Re: [PATCH 4/7] arch/nios: replace "__auto_type" with "auto"

[Linus Torvalds]

On Fri, 18 Jul 2025 at 14:34, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>
> -       __auto_type __pu_ptr = (ptr);                                   \
> +       auto __pu_ptr = (ptr);                                  \
>         typeof(*__pu_ptr) __pu_val = (typeof(*__pu_ptr))(x);            \

Side note: I think some coccinelle (or sed) script that replaces that
older form of

       typeof(x) Y = (typeof(x))(Z);

or

        typeof(Z) Y = Z;


with just

        auto Y = Z;

is also worthwhile at some point.

We have more of those, because that's the really traditional gcc way
to do things that predates __auto_type.

And the patterns are a bit more complicated, so they need care: not
all of the "typeof (x) Z = Y" patterns have the same type in the
assignment.

So it's not the universal case, but it's the _common_ case, I think.

For example, it's obviously the case in the above, where we use the
exact same "typeof" on both sides, but in other uaccess.h files we
also have patterns like

        __typeof__(*(ptr)) __x = (x); /* eval x once */
        __typeof__(ptr) __ptr = (ptr); /* eval ptr once */

where that *first* case very much needs to use that "__typeof__"
model, because 'x' typically does not necessarily have the same type
as '*(ptr)' (and we absolutely do not want to use a cast: we want
integer types to convert naturally, but we very much want warnings if
somebody were to mix types wrong).

But that second case obviously is exactly the "auto type" case, just
written using __typeof__.

               Linus