From: hokomo via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
To: 67883@debbugs.gnu.org
Subject: bug#67883: 29.1.90; Native compiler hangs when compiling code with circular objects
Date: Mon, 18 Dec 2023 18:22:41 +0100 [thread overview]
Message-ID: <87a5q7bc2f.fsf@disroot.org> (raw)
Hello,
The Emacs Lisp native compiler goes into an infinite loop when
compiling code that contains circular objects.
For example, put the following into a file and use M-x
emacs-lisp-native-compile; it should hang:
(defun test1 ()
'#1=(1 2 3 . #1#))
It seems like this only happens for certain top-level forms, such
as `defun' (which may be expected behavior, due to the way the
file compiler processes top-level forms). For example, this
doesn't hang:
(lambda ()
'#1=(1 2 3 . #1#))
Here's a more interesting example, which is how I stumbled upon
this issue in the first place:
(defun cycle-pure (list)
(declare (pure t) (side-effect-free t))
(let ((newlist (append list ())))
(nconc newlist newlist)))
(defun test2 ()
(cycle-pure '(1 2 3)))
(The definition of `cycle-pure' is copied from the `-cycle'
function from the dash.el package.)
If `cycle-pure' is not yet defined when compiling, the compiler
doesn't hang.
However, if `cycle-pure' is defined (e.g. via M-x eval-defun), the
compiler hangs. This is weird because, unlike `test1' above,
`test2' doesn't contain a circular list itself; it only builds it
at run-time.
In contrast, this example doesn't hang, regardless of whether
`cycle' is defined or not (note the removed declarations):
(defun cycle (list)
(let ((newlist (append list ())))
(nconc newlist newlist)))
(defun test3 ()
(cycle '(1 2 3)))
My conjecture is that the `pure' and `side-effect-free'
declarations within `cycle-pure' (which I assume are picked up
only once the function definition is loaded) allow the compiler to
do some constant folding when it sees the expression `(cycle-pure
'(1 2 3))'. This results in the compiler manipulating a circular
list at compile-time, just like in `test1', and leads to a hang.
Kind regards,
hokomo
next reply other threads:[~2023-12-18 17:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-18 17:22 hokomo via Bug reports for GNU Emacs, the Swiss army knife of text editors [this message]
2023-12-19 12:48 ` bug#67883: 29.1.90; Native compiler hangs when compiling code with circular objects Andrea Corallo
2023-12-19 13:29 ` Andrea Corallo
2023-12-24 19:41 ` Stefan Kangas
2023-12-26 8:23 ` Andrea Corallo
2023-12-26 15:36 ` Stefan Kangas
2023-12-27 18:48 ` hokomo via Bug reports for GNU Emacs, the Swiss army knife of text editors
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87a5q7bc2f.fsf@disroot.org \
--to=bug-gnu-emacs@gnu.org \
--cc=67883@debbugs.gnu.org \
--cc=hokomo@disroot.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.