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* [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr
@ 2021-06-08 17:46 jason at gcc dot gnu.org
2021-06-08 17:46 ` [Bug c++/100976] " mpolacek at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: jason at gcc dot gnu.org @ 2021-06-08 17:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
Bug ID: 100976
Summary: [C++23] Make constexpr reference temp constexpr
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jason at gcc dot gnu.org
Blocks: 98940
Target Milestone: ---
https://wg21.link/cwg2481
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98940
[Bug 98940] Implement C++23 language features
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
@ 2021-06-08 17:46 ` mpolacek at gcc dot gnu.org
2021-06-08 18:45 ` jason at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2021-06-08 17:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2021-06-08
CC| |mpolacek at gcc dot gnu.org
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
2021-06-08 17:46 ` [Bug c++/100976] " mpolacek at gcc dot gnu.org
@ 2021-06-08 18:45 ` jason at gcc dot gnu.org
2021-06-08 20:51 ` jason at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: jason at gcc dot gnu.org @ 2021-06-08 18:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> ---
constexpr const int &r = 42;
static_assert(r == 42);
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
2021-06-08 17:46 ` [Bug c++/100976] " mpolacek at gcc dot gnu.org
2021-06-08 18:45 ` jason at gcc dot gnu.org
@ 2021-06-08 20:51 ` jason at gcc dot gnu.org
2021-07-01 16:55 ` mpolacek at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: jason at gcc dot gnu.org @ 2021-06-08 20:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Or rather,
int main()
{
constexpr const int &r = 42;
static_assert(r == 42); // { dg-bogus "" }
}
[expr.const]/4.7 says that "a temporary object of non-volatile const-qualified
literal type whose lifetime is extended to that
of a variable that is usable in constant expressions" is usable in a constant
expression.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
` (2 preceding siblings ...)
2021-06-08 20:51 ` jason at gcc dot gnu.org
@ 2021-07-01 16:55 ` mpolacek at gcc dot gnu.org
2021-07-01 20:09 ` mpolacek at gcc dot gnu.org
2021-07-19 13:59 ` mpolacek at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2021-07-01 16:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |mpolacek at gcc dot gnu.org
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
` (3 preceding siblings ...)
2021-07-01 16:55 ` mpolacek at gcc dot gnu.org
@ 2021-07-01 20:09 ` mpolacek at gcc dot gnu.org
2021-07-19 13:59 ` mpolacek at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2021-07-01 20:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #2)
> Or rather,
>
> int main()
> {
> constexpr const int &r = 42;
> static_assert(r == 42); // { dg-bogus "" }
> }
>
> [expr.const]/4.7 says that "a temporary object of non-volatile
> const-qualified literal type whose lifetime is extended to that
> of a variable that is usable in constant expressions" is usable in a
> constant expression.
This was actually CWG 2126 which we don't seem to fully implement:
struct A { int n; };
const A &a = {1}; // const temporary
A &b = (A &)(const A &)A{1}; // const temporary
A &&c = (A &&)(const A &)A{1}; // const temporary
static_assert(a.n == 1, "");
static_assert(b.n == 1, "");
static_assert(c.n == 1, "");
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/100976] [C++23] Make constexpr reference temp constexpr
2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
` (4 preceding siblings ...)
2021-07-01 20:09 ` mpolacek at gcc dot gnu.org
@ 2021-07-19 13:59 ` mpolacek at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2021-07-19 13:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100976
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |WORKSFORME
Status|ASSIGNED |RESOLVED
--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Turned out we already implement CWG 2481. If anyone has a test for something
we don't handle, please open a PR.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-07-19 13:59 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2021-06-08 17:46 [Bug c++/100976] New: [C++23] Make constexpr reference temp constexpr jason at gcc dot gnu.org
2021-06-08 17:46 ` [Bug c++/100976] " mpolacek at gcc dot gnu.org
2021-06-08 18:45 ` jason at gcc dot gnu.org
2021-06-08 20:51 ` jason at gcc dot gnu.org
2021-07-01 16:55 ` mpolacek at gcc dot gnu.org
2021-07-01 20:09 ` mpolacek at gcc dot gnu.org
2021-07-19 13:59 ` mpolacek at gcc dot gnu.org
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