void HGraphBuilder::GenerateStringAdd(CallRuntime* call) {
  ASSERT_EQ(2, call->arguments()->length());
  CHECK_ALIVE(VisitArgumentList(call->arguments()));
  HValue* context = environment()->LookupContext();
  HCallStub* result = new(zone()) HCallStub(context, CodeStub::StringAdd, 2);
  Drop(2);
  return ast_context()->ReturnInstruction(result, call->id());
}
void HGraphBuilder::GenerateStringAdd(CallRuntime* call) {
  ASSERT_EQ(2, call->arguments()->length());
  CHECK_ALIVE(VisitArgumentList(call->arguments()));
  HValue* context = environment()->LookupContext();
  HCallStub* result = new(zone()) HCallStub(context, CodeStub::StringAdd, 2);
  Drop(2);
  return ast_context()->ReturnInstruction(result, call->id());
}