x86-64: Optimize memrchr with AVX2

Optimize memrchr with AVX2 to search 32 bytes with a single vector
compare instruction.  It is as fast as SSE2 memrchr for small data
sizes and up to 1X faster for large data sizes on Haswell.  Select
AVX2 memrchr on AVX2 machines where vzeroupper is preferred and AVX
unaligned load is fast.

	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
	memrchr-sse2 and memrchr-avx2.
	* sysdeps/x86_64/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Add tests for __memrchr_avx2 and
	__memrchr_sse2.
	* sysdeps/x86_64/multiarch/memrchr-avx2.S: New file.
	* sysdeps/x86_64/multiarch/memrchr-sse2.S: Likewise.
	* sysdeps/x86_64/multiarch/memrchr.c: Likewise.

5 files changed, 424 insertions, 0 deletions

diff --git a/sysdeps/x86_64/multiarch/Makefile b/sysdeps/x86_64/multiarch/Makefile
index 4523f51095..2fa390b3dd 100644
--- a/sysdeps/x86_64/multiarch/Makefile
+++ b/sysdeps/x86_64/multiarch/Makefile
@@ -7,6 +7,7 @@ ifeq ($(subdir),string)
 sysdep_routines += strncat-c stpncpy-c strncpy-c strcmp-ssse3 \
 		   strcmp-sse2-unaligned strncmp-ssse3 \
 		   memchr-sse2 rawmemchr-sse2 memchr-avx2 rawmemchr-avx2 \
+		   memrchr-sse2 memrchr-avx2 \
 		   memcmp-avx2-movbe \
 		   memcmp-sse4 memcpy-ssse3 \
 		   memmove-ssse3 \
diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index 8dda1b040a..5670eb7e9e 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -112,6 +112,13 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 	      IFUNC_IMPL_ADD (array, i, memmove, 1,
 			      __memmove_sse2_unaligned_erms))
 
+  /* Support sysdeps/x86_64/multiarch/memrchr.S.  */
+  IFUNC_IMPL (i, name, memrchr,
+	      IFUNC_IMPL_ADD (array, i, memrchr,
+			      HAS_ARCH_FEATURE (AVX2_Usable),
+			      __memrchr_avx2)
+	      IFUNC_IMPL_ADD (array, i, memrchr, 1, __memrchr_sse2))
+
   /* Support sysdeps/x86_64/multiarch/memset_chk.S.  */
   IFUNC_IMPL (i, name, __memset_chk,
 	      IFUNC_IMPL_ADD (array, i, __memset_chk, 1,
diff --git a/sysdeps/x86_64/multiarch/memrchr-avx2.S b/sysdeps/x86_64/multiarch/memrchr-avx2.S
new file mode 100644
index 0000000000..3ee02e1cc3
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memrchr-avx2.S
@@ -0,0 +1,359 @@
+/* memrchr 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)
+
+# include <sysdep.h>
+
+# ifndef VZEROUPPER
+#  define VZEROUPPER	vzeroupper
+# endif
+
+# define VEC_SIZE 32
+
+	.section .text.avx,"ax",@progbits
+ENTRY (__memrchr_avx2)
+	/* Broadcast CHAR to YMM0.  */
+	vmovd	%esi, %xmm0
+	vpbroadcastb %xmm0, %ymm0
+
+	subq	$VEC_SIZE, %rdx
+	jbe	L(last_vec_or_less)
+
+	addq	%rdx, %rdi
+
+	/* Check the last VEC_SIZE bytes.  */
+	vpcmpeqb (%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x0)
+
+	subq	$(VEC_SIZE * 4), %rdi
+	movl	%edi, %ecx
+	andl	$(VEC_SIZE - 1), %ecx
+	jz	L(aligned_more)
+
+	/* Align data for aligned loads in the loop.  */
+	addq	$VEC_SIZE, %rdi
+	addq	$VEC_SIZE, %rdx
+	andq	$-VEC_SIZE, %rdi
+	subq	%rcx, %rdx
+
+	.p2align 4
+L(aligned_more):
+	subq	$(VEC_SIZE * 4), %rdx
+	jbe	L(last_4x_vec_or_less)
+
+	/* Check the last 4 * VEC_SIZE.  Only one VEC_SIZE at a time
+	   since data is only aligned to VEC_SIZE.  */
+	vpcmpeqb (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x3)
+
+	vpcmpeqb (VEC_SIZE * 2)(%rdi), %ymm0, %ymm2
+	vpmovmskb %ymm2, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x2)
+
+	vpcmpeqb VEC_SIZE(%rdi), %ymm0, %ymm3
+	vpmovmskb %ymm3, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x1)
+
+	vpcmpeqb (%rdi), %ymm0, %ymm4
+	vpmovmskb %ymm4, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x0)
+
+	/* Align data to 4 * VEC_SIZE for loop with fewer branches.
+	   There are some overlaps with above if data isn't aligned
+	   to 4 * VEC_SIZE.  */
+	movl	%edi, %ecx
+	andl	$(VEC_SIZE * 4 - 1), %ecx
+	jz	L(loop_4x_vec)
+
+	addq	$(VEC_SIZE * 4), %rdi
+	addq	$(VEC_SIZE * 4), %rdx
+	andq	$-(VEC_SIZE * 4), %rdi
+	subq	%rcx, %rdx
+
+	.p2align 4
+L(loop_4x_vec):
+	/* Compare 4 * VEC at a time forward.  */
+	subq	$(VEC_SIZE * 4), %rdi
+	subq	$(VEC_SIZE * 4), %rdx
+	jbe	L(last_4x_vec_or_less)
+
+	vmovdqa	(%rdi), %ymm1
+	vmovdqa	VEC_SIZE(%rdi), %ymm2
+	vmovdqa	(VEC_SIZE * 2)(%rdi), %ymm3
+	vmovdqa	(VEC_SIZE * 3)(%rdi), %ymm4
+
+	vpcmpeqb %ymm1, %ymm0, %ymm1
+	vpcmpeqb %ymm2, %ymm0, %ymm2
+	vpcmpeqb %ymm3, %ymm0, %ymm3
+	vpcmpeqb %ymm4, %ymm0, %ymm4
+
+	vpor	%ymm1, %ymm2, %ymm5
+	vpor	%ymm3, %ymm4, %ymm6
+	vpor	%ymm5, %ymm6, %ymm5
+
+	vpmovmskb %ymm5, %eax
+	testl	%eax, %eax
+	jz	L(loop_4x_vec)
+
+	/* There is a match.  */
+	vpmovmskb %ymm4, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x3)
+
+	vpmovmskb %ymm3, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x2)
+
+	vpmovmskb %ymm2, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x1)
+
+	vpmovmskb %ymm1, %eax
+	bsrl	%eax, %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_4x_vec_or_less):
+	addl	$(VEC_SIZE * 4), %edx
+	cmpl	$(VEC_SIZE * 2), %edx
+	jbe	L(last_2x_vec)
+
+	vpcmpeqb (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x3)
+
+	vpcmpeqb (VEC_SIZE * 2)(%rdi), %ymm0, %ymm2
+	vpmovmskb %ymm2, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x2)
+
+	vpcmpeqb VEC_SIZE(%rdi), %ymm0, %ymm3
+	vpmovmskb %ymm3, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x1_check)
+	cmpl	$(VEC_SIZE * 3), %edx
+	jbe	L(zero)
+
+	vpcmpeqb (%rdi), %ymm0, %ymm4
+	vpmovmskb %ymm4, %eax
+	testl	%eax, %eax
+	jz	L(zero)
+	bsrl	%eax, %eax
+	subq	$(VEC_SIZE * 4), %rdx
+	addq	%rax, %rdx
+	jl	L(zero)
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_2x_vec):
+	vpcmpeqb (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x3_check)
+	cmpl	$VEC_SIZE, %edx
+	jbe	L(zero)
+
+	vpcmpeqb (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jz	L(zero)
+	bsrl	%eax, %eax
+	subq	$(VEC_SIZE * 2), %rdx
+	addq	%rax, %rdx
+	jl	L(zero)
+	addl	$(VEC_SIZE * 2), %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_x0):
+	bsrl	%eax, %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_x1):
+	bsrl	%eax, %eax
+	addl	$VEC_SIZE, %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_x2):
+	bsrl	%eax, %eax
+	addl	$(VEC_SIZE * 2), %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_x3):
+	bsrl	%eax, %eax
+	addl	$(VEC_SIZE * 3), %eax
+	addq	%rdi, %rax
+	ret
+
+	.p2align 4
+L(last_vec_x1_check):
+	bsrl	%eax, %eax
+	subq	$(VEC_SIZE * 3), %rdx
+	addq	%rax, %rdx
+	jl	L(zero)
+	addl	$VEC_SIZE, %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_x3_check):
+	bsrl	%eax, %eax
+	subq	$VEC_SIZE, %rdx
+	addq	%rax, %rdx
+	jl	L(zero)
+	addl	$(VEC_SIZE * 3), %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(zero):
+	VZEROUPPER
+L(null):
+	xorl	%eax, %eax
+	ret
+
+	.p2align 4
+L(last_vec_or_less_aligned):
+	movl	%edx, %ecx
+
+	vpcmpeqb (%rdi), %ymm0, %ymm1
+
+	movl	$1, %edx
+	/* Support rdx << 32.  */
+	salq	%cl, %rdx
+	subq	$1, %rdx
+
+	vpmovmskb %ymm1, %eax
+
+	/* Remove the trailing bytes.  */
+	andl	%edx, %eax
+	testl	%eax, %eax
+	jz	L(zero)
+
+	bsrl	%eax, %eax
+	addq	%rdi, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_or_less):
+	addl	$VEC_SIZE, %edx
+
+	/* Check for zero length.  */
+	testl	%edx, %edx
+	jz	L(null)
+
+	movl	%edi, %ecx
+	andl	$(VEC_SIZE - 1), %ecx
+	jz	L(last_vec_or_less_aligned)
+
+	movl	%ecx, %esi
+	movl	%ecx, %r8d
+	addl	%edx, %esi
+	andq	$-VEC_SIZE, %rdi
+
+	subl	$VEC_SIZE, %esi
+	ja	L(last_vec_2x_aligned)
+
+	/* Check the last VEC.  */
+	vpcmpeqb (%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+
+	/* Remove the leading and trailing bytes.  */
+	sarl	%cl, %eax
+	movl	%edx, %ecx
+
+	movl	$1, %edx
+	sall	%cl, %edx
+	subl	$1, %edx
+
+	andl	%edx, %eax
+	testl	%eax, %eax
+	jz	L(zero)
+
+	bsrl	%eax, %eax
+	addq	%rdi, %rax
+	addq	%r8, %rax
+	VZEROUPPER
+	ret
+
+	.p2align 4
+L(last_vec_2x_aligned):
+	movl	%esi, %ecx
+
+	/* Check the last VEC.  */
+	vpcmpeqb VEC_SIZE(%rdi), %ymm0, %ymm1
+
+	movl	$1, %edx
+	sall	%cl, %edx
+	subl	$1, %edx
+
+	vpmovmskb %ymm1, %eax
+
+	/* Remove the trailing bytes.  */
+	andl	%edx, %eax
+
+	testl	%eax, %eax
+	jnz	L(last_vec_x1)
+
+	/* Check the second last VEC.  */
+	vpcmpeqb (%rdi), %ymm0, %ymm1
+
+	movl	%r8d, %ecx
+
+	vpmovmskb %ymm1, %eax
+
+	/* Remove the leading bytes.  Must use unsigned right shift for
+	   bsrl below.  */
+	shrl	%cl, %eax
+	testl	%eax, %eax
+	jz	L(zero)
+
+	bsrl	%eax, %eax
+	addq	%rdi, %rax
+	addq	%r8, %rax
+	VZEROUPPER
+	ret
+END (__memrchr_avx2)
+#endif
diff --git a/sysdeps/x86_64/multiarch/memrchr-sse2.S b/sysdeps/x86_64/multiarch/memrchr-sse2.S
new file mode 100644
index 0000000000..f518819c87
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memrchr-sse2.S
@@ -0,0 +1,26 @@
+/* memrchr optimized with SSE2.
+   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)
+# define __memrchr __memrchr_sse2
+
+# undef weak_alias
+# define weak_alias(__memrchr, memrchr)
+#endif
+
+#include "../memrchr.S"
diff --git a/sysdeps/x86_64/multiarch/memrchr.c b/sysdeps/x86_64/multiarch/memrchr.c
new file mode 100644
index 0000000000..003d403106
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memrchr.c
@@ -0,0 +1,31 @@
+/* Multiple versions of memrchr
+   All versions must be listed in ifunc-impl-list.c.
+   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/>.  */
+
+/* Define multiple versions only for the definition in libc. */
+#if IS_IN (libc)
+# define memrchr __redirect_memrchr
+# include <string.h>
+# undef memrchr
+
+# define SYMBOL_NAME memrchr
+# include "ifunc-avx2.h"
+
+libc_ifunc_redirected (__redirect_memrchr, __memrchr, IFUNC_SELECTOR ());
+weak_alias (__memrchr, memrchr)
+#endif