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x86-64: Optimize memcmp/wmemcmp with AVX2 and MOVBE 

Optimize x86-64 memcmp/wmemcmp with AVX2.  It uses vector compare as
much as possible.  It is as fast as SSE4 memcmp for size <= 16 bytes
and up to 2X faster for size > 16 bytes on Haswell and Skylake.  Select
AVX2 memcmp/wmemcmp on AVX2 machines where vzeroupper is preferred and
AVX unaligned load is fast.

NB: It uses TZCNT instead of BSF since TZCNT produces the same result
as BSF for non-zero input.  TZCNT is faster than BSF and is executed
as BSF if machine doesn't support TZCNT.

Key features:

1. For size from 2 to 7 bytes, load as big endian with movbe and bswap
   to avoid branches.
2. Use overlapping compare to avoid branch.
3. Use vector compare when size >= 4 bytes for memcmp or size >= 8
   bytes for wmemcmp.
4. If size is 8 * VEC_SIZE or less, unroll the loop.
5. Compare 4 * VEC_SIZE at a time with the aligned first memory area.
6. Use 2 vector compares when size is 2 * VEC_SIZE or less.
7. Use 4 vector compares when size is 4 * VEC_SIZE or less.
8. Use 8 vector compares when size is 8 * VEC_SIZE or less.

	* sysdeps/x86/cpu-features.h (index_cpu_MOVBE): New.
	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
	memcmp-avx2 and wmemcmp-avx2.
	* sysdeps/x86_64/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Test __memcmp_avx2 and __wmemcmp_avx2.
	* sysdeps/x86_64/multiarch/memcmp-avx2.S: New file.
	* sysdeps/x86_64/multiarch/wmemcmp-avx2.S: Likewise.
	* sysdeps/x86_64/multiarch/memcmp.S: Use __memcmp_avx2 on AVX
	2 machines if AVX unaligned load is fast and vzeroupper is
	preferred.
	* sysdeps/x86_64/multiarch/wmemcmp.S: Use __wmemcmp_avx2 on AVX
	2 machines if AVX unaligned load is fast and vzeroupper is
	preferred.
This commit is contained in:
H.J. Lu 2017-06-05 12:52:41 -07:00
parent ef9c4cb6c7
commit 935971ba6b
8 changed files with 482 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
ChangeLog
View File

@ -1,3 +1,19 @@
2017-06-05 H.J. Lu <hongjiu.lu@intel.com>
* sysdeps/x86/cpu-features.h (index_cpu_MOVBE): New.
* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
memcmp-avx2 and wmemcmp-avx2.
* sysdeps/x86_64/multiarch/ifunc-impl-list.c
(__libc_ifunc_impl_list): Test __memcmp_avx2 and __wmemcmp_avx2.
* sysdeps/x86_64/multiarch/memcmp-avx2.S: New file.
* sysdeps/x86_64/multiarch/wmemcmp-avx2.S: Likewise.
* sysdeps/x86_64/multiarch/memcmp.S: Use __memcmp_avx2 on AVX
2 machines if AVX unaligned load is fast and vzeroupper is
preferred.
* sysdeps/x86_64/multiarch/wmemcmp.S: Use __wmemcmp_avx2 on AVX
2 machines if AVX unaligned load is fast and vzeroupper is
preferred.
2017-06-05 H.J. Lu <hongjiu.lu@intel.com>
* include/wchar.h (__wmemset_chk): New.

1
sysdeps/x86/cpu-features.h
View File

@ -102,6 +102,7 @@
# define index_cpu_AVX COMMON_CPUID_INDEX_1*CPUID_SIZE+CPUID_ECX_OFFSET
# define index_cpu_AVX2 COMMON_CPUID_INDEX_7*CPUID_SIZE+CPUID_EBX_OFFSET
# define index_cpu_ERMS COMMON_CPUID_INDEX_7*CPUID_SIZE+CPUID_EBX_OFFSET
# define index_cpu_MOVBE COMMON_CPUID_INDEX_1*CPUID_SIZE+CPUID_ECX_OFFSET
# define index_arch_Fast_Rep_String FEATURE_INDEX_1*FEATURE_SIZE
# define index_arch_Fast_Copy_Backward FEATURE_INDEX_1*FEATURE_SIZE

5
sysdeps/x86_64/multiarch/Makefile
View File

@ -6,6 +6,7 @@ ifeq ($(subdir),string)
sysdep_routines += strncat-c stpncpy-c strncpy-c strcmp-ssse3 \
strcmp-sse2-unaligned strncmp-ssse3 \
memcmp-avx2-movbe \
memcmp-sse4 memcpy-ssse3 \
memmove-ssse3 \
memcpy-ssse3-back \
@ -30,7 +31,9 @@ CFLAGS-strspn-c.c += -msse4
endif
ifeq ($(subdir),wcsmbs)
sysdep_routines += wmemcmp-sse4 wmemcmp-ssse3 wmemcmp-c wcscpy-ssse3 wcscpy-c
sysdep_routines += wmemcmp-sse4 wmemcmp-ssse3 wmemcmp-c \
wmemcmp-avx2-movbe \
wcscpy-ssse3 wcscpy-c
endif
ifeq ($(subdir),debug)

8
sysdeps/x86_64/multiarch/ifunc-impl-list.c
View File

@ -40,6 +40,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
/* Support sysdeps/x86_64/multiarch/memcmp.S. */
IFUNC_IMPL (i, name, memcmp,
IFUNC_IMPL_ADD (array, i, memcmp,
(HAS_ARCH_FEATURE (AVX2_Usable)
&& HAS_CPU_FEATURE (MOVBE)),
__memcmp_avx2_movbe)
IFUNC_IMPL_ADD (array, i, memcmp, HAS_CPU_FEATURE (SSE4_1),
__memcmp_sse4_1)
IFUNC_IMPL_ADD (array, i, memcmp, HAS_CPU_FEATURE (SSSE3),
@ -294,6 +298,10 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
/* Support sysdeps/x86_64/multiarch/wmemcmp.S. */
IFUNC_IMPL (i, name, wmemcmp,
IFUNC_IMPL_ADD (array, i, wmemcmp,
(HAS_ARCH_FEATURE (AVX2_Usable)
&& HAS_CPU_FEATURE (MOVBE)),
__wmemcmp_avx2_movbe)
IFUNC_IMPL_ADD (array, i, wmemcmp, HAS_CPU_FEATURE (SSE4_1),
__wmemcmp_sse4_1)
IFUNC_IMPL_ADD (array, i, wmemcmp, HAS_CPU_FEATURE (SSSE3),

425
sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S Normal file
View File

@ -0,0 +1,425 @@
/* memcmp/wmemcmp optimized with AVX2.
Copyright (C) 2017 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/>. */
#if IS_IN (libc)
/* memcmp/wmemcmp is implemented as:
1. For size from 2 to 7 bytes, load as big endian with movbe and bswap
to avoid branches.
2. Use overlapping compare to avoid branch.
3. Use vector compare when size >= 4 bytes for memcmp or size >= 8
bytes for wmemcmp.
4. If size is 8 * VEC_SIZE or less, unroll the loop.
5. Compare 4 * VEC_SIZE at a time with the aligned first memory
area.
6. Use 2 vector compares when size is 2 * VEC_SIZE or less.
7. Use 4 vector compares when size is 4 * VEC_SIZE or less.
8. Use 8 vector compares when size is 8 * VEC_SIZE or less. */
# include <sysdep.h>
# ifndef MEMCMP
# define MEMCMP __memcmp_avx2_movbe
# endif
# ifdef USE_AS_WMEMCMP
# define VPCMPEQ vpcmpeqd
# else
# define VPCMPEQ vpcmpeqb
# endif
# ifndef VZEROUPPER
# define VZEROUPPER vzeroupper
# endif
# define VEC_SIZE 32
# define VEC_MASK ((1 << VEC_SIZE) - 1)
/* Warning!
wmemcmp has to use SIGNED comparison for elements.
memcmp has to use UNSIGNED comparison for elemnts.
*/
.section .text.avx,"ax",@progbits
ENTRY (MEMCMP)
# ifdef USE_AS_WMEMCMP
shl $2, %rdx
# endif
cmpq $VEC_SIZE, %rdx
jb L(less_vec)
cmpq $(VEC_SIZE * 2), %rdx
ja L(more_2x_vec)
L(last_2x_vec):
/* From VEC to 2 * VEC. No branch when size == VEC_SIZE. */
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
L(last_vec):
/* Use overlapping loads to avoid branches. */
leaq -VEC_SIZE(%rdi, %rdx), %rdi
leaq -VEC_SIZE(%rsi, %rdx), %rsi
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
VZEROUPPER
ret
.p2align 4
L(first_vec):
/* A byte or int32 is different within 16 or 32 bytes. */
tzcntl %eax, %ecx
# ifdef USE_AS_WMEMCMP
xorl %eax, %eax
movl (%rdi, %rcx), %edx
cmpl (%rsi, %rcx), %edx
L(wmemcmp_return):
setl %al
negl %eax
orl $1, %eax
# else
movzbl (%rdi, %rcx), %eax
movzbl (%rsi, %rcx), %edx
sub %edx, %eax
# endif
VZEROUPPER
ret
# ifdef USE_AS_WMEMCMP
.p2align 4
L(4):
xorl %eax, %eax
movl (%rdi), %edx
cmpl (%rsi), %edx
jne L(wmemcmp_return)
ret
# else
.p2align 4
L(between_4_7):
/* Load as big endian with overlapping movbe to avoid branches. */
movbe (%rdi), %eax
movbe (%rsi), %ecx
shlq $32, %rax
shlq $32, %rcx
movbe -4(%rdi, %rdx), %edi
movbe -4(%rsi, %rdx), %esi
orq %rdi, %rax
orq %rsi, %rcx
subq %rcx, %rax
je L(exit)
sbbl %eax, %eax
orl $1, %eax
ret
.p2align 4
L(exit):
ret
.p2align 4
L(between_2_3):
/* Load as big endian with overlapping loads and bswap to avoid
branches. */
movzwl -2(%rdi, %rdx), %eax
movzwl -2(%rsi, %rdx), %ecx
shll $16, %eax
shll $16, %ecx
movzwl (%rdi), %edi
movzwl (%rsi), %esi
orl %edi, %eax
orl %esi, %ecx
bswap %eax
bswap %ecx
subl %ecx, %eax
ret
.p2align 4
L(1):
movzbl (%rdi), %eax
movzbl (%rsi), %ecx
subl %ecx, %eax
ret
# endif
.p2align 4
L(zero):
xorl %eax, %eax
ret
.p2align 4
L(less_vec):
# ifdef USE_AS_WMEMCMP
/* It can only be 0, 4, 8, 12, 16, 20, 24, 28 bytes. */
cmpb $4, %dl
je L(4)
jb L(zero)
# else
cmpb $1, %dl
je L(1)
jb L(zero)
cmpb $4, %dl
jb L(between_2_3)
cmpb $8, %dl
jb L(between_4_7)
# endif
cmpb $16, %dl
jae L(between_16_31)
/* It is between 8 and 15 bytes. */
vmovq (%rdi), %xmm1
vmovq (%rsi), %xmm2
VPCMPEQ %xmm1, %xmm2, %xmm2
vpmovmskb %xmm2, %eax
subl $0xffff, %eax
jnz L(first_vec)
/* Use overlapping loads to avoid branches. */
leaq -8(%rdi, %rdx), %rdi
leaq -8(%rsi, %rdx), %rsi
vmovq (%rdi), %xmm1
vmovq (%rsi), %xmm2
VPCMPEQ %xmm1, %xmm2, %xmm2
vpmovmskb %xmm2, %eax
subl $0xffff, %eax
jnz L(first_vec)
ret
.p2align 4
L(between_16_31):
/* From 16 to 31 bytes. No branch when size == 16. */
vmovdqu (%rsi), %xmm2
VPCMPEQ (%rdi), %xmm2, %xmm2
vpmovmskb %xmm2, %eax
subl $0xffff, %eax
jnz L(first_vec)
/* Use overlapping loads to avoid branches. */
leaq -16(%rdi, %rdx), %rdi
leaq -16(%rsi, %rdx), %rsi
vmovdqu (%rsi), %xmm2
VPCMPEQ (%rdi), %xmm2, %xmm2
vpmovmskb %xmm2, %eax
subl $0xffff, %eax
jnz L(first_vec)
ret
.p2align 4
L(more_2x_vec):
/* More than 2 * VEC. */
cmpq $(VEC_SIZE * 8), %rdx
ja L(more_8x_vec)
cmpq $(VEC_SIZE * 4), %rdx
jb L(last_4x_vec)
/* From 4 * VEC to 8 * VEC, inclusively. */
vmovdqu (%rsi), %ymm1
VPCMPEQ (%rdi), %ymm1, %ymm1
vmovdqu VEC_SIZE(%rsi), %ymm2
VPCMPEQ VEC_SIZE(%rdi), %ymm2, %ymm2
vmovdqu (VEC_SIZE * 2)(%rsi), %ymm3
VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm3, %ymm3
vmovdqu (VEC_SIZE * 3)(%rsi), %ymm4
VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm4, %ymm4
vpand %ymm1, %ymm2, %ymm5
vpand %ymm3, %ymm4, %ymm6
vpand %ymm5, %ymm6, %ymm5
vpmovmskb %ymm5, %eax
subl $VEC_MASK, %eax
jnz L(4x_vec_end)
leaq -(4 * VEC_SIZE)(%rdi, %rdx), %rdi
leaq -(4 * VEC_SIZE)(%rsi, %rdx), %rsi
vmovdqu (%rsi), %ymm1
VPCMPEQ (%rdi), %ymm1, %ymm1
vmovdqu VEC_SIZE(%rsi), %ymm2
VPCMPEQ VEC_SIZE(%rdi), %ymm2, %ymm2
vpand %ymm2, %ymm1, %ymm5
vmovdqu (VEC_SIZE * 2)(%rsi), %ymm3
VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm3, %ymm3
vpand %ymm3, %ymm5, %ymm5
vmovdqu (VEC_SIZE * 3)(%rsi), %ymm4
VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm4, %ymm4
vpand %ymm4, %ymm5, %ymm5
vpmovmskb %ymm5, %eax
subl $VEC_MASK, %eax
jnz L(4x_vec_end)
VZEROUPPER
ret
.p2align 4
L(more_8x_vec):
/* More than 8 * VEC. Check the first VEC. */
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
/* Align the first memory area for aligned loads in the loop.
Compute how much the first memory area is misaligned. */
movq %rdi, %rcx
andl $(VEC_SIZE - 1), %ecx
/* Get the negative of offset for alignment. */
subq $VEC_SIZE, %rcx
/* Adjust the second memory area. */
subq %rcx, %rsi
/* Adjust the first memory area which should be aligned now. */
subq %rcx, %rdi
/* Adjust length. */
addq %rcx, %rdx
L(loop_4x_vec):
/* Compare 4 * VEC at a time forward. */
vmovdqu (%rsi), %ymm1
VPCMPEQ (%rdi), %ymm1, %ymm1
vmovdqu VEC_SIZE(%rsi), %ymm2
VPCMPEQ VEC_SIZE(%rdi), %ymm2, %ymm2
vpand %ymm2, %ymm1, %ymm5
vmovdqu (VEC_SIZE * 2)(%rsi), %ymm3
VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm3, %ymm3
vpand %ymm3, %ymm5, %ymm5
vmovdqu (VEC_SIZE * 3)(%rsi), %ymm4
VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm4, %ymm4
vpand %ymm4, %ymm5, %ymm5
vpmovmskb %ymm5, %eax
subl $VEC_MASK, %eax
jnz L(4x_vec_end)
addq $(VEC_SIZE * 4), %rdi
addq $(VEC_SIZE * 4), %rsi
subq $(VEC_SIZE * 4), %rdx
cmpq $(VEC_SIZE * 4), %rdx
jae L(loop_4x_vec)
/* Less than 4 * VEC. */
cmpq $VEC_SIZE, %rdx
jbe L(last_vec)
cmpq $(VEC_SIZE * 2), %rdx
jbe L(last_2x_vec)
L(last_4x_vec):
/* From 2 * VEC to 4 * VEC. */
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
addq $VEC_SIZE, %rdi
addq $VEC_SIZE, %rsi
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
/* Use overlapping loads to avoid branches. */
leaq -(3 * VEC_SIZE)(%rdi, %rdx), %rdi
leaq -(3 * VEC_SIZE)(%rsi, %rdx), %rsi
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
addq $VEC_SIZE, %rdi
addq $VEC_SIZE, %rsi
vmovdqu (%rsi), %ymm2
VPCMPEQ (%rdi), %ymm2, %ymm2
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
VZEROUPPER
ret
.p2align 4
L(4x_vec_end):
vpmovmskb %ymm1, %eax
subl $VEC_MASK, %eax
jnz L(first_vec)
vpmovmskb %ymm2, %eax
subl $VEC_MASK, %eax
jnz L(first_vec_x1)
vpmovmskb %ymm3, %eax
subl $VEC_MASK, %eax
jnz L(first_vec_x2)
vpmovmskb %ymm4, %eax
subl $VEC_MASK, %eax
tzcntl %eax, %ecx
# ifdef USE_AS_WMEMCMP
xorl %eax, %eax
movl (VEC_SIZE * 3)(%rdi, %rcx), %edx
cmpl (VEC_SIZE * 3)(%rsi, %rcx), %edx
jmp L(wmemcmp_return)
# else
movzbl (VEC_SIZE * 3)(%rdi, %rcx), %eax
movzbl (VEC_SIZE * 3)(%rsi, %rcx), %edx
sub %edx, %eax
# endif
VZEROUPPER
ret
.p2align 4
L(first_vec_x1):
tzcntl %eax, %ecx
# ifdef USE_AS_WMEMCMP
xorl %eax, %eax
movl VEC_SIZE(%rdi, %rcx), %edx
cmpl VEC_SIZE(%rsi, %rcx), %edx
jmp L(wmemcmp_return)
# else
movzbl VEC_SIZE(%rdi, %rcx), %eax
movzbl VEC_SIZE(%rsi, %rcx), %edx
sub %edx, %eax
# endif
VZEROUPPER
ret
.p2align 4
L(first_vec_x2):
tzcntl %eax, %ecx
# ifdef USE_AS_WMEMCMP
xorl %eax, %eax
movl (VEC_SIZE * 2)(%rdi, %rcx), %edx
cmpl (VEC_SIZE * 2)(%rsi, %rcx), %edx
jmp L(wmemcmp_return)
# else
movzbl (VEC_SIZE * 2)(%rdi, %rcx), %eax
movzbl (VEC_SIZE * 2)(%rsi, %rcx), %edx
sub %edx, %eax
# endif
VZEROUPPER
ret
END (MEMCMP)
#endif

13
sysdeps/x86_64/multiarch/memcmp.S
View File

@ -27,7 +27,18 @@
ENTRY(memcmp)
.type memcmp, @gnu_indirect_function
LOAD_RTLD_GLOBAL_RO_RDX
HAS_CPU_FEATURE (SSSE3)
HAS_ARCH_FEATURE (Prefer_No_VZEROUPPER)
jnz 1f
HAS_ARCH_FEATURE (AVX2_Usable)
jz 1f
HAS_CPU_FEATURE (MOVBE)
jz 1f
HAS_ARCH_FEATURE (AVX_Fast_Unaligned_Load)
jz 1f
leaq __memcmp_avx2_movbe(%rip), %rax
ret
1: HAS_CPU_FEATURE (SSSE3)
jnz 2f
leaq __memcmp_sse2(%rip), %rax
ret

4
sysdeps/x86_64/multiarch/wmemcmp-avx2-movbe.S Normal file
View File

@ -0,0 +1,4 @@
#define MEMCMP __wmemcmp_avx2_movbe
#define USE_AS_WMEMCMP 1
#include "memcmp-avx2-movbe.S"

13
sysdeps/x86_64/multiarch/wmemcmp.S
View File

@ -27,7 +27,18 @@
ENTRY(wmemcmp)
.type wmemcmp, @gnu_indirect_function
LOAD_RTLD_GLOBAL_RO_RDX
HAS_CPU_FEATURE (SSSE3)
HAS_ARCH_FEATURE (Prefer_No_VZEROUPPER)
jnz 1f
HAS_ARCH_FEATURE (AVX2_Usable)
jz 1f
HAS_CPU_FEATURE (MOVBE)
jz 1f
HAS_ARCH_FEATURE (AVX_Fast_Unaligned_Load)
jz 1f
leaq __wmemcmp_avx2_movbe(%rip), %rax
ret
1: HAS_CPU_FEATURE (SSSE3)
jnz 2f
leaq __wmemcmp_sse2(%rip), %rax
ret