[Bug tree-optimization/25243] [4.1/4.2 Regression] Jump threading opportunity missed in tree-ssa but caught in jump1

[law at redhat dot com]

------- Comment #8 from law at redhat dot com  2005-12-05 18:18 -------
Subject: Re:  [4.1/4.2 Regression] Jump
        threading opportunity missed in tree-ssa but caught in jump1

On Mon, 2005-12-05 at 18:05 +0000, steven at gcc dot gnu dot org wrote:
> 
> ------- Comment #7 from steven at gcc dot gnu dot org  2005-12-05 18:05 -------
> Created an attachment (id=10410)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10410&action=view)
>  --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10410&action=view)
> follow SSA_NAME_VALUE deep
> 
> Hmmwell, the attached patch does bootstrap on i686,ia64, and x86-64, and it
> passes regression testing on those targets too.  Jeff, do you have an example
> of when this could go into an infinite loop?
Try putting it in lookup_avail_expr.  ie, instead of following one chain
back, make it a loop.

I'd also really rather look at moving away from the equivalency chains,
which would also address this problem.  What's preventing that is things
actually get slower when we fully propagate constants/copies as they are
discovered.

jeff


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25243