[llvm] ValueTracking: generalize isNonEqualPHIs (PR #108820)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

I see the following:

```cpp
  case Instruction::PHI: {
    const PHINode *P = cast<PHINode>(Op);
    // Unreachable blocks may have zero-operand PHI nodes.
    if (P->getNumIncomingValues() == 0)
      break;

    // Otherwise take the unions of the known bit sets of the operands,
    // taking conservative care to avoid excessive recursion.
    const unsigned PhiRecursionLimit = MaxAnalysisRecursionDepth - 2;
```

I'll push a change, and you can check it.

https://github.com/llvm/llvm-project/pull/108820