[tip:timers/vdso 1/4] include/vdso/math64.h:14:17: error: implicit declaration of function 'OPTIMIZER_HIDE_VAR'

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

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/vdso
head:   ca46a07c4b68246c4e400ce3649ab7228a878d8f
commit: 37db375ad90467d7e3ce4e450b3d1c4f297d4ed3 [1/4] vdso/math64: Use OPTIMIZER_HIDE_VAR() in __iter_div_u64_rem()
config: m68k-atari_defconfig (https://download.01.org/0day-ci/archive/20260930/202609301300.uAawkHuh-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 16.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260930/202609301300.uAawkHuh-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/202609301300.uAawkHuh-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from include/linux/math64.h:8,
                    from include/linux/time.h:6,
                    from include/linux/stat.h:19,
                    from include/linux/fs_dirent.h:5,
                    from include/linux/fs/super_types.h:5,
                    from include/linux/fs/super.h:5,
                    from include/linux/fs.h:5,
                    from include/linux/highmem.h:5,
                    from include/linux/bvec.h:10,
                    from include/linux/blk_types.h:10,
                    from include/linux/blkdev.h:9,
                    from drivers/md/md-linear.c:7:
   include/vdso/math64.h: In function '__iter_div_u64_rem':
>> include/vdso/math64.h:14:17: error: implicit declaration of function 'OPTIMIZER_HIDE_VAR' [-Wimplicit-function-declaration]
      14 |                 OPTIMIZER_HIDE_VAR(dividend);
         |                 ^~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/math64.h:8,
                    from include/linux/time.h:6,
                    from include/linux/stat.h:19,
                    from include/linux/fs_dirent.h:5,
                    from include/linux/fs/super_types.h:5,
                    from include/linux/fs/super.h:5,
                    from include/linux/fs.h:5,
                    from include/linux/highmem.h:5,
                    from include/linux/bvec.h:10,
                    from include/linux/blk_types.h:10,
                    from include/linux/blkdev.h:9,
                    from drivers/md/raid5.c:38:
   include/vdso/math64.h: In function '__iter_div_u64_rem':
>> include/vdso/math64.h:14:17: error: implicit declaration of function 'OPTIMIZER_HIDE_VAR' [-Wimplicit-function-declaration]
      14 |                 OPTIMIZER_HIDE_VAR(dividend);
         |                 ^~~~~~~~~~~~~~~~~~
   drivers/md/raid5.c: In function 'handle_stripe_dirtying':
   drivers/md/raid5.c:4306:21: warning: variable 'qread' set but not used [-Wunused-but-set-variable=]
    4306 |                 int qread =0;
         |                     ^~~~~
--
   In file included from include/linux/math64.h:8,
                    from include/linux/time.h:6,
                    from include/linux/stat.h:19,
                    from include/linux/fs_dirent.h:5,
                    from include/linux/fs/super_types.h:5,
                    from include/linux/fs/super.h:5,
                    from include/linux/fs.h:5,
                    from include/linux/highmem.h:5,
                    from include/linux/bvec.h:10,
                    from include/linux/blk_types.h:10,
                    from include/linux/blkdev.h:9,
                    from raid5.c:38:
   include/vdso/math64.h: In function '__iter_div_u64_rem':
>> include/vdso/math64.h:14:17: error: implicit declaration of function 'OPTIMIZER_HIDE_VAR' [-Wimplicit-function-declaration]
      14 |                 OPTIMIZER_HIDE_VAR(dividend);
         |                 ^~~~~~~~~~~~~~~~~~
   raid5.c: In function 'handle_stripe_dirtying':
   raid5.c:4306:21: warning: variable 'qread' set but not used [-Wunused-but-set-variable=]
    4306 |                 int qread =0;
         |                     ^~~~~


vim +/OPTIMIZER_HIDE_VAR +14 include/vdso/math64.h

     4	
     5	static __always_inline u32 __iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
     6	{
     7		u32 ret = 0;
     8	
     9		while (dividend >= divisor) {
    10			/*
    11			 * Prevent the compiler from optimising this loop into a
    12			 * modulo operation.
    13			 */
  > 14			OPTIMIZER_HIDE_VAR(dividend);
    15	
    16			dividend -= divisor;
    17			ret++;
    18		}
    19	
    20		*remainder = dividend;
    21	
    22		return ret;
    23	}
    24	

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