Preheat oven to 350°. In a bowl, combine cornflake crumbs, sugar and butter. Press into a greased 9-in. square baking dish. Bake 10 minutes. Cool on a wire rack., In a saucepan, combine cornstarch and pineapple until blended. Bring to a boil; cook and stir 2 minutes or until thickened. Cool. , In a bowl, beat ice cream and pudding mix on low speed 2 minutes or until blended and thickened. Spoon over crust. Top with pineapple mixture. Refrigerate until serving. If desired, serve with whipped topping.