diff --git a/sys/x86/include/endian.h b/sys/x86/include/endian.h
index 9c39f4fddf80..18d52fb8a6fa 100644
--- a/sys/x86/include/endian.h
+++ b/sys/x86/include/endian.h
@@ -1,133 +1,77 @@
 /*-
  * SPDX-License-Identifier: BSD-3-Clause
  *
  * Copyright (c) 1987, 1991 Regents of the University of California.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. Neither the name of the University nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
  *	@(#)endian.h	7.8 (Berkeley) 4/3/91
  * $FreeBSD$
  */
 
 #ifndef _MACHINE_ENDIAN_H_
 #define	_MACHINE_ENDIAN_H_
 
 #include <sys/cdefs.h>
 #include <sys/_types.h>
 
 /*
  * Define the order of 32-bit words in 64-bit words.
  */
 #define	_QUAD_HIGHWORD 1
 #define	_QUAD_LOWWORD 0
 
 /*
  * Definitions for byte order, according to byte significance from low
  * address to high.
  */
 #define	_LITTLE_ENDIAN	1234	/* LSB first: i386, vax */
 #define	_BIG_ENDIAN	4321	/* MSB first: 68000, ibm, net */
 #define	_PDP_ENDIAN	3412	/* LSB first in word, MSW first in long */
 
 #define	_BYTE_ORDER	_LITTLE_ENDIAN
 
 /*
  * Deprecated variants that don't have enough underscores to be useful in more
  * strict namespaces.
  */
 #if __BSD_VISIBLE
 #define	LITTLE_ENDIAN	_LITTLE_ENDIAN
 #define	BIG_ENDIAN	_BIG_ENDIAN
 #define	PDP_ENDIAN	_PDP_ENDIAN
 #define	BYTE_ORDER	_BYTE_ORDER
 #endif
 
-#define	__bswap16_gen(x)	(__uint16_t)((x) << 8 | (x) >> 8)
-#define	__bswap32_gen(x)		\
-	(((__uint32_t)__bswap16((x) & 0xffff) << 16) | __bswap16((x) >> 16))
-#define	__bswap64_gen(x)		\
-	(((__uint64_t)__bswap32((x) & 0xffffffff) << 32) | __bswap32((x) >> 32))
-
-#ifdef __GNUCLIKE_BUILTIN_CONSTANT_P
-#define	__bswap16(x)				\
-	((__uint16_t)(__builtin_constant_p(x) ?	\
-	    __bswap16_gen((__uint16_t)(x)) : __bswap16_var(x)))
-#define	__bswap32(x)			\
-	(__builtin_constant_p(x) ?	\
-	    __bswap32_gen((__uint32_t)(x)) : __bswap32_var(x))
-#define	__bswap64(x)			\
-	(__builtin_constant_p(x) ?	\
-	    __bswap64_gen((__uint64_t)(x)) : __bswap64_var(x))
-#else
-/* XXX these are broken for use in static initializers. */
-#define	__bswap16(x)	__bswap16_var(x)
-#define	__bswap32(x)	__bswap32_var(x)
-#define	__bswap64(x)	__bswap64_var(x)
-#endif
-
-/* These are defined as functions to avoid multiple evaluation of x. */
-
-static __inline __uint16_t
-__bswap16_var(__uint16_t _x)
-{
-
-	return (__bswap16_gen(_x));
-}
-
-static __inline __uint32_t
-__bswap32_var(__uint32_t _x)
-{
-
-#ifdef __GNUCLIKE_ASM
-	__asm("bswap %0" : "+r" (_x));
-	return (_x);
-#else
-	return (__bswap32_gen(_x));
-#endif
-}
-
-static __inline __uint64_t
-__bswap64_var(__uint64_t _x)
-{
-
-#if defined(__amd64__) && defined(__GNUCLIKE_ASM)
-	__asm("bswap %0" : "+r" (_x));
-	return (_x);
-#else
-	/*
-	 * It is important for the optimizations that the following is not
-	 * really generic, but expands to 2 __bswap32_var()'s.
-	 */
-	return (__bswap64_gen(_x));
-#endif
-}
+#define	__bswap16(x)	__builtin_bswap16(x)
+#define	__bswap32(x)	__builtin_bswap32(x)
+#define	__bswap64(x)	__builtin_bswap64(x)
 
 #define	__htonl(x)	__bswap32(x)
 #define	__htons(x)	__bswap16(x)
 #define	__ntohl(x)	__bswap32(x)
 #define	__ntohs(x)	__bswap16(x)
 
 #endif /* !_MACHINE_ENDIAN_H_ */