[Bug sanitizer/97868] warn about using fences with TSAN

[ispavlick at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97868

pavlick <ispavlick at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ispavlick at gmail dot com

--- Comment #5 from pavlick <ispavlick at gmail dot com> ---
Why is there false positive and no warning about the unsupported feature
(atomic_thread_fence)?

[code]
#include <thread>
#include <atomic>
#include <vector>
#include <chrono>
using namespace std;

class Test {
        atomic_flag m_spin_lock;
        vector<int> m_data;
public:
        void add() {
                while (m_spin_lock.test_and_set(memory_order_relaxed))
                        this_thread::yield();
                atomic_thread_fence(memory_order_acquire);
                while (true) {
                        this_thread::sleep_for(300ms);
                        m_data.push_back(4);
                }
                m_spin_lock.clear(memory_order_release);
        }
        void read() {
                size_t sz;
                if (! m_spin_lock.test_and_set(std::memory_order_acquire)) {
                        sz = m_data.size();
                        m_spin_lock.clear(std::memory_order_release);
                }
                (void)sz;
        }
}test;

int main() {
        jthread rt(&Test::read, &test);
        this_thread::sleep_for(10ms);
        test.add();
}

[/code]

$ g++ 3.cc -std=c++20 -Wtsan -Wall -fsanitize=thread