https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126425
Bug ID: 126425
Summary: [C++26] GCC incorrectly treats deleting an object
outside its lifetime as a constant expression
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: painthingy at gmail dot com
Target Milestone: ---
Version: trunk (17.0.0 20260726, experimental)
Reproducer: https://godbolt.org/z/s9s9T4af9
```cpp
#include <memory>
struct Base {
constexpr ~Base() {}
};
struct Derived : Base {
~Derived() = default;
};
consteval {
Derived* ptr = new Derived();
std::destroy_at((Base*)ptr);
// std::construct_at((Base*)ptr); // remove -> GCC still accepts
delete ptr;
}
int main() {}
```
Compile options (GCC): -std=c++26 -freflection -O0 -Wall
Expected behavior:
After std::destroy_at((Base*)ptr) ends *ptr's lifetime, the subsequent delete
ptr; calls ~Derived() (and eventually deallocates) an object whose lifetime has
already ended. This is not a constant expression, since destroying or otherwise
using an object outside its lifetime during constant evaluation is one of the
operations explicitly disallowed by [expr.const]. Clang (clang-p2996, based on
clang 21) correctly rejects this program during evaluation of the consteval
block:
```
<source>:11:1: error: evaluating expression of a consteval block must be a
constant expression
<source>:17:5: note: destroying object '{*new Derived#0}' whose lifetime has
already ended
<source>:17:5: note: in call to '{*new Derived#0}.~Derived()'
```
Actual behavior:
GCC trunk accepts the program without diagnostic, silently allowing delete to
run the destructor and deallocation on an object whose lifetime has already
ended via the earlier std::destroy_at call. This holds whether or not the
commented-out std::construct_at((Base*)ptr) (which would legitimately restart
the object's lifetime) is present — GCC's acceptance doesn't change either way,
suggesting it isn't tracking lifetime-end at all in this context.
Additional info:
This looks related to bug 122336
GCC version details:
g++
(Compiler-Explorer-Build-gcc-7149f5ebd52eee6ad29a06f6d46c4142d0eccf46-binutils-2.44)
17.0.0 20260726 (experimental)
Clang (for comparison) version details:
clang version 21.0.0git (https://github.com/Bloomberg/clang-p2996
7220baffd57ea5b0f8cf59bee494dd5b7cc2b748)
Target: x86_64-unknown-linux-gnu
Clang compile options: -std=c++26 -freflection -fparameter-reflection
-freflection-latest -O0
