[turbofan] Build s/NULL/nullptr/g and CHECK(x != nullptr) to CHECK_NOT_NULL(x).

src/compiler/graph-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_GRAPH_REDUCER_H_
 #define V8_COMPILER_GRAPH_REDUCER_H_
 
 #include "src/compiler/node-marker.h"
 #include "src/zone-containers.h"
 
@@ skipping 55 matching lines @@
   // Observe the actions of this reducer.
   class Editor {
    public:
     virtual ~Editor() {}
 
     // Replace {node} with {replacement}.
     virtual void Replace(Node* node, Node* replacement) = 0;
     // Revisit the {node} again later.
     virtual void Revisit(Node* node) = 0;
     // Replace value uses of {node} with {value} and effect uses of {node} with
-    // {effect}. If {effect == NULL}, then use the effect input to {node}. All
+    // {effect}. If {effect == nullptr}, then use the effect input to {node}.
+    // All
     // control uses will be relaxed assuming {node} cannot throw.
     virtual void ReplaceWithValue(Node* node, Node* value, Node* effect,
                                   Node* control) = 0;
   };
 
   explicit AdvancedReducer(Editor* editor) : editor_(editor) {}
 
  protected:
   // Helper functions for subclasses to produce reductions for a node.
   static Reduction Replace(Node* node) { return Reducer::Replace(node); }
@@ skipping 55 matching lines @@
 
   // Reduce a single node.
   Reduction Reduce(Node* const);
   // Reduce the node on top of the stack.
   void ReduceTop();
 
   // Replace {node} with {replacement}.
   void Replace(Node* node, Node* replacement) final;
 
   // Replace value uses of {node} with {value} and effect uses of {node} with
-  // {effect}. If {effect == NULL}, then use the effect input to {node}. All
+  // {effect}. If {effect == nullptr}, then use the effect input to {node}. All
   // control uses will be relaxed assuming {node} cannot throw.
   void ReplaceWithValue(Node* node, Node* value, Node* effect,
                         Node* control) final;
 
   // Replace all uses of {node} with {replacement} if the id of {replacement} is
   // less than or equal to {max_id}. Otherwise, replace all uses of {node} whose
   // id is less than or equal to {max_id} with the {replacement}.
   void Replace(Node* node, Node* replacement, NodeId max_id);
 
   // Node stack operations.
@@ skipping 12 matching lines @@
   ZoneStack<NodeState> stack_;
 
   DISALLOW_COPY_AND_ASSIGN(GraphReducer);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_GRAPH_REDUCER_H_