x86-64: Optimize strcmp/wcscmp and strncmp/wcsncmp with AVX2

Optimize x86-64 strcmp/wcscmp and strncmp/wcsncmp with AVX2. It uses vector
comparison as much as possible. Peak performance observed on a SkyLake
machine: 9x, 3x, 2.5x and 5.5x for strcmp, strncmp, wcscmp and wcsncmp,
respectively. The larger the comparison length, the more benefit using
avx2 functions, except on the strcmp, where peak is observed at length
== 32 bytes. Select AVX2 strcmp/wcscmp 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.

	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
	strcmp-avx2, strncmp-avx2, wcscmp-avx2, wcscmp-sse2, wcsncmp-avx2 and
	wcsncmp-sse2.
	* sysdeps/x86_64/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Add tests for __strcmp_avx2,
	__strncmp_avx2,	__wcscmp_avx2, __wcsncmp_avx2, __wcscmp_sse2
	and __wcsncmp_sse2.
	* sysdeps/x86_64/multiarch/strcmp.c (OPTIMIZE (avx2)):
	(IFUNC_SELECTOR): Return OPTIMIZE (avx2) on AVX 2 machines if
	AVX unaligned load is fast and vzeroupper is preferred.
	* sysdeps/x86_64/multiarch/strncmp.c: Likewise.
	* sysdeps/x86_64/multiarch/strcmp-avx2.S: New file.
	* sysdeps/x86_64/multiarch/strncmp-avx2.S: Likewise.
	* sysdeps/x86_64/multiarch/wcscmp-avx2.S: Likewise.
	* sysdeps/x86_64/multiarch/wcscmp-sse2.S: Likewise.
	* sysdeps/x86_64/multiarch/wcscmp.c: Likewise.
	* sysdeps/x86_64/multiarch/wcsncmp-avx2.S: Likewise.
	* sysdeps/x86_64/multiarch/wcsncmp-sse2.c: Likewise.
	* sysdeps/x86_64/multiarch/wcsncmp.c: Likewise.
	* sysdeps/x86_64/wcscmp.S (__wcscmp): Add alias only if __wcscmp
	is undefined.

1 files changed, 847 insertions, 0 deletions

diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
new file mode 100644
index 0000000000..e8397f3b05
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
@@ -0,0 +1,847 @@
+/* strcmp/wcscmp/strncmp/wcsncmp optimized with AVX2.
+   Copyright (C) 2018 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)
+
+# include <sysdep.h>
+
+# ifndef STRCMP
+#  define STRCMP	__strcmp_avx2
+# endif
+
+# define PAGE_SIZE	4096
+
+/* VEC_SIZE = Number of bytes in a ymm register */
+# define VEC_SIZE	32
+
+/* Shift for dividing by (VEC_SIZE * 4).  */
+# define DIVIDE_BY_VEC_4_SHIFT	7
+# if (VEC_SIZE * 4) != (1 << DIVIDE_BY_VEC_4_SHIFT)
+#  error (VEC_SIZE * 4) != (1 << DIVIDE_BY_VEC_4_SHIFT)
+# endif
+
+# ifdef USE_AS_WCSCMP
+/* Compare packed dwords.  */
+#  define VPCMPEQ	vpcmpeqd
+/* Compare packed dwords and store minimum.  */
+#  define VPMINU	vpminud
+/* 1 dword char == 4 bytes.  */
+#  define SIZE_OF_CHAR	4
+# else
+/* Compare packed bytes.  */
+#  define VPCMPEQ	vpcmpeqb
+/* Compare packed bytes and store minimum.  */
+#  define VPMINU	vpminub
+/* 1 byte char == 1 byte.  */
+#  define SIZE_OF_CHAR	1
+# endif
+
+# ifndef VZEROUPPER
+#  define VZEROUPPER	vzeroupper
+# endif
+
+/* Warning!
+           wcscmp/wcsncmp have to use SIGNED comparison for elements.
+           strcmp/strncmp have to use UNSIGNED comparison for elements.
+*/
+
+/* The main idea of the string comparison (byte or dword) using AVX2
+   consists of comparing (VPCMPEQ) two ymm vectors. The latter can be on
+   either packed bytes or dwords depending on USE_AS_WCSCMP. In order
+   to check the null char, algorithm keeps the matched bytes/dwords,
+   requiring two more AVX2 instructions (VPMINU and VPCMPEQ). In general,
+   the costs of comparing VEC_SIZE bytes (32-bytes) are two VPCMPEQ and
+   one VPMINU instructions, together with movdqu and testl instructions.
+   Main loop (away from from page boundary) compares 4 vectors are a time,
+   effectively comparing 4 x VEC_SIZE bytes (128 bytes) on each loop.
+
+   The routine strncmp/wcsncmp (enabled by defining USE_AS_STRNCMP) logic
+   is the same as strcmp, except that an a maximum offset is tracked.  If
+   the maximum offset is reached before a difference is found, zero is
+   returned.  */
+
+	.section .text.avx,"ax",@progbits
+ENTRY (STRCMP)
+# ifdef USE_AS_STRNCMP
+	/* Check for simple cases (0 or 1) in offset.  */
+	cmp	$1, %rdx
+	je	L(char0)
+	jb	L(zero)
+#  ifdef USE_AS_WCSCMP
+	/* Convert units: from wide to byte char.  */
+	shl	$2, %rdx
+#  endif
+	/* Register %r11 tracks the maximum offset.  */
+	movq	%rdx, %r11
+# endif
+	movl	%edi, %eax
+	xorl	%edx, %edx
+	/* Make %ymm7 all zeros in this function.  */
+	vpxor	%ymm7, %ymm7, %ymm7
+	orl	%esi, %eax
+	andl	$(PAGE_SIZE - 1), %eax
+	cmpl	$(PAGE_SIZE - (VEC_SIZE * 4)), %eax
+	jg	L(cross_page)
+	/* Start comparing 4 vectors.  */
+	vmovdqu	(%rdi), %ymm1
+	VPCMPEQ	(%rsi), %ymm1, %ymm0
+	VPMINU	%ymm1, %ymm0, %ymm0
+	VPCMPEQ	%ymm7, %ymm0, %ymm0
+	vpmovmskb %ymm0, %ecx
+	testl	%ecx, %ecx
+	je	L(next_3_vectors)
+	tzcntl	%ecx, %edx
+# ifdef USE_AS_STRNCMP
+	/* Return 0 if the mismatched index (%rdx) is after the maximum
+	   offset (%r11).   */
+	cmpq	%r11, %rdx
+	jae	L(zero)
+# endif
+# ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(%rdi, %rdx), %ecx
+	cmpl	(%rsi, %rdx), %ecx
+	je	L(return)
+L(wcscmp_return):
+	setl	%al
+	negl	%eax
+	orl	$1, %eax
+L(return):
+# else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %edx
+	subl	%edx, %eax
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(return_vec_size):
+	tzcntl	%ecx, %edx
+# ifdef USE_AS_STRNCMP
+	/* Return 0 if the mismatched index (%rdx + VEC_SIZE) is after
+	   the maximum offset (%r11).  */
+	addq	$VEC_SIZE, %rdx
+	cmpq	%r11, %rdx
+	jae	L(zero)
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(%rdi, %rdx), %ecx
+	cmpl	(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	VEC_SIZE(%rdi, %rdx), %ecx
+	cmpl	VEC_SIZE(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	VEC_SIZE(%rdi, %rdx), %eax
+	movzbl	VEC_SIZE(%rsi, %rdx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(return_2_vec_size):
+	tzcntl	%ecx, %edx
+# ifdef USE_AS_STRNCMP
+	/* Return 0 if the mismatched index (%rdx + 2 * VEC_SIZE) is
+	   after the maximum offset (%r11).  */
+	addq	$(VEC_SIZE * 2), %rdx
+	cmpq	%r11, %rdx
+	jae	L(zero)
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(%rdi, %rdx), %ecx
+	cmpl	(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(VEC_SIZE * 2)(%rdi, %rdx), %ecx
+	cmpl	(VEC_SIZE * 2)(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(VEC_SIZE * 2)(%rdi, %rdx), %eax
+	movzbl	(VEC_SIZE * 2)(%rsi, %rdx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(return_3_vec_size):
+	tzcntl	%ecx, %edx
+# ifdef USE_AS_STRNCMP
+	/* Return 0 if the mismatched index (%rdx + 3 * VEC_SIZE) is
+	   after the maximum offset (%r11).  */
+	addq	$(VEC_SIZE * 3), %rdx
+	cmpq	%r11, %rdx
+	jae	L(zero)
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(%rdi, %rdx), %ecx
+	cmpl	(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(VEC_SIZE * 3)(%rdi, %rdx), %ecx
+	cmpl	(VEC_SIZE * 3)(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(VEC_SIZE * 3)(%rdi, %rdx), %eax
+	movzbl	(VEC_SIZE * 3)(%rsi, %rdx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(next_3_vectors):
+	vmovdqu	VEC_SIZE(%rdi), %ymm6
+	VPCMPEQ	VEC_SIZE(%rsi), %ymm6, %ymm3
+	VPMINU	%ymm6, %ymm3, %ymm3
+	VPCMPEQ	%ymm7, %ymm3, %ymm3
+	vpmovmskb %ymm3, %ecx
+	testl	%ecx, %ecx
+	jne	L(return_vec_size)
+	vmovdqu	(VEC_SIZE * 2)(%rdi), %ymm5
+	vmovdqu	(VEC_SIZE * 3)(%rdi), %ymm4
+	vmovdqu	(VEC_SIZE * 3)(%rsi), %ymm0
+	VPCMPEQ	(VEC_SIZE * 2)(%rsi), %ymm5, %ymm2
+	VPMINU	%ymm5, %ymm2, %ymm2
+	VPCMPEQ	%ymm4, %ymm0, %ymm0
+	VPCMPEQ	%ymm7, %ymm2, %ymm2
+	vpmovmskb %ymm2, %ecx
+	testl	%ecx, %ecx
+	jne	L(return_2_vec_size)
+	VPMINU	%ymm4, %ymm0, %ymm0
+	VPCMPEQ	%ymm7, %ymm0, %ymm0
+	vpmovmskb %ymm0, %ecx
+	testl	%ecx, %ecx
+	jne	L(return_3_vec_size)
+L(main_loop_header):
+	leaq	(VEC_SIZE * 4)(%rdi), %rdx
+	movl	$PAGE_SIZE, %ecx
+	/* Align load via RAX.  */
+	andq	$-(VEC_SIZE * 4), %rdx
+	subq	%rdi, %rdx
+	leaq	(%rdi, %rdx), %rax
+# ifdef USE_AS_STRNCMP
+	/* Starting from this point, the maximum offset, or simply the
+	   'offset', DECREASES by the same amount when base pointers are
+	   moved forward.  Return 0 when:
+	     1) On match: offset <= the matched vector index.
+	     2) On mistmach, offset is before the mistmatched index.
+	 */
+	subq	%rdx, %r11
+	jbe	L(zero)
+# endif
+	addq	%rsi, %rdx
+	movq	%rdx, %rsi
+	andl	$(PAGE_SIZE - 1), %esi
+	/* Number of bytes before page crossing.  */
+	subq	%rsi, %rcx
+	/* Number of VEC_SIZE * 4 blocks before page crossing.  */
+	shrq	$DIVIDE_BY_VEC_4_SHIFT, %rcx
+	/* ESI: Number of VEC_SIZE * 4 blocks before page crossing.   */
+	movl	%ecx, %esi
+	jmp	L(loop_start)
+
+	.p2align 4
+L(loop):
+# ifdef USE_AS_STRNCMP
+	/* Base pointers are moved forward by 4 * VEC_SIZE.  Decrease
+	   the maximum offset (%r11) by the same amount.  */
+	subq	$(VEC_SIZE * 4), %r11
+	jbe	L(zero)
+# endif
+	addq	$(VEC_SIZE * 4), %rax
+	addq	$(VEC_SIZE * 4), %rdx
+L(loop_start):
+	testl	%esi, %esi
+	leal	-1(%esi), %esi
+	je	L(loop_cross_page)
+L(back_to_loop):
+	/* Main loop, comparing 4 vectors are a time.  */
+	vmovdqa	(%rax), %ymm0
+	vmovdqa	VEC_SIZE(%rax), %ymm3
+	VPCMPEQ	(%rdx), %ymm0, %ymm4
+	VPCMPEQ	VEC_SIZE(%rdx), %ymm3, %ymm1
+	VPMINU	%ymm0, %ymm4, %ymm4
+	VPMINU	%ymm3, %ymm1, %ymm1
+	vmovdqa	(VEC_SIZE * 2)(%rax), %ymm2
+	VPMINU	%ymm1, %ymm4, %ymm0
+	vmovdqa	(VEC_SIZE * 3)(%rax), %ymm3
+	VPCMPEQ	(VEC_SIZE * 2)(%rdx), %ymm2, %ymm5
+	VPCMPEQ	(VEC_SIZE * 3)(%rdx), %ymm3, %ymm6
+	VPMINU	%ymm2, %ymm5, %ymm5
+	VPMINU	%ymm3, %ymm6, %ymm6
+	VPMINU	%ymm5, %ymm0, %ymm0
+	VPMINU	%ymm6, %ymm0, %ymm0
+	VPCMPEQ	%ymm7, %ymm0, %ymm0
+
+	/* Test each mask (32 bits) individually because for VEC_SIZE
+	   == 32 is not possible to OR the four masks and keep all bits
+	   in a 64-bit integer register, differing from SSE2 strcmp
+	   where ORing is possible.  */
+	vpmovmskb %ymm0, %ecx
+	testl	%ecx, %ecx
+	je	L(loop)
+	VPCMPEQ	%ymm7, %ymm4, %ymm0
+	vpmovmskb %ymm0, %edi
+	testl	%edi, %edi
+	je	L(test_vec)
+	tzcntl	%edi, %ecx
+# ifdef USE_AS_STRNCMP
+	cmpq	%rcx, %r11
+	jbe	L(zero)
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rcx), %edi
+	cmpl	(%rdx, %rcx), %edi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rcx), %eax
+	movzbl	(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rcx), %edi
+	cmpl	(%rdx, %rcx), %edi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rcx), %eax
+	movzbl	(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(test_vec):
+# ifdef USE_AS_STRNCMP
+	/* The first vector matched.  Return 0 if the maximum offset
+	   (%r11) <= VEC_SIZE.  */
+	cmpq	$VEC_SIZE, %r11
+	jbe	L(zero)
+# endif
+	VPCMPEQ	%ymm7, %ymm1, %ymm1
+	vpmovmskb %ymm1, %ecx
+	testl	%ecx, %ecx
+	je	L(test_2_vec)
+	tzcntl	%ecx, %edi
+# ifdef USE_AS_STRNCMP
+	addq	$VEC_SIZE, %rdi
+	cmpq	%rdi, %r11
+	jbe	L(zero)
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rdi), %ecx
+	cmpl	(%rdx, %rdi), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rdi), %eax
+	movzbl	(%rdx, %rdi), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	VEC_SIZE(%rsi, %rdi), %ecx
+	cmpl	VEC_SIZE(%rdx, %rdi), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	VEC_SIZE(%rax, %rdi), %eax
+	movzbl	VEC_SIZE(%rdx, %rdi), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(test_2_vec):
+# ifdef USE_AS_STRNCMP
+	/* The first 2 vectors matched.  Return 0 if the maximum offset
+	   (%r11) <= 2 * VEC_SIZE.  */
+	cmpq	$(VEC_SIZE * 2), %r11
+	jbe	L(zero)
+# endif
+	VPCMPEQ	%ymm7, %ymm5, %ymm5
+	vpmovmskb %ymm5, %ecx
+	testl	%ecx, %ecx
+	je	L(test_3_vec)
+	tzcntl	%ecx, %edi
+# ifdef USE_AS_STRNCMP
+	addq	$(VEC_SIZE * 2), %rdi
+	cmpq	%rdi, %r11
+	jbe	L(zero)
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rdi), %ecx
+	cmpl	(%rdx, %rdi), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rdi), %eax
+	movzbl	(%rdx, %rdi), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(VEC_SIZE * 2)(%rsi, %rdi), %ecx
+	cmpl	(VEC_SIZE * 2)(%rdx, %rdi), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(VEC_SIZE * 2)(%rax, %rdi), %eax
+	movzbl	(VEC_SIZE * 2)(%rdx, %rdi), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(test_3_vec):
+# ifdef USE_AS_STRNCMP
+	/* The first 3 vectors matched.  Return 0 if the maximum offset
+	   (%r11) <= 3 * VEC_SIZE.  */
+	cmpq	$(VEC_SIZE * 3), %r11
+	jbe	L(zero)
+# endif
+	VPCMPEQ	%ymm7, %ymm6, %ymm6
+	vpmovmskb %ymm6, %esi
+	tzcntl	%esi, %ecx
+# ifdef USE_AS_STRNCMP
+	addq	$(VEC_SIZE * 3), %rcx
+	cmpq	%rcx, %r11
+	jbe	L(zero)
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rcx), %esi
+	cmpl	(%rdx, %rcx), %esi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rcx), %eax
+	movzbl	(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(VEC_SIZE * 3)(%rsi, %rcx), %esi
+	cmpl	(VEC_SIZE * 3)(%rdx, %rcx), %esi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(VEC_SIZE * 3)(%rax, %rcx), %eax
+	movzbl	(VEC_SIZE * 3)(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(loop_cross_page):
+	xorl	%r10d, %r10d
+	movq	%rdx, %rcx
+	/* Align load via RDX.  We load the extra ECX bytes which should
+	   be ignored.  */
+	andl	$((VEC_SIZE * 4) - 1), %ecx
+	/* R10 is -RCX.  */
+	subq	%rcx, %r10
+
+	/* This works only if VEC_SIZE * 2 == 64. */
+# if (VEC_SIZE * 2) != 64
+#  error (VEC_SIZE * 2) != 64
+# endif
+
+	/* Check if the first VEC_SIZE * 2 bytes should be ignored.  */
+	cmpl	$(VEC_SIZE * 2), %ecx
+	jge	L(loop_cross_page_2_vec)
+
+	vmovdqu	(%rax, %r10), %ymm2
+	vmovdqu	VEC_SIZE(%rax, %r10), %ymm3
+	VPCMPEQ	(%rdx, %r10), %ymm2, %ymm0
+	VPCMPEQ	VEC_SIZE(%rdx, %r10), %ymm3, %ymm1
+	VPMINU	%ymm2, %ymm0, %ymm0
+	VPMINU	%ymm3, %ymm1, %ymm1
+	VPCMPEQ	%ymm7, %ymm0, %ymm0
+	VPCMPEQ	%ymm7, %ymm1, %ymm1
+
+	vpmovmskb %ymm0, %edi
+	vpmovmskb %ymm1, %esi
+
+	salq	$32, %rsi
+	xorq	%rsi, %rdi
+
+	/* Since ECX < VEC_SIZE * 2, simply skip the first ECX bytes.  */
+	shrq	%cl, %rdi
+
+	testq	%rdi, %rdi
+	je	L(loop_cross_page_2_vec)
+	tzcntq	%rdi, %rcx
+# ifdef USE_AS_STRNCMP
+	cmpq	%rcx, %r11
+	jbe	L(zero)
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rcx), %edi
+	cmpl	(%rdx, %rcx), %edi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rcx), %eax
+	movzbl	(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rcx), %edi
+	cmpl	(%rdx, %rcx), %edi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rcx), %eax
+	movzbl	(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(loop_cross_page_2_vec):
+	/* The first VEC_SIZE * 2 bytes match or are ignored.  */
+	vmovdqu	(VEC_SIZE * 2)(%rax, %r10), %ymm2
+	vmovdqu	(VEC_SIZE * 3)(%rax, %r10), %ymm3
+	VPCMPEQ	(VEC_SIZE * 2)(%rdx, %r10), %ymm2, %ymm5
+	VPMINU	%ymm2, %ymm5, %ymm5
+	VPCMPEQ	(VEC_SIZE * 3)(%rdx, %r10), %ymm3, %ymm6
+	VPCMPEQ	%ymm7, %ymm5, %ymm5
+	VPMINU	%ymm3, %ymm6, %ymm6
+	VPCMPEQ	%ymm7, %ymm6, %ymm6
+
+	vpmovmskb %ymm5, %edi
+	vpmovmskb %ymm6, %esi
+
+	salq	$32, %rsi
+	xorq	%rsi, %rdi
+
+	xorl	%r8d, %r8d
+	/* If ECX > VEC_SIZE * 2, skip ECX - (VEC_SIZE * 2) bytes.  */
+	subl	$(VEC_SIZE * 2), %ecx
+	jle	1f
+	/* Skip ECX bytes.  */
+	shrq	%cl, %rdi
+	/* R8 has number of bytes skipped.  */
+	movl	%ecx, %r8d
+1:
+	/* Before jumping back to the loop, set ESI to the number of
+	   VEC_SIZE * 4 blocks before page crossing.  */
+	movl	$(PAGE_SIZE / (VEC_SIZE * 4) - 1), %esi
+
+	testq	%rdi, %rdi
+	je	L(back_to_loop)
+	tzcntq	%rdi, %rcx
+	addq	%r10, %rcx
+	/* Adjust for number of bytes skipped.  */
+	addq	%r8, %rcx
+# ifdef USE_AS_STRNCMP
+	addq	$(VEC_SIZE * 2), %rcx
+	subq	%rcx, %r11
+	jbe	L(zero)
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(%rsi, %rcx), %edi
+	cmpl	(%rdx, %rcx), %edi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rax, %rcx), %eax
+	movzbl	(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# else
+#  ifdef USE_AS_WCSCMP
+	movq	%rax, %rsi
+	xorl	%eax, %eax
+	movl	(VEC_SIZE * 2)(%rsi, %rcx), %edi
+	cmpl	(VEC_SIZE * 2)(%rdx, %rcx), %edi
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(VEC_SIZE * 2)(%rax, %rcx), %eax
+	movzbl	(VEC_SIZE * 2)(%rdx, %rcx), %edx
+	subl	%edx, %eax
+#  endif
+# endif
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(cross_page_loop):
+	/* Check one byte/dword at a time.  */
+# ifdef USE_AS_WCSCMP
+	cmpl	%ecx, %eax
+# else
+	subl	%ecx, %eax
+# endif
+	jne	L(different)
+	addl	$SIZE_OF_CHAR, %edx
+	cmpl	$(VEC_SIZE * 4), %edx
+	je	L(main_loop_header)
+# ifdef USE_AS_STRNCMP
+	cmpq	%r11, %rdx
+	jae	L(zero)
+# endif
+# ifdef USE_AS_WCSCMP
+	movl	(%rdi, %rdx), %eax
+	movl	(%rsi, %rdx), %ecx
+# else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %ecx
+# endif
+	/* Check null char.  */
+	testl	%eax, %eax
+	jne	L(cross_page_loop)
+	/* Since %eax == 0, subtract is OK for both SIGNED and UNSIGNED
+	   comparisons.  */
+	subl	%ecx, %eax
+# ifndef USE_AS_WCSCMP
+L(different):
+# endif
+	VZEROUPPER
+	ret
+
+# ifdef USE_AS_WCSCMP
+	.p2align 4
+L(different):
+	/* Use movl to avoid modifying EFLAGS.  */
+	movl	$0, %eax
+	setl	%al
+	negl	%eax
+	orl	$1, %eax
+	VZEROUPPER
+	ret
+# endif
+
+# ifdef USE_AS_STRNCMP
+	.p2align 4
+L(zero):
+	xorl	%eax, %eax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(char0):
+#  ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(%rdi), %ecx
+	cmpl	(%rsi), %ecx
+	jne	L(wcscmp_return)
+#  else
+	movzbl	(%rsi), %ecx
+	movzbl	(%rdi), %eax
+	subl	%ecx, %eax
+#  endif
+	VZEROUPPER
+	ret
+# endif
+
+	.p2align 4
+L(last_vector):
+	addq	%rdx, %rdi
+	addq	%rdx, %rsi
+# ifdef USE_AS_STRNCMP
+	subq	%rdx, %r11
+# endif
+	tzcntl	%ecx, %edx
+# ifdef USE_AS_STRNCMP
+	cmpq	%r11, %rdx
+	jae	L(zero)
+# endif
+# ifdef USE_AS_WCSCMP
+	xorl	%eax, %eax
+	movl	(%rdi, %rdx), %ecx
+	cmpl	(%rsi, %rdx), %ecx
+	jne	L(wcscmp_return)
+# else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %edx
+	subl	%edx, %eax
+# endif
+	VZEROUPPER
+	ret
+
+	/* Comparing on page boundary region requires special treatment:
+	   It must done one vector at the time, starting with the wider
+	   ymm vector if possible, if not, with xmm. If fetching 16 bytes
+	   (xmm) still passes the boundary, byte comparison must be done.
+	 */
+	.p2align 4
+L(cross_page):
+	/* Try one ymm vector at a time.  */
+	cmpl	$(PAGE_SIZE - VEC_SIZE), %eax
+	jg	L(cross_page_1_vector)
+L(loop_1_vector):
+	vmovdqu	(%rdi, %rdx), %ymm1
+	VPCMPEQ	(%rsi, %rdx), %ymm1, %ymm0
+	VPMINU	%ymm1, %ymm0, %ymm0
+	VPCMPEQ	%ymm7, %ymm0, %ymm0
+	vpmovmskb %ymm0, %ecx
+	testl	%ecx, %ecx
+	jne	L(last_vector)
+
+	addl	$VEC_SIZE, %edx
+
+	addl	$VEC_SIZE, %eax
+# ifdef USE_AS_STRNCMP
+	/* Return 0 if the current offset (%rdx) >= the maximum offset
+	   (%r11).  */
+	cmpq	%r11, %rdx
+	jae	L(zero)
+# endif
+	cmpl	$(PAGE_SIZE - VEC_SIZE), %eax
+	jle	L(loop_1_vector)
+L(cross_page_1_vector):
+	/* Less than 32 bytes to check, try one xmm vector.  */
+	cmpl	$(PAGE_SIZE - 16), %eax
+	jg	L(cross_page_1_xmm)
+	vmovdqu	(%rdi, %rdx), %xmm1
+	VPCMPEQ	(%rsi, %rdx), %xmm1, %xmm0
+	VPMINU	%xmm1, %xmm0, %xmm0
+	VPCMPEQ	%xmm7, %xmm0, %xmm0
+	vpmovmskb %xmm0, %ecx
+	testl	%ecx, %ecx
+	jne	L(last_vector)
+
+	addl	$16, %edx
+# ifndef USE_AS_WCSCMP
+	addl	$16, %eax
+# endif
+# ifdef USE_AS_STRNCMP
+	/* Return 0 if the current offset (%rdx) >= the maximum offset
+	   (%r11).  */
+	cmpq	%r11, %rdx
+	jae	L(zero)
+# endif
+
+L(cross_page_1_xmm):
+# ifndef USE_AS_WCSCMP
+	/* Less than 16 bytes to check, try 8 byte vector.  NB: No need
+	   for wcscmp nor wcsncmp since wide char is 4 bytes.   */
+	cmpl	$(PAGE_SIZE - 8), %eax
+	jg	L(cross_page_8bytes)
+	vmovq	(%rdi, %rdx), %xmm1
+	vmovq	(%rsi, %rdx), %xmm0
+	VPCMPEQ	%xmm0, %xmm1, %xmm0
+	VPMINU	%xmm1, %xmm0, %xmm0
+	VPCMPEQ	%xmm7, %xmm0, %xmm0
+	vpmovmskb %xmm0, %ecx
+	/* Only last 8 bits are valid.  */
+	andl	$0xff, %ecx
+	testl	%ecx, %ecx
+	jne	L(last_vector)
+
+	addl	$8, %edx
+	addl	$8, %eax
+#  ifdef USE_AS_STRNCMP
+	/* Return 0 if the current offset (%rdx) >= the maximum offset
+	   (%r11).  */
+	cmpq	%r11, %rdx
+	jae	L(zero)
+#  endif
+
+L(cross_page_8bytes):
+	/* Less than 8 bytes to check, try 4 byte vector.  */
+	cmpl	$(PAGE_SIZE - 4), %eax
+	jg	L(cross_page_4bytes)
+	vmovd	(%rdi, %rdx), %xmm1
+	vmovd	(%rsi, %rdx), %xmm0
+	VPCMPEQ	%xmm0, %xmm1, %xmm0
+	VPMINU	%xmm1, %xmm0, %xmm0
+	VPCMPEQ	%xmm7, %xmm0, %xmm0
+	vpmovmskb %xmm0, %ecx
+	/* Only last 4 bits are valid.  */
+	andl	$0xf, %ecx
+	testl	%ecx, %ecx
+	jne	L(last_vector)
+
+	addl	$4, %edx
+#  ifdef USE_AS_STRNCMP
+	/* Return 0 if the current offset (%rdx) >= the maximum offset
+	   (%r11).  */
+	cmpq	%r11, %rdx
+	jae	L(zero)
+#  endif
+
+L(cross_page_4bytes):
+# endif
+	/* Less than 4 bytes to check, try one byte/dword at a time.  */
+# ifdef USE_AS_STRNCMP
+	cmpq	%r11, %rdx
+	jae	L(zero)
+# endif
+# ifdef USE_AS_WCSCMP
+	movl	(%rdi, %rdx), %eax
+	movl	(%rsi, %rdx), %ecx
+# else
+	movzbl	(%rdi, %rdx), %eax
+	movzbl	(%rsi, %rdx), %ecx
+# endif
+	testl	%eax, %eax
+	jne	L(cross_page_loop)
+	subl	%ecx, %eax
+	VZEROUPPER
+	ret
+END (STRCMP)
+#endif