From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 827 invoked by alias); 10 Mar 2015 11:51:00 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 776 invoked by uid 48); 10 Mar 2015 11:50:56 -0000 From: "vries at gcc dot 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 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 5.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: minor X-Bugzilla-Who: vries at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2015-03/txt/msg01105.txt.bz2 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.