Support Null type in Class::TypeTest and simplify Instance::IsInstanceOf.

runtime/vm/flow_graph_optimizer.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/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 1246 matching lines @@
   ASSERT(ic_data.num_args_tested() == 1);  // Unary checks only.
   if (!type.IsInstantiated() || type.IsMalformed()) return Bool::null();
   const Class& type_class = Class::Handle(type.type_class());
   if (type_class.HasTypeArguments()) return Bool::null();
   const ClassTable& class_table = *Isolate::Current()->class_table();
   Bool& prev = Bool::Handle();
   Class& cls = Class::Handle();
   for (int i = 0; i < ic_data.NumberOfChecks(); i++) {
     cls = class_table.At(ic_data.GetReceiverClassIdAt(i));
     if (cls.HasTypeArguments()) return Bool::null();
-    bool is_subtype = false;
-    if (cls.IsNullClass()) {
-      is_subtype = type_class.IsDynamicClass() || type_class.IsObjectClass();
-    } else {
-      is_subtype = cls.IsSubtypeOf(TypeArguments::Handle(),
-                                   type_class,
-                                   TypeArguments::Handle(),
-                                   NULL);
-    }
+    const bool is_subtype = cls.IsSubtypeOf(TypeArguments::Handle(),
+                                            type_class,
+                                            TypeArguments::Handle(),
+                                            NULL);
     if (prev.IsNull()) {
       prev = is_subtype ? Bool::True().raw() : Bool::False().raw();
     } else {
       if (is_subtype != prev.value()) return Bool::null();
     }
   }
   return prev.raw();
 }
 
 
@@ skipping 3141 matching lines @@
 
   if (FLAG_trace_constant_propagation) {
     OS::Print("\n==== After constant propagation ====\n");
     FlowGraphPrinter printer(*graph_);
     printer.PrintBlocks();
   }
 }
 
 
 }  // namespace dart