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Re: Excessive use of `eassert`
From: |
Eli Zaretskii |
Subject: |
Re: Excessive use of `eassert` |
Date: |
Fri, 19 Jan 2024 17:02:06 +0200 |
> 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.
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.
- Excessive use of `eassert`, Stefan Monnier, 2024/01/18
- Re: Excessive use of `eassert`, Eli Zaretskii, 2024/01/19
- Re: Excessive use of `eassert`, Alan Mackenzie, 2024/01/19
- Re: Excessive use of `eassert`, Eli Zaretskii, 2024/01/19
- Re: Excessive use of `eassert`, Paul Eggert, 2024/01/20
- Re: Excessive use of `eassert`, Eli Zaretskii, 2024/01/21
- Re: Excessive use of `eassert`, Paul Eggert, 2024/01/21
- Re: Excessive use of `eassert`, Alan Mackenzie, 2024/01/21
- Re: Excessive use of `eassert`, Paul Eggert, 2024/01/22