In-object double fields unboxing (for 64-bit only).

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 2ff1ce98500e5aa6e9c03faad4bd07b3c3736a8b..c9f68e4771b9797eb0da5fb9ec30583b72552469 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -2830,6 +2830,12 @@ void MarkCompactCollector::MigrateObject(HeapObject* dst,
     Address dst_slot = dst_addr;
     ASSERT(IsAligned(size, kPointerSize));
 
+    bool has_only_tagged_fields = !src->IsConstantPoolArray();
+#if V8_DOUBLE_FIELDS_UNBOXING
+    InobjectPropertiesHelper helper(src->map());
+    has_only_tagged_fields =
+        has_only_tagged_fields && helper.all_fields_tagged();
+#endif
     for (int remaining = size / kPointerSize; remaining > 0; remaining--) {
       Object* value = Memory::Object_at(src_slot);
 
@@ -2838,7 +2844,11 @@ void MarkCompactCollector::MigrateObject(HeapObject* dst,
       // We special case ConstantPoolArrays below since they could contain
       // integers value entries which look like tagged pointers.
       // TODO(mstarzinger): restructure this code to avoid this special-casing.
-      if (!src->IsConstantPoolArray()) {
+      if (has_only_tagged_fields
+#if V8_DOUBLE_FIELDS_UNBOXING
+          || helper.IsTagged(src_slot - src_addr)

[Toon Verwaest, 2014/07/29 15:02:08]

#if V8_DOUBLE_FIELDS_UNBOXING
 if (.. || ) {
#else
 if (..) {
#endif

[Igor Sheludko, 2014/10/30 14:23:43]

Done.

+#endif
+          ) {
         RecordMigratedSlot(value, dst_slot);
       }