- Remember the fact that an object has been added to the

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
===================================================================
--- runtime/vm/raw_object.h	(revision 22083)
+++ runtime/vm/raw_object.h	(working copy)
@@ -224,8 +224,9 @@
     kCanonicalBit = 2,
     kFromSnapshotBit = 3,
     kWatchedBit = 4,

[siva, 2013/04/27 00:49:37]

The WatchedBit is only used during GC right so we could swap it with kFreeBit.

-    kReservedTagBit = 5,  // kReservedBit{10K,100K,1M,10M}
-    kReservedTagSize = 3,
+    kRememberedBit = 5,
+    kReservedTagBit = 6,  // kReservedBit{10K,100K,1M,10M}
+    kReservedTagSize = 2,
     kSizeTagBit = 8,
     kSizeTagSize = 8,
     kClassIdTagBit = kSizeTagBit + kSizeTagSize,
@@ -299,19 +300,18 @@
     ptr()->tags_ = MarkBit::update(false, tags);
   }
 
-  // Support for GC watched bit.
-  bool IsWatched() const {
-    return WatchedBit::decode(ptr()->tags_);
+  // Support for remembered bit.
+  bool IsRemembered() const {
+    return RememberedBit::decode(ptr()->tags_);
   }
-  void SetWatchedBit() {
-    ASSERT(!IsWatched());
+  void SetRememberedBit() {
+    ASSERT(!IsRemembered());
     uword tags = ptr()->tags_;
-    ptr()->tags_ = WatchedBit::update(true, tags);
+    ptr()->tags_ = RememberedBit::update(true, tags);
   }
-  void ClearWatchedBit() {
-    ASSERT(IsWatched());
+  void ClearRememberedBit() {
     uword tags = ptr()->tags_;
-    ptr()->tags_ = WatchedBit::update(false, tags);
+    ptr()->tags_ = RememberedBit::update(false, tags);
   }
 
   // Support for object tags.
@@ -330,6 +330,21 @@
     ptr()->tags_ = CreatedFromSnapshotTag::update(true, tags);
   }
 
+  // Support for GC watched bit.
+  bool IsWatched() const {
+    return WatchedBit::decode(ptr()->tags_);
+  }
+  void SetWatchedBit() {
+    ASSERT(!IsWatched());
+    uword tags = ptr()->tags_;
+    ptr()->tags_ = WatchedBit::update(true, tags);
+  }
+  void ClearWatchedBit() {
+    ASSERT(IsWatched());
+    uword tags = ptr()->tags_;
+    ptr()->tags_ = WatchedBit::update(false, tags);
+  }
+
   bool IsDartInstance() {
     return (!IsHeapObject() || (GetClassId() >= kInstanceCid));
   }
@@ -386,10 +401,10 @@
  private:
   uword tags_;  // Various object tags (bits).
 
-  class FreeBit : public BitField<bool, kFreeBit, 1> {};
-
   class MarkBit : public BitField<bool, kMarkBit, 1> {};
 
+  class RememberedBit : public BitField<bool, kRememberedBit, 1> {};
+
   class WatchedBit : public BitField<bool, kWatchedBit, 1> {};
 
   class CanonicalObjectTag : public BitField<bool, kCanonicalBit, 1> {};