cmd/gc: remove an incorrect assertion in escape analysis.

A fatal error used to happen when escassign-ing a multiple
function return to a single node. However, the situation
naturally appears when using "go f(g())" or "defer f(g())",
because g() is escassign-ed to sink.

Fixes #4529.

R=golang-dev, lvd, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/6920060

src/cmd/gc/esc.c

@@ -639,6 +639,7 @@ static void
 escassign(EscState *e, Node *dst, Node *src)
 {
 	int lno;
+	NodeList *ll;
 
 	if(isblank(dst) || dst == N || src == N || src->op == ONONAME || src->op == OXXX)
 		return;
@@ -715,9 +716,10 @@ escassign(EscState *e, Node *dst, Node *src)
 	case OCALLMETH:
 	case OCALLFUNC:
 	case OCALLINTER:
-		if(count(src->escretval) != 1)
-			fatal("escassign from call %+N", src);
-		escflows(e, dst, src->escretval->n);
+		// Flowing multiple returns to a single dst happens when
+		// analyzing "go f(g())": here g() flows to sink (issue 4529).
+		for(ll=src->escretval; ll; ll=ll->next)
+			escflows(e, dst, ll->n);
 		break;
 
 	case ODOT:

test/escape2.go

@@ -142,13 +142,13 @@ func (b Bar) AlsoLeak() *int { // ERROR "leaking param: b"
 }
 
 func (b Bar) LeaksToo() *int { // ERROR "leaking param: b"
-	v := 0	// ERROR "moved to heap: v"
+	v := 0    // ERROR "moved to heap: v"
 	b.ii = &v // ERROR "&v escapes"
 	return b.ii
 }
 
 func (b *Bar) LeaksABit() *int { // ERROR "b does not escape"
-	v := 0	// ERROR "moved to heap: v"
+	v := 0    // ERROR "moved to heap: v"
 	b.ii = &v // ERROR "&v escapes"
 	return b.ii
 }
@@ -574,7 +574,7 @@ func foo75esc(z *int) { // ERROR "leaking param: z"
 }
 
 func foo75aesc(z *int) { // ERROR "z does not escape"
-	var ppi **interface{}   // assignments to pointer dereferences lose track
+	var ppi **interface{}       // assignments to pointer dereferences lose track
 	*ppi = myprint1(z, 1, 2, 3) // ERROR "[.][.][.] argument escapes to heap"
 }
 
@@ -660,6 +660,21 @@ func foo81() *int {
 	return nil
 }
 
+func tee(p *int) (x, y *int) { return p, p } // ERROR "leaking param"
+
+func noop(x, y *int) {} // ERROR "does not escape"
+
+func foo82() {
+	var x, y, z int  // ERROR "moved to heap"
+	go noop(tee(&z)) // ERROR "&z escapes to heap"
+	go noop(&x, &y)  // ERROR "escapes to heap"
+	for {
+		var u, v, w int     // ERROR "moved to heap"
+		defer noop(tee(&u)) // ERROR "&u escapes to heap"
+		defer noop(&v, &w)  // ERROR "escapes to heap"
+	}
+}
+
 type Fooer interface {
 	Foo()
 }
@@ -1093,29 +1108,29 @@ L1:
 	_ = i
 }
 
-func foo124(x **int) {	// ERROR "x does not escape"
-	var i int	// ERROR "moved to heap: i"
-	p := &i 	// ERROR "&i escapes"
-	func() {	// ERROR "func literal does not escape"
-		*x = p	// ERROR "leaking closure reference p"
+func foo124(x **int) { // ERROR "x does not escape"
+	var i int // ERROR "moved to heap: i"
+	p := &i   // ERROR "&i escapes"
+	func() {  // ERROR "func literal does not escape"
+		*x = p // ERROR "leaking closure reference p"
 	}()
 }
 
-func foo125(ch chan *int) {	// ERROR "does not escape"
-	var i int	// ERROR "moved to heap"
-	p := &i 	// ERROR "&i escapes to heap"
-	func() {	// ERROR "func literal does not escape"
-		ch <- p	// ERROR "leaking closure reference p"
+func foo125(ch chan *int) { // ERROR "does not escape"
+	var i int // ERROR "moved to heap"
+	p := &i   // ERROR "&i escapes to heap"
+	func() {  // ERROR "func literal does not escape"
+		ch <- p // ERROR "leaking closure reference p"
 	}()
 }
 
 func foo126() {
-	var px *int  // loopdepth 0
+	var px *int // loopdepth 0
 	for {
 		// loopdepth 1
-		var i int  // ERROR "moved to heap"
+		var i int // ERROR "moved to heap"
 		func() {  // ERROR "func literal does not escape"
-			px = &i  // ERROR "&i escapes"
+			px = &i // ERROR "&i escapes"
 		}()
 	}
 }
@@ -1123,8 +1138,8 @@ func foo126() {
 var px *int
 
 func foo127() {
-	var i int  // ERROR "moved to heap: i"
-	p := &i  // ERROR "&i escapes to heap"
+	var i int // ERROR "moved to heap: i"
+	p := &i   // ERROR "&i escapes to heap"
 	q := p
 	px = q
 }
@@ -1137,12 +1152,12 @@ func foo128() {
 }
 
 func foo129() {
-	var i int  // ERROR "moved to heap: i"
-	p := &i  // ERROR "&i escapes to heap"
+	var i int // ERROR "moved to heap: i"
+	p := &i   // ERROR "&i escapes to heap"
 	func() {  // ERROR "func literal does not escape"
-		q := p  // ERROR "leaking closure reference p"
-		func() {  // ERROR "func literal does not escape"
-			r := q  // ERROR "leaking closure reference q"
+		q := p   // ERROR "leaking closure reference p"
+		func() { // ERROR "func literal does not escape"
+			r := q // ERROR "leaking closure reference q"
 			px = r
 		}()
 	}()
@@ -1150,40 +1165,40 @@ func foo129() {
 
 func foo130() {
 	for {
-		var i int  // ERROR "moved to heap"
+		var i int // ERROR "moved to heap"
 		func() {  // ERROR "func literal does not escape"
-			px = &i  // ERROR "&i escapes" "leaking closure reference i"
+			px = &i // ERROR "&i escapes" "leaking closure reference i"
 		}()
 	}
 }
 
 func foo131() {
-	var i int  // ERROR "moved to heap"
+	var i int // ERROR "moved to heap"
 	func() {  // ERROR "func literal does not escape"
-		px = &i  // ERROR "&i escapes" "leaking closure reference i"
+		px = &i // ERROR "&i escapes" "leaking closure reference i"
 	}()
 }
 
 func foo132() {
-	var i int  // ERROR "moved to heap"
-	go func() {  // ERROR "func literal escapes to heap"
-		px = &i  // ERROR "&i escapes" "leaking closure reference i"
+	var i int   // ERROR "moved to heap"
+	go func() { // ERROR "func literal escapes to heap"
+		px = &i // ERROR "&i escapes" "leaking closure reference i"
 	}()
 }
 
 func foo133() {
-	var i int  // ERROR "moved to heap"
-	defer func() {  // ERROR "func literal does not escape"
-		px = &i  // ERROR "&i escapes" "leaking closure reference i"
+	var i int      // ERROR "moved to heap"
+	defer func() { // ERROR "func literal does not escape"
+		px = &i // ERROR "&i escapes" "leaking closure reference i"
 	}()
 }
 
 func foo134() {
 	var i int
 	p := &i  // ERROR "&i does not escape"
-	func() {  // ERROR "func literal does not escape"
+	func() { // ERROR "func literal does not escape"
 		q := p
-		func() {  // ERROR "func literal does not escape"
+		func() { // ERROR "func literal does not escape"
 			r := q
 			_ = r
 		}()
@@ -1191,11 +1206,11 @@ func foo134() {
 }
 
 func foo135() {
-	var i int  // ERROR "moved to heap: i"
-	p := &i  // ERROR "&i escapes to heap" "moved to heap: p"
-	go func() {  // ERROR "func literal escapes to heap"
-		q := p  // ERROR "&p escapes to heap"
-		func() {  // ERROR "func literal does not escape"
+	var i int   // ERROR "moved to heap: i"
+	p := &i     // ERROR "&i escapes to heap" "moved to heap: p"
+	go func() { // ERROR "func literal escapes to heap"
+		q := p   // ERROR "&p escapes to heap"
+		func() { // ERROR "func literal does not escape"
 			r := q
 			_ = r
 		}()
@@ -1203,11 +1218,11 @@ func foo135() {
 }
 
 func foo136() {
-	var i int  // ERROR "moved to heap: i"
-	p := &i  // ERROR "&i escapes to heap" "moved to heap: p"
-	go func() {  // ERROR "func literal escapes to heap"
-		q := p  // ERROR "&p escapes to heap" "leaking closure reference p"
-		func() {  // ERROR "func literal does not escape"
+	var i int   // ERROR "moved to heap: i"
+	p := &i     // ERROR "&i escapes to heap" "moved to heap: p"
+	go func() { // ERROR "func literal escapes to heap"
+		q := p   // ERROR "&p escapes to heap" "leaking closure reference p"
+		func() { // ERROR "func literal does not escape"
 			r := q // ERROR "leaking closure reference q"
 			px = r
 		}()
@@ -1215,12 +1230,12 @@ func foo136() {
 }
 
 func foo137() {
-	var i int  // ERROR "moved to heap: i"
-	p := &i  // ERROR "&i escapes to heap"
+	var i int // ERROR "moved to heap: i"
+	p := &i   // ERROR "&i escapes to heap"
 	func() {  // ERROR "func literal does not escape"
-		q := p  // ERROR "leaking closure reference p" "moved to heap: q"
+		q := p      // ERROR "leaking closure reference p" "moved to heap: q"
 		go func() { // ERROR "func literal escapes to heap"
-			r := q  // ERROR "&q escapes to heap"
+			r := q // ERROR "&q escapes to heap"
 			_ = r
 		}()
 	}()
@@ -1230,7 +1245,7 @@ func foo138() *byte {
 	type T struct {
 		x [1]byte
 	}
-	t := new(T) // ERROR "new.T. escapes to heap"
+	t := new(T)    // ERROR "new.T. escapes to heap"
 	return &t.x[0] // ERROR "&t.x.0. escapes to heap"
 }
 
@@ -1240,6 +1255,6 @@ func foo139() *byte {
 			y byte
 		}
 	}
-	t := new(T) // ERROR "new.T. escapes to heap"
+	t := new(T)   // ERROR "new.T. escapes to heap"
 	return &t.x.y // ERROR "&t.x.y escapes to heap"
 }

test/fixedbugs/issue4529.go

+// compile
+
+// 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.
+
+// Issue 4529: escape analysis crashes on "go f(g())"
+// when g has multiple returns.
+
+package main
+
+type M interface{}
+
+type A struct {
+	a string
+	b chan M
+}
+
+func (a *A) I() (b <-chan M, c chan<- M) {
+	a.b, c = make(chan M), make(chan M)
+	b = a.b
+
+	return
+}
+
+func Init(a string, b *A, c interface {
+	I() (<-chan M, chan<- M)
+}) {
+	b.a = a
+	go b.c(c.I())
+}
+
+func (a *A) c(b <-chan M, _ chan<- M) {}