Bounds modelling and compiler optimizations for superscalar performance tuning

Abstract

We consider the floating point microarchitecture support in RISC superscalar processors. We briefly review the fundamental performance trade-offs in the design of such microarchitecutres. We propose a simple, yet effective bounds model to deduce the "best-case" loop performance limits for these processors. We compare these bounds to simulated and real performance measurements. From this study, we identify several loop tuning opportunities. In particular, we illustrate the use of this analysis in suggesting loop unrolling and scheduling heuristics. We report our experimental results in the context of a set of application-based loop test cases. These are designed to stress various resource limits in the core (infinite cache) microarchitecture.