Deriving descriptions of possible values of program variables by means of abstract interpretation

AbstractA PROLOG compiler specializes the code for unification between calls and clause heads as they appear in the program. This code could be further specialized, yielding more efficient code, if more precise information about possible values for actual arguments were available. This paper addresses the problem of gathering such information. It develops a method for obtaining descriptions of possible values of program variables. The method is based upon a framework for abstract interpretation. The descriptions can be regarded as extended modes or a kind of type information. An important issue in the method is the treatment of free variables and the sharing of free variables between different values of program variables