StrSolve: solving string constraints lazily

Reasoning about strings is becoming a key step at the heart of many program analysis and testing frameworks. Stand-alone string constraint solving tools, called decision procedures, have been the focus of recent research in this area. The aim of this work is to provide algorithms and implementations that can be used by a variety of program analyses through a well-defined interface. This separation enables independent improvement of string constraint solving algorithms and reduces client effort. We present StrSolve, a decision procedure that reasons about equations over string variables. Our approach scales well with respect to the size of the input constraints, especially compared to other contemporary techniques. Our approach performs an explicit search for a satisfying assignment, but constructs the search space lazily based on an automata representation. We empirically evaluate our approach by comparing it with four existing string decision procedures on a number of tasks. We find that our prototype is, on average, several orders of magnitude faster than the fastest existing approaches, and present evidence that our lazy search space enumeration accounts for most of that benefit.