[Interpreter] Optimize code of the form 'if (x === undefined)'.

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 91 matching lines @@
 
   void BuildVariableLoad(Variable* variable, FeedbackSlot slot,
                          HoleCheckMode hole_check_mode,
                          TypeofMode typeof_mode = NOT_INSIDE_TYPEOF);
   void BuildVariableLoadForAccumulatorValue(
       Variable* variable, FeedbackSlot slot, HoleCheckMode hole_check_mode,
       TypeofMode typeof_mode = NOT_INSIDE_TYPEOF);
   void BuildVariableAssignment(Variable* variable, Token::Value op,
                                FeedbackSlot slot,
                                HoleCheckMode hole_check_mode);
-
+  void BuildLiteralCompareNil(Token::Value compare_op, NilValue nil);
   void BuildReturn();
   void BuildAsyncReturn();
   void BuildAsyncGeneratorReturn();
   void BuildReThrow();
   void BuildAbort(BailoutReason bailout_reason);
   void BuildThrowIfHole(Variable* variable);
   void BuildThrowReferenceError(const AstRawString* name);
   void BuildHoleCheckForVariableAssignment(Variable* variable, Token::Value op);
 
   // Build jump to targets[value], where
@@ skipping 109 matching lines @@
   ZoneVector<BytecodeLabel> generator_resume_points_;
   Register generator_state_;
   int loop_depth_;
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_GENERATOR_H_