Safe Delay Optimization for Physical Synthesis

Abstract

Physical synthesis is a relatively young field in electronic design automation. Many published optimizations for physical synthesis end up hurting the final result, often by neglecting important physical aspects of the layout, such as long wires or routing congestion. In this work we propose SafeResynth, a safe resynthesis technique, which provides immediately-measurable delay improvement without altering the design's functionality. It can enhance circuit timing without detrimental effects on route length and congestion. When applied to IWLS'05 benchmarks, SafeResynth improves circuit delay by 11% on average after routing, while increasing route length and via count by less than 0.2%. Our resynthesis can also be used in an unsafe mode, akin to more traditional physical synthesis algorithms popular in commercial tools. Applied together, our safe and unsafe transformations achieve 24% average delay improvement for seven large benchmarks from the OpenCores suite. The relative contribution of safe and unsafe techniques varies depending on the amount of whitespace in the layout.