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* [Bug c++/102163] New: std::variant rejects valid constant expression
@ 2021-09-01 16:57 hewillk at gmail dot com
2021-09-01 20:55 ` [Bug c++/102163] [10/11/12 Regression] " ppalka at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: hewillk at gmail dot com @ 2021-09-01 16:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
Bug ID: 102163
Summary: std::variant rejects valid constant expression
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
#include <variant>
struct O {
O() = default;
O(O&&) = default;
O(const O&) = default;
O& operator=(const O&) = default;
O& operator=(O&&) = default;
~O() = default;
constexpr O(int x) {}
};
constexpr std::variant<float, O> v{42};
https://godbolt.org/z/PdEx4z7rf
GCC-trunk rejected it under -std=c++20, it seems to be a language feature bug.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10/11/12 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
@ 2021-09-01 20:55 ` ppalka at gcc dot gnu.org
2021-09-01 21:08 ` pinskia at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-09-01 20:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |10.4
Last reconfirmed| |2021-09-01
CC| |ppalka at gcc dot gnu.org
Ever confirmed|0 |1
Known to work| |9.4.0
Status|UNCONFIRMED |ASSIGNED
Known to fail| |10.3.0, 11.2.0, 12.0
Summary|std::variant rejects valid |[10/11/12 Regression]
|constant expression |std::variant rejects valid
| |constant expression
--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Reduced rejects-valid testcase:
struct O {
constexpr O(int) {}
};
union _Variadic_union
{
constexpr _Variadic_union() : _M_rest(42) { }
O _M_rest;
};
constexpr _Variadic_union w;
Started with r10-7313.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10/11/12 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
2021-09-01 20:55 ` [Bug c++/102163] [10/11/12 Regression] " ppalka at gcc dot gnu.org
@ 2021-09-01 21:08 ` pinskia at gcc dot gnu.org
2021-09-01 21:09 ` pinskia at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-01 21:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
PR 97665 is related but it does not have an intializer for _M_rest.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10/11/12 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
2021-09-01 20:55 ` [Bug c++/102163] [10/11/12 Regression] " ppalka at gcc dot gnu.org
2021-09-01 21:08 ` pinskia at gcc dot gnu.org
@ 2021-09-01 21:09 ` pinskia at gcc dot gnu.org
2021-09-14 15:23 ` cvs-commit at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-01 21:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note this works:
struct O {
constexpr O() {}
};
union _Variadic_union
{
constexpr _Variadic_union() : _M_rest() { }
O _M_rest;
};
constexpr _Variadic_union w;
----- CUT ---
But this fails:
struct O {
constexpr O() {}
};
union _Variadic_union
{
constexpr _Variadic_union() : _M_rest{} { }
O _M_rest;
};
constexpr _Variadic_union w;
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10/11/12 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
` (2 preceding siblings ...)
2021-09-01 21:09 ` pinskia at gcc dot gnu.org
@ 2021-09-14 15:23 ` cvs-commit at gcc dot gnu.org
2021-10-06 14:15 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-09-14 15:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:de07cff96abd43f6f65dcf333958899c2ec42598
commit r12-3527-gde07cff96abd43f6f65dcf333958899c2ec42598
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Sep 14 11:22:12 2021 -0400
c++: empty union member activation during constexpr [PR102163]
Here, the union's constructor is defined to activate its empty data
member _M_rest, but during constexpr evaluation of this constructor the
subobject constructor call O::O(&_M_rest, 42) doesn't produce a side
effect that actually activates the member, so the union still appears
uninitialized after its constructor has run. This patch fixes this by
using a dummy MODIFY_EXPR in this situation, whose evaluation ensures
the member gets activated.
PR c++/102163
gcc/cp/ChangeLog:
* constexpr.c (cxx_eval_call_expression): After evaluating a
subobject constructor call for an empty union member, produce a
side effect that makes sure the member gets activated.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-empty17.C: New test.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10/11/12 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
` (3 preceding siblings ...)
2021-09-14 15:23 ` cvs-commit at gcc dot gnu.org
@ 2021-10-06 14:15 ` cvs-commit at gcc dot gnu.org
2021-10-06 14:17 ` [Bug c++/102163] [10 " ppalka at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-10-06 14:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:59c6831682dfa8bec2b5a62bdc85739924970808
commit r11-9080-g59c6831682dfa8bec2b5a62bdc85739924970808
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Sep 14 11:22:12 2021 -0400
c++: empty union member activation during constexpr [PR102163]
Here, the union's constructor is defined to activate its empty data
member _M_rest, but during constexpr evaluation of this constructor the
subobject constructor call O::O(&_M_rest, 42) doesn't produce a side
effect that actually activates the member, so the union still appears
uninitialized after its constructor has run. This patch fixes this by
using a dummy MODIFY_EXPR in this situation, whose evaluation ensures
the member gets activated.
PR c++/102163
gcc/cp/ChangeLog:
* constexpr.c (cxx_eval_call_expression): After evaluating a
subobject constructor call for an empty union member, produce a
side effect that makes sure the member gets activated.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-empty17.C: New test.
(cherry picked from commit de07cff96abd43f6f65dcf333958899c2ec42598)
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
` (4 preceding siblings ...)
2021-10-06 14:15 ` cvs-commit at gcc dot gnu.org
@ 2021-10-06 14:17 ` ppalka at gcc dot gnu.org
2022-06-28 10:46 ` jakub at gcc dot gnu.org
2023-07-07 9:46 ` rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-10-06 14:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[10/11/12 Regression] |[10 Regression]
|std::variant rejects valid |std::variant rejects valid
|constant expression |constant expression
--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 11.3 and 12 so far.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
` (5 preceding siblings ...)
2021-10-06 14:17 ` [Bug c++/102163] [10 " ppalka at gcc dot gnu.org
@ 2022-06-28 10:46 ` jakub at gcc dot gnu.org
2023-07-07 9:46 ` rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-06-28 10:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.4 |10.5
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/102163] [10 Regression] std::variant rejects valid constant expression
2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
` (6 preceding siblings ...)
2022-06-28 10:46 ` jakub at gcc dot gnu.org
@ 2023-07-07 9:46 ` rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-07-07 9:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102163
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Known to work| |11.3.0, 12.1.0
Target Milestone|10.5 |11.3
Known to fail|12.0 |10.5.0
Resolution|--- |FIXED
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
fixed
^ permalink raw reply [flat|nested] 9+ messages in thread
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2021-09-01 16:57 [Bug c++/102163] New: std::variant rejects valid constant expression hewillk at gmail dot com
2021-09-01 20:55 ` [Bug c++/102163] [10/11/12 Regression] " ppalka at gcc dot gnu.org
2021-09-01 21:08 ` pinskia at gcc dot gnu.org
2021-09-01 21:09 ` pinskia at gcc dot gnu.org
2021-09-14 15:23 ` cvs-commit at gcc dot gnu.org
2021-10-06 14:15 ` cvs-commit at gcc dot gnu.org
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