Partial redundancy elimination is a code optimization with a long history of literature and implementation. In practice, its effectiveness depends on issues of naming and code shape. This paper shows that a combination of global reassociation and global value numbering can increase the effectiveness of partial redundancy elimination. By imposing a discipline on the choice of names and the shape of expressions, we are able to expose more redundancies. As part of the work, we introduce a new algorithm for global reassociation of expressions. It uses global information to reorder expressions, creating opportunities for other optimizations. The new algorithm generalizes earlier work that ordered FORTRAN array address expressions to improve optimization [25]. 1 Introduction Partial redundancy elimination is a powerful optimization that has been discussed in the literature for many years (e.g., [21, 8, 14, 12, 18]). Unfortunately, partial redundancy elimination has two serious limitations...