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