This paper describes the design and implementation of Gordini, a performance analysis tool that is capable of automatically locating places in the source code where a communication optimization technique can be applied for performance debugging of message passing parallel programs. Our automatic search approach is based on data dependence analysis on trace files. It currently supports three techniques: communication-computation overlap, message aggregation, and collective communication. In case studies, Gordini assists us in improving the performance of sophisticated programs coded by experts, the two first prize winners of software contests. Therefore, we believe that our automatic approach is useful for application developers to locate communication bottlenecks in programs.