Re: [PATCH v4 1/3] math.h: add DIV_ROUND_UP_NO_OVERFLOW

[Linus Torvalds]

On Wed, 25 Oct 2023 at 22:57, David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> Doesn't that version end up calling inline functions?
> So won't be usable in static initialisers - the same as statement functions.

David, please either read what I write, or actually test things out,
instead of just adding noise.

It is not a problem to have a _Generic() - or a
__builtin_chooise_expr() - that has an inline function that doesn't
get used. The compiler will remove it.

The problem is literally that you can't use "__auto_type", because
*STATEMENT EXPRESSIONS* do not work outside of function definitions,
because gcc won't even *parse* them, and just says

  error: braced-group within expression allowed only inside a function

exactly like I explained in the comment of the patch that does the _Generic().

Which is why my solution ended up using those inline functions, and
splitting manually by type, instead of an expression statement and
__auto_type.

Whether you then split into different expressions with _Generic() or
by using __builtin_choose_expr() is irrelevant, although once you do
"split by type", _Generic() ends up being much more convenient because
that's what it's designed for (and you don't end up trying to figure
out the size with sizeof() and typeof tricks).

               Linus