Fix bugs in load elimination and type propagation.

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 177 matching lines @@
       v.x = i - 1;
       v.y = i - 1;
     }
     sum += v.x + v.y;
   }
   Expect.equals(4, sum);
   Expect.equals(2, u.x);
   Expect.equals(2, u.y);
 }
 
+
+testPhiMultipleRepresentations(f, arr) {
+  var w;
+  if (f) {
+    w = arr[0] + arr[1];
+  } else {
+    w = arr[0] - arr[1];
+  }
+  var v;
+  if (f) {
+    v = arr[0];
+  } else {
+    v = arr[0];
+  }
+  return v + w;
+}
+
+
 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);
@@ skipping 21 matching lines @@
   final u32List = new Uint32List(3);
   u32List[0] = 0;
   u32List[1] = 0x3FFFFFFF;
   u32List[2] = 0x7FFFFFFF;
 
   for (var i = 0; i < 20; i++) {
     testPhiConvertions(true, u32List);
     testPhiConvertions(false, u32List);
   }
 
+  for (var i = 0; i < 20; i++) {
+    Expect.equals(0.0, testPhiMultipleRepresentations(true, f64List));
+    Expect.equals(0, testPhiMultipleRepresentations(false, const [1,2]));
+  }
+
   final escape = new List(1);
   for (var i = 0; i < 20; i++) {
     fakeAliasing(escape);
   }
 }