vect: Fix wrong shift_n after widening on BE [PR107338]

[Richard Biener]

On Mon, Oct 24, 2022 at 12:43 PM Kewen.Lin <linkw@linux.ibm.com> wrote:
>
> Hi,
>
> As PR107338 shows, with the use of widening loads, the
> container_type can become a wider type, it causes us to
> get wrong shift_n since the BIT_FIELD_REF offset actually
> becomes bigger on BE.  Taking the case in PR107338 as
> example, at the beginning the container type is short and
> BIT_FIELD_REF offset is 8 and size is 4, with unpacking to
> wider type int, the high 16 bits are zero, by viewing it
> as type int, its offset actually becomes to 24.  So the
> shift_n should be 4 (32 - 24 - 4) instead of 20 (32 - 8
> - 4).
>
> I noticed that if we move shift_n calculation early
> before the adjustments for widening loads (container type
> change), it's based on all the stuffs of the original
> container, the shfit_n calculated there is exactly what
> we want, it can be independent of widening.  Besides, I
> add prec adjustment together with the current adjustments
> for widening loads, although prec's subsequent uses don't
> require this change for now, since the container type gets
> changed, we should keep the corresponding prec consistent.
>
> Bootstrapped and regtested on x86_64-redhat-linux,
> aarch64-linux-gnu, powerpc64-linux-gnu P7 and P8 and
> powerpc64le-linux-gnu P9 and P10.
>
> Is it ok for trunk?

OK.

Richard.

> BR,
> Kewen
> -----
>
>         PR tree-optimization/107338
>
> gcc/ChangeLog:
>
>         * tree-vect-patterns.cc (vect_recog_bitfield_ref_pattern): Move
>         shfit_n calculation before the adjustments for widening loads.
> ---
>  gcc/tree-vect-patterns.cc | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> index 777ba2f5903..01094e8cb86 100644
> --- a/gcc/tree-vect-patterns.cc
> +++ b/gcc/tree-vect-patterns.cc
> @@ -1925,6 +1925,16 @@ vect_recog_bitfield_ref_pattern (vec_info *vinfo, stmt_vec_info stmt_info,
>    tree container_type = TREE_TYPE (container);
>    tree vectype = get_vectype_for_scalar_type (vinfo, container_type);
>
> +  /* Calculate shift_n before the adjustments for widening loads, otherwise
> +     the container may change and we have to consider offset change for
> +     widening loads on big endianness.  The shift_n calculated here can be
> +     independent of widening.  */
> +  unsigned HOST_WIDE_INT shift_n = bit_field_offset (bf_ref).to_constant ();
> +  unsigned HOST_WIDE_INT mask_width = bit_field_size (bf_ref).to_constant ();
> +  unsigned HOST_WIDE_INT prec = tree_to_uhwi (TYPE_SIZE (container_type));
> +  if (BYTES_BIG_ENDIAN)
> +    shift_n = prec - shift_n - mask_width;
> +
>    /* We move the conversion earlier if the loaded type is smaller than the
>       return type to enable the use of widening loads.  */
>    if (TYPE_PRECISION (TREE_TYPE (container)) < TYPE_PRECISION (ret_type)
> @@ -1935,6 +1945,7 @@ vect_recog_bitfield_ref_pattern (vec_info *vinfo, stmt_vec_info stmt_info,
>                                NOP_EXPR, container);
>        container = gimple_get_lhs (pattern_stmt);
>        container_type = TREE_TYPE (container);
> +      prec = tree_to_uhwi (TYPE_SIZE (container_type));
>        vectype = get_vectype_for_scalar_type (vinfo, container_type);
>        append_pattern_def_seq (vinfo, stmt_info, pattern_stmt, vectype);
>      }
> @@ -1953,12 +1964,6 @@ vect_recog_bitfield_ref_pattern (vec_info *vinfo, stmt_vec_info stmt_info,
>         shift_first = false;
>      }
>
> -  unsigned HOST_WIDE_INT shift_n = bit_field_offset (bf_ref).to_constant ();
> -  unsigned HOST_WIDE_INT mask_width = bit_field_size (bf_ref).to_constant ();
> -  unsigned HOST_WIDE_INT prec = tree_to_uhwi (TYPE_SIZE (container_type));
> -  if (BYTES_BIG_ENDIAN)
> -    shift_n = prec - shift_n - mask_width;
> -
>    /* If we don't have to shift we only generate the mask, so just fix the
>       code-path to shift_first.  */
>    if (shift_n == 0)
> --
> 2.35.4