compiler: add support for channel operations

Support for channels is not complete. The following pieces are missing:

  * Channels with values bigger than int. An int in TinyGo can always
    contain at least a pointer, so pointers are okay to send.
  * Buffered channels.
  * The select statement.

testdata/channel.go

@@ -0,0 +1,95 @@
+package main
+
+import "time"
+
+func main() {
+	ch := make(chan int)
+	println("len, cap of channel:", len(ch), cap(ch))
+	go sender(ch)
+
+	n, ok := <-ch
+	println("recv from open channel:", n, ok)
+
+	for n := range ch {
+		if n == 6 {
+			time.Sleep(time.Microsecond)
+		}
+		println("received num:", n)
+	}
+
+	n, ok = <-ch
+	println("recv from closed channel:", n, ok)
+
+	// Test multi-sender.
+	ch = make(chan int)
+	go fastsender(ch)
+	go fastsender(ch)
+	go fastsender(ch)
+	slowreceiver(ch)
+
+	// Test multi-receiver.
+	ch = make(chan int)
+	go fastreceiver(ch)
+	go fastreceiver(ch)
+	go fastreceiver(ch)
+	slowsender(ch)
+
+	// Test iterator style channel.
+	ch = make(chan int)
+	go iterator(ch, 100)
+	sum := 0
+	for i := range ch {
+		sum += i
+	}
+	println("sum(100):", sum)
+
+	// Allow goroutines to exit.
+	time.Sleep(time.Microsecond)
+}
+
+func sender(ch chan int) {
+	for i := 1; i <= 8; i++ {
+		if i == 4 {
+			time.Sleep(time.Microsecond)
+			println("slept")
+		}
+		ch <- i
+	}
+	close(ch)
+}
+
+func fastsender(ch chan int) {
+	ch <- 10
+	ch <- 11
+}
+
+func slowreceiver(ch chan int) {
+	for i := 0; i < 6; i++ {
+		n := <-ch
+		println("got n:", n)
+		time.Sleep(time.Microsecond)
+	}
+}
+
+func slowsender(ch chan int) {
+	for n := 0; n < 6; n++ {
+		time.Sleep(time.Microsecond)
+		ch <- 12 + n
+	}
+}
+
+func fastreceiver(ch chan int) {
+	sum := 0
+	for i := 0; i < 2; i++ {
+		n := <-ch
+		sum += n
+	}
+	println("sum:", sum)
+}
+
+func iterator(ch chan int, top int) {
+	for i := 0; i < top; i++ {
+		ch <- i
+	}
+	close(ch)
+}

testdata/channel.txt

@@ -0,0 +1,21 @@
+len, cap of channel: 0 0
+recv from open channel: 1 true
+received num: 2
+received num: 3
+slept
+received num: 4
+received num: 5
+received num: 6
+received num: 7
+received num: 8
+recv from closed channel: 0 false
+got n: 10
+got n: 11
+got n: 10
+got n: 11
+got n: 10
+got n: 11
+sum: 25
+sum: 29
+sum: 33
+sum(100): 4950