An Exact Method for Analysis of Value-based Array Data Dependences

Abstract

Standard array data dependence testing algorithms give information about the aliasing of array references. If statement 1 writes a[5], and statement 2 later reads a[5], standard techniques described this as a flow dependence, even if there was an intervening write. We call a dependence between two references to the same memory location a memory-based dependence. In contrast, if there are no intervening writes, the references touch the same value and we call the dependence a value-based dependence. There has been a surge of recent work on value-based array data dependence analysis (also referred to as computation of array data-flow dependence information). In this paper, we describe a technique that is exact over programs without control flow (other than loops) and non-linear references. We compare our proposal with the technique proposed by Paul Feautrier, which is the other technique that is complete over the same domain as ours. We also compare our work with that of Tu and Padua, a representative approximate scheme for array privatization. (Also cross-referenced as UMIACS-TR-93-137)