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

[jakub at gcc dot gnu.org]

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

--- Comment #20 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Testcase I've been eyeballing so far:
unsigned f1 (unsigned x) { return (x % 679U) == 0; }
unsigned f2 (unsigned x, unsigned *y) { *y = x / 679U; return (x % 679U) == 0;
}
unsigned f3 (unsigned x) { return (x % 1738U) == 0; }
void bar (void);
void f4 (unsigned x) { if (x % 3 == 0) bar (); }
void f5 (unsigned x) { if (x % 3 == 1) bar (); }
void f6 (unsigned x) { if (x % 3 == 2) bar (); }