commit 306a7dd0d24815a5b329543372d89c0715fb0f03
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date:   Wed Jan 13 06:10:11 2021 +0000

    Use compiler builtins for __bitcount primitives.
    
    The previous code would only do it if __POPCNT__ was defined, which was
    never true at least for the kernel build.

diff --git a/sys/sys/types.h b/sys/sys/types.h
index c026fa023bd0..a90d518889d4 100644
--- a/sys/sys/types.h
+++ b/sys/sys/types.h
@@ -309,67 +309,11 @@ typedef	_Bool	bool;
  * since its purpose is to provide typedefs, not miscellaneous doodads.
  */
 
-#ifdef __POPCNT__
 #define	__bitcount64(x)	__builtin_popcountll((__uint64_t)(x))
 #define	__bitcount32(x)	__builtin_popcount((__uint32_t)(x))
 #define	__bitcount16(x)	__builtin_popcount((__uint16_t)(x))
 #define	__bitcountl(x)	__builtin_popcountl((unsigned long)(x))
 #define	__bitcount(x)	__builtin_popcount((unsigned int)(x))
-#else
-/*
- * Population count algorithm using SWAR approach
- * - "SIMD Within A Register".
- */
-static __inline __uint16_t
-__bitcount16(__uint16_t _x)
-{
-
-	_x = (_x & 0x5555) + ((_x & 0xaaaa) >> 1);
-	_x = (_x & 0x3333) + ((_x & 0xcccc) >> 2);
-	_x = (_x + (_x >> 4)) & 0x0f0f;
-	_x = (_x + (_x >> 8)) & 0x00ff;
-	return (_x);
-}
-
-static __inline __uint32_t
-__bitcount32(__uint32_t _x)
-{
-
-	_x = (_x & 0x55555555) + ((_x & 0xaaaaaaaa) >> 1);
-	_x = (_x & 0x33333333) + ((_x & 0xcccccccc) >> 2);
-	_x = (_x + (_x >> 4)) & 0x0f0f0f0f;
-	_x = (_x + (_x >> 8));
-	_x = (_x + (_x >> 16)) & 0x000000ff;
-	return (_x);
-}
-
-#ifdef __LP64__
-static __inline __uint64_t
-__bitcount64(__uint64_t _x)
-{
-
-	_x = (_x & 0x5555555555555555) + ((_x & 0xaaaaaaaaaaaaaaaa) >> 1);
-	_x = (_x & 0x3333333333333333) + ((_x & 0xcccccccccccccccc) >> 2);
-	_x = (_x + (_x >> 4)) & 0x0f0f0f0f0f0f0f0f;
-	_x = (_x + (_x >> 8));
-	_x = (_x + (_x >> 16));
-	_x = (_x + (_x >> 32)) & 0x000000ff;
-	return (_x);
-}
-
-#define	__bitcountl(x)	__bitcount64((unsigned long)(x))
-#else
-static __inline __uint64_t
-__bitcount64(__uint64_t _x)
-{
-
-	return (__bitcount32(_x >> 32) + __bitcount32(_x));
-}
-
-#define	__bitcountl(x)	__bitcount32((unsigned long)(x))
-#endif
-#define	__bitcount(x)	__bitcount32((unsigned int)(x))
-#endif
 
 #if __BSD_VISIBLE