From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 25739 invoked by alias); 13 May 2015 08:54:03 -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 25691 invoked by uid 48); 13 May 2015 08:53:59 -0000 From: "rguenth at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/66090] Wrong loop code generation with -O2 on ARM Date: Wed, 13 May 2015 08:54:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: 4.9.2 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: rguenth at gcc dot gnu.org X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: cc 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: 2015-05/txt/msg01029.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66090 Richard Biener changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jsm28 at gcc dot gnu.org --- Comment #4 from Richard Biener --- The testcase computes ptr + 1024 which evaluates to zero (even without IVOPTs coming into play). This invokes undefined behavior as even if you consider ptr + 1024 being "one after the last array element and not dereferenced" (the NULL pointer is special in C, if you want to lift this restriction you need to provide -fno-delete-null-pointer-checks). Joseph may be able to provide more C standard legalise wording here. But it's certainly how the middle-end works.