From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 29586 invoked by alias); 26 Jul 2011 17:31:45 -0000 Received: (qmail 29565 invoked by uid 22791); 26 Jul 2011 17:31:44 -0000 X-SWARE-Spam-Status: No, hits=-7.2 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,SPF_HELO_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 26 Jul 2011 17:31:29 +0000 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p6QHTwoV019644 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 26 Jul 2011 13:31:29 -0400 Received: from zebedee.pink (ovpn-116-36.ams2.redhat.com [10.36.116.36]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id p6QGbSRf022647; Tue, 26 Jul 2011 12:37:30 -0400 Message-ID: <4E2EED47.2010806@redhat.com> Date: Tue, 26 Jul 2011 17:31:00 -0000 From: Andrew Haley User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110621 Fedora/3.1.11-1.fc14 Thunderbird/3.1.11 MIME-Version: 1.0 To: gcc-help@gcc.gnu.org Subject: Re: Is it OK that gcc optimizes away overflow check? References: <4E2B2B72.9050504@agner.org> <4E2E8B12.1090204@agner.org> <4E2E9873.7060902@redhat.com> In-Reply-To: <4E2E9873.7060902@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact gcc-help-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-help-owner@gcc.gnu.org X-SW-Source: 2011-07/txt/msg00270.txt.bz2 On 07/26/2011 11:35 AM, Andrew Haley wrote: > Consider > > for (i = 0; i < limit; i++) > f(i * 2); > > which can be rewritten to > > tmp = limit * 2; > for (i = 0; i < tmp; i++) > f(i); duh. int tmp = limit * 2; for (i = 0; i < tmp; i += 2) f(i); Andrew.