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

[Xinliang David Li]

This means O3 level inlining should be turned on also for lto build by
default -- as -O2 lto performance is too unimpressive.

David

On Mon, Nov 15, 2010 at 3:36 PM, Xinliang David Li <davidxl@google.com> wrote:
> Just measured: lto +O3 improves over O2 by a decent 4.8% geomean. More
> data come later.
>
>            164.gzip                1324                1322     -0.10%
>             175.vpr                1694                1703      0.51%
>             176.gcc                2293                2347      2.34%
>             181.mcf                1772                1797      1.43%
>          186.crafty                2320                2486      7.12%
>          197.parser                1166                1236      6.02%
>             252.eon                2443                2810     14.98%
>         253.perlbmk                2410                2407     -0.16%
>             254.gap                1987                2024      1.82%
>          255.vortex                2392                2826     18.13%
>           256.bzip2                1719                1760      2.38%
>           300.twolf                2288                2394      4.63%
>
>
> David
>
>
> On Mon, Nov 15, 2010 at 2:38 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>>> I did some measurement (64bit).
>>>
>>> Experiment 1:
>>>
>>> -O2 -funroll-loops vs -O2
>>>
>>> It improves performance (geomean) by 0.56%, not too much:
>>>                                          O2                 O2 unroll-loops
>>>             164.gzip                1324                1331      0.56%
>>>              175.vpr                1694                1605     -5.24%
>>>              176.gcc                2293                2350      2.47%
>>>              181.mcf                1772                1788      0.90%
>>>           186.crafty                2320                2326      0.26%
>>>           197.parser                1166                1162     -0.32%
>>>              252.eon                2443                2529      3.50%
>>>          253.perlbmk                2410                2460      2.07%
>>>              254.gap                1987                2019      1.58%
>>>           255.vortex                2392                2406      0.58%
>>>            256.bzip2                1719                1715     -0.25%
>>>            300.twolf                2288                2308      0.88%
>>
>> Can you also try -funroll-all-loops?  As for pretty small programs, like
>> spec2k, -funroll-all-loops is often win.  In just few loops we can work out
>> number of iterations.
>>
>>>
>>> Experiment 3:    O2 lto vs O2:    geomean 0.72%
>>>                                         O2                   O2 LTO
>>>            164.gzip                1324                1317     -0.53%
>>>              175.vpr                1694                1697      0.18%
>>>              176.gcc                2293                2291     -0.08%
>>>              181.mcf                1772                1760     -0.65%
>>>           186.crafty                2320                2245     -3.26%
>>>           197.parser                1166                1163     -0.29%
>>>              252.eon                2443                2576      5.44%
>>>          253.perlbmk                2410                2433      0.93%
>>>              254.gap                1987                1995      0.36%
>>>           255.vortex                2392                2588      8.19%
>>>            256.bzip2                1719                1729      0.56%
>>>            300.twolf                2288                2248     -1.77%
>>
>> You need -O3 -fwhole-program -flto for resonable cross module inlining to happen.
>> -fwhole-program is quite essential to get resonable win from LTO (w/o profile feedback).
>>
>> At least our nightly tester then gets quite nice improvements on few benchmark at spec2k,
>> see also my gccsummit slides.
>>
>> Honza
>>
>