I believe GP is talking about -fbounds-safety [0, 1]. From my understanding this will cause the compiler to emit an error if it can't figure out how to bounds check a pointer access at either compile time or run time. You then need to either add appropriate annotations to provide the missing information or otherwise restructure the code to satisfy the compiler.

[0]: https://clang.llvm.org/docs/BoundsSafety.html

[1]: https://clang.llvm.org/docs/BoundsSafetyAdoptionGuide.html