An analysis of the search spaces for generate and validate patch generation systems

We present the first systematic analysis of key characteristics of patch search spaces for automatic patch generation systems. We analyze sixteen different configurations of the patch search spaces of SPR and Prophet, two current state-of-the-art patch generation systems. The analysis shows that 1) correct patches are sparse in the search spaces (typically at most one correct patch per search space per defect), 2) incorrect patches that nevertheless pass all of the test cases in the validation test suite are typically orders of magnitude more abundant, and 3) leveraging information other than the test suite is therefore critical for enabling the system to successfully isolate correct patches.