[Bug tree-optimization/68021] [6 Regression] ice in rewrite_use_nonlinear_expr with -O3

["ysrumyan at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68021

--- Comment #4 from Yuri Rumyantsev <ysrumyan at gmail dot com> ---
Indeed, there is an issue with outer-loop unswitching - it should not be
performed for infinite loops. But if we slightly modify test if finite
outer-loop we will get the same error: 
char a;
void fn1(char *p1, int p2, int p3) {
  int i, x;
  for (i = 0; i < 10; i++) {
    for (x = 0; x < p3; x++) {
      *p1 = a;
      p1--;
    }
    p1 += p2;
  }
}

I assume that  sccp is responsible for it.