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Re: Comparison of GCC-4.6.1 and LLVM-2.9 on x86/x86-64 targets

On 09/07/2011 11:55 AM, Xinliang David Li wrote: 
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.

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).

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.

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