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* [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation
@ 2021-09-10 20:57 johelegp at gmail dot com
2021-09-10 21:23 ` [Bug c++/102284] " johelegp at gmail dot com
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2021-09-10 20:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
Bug ID: 102284
Summary: Can access object outside of its lifetime during
constant evaluation
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: johelegp at gmail dot com
CC: johelegp at gmail dot com
Target Milestone: ---
This is prohibited at https://eel.is/c++draft/basic.life#7.1.
See https://godbolt.org/z/exKnnT935.
```C++
#include <memory>
struct X { int x; };
int main() {
[]() consteval {
{
X x{};
x.~X();
++x.x;
std::construct_at(&x);
}
{
union { X x{}; };
x.~X();
++x.x;
}
}();
}
```
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
@ 2021-09-10 21:23 ` johelegp at gmail dot com
2021-09-10 21:24 ` johelegp at gmail dot com
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2021-09-10 21:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
--- Comment #1 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
There's also https://eel.is/c++draft/basic.life#9.sentence-1 to consider.
See https://godbolt.org/z/P97Kaqhv8.
```C++
struct X { int x; };
int main() {
[]() consteval {
X x{};
x.~X();
}();
}
```
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
2021-09-10 21:23 ` [Bug c++/102284] " johelegp at gmail dot com
@ 2021-09-10 21:24 ` johelegp at gmail dot com
2021-09-10 21:26 ` pinskia at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2021-09-10 21:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
--- Comment #2 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Fixed that: https://godbolt.org/z/YGf4GTP5P.
```C++
struct X { constexpr ~X() { } };
int main() {
[]() consteval {
X x{};
x.~X();
}();
}
```
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
2021-09-10 21:23 ` [Bug c++/102284] " johelegp at gmail dot com
2021-09-10 21:24 ` johelegp at gmail dot com
@ 2021-09-10 21:26 ` pinskia at gcc dot gnu.org
2021-09-11 1:04 ` johelegp at gmail dot com
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-10 21:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think there might be a dup of this bug.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
` (2 preceding siblings ...)
2021-09-10 21:26 ` pinskia at gcc dot gnu.org
@ 2021-09-11 1:04 ` johelegp at gmail dot com
2022-01-17 11:12 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2021-09-11 1:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
--- Comment #4 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
If there is, I confirmed it's not in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55004.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
` (3 preceding siblings ...)
2021-09-11 1:04 ` johelegp at gmail dot com
@ 2022-01-17 11:12 ` pinskia at gcc dot gnu.org
2022-09-24 20:11 ` johelegp at gmail dot com
2022-09-27 1:40 ` johelegp at gmail dot com
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-01-17 11:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2022-01-17
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=102623
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
` (4 preceding siblings ...)
2022-01-17 11:12 ` pinskia at gcc dot gnu.org
@ 2022-09-24 20:11 ` johelegp at gmail dot com
2022-09-27 1:40 ` johelegp at gmail dot com
6 siblings, 0 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2022-09-24 20:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
--- Comment #6 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Another example.
Simplified: https://godbolt.org/z/z781c56PM.
```C++
struct ratio {
int numerator;
};
template<auto> struct constant;
template<auto F> concept constant_invocable = requires { typename
constant<(F(), 0)>; };
static_assert(not constant_invocable<[] {
ratio r;
(void)int{r.*&ratio::numerator};
}>);
```
```
<source>:9:15: error: static assertion failed
9 | static_assert(not constant_invocable<[] {
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
10 | ratio r;
| ~~~~~~~~
11 | (void)int{r.*&ratio::numerator};
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
12 | }>);
| ~~
Compiler returned: 1
```
Found while opening https://github.com/llvm/llvm-project/issues/57958:
https://godbolt.org/z/KWfvEnaae.
```C++
#include <concepts>
#include <cstdint>
#include <functional>
#include <type_traits>
struct ratio {
std::intmax_t numerator;
std::intmax_t denominator{1};
};
template<auto F> concept constant_invocable = requires { typename
std::integral_constant<int, (F(), 0)>; };
template<auto P> requires std::is_member_object_pointer_v<decltype(P)>
inline constexpr bool default_initialization_leaves_uninitialized =
[]<class T, class M>(M T::*) {
return not constant_invocable<[]() {
T v;
(void)M{v.*P};
}>;
}(P);
static_assert(default_initialization_leaves_uninitialized<&ratio::numerator>);
static_assert(not
default_initialization_leaves_uninitialized<&ratio::denominator>);
```
```
<source>:22:15: error: static assertion failed
22 |
static_assert(default_initialization_leaves_uninitialized<&ratio::numerator>);
|
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Compiler returned: 1
```
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/102284] Can access object outside of its lifetime during constant evaluation
2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
` (5 preceding siblings ...)
2022-09-24 20:11 ` johelegp at gmail dot com
@ 2022-09-27 1:40 ` johelegp at gmail dot com
6 siblings, 0 replies; 8+ messages in thread
From: johelegp at gmail dot com @ 2022-09-27 1:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102284
--- Comment #7 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
This may be related. Assigning to another member doesn't end the lifetime of
the active one: https://godbolt.org/z/eMGY5ehnb.
```C++
#include <memory>
struct symbol { };
constexpr symbol one{};
struct unit {
const struct symbol* symbol = &one;
struct not_one_t { };
union to_the {
not_one_t not_one = {}; // Omits ¹ from NTTP.
int i;
to_the() = default;
constexpr to_the(int i) : i{i} {
if (i == 1) {
// std::destroy_at(&this->i); // On GCC, doesn't help.
not_one = {};
// std::construct_at(¬_one); // On GCC, initializes `not_one`,
doesn't end the lifetime of `i`.
}
}
} exponent = {};
constexpr unit(const struct symbol& s)
: symbol{&s} { }
constexpr unit(const struct symbol& s, auto e)
: symbol{&s}, exponent{e} { }
};
template<auto> void print() { }
int main() {
constexpr auto U = unit{one, 1};
print<U>();
print<unit{one}>();
static_assert(&U.exponent.not_one);
// static_assert(U.exponent.i == 1); // Works on GCC (and MSVC).
}
```
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2022-09-27 1:40 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
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2021-09-10 20:57 [Bug c++/102284] New: Can access object outside of its lifetime during constant evaluation johelegp at gmail dot com
2021-09-10 21:23 ` [Bug c++/102284] " johelegp at gmail dot com
2021-09-10 21:24 ` johelegp at gmail dot com
2021-09-10 21:26 ` pinskia at gcc dot gnu.org
2021-09-11 1:04 ` johelegp at gmail dot com
2022-01-17 11:12 ` pinskia at gcc dot gnu.org
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