From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 23748 invoked by alias); 22 Aug 2012 08:48:31 -0000 Received: (qmail 23641 invoked by uid 22791); 22 Aug 2012 08:48:30 -0000 X-SWARE-Spam-Status: No, hits=-4.3 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00,KHOP_THREADED X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 22 Aug 2012 08:47:43 +0000 From: "rguenth at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/53676] [4.7 regression] empty loop is not always removed now Date: Wed, 22 Aug 2012 08:48:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: middle-end X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: normal X-Bugzilla-Who: rguenth at gcc dot gnu.org X-Bugzilla-Status: ASSIGNED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: rguenth at gcc dot gnu.org X-Bugzilla-Target-Milestone: 4.7.2 X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 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 X-SW-Source: 2012-08/txt/msg01521.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53676 --- Comment #13 from Richard Guenther 2012-08-22 08:46:54 UTC --- (In reply to comment #12) > I've been doing research into LLVM 3.1 and other GCC versions. LLVM 3.1 > correctly eliminate the (near) empty loop, and their current trunk does not > regress like 4.7 has. > > Is the trunk patch coupled to other changes that are too invasive for 4.7? I'm > confused and curious about what optimization regressions are serious enough to > warrant a back port, if any. No, it's only the commit referenced in this PR. No optimization regressions warrant a backport as they always come with the risk of regressing something worse than performance. Trivial restoring of old behavior might be worth backporting but the patch introduces a completely new non-trivial transform into a core analysis engine that is shared among many passes.