Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1347,6 +1347,27 @@
     return emitUnaryFloatFnCall(Expo, TLI, LibFunc_exp10, LibFunc_exp10f,
                                 LibFunc_exp10l, B, Attrs);
 
+  // pow(C,x) -> exp2(log2(C)*x) if C > 0, C != inf, C != NaN
+  if (Pow->hasOneUse() && Pow->hasApproxFunc() && BaseF->isNormal() &&
+      !BaseF->isNegative()) {
+    Value *Log = nullptr;
+    if (Ty->isFloatTy())
+      Log = ConstantFP::get(Ty, std::log(BaseF->convertToFloat()));
+    else if (Ty->isDoubleTy())
+      Log = ConstantFP::get(Ty, std::log(BaseF->convertToDouble()));
+    if (Log) {
+      Value *FMul = B.CreateFMul(Log, Expo, "logmul");
+      if (Pow->doesNotAccessMemory()) {
+        return B.CreateCall(Intrinsic::getDeclaration(Mod, Intrinsic::exp2, Ty),
+                            FMul, "exp2");
+      } else {
+        if (hasUnaryFloatFn(TLI, Ty, LibFunc_exp2, LibFunc_exp2f,
+                            LibFunc_exp2l))
+          return emitUnaryFloatFnCall(FMul, TLI, LibFunc_exp2, LibFunc_exp2f,
+                                      LibFunc_exp2l, B, Attrs);
+      }
+    }
+  }
   return nullptr;
 }
 
Index: test/Transforms/InstCombine/pow-exp.ll
===================================================================
--- test/Transforms/InstCombine/pow-exp.ll
+++ test/Transforms/InstCombine/pow-exp.ll
@@ -205,6 +205,228 @@
   ret double %pow
 }
 
+declare void @use_d(double)
+declare void @use_f(float)
+
+define double @pow_ok_base(double %e) {
+; CHECK-LABEL: @pow_ok_base(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn double [[E:%.*]], 0xBFD6D3C324E13F50
+; CHECK-NEXT:    [[EXP2:%.*]] = call afn double @exp2(double [[LOGMUL]])
+; CHECK-NEXT:    ret double [[EXP2]]
+;
+  %call = tail call afn double @pow(double 0x3FE6666666666666, double %e)
+  ret double %call
+}
+
+define double @pow_ok_base2(double %e) {
+; CHECK-LABEL: @pow_ok_base2(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn double [[E:%.*]], 0x4006FD0F752F7F61
+; CHECK-NEXT:    [[EXP2:%.*]] = call afn double @exp2(double [[LOGMUL]])
+; CHECK-NEXT:    ret double [[EXP2]]
+;
+  %call = tail call afn double @pow(double 1.770000e+01, double %e)
+  ret double %call
+}
+
+define double @pow_ok_base3(double %e) {
+; CHECK-LABEL: @pow_ok_base3(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn double [[E:%.*]], 0x4002801292821F4C
+; CHECK-NEXT:    [[EXP2:%.*]] = call afn double @exp2(double [[LOGMUL]])
+; CHECK-NEXT:    ret double [[EXP2]]
+;
+  %call = tail call afn double @pow(double 1.010000e+01, double %e)
+  ret double %call
+}
+
+define double @pow_ok_ten_base(double %e) {
+; CHECK-LABEL: @pow_ok_ten_base(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn double [[E:%.*]], 0x40026BB1BBB55516
+; CHECK-NEXT:    [[EXP2:%.*]] = call afn double @exp2(double [[LOGMUL]])
+; CHECK-NEXT:    ret double [[EXP2]]
+;
+  %call = tail call afn double @pow(double 1.000000e+01, double %e)
+  ret double %call
+}
+
+define float @powf_ok_base(float %e) {
+; CHECK-LABEL: @powf_ok_base(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn float [[E:%.*]], 0xBFD6D3C340000000
+; CHECK-NEXT:    [[EXP2F:%.*]] = call afn float @exp2f(float [[LOGMUL]])
+; CHECK-NEXT:    ret float [[EXP2F]]
+;
+  %call = tail call afn float @powf(float 0x3FE6666660000000, float %e)
+  ret float %call
+}
+
+define float @powf_ok_base2(float %e) {
+; CHECK-LABEL: @powf_ok_base2(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn float [[E:%.*]], 0x4006FD0F80000000
+; CHECK-NEXT:    [[EXP2F:%.*]] = call afn float @exp2f(float [[LOGMUL]])
+; CHECK-NEXT:    ret float [[EXP2F]]
+;
+  %call = tail call afn float @powf(float 0x4031B33340000000, float %e)
+  ret float %call
+}
+
+define float @powf_ok_base3(float %e) {
+; CHECK-LABEL: @powf_ok_base3(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn float [[E:%.*]], 0x40028012A0000000
+; CHECK-NEXT:    [[EXP2F:%.*]] = call afn float @exp2f(float [[LOGMUL]])
+; CHECK-NEXT:    ret float [[EXP2F]]
+;
+  %call = tail call afn float @powf(float 0x4024333340000000, float %e)
+  ret float %call
+}
+
+define float @powf_ok_ten_base(float %e) {
+; CHECK-LABEL: @powf_ok_ten_base(
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul afn float [[E:%.*]], 0x40026BB1C0000000
+; CHECK-NEXT:    [[EXP2F:%.*]] = call afn float @exp2f(float [[LOGMUL]])
+; CHECK-NEXT:    ret float [[EXP2F]]
+;
+  %call = tail call afn float @powf(float 1.000000e+01, float %e)
+  ret float %call
+}
+
+define double @pow_zero_base(double %e) {
+; CHECK-LABEL: @pow_zero_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn double @pow(double 0.000000e+00, double [[E:%.*]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call afn double @pow(double 0.000000e+00, double %e)
+  ret double %call
+}
+
+define double @pow_zero_base2(double %e) {
+; CHECK-LABEL: @pow_zero_base2(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn double @pow(double -0.000000e+00, double [[E:%.*]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call afn double @pow(double -0.000000e+00, double %e)
+  ret double %call
+}
+
+define double @pow_inf_base(double %e) {
+; CHECK-LABEL: @pow_inf_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn double @pow(double 0x7FF0000000000000, double [[E:%.*]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call afn double @pow(double 0x7FF0000000000000, double %e)
+  ret double %call
+}
+
+define double @pow_nan_base(double %e) {
+; CHECK-LABEL: @pow_nan_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn double @pow(double 0x7FF8000000000000, double [[E:%.*]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call afn double @pow(double 0x7FF8000000000000, double %e)
+  ret double %call
+}
+
+define double @pow_negative_base(double %e) {
+; CHECK-LABEL: @pow_negative_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn double @pow(double -4.000000e+00, double [[E:%.*]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call afn double @pow(double -4.000000e+00, double %e)
+  ret double %call
+}
+
+define double @pow_multiuse(double %e) {
+; CHECK-LABEL: @pow_multiuse(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn double @pow(double 5.000000e+00, double [[E:%.*]])
+; CHECK-NEXT:    tail call void @use_d(double [[CALL]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call afn double @pow(double 5.000000e+00, double %e)
+  tail call void @use_d(double %call)
+  ret double %call
+}
+
+define double @pow_ok_base_no_afn(double %e) {
+; CHECK-LABEL: @pow_ok_base_no_afn(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call double @pow(double 0x3FE6666666666666, double [[E:%.*]])
+; CHECK-NEXT:    ret double [[CALL]]
+;
+  %call = tail call double @pow(double 0x3FE6666666666666, double %e)
+  ret double %call
+}
+
+define float @powf_zero_base(float %e) {
+; CHECK-LABEL: @powf_zero_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn float @powf(float 0.000000e+00, float [[E:%.*]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call afn float @powf(float 0.000000e+00, float %e)
+  ret float %call
+}
+
+define float @powf_zero_base2(float %e) {
+; CHECK-LABEL: @powf_zero_base2(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn float @powf(float -0.000000e+00, float [[E:%.*]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call afn float @powf(float -0.000000e+00, float %e)
+  ret float %call
+}
+
+define float @powf_inf_base(float %e) {
+; CHECK-LABEL: @powf_inf_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn float @powf(float 0x7FF0000000000000, float [[E:%.*]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call afn float @powf(float 0x7FF0000000000000, float %e)
+  ret float %call
+}
+
+define float @powf_nan_base(float %e) {
+; CHECK-LABEL: @powf_nan_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn float @powf(float 0x7FF8000000000000, float [[E:%.*]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call afn float @powf(float 0x7FF8000000000000, float %e)
+  ret float %call
+}
+
+define float @powf_negative_base(float %e) {
+; CHECK-LABEL: @powf_negative_base(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn float @powf(float -4.000000e+00, float [[E:%.*]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call afn float @powf(float -4.000000e+00, float %e)
+  ret float %call
+}
+
+define float @powf_multiuse(float %e) {
+; CHECK-LABEL: @powf_multiuse(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn float @powf(float 5.000000e+00, float [[E:%.*]])
+; CHECK-NEXT:    tail call void @use_f(float [[CALL]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call afn float @powf(float 5.000000e+00, float %e)
+  tail call void @use_f(float %call)
+  ret float %call
+}
+
+define float @powf_ok_base_no_afn(float %e) {
+; CHECK-LABEL: @powf_ok_base_no_afn(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call float @powf(float 0x3FE6666660000000, float [[E:%.*]])
+; CHECK-NEXT:    ret float [[CALL]]
+;
+  %call = tail call float @powf(float 0x3FE6666660000000, float %e)
+  ret float %call
+}
+
+define fp128 @powl_long_dbl_no_fold(fp128 %e) {
+; CHECK-LABEL: @powl_long_dbl_no_fold(
+; CHECK-NEXT:    [[CALL:%.*]] = tail call afn fp128 @powl(fp128 0xL00000000000000005001000000000000, fp128 [[E:%.*]])
+; CHECK-NEXT:    ret fp128 [[CALL]]
+;
+  %call = tail call afn fp128 @powl(fp128 0xL00000000000000005001000000000000, fp128 %e)
+  ret fp128 %call
+}
+
 declare float @expf(float)
 declare double @exp(double)
 declare fp128 @expl(fp128)
Index: test/Transforms/InstCombine/pow_fp_int.ll
===================================================================
--- test/Transforms/InstCombine/pow_fp_int.ll
+++ test/Transforms/InstCombine/pow_fp_int.ll
@@ -196,8 +196,9 @@
 define double @pow_uitofp_const_base_fast_i32(i32 %x) {
 ; CHECK-LABEL: @pow_uitofp_const_base_fast_i32(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
-; CHECK-NEXT:    [[POW:%.*]] = tail call fast float @llvm.pow.f32(float 7.000000e+00, float [[SUBFP]])
-; CHECK-NEXT:    [[RES:%.*]] = fpext float [[POW]] to double
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul fast float [[SUBFP]], 0x3FFF2272A0000000
+; CHECK-NEXT:    [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[LOGMUL]])
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[EXP2]] to double
 ; CHECK-NEXT:    ret double [[RES]]
 ;
   %subfp = uitofp i32 %x to float
@@ -247,8 +248,9 @@
 define double @pow_sitofp_const_base_fast_i64(i64 %x) {
 ; CHECK-LABEL: @pow_sitofp_const_base_fast_i64(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = sitofp i64 [[X:%.*]] to float
-; CHECK-NEXT:    [[POW:%.*]] = tail call fast float @llvm.pow.f32(float 7.000000e+00, float [[SUBFP]])
-; CHECK-NEXT:    [[RES:%.*]] = fpext float [[POW]] to double
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul fast float [[SUBFP]], 0x3FFF2272A0000000
+; CHECK-NEXT:    [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[LOGMUL]])
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[EXP2]] to double
 ; CHECK-NEXT:    ret double [[RES]]
 ;
   %subfp = sitofp i64 %x to float
@@ -260,8 +262,9 @@
 define double @pow_uitofp_const_base_fast_i64(i64 %x) {
 ; CHECK-LABEL: @pow_uitofp_const_base_fast_i64(
 ; CHECK-NEXT:    [[SUBFP:%.*]] = uitofp i64 [[X:%.*]] to float
-; CHECK-NEXT:    [[POW:%.*]] = tail call fast float @llvm.pow.f32(float 7.000000e+00, float [[SUBFP]])
-; CHECK-NEXT:    [[RES:%.*]] = fpext float [[POW]] to double
+; CHECK-NEXT:    [[LOGMUL:%.*]] = fmul fast float [[SUBFP]], 0x3FFF2272A0000000
+; CHECK-NEXT:    [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[LOGMUL]])
+; CHECK-NEXT:    [[RES:%.*]] = fpext float [[EXP2]] to double
 ; CHECK-NEXT:    ret double [[RES]]
 ;
   %subfp = uitofp i64 %x to float