[Bug middle-end/82853] Optimize x % 3 == 0 without modulo

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82853

--- Comment #8 from Andi Kleen <andi-gcc at firstfloor dot org> ---
I'm not sure if it works with other numbers too.

(need to dig through Hacker's delight & Matters Computational to see if they
have anything on it)

But it could be extended for other word lengths at least

BTW there are some other cases, will file a bug shortly on those too.