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.

1 files changed, 425 insertions, 0 deletions

diff --git a/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S b/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S
new file mode 100644
index 0000000000..47630dd97b
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memcmp-avx2-movbe.S
@@ -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