Software programs evolve throughout their lifetime undergoing various changes. While making these changes, software developers may introduce regression faults. It is desirable to detect these faults as quickly as possible to reduce the cost involved in fixing them. One existing solution is continuous testing, which runs an existing test suite to quickly find regression faults as soon as code changes are saved. However, the effectiveness of continuous testing depends on the capability of the existing test suite for finding behavioral differences across versions. To address the issue, we propose an approach, called eXpress, that conducts efficient regression test generation based on a path-exploration-based test generation (PBTG) technique, such as dynamic symbolic execution. eXpress prunes various irrelevant paths with respect to detecting behavioral differences to optimize the search strategy of a PBTG technique. As a result, the PBTG technique focuses its efforts on regression test generation. In addition, eXpress leverages the existing test suite (if available) for the original version to efficiently execute the changed code regions of the program and infect program states. Experimental results on 67 versions (in total) of four programs (two from the subject infrastructure repository and two from real-world open source projects) show that, using eXpress, a state-of-the-art PBTG technique, called Pex, requires about 36% less amount of time (on average) to detect behavioral differences than without using eXpress. In addition, Pex using eXpress detects four behavioral differences that could not be detected without using eXpress (within a time bound). Furthermore, Pex requires 67% less amount of time to find behavioral differences by exploiting an existing test suite than exploration without using the test suite.