A Network-Flow Approach to Timing-Driven Incremental Placement for ASICs

We present a novel incremental placement methodology called FlowPlace for significantly reducing critical path delays of placed standard-cell circuits. FlowPlace includes: a) a timing-driven (TD) analytical global placer TAN that uses accurate delay functions and minimizes a combination of linear and quadratic objective functions; b) a network flow based detailed placer TIF that has new and effective techniques for performing TD incremental placement and satisfying row-length (white space) constraints. We have obtained results on three sets of benchmarks: i) TD versions of the ibm benchmark suite that we have constructed; ii) benchmarks used in TD-Dragon; iii) the Faraday benchmarks. Results show that starting with Dragon-placed circuits, we are able to obtain up to 34% and an average of 18% improvement in critical path delays, at an average of 17.5% of the run-time of the Dragon placer. Starting with a state-of-the-art TD placer TD-Dragon, for the TD-Dragon benchmarks we obtain up to about 10% and an average of 4.3% delay improvement with 12% of TD-Dragon´s run times; this is significant as we are extracting performance improvements from a performance-optimized layout. Wire length deterioration on the average over all benchmark suites is less than 8%