While working on test cases for JDK-8373134 I discovered a missing optimisation for arithmetic or. Max node implementations get the Max(A, Max(A, B)) == Max(A, B) optimisation via MaxNode::find_identity_operation. However, this is not present for arithmetic or. E.g.

```
    // int c = a * i; is going to optimize to c = a;
    // So this effectively becomes (a | (b | a))
    // Since (a | a) is a, it should be possible to
    // reduce to (a | b)
    private static int test(int b, int a)
    {
        int i;
        for (i = -10; i < 1; i++)
        {
        }
        int c = a * i;
        return a | (b | c);
    }
```

The above results in this IR nodes at the end of gvn. With the optimisation we should expect to find a single Or with 10 and 11.

```
 114 OrI === _ 10 11 [[ 115 ]] !jvms: TestIntOr::test @ bci:21 (line 21)
 115 OrI === _ 11 114 [[ 116 ]] !jvms: TestIntOr::test @ bci:22 (line 21)
```