Re: [PATCH] longlong.h: Do no use asm input cast for clang

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Dec 1, 2022 at 12:26 AM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> Hi!
>
> On Wed, Nov 30, 2022 at 03:16:25PM -0300, Adhemerval Zanella via Gcc-patches wrote:
> > clang by default rejects the input casts with:
> >
> >   error: invalid use of a cast in a inline asm context requiring an
> >   lvalue: remove the cast or build with -fheinous-gnu-extensions
> >
> > And even with -fheinous-gnu-extensions clang still throws an warning
> > and also states that this option might be removed in the future.
> > For gcc the cast are still useful somewhat [1], so just remove it
> > clang is used.
>
> This is one of the things in inline asm that is tightly tied to GCC
> internals.  You should emulate GCC's behaviour faithfully if you want
> to claim you implement the inline asm GNU C extension.

I understand that the casts should be no-ops on the asm side (maybe they
change the sign) and they are present as type-checking.  Can we implement
this type-checking in a different (portable) way?  I think the macro you use
should be named like __asm_output_check_type (..) or so to indicate the
intended purpose.

Richard.

> > --- a/include/ChangeLog
> > +++ b/include/ChangeLog
>
> That should not be part of the patch?  Changelog entries should be
> verbatim in the message you send.
>
> The size of this patch already makes clear this is a bad idea, imo.
> This code is already hard enough to read.
>
>
> Segher