bug#67005: 30.0.50; improve nadivce/comp/trampoline handling

[Jens Schmidt]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Only slightly off-topic: When changing the default value of user option
>> `native-comp-never-optimize-functions', which now both Andrea and I have
>> done, does one also need to bump the :version?  Or is this taken care of
>> automagically?  If it needs to be done manually, to which value should
>> we/I set it?
>
> I guess you should change it to the version in which the new value will
> be released (i.e. "30.1").

Andrea has already seen to that, thanks.

>> And here is another comment question: Do you think this snippet that
>> made me so upset:
>>
>>       (let* ((f (if (symbolp callee)
>>                     (symbol-function callee)
>>                   (cl-assert (byte-code-function-p callee))
>>                   callee))
>>              (subrp (subrp f))
>>              (comp-func-callee (comp-func-in-unit callee)))
>>
>> deserves some explanation?
>
> A comment would make sense, since the code got you confused, yes.

That comment added, others removed and shortened.  Please review.

Thanks

>From 8758a6b4f7eff990dea45b651eaa2b7e94db730e Mon Sep 17 00:00:00 2001
From: Jens Schmidt <jschmidt4gnu@vodafonemail.de>
Date: Mon, 20 Nov 2023 23:42:01 +0100
Subject: [PATCH] Improve handling of advices and trampoline generation

* lisp/emacs-lisp/comp-common.el
(native-comp-never-optimize-functions): Remove macroexpand and
rename-buffer from default value.
* lisp/emacs-lisp/comp.el (comp-call-optim-form-call): Document call
optimization for advised primitives.
* lisp/emacs-lisp/nadvice.el (advice-add): Disallow advices during
bootstrap.  (Bug#67005)
---
 lisp/emacs-lisp/comp-common.el | 9 ++++-----
 lisp/emacs-lisp/comp.el        | 8 ++++++++
 lisp/emacs-lisp/nadvice.el     | 9 +++++++--
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/lisp/emacs-lisp/comp-common.el b/lisp/emacs-lisp/comp-common.el
index 6d94d1bd82e..cc7f21900e8 100644
--- a/lisp/emacs-lisp/comp-common.el
+++ b/lisp/emacs-lisp/comp-common.el
@@ -49,11 +49,10 @@ native-comp-verbose
   :version "28.1")

 (defcustom native-comp-never-optimize-functions
-  '(eval
-    ;; The following two are mandatory for Emacs to be working
-    ;; correctly (see comment in `advice--add-function'). DO NOT
-    ;; REMOVE.
-    macroexpand rename-buffer)
+  ;; We used to list those functions here that were advised during
+  ;; preload, but we now prefer to disallow preload advices in
+  ;; `advice-add' (bug#67005).
+  '(eval)
   "Primitive functions to exclude from trampoline optimization.

 Primitive functions included in this list will not be called
diff --git a/lisp/emacs-lisp/comp.el b/lisp/emacs-lisp/comp.el
index 73764eb1d79..9d537cbcfa7 100644
--- a/lisp/emacs-lisp/comp.el
+++ b/lisp/emacs-lisp/comp.el
@@ -2783,6 +2783,14 @@ comp-call-optim-form-call
                     (symbol-function callee)
                   (cl-assert (byte-code-function-p callee))
                   callee))
+             ;; Below call to `subrp' returns nil on an advised
+             ;; primitive F, so that we do not optimize calls to F
+             ;; with the funcall trampoline removal below.  But if F
+             ;; is advised while we compile its call, it is very
+             ;; likely to be advised also when that call is executed.
+             ;; And in that case an "unoptimized" call to F is
+             ;; actually cheaper since it avoids the call to the
+             ;; intermediate native trampoline (bug#67005).
              (subrp (subrp f))
              (comp-func-callee (comp-func-in-unit callee)))
         (cond
diff --git a/lisp/emacs-lisp/nadvice.el b/lisp/emacs-lisp/nadvice.el
index 42027c01491..c43d1b86752 100644
--- a/lisp/emacs-lisp/nadvice.el
+++ b/lisp/emacs-lisp/nadvice.el
@@ -507,10 +507,15 @@ advice-add
 is defined as a macro, alias, command, ...
 HOW can be one of:
 <<>>"
+  ;; Actively disallow function advices during bootstrap for the
+  ;; following reasons:
+  ;; - Advices in Emacs' core are generally considered bad style.
+  ;; - `Snarf-documentation' looses docstrings of advised dumped
+  ;;   functions (bug#66032#20).
   ;; TODO:
   ;; - record the advice location, to display in describe-function.
-  ;; - change all defadvice in lisp/**/*.el.
-  ;; - obsolete advice.el.
+  (when purify-flag
+    (error "Invalid pre-dump advice on %s" symbol))
   (let* ((f (symbol-function symbol))
         (nf (advice--normalize symbol f)))
     (unless (eq f nf) (fset symbol nf))
--
2.30.2