An Effective Floorplan-Guided Placement Algorithm for Large-Scale Mixed-Size Designs

In this article we propose an effective algorithm flow to handle modern large-scale mixed-size placement, both with and without geometry constraints. The basic idea is to use floorplanning to guide the placement of objects at the global level. The flow consists of four steps: (1) The objects in the original netlist are clustered into blocks; (2) floorplanning is performed on the blocks; (3) the blocks are shifted within the chip region to further optimize the wirelength; (4) with large macro-locations fixed, incremental placement is applied to place the remaining objects. There are several advantages to handling placement at the global level with a floorplanning technique. First, the problem size can be significantly reduced. Second, exact Half-Perimeter WireLength (HPWL) can be minimized. Third, better object distribution can be achieved so that legalization only needs to handle minor overlaps among small objects in a block. Fourth, macro-rotation and various geometry constraints can be handled. To demonstrate the effectiveness of this new flow, we implement a high-quality and efficient floorplan-guided placer called FLOP. We also construct the Modern Mixed-Size (MMS) placement benchmarks that can effectively represent the complexities of modern mixed-size designs and the challenges faced by modern mixed-size placers. Compared with most state-of-the-art mixed-size placers and leading macroplacers, experimental results show that FLOP achieves the best HPWL and easily obtains legal solutions on all circuits with all geometry constraints satisfied.