Big differences on SpecFP results for gcc and icc

[Daniel Berlin]

On Sun, 2005-06-12 at 11:21 +0200, Uros Bizjak wrote:
> 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

SSE Vectorization, I believe.
> -178.galgel, where icc is again 40% faster

This is because of a better fortran *library*, not compiler.
IIRC, it's all in matmul.

> -179.art, where llvm is more than 1.5x faster than both gcc and icc

taken care of on struct-reorg.

> -187.facere, where icc is 100% faster than gcc
No idea.

> -189.lucas, where icc is 60% faster
No idea, though i'd imagine its the same issue.

> 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?

I could tell you why for PPC (where we aren't that far behind xlc or icc
on a lot of them, if you use the right options), but no clue for x86.

> 
> Uros.