Unify the handling of comparinsons against null and undefined.

src/hydrogen.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 892 matching lines @@
   void HandleCompoundAssignment(Assignment* expr);
   void HandlePolymorphicStoreNamedField(Assignment* expr,
                                         HValue* object,
                                         HValue* value,
                                         SmallMapList* types,
                                         Handle<String> name);
   void HandlePolymorphicCallNamed(Call* expr,
                                   HValue* receiver,
                                   SmallMapList* types,
                                   Handle<String> name);
-  void HandleLiteralCompareTypeof(CompareOperation* compare_expr,
-                                  Expression* expr,
+  bool TryLiteralCompare(CompareOperation* expr);
+  void HandleLiteralCompareTypeof(CompareOperation* expr,
+                                  Expression* sub_expr,
                                   Handle<String> check);
-  void HandleLiteralCompareUndefined(CompareOperation* compare_expr,
-                                     Expression* expr);
-  void HandleLiteralCompareNull(CompareOperation* compare_expr,
-                                Expression* expr);
+  void HandleLiteralCompareNil(CompareOperation* expr,
+                               Expression* sub_expr,
+                               NilValue nil);
 
   HStringCharCodeAt* BuildStringCharCodeAt(HValue* context,
                                            HValue* string,
                                            HValue* index);
   HInstruction* BuildBinaryOperation(BinaryOperation* expr,
                                      HValue* left,
                                      HValue* right);
   HInstruction* BuildIncrement(bool returns_original_input,
                                CountOperation* expr);
   HLoadNamedField* BuildLoadNamedField(HValue* object,
@@ skipping 304 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_