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RE: [RFC PATCH, x86_64] Use -mno-sse[,2] to fall back to x87 FP argument passing convention


> To respond to the issue of apples vs. oranges comparisons, I'll post
> the whetstone figures for a recent mainline GCC on current 
> 64-bit CPUs.

Thanks for the data.
> On a Core2 6600 @ 2.4GHz
> -O3 -ffast-math -mfpmath=387		2799 MWIPS
> -O3 -ffast-math -mfpmath=387,sse	2702 MWIPS
> -O3 -ffast-math                         2501 MWIPS
> On an Opteron 248 @ 2.21GHz
> -O3 -ffast-math -mfpmath=387		2578 MWIPS
> -O3 -ffast-math                         2213 MWIPS
> This shows that x87 math is 12-16% faster on 64-bit code on this
> particular benchmark.

It isn't clear yet whether the comparison is x87 vs. SSE or x87 microcode vs. poor GLIBC transcendentals...

> This is on RedHat 4.2 with glibc 2.3.4, so it's possible some
> performance may be lost via a poor libm implementation, but
> that's doubtful, and this OS configuration is "realistic".

I'd like to try it on SUSE 9.x...

Evandro Menezes               AMD            Austin, TX

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