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

src/interpreter/mkpeephole.cc

 // Copyright 2016 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.
 
 #include <array>
 #include <fstream>
 #include <map>
 #include <string>
 #include <vector>
 
@@ skipping 174 matching lines @@
             Bytecode::kShiftLeftSmi};
       case Bytecode::kShiftRight:
         return {
             PeepholeAction::kTransformLdaZeroBinaryOpToBinaryOpWithZeroAction,
             Bytecode::kShiftRightSmi};
       default:
         break;
     }
   }
 
-  // Fuse LdaNull/LdaUndefined followed by a equality comparison with test
-  // undetectable. Testing undetectable is a simple check on the map which is
-  // more efficient than the full comparison operation.
-  if (last == Bytecode::kLdaNull || last == Bytecode::kLdaUndefined) {
-    if (current == Bytecode::kTestEqual) {
-      return {PeepholeAction::kTransformEqualityWithNullOrUndefinedAction,
-              Bytecode::kTestUndetectable};
-    }
-  }
-
-  // Fuse LdaNull/LdaUndefined followed by a strict equals with
-  // TestNull/TestUndefined.
-  if (current == Bytecode::kTestEqualStrict) {
-    if (last == Bytecode::kLdaNull) {
-      return {PeepholeAction::kTransformEqualityWithNullOrUndefinedAction,
-              Bytecode::kTestNull};
-    } else if (last == Bytecode::kLdaUndefined) {
-      return {PeepholeAction::kTransformEqualityWithNullOrUndefinedAction,
-              Bytecode::kTestUndefined};
-    }
-  }
-
   // If there is no last bytecode to optimize against, store the incoming
   // bytecode or for jumps emit incoming bytecode immediately.
   if (last == Bytecode::kIllegal) {
     if (Bytecodes::IsJump(current)) {
       return {PeepholeAction::kUpdateLastJumpAction, Bytecode::kIllegal};
     } else if (current == Bytecode::kNop) {
       return {PeepholeAction::kUpdateLastIfSourceInfoPresentAction,
               Bytecode::kIllegal};
     } else {
       return {PeepholeAction::kUpdateLastAction, Bytecode::kIllegal};
@@ skipping 145 matching lines @@
 
   std::ofstream ofs(argv[1], std::ofstream::trunc);
   v8::internal::interpreter::PeepholeActionTableWriter writer;
   writer.BuildTable();
   writer.Write(ofs);
   ofs.flush();
   ofs.close();
 
   return 0;
 }