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

tests/language/vm/integer_type_propagation2_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=--enable-inlining-annotations --no-background-compilation --optimization-counter-threshold=1000
+
+import "package:expect/expect.dart";
+import "dart:typed_data";
+
+const noInline = "NeverInline";
+const alwaysInline = "AlwaysInline";
+
+var list = new Uint32List(1);
+
+@noInline
+testuint32(bool b) {
+  var t;
+  if (b) {
+    t = list[0];
+  }
+  if (t != null) {
+    return t & 0x7fffffff;
+  }
+  return -1;
+}
+
+main() {
+  var s = 0;
+  testuint32(true);
+  testuint32(false);
+  for (int i = 0; i < 10000; ++i) {
+    testuint32(true);
+  }
+  Expect.equals(0, testuint32(true));
+  Expect.equals(-1, testuint32(false));
+}