Efficient global fanout optimization algorithms

Fanout optimization is a fundamental problem in timing optimization. Most of the research has focussed on the fanout optimization problem for a single net (or the local fanout optimization problem-LFO). The real goal, however, is to optimize the delay through the entire circuit by fanout optimization incurring minimum area penalty and without violating the pin loading constraints. This is known as the global fanout optimization (GFO) problem. In this paper, we show that the techniques proposed so far in the literature are either impractical or ineffective for large designs. We propose simple yet efficient and effective schemes for GFO and show that they outperform the "nearly-optimum" reverse topological (RT) algorithm on large industrial designs. One of these schemes yields only 0.3% worse circuit delay on average, but incurs only 18.5% of the area penalty as compared to the RT algorithm and is about 3 times faster. A popularly used mincut-based strategy was not found to be effective.