On Wed, Sep 7, 2011 at 6:23 PM, Vladimir Makarov <vmaka...@redhat.com> wrote: > 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).
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. >
