Directly embed small strings in zvals

Hello everyone, I was wondering if it would make sense to store small strings (length <= 7) directly inside the zval struct, thereby avoiding the need to extra allocate a zend_string, which would also not entail any costly indirection and refcounting for such strings. The idea would be to add a new sruct `struct { uint8_t len; char val[7]; } sval` to the _zend_value union type in order to embed it directly into the zval struct and use a type flag (zval.u1.v.type_flags) such as IS_SMALL_STRING to destinguish between a regular heap allocated zend_string and the directly embedded compact representation. Small strings are quite common IMHO. In fact quickly sampling my company's PHP code base I found well over 50% of the strings to be of length <= 7. It would save a lot of memory allocations as well as pointer indirection, and could also bypass refcounting logic. Also, comparing small strings for equality would become a trivial operation (just comparing two pre-aligned 64bit integers) - no more need to keep small strings interned. Of course it wouldn't longer be possible to also persistently store the hash value of a small string, though calculating the hash value for small strings is less costly anyways because less characters equals less iterations, so that might not be an issue in practice. I don't see such an idea in https://wiki.php.net/php-7.1-ideas and I was wondering: Has anybody experimented with that approach yet? Is it worth discussing? Please let me know your thoughts, Ben -- Bejamin Coutu ben.coutu@zeyos.com ZeyOS, Inc. http://www.zeyos.com