[Bug rtl-optimization/48496] [4.7/4.8 Regression] 'asm' operand requires impossible reload

["ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48496

--- Comment #19 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-04-09 08:04:40 UTC ---
> However, recog.c contains in various places checks that will *accept* -during
> reload- a pseudo in places where a memory constraint is required; exactly
> because such pseudos will actually get replaced by a MEM:
> 
>               case TARGET_MEM_CONSTRAINT:
> [snip]
>                 /* During reload, accept a pseudo  */
>                 else if (reload_in_progress && REG_P (op)
>                          && REGNO (op) >= FIRST_PSEUDO_REGISTER)
>                   win = 1;
> 
> Note that those checks were originally added in the same patch that added this
> asm validity check ...

OK, this makes sense.

> So really that validity check shouldn't have failed just because of the
> presence of a spilled pseudo.  The question is, why doesn't this work for the
> ia64 test case as expected?

Because the reload insns are of the form:

(insn 119 66 120 4 (set (reg:DI 136 f8)
        (reg:DI 406 [ MEM[(const mp_limb_t *)mip_6(D) + 8B] ])) pr52657.c:27 5
{movdi_internal}

and the matching alternative would be (f, Q) with

;; Note that while this accepts mem, it only accepts non-volatile mem,
;; and so cannot be "fixed" by adjusting the address.  Thus it cannot
;; and does not use define_memory_constraint.
(define_constraint "Q"
  "Non-volatile memory for FP_REG loads/stores"
  (and (match_operand 0 "memory_operand")
       (match_test "!MEM_VOLATILE_P (op)")))

bool
insn_extra_memory_constraint (enum constraint_num c)
{
  switch (c)
    {
    case CONSTRAINT_S:
      return true;

    default: break;
    }
  return false;
}