[turbofan] Make sure value numbering only narrows types.

src/compiler/value-numbering-reducer.h

Index: src/compiler/value-numbering-reducer.h
diff --git a/src/compiler/value-numbering-reducer.h b/src/compiler/value-numbering-reducer.h
index 822b6075c5ff4b5c6801f1e212cc408c6188f639..f700c85bc00dec321fa8948799f8e24aab4e880d 100644
--- a/src/compiler/value-numbering-reducer.h
+++ b/src/compiler/value-numbering-reducer.h
@@ -13,7 +13,7 @@ namespace compiler {
 
 class ValueNumberingReducer final : public Reducer {
  public:
-  explicit ValueNumberingReducer(Zone* zone);
+  explicit ValueNumberingReducer(Zone* temp_zone, Zone* graph_zone);
   ~ValueNumberingReducer();
 
   Reduction Reduce(Node* node) override;
@@ -22,12 +22,14 @@ class ValueNumberingReducer final : public Reducer {
   enum { kInitialCapacity = 256u, kCapacityToSizeRatio = 2u };
 
   void Grow();
-  Zone* zone() const { return zone_; }
+  Zone* temp_zone() const { return temp_zone_; }
+  Zone* graph_zone() const { return graph_zone_; }
 
   Node** entries_;
   size_t capacity_;
   size_t size_;
-  Zone* zone_;
+  Zone* temp_zone_;
+  Zone* graph_zone_;
 };
 
 }  // namespace compiler