if( ! function_exists( 'wphelp_dns_prefetch' ) ) :
 
    function wphelp_dns_prefetch(){
         
        if ( is_singular() ) { 
                  echo '<link rel="prefetch" href="' .esc_url( home_url() ) . '">';               
                   echo '<link rel="prerender" href="' .esc_url( home_url() ) . '">';             
        }
 
    }
 
endif;
 
add_action('wp_head', 'wphelp_dns_prefetch');