High-level synthesis with behavioral level multi-cycle path analysis

High-level synthesis (HLS) tools generate register transfer level (RTL) hardware descriptions through a process of resource allocation, scheduling and binding. Intuitively, RTL quality influences the logic synthesis quality. Specifically, the achievable clock rate, area, and latency in clock cycles will be determined by the RTL description. However, not all paths should receive equal logic synthesis effort - multi-cycle paths represent an opportunity to spend logic synthesis effort elsewhere to achieve better design quality. In this paper, we perform multi-cycle optimisation on chained functional operations. We couple HLS and logic synthesis synergistically so multi-cycle paths can be identified and optimised coherently across both behavioral and logic levels. In addition, we perform multi-cycle path analysis at the behavioral level efficiently. We prove that our technique examines all reachable circuit state and finds multi-cycle paths including control flow and guarding conditions that improve the flexibility and power of the technique. Compared to LegUp, we achieve average 55% execution time improvement, 29% area improvement, and 68% time-area product improvement targeting FPGA architecture.