Add support for adding an external and a tagged pointer

src/mips/lithium-mips.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_MIPS
 
@@ skipping 1591 matching lines @@
     LOperand* left = UseRegisterAtStart(instr->BetterLeftOperand());
     LOperand* right = UseOrConstantAtStart(instr->BetterRightOperand());
     LAddI* add = new(zone()) LAddI(left, right);
     LInstruction* result = DefineAsRegister(add);
     if (instr->CheckFlag(HValue::kCanOverflow)) {
       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));
     LOperand* left = UseRegisterAtStart(instr->left());
     LOperand* right = UseOrConstantAtStart(instr->right());
     LAddI* add = new(zone()) LAddI(left, right);
     LInstruction* result = DefineAsRegister(add);
     return result;
   } else if (instr->representation().IsDouble()) {
     if (IsMipsArchVariant(kMips32r2)) {
       if (instr->left()->IsMul())
         return DoMultiplyAdd(HMul::cast(instr->left()), instr->right());
@@ skipping 1017 matching lines @@
   LOperand* function = UseRegisterAtStart(instr->function());
   LAllocateBlockContext* result =
       new(zone()) LAllocateBlockContext(context, function);
   return MarkAsCall(DefineFixed(result, cp), instr);
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS