Support string add in crankshaft:

src/arm/lithium-arm.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1927 matching lines @@
 
 LInstruction* LChunkBuilder::DoStoreNamedGeneric(HStoreNamedGeneric* instr) {
   LOperand* obj = UseFixed(instr->object(), r1);
   LOperand* val = UseFixed(instr->value(), r0);
 
   LInstruction* result = new LStoreNamedGeneric(obj, val);
   return MarkAsCall(result, instr);
 }
 
 
+LInstruction* LChunkBuilder::DoStringAdd(HStringAdd* instr) {
+  LOperand* left = UseRegisterAtStart(instr->left());
+  LOperand* right = UseRegisterAtStart(instr->right());
+  return MarkAsCall(DefineFixed(new LStringAdd(left, right), r0), instr);
+}
+
+
 LInstruction* LChunkBuilder::DoStringCharCodeAt(HStringCharCodeAt* instr) {
   LOperand* string = UseRegister(instr->string());
   LOperand* index = UseRegisterOrConstant(instr->index());
   LStringCharCodeAt* result = new LStringCharCodeAt(string, index);
   return AssignEnvironment(AssignPointerMap(DefineAsRegister(result)));
 }
 
 
 LInstruction* LChunkBuilder::DoStringCharFromCode(HStringCharFromCode* instr) {
   LOperand* char_code = UseRegister(instr->value());
@@ skipping 152 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoLeaveInlined(HLeaveInlined* instr) {
   HEnvironment* outer = current_block_->last_environment()->outer();
   current_block_->UpdateEnvironment(outer);
   return NULL;
 }
 
 
 } }  // namespace v8::internal