Re: [PATCH next] minmax.h: Use auto for variables in __minmax_array()

[Marco Elver]

On Sat, 7 Feb 2026 at 11:50, David Laight <david.laight.linux@xxxxxxxxx> wrote:
>
> On Fri,  6 Feb 2026 22:25:54 +0000
> david.laight.linux@xxxxxxxxx wrote:
>
> Cc the people discussing unqual_scalar_typeof() for arm64 LTO READ_ONCE().
>
>
> > From: David Laight <david.laight.linux@xxxxxxxxx>
> >
> > While 'auto __element = _array[--__len]' should remove 'const',
> > gcc prior to version 11 are buggy and retain it.
> > However forcing an integer promotion by adding zero does work.
> >
> > Promoting signed/unsigned char and short to int doesn't matter here,
> > that happens as soon as the value is used.
> >
> > Type type of the result (for char/short arrays) changes, but the value
> > will always be promoted to int before it is used (for any purpose) so
> > it isn't even worth casting the type back - all that is likely to do
> > is make the compiler explicitly mask it to 8/16 bits before it is
> > immediately promoted back to int.
> >
> > Signed-off-by: David Laight <david.laight.linux@xxxxxxxxx>

Acked-by: Marco Elver <elver@xxxxxxxxxx>

I'm looking forward to the day we can delete __unqual_scalar_typeof()
and all the other hacks.

Thanks!

> > ---
> >  include/linux/minmax.h | 19 ++++++-------------
> >  1 file changed, 6 insertions(+), 13 deletions(-)
> >
> > diff --git a/include/linux/minmax.h b/include/linux/minmax.h
> > index a0158db54a04..7d437f73a6d6 100644
> > --- a/include/linux/minmax.h
> > +++ b/include/linux/minmax.h
> > @@ -239,20 +239,13 @@
> >   * ...
> >   * min = min_array(buff, nb_items);
> >   * --- 8< ---
> > - *
> > - * The first typeof(&(array)[0]) is needed in order to support arrays of both
> > - * 'int *buff' and 'int buff[N]' types.
> > - *
> > - * The array can be an array of const items.
> > - * typeof() keeps the const qualifier. Use __unqual_scalar_typeof() in order
> > - * to discard the const qualifier for the __element variable.
> >   */
> > -#define __minmax_array(op, array, len) ({                            \
> > -     typeof(&(array)[0]) __array = (array);                          \
> > -     typeof(len) __len = (len);                                      \
> > -     __unqual_scalar_typeof(__array[0]) __element = __array[--__len];\
> > -     while (__len--)                                                 \
> > -             __element = op(__element, __array[__len]);              \
> > +#define __minmax_array(op, array, len) ({                    \
> > +     auto __array = &(array)[0];                             \
> > +     auto __len = len;                                       \
> > +     auto __element = __array[--__len] + 0;                  \
> > +     while (__len--)                                         \
> > +             __element = op(__element, __array[__len]);      \
> >       __element; })
> >
> >  /**
>