runtime: support memclr/memmove for linux/loong64

Contributors to the loong64 port are:
  Weining Lu <luweining@loongson.cn>
  Lei Wang <wanglei@loongson.cn>
  Lingqin Gong <gonglingqin@loongson.cn>
  Xiaolin Zhao <zhaoxiaolin@loongson.cn>
  Meidan Li <limeidan@loongson.cn>
  Xiaojuan Zhai <zhaixiaojuan@loongson.cn>
  Qiyuan Pu <puqiyuan@loongson.cn>
  Guoqi Chen <chenguoqi@loongson.cn>

This port has been updated to Go 1.15.6:
  https://github.com/loongson/go

Updates #46229

Change-Id: I7c1f39670034db6714630d479bc41b6620ba2b1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/368079
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/runtime/memclr_loong64.s

@@ -0,0 +1,41 @@
+// Copyright 2022 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 "go_asm.h"
+#include "textflag.h"
+
+// func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)
+TEXT runtime·memclrNoHeapPointers(SB),NOSPLIT,$0-16
+	MOVV	ptr+0(FP), R6
+	MOVV	n+8(FP), R7
+	ADDV	R6, R7, R4
+
+	// if less than 8 bytes, do one byte at a time
+	SGTU	$8, R7, R8
+	BNE	R8, out
+
+	// do one byte at a time until 8-aligned
+	AND	$7, R6, R8
+	BEQ	R8, words
+	MOVB	R0, (R6)
+	ADDV	$1, R6
+	JMP	-4(PC)
+
+words:
+	// do 8 bytes at a time if there is room
+	ADDV	$-7, R4, R7
+
+	SGTU	R7, R6, R8
+	BEQ	R8, out
+	MOVV	R0, (R6)
+	ADDV	$8, R6
+	JMP	-4(PC)
+
+out:
+	BEQ	R6, R4, done
+	MOVB	R0, (R6)
+	ADDV	$1, R6
+	JMP	-3(PC)
+done:
+	RET

src/runtime/memmove_loong64.s

@@ -0,0 +1,105 @@
+// Copyright 2022 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"
+
+// See memmove Go doc for important implementation constraints.
+
+// func memmove(to, from unsafe.Pointer, n uintptr)
+TEXT runtime·memmove(SB), NOSPLIT|NOFRAME, $0-24
+	MOVV	to+0(FP), R4
+	MOVV	from+8(FP), R5
+	MOVV	n+16(FP), R6
+	BNE	R6, check
+	RET
+
+check:
+	SGTU	R4, R5, R7
+	BNE	R7, backward
+
+	ADDV	R4, R6, R9 // end pointer
+
+	// if the two pointers are not of same alignments, do byte copying
+	SUBVU	R5, R4, R7
+	AND	$7, R7
+	BNE	R7, out
+
+	// if less than 8 bytes, do byte copying
+	SGTU	$8, R6, R7
+	BNE	R7, out
+
+	// do one byte at a time until 8-aligned
+	AND	$7, R4, R8
+	BEQ	R8, words
+	MOVB	(R5), R7
+	ADDV	$1, R5
+	MOVB	R7, (R4)
+	ADDV	$1, R4
+	JMP	-6(PC)
+
+words:
+	// do 8 bytes at a time if there is room
+	ADDV	$-7, R9, R6 // R6 is end pointer-7
+
+	SGTU	R6, R4, R8
+	BEQ	R8, out
+	MOVV	(R5), R7
+	ADDV	$8, R5
+	MOVV	R7, (R4)
+	ADDV	$8, R4
+	JMP	-6(PC)
+
+out:
+	BEQ	R4, R9, done
+	MOVB	(R5), R7
+	ADDV	$1, R5
+	MOVB	R7, (R4)
+	ADDV	$1, R4
+	JMP	-5(PC)
+done:
+	RET
+
+backward:
+	ADDV	R6, R5 // from-end pointer
+	ADDV	R4, R6, R9 // to-end pointer
+
+	// if the two pointers are not of same alignments, do byte copying
+	SUBVU	R9, R5, R7
+	AND	$7, R7
+	BNE	R7, out1
+
+	// if less than 8 bytes, do byte copying
+	SGTU	$8, R6, R7
+	BNE	R7, out1
+
+	// do one byte at a time until 8-aligned
+	AND	$7, R9, R8
+	BEQ	R8, words1
+	ADDV	$-1, R5
+	MOVB	(R5), R7
+	ADDV	$-1, R9
+	MOVB	R7, (R9)
+	JMP	-6(PC)
+
+words1:
+	// do 8 bytes at a time if there is room
+	ADDV	$7, R4, R6 // R6 is start pointer+7
+
+	SGTU	R9, R6, R8
+	BEQ	R8, out1
+	ADDV	$-8, R5
+	MOVV	(R5), R7
+	ADDV	$-8, R9
+	MOVV	R7, (R9)
+	JMP	-6(PC)
+
+out1:
+	BEQ	R4, R9, done1
+	ADDV	$-1, R5
+	MOVB	(R5), R7
+	ADDV	$-1, R9
+	MOVB	R7, (R9)
+	JMP	-5(PC)
+done1:
+	RET