From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 59207 invoked by alias); 20 May 2015 10:55:00 -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 Received: (qmail 58759 invoked by uid 48); 20 May 2015 10:54:52 -0000 From: "gil.hur at sf dot snu.ac.kr" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/65752] Too strong optimizations int -> pointer casts Date: Wed, 20 May 2015 10:55:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 4.9.2 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: gil.hur at sf dot snu.ac.kr 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: 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/msg01616.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65752 --- Comment #26 from Chung-Kil Hur --- Thanks for the detailed explanations. > The C standard only guarantees that you can convert a pointer to uintptr_t > and back, it doesn't guarantee that you can convert a modified uintptr_t > back to > a pointer that is valid. > > Thus, doing (int *)((xp + i) - j) is invoking undefined behavior. > I didn't know about this rule. I thought this cast is valid because "(xp+i)-j" is even "safely-derived". Could you give a reference for that rule in the standard? Thanks!