Revert r1529, which failed on some of the benchmarks.

src/virtual-frame.h

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 83 matching lines @@
     ASSERT(type() != MEMORY);
     type_ = (type_ & ~SyncField::mask()) | SyncField::encode(NOT_SYNCED);
   }
 
   bool is_valid() const { return type() != INVALID; }
   bool is_memory() const { return type() == MEMORY; }
   bool is_register() const { return type() == REGISTER; }
   bool is_constant() const { return type() == CONSTANT; }
   bool is_copy() const { return type() == COPY; }
 
-  bool is_copied() const { return IsCopiedField::decode(type_); }
-
-  void set_copied() {
-    type_ = (type_ & ~IsCopiedField::mask()) | IsCopiedField::encode(true);
-  }
-
-  void clear_copied() {
-    type_ = (type_ & ~IsCopiedField::mask()) | IsCopiedField::encode(false);
-  }
-
   Register reg() const {
     ASSERT(is_register());
     return data_.reg_;
   }
 
   Handle<Object> handle() const {
     ASSERT(is_constant());
     return Handle<Object>(data_.handle_);
   }
 
   int index() const {
     ASSERT(is_copy());
     return data_.index_;
   }
 
   bool Equals(FrameElement other);
 
  private:
   enum Type {
     INVALID,
     MEMORY,
     REGISTER,
     CONSTANT,
     COPY
   };
 
   // BitField is <type, shift, size>.
   class SyncField : public BitField<SyncFlag, 0, 1> {};
-  class IsCopiedField : public BitField<bool, 1, 1> {};
-  class TypeField : public BitField<Type, 2, 32 - 2> {};
+  class TypeField : public BitField<Type, 1, 32 - 1> {};
 
   Type type() const { return TypeField::decode(type_); }
 
   // The element's type and a dirty bit.  The dirty bit can be cleared
   // for non-memory elements to indicate that the element agrees with
   // the value in memory in the actual frame.
   int type_;
 
   union {
     Register reg_;
     Object** handle_;
     int index_;
   } data_;
 
+  // The index of the next element in a list of copies, or the frame's
+  // illegal index if there is no next element.
+  int next_;
+
   // Used to construct memory and register elements.
   FrameElement(Type type, Register reg, SyncFlag is_synced) {
     Initialize(type, reg, is_synced);
   }
 
   // Used to construct constant elements.
   inline FrameElement(Handle<Object> value, SyncFlag is_synced);
 
   // Used to initialize invalid, memory, and register elements.
   inline void Initialize(Type type, Register reg, SyncFlag is_synced);
 
   friend class VirtualFrame;
 };
 
 
 } }  // namespace v8::internal
 
 #ifdef ARM
 #include "virtual-frame-arm.h"
 #else  // ia32
 #include "virtual-frame-ia32.h"
 #endif
 
 
 namespace v8 { namespace internal {
 
 FrameElement::FrameElement(Handle<Object> value, SyncFlag is_synced) {
-  type_ = TypeField::encode(CONSTANT)
-          | IsCopiedField::encode(false)
-          | SyncField::encode(is_synced);
+  type_ = TypeField::encode(CONSTANT) | SyncField::encode(is_synced);
   data_.handle_ = value.location();
+  next_ = VirtualFrame::kIllegalIndex;
 }
 
 
 void FrameElement::Initialize(Type type, Register reg, SyncFlag is_synced) {
-  type_ = TypeField::encode(type)
-          | IsCopiedField::encode(false)
-          | SyncField::encode(is_synced);
+  type_ = TypeField::encode(type) | SyncField::encode(is_synced);
   data_.reg_ = reg;
+  next_ = VirtualFrame::kIllegalIndex;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_VIRTUAL_FRAME_H_