Deadlock-Free Absorption of Barrier Synchronisations

This paper validates and generalises an optimisation arising in the compilation of while loops in data-parallel languages for MIMD shared memory architectures. Dependencies in the source program force the introduction of global synchronisations in the target MIMD program; yet, an efficient compilation must decrease the number of these costly operations. In this context, Hatcher and Quinn have proposed an optimisation that consists in splitting the original loop in two consecutive loops: a computation loop without additional control dependencies and a waiting loop to ensure global termination. We prove its correctness in the axiomatic semantics of Owicki and Gries. We observe that the loops are independent and conclude that this property is more generally applicable than suggested by Hatcher and Quinn's method. Keywords Compilers, Parallel Processing, Program Correctness. Introduction In their description of the data-parallel C language (DPC [5]), Hatcher and Quinn propose an origi..