[libcxx-commits] [libcxx] Fix bug in atomic_ref's calculation of lock_free-ness. (PR #93427)

[Louis Dionne via libcxx-commits]

================
@@ -11,9 +11,104 @@
 
 #include <cassert>
 #include <cstdint>
+#include <cstddef>
+#include <type_traits>
 
 #include "test_macros.h"
 
+#if defined(TEST_COMPILER_CLANG)
+#  define TEST_ATOMIC_CHAR_LOCK_FREE __CLANG_ATOMIC_CHAR_LOCK_FREE
+#  define TEST_ATOMIC_SHORT_LOCK_FREE __CLANG_ATOMIC_SHORT_LOCK_FREE
+#  define TEST_ATOMIC_INT_LOCK_FREE __CLANG_ATOMIC_INT_LOCK_FREE
+#  define TEST_ATOMIC_LONG_LOCK_FREE __CLANG_ATOMIC_LONG_LOCK_FREE
+#  define TEST_ATOMIC_LLONG_LOCK_FREE __CLANG_ATOMIC_LLONG_LOCK_FREE
+#  define TEST_ATOMIC_POINTER_LOCK_FREE __CLANG_ATOMIC_POINTER_LOCK_FREE
+#elif defined(TEST_COMPILER_GCC)
+#  define TEST_ATOMIC_CHAR_LOCK_FREE __GCC_ATOMIC_CHAR_LOCK_FREE
+#  define TEST_ATOMIC_SHORT_LOCK_FREE __GCC_ATOMIC_SHORT_LOCK_FREE
+#  define TEST_ATOMIC_INT_LOCK_FREE __GCC_ATOMIC_INT_LOCK_FREE
+#  define TEST_ATOMIC_LONG_LOCK_FREE __GCC_ATOMIC_LONG_LOCK_FREE
+#  define TEST_ATOMIC_LLONG_LOCK_FREE __GCC_ATOMIC_LLONG_LOCK_FREE
+#  define TEST_ATOMIC_POINTER_LOCK_FREE __GCC_ATOMIC_POINTER_LOCK_FREE
+#elif TEST_COMPILER_MSVC
+// This is lifted from STL/stl/inc/atomic on github for the purposes of
+// keeping the tests compiling for MSVC's STL. It's not a perfect solution
+// but at least the tests will keep running.
+//
+// Note MSVC's STL never produces a type that is sometimes lock free, but not always lock free.
+template <class T, size_t Size = sizeof(T)>
+constexpr bool msvc_is_lock_free_macro_value() {
+  return (Size <= 8 && (Size & Size - 1) == 0) ? 2 : 0;
+}
+#  define TEST_ATOMIC_CHAR_LOCK_FREE ::msvc_is_lock_free_macro_value<char>()
+#  define TEST_ATOMIC_SHORT_LOCK_FREE ::msvc_is_lock_free_macro_value<short>()
+#  define TEST_ATOMIC_INT_LOCK_FREE ::msvc_is_lock_free_macro_value<int>()
+#  define TEST_ATOMIC_LONG_LOCK_FREE ::msvc_is_lock_free_macro_value<long>()
+#  define TEST_ATOMIC_LLONG_LOCK_FREE ::msvc_is_lock_free_macro_value<long long>()
+#  define TEST_ATOMIC_POINTER_LOCK_FREE ::msvc_is_lock_free_macro_value<void*>()
+#else
+#  error "Unknown compiler"
+#endif
+
+#ifdef TEST_COMPILER_CLANG
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wc++11-extensions"
+#endif
+// The entire LockFreeStatus/LockFreeStatusEnum/LockFreeStatusType exists entirely to work around the support
+// for C++03, which many of our atomic tests run under. This is a bit of a hack, but it's the best we can do.
+//
+// We could limit the testing involving these things to C++11 or greater? But test coverage in C++03 seems important too.
+
+enum class LockFreeStatus : int { unknown = -1, never = 0, sometimes = 1, always = 2 };
+#define COMPARE_TYPES(T1, T2) (sizeof(T1) == sizeof(T2) && TEST_ALIGNOF(T1) >= TEST_ALIGNOF(T2))
+
+template <class T>
+struct LockFreeStatusInfo {
+  static const LockFreeStatus value = LockFreeStatus(
+      COMPARE_TYPES(T, char)
+          ? TEST_ATOMIC_CHAR_LOCK_FREE
+          : (COMPARE_TYPES(T, short)
+                 ? TEST_ATOMIC_SHORT_LOCK_FREE
+                 : (COMPARE_TYPES(T, int)
+                        ? TEST_ATOMIC_INT_LOCK_FREE
+                        : (COMPARE_TYPES(T, long)
+                               ? TEST_ATOMIC_LONG_LOCK_FREE
+                               : (COMPARE_TYPES(T, long long)
+                                      ? TEST_ATOMIC_LLONG_LOCK_FREE
+                                      : (COMPARE_TYPES(T, void*) ? TEST_ATOMIC_POINTER_LOCK_FREE : -1))))));
+
+  static const bool status_known = LockFreeStatusInfo::value != LockFreeStatus::unknown;
+};
+
+// IDK why this blows up in C++03, but it does. So we'll just disable it.
+#if TEST_STD_VER >= 11
+static_assert(LockFreeStatusInfo<char>::status_known, "");
+static_assert(LockFreeStatusInfo<short>::status_known, "");
+static_assert(LockFreeStatusInfo<int>::status_known, "");
+static_assert(LockFreeStatusInfo<long>::status_known, "");
+static_assert(LockFreeStatusInfo<long long>::status_known, "");
+static_assert(LockFreeStatusInfo<void*>::status_known, "");
+
+// I think these are always supposed to be lock free, and it's worth trying to hardcode expected values.
+static_assert(LockFreeStatusInfo<char>::value == LockFreeStatus::always, "");
+static_assert(LockFreeStatusInfo<short>::value == LockFreeStatus::always, "");
+static_assert(LockFreeStatusInfo<int>::value == LockFreeStatus::always,
+              ""); // This one may not always be lock free, but we'll let the CI decide.
+#endif
+
+// These macros are somewhat suprising to use, since they take the values 0, 1, or 2.
+// To make the tests clearer, get rid of them in preference of AtomicInfo.
----------------
ldionne wrote:

```suggestion
// To make the tests clearer, get rid of them in preference of LockFreeStatusInfo.
```

Or did I miss a class called `AtomicInfo`?

https://github.com/llvm/llvm-project/pull/93427