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

src/interpreter/bytecode-generator.cc

 // Copyright 2015 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-generator.h"
 
 #include "src/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compilation-info.h"
@@ skipping 570 matching lines @@
       execution_result_(nullptr),
       generator_resume_points_(info->literal()->yield_count(), info->zone()),
       generator_state_(),
       loop_depth_(0),
       home_object_symbol_(info->isolate()->factory()->home_object_symbol()),
       empty_fixed_array_(info->isolate()->factory()->empty_fixed_array()) {
   AstValueFactory* ast_value_factory = info->parse_info()->ast_value_factory();
   const AstRawString* prototype_string = ast_value_factory->prototype_string();
   ast_value_factory->Internalize(info->isolate());
   prototype_string_ = prototype_string->string();
+  undefined_string_ = ast_value_factory->undefined_string();
 }
 
 Handle<BytecodeArray> BytecodeGenerator::FinalizeBytecode(Isolate* isolate) {
   AllocateDeferredConstants();
   if (HasStackOverflow()) return Handle<BytecodeArray>();
   return builder()->ToBytecodeArray(isolate);
 }
 
 void BytecodeGenerator::AllocateDeferredConstants() {
   // Build global declaration pair arrays.
@@ skipping 1223 matching lines @@
       // We need to load the variable into the accumulator, even when in a
       // VisitForRegisterScope, in order to avoid register aliasing if
       // subsequent expressions assign to the same variable.
       builder()->LoadAccumulatorWithRegister(source);
       if (hole_check_mode == HoleCheckMode::kRequired) {
         BuildThrowIfHole(variable->name());
       }
       break;
     }
     case VariableLocation::UNALLOCATED: {
-      builder()->LoadGlobal(variable->name(), feedback_index(slot),
-                            typeof_mode);
+      // The global identifier "undefined" is immutable. Everything
+      // else could be reassigned. For performance, we do a pointer comparison
+      // rather than checking if the raw_name is really "undefined".
+      if (variable->raw_name() == undefined_string()) {
+        builder()->LoadUndefined();
+      } else {
+        builder()->LoadGlobal(variable->name(), feedback_index(slot),
+                              typeof_mode);
+      }
       break;
     }
     case VariableLocation::CONTEXT: {
       int depth = execution_context()->ContextChainDepth(variable->scope());
       ContextScope* context = execution_context()->Previous(depth);
       Register context_reg;
       if (context) {
         context_reg = context->reg();
         depth = 0;
       } else {
@@ skipping 1352 matching lines @@
 }
 
 Runtime::FunctionId BytecodeGenerator::StoreKeyedToSuperRuntimeId() {
   return is_strict(language_mode()) ? Runtime::kStoreKeyedToSuper_Strict
                                     : Runtime::kStoreKeyedToSuper_Sloppy;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8