1. A circuit design support method, comprising: obtaining, by a computer, shared circuit information indicating various types of shared circuits each executing at least any one of various types of logical computations to enable a plurality of signal lines to share an observation point at which a signal value is observable; determining, for each of the plurality of signal lines to be observed in a circuit under-design, a value based on controllability representing ease of control to set a value of a corresponding signal line to a specific value; selecting any one shared circuit among the various types of shared circuits, based on the obtained shared circuit information, the selecting including selecting any one shared circuit based on a sequence indicated by the obtained shared circuit information; 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 that has a value determined therefor equal to a non-controlling value of a logical computation executed for an input signal input into the input terminal, wherein the shared circuit information indicates order of the various types of shared circuit based on an area and a number of input terminals of each of the various types of shared circuits.