[ptr-traits] Implement the base pointer traits using the actual

[oota-llvm.git] / include / llvm / Support / PointerLikeTypeTraits.h

diff --git a/include/llvm/Support/PointerLikeTypeTraits.h b/include/llvm/Support/PointerLikeTypeTraits.h
index 95d735869f2045f230a37f3b1eb3e26bdfe6497a..c12d237b2796a015633305d789240850c95ebf51 100644 (file)
--- a/include/llvm/Support/PointerLikeTypeTraits.h
+++ b/include/llvm/Support/PointerLikeTypeTraits.h
@@ -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 PointerLikeTypeTraits {
   // 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.