public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug libstdc++/111172] New: Dead code in std::get for variant?
@ 2023-08-27 15:19 hewillk at gmail dot com
2023-09-12 20:24 ` [Bug libstdc++/111172] " redi at gcc dot gnu.org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: hewillk at gmail dot com @ 2023-08-27 15:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
Bug ID: 111172
Summary: Dead code in std::get for variant?
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
In libstdc++'s implementation of variant's std::get, there are static_asserts
that require T not to be void, for example:
template<typename _Tp, typename... _Types>
constexpr _Tp&
get(variant<_Types...>& __v)
{
static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
"T must occur exactly once in alternatives");
static_assert(!is_void_v<_Tp>, "_Tp must not be void");
constexpr size_t __n = std::__find_uniq_type_in_pack<_Tp, _Types...>();
return std::get<__n>(__v);
}
But it looks like such static_asserts are *never* fired because the return type
already causes a compile error of forming reference to void when T is void.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
@ 2023-09-12 20:24 ` redi at gcc dot gnu.org
2023-09-15 9:24 ` cvs-commit at gcc dot gnu.org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: redi at gcc dot gnu.org @ 2023-09-12 20:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2023-09-12
Status|UNCONFIRMED |NEW
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
2023-09-12 20:24 ` [Bug libstdc++/111172] " redi at gcc dot gnu.org
@ 2023-09-15 9:24 ` cvs-commit at gcc dot gnu.org
2023-09-17 21:03 ` redi at gcc dot gnu.org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-09-15 9:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:
https://gcc.gnu.org/g:d19bdf8874059457fdfe50a9e14dad8f8b8cecbb
commit r14-4012-gd19bdf8874059457fdfe50a9e14dad8f8b8cecbb
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Sep 12 21:28:38 2023 +0100
libstdc++: Remove non-void static assertions in variant's std::get
[PR111172]
A void template argument would cause a substitution failure when trying
to form a reference for the return type, so the function body would
never be instantiated.
libstdc++-v3/ChangeLog:
PR libstdc++/111172
* include/std/variant (get<T>): Remove !is_void static
assertions.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
2023-09-12 20:24 ` [Bug libstdc++/111172] " redi at gcc dot gnu.org
2023-09-15 9:24 ` cvs-commit at gcc dot gnu.org
@ 2023-09-17 21:03 ` redi at gcc dot gnu.org
2023-11-09 8:09 ` cvs-commit at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: redi at gcc dot gnu.org @ 2023-09-17 21:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
Target Milestone|--- |14.0
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed for GCC 14. Thanks for the report.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
` (2 preceding siblings ...)
2023-09-17 21:03 ` redi at gcc dot gnu.org
@ 2023-11-09 8:09 ` cvs-commit at gcc dot gnu.org
2023-11-09 10:02 ` redi at gcc dot gnu.org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-11-09 8:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:
https://gcc.gnu.org/g:9847a4e9f025e66bfd09e0174e8bd32aa01939af
commit r13-8021-g9847a4e9f025e66bfd09e0174e8bd32aa01939af
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Sep 12 21:28:38 2023 +0100
libstdc++: Remove non-void static assertions in variant's std::get
[PR111172]
A void template argument would cause a substitution failure when trying
to form a reference for the return type, so the function body would
never be instantiated.
libstdc++-v3/ChangeLog:
PR libstdc++/111172
* include/std/variant (get<T>): Remove !is_void static
assertions.
(cherry picked from commit d19bdf8874059457fdfe50a9e14dad8f8b8cecbb)
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
` (3 preceding siblings ...)
2023-11-09 8:09 ` cvs-commit at gcc dot gnu.org
@ 2023-11-09 10:02 ` redi at gcc dot gnu.org
2024-03-18 14:06 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: redi at gcc dot gnu.org @ 2023-11-09 10:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|14.0 |13.3
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
` (4 preceding siblings ...)
2023-11-09 10:02 ` redi at gcc dot gnu.org
@ 2024-03-18 14:06 ` cvs-commit at gcc dot gnu.org
2024-03-18 14:15 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-03-18 14:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:
https://gcc.gnu.org/g:15c517049c0d8b6319990445939a69bb36fdc678
commit r12-10253-g15c517049c0d8b6319990445939a69bb36fdc678
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Sep 12 21:28:38 2023 +0100
libstdc++: Remove non-void static assertions in variant's std::get
[PR111172]
A void template argument would cause a substitution failure when trying
to form a reference for the return type, so the function body would
never be instantiated.
libstdc++-v3/ChangeLog:
PR libstdc++/111172
* include/std/variant (get<T>): Remove !is_void static
assertions.
(cherry picked from commit d19bdf8874059457fdfe50a9e14dad8f8b8cecbb)
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
` (5 preceding siblings ...)
2024-03-18 14:06 ` cvs-commit at gcc dot gnu.org
@ 2024-03-18 14:15 ` redi at gcc dot gnu.org
2024-03-18 14:16 ` redi at gcc dot gnu.org
2024-08-20 10:41 ` redi at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: redi at gcc dot gnu.org @ 2024-03-18 14:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed for 13.3 and 12.4 too.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
` (6 preceding siblings ...)
2024-03-18 14:15 ` redi at gcc dot gnu.org
@ 2024-03-18 14:16 ` redi at gcc dot gnu.org
2024-08-20 10:41 ` redi at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: redi at gcc dot gnu.org @ 2024-03-18 14:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|13.3 |12.4
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug libstdc++/111172] Dead code in std::get for variant?
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
` (7 preceding siblings ...)
2024-03-18 14:16 ` redi at gcc dot gnu.org
@ 2024-08-20 10:41 ` redi at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: redi at gcc dot gnu.org @ 2024-08-20 10:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111172
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=116381
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For the record:
The original design for std::variant allowed alternatives of cv void type, but
that was removed by
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0510r0.html during
C++17 ballot resolution. g:7b277e8b464b implemented that change, but left these
unnecessary checks.
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2024-08-20 10:41 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-08-27 15:19 [Bug libstdc++/111172] New: Dead code in std::get for variant? hewillk at gmail dot com
2023-09-12 20:24 ` [Bug libstdc++/111172] " redi at gcc dot gnu.org
2023-09-15 9:24 ` cvs-commit at gcc dot gnu.org
2023-09-17 21:03 ` redi at gcc dot gnu.org
2023-11-09 8:09 ` cvs-commit at gcc dot gnu.org
2023-11-09 10:02 ` redi at gcc dot gnu.org
2024-03-18 14:06 ` cvs-commit at gcc dot gnu.org
2024-03-18 14:15 ` redi at gcc dot gnu.org
2024-03-18 14:16 ` redi at gcc dot gnu.org
2024-08-20 10:41 ` redi at gcc dot gnu.org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).