Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1235,8 +1235,8 @@
 }
 
 /// Use exp{,2}(x * y) for pow(exp{,2}(x), y);
-/// exp2(n * x) for pow(2.0 ** n, x); exp10(x) for pow(10.0, x);
-/// exp2(log2(n) * x) for pow(n, x).
+/// ldexp(1.0, x) for pow(2.0, itofp(x)); exp2(n * x) for pow(2.0 ** n, x);
+/// exp10(x) for pow(10.0, x); exp2(log2(n) * x) for pow(n, x).
 Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {
   Value *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
   AttributeList Attrs = Pow->getCalledFunction()->getAttributes();
@@ -1318,6 +1318,24 @@
   if (!match(Pow->getArgOperand(0), m_APFloat(BaseF)))
     return nullptr;
 
+  // pow(2.0, itofp(x)) -> ldexp(1.0, x)
+  if (match(Base, m_SpecificFP(2.0)) &&
+      (isa<SIToFPInst>(Expo) || isa<UIToFPInst>(Expo)) &&
+      hasFloatFn(TLI, Ty, LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl)) {
+    Value *ExpoI = cast<Instruction>(Expo)->getOperand(0);
+    // Make sure that the exponent fits inside an int32_t,
+    // thus avoiding any range issues that the original expression has not.
+    unsigned BitWidth = ExpoI->getType()->getPrimitiveSizeInBits();
+    if (BitWidth < 32 ||
+        (BitWidth == 32 && isa<SIToFPInst>(Expo))) {
+      ExpoI = isa<SIToFPInst>(Expo) ? B.CreateSExt(ExpoI, B.getInt32Ty())
+                                    : B.CreateZExt(ExpoI, B.getInt32Ty());
+      return emitBinaryFloatFnCall(ConstantFP::get(Ty, 1.0), ExpoI, TLI,
+                                   LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl,
+                                   B, Attrs);
+    }
+  }
+
   // pow(2.0 ** n, x) -> exp2(n * x)
   if (hasFloatFn(TLI, Ty, LibFunc_exp2, LibFunc_exp2f, LibFunc_exp2l)) {
     APFloat BaseR = APFloat(1.0);
Index: llvm/test/Transforms/InstCombine/pow_fp_int.ll
===================================================================
--- llvm/test/Transforms/InstCombine/pow_fp_int.ll
+++ llvm/test/Transforms/InstCombine/pow_fp_int.ll
@@ -49,6 +49,18 @@
   ret double %pow
 }
 
+define double @pow_sitofp_double_const_base_2_fast(i32 %x) {
+; CHECK-LABEL: @pow_sitofp_double_const_base_2_fast(
+; CHECK-NEXT:    [[LDEXPF:%.*]] = call afn float @ldexpf(float 1.000000e+00, i32 [[X:%.*]]) #1
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[LDEXPF]] to double
+; CHECK-NEXT:    ret double [[RES]]
+;
+  %subfp = sitofp i32 %x to float
+  %pow = tail call afn float @llvm.pow.f32(float 2.000000e+00, float %subfp)
+  %res = fpext float %pow to double
+  ret double %res
+}
+
 define double @pow_sitofp_double_const_base_power_of_2_fast(i32 %x) {
 ; CHECK-LABEL: @pow_sitofp_double_const_base_power_of_2_fast(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = sitofp i32 [[X:%.*]] to float
@@ -63,6 +75,19 @@
   ret double %res
 }
 
+define double @pow_uitofp_const_base_2_fast(i31 %x) {
+; CHECK-LABEL: @pow_uitofp_const_base_2_fast(
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i31 [[X:%.*]] to i32
+; CHECK-NEXT:    [[LDEXPF:%.*]] = call afn float @ldexpf(float 1.000000e+00, i32 [[TMP1]]) #1
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[LDEXPF]] to double
+; CHECK-NEXT:    ret double [[RES]]
+;
+  %subfp = uitofp i31 %x to float
+  %pow = tail call afn float @llvm.pow.f32(float 2.000000e+00, float %subfp)
+  %res = fpext float %pow to double
+  ret double %res
+}
+
 define double @pow_uitofp_const_base_power_of_2_fast(i31 %x) {
 ; CHECK-LABEL: @pow_uitofp_const_base_power_of_2_fast(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i31 [[X:%.*]] to float
@@ -210,6 +235,19 @@
   ret double %res
 }
 
+define double @pow_uitofp_const_base_2_fast_i32(i32 %x) {
+; CHECK-LABEL: @pow_uitofp_const_base_2_fast_i32(
+; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
+; CHECK-NEXT:    [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[SUBFP]])
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[EXP2]] to double
+; CHECK-NEXT:    ret double [[RES]]
+;
+  %subfp = uitofp i32 %x to float
+  %pow = tail call fast float @llvm.pow.f32(float 2.000000e+00, float %subfp)
+  %res = fpext float %pow to double
+  ret double %res
+}
+
 define double @pow_uitofp_const_base_power_of_2_fast_i32(i32 %x) {
 ; CHECK-LABEL: @pow_uitofp_const_base_power_of_2_fast_i32(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
@@ -302,6 +340,18 @@
   ret double %res
 }
 
+define double @pow_sitofp_const_base_2_no_fast(i32 %x) {
+; CHECK-LABEL: @pow_sitofp_const_base_2_no_fast(
+; CHECK-NEXT:    [[LDEXPF:%.*]] = call float @ldexpf(float 1.000000e+00, i32 [[X:%.*]]) #1
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[LDEXPF]] to double
+; CHECK-NEXT:    ret double [[RES]]
+;
+  %subfp = sitofp i32 %x to float
+  %pow = tail call float @llvm.pow.f32(float 2.000000e+00, float %subfp)
+  %res = fpext float %pow to double
+  ret double %res
+}
+
 define double @pow_sitofp_const_base_power_of_2_no_fast(i32 %x) {
 ; CHECK-LABEL: @pow_sitofp_const_base_power_of_2_no_fast(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = sitofp i32 [[X:%.*]] to float
@@ -316,6 +366,19 @@
   ret double %res
 }
 
+define double @pow_uitofp_const_base_2_no_fast(i32 %x) {
+; CHECK-LABEL: @pow_uitofp_const_base_2_no_fast(
+; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
+; CHECK-NEXT:    [[EXP2:%.*]] = call float @llvm.exp2.f32(float [[SUBFP]])
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[EXP2]] to double
+; CHECK-NEXT:    ret double [[RES]]
+;
+  %subfp = uitofp i32 %x to float
+  %pow = tail call float @llvm.pow.f32(float 2.000000e+00, float %subfp)
+  %res = fpext float %pow to double
+  ret double %res
+}
+
 define double @pow_uitofp_const_base_power_of_2_no_fast(i32 %x) {
 ; CHECK-LABEL: @pow_uitofp_const_base_power_of_2_no_fast(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float