Remove ARGUMENTS_VARIABLE and fix crankshaft to properly detect the arguments object and keep it al…

src/ast/scopes.cc

 // Copyright 2012 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/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/ast/ast.h"
@@ skipping 568 matching lines @@
       zone(), this, ast_value_factory->this_string(),
       subclass_constructor ? CONST : VAR, THIS_VARIABLE,
       subclass_constructor ? kNeedsInitialization : kCreatedInitialized);
   receiver_ = var;
 }
 
 void DeclarationScope::DeclareArguments(AstValueFactory* ast_value_factory) {
   DCHECK(is_function_scope());
   DCHECK(!is_arrow_scope());
 
-  // Check if there's lexically declared variable named arguments to avoid
-  // redeclaration. See ES#sec-functiondeclarationinstantiation, step 20.
-  Variable* arg_variable = LookupLocal(ast_value_factory->arguments_string());
-  if (arg_variable != nullptr && IsLexicalVariableMode(arg_variable->mode())) {
-    return;
-  }
-
-  // Declare 'arguments' variable which exists in all non arrow functions.
-  // Note that it might never be accessed, in which case it won't be
-  // allocated during variable allocation.
-  if (arg_variable == nullptr) {
+  arguments_ = LookupLocal(ast_value_factory->arguments_string());
+  if (arguments_ == nullptr) {
+    // Declare 'arguments' variable which exists in all non arrow functions.
+    // Note that it might never be accessed, in which case it won't be
+    // allocated during variable allocation.
     arguments_ = Declare(zone(), this, ast_value_factory->arguments_string(),
-                         VAR, ARGUMENTS_VARIABLE, kCreatedInitialized);
-  } else {
-    arguments_ = arg_variable;
+                         VAR, NORMAL_VARIABLE, kCreatedInitialized);
+  } else if (IsLexicalVariableMode(arguments_->mode())) {
+    // Check if there's lexically declared variable named arguments to avoid
+    // redeclaration. See ES#sec-functiondeclarationinstantiation, step 20.
+    arguments_ = nullptr;
   }
 }
 
 void DeclarationScope::DeclareDefaultFunctionVariables(
     AstValueFactory* ast_value_factory) {
   DCHECK(is_function_scope());
   DCHECK(!is_arrow_scope());
 
   new_target_ = Declare(zone(), this, ast_value_factory->new_target_string(),
                         CONST, NORMAL_VARIABLE, kCreatedInitialized);
@@ skipping 1217 matching lines @@
   Variable* function =
       is_function_scope() ? AsDeclarationScope()->function_var() : nullptr;
   bool is_function_var_in_context =
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
          (is_function_var_in_context ? 1 : 0);
 }
 
 }  // namespace internal
 }  // namespace v8