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https://github.com/golang/go
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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>
155 lines
1.7 KiB
ArmAsm
155 lines
1.7 KiB
ArmAsm
// Copyright 2018 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, $0-24
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MOVD to+0(FP), R0
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MOVD from+8(FP), R1
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MOVD n+16(FP), R2
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Get R0
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Get R1
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I64LtU
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If // forward
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exit_forward_64:
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Block
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loop_forward_64:
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Loop
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Get R2
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I64Const $8
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I64LtU
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BrIf exit_forward_64
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MOVD 0(R1), 0(R0)
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Get R0
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I64Const $8
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I64Add
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Set R0
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Get R1
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I64Const $8
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I64Add
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Set R1
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Get R2
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I64Const $8
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I64Sub
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Set R2
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Br loop_forward_64
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End
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End
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loop_forward_8:
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Loop
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Get R2
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I64Eqz
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If
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RET
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End
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Get R0
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I32WrapI64
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I64Load8U (R1)
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I64Store8 $0
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Get R0
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I64Const $1
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I64Add
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Set R0
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Get R1
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I64Const $1
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I64Add
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Set R1
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Get R2
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I64Const $1
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I64Sub
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Set R2
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Br loop_forward_8
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End
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Else
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// backward
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Get R0
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Get R2
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I64Add
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Set R0
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Get R1
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Get R2
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I64Add
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Set R1
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exit_backward_64:
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Block
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loop_backward_64:
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Loop
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Get R2
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I64Const $8
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I64LtU
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BrIf exit_backward_64
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Get R0
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I64Const $8
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I64Sub
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Set R0
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Get R1
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I64Const $8
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I64Sub
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Set R1
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Get R2
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I64Const $8
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I64Sub
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Set R2
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MOVD 0(R1), 0(R0)
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Br loop_backward_64
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End
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End
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loop_backward_8:
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Loop
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Get R2
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I64Eqz
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If
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RET
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End
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Get R0
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I64Const $1
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I64Sub
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Set R0
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Get R1
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I64Const $1
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I64Sub
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Set R1
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Get R2
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I64Const $1
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I64Sub
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Set R2
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Get R0
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I32WrapI64
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I64Load8U (R1)
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I64Store8 $0
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Br loop_backward_8
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End
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End
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UNDEF
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