Is vec_init<mode> allowed to FAIL?

["Jan Hoogerbrugge" <jan dot hoogerbrugge at gmail dot com>]

Hi,

I am trying to define vec_init<mode>. I can only do splats on register
values. So
operands[1] of vec_init should be registers and those registers should
be the same.

Here is some code:

(define_expand "vec_init<mode>"
        [(match_operand:VEC_MODE32 0 "register_operand" "")
         (match_operand 1 "register_operand" "")]
        ""
        {
                if(trimedia_expand_vector_init(operands[0], operands[1]))
                        DONE;
                else
                        FAIL;
        }
)

int
trimedia_expand_vector_init (rtx target, rtx vals)
{
  enum machine_mode mode = GET_MODE (target);
  enum machine_mode inner_mode = GET_MODE_INNER (mode);
  int n_elts = GET_MODE_NUNITS (mode);
  rtx elem, tmp1, tmp2;
  int i;

  for (i = 0; i < n_elts; ++i)
    {
      elem = XVECEXP (vals, 0, i);
      if (CONSTANT_P (elem))
        return 0;
      if (!rtx_equal_p (elem, XVECEXP (vals, 0, 0)))
        return 0;
    }

  tmp1 = gen_reg_rtx (SImode);
  tmp2 = gen_reg_rtx (SImode);

  if (GET_MODE_SIZE (mode) == 4)
    {
      if (inner_mode == QImode)
        {
          emit_insn (gen_packqi (tmp1, elem, elem));
          emit_insn (gen_packhi (target, tmp1, tmp1));
          return 1;
        }
      else if (inner_mode == HImode)
        {
          emit_insn (gen_packhi (target, elem, elem));
          return 1;
        }
    }
  else if (GET_MODE_SIZE (mode) == 8)
    {
      if (inner_mode == QImode)
        {
          emit_insn (gen_packqi (tmp1, elem, elem));
          emit_insn (gen_packhi (tmp2, tmp1, tmp1));
          emit_insn (gen_packsi (target, tmp2, tmp2));
          return 1;
        }
      else if (inner_mode == HImode)
        {
          emit_insn (gen_packhi (tmp2, elem, elem));
          emit_insn (gen_packsi (target, tmp2, tmp2));
          return 1;
        }
    }

  return 0;
}

I see however that no code is generated if trimedia_expand_vector_init()
returns 0 and the define_expand FAILs. I also see in other targets that a
vec_init always ends with a DONE. Could it be that vec_init is not allowed to
FAIL?

Regards,
Jan