From: Dmitry Antipov <dmantipov@yandex.ru>
To: Paul Eggert <eggert@cs.ucla.edu>
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 19:39:13 +0400 [thread overview]
Message-ID: <54073621.2040403@yandex.ru> (raw)
In-Reply-To: <5407281C.3090302@cs.ucla.edu>
On 09/03/2014 06:39 PM, Paul Eggert wrote:
> 3. It's often better (i.e., faster and/or less memory-intensive) to use a block-scope object,
> which is reclaimed on block exit rather than function exit. This suggests that we should have
> two forms of cons stack allocation, one block-scope and one function-scope, depending on the
> lifetime that the caller wants. For a block-scope cons we can use a C99-style compound literal,
> which (unlike alloca) would be safe as an expression. (We're assuming C99 in the trunk now.)
OK. So, for the simplest object (cons) we can have:
1) Function-scoped version using alloca (assuming statement expressions):
#define alloca_cons(head, tail) \
({ struct Lisp_Cons *_c = alloca (sizeof *_c); \
eassert (pointer_valid_for_lisp_object (_c)); \
_c->car = (head), _c->u.cdr = (tail); \
make_lisp_ptr (_c, Lisp_Cons); })
2) Block-scoped version using implicit stack allocation (assuming statement expressions):
#define scoped_cons(head, tail) \
({ struct Lisp_Cons alignas (GCALIGNMENT) _c; \
_c.car = (head), _c.u.cdr = (tail); \
make_lisp_ptr (&_c, Lisp_Cons); })
3) Block-scoped version assuming no statement expression but compound literals:
#define scoped_cons_2(head, tail) \
make_lisp_ptr (&((struct Lisp_Cons) { head, { tail } }), Lisp_Cons)
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?
In 3), how we can be sure that Lisp_Cons is properly aligned on stack?
Dmitry
next prev parent reply other threads:[~2014-09-03 15:39 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 [this message]
2014-09-03 16:42 ` Paul Eggert
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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