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[Bug target/29256] [6/7/8 regression] loop performance regression
- From: "wilco at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 19 Feb 2018 15:37:46 +0000
- Subject: [Bug target/29256] [6/7/8 regression] loop performance regression
- Auto-submitted: auto-generated
- References: <bug-29256-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=29256
Wilco <wilco at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |wilco at gcc dot gnu.org
--- Comment #66 from Wilco <wilco at gcc dot gnu.org> ---
(In reply to Aldy Hernandez from comment #65)
> (In reply to Jeffrey A. Law from comment #45)
> > This problem still exists and can be seen by making the arrays external and
> > using -fno-tree-loop-distribute-patterns.
>
> Still a problem. I get the same code Jeff got for comment 45.
A simple workaround for GCC8 might be to tweak the address costs when loop
unrolling is enabled, so offsets are preferred over indexing (either in IVOpt
or backend). For GCC9 a tree level loop optimization has been proposed which
will fix this issue.