sync/atomic: add support for GOARCH=arm64

Change-Id: I11cd4b5e8daf3805af0eaa83b55b20da889702f4
Reviewed-on: https://go-review.googlesource.com/7145Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Russ Cox <rsc@golang.org>

src/sync/atomic/asm_arm64.s

+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "textflag.h"
+
+TEXT ·SwapInt32(SB),NOSPLIT,$0-20
+	B	·SwapUint32(SB)
+
+TEXT ·SwapUint32(SB),NOSPLIT,$0-20
+	MOVD	addr+0(FP), R0
+	MOVW	new+8(FP), R1
+again:
+	LDAXRW	(R0), R2
+	STLXRW	R1, (R0), R3
+	CBNZ	R3, again
+	MOVW	R2, old+16(FP)
+	RET
+
+TEXT ·SwapInt64(SB),NOSPLIT,$0-24
+	B	·SwapUint64(SB)
+
+TEXT ·SwapUint64(SB),NOSPLIT,$0-24
+	MOVD	addr+0(FP), R0
+	MOVD	new+8(FP), R1
+again:
+	LDAXR	(R0), R2
+	STLXR	R1, (R0), R3
+	CBNZ	R3, again
+	MOVD	R2, old+16(FP)
+	RET
+
+TEXT ·SwapUintptr(SB),NOSPLIT,$0-24
+	B	·SwapUint64(SB)
+
+TEXT ·CompareAndSwapInt32(SB),NOSPLIT,$0-17
+	B	·CompareAndSwapUint32(SB)
+
+TEXT ·CompareAndSwapUint32(SB),NOSPLIT,$0-17
+	MOVD	addr+0(FP), R0
+	MOVW	old+8(FP), R1
+	MOVW	new+12(FP), R2
+again:
+	LDAXRW	(R0), R3
+	CMPW	R1, R3
+	BNE	ok
+	STLXRW	R2, (R0), R3
+	CBNZ	R3, again
+ok:
+	CSET	EQ, R0
+	MOVB	R0, swapped+16(FP)
+	RET
+
+TEXT ·CompareAndSwapUintptr(SB),NOSPLIT,$0-25
+	B	·CompareAndSwapUint64(SB)
+
+TEXT ·CompareAndSwapInt64(SB),NOSPLIT,$0-25
+	B	·CompareAndSwapUint64(SB)
+
+TEXT ·CompareAndSwapUint64(SB),NOSPLIT,$0-25
+	MOVD	addr+0(FP), R0
+	MOVD	old+8(FP), R1
+	MOVD	new+16(FP), R2
+again:
+	LDAXR	(R0), R3
+	CMP	R1, R3
+	BNE	ok
+	STLXR	R2, (R0), R3
+	CBNZ	R3, again
+ok:
+	CSET	EQ, R0
+	MOVB	R0, swapped+24(FP)
+	RET
+
+TEXT ·AddInt32(SB),NOSPLIT,$0-20
+	B	·AddUint32(SB)
+
+TEXT ·AddUint32(SB),NOSPLIT,$0-20
+	MOVD	addr+0(FP), R0
+	MOVW	delta+8(FP), R1
+again:
+	LDAXRW	(R0), R2
+	ADDW	R2, R1, R2
+	STLXRW	R2, (R0), R3
+	CBNZ	R3, again
+	MOVW	R2, new+16(FP)
+	RET
+
+TEXT ·AddUintptr(SB),NOSPLIT,$0-24
+	B	·AddUint64(SB)
+
+TEXT ·AddInt64(SB),NOSPLIT,$0-24
+	B	·AddUint64(SB)
+
+TEXT ·AddUint64(SB),NOSPLIT,$0-24
+	MOVD	addr+0(FP), R0
+	MOVD	delta+8(FP), R1
+again:
+	LDAXR	(R0), R2
+	ADD	R2, R1, R2
+	STLXR	R2, (R0), R3
+	CBNZ	R3, again
+	MOVD	R2, new+16(FP)
+	RET
+
+TEXT ·LoadInt32(SB),NOSPLIT,$0-12
+	B	·LoadUint32(SB)
+
+TEXT ·LoadUint32(SB),NOSPLIT,$0-12
+	MOVD	addr+0(FP), R0
+	LDARW	(R0), R0
+	MOVW	R0, val+8(FP)
+	RET
+
+TEXT ·LoadInt64(SB),NOSPLIT,$0-16
+	B	·LoadUint64(SB)
+
+TEXT ·LoadUint64(SB),NOSPLIT,$0-16
+	MOVD	addr+0(FP), R0
+	LDAR	(R0), R0
+	MOVD	R0, val+8(FP)
+	RET
+
+TEXT ·LoadUintptr(SB),NOSPLIT,$0-16
+	B	·LoadPointer(SB)
+
+TEXT ·LoadPointer(SB),NOSPLIT,$0-16
+	B	·LoadUint64(SB)
+
+TEXT ·StoreInt32(SB),NOSPLIT,$0-12
+	B	·StoreUint32(SB)
+
+TEXT ·StoreUint32(SB),NOSPLIT,$0-12
+	MOVD	addr+0(FP), R0
+	MOVW	val+8(FP), R1
+	STLRW	R1, (R0)
+	RET
+
+TEXT ·StoreInt64(SB),NOSPLIT,$0-16
+	B	·StoreUint64(SB)
+
+TEXT ·StoreUint64(SB),NOSPLIT,$0-16
+	MOVD	addr+0(FP), R0
+	MOVD	val+8(FP), R1
+	STLR	R1, (R0)
+	RET
+
+TEXT ·StoreUintptr(SB),NOSPLIT,$0-16
+	B	·StoreUint64(SB)