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

[David Laight <David.Laight@ACULAB.COM>]

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@intel.com/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.

	David

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