On 6/1/12, Ian Lance Taylor <iant@xxxxxxxxxx> wrote: > ohav chochmah <philomath868@xxxxxxxxx> writes: > >> On 6/1/12, Ian Lance Taylor <iant@xxxxxxxxxx> wrote: >> >>> When optimizing on x86 or x86_64, -fomit-frame-pointer is the default >>> anyhow. -fomit-frame-pointer essentially implies >>> -momit-leaf-frame-pointer. >>> >> >> I was sure that's the answer, but then is GCC lying to me? >> ~ $ gcc -S tst.c -O2 -march=native -Q --help=optimizers | grep omit >> -fomit-frame-pointer [disabled] > > Basically, it's a bug. When you use the --help=optimizers option, GCC > doesn't actually compile the file. That means that it doesn't run > through the target specific code that causes -O2 to turn on > -fomit-frame-pointer. And that means that the display is invalid. > > Please file a bug report at http://gcc.gnu.org/bugzilla if there isn't > one open already. Thanks. > > >>> For x86_64 -mfpmath=sse is the default. >>> >> here again: >> ~ $ gcc -S tst.c -O2 -march=native -Q --help=target | grep 'mfpmath=' >> -mfpmath= 387 > > Same answer. The -mfpmath setting is done in target specific code that > is not run when using --help. > > >>>> why is msse disabled by default even after march=native, while >>>> msse[234], msse4.[12] and mssse3 are all enabled? >>> >>> Not sure--what makes you think this is the case? >>> >> sorry, 's/msse/mmmx/'. >> ~ $ gcc -S tst.c -O2 -march=native -Q --help=target | grep mmx >> -mmmx [disabled] >> >> ~ $ sudo x86info -a -v | grep -i mmx >> mmx MMX support >> >>>> isn't the CRC32 instruction part of sse4.2?, why is mcrc32 disabled by >>>> default even when sse4.2 is enabled? > > Same answer. Target specific code turns on -mmmx if -msse is on. > > Ian > thanks, done at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53554 . glad to contribute back something tiny... cheers.
