- 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 145 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);
   }
 
   void Validate() const;
   intptr_t Size() const;
   intptr_t VisitPointers(ObjectPointerVisitor* visitor);
 
   static RawObject* FromAddr(uword addr) {
     // We expect the untagged address here.
     ASSERT((addr & kSmiTagMask) != kHeapObjectTag);
     return reinterpret_cast<RawObject*>(addr + kHeapObjectTag);
   }
 
   static uword ToAddr(RawObject* raw_obj) {
     return reinterpret_cast<uword>(raw_obj->ptr());
   }
 
  protected:
   RawClass* class_;
 
  private:
   enum {
     kMarkingMask = 3,
     kNotMarked = 1,  // Tagged pointer.
     kMarked = 3,  // Tagged pointer and forwarding bit set.
+    kMarkBit = 2,
   };
 
   RawObject* ptr() const {
     ASSERT(IsHeapObject());
     return reinterpret_cast<RawObject*>(
         reinterpret_cast<uword>(this) - kHeapObjectTag);
   }
 
   intptr_t tags_;  // Various object tags (bits).
 
@@ skipping 661 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_