In the process of designing an integrated circuit (IC), it is often the case that a functional description is converted into multiplexers. In some cases it would be more efficient to combine two or more multiplexers into a larger multiplexer to identify potential design problems in the original register transfer level (RTL). Such early detection can prevent routing congestion problem that would be too expensive to fix later. A large multiplexer is defined as a multiplexer having a number of inputs and control signals that is above a predetermined threshold. When such a multiplexing functionality is detected that function may be replaced in the circuit with a large multiplexer that would be a more efficient implementation. Accordingly the circuit is checked for existence of multiplexing functions, and merging, when possible, of such multiplexing functions to achieve the ability to instantiate the multiplexing functionality with a large multiplexer.