Re: [PATCH 2/3] s390/bitops: Limit return value range of __flogr()

[kernel test robot <lkp@intel.com>]

Hi Heiko,

kernel test robot noticed the following build errors:

[auto build test ERROR on s390/features]
[also build test ERROR on next-20250911]
[cannot apply to linus/master v6.17-rc5]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Heiko-Carstens/Compiler-Attributes-Add-__assume-macro/20250910-231949
base:   https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git features
patch link:    https://lore.kernel.org/r/20250910151216.646600-3-hca%40linux.ibm.com
patch subject: [PATCH 2/3] s390/bitops: Limit return value range of __flogr()
config: s390-randconfig-002-20250911 (https://download.01.org/0day-ci/archive/20250911/202509112018.eZI47cSy-lkp@intel.com/config)
compiler: clang version 16.0.6 (https://github.com/llvm/llvm-project 7cbf1a2591520c2491aa35339f227775f4d3adf6)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250911/202509112018.eZI47cSy-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509112018.eZI47cSy-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from kernel/bounds.c:13:
   In file included from include/linux/log2.h:12:
   In file included from include/linux/bitops.h:67:
>> arch/s390/include/asm/bitops.h:174:3: error: '__assume__' attribute cannot be applied to a statement
                   __assume(bit <= 64);
                   ^                  ~
   include/linux/compiler_attributes.h:68:56: note: expanded from macro '__assume'
   # define __assume(expr)                 __attribute__((__assume__(expr)))
                                                          ^
   1 error generated.
   make[3]: *** [scripts/Makefile.build:182: kernel/bounds.s] Error 1 shuffle=1723937077
   make[3]: Target 'prepare' not remade because of errors.
   make[2]: *** [Makefile:1282: prepare0] Error 2 shuffle=1723937077
   make[2]: Target 'prepare' not remade because of errors.
   make[1]: *** [Makefile:248: __sub-make] Error 2 shuffle=1723937077
   make[1]: Target 'prepare' not remade because of errors.
   make: *** [Makefile:248: __sub-make] Error 2 shuffle=1723937077
   make: Target 'prepare' not remade because of errors.


vim +/__assume__ +174 arch/s390/include/asm/bitops.h

   124	
   125	/**
   126	 * __flogr - find leftmost one
   127	 * @word - The word to search
   128	 *
   129	 * Returns the bit number of the most significant bit set,
   130	 * where the most significant bit has bit number 0.
   131	 * If no bit is set this function returns 64.
   132	 */
   133	static __always_inline __attribute_const__ unsigned long __flogr(unsigned long word)
   134	{
   135		unsigned long bit;
   136	
   137		if (__builtin_constant_p(word)) {
   138			bit = 0;
   139			if (!word)
   140				return 64;
   141			if (!(word & 0xffffffff00000000UL)) {
   142				word <<= 32;
   143				bit += 32;
   144			}
   145			if (!(word & 0xffff000000000000UL)) {
   146				word <<= 16;
   147				bit += 16;
   148			}
   149			if (!(word & 0xff00000000000000UL)) {
   150				word <<= 8;
   151				bit += 8;
   152			}
   153			if (!(word & 0xf000000000000000UL)) {
   154				word <<= 4;
   155				bit += 4;
   156			}
   157			if (!(word & 0xc000000000000000UL)) {
   158				word <<= 2;
   159				bit += 2;
   160			}
   161			if (!(word & 0x8000000000000000UL)) {
   162				word <<= 1;
   163				bit += 1;
   164			}
   165			return bit;
   166		} else {
   167			union register_pair rp __uninitialized;
   168	
   169			rp.even = word;
   170			asm volatile(
   171				"       flogr   %[rp],%[rp]\n"
   172				: [rp] "+d" (rp.pair) : : "cc");
   173			bit = rp.even;
 > 174			__assume(bit <= 64);
   175			return bit & 127;
   176		}
   177	}
   178	

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