[Bug target/63805] ICE: in extract_insn, at recog.c:2327 with -mcpu=power8

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63805

--- Comment #13 from Alan Modra <amodra at gmail dot com> ---
Note that testcases with smaller atomic ops fail too, but at runtime.  For
example:

struct foo { char pad; char x[4]; } a;

int
bar (int val)
{
  int ret;
  __atomic_exchange (&a.x, &val, &ret, 5);
  return  ret;
}

int main ()
{
  return bar (42);
}

Fails with a bus error.