Re: [PATCH v3 1/2] op_by_pieces_d::run: Change a while loop to a do-while loop

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

On Tue, Apr 27, 2021 at 3:14 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Change a while loop in op_by_pieces_d::run to a do-while loop to prepare
> for offset adjusted operation for the remaining bytes on the last piece
> operation of a memory region.

OK.

Thanks,
Richard.

>         PR middl-end/90773
>         * expr.c (op_by_pieces_d::get_usable_mode): New member function.
>         (op_by_pieces_d::run): Cange a while loop to a do-while loop.
> ---
>  gcc/expr.c | 76 +++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 53 insertions(+), 23 deletions(-)
>
> diff --git a/gcc/expr.c b/gcc/expr.c
> index a0e19465965..07cb64427c9 100644
> --- a/gcc/expr.c
> +++ b/gcc/expr.c
> @@ -1041,6 +1041,9 @@ pieces_addr::maybe_postinc (HOST_WIDE_INT size)
>
>  class op_by_pieces_d
>  {
> + private:
> +  scalar_int_mode get_usable_mode (scalar_int_mode mode, unsigned int);
> +
>   protected:
>    pieces_addr m_to, m_from;
>    unsigned HOST_WIDE_INT m_len;
> @@ -1108,6 +1111,25 @@ op_by_pieces_d::op_by_pieces_d (rtx to, bool to_load,
>    m_align = align;
>  }
>
> +/* This function returns the largest usable integer mode for LEN bytes
> +   whose size is no bigger than size of MODE.  */
> +
> +scalar_int_mode
> +op_by_pieces_d::get_usable_mode (scalar_int_mode mode, unsigned int len)
> +{
> +  unsigned int size;
> +  do
> +    {
> +      size = GET_MODE_SIZE (mode);
> +      if (len >= size && prepare_mode (mode, m_align))
> +       break;
> +      /* NB: widest_int_mode_for_size checks SIZE > 1.  */
> +      mode = widest_int_mode_for_size (size);
> +    }
> +  while (1);
> +  return mode;
> +}
> +
>  /* This function contains the main loop used for expanding a block
>     operation.  First move what we can in the largest integer mode,
>     then go to successively smaller modes.  For every access, call
> @@ -1116,42 +1138,50 @@ op_by_pieces_d::op_by_pieces_d (rtx to, bool to_load,
>  void
>  op_by_pieces_d::run ()
>  {
> -  while (m_max_size > 1 && m_len > 0)
> +  if (m_len == 0)
> +    return;
> +
> +  /* NB: widest_int_mode_for_size checks M_MAX_SIZE > 1.  */
> +  scalar_int_mode mode = widest_int_mode_for_size (m_max_size);
> +  mode = get_usable_mode (mode, m_len);
> +
> +  do
>      {
> -      scalar_int_mode mode = widest_int_mode_for_size (m_max_size);
> +      unsigned int size = GET_MODE_SIZE (mode);
> +      rtx to1 = NULL_RTX, from1;
>
> -      if (prepare_mode (mode, m_align))
> +      while (m_len >= size)
>         {
> -         unsigned int size = GET_MODE_SIZE (mode);
> -         rtx to1 = NULL_RTX, from1;
> +         if (m_reverse)
> +           m_offset -= size;
>
> -         while (m_len >= size)
> -           {
> -             if (m_reverse)
> -               m_offset -= size;
> +         to1 = m_to.adjust (mode, m_offset);
> +         from1 = m_from.adjust (mode, m_offset);
>
> -             to1 = m_to.adjust (mode, m_offset);
> -             from1 = m_from.adjust (mode, m_offset);
> +         m_to.maybe_predec (-(HOST_WIDE_INT)size);
> +         m_from.maybe_predec (-(HOST_WIDE_INT)size);
>
> -             m_to.maybe_predec (-(HOST_WIDE_INT)size);
> -             m_from.maybe_predec (-(HOST_WIDE_INT)size);
> +         generate (to1, from1, mode);
>
> -             generate (to1, from1, mode);
> +         m_to.maybe_postinc (size);
> +         m_from.maybe_postinc (size);
>
> -             m_to.maybe_postinc (size);
> -             m_from.maybe_postinc (size);
> +         if (!m_reverse)
> +           m_offset += size;
>
> -             if (!m_reverse)
> -               m_offset += size;
> +         m_len -= size;
> +       }
>
> -             m_len -= size;
> -           }
> +      finish_mode (mode);
>
> -         finish_mode (mode);
> -       }
> +      if (m_len == 0)
> +       return;
>
> -      m_max_size = GET_MODE_SIZE (mode);
> +      /* NB: widest_int_mode_for_size checks SIZE > 1.  */
> +      mode = widest_int_mode_for_size (size);
> +      mode = get_usable_mode (mode, m_len);
>      }
> +  while (1);
>
>    /* The code above should have handled everything.  */
>    gcc_assert (!m_len);
> --
> 2.31.1
>