--- Comment #6 from Peter Bergner <bergner at gcc dot> ---
(In reply to Segher Boessenkool from comment #5)
> I think you should do this check inside address_offset?

I don't think that is possible.  The callers of address_offset assume if
address_offset returns a non-NULL rtx, then it *IS* a constant (eg, they use
INTVAL() on its return value).  The problematical address we have here doesn't
have constant offset, so to "change" anything, we'd have to return non-NULL
(otherwise we return true from mem_operand_gpr) and that would cause issues
with INTVAL...or I'd have to guard all return values of address_offset.

I'll also note that the patch also matches the usage of mem_operand_ds_form()
which also has an early out for an unsupported case before it calls

mem_operand_ds_form (rtx op, machine_mode mode)
  unsigned HOST_WIDE_INT offset;
  int extra;
  rtx addr = XEXP (op, 0);

  if (!offsettable_address_p (false, mode, addr))
    return false;

  op = address_offset (addr);
  if (op == NULL_RTX)
    return true;


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