gc: treat DOTMETH like DOT in escape analysis.

Fixes #2225

R=rsc, nigeltao, dave
CC=bradfitz, golang-dev, mikioh.mikioh
https://golang.org/cl/4972056

src/cmd/gc/esc.c

@@ -398,6 +398,8 @@ escassign(Node *dst, Node *src)
 	case OCONVIFACE:
 	case OCONVNOP:
 	case ODOT:
+	case ODOTMETH:	// treat recv.meth as a value with recv in it, only happens in ODEFER and OPROC
+			// iface.method already leaks iface in esccall, no need to put in extra ODOTINTER edge here
 	case ODOTTYPE:
 	case ODOTTYPE2:
 	case OSLICE:

test/escape2.go

@@ -127,6 +127,10 @@ func (b *Bar) AlsoNoLeak() *int { // ERROR "b does not escape"
 	return b.ii
 }
 
+func goLeak(b *Bar) {  // ERROR "leaking param: NAME-b"
+	go b.NoLeak()
+}
+
 type Bar2 struct {
 	i  [12]int
 	ii []int
@@ -395,6 +399,10 @@ func foo64(m M) { // ERROR "leaking param: NAME-m"
 	m.M()
 }
 
+func foo64b(m M) { // ERROR "leaking param: NAME-m"
+	defer m.M()
+}
+
 type MV int
 
 func (MV) M() {}