On Mon, Jun 13, 2022 at 12:02 PM Kewen.Lin <li...@linux.ibm.com> wrote:
>
> Hi,
>
> As PR105940 shown, when rs6000 port tries to assign
> m_suggested_unroll_factor by 4 or so, there will be ICE
> on below statement:
>
> exact_div (LOOP_VINFO_VECT_FACTOR (loop_vinfo),
> loop_vinfo->suggested_unroll_factor);
>
> In function vect_analyze_loop_2, the current place of
> suggested_unroll_factor applying can't guarantee it's
> applied for all cases. As the case shows, vectorizer
> could retry with SLP forced off, the vf is reset by
> saved_vectorization_factor which isn't applied with
> suggested_unroll_factor before. It means it can end
> up with one vf which neglects suggested_unroll_factor.
> I think it's off design, we should move the applying
> of suggested_unroll_factor after start_over.
>
> Bootstrapped and regtested on x86_64-redhat-linux,
> aarch64-linux-gnu and powerpc64{,le}-linux-gnu.
>
> Is it ok for trunk?
OK (I think the GCC 12 branch is also affected).
Richard.
>
> BR,
> Kewen
> -----
> PR tree-optimization/105940
>
> gcc/ChangeLog:
>
> * tree-vect-loop.cc (vect_analyze_loop_2): Move the place of
> applying suggested_unroll_factor after start_over.
> ---
> gcc/tree-vect-loop.cc | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 896218f23ea..af955d26f8d 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -2393,15 +2393,15 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo, bool
> &fatal,
> set of rgroups. */
> gcc_assert (LOOP_VINFO_MASKS (loop_vinfo).is_empty ());
>
> + /* This is the point where we can re-start analysis with SLP forced off.
> */
> +start_over:
> +
> /* Apply the suggested unrolling factor, this was determined by the backend
> during finish_cost the first time we ran the analyzis for this
> vector mode. */
> if (loop_vinfo->suggested_unroll_factor > 1)
> LOOP_VINFO_VECT_FACTOR (loop_vinfo) *=
> loop_vinfo->suggested_unroll_factor;
>
> - /* This is the point where we can re-start analysis with SLP forced off.
> */
> -start_over:
> -
> /* Now the vectorization factor is final. */
> poly_uint64 vectorization_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
> gcc_assert (known_ne (vectorization_factor, 0U));
> --
> 2.27.0
