array_values should be a no-op for packed layout arrays

I noticed this commit <https://github.com/facebook/hhvm/commit/4167d66fcfa81a1c2a19e853282fac968d9cd454> recently in HHVM, which makes array_values() return the same array back if it's packed instead of building a copy. My understanding is PHP 7 also has packed arrays like HHVM, and my reading of PHP's array_values() implementation (here <https://github.com/php/php-src/blob/c6982995504b6e21e8a5ade29cfb16a55196dc43/ext/standard/array.c#L4000>) is that it always creates a copy of the array, even if it's packed. Would this be a worthwhile optimisation to make in PHP as well?