Fix bugs in load elimination and type propagation.

tests/language/vm/load_to_load_forwarding_vm_test.dart

Index: tests/language/vm/load_to_load_forwarding_vm_test.dart
===================================================================
--- tests/language/vm/load_to_load_forwarding_vm_test.dart	(revision 28924)
+++ tests/language/vm/load_to_load_forwarding_vm_test.dart	(working copy)
@@ -195,6 +195,24 @@
   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 = [];
@@ -236,6 +254,11 @@
     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);