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

[Jonas Paulsson via llvm-commits]

================
@@ -1323,25 +1324,43 @@ SystemZTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
 }
 
 bool SystemZTTIImpl::shouldExpandReduction(const IntrinsicInst *II) const {
-  // Always expand on Subtargets without vector instructions
+  // Always expand on Subtargets without vector instructions.
   if (!ST->hasVector())
     return true;
 
-  // Always expand for operands that do not fill one vector reg
-  auto *Type = cast<FixedVectorType>(II->getOperand(0)->getType());
-  unsigned NumElts = Type->getNumElements();
-  unsigned ScalarSize = Type->getScalarSizeInBits();
+  // Find the type of the vector operand of the intrinsic
+  // This assumes that each vector reduction intrinsic only
+  // has one vector operand.
+  FixedVectorType *VType = 0x0;
+  for (unsigned I = 0; I < II->getNumOperands(); ++I) {
+    auto *T = II->getOperand(I)->getType();
+    if (T->isVectorTy()) {
+      VType = cast<FixedVectorType>(T);
+      break;
+    }
+  }
+
+  // If we did not find a vector operand, do not continue.
+  if (VType == 0x0)
+    return true;
+
+  // If the vector operand is not a full vector, the reduction
+  // should be expanded.
+  unsigned NumElts = VType->getNumElements();
+  unsigned ScalarSize = VType->getScalarSizeInBits();
   unsigned MaxElts = SystemZ::VectorBits / ScalarSize;
   if (NumElts < MaxElts)
     return true;
 
-  // Otherwise
+  // Handling of full vector operands depends on the
+  // individual intrinsic.
   switch (II->getIntrinsicID()) {
-  // Do not expand vector.reduce.add
-  case Intrinsic::vector_reduce_add:
-    // Except for i64, since the performance benefit is dubious there
-    return ScalarSize >= 64;
   default:
     return true;
+  // Do not expand vector.reduce.add...
+  case Intrinsic::vector_reduce_add:
----------------
JonPsson1 wrote:

I think generally we might want to keep the code as simple as possible until we actually need something more complex. In this case it is slightly confusing to me to go through the switch and all, when there is actually only one intrinsic handled... But not sure if this is just my opinion... 

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