Object representatives: a uniform abstraction for pointer information

Abstract

Pointer analyses enable many subsequent program analyses and transformations by statically disambiguating references to the heap. However, different client analyses may have different sets of pointer analysis needs, and each must pick some pointer analysis along the cost/precision spectrum to meet those needs. Some analysis clients employ combinations of pointer analyses to obtain better precision with reduced analysis times. Our goal is to ease the task of developing client analyses by enabling composition and substitutability for pointer analyses. We therefore propose object representatives, which statically represent runtime objects. A representative encapsulates the notion of object identity, as observed through the representative's aliasing relations with other representatives. Object representatives enable pointer analysis clients to disambiguate references to the heap in a uniform yet flexible way. Representatives can be generated from many combinations of pointer analyses, and pointer analyses can be freely exchanged and combined without changing client code. We believe that the use of object representatives brings many software engineering benefits to compiler implementations because, at compile time, object representatives are Java objects. We discuss our motivating case for object representatives, namely, the development of an abstract interpreter for tracematches, a language feature for runtime monitoring. We explain one particular algorithm for computing object representatives which combines flow-sensitive intraprocedural must-alias and must-not-alias analyses with a flow-insensitive, context-sensitive whole-program points-to analysis. In our experience, client analysis implementations can almost directly substitute object representatives for runtime objects, simplifying the design and implementation of such analyses.