A case for precise, fine-grained pointer synthesis in high-level synthesis

Abstract

This article combines two practical approaches to improve pointer synthesis within HLS tools. Both approaches focus on inefficiencies in how HLS tools treat the points-to graph – a mapping that connects each instruction to the memory locations that it might access at runtime. HLS pointer synthesis first compute the points-to graph via pointer analysis and then implements its connections in hardware, which gives rise to two inefficiencies. Firstly, HLS tools typically favour pointer analysis that is fast, sacrificing precision. Secondly, they also favour centralising memory connections in hardware for instructions that can point to more than one location. In this article, we demonstrate that a more precise pointer analysis coupled with decentralised memory connections in hardware can substantially reduce the unnecessary sharing of memory resources. We implement both flow- and context-sensitive pointer analysis and fine-grained memory connections in two modern HLS tools, LegUp and Vitis HLS. An evaluation on three benchmark suites, ranging from non-trivial pointer use to standard HLS benchmarks, indicates that when we improve both precision and granularity of pointer synthesis, on average, we can reduce area and latency by around 42% and 37% respectively.