1. A method for designing a system on a target device, comprising: identifying an exclusive-OR (XOR) network in a design for the system that matches an XOR network in a library having a corresponding preferred XOR network; presenting a user with a plurality of preferred XOR networks that is available to be used to replace the XOR network identified, and objectives achieved by the preferred XOR networks; replacing the XOR network identified in the design with one of the preferred XOR networks in the library in response to an objective identified by the user from the objectives presented, wherein the identifying and replacing is performed during synthesis prior to placing and routing the system on the target device; generating a program file that includes the design; and programming the target device with the program file to transform programmable resources to implement the design, wherein the target device has been implemented on a die.