asm-generic: unaligned: remove byteshift helpers

In theory, compilers should be able to work this out themselves so we
can use a simpler version based on the swab() helpers.

I have verified that this works on all supported compiler versions
(gcc-4.9 and up, clang-10 and up). Looking at the object code produced by
gcc-11, I found that the impact is mostly a change in inlining decisions
that lead to slightly larger code.

In other cases, this version produces explicit byte swaps in place of
separate byte access, or comparing against pre-swapped constants.

While the source code is clearly simpler, I have not seen an indication
of the new version actually producing better code on Arm, so maybe
we want to skip this after all. From what I can tell, gcc recognizes
the byteswap pattern in the byteshift.h header and can turn it into
explicit instructions, but it does not turn a __builtin_bswap32() back
into individual bytes when that would result in better output, e.g.
when storing a byte-reversed constant.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 0 insertions, 71 deletions

diff --git a/include/linux/unaligned/be_byteshift.h b/include/linux/unaligned/be_byteshift.h
deleted file mode 100644
index c43ff5918c8a..000000000000
--- a/include/linux/unaligned/be_byteshift.h
+++ /dev/null
@@ -1,71 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_UNALIGNED_BE_BYTESHIFT_H
-#define _LINUX_UNALIGNED_BE_BYTESHIFT_H
-
-#include <linux/types.h>
-
-static inline u16 __get_unaligned_be16(const u8 *p)
-{
-	return p[0] << 8 | p[1];
-}
-
-static inline u32 __get_unaligned_be32(const u8 *p)
-{
-	return p[0] << 24 | p[1] << 16 | p[2] << 8 | p[3];
-}
-
-static inline u64 __get_unaligned_be64(const u8 *p)
-{
-	return (u64)__get_unaligned_be32(p) << 32 |
-	       __get_unaligned_be32(p + 4);
-}
-
-static inline void __put_unaligned_be16(u16 val, u8 *p)
-{
-	*p++ = val >> 8;
-	*p++ = val;
-}
-
-static inline void __put_unaligned_be32(u32 val, u8 *p)
-{
-	__put_unaligned_be16(val >> 16, p);
-	__put_unaligned_be16(val, p + 2);
-}
-
-static inline void __put_unaligned_be64(u64 val, u8 *p)
-{
-	__put_unaligned_be32(val >> 32, p);
-	__put_unaligned_be32(val, p + 4);
-}
-
-static inline u16 get_unaligned_be16(const void *p)
-{
-	return __get_unaligned_be16(p);
-}
-
-static inline u32 get_unaligned_be32(const void *p)
-{
-	return __get_unaligned_be32(p);
-}
-
-static inline u64 get_unaligned_be64(const void *p)
-{
-	return __get_unaligned_be64(p);
-}
-
-static inline void put_unaligned_be16(u16 val, void *p)
-{
-	__put_unaligned_be16(val, p);
-}
-
-static inline void put_unaligned_be32(u32 val, void *p)
-{
-	__put_unaligned_be32(val, p);
-}
-
-static inline void put_unaligned_be64(u64 val, void *p)
-{
-	__put_unaligned_be64(val, p);
-}
-
-#endif /* _LINUX_UNALIGNED_BE_BYTESHIFT_H */