From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 084DA3858C78; Tue, 1 Mar 2022 07:58:02 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 084DA3858C78 From: "rguenth at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/104711] Unnecessary -Wshift-negative-value warning Date: Tue, 01 Mar 2022 07:58:02 +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: unknown X-Bugzilla-Keywords: documentation X-Bugzilla-Severity: normal X-Bugzilla-Who: rguenth at gcc dot gnu.org X-Bugzilla-Status: NEW 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: 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: Tue, 01 Mar 2022 07:58:03 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104711 --- Comment #5 from Richard Biener --- I agree that -fwrapv should make left-shift of positive values when the res= ult is not representable well-defined but I'm not sure about the negative value case - the standard does not provide enough reasoning to suggest the undefinedness is because of actual overflow - in fact the standard allows E= 1 << 0 and there's definitely no overflow for negative E1 in that case. Supposedly the standard simply chickened out for non-twos-complement archs here again and unfortunately didn't leave the door open for implementation-defined behavior. I suppose you are asking for an option to turn all left shifts into logical shifts?=