bug#69480: Emacs Lisp needs, for its great 'native-compile', 'declare' and 'the' for fixnums and arrays.

[Stephen Berman]

On Fri, 01 Mar 2024 07:18:29 -0500 Andrea Corallo <acorallo@gnu.org> wrote:

> Stephen Berman via "Bug reports for GNU Emacs, the Swiss army knife of
> text editors" <bug-gnu-emacs@gnu.org> writes:
>
>> On Thu, 29 Feb 2024 22:10:27 +0200 Eli Zaretskii <eliz@gnu.org> wrote:
>>
>>>> From: Robert Boyer <robertstephenboyer@gmail.com>
>>>> Date: Thu, 29 Feb 2024 13:40:14 -0600
>>>>
>>>> Consider this form:
>>>>
>>>> (progn (emacs-lisp-native-compile-and-load) (benchmark (build-sieve (expt 
>>>> 10
>>>> 8)) 1))
>>>>
>>>> First of all, 'benchmark' has an obvious bug because it reports a time of
>>>> .000005 seconds.
>>>
>>> You use benchmark incorrectly.  And you should use benchmark-run
>>> instead, anyway.
>>>
>>>> After finding the file eratosthenese.el, the evaluation of the form above
>>>> takes 69 seconds in Emacs.
>>>>
>>>> After entering SBCL and loading eratosthenese.lisp, (build-sieve (expt 10 
>>>> 8))
>>>> takes 8 seconds.
>>>
>>> It takes 16.7 sec on my system.
>>
>> I was curious to see how long it takes on my system, compared to the
>> byte-compiled and uncompiled files, and the results surprised me.
>> First, I visited the file eratosthenes.el, ran `eval-buffer' and then
>> `M-: (benchmark-run nil (build-sieve (expt 10 8)))', with this result:
>>
>> (143.326808051 1 0.344846223)
>>
>> Then I ran `M-: (progn (emacs-lisp-native-compile-and-load)
>> (benchmark-run nil (build-sieve (expt 10 8))))', with this result:
>>
>> (37.457440511 1 0.36922945500000004)
>>
>> The native compilation also produced a byte-compiled file
>> eratosthenes.elc, so I then loaded that file and again ran `M-:
>> (benchmark-run nil (build-sieve (expt 10 8)))', with this result:
>>
>> (21.854069551000002 1 0.3595161699999999)
>>
>> I was surprised that this was much faster than the run with native
>> compilation, but I thought perhaps this was due to the time spent
>> producing both the native and byte-compiled files (though more than 15
>> seconds for that seemed unlikely), so I ran `M-: (progn
>> (emacs-lisp-native-compile-and-load) (benchmark-run nil (build-sieve
>> (expt 10 8))))' again, which just loaded the already native-compiled
>> file (and updated its timestamp), but the result was practically the
>> same as the first time:
>>
>> (37.095767574 1 0.36986937500000017)
>>
>> Why is the timing with native compilation so much slower than with byte
>> compilation?
>
> Because the file is not lexically scoped so we are not running
> optimizations.

Ah, ok.

> On my laptop I see:
>
> 11 secs byte compiled
> 18 secs native compiled
>
> 7 secs byte compiled with lexical scope
> 5 secs  native compiled with lexical scope.

I got these timings with lexical scope:

native compiled: (12.717023709000001 1 0.34653286699999997)
  byte compiled: (9.597325325 1 0.38987931)

It's still slower with native compilation than with byte compilation on
my machine, unlike on yours.  Do you have any idea why?

Steve Berman