test: add tests for indirection level computation in escape analysis

The false positive (var incorrectly escapes to heap) is marked with BAD.

Change-Id: I11877fa8e976094b31a221abd88ae32d351c85ee
Reviewed-on: https://go-review.googlesource.com/5292Reviewed-by: Keith Randall <khr@golang.org>

test/escape_level.go

+// errorcheck -0 -m -l
+
+// Copyright 2015 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 indirection level computation in escape analysis.
+
+package escape
+
+var sink interface{}
+
+func level0() {
+	i := 0     // ERROR "moved to heap: i"
+	p0 := &i   // ERROR "moved to heap: p0" "&i escapes to heap"
+	p1 := &p0  // ERROR "moved to heap: p1" "&p0 escapes to heap"
+	p2 := &p1  // ERROR "moved to heap: p2" "&p1 escapes to heap"
+	sink = &p2 // ERROR "&p2 escapes to heap"
+}
+
+func level1() {
+	i := 0    // ERROR "moved to heap: i"
+	p0 := &i  // ERROR "moved to heap: p0" "&i escapes to heap"
+	p1 := &p0 // ERROR "moved to heap: p1" "&p0 escapes to heap"
+	p2 := &p1 // ERROR "&p1 escapes to heap"
+	sink = p2
+}
+
+func level2() {
+	i := 0    // ERROR "moved to heap: i"
+	p0 := &i  // ERROR "moved to heap: p0" "&i escapes to heap"
+	p1 := &p0 // ERROR "&p0 escapes to heap"
+	p2 := &p1 // ERROR "&p1 does not escape"
+	sink = *p2
+}
+
+func level3() {
+	i := 0    // ERROR "moved to heap: i"
+	p0 := &i  // ERROR "&i escapes to heap"
+	p1 := &p0 // ERROR "&p0 does not escape"
+	p2 := &p1 // ERROR "&p1 does not escape"
+	sink = **p2
+}
+
+func level4() {
+	i := 0     // ERROR "moved to heap: i"
+	p0 := &i   // ERROR "moved to heap: p0" "&i escapes to heap"
+	p1 := &p0  // ERROR "&p0 escapes to heap"
+	p2 := p1   // ERROR "moved to heap: p2"
+	sink = &p2 // ERROR "&p2 escapes to heap"
+}
+
+func level5() {
+	i := 0    // ERROR "moved to heap: i"
+	p0 := &i  // ERROR "moved to heap: p0" "&i escapes to heap"
+	p1 := &p0 // ERROR "&p0 escapes to heap"
+	p2 := p1
+	sink = p2
+}
+
+func level6() {
+	i := 0    // ERROR "moved to heap: i"
+	p0 := &i  // ERROR "&i escapes to heap"
+	p1 := &p0 // ERROR "&p0 does not escape"
+	p2 := p1
+	sink = *p2
+}
+
+func level7() {
+	i := 0     // ERROR "moved to heap: i"
+	p0 := &i   // ERROR "moved to heap: p0" "&i escapes to heap"
+	// BAD: p0 should not escape here
+	p1 := &p0  // ERROR "&p0 escapes to heap"
+	p2 := *p1  // ERROR "moved to heap: p2"
+	sink = &p2 // ERROR "&p2 escapes to heap"
+}
+
+func level8() {
+	i := 0    // ERROR "moved to heap: i"
+	p0 := &i  // ERROR "&i escapes to heap"
+	p1 := &p0 // ERROR "&p0 does not escape"
+	p2 := *p1
+	sink = p2
+}
+
+func level9() {
+	i := 0
+	p0 := &i  // ERROR "&i does not escape"
+	p1 := &p0 // ERROR "&p0 does not escape"
+	p2 := *p1
+	sink = *p2
+}
+
+func level10() {
+	i := 0
+	p0 := &i // ERROR "&i does not escape"
+	p1 := *p0
+	p2 := &p1 // ERROR "&p1 does not escape"
+	sink = *p2
+}
+
+func level11() {
+	i := 0
+	p0 := &i   // ERROR "&i does not escape"
+	p1 := &p0  // ERROR "&p0 does not escape"
+	p2 := **p1 // ERROR "moved to heap: p2"
+	sink = &p2 // ERROR "&p2 escapes to heap"
+}