1. A circuit design support method comprising: obtaining shared circuit information indicating various types of shared circuits each executing at least any one of various types of logical computations and causing a plurality of signal lines to share thereamong an observation point at which a signal value is observable; determining for each of the signal lines to be observed in a circuit under-design, a value based on controllability representing ease of control to set a value of the signal line to be a specific value; selecting based on the obtained shared circuit information, any one shared circuit among the various types of shared circuits; and generating correlation information that correlates each input terminal of the selected shared circuit with a signal line among the signal lines to be observed and whose value determined therefor is equal to a non-controlling value of a logical computation executed for an input signal input into the input terminal, wherein the circuit design support method is executed by a computer.