Re: [Emacs-diffs] feature/byte-switch 086c4ea: * src/bytecode.c: (exec_byte_code) Use hash_lookup for Bswitch

[Vibhav Pant <vibhavp@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1516 bytes --]

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
>

[-- Attachment #2: Type: text/html, Size: 2819 bytes --]