MIPS: Ensure proper alignment of LazyInstance objects.

src/lazy-instance.h

Index: src/lazy-instance.h
diff --git a/src/lazy-instance.h b/src/lazy-instance.h
index 4beb55c0a291b05cf91bde23ffd8af03f1be9f6a..d0893e560470ee345adbd1af45cd295b998fc610 100644
--- a/src/lazy-instance.h
+++ b/src/lazy-instance.h
@@ -107,9 +107,17 @@ 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);
@@ -121,6 +129,8 @@ struct StaticallyAllocatedInstanceTrait {
   }
 };
 
+#undef LAZY_ALIGN
+
 
 template <typename T>
 struct DynamicallyAllocatedInstanceTrait {
@@ -208,7 +218,8 @@ 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_;
 };