Method of prefetching data for references with multiple stride directions

Abstract

There are two separate, yet related, prefetching strategies used for data references used having multiple strides, which typically occur in data references within nested loop structures. The first approach attempts to reverse one or more of the nested loops so that the strides of the reference are in the same direction. Once the loop or loops are reversed, data elements can be prefetched in the common loop direction. Preferably, the inner loops are reversed as compared with the outer loops, but this is not essential. The second approach is used where the data reference has multiple strides and the loops cannot be reversed. In this case, the prefetching method prefetches in the opposite direction of the innermost loop that surrounds the data reference. The second approach is used when the first approach cannot be used and where the strides of the reference have different directions and the inner loop is expected to iterate relatively few times. In such a case the second approach produces better results than the prior art.