[PATCH] aarch64: Optimized implementation of pthread_spin_trylock

[Xuelei Zhang <zhangxuelei4 at huawei dot com>]

Judge the value of ldaxr before stxr, to reduce the memmory store
operation in the case spin_lock is already used by other threads.
---
 sysdeps/aarch64/nptl/pthread_spin_trylock.S | 46 +++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 sysdeps/aarch64/nptl/pthread_spin_trylock.S

diff --git a/sysdeps/aarch64/nptl/pthread_spin_trylock.S b/sysdeps/aarch64/nptl/pthread_spin_trylock.S
new file mode 100644
index 00000000000..408861dd9f7
--- /dev/null
+++ b/sysdeps/aarch64/nptl/pthread_spin_trylock.S
@@ -0,0 +1,46 @@
+/* pthread_spin_trylock -- trylock a spin lock. Generic version.
+   Copyright (C) 2012-2019 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/>.  */
+
+#include <sysdep.h>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ */
+
+ENTRY (pthread_spin_trylock)
+	DELOUSE (0)
+	mov w1, #0x1
+	
+L(spin):
+	ldaxr   w2, [x0]
+	cbnz    w2, L(fail)
+	stxr    w3, w1, [x0]
+	cbnz    w3, L(spin)
+	mov w0, #0
+	ret
+	nop
+
+L(fail):
+	mov	w0, #16
+	ret
+
+END (pthread_spin_trylock)
+libc_hidden_builtin_def (pthread_spin_trylock)
+weak_alias (pthread_spin_trylock, index)
+
-- 
2.14.1.windows.1