[Bug tree-optimization/126877] New: a==b imples (a+b)&1 is known to 0

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126877

            Bug ID: 126877
           Summary: a==b imples (a+b)&1 is known to 0
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: easyhack, missed-optimization, TREE
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 85316
  Target Milestone: ---

Take:
```
signed f(signed a, signed b)
{
    if (a == b)
    {
      signed c = a + b;
      return c&1;
    }
    return 1;
}
```

This should optimize to return a == b. which it does on the RTL level.


A operator_plus::op1_op2_relation_effect needs to be implemented though the
range that is being intersection with is one with a bitmask/value rather than
zero/nonegative (etc.).


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases