[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

1 files changed, 39 insertions, 0 deletions

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"