Add support for adding an external and a tagged pointer

src/x64/lithium-x64.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 <sstream>
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
@@ skipping 1588 matching lines @@
     LAddI* add = new(zone()) LAddI(left, right);
     bool can_overflow = instr->CheckFlag(HValue::kCanOverflow);
     LInstruction* result = use_lea ? DefineAsRegister(add)
                                    : DefineSameAsFirst(add);
     if (can_overflow) {
       result = AssignEnvironment(result);
     }
     return result;
   } else if (instr->representation().IsExternal()) {
     DCHECK(instr->left()->representation().IsExternal());
-    DCHECK(instr->right()->representation().IsInteger32());
+    DCHECK(instr->right()->representation().IsInteger32() ||
+           instr->right()->representation().IsTagged());
     DCHECK(!instr->CheckFlag(HValue::kCanOverflow));
     bool use_lea = LAddI::UseLea(instr);
     LOperand* left = UseRegisterAtStart(instr->left());
     HValue* right_candidate = instr->right();
     LOperand* right = use_lea
         ? UseRegisterOrConstantAtStart(right_candidate)
         : UseOrConstantAtStart(right_candidate);
     LAddI* add = new(zone()) LAddI(left, right);
     LInstruction* result = use_lea
         ? DefineAsRegister(add)
@@ skipping 1117 matching lines @@
   LAllocateBlockContext* result =
       new(zone()) LAllocateBlockContext(context, function);
   return MarkAsCall(DefineFixed(result, rsi), instr);
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64