For each statement ID, convert 'default' to (last_stmt_idx+1)

        :param block_addr:  The block address.
        :param stmt_idx:    Statement ID.
        :returns:           New statement ID.

def _normalize_stmt_idx(self, block_addr, stmt_idx):
        """
        For each statement ID, convert 'default' to (last_stmt_idx+1)

        :param block_addr:  The block address.
        :param stmt_idx:    Statement ID.
        :returns:           New statement ID.
        """

        if type(stmt_idx) is int:
            return stmt_idx

        if stmt_idx == DEFAULT_STATEMENT:
            vex_block = self.project.factory.block(block_addr).vex
            return len(vex_block.statements)

        raise AngrBackwardSlicingError('Unsupported statement ID "%s"' % stmt_idx)