Efficient implementation of portable C*-like data-parallel library in C++

Abstract

The C* language is a data-parallel extension of the C language which incorporates parallel data types. Since the C++ language provides operator overloading, a C++ library can implement the C* parallel extensions with a similar syntax. Although library implementations are highly portable, some overheads make them impractical. The two major overheads incurred are temporaries in each operator application and the inability to detect regular communication patterns. The C++ overloading mechanism forces a temporary for each operator application. Also, regular communications in C* are syntactically indistinguishable from general point-to-point communications. We tackled these problems extensively in a library. The template mechanism, a type parameterization in C++, is used to eliminate temporaries by delaying operator application and evaluating the entire expression at once. The polymorphic type dispatch mechanism is used to detect regular communications by assigning particular types to potentially regular communications. We have implemented the library on the CM-5, and compared its performance with the C* compiler using three simple examples. The techniques presented offers improved performance comparable to the C* compiler, which is close or 1.5 times slower in two examples, and even faster in one example.