message: Explicitly replace dummy root instruction.
diff: @@ -343,7 +343,7 @@ Status HorizontalFusionImpl::CreateFusedComputation(
  }
  // Always create a dummy tuple instruction to serve as the root of the
  // computation, as the existence of a root instruction is required by the
  - // HloComputation. The real root instruction will be provided below.
  + // HloComputation. The real root instruction will replace it below.
  auto dummy_root = b.AddInstruction(
  HloInstruction::CreateTuple(std::vector<HloInstruction*>{}));
  *uniq_computation = b.Build(dummy_root);
  @@ -426,6 +426,7 @@ Status HorizontalFusionImpl::CreateFusedComputation(
  // Make a tuple of output_slices.
  auto tuple = comp->AddInstruction(HloInstruction::CreateTuple(output_slices));
  comp->set_root_instruction(tuple, /*accept_different_shape=*/true);
  + comp->RemoveInstruction(dummy_root);
  return Status::OK();
  }
  