From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 27249 invoked by alias); 7 Jan 2012 18:25:36 -0000 Received: (qmail 27233 invoked by uid 22791); 7 Jan 2012 18:25:35 -0000 X-SWARE-Spam-Status: No, hits=-2.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 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; Sat, 07 Jan 2012 18:25:23 +0000 From: "pinskia at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/51783] Missed optimization for X ==/!= (signed type) ((unsigned type) Y + Z) Date: Sat, 07 Jan 2012 18:25:00 -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-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: pinskia at gcc dot gnu.org X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- 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: 2012-01/txt/msg00741.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51783 --- Comment #1 from Andrew Pinski 2012-01-07 18:25:19 UTC --- I think that would be an invalid transformation except when -fwrapv is used. The reason is: x.0_2 = (unsigned int) x_1(D); D.2715_4 = z_3(D) + x.0_2; <--- wrapping semantics c_5 = (int) D.2715_4; While: D.1720_10 = (int) z_3(D); c_5 = x_1(D) + D.1720_10; Was undefined semantics for overflow. This cannot happen until we have signed operations which also have wrapping semantics.