[llvm] r256656 - Revert "Revert "[ptr-traits] Implement the base pointer traits using the actual""

[Chandler Carruth via llvm-commits]

Author: chandlerc
Date: Wed Dec 30 17:37:25 2015
New Revision: 256656

URL: http://llvm.org/viewvc/llvm-project?rev=256656&view=rev
Log:
Revert "Revert "[ptr-traits] Implement the base pointer traits using the actual""

This reverts commit r256642 and restores r256620 now that Tobias has
updated Polly.

There are still some potential problems with the code in Polly that I've
sent post-commit review about, but they're unlikely to break anything in
practice, and I'd like to avoid the rest of LLVM and Clang regressing
here.

Modified:
    llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h

Modified: llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h?rev=256656&r1=256655&r2=256656&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h (original)
+++ llvm/trunk/include/llvm/Support/PointerLikeTypeTraits.h Wed Dec 30 17:37:25 2015
@@ -15,6 +15,7 @@
 #ifndef LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
 #define LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
 
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/DataTypes.h"
 
 namespace llvm {
@@ -27,15 +28,32 @@ template <typename T> class PointerLikeT
   // getNumLowBitsAvailable
 };
 
+namespace detail {
+/// A tiny meta function to compute the log2 of a compile time constant.
+template <size_t N>
+struct ConstantLog2
+    : std::integral_constant<size_t, ConstantLog2<N / 2>::value + 1> {};
+template <> struct ConstantLog2<1> : std::integral_constant<size_t, 0> {};
+}
+
 // Provide PointerLikeTypeTraits for non-cvr pointers.
-template <typename T> class PointerLikeTypeTraits<T *> {
-public:
+template <typename T> struct PointerLikeTypeTraits<T *> {
   static inline void *getAsVoidPointer(T *P) { return P; }
   static inline T *getFromVoidPointer(void *P) { return static_cast<T *>(P); }
 
-  /// Note, we assume here that malloc returns objects at least 4-byte aligned.
-  /// However, this may be wrong, or pointers may be from something other than
-  /// malloc.  In this case, you should specialize this template to reduce this.
+  enum {
+    NumLowBitsAvailable = detail::ConstantLog2<AlignOf<T>::Alignment>::value
+  };
+};
+
+template <> struct PointerLikeTypeTraits<void *> {
+  static inline void *getAsVoidPointer(void *P) { return P; }
+  static inline void *getFromVoidPointer(void *P) { return P; }
+
+  /// Note, we assume here that void* is related to raw malloc'ed memory and
+  /// that malloc returns objects at least 4-byte aligned. However, this may be
+  /// wrong, or pointers may be from something other than malloc. In this case,
+  /// you should specify a real typed pointer or avoid this template.
   ///
   /// All clients should use assertions to do a run-time check to ensure that
   /// this is actually true.