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* [Bug c++/110714] New: constexpr lifetime error: base class this pointer
@ 2023-07-18 11:39 pkeir at outlook dot com
2023-07-18 12:46 ` [Bug c++/110714] " pinskia at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: pkeir at outlook dot com @ 2023-07-18 11:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
Bug ID: 110714
Summary: constexpr lifetime error: base class this pointer
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: pkeir at outlook dot com
Target Milestone: ---
Compiling the C++20 MRE code below fails:
struct Base
{
constexpr virtual ~Base() {}
constexpr Base* get_this() { return this; }
int x;
};
struct Derived : public Base {};
constexpr bool test()
{
Derived* pf = new Derived;
delete pf->get_this();
return true;
}
constexpr bool b = test();
...with the following error message:
2$ /opt/gcc-latest/bin/g++ -std=c++20 -c ce_base_alloc2.cpp
ce_base_alloc2.cpp:17:24: in ‘constexpr’ expansion of ‘test()’
ce_base_alloc2.cpp:13:23: in ‘constexpr’ expansion of
‘pf->Derived::<anonymous>.Base::get_this()->Base::~Base()’
ce_base_alloc2.cpp:8:8: error: deallocation of storage that was not previously
allocated
8 | struct Derived : public Base {};
| ^~~~~~~
I have tried with GCC trunk (14.0.0) and also version 12.2.0.
I suspect that the this pointer in the base class is not tracking the constexpr
dynamic allocation. Clang and MSVC both compile successfully. Clang requires
the virtual destructor.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/110714] constexpr lifetime error: base class this pointer
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
@ 2023-07-18 12:46 ` pinskia at gcc dot gnu.org
2023-07-18 12:58 ` pkeir at outlook dot com
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-07-18 12:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2023-07-18
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note this works on the trunk:
```
struct Base
{
constexpr virtual ~Base() {}
// constexpr Base* get_this() { return this; }
int x;
};
struct Derived : public Base {};
constexpr bool test()
{
Derived* pf = new Derived;
Base* t = pf;
delete t;
return true;
}
constexpr bool b = test();
```
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/110714] constexpr lifetime error: base class this pointer
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
2023-07-18 12:46 ` [Bug c++/110714] " pinskia at gcc dot gnu.org
@ 2023-07-18 12:58 ` pkeir at outlook dot com
2023-07-18 13:16 ` pkeir at outlook dot com
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pkeir at outlook dot com @ 2023-07-18 12:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
--- Comment #2 from Paul Keir <pkeir at outlook dot com> ---
I know. `delete pf` also works. The issue seems to be with the use of the this
pointer within the member function. This is just the MRE - I've come across
this issue twice now in our code base.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/110714] constexpr lifetime error: base class this pointer
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
2023-07-18 12:46 ` [Bug c++/110714] " pinskia at gcc dot gnu.org
2023-07-18 12:58 ` pkeir at outlook dot com
@ 2023-07-18 13:16 ` pkeir at outlook dot com
2024-03-22 0:53 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: pkeir at outlook dot com @ 2023-07-18 13:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
--- Comment #3 from Paul Keir <pkeir at outlook dot com> ---
Actually, there's no need here to delete through the base pointer; so this is
perhaps simpler:
struct Base
{
constexpr Base* get_this() { return this; }
int x;
};
struct Derived : public Base {};
constexpr bool test()
{
Derived* pf = new Derived;
delete static_cast<Derived*>(pf->get_this());
return true;
}
constexpr bool b = test();
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/110714] constexpr lifetime error: base class this pointer
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
` (2 preceding siblings ...)
2023-07-18 13:16 ` pkeir at outlook dot com
@ 2024-03-22 0:53 ` redi at gcc dot gnu.org
2024-03-22 0:54 ` redi at gcc dot gnu.org
2024-03-25 21:13 ` ppalka at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2024-03-22 0:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed|2023-07-18 00:00:00 |2024-3-22
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I encountered this using std::pointer_traits<P>::pointer_to in constexpr code
like so:
#include <memory>
struct B { constexpr virtual ~B() = default; };
struct D : B { };
consteval void f()
{
delete std::pointer_traits<B*>::pointer_to(*new D());
}
int main()
{
f();
}
Which can be simplified to:
struct B { constexpr virtual ~B() = default; };
struct D : B { };
consteval void f()
{
delete &(B&)*new D();
}
int main()
{
f();
}
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/110714] constexpr lifetime error: base class this pointer
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
` (3 preceding siblings ...)
2024-03-22 0:53 ` redi at gcc dot gnu.org
@ 2024-03-22 0:54 ` redi at gcc dot gnu.org
2024-03-25 21:13 ` ppalka at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2024-03-22 0:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This works with Clang and EDG.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/110714] constexpr lifetime error: base class this pointer
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
` (4 preceding siblings ...)
2024-03-22 0:54 ` redi at gcc dot gnu.org
@ 2024-03-25 21:13 ` ppalka at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: ppalka at gcc dot gnu.org @ 2024-03-25 21:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org,
| |ppalka at gcc dot gnu.org
--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
For the original testcase, evaluation of pf->get_this(); yields &heap [0]
instead of the expected &heap, which we don't recognize as a valid constexpr
heap pointer thus leading to the error.
This heap[0] term gets built from cxx_fold_indirect_ref which folds '*(struct
Derived *) &heap' into 'heap[0]' (where 'heap' has type Derived[1]), which
doesn't seem like a sound transformation? I'd expect it to get folded to
simply 'heap'.
Then again this intermediate (Derived *) cast seems unsound in the first place
since we're casting something of type Derived[1]* to Derived*. I don't know
what to make of that.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-03-25 21:13 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-07-18 11:39 [Bug c++/110714] New: constexpr lifetime error: base class this pointer pkeir at outlook dot com
2023-07-18 12:46 ` [Bug c++/110714] " pinskia at gcc dot gnu.org
2023-07-18 12:58 ` pkeir at outlook dot com
2023-07-18 13:16 ` pkeir at outlook dot com
2024-03-22 0:53 ` redi at gcc dot gnu.org
2024-03-22 0:54 ` redi at gcc dot gnu.org
2024-03-25 21:13 ` ppalka at gcc dot gnu.org
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