Mixed-size placement via line search

We describe a remarkably simple yet very effective line search technique for cell placement. Our method "corrects" errors in force scaling by sampling different force weights in each iteration of placement and selecting the best candidate placements based on an objective function. Our technique is not only very fast, but it does away with the need for the ad hoc scaling that has plagued prior force-directed methods. We describe the implementation of our method within a multilevel flow and show that it can achieve good wire lengths with competitive run-times compared to other academic tools. Specifically, we produce placements with 12% and 15% better HPWL than FengShui 5.0 and Capo 9.1, respectively, on the ICCAD04 mixed-size benchmarks, while presenting run-times that are 37% faster than Capo 9.1.