[aarch64] Add an ASIMD variant of strlen for falkor

This variant of strlen uses vector loads and operations to reduce the
size of the code and also eliminate the non-ascii fallback.  This
works very well for falkor because of its two vector units and
efficient vector ops.  In the best case it reduces latency of cases in
bench-strlen by 48%, with gains throughout the benchmark.
strlen-walk also sees uniform gains in the 5%-15% range.

Overall the routine appears to work better than the stock one for falkor
regardless of the benchmark, length of string or cache state.

The same cannot be said of a53 and a72 though.  a53 performance was
greatly reduced and for a72 it was a bit of a mixed bag, slightly on the
negative side but I reckon it might be fast in some situations.

	* sysdeps/aarch64/strlen.S (__strlen): Rename to STRLEN.
	[!STRLEN](STRLEN): Set to __strlen.
	* sysdeps/aarch64/multiarch/strlen.c: New file.
	* sysdeps/aarch64/multiarch/strlen_generic.S: Likewise.
	* sysdeps/aarch64/multiarch/strlen_asimd.S: Likewise.
	* sysdeps/aarch64/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Add strlen.
	* sysdeps/aarch64/multiarch/Makefile (sysdep_routines): Add
	strlen_generic and strlen_asimd.

Reviewed-By: szabolcs.nagy@arm.com
CC: pinskia@gmail.com

5 files changed, 254 insertions, 1 deletions

diff --git a/sysdeps/aarch64/multiarch/Makefile b/sysdeps/aarch64/multiarch/Makefile
index 57ffdf7238..b1a5f59fcd 100644
--- a/sysdeps/aarch64/multiarch/Makefile
+++ b/sysdeps/aarch64/multiarch/Makefile
@@ -1,4 +1,5 @@
 ifeq ($(subdir),string)
 sysdep_routines += memcpy_generic memcpy_thunderx memcpy_thunderx2 \
-		   memcpy_falkor memmove_falkor memset_generic memset_falkor
+		   memcpy_falkor memmove_falkor memset_generic memset_falkor \
+		   strlen_generic strlen_asimd
 endif
diff --git a/sysdeps/aarch64/multiarch/ifunc-impl-list.c b/sysdeps/aarch64/multiarch/ifunc-impl-list.c
index e55be80103..af446650a6 100644
--- a/sysdeps/aarch64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/aarch64/multiarch/ifunc-impl-list.c
@@ -53,5 +53,9 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 	      IFUNC_IMPL_ADD (array, i, memset, (zva_size == 64), __memset_falkor)
 	      IFUNC_IMPL_ADD (array, i, memset, 1, __memset_generic))
 
+  IFUNC_IMPL (i, name, strlen,
+	      IFUNC_IMPL_ADD (array, i, strlen, 1, __strlen_asimd)
+	      IFUNC_IMPL_ADD (array, i, strlen, 1, __strlen_generic))
+
   return i;
 }
diff --git a/sysdeps/aarch64/multiarch/strlen.c b/sysdeps/aarch64/multiarch/strlen.c
new file mode 100644
index 0000000000..6c62d684c8
--- /dev/null
+++ b/sysdeps/aarch64/multiarch/strlen.c
@@ -0,0 +1,41 @@
+/* Multiple versions of strlen. AARCH64 version.
+   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/>.  */
+
+/* Define multiple versions only for the definition in libc.  */
+
+#if IS_IN (libc)
+/* Redefine strlen so that the compiler won't complain about the type
+   mismatch with the IFUNC selector in strong_alias, below.  */
+# undef strlen
+# define strlen __redirect_strlen
+# include <string.h>
+# include <init-arch.h>
+
+#define USE_ASIMD_STRLEN() IS_FALKOR (midr)
+
+extern __typeof (__redirect_strlen) __strlen;
+
+extern __typeof (__redirect_strlen) __strlen_generic attribute_hidden;
+extern __typeof (__redirect_strlen) __strlen_asimd attribute_hidden;
+
+libc_ifunc (__strlen,
+	    (USE_ASIMD_STRLEN () ? __strlen_asimd : __strlen_generic));
+
+# undef strlen
+strong_alias (__strlen, strlen);
+#endif
diff --git a/sysdeps/aarch64/multiarch/strlen_asimd.S b/sysdeps/aarch64/multiarch/strlen_asimd.S
new file mode 100644
index 0000000000..ca37b931cb
--- /dev/null
+++ b/sysdeps/aarch64/multiarch/strlen_asimd.S
@@ -0,0 +1,168 @@
+/* Strlen implementation that uses ASIMD instructions for load and NULL checks.
+   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/>.  */
+
+#include <sysdep.h>
+
+/* Assumptions:
+
+   ARMv8-a, AArch64, ASIMD, unaligned accesses, min page size 4k.  */
+
+/* To test the page crossing code path more thoroughly, compile with
+   -DTEST_PAGE_CROSS - this will force all calls through the slower
+   entry path.  This option is not intended for production use.  */
+
+/* Arguments and results.  */
+#define srcin		x0
+#define len		x0
+
+/* Locals and temporaries.  */
+#define src		x1
+#define data1		x2
+#define data2		x3
+#define has_nul1	x4
+#define has_nul2	x5
+#define tmp1		x4
+#define tmp2		x5
+#define tmp3		x6
+#define tmp4		x7
+#define zeroones	x8
+#define dataq		q2
+#define datav		v2
+#define datab2		b3
+#define dataq2		q3
+#define datav2		v3
+
+#ifdef TEST_PAGE_CROSS
+# define MIN_PAGE_SIZE 16
+#else
+# define MIN_PAGE_SIZE 4096
+#endif
+
+	/* Since strings are short on average, we check the first 16 bytes
+	   of the string for a NUL character.  In order to do an unaligned load
+	   safely we have to do a page cross check first.  If there is a NUL
+	   byte we calculate the length from the 2 8-byte words using
+	   conditional select to reduce branch mispredictions (it is unlikely
+	   strlen_asimd will be repeatedly called on strings with the same
+	   length).
+
+	   If the string is longer than 16 bytes, we align src so don't need
+	   further page cross checks, and process 16 bytes per iteration.
+
+	   If the page cross check fails, we read 16 bytes from an aligned
+	   address, remove any characters before the string, and continue
+	   in the main loop using aligned loads.  Since strings crossing a
+	   page in the first 16 bytes are rare (probability of
+	   16/MIN_PAGE_SIZE ~= 0.4%), this case does not need to be optimized.
+
+	   AArch64 systems have a minimum page size of 4k.  We don't bother
+	   checking for larger page sizes - the cost of setting up the correct
+	   page size is just not worth the extra gain from a small reduction in
+	   the cases taking the slow path.  Note that we only care about
+	   whether the first fetch, which may be misaligned, crosses a page
+	   boundary.  */
+
+ENTRY_ALIGN (__strlen_asimd, 6)
+	DELOUSE (0)
+	DELOUSE (1)
+	and	tmp1, srcin, MIN_PAGE_SIZE - 1
+	cmp	tmp1, MIN_PAGE_SIZE - 16
+	b.gt	L(page_cross)
+	ldr	dataq, [srcin]
+#ifdef __AARCH64EB__
+	rev64	datav.16b, datav.16b
+#endif
+
+	/* Get the minimum value and keep going if it is not zero.  */
+	uminv	datab2, datav.16b
+	mov	tmp1, datav2.d[0]
+	cbnz	tmp1, L(main_loop_entry)
+
+	cmeq	datav.16b, datav.16b, #0
+	mov	data1, datav.d[0]
+	mov	data2, datav.d[1]
+	cmp	data1, 0
+	csel	data1, data1, data2, ne
+	mov	len, 8
+	rev	data1, data1
+	clz	tmp1, data1
+	csel	len, xzr, len, ne
+	add	len, len, tmp1, lsr 3
+	ret
+
+L(main_loop_entry):
+	bic	src, srcin, 15
+
+L(main_loop):
+	ldr	dataq, [src, 16]!
+L(page_cross_entry):
+	/* Get the minimum value and keep going if it is not zero.  */
+	uminv	datab2, datav.16b
+	mov	tmp1, datav2.d[0]
+	cbnz	tmp1, L(main_loop)
+
+L(tail):
+#ifdef __AARCH64EB__
+	rev64	datav.16b, datav.16b
+#endif
+	/* Set te NULL byte as 0xff and the rest as 0x00, move the data into a
+	   pair of scalars and then compute the length from the earliest NULL
+	   byte.  */
+	cmeq	datav.16b, datav.16b, #0
+	mov	data1, datav.d[0]
+	mov	data2, datav.d[1]
+	cmp	data1, 0
+	csel	data1, data1, data2, ne
+	sub	len, src, srcin
+	rev	data1, data1
+	add	tmp2, len, 8
+	clz	tmp1, data1
+	csel	len, len, tmp2, ne
+	add	len, len, tmp1, lsr 3
+	ret
+
+	/* Load 16 bytes from [srcin & ~15] and force the bytes that precede
+	   srcin to 0xff, so we ignore any NUL bytes before the string.
+	   Then continue in the aligned loop.  */
+L(page_cross):
+	mov	tmp3, 63
+	bic	src, srcin, 15
+	and	tmp1, srcin, 7
+	ands	tmp2, srcin, 8
+	ldr	dataq, [src]
+	lsl	tmp1, tmp1, 3
+	csel	tmp2, tmp2, tmp1, eq
+	csel	tmp1, tmp1, tmp3, eq
+	mov	tmp4, -1
+#ifdef __AARCH64EB__
+	/* Big-endian.  Early bytes are at MSB.  */
+	lsr	tmp1, tmp4, tmp1
+	lsr	tmp2, tmp4, tmp2
+#else
+	/* Little-endian.  Early bytes are at LSB.  */
+	lsl	tmp1, tmp4, tmp1
+	lsl	tmp2, tmp4, tmp2
+#endif
+	mov	datav2.d[0], tmp1
+	mov	datav2.d[1], tmp2
+	orn	datav.16b, datav.16b, datav2.16b
+	b	L(page_cross_entry)
+END (__strlen_asimd)
+weak_alias (__strlen_asimd, strlen_asimd)
+libc_hidden_builtin_def (strlen_asimd)
diff --git a/sysdeps/aarch64/multiarch/strlen_generic.S b/sysdeps/aarch64/multiarch/strlen_generic.S
new file mode 100644
index 0000000000..4234948eba
--- /dev/null
+++ b/sysdeps/aarch64/multiarch/strlen_generic.S
@@ -0,0 +1,39 @@
+/* A Generic Optimized strlen implementation for AARCH64.
+   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/>.  */
+
+/* The actual strlen code is in ../strlen.S.  If we are building libc this file
+   defines __strlen_generic.  Otherwise the include of ../strlen.S will define
+   the normal __strlen  entry points.  */
+
+#include <sysdep.h>
+
+#if IS_IN (libc)
+
+# define STRLEN __strlen_generic
+
+/* Do not hide the generic version of strlen, we use it internally.  */
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name)
+
+# ifdef SHARED
+/* It doesn't make sense to send libc-internal strlen calls through a PLT. */
+	.globl __GI_strlen; __GI_strlen = __strlen_generic
+# endif
+#endif
+
+#include "../strlen.S"