MIPS: Ensure proper alignment of LazyInstance objects.

The template system converts the actual struct type to an array of chars.
Make sure the alignment is kept by the compiler.

This fixes a lot of serialization-related HW tests, for example cctest test-serialize/Serialize.

BUG=
TEST=cctest test-serialize

Review URL: https://chromiumcodereview.appspot.com/9702114
Patch from Daniel Kalmar <kalmard@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11240 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/lazy-instance.h

@@ -111,9 +111,17 @@ struct LeakyInstanceTrait {
 
 // Traits that define how an instance is allocated and accessed.
 
+// TODO(kalmard): __alignof__ is only defined for GCC > 4.2. Fix alignment issue
+// on MIPS with other compilers.
+#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2))
+#define LAZY_ALIGN(x) __attribute__((aligned(__alignof__(x))))
+#else
+#define LAZY_ALIGN(x)
+#endif
+
 template <typename T>
 struct StaticallyAllocatedInstanceTrait {
-  typedef char StorageType[sizeof(T)];
+  typedef char StorageType[sizeof(T)] LAZY_ALIGN(T);
 
   static T* MutableInstance(StorageType* storage) {
     return reinterpret_cast<T*>(storage);
@@ -125,6 +133,8 @@ struct StaticallyAllocatedInstanceTrait {
   }
 };
 
+#undef LAZY_ALIGN
+
 
 template <typename T>
 struct DynamicallyAllocatedInstanceTrait {
@@ -212,7 +222,8 @@ struct LazyInstanceImpl {
 
   mutable OnceType once_;
   // Note that the previous field, OnceType, is an AtomicWord which guarantees
-  // the correct alignment of the storage field below.
+  // 4-byte alignment of the storage field below. If compiling with GCC (>4.2),
+  // the LAZY_ALIGN macro above will guarantee correctness for any alignment.
   mutable StorageType storage_;
 };