PolyAPM - comparative parallel programming with abstract parallel machines

A parallelising compilation consists of many translation and optimisation stages. The programmer may steer the compiler through these stages by supplying directives with the source code or setting compiler switches. However, for an evaluation of the effects of individual stages, their selection and their best order, this approach is not optimal. To solve this problem, we propose the following method. The compilation is cast as a sequence of program transformations. Each intermediate program runs on anAbstract Parallel Machine (APM), while the program generated by the final transformation runs on the target architecture. Our intermediate programs are all in the same language, Haskell. Thus, each program is executable and still abstract enough to be legible, which enables the evaluation of the transformation that generated it. This evaluation is supported by a cost model, which makes a performance prediction of the abstract program for a real machine. Our project, PolyAPM, provides an acyclic directed graph – usually a tree – of APMs whose traversal specifies different combinations and orders of transformations. From one source program, several target programs can be constructed. Their run time characteristics can be evaluated and compared. The goal of PolyAPM is not to support the one-off construction of parallel application programs. For the method’s overhead to pay off, the project aims rather at supporting the construction and comparison of many similar variations of a parallel program and a comparative evaluation of parallelisation techniques. With the automation of transformations, PolyAPM can also be used to construct semi-automatic compilation systems.