https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122084
Bug ID: 122084
Summary: Self-referential objects work poorly in constexpr
dtors
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: blubban at gmail dot com
Target Milestone: ---
struct iterator {
iterator* next;
//iterator* keepalive = this;
constexpr explicit iterator() {
next = this;
}
constexpr explicit iterator(iterator* prev) {
next = prev->next;
prev->next = this;
}
constexpr iterator(const iterator&) = delete;
iterator& operator=(const iterator&) = delete;
constexpr ~iterator() {
iterator* it = next;
while (true)
{
if (it->next == this) {
it->next = next;
break;
}
it = it->next;
}
}
};
constexpr iterator copy(iterator* first) {
return iterator(first);
}
constexpr bool test() {
iterator root;
iterator it { copy(&root) };
return true;
}
static_assert(test());
-std=c++20
Expected: Compile successfully, as under Clang and MSVC.
https://godbolt.org/z/7bKxbdqb9
Actual:
<source>:39:19: error: non-constant condition for static assertion
39 | static_assert(test());
| ~~~~^~
<source>:39:19: in 'constexpr' expansion of 'test()'
<source>:37:1: in 'constexpr' expansion of '(& it)->iterator::~iterator()'
<source>:20:21: error: ''result_decl' not supported by dump_expr<expression
error>' is not a constant expression
20 | if (it->next == this) {
| ~~~~^~~~
Oddly enough, it compiles successfully if I uncomment the keepalive member.
