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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114551] [14 Regression] wrong code at -O3 on
 x86_64-linux-gnu since r14-2944
Date: Wed, 03 Apr 2024 12:27:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114551

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot =
gnu.org

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
It can be reproduced with -O2 -funswitch-loops -fsplit-loops.

Loop splitting emits

  <bb 2> [local count: 14598063]:
  a.0_1 =3D a;
  _2 =3D a.0_1 + -1;
  a =3D _2;
  _24 =3D _2 <=3D 0;
  _10 =3D 2147483647 - _2;
  if (_10 <=3D 2)

and the 2147483647 - _2 expression then overflows, so that's definitely
wrong.  This is built here:

        /* Build a condition that will skip the first loop when the
           guard condition won't ever be true (or false).  */
        gimple_seq stmts2;
        border =3D force_gimple_operand (border, &stmts2, true, NULL_TREE);
        if (stmts2)=20=20=20=20=20=20=20=20=20=20=20=20=20=20

or rather in split_at_bb_p and put into '*border'=