[Bug d/119139] Regression with struct invariants

[ibuclaw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119139

--- Comment #2 from Iain Buclaw <ibuclaw at gcc dot gnu.org> ---
Both gdc-11 and gdc-12 seem to produce the same tree structures from initial
dump.

```
struct  toString ()
{
  return <retval> = {.length=1, .ptr="1"};
}


void __invariant1 (const struct B & this)
{
  return;
}


struct  str (struct B & this)
{
  void __returnLabel = <<< error >>>;
  const struct  __result;

  __invariant ((struct B *) this);
  if (this->n == 0)
    {
      __result = {.length=1, .ptr="0"};
      goto __returnLabel;
    }
  __result = toString ();
  goto __returnLabel;
  __returnLabel:;
  __invariant ((struct B *) this);
  return <retval> = __result;
}


void __invariant (const struct B & this)
{
  __invariant1 ((const struct B *) this);
}


int main ()
{
  struct B b;

  b = {.n=2};
  str (&b);
  return <retval> = 0;
}
```