Re: Finalizing 'inhibit-automatic-native-compilation'

[Aymeric Agon-Rambosson <aymeric.agon@yandex.com>]

Le jeudi 9 février 2023 à 12:11, Eli Zaretskii <eliz@gnu.org> a 
écrit :

>> Would it possible to add a constant value, like 
>> 'compile-but-no-output, that would have exactly the second 
>> behaviour I was mentioning before, that is compiling 
>> trampolines 
>> but not even trying to output them anywhere, by passing nil as 
>> the 
>> last argument of `comp--native-compile' ?
>
> Argh, the last argument to comp--native-compile is not 
> documented.
> AFAIR, setting it to nil means the trampoline will be written to
> temporary-file-directory, right?  Because I don't think we can 
> compile
> a trampoline without writing it to some file, from which we will
> thereafter load it.  (Andrea, please correct me if I'm wrong.) 
> If so,
> we could assume Lisp programs will use temporary-file-directory 
> if
> they need this, would that be good enough?

I'm asking this because this is already what 
`inhibit-automatic-native-compilation' does :

(defun comp-trampoline-compile (subr-name)
  "Synthesize compile and return a trampoline for SUBR-NAME."
  (let* ((lambda-list (comp-make-lambda-list-from-subr
                       (symbol-function subr-name)))
         ;; The synthesized trampoline must expose the exact same 
         ABI of
         ;; the primitive we are replacing in the function reloc 
         table.
         (form `(lambda ,lambda-list
                  (let ((f #',subr-name))
                    (,(if (memq '&rest lambda-list) #'apply 
                    'funcall)
                     f
                     ,@(cl-loop
                        for arg in lambda-list
                        unless (memq arg '(&optional &rest))
                        collect arg)))))
         ;; Use speed 1 for compilation speed and not to optimize 
         away
         ;; funcall calls!
         (byte-optimize nil)
         (native-comp-speed 1)
         (lexical-binding t))
    (comp--native-compile
     form nil
     ;; If we've disabled nativecomp, don't write the trampolines 
     to
     ;; the eln cache (but create them).
     (unless inhibit-automatic-native-compilation
       (cl-loop
        for dir in (if native-compile-target-directory
                       (list (expand-file-name 
                       comp-native-version-dir
                                               native-compile-target-directory))
                     (comp-eln-load-path-eff))
        for f = (expand-file-name
                 (comp-trampoline-filename subr-name)
                 dir)
        unless (file-exists-p dir)
          do (ignore-errors
               (make-directory dir t)
               (cl-return f))
        when (file-writable-p f)
          do (cl-return f)
        finally (error "Cannot find suitable directory for output 
        in \
`native-comp-eln-load-path'"))))))

The line :

(unless inhibit-automatic-native-compilation

Could be replaced with :

(unless (equal comp-enable-subr-trampolines 
'compile-but-no-output)

To the same effect (the current effect of 
`inhibit-automatic-native-compilation', with which we haven't had 
issues so far).

As a side note, Lars' comment seems to say that it is completely 
possible to attach a trampoline to a primitive without saving said 
trampoline anywhere (not even in `temporary-file-directory').

This is supported by the fact the *optional* outputting of the 
trampoline to the file system is done by the function 
`comp--native-compile', with last argument set to a filename, 
while the association of this trampoline with the primitive is 
done by the (primitive) function `comp--trampoline-install'. So 
these two actions (outputting and attaching) are independent.

I completely agree that the last argument of 
`comp--native-compile' could be documented, particularly what 
exactly happens when it is set to nil.

Best,

Aymeric