Mix together flour, sugar, butter, and pecans and pat down in a 9x13 inch cake pan. Bake at 400 F for 12 to 15 minutes. Cool and break into bite-size pieces. Put back in pan. To make filling, mix an 8 ounce package cream cheese with 1/2 cup powdered sugar. Prepare Dream Whip as directed on package. Add cream cheese mixture. Mix well. Pour over crust. Add 1 can cherry pie filling over top.