Address review comments

Author: david-arm

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -5342,10 +5342,10 @@ LoopVectorizationCostModel::getUniformMemOpCost(Instruction *I,
   StoreInst *SI = cast<StoreInst>(I);
 
   bool IsLoopInvariantStoreValue = Legal->isInvariant(SI->getValueOperand());
-  // TODO: We have tests that request the cost of extracting element
-  // VF.getKnownMinValue() - 1 from a scalable vector. This is actually
-  // meaningless, given what we actually want is the last lane and is likely
-  // to be more expensive.
+  // TODO: We have existing tests that request the cost of extracting element
+  // VF.getKnownMinValue() - 1 from a scalable vector. This does not represent
+  // the actual generated code, which involves extracting the last element of
+  // a scalable vector where the lane to extract is unknown at compile time.
   return TTI.getAddressComputationCost(ValTy) +
          TTI.getMemoryOpCost(Instruction::Store, ValTy, Alignment, AS,
                              CostKind) +

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -3495,6 +3495,7 @@ void VPInterleaveRecipe::execute(VPTransformState &State) {
 
       return;
     }
+    assert(!State.VF.isScalable() && "VF is assumed to be non scalable.");
 
     // For each member in the group, shuffle out the appropriate data from the
     // wide loads.