This code removes all products that are on sale at the moment of creation of coupon.

new_gist_file.php

<?php

add_filter('ywrac_coupon_args','ywrac_coupon_args');
function ywrac_coupon_args( $args ){

	$product_on_sale = wc_get_product_ids_on_sale();
	if( is_array( $product_on_sale) && !empty( $product_on_sale ) ){
		$args['exclude_product_ids'] = implode( ',', $product_on_sale );
	}

	return $args;
}