Demand-driven Alias Analysis Implementation Based on Open64

In this paper, an implementation of a demand-driven alias analysis [7] in Open64 is presented. In the algorithm, a program expression graph is constructed based on all the expressions and assignments in the program, and the memory alias problem is formulated as a CFL-reachability problem. To deal with field accesses of structs which are common in multi-media applications, a field-sensitive extension of the original algorithm is also implemented. Currently, the field-sensitivity assumes ansi-compliant programs. By evaluating the implementation using some spec2000 programs, we found that the scalability of the original algorithm is not able to give enough precision in a reasonable compile time. To improve the scalability, a new one-level flow demand driven algorithm is developed, in which the hierarchical state machine is simplified by making machine M transitive while still keeping machine V non-transitive. The algorithm can achieve the same precision as Das’s algorithm [3], but uses a demand driven approach. Although the new one-level flow algorithm lost some of the precision for making machine M transitive, it can finish analysis of more queries for a given reasonable compile time and give more definite alias results. In other words, it can give better precision than the original algorithm and is more practical for product compiler. From experiment results, we can see that the algorithm can finish about half of the queries in a short compile time, and give much more “not aliased” results than the original algorithm.