Re: [PATCH] Abstract out calculation of max HWIs per wide int.

[Andrew Pinski <pinskia@gmail.com>]

On Mon, Apr 17, 2023 at 11:44 AM Aldy Hernandez via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> I'm about to add one more use of the same snippet of code, for a total
> of 4 identical calculations in the code base.
>
> This seems safe enough even before the release, since this file hardly
> changes and I'm pretty much the only one who's touched it this year.
>
> OK for trunk?
>
> gcc/ChangeLog:
>
>         * wide-int.h (WIDE_INT_MAX_HWIS): New.
>         (class fixed_wide_int_storage): Use it.
>         (trailing_wide_ints <N>::set_precision): Use it.
>         (trailing_wide_ints <N>::extra_size): Use it.
> ---
>  gcc/wide-int.h | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/wide-int.h b/gcc/wide-int.h
> index a450a744c9f..6be343c0eb5 100644
> --- a/gcc/wide-int.h
> +++ b/gcc/wide-int.h
> @@ -264,6 +264,10 @@ along with GCC; see the file COPYING3.  If not see
>  /* The number of HWIs needed to store an offset_int.  */
>  #define OFFSET_INT_ELTS (ADDR_MAX_PRECISION / HOST_BITS_PER_WIDE_INT)
>
> +/* The max number of HWIs needed to store a wide_int of PRECISION.  */
> +#define WIDE_INT_MAX_HWIS(PRECISION) \
> +  ((PRECISION + HOST_BITS_PER_WIDE_INT - 1) / HOST_BITS_PER_WIDE_INT)

Does it make sense to use an constexpr inline function instead of a
define here since GCC is written in C++11 after all?
That is:
constexpr inline unsigned WIDE_INT_MAX_HWIS(unsigned precision)
{
  return ((precision + HOST_BITS_PER_WIDE_INT - 1) / HOST_BITS_PER_WIDE_INT);
}

Thanks,
Andrew Pinski

> +
>  /* The type of result produced by a binary operation on types T1 and T2.
>     Defined purely for brevity.  */
>  #define WI_BINARY_RESULT(T1, T2) \
> @@ -1214,7 +1218,7 @@ template <int N>
>  class GTY(()) fixed_wide_int_storage
>  {
>  private:
> -  HOST_WIDE_INT val[(N + HOST_BITS_PER_WIDE_INT + 1) / HOST_BITS_PER_WIDE_INT];
> +  HOST_WIDE_INT val[WIDE_INT_MAX_HWIS (N)];
>    unsigned int len;
>
>  public:
> @@ -1475,8 +1479,7 @@ trailing_wide_ints <N>::set_precision (unsigned int precision,
>    gcc_checking_assert (num_elements <= N);
>    m_num_elements = num_elements;
>    m_precision = precision;
> -  m_max_len = ((precision + HOST_BITS_PER_WIDE_INT - 1)
> -              / HOST_BITS_PER_WIDE_INT);
> +  m_max_len = WIDE_INT_MAX_HWIS (precision);
>  }
>
>  /* Return a reference to element INDEX.  */
> @@ -1505,8 +1508,7 @@ inline size_t
>  trailing_wide_ints <N>::extra_size (unsigned int precision,
>                                     unsigned int num_elements)
>  {
> -  unsigned int max_len = ((precision + HOST_BITS_PER_WIDE_INT - 1)
> -                         / HOST_BITS_PER_WIDE_INT);
> +  unsigned int max_len = WIDE_INT_MAX_HWIS (precision);
>    gcc_checking_assert (num_elements <= N);
>    return (num_elements * max_len - 1) * sizeof (HOST_WIDE_INT);
>  }
> --
> 2.39.2
>