Buffer insertion with adaptive blockage avoidance

Buffer insertion is a fundamental technology for VLSI interconnect optimization. Several existing buffer insertion algorithms have evolved from van Ginneken's classic algorithm. In this work, we extend van Ginneken's algorithm to handle blockages in the layout. Given a Steiner tree containing a Steiner point that overlaps a blockage, a local adjustment is made to the tree topology that enables additional buffer insertion candidates to be considered. This adjustment is adaptive to the demand on buffer insertion and is incurred only when it facilitates the maximal slack solution. This approach can be combined with any performance-driven Steiner tree construction. The overall time complexity has linear dependence on the number of blockages and quadratic dependence on the number of potential buffer locations. Experiments on several large nets confirm that high-quality solutions can be obtained through this technique with little CPU cost.