bug#68244: hash-table improvements

[Stefan Kangas]

Mattias Engdegård <mattias.engdegard@gmail.com> writes:

> Maybe we should promote equal-including-properties to a first-class
> hash table test? It's defined as a user test in two places in the
> Emacs tree, and user tests are much slower than built-in ones.

It might be worth a try.  I see that it's used in the native compiler,
for example, and we're obviously very happy if we can make that stuff
more performant.