From f346a4c44c7200454d01c05879fbcd76a1ca9237 Mon Sep 17 00:00:00 2001
From: Matthew Dempsky <mdempsky@google.com>
Date: Tue, 24 Sep 2019 17:35:15 -0700
Subject: [PATCH] test: add regress test for #27557

This commit just adds a regress test for a few of the important corner
cases that I identified in #27557, which turn out to not be tested
anywhere.

While here, annotate a few of the existing test cases where we could
improve escape analysis.

Updates #27557.

Change-Id: Ie57792a538f7899bb17915485fabc86100f469a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/197137
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
---
 src/cmd/compile/internal/gc/escape.go |  5 +---
 test/escape2.go                       |  1 +
 test/escape2n.go                      |  1 +
 test/fixedbugs/issue21709.go          |  2 ++
 test/fixedbugs/issue27557.go          | 42 +++++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 4 deletions(-)
 create mode 100644 test/fixedbugs/issue27557.go

diff --git a/src/cmd/compile/internal/gc/escape.go b/src/cmd/compile/internal/gc/escape.go
index 85a495a769..106b877349 100644
--- a/src/cmd/compile/internal/gc/escape.go
+++ b/src/cmd/compile/internal/gc/escape.go
@@ -505,10 +505,7 @@ func (e *Escape) exprSkipInit(k EscHole, n *Node) {
 	case OCALLPART:
 		e.spill(k, n)
 
-		// esc.go says "Contents make it to memory, lose
-		// track."  I think we can just flow n.Left to our
-		// spilled location though.
-		// TODO(mdempsky): Try that.
+		// TODO(mdempsky): We can do better here. See #27557.
 		e.assignHeap(n.Left, "call part", n)
 
 	case OPTRLIT:
diff --git a/test/escape2.go b/test/escape2.go
index b7cd914c22..4e30331380 100644
--- a/test/escape2.go
+++ b/test/escape2.go
@@ -1386,6 +1386,7 @@ func (t *Tm) M() { // ERROR "t does not escape$"
 func foo141() {
 	var f func()
 
+	// BAD: new(Tm) should not escape
 	t := new(Tm) // ERROR "new\(Tm\) escapes to heap$"
 	f = t.M      // ERROR "t.M does not escape$"
 	_ = f
diff --git a/test/escape2n.go b/test/escape2n.go
index 42312fe41d..26b0a1d8c5 100644
--- a/test/escape2n.go
+++ b/test/escape2n.go
@@ -1386,6 +1386,7 @@ func (t *Tm) M() { // ERROR "t does not escape$"
 func foo141() {
 	var f func()
 
+	// BAD: new(Tm) should not escape
 	t := new(Tm) // ERROR "new\(Tm\) escapes to heap$"
 	f = t.M      // ERROR "t.M does not escape$"
 	_ = f
diff --git a/test/fixedbugs/issue21709.go b/test/fixedbugs/issue21709.go
index 10f5660e1b..abc9e767e5 100644
--- a/test/fixedbugs/issue21709.go
+++ b/test/fixedbugs/issue21709.go
@@ -14,6 +14,7 @@ func (s *S) Inc() {} // ERROR "s does not escape"
 var N int
 
 func F1() {
+	// BAD: s should not escape
 	var s S // ERROR "moved to heap: s"
 	for i := 0; i < N; i++ {
 		fs := []func(){ // ERROR "\[\]func\(\) literal does not escape"
@@ -26,6 +27,7 @@ func F1() {
 }
 
 func F2() {
+	// BAD: s should not escape
 	var s S // ERROR "moved to heap: s"
 	for i := 0; i < N; i++ {
 		for _, f := range []func(){ // ERROR "\[\]func\(\) literal does not escape"
diff --git a/test/fixedbugs/issue27557.go b/test/fixedbugs/issue27557.go
new file mode 100644
index 0000000000..11a23f6932
--- /dev/null
+++ b/test/fixedbugs/issue27557.go
@@ -0,0 +1,42 @@
+// errorcheck -0 -l -m
+
+// 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.
+
+package p
+
+var sink interface{}
+
+func _() {
+	// BAD: t should not escape
+	var t T         // ERROR "moved to heap"
+	f := t.noescape // ERROR "t.noescape does not escape"
+	f()
+}
+
+func _() {
+	var t T       // ERROR "moved to heap"
+	f := t.escape // ERROR "t.escape does not escape"
+	f()
+}
+
+func _() {
+	var t T        // ERROR "moved to heap"
+	f := t.returns // ERROR "t.returns does not escape"
+	sink = f()
+}
+
+type T struct{}
+
+func (t *T) noescape()   {}           // ERROR "t does not escape"
+func (t *T) escape()     { sink = t } // ERROR "leaking param: t$"
+func (t *T) returns() *T { return t } // ERROR "leaking param: t to result ~r0 level=0"
+
+func (t *T) recursive() { // ERROR "leaking param: t$"
+	sink = t
+
+	var t2 T          // ERROR "moved to heap"
+	f := t2.recursive // ERROR "t2.recursive does not escape"
+	f()
+}
-- 
2.50.0