Supporting data-level and processor-level parallelism in data-parallel programming languages

The dataparallel C and C* languages do not allow the programmer to express both data-level and processor-level parallelism. Instead, the programmer must choose between them. Choosing data-level parallelism prevents the programmer from applying efficient sequential algorithms to data aggregates and causes unacceptable performance. Choosing processor-level parallelism forces the programmer to sequentialize fundamentally parallel data permutation or reduction operations through the use of `for´ loops. The authors give several prototypical examples that demonstrate how data-parallel algorithms can exhibit both data-level and processor-level parallelism. They suggest several ways that data-parallel programming languages or their compilers could be extended to support both kinds of parallelism, and discuss the advantages and disadvantages of each approach