The limits of alias analysis for scalar optimizations

In theory, increasing alias analysis precision should improve compiler optimizations on C programs. This paper compares alias analysis algorithms on scalar optimizations, including an analysis that assumes no aliases, to establish a very loose upper bound on optimization opportunities. We then measure optimization opportunities on thirty-six C programs. In practice, the optimizations are rarely inhibited due to the precision of the alias analyses. Previous work finds similarly that the increased precision of specific alias algorithms provide little benefit for scalar optimizations, and that simple static alias algorithms find almost all dynamically determined aliases. This paper, however, is the first to provide a static methodology that indicates that additional precision is unlikely to yield improvements for a set of optimizations. For clients with higher alias accuracy demands, this methodology can help pinpoint the need for additional accuracy.