We previously presented a fault localization technique called Value Replacement that repeatedly alters the state of an executing program to locate a faulty statement [9]. The technique searches for program statements involving values that can be altered during runtime to cause the incorrect output of a failing run to become correct. We showed that highly effective fault localization results could be achieved by the technique on programs containing single faults. In the current work, we generalize Value Replacement so that it can also perform effectively in the presence of multiple faults. We improve scalability by describing two techniques that significantly improve the efficiency of Value Replacement. In our experimental study, our generalized technique effectively isolates multiple simultaneous faults in time on the order of minutes in each case, whereas in [9], the technique had sometimes required time on the order of hours to isolate only single faults.
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