Routability-Driven and Fence-Aware Legalization for Mixed-Cell-Height Circuits

Placement is one of the most critical stages in the physical synthesis flow. Circuits with increasing numbers of cells of multi-row height have brought challenges to traditional placers on efficiency and effectiveness. Furthermore, constraints on fence region and routability (e.g., edge spacing, pin access/short) should be considered, besides providing an overlap-free solution close to the global placement (GP) solution and fulfilling the power and ground (P/G) alignments. In this paper, we propose a legalization method for mixed-cell-height circuits by a window-based cell insertion technique and two post-processing network-flow-based optimizations. Compared with the champion of the IC/CAD 2017 Contest, our algorithm achieves 18% and 12% less average and maximum displacement respectively as well as significantly fewer routability violations. Comparing our algorithm with the state-of-the-art algorithms on this problem, there is a 9% improvement in total displacement with 20% less running time.