GNU bug report logs - #14769
24.3.50; [PATCH] optimize `concat's literals

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From: Noam Postavsky <npostavs <at> gmail.com>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: Lars Ingebrigtsen <larsi <at> gnus.org>, Stefan Monnier <monnier <at> iro.umontreal.ca>, 14769 <at> debbugs.gnu.org, shigeru.fukaya <at> gmail.com
Subject: bug#14769: [PATCH] optimize `concat's literals
Date: Tue, 18 Jun 2019 21:43:32 -0400

Mattias Engdegård <mattiase <at> acm.org> writes:

> +    (dolist (arg (cdr form))

> +                   (let ((val (eval arg)))

> +                          ;; Constant arg: concat with previous.
> +                          (setq accum (concat accum val)))))

Hmm, I think the OP's patch is careful not to concat in a loop like
this: it's O(n^2).  I guess for most human written code n is small
enough that it doesn't matter, but I could imagine this slowing
compilation of a very big rx macro.

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