From: Daniel Colascione <dancol@dancol.org>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: Philipp Stephani <p.stephani2@gmail.com>,
Paul Eggert <eggert@cs.ucla.edu>,
emacs-devel@gnu.org
Subject: Re: [Emacs-diffs] emacs-25 3eb93c0: Rely on conservative stack scanning to find "emacs_value"s
Date: Fri, 1 Apr 2016 11:34:16 -0700 [thread overview]
Message-ID: <56FEBF28.40900@dancol.org> (raw)
In-Reply-To: <jwvpoua4a10.fsf-monnier+emacsdiffs@gnu.org>
[-- Attachment #1.1: Type: text/plain, Size: 711 bytes --]
On 03/31/2016 02:29 PM, Stefan Monnier wrote:
>> That's cheap: you can do it with linear allocation out of an array.
>> Why would that be expensive?
>
> That's very expensive compared to doing nothing.
>
> It means that you have to allocate a new array,
Once.
> loop through the old one
> calling your "cheap allocation" function on each element, instead of
> just passing the array pointer untouched.
It's a pointer comparison of something that will be in L1 cache anyway.
Of course it's slower than doing nothing. But you have not demonstrated
that it is meaningfully slower, meanwhile, you're ignoring the
compatibility benefits and consigning everyone to stack scanning forever.
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]
next prev parent reply other threads:[~2016-04-01 18:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20151130193446.22218.14685@vcs.savannah.gnu.org>
[not found] ` <E1a3UDm-0005my-HI@vcs.savannah.gnu.org>
2016-01-03 13:59 ` [Emacs-diffs] emacs-25 3eb93c0: Rely on conservative stack scanning to find "emacs_value"s Daniel Colascione
2016-01-03 15:45 ` Paul Eggert
2016-03-29 10:07 ` Philipp Stephani
2016-03-29 12:59 ` Stefan Monnier
2016-03-30 1:35 ` Paul Eggert
2016-03-30 18:26 ` Philipp Stephani
2016-03-30 18:28 ` Daniel Colascione
2016-03-30 18:42 ` Paul Eggert
2016-03-30 18:48 ` Daniel Colascione
2016-03-30 21:13 ` Stefan Monnier
2016-03-30 21:18 ` Daniel Colascione
2016-03-30 21:30 ` Stefan Monnier
2016-03-31 18:46 ` Philipp Stephani
2016-03-31 19:24 ` Daniel Colascione
2016-03-31 21:29 ` Stefan Monnier
2016-04-01 18:34 ` Daniel Colascione [this message]
2016-04-01 19:05 ` Stefan Monnier
2016-04-01 19:15 ` Daniel Colascione
2016-04-01 22:46 ` Stefan Monnier
2016-04-03 1:11 ` Daniel Colascione
2016-04-03 5:49 ` Stefan Monnier
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56FEBF28.40900@dancol.org \
--to=dancol@dancol.org \
--cc=eggert@cs.ucla.edu \
--cc=emacs-devel@gnu.org \
--cc=monnier@iro.umontreal.ca \
--cc=p.stephani2@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.