https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103501
Bug ID: 103501
Summary: associative containers left invalid after
allocator-extended move construction
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
#include <set>
#include <iostream>
template<typename T>
struct Alloc : std::allocator<T>
{
template<typename U> struct rebind { using other = Alloc<U>; };
Alloc(int i) : id(i) { }
template<typename U>
Alloc(const Alloc<U>& a) : id(a.id) { }
int id;
using is_always_equal = std::false_type;
bool operator==(const Alloc& a) const { return id == a.id; }
bool operator!=(const Alloc& a) const { return id != a.id; }
};
struct X
{
int i;
X(int i) : i(i) { }
X(const X& x) noexcept : i(x.i) { }
X(X&& x) noexcept : i(x.i) { x.i = -1; }
bool operator<(const X& rhs) const { return i < rhs.i; }
};
struct Y
{
int i;
Y(int i) : i(i) { }
Y(const Y& y) noexcept : i(y.i) { }
Y(Y&& y) noexcept : i(y.i) { y.i = -y.i; }
bool operator<(const Y& rhs) const { return i < rhs.i; }
};
int main()
{
std::set<X, std::less<>, Alloc<X>> s1{ {1, 2, 3}, Alloc<X>(1)};
std::set<X, std::less<>, Alloc<X>> s2{ std::move(s1), Alloc<X>(2) };
for (auto& x : s1)
std::cout << x.i << '\n';
std::cout << '\n';
std::multiset<Y, std::less<>, Alloc<Y>> m1{ {1, 2, 3}, Alloc<Y>(1)};
std::multiset<Y, std::less<>, Alloc<Y>> m2{ std::move(m1), Alloc<Y>(2) };
for (auto& y : m1)
std::cout << y.i << '\n';
}
The sets are left with broken invariants, printing:
-1
-1
-1
-1
-2
-3
(the std::set has non-unique elements, the std::multiset has elements in
non-increasing order).
The problem is that we move each individual element when the allocators are not
equal, and that can leave non-unique elements behind.
I think we need to clear the moved-from sets in this case.
I haven't checked the unordered containers yet to see if they have the same
issue.
