[llvm] [SystemZ] Fix Operand Retrieval for Vector Reduction Intrinsic in `shouldExpandReduction` (PR #88874)

[Dominik Steenken via llvm-commits]

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@@ -1322,26 +1323,30 @@ SystemZTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
   return BaseT::getIntrinsicInstrCost(ICA, CostKind);
 }
 
+// Find the type of the vector operand indicated by index.
+// Asserts that the operand indicated is actually a vector.
+FixedVectorType *getOperandVectorType(const IntrinsicInst *II, unsigned Index) {
+  auto *T = II->getOperand(Index)->getType();
+  assert(T->isVectorTy());
+  return cast<FixedVectorType>(T);
+}
+
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dominik-steenken wrote:

The vectors can also have float values, but that would not preclude the `FixedVectorType`. The idea behind the assert was that when you use this function to get the operand type for a given intrinsics vector operand, to check that you supplied the correct operand index, so we don't run into the same error that motivated this PR in the first place.

https://github.com/llvm/llvm-project/pull/88874