I think sanitizer usefulness for defined behaviors is going to depend a lot on how frequently those behaviors are intentionally used and how easy/hard it would

I think sanitizer usefulness for defined behaviors is going to depend a lot on how frequently those behaviors are intentionally used and how easy/hard it would be to suppress false positives. There might be some behaviors that sanitizers don't currently catch but are used for optimizations as well, and boringcc/friendly C might be useful for those? Not entirely sure what those might be, if they even exist, though; IIRC sanitizers don't currently flag strict aliasing violations, but -fno-strict-aliasing exists so there's no need for a new compiler/dialect (for GCC/Clang?)