diff options
| author | Arnd Bergmann <arnd@arndb.de> | 2021-05-08 00:07:51 +0200 |
|---|---|---|
| committer | Arnd Bergmann <arnd@arndb.de> | 2021-05-10 17:50:47 +0200 |
| commit | 0652035a57945e14e611dafae2ec5b46a05bc1d1 (patch) | |
| tree | 0c34544a7755bc1ee0a822e86458d3ed9215533f /include/asm-generic | |
| parent | f12d3ff3f41cc92f67cfaf29697685e8834fe4a4 (diff) | |
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>
Diffstat (limited to 'include/asm-generic')
| -rw-r--r-- | include/asm-generic/unaligned.h | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h index 374c940e9be1..d79df721ae60 100644 --- a/include/asm-generic/unaligned.h +++ b/include/asm-generic/unaligned.h @@ -16,7 +16,6 @@ #if defined(__LITTLE_ENDIAN) # ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS # include <linux/unaligned/le_struct.h> -# include <linux/unaligned/be_byteshift.h> # endif # include <linux/unaligned/generic.h> # define get_unaligned __get_unaligned_le @@ -24,7 +23,6 @@ #elif defined(__BIG_ENDIAN) # ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS # include <linux/unaligned/be_struct.h> -# include <linux/unaligned/le_byteshift.h> # endif # include <linux/unaligned/generic.h> # define get_unaligned __get_unaligned_be |