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Big differences on SpecFP results for gcc and icc


Hello!

There is an interesting comparison of SPEC scores between gcc and icc: http://people.redhat.com/dnovillo/spec2000.i686/gcc/individual-run-ratio.html . A quick look at the graphs shows a big differences in achieved scores between gcc and icc, mostly in SpecFP tests. I was trying to find some information on this matter, but none can be found in the archives on gcc's site.

An interesting examples are:
-177.mesa (this is a c test), where icc is almost 40% faster
-178.galgel, where icc is again 40% faster
-179.art, where llvm is more than 1.5x faster than both gcc and icc
-187.facere, where icc is 100% faster than gcc
-189.lucas, where icc is 60% faster

I know that these graphs don't show the results of most aggresive optimization options for gcc, but that is also the case with icc (only -O2). However, it looks that gcc and icc are not even in the same class regarding FP performance. Perhaps there is some critical optimizations, that are not present in gcc?

I think I'm not the only person, that finds these results rather "dissapointing". As Scott is currently writing a paper on gcc's FP performance, perhaps someone has an explanation, why gcc's results are so low on Pentium4 for these tests?

Uros.


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