From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 29165 invoked by alias); 15 Dec 2014 20:46:45 -0000 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 Received: (qmail 29092 invoked by uid 48); 15 Dec 2014 20:46:42 -0000 From: "jakub at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/64309] if (1 & (1 << n)) not simplified to if (n == 0) Date: Mon, 15 Dec 2014 20:46:00 -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-Version: 5.0 X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: normal X-Bugzilla-Who: jakub at gcc dot gnu.org X-Bugzilla-Status: ASSIGNED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: mpolacek at gcc dot gnu.org X-Bugzilla-Target-Milestone: 5.0 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2014-12/txt/msg01821.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64309 --- Comment #9 from Jakub Jelinek --- (1 << n) & 5 != 0 -> n == 0 || n == 2 (not beneficial) Not only that, we actually emit similar comparisons as a bit test intentionally even if you write it in a switch or series of ifs that way, so undoing that optimization would be a bad idea.