message: XLA: Print nicer message when trying to traverse HLO computation
diff: @@ -380,6 +380,9 @@ void HloComputation::ComputeInstructionPostOrder(
  dfs_stack.push_back(root);
  while (!dfs_stack.empty()) {
  const auto current = dfs_stack.back();
  + CHECK_EQ(current->parent(), this)
  + << "Instruction " << current->name()
  + << " is not in the current computation (" << name() << ").";
  auto it = visited->find(current);
  if (it != visited->end()) {
  if (it->second == kVisited) {
  