message: Allow scalars to be passed as-is to the poplar fusions
  Summary:
  Check that number of tensor elements is 1 and allow pass-through for scalars.
  Fix T39214.
  Test Plan: CI
  Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, georgep
  Maniphest Tasks: T39214
diff: @@ -117,10 +117,15 @@ StatusOr<ExpressionInput> GetElementwiseInput(
  TF_ASSIGN_OR_RETURN(auto expr_input,
  GetTensorInput(res, inst, tensor_map, operand_idx,
  input_idx, seq, debug_name_and_id));
  +
  + // Allow passing scalars to the underlying op and let poplar broadcast.
  + if (expr_input.tensor->numElements() > 1) {
  // Broadcast the tensor internally to the right shape.
  - TF_ASSIGN_OR_RETURN(expr_input.tensor,
  + TF_ASSIGN_OR_RETURN(
  + expr_input.tensor,
  BroadcastTensor(*expr_input.tensor, input->shape(),
  input->dimensions()));
  + }
  return expr_input;
  }
  } else {
  