implement null aware ops, fixes #249

test/codegen/language/nullaware_opt_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// VMOptions=--optimization_counter_threshold=5
+//
+// Basic null-aware operator test that invokes the optimizing compiler.
+
+import "package:expect/expect.dart";
+
+class C {
+  C(this.f);
+  var f;
+  m(a) => a;
+}
+
+bomb() {
+  Expect.fail('Should not be executed');
+  return 100;
+}
+
+getNull() => null;
+
+test() {
+  var c;
+  var d = new C(5);
+  Expect.equals(null, c?.m(bomb()));
+  Expect.equals(null, getNull()?.anything(bomb()));
+  Expect.equals(1, d?.m(1));
+
+  Expect.equals(1, new C(1)?.f);
+  Expect.equals(null, c?.v);
+  Expect.equals(10, c ?? 10);
+  Expect.equals(d, d ?? bomb());
+
+  var e;
+  // The assignment to e is not executed since d != null.
+  d ??= e ??= new C(100);
+  Expect.equals(null, e);
+  e ??= new C(100);
+  Expect.equals(100, e?.f);
+  e?.f ??= 200;
+  Expect.equals(100, e?.f);
+
+  e.f = null;
+  e?.f ??= 200;
+  Expect.equals(200, e?.f);
+
+  c?.f ??= 400;
+  Expect.equals(null, c?.f);
+  Expect.equals(null, c?.f++);
+  e?.f++;
+  Expect.equals(201, e.f);
+
+  var x = 5 ?? bomb();
+}
+
+// Check that instructions without result do not crash.
+test2() {
+  var c;
+  c?.v;
+  c?.m(bomb());
+}
+
+main() {
+  for (int i = 0; i < 10; i++) {
+    test();
+    test2();
+  }
+}