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Re: C Compiler benchmark: gcc 4.6.3 vs. Intel v11 and others

On 1/19/2012 9:24 PM, wrote:
On 1/18/2012 10:37 PM, Marc Glisse wrote:
On Wed, 18 Jan 2012, wrote:

For those who might be interested, I've recently benchmarked gcc
4.6.3 (and 3.4.2) vs. Intel v11 and Microsoft (in Windows 7) here:

For the math functions, this is normally more a libc feature, so you
might get very different results on different OS. Then again, by using
-ffast-math, you allow the math functions to return any random value,
so I can think of ways to make it even faster ;-)

I use -ffast-math all the time and have always gotten virtually
identical results to when I turn it off. The speed difference is
important for me.
The default for the Intel compiler is more aggressive than gcc -ffast-math -fno-cx-limited-range, as long as you don't use one of the old buggy mathinline.h header files. For a fair comparison, you need detailed attention to comparable options. If you don't set gcc -ffast-math, you will want icc -fp-model-source.
It's good to have in mind what you want from the more aggressive options, e.g. auto-vectorization of sum reduction.
If you do want gcc -fcx-limited range, icc spells it -complex-limited-range.

Tim Prince

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