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

test/unittests/interpreter/bytecode-peephole-optimizer-unittest.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 "src/v8.h"
 
 #include "src/factory.h"
 #include "src/interpreter/bytecode-label.h"
 #include "src/interpreter/bytecode-peephole-optimizer.h"
 #include "src/objects-inl.h"
@@ skipping 385 matching lines @@
     CHECK_EQ(write_count(), 1);
     CHECK_EQ(last_written().bytecode(), operator_replacement[1]);
     CHECK_EQ(last_written().operand_count(), 3);
     CHECK_EQ(last_written().operand(0), 0u);
     CHECK_EQ(last_written().operand(1), reg_operand);
     CHECK_EQ(last_written().operand(2), idx_operand);
     Reset();
   }
 }
 
+TEST_F(BytecodePeepholeOptimizerTest, MergeLdaNullOrUndefinedWithCompareOp) {
+  Bytecode first_bytecodes[] = {Bytecode::kLdaUndefined, Bytecode::kLdaNull};
+
+  for (auto first_bytecode : first_bytecodes) {
+    uint32_t reg_operand = Register(0).ToOperand();
+    uint32_t idx_operand = 1;
+    BytecodeNode first(first_bytecode);
+    BytecodeNode second(Bytecode::kTestEqual, reg_operand, idx_operand);
+    optimizer()->Write(&first);
+    optimizer()->Write(&second);
+    Flush();
+    CHECK_EQ(write_count(), 1);
+    CHECK_EQ(last_written().bytecode(), Bytecode::kTestUndetectable);
+    CHECK_EQ(last_written().operand_count(), 1);
+    CHECK_EQ(last_written().operand(0), reg_operand);
+    Reset();
+  }
+}
+
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8