False positive Wreturn-type warning when a function either returns or throws

[TiborGY]

Clang does not appear to be able to deduce that a function that always throws is effectively [[noreturn]], not even in seemingly trivial cases. Consider this:

void throwError(const std::string& msg){
    throw std::runtime_error(msg);
}

int ensureZero(const int i){
    if (i == 0) return 0;
    throwError("ERROR");
}

Compiling with -Wall -Wextra -O3 -std=c++2c yields a false positive warning:
warning: non-void function does not return a value in all control paths [-Wreturn-type]

PS. https://godbolt.org/z/hdTb6bGcr

[snarang181]

Hi, I have a PR up for this #145166