Prototyping the automatic generation of MPI code from OpenMP programs in GCC

Abstract. Multiprocessor architectures comprising various memory organizations and communi-cation schemes are now widely deployed. Hence, powerful programming tools are expressly needed in order to fully exploit the computation capabilities of such architectures. Classically, a parallel program must strictly conform to a unique parallel paradigm (either shared memory or message passing). However it is clear that this approach is far from being suited to current architectures. The shared-memory paradigm is restricted to certain hardware architectures while the message-passing paradigm prevents the application from evolution. In this paper we investigated the use of GCC as a compiler to transform an OpenMP program into a MPI program. OpenMP directives are used to express parallelism in the application and to provide data dependence information to the compiler. We deeply analyze GOMP, the OpenMP implementation in GCC, providing code trans-formations in the GIMPLE representation and compare them to those necessary for transforming a shared-memory program (annotated with OpenMP pragmas) to a message-passing MPI-based program. In order to test some ideas, we have developed a limited prototype. The result is that, in addition to GOMP providing parser and code transformation, additional data dependency analyses are necessary to generate communications.