gc: fix send precedence

Test and fix case found by Robert.
Add receive inside send to tree too.

R=ken2
CC=golang-dev
https://golang.org/cl/3973052

src/cmd/gc/go.y

@@ -93,9 +93,10 @@ static void fixlbrace(int);
 %type	<type>	hidden_type_func
 %type	<type>	hidden_type_recv_chan hidden_type_non_recv_chan
 
+%left		LCOMM	/* outside the usual hierarchy; here for good error messages */
+
 %left		LOROR
 %left		LANDAND
-%left		LCOMM
 %left		LEQ LNE LLE LGE LLT LGT
 %left		'+' '-' '|' '^'
 %left		'*' '/' '%' '&' LLSH LRSH LANDNOT

test/chan/sendstmt.go

@@ -0,0 +1,37 @@
+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2011 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.
+
+// Test various parsing cases that are a little
+// different now that send is a statement, not a expression.
+
+package main
+
+func main() {
+	chanchan()
+	sendprec()
+}
+
+func chanchan() {
+	cc := make(chan chan int, 1)
+	c := make(chan int, 1)
+	cc <- c
+	select {
+	case <-cc <- 2:
+	default:
+		panic("nonblock")
+	}
+	if <-c != 2 {
+		panic("bad receive")
+	}
+}
+
+func sendprec() {
+	c := make(chan bool, 1)
+	c <- false || true	// not a syntax error: same as c <- (false || true)
+	if !<-c {
+		panic("sent false")
+	}
+}