Optimal End-Case Partitioners and Placers for Standard-Cell Layout

We develop new optimal partitioning and placement codes for end-case processing in top-down standard-cell placement. Such codes are based on either enumeration or branch-and-bound, and are invoked for instances below prescribed size thresholds (e.g., < 30 cells for partitioning, or < 10 cells for placement). Our optimal partitioners handle tight balance constraints and uneven cell sizes transparently, while achieving substantial speedups over single FM starts. Optimal cutsizes for small instances (between 10 and 35 movable nodes) are typically found to be at least 40% smaller than what FM will achieve in several starts. Our optimal placers use branch-and-bound to achieve substantial speedups over even Gray code based enumeration. In the context of a top-down global placer, the right combination of optimal partitioners and placers can achieve up to an average of 10% wirelength reduction and 50% CPU time savings for a set of industry testcases. The paper concludes with directions for future research.