From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 9709 invoked by alias); 12 Jul 2002 11:26:02 -0000 Mailing-List: contact gcc-prs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-prs-owner@gcc.gnu.org Received: (qmail 9689 invoked by uid 71); 12 Jul 2002 11:26:01 -0000 Resent-Date: 12 Jul 2002 11:26:01 -0000 Resent-Message-ID: <20020712112601.9688.qmail@sources.redhat.com> Resent-From: gcc-gnats@gcc.gnu.org (GNATS Filer) Resent-To: nobody@gcc.gnu.org Resent-Cc: gcc-prs@gcc.gnu.org, gcc-bugs@gcc.gnu.org Resent-Reply-To: gcc-gnats@gcc.gnu.org, algrant@acm.org Received: (qmail 9570 invoked by uid 61); 12 Jul 2002 11:25:26 -0000 Message-Id: <20020712112526.9569.qmail@sources.redhat.com> Date: Fri, 12 Jul 2002 04:26:00 -0000 From: algrant@acm.org Reply-To: algrant@acm.org To: gcc-gnats@gcc.gnu.org X-Send-Pr-Version: gnatsweb-2.9.3 (1.1.1.1.2.31) Subject: c/7284: incorrectly simplifies leftshift followed by signed power-of-2 division X-SW-Source: 2002-07/txt/msg00373.txt.bz2 List-Id: >Number: 7284 >Category: c >Synopsis: incorrectly simplifies leftshift followed by signed power-of-2 division >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: wrong-code >Submitter-Id: net >Arrival-Date: Fri Jul 12 04:26:00 PDT 2002 >Closed-Date: >Last-Modified: >Originator: Al Grant >Release: 3.1 >Organization: >Environment: SunOS 5.5.1 Generic_103640-31 sun4u sparc SUNW,Ultra-5_10 >Description: Incorrect simplification of signed (n << 24) / (1 << 23) to a single left shift. Should sign-extend from bit 8. >How-To-Repeat: #include int f(int n) { return (n<<24) / (1<<23); } int main(void) { if (f(128) != -256) printf("Broken\n"); return 0; } >Fix: Replace with left shift followed by signed right shift. This can be done in source as a workaround. >Release-Note: >Audit-Trail: >Unformatted: