Re: [PATCH] compiler_types: Introduce inline_for_performance

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

Hi Eric,

kernel test robot noticed the following build warnings:

[auto build test WARNING on e84d960149e71e8d5e4db69775ce31305898ed0c]

url:    https://github.com/intel-lab-lkp/linux/commits/Eric-Dumazet/compiler_types-Introduce-inline_for_performance/20260118-232653
base:   e84d960149e71e8d5e4db69775ce31305898ed0c
patch link:    https://lore.kernel.org/r/20260118152448.2560414-1-edumazet%40google.com
patch subject: [PATCH] compiler_types: Introduce inline_for_performance
config: m68k-amcore_defconfig (https://download.01.org/0day-ci/archive/20260119/202601190247.dDAvbbMH-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260119/202601190247.dDAvbbMH-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/202601190247.dDAvbbMH-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from arch/m68k/include/asm/div64.h:6,
                    from include/linux/math.h:6,
                    from include/linux/kernel.h:27,
                    from arch/m68k/coldfire/cache.c:12:
>> include/asm-generic/div64.h:138:10: warning: '__arch_xprod_64' defined but not used [-Wunused-function]
     138 | uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
         |          ^~~~~~~~~~~~~~~


vim +/__arch_xprod_64 +138 include/asm-generic/div64.h

461a5e51060c93 Nicolas Pitre 2015-10-30  125  
f682b27c57aec2 Nicolas Pitre 2015-10-30  126  #ifndef __arch_xprod_64
f682b27c57aec2 Nicolas Pitre 2015-10-30  127  /*
f682b27c57aec2 Nicolas Pitre 2015-10-30  128   * Default C implementation for __arch_xprod_64()
f682b27c57aec2 Nicolas Pitre 2015-10-30  129   *
f682b27c57aec2 Nicolas Pitre 2015-10-30  130   * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
f682b27c57aec2 Nicolas Pitre 2015-10-30  131   * Semantic:  retval = ((bias ? m : 0) + m * n) >> 64
f682b27c57aec2 Nicolas Pitre 2015-10-30  132   *
f682b27c57aec2 Nicolas Pitre 2015-10-30  133   * The product is a 128-bit value, scaled down to 64 bits.
00a31dd3acea0f Nicolas Pitre 2024-10-03  134   * Hoping for compile-time optimization of  conditional code.
f682b27c57aec2 Nicolas Pitre 2015-10-30  135   * Architectures may provide their own optimized assembly implementation.
f682b27c57aec2 Nicolas Pitre 2015-10-30  136   */
5f712d70e20a46 Eric Dumazet  2026-01-18  137  static inline_for_performance
d533cb2d2af400 Nicolas Pitre 2024-10-03 @138  uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
f682b27c57aec2 Nicolas Pitre 2015-10-30  139  {
f682b27c57aec2 Nicolas Pitre 2015-10-30  140  	uint32_t m_lo = m;
f682b27c57aec2 Nicolas Pitre 2015-10-30  141  	uint32_t m_hi = m >> 32;
f682b27c57aec2 Nicolas Pitre 2015-10-30  142  	uint32_t n_lo = n;
f682b27c57aec2 Nicolas Pitre 2015-10-30  143  	uint32_t n_hi = n >> 32;
00a31dd3acea0f Nicolas Pitre 2024-10-03  144  	uint64_t x, y;
f682b27c57aec2 Nicolas Pitre 2015-10-30  145  
00a31dd3acea0f Nicolas Pitre 2024-10-03  146  	/* Determine if overflow handling can be dispensed with. */
00a31dd3acea0f Nicolas Pitre 2024-10-03  147  	bool no_ovf = __builtin_constant_p(m) &&
00a31dd3acea0f Nicolas Pitre 2024-10-03  148  		      ((m >> 32) + (m & 0xffffffff) < 0x100000000);
f682b27c57aec2 Nicolas Pitre 2015-10-30  149  
00a31dd3acea0f Nicolas Pitre 2024-10-03  150  	if (no_ovf) {
00a31dd3acea0f Nicolas Pitre 2024-10-03  151  		x = (uint64_t)m_lo * n_lo + (bias ? m : 0);
00a31dd3acea0f Nicolas Pitre 2024-10-03  152  		x >>= 32;
00a31dd3acea0f Nicolas Pitre 2024-10-03  153  		x += (uint64_t)m_lo * n_hi;
00a31dd3acea0f Nicolas Pitre 2024-10-03  154  		x += (uint64_t)m_hi * n_lo;
00a31dd3acea0f Nicolas Pitre 2024-10-03  155  		x >>= 32;
00a31dd3acea0f Nicolas Pitre 2024-10-03  156  		x += (uint64_t)m_hi * n_hi;
f682b27c57aec2 Nicolas Pitre 2015-10-30  157  	} else {
00a31dd3acea0f Nicolas Pitre 2024-10-03  158  		x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0);
00a31dd3acea0f Nicolas Pitre 2024-10-03  159  		y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0);
00a31dd3acea0f Nicolas Pitre 2024-10-03  160  		x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32);
00a31dd3acea0f Nicolas Pitre 2024-10-03  161  		y = (uint64_t)m_hi * n_lo + (uint32_t)y;
00a31dd3acea0f Nicolas Pitre 2024-10-03  162  		x += (uint32_t)(y >> 32);
f682b27c57aec2 Nicolas Pitre 2015-10-30  163  	}
f682b27c57aec2 Nicolas Pitre 2015-10-30  164  
00a31dd3acea0f Nicolas Pitre 2024-10-03  165  	return x;
f682b27c57aec2 Nicolas Pitre 2015-10-30  166  }
f682b27c57aec2 Nicolas Pitre 2015-10-30  167  #endif
f682b27c57aec2 Nicolas Pitre 2015-10-30  168  

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