Add support for adding an external and a tagged pointer

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/base/bits.h"
 #include "src/double.h"
 #include "src/elements.h"
 #include "src/factory.h"
@@ skipping 1425 matching lines @@
     return Representation::External();
   }
   return HArithmeticBinaryOperation::RepresentationFromInputs();
 }
 
 
 Representation HAdd::RequiredInputRepresentation(int index) {
   if (index == 2) {
     Representation left_rep = left()->representation();
     if (left_rep.IsExternal()) {
-      return Representation::Integer32();
+      // Either Tagged or Integer32.
+      return Representation::None();
     }
   }
   return HArithmeticBinaryOperation::RequiredInputRepresentation(index);
 }
 
 
 static bool IsIdentityOperation(HValue* arg1, HValue* arg2, int32_t identity) {
   return arg1->representation().IsSpecialization() &&
     arg2->EqualsInteger32Constant(identity);
 }
@@ skipping 3254 matching lines @@
     case HObjectAccess::kExternalMemory:
       os << "[external-memory]";
       break;
   }
 
   return os << "@" << access.offset();
 }
 
 }  // namespace internal
 }  // namespace v8