c8cebc5533
In the _zero, _fill and _copy functions, the small_const_nbits branch is
redundant. If nbits is small and const, gcc knows full well that
BITS_TO_LONGS(nbits) is 1, so len is also a compile-time constant
(sizeof(long)), and calling memset or memcpy with a length argument of
sizeof(long) makes gcc generate the expected code anyway:
#include <string.h>
void a(unsigned long *x) { memset(x, 0, 8); }
void b(unsigned long *x) { memset(x, 0xff, 8); }
void c(unsigned long *x, const unsigned long *y) { memcpy(x, y, 8); }
turns into
0000000000000000 <a>:
0: 48 c7 07 00 00 00 00 movq $0x0,(%rdi)
7: c3 retq
8: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
f: 00
0000000000000010 <b>:
10: 48 c7 07 ff ff ff ff movq $0xffffffffffffffff,(%rdi)
17: c3 retq
18: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
1f: 00
0000000000000020 <c>:
20: 48 8b 06 mov (%rsi),%rax
23: 48 89 07 mov %rax,(%rdi)
26: c3 retq
Link: http://lkml.kernel.org/r/20180818131623.8755-4-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Yury Norov <ynorov@caviumnetworks.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.