[llvm] [CodeExtractor] Optimize PHI incoming value removal using reverse iteration (NFC) (PR #171956)

[via llvm-commits]

int-zjt wrote:

> Same question here. I believe this should be using removeIncomingValueIf() instead.

Apologies, I got my replies crossed between two patches. This is actually the place I intended to discuss regarding the `addIncoming` side effect.

As mentioned, using `removeIncomingValueIf` here would require embedding the move logic into the lambda:

```cpp
PN->removeIncomingValueIf([&](unsigned i) {
  if (Blocks.count(PN->getIncomingBlock(i))) {
    // Side effect: moving to NewPN
    NewPN->addIncoming(PN->getIncomingValue(i), PN->getIncomingBlock(i));
    return true;
  }
  return false;
});
```

I feel the explicit loop makes the 'move' semantics clearer than hiding it inside a removal predicate. What do you think?

https://github.com/llvm/llvm-project/pull/171956