Re: [PATCH next v2 2/5] minmax: Allow min()/max()/clamp() if the arguments have the same signedness.

[Nathan Chancellor]

On Sun, Jul 30, 2023 at 02:55:50PM +0000, David Laight wrote:
> From: kernel test robot
> > Sent: 29 July 2023 03:01
> > 
> > kernel test robot noticed the following build errors:
> > 
> ...)
> > compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project.git
> > 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
> > reproduce: (https://download.01.org/0day-ci/archive/20230729/202307290943.ODVeyeK6-
> > lkp@xxxxxxxxx/reproduce)
> > 
> ...
> > >> mm/percpu.c:3102:10: error: static assertion expression is not an integral constant expression
> >                    base = min(ptr, base);
> >                           ^~~~~~~~~~~~~~
> ...                    ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
> >    include/linux/minmax.h:23:2: note: expanded from macro '__types_ok'
> >            (is_signed_type(typeof(x)) == is_signed_type(typeof(y)))
> >            ^
> ...
> >    mm/percpu.c:3102:10: note: cast that performs the conversions of a reinterpret_cast is not allowed
> > in a constant expression
> 
> That is a C++ error that seems to have crept into C.
> The relevant definition is:
> 
> #define is_signed_type(type)  (((type)(-1)) < (type)1)
> 
> This seems to have been fixed in clang 16.0.0.

Indeed, it looks like

https://github.com/llvm/llvm-project/commit/a181de452df311d7647329120d05f4eb9c158b6c

fixed this as a result of the discussion at

https://github.com/llvm/llvm-project/issues/57687, which certainly makes
sense.

Cheers,
Nathan