That flag catches four specific instances of undefined behavior, a tiny speck in a sea of all possible ways that undefined behavior can be invoked.

If you are building your project with Clang, and find that your code causes undefined behavior not caught by any existing in-compiler test, and you can reproduce it, you might want to ...

- sign up for the developers' list at http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev ,

- skim over http://clang.llvm.org/hacking.html ,

- build from 'trunk' by carefully following a few simple steps in http://clang.llvm.org/get_started.html ,

- wade in and reproduce your bug ,

... and then share your findings.

Together we can build better tools. Anyone with patience and interest can help.

I think we may have our wires crossed. I'm concerned about undefined behavior in my own programs, not undefined behavior in Clang itself. Someone mentioned Clang as a tool that can help detect UB in other programs, but I mentioned that these checks are far from exhaustive.

Sorry, the fault is mine alone. I used an ambiguous description above, now edited.

The only point I wanted to make was that a collective effort might help cut down on ambiguity in expression that the compiler does not identify. I think we could use "more warnings".

He means to say you're welcome to submit patches to make them more exhaustive.