Source

File: wp-includes/class-wp-query.php

private function set_found_posts( $q, $limits ) {
		global $wpdb;
		// Bail if posts is an empty array. Continue if posts is an empty string,
		// null, or false to accommodate caching plugins that fill posts later.
		if ( $q['no_found_rows'] || ( is_array( $this->posts ) && ! $this->posts ) ) {
			return;
		}

		if ( ! empty( $limits ) ) {
			/**
			 * Filters the query to run for retrieving the found posts.
			 *
			 * @since 2.1.0
			 *
			 * @param string   $found_posts_query The query to run to find the found posts.
			 * @param WP_Query $this              The WP_Query instance (passed by reference).
			 */
			$found_posts_query = apply_filters_ref_array( 'found_posts_query', array( 'SELECT FOUND_ROWS()', &$this ) );

			$this->found_posts = (int) $wpdb->get_var( $found_posts_query );
		} else {
			if ( is_array( $this->posts ) ) {
				$this->found_posts = count( $this->posts );
			} else {
				if ( null === $this->posts ) {
					$this->found_posts = 0;
				} else {
					$this->found_posts = 1;
				}
			}
		}

		/**
		 * Filters the number of found posts for the query.
		 *
		 * @since 2.1.0
		 *
		 * @param int      $found_posts The number of posts found.
		 * @param WP_Query $this        The WP_Query instance (passed by reference).
		 */
		$this->found_posts = (int) apply_filters_ref_array( 'found_posts', array( $this->found_posts, &$this ) );

		if ( ! empty( $limits ) ) {
			$this->max_num_pages = ceil( $this->found_posts / $q['posts_per_page'] );
		}
	}