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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53967

--- Comment #8 from bfriesen at simple dot dallas.tx.us 2012-07-16 14:16:46 UTC ---
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.


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