Revert r1529, which failed on some of the benchmarks.

src/virtual-frame.cc

 // Copyright 2009 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 75 matching lines @@
       // We do not allow copies of copies, so we follow one link to
       // the actual backing store of a copy before making a copy.
       index = target.index();
       ASSERT(elements_[index].is_memory() || elements_[index].is_register());
       // Fall through.
 
     case FrameElement::MEMORY:  // Fall through.
     case FrameElement::REGISTER:
       // All copies are backed by memory or register locations.
       result.type_ =
-          FrameElement::TypeField::encode(FrameElement::COPY)
-          | FrameElement::IsCopiedField::encode(false)
-          | FrameElement::SyncField::encode(FrameElement::NOT_SYNCED);
+          FrameElement::TypeField::encode(FrameElement::COPY) |
+          FrameElement::SyncField::encode(FrameElement::NOT_SYNCED);
       result.data_.index_ = index;
-      elements_[index].set_copied();
       break;
 
     case FrameElement::INVALID:
       // We should not try to copy invalid elements.
       UNREACHABLE();
       break;
   }
   return result;
 }
 
@@ skipping 251 matching lines @@
   bool same_constant = original.is_constant()
                     && value->is_constant()
                     && original.handle().is_identical_to(value->handle());
   if (same_register || same_constant) {
     value->Unuse();
     return;
   }
 
   // If the original may be a copy, adjust to preserve the copy-on-write
   // semantics of copied elements.
-  if (original.is_copied() &&
-      (original.is_register() || original.is_memory())) {
+  if (original.is_register() || original.is_memory()) {
     FrameElement ignored = AdjustCopies(frame_index);
   }
 
   // If the original is a register reference, deallocate it.
   if (original.is_register()) {
     Unuse(original.reg());
   }
 
   FrameElement new_element;
   if (value->is_register()) {
@@ skipping 174 matching lines @@
   for (int i = 0; i < kNumRegisters; i++) {
     if (frame_registers_.count(i) != other->frame_registers_.count(i)) {
       return false;
     }
   }
 
   return true;
 }
 
 } }  // namespace v8::internal