From 0652035a57945e14e611dafae2ec5b46a05bc1d1 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Sat, 8 May 2021 00:07:51 +0200 Subject: 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 Signed-off-by: Arnd Bergmann --- include/asm-generic/unaligned.h | 2 -- 1 file changed, 2 deletions(-) (limited to 'include/asm-generic/unaligned.h') 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 -# include # endif # include # define get_unaligned __get_unaligned_le @@ -24,7 +23,6 @@ #elif defined(__BIG_ENDIAN) # ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS # include -# include # endif # include # define get_unaligned __get_unaligned_be -- cgit v1.2.3