From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id BD80F3985C15; Mon, 28 Jun 2021 14:53:48 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org BD80F3985C15 From: "vincent-gcc at vinc17 dot net" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/38470] value range propagation (VRP) would improve -Wsign-compare Date: Mon, 28 Jun 2021 14:53:48 +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: diagnostic X-Bugzilla-Severity: enhancement X-Bugzilla-Who: vincent-gcc at vinc17 dot net 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: Mon, 28 Jun 2021 14:53:48 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D38470 --- Comment #28 from Vincent Lef=C3=A8vre -= -- (In reply to Matthias Kretz (Vir) from comment #27) > Fair enough. But how can the compiler be certain that the developer reali= zed > u and u % 100 is unsigned? Maybe when (s)he wrote the code the expectation > was for the RHS to be within [-99..99]. Indeed. (I never use % when its LHS can be either positive or negative, so = that I didn't think about this case.) Now, the cause of the bug in such a case would be that the user messed up w= ith the signedness of u, not because he forgot about the promotion rule. This is something rather different.=