Dependence analysis for pointer variables

Our concern is how to determine data dependencies between program constructs in programming languages with pointer variables. We are particularly interested in computing data dependencies for languages that manipulate heap-allocated storage, such as Lisp and Pascal. We have defined a family of algorithms that compute safe approximations to the flow, output, and anti-dependencies of a program written in such a language. Our algorithms account for destructive updates to fields of a structure and thus are not limited to the cases where all structures are trees or acyclic graphs; they are applicable to programs that build cyclic structures. Our technique extends an analysis method described by Jones and Muchnick that determines an approximation to the actual layouts of memory that can arise at each program point during execution. We extend the domain used in their abstract interpretation so that the (abstract) memory locations are labeled by the program points that set their contents. Data dependencies are then determined from these memory layouts according to the component labels found along the access paths that must be traversed during execution to evaluate the program's statements and predicates. For structured programming constructs, the technique can be extended to distinguish between loop-carried and loop-independent dependencies, as well as to determine lower bounds on minimum distances for loop-carried dependencies.