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[Bug target/53967] GCC produces slow code for convolution algorithm with -mfpmath=sse (the AMD_64 default)
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 16 Jul 2012 14:56:59 +0000
- Subject: [Bug target/53967] GCC produces slow code for convolution algorithm with -mfpmath=sse (the AMD_64 default)
- Auto-submitted: auto-generated
- References: <bug-53967-4@http.gcc.gnu.org/bugzilla/>
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)?