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Data Distribution Features

Modern parallel and sequential architectures attain their highest speed when the data accessed exhibits locality of reference. The sequential storage order implied by FORTRAN 77 and Fortran 90 often conflicts with the locality demanded by the architecture. To avoid this, HPF includes features which describe the collocation of data (ALIGN) and the partitioning of data among memory regions or abstract processors (DISTRIBUTE). Compilers may interpret these annotations to improve storage allocation for data, subject to the constraint that semantically every data object has a single value at any point in the program. In all cases, users should expect the compiler to arrange the computation to minimize communication while retaining parallelism. Section describes the distribution features.