From: Alan Mackenzie <acm@muc.de>
To: Eli Zaretskii <eliz@gnu.org>
Cc: Stefan Monnier <monnier@iro.umontreal.ca>,
Paul Eggert <eggert@cs.ucla.edu>,
emacs-devel@gnu.org
Subject: Re: Excessive use of `eassert`
Date: Fri, 19 Jan 2024 19:42:39 +0000 [thread overview]
Message-ID: <ZarQr591SsuIZwNs@ACM> (raw)
In-Reply-To: <83sf2tv029.fsf@gnu.org>
Hello, Eli.
On Fri, Jan 19, 2024 at 17:02:06 +0200, Eli Zaretskii wrote:
> > From: Stefan Monnier <monnier@iro.umontreal.ca>
> > Cc: emacs-devel@gnu.org
> > Date: Fri, 19 Jan 2024 08:01:47 -0500
> > >> shows that `make_lisp_symbol` is not inlined, so NILP(x) ends up being
> > >> an actual function call to a function calling another function ....
> > >> which I think is definitely in the "excessive" camp :-)
> > > I'm not sure I follow. Can you elaborate? Are you saying that the
> > > assertion causes make_lisp_symbol not to be inlined? And what
> > > functions are called by NILP?
> > AFAICT it's worse than just `NILP`, I think, because every `Qnil` (same
> > thing with all other `Q<something>`, I guess) becomes a call to
> > `builtin_lisp_symbol` which itself has a call to `make_lisp_symbol`.
> Then how come this is suddenly an issue? We've had that assertion
> since 2016. I use an Emacs build with ENABLE_CHECKING and without
> optimizations every day, and while it is indeed slower than the
> production build by a factor of 3.5, it is not unbearably slow.
> > >> The patch below seems to address this specific issue, tho I haven't
> > >> measured its performance impact yet.
> > > Is this specifically about NILP? Or are there other situations where
> > > this assertion slows us down considerably. I wouldn't want to drop
> > > this assertion so summarily, if possible.
> > Why do you find this specific assertion important? When building other
> > `Lisp_Object`s (like `make_fixnum`) we don't seem to have any
> > corresponding assertion that the revere operation (e.g. XFIXNUM) returns
> > the original value.
> make_fixnum is a trivial bit-shuffling, whereas make_lisp_symbol is
> much trickier. Perhaps especially so now that we have
> symbols-with-positions as well as bare symbols.
Not really. Symbols with positions don't belong in the obarray. If they
somehow get there, then that's a bug to be fixed.
> I have added Paul, who introduced that assertion (and the code around
> it). Paul, do you think this assertion is important to keep?
> I also added Alan, in case he has comments.
--
Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2024-01-19 19:42 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-18 22:35 Excessive use of `eassert` Stefan Monnier
2024-01-19 7:04 ` Eli Zaretskii
2024-01-19 13:01 ` Stefan Monnier
2024-01-19 15:02 ` Eli Zaretskii
2024-01-19 15:50 ` Stefan Monnier
2024-01-19 16:23 ` Eli Zaretskii
2024-01-19 17:44 ` Stefan Monnier
2024-01-19 19:42 ` Alan Mackenzie [this message]
2024-01-19 19:56 ` Eli Zaretskii
2024-01-21 1:41 ` Paul Eggert
2024-01-21 9:57 ` Eli Zaretskii
2024-01-21 20:35 ` Paul Eggert
2024-01-21 10:59 ` Alan Mackenzie
2024-01-22 5:19 ` Paul Eggert
2024-01-22 13:07 ` Stefan Monnier
2024-01-22 14:37 ` Alan Mackenzie
2024-01-23 7:51 ` Paul Eggert
2024-01-23 11:42 ` Alan Mackenzie
2024-01-24 1:04 ` Paul Eggert
2024-01-24 15:09 ` Alan Mackenzie
2024-01-26 8:06 ` Paul Eggert
2024-01-21 15:54 ` Stefan Monnier
2024-01-22 4:12 ` Paul Eggert
2024-01-22 13:20 ` Stefan Monnier
2024-01-23 8:15 ` Paul Eggert
2024-01-23 17:11 ` Stefan Monnier
2024-01-24 7:45 ` Paul Eggert
2024-01-23 18:16 ` Eli Zaretskii
2024-01-23 19:50 ` Stefan Monnier
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