[gcc r13-5119] libstdc++: Use lock-free type for __platform_wait_t

[gcc r13-5119] libstdc++: Use lock-free type for __platform_wait_t

[Jonathan Wakely]

https://gcc.gnu.org/g:dc22cf461278ace754042d9388a62afb002dfa0e

commit r13-5119-gdc22cf461278ace754042d9388a62afb002dfa0e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jan 5 20:23:26 2023 +0000

    libstdc++: Use lock-free type for __platform_wait_t
    
    For non-futex targets the __platform_wait_t type is currently uint64_t,
    but that requires a lock in libatomic for some 32-bit targets. We don't
    really need a 64-bit type, so use unsigned long if that is lock-free,
    and int otherwise. This should mean it's lock-free on a wider set of
    targets.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/atomic_wait.h (__detail::__platform_wait_t):
            Define as unsigned long if always lock-free, and unsigned int
            otherwise.

Diff:
---
 libstdc++-v3/include/bits/atomic_wait.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index bd1ed56d157..1d7a034a165 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -64,7 +64,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 // and __platform_notify() if there is a more efficient primitive supported
 // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than
 // a mutex/condvar based wait.
-    using __platform_wait_t = uint64_t;
+# if ATOMIC_LONG_LOCK_FREE == 2
+    using __platform_wait_t = unsigned long;
+# else
+    using __platform_wait_t = unsigned int;
+# endif
     inline constexpr size_t __platform_wait_alignment
       = __alignof__(__platform_wait_t);
 #endif