Switch from template functions overloading to partial template specialization.

This should fix compilation on old GCC.

Review URL: http://codereview.chromium.org/6350012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6563 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/utils.h

@@ -760,20 +760,32 @@ static inline int TenToThe(int exponent) {
 // you can use BitCast to cast one pointer type to another.  This confuses gcc
 // enough that it can no longer see that you have cast one pointer type to
 // another thus avoiding the warning.
+
+// We need different implementations of BitCast for pointer and non-pointer
+// values. We use partial specialization of auxiliary struct to work around
+// issues with template functions overloading.
+template <class Dest, class Source>
+struct BitCastHelper {
+  STATIC_ASSERT(sizeof(Dest) == sizeof(Source));
+
+  INLINE(static Dest cast(const Source& source)) {
+    Dest dest;
+    memcpy(&dest, &source, sizeof(dest));
+    return dest;
+  }
+};
+
+template <class Dest, class Source>
+struct BitCastHelper<Dest, Source*> {
+  INLINE(static Dest cast(Source* source)) {
+    return BitCastHelper<Dest, uintptr_t>::
+        cast(reinterpret_cast<uintptr_t>(source));
+  }
+};
+
 template <class Dest, class Source>
 inline Dest BitCast(const Source& source) {
-  // Compile time assertion: sizeof(Dest) == sizeof(Source)
-  // A compile error here means your Dest and Source have different sizes.
-  typedef char VerifySizesAreEqual[sizeof(Dest) == sizeof(Source) ? 1 : -1];
-
-  Dest dest;
-  memcpy(&dest, &source, sizeof(dest));
-  return dest;
-}
-
-template <class Dest, class Source>
-inline Dest BitCast(Source* source) {
-  return BitCast<Dest>(reinterpret_cast<uintptr_t>(source));
+  return BitCastHelper<Dest, Source>::cast(source);
 }
 
 } }  // namespace v8::internal