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 @@ public:
         }
     }
 
-    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 @@ private:
     // 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 @@ private:
     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);