Attach sharding to `tuple` in mhlo -> hlo conversion when the following two conditions are true.
Attach sharding to `tuple` in mhlo -> hlo conversion when the following two conditions are true.
1. converting `mhlo::ReturnOp` or `mlir::func::ReturnOp`
2. `num_return_values == 1`
3. `!return_tuple || !is_entry_function`
