Commit 9d8e2277 authored Jan 26, 2012 by Jan Beulich Committed by Ingo Molnar Jan 26, 2012

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: Jan 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: Ingo 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

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