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

src/interpreter/bytecode-peephole-optimizer.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/interpreter/bytecode-peephole-optimizer.h"
 
 #include "src/objects-inl.h"
 #include "src/objects.h"
 
 namespace v8 {
@@ skipping 120 matching lines @@
                                                 BytecodeNode* const last,
                                                 BytecodeNode* const current) {
   DCHECK_EQ(last->bytecode(), Bytecode::kLdaZero);
   current->set_bytecode(new_bytecode, 0, current->operand(0),
                         current->operand(1));
   if (last->source_info().is_valid()) {
     current->set_source_info(last->source_info());
   }
 }
 
+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(
     BytecodeNode* const node, const PeepholeActionAndData* action_data) {
   DCHECK(LastIsValid());
   DCHECK(!Bytecodes::IsJump(node->bytecode()));
 
   next_stage()->Write(last());
   SetLast(node);
 }
@@ skipping 93 matching lines @@
   if (!node->source_info().is_valid() || !last()->source_info().is_valid()) {
     // Fused last and current into current.
     TransformLdaZeroBinaryOpToBinaryOpWithZero(action_data->bytecode, last(),
                                                node);
     SetLast(node);
   } else {
     DefaultAction(node);
   }
 }
 
+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());
   DCHECK(Bytecodes::IsJump(node->bytecode()));
 
   next_stage()->Write(last());
   InvalidateLast();
 }
 
 void BytecodePeepholeOptimizer::UpdateLastJumpAction(
@@ skipping 42 matching lines @@
 #undef CASE
     default:
       UNREACHABLE();
       break;
   }
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8