diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
@@ -112,6 +112,11 @@
                                              Optional<FastMathFlags> FMF,
                                              TTI::TargetCostKind CostKind);
 
+  InstructionCost getExtendedReductionCost(unsigned Opcode, bool IsUnsigned,
+                                           Type *ResTy, VectorType *ValTy,
+                                           Optional<FastMathFlags> FMF,
+                                           TTI::TargetCostKind CostKind);
+
   bool isElementTypeLegalForScalableVector(Type *Ty) const {
     return TLI->isLegalElementTypeForRVV(Ty);
   }
diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -377,6 +377,32 @@
   return (LT.first - 1) + BaseCost + Log2_32_Ceil(VL);
 }
 
+InstructionCost RISCVTTIImpl::getExtendedReductionCost(
+    unsigned Opcode, bool IsUnsigned, Type *ResTy, VectorType *ValTy,
+    Optional<FastMathFlags> FMF, TTI::TargetCostKind CostKind) {
+  if (isa<FixedVectorType>(ValTy) && !ST->useRVVForFixedLengthVectors())
+    return BaseT::getExtendedReductionCost(Opcode, IsUnsigned, ResTy, ValTy,
+                                           FMF, CostKind);
+
+  // Skip if scalar size of ResTy is bigger than ELEN.
+  if (ResTy->getScalarSizeInBits() > ST->getELEN())
+    return BaseT::getExtendedReductionCost(Opcode, IsUnsigned, ResTy, ValTy,
+                                           FMF, CostKind);
+
+  if (Opcode != Instruction::Add && Opcode != Instruction::FAdd)
+    return BaseT::getExtendedReductionCost(Opcode, IsUnsigned, ResTy, ValTy,
+                                           FMF, CostKind);
+
+  std::pair<InstructionCost, MVT> LT = TLI->getTypeLegalizationCost(DL, ValTy);
+
+  if (ResTy->getScalarSizeInBits() != 2 * LT.second.getScalarSizeInBits())
+    return BaseT::getExtendedReductionCost(Opcode, IsUnsigned, ResTy, ValTy,
+                                           FMF, CostKind);
+
+  return (LT.first - 1) +
+         getArithmeticReductionCost(Opcode, ValTy, FMF, CostKind);
+}
+
 void RISCVTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
                                            TTI::UnrollingPreferences &UP,
                                            OptimizationRemarkEmitter *ORE) {