GNU bug report logs - #66816
[PATCH] Delete redundant lambdas around unary functions

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: [PATCH] Delete redundant lambdas around unary functions
Date: Sun, 29 Oct 2023 06:02:38 -0700

[Message part 1 (text/plain, inline)]

Severity: wishlist

Please see the attached patch.

I've been able to measure around 10% better performance in the few cases
I looked into.  Here's an example:

    (benchmark-run 1000
      (seq-filter (lambda (n) (bufferp n))
                  (number-sequence 0 100000)))
    => (69.007736 333 47.018879999999996)

    (benchmark-run 1000
      (seq-filter #'bufferp
                  (number-sequence 0 100000)))
    => (61.541616 333 47.673137)

[0001-Delete-redundant-lambdas-around-unary-functions.patch (text/x-patch, attachment)]

Message #8 received at 66816 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Stefan Kangas <stefankangas <at> gmail.com>
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>, 66816 <at> debbugs.gnu.org
Subject: bug#66816: [PATCH] Delete redundant lambdas around unary functions
Date: Sun, 29 Oct 2023 20:03:16 +0100

> I've been able to measure around 10% better performance in the few cases
> I looked into.  Here's an example:
> 
>     (benchmark-run 1000
>       (seq-filter (lambda (n) (bufferp n))
>                   (number-sequence 0 100000)))

(This would be less of a problem if we could inline functions on the Lisp level...)

We could also have the compiler η-reduce automatically. I investigated this very briefly some time ago. Maybe I can dig up the patch.

One problem is that the arity isn't necessarily preserved. Most of the time this isn't a problem but it could be something to watch out for if doing the η-reduction by hand.

Message #11 received at 66816 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>
Cc: Stefan Kangas <stefankangas <at> gmail.com>, 66816 <at> debbugs.gnu.org
Subject: Re: bug#66816: [PATCH] Delete redundant lambdas around unary functions
Date: Sun, 29 Oct 2023 17:55:27 -0400

The patch looks good to me.

> We could also have the compiler η-reduce automatically. I investigated this
> very briefly some time ago. Maybe I can dig up the patch.
> One problem is that the arity isn't necessarily preserved.

And even if we check the arity before performing the rewrite, the arity
at compile-time may be different from the arity at run-time, so it's not
a safe optimization.

OTOH we could emit a warning :-)

> Most of the time this isn't a problem but it could be something to
> watch out for if doing the η-reduction by hand.

I've been bitten a few times, indeed.


        Stefan

Message #14 received at 66816 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: Stefan Kangas <stefankangas <at> gmail.com>, 66816 <at> debbugs.gnu.org
Subject: Re: bug#66816: [PATCH] Delete redundant lambdas around unary functions
Date: Mon, 30 Oct 2023 09:56:01 +0100

29 okt. 2023 kl. 22.55 skrev Stefan Monnier <monnier <at> iro.umontreal.ca>:

> The patch looks good to me.

To me, too -- good work.

One version that the patch doesn't seem to include is

  (lambda (X...) (funcall F X...)) -> F

which is less safe in general (since the value of the expression F could change between the closure creation and application) but sometimes obviously fine, as when the function is a parameter to `mapcar`.

The patch also appears limited to unary functions.

Message #17 received at 66816 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Stefan Kangas <stefankangas <at> gmail.com>
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>, 66816 <at> debbugs.gnu.org
Subject: Re: bug#66816: [PATCH] Delete redundant lambdas around unary functions
Date: Mon, 30 Oct 2023 16:00:34 +0100

[Message part 1 (text/plain, inline)]

Since I had a tool for it handy, I scanned the Emacs tree. Output attached, in case it might be of use.
Caution: it has not been vetted in any way and definitely contains plenty of false positives.

[eta-opportunities.log (application/octet-stream, attachment)]

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