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Re: [BENCHMARK]-mfpmath=sse should disable x387 intrinsics


[Sorry, sent this to the wrong list]

Roger Sayle wrote:

Could you present the performance results for your testcase with
"-mfpmath=387", "-mfpmath=sse" and "-mfpmath=sse,387"?  It's relatively
rare for "-mfpmath=sse" to be a win on a Pentium4 benchmark, and to quote
Robert Scott Ladd from his Coyote Gulch benchmarking:

From http://www.coyotegulch.com/products/acovea/acovea_4.html
Much to my surprise, I have yet to find any consistent evidence that
options like -mfpmath=sse improve program performance. Thus Acovea
bears out my personal experience, though it does not explain why so
many people continue to suggest that I should use -mfpmath=sse to
generate floating-point code. If someone could suggest a good
"-mfpmath=sse", I'd appreciate seeing it.

I have a real-world C++ code which gets a 10% performance gain on a P4 when compiled with -mfpmath=sse (using the mainline compiler of 20041125). Its critical inner loop consists of multiplications, additions and subtractions only. Hopefully this code will be open-sourced soon; as soon as that happens, I could contribute it as a floating-point benchmark.

Cheers,
  Martin


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