SSI Revisited

The static single information (SSI) form, proposed by Ananian, then in a more general form by Singer, is an extension of the static single assignment (SSA) form. The latter is a well-established compiler intermediate representation that has been successfully used for numerous compiler analysis and optimizations. Several interesting results have also been shown for SSI concerning liveness analysis and representation of live-ranges of variables, which could make SSI appealing for just-in-time compilation. Unfortunately, previous literature on the SSI form is sparse and appears to be partly incorrect. Our paper corrects some of the mistakes that have been made. Our main result is a complete proof that, even for the most general definition of SSI, basic blocks, and thus program points, can be totally ordered so that live-ranges of variables correspond to intervals. This corrects the erroneous proof of Brisk and Sarrafzadeh