From: Paul Eggert <eggert@cs.ucla.edu>
To: Dmitry Antipov <dmantipov@yandex.ru>
Cc: Emacs development discussions <emacs-devel@gnu.org>
Subject: Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings]
Date: Wed, 03 Sep 2014 09:42:29 -0700 [thread overview]
Message-ID: <540744F5.2010804@cs.ucla.edu> (raw)
In-Reply-To: <54073621.2040403@yandex.ru>
Dmitry Antipov wrote:
> 1) Function-scoped version using alloca (assuming statement expressions):
> ...
> 2) Block-scoped version using implicit stack allocation (assuming
> statement expressions):
> ...
> 3) Block-scoped version assuming no statement expression but compound
> literals:
> ...
> If we have 2), why we need 1) at all? 2) in a top-level function scope
> is an equivalent to 1), isn't it?
Correct. We'd need (1) e.g. to build up a list in a loop, and have the
list survive until function exit. But on further thought this is
probably a dangerous feature, since it'll be too tempting to write
unbounded loops. So let's not do (1).
> In 3), how we can be sure that Lisp_Cons is properly aligned on stack?
For GCC, we can define struct Lisp_Cons via 'struct __attribute__
((aligned (GCALIGNMENT))) Lisp_Cons { ... };'. For compilers that don't
support this syntax we can align the struct by hand, by using a
character-array compound literal that's a bit too large, aligning the
resulting pointer by hand, and then using the aligned pointer.
next prev parent reply other threads:[~2014-09-03 16:42 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-02 12:55 [RFC] temporary Lisp_Strings Dmitry Antipov
2014-09-02 13:21 ` Andreas Schwab
2014-09-02 13:47 ` Dmitry Antipov
2014-09-02 14:14 ` Andreas Schwab
2014-09-02 15:00 ` Eli Zaretskii
2014-09-02 14:00 ` Stefan Monnier
2014-09-02 15:13 ` Dmitry Antipov
2014-09-02 17:32 ` Stefan Monnier
2014-09-03 10:23 ` Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings] Dmitry Antipov
2014-09-03 13:14 ` Stefan Monnier
2014-09-03 14:39 ` Paul Eggert
2014-09-03 15:39 ` Dmitry Antipov
2014-09-03 16:42 ` Paul Eggert [this message]
2014-09-03 17:47 ` Stefan Monnier
2014-09-03 18:00 ` Paul Eggert
2014-09-04 4:59 ` Dmitry Antipov
2014-09-04 5:13 ` Paul Eggert
2014-09-04 5:51 ` Dmitry Antipov
2014-09-04 6:45 ` Paul Eggert
2014-09-04 13:11 ` Stefan Monnier
2014-09-04 13:37 ` Dmitry Antipov
2014-09-04 14:46 ` Dmitry Antipov
2014-09-04 16:03 ` Paul Eggert
2014-09-05 4:00 ` Dmitry Antipov
2014-09-05 4:24 ` Stefan Monnier
2014-09-05 9:28 ` Dmitry Antipov
2014-09-05 7:15 ` Paul Eggert
2014-09-05 9:16 ` Dmitry Antipov
2014-09-05 14:35 ` Paul Eggert
2014-09-05 15:35 ` Stefan Monnier
2014-09-08 10:33 ` Dmitry Antipov
2014-09-08 12:01 ` Dmitry Antipov
2014-09-08 13:30 ` Stefan Monnier
2014-09-08 12:44 ` Stefan Monnier
2014-09-08 13:30 ` Stefan Monnier
2014-09-02 14:37 ` [RFC] temporary Lisp_Strings Paul Eggert
2014-09-02 15:24 ` Dmitry Antipov
2014-09-02 15:28 ` Dmitry Antipov
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