[jpirko-mlxsw:combined_queue 4/24] drivers/net/ethernet/mellanox/mlxsw/item.h:221:6: warning: variable 'be_index' is used uninitialized whenever 'if' condition is false

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

tree:   https://github.com/jpirko/linux_mlxsw combined_queue
head:   ff8aee5108029aa150fba69c00891450d992c987
commit: ad44ce5de61e6ce62c21243a8dac3ec5d83bd2eb [4/24] Fixup to "mlxsw: Warn about invalid accesses to array fields" ?
config: i386-buildonly-randconfig-002-20240707 (https://download.01.org/0day-ci/archive/20240708/202407080205.GiAzZkxA-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240708/202407080205.GiAzZkxA-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/202407080205.GiAzZkxA-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from drivers/net/ethernet/mellanox/mlxsw/i2c.c:15:
   In file included from drivers/net/ethernet/mellanox/mlxsw/cmd.h:7:
>> drivers/net/ethernet/mellanox/mlxsw/item.h:221:6: warning: variable 'be_index' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
     221 |         if (WARN_ONCE(index > max_index,
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
     222 |                       "name=%s,index=%u,max_index=%u\n", item->name, index,
         |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     223 |                       max_index))
         |                       ~~~~~~~~~~
   include/asm-generic/bug.h:152:2: note: expanded from macro 'WARN_ONCE'
     152 |         DO_ONCE_LITE_IF(condition, WARN, 1, format)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/once_lite.h:27:2: note: expanded from macro 'DO_ONCE_LITE_IF'
      27 |         ({                                                              \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      28 |                 bool __ret_do_once = !!(condition);                     \
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      29 |                                                                         \
         |                                                                         ~
      30 |                 if (__ONCE_LITE_IF(__ret_do_once))                      \
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      31 |                         func(__VA_ARGS__);                              \
         |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      32 |                                                                         \
         |                                                                         ~
      33 |                 unlikely(__ret_do_once);                                \
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      34 |         })
         |         ~~
   drivers/net/ethernet/mellanox/mlxsw/item.h:225:11: note: uninitialized use occurs here
     225 |         offset = be_index * item->element_size >> 3;
         |                  ^~~~~~~~
   drivers/net/ethernet/mellanox/mlxsw/item.h:221:2: note: remove the 'if' if its condition is always true
     221 |         if (WARN_ONCE(index > max_index,
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     222 |                       "name=%s,index=%u,max_index=%u\n", item->name, index,
         |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     223 |                       max_index))
         |                       ~~~~~~~~~~~
     224 |         be_index = max_index - index;
   drivers/net/ethernet/mellanox/mlxsw/item.h:208:25: note: initialize the variable 'be_index' to silence this warning
     208 |         u16 max_index, be_index;
         |                                ^
         |                                 = 0
   1 warning generated.


vim +221 drivers/net/ethernet/mellanox/mlxsw/item.h

   203	
   204	static inline u16
   205	__mlxsw_item_bit_array_offset(const struct mlxsw_item *item,
   206				      u16 index, u8 *shift)
   207	{
   208		u16 max_index, be_index;
   209		u16 offset;		/* byte offset inside the array */
   210		u8 in_byte_index;
   211	
   212		BUG_ON(index && !item->element_size);
   213		if (item->offset % sizeof(u32) != 0 ||
   214		    BITS_PER_BYTE % item->element_size != 0) {
   215			pr_err("mlxsw: item bug (name=%s,offset=%x,element_size=%x)\n",
   216			       item->name, item->offset, item->element_size);
   217			BUG();
   218		}
   219	
   220		max_index = (item->size.bytes << 3) / item->element_size - 1;
 > 221		if (WARN_ONCE(index > max_index,
   222			      "name=%s,index=%u,max_index=%u\n", item->name, index,
   223			      max_index))
   224		be_index = max_index - index;
   225		offset = be_index * item->element_size >> 3;
   226		in_byte_index  = index % (BITS_PER_BYTE / item->element_size);
   227		*shift = in_byte_index * item->element_size;
   228	
   229		return item->offset + offset;
   230	}
   231	

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