MIPS: Ensure proper alignment of LazyInstance objects.

src/lazy-instance.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 89 matching lines @@
 
 
 template <typename T>
 struct LeakyInstanceTrait {
   static void Destroy(T* /* instance */) {}
 };
 
 
 // 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);
   }
 
   template <typename ConstructTrait>
   static void InitStorageUsingTrait(StorageType* storage) {
     ConstructTrait::Construct(MutableInstance(storage));
   }
 };
 
+#undef LAZY_ALIGN
+
 
 template <typename T>
 struct DynamicallyAllocatedInstanceTrait {
   typedef T* StorageType;
 
   static T* MutableInstance(StorageType* storage) {
     return *storage;
   }
 
   template <typename CreateTrait>
@@ skipping 67 matching lines @@
     return AllocationTrait::MutableInstance(&storage_);
   }
 
   const T& Get() const {
     Init();
     return *AllocationTrait::MutableInstance(&storage_);
   }
 
   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_;
 };
 
 
 template <typename T,
           typename CreateTrait = DefaultConstructTrait<T>,
           typename InitOnceTrait = SingleThreadInitOnceTrait,
           typename DestroyTrait = LeakyInstanceTrait<T> >
 struct LazyStaticInstance {
   typedef LazyInstanceImpl<T, StaticallyAllocatedInstanceTrait<T>,
@@ skipping 17 matching lines @@
           typename InitOnceTrait = SingleThreadInitOnceTrait,
           typename DestroyTrait = LeakyInstanceTrait<T> >
 struct LazyDynamicInstance {
   typedef LazyInstanceImpl<T, DynamicallyAllocatedInstanceTrait<T>,
       CreateTrait, InitOnceTrait, DestroyTrait> type;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_LAZY_INSTANCE_H_