Environment sets the environment position when copying to maintain the use lists.

runtime/vm/intermediate_language.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_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 3327 matching lines @@
 
   Location* LocationSlotAt(intptr_t ix) const {
     ASSERT((ix >= 0) && (ix < values_.length()));
     return &locations_[ix];
   }
 
   intptr_t fixed_parameter_count() const {
     return fixed_parameter_count_;
   }
 
-  Environment* Copy() const;
+  void CopyTo(Instruction* instr) const;
 
   void PrintTo(BufferFormatter* f) const;
 
  private:
   Environment(intptr_t length, intptr_t fixed_parameter_count)
       : values_(length),
         locations_(NULL),
         fixed_parameter_count_(fixed_parameter_count) { }
 
   GrowableArray<Value*> values_;
@@ skipping 39 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_