libstdc++: Add missing free functions for atomic_flag [PR103934]

This patch adds -
  atomic_flag_test
  atomic_flag_test_explicit

Which were missed when commit 491ba6 introduced C++20 atomic flag
test.

libstdc++-v3/ChangeLog:

	PR libstdc++/103934
	* include/std/atomic (atomic_flag_test): Add.
	(atomic_flag_test_explicit): Add.
	* testsuite/29_atomics/atomic_flag/test/explicit.cc: Add
	test case to cover missing atomic_flag free functions.
	* testsuite/29_atomics/atomic_flag/test/implicit.cc:
	Likewise.

3 files changed, 70 insertions, 2 deletions

diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 1c27c8c41e1..1edd3ae16fa 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -1214,6 +1214,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 				    memory_order __m) noexcept
   { return __a->test_and_set(__m); }
 
+#if __cpp_lib_atomic_flag_test
+  inline bool
+  atomic_flag_test(const atomic_flag* __a) noexcept
+  { return __a->test(); }
+
+  inline bool
+  atomic_flag_test(const volatile atomic_flag* __a) noexcept
+  { return __a->test(); }
+
+  inline bool
+  atomic_flag_test_explicit(const atomic_flag* __a,
+			    memory_order __m) noexcept
+  { return __a->test(__m); }
+
+  inline bool
+  atomic_flag_test_explicit(const volatile atomic_flag* __a,
+			    memory_order __m) noexcept
+  { return __a->test(__m); }
+#endif
+
   inline void
   atomic_flag_clear_explicit(atomic_flag* __a, memory_order __m) noexcept
   { __a->clear(__m); }
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc
index 380bd36ac47..fc8d6589707 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc
@@ -22,7 +22,8 @@
 #include <atomic>
 #include <testsuite_hooks.h>
 
-int main()
+void
+test01()
 {
   using namespace std;
 
@@ -38,3 +39,26 @@ int main()
   VERIFY( ! af.test(memory_order_acquire) );
   VERIFY( ! caf.test(memory_order_acquire) );
 }
+
+void
+test02()
+{
+  using namespace std;
+
+  atomic_flag af{true};
+  const atomic_flag& caf = af;
+
+  VERIFY( atomic_flag_test_explicit(&af, memory_order_acquire) );
+  VERIFY( atomic_flag_test_explicit(&caf, memory_order_acquire) );
+  af.clear(memory_order_release);
+  VERIFY( ! atomic_flag_test_explicit(&af, memory_order_acquire) );
+  VERIFY( ! atomic_flag_test_explicit(&caf, memory_order_acquire) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc
index cce873fa553..2840055433f 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc
@@ -22,7 +22,8 @@
 #include <atomic>
 #include <testsuite_hooks.h>
 
-int main()
+void
+test01()
 {
   using namespace std;
 
@@ -38,3 +39,26 @@ int main()
   VERIFY( ! af.test() );
   VERIFY( ! caf.test() );
 }
+
+void
+test02()
+{
+  using namespace std;
+
+  atomic_flag af{true};
+  const atomic_flag& caf = af;
+
+  VERIFY( atomic_flag_test(&af) );
+  VERIFY( atomic_flag_test(&caf) );
+  af.clear(memory_order_release);
+  VERIFY( ! atomic_flag_test(&af) );
+  VERIFY( ! atomic_flag_test(&caf) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  return 0;
+}