[committed] libstdc++: Fix std::atomic> for AIX [PR104101]

[Jonathan Wakely via Gcc-patches]

Tested powerpc64le-linux, powerpc-aix, pushed to trunk.


This fixes a testsuite failure on AIX.

The lock function currently just spins, which should be changed to use
back-off, and maybe then _M_val.wait(__current) when supported.

libstdc++-v3/ChangeLog:

        PR libstdc++/104101
        * include/bits/shared_ptr_atomic.h (_Sp_atomic::_Atomic_count::lock):
        Only use __thread_relax if __cpp_lib_atomic_wait is defined.
---
 libstdc++-v3/include/bits/shared_ptr_atomic.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libstdc++-v3/include/bits/shared_ptr_atomic.h 
b/libstdc++-v3/include/bits/shared_ptr_atomic.h
index 50aa46370ca..35f781dc9a0 100644
--- a/libstdc++-v3/include/bits/shared_ptr_atomic.h
+++ b/libstdc++-v3/include/bits/shared_ptr_atomic.h
@@ -392,7 +392,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          auto __current = _M_val.load(memory_order_relaxed);
          while (__current & _S_lock_bit)
            {
+#if __cpp_lib_atomic_wait
              __detail::__thread_relax();
+#endif
              __current = _M_val.load(memory_order_relaxed);
            }
 
@@ -401,7 +403,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                                                 __o,
                                                 memory_order_relaxed))
            {
+#if __cpp_lib_atomic_wait
              __detail::__thread_relax();
+#endif
              __current = __current & ~_S_lock_bit;
            }
          return reinterpret_cast<pointer>(__current);
-- 
2.31.1