamicstack  -mstack-size -mstack-guard
519
520           Score Options -meb -mel -mnhwloop -muls -mmac -mscore5 -mscore5u
521           -mscore7 -mscore7d
522
523           SH Options -m1  -m2  -m2e -m2a-nofpu -m2a-single-only -m2a-single
524           -m2a -m3  -m3e -m4-nofpu  -m4-single-only  -m4-single  -m4
525           -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -m5-64media
526           -m5-64media-nofpu -m5-32media  -m5-32media-nofpu -m5-compact
527           -m5-compact-nofpu -mb  -ml  -mdalign  -mrelax -mbigtable -mfmovd
528           -mhitachi -mrenesas -mno-renesas -mnomacsave -mieee  -mbitops
529           -misize  -minline-ic_invalidate -mpadstruct  -mspace -mprefergot
530           -musermode -multcost=number -mdiv=strategy -mdivsi3_libfunc=name
531           -mfixed-range=register-range -madjust-unroll -mindexed-addressing
532           -mgettrcost=number -mpt-fixed -minvalid-symbols
533
534           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
535           -m32  -m64  -mapp-regs  -mno-app-regs -mfaster-structs
536           -mno-faster-structs -mfpu  -mno-fpu  -mhard-float  -msoft-float
537           -mhard-quad-float  -msoft-quad-float -mimpure-text
538           -mno-impure-text  -mlittle-endian -mstack-bias  -mno-stack-bias
539           -munaligned-doubles  -mno-unaligned-doubles -mv8plus  -mno-v8plus
540           -mvis  -mno-vis -threads -pthreads -pthread
541
542           SPU Options -mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma
543           -mbranch-hints -msmall-mem -mlarge-mem -mstdmain
544           -mfixed-range=register-range -mea32 -mea64
545           -maddress-space-conversion -mno-address-space-conversion
546           -mcache-size=cache-size -matomic-updates -mno-atomic-updates
547
548           System V Options -Qy  -Qn  -YP,paths  -Ym,dir
549
550           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep
551           -mprolog-function  -mno-prolog-function  -mspace -mtda=n  -msda=n
552           -mzda=n -mapp-regs  -mno-app-regs -mdisable-callt
553           -mno-disable-callt -mv850e1 -mv850e -mv850  -mbig-switch
554
555           VAX Options -mg  -mgnu  -munix
556
557           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy
558           -Xbind-now
559
560           x86-64 Options See i386 and x86-64 Options.
561
562           i386 and x86-64 Windows Options -mconsole -mcygwin -mno-cygwin
563           -mdll -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows
564           -fno-set-stack-executable
565
566           Xstormy16 Options -msim
567
568           Xtensa Options -mconst16 -mno-const16 -mfused-madd  -mno-fused-madd
569           -mserialize-volatile  -mno-serialize-volatile
570           -mtext-section-literals  -mno-text-section-literals -mtarget-align
571           -mno-target-align -mlongcalls  -mno-longcalls
572
573           zSeries Options See S/390 and zSeries Options.
574
575       Code Generation Options
576           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
577           -fnon-call-exceptions  -funwind-tables -fasynchronous-unwind-tables
578           -finhibit-size-directive  -finstrument-functions
579           -finstrument-functions-exclude-function-list=sym,sym,...
580           -finstrument-functions-exclude-file-list=file,file,...  -fno-common
581           -fno-ident -fpcc-struct-return  -fpic  -fPIC -fpie -fPIE
582           -fno-jump-tables -frecord-gcc-switches -freg-struct-return
583           -fshort-enums -fshort-double  -fshort-wchar -fverbose-asm
584           -fpack-struct[=n]  -fstack-check -fstack-limit-register=reg
585           -fstack-limit-symbol=sym -fno-stack-limit  -fargument-alias
586           -fargument-noalias -fargument-noalias-global
587           -fargument-noalias-anything -fleading-underscore  -ftls-model=model
588           -ftrapv  -fwrapv  -fbounds-check -fvisibility
589
590   Options Controlling the Kind of Output
591       Compilation can involve up to four stages: preprocessing, compilation
592       proper, assembly and linking, always in that order.  GCC is capable of
593       preprocessing and compiling several files either into several assembler
594       input files, or into one assembler input file; then each assembler
595       input file produces an object file, and linking combines all the object
596       files (those newly compiled, and those specified as input) into an
597       executable file.
598
599       For any given input file, the file name suffix determines what kind of
600       compilation is done:
601
602       file.c
603           C source code which must be preprocessed.
604
605       file.i
606           C source code which should not be preprocessed.
607
608       file.ii
609           C++ source code which should not be preprocessed.
610
611       file.m
612           Objective-C source code.  Note that you must link with the libobjc
613           library to make an Objective-C program work.
614
615       file.mi
616           Objective-C source code which should not be preprocessed.
617
618       file.mm
619       file.M
620           Objective-C++ source code.  Note that you must link with the
621           libobjc library to make an Objective-C++ program work.  Note that
622           .M refers to a literal capital M.
623
624       file.mii
625           Objective-C++ source code which should not be preprocessed.
626
627       file.h
628           C, C++, Objective-C or Objective-C++ header file to be turned into
629           a precompiled header.
630
631       file.cc
632       file.cp
633       file.cxx
634       file.cpp
635       file.CPP
636       file.c++
637       file.C
638           C++ source code which must be preprocessed.  Note that in .cxx, the
639           last two letters must both be literally x.  Likewise, .C refers to
640           a literal capital C.
641
642       file.mm
643       file.M
644           Objective-C++ source code which must be preprocessed.
645
646       file.mii
647           Objective-C++ source code which should not be preprocessed.
648
649       file.hh
650       file.H
651       file.hp
652       file.hxx
653       file.hpp
654       file.HPP
655       file.h++
656       file.tcc
657           C++ header file to be turned into a precompiled header.
658
659       file.f
660       file.for
661       file.ftn
662           Fixed form Fortran source code which should not be preprocessed.
663
664       file.F
665       file.FOR
666       file.fpp
667       file.FPP
668       file.FTN
669           Fixed form Fortran source code which must be preprocessed (with the
670           traditional preprocessor).
671
672       file.f90
673       file.f95
674       file.f03
675       file.f08
676           Free form Fortran source code which should not be preprocessed.
677
678       file.F90
679       file.F95
680       file.F03
681       file.F08
682           Free form Fortran source code which must be preprocessed (with the
683           traditional preprocessor).
684
685       file.ads
686           Ada source code file which contains a library unit declaration (a
687           declaration of a package, subprogram, or generic, or a generic
688           instantiation), or a library unit renaming declaration (a package,
689           generic, or subprogram renaming declaration).  Such files are also
690           called specs.
691
692       file.adb
693           Ada source code file containing a library unit body (a subprogram
694           or package body).  Such files are also called bodies.
695
696       file.s
697           Assembler code.
698
699       file.S
700       file.sx
701           Assembler code which must be preprocessed.
702
703       other
704           An object file to be fed straight into linking.  Any file name with
705           no recognized suffix is treated this way.
706
707       You can specify the input language explicitly with the -x option:
708
709       -x language
710           Specify explicitly the language for the following input files
711           (rather than letting the compiler choose a default based on the
712           file name suffix).  This option applies to all following input
713           files until the next -x option.  Possible values for language are:
714
715                   c  c-header  c-cpp-output
716                   c++  c++-header  c++-cpp-output
717                   objective-c  objective-c-header  objective-c-cpp-output
718                   objective-c++ objective-c++-header objective-c++-cpp-output
719                   assembler  assembler-with-cpp
720                   ada
721                   f77  f77-cpp-input f95  f95-cpp-input
722                   java
723
724       -x none
725           Turn off any specification of a language, so that subsequent files
726           are handled according to their file name suffixes (as they are if
727           -x has not been used at all).
728
729       -pass-exit-codes
730           Normally the gcc program will exit with the code of 1 if any phase
731           of the compiler returns a non-success return code.  If you specify
732           -pass-exit-codes, the gcc program will instead return with
733           numerically highest error produced by any phase that returned an
734           error indication.  The C, C++, and Fortran frontends return 4, if
735           an internal compiler error is encountered.
736
737       If you only want some of the stages of compilation, you can use -x (or
738       filename suffixes) to tell gcc where to start, and one of the options
739       -c, -S, or -E to say where gcc is to stop.  Note that some combinations
740       (for example, -x cpp-output -E) instruct gcc to do nothing at all.
741
742       -c  Compile or assemble the source files, but do not link.  The linking
743           stage simply is not done.  The ultimate output is in the form of an
744           object file for each source file.
745
746           By default, the object file name for a source file is made by
747           replacing the suffix .c, .i, .s, etc., with .o.
748
749           Unrecognized input files, not requiring compilation or assembly,
750           are ignored.
751
752       -S  Stop after the stage of compilation proper; do not assemble.  The
753           output is in the form of an assembler code file for each non-
754           assembler input file specified.
755
756           By default, the assembler file name for a source file is made by
757           replacing the suffix .c, .i, etc., with .s.
758
759           Input files that don't require compilation are ignored.
760
761       -E  Stop after the preprocessing stage; do not run the compiler proper.
762           The output is in the form of preprocessed source code, which is
763           sent to the standard output.
764
765           Input files which don't require preprocessing are ignored.
766
767       -o file
768           Place output in file file.  This applies regardless to whatever
769           sort of output is being produced, whether it be an executable file,
770           an object file, an assembler file or preprocessed C code.
771
772           If -o is not specified, the default is to put an executable file in
773           a.out, the object file for source.suffix in source.o, its assembler
774           file in source.s, a precompiled header file in source.suffix.gch,
775           and all preprocessed C source on standard output.
776
777       -v  Print (on standard error output) the commands executed to run the
778           stages of compilation.  Also print the version number of the
779           compiler driver program and of the preprocessor and the compiler
780           proper.
781
782       -###
783           Like -v except the commands are not executed and all command
784           arguments are quoted.  This is useful for shell scripts to capture
785           the driver-generated command lines.
786
787       -pipe
788           Use pipes rather than temporary files for communication between the
789           various stages of compilation.  This fails to work on some systems
790           where the assembler is unable to read from a pipe; but the GNU
791           assembler has no trouble.
792
793       -combine
794           If you are compiling multiple source files, this option tells the
795           driver to pass all the source files to the compiler at once (for
796           those languages for which the compiler can handle this).  This will
797           allow intermodule analysis (IMA) to be performed by the compiler.
798           Currently the only language for which this is supported is C.  If
799           you pass source files for multiple languages to the driver, using
800           this option, the driver will invoke the compiler(s) that support
801           IMA once each, passing each compiler all the source files
802           appropriate for it.  For those languages that do not support IMA
803           this option will be ignored, and the compiler will be invoked once
804           for each source file in that language.  If you use this option in
805           conjunction with -save-temps, the compiler will generate multiple
806           pre-processed files (one for each source file), but only one
807           (combined) .o or .s file.
808
809       --help
810           Print (on the standard output) a description of the command line
811           options understood by gcc.  If the -v option is also specified then
812           --help will also be passed on to the various processes invoked by
813           gcc, so that they can display the command line options they accept.
814           If the -Wextra option has also been specified (prior to the --help
815           option), then command line options which have no documentation
816           associated with them will also be displayed.
817
818       --target-help
819           Print (on the standard output) a description of target-specific
820           command line options for each tool.  For some targets extra target-
821           specific information may also be printed.
822
823       --help={class|[^]qualifier}[,...]
824           Print (on the standard output) a description of the command line
825           options understood by the compiler that fit into all specified
826           classes and qualifiers.  These are the supported classes:
827
828           optimizers
829               This will display all of the optimization options supported by
830               the compiler.
831
832           warnings
833               This will display all of the options controlling warning
834               messages produced by the compiler.
835
836           target
837               This will display target-specific options.  Unlike the
838               --target-help option however, target-specific options of the
839               linker and assembler will not be displayed.  This is because
840               those tools do not currently support the extended --help=
841               syntax.
842
843           params
844               This will display the values recognized by the --param option.
845
846           language
847               This will display the options supported for language, where
848               language is the name of one of the languages supported in this
849               version of GCC.
850
851           common
852               This will display the options that are common to all languages.
853
854           These are the supported qualifiers:
855
856           undocumented
857               Display only those options which are undocumented.
858
859           joined
860               Display options which take an argument that appears after an
861               equal sign in the same continuous piece of text, such as:
862               --help=target.
863
864           separate
865               Display options which take an argument that appears as a
866               separate word following the original option, such as: -o
867               output-file.
868
869           Thus for example to display all the undocumented target-specific
870           switches supported by the compiler the following can be used:
871
872                   --help=target,undocumented
873
874           The sense of a qualifier can be inverted by prefixing it with the ^
875           character, so for example to display all binary warning options
876           (i.e., ones that are either on or off and that do not take an
877           argument), which have a description the following can be used:
878
879                   --help=warnings,^joined,^undocumented
880
881           The argument to --help= should not consist solely of inverted
882           qualifiers.
883
884           Combining several classes is possible, although this usually
885           restricts the output by so much that there is nothing to display.
886           One case where it does work however is when one of the classes is
887           target.  So for example to display all the target-specific
888           optimization options the following can be used:
889
890                   --help=target,optimizers
891
892           The --help= option can be repeated on the command line.  Each
893           successive use will display its requested class of options,
894           skipping those that have already been displayed.
895
896           If the -Q option appears on the command line before the --help=
897           option, then the descriptive text displayed by --help= is changed.
898           Instead of describing the displayed options, an indication is given
899           as to whether the option is enabled, disabled or set to a specific
900           value (assuming that the compiler knows this at the point where the
901           --help= option is used).
902
903           Here is a truncated example from the ARM port of gcc:
904
905                     % gcc -Q -mabi=2 --help=target -c
906                     The following options are target specific:
907                     -mabi=                                2
908                     -mabort-on-noreturn                   [disabled]
909                     -mapcs                                [disabled]
910
911           The output is sensitive to the effects of previous command line
912           options, so for example it is possible to find out which
913           optimizations are enabled at -O2 by using:
914
915                   -Q -O2 --help=optimizers
916
917           Alternatively you can discover which binary optimizations are
918           enabled by -O3 by using:
919
920                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
921                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
922                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled
923
924       -no-canonical-prefixes
925           Do not expand any symbolic links, resolve references to /../ or
926           /./, or make the path absolute when generating a relative prefix.
927
928       --version
929           Display the version number and copyrights of the invoked GCC.
930
931       -wrapper
932           Invoke all subcommands under a wrapper program. It takes a single
933           comma separated list as an argument, which will be used to invoke
934           the wrapper:
935
936                   gcc -c t.c -wrapper gdb,--args
937
938           This will invoke all subprograms of gcc under "gdb --args", thus
939           cc1 invocation will be "gdb --args cc1 ...".
940
941       -fplugin=name.so
942           Load the plugin code in file name.so, assumed to be a shared object
943           to be dlopen'd by the compiler.  The base name of the shared object
944           file is used to identify the plugin for the purposes of argument
945           parsing (See -fplugin-arg-name-key=value below).  Each plugin
946           should define the callback functions specified in the Plugins API.
947
948       -fplugin-arg-name-key=value
949           Define an argument called key with a value of value for the plugin
950           called name.
951
952       @file
953           Read command-line options from file.  The options read are inserted
954           in place of the original @file option.  If file does not exist, or
955           cannot be read, then the option will be treated literally, and not
956           removed.
957
958           Options in file are separated by whitespace.  A whitespace
959           character may be included in an option by surrounding the entire
960           option in either single or double quotes.  Any character (including
961           a backslash) may be included by prefixing the character to be
962           included with a backslash.  The file may itself contain additional
963           @file options; any such options will be processed recursively.
964
965   Compiling C++ Programs
966       C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
967       .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
968       (for shared template code) .tcc; and preprocessed C++ files use the
969       suffix .ii.  GCC recognizes files with these names and compiles them as
970       C++ programs even if you call the compiler the same way as for
971       compiling C programs (usually with the name gcc).
972
973       However, the use of gcc does not add the C++ library.  g++ is a program
974       that calls GCC and treats .c, .h and .i files as C++ source files
975       instead of C source files unless -x is used, and automatically
976       specifies linking against the C++ library.  This program is also useful
977       when precompiling a C header file with a .h extension for use in C++
978       compilations.  On many systems, g++ is also installed with the name
979       c++.
980
981       When you compile C++ programs, you may specify many of the same
982       command-line options that you use for compiling programs in any
983       language; or command-line options meaningful for C and related
984       languages; or options that are meaningful only for C++ programs.
985
986   Options Controlling C Dialect
987       The following options control the dialect of C (or languages derived
988       from C, such as C++, Objective-C and Objective-C++) that the compiler
989       accepts:
990
991       -ansi
992           In C mode, this is equivalent to -std=c90. In C++ mode, it is
993           equivalent to -std=c++98.
994
995           This turns off certain features of GCC that are incompatible with
996           ISO C90 (when compiling C code), or of standard C++ (when compiling
997           C++ code), such as the "asm" and "typeof" keywords, and predefined
998           macros such as "unix" and "vax" that identify the type of system
999           you are using.  It also enables the undesirable and rarely used ISO
1000           trigraph feature.  For the C compiler, it disables recognition of
1001           C++ style // comments as well as the "inline" keyword.
1002
1003           The alternate keywords "__asm__", "__extension__", "__inline__" and
1004           "__typeof__" continue to work despite -ansi.  You would not want to
1005           use them in an ISO C program, of course, but it is useful to put
1006           them in header files that might be included in compilations done
1007           with -ansi.  Alternate predefined macros such as "__unix__" and
1008           "__vax__" are also available, with or without -ansi.
1009
1010           The -ansi option does not cause non-ISO programs to be rejected
1011           gratuitously.  For that, -pedantic is required in addition to
1012           -ansi.
1013
1014           The macro "__STRICT_ANSI__" is predefined when the -ansi option is
1015           used.  Some header files may notice this macro and refrain from
1016           declaring certain functions or defining certain macros that the ISO
1017           standard doesn't call for; this is to avoid interfering with any
1018           programs that might use these names for other things.
1019
1020           Functions that would normally be built in but do not have semantics
1021           defined by ISO C (such as "alloca" and "ffs") are not built-in
1022           functions when -ansi is used.
1023
1024       -std=
1025           Determine the language standard.   This option is currently only
1026           supported when compiling C or C++.
1027
1028           The compiler can accept several base standards, such as c90 or
1029           c++98, and GNU dialects of those standards, such as gnu90 or
1030           gnu++98.  By specifying a base standard, the compiler will accept
1031           all programs following that standard and those using GNU extensions
1032           that do not contradict it.  For example, -std=c90 turns off certain
1033           features of GCC that are incompatible with ISO C90, such as the
1034           "asm" and "typeof" keywords, but not other GNU extensions that do
1035           not have a meaning in ISO C90, such as omitting the middle term of
1036           a "?:" expression. On the other hand, by specifying a GNU dialect
1037           of a standard, all features the compiler support are enabled, even
1038           when those features change the meaning of the base standard and
1039           some strict-conforming programs may be rejected.  The particular
1040           standard is used by -pedantic to identify which features are GNU
1041           extensions given that version of the standard. For example
1042           -std=gnu90 -pedantic would warn about C++ style // comments, while
1043           -std=gnu99 -pedantic would not.
1044
1045           A value for this option must be provided; possible values are
1046
1047           c90
1048           c89
1049           iso9899:1990
1050               Support all ISO C90 programs (certain GNU extensions that
1051               conflict with ISO C90 are disabled). Same as -ansi for C code.
1052
1053           iso9899:199409
1054               ISO C90 as modified in amendment 1.
1055
1056           c99
1057           c9x
1058           iso9899:1999
1059           iso9899:199x
1060               ISO C99.  Note that this standard is not yet fully supported;
1061               see <http://gcc.gnu.org/gcc-4.5/c99status.html> for more
1062               information.  The names c9x and iso9899:199x are deprecated.
1063
1064           gnu90
1065           gnu89
1066               GNU dialect of ISO C90 (including some C99 features). This is
1067               the default for C code.
1068
1069           gnu99
1070           gnu9x
1071               GNU dialect of ISO C99.  When ISO C99 is fully implemented in
1072               GCC, this will become the default.  The name gnu9x is
1073               deprecated.
1074
1075           c++98
1076               The 1998 ISO C++ standard plus amendments. Same as -ansi for
1077               C++ code.
1078
1079           gnu++98
1080               GNU dialect of -std=c++98.  This is the default for C++ code.
1081
1082           c++0x
1083               The working draft of the upcoming ISO C++0x standard. This
1084               option enables experimental features that are likely to be
1085               included in C++0x. The working draft is constantly changing,
1086               and any feature that is enabled by this flag may be removed
1087               from future versions of GCC if it is not part of the C++0x
1088               standard.
1089
1090           gnu++0x
1091               GNU dialect of -std=c++0x. This option enables experimental
1092               features that may be removed in future versions of GCC.
1093
1094       -fgnu89-inline
1095           The option -fgnu89-inline tells GCC to use the traditional GNU
1096           semantics for "inline" functions when in C99 mode.
1097             This option is accepted and ignored by GCC versions 4.1.3 up to
1098           but not including 4.3.  In GCC versions 4.3 and later it changes
1099           the behavior of GCC in C99 mode.  Using this option is roughly
1100           equivalent to adding the "gnu_inline" function attribute to all
1101           inline functions.
1102
1103           The option -fno-gnu89-inline explicitly tells GCC to use the C99
1104           semantics for "inline" when in C99 or gnu99 mode (i.e., it
1105           specifies the default behavior).  This option was first supported
1106           in GCC 4.3.  This option is not supported in -std=c90 or -std=gnu90
1107           mode.
1108
1109           The preprocessor macros "__GNUC_GNU_INLINE__" and
1110           "__GNUC_STDC_INLINE__" may be used to check which semantics are in
1111           effect for "inline" functions.
1112
1113       -aux-info filename
1114           Output to the given filename prototyped declarations for all
1115           functions declared and/or defined in a translation unit, including
1116           those in header files.  This option is silently ignored in any
1117           language other than C.
1118
1119           Besides declarations, the file indicates, in comments, the origin
1120           of each declaration (source file and line), whether the declaration
1121           was implicit, prototyped or unprototyped (I, N for new or O for
1122           old, respectively, in the first character after the line number and
1123           the colon), and whether it came from a declaration or a definition
1124           (C or F, respectively, in the following character).  In the case of
1125           function definitions, a K&R-style list of arguments followed by
1126           their declarations is also provided, inside comments, after the
1127           declaration.
1128
1129       -fno-asm
1130           Do not recognize "asm", "inline" or "typeof" as a keyword, so that
1131           code can use these words as identifiers.  You can use the keywords
1132           "__asm__", "__inline__" and "__typeof__" instead.  -ansi implies
1133           -fno-asm.
1134
1135           In C++, this switch only affects the "typeof" keyword, since "asm"
1136           and "inline" are standard keywords.  You may want to use the
1137           -fno-gnu-keywords flag instead, which has the same effect.  In C99
1138           mode (-std=c99 or -std=gnu99), this switch only affects the "asm"
1139           and "typeof" keywords, since "inline" is a standard keyword in ISO
1140           C99.
1141
1142       -fno-builtin
1143       -fno-builtin-function
1144           Don't recognize built-in functions that do not begin with
1145           __builtin_ as prefix.
1146
1147           GCC normally generates special code to handle certain built-in
1148           functions more efficiently; for instance, calls to "alloca" may
1149           become single instructions that adjust the stack directly, and
1150           calls to "memcpy" may become inline copy loops.  The resulting code
1151           is often both smaller and faster, but since the function calls no
1152           longer appear as such, you cannot set a breakpoint on those calls,
1153           nor can you change the behavior of the functions by linking with a
1154           different library.  In addition, when a function is recognized as a
1155           built-in function, GCC may use information about that function to
1156           warn about problems with calls to that function, or to generate
1157           more efficient code, even if the resulting code still contains
1158           calls to that function.  For example, warnings are given with
1159           -Wformat for bad calls to "printf", when "printf" is built in, and
1160           "strlen" is known not to modify global memory.
1161
1162           With the -fno-builtin-function option only the built-in function
1163           function is disabled.  function must not begin with __builtin_.  If
1164           a function is named that is not built-in in this version of GCC,
1165           this option is ignored.  There is no corresponding
1166           -fbuiltin-function option; if you wish to enable built-in functions
1167           selectively when using -fno-builtin or -ffreestanding, you may
1168           define macros such as:
1169
1170                   #define abs(n)          __builtin_abs ((n))
1171                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))
1172
1173       -fhosted
1174           Assert that compilation takes place in a hosted environment.  This
1175           implies -fbuiltin.  A hosted environment is one in which the entire
1176           standard library is available, and in which "main" has a return
1177           type of "int".  Examples are nearly everything except a kernel.
1178           This is equivalent to -fno-freestanding.
1179
1180       -ffreestanding
1181           Assert that compilation takes place in a freestanding environment.
1182           This implies -fno-builtin.  A freestanding environment is one in
1183           which the standard library may not exist, and program startup may
1184           not necessarily be at "main".  The most obvious example is an OS
1185           kernel.  This is equivalent to -fno-hosted.
1186
1187       -fopenmp
1188           Enable handling of OpenMP directives "#pragma omp" in C/C++ and
1189           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
1190           generates parallel code according to the OpenMP Application Program
1191           Interface v3.0 <http://www.openmp.org/>.  This option implies
1192           -pthread, and thus is only supported on targets that have support
1193           for -pthread.
1194
1195       -fms-extensions
1196           Accept some non-standard constructs used in Microsoft header files.
1197
1198           Some cases of unnamed fields in structures and unions are only
1199           accepted with this option.
1200
1201       -trigraphs
1202           Support ISO C trigraphs.  The -ansi option (and -std options for
1203           strict ISO C conformance) implies -trigraphs.
1204
1205       -no-integrated-cpp
1206           Performs a compilation in two passes: preprocessing and compiling.
1207           This option allows a user supplied "cc1", "cc1plus", or "cc1obj"
1208           via the -B option.  The user supplied compilation step can then add
1209           in an additional preprocessing step after normal preprocessing but
1210           before compiling.  The default is to use the integrated cpp
1211           (internal cpp)
1212
1213           The semantics of this option will change if "cc1", "cc1plus", and
1214           "cc1obj" are merged.
1215
1216       -traditional
1217       -traditional-cpp
1218           Formerly, these options caused GCC to attempt to emulate a pre-
1219           standard C compiler.  They are now only supported with the -E
1220           switch.  The preprocessor continues to support a pre-standard mode.
1221           See the GNU CPP manual for details.
1222
1223       -fcond-mismatch
1224           Allow conditional expressions with mismatched types in the second
1225           and third arguments.  The value of such an expression is void.
1226           This option is not supported for C++.
1227
1228       -flax-vector-conversions
1229           Allow implicit conversions between vectors with differing numbers
1230           of elements and/or incompatible element types.  This option should
1231           not be used for new code.
1232
1233       -funsigned-char
1234           Let the type "char" be unsigned, like "unsigned char".
1235
1236           Each kind of machine has a default for what "char" should be.  It
1237           is either like "unsigned char" by default or like "signed char" by
1238           default.
1239
1240           Ideally, a portable program should always use "signed char" or
1241           "unsigned char" when it depends on the signedness of an object.
1242           But many programs have been written to use plain "char" and expect
1243           it to be signed, or expect it to be unsigned, depending on the
1244           machines they were written for.  This option, and its inverse, let
1245           you make such a program work with the opposite default.
1246
1247           The type "char" is always a distinct type from each of "signed
1248           char" or "unsigned char", even though its behavior is always just
1249           like one of those two.
1250
1251       -fsigned-char
1252           Let the type "char" be signed, like "signed char".
1253
1254           Note that this is equivalent to -fno-unsigned-char, which is the
1255           negative form of -funsigned-char.  Likewise, the option
1256           -fno-signed-char is equivalent to -funsigned-char.
1257
1258       -fsigned-bitfields
1259       -funsigned-bitfields
1260       -fno-signed-bitfields
1261       -fno-unsigned-bitfields
1262           These options control whether a bit-field is signed or unsigned,
1263           when the declaration does not use either "signed" or "unsigned".
1264           By default, such a bit-field is signed, because this is consistent:
1265           the basic integer types such as "int" are signed types.
1266
1267   Options Controlling C++ Dialect
1268       This section describes the command-line options that are only
1269       meaningful for C++ programs; but you can also use most of the GNU
1270       compiler options regardless of what language your program is in.  For
1271       example, you might compile a file "firstClass.C" like this:
1272
1273               g++ -g -frepo -O -c firstClass.C
1274
1275       In this example, only -frepo is an option meant only for C++ programs;
1276       you can use the other options with any language supported by GCC.
1277
1278       Here is a list of options that are only for compiling C++ programs:
1279
1280       -fabi-version=n
1281           Use version n of the C++ ABI.  Version 2 is the version of the C++
1282           ABI that first appeared in G++ 3.4.  Version 1 is the version of
1283           the C++ ABI that first appeared in G++ 3.2.  Version 0 will always
1284           be the version that conforms most closely to the C++ ABI
1285           specification.  Therefore, the ABI obtained using version 0 will
1286           change as ABI bugs are fixed.
1287
1288           The default is version 2.
1289
1290           Version 3 corrects an error in mangling a constant address as a
1291           template argument.
1292
1293           Version 4 implements a standard mangling for vector types.
1294
1295           See also -Wabi.
1296
1297       -fno-access-control
1298           Turn off all access checking.  This switch is mainly useful for
1299           working around bugs in the access control code.
1300
1301       -fcheck-new
1302           Check that the pointer returned by "operator new" is non-null
1303           before attempting to modify the storage allocated.  This check is
1304           normally unnecessary because the C++ standard specifies that
1305           "operator new" will only return 0 if it is declared throw(), in
1306           which case the compiler will always check the return value even
1307           without this option.  In all other cases, when "operator new" has a
1308           non-empty exception specification, memory exhaustion is signalled
1309           by throwing "std::bad_alloc".  See also new (nothrow).
1310
1311       -fconserve-space
1312           Put uninitialized or runtime-initialized global variables into the
1313           common segment, as C does.  This saves space in the executable at
1314           the cost of not diagnosing duplicate definitions.  If you compile
1315           with this flag and your program mysteriously crashes after "main()"
1316           has completed, you may have an object that is being destroyed twice
1317           because two definitions were merged.
1318
1319           This option is no longer useful on most targets, now that support
1320           has been added for putting variables into BSS without making them
1321           common.
1322
1323       -fno-deduce-init-list
1324           Disable deduction of a template type parameter as
1325           std::initializer_list from a brace-enclosed initializer list, i.e.
1326
1327                   template <class T> auto forward(T t) -> decltype (realfn (t))
1328                   {
1329                     return realfn (t);
1330                   }
1331
1332                   void f()
1333                   {
1334                     forward({1,2}); // call forward<std::initializer_list<int>>
1335                   }
1336
1337           This option is present because this deduction is an extension to
1338           the current specification in the C++0x working draft, and there was
1339           some concern about potential overload resolution problems.
1340
1341       -ffriend-injection
1342           Inject friend functions into the enclosing namespace, so that they
1343           are visible outside the scope of the class in which they are
1344           declared.  Friend functions were documented to work this way in the
1345           old Annotated C++ Reference Manual, and versions of G++ before 4.1
1346           always worked that way.  However, in ISO C++ a friend function
1347           which is not declared in an enclosing scope can only be found using
1348           argument dependent lookup.  This option causes friends to be
1349           injected as they were in earlier releases.
1350
1351           This option is for compatibility, and may be removed in a future
1352           release of G++.
1353
1354       -fno-elide-constructors
1355           The C++ standard allows an implementation to omit creating a
1356           temporary which is only used to initialize another object of the
1357           same type.  Specifying this option disables that optimization, and
1358           forces G++ to call the copy constructor in all cases.
1359
1360       -fno-enforce-eh-specs
1361           Don't generate code to check for violation of exception
1362           specifications at runtime.  This option violates the C++ standard,
1363           but may be useful for reducing code size in production builds, much
1364           like defining NDEBUG.  This does not give user code permission to
1365           throw exceptions in violation of the exception specifications; the
1366           compiler will still optimize based on the specifications, so
1367           throwing an unexpected exception will result in undefined behavior.
1368
1369       -ffor-scope
1370       -fno-for-scope
1371           If -ffor-scope is specified, the scope of variables declared in a
1372           for-init-statement is limited to the for loop itself, as specified
1373           by the C++ standard.  If -fno-for-scope is specified, the scope of
1374           variables declared in a for-init-statement extends to the end of
1375           the enclosing scope, as was the case in old versions of G++, and
1376           other (traditional) implementations of C++.
1377
1378           The default if neither flag is given to follow the standard, but to
1379           allow and give a warning for old-style code that would otherwise be
1380           invalid, or have different behavior.
1381
1382       -fno-gnu-keywords
1383           Do not recognize "typeof" as a keyword, so that code can use this
1384           word as an identifier.  You can use the keyword "__typeof__"
1385           instead.  -ansi implies -fno-gnu-keywords.
1386
1387       -fno-implicit-templates
1388           Never emit code for non-inline templates which are instantiated
1389           implicitly (i.e. by use); only emit code for explicit
1390           instantiations.
1391
1392       -fno-implicit-inline-templates
1393           Don't emit code for implicit instantiations of inline templates,
1394           either.  The default is to handle inlines differently so that
1395           compiles with and without optimization will need the same set of
1396           explicit instantiations.
1397
1398       -fno-implement-inlines
1399           To save space, do not emit out-of-line copies of inline functions
1400           controlled by #pragma implementation.  This will cause linker
1401           errors if these functions are not inlined everywhere they are
1402           called.
1403
1404       -fms-extensions
1405           Disable pedantic warnings about constructs used in MFC, such as
1406           implicit int and getting a pointer to member function via non-
1407           standard syntax.
1408
1409       -fno-nonansi-builtins
1410           Disable built-in declarations of functions that are not mandated by
1411           ANSI/ISO C.  These include "ffs", "alloca", "_exit", "index",
1412           "bzero", "conjf", and other related functions.
1413
1414       -fno-operator-names
1415           Do not treat the operator name keywords "and", "bitand", "bitor",
1416           "compl", "not", "or" and "xor" as synonyms as keywords.
1417
1418       -fno-optional-diags
1419           Disable diagnostics that the standard says a compiler does not need
1420           to issue.  Currently, the only such diagnostic issued by G++ is the
1421           one for a name having multiple meanings within a class.
1422
1423       -fpermissive
1424           Downgrade some diagnostics about nonconformant code from errors to
1425           warnings.  Thus, using -fpermissive will allow some nonconforming
1426           code to compile.
1427
1428       -fno-pretty-templates
1429           When an error message refers to a specialization of a function
1430           template, the compiler will normally print the signature of the
1431           template followed by the template arguments and any typedefs or
1432           typenames in the signature (e.g. "void f(T) [with T = int]" rather
1433           than "void f(int)") so that it's clear which template is involved.
1434           When an error message refers to a specialization of a class
1435           template, the compiler will omit any template arguments which match
1436           the default template arguments for that template.  If either of
1437           these behaviors make it harder to understand the error message
1438           rather than easier, using -fno-pretty-templates will disable them.
1439
1440       -frepo
1441           Enable automatic template instantiation at link time.  This option
1442           also implies -fno-implicit-templates.
1443
1444       -fno-rtti
1445           Disable generation of information about every class with virtual
1446           functions for use by the C++ runtime type identification features
1447           (dynamic_cast and typeid).  If you don't use those parts of the
1448           language, you can save some space by using this flag.  Note that
1449           exception handling uses the same information, but it will generate
1450           it as needed. The dynamic_cast operator can still be used for casts
1451           that do not require runtime type information, i.e. casts to "void
1452           *" or to unambiguous base classes.
1453
1454       -fstats
1455           Emit statistics about front-end processing at the end of the
1456           compilation.  This information is generally only useful to the G++
1457           development team.
1458
1459       -ftemplate-depth=n
1460           Set the maximum instantiation depth for template classes to n.  A
1461           limit on the template instantiation depth is needed to detect
1462           endless recursions during template class instantiation.  ANSI/ISO
1463           C++ conforming programs must not rely on a maximum depth greater
1464           than 17 (changed to 1024 in C++0x).
1465
1466       -fno-threadsafe-statics
1467           Do not emit the extra code to use the routines specified in the C++
1468           ABI for thread-safe initialization of local statics.  You can use
1469           this option to reduce code size slightly in code that doesn't need
1470           to be thread-safe.
1471
1472       -fuse-cxa-atexit
1473           Register destructors for objects with static storage duration with
1474           the "__cxa_atexit" function rather than the "atexit" function.
1475           This option is required for fully standards-compliant handling of
1476           static destructors, but will only work if your C library supports
1477           "__cxa_atexit".
1478
1479       -fno-use-cxa-get-exception-ptr
1480           Don't use the "__cxa_get_exception_ptr" runtime routine.  This will
1481           cause "std::uncaught_exception" to be incorrect, but is necessary
1482           if the runtime routine is not available.
1483
1484       -fvisibility-inlines-hidden
1485           This switch declares that the user does not attempt to compare
1486           pointers to inline methods where the addresses of the two functions
1487           were taken in different shared objects.
1488
1489           The effect of this is that GCC may, effectively, mark inline
1490           methods with "__attribute__ ((visibility ("hidden")))" so that they
1491           do not appear in the export table of a DSO and do not require a PLT
1492           indirection when used within the DSO.  Enabling this option can
1493           have a dramatic effect on load and link times of a DSO as it
1494           massively reduces the size of the dynamic export table when the
1495           library makes heavy use of templates.
1496
1497           The behavior of this switch is not quite the same as marking the
1498           methods as hidden directly, because it does not affect static
1499           variables local to the function or cause the compiler to deduce
1500           that the function is defined in only one shared object.
1501
1502           You may mark a method as having a visibility explicitly to negate
1503           the effect of the switch for that method.  For example, if you do
1504           want to compare pointers to a particular inline method, you might
1505           mark it as having default visibility.  Marking the enclosing class
1506           with explicit visibility will have no effect.
1507
1508           Explicitly instantiated inline methods are unaffected by this
1509           option as their linkage might otherwise cross a shared library
1510           boundary.
1511
1512       -fvisibility-ms-compat
1513           This flag attempts to use visibility settings to make GCC's C++
1514           linkage model compatible with that of Microsoft Visual Studio.
1515
1516           The flag makes these changes to GCC's linkage model:
1517
1518           1.  It sets the default visibility to "hidden", like
1519               -fvisibility=hidden.
1520
1521           2.  Types, but not their members, are not hidden by default.
1522
1523           3.  The One Definition Rule is relaxed for types without explicit
1524               visibility specifications which are defined in more than one
1525               different shared object: those declarations are permitted if
1526               they would have been permitted when this option was not used.
1527
1528           In new code it is better to use -fvisibility=hidden and export
1529           those classes which are intended to be externally visible.
1530           Unfortunately it is possible for code to rely, perhaps
1531           accidentally, on the Visual Studio behavior.
1532
1533           Among the consequences of these changes are that static data
1534           members of the same type with the same name but defined in
1535           different shared objects will be different, so changing one will
1536           not change the other; and that pointers to function members defined
1537           in different shared objects may not compare equal.  When this flag
1538           is given, it is a violation of the ODR to define types with the
1539           same name differently.
1540
1541       -fno-weak
1542           Do not use weak symbol support, even if it is provided by the
1543           linker.  By default, G++ will use weak symbols if they are
1544           available.  This option exists only for testing, and should not be
1545           used by end-users; it will result in inferior code and has no
1546           benefits.  This option may be removed in a future release of G++.
1547
1548       -nostdinc++
1549           Do not search for header files in the standard directories specific
1550           to C++, but do still search the other standard directories.  (This
1551           option is used when building the C++ library.)
1552
1553       In addition, these optimization, warning, and code generation options
1554       have meanings only for C++ programs:
1555
1556       -fno-default-inline
1557           Do not assume inline for functions defined inside a class scope.
1558             Note that these functions will have linkage like inline
1559           functions; they just won't be inlined by default.
1560
1561       -Wabi (C, Objective-C, C++ and Objective-C++ only)
1562           Warn when G++ generates code that is probably not compatible with
1563           the vendor-neutral C++ ABI.  Although an effort has been made to
1564           warn about all such cases, there are probably some cases that are
1565           not warned about, even though G++ is generating incompatible code.
1566           There may also be cases where warnings are emitted even though the
1567           code that is generated will be compatible.
1568
1569           You should rewrite your code to avoid these warnings if you are
1570           concerned about the fact that code generated by G++ may not be
1571           binary compatible with code generated by other compilers.
1572
1573           The known incompatibilities in -fabi-version=2 (the default)
1574           include:
1575
1576           ·   A template with a non-type template parameter of reference type
1577               is mangled incorrectly:
1578
1579                       extern int N;
1580                       template <int &> struct S {};
1581                       void n (S<N>) {2}
1582
1583               This is fixed in -fabi-version=3.
1584
1585           ·   SIMD vector types declared using "__attribute ((vector_size))"
1586               are mangled in a non-standard way that does not allow for
1587               overloading of functions taking vectors of different sizes.
1588
1589               The mangling is changed in -fabi-version=4.
1590
1591           The known incompatibilities in -fabi-version=1 include:
1592
1593           ·   Incorrect handling of tail-padding for bit-fields.  G++ may
1594               attempt to pack data into the same byte as a base class.  For
1595               example:
1596
1597                       struct A { virtual void f(); int f1 : 1; };
1598                       struct B : public A { int f2 : 1; };
1599
1600               In this case, G++ will place "B::f2" into the same byte
1601               as"A::f1"; other compilers will not.  You can avoid this
1602               problem by explicitly padding "A" so that its size is a
1603               multiple of the byte size on your platform; that will cause G++
1604               and other compilers to layout "B" identically.
1605
1606           ·   Incorrect handling of tail-padding for virtual bases.  G++ does
1607               not use tail padding when laying out virtual bases.  For
1608               example:
1609
1610                       struct A { virtual void f(); char c1; };
1611                       struct B { B(); char c2; };
1612                       struct C : public A, public virtual B {};
1613
1614               In this case, G++ will not place "B" into the tail-padding for
1615               "A"; other compilers will.  You can avoid this problem by
1616               explicitly padding "A" so that its size is a multiple of its
1617               alignment (ignoring virtual base classes); that will cause G++
1618               and other compilers to layout "C" identically.
1619
1620           ·   Incorrect handling of bit-fields with declared widths greater
1621               than that of their underlying types, when the bit-fields appear
1622               in a union.  For example:
1623
1624                       union U { int i : 4096; };
1625
1626               Assuming that an "int" does not have 4096 bits, G++ will make
1627               the union too small by the number of bits in an "int".
1628
1629           ·   Empty classes can be placed at incorrect offsets.  For example:
1630
1631                       struct A {};
1632
1633                       struct B {
1634                         A a;
1635                         virtual void f ();
1636                       };
1637
1638                       struct C : public B, public A {};
1639
1640               G++ will place the "A" base class of "C" at a nonzero offset;
1641               it should be placed at offset zero.  G++ mistakenly believes
1642               that the "A" data member of "B" is already at offset zero.
1643
1644           ·   Names of template functions whose types involve "typename" or
1645               template template parameters can be mangled incorrectly.
1646
1647                       template <typename Q>
1648                       void f(typename Q::X) {}
1649
1650                       template <template <typename> class Q>
1651                       void f(typename Q<int>::X) {}
1652
1653               Instantiations of these templates may be mangled incorrectly.
1654
1655           It also warns psABI related changes.  The known psABI changes at
1656           this point include:
1657
1658           ·   For SYSV/x86-64, when passing union with long double, it is
1659               changed to pass in memory as specified in psABI.  For example:
1660
1661                       union U {
1662                         long double ld;
1663                         int i;
1664                       };
1665
1666               "union U" will always be passed in memory.
1667
1668       -Wctor-dtor-privacy (C++ and Objective-C++ only)
1669           Warn when a class seems unusable because all the constructors or
1670           destructors in that class are private, and it has neither friends
1671           nor public static member functions.
1672
1673       -Wnon-virtual-dtor (C++ and Objective-C++ only)
1674           Warn when a class has virtual functions and accessible non-virtual
1675           destructor, in which case it would be possible but unsafe to delete
1676           an instance of a derived class through a pointer to the base class.
1677           This warning is also enabled if -Weffc++ is specified.
1678
1679       -Wreorder (C++ and Objective-C++ only)
1680           Warn when the order of member initializers given in the code does
1681           not match the order in which they must be executed.  For instance:
1682
1683                   struct A {
1684                     int i;
1685                     int j;
1686                     A(): j (0), i (1) { }
1687                   };
1688
1689           The compiler will rearrange the member initializers for i and j to
1690           match the declaration order of the members, emitting a warning to
1691           that effect.  This warning is enabled by -Wall.
1692
1693       The following -W... options are not affected by -Wall.
1694
1695       -Weffc++ (C++ and Objective-C++ only)
1696           Warn about violations of the following style guidelines from Scott
1697           Meyers' Effective C++ book:
1698
1699           ·   Item 11:  Define a copy constructor and an assignment operator
1700               for classes with dynamically allocated memory.
1701
1702           ·   Item 12:  Prefer initialization to assignment in constructors.
1703
1704           ·   Item 14:  Make destructors virtual in base classes.
1705
1706           ·   Item 15:  Have "operator=" return a reference to *this.
1707
1708           ·   Item 23:  Don't try to return a reference when you must return
1709               an object.
1710
1711           Also warn about violations of the following style guidelines from
1712           Scott Meyers' More Effective C++ book:
1713
1714           ·   Item 6:  Distinguish between prefix and postfix forms of
1715               increment and decrement operators.
1716
1717           ·   Item 7:  Never overload "&&", "||", or ",".
1718
1719           When selecting this option, be aware that the standard library
1720           headers do not obey all of these guidelines; use grep -v to filter
1721           out those warnings.
1722
1723       -Wstrict-null-sentinel (C++ and Objective-C++ only)
1724           Warn also about the use of an uncasted "NULL" as sentinel.  When
1725           compiling only with GCC this is a valid sentinel, as "NULL" is
1726           defined to "__null".  Although it is a null pointer constant not a
1727           null pointer, it is guaranteed to be of the same size as a pointer.
1728           But this use is not portable across different compilers.
1729
1730       -Wno-non-template-friend (C++ and Objective-C++ only)
1731           Disable warnings when non-templatized friend functions are declared
1732           within a template.  Since the advent of explicit template
1733           specification support in G++, if the name of the friend is an
1734           unqualified-id (i.e., friend foo(int)), the C++ language
1735           specification demands that the friend declare or define an
1736           ordinary, nontemplate function.  (Section 14.5.3).  Before G++
1737           implemented explicit specification, unqualified-ids could be
1738           interpreted as a particular specialization of a templatized
1739           function.  Because this non-conforming behavior is no longer the
1740           default behavior for G++, -Wnon-template-friend allows the compiler
1741           to check existing code for potential trouble spots and is on by
1742           default.  This new compiler behavior can be turned off with
1743           -Wno-non-template-friend which keeps the conformant compiler code
1744           but disables the helpful warning.
1745
1746       -Wold-style-cast (C++ and Objective-C++ only)
1747           Warn if an old-style (C-style) cast to a non-void type is used
1748           within a C++ program.  The new-style casts (dynamic_cast,
1749           static_cast, reinterpret_cast, and const_cast) are less vulnerable
1750           to unintended effects and much easier to search for.
1751
1752       -Woverloaded-virtual (C++ and Objective-C++ only)
1753           Warn when a function declaration hides virtual functions from a
1754           base class.  For example, in:
1755
1756                   struct A {
1757                     virtual void f();
1758                   };
1759
1760                   struct B: public A {
1761                     void f(int);
1762                   };
1763
1764           the "A" class version of "f" is hidden in "B", and code like:
1765
1766                   B* b;
1767                   b->f();
1768
1769           will fail to compile.
1770
1771       -Wno-pmf-conversions (C++ and Objective-C++ only)
1772           Disable the diagnostic for converting a bound pointer to member
1773           function to a plain pointer.
1774
1775       -Wsign-promo (C++ and Objective-C++ only)
1776           Warn when overload resolution chooses a promotion from unsigned or
1777           enumerated type to a signed type, over a conversion to an unsigned
1778           type of the same size.  Previous versions of G++ would try to
1779           preserve unsignedness, but the standard mandates the current
1780           behavior.
1781
1782                   struct A {
1783                     operator int ();
1784                     A& operator = (int);
1785                   };
1786
1787                   main ()
1788                   {
1789                     A a,b;
1790                     a = b;
1791                   }
1792
1793           In this example, G++ will synthesize a default A& operator = (const
1794           A&);, while cfront will use the user-defined operator =.
1795
1796   Options Controlling Objective-C and Objective-C++ Dialects
1797       (NOTE: This manual does not describe the Objective-C and Objective-C++
1798       languages themselves.  See
1799
1800       This section describes the command-line options that are only
1801       meaningful for Objective-C and Objective-C++ programs, but you can also
1802       use most of the language-independent GNU compiler options.  For
1803       example, you might compile a file "some_class.m" like this:
1804
1805               gcc -g -fgnu-runtime -O -c some_class.m
1806
1807       In this example, -fgnu-runtime is an option meant only for Objective-C
1808       and Objective-C++ programs; you can use the other options with any
1809       language supported by GCC.
1810
1811       Note that since Objective-C is an extension of the C language,
1812       Objective-C compilations may also use options specific to the C front-
1813       end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may
1814       use C++-specific options (e.g., -Wabi).
1815
1816       Here is a list of options that are only for compiling Objective-C and
1817       Objective-C++ programs:
1818
1819       -fconstant-string-class=class-name
1820           Use class-name as the name of the class to instantiate for each
1821           literal string specified with the syntax "@"..."".  The default
1822           class name is "NXConstantString" if the GNU runtime is being used,
1823           and "NSConstantString" if the NeXT runtime is being used (see
1824           below).  The -fconstant-cfstrings option, if also present, will
1825           override the -fconstant-string-class setting and cause "@"...""
1826           literals to be laid out as constant CoreFoundation strings.
1827
1828       -fgnu-runtime
1829           Generate object code compatible with the standard GNU Objective-C
1830           runtime.  This is the default for most types of systems.
1831
1832       -fnext-runtime
1833           Generate output compatible with the NeXT runtime.  This is the
1834           default for NeXT-based systems, including Darwin and Mac OS X.  The
1835           macro "__NEXT_RUNTIME__" is predefined if (and only if) this option
1836           is used.
1837
1838       -fno-nil-receivers
1839           Assume that all Objective-C message dispatches (e.g., "[receiver
1840           message:arg]") in this translation unit ensure that the receiver is
1841           not "nil".  This allows for more efficient entry points in the
1842           runtime to be used.  Currently, this option is only available in
1843           conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1844
1845       -fobjc-call-cxx-cdtors
1846           For each Objective-C class, check if any of its instance variables
1847           is a C++ object with a non-trivial default constructor.  If so,
1848           synthesize a special "- (id) .cxx_construct" instance method that
1849           will run non-trivial default constructors on any such instance
1850           variables, in order, and then return "self".  Similarly, check if
1851           any instance variable is a C++ object with a non-trivial
1852           destructor, and if so, synthesize a special "- (void)
1853           .cxx_destruct" method that will run all such default destructors,
1854           in reverse order.
1855
1856           The "- (id) .cxx_construct" and/or "- (void) .cxx_destruct" methods
1857           thusly generated will only operate on instance variables declared
1858           in the current Objective-C class, and not those inherited from
1859           superclasses.  It is the responsibility of the Objective-C runtime
1860           to invoke all such methods in an object's inheritance hierarchy.
1861           The "- (id) .cxx_construct" methods will be invoked by the runtime
1862           immediately after a new object instance is allocated; the "- (void)
1863           .cxx_destruct" methods will be invoked immediately before the
1864           runtime deallocates an object instance.
1865
1866           As of this writing, only the NeXT runtime on Mac OS X 10.4 and
1867           later has support for invoking the "- (id) .cxx_construct" and "-
1868           (void) .cxx_destruct" methods.
1869
1870       -fobjc-direct-dispatch
1871           Allow fast jumps to the message dispatcher.  On Darwin this is
1872           accomplished via the comm page.
1873
1874       -fobjc-exceptions
1875           Enable syntactic support for structured exception handling in
1876           Objective-C, similar to what is offered by C++ and Java.  This
1877           option is unavailable in conjunction with the NeXT runtime on Mac
1878           OS X 10.2 and earlier.
1879
1880                     @try {
1881                       ...
1882                          @throw expr;
1883                       ...
1884                     }
1885                     @catch (AnObjCClass *exc) {
1886                       ...
1887                         @throw expr;
1888                       ...
1889                         @throw;
1890                       ...
1891                     }
1892                     @catch (AnotherClass *exc) {
1893                       ...
1894                     }
1895                     @catch (id allOthers) {
1896                       ...
1897                     }
1898                     @finally {
1899                       ...
1900                         @throw expr;
1901                       ...
1902                     }
1903
1904           The @throw statement may appear anywhere in an Objective-C or
1905           Objective-C++ program; when used inside of a @catch block, the
1906           @throw may appear without an argument (as shown above), in which
1907           case the object caught by the @catch will be rethrown.
1908
1909           Note that only (pointers to) Objective-C objects may be thrown and
1910           caught using this scheme.  When an object is thrown, it will be
1911           caught by the nearest @catch clause capable of handling objects of
1912           that type, analogously to how "catch" blocks work in C++ and Java.
1913           A "@catch(id ...)" clause (as shown above) may also be provided to
1914           catch any and all Objective-C exceptions not caught by previous
1915           @catch clauses (if any).
1916
1917           The @finally clause, if present, will be executed upon exit from
1918           the immediately preceding "@try ... @catch" section.  This will
1919           happen regardless of whether any exceptions are thrown, caught or
1920           rethrown inside the "@try ... @catch" section, analogously to the
1921           behavior of the "finally" clause in Java.
1922
1923           There are several caveats to using the new exception mechanism:
1924
1925           ·   Although currently designed to be binary compatible with
1926               "NS_HANDLER"-style idioms provided by the "NSException" class,
1927               the new exceptions can only be used on Mac OS X 10.3 (Panther)
1928               and later systems, due to additional functionality needed in
1929               the (NeXT) Objective-C runtime.
1930
1931           ·   As mentioned above, the new exceptions do not support handling
1932               types other than Objective-C objects.   Furthermore, when used
1933               from Objective-C++, the Objective-C exception model does not
1934               interoperate with C++ exceptions at this time.  This means you
1935               cannot @throw an exception from Objective-C and "catch" it in
1936               C++, or vice versa (i.e., "throw ... @catch").
1937
1938           The -fobjc-exceptions switch also enables the use of
1939           synchronization blocks for thread-safe execution:
1940
1941                     @synchronized (ObjCClass *guard) {
1942                       ...
1943                     }
1944
1945           Upon entering the @synchronized block, a thread of execution shall
1946           first check whether a lock has been placed on the corresponding
1947           "guard" object by another thread.  If it has, the current thread
1948           shall wait until the other thread relinquishes its lock.  Once
1949           "guard" becomes available, the current thread will place its own
1950           lock on it, execute the code contained in the @synchronized block,
1951           and finally relinquish the lock (thereby making "guard" available
1952           to other threads).
1953
1954           Unlike Java, Objective-C does not allow for entire methods to be
1955           marked @synchronized.  Note that throwing exceptions out of
1956           @synchronized blocks is allowed, and will cause the guarding object
1957           to be unlocked properly.
1958
1959       -fobjc-gc
1960           Enable garbage collection (GC) in Objective-C and Objective-C++
1961           programs.
1962
1963       -freplace-objc-classes
1964           Emit a special marker instructing ld(1) not to statically link in
1965           the resulting object file, and allow dyld(1) to load it in at run
1966           time instead.  This is used in conjunction with the Fix-and-
1967           Continue debugging mode, where the object file in question may be
1968           recompiled and dynamically reloaded in the course of program
1969           execution, without the need to restart the program itself.
1970           Currently, Fix-and-Continue functionality is only available in
1971           conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1972
1973       -fzero-link
1974           When compiling for the NeXT runtime, the compiler ordinarily
1975           replaces calls to "objc_getClass("...")" (when the name of the
1976           class is known at compile time) with static class references that
1977           get initialized at load time, which improves run-time performance.
1978           Specifying the -fzero-link flag suppresses this behavior and causes
1979           calls to "objc_getClass("...")"  to be retained.  This is useful in
1980           Zero-Link debugging mode, since it allows for individual class
1981           implementations to be modified during program execution.
1982
1983       -gen-decls
1984           Dump interface declarations for all classes seen in the source file
1985           to a file named sourcename.decl.
1986
1987       -Wassign-intercept (Objective-C and Objective-C++ only)
1988           Warn whenever an Objective-C assignment is being intercepted by the
1989           garbage collector.
1990
1991       -Wno-protocol (Objective-C and Objective-C++ only)
1992           If a class is declared to implement a protocol, a warning is issued
1993           for every method in the protocol that is not implemented by the
1994           class.  The default behavior is to issue a warning for every method
1995           not explicitly implemented in the class, even if a method
1996           implementation is inherited from the superclass.  If you use the
1997           -Wno-protocol option, then methods inherited from the superclass
1998           are considered to be implemented, and no warning is issued for
1999           them.
2000
2001       -Wselector (Objective-C and Objective-C++ only)
2002           Warn if multiple methods of different types for the same selector
2003           are found during compilation.  The check is performed on the list
2004           of methods in the final stage of compilation.  Additionally, a
2005           check is performed for each selector appearing in a
2006           "@selector(...)"  expression, and a corresponding method for that
2007           selector has been found during compilation.  Because these checks
2008           scan the method table only at the end of compilation, these
2009           warnings are not produced if the final stage of compilation is not
2010           reached, for example because an error is found during compilation,
2011           or because the -fsyntax-only option is being used.
2012
2013       -Wstrict-selector-match (Objective-C and Objective-C++ only)
2014           Warn if multiple methods with differing argument and/or return
2015           types are found for a given selector when attempting to send a
2016           message using this selector to a receiver of type "id" or "Class".
2017           When this flag is off (which is the default behavior), the compiler
2018           will omit such warnings if any differences found are confined to
2019           types which share the same size and alignment.
2020
2021       -Wundeclared-selector (Objective-C and Objective-C++ only)
2022           Warn if a "@selector(...)" expression referring to an undeclared
2023           selector is found.  A selector is considered undeclared if no
2024           method with that name has been declared before the "@selector(...)"
2025           expression, either explicitly in an @interface or @protocol
2026           declaration, or implicitly in an @implementation section.  This
2027           option always performs its checks as soon as a "@selector(...)"
2028           expression is found, while -Wselector only performs its checks in
2029           the final stage of compilation.  This also enforces the coding
2030           style convention that methods and selectors must be declared before
2031           being used.
2032
2033       -print-objc-runtime-info
2034           Generate C header describing the largest structure that is passed
2035           by value, if any.
2036
2037   Options to Control Diagnostic Messages Formatting
2038       Traditionally, diagnostic messages have been formatted irrespective of
2039       the output device's aspect (e.g. its width, ...).  The options
2040       described below can be used to control the diagnostic messages
2041       formatting algorithm, e.g. how many characters per line, how often
2042       source location information should be reported.  Right now, only the
2043       C++ front end can honor these options.  However it is expected, in the
2044       near future, that the remaining front ends would be able to digest them
2045       correctly.
2046
2047       -fmessage-length=n
2048           Try to format error messages so that they fit on lines of about n
2049           characters.  The default is 72 characters for g++ and 0 for the
2050           rest of the front ends supported by GCC.  If n is zero, then no
2051           line-wrapping will be done; each error message will appear on a
2052           single line.
2053
2054       -fdiagnostics-show-location=once
2055           Only meaningful in line-wrapping mode.  Instructs the diagnostic
2056           messages reporter to emit once source location information; that
2057           is, in case the message is too long to fit on a single physical
2058           line and has to be wrapped, the source location won't be emitted
2059           (as prefix) again, over and over, in subsequent continuation lines.
2060           This is the default behavior.
2061
2062       -fdiagnostics-show-location=every-line
2063           Only meaningful in line-wrapping mode.  Instructs the diagnostic
2064           messages reporter to emit the same source location information (as
2065           prefix) for physical lines that result from the process of breaking
2066           a message which is too long to fit on a single line.
2067
2068       -fdiagnostics-show-option
2069           This option instructs the diagnostic machinery to add text to each
2070           diagnostic emitted, which indicates which command line option
2071           directly controls that diagnostic, when such an option is known to
2072           the diagnostic machinery.
2073
2074       -Wcoverage-mismatch
2075           Warn if feedback profiles do not match when using the -fprofile-use
2076           option.  If a source file was changed between -fprofile-gen and
2077           -fprofile-use, the files with the profile feedback can fail to
2078           match the source file and GCC can not use the profile feedback
2079           information.  By default, GCC emits an error message in this case.
2080           The option -Wcoverage-mismatch emits a warning instead of an error.
2081           GCC does not use appropriate feedback profiles, so using this
2082           option can result in poorly optimized code.  This option is useful
2083           only in the case of very minor changes such as bug fixes to an
2084           existing code-base.
2085
2086   Options to Request or Suppress Warnings
2087       Warnings are diagnostic messages that report constructions which are
2088       not inherently erroneous but which are risky or suggest there may have
2089       been an error.
2090
2091       The following language-independent options do not enable specific
2092       warnings but control the kinds of diagnostics produced by GCC.
2093
2094       -fsyntax-only
2095           Check the code for syntax errors, but don't do anything beyond
2096           that.
2097
2098       -w  Inhibit all warning messages.
2099
2100       -Werror
2101           Make all warnings into errors.
2102
2103       -Werror=
2104           Make the specified warning into an error.  The specifier for a
2105           warning is appended, for example -Werror=switch turns the warnings
2106           controlled by -Wswitch into errors.  This switch takes a negative
2107           form, to be used to negate -Werror for specific warnings, for
2108           example -Wno-error=switch makes -Wswitch warnings not be errors,
2109           even when -Werror is in effect.  You can use the
2110           -fdiagnostics-show-option option to have each controllable warning
2111           amended with the option which controls it, to determine what to use
2112           with this option.
2113
2114           Note that specifying -Werror=foo automatically implies -Wfoo.
2115           However, -Wno-error=foo does not imply anything.
2116
2117       -Wfatal-errors
2118           This option causes the compiler to abort compilation on the first
2119           error occurred rather than trying to keep going and printing
2120           further error messages.
2121
2122       You can request many specific warnings with options beginning -W, for
2123       example -Wimplicit to request warnings on implicit declarations.  Each
2124       of these specific warning options also has a negative form beginning
2125       -Wno- to turn off warnings; for example, -Wno-implicit.  This manual
2126       lists only one of the two forms, whichever is not the default.  For
2127       further, language-specific options also refer to C++ Dialect Options
2128       and Objective-C and Objective-C++ Dialect Options.
2129
2130       -pedantic
2131           Issue all the warnings demanded by strict ISO C and ISO C++; reject
2132           all programs that use forbidden extensions, and some other programs
2133           that do not follow ISO C and ISO C++.  For ISO C, follows the
2134           version of the ISO C standard specified by any -std option used.
2135
2136           Valid ISO C and ISO C++ programs should compile properly with or
2137           without this option (though a rare few will require -ansi or a -std
2138           option specifying the required version of ISO C).  However, without
2139           this option, certain GNU extensions and traditional C and C++
2140           features are supported as well.  With this option, they are
2141           rejected.
2142
2143           -pedantic does not cause warning messages for use of the alternate
2144           keywords whose names begin and end with __.  Pedantic warnings are
2145           also disabled in the expression that follows "__extension__".
2146           However, only system header files should use these escape routes;
2147           application programs should avoid them.
2148
2149           Some users try to use -pedantic to check programs for strict ISO C
2150           conformance.  They soon find that it does not do quite what they
2151           want: it finds some non-ISO practices, but not all---only those for
2152           which ISO C requires a diagnostic, and some others for which
2153           diagnostics have been added.
2154
2155           A feature to report any failure to conform to ISO C might be useful
2156           in some instances, but would require considerable additional work
2157           and would be quite different from -pedantic.  We don't have plans
2158           to support such a feature in the near future.
2159
2160           Where the standard specified with -std represents a GNU extended
2161           dialect of C, such as gnu90 or gnu99, there is a corresponding base
2162           standard, the version of ISO C on which the GNU extended dialect is
2163           based.  Warnings from -pedantic are given where they are required
2164           by the base standard.  (It would not make sense for such warnings
2165           to be given only for features not in the specified GNU C dialect,
2166           since by definition the GNU dialects of C include all features the
2167           compiler supports with the given option, and there would be nothing
2168           to warn about.)
2169
2170       -pedantic-errors
2171           Like -pedantic, except that errors are produced rather than
2172           warnings.
2173
2174       -Wall
2175           This enables all the warnings about constructions that some users
2176           consider questionable, and that are easy to avoid (or modify to
2177           prevent the warning), even in conjunction with macros.  This also
2178           enables some language-specific warnings described in C++ Dialect
2179           Options and Objective-C and Objective-C++ Dialect Options.
2180
2181           -Wall turns on the following warning flags:
2182
2183           -Waddress -Warray-bounds (only with -O2) -Wc++0x-compat
2184           -Wchar-subscripts -Wenum-compare (in C/Objc; this is on by default
2185           in C++) -Wimplicit-int -Wimplicit-function-declaration -Wcomment
2186           -Wformat -Wmain (only for C/ObjC and unless -ffreestanding)
2187           -Wmissing-braces -Wnonnull -Wparentheses -Wpointer-sign -Wreorder
2188           -Wreturn-type -Wsequence-point -Wsign-compare (only in C++)
2189           -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch -Wtrigraphs
2190           -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label
2191           -Wunused-value -Wunused-variable -Wvolatile-register-var
2192
2193           Note that some warning flags are not implied by -Wall.  Some of
2194           them warn about constructions that users generally do not consider
2195           questionable, but which occasionally you might wish to check for;
2196           others warn about constructions that are necessary or hard to avoid
2197           in some cases, and there is no simple way to modify the code to
2198           suppress the warning. Some of them are enabled by -Wextra but many
2199           of them must be enabled individually.
2200
2201       -Wextra
2202           This enables some extra warning flags that are not enabled by
2203           -Wall. (This option used to be called -W.  The older name is still
2204           supported, but the newer name is more descriptive.)
2205
2206           -Wclobbered -Wempty-body -Wignored-qualifiers
2207           -Wmissing-field-initializers -Wmissing-parameter-type (C only)
2208           -Wold-style-declaration (C only) -Woverride-init -Wsign-compare
2209           -Wtype-limits -Wuninitialized -Wunused-parameter (only with
2210           -Wunused or -Wall)
2211
2212           The option -Wextra also prints warning messages for the following
2213           cases:
2214
2215           ·   A pointer is compared against integer zero with <, <=, >, or
2216               >=.
2217
2218           ·   (C++ only) An enumerator and a non-enumerator both appear in a
2219               conditional expression.
2220
2221           ·   (C++ only) Ambiguous virtual bases.
2222
2223           ·   (C++ only) Subscripting an array which has been declared
2224               register.
2225
2226           ·   (C++ only) Taking the address of a variable which has been
2227               declared register.
2228
2229           ·   (C++ only) A base class is not initialized in a derived class'
2230               copy constructor.
2231
2232       -Wchar-subscripts
2233           Warn if an array subscript has type "char".  This is a common cause
2234           of error, as programmers often forget that this type is signed on
2235           some machines.  This warning is enabled by -Wall.
2236
2237       -Wcomment
2238           Warn whenever a comment-start sequence /* appears in a /* comment,
2239           or whenever a Backslash-Newline appears in a // comment.  This
2240           warning is enabled by -Wall.
2241
2242       -Wformat
2243           Check calls to "printf" and "scanf", etc., to make sure that the
2244           arguments supplied have types appropriate to the format string
2245           specified, and that the conversions specified in the format string
2246           make sense.  This includes standard functions, and others specified
2247           by format attributes, in the "printf", "scanf", "strftime" and
2248           "strfmon" (an X/Open extension, not in the C standard) families (or
2249           other target-specific families).  Which functions are checked
2250           without format attributes having been specified depends on the
2251           standard version selected, and such checks of functions without the
2252           attribute specified are disabled by -ffreestanding or -fno-builtin.
2253
2254           The formats are checked against the format features supported by
2255           GNU libc version 2.2.  These include all ISO C90 and C99 features,
2256           as well as features from the Single Unix Specification and some BSD
2257           and GNU extensions.  Other library implementations may not support
2258           all these features; GCC does not support warning about features
2259           that go beyond a particular library's limitations.  However, if
2260           -pedantic is used with -Wformat, warnings will be given about
2261           format features not in the selected standard version (but not for
2262           "strfmon" formats, since those are not in any version of the C
2263           standard).
2264
2265           Since -Wformat also checks for null format arguments for several
2266           functions, -Wformat also implies -Wnonnull.
2267
2268           -Wformat is included in -Wall.  For more control over some aspects
2269           of format checking, the options -Wformat-y2k,
2270           -Wno-format-extra-args, -Wno-format-zero-length,
2271           -Wformat-nonliteral, -Wformat-security, and -Wformat=2 are
2272           available, but are not included in -Wall.
2273
2274       -Wformat-y2k
2275           If -Wformat is specified, also warn about "strftime" formats which
2276           may yield only a two-digit year.
2277
2278       -Wno-format-contains-nul
2279           If -Wformat is specified, do not warn about format strings that
2280           contain NUL bytes.
2281
2282       -Wno-format-extra-args
2283           If -Wformat is specified, do not warn about excess arguments to a
2284           "printf" or "scanf" format function.  The C standard specifies that
2285           such arguments are ignored.
2286
2287           Where the unused arguments lie between used arguments that are
2288           specified with $ operand number specifications, normally warnings
2289           are still given, since the implementation could not know what type
2290           to pass to "va_arg" to skip the unused arguments.  However, in the
2291           case of "scanf" formats, this option will suppress the warning if
2292           the unused arguments are all pointers, since the Single Unix
2293           Specification says that such unused arguments are allowed.
2294
2295       -Wno-format-zero-length (C and Objective-C only)
2296           If -Wformat is specified, do not warn about zero-length formats.
2297           The C standard specifies that zero-length formats are allowed.
2298
2299       -Wformat-nonliteral
2300           If -Wformat is specified, also warn if the format string is not a
2301           string literal and so cannot be checked, unless the format function
2302           takes its format arguments as a "va_list".
2303
2304       -Wformat-security
2305           If -Wformat is specified, also warn about uses of format functions
2306           that represent possible security problems.  At present, this warns
2307           about calls to "printf" and "scanf" functions where the format
2308           string is not a string literal and there are no format arguments,
2309           as in "printf (foo);".  This may be a security hole if the format
2310           string came from untrusted input and contains %n.  (This is
2311           currently a subset of what -Wformat-nonliteral warns about, but in
2312           future warnings may be added to -Wformat-security that are not
2313           included in -Wformat-nonliteral.)
2314
2315       -Wformat=2
2316           Enable -Wformat plus format checks not included in -Wformat.
2317           Currently equivalent to -Wformat -Wformat-nonliteral
2318           -Wformat-security -Wformat-y2k.
2319
2320       -Wnonnull (C and Objective-C only)
2321           Warn about passing a null pointer for arguments marked as requiring
2322           a non-null value by the "nonnull" function attribute.
2323
2324           -Wnonnull is included in -Wall and -Wformat.  It can be disabled
2325           with the -Wno-nonnull option.
2326
2327       -Winit-self (C, C++, Objective-C and Objective-C++ only)
2328           Warn about uninitialized variables which are initialized with
2329           themselves.  Note this option can only be used with the
2330           -Wuninitialized option.
2331
2332           For example, GCC will warn about "i" being uninitialized in the
2333           following snippet only when -Winit-self has been specified:
2334
2335                   int f()
2336                   {
2337                     int i = i;
2338                     return i;
2339                   }
2340
2341       -Wimplicit-int (C and Objective-C only)
2342           Warn when a declaration does not specify a type.  This warning is
2343           enabled by -Wall.
2344
2345       -Wimplicit-function-declaration (C and Objective-C only)
2346           Give a warning whenever a function is used before being declared.
2347           In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by
2348           default and it is made into an error by -pedantic-errors. This
2349           warning is also enabled by -Wall.
2350
2351       -Wimplicit
2352           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
2353           warning is enabled by -Wall.
2354
2355       -Wignored-qualifiers (C and C++ only)
2356           Warn if the return type of a function has a type qualifier such as
2357           "const".  For ISO C such a type qualifier has no effect, since the
2358           value returned by a function is not an lvalue.  For C++, the
2359           warning is only emitted for scalar types or "void".  ISO C
2360           prohibits qualified "void" return types on function definitions, so
2361           such return types always receive a warning even without this
2362           option.
2363
2364           This warning is also enabled by -Wextra.
2365
2366       -Wmain
2367           Warn if the type of main is suspicious.  main should be a function
2368           with external linkage, returning int, taking either zero arguments,
2369           two, or three arguments of appropriate types.  This warning is
2370           enabled by default in C++ and is enabled by either -Wall or
2371           -pedantic.
2372
2373       -Wmissing-braces
2374           Warn if an aggregate or union initializer is not fully bracketed.
2375           In the following example, the initializer for a is not fully
2376           bracketed, but that for b is fully bracketed.
2377
2378                   int a[2][2] = { 0, 1, 2, 3 };
2379                   int b[2][2] = { { 0, 1 }, { 2, 3 } };
2380
2381           This warning is enabled by -Wall.
2382
2383       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
2384           Warn if a user-supplied include directory does not exist.
2385
2386       -Wparentheses
2387           Warn if parentheses are omitted in certain contexts, such as when
2388           there is an assignment in a context where a truth value is
2389           expected, or when operators are nested whose precedence people
2390           often get confused about.
2391
2392           Also warn if a comparison like x<=y<=z appears; this is equivalent
2393           to (x<=y ? 1 : 0) <= z, which is a different interpretation from
2394           that of ordinary mathematical notation.
2395
2396           Also warn about constructions where there may be confusion to which
2397           "if" statement an "else" branch belongs.  Here is an example of
2398           such a case:
2399
2400                   {
2401                     if (a)
2402                       if (b)
2403                         foo ();
2404                     else
2405                       bar ();
2406                   }
2407
2408           In C/C++, every "else" branch belongs to the innermost possible
2409           "if" statement, which in this example is "if (b)".  This is often
2410           not what the programmer expected, as illustrated in the above
2411           example by indentation the programmer chose.  When there is the
2412           potential for this confusion, GCC will issue a warning when this
2413           flag is specified.  To eliminate the warning, add explicit braces
2414           around the innermost "if" statement so there is no way the "else"
2415           could belong to the enclosing "if".  The resulting code would look
2416           like this:
2417
2418                   {
2419                     if (a)
2420                       {
2421                         if (b)
2422                           foo ();
2423                         else
2424                           bar ();
2425                       }
2426                   }
2427
2428           This warning is enabled by -Wall.
2429
2430       -Wsequence-point
2431           Warn about code that may have undefined semantics because of
2432           violations of sequence point rules in the C and C++ standards.
2433
2434           The C and C++ standards defines the order in which expressions in a
2435           C/C++ program are evaluated in terms of sequence points, which
2436           represent a partial ordering between the execution of parts of the
2437           program: those executed before the sequence point, and those
2438           executed after it.  These occur after the evaluation of a full
2439           expression (one which is not part of a larger expression), after
2440           the evaluation of the first operand of a "&&", "||", "? :" or ","
2441           (comma) operator, before a function is called (but after the
2442           evaluation of its arguments and the expression denoting the called
2443           function), and in certain other places.  Other than as expressed by
2444           the sequence point rules, the order of evaluation of subexpressions
2445           of an expression is not specified.  All these rules describe only a
2446           partial order rather than a total order, since, for example, if two
2447           functions are called within one expression with no sequence point
2448           between them, the order in which the functions are called is not
2449           specified.  However, the standards committee have ruled that
2450           function calls do not overlap.
2451
2452           It is not specified when between sequence points modifications to
2453           the values of objects take effect.  Programs whose behavior depends
2454           on this have undefined behavior; the C and C++ standards specify
2455           that "Between the previous and next sequence point an object shall
2456           have its stored value modified at most once by the evaluation of an
2457           expression.  Furthermore, the prior value shall be read only to
2458           determine the value to be stored.".  If a program breaks these
2459           rules, the results on any particular implementation are entirely
2460           unpredictable.
2461
2462           Examples of code with undefined behavior are "a = a++;", "a[n] =
2463           b[n++]" and "a[i++] = i;".  Some more complicated cases are not
2464           diagnosed by this option, and it may give an occasional false
2465           positive result, but in general it has been found fairly effective
2466           at detecting this sort of problem in programs.
2467
2468           The standard is worded confusingly, therefore there is some debate
2469           over the precise meaning of the sequence point rules in subtle
2470           cases.  Links to discussions of the problem, including proposed
2471           formal definitions, may be found on the GCC readings page, at
2472           <http://gcc.gnu.org/readings.html>.
2473
2474           This warning is enabled by -Wall for C and C++.
2475
2476       -Wreturn-type
2477           Warn whenever a function is defined with a return-type that
2478           defaults to "int".  Also warn about any "return" statement with no
2479           return-value in a function whose return-type is not "void" (falling
2480           off the end of the function body is considered returning without a
2481           value), and about a "return" statement with an expression in a
2482           function whose return-type is "void".
2483
2484           For C++, a function without return type always produces a
2485           diagnostic message, even when -Wno-return-type is specified.  The
2486           only exceptions are main and functions defined in system headers.
2487
2488           This warning is enabled by -Wall.
2489
2490       -Wswitch
2491           Warn whenever a "switch" statement has an index of enumerated type
2492           and lacks a "case" for one or more of the named codes of that
2493           enumeration.  (The presence of a "default" label prevents this
2494           warning.)  "case" labels outside the enumeration range also provoke
2495           warnings when this option is used (even if there is a "default"
2496           label).  This warning is enabled by -Wall.
2497
2498       -Wswitch-default
2499           Warn whenever a "switch" statement does not have a "default" case.
2500
2501       -Wswitch-enum
2502           Warn whenever a "switch" statement has an index of enumerated type
2503           and lacks a "case" for one or more of the named codes of that
2504           enumeration.  "case" labels outside the enumeration range also
2505           provoke warnings when this option is used.  The only difference
2506           between -Wswitch and this option is that this option gives a
2507           warning about an omitted enumeration code even if there is a
2508           "default" label.
2509
2510       -Wsync-nand (C and C++ only)
2511           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch"
2512           built-in functions are used.  These functions changed semantics in
2513           GCC 4.4.
2514
2515       -Wtrigraphs
2516           Warn if any trigraphs are encountered that might change the meaning
2517           of the program (trigraphs within comments are not warned about).
2518           This warning is enabled by -Wall.
2519
2520       -Wunused-function
2521           Warn whenever a static function is declared but not defined or a
2522           non-inline static function is unused.  This warning is enabled by
2523           -Wall.
2524
2525       -Wunused-label
2526           Warn whenever a label is declared but not used.  This warning is
2527           enabled by -Wall.
2528
2529           To suppress this warning use the unused attribute.
2530
2531       -Wunused-parameter
2532           Warn whenever a function parameter is unused aside from its
2533           declaration.
2534
2535           To suppress this warning use the unused attribute.
2536
2537       -Wno-unused-result
2538           Do not warn if a caller of a function marked with attribute
2539           "warn_unused_result" does not use its return value. The default is
2540           -Wunused-result.
2541
2542       -Wunused-variable
2543           Warn whenever a local variable or non-constant static variable is
2544           unused aside from its declaration.  This warning is enabled by
2545           -Wall.
2546
2547           To suppress this warning use the unused attribute.
2548
2549       -Wunused-value
2550           Warn whenever a statement computes a result that is explicitly not
2551           used. To suppress this warning cast the unused expression to void.
2552           This includes an expression-statement or the left-hand side of a
2553           comma expression that contains no side effects. For example, an
2554           expression such as x[i,j] will cause a warning, while x[(void)i,j]
2555           will not.
2556
2557           This warning is enabled by -Wall.
2558
2559       -Wunused
2560           All the above -Wunused options combined.
2561
2562           In order to get a warning about an unused function parameter, you
2563           must either specify -Wextra -Wunused (note that -Wall implies
2564           -Wunused), or separately specify -Wunused-parameter.
2565
2566       -Wuninitialized
2567           Warn if an automatic variable is used without first being
2568           initialized or if a variable may be clobbered by a "setjmp" call.
2569           In C++, warn if a non-static reference or non-static const member
2570           appears in a class without constructors.
2571
2572           If you want to warn about code which uses the uninitialized value
2573           of the variable in its own initializer, use the -Winit-self option.
2574
2575           These warnings occur for individual uninitialized or clobbered
2576           elements of structure, union or array variables as well as for
2577           variables which are uninitialized or clobbered as a whole.  They do
2578           not occur for variables or elements declared "volatile".  Because
2579           these warnings depend on optimization, the exact variables or
2580           elements for which there are warnings will depend on the precise
2581           optimization options and version of GCC used.
2582
2583           Note that there may be no warning about a variable that is used
2584           only to compute a value that itself is never used, because such
2585           computations may be deleted by data flow analysis before the
2586           warnings are printed.
2587
2588           These warnings are made optional because GCC is not smart enough to
2589           see all the reasons why the code might be correct despite appearing
2590           to have an error.  Here is one example of how this can happen:
2591
2592                   {
2593                     int x;
2594                     switch (y)
2595                       {
2596                       case 1: x = 1;
2597                         break;
2598                       case 2: x = 4;
2599                         break;
2600                       case 3: x = 5;
2601                       }
2602                     foo (x);
2603                   }
2604
2605           If the value of "y" is always 1, 2 or 3, then "x" is always
2606           initialized, but GCC doesn't know this.  Here is another common
2607           case:
2608
2609                   {
2610                     int save_y;
2611                     if (change_y) save_y = y, y = new_y;
2612                     ...
2613                     if (change_y) y = save_y;
2614                   }
2615
2616           This has no bug because "save_y" is used only if it is set.
2617
2618           This option also warns when a non-volatile automatic variable might
2619           be changed by a call to "longjmp".  These warnings as well are
2620           possible only in optimizing compilation.
2621
2622           The compiler sees only the calls to "setjmp".  It cannot know where
2623           "longjmp" will be called; in fact, a signal handler could call it
2624           at any point in the code.  As a result, you may get a warning even
2625           when there is in fact no problem because "longjmp" cannot in fact
2626           be called at the place which would cause a problem.
2627
2628           Some spurious warnings can be avoided if you declare all the
2629           functions you use that never return as "noreturn".
2630
2631           This warning is enabled by -Wall or -Wextra.
2632
2633       -Wunknown-pragmas
2634           Warn when a #pragma directive is encountered which is not
2635           understood by GCC.  If this command line option is used, warnings
2636           will even be issued for unknown pragmas in system header files.
2637           This is not the case if the warnings were only enabled by the -Wall
2638           command line option.
2639
2640       -Wno-pragmas
2641           Do not warn about misuses of pragmas, such as incorrect parameters,
2642           invalid syntax, or conflicts between pragmas.  See also
2643           -Wunknown-pragmas.
2644
2645       -Wstrict-aliasing
2646           This option is only active when -fstrict-aliasing is active.  It
2647           warns about code which might break the strict aliasing rules that
2648           the compiler is using for optimization.  The warning does not catch
2649           all cases, but does attempt to catch the more common pitfalls.  It
2650           is included in -Wall.  It is equivalent to -Wstrict-aliasing=3
2651
2652       -Wstrict-aliasing=n
2653           This option is only active when -fstrict-aliasing is active.  It
2654           warns about code which might break the strict aliasing rules that
2655           the compiler is using for optimization.  Higher levels correspond
2656           to higher accuracy (fewer false positives).  Higher levels also
2657           correspond to more effort, similar to the way -O works.
2658           -Wstrict-aliasing is equivalent to -Wstrict-aliasing=n, with n=3.
2659
2660           Level 1: Most aggressive, quick, least accurate.  Possibly useful
2661           when higher levels do not warn but -fstrict-aliasing still breaks
2662           the code, as it has very few false negatives.  However, it has many
2663           false positives.  Warns for all pointer conversions between
2664           possibly incompatible types, even if never dereferenced.  Runs in
2665           the frontend only.
2666
2667           Level 2: Aggressive, quick, not too precise.  May still have many
2668           false positives (not as many as level 1 though), and few false
2669           negatives (but possibly more than level 1).  Unlike level 1, it
2670           only warns when an address is taken.  Warns about incomplete types.
2671           Runs in the frontend only.
2672
2673           Level 3 (default for -Wstrict-aliasing): Should have very few false
2674           positives and few false negatives.  Slightly slower than levels 1
2675           or 2 when optimization is enabled.  Takes care of the common
2676           pun+dereference pattern in the frontend: "*(int*)&some_float".  If
2677           optimization is enabled, it also runs in the backend, where it
2678           deals with multiple statement cases using flow-sensitive points-to
2679           information.  Only warns when the converted pointer is
2680           dereferenced.  Does not warn about incomplete types.
2681
2682       -Wstrict-overflow
2683       -Wstrict-overflow=n
2684           This option is only active when -fstrict-overflow is active.  It
2685           warns about cases where the compiler optimizes based on the
2686           assumption that signed overflow does not occur.  Note that it does
2687           not warn about all cases where the code might overflow: it only
2688           warns about cases where the compiler implements some optimization.
2689           Thus this warning depends on the optimization level.
2690
2691           An optimization which assumes that signed overflow does not occur
2692           is perfectly safe if the values of the variables involved are such
2693           that overflow never does, in fact, occur.  Therefore this warning
2694           can easily give a false positive: a warning about code which is not
2695           actually a problem.  To help focus on important issues, several
2696           warning levels are defined.  No warnings are issued for the use of
2697           undefined signed overflow when estimating how many iterations a
2698           loop will require, in particular when determining whether a loop
2699           will be executed at all.
2700
2701           -Wstrict-overflow=1
2702               Warn about cases which are both questionable and easy to avoid.
2703               For example: "x + 1 > x"; with -fstrict-overflow, the compiler
2704               will simplify this to 1.  This level of -Wstrict-overflow is
2705               enabled by -Wall; higher levels are not, and must be explicitly
2706               requested.
2707
2708           -Wstrict-overflow=2
2709               Also warn about other cases where a comparison is simplified to
2710               a constant.  For example: "abs (x) >= 0".  This can only be
2711               simplified when -fstrict-overflow is in effect, because "abs
2712               (INT_MIN)" overflows to "INT_MIN", which is less than zero.
2713               -Wstrict-overflow (with no level) is the same as
2714               -Wstrict-overflow=2.
2715
2716           -Wstrict-overflow=3
2717               Also warn about other cases where a comparison is simplified.
2718               For example: "x + 1 > 1" will be simplified to "x > 0".
2719
2720           -Wstrict-overflow=4
2721               Also warn about other simplifications not covered by the above
2722               cases.  For example: "(x * 10) / 5" will be simplified to "x *
2723               2".
2724
2725           -Wstrict-overflow=5
2726               Also warn about cases where the compiler reduces the magnitude
2727               of a constant involved in a comparison.  For example: "x + 2 >
2728               y" will be simplified to "x + 1 >= y".  This is reported only
2729               at the highest warning level because this simplification
2730               applies to many comparisons, so this warning level will give a
2731               very large number of false positives.
2732
2733       -Warray-bounds
2734           This option is only active when -ftree-vrp is active (default for
2735           -O2 and above). It warns about subscripts to arrays that are always
2736           out of bounds. This warning is enabled by -Wall.
2737
2738       -Wno-div-by-zero
2739           Do not warn about compile-time integer division by zero.  Floating
2740           point division by zero is not warned about, as it can be a
2741           legitimate way of obtaining infinities and NaNs.
2742
2743       -Wsystem-headers
2744           Print warning messages for constructs found in system header files.
2745           Warnings from system headers are normally suppressed, on the
2746           assumption that they usually do not indicate real problems and
2747           would only make the compiler output harder to read.  Using this
2748           command line option tells GCC to emit warnings from system headers
2749           as if they occurred in user code.  However, note that using -Wall
2750           in conjunction with this option will not warn about unknown pragmas
2751           in system headers---for that, -Wunknown-pragmas must also be used.
2752
2753       -Wfloat-equal
2754           Warn if floating point values are used in equality comparisons.
2755
2756           The idea behind this is that sometimes it is convenient (for the
2757           programmer) to consider floating-point values as approximations to
2758           infinitely precise real numbers.  If you are doing this, then you
2759           need to compute (by analyzing the code, or in some other way) the
2760           maximum or likely maximum error that the computation introduces,
2761           and allow for it when performing comparisons (and when producing
2762           output, but that's a different problem).  In particular, instead of
2763           testing for equality, you would check to see whether the two values
2764           have ranges that overlap; and this is done with the relational
2765           operators, so equality comparisons are probably mistaken.
2766
2767       -Wtraditional (C and Objective-C only)
2768           Warn about certain constructs that behave differently in
2769           traditional and ISO C.  Also warn about ISO C constructs that have
2770           no traditional C equivalent, and/or problematic constructs which
2771           should be avoided.
2772
2773           ·   Macro parameters that appear within string literals in the
2774               macro body.  In traditional C macro replacement takes place
2775               within string literals, but does not in ISO C.
2776
2777           ·   In traditional C, some preprocessor directives did not exist.
2778               Traditional preprocessors would only consider a line to be a
2779               directive if the # appeared in column 1 on the line.  Therefore
2780               -Wtraditional warns about directives that traditional C
2781               understands but would ignore because the # does not appear as
2782               the first character on the line.  It also suggests you hide
2783               directives like #pragma not understood by traditional C by
2784               indenting them.  Some traditional implementations would not
2785               recognize #elif, so it suggests avoiding it altogether.
2786
2787           ·   A function-like macro that appears without arguments.
2788
2789           ·   The unary plus operator.
2790
2791           ·   The U integer constant suffix, or the F or L floating point
2792               constant suffixes.  (Traditional C does support the L suffix on
2793               integer constants.)  Note, these suffixes appear in macros
2794               defined in the system headers of most modern systems, e.g. the
2795               _MIN/_MAX macros in "<limits.h>".  Use of these macros in user
2796               code might normally lead to spurious warnings, however GCC's
2797               integrated preprocessor has enough context to avoid warning in
2798               these cases.
2799
2800           ·   A function declared external in one block and then used after
2801               the end of the block.
2802
2803           ·   A "switch" statement has an operand of type "long".
2804
2805           ·   A non-"static" function declaration follows a "static" one.
2806               This construct is not accepted by some traditional C compilers.
2807
2808           ·   The ISO type of an integer constant has a different width or
2809               signedness from its traditional type.  This warning is only
2810               issued if the base of the constant is ten.  I.e. hexadecimal or
2811               octal values, which typically represent bit patterns, are not
2812               warned about.
2813
2814           ·   Usage of ISO string concatenation is detected.
2815
2816           ·   Initialization of automatic aggregates.
2817
2818           ·   Identifier conflicts with labels.  Traditional C lacks a
2819               separate namespace for labels.
2820
2821           ·   Initialization of unions.  If the initializer is zero, the
2822               warning is omitted.  This is done under the assumption that the
2823               zero initializer in user code appears conditioned on e.g.
2824               "__STDC__" to avoid missing initializer warnings and relies on
2825               default initialization to zero in the traditional C case.
2826
2827           ·   Conversions by prototypes between fixed/floating point values
2828               and vice versa.  The absence of these prototypes when compiling
2829               with traditional C would cause serious problems.  This is a
2830               subset of the possible conversion warnings, for the full set
2831               use -Wtraditional-conversion.
2832
2833           ·   Use of ISO C style function definitions.  This warning
2834               intentionally is not issued for prototype declarations or
2835               variadic functions because these ISO C features will appear in
2836               your code when using libiberty's traditional C compatibility
2837               macros, "PARAMS" and "VPARAMS".  This warning is also bypassed
2838               for nested functions because that feature is already a GCC
2839               extension and thus not relevant to traditional C compatibility.
2840
2841       -Wtraditional-conversion (C and Objective-C only)
2842           Warn if a prototype causes a type conversion that is different from
2843           what would happen to the same argument in the absence of a
2844           prototype.  This includes conversions of fixed point to floating
2845           and vice versa, and conversions changing the width or signedness of
2846           a fixed point argument except when the same as the default
2847           promotion.
2848
2849       -Wdeclaration-after-statement (C and Objective-C only)
2850           Warn when a declaration is found after a statement in a block.
2851           This construct, known from C++, was introduced with ISO C99 and is
2852           by default allowed in GCC.  It is not supported by ISO C90 and was
2853           not supported by GCC versions before GCC 3.0.
2854
2855       -Wundef
2856           Warn if an undefined identifier is evaluated in an #if directive.
2857
2858       -Wno-endif-labels
2859           Do not warn whenever an #else or an #endif are followed by text.
2860
2861       -Wshadow
2862           Warn whenever a local variable shadows another local variable,
2863           parameter or global variable or whenever a built-in function is
2864           shadowed.
2865
2866       -Wlarger-than=len
2867           Warn whenever an object of larger than len bytes is defined.
2868
2869       -Wframe-larger-than=len
2870           Warn if the size of a function frame is larger than len bytes.  The
2871           computation done to determine the stack frame size is approximate
2872           and not conservative.  The actual requirements may be somewhat
2873           greater than len even if you do not get a warning.  In addition,
2874           any space allocated via "alloca", variable-length arrays, or
2875           related constructs is not included by the compiler when determining
2876           whether or not to issue a warning.
2877
2878       -Wunsafe-loop-optimizations
2879           Warn if the loop cannot be optimized because the compiler could not
2880           assume anything on the bounds of the loop indices.  With
2881           -funsafe-loop-optimizations warn if the compiler made such
2882           assumptions.
2883
2884       -Wno-pedantic-ms-format (MinGW targets only)
2885           Disables the warnings about non-ISO "printf" / "scanf" format width
2886           specifiers "I32", "I64", and "I" used on Windows targets depending
2887           on the MS runtime, when you are using the options -Wformat and
2888           -pedantic without gnu-extensions.
2889
2890       -Wpointer-arith
2891           Warn about anything that depends on the "size of" a function type
2892           or of "void".  GNU C assigns these types a size of 1, for
2893           convenience in calculations with "void *" pointers and pointers to
2894           functions.  In C++, warn also when an arithmetic operation involves
2895           "NULL".  This warning is also enabled by -pedantic.
2896
2897       -Wtype-limits
2898           Warn if a comparison is always true or always false due to the
2899           limited range of the data type, but do not warn for constant
2900           expressions.  For example, warn if an unsigned variable is compared
2901           against zero with < or >=.  This warning is also enabled by
2902           -Wextra.
2903
2904       -Wbad-function-cast (C and Objective-C only)
2905           Warn whenever a function call is cast to a non-matching type.  For
2906           example, warn if "int malloc()" is cast to "anything *".
2907
2908       -Wc++-compat (C and Objective-C only)
2909           Warn about ISO C constructs that are outside of the common subset
2910           of ISO C and ISO C++, e.g. request for implicit conversion from
2911           "void *" to a pointer to non-"void" type.
2912
2913       -Wc++0x-compat (C++ and Objective-C++ only)
2914           Warn about C++ constructs whose meaning differs between ISO C++
2915           1998 and ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will
2916           become keywords in ISO C++ 200x.  This warning is enabled by -Wall.
2917
2918       -Wcast-qual
2919           Warn whenever a pointer is cast so as to remove a type qualifier
2920           from the target type.  For example, warn if a "const char *" is
2921           cast to an ordinary "char *".
2922
2923           Also warn when making a cast which introduces a type qualifier in
2924           an unsafe way.  For example, casting "char **" to "const char **"
2925           is unsafe, as in this example:
2926
2927                     /* p is char ** value.  */
2928                     const char **q = (const char **) p;
2929                     /* Assignment of readonly string to const char * is OK.  */
2930                     *q = "string";
2931                     /* Now char** pointer points to read-only memory.  */
2932                     **p = 'b';
2933
2934       -Wcast-align
2935           Warn whenever a pointer is cast such that the required alignment of
2936           the target is increased.  For example, warn if a "char *" is cast
2937           to an "int *" on machines where integers can only be accessed at
2938           two- or four-byte boundaries.
2939
2940       -Wwrite-strings
2941           When compiling C, give string constants the type "const
2942           char[length]" so that copying the address of one into a non-"const"
2943           "char *" pointer will get a warning.  These warnings will help you
2944           find at compile time code that can try to write into a string
2945           constant, but only if you have been very careful about using
2946           "const" in declarations and prototypes.  Otherwise, it will just be
2947           a nuisance. This is why we did not make -Wall request these
2948           warnings.
2949
2950           When compiling C++, warn about the deprecated conversion from
2951           string literals to "char *".  This warning is enabled by default
2952           for C++ programs.
2953
2954       -Wclobbered
2955           Warn for variables that might be changed by longjmp or vfork.  This
2956           warning is also enabled by -Wextra.
2957
2958       -Wconversion
2959           Warn for implicit conversions that may alter a value. This includes
2960           conversions between real and integer, like "abs (x)" when "x" is
2961           "double"; conversions between signed and unsigned, like "unsigned
2962           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
2963           not warn for explicit casts like "abs ((int) x)" and "ui =
2964           (unsigned) -1", or if the value is not changed by the conversion
2965           like in "abs (2.0)".  Warnings about conversions between signed and
2966           unsigned integers can be disabled by using -Wno-sign-conversion.
2967
2968           For C++, also warn for confusing overload resolution for user-
2969           defined conversions; and conversions that will never use a type
2970           conversion operator: conversions to "void", the same type, a base
2971           class or a reference to them. Warnings about conversions between
2972           signed and unsigned integers are disabled by default in C++ unless
2973           -Wsign-conversion is explicitly enabled.
2974
2975       -Wno-conversion-null (C++ and Objective-C++ only)
2976           Do not warn for conversions between "NULL" and non-pointer types.
2977           -Wconversion-null is enabled by default.
2978
2979       -Wempty-body
2980           Warn if an empty body occurs in an if, else or do while statement.
2981           This warning is also enabled by -Wextra.
2982
2983       -Wenum-compare
2984           Warn about a comparison between values of different enum types. In
2985           C++ this warning is enabled by default.  In C this warning is
2986           enabled by -Wall.
2987
2988       -Wjump-misses-init (C, Objective-C only)
2989           Warn if a "goto" statement or a "switch" statement jumps forward
2990           across the initialization of a variable, or jumps backward to a
2991           label after the variable has been initialized.  This only warns
2992           about variables which are initialized when they are declared.  This
2993           warning is only supported for C and Objective C; in C++ this sort
2994           of branch is an error in any case.
2995
2996           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled
2997           with the -Wno-jump-misses-init option.
2998
2999       -Wsign-compare
3000           Warn when a comparison between signed and unsigned values could
3001           produce an incorrect result when the signed value is converted to
3002           unsigned.  This warning is also enabled by -Wextra; to get the
3003           other warnings of -Wextra without this warning, use -Wextra
3004           -Wno-sign-compare.
3005
3006       -Wsign-conversion
3007           Warn for implicit conversions that may change the sign of an
3008           integer value, like assigning a signed integer expression to an
3009           unsigned integer variable. An explicit cast silences the warning.
3010           In C, this option is enabled also by -Wconversion.
3011
3012       -Waddress
3013           Warn about suspicious uses of memory addresses. These include using
3014           the address of a function in a conditional expression, such as
3015           "void func(void); if (func)", and comparisons against the memory
3016           address of a string literal, such as "if (x == "abc")".  Such uses
3017           typically indicate a programmer error: the address of a function
3018           always evaluates to true, so their use in a conditional usually
3019           indicate that the programmer forgot the parentheses in a function
3020           call; and comparisons against string literals result in unspecified
3021           behavior and are not portable in C, so they usually indicate that
3022           the programmer intended to use "strcmp".  This warning is enabled
3023           by -Wall.
3024
3025       -Wlogical-op
3026           Warn about suspicious uses of logical operators in expressions.
3027           This includes using logical operators in contexts where a bit-wise
3028           operator is likely to be expected.
3029
3030       -Waggregate-return
3031           Warn if any functions that return structures or unions are defined
3032           or called.  (In languages where you can return an array, this also
3033           elicits a warning.)
3034
3035       -Wno-attributes
3036           Do not warn if an unexpected "__attribute__" is used, such as
3037           unrecognized attributes, function attributes applied to variables,
3038           etc.  This will not stop errors for incorrect use of supported
3039           attributes.
3040
3041       -Wno-builtin-macro-redefined
3042           Do not warn if certain built-in macros are redefined.  This
3043           suppresses warnings for redefinition of "__TIMESTAMP__",
3044           "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".
3045
3046       -Wstrict-prototypes (C and Objective-C only)
3047           Warn if a function is declared or defined without specifying the
3048           argument types.  (An old-style function definition is permitted
3049           without a warning if preceded by a declaration which specifies the
3050           argument types.)
3051
3052       -Wold-style-declaration (C and Objective-C only)
3053           Warn for obsolescent usages, according to the C Standard, in a
3054           declaration. For example, warn if storage-class specifiers like
3055           "static" are not the first things in a declaration.  This warning
3056           is also enabled by -Wextra.
3057
3058       -Wold-style-definition (C and Objective-C only)
3059           Warn if an old-style function definition is used.  A warning is
3060           given even if there is a previous prototype.
3061
3062       -Wmissing-parameter-type (C and Objective-C only)
3063           A function parameter is declared without a type specifier in
3064           K&R-style functions:
3065
3066                   void foo(bar) { }
3067
3068           This warning is also enabled by -Wextra.
3069
3070       -Wmissing-prototypes (C and Objective-C only)
3071           Warn if a global function is defined without a previous prototype
3072           declaration.  This warning is issued even if the definition itself
3073           provides a prototype.  The aim is to detect global functions that
3074           fail to be declared in header files.
3075
3076       -Wmissing-declarations
3077           Warn if a global function is defined without a previous
3078           declaration.  Do so even if the definition itself provides a
3079           prototype.  Use this option to detect global functions that are not
3080           declared in header files.  In C++, no warnings are issued for
3081           function templates, or for inline functions, or for functions in
3082           anonymous namespaces.
3083
3084       -Wmissing-field-initializers
3085           Warn if a structure's initializer has some fields missing.  For
3086           example, the following code would cause such a warning, because
3087           "x.h" is implicitly zero:
3088
3089                   struct s { int f, g, h; };
3090                   struct s x = { 3, 4 };
3091
3092           This option does not warn about designated initializers, so the
3093           following modification would not trigger a warning:
3094
3095                   struct s { int f, g, h; };
3096                   struct s x = { .f = 3, .g = 4 };
3097
3098           This warning is included in -Wextra.  To get other -Wextra warnings
3099           without this one, use -Wextra -Wno-missing-field-initializers.
3100
3101       -Wmissing-noreturn
3102           Warn about functions which might be candidates for attribute
3103           "noreturn".  Note these are only possible candidates, not absolute
3104           ones.  Care should be taken to manually verify functions actually
3105           do not ever return before adding the "noreturn" attribute,
3106           otherwise subtle code generation bugs could be introduced.  You
3107           will not get a warning for "main" in hosted C environments.
3108
3109       -Wmissing-format-attribute
3110           Warn about function pointers which might be candidates for "format"
3111           attributes.  Note these are only possible candidates, not absolute
3112           ones.  GCC will guess that function pointers with "format"
3113           attributes that are used in assignment, initialization, parameter
3114           passing or return statements should have a corresponding "format"
3115           attribute in the resulting type.  I.e. the left-hand side of the
3116           assignment or initialization, the type of the parameter variable,
3117           or the return type of the containing function respectively should
3118           also have a "format" attribute to avoid the warning.
3119
3120           GCC will also warn about function definitions which might be
3121           candidates for "format" attributes.  Again, these are only possible
3122           candidates.  GCC will guess that "format" attributes might be
3123           appropriate for any function that calls a function like "vprintf"
3124           or "vscanf", but this might not always be the case, and some
3125           functions for which "format" attributes are appropriate may not be
3126           detected.
3127
3128       -Wno-multichar
3129           Do not warn if a multicharacter constant ('FOOF') is used.  Usually
3130           they indicate a typo in the user's code, as they have
3131           implementation-defined values, and should not be used in portable
3132           code.
3133
3134       -Wnormalized=<none|id|nfc|nfkc>
3135           In ISO C and ISO C++, two identifiers are different if they are
3136           different sequences of characters.  However, sometimes when
3137           characters outside the basic ASCII character set are used, you can
3138           have two different character sequences that look the same.  To
3139           avoid confusion, the ISO 10646 standard sets out some normalization
3140           rules which when applied ensure that two sequences that look the
3141           same are turned into the same sequence.  GCC can warn you if you
3142           are using identifiers which have not been normalized; this option
3143           controls that warning.
3144
3145           There are four levels of warning that GCC supports.  The default is
3146           -Wnormalized=nfc, which warns about any identifier which is not in
3147           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
3148           form for most uses.
3149
3150           Unfortunately, there are some characters which ISO C and ISO C++
3151           allow in identifiers that when turned into NFC aren't allowable as
3152           identifiers.  That is, there's no way to use these symbols in
3153           portable ISO C or C++ and have all your identifiers in NFC.
3154           -Wnormalized=id suppresses the warning for these characters.  It is
3155           hoped that future versions of the standards involved will correct
3156           this, which is why this option is not the default.
3157
3158           You can switch the warning off for all characters by writing
3159           -Wnormalized=none.  You would only want to do this if you were
3160           using some other normalization scheme (like "D"), because otherwise
3161           you can easily create bugs that are literally impossible to see.
3162
3163           Some characters in ISO 10646 have distinct meanings but look
3164           identical in some fonts or display methodologies, especially once
3165           formatting has been applied.  For instance "\u207F", "SUPERSCRIPT
3166           LATIN SMALL LETTER N", will display just like a regular "n" which
3167           has been placed in a superscript.  ISO 10646 defines the NFKC
3168           normalization scheme to convert all these into a standard form as
3169           well, and GCC will warn if your code is not in NFKC if you use
3170           -Wnormalized=nfkc.  This warning is comparable to warning about
3171           every identifier that contains the letter O because it might be
3172           confused with the digit 0, and so is not the default, but may be
3173           useful as a local coding convention if the programming environment
3174           is unable to be fixed to display these characters distinctly.
3175
3176       -Wno-deprecated
3177           Do not warn about usage of deprecated features.
3178
3179       -Wno-deprecated-declarations
3180           Do not warn about uses of functions, variables, and types marked as
3181           deprecated by using the "deprecated" attribute.
3182
3183       -Wno-overflow
3184           Do not warn about compile-time overflow in constant expressions.
3185
3186       -Woverride-init (C and Objective-C only)
3187           Warn if an initialized field without side effects is overridden
3188           when using designated initializers.
3189
3190           This warning is included in -Wextra.  To get other -Wextra warnings
3191           without this one, use -Wextra -Wno-override-init.
3192
3193       -Wpacked
3194           Warn if a structure is given the packed attribute, but the packed
3195           attribute has no effect on the layout or size of the structure.
3196           Such structures may be mis-aligned for little benefit.  For
3197           instance, in this code, the variable "f.x" in "struct bar" will be
3198           misaligned even though "struct bar" does not itself have the packed
3199           attribute:
3200
3201                   struct foo {
3202                     int x;
3203                     char a, b, c, d;
3204                   } __attribute__((packed));
3205                   struct bar {
3206                     char z;
3207                     struct foo f;
3208                   };
3209
3210       -Wpacked-bitfield-compat
3211           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
3212           bit-fields of type "char".  This has been fixed in GCC 4.4 but the
3213           change can lead to differences in the structure layout.  GCC
3214           informs you when the offset of such a field has changed in GCC 4.4.
3215           For example there is no longer a 4-bit padding between field "a"
3216           and "b" in this structure:
3217
3218                   struct foo
3219                   {
3220                     char a:4;
3221                     char b:8;
3222                   } __attribute__ ((packed));
3223
3224           This warning is enabled by default.  Use
3225           -Wno-packed-bitfield-compat to disable this warning.
3226
3227       -Wpadded
3228           Warn if padding is included in a structure, either to align an
3229           element of the structure or to align the whole structure.
3230           Sometimes when this happens it is possible to rearrange the fields
3231           of the structure to reduce the padding and so make the structure
3232           smaller.
3233
3234       -Wredundant-decls
3235           Warn if anything is declared more than once in the same scope, even
3236           in cases where multiple declaration is valid and changes nothing.
3237
3238       -Wnested-externs (C and Objective-C only)
3239           Warn if an "extern" declaration is encountered within a function.
3240
3241       -Winline
3242           Warn if a function can not be inlined and it was declared as
3243           inline.  Even with this option, the compiler will not warn about
3244           failures to inline functions declared in system headers.
3245
3246           The compiler uses a variety of heuristics to determine whether or
3247           not to inline a function.  For example, the compiler takes into
3248           account the size of the function being inlined and the amount of
3249           inlining that has already been done in the current function.
3250           Therefore, seemingly insignificant changes in the source program
3251           can cause the warnings produced by -Winline to appear or disappear.
3252
3253       -Wno-invalid-offsetof (C++ and Objective-C++ only)
3254           Suppress warnings from applying the offsetof macro to a non-POD
3255           type.  According to the 1998 ISO C++ standard, applying offsetof to
3256           a non-POD type is undefined.  In existing C++ implementations,
3257           however, offsetof typically gives meaningful results even when
3258           applied to certain kinds of non-POD types. (Such as a simple struct
3259           that fails to be a POD type only by virtue of having a
3260           constructor.)  This flag is for users who are aware that they are
3261           writing nonportable code and who have deliberately chosen to ignore
3262           the warning about it.
3263
3264           The restrictions on offsetof may be relaxed in a future version of
3265           the C++ standard.
3266
3267       -Wno-int-to-pointer-cast (C and Objective-C only)
3268           Suppress warnings from casts to pointer type of an integer of a
3269           different size.
3270
3271       -Wno-pointer-to-int-cast (C and Objective-C only)
3272           Suppress warnings from casts from a pointer to an integer type of a
3273           different size.
3274
3275       -Winvalid-pch
3276           Warn if a precompiled header is found in the search path but can't
3277           be used.
3278
3279       -Wlong-long
3280           Warn if long long type is used.  This is enabled by either
3281           -pedantic or -Wtraditional in ISO C90 and C++98 modes.  To inhibit
3282           the warning messages, use -Wno-long-long.
3283
3284       -Wvariadic-macros
3285           Warn if variadic macros are used in pedantic ISO C90 mode, or the
3286           GNU alternate syntax when in pedantic ISO C99 mode.  This is
3287           default.  To inhibit the warning messages, use
3288           -Wno-variadic-macros.
3289
3290       -Wvla
3291           Warn if variable length array is used in the code.  -Wno-vla will
3292           prevent the -pedantic warning of the variable length array.
3293
3294       -Wvolatile-register-var
3295           Warn if a register variable is declared volatile.  The volatile
3296           modifier does not inhibit all optimizations that may eliminate
3297           reads and/or writes to register variables.  This warning is enabled
3298           by -Wall.
3299
3300       -Wdisabled-optimization
3301           Warn if a requested optimization pass is disabled.  This warning
3302           does not generally indicate that there is anything wrong with your
3303           code; it merely indicates that GCC's optimizers were unable to
3304           handle the code effectively.  Often, the problem is that your code
3305           is too big or too complex; GCC will refuse to optimize programs
3306           when the optimization itself is likely to take inordinate amounts
3307           of time.
3308
3309       -Wpointer-sign (C and Objective-C only)
3310           Warn for pointer argument passing or assignment with different
3311           signedness.  This option is only supported for C and Objective-C.
3312           It is implied by -Wall and by -pedantic, which can be disabled with
3313           -Wno-pointer-sign.
3314
3315       -Wstack-protector
3316           This option is only active when -fstack-protector is active.  It
3317           warns about functions that will not be protected against stack
3318           smashing.
3319
3320       -Wno-mudflap
3321           Suppress warnings about constructs that cannot be instrumented by
3322           -fmudflap.
3323
3324       -Woverlength-strings
3325           Warn about string constants which are longer than the "minimum
3326           maximum" length specified in the C standard.  Modern compilers
3327           generally allow string constants which are much longer than the
3328           standard's minimum limit, but very portable programs should avoid
3329           using longer strings.
3330
3331           The limit applies after string constant concatenation, and does not
3332           count the trailing NUL.  In C90, the limit was 509 characters; in
3333           C99, it was raised to 4095.  C++98 does not specify a normative
3334           minimum maximum, so we do not diagnose overlength strings in C++.
3335
3336           This option is implied by -pedantic, and can be disabled with
3337           -Wno-overlength-strings.
3338
3339       -Wunsuffixed-float-constants (C and Objective-C only)
3340           GCC will issue a warning for any floating constant that does not
3341           have a suffix.  When used together with -Wsystem-headers it will
3342           warn about such constants in system header files.  This can be
3343           useful when preparing code to use with the "FLOAT_CONST_DECIMAL64"
3344           pragma from the decimal floating-point extension to C99.
3345
3346   Options for Debugging Your Program or GCC
3347       GCC has various special options that are used for debugging either your
3348       program or GCC:
3349
3350       -g  Produce debugging information in the operating system's native
3351           format (stabs, COFF, XCOFF, or DWARF 2).  GDB can work with this
3352           debugging information.
3353
3354           On most systems that use stabs format, -g enables use of extra
3355           debugging information that only GDB can use; this extra information
3356           makes debugging work better in GDB but will probably make other
3357           debuggers crash or refuse to read the program.  If you want to
3358           control for certain whether to generate the extra information, use
3359           -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
3360
3361           GCC allows you to use -g with -O.  The shortcuts taken by optimized
3362           code may occasionally produce surprising results: some variables
3363           you declared may not exist at all; flow of control may briefly move
3364           where you did not expect it; some statements may not be executed
3365           because they compute constant results or their values were already
3366           at hand; some statements may execute in different places because
3367           they were moved out of loops.
3368
3369           Nevertheless it proves possible to debug optimized output.  This
3370           makes it reasonable to use the optimizer for programs that might
3371           have bugs.
3372
3373           The following options are useful when GCC is generated with the
3374           capability for more than one debugging format.
3375
3376       -ggdb
3377           Produce debugging information for use by GDB.  This means to use
3378           the most expressive format available (DWARF 2, stabs, or the native
3379           format if neither of those are supported), including GDB extensions
3380           if at all possible.
3381
3382       -gstabs
3383           Produce debugging information in stabs format (if that is
3384           supported), without GDB extensions.  This is the format used by DBX
3385           on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
3386           this option produces stabs debugging output which is not understood
3387           by DBX or SDB.  On System V Release 4 systems this option requires
3388           the GNU assembler.
3389
3390       -feliminate-unused-debug-symbols
3391           Produce debugging information in stabs format (if that is
3392           supported), for only symbols that are actually used.
3393
3394       -femit-class-debug-always
3395           Instead of emitting debugging information for a C++ class in only
3396           one object file, emit it in all object files using the class.  This
3397           option should be used only with debuggers that are unable to handle
3398           the way GCC normally emits debugging information for classes
3399           because using this option will increase the size of debugging
3400           information by as much as a factor of two.
3401
3402       -gstabs+
3403           Produce debugging information in stabs format (if that is
3404           supported), using GNU extensions understood only by the GNU
3405           debugger (GDB).  The use of these extensions is likely to make
3406           other debuggers crash or refuse to read the program.
3407
3408       -gcoff
3409           Produce debugging information in COFF format (if that is
3410           supported).  This is the format used by SDB on most System V
3411           systems prior to System V Release 4.
3412
3413       -gxcoff
3414           Produce debugging information in XCOFF format (if that is
3415           supported).  This is the format used by the DBX debugger on IBM
3416           RS/6000 systems.
3417
3418       -gxcoff+
3419           Produce debugging information in XCOFF format (if that is
3420           supported), using GNU extensions understood only by the GNU
3421           debugger (GDB).  The use of these extensions is likely to make
3422           other debuggers crash or refuse to read the program, and may cause
3423           assemblers other than the GNU assembler (GAS) to fail with an
3424           error.
3425
3426       -gdwarf-version
3427           Produce debugging information in DWARF format (if that is
3428           supported).  This is the format used by DBX on IRIX 6.  The value
3429           of version may be either 2, 3 or 4; the default version is 2.
3430
3431           Note that with DWARF version 2 some ports require, and will always
3432           use, some non-conflicting DWARF 3 extensions in the unwind tables.
3433
3434           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for
3435           maximum benefit.
3436
3437       -gstrict-dwarf
3438           Disallow using extensions of later DWARF standard version than
3439           selected with -gdwarf-version.  On most targets using non-
3440           conflicting DWARF extensions from later standard versions is
3441           allowed.
3442
3443       -gno-strict-dwarf
3444           Allow using extensions of later DWARF standard version than
3445           selected with -gdwarf-version.
3446
3447       -gvms
3448           Produce debugging information in VMS debug format (if that is
3449           supported).  This is the format used by DEBUG on VMS systems.
3450
3451       -glevel
3452       -ggdblevel
3453       -gstabslevel
3454       -gcofflevel
3455       -gxcofflevel
3456       -gvmslevel
3457           Request debugging information and also use level to specify how
3458           much information.  The default level is 2.
3459
3460           Level 0 produces no debug information at all.  Thus, -g0 negates
3461           -g.
3462
3463           Level 1 produces minimal information, enough for making backtraces
3464           in parts of the program that you don't plan to debug.  This
3465           includes descriptions of functions and external variables, but no
3466           information about local variables and no line numbers.
3467
3468           Level 3 includes extra information, such as all the macro
3469           definitions present in the program.  Some debuggers support macro
3470           expansion when you use -g3.
3471
3472           -gdwarf-2 does not accept a concatenated debug level, because GCC
3473           used to support an option -gdwarf that meant to generate debug
3474           information in version 1 of the DWARF format (which is very
3475           different from version 2), and it would have been too confusing.
3476           That debug format is long obsolete, but the option cannot be
3477           changed now.  Instead use an additional -glevel option to change
3478           the debug level for DWARF.
3479
3480       -gtoggle
3481           Turn off generation of debug info, if leaving out this option would
3482           have generated it, or turn it on at level 2 otherwise.  The
3483           position of this argument in the command line does not matter, it
3484           takes effect after all other options are processed, and it does so
3485           only once, no matter how many times it is given.  This is mainly
3486           intended to be used with -fcompare-debug.
3487
3488       -fdump-final-insns[=file]
3489           Dump the final internal representation (RTL) to file.  If the
3490           optional argument is omitted (or if file is "."), the name of the
3491           dump file will be determined by appending ".gkd" to the compilation
3492           output file name.
3493
3494       -fcompare-debug[=opts]
3495           If no error occurs during compilation, run the compiler a second
3496           time, adding opts and -fcompare-debug-second to the arguments
3497           passed to the second compilation.  Dump the final internal
3498           representation in both compilations, and print an error if they
3499           differ.
3500
3501           If the equal sign is omitted, the default -gtoggle is used.
3502
3503           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
3504           and nonzero, implicitly enables -fcompare-debug.  If
3505           GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
3506           it is used for opts, otherwise the default -gtoggle is used.
3507
3508           -fcompare-debug=, with the equal sign but without opts, is
3509           equivalent to -fno-compare-debug, which disables the dumping of the
3510           final representation and the second compilation, preventing even
3511           GCC_COMPARE_DEBUG from taking effect.
3512
3513           To verify full coverage during -fcompare-debug testing, set
3514           GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC
3515           will reject as an invalid option in any actual compilation (rather
3516           than preprocessing, assembly or linking).  To get just a warning,
3517           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
3518           will do.
3519
3520       -fcompare-debug-second
3521           This option is implicitly passed to the compiler for the second
3522           compilation requested by -fcompare-debug, along with options to
3523           silence warnings, and omitting other options that would cause side-
3524           effect compiler outputs to files or to the standard output.  Dump
3525           files and preserved temporary files are renamed so as to contain
3526           the ".gk" additional extension during the second compilation, to
3527           avoid overwriting those generated by the first.
3528
3529           When this option is passed to the compiler driver, it causes the
3530           first compilation to be skipped, which makes it useful for little
3531           other than debugging the compiler proper.
3532
3533       -feliminate-dwarf2-dups
3534           Compress DWARF2 debugging information by eliminating duplicated
3535           information about each symbol.  This option only makes sense when
3536           generating DWARF2 debugging information with -gdwarf-2.
3537
3538       -femit-struct-debug-baseonly
3539           Emit debug information for struct-like types only when the base
3540           name of the compilation source file matches the base name of file
3541           in which the struct was defined.
3542
3543           This option substantially reduces the size of debugging
3544           information, but at significant potential loss in type information
3545           to the debugger.  See -femit-struct-debug-reduced for a less
3546           aggressive option.  See -femit-struct-debug-detailed for more
3547           detailed control.
3548
3549           This option works only with DWARF 2.
3550
3551       -femit-struct-debug-reduced
3552           Emit debug information for struct-like types only when the base
3553           name of the compilation source file matches the base name of file
3554           in which the type was defined, unless the struct is a template or
3555           defined in a system header.
3556
3557           This option significantly reduces the size of debugging
3558           information, with some potential loss in type information to the
3559           debugger.  See -femit-struct-debug-baseonly for a more aggressive
3560           option.  See -femit-struct-debug-detailed for more detailed
3561           control.
3562
3563           This option works only with DWARF 2.
3564
3565       -femit-struct-debug-detailed[=spec-list]
3566           Specify the struct-like types for which the compiler will generate
3567           debug information.  The intent is to reduce duplicate struct debug
3568           information between different object files within the same program.
3569
3570           This option is a detailed version of -femit-struct-debug-reduced
3571           and -femit-struct-debug-baseonly, which will serve for most needs.
3572
3573           A specification has the syntax
3574           [dir:|ind:][ord:|gen:](any|sys|base|none)
3575
3576           The optional first word limits the specification to structs that
3577           are used directly (dir:) or used indirectly (ind:).  A struct type
3578           is used directly when it is the type of a variable, member.
3579           Indirect uses arise through pointers to structs.  That is, when use
3580           of an incomplete struct would be legal, the use is indirect.  An
3581           example is struct one direct; struct two * indirect;.
3582
3583           The optional second word limits the specification to ordinary
3584           structs (ord:) or generic structs (gen:).  Generic structs are a
3585           bit complicated to explain.  For C++, these are non-explicit
3586           specializations of template classes, or non-template classes within
3587           the above.  Other programming languages have generics, but
3588           -femit-struct-debug-detailed does not yet implement them.
3589
3590           The third word specifies the source files for those structs for
3591           which the compiler will emit debug information.  The values none
3592           and any have the normal meaning.  The value base means that the
3593           base of name of the file in which the type declaration appears must
3594           match the base of the name of the main compilation file.  In
3595           practice, this means that types declared in foo.c and foo.h will
3596           have debug information, but types declared in other header will
3597           not.  The value sys means those types satisfying base or declared
3598           in system or compiler headers.
3599
3600           You may need to experiment to determine the best settings for your
3601           application.
3602
3603           The default is -femit-struct-debug-detailed=all.
3604
3605           This option works only with DWARF 2.
3606
3607       -fenable-icf-debug
3608           Generate additional debug information to support identical code
3609           folding (ICF).  This option only works with DWARF version 2 or
3610           higher.
3611
3612       -fno-merge-debug-strings
3613           Direct the linker to not merge together strings in the debugging
3614           information which are identical in different object files.  Merging
3615           is not supported by all assemblers or linkers.  Merging decreases
3616           the size of the debug information in the output file at the cost of
3617           increasing link processing time.  Merging is enabled by default.
3618
3619       -fdebug-prefix-map=old=new
3620           When compiling files in directory old, record debugging information
3621           describing them as in new instead.
3622
3623       -fno-dwarf2-cfi-asm
3624           Emit DWARF 2 unwind info as compiler generated ".eh_frame" section
3625           instead of using GAS ".cfi_*" directives.
3626
3627       -p  Generate extra code to write profile information suitable for the
3628           analysis program prof.  You must use this option when compiling the
3629           source files you want data about, and you must also use it when
3630           linking.
3631
3632       -pg Generate extra code to write profile information suitable for the
3633           analysis program gprof.  You must use this option when compiling
3634           the source files you want data about, and you must also use it when
3635           linking.
3636
3637       -Q  Makes the compiler print out each function name as it is compiled,
3638           and print some statistics about each pass when it finishes.
3639
3640       -ftime-report
3641           Makes the compiler print some statistics about the time consumed by
3642           each pass when it finishes.
3643
3644       -fmem-report
3645           Makes the compiler print some statistics about permanent memory
3646           allocation when it finishes.
3647
3648       -fpre-ipa-mem-report
3649       -fpost-ipa-mem-report
3650           Makes the compiler print some statistics about permanent memory
3651           allocation before or after interprocedural optimization.
3652
3653       -fprofile-arcs
3654           Add code so that program flow arcs are instrumented.  During
3655           execution the program records how many times each branch and call
3656           is executed and how many times it is taken or returns.  When the
3657           compiled program exits it saves this data to a file called
3658           auxname.gcda for each source file.  The data may be used for
3659           profile-directed optimizations (-fbranch-probabilities), or for
3660           test coverage analysis (-ftest-coverage).  Each object file's
3661           auxname is generated from the name of the output file, if
3662           explicitly specified and it is not the final executable, otherwise
3663           it is the basename of the source file.  In both cases any suffix is
3664           removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda
3665           for output file specified as -o dir/foo.o).
3666
3667       --coverage
3668           This option is used to compile and link code instrumented for
3669           coverage analysis.  The option is a synonym for -fprofile-arcs
3670           -ftest-coverage (when compiling) and -lgcov (when linking).  See
3671           the documentation for those options for more details.
3672
3673           ·   Compile the source files with -fprofile-arcs plus optimization
3674               and code generation options.  For test coverage analysis, use
3675               the additional -ftest-coverage option.  You do not need to
3676               profile every source file in a program.
3677
3678           ·   Link your object files with -lgcov or -fprofile-arcs (the
3679               latter implies the former).
3680
3681           ·   Run the program on a representative workload to generate the
3682               arc profile information.  This may be repeated any number of
3683               times.  You can run concurrent instances of your program, and
3684               provided that the file system supports locking, the data files
3685               will be correctly updated.  Also "fork" calls are detected and
3686               correctly handled (double counting will not happen).
3687
3688           ·   For profile-directed optimizations, compile the source files
3689               again with the same optimization and code generation options
3690               plus -fbranch-probabilities.
3691
3692           ·   For test coverage analysis, use gcov to produce human readable
3693               information from the .gcno and .gcda files.  Refer to the gcov
3694               documentation for further information.
3695
3696           With -fprofile-arcs, for each function of your program GCC creates
3697           a program flow graph, then finds a spanning tree for the graph.
3698           Only arcs that are not on the spanning tree have to be
3699           instrumented: the compiler adds code to count the number of times
3700           that these arcs are executed.  When an arc is the only exit or only
3701           entrance to a block, the instrumentation code can be added to the
3702           block; otherwise, a new basic block must be created to hold the
3703           instrumentation code.
3704
3705       -ftest-coverage
3706           Produce a notes file that the gcov code-coverage utility can use to
3707           show program coverage.  Each source file's note file is called
3708           auxname.gcno.  Refer to the -fprofile-arcs option above for a
3709           description of auxname and instructions on how to generate test
3710           coverage data.  Coverage data will match the source files more
3711           closely, if you do not optimize.
3712
3713       -fdbg-cnt-list
3714           Print the name and the counter upperbound for all debug counters.
3715
3716       -fdbg-cnt=counter-value-list
3717           Set the internal debug counter upperbound. counter-value-list is a
3718           comma-separated list of name:value pairs which sets the upperbound
3719           of each debug counter name to value.  All debug counters have the
3720           initial upperbound of UINT_MAX, thus dbg_cnt() returns true always
3721           unless the upperbound is set by this option.  e.g. With
3722           -fdbg-cnt=dce:10,tail_call:0 dbg_cnt(dce) will return true only for
3723           first 10 invocations and dbg_cnt(tail_call) will return false
3724           always.
3725
3726       -dletters
3727       -fdump-rtl-pass
3728           Says to make debugging dumps during compilation at times specified
3729           by letters.  This is used for debugging the RTL-based passes of the
3730           compiler.  The file names for most of the dumps are made by
3731           appending a pass number and a word to the dumpname, and the files
3732           are created in the directory of the output file.  dumpname is
3733           generated from the name of the output file, if explicitly specified
3734           and it is not an executable, otherwise it is the basename of the
3735           source file. These switches may have different effects when -E is
3736           used for preprocessing.
3737
3738           Debug dumps can be enabled with a -fdump-rtl switch or some -d
3739           option letters.  Here are the possible letters for use in pass and
3740           letters, and their meanings:
3741
3742           -fdump-rtl-alignments
3743               Dump after branch alignments have been computed.
3744
3745           -fdump-rtl-asmcons
3746               Dump after fixing rtl statements that have unsatisfied in/out
3747               constraints.
3748
3749           -fdump-rtl-auto_inc_dec
3750               Dump after auto-inc-dec discovery.  This pass is only run on
3751               architectures that have auto inc or auto dec instructions.
3752
3753           -fdump-rtl-barriers
3754               Dump after cleaning up the barrier instructions.
3755
3756           -fdump-rtl-bbpart
3757               Dump after partitioning hot and cold basic blocks.
3758
3759           -fdump-rtl-bbro
3760               Dump after block reordering.
3761
3762           -fdump-rtl-btl1
3763           -fdump-rtl-btl2
3764               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
3765               two branch target load optimization passes.
3766
3767           -fdump-rtl-bypass
3768               Dump after jump bypassing and control flow optimizations.
3769
3770           -fdump-rtl-combine
3771               Dump after the RTL instruction combination pass.
3772
3773           -fdump-rtl-compgotos
3774               Dump after duplicating the computed gotos.
3775
3776           -fdump-rtl-ce1
3777           -fdump-rtl-ce2
3778           -fdump-rtl-ce3
3779               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
3780               dumping after the three if conversion passes.
3781
3782           -fdump-rtl-cprop_hardreg
3783               Dump after hard register copy propagation.
3784
3785           -fdump-rtl-csa
3786               Dump after combining stack adjustments.
3787
3788           -fdump-rtl-cse1
3789           -fdump-rtl-cse2
3790               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
3791               two common sub-expression elimination passes.
3792
3793           -fdump-rtl-dce
3794               Dump after the standalone dead code elimination passes.
3795
3796           -fdump-rtl-dbr
3797               Dump after delayed branch scheduling.
3798
3799           -fdump-rtl-dce1
3800           -fdump-rtl-dce2
3801               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
3802               two dead store elimination passes.
3803
3804           -fdump-rtl-eh
3805               Dump after finalization of EH handling code.
3806
3807           -fdump-rtl-eh_ranges
3808               Dump after conversion of EH handling range regions.
3809
3810           -fdump-rtl-expand
3811               Dump after RTL generation.
3812
3813           -fdump-rtl-fwprop1
3814           -fdump-rtl-fwprop2
3815               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
3816               the two forward propagation passes.
3817
3818           -fdump-rtl-gcse1
3819           -fdump-rtl-gcse2
3820               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
3821               global common subexpression elimination.
3822
3823           -fdump-rtl-init-regs
3824               Dump after the initialization of the registers.
3825
3826           -fdump-rtl-initvals
3827               Dump after the computation of the initial value sets.
3828
3829           -fdump-rtl-into_cfglayout
3830               Dump after converting to cfglayout mode.
3831
3832           -fdump-rtl-ira
3833               Dump after iterated register allocation.
3834
3835           -fdump-rtl-jump
3836               Dump after the second jump optimization.
3837
3838           -fdump-rtl-loop2
3839               -fdump-rtl-loop2 enables dumping after the rtl loop
3840               optimization passes.
3841
3842           -fdump-rtl-mach
3843               Dump after performing the machine dependent reorganization
3844               pass, if that pass exists.
3845
3846           -fdump-rtl-mode_sw
3847               Dump after removing redundant mode switches.
3848
3849           -fdump-rtl-rnreg
3850               Dump after register renumbering.
3851
3852           -fdump-rtl-outof_cfglayout
3853               Dump after converting from cfglayout mode.
3854
3855           -fdump-rtl-peephole2
3856               Dump after the peephole pass.
3857
3858           -fdump-rtl-postreload
3859               Dump after post-reload optimizations.
3860
3861           -fdump-rtl-pro_and_epilogue
3862               Dump after generating the function pro and epilogues.
3863
3864           -fdump-rtl-regmove
3865               Dump after the register move pass.
3866
3867           -fdump-rtl-sched1
3868           -fdump-rtl-sched2
3869               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
3870               the basic block scheduling passes.
3871
3872           -fdump-rtl-see
3873               Dump after sign extension elimination.
3874
3875           -fdump-rtl-seqabstr
3876               Dump after common sequence discovery.
3877
3878           -fdump-rtl-shorten
3879               Dump after shortening branches.
3880
3881           -fdump-rtl-sibling
3882               Dump after sibling call optimizations.
3883
3884           -fdump-rtl-split1
3885           -fdump-rtl-split2
3886           -fdump-rtl-split3
3887           -fdump-rtl-split4
3888           -fdump-rtl-split5
3889               -fdump-rtl-split1, -fdump-rtl-split2, -fdump-rtl-split3,
3890               -fdump-rtl-split4 and -fdump-rtl-split5 enable dumping after
3891               five rounds of instruction splitting.
3892
3893           -fdump-rtl-sms
3894               Dump after modulo scheduling.  This pass is only run on some
3895               architectures.
3896
3897           -fdump-rtl-stack
3898               Dump after conversion from GCC's "flat register file" registers
3899               to the x87's stack-like registers.  This pass is only run on
3900               x86 variants.
3901
3902           -fdump-rtl-subreg1
3903           -fdump-rtl-subreg2
3904               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
3905               the two subreg expansion passes.
3906
3907           -fdump-rtl-unshare
3908               Dump after all rtl has been unshared.
3909
3910           -fdump-rtl-vartrack
3911               Dump after variable tracking.
3912
3913           -fdump-rtl-vregs
3914               Dump after converting virtual registers to hard registers.
3915
3916           -fdump-rtl-web
3917               Dump after live range splitting.
3918
3919           -fdump-rtl-regclass
3920           -fdump-rtl-subregs_of_mode_init
3921           -fdump-rtl-subregs_of_mode_finish
3922           -fdump-rtl-dfinit
3923           -fdump-rtl-dfinish
3924               These dumps are defined but always produce empty files.
3925
3926           -fdump-rtl-all
3927               Produce all the dumps listed above.
3928
3929           -dA Annotate the assembler output with miscellaneous debugging
3930               information.
3931
3932           -dD Dump all macro definitions, at the end of preprocessing, in
3933               addition to normal output.
3934
3935           -dH Produce a core dump whenever an error occurs.
3936
3937           -dm Print statistics on memory usage, at the end of the run, to
3938               standard error.
3939
3940           -dp Annotate the assembler output with a comment indicating which
3941               pattern and alternative was used.  The length of each
3942               instruction is also printed.
3943
3944           -dP Dump the RTL in the assembler output as a comment before each
3945               instruction.  Also turns on -dp annotation.
3946
3947           -dv For each of the other indicated dump files (-fdump-rtl-pass),
3948               dump a representation of the control flow graph suitable for
3949               viewing with VCG to file.pass.vcg.
3950
3951           -dx Just generate RTL for a function instead of compiling it.
3952               Usually used with -fdump-rtl-expand.
3953
3954           -dy Dump debugging information during parsing, to standard error.
3955
3956       -fdump-noaddr
3957           When doing debugging dumps, suppress address output.  This makes it
3958           more feasible to use diff on debugging dumps for compiler
3959           invocations with different compiler binaries and/or different text
3960           / bss / data / heap / stack / dso start locations.
3961
3962       -fdump-unnumbered
3963           When doing debugging dumps, suppress instruction numbers and
3964           address output.  This makes it more feasible to use diff on
3965           debugging dumps for compiler invocations with different options, in
3966           particular with and without -g.
3967
3968       -fdump-unnumbered-links
3969           When doing debugging dumps (see -d option above), suppress
3970           instruction numbers for the links to the previous and next
3971           instructions in a sequence.
3972
3973       -fdump-translation-unit (C++ only)
3974       -fdump-translation-unit-options (C++ only)
3975           Dump a representation of the tree structure for the entire
3976           translation unit to a file.  The file name is made by appending .tu
3977           to the source file name, and the file is created in the same
3978           directory as the output file.  If the -options form is used,
3979           options controls the details of the dump as described for the
3980           -fdump-tree options.
3981
3982       -fdump-class-hierarchy (C++ only)
3983       -fdump-class-hierarchy-options (C++ only)
3984           Dump a representation of each class's hierarchy and virtual
3985           function table layout to a file.  The file name is made by
3986           appending .class to the source file name, and the file is created
3987           in the same directory as the output file.  If the -options form is
3988           used, options controls the details of the dump as described for the
3989           -fdump-tree options.
3990
3991       -fdump-ipa-switch
3992           Control the dumping at various stages of inter-procedural analysis
3993           language tree to a file.  The file name is generated by appending a
3994           switch specific suffix to the source file name, and the file is
3995           created in the same directory as the output file.  The following
3996           dumps are possible:
3997
3998           all Enables all inter-procedural analysis dumps.
3999
4000           cgraph
4001               Dumps information about call-graph optimization, unused
4002               function removal, and inlining decisions.
4003
4004           inline
4005               Dump after function inlining.
4006
4007       -fdump-statistics-option
4008           Enable and control dumping of pass statistics in a separate file.
4009           The file name is generated by appending a suffix ending in
4010           .statistics to the source file name, and the file is created in the
4011           same directory as the output file.  If the -option form is used,
4012           -stats will cause counters to be summed over the whole compilation
4013           unit while -details will dump every event as the passes generate
4014           them.  The default with no option is to sum counters for each
4015           function compiled.
4016
4017       -fdump-tree-switch
4018       -fdump-tree-switch-options
4019           Control the dumping at various stages of processing the
4020           intermediate language tree to a file.  The file name is generated
4021           by appending a switch specific suffix to the source file name, and
4022           the file is created in the same directory as the output file.  If
4023           the -options form is used, options is a list of - separated options
4024           that control the details of the dump.  Not all options are
4025           applicable to all dumps, those which are not meaningful will be
4026           ignored.  The following options are available
4027
4028           address
4029               Print the address of each node.  Usually this is not meaningful
4030               as it changes according to the environment and source file.
4031               Its primary use is for tying up a dump file with a debug
4032               environment.
4033
4034           asmname
4035               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
4036               that in the dump instead of "DECL_NAME".  Its primary use is
4037               ease of use working backward from mangled names in the assembly
4038               file.
4039
4040           slim
4041               Inhibit dumping of members of a scope or body of a function
4042               merely because that scope has been reached.  Only dump such
4043               items when they are directly reachable by some other path.
4044               When dumping pretty-printed trees, this option inhibits dumping
4045               the bodies of control structures.
4046
4047           raw Print a raw representation of the tree.  By default, trees are
4048               pretty-printed into a C-like representation.
4049
4050           details
4051               Enable more detailed dumps (not honored by every dump option).
4052
4053           stats
4054               Enable dumping various statistics about the pass (not honored
4055               by every dump option).
4056
4057           blocks
4058               Enable showing basic block boundaries (disabled in raw dumps).
4059
4060           vops
4061               Enable showing virtual operands for every statement.
4062
4063           lineno
4064               Enable showing line numbers for statements.
4065
4066           uid Enable showing the unique ID ("DECL_UID") for each variable.
4067
4068           verbose
4069               Enable showing the tree dump for each statement.
4070
4071           eh  Enable showing the EH region number holding each statement.
4072
4073           all Turn on all options, except raw, slim, verbose and lineno.
4074
4075           The following tree dumps are possible:
4076
4077           original
4078               Dump before any tree based optimization, to file.original.
4079
4080           optimized
4081               Dump after all tree based optimization, to file.optimized.
4082
4083           gimple
4084               Dump each function before and after the gimplification pass to
4085               a file.  The file name is made by appending .gimple to the
4086               source file name.
4087
4088           cfg Dump the control flow graph of each function to a file.  The
4089               file name is made by appending .cfg to the source file name.
4090
4091           vcg Dump the control flow graph of each function to a file in VCG
4092               format.  The file name is made by appending .vcg to the source
4093               file name.  Note that if the file contains more than one
4094               function, the generated file cannot be used directly by VCG.
4095               You will need to cut and paste each function's graph into its
4096               own separate file first.
4097
4098           ch  Dump each function after copying loop headers.  The file name
4099               is made by appending .ch to the source file name.
4100
4101           ssa Dump SSA related information to a file.  The file name is made
4102               by appending .ssa to the source file name.
4103
4104           alias
4105               Dump aliasing information for each function.  The file name is
4106               made by appending .alias to the source file name.
4107
4108           ccp Dump each function after CCP.  The file name is made by
4109               appending .ccp to the source file name.
4110
4111           storeccp
4112               Dump each function after STORE-CCP.  The file name is made by
4113               appending .storeccp to the source file name.
4114
4115           pre Dump trees after partial redundancy elimination.  The file name
4116               is made by appending .pre to the source file name.
4117
4118           fre Dump trees after full redundancy elimination.  The file name is
4119               made by appending .fre to the source file name.
4120
4121           copyprop
4122               Dump trees after copy propagation.  The file name is made by
4123               appending .copyprop to the source file name.
4124
4125           store_copyprop
4126               Dump trees after store copy-propagation.  The file name is made
4127               by appending .store_copyprop to the source file name.
4128
4129           dce Dump each function after dead code elimination.  The file name
4130               is made by appending .dce to the source file name.
4131
4132           mudflap
4133               Dump each function after adding mudflap instrumentation.  The
4134               file name is made by appending .mudflap to the source file
4135               name.
4136
4137           sra Dump each function after performing scalar replacement of
4138               aggregates.  The file name is made by appending .sra to the
4139               source file name.
4140
4141           sink
4142               Dump each function after performing code sinking.  The file
4143               name is made by appending .sink to the source file name.
4144
4145           dom Dump each function after applying dominator tree optimizations.
4146               The file name is made by appending .dom to the source file
4147               name.
4148
4149           dse Dump each function after applying dead store elimination.  The
4150               file name is made by appending .dse to the source file name.
4151
4152           phiopt
4153               Dump each function after optimizing PHI nodes into straightline
4154               code.  The file name is made by appending .phiopt to the source
4155               file name.
4156
4157           forwprop
4158               Dump each function after forward propagating single use
4159               variables.  The file name is made by appending .forwprop to the
4160               source file name.
4161
4162           copyrename
4163               Dump each function after applying the copy rename optimization.
4164               The file name is made by appending .copyrename to the source
4165               file name.
4166
4167           nrv Dump each function after applying the named return value
4168               optimization on generic trees.  The file name is made by
4169               appending .nrv to the source file name.
4170
4171           vect
4172               Dump each function after applying vectorization of loops.  The
4173               file name is made by appending .vect to the source file name.
4174
4175           slp Dump each function after applying vectorization of basic
4176               blocks.  The file name is made by appending .slp to the source
4177               file name.
4178
4179           vrp Dump each function after Value Range Propagation (VRP).  The
4180               file name is made by appending .vrp to the source file name.
4181
4182           all Enable all the available tree dumps with the flags provided in
4183               this option.
4184
4185       -ftree-vectorizer-verbose=n
4186           This option controls the amount of debugging output the vectorizer
4187           prints.  This information is written to standard error, unless
4188           -fdump-tree-all or -fdump-tree-vect is specified, in which case it
4189           is output to the usual dump listing file, .vect.  For n=0 no
4190           diagnostic information is reported.  If n=1 the vectorizer reports
4191           each loop that got vectorized, and the total number of loops that
4192           got vectorized.  If n=2 the vectorizer also reports non-vectorized
4193           loops that passed the first analysis phase (vect_analyze_loop_form)
4194           - i.e. countable, inner-most, single-bb, single-entry/exit loops.
4195           This is the same verbosity level that -fdump-tree-vect-stats uses.
4196           Higher verbosity levels mean either more information dumped for
4197           each reported loop, or same amount of information reported for more
4198           loops: if n=3, vectorizer cost model information is reported.  If
4199           n=4, alignment related information is added to the reports.  If
4200           n=5, data-references related information (e.g. memory dependences,
4201           memory access-patterns) is added to the reports.  If n=6, the
4202           vectorizer reports also non-vectorized inner-most loops that did
4203           not pass the first analysis phase (i.e., may not be countable, or
4204           may have complicated control-flow).  If n=7, the vectorizer reports
4205           also non-vectorized nested loops.  If n=8, SLP related information
4206           is added to the reports.  For n=9, all the information the
4207           vectorizer generates during its analysis and transformation is
4208           reported.  This is the same verbosity level that
4209           -fdump-tree-vect-details uses.
4210
4211       -frandom-seed=string
4212           This option provides a seed that GCC uses when it would otherwise
4213           use random numbers.  It is used to generate certain symbol names
4214           that have to be different in every compiled file.  It is also used
4215           to place unique stamps in coverage data files and the object files
4216           that produce them.  You can use the -frandom-seed option to produce
4217           reproducibly identical object files.
4218
4219           The string should be different for every file you compile.
4220
4221       -fsched-verbose=n
4222           On targets that use instruction scheduling, this option controls
4223           the amount of debugging output the scheduler prints.  This
4224           information is written to standard error, unless -fdump-rtl-sched1
4225           or -fdump-rtl-sched2 is specified, in which case it is output to
4226           the usual dump listing file, .sched1 or .sched2 respectively.
4227           However for n greater than nine, the output is always printed to
4228           standard error.
4229
4230           For n greater than zero, -fsched-verbose outputs the same
4231           information as -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n
4232           greater than one, it also output basic block probabilities,
4233           detailed ready list information and unit/insn info.  For n greater
4234           than two, it includes RTL at abort point, control-flow and regions
4235           info.  And for n over four, -fsched-verbose also includes
4236           dependence info.
4237
4238       -save-temps
4239       -save-temps=cwd
4240           Store the usual "temporary" intermediate files permanently; place
4241           them in the current directory and name them based on the source
4242           file.  Thus, compiling foo.c with -c -save-temps would produce
4243           files foo.i and foo.s, as well as foo.o.  This creates a
4244           preprocessed foo.i output file even though the compiler now
4245           normally uses an integrated preprocessor.
4246
4247           When used in combination with the -x command line option,
4248           -save-temps is sensible enough to avoid over writing an input
4249           source file with the same extension as an intermediate file.  The
4250           corresponding intermediate file may be obtained by renaming the
4251           source file before using -save-temps.
4252
4253           If you invoke GCC in parallel, compiling several different source
4254           files that share a common base name in different subdirectories or
4255           the same source file compiled for multiple output destinations, it
4256           is likely that the different parallel compilers will interfere with
4257           each other, and overwrite the temporary files.  For instance:
4258
4259                   gcc -save-temps -o outdir1/foo.o indir1/foo.c&
4260                   gcc -save-temps -o outdir2/foo.o indir2/foo.c&
4261
4262           may result in foo.i and foo.o being written to simultaneously by
4263           both compilers.
4264
4265       -save-temps=obj
4266           Store the usual "temporary" intermediate files permanently.  If the
4267           -o option is used, the temporary files are based on the object
4268           file.  If the -o option is not used, the -save-temps=obj switch
4269           behaves like -save-temps.
4270
4271           For example:
4272
4273                   gcc -save-temps=obj -c foo.c
4274                   gcc -save-temps=obj -c bar.c -o dir/xbar.o
4275                   gcc -save-temps=obj foobar.c -o dir2/yfoobar
4276
4277           would create foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i,
4278           dir2/yfoobar.s, and dir2/yfoobar.o.
4279
4280       -time[=file]
4281           Report the CPU time taken by each subprocess in the compilation
4282           sequence.  For C source files, this is the compiler proper and
4283           assembler (plus the linker if linking is done).
4284
4285           Without the specification of an output file, the output looks like
4286           this:
4287
4288                   # cc1 0.12 0.01
4289                   # as 0.00 0.01
4290
4291           The first number on each line is the "user time", that is time
4292           spent executing the program itself.  The second number is "system
4293           time", time spent executing operating system routines on behalf of
4294           the program.  Both numbers are in seconds.
4295
4296           With the specification of an output file, the output is appended to
4297           the named file, and it looks like this:
4298
4299                   0.12 0.01 cc1 <options>
4300                   0.00 0.01 as <options>
4301
4302           The "user time" and the "system time" are moved before the program
4303           name, and the options passed to the program are displayed, so that
4304           one can later tell what file was being compiled, and with which
4305           options.
4306
4307       -fvar-tracking
4308           Run variable tracking pass.  It computes where variables are stored
4309           at each position in code.  Better debugging information is then
4310           generated (if the debugging information format supports this
4311           information).
4312
4313           It is enabled by default when compiling with optimization (-Os, -O,
4314           -O2, ...), debugging information (-g) and the debug info format
4315           supports it.
4316
4317       -fvar-tracking-assignments
4318           Annotate assignments to user variables early in the compilation and
4319           attempt to carry the annotations over throughout the compilation
4320           all the way to the end, in an attempt to improve debug information
4321           while optimizing.  Use of -gdwarf-4 is recommended along with it.
4322
4323           It can be enabled even if var-tracking is disabled, in which case
4324           annotations will be created and maintained, but discarded at the
4325           end.
4326
4327       -fvar-tracking-assignments-toggle
4328           Toggle -fvar-tracking-assignments, in the same way that -gtoggle
4329           toggles -g.
4330
4331       -print-file-name=library
4332           Print the full absolute name of the library file library that would
4333           be used when linking---and don't do anything else.  With this
4334           option, GCC does not compile or link anything; it just prints the
4335           file name.
4336
4337       -print-multi-directory
4338           Print the directory name corresponding to the multilib selected by
4339           any other switches present in the command line.  This directory is
4340           supposed to exist in GCC_EXEC_PREFIX.
4341
4342       -print-multi-lib
4343           Print the mapping from multilib directory names to compiler
4344           switches that enable them.  The directory name is separated from
4345           the switches by ;, and each switch starts with an @} instead of the
4346           @samp{-, without spaces between multiple switches.  This is
4347           supposed to ease shell-processing.
4348
4349       -print-multi-os-directory
4350           Print the path to OS libraries for the selected multilib, relative
4351           to some lib subdirectory.  If OS libraries are present in the lib
4352           subdirectory and no multilibs are used, this is usually just ., if
4353           OS libraries are present in libsuffix sibling directories this
4354           prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
4355           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
4356           or ev6.
4357
4358       -print-prog-name=program
4359           Like -print-file-name, but searches for a program such as cpp.
4360
4361       -print-libgcc-file-name
4362           Same as -print-file-name=libgcc.a.
4363
4364           This is useful when you use -nostdlib or -nodefaultlibs but you do
4365           want to link with libgcc.a.  You can do
4366
4367                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`
4368
4369       -print-search-dirs
4370           Print the name of the configured installation directory and a list
4371           of program and library directories gcc will search---and don't do
4372           anything else.
4373
4374           This is useful when gcc prints the error message installation
4375           problem, cannot exec cpp0: No such file or directory.  To resolve
4376           this you either need to put cpp0 and the other compiler components
4377           where gcc expects to find them, or you can set the environment
4378           variable GCC_EXEC_PREFIX to the directory where you installed them.
4379           Don't forget the trailing /.
4380
4381       -print-sysroot
4382           Print the target sysroot directory that will be used during
4383           compilation.  This is the target sysroot specified either at
4384           configure time or using the --sysroot option, possibly with an
4385           extra suffix that depends on compilation options.  If no target
4386           sysroot is specified, the option prints nothing.
4387
4388       -print-sysroot-headers-suffix
4389           Print the suffix added to the target sysroot when searching for
4390           headers, or give an error if the compiler is not configured with
4391           such a suffix---and don't do anything else.
4392
4393       -dumpmachine
4394           Print the compiler's target machine (for example,
4395           i686-pc-linux-gnu)---and don't do anything else.
4396
4397       -dumpversion
4398           Print the compiler version (for example, 3.0)---and don't do
4399           anything else.
4400
4401       -dumpspecs
4402           Print the compiler's built-in specs---and don't do anything else.
4403           (This is used when GCC itself is being built.)
4404
4405       -feliminate-unused-debug-types
4406           Normally, when producing DWARF2 output, GCC will emit debugging
4407           information for all types declared in a compilation unit,
4408           regardless of whether or not they are actually used in that
4409           compilation unit.  Sometimes this is useful, such as if, in the
4410           debugger, you want to cast a value to a type that is not actually
4411           used in your program (but is declared).  More often, however, this
4412           results in a significant amount of wasted space.  With this option,
4413           GCC will avoid producing debug symbol output for types that are
4414           nowhere used in the source file being compiled.
4415
4416   Options That Control Optimization
4417       These options control various sorts of optimizations.
4418
4419       Without any optimization option, the compiler's goal is to reduce the
4420       cost of compilation and to make debugging produce the expected results.
4421       Statements are independent: if you stop the program with a breakpoint
4422       between statements, you can then assign a new value to any variable or
4423       change the program counter to any other statement in the function and
4424       get exactly the results you would expect from the source code.
4425
4426       Turning on optimization flags makes the compiler attempt to improve the
4427       performance and/or code size at the expense of compilation time and
4428       possibly the ability to debug the program.
4429
4430       The compiler performs optimization based on the knowledge it has of the
4431       program.  Compiling multiple files at once to a single output file mode
4432       allows the compiler to use information gained from all of the files
4433       when compiling each of them.
4434
4435       Not all optimizations are controlled directly by a flag.  Only
4436       optimizations that have a flag are listed in this section.
4437
4438       Most optimizations are only enabled if an -O level is set on the
4439       command line.  Otherwise they are disabled, even if individual
4440       optimization flags are specified.
4441
4442       Depending on the target and how GCC was configured, a slightly
4443       different set of optimizations may be enabled at each -O level than
4444       those listed here.  You can invoke GCC with -Q --help=optimizers to
4445       find out the exact set of optimizations that are enabled at each level.
4446
4447       -O
4448       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
4449           lot more memory for a large function.
4450
4451           With -O, the compiler tries to reduce code size and execution time,
4452           without performing any optimizations that take a great deal of
4453           compilation time.
4454
4455           -O turns on the following optimization flags:
4456
4457           -fauto-inc-dec -fcprop-registers -fdce -fdefer-pop -fdelayed-branch
4458           -fdse -fguess-branch-probability -fif-conversion2 -fif-conversion
4459           -fipa-pure-const -fipa-reference -fmerge-constants
4460           -fsplit-wide-types -ftree-builtin-call-dce -ftree-ccp -ftree-ch
4461           -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse
4462           -ftree-forwprop -ftree-fre -ftree-phiprop -ftree-sra -ftree-pta
4463           -ftree-ter -funit-at-a-time
4464
4465           -O also turns on -fomit-frame-pointer on machines where doing so
4466           does not interfere with debugging.
4467
4468       -O2 Optimize even more.  GCC performs nearly all supported
4469           optimizations that do not involve a space-speed tradeoff.  As
4470           compared to -O, this option increases both compilation time and the
4471           performance of the generated code.
4472
4473           -O2 turns on all optimization flags specified by -O.  It also turns
4474           on the following optimization flags: -fthread-jumps
4475           -falign-functions  -falign-jumps -falign-loops  -falign-labels
4476           -fcaller-saves -fcrossjumping -fcse-follow-jumps  -fcse-skip-blocks
4477           -fdelete-null-pointer-checks -fexpensive-optimizations -fgcse
4478           -fgcse-lm -finline-small-functions -findirect-inlining -fipa-sra
4479           -foptimize-sibling-calls -fpeephole2 -fregmove -freorder-blocks
4480           -freorder-functions -frerun-cse-after-loop -fsched-interblock
4481           -fsched-spec -fschedule-insns  -fschedule-insns2 -fstrict-aliasing
4482           -fstrict-overflow -ftree-switch-conversion -ftree-pre -ftree-vrp
4483
4484           Please note the warning under -fgcse about invoking -O2 on programs
4485           that use computed gotos.
4486
4487       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
4488           and also turns on the -finline-functions, -funswitch-loops,
4489           -fpredictive-commoning, -fgcse-after-reload and -ftree-vectorize
4490           options.
4491
4492       -O0 Reduce compilation time and make debugging produce the expected
4493           results.  This is the default.
4494
4495       -Os Optimize for size.  -Os enables all -O2 optimizations that do not
4496           typically increase code size.  It also performs further
4497           optimizations designed to reduce code size.
4498
4499           -Os disables the following optimization flags: -falign-functions
4500           -falign-jumps  -falign-loops -falign-labels  -freorder-blocks
4501           -freorder-blocks-and-partition -fprefetch-loop-arrays
4502           -ftree-vect-loop-version
4503
4504           If you use multiple -O options, with or without level numbers, the
4505           last such option is the one that is effective.
4506
4507       Options of the form -fflag specify machine-independent flags.  Most
4508       flags have both positive and negative forms; the negative form of -ffoo
4509       would be -fno-foo.  In the table below, only one of the forms is
4510       listed---the one you typically will use.  You can figure out the other
4511       form by either removing no- or adding it.
4512
4513       The following options control specific optimizations.  They are either
4514       activated by -O options or are related to ones that are.  You can use
4515       the following flags in the rare cases when "fine-tuning" of
4516       optimizations to be performed is desired.
4517
4518       -fno-default-inline
4519           Do not make member functions inline by default merely because they
4520           are defined inside the class scope (C++ only).  Otherwise, when you
4521           specify -O, member functions defined inside class scope are
4522           compiled inline by default; i.e., you don't need to add inline in
4523           front of the member function name.
4524
4525       -fno-defer-pop
4526           Always pop the arguments to each function call as soon as that
4527           function returns.  For machines which must pop arguments after a
4528           function call, the compiler normally lets arguments accumulate on
4529           the stack for several function calls and pops them all at once.
4530
4531           Disabled at levels -O, -O2, -O3, -Os.
4532
4533       -fforward-propagate
4534           Perform a forward propagation pass on RTL.  The pass tries to
4535           combine two instructions and checks if the result can be
4536           simplified.  If loop unrolling is active, two passes are performed
4537           and the second is scheduled after loop unrolling.
4538
4539           This option is enabled by default at optimization levels -O, -O2,
4540           -O3, -Os.
4541
4542       -fomit-frame-pointer
4543           Don't keep the frame pointer in a register for functions that don't
4544           need one.  This avoids the instructions to save, set up and restore
4545           frame pointers; it also makes an extra register available in many
4546           functions.  It also makes debugging impossible on some machines.
4547
4548           On some machines, such as the VAX, this flag has no effect, because
4549           the standard calling sequence automatically handles the frame
4550           pointer and nothing is saved by pretending it doesn't exist.  The
4551           machine-description macro "FRAME_POINTER_REQUIRED" controls whether
4552           a target machine supports this flag.
4553
4554           Enabled at levels -O, -O2, -O3, -Os.
4555
4556       -foptimize-sibling-calls
4557           Optimize sibling and tail recursive calls.
4558
4559           Enabled at levels -O2, -O3, -Os.
4560
4561       -fno-inline
4562           Don't pay attention to the "inline" keyword.  Normally this option
4563           is used to keep the compiler from expanding any functions inline.
4564           Note that if you are not optimizing, no functions can be expanded
4565           inline.
4566
4567       -finline-small-functions
4568           Integrate functions into their callers when their body is smaller
4569           than expected function call code (so overall size of program gets
4570           smaller).  The compiler heuristically decides which functions are
4571           simple enough to be worth integrating in this way.
4572
4573           Enabled at level -O2.
4574
4575       -findirect-inlining
4576           Inline also indirect calls that are discovered to be known at
4577           compile time thanks to previous inlining.  This option has any
4578           effect only when inlining itself is turned on by the
4579           -finline-functions or -finline-small-functions options.
4580
4581           Enabled at level -O2.
4582
4583       -finline-functions
4584           Integrate all simple functions into their callers.  The compiler
4585           heuristically decides which functions are simple enough to be worth
4586           integrating in this way.
4587
4588           If all calls to a given function are integrated, and the function
4589           is declared "static", then the function is normally not output as
4590           assembler code in its own right.
4591
4592           Enabled at level -O3.
4593
4594       -finline-functions-called-once
4595           Consider all "static" functions called once for inlining into their
4596           caller even if they are not marked "inline".  If a call to a given
4597           function is integrated, then the function is not output as
4598           assembler code in its own right.
4599
4600           Enabled at levels -O1, -O2, -O3 and -Os.
4601
4602       -fearly-inlining
4603           Inline functions marked by "always_inline" and functions whose body
4604           seems smaller than the function call overhead early before doing
4605           -fprofile-generate instrumentation and real inlining pass.  Doing
4606           so makes profiling significantly cheaper and usually inlining
4607           faster on programs having large chains of nested wrapper functions.
4608
4609           Enabled by default.
4610
4611       -fipa-sra
4612           Perform interprocedural scalar replacement of aggregates, removal
4613           of unused parameters and replacement of parameters passed by
4614           reference by parameters passed by value.
4615
4616           Enabled at levels -O2, -O3 and -Os.
4617
4618       -finline-limit=n
4619           By default, GCC limits the size of functions that can be inlined.
4620           This flag allows coarse control of this limit.  n is the size of
4621           functions that can be inlined in number of pseudo instructions.
4622
4623           Inlining is actually controlled by a number of parameters, which
4624           may be specified individually by using --param name=value.  The
4625           -finline-limit=n option sets some of these parameters as follows:
4626
4627           max-inline-insns-single
4628               is set to n/2.
4629
4630           max-inline-insns-auto
4631               is set to n/2.
4632
4633           See below for a documentation of the individual parameters
4634           controlling inlining and for the defaults of these parameters.
4635
4636           Note: there may be no value to -finline-limit that results in
4637           default behavior.
4638
4639           Note: pseudo instruction represents, in this particular context, an
4640           abstract measurement of function's size.  In no way does it
4641           represent a count of assembly instructions and as such its exact
4642           meaning might change from one release to an another.
4643
4644       -fkeep-inline-functions
4645           In C, emit "static" functions that are declared "inline" into the
4646           object file, even if the function has been inlined into all of its
4647           callers.  This switch does not affect functions using the "extern
4648           inline" extension in GNU C90.  In C++, emit any and all inline
4649           functions into the object file.
4650
4651       -fkeep-static-consts
4652           Emit variables declared "static const" when optimization isn't
4653           turned on, even if the variables aren't referenced.
4654
4655           GCC enables this option by default.  If you want to force the
4656           compiler to check if the variable was referenced, regardless of
4657           whether or not optimization is turned on, use the
4658           -fno-keep-static-consts option.
4659
4660       -fmerge-constants
4661           Attempt to merge identical constants (string constants and floating
4662           point constants) across compilation units.
4663
4664           This option is the default for optimized compilation if the
4665           assembler and linker support it.  Use -fno-merge-constants to
4666           inhibit this behavior.
4667
4668           Enabled at levels -O, -O2, -O3, -Os.
4669
4670       -fmerge-all-constants
4671           Attempt to merge identical constants and identical variables.
4672
4673           This option implies -fmerge-constants.  In addition to
4674           -fmerge-constants this considers e.g. even constant initialized
4675           arrays or initialized constant variables with integral or floating
4676           point types.  Languages like C or C++ require each variable,
4677           including multiple instances of the same variable in recursive
4678           calls, to have distinct locations, so using this option will result
4679           in non-conforming behavior.
4680
4681       -fmodulo-sched
4682           Perform swing modulo scheduling immediately before the first
4683           scheduling pass.  This pass looks at innermost loops and reorders
4684           their instructions by overlapping different iterations.
4685
4686       -fmodulo-sched-allow-regmoves
4687           Perform more aggressive SMS based modulo scheduling with register
4688           moves allowed.  By setting this flag certain anti-dependences edges
4689           will be deleted which will trigger the generation of reg-moves
4690           based on the life-range analysis.  This option is effective only
4691           with -fmodulo-sched enabled.
4692
4693       -fno-branch-count-reg
4694           Do not use "decrement and branch" instructions on a count register,
4695           but instead generate a sequence of instructions that decrement a
4696           register, compare it against zero, then branch based upon the
4697           result.  This option is only meaningful on architectures that
4698           support such instructions, which include x86, PowerPC, IA-64 and
4699           S/390.
4700
4701           The default is -fbranch-count-reg.
4702
4703       -fno-function-cse
4704           Do not put function addresses in registers; make each instruction
4705           that calls a constant function contain the function's address
4706           explicitly.
4707
4708           This option results in less efficient code, but some strange hacks
4709           that alter the assembler output may be confused by the
4710           optimizations performed when this option is not used.
4711
4712           The default is -ffunction-cse
4713
4714       -fno-zero-initialized-in-bss
4715           If the target supports a BSS section, GCC by default puts variables
4716           that are initialized to zero into BSS.  This can save space in the
4717           resulting code.
4718
4719           This option turns off this behavior because some programs
4720           explicitly rely on variables going to the data section.  E.g., so
4721           that the resulting executable can find the beginning of that
4722           section and/or make assumptions based on that.
4723
4724           The default is -fzero-initialized-in-bss.
4725
4726       -fmudflap -fmudflapth -fmudflapir
4727           For front-ends that support it (C and C++), instrument all risky
4728           pointer/array dereferencing operations, some standard library
4729           string/heap functions, and some other associated constructs with
4730           range/validity tests.  Modules so instrumented should be immune to
4731           buffer overflows, invalid heap use, and some other classes of C/C++
4732           programming errors.  The instrumentation relies on a separate
4733           runtime library (libmudflap), which will be linked into a program
4734           if -fmudflap is given at link time.  Run-time behavior of the
4735           instrumented program is controlled by the MUDFLAP_OPTIONS
4736           environment variable.  See "env MUDFLAP_OPTIONS=-help a.out" for
4737           its options.
4738
4739           Use -fmudflapth instead of -fmudflap to compile and to link if your
4740           program is multi-threaded.  Use -fmudflapir, in addition to
4741           -fmudflap or -fmudflapth, if instrumentation should ignore pointer
4742           reads.  This produces less instrumentation (and therefore faster
4743           execution) and still provides some protection against outright
4744           memory corrupting writes, but allows erroneously read data to
4745           propagate within a program.
4746
4747       -fthread-jumps
4748           Perform optimizations where we check to see if a jump branches to a
4749           location where another comparison subsumed by the first is found.
4750           If so, the first branch is redirected to either the destination of
4751           the second branch or a point immediately following it, depending on
4752           whether the condition is known to be true or false.
4753
4754           Enabled at levels -O2, -O3, -Os.
4755
4756       -fsplit-wide-types
4757           When using a type that occupies multiple registers, such as "long
4758           long" on a 32-bit system, split the registers apart and allocate
4759           them independently.  This normally generates better code for those
4760           types, but may make debugging more difficult.
4761
4762           Enabled at levels -O, -O2, -O3, -Os.
4763
4764       -fcse-follow-jumps
4765           In common subexpression elimination (CSE), scan through jump
4766           instructions when the target of the jump is not reached by any
4767           other path.  For example, when CSE encounters an "if" statement
4768           with an "else" clause, CSE will follow the jump when the condition
4769           tested is false.
4770
4771           Enabled at levels -O2, -O3, -Os.
4772
4773       -fcse-skip-blocks
4774           This is similar to -fcse-follow-jumps, but causes CSE to follow
4775           jumps which conditionally skip over blocks.  When CSE encounters a
4776           simple "if" statement with no else clause, -fcse-skip-blocks causes
4777           CSE to follow the jump around the body of the "if".
4778
4779           Enabled at levels -O2, -O3, -Os.
4780
4781       -frerun-cse-after-loop
4782           Re-run common subexpression elimination after loop optimizations
4783           has been performed.
4784
4785           Enabled at levels -O2, -O3, -Os.
4786
4787       -fgcse
4788           Perform a global common subexpression elimination pass.  This pass
4789           also performs global constant and copy propagation.
4790
4791           Note: When compiling a program using computed gotos, a GCC
4792           extension, you may get better runtime performance if you disable
4793           the global common subexpression elimination pass by adding
4794           -fno-gcse to the command line.
4795
4796           Enabled at levels -O2, -O3, -Os.
4797
4798       -fgcse-lm
4799           When -fgcse-lm is enabled, global common subexpression elimination
4800           will attempt to move loads which are only killed by stores into
4801           themselves.  This allows a loop containing a load/store sequence to
4802           be changed to a load outside the loop, and a copy/store within the
4803           loop.
4804
4805           Enabled by default when gcse is enabled.
4806
4807       -fgcse-sm
4808           When -fgcse-sm is enabled, a store motion pass is run after global
4809           common subexpression elimination.  This pass will attempt to move
4810           stores out of loops.  When used in conjunction with -fgcse-lm,
4811           loops containing a load/store sequence can be changed to a load
4812           before the loop and a store after the loop.
4813
4814           Not enabled at any optimization level.
4815
4816       -fgcse-las
4817           When -fgcse-las is enabled, the global common subexpression
4818           elimination pass eliminates redundant loads that come after stores
4819           to the same memory location (both partial and full redundancies).
4820
4821           Not enabled at any optimization level.
4822
4823       -fgcse-after-reload
4824           When -fgcse-after-reload is enabled, a redundant load elimination
4825           pass is performed after reload.  The purpose of this pass is to
4826           cleanup redundant spilling.
4827
4828       -funsafe-loop-optimizations
4829           If given, the loop optimizer will assume that loop indices do not
4830           overflow, and that the loops with nontrivial exit condition are not
4831           infinite.  This enables a wider range of loop optimizations even if
4832           the loop optimizer itself cannot prove that these assumptions are
4833           valid.  Using -Wunsafe-loop-optimizations, the compiler will warn
4834           you if it finds this kind of loop.
4835
4836       -fcrossjumping
4837           Perform cross-jumping transformation.  This transformation unifies
4838           equivalent code and save code size.  The resulting code may or may
4839           not perform better than without cross-jumping.
4840
4841           Enabled at levels -O2, -O3, -Os.
4842
4843       -fauto-inc-dec
4844           Combine increments or decrements of addresses with memory accesses.
4845           This pass is always skipped on architectures that do not have
4846           instructions to support this.  Enabled by default at -O and higher
4847           on architectures that support this.
4848
4849       -fdce
4850           Perform dead code elimination (DCE) on RTL.  Enabled by default at
4851           -O and higher.
4852
4853       -fdse
4854           Perform dead store elimination (DSE) on RTL.  Enabled by default at
4855           -O and higher.
4856
4857       -fif-conversion
4858           Attempt to transform conditional jumps into branch-less
4859           equivalents.  This include use of conditional moves, min, max, set
4860           flags and abs instructions, and some tricks doable by standard
4861           arithmetics.  The use of conditional execution on chips where it is
4862           available is controlled by "if-conversion2".
4863
4864           Enabled at levels -O, -O2, -O3, -Os.
4865
4866       -fif-conversion2
4867           Use conditional execution (where available) to transform
4868           conditional jumps into branch-less equivalents.
4869
4870           Enabled at levels -O, -O2, -O3, -Os.
4871
4872       -fdelete-null-pointer-checks
4873           Assume that programs cannot safely dereference null pointers, and
4874           that no code or data element resides there.  This enables simple
4875           constant folding optimizations at all optimization levels.  In
4876           addition, other optimization passes in GCC use this flag to control
4877           global dataflow analyses that eliminate useless checks for null
4878           pointers; these assume that if a pointer is checked after it has
4879           already been dereferenced, it cannot be null.
4880
4881           Note however that in some environments this assumption is not true.
4882           Use -fno-delete-null-pointer-checks to disable this optimization
4883           for programs which depend on that behavior.
4884
4885           Some targets, especially embedded ones, disable this option at all
4886           levels.  Otherwise it is enabled at all levels: -O0, -O1, -O2, -O3,
4887           -Os.  Passes that use the information are enabled independently at
4888           different optimization levels.
4889
4890       -fexpensive-optimizations
4891           Perform a number of minor optimizations that are relatively
4892           expensive.
4893
4894           Enabled at levels -O2, -O3, -Os.
4895
4896       -foptimize-register-move
4897       -fregmove
4898           Attempt to reassign register numbers in move instructions and as
4899           operands of other simple instructions in order to maximize the
4900           amount of register tying.  This is especially helpful on machines
4901           with two-operand instructions.
4902
4903           Note -fregmove and -foptimize-register-move are the same
4904           optimization.
4905
4906           Enabled at levels -O2, -O3, -Os.
4907
4908       -fira-algorithm=algorithm
4909           Use specified coloring algorithm for the integrated register
4910           allocator.  The algorithm argument should be "priority" or "CB".
4911           The first algorithm specifies Chow's priority coloring, the second
4912           one specifies Chaitin-Briggs coloring.  The second algorithm can be
4913           unimplemented for some architectures.  If it is implemented, it is
4914           the default because Chaitin-Briggs coloring as a rule generates a
4915           better code.
4916
4917       -fira-region=region
4918           Use specified regions for the integrated register allocator.  The
4919           region argument should be one of "all", "mixed", or "one".  The
4920           first value means using all loops as register allocation regions,
4921           the second value which is the default means using all loops except
4922           for loops with small register pressure as the regions, and third
4923           one means using all function as a single region.  The first value
4924           can give best result for machines with small size and irregular
4925           register set, the third one results in faster and generates decent
4926           code and the smallest size code, and the default value usually give
4927           the best results in most cases and for most architectures.
4928
4929       -fira-coalesce
4930           Do optimistic register coalescing.  This option might be profitable
4931           for architectures with big regular register files.
4932
4933       -fira-loop-pressure
4934           Use IRA to evaluate register pressure in loops for decision to move
4935           loop invariants.  Usage of this option usually results in
4936           generation of faster and smaller code on machines with big register
4937           files (>= 32 registers) but it can slow compiler down.
4938
4939           This option is enabled at level -O3 for some targets.
4940
4941       -fno-ira-share-save-slots
4942           Switch off sharing stack slots used for saving call used hard
4943           registers living through a call.  Each hard register will get a
4944           separate stack slot and as a result function stack frame will be
4945           bigger.
4946
4947       -fno-ira-share-spill-slots
4948           Switch off sharing stack slots allocated for pseudo-registers.
4949           Each pseudo-register which did not get a hard register will get a
4950           separate stack slot and as a result function stack frame will be
4951           bigger.
4952
4953       -fira-verbose=n
4954           Set up how verbose dump file for the integrated register allocator
4955           will be.  Default value is 5.  If the value is greater or equal to
4956           10, the dump file will be stderr as if the value were n minus 10.
4957
4958       -fdelayed-branch
4959           If supported for the target machine, attempt to reorder
4960           instructions to exploit instruction slots available after delayed
4961           branch instructions.
4962
4963           Enabled at levels -O, -O2, -O3, -Os.
4964
4965       -fschedule-insns
4966           If supported for the target machine, attempt to reorder
4967           instructions to eliminate execution stalls due to required data
4968           being unavailable.  This helps machines that have slow floating
4969           point or memory load instructions by allowing other instructions to
4970           be issued until the result of the load or floating point
4971           instruction is required.
4972
4973           Enabled at levels -O2, -O3.
4974
4975       -fschedule-insns2
4976           Similar to -fschedule-insns, but requests an additional pass of
4977           instruction scheduling after register allocation has been done.
4978           This is especially useful on machines with a relatively small
4979           number of registers and where memory load instructions take more
4980           than one cycle.
4981
4982           Enabled at levels -O2, -O3, -Os.
4983
4984       -fno-sched-interblock
4985           Don't schedule instructions across basic blocks.  This is normally
4986           enabled by default when scheduling before register allocation, i.e.
4987           with -fschedule-insns or at -O2 or higher.
4988
4989       -fno-sched-spec
4990           Don't allow speculative motion of non-load instructions.  This is
4991           normally enabled by default when scheduling before register
4992           allocation, i.e.  with -fschedule-insns or at -O2 or higher.
4993
4994       -fsched-pressure
4995           Enable register pressure sensitive insn scheduling before the
4996           register allocation.  This only makes sense when scheduling before
4997           register allocation is enabled, i.e. with -fschedule-insns or at
4998           -O2 or higher.  Usage of this option can improve the generated code
4999           and decrease its size by preventing register pressure increase
5000           above the number of available hard registers and as a consequence
5001           register spills in the register allocation.
5002
5003       -fsched-spec-load
5004           Allow speculative motion of some load instructions.  This only
5005           makes sense when scheduling before register allocation, i.e. with
5006           -fschedule-insns or at -O2 or higher.
5007
5008       -fsched-spec-load-dangerous
5009           Allow speculative motion of more load instructions.  This only
5010           makes sense when scheduling before register allocation, i.e. with
5011           -fschedule-insns or at -O2 or higher.
5012
5013       -fsched-stalled-insns
5014       -fsched-stalled-insns=n
5015           Define how many insns (if any) can be moved prematurely from the
5016           queue of stalled insns into the ready list, during the second
5017           scheduling pass.  -fno-sched-stalled-insns means that no insns will
5018           be moved prematurely, -fsched-stalled-insns=0 means there is no
5019           limit on how many queued insns can be moved prematurely.
5020           -fsched-stalled-insns without a value is equivalent to
5021           -fsched-stalled-insns=1.
5022
5023       -fsched-stalled-insns-dep
5024       -fsched-stalled-insns-dep=n
5025           Define how many insn groups (cycles) will be examined for a
5026           dependency on a stalled insn that is candidate for premature
5027           removal from the queue of stalled insns.  This has an effect only
5028           during the second scheduling pass, and only if
5029           -fsched-stalled-insns is used.  -fno-sched-stalled-insns-dep is
5030           equivalent to -fsched-stalled-insns-dep=0.
5031           -fsched-stalled-insns-dep without a value is equivalent to
5032           -fsched-stalled-insns-dep=1.
5033
5034       -fsched2-use-superblocks
5035           When scheduling after register allocation, do use superblock
5036           scheduling algorithm.  Superblock scheduling allows motion across
5037           basic block boundaries resulting on faster schedules.  This option
5038           is experimental, as not all machine descriptions used by GCC model
5039           the CPU closely enough to avoid unreliable results from the
5040           algorithm.
5041
5042           This only makes sense when scheduling after register allocation,
5043           i.e. with -fschedule-insns2 or at -O2 or higher.
5044
5045       -fsched-group-heuristic
5046           Enable the group heuristic in the scheduler.  This heuristic favors
5047           the instruction that belongs to a schedule group.  This is enabled
5048           by default when scheduling is enabled, i.e. with -fschedule-insns
5049           or -fschedule-insns2 or at -O2 or higher.
5050
5051       -fsched-critical-path-heuristic
5052           Enable the critical-path heuristic in the scheduler.  This
5053           heuristic favors instructions on the critical path.  This is
5054           enabled by default when scheduling is enabled, i.e. with
5055           -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
5056
5057       -fsched-spec-insn-heuristic
5058           Enable the speculative instruction heuristic in the scheduler.
5059           This heuristic favors speculative instructions with greater
5060           dependency weakness.  This is enabled by default when scheduling is
5061           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
5062           or higher.
5063
5064       -fsched-rank-heuristic
5065           Enable the rank heuristic in the scheduler.  This heuristic favors
5066           the instruction belonging to a basic block with greater size or
5067           frequency.  This is enabled by default when scheduling is enabled,
5068           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or
5069           higher.
5070
5071       -fsched-last-insn-heuristic
5072           Enable the last-instruction heuristic in the scheduler.  This
5073           heuristic favors the instruction that is less dependent on the last
5074           instruction scheduled.  This is enabled by default when scheduling
5075           is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at
5076           -O2 or higher.
5077
5078       -fsched-dep-count-heuristic
5079           Enable the dependent-count heuristic in the scheduler.  This
5080           heuristic favors the instruction that has more instructions
5081           depending on it.  This is enabled by default when scheduling is
5082           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
5083           or higher.
5084
5085       -freschedule-modulo-scheduled-loops
5086           The modulo scheduling comes before the traditional scheduling, if a
5087           loop was modulo scheduled we may want to prevent the later
5088           scheduling passes from changing its schedule, we use this option to
5089           control that.
5090
5091       -fselective-scheduling
5092           Schedule instructions using selective scheduling algorithm.
5093           Selective scheduling runs instead of the first scheduler pass.
5094
5095       -fselective-scheduling2
5096           Schedule instructions using selective scheduling algorithm.
5097           Selective scheduling runs instead of the second scheduler pass.
5098
5099       -fsel-sched-pipelining
5100           Enable software pipelining of innermost loops during selective
5101           scheduling.  This option has no effect until one of
5102           -fselective-scheduling or -fselective-scheduling2 is turned on.
5103
5104       -fsel-sched-pipelining-outer-loops
5105           When pipelining loops during selective scheduling, also pipeline
5106           outer loops.  This option has no effect until
5107           -fsel-sched-pipelining is turned on.
5108
5109       -fcaller-saves
5110           Enable values to be allocated in registers that will be clobbered
5111           by function calls, by emitting extra instructions to save and
5112           restore the registers around such calls.  Such allocation is done
5113           only when it seems to result in better code than would otherwise be
5114           produced.
5115
5116           This option is always enabled by default on certain machines,
5117           usually those which have no call-preserved registers to use
5118           instead.
5119
5120           Enabled at levels -O2, -O3, -Os.
5121
5122       -fconserve-stack
5123           Attempt to minimize stack usage.  The compiler will attempt to use
5124           less stack space, even if that makes the program slower.  This
5125           option implies setting the large-stack-frame parameter to 100 and
5126           the large-stack-frame-growth parameter to 400.
5127
5128       -ftree-reassoc
5129           Perform reassociation on trees.  This flag is enabled by default at
5130           -O and higher.
5131
5132       -ftree-pre
5133           Perform partial redundancy elimination (PRE) on trees.  This flag
5134           is enabled by default at -O2 and -O3.
5135
5136       -ftree-forwprop
5137           Perform forward propagation on trees.  This flag is enabled by
5138           default at -O and higher.
5139
5140       -ftree-fre
5141           Perform full redundancy elimination (FRE) on trees.  The difference
5142           between FRE and PRE is that FRE only considers expressions that are
5143           computed on all paths leading to the redundant computation.  This
5144           analysis is faster than PRE, though it exposes fewer redundancies.
5145           This flag is enabled by default at -O and higher.
5146
5147       -ftree-phiprop
5148           Perform hoisting of loads from conditional pointers on trees.  This
5149           pass is enabled by default at -O and higher.
5150
5151       -ftree-copy-prop
5152           Perform copy propagation on trees.  This pass eliminates
5153           unnecessary copy operations.  This flag is enabled by default at -O
5154           and higher.
5155
5156       -fipa-pure-const
5157           Discover which functions are pure or constant.  Enabled by default
5158           at -O and higher.
5159
5160       -fipa-reference
5161           Discover which static variables do not escape cannot escape the
5162           compilation unit.  Enabled by default at -O and higher.
5163
5164       -fipa-struct-reorg
5165           Perform structure reorganization optimization, that change C-like
5166           structures layout in order to better utilize spatial locality.
5167           This transformation is affective for programs containing arrays of
5168           structures.  Available in two compilation modes: profile-based
5169           (enabled with -fprofile-generate) or static (which uses built-in
5170           heuristics).  Require -fipa-type-escape to provide the safety of
5171           this transformation.  It works only in whole program mode, so it
5172           requires -fwhole-program and -combine to be enabled.  Structures
5173           considered cold by this transformation are not affected (see
5174           --param struct-reorg-cold-struct-ratio=value).
5175
5176           With this flag, the program debug info reflects a new structure
5177           layout.
5178
5179       -fipa-pta
5180           Perform interprocedural pointer analysis.  This option is
5181           experimental and does not affect generated code.
5182
5183       -fipa-cp
5184           Perform interprocedural constant propagation.  This optimization
5185           analyzes the program to determine when values passed to functions
5186           are constants and then optimizes accordingly.  This optimization
5187           can substantially increase performance if the application has
5188           constants passed to functions.  This flag is enabled by default at
5189           -O2, -Os and -O3.
5190
5191       -fipa-cp-clone
5192           Perform function cloning to make interprocedural constant
5193           propagation stronger.  When enabled, interprocedural constant
5194           propagation will perform function cloning when externally visible
5195           function can be called with constant arguments.  Because this
5196           optimization can create multiple copies of functions, it may
5197           significantly increase code size (see --param
5198           ipcp-unit-growth=value).  This flag is enabled by default at -O3.
5199
5200       -fipa-matrix-reorg
5201           Perform matrix flattening and transposing.  Matrix flattening tries
5202           to replace an m-dimensional matrix with its equivalent
5203           n-dimensional matrix, where n < m.  This reduces the level of
5204           indirection needed for accessing the elements of the matrix. The
5205           second optimization is matrix transposing that attempts to change
5206           the order of the matrix's dimensions in order to improve cache
5207           locality.  Both optimizations need the -fwhole-program flag.
5208           Transposing is enabled only if profiling information is available.
5209
5210       -ftree-sink
5211           Perform forward store motion  on trees.  This flag is enabled by
5212           default at -O and higher.
5213
5214       -ftree-ccp
5215           Perform sparse conditional constant propagation (CCP) on trees.
5216           This pass only operates on local scalar variables and is enabled by
5217           default at -O and higher.
5218
5219       -ftree-switch-conversion
5220           Perform conversion of simple initializations in a switch to
5221           initializations from a scalar array.  This flag is enabled by
5222           default at -O2 and higher.
5223
5224       -ftree-dce
5225           Perform dead code elimination (DCE) on trees.  This flag is enabled
5226           by default at -O and higher.
5227
5228       -ftree-builtin-call-dce
5229           Perform conditional dead code elimination (DCE) for calls to
5230           builtin functions that may set "errno" but are otherwise side-
5231           effect free.  This flag is enabled by default at -O2 and higher if
5232           -Os is not also specified.
5233
5234       -ftree-dominator-opts
5235           Perform a variety of simple scalar cleanups (constant/copy
5236           propagation, redundancy elimination, range propagation and
5237           expression simplification) based on a dominator tree traversal.
5238           This also performs jump threading (to reduce jumps to jumps). This
5239           flag is enabled by default at -O and higher.
5240
5241       -ftree-dse
5242           Perform dead store elimination (DSE) on trees.  A dead store is a
5243           store into a memory location which will later be overwritten by
5244           another store without any intervening loads.  In this case the
5245           earlier store can be deleted.  This flag is enabled by default at
5246           -O and higher.
5247
5248       -ftree-ch
5249           Perform loop header copying on trees.  This is beneficial since it
5250           increases effectiveness of code motion optimizations.  It also
5251           saves one jump.  This flag is enabled by default at -O and higher.
5252           It is not enabled for -Os, since it usually increases code size.
5253
5254       -ftree-loop-optimize
5255           Perform loop optimizations on trees.  This flag is enabled by
5256           default at -O and higher.
5257
5258       -ftree-loop-linear
5259           Perform linear loop transformations on tree.  This flag can improve
5260           cache performance and allow further loop optimizations to take
5261           place.
5262
5263       -floop-interchange
5264           Perform loop interchange transformations on loops.  Interchanging
5265           two nested loops switches the inner and outer loops.  For example,
5266           given a loop like:
5267
5268                   DO J = 1, M
5269                     DO I = 1, N
5270                       A(J, I) = A(J, I) * C
5271                     ENDDO
5272                   ENDDO
5273
5274           loop interchange will transform the loop as if the user had
5275           written:
5276
5277                   DO I = 1, N
5278                     DO J = 1, M
5279                       A(J, I) = A(J, I) * C
5280                     ENDDO
5281                   ENDDO
5282
5283           which can be beneficial when "N" is larger than the caches, because
5284           in Fortran, the elements of an array are stored in memory
5285           contiguously by column, and the original loop iterates over rows,
5286           potentially creating at each access a cache miss.  This
5287           optimization applies to all the languages supported by GCC and is
5288           not limited to Fortran.  To use this code transformation, GCC has
5289           to be configured with --with-ppl and --with-cloog to enable the
5290           Graphite loop transformation infrastructure.
5291
5292       -floop-strip-mine
5293           Perform loop strip mining transformations on loops.  Strip mining
5294           splits a loop into two nested loops.  The outer loop has strides
5295           equal to the strip size and the inner loop has strides of the
5296           original loop within a strip.  The strip length can be changed
5297           using the loop-block-tile-size parameter.  For example, given a
5298           loop like:
5299
5300                   DO I = 1, N
5301                     A(I) = A(I) + C
5302                   ENDDO
5303
5304           loop strip mining will transform the loop as if the user had
5305           written:
5306
5307                   DO II = 1, N, 51
5308                     DO I = II, min (II + 50, N)
5309                       A(I) = A(I) + C
5310                     ENDDO
5311                   ENDDO
5312
5313           This optimization applies to all the languages supported by GCC and
5314           is not limited to Fortran.  To use this code transformation, GCC
5315           has to be configured with --with-ppl and --with-cloog to enable the
5316           Graphite loop transformation infrastructure.
5317
5318       -floop-block
5319           Perform loop blocking transformations on loops.  Blocking strip
5320           mines each loop in the loop nest such that the memory accesses of
5321           the element loops fit inside caches.  The strip length can be
5322           changed using the loop-block-tile-size parameter.  For example,
5323           given a loop like:
5324
5325                   DO I = 1, N
5326                     DO J = 1, M
5327                       A(J, I) = B(I) + C(J)
5328                     ENDDO
5329                   ENDDO
5330
5331           loop blocking will transform the loop as if the user had written:
5332
5333                   DO II = 1, N, 51
5334                     DO JJ = 1, M, 51
5335                       DO I = II, min (II + 50, N)
5336                         DO J = JJ, min (JJ + 50, M)
5337                           A(J, I) = B(I) + C(J)
5338                         ENDDO
5339                       ENDDO
5340                     ENDDO
5341                   ENDDO
5342
5343           which can be beneficial when "M" is larger than the caches, because
5344           the innermost loop will iterate over a smaller amount of data that
5345           can be kept in the caches.  This optimization applies to all the
5346           languages supported by GCC and is not limited to Fortran.  To use
5347           this code transformation, GCC has to be configured with --with-ppl
5348           and --with-cloog to enable the Graphite loop transformation
5349           infrastructure.
5350
5351       -fgraphite-identity
5352           Enable the identity transformation for graphite.  For every SCoP we
5353           generate the polyhedral representation and transform it back to
5354           gimple.  Using -fgraphite-identity we can check the costs or
5355           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
5356           minimal optimizations are also performed by the code generator
5357           CLooG, like index splitting and dead code elimination in loops.
5358
5359       -floop-parallelize-all
5360           Use the Graphite data dependence analysis to identify loops that
5361           can be parallelized.  Parallelize all the loops that can be
5362           analyzed to not contain loop carried dependences without checking
5363           that it is profitable to parallelize the loops.
5364
5365       -fcheck-data-deps
5366           Compare the results of several data dependence analyzers.  This
5367           option is used for debugging the data dependence analyzers.
5368
5369       -ftree-loop-distribution
5370           Perform loop distribution.  This flag can improve cache performance
5371           on big loop bodies and allow further loop optimizations, like
5372           parallelization or vectorization, to take place.  For example, the
5373           loop
5374
5375                   DO I = 1, N
5376                     A(I) = B(I) + C
5377                     D(I) = E(I) * F
5378                   ENDDO
5379
5380           is transformed to
5381
5382                   DO I = 1, N
5383                      A(I) = B(I) + C
5384                   ENDDO
5385                   DO I = 1, N
5386                      D(I) = E(I) * F
5387                   ENDDO
5388
5389       -ftree-loop-im
5390           Perform loop invariant motion on trees.  This pass moves only
5391           invariants that would be hard to handle at RTL level (function
5392           calls, operations that expand to nontrivial sequences of insns).
5393           With -funswitch-loops it also moves operands of conditions that are
5394           invariant out of the loop, so that we can use just trivial
5395           invariantness analysis in loop unswitching.  The pass also includes
5396           store motion.
5397
5398       -ftree-loop-ivcanon
5399           Create a canonical counter for number of iterations in the loop for
5400           that determining number of iterations requires complicated
5401           analysis.  Later optimizations then may determine the number
5402           easily.  Useful especially in connection with unrolling.
5403
5404       -fivopts
5405           Perform induction variable optimizations (strength reduction,
5406           induction variable merging and induction variable elimination) on
5407           trees.
5408
5409       -ftree-parallelize-loops=n
5410           Parallelize loops, i.e., split their iteration space to run in n
5411           threads.  This is only possible for loops whose iterations are
5412           independent and can be arbitrarily reordered.  The optimization is
5413           only profitable on multiprocessor machines, for loops that are CPU-
5414           intensive, rather than constrained e.g. by memory bandwidth.  This
5415           option implies -pthread, and thus is only supported on targets that
5416           have support for -pthread.
5417
5418       -ftree-pta
5419           Perform function-local points-to analysis on trees.  This flag is
5420           enabled by default at -O and higher.
5421
5422       -ftree-sra
5423           Perform scalar replacement of aggregates.  This pass replaces
5424           structure references with scalars to prevent committing structures
5425           to memory too early.  This flag is enabled by default at -O and
5426           higher.
5427
5428       -ftree-copyrename
5429           Perform copy renaming on trees.  This pass attempts to rename
5430           compiler temporaries to other variables at copy locations, usually
5431           resulting in variable names which more closely resemble the
5432           original variables.  This flag is enabled by default at -O and
5433           higher.
5434
5435       -ftree-ter
5436           Perform temporary expression replacement during the SSA->normal
5437           phase.  Single use/single def temporaries are replaced at their use
5438           location with their defining expression.  This results in non-
5439           GIMPLE code, but gives the expanders much more complex trees to
5440           work on resulting in better RTL generation.  This is enabled by
5441           default at -O and higher.
5442
5443       -ftree-vectorize
5444           Perform loop vectorization on trees. This flag is enabled by
5445           default at -O3.
5446
5447       -ftree-slp-vectorize
5448           Perform basic block vectorization on trees. This flag is enabled by
5449           default at -O3 and when -ftree-vectorize is enabled.
5450
5451       -ftree-vect-loop-version
5452           Perform loop versioning when doing loop vectorization on trees.
5453           When a loop appears to be vectorizable except that data alignment
5454           or data dependence cannot be determined at compile time then
5455           vectorized and non-vectorized versions of the loop are generated
5456           along with runtime checks for alignment or dependence to control
5457           which version is executed.  This option is enabled by default
5458           except at level -Os where it is disabled.
5459
5460       -fvect-cost-model
5461           Enable cost model for vectorization.
5462
5463       -ftree-vrp
5464           Perform Value Range Propagation on trees.  This is similar to the
5465           constant propagation pass, but instead of values, ranges of values
5466           are propagated.  This allows the optimizers to remove unnecessary
5467           range checks like array bound checks and null pointer checks.  This
5468           is enabled by default at -O2 and higher.  Null pointer check
5469           elimination is only done if -fdelete-null-pointer-checks is
5470           enabled.
5471
5472       -ftracer
5473           Perform tail duplication to enlarge superblock size.  This
5474           transformation simplifies the control flow of the function allowing
5475           other optimizations to do better job.
5476
5477       -funroll-loops
5478           Unroll loops whose number of iterations can be determined at
5479           compile time or upon entry to the loop.  -funroll-loops implies
5480           -frerun-cse-after-loop.  This option makes code larger, and may or
5481           may not make it run faster.
5482
5483       -funroll-all-loops
5484           Unroll all loops, even if their number of iterations is uncertain
5485           when the loop is entered.  This usually makes programs run more
5486           slowly.  -funroll-all-loops implies the same options as
5487           -funroll-loops,
5488
5489       -fsplit-ivs-in-unroller
5490           Enables expressing of values of induction variables in later
5491           iterations of the unrolled loop using the value in the first
5492           iteration.  This breaks long dependency chains, thus improving
5493           efficiency of the scheduling passes.
5494
5495           Combination of -fweb and CSE is often sufficient to obtain the same
5496           effect.  However in cases the loop body is more complicated than a
5497           single basic block, this is not reliable.  It also does not work at
5498           all on some of the architectures due to restrictions in the CSE
5499           pass.
5500
5501           This optimization is enabled by default.
5502
5503       -fvariable-expansion-in-unroller
5504           With this option, the compiler will create multiple copies of some
5505           local variables when unrolling a loop which can result in superior
5506           code.
5507
5508       -fpredictive-commoning
5509           Perform predictive commoning optimization, i.e., reusing
5510           computations (especially memory loads and stores) performed in
5511           previous iterations of loops.
5512
5513           This option is enabled at level -O3.
5514
5515       -fprefetch-loop-arrays
5516           If supported by the target machine, generate instructions to
5517           prefetch memory to improve the performance of loops that access
5518           large arrays.
5519
5520           This option may generate better or worse code; results are highly
5521           dependent on the structure of loops within the source code.
5522
5523           Disabled at level -Os.
5524
5525       -fno-peephole
5526       -fno-peephole2
5527           Disable any machine-specific peephole optimizations.  The
5528           difference between -fno-peephole and -fno-peephole2 is in how they
5529           are implemented in the compiler; some targets use one, some use the
5530           other, a few use both.
5531
5532           -fpeephole is enabled by default.  -fpeephole2 enabled at levels
5533           -O2, -O3, -Os.
5534
5535       -fno-guess-branch-probability
5536           Do not guess branch probabilities using heuristics.
5537
5538           GCC will use heuristics to guess branch probabilities if they are
5539           not provided by profiling feedback (-fprofile-arcs).  These
5540           heuristics are based on the control flow graph.  If some branch
5541           probabilities are specified by __builtin_expect, then the
5542           heuristics will be used to guess branch probabilities for the rest
5543           of the control flow graph, taking the __builtin_expect info into
5544           account.  The interactions between the heuristics and
5545           __builtin_expect can be complex, and in some cases, it may be
5546           useful to disable the heuristics so that the effects of
5547           __builtin_expect are easier to understand.
5548
5549           The default is -fguess-branch-probability at levels -O, -O2, -O3,
5550           -Os.
5551
5552       -freorder-blocks
5553           Reorder basic blocks in the compiled function in order to reduce
5554           number of taken branches and improve code locality.
5555
5556           Enabled at levels -O2, -O3.
5557
5558       -freorder-blocks-and-partition
5559           In addition to reordering basic blocks in the compiled function, in
5560           order to reduce number of taken branches, partitions hot and cold
5561           basic blocks into separate sections of the assembly and .o files,
5562           to improve paging and cache locality performance.
5563
5564           This optimization is automatically turned off in the presence of
5565           exception handling, for linkonce sections, for functions with a
5566           user-defined section attribute and on any architecture that does
5567           not support named sections.
5568
5569       -freorder-functions
5570           Reorder functions in the object file in order to improve code
5571           locality.  This is implemented by using special subsections
5572           ".text.hot" for most frequently executed functions and
5573           ".text.unlikely" for unlikely executed functions.  Reordering is
5574           done by the linker so object file format must support named
5575           sections and linker must place them in a reasonable way.
5576
5577           Also profile feedback must be available in to make this option
5578           effective.  See -fprofile-arcs for details.
5579
5580           Enabled at levels -O2, -O3, -Os.
5581
5582       -fstrict-aliasing
5583           Allow the compiler to assume the strictest aliasing rules
5584           applicable to the language being compiled.  For C (and C++), this
5585           activates optimizations based on the type of expressions.  In
5586           particular, an object of one type is assumed never to reside at the
5587           same address as an object of a different type, unless the types are
5588           almost the same.  For example, an "unsigned int" can alias an
5589           "int", but not a "void*" or a "double".  A character type may alias
5590           any other type.
5591
5592           Pay special attention to code like this:
5593
5594                   union a_union {
5595                     int i;
5596                     double d;
5597                   };
5598
5599                   int f() {
5600                     union a_union t;
5601                     t.d = 3.0;
5602                     return t.i;
5603                   }
5604
5605           The practice of reading from a different union member than the one
5606           most recently written to (called "type-punning") is common.  Even
5607           with -fstrict-aliasing, type-punning is allowed, provided the
5608           memory is accessed through the union type.  So, the code above will
5609           work as expected.    However, this code might not:
5610
5611                   int f() {
5612                     union a_union t;
5613                     int* ip;
5614                     t.d = 3.0;
5615                     ip = &t.i;
5616                     return *ip;
5617                   }
5618
5619           Similarly, access by taking the address, casting the resulting
5620           pointer and dereferencing the result has undefined behavior, even
5621           if the cast uses a union type, e.g.:
5622
5623                   int f() {
5624                     double d = 3.0;
5625                     return ((union a_union *) &d)->i;
5626                   }
5627
5628           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.
5629
5630       -fstrict-overflow
5631           Allow the compiler to assume strict signed overflow rules,
5632           depending on the language being compiled.  For C (and C++) this
5633           means that overflow when doing arithmetic with signed numbers is
5634           undefined, which means that the compiler may assume that it will
5635           not happen.  This permits various optimizations.  For example, the
5636           compiler will assume that an expression like "i + 10 > i" will
5637           always be true for signed "i".  This assumption is only valid if
5638           signed overflow is undefined, as the expression is false if "i +
5639           10" overflows when using twos complement arithmetic.  When this
5640           option is in effect any attempt to determine whether an operation
5641           on signed numbers will overflow must be written carefully to not
5642           actually involve overflow.
5643
5644           This option also allows the compiler to assume strict pointer
5645           semantics: given a pointer to an object, if adding an offset to
5646           that pointer does not produce a pointer to the same object, the
5647           addition is undefined.  This permits the compiler to conclude that
5648           "p + u > p" is always true for a pointer "p" and unsigned integer
5649           "u".  This assumption is only valid because pointer wraparound is
5650           undefined, as the expression is false if "p + u" overflows using
5651           twos complement arithmetic.
5652
5653           See also the -fwrapv option.  Using -fwrapv means that integer
5654           signed overflow is fully defined: it wraps.  When -fwrapv is used,
5655           there is no difference between -fstrict-overflow and
5656           -fno-strict-overflow for integers.  With -fwrapv certain types of
5657           overflow are permitted.  For example, if the compiler gets an
5658           overflow when doing arithmetic on constants, the overflowed value
5659           can still be used with -fwrapv, but not otherwise.
5660
5661           The -fstrict-overflow option is enabled at levels -O2, -O3, -Os.
5662
5663       -falign-functions
5664       -falign-functions=n
5665           Align the start of functions to the next power-of-two greater than
5666           n, skipping up to n bytes.  For instance, -falign-functions=32
5667           aligns functions to the next 32-byte boundary, but
5668           -falign-functions=24 would align to the next 32-byte boundary only
5669           if this can be done by skipping 23 bytes or less.
5670
5671           -fno-align-functions and -falign-functions=1 are equivalent and
5672           mean that functions will not be aligned.
5673
5674           Some assemblers only support this flag when n is a power of two; in
5675           that case, it is rounded up.
5676
5677           If n is not specified or is zero, use a machine-dependent default.
5678
5679           Enabled at levels -O2, -O3.
5680
5681       -falign-labels
5682       -falign-labels=n
5683           Align all branch targets to a power-of-two boundary, skipping up to
5684           n bytes like -falign-functions.  This option can easily make code
5685           slower, because it must insert dummy operations for when the branch
5686           target is reached in the usual flow of the code.
5687
5688           -fno-align-labels and -falign-labels=1 are equivalent and mean that
5689           labels will not be aligned.
5690
5691           If -falign-loops or -falign-jumps are applicable and are greater
5692           than this value, then their values are used instead.
5693
5694           If n is not specified or is zero, use a machine-dependent default
5695           which is very likely to be 1, meaning no alignment.
5696
5697           Enabled at levels -O2, -O3.
5698
5699       -falign-loops
5700       -falign-loops=n
5701           Align loops to a power-of-two boundary, skipping up to n bytes like
5702           -falign-functions.  The hope is that the loop will be executed many
5703           times, which will make up for any execution of the dummy
5704           operations.
5705
5706           -fno-align-loops and -falign-loops=1 are equivalent and mean that
5707           loops will not be aligned.
5708
5709           If n is not specified or is zero, use a machine-dependent default.
5710
5711           Enabled at levels -O2, -O3.
5712
5713       -falign-jumps
5714       -falign-jumps=n
5715           Align branch targets to a power-of-two boundary, for branch targets
5716           where the targets can only be reached by jumping, skipping up to n
5717           bytes like -falign-functions.  In this case, no dummy operations
5718           need be executed.
5719
5720           -fno-align-jumps and -falign-jumps=1 are equivalent and mean that
5721           loops will not be aligned.
5722
5723           If n is not specified or is zero, use a machine-dependent default.
5724
5725           Enabled at levels -O2, -O3.
5726
5727       -funit-at-a-time
5728           This option is left for compatibility reasons. -funit-at-a-time has
5729           no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder
5730           and -fno-section-anchors.
5731
5732           Enabled by default.
5733
5734       -fno-toplevel-reorder
5735           Do not reorder top-level functions, variables, and "asm"
5736           statements.  Output them in the same order that they appear in the
5737           input file.  When this option is used, unreferenced static
5738           variables will not be removed.  This option is intended to support
5739           existing code which relies on a particular ordering.  For new code,
5740           it is better to use attributes.
5741
5742           Enabled at level -O0.  When disabled explicitly, it also imply
5743           -fno-section-anchors that is otherwise enabled at -O0 on some
5744           targets.
5745
5746       -fweb
5747           Constructs webs as commonly used for register allocation purposes
5748           and assign each web individual pseudo register.  This allows the
5749           register allocation pass to operate on pseudos directly, but also
5750           strengthens several other optimization passes, such as CSE, loop
5751           optimizer and trivial dead code remover.  It can, however, make
5752           debugging impossible, since variables will no longer stay in a
5753           "home register".
5754
5755           Enabled by default with -funroll-loops.
5756
5757       -fwhole-program
5758           Assume that the current compilation unit represents the whole
5759           program being compiled.  All public functions and variables with
5760           the exception of "main" and those merged by attribute
5761           "externally_visible" become static functions and in effect are
5762           optimized more aggressively by interprocedural optimizers.  While
5763           this option is equivalent to proper use of the "static" keyword for
5764           programs consisting of a single file, in combination with option
5765           -combine, -flto or -fwhopr this flag can be used to compile many
5766           smaller scale programs since the functions and variables become
5767           local for the whole combined compilation unit, not for the single
5768           source file itself.
5769
5770           This option implies -fwhole-file for Fortran programs.
5771
5772       -flto
5773           This option runs the standard link-time optimizer.  When invoked
5774           with source code, it generates GIMPLE (one of GCC's internal
5775           representations) and writes it to special ELF sections in the
5776           object file.  When the object files are linked together, all the
5777           function bodies are read from these ELF sections and instantiated
5778           as if they had been part of the same translation unit.
5779
5780           To use the link-timer optimizer, -flto needs to be specified at
5781           compile time and during the final link.  For example,
5782
5783                   gcc -c -O2 -flto foo.c
5784                   gcc -c -O2 -flto bar.c
5785                   gcc -o myprog -flto -O2 foo.o bar.o
5786
5787           The first two invocations to GCC will save a bytecode
5788           representation of GIMPLE into special ELF sections inside foo.o and
5789           bar.o.  The final invocation will read the GIMPLE bytecode from
5790           foo.o and bar.o, merge the two files into a single internal image,
5791           and compile the result as usual.  Since both foo.o and bar.o are
5792           merged into a single image, this causes all the inter-procedural
5793           analyses and optimizations in GCC to work across the two files as
5794           if they were a single one.  This means, for example, that the
5795           inliner will be able to inline functions in bar.o into functions in
5796           foo.o and vice-versa.
5797
5798           Another (simpler) way to enable link-time optimization is,
5799
5800                   gcc -o myprog -flto -O2 foo.c bar.c
5801
5802           The above will generate bytecode for foo.c and bar.c, merge them
5803           together into a single GIMPLE representation and optimize them as
5804           usual to produce myprog.
5805
5806           The only important thing to keep in mind is that to enable link-
5807           time optimizations the -flto flag needs to be passed to both the
5808           compile and the link commands.
5809
5810           Note that when a file is compiled with -flto, the generated object
5811           file will be larger than a regular object file because it will
5812           contain GIMPLE bytecodes and the usual final code.  This means that
5813           object files with LTO information can be linked as a normal object
5814           file.  So, in the previous example, if the final link is done with
5815
5816                   gcc -o myprog foo.o bar.o
5817
5818           The only difference will be that no inter-procedural optimizations
5819           will be applied to produce myprog.  The two object files foo.o and
5820           bar.o will be simply sent to the regular linker.
5821
5822           Additionally, the optimization flags used to compile individual
5823           files are not necessarily related to those used at link-time.  For
5824           instance,
5825
5826                   gcc -c -O0 -flto foo.c
5827                   gcc -c -O0 -flto bar.c
5828                   gcc -o myprog -flto -O3 foo.o bar.o
5829
5830           This will produce individual object files with unoptimized
5831           assembler code, but the resulting binary myprog will be optimized
5832           at -O3.  Now, if the final binary is generated without -flto, then
5833           myprog will not be optimized.
5834
5835           When producing the final binary with -flto, GCC will only apply
5836           link-time optimizations to those files that contain bytecode.
5837           Therefore, you can mix and match object files and libraries with
5838           GIMPLE bytecodes and final object code.  GCC will automatically
5839           select which files to optimize in LTO mode and which files to link
5840           without further processing.
5841
5842           There are some code generation flags that GCC will preserve when
5843           generating bytecodes, as they need to be used during the final link
5844           stage.  Currently, the following options are saved into the GIMPLE
5845           bytecode files: -fPIC, -fcommon and all the -m target flags.
5846
5847           At link time, these options are read-in and reapplied.  Note that
5848           the current implementation makes no attempt at recognizing
5849           conflicting values for these options.  If two or more files have a
5850           conflicting value (e.g., one file is compiled with -fPIC and
5851           another isn't), the compiler will simply use the last value read
5852           from the bytecode files.  It is recommended, then, that all the
5853           files participating in the same link be compiled with the same
5854           options.
5855
5856           Another feature of LTO is that it is possible to apply
5857           interprocedural optimizations on files written in different
5858           languages.  This requires some support in the language front end.
5859           Currently, the C, C++ and Fortran front ends are capable of
5860           emitting GIMPLE bytecodes, so something like this should work
5861
5862                   gcc -c -flto foo.c
5863                   g++ -c -flto bar.cc
5864                   gfortran -c -flto baz.f90
5865                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
5866
5867           Notice that the final link is done with g++ to get the C++ runtime
5868           libraries and -lgfortran is added to get the Fortran runtime
5869           libraries.  In general, when mixing languages in LTO mode, you
5870           should use the same link command used when mixing languages in a
5871           regular (non-LTO) compilation.  This means that if your build
5872           process was mixing languages before, all you need to add is -flto
5873           to all the compile and link commands.
5874
5875           If LTO encounters objects with C linkage declared with incompatible
5876           types in separate translation units to be linked together
5877           (undefined behavior according to ISO C99 6.2.7), a non-fatal
5878           diagnostic may be issued.  The behavior is still undefined at
5879           runtime.
5880
5881           If object files containing GIMPLE bytecode are stored in a library
5882           archive, say libfoo.a, it is possible to extract and use them in an
5883           LTO link if you are using gold as the linker (which, in turn
5884           requires GCC to be configured with --enable-gold).  To enable this
5885           feature, use the flag -fuse-linker-plugin at link-time:
5886
5887                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
5888
5889           With the linker plugin enabled, gold will extract the needed GIMPLE
5890           files from libfoo.a and pass them on to the running GCC to make
5891           them part of the aggregated GIMPLE image to be optimized.
5892
5893           If you are not using gold and/or do not specify -fuse-linker-plugin
5894           then the objects inside libfoo.a will be extracted and linked as
5895           usual, but they will not participate in the LTO optimization
5896           process.
5897
5898           Link time optimizations do not require the presence of the whole
5899           program to operate.  If the program does not require any symbols to
5900           be exported, it is possible to combine -flto and -fwhopr with
5901           -fwhole-program to allow the interprocedural optimizers to use more
5902           aggressive assumptions which may lead to improved optimization
5903           opportunities.
5904
5905           Regarding portability: the current implementation of LTO makes no
5906           attempt at generating bytecode that can be ported between different
5907           types of hosts.  The bytecode files are versioned and there is a
5908           strict version check, so bytecode files generated in one version of
5909           GCC will not work with an older/newer version of GCC.
5910
5911           Link time optimization does not play well with generating debugging
5912           information.  Combining -flto or -fwhopr with -g is experimental.
5913
5914           This option is disabled by default.
5915
5916       -fwhopr
5917           This option is identical in functionality to -flto but it differs
5918           in how the final link stage is executed.  Instead of loading all
5919           the function bodies in memory, the callgraph is analyzed and
5920           optimization decisions are made (whole program analysis or WPA).
5921           Once optimization decisions are made, the callgraph is partitioned
5922           and the different sections are compiled separately (local
5923           transformations or LTRANS).  This process allows optimizations on
5924           very large programs that otherwise would not fit in memory.  This
5925           option enables -fwpa and -fltrans automatically.
5926
5927           Disabled by default.
5928
5929           This option is experimental.
5930
5931       -fwpa
5932           This is an internal option used by GCC when compiling with -fwhopr.
5933           You should never need to use it.
5934
5935           This option runs the link-time optimizer in the whole-program-
5936           analysis (WPA) mode, which reads in summary information from all
5937           inputs and performs a whole-program analysis based on summary
5938           information only.  It generates object files for subsequent runs of
5939           the link-time optimizer where individual object files are optimized
5940           using both summary information from the WPA mode and the actual
5941           function bodies.  It then drives the LTRANS phase.
5942
5943           Disabled by default.
5944
5945       -fltrans
5946           This is an internal option used by GCC when compiling with -fwhopr.
5947           You should never need to use it.
5948
5949           This option runs the link-time optimizer in the local-
5950           transformation (LTRANS) mode, which reads in output from a previous
5951           run of the LTO in WPA mode.  In the LTRANS mode, LTO optimizes an
5952           object and produces the final assembly.
5953
5954           Disabled by default.
5955
5956       -fltrans-output-list=file
5957           This is an internal option used by GCC when compiling with -fwhopr.
5958           You should never need to use it.
5959
5960           This option specifies a file to which the names of LTRANS output
5961           files are written.  This option is only meaningful in conjunction
5962           with -fwpa.
5963
5964           Disabled by default.
5965
5966       -flto-compression-level=n
5967           This option specifies the level of compression used for
5968           intermediate language written to LTO object files, and is only
5969           meaningful in conjunction with LTO mode (-fwhopr, -flto).  Valid
5970           values are 0 (no compression) to 9 (maximum compression).  Values
5971           outside this range are clamped to either 0 or 9.  If the option is
5972           not given, a default balanced compression setting is used.
5973
5974       -flto-report
5975           Prints a report with internal details on the workings of the link-
5976           time optimizer.  The contents of this report vary from version to
5977           version, it is meant to be useful to GCC developers when processing
5978           object files in LTO mode (via -fwhopr or -flto).
5979
5980           Disabled by default.
5981
5982       -fuse-linker-plugin
5983           Enables the extraction of objects with GIMPLE bytecode information
5984           from library archives.  This option relies on features available
5985           only in gold, so to use this you must configure GCC with
5986           --enable-gold.  See -flto for a description on the effect of this
5987           flag and how to use it.
5988
5989           Disabled by default.
5990
5991       -fcprop-registers
5992           After register allocation and post-register allocation instruction
5993           splitting, we perform a copy-propagation pass to try to reduce
5994           scheduling dependencies and occasionally eliminate the copy.
5995
5996           Enabled at levels -O, -O2, -O3, -Os.
5997
5998       -fprofile-correction
5999           Profiles collected using an instrumented binary for multi-threaded
6000           programs may be inconsistent due to missed counter updates. When
6001           this option is specified, GCC will use heuristics to correct or
6002           smooth out such inconsistencies. By default, GCC will emit an error
6003           message when an inconsistent profile is detected.
6004
6005       -fprofile-dir=path
6006           Set the directory to search the profile data files in to path.
6007           This option affects only the profile data generated by
6008           -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
6009           -fprofile-use and -fbranch-probabilities and its related options.
6010           By default, GCC will use the current directory as path thus the
6011           profile data file will appear in the same directory as the object
6012           file.
6013
6014       -fprofile-generate
6015       -fprofile-generate=path
6016           Enable options usually used for instrumenting application to
6017           produce profile useful for later recompilation with profile
6018           feedback based optimization.  You must use -fprofile-generate both
6019           when compiling and when linking your program.
6020
6021           The following options are enabled: "-fprofile-arcs",
6022           "-fprofile-values", "-fvpt".
6023
6024           If path is specified, GCC will look at the path to find the profile
6025           feedback data files. See -fprofile-dir.
6026
6027       -fprofile-use
6028       -fprofile-use=path
6029           Enable profile feedback directed optimizations, and optimizations
6030           generally profitable only with profile feedback available.
6031
6032           The following options are enabled: "-fbranch-probabilities",
6033           "-fvpt", "-funroll-loops", "-fpeel-loops", "-ftracer"
6034
6035           By default, GCC emits an error message if the feedback profiles do
6036           not match the source code.  This error can be turned into a warning
6037           by using -Wcoverage-mismatch.  Note this may result in poorly
6038           optimized code.
6039
6040           If path is specified, GCC will look at the path to find the profile
6041           feedback data files. See -fprofile-dir.
6042
6043       The following options control compiler behavior regarding floating
6044       point arithmetic.  These options trade off between speed and
6045       correctness.  All must be specifically enabled.
6046
6047       -ffloat-store
6048           Do not store floating point variables in registers, and inhibit
6049           other options that might change whether a floating point value is
6050           taken from a register or memory.
6051
6052           This option prevents undesirable excess precision on machines such
6053           as the 68000 where the floating registers (of the 68881) keep more
6054           precision than a "double" is supposed to have.  Similarly for the
6055           x86 architecture.  For most programs, the excess precision does
6056           only good, but a few programs rely on the precise definition of
6057           IEEE floating point.  Use -ffloat-store for such programs, after
6058           modifying them to store all pertinent intermediate computations
6059           into variables.
6060
6061       -fexcess-precision=style
6062           This option allows further control over excess precision on
6063           machines where floating-point registers have more precision than
6064           the IEEE "float" and "double" types and the processor does not
6065           support operations rounding to those types.  By default,
6066           -fexcess-precision=fast is in effect; this means that operations
6067           are carried out in the precision of the registers and that it is
6068           unpredictable when rounding to the types specified in the source
6069           code takes place.  When compiling C, if -fexcess-precision=standard
6070           is specified then excess precision will follow the rules specified
6071           in ISO C99; in particular, both casts and assignments cause values
6072           to be rounded to their semantic types (whereas -ffloat-store only
6073           affects assignments).  This option is enabled by default for C if a
6074           strict conformance option such as -std=c99 is used.
6075
6076           -fexcess-precision=standard is not implemented for languages other
6077           than C, and has no effect if -funsafe-math-optimizations or
6078           -ffast-math is specified.  On the x86, it also has no effect if
6079           -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case,
6080           IEEE semantics apply without excess precision, and in the latter,
6081           rounding is unpredictable.
6082
6083       -ffast-math
6084           Sets -fno-math-errno, -funsafe-math-optimizations,
6085           -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans and
6086           -fcx-limited-range.
6087
6088           This option causes the preprocessor macro "__FAST_MATH__" to be
6089           defined.
6090
6091           This option is not turned on by any -O option since it can result
6092           in incorrect output for programs which depend on an exact
6093           implementation of IEEE or ISO rules/specifications for math
6094           functions. It may, however, yield faster code for programs that do
6095           not require the guarantees of these specifications.
6096
6097       -fno-math-errno
6098           Do not set ERRNO after calling math functions that are executed
6099           with a single instruction, e.g., sqrt.  A program that relies on
6100           IEEE exceptions for math error handling may want to use this flag
6101           for speed while maintaining IEEE arithmetic compatibility.
6102
6103           This option is not turned on by any -O option since it can result
6104           in incorrect output for programs which depend on an exact
6105           implementation of IEEE or ISO rules/specifications for math
6106           functions. It may, however, yield faster code for programs that do
6107           not require the guarantees of these specifications.
6108
6109           The default is -fmath-errno.
6110
6111           On Darwin systems, the math library never sets "errno".  There is
6112           therefore no reason for the compiler to consider the possibility
6113           that it might, and -fno-math-errno is the default.
6114
6115       -funsafe-math-optimizations
6116           Allow optimizations for floating-point arithmetic that (a) assume
6117           that arguments and results are valid and (b) may violate IEEE or
6118           ANSI standards.  When used at link-time, it may include libraries
6119           or startup files that change the default FPU control word or other
6120           similar optimizations.
6121
6122           This option is not turned on by any -O option since it can result
6123           in incorrect output for programs which depend on an exact
6124           implementation of IEEE or ISO rules/specifications for math
6125           functions. It may, however, yield faster code for programs that do
6126           not require the guarantees of these specifications.  Enables
6127           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and
6128           -freciprocal-math.
6129
6130           The default is -fno-unsafe-math-optimizations.
6131
6132       -fassociative-math
6133           Allow re-association of operands in series of floating-point
6134           operations.  This violates the ISO C and C++ language standard by
6135           possibly changing computation result.  NOTE: re-ordering may change
6136           the sign of zero as well as ignore NaNs and inhibit or create
6137           underflow or overflow (and thus cannot be used on a code which
6138           relies on rounding behavior like "(x + 2**52) - 2**52)".  May also
6139           reorder floating-point comparisons and thus may not be used when
6140           ordered comparisons are required.  This option requires that both
6141           -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover,
6142           it doesn't make much sense with -frounding-math. For Fortran the
6143           option is automatically enabled when both -fno-signed-zeros and
6144           -fno-trapping-math are in effect.
6145
6146           The default is -fno-associative-math.
6147
6148       -freciprocal-math
6149           Allow the reciprocal of a value to be used instead of dividing by
6150           the value if this enables optimizations.  For example "x / y" can
6151           be replaced with "x * (1/y)" which is useful if "(1/y)" is subject
6152           to common subexpression elimination.  Note that this loses
6153           precision and increases the number of flops operating on the value.
6154
6155           The default is -fno-reciprocal-math.
6156
6157       -ffinite-math-only
6158           Allow optimizations for floating-point arithmetic that assume that
6159           arguments and results are not NaNs or +-Infs.
6160
6161           This option is not turned on by any -O option since it can result
6162           in incorrect output for programs which depend on an exact
6163           implementation of IEEE or ISO rules/specifications for math
6164           functions. It may, however, yield faster code for programs that do
6165           not require the guarantees of these specifications.
6166
6167           The default is -fno-finite-math-only.
6168
6169       -fno-signed-zeros
6170           Allow optimizations for floating point arithmetic that ignore the
6171           signedness of zero.  IEEE arithmetic specifies the behavior of
6172           distinct +0.0 and -0.0 values, which then prohibits simplification
6173           of expressions such as x+0.0 or 0.0*x (even with
6174           -ffinite-math-only).  This option implies that the sign of a zero
6175           result isn't significant.
6176
6177           The default is -fsigned-zeros.
6178
6179       -fno-trapping-math
6180           Compile code assuming that floating-point operations cannot
6181           generate user-visible traps.  These traps include division by zero,
6182           overflow, underflow, inexact result and invalid operation.  This
6183           option requires that -fno-signaling-nans be in effect.  Setting
6184           this option may allow faster code if one relies on "non-stop" IEEE
6185           arithmetic, for example.
6186
6187           This option should never be turned on by any -O option since it can
6188           result in incorrect output for programs which depend on an exact
6189           implementation of IEEE or ISO rules/specifications for math
6190           functions.
6191
6192           The default is -ftrapping-math.
6193
6194       -frounding-math
6195           Disable transformations and optimizations that assume default
6196           floating point rounding behavior.  This is round-to-zero for all
6197           floating point to integer conversions, and round-to-nearest for all
6198           other arithmetic truncations.  This option should be specified for
6199           programs that change the FP rounding mode dynamically, or that may
6200           be executed with a non-default rounding mode.  This option disables
6201           constant folding of floating point expressions at compile-time
6202           (which may be affected by rounding mode) and arithmetic
6203           transformations that are unsafe in the presence of sign-dependent
6204           rounding modes.
6205
6206           The default is -fno-rounding-math.
6207
6208           This option is experimental and does not currently guarantee to
6209           disable all GCC optimizations that are affected by rounding mode.
6210           Future versions of GCC may provide finer control of this setting
6211           using C99's "FENV_ACCESS" pragma.  This command line option will be
6212           used to specify the default state for "FENV_ACCESS".
6213
6214       -fsignaling-nans
6215           Compile code assuming that IEEE signaling NaNs may generate user-
6216           visible traps during floating-point operations.  Setting this
6217           option disables optimizations that may change the number of
6218           exceptions visible with signaling NaNs.  This option implies
6219           -ftrapping-math.
6220
6221           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
6222           defined.
6223
6224           The default is -fno-signaling-nans.
6225
6226           This option is experimental and does not currently guarantee to
6227           disable all GCC optimizations that affect signaling NaN behavior.
6228
6229       -fsingle-precision-constant
6230           Treat floating point constant as single precision constant instead
6231           of implicitly converting it to double precision constant.
6232
6233       -fcx-limited-range
6234           When enabled, this option states that a range reduction step is not
6235           needed when performing complex division.  Also, there is no
6236           checking whether the result of a complex multiplication or division
6237           is "NaN + I*NaN", with an attempt to rescue the situation in that
6238           case.  The default is -fno-cx-limited-range, but is enabled by
6239           -ffast-math.
6240
6241           This option controls the default setting of the ISO C99
6242           "CX_LIMITED_RANGE" pragma.  Nevertheless, the option applies to all
6243           languages.
6244
6245       -fcx-fortran-rules
6246           Complex multiplication and division follow Fortran rules.  Range
6247           reduction is done as part of complex division, but there is no
6248           checking whether the result of a complex multiplication or division
6249           is "NaN + I*NaN", with an attempt to rescue the situation in that
6250           case.
6251
6252           The default is -fno-cx-fortran-rules.
6253
6254       The following options control optimizations that may improve
6255       performance, but are not enabled by any -O options.  This section
6256       includes experimental options that may produce broken code.
6257
6258       -fbranch-probabilities
6259           After running a program compiled with -fprofile-arcs, you can
6260           compile it a second time using -fbranch-probabilities, to improve
6261           optimizations based on the number of times each branch was taken.
6262           When the program compiled with -fprofile-arcs exits it saves arc
6263           execution counts to a file called sourcename.gcda for each source
6264           file.  The information in this data file is very dependent on the
6265           structure of the generated code, so you must use the same source
6266           code and the same optimization options for both compilations.
6267
6268           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
6269           JUMP_INSN and CALL_INSN.  These can be used to improve
6270           optimization.  Currently, they are only used in one place: in
6271           reorg.c, instead of guessing which path a branch is mostly to take,
6272           the REG_BR_PROB values are used to exactly determine which path is
6273           taken more often.
6274
6275       -fprofile-values
6276           If combined with -fprofile-arcs, it adds code so that some data
6277           about values of expressions in the program is gathered.
6278
6279           With -fbranch-probabilities, it reads back the data gathered from
6280           profiling values of expressions and adds REG_VALUE_PROFILE notes to
6281           instructions for their later usage in optimizations.
6282
6283           Enabled with -fprofile-generate and -fprofile-use.
6284
6285       -fvpt
6286           If combined with -fprofile-arcs, it instructs the compiler to add a
6287           code to gather information about values of expressions.
6288
6289           With -fbranch-probabilities, it reads back the data gathered and
6290           actually performs the optimizations based on them.  Currently the
6291           optimizations include specialization of division operation using
6292           the knowledge about the value of the denominator.
6293
6294       -frename-registers
6295           Attempt to avoid false dependencies in scheduled code by making use
6296           of registers left over after register allocation.  This
6297           optimization will most benefit processors with lots of registers.
6298           Depending on the debug information format adopted by the target,
6299           however, it can make debugging impossible, since variables will no
6300           longer stay in a "home register".
6301
6302           Enabled by default with -funroll-loops and -fpeel-loops.
6303
6304       -ftracer
6305           Perform tail duplication to enlarge superblock size.  This
6306           transformation simplifies the control flow of the function allowing
6307           other optimizations to do better job.
6308
6309           Enabled with -fprofile-use.
6310
6311       -funroll-loops
6312           Unroll loops whose number of iterations can be determined at
6313           compile time or upon entry to the loop.  -funroll-loops implies
6314           -frerun-cse-after-loop, -fweb and -frename-registers.  It also
6315           turns on complete loop peeling (i.e. complete removal of loops with
6316           small constant number of iterations).  This option makes code
6317           larger, and may or may not make it run faster.
6318
6319           Enabled with -fprofile-use.
6320
6321       -funroll-all-loops
6322           Unroll all loops, even if their number of iterations is uncertain
6323           when the loop is entered.  This usually makes programs run more
6324           slowly.  -funroll-all-loops implies the same options as
6325           -funroll-loops.
6326
6327       -fpeel-loops
6328           Peels the loops for that there is enough information that they do
6329           not roll much (from profile feedback).  It also turns on complete
6330           loop peeling (i.e. complete removal of loops with small constant
6331           number of iterations).
6332
6333           Enabled with -fprofile-use.
6334
6335       -fmove-loop-invariants
6336           Enables the loop invariant motion pass in the RTL loop optimizer.
6337           Enabled at level -O1
6338
6339       -funswitch-loops
6340           Move branches with loop invariant conditions out of the loop, with
6341           duplicates of the loop on both branches (modified according to
6342           result of the condition).
6343
6344       -ffunction-sections
6345       -fdata-sections
6346           Place each function or data item into its own section in the output
6347           file if the target supports arbitrary sections.  The name of the
6348           function or the name of the data item determines the section's name
6349           in the output file.
6350
6351           Use these options on systems where the linker can perform
6352           optimizations to improve locality of reference in the instruction
6353           space.  Most systems using the ELF object format and SPARC
6354           processors running Solaris 2 have linkers with such optimizations.
6355           AIX may have these optimizations in the future.
6356
6357           Only use these options when there are significant benefits from
6358           doing so.  When you specify these options, the assembler and linker
6359           will create larger object and executable files and will also be
6360           slower.  You will not be able to use "gprof" on all systems if you
6361           specify this option and you may have problems with debugging if you
6362           specify both this option and -g.
6363
6364       -fbranch-target-load-optimize
6365           Perform branch target register load optimization before prologue /
6366           epilogue threading.  The use of target registers can typically be
6367           exposed only during reload, thus hoisting loads out of loops and
6368           doing inter-block scheduling needs a separate optimization pass.
6369
6370       -fbranch-target-load-optimize2
6371           Perform branch target register load optimization after prologue /
6372           epilogue threading.
6373
6374       -fbtr-bb-exclusive
6375           When performing branch target register load optimization, don't
6376           reuse branch target registers in within any basic block.
6377
6378       -fstack-protector
6379           Emit extra code to check for buffer overflows, such as stack
6380           smashing attacks.  This is done by adding a guard variable to
6381           functions with vulnerable objects.  This includes functions that
6382           call alloca, and functions with buffers larger than 8 bytes.  The
6383           guards are initialized when a function is entered and then checked
6384           when the function exits.  If a guard check fails, an error message
6385           is printed and the program exits.
6386
6387       -fstack-protector-all
6388           Like -fstack-protector except that all functions are protected.
6389
6390       -fsection-anchors
6391           Try to reduce the number of symbolic address calculations by using
6392           shared "anchor" symbols to address nearby objects.  This
6393           transformation can help to reduce the number of GOT entries and GOT
6394           accesses on some targets.
6395
6396           For example, the implementation of the following function "foo":
6397
6398                   static int a, b, c;
6399                   int foo (void) { return a + b + c; }
6400
6401           would usually calculate the addresses of all three variables, but
6402           if you compile it with -fsection-anchors, it will access the
6403           variables from a common anchor point instead.  The effect is
6404           similar to the following pseudocode (which isn't valid C):
6405
6406                   int foo (void)
6407                   {
6408                     register int *xr = &x;
6409                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
6410                   }
6411
6412           Not all targets support this option.
6413
6414       --param name=value
6415           In some places, GCC uses various constants to control the amount of
6416           optimization that is done.  For example, GCC will not inline
6417           functions that contain more that a certain number of instructions.
6418           You can control some of these constants on the command-line using
6419           the --param option.
6420
6421           The names of specific parameters, and the meaning of the values,
6422           are tied to the internals of the compiler, and are subject to
6423           change without notice in future releases.
6424
6425           In each case, the value is an integer.  The allowable choices for
6426           name are given in the following table:
6427
6428           struct-reorg-cold-struct-ratio
6429               The threshold ratio (as a percentage) between a structure
6430               frequency and the frequency of the hottest structure in the
6431               program.  This parameter is used by struct-reorg optimization
6432               enabled by -fipa-struct-reorg.  We say that if the ratio of a
6433               structure frequency, calculated by profiling, to the hottest
6434               structure frequency in the program is less than this parameter,
6435               then structure reorganization is not applied to this structure.
6436               The default is 10.
6437
6438           predictable-branch-outcome
6439               When branch is predicted to be taken with probability lower
6440               than this threshold (in percent), then it is considered well
6441               predictable. The default is 10.
6442
6443           max-crossjump-edges
6444               The maximum number of incoming edges to consider for
6445               crossjumping.  The algorithm used by -fcrossjumping is O(N^2)
6446               in the number of edges incoming to each block.  Increasing
6447               values mean more aggressive optimization, making the compile
6448               time increase with probably small improvement in executable
6449               size.
6450
6451           min-crossjump-insns
6452               The minimum number of instructions which must be matched at the
6453               end of two blocks before crossjumping will be performed on
6454               them.  This value is ignored in the case where all instructions
6455               in the block being crossjumped from are matched.  The default
6456               value is 5.
6457
6458           max-grow-copy-bb-insns
6459               The maximum code size expansion factor when copying basic
6460               blocks instead of jumping.  The expansion is relative to a jump
6461               instruction.  The default value is 8.
6462
6463           max-goto-duplication-insns
6464               The maximum number of instructions to duplicate to a block that
6465               jumps to a computed goto.  To avoid O(N^2) behavior in a number
6466               of passes, GCC factors computed gotos early in the compilation
6467               process, and unfactors them as late as possible.  Only computed
6468               jumps at the end of a basic blocks with no more than max-goto-
6469               duplication-insns are unfactored.  The default value is 8.
6470
6471           max-delay-slot-insn-search
6472               The maximum number of instructions to consider when looking for
6473               an instruction to fill a delay slot.  If more than this
6474               arbitrary number of instructions is searched, the time savings
6475               from filling the delay slot will be minimal so stop searching.
6476               Increasing values mean more aggressive optimization, making the
6477               compile time increase with probably small improvement in
6478               executable run time.
6479
6480           max-delay-slot-live-search
6481               When trying to fill delay slots, the maximum number of
6482               instructions to consider when searching for a block with valid
6483               live register information.  Increasing this arbitrarily chosen
6484               value means more aggressive optimization, increasing the
6485               compile time.  This parameter should be removed when the delay
6486               slot code is rewritten to maintain the control-flow graph.
6487
6488           max-gcse-memory
6489               The approximate maximum amount of memory that will be allocated
6490               in order to perform the global common subexpression elimination
6491               optimization.  If more memory than specified is required, the
6492               optimization will not be done.
6493
6494           max-pending-list-length
6495               The maximum number of pending dependencies scheduling will
6496               allow before flushing the current state and starting over.
6497               Large functions with few branches or calls can create
6498               excessively large lists which needlessly consume memory and
6499               resources.
6500
6501           max-inline-insns-single
6502               Several parameters control the tree inliner used in gcc.  This
6503               number sets the maximum number of instructions (counted in
6504               GCC's internal representation) in a single function that the
6505               tree inliner will consider for inlining.  This only affects
6506               functions declared inline and methods implemented in a class
6507               declaration (C++).  The default value is 300.
6508
6509           max-inline-insns-auto
6510               When you use -finline-functions (included in -O3), a lot of
6511               functions that would otherwise not be considered for inlining
6512               by the compiler will be investigated.  To those functions, a
6513               different (more restrictive) limit compared to functions
6514               declared inline can be applied.  The default value is 50.
6515
6516           large-function-insns
6517               The limit specifying really large functions.  For functions
6518               larger than this limit after inlining, inlining is constrained
6519               by --param large-function-growth.  This parameter is useful
6520               primarily to avoid extreme compilation time caused by non-
6521               linear algorithms used by the backend.  The default value is
6522               2700.
6523
6524           large-function-growth
6525               Specifies maximal growth of large function caused by inlining
6526               in percents.  The default value is 100 which limits large
6527               function growth to 2.0 times the original size.
6528
6529           large-unit-insns
6530               The limit specifying large translation unit.  Growth caused by
6531               inlining of units larger than this limit is limited by --param
6532               inline-unit-growth.  For small units this might be too tight
6533               (consider unit consisting of function A that is inline and B
6534               that just calls A three time.  If B is small relative to A, the
6535               growth of unit is 300\% and yet such inlining is very sane.
6536               For very large units consisting of small inlineable functions
6537               however the overall unit growth limit is needed to avoid
6538               exponential explosion of code size.  Thus for smaller units,
6539               the size is increased to --param large-unit-insns before
6540               applying --param inline-unit-growth.  The default is 10000
6541
6542           inline-unit-growth
6543               Specifies maximal overall growth of the compilation unit caused
6544               by inlining.  The default value is 30 which limits unit growth
6545               to 1.3 times the original size.
6546
6547           ipcp-unit-growth
6548               Specifies maximal overall growth of the compilation unit caused
6549               by interprocedural constant propagation.  The default value is
6550               10 which limits unit growth to 1.1 times the original size.
6551
6552           large-stack-frame
6553               The limit specifying large stack frames.  While inlining the
6554               algorithm is trying to not grow past this limit too much.
6555               Default value is 256 bytes.
6556
6557           large-stack-frame-growth
6558               Specifies maximal growth of large stack frames caused by
6559               inlining in percents.  The default value is 1000 which limits
6560               large stack frame growth to 11 times the original size.
6561
6562           max-inline-insns-recursive
6563           max-inline-insns-recursive-auto
6564               Specifies maximum number of instructions out-of-line copy of
6565               self recursive inline function can grow into by performing
6566               recursive inlining.
6567
6568               For functions declared inline --param max-inline-insns-
6569               recursive is taken into account.  For function not declared
6570               inline, recursive inlining happens only when -finline-functions
6571               (included in -O3) is enabled and --param max-inline-insns-
6572               recursive-auto is used.  The default value is 450.
6573
6574           max-inline-recursive-depth
6575           max-inline-recursive-depth-auto
6576               Specifies maximum recursion depth used by the recursive
6577               inlining.
6578
6579               For functions declared inline --param max-inline-recursive-
6580               depth is taken into account.  For function not declared inline,
6581               recursive inlining happens only when -finline-functions
6582               (included in -O3) is enabled and --param max-inline-recursive-
6583               depth-auto is used.  The default value is 8.
6584
6585           min-inline-recursive-probability
6586               Recursive inlining is profitable only for function having deep
6587               recursion in average and can hurt for function having little
6588               recursion depth by increasing the prologue size or complexity
6589               of function body to other optimizers.
6590
6591               When profile feedback is available (see -fprofile-generate) the
6592               actual recursion depth can be guessed from probability that
6593               function will recurse via given call expression.  This
6594               parameter limits inlining only to call expression whose
6595               probability exceeds given threshold (in percents).  The default
6596               value is 10.
6597
6598           early-inlining-insns
6599               Specify growth that early inliner can make.  In effect it
6600               increases amount of inlining for code having large abstraction
6601               penalty.  The default value is 8.
6602
6603           max-early-inliner-iterations
6604           max-early-inliner-iterations
6605               Limit of iterations of early inliner.  This basically bounds
6606               number of nested indirect calls early inliner can resolve.
6607               Deeper chains are still handled by late inlining.
6608
6609           min-vect-loop-bound
6610               The minimum number of iterations under which a loop will not
6611               get vectorized when -ftree-vectorize is used.  The number of
6612               iterations after vectorization needs to be greater than the
6613               value specified by this option to allow vectorization.  The
6614               default value is 0.
6615
6616           max-unrolled-insns
6617               The maximum number of instructions that a loop should have if
6618               that loop is unrolled, and if the loop is unrolled, it
6619               determines how many times the loop code is unrolled.
6620
6621           max-average-unrolled-insns
6622               The maximum number of instructions biased by probabilities of
6623               their execution that a loop should have if that loop is
6624               unrolled, and if the loop is unrolled, it determines how many
6625               times the loop code is unrolled.
6626
6627           max-unroll-times
6628               The maximum number of unrollings of a single loop.
6629
6630           max-peeled-insns
6631               The maximum number of instructions that a loop should have if
6632               that loop is peeled, and if the loop is peeled, it determines
6633               how many times the loop code is peeled.
6634
6635           max-peel-times
6636               The maximum number of peelings of a single loop.
6637
6638           max-completely-peeled-insns
6639               The maximum number of insns of a completely peeled loop.
6640
6641           max-completely-peel-times
6642               The maximum number of iterations of a loop to be suitable for
6643               complete peeling.
6644
6645           max-completely-peel-loop-nest-depth
6646               The maximum depth of a loop nest suitable for complete peeling.
6647
6648           max-unswitch-insns
6649               The maximum number of insns of an unswitched loop.
6650
6651           max-unswitch-level
6652               The maximum number of branches unswitched in a single loop.
6653
6654           lim-expensive
6655               The minimum cost of an expensive expression in the loop
6656               invariant motion.
6657
6658           iv-consider-all-candidates-bound
6659               Bound on number of candidates for induction variables below
6660               that all candidates are considered for each use in induction
6661               variable optimizations.  Only the most relevant candidates are
6662               considered if there are more candidates, to avoid quadratic
6663               time complexity.
6664
6665           iv-max-considered-uses
6666               The induction variable optimizations give up on loops that
6667               contain more induction variable uses.
6668
6669           iv-always-prune-cand-set-bound
6670               If number of candidates in the set is smaller than this value,
6671               we always try to remove unnecessary ivs from the set during its
6672               optimization when a new iv is added to the set.
6673
6674           scev-max-expr-size
6675               Bound on size of expressions used in the scalar evolutions
6676               analyzer.  Large expressions slow the analyzer.
6677
6678           omega-max-vars
6679               The maximum number of variables in an Omega constraint system.
6680               The default value is 128.
6681
6682           omega-max-geqs
6683               The maximum number of inequalities in an Omega constraint
6684               system.  The default value is 256.
6685
6686           omega-max-eqs
6687               The maximum number of equalities in an Omega constraint system.
6688               The default value is 128.
6689
6690           omega-max-wild-cards
6691               The maximum number of wildcard variables that the Omega solver
6692               will be able to insert.  The default value is 18.
6693
6694           omega-hash-table-size
6695               The size of the hash table in the Omega solver.  The default
6696               value is 550.
6697
6698           omega-max-keys
6699               The maximal number of keys used by the Omega solver.  The
6700               default value is 500.
6701
6702           omega-eliminate-redundant-constraints
6703               When set to 1, use expensive methods to eliminate all redundant
6704               constraints.  The default value is 0.
6705
6706           vect-max-version-for-alignment-checks
6707               The maximum number of runtime checks that can be performed when
6708               doing loop versioning for alignment in the vectorizer.  See
6709               option ftree-vect-loop-version for more information.
6710
6711           vect-max-version-for-alias-checks
6712               The maximum number of runtime checks that can be performed when
6713               doing loop versioning for alias in the vectorizer.  See option
6714               ftree-vect-loop-version for more information.
6715
6716           max-iterations-to-track
6717               The maximum number of iterations of a loop the brute force
6718               algorithm for analysis of # of iterations of the loop tries to
6719               evaluate.
6720
6721           hot-bb-count-fraction
6722               Select fraction of the maximal count of repetitions of basic
6723               block in program given basic block needs to have to be
6724               considered hot.
6725
6726           hot-bb-frequency-fraction
6727               Select fraction of the maximal frequency of executions of basic
6728               block in function given basic block needs to have to be
6729               considered hot
6730
6731           max-predicted-iterations
6732               The maximum number of loop iterations we predict statically.
6733               This is useful in cases where function contain single loop with
6734               known bound and other loop with unknown.  We predict the known
6735               number of iterations correctly, while the unknown number of
6736               iterations average to roughly 10.  This means that the loop
6737               without bounds would appear artificially cold relative to the
6738               other one.
6739
6740           align-threshold
6741               Select fraction of the maximal frequency of executions of basic
6742               block in function given basic block will get aligned.
6743
6744           align-loop-iterations
6745               A loop expected to iterate at lest the selected number of
6746               iterations will get aligned.
6747
6748           tracer-dynamic-coverage
6749           tracer-dynamic-coverage-feedback
6750               This value is used to limit superblock formation once the given
6751               percentage of executed instructions is covered.  This limits
6752               unnecessary code size expansion.
6753
6754               The tracer-dynamic-coverage-feedback is used only when profile
6755               feedback is available.  The real profiles (as opposed to
6756               statically estimated ones) are much less balanced allowing the
6757               threshold to be larger value.
6758
6759           tracer-max-code-growth
6760               Stop tail duplication once code growth has reached given
6761               percentage.  This is rather hokey argument, as most of the
6762               duplicates will be eliminated later in cross jumping, so it may
6763               be set to much higher values than is the desired code growth.
6764
6765           tracer-min-branch-ratio
6766               Stop reverse growth when the reverse probability of best edge
6767               is less than this threshold (in percent).
6768
6769           tracer-min-branch-ratio
6770           tracer-min-branch-ratio-feedback
6771               Stop forward growth if the best edge do have probability lower
6772               than this threshold.
6773
6774               Similarly to tracer-dynamic-coverage two values are present,
6775               one for compilation for profile feedback and one for
6776               compilation without.  The value for compilation with profile
6777               feedback needs to be more conservative (higher) in order to
6778               make tracer effective.
6779
6780           max-cse-path-length
6781               Maximum number of basic blocks on path that cse considers.  The
6782               default is 10.
6783
6784           max-cse-insns
6785               The maximum instructions CSE process before flushing. The
6786               default is 1000.
6787
6788           ggc-min-expand
6789               GCC uses a garbage collector to manage its own memory
6790               allocation.  This parameter specifies the minimum percentage by
6791               which the garbage collector's heap should be allowed to expand
6792               between collections.  Tuning this may improve compilation
6793               speed; it has no effect on code generation.
6794
6795               The default is 30% + 70% * (RAM/1GB) with an upper bound of
6796               100% when RAM >= 1GB.  If "getrlimit" is available, the notion
6797               of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or
6798               "RLIMIT_AS".  If GCC is not able to calculate RAM on a
6799               particular platform, the lower bound of 30% is used.  Setting
6800               this parameter and ggc-min-heapsize to zero causes a full
6801               collection to occur at every opportunity.  This is extremely
6802               slow, but can be useful for debugging.
6803
6804           ggc-min-heapsize
6805               Minimum size of the garbage collector's heap before it begins
6806               bothering to collect garbage.  The first collection occurs
6807               after the heap expands by ggc-min-expand% beyond ggc-min-
6808               heapsize.  Again, tuning this may improve compilation speed,
6809               and has no effect on code generation.
6810
6811               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
6812               which tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
6813               exceeded, but with a lower bound of 4096 (four megabytes) and
6814               an upper bound of 131072 (128 megabytes).  If GCC is not able
6815               to calculate RAM on a particular platform, the lower bound is
6816               used.  Setting this parameter very large effectively disables
6817               garbage collection.  Setting this parameter and ggc-min-expand
6818               to zero causes a full collection to occur at every opportunity.
6819
6820           max-reload-search-insns
6821               The maximum number of instruction reload should look backward
6822               for equivalent register.  Increasing values mean more
6823               aggressive optimization, making the compile time increase with
6824               probably slightly better performance.  The default value is
6825               100.
6826
6827           max-cselib-memory-locations
6828               The maximum number of memory locations cselib should take into
6829               account.  Increasing values mean more aggressive optimization,
6830               making the compile time increase with probably slightly better
6831               performance.  The default value is 500.
6832
6833           reorder-blocks-duplicate
6834           reorder-blocks-duplicate-feedback
6835               Used by basic block reordering pass to decide whether to use
6836               unconditional branch or duplicate the code on its destination.
6837               Code is duplicated when its estimated size is smaller than this
6838               value multiplied by the estimated size of unconditional jump in
6839               the hot spots of the program.
6840
6841               The reorder-block-duplicate-feedback is used only when profile
6842               feedback is available and may be set to higher values than
6843               reorder-block-duplicate since information about the hot spots
6844               is more accurate.
6845
6846           max-sched-ready-insns
6847               The maximum number of instructions ready to be issued the
6848               scheduler should consider at any given time during the first
6849               scheduling pass.  Increasing values mean more thorough
6850               searches, making the compilation time increase with probably
6851               little benefit.  The default value is 100.
6852
6853           max-sched-region-blocks
6854               The maximum number of blocks in a region to be considered for
6855               interblock scheduling.  The default value is 10.
6856
6857           max-pipeline-region-blocks
6858               The maximum number of blocks in a region to be considered for
6859               pipelining in the selective scheduler.  The default value is
6860               15.
6861
6862           max-sched-region-insns
6863               The maximum number of insns in a region to be considered for
6864               interblock scheduling.  The default value is 100.
6865
6866           max-pipeline-region-insns
6867               The maximum number of insns in a region to be considered for
6868               pipelining in the selective scheduler.  The default value is
6869               200.
6870
6871           min-spec-prob
6872               The minimum probability (in percents) of reaching a source
6873               block for interblock speculative scheduling.  The default value
6874               is 40.
6875
6876           max-sched-extend-regions-iters
6877               The maximum number of iterations through CFG to extend regions.
6878               0 - disable region extension, N - do at most N iterations.  The
6879               default value is 0.
6880
6881           max-sched-insn-conflict-delay
6882               The maximum conflict delay for an insn to be considered for
6883               speculative motion.  The default value is 3.
6884
6885           sched-spec-prob-cutoff
6886               The minimal probability of speculation success (in percents),
6887               so that speculative insn will be scheduled.  The default value
6888               is 40.
6889
6890           sched-mem-true-dep-cost
6891               Minimal distance (in CPU cycles) between store and load
6892               targeting same memory locations.  The default value is 1.
6893
6894           selsched-max-lookahead
6895               The maximum size of the lookahead window of selective
6896               scheduling.  It is a depth of search for available
6897               instructions.  The default value is 50.
6898
6899           selsched-max-sched-times
6900               The maximum number of times that an instruction will be
6901               scheduled during selective scheduling.  This is the limit on
6902               the number of iterations through which the instruction may be
6903               pipelined.  The default value is 2.
6904
6905           selsched-max-insns-to-rename
6906               The maximum number of best instructions in the ready list that
6907               are considered for renaming in the selective scheduler.  The
6908               default value is 2.
6909
6910           max-last-value-rtl
6911               The maximum size measured as number of RTLs that can be
6912               recorded in an expression in combiner for a pseudo register as
6913               last known value of that register.  The default is 10000.
6914
6915           integer-share-limit
6916               Small integer constants can use a shared data structure,
6917               reducing the compiler's memory usage and increasing its speed.
6918               This sets the maximum value of a shared integer constant.  The
6919               default value is 256.
6920
6921           min-virtual-mappings
6922               Specifies the minimum number of virtual mappings in the
6923               incremental SSA updater that should be registered to trigger
6924               the virtual mappings heuristic defined by virtual-mappings-
6925               ratio.  The default value is 100.
6926
6927           virtual-mappings-ratio
6928               If the number of virtual mappings is virtual-mappings-ratio
6929               bigger than the number of virtual symbols to be updated, then
6930               the incremental SSA updater switches to a full update for those
6931               symbols.  The default ratio is 3.
6932
6933           ssp-buffer-size
6934               The minimum size of buffers (i.e. arrays) that will receive
6935               stack smashing protection when -fstack-protection is used.
6936
6937           max-jump-thread-duplication-stmts
6938               Maximum number of statements allowed in a block that needs to
6939               be duplicated when threading jumps.
6940
6941           max-fields-for-field-sensitive
6942               Maximum number of fields in a structure we will treat in a
6943               field sensitive manner during pointer analysis.  The default is
6944               zero for -O0, and -O1 and 100 for -Os, -O2, and -O3.
6945
6946           prefetch-latency
6947               Estimate on average number of instructions that are executed
6948               before prefetch finishes.  The distance we prefetch ahead is
6949               proportional to this constant.  Increasing this number may also
6950               lead to less streams being prefetched (see simultaneous-
6951               prefetches).
6952
6953           simultaneous-prefetches
6954               Maximum number of prefetches that can run at the same time.
6955
6956           l1-cache-line-size
6957               The size of cache line in L1 cache, in bytes.
6958
6959           l1-cache-size
6960               The size of L1 cache, in kilobytes.
6961
6962           l2-cache-size
6963               The size of L2 cache, in kilobytes.
6964
6965           min-insn-to-prefetch-ratio
6966               The minimum ratio between the number of instructions and the
6967               number of prefetches to enable prefetching in a loop with an
6968               unknown trip count.
6969
6970           prefetch-min-insn-to-mem-ratio
6971               The minimum ratio between the number of instructions and the
6972               number of memory references to enable prefetching in a loop.
6973
6974           use-canonical-types
6975               Whether the compiler should use the "canonical" type system.
6976               By default, this should always be 1, which uses a more
6977               efficient internal mechanism for comparing types in C++ and
6978               Objective-C++.  However, if bugs in the canonical type system
6979               are causing compilation failures, set this value to 0 to
6980               disable canonical types.
6981
6982           switch-conversion-max-branch-ratio
6983               Switch initialization conversion will refuse to create arrays
6984               that are bigger than switch-conversion-max-branch-ratio times
6985               the number of branches in the switch.
6986
6987           max-partial-antic-length
6988               Maximum length of the partial antic set computed during the
6989               tree partial redundancy elimination optimization (-ftree-pre)
6990               when optimizing at -O3 and above.  For some sorts of source
6991               code the enhanced partial redundancy elimination optimization
6992               can run away, consuming all of the memory available on the host
6993               machine.  This parameter sets a limit on the length of the sets
6994               that are computed, which prevents the runaway behavior.
6995               Setting a value of 0 for this parameter will allow an unlimited
6996               set length.
6997
6998           sccvn-max-scc-size
6999               Maximum size of a strongly connected component (SCC) during
7000               SCCVN processing.  If this limit is hit, SCCVN processing for
7001               the whole function will not be done and optimizations depending
7002               on it will be disabled.  The default maximum SCC size is 10000.
7003
7004           ira-max-loops-num
7005               IRA uses a regional register allocation by default.  If a
7006               function contains loops more than number given by the
7007               parameter, only at most given number of the most frequently
7008               executed loops will form regions for the regional register
7009               allocation.  The default value of the parameter is 100.
7010
7011           ira-max-conflict-table-size
7012               Although IRA uses a sophisticated algorithm of compression
7013               conflict table, the table can be still big for huge functions.
7014               If the conflict table for a function could be more than size in
7015               MB given by the parameter, the conflict table is not built and
7016               faster, simpler, and lower quality register allocation
7017               algorithm will be used.  The algorithm do not use pseudo-
7018               register conflicts.  The default value of the parameter is
7019               2000.
7020
7021           ira-loop-reserved-regs
7022               IRA can be used to evaluate more accurate register pressure in
7023               loops for decision to move loop invariants (see -O3).  The
7024               number of available registers reserved for some other purposes
7025               is described by this parameter.  The default value of the
7026               parameter is 2 which is minimal number of registers needed for
7027               execution of typical instruction.  This value is the best found
7028               from numerous experiments.
7029
7030           loop-invariant-max-bbs-in-loop
7031               Loop invariant motion can be very expensive, both in compile
7032               time and in amount of needed compile time memory, with very
7033               large loops.  Loops with more basic blocks than this parameter
7034               won't have loop invariant motion optimization performed on
7035               them.  The default value of the parameter is 1000 for -O1 and
7036               10000 for -O2 and above.
7037
7038           max-vartrack-size
7039               Sets a maximum number of hash table slots to use during
7040               variable tracking dataflow analysis of any function.  If this
7041               limit is exceeded with variable tracking at assignments
7042               enabled, analysis for that function is retried without it,
7043               after removing all debug insns from the function.  If the limit
7044               is exceeded even without debug insns, var tracking analysis is
7045               completely disabled for the function.  Setting the parameter to
7046               zero makes it unlimited.
7047
7048           min-nondebug-insn-uid
7049               Use uids starting at this parameter for nondebug insns.  The
7050               range below the parameter is reserved exclusively for debug
7051               insns created by -fvar-tracking-assignments, but debug insns
7052               may get (non-overlapping) uids above it if the reserved range
7053               is exhausted.
7054
7055           ipa-sra-ptr-growth-factor
7056               IPA-SRA will replace a pointer to an aggregate with one or more
7057               new parameters only when their cumulative size is less or equal
7058               to ipa-sra-ptr-growth-factor times the size of the original
7059               pointer parameter.
7060
7061           graphite-max-nb-scop-params
7062               To avoid exponential effects in the Graphite loop transforms,
7063               the number of parameters in a Static Control Part (SCoP) is
7064               bounded.  The default value is 10 parameters.  A variable whose
7065               value is unknown at compile time and defined outside a SCoP is
7066               a parameter of the SCoP.
7067
7068           graphite-max-bbs-per-function
7069               To avoid exponential effects in the detection of SCoPs, the
7070               size of the functions analyzed by Graphite is bounded.  The
7071               default value is 100 basic blocks.
7072
7073           loop-block-tile-size
7074               Loop blocking or strip mining transforms, enabled with
7075               -floop-block or -floop-strip-mine, strip mine each loop in the
7076               loop nest by a given number of iterations.  The strip length
7077               can be changed using the loop-block-tile-size parameter.  The
7078               default value is 51 iterations.
7079
7080   Options Controlling the Preprocessor
7081       These options control the C preprocessor, which is run on each C source
7082       file before actual compilation.
7083
7084       If you use the -E option, nothing is done except preprocessing.  Some
7085       of these options make sense only together with -E because they cause
7086       the preprocessor output to be unsuitable for actual compilation.
7087
7088       -Wp,option
7089           You can use -Wp,option to bypass the compiler driver and pass
7090           option directly through to the preprocessor.  If option contains
7091           commas, it is split into multiple options at the commas.  However,
7092           many options are modified, translated or interpreted by the
7093           compiler driver before being passed to the preprocessor, and -Wp
7094           forcibly bypasses this phase.  The preprocessor's direct interface
7095           is undocumented and subject to change, so whenever possible you
7096           should avoid using -Wp and let the driver handle the options
7097           instead.
7098
7099       -Xpreprocessor option
7100           Pass option as an option to the preprocessor.  You can use this to
7101           supply system-specific preprocessor options which GCC does not know
7102           how to recognize.
7103
7104           If you want to pass an option that takes an argument, you must use
7105           -Xpreprocessor twice, once for the option and once for the
7106           argument.
7107
7108       -D name
7109           Predefine name as a macro, with definition 1.
7110
7111       -D name=definition
7112           The contents of definition are tokenized and processed as if they
7113           appeared during translation phase three in a #define directive.  In
7114           particular, the definition will be truncated by embedded newline
7115           characters.
7116
7117           If you are invoking the preprocessor from a shell or shell-like
7118           program you may need to use the shell's quoting syntax to protect
7119           characters such as spaces that have a meaning in the shell syntax.
7120
7121           If you wish to define a function-like macro on the command line,
7122           write its argument list with surrounding parentheses before the
7123           equals sign (if any).  Parentheses are meaningful to most shells,
7124           so you will need to quote the option.  With sh and csh,
7125           -D'name(args...)=definition' works.
7126
7127           -D and -U options are processed in the order they are given on the
7128           command line.  All -imacros file and -include file options are
7129           processed after all -D and -U options.
7130
7131       -U name
7132           Cancel any previous definition of name, either built in or provided
7133           with a -D option.
7134
7135       -undef
7136           Do not predefine any system-specific or GCC-specific macros.  The
7137           standard predefined macros remain defined.
7138
7139       -I dir
7140           Add the directory dir to the list of directories to be searched for
7141           header files.  Directories named by -I are searched before the
7142           standard system include directories.  If the directory dir is a
7143           standard system include directory, the option is ignored to ensure
7144           that the default search order for system directories and the
7145           special treatment of system headers are not defeated .  If dir
7146           begins with "=", then the "=" will be replaced by the sysroot
7147           prefix; see --sysroot and -isysroot.
7148
7149       -o file
7150           Write output to file.  This is the same as specifying file as the
7151           second non-option argument to cpp.  gcc has a different
7152           interpretation of a second non-option argument, so you must use -o
7153           to specify the output file.
7154
7155       -Wall
7156           Turns on all optional warnings which are desirable for normal code.
7157           At present this is -Wcomment, -Wtrigraphs, -Wmultichar and a
7158           warning about integer promotion causing a change of sign in "#if"
7159           expressions.  Note that many of the preprocessor's warnings are on
7160           by default and have no options to control them.
7161
7162       -Wcomment
7163       -Wcomments
7164           Warn whenever a comment-start sequence /* appears in a /* comment,
7165           or whenever a backslash-newline appears in a // comment.  (Both
7166           forms have the same effect.)
7167
7168       -Wtrigraphs
7169           Most trigraphs in comments cannot affect the meaning of the
7170           program.  However, a trigraph that would form an escaped newline
7171           (??/ at the end of a line) can, by changing where the comment
7172           begins or ends.  Therefore, only trigraphs that would form escaped
7173           newlines produce warnings inside a comment.
7174
7175           This option is implied by -Wall.  If -Wall is not given, this
7176           option is still enabled unless trigraphs are enabled.  To get
7177           trigraph conversion without warnings, but get the other -Wall
7178           warnings, use -trigraphs -Wall -Wno-trigraphs.
7179
7180       -Wtraditional
7181           Warn about certain constructs that behave differently in
7182           traditional and ISO C.  Also warn about ISO C constructs that have
7183           no traditional C equivalent, and problematic constructs which
7184           should be avoided.
7185
7186       -Wundef
7187           Warn whenever an identifier which is not a macro is encountered in
7188           an #if directive, outside of defined.  Such identifiers are
7189           replaced with zero.
7190
7191       -Wunused-macros
7192           Warn about macros defined in the main file that are unused.  A
7193           macro is used if it is expanded or tested for existence at least
7194           once.  The preprocessor will also warn if the macro has not been
7195           used at the time it is redefined or undefined.
7196
7197           Built-in macros, macros defined on the command line, and macros
7198           defined in include files are not warned about.
7199
7200           Note: If a macro is actually used, but only used in skipped
7201           conditional blocks, then CPP will report it as unused.  To avoid
7202           the warning in such a case, you might improve the scope of the
7203           macro's definition by, for example, moving it into the first
7204           skipped block.  Alternatively, you could provide a dummy use with
7205           something like:
7206
7207                   #if defined the_macro_causing_the_warning
7208                   #endif
7209
7210       -Wendif-labels
7211           Warn whenever an #else or an #endif are followed by text.  This
7212           usually happens in code of the form
7213
7214                   #if FOO
7215                   ...
7216                   #else FOO
7217                   ...
7218                   #endif FOO
7219
7220           The second and third "FOO" should be in comments, but often are not
7221           in older programs.  This warning is on by default.
7222
7223       -Werror
7224           Make all warnings into hard errors.  Source code which triggers
7225           warnings will be rejected.
7226
7227       -Wsystem-headers
7228           Issue warnings for code in system headers.  These are normally
7229           unhelpful in finding bugs in your own code, therefore suppressed.
7230           If you are responsible for the system library, you may want to see
7231           them.
7232
7233       -w  Suppress all warnings, including those which GNU CPP issues by
7234           default.
7235
7236       -pedantic
7237           Issue all the mandatory diagnostics listed in the C standard.  Some
7238           of them are left out by default, since they trigger frequently on
7239           harmless code.
7240
7241       -pedantic-errors
7242           Issue all the mandatory diagnostics, and make all mandatory
7243           diagnostics into errors.  This includes mandatory diagnostics that
7244           GCC issues without -pedantic but treats as warnings.
7245
7246       -M  Instead of outputting the result of preprocessing, output a rule
7247           suitable for make describing the dependencies of the main source
7248           file.  The preprocessor outputs one make rule containing the object
7249           file name for that source file, a colon, and the names of all the
7250           included files, including those coming from -include or -imacros
7251           command line options.
7252
7253           Unless specified explicitly (with -MT or -MQ), the object file name
7254           consists of the name of the source file with any suffix replaced
7255           with object file suffix and with any leading directory parts
7256           removed.  If there are many included files then the rule is split
7257           into several lines using \-newline.  The rule has no commands.
7258
7259           This option does not suppress the preprocessor's debug output, such
7260           as -dM.  To avoid mixing such debug output with the dependency
7261           rules you should explicitly specify the dependency output file with
7262           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
7263           Debug output will still be sent to the regular output stream as
7264           normal.
7265
7266           Passing -M to the driver implies -E, and suppresses warnings with
7267           an implicit -w.
7268
7269       -MM Like -M but do not mention header files that are found in system
7270           header directories, nor header files that are included, directly or
7271           indirectly, from such a header.
7272
7273           This implies that the choice of angle brackets or double quotes in
7274           an #include directive does not in itself determine whether that
7275           header will appear in -MM dependency output.  This is a slight
7276           change in semantics from GCC versions 3.0 and earlier.
7277
7278       -MF file
7279           When used with -M or -MM, specifies a file to write the
7280           dependencies to.  If no -MF switch is given the preprocessor sends
7281           the rules to the same place it would have sent preprocessed output.
7282
7283           When used with the driver options -MD or -MMD, -MF overrides the
7284           default dependency output file.
7285
7286       -MG In conjunction with an option such as -M requesting dependency
7287           generation, -MG assumes missing header files are generated files
7288           and adds them to the dependency list without raising an error.  The
7289           dependency filename is taken directly from the "#include" directive
7290           without prepending any path.  -MG also suppresses preprocessed
7291           output, as a missing header file renders this useless.
7292
7293           This feature is used in automatic updating of makefiles.
7294
7295       -MP This option instructs CPP to add a phony target for each dependency
7296           other than the main file, causing each to depend on nothing.  These
7297           dummy rules work around errors make gives if you remove header
7298           files without updating the Makefile to match.
7299
7300           This is typical output:
7301
7302                   test.o: test.c test.h
7303
7304                   test.h:
7305
7306       -MT target
7307           Change the target of the rule emitted by dependency generation.  By
7308           default CPP takes the name of the main input file, deletes any
7309           directory components and any file suffix such as .c, and appends
7310           the platform's usual object suffix.  The result is the target.
7311
7312           An -MT option will set the target to be exactly the string you
7313           specify.  If you want multiple targets, you can specify them as a
7314           single argument to -MT, or use multiple -MT options.
7315
7316           For example, -MT '$(objpfx)foo.o' might give
7317
7318                   $(objpfx)foo.o: foo.c
7319
7320       -MQ target
7321           Same as -MT, but it quotes any characters which are special to
7322           Make.  -MQ '$(objpfx)foo.o' gives
7323
7324                   $$(objpfx)foo.o: foo.c
7325
7326           The default target is automatically quoted, as if it were given
7327           with -MQ.
7328
7329       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
7330           The driver determines file based on whether an -o option is given.
7331           If it is, the driver uses its argument but with a suffix of .d,
7332           otherwise it takes the name of the input file, removes any
7333           directory components and suffix, and applies a .d suffix.
7334
7335           If -MD is used in conjunction with -E, any -o switch is understood
7336           to specify the dependency output file, but if used without -E, each
7337           -o is understood to specify a target object file.
7338
7339           Since -E is not implied, -MD can be used to generate a dependency
7340           output file as a side-effect of the compilation process.
7341
7342       -MMD
7343           Like -MD except mention only user header files, not system header
7344           files.
7345
7346       -fpch-deps
7347           When using precompiled headers, this flag will cause the
7348           dependency-output flags to also list the files from the precompiled
7349           header's dependencies.  If not specified only the precompiled
7350           header would be listed and not the files that were used to create
7351           it because those files are not consulted when a precompiled header
7352           is used.
7353
7354       -fpch-preprocess
7355           This option allows use of a precompiled header together with -E.
7356           It inserts a special "#pragma", "#pragma GCC pch_preprocess
7357           "<filename>"" in the output to mark the place where the precompiled
7358           header was found, and its filename.  When -fpreprocessed is in use,
7359           GCC recognizes this "#pragma" and loads the PCH.
7360
7361           This option is off by default, because the resulting preprocessed
7362           output is only really suitable as input to GCC.  It is switched on
7363           by -save-temps.
7364
7365           You should not write this "#pragma" in your own code, but it is
7366           safe to edit the filename if the PCH file is available in a
7367           different location.  The filename may be absolute or it may be
7368           relative to GCC's current directory.
7369
7370       -x c
7371       -x c++
7372       -x objective-c
7373       -x assembler-with-cpp
7374           Specify the source language: C, C++, Objective-C, or assembly.
7375           This has nothing to do with standards conformance or extensions; it
7376           merely selects which base syntax to expect.  If you give none of
7377           these options, cpp will deduce the language from the extension of
7378           the source file: .c, .cc, .m, or .S.  Some other common extensions
7379           for C++ and assembly are also recognized.  If cpp does not
7380           recognize the extension, it will treat the file as C; this is the
7381           most generic mode.
7382
7383           Note: Previous versions of cpp accepted a -lang option which
7384           selected both the language and the standards conformance level.
7385           This option has been removed, because it conflicts with the -l
7386           option.
7387
7388       -std=standard
7389       -ansi
7390           Specify the standard to which the code should conform.  Currently
7391           CPP knows about C and C++ standards; others may be added in the
7392           future.
7393
7394           standard may be one of:
7395
7396           "c90"
7397           "c89"
7398           "iso9899:1990"
7399               The ISO C standard from 1990.  c90 is the customary shorthand
7400               for this version of the standard.
7401
7402               The -ansi option is equivalent to -std=c90.
7403
7404           "iso9899:199409"
7405               The 1990 C standard, as amended in 1994.
7406
7407           "iso9899:1999"
7408           "c99"
7409           "iso9899:199x"
7410           "c9x"
7411               The revised ISO C standard, published in December 1999.  Before
7412               publication, this was known as C9X.
7413
7414           "gnu90"
7415           "gnu89"
7416               The 1990 C standard plus GNU extensions.  This is the default.
7417
7418           "gnu99"
7419           "gnu9x"
7420               The 1999 C standard plus GNU extensions.
7421
7422           "c++98"
7423               The 1998 ISO C++ standard plus amendments.
7424
7425           "gnu++98"
7426               The same as -std=c++98 plus GNU extensions.  This is the
7427               default for C++ code.
7428
7429       -I- Split the include path.  Any directories specified with -I options
7430           before -I- are searched only for headers requested with
7431           "#include "file""; they are not searched for "#include <file>".  If
7432           additional directories are specified with -I options after the -I-,
7433           those directories are searched for all #include directives.
7434
7435           In addition, -I- inhibits the use of the directory of the current
7436           file directory as the first search directory for "#include "file"".
7437           This option has been deprecated.
7438
7439       -nostdinc
7440           Do not search the standard system directories for header files.
7441           Only the directories you have specified with -I options (and the
7442           directory of the current file, if appropriate) are searched.
7443
7444       -nostdinc++
7445           Do not search for header files in the C++-specific standard
7446           directories, but do still search the other standard directories.
7447           (This option is used when building the C++ library.)
7448
7449       -include file
7450           Process file as if "#include "file"" appeared as the first line of
7451           the primary source file.  However, the first directory searched for
7452           file is the preprocessor's working directory instead of the
7453           directory containing the main source file.  If not found there, it
7454           is searched for in the remainder of the "#include "..."" search
7455           chain as normal.
7456
7457           If multiple -include options are given, the files are included in
7458           the order they appear on the command line.
7459
7460       -imacros file
7461           Exactly like -include, except that any output produced by scanning
7462           file is thrown away.  Macros it defines remain defined.  This
7463           allows you to acquire all the macros from a header without also
7464           processing its declarations.
7465
7466           All files specified by -imacros are processed before all files
7467           specified by -include.
7468
7469       -idirafter dir
7470           Search dir for header files, but do it after all directories
7471           specified with -I and the standard system directories have been
7472           exhausted.  dir is treated as a system include directory.  If dir
7473           begins with "=", then the "=" will be replaced by the sysroot
7474           prefix; see --sysroot and -isysroot.
7475
7476       -iprefix prefix
7477           Specify prefix as the prefix for subsequent -iwithprefix options.
7478           If the prefix represents a directory, you should include the final
7479           /.
7480
7481       -iwithprefix dir
7482       -iwithprefixbefore dir
7483           Append dir to the prefix specified previously with -iprefix, and
7484           add the resulting directory to the include search path.
7485           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
7486           puts it where -idirafter would.
7487
7488       -isysroot dir
7489           This option is like the --sysroot option, but applies only to
7490           header files.  See the --sysroot option for more information.
7491
7492       -imultilib dir
7493           Use dir as a subdirectory of the directory containing target-
7494           specific C++ headers.
7495
7496       -isystem dir
7497           Search dir for header files, after all directories specified by -I
7498           but before the standard system directories.  Mark it as a system
7499           directory, so that it gets the same special treatment as is applied
7500           to the standard system directories.  If dir begins with "=", then
7501           the "=" will be replaced by the sysroot prefix; see --sysroot and
7502           -isysroot.
7503
7504       -iquote dir
7505           Search dir only for header files requested with "#include "file"";
7506           they are not searched for "#include <file>", before all directories
7507           specified by -I and before the standard system directories.  If dir
7508           begins with "=", then the "=" will be replaced by the sysroot
7509           prefix; see --sysroot and -isysroot.
7510
7511       -fdirectives-only
7512           When preprocessing, handle directives, but do not expand macros.
7513
7514           The option's behavior depends on the -E and -fpreprocessed options.
7515
7516           With -E, preprocessing is limited to the handling of directives
7517           such as "#define", "#ifdef", and "#error".  Other preprocessor
7518           operations, such as macro expansion and trigraph conversion are not
7519           performed.  In addition, the -dD option is implicitly enabled.
7520
7521           With -fpreprocessed, predefinition of command line and most builtin
7522           macros is disabled.  Macros such as "__LINE__", which are
7523           contextually dependent, are handled normally.  This enables
7524           compilation of files previously preprocessed with "-E
7525           -fdirectives-only".
7526
7527           With both -E and -fpreprocessed, the rules for -fpreprocessed take
7528           precedence.  This enables full preprocessing of files previously
7529           preprocessed with "-E -fdirectives-only".
7530
7531       -fdollars-in-identifiers
7532           Accept $ in identifiers.
7533
7534       -fextended-identifiers
7535           Accept universal character names in identifiers.  This option is
7536           experimental; in a future version of GCC, it will be enabled by
7537           default for C99 and C++.
7538
7539       -fpreprocessed
7540           Indicate to the preprocessor that the input file has already been
7541           preprocessed.  This suppresses things like macro expansion,
7542           trigraph conversion, escaped newline splicing, and processing of
7543           most directives.  The preprocessor still recognizes and removes
7544           comments, so that you can pass a file preprocessed with -C to the
7545           compiler without problems.  In this mode the integrated
7546           preprocessor is little more than a tokenizer for the front ends.
7547
7548           -fpreprocessed is implicit if the input file has one of the
7549           extensions .i, .ii or .mi.  These are the extensions that GCC uses
7550           for preprocessed files created by -save-temps.
7551
7552       -ftabstop=width
7553           Set the distance between tab stops.  This helps the preprocessor
7554           report correct column numbers in warnings or errors, even if tabs
7555           appear on the line.  If the value is less than 1 or greater than
7556           100, the option is ignored.  The default is 8.
7557
7558       -fexec-charset=charset
7559           Set the execution character set, used for string and character
7560           constants.  The default is UTF-8.  charset can be any encoding
7561           supported by the system's "iconv" library routine.
7562
7563       -fwide-exec-charset=charset
7564           Set the wide execution character set, used for wide string and
7565           character constants.  The default is UTF-32 or UTF-16, whichever
7566           corresponds to the width of "wchar_t".  As with -fexec-charset,
7567           charset can be any encoding supported by the system's "iconv"
7568           library routine; however, you will have problems with encodings
7569           that do not fit exactly in "wchar_t".
7570
7571       -finput-charset=charset
7572           Set the input character set, used for translation from the
7573           character set of the input file to the source character set used by
7574           GCC.  If the locale does not specify, or GCC cannot get this
7575           information from the locale, the default is UTF-8.  This can be
7576           overridden by either the locale or this command line option.
7577           Currently the command line option takes precedence if there's a
7578           conflict.  charset can be any encoding supported by the system's
7579           "iconv" library routine.
7580
7581       -fworking-directory
7582           Enable generation of linemarkers in the preprocessor output that
7583           will let the compiler know the current working directory at the
7584           time of preprocessing.  When this option is enabled, the
7585           preprocessor will emit, after the initial linemarker, a second
7586           linemarker with the current working directory followed by two
7587           slashes.  GCC will use this directory, when it's present in the
7588           preprocessed input, as the directory emitted as the current working
7589           directory in some debugging information formats.  This option is
7590           implicitly enabled if debugging information is enabled, but this
7591           can be inhibited with the negated form -fno-working-directory.  If
7592           the -P flag is present in the command line, this option has no
7593           effect, since no "#line" directives are emitted whatsoever.
7594
7595       -fno-show-column
7596           Do not print column numbers in diagnostics.  This may be necessary
7597           if diagnostics are being scanned by a program that does not
7598           understand the column numbers, such as dejagnu.
7599
7600       -A predicate=answer
7601           Make an assertion with the predicate predicate and answer answer.
7602           This form is preferred to the older form -A predicate(answer),
7603           which is still supported, because it does not use shell special
7604           characters.
7605
7606       -A -predicate=answer
7607           Cancel an assertion with the predicate predicate and answer answer.
7608
7609       -dCHARS
7610           CHARS is a sequence of one or more of the following characters, and
7611           must not be preceded by a space.  Other characters are interpreted
7612           by the compiler proper, or reserved for future versions of GCC, and
7613           so are silently ignored.  If you specify characters whose behavior
7614           conflicts, the result is undefined.
7615
7616           M   Instead of the normal output, generate a list of #define
7617               directives for all the macros defined during the execution of
7618               the preprocessor, including predefined macros.  This gives you
7619               a way of finding out what is predefined in your version of the
7620               preprocessor.  Assuming you have no file foo.h, the command
7621
7622                       touch foo.h; cpp -dM foo.h
7623
7624               will show all the predefined macros.
7625
7626               If you use -dM without the -E option, -dM is interpreted as a
7627               synonym for -fdump-rtl-mach.
7628
7629           D   Like M except in two respects: it does not include the
7630               predefined macros, and it outputs both the #define directives
7631               and the result of preprocessing.  Both kinds of output go to
7632               the standard output file.
7633
7634           N   Like D, but emit only the macro names, not their expansions.
7635
7636           I   Output #include directives in addition to the result of
7637               preprocessing.
7638
7639           U   Like D except that only macros that are expanded, or whose
7640               definedness is tested in preprocessor directives, are output;
7641               the output is delayed until the use or test of the macro; and
7642               #undef directives are also output for macros tested but
7643               undefined at the time.
7644
7645       -P  Inhibit generation of linemarkers in the output from the
7646           preprocessor.  This might be useful when running the preprocessor
7647           on something that is not C code, and will be sent to a program
7648           which might be confused by the linemarkers.
7649
7650       -C  Do not discard comments.  All comments are passed through to the
7651           output file, except for comments in processed directives, which are
7652           deleted along with the directive.
7653
7654           You should be prepared for side effects when using -C; it causes
7655           the preprocessor to treat comments as tokens in their own right.
7656           For example, comments appearing at the start of what would be a
7657           directive line have the effect of turning that line into an
7658           ordinary source line, since the first token on the line is no
7659           longer a #.
7660
7661       -CC Do not discard comments, including during macro expansion.  This is
7662           like -C, except that comments contained within macros are also
7663           passed through to the output file where the macro is expanded.
7664
7665           In addition to the side-effects of the -C option, the -CC option
7666           causes all C++-style comments inside a macro to be converted to
7667           C-style comments.  This is to prevent later use of that macro from
7668           inadvertently commenting out the remainder of the source line.
7669
7670           The -CC option is generally used to support lint comments.
7671
7672       -traditional-cpp
7673           Try to imitate the behavior of old-fashioned C preprocessors, as
7674           opposed to ISO C preprocessors.
7675
7676       -trigraphs
7677           Process trigraph sequences.  These are three-character sequences,
7678           all starting with ??, that are defined by ISO C to stand for single
7679           characters.  For example, ??/ stands for \, so '??/n' is a
7680           character constant for a newline.  By default, GCC ignores
7681           trigraphs, but in standard-conforming modes it converts them.  See
7682           the -std and -ansi options.
7683
7684           The nine trigraphs and their replacements are
7685
7686                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
7687                   Replacement:      [    ]    {    }    #    \    ^    |    ~
7688
7689       -remap
7690           Enable special code to work around file systems which only permit
7691           very short file names, such as MS-DOS.
7692
7693       --help
7694       --target-help
7695           Print text describing all the command line options instead of
7696           preprocessing anything.
7697
7698       -v  Verbose mode.  Print out GNU CPP's version number at the beginning
7699           of execution, and report the final form of the include path.
7700
7701       -H  Print the name of each header file used, in addition to other
7702           normal activities.  Each name is indented to show how deep in the
7703           #include stack it is.  Precompiled header files are also printed,
7704           even if they are found to be invalid; an invalid precompiled header
7705           file is printed with ...x and a valid one with ...! .
7706
7707       -version
7708       --version
7709           Print out GNU CPP's version number.  With one dash, proceed to
7710           preprocess as normal.  With two dashes, exit immediately.
7711
7712   Passing Options to the Assembler
7713       You can pass options to the assembler.
7714
7715       -Wa,option
7716           Pass option as an option to the assembler.  If option contains
7717           commas, it is split into multiple options at the commas.
7718
7719       -Xassembler option
7720           Pass option as an option to the assembler.  You can use this to
7721           supply system-specific assembler options which GCC does not know
7722           how to recognize.
7723
7724           If you want to pass an option that takes an argument, you must use
7725           -Xassembler twice, once for the option and once for the argument.
7726
7727   Options for Linking
7728       These options come into play when the compiler links object files into
7729       an executable output file.  They are meaningless if the compiler is not
7730       doing a link step.
7731
7732       object-file-name
7733           A file name that does not end in a special recognized suffix is
7734           considered to name an object file or library.  (Object files are
7735           distinguished from libraries by the linker according to the file
7736           contents.)  If linking is done, these object files are used as
7737           input to the linker.
7738
7739       -c
7740       -S
7741       -E  If any of these options is used, then the linker is not run, and
7742           object file names should not be used as arguments.
7743
7744       -llibrary
7745       -l library
7746           Search the library named library when linking.  (The second
7747           alternative with the library as a separate argument is only for
7748           POSIX compliance and is not recommended.)
7749
7750           It makes a difference where in the command you write this option;
7751           the linker searches and processes libraries and object files in the
7752           order they are specified.  Thus, foo.o -lz bar.o searches library z
7753           after file foo.o but before bar.o.  If bar.o refers to functions in
7754           z, those functions may not be loaded.
7755
7756           The linker searches a standard list of directories for the library,
7757           which is actually a file named liblibrary.a.  The linker then uses
7758           this file as if it had been specified precisely by name.
7759
7760           The directories searched include several standard system
7761           directories plus any that you specify with -L.
7762
7763           Normally the files found this way are library files---archive files
7764           whose members are object files.  The linker handles an archive file
7765           by scanning through it for members which define symbols that have
7766           so far been referenced but not defined.  But if the file that is
7767           found is an ordinary object file, it is linked in the usual
7768           fashion.  The only difference between using an -l option and
7769           specifying a file name is that -l surrounds library with lib and .a
7770           and searches several directories.
7771
7772       -lobjc
7773           You need this special case of the -l option in order to link an
7774           Objective-C or Objective-C++ program.
7775
7776       -nostartfiles
7777           Do not use the standard system startup files when linking.  The
7778           standard system libraries are used normally, unless -nostdlib or
7779           -nodefaultlibs is used.
7780
7781       -nodefaultlibs
7782           Do not use the standard system libraries when linking.  Only the
7783           libraries you specify will be passed to the linker, options
7784           specifying linkage of the system libraries, such as
7785           "-static-libgcc" or "-shared-libgcc", will be ignored.  The
7786           standard startup files are used normally, unless -nostartfiles is
7787           used.  The compiler may generate calls to "memcmp", "memset",
7788           "memcpy" and "memmove".  These entries are usually resolved by
7789           entries in libc.  These entry points should be supplied through
7790           some other mechanism when this option is specified.
7791
7792       -nostdlib
7793           Do not use the standard system startup files or libraries when
7794           linking.  No startup files and only the libraries you specify will
7795           be passed to the linker, options specifying linkage of the system
7796           libraries, such as "-static-libgcc" or "-shared-libgcc", will be
7797           ignored.  The compiler may generate calls to "memcmp", "memset",
7798           "memcpy" and "memmove".  These entries are usually resolved by
7799           entries in libc.  These entry points should be supplied through
7800           some other mechanism when this option is specified.
7801
7802           One of the standard libraries bypassed by -nostdlib and
7803           -nodefaultlibs is libgcc.a, a library of internal subroutines that
7804           GCC uses to overcome shortcomings of particular machines, or
7805           special needs for some languages.
7806
7807           In most cases, you need libgcc.a even when you want to avoid other
7808           standard libraries.  In other words, when you specify -nostdlib or
7809           -nodefaultlibs you should usually specify -lgcc as well.  This
7810           ensures that you have no unresolved references to internal GCC
7811           library subroutines.  (For example, __main, used to ensure C++
7812           constructors will be called.)
7813
7814       -pie
7815           Produce a position independent executable on targets which support
7816           it.  For predictable results, you must also specify the same set of
7817           options that were used to generate code (-fpie, -fPIE, or model
7818           suboptions) when you specify this option.
7819
7820       -rdynamic
7821           Pass the flag -export-dynamic to the ELF linker, on targets that
7822           support it. This instructs the linker to add all symbols, not only
7823           used ones, to the dynamic symbol table. This option is needed for
7824           some uses of "dlopen" or to allow obtaining backtraces from within
7825           a program.
7826
7827       -s  Remove all symbol table and relocation information from the
7828           executable.
7829
7830       -static
7831           On systems that support dynamic linking, this prevents linking with
7832           the shared libraries.  On other systems, this option has no effect.
7833
7834       -shared
7835           Produce a shared object which can then be linked with other objects
7836           to form an executable.  Not all systems support this option.  For
7837           predictable results, you must also specify the same set of options
7838           that were used to generate code (-fpic, -fPIC, or model suboptions)
7839           when you specify this option.[1]
7840
7841       -shared-libgcc
7842       -static-libgcc
7843           On systems that provide libgcc as a shared library, these options
7844           force the use of either the shared or static version respectively.
7845           If no shared version of libgcc was built when the compiler was
7846           configured, these options have no effect.
7847
7848           There are several situations in which an application should use the
7849           shared libgcc instead of the static version.  The most common of
7850           these is when the application wishes to throw and catch exceptions
7851           across different shared libraries.  In that case, each of the
7852           libraries as well as the application itself should use the shared
7853           libgcc.
7854
7855           Therefore, the G++ and GCJ drivers automatically add -shared-libgcc
7856           whenever you build a shared library or a main executable, because
7857           C++ and Java programs typically use exceptions, so this is the
7858           right thing to do.
7859
7860           If, instead, you use the GCC driver to create shared libraries, you
7861           may find that they will not always be linked with the shared
7862           libgcc.  If GCC finds, at its configuration time, that you have a
7863           non-GNU linker or a GNU linker that does not support option
7864           --eh-frame-hdr, it will link the shared version of libgcc into
7865           shared libraries by default.  Otherwise, it will take advantage of
7866           the linker and optimize away the linking with the shared version of
7867           libgcc, linking with the static version of libgcc by default.  This
7868           allows exceptions to propagate through such shared libraries,
7869           without incurring relocation costs at library load time.
7870
7871           However, if a library or main executable is supposed to throw or
7872           catch exceptions, you must link it using the G++ or GCJ driver, as
7873           appropriate for the languages used in the program, or using the
7874           option -shared-libgcc, such that it is linked with the shared
7875           libgcc.
7876
7877       -static-libstdc++
7878           When the g++ program is used to link a C++ program, it will
7879           normally automatically link against libstdc++.  If libstdc++ is
7880           available as a shared library, and the -static option is not used,
7881           then this will link against the shared version of libstdc++.  That
7882           is normally fine.  However, it is sometimes useful to freeze the
7883           version of libstdc++ used by the program without going all the way
7884           to a fully static link.  The -static-libstdc++ option directs the
7885           g++ driver to link libstdc++ statically, without necessarily
7886           linking other libraries statically.
7887
7888       -symbolic
7889           Bind references to global symbols when building a shared object.
7890           Warn about any unresolved references (unless overridden by the link
7891           editor option -Xlinker -z -Xlinker defs).  Only a few systems
7892           support this option.
7893
7894       -T script
7895           Use script as the linker script.  This option is supported by most
7896           systems using the GNU linker.  On some targets, such as bare-board
7897           targets without an operating system, the -T option may be required
7898           when linking to avoid references to undefined symbols.
7899
7900       -Xlinker option
7901           Pass option as an option to the linker.  You can use this to supply
7902           system-specific linker options which GCC does not know how to
7903           recognize.
7904
7905           If you want to pass an option that takes a separate argument, you
7906           must use -Xlinker twice, once for the option and once for the
7907           argument.  For example, to pass -assert definitions, you must write
7908           -Xlinker -assert -Xlinker definitions.  It does not work to write
7909           -Xlinker "-assert definitions", because this passes the entire
7910           string as a single argument, which is not what the linker expects.
7911
7912           When using the GNU linker, it is usually more convenient to pass
7913           arguments to linker options using the option=value syntax than as
7914           separate arguments.  For example, you can specify -Xlinker
7915           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
7916           Other linkers may not support this syntax for command-line options.
7917
7918       -Wl,option
7919           Pass option as an option to the linker.  If option contains commas,
7920           it is split into multiple options at the commas.  You can use this
7921           syntax to pass an argument to the option.  For example,
7922           -Wl,-Map,output.map passes -Map output.map to the linker.  When
7923           using the GNU linker, you can also get the same effect with
7924           -Wl,-Map=output.map.
7925
7926       -u symbol
7927           Pretend the symbol symbol is undefined, to force linking of library
7928           modules to define it.  You can use -u multiple times with different
7929           symbols to force loading of additional library modules.
7930
7931   Options for Directory Search
7932       These options specify directories to search for header files, for
7933       libraries and for parts of the compiler:
7934
7935       -Idir
7936           Add the directory dir to the head of the list of directories to be
7937           searched for header files.  This can be used to override a system
7938           header file, substituting your own version, since these directories
7939           are searched before the system header file directories.  However,
7940           you should not use this option to add directories that contain
7941           vendor-supplied system header files (use -isystem for that).  If
7942           you use more than one -I option, the directories are scanned in
7943           left-to-right order; the standard system directories come after.
7944
7945           If a standard system include directory, or a directory specified
7946           with -isystem, is also specified with -I, the -I option will be
7947           ignored.  The directory will still be searched but as a system
7948           directory at its normal position in the system include chain.  This
7949           is to ensure that GCC's procedure to fix buggy system headers and
7950           the ordering for the include_next directive are not inadvertently
7951           changed.  If you really need to change the search order for system
7952           directories, use the -nostdinc and/or -isystem options.
7953
7954       -iquotedir
7955           Add the directory dir to the head of the list of directories to be
7956           searched for header files only for the case of #include "file";
7957           they are not searched for #include <file>, otherwise just like -I.
7958
7959       -Ldir
7960           Add directory dir to the list of directories to be searched for -l.
7961
7962       -Bprefix
7963           This option specifies where to find the executables, libraries,
7964           include files, and data files of the compiler itself.
7965
7966           The compiler driver program runs one or more of the subprograms
7967           cpp, cc1, as and ld.  It tries prefix as a prefix for each program
7968           it tries to run, both with and without machine/version/.
7969
7970           For each subprogram to be run, the compiler driver first tries the
7971           -B prefix, if any.  If that name is not found, or if -B was not
7972           specified, the driver tries two standard prefixes, which are
7973           /usr/lib/gcc/ and /usr/local/lib/gcc/.  If neither of those results
7974           in a file name that is found, the unmodified program name is
7975           searched for using the directories specified in your PATH
7976           environment variable.
7977
7978           The compiler will check to see if the path provided by the -B
7979           refers to a directory, and if necessary it will add a directory
7980           separator character at the end of the path.
7981
7982           -B prefixes that effectively specify directory names also apply to
7983           libraries in the linker, because the compiler translates these
7984           options into -L options for the linker.  They also apply to
7985           includes files in the preprocessor, because the compiler translates
7986           these options into -isystem options for the preprocessor.  In this
7987           case, the compiler appends include to the prefix.
7988
7989           The run-time support file libgcc.a can also be searched for using
7990           the -B prefix, if needed.  If it is not found there, the two
7991           standard prefixes above are tried, and that is all.  The file is
7992           left out of the link if it is not found by those means.
7993
7994           Another way to specify a prefix much like the -B prefix is to use
7995           the environment variable GCC_EXEC_PREFIX.
7996
7997           As a special kludge, if the path provided by -B is [dir/]stageN/,
7998           where N is a number in the range 0 to 9, then it will be replaced
7999           by [dir/]include.  This is to help with boot-strapping the
8000           compiler.
8001
8002       -specs=file
8003           Process file after the compiler reads in the standard specs file,
8004           in order to override the defaults that the gcc driver program uses
8005           when determining what switches to pass to cc1, cc1plus, as, ld,
8006           etc.  More than one -specs=file can be specified on the command
8007           line, and they are processed in order, from left to right.
8008
8009       --sysroot=dir
8010           Use dir as the logical root directory for headers and libraries.
8011           For example, if the compiler would normally search for headers in
8012           /usr/include and libraries in /usr/lib, it will instead search
8013           dir/usr/include and dir/usr/lib.
8014
8015           If you use both this option and the -isysroot option, then the
8016           --sysroot option will apply to libraries, but the -isysroot option
8017           will apply to header files.
8018
8019           The GNU linker (beginning with version 2.16) has the necessary
8020           support for this option.  If your linker does not support this
8021           option, the header file aspect of --sysroot will still work, but
8022           the library aspect will not.
8023
8024       -I- This option has been deprecated.  Please use -iquote instead for -I
8025           directories before the -I- and remove the -I-.  Any directories you
8026           specify with -I options before the -I- option are searched only for
8027           the case of #include "file"; they are not searched for #include
8028           <file>.
8029
8030           If additional directories are specified with -I options after the
8031           -I-, these directories are searched for all #include directives.
8032           (Ordinarily all -I directories are used this way.)
8033
8034           In addition, the -I- option inhibits the use of the current
8035           directory (where the current input file came from) as the first
8036           search directory for #include "file".  There is no way to override
8037           this effect of -I-.  With -I. you can specify searching the
8038           directory which was current when the compiler was invoked.  That is
8039           not exactly the same as what the preprocessor does by default, but
8040           it is often satisfactory.
8041
8042           -I- does not inhibit the use of the standard system directories for
8043           header files.  Thus, -I- and -nostdinc are independent.
8044
8045   Specifying Target Machine and Compiler Version
8046       The usual way to run GCC is to run the executable called gcc, or
8047       <machine>-gcc when cross-compiling, or <machine>-gcc-<version> to run a
8048       version other than the one that was installed last.  Sometimes this is
8049       inconvenient, so GCC provides options that will switch to another
8050       cross-compiler or version.
8051
8052       -b machine
8053           The argument machine specifies the target machine for compilation.
8054
8055           The value to use for machine is the same as was specified as the
8056           machine type when configuring GCC as a cross-compiler.  For
8057           example, if a cross-compiler was configured with configure arm-elf,
8058           meaning to compile for an arm processor with elf binaries, then you
8059           would specify -b arm-elf to run that cross compiler.  Because there
8060           are other options beginning with -b, the configuration must contain
8061           a hyphen, or -b alone should be one argument followed by the
8062           configuration in the next argument.
8063
8064       -V version
8065           The argument version specifies which version of GCC to run.  This
8066           is useful when multiple versions are installed.  For example,
8067           version might be 4.0, meaning to run GCC version 4.0.
8068
8069       The -V and -b options work by running the <machine>-gcc-<version>
8070       executable, so there's no real reason to use them if you can just run
8071       that directly.
8072
8073   Hardware Models and Configurations
8074       Earlier we discussed the standard option -b which chooses among
8075       different installed compilers for completely different target machines,
8076       such as VAX vs. 68000 vs. 80386.
8077
8078       In addition, each of these target machine types can have its own
8079       special options, starting with -m, to choose among various hardware
8080       models or configurations---for example, 68010 vs 68020, floating
8081       coprocessor or none.  A single installed version of the compiler can
8082       compile for any model or configuration, according to the options
8083       specified.
8084
8085       Some configurations of the compiler also support additional special
8086       options, usually for compatibility with other compilers on the same
8087       platform.
8088
8089       ARC Options
8090
8091       These options are defined for ARC implementations:
8092
8093       -EL Compile code for little endian mode.  This is the default.
8094
8095       -EB Compile code for big endian mode.
8096
8097       -mmangle-cpu
8098           Prepend the name of the cpu to all public symbol names.  In
8099           multiple-processor systems, there are many ARC variants with
8100           different instruction and register set characteristics.  This flag
8101           prevents code compiled for one cpu to be linked with code compiled
8102           for another.  No facility exists for handling variants that are
8103           "almost identical".  This is an all or nothing option.
8104
8105       -mcpu=cpu
8106           Compile code for ARC variant cpu.  Which variants are supported
8107           depend on the configuration.  All variants support -mcpu=base, this
8108           is the default.
8109
8110       -mtext=text-section
8111       -mdata=data-section
8112       -mrodata=readonly-data-section
8113           Put functions, data, and readonly data in text-section, data-
8114           section, and readonly-data-section respectively by default.  This
8115           can be overridden with the "section" attribute.
8116
8117       -mfix-cortex-m3-ldrd
8118           Some Cortex-M3 cores can cause data corruption when "ldrd"
8119           instructions with overlapping destination and base registers are
8120           used.  This option avoids generating these instructions.  This
8121           option is enabled by default when -mcpu=cortex-m3 is specified.
8122
8123       ARM Options
8124
8125       These -m options are defined for Advanced RISC Machines (ARM)
8126       architectures:
8127
8128       -mabi=name
8129           Generate code for the specified ABI.  Permissible values are: apcs-
8130           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.
8131
8132       -mapcs-frame
8133           Generate a stack frame that is compliant with the ARM Procedure
8134           Call Standard for all functions, even if this is not strictly
8135           necessary for correct execution of the code.  Specifying
8136           -fomit-frame-pointer with this option will cause the stack frames
8137           not to be generated for leaf functions.  The default is
8138           -mno-apcs-frame.
8139
8140       -mapcs
8141           This is a synonym for -mapcs-frame.
8142
8143       -mthumb-interwork
8144           Generate code which supports calling between the ARM and Thumb
8145           instruction sets.  Without this option the two instruction sets
8146           cannot be reliably used inside one program.  The default is
8147           -mno-thumb-interwork, since slightly larger code is generated when
8148           -mthumb-interwork is specified.
8149
8150       -mno-sched-prolog
8151           Prevent the reordering of instructions in the function prolog, or
8152           the merging of those instruction with the instructions in the
8153           function's body.  This means that all functions will start with a
8154           recognizable set of instructions (or in fact one of a choice from a
8155           small set of different function prologues), and this information
8156           can be used to locate the start if functions inside an executable
8157           piece of code.  The default is -msched-prolog.
8158
8159       -mfloat-abi=name
8160           Specifies which floating-point ABI to use.  Permissible values are:
8161           soft, softfp and hard.
8162
8163           Specifying soft causes GCC to generate output containing library
8164           calls for floating-point operations.  softfp allows the generation
8165           of code using hardware floating-point instructions, but still uses
8166           the soft-float calling conventions.  hard allows generation of
8167           floating-point instructions and uses FPU-specific calling
8168           conventions.
8169
8170           The default depends on the specific target configuration.  Note
8171           that the hard-float and soft-float ABIs are not link-compatible;
8172           you must compile your entire program with the same ABI, and link
8173           with a compatible set of libraries.
8174
8175       -mhard-float
8176           Equivalent to -mfloat-abi=hard.
8177
8178       -msoft-float
8179           Equivalent to -mfloat-abi=soft.
8180
8181       -mlittle-endian
8182           Generate code for a processor running in little-endian mode.  This
8183           is the default for all standard configurations.
8184
8185       -mbig-endian
8186           Generate code for a processor running in big-endian mode; the
8187           default is to compile code for a little-endian processor.
8188
8189       -mwords-little-endian
8190           This option only applies when generating code for big-endian
8191           processors.  Generate code for a little-endian word order but a
8192           big-endian byte order.  That is, a byte order of the form 32107654.
8193           Note: this option should only be used if you require compatibility
8194           with code for big-endian ARM processors generated by versions of
8195           the compiler prior to 2.8.
8196
8197       -mcpu=name
8198           This specifies the name of the target ARM processor.  GCC uses this
8199           name to determine what kind of instructions it can emit when
8200           generating assembly code.  Permissible names are: arm2, arm250,
8201           arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d,
8202           arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i, arm710, arm710c,
8203           arm7100, arm720, arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm710t,
8204           arm720t, arm740t, strongarm, strongarm110, strongarm1100,
8205           strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t,
8206           arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi,
8207           arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e,
8208           arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s,
8209           arm1156t2f-s, arm1176jz-s, arm1176jzf-s, cortex-a5, cortex-a8,
8210           cortex-a9, cortex-r4, cortex-r4f, cortex-m3, cortex-m1, cortex-m0,
8211           xscale, iwmmxt, iwmmxt2, ep9312.
8212
8213       -mtune=name
8214           This option is very similar to the -mcpu= option, except that
8215           instead of specifying the actual target processor type, and hence
8216           restricting which instructions can be used, it specifies that GCC
8217           should tune the performance of the code as if the target were of
8218           the type specified in this option, but still choosing the
8219           instructions that it will generate based on the cpu specified by a
8220           -mcpu= option.  For some ARM implementations better performance can
8221           be obtained by using this option.
8222
8223       -march=name
8224           This specifies the name of the target ARM architecture.  GCC uses
8225           this name to determine what kind of instructions it can emit when
8226           generating assembly code.  This option can be used in conjunction
8227           with or instead of the -mcpu= option.  Permissible names are:
8228           armv2, armv2a, armv3, armv3m, armv4, armv4t, armv5, armv5t, armv5e,
8229           armv5te, armv6, armv6j, armv6t2, armv6z, armv6zk, armv6-m, armv7,
8230           armv7-a, armv7-r, armv7-m, iwmmxt, iwmmxt2, ep9312.
8231
8232       -mfpu=name
8233       -mfpe=number
8234       -mfp=number
8235           This specifies what floating point hardware (or hardware emulation)
8236           is available on the target.  Permissible names are: fpa, fpe2,
8237           fpe3, maverick, vfp, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16,
8238           vfpv3xd, vfpv3xd-fp16, neon, neon-fp16, vfpv4, vfpv4-d16,
8239           fpv4-sp-d16 and neon-vfpv4.  -mfp and -mfpe are synonyms for
8240           -mfpu=fpenumber, for compatibility with older versions of GCC.
8241
8242           If -msoft-float is specified this specifies the format of floating
8243           point values.
8244
8245       -mfp16-format=name
8246           Specify the format of the "__fp16" half-precision floating-point
8247           type.  Permissible names are none, ieee, and alternative; the
8248           default is none, in which case the "__fp16" type is not defined.
8249
8250       -mstructure-size-boundary=n
8251           The size of all structures and unions will be rounded up to a
8252           multiple of the number of bits set by this option.  Permissible
8253           values are 8, 32 and 64.  The default value varies for different
8254           toolchains.  For the COFF targeted toolchain the default value is
8255           8.  A value of 64 is only allowed if the underlying ABI supports
8256           it.
8257
8258           Specifying the larger number can produce faster, more efficient
8259           code, but can also increase the size of the program.  Different
8260           values are potentially incompatible.  Code compiled with one value
8261           cannot necessarily expect to work with code or libraries compiled
8262           with another value, if they exchange information using structures
8263           or unions.
8264
8265       -mabort-on-noreturn
8266           Generate a call to the function "abort" at the end of a "noreturn"
8267           function.  It will be executed if the function tries to return.
8268
8269       -mlong-calls
8270       -mno-long-calls
8271           Tells the compiler to perform function calls by first loading the
8272           address of the function into a register and then performing a
8273           subroutine call on this register.  This switch is needed if the
8274           target function will lie outside of the 64 megabyte addressing
8275           range of the offset based version of subroutine call instruction.
8276
8277           Even if this switch is enabled, not all function calls will be
8278           turned into long calls.  The heuristic is that static functions,
8279           functions which have the short-call attribute, functions that are
8280           inside the scope of a #pragma no_long_calls directive and functions
8281           whose definitions have already been compiled within the current
8282           compilation unit, will not be turned into long calls.  The
8283           exception to this rule is that weak function definitions, functions
8284           with the long-call attribute or the section attribute, and
8285           functions that are within the scope of a #pragma long_calls
8286           directive, will always be turned into long calls.
8287
8288           This feature is not enabled by default.  Specifying -mno-long-calls
8289           will restore the default behavior, as will placing the function
8290           calls within the scope of a #pragma long_calls_off directive.  Note
8291           these switches have no effect on how the compiler generates code to
8292           handle function calls via function pointers.
8293
8294       -msingle-pic-base
8295           Treat the register used for PIC addressing as read-only, rather
8296           than loading it in the prologue for each function.  The run-time
8297           system is responsible for initializing this register with an
8298           appropriate value before execution begins.
8299
8300       -mpic-register=reg
8301           Specify the register to be used for PIC addressing.  The default is
8302           R10 unless stack-checking is enabled, when R9 is used.
8303
8304       -mcirrus-fix-invalid-insns
8305           Insert NOPs into the instruction stream to in order to work around
8306           problems with invalid Maverick instruction combinations.  This
8307           option is only valid if the -mcpu=ep9312 option has been used to
8308           enable generation of instructions for the Cirrus Maverick floating
8309           point co-processor.  This option is not enabled by default, since
8310           the problem is only present in older Maverick implementations.  The
8311           default can be re-enabled by use of the
8312           -mno-cirrus-fix-invalid-insns switch.
8313
8314       -mpoke-function-name
8315           Write the name of each function into the text section, directly
8316           preceding the function prologue.  The generated code is similar to
8317           this:
8318
8319                        t0
8320                            .ascii "arm_poke_function_name", 0
8321                            .align
8322                        t1
8323                            .word 0xff000000 + (t1 - t0)
8324                        arm_poke_function_name
8325                            mov     ip, sp
8326                            stmfd   sp!, {fp, ip, lr, pc}
8327                            sub     fp, ip, #4
8328
8329           When performing a stack backtrace, code can inspect the value of
8330           "pc" stored at "fp + 0".  If the trace function then looks at
8331           location "pc - 12" and the top 8 bits are set, then we know that
8332           there is a function name embedded immediately preceding this
8333           location and has length "((pc[-3]) & 0xff000000)".
8334
8335       -mthumb
8336           Generate code for the Thumb instruction set.  The default is to use
8337           the 32-bit ARM instruction set.  This option automatically enables
8338           either 16-bit Thumb-1 or mixed 16/32-bit Thumb-2 instructions based
8339           on the -mcpu=name and -march=name options.  This option is not
8340           passed to the assembler. If you want to force assembler files to be
8341           interpreted as Thumb code, either add a .thumb directive to the
8342           source or pass the -mthumb option directly to the assembler by
8343           prefixing it with -Wa.
8344
8345       -mtpcs-frame
8346           Generate a stack frame that is compliant with the Thumb Procedure
8347           Call Standard for all non-leaf functions.  (A leaf function is one
8348           that does not call any other functions.)  The default is
8349           -mno-tpcs-frame.
8350
8351       -mtpcs-leaf-frame
8352           Generate a stack frame that is compliant with the Thumb Procedure
8353           Call Standard for all leaf functions.  (A leaf function is one that
8354           does not call any other functions.)  The default is
8355           -mno-apcs-leaf-frame.
8356
8357       -mcallee-super-interworking
8358           Gives all externally visible functions in the file being compiled
8359           an ARM instruction set header which switches to Thumb mode before
8360           executing the rest of the function.  This allows these functions to
8361           be called from non-interworking code.  This option is not valid in
8362           AAPCS configurations because interworking is enabled by default.
8363
8364       -mcaller-super-interworking
8365           Allows calls via function pointers (including virtual functions) to
8366           execute correctly regardless of whether the target code has been
8367           compiled for interworking or not.  There is a small overhead in the
8368           cost of executing a function pointer if this option is enabled.
8369           This option is not valid in AAPCS configurations because
8370           interworking is enabled by default.
8371
8372       -mtp=name
8373           Specify the access model for the thread local storage pointer.  The
8374           valid models are soft, which generates calls to "__aeabi_read_tp",
8375           cp15, which fetches the thread pointer from "cp15" directly
8376           (supported in the arm6k architecture), and auto, which uses the
8377           best available method for the selected processor.  The default
8378           setting is auto.
8379
8380       -mword-relocations
8381           Only generate absolute relocations on word sized values (i.e.
8382           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
8383           SymbianOS) where the runtime loader imposes this restriction, and
8384           when -fpic or -fPIC is specified.
8385
8386       AVR Options
8387
8388       These options are defined for AVR implementations:
8389
8390       -mmcu=mcu
8391           Specify ATMEL AVR instruction set or MCU type.
8392
8393           Instruction set avr1 is for the minimal AVR core, not supported by
8394           the C compiler, only for assembler programs (MCU types: at90s1200,
8395           attiny10, attiny11, attiny12, attiny15, attiny28).
8396
8397           Instruction set avr2 (default) is for the classic AVR core with up
8398           to 8K program memory space (MCU types: at90s2313, at90s2323,
8399           attiny22, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434,
8400           at90s8515, at90c8534, at90s8535).
8401
8402           Instruction set avr3 is for the classic AVR core with up to 128K
8403           program memory space (MCU types: atmega103, atmega603, at43usb320,
8404           at76c711).
8405
8406           Instruction set avr4 is for the enhanced AVR core with up to 8K
8407           program memory space (MCU types: atmega8, atmega83, atmega85).
8408
8409           Instruction set avr5 is for the enhanced AVR core with up to 128K
8410           program memory space (MCU types: atmega16, atmega161, atmega163,
8411           atmega32, atmega323, atmega64, atmega128, at43usb355, at94k).
8412
8413       -mno-interrupts
8414           Generated code is not compatible with hardware interrupts.  Code
8415           size will be smaller.
8416
8417       -mcall-prologues
8418           Functions prologues/epilogues expanded as call to appropriate
8419           subroutines.  Code size will be smaller.
8420
8421       -mtiny-stack
8422           Change only the low 8 bits of the stack pointer.
8423
8424       -mint8
8425           Assume int to be 8 bit integer.  This affects the sizes of all
8426           types: A char will be 1 byte, an int will be 1 byte, a long will be
8427           2 bytes and long long will be 4 bytes.  Please note that this
8428           option does not comply to the C standards, but it will provide you
8429           with smaller code size.
8430
8431       Blackfin Options
8432
8433       -mcpu=cpu[-sirevision]
8434           Specifies the name of the target Blackfin processor.  Currently,
8435           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
8436           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
8437           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
8438           bf547m, bf548m, bf549m, bf561.  The optional sirevision specifies
8439           the silicon revision of the target Blackfin processor.  Any
8440           workarounds available for the targeted silicon revision will be
8441           enabled.  If sirevision is none, no workarounds are enabled.  If
8442           sirevision is any, all workarounds for the targeted processor will
8443           be enabled.  The "__SILICON_REVISION__" macro is defined to two
8444           hexadecimal digits representing the major and minor numbers in the
8445           silicon revision.  If sirevision is none, the
8446           "__SILICON_REVISION__" is not defined.  If sirevision is any, the
8447           "__SILICON_REVISION__" is defined to be 0xffff.  If this optional
8448           sirevision is not used, GCC assumes the latest known silicon
8449           revision of the targeted Blackfin processor.
8450
8451           Support for bf561 is incomplete.  For bf561, Only the processor
8452           macro is defined.  Without this option, bf532 is used as the
8453           processor by default.  The corresponding predefined processor
8454           macros for cpu is to be defined.  And for bfin-elf toolchain, this
8455           causes the hardware BSP provided by libgloss to be linked in if
8456           -msim is not given.
8457
8458       -msim
8459           Specifies that the program will be run on the simulator.  This
8460           causes the simulator BSP provided by libgloss to be linked in.
8461           This option has effect only for bfin-elf toolchain.  Certain other
8462           options, such as -mid-shared-library and -mfdpic, imply -msim.
8463
8464       -momit-leaf-frame-pointer
8465           Don't keep the frame pointer in a register for leaf functions.
8466           This avoids the instructions to save, set up and restore frame
8467           pointers and makes an extra register available in leaf functions.
8468           The option -fomit-frame-pointer removes the frame pointer for all
8469           functions which might make debugging harder.
8470
8471       -mspecld-anomaly
8472           When enabled, the compiler will ensure that the generated code does
8473           not contain speculative loads after jump instructions. If this
8474           option is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.
8475
8476       -mno-specld-anomaly
8477           Don't generate extra code to prevent speculative loads from
8478           occurring.
8479
8480       -mcsync-anomaly
8481           When enabled, the compiler will ensure that the generated code does
8482           not contain CSYNC or SSYNC instructions too soon after conditional
8483           branches.  If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS"
8484           is defined.
8485
8486       -mno-csync-anomaly
8487           Don't generate extra code to prevent CSYNC or SSYNC instructions
8488           from occurring too soon after a conditional branch.
8489
8490       -mlow-64k
8491           When enabled, the compiler is free to take advantage of the
8492           knowledge that the entire program fits into the low 64k of memory.
8493
8494       -mno-low-64k
8495           Assume that the program is arbitrarily large.  This is the default.
8496
8497       -mstack-check-l1
8498           Do stack checking using information placed into L1 scratchpad
8499           memory by the uClinux kernel.
8500
8501       -mid-shared-library
8502           Generate code that supports shared libraries via the library ID
8503           method.  This allows for execute in place and shared libraries in
8504           an environment without virtual memory management.  This option
8505           implies -fPIC.  With a bfin-elf target, this option implies -msim.
8506
8507       -mno-id-shared-library
8508           Generate code that doesn't assume ID based shared libraries are
8509           being used.  This is the default.
8510
8511       -mleaf-id-shared-library
8512           Generate code that supports shared libraries via the library ID
8513           method, but assumes that this library or executable won't link
8514           against any other ID shared libraries.  That allows the compiler to
8515           use faster code for jumps and calls.
8516
8517       -mno-leaf-id-shared-library
8518           Do not assume that the code being compiled won't link against any
8519           ID shared libraries.  Slower code will be generated for jump and
8520           call insns.
8521
8522       -mshared-library-id=n
8523           Specified the identification number of the ID based shared library
8524           being compiled.  Specifying a value of 0 will generate more compact
8525           code, specifying other values will force the allocation of that
8526           number to the current library but is no more space or time
8527           efficient than omitting this option.
8528
8529       -msep-data
8530           Generate code that allows the data segment to be located in a
8531           different area of memory from the text segment.  This allows for
8532           execute in place in an environment without virtual memory
8533           management by eliminating relocations against the text section.
8534
8535       -mno-sep-data
8536           Generate code that assumes that the data segment follows the text
8537           segment.  This is the default.
8538
8539       -mlong-calls
8540       -mno-long-calls
8541           Tells the compiler to perform function calls by first loading the
8542           address of the function into a register and then performing a
8543           subroutine call on this register.  This switch is needed if the
8544           target function will lie outside of the 24 bit addressing range of
8545           the offset based version of subroutine call instruction.
8546
8547           This feature is not enabled by default.  Specifying -mno-long-calls
8548           will restore the default behavior.  Note these switches have no
8549           effect on how the compiler generates code to handle function calls
8550           via function pointers.
8551
8552       -mfast-fp
8553           Link with the fast floating-point library. This library relaxes
8554           some of the IEEE floating-point standard's rules for checking
8555           inputs against Not-a-Number (NAN), in the interest of performance.
8556
8557       -minline-plt
8558           Enable inlining of PLT entries in function calls to functions that
8559           are not known to bind locally.  It has no effect without -mfdpic.
8560
8561       -mmulticore
8562           Build standalone application for multicore Blackfin processor.
8563           Proper start files and link scripts will be used to support
8564           multicore.  This option defines "__BFIN_MULTICORE". It can only be
8565           used with -mcpu=bf561[-sirevision]. It can be used with -mcorea or
8566           -mcoreb. If it's used without -mcorea or -mcoreb, single
8567           application/dual core programming model is used. In this model, the
8568           main function of Core B should be named as coreb_main. If it's used
8569           with -mcorea or -mcoreb, one application per core programming model
8570           is used.  If this option is not used, single core application
8571           programming model is used.
8572
8573       -mcorea
8574           Build standalone application for Core A of BF561 when using one
8575           application per core programming model. Proper start files and link
8576           scripts will be used to support Core A. This option defines
8577           "__BFIN_COREA". It must be used with -mmulticore.
8578
8579       -mcoreb
8580           Build standalone application for Core B of BF561 when using one
8581           application per core programming model. Proper start files and link
8582           scripts will be used to support Core B. This option defines
8583           "__BFIN_COREB". When this option is used, coreb_main should be used
8584           instead of main. It must be used with -mmulticore.
8585
8586       -msdram
8587           Build standalone application for SDRAM. Proper start files and link
8588           scripts will be used to put the application into SDRAM.  Loader
8589           should initialize SDRAM before loading the application into SDRAM.
8590           This option defines "__BFIN_SDRAM".
8591
8592       -micplb
8593           Assume that ICPLBs are enabled at runtime.  This has an effect on
8594           certain anomaly workarounds.  For Linux targets, the default is to
8595           assume ICPLBs are enabled; for standalone applications the default
8596           is off.
8597
8598       CRIS Options
8599
8600       These options are defined specifically for the CRIS ports.
8601
8602       -march=architecture-type
8603       -mcpu=architecture-type
8604           Generate code for the specified architecture.  The choices for
8605           architecture-type are v3, v8 and v10 for respectively ETRAX 4,
8606           ETRAX 100, and ETRAX 100 LX.  Default is v0 except for cris-axis-
8607           linux-gnu, where the default is v10.
8608
8609       -mtune=architecture-type
8610           Tune to architecture-type everything applicable about the generated
8611           code, except for the ABI and the set of available instructions.
8612           The choices for architecture-type are the same as for
8613           -march=architecture-type.
8614
8615       -mmax-stack-frame=n
8616           Warn when the stack frame of a function exceeds n bytes.
8617
8618       -metrax4
8619       -metrax100
8620           The options -metrax4 and -metrax100 are synonyms for -march=v3 and
8621           -march=v8 respectively.
8622
8623       -mmul-bug-workaround
8624       -mno-mul-bug-workaround
8625           Work around a bug in the "muls" and "mulu" instructions for CPU
8626           models where it applies.  This option is active by default.
8627
8628       -mpdebug
8629           Enable CRIS-specific verbose debug-related information in the
8630           assembly code.  This option also has the effect to turn off the
8631           #NO_APP formatted-code indicator to the assembler at the beginning
8632           of the assembly file.
8633
8634       -mcc-init
8635           Do not use condition-code results from previous instruction; always
8636           emit compare and test instructions before use of condition codes.
8637
8638       -mno-side-effects
8639           Do not emit instructions with side-effects in addressing modes
8640           other than post-increment.
8641
8642       -mstack-align
8643       -mno-stack-align
8644       -mdata-align
8645       -mno-data-align
8646       -mconst-align
8647       -mno-const-align
8648           These options (no-options) arranges (eliminate arrangements) for
8649           the stack-frame, individual data and constants to be aligned for
8650           the maximum single data access size for the chosen CPU model.  The
8651           default is to arrange for 32-bit alignment.  ABI details such as
8652           structure layout are not affected by these options.
8653
8654       -m32-bit
8655       -m16-bit
8656       -m8-bit
8657           Similar to the stack- data- and const-align options above, these
8658           options arrange for stack-frame, writable data and constants to all
8659           be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
8660           alignment.
8661
8662       -mno-prologue-epilogue
8663       -mprologue-epilogue
8664           With -mno-prologue-epilogue, the normal function prologue and
8665           epilogue that sets up the stack-frame are omitted and no return
8666           instructions or return sequences are generated in the code.  Use
8667           this option only together with visual inspection of the compiled
8668           code: no warnings or errors are generated when call-saved registers
8669           must be saved, or storage for local variable needs to be allocated.
8670
8671       -mno-gotplt
8672       -mgotplt
8673           With -fpic and -fPIC, don't generate (do generate) instruction
8674           sequences that load addresses for functions from the PLT part of
8675           the GOT rather than (traditional on other architectures) calls to
8676           the PLT.  The default is -mgotplt.
8677
8678       -melf
8679           Legacy no-op option only recognized with the cris-axis-elf and
8680           cris-axis-linux-gnu targets.
8681
8682       -mlinux
8683           Legacy no-op option only recognized with the cris-axis-linux-gnu
8684           target.
8685
8686       -sim
8687           This option, recognized for the cris-axis-elf arranges to link with
8688           input-output functions from a simulator library.  Code, initialized
8689           data and zero-initialized data are allocated consecutively.
8690
8691       -sim2
8692           Like -sim, but pass linker options to locate initialized data at
8693           0x40000000 and zero-initialized data at 0x80000000.
8694
8695       CRX Options
8696
8697       These options are defined specifically for the CRX ports.
8698
8699       -mmac
8700           Enable the use of multiply-accumulate instructions. Disabled by
8701           default.
8702
8703       -mpush-args
8704           Push instructions will be used to pass outgoing arguments when
8705           functions are called. Enabled by default.
8706
8707       Darwin Options
8708
8709       These options are defined for all architectures running the Darwin
8710       operating system.
8711
8712       FSF GCC on Darwin does not create "fat" object files; it will create an
8713       object file for the single architecture that it was built to target.
8714       Apple's GCC on Darwin does create "fat" files if multiple -arch options
8715       are used; it does so by running the compiler or linker multiple times
8716       and joining the results together with lipo.
8717
8718       The subtype of the file created (like ppc7400 or ppc970 or i686) is
8719       determined by the flags that specify the ISA that GCC is targetting,
8720       like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
8721       override this.
8722
8723       The Darwin tools vary in their behavior when presented with an ISA
8724       mismatch.  The assembler, as, will only permit instructions to be used
8725       that are valid for the subtype of the file it is generating, so you
8726       cannot put 64-bit instructions in a ppc750 object file.  The linker for
8727       shared libraries, /usr/bin/libtool, will fail and print an error if
8728       asked to create a shared library with a less restrictive subtype than
8729       its input files (for instance, trying to put a ppc970 object file in a
8730       ppc7400 library).  The linker for executables, ld, will quietly give
8731       the executable the most restrictive subtype of any of its input files.
8732
8733       -Fdir
8734           Add the framework directory dir to the head of the list of
8735           directories to be searched for header files.  These directories are
8736           interleaved with those specified by -I options and are scanned in a
8737           left-to-right order.
8738
8739           A framework directory is a directory with frameworks in it.  A
8740           framework is a directory with a "Headers" and/or "PrivateHeaders"
8741           directory contained directly in it that ends in ".framework".  The
8742           name of a framework is the name of this directory excluding the
8743           ".framework".  Headers associated with the framework are found in
8744           one of those two directories, with "Headers" being searched first.
8745           A subframework is a framework directory that is in a framework's
8746           "Frameworks" directory.  Includes of subframework headers can only
8747           appear in a header of a framework that contains the subframework,
8748           or in a sibling subframework header.  Two subframeworks are
8749           siblings if they occur in the same framework.  A subframework
8750           should not have the same name as a framework, a warning will be
8751           issued if this is violated.  Currently a subframework cannot have
8752           subframeworks, in the future, the mechanism may be extended to
8753           support this.  The standard frameworks can be found in
8754           "/System/Library/Frameworks" and "/Library/Frameworks".  An example
8755           include looks like "#include <Framework/header.h>", where Framework
8756           denotes the name of the framework and header.h is found in the
8757           "PrivateHeaders" or "Headers" directory.
8758
8759       -iframeworkdir
8760           Like -F except the directory is a treated as a system directory.
8761           The main difference between this -iframework and -F is that with
8762           -iframework the compiler does not warn about constructs contained
8763           within header files found via dir.  This option is valid only for
8764           the C family of languages.
8765
8766       -gused
8767           Emit debugging information for symbols that are used.  For STABS
8768           debugging format, this enables -feliminate-unused-debug-symbols.
8769           This is by default ON.
8770
8771       -gfull
8772           Emit debugging information for all symbols and types.
8773
8774       -mmacosx-version-min=version
8775           The earliest version of MacOS X that this executable will run on is
8776           version.  Typical values of version include 10.1, 10.2, and 10.3.9.
8777
8778           If the compiler was built to use the system's headers by default,
8779           then the default for this option is the system version on which the
8780           compiler is running, otherwise the default is to make choices which
8781           are compatible with as many systems and code bases as possible.
8782
8783       -mkernel
8784           Enable kernel development mode.  The -mkernel option sets -static,
8785           -fno-common, -fno-cxa-atexit, -fno-exceptions,
8786           -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
8787           where applicable.  This mode also sets -mno-altivec, -msoft-float,
8788           -fno-builtin and -mlong-branch for PowerPC targets.
8789
8790       -mone-byte-bool
8791           Override the defaults for bool so that sizeof(bool)==1.  By default
8792           sizeof(bool) is 4 when compiling for Darwin/PowerPC and 1 when
8793           compiling for Darwin/x86, so this option has no effect on x86.
8794
8795           Warning: The -mone-byte-bool switch causes GCC to generate code
8796           that is not binary compatible with code generated without that
8797           switch.  Using this switch may require recompiling all other
8798           modules in a program, including system libraries.  Use this switch
8799           to conform to a non-default data model.
8800
8801       -mfix-and-continue
8802       -ffix-and-continue
8803       -findirect-data
8804           Generate code suitable for fast turn around development.  Needed to
8805           enable gdb to dynamically load ".o" files into already running
8806           programs.  -findirect-data and -ffix-and-continue are provided for
8807           backwards compatibility.
8808
8809       -all_load
8810           Loads all members of static archive libraries.  See man ld(1) for
8811           more information.
8812
8813       -arch_errors_fatal
8814           Cause the errors having to do with files that have the wrong
8815           architecture to be fatal.
8816
8817       -bind_at_load
8818           Causes the output file to be marked such that the dynamic linker
8819           will bind all undefined references when the file is loaded or
8820           launched.
8821
8822       -bundle
8823           Produce a Mach-o bundle format file.  See man ld(1) for more
8824           information.
8825
8826       -bundle_loader executable
8827           This option specifies the executable that will be loading the build
8828           output file being linked.  See man ld(1) for more information.
8829
8830       -dynamiclib
8831           When passed this option, GCC will produce a dynamic library instead
8832           of an executable when linking, using the Darwin libtool command.
8833
8834       -force_cpusubtype_ALL
8835           This causes GCC's output file to have the ALL subtype, instead of
8836           one controlled by the -mcpu or -march option.
8837
8838       -allowable_client  client_name
8839       -client_name
8840       -compatibility_version
8841       -current_version
8842       -dead_strip
8843       -dependency-file
8844       -dylib_file
8845       -dylinker_install_name
8846       -dynamic
8847       -exported_symbols_list
8848       -filelist
8849       -flat_namespace
8850       -force_flat_namespace
8851       -headerpad_max_install_names
8852       -image_base
8853       -init
8854       -install_name
8855       -keep_private_externs
8856       -multi_module
8857       -multiply_defined
8858       -multiply_defined_unused
8859       -noall_load
8860       -no_dead_strip_inits_and_terms
8861       -nofixprebinding
8862       -nomultidefs
8863       -noprebind
8864       -noseglinkedit
8865       -pagezero_size
8866       -prebind
8867       -prebind_all_twolevel_modules
8868       -private_bundle
8869       -read_only_relocs
8870       -sectalign
8871       -sectobjectsymbols
8872       -whyload
8873       -seg1addr
8874       -sectcreate
8875       -sectobjectsymbols
8876       -sectorder
8877       -segaddr
8878       -segs_read_only_addr
8879       -segs_read_write_addr
8880       -seg_addr_table
8881       -seg_addr_table_filename
8882       -seglinkedit
8883       -segprot
8884       -segs_read_only_addr
8885       -segs_read_write_addr
8886       -single_module
8887       -static
8888       -sub_library
8889       -sub_umbrella
8890       -twolevel_namespace
8891       -umbrella
8892       -undefined
8893       -unexported_symbols_list
8894       -weak_reference_mismatches
8895       -whatsloaded
8896           These options are passed to the Darwin linker.  The Darwin linker
8897           man page describes them in detail.
8898
8899       DEC Alpha Options
8900
8901       These -m options are defined for the DEC Alpha implementations:
8902
8903       -mno-soft-float
8904       -msoft-float
8905           Use (do not use) the hardware floating-point instructions for
8906           floating-point operations.  When -msoft-float is specified,
8907           functions in libgcc.a will be used to perform floating-point
8908           operations.  Unless they are replaced by routines that emulate the
8909           floating-point operations, or compiled in such a way as to call
8910           such emulations routines, these routines will issue floating-point
8911           operations.   If you are compiling for an Alpha without floating-
8912           point operations, you must ensure that the library is built so as
8913           not to call them.
8914
8915           Note that Alpha implementations without floating-point operations
8916           are required to have floating-point registers.
8917
8918       -mfp-reg
8919       -mno-fp-regs
8920           Generate code that uses (does not use) the floating-point register
8921           set.  -mno-fp-regs implies -msoft-float.  If the floating-point
8922           register set is not used, floating point operands are passed in
8923           integer registers as if they were integers and floating-point
8924           results are passed in $0 instead of $f0.  This is a non-standard
8925           calling sequence, so any function with a floating-point argument or
8926           return value called by code compiled with -mno-fp-regs must also be
8927           compiled with that option.
8928
8929           A typical use of this option is building a kernel that does not
8930           use, and hence need not save and restore, any floating-point
8931           registers.
8932
8933       -mieee
8934           The Alpha architecture implements floating-point hardware optimized
8935           for maximum performance.  It is mostly compliant with the IEEE
8936           floating point standard.  However, for full compliance, software
8937           assistance is required.  This option generates code fully IEEE
8938           compliant code except that the inexact-flag is not maintained (see
8939           below).  If this option is turned on, the preprocessor macro
8940           "_IEEE_FP" is defined during compilation.  The resulting code is
8941           less efficient but is able to correctly support denormalized
8942           numbers and exceptional IEEE values such as not-a-number and
8943           plus/minus infinity.  Other Alpha compilers call this option
8944           -ieee_with_no_inexact.
8945
8946       -mieee-with-inexact
8947           This is like -mieee except the generated code also maintains the
8948           IEEE inexact-flag.  Turning on this option causes the generated
8949           code to implement fully-compliant IEEE math.  In addition to
8950           "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
8951           On some Alpha implementations the resulting code may execute
8952           significantly slower than the code generated by default.  Since
8953           there is very little code that depends on the inexact-flag, you
8954           should normally not specify this option.  Other Alpha compilers
8955           call this option -ieee_with_inexact.
8956
8957       -mfp-trap-mode=trap-mode
8958           This option controls what floating-point related traps are enabled.
8959           Other Alpha compilers call this option -fptm trap-mode.  The trap
8960           mode can be set to one of four values:
8961
8962           n   This is the default (normal) setting.  The only traps that are
8963               enabled are the ones that cannot be disabled in software (e.g.,
8964               division by zero trap).
8965
8966           u   In addition to the traps enabled by n, underflow traps are
8967               enabled as well.
8968
8969           su  Like u, but the instructions are marked to be safe for software
8970               completion (see Alpha architecture manual for details).
8971
8972           sui Like su, but inexact traps are enabled as well.
8973
8974       -mfp-rounding-mode=rounding-mode
8975           Selects the IEEE rounding mode.  Other Alpha compilers call this
8976           option -fprm rounding-mode.  The rounding-mode can be one of:
8977
8978           n   Normal IEEE rounding mode.  Floating point numbers are rounded
8979               towards the nearest machine number or towards the even machine
8980               number in case of a tie.
8981
8982           m   Round towards minus infinity.
8983
8984           c   Chopped rounding mode.  Floating point numbers are rounded
8985               towards zero.
8986
8987           d   Dynamic rounding mode.  A field in the floating point control
8988               register (fpcr, see Alpha architecture reference manual)
8989               controls the rounding mode in effect.  The C library
8990               initializes this register for rounding towards plus infinity.
8991               Thus, unless your program modifies the fpcr, d corresponds to
8992               round towards plus infinity.
8993
8994       -mtrap-precision=trap-precision
8995           In the Alpha architecture, floating point traps are imprecise.
8996           This means without software assistance it is impossible to recover
8997           from a floating trap and program execution normally needs to be
8998           terminated.  GCC can generate code that can assist operating system
8999           trap handlers in determining the exact location that caused a
9000           floating point trap.  Depending on the requirements of an
9001           application, different levels of precisions can be selected:
9002
9003           p   Program precision.  This option is the default and means a trap
9004               handler can only identify which program caused a floating point
9005               exception.
9006
9007           f   Function precision.  The trap handler can determine the
9008               function that caused a floating point exception.
9009
9010           i   Instruction precision.  The trap handler can determine the
9011               exact instruction that caused a floating point exception.
9012
9013           Other Alpha compilers provide the equivalent options called
9014           -scope_safe and -resumption_safe.
9015
9016       -mieee-conformant
9017           This option marks the generated code as IEEE conformant.  You must
9018           not use this option unless you also specify -mtrap-precision=i and
9019           either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect is
9020           to emit the line .eflag 48 in the function prologue of the
9021           generated assembly file.  Under DEC Unix, this has the effect that
9022           IEEE-conformant math library routines will be linked in.
9023
9024       -mbuild-constants
9025           Normally GCC examines a 32- or 64-bit integer constant to see if it
9026           can construct it from smaller constants in two or three
9027           instructions.  If it cannot, it will output the constant as a
9028           literal and generate code to load it from the data segment at
9029           runtime.
9030
9031           Use this option to require GCC to construct all integer constants
9032           using code, even if it takes more instructions (the maximum is
9033           six).
9034
9035           You would typically use this option to build a shared library
9036           dynamic loader.  Itself a shared library, it must relocate itself
9037           in memory before it can find the variables and constants in its own
9038           data segment.
9039
9040       -malpha-as
9041       -mgas
9042           Select whether to generate code to be assembled by the vendor-
9043           supplied assembler (-malpha-as) or by the GNU assembler -mgas.
9044
9045       -mbwx
9046       -mno-bwx
9047       -mcix
9048       -mno-cix
9049       -mfix
9050       -mno-fix
9051       -mmax
9052       -mno-max
9053           Indicate whether GCC should generate code to use the optional BWX,
9054           CIX, FIX and MAX instruction sets.  The default is to use the
9055           instruction sets supported by the CPU type specified via -mcpu=
9056           option or that of the CPU on which GCC was built if none was
9057           specified.
9058
9059       -mfloat-vax
9060       -mfloat-ieee
9061           Generate code that uses (does not use) VAX F and G floating point
9062           arithmetic instead of IEEE single and double precision.
9063
9064       -mexplicit-relocs
9065       -mno-explicit-relocs
9066           Older Alpha assemblers provided no way to generate symbol
9067           relocations except via assembler macros.  Use of these macros does
9068           not allow optimal instruction scheduling.  GNU binutils as of
9069           version 2.12 supports a new syntax that allows the compiler to
9070           explicitly mark which relocations should apply to which
9071           instructions.  This option is mostly useful for debugging, as GCC
9072           detects the capabilities of the assembler when it is built and sets
9073           the default accordingly.
9074
9075       -msmall-data
9076       -mlarge-data
9077           When -mexplicit-relocs is in effect, static data is accessed via
9078           gp-relative relocations.  When -msmall-data is used, objects 8
9079           bytes long or smaller are placed in a small data area (the ".sdata"
9080           and ".sbss" sections) and are accessed via 16-bit relocations off
9081           of the $gp register.  This limits the size of the small data area
9082           to 64KB, but allows the variables to be directly accessed via a
9083           single instruction.
9084
9085           The default is -mlarge-data.  With this option the data area is
9086           limited to just below 2GB.  Programs that require more than 2GB of
9087           data must use "malloc" or "mmap" to allocate the data in the heap
9088           instead of in the program's data segment.
9089
9090           When generating code for shared libraries, -fpic implies
9091           -msmall-data and -fPIC implies -mlarge-data.
9092
9093       -msmall-text
9094       -mlarge-text
9095           When -msmall-text is used, the compiler assumes that the code of
9096           the entire program (or shared library) fits in 4MB, and is thus
9097           reachable with a branch instruction.  When -msmall-data is used,
9098           the compiler can assume that all local symbols share the same $gp
9099           value, and thus reduce the number of instructions required for a
9100           function call from 4 to 1.
9101
9102           The default is -mlarge-text.
9103
9104       -mcpu=cpu_type
9105           Set the instruction set and instruction scheduling parameters for
9106           machine type cpu_type.  You can specify either the EV style name or
9107           the corresponding chip number.  GCC supports scheduling parameters
9108           for the EV4, EV5 and EV6 family of processors and will choose the
9109           default values for the instruction set from the processor you
9110           specify.  If you do not specify a processor type, GCC will default
9111           to the processor on which the compiler was built.
9112
9113           Supported values for cpu_type are
9114
9115           ev4
9116           ev45
9117           21064
9118               Schedules as an EV4 and has no instruction set extensions.
9119
9120           ev5
9121           21164
9122               Schedules as an EV5 and has no instruction set extensions.
9123
9124           ev56
9125           21164a
9126               Schedules as an EV5 and supports the BWX extension.
9127
9128           pca56
9129           21164pc
9130           21164PC
9131               Schedules as an EV5 and supports the BWX and MAX extensions.
9132
9133           ev6
9134           21264
9135               Schedules as an EV6 and supports the BWX, FIX, and MAX
9136               extensions.
9137
9138           ev67
9139           21264a
9140               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
9141               extensions.
9142
9143           Native Linux/GNU toolchains also support the value native, which
9144           selects the best architecture option for the host processor.
9145           -mcpu=native has no effect if GCC does not recognize the processor.
9146
9147       -mtune=cpu_type
9148           Set only the instruction scheduling parameters for machine type
9149           cpu_type.  The instruction set is not changed.
9150
9151           Native Linux/GNU toolchains also support the value native, which
9152           selects the best architecture option for the host processor.
9153           -mtune=native has no effect if GCC does not recognize the
9154           processor.
9155
9156       -mmemory-latency=time
9157           Sets the latency the scheduler should assume for typical memory
9158           references as seen by the application.  This number is highly
9159           dependent on the memory access patterns used by the application and
9160           the size of the external cache on the machine.
9161
9162           Valid options for time are
9163
9164           number
9165               A decimal number representing clock cycles.
9166
9167           L1
9168           L2
9169           L3
9170           main
9171               The compiler contains estimates of the number of clock cycles
9172               for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9173               (also called Dcache, Scache, and Bcache), as well as to main
9174               memory.  Note that L3 is only valid for EV5.
9175
9176       DEC Alpha/VMS Options
9177
9178       These -m options are defined for the DEC Alpha/VMS implementations:
9179
9180       -mvms-return-codes
9181           Return VMS condition codes from main.  The default is to return
9182           POSIX style condition (e.g. error) codes.
9183
9184       -mdebug-main=prefix
9185           Flag the first routine whose name starts with prefix as the main
9186           routine for the debugger.
9187
9188       -mmalloc64
9189           Default to 64bit memory allocation routines.
9190
9191       FR30 Options
9192
9193       These options are defined specifically for the FR30 port.
9194
9195       -msmall-model
9196           Use the small address space model.  This can produce smaller code,
9197           but it does assume that all symbolic values and addresses will fit
9198           into a 20-bit range.
9199
9200       -mno-lsim
9201           Assume that run-time support has been provided and so there is no
9202           need to include the simulator library (libsim.a) on the linker
9203           command line.
9204
9205       FRV Options
9206
9207       -mgpr-32
9208           Only use the first 32 general purpose registers.
9209
9210       -mgpr-64
9211           Use all 64 general purpose registers.
9212
9213       -mfpr-32
9214           Use only the first 32 floating point registers.
9215
9216       -mfpr-64
9217           Use all 64 floating point registers
9218
9219       -mhard-float
9220           Use hardware instructions for floating point operations.
9221
9222       -msoft-float
9223           Use library routines for floating point operations.
9224
9225       -malloc-cc
9226           Dynamically allocate condition code registers.
9227
9228       -mfixed-cc
9229           Do not try to dynamically allocate condition code registers, only
9230           use "icc0" and "fcc0".
9231
9232       -mdword
9233           Change ABI to use double word insns.
9234
9235       -mno-dword
9236           Do not use double word instructions.
9237
9238       -mdouble
9239           Use floating point double instructions.
9240
9241       -mno-double
9242           Do not use floating point double instructions.
9243
9244       -mmedia
9245           Use media instructions.
9246
9247       -mno-media
9248           Do not use media instructions.
9249
9250       -mmuladd
9251           Use multiply and add/subtract instructions.
9252
9253       -mno-muladd
9254           Do not use multiply and add/subtract instructions.
9255
9256       -mfdpic
9257           Select the FDPIC ABI, that uses function descriptors to represent
9258           pointers to functions.  Without any PIC/PIE-related options, it
9259           implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and
9260           small data are within a 12-bit range from the GOT base address;
9261           with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
9262           bfin-elf target, this option implies -msim.
9263
9264       -minline-plt
9265           Enable inlining of PLT entries in function calls to functions that
9266           are not known to bind locally.  It has no effect without -mfdpic.
9267           It's enabled by default if optimizing for speed and compiling for
9268           shared libraries (i.e., -fPIC or -fpic), or when an optimization
9269           option such as -O3 or above is present in the command line.
9270
9271       -mTLS
9272           Assume a large TLS segment when generating thread-local code.
9273
9274       -mtls
9275           Do not assume a large TLS segment when generating thread-local
9276           code.
9277
9278       -mgprel-ro
9279           Enable the use of "GPREL" relocations in the FDPIC ABI for data
9280           that is known to be in read-only sections.  It's enabled by
9281           default, except for -fpic or -fpie: even though it may help make
9282           the global offset table smaller, it trades 1 instruction for 4.
9283           With -fPIC or -fPIE, it trades 3 instructions for 4, one of which
9284           may be shared by multiple symbols, and it avoids the need for a GOT
9285           entry for the referenced symbol, so it's more likely to be a win.
9286           If it is not, -mno-gprel-ro can be used to disable it.
9287
9288       -multilib-library-pic
9289           Link with the (library, not FD) pic libraries.  It's implied by
9290           -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic.  You
9291           should never have to use it explicitly.
9292
9293       -mlinked-fp
9294           Follow the EABI requirement of always creating a frame pointer
9295           whenever a stack frame is allocated.  This option is enabled by
9296           default and can be disabled with -mno-linked-fp.
9297
9298       -mlong-calls
9299           Use indirect addressing to call functions outside the current
9300           compilation unit.  This allows the functions to be placed anywhere
9301           within the 32-bit address space.
9302
9303       -malign-labels
9304           Try to align labels to an 8-byte boundary by inserting nops into
9305           the previous packet.  This option only has an effect when VLIW
9306           packing is enabled.  It doesn't create new packets; it merely adds
9307           nops to existing ones.
9308
9309       -mlibrary-pic
9310           Generate position-independent EABI code.
9311
9312       -macc-4
9313           Use only the first four media accumulator registers.
9314
9315       -macc-8
9316           Use all eight media accumulator registers.
9317
9318       -mpack
9319           Pack VLIW instructions.
9320
9321       -mno-pack
9322           Do not pack VLIW instructions.
9323
9324       -mno-eflags
9325           Do not mark ABI switches in e_flags.
9326
9327       -mcond-move
9328           Enable the use of conditional-move instructions (default).
9329
9330           This switch is mainly for debugging the compiler and will likely be
9331           removed in a future version.
9332
9333       -mno-cond-move
9334           Disable the use of conditional-move instructions.
9335
9336           This switch is mainly for debugging the compiler and will likely be
9337           removed in a future version.
9338
9339       -mscc
9340           Enable the use of conditional set instructions (default).
9341
9342           This switch is mainly for debugging the compiler and will likely be
9343           removed in a future version.
9344
9345       -mno-scc
9346           Disable the use of conditional set instructions.
9347
9348           This switch is mainly for debugging the compiler and will likely be
9349           removed in a future version.
9350
9351       -mcond-exec
9352           Enable the use of conditional execution (default).
9353
9354           This switch is mainly for debugging the compiler and will likely be
9355           removed in a future version.
9356
9357       -mno-cond-exec
9358           Disable the use of conditional execution.
9359
9360           This switch is mainly for debugging the compiler and will likely be
9361           removed in a future version.
9362
9363       -mvliw-branch
9364           Run a pass to pack branches into VLIW instructions (default).
9365
9366           This switch is mainly for debugging the compiler and will likely be
9367           removed in a future version.
9368
9369       -mno-vliw-branch
9370           Do not run a pass to pack branches into VLIW instructions.
9371
9372           This switch is mainly for debugging the compiler and will likely be
9373           removed in a future version.
9374
9375       -mmulti-cond-exec
9376           Enable optimization of "&&" and "||" in conditional execution
9377           (default).
9378
9379           This switch is mainly for debugging the compiler and will likely be
9380           removed in a future version.
9381
9382       -mno-multi-cond-exec
9383           Disable optimization of "&&" and "||" in conditional execution.
9384
9385           This switch is mainly for debugging the compiler and will likely be
9386           removed in a future version.
9387
9388       -mnested-cond-exec
9389           Enable nested conditional execution optimizations (default).
9390
9391           This switch is mainly for debugging the compiler and will likely be
9392           removed in a future version.
9393
9394       -mno-nested-cond-exec
9395           Disable nested conditional execution optimizations.
9396
9397           This switch is mainly for debugging the compiler and will likely be
9398           removed in a future version.
9399
9400       -moptimize-membar
9401           This switch removes redundant "membar" instructions from the
9402           compiler generated code.  It is enabled by default.
9403
9404       -mno-optimize-membar
9405           This switch disables the automatic removal of redundant "membar"
9406           instructions from the generated code.
9407
9408       -mtomcat-stats
9409           Cause gas to print out tomcat statistics.
9410
9411       -mcpu=cpu
9412           Select the processor type for which to generate code.  Possible
9413           values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300
9414           and simple.
9415
9416       GNU/Linux Options
9417
9418       These -m options are defined for GNU/Linux targets:
9419
9420       -mglibc
9421           Use the GNU C library instead of uClibc.  This is the default
9422           except on *-*-linux-*uclibc* targets.
9423
9424       -muclibc
9425           Use uClibc instead of the GNU C library.  This is the default on
9426           *-*-linux-*uclibc* targets.
9427
9428       H8/300 Options
9429
9430       These -m options are defined for the H8/300 implementations:
9431
9432       -mrelax
9433           Shorten some address references at link time, when possible; uses
9434           the linker option -relax.
9435
9436       -mh Generate code for the H8/300H.
9437
9438       -ms Generate code for the H8S.
9439
9440       -mn Generate code for the H8S and H8/300H in the normal mode.  This
9441           switch must be used either with -mh or -ms.
9442
9443       -ms2600
9444           Generate code for the H8S/2600.  This switch must be used with -ms.
9445
9446       -mint32
9447           Make "int" data 32 bits by default.
9448
9449       -malign-300
9450           On the H8/300H and H8S, use the same alignment rules as for the
9451           H8/300.  The default for the H8/300H and H8S is to align longs and
9452           floats on 4 byte boundaries.  -malign-300 causes them to be aligned
9453           on 2 byte boundaries.  This option has no effect on the H8/300.
9454
9455       HPPA Options
9456
9457       These -m options are defined for the HPPA family of computers:
9458
9459       -march=architecture-type
9460           Generate code for the specified architecture.  The choices for
9461           architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for
9462           PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX
9463           system to determine the proper architecture option for your
9464           machine.  Code compiled for lower numbered architectures will run
9465           on higher numbered architectures, but not the other way around.
9466
9467       -mpa-risc-1-0
9468       -mpa-risc-1-1
9469       -mpa-risc-2-0
9470           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.
9471
9472       -mbig-switch
9473           Generate code suitable for big switch tables.  Use this option only
9474           if the assembler/linker complain about out of range branches within
9475           a switch table.
9476
9477       -mjump-in-delay
9478           Fill delay slots of function calls with unconditional jump
9479           instructions by modifying the return pointer for the function call
9480           to be the target of the conditional jump.
9481
9482       -mdisable-fpregs
9483           Prevent floating point registers from being used in any manner.
9484           This is necessary for compiling kernels which perform lazy context
9485           switching of floating point registers.  If you use this option and
9486           attempt to perform floating point operations, the compiler will
9487           abort.
9488
9489       -mdisable-indexing
9490           Prevent the compiler from using indexing address modes.  This
9491           avoids some rather obscure problems when compiling MIG generated
9492           code under MACH.
9493
9494       -mno-space-regs
9495           Generate code that assumes the target has no space registers.  This
9496           allows GCC to generate faster indirect calls and use unscaled index
9497           address modes.
9498
9499           Such code is suitable for level 0 PA systems and kernels.
9500
9501       -mfast-indirect-calls
9502           Generate code that assumes calls never cross space boundaries.
9503           This allows GCC to emit code which performs faster indirect calls.
9504
9505           This option will not work in the presence of shared libraries or
9506           nested functions.
9507
9508       -mfixed-range=register-range
9509           Generate code treating the given register range as fixed registers.
9510           A fixed register is one that the register allocator can not use.
9511           This is useful when compiling kernel code.  A register range is
9512           specified as two registers separated by a dash.  Multiple register
9513           ranges can be specified separated by a comma.
9514
9515       -mlong-load-store
9516           Generate 3-instruction load and store sequences as sometimes
9517           required by the HP-UX 10 linker.  This is equivalent to the +k
9518           option to the HP compilers.
9519
9520       -mportable-runtime
9521           Use the portable calling conventions proposed by HP for ELF
9522           systems.
9523
9524       -mgas
9525           Enable the use of assembler directives only GAS understands.
9526
9527       -mschedule=cpu-type
9528           Schedule code according to the constraints for the machine type
9529           cpu-type.  The choices for cpu-type are 700 7100, 7100LC, 7200,
9530           7300 and 8000.  Refer to /usr/lib/sched.models on an HP-UX system
9531           to determine the proper scheduling option for your machine.  The
9532           default scheduling is 8000.
9533
9534       -mlinker-opt
9535           Enable the optimization pass in the HP-UX linker.  Note this makes
9536           symbolic debugging impossible.  It also triggers a bug in the HP-UX
9537           8 and HP-UX 9 linkers in which they give bogus error messages when
9538           linking some programs.
9539
9540       -msoft-float
9541           Generate output containing library calls for floating point.
9542           Warning: the requisite libraries are not available for all HPPA
9543           targets.  Normally the facilities of the machine's usual C compiler
9544           are used, but this cannot be done directly in cross-compilation.
9545           You must make your own arrangements to provide suitable library
9546           functions for cross-compilation.
9547
9548           -msoft-float changes the calling convention in the output file;
9549           therefore, it is only useful if you compile all of a program with
9550           this option.  In particular, you need to compile libgcc.a, the
9551           library that comes with GCC, with -msoft-float in order for this to
9552           work.
9553
9554       -msio
9555           Generate the predefine, "_SIO", for server IO.  The default is
9556           -mwsio.  This generates the predefines, "__hp9000s700",
9557           "__hp9000s700__" and "_WSIO", for workstation IO.  These options
9558           are available under HP-UX and HI-UX.
9559
9560       -mgnu-ld
9561           Use GNU ld specific options.  This passes -shared to ld when
9562           building a shared library.  It is the default when GCC is
9563           configured, explicitly or implicitly, with the GNU linker.  This
9564           option does not have any affect on which ld is called, it only
9565           changes what parameters are passed to that ld.  The ld that is
9566           called is determined by the --with-ld configure option, GCC's
9567           program search path, and finally by the user's PATH.  The linker
9568           used by GCC can be printed using which `gcc -print-prog-name=ld`.
9569           This option is only available on the 64 bit HP-UX GCC, i.e.
9570           configured with hppa*64*-*-hpux*.
9571
9572       -mhp-ld
9573           Use HP ld specific options.  This passes -b to ld when building a
9574           shared library and passes +Accept TypeMismatch to ld on all links.
9575           It is the default when GCC is configured, explicitly or implicitly,
9576           with the HP linker.  This option does not have any affect on which
9577           ld is called, it only changes what parameters are passed to that
9578           ld.  The ld that is called is determined by the --with-ld configure
9579           option, GCC's program search path, and finally by the user's PATH.
9580           The linker used by GCC can be printed using which `gcc
9581           -print-prog-name=ld`.  This option is only available on the 64 bit
9582           HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.
9583
9584       -mlong-calls
9585           Generate code that uses long call sequences.  This ensures that a
9586           call is always able to reach linker generated stubs.  The default
9587           is to generate long calls only when the distance from the call site
9588           to the beginning of the function or translation unit, as the case
9589           may be, exceeds a predefined limit set by the branch type being
9590           used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
9591           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
9592           always limited at 240,000 bytes.
9593
9594           Distances are measured from the beginning of functions when using
9595           the -ffunction-sections option, or when using the -mgas and
9596           -mno-portable-runtime options together under HP-UX with the SOM
9597           linker.
9598
9599           It is normally not desirable to use this option as it will degrade
9600           performance.  However, it may be useful in large applications,
9601           particularly when partial linking is used to build the application.
9602
9603           The types of long calls used depends on the capabilities of the
9604           assembler and linker, and the type of code being generated.  The
9605           impact on systems that support long absolute calls, and long pic
9606           symbol-difference or pc-relative calls should be relatively small.
9607           However, an indirect call is used on 32-bit ELF systems in pic code
9608           and it is quite long.
9609
9610       -munix=unix-std
9611           Generate compiler predefines and select a startfile for the
9612           specified UNIX standard.  The choices for unix-std are 93, 95 and
9613           98.  93 is supported on all HP-UX versions.  95 is available on HP-
9614           UX 10.10 and later.  98 is available on HP-UX 11.11 and later.  The
9615           default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to
9616           11.00, and 98 for HP-UX 11.11 and later.
9617
9618           -munix=93 provides the same predefines as GCC 3.3 and 3.4.
9619           -munix=95 provides additional predefines for "XOPEN_UNIX" and
9620           "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o.  -munix=98
9621           provides additional predefines for "_XOPEN_UNIX",
9622           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
9623           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.
9624
9625           It is important to note that this option changes the interfaces for
9626           various library routines.  It also affects the operational behavior
9627           of the C library.  Thus, extreme care is needed in using this
9628           option.
9629
9630           Library code that is intended to operate with more than one UNIX
9631           standard must test, set and restore the variable
9632           __xpg4_extended_mask as appropriate.  Most GNU software doesn't
9633           provide this capability.
9634
9635       -nolibdld
9636           Suppress the generation of link options to search libdld.sl when
9637           the -static option is specified on HP-UX 10 and later.
9638
9639       -static
9640           The HP-UX implementation of setlocale in libc has a dependency on
9641           libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
9642           when the -static option is specified, special link options are
9643           needed to resolve this dependency.
9644
9645           On HP-UX 10 and later, the GCC driver adds the necessary options to
9646           link with libdld.sl when the -static option is specified.  This
9647           causes the resulting binary to be dynamic.  On the 64-bit port, the
9648           linkers generate dynamic binaries by default in any case.  The
9649           -nolibdld option can be used to prevent the GCC driver from adding
9650           these link options.
9651
9652       -threads
9653           Add support for multithreading with the dce thread library under
9654           HP-UX.  This option sets flags for both the preprocessor and
9655           linker.
9656
9657       Intel 386 and AMD x86-64 Options
9658
9659       These -m options are defined for the i386 and x86-64 family of
9660       computers:
9661
9662       -mtune=cpu-type
9663           Tune to cpu-type everything applicable about the generated code,
9664           except for the ABI and the set of available instructions.  The
9665           choices for cpu-type are:
9666
9667           generic
9668               Produce code optimized for the most common IA32/AMD64/EM64T
9669               processors.  If you know the CPU on which your code will run,
9670               then you should use the corresponding -mtune option instead of
9671               -mtune=generic.  But, if you do not know exactly what CPU users
9672               of your application will have, then you should use this option.
9673
9674               As new processors are deployed in the marketplace, the behavior
9675               of this option will change.  Therefore, if you upgrade to a
9676               newer version of GCC, the code generated option will change to
9677               reflect the processors that were most common when that version
9678               of GCC was released.
9679
9680               There is no -march=generic option because -march indicates the
9681               instruction set the compiler can use, and there is no generic
9682               instruction set applicable to all processors.  In contrast,
9683               -mtune indicates the processor (or, in this case, collection of
9684               processors) for which the code is optimized.
9685
9686           native
9687               This selects the CPU to tune for at compilation time by
9688               determining the processor type of the compiling machine.  Using
9689               -mtune=native will produce code optimized for the local machine
9690               under the constraints of the selected instruction set.  Using
9691               -march=native will enable all instruction subsets supported by
9692               the local machine (hence the result might not run on different
9693               machines).
9694
9695           i386
9696               Original Intel's i386 CPU.
9697
9698           i486
9699               Intel's i486 CPU.  (No scheduling is implemented for this
9700               chip.)
9701
9702           i586, pentium
9703               Intel Pentium CPU with no MMX support.
9704
9705           pentium-mmx
9706               Intel PentiumMMX CPU based on Pentium core with MMX instruction
9707               set support.
9708
9709           pentiumpro
9710               Intel PentiumPro CPU.
9711
9712           i686
9713               Same as "generic", but when used as "march" option, PentiumPro
9714               instruction set will be used, so the code will run on all i686
9715               family chips.
9716
9717           pentium2
9718               Intel Pentium2 CPU based on PentiumPro core with MMX
9719               instruction set support.
9720
9721           pentium3, pentium3m
9722               Intel Pentium3 CPU based on PentiumPro core with MMX and SSE
9723               instruction set support.
9724
9725           pentium-m
9726               Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2
9727               instruction set support.  Used by Centrino notebooks.
9728
9729           pentium4, pentium4m
9730               Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set
9731               support.
9732
9733           prescott
9734               Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and
9735               SSE3 instruction set support.
9736
9737           nocona
9738               Improved version of Intel Pentium4 CPU with 64-bit extensions,
9739               MMX, SSE, SSE2 and SSE3 instruction set support.
9740
9741           core2
9742               Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
9743               and SSSE3 instruction set support.
9744
9745           atom
9746               Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and
9747               SSSE3 instruction set support.
9748
9749           k6  AMD K6 CPU with MMX instruction set support.
9750
9751           k6-2, k6-3
9752               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction
9753               set support.
9754
9755           athlon, athlon-tbird
9756               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
9757               prefetch instructions support.
9758
9759           athlon-4, athlon-xp, athlon-mp
9760               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
9761               full SSE instruction set support.
9762
9763           k8, opteron, athlon64, athlon-fx
9764               AMD K8 core based CPUs with x86-64 instruction set support.
9765               (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow! and
9766               64-bit instruction set extensions.)
9767
9768           k8-sse3, opteron-sse3, athlon64-sse3
9769               Improved versions of k8, opteron and athlon64 with SSE3
9770               instruction set support.
9771
9772           amdfam10, barcelona
9773               AMD Family 10h core based CPUs with x86-64 instruction set
9774               support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
9775               enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
9776
9777           winchip-c6
9778               IDT Winchip C6 CPU, dealt in same way as i486 with additional
9779               MMX instruction set support.
9780
9781           winchip2
9782               IDT Winchip2 CPU, dealt in same way as i486 with additional MMX
9783               and 3DNow!  instruction set support.
9784
9785           c3  Via C3 CPU with MMX and 3DNow! instruction set support.  (No
9786               scheduling is implemented for this chip.)
9787
9788           c3-2
9789               Via C3-2 CPU with MMX and SSE instruction set support.  (No
9790               scheduling is implemented for this chip.)
9791
9792           geode
9793               Embedded AMD CPU with MMX and 3DNow! instruction set support.
9794
9795           While picking a specific cpu-type will schedule things
9796           appropriately for that particular chip, the compiler will not
9797           generate any code that does not run on the i386 without the
9798           -march=cpu-type option being used.
9799
9800       -march=cpu-type
9801           Generate instructions for the machine type cpu-type.  The choices
9802           for cpu-type are the same as for -mtune.  Moreover, specifying
9803           -march=cpu-type implies -mtune=cpu-type.
9804
9805       -mcpu=cpu-type
9806           A deprecated synonym for -mtune.
9807
9808       -mfpmath=unit
9809           Generate floating point arithmetics for selected unit unit.  The
9810           choices for unit are:
9811
9812           387 Use the standard 387 floating point coprocessor present
9813               majority of chips and emulated otherwise.  Code compiled with
9814               this option will run almost everywhere.  The temporary results
9815               are computed in 80bit precision instead of precision specified
9816               by the type resulting in slightly different results compared to
9817               most of other chips.  See -ffloat-store for more detailed
9818               description.
9819
9820               This is the default choice for i386 compiler.
9821
9822           sse Use scalar floating point instructions present in the SSE
9823               instruction set.  This instruction set is supported by Pentium3
9824               and newer chips, in the AMD line by Athlon-4, Athlon-xp and
9825               Athlon-mp chips.  The earlier version of SSE instruction set
9826               supports only single precision arithmetics, thus the double and
9827               extended precision arithmetics is still done using 387.  Later
9828               version, present only in Pentium4 and the future AMD x86-64
9829               chips supports double precision arithmetics too.
9830
9831               For the i386 compiler, you need to use -march=cpu-type, -msse
9832               or -msse2 switches to enable SSE extensions and make this
9833               option effective.  For the x86-64 compiler, these extensions
9834               are enabled by default.
9835
9836               The resulting code should be considerably faster in the
9837               majority of cases and avoid the numerical instability problems
9838               of 387 code, but may break some existing code that expects
9839               temporaries to be 80bit.
9840
9841               This is the default choice for the x86-64 compiler.
9842
9843           sse,387
9844           sse+387
9845           both
9846               Attempt to utilize both instruction sets at once.  This
9847               effectively double the amount of available registers and on
9848               chips with separate execution units for 387 and SSE the
9849               execution resources too.  Use this option with care, as it is
9850               still experimental, because the GCC register allocator does not
9851               model separate functional units well resulting in instable
9852               performance.
9853
9854       -masm=dialect
9855           Output asm instructions using selected dialect.  Supported choices
9856           are intel or att (the default one).  Darwin does not support intel.
9857
9858       -mieee-fp
9859       -mno-ieee-fp
9860           Control whether or not the compiler uses IEEE floating point
9861           comparisons.  These handle correctly the case where the result of a
9862           comparison is unordered.
9863
9864       -msoft-float
9865           Generate output containing library calls for floating point.
9866           Warning: the requisite libraries are not part of GCC.  Normally the
9867           facilities of the machine's usual C compiler are used, but this
9868           can't be done directly in cross-compilation.  You must make your
9869           own arrangements to provide suitable library functions for cross-
9870           compilation.
9871
9872           On machines where a function returns floating point results in the
9873           80387 register stack, some floating point opcodes may be emitted
9874           even if -msoft-float is used.
9875
9876       -mno-fp-ret-in-387
9877           Do not use the FPU registers for return values of functions.
9878
9879           The usual calling convention has functions return values of types
9880           "float" and "double" in an FPU register, even if there is no FPU.
9881           The idea is that the operating system should emulate an FPU.
9882
9883           The option -mno-fp-ret-in-387 causes such values to be returned in
9884           ordinary CPU registers instead.
9885
9886       -mno-fancy-math-387
9887           Some 387 emulators do not support the "sin", "cos" and "sqrt"
9888           instructions for the 387.  Specify this option to avoid generating
9889           those instructions.  This option is the default on FreeBSD, OpenBSD
9890           and NetBSD.  This option is overridden when -march indicates that
9891           the target cpu will always have an FPU and so the instruction will
9892           not need emulation.  As of revision 2.6.1, these instructions are
9893           not generated unless you also use the -funsafe-math-optimizations
9894           switch.
9895
9896       -malign-double
9897       -mno-align-double
9898           Control whether GCC aligns "double", "long double", and "long long"
9899           variables on a two word boundary or a one word boundary.  Aligning
9900           "double" variables on a two word boundary will produce code that
9901           runs somewhat faster on a Pentium at the expense of more memory.
9902
9903           On x86-64, -malign-double is enabled by default.
9904
9905           Warning: if you use the -malign-double switch, structures
9906           containing the above types will be aligned differently than the
9907           published application binary interface specifications for the 386
9908           and will not be binary compatible with structures in code compiled
9909           without that switch.
9910
9911       -m96bit-long-double
9912       -m128bit-long-double
9913           These switches control the size of "long double" type.  The i386
9914           application binary interface specifies the size to be 96 bits, so
9915           -m96bit-long-double is the default in 32 bit mode.
9916
9917           Modern architectures (Pentium and newer) would prefer "long double"
9918           to be aligned to an 8 or 16 byte boundary.  In arrays or structures
9919           conforming to the ABI, this would not be possible.  So specifying a
9920           -m128bit-long-double will align "long double" to a 16 byte boundary
9921           by padding the "long double" with an additional 32 bit zero.
9922
9923           In the x86-64 compiler, -m128bit-long-double is the default choice
9924           as its ABI specifies that "long double" is to be aligned on 16 byte
9925           boundary.
9926
9927           Notice that neither of these options enable any extra precision
9928           over the x87 standard of 80 bits for a "long double".
9929
9930           Warning: if you override the default value for your target ABI, the
9931           structures and arrays containing "long double" variables will
9932           change their size as well as function calling convention for
9933           function taking "long double" will be modified.  Hence they will
9934           not be binary compatible with arrays or structures in code compiled
9935           without that switch.
9936
9937       -mlarge-data-threshold=number
9938           When -mcmodel=medium is specified, the data greater than threshold
9939           are placed in large data section.  This value must be the same
9940           across all object linked into the binary and defaults to 65535.
9941
9942       -mrtd
9943           Use a different function-calling convention, in which functions
9944           that take a fixed number of arguments return with the "ret" num
9945           instruction, which pops their arguments while returning.  This
9946           saves one instruction in the caller since there is no need to pop
9947           the arguments there.
9948
9949           You can specify that an individual function is called with this
9950           calling sequence with the function attribute stdcall.  You can also
9951           override the -mrtd option by using the function attribute cdecl.
9952
9953           Warning: this calling convention is incompatible with the one
9954           normally used on Unix, so you cannot use it if you need to call
9955           libraries compiled with the Unix compiler.
9956
9957           Also, you must provide function prototypes for all functions that
9958           take variable numbers of arguments (including "printf"); otherwise
9959           incorrect code will be generated for calls to those functions.
9960
9961           In addition, seriously incorrect code will result if you call a
9962           function with too many arguments.  (Normally, extra arguments are
9963           harmlessly ignored.)
9964
9965       -mregparm=num
9966           Control how many registers are used to pass integer arguments.  By
9967           default, no registers are used to pass arguments, and at most 3
9968           registers can be used.  You can control this behavior for a
9969           specific function by using the function attribute regparm.
9970
9971           Warning: if you use this switch, and num is nonzero, then you must
9972           build all modules with the same value, including any libraries.
9973           This includes the system libraries and startup modules.
9974
9975       -msseregparm
9976           Use SSE register passing conventions for float and double arguments
9977           and return values.  You can control this behavior for a specific
9978           function by using the function attribute sseregparm.
9979
9980           Warning: if you use this switch then you must build all modules
9981           with the same value, including any libraries.  This includes the
9982           system libraries and startup modules.
9983
9984       -mpc32
9985       -mpc64
9986       -mpc80
9987           Set 80387 floating-point precision to 32, 64 or 80 bits.  When
9988           -mpc32 is specified, the significands of results of floating-point
9989           operations are rounded to 24 bits (single precision); -mpc64 rounds
9990           the significands of results of floating-point operations to 53 bits
9991           (double precision) and -mpc80 rounds the significands of results of
9992           floating-point operations to 64 bits (extended double precision),
9993           which is the default.  When this option is used, floating-point
9994           operations in higher precisions are not available to the programmer
9995           without setting the FPU control word explicitly.
9996
9997           Setting the rounding of floating-point operations to less than the
9998           default 80 bits can speed some programs by 2% or more.  Note that
9999           some mathematical libraries assume that extended precision (80 bit)
10000           floating-point operations are enabled by default; routines in such
10001           libraries could suffer significant loss of accuracy, typically
10002           through so-called "catastrophic cancellation", when this option is
10003           used to set the precision to less than extended precision.
10004
10005       -mstackrealign
10006           Realign the stack at entry.  On the Intel x86, the -mstackrealign
10007           option will generate an alternate prologue and epilogue that
10008           realigns the runtime stack if necessary.  This supports mixing
10009           legacy codes that keep a 4-byte aligned stack with modern codes
10010           that keep a 16-byte stack for SSE compatibility.  See also the
10011           attribute "force_align_arg_pointer", applicable to individual
10012           functions.
10013
10014       -mpreferred-stack-boundary=num
10015           Attempt to keep the stack boundary aligned to a 2 raised to num
10016           byte boundary.  If -mpreferred-stack-boundary is not specified, the
10017           default is 4 (16 bytes or 128 bits).
10018
10019       -mincoming-stack-boundary=num
10020           Assume the incoming stack is aligned to a 2 raised to num byte
10021           boundary.  If -mincoming-stack-boundary is not specified, the one
10022           specified by -mpreferred-stack-boundary will be used.
10023
10024           On Pentium and PentiumPro, "double" and "long double" values should
10025           be aligned to an 8 byte boundary (see -malign-double) or suffer
10026           significant run time performance penalties.  On Pentium III, the
10027           Streaming SIMD Extension (SSE) data type "__m128" may not work
10028           properly if it is not 16 byte aligned.
10029
10030           To ensure proper alignment of this values on the stack, the stack
10031           boundary must be as aligned as that required by any value stored on
10032           the stack.  Further, every function must be generated such that it
10033           keeps the stack aligned.  Thus calling a function compiled with a
10034           higher preferred stack boundary from a function compiled with a
10035           lower preferred stack boundary will most likely misalign the stack.
10036           It is recommended that libraries that use callbacks always use the
10037           default setting.
10038
10039           This extra alignment does consume extra stack space, and generally
10040           increases code size.  Code that is sensitive to stack space usage,
10041           such as embedded systems and operating system kernels, may want to
10042           reduce the preferred alignment to -mpreferred-stack-boundary=2.
10043
10044       -mmmx
10045       -mno-mmx
10046       -msse
10047       -mno-sse
10048       -msse2
10049       -mno-sse2
10050       -msse3
10051       -mno-sse3
10052       -mssse3
10053       -mno-ssse3
10054       -msse4.1
10055       -mno-sse4.1
10056       -msse4.2
10057       -mno-sse4.2
10058       -msse4
10059       -mno-sse4
10060       -mavx
10061       -mno-avx
10062       -maes
10063       -mno-aes
10064       -mpclmul
10065       -mno-pclmul
10066       -msse4a
10067       -mno-sse4a
10068       -mfma4
10069       -mno-fma4
10070       -mxop
10071       -mno-xop
10072       -mlwp
10073       -mno-lwp
10074       -m3dnow
10075       -mno-3dnow
10076       -mpopcnt
10077       -mno-popcnt
10078       -mabm
10079       -mno-abm
10080           These switches enable or disable the use of instructions in the
10081           MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, FMA4,
10082           XOP, LWP, ABM or 3DNow! extended instruction sets.  These
10083           extensions are also available as built-in functions: see X86 Built-
10084           in Functions, for details of the functions enabled and disabled by
10085           these switches.
10086
10087           To have SSE/SSE2 instructions generated automatically from
10088           floating-point code (as opposed to 387 instructions), see
10089           -mfpmath=sse.
10090
10091           GCC depresses SSEx instructions when -mavx is used. Instead, it
10092           generates new AVX instructions or AVX equivalence for all SSEx
10093           instructions when needed.
10094
10095           These options will enable GCC to use these extended instructions in
10096           generated code, even without -mfpmath=sse.  Applications which
10097           perform runtime CPU detection must compile separate files for each
10098           supported architecture, using the appropriate flags.  In
10099           particular, the file containing the CPU detection code should be
10100           compiled without these options.
10101
10102       -mfused-madd
10103       -mno-fused-madd
10104           Do (don't) generate code that uses the fused multiply/add or
10105           multiply/subtract instructions.  The default is to use these
10106           instructions.
10107
10108       -mcld
10109           This option instructs GCC to emit a "cld" instruction in the
10110           prologue of functions that use string instructions.  String
10111           instructions depend on the DF flag to select between autoincrement
10112           or autodecrement mode.  While the ABI specifies the DF flag to be
10113           cleared on function entry, some operating systems violate this
10114           specification by not clearing the DF flag in their exception
10115           dispatchers.  The exception handler can be invoked with the DF flag
10116           set which leads to wrong direction mode, when string instructions
10117           are used.  This option can be enabled by default on 32-bit x86
10118           targets by configuring GCC with the --enable-cld configure option.
10119           Generation of "cld" instructions can be suppressed with the
10120           -mno-cld compiler option in this case.
10121
10122       -mcx16
10123           This option will enable GCC to use CMPXCHG16B instruction in
10124           generated code.  CMPXCHG16B allows for atomic operations on 128-bit
10125           double quadword (or oword) data types.  This is useful for high
10126           resolution counters that could be updated by multiple processors
10127           (or cores).  This instruction is generated as part of atomic built-
10128           in functions: see Atomic Builtins for details.
10129
10130       -msahf
10131           This option will enable GCC to use SAHF instruction in generated
10132           64-bit code.  Early Intel CPUs with Intel 64 lacked LAHF and SAHF
10133           instructions supported by AMD64 until introduction of Pentium 4 G1
10134           step in December 2005.  LAHF and SAHF are load and store
10135           instructions, respectively, for certain status flags.  In 64-bit
10136           mode, SAHF instruction is used to optimize "fmod", "drem" or
10137           "remainder" built-in functions: see Other Builtins for details.
10138
10139       -mmovbe
10140           This option will enable GCC to use movbe instruction to implement
10141           "__builtin_bswap32" and "__builtin_bswap64".
10142
10143       -mcrc32
10144           This option will enable built-in functions,
10145           "__builtin_ia32_crc32qi", "__builtin_ia32_crc32hi".
10146           "__builtin_ia32_crc32si" and "__builtin_ia32_crc32di" to generate
10147           the crc32 machine instruction.
10148
10149       -mrecip
10150           This option will enable GCC to use RCPSS and RSQRTSS instructions
10151           (and their vectorized variants RCPPS and RSQRTPS) with an
10152           additional Newton-Raphson step to increase precision instead of
10153           DIVSS and SQRTSS (and their vectorized variants) for single
10154           precision floating point arguments.  These instructions are
10155           generated only when -funsafe-math-optimizations is enabled together
10156           with -finite-math-only and -fno-trapping-math.  Note that while the
10157           throughput of the sequence is higher than the throughput of the
10158           non-reciprocal instruction, the precision of the sequence can be
10159           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
10160           0.99999994).
10161
10162           Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS (or
10163           RSQRTPS) already with -ffast-math (or the above option
10164           combination), and doesn't need -mrecip.
10165
10166       -mveclibabi=type
10167           Specifies the ABI type to use for vectorizing intrinsics using an
10168           external library.  Supported types are "svml" for the Intel short
10169           vector math library and "acml" for the AMD math core library style
10170           of interfacing.  GCC will currently emit calls to "vmldExp2",
10171           "vmldLn2", "vmldLog102", "vmldLog102", "vmldPow2", "vmldTanh2",
10172           "vmldTan2", "vmldAtan2", "vmldAtanh2", "vmldCbrt2", "vmldSinh2",
10173           "vmldSin2", "vmldAsinh2", "vmldAsin2", "vmldCosh2", "vmldCos2",
10174           "vmldAcosh2", "vmldAcos2", "vmlsExp4", "vmlsLn4", "vmlsLog104",
10175           "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4", "vmlsAtan4",
10176           "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4", "vmlsAsinh4",
10177           "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4" and "vmlsAcos4"
10178           for corresponding function type when -mveclibabi=svml is used and
10179           "__vrd2_sin", "__vrd2_cos", "__vrd2_exp", "__vrd2_log",
10180           "__vrd2_log2", "__vrd2_log10", "__vrs4_sinf", "__vrs4_cosf",
10181           "__vrs4_expf", "__vrs4_logf", "__vrs4_log2f", "__vrs4_log10f" and
10182           "__vrs4_powf" for corresponding function type when -mveclibabi=acml
10183           is used. Both -ftree-vectorize and -funsafe-math-optimizations have
10184           to be enabled. A SVML or ACML ABI compatible library will have to
10185           be specified at link time.
10186
10187       -mabi=name
10188           Generate code for the specified calling convention.  Permissible
10189           values are: sysv for the ABI used on GNU/Linux and other systems
10190           and ms for the Microsoft ABI.  The default is to use the Microsoft
10191           ABI when targeting Windows.  On all other systems, the default is
10192           the SYSV ABI.  You can control this behavior for a specific
10193           function by using the function attribute ms_abi/sysv_abi.
10194
10195       -mpush-args
10196       -mno-push-args
10197           Use PUSH operations to store outgoing parameters.  This method is
10198           shorter and usually equally fast as method using SUB/MOV operations
10199           and is enabled by default.  In some cases disabling it may improve
10200           performance because of improved scheduling and reduced
10201           dependencies.
10202
10203       -maccumulate-outgoing-args
10204           If enabled, the maximum amount of space required for outgoing
10205           arguments will be computed in the function prologue.  This is
10206           faster on most modern CPUs because of reduced dependencies,
10207           improved scheduling and reduced stack usage when preferred stack
10208           boundary is not equal to 2.  The drawback is a notable increase in
10209           code size.  This switch implies -mno-push-args.
10210
10211       -mthreads
10212           Support thread-safe exception handling on Mingw32.  Code that
10213           relies on thread-safe exception handling must compile and link all
10214           code with the -mthreads option.  When compiling, -mthreads defines
10215           -D_MT; when linking, it links in a special thread helper library
10216           -lmingwthrd which cleans up per thread exception handling data.
10217
10218       -mno-align-stringops
10219           Do not align destination of inlined string operations.  This switch
10220           reduces code size and improves performance in case the destination
10221           is already aligned, but GCC doesn't know about it.
10222
10223       -minline-all-stringops
10224           By default GCC inlines string operations only when destination is
10225           known to be aligned at least to 4 byte boundary.  This enables more
10226           inlining, increase code size, but may improve performance of code
10227           that depends on fast memcpy, strlen and memset for short lengths.
10228
10229       -minline-stringops-dynamically
10230           For string operation of unknown size, inline runtime checks so for
10231           small blocks inline code is used, while for large blocks library
10232           call is used.
10233
10234       -mstringop-strategy=alg
10235           Overwrite internal decision heuristic about particular algorithm to
10236           inline string operation with.  The allowed values are "rep_byte",
10237           "rep_4byte", "rep_8byte" for expanding using i386 "rep" prefix of
10238           specified size, "byte_loop", "loop", "unrolled_loop" for expanding
10239           inline loop, "libcall" for always expanding library call.
10240
10241       -momit-leaf-frame-pointer
10242           Don't keep the frame pointer in a register for leaf functions.
10243           This avoids the instructions to save, set up and restore frame
10244           pointers and makes an extra register available in leaf functions.
10245           The option -fomit-frame-pointer removes the frame pointer for all
10246           functions which might make debugging harder.
10247
10248       -mtls-direct-seg-refs
10249       -mno-tls-direct-seg-refs
10250           Controls whether TLS variables may be accessed with offsets from
10251           the TLS segment register (%gs for 32-bit, %fs for 64-bit), or
10252           whether the thread base pointer must be added.  Whether or not this
10253           is legal depends on the operating system, and whether it maps the
10254           segment to cover the entire TLS area.
10255
10256           For systems that use GNU libc, the default is on.
10257
10258       -msse2avx
10259       -mno-sse2avx
10260           Specify that the assembler should encode SSE instructions with VEX
10261           prefix.  The option -mavx turns this on by default.
10262
10263       These -m switches are supported in addition to the above on AMD x86-64
10264       processors in 64-bit environments.
10265
10266       -m32
10267       -m64
10268           Generate code for a 32-bit or 64-bit environment.  The 32-bit
10269           environment sets int, long and pointer to 32 bits and generates
10270           code that runs on any i386 system.  The 64-bit environment sets int
10271           to 32 bits and long and pointer to 64 bits and generates code for
10272           AMD's x86-64 architecture. For darwin only the -m64 option turns
10273           off the -fno-pic and -mdynamic-no-pic options.
10274
10275       -mno-red-zone
10276           Do not use a so called red zone for x86-64 code.  The red zone is
10277           mandated by the x86-64 ABI, it is a 128-byte area beyond the
10278           location of the stack pointer that will not be modified by signal
10279           or interrupt handlers and therefore can be used for temporary data
10280           without adjusting the stack pointer.  The flag -mno-red-zone
10281           disables this red zone.
10282
10283       -mcmodel=small
10284           Generate code for the small code model: the program and its symbols
10285           must be linked in the lower 2 GB of the address space.  Pointers
10286           are 64 bits.  Programs can be statically or dynamically linked.
10287           This is the default code model.
10288
10289       -mcmodel=kernel
10290           Generate code for the kernel code model.  The kernel runs in the
10291           negative 2 GB of the address space.  This model has to be used for
10292           Linux kernel code.
10293
10294       -mcmodel=medium
10295           Generate code for the medium model: The program is linked in the
10296           lower 2 GB of the address space.  Small symbols are also placed
10297           there.  Symbols with sizes larger than -mlarge-data-threshold are
10298           put into large data or bss sections and can be located above 2GB.
10299           Programs can be statically or dynamically linked.
10300
10301       -mcmodel=large
10302           Generate code for the large model: This model makes no assumptions
10303           about addresses and sizes of sections.
10304
10305       IA-64 Options
10306
10307       These are the -m options defined for the Intel IA-64 architecture.
10308
10309       -mbig-endian
10310           Generate code for a big endian target.  This is the default for HP-
10311           UX.
10312
10313       -mlittle-endian
10314           Generate code for a little endian target.  This is the default for
10315           AIX5 and GNU/Linux.
10316
10317       -mgnu-as
10318       -mno-gnu-as
10319           Generate (or don't) code for the GNU assembler.  This is the
10320           default.
10321
10322       -mgnu-ld
10323       -mno-gnu-ld
10324           Generate (or don't) code for the GNU linker.  This is the default.
10325
10326       -mno-pic
10327           Generate code that does not use a global pointer register.  The
10328           result is not position independent code, and violates the IA-64
10329           ABI.
10330
10331       -mvolatile-asm-stop
10332       -mno-volatile-asm-stop
10333           Generate (or don't) a stop bit immediately before and after
10334           volatile asm statements.
10335
10336       -mregister-names
10337       -mno-register-names
10338           Generate (or don't) in, loc, and out register names for the stacked
10339           registers.  This may make assembler output more readable.
10340
10341       -mno-sdata
10342       -msdata
10343           Disable (or enable) optimizations that use the small data section.
10344           This may be useful for working around optimizer bugs.
10345
10346       -mconstant-gp
10347           Generate code that uses a single constant global pointer value.
10348           This is useful when compiling kernel code.
10349
10350       -mauto-pic
10351           Generate code that is self-relocatable.  This implies
10352           -mconstant-gp.  This is useful when compiling firmware code.
10353
10354       -minline-float-divide-min-latency
10355           Generate code for inline divides of floating point values using the
10356           minimum latency algorithm.
10357
10358       -minline-float-divide-max-throughput
10359           Generate code for inline divides of floating point values using the
10360           maximum throughput algorithm.
10361
10362       -mno-inline-float-divide
10363           Do not generate inline code for divides of floating point values.
10364
10365       -minline-int-divide-min-latency
10366           Generate code for inline divides of integer values using the
10367           minimum latency algorithm.
10368
10369       -minline-int-divide-max-throughput
10370           Generate code for inline divides of integer values using the
10371           maximum throughput algorithm.
10372
10373       -mno-inline-int-divide
10374           Do not generate inline code for divides of integer values.
10375
10376       -minline-sqrt-min-latency
10377           Generate code for inline square roots using the minimum latency
10378           algorithm.
10379
10380       -minline-sqrt-max-throughput
10381           Generate code for inline square roots using the maximum throughput
10382           algorithm.
10383
10384       -mno-inline-sqrt
10385           Do not generate inline code for sqrt.
10386
10387       -mfused-madd
10388       -mno-fused-madd
10389           Do (don't) generate code that uses the fused multiply/add or
10390           multiply/subtract instructions.  The default is to use these
10391           instructions.
10392
10393       -mno-dwarf2-asm
10394       -mdwarf2-asm
10395           Don't (or do) generate assembler code for the DWARF2 line number
10396           debugging info.  This may be useful when not using the GNU
10397           assembler.
10398
10399       -mearly-stop-bits
10400       -mno-early-stop-bits
10401           Allow stop bits to be placed earlier than immediately preceding the
10402           instruction that triggered the stop bit.  This can improve
10403           instruction scheduling, but does not always do so.
10404
10405       -mfixed-range=register-range
10406           Generate code treating the given register range as fixed registers.
10407           A fixed register is one that the register allocator can not use.
10408           This is useful when compiling kernel code.  A register range is
10409           specified as two registers separated by a dash.  Multiple register
10410           ranges can be specified separated by a comma.
10411
10412       -mtls-size=tls-size
10413           Specify bit size of immediate TLS offsets.  Valid values are 14,
10414           22, and 64.
10415
10416       -mtune=cpu-type
10417           Tune the instruction scheduling for a particular CPU, Valid values
10418           are itanium, itanium1, merced, itanium2, and mckinley.
10419
10420       -milp32
10421       -mlp64
10422           Generate code for a 32-bit or 64-bit environment.  The 32-bit
10423           environment sets int, long and pointer to 32 bits.  The 64-bit
10424           environment sets int to 32 bits and long and pointer to 64 bits.
10425           These are HP-UX specific flags.
10426
10427       -mno-sched-br-data-spec
10428       -msched-br-data-spec
10429           (Dis/En)able data speculative scheduling before reload.  This will
10430           result in generation of the ld.a instructions and the corresponding
10431           check instructions (ld.c / chk.a).  The default is 'disable'.
10432
10433       -msched-ar-data-spec
10434       -mno-sched-ar-data-spec
10435           (En/Dis)able data speculative scheduling after reload.  This will
10436           result in generation of the ld.a instructions and the corresponding
10437           check instructions (ld.c / chk.a).  The default is 'enable'.
10438
10439       -mno-sched-control-spec
10440       -msched-control-spec
10441           (Dis/En)able control speculative scheduling.  This feature is
10442           available only during region scheduling (i.e. before reload).  This
10443           will result in generation of the ld.s instructions and the
10444           corresponding check instructions chk.s .  The default is 'disable'.
10445
10446       -msched-br-in-data-spec
10447       -mno-sched-br-in-data-spec
10448           (En/Dis)able speculative scheduling of the instructions that are
10449           dependent on the data speculative loads before reload.  This is
10450           effective only with -msched-br-data-spec enabled.  The default is
10451           'enable'.
10452
10453       -msched-ar-in-data-spec
10454       -mno-sched-ar-in-data-spec
10455           (En/Dis)able speculative scheduling of the instructions that are
10456           dependent on the data speculative loads after reload.  This is
10457           effective only with -msched-ar-data-spec enabled.  The default is
10458           'enable'.
10459
10460       -msched-in-control-spec
10461       -mno-sched-in-control-spec
10462           (En/Dis)able speculative scheduling of the instructions that are
10463           dependent on the control speculative loads.  This is effective only
10464           with -msched-control-spec enabled.  The default is 'enable'.
10465
10466       -mno-sched-prefer-non-data-spec-insns
10467       -msched-prefer-non-data-spec-insns
10468           If enabled, data speculative instructions will be chosen for
10469           schedule only if there are no other choices at the moment.  This
10470           will make the use of the data speculation much more conservative.
10471           The default is 'disable'.
10472
10473       -mno-sched-prefer-non-control-spec-insns
10474       -msched-prefer-non-control-spec-insns
10475           If enabled, control speculative instructions will be chosen for
10476           schedule only if there are no other choices at the moment.  This
10477           will make the use of the control speculation much more
10478           conservative.  The default is 'disable'.
10479
10480       -mno-sched-count-spec-in-critical-path
10481       -msched-count-spec-in-critical-path
10482           If enabled, speculative dependencies will be considered during
10483           computation of the instructions priorities.  This will make the use
10484           of the speculation a bit more conservative.  The default is
10485           'disable'.
10486
10487       -msched-spec-ldc
10488           Use a simple data speculation check.  This option is on by default.
10489
10490       -msched-control-spec-ldc
10491           Use a simple check for control speculation.  This option is on by
10492           default.
10493
10494       -msched-stop-bits-after-every-cycle
10495           Place a stop bit after every cycle when scheduling.  This option is
10496           on by default.
10497
10498       -msched-fp-mem-deps-zero-cost
10499           Assume that floating-point stores and loads are not likely to cause
10500           a conflict when placed into the same instruction group.  This
10501           option is disabled by default.
10502
10503       -msel-sched-dont-check-control-spec
10504           Generate checks for control speculation in selective scheduling.
10505           This flag is disabled by default.
10506
10507       -msched-max-memory-insns=max-insns
10508           Limit on the number of memory insns per instruction group, giving
10509           lower priority to subsequent memory insns attempting to schedule in
10510           the same instruction group. Frequently useful to prevent cache bank
10511           conflicts.  The default value is 1.
10512
10513       -msched-max-memory-insns-hard-limit
10514           Disallow more than `msched-max-memory-insns' in instruction group.
10515           Otherwise, limit is `soft' meaning that we would prefer non-memory
10516           operations when limit is reached but may still schedule memory
10517           operations.
10518
10519       IA-64/VMS Options
10520
10521       These -m options are defined for the IA-64/VMS implementations:
10522
10523       -mvms-return-codes
10524           Return VMS condition codes from main. The default is to return
10525           POSIX style condition (e.g. error) codes.
10526
10527       -mdebug-main=prefix
10528           Flag the first routine whose name starts with prefix as the main
10529           routine for the debugger.
10530
10531       -mmalloc64
10532           Default to 64bit memory allocation routines.
10533
10534       LM32 Options
10535
10536       These -m options are defined for the Lattice Mico32 architecture:
10537
10538       -mbarrel-shift-enabled
10539           Enable barrel-shift instructions.
10540
10541       -mdivide-enabled
10542           Enable divide and modulus instructions.
10543
10544       -mmultiply-enabled
10545           Enable multiply instructions.
10546
10547       -msign-extend-enabled
10548           Enable sign extend instructions.
10549
10550       -muser-enabled
10551           Enable user-defined instructions.
10552
10553       M32C Options
10554
10555       -mcpu=name
10556           Select the CPU for which code is generated.  name may be one of r8c
10557           for the R8C/Tiny series, m16c for the M16C (up to /60) series,
10558           m32cm for the M16C/80 series, or m32c for the M32C/80 series.
10559
10560       -msim
10561           Specifies that the program will be run on the simulator.  This
10562           causes an alternate runtime library to be linked in which supports,
10563           for example, file I/O.  You must not use this option when
10564           generating programs that will run on real hardware; you must
10565           provide your own runtime library for whatever I/O functions are
10566           needed.
10567
10568       -memregs=number
10569           Specifies the number of memory-based pseudo-registers GCC will use
10570           during code generation.  These pseudo-registers will be used like
10571           real registers, so there is a tradeoff between GCC's ability to fit
10572           the code into available registers, and the performance penalty of
10573           using memory instead of registers.  Note that all modules in a
10574           program must be compiled with the same value for this option.
10575           Because of that, you must not use this option with the default
10576           runtime libraries gcc builds.
10577
10578       M32R/D Options
10579
10580       These -m options are defined for Renesas M32R/D architectures:
10581
10582       -m32r2
10583           Generate code for the M32R/2.
10584
10585       -m32rx
10586           Generate code for the M32R/X.
10587
10588       -m32r
10589           Generate code for the M32R.  This is the default.
10590
10591       -mmodel=small
10592           Assume all objects live in the lower 16MB of memory (so that their
10593           addresses can be loaded with the "ld24" instruction), and assume
10594           all subroutines are reachable with the "bl" instruction.  This is
10595           the default.
10596
10597           The addressability of a particular object can be set with the
10598           "model" attribute.
10599
10600       -mmodel=medium
10601           Assume objects may be anywhere in the 32-bit address space (the
10602           compiler will generate "seth/add3" instructions to load their
10603           addresses), and assume all subroutines are reachable with the "bl"
10604           instruction.
10605
10606       -mmodel=large
10607           Assume objects may be anywhere in the 32-bit address space (the
10608           compiler will generate "seth/add3" instructions to load their
10609           addresses), and assume subroutines may not be reachable with the
10610           "bl" instruction (the compiler will generate the much slower
10611           "seth/add3/jl" instruction sequence).
10612
10613       -msdata=none
10614           Disable use of the small data area.  Variables will be put into one
10615           of .data, bss, or .rodata (unless the "section" attribute has been
10616           specified).  This is the default.
10617
10618           The small data area consists of sections .sdata and .sbss.  Objects
10619           may be explicitly put in the small data area with the "section"
10620           attribute using one of these sections.
10621
10622       -msdata=sdata
10623           Put small global and static data in the small data area, but do not
10624           generate special code to reference them.
10625
10626       -msdata=use
10627           Put small global and static data in the small data area, and
10628           generate special instructions to reference them.
10629
10630       -G num
10631           Put global and static objects less than or equal to num bytes into
10632           the small data or bss sections instead of the normal data or bss
10633           sections.  The default value of num is 8.  The -msdata option must
10634           be set to one of sdata or use for this option to have any effect.
10635
10636           All modules should be compiled with the same -G num value.
10637           Compiling with different values of num may or may not work; if it
10638           doesn't the linker will give an error message---incorrect code will
10639           not be generated.
10640
10641       -mdebug
10642           Makes the M32R specific code in the compiler display some
10643           statistics that might help in debugging programs.
10644
10645       -malign-loops
10646           Align all loops to a 32-byte boundary.
10647
10648       -mno-align-loops
10649           Do not enforce a 32-byte alignment for loops.  This is the default.
10650
10651       -missue-rate=number
10652           Issue number instructions per cycle.  number can only be 1 or 2.
10653
10654       -mbranch-cost=number
10655           number can only be 1 or 2.  If it is 1 then branches will be
10656           preferred over conditional code, if it is 2, then the opposite will
10657           apply.
10658
10659       -mflush-trap=number
10660           Specifies the trap number to use to flush the cache.  The default
10661           is 12.  Valid numbers are between 0 and 15 inclusive.
10662
10663       -mno-flush-trap
10664           Specifies that the cache cannot be flushed by using a trap.
10665
10666       -mflush-func=name
10667           Specifies the name of the operating system function to call to
10668           flush the cache.  The default is _flush_cache, but a function call
10669           will only be used if a trap is not available.
10670
10671       -mno-flush-func
10672           Indicates that there is no OS function for flushing the cache.
10673
10674       M680x0 Options
10675
10676       These are the -m options defined for M680x0 and ColdFire processors.
10677       The default settings depend on which architecture was selected when the
10678       compiler was configured; the defaults for the most common choices are
10679       given below.
10680
10681       -march=arch
10682           Generate code for a specific M680x0 or ColdFire instruction set
10683           architecture.  Permissible values of arch for M680x0 architectures
10684           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
10685           architectures are selected according to Freescale's ISA
10686           classification and the permissible values are: isaa, isaaplus, isab
10687           and isac.
10688
10689           gcc defines a macro __mcfarch__ whenever it is generating code for
10690           a ColdFire target.  The arch in this macro is one of the -march
10691           arguments given above.
10692
10693           When used together, -march and -mtune select code that runs on a
10694           family of similar processors but that is optimized for a particular
10695           microarchitecture.
10696
10697       -mcpu=cpu
10698           Generate code for a specific M680x0 or ColdFire processor.  The
10699           M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302,
10700           68332 and cpu32.  The ColdFire cpus are given by the table below,
10701           which also classifies the CPUs into families:
10702
10703           Family : -mcpu arguments
10704           51 : 51 51ac 51cn 51em 51qe
10705           5206 : 5202 5204 5206
10706           5206e : 5206e
10707           5208 : 5207 5208
10708           5211a : 5210a 5211a
10709           5213 : 5211 5212 5213
10710           5216 : 5214 5216
10711           52235 : 52230 52231 52232 52233 52234 52235
10712           5225 : 5224 5225
10713           52259 : 52252 52254 52255 52256 52258 52259
10714           5235 : 5232 5233 5234 5235 523x
10715           5249 : 5249
10716           5250 : 5250
10717           5271 : 5270 5271
10718           5272 : 5272
10719           5275 : 5274 5275
10720           5282 : 5280 5281 5282 528x
10721           53017 : 53011 53012 53013 53014 53015 53016 53017
10722           5307 : 5307
10723           5329 : 5327 5328 5329 532x
10724           5373 : 5372 5373 537x
10725           5407 : 5407
10726           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484
10727           5485
10728
10729           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.
10730           Other combinations of -mcpu and -march are rejected.
10731
10732           gcc defines the macro __mcf_cpu_cpu when ColdFire target cpu is
10733           selected.  It also defines __mcf_family_family, where the value of
10734           family is given by the table above.
10735
10736       -mtune=tune
10737           Tune the code for a particular microarchitecture, within the
10738           constraints set by -march and -mcpu.  The M680x0 microarchitectures
10739           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  The
10740           ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.
10741
10742           You can also use -mtune=68020-40 for code that needs to run
10743           relatively well on 68020, 68030 and 68040 targets.  -mtune=68020-60
10744           is similar but includes 68060 targets as well.  These two options
10745           select the same tuning decisions as -m68020-40 and -m68020-60
10746           respectively.
10747
10748           gcc defines the macros __mcarch and __mcarch__ when tuning for
10749           680x0 architecture arch.  It also defines mcarch unless either
10750           -ansi or a non-GNU -std option is used.  If gcc is tuning for a
10751           range of architectures, as selected by -mtune=68020-40 or
10752           -mtune=68020-60, it defines the macros for every architecture in
10753           the range.
10754
10755           gcc also defines the macro __muarch__ when tuning for ColdFire
10756           microarchitecture uarch, where uarch is one of the arguments given
10757           above.
10758
10759       -m68000
10760       -mc68000
10761           Generate output for a 68000.  This is the default when the compiler
10762           is configured for 68000-based systems.  It is equivalent to
10763           -march=68000.
10764
10765           Use this option for microcontrollers with a 68000 or EC000 core,
10766           including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
10767
10768       -m68010
10769           Generate output for a 68010.  This is the default when the compiler
10770           is configured for 68010-based systems.  It is equivalent to
10771           -march=68010.
10772
10773       -m68020
10774       -mc68020
10775           Generate output for a 68020.  This is the default when the compiler
10776           is configured for 68020-based systems.  It is equivalent to
10777           -march=68020.
10778
10779       -m68030
10780           Generate output for a 68030.  This is the default when the compiler
10781           is configured for 68030-based systems.  It is equivalent to
10782           -march=68030.
10783
10784       -m68040
10785           Generate output for a 68040.  This is the default when the compiler
10786           is configured for 68040-based systems.  It is equivalent to
10787           -march=68040.
10788
10789           This option inhibits the use of 68881/68882 instructions that have
10790           to be emulated by software on the 68040.  Use this option if your
10791           68040 does not have code to emulate those instructions.
10792
10793       -m68060
10794           Generate output for a 68060.  This is the default when the compiler
10795           is configured for 68060-based systems.  It is equivalent to
10796           -march=68060.
10797
10798           This option inhibits the use of 68020 and 68881/68882 instructions
10799           that have to be emulated by software on the 68060.  Use this option
10800           if your 68060 does not have code to emulate those instructions.
10801
10802       -mcpu32
10803           Generate output for a CPU32.  This is the default when the compiler
10804           is configured for CPU32-based systems.  It is equivalent to
10805           -march=cpu32.
10806
10807           Use this option for microcontrollers with a CPU32 or CPU32+ core,
10808           including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
10809           68341, 68349 and 68360.
10810
10811       -m5200
10812           Generate output for a 520X ColdFire CPU.  This is the default when
10813           the compiler is configured for 520X-based systems.  It is
10814           equivalent to -mcpu=5206, and is now deprecated in favor of that
10815           option.
10816
10817           Use this option for microcontroller with a 5200 core, including the
10818           MCF5202, MCF5203, MCF5204 and MCF5206.
10819
10820       -m5206e
10821           Generate output for a 5206e ColdFire CPU.  The option is now
10822           deprecated in favor of the equivalent -mcpu=5206e.
10823
10824       -m528x
10825           Generate output for a member of the ColdFire 528X family.  The
10826           option is now deprecated in favor of the equivalent -mcpu=528x.
10827
10828       -m5307
10829           Generate output for a ColdFire 5307 CPU.  The option is now
10830           deprecated in favor of the equivalent -mcpu=5307.
10831
10832       -m5407
10833           Generate output for a ColdFire 5407 CPU.  The option is now
10834           deprecated in favor of the equivalent -mcpu=5407.
10835
10836       -mcfv4e
10837           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
10838           This includes use of hardware floating point instructions.  The
10839           option is equivalent to -mcpu=547x, and is now deprecated in favor
10840           of that option.
10841
10842       -m68020-40
10843           Generate output for a 68040, without using any of the new
10844           instructions.  This results in code which can run relatively
10845           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
10846           generated code does use the 68881 instructions that are emulated on
10847           the 68040.
10848
10849           The option is equivalent to -march=68020 -mtune=68020-40.
10850
10851       -m68020-60
10852           Generate output for a 68060, without using any of the new
10853           instructions.  This results in code which can run relatively
10854           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
10855           generated code does use the 68881 instructions that are emulated on
10856           the 68060.
10857
10858           The option is equivalent to -march=68020 -mtune=68020-60.
10859
10860       -mhard-float
10861       -m68881
10862           Generate floating-point instructions.  This is the default for
10863           68020 and above, and for ColdFire devices that have an FPU.  It
10864           defines the macro __HAVE_68881__ on M680x0 targets and __mcffpu__
10865           on ColdFire targets.
10866
10867       -msoft-float
10868           Do not generate floating-point instructions; use library calls
10869           instead.  This is the default for 68000, 68010, and 68832 targets.
10870           It is also the default for ColdFire devices that have no FPU.
10871
10872       -mdiv
10873       -mno-div
10874           Generate (do not generate) ColdFire hardware divide and remainder
10875           instructions.  If -march is used without -mcpu, the default is "on"
10876           for ColdFire architectures and "off" for M680x0 architectures.
10877           Otherwise, the default is taken from the target CPU (either the
10878           default CPU, or the one specified by -mcpu).  For example, the
10879           default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.
10880
10881           gcc defines the macro __mcfhwdiv__ when this option is enabled.
10882
10883       -mshort
10884           Consider type "int" to be 16 bits wide, like "short int".
10885           Additionally, parameters passed on the stack are also aligned to a
10886           16-bit boundary even on targets whose API mandates promotion to
10887           32-bit.
10888
10889       -mno-short
10890           Do not consider type "int" to be 16 bits wide.  This is the
10891           default.
10892
10893       -mnobitfield
10894       -mno-bitfield
10895           Do not use the bit-field instructions.  The -m68000, -mcpu32 and
10896           -m5200 options imply -mnobitfield.
10897
10898       -mbitfield
10899           Do use the bit-field instructions.  The -m68020 option implies
10900           -mbitfield.  This is the default if you use a configuration
10901           designed for a 68020.
10902
10903       -mrtd
10904           Use a different function-calling convention, in which functions
10905           that take a fixed number of arguments return with the "rtd"
10906           instruction, which pops their arguments while returning.  This
10907           saves one instruction in the caller since there is no need to pop
10908           the arguments there.
10909
10910           This calling convention is incompatible with the one normally used
10911           on Unix, so you cannot use it if you need to call libraries
10912           compiled with the Unix compiler.
10913
10914           Also, you must provide function prototypes for all functions that
10915           take variable numbers of arguments (including "printf"); otherwise
10916           incorrect code will be generated for calls to those functions.
10917
10918           In addition, seriously incorrect code will result if you call a
10919           function with too many arguments.  (Normally, extra arguments are
10920           harmlessly ignored.)
10921
10922           The "rtd" instruction is supported by the 68010, 68020, 68030,
10923           68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
10924
10925       -mno-rtd
10926           Do not use the calling conventions selected by -mrtd.  This is the
10927           default.
10928
10929       -malign-int
10930       -mno-align-int
10931           Control whether GCC aligns "int", "long", "long long", "float",
10932           "double", and "long double" variables on a 32-bit boundary
10933           (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning
10934           variables on 32-bit boundaries produces code that runs somewhat
10935           faster on processors with 32-bit busses at the expense of more
10936           memory.
10937
10938           Warning: if you use the -malign-int switch, GCC will align
10939           structures containing the above types  differently than most
10940           published application binary interface specifications for the m68k.
10941
10942       -mpcrel
10943           Use the pc-relative addressing mode of the 68000 directly, instead
10944           of using a global offset table.  At present, this option implies
10945           -fpic, allowing at most a 16-bit offset for pc-relative addressing.
10946           -fPIC is not presently supported with -mpcrel, though this could be
10947           supported for 68020 and higher processors.
10948
10949       -mno-strict-align
10950       -mstrict-align
10951           Do not (do) assume that unaligned memory references will be handled
10952           by the system.
10953
10954       -msep-data
10955           Generate code that allows the data segment to be located in a
10956           different area of memory from the text segment.  This allows for
10957           execute in place in an environment without virtual memory
10958           management.  This option implies -fPIC.
10959
10960       -mno-sep-data
10961           Generate code that assumes that the data segment follows the text
10962           segment.  This is the default.
10963
10964       -mid-shared-library
10965           Generate code that supports shared libraries via the library ID
10966           method.  This allows for execute in place and shared libraries in
10967           an environment without virtual memory management.  This option
10968           implies -fPIC.
10969
10970       -mno-id-shared-library
10971           Generate code that doesn't assume ID based shared libraries are
10972           being used.  This is the default.
10973
10974       -mshared-library-id=n
10975           Specified the identification number of the ID based shared library
10976           being compiled.  Specifying a value of 0 will generate more compact
10977           code, specifying other values will force the allocation of that
10978           number to the current library but is no more space or time
10979           efficient than omitting this option.
10980
10981       -mxgot
10982       -mno-xgot
10983           When generating position-independent code for ColdFire, generate
10984           code that works if the GOT has more than 8192 entries.  This code
10985           is larger and slower than code generated without this option.  On
10986           M680x0 processors, this option is not needed; -fPIC suffices.
10987
10988           GCC normally uses a single instruction to load values from the GOT.
10989           While this is relatively efficient, it only works if the GOT is
10990           smaller than about 64k.  Anything larger causes the linker to
10991           report an error such as:
10992
10993                   relocation truncated to fit: R_68K_GOT16O foobar
10994
10995           If this happens, you should recompile your code with -mxgot.  It
10996           should then work with very large GOTs.  However, code generated
10997           with -mxgot is less efficient, since it takes 4 instructions to
10998           fetch the value of a global symbol.
10999
11000           Note that some linkers, including newer versions of the GNU linker,
11001           can create multiple GOTs and sort GOT entries.  If you have such a
11002           linker, you should only need to use -mxgot when compiling a single
11003           object file that accesses more than 8192 GOT entries.  Very few do.
11004
11005           These options have no effect unless GCC is generating position-
11006           independent code.
11007
11008       M68hc1x Options
11009
11010       These are the -m options defined for the 68hc11 and 68hc12
11011       microcontrollers.  The default values for these options depends on
11012       which style of microcontroller was selected when the compiler was
11013       configured; the defaults for the most common choices are given below.
11014
11015       -m6811
11016       -m68hc11
11017           Generate output for a 68HC11.  This is the default when the
11018           compiler is configured for 68HC11-based systems.
11019
11020       -m6812
11021       -m68hc12
11022           Generate output for a 68HC12.  This is the default when the
11023           compiler is configured for 68HC12-based systems.
11024
11025       -m68S12
11026       -m68hcs12
11027           Generate output for a 68HCS12.
11028
11029       -mauto-incdec
11030           Enable the use of 68HC12 pre and post auto-increment and auto-
11031           decrement addressing modes.
11032
11033       -minmax
11034       -mnominmax
11035           Enable the use of 68HC12 min and max instructions.
11036
11037       -mlong-calls
11038       -mno-long-calls
11039           Treat all calls as being far away (near).  If calls are assumed to
11040           be far away, the compiler will use the "call" instruction to call a
11041           function and the "rtc" instruction for returning.
11042
11043       -mshort
11044           Consider type "int" to be 16 bits wide, like "short int".
11045
11046       -msoft-reg-count=count
11047           Specify the number of pseudo-soft registers which are used for the
11048           code generation.  The maximum number is 32.  Using more pseudo-soft
11049           register may or may not result in better code depending on the
11050           program.  The default is 4 for 68HC11 and 2 for 68HC12.
11051
11052       MCore Options
11053
11054       These are the -m options defined for the Motorola M*Core processors.
11055
11056       -mhardlit
11057       -mno-hardlit
11058           Inline constants into the code stream if it can be done in two
11059           instructions or less.
11060
11061       -mdiv
11062       -mno-div
11063           Use the divide instruction.  (Enabled by default).
11064
11065       -mrelax-immediate
11066       -mno-relax-immediate
11067           Allow arbitrary sized immediates in bit operations.
11068
11069       -mwide-bitfields
11070       -mno-wide-bitfields
11071           Always treat bit-fields as int-sized.
11072
11073       -m4byte-functions
11074       -mno-4byte-functions
11075           Force all functions to be aligned to a four byte boundary.
11076
11077       -mcallgraph-data
11078       -mno-callgraph-data
11079           Emit callgraph information.
11080
11081       -mslow-bytes
11082       -mno-slow-bytes
11083           Prefer word access when reading byte quantities.
11084
11085       -mlittle-endian
11086       -mbig-endian
11087           Generate code for a little endian target.
11088
11089       -m210
11090       -m340
11091           Generate code for the 210 processor.
11092
11093       -mno-lsim
11094           Assume that run-time support has been provided and so omit the
11095           simulator library (libsim.a) from the linker command line.
11096
11097       -mstack-increment=size
11098           Set the maximum amount for a single stack increment operation.
11099           Large values can increase the speed of programs which contain
11100           functions that need a large amount of stack space, but they can
11101           also trigger a segmentation fault if the stack is extended too
11102           much.  The default value is 0x1000.
11103
11104       MeP Options
11105
11106       -mabsdiff
11107           Enables the "abs" instruction, which is the absolute difference
11108           between two registers.
11109
11110       -mall-opts
11111           Enables all the optional instructions - average, multiply, divide,
11112           bit operations, leading zero, absolute difference, min/max, clip,
11113           and saturation.
11114
11115       -maverage
11116           Enables the "ave" instruction, which computes the average of two
11117           registers.
11118
11119       -mbased=n
11120           Variables of size n bytes or smaller will be placed in the ".based"
11121           section by default.  Based variables use the $tp register as a base
11122           register, and there is a 128 byte limit to the ".based" section.
11123
11124       -mbitops
11125           Enables the bit operation instructions - bit test ("btstm"), set
11126           ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set
11127           ("tas").
11128
11129       -mc=name
11130           Selects which section constant data will be placed in.  name may be
11131           "tiny", "near", or "far".
11132
11133       -mclip
11134           Enables the "clip" instruction.  Note that "-mclip" is not useful
11135           unless you also provide "-mminmax".
11136
11137       -mconfig=name
11138           Selects one of the build-in core configurations.  Each MeP chip has
11139           one or more modules in it; each module has a core CPU and a variety
11140           of coprocessors, optional instructions, and peripherals.  The
11141           "MeP-Integrator" tool, not part of GCC, provides these
11142           configurations through this option; using this option is the same
11143           as using all the corresponding command line options.  The default
11144           configuration is "default".
11145
11146       -mcop
11147           Enables the coprocessor instructions.  By default, this is a 32-bit
11148           coprocessor.  Note that the coprocessor is normally enabled via the
11149           "-mconfig=" option.
11150
11151       -mcop32
11152           Enables the 32-bit coprocessor's instructions.
11153
11154       -mcop64
11155           Enables the 64-bit coprocessor's instructions.
11156
11157       -mivc2
11158           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.
11159
11160       -mdc
11161           Causes constant variables to be placed in the ".near" section.
11162
11163       -mdiv
11164           Enables the "div" and "divu" instructions.
11165
11166       -meb
11167           Generate big-endian code.
11168
11169       -mel
11170           Generate little-endian code.
11171
11172       -mio-volatile
11173           Tells the compiler that any variable marked with the "io" attribute
11174           is to be considered volatile.
11175
11176       -ml Causes variables to be assigned to the ".far" section by default.
11177
11178       -mleadz
11179           Enables the "leadz" (leading zero) instruction.
11180
11181       -mm Causes variables to be assigned to the ".near" section by default.
11182
11183       -mminmax
11184           Enables the "min" and "max" instructions.
11185
11186       -mmult
11187           Enables the multiplication and multiply-accumulate instructions.
11188
11189       -mno-opts
11190           Disables all the optional instructions enabled by "-mall-opts".
11191
11192       -mrepeat
11193           Enables the "repeat" and "erepeat" instructions, used for low-
11194           overhead looping.
11195
11196       -ms Causes all variables to default to the ".tiny" section.  Note that
11197           there is a 65536 byte limit to this section.  Accesses to these
11198           variables use the %gp base register.
11199
11200       -msatur
11201           Enables the saturation instructions.  Note that the compiler does
11202           not currently generate these itself, but this option is included
11203           for compatibility with other tools, like "as".
11204
11205       -msdram
11206           Link the SDRAM-based runtime instead of the default ROM-based
11207           runtime.
11208
11209       -msim
11210           Link the simulator runtime libraries.
11211
11212       -msimnovec
11213           Link the simulator runtime libraries, excluding built-in support
11214           for reset and exception vectors and tables.
11215
11216       -mtf
11217           Causes all functions to default to the ".far" section.  Without
11218           this option, functions default to the ".near" section.
11219
11220       -mtiny=n
11221           Variables that are n bytes or smaller will be allocated to the
11222           ".tiny" section.  These variables use the $gp base register.  The
11223           default for this option is 4, but note that there's a 65536 byte
11224           limit to the ".tiny" section.
11225
11226       MIPS Options
11227
11228       -EB Generate big-endian code.
11229
11230       -EL Generate little-endian code.  This is the default for mips*el-*-*
11231           configurations.
11232
11233       -march=arch
11234           Generate code that will run on arch, which can be the name of a
11235           generic MIPS ISA, or the name of a particular processor.  The ISA
11236           names are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips64 and
11237           mips64r2.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec,
11238           4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec,
11239           24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 74kc, 74kf2_1, 74kf1_1,
11240           74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, loongson2e, loongson2f, m4k,
11241           octeon, orion, r2000, r3000, r3900, r4000, r4400, r4600, r4650,
11242           r6000, r8000, rm7000, rm9000, r10000, r12000, r14000, r16000, sb1,
11243           sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400,
11244           vr5500 and xlr.  The special value from-abi selects the most
11245           compatible architecture for the selected ABI (that is, mips1 for
11246           32-bit ABIs and mips3 for 64-bit ABIs).
11247
11248           Native Linux/GNU toolchains also support the value native, which
11249           selects the best architecture option for the host processor.
11250           -march=native has no effect if GCC does not recognize the
11251           processor.
11252
11253           In processor names, a final 000 can be abbreviated as k (for
11254           example, -march=r2k).  Prefixes are optional, and vr may be written
11255           r.
11256
11257           Names of the form nf2_1 refer to processors with FPUs clocked at
11258           half the rate of the core, names of the form nf1_1 refer to
11259           processors with FPUs clocked at the same rate as the core, and
11260           names of the form nf3_2 refer to processors with FPUs clocked a
11261           ratio of 3:2 with respect to the core.  For compatibility reasons,
11262           nf is accepted as a synonym for nf2_1 while nx and bfx are accepted
11263           as synonyms for nf1_1.
11264
11265           GCC defines two macros based on the value of this option.  The
11266           first is _MIPS_ARCH, which gives the name of target architecture,
11267           as a string.  The second has the form _MIPS_ARCH_foo, where foo is
11268           the capitalized value of _MIPS_ARCH.  For example, -march=r2000
11269           will set _MIPS_ARCH to "r2000" and define the macro
11270           _MIPS_ARCH_R2000.
11271
11272           Note that the _MIPS_ARCH macro uses the processor names given
11273           above.  In other words, it will have the full prefix and will not
11274           abbreviate 000 as k.  In the case of from-abi, the macro names the
11275           resolved architecture (either "mips1" or "mips3").  It names the
11276           default architecture when no -march option is given.
11277
11278       -mtune=arch
11279           Optimize for arch.  Among other things, this option controls the
11280           way instructions are scheduled, and the perceived cost of
11281           arithmetic operations.  The list of arch values is the same as for
11282           -march.
11283
11284           When this option is not used, GCC will optimize for the processor
11285           specified by -march.  By using -march and -mtune together, it is
11286           possible to generate code that will run on a family of processors,
11287           but optimize the code for one particular member of that family.
11288
11289           -mtune defines the macros _MIPS_TUNE and _MIPS_TUNE_foo, which work
11290           in the same way as the -march ones described above.
11291
11292       -mips1
11293           Equivalent to -march=mips1.
11294
11295       -mips2
11296           Equivalent to -march=mips2.
11297
11298       -mips3
11299           Equivalent to -march=mips3.
11300
11301       -mips4
11302           Equivalent to -march=mips4.
11303
11304       -mips32
11305           Equivalent to -march=mips32.
11306
11307       -mips32r2
11308           Equivalent to -march=mips32r2.
11309
11310       -mips64
11311           Equivalent to -march=mips64.
11312
11313       -mips64r2
11314           Equivalent to -march=mips64r2.
11315
11316       -mips16
11317       -mno-mips16
11318           Generate (do not generate) MIPS16 code.  If GCC is targetting a
11319           MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE.
11320
11321           MIPS16 code generation can also be controlled on a per-function
11322           basis by means of "mips16" and "nomips16" attributes.
11323
11324       -mflip-mips16
11325           Generate MIPS16 code on alternating functions.  This option is
11326           provided for regression testing of mixed MIPS16/non-MIPS16 code
11327           generation, and is not intended for ordinary use in compiling user
11328           code.
11329
11330       -minterlink-mips16
11331       -mno-interlink-mips16
11332           Require (do not require) that non-MIPS16 code be link-compatible
11333           with MIPS16 code.
11334
11335           For example, non-MIPS16 code cannot jump directly to MIPS16 code;
11336           it must either use a call or an indirect jump.  -minterlink-mips16
11337           therefore disables direct jumps unless GCC knows that the target of
11338           the jump is not MIPS16.
11339
11340       -mabi=32
11341       -mabi=o64
11342       -mabi=n32
11343       -mabi=64
11344       -mabi=eabi
11345           Generate code for the given ABI.
11346
11347           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
11348           generates 64-bit code when you select a 64-bit architecture, but
11349           you can use -mgp32 to get 32-bit code instead.
11350
11351           For information about the O64 ABI, see
11352           <http://gcc.gnu.org/projects/mipso64-abi.html>.
11353
11354           GCC supports a variant of the o32 ABI in which floating-point
11355           registers are 64 rather than 32 bits wide.  You can select this
11356           combination with -mabi=32 -mfp64.  This ABI relies on the mthc1 and
11357           mfhc1 instructions and is therefore only supported for MIPS32R2
11358           processors.
11359
11360           The register assignments for arguments and return values remain the
11361           same, but each scalar value is passed in a single 64-bit register
11362           rather than a pair of 32-bit registers.  For example, scalar
11363           floating-point values are returned in $f0 only, not a $f0/$f1 pair.
11364           The set of call-saved registers also remains the same, but all 64
11365           bits are saved.
11366
11367       -mabicalls
11368       -mno-abicalls
11369           Generate (do not generate) code that is suitable for SVR4-style
11370           dynamic objects.  -mabicalls is the default for SVR4-based systems.
11371
11372       -mshared
11373       -mno-shared
11374           Generate (do not generate) code that is fully position-independent,
11375           and that can therefore be linked into shared libraries.  This
11376           option only affects -mabicalls.
11377
11378           All -mabicalls code has traditionally been position-independent,
11379           regardless of options like -fPIC and -fpic.  However, as an
11380           extension, the GNU toolchain allows executables to use absolute
11381           accesses for locally-binding symbols.  It can also use shorter GP
11382           initialization sequences and generate direct calls to locally-
11383           defined functions.  This mode is selected by -mno-shared.
11384
11385           -mno-shared depends on binutils 2.16 or higher and generates
11386           objects that can only be linked by the GNU linker.  However, the
11387           option does not affect the ABI of the final executable; it only
11388           affects the ABI of relocatable objects.  Using -mno-shared will
11389           generally make executables both smaller and quicker.
11390
11391           -mshared is the default.
11392
11393       -mplt
11394       -mno-plt
11395           Assume (do not assume) that the static and dynamic linkers support
11396           PLTs and copy relocations.  This option only affects -mno-shared
11397           -mabicalls.  For the n64 ABI, this option has no effect without
11398           -msym32.
11399
11400           You can make -mplt the default by configuring GCC with
11401           --with-mips-plt.  The default is -mno-plt otherwise.
11402
11403       -mxgot
11404       -mno-xgot
11405           Lift (do not lift) the usual restrictions on the size of the global
11406           offset table.
11407
11408           GCC normally uses a single instruction to load values from the GOT.
11409           While this is relatively efficient, it will only work if the GOT is
11410           smaller than about 64k.  Anything larger will cause the linker to
11411           report an error such as:
11412
11413                   relocation truncated to fit: R_MIPS_GOT16 foobar
11414
11415           If this happens, you should recompile your code with -mxgot.  It
11416           should then work with very large GOTs, although it will also be
11417           less efficient, since it will take three instructions to fetch the
11418           value of a global symbol.
11419
11420           Note that some linkers can create multiple GOTs.  If you have such
11421           a linker, you should only need to use -mxgot when a single object
11422           file accesses more than 64k's worth of GOT entries.  Very few do.
11423
11424           These options have no effect unless GCC is generating position
11425           independent code.
11426
11427       -mgp32
11428           Assume that general-purpose registers are 32 bits wide.
11429
11430       -mgp64
11431           Assume that general-purpose registers are 64 bits wide.
11432
11433       -mfp32
11434           Assume that floating-point registers are 32 bits wide.
11435
11436       -mfp64
11437           Assume that floating-point registers are 64 bits wide.
11438
11439       -mhard-float
11440           Use floating-point coprocessor instructions.
11441
11442       -msoft-float
11443           Do not use floating-point coprocessor instructions.  Implement
11444           floating-point calculations using library calls instead.
11445
11446       -msingle-float
11447           Assume that the floating-point coprocessor only supports single-
11448           precision operations.
11449
11450       -mdouble-float
11451           Assume that the floating-point coprocessor supports double-
11452           precision operations.  This is the default.
11453
11454       -mllsc
11455       -mno-llsc
11456           Use (do not use) ll, sc, and sync instructions to implement atomic
11457           memory built-in functions.  When neither option is specified, GCC
11458           will use the instructions if the target architecture supports them.
11459
11460           -mllsc is useful if the runtime environment can emulate the
11461           instructions and -mno-llsc can be useful when compiling for
11462           nonstandard ISAs.  You can make either option the default by
11463           configuring GCC with --with-llsc and --without-llsc respectively.
11464           --with-llsc is the default for some configurations; see the
11465           installation documentation for details.
11466
11467       -mdsp
11468       -mno-dsp
11469           Use (do not use) revision 1 of the MIPS DSP ASE.
11470             This option defines the preprocessor macro __mips_dsp.  It also
11471           defines __mips_dsp_rev to 1.
11472
11473       -mdspr2
11474       -mno-dspr2
11475           Use (do not use) revision 2 of the MIPS DSP ASE.
11476             This option defines the preprocessor macros __mips_dsp and
11477           __mips_dspr2.  It also defines __mips_dsp_rev to 2.
11478
11479       -msmartmips
11480       -mno-smartmips
11481           Use (do not use) the MIPS SmartMIPS ASE.
11482
11483       -mpaired-single
11484       -mno-paired-single
11485           Use (do not use) paired-single floating-point instructions.
11486             This option requires hardware floating-point support to be
11487           enabled.
11488
11489       -mdmx
11490       -mno-mdmx
11491           Use (do not use) MIPS Digital Media Extension instructions.  This
11492           option can only be used when generating 64-bit code and requires
11493           hardware floating-point support to be enabled.
11494
11495       -mips3d
11496       -mno-mips3d
11497           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies
11498           -mpaired-single.
11499
11500       -mmt
11501       -mno-mt
11502           Use (do not use) MT Multithreading instructions.
11503
11504       -mlong64
11505           Force "long" types to be 64 bits wide.  See -mlong32 for an
11506           explanation of the default and the way that the pointer size is
11507           determined.
11508
11509       -mlong32
11510           Force "long", "int", and pointer types to be 32 bits wide.
11511
11512           The default size of "int"s, "long"s and pointers depends on the
11513           ABI.  All the supported ABIs use 32-bit "int"s.  The n64 ABI uses
11514           64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
11515           "long"s.  Pointers are the same size as "long"s, or the same size
11516           as integer registers, whichever is smaller.
11517
11518       -msym32
11519       -mno-sym32
11520           Assume (do not assume) that all symbols have 32-bit values,
11521           regardless of the selected ABI.  This option is useful in
11522           combination with -mabi=64 and -mno-abicalls because it allows GCC
11523           to generate shorter and faster references to symbolic addresses.
11524
11525       -G num
11526           Put definitions of externally-visible data in a small data section
11527           if that data is no bigger than num bytes.  GCC can then access the
11528           data more efficiently; see -mgpopt for details.
11529
11530           The default -G option depends on the configuration.
11531
11532       -mlocal-sdata
11533       -mno-local-sdata
11534           Extend (do not extend) the -G behavior to local data too, such as
11535           to static variables in C.  -mlocal-sdata is the default for all
11536           configurations.
11537
11538           If the linker complains that an application is using too much small
11539           data, you might want to try rebuilding the less performance-
11540           critical parts with -mno-local-sdata.  You might also want to build
11541           large libraries with -mno-local-sdata, so that the libraries leave
11542           more room for the main program.
11543
11544       -mextern-sdata
11545       -mno-extern-sdata
11546           Assume (do not assume) that externally-defined data will be in a
11547           small data section if that data is within the -G limit.
11548           -mextern-sdata is the default for all configurations.
11549
11550           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and
11551           Mod references a variable Var that is no bigger than num bytes, you
11552           must make sure that Var is placed in a small data section.  If Var
11553           is defined by another module, you must either compile that module
11554           with a high-enough -G setting or attach a "section" attribute to
11555           Var's definition.  If Var is common, you must link the application
11556           with a high-enough -G setting.
11557
11558           The easiest way of satisfying these restrictions is to compile and
11559           link every module with the same -G option.  However, you may wish
11560           to build a library that supports several different small data
11561           limits.  You can do this by compiling the library with the highest
11562           supported -G setting and additionally using -mno-extern-sdata to
11563           stop the library from making assumptions about externally-defined
11564           data.
11565
11566       -mgpopt
11567       -mno-gpopt
11568           Use (do not use) GP-relative accesses for symbols that are known to
11569           be in a small data section; see -G, -mlocal-sdata and
11570           -mextern-sdata.  -mgpopt is the default for all configurations.
11571
11572           -mno-gpopt is useful for cases where the $gp register might not
11573           hold the value of "_gp".  For example, if the code is part of a
11574           library that might be used in a boot monitor, programs that call
11575           boot monitor routines will pass an unknown value in $gp.  (In such
11576           situations, the boot monitor itself would usually be compiled with
11577           -G0.)
11578
11579           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
11580
11581       -membedded-data
11582       -mno-embedded-data
11583           Allocate variables to the read-only data section first if possible,
11584           then next in the small data section if possible, otherwise in data.
11585           This gives slightly slower code than the default, but reduces the
11586           amount of RAM required when executing, and thus may be preferred
11587           for some embedded systems.
11588
11589       -muninit-const-in-rodata
11590       -mno-uninit-const-in-rodata
11591           Put uninitialized "const" variables in the read-only data section.
11592           This option is only meaningful in conjunction with -membedded-data.
11593
11594       -mcode-readable=setting
11595           Specify whether GCC may generate code that reads from executable
11596           sections.  There are three possible settings:
11597
11598           -mcode-readable=yes
11599               Instructions may freely access executable sections.  This is
11600               the default setting.
11601
11602           -mcode-readable=pcrel
11603               MIPS16 PC-relative load instructions can access executable
11604               sections, but other instructions must not do so.  This option
11605               is useful on 4KSc and 4KSd processors when the code TLBs have
11606               the Read Inhibit bit set.  It is also useful on processors that
11607               can be configured to have a dual instruction/data SRAM
11608               interface and that, like the M4K, automatically redirect PC-
11609               relative loads to the instruction RAM.
11610
11611           -mcode-readable=no
11612               Instructions must not access executable sections.  This option
11613               can be useful on targets that are configured to have a dual
11614               instruction/data SRAM interface but that (unlike the M4K) do
11615               not automatically redirect PC-relative loads to the instruction
11616               RAM.
11617
11618       -msplit-addresses
11619       -mno-split-addresses
11620           Enable (disable) use of the "%hi()" and "%lo()" assembler
11621           relocation operators.  This option has been superseded by
11622           -mexplicit-relocs but is retained for backwards compatibility.
11623
11624       -mexplicit-relocs
11625       -mno-explicit-relocs
11626           Use (do not use) assembler relocation operators when dealing with
11627           symbolic addresses.  The alternative, selected by
11628           -mno-explicit-relocs, is to use assembler macros instead.
11629
11630           -mexplicit-relocs is the default if GCC was configured to use an
11631           assembler that supports relocation operators.
11632
11633       -mcheck-zero-division
11634       -mno-check-zero-division
11635           Trap (do not trap) on integer division by zero.
11636
11637           The default is -mcheck-zero-division.
11638
11639       -mdivide-traps
11640       -mdivide-breaks
11641           MIPS systems check for division by zero by generating either a
11642           conditional trap or a break instruction.  Using traps results in
11643           smaller code, but is only supported on MIPS II and later.  Also,
11644           some versions of the Linux kernel have a bug that prevents trap
11645           from generating the proper signal ("SIGFPE").  Use -mdivide-traps
11646           to allow conditional traps on architectures that support them and
11647           -mdivide-breaks to force the use of breaks.
11648
11649           The default is usually -mdivide-traps, but this can be overridden
11650           at configure time using --with-divide=breaks.  Divide-by-zero
11651           checks can be completely disabled using -mno-check-zero-division.
11652
11653       -mmemcpy
11654       -mno-memcpy
11655           Force (do not force) the use of "memcpy()" for non-trivial block
11656           moves.  The default is -mno-memcpy, which allows GCC to inline most
11657           constant-sized copies.
11658
11659       -mlong-calls
11660       -mno-long-calls
11661           Disable (do not disable) use of the "jal" instruction.  Calling
11662           functions using "jal" is more efficient but requires the caller and
11663           callee to be in the same 256 megabyte segment.
11664
11665           This option has no effect on abicalls code.  The default is
11666           -mno-long-calls.
11667
11668       -mmad
11669       -mno-mad
11670           Enable (disable) use of the "mad", "madu" and "mul" instructions,
11671           as provided by the R4650 ISA.
11672
11673       -mfused-madd
11674       -mno-fused-madd
11675           Enable (disable) use of the floating point multiply-accumulate
11676           instructions, when they are available.  The default is
11677           -mfused-madd.
11678
11679           When multiply-accumulate instructions are used, the intermediate
11680           product is calculated to infinite precision and is not subject to
11681           the FCSR Flush to Zero bit.  This may be undesirable in some
11682           circumstances.
11683
11684       -nocpp
11685           Tell the MIPS assembler to not run its preprocessor over user
11686           assembler files (with a .s suffix) when assembling them.
11687
11688       -mfix-r4000
11689       -mno-fix-r4000
11690           Work around certain R4000 CPU errata:
11691
11692           -   A double-word or a variable shift may give an incorrect result
11693               if executed immediately after starting an integer division.
11694
11695           -   A double-word or a variable shift may give an incorrect result
11696               if executed while an integer multiplication is in progress.
11697
11698           -   An integer division may give an incorrect result if started in
11699               a delay slot of a taken branch or a jump.
11700
11701       -mfix-r4400
11702       -mno-fix-r4400
11703           Work around certain R4400 CPU errata:
11704
11705           -   A double-word or a variable shift may give an incorrect result
11706               if executed immediately after starting an integer division.
11707
11708       -mfix-r10000
11709       -mno-fix-r10000
11710           Work around certain R10000 errata:
11711
11712           -   "ll"/"sc" sequences may not behave atomically on revisions
11713               prior to 3.0.  They may deadlock on revisions 2.6 and earlier.
11714
11715           This option can only be used if the target architecture supports
11716           branch-likely instructions.  -mfix-r10000 is the default when
11717           -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
11718
11719       -mfix-vr4120
11720       -mno-fix-vr4120
11721           Work around certain VR4120 errata:
11722
11723           -   "dmultu" does not always produce the correct result.
11724
11725           -   "div" and "ddiv" do not always produce the correct result if
11726               one of the operands is negative.
11727
11728           The workarounds for the division errata rely on special functions
11729           in libgcc.a.  At present, these functions are only provided by the
11730           "mips64vr*-elf" configurations.
11731
11732           Other VR4120 errata require a nop to be inserted between certain
11733           pairs of instructions.  These errata are handled by the assembler,
11734           not by GCC itself.
11735
11736       -mfix-vr4130
11737           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are
11738           implemented by the assembler rather than by GCC, although GCC will
11739           avoid using "mflo" and "mfhi" if the VR4130 "macc", "macchi",
11740           "dmacc" and "dmacchi" instructions are available instead.
11741
11742       -mfix-sb1
11743       -mno-fix-sb1
11744           Work around certain SB-1 CPU core errata.  (This flag currently
11745           works around the SB-1 revision 2 "F1" and "F2" floating point
11746           errata.)
11747
11748       -mr10k-cache-barrier=setting
11749           Specify whether GCC should insert cache barriers to avoid the side-
11750           effects of speculation on R10K processors.
11751
11752           In common with many processors, the R10K tries to predict the
11753           outcome of a conditional branch and speculatively executes
11754           instructions from the "taken" branch.  It later aborts these
11755           instructions if the predicted outcome was wrong.  However, on the
11756           R10K, even aborted instructions can have side effects.
11757
11758           This problem only affects kernel stores and, depending on the
11759           system, kernel loads.  As an example, a speculatively-executed
11760           store may load the target memory into cache and mark the cache line
11761           as dirty, even if the store itself is later aborted.  If a DMA
11762           operation writes to the same area of memory before the "dirty" line
11763           is flushed, the cached data will overwrite the DMA-ed data.  See
11764           the R10K processor manual for a full description, including other
11765           potential problems.
11766
11767           One workaround is to insert cache barrier instructions before every
11768           memory access that might be speculatively executed and that might
11769           have side effects even if aborted.  -mr10k-cache-barrier=setting
11770           controls GCC's implementation of this workaround.  It assumes that
11771           aborted accesses to any byte in the following regions will not have
11772           side effects:
11773
11774           1.  the memory occupied by the current function's stack frame;
11775
11776           2.  the memory occupied by an incoming stack argument;
11777
11778           3.  the memory occupied by an object with a link-time-constant
11779               address.
11780
11781           It is the kernel's responsibility to ensure that speculative
11782           accesses to these regions are indeed safe.
11783
11784           If the input program contains a function declaration such as:
11785
11786                   void foo (void);
11787
11788           then the implementation of "foo" must allow "j foo" and "jal foo"
11789           to be executed speculatively.  GCC honors this restriction for
11790           functions it compiles itself.  It expects non-GCC functions (such
11791           as hand-written assembly code) to do the same.
11792
11793           The option has three forms:
11794
11795           -mr10k-cache-barrier=load-store
11796               Insert a cache barrier before a load or store that might be
11797               speculatively executed and that might have side effects even if
11798               aborted.
11799
11800           -mr10k-cache-barrier=store
11801               Insert a cache barrier before a store that might be
11802               speculatively executed and that might have side effects even if
11803               aborted.
11804
11805           -mr10k-cache-barrier=none
11806               Disable the insertion of cache barriers.  This is the default
11807               setting.
11808
11809       -mflush-func=func
11810       -mno-flush-func
11811           Specifies the function to call to flush the I and D caches, or to
11812           not call any such function.  If called, the function must take the
11813           same arguments as the common "_flush_func()", that is, the address
11814           of the memory range for which the cache is being flushed, the size
11815           of the memory range, and the number 3 (to flush both caches).  The
11816           default depends on the target GCC was configured for, but commonly
11817           is either _flush_func or __cpu_flush.
11818
11819       mbranch-cost=num
11820           Set the cost of branches to roughly num "simple" instructions.
11821           This cost is only a heuristic and is not guaranteed to produce
11822           consistent results across releases.  A zero cost redundantly
11823           selects the default, which is based on the -mtune setting.
11824
11825       -mbranch-likely
11826       -mno-branch-likely
11827           Enable or disable use of Branch Likely instructions, regardless of
11828           the default for the selected architecture.  By default, Branch
11829           Likely instructions may be generated if they are supported by the
11830           selected architecture.  An exception is for the MIPS32 and MIPS64
11831           architectures and processors which implement those architectures;
11832           for those, Branch Likely instructions will not be generated by
11833           default because the MIPS32 and MIPS64 architectures specifically
11834           deprecate their use.
11835
11836       -mfp-exceptions
11837       -mno-fp-exceptions
11838           Specifies whether FP exceptions are enabled.  This affects how we
11839           schedule FP instructions for some processors.  The default is that
11840           FP exceptions are enabled.
11841
11842           For instance, on the SB-1, if FP exceptions are disabled, and we
11843           are emitting 64-bit code, then we can use both FP pipes.
11844           Otherwise, we can only use one FP pipe.
11845
11846       -mvr4130-align
11847       -mno-vr4130-align
11848           The VR4130 pipeline is two-way superscalar, but can only issue two
11849           instructions together if the first one is 8-byte aligned.  When
11850           this option is enabled, GCC will align pairs of instructions that
11851           it thinks should execute in parallel.
11852
11853           This option only has an effect when optimizing for the VR4130.  It
11854           normally makes code faster, but at the expense of making it bigger.
11855           It is enabled by default at optimization level -O3.
11856
11857       -msynci
11858       -mno-synci
11859           Enable (disable) generation of "synci" instructions on
11860           architectures that support it.  The "synci" instructions (if
11861           enabled) will be generated when "__builtin___clear_cache()" is
11862           compiled.
11863
11864           This option defaults to "-mno-synci", but the default can be
11865           overridden by configuring with "--with-synci".
11866
11867           When compiling code for single processor systems, it is generally
11868           safe to use "synci".  However, on many multi-core (SMP) systems, it
11869           will not invalidate the instruction caches on all cores and may
11870           lead to undefined behavior.
11871
11872       -mrelax-pic-calls
11873       -mno-relax-pic-calls
11874           Try to turn PIC calls that are normally dispatched via register $25
11875           into direct calls.  This is only possible if the linker can resolve
11876           the destination at link-time and if the destination is within range
11877           for a direct call.
11878
11879           -mrelax-pic-calls is the default if GCC was configured to use an
11880           assembler and a linker that supports the ".reloc" assembly
11881           directive and "-mexplicit-relocs" is in effect.  With
11882           "-mno-explicit-relocs", this optimization can be performed by the
11883           assembler and the linker alone without help from the compiler.
11884
11885       -mmcount-ra-address
11886       -mno-mcount-ra-address
11887           Emit (do not emit) code that allows "_mcount" to modify the calling
11888           function's return address.  When enabled, this option extends the
11889           usual "_mcount" interface with a new ra-address parameter, which
11890           has type "intptr_t *" and is passed in register $12.  "_mcount" can
11891           then modify the return address by doing both of the following:
11892
11893           ·   Returning the new address in register $31.
11894
11895           ·   Storing the new address in "*ra-address", if ra-address is
11896               nonnull.
11897
11898           The default is -mno-mcount-ra-address.
11899
11900       MMIX Options
11901
11902       These options are defined for the MMIX:
11903
11904       -mlibfuncs
11905       -mno-libfuncs
11906           Specify that intrinsic library functions are being compiled,
11907           passing all values in registers, no matter the size.
11908
11909       -mepsilon
11910       -mno-epsilon
11911           Generate floating-point comparison instructions that compare with
11912           respect to the "rE" epsilon register.
11913
11914       -mabi=mmixware
11915       -mabi=gnu
11916           Generate code that passes function parameters and return values
11917           that (in the called function) are seen as registers $0 and up, as
11918           opposed to the GNU ABI which uses global registers $231 and up.
11919
11920       -mzero-extend
11921       -mno-zero-extend
11922           When reading data from memory in sizes shorter than 64 bits, use
11923           (do not use) zero-extending load instructions by default, rather
11924           than sign-extending ones.
11925
11926       -mknuthdiv
11927       -mno-knuthdiv
11928           Make the result of a division yielding a remainder have the same
11929           sign as the divisor.  With the default, -mno-knuthdiv, the sign of
11930           the remainder follows the sign of the dividend.  Both methods are
11931           arithmetically valid, the latter being almost exclusively used.
11932
11933       -mtoplevel-symbols
11934       -mno-toplevel-symbols
11935           Prepend (do not prepend) a : to all global symbols, so the assembly
11936           code can be used with the "PREFIX" assembly directive.
11937
11938       -melf
11939           Generate an executable in the ELF format, rather than the default
11940           mmo format used by the mmix simulator.
11941
11942       -mbranch-predict
11943       -mno-branch-predict
11944           Use (do not use) the probable-branch instructions, when static
11945           branch prediction indicates a probable branch.
11946
11947       -mbase-addresses
11948       -mno-base-addresses
11949           Generate (do not generate) code that uses base addresses.  Using a
11950           base address automatically generates a request (handled by the
11951           assembler and the linker) for a constant to be set up in a global
11952           register.  The register is used for one or more base address
11953           requests within the range 0 to 255 from the value held in the
11954           register.  The generally leads to short and fast code, but the
11955           number of different data items that can be addressed is limited.
11956           This means that a program that uses lots of static data may require
11957           -mno-base-addresses.
11958
11959       -msingle-exit
11960       -mno-single-exit
11961           Force (do not force) generated code to have a single exit point in
11962           each function.
11963
11964       MN10300 Options
11965
11966       These -m options are defined for Matsushita MN10300 architectures:
11967
11968       -mmult-bug
11969           Generate code to avoid bugs in the multiply instructions for the
11970           MN10300 processors.  This is the default.
11971
11972       -mno-mult-bug
11973           Do not generate code to avoid bugs in the multiply instructions for
11974           the MN10300 processors.
11975
11976       -mam33
11977           Generate code which uses features specific to the AM33 processor.
11978
11979       -mno-am33
11980           Do not generate code which uses features specific to the AM33
11981           processor.  This is the default.
11982
11983       -mreturn-pointer-on-d0
11984           When generating a function which returns a pointer, return the
11985           pointer in both "a0" and "d0".  Otherwise, the pointer is returned
11986           only in a0, and attempts to call such functions without a prototype
11987           would result in errors.  Note that this option is on by default;
11988           use -mno-return-pointer-on-d0 to disable it.
11989
11990       -mno-crt0
11991           Do not link in the C run-time initialization object file.
11992
11993       -mrelax
11994           Indicate to the linker that it should perform a relaxation
11995           optimization pass to shorten branches, calls and absolute memory
11996           addresses.  This option only has an effect when used on the command
11997           line for the final link step.
11998
11999           This option makes symbolic debugging impossible.
12000
12001       PDP-11 Options
12002
12003       These options are defined for the PDP-11:
12004
12005       -mfpu
12006           Use hardware FPP floating point.  This is the default.  (FIS
12007           floating point on the PDP-11/40 is not supported.)
12008
12009       -msoft-float
12010           Do not use hardware floating point.
12011
12012       -mac0
12013           Return floating-point results in ac0 (fr0 in Unix assembler
12014           syntax).
12015
12016       -mno-ac0
12017           Return floating-point results in memory.  This is the default.
12018
12019       -m40
12020           Generate code for a PDP-11/40.
12021
12022       -m45
12023           Generate code for a PDP-11/45.  This is the default.
12024
12025       -m10
12026           Generate code for a PDP-11/10.
12027
12028       -mbcopy-builtin
12029           Use inline "movmemhi" patterns for copying memory.  This is the
12030           default.
12031
12032       -mbcopy
12033           Do not use inline "movmemhi" patterns for copying memory.
12034
12035       -mint16
12036       -mno-int32
12037           Use 16-bit "int".  This is the default.
12038
12039       -mint32
12040       -mno-int16
12041           Use 32-bit "int".
12042
12043       -mfloat64
12044       -mno-float32
12045           Use 64-bit "float".  This is the default.
12046
12047       -mfloat32
12048       -mno-float64
12049           Use 32-bit "float".
12050
12051       -mabshi
12052           Use "abshi2" pattern.  This is the default.
12053
12054       -mno-abshi
12055           Do not use "abshi2" pattern.
12056
12057       -mbranch-expensive
12058           Pretend that branches are expensive.  This is for experimenting
12059           with code generation only.
12060
12061       -mbranch-cheap
12062           Do not pretend that branches are expensive.  This is the default.
12063
12064       -msplit
12065           Generate code for a system with split I&D.
12066
12067       -mno-split
12068           Generate code for a system without split I&D.  This is the default.
12069
12070       -munix-asm
12071           Use Unix assembler syntax.  This is the default when configured for
12072           pdp11-*-bsd.
12073
12074       -mdec-asm
12075           Use DEC assembler syntax.  This is the default when configured for
12076           any PDP-11 target other than pdp11-*-bsd.
12077
12078       picoChip Options
12079
12080       These -m options are defined for picoChip implementations:
12081
12082       -mae=ae_type
12083           Set the instruction set, register set, and instruction scheduling
12084           parameters for array element type ae_type.  Supported values for
12085           ae_type are ANY, MUL, and MAC.
12086
12087           -mae=ANY selects a completely generic AE type.  Code generated with
12088           this option will run on any of the other AE types.  The code will
12089           not be as efficient as it would be if compiled for a specific AE
12090           type, and some types of operation (e.g., multiplication) will not
12091           work properly on all types of AE.
12092
12093           -mae=MUL selects a MUL AE type.  This is the most useful AE type
12094           for compiled code, and is the default.
12095
12096           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this
12097           option may suffer from poor performance of byte (char)
12098           manipulation, since the DSP AE does not provide hardware support
12099           for byte load/stores.
12100
12101       -msymbol-as-address
12102           Enable the compiler to directly use a symbol name as an address in
12103           a load/store instruction, without first loading it into a register.
12104           Typically, the use of this option will generate larger programs,
12105           which run faster than when the option isn't used.  However, the
12106           results vary from program to program, so it is left as a user
12107           option, rather than being permanently enabled.
12108
12109       -mno-inefficient-warnings
12110           Disables warnings about the generation of inefficient code.  These
12111           warnings can be generated, for example, when compiling code which
12112           performs byte-level memory operations on the MAC AE type.  The MAC
12113           AE has no hardware support for byte-level memory operations, so all
12114           byte load/stores must be synthesized from word load/store
12115           operations.  This is inefficient and a warning will be generated
12116           indicating to the programmer that they should rewrite the code to
12117           avoid byte operations, or to target an AE type which has the
12118           necessary hardware support.  This option enables the warning to be
12119           turned off.
12120
12121       PowerPC Options
12122
12123       These are listed under
12124
12125       IBM RS/6000 and PowerPC Options
12126
12127       These -m options are defined for the IBM RS/6000 and PowerPC:
12128
12129       -mpower
12130       -mno-power
12131       -mpower2
12132       -mno-power2
12133       -mpowerpc
12134       -mno-powerpc
12135       -mpowerpc-gpopt
12136       -mno-powerpc-gpopt
12137       -mpowerpc-gfxopt
12138       -mno-powerpc-gfxopt
12139       -mpowerpc64
12140       -mno-powerpc64
12141       -mmfcrf
12142       -mno-mfcrf
12143       -mpopcntb
12144       -mno-popcntb
12145       -mpopcntd
12146       -mno-popcntd
12147       -mfprnd
12148       -mno-fprnd
12149       -mcmpb
12150       -mno-cmpb
12151       -mmfpgpr
12152       -mno-mfpgpr
12153       -mhard-dfp
12154       -mno-hard-dfp
12155           GCC supports two related instruction set architectures for the
12156           RS/6000 and PowerPC.  The POWER instruction set are those
12157           instructions supported by the rios chip set used in the original
12158           RS/6000 systems and the PowerPC instruction set is the architecture
12159           of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and the
12160           IBM 4xx, 6xx, and follow-on microprocessors.
12161
12162           Neither architecture is a subset of the other.  However there is a
12163           large common subset of instructions supported by both.  An MQ
12164           register is included in processors supporting the POWER
12165           architecture.
12166
12167           You use these options to specify which instructions are available
12168           on the processor you are using.  The default value of these options
12169           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
12170           overrides the specification of these options.  We recommend you use
12171           the -mcpu=cpu_type option rather than the options listed above.
12172
12173           The -mpower option allows GCC to generate instructions that are
12174           found only in the POWER architecture and to use the MQ register.
12175           Specifying -mpower2 implies -power and also allows GCC to generate
12176           instructions that are present in the POWER2 architecture but not
12177           the original POWER architecture.
12178
12179           The -mpowerpc option allows GCC to generate instructions that are
12180           found only in the 32-bit subset of the PowerPC architecture.
12181           Specifying -mpowerpc-gpopt implies -mpowerpc and also allows GCC to
12182           use the optional PowerPC architecture instructions in the General
12183           Purpose group, including floating-point square root.  Specifying
12184           -mpowerpc-gfxopt implies -mpowerpc and also allows GCC to use the
12185           optional PowerPC architecture instructions in the Graphics group,
12186           including floating-point select.
12187
12188           The -mmfcrf option allows GCC to generate the move from condition
12189           register field instruction implemented on the POWER4 processor and
12190           other processors that support the PowerPC V2.01 architecture.  The
12191           -mpopcntb option allows GCC to generate the popcount and double
12192           precision FP reciprocal estimate instruction implemented on the
12193           POWER5 processor and other processors that support the PowerPC
12194           V2.02 architecture.  The -mpopcntd option allows GCC to generate
12195           the popcount instruction implemented on the POWER7 processor and
12196           other processors that support the PowerPC V2.06 architecture.  The
12197           -mfprnd option allows GCC to generate the FP round to integer
12198           instructions implemented on the POWER5+ processor and other
12199           processors that support the PowerPC V2.03 architecture.  The -mcmpb
12200           option allows GCC to generate the compare bytes instruction
12201           implemented on the POWER6 processor and other processors that
12202           support the PowerPC V2.05 architecture.  The -mmfpgpr option allows
12203           GCC to generate the FP move to/from general purpose register
12204           instructions implemented on the POWER6X processor and other
12205           processors that support the extended PowerPC V2.05 architecture.
12206           The -mhard-dfp option allows GCC to generate the decimal floating
12207           point instructions implemented on some POWER processors.
12208
12209           The -mpowerpc64 option allows GCC to generate the additional 64-bit
12210           instructions that are found in the full PowerPC64 architecture and
12211           to treat GPRs as 64-bit, doubleword quantities.  GCC defaults to
12212           -mno-powerpc64.
12213
12214           If you specify both -mno-power and -mno-powerpc, GCC will use only
12215           the instructions in the common subset of both architectures plus
12216           some special AIX common-mode calls, and will not use the MQ
12217           register.  Specifying both -mpower and -mpowerpc permits GCC to use
12218           any instruction from either architecture and to allow use of the MQ
12219           register; specify this for the Motorola MPC601.
12220
12221       -mnew-mnemonics
12222       -mold-mnemonics
12223           Select which mnemonics to use in the generated assembler code.
12224           With -mnew-mnemonics, GCC uses the assembler mnemonics defined for
12225           the PowerPC architecture.  With -mold-mnemonics it uses the
12226           assembler mnemonics defined for the POWER architecture.
12227           Instructions defined in only one architecture have only one
12228           mnemonic; GCC uses that mnemonic irrespective of which of these
12229           options is specified.
12230
12231           GCC defaults to the mnemonics appropriate for the architecture in
12232           use.  Specifying -mcpu=cpu_type sometimes overrides the value of
12233           these option.  Unless you are building a cross-compiler, you should
12234           normally not specify either -mnew-mnemonics or -mold-mnemonics, but
12235           should instead accept the default.
12236
12237       -mcpu=cpu_type
12238           Set architecture type, register usage, choice of mnemonics, and
12239           instruction scheduling parameters for machine type cpu_type.
12240           Supported values for cpu_type are 401, 403, 405, 405fp, 440, 440fp,
12241           464, 464fp, 476, 476fp, 505, 601, 602, 603, 603e, 604, 604e, 620,
12242           630, 740, 7400, 7450, 750, 801, 821, 823, 860, 970, 8540, a2,
12243           e300c2, e300c3, e500mc, e500mc64, ec603e, G3, G4, G5, power,
12244           power2, power3, power4, power5, power5+, power6, power6x, power7,
12245           common, powerpc, powerpc64, rios, rios1, rios2, rsc, and rs64.
12246
12247           -mcpu=common selects a completely generic processor.  Code
12248           generated under this option will run on any POWER or PowerPC
12249           processor.  GCC will use only the instructions in the common subset
12250           of both architectures, and will not use the MQ register.  GCC
12251           assumes a generic processor model for scheduling purposes.
12252
12253           -mcpu=power, -mcpu=power2, -mcpu=powerpc, and -mcpu=powerpc64
12254           specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not
12255           MPC601), and 64-bit PowerPC architecture machine types, with an
12256           appropriate, generic processor model assumed for scheduling
12257           purposes.
12258
12259           The other options specify a specific processor.  Code generated
12260           under those options will run best on that processor, and may not
12261           run at all on others.
12262
12263           The -mcpu options automatically enable or disable the following
12264           options:
12265
12266           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple
12267           -mnew-mnemonics  -mpopcntb -mpopcntd  -mpower  -mpower2
12268           -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt  -msingle-float
12269           -mdouble-float -msimple-fpu -mstring  -mmulhw  -mdlmzb  -mmfpgpr
12270           -mvsx
12271
12272           The particular options set for any particular CPU will vary between
12273           compiler versions, depending on what setting seems to produce
12274           optimal code for that CPU; it doesn't necessarily reflect the
12275           actual hardware's capabilities.  If you wish to set an individual
12276           option to a particular value, you may specify it after the -mcpu
12277           option, like -mcpu=970 -mno-altivec.
12278
12279           On AIX, the -maltivec and -mpowerpc64 options are not enabled or
12280           disabled by the -mcpu option at present because AIX does not have
12281           full support for these options.  You may still enable or disable
12282           them individually if you're sure it'll work in your environment.
12283
12284       -mtune=cpu_type
12285           Set the instruction scheduling parameters for machine type
12286           cpu_type, but do not set the architecture type, register usage, or
12287           choice of mnemonics, as -mcpu=cpu_type would.  The same values for
12288           cpu_type are used for -mtune as for -mcpu.  If both are specified,
12289           the code generated will use the architecture, registers, and
12290           mnemonics set by -mcpu, but the scheduling parameters set by
12291           -mtune.
12292
12293       -mswdiv
12294       -mno-swdiv
12295           Generate code to compute division as reciprocal estimate and
12296           iterative refinement, creating opportunities for increased
12297           throughput.  This feature requires: optional PowerPC Graphics
12298           instruction set for single precision and FRE instruction for double
12299           precision, assuming divides cannot generate user-visible traps, and
12300           the domain values not include Infinities, denormals or zero
12301           denominator.
12302
12303       -maltivec
12304       -mno-altivec
12305           Generate code that uses (does not use) AltiVec instructions, and
12306           also enable the use of built-in functions that allow more direct
12307           access to the AltiVec instruction set.  You may also need to set
12308           -mabi=altivec to adjust the current ABI with AltiVec ABI
12309           enhancements.
12310
12311       -mvrsave
12312       -mno-vrsave
12313           Generate VRSAVE instructions when generating AltiVec code.
12314
12315       -mgen-cell-microcode
12316           Generate Cell microcode instructions
12317
12318       -mwarn-cell-microcode
12319           Warning when a Cell microcode instruction is going to emitted.  An
12320           example of a Cell microcode instruction is a variable shift.
12321
12322       -msecure-plt
12323           Generate code that allows ld and ld.so to build executables and
12324           shared libraries with non-exec .plt and .got sections.  This is a
12325           PowerPC 32-bit SYSV ABI option.
12326
12327       -mbss-plt
12328           Generate code that uses a BSS .plt section that ld.so fills in, and
12329           requires .plt and .got sections that are both writable and
12330           executable.  This is a PowerPC 32-bit SYSV ABI option.
12331
12332       -misel
12333       -mno-isel
12334           This switch enables or disables the generation of ISEL
12335           instructions.
12336
12337       -misel=yes/no
12338           This switch has been deprecated.  Use -misel and -mno-isel instead.
12339
12340       -mspe
12341       -mno-spe
12342           This switch enables or disables the generation of SPE simd
12343           instructions.
12344
12345       -mpaired
12346       -mno-paired
12347           This switch enables or disables the generation of PAIRED simd
12348           instructions.
12349
12350       -mspe=yes/no
12351           This option has been deprecated.  Use -mspe and -mno-spe instead.
12352
12353       -mvsx
12354       -mno-vsx
12355           Generate code that uses (does not use) vector/scalar (VSX)
12356           instructions, and also enable the use of built-in functions that
12357           allow more direct access to the VSX instruction set.
12358
12359       -mfloat-gprs=yes/single/double/no
12360       -mfloat-gprs
12361           This switch enables or disables the generation of floating point
12362           operations on the general purpose registers for architectures that
12363           support it.
12364
12365           The argument yes or single enables the use of single-precision
12366           floating point operations.
12367
12368           The argument double enables the use of single and double-precision
12369           floating point operations.
12370
12371           The argument no disables floating point operations on the general
12372           purpose registers.
12373
12374           This option is currently only available on the MPC854x.
12375
12376       -m32
12377       -m64
12378           Generate code for 32-bit or 64-bit environments of Darwin and SVR4
12379           targets (including GNU/Linux).  The 32-bit environment sets int,
12380           long and pointer to 32 bits and generates code that runs on any
12381           PowerPC variant.  The 64-bit environment sets int to 32 bits and
12382           long and pointer to 64 bits, and generates code for PowerPC64, as
12383           for -mpowerpc64.
12384
12385       -mfull-toc
12386       -mno-fp-in-toc
12387       -mno-sum-in-toc
12388       -mminimal-toc
12389           Modify generation of the TOC (Table Of Contents), which is created
12390           for every executable file.  The -mfull-toc option is selected by
12391           default.  In that case, GCC will allocate at least one TOC entry
12392           for each unique non-automatic variable reference in your program.
12393           GCC will also place floating-point constants in the TOC.  However,
12394           only 16,384 entries are available in the TOC.
12395
12396           If you receive a linker error message that saying you have
12397           overflowed the available TOC space, you can reduce the amount of
12398           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
12399           -mno-fp-in-toc prevents GCC from putting floating-point constants
12400           in the TOC and -mno-sum-in-toc forces GCC to generate code to
12401           calculate the sum of an address and a constant at run-time instead
12402           of putting that sum into the TOC.  You may specify one or both of
12403           these options.  Each causes GCC to produce very slightly slower and
12404           larger code at the expense of conserving TOC space.
12405
12406           If you still run out of space in the TOC even when you specify both
12407           of these options, specify -mminimal-toc instead.  This option
12408           causes GCC to make only one TOC entry for every file.  When you
12409           specify this option, GCC will produce code that is slower and
12410           larger but which uses extremely little TOC space.  You may wish to
12411           use this option only on files that contain less frequently executed
12412           code.
12413
12414       -maix64
12415       -maix32
12416           Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
12417           64-bit "long" type, and the infrastructure needed to support them.
12418           Specifying -maix64 implies -mpowerpc64 and -mpowerpc, while -maix32
12419           disables the 64-bit ABI and implies -mno-powerpc64.  GCC defaults
12420           to -maix32.
12421
12422       -mxl-compat
12423       -mno-xl-compat
12424           Produce code that conforms more closely to IBM XL compiler
12425           semantics when using AIX-compatible ABI.  Pass floating-point
12426           arguments to prototyped functions beyond the register save area
12427           (RSA) on the stack in addition to argument FPRs.  Do not assume
12428           that most significant double in 128-bit long double value is
12429           properly rounded when comparing values and converting to double.
12430           Use XL symbol names for long double support routines.
12431
12432           The AIX calling convention was extended but not initially
12433           documented to handle an obscure K&R C case of calling a function
12434           that takes the address of its arguments with fewer arguments than
12435           declared.  IBM XL compilers access floating point arguments which
12436           do not fit in the RSA from the stack when a subroutine is compiled
12437           without optimization.  Because always storing floating-point
12438           arguments on the stack is inefficient and rarely needed, this
12439           option is not enabled by default and only is necessary when calling
12440           subroutines compiled by IBM XL compilers without optimization.
12441
12442       -mpe
12443           Support IBM RS/6000 SP Parallel Environment (PE).  Link an
12444           application written to use message passing with special startup
12445           code to enable the application to run.  The system must have PE
12446           installed in the standard location (/usr/lpp/ppe.poe/), or the
12447           specs file must be overridden with the -specs= option to specify
12448           the appropriate directory location.  The Parallel Environment does
12449           not support threads, so the -mpe option and the -pthread option are
12450           incompatible.
12451
12452       -malign-natural
12453       -malign-power
12454           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
12455           -malign-natural overrides the ABI-defined alignment of larger
12456           types, such as floating-point doubles, on their natural size-based
12457           boundary.  The option -malign-power instructs GCC to follow the
12458           ABI-specified alignment rules.  GCC defaults to the standard
12459           alignment defined in the ABI.
12460
12461           On 64-bit Darwin, natural alignment is the default, and
12462           -malign-power is not supported.
12463
12464       -msoft-float
12465       -mhard-float
12466           Generate code that does not use (uses) the floating-point register
12467           set.  Software floating point emulation is provided if you use the
12468           -msoft-float option, and pass the option to GCC when linking.
12469
12470       -msingle-float
12471       -mdouble-float
12472           Generate code for single or double-precision floating point
12473           operations.  -mdouble-float implies -msingle-float.
12474
12475       -msimple-fpu
12476           Do not generate sqrt and div instructions for hardware floating
12477           point unit.
12478
12479       -mfpu
12480           Specify type of floating point unit.  Valid values are sp_lite
12481           (equivalent to -msingle-float -msimple-fpu), dp_lite (equivalent to
12482           -mdouble-float -msimple-fpu), sp_full (equivalent to
12483           -msingle-float), and dp_full (equivalent to -mdouble-float).
12484
12485       -mxilinx-fpu
12486           Perform optimizations for floating point unit on Xilinx PPC
12487           405/440.
12488
12489       -mmultiple
12490       -mno-multiple
12491           Generate code that uses (does not use) the load multiple word
12492           instructions and the store multiple word instructions.  These
12493           instructions are generated by default on POWER systems, and not
12494           generated on PowerPC systems.  Do not use -mmultiple on little
12495           endian PowerPC systems, since those instructions do not work when
12496           the processor is in little endian mode.  The exceptions are PPC740
12497           and PPC750 which permit the instructions usage in little endian
12498           mode.
12499
12500       -mstring
12501       -mno-string
12502           Generate code that uses (does not use) the load string instructions
12503           and the store string word instructions to save multiple registers
12504           and do small block moves.  These instructions are generated by
12505           default on POWER systems, and not generated on PowerPC systems.  Do
12506           not use -mstring on little endian PowerPC systems, since those
12507           instructions do not work when the processor is in little endian
12508           mode.  The exceptions are PPC740 and PPC750 which permit the
12509           instructions usage in little endian mode.
12510
12511       -mupdate
12512       -mno-update
12513           Generate code that uses (does not use) the load or store
12514           instructions that update the base register to the address of the
12515           calculated memory location.  These instructions are generated by
12516           default.  If you use -mno-update, there is a small window between
12517           the time that the stack pointer is updated and the address of the
12518           previous frame is stored, which means code that walks the stack
12519           frame across interrupts or signals may get corrupted data.
12520
12521       -mavoid-indexed-addresses
12522       -mno-avoid-indexed-addresses
12523           Generate code that tries to avoid (not avoid) the use of indexed
12524           load or store instructions. These instructions can incur a
12525           performance penalty on Power6 processors in certain situations,
12526           such as when stepping through large arrays that cross a 16M
12527           boundary.  This option is enabled by default when targetting Power6
12528           and disabled otherwise.
12529
12530       -mfused-madd
12531       -mno-fused-madd
12532           Generate code that uses (does not use) the floating point multiply
12533           and accumulate instructions.  These instructions are generated by
12534           default if hardware floating is used.
12535
12536       -mmulhw
12537       -mno-mulhw
12538           Generate code that uses (does not use) the half-word multiply and
12539           multiply-accumulate instructions on the IBM 405, 440, 464 and 476
12540           processors.  These instructions are generated by default when
12541           targetting those processors.
12542
12543       -mdlmzb
12544       -mno-dlmzb
12545           Generate code that uses (does not use) the string-search dlmzb
12546           instruction on the IBM 405, 440, 464 and 476 processors.  This
12547           instruction is generated by default when targetting those
12548           processors.
12549
12550       -mno-bit-align
12551       -mbit-align
12552           On System V.4 and embedded PowerPC systems do not (do) force
12553           structures and unions that contain bit-fields to be aligned to the
12554           base type of the bit-field.
12555
12556           For example, by default a structure containing nothing but 8
12557           "unsigned" bit-fields of length 1 would be aligned to a 4 byte
12558           boundary and have a size of 4 bytes.  By using -mno-bit-align, the
12559           structure would be aligned to a 1 byte boundary and be one byte in
12560           size.
12561
12562       -mno-strict-align
12563       -mstrict-align
12564           On System V.4 and embedded PowerPC systems do not (do) assume that
12565           unaligned memory references will be handled by the system.
12566
12567       -mrelocatable
12568       -mno-relocatable
12569           On embedded PowerPC systems generate code that allows (does not
12570           allow) the program to be relocated to a different address at
12571           runtime.  If you use -mrelocatable on any module, all objects
12572           linked together must be compiled with -mrelocatable or
12573           -mrelocatable-lib.
12574
12575       -mrelocatable-lib
12576       -mno-relocatable-lib
12577           On embedded PowerPC systems generate code that allows (does not
12578           allow) the program to be relocated to a different address at
12579           runtime.  Modules compiled with -mrelocatable-lib can be linked
12580           with either modules compiled without -mrelocatable and
12581           -mrelocatable-lib or with modules compiled with the -mrelocatable
12582           options.
12583
12584       -mno-toc
12585       -mtoc
12586           On System V.4 and embedded PowerPC systems do not (do) assume that
12587           register 2 contains a pointer to a global area pointing to the
12588           addresses used in the program.
12589
12590       -mlittle
12591       -mlittle-endian
12592           On System V.4 and embedded PowerPC systems compile code for the
12593           processor in little endian mode.  The -mlittle-endian option is the
12594           same as -mlittle.
12595
12596       -mbig
12597       -mbig-endian
12598           On System V.4 and embedded PowerPC systems compile code for the
12599           processor in big endian mode.  The -mbig-endian option is the same
12600           as -mbig.
12601
12602       -mdynamic-no-pic
12603           On Darwin and Mac OS X systems, compile code so that it is not
12604           relocatable, but that its external references are relocatable.  The
12605           resulting code is suitable for applications, but not shared
12606           libraries.
12607
12608       -mprioritize-restricted-insns=priority
12609           This option controls the priority that is assigned to dispatch-slot
12610           restricted instructions during the second scheduling pass.  The
12611           argument priority takes the value 0/1/2 to assign
12612           no/highest/second-highest priority to dispatch slot restricted
12613           instructions.
12614
12615       -msched-costly-dep=dependence_type
12616           This option controls which dependences are considered costly by the
12617           target during instruction scheduling.  The argument dependence_type
12618           takes one of the following values: no: no dependence is costly,
12619           all: all dependences are costly, true_store_to_load: a true
12620           dependence from store to load is costly, store_to_load: any
12621           dependence from store to load is costly, number: any dependence
12622           which latency >= number is costly.
12623
12624       -minsert-sched-nops=scheme
12625           This option controls which nop insertion scheme will be used during
12626           the second scheduling pass.  The argument scheme takes one of the
12627           following values: no: Don't insert nops.  pad: Pad with nops any
12628           dispatch group which has vacant issue slots, according to the
12629           scheduler's grouping.  regroup_exact: Insert nops to force costly
12630           dependent insns into separate groups.  Insert exactly as many nops
12631           as needed to force an insn to a new group, according to the
12632           estimated processor grouping.  number: Insert nops to force costly
12633           dependent insns into separate groups.  Insert number nops to force
12634           an insn to a new group.
12635
12636       -mcall-sysv
12637           On System V.4 and embedded PowerPC systems compile code using
12638           calling conventions that adheres to the March 1995 draft of the
12639           System V Application Binary Interface, PowerPC processor
12640           supplement.  This is the default unless you configured GCC using
12641           powerpc-*-eabiaix.
12642
12643       -mcall-sysv-eabi
12644       -mcall-eabi
12645           Specify both -mcall-sysv and -meabi options.
12646
12647       -mcall-sysv-noeabi
12648           Specify both -mcall-sysv and -mno-eabi options.
12649
12650       -mcall-aixdesc
12651           On System V.4 and embedded PowerPC systems compile code for the AIX
12652           operating system.
12653
12654       -mcall-linux
12655           On System V.4 and embedded PowerPC systems compile code for the
12656           Linux-based GNU system.
12657
12658       -mcall-gnu
12659           On System V.4 and embedded PowerPC systems compile code for the
12660           Hurd-based GNU system.
12661
12662       -mcall-freebsd
12663           On System V.4 and embedded PowerPC systems compile code for the
12664           FreeBSD operating system.
12665
12666       -mcall-netbsd
12667           On System V.4 and embedded PowerPC systems compile code for the
12668           NetBSD operating system.
12669
12670       -mcall-openbsd
12671           On System V.4 and embedded PowerPC systems compile code for the
12672           OpenBSD operating system.
12673
12674       -maix-struct-return
12675           Return all structures in memory (as specified by the AIX ABI).
12676
12677       -msvr4-struct-return
12678           Return structures smaller than 8 bytes in registers (as specified
12679           by the SVR4 ABI).
12680
12681       -mabi=abi-type
12682           Extend the current ABI with a particular extension, or remove such
12683           extension.  Valid values are altivec, no-altivec, spe, no-spe,
12684           ibmlongdouble, ieeelongdouble.
12685
12686       -mabi=spe
12687           Extend the current ABI with SPE ABI extensions.  This does not
12688           change the default ABI, instead it adds the SPE ABI extensions to
12689           the current ABI.
12690
12691       -mabi=no-spe
12692           Disable Booke SPE ABI extensions for the current ABI.
12693
12694       -mabi=ibmlongdouble
12695           Change the current ABI to use IBM extended precision long double.
12696           This is a PowerPC 32-bit SYSV ABI option.
12697
12698       -mabi=ieeelongdouble
12699           Change the current ABI to use IEEE extended precision long double.
12700           This is a PowerPC 32-bit Linux ABI option.
12701
12702       -mprototype
12703       -mno-prototype
12704           On System V.4 and embedded PowerPC systems assume that all calls to
12705           variable argument functions are properly prototyped.  Otherwise,
12706           the compiler must insert an instruction before every non prototyped
12707           call to set or clear bit 6 of the condition code register (CR) to
12708           indicate whether floating point values were passed in the floating
12709           point registers in case the function takes a variable arguments.
12710           With -mprototype, only calls to prototyped variable argument
12711           functions will set or clear the bit.
12712
12713       -msim
12714           On embedded PowerPC systems, assume that the startup module is
12715           called sim-crt0.o and that the standard C libraries are libsim.a
12716           and libc.a.  This is the default for powerpc-*-eabisim
12717           configurations.
12718
12719       -mmvme
12720           On embedded PowerPC systems, assume that the startup module is
12721           called crt0.o and the standard C libraries are libmvme.a and
12722           libc.a.
12723
12724       -mads
12725           On embedded PowerPC systems, assume that the startup module is
12726           called crt0.o and the standard C libraries are libads.a and libc.a.
12727
12728       -myellowknife
12729           On embedded PowerPC systems, assume that the startup module is
12730           called crt0.o and the standard C libraries are libyk.a and libc.a.
12731
12732       -mvxworks
12733           On System V.4 and embedded PowerPC systems, specify that you are
12734           compiling for a VxWorks system.
12735
12736       -memb
12737           On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
12738           header to indicate that eabi extended relocations are used.
12739
12740       -meabi
12741       -mno-eabi
12742           On System V.4 and embedded PowerPC systems do (do not) adhere to
12743           the Embedded Applications Binary Interface (eabi) which is a set of
12744           modifications to the System V.4 specifications.  Selecting -meabi
12745           means that the stack is aligned to an 8 byte boundary, a function
12746           "__eabi" is called to from "main" to set up the eabi environment,
12747           and the -msdata option can use both "r2" and "r13" to point to two
12748           separate small data areas.  Selecting -mno-eabi means that the
12749           stack is aligned to a 16 byte boundary, do not call an
12750           initialization function from "main", and the -msdata option will
12751           only use "r13" to point to a single small data area.  The -meabi
12752           option is on by default if you configured GCC using one of the
12753           powerpc*-*-eabi* options.
12754
12755       -msdata=eabi
12756           On System V.4 and embedded PowerPC systems, put small initialized
12757           "const" global and static data in the .sdata2 section, which is
12758           pointed to by register "r2".  Put small initialized non-"const"
12759           global and static data in the .sdata section, which is pointed to
12760           by register "r13".  Put small uninitialized global and static data
12761           in the .sbss section, which is adjacent to the .sdata section.  The
12762           -msdata=eabi option is incompatible with the -mrelocatable option.
12763           The -msdata=eabi option also sets the -memb option.
12764
12765       -msdata=sysv
12766           On System V.4 and embedded PowerPC systems, put small global and
12767           static data in the .sdata section, which is pointed to by register
12768           "r13".  Put small uninitialized global and static data in the .sbss
12769           section, which is adjacent to the .sdata section.  The -msdata=sysv
12770           option is incompatible with the -mrelocatable option.
12771
12772       -msdata=default
12773       -msdata
12774           On System V.4 and embedded PowerPC systems, if -meabi is used,
12775           compile code the same as -msdata=eabi, otherwise compile code the
12776           same as -msdata=sysv.
12777
12778       -msdata=data
12779           On System V.4 and embedded PowerPC systems, put small global data
12780           in the .sdata section.  Put small uninitialized global data in the
12781           .sbss section.  Do not use register "r13" to address small data
12782           however.  This is the default behavior unless other -msdata options
12783           are used.
12784
12785       -msdata=none
12786       -mno-sdata
12787           On embedded PowerPC systems, put all initialized global and static
12788           data in the .data section, and all uninitialized data in the .bss
12789           section.
12790
12791       -G num
12792           On embedded PowerPC systems, put global and static items less than
12793           or equal to num bytes into the small data or bss sections instead
12794           of the normal data or bss section.  By default, num is 8.  The -G
12795           num switch is also passed to the linker.  All modules should be
12796           compiled with the same -G num value.
12797
12798       -mregnames
12799       -mno-regnames
12800           On System V.4 and embedded PowerPC systems do (do not) emit
12801           register names in the assembly language output using symbolic
12802           forms.
12803
12804       -mlongcall
12805       -mno-longcall
12806           By default assume that all calls are far away so that a longer more
12807           expensive calling sequence is required.  This is required for calls
12808           further than 32 megabytes (33,554,432 bytes) from the current
12809           location.  A short call will be generated if the compiler knows the
12810           call cannot be that far away.  This setting can be overridden by
12811           the "shortcall" function attribute, or by "#pragma longcall(0)".
12812
12813           Some linkers are capable of detecting out-of-range calls and
12814           generating glue code on the fly.  On these systems, long calls are
12815           unnecessary and generate slower code.  As of this writing, the AIX
12816           linker can do this, as can the GNU linker for PowerPC/64.  It is
12817           planned to add this feature to the GNU linker for 32-bit PowerPC
12818           systems as well.
12819
12820           On Darwin/PPC systems, "#pragma longcall" will generate "jbsr
12821           callee, L42", plus a "branch island" (glue code).  The two target
12822           addresses represent the callee and the "branch island".  The
12823           Darwin/PPC linker will prefer the first address and generate a "bl
12824           callee" if the PPC "bl" instruction will reach the callee directly;
12825           otherwise, the linker will generate "bl L42" to call the "branch
12826           island".  The "branch island" is appended to the body of the
12827           calling function; it computes the full 32-bit address of the callee
12828           and jumps to it.
12829
12830           On Mach-O (Darwin) systems, this option directs the compiler emit
12831           to the glue for every direct call, and the Darwin linker decides
12832           whether to use or discard it.
12833
12834           In the future, we may cause GCC to ignore all longcall
12835           specifications when the linker is known to generate glue.
12836
12837       -mtls-markers
12838       -mno-tls-markers
12839           Mark (do not mark) calls to "__tls_get_addr" with a relocation
12840           specifying the function argument.  The relocation allows ld to
12841           reliably associate function call with argument setup instructions
12842           for TLS optimization, which in turn allows gcc to better schedule
12843           the sequence.
12844
12845       -pthread
12846           Adds support for multithreading with the pthreads library.  This
12847           option sets flags for both the preprocessor and linker.
12848
12849       RX Options
12850
12851       These command line options are defined for RX targets:
12852
12853       -m64bit-doubles
12854       -m32bit-doubles
12855           Make the "double" data type be 64-bits (-m64bit-doubles) or 32-bits
12856           (-m32bit-doubles) in size.  The default is -m32bit-doubles.  Note
12857           RX floating point hardware only works on 32-bit values, which is
12858           why the default is -m32bit-doubles.
12859
12860       -fpu
12861       -nofpu
12862           Enables (-fpu) or disables (-nofpu) the use of RX floating point
12863           hardware.  The default is enabled for the RX600 series and disabled
12864           for the RX200 series.
12865
12866           Floating point instructions will only be generated for 32-bit
12867           floating point values however, so if the -m64bit-doubles option is
12868           in use then the FPU hardware will not be used for doubles.
12869
12870           Note If the -fpu option is enabled then -funsafe-math-optimizations
12871           is also enabled automatically.  This is because the RX FPU
12872           instructions are themselves unsafe.
12873
12874       -mcpu=name
12875       -patch=name
12876           Selects the type of RX CPU to be targeted.  Currently three types
12877           are supported, the generic RX600 and RX200 series hardware and the
12878           specific RX610 cpu.  The default is RX600.
12879
12880           The only difference between RX600 and RX610 is that the RX610 does
12881           not support the "MVTIPL" instruction.
12882
12883           The RX200 series does not have a hardware floating point unit and
12884           so -nofpu is enabled by default when this type is selected.
12885
12886       -mbig-endian-data
12887       -mlittle-endian-data
12888           Store data (but not code) in the big-endian format.  The default is
12889           -mlittle-endian-data, ie to store data in the little endian format.
12890
12891       -msmall-data-limit=N
12892           Specifies the maximum size in bytes of global and static variables
12893           which can be placed into the small data area.  Using the small data
12894           area can lead to smaller and faster code, but the size of area is
12895           limited and it is up to the programmer to ensure that the area does
12896           not overflow.  Also when the small data area is used one of the
12897           RX's registers ("r13") is reserved for use pointing to this area,
12898           so it is no longer available for use by the compiler.  This could
12899           result in slower and/or larger code if variables which once could
12900           have been held in "r13" are now pushed onto the stack.
12901
12902           Note, common variables (variables which have not been initialised)
12903           and constants are not placed into the small data area as they are
12904           assigned to other sections in the output executable.
12905
12906           The default value is zero, which disables this feature.  Note, this
12907           feature is not enabled by default with higher optimization levels
12908           (-O2 etc) because of the potentially detrimental effects of
12909           reserving register "r13".  It is up to the programmer to experiment
12910           and discover whether this feature is of benefit to their program.
12911
12912       -msim
12913       -mno-sim
12914           Use the simulator runtime.  The default is to use the libgloss
12915           board specific runtime.
12916
12917       -mas100-syntax
12918       -mno-as100-syntax
12919           When generating assembler output use a syntax that is compatible
12920           with Renesas's AS100 assembler.  This syntax can also be handled by
12921           the GAS assembler but it has some restrictions so generating it is
12922           not the default option.
12923
12924       -mmax-constant-size=N
12925           Specifies the maximum size, in bytes, of a constant that can be
12926           used as an operand in a RX instruction.  Although the RX
12927           instruction set does allow constants of up to 4 bytes in length to
12928           be used in instructions, a longer value equates to a longer
12929           instruction.  Thus in some circumstances it can be beneficial to
12930           restrict the size of constants that are used in instructions.
12931           Constants that are too big are instead placed into a constant pool
12932           and referenced via register indirection.
12933
12934           The value N can be between 0 and 4.  A value of 0 (the default) or
12935           4 means that constants of any size are allowed.
12936
12937       -mrelax
12938           Enable linker relaxation.  Linker relaxation is a process whereby
12939           the linker will attempt to reduce the size of a program by finding
12940           shorter versions of various instructions.  Disabled by default.
12941
12942       -mint-register=N
12943           Specify the number of registers to reserve for fast interrupt
12944           handler functions.  The value N can be between 0 and 4.  A value of
12945           1 means that register "r13" will be reserved for the exclusive use
12946           of fast interrupt handlers.  A value of 2 reserves "r13" and "r12".
12947           A value of 3 reserves "r13", "r12" and "r11", and a value of 4
12948           reserves "r13" through "r10".  A value of 0, the default, does not
12949           reserve any registers.
12950
12951       -msave-acc-in-interrupts
12952           Specifies that interrupt handler functions should preserve the
12953           accumulator register.  This is only necessary if normal code might
12954           use the accumulator register, for example because it performs
12955           64-bit multiplications.  The default is to ignore the accumulator
12956           as this makes the interrupt handlers faster.
12957
12958       Note: The generic GCC command line -ffixed-reg has special significance
12959       to the RX port when used with the "interrupt" function attribute.  This
12960       attribute indicates a function intended to process fast interrupts.
12961       GCC will will ensure that it only uses the registers "r10", "r11",
12962       "r12" and/or "r13" and only provided that the normal use of the
12963       corresponding registers have been restricted via the -ffixed-reg or
12964       -mint-register command line options.
12965
12966       S/390 and zSeries Options
12967
12968       These are the -m options defined for the S/390 and zSeries
12969       architecture.
12970
12971       -mhard-float
12972       -msoft-float
12973           Use (do not use) the hardware floating-point instructions and
12974           registers for floating-point operations.  When -msoft-float is
12975           specified, functions in libgcc.a will be used to perform floating-
12976           point operations.  When -mhard-float is specified, the compiler
12977           generates IEEE floating-point instructions.  This is the default.
12978
12979       -mhard-dfp
12980       -mno-hard-dfp
12981           Use (do not use) the hardware decimal-floating-point instructions
12982           for decimal-floating-point operations.  When -mno-hard-dfp is
12983           specified, functions in libgcc.a will be used to perform decimal-
12984           floating-point operations.  When -mhard-dfp is specified, the
12985           compiler generates decimal-floating-point hardware instructions.
12986           This is the default for -march=z9-ec or higher.
12987
12988       -mlong-double-64
12989       -mlong-double-128
12990           These switches control the size of "long double" type. A size of
12991           64bit makes the "long double" type equivalent to the "double" type.
12992           This is the default.
12993
12994       -mbackchain
12995       -mno-backchain
12996           Store (do not store) the address of the caller's frame as backchain
12997           pointer into the callee's stack frame.  A backchain may be needed
12998           to allow debugging using tools that do not understand DWARF-2 call
12999           frame information.  When -mno-packed-stack is in effect, the
13000           backchain pointer is stored at the bottom of the stack frame; when
13001           -mpacked-stack is in effect, the backchain is placed into the
13002           topmost word of the 96/160 byte register save area.
13003
13004           In general, code compiled with -mbackchain is call-compatible with
13005           code compiled with -mmo-backchain; however, use of the backchain
13006           for debugging purposes usually requires that the whole binary is
13007           built with -mbackchain.  Note that the combination of -mbackchain,
13008           -mpacked-stack and -mhard-float is not supported.  In order to
13009           build a linux kernel use -msoft-float.
13010
13011           The default is to not maintain the backchain.
13012
13013       -mpacked-stack
13014       -mno-packed-stack
13015           Use (do not use) the packed stack layout.  When -mno-packed-stack
13016           is specified, the compiler uses the all fields of the 96/160 byte
13017           register save area only for their default purpose; unused fields
13018           still take up stack space.  When -mpacked-stack is specified,
13019           register save slots are densely packed at the top of the register
13020           save area; unused space is reused for other purposes, allowing for
13021           more efficient use of the available stack space.  However, when
13022           -mbackchain is also in effect, the topmost word of the save area is
13023           always used to store the backchain, and the return address register
13024           is always saved two words below the backchain.
13025
13026           As long as the stack frame backchain is not used, code generated
13027           with -mpacked-stack is call-compatible with code generated with
13028           -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95 for
13029           S/390 or zSeries generated code that uses the stack frame backchain
13030           at run time, not just for debugging purposes.  Such code is not
13031           call-compatible with code compiled with -mpacked-stack.  Also, note
13032           that the combination of -mbackchain, -mpacked-stack and
13033           -mhard-float is not supported.  In order to build a linux kernel
13034           use -msoft-float.
13035
13036           The default is to not use the packed stack layout.
13037
13038       -msmall-exec
13039       -mno-small-exec
13040           Generate (or do not generate) code using the "bras" instruction to
13041           do subroutine calls.  This only works reliably if the total
13042           executable size does not exceed 64k.  The default is to use the
13043           "basr" instruction instead, which does not have this limitation.
13044
13045       -m64
13046       -m31
13047           When -m31 is specified, generate code compliant to the GNU/Linux
13048           for S/390 ABI.  When -m64 is specified, generate code compliant to
13049           the GNU/Linux for zSeries ABI.  This allows GCC in particular to
13050           generate 64-bit instructions.  For the s390 targets, the default is
13051           -m31, while the s390x targets default to -m64.
13052
13053       -mzarch
13054       -mesa
13055           When -mzarch is specified, generate code using the instructions
13056           available on z/Architecture.  When -mesa is specified, generate
13057           code using the instructions available on ESA/390.  Note that -mesa
13058           is not possible with -m64.  When generating code compliant to the
13059           GNU/Linux for S/390 ABI, the default is -mesa.  When generating
13060           code compliant to the GNU/Linux for zSeries ABI, the default is
13061           -mzarch.
13062
13063       -mmvcle
13064       -mno-mvcle
13065           Generate (or do not generate) code using the "mvcle" instruction to
13066           perform block moves.  When -mno-mvcle is specified, use a "mvc"
13067           loop instead.  This is the default unless optimizing for size.
13068
13069       -mdebug
13070       -mno-debug
13071           Print (or do not print) additional debug information when
13072           compiling.  The default is to not print debug information.
13073
13074       -march=cpu-type
13075           Generate code that will run on cpu-type, which is the name of a
13076           system representing a certain processor type.  Possible values for
13077           cpu-type are g5, g6, z900, z990, z9-109, z9-ec and z10.  When
13078           generating code using the instructions available on z/Architecture,
13079           the default is -march=z900.  Otherwise, the default is -march=g5.
13080
13081       -mtune=cpu-type
13082           Tune to cpu-type everything applicable about the generated code,
13083           except for the ABI and the set of available instructions.  The list
13084           of cpu-type values is the same as for -march.  The default is the
13085           value used for -march.
13086
13087       -mtpf-trace
13088       -mno-tpf-trace
13089           Generate code that adds (does not add) in TPF OS specific branches
13090           to trace routines in the operating system.  This option is off by
13091           default, even when compiling for the TPF OS.
13092
13093       -mfused-madd
13094       -mno-fused-madd
13095           Generate code that uses (does not use) the floating point multiply
13096           and accumulate instructions.  These instructions are generated by
13097           default if hardware floating point is used.
13098
13099       -mwarn-framesize=framesize
13100           Emit a warning if the current function exceeds the given frame
13101           size.  Because this is a compile time check it doesn't need to be a
13102           real problem when the program runs.  It is intended to identify
13103           functions which most probably cause a stack overflow.  It is useful
13104           to be used in an environment with limited stack size e.g. the linux
13105           kernel.
13106
13107       -mwarn-dynamicstack
13108           Emit a warning if the function calls alloca or uses dynamically
13109           sized arrays.  This is generally a bad idea with a limited stack
13110           size.
13111
13112       -mstack-guard=stack-guard
13113       -mstack-size=stack-size
13114           If these options are provided the s390 back end emits additional
13115           instructions in the function prologue which trigger a trap if the
13116           stack size is stack-guard bytes above the stack-size (remember that
13117           the stack on s390 grows downward).  If the stack-guard option is
13118           omitted the smallest power of 2 larger than the frame size of the
13119           compiled function is chosen.  These options are intended to be used
13120           to help debugging stack overflow problems.  The additionally
13121           emitted code causes only little overhead and hence can also be used
13122           in production like systems without greater performance degradation.
13123           The given values have to be exact powers of 2 and stack-size has to
13124           be greater than stack-guard without exceeding 64k.  In order to be
13125           efficient the extra code makes the assumption that the stack starts
13126           at an address aligned to the value given by stack-size.  The stack-
13127           guard option can only be used in conjunction with stack-size.
13128
13129       Score Options
13130
13131       These options are defined for Score implementations:
13132
13133       -meb
13134           Compile code for big endian mode.  This is the default.
13135
13136       -mel
13137           Compile code for little endian mode.
13138
13139       -mnhwloop
13140           Disable generate bcnz instruction.
13141
13142       -muls
13143           Enable generate unaligned load and store instruction.
13144
13145       -mmac
13146           Enable the use of multiply-accumulate instructions. Disabled by
13147           default.
13148
13149       -mscore5
13150           Specify the SCORE5 as the target architecture.
13151
13152       -mscore5u
13153           Specify the SCORE5U of the target architecture.
13154
13155       -mscore7
13156           Specify the SCORE7 as the target architecture. This is the default.
13157
13158       -mscore7d
13159           Specify the SCORE7D as the target architecture.
13160
13161       SH Options
13162
13163       These -m options are defined for the SH implementations:
13164
13165       -m1 Generate code for the SH1.
13166
13167       -m2 Generate code for the SH2.
13168
13169       -m2e
13170           Generate code for the SH2e.
13171
13172       -m2a-nofpu
13173           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
13174           way that the floating-point unit is not used.
13175
13176       -m2a-single-only
13177           Generate code for the SH2a-FPU, in such a way that no double-
13178           precision floating point operations are used.
13179
13180       -m2a-single
13181           Generate code for the SH2a-FPU assuming the floating-point unit is
13182           in single-precision mode by default.
13183
13184       -m2a
13185           Generate code for the SH2a-FPU assuming the floating-point unit is
13186           in double-precision mode by default.
13187
13188       -m3 Generate code for the SH3.
13189
13190       -m3e
13191           Generate code for the SH3e.
13192
13193       -m4-nofpu
13194           Generate code for the SH4 without a floating-point unit.
13195
13196       -m4-single-only
13197           Generate code for the SH4 with a floating-point unit that only
13198           supports single-precision arithmetic.
13199
13200       -m4-single
13201           Generate code for the SH4 assuming the floating-point unit is in
13202           single-precision mode by default.
13203
13204       -m4 Generate code for the SH4.
13205
13206       -m4a-nofpu
13207           Generate code for the SH4al-dsp, or for a SH4a in such a way that
13208           the floating-point unit is not used.
13209
13210       -m4a-single-only
13211           Generate code for the SH4a, in such a way that no double-precision
13212           floating point operations are used.
13213
13214       -m4a-single
13215           Generate code for the SH4a assuming the floating-point unit is in
13216           single-precision mode by default.
13217
13218       -m4a
13219           Generate code for the SH4a.
13220
13221       -m4al
13222           Same as -m4a-nofpu, except that it implicitly passes -dsp to the
13223           assembler.  GCC doesn't generate any DSP instructions at the
13224           moment.
13225
13226       -mb Compile code for the processor in big endian mode.
13227
13228       -ml Compile code for the processor in little endian mode.
13229
13230       -mdalign
13231           Align doubles at 64-bit boundaries.  Note that this changes the
13232           calling conventions, and thus some functions from the standard C
13233           library will not work unless you recompile it first with -mdalign.
13234
13235       -mrelax
13236           Shorten some address references at link time, when possible; uses
13237           the linker option -relax.
13238
13239       -mbigtable
13240           Use 32-bit offsets in "switch" tables.  The default is to use
13241           16-bit offsets.
13242
13243       -mbitops
13244           Enable the use of bit manipulation instructions on SH2A.
13245
13246       -mfmovd
13247           Enable the use of the instruction "fmovd".  Check -mdalign for
13248           alignment constraints.
13249
13250       -mhitachi
13251           Comply with the calling conventions defined by Renesas.
13252
13253       -mrenesas
13254           Comply with the calling conventions defined by Renesas.
13255
13256       -mno-renesas
13257           Comply with the calling conventions defined for GCC before the
13258           Renesas conventions were available.  This option is the default for
13259           all targets of the SH toolchain except for sh-symbianelf.
13260
13261       -mnomacsave
13262           Mark the "MAC" register as call-clobbered, even if -mhitachi is
13263           given.
13264
13265       -mieee
13266           Increase IEEE-compliance of floating-point code.  At the moment,
13267           this is equivalent to -fno-finite-math-only.  When generating 16
13268           bit SH opcodes, getting IEEE-conforming results for comparisons of
13269           NANs / infinities incurs extra overhead in every floating point
13270           comparison, therefore the default is set to -ffinite-math-only.
13271
13272       -minline-ic_invalidate
13273           Inline code to invalidate instruction cache entries after setting
13274           up nested function trampolines.  This option has no effect if
13275           -musermode is in effect and the selected code generation option
13276           (e.g. -m4) does not allow the use of the icbi instruction.  If the
13277           selected code generation option does not allow the use of the icbi
13278           instruction, and -musermode is not in effect, the inlined code will
13279           manipulate the instruction cache address array directly with an
13280           associative write.  This not only requires privileged mode, but it
13281           will also fail if the cache line had been mapped via the TLB and
13282           has become unmapped.
13283
13284       -misize
13285           Dump instruction size and location in the assembly code.
13286
13287       -mpadstruct
13288           This option is deprecated.  It pads structures to multiple of 4
13289           bytes, which is incompatible with the SH ABI.
13290
13291       -mspace
13292           Optimize for space instead of speed.  Implied by -Os.
13293
13294       -mprefergot
13295           When generating position-independent code, emit function calls
13296           using the Global Offset Table instead of the Procedure Linkage
13297           Table.
13298
13299       -musermode
13300           Don't generate privileged mode only code; implies
13301           -mno-inline-ic_invalidate if the inlined code would not work in
13302           user mode.  This is the default when the target is "sh-*-linux*".
13303
13304       -multcost=number
13305           Set the cost to assume for a multiply insn.
13306
13307       -mdiv=strategy
13308           Set the division strategy to use for SHmedia code.  strategy must
13309           be one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l,
13310           inv:call, inv:call2, inv:fp .  "fp" performs the operation in
13311           floating point.  This has a very high latency, but needs only a few
13312           instructions, so it might be a good choice if your code has enough
13313           easily exploitable ILP to allow the compiler to schedule the
13314           floating point instructions together with other instructions.
13315           Division by zero causes a floating point exception.  "inv" uses
13316           integer operations to calculate the inverse of the divisor, and
13317           then multiplies the dividend with the inverse.  This strategy
13318           allows cse and hoisting of the inverse calculation.  Division by
13319           zero calculates an unspecified result, but does not trap.
13320           "inv:minlat" is a variant of "inv" where if no cse / hoisting
13321           opportunities have been found, or if the entire operation has been
13322           hoisted to the same place, the last stages of the inverse
13323           calculation are intertwined with the final multiply to reduce the
13324           overall latency, at the expense of using a few more instructions,
13325           and thus offering fewer scheduling opportunities with other code.
13326           "call" calls a library function that usually implements the
13327           inv:minlat strategy.  This gives high code density for
13328           m5-*media-nofpu compilations.  "call2" uses a different entry point
13329           of the same library function, where it assumes that a pointer to a
13330           lookup table has already been set up, which exposes the pointer
13331           load to cse / code hoisting optimizations.  "inv:call", "inv:call2"
13332           and "inv:fp" all use the "inv" algorithm for initial code
13333           generation, but if the code stays unoptimized, revert to the
13334           "call", "call2", or "fp" strategies, respectively.  Note that the
13335           potentially-trapping side effect of division by zero is carried by
13336           a separate instruction, so it is possible that all the integer
13337           instructions are hoisted out, but the marker for the side effect
13338           stays where it is.  A recombination to fp operations or a call is
13339           not possible in that case.  "inv20u" and "inv20l" are variants of
13340           the "inv:minlat" strategy.  In the case that the inverse
13341           calculation was nor separated from the multiply, they speed up
13342           division where the dividend fits into 20 bits (plus sign where
13343           applicable), by inserting a test to skip a number of operations in
13344           this case; this test slows down the case of larger dividends.
13345           inv20u assumes the case of a such a small dividend to be unlikely,
13346           and inv20l assumes it to be likely.
13347
13348       -mdivsi3_libfunc=name
13349           Set the name of the library function used for 32 bit signed
13350           division to name.  This only affect the name used in the call and
13351           inv:call division strategies, and the compiler will still expect
13352           the same sets of input/output/clobbered registers as if this option
13353           was not present.
13354
13355       -mfixed-range=register-range
13356           Generate code treating the given register range as fixed registers.
13357           A fixed register is one that the register allocator can not use.
13358           This is useful when compiling kernel code.  A register range is
13359           specified as two registers separated by a dash.  Multiple register
13360           ranges can be specified separated by a comma.
13361
13362       -madjust-unroll
13363           Throttle unrolling to avoid thrashing target registers.  This
13364           option only has an effect if the gcc code base supports the
13365           TARGET_ADJUST_UNROLL_MAX target hook.
13366
13367       -mindexed-addressing
13368           Enable the use of the indexed addressing mode for
13369           SHmedia32/SHcompact.  This is only safe if the hardware and/or OS
13370           implement 32 bit wrap-around semantics for the indexed addressing
13371           mode.  The architecture allows the implementation of processors
13372           with 64 bit MMU, which the OS could use to get 32 bit addressing,
13373           but since no current hardware implementation supports this or any
13374           other way to make the indexed addressing mode safe to use in the 32
13375           bit ABI, the default is -mno-indexed-addressing.
13376
13377       -mgettrcost=number
13378           Set the cost assumed for the gettr instruction to number.  The
13379           default is 2 if -mpt-fixed is in effect, 100 otherwise.
13380
13381       -mpt-fixed
13382           Assume pt* instructions won't trap.  This will generally generate
13383           better scheduled code, but is unsafe on current hardware.  The
13384           current architecture definition says that ptabs and ptrel trap when
13385           the target anded with 3 is 3.  This has the unintentional effect of
13386           making it unsafe to schedule ptabs / ptrel before a branch, or
13387           hoist it out of a loop.  For example, __do_global_ctors, a part of
13388           libgcc that runs constructors at program startup, calls functions
13389           in a list which is delimited by -1.  With the -mpt-fixed option,
13390           the ptabs will be done before testing against -1.  That means that
13391           all the constructors will be run a bit quicker, but when the loop
13392           comes to the end of the list, the program crashes because ptabs
13393           loads -1 into a target register.  Since this option is unsafe for
13394           any hardware implementing the current architecture specification,
13395           the default is -mno-pt-fixed.  Unless the user specifies a specific
13396           cost with -mgettrcost, -mno-pt-fixed also implies -mgettrcost=100;
13397           this deters register allocation using target registers for storing
13398           ordinary integers.
13399
13400       -minvalid-symbols
13401           Assume symbols might be invalid.  Ordinary function symbols
13402           generated by the compiler will always be valid to load with
13403           movi/shori/ptabs or movi/shori/ptrel, but with assembler and/or
13404           linker tricks it is possible to generate symbols that will cause
13405           ptabs / ptrel to trap.  This option is only meaningful when
13406           -mno-pt-fixed is in effect.  It will then prevent cross-basic-block
13407           cse, hoisting and most scheduling of symbol loads.  The default is
13408           -mno-invalid-symbols.
13409
13410       SPARC Options
13411
13412       These -m options are supported on the SPARC:
13413
13414       -mno-app-regs
13415       -mapp-regs
13416           Specify -mapp-regs to generate output using the global registers 2
13417           through 4, which the SPARC SVR4 ABI reserves for applications.
13418           This is the default.
13419
13420           To be fully SVR4 ABI compliant at the cost of some performance
13421           loss, specify -mno-app-regs.  You should compile libraries and
13422           system software with this option.
13423
13424       -mfpu
13425       -mhard-float
13426           Generate output containing floating point instructions.  This is
13427           the default.
13428
13429       -mno-fpu
13430       -msoft-float
13431           Generate output containing library calls for floating point.
13432           Warning: the requisite libraries are not available for all SPARC
13433           targets.  Normally the facilities of the machine's usual C compiler
13434           are used, but this cannot be done directly in cross-compilation.
13435           You must make your own arrangements to provide suitable library
13436           functions for cross-compilation.  The embedded targets sparc-*-aout
13437           and sparclite-*-* do provide software floating point support.
13438
13439           -msoft-float changes the calling convention in the output file;
13440           therefore, it is only useful if you compile all of a program with
13441           this option.  In particular, you need to compile libgcc.a, the
13442           library that comes with GCC, with -msoft-float in order for this to
13443           work.
13444
13445       -mhard-quad-float
13446           Generate output containing quad-word (long double) floating point
13447           instructions.
13448
13449       -msoft-quad-float
13450           Generate output containing library calls for quad-word (long
13451           double) floating point instructions.  The functions called are
13452           those specified in the SPARC ABI.  This is the default.
13453
13454           As of this writing, there are no SPARC implementations that have
13455           hardware support for the quad-word floating point instructions.
13456           They all invoke a trap handler for one of these instructions, and
13457           then the trap handler emulates the effect of the instruction.
13458           Because of the trap handler overhead, this is much slower than
13459           calling the ABI library routines.  Thus the -msoft-quad-float
13460           option is the default.
13461
13462       -mno-unaligned-doubles
13463       -munaligned-doubles
13464           Assume that doubles have 8 byte alignment.  This is the default.
13465
13466           With -munaligned-doubles, GCC assumes that doubles have 8 byte
13467           alignment only if they are contained in another type, or if they
13468           have an absolute address.  Otherwise, it assumes they have 4 byte
13469           alignment.  Specifying this option avoids some rare compatibility
13470           problems with code generated by other compilers.  It is not the
13471           default because it results in a performance loss, especially for
13472           floating point code.
13473
13474       -mno-faster-structs
13475       -mfaster-structs
13476           With -mfaster-structs, the compiler assumes that structures should
13477           have 8 byte alignment.  This enables the use of pairs of "ldd" and
13478           "std" instructions for copies in structure assignment, in place of
13479           twice as many "ld" and "st" pairs.  However, the use of this
13480           changed alignment directly violates the SPARC ABI.  Thus, it's
13481           intended only for use on targets where the developer acknowledges
13482           that their resulting code will not be directly in line with the
13483           rules of the ABI.
13484
13485       -mimpure-text
13486           -mimpure-text, used in addition to -shared, tells the compiler to
13487           not pass -z text to the linker when linking a shared object.  Using
13488           this option, you can link position-dependent code into a shared
13489           object.
13490
13491           -mimpure-text suppresses the "relocations remain against
13492           allocatable but non-writable sections" linker error message.
13493           However, the necessary relocations will trigger copy-on-write, and
13494           the shared object is not actually shared across processes.  Instead
13495           of using -mimpure-text, you should compile all source code with
13496           -fpic or -fPIC.
13497
13498           This option is only available on SunOS and Solaris.
13499
13500       -mcpu=cpu_type
13501           Set the instruction set, register set, and instruction scheduling
13502           parameters for machine type cpu_type.  Supported values for
13503           cpu_type are v7, cypress, v8, supersparc, sparclite, f930, f934,
13504           hypersparc, sparclite86x, sparclet, tsc701, v9, ultrasparc,
13505           ultrasparc3, niagara and niagara2.
13506
13507           Default instruction scheduling parameters are used for values that
13508           select an architecture and not an implementation.  These are v7,
13509           v8, sparclite, sparclet, v9.
13510
13511           Here is a list of each supported architecture and their supported
13512           implementations.
13513
13514                       v7:             cypress
13515                       v8:             supersparc, hypersparc
13516                       sparclite:      f930, f934, sparclite86x
13517                       sparclet:       tsc701
13518                       v9:             ultrasparc, ultrasparc3, niagara, niagara2
13519
13520           By default (unless configured otherwise), GCC generates code for
13521           the V7 variant of the SPARC architecture.  With -mcpu=cypress, the
13522           compiler additionally optimizes it for the Cypress CY7C602 chip, as
13523           used in the SPARCStation/SPARCServer 3xx series.  This is also
13524           appropriate for the older SPARCStation 1, 2, IPX etc.
13525
13526           With -mcpu=v8, GCC generates code for the V8 variant of the SPARC
13527           architecture.  The only difference from V7 code is that the
13528           compiler emits the integer multiply and integer divide instructions
13529           which exist in SPARC-V8 but not in SPARC-V7.  With
13530           -mcpu=supersparc, the compiler additionally optimizes it for the
13531           SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
13532           series.
13533
13534           With -mcpu=sparclite, GCC generates code for the SPARClite variant
13535           of the SPARC architecture.  This adds the integer multiply, integer
13536           divide step and scan ("ffs") instructions which exist in SPARClite
13537           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally
13538           optimizes it for the Fujitsu MB86930 chip, which is the original
13539           SPARClite, with no FPU.  With -mcpu=f934, the compiler additionally
13540           optimizes it for the Fujitsu MB86934 chip, which is the more recent
13541           SPARClite with FPU.
13542
13543           With -mcpu=sparclet, GCC generates code for the SPARClet variant of
13544           the SPARC architecture.  This adds the integer multiply,
13545           multiply/accumulate, integer divide step and scan ("ffs")
13546           instructions which exist in SPARClet but not in SPARC-V7.  With
13547           -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC
13548           SPARClet chip.
13549
13550           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC
13551           architecture.  This adds 64-bit integer and floating-point move
13552           instructions, 3 additional floating-point condition code registers
13553           and conditional move instructions.  With -mcpu=ultrasparc, the
13554           compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
13555           chips.  With -mcpu=ultrasparc3, the compiler additionally optimizes
13556           it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.  With
13557           -mcpu=niagara, the compiler additionally optimizes it for Sun
13558           UltraSPARC T1 chips.  With -mcpu=niagara2, the compiler
13559           additionally optimizes it for Sun UltraSPARC T2 chips.
13560
13561       -mtune=cpu_type
13562           Set the instruction scheduling parameters for machine type
13563           cpu_type, but do not set the instruction set or register set that
13564           the option -mcpu=cpu_type would.
13565
13566           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type,
13567           but the only useful values are those that select a particular cpu
13568           implementation.  Those are cypress, supersparc, hypersparc, f930,
13569           f934, sparclite86x, tsc701, ultrasparc, ultrasparc3, niagara, and
13570           niagara2.
13571
13572       -mv8plus
13573       -mno-v8plus
13574           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The
13575           difference from the V8 ABI is that the global and out registers are
13576           considered 64-bit wide.  This is enabled by default on Solaris in
13577           32-bit mode for all SPARC-V9 processors.
13578
13579       -mvis
13580       -mno-vis
13581           With -mvis, GCC generates code that takes advantage of the
13582           UltraSPARC Visual Instruction Set extensions.  The default is
13583           -mno-vis.
13584
13585       These -m options are supported in addition to the above on SPARC-V9
13586       processors in 64-bit environments:
13587
13588       -mlittle-endian
13589           Generate code for a processor running in little-endian mode.  It is
13590           only available for a few configurations and most notably not on
13591           Solaris and Linux.
13592
13593       -m32
13594       -m64
13595           Generate code for a 32-bit or 64-bit environment.  The 32-bit
13596           environment sets int, long and pointer to 32 bits.  The 64-bit
13597           environment sets int to 32 bits and long and pointer to 64 bits.
13598
13599       -mcmodel=medlow
13600           Generate code for the Medium/Low code model: 64-bit addresses,
13601           programs must be linked in the low 32 bits of memory.  Programs can
13602           be statically or dynamically linked.
13603
13604       -mcmodel=medmid
13605           Generate code for the Medium/Middle code model: 64-bit addresses,
13606           programs must be linked in the low 44 bits of memory, the text and
13607           data segments must be less than 2GB in size and the data segment
13608           must be located within 2GB of the text segment.
13609
13610       -mcmodel=medany
13611           Generate code for the Medium/Anywhere code model: 64-bit addresses,
13612           programs may be linked anywhere in memory, the text and data
13613           segments must be less than 2GB in size and the data segment must be
13614           located within 2GB of the text segment.
13615
13616       -mcmodel=embmedany
13617           Generate code for the Medium/Anywhere code model for embedded
13618           systems: 64-bit addresses, the text and data segments must be less
13619           than 2GB in size, both starting anywhere in memory (determined at
13620           link time).  The global register %g4 points to the base of the data
13621           segment.  Programs are statically linked and PIC is not supported.
13622
13623       -mstack-bias
13624       -mno-stack-bias
13625           With -mstack-bias, GCC assumes that the stack pointer, and frame
13626           pointer if present, are offset by -2047 which must be added back
13627           when making stack frame references.  This is the default in 64-bit
13628           mode.  Otherwise, assume no such offset is present.
13629
13630       These switches are supported in addition to the above on Solaris:
13631
13632       -threads
13633           Add support for multithreading using the Solaris threads library.
13634           This option sets flags for both the preprocessor and linker.  This
13635           option does not affect the thread safety of object code produced by
13636           the compiler or that of libraries supplied with it.
13637
13638       -pthreads
13639           Add support for multithreading using the POSIX threads library.
13640           This option sets flags for both the preprocessor and linker.  This
13641           option does not affect the thread safety of object code produced
13642           by the compiler or that of libraries supplied with it.
13643
13644       -pthread
13645           This is a synonym for -pthreads.
13646
13647       SPU Options
13648
13649       These -m options are supported on the SPU:
13650
13651       -mwarn-reloc
13652       -merror-reloc
13653           The loader for SPU does not handle dynamic relocations.  By
13654           default, GCC will give an error when it generates code that
13655           requires a dynamic relocation.  -mno-error-reloc disables the
13656           error, -mwarn-reloc will generate a warning instead.
13657
13658       -msafe-dma
13659       -munsafe-dma
13660           Instructions which initiate or test completion of DMA must not be
13661           reordered with respect to loads and stores of the memory which is
13662           being accessed.  Users typically address this problem using the
13663           volatile keyword, but that can lead to inefficient code in places
13664           where the memory is known to not change.  Rather than mark the
13665           memory as volatile we treat the DMA instructions as potentially
13666           effecting all memory.  With -munsafe-dma users must use the
13667           volatile keyword to protect memory accesses.
13668
13669       -mbranch-hints
13670           By default, GCC will generate a branch hint instruction to avoid
13671           pipeline stalls for always taken or probably taken branches.  A
13672           hint will not be generated closer than 8 instructions away from its
13673           branch.  There is little reason to disable them, except for
13674           debugging purposes, or to make an object a little bit smaller.
13675
13676       -msmall-mem
13677       -mlarge-mem
13678           By default, GCC generates code assuming that addresses are never
13679           larger than 18 bits.  With -mlarge-mem code is generated that
13680           assumes a full 32 bit address.
13681
13682       -mstdmain
13683           By default, GCC links against startup code that assumes the SPU-
13684           style main function interface (which has an unconventional
13685           parameter list).  With -mstdmain, GCC will link your program
13686           against startup code that assumes a C99-style interface to "main",
13687           including a local copy of "argv" strings.
13688
13689       -mfixed-range=register-range
13690           Generate code treating the given register range as fixed registers.
13691           A fixed register is one that the register allocator can not use.
13692           This is useful when compiling kernel code.  A register range is
13693           specified as two registers separated by a dash.  Multiple register
13694           ranges can be specified separated by a comma.
13695
13696       -mea32
13697       -mea64
13698           Compile code assuming that pointers to the PPU address space
13699           accessed via the "__ea" named address space qualifier are either 32
13700           or 64 bits wide.  The default is 32 bits.  As this is an ABI
13701           changing option, all object code in an executable must be compiled
13702           with the same setting.
13703
13704       -maddress-space-conversion
13705       -mno-address-space-conversion
13706           Allow/disallow treating the "__ea" address space as superset of the
13707           generic address space.  This enables explicit type casts between
13708           "__ea" and generic pointer as well as implicit conversions of
13709           generic pointers to "__ea" pointers.  The default is to allow
13710           address space pointer conversions.
13711
13712       -mcache-size=cache-size
13713           This option controls the version of libgcc that the compiler links
13714           to an executable and selects a software-managed cache for accessing
13715           variables in the "__ea" address space with a particular cache size.
13716           Possible options for cache-size are 8, 16, 32, 64 and 128.  The
13717           default cache size is 64KB.
13718
13719       -matomic-updates
13720       -mno-atomic-updates
13721           This option controls the version of libgcc that the compiler links
13722           to an executable and selects whether atomic updates to the
13723           software-managed cache of PPU-side variables are used.  If you use
13724           atomic updates, changes to a PPU variable from SPU code using the
13725           "__ea" named address space qualifier will not interfere with
13726           changes to other PPU variables residing in the same cache line from
13727           PPU code.  If you do not use atomic updates, such interference may
13728           occur; however, writing back cache lines will be more efficient.
13729           The default behavior is to use atomic updates.
13730
13731       -mdual-nops
13732       -mdual-nops=n
13733           By default, GCC will insert nops to increase dual issue when it
13734           expects it to increase performance.  n can be a value from 0 to 10.
13735           A smaller n will insert fewer nops.  10 is the default, 0 is the
13736           same as -mno-dual-nops.  Disabled with -Os.
13737
13738       -mhint-max-nops=n
13739           Maximum number of nops to insert for a branch hint.  A branch hint
13740           must be at least 8 instructions away from the branch it is
13741           effecting.  GCC will insert up to n nops to enforce this, otherwise
13742           it will not generate the branch hint.
13743
13744       -mhint-max-distance=n
13745           The encoding of the branch hint instruction limits the hint to be
13746           within 256 instructions of the branch it is effecting.  By default,
13747           GCC makes sure it is within 125.
13748
13749       -msafe-hints
13750           Work around a hardware bug which causes the SPU to stall
13751           indefinitely.  By default, GCC will insert the "hbrp" instruction
13752           to make sure this stall won't happen.
13753
13754       Options for System V
13755
13756       These additional options are available on System V Release 4 for
13757       compatibility with other compilers on those systems:
13758
13759       -G  Create a shared object.  It is recommended that -symbolic or
13760           -shared be used instead.
13761
13762       -Qy Identify the versions of each tool used by the compiler, in a
13763           ".ident" assembler directive in the output.
13764
13765       -Qn Refrain from adding ".ident" directives to the output file (this is
13766           the default).
13767
13768       -YP,dirs
13769           Search the directories dirs, and no others, for libraries specified
13770           with -l.
13771
13772       -Ym,dir
13773           Look in the directory dir to find the M4 preprocessor.  The
13774           assembler uses this option.
13775
13776       V850 Options
13777
13778       These -m options are defined for V850 implementations:
13779
13780       -mlong-calls
13781       -mno-long-calls
13782           Treat all calls as being far away (near).  If calls are assumed to
13783           be far away, the compiler will always load the functions address up
13784           into a register, and call indirect through the pointer.
13785
13786       -mno-ep
13787       -mep
13788           Do not optimize (do optimize) basic blocks that use the same index
13789           pointer 4 or more times to copy pointer into the "ep" register, and
13790           use the shorter "sld" and "sst" instructions.  The -mep option is
13791           on by default if you optimize.
13792
13793       -mno-prolog-function
13794       -mprolog-function
13795           Do not use (do use) external functions to save and restore
13796           registers at the prologue and epilogue of a function.  The external
13797           functions are slower, but use less code space if more than one
13798           function saves the same number of registers.  The -mprolog-function
13799           option is on by default if you optimize.
13800
13801       -mspace
13802           Try to make the code as small as possible.  At present, this just
13803           turns on the -mep and -mprolog-function options.
13804
13805       -mtda=n
13806           Put static or global variables whose size is n bytes or less into
13807           the tiny data area that register "ep" points to.  The tiny data
13808           area can hold up to 256 bytes in total (128 bytes for byte
13809           references).
13810
13811       -msda=n
13812           Put static or global variables whose size is n bytes or less into
13813           the small data area that register "gp" points to.  The small data
13814           area can hold up to 64 kilobytes.
13815
13816       -mzda=n
13817           Put static or global variables whose size is n bytes or less into
13818           the first 32 kilobytes of memory.
13819
13820       -mv850
13821           Specify that the target processor is the V850.
13822
13823       -mbig-switch
13824           Generate code suitable for big switch tables.  Use this option only
13825           if the assembler/linker complain about out of range branches within
13826           a switch table.
13827
13828       -mapp-regs
13829           This option will cause r2 and r5 to be used in the code generated
13830           by the compiler.  This setting is the default.
13831
13832       -mno-app-regs
13833           This option will cause r2 and r5 to be treated as fixed registers.
13834
13835       -mv850e1
13836           Specify that the target processor is the V850E1.  The preprocessor
13837           constants __v850e1__ and __v850e__ will be defined if this option
13838           is used.
13839
13840       -mv850e
13841           Specify that the target processor is the V850E.  The preprocessor
13842           constant __v850e__ will be defined if this option is used.
13843
13844           If neither -mv850 nor -mv850e nor -mv850e1 are defined then a
13845           default target processor will be chosen and the relevant __v850*__
13846           preprocessor constant will be defined.
13847
13848           The preprocessor constants __v850 and __v851__ are always defined,
13849           regardless of which processor variant is the target.
13850
13851       -mdisable-callt
13852           This option will suppress generation of the CALLT instruction for
13853           the v850e and v850e1 flavors of the v850 architecture.  The default
13854           is -mno-disable-callt which allows the CALLT instruction to be
13855           used.
13856
13857       VAX Options
13858
13859       These -m options are defined for the VAX:
13860
13861       -munix
13862           Do not output certain jump instructions ("aobleq" and so on) that
13863           the Unix assembler for the VAX cannot handle across long ranges.
13864
13865       -mgnu
13866           Do output those jump instructions, on the assumption that you will
13867           assemble with the GNU assembler.
13868
13869       -mg Output code for g-format floating point numbers instead of
13870           d-format.
13871
13872       VxWorks Options
13873
13874       The options in this section are defined for all VxWorks targets.
13875       Options specific to the target hardware are listed with the other
13876       options for that target.
13877
13878       -mrtp
13879           GCC can generate code for both VxWorks kernels and real time
13880           processes (RTPs).  This option switches from the former to the
13881           latter.  It also defines the preprocessor macro "__RTP__".
13882
13883       -non-static
13884           Link an RTP executable against shared libraries rather than static
13885           libraries.  The options -static and -shared can also be used for
13886           RTPs; -static is the default.
13887
13888       -Bstatic
13889       -Bdynamic
13890           These options are passed down to the linker.  They are defined for
13891           compatibility with Diab.
13892
13893       -Xbind-lazy
13894           Enable lazy binding of function calls.  This option is equivalent
13895           to -Wl,-z,now and is defined for compatibility with Diab.
13896
13897       -Xbind-now
13898           Disable lazy binding of function calls.  This option is the default
13899           and is defined for compatibility with Diab.
13900
13901       x86-64 Options
13902
13903       These are listed under
13904
13905       i386 and x86-64 Windows Options
13906
13907       These additional options are available for Windows targets:
13908
13909       -mconsole
13910           This option is available for Cygwin and MinGW targets.  It
13911           specifies that a console application is to be generated, by
13912           instructing the linker to set the PE header subsystem type required
13913           for console applications.  This is the default behavior for Cygwin
13914           and MinGW targets.
13915
13916       -mcygwin
13917           This option is available for Cygwin targets.  It specifies that the
13918           Cygwin internal interface is to be used for predefined preprocessor
13919           macros, C runtime libraries and related linker paths and options.
13920           For Cygwin targets this is the default behavior.  This option is
13921           deprecated and will be removed in a future release.
13922
13923       -mno-cygwin
13924           This option is available for Cygwin targets.  It specifies that the
13925           MinGW internal interface is to be used instead of Cygwin's, by
13926           setting MinGW-related predefined macros and linker paths and
13927           default library options.  This option is deprecated and will be
13928           removed in a future release.
13929
13930       -mdll
13931           This option is available for Cygwin and MinGW targets.  It
13932           specifies that a DLL - a dynamic link library - is to be generated,
13933           enabling the selection of the required runtime startup object and
13934           entry point.
13935
13936       -mnop-fun-dllimport
13937           This option is available for Cygwin and MinGW targets.  It
13938           specifies that the dllimport attribute should be ignored.
13939
13940       -mthread
13941           This option is available for MinGW targets. It specifies that
13942           MinGW-specific thread support is to be used.
13943
13944       -municode
13945           This option is available for mingw-w64 targets.  It specifies that
13946           the UNICODE macro is getting pre-defined and that the unicode
13947           capable runtime startup code is chosen.
13948
13949       -mwin32
13950           This option is available for Cygwin and MinGW targets.  It
13951           specifies that the typical Windows pre-defined macros are to be set
13952           in the pre-processor, but does not influence the choice of runtime
13953           library/startup code.
13954
13955       -mwindows
13956           This option is available for Cygwin and MinGW targets.  It
13957           specifies that a GUI application is to be generated by instructing
13958           the linker to set the PE header subsystem type appropriately.
13959
13960       -fno-set-stack-executable
13961           This option is available for MinGW targets. It specifies that the
13962           executable flag for stack used by nested functions isn't set. This
13963           is necessary for binaries running in kernel mode of Windows, as
13964           there the user32 API, which is used to set executable privileges,
13965           isn't available.
13966
13967       -mpe-aligned-commons
13968           This option is available for Cygwin and MinGW targets.  It
13969           specifies that the GNU extension to the PE file format that permits
13970           the correct alignment of COMMON variables should be used when
13971           generating code.  It will be enabled by default if GCC detects that
13972           the target assembler found during configuration supports the
13973           feature.
13974
13975       See also under i386 and x86-64 Options for standard options.
13976
13977       Xstormy16 Options
13978
13979       These options are defined for Xstormy16:
13980
13981       -msim
13982           Choose startup files and linker script suitable for the simulator.
13983
13984       Xtensa Options
13985
13986       These options are supported for Xtensa targets:
13987
13988       -mconst16
13989       -mno-const16
13990           Enable or disable use of "CONST16" instructions for loading
13991           constant values.  The "CONST16" instruction is currently not a
13992           standard option from Tensilica.  When enabled, "CONST16"
13993           instructions are always used in place of the standard "L32R"
13994           instructions.  The use of "CONST16" is enabled by default only if
13995           the "L32R" instruction is not available.
13996
13997       -mfused-madd
13998       -mno-fused-madd
13999           Enable or disable use of fused multiply/add and multiply/subtract
14000           instructions in the floating-point option.  This has no effect if
14001           the floating-point option is not also enabled.  Disabling fused
14002           multiply/add and multiply/subtract instructions forces the compiler
14003           to use separate instructions for the multiply and add/subtract
14004           operations.  This may be desirable in some cases where strict IEEE
14005           754-compliant results are required: the fused multiply add/subtract
14006           instructions do not round the intermediate result, thereby
14007           producing results with more bits of precision than specified by the
14008           IEEE standard.  Disabling fused multiply add/subtract instructions
14009           also ensures that the program output is not sensitive to the
14010           compiler's ability to combine multiply and add/subtract operations.
14011
14012       -mserialize-volatile
14013       -mno-serialize-volatile
14014           When this option is enabled, GCC inserts "MEMW" instructions before
14015           "volatile" memory references to guarantee sequential consistency.
14016           The default is -mserialize-volatile.  Use -mno-serialize-volatile
14017           to omit the "MEMW" instructions.
14018
14019       -mtext-section-literals
14020       -mno-text-section-literals
14021           Control the treatment of literal pools.  The default is
14022           -mno-text-section-literals, which places literals in a separate
14023           section in the output file.  This allows the literal pool to be
14024           placed in a data RAM/ROM, and it also allows the linker to combine
14025           literal pools from separate object files to remove redundant
14026           literals and improve code size.  With -mtext-section-literals, the
14027           literals are interspersed in the text section in order to keep them
14028           as close as possible to their references.  This may be necessary
14029           for large assembly files.
14030
14031       -mtarget-align
14032       -mno-target-align
14033           When this option is enabled, GCC instructs the assembler to
14034           automatically align instructions to reduce branch penalties at the
14035           expense of some code density.  The assembler attempts to widen
14036           density instructions to align branch targets and the instructions
14037           following call instructions.  If there are not enough preceding
14038           safe density instructions to align a target, no widening will be
14039           performed.  The default is -mtarget-align.  These options do not
14040           affect the treatment of auto-aligned instructions like "LOOP",
14041           which the assembler will always align, either by widening density
14042           instructions or by inserting no-op instructions.
14043
14044       -mlongcalls
14045       -mno-longcalls
14046           When this option is enabled, GCC instructs the assembler to
14047           translate direct calls to indirect calls unless it can determine
14048           that the target of a direct call is in the range allowed by the
14049           call instruction.  This translation typically occurs for calls to
14050           functions in other source files.  Specifically, the assembler
14051           translates a direct "CALL" instruction into an "L32R" followed by a
14052           "CALLX" instruction.  The default is -mno-longcalls.  This option
14053           should be used in programs where the call target can potentially be
14054           out of range.  This option is implemented in the assembler, not the
14055           compiler, so the assembly code generated by GCC will still show
14056           direct call instructions---look at the disassembled object code to
14057           see the actual instructions.  Note that the assembler will use an
14058           indirect call for every cross-file call, not just those that really
14059           will be out of range.
14060
14061       zSeries Options
14062
14063       These are listed under
14064
14065   Options for Code Generation Conventions
14066       These machine-independent options control the interface conventions
14067       used in code generation.
14068
14069       Most of them have both positive and negative forms; the negative form
14070       of -ffoo would be -fno-foo.  In the table below, only one of the forms
14071       is listed---the one which is not the default.  You can figure out the
14072       other form by either removing no- or adding it.
14073
14074       -fbounds-check
14075           For front-ends that support it, generate additional code to check
14076           that indices used to access arrays are within the declared range.
14077           This is currently only supported by the Java and Fortran front-
14078           ends, where this option defaults to true and false respectively.
14079
14080       -ftrapv
14081           This option generates traps for signed overflow on addition,
14082           subtraction, multiplication operations.
14083
14084       -fwrapv
14085           This option instructs the compiler to assume that signed arithmetic
14086           overflow of addition, subtraction and multiplication wraps around
14087           using twos-complement representation.  This flag enables some
14088           optimizations and disables others.  This option is enabled by
14089           default for the Java front-end, as required by the Java language
14090           specification.
14091
14092       -fexceptions
14093           Enable exception handling.  Generates extra code needed to
14094           propagate exceptions.  For some targets, this implies GCC will
14095           generate frame unwind information for all functions, which can
14096           produce significant data size overhead, although it does not affect
14097           execution.  If you do not specify this option, GCC will enable it
14098           by default for languages like C++ which normally require exception
14099           handling, and disable it for languages like C that do not normally
14100           require it.  However, you may need to enable this option when
14101           compiling C code that needs to interoperate properly with exception
14102           handlers written in C++.  You may also wish to disable this option
14103           if you are compiling older C++ programs that don't use exception
14104           handling.
14105
14106       -fnon-call-exceptions
14107           Generate code that allows trapping instructions to throw
14108           exceptions.  Note that this requires platform-specific runtime
14109           support that does not exist everywhere.  Moreover, it only allows
14110           trapping instructions to throw exceptions, i.e. memory references
14111           or floating point instructions.  It does not allow exceptions to be
14112           thrown from arbitrary signal handlers such as "SIGALRM".
14113
14114       -funwind-tables
14115           Similar to -fexceptions, except that it will just generate any
14116           needed static data, but will not affect the generated code in any
14117           other way.  You will normally not enable this option; instead, a
14118           language processor that needs this handling would enable it on your
14119           behalf.
14120
14121       -fasynchronous-unwind-tables
14122           Generate unwind table in dwarf2 format, if supported by target
14123           machine.  The table is exact at each instruction boundary, so it
14124           can be used for stack unwinding from asynchronous events (such as
14125           debugger or garbage collector).
14126
14127       -fpcc-struct-return
14128           Return "short" "struct" and "union" values in memory like longer
14129           ones, rather than in registers.  This convention is less efficient,
14130           but it has the advantage of allowing intercallability between GCC-
14131           compiled files and files compiled with other compilers,
14132           particularly the Portable C Compiler (pcc).
14133
14134           The precise convention for returning structures in memory depends
14135           on the target configuration macros.
14136
14137           Short structures and unions are those whose size and alignment
14138           match that of some integer type.
14139
14140           Warning: code compiled with the -fpcc-struct-return switch is not
14141           binary compatible with code compiled with the -freg-struct-return
14142           switch.  Use it to conform to a non-default application binary
14143           interface.
14144
14145       -freg-struct-return
14146           Return "struct" and "union" values in registers when possible.
14147           This is more efficient for small structures than
14148           -fpcc-struct-return.
14149
14150           If you specify neither -fpcc-struct-return nor -freg-struct-return,
14151           GCC defaults to whichever convention is standard for the target.
14152           If there is no standard convention, GCC defaults to
14153           -fpcc-struct-return, except on targets where GCC is the principal
14154           compiler.  In those cases, we can choose the standard, and we chose
14155           the more efficient register return alternative.
14156
14157           Warning: code compiled with the -freg-struct-return switch is not
14158           binary compatible with code compiled with the -fpcc-struct-return
14159           switch.  Use it to conform to a non-default application binary
14160           interface.
14161
14162       -fshort-enums
14163           Allocate to an "enum" type only as many bytes as it needs for the
14164           declared range of possible values.  Specifically, the "enum" type
14165           will be equivalent to the smallest integer type which has enough
14166           room.
14167
14168           Warning: the -fshort-enums switch causes GCC to generate code that
14169           is not binary compatible with code generated without that switch.
14170           Use it to conform to a non-default application binary interface.
14171
14172       -fshort-double
14173           Use the same size for "double" as for "float".
14174
14175           Warning: the -fshort-double switch causes GCC to generate code that
14176           is not binary compatible with code generated without that switch.
14177           Use it to conform to a non-default application binary interface.
14178
14179       -fshort-wchar
14180           Override the underlying type for wchar_t to be short unsigned int
14181           instead of the default for the target.  This option is useful for
14182           building programs to run under WINE.
14183
14184           Warning: the -fshort-wchar switch causes GCC to generate code that
14185           is not binary compatible with code generated without that switch.
14186           Use it to conform to a non-default application binary interface.
14187
14188       -fno-common
14189           In C code, controls the placement of uninitialized global
14190           variables.  Unix C compilers have traditionally permitted multiple
14191           definitions of such variables in different compilation units by
14192           placing the variables in a common block.  This is the behavior
14193           specified by -fcommon, and is the default for GCC on most targets.
14194           On the other hand, this behavior is not required by ISO C, and on
14195           some targets may carry a speed or code size penalty on variable
14196           references.  The -fno-common option specifies that the compiler
14197           should place uninitialized global variables in the data section of
14198           the object file, rather than generating them as common blocks.
14199           This has the effect that if the same variable is declared (without
14200           "extern") in two different compilations, you will get a multiple-
14201           definition error when you link them.  In this case, you must
14202           compile with -fcommon instead.  Compiling with -fno-common is
14203           useful on targets for which it provides better performance, or if
14204           you wish to verify that the program will work on other systems
14205           which always treat uninitialized variable declarations this way.
14206
14207       -fno-ident
14208           Ignore the #ident directive.
14209
14210       -finhibit-size-directive
14211           Don't output a ".size" assembler directive, or anything else that
14212           would cause trouble if the function is split in the middle, and the
14213           two halves are placed at locations far apart in memory.  This
14214           option is used when compiling crtstuff.c; you should not need to
14215           use it for anything else.
14216
14217       -fverbose-asm
14218           Put extra commentary information in the generated assembly code to
14219           make it more readable.  This option is generally only of use to
14220           those who actually need to read the generated assembly code
14221           (perhaps while debugging the compiler itself).
14222
14223           -fno-verbose-asm, the default, causes the extra information to be
14224           omitted and is useful when comparing two assembler files.
14225
14226       -frecord-gcc-switches
14227           This switch causes the command line that was used to invoke the
14228           compiler to be recorded into the object file that is being created.
14229           This switch is only implemented on some targets and the exact
14230           format of the recording is target and binary file format dependent,
14231           but it usually takes the form of a section containing ASCII text.
14232           This switch is related to the -fverbose-asm switch, but that switch
14233           only records information in the assembler output file as comments,
14234           so it never reaches the object file.
14235
14236       -fpic
14237           Generate position-independent code (PIC) suitable for use in a
14238           shared library, if supported for the target machine.  Such code
14239           accesses all constant addresses through a global offset table
14240           (GOT).  The dynamic loader resolves the GOT entries when the
14241           program starts (the dynamic loader is not part of GCC; it is part
14242           of the operating system).  If the GOT size for the linked
14243           executable exceeds a machine-specific maximum size, you get an
14244           error message from the linker indicating that -fpic does not work;
14245           in that case, recompile with -fPIC instead.  (These maximums are 8k
14246           on the SPARC and 32k on the m68k and RS/6000.  The 386 has no such
14247           limit.)
14248
14249           Position-independent code requires special support, and therefore
14250           works only on certain machines.  For the 386, GCC supports PIC for
14251           System V but not for the Sun 386i.  Code generated for the IBM
14252           RS/6000 is always position-independent.
14253
14254           When this flag is set, the macros "__pic__" and "__PIC__" are
14255           defined to 1.
14256
14257       -fPIC
14258           If supported for the target machine, emit position-independent
14259           code, suitable for dynamic linking and avoiding any limit on the
14260           size of the global offset table.  This option makes a difference on
14261           the m68k, PowerPC and SPARC.
14262
14263           Position-independent code requires special support, and therefore
14264           works only on certain machines.
14265
14266           When this flag is set, the macros "__pic__" and "__PIC__" are
14267           defined to 2.
14268
14269       -fpie
14270       -fPIE
14271           These options are similar to -fpic and -fPIC, but generated
14272           position independent code can be only linked into executables.
14273           Usually these options are used when -pie GCC option will be used
14274           during linking.
14275
14276           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".
14277           The macros have the value 1 for -fpie and 2 for -fPIE.
14278
14279       -fno-jump-tables
14280           Do not use jump tables for switch statements even where it would be
14281           more efficient than other code generation strategies.  This option
14282           is of use in conjunction with -fpic or -fPIC for building code
14283           which forms part of a dynamic linker and cannot reference the
14284           address of a jump table.  On some targets, jump tables do not
14285           require a GOT and this option is not needed.
14286
14287       -ffixed-reg
14288           Treat the register named reg as a fixed register; generated code
14289           should never refer to it (except perhaps as a stack pointer, frame
14290           pointer or in some other fixed role).
14291
14292           reg must be the name of a register.  The register names accepted
14293           are machine-specific and are defined in the "REGISTER_NAMES" macro
14294           in the machine description macro file.
14295
14296           This flag does not have a negative form, because it specifies a
14297           three-way choice.
14298
14299       -fcall-used-reg
14300           Treat the register named reg as an allocable register that is
14301           clobbered by function calls.  It may be allocated for temporaries
14302           or variables that do not live across a call.  Functions compiled
14303           this way will not save and restore the register reg.
14304
14305           It is an error to used this flag with the frame pointer or stack
14306           pointer.  Use of this flag for other registers that have fixed
14307           pervasive roles in the machine's execution model will produce
14308           disastrous results.
14309
14310           This flag does not have a negative form, because it specifies a
14311           three-way choice.
14312
14313       -fcall-saved-reg
14314           Treat the register named reg as an allocable register saved by
14315           functions.  It may be allocated even for temporaries or variables
14316           that live across a call.  Functions compiled this way will save and
14317           restore the register reg if they use it.
14318
14319           It is an error to used this flag with the frame pointer or stack
14320           pointer.  Use of this flag for other registers that have fixed
14321           pervasive roles in the machine's execution model will produce
14322           disastrous results.
14323
14324           A different sort of disaster will result from the use of this flag
14325           for a register in which function values may be returned.
14326
14327           This flag does not have a negative form, because it specifies a
14328           three-way choice.
14329
14330       -fpack-struct[=n]
14331           Without a value specified, pack all structure members together
14332           without holes.  When a value is specified (which must be a small
14333           power of two), pack structure members according to this value,
14334           representing the maximum alignment (that is, objects with default
14335           alignment requirements larger than this will be output potentially
14336           unaligned at the next fitting location.
14337
14338           Warning: the -fpack-struct switch causes GCC to generate code that
14339           is not binary compatible with code generated without that switch.
14340           Additionally, it makes the code suboptimal.  Use it to conform to a
14341           non-default application binary interface.
14342
14343       -finstrument-functions
14344           Generate instrumentation calls for entry and exit to functions.
14345           Just after function entry and just before function exit, the
14346           following profiling functions will be called with the address of
14347           the current function and its call site.  (On some platforms,
14348           "__builtin_return_address" does not work beyond the current
14349           function, so the call site information may not be available to the
14350           profiling functions otherwise.)
14351
14352                   void __cyg_profile_func_enter (void *this_fn,
14353                                                  void *call_site);
14354                   void __cyg_profile_func_exit  (void *this_fn,
14355                                                  void *call_site);
14356
14357           The first argument is the address of the start of the current
14358           function, which may be looked up exactly in the symbol table.
14359
14360           This instrumentation is also done for functions expanded inline in
14361           other functions.  The profiling calls will indicate where,
14362           conceptually, the inline function is entered and exited.  This
14363           means that addressable versions of such functions must be
14364           available.  If all your uses of a function are expanded inline,
14365           this may mean an additional expansion of code size.  If you use
14366           extern inline in your C code, an addressable version of such
14367           functions must be provided.  (This is normally the case anyways,
14368           but if you get lucky and the optimizer always expands the functions
14369           inline, you might have gotten away without providing static
14370           copies.)
14371
14372           A function may be given the attribute "no_instrument_function", in
14373           which case this instrumentation will not be done.  This can be
14374           used, for example, for the profiling functions listed above, high-
14375           priority interrupt routines, and any functions from which the
14376           profiling functions cannot safely be called (perhaps signal
14377           handlers, if the profiling routines generate output or allocate
14378           memory).
14379
14380       -finstrument-functions-exclude-file-list=file,file,...
14381           Set the list of functions that are excluded from instrumentation
14382           (see the description of "-finstrument-functions").  If the file
14383           that contains a function definition matches with one of file, then
14384           that function is not instrumented.  The match is done on
14385           substrings: if the file parameter is a substring of the file name,
14386           it is considered to be a match.
14387
14388           For example,
14389           "-finstrument-functions-exclude-file-list=/bits/stl,include/sys"
14390           will exclude any inline function defined in files whose pathnames
14391           contain "/bits/stl" or "include/sys".
14392
14393           If, for some reason, you want to include letter ',' in one of sym,
14394           write ','. For example,
14395           "-finstrument-functions-exclude-file-list=',,tmp'" (note the single
14396           quote surrounding the option).
14397
14398       -finstrument-functions-exclude-function-list=sym,sym,...
14399           This is similar to "-finstrument-functions-exclude-file-list", but
14400           this option sets the list of function names to be excluded from
14401           instrumentation.  The function name to be matched is its user-
14402           visible name, such as "vector<int> blah(const vector<int> &)", not
14403           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The
14404           match is done on substrings: if the sym parameter is a substring of
14405           the function name, it is considered to be a match.  For C99 and C++
14406           extended identifiers, the function name must be given in UTF-8, not
14407           using universal character names.
14408
14409       -fstack-check
14410           Generate code to verify that you do not go beyond the boundary of
14411           the stack.  You should specify this flag if you are running in an
14412           environment with multiple threads, but only rarely need to specify
14413           it in a single-threaded environment since stack overflow is
14414           automatically detected on nearly all systems if there is only one
14415           stack.
14416
14417           Note that this switch does not actually cause checking to be done;
14418           the operating system or the language runtime must do that.  The
14419           switch causes generation of code to ensure that they see the stack
14420           being extended.
14421
14422           You can additionally specify a string parameter: "no" means no
14423           checking, "generic" means force the use of old-style checking,
14424           "specific" means use the best checking method and is equivalent to
14425           bare -fstack-check.
14426
14427           Old-style checking is a generic mechanism that requires no specific
14428           target support in the compiler but comes with the following
14429           drawbacks:
14430
14431           1.  Modified allocation strategy for large objects: they will
14432               always be allocated dynamically if their size exceeds a fixed
14433               threshold.
14434
14435           2.  Fixed limit on the size of the static frame of functions: when
14436               it is topped by a particular function, stack checking is not
14437               reliable and a warning is issued by the compiler.
14438
14439           3.  Inefficiency: because of both the modified allocation strategy
14440               and the generic implementation, the performances of the code
14441               are hampered.
14442
14443           Note that old-style stack checking is also the fallback method for
14444           "specific" if no target support has been added in the compiler.
14445
14446       -fstack-limit-register=reg
14447       -fstack-limit-symbol=sym
14448       -fno-stack-limit
14449           Generate code to ensure that the stack does not grow beyond a
14450           certain value, either the value of a register or the address of a
14451           symbol.  If the stack would grow beyond the value, a signal is
14452           raised.  For most targets, the signal is raised before the stack
14453           overruns the boundary, so it is possible to catch the signal
14454           without taking special precautions.
14455
14456           For instance, if the stack starts at absolute address 0x80000000
14457           and grows downwards, you can use the flags
14458           -fstack-limit-symbol=__stack_limit and
14459           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of
14460           128KB.  Note that this may only work with the GNU linker.
14461
14462       -fargument-alias
14463       -fargument-noalias
14464       -fargument-noalias-global
14465       -fargument-noalias-anything
14466           Specify the possible relationships among parameters and between
14467           parameters and global data.
14468
14469           -fargument-alias specifies that arguments (parameters) may alias
14470           each other and may alias global storage.-fargument-noalias
14471           specifies that arguments do not alias each other, but may alias
14472           global storage.-fargument-noalias-global specifies that arguments
14473           do not alias each other and do not alias global storage.
14474           -fargument-noalias-anything specifies that arguments do not alias
14475           any other storage.
14476
14477           Each language will automatically use whatever option is required by
14478           the language standard.  You should not need to use these options
14479           yourself.
14480
14481       -fleading-underscore
14482           This option and its counterpart, -fno-leading-underscore, forcibly
14483           change the way C symbols are represented in the object file.  One
14484           use is to help link with legacy assembly code.
14485
14486           Warning: the -fleading-underscore switch causes GCC to generate
14487           code that is not binary compatible with code generated without that
14488           switch.  Use it to conform to a non-default application binary
14489           interface.  Not all targets provide complete support for this
14490           switch.
14491
14492       -ftls-model=model
14493           Alter the thread-local storage model to be used.  The model
14494           argument should be one of "global-dynamic", "local-dynamic",
14495           "initial-exec" or "local-exec".
14496
14497           The default without -fpic is "initial-exec"; with -fpic the default
14498           is "global-dynamic".
14499
14500       -fvisibility=default|internal|hidden|protected
14501           Set the default ELF image symbol visibility to the specified
14502           option---all symbols will be marked with this unless overridden
14503           within the code.  Using this feature can very substantially improve
14504           linking and load times of shared object libraries, produce more
14505           optimized code, provide near-perfect API export and prevent symbol
14506           clashes.  It is strongly recommended that you use this in any
14507           shared objects you distribute.
14508
14509           Despite the nomenclature, "default" always means public ie;
14510           available to be linked against from outside the shared object.
14511           "protected" and "internal" are pretty useless in real-world usage
14512           so the only other commonly used option will be "hidden".  The
14513           default if -fvisibility isn't specified is "default", i.e., make
14514           every symbol public---this causes the same behavior as previous
14515           versions of GCC.
14516
14517           A good explanation of the benefits offered by ensuring ELF symbols
14518           have the correct visibility is given by "How To Write Shared
14519           Libraries" by Ulrich Drepper (which can be found at
14520           <http://people.redhat.com/~drepper/>)---however a superior solution
14521           made possible by this option to marking things hidden when the
14522           default is public is to make the default hidden and mark things
14523           public.  This is the norm with DLL's on Windows and with
14524           -fvisibility=hidden and "__attribute__ ((visibility("default")))"
14525           instead of "__declspec(dllexport)" you get almost identical
14526           semantics with identical syntax.  This is a great boon to those
14527           working with cross-platform projects.
14528
14529           For those adding visibility support to existing code, you may find
14530           #pragma GCC visibility of use.  This works by you enclosing the
14531           declarations you wish to set visibility for with (for example)
14532           #pragma GCC visibility push(hidden) and #pragma GCC visibility pop.
14533           Bear in mind that symbol visibility should be viewed as part of the
14534           API interface contract and thus all new code should always specify
14535           visibility when it is not the default ie; declarations only for use
14536           within the local DSO should always be marked explicitly as hidden
14537           as so to avoid PLT indirection overheads---making this abundantly
14538           clear also aids readability and self-documentation of the code.
14539           Note that due to ISO C++ specification requirements, operator new
14540           and operator delete must always be of default visibility.
14541
14542           Be aware that headers from outside your project, in particular
14543           system headers and headers from any other library you use, may not
14544           be expecting to be compiled with visibility other than the default.
14545           You may need to explicitly say #pragma GCC visibility push(default)
14546           before including any such headers.
14547
14548           extern declarations are not affected by -fvisibility, so a lot of
14549           code can be recompiled with -fvisibility=hidden with no
14550           modifications.  However, this means that calls to extern functions
14551           with no explicit visibility will use the PLT, so it is more
14552           effective to use __attribute ((visibility)) and/or #pragma GCC
14553           visibility to tell the compiler which extern declarations should be
14554           treated as hidden.
14555
14556           Note that -fvisibility does affect C++ vague linkage entities. This
14557           means that, for instance, an exception class that will be thrown
14558           between DSOs must be explicitly marked with default visibility so
14559           that the type_info nodes will be unified between the DSOs.
14560
14561           An overview of these techniques, their benefits and how to use them
14562           is at <http://gcc.gnu.org/wiki/Visibility>.
14563

ENVIRONMENT

14565       This section describes several environment variables that affect how
14566       GCC operates.  Some of them work by specifying directories or prefixes
14567       to use when searching for various kinds of files.  Some are used to
14568       specify other aspects of the compilation environment.
14569
14570       Note that you can also specify places to search using options such as
14571       -B, -I and -L.  These take precedence over places specified using
14572       environment variables, which in turn take precedence over those
14573       specified by the configuration of GCC.
14574
14575       LANG
14576       LC_CTYPE
14577       LC_MESSAGES
14578       LC_ALL
14579           These environment variables control the way that GCC uses
14580           localization information that allow GCC to work with different
14581           national conventions.  GCC inspects the locale categories LC_CTYPE
14582           and LC_MESSAGES if it has been configured to do so.  These locale
14583           categories can be set to any value supported by your installation.
14584           A typical value is en_GB.UTF-8 for English in the United Kingdom
14585           encoded in UTF-8.
14586
14587           The LC_CTYPE environment variable specifies character
14588           classification.  GCC uses it to determine the character boundaries
14589           in a string; this is needed for some multibyte encodings that
14590           contain quote and escape characters that would otherwise be
14591           interpreted as a string end or escape.
14592
14593           The LC_MESSAGES environment variable specifies the language to use
14594           in diagnostic messages.
14595
14596           If the LC_ALL environment variable is set, it overrides the value
14597           of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES
14598           default to the value of the LANG environment variable.  If none of
14599           these variables are set, GCC defaults to traditional C English
14600           behavior.
14601
14602       TMPDIR
14603           If TMPDIR is set, it specifies the directory to use for temporary
14604           files.  GCC uses temporary files to hold the output of one stage of
14605           compilation which is to be used as input to the next stage: for
14606           example, the output of the preprocessor, which is the input to the
14607           compiler proper.
14608
14609       GCC_EXEC_PREFIX
14610           If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the
14611           names of the subprograms executed by the compiler.  No slash is
14612           added when this prefix is combined with the name of a subprogram,
14613           but you can specify a prefix that ends with a slash if you wish.
14614
14615           If GCC_EXEC_PREFIX is not set, GCC will attempt to figure out an
14616           appropriate prefix to use based on the pathname it was invoked
14617           with.
14618
14619           If GCC cannot find the subprogram using the specified prefix, it
14620           tries looking in the usual places for the subprogram.
14621
14622           The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where
14623           prefix is the prefix to the installed compiler. In many cases
14624           prefix is the value of "prefix" when you ran the configure script.
14625
14626           Other prefixes specified with -B take precedence over this prefix.
14627
14628           This prefix is also used for finding files such as crt0.o that are
14629           used for linking.
14630
14631           In addition, the prefix is used in an unusual way in finding the
14632           directories to search for header files.  For each of the standard
14633           directories whose name normally begins with /usr/local/lib/gcc
14634           (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries
14635           replacing that beginning with the specified prefix to produce an
14636           alternate directory name.  Thus, with -Bfoo/, GCC will search
14637           foo/bar where it would normally search /usr/local/lib/bar.  These
14638           alternate directories are searched first; the standard directories
14639           come next. If a standard directory begins with the configured
14640           prefix then the value of prefix is replaced by GCC_EXEC_PREFIX when
14641           looking for header files.
14642
14643       COMPILER_PATH
14644           The value of COMPILER_PATH is a colon-separated list of
14645           directories, much like PATH.  GCC tries the directories thus
14646           specified when searching for subprograms, if it can't find the
14647           subprograms using GCC_EXEC_PREFIX.
14648
14649       LIBRARY_PATH
14650           The value of LIBRARY_PATH is a colon-separated list of directories,
14651           much like PATH.  When configured as a native compiler, GCC tries
14652           the directories thus specified when searching for special linker
14653           files, if it can't find them using GCC_EXEC_PREFIX.  Linking using
14654           GCC also uses these directories when searching for ordinary
14655           libraries for the -l option (but directories specified with -L come
14656           first).
14657
14658       LANG
14659           This variable is used to pass locale information to the compiler.
14660           One way in which this information is used is to determine the
14661           character set to be used when character literals, string literals
14662           and comments are parsed in C and C++.  When the compiler is
14663           configured to allow multibyte characters, the following values for
14664           LANG are recognized:
14665
14666           C-JIS
14667               Recognize JIS characters.
14668
14669           C-SJIS
14670               Recognize SJIS characters.
14671
14672           C-EUCJP
14673               Recognize EUCJP characters.
14674
14675           If LANG is not defined, or if it has some other value, then the
14676           compiler will use mblen and mbtowc as defined by the default locale
14677           to recognize and translate multibyte characters.
14678
14679       Some additional environments variables affect the behavior of the
14680       preprocessor.
14681
14682       CPATH
14683       C_INCLUDE_PATH
14684       CPLUS_INCLUDE_PATH
14685       OBJC_INCLUDE_PATH
14686           Each variable's value is a list of directories separated by a
14687           special character, much like PATH, in which to look for header
14688           files.  The special character, "PATH_SEPARATOR", is target-
14689           dependent and determined at GCC build time.  For Microsoft Windows-
14690           based targets it is a semicolon, and for almost all other targets
14691           it is a colon.
14692
14693           CPATH specifies a list of directories to be searched as if
14694           specified with -I, but after any paths given with -I options on the
14695           command line.  This environment variable is used regardless of
14696           which language is being preprocessed.
14697
14698           The remaining environment variables apply only when preprocessing
14699           the particular language indicated.  Each specifies a list of
14700           directories to be searched as if specified with -isystem, but after
14701           any paths given with -isystem options on the command line.
14702
14703           In all these variables, an empty element instructs the compiler to
14704           search its current working directory.  Empty elements can appear at
14705           the beginning or end of a path.  For instance, if the value of
14706           CPATH is ":/special/include", that has the same effect as
14707           -I. -I/special/include.
14708
14709       DEPENDENCIES_OUTPUT
14710           If this variable is set, its value specifies how to output
14711           dependencies for Make based on the non-system header files
14712           processed by the compiler.  System header files are ignored in the
14713           dependency output.
14714
14715           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
14716           case the Make rules are written to that file, guessing the target
14717           name from the source file name.  Or the value can have the form
14718           file target, in which case the rules are written to file file using
14719           target as the target name.
14720
14721           In other words, this environment variable is equivalent to
14722           combining the options -MM and -MF, with an optional -MT switch too.
14723
14724       SUNPRO_DEPENDENCIES
14725           This variable is the same as DEPENDENCIES_OUTPUT (see above),
14726           except that system header files are not ignored, so it implies -M
14727           rather than -MM.  However, the dependence on the main input file is
14728           omitted.
14729

BUGS

14731       For instructions on reporting bugs, see
14732       <http://bugzilla.redhat.com/bugzilla>.
14733

FOOTNOTES

14735       1.  On some systems, gcc -shared needs to build supplementary stub code
14736           for constructors to work.  On multi-libbed systems, gcc -shared
14737           must select the correct support libraries to link against.  Failing
14738           to supply the correct flags may lead to subtle defects.  Supplying
14739           them in cases where they are not necessary is innocuous.
14740

SEE ALSO

14742       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1),
14743       adb(1), dbx(1), sdb(1) and the Info entries for gcc, cpp, as, ld,
14744       binutils and gdb.
14745

AUTHOR

14747       See the Info entry for gcc, or
14748       <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors
14749       to GCC.
14750
14752       Copyright (c) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14753       1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
14754       Free Software Foundation, Inc.
14755
14756       Permission is granted to copy, distribute and/or modify this document
14757       under the terms of the GNU Free Documentation License, Version 1.2 or
14758       any later version published by the Free Software Foundation; with the
14759       Invariant Sections being "GNU General Public License" and "Funding Free
14760       Software", the Front-Cover texts being (a) (see below), and with the
14761       Back-Cover Texts being (b) (see below).  A copy of the license is
14762       included in the gfdl(7) man page.
14763
14764       (a) The FSF's Front-Cover Text is:
14765
14766            A GNU Manual
14767
14768       (b) The FSF's Back-Cover Text is:
14769
14770            You have freedom to copy and modify this GNU Manual, like GNU
14771            software.  Copies published by the Free Software Foundation raise
14772            funds for GNU development.
14773
14774
14775
14776gcc-4.5.0                         2010-05-13                            GCC(1)
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