cmd/compile: preserve loop depth when evaluating block

Add block method to preserve loop depth when evaluating statements in a
block, so escape analysis can handle looping label more precisely.

Updates #22438

Change-Id: I39b306544a6c0ee3fcbebbe0d0ee735cb71773e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/193517
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/test/escape_goto.go b/test/escape_goto.go
new file mode 100644
index 0000000000..f024a9afe3
--- /dev/null
+++ b/test/escape_goto.go
@@ -0,0 +1,44 @@
+// errorcheck -0 -m -l
+
+// 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.
+
+// Test escape analysis for goto statements.
+
+package escape
+
+var x bool
+
+func _() {
+	var p *int
+loop:
+	if x {
+		goto loop
+	}
+	// BAD: We should be able to recognize that there
+	// aren't any more "goto loop" after here.
+	p = new(int) // ERROR "escapes to heap"
+	_ = p
+}
+
+func _() {
+	var p *int
+	if x {
+	loop:
+		goto loop
+	} else {
+		p = new(int) // ERROR "does not escape"
+	}
+	_ = p
+}
+
+func _() {
+	var p *int
+	if x {
+	loop:
+		goto loop
+	}
+	p = new(int) // ERROR "does not escape"
+	_ = p
+}