[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495
--- Comment #1 from Luke Dalessandro ---
A short-term workaround for this appears to be explicit allocator usage (works
back at least to 10.2).
```
#include
struct Foo {
constexpr virtual ~Foo() {}
};
constexpr bool foo() {
std::allocator alloc = {};
Foo *ptr = alloc.allocate(1);
std::construct_at(ptr);
std::destroy_at(ptr);
alloc.deallocate(ptr, 1);
return true;
}
static_assert(foo());
```
https://godbolt.org/z/ohKE6h3Px
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495
--- Comment #2 from Luke Dalessandro ---
It's also possible to workaround this with array allocation.
```
struct Foo {
constexpr virtual ~Foo() {}
};
constexpr bool foo() {
Foo *ptr = new Foo[1]{};
delete [] ptr;
return true;
}
static_assert(foo());
```
Obviously both of the workarounds require that we be able to cast from a `Foo*`
to our derived pointer, at which point we might as well skip the virtual
destructor and add an abstract `virtual void destroy() = 0` member where we can
just call `delete this` anyway.
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 Jakub Jelinek changed: What|Removed |Added CC||jakub at gcc dot gnu.org, ||jason at gcc dot gnu.org Status|UNCONFIRMED |NEW Ever confirmed|0 |1 Last reconfirmed||2021-05-10 --- Comment #3 from Jakub Jelinek --- constexpr.c (cxx_eval_call_expression) has: if (DECL_CLONED_FUNCTION_P (fun)) fun = DECL_CLONED_FUNCTION (fun); and similarly constexpr.c (maybe_save_constexpr_fundef) has: if (processing_template_decl || !DECL_DECLARED_CONSTEXPR_P (fun) || cp_function_chain->invalid_constexpr || DECL_CLONED_FUNCTION_P (fun)) return; which means instead of calling during constexpr evaluation the deleting destructor (_ZN3FooD0Ev) we call the destructor it is cloned from (_ZN3FooD4Ev) and that means we don't constexpr evaluate the actual delete operator call. I guess it would be possible to remember DECL_DELETING_DESTRUCTOR_P (fun) from before the fun = DECL_CLONED_FUNCTION (fun); and constexpr evaluate a delete operator call, but I'm afraid I have no idea how this works for constructors or any other cloned function either, how do we figure out what arguments to bind to e.g. in_chrg argument etc.?
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 Andrew Pinski changed: What|Removed |Added CC||friedkeenan at protonmail dot com --- Comment #4 from Andrew Pinski --- *** Bug 102167 has been marked as a duplicate of this bug. ***
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 --- Comment #5 from Jakub Jelinek --- Ah, for constructors this is likely a non-issue, because in_chrg etc. only appears on constructors of classes with virtual bases and such constructors are not constexpr.
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 Jakub Jelinek changed: What|Removed |Added Status|NEW |ASSIGNED Assignee|unassigned at gcc dot gnu.org |jakub at gcc dot gnu.org --- Comment #6 from Jakub Jelinek --- Created attachment 51415 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51415&action=edit gcc12-pr100495.patch The easiest fix seems to be to just remember the deleting dtor bodies and constexpr evaluating them, they are quite special anyway, as they are created by build_delete_destructor_body and essentially contain just two calls, so there is no user code in those and thus practically they aren't really clones of those user functions - they just call some other dtor fndecl (with the user code in it) and delete.
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 --- Comment #7 from CVS Commits --- The master branch has been updated by Jakub Jelinek : https://gcc.gnu.org/g:81f9718139cb1cc164ada411ada8cca9f32b8be8 commit r12-3387-g81f9718139cb1cc164ada411ada8cca9f32b8be8 Author: Jakub Jelinek Date: Tue Sep 7 19:33:28 2021 +0200 c++: Fix up constexpr evaluation of deleting dtors [PR100495] We do not save bodies of constexpr clones and instead evaluate the bodies of the constexpr functions they were cloned from. I believe that is just fine for constructors because complete vs. base ctors differ only in classes that have virtual bases and such constructors aren't constexpr, similarly complete/base destructors. But as the testcase below shows, for deleting destructors it is not fine, deleting dtors while marked as clones in fact are just artificial functions with synthetized body which calls the user destructor and deallocation. So, either we'd need to evaluate the destructor and afterwards synthetize and evaluate the deallocation, or we can just save and use the deleting dtors bodies. The latter seems much easier to me. 2021-09-07 Jakub Jelinek PR c++/100495 * constexpr.c (maybe_save_constexpr_fundef): Save body even for constexpr deleting dtors. (cxx_eval_call_expression): Don't use DECL_CLONED_FUNCTION for deleting dtors. * g++.dg/cpp2a/constexpr-new21.C: New test.
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 --- Comment #8 from CVS Commits --- The releases/gcc-11 branch has been updated by Jakub Jelinek : https://gcc.gnu.org/g:9f300873f6bf8456ebdbd40d0211aefe57f95cb5 commit r11-8968-g9f300873f6bf8456ebdbd40d0211aefe57f95cb5 Author: Jakub Jelinek Date: Tue Sep 7 19:33:28 2021 +0200 c++: Fix up constexpr evaluation of deleting dtors [PR100495] We do not save bodies of constexpr clones and instead evaluate the bodies of the constexpr functions they were cloned from. I believe that is just fine for constructors because complete vs. base ctors differ only in classes that have virtual bases and such constructors aren't constexpr, similarly complete/base destructors. But as the testcase below shows, for deleting destructors it is not fine, deleting dtors while marked as clones in fact are just artificial functions with synthetized body which calls the user destructor and deallocation. So, either we'd need to evaluate the destructor and afterwards synthetize and evaluate the deallocation, or we can just save and use the deleting dtors bodies. The latter seems much easier to me. 2021-09-07 Jakub Jelinek PR c++/100495 * constexpr.c (maybe_save_constexpr_fundef): Save body even for constexpr deleting dtors. (cxx_eval_call_expression): Don't use DECL_CLONED_FUNCTION for deleting dtors. * g++.dg/cpp2a/constexpr-new21.C: New test. (cherry picked from commit 81f9718139cb1cc164ada411ada8cca9f32b8be8)
[Bug c++/100495] constexpr virtual destructor incorrectly reports memory leak
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100495 --- Comment #9 from Jakub Jelinek --- Fixed for 11.3+/12+ so far, probably should be backported for 10.4 too.
