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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/109637] unnecessary range check in complete
 switch on bitfield
Date: Wed, 26 Apr 2023 18:52:58 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109637

Andrew Macleod <amacleod at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com

--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
I think the bigger questions is why did switch conv change:

  1 =3D s_5(D)->x;
  switch (_1) <default: <L5> [INV], case 1: <L1> [INV], case 2: <L2> [INV],
case 3: <L3> [INV]>

  <bb 3> :
<L1>:
  goto <bb 6>; [INV]

  <bb 4> :
<L2>:
  goto <bb 6>; [INV]

  <bb 5> :
<L3>:

  <bb 6> :
  # _3 =3D PHI <0(2), 1(3), 2(4), 3(5)>
<L5>:
  return _3;


to=20


  <bb 2> :
  _1 =3D s_5(D)->x;
  _6 =3D (unsigned char) _1;
  _2 =3D _6 + 255;
  if (_2 <=3D 2)
    goto <bb 4>; [INV]
  else
    goto <bb 3>; [INV]

  <bb 3> :
<L6>:
  _10 =3D 0;
  goto <bb 5>; [100.00%]

  <bb 4> :
<L7>:
  _8 =3D (unsigned int) _1;
  _9 =3D (int) _1;
  _7 =3D _9;

  <bb 5> :
  # _3 =3D PHI <_10(3), _7(4)>
<L8>:
<L5>:
  return _3;


Why are we adding -1 to [0,3] ?  Thats the root of this issue I think?  see=
ms
strange=