A method and apparatus for to blocking nested loops having feedback or feedforward indexing. An embodiment of a method includes receiving a computer code segment, the segment including a first inner loop and a second outer loop, the inner loop being within the outer loop and the inn loops having a one-dimensional iteration space that is independent of the outer loop. The first loop is indexed by a variable I over a contiguous one-dimensional iteration space and addresses one or more data arrays with a shift in the index. The method further includes dividing a two-dimensional iteration space of the first loop and the second loop into multiple contiguous windows, where the second loop uses only one window of the plurality of windows during each iteration and the plurality of windows cover the iteration space. The method includes modifying the computer code segment by adding a third outer loop outside the second loop of the segment, the third loop encompassing the first loop and the second loop.