Do not reuse tags_ field to store next_ pointer of FreeListElement.

runtime/vm/raw_object.h

 // Copyright (c) 2012, 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 "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/token.h"
@@ skipping 171 matching lines @@
     kReservedBit10K = 4,
     kReservedBit100K = 5,
     kReservedBit1M = 6,
     kReservedBit10M = 7,
     kSizeTagBit = 8,
     kSizeTagSize = 8,
     kClassIdTagBit = kSizeTagBit + kSizeTagSize,
     kClassIdTagSize = 16
   };
 
+  class FreeBit : public BitField<bool, kFreeBit, 1> {};

[Ivan Posva, 2012/06/08 12:50:20]

Do you still need to make this public?

[Vyacheslav Egorov (Google), 2012/06/08 12:58:27]

We still initialize it in the FreeListElement::AsElement.

Moved to private, made FreeListElement a friend of RawClass.

+
   // Encodes the object size in the tag in units of object alignment.
   class SizeTag {
    public:
     static const intptr_t kMaxSizeTag =
         ((1 << RawObject::kSizeTagSize) - 1) << kObjectAlignmentLog2;
 
     static uword encode(intptr_t size) {
       return SizeBits::encode(SizeToTagValue(size));
     }
 
@@ skipping 63 matching lines @@
     return CreatedFromSnapshotTag::decode(ptr()->tags_);
   }
   void SetCreatedFromSnapshot() {
     uword tags = ptr()->tags_;
     ptr()->tags_ = CreatedFromSnapshotTag::update(true, tags);
   }
 
   intptr_t Size() const {
     uword tags = ptr()->tags_;
     intptr_t result = SizeTag::decode(tags);
-    if ((result != 0) && !FreeBit::decode(tags)) {
+    if (result != 0) {
       ASSERT(result == SizeFromClass());
       return result;
     }
     result = SizeFromClass();
-    ASSERT((result > SizeTag::kMaxSizeTag) || FreeBit::decode(tags));
+    ASSERT(result > SizeTag::kMaxSizeTag);
     return result;
   }
 
   void Validate(Isolate* isolate) const;
   intptr_t VisitPointers(ObjectPointerVisitor* visitor);
   bool FindObject(FindObjectVisitor* visitor);
 
   static RawObject* FromAddr(uword addr) {
     // We expect the untagged address here.
     ASSERT((addr & kSmiTagMask) != kHeapObjectTag);
@@ skipping 20 matching lines @@
   static bool IsOneByteStringClassId(intptr_t index);
   static bool IsTwoByteStringClassId(intptr_t index);
   static bool IsExternalStringClassId(intptr_t index);
   static bool IsBuiltinListClassId(intptr_t index);
   static bool IsByteArrayClassId(intptr_t index);
 
  protected:
   uword tags_;  // Various object tags (bits).
 
  private:
-  class FreeBit : public BitField<bool, kFreeBit, 1> {};
-
   class MarkBit : public BitField<bool, kMarkBit, 1> {};
 
   class CanonicalObjectTag : public BitField<bool, kCanonicalBit, 1> {};
 
   class CreatedFromSnapshotTag : public BitField<bool, kFromSnapshotBit, 1> {};
 
   RawObject* ptr() const {
     ASSERT(IsHeapObject());
     return reinterpret_cast<RawObject*>(
         reinterpret_cast<uword>(this) - kHeapObjectTag);
   }
 
   intptr_t SizeFromClass() const;
 
   intptr_t GetClassId() const {
     uword tags = ptr()->tags_;
-    // TODO(vegorov): stop destroying tags_ when creating FreeListElement.
-    ASSERT(!FreeBit::decode(tags));
     return ClassIdTag::decode(tags);
   }
 
   friend class Api;
   friend class Array;
   friend class Heap;
   friend class MarkingVisitor;
   friend class Object;
   friend class RawInstructions;
   friend class RawInstance;
@@ skipping 1149 matching lines @@
          kExternalUint64Array == kByteArray + 18 &&
          kExternalFloat32Array == kByteArray + 19 &&
          kExternalFloat64Array == kByteArray + 20 &&
          kClosure == kByteArray + 21);
   return (index >= kByteArray && index <= kClosure);
 }
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_