[PATCH][AArch64] Add rawmemchr

[Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>]

Add a simple rawmemchr implementation. Use strlen for rawmemchr(s, '\0') as
it is the fastest way to search for '\0'.  Otherwise use memchr with an infinite size.
This is 3x faster on benchtests for large sizes.

Passes GLIBC tests, OK for commit?

ChangeLog:
2016-05-27  Wilco Dijkstra  <wdijkstr@arm.com>

	* sysdeps/aarch64/rawmemchr.S (__rawmemchr): New file.
	* sysdeps/aarch64/strlen.S (__strlen): Change to __strlen to avoid PLT.

---
 sysdeps/aarch64/rawmemchr.S | 42 ++++++++++++++++++++++++++++++++++++++++++
 sysdeps/aarch64/strlen.S    |  5 +++--
 2 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 sysdeps/aarch64/rawmemchr.S

diff --git a/sysdeps/aarch64/rawmemchr.S b/sysdeps/aarch64/rawmemchr.S
new file mode 100644
index 0000000..ec958e8
--- /dev/null
+++ b/sysdeps/aarch64/rawmemchr.S
@@ -0,0 +1,42 @@
+/* rawmemchr - find a character in a memory zone
+
+   Copyright (C) 2015-2016 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>
+
+/* Special case rawmemchr (s, 0) as strlen, otherwise tailcall memchr.
+   Call strlen without setting up a full frame - it preserves x14/x15.
+*/
+
+ENTRY (__rawmemchr)
+	cbz	w1, L(do_strlen)
+	mov	x2, -1
+	b	__memchr
+
+L(do_strlen):
+	mov	x15, x30
+	cfi_return_column (x15)
+	mov	x14, x0
+	bl	__strlen
+	add	x0, x14, x0
+	ret	x15
+
+END (__rawmemchr)
+weak_alias (__rawmemchr, rawmemchr)
+libc_hidden_builtin_def (__rawmemchr)
diff --git a/sysdeps/aarch64/strlen.S b/sysdeps/aarch64/strlen.S
index feb9e48..e2a4363 100644
--- a/sysdeps/aarch64/strlen.S
+++ b/sysdeps/aarch64/strlen.S
@@ -84,7 +84,7 @@
 	   whether the first fetch, which may be misaligned, crosses a page
 	   boundary.  */
 
-ENTRY_ALIGN (strlen, 6)
+ENTRY_ALIGN (__strlen, 6)
 	and	tmp1, srcin, MIN_PAGE_SIZE - 1
 	mov	zeroones, REP8_01
 	cmp	tmp1, MIN_PAGE_SIZE - 16
@@ -213,5 +213,6 @@ L(page_cross):
 	csel	data1, data1, tmp4, eq
 	csel	data2, data2, tmp2, eq
 	b	L(page_cross_entry)
-END (strlen)
+END (__strlen)
+weak_alias (__strlen, strlen)
 libc_hidden_builtin_def (strlen)
-- 
1.9.1