On the Correlation between Resource Minimization and Interconnect Complexities in High-Level Synthesis

As the technology node of VLSI designs advances to sub10 nm, two interconnect-centric metrics of a circuit, the interconnect complexity (either number of interconnects or wirelength/WL) and congestion, become critically important across all design stages alongside conventional resource or function-unit (FU)-centric metrics like area/number-of-FUs and leakage power. High Level synthesis (HLS), one of the earliest and most impactful design stages, rarely monitors interconnect metrics, which makes their recovery at later stages very difficult. HLS algorithms and tools typically perform FU-centric minimization via operation scheduling, module selection (SMS) and binding. As a consequence, it mostly overlooks interconnect-based metrics. In this paper, we explore whether this can adversely affect interconnect metrics, and in general explore the correlation between FU-centric optimization in SMS, and the resulting interconnect metrics co-optimized (along with FU metrics) in the later binding stage(s). For this purpose we develop a probabilistic analysis for post-scheduling binding to estimate interconnect metrics, and verify its accuracy by comparison to empirical results across different scheduling techniques that generate different degrees of FU optimization. Based on both empirical and analytical results we predict how interconnects metrics will pan out with different degrees of FU optimization. Finally, based on our analysis, we also provide suggestions to improve interconnect metrics for whatever FU optimization degree an available SMS technique can achieve.