lib/test_bitmap.c:920:2: error: call to __compiletime_assert_348 declared with 'error' attribute: BUILD_BUG_ON failed: !__builtin_constant_p(res)

Hi Alexander,

FYI, the error/warning still remains.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   fdf0eaf11452d72945af31804e2a1048ee1b574c
commit: dc34d5036692c614eef23c1130ee42a201c316bf lib: test_bitmap: add compile-time optimization/evaluations assertions
date:   1 year, 1 month ago
config: arm64-randconfig-r031-20230717 (https://download.01.org/0day-ci/archive/20230717/[email protected]/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project.git f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce: (https://download.01.org/0day-ci/archive/20230717/[email protected]/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 <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All errors (new ones prefixed by >>):

>> lib/test_bitmap.c:920:2: error: call to __compiletime_assert_348 declared with 'error' attribute: BUILD_BUG_ON failed: !__builtin_constant_p(res)
           BUILD_BUG_ON(!__builtin_constant_p(res));
           ^
   include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
           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'
   #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                       ^
   include/linux/compiler_types.h:352:2: note: expanded from macro 'compiletime_assert'
           _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
           ^
   include/linux/compiler_types.h:340:2: note: expanded from macro '_compiletime_assert'
           __compiletime_assert(condition, msg, prefix, suffix)
           ^
   include/linux/compiler_types.h:333:4: note: expanded from macro '__compiletime_assert'
                           prefix ## suffix();                             \
                           ^

<scratch space>:287:1: note: expanded from here __compiletime_assert_348
^
1 error generated.

vim +/error +920 lib/test_bitmap.c

871
872 static void __init test_bitmap_const_eval(void)
873 {
874 DECLARE_BITMAP(bitmap, BITS_PER_LONG);
875 unsigned long initvar = BIT(2);
876 unsigned long bitopvar = 0;
877 unsigned long var = 0;
878 int res;
879
880 /*
881 * Compilers must be able to optimize all of those to compile-time
882 * constants on any supported optimization level (-O2, -Os) and any
883 * architecture. Otherwise, trigger a build bug.
884 * The whole function gets optimized out then, there's nothing to do
885 * in runtime.
886 */
887
888 /*
889 * Equals to unsigned long bitmap[1] = { GENMASK(6, 5), }.
890 * Clang on s390 optimizes bitops at compile-time as intended, but at
891 * the same time stops treating @bitmap and @bitopvar as compile-time
892 * constants after regular test_bit() is executed, thus triggering the
893 * build bugs below. So, call const_test_bit() there directly until
894 * the compiler is fixed.
895 */
896 bitmap_clear(bitmap, 0, BITS_PER_LONG);
897 #if defined(__s390__) && defined(__clang__)
898 if (!const_test_bit(7, bitmap))
899 #else
900 if (!test_bit(7, bitmap))
901 #endif
902 bitmap_set(bitmap, 5, 2);
903
904 /* Equals to unsigned long bitopvar = BIT(20) */
905 __change_bit(31, &bitopvar);
906 bitmap_shift_right(&bitopvar, &bitopvar, 11, BITS_PER_LONG);
907
908 /* Equals to unsigned long var = BIT(25) */
909 var |= BIT(25);
910 if (var & BIT(0))
911 var ^= GENMASK(9, 6);
912
913 /* __const_hweight<32|64>(GENMASK(6, 5)) == 2 */
914 res = bitmap_weight(bitmap, 20);
915 BUILD_BUG_ON(!__builtin_constant_p(res));
916 BUILD_BUG_ON(res != 2);
917
918 /* !(BIT(31) & BIT(18)) == 1 */
919 res = !test_bit(18, &bitopvar);

 > 920		BUILD_BUG_ON(!__builtin_constant_p(res));

921 BUILD_BUG_ON(!res);
922
923 /* BIT(2) & GENMASK(14, 8) == 0 */
924 res = initvar & GENMASK(14, 8);
925 BUILD_BUG_ON(!__builtin_constant_p(res));
926 BUILD_BUG_ON(res);
927
928 /* ~BIT(25) */
929 BUILD_BUG_ON(!__builtin_constant_p(~var));
930 BUILD_BUG_ON(~var != ~BIT(25));
931 }
932

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