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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/79119] absolute value of a pointer difference
 can be assumed to be less than or equal to PTRDIFF_MAX
Date: Thu, 27 Apr 2023 22:31:48 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D79119

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So a couple of things need to happen really:
optimized now:
  if (p_10 < q_12)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870913]:
  _3 =3D _22 - _21;
  _4 =3D _3 /[ex] 4;
  iftmp.0_14 =3D (long unsigned int) _4;
  goto <bb 5>; [100.00%]

  <bb 4> [local count: 536870913]:
  _5 =3D _21 - _22;
  _6 =3D _5 /[ex] 4;
  iftmp.0_13 =3D (long unsigned int) _6;

  <bb 5> [local count: 1073741824]:
  # iftmp.0_7 =3D PHI <iftmp.0_14(3), iftmp.0_13(4)>

I have a patch which is able to move the cast out of the PHI (will be posti=
ng
it today or tomorrow).
The next thing is we need to move the /[ext] 4 out of the PHI, I have not
extended PHIOPT to do that just yet (just extended it to handle unary
operations though).
And then we have to see the abs but with _22/_21 being unrelated to p_10/q_=
12
except with a cast, it might be hard. I am looking into a patch for the case
where if _22/_21 was in the conditional.=