PTR-PLUS merge into the mainline

Daniel Berlin dberlin@dberlin.org
Thu Jul 5 20:45:00 GMT 2007


On 7/5/07, Richard Guenther <rguenther@suse.de> wrote:
> On Thu, 5 Jul 2007, Roman Zippel wrote:
>
> > Hi,
> >
> > On Thu, 5 Jul 2007, Richard Guenther wrote:
> >
> > > If there is anything to fix, then all those variants should produce
> > > the same code, not just foo3 and foo4.  So for these cases we should
> > > make sure that value-numbering sees them as computing the same value
> > > and extend combine to choose the instructions with the least cost.
> > >
> > > Changing fold isn't a real fix.  It's a workaround for a specific
> > > testcase.
> >
> > What do you suggest now specifically?
> > combine isn't the problem here, at the time we reach RTL this should
> > already be done. Your patch only catches specific cases and pessimises
> > others.
>
> Well, that's always the nature of any canonicalization.
>
> The following actually makes SCCVN notice that tmp1 == tmp2 in

I posted a general patch to do this for all expressions in one of the
bug reports.

I simply didn't do it in the initial sccvn patch  because it's
somewhat memory expensive, and i hadn't measured it's performance.

But as you say, it is certainly possible.



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