[Bug tree-optimization/102872] New: If statement is always false but not figured out at gimple level

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102872

            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 = 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 = (short unsigned int) a.3_5;
  _9 = a.3_5 & 65535;
  if (_9 == 0)
    goto <bb 4>; [50.00%]
  else
    goto <bb 6>; [50.00%]

  <bb 4> [local count: 477815112]:
  if (d_10 != 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.