DAG-Aware Synthesis Orchestration

Modern logic synthesis techniques use multilevel technology-independent representations like and-inverter-graphs (AIGs) for digital logic. This involves structural rewriting, resubstitution, and refactoring based on directed-acyclic-graph (DAGs) traversal. Existing DAG-aware logic synthesis algorithms are designed to perform one specific optimization during a single DAG traversal. However, we empirically identify and demonstrate that these algorithms are limited in quality-of-results due to the solely considered optimization operation in the design concept. This work proposes synthesis orchestration, which is a fine-grained node-level optimization implying multiple optimizations during the single traversal of the graph. Our experimental results are comprehensively conducted on all 104 designs collected from ISCAS'85/89/99, VTR, and EPFL benchmark suites. The orchestration algorithms consistently outperform existing optimizations, rewriting, resubstitution, and refactoring, leading to an average of 4% more node reduction with reasonable runtime cost for the single optimization. Moreover, we evaluate the orchestration algorithm in the sequential optimization, and as a plug-in algorithm in resyn and resyn3 flows in ABC, which demonstrate consistent logic minimization improvements (1%, 4.7% and 11.5% more node reduction on average). Finally, we integrate the orchestration into OpenROAD for end-to-end performance evaluations. Our results demonstrate the advantages of the orchestration optimization techniques, even after technology mapping and post-routing in the design flow.