Re: Shrinking the C core

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: ams@gnu.org, incal@dataswamp.org, emacs-devel@gnu.org
> Date: Mon, 21 Aug 2023 08:48:55 +0000
> 
> >> Then, I conclude that the example with CL version of `car' is actually
> >> not worse in Elisp:
> >
> > I think you forget the price of running the interpreter.  After
> > computing the value of 'car', the code must use it, and that's where
> > the difference comes from.  Look at bytecode.c, from which I quoted a
> > tiny fragment, to see what Emacs does with the results of each
> > op-code.  (It's actually what every byte-code machine out there does.)
> 
> Do I understand correctly that the extra staff that has to be done by
> the byte-code machine is register manipulation?

Which registers do you have in mind here?

bytecode.c implements a stack-based machine, see the comments and
"ASCII-art" picture around line 340 in bytecode.c.  Then study the
macros used in bytecode.c, like TOP, PUSH, etc., and you will see what
I mean.

> If so, the assembly will probably look similar

I don't think so.  You can compare the GDB disassembly with the
results of byte-code disassembly (the "M-x disassemble" command in
Emacs), and I'm quite sure you will see the results are very
different.