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

test/cctest/interpreter/bytecode_expectations/Generators.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 wrap: no
 test function name: f
 
 ---
 snippet: "
@@ skipping 259 matching lines @@
   [46, 225, 231],
 ]
 
 ---
 snippet: "
   function* f() { for (let x of [42]) yield x }
   f();
 "
 frame size: 17
 parameter count: 1
-bytecode array length: 771
+bytecode array length: 769
 bytecodes: [
                 B(Ldar), R(new_target),
                 B(JumpIfUndefined), U8(28),
                 B(ResumeGenerator), R(new_target),
                 B(Star), R(3),
                 B(LdaZero),
                 B(TestEqualStrict), R(3), U8(0),
                 B(JumpIfTrue), U8(60),
                 B(LdaSmi), U8(1),
                 B(TestEqualStrict), R(3), U8(0),
@@ skipping 177 matching lines @@
                 B(Star), R(10),
                 B(LdaZero),
                 B(TestEqualStrict), R(10), U8(15),
                 B(JumpIfTrueConstant), U8(17),
                 B(LdaContextSlot), R(1), U8(7), U8(0),
                 B(Star), R(10),
                 B(LdaNamedProperty), R(10), U8(12), U8(16),
                 B(StaContextSlot), R(1), U8(11), U8(0),
                 B(LdaContextSlot), R(1), U8(11), U8(0),
                 B(Star), R(10),
-                B(LdaNull),
-                B(TestEqual), R(10), U8(18),
-                B(JumpIfFalse), U8(4),
+                B(TestUndetectable), R(10),
+                B(JumpIfToBooleanFalse), U8(4),

[rmcilroy, 2016/12/05 10:57:19]

Could you add an explicit BytecodeGeneratorTest for this logic please?

[mythria, 2016/12/05 14:53:11]

Done.

                 B(JumpConstant), U8(16),
                 B(LdaContextSlot), R(1), U8(9), U8(0),
                 B(Star), R(10),
                 B(LdaSmi), U8(1),
                 B(TestEqualStrict), R(10), U8(19),
                 B(JumpIfFalse), U8(75),
                 B(LdaContextSlot), R(1), U8(11), U8(0),
                 B(TypeOf),
                 B(Star), R(10),
                 B(LdaConstant), U8(13),
@@ skipping 122 matching lines @@
   FIXED_ARRAY_TYPE,
   Smi [135],
   Smi [152],
   ONE_BYTE_INTERNALIZED_STRING_TYPE [".catch"],
   FIXED_ARRAY_TYPE,
   ONE_BYTE_INTERNALIZED_STRING_TYPE ["return"],
   ONE_BYTE_INTERNALIZED_STRING_TYPE ["function"],
   ONE_BYTE_INTERNALIZED_STRING_TYPE [""],
   FIXED_ARRAY_TYPE,
   Smi [133],
-  Smi [161],
-  Smi [581],
+  Smi [159],
+  Smi [579],
 ]
 handlers: [
-  [46, 690, 696],
+  [46, 688, 694],
   [143, 438, 444],
   [146, 394, 396],
-  [542, 558, 560],
+  [540, 556, 558],
 ]