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[Bug tree-optimization/28868] [4.0/4.1/4.2/4.3 Regression] Not elimintating the PHIs which have the same arguments
- From: "dberlin at dberlin dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 4 Nov 2007 19:24:41 -0000
- Subject: [Bug tree-optimization/28868] [4.0/4.1/4.2/4.3 Regression] Not elimintating the PHIs which have the same arguments
- References: <bug-28868-6528@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #11 from dberlin at gcc dot gnu dot org 2007-11-04 19:24 -------
Subject: Re: [4.0/4.1/4.2/4.3 Regression] Not elimintating the PHIs which have
the same arguments
On 4 Nov 2007 15:45:59 -0000, rguenth at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #10 from rguenth at gcc dot gnu dot org 2007-11-04 15:45 -------
> FRE doesn't replace a SSA_NAME with another SSA_NAME
Also true. It will only replace non-ssa names with ssa-names.
This is to avoid lengthening the range of variables.
Replacing ssa names with other ssa names willy-nilly is not always a
win. We eventually ended up with heuristics to not change loop depths
of ssa names, etc.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28868