From: Duncan Sands <baldrick@free.fr>
To: gcc@gcc.gnu.org
Subject: Re: Comparison of GCC-4.6.1 and LLVM-2.9 on x86/x86-64 targets
Date: Thu, 08 Sep 2011 09:22:00 -0000 [thread overview]
Message-ID: <4E688926.7080607@free.fr> (raw)
In-Reply-To: <CAFiYyc29nUcPvC0fk7B1d7J-gP-7S9q8KYBnL9q3T0tCq9YBuw@mail.gmail.com>
>>> Why is lto/whole program mode not used in LLVM for peak performance
>>> comparison? (of course, peak performance should really use FDO..)
>>>
>> Thanks for the feedback. I did not manage to use LTO for LLVM as it
>> described on
>>
>> http://llvm.org/docs/LinkTimeOptimization.html#lto
>>
>> I am getting 'file not recognized: File format not recognized' during the
>> linkage pass.
Note that these are the instructions to follow on linux for LTO with llvm-gcc:
http://llvm.org/docs/GoldPlugin.html
Ciao, Duncan.
>>
>> You probably right that I should use -Ofast without -flto for gcc then.
>> Although I don't think that it significantly change GCC peak performance.
>> Still I am going to run SPEC2000 without -flto and post the data (probably
>> on the next week).
>
> Note that due to a bug in 4.6.x -Ofast is not equivalent to -O3 -ffast-math
> (it doesn't use crtfastmath.o). I'll backport the fix.
>
>> As for FDO, unfortunately for some tests SPEC uses different training sets
>> and it gives sometimes wrong info for the further optimizations.
>>
>> I do not look at this comparison as finished work and am going to run more
>> SPEC2000 tests and change the results if I have serious reasonable
>> objections for the current comparison.
>>
next prev parent reply other threads:[~2011-09-08 9:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-07 15:16 Vladimir Makarov
2011-09-07 15:29 ` Duncan Sands
2011-09-07 16:59 ` Vladimir Makarov
2011-09-07 15:55 ` Xinliang David Li
2011-09-07 16:24 ` Vladimir Makarov
2011-09-08 8:23 ` Richard Guenther
2011-09-08 9:22 ` Duncan Sands [this message]
2011-09-09 14:02 ` Vladimir Makarov
2011-09-07 17:01 ` Duncan Sands
2011-09-08 8:47 ` Jakub Jelinek
2011-09-09 14:26 ` Vladimir Makarov
2011-09-09 14:36 ` Jakub Jelinek
2011-09-09 23:30 ` Lawrence Crowl
2011-09-10 13:22 ` Gabriel Dos Reis
2011-09-12 16:40 ` Vladimir Makarov
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