From: Dmitry Antipov <dmantipov@yandex.ru>
To: Ken Raeburn <raeburn@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: Small LAP peephole optimization
Date: Thu, 10 May 2007 18:21:07 +0400 [thread overview]
Message-ID: <46432A53.5080906@yandex.ru> (raw)
In-Reply-To: <8835CE25-48D2-4F9A-9DC3-81BC3CE49F4E@gnu.org>
Ken Raeburn wrote:
> Now if the author of "foo" isn't sure that "quux" is going to return a
> numeric value, removing the addition changes the semantics of "foo".
Yes. I understand this myself after a short meditation around the comment
above 'byte-compile-associative' :-).
> I would guess that in most of these cases it's a safe optimization, but
> you should really check.
What do you think about such 'unsafe' optimizations in general ? As I know,
some CL systems (such as from Franz) allows byte compiler to be very aggressive
at the cost of safety.
> If the previous operation is guaranteed to leave a numeric value at the top
> of the stack, as in your example, and no other code can branch to the +0 sequence,
> then you can do the optimization; otherwise, you probably shouldn't.
As I understand, branching to +0 is impossible if there is no TAG between
previous byteop an (byte-constant 0), so we might safely optimize the
sequences like
<numeric-on-top-op> (byte-constant 0) (byte-plus . 0) -> <numeric-on-top-op>
Less obvious cases are also interesting, but I'm not sure that saving 2 ops
might push someone to implement substantially more complex logic.
Dmitry
next prev parent reply other threads:[~2007-05-10 14:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-09 10:19 Small LAP peephole optimization Dmitry Antipov
2007-05-09 16:54 ` Ken Raeburn
2007-05-10 14:21 ` Dmitry Antipov [this message]
2007-05-10 20:10 ` Ken Raeburn
2007-05-09 21:34 ` Richard Stallman
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
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=46432A53.5080906@yandex.ru \
--to=dmantipov@yandex.ru \
--cc=emacs-devel@gnu.org \
--cc=raeburn@gnu.org \
/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 public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).