Scheduling Transformation and Dependence Tests for Recursive Programs

Scheduling transformations reorder the execution of operations in a program to improve locality and/or parallelism. The polyhedral model provides a general framework for performing instance-wise scheduling transformations for regular programs, reordering the iterations of loops that operate over dense arrays through transformations like tiling. There is no analogous framework for recursive programs—despite recent interest in optimizations like tiling and fusion for recursive applications. This paper presents PolyRec, the first general framework for applying scheduling transformations—like inlining, interchange, and code motion—to nested recursive programs and reasoning about their correctness. We describe the phases of PolyRec—representing dynamic instances, applying transformations, reasoning about correctness—and show that PolyRec is able to apply sophisticated, composed transformations to complex, nested recursive programs and improve performance through enhanced locality