Exact Dependence Analysis for Increased Communication Overlap

MPI programs are often challenged to scale up to several million cores. In doing so, the programmer tunes every aspect of the application code. However, for large applications, this is often not practical and expensive tracing tools and post-mortem analysis are employed to guide the tuning efforts finding hot-spots and performance bottlenecks. In this paper we revive the use of compiler analysis techniques to automatically unveil opportunities for communication/computation overlap using the result of exact data dependence analysis provided by the polyhedral model. We apply our technique to a 5-point stencil code showing performance improvements up to 28% using 512 cores.