diff --git a/llvm/include/llvm/Analysis/TargetTransformInfo.h b/llvm/include/llvm/Analysis/TargetTransformInfo.h
--- a/llvm/include/llvm/Analysis/TargetTransformInfo.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfo.h
@@ -1290,7 +1290,7 @@
   /// Calculate the cost of an extended reduction pattern, similar to
   /// getArithmeticReductionCost of a reduction with an extension.
   /// This is the cost of as:
-  /// ResTy vecreduce(ext(Ty A)).
+  /// ResTy vecreduce.opcode(ext(Ty A)).
   InstructionCost getExtendedReductionCost(
       unsigned Opcode, bool IsUnsigned, Type *ResTy, VectorType *Ty,
       Optional<FastMathFlags> FMF,
diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
--- a/llvm/include/llvm/CodeGen/BasicTTIImpl.h
+++ b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -2329,7 +2329,7 @@
                                            Optional<FastMathFlags> FMF,
                                            TTI::TargetCostKind CostKind) {
     // Without any native support, this is equivalent to the cost of
-    // vecreduce.op(ext).
+    // vecreduce.opcode(ext(Ty A)).
     VectorType *ExtTy = VectorType::get(ResTy, Ty);
     InstructionCost RedCost =
         thisT()->getArithmeticReductionCost(Opcode, ExtTy, FMF, CostKind);
@@ -2344,7 +2344,8 @@
                                          VectorType *Ty,
                                          TTI::TargetCostKind CostKind) {
     // Without any native support, this is equivalent to the cost of
-    // vecreduce.add(mul(ext, ext)).
+    // vecreduce.add(mul(ext(Ty A), ext(Ty B))) or
+    // vecreduce.add(mul(A, B)).
     VectorType *ExtTy = VectorType::get(ResTy, Ty);
     InstructionCost RedCost = thisT()->getArithmeticReductionCost(
         Instruction::Add, ExtTy, None, CostKind);