[llvm] [SLP] NFC. Use InstructionsState::valid if users just want to know whether VL has same opcode. (PR #120217)

[Han-Kuan Chen via llvm-commits]

================
@@ -8144,9 +8147,8 @@ void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
   }
 
   // Don't handle scalable vectors
-  if (S.getOpcode() == Instruction::ExtractElement &&
-      isa<ScalableVectorType>(
-          cast<ExtractElementInst>(S.getMainOp())->getVectorOperandType())) {
+  if (auto *EE = dyn_cast_if_present<ExtractElementInst>(S.getMainOp());
----------------
HanKuanChen wrote:

1. The origin code check MainOp opcode (`S.getOpcode() == Instruction::ExtractElement`) and use `cast` later. I think use `dyn_cast_if_present` is better.
```
  if (S.getOpcode() == Instruction::ExtractElement &&
      isa<ScalableVectorType>(
          cast<ExtractElementInst>(S.getMainOp())->getVectorOperandType())) {
```
2. There is a case which uses `isa_and_present`. Follow the same idea, I use `dyn_cast_if_present` here.
```
  bool AreAllSameInsts = AreAllSameBlock || AreScatterAllGEPSameBlock;
  if (!AreAllSameInsts || (!S && allConstant(VL)) || isSplat(VL) ||
      (isa_and_present<InsertElementInst, ExtractValueInst, ExtractElementInst>(
           S.getMainOp()) &&
       !all_of(VL, isVectorLikeInstWithConstOps)) ||
      NotProfitableForVectorization(VL)) {
```

https://github.com/llvm/llvm-project/pull/120217