"[email protected]" <[email protected]> writes:
> Hi， Richard. Thanks for the comments.
>
>>> if (!LOOP_VINFO_USING_DECREMENTING_IV_P (loop_vinfo)
>>> || !iv_rgc
>>> || (iv_rgc->max_nscalars_per_iter * iv_rgc->factor
>>> != rgc->max_nscalars_per_iter * rgc->factor))
>>> {
> >> /* See whether zero-based IV would ever generate all-false
> masks
> >> or zero length before wrapping around. */
> >> bool might_wrap_p = vect_rgroup_iv_might_wrap_p (loop_vinfo,
> rgc);
>
> >> /* Set up all controls for this group. */
> >> test_ctrl = vect_set_loop_controls_directly (loop, loop_vinfo,
> >> &preheader_seq,
> >> &header_seq,
> >> loop_cond_gsi,
> rgc,
> >> niters,
> niters_skip,
> >> might_wrap_p);
>
> >> iv_rgc = rgc;
> >> }
>
>
> Could you tell me why you add:
> (iv_rgc->max_nscalars_per_iter * iv_rgc->factor
>>> != rgc->max_nscalars_per_iter * rgc->factor) ?
The patch creates IVs with the following step:
gimple_seq_add_stmt (header_seq, gimple_build_assign (step, MIN_EXPR,
index_before_incr,
nitems_step));
If nitems_step is the same for two IVs, those IVs will always be equal.
So having multiple IVs with the same nitems_step is redundant.
nitems_step is calculated as follows:
unsigned int nitems_per_iter = rgc->max_nscalars_per_iter * rgc->factor;
...
poly_uint64 vf = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
...
if (nitems_per_iter != 1)
{
...
tree iv_factor = build_int_cst (iv_type, nitems_per_iter);
...
nitems_step = gimple_build (preheader_seq, MULT_EXPR, iv_type,
nitems_step, iv_factor);
...
}
so nitems_per_step is equal to:
rgc->max_nscalars_per_iter * rgc->factor * VF
VF is fixed for a loop, so nitems_step is equal for two different
rgroup_controls if:
rgc->max_nscalars_per_iter * rgc->factor
is the same for those rgroup_controls.
Please try the example I posted earlier today. I think you'll see that,
without the:
(iv_rgc->max_nscalars_per_iter * iv_rgc->factor
!= rgc->max_nscalars_per_iter * rgc->factor)
you'll have two IVs with the same step (because their MIN_EXPRs have
the same bound).
Thanks,
Richard
