Dartagnan: Leveraging Compiler Optimizations and the Price of Precision (Competition Contribution)

We describe the new features of the bounded model checker Dartagnan for SV-COMP ’21. We participate, for the first time, in the ReachSafety category on the verification of sequential programs. In some of these verification tasks, bugs only show up after many loop iterations, which is a challenge for bounded model checking. We address the challenge by simplifying the structure of the input program while preserving its semantics. For simplification, we leverage common compiler optimizations, which we get for free by using LLVM. Yet, there is a price to pay. Compiler optimizations may introduce bitwise operations, which require bit-precise reasoning. We evaluated an SMT encoding based on the theory of integers + bit conversions against one based on the theory of bit-vectors and found that the latter yields better performance. Compared to the unoptimized version of Dartagnan, the combination of compiler optimizations and bit-vectors yields a speed-up of an order of magnitude on average.