Perturb+mutate: Semisynthetic circuit generation for incremental placement and routing

CAD tool designers are always searching for more benchmark circuits to stress their software. In this article we present a heuristic method to generate benchmark circuits specially suited for incremental place-and-route tools. The method removes part of a real circuit and replaces it with an altered version of the same circuit to mimic an incremental design change. The alteration consists of two steps: mutate followed by perturb. The perturb step exactly preserves as many circuit characteristics as possible. While perturbing, reproduction of interconnect locality, a characteristic that is difficult to measure reliably or reproduce exactly, is controlled using a new technique, ancestor depth control (ADC). Perturbing with ADC produces circuits with postrouting properties that match the best techniques known to-date. The mutate step produces targetted mutations resulting in controlled changes to specific circuit properties (while keeping other properties constant). We demonstrate one targetted mutation heuristic, scale, to significantly change circuit size with little change to other circuit characteristics. The method is simple enough for inclusion in a CAD tool directly, and fast enough for use in on-the-fly benchmark generation.