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9b5bd30716
Unlike C's memmove, Go's memmove must be careful to do indivisible writes of pointer values because it may be racing with the garbage collector reading the heap. We've had various bugs related to this over the years (#36101, #13160, #12552). Indeed, memmove is a great target for optimization and it's easy to forget the special requirements of Go's memmove. The CL documents these (currently unwritten!) requirements. We're also adding a test that should hopefully keep everyone honest going forward, though it's hard to be sure we're hitting all cases of memmove. Change-Id: I2f59f8d8d6fb42d2f10006b55d605b5efd8ddc24 Reviewed-on: https://go-review.googlesource.com/c/go/+/213418 Reviewed-by: Cherry Zhang <cherryyz@google.com>
192 lines
2.9 KiB
ArmAsm
192 lines
2.9 KiB
ArmAsm
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#include "textflag.h"
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// See memmove Go doc for important implementation constraints.
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// func memmove(to, from unsafe.Pointer, n uintptr)
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TEXT runtime·memmove(SB),NOSPLIT|NOFRAME,$0-24
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MOVD to+0(FP), R6
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MOVD from+8(FP), R4
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MOVD n+16(FP), R5
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CMPBEQ R6, R4, done
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start:
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CMPBLE R5, $3, move0to3
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CMPBLE R5, $7, move4to7
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CMPBLE R5, $11, move8to11
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CMPBLE R5, $15, move12to15
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CMPBNE R5, $16, movemt16
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MOVD 0(R4), R7
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MOVD 8(R4), R8
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MOVD R7, 0(R6)
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MOVD R8, 8(R6)
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RET
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movemt16:
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CMPBGT R4, R6, forwards
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ADD R5, R4, R7
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CMPBLE R7, R6, forwards
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ADD R5, R6, R8
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backwards:
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MOVD -8(R7), R3
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MOVD R3, -8(R8)
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MOVD -16(R7), R3
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MOVD R3, -16(R8)
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ADD $-16, R5
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ADD $-16, R7
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ADD $-16, R8
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CMP R5, $16
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BGE backwards
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BR start
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forwards:
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CMPBGT R5, $64, forwards_fast
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MOVD 0(R4), R3
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MOVD R3, 0(R6)
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MOVD 8(R4), R3
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MOVD R3, 8(R6)
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ADD $16, R4
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ADD $16, R6
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ADD $-16, R5
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CMP R5, $16
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BGE forwards
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BR start
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forwards_fast:
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CMP R5, $256
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BLE forwards_small
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MVC $256, 0(R4), 0(R6)
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ADD $256, R4
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ADD $256, R6
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ADD $-256, R5
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BR forwards_fast
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forwards_small:
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CMPBEQ R5, $0, done
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ADD $-1, R5
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EXRL $memmove_exrl_mvc<>(SB), R5
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RET
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move0to3:
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CMPBEQ R5, $0, done
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move1:
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CMPBNE R5, $1, move2
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MOVB 0(R4), R3
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MOVB R3, 0(R6)
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RET
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move2:
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CMPBNE R5, $2, move3
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MOVH 0(R4), R3
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MOVH R3, 0(R6)
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RET
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move3:
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MOVH 0(R4), R3
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MOVB 2(R4), R7
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MOVH R3, 0(R6)
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MOVB R7, 2(R6)
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RET
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move4to7:
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CMPBNE R5, $4, move5
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MOVW 0(R4), R3
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MOVW R3, 0(R6)
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RET
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move5:
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CMPBNE R5, $5, move6
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MOVW 0(R4), R3
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MOVB 4(R4), R7
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MOVW R3, 0(R6)
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MOVB R7, 4(R6)
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RET
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move6:
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CMPBNE R5, $6, move7
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MOVW 0(R4), R3
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MOVH 4(R4), R7
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MOVW R3, 0(R6)
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MOVH R7, 4(R6)
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RET
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move7:
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MOVW 0(R4), R3
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MOVH 4(R4), R7
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MOVB 6(R4), R8
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MOVW R3, 0(R6)
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MOVH R7, 4(R6)
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MOVB R8, 6(R6)
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RET
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move8to11:
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CMPBNE R5, $8, move9
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MOVD 0(R4), R3
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MOVD R3, 0(R6)
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RET
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move9:
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CMPBNE R5, $9, move10
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MOVD 0(R4), R3
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MOVB 8(R4), R7
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MOVD R3, 0(R6)
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MOVB R7, 8(R6)
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RET
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move10:
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CMPBNE R5, $10, move11
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MOVD 0(R4), R3
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MOVH 8(R4), R7
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MOVD R3, 0(R6)
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MOVH R7, 8(R6)
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RET
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move11:
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MOVD 0(R4), R3
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MOVH 8(R4), R7
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MOVB 10(R4), R8
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MOVD R3, 0(R6)
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MOVH R7, 8(R6)
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MOVB R8, 10(R6)
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RET
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move12to15:
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CMPBNE R5, $12, move13
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MOVD 0(R4), R3
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MOVW 8(R4), R7
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MOVD R3, 0(R6)
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MOVW R7, 8(R6)
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RET
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move13:
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CMPBNE R5, $13, move14
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MOVD 0(R4), R3
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MOVW 8(R4), R7
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MOVB 12(R4), R8
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MOVD R3, 0(R6)
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MOVW R7, 8(R6)
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MOVB R8, 12(R6)
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RET
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move14:
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CMPBNE R5, $14, move15
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MOVD 0(R4), R3
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MOVW 8(R4), R7
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MOVH 12(R4), R8
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MOVD R3, 0(R6)
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MOVW R7, 8(R6)
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MOVH R8, 12(R6)
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RET
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move15:
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MOVD 0(R4), R3
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MOVW 8(R4), R7
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MOVH 12(R4), R8
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MOVB 14(R4), R10
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MOVD R3, 0(R6)
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MOVW R7, 8(R6)
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MOVH R8, 12(R6)
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MOVB R10, 14(R6)
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done:
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RET
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// DO NOT CALL - target for exrl (execute relative long) instruction.
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TEXT memmove_exrl_mvc<>(SB),NOSPLIT|NOFRAME,$0-0
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MVC $1, 0(R4), 0(R6)
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MOVD R0, 0(R0)
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RET
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