Fix incorrect handling of refined aliases during load forwarding.

tests/language/vm/load_to_load_forwarding_vm_test.dart

 // Copyright (c) 2012, 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 correctness of side effects tracking used by load to load forwarding.
 
 // VMOptions=--optimization-counter-threshold=10
 
 import "package:expect/expect.dart";
 import "dart:typed_data";
 
@@ skipping 453 matching lines @@
   global_array[0].x++;
 }
 
 testAliasingStoreIndexed(array) {
   var z = new Z();
   array[0] = z;
   side_effect();
   return z.x;
 }
 
+class ZZ {
+  var f;
+}
+
+var zz, f0 = 42;
+
+testAliasesRefinement() {
+  zz = new ZZ();
+  var b = zz;
+  if (b.f == null) {
+    b.f = f0;
+  }
+  return b.f;
+}
+
 main() {
   final fixed = new List(10);
   final growable = [];
   testImmutableVMFields(fixed, true);
   testImmutableVMFields(growable, false);
   testImmutableVMFields(growable, false);
 
   final f64List = new Float64List(2);
   testPhiRepresentation(true, f64List);
   testPhiRepresentation(false, f64List);
 
   final obj = new X(new X(new X(null)));
 
   final cs = new C(0, new C(1, new C(2, null)));
 
   for (var i = 0; i < 20; i++) {
     Expect.listEquals([0x02010000, 0x03020100], foo(new A(0, 0)));
     Expect.listEquals([0x02010000, 0x03020100], bar(new A(0, 0), false));
     Expect.listEquals([0x04020000, 0x03020100], bar(new A(0, 0), true));
     testImmutableVMFields(fixed, true);
     testPhiRepresentation(true, f64List);
     testPhiForwarding(obj);
     testPhiForwarding2(obj);
     testPhiForwarding3();
     testPhiForwarding4();
     Expect.equals(4, testPhiForwarding5(cs));
     testEqualPhisElimination();
+    Expect.equals(f0, testAliasesRefinement());
   }
 
   Expect.equals(1, testImmutableVMFields([], false));
   Expect.equals(2, testImmutableVMFields([1], false));
   Expect.equals(2, testImmutableVMFields([1, 2], false));
   Expect.equals(3, testImmutableVMFields([1, 2, 3], false));
 
   final u32List = new Uint32List(3);
   u32List[0] = 0;
   u32List[1] = 0x3FFFFFFF;
@@ skipping 19 matching lines @@
     Expect.equals(3, testIndexedNoAlias(array));
   }
 
   testIndexedAliasedStores();
 
   var test_array = new List(1);
   for (var i = 0; i < 20; i++) {
     Expect.equals(43, testAliasingStoreIndexed(global_array));
   }
 }