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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109637] unnecessary range check in complete
 switch on bitfield
Date: Wed, 26 Apr 2023 18:28:13 +0000
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X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.1.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109637

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-04-26
          Component|middle-end                  |tree-optimization
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  # RANGE [irange] unsigned char [0, 3] NONZERO 0x3
  _6 =3D (unsigned charD.30) _1;
  # RANGE [irange] unsigned char [0, 2][+INF, +INF]
  _2 =3D _6 + 255;

  if (_2 <=3D 2)

VRP Should have changed _2 <=3D 2 to just _2 !=3D 255 which then gets folde=
d into
_6 !=3D 0 which then will get folded into _1 !=3D 0

and then phiopt could also have sunk the cast:
  if (_2 <=3D 2)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870913]:
<L7>:
  _9 =3D (int) _1;

  <bb 4> [local count: 1073741824]:
  # _3 =3D PHI <0(2), _9(3)>

Which then would get simplified into just:
_3 =3D (int)_1;

So there are a few things that needed to be done here ...=