[Bug tree-optimization/59642] Performance regression (4.7/4.8) with -ftree-loop-distribute-patterns

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59642

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
I've noticed the same in other PRs, normally we manage to track the actual
value of *p, but we don't manage that when *p was written by __builtin_mem*,
which should still be doable:
int f(int*p){
  __builtin_memset(p,0,4);
  return *p;
}

gives the following .optimized:

  __builtin_memset (p_2(D), 0, 4);
  _4 = *p_2(D);
  return _4;

(RTL fixes things later in this simple case)