function.php

/*
 * 投稿にアーカイブ(投稿一覧)を持たせるようにします。
 * ※ 記載後にパーマリンク設定で「変更を保存」してください。
 */
function post_has_archive( $args, $post_type ) {
	if ( 'post' == $post_type ) {
		$args['rewrite'] = true;
		$args['has_archive'] = 'newsrelease'; // ページ名
	}
	return $args;
}
add_filter( 'register_post_type_args', 'post_has_archive', 10, 2 );

function get_archives_by_fiscal_year( $args = '' ) {
    global $wpdb, $wp_locale;
    $defaults = array (
        'post_type' => 'post',
        'limit' => '',
        'format' => 'html',
        'before' => '',
        'after' => '',
        'show_post_count' => false,
        'echo' => 1
    );
    $r = wp_parse_args( $args, $defaults );
    extract ( $r, EXTR_SKIP );
    if ( '' != $limit ) {
        $limit = absint( $limit );
        $limit = ' LIMIT ' . $limit;
    }
    $arcresults = (array) $wpdb->get_results(
        "SELECT YEAR(ADDDATE(post_date, INTERVAL -3 MONTH)) AS `year`, COUNT(ID) AS `posts`
        FROM $wpdb->posts
        WHERE post_type = '$post_type' AND post_status = 'publish'
        GROUP BY YEAR(ADDDATE(post_date, INTERVAL -3 MONTH))
        ORDER BY post_date DESC
        $limit"
    );
    return $arcresults;
}