github.com/sanprasirt/go@v0.0.0-20170607001320-a027466e4b6d/src/runtime/memmove_amd64.s

// Derived from Inferno's libkern/memmove-386.s (adapted for amd64)
// https://bitbucket.org/inferno-os/inferno-os/src/default/libkern/memmove-386.s
//
//         Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
//         Revisions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com).  All rights reserved.
//         Portions Copyright 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

// +build !plan9

#include "textflag.h"

// void runtime·memmove(void*, void*, uintptr)
TEXT runtime·memmove(SB), NOSPLIT, $0-24

	MOVQ	to+0(FP), DI
	MOVQ	from+8(FP), SI
	MOVQ	n+16(FP), BX

	// REP instructions have a high startup cost, so we handle small sizes
	// with some straightline code. The REP MOVSQ instruction is really fast
	// for large sizes. The cutover is approximately 2K.
tail:
	// move_129through256 or smaller work whether or not the source and the
	// destination memory regions overlap because they load all data into
	// registers before writing it back.  move_256through2048 on the other
	// hand can be used only when the memory regions don't overlap or the copy
	// direction is forward.
	TESTQ	BX, BX
	JEQ	move_0
	CMPQ	BX, $2
	JBE	move_1or2
	CMPQ	BX, $4
	JBE	move_3or4
	CMPQ	BX, $8
	JB	move_5through7
	JE	move_8
	CMPQ	BX, $16
	JBE	move_9through16
	CMPQ	BX, $32
	JBE	move_17through32
	CMPQ	BX, $64
	JBE	move_33through64
	CMPQ	BX, $128
	JBE	move_65through128
	CMPQ	BX, $256
	JBE	move_129through256
	// TODO: use branch table and BSR to make this just a single dispatch

	TESTB	$1, runtime·useAVXmemmove(SB)
	JNZ	avxUnaligned

/*
 * check and set for backwards
 */
	CMPQ	SI, DI
	JLS	back

/*
 * forward copy loop
 */
forward:
	CMPQ	BX, $2048
	JLS	move_256through2048

	// If REP MOVSB isn't fast, don't use it
	CMPB	runtime·support_erms(SB), $1 // enhanced REP MOVSB/STOSB
	JNE	fwdBy8

	// Check alignment
	MOVL	SI, AX
	ORL	DI, AX
	TESTL	$7, AX
	JEQ	fwdBy8

	// Do 1 byte at a time
	MOVQ	BX, CX
	REP;	MOVSB
	RET

fwdBy8:
	// Do 8 bytes at a time
	MOVQ	BX, CX
	SHRQ	$3, CX
	ANDQ	$7, BX
	REP;	MOVSQ
	JMP	tail

back:
/*
 * check overlap
 */
	MOVQ	SI, CX
	ADDQ	BX, CX
	CMPQ	CX, DI
	JLS	forward
/*
 * whole thing backwards has
 * adjusted addresses
 */
	ADDQ	BX, DI
	ADDQ	BX, SI
	STD

/*
 * copy
 */
	MOVQ	BX, CX
	SHRQ	$3, CX
	ANDQ	$7, BX

	SUBQ	$8, DI
	SUBQ	$8, SI
	REP;	MOVSQ

	CLD
	ADDQ	$8, DI
	ADDQ	$8, SI
	SUBQ	BX, DI
	SUBQ	BX, SI
	JMP	tail

move_1or2:
	MOVB	(SI), AX
	MOVB	-1(SI)(BX*1), CX
	MOVB	AX, (DI)
	MOVB	CX, -1(DI)(BX*1)
	RET
move_0:
	RET
move_3or4:
	CMPQ	BX, $4
	JB	move_3
	MOVL	(SI), AX
	MOVL	AX, (DI)
	RET
move_3:
	MOVW	(SI), AX
	MOVB	2(SI), CX
	MOVW	AX, (DI)
	MOVB	CX, 2(DI)
	RET
move_5through7:
	MOVL	(SI), AX
	MOVL	-4(SI)(BX*1), CX
	MOVL	AX, (DI)
	MOVL	CX, -4(DI)(BX*1)
	RET
move_8:
	// We need a separate case for 8 to make sure we write pointers atomically.
	MOVQ	(SI), AX
	MOVQ	AX, (DI)
	RET
move_9through16:
	MOVQ	(SI), AX
	MOVQ	-8(SI)(BX*1), CX
	MOVQ	AX, (DI)
	MOVQ	CX, -8(DI)(BX*1)
	RET
move_17through32:
	MOVOU	(SI), X0
	MOVOU	-16(SI)(BX*1), X1
	MOVOU	X0, (DI)
	MOVOU	X1, -16(DI)(BX*1)
	RET
move_33through64:
	MOVOU	(SI), X0
	MOVOU	16(SI), X1
	MOVOU	-32(SI)(BX*1), X2
	MOVOU	-16(SI)(BX*1), X3
	MOVOU	X0, (DI)
	MOVOU	X1, 16(DI)
	MOVOU	X2, -32(DI)(BX*1)
	MOVOU	X3, -16(DI)(BX*1)
	RET
move_65through128:
	MOVOU	(SI), X0
	MOVOU	16(SI), X1
	MOVOU	32(SI), X2
	MOVOU	48(SI), X3
	MOVOU	-64(SI)(BX*1), X4
	MOVOU	-48(SI)(BX*1), X5
	MOVOU	-32(SI)(BX*1), X6
	MOVOU	-16(SI)(BX*1), X7
	MOVOU	X0, (DI)
	MOVOU	X1, 16(DI)
	MOVOU	X2, 32(DI)
	MOVOU	X3, 48(DI)
	MOVOU	X4, -64(DI)(BX*1)
	MOVOU	X5, -48(DI)(BX*1)
	MOVOU	X6, -32(DI)(BX*1)
	MOVOU	X7, -16(DI)(BX*1)
	RET
move_129through256:
	MOVOU	(SI), X0
	MOVOU	16(SI), X1
	MOVOU	32(SI), X2
	MOVOU	48(SI), X3
	MOVOU	64(SI), X4
	MOVOU	80(SI), X5
	MOVOU	96(SI), X6
	MOVOU	112(SI), X7
	MOVOU	-128(SI)(BX*1), X8
	MOVOU	-112(SI)(BX*1), X9
	MOVOU	-96(SI)(BX*1), X10
	MOVOU	-80(SI)(BX*1), X11
	MOVOU	-64(SI)(BX*1), X12
	MOVOU	-48(SI)(BX*1), X13
	MOVOU	-32(SI)(BX*1), X14
	MOVOU	-16(SI)(BX*1), X15
	MOVOU	X0, (DI)
	MOVOU	X1, 16(DI)
	MOVOU	X2, 32(DI)
	MOVOU	X3, 48(DI)
	MOVOU	X4, 64(DI)
	MOVOU	X5, 80(DI)
	MOVOU	X6, 96(DI)
	MOVOU	X7, 112(DI)
	MOVOU	X8, -128(DI)(BX*1)
	MOVOU	X9, -112(DI)(BX*1)
	MOVOU	X10, -96(DI)(BX*1)
	MOVOU	X11, -80(DI)(BX*1)
	MOVOU	X12, -64(DI)(BX*1)
	MOVOU	X13, -48(DI)(BX*1)
	MOVOU	X14, -32(DI)(BX*1)
	MOVOU	X15, -16(DI)(BX*1)
	RET
move_256through2048:
	SUBQ	$256, BX
	MOVOU	(SI), X0
	MOVOU	16(SI), X1
	MOVOU	32(SI), X2
	MOVOU	48(SI), X3
	MOVOU	64(SI), X4
	MOVOU	80(SI), X5
	MOVOU	96(SI), X6
	MOVOU	112(SI), X7
	MOVOU	128(SI), X8
	MOVOU	144(SI), X9
	MOVOU	160(SI), X10
	MOVOU	176(SI), X11
	MOVOU	192(SI), X12
	MOVOU	208(SI), X13
	MOVOU	224(SI), X14
	MOVOU	240(SI), X15
	MOVOU	X0, (DI)
	MOVOU	X1, 16(DI)
	MOVOU	X2, 32(DI)
	MOVOU	X3, 48(DI)
	MOVOU	X4, 64(DI)
	MOVOU	X5, 80(DI)
	MOVOU	X6, 96(DI)
	MOVOU	X7, 112(DI)
	MOVOU	X8, 128(DI)
	MOVOU	X9, 144(DI)
	MOVOU	X10, 160(DI)
	MOVOU	X11, 176(DI)
	MOVOU	X12, 192(DI)
	MOVOU	X13, 208(DI)
	MOVOU	X14, 224(DI)
	MOVOU	X15, 240(DI)
	CMPQ	BX, $256
	LEAQ	256(SI), SI
	LEAQ	256(DI), DI
	JGE	move_256through2048
	JMP	tail

avxUnaligned:
	// There are two implementations of move algorithm.
	// The first one for non-ovelapped memory regions. It uses forward copying.
	// The second one for overlapped regions. It uses backward copying
	MOVQ	DI, CX
	SUBQ	SI, CX
	// Now CX contains distance between SRC and DEST
	CMPQ	CX, BX
	// If the distance lesser than region length it means that regions are overlapped
	JC	copy_backward

	// Non-temporal copy would be better for big sizes.
	CMPQ	BX, $0x100000
	JAE	gobble_big_data_fwd

	// Memory layout on the source side
	// SI                                       CX
	// |<---------BX before correction--------->|
	// |       |<--BX corrected-->|             |
	// |       |                  |<--- AX  --->|
	// |<-R11->|                  |<-128 bytes->|
	// +----------------------------------------+
	// | Head  | Body             | Tail        |
	// +-------+------------------+-------------+
	// ^       ^                  ^
	// |       |                  |
	// Save head into Y4          Save tail into X5..X12
	//         |
	//         SI+R11, where R11 = ((DI & -32) + 32) - DI
	// Algorithm:
	// 1. Unaligned save of the tail's 128 bytes
	// 2. Unaligned save of the head's 32  bytes
	// 3. Destination-aligned copying of body (128 bytes per iteration)
	// 4. Put head on the new place
	// 5. Put the tail on the new place
	// It can be important to satisfy processor's pipeline requirements for
	// small sizes as the cost of unaligned memory region copying is
	// comparable with the cost of main loop. So code is slightly messed there.
	// There is more clean implementation of that algorithm for bigger sizes
	// where the cost of unaligned part copying is negligible.
	// You can see it after gobble_big_data_fwd label.
	LEAQ	(SI)(BX*1), CX
	MOVQ	DI, R10
	// CX points to the end of buffer so we need go back slightly. We will use negative offsets there.
	MOVOU	-0x80(CX), X5
	MOVOU	-0x70(CX), X6
	MOVQ	$0x80, AX
	// Align destination address
	ANDQ	$-32, DI
	ADDQ	$32, DI
	// Continue tail saving.
	MOVOU	-0x60(CX), X7
	MOVOU	-0x50(CX), X8
	// Make R11 delta between aligned and unaligned destination addresses.
	MOVQ	DI, R11
	SUBQ	R10, R11
	// Continue tail saving.
	MOVOU	-0x40(CX), X9
	MOVOU	-0x30(CX), X10
	// Let's make bytes-to-copy value adjusted as we've prepared unaligned part for copying.
	SUBQ	R11, BX
	// Continue tail saving.
	MOVOU	-0x20(CX), X11
	MOVOU	-0x10(CX), X12
	// The tail will be put on it's place after main body copying.
	// It's time for the unaligned heading part.
	VMOVDQU	(SI), Y4
	// Adjust source address to point past head.
	ADDQ	R11, SI
	SUBQ	AX, BX
	// Aligned memory copying there
gobble_128_loop:
	VMOVDQU	(SI), Y0
	VMOVDQU	0x20(SI), Y1
	VMOVDQU	0x40(SI), Y2
	VMOVDQU	0x60(SI), Y3
	ADDQ	AX, SI
	VMOVDQA	Y0, (DI)
	VMOVDQA	Y1, 0x20(DI)
	VMOVDQA	Y2, 0x40(DI)
	VMOVDQA	Y3, 0x60(DI)
	ADDQ	AX, DI
	SUBQ	AX, BX
	JA	gobble_128_loop
	// Now we can store unaligned parts.
	ADDQ	AX, BX
	ADDQ	DI, BX
	VMOVDQU	Y4, (R10)
	VZEROUPPER
	MOVOU	X5, -0x80(BX)
	MOVOU	X6, -0x70(BX)
	MOVOU	X7, -0x60(BX)
	MOVOU	X8, -0x50(BX)
	MOVOU	X9, -0x40(BX)
	MOVOU	X10, -0x30(BX)
	MOVOU	X11, -0x20(BX)
	MOVOU	X12, -0x10(BX)
	RET

gobble_big_data_fwd:
	// There is forward copying for big regions.
	// It uses non-temporal mov instructions.
	// Details of this algorithm are commented previously for small sizes.
	LEAQ	(SI)(BX*1), CX
	MOVOU	-0x80(SI)(BX*1), X5
	MOVOU	-0x70(CX), X6
	MOVOU	-0x60(CX), X7
	MOVOU	-0x50(CX), X8
	MOVOU	-0x40(CX), X9
	MOVOU	-0x30(CX), X10
	MOVOU	-0x20(CX), X11
	MOVOU	-0x10(CX), X12
	VMOVDQU	(SI), Y4
	MOVQ	DI, R8
	ANDQ	$-32, DI
	ADDQ	$32, DI
	MOVQ	DI, R10
	SUBQ	R8, R10
	SUBQ	R10, BX
	ADDQ	R10, SI
	LEAQ	(DI)(BX*1), CX
	SUBQ	$0x80, BX
gobble_mem_fwd_loop:
	PREFETCHNTA 0x1C0(SI)
	PREFETCHNTA 0x280(SI)
	// Prefetch values were chosen empirically.
	// Approach for prefetch usage as in 7.6.6 of [1]
	// [1] 64-ia-32-architectures-optimization-manual.pdf
	// http://www.intel.ru/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf
	VMOVDQU	(SI), Y0
	VMOVDQU	0x20(SI), Y1
	VMOVDQU	0x40(SI), Y2
	VMOVDQU	0x60(SI), Y3
	ADDQ	$0x80, SI
	VMOVNTDQ Y0, (DI)
	VMOVNTDQ Y1, 0x20(DI)
	VMOVNTDQ Y2, 0x40(DI)
	VMOVNTDQ Y3, 0x60(DI)
	ADDQ	$0x80, DI
	SUBQ	$0x80, BX
	JA		gobble_mem_fwd_loop
	// NT instructions don't follow the normal cache-coherency rules.
	// We need SFENCE there to make copied data available timely.
	SFENCE
	VMOVDQU	Y4, (R8)
	VZEROUPPER
	MOVOU	X5, -0x80(CX)
	MOVOU	X6, -0x70(CX)
	MOVOU	X7, -0x60(CX)
	MOVOU	X8, -0x50(CX)
	MOVOU	X9, -0x40(CX)
	MOVOU	X10, -0x30(CX)
	MOVOU	X11, -0x20(CX)
	MOVOU	X12, -0x10(CX)
	RET

copy_backward:
	MOVQ	DI, AX
	// Backward copying is about the same as the forward one.
	// Firstly we load unaligned tail in the beginning of region.
	MOVOU	(SI), X5
	MOVOU	0x10(SI), X6
	ADDQ	BX, DI
	MOVOU	0x20(SI), X7
	MOVOU	0x30(SI), X8
	LEAQ	-0x20(DI), R10
	MOVQ	DI, R11
	MOVOU	0x40(SI), X9
	MOVOU	0x50(SI), X10
	ANDQ	$0x1F, R11
	MOVOU	0x60(SI), X11
	MOVOU	0x70(SI), X12
	XORQ	R11, DI
	// Let's point SI to the end of region
	ADDQ	BX, SI
	// and load unaligned head into X4.
	VMOVDQU	-0x20(SI), Y4
	SUBQ	R11, SI
	SUBQ	R11, BX
	// If there is enough data for non-temporal moves go to special loop
	CMPQ	BX, $0x100000
	JA		gobble_big_data_bwd
	SUBQ	$0x80, BX
gobble_mem_bwd_loop:
	VMOVDQU	-0x20(SI), Y0
	VMOVDQU	-0x40(SI), Y1
	VMOVDQU	-0x60(SI), Y2
	VMOVDQU	-0x80(SI), Y3
	SUBQ	$0x80, SI
	VMOVDQA	Y0, -0x20(DI)
	VMOVDQA	Y1, -0x40(DI)
	VMOVDQA	Y2, -0x60(DI)
	VMOVDQA	Y3, -0x80(DI)
	SUBQ	$0x80, DI
	SUBQ	$0x80, BX
	JA		gobble_mem_bwd_loop
	// Let's store unaligned data
	VMOVDQU	Y4, (R10)
	VZEROUPPER
	MOVOU	X5, (AX)
	MOVOU	X6, 0x10(AX)
	MOVOU	X7, 0x20(AX)
	MOVOU	X8, 0x30(AX)
	MOVOU	X9, 0x40(AX)
	MOVOU	X10, 0x50(AX)
	MOVOU	X11, 0x60(AX)
	MOVOU	X12, 0x70(AX)
	RET

gobble_big_data_bwd:
	SUBQ	$0x80, BX
gobble_big_mem_bwd_loop:
	PREFETCHNTA -0x1C0(SI)
	PREFETCHNTA -0x280(SI)
	VMOVDQU	-0x20(SI), Y0
	VMOVDQU	-0x40(SI), Y1
	VMOVDQU	-0x60(SI), Y2
	VMOVDQU	-0x80(SI), Y3
	SUBQ	$0x80, SI
	VMOVNTDQ	Y0, -0x20(DI)
	VMOVNTDQ	Y1, -0x40(DI)
	VMOVNTDQ	Y2, -0x60(DI)
	VMOVNTDQ	Y3, -0x80(DI)
	SUBQ	$0x80, DI
	SUBQ	$0x80, BX
	JA	gobble_big_mem_bwd_loop
	SFENCE
	VMOVDQU	Y4, (R10)
	VZEROUPPER
	MOVOU	X5, (AX)
	MOVOU	X6, 0x10(AX)
	MOVOU	X7, 0x20(AX)
	MOVOU	X8, 0x30(AX)
	MOVOU	X9, 0x40(AX)
	MOVOU	X10, 0x50(AX)
	MOVOU	X11, 0x60(AX)
	MOVOU	X12, 0x70(AX)
	RET