No safeguards?

I have a set of shell scripts that will go through source code and make varrious mutations one at a time such as change + to -, replace && with ||, replace 0 with ~0, change 1 to 2 or 2 to 1, swaps <, >, and =, inserts negations, blanks a line entirely, etc. Then it attempts to compile the code with optimizations. If it compiles, the script checks the sha256sum of the resulting binary against all the hashes it's seen before and if it's a new hash it runs the tests. If the tests pass the source is saved off for my manual inspection later.

The single point changes tend to not make errors which self cancel out, and usually if an error does cancel out or the change is in code that doesn't do anything the binary will not change. In code where tests have good condition/decision branch coverage most things this procedure catches are test omissions or bugs.

This approach is super slow and kludgy, I've been repeatedly surprised and frustrated that no one has made a C-syntax aware tool to do similar testing without wasting tons of time on stuff that won't compile or won't make a difference (e.g. mutating comments.. though sometimes I've addressed this by first running the code through something that removes all the comments).

But it's worked well enough for me and parsing C syntax is far enough away from the kind of programming I enjoy that I haven't bothered trying to close this gap myself.