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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107500] Useless atexit entry for ~constant_init in
 eh_globals.cc
Date: Wed, 02 Nov 2022 13:09:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107500

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to R. Diez from comment #5)
> First of all, GCC seems unable to generate an empty routine or destructor,
> or at least flag it as being effectively empty. The caller should then
> realise that it is empty, so it is not worth generating an atexit call for
> it.

The object has a user-provided destructor, which is necessary for the
immortalization trick to work. Being user-provided means it's non-trivial a=
nd
that means the destructor must be run. To destroy a gobal object, atexit it
used.

Now if the compiler can tell that the destructor actually has no side effec=
ts,
it's unobservable whether the atexit call ever happens. But that takes
non-trivial analysis of the destructor body and hard-coded knowledge that
atexit has no *other* observable side effects except registering the destru=
ctor
This all requires special case handling in the compiler, not just "turn on =
-Os
and all the code gets removed".=