On Tue, Oct 15, 2013 at 4:58 PM, Igor Zamyatin <izamya...@gmail.com> wrote: > Hi All! > > Is there any particular reason that matmul* modules from libgfortran > are compiled with -O2 -ftree-vectorize?
Yes, testing showed that it improved performance compared to the default options. See the thread starting at http://gcc.gnu.org/ml/fortran/2005-11/msg00366.html In the almost 8 years (!!) since the patch was merged, I believe the importance of vectorization for utilizing current processors has only increased. [snip] > Why not just use O3 for those modules? Back when the change was made, -ftree-vectorize wasn't enabled by -O3. IIRC I did some tests, and -O3 didn't really improve things beyond what "-O2 -funroll-loops -ftree-vectorize" already did. That was a while ago however, so if somebody (*wink*) would care to redo the benchmarks things might look different with today's GCC on today's hardware. Hope this helps, -- Janne Blomqvist
