Inline instanceOf and 'as' operations; fix a bug in code emission

runtime/vm/flow_graph_compiler_x64.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/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 586 matching lines @@
   // checking whether the tested instance is a Smi.
   if (type.IsInstantiated()) {
     // A null object is only an instance of Object and dynamic, which has
     // already been checked above (if the type is instantiated). So we can
     // return false here if the instance is null (and if the type is
     // instantiated).
     // We can only inline this null check if the type is instantiated at compile
     // time, since an uninstantiated type at compile time could be Object or
     // dynamic at run time.
     __ CompareObject(RAX, Object::null_object(), PP);
-    __ j(EQUAL, &is_not_instance);
+    __ j(EQUAL, type.IsNullType() ? &is_instance : &is_not_instance);
   }
 
   // Generate inline instanceof test.
   SubtypeTestCache& test_cache = SubtypeTestCache::ZoneHandle();
   test_cache = GenerateInlineInstanceof(token_pos, type,
                                         &is_instance, &is_not_instance);
 
   // test_cache is null if there is no fall-through.
   Label done;
   if (!test_cache.IsNull()) {
@@ skipping 1133 matching lines @@
   __ movups(reg, Address(RSP, 0));
   __ AddImmediate(RSP, Immediate(kFpuRegisterSize), PP);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64