Remove log2 dependency when building against Android API-9 SDK

[pasaulais]

Summary

Android's API-9 SDK is missing log2 builtins. A previous commit added support for building against this API revision but this requires log2l to be present. This patch removes the dependency on log2l when HAVE_LOG2 is zero.

[pasaulais]

Forgot to add suscribers.

[chandlerc]

This commit doesn't really make sense to me as at no point does it define HAVE_LOG2....

[pasaulais]

This comment was removed by pasaulais.

[pasaulais]

That's true, this commit would require manually setting HAVE_LOG2 to zero on Android. Since HAVE_LOG2 and other macros have been dropped (r231679) I was trying not to pull the autoconf/CMake changes back. I see two solutions:

1. Use 'log(n) / log(2)' instead of log2l on Android, don't use HAVE_LOG2 at all.
2. Reintroduce HAVE_LOG2 through CMake and autoconf. Remove the Android-specific changes added by Vince.

I am uploading a new patch that does 1) since that's the least intrusive change.

[chandlerc]

Looks good to me.

[pasaulais]

Thanks, Chandler. I don't have commit rights, could you commit it for me?

[vharron]

I needed this patch so I was able to verify and submit. Thanks Pierre-Andre!

[pasaulais]

Thanks for committing the patch, Vince!

llvm/trunk/include/llvm/Support/MathExtras.h

static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
   return detail::PopulationCounter<T, sizeof(T)>::count(Value);
 }
 
 /// Log2 - This function returns the log base 2 of the specified value
 inline double Log2(double Value) {
 #if defined(__ANDROID_API__) && __ANDROID_API__ < 18
-  return (double)__builtin_log2l(Value);
+  return __builtin_log(Value) / __builtin_log(2.0);
 #else
   return log2(Value);
 #endif
 }
 
 /// Log2_32 - This function returns 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