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

From: Aymeric Agon-Rambosson
Subject: Re: Finalizing 'inhibit-automatic-native-compilation'
Date: Fri, 10 Feb 2023 09:37:16 +0100
User-agent: mu4e 1.6.10; emacs 28.1

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)
                       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))
    form nil
;; If we've disabled nativecomp, don't write the trampolines to
    ;; the eln cache (but create them).
    (unless inhibit-automatic-native-compilation
       for dir in (if native-compile-target-directory
(list (expand-file-name comp-native-version-dir
       for f = (expand-file-name
                (comp-trampoline-filename subr-name)
       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 \

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.



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