Structural gate decomposition for depth-optimal technology mapping in LUT-based FPGA design

In this paper, we study the problem of decomposing gates in fanin-unbounded or K-bounded networks such that the K-input LUT mapping solutions computed by a depth-optimal mapper have minimum depth. We show (1) any decomposition leads to a smaller or equal mapping depth regardless the decomposition algorithm used, and (2) the problem is NP-hard for unbounded networks when K⩾3 and remains NP-hard for K-bounded networks when K⩾5. We propose a gate decomposition algorithm, named DOGMA, which combines level-driven node packing technique (Chortle-d) and the network flow based optimal labeling technique (FlowMap). Experimental results show that networks decomposed by DOGMA allow depth-optimal technology mappers to improve the mapping solutions by up to 11% in depth and up to 35% in area comparing to the mapping results of networks decomposed by other existing decomposition algorithms