Increasing hardware efficiency with multifunction loop accelerators

To meet the conflicting goals of high-performance low-cost embedded systems, critical application loop nests are commonly executed on specialized hardware accelerators. These loop accelerators are traditionally designed in a single-function manner, wherein each loop nest is implemented as a dedicated hardware block. This paper focuses on hardware sharing across loop nests by creating multifunction loop accelerators, or accelerators capable of executing multiple algorithms. A compiler-based system for automatically synthesizing multifunction loop accelerator architectures from C code is presented. We compare the effectiveness of three architecture synthesis approaches with varying levels of complexity: sum of individual accelerators, union of individual accelerators, and joint accelerator synthesis. Experiments show that multifunction accelerators achieve substantial hardware savings over combinations of single-function designs. In addition, the union approach to multifunction synthesis is shown to be effective at creating low-cost hardware by exploiting hardware sharing, while remaining computationally tractable.