internal_error in loop-iv.c

[Frederic Riss]

Hi,

My port hits this assertion in loop-iv.c:799:

gcc_assert ((*inner_mode == *outer_mode) != (*extend != UNKNOWN));

It's in the function get_biv_step:

static bool
get_biv_step (df_ref last_def, rtx reg, rtx *inner_step,
              enum machine_mode *inner_mode, enum rtx_code *extend,
              enum machine_mode *outer_mode, rtx *outer_step)
{
  *outer_mode = GET_MODE (reg);

  if (!get_biv_step_1 (last_def, reg,
                       inner_step, inner_mode, extend, *outer_mode,
                       outer_step))
    return false;

  gcc_assert ((*inner_mode == *outer_mode) != (*extend != UNKNOWN));
  gcc_assert (*inner_mode != *outer_mode || *outer_step == const0_rtx);

  return true;
}

The analyzed register is SImode (outer_mode), but the step determined
by the biv step analysis returns a V2HI (inner_mode) step value. As
the register is modified through a subreg, there's no extension. The
vector mode comes from the analysis of the following insn:

(insn 170 169 171 12 /work1-disk/dft/src/dft.c:99 (set (subreg:V2HI
(reg:SI 544 [ vect_vec_iv_.173 ]) 0)
        (plus:V2HI (subreg:V2HI (reg:SI 540 [ vect_vec_iv_.173 ]) 0)
            (subreg:V2HI (reg:SI 542 [ vect_cst_.172 ]) 0))) 347
{addv2hi3} (expr_list:REG_DEAD (reg:SI 542 [ vect_cst_.172 ])
        (expr_list:REG_EQUAL (plus:V2HI (subreg:V2HI (reg:SI 540 [
vect_vec_iv_.173 ]) 0)
                (const_vector:V2HI [
                        (const_int 4 [0x4])
                        (const_int 4 [0x4])
                    ]))
            (nil))))

The code looks OK to me, but I thought there might be some rule about
vector subregs that I don't know about.

If the code is OK, should get_biv_step return true or false?

Many thanks,
Fred