From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22797 invoked by alias); 30 Nov 2010 15:41:53 -0000 Received: (qmail 22781 invoked by uid 22791); 30 Nov 2010 15:41:52 -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; Tue, 30 Nov 2010 15:41:47 +0000 From: "rguenther at suse dot de" To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/46488] [4.5 regression] server/core_filters.c from apache httpd 2.2.17 miscompiled at -O3 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: middle-end X-Bugzilla-Keywords: X-Bugzilla-Severity: major X-Bugzilla-Who: rguenther at suse dot de X-Bugzilla-Status: ASSIGNED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: ebotcazou at gcc dot gnu.org X-Bugzilla-Target-Milestone: 4.5.2 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 Date: Tue, 30 Nov 2010 15:47:00 -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 X-SW-Source: 2010-11/txt/msg03693.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46488 --- Comment #33 from rguenther at suse dot de 2010-11-30 15:41:36 UTC --- On Tue, 30 Nov 2010, ebotcazou at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46488 > > --- Comment #32 from Eric Botcazou 2010-11-30 15:10:58 UTC --- > The problem appears to be deeply rooted in the Ring construct, more precisely > in the HEAD trick. IIUC the idea is to "attach" a doubly-linked list to > another structure by means of a "virtual" member overlaid on top of the > structure; the only thing they actually share is a special APR_RING_ENTRY (the > APR_RING_HEAD). But this overlay fundamentally violates the aliasing rules > even if one try to narrow the accesses to just the shared part. > > Richard, is that how the aliasing rules are implemented in the 4.5.x series? Yes, also in 4.4 and 4.3, but maybe you need to be more lucky to trigger the problem there. > Has this been changed in 4.6.0? No. But with 4.6 we can ignore pointer types when doing copy-propagation and thus we probably see that they must-alias (in which case we will not apply TBAA to be more nice to our users). Richard.