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

[Aymeric Agon-Rambosson]

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