[rurban]

Certainly not with open addressing as it will destroy all the cache-line advantages. with seperate chaining it's very common, esp. for resizing.

[barrkel]

The key is usually indirected, which means a pointer, which is usually bigger than the hash code.

(And of course you could use parallel arrays if you're super concerned about cache lines, though the tradeoffs would very much depend on whether hash misses or hits are the expected mode.)

[senderista]

And if it’s not a pointer but a word-size integer, just use an invertible hash function (aka permutation aka block cipher) so you can store the hash code in place of the key :)