gc: issue 1231

Fixes #1231.

R=ken2
CC=golang-dev
https://golang.org/cl/3627041

src/cmd/gc/gen.c

@@ -433,7 +433,7 @@ cgen_discard(Node *nr)
 
 	switch(nr->op) {
 	case ONAME:
-		if(!(nr->class & PHEAP) && nr->class != PEXTERN && nr->class != PFUNC)
+		if(!(nr->class & PHEAP) && nr->class != PEXTERN && nr->class != PFUNC && nr->class != PPARAMREF)
 			gused(nr);
 		break;
 

test/closure.go

@@ -98,4 +98,15 @@ func main() {
 		println("newfunc returned broken funcs")
 		panic("fail")
 	}
+
+	ff(1)
+}
+
+func ff(x int) {
+	call(func() {
+		_ = x
+	})
+}
+
+func call(func()) {
 }