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

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 3405)
+++ src/objects-inl.h	(working copy)
@@ -704,13 +704,15 @@
 #define FIELD_ADDR(p, offset) \
   (reinterpret_cast<byte*>(p) + offset - kHeapObjectTag)
 
+#define FIELD_ADDR_ALIGNED_8(p, offset) \
+  (reinterpret_cast<byte*>((reinterpret_cast<intptr_t>(p) + offset - kHeapObjectTag + 4) & -8))
+
 #define READ_FIELD(p, offset) \
   (*reinterpret_cast<Object**>(FIELD_ADDR(p, offset)))
 
 #define WRITE_FIELD(p, offset, value) \
   (*reinterpret_cast<Object**>(FIELD_ADDR(p, offset)) = value)
 
-
 #define WRITE_BARRIER(object, offset) \
   Heap::RecordWrite(object->address(), offset);
 
@@ -725,11 +727,11 @@
            !Heap::InNewSpace(READ_FIELD(object, offset))); \
   }
 
-#define READ_DOUBLE_FIELD(p, offset) \
-  (*reinterpret_cast<double*>(FIELD_ADDR(p, offset)))
+#define READ_HEAP_NUMBER_FIELD(p, offset) \
+  (*reinterpret_cast<double*>(FIELD_ADDR_ALIGNED_8(p, offset)))
 
-#define WRITE_DOUBLE_FIELD(p, offset, value) \
-  (*reinterpret_cast<double*>(FIELD_ADDR(p, offset)) = value)
+#define WRITE_HEAP_NUMBER_FIELD(p, offset, value) \
+  (*reinterpret_cast<double*>(FIELD_ADDR_ALIGNED_8(p, offset)) = value)
 
 #define READ_INT_FIELD(p, offset) \
   (*reinterpret_cast<int*>(FIELD_ADDR(p, offset)))
@@ -1099,12 +1101,12 @@
 
 
 double HeapNumber::value() {
-  return READ_DOUBLE_FIELD(this, kValueOffset);
+  return READ_HEAP_NUMBER_FIELD(this, kValueMinimumOffset);
 }
 
 
 void HeapNumber::set_value(double value) {
-  WRITE_DOUBLE_FIELD(this, kValueOffset, value);
+  WRITE_HEAP_NUMBER_FIELD(this, kValueMinimumOffset, value);
 }
 
 
@@ -3020,12 +3022,13 @@
 #undef FIELD_ADDR
 #undef READ_FIELD
 #undef WRITE_FIELD
+#undef FIELD_ADDR_ALIGNED_8
 #undef WRITE_BARRIER
 #undef CONDITIONAL_WRITE_BARRIER
 #undef READ_MEMADDR_FIELD
 #undef WRITE_MEMADDR_FIELD
-#undef READ_DOUBLE_FIELD
-#undef WRITE_DOUBLE_FIELD
+#undef READ_HEAP_NUMBER_FIELD
+#undef WRITE_HEAP_NUMBER_FIELD
 #undef READ_INT_FIELD
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD