A new incremental placement algorithm and its application to congestion-aware divisor extraction

This work presents two contributions. The first is an incremental placement algorithm for placement-aware logic synthesis along with a proof of optimality. The algorithm can efficiently compute the optimum location for a newly introduced node in a network that minimizes the incremental increase in the total half-perimeter wire-length of the network. The algorithm can be applied in a variety of placement-aware optimization contexts. The second contribution is a specific application of this algorithm to placement-aware common divisor extraction. We evaluate the effectiveness of the proposed extraction procedure by using it in an otherwise non-placement-aware flow with two different final placers. The first flow uses an industrial congestion-driven placer and results in an average reduction of 21% in congestion as measured by the global router. The second flow uses an academic wire-length-driven placer and results in an average reduction of 11% for a tool-specific measure of congestion estimated from the placement. Our experiments also reveal a rather surprising phenomenon: in many cases the attempt to minimize the wire-length results in fewer literals after extraction than with a conventional literal-driven approach.