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Commit 9d8e2277 authored by Jan Beulich's avatar Jan Beulich Committed by Ingo Molnar
Browse files

x86-64: Handle byte-wise tail copying in memcpy() without a loop 



While hard to measure, reducing the number of possibly/likely
mis-predicted branches can generally be expected to be slightly
better.

Other than apparent at the first glance, this also doesn't grow
the function size (the alignment gap to the next function just
gets smaller).

Signed-off-by: default avatarJan Beulich <jbeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/4F218584020000780006F422@nat28.tlf.novell.com


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2ab56091

arch/x86/lib/memcpy_64.S

+10 −9
Original line number Diff line number Diff line
@@ -164,18 +164,19 @@ ENTRY(memcpy) 
	retq

	.p2align 4

.Lless_3bytes:

	cmpl $0, %edx

	je .Lend

	subl $1, %edx

	jb .Lend

	/*

	 * Move data from 1 bytes to 3 bytes.

	 */

.Lloop_1:

	movb (%rsi), %r8b

	movb %r8b, (%rdi)

	incq %rdi

	incq %rsi

	decl %edx

	jnz .Lloop_1

	movzbl (%rsi), %ecx

	jz .Lstore_1byte

	movzbq 1(%rsi), %r8

	movzbq (%rsi, %rdx), %r9

	movb %r8b, 1(%rdi)

	movb %r9b, (%rdi, %rdx)

.Lstore_1byte:

	movb %cl, (%rdi)



.Lend:

	retq