PR19039 causes regression of 3.9% in SPEC int

Steven Bosscher
Fri Dec 24 14:54:00 GMT 2004

On Friday 24 December 2004 11:02, Roger Sayle wrote:
> On Fri, 24 Dec 2004, Mostafa Hagog wrote:
> > Performing the loop-header-copying is a sort of "work around" to this PR,
> > I have ported the loop-header-copying from tree's to RTL.  This caused a
> > total 3.9% improvements with the rtl loop header copying (lhc).
> That's PR tree-optimization/19038, *not* PR target/19039. for the quick link lovers.

> Would you mind posting your RTL-based loop header copying patch to
> gcc-patches?  Not only might it be catching more optimizations than
> out-of-ssa is causing, but as a solution it might be more suitable
> for gcc 4.0 (depending upon compile-time performance impact, ugliness,
> intrusivenss, corrections to Andrew's "quick fix", etc...).

I'm unimpressed by either RTL loop header copying, or Andrew's fix,
both just paper over the underlying problem.  The real problem is
that apparently we are creating a situation where copy propagation
makes coalescing impossible.  Fix that and you don't get the extra
basic block - bug fixed, done.

> Very impressive performance numbers though.

Indeed.  We really should fix this one way or another for GCC 4.0.


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