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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/102872] New: If statement is always false but
 not figured out at gimple level
Date: Thu, 21 Oct 2021 08:25:31 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102872

            Bug ID: 102872
           Summary: If statement is always false but not figured out at
                    gimple level
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, TREE
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
void foo(void);

static int a, b;
int main() {
  for (; a; ++a) {
    unsigned short d =3D a;
    if (!(b | d) && d)
      foo();
  }
}
---- CUT ---
This is the reduced testcase of PR 102703 but without the store to a static
variable which then was removed.

In VRP1 we have:
  d_10 =3D (short unsigned int) a.3_5;
  _9 =3D a.3_5 & 65535;
  if (_9 =3D=3D 0)
    goto <bb 4>; [50.00%]
  else
    goto <bb 6>; [50.00%]

  <bb 4> [local count: 477815112]:
  if (d_10 !=3D 0)
    goto <bb 5>; [33.00%]
  else
    goto <bb 6>; [67.00%]

  <bb 5> [local count: 157678986]:
  foo ();

_9 and d_10 have the same value though different types.=