SFO: A Scalable Approach to Fanout-Bounded Logic Synthesis for Emerging Technologies

Fanouts are an essential element for signal cloning to achieve logic sharing, but can be a very limited resource in certain emerging technologies, such as quantum circuits, superconducting electronic circuits, photonic integrated circuits, and biological circuits. Although fanout synthesis has been intensively studied for high performance circuit synthesis, prior methods often treat fanout as a soft constraint for critical path optimization or target on specific high-fanout nets such as clock and reset signals. They are not particularly suited for circuit synthesis of these emerging technologies. By treating fanouts as first class citizens, the problem of fanout-bounded logic synthesis was posed as a challenge in the 2019 IWLS Programming Contest. In this paper, we present our winning method, which achieved the overall best quality in the competition, based on fanout load redistribution among existing or expanded equivalent signals.