bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?

[Andrea Corallo]

Mattias Engdegård <mattiase@acm.org> writes:

>> I thought the reason why cons is not constant folded is to respect the
>> allocation side effect, at least that's what I convinced my-self of :)
>
> Yes, in the sense that
>
>  (defun f () (cons 'a 'b))
>
> produces a fresh (a . b) each time (f) is called, because the returned
> values can be distinguished both explicitly by 'eq' and by mutating it
> and observing whether the change affects previously returned values or
> not. Neither works for numbers.

Understand makes perfectly sense.  Cons allocation is something
very visible in Lisp.

  Andrea