- Implement the old sweeper.

vm/raw_object.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_RAW_OBJECT_H_
 #define VM_RAW_OBJECT_H_
 
 #include "vm/assert.h"
 #include "vm/globals.h"
 #include "vm/snapshot.h"
@@ skipping 154 matching lines @@
     return mark_bits == kMarked;
   }
   void SetMarkBit() {
     ASSERT(!IsMarked());
     uword header_bits = reinterpret_cast<uword>(ptr()->class_);
     ptr()->class_ = reinterpret_cast<RawClass*>(header_bits | kMarked);
   }
   void ClearMarkBit() {
     ASSERT(IsMarked());
     uword header_bits = reinterpret_cast<uword>(ptr()->class_);
-    ptr()->class_ = reinterpret_cast<RawClass*>(header_bits ^ kMarked);
+    ptr()->class_ = reinterpret_cast<RawClass*>(header_bits ^ kMarkBit);
   }
 
   // Support for object tags.
   bool IsCanonical() const {
     return CanonicalObjectTag::decode(ptr()->tags_);
   }
   void SetCanonical() {
     intptr_t tags = ptr()->tags_;
     ptr()->tags_ = CanonicalObjectTag::update(true, tags);
   }
@@ skipping 29 matching lines @@
 
  protected:
   RawClass* class_;
   intptr_t tags_;  // Various object tags (bits).
 
  private:
   enum {
     kMarkingMask = 3,
     kNotMarked = 1,  // Tagged pointer.
     kMarked = 3,  // Tagged pointer and forwarding bit set.
+    kMarkBit = 2,
   };
 
   class CanonicalObjectTag : public BitField<bool, 2, 1> {
   };
 
   class CreatedFromSnapshotTag : public BitField<bool, 3, 1> {
   };
 
   RawObject* ptr() const {
     ASSERT(IsHeapObject());
@@ skipping 664 matching lines @@
   intptr_t type_;  // Uninitialized, simple or complex.
   intptr_t flags_;  // Represents global/local, case insensitive, multiline.
 
   // Variable length data follows here.
   uint8_t data_[0];
 };
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_