[llvm] [VPlan] Use VPInstruction for VPScalarPHIRecipe. (NFCI) (PR #129767)

[via llvm-commits]

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@@ -418,6 +423,7 @@ bool VPInstruction::canGenerateScalarForFirstLane() const {
   if (isSingleScalar() || isVectorToScalar())
     return true;
   switch (Opcode) {
+  case Instruction::PHI:
   case Instruction::ICmp:
----------------
ayalz wrote:

```suggestion
  case Instruction::ICmp:
  case Instruction::PHI:
```
lex order?

https://github.com/llvm/llvm-project/pull/129767