SPIRE: A retiming-based physical-synthesis transformation system

The impact of physical synthesis on design performance is increasing as process technology scales. Current physical synthesis flows generally perform a series of individual netlist transformations based on local timing conditions. However, such optimizations lack sufficient perspective or scope to achieve timing closure in many cases. To address these issues, we develop an integrated transformation system that performs multiple optimizations simultaneously on larger design partitions than existing approaches. Our system, SPIRE, combines physically-aware register retiming, along with a novel form of cloning and register placement. SPIRE also incorporates a placement-dependent static timing analyzer (STA) with a delay model that accounts for buffering and is suitable for physical synthesis. Empirical results on 45nm microprocessor designs show 8% improvement in worst-case slack and 69% improvement in total negative slack after an industrial physical synthesis flow was already completed.