[PATCH 3/5] std::__atomic_wait: don't use __detail::__waiter with futex

[Thiago Macieira via Gcc-patches]

That violates "don't pay for what you don't need" rule of C++. Users of
std::atomic<T>::wait will often have some bit in their atomic indicate
whether the value is contended or not, so we don't need libstdc++ to do
double book-keeping for us.
---
 libstdc++-v3/include/bits/atomic_wait.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/libstdc++-v3/include/bits/atomic_wait.h 
b/libstdc++-v3/include/bits/atomic_wait.h
index 1c6bda2e2b6..4d240f44faf 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -258,14 +258,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       if (std::__atomic_spin(__pred))
        return;
 
-      __waiter __w(__addr);
-      while (!__pred())
+      if constexpr (__platform_wait_uses_type<_Tp>)
        {
-         if constexpr (__platform_wait_uses_type<_Tp>)
-           {
-             __platform_wait(__addr, __old);
-           }
-         else
+         __platform_wait(__addr, __old);
+       }
+      else
+       {
+         __waiter __w(__addr);
+         while (!__pred())
            {
              // TODO support timed backoff when this can be moved into the lib
              __w._M_do_wait();
@@ -274,13 +274,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp>
-    void
+    inline void
     __atomic_notify(const _Tp* __addr, bool __all) noexcept
     {
       using namespace __detail;
-      auto& __w = __waiters::_S_for((void*)__addr);
-      if (!__w._M_waiting())
-       return;
 
 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
       if constexpr (__platform_wait_uses_type<_Tp>)
@@ -290,6 +287,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       else
 #endif
        {
+         auto& __w = __waiters::_S_for((void*)__addr);
+         if (!__w._M_waiting())
+           return;
          __w._M_notify(__all);
        }
     }
-- 
2.30.1