From: Vibhav Pant <vibhavp@gmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: "emacs-devel@gnu.org" <emacs-devel@gnu.org>
Subject: Re: [Emacs-diffs] feature/byte-switch 086c4ea: * src/bytecode.c: (exec_byte_code) Use hash_lookup for Bswitch
Date: Thu, 19 Jan 2017 17:53:50 +0000 [thread overview]
Message-ID: <CA+T2Sh1sv482AJ0Nm-JHJQqMjAF+XSG6fyBQJxcOj=ifTRXy+w@mail.gmail.com> (raw)
In-Reply-To: <jwvd1fjau78.fsf-monnier+emacsdiffs@gnu.org>
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I see. For now, I've made the type check only work when BYTE_CODE_SAFE is
defined at compile time. I'll make it a part of the regular code once the
byte-switch is implemented and there are no performance issues with doing
so.
On Thu, 19 Jan 2017, 22:04 Stefan Monnier, <monnier@iro.umontreal.ca> wrote:
> > On another thought, `byte-switch` is used while compiling certain
> > `cond` forms. It
> > replaces the traditional goto-if-nil bytecode by using a hash table
> mapping
> > values to addresses/tags to be jumped to. Since `byte-switch` is
> essentially a
> > "dynamic" goto (in the sense that the address/tag cannot be known at
> > compile time),
> > wouldn't doing a runtime type check in the bytecode VM for what is a
> > hash table lookup + goto have a significant performance penalty?
>
> I don't know. Only measurement can tell. My guess is that hash_lookup
> already takes a significant amount of time, so a HASH_TABLE_P test would be
> negligible in comparison.
>
>
> Stefan
>
>
> > On Wed, Jan 18, 2017 at 11:18 PM, Stefan Monnier
> > <monnier@iro.umontreal.ca> wrote:
> >>> * src/bytecode.c: (exec_byte_code) Use hash_lookup for Bswitch
> >>> Fgethash type checks the provided table object, which is unnecessary
> >>> for compiled bytecode.
> >>
> >> While it's true that we can cause a core dump of Emacs if we feed it an
> >> invalid .elc file, that's a "feature" I'd rather shrink rather
> >> than generalize.
> >>
> >>
> >> Stefan
>
>
>
> > --
> > Vibhav Pant
> > vibhavp@gmail.com
>
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next prev parent reply other threads:[~2017-01-19 17:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170118171311.10996.72260@vcs.savannah.gnu.org>
[not found] ` <20170118171311.A84EA220125@vcs.savannah.gnu.org>
2017-01-18 17:48 ` [Emacs-diffs] feature/byte-switch 086c4ea: * src/bytecode.c: (exec_byte_code) Use hash_lookup for Bswitch Stefan Monnier
2017-01-18 18:19 ` Vibhav Pant
2017-01-19 12:16 ` Vibhav Pant
2017-01-19 16:34 ` Stefan Monnier
2017-01-19 17:53 ` Vibhav Pant [this message]
2017-01-20 9:10 ` Daniel Colascione
2017-01-20 14:53 ` Stefan Monnier
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