Re: [PATCH 2/2, i386]: Implement TARGET_EXPAND_DIVMOD_LIBFUNC

[Uros Bizjak <ubizjak at gmail dot com>]

On Thu, Nov 3, 2016 at 1:58 PM, Eric Botcazou <ebotcazou@adacore.com> wrote:
>> libfunc, as in "__{,u}divmod{di,ti}4 library function" is already
>> implemented in libgcc. But the enablement of this function inside the
>> compiler has to be performed by each target.
>
> So can we do it generically instead of duplicating it ~50 times?

I guess it can be done. Currently the expander goes:

--cut here--
  /* Check if optab_handler exists for divmod_optab for given mode.  */
  if (optab_handler (tab, mode) != CODE_FOR_nothing)
    {
      quotient = gen_reg_rtx (mode);
      remainder = gen_reg_rtx (mode);
      expand_twoval_binop (tab, op0, op1, quotient, remainder, unsignedp);
    }

  /* Generate call to divmod libfunc if it exists.  */
  else if ((libfunc = optab_libfunc (tab, mode)) != NULL_RTX)
    targetm.expand_divmod_libfunc (libfunc, mode, op0, op1,
                   &quotient, &remainder);

  else
    gcc_unreachable ();
--cut here--

so, by declaring divmod libfunc, the target also has to provide target hook.

Let's ask authors of the original divmod patch for the details.

Uros.