[llvm] [SLP] NFC. Refactor getSameOpcode and reduce for loop iterations. (PR #122241)

[Han-Kuan Chen via llvm-commits]

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@@ -915,24 +915,22 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
   if (It == VL.end())
     return InstructionsState::invalid();
 
-  Value *V = *It;
+  Instruction *MainOp = cast<Instruction>(*It);
   unsigned InstCnt = std::count_if(It, VL.end(), IsaPred<Instruction>);
-  if ((VL.size() > 2 && !isa<PHINode>(V) && InstCnt < VL.size() / 2) ||
+  if ((VL.size() > 2 && !isa<PHINode>(MainOp) && InstCnt < VL.size() / 2) ||
       (VL.size() == 2 && InstCnt < 2))
     return InstructionsState::invalid();
 
-  bool IsCastOp = isa<CastInst>(V);
-  bool IsBinOp = isa<BinaryOperator>(V);
-  bool IsCmpOp = isa<CmpInst>(V);
-  CmpInst::Predicate BasePred =
-      IsCmpOp ? cast<CmpInst>(V)->getPredicate() : CmpInst::BAD_ICMP_PREDICATE;
-  unsigned Opcode = cast<Instruction>(V)->getOpcode();
+  bool IsCastOp = isa<CastInst>(MainOp);
+  bool IsBinOp = isa<BinaryOperator>(MainOp);
+  bool IsCmpOp = isa<CmpInst>(MainOp);
+  CmpInst::Predicate BasePred = IsCmpOp ? cast<CmpInst>(MainOp)->getPredicate()
+                                        : CmpInst::BAD_ICMP_PREDICATE;
+  Instruction *AltOp = MainOp;
+  unsigned Opcode = MainOp->getOpcode();
   unsigned AltOpcode = Opcode;
-  unsigned AltIndex = std::distance(VL.begin(), It);
 
-  bool SwappedPredsCompatible = [&]() {
-    if (!IsCmpOp)
-      return false;
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HanKuanChen wrote:

Why not use `bool SwappedPredsCompatible = IsCmpOp && [&]() {`? The `&&` performs short-circuit evaluation, which can make the code clearer.

https://github.com/llvm/llvm-project/pull/122241