Add a use list iterator that allows mutation of current.

runtime/vm/intermediate_language.h

 // Copyright (c) 2013, 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 53 matching lines @@
 #undef DEFINE_ENUM_LIST
   };
 
   static Kind RecognizeKind(const Function& function);
   static const char* KindToCString(Kind kind);
 };
 
 
 class Value : public ZoneAllocated {
  public:
+  // A forward iterator that allows removing the current value from the
+  // underlying use list during iteration.
+  class Iterator {

[srdjan, 2013/02/04 21:38:17]

public ValueObject?

+   public:
+    explicit Iterator(Value* head) : next_(head) { Advance(); }
+    Value* Current() const { return current_; }
+    bool Done() const { return current_ == NULL; }
+    void Advance() {
+      // Pre-fetch next on advance and cache it.
+      current_ = next_;
+      if (next_ != NULL) next_ = next_->next_use();
+    }
+   private:
+    Value* current_;
+    Value* next_;
+  };
+
   explicit Value(Definition* definition)
       : definition_(definition),
         previous_use_(NULL),
         next_use_(NULL),
         instruction_(NULL),
         use_index_(-1),
         reaching_cid_(kIllegalCid) { }
 
   Definition* definition() const { return definition_; }
   void set_definition(Definition* definition) { definition_ = definition; }
@@ skipping 4393 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_