function bbp_delete_topic_replies( $topic_id = 0 ) {

	// Validate topic ID
	$topic_id = bbp_get_topic_id( $topic_id );

	// Topic is being permanently deleted, so its replies gotta go too
	// Note that we get all post statuses here
	$replies = new WP_Query( array(
		'fields'         => 'id=>parent',
		'post_type'      => bbp_get_reply_post_type(),
		'post_status'    => array_keys( get_post_stati() ),
		'post_parent'    => $topic_id,
		'posts_per_page' => -1,

		// Performance
		'nopaging'               => true,
		'suppress_filters'       => true,
		'update_post_term_cache' => false,
		'update_post_meta_cache' => false,
		'ignore_sticky_posts'    => true,
		'no_found_rows'          => true
	) );

	// Loop through and delete child replies
	if ( ! empty( $replies->posts ) ) {
		foreach ( $replies->posts as $reply ) {
			wp_delete_post( $reply->ID, true );
		}

		// Reset the $post global
		wp_reset_postdata();
	}
}