From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 797E73857815; Thu, 26 Nov 2020 00:20:26 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 797E73857815 From: "redi at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/97976] Optimization relating to NULL pointer assumptions in gcc 9.1 Date: Thu, 26 Nov 2020 00:20:26 +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: 9.1.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: redi at gcc dot gnu.org X-Bugzilla-Status: RESOLVED X-Bugzilla-Resolution: INVALID 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: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 26 Nov 2020 00:20:26 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97976 --- Comment #9 from Jonathan Wakely --- 6.3.2.3 p3 says a null pointer compares unequal to any pointer to an object= , so that means no object can ever be at address 0 in a valid C program. If you'= re not using the -fno-delete-null-pointer-checks option then GCC is perfectly justified to assume no object is at address 0 (because the standards say th= at's not possible). The footnote on 6.5.3.2 clarifies that a null pointer is not a valid operand for the unary * operator.=20 For C++, [basic.compound] says a pointer can point to an object or be null,= not both.=