[Bug middle-end/68870] [6 Regression] ICE on valid code at -O1, -O2 and -O3 on x86_64-linux-gnu

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68870

--- Comment #8 from Arseny Solokha <asolokha at gmx dot com> ---
I believe the following reproducer is for the issue reported here. Its further
minimization yields backtrace listed in #c0.

The only difference is that w/ the following not minimized snippet gcc ICEs in
tree_nop_conversion_p(tree_node const*, tree_node const*) when compiling it at
-O1:

int w3, ao, k9, nl;

static int
oy(void)
{
  static int pe;
  int ht;
  for (ao = 0; ao < 1; ++ao)
    for (ht = 0; ht < 1; ++ht)
      for (w3 = 0; w3 < 1; ++w3)
        for (k9 = 0; k9 < 1; ++k9)
          if (pe < 1)
            return 0;
  return (ht > 1) || nl;
}

int
ct(void)
{
  return oy();
}