From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 9207 invoked by alias); 12 Mar 2012 15:01:55 -0000 Received: (qmail 9198 invoked by uid 22791); 12 Mar 2012 15:01:54 -0000 X-SWARE-Spam-Status: No, hits=-2.8 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; Mon, 12 Mar 2012 15:01:41 +0000 From: "rguenth at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/52558] write introduction incorrect wrt the C++11 memory model Date: Mon, 12 Mar 2012 15:01:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: rguenth at gcc dot gnu.org X-Bugzilla-Status: NEW 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: 2012-03/txt/msg00885.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52558 --- Comment #2 from Richard Guenther 2012-03-12 15:01:36 UTC --- (In reply to comment #1) > Richi, is this something that should also be fixed for 4.7 as well? There is a > write to g_2 that is introduced on paths that did not have it. So this is not > just a load/load data race. No, we don't want to fix this for 4.7 as this is not a regression. Yes, LIM only avoids introducing traps, not data-races. This was discussed in the past already, btw, and we do not want to generally disallow this optimization. [The C++ memory model is stupid here, it should not treat every variable raceable but only specially marked ones, oh well ...] There will be very many other passes that are affected by this, and even more very many passes that will be affected by load data-races. You will for example slow down SPEC CPU 2006 quite a bit (though technically it does not include C++11 benchmarks).