Revert r1529, which failed on some of the benchmarks.

src/virtual-frame.h

Index: src/virtual-frame.h
===================================================================
--- src/virtual-frame.h	(revision 1531)
+++ src/virtual-frame.h	(working copy)
@@ -101,16 +101,6 @@
   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_;
@@ -139,8 +129,7 @@
 
   // 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_); }
 
@@ -155,6 +144,10 @@
     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);
@@ -182,18 +175,16 @@
 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;
 }