Pointer Analysis for Programs with Structures and Casting

Type casting allows a program to access an object as if it had a type different from its declared type. This complicates the design of a pointer-analysis algorithm that treats structure fields as separate objects; therefore, some previous pointer-analysis algorithms "collapse" a structure into a single variable. The disadvantage of this approach is that it can lead to very imprecise points-to information. Other algorithms treat each field as a separate object based on its offset and size. While this approach leads to more precise results, the results are not portable because the memory layout of structures is implementation dependent. This paper first describes the complications introduced by type casting, then presents a tunable pointer-analysis framework for handling structures in the presence of casting. Different instances of this framework produce algorithms with different levels of precision, portability, and efficiency. Experimental results from running our implementations of four instances of this framework show that (i) it is important to distinguish fields of structures in pointer analysis, but (ii) making conservative approximations when casting is involved usually does not cost much in terms of time, space, or the precision of the results.