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Re: vortex peak performance regression
> > Zoltan,
> > It looks like your patch:
> > + 2001-11-30 Zoltan Hidvegi <hzoli@hzoli.2y.net>
> > +
> > + * unroll.c (unroll_loop): Correct special exit cases.
> > +
> > causes regression in the spec2000 tester - most importantly the vortex
> > benchmark (- see www.suse.de/~aj/SPEC
> >
> > It is not obvious for me why, but can you please double check
> > whether the regression is unavoidable.
>
> I have to think more about it, as I was unable to quickly produce a
> testcase to show it is necessary. But it only adds a single increment
> to the loop, but that also requires an extra register, that may be
> just enough to run out of registers. I have no more time to think
The difference is small enought to make this possible explanation.
> about this today, I'll try to look at it tomorrow. Which architecture
> did you run the test? It can make a difference if it has
You may look at the pages for details - it is Athlon, so the register
pressure definitly does make sense.
Honza
> count-regiter loop or not.
>
> Zoli