Index: llvm/lib/Target/RISCV/RISCVISelLowering.h
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.h
+++ llvm/lib/Target/RISCV/RISCVISelLowering.h
@@ -185,6 +185,9 @@
   bool mayBeEmittedAsTailCall(const CallInst *CI) const override;
   bool shouldConsiderGEPOffsetSplit() const override { return true; }
 
+  bool decomposeMulByConstant(LLVMContext &Context, EVT VT,
+                              SDValue C) const override;
+
   TargetLowering::AtomicExpansionKind
   shouldExpandAtomicRMWInIR(AtomicRMWInst *AI) const override;
   Value *emitMaskedAtomicRMWIntrinsic(IRBuilder<> &Builder, AtomicRMWInst *AI,
Index: llvm/lib/Target/RISCV/RISCVISelLowering.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -34,6 +34,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/MathExtras.h"
 
 using namespace llvm;
 
@@ -2978,6 +2979,24 @@
   return true;
 }
 
+bool RISCVTargetLowering::decomposeMulByConstant(LLVMContext &Context, EVT VT,
+                                                 SDValue C) const {
+  // Check integral scalar types.
+  if (VT.isScalarInteger()) {
+    // Do not optimize mul on riscv32 with the M extension.
+    if (!Subtarget.is64Bit() && Subtarget.hasStdExtM())
+      return false;
+    if (auto *ConstNode = dyn_cast<ConstantSDNode>(C.getNode())) {
+      int64_t Imm = ConstNode->getSExtValue();
+      if (isPowerOf2_64(Imm + 1) || isPowerOf2_64(Imm - 1) ||
+          isPowerOf2_64(1 - Imm) || isPowerOf2_64(-1 - Imm))
+        return true;
+    }
+  }
+
+  return false;
+}
+
 #define GET_REGISTER_MATCHER
 #include "RISCVGenAsmMatcher.inc"
 
Index: llvm/test/CodeGen/RISCV/mul.ll
===================================================================
--- llvm/test/CodeGen/RISCV/mul.ll
+++ llvm/test/CodeGen/RISCV/mul.ll
@@ -79,12 +79,8 @@
 define signext i32 @mul_constant(i32 %a) nounwind {
 ; RV32I-LABEL: mul_constant:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a1, zero, 5
-; RV32I-NEXT:    call __mulsi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a1, a0, 2
+; RV32I-NEXT:    add a0, a1, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: mul_constant:
@@ -95,19 +91,14 @@
 ;
 ; RV64I-LABEL: mul_constant:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, 5
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    sext.w a0, a0
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 2
+; RV64I-NEXT:    addw a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: mul_constant:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, 5
-; RV64IM-NEXT:    mulw a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 2
+; RV64IM-NEXT:    addw a0, a1, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i32 %a, 5
   ret i32 %1
@@ -177,13 +168,15 @@
 define i64 @mul64_constant(i64 %a) nounwind {
 ; RV32I-LABEL: mul64_constant:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a2, zero, 5
-; RV32I-NEXT:    mv a3, zero
-; RV32I-NEXT:    call __muldi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a3, a0, 2
+; RV32I-NEXT:    add a2, a3, a0
+; RV32I-NEXT:    sltu a3, a2, a3
+; RV32I-NEXT:    srli a0, a0, 30
+; RV32I-NEXT:    slli a4, a1, 2
+; RV32I-NEXT:    or a0, a4, a0
+; RV32I-NEXT:    add a0, a0, a1
+; RV32I-NEXT:    add a1, a0, a3
+; RV32I-NEXT:    mv a0, a2
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: mul64_constant:
@@ -197,18 +190,14 @@
 ;
 ; RV64I-LABEL: mul64_constant:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, 5
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 2
+; RV64I-NEXT:    add a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: mul64_constant:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, 5
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 2
+; RV64IM-NEXT:    add a0, a1, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i64 %a, 5
   ret i64 %1
@@ -305,12 +294,8 @@
 define i32 @muli32_p65(i32 %a) nounwind {
 ; RV32I-LABEL: muli32_p65:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a1, zero, 65
-; RV32I-NEXT:    call __mulsi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a1, a0, 6
+; RV32I-NEXT:    add a0, a1, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli32_p65:
@@ -321,18 +306,14 @@
 ;
 ; RV64I-LABEL: muli32_p65:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, 65
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    addw a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli32_p65:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, 65
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    addw a0, a1, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i32 %a, 65
   ret i32 %1
@@ -341,12 +322,8 @@
 define i32 @muli32_p63(i32 %a) nounwind {
 ; RV32I-LABEL: muli32_p63:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a1, zero, 63
-; RV32I-NEXT:    call __mulsi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a1, a0, 6
+; RV32I-NEXT:    sub a0, a1, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli32_p63:
@@ -357,18 +334,14 @@
 ;
 ; RV64I-LABEL: muli32_p63:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, 63
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    subw a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli32_p63:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, 63
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    subw a0, a1, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i32 %a, 63
   ret i32 %1
@@ -377,13 +350,15 @@
 define i64 @muli64_p65(i64 %a) nounwind {
 ; RV32I-LABEL: muli64_p65:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a2, zero, 65
-; RV32I-NEXT:    mv a3, zero
-; RV32I-NEXT:    call __muldi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a3, a0, 6
+; RV32I-NEXT:    add a2, a3, a0
+; RV32I-NEXT:    sltu a3, a2, a3
+; RV32I-NEXT:    srli a0, a0, 26
+; RV32I-NEXT:    slli a4, a1, 6
+; RV32I-NEXT:    or a0, a4, a0
+; RV32I-NEXT:    add a0, a0, a1
+; RV32I-NEXT:    add a1, a0, a3
+; RV32I-NEXT:    mv a0, a2
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli64_p65:
@@ -397,18 +372,14 @@
 ;
 ; RV64I-LABEL: muli64_p65:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, 65
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    add a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli64_p65:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, 65
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    add a0, a1, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i64 %a, 65
   ret i64 %1
@@ -417,13 +388,14 @@
 define i64 @muli64_p63(i64 %a) nounwind {
 ; RV32I-LABEL: muli64_p63:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a2, zero, 63
-; RV32I-NEXT:    mv a3, zero
-; RV32I-NEXT:    call __muldi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a2, a0, 6
+; RV32I-NEXT:    sltu a3, a2, a0
+; RV32I-NEXT:    srli a4, a0, 26
+; RV32I-NEXT:    slli a5, a1, 6
+; RV32I-NEXT:    or a4, a5, a4
+; RV32I-NEXT:    sub a1, a4, a1
+; RV32I-NEXT:    sub a1, a1, a3
+; RV32I-NEXT:    sub a0, a2, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli64_p63:
@@ -437,18 +409,14 @@
 ;
 ; RV64I-LABEL: muli64_p63:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, 63
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    sub a0, a1, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli64_p63:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, 63
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    sub a0, a1, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i64 %a, 63
   ret i64 %1
@@ -457,12 +425,8 @@
 define i32 @muli32_m63(i32 %a) nounwind {
 ; RV32I-LABEL: muli32_m63:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a1, zero, -63
-; RV32I-NEXT:    call __mulsi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a1, a0, 6
+; RV32I-NEXT:    sub a0, a0, a1
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli32_m63:
@@ -473,18 +437,14 @@
 ;
 ; RV64I-LABEL: muli32_m63:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, -63
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    subw a0, a0, a1
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli32_m63:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, -63
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    subw a0, a0, a1
 ; RV64IM-NEXT:    ret
   %1 = mul i32 %a, -63
   ret i32 %1
@@ -493,12 +453,9 @@
 define i32 @muli32_m65(i32 %a) nounwind {
 ; RV32I-LABEL: muli32_m65:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a1, zero, -65
-; RV32I-NEXT:    call __mulsi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a1, a0, 6
+; RV32I-NEXT:    add a0, a1, a0
+; RV32I-NEXT:    neg a0, a0
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli32_m65:
@@ -509,18 +466,16 @@
 ;
 ; RV64I-LABEL: muli32_m65:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, -65
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    add a0, a1, a0
+; RV64I-NEXT:    negw a0, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli32_m65:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, -65
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    add a0, a1, a0
+; RV64IM-NEXT:    negw a0, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i32 %a, -65
   ret i32 %1
@@ -529,13 +484,14 @@
 define i64 @muli64_m63(i64 %a) nounwind {
 ; RV32I-LABEL: muli64_m63:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a2, zero, -63
-; RV32I-NEXT:    addi a3, zero, -1
-; RV32I-NEXT:    call __muldi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a2, a0, 6
+; RV32I-NEXT:    sltu a3, a0, a2
+; RV32I-NEXT:    srli a4, a0, 26
+; RV32I-NEXT:    slli a5, a1, 6
+; RV32I-NEXT:    or a4, a5, a4
+; RV32I-NEXT:    sub a1, a1, a4
+; RV32I-NEXT:    sub a1, a1, a3
+; RV32I-NEXT:    sub a0, a0, a2
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli64_m63:
@@ -550,18 +506,14 @@
 ;
 ; RV64I-LABEL: muli64_m63:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, -63
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    sub a0, a0, a1
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli64_m63:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, -63
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    sub a0, a0, a1
 ; RV64IM-NEXT:    ret
   %1 = mul i64 %a, -63
   ret i64 %1
@@ -570,13 +522,18 @@
 define i64 @muli64_m65(i64 %a) nounwind {
 ; RV32I-LABEL: muli64_m65:
 ; RV32I:       # %bb.0:
-; RV32I-NEXT:    addi sp, sp, -16
-; RV32I-NEXT:    sw ra, 12(sp)
-; RV32I-NEXT:    addi a2, zero, -65
-; RV32I-NEXT:    addi a3, zero, -1
-; RV32I-NEXT:    call __muldi3
-; RV32I-NEXT:    lw ra, 12(sp)
-; RV32I-NEXT:    addi sp, sp, 16
+; RV32I-NEXT:    slli a2, a0, 6
+; RV32I-NEXT:    add a3, a2, a0
+; RV32I-NEXT:    sltu a2, a3, a2
+; RV32I-NEXT:    srli a0, a0, 26
+; RV32I-NEXT:    slli a4, a1, 6
+; RV32I-NEXT:    or a0, a4, a0
+; RV32I-NEXT:    add a0, a0, a1
+; RV32I-NEXT:    add a0, a0, a2
+; RV32I-NEXT:    snez a1, a3
+; RV32I-NEXT:    add a0, a0, a1
+; RV32I-NEXT:    neg a1, a0
+; RV32I-NEXT:    neg a0, a3
 ; RV32I-NEXT:    ret
 ;
 ; RV32IM-LABEL: muli64_m65:
@@ -591,18 +548,16 @@
 ;
 ; RV64I-LABEL: muli64_m65:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    addi sp, sp, -16
-; RV64I-NEXT:    sd ra, 8(sp)
-; RV64I-NEXT:    addi a1, zero, -65
-; RV64I-NEXT:    call __muldi3
-; RV64I-NEXT:    ld ra, 8(sp)
-; RV64I-NEXT:    addi sp, sp, 16
+; RV64I-NEXT:    slli a1, a0, 6
+; RV64I-NEXT:    add a0, a1, a0
+; RV64I-NEXT:    neg a0, a0
 ; RV64I-NEXT:    ret
 ;
 ; RV64IM-LABEL: muli64_m65:
 ; RV64IM:       # %bb.0:
-; RV64IM-NEXT:    addi a1, zero, -65
-; RV64IM-NEXT:    mul a0, a0, a1
+; RV64IM-NEXT:    slli a1, a0, 6
+; RV64IM-NEXT:    add a0, a1, a0
+; RV64IM-NEXT:    neg a0, a0
 ; RV64IM-NEXT:    ret
   %1 = mul i64 %a, -65
   ret i64 %1