Placement feedback: a concept and method for better min-cut placements

Abstract

The advent of strong multi-level partitioners has made topdown min-cut placers a favored choice for modern placer implementations. We examine terminal propagation, an important step in min-cut placers, because it is responsible for translating partitioning results into global placement wirelength assumptions. In this work, we identify a previously overlooked problem - ambiguous terminal propagation - and propose a solution based on the concept of feedback from automatic control systems. Implementing our approach in Capo (version 8.7 [5, 10]) and applying it to standard benchmark circuits yields up to 14% wirelength reductions for the IBM benchmarks and 10% reductions for PEKO instances. Experiments also show consistent improvements for routed wirelength, yielding up to 9% wirelength reductions with practical increase in placement runtime. In addition, our method significantly improves routability without building congestion maps, and reduces the number of vias.