From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 4AF3A3858004; Mon, 22 Mar 2021 11:18:51 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4AF3A3858004 From: "vincent-gcc at vinc17 dot net" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/99707] missing -Woverflow warning in floating-point to integer conversion for known but non-constant value Date: Mon, 22 Mar 2021 11:18:51 +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: 10.2.1 X-Bugzilla-Keywords: diagnostic X-Bugzilla-Severity: normal X-Bugzilla-Who: vincent-gcc at vinc17 dot net 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: 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, 22 Mar 2021 11:18:51 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99707 --- Comment #3 from Vincent Lef=C3=A8vre --- (In reply to Andrew Pinski from comment #1) > Gcc does not know that x will be negative. Actually, the code should have been (without the volatile): #include int main (void) { double x =3D -1.0; unsigned int i =3D x; printf ("%u\n", i); if (x =3D=3D -1.0) printf ("%u\n", i); return 0; } I don't get the warning either, and due to the "double x =3D -1.0;", GCC kn= ows that x is negative. > -Wconversion might warn about this but I have not tried. The test is done with -Wconversion. (In reply to Andrew Pinski from comment #2) > Also this might be caught at runtime with -fsanitizer=3Dundefined but I h= ave > not tried yet. Since this is undefined behavior in this case unlike the > original PR93806. After checking... This is not undefined behavior, but the value is unspecif= ied. F.4: "[...] if the floating value is infinite or NaN or if the integral par= t of the floating value exceeds the range of the integer type, then the =E2=80= =9Cinvalid=E2=80=9D floating-point exception is raised and the resulting value is unspecified."=