cmd/gc: escape analysis to track flow of in to out parameters.

includes step 0: synthesize outparams, from 6600044
includes step 1,2: give outparams loopdepth 0 and verify unchanged results
         generate esc:$mask tags, but still tie to sink if a param has mask != 0
from 6610054

adds final steps:
- have esccall generate n->escretval, a list of nodes the function results flow to
- use these in esccall and ORETURN/OAS2FUNC/and f(g())
- only tie parameters to sink if tag is absent, otherwise according to mask, tie them to escretval

R=rsc, bradfitz
CC=dave, gobot, golang-dev, iant, rsc
https://golang.org/cl/6741044

1 files changed, 119 insertions, 0 deletions

diff --git a/test/escape5.go b/test/escape5.go
new file mode 100644
index 0000000000..22c324f902
--- /dev/null
+++ b/test/escape5.go
@@ -0,0 +1,119 @@
+// errorcheck -0 -m -l
+
+// Copyright 2012 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, using compiler diagnostic flags, that the escape analysis is working.
+// Compiles but does not run.  Inlining is disabled.
+
+package foo
+
+func noleak(p *int) int { // ERROR "p does not escape"
+	return *p
+}
+
+func leaktoret(p *int) *int { // ERROR "leaking param: p to result"
+	return p
+}
+
+func leaktoret2(p *int) (*int, *int) { // ERROR "leaking param: p to result .anon1" "leaking param: p to result .anon2"
+	return p, p
+}
+
+func leaktoret22(p, q *int) (*int, *int) { // ERROR "leaking param: p to result .anon2" "leaking param: q to result .anon3"
+	return p, q
+}
+
+func leaktoret22b(p, q *int) (*int, *int) { // ERROR "leaking param: p to result .anon3" "leaking param: q to result .anon2"
+	return leaktoret22(q, p)
+}
+
+func leaktoret22c(p, q *int) (*int, *int) { // ERROR "leaking param: p to result .anon3" "leaking param: q to result .anon2"
+	r, s := leaktoret22(q, p)
+	return r, s
+}
+
+func leaktoret22d(p, q *int) (r, s *int) { // ERROR "leaking param: p to result s" "leaking param: q to result r"
+	r, s = leaktoret22(q, p)
+	return
+}
+
+func leaktoret22e(p, q *int) (r, s *int) { // ERROR "leaking param: p to result s" "leaking param: q to result r"
+	r, s = leaktoret22(q, p)
+	return r, s
+}
+
+func leaktoret22f(p, q *int) (r, s *int) { // ERROR "leaking param: p to result s" "leaking param: q to result r"
+	rr, ss := leaktoret22(q, p)
+	return rr, ss
+}
+
+var gp *int
+
+func leaktosink(p *int) *int { // ERROR "leaking param: p"
+	gp = p
+	return p
+}
+
+func f1() {
+	var x int
+	p := noleak(&x) // ERROR "&x does not escape"
+	_ = p
+}
+
+func f2() {
+	var x int
+	p := leaktoret(&x) // ERROR "&x does not escape"
+	_ = p
+}
+
+func f3() {
+	var x int          // ERROR "moved to heap: x"
+	p := leaktoret(&x) // ERROR "&x escapes to heap"
+	gp = p
+}
+
+func f4() {
+	var x int              // ERROR "moved to heap: x"
+	p, q := leaktoret2(&x) // ERROR "&x escapes to heap"
+	gp = p
+	gp = q
+}
+
+func f5() {
+	var x int
+	leaktoret22(leaktoret2(&x)) // ERROR "&x does not escape"
+}
+
+func f6() {
+	var x int                               // ERROR "moved to heap: x"
+	px1, px2 := leaktoret22(leaktoret2(&x)) // ERROR "&x escapes to heap"
+	gp = px1
+	_ = px2
+}
+
+type T struct{ x int }
+
+func (t *T) Foo(u int) (*T, bool) { // ERROR "leaking param: t to result"
+	t.x += u
+	return t, true
+}
+
+func f7() *T {
+	r, _ := new(T).Foo(42) // ERROR "new.T. escapes to heap"
+	return r
+}
+
+func leakrecursive1(p, q *int) (*int, *int) { // ERROR "leaking param: p" "leaking param: q"
+	return leakrecursive2(q, p)
+}
+
+func leakrecursive2(p, q *int) (*int, *int) { // ERROR "leaking param: p" "leaking param: q"
+	if *p > *q {
+		return leakrecursive1(q, p)
+	}
+	// without this, leakrecursive? are safe for p and q, b/c in fact their graph does not have leaking edges.
+	return p, q
+}
+