[PATCH] faster memcpy on x64.

[OndÅej BÃlka <neleai at seznam dot cz>]

Hi,

I was occupied for last few week on analyzing memcpy and memset and I
have better implementations than current. This patch is about memcpy.

Benchmark results are at 
http://kam.mff.cuni.cz/~ondra/memcpy_profile.html
or archived at 
http://kam.mff.cuni.cz/~ondra/memcpy_profile_result27_04_13.tar.bz2

I tried to modify this for  memmove and I found that additional 
cost is close to zero when not overlapping.
So this implementation can be aliased to memmove.

Important part there is test of memcpy in hooked gcc which shows small
but real speedup. A memcpy_new 1) is faster on newer processors while
memcpy_new_small on slower.

Could we test 2) on wider range of usecases and report results?

Here we hit fact that strings in practice are small and there is we hit
latency to get data.

The microbenchmarks tests look much better.

Main speedup is obtained by avoiding computed loops and simplify control
flow for better speculative execution. 1)

This gives 20% speedup for 32-1000 byte strings.

Second is that loop that I use is in most architectures asymptoticaly
faster than gcc one for data in L1, L2, L3 cache. 
When data is in memory then memory is bottleneck and choice of
implementation can give at most 1%.

I tested avx version which is slower on current processors due fact that 
it is faster to load high and low half separately.

1) Except core2,athlon where I need even simpler control flow
(memcpy_new_small) to get that speedup.

I attached file from which I generated this patch. There are few
mistakes made by gcc, I could post diff againist vanilla version.

I did not tried optimize for atom yet so I keep ifunc for it.

Passes testsuite. OK for 2.18?

Ondra

1) File variant/memcpy_new_small.s in 2)
2) http://kam.mff.cuni.cz/~ondra/memcpy_profile27_04_13.tar.bz2


	* sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S: New file.
	* sysdeps/x86_64/multiarch/memcpy.S (__new_memcpy): Add
	__memcpy_sse2_unaligned ifunc selection. 
	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines):
	Add memcpy-sse2-unaligned.S.
	sysdeps/x86_64/multiarch/ifunc-impl-list.c: __memcpy_sse2_unaligned.

---
 sysdeps/x86_64/multiarch/Makefile                |    2 +-
 sysdeps/x86_64/multiarch/ifunc-impl-list.c       |    1 +
 sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S |  176 ++++++++++++++++++++++
 sysdeps/x86_64/multiarch/memcpy.S                |   15 +-
 4 files changed, 186 insertions(+), 8 deletions(-)
 create mode 100644 sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S

diff --git a/sysdeps/x86_64/multiarch/Makefile b/sysdeps/x86_64/multiarch/Makefile
index 86787ee..203d16e 100644
--- a/sysdeps/x86_64/multiarch/Makefile
+++ b/sysdeps/x86_64/multiarch/Makefile
@@ -7,7 +7,7 @@ endif
 ifeq ($(subdir),string)
 
 sysdep_routines += strncat-c stpncpy-c strncpy-c strcmp-ssse3 strncmp-ssse3 \
-		   strend-sse4 memcmp-sse4 memcpy-ssse3 mempcpy-ssse3 \
+		   strend-sse4 memcmp-sse4 memcpy-ssse3 memcpy-sse2-unaligned mempcpy-ssse3 \
 		   memmove-ssse3 memcpy-ssse3-back mempcpy-ssse3-back \
 		   memmove-ssse3-back strcasestr-nonascii strcasecmp_l-ssse3 \
 		   strncase_l-ssse3 strcat-ssse3 strncat-ssse3\
diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index 05315fd..28d3579 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -227,6 +227,7 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 	      IFUNC_IMPL_ADD (array, i, memcpy, HAS_SSSE3,
 			      __memcpy_ssse3_back)
 	      IFUNC_IMPL_ADD (array, i, memcpy, HAS_SSSE3, __memcpy_ssse3)
+	      IFUNC_IMPL_ADD (array, i, memcpy, 1, __memcpy_sse2_unaligned)
 	      IFUNC_IMPL_ADD (array, i, memcpy, 1, __memcpy_sse2))
 
   /* Support sysdeps/x86_64/multiarch/mempcpy_chk.S.  */
diff --git a/sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S b/sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S
new file mode 100644
index 0000000..1b86c41
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memcpy-sse2-unaligned.S
@@ -0,0 +1,176 @@
+/* memcpy with unaliged loads
+   Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#include "asm-syntax.h"
+
+#ifndef ALIGN
+# define ALIGN(n)	.p2align n
+#endif
+
+
+ENTRY(__memcpy_sse2_unaligned)
+	movq	%rsi, %rax
+	leaq	(%rdx,%rdx), %rcx
+	subq	%rdi, %rax
+	subq	%rdx, %rax
+	cmpq	%rcx, %rax
+	jb	L(overlapping)
+	cmpq	$16, %rdx
+	jbe	L(less_16)
+	movdqu	(%rsi), %xmm8
+	cmpq	$32, %rdx
+	movdqu	%xmm8, (%rdi)
+	movdqu	-16(%rsi,%rdx), %xmm8
+	movdqu	%xmm8, -16(%rdi,%rdx)
+	ja	.L31
+L(return):
+	movq	%rdi, %rax
+	ret
+	.p2align 4,,10
+	ALIGN(4)
+.L31:
+	movdqu	16(%rsi), %xmm8
+	cmpq	$64, %rdx
+	movdqu	%xmm8, 16(%rdi)
+	movdqu	-32(%rsi,%rdx), %xmm8
+	movdqu	%xmm8, -32(%rdi,%rdx)
+	jbe	L(return)
+	movdqu	32(%rsi), %xmm8
+	cmpq	$128, %rdx
+	movdqu	%xmm8, 32(%rdi)
+	movdqu	-48(%rsi,%rdx), %xmm8
+	movdqu	%xmm8, -48(%rdi,%rdx)
+	movdqu	48(%rsi), %xmm8
+	movdqu	%xmm8, 48(%rdi)
+	movdqu	-64(%rsi,%rdx), %xmm8
+	movdqu	%xmm8, -64(%rdi,%rdx)
+	jbe	L(return)
+	leaq	64(%rdi), %rcx
+	addq	%rdi, %rdx
+	andq	$-64, %rdx
+	andq	$-64, %rcx
+	movq	%rcx, %rax
+	subq	%rdi, %rax
+	addq	%rax, %rsi
+	cmpq	%rdx, %rcx
+	je	L(return)
+	movq	%rsi, %r10
+	subq	%rcx, %r10
+	leaq	16(%r10), %r9
+	leaq	32(%r10), %r8
+	leaq	48(%r10), %rax
+	.p2align 4,,10
+	ALIGN(4)
+L(loop):
+	movdqu	(%rcx,%r10), %xmm8
+	movdqa	%xmm8, (%rcx)
+	movdqu	(%rcx,%r9), %xmm8
+	movdqa	%xmm8, 16(%rcx)
+	movdqu	(%rcx,%r8), %xmm8
+	movdqa	%xmm8, 32(%rcx)
+	movdqu	(%rcx,%rax), %xmm8
+	movdqa	%xmm8, 48(%rcx)
+	addq	$64, %rcx
+	cmpq	%rcx, %rdx
+	jne	L(loop)
+	jmp	L(return)
+L(overlapping):
+	cmpq	%rsi, %rdi
+	jae	.L3
+	testq	%rdx, %rdx
+	.p2align 4,,5
+	je	L(return)
+	movq	%rdx, %r9
+	leaq	16(%rsi), %rcx
+	leaq	16(%rdi), %r8
+	shrq	$4, %r9
+	movq	%r9, %rax
+	salq	$4, %rax
+	cmpq	%rcx, %rdi
+	setae	%cl
+	cmpq	%r8, %rsi
+	setae	%r8b
+	orl	%r8d, %ecx
+	cmpq	$15, %rdx
+	seta	%r8b
+	testb	%r8b, %cl
+	je	.L16
+	testq	%rax, %rax
+	je	.L16
+	xorl	%ecx, %ecx
+	xorl	%r8d, %r8d
+.L7:
+	movdqu	(%rsi,%rcx), %xmm8
+	addq	$1, %r8
+	movdqu	%xmm8, (%rdi,%rcx)
+	addq	$16, %rcx
+	cmpq	%r8, %r9
+	ja	.L7
+	cmpq	%rax, %rdx
+	je	L(return)
+.L21:
+	movzbl	(%rsi,%rax), %ecx
+	movb	%cl, (%rdi,%rax)
+	addq	$1, %rax
+	cmpq	%rax, %rdx
+	ja	.L21
+	jmp	L(return)
+L(less_16):
+	testb	$24, %dl
+	jne	L(between_9_16)
+	testb	$4, %dl
+	.p2align 4,,5
+	jne	L(between_5_8)
+	testq	%rdx, %rdx
+	.p2align 4,,2
+	je	L(return)
+	movzbl	(%rsi), %eax
+	testb	$2, %dl
+	movb	%al, (%rdi)
+	je	L(return)
+	movzwl	-2(%rsi,%rdx), %eax
+	movw	%ax, -2(%rdi,%rdx)
+	jmp	L(return)
+.L3:
+	leaq	-1(%rdx), %rax
+	.p2align 4,,10
+	ALIGN(4)
+.L11:
+	movzbl	(%rsi,%rax), %edx
+	movb	%dl, (%rdi,%rax)
+	subq	$1, %rax
+	jmp	.L11
+L(between_9_16):
+	movq	(%rsi), %rax
+	movq	%rax, (%rdi)
+	movq	-8(%rsi,%rdx), %rax
+	movq	%rax, -8(%rdi,%rdx)
+	jmp	L(return)
+.L16:
+	xorl	%eax, %eax
+	jmp	.L21
+L(between_5_8):
+	movl	(%rsi), %eax
+	movl	%eax, (%rdi)
+	movl	-4(%rsi,%rdx), %eax
+	movl	%eax, -4(%rdi,%rdx)
+	jmp	L(return)
+END(__memcpy_sse2_unaligned)
+
diff --git a/sysdeps/x86_64/multiarch/memcpy.S b/sysdeps/x86_64/multiarch/memcpy.S
index b452f53..a1e5031 100644
--- a/sysdeps/x86_64/multiarch/memcpy.S
+++ b/sysdeps/x86_64/multiarch/memcpy.S
@@ -33,13 +33,14 @@ ENTRY(__new_memcpy)
 	jne	1f
 	call	__init_cpu_features
 1:	leaq	__memcpy_sse2(%rip), %rax
-	testl	$bit_SSSE3, __cpu_features+CPUID_OFFSET+index_SSSE3(%rip)
-	jz	2f
-	leaq	__memcpy_ssse3(%rip), %rax
-	testl	$bit_Fast_Copy_Backward, __cpu_features+FEATURE_OFFSET+index_Fast_Copy_Backward(%rip)
-	jz	2f
-	leaq	__memcpy_ssse3_back(%rip), %rax
-2:	ret
+	testl	$bit_Slow_BSF, __cpu_features+FEATURE_OFFSET+index_Slow_BSF(%rip)
+	jnz	2f
+	leaq	__memcpy_sse2_unaligned(%rip), %rax
+	ret
+2:	testl   $bit_SSSE3, __cpu_features+CPUID_OFFSET+index_SSSE3(%rip)
+	jz 3f
+	leaq    __memcpy_ssse3(%rip), %rax
+3:	ret
 END(__new_memcpy)
 
 # undef ENTRY
-- 
1.7.4.4

Attachment: memcpy_new.c
Description: Text document