x86_64: Implement evex512 version of strlen, strnlen, wcslen and wcsnlen

This patch implements following evex512 version of string functions.
Perf gain for evex512 version is up to 50% as compared to evex,
depending on length and alignment.

Placeholder function, not used by any processor at the moment.

- String length function using 512 bit vectors.
- String N length using 512 bit vectors.
- Wide string length using 512 bit vectors.
- Wide string N length using 512 bit vectors.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
(cherry picked from commit 9c66efb86f)

sysdeps/x86_64/multiarch/Makefile

@@ -87,6 +87,7 @@ sysdep_routines += \
   strlen-avx2 \
   strlen-avx2-rtm \
   strlen-evex \
+  strlen-evex512 \
   strlen-sse2 \
   strncase_l-avx2 \
   strncase_l-avx2-rtm \
@@ -115,6 +116,7 @@ sysdep_routines += \
   strnlen-avx2 \
   strnlen-avx2-rtm \
   strnlen-evex \
+  strnlen-evex512 \
   strnlen-sse2 \
   strpbrk-c \
   strpbrk-sse2 \
@@ -148,6 +150,7 @@ sysdep_routines += \
   wcslen-avx2 \
   wcslen-avx2-rtm \
   wcslen-evex \
+  wcslen-evex512 \
   wcslen-sse2 \
   wcslen-sse4_1 \
   wcsncmp-avx2 \
@@ -158,6 +161,7 @@ sysdep_routines += \
   wcsnlen-avx2-rtm \
   wcsnlen-c \
   wcsnlen-evex \
+  wcsnlen-evex512 \
   wcsnlen-sse4_1 \
   wcsrchr-avx2 \
   wcsrchr-avx2-rtm \

sysdeps/x86_64/multiarch/ifunc-impl-list.c

@@ -317,6 +317,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __strlen_evex)
+	      IFUNC_IMPL_ADD (array, i, strlen,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __strlen_evex512)
 	      IFUNC_IMPL_ADD (array, i, strlen, 1, __strlen_sse2))
 
   /* Support sysdeps/x86_64/multiarch/strnlen.c.  */
@@ -335,6 +340,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __strnlen_evex)
+	      IFUNC_IMPL_ADD (array, i, strnlen,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __strnlen_evex512)
 	      IFUNC_IMPL_ADD (array, i, strnlen, 1, __strnlen_sse2))
 
   /* Support sysdeps/x86_64/multiarch/stpncpy.c.  */
@@ -714,6 +724,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wcslen_evex)
+	      IFUNC_IMPL_ADD (array, i, wcslen,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __wcslen_evex512)
 	      IFUNC_IMPL_ADD (array, i, wcslen,
 			      CPU_FEATURE_USABLE (SSE4_1),
 			      __wcslen_sse4_1)
@@ -735,6 +750,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wcsnlen_evex)
+	      IFUNC_IMPL_ADD (array, i, wcsnlen,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __wcsnlen_evex512)
 	      IFUNC_IMPL_ADD (array, i, wcsnlen,
 			      CPU_FEATURE_USABLE (SSE4_1),
 			      __wcsnlen_sse4_1)

sysdeps/x86_64/multiarch/strlen-evex-base.S

@@ -0,0 +1,302 @@
+/* Placeholder function, not used by any processor at the moment.
+   Copyright (C) 2022 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
+   <https://www.gnu.org/licenses/>.  */
+
+#if IS_IN (libc)
+
+# include <sysdep.h>
+
+# ifdef USE_AS_WCSLEN
+#  define VPCMP		vpcmpd
+#  define VPTESTN	vptestnmd
+#  define VPMINU	vpminud
+#  define CHAR_SIZE	4
+# else
+#  define VPCMP		vpcmpb
+#  define VPTESTN	vptestnmb
+#  define VPMINU	vpminub
+#  define CHAR_SIZE	1
+# endif
+
+# define XMM0		xmm16
+# define PAGE_SIZE	4096
+# define CHAR_PER_VEC	(VEC_SIZE / CHAR_SIZE)
+
+# if VEC_SIZE == 64
+#  define KMOV		kmovq
+#  define KORTEST	kortestq
+#  define RAX		rax
+#  define RCX		rcx
+#  define RDX		rdx
+#  define SHR		shrq
+#  define TEXTSUFFIX	evex512
+#  define VMM0		zmm16
+#  define VMM1		zmm17
+#  define VMM2		zmm18
+#  define VMM3		zmm19
+#  define VMM4		zmm20
+#  define VMOVA		vmovdqa64
+# elif VEC_SIZE == 32
+/* Currently Unused.  */
+#  define KMOV		kmovd
+#  define KORTEST	kortestd
+#  define RAX		eax
+#  define RCX		ecx
+#  define RDX		edx
+#  define SHR		shrl
+#  define TEXTSUFFIX	evex256
+#  define VMM0		ymm16
+#  define VMM1		ymm17
+#  define VMM2		ymm18
+#  define VMM3		ymm19
+#  define VMM4		ymm20
+#  define VMOVA		vmovdqa32
+# endif
+
+	.section .text.TEXTSUFFIX, "ax", @progbits
+/* Aligning entry point to 64 byte, provides better performance for
+   one vector length string.  */
+ENTRY_P2ALIGN (STRLEN, 6)
+# ifdef USE_AS_STRNLEN
+	/* Check zero length.  */
+	test	%RSI_LP, %RSI_LP
+	jz	L(ret_max)
+#  ifdef __ILP32__
+	/* Clear the upper 32 bits.  */
+	movl	%esi, %esi
+#  endif
+# endif
+
+	movl	%edi, %eax
+	vpxorq	%XMM0, %XMM0, %XMM0
+	andl	$(PAGE_SIZE - 1), %eax
+	cmpl	$(PAGE_SIZE - VEC_SIZE), %eax
+	ja	L(page_cross)
+
+	/* Compare [w]char for null, mask bit will be set for match.  */
+	VPCMP	$0, (%rdi), %VMM0, %k0
+	KMOV	%k0, %RAX
+	test	%RAX, %RAX
+	jz	L(align_more)
+
+	bsf	%RAX, %RAX
+# ifdef USE_AS_STRNLEN
+	cmpq	%rsi, %rax
+	cmovnb	%rsi, %rax
+# endif
+	ret
+
+	/* At this point vector max length reached.  */
+# ifdef USE_AS_STRNLEN
+	.p2align 4,,3
+L(ret_max):
+	movq	%rsi, %rax
+	ret
+# endif
+
+L(align_more):
+	leaq	VEC_SIZE(%rdi), %rax
+	/* Align rax to VEC_SIZE.  */
+	andq	$-VEC_SIZE, %rax
+# ifdef USE_AS_STRNLEN
+	movq	%rax, %rdx
+	subq	%rdi, %rdx
+#  ifdef USE_AS_WCSLEN
+	SHR	$2, %RDX
+#  endif
+	/* At this point rdx contains [w]chars already compared.  */
+	subq	%rsi, %rdx
+	jae	L(ret_max)
+	negq	%rdx
+	/* At this point rdx contains number of w[char] needs to go.
+	   Now onwards rdx will keep decrementing with each compare.  */
+# endif
+
+	/* Loop unroll 4 times for 4 vector loop.  */
+	VPCMP	$0, (%rax), %VMM0, %k0
+	KMOV	%k0, %RCX
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x1)
+
+# ifdef USE_AS_STRNLEN
+	subq	$CHAR_PER_VEC, %rdx
+	jbe	L(ret_max)
+# endif
+
+	VPCMP	$0, VEC_SIZE(%rax), %VMM0, %k0
+	KMOV	%k0, %RCX
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x2)
+
+# ifdef USE_AS_STRNLEN
+	subq	$CHAR_PER_VEC, %rdx
+	jbe	L(ret_max)
+# endif
+
+	VPCMP	$0, (VEC_SIZE * 2)(%rax), %VMM0, %k0
+	KMOV	%k0, %RCX
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x3)
+
+# ifdef USE_AS_STRNLEN
+	subq	$CHAR_PER_VEC, %rdx
+	jbe	L(ret_max)
+# endif
+
+	VPCMP	$0, (VEC_SIZE * 3)(%rax), %VMM0, %k0
+	KMOV	%k0, %RCX
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x4)
+
+# ifdef USE_AS_STRNLEN
+	subq	$CHAR_PER_VEC, %rdx
+	jbe	L(ret_max)
+	/* Save pointer before 4 x VEC_SIZE alignment.  */
+	movq	%rax, %rcx
+# endif
+
+	/* Align address to VEC_SIZE * 4 for loop.  */
+	andq	$-(VEC_SIZE * 4), %rax
+
+# ifdef USE_AS_STRNLEN
+	subq	%rax, %rcx
+#  ifdef USE_AS_WCSLEN
+	SHR	$2, %RCX
+#  endif
+	/* rcx contains number of [w]char will be recompared due to
+	   alignment fixes.  rdx must be incremented by rcx to offset
+	   alignment adjustment.  */
+	addq	%rcx, %rdx
+	/* Need jump as we don't want to add/subtract rdx for first
+	   iteration of 4 x VEC_SIZE aligned loop.  */
+	jmp	L(loop_entry)
+# endif
+
+	.p2align 4,,11
+L(loop):
+# ifdef USE_AS_STRNLEN
+	subq	$(CHAR_PER_VEC * 4), %rdx
+	jbe	L(ret_max)
+L(loop_entry):
+# endif
+	/* VPMINU and VPCMP combination provide better performance as
+	   compared to alternative combinations.  */
+	VMOVA	(VEC_SIZE * 4)(%rax), %VMM1
+	VPMINU	(VEC_SIZE * 5)(%rax), %VMM1, %VMM2
+	VMOVA	(VEC_SIZE * 6)(%rax), %VMM3
+	VPMINU	(VEC_SIZE * 7)(%rax), %VMM3, %VMM4
+
+	VPTESTN	%VMM2, %VMM2, %k0
+	VPTESTN	%VMM4, %VMM4, %k1
+
+	subq	$-(VEC_SIZE * 4), %rax
+	KORTEST	%k0, %k1
+	jz	L(loop)
+
+	VPTESTN	%VMM1, %VMM1, %k2
+	KMOV	%k2, %RCX
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x1)
+
+	KMOV	%k0, %RCX
+	/* At this point, if k0 is non zero, null char must be in the
+	   second vector.  */
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x2)
+
+	VPTESTN	%VMM3, %VMM3, %k3
+	KMOV	%k3, %RCX
+	test	%RCX, %RCX
+	jnz	L(ret_vec_x3)
+	/* At this point null [w]char must be in the fourth vector so no
+	   need to check.  */
+	KMOV	%k1, %RCX
+
+	/* Fourth, third, second vector terminating are pretty much
+	   same, implemented this way to avoid branching and reuse code
+	   from pre loop exit condition.  */
+L(ret_vec_x4):
+	bsf	%RCX, %RCX
+	subq	%rdi, %rax
+# ifdef USE_AS_WCSLEN
+	subq	$-(VEC_SIZE * 3), %rax
+	shrq	$2, %rax
+	addq	%rcx, %rax
+# else
+	leaq	(VEC_SIZE * 3)(%rcx, %rax), %rax
+# endif
+# ifdef USE_AS_STRNLEN
+	cmpq	%rsi, %rax
+	cmovnb	%rsi, %rax
+# endif
+	ret
+
+L(ret_vec_x3):
+	bsf	%RCX, %RCX
+	subq	%rdi, %rax
+# ifdef USE_AS_WCSLEN
+	subq	$-(VEC_SIZE * 2), %rax
+	shrq	$2, %rax
+	addq	%rcx, %rax
+# else
+	leaq	(VEC_SIZE * 2)(%rcx, %rax), %rax
+# endif
+# ifdef USE_AS_STRNLEN
+	cmpq	%rsi, %rax
+	cmovnb	%rsi, %rax
+# endif
+	ret
+
+L(ret_vec_x2):
+	subq	$-VEC_SIZE, %rax
+L(ret_vec_x1):
+	bsf	%RCX, %RCX
+	subq	%rdi, %rax
+# ifdef USE_AS_WCSLEN
+	shrq	$2, %rax
+# endif
+	addq	%rcx, %rax
+# ifdef USE_AS_STRNLEN
+	cmpq	%rsi, %rax
+	cmovnb	%rsi, %rax
+# endif
+	ret
+
+L(page_cross):
+	movl	%eax, %ecx
+# ifdef USE_AS_WCSLEN
+	andl	$(VEC_SIZE - 1), %ecx
+	sarl	$2, %ecx
+# endif
+	/* ecx contains number of w[char] to be skipped as a result
+	   of address alignment.  */
+	xorq	%rdi, %rax
+	VPCMP	$0, (PAGE_SIZE - VEC_SIZE)(%rax), %VMM0, %k0
+	KMOV	%k0, %RAX
+	/* Ignore number of character for alignment adjustment.  */
+	SHR	%cl, %RAX
+	jz	L(align_more)
+
+	bsf	%RAX, %RAX
+# ifdef USE_AS_STRNLEN
+	cmpq	%rsi, %rax
+	cmovnb	%rsi, %rax
+# endif
+	ret
+
+END (STRLEN)
+#endif

sysdeps/x86_64/multiarch/strlen-evex512.S

@@ -0,0 +1,7 @@
+#ifndef STRLEN
+# define STRLEN		__strlen_evex512
+#endif
+
+#define VEC_SIZE	64
+
+#include "strlen-evex-base.S"

sysdeps/x86_64/multiarch/strnlen-evex512.S

@@ -0,0 +1,4 @@
+#define STRLEN __strnlen_evex512
+#define USE_AS_STRNLEN 1
+
+#include "strlen-evex512.S"

sysdeps/x86_64/multiarch/wcslen-evex512.S

@@ -0,0 +1,4 @@
+#define STRLEN __wcslen_evex512
+#define USE_AS_WCSLEN 1
+
+#include "strlen-evex512.S"

sysdeps/x86_64/multiarch/wcsnlen-evex512.S

@@ -0,0 +1,5 @@
+#define STRLEN __wcsnlen_evex512
+#define USE_AS_WCSLEN 1
+#define USE_AS_STRNLEN 1
+
+#include "strlen-evex512.S"