[Bug target/53967] GCC produces slow code for convolution algorithm with -mfpmath=sse (the AMD_64 default)

[rguenth at gcc dot gnu.org]

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)?