Cycle collector. (#175)

backend.native/tests/runtime/memory/cycles0.kt

@@ -0,0 +1,45 @@
+data class Node(val data: Int, var next: Node?, var prev: Node?, val outer: Node?)
+
+fun makeCycle(len: Int, outer: Node?): Node {
+    val start = Node(0, null, null, outer)
+    var prev = start
+    for (i in 1 .. len - 1) {
+        prev = Node(i, prev, null, outer)
+    }
+    start.next = prev
+    return start
+}
+
+fun makeDoubleCycle(len: Int): Node {
+    val start = makeCycle(len, null)
+    var prev = start
+    var cur = prev.next
+    while (cur != start) {
+        cur!!.prev = prev
+        prev = cur
+        cur = cur.next
+    }
+    start.prev = prev
+    return start
+}
+
+fun createCycles(junk: Node) {
+    val cycle1 = makeCycle(1, junk)
+    val cycle2 = makeCycle(2, junk)
+    val cycle10 = makeCycle(10, junk)
+    val cycle100 = makeCycle(100, junk)
+    val dcycle1 = makeDoubleCycle(1)
+    val dcycle2 = makeDoubleCycle(2)
+    val dcycle10 = makeDoubleCycle(10)
+    val dcycle100 = makeDoubleCycle(100)
+
+}
+
+fun main(args : Array<String>) {
+    // Create outer link from cyclic garbage.
+    val outer = Node(42, null, null, null)
+    createCycles(outer)
+    konan.internal.GC.collect()
+    // Ensure outer is not collected.
+    println(outer.data)
+}