RE: Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM

[Bingfeng Mei <bmei at broadcom dot com>]

Thanks for nice benchmarks. Vladimir.

Why is GCC code size so much bigger than LLVM? Does -Ofast have more unrolling
on GCC? It doesn't seem increasing code size help performance (164.gzip & 197.parser)
Is there comparisons for O2? I guess that is more useful for typical
mobile/embedded programmers.

Bingfeng

> -----Original Message-----
> From: gcc-owner@gcc.gnu.org [mailto:gcc-owner@gcc.gnu.org] On Behalf Of
> Vladimir Makarov
> Sent: 24 June 2014 16:07
> To: Ramana Radhakrishnan; gcc.gcc.gnu.org
> Subject: Re: Comparison of GCC-4.9 and LLVM-3.4 performance on
> SPECInt2000 for x86-64 and ARM
> 
> On 06/24/2014 10:57 AM, Ramana Radhakrishnan wrote:
> >
> > The ball-park number you have probably won't change much.
> >
> >>>
> >> Unfortunately, that is the configuration I can use on my system
> because
> >> of lack of libraries for other configurations.
> >
> > Using --with-fpu={neon / neon-vfpv4} shouldn't cause you ABI issues
> > with libraries for any other configurations. neon / neon-vfpv4 enable
> > use of the neon unit in a manner that is ABI compatible with the rest
> > of the system.
> >
> > For more on command line options for AArch32 and how they map to
> > various CPU's you might find this blog interesting.
> >
> > http://community.arm.com/groups/tools/blog/2013/04/15/arm-cortex-a-
> processors-and-gcc-command-lines
> >
> >
> >>
> >> I don't think Neon can improve score for SPECInt2000 significantly
> but
> >> may be I am wrong.
> >
> > It won't probably improve the overall score by a large amount but some
> > individual benchmarks will get some help.
> >
> There are some few benchmarks which benefit from autovectorization (eon
> particularly).
> >>> Did you add any other architecture specific options to your SPEC2k
> >>> runs ?
> >>>
> >>>
> >> No.  The only options I used are -Ofast.
> >>
> >> Could you recommend me what best options you think I should use for
> this
> >> processor.
> >>
> >
> > I would personally use --with-cpu=cortex-a15 --with-fpu=neon-vfpv4
> > --with-float=hard on this processor as that maps with the processor
> > available on that particular piece of Silicon.
> Thanks, Ramana.  Next time, I'll try these options.
> >
> > Also given it's a big LITTLE system with probably kernel switching -
> > it may be better to also make sure that you are always running on the
> > big core.
> >
> The results are pretty stable.  Also this version of Fedora does not
> implement switching from Big to Little processors.