From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 29836 invoked by alias); 12 Mar 2012 15:29:59 -0000 Received: (qmail 29826 invoked by uid 22791); 12 Mar 2012 15:29:58 -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 15:29:45 +0000 From: "aldyh 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 15:29:00 -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: aldyh 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/msg00893.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52558 --- Comment #4 from Aldy Hernandez 2012-03-12 15:29:06 UTC --- > 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). I thought we ignored *load* data races, but still cared about introducing write data races. This test case has both. I don't understand why we would allow introducing writes on paths that did not have it, but I will defer to you.