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

src/interpreter/bytecode-peephole-optimizer.cc

Index: src/interpreter/bytecode-peephole-optimizer.cc
diff --git a/src/interpreter/bytecode-peephole-optimizer.cc b/src/interpreter/bytecode-peephole-optimizer.cc
index 40552943f75dcb3b07d196b910f00cfd321d2946..bccba16b7857ab5a5834c02003af4566b02a71ec 100644
--- a/src/interpreter/bytecode-peephole-optimizer.cc
+++ b/src/interpreter/bytecode-peephole-optimizer.cc
@@ -138,6 +138,17 @@ void TransformLdaZeroBinaryOpToBinaryOpWithZero(Bytecode new_bytecode,
   }
 }
 
+void TransformEqualityWithNullOrUndefinedToTestUndetectable(
+    Bytecode new_bytecode, BytecodeNode* const last,
+    BytecodeNode* const current) {
+  DCHECK((last->bytecode() == Bytecode::kLdaNull) ||
+         (last->bytecode() == Bytecode::kLdaUndefined));
+  current->set_bytecode(new_bytecode, current->operand(0));

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

I don't think you need to pass the new_bytecode  (or have it as action data on
the peephole table) since it should always be TestUndetectable, right? Could you
change to remove the action data? 

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

Yes, we don't need action data. I did not think about that.

Done.

+  if (last->source_info().is_valid()) {
+    current->set_source_info(last->source_info());
+  }
+}
+
 }  // namespace
 
 void BytecodePeepholeOptimizer::DefaultAction(
@@ -251,6 +262,21 @@ void BytecodePeepholeOptimizer::
   }
 }
 
+void BytecodePeepholeOptimizer::
+    TransformEqualityWithNullOrUndefinedToTestUndetectableAction(
+        BytecodeNode* const node, const PeepholeActionAndData* action_data) {
+  DCHECK(LastIsValid());
+  DCHECK(!Bytecodes::IsJump(node->bytecode()));
+  if (!node->source_info().is_valid() || !last()->source_info().is_valid()) {

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

Do we need to do this check? LdaUndefined/null can never through, so I don't
think the first source position is ever observable.

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

I don't think we need, because if my understanding is correct the last source
info can only be ExpressionPosition and LdaNull/Undefined cannot throw. I also
think we don't need them for BinaryOpWithSmi or BinaryOpWithZero optimizations.
Since LdaSmi/LdaZero also cannot throw. I removed the check here. If you think
we also don't need it with BinaryOps, I will also remove them.

[rmcilroy, 2016/12/05 19:08:09]

Yeah we could think about removing for BinaryOpWithSmi or BinaryOpWithZero.
Please do this in another CL if you want do do it.

+    // Fused last and current into current.
+    TransformEqualityWithNullOrUndefinedToTestUndetectable(
+        action_data->bytecode, last(), node);
+    SetLast(node);
+  } else {
+    DefaultAction(node);
+  }
+}
+
 void BytecodePeepholeOptimizer::DefaultJumpAction(
     BytecodeNode* const node, const PeepholeActionAndData* action_data) {
   DCHECK(LastIsValid());