Align double array backing store during compaction and mark-sweep promotion.

src/heap-inl.h

Index: src/heap-inl.h
diff --git a/src/heap-inl.h b/src/heap-inl.h
index ad6f44f935f1af9349d99f0cc670017a3cd7f192..e75248e47168bd64895f239a6134442ae27cfd92 100644
--- a/src/heap-inl.h
+++ b/src/heap-inl.h
@@ -373,6 +373,28 @@ void Heap::RecordWrites(Address address, int start, int len) {
 }
 
 
+STATIC_ASSERT((FixedDoubleArray::kHeaderSize & kDoubleAlignmentMask) == 0);
+STATIC_ASSERT((ConstantPoolArray::kHeaderSize & kDoubleAlignmentMask) == 0);
+
+
+HeapObject* Heap::EnsureDoubleAligned(HeapObject* object, int size) {
+  if ((OffsetFrom(object->address()) & kDoubleAlignmentMask) != 0) {
+    CreateFillerObjectAt(object->address(), kPointerSize);
+    return HeapObject::FromAddress(object->address() + kPointerSize);
+  } else {
+    CreateFillerObjectAt(object->address() + size - kPointerSize,
+                         kPointerSize);
+    return object;
+  }
+}
+
+
+bool Heap::MustBeDoubleAligned(HeapObject* object) {
+  return  object->IsFixedDoubleArray() &&
+      (kObjectAlignment != kDoubleAlignment);
+}
+
+
 OldSpace* Heap::TargetSpace(HeapObject* object) {
   InstanceType type = object->map()->instance_type();
   AllocationSpace space = TargetSpaceId(type);