LibJS: Skip ordinary_call_bind_this() when possible

If during parsing it was found that function won't use `this` then
there is no need to initialise `this_value` during call.

Userland/Libraries/LibJS/AST.cpp

@@ -242,6 +242,7 @@ ThrowCompletionOr<ClassElement::ClassValue> ClassField::class_element_evaluation
  auto function_code = create_ast_node<ClassFieldInitializerStatement>(m_initializer->source_range(), copy_initializer.release_nonnull(), name);
  FunctionParsingInsights parsing_insights;
  parsing_insights.uses_this_from_environment = true;
+ parsing_insights.uses_this = true;
  initializer = make_handle(*ECMAScriptFunctionObject::create(realm, "field", ByteString::empty(), *function_code, {}, 0, {}, vm.lexical_environment(), vm.running_execution_context().private_environment, FunctionKind::Normal, true, parsing_insights, false, property_key_or_private_name));
  initializer->make_method(target);
  }
@@ -288,6 +289,7 @@ ThrowCompletionOr<ClassElement::ClassValue> StaticInitializer::class_element_eva
  // Note: The function bodyFunction is never directly accessible to ECMAScript code.
  FunctionParsingInsights parsing_insights;
  parsing_insights.uses_this_from_environment = true;
+ parsing_insights.uses_this = true;
  auto body_function = ECMAScriptFunctionObject::create(realm, ByteString::empty(), ByteString::empty(), *m_function_body, {}, 0, m_function_body->local_variables_names(), lexical_environment, private_environment, FunctionKind::Normal, true, parsing_insights, false);
 
  // 6. Perform MakeMethod(bodyFunction, homeObject).
@@ -337,6 +339,7 @@ ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::create_class_const
  auto const& constructor = *m_constructor;
  auto parsing_insights = constructor.parsing_insights();
  parsing_insights.uses_this_from_environment = true;
+ parsing_insights.uses_this = true;
  auto class_constructor = ECMAScriptFunctionObject::create(
  realm,
  constructor.name(),

Userland/Libraries/LibJS/AST.h

@@ -694,6 +694,7 @@ struct FunctionParameter {
 };
 
 struct FunctionParsingInsights {
+ bool uses_this { false };
  bool uses_this_from_environment { false };
  bool contains_direct_call_to_eval { false };
  bool might_need_arguments_object { false };

Userland/Libraries/LibJS/Parser.cpp

@@ -433,32 +433,29 @@ class ScopePusher {
  }
  }
 
- bool uses_this_from_environment() const
- {
- return m_uses_this_from_environment;
- }
+ bool uses_this() const { return m_uses_this; }
+ bool uses_this_from_environment() const { return m_uses_this_from_environment; }
 
  void set_uses_this()
  {
  auto const* closest_function_scope = last_function_scope();
- if (!closest_function_scope || !closest_function_scope->m_is_arrow_function)
- return;
-
+ auto uses_this_from_environment = closest_function_scope && closest_function_scope->m_is_arrow_function;
  for (auto* scope_ptr = this; scope_ptr; scope_ptr = scope_ptr->m_parent_scope) {
- if (scope_ptr->m_uses_this_from_environment)
- break;
- if (scope_ptr->m_type == ScopeType::Function)
- scope_ptr->m_uses_this_from_environment = true;
+ if (scope_ptr->m_type == ScopeType::Function) {
+ scope_ptr->m_uses_this = true;
+ if (uses_this_from_environment)
+ scope_ptr->m_uses_this_from_environment = true;
+ }
  }
  }
 
  void set_uses_new_target()
  {
  for (auto* scope_ptr = this; scope_ptr; scope_ptr = scope_ptr->m_parent_scope) {
- if (scope_ptr->m_uses_this_from_environment)
- break;
- if (scope_ptr->m_type == ScopeType::Function)
+ if (scope_ptr->m_type == ScopeType::Function) {
+ scope_ptr->m_uses_this = true;
  scope_ptr->m_uses_this_from_environment = true;
+ }
  }
  }
 
@@ -512,6 +509,7 @@ class ScopePusher {
  // 1. It's an arrow function or establish parent scope for an arrow function
  // 2. Uses new.target
  bool m_uses_this_from_environment { false };
+ bool m_uses_this { false };
  bool m_is_arrow_function { false };
 };
 
@@ -2307,6 +2305,7 @@ NonnullRefPtr<Expression const> Parser::parse_expression(int min_precedence, Ass
  auto& callee = static_ptr_cast<CallExpression const>(expression)->callee();
  if (is<Identifier>(callee) && static_cast<Identifier const&>(callee).string() == "eval"sv) {
  m_state.current_scope_pusher->set_contains_direct_call_to_eval();
+ m_state.current_scope_pusher->set_uses_this();
  }
  }
 
@@ -2845,6 +2844,7 @@ NonnullRefPtr<FunctionBody const> Parser::parse_function_body(Vector<FunctionPar
  VERIFY(m_state.current_scope_pusher->type() == ScopePusher::ScopeType::Function);
  parsing_insights.contains_direct_call_to_eval = m_state.current_scope_pusher->contains_direct_call_to_eval();
  parsing_insights.uses_this_from_environment = m_state.current_scope_pusher->uses_this_from_environment();
+ parsing_insights.uses_this = m_state.current_scope_pusher->uses_this();
  return function_body;
 }
 

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -332,6 +332,7 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(DeprecatedFlyString name, Byt
  }
 
  m_function_environment_needed = arguments_object_needs_binding || m_function_environment_bindings_count > 0 || m_var_environment_bindings_count > 0 || m_lex_environment_bindings_count > 0 || parsing_insights.uses_this_from_environment || m_contains_direct_call_to_eval;
+ m_uses_this = parsing_insights.uses_this;
 }
 
 void ECMAScriptFunctionObject::initialize(Realm& realm)
@@ -414,7 +415,8 @@ ThrowCompletionOr<Value> ECMAScriptFunctionObject::internal_call(Value this_argu
  }
 
  // 5. Perform OrdinaryCallBindThis(F, calleeContext, thisArgument).
- ordinary_call_bind_this(*callee_context, this_argument);
+ if (m_uses_this)
+ ordinary_call_bind_this(*callee_context, this_argument);
 
  // 6. Let result be Completion(OrdinaryCallEvaluateBody(F, argumentsList)).
  auto result = ordinary_call_evaluate_body();
@@ -477,7 +479,8 @@ ThrowCompletionOr<NonnullGCPtr<Object>> ECMAScriptFunctionObject::internal_const
  // 6. If kind is base, then
  if (kind == ConstructorKind::Base) {
  // a. Perform OrdinaryCallBindThis(F, calleeContext, thisArgument).
- ordinary_call_bind_this(*callee_context, this_argument);
+ if (m_uses_this)
+ ordinary_call_bind_this(*callee_context, this_argument);
 
  // b. Let initializeResult be Completion(InitializeInstanceElements(thisArgument, F)).
  auto initialize_result = this_argument->initialize_instance_elements(*this);

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h

@@ -164,6 +164,7 @@ class ECMAScriptFunctionObject final : public FunctionObject {
  bool m_arguments_object_needed { false };
  bool m_is_module_wrapper { false };
  bool m_function_environment_needed { false };
+ bool m_uses_this { false };
  Vector<VariableNameToInitialize> m_var_names_to_initialize_binding;
  Vector<DeprecatedFlyString> m_function_names_to_initialize_binding;
 

Userland/Libraries/LibJS/SourceTextModule.cpp

@@ -760,6 +760,7 @@ ThrowCompletionOr<void> SourceTextModule::execute_module(VM& vm, GCPtr<PromiseCa
 
  FunctionParsingInsights parsing_insights;
  parsing_insights.uses_this_from_environment = true;
+ parsing_insights.uses_this = true;
  auto module_wrapper_function = ECMAScriptFunctionObject::create(
  realm(), "module code with top-level await", StringView {}, this->m_ecmascript_code,
  {}, 0, {}, environment(), nullptr, FunctionKind::Async, true, parsing_insights);