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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/101223] [11/12 Regression] evrp produces wrong code since r11-3685-gfcae5121154d1c33 Date: Mon, 28 Jun 2021 14:19:00 +0000 [thread overview] Message-ID: <bug-101223-4-kHfdWpjC75@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-101223-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101223 --- Comment #7 from Andrew Macleod <amacleod at redhat dot com> --- I think this is our old friend 1-bit signed overflow. for 1 signed bit values, varying is [-1, 0] range-op::build_lt checks to see if UB - 1 overflows, and if it does, then the result is undefined. wi::sub sets the overflow flag for 0 - 1 with 1 bit signed... so the comparison ends up being undefined, and we then make incorrect choices because we think we can. I think we need to, yet again, special case 1-bit signed values here, and probably in build_gt as well.
next prev parent reply other threads:[~2021-06-28 14:19 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-26 12:44 [Bug tree-optimization/101223] New: wrong code at -Os and above on x86_64-linux-gnu zhendong.su at inf dot ethz.ch 2021-06-28 2:34 ` [Bug tree-optimization/101223] [11/12 Regression] " pinskia at gcc dot gnu.org 2021-06-28 3:00 ` [Bug tree-optimization/101223] [11/12 Regression] evrp produces wrong code pinskia at gcc dot gnu.org 2021-06-28 3:03 ` pinskia at gcc dot gnu.org 2021-06-28 7:02 ` rguenth at gcc dot gnu.org 2021-06-28 7:27 ` [Bug tree-optimization/101223] [11/12 Regression] evrp produces wrong code since r11-3685-gfcae5121154d1c33 marxin at gcc dot gnu.org 2021-06-28 10:57 ` aldyh at gcc dot gnu.org 2021-06-28 10:58 ` jakub at gcc dot gnu.org 2021-06-28 10:59 ` aldyh at gcc dot gnu.org 2021-06-28 14:19 ` amacleod at redhat dot com [this message] 2021-07-02 13:03 ` rsandifo at gcc dot gnu.org 2021-07-02 13:14 ` jakub at gcc dot gnu.org 2021-07-02 13:18 ` rsandifo at gcc dot gnu.org 2021-07-02 15:35 ` cvs-commit at gcc dot gnu.org 2021-07-02 15:37 ` amacleod at redhat dot com 2021-07-02 20:31 ` [Bug tree-optimization/101223] [11 " pinskia at gcc dot gnu.org 2021-07-14 21:58 ` cvs-commit at gcc dot gnu.org 2021-07-14 22:16 ` amacleod at redhat dot com
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