Re: [PATCH v2] lib: test_bitops: add compile-time optimization/evaluations assertions

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

Hi Vincent,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v6.7-rc4 next-20231206]
[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/Vincent-Mailhol/lib-test_bitops-add-compile-time-optimization-evaluations-assertions/20231130-182837
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20231130102717.1297492-1-mailhol.vincent%40wanadoo.fr
patch subject: [PATCH v2] lib: test_bitops: add compile-time optimization/evaluations assertions
config: hexagon-allmodconfig (https://download.01.org/0day-ci/archive/20231206/202312062158.60c1e6yt-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231206/202312062158.60c1e6yt-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/202312062158.60c1e6yt-lkp@intel.com/

All errors (new ones prefixed by >>):

>> lib/test_bitops.c:74:2: error: call to '__compiletime_assert_178' declared with 'error' attribute: BUILD_BUG_ON failed: !__builtin_constant_p(__test_expr)
      74 |         test_const_eval(__ffs(BIT(n)) == n);
         |         ^
   lib/test_bitops.c:59:2: note: expanded from macro 'test_const_eval'
      59 |         BUILD_BUG_ON(!__builtin_constant_p(__test_expr));       \
         |         ^
   include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
      50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
         |         ^
   include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
      39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
         |                                     ^
   note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
   include/linux/compiler_types.h:423:2: note: expanded from macro '_compiletime_assert'
     423 |         __compiletime_assert(condition, msg, prefix, suffix)
         |         ^
   include/linux/compiler_types.h:416:4: note: expanded from macro '__compiletime_assert'
     416 |                         prefix ## suffix();                             \
         |                         ^
   <scratch space>:18:1: note: expanded from here
      18 | __compiletime_assert_178
         | ^
   1 error generated.


vim +74 lib/test_bitops.c

    62	
    63	static void test_bitops_const_eval(void)
    64	{
    65		/*
    66		 * On any supported optimization level (-O2, -Os) and if
    67		 * invoked with a compile-time constant argument, the compiler
    68		 * must be able to fold into a constant expression all the bit
    69		 * find functions. Namely: __ffs(), ffs(), ffz(), __fls(),
    70		 * fls() and fls64(). Otherwise, trigger a build bug.
    71		 */
    72		const int n = 10;
    73	
  > 74		test_const_eval(__ffs(BIT(n)) == n);
    75		test_const_eval(ffs(BIT(n)) == n + 1);
    76		test_const_eval(ffz(~BIT(n)) == n);
    77		test_const_eval(__fls(BIT(n)) == n);
    78		test_const_eval(fls(BIT(n)) == n + 1);
    79		test_const_eval(fls64(BIT_ULL(n)) == n + 1);
    80	}
    81	

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