Bagman suddenly spotted Harry, got up quickly, and bounded forward.
“Ah, here he is! Champion number four! In you come, Harry, in you come … nothing to worry about, it's just the wand weighing ceremony, the rest of the judges will be here in a moment –“ (p303, Harry Potter 4, US edition)
I’d like to know the meaning of 'in you come' by comparing and contrasting it with two other expressions 'come on in' and 'do come in'. These three expressions are vaguely mixed in my mind. I know they are emphasizing 'come in', but are they equal in every way? If there's any difference, when should they be used?