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* [Bug c++/107544] New: Friended struct with concept gives different output in clang/gcc/MSVC
@ 2022-11-06 21:45 danakj at orodu dot net
2022-11-06 21:47 ` [Bug c++/107544] " danakj at orodu dot net
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: danakj at orodu dot net @ 2022-11-06 21:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107544
Bug ID: 107544
Summary: Friended struct with concept gives different output in
clang/gcc/MSVC
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: danakj at orodu dot net
Target Milestone: ---
I don't know which compiler is right, but all three give a different output. So
I will report it here, as the GCC result looks wrong and exposes private data.
https://godbolt.org/z/7Pq3eWhc8
```
#include <compare>
#include <concepts>
#include <iostream>
template <class T>
concept HasTag = requires {
T::Tag;
requires std::same_as<decltype(T::Tag), const bool>;
};
template <class T>
struct check_tag final {
static constexpr bool value()
requires(!HasTag<T>)
{
return false;
}
static constexpr bool value()
requires(HasTag<T>)
{
return T::Tag;
};
};
struct S {
private:
template <class T>
friend struct check_tag;
static constexpr bool Tag = true;
};
int main() {
std::cout << HasTag<S> << "\n";
std::cout << check_tag<S>::value() << "\n";
}
```
Clang output (the concept sees private data if used in friend):
0
1
GCC output (the concept always sees private data):
1
1
MSVC output (the concept never sees private data):
0
0
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/107544] Friended struct with concept gives different output in clang/gcc/MSVC
2022-11-06 21:45 [Bug c++/107544] New: Friended struct with concept gives different output in clang/gcc/MSVC danakj at orodu dot net
@ 2022-11-06 21:47 ` danakj at orodu dot net
2022-11-06 21:49 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: danakj at orodu dot net @ 2022-11-06 21:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107544
--- Comment #1 from danakj at orodu dot net ---
Clang report: https://github.com/llvm/llvm-project/issues/58833
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/107544] Friended struct with concept gives different output in clang/gcc/MSVC
2022-11-06 21:45 [Bug c++/107544] New: Friended struct with concept gives different output in clang/gcc/MSVC danakj at orodu dot net
2022-11-06 21:47 ` [Bug c++/107544] " danakj at orodu dot net
@ 2022-11-06 21:49 ` pinskia at gcc dot gnu.org
2022-11-06 21:49 ` pinskia at gcc dot gnu.org
2022-11-06 21:55 ` danakj at orodu dot net
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-11-06 21:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107544
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=104111
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a dup of bug 104111.
Specifically there is an issue reported against the C++ standard too:
https://cplusplus.github.io/CWG/issues/2589.html
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a dup of bug 104111.
Specifically there is an issue reported against the C++ standard too:
https://cplusplus.github.io/CWG/issues/2589.html
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/107544] Friended struct with concept gives different output in clang/gcc/MSVC
2022-11-06 21:45 [Bug c++/107544] New: Friended struct with concept gives different output in clang/gcc/MSVC danakj at orodu dot net
2022-11-06 21:47 ` [Bug c++/107544] " danakj at orodu dot net
2022-11-06 21:49 ` pinskia at gcc dot gnu.org
@ 2022-11-06 21:49 ` pinskia at gcc dot gnu.org
2022-11-06 21:55 ` danakj at orodu dot net
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-11-06 21:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107544
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=104111
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a dup of bug 104111.
Specifically there is an issue reported against the C++ standard too:
https://cplusplus.github.io/CWG/issues/2589.html
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a dup of bug 104111.
Specifically there is an issue reported against the C++ standard too:
https://cplusplus.github.io/CWG/issues/2589.html
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/107544] Friended struct with concept gives different output in clang/gcc/MSVC
2022-11-06 21:45 [Bug c++/107544] New: Friended struct with concept gives different output in clang/gcc/MSVC danakj at orodu dot net
` (2 preceding siblings ...)
2022-11-06 21:49 ` pinskia at gcc dot gnu.org
@ 2022-11-06 21:55 ` danakj at orodu dot net
3 siblings, 0 replies; 5+ messages in thread
From: danakj at orodu dot net @ 2022-11-06 21:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107544
--- Comment #4 from danakj at orodu dot net ---
It looks related but I am not sure it is a duplicate. In this case, the concept
is being used from a non-friend context first and still accessing the private
data. In that bug, they demonstrate clang having the same output, but here
clang and GCC differ as well.
```
std::cout << HasTag<S> << "\n";
std::cout << check_tag<S>::value() << "\n";
```
Reordering these statements does not change the output.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-11-06 21:55 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2022-11-06 21:45 [Bug c++/107544] New: Friended struct with concept gives different output in clang/gcc/MSVC danakj at orodu dot net
2022-11-06 21:47 ` [Bug c++/107544] " danakj at orodu dot net
2022-11-06 21:49 ` pinskia at gcc dot gnu.org
2022-11-06 21:49 ` pinskia at gcc dot gnu.org
2022-11-06 21:55 ` danakj at orodu dot net
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