Mountain-mover: An intuitive logic shifting heuristic for improving timing slack violating paths

Based on a simple intuitive notion, in this paper, we propose an efficient post-placement improvement scheme. Based on the given timing slack distribution of a circuit, a corresponding “slack mountain map” can be visualized with peaks representing most violating (negative) slacks and valleys representing non-critical (positive) slacks respectively. Guided by this map, violating paths are eliminated or improved when slack mountains are flattened by applying a local logic perturbation technique (rewiring) iteratively to shift logic resources from critical to non-critical areas. Due to the locality property of the rewiring technique, to better avoid being stuck at local minimums, instead of running rewiring operations from the peak top towards lower areas, we do this local logic shifting starting from “sea areas” (most non-critical) towards peak (most critical) areas. At the end, as the slack map is more flattened, a circuit with slack violations more evenly distributed can be yielded. Comparing to the recent work [1], our experimental results demonstrate that this scheme can obtain a better or comparable delay reduction but with CPU time one order of magnitude smaller.