Introduce a VM type cast to avoid repeating a type test and spare a handle.

runtime/vm/flow_graph_compiler_x64.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/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "lib/error.h"
@@ skipping 294 matching lines @@
     intptr_t cid,
     intptr_t token_pos,
     const AbstractType& type,
     Label* is_instance_lbl,
     Label* is_not_instance_lbl) {
   ASSERT(!type.IsInstantiated());
   // Skip check if destination is a dynamic type.
   const Immediate raw_null =
       Immediate(reinterpret_cast<intptr_t>(Object::null()));
   if (type.IsTypeParameter()) {
-    // TODO(regis): Introduce and use TypeParameter::Cast().
-    const TypeParameter* type_param =
-        reinterpret_cast<const TypeParameter*>(&type);
+    const TypeParameter& type_param = TypeParameter::Cast(type);
     // Load instantiator (or null) and instantiator type arguments on stack.
     __ movq(RDX, Address(RSP, 0));  // Get instantiator type arguments.
     // RDX: instantiator type arguments.
     // Check if type argument is Dynamic.
     __ cmpq(RDX, raw_null);
     __ j(EQUAL, is_instance_lbl);
     // Can handle only type arguments that are instances of TypeArguments.
     // (runtime checks canonicalize type arguments).
     Label fall_through;
     __ CompareClassId(RDX, kTypeArguments);
     __ j(NOT_EQUAL, &fall_through);
     __ movq(RDI,
-        FieldAddress(RDX, TypeArguments::type_at_offset(type_param->index())));
+        FieldAddress(RDX, TypeArguments::type_at_offset(type_param.index())));
     // RDI: Concrete type of type.
     // Check if type argument is dynamic.
     __ CompareObject(RDI, Type::ZoneHandle(Type::DynamicType()));
     __ j(EQUAL,  is_instance_lbl);
     __ cmpq(RDI, raw_null);
     __ j(EQUAL,  is_instance_lbl);
     const Type& object_type = Type::ZoneHandle(Type::ObjectType());
     __ CompareObject(RDI, object_type);
     __ j(EQUAL,  is_instance_lbl);
 
@@ skipping 739 matching lines @@
   __ cvtsi2sd(result, temp);
   __ Bind(&done);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64