Re: [PATCH V16] VECT: Add decrement IV iteration loop control by variable amount support

[Richard Sandiford via Gcc-patches]

This looks good to me.  Just a couple of very minor cosmetic things:

juzhe.zh...@rivai.ai writes:
> @@ -753,17 +846,35 @@ vect_set_loop_condition_partial_vectors (class loop 
> *loop,
>             continue;
>         }
>  
> -     /* 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);
> +     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))

Coding style is to put each subcondition on a separate line when the
whole condition doesn't fit on a single line.  So:

        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))

> @@ -2725,6 +2726,17 @@ start_over:
>        && !vect_verify_loop_lens (loop_vinfo))
>      LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) = false;
>  
> +  /* If we're vectorizing an loop that uses length "controls" and

s/an loop/a loop/    (Sorry for not noticing earlier.)

OK for trunk from my POV with those changes; no need to repost unless
your policies require it.  Please give Richi a chance to comment too
though.

Thanks for your patience with the review process.  The final result
seems pretty clean to me.

Richard