An effective legalization approach based on multiple ordering

Abstract

With the rapid increase of scale in IC design, the large scale IC placement has become more and more important. After global distribution and some objectives optimized, legalization is a core task to remove the overlap, align cells to sites, and try to preserve the optimal solution from global placement simultaneously. As we know, in large scale IC design, blind alignment will damage global placement solution and increase the wire length greatly. In nowadays research, cells managing order is often underemphasized and most of the legalizers choose the natural cells ordering. However, it is observed that a good choice of managing order would be beneficial for the placement solution. In this paper, a wire length driven legalization for standard cells is proposed, which guides cells distribution with different managing ordering in different stages and optimizes wire length by subsection optimization. In addition, a bounding box is built to narrow the searching area of optimal position in invalid cell instances relocation stage. Experimental results show that our legalizer gets 8% of the average wire length reduction over FastPlace3.0 (Agnihorti et al., 2003) on the ISPD2005 benchmarks.