From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 16743 invoked by alias); 25 Jun 2012 13:41:07 -0000 Received: (qmail 16692 invoked by uid 22791); 25 Jun 2012 13:41:06 -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; Mon, 25 Jun 2012 13:40:19 +0000 From: "rguenth at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/53676] [4.7/4.8 regression] empty loop is not always removed now Date: Mon, 25 Jun 2012 13:41:00 -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: 2012-06/txt/msg01641.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53676 --- Comment #7 from Richard Guenther 2012-06-25 13:39:29 UTC --- In SCEV analysis we'd need to detect the pattern feeding the truncation tem_3 = (int) result_2; tem_4 = tem_3 + 2; result_5 = (signed char) tem_4; in interpret_rhs_expr - otherwise we ask for the evolution of tem_4 which we cannot express properly because tem_3's chrec wraps. So we'd need to handle result_5 = (signed char) ((int) result_2 + 2) as if it were done without the intermediate tem_4.