[turbofan] Reenable value numbering.

src/compiler/value-numbering-reducer.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_VALUE_NUMBERING_REDUCER_H_
 #define V8_COMPILER_VALUE_NUMBERING_REDUCER_H_
 
 #include "src/compiler/graph-reducer.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class ValueNumberingReducer FINAL : public Reducer {
  public:
   explicit ValueNumberingReducer(Zone* zone);
   ~ValueNumberingReducer();
 
   virtual Reduction Reduce(Node* node) OVERRIDE;
 
  private:
+  enum { kInitialCapacity = 256u, kCapacityToSizeRatio = 2u };
+
+  void Grow();
   Zone* zone() const { return zone_; }
 
-  // TODO(turbofan): We currently use separate chaining with linked lists here,
-  // we may want to replace that with a more sophisticated data structure at
-  // some point in the future.
-  class Entry;
-  Entry* buckets_[117u];
+  Node** entries_;
+  size_t capacity_;
+  size_t size_;
   Zone* zone_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_VALUE_NUMBERING_REDUCER_H_