Reland "VM: Handle null-comparisons in the flow graph type propagation"

tests/language/vm/integer_type_propagation_test.dart

+// Copyright (c) 2017, 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 various optimizations and deoptimizations of optimizing compiler..
+// VMOptions=--checked --enable-inlining-annotations --no-background-compilation --optimization-counter-threshold=1000
+
+import "package:expect/expect.dart";
+
+const noInline = "NeverInline";
+
+@noInline
+testuint32(y) {
+  int x = y;
+  if (x != null) {
+    return x & 0xffff;
+  }
+}
+
+main() {
+  var s = 0;
+  testuint32(0x7fffffff);
+  for (int i = 0; i < 10000; ++i) {
+    testuint32(i);
+  }
+  Expect.equals(65535, testuint32(0x7fffffff));
+  Expect.equals(65535, testuint32(0x7fff23452435245ffff));
+}