cmd/gc: fix pointer composite literals in exported if statements.

Fixes #4230 (again).

R=rsc, golang-dev, r
CC=golang-dev
https://golang.org/cl/10470043

src/cmd/gc/fmt.c

@@ -1222,7 +1222,7 @@ exprfmt(Fmt *f, Node *n, int prec)
 		}
 		if(fmtmode == FExp && ptrlit)
 			// typecheck has overwritten OIND by OTYPE with pointer type.
-			return fmtprint(f, "&%T{ %,H }", n->right->type->type, n->list);
+			return fmtprint(f, "(&%T{ %,H })", n->right->type->type, n->list);
 		return fmtprint(f, "(%N{ %,H })", n->right, n->list);
 
 	case OPTRLIT:

test/fixedbugs/bug465.dir/a.go

@@ -59,3 +59,18 @@ func F7() int {
 	}
 	return 0
 }
+
+func F8() int {
+	if a := (&T{1, 1}); a != nil {
+		return 1
+	}
+	return 0
+}
+
+func F9() int {
+	var a *T
+	if a = (&T{1, 1}); a != nil {
+		return 1
+	}
+	return 0
+}

test/fixedbugs/bug465.dir/b.go

@@ -9,7 +9,7 @@ import "./a"
 func main() {
 	for _, f := range []func() int{
 		a.F1, a.F2, a.F3, a.F4,
-		a.F5, a.F6, a.F7} {
+		a.F5, a.F6, a.F7, a.F8, a.F9} {
 		if f() > 1 {
 			panic("f() > 1")
 		}