[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #127450)

[Alexey Bataev via llvm-commits]

================
@@ -12369,14 +12689,22 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
       if (isa<PoisonValue>(UniqueValues[Idx]))
         return InstructionCost(TTI::TCC_Free);
 
-      auto *VI = cast<Instruction>(UniqueValues[Idx]);
-      unsigned OpIdx = isa<UnaryOperator>(VI) ? 0 : 1;
-      TTI::OperandValueInfo Op1Info = TTI::getOperandInfo(VI->getOperand(0));
-      TTI::OperandValueInfo Op2Info =
-          TTI::getOperandInfo(VI->getOperand(OpIdx));
-      SmallVector<const Value *> Operands(VI->operand_values());
+      // We cannot retrieve the operand from UniqueValues[Idx] because an
+      // interchangeable instruction may be used. The order and the actual
+      // operand might differ from what is retrieved from UniqueValues[Idx].
+      Value *Op1 = E->getOperand(0)[Idx];
+      Value *Op2;
+      SmallVector<const Value *, 2> Operands({Op1});
----------------
alexey-bataev wrote:

```suggestion
      SmallVector<const Value *, 2> Operands(1, Op1);
```

https://github.com/llvm/llvm-project/pull/127450