Index: llvm/lib/Transforms/Utils/BuildLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/BuildLibCalls.cpp
+++ llvm/lib/Transforms/Utils/BuildLibCalls.cpp
@@ -1269,7 +1269,7 @@
   assert((Name != "") && "Must specify Name to emitBinaryFloatFnCall");
 
   Module *M = B.GetInsertBlock()->getModule();
-  FunctionCallee Callee = M->getOrInsertFunction(Name, Op1->getType(),
+  FunctionCallee Callee = M->getOrInsertFunction(Name, Attrs, Op1->getType(),
                                                  Op1->getType(), Op2->getType());
   CallInst *CI = B.CreateCall(Callee, { Op1, Op2 }, Name);
 
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1450,12 +1450,25 @@
   return nullptr;
 }
 
+// Return an AttributeList containing SExt or ZExt for argument ArgNo,
+// depending on the opcode of Op.
+static AttributeList getExtAttrForArg(unsigned ArgNo, Value *Op) {
+  assert((isa<SIToFPInst>(Op) || isa<UIToFPInst>(Op)) &&
+         "Op expected to be an sitofp/uitfp instruction.");
+  Attribute::AttrKind A = isa<SIToFPInst>(Op) ? Attribute::AttrKind::SExt
+                                              : Attribute::AttrKind::ZExt;
+  SmallVector<std::pair<unsigned, Attribute>, 1> ArgAttrs;
+  ArgAttrs.push_back(std::make_pair(AttributeList::FirstArgIndex + ArgNo,
+                                    Attribute::get(Op->getContext(), A)));
+  return AttributeList::get(Op->getContext(), ArgAttrs);
+}
+
 /// Use exp{,2}(x * y) for pow(exp{,2}(x), y);
 /// 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, IRBuilderBase &B) {
   Value *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
-  AttributeList Attrs; // Attributes are only meaningful on the original call
+  AttributeList NoAttrs;
   Module *Mod = Pow->getModule();
   Type *Ty = Pow->getType();
   bool Ignored;
@@ -1536,8 +1549,8 @@
       hasFloatFn(TLI, Ty, LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl)) {
     if (Value *ExpoI = getIntToFPVal(Expo, B))
       return emitBinaryFloatFnCall(ConstantFP::get(Ty, 1.0), ExpoI, TLI,
-                                   LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl,
-                                   B, Attrs);
+                                   LibFunc_ldexp, LibFunc_ldexpf,
+                                   LibFunc_ldexpl, B, getExtAttrForArg(1, Expo));
   }
 
   // pow(2.0 ** n, x) -> exp2(n * x)
@@ -1559,7 +1572,7 @@
                             FMul, "exp2");
       else
         return emitUnaryFloatFnCall(FMul, TLI, LibFunc_exp2, LibFunc_exp2f,
-                                    LibFunc_exp2l, B, Attrs);
+                                    LibFunc_exp2l, B, NoAttrs);
     }
   }
 
@@ -1568,7 +1581,7 @@
   if (match(Base, m_SpecificFP(10.0)) &&
       hasFloatFn(TLI, Ty, LibFunc_exp10, LibFunc_exp10f, LibFunc_exp10l))
     return emitUnaryFloatFnCall(Expo, TLI, LibFunc_exp10, LibFunc_exp10f,
-                                LibFunc_exp10l, B, Attrs);
+                                LibFunc_exp10l, B, NoAttrs);
 
   // pow(x, y) -> exp2(log2(x) * y)
   if (Pow->hasApproxFunc() && Pow->hasNoNaNs() && BaseF->isFiniteNonZero() &&
@@ -1591,7 +1604,7 @@
                             FMul, "exp2");
       else if (hasFloatFn(TLI, Ty, LibFunc_exp2, LibFunc_exp2f, LibFunc_exp2l))
         return emitUnaryFloatFnCall(FMul, TLI, LibFunc_exp2, LibFunc_exp2f,
-                                    LibFunc_exp2l, B, Attrs);
+                                    LibFunc_exp2l, B, NoAttrs);
     }
   }
 
@@ -1803,7 +1816,6 @@
 
 Value *LibCallSimplifier::optimizeExp2(CallInst *CI, IRBuilderBase &B) {
   Function *Callee = CI->getCalledFunction();
-  AttributeList Attrs; // Attributes are only meaningful on the original call
   StringRef Name = Callee->getName();
   Value *Ret = nullptr;
   if (UnsafeFPShrink && Name == TLI->getName(LibFunc_exp2) &&
@@ -1819,8 +1831,8 @@
       hasFloatFn(TLI, Ty, LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl)) {
     if (Value *Exp = getIntToFPVal(Op, B))
       return emitBinaryFloatFnCall(ConstantFP::get(Ty, 1.0), Exp, TLI,
-                                   LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl,
-                                   B, Attrs);
+                                   LibFunc_ldexp, LibFunc_ldexpf,
+                                   LibFunc_ldexpl, B, getExtAttrForArg(1, Op));
   }
 
   return Ret;
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
@@ -51,7 +51,7 @@
 
 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:%.*]])
+; CHECK-NEXT:    [[LDEXPF:%.*]] = call afn float @ldexpf(float 1.000000e+00, i32 signext [[X:%.*]])
 ; CHECK-NEXT:    [[RES:%.*]] = fpext float [[LDEXPF]] to double
 ; CHECK-NEXT:    ret double [[RES]]
 ;
@@ -78,7 +78,7 @@
 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]])
+; CHECK-NEXT:    [[LDEXPF:%.*]] = call afn float @ldexpf(float 1.000000e+00, i32 zeroext [[TMP1]])
 ; CHECK-NEXT:    [[RES:%.*]] = fpext float [[LDEXPF]] to double
 ; CHECK-NEXT:    ret double [[RES]]
 ;
@@ -343,7 +343,7 @@
 
 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:%.*]])
+; CHECK-NEXT:    [[LDEXPF:%.*]] = call float @ldexpf(float 1.000000e+00, i32 signext [[X:%.*]])
 ; CHECK-NEXT:    [[RES:%.*]] = fpext float [[LDEXPF]] to double
 ; CHECK-NEXT:    ret double [[RES]]
 ;
Index: llvm/test/Transforms/InstCombine/simplify-libcalls.ll
===================================================================
--- llvm/test/Transforms/InstCombine/simplify-libcalls.ll
+++ llvm/test/Transforms/InstCombine/simplify-libcalls.ll
@@ -189,7 +189,7 @@
 }
 define double @fake_ldexp(i32 %x) {
 ; CHECK-LABEL: @fake_ldexp(
-; CHECK-NEXT:    [[Z:%.*]] = call double @ldexp(double 1.0{{.*}}, i32 %x)
+; CHECK-NEXT:    [[Z:%.*]] = call double @ldexp(double 1.0{{.*}}, i32 signext %x)
 ; CHECK-NEXT:    ret double [[Z]]
 
   %y = sitofp i32 %x to double