src/runtime/memclr_riscv64.s

// Copyright 2016 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 memclrNoHeapPointers Go doc for important implementation constraints.

// void runtime·memclrNoHeapPointers(void*, uintptr)
TEXT runtime·memclrNoHeapPointers<ABIInternal>(SB),NOSPLIT,$0-16
	// X10 = ptr
	// X11 = n

	// If less than 8 bytes, do single byte zeroing.
	MOV	$8, X9
	BLT	X11, X9, check4

	// Check alignment
	AND	$7, X10, X5
	BEQZ	X5, aligned

	// Zero one byte at a time until we reach 8 byte alignment.
	SUB	X5, X9, X5
	SUB	X5, X11, X11
align:
	SUB	$1, X5
	MOVB	ZERO, 0(X10)
	ADD	$1, X10
	BNEZ	X5, align

aligned:
	// X9 already contains $8
	BLT	X11, X9, check4
	MOV	$16, X9
	BLT	X11, X9, zero8
	MOV	$32, X9
	BLT	X11, X9, zero16
	MOV	$64, X9
	BLT	X11, X9, zero32
loop64:
	MOV	ZERO, 0(X10)
	MOV	ZERO, 8(X10)
	MOV	ZERO, 16(X10)
	MOV	ZERO, 24(X10)
	MOV	ZERO, 32(X10)
	MOV	ZERO, 40(X10)
	MOV	ZERO, 48(X10)
	MOV	ZERO, 56(X10)
	ADD	$64, X10
	SUB	$64, X11
	BGE	X11, X9, loop64
	BEQZ	X11, done

check32:
	MOV	$32, X9
	BLT	X11, X9, check16
zero32:
	MOV	ZERO, 0(X10)
	MOV	ZERO, 8(X10)
	MOV	ZERO, 16(X10)
	MOV	ZERO, 24(X10)
	ADD	$32, X10
	SUB	$32, X11
	BEQZ	X11, done

check16:
	MOV	$16, X9
	BLT	X11, X9, check8
zero16:
	MOV	ZERO, 0(X10)
	MOV	ZERO, 8(X10)
	ADD	$16, X10
	SUB	$16, X11
	BEQZ	X11, done

check8:
	MOV	$8, X9
	BLT	X11, X9, check4
zero8:
	MOV	ZERO, 0(X10)
	ADD	$8, X10
	SUB	$8, X11
	BEQZ	X11, done

check4:
	MOV	$4, X9
	BLT	X11, X9, loop1
zero4:
	MOVB	ZERO, 0(X10)
	MOVB	ZERO, 1(X10)
	MOVB	ZERO, 2(X10)
	MOVB	ZERO, 3(X10)
	ADD	$4, X10
	SUB	$4, X11

loop1:
	BEQZ	X11, done
	MOVB	ZERO, 0(X10)
	ADD	$1, X10
	SUB	$1, X11
	JMP	loop1

done:
	RET