Verifying Semantic Conflict-Freedom in Three-Way Program Merges

Abstract

Even though many programmers rely on 3-way merge tools to integrate changes from different branches, such tools can introduce subtle bugs in the integration process. This paper aims to mitigate this problem by defining a semantic notion of confict-freedom, which ensures that the merged program does not introduce new unwanted behaviors. We also show how to verify this property using a novel, compositional algorithm that combines lightweight dependence analysis for shared program fragments and precise relational reasoning for the modifications. We evaluate our tool called SafeMerge on 52 real-world merge scenarios obtained from Github and compare the results against a textual merge tool. The experimental results demonstrate the benefits of our approach over syntactic confict-freedom and indicate that SafeMerge is both precise and practical.