cmd/compile: fix -m=2 infinite loop in escape.go
This CL detects infinite loops due to negative dereference cycles
during escape analysis, and terminates the loop gracefully. We still
fail to print a complete explanation of the escape path, but esc.go
didn't print *any* explanation for these test cases, so the release
blocking issue here is simply that we don't infinite loop.
Updates #35518.
Change-Id: I39beed036e5a685706248852f1fa619af3b7abbc
Reviewed-on: https://go-review.googlesource.com/c/go/+/206619
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/gc/escape.go b/src/cmd/compile/internal/gc/escape.go
index 0f71f99..76c91ba 100644
--- a/src/cmd/compile/internal/gc/escape.go
+++ b/src/cmd/compile/internal/gc/escape.go
@@ -1226,8 +1226,17 @@
// explainPath prints an explanation of how src flows to the walk root.
func (e *Escape) explainPath(root, src *EscLocation) {
+ visited := make(map[*EscLocation]bool)
+
pos := linestr(src.n.Pos)
for {
+ // Prevent infinite loop.
+ if visited[src] {
+ fmt.Printf("%s: warning: truncated explanation due to assignment cycle; see golang.org/issue/35518\n", pos)
+ break
+ }
+ visited[src] = true
+
dst := src.dst
edge := &dst.edges[src.dstEdgeIdx]
if edge.src != src {
diff --git a/test/fixedbugs/issue35518.go b/test/fixedbugs/issue35518.go
new file mode 100644
index 0000000..18a02d4
--- /dev/null
+++ b/test/fixedbugs/issue35518.go
@@ -0,0 +1,36 @@
+// errorcheck -0 -l -m=2
+
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This test makes sure that -m=2's escape analysis diagnostics don't
+// go into an infinite loop when handling negative dereference
+// cycles. The critical thing being tested here is that compilation
+// succeeds ("errorcheck -0"), not any particular diagnostic output,
+// hence the very lax ERROR patterns below.
+
+package p
+
+type Node struct {
+ Orig *Node
+}
+
+var sink *Node
+
+func f1() {
+ var n Node // ERROR "."
+ n.Orig = &n
+
+ m := n // ERROR "."
+ sink = &m
+}
+
+func f2() {
+ var n1, n2 Node // ERROR "."
+ n1.Orig = &n2
+ n2 = n1
+
+ m := n2 // ERROR "."
+ sink = &m
+}
