From 9d8e22777e66f420e46490e9fc6f8cb7e0e2222b Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Thu, 26 Jan 2012 15:55:32 +0000 Subject: [PATCH] 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 Cc: Linus Torvalds Link: http://lkml.kernel.org/r/4F218584020000780006F422@nat28.tlf.novell.com Signed-off-by: Ingo Molnar --- arch/x86/lib/memcpy_64.S | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S index 1235b04..1c273be 100644 --- a/arch/x86/lib/memcpy_64.S +++ b/arch/x86/lib/memcpy_64.S @@ -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 -- 2.7.4