Wirelength minimization for min-cut placements via placement feedback

The advent of strong multilevel partitioners has made top-down min-cut placers a favored choice for modern placer implementations. Terminal propagation is an important step in min-cut placers because it translates partitioning results into global-placement wirelength assumptions. In this work, the repartitioning problem is carefully reexamined (Proc. ACM/IEEE Int. Symp. Physical Design, p. 18, 1997) in the context of terminal propagation and studied in an in-depth manner. Abstractly, it was observed that in repartitioning, future cell locations are used for present terminal propagations and that this can be conceptually regarded as a form of placement feedback. This concept was utilized to achieve accurate terminal propagation via feedback iteration and controller insertion to fine-tune the feedback response. This yields substantial reductions in placement wirelength. Implementing our approach in Capo [version 8.7 (Proc. ACM/IEEE Design Automation Conf., p. 477, 2000 and GSRC Bookshelf)] and applying it to standard benchmark circuits yields up to 14% wirelength reductions for the IBM benchmarks with an average improvement of 5.5% and up to 10% reductions for the Peko benchmarks with an average improvement of 5.37%. Experiments also show consistent improvements for routed wirelength, yielding up to 9% wirelength reductions and 5.8% average reduction with acceptable increase in placement runtime. In practice, the method proposed significantly improves routability without building congestion maps and also reduces the number of vias