About the Relevance of Multispeculation in High- Level Synthesis

Nowadays circuits possess stringent area or power constraints. Nevertheless, the increase of performance is still an obligation while designing them. The recent appearance of Variable Latency Functional Units (VLFUs) has raised the possibilities for designers because they offer a good tradeoff. However, the VLFU behaviour depends on the inputs, so the use of many of them increases the probability of working in long latency mode. In this paper we propose the use of Multispeculative FUs to improve performance with a negligible area penalty. By judiciously speculating the carry vectors of concrete operations, and hiding the possible mispredictions, the probability of working in long latency mode is reduced. Hence, the average latency is diminished and thus performance is increased. Our experiments show a 24% improvement on execution time when considering logarithmic modules.