GNU bug report logs - #42147
28.0.50; pure vs side-effect-free, missing optimizations?

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Package: emacs;

Reported by: Andrea Corallo <andrea_corallo <at> yahoo.it>

Date: Tue, 30 Jun 2020 22:28:02 UTC

Severity: normal

Found in version 28.0.50

Done: Mattias Engdegård <mattiase <at> acm.org>

Bug is archived. No further changes may be made.

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From: Andrea Corallo <andrea_corallo <at> yahoo.it>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: Paul Eggert <eggert <at> cs.ucla.edu>, Stefan Monnier <monnier <at> iro.umontreal.ca>, 42147 <at> debbugs.gnu.org
Subject: bug#42147: 28.0.50; pure vs side-effect-free, missing optimizations?
Date: Thu, 2 Jul 2020 15:32:48 +0000 (UTC)

Mattias Engdegård <mattiase <at> 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
This bug report was last modified 4 years and 282 days ago.

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