def forward(self, memory_bank, tgt, seg):
        """
        Args:
            memory_bank: [batch_size x seq_length x hidden_size]
            tgt: [batch_size x seq_length]

        Returns:
            loss: Masked language modeling loss.
            correct: Number of words that are predicted correctly.
            denominator: Number of masked words.
        """

        # Masked language model (MLM).
        loss, correct, denominator = self.mlm(memory_bank, tgt)

        return loss, correct, denominator

        Args:
            memory_bank: [batch_size x seq_length x hidden_size]
            tgt: [batch_size x seq_length]

        Returns:
            loss: Masked language modeling loss.
            correct: Number of words that are predicted correctly.
            denominator: Number of masked words.
        
uer/targets/mlm_target.py