Implement a variation of scalar replacement for non-escaping allocations.

tests/language/load_to_load_forwarding_test.dart

Index: tests/language/load_to_load_forwarding_test.dart
diff --git a/tests/language/load_to_load_forwarding_test.dart b/tests/language/load_to_load_forwarding_test.dart
index 6c7d8b426747625c0e6549c1cb877203edd9fd0d..cade3c6e9af31a75ac7e96ce7aa0cac166560e7d 100644
--- a/tests/language/load_to_load_forwarding_test.dart
+++ b/tests/language/load_to_load_forwarding_test.dart
@@ -35,10 +35,37 @@ bar(a, mode) {
   return [value1, value2];
 }
 
+// Verify that immutable and mutable VM fields (array length in this case)
+// are not confused by load forwarding even if the access the same offset
+// in the object.
+testImmutableVMFields(arr, immutable) {
+  if (immutable) {
+    return arr.length;  // Immutable length load.
+  }
+
+  if (arr.length < 2) {  // Mutable length load, should not be forwarded.
+    arr.add(null);
+  }
+
+  return arr.length;
+}
+
 main() {
+  final fixed = new List(10);
+  final growable = [];
+  testImmutableVMFields(fixed, true);
+  testImmutableVMFields(growable, false);
+  testImmutableVMFields(growable, false);
+
   for (var i = 0; i < 2000; 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);
   }
+
+  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));
 }