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Re: Loop unrolling-related SPEC regressions?

Jan Hubicka wrote:

> >
> > > browsing the latest results from Andreas, it looks like a few of them (e.g.,
> > > 164.gzip, 186.crafty, 200.sixtrack) are showing a definite regression in the
> > > PEAK case, characterized by -funroll-all-loops.
> >
> > It's not clear to me that -funroll-all-loops is the correct setting for
> > PEAK, as bloating out the code may make the cache perform worse.
> We do use them in the testing runs for exactly these purposes.
> It tends to show the "bugs" that causes unnecesary code growth in some
> areas unnoticed by other benchmarks.
> THe base/peak flags are not supposed to bring best performance,
> but be good for testing majority of gcc features.

That's really enlightening Honza! Thanks for the clarification.
We should also remember this when someone compares the SPEC numbers made available
by other compiler producers with those of GCC: my guess is that this kind of
rationale for choosing the PEAK flags it's unfortunately not so widespread...


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