From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 9EFC03857C60; Wed, 24 Mar 2021 23:48:19 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 9EFC03857C60 From: "msebor at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/99756] New: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional Date: Wed, 24 Mar 2021 23:48:19 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 11.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: msebor 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: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: 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: Wed, 24 Mar 2021 23:48:19 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99756 Bug ID: 99756 Summary: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: msebor at gcc dot gnu.org Target Milestone: --- The following code triggers a spurious -Wmaybe-uninitialized. There are two underlying problems: one is a limitation of the uninitialized pass and anot= her is a missed optimization opportunity described in PR 99755 (the second test= for k results in another read from it instead of reusing the value read previou= sly in the first conditional). $ cat t.c && gcc -O2 -S -Wall t.c extern int a[], i, j, k; void f (void) { int x; if (i > 1 && j > 2 && k > 3) x =3D i + 1; if (i =3D=3D 2 && j =3D=3D 3 && k =3D=3D 4) a[x] =3D 0; // { dg-bogus "Wmaybe-uninitialized" } } t.c: In function =E2=80=98f3=E2=80=99: t.c:28:10: warning: =E2=80=98x=E2=80=99 may be used uninitialized in this f= unction [-Wmaybe-uninitialized] 28 | a[x] =3D 0; // { dg-bogus "Wmaybe-uninitialized= " } | ~~~~~^~~=