Modern Fixed-Outline Floorplanning with Rectilinear Soft Modules

To better utilize space and reduce wirelength within a fixed-outline with preplaced modules, modern floorplanning is desired to be able to handle rectilinear soft modules. Nevertheless, the induced special shape constraints have not been fully explored in the literature. In this paper, we propose a novel analytical-based approach to address the challenges of fixed-outline, preplaced modules, and rectilinear soft modules. Unlike most previous work, which abstracts modules as circles during global floorplanning, we treat modules as shape-adjustable rectangles and propose a differentiable shape mechanism to capture the impact of shaping on the floorplan quality. For legalization, we first construct an overlap graph to extract the neighborhood of overlaps, modules, and whitespaces. Then, a shortest-path based algorithm effectively migrates area from overlaps through a chain of modules to whitespaces while carefully considering the shape constraints. Finally, we iteratively expand and shrink the bounding boxes of modules to further refine the wirelength by improving area utilization. Our legalization and refinement allows rectilinear shapes to form naturally. Based on the experiments conducted on the GSRC, MCNC, and CAD contest benchmark suites, our results show that our approach achieves superior wirelength and runtime to the state-of-the-art works and the contest winning team, demonstrating its effectiveness and efficiency.