WooCommerce - Number of products on sale

<?php
  // get the number of products in the shop which are on sale
  // usage: We have [products_available] available!
  // code goes in functions.php for your child theme
  add_shortcode('products_available', 'products_available');
  function products_available() {
    $args = array(
      'post_type' => 'product',
      'posts_per_page' => -1,
      'orderby' => '',
      'order' => '',
      'meta_query' => array(
        array(
        'key' => '_stock_status',
        'value' => 'instock',
        'compare' => '='
        )
      )
    );
    $loop = new WP_Query( $args );
    $products = $loop->posts;
    wp_reset_postdata();
    return count($products);
  }