__xg
: "=&d" (x) : "d" (x), "m" (*__xg(u8, ptr)) : "memory");
: "=&d" (x) : "d" (x), "m" (*__xg(u16, ptr)) : "memory");
: "=&d" (x) : "d" (x), "m" (*__xg(u32, ptr)) : "memory");