The first interprocedural modification side-effects analysis for C (MOD C ) that obtains better than worst-case precision on programs with general-purpose pointer usage is presented with empirical results. The analysis consists of an algorithm schema corresponding to a family of MOD C algorithms with two independent phases: one for determining pointer-induced aliases and a subsequent one for propagating interprocedural side effects. These MOD C algorithms are parameterized by the aliasing method used. The empirical results compare the performance of two dissimilar MOD C algorithms: MOD C ( FSAlias ) uses a flow-sensitive, calling-context-sensitive interprocedural alias analysis; MOD C ( FIAlias uses a flow-insensitive, calling-context-insensitive alias analysis which is much faster, but less accurate. These two algorithms were profiled on 45 programs ranging in size from 250 to 30,000 lines of C code, and the results demonstrate dramatically the possible cost-precision trade-offs. This first comparative implementation of MOD C analyses offers insight into the differences between flow-/context-sensitive and flow-/context-insensitive analyses. The analysis cost versus precision trade-offs in side-effect information obtained are reported. The results show surprisingly that the precision of flow-sensitive side-effect analysis is not always prohibitive in cost, and that the precision of flow-insensitive analysis is substantially better than worst-case estimates and seems sufficient for certain applications. On average MOD C ( FSAlias ) for procedures and calls is in the range of 20% more precise than MOD C ( FIAlias ); however, the performance was found to be at least an order of magnitude slower than MOD C ( FIAlias ).

The paper presents methods that we have implemented to improve the quality of the def-uses reported for dynamically allocated locations. The methods presented are based on the Ruggieri/Murtagh naming scheme for dynamically created locations. We expand upon this scheme to name dynamically allocated locations for some user written allocation routines. Using this expanded naming scheme, we introduce an inexpensive, non-iterative, and localized calculation of extended must alias analysis to handle dynamically allocated locations, and show how this information can be used to improve def-use information. This is the first attempt to specify must alias information for names which represent a set of dynamically allocated locations. Empirical results are presented to illustrate the usefulness of our method. We consider this work a step towards developing practical re-engineering tools for C.