This is tis-interpreter, an interpreter of C for detecting undefined behavior.
tis-interpreter detects subtle bugs in C programs that may not have eye-visible effects when executing the same programs compiled in the traditional way. Some of the bugs that are discovered lead to security vulnerabilities. Fortunately, most don’t.
tis-interpreter works by interpreting C programs statement by statement from beginning to end, verifying at each statement whether the program can invoke undefined behavior. This makes it comparable to Valgrind and C compiler sanitizers (UBSan, ASan, …). The recommended use is to apply tis-interpreter to existing tests for security-sensitive C code in which a bug could have dramatic consequences. tis-interpreter can detect violations of the C standard even when applied to regression tests that have never revealed any problem.
At this stage, the best uses for tis-interpreter are pure C libraries with as few dependencies as possible and existing tests. After compilation (or after downloading a binary snapshot), you can experiment with examples of increasing difficulty.