Always 64-bit align floating point values in heap numbers....

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 3405)
+++ src/heap.cc	(working copy)
@@ -773,6 +773,9 @@
       // Copy the from-space object to its new location (given by the
       // forwarding address) and fix its map.
       HeapObject* target = source->map_word().ToForwardingAddress();
+      // We don't need to worry about alignment and HeapNumbers here because
+      // a heap number is put in data space directly and not queued up for
+      // copying and scanning for pointers here.
       CopyBlock(reinterpret_cast<Object**>(target->address()),
                 reinterpret_cast<Object**>(source->address()),
                 source->SizeFromMap(map));
@@ -936,11 +939,21 @@
 
 HeapObject* Heap::MigrateObject(HeapObject* source,
                                 HeapObject* target,
-                                int size) {
-  // Copy the content of source to target.
-  CopyBlock(reinterpret_cast<Object**>(target->address()),
-            reinterpret_cast<Object**>(source->address()),
-            size);
+                                int size,
+                                MapWord first_word) {
+  if (kObjectAlignment == 4 &&
+      size == HeapNumber::kSize &&
+      ((reinterpret_cast<intptr_t>(source) & 7) !=
+       (reinterpret_cast<intptr_t>(target) & 7)) &&
+      first_word.ToMap() == Heap::heap_number_map()) {
+    target->set_map_word(first_word);
+    reinterpret_cast<HeapNumber*>(source)->CopyBodyTo(target);
+  } else {
+    // Copy the content of source to target.
+    CopyBlock(reinterpret_cast<Object**>(target->address()),
+              reinterpret_cast<Object**>(source->address()),
+              size);
+  }
 
   // Set the forwarding address.
   source->set_map_word(MapWord::FromForwardingAddress(target));
@@ -1039,7 +1052,7 @@
           // and not revisited---we will never sweep that space for
           // pointers and the copied objects do not contain pointers to
           // new space objects.
-          *p = MigrateObject(object, target, object_size);
+          *p = MigrateObject(object, target, object_size, first_word);
 #ifdef DEBUG
           VerifyNonPointerSpacePointersVisitor v;
           (*p)->Iterate(&v);
@@ -1053,7 +1066,11 @@
   Object* result = new_space_.AllocateRaw(object_size);
   // Failed allocation at this point is utterly unexpected.
   ASSERT(!result->IsFailure());
-  *p = MigrateObject(object, HeapObject::cast(result), object_size);
+  HeapObject* target = HeapObject::cast(result);
+  *p = MigrateObject(object,
+                     HeapObject::cast(target),
+                     object_size,
+                     first_word);
 }