AiTO: Simultaneous gate sizing and buffer insertion for timing optimization with GNNs and RL

Gate sizing and buffer insertion for timing optimization are performed extensively in electronic design automation (EDA) flows. Both of them aim to adjust the upstream and downstream capacitances of gates/buffers to minimize delay. However, most of existing work focuses on gate sizing or buffer insertion independently. This paper proposes a learning-based timing optimization framework, AiTO, that combines reinforcement learning with graph neural network, to perform simultaneously gate sizing and buffer insertion. We model buffer insertion as a special gate sizing by determining possible buffer locations in advance and treating the buffer insertion and gate sizing as an RL process. Experimental results on 10 real designs (28-nm and 110-nm) show that, AiTO can achieve better worst negative slack (WNS) optimization results than OpenROAD while being able to improve the results of the commercial tool, Innovus, to some extent. Moreover, ablation studies demonstrate the benefits of performing simultaneous gate sizing and buffer insertion for timing optimization.