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


On Wed, Jun 25, 2014 at 5:26 PM, Bingfeng Mei <bmei@broadcom.com> wrote:
> Thanks for nice benchmarks. Vladimir.
>
> Why is GCC code size so much bigger than LLVM? Does -Ofast have more unrolling
On the contrary, I don't think rtl unrolling is enabled by default on
GCC with level O3/Ofast. There is no unroll dump file at all unless
-funroll-loops/-funroll-all-loops is explicitly specified.

Thanks,
bin

> 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.
>


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