Fix tree-optimization/20920

[Jeffrey A Law]

On Sat, 2005-04-09 at 23:27 -0400, Diego Novillo wrote:
> Sigh.  Another SSA_NAME flowing through EH edges getting in the
> way.
> 
> I'm starting to think that it would be much better to make these
> SSA_NAME_OCCURS_IN_ABNORMAL_PHI into virtuals.  We would avoid
> all the monkeying around that optimizers have to do.  It would
> involve a bit of trickery because we only detect them when they
> first go into SSA form, but it's doable.  Comments from EH folks?
I think that would have a rather bad effect on C++ and Java code.

One of the nice things about the current approach is that it is very
fine grained -- ie, the flag bit appears on SSA_NAMEs and thus has
a relatively limited affect on optimization.

Your approach would in effect penalize all other instances of a _DECL
just because one instance happened to flow through an EH edge.

Jeff