On finding functionally identical and functionally opposite lines in combinational logic circuits

Given a combinational logic circuit, we find a subset of lines R that has the following property. Every line g in the circuit has a representative line r∈R such that g and r carry identical values for any input combination of the circuit. This problem has applications in logic optimization as well as in testing. We define the problem, discuss its applications, describe a solution based on structural analysis and on functional analysis that uses logic simulation, and present experimental results. Considering logic optimization, every line g in the circuit can be replaced by a fanout branch of its representative r, and the logic driving g can be removed. Circuit size is thus reduced. We demonstrate that circuit reduction based on the set R can be used as a preprocessing step to reduce the run time of logic optimization procedures, without compromising solution quality. We also consider pairs of lines that always carry opposite values and show how they can be used to further reduce circuit size