Declare the arguments object before creating the function var, to make sure it masks it

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 1200 matching lines @@
   migrate_to->set_start_position(start_position_);
   migrate_to->set_end_position(end_position_);
   migrate_to->set_language_mode(language_mode());
   migrate_to->arity_ = arity_;
   migrate_to->force_context_allocation_ = force_context_allocation_;
   outer_scope_->RemoveInnerScope(this);
   DCHECK_EQ(outer_scope_, migrate_to->outer_scope_);
   DCHECK_EQ(outer_scope_->zone(), migrate_to->zone());
   DCHECK_EQ(NeedsHomeObject(), migrate_to->NeedsHomeObject());
   DCHECK_EQ(asm_function_, migrate_to->asm_function_);
-  DCHECK_EQ(arguments() != nullptr, migrate_to->arguments() != nullptr);
 }
 
 #ifdef DEBUG
 static const char* Header(ScopeType scope_type, FunctionKind function_kind,
                           bool is_declaration_scope) {
   switch (scope_type) {
     case EVAL_SCOPE: return "eval";
     // TODO(adamk): Should we print concise method scopes specially?
     case FUNCTION_SCOPE:
       if (IsGeneratorFunction(function_kind)) return "function*";
@@ skipping 600 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