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 17:46:16 +0530 [thread overview]
Message-ID: <CA+T2Sh3yww1NF_pmhkD5FD56qsGC7WF=o+62pAvEKjaZMGTZ4w@mail.gmail.com> (raw)
In-Reply-To: <jwv37ggclak.fsf-monnier+emacsdiffs@gnu.org>
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?
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
next prev parent reply other threads:[~2017-01-19 12:16 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 [this message]
2017-01-19 16:34 ` Stefan Monnier
2017-01-19 17:53 ` Vibhav Pant
2017-01-20 9:10 ` Daniel Colascione
2017-01-20 14:53 ` Stefan Monnier
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