A language for the compact representation of multiple program versions

Abstract. As processor complexity increases compilers tend to deliver subopti-mal performance. Library generators such as ATLAS, FFTW and SPIRAL over-come this issue by empirically searching in the space of possible program ver-sions for the one that performs the best. Empirical search can also be applied by programmers, but because they lack a tool to automate the process, programmers need to manually re-write the application in terms of several parameters whose best value will be determined by the empirical search in the target machine. In this paper, we present the design of an annotation language, meant to be used either as an intermediate representation within library generators or directly by the programmer. This language that we call X represents parameterized programs in a compact and natural way. It provides an powerful optimization framework for high performance computing.