Mongrel: hybrid techniques for standard cell placement

We give an overview of a standard-cell placer Mongrel. The prototype tool adopts a middle-down methodology in which a grid is imposed over the layout area and cells are assigned to bins forming a global placement. The optimization technique applied in this phase is based on the Relaxation-Based Local Search (RBLS) framework in which a combinatorial search mechanism is driven by an analytical engine. This enables a more global view of the problem and results in complex modifications of the placement in a single search "move". Details of this approach including a novel placement legalization procedure are presented. When a global placement has converged, a detailed placement is formed and further optimized by the proposed optimal interleaving technique. Experimental results are presented and are quite promising, demonstrating that there is significant room for improvement in state of the art placement.