http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53967
--- Comment #8 from bfriesen at simple dot dallas.tx.us 2012-07-16 14:16:46 UTC --- 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.
