diff --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -22,10 +22,6 @@
 #include <limits>
 #include <type_traits>
 
-#ifdef __ANDROID_NDK__
-#include <android/api-level.h>
-#endif
-
 #ifdef _MSC_VER
 // Declare these intrinsics manually rather including intrin.h. It's very
 // expensive, and MathExtras.h is popular.
@@ -608,15 +604,6 @@
 
 template <> constexpr inline size_t CTLog2<1>() { return 0; }
 
-/// Return the log base 2 of the specified value.
-inline double Log2(double Value) {
-#if defined(__ANDROID_API__) && __ANDROID_API__ < 18
-  return __builtin_log(Value) / __builtin_log(2.0);
-#else
-  return log2(Value);
-#endif
-}
-
 /// Return the floor log base 2 of the specified value, -1 if the value is zero.
 /// (32 bit edition.)
 /// Ex. Log2_32(32) == 5, Log2_32(1) == 0, Log2_32(0) == -1, Log2_32(6) == 2
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -2150,7 +2150,7 @@
         return ConstantFoldFP(log, APF, Ty);
       case Intrinsic::log2:
         // TODO: What about hosts that lack a C99 library?
-        return ConstantFoldFP(Log2, APF, Ty);
+        return ConstantFoldFP(log2, APF, Ty);
       case Intrinsic::log10:
         // TODO: What about hosts that lack a C99 library?
         return ConstantFoldFP(log10, APF, Ty);
@@ -2279,7 +2279,7 @@
     case LibFunc_log2f_finite:
       if (!APF.isNegative() && !APF.isZero() && TLI->has(Func))
         // TODO: What about hosts that lack a C99 library?
-        return ConstantFoldFP(Log2, APF, Ty);
+        return ConstantFoldFP(log2, APF, Ty);
       break;
     case LibFunc_log10:
     case LibFunc_log10f: