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

tests/language/load_to_load_forwarding_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.
 
 import "package:expect/expect.dart";
 
 class A {
   var x, y;
   A(this.x, this.y);
@@ skipping 17 matching lines @@
   for (var j = 1; j < 4; j++) {
     value1 |= a.x << (j * 8);
     a.y += 1;
     if (mode) a.x += 1;
     a.x += 1;
     value2 |= a.y << (j * 8);
   }
   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));
 }