[llvm] [VPlan] Replace ExtractLast(Elem|LanePerPart) with ExtractLast(Lane/Part) (PR #164124)

[David Sherwood via llvm-commits]

================
@@ -116,14 +116,18 @@ Type *VPTypeAnalysis::inferScalarTypeForRecipe(const VPInstruction *R) {
     return inferScalarType(R->getOperand(1));
   case VPInstruction::FirstActiveLane:
     return Type::getIntNTy(Ctx, 64);
-  case VPInstruction::ExtractLastElement:
-  case VPInstruction::ExtractLastLanePerPart:
+  case VPInstruction::ExtractLastLane:
----------------
david-arm wrote:

The comment above `ExtractLastLane` suggests this is exclusively for vector operands. It's probably worth either having it as a separate case like this:

```
  case VPInstruction::ExtractLastLane: {
    Type *BaseTy = inferScalarType(R->getOperand(0));
    return cast<VectorType>(BaseTy)->getElementType();
  }
```

or asserting that `VecTy` is not null for ExtractLastLane.

https://github.com/llvm/llvm-project/pull/164124