Re: [PATCH 2/2] PR 110487: `(a !=/== CST1 ? CST2 : CST3)` pattern for type safety

[Richard Biener <richard.guenther@gmail.com>]

On Sat, Jul 1, 2023 at 10:23 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The problem here is we might produce some values out of the type's
> min/max (and/or valid values, e.g. signed booleans). The fix is to
> use an integer type which has the same precision and signedness
> as the original type.
>
> Note two_value_replacement in phiopt had the same issue in previous
> versions; though I don't know if a problem will show up there.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu.

OK.

> gcc/ChangeLog:
>
>         PR tree-optimization/110487
>         * match.pd (a !=/== CST1 ? CST2 : CST3): Always
>         build a nonstandard integer and use that.
> ---
>  gcc/match.pd | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index a0d114f6a16..9748ad8466e 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -4797,24 +4797,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         tree type1;
>         if ((eqne == EQ_EXPR) ^ (wi::to_wide (@1) == min))
>           std::swap (arg0, arg1);
> -       if (TYPE_PRECISION (TREE_TYPE (@0)) == TYPE_PRECISION (type))
> -        {
> -          /* Avoid performing the arithmetics in bool type which has different
> -             semantics, otherwise prefer unsigned types from the two with
> -            the same precision.  */
> -          if (TREE_CODE (TREE_TYPE (arg0)) == BOOLEAN_TYPE
> -              || !TYPE_UNSIGNED (type))
> -            type1 = TREE_TYPE (@0);
> -          else
> -            type1 = TREE_TYPE (arg0);
> -        }
> -       else if (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (type))
> +       if (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (type))
>          type1 = TREE_TYPE (@0);
>         else
>          type1 = type;
> -       min = wide_int::from (min, TYPE_PRECISION (type1),
> +       auto prec = TYPE_PRECISION (type1);
> +       auto unsign = TYPE_UNSIGNED (type1);
> +       type1 = build_nonstandard_integer_type (prec, unsign);
> +       min = wide_int::from (min, prec,
>                              TYPE_SIGN (TREE_TYPE (@0)));
> -       wide_int a = wide_int::from (wi::to_wide (arg0), TYPE_PRECISION (type1),
> +       wide_int a = wide_int::from (wi::to_wide (arg0), prec,
>                                     TYPE_SIGN (type));
>         enum tree_code code;
>         wi::overflow_type ovf;
> @@ -4822,7 +4814,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>          {
>            code = PLUS_EXPR;
>            a -= min;
> -          if (!TYPE_UNSIGNED (type1))
> +          if (!unsign)
>              {
>                /* lhs is known to be in range [min, min+1] and we want to add a
>                   to it.  Check if that operation can overflow for those 2 values
> @@ -4836,7 +4828,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>          {
>            code = MINUS_EXPR;
>            a += min;
> -          if (!TYPE_UNSIGNED (type1))
> +          if (!unsign)
>              {
>                /* lhs is known to be in range [min, min+1] and we want to subtract
>                   it from a.  Check if that operation can overflow for those 2
> --
> 2.31.1
>