LibJS: Elide function wrapper for class field literal initializers

If a class field initializer is just a simple literal, we can skip
creating (and calling) a wrapper function for it entirely.

1.44x speedup on JetStream3/raytrace-private-class-fields.js
1.53x speedup on JetStream3/raytrace-public-class-fields.js

Libraries/LibJS/AST.cpp

@@ -225,24 +225,35 @@ ThrowCompletionOr<ClassElement::ClassValue> ClassField::class_element_evaluation
     auto& realm = *vm.current_realm();
 
     auto property_key_or_private_name = TRY(class_key_to_property_name(vm, *m_key, property_key));
-    GC::Ptr<ECMAScriptFunctionObject> initializer;
+    Variant<GC::Ref<ECMAScriptFunctionObject>, Value, Empty> initializer;
     if (m_initializer) {
-        auto copy_initializer = m_initializer;
-        auto name = property_key_or_private_name.visit(
-            [&](PropertyKey const& property_key) -> String {
-                return property_key.is_number() ? property_key.to_string() : property_key.to_string_or_symbol().to_display_string();
-            },
-            [&](PrivateName const& private_name) -> String {
-                return private_name.description.to_string();
-            });
+        if (auto const* literal = as_if<NumericLiteral>(*m_initializer)) {
+            initializer = literal->value();
+        } else if (auto const* literal = as_if<BooleanLiteral>(*m_initializer)) {
+            initializer = literal->value();
+        } else if (auto const* literal = as_if<NullLiteral>(*m_initializer)) {
+            initializer = literal->value();
+        } else if (auto const* literal = as_if<StringLiteral>(*m_initializer)) {
+            initializer = Value(PrimitiveString::create(vm, literal->value()));
+        } else {
+            auto copy_initializer = m_initializer;
+            auto name = property_key_or_private_name.visit(
+                [&](PropertyKey const& property_key) -> String {
+                    return property_key.is_number() ? property_key.to_string() : property_key.to_string_or_symbol().to_display_string();
+                },
+                [&](PrivateName const& private_name) -> String {
+                    return private_name.description.to_string();
+                });
 
-        // FIXME: A potential optimization is not creating the functions here since these are never directly accessible.
-        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 = ECMAScriptFunctionObject::create(realm, "field"_string, ByteString::empty(), *function_code, FunctionParameters::empty(), 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);
+            // FIXME: A potential optimization is not creating the functions here since these are never directly accessible.
+            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;
+            auto function = ECMAScriptFunctionObject::create(realm, "field"_string, ByteString::empty(), *function_code, FunctionParameters::empty(), 0, {}, vm.lexical_environment(), vm.running_execution_context().private_environment, FunctionKind::Normal, true, parsing_insights, false, property_key_or_private_name);
+            function->make_method(target);
+            initializer = function;
+        }
     }
 
     return ClassValue {

Libraries/LibJS/AST.h

@@ -94,6 +94,8 @@ public:
     virtual bool is_object_expression() const { return false; }
     virtual bool is_numeric_literal() const { return false; }
     virtual bool is_string_literal() const { return false; }
+    virtual bool is_boolean_literal() const { return false; }
+    virtual bool is_null_literal() const { return false; }
     virtual bool is_update_expression() const { return false; }
     virtual bool is_call_expression() const { return false; }
     virtual bool is_labelled_statement() const { return false; }
@@ -1214,6 +1216,8 @@ public:
     virtual Value value() const override { return Value(m_value); }
 
 private:
+    virtual bool is_boolean_literal() const override { return true; }
+
     bool m_value { false };
 };
 
@@ -1281,6 +1285,9 @@ public:
     virtual Bytecode::CodeGenerationErrorOr<Optional<Bytecode::ScopedOperand>> generate_bytecode(Bytecode::Generator&, Optional<Bytecode::ScopedOperand> preferred_dst = {}) const override;
 
     virtual Value value() const override { return js_null(); }
+
+private:
+    virtual bool is_null_literal() const override { return true; }
 };
 
 class RegExpLiteral final : public Expression {
@@ -2267,6 +2274,15 @@ inline bool ASTNode::fast_is<ObjectExpression>() const { return is_object_expres
 template<>
 inline bool ASTNode::fast_is<ImportCall>() const { return is_import_call(); }
 
+template<>
+inline bool ASTNode::fast_is<NumericLiteral>() const { return is_numeric_literal(); }
+
+template<>
+inline bool ASTNode::fast_is<BooleanLiteral>() const { return is_boolean_literal(); }
+
+template<>
+inline bool ASTNode::fast_is<NullLiteral>() const { return is_null_literal(); }
+
 template<>
 inline bool ASTNode::fast_is<StringLiteral>() const { return is_string_literal(); }
 

Libraries/LibJS/Runtime/ClassFieldDefinition.h

@@ -17,8 +17,8 @@ using ClassElementName = Variant<PropertyKey, PrivateName>;
 
 // 6.2.10 The ClassFieldDefinition Record Specification Type, https://tc39.es/ecma262/#sec-classfielddefinition-record-specification-type
 struct ClassFieldDefinition {
-    ClassElementName name;                         // [[Name]]
-    GC::Ptr<ECMAScriptFunctionObject> initializer; // [[Initializer]]
+    ClassElementName name;                                                // [[Name]]
+    Variant<GC::Ref<ECMAScriptFunctionObject>, Value, Empty> initializer; // [[Initializer]]
 };
 
 }

Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -553,7 +553,14 @@ void ECMAScriptFunctionObject::visit_edges(Visitor& visitor)
     visitor.visit(m_bytecode_executable);
 
     for (auto& field : m_fields) {
-        visitor.visit(field.initializer);
+        field.initializer.visit(
+            [&visitor](GC::Ref<ECMAScriptFunctionObject>& initializer) {
+                visitor.visit(initializer);
+            },
+            [&visitor](Value initializer) {
+                visitor.visit(initializer);
+            },
+            [](Empty) {});
         if (auto* property_key_ptr = field.name.get_pointer<PropertyKey>(); property_key_ptr && property_key_ptr->is_symbol())
             visitor.visit(property_key_ptr->as_symbol());
     }

Libraries/LibJS/Runtime/Object.cpp

@@ -669,9 +669,14 @@ ThrowCompletionOr<void> Object::define_field(ClassFieldDefinition const& field)
     auto init_value = js_undefined();
 
     // 3. If initializer is not empty, then
-    if (initializer) {
-        // a. Let initValue be ? Call(initializer, receiver).
-        init_value = TRY(call(vm, initializer, this));
+    if (!initializer.has<Empty>()) {
+        // OPTIMIZATION: If the initializer is a value (from a literal), we can skip the call.
+        if (auto const* initializer_value = initializer.get_pointer<Value>()) {
+            init_value = *initializer_value;
+        } else {
+            // a. Let initValue be ? Call(initializer, receiver).
+            init_value = TRY(call(vm, *initializer.get<GC::Ref<ECMAScriptFunctionObject>>(), this));
+        }
     }
     // 4. Else, let initValue be undefined.