Re: [PATCH] vect: Use xor to invert oversized vector masks

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Mar 14, 2024 at 11:42 PM Andrew Stubbs <ams@baylibre.com> wrote:
>
> Don't enable excess lanes when inverting vector bit-masks smaller than the
> integer mode.  This is yet another case of wrong-code due to mishandling
> of oversized bitmasks.
>
> This issue shows up in vect/tsvc/vect-tsvc-s278.c and
> vect/tsvc/vect-tsvc-s279.c if I set the preferred vector size to V32
> (down from V64) on amdgcn.
>
> OK for mainline?
>
> Andrew
>
> gcc/ChangeLog:
>
>         * expr.cc (expand_expr_real_2): Use xor to invert vector masks.
> ---
>  gcc/expr.cc | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/gcc/expr.cc b/gcc/expr.cc
> index 403eeaa108e4..3540327d879e 100644
> --- a/gcc/expr.cc
> +++ b/gcc/expr.cc
> @@ -10497,6 +10497,17 @@ expand_expr_real_2 (sepops ops, rtx target, machine_mode tmode,
>                                immed_wide_int_const (mask, int_mode),
>                                target, 1, OPTAB_LIB_WIDEN);
>         }
> +      /* If it's a vector mask don't enable excess bits.  */
> +      else if (VECTOR_BOOLEAN_TYPE_P (type)
> +              && SCALAR_INT_MODE_P (mode)
> +              && maybe_ne (GET_MODE_PRECISION (mode),
> +                           TYPE_VECTOR_SUBPARTS (type).to_constant ()))
> +       {
> +         auto nunits = TYPE_VECTOR_SUBPARTS (type).to_constant ();
> +         temp = expand_binop (mode, xor_optab, op0,
> +                              GEN_INT ((HOST_WIDE_INT_1U << nunits) - 1),
> +                              target, true, OPTAB_WIDEN);
> +       }
Not review, just curious, should the issue be fixed by the commit in PR113576.
Also wonder besides cbranch, excess land bits also matter?
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113576#c35
>        else
>         temp = expand_unop (mode, one_cmpl_optab, op0, target, 1);
>        gcc_assert (temp);
> --
> 2.41.0
>


-- 
BR,
Hongtao