From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 56B143858C39; Thu, 7 Oct 2021 08:21:08 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 56B143858C39 From: "aldyh at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/102631] -Wmaybe-uninitialized cannot see through a series of PHIs Date: Thu, 07 Oct 2021 08:21:08 +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: 12.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: aldyh at gcc dot gnu.org 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: Thu, 07 Oct 2021 08:21:08 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102631 --- Comment #4 from Aldy Hernandez --- For the calls-aarch64.ii testcase, there's some additional information in t= he upstream thread. Quoted here for convenience: There's some missing context. The only way to get to BB101->BB102 is through: if (_6711 !=3D 0) goto ; [5.50%] else goto ; [94.50%] And there's an implicit relation between _6711 and _811: ... if (_6711 !=3D 0) goto ; [5.50%] else goto ; [94.50%] [local count: 17344687]: goto ; [100.00%] [local count: 298013267]: [local count: 315357954]: # _881 =3D PHI <1(87), 0(287)> That is, _6711 =3D=3D !_881. Presumably the threader shuffled things sufficiently so that the above relationship is difficult to devise. It seemsthat it's having a hard time noticing that the _6711 and _811 guards are inversely related.=