LibJS: Get this from execution context for non-arrow functions

Allows to skip function environment allocation for non-arrow functions
if the only reason it is needed is to hold `this` binding.

The parser is changed to do following:
- If a function is an arrow function and uses `this` then all functions
  in a scope chain are marked to allocate function environment for
  `this` binding.
- If a function uses `new.target` then all functions in a scope chain
  are marked to allocate function environment.

`ordinary_call_bind_this()` is changed to put `this` value in execution
context when function environment allocation is skipped.

35% improvement in Octane/typescript.js
50% improvement in Octane/deltablue.js
19% improvement in Octane/raytrace.js

Userland/Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -1562,6 +1562,14 @@ ThrowCompletionOr<void> DeleteByIdWithThis::execute_impl(Bytecode::Interpreter&
 
 ThrowCompletionOr<void> ResolveThisBinding::execute_impl(Bytecode::Interpreter& interpreter) const
 {
+    auto& running_execution_context = interpreter.vm().running_execution_context();
+    if (running_execution_context.function && is<ECMAScriptFunctionObject>(*running_execution_context.function)) {
+        auto const& esfo = static_cast<ECMAScriptFunctionObject&>(*running_execution_context.function);
+        if (!esfo.allocates_function_environment()) {
+            interpreter.set(dst(), running_execution_context.this_value);
+            return {};
+        }
+    }
     auto& cached_this_value = interpreter.reg(Register::this_value());
     if (cached_this_value.is_empty()) {
         // OPTIMIZATION: Because the value of 'this' cannot be reassigned during a function execution, it's

Userland/Libraries/LibJS/Parser.cpp

@@ -440,7 +440,19 @@ class ScopePusher {
 
     void set_uses_this()
     {
-        for (auto scope_ptr = this; scope_ptr; scope_ptr = scope_ptr->m_parent_scope) {
+        auto const* closest_function_scope = last_function_scope();
+        if (!closest_function_scope || !closest_function_scope->m_is_arrow_function)
+            return;
+
+        for (auto* scope_ptr = this; scope_ptr; scope_ptr = scope_ptr->m_parent_scope) {
+            if (scope_ptr->m_type == ScopeType::Function)
+                scope_ptr->m_uses_this = true;
+        }
+    }
+
+    void set_uses_new_target()
+    {
+        for (auto* scope_ptr = this; scope_ptr; scope_ptr = scope_ptr->m_parent_scope) {
             if (scope_ptr->m_type == ScopeType::Function)
                 scope_ptr->m_uses_this = true;
         }
@@ -1217,7 +1229,7 @@ RefPtr<MetaProperty const> Parser::try_parse_new_target_expression()
     discard_saved_state();
 
     if (m_state.current_scope_pusher)
-        m_state.current_scope_pusher->set_uses_this();
+        m_state.current_scope_pusher->set_uses_new_target();
 
     return create_ast_node<MetaProperty>({ m_source_code, rule_start.position(), position() }, MetaProperty::Type::NewTarget);
 }
@@ -1677,7 +1689,7 @@ Parser::PrimaryExpressionParseResult Parser::parse_primary_expression()
         if (!m_state.allow_super_property_lookup)
             syntax_error("'super' keyword unexpected here");
         if (m_state.current_scope_pusher)
-            m_state.current_scope_pusher->set_uses_this();
+            m_state.current_scope_pusher->set_uses_new_target();
         return { create_ast_node<SuperExpression>({ m_source_code, rule_start.position(), position() }) };
     case TokenType::EscapedKeyword:
         if (match_invalid_escaped_keyword())

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -414,8 +414,7 @@ ThrowCompletionOr<Value> ECMAScriptFunctionObject::internal_call(Value this_argu
     }
 
     // 5. Perform OrdinaryCallBindThis(F, calleeContext, thisArgument).
-    if (m_function_environment_needed)
-        ordinary_call_bind_this(*callee_context, this_argument);
+    ordinary_call_bind_this(*callee_context, this_argument);
 
     // 6. Let result be Completion(OrdinaryCallEvaluateBody(F, argumentsList)).
     auto result = ordinary_call_evaluate_body();
@@ -478,8 +477,7 @@ ThrowCompletionOr<NonnullGCPtr<Object>> ECMAScriptFunctionObject::internal_const
     // 6. If kind is base, then
     if (kind == ConstructorKind::Base) {
         // a. Perform OrdinaryCallBindThis(F, calleeContext, thisArgument).
-        if (m_function_environment_needed)
-            ordinary_call_bind_this(*callee_context, this_argument);
+        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);
@@ -699,7 +697,10 @@ void ECMAScriptFunctionObject::ordinary_call_bind_this(ExecutionContext& callee_
     // 7. Assert: localEnv is a function Environment Record.
     // 8. Assert: The next step never returns an abrupt completion because localEnv.[[ThisBindingStatus]] is not initialized.
     // 9. Perform ! localEnv.BindThisValue(thisValue).
-    MUST(verify_cast<FunctionEnvironment>(*local_env).bind_this_value(vm, this_value));
+    if (m_function_environment_needed)
+        MUST(verify_cast<FunctionEnvironment>(*local_env).bind_this_value(vm, this_value));
+    else
+        callee_context.this_value = this_value;
 
     // 10. Return unused.
 }

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h

@@ -99,6 +99,8 @@ class ECMAScriptFunctionObject final : public FunctionObject {
 
     Variant<PropertyKey, PrivateName, Empty> const& class_field_initializer_name() const { return m_class_field_initializer_name; }
 
+    bool allocates_function_environment() const { return m_function_environment_needed; }
+
     friend class Bytecode::Generator;
 
 protected: