https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124117
Bug ID: 124117
Summary: constexpr evaluator fails to deallocate copy of
pointer
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ivan.lazaric.gcc at gmail dot com
Target Milestone: ---
```
#include <memory>
#include <cassert>
struct NodeBase
{
int data;
constexpr NodeBase* base_ptr() { return this; }
};
struct Node : NodeBase {};
consteval bool deallocate_copy() {
std::allocator<Node> alloc;
Node* node_ptr = alloc.allocate(1);
new (node_ptr) Node;
NodeBase* base_ptr = node_ptr->base_ptr();
Node* node_ptr_copy = static_cast<Node*>(base_ptr);
assert(node_ptr == node_ptr_copy); // passes
alloc.deallocate(node_ptr_copy, 1); // fails
return true;
}
static_assert(deallocate_copy());
```
Despite `node_ptr` and `node_ptr_copy` comparing equal,
deallocating `node_ptr_copy` fails, while
deallocating `node_ptr` succeeds
Clang accepts this code
Godbolt of this example:
https://godbolt.org/z/8T7xhrbEe
This example is rather sensitive
Removing the `data` member variable makes it pass
`NodeBase* base_ptr = node_ptr;` also passes
I believe this issue is relevant to libstdc++,
to constexpr-ifying `std::{set,map}`
