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.

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
>
>
>