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cmd/compile: clear hidden value at end of channel range body
While we’re here, clean up a few comments. Fixes #15281 Change-Id: Ia6173e9941133db08f57bc80bdd3c5722122bfdb Reviewed-on: https://go-review.googlesource.com/22082 Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>
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@ -154,7 +154,7 @@ func walkrange(n *Node) {
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v2 = n.List.Second()
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v2 = n.List.Second()
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}
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}
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// n->list has no meaning anymore, clear it
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// n.List has no meaning anymore, clear it
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// to avoid erroneous processing by racewalk.
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// to avoid erroneous processing by racewalk.
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n.List.Set(nil)
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n.List.Set(nil)
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@ -217,9 +217,9 @@ func walkrange(n *Node) {
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n.Right.Ninit.Set1(a)
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n.Right.Ninit.Set1(a)
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}
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}
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// orderstmt allocated the iterator for us.
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// we only use a once, so no copy needed.
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case TMAP:
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case TMAP:
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// orderstmt allocated the iterator for us.
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// we only use a once, so no copy needed.
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ha := a
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ha := a
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th := hiter(t)
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th := hiter(t)
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@ -254,8 +254,8 @@ func walkrange(n *Node) {
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body = []*Node{a}
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body = []*Node{a}
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}
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}
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// orderstmt arranged for a copy of the channel variable.
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case TCHAN:
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case TCHAN:
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// orderstmt arranged for a copy of the channel variable.
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ha := a
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ha := a
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n.Left = nil
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n.Left = nil
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@ -278,9 +278,13 @@ func walkrange(n *Node) {
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} else {
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} else {
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body = []*Node{Nod(OAS, v1, hv1)}
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body = []*Node{Nod(OAS, v1, hv1)}
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}
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}
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// Zero hv1. This prevents hv1 from being the sole, inaccessible
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// reference to an otherwise GC-able value during the next channel receive.
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// See issue 15281.
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body = append(body, Nod(OAS, hv1, nil))
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// orderstmt arranged for a copy of the string variable.
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case TSTRING:
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case TSTRING:
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// orderstmt arranged for a copy of the string variable.
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ha := a
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ha := a
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ohv1 := temp(Types[TINT])
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ohv1 := temp(Types[TINT])
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64
test/fixedbugs/issue15281.go
Normal file
64
test/fixedbugs/issue15281.go
Normal file
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@ -0,0 +1,64 @@
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// run
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// 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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package main
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import "runtime"
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func main() {
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{
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x := inuse()
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c := make(chan []byte, 10)
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c <- make([]byte, 10<<20)
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close(c)
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f1(c, x)
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}
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{
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x := inuse()
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c := make(chan []byte, 10)
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c <- make([]byte, 10<<20)
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close(c)
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f2(c, x)
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}
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}
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func f1(c chan []byte, start int64) {
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for x := range c {
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if delta := inuse() - start; delta < 9<<20 {
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println("BUG: f1: after alloc: expected delta at least 9MB, got: ", delta)
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println(x)
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}
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x = nil
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if delta := inuse() - start; delta > 1<<20 {
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println("BUG: f1: after alloc: expected delta below 1MB, got: ", delta)
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println(x)
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}
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}
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}
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func f2(c chan []byte, start int64) {
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for {
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x, ok := <-c
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if !ok {
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break
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}
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if delta := inuse() - start; delta < 9<<20 {
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println("BUG: f2: after alloc: expected delta at least 9MB, got: ", delta)
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println(x)
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}
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x = nil
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if delta := inuse() - start; delta > 1<<20 {
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println("BUG: f2: after alloc: expected delta below 1MB, got: ", delta)
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println(x)
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}
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}
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}
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func inuse() int64 {
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runtime.GC()
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var st runtime.MemStats
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runtime.ReadMemStats(&st)
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return int64(st.Alloc)
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}
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