Continue work on type propagation in optimizing compiler (still WIP).

runtime/vm/object.cc

 // 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/bigint_operations.h"
@@ skipping 1735 matching lines @@
     Error* malformed_error) const {
   ASSERT(!IsVoidClass());
   // Check for DynamicType.
   // Each occurrence of DynamicType in type T is interpreted as the Dynamic
   // type, a supertype of all types.
   if (other.IsDynamicClass()) {
     return true;
   }
   // In the case of a subtype test, each occurrence of DynamicType in type S is
   // interpreted as the bottom type, a subtype of all types.
+  // However, DynamicType is not more specific than any type.
   if (IsDynamicClass()) {
     return test_kind == kIsSubtypeOf;
   }
+  // Check for NullType, which is not a subtype of any type, but is more
+  // specific than any type.
+  if (IsNullClass()) {
+    return test_kind == kIsMoreSpecificThan;
+  }
   // Check for reflexivity.
   if (raw() == other.raw()) {
     const intptr_t len = NumTypeArguments();
     if (len == 0) {
       return true;
     }
     // Since we do not truncate the type argument vector of a subclass (see
     // below), we only check a prefix of the proper length.
     // Check for covariance.
     if (other_type_arguments.IsNull() ||
@@ skipping 9216 matching lines @@
 const char* JSRegExp::ToCString() const {
   const String& str = String::Handle(pattern());
   const char* format = "JSRegExp: pattern=%s flags=%s";
   intptr_t len = OS::SNPrint(NULL, 0, format, str.ToCString(), Flags());
   char* chars = Isolate::Current()->current_zone()->Alloc<char>(len + 1);
   OS::SNPrint(chars, (len + 1), format, str.ToCString(), Flags());
   return chars;
 }
 
 }  // namespace dart