[forwarded from https://launchpad.net/bugs/291780]

When compiling a small test program, the compiler shows a warning I would either not expect at all, or expect it to appear for all four if-statements used in my example:

$ gcc -Wextra -c promotion.c
promotion.c: In function ‘main’:
promotion.c:10: warning: comparison of promoted ~unsigned with unsigned

promotion.c:
typedef unsigned char uint8_t;

int main(void)
{
        uint8_t a = 0;
        uint8_t b = 0;
        unsigned char c = 0;
        unsigned char d = 0;

        if (a == (b ^ 0xff)) { }
        if (a == (d ^ 0xff)) { }
        if (c == (b ^ 0xff)) { }
        if (c == (d ^ 0xff)) { }

        return 0;
}