[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #133888)

[Alexey Bataev via llvm-commits]

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@@ -599,6 +599,28 @@ static std::optional<unsigned> getElementIndex(const Value *Inst,
   return Index;
 }
 
+/// \returns true if all of the values in \p VL use the same opcode.
+/// For comparison instructions, also checks if predicates match.
+/// PoisonValues are considered matching.
+/// Interchangeable instructions are not considered.
+static bool allSameOpcode(ArrayRef<Value *> VL) {
+  auto *It = find_if(VL, IsaPred<Instruction>);
+  if (It == VL.end())
+    return true;
+  Instruction *MainOp = cast<Instruction>(*It);
+  unsigned Opcode = MainOp->getOpcode();
+  bool IsCmpOp = isa<CmpInst>(MainOp);
+  CmpInst::Predicate BasePred = IsCmpOp ? cast<CmpInst>(MainOp)->getPredicate()
+                                        : CmpInst::BAD_ICMP_PREDICATE;
+  return std::all_of(It, VL.end(), [&](Value *V) {
+    if (auto *CI = dyn_cast<CmpInst>(V))
+      return BasePred == CI->getPredicate();
+    if (auto *I = dyn_cast<Instruction>(V))
+      return I->getOpcode() == Opcode;
+    return isa<PoisonValue>(V);
+  });
+}
+
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alexey-bataev wrote:

We have a function `isAlternateInstruction`, can we use it here?

https://github.com/llvm/llvm-project/pull/133888