How to get GCC on par with ICC?

[Marc Glisse]

On Fri, 8 Jun 2018, Steve Ellcey wrote:

> On Thu, 2018-06-07 at 12:01 +0200, Richard Biener wrote:
>> Â 
>> When we do our own comparisons of GCC vs. ICC on benchmarks
>> like SPEC CPU 2006/2017 ICC doesn't have a big lead over GCC
>> (in fact it even trails in some benchmarks) unless you get to
>> "SPEC tricks" like data structure re-organization optimizations that
>> probably never apply in practice on real-world code (and people
>> should fix such things at the source level being pointed at them
>> via actually profiling their codes).
>
> Richard,
>
> I was wondering if you have any more details about these comparisions
> you have done that you can share? Â Compiler versions, options used,
> hardware, etc  Also, were there any tests that stood out in terms of
> icc outperforming GCC?
>
> I did a compare of SPEC 2017 rate using GCC 8.* (pre release) and
> a recent ICC (2018.0.128?) on my desktop (Xeon CPU E5-1650 v4).
> I used '-xHost -O3' for icc and '-march=native -mtune=native -O3'
> for gcc.

You should use -Ofast for gcc. As mentionned earlier in the discussion, 
ICC has some equivalent of -ffast-math by default.

> The int rate numbers (running 1 copy only) were not too bad, GCC was
> only about 2% slower and only 525.x264_r seemed way slower with GCC.
> The fp rate numbers (again only 1 copy) showed a larger difference, 
> around 20%.  521.wrf_r was more than twice as slow when compiled with
> GCC instead of ICC and 503.bwaves_r and 510.parest_r also showed
> significant slowdowns when compiled with GCC vs. ICC.

-- 
Marc Glisse