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Re: GCC-4.5.0 comparison with previous releases and LLVM-2.7 on SPEC2000 for x86/x86_64


On Thu, Apr 29, 2010 at 9:25 AM, Vladimir Makarov <vmakarov@redhat.com> wrote:
> ?GCC-4.5.0 and LLVM-2.7 were released recently. ?To understand
> where we stand after releasing GCC-4.5.0 I benchmarked it on SPEC2000
> for x86/x86-64 and posted the comparison of it with the
> previous GCC releases and LLVM-2.7.
>
> ?Even benchmarking SPEC2000 takes a lot of time on the fastest
> machine I have. So I don't plan to use SPEC2006 for this in near
> future.
>
> ?You can find the comparison on
> http://vmakarov.fedorapeople.org/spec/ (please just click links at the
> bottom of the left frame starting with link "GCC release comparison").
>
> ?If you need exact numbers, please use the tables (the links to them
> are also given) which were used to generate the corresponding bar
> graphs.
>
>
> ?In general GCC-4.5.0 became faster (upto 10%) in -O2 mode. ?This is
> first considerable compilation speed improvement since GCC-4.2.
> GCC-4.5.0 generates a better (1-2% in average upto 4% for x86-64
> SPECFP2000 in -O2 mode) code too in comparison with the previous
> release. ?That is not including LTO and Graphite which can gives even
> more (especially LTO) in many cases.
>
> ?GCC-4.5.0 has new big optimizations LTO and Graphite (more
> accurately graphite was introduced in the previous release).
> Therefore I ran additional benchmarks to test them.
>
> ?LTO is a promising technology especially for integer benchmarks for
> which it results in smaller and faster code. ?But it might result in
> degradations too on SPECFP2000 mainly because of big degradations on a
> few benchmarks like wupwise or facerec. ?Another annoying thing about
> LTO, it considerably slows down the compiler.


The LTO improvement on spec2000int is is only 1.86%

                4.5     4.5+lto Improvement
164.gzip        955     950     -0.52%       <-- degrade
175.vpr         588     594     1.02%
176.gcc         1211    1216    0.41%
181.mcf         699     698     -0.14%
186.crafty      1011    987     -2.37%    <--- degrade
197.parser      792     813     2.65%
252.eon         1026    1023    -0.29%   <-- degrade
253.perlbmk     1312    1294    -1.37%  <-- degrade
254.gap         1021    1037    1.57%
255.vortex      1123    1319    17.45%
256.bzip2       737     768     4.21%
300.twolf       773     779     0.78%
-----------------------------------------------------
SPECint2000     913     930     1.86%


This matches our previous observation that to bring the best out of
LTO, FDO is also needed. (As a reference, LIPO improves over plain FDO
by ~4.5%, vortex improves 23%).  You will probably see even smaller
improvement in SPEC2006.

It would be great if there is number collected comparing LTO + FDO vs
plain FDO in the same setup.

Thanks,

David




>
> ?Currently Graphite gives small improvements on x86 (one exception is
> 2% for peak x86 SPECFP2000) and mostly degradation on x86_64 (with
> maximum one more than 10% for SPECFP2000 because of big degradations
> on mgrid and swim). ?So further work is needed on the project because
> it seems not mature yet.
>
> ?As for LLVM, LLVM became slower (e.g. in comparison with llvm-2.5 on
> 15%-50% for x86-64). ?So the gap between compilation speed of GCC and
> LLVM decreased and sometimes achieves 4% on x86_64 and 8% on x86 (both
> for SPECInt2000 in -O2 mode). ?May be I am wrong but I don't think
> CLANG will improve this situation significantly (in -O2 and -O3 mode)
> because optimizations still take most of time of any serious
> optimizing compiler.
>
> ?LLVM did a progress in code performance especially for floating
> point benchmarks. ?But the gap between LLVM-2.7 and GCC-4.5 in peak
> performance (not including GCC LTO and Graphite) still 6-7% on
> SPECInt200 and 13-17% on SPECFP2000.
>
> ?In general, IMHO GCC-4.5.0 is a good and promising release.
>
>


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