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From: "vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/65363] trivial redundant code reordering makes code less optimal
Date: Tue, 10 Mar 2015 11:51:00 -0000	[thread overview]
Message-ID: <bug-65363-4-VZaR9OAHXW@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-65363-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65363

--- Comment #3 from vries at gcc dot gnu.org ---
(In reply to Richard Biener from comment #1)
> FRE can only eliminate the dominated one (obviously), so the first one is
> the one prevailing. 

I don't understand that.

Say we have load A (loading into tmp.a) and load B (loading into tmp.b).

If load A dominates load B, then we can replace the uses of tmp.b with uses of
tmp.a, since the domination relation guarantees that tmp.a is available at all
uses of tmp.b.

However, if load A dominates load B, but load B dominates the uses of tmp.a,
then we can replace the uses of tmp.a with uses of tmp.b.


      parent reply	other threads:[~2015-03-10 11:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 16:41 [Bug tree-optimization/65363] New: " vries at gcc dot gnu.org
2015-03-10  9:11 ` [Bug tree-optimization/65363] " rguenth at gcc dot gnu.org
2015-03-10  9:13 ` jakub at gcc dot gnu.org
2015-03-10 11:51 ` vries at gcc dot gnu.org [this message]

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