[Bug c++/113852] -Wsign-compare doesn't warn on unsigned result types

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113852

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

int main()
{
    unsigned short a1 = (1u << 16) - 1;
    unsigned short a2 = a1;

    /* a1 * a2 should be 4294836225 in math terms */
    unsigned long long a3 = 4294836225;

    /*
     * The result of (a1 * a2) is of type int and the result is negative.
     * (a1 * a2) ends up as some bogus high number because the common
     * type here ends up as uint64_t and sign-extension occurs.
     */
    if ((a1 * a2) > a3) {
        __builtin_abort();
    }
}