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From: "kristerw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/106884] New: ifcombine may move shift so it shifts more than bitwidth Date: Thu, 08 Sep 2022 00:20:48 +0000 [thread overview] Message-ID: <bug-106884-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106884 Bug ID: 106884 Summary: ifcombine may move shift so it shifts more than bitwidth Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: kristerw at gcc dot gnu.org Target Milestone: --- The function foo from gcc.dg/tree-ssa/ssa-ifcombine-1.c can be called as foo(1, 1, 33) without invoking undefined behavior int foo (int x, int a, int b) { int c = 1 << a; if (x & c) if (x & (1 << b)) return 2; return 0; } But ifcombine transforms this to int foo (int x, int a, int b) { int c; int _4; int _10; int _11; int _12; int _13; <bb 2>: _10 = 1 << b_8(D); _11 = 1 << a_5(D); _12 = _10 | _11; _13 = x_7(D) & _12; if (_12 == _13) goto <bb 3>; else goto <bb 4>; <bb 3>: <bb 4>: # _4 = PHI <2(3), 0(2)> return _4; } and this will now calculate 1 << 33 unconditionally for _10.
next reply other threads:[~2022-09-08 0:20 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-08 0:20 kristerw at gcc dot gnu.org [this message] 2022-09-08 9:52 ` [Bug tree-optimization/106884] " rguenth at gcc dot gnu.org 2022-09-08 10:53 ` kristerw at gcc dot gnu.org 2022-09-30 11:34 ` kristerw at gcc dot gnu.org 2023-07-11 9:45 ` rguenth at gcc dot gnu.org 2023-07-11 15:36 ` pinskia at gcc dot gnu.org 2023-08-06 0:07 ` kristerw at gcc dot gnu.org 2023-11-01 15:57 ` pinskia at gcc dot gnu.org
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