Eli Zaretskii <eliz@gnu.org> schrieb am So., 17. Sep. 2017 um 16:31 Uhr:

> > Cc: andrewjmoreton@gmail.com, emacs-devel@gnu.org
> > From: Paul Eggert <eggert@cs.ucla.edu>
> > Date: Sun, 17 Sep 2017 00:01:09 -0700
> >
> > Why was the attached patch needed? What warning did it suppress?
>
> I wrote about that in
>
>   http://lists.gnu.org/archive/html/emacs-devel/2017-09/msg00448.html
>
> The warning is this:
>
>   ../../emacs/src/data.c: In function 'minmax_driver':
>   ../../emacs/src/data.c:3022:9: warning: 'accum.i' may be used
> uninitialized in this function [-Wmaybe-uninitialized]
>   return accum;
>   ^~~~~
>
> Which seems to mean that even eassume is sometimes not enough to
> convince GCC 7 that the code is correct:
>
>   static Lisp_Object
>   minmax_driver (ptrdiff_t nargs, Lisp_Object *args,
>                  enum Arith_Comparison comparison)
>   {
>     eassume (0 < nargs);  <<<<<<<<<<<<<<<<<<<<<<<
>     Lisp_Object accum;
>     for (ptrdiff_t argnum = 0; argnum < nargs; argnum++)
>       {
>         Lisp_Object val = args[argnum];
>         CHECK_NUMBER_OR_FLOAT_COERCE_MARKER (val);
>         if (argnum == 0 || !NILP (arithcompare (val, accum, comparison)))
>           accum = val;
>         else if (FLOATP (accum) && isnan (XFLOAT_DATA (accum)))
>           return accum;
>       }
>     return accum;
>   }
>
> Since nargs > 0, the loop is always entered, but GCC seems to miss that.
>

How about rewriting the function body like this:

{
  Lisp_Object accum = args[0];
  CHECK_NUMBER_OR_FLOAT_COERCE_MARKER (accum);
  for (ptrdiff_t argnum = 1; ...)
    {
      if (FLOATP (accum) && isnan (...)) break;
      ...
    }
  return accum;
}