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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/108360] [13 Regression] Dead Code Elimination
 Regression at -Os since r13-2048-g418b71c0d535bf
Date: Tue, 10 Jan 2023 19:26:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108360

--- Comment #5 from Andrew Macleod <amacleod at redhat dot com> ---
The key change is that condition:
   _6 =3D f.5_5 << 4;
    e =3D _6;
    h_23 =3D (short int) _6;

    if (_21 =3D=3D -1)
      goto <bb 3>; [50.00%]
    else
      goto <bb 4>; [50.00%]

On the false edge, we lose the ability to determine that h_23 is [16,16], a=
nd
instead, it remains [0,0][16,16]..    that causes us to not be able to
eliminate the branch=