https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97566
Bug ID: 97566
Summary: [[no_unique_address]] causes miscompiles when mixed
with EBO in constexpr context
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: natattak at gmail dot com
Target Milestone: ---
Example: (https://godbolt.org/z/Y5q5br)
#include <memory>
#include <cassert>
// error disappears if E doesn't inherit from B
struct B {};
struct E : B {};
struct counter {
constexpr counter() = default;
constexpr void inc() {
size++;
}
// error disappears if you remove or reorder this value
int unused = 0;
int size = 0;
[[no_unique_address]] E empty = {};
};
constexpr int test() {
counter x;
x.inc();
return x.size;
}
int main() {
assert(test() == 1); // works, unless optimisations enabled
static_assert(test() == 1); // fails, always
}
In particular, the runtime assertion only passes on -O0; any higher
optimisation e.g. -O1 causes it to fail.
Compiled as `g++ -std=c++20`.
