[patch] fix pr22550

[Diego Novillo]

On Thu, Jul 28, 2005 at 06:10:18PM +0200, Richard Guenther wrote:

> > In fact, looking at the cleanup code, it would not be hard to
> > teach it to flag an SSA update if it needed to.  This would
> > harden CFG cleanup from messing up the SSA form.  There was a PR
> > for it which Andrew had fixed by preventing CFG cleanup from
> > propagating constants.  Andrew, remember the number?  It may be
> > worth exploring that route.
> 
> I remember it was with a custom patch applied.  Also I hit the same
> problem with tree_merge_blocks propagating a const into an ARRAY_REF
> index with the salias for arrays patch.
> 
> So, the don't-propagate patch looks like if it is going to fix this problem
> as well, which I kind of like ;)
> 
No, that wasn't the point.  Both patches fix the problem.

This final point is not directly related to the problem.
Currently, CFG cleanup will stop itself from doing certain
propagations because it is not ready to deal with an out-of-date
SSA form after itself.

My point is that we could teach it to update the SSA form, if
needed.