https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81616
Martin Jambor <jamborm at gcc dot gnu.org> changed:
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CC| |jamborm at gcc dot gnu.org
--- Comment #38 from Martin Jambor <jamborm at gcc dot gnu.org> ---
Created attachment 42872
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42872&action=edit
Untested fix for harmful FMAs
(In reply to Jan Hubicka from comment #25)
> Hi, I agree that the matric multiplication fma issue is
> important and hopefully it will be fixed for GCC 8. See
> https://gcc.gnu.org/ml/gcc-patches/2017-11/msg00437.html
I am testing the attached patch to address the FMA generation. I plan
to submit it to the mailing list this week if everything goes fine but
I would be very grateful for any comments or additional
testing/benchmarking.
The patch brings the run-time of the matrix.c testcase with native
znver1 tuning down to the levels seen with generic tuning, without it
I see 60% regressions at both -O2 and -O3. (Even with the patch,
using -mprefer-vector-width=256 can still do quite a bit better but at
least the difference is now 20% and not 100%).
