Re: Performance issue w/ `cl-loop`s `collect...into`

[Tianxiang Xiong <tianxiang.xiong@gmail.com>]

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Is there a function to easily time operations in Emacs Lisp? Something like
Clojure's `core/time`?

`profile-*` a chore to use for short stuff.

On Sun, Apr 8, 2018 at 7:20 PM, Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> > IIUC the `(eq var cl--loop-accum-var)` is used to test whether the
> > accumulation is `into` or not. If not, clauses like `collect(ing)` use a
> > `cons-nreverse` rather than `nconc` algorithm, which is O(n) instead of
> > O(n^2). Since we're doing `setcdr` in all cases where the accumulation is
> > into a list, we're always O(n), so the optimization is unnecessary.
>
> I agree that the algorithmic complexity of "cons+nreverse" is no better
> than that of the setcdr, but that doesn't mean that it's the same speed.
> Since (eq var cl--loop-accum-var) is expected to be the most common
> case, it'd be good to make sure that your patch doesn't make the
> code slower, hence the need to test the performance.
>
>
>         Stefan
>
>
> > Attached is a new patch that uses `(cl--loop-accum-var)`.
> >
> > On Sun, Apr 8, 2018 at 6:59 PM, Stefan Monnier <monnier@iro.umontreal.ca
> >
> > wrote:
> >
> >> > Here's a second, cleaner attempt that separates the
> >> `cl--loop-handle-accum`
> >> > function into two functions, one to deal with lists and one to deal w/
> >> > non-lists.
> >> > The tail-tracking optimizing is also applied to `append(ing)` and
> >> > `nconc(ing)`.
> >>
> >> Thanks.  Looks good.
> >> I see you've dropped the (eq var cl--loop-accum-var) optimization.
> >> Have you tried to measure the effect?
> >>
> >>
> >>         Stefan
> >>
> >>
> >> > +(defun cl--loop-handle-accum (def)
> >> [...]
> >> > +  (cond
> >> [...]
> >> > +    (cl--loop-accum-var cl--loop-accum-var)
> >>
> >> You can write this line as just
> >>
> >>        (cl--loop-accum-var)
> >>
> >>
> >> -- Stefan
> >>
> >>
> >>
>

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