Strengthen type assertions post-dominated by checks during type propagation.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, 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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 1093 matching lines @@
   return this;
 }
 
 
 Definition* AssertAssignableInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   if (FLAG_eliminate_type_checks &&
       value()->Type()->IsAssignableTo(dst_type())) {
     return value()->definition();
   }
 
-  // (3) For uninstantiated target types: If the instantiator type arguments
+  // For uninstantiated target types: If the instantiator type arguments
   // are constant, instantiate the target type here.
   if (dst_type().IsInstantiated()) return this;
 
   ConstantInstr* constant_type_args =
       instantiator_type_arguments()->definition()->AsConstant();
   if (constant_type_args != NULL &&
       !constant_type_args->value().IsNull() &&
       constant_type_args->value().IsTypeArguments()) {
     const TypeArguments& instantiator_type_args =
         TypeArguments::Cast(constant_type_args->value());
@@ skipping 1076 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart