[Bug tree-optimization/112104] New: loop of ^1 should just be reduced to ^(n&1)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112104

            Bug ID: 112104
           Summary: loop of ^1 should just be reduced to ^(n&1)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
int
foo(long n3) {
  int j = 0;
  for(int i=0; i<n3; i++)
    j=j^1;
  return j;
}

int
foo1(long n3) {
  int j = 0;
  if (n3>=0)
    j = j ^ (n3&1);
  return j;
}
```

We should figure out that j as the result is just alternating between 0 and 1
(VRP figures that that is the range) in SCCP pattern matching.

I Noticed this while looking into PR 111972