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cmd/link: propagate UsedInIface through method descriptor
The linker prunes methods that are not directly reachable if the receiver type is never converted to interface. A type can be converted to interface using reflection through other types. The linker already takes this into consideration but it missed the case that the intermediate is a method descriptor. Handle this case. Change-Id: I590efc5da163c326db8d43583908a2ef67f65d9d Reviewed-on: https://go-review.googlesource.com/c/go/+/255858 Trust: Cherry Zhang <cherryyz@google.com> Run-TryBot: Cherry Zhang <cherryyz@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com> Reviewed-by: Jeremy Faller <jeremy@golang.org>
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@ -130,6 +130,19 @@ func (d *deadcodePass) flood() {
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}
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}
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if usedInIface {
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if usedInIface {
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methods = append(methods, methodref{src: symIdx, r: i})
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methods = append(methods, methodref{src: symIdx, r: i})
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// The method descriptor is itself a type descriptor, and
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// it can be used to reach other types, e.g. by using
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// reflect.Type.Method(i).Type.In(j). We need to traverse
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// its child types with UsedInIface set. (See also the
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// comment below.)
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rs := r.Sym()
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if !d.ldr.AttrUsedInIface(rs) {
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d.ldr.SetAttrUsedInIface(rs, true)
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if d.ldr.AttrReachable(rs) {
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d.ldr.SetAttrReachable(rs, false)
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d.mark(rs, symIdx)
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}
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}
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}
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}
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i += 2
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i += 2
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continue
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continue
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@ -215,9 +228,15 @@ func (d *deadcodePass) mark(symIdx, parent loader.Sym) {
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if *flagDumpDep {
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if *flagDumpDep {
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to := d.ldr.SymName(symIdx)
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to := d.ldr.SymName(symIdx)
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if to != "" {
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if to != "" {
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if d.ldr.AttrUsedInIface(symIdx) {
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to += " <UsedInIface>"
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}
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from := "_"
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from := "_"
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if parent != 0 {
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if parent != 0 {
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from = d.ldr.SymName(parent)
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from = d.ldr.SymName(parent)
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if d.ldr.AttrUsedInIface(parent) {
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from += " <UsedInIface>"
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}
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}
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}
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fmt.Printf("%s -> %s\n", from, to)
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fmt.Printf("%s -> %s\n", from, to)
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}
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}
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@ -32,6 +32,7 @@ func TestDeadcode(t *testing.T) {
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{"typedesc", "", "type.main.T"},
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{"typedesc", "", "type.main.T"},
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{"ifacemethod", "", "main.T.M"},
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{"ifacemethod", "", "main.T.M"},
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{"ifacemethod2", "main.T.M", ""},
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{"ifacemethod2", "main.T.M", ""},
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{"ifacemethod3", "main.S.M", ""},
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}
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}
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for _, test := range tests {
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for _, test := range tests {
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test := test
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test := test
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29
src/cmd/link/internal/ld/testdata/deadcode/ifacemethod3.go
vendored
Normal file
29
src/cmd/link/internal/ld/testdata/deadcode/ifacemethod3.go
vendored
Normal file
@ -0,0 +1,29 @@
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// Copyright 2020 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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// Like ifacemethod2.go, this tests that a method *is* live
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// if the type is "indirectly" converted to an interface
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// using reflection with a method descriptor as intermediate.
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package main
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import "reflect"
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type S int
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func (s S) M() { println("S.M") }
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type I interface { M() }
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type T float64
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func (t T) F(s S) {}
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func main() {
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var t T
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ft := reflect.TypeOf(t).Method(0).Type
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at := ft.In(1)
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v := reflect.New(at).Elem()
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v.Interface().(I).M()
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}
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