Fix bug with guarded fields and deserialization.

tests/language/vm/optimized_guarded_field_test.dart

 // Copyright (c) 2013, 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.
 // Test correct handling of phis with only environment uses that were inserted
 // by store to load forwarding.
 // VMOptions=--optimization_counter_threshold=10
 
 import "package:expect/expect.dart";
 
 class A {
@@ skipping 14 matching lines @@
   test(a);
   test(b);
   for (var i = 0; i < 20; ++i) test(a);
   Expect.equals("null", test(a));
   Expect.equals("null", test(b));
 
   // Store a non-null object into foo to trigger deoptimization of test.
   a.foo = 123;
   Expect.equals("other", test(a));
   Expect.equals("null", test(b));
+
+  // Test guarded fields with allocation sinking and deoptimization.
+  Expect.equals(43, test_deopt(42, 1));
+  for (var i = 0; i < 20; i++) test_deopt(42, 1);
+  Expect.equals(43, test_deopt(42, 1));
+  Expect.equals("aaabbb", test_deopt("aaa", "bbb"));
 }
+
+
+class C {
+  C(this.x, this.y);
+  final x;
+  final y;
+}
+
+
+test_deopt(a, b) {
+  var c = new C(a, b);
+  return c.x + c.y;
+}