Weak references. (#1459)

backend.native/tests/build.gradle

@@ -2076,6 +2076,11 @@ task memory_escape2(type: RunKonanTest) {
     source = "runtime/memory/escape2.kt"
 }
 
+task memory_weak0(type: RunKonanTest) {
+    goldValue = "Data(s=Hello)\nnull\nOK\n"
+    source = "runtime/memory/weak0.kt"
+}
+
 task mpp1(type: RunStandaloneKonanTest) {
     source = "codegen/mpp/mpp1.kt"
     flags = ['-tr', '-Xmulti-platform']

backend.native/tests/runtime/memory/weak0.kt

@@ -0,0 +1,35 @@
+package runtime.memory.weak0
+
+import kotlin.test.*
+import konan.ref.*
+
+data class Data(val s: String)
+
+fun localWeak(): WeakReference<Data>  {
+    val x = Data("Hello")
+    val weak = WeakReference(x)
+
+    println(weak.get())
+    return weak
+}
+
+fun multiWeak(): Array<WeakReference<Data>>  {
+    val x = Data("Hello")
+    val weaks = Array(100, { WeakReference(x) } )
+    weaks.forEach {
+        it -> if (it.get()?.s != "Hello") throw Error("bad reference")
+    }
+    return weaks
+}
+
+@Test fun runTest() {
+    val weak = localWeak()
+    val value = weak.get()
+    println(value?.toString())
+
+    val weaks = multiWeak()
+    weaks.forEach {
+        it -> if (it.get()?.s != null) throw Error("not null")
+    }
+    println("OK")
+}