Dynamic tile free scheduling for code with acyclic inter-tile dependence graphs

Free scheduling is a task ordering technique under which instructions are executed as soon as their operands become available. Coarsening the grain of computations under the free schedule, by means of using groups of loop nest statement instances (tiles) in place of single statement instances, increases the locality of data accesses and reduces the number of synchronization events, and as a consequence improves program performance. The paper presents an approach for code generation that allows for the free schedule for tiles of arbitrarily nested affine loops at run-time. The scope of the applicability of the introduced algorithms is limited to tiled loop nests whose inter-tile dependence graphs are cycle-free. The approach is based on the polyhedral model. Results of experiments with the PolyBench benchmark suite, demonstrating significant tiled code speed-up, are discussed.