From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 26 Feb 2024 13:17:32 +0000 (+0000)
Subject: libstdc++: Do not define lock-free atomic aliases if not fully lock-free [PR114103]
X-Git-Tag: basepoints/gcc-15~768
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e162b2ff52c5e20f6624ff6b66845fe573cef183;p=thirdparty%2Fgcc.git

libstdc++: Do not define lock-free atomic aliases if not fully lock-free [PR114103]

The whole point of these typedefs is to guarantee lock-freedom, so if
the target has no such types, we shouldn't defined the typedefs at all.

libstdc++-v3/ChangeLog:

	PR libstdc++/114103
	* include/bits/version.def (atomic_lock_free_type_aliases): Add
	extra_cond to check for at least one always-lock-free type.
	* include/bits/version.h: Regenerate.
	* include/std/atomic (atomic_signed_lock_free)
	(atomic_unsigned_lock_free): Only use always-lock-free types.
	* src/c++20/tzdb.cc (time_zone::_Impl::RulesCounter): Don't use
	atomic counter if lock-free aliases aren't available.
	* testsuite/29_atomics/atomic/lock_free_aliases.cc: XFAIL for
	targets without lock-free word-size compare_exchange.
---

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 502961eb2699..d298420121b8 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -739,6 +739,7 @@ ftms = {
   values = {
     v = 201907;
     cxxmin = 20;
+    extra_cond = "(__GCC_ATOMIC_INT_LOCK_FREE | __GCC_ATOMIC_LONG_LOCK_FREE | __GCC_ATOMIC_CHAR_LOCK_FREE) & 2";
   };
 };
 
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index 7a6fbd35e2ef..9107b45a4841 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -819,7 +819,7 @@
 #undef __glibcxx_want_atomic_float
 
 #if !defined(__cpp_lib_atomic_lock_free_type_aliases)
-# if (__cplusplus >= 202002L)
+# if (__cplusplus >= 202002L) && ((__GCC_ATOMIC_INT_LOCK_FREE | __GCC_ATOMIC_LONG_LOCK_FREE | __GCC_ATOMIC_CHAR_LOCK_FREE) & 2)
 #  define __glibcxx_atomic_lock_free_type_aliases 201907L
 #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_atomic_lock_free_type_aliases)
 #   define __cpp_lib_atomic_lock_free_type_aliases 201907L
diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 559f8370459e..1462cf5ec23f 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -1774,13 +1774,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     = atomic<make_signed_t<__detail::__platform_wait_t>>;
   using atomic_unsigned_lock_free
     = atomic<make_unsigned_t<__detail::__platform_wait_t>>;
-# elif ATOMIC_INT_LOCK_FREE || !(ATOMIC_LONG_LOCK_FREE || ATOMIC_CHAR_LOCK_FREE)
+# elif ATOMIC_INT_LOCK_FREE == 2
   using atomic_signed_lock_free = atomic<signed int>;
   using atomic_unsigned_lock_free = atomic<unsigned int>;
-# elif ATOMIC_LONG_LOCK_FREE
+# elif ATOMIC_LONG_LOCK_FREE == 2
   using atomic_signed_lock_free = atomic<signed long>;
   using atomic_unsigned_lock_free = atomic<unsigned long>;
-# elif ATOMIC_CHAR_LOCK_FREE
+# elif ATOMIC_CHAR_LOCK_FREE == 2
   using atomic_signed_lock_free = atomic<signed char>;
   using atomic_unsigned_lock_free = atomic<unsigned char>;
 # else
diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index e03f4a5c32ac..890a4c53e2d4 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -651,7 +651,7 @@ namespace std::chrono
     template<typename _Tp> requires _Tp::is_always_lock_free
       struct RulesCounter<_Tp>
       {
-	atomic_signed_lock_free counter{0};
+	_Tp counter{0};
 
 	void
 	increment()
@@ -703,7 +703,12 @@ namespace std::chrono
       };
 #endif // __GTHREADS && __cpp_lib_atomic_wait
 
+#if __cpp_lib_atomic_lock_free_type_aliases
     RulesCounter<atomic_signed_lock_free> rules_counter;
+#else
+    RulesCounter<void> rules_counter;
+#endif
+
 #else // TZDB_DISABLED
     _Impl(weak_ptr<tzdb_list::_Node>) { }
     struct {
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/lock_free_aliases.cc b/libstdc++-v3/testsuite/29_atomics/atomic/lock_free_aliases.cc
index 372a63129ff7..489d181d136f 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/lock_free_aliases.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/lock_free_aliases.cc
@@ -1,5 +1,6 @@
 // { dg-do compile { target c++20 } }
 // { dg-add-options no_pch }
+// { dg-require-atomic-cmpxchg-word "PR libstdc++/114103" }
 
 #include <atomic>