[Bug tree-optimization/64454] optimize (x%5)%5

["glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64454

--- Comment #9 from Marc Glisse <glisse at gcc dot gnu.org> ---
VRP could still do better:

typedef unsigned short T;
T f(T x, T y){
  // Avoid narrowing in the front-end
  int ix=x;
  int iy=y;
  T z=ix%iy;
  int iz=z;
  return z%iy;
}

ix and iy both have range [0, 65535], but we don't optimize

_9 = _5 & 65535;

because

Visiting statement:
_5 = ix_2 % iy_4;
Found new range for _5: VARYING

Whereas (since the type is unsigned, the signed case is slightly more
complicated but should still be doable) the range for _5 should be the
intersection of [0, 65535] (at most max(ix_2)) and [0, 65534] (at most
max(iy_4)-1).

Even in the constant case, if x has range [0, 3], VRP currently says that x%7
has range [0, 6].