http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53967
--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-07-16 14:56:59 UTC --- (In reply to comment #8) > I used -march=native in this case. It is interesting that this enabled AVX > (this particular CPU does support it). > > To be clear, the problem also occurs with > > -m64 -mtune=generic -march=x86-64 -mfpmath=sse > > vs > > -m64 -mtune=generic -march=x86-64 -mfpmath=387 > > and is also observed on a 5-year old Opteron. > > With GCC 4.7.1, and for a specific application benchmark case and with generic > architecture and tuning, -mfpmath=387 produces 0.133 iter/s and -mfpmath=sse > produces 0.047 iter/s. A different (non-GCC) compiler on the same system > produces 0.155 iter/s. > > In the course of testing, I have indeed tried -march=corei7 and it did not > provide an improvement. What kind of optimization options are you using? -O3? Or are you really using -O0 (aka nothing)?
