[Bug tree-optimization/29738] Missed constant propagation into loops

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from rguenther at suse dot de  2006-11-06 12:37 -------
Subject: Re:  Missed constant propagation into
 loops

On Mon, 6 Nov 2006, rakdver at atrey dot karlin dot mff dot cuni dot cz wrote:

> 
> 
> ------- Comment #7 from rakdver at atrey dot karlin dot mff dot cuni dot cz  2006-11-06 12:33 -------
> Subject: Re:  Missed constant propagation into loops
> 
> > But obviously for real operands, foo () won't clobber them.  I.e. the following
> > also could be optimized but is not:
> > 
> > void foo (int *);
> > void bar (void)
> > {
> >   int j;
> >   int i;
> >   i = 0;
> >   for (j = 0; j < 10000; j++)
> >     if (i)
> >       foo (&i);
> > }
> > 
> > foo () will be never executed, so the clobbering of i is not "executed",
> > so we don't need i as PHI arg/result for the loop.  This is what I'm looking
> > for as optimization.
> 
> now you have lost me, I have no idea what you are trying to tell.  What
> I mean is that this is exactly the same case like
> 
> void bar (void)
> {
>   int j;
>   int i;
>   i = 0;
>   for (j = 0; j < 10000; j++)
>     if (i)
>       i = 1;
> }
> 
> Except that in the testcase for the PR, "i" is not a real operand.
> Since we already have some support for virtual operands in ccp, it
> should not be too difficult to make it handle this case as well.

Ah, I see.  You are of course completely right.  Now the question is,
why does store_ccp not handle it?  (Maybe it is as dis-functional as
store_copyprop was until I fixed it?)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29738