Re: PR19038 causes regression of 3.9% in SPEC int

[Jeffrey A Law <law at redhat dot com>]

On Fri, 2004-12-24 at 14:26 +0100, Steven Bosscher wrote:
> 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.
> 
> http://gcc.gnu.org/PR19038 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.
Well, this ought to fix the poor placement of the copy instruction.

Bootstrapped and regression tested on i686-pc-linux-gnu.

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