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

src/compiler/ast-graph-builder.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_AST_GRAPH_BUILDER_H_
 #define V8_COMPILER_AST_GRAPH_BUILDER_H_
 
 #include "src/ast/ast.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/liveness-analyzer.h"
@@ skipping 151 matching lines @@
   Node* GetFunctionClosure();
 
   // Get or create the node that represents the incoming function context.
   Node* GetFunctionContext();
 
   // Get or create the node that represents the incoming new target value.
   Node* GetNewTarget();
 
   // Node creation helpers.
   Node* NewNode(const Operator* op, bool incomplete = false) {
-    return MakeNode(op, 0, static_cast<Node**>(NULL), incomplete);
+    return MakeNode(op, 0, static_cast<Node**>(nullptr), incomplete);
   }
 
   Node* NewNode(const Operator* op, Node* n1) {
     return MakeNode(op, 1, &n1, false);
   }
 
   Node* NewNode(const Operator* op, Node* n1, Node* n2) {
     Node* buffer[] = {n1, n2};
     return MakeNode(op, arraysize(buffer), buffer, false);
   }
@@ skipping 175 matching lines @@
   // Builders for binary operations.
   Node* BuildBinaryOp(Node* left, Node* right, Token::Value op,
                       TypeFeedbackId feedback_id);
 
   // Process arguments to a call by popping {arity} elements off the operand
   // stack and build a call node using the given call operator.
   Node* ProcessArguments(const Operator* op, int arity);
 
   // ===========================================================================
   // The following build methods have the same contract as the above ones, but
-  // they can also return {NULL} to indicate that no fragment was built. Note
+  // they can also return {nullptr} to indicate that no fragment was built. Note
   // that these are optimizations, disabling any of them should still produce
   // correct graphs.
 
   // Optimization for variable load from global object.
   Node* TryLoadGlobalConstant(Handle<Name> name);
 
   // Optimization for variable load of dynamic lookup slot that is most likely
   // to resolve to a global slot or context slot (inferred from scope chain).
   Node* TryLoadDynamicVariable(Variable* variable, Handle<String> name,
                                BailoutId bailout_id,
@@ skipping 205 matching lines @@
 
   // Prepare environment to be used as loop header.
   void PrepareForLoop(BitVector* assigned, bool is_osr = false);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_AST_GRAPH_BUILDER_H_