runtime: select bug

The sanity checking in pass 2 is wrong
when a select is offering to communicate in
either direction on a channel and neither case
is immediately ready.

R=ken2
CC=golang-dev
https://golang.org/cl/3991047

src/pkg/runtime/chan.c

@@ -732,25 +732,12 @@ loop:
 
 		switch(cas->send) {
 		case 0:	// recv
-			if(c->dataqsiz > 0) {
-				if(c->qcount > 0)
-					runtime·throw("select: pass 2 async recv");
-			} else {
-				if(dequeue(&c->sendq, c))
-					runtime·throw("select: pass 2 sync recv");
-			}
 			enqueue(&c->recvq, sg);
 			break;
 		
 		case 1:	// send
-			if(c->dataqsiz > 0) {
-				if(c->qcount < c->dataqsiz)
-					runtime·throw("select: pass 2 async send");
-			} else {
-				if(dequeue(&c->recvq, c))
-					runtime·throw("select: pass 2 sync send");
+			if(c->dataqsiz == 0)
 				c->elemalg->copy(c->elemsize, sg->elem, cas->u.elem);
-			}
 			enqueue(&c->sendq, sg);
 			break;
 		}

test/chan/select3.go

@@ -196,4 +196,13 @@ func main() {
 		case closedch <- 7:
 		}
 	})
+	
+	// select should not get confused if it sees itself
+	testBlock(always, func() {
+		c := make(chan int)
+		select {
+		case c <- 1:
+		case <-c:
+		}
+	})
 }