Answer: Nothing. An irreversible process can not be drawn on the T-s diagram. Every process drawn on the T-s diagram must be reversible. If we have to represent an irreversible process on the T-s diagram then it is drawn as the dotted line as shown in the figure above.
For example, throttling is a highly irreversible process but to show it in the vapor compression cycle we draw it as a dotted line on the T-s diagram.