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

[Tim Prince <n8tm at aol dot com>]

On 1/19/2012 9:24 PM, willus.com wrote:
> On 1/18/2012 10:37 PM, Marc Glisse wrote:
> > On Wed, 18 Jan 2012, willus.com 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:
> > >
> > > http://willus.com/ccomp_benchmark2.shtml
> >
> > http://en.wikipedia.org/wiki/Microsoft_Windows_SDK#64-bit_development
> >
> > 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