From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30267 invoked by alias); 20 Aug 2011 19:45:32 -0000 Received: (qmail 30259 invoked by uid 22791); 20 Aug 2011 19:45:32 -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, 20 Aug 2011 19:45:19 +0000 From: "hjl.tools at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug target/50131] Optimize x = -1 with "or" for -O Date: Sat, 20 Aug 2011 20:04:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: target X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: hjl.tools at gmail dot com 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: 2011-08/txt/msg01737.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50131 --- Comment #3 from H.J. Lu 2011-08-20 19:44:49 UTC --- (In reply to comment #2) > Is or $-1, reg on all CPUs equally expensive to mov $-1, reg though (as or > generally needs the previous reg content while mov does not; I know some CPUs > special case xor reg, reg, but I doubt or $-1, reg is special cased)? We should add a new x86 optimization flag and turn it on only if it helps for the processor to be optimized.