[Interpreter] Optimize equality check with null/undefined with a check on the map.

src/interpreter/bytecode-generator.h

 // Copyright 2015 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_INTERPRETER_BYTECODE_GENERATOR_H_
 #define V8_INTERPRETER_BYTECODE_GENERATOR_H_
 
 #include "src/ast/ast.h"
 #include "src/interpreter/bytecode-array-builder.h"
 #include "src/interpreter/bytecode-label.h"
@@ skipping 177 matching lines @@
     return builder()->register_allocator();
   }
 
   GlobalDeclarationsBuilder* globals_builder() { return globals_builder_; }
   inline LanguageMode language_mode() const;
   int feedback_index(FeedbackVectorSlot slot) const;
 
   Handle<Name> home_object_symbol() const { return home_object_symbol_; }
   Handle<Name> prototype_string() const { return prototype_string_; }
   Handle<FixedArray> empty_fixed_array() const { return empty_fixed_array_; }
+  const AstRawString* undefined_string() const { return undefined_string_; }
 
   Zone* zone_;
   BytecodeArrayBuilder* builder_;
   CompilationInfo* info_;
   DeclarationScope* scope_;
 
   GlobalDeclarationsBuilder* globals_builder_;
   ZoneVector<GlobalDeclarationsBuilder*> global_declarations_;
   ZoneVector<std::pair<FunctionLiteral*, size_t>> function_literals_;
   ZoneVector<std::pair<NativeFunctionLiteral*, size_t>>
       native_function_literals_;
 
   ControlScope* execution_control_;
   ContextScope* execution_context_;
   ExpressionResultScope* execution_result_;
 
   ZoneVector<BytecodeLabel> generator_resume_points_;
   Register generator_state_;
   int loop_depth_;
 
   Handle<Name> home_object_symbol_;
   Handle<Name> prototype_string_;
   Handle<FixedArray> empty_fixed_array_;
+  const AstRawString* undefined_string_;
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_GENERATOR_H_