Data dependence distance is widely used to characterize data dependences in advance optimizing compilers. The standard definition of dependence distance assumes that loops are normalized (have constant lower bounds and a step of 1); there is not a commonly accepted definition for unnormalized loops. We have identified several potential definitions, all of which give the same answer for normalized loops. There are a number of subtleties involved in choosing between these definitions, and no one definition is suitable for all applications.
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