NTUplace3: An Analytical Placer for Large-Scale Mixed-Size Designs With Preplaced Blocks and Density Constraints

TLDR

Modern placers must account for constraints beyond wirelength, notably preplaced blocks and density. The authors propose a high‑quality analytical placer that optimizes wirelength while handling preplaced blocks and density using a log‑sum‑exp model within a multilevel framework. The algorithm employs two‑stage Gaussian and level smoothing for block spreading, white‑space reallocation with partitioning and cut‑line shifting during global placement, cell sliding in detailed placement, conjugate‑gradient optimization with dynamic step size, and macro shifting to improve macro placement. Experiments demonstrate that the placer achieves very high‑quality placement results.

Abstract

In addition to wirelength, modern placers need to consider various constraints such as preplaced blocks and density. We propose a high-quality analytical placement algorithm considering wirelength, preplaced blocks, and density based on the log-sum-exp wirelength model proposed by Naylor and the multilevel framework. To handle preplaced blocks, we use a two-stage smoothing technique, i.e., Gaussian smoothing followed by level smoothing, to facilitate block spreading during global placement (GP). The density is controlled by white-space reallocation using partitioning and cut-line shifting during GP and cell sliding during detailed placement. We further use the conjugate gradient method with dynamic step-size control to speed up the GP and macro shifting to find better macro positions. Experimental results show that our placer obtains very high-quality results.