On 16/10/13 10:37, pins...@gmail.com wrote:
On Oct 15, 2013, at 6:58 AM, Igor Zamyatin <izamya...@gmail.com> wrote:
Hi All!
Is there any particular reason that matmul* modules from libgfortran
are compiled with -O2 -ftree-vectorize?
I see some regressions on Atom processor after r202980
(http://gcc.gnu.org/ml/gcc-cvs/2013-09/msg00846.html)
Why not just use O3 for those modules?
-O3 and -O2 -ftree-vectorize won't give much performance difference. What you
are seeing is the cost model needs improvement; at least for atom.
Hi all,
I think http://gcc.gnu.org/ml/gcc-patches/2013-09/msg01908.html introduced the
new "cheap" vectoriser cost model that favors compilation time over runtime
performance and is set as default for -O2. -O3 uses the "dynamic" model which
potentially gives better runtime performance in exchange for longer compile
times (if I understand the new rules correctly).
Therefore, I'd expect -O3 to give a better vector performance than -O2...
Kyrill
