fixup! 5ed6c49e84adba6a0fdace8103596b7a90c45691 non-x86 friendliness

Let us prefer fetch_or() to compare_exchange_weak() on ISAs that
can support it efficiently. Even on IA-32 and AMD64 it would be
possible to emit LOCK BTS, but unfortunately the contemporary
compilers do not support that.

1 files changed, 27 insertions, 0 deletions

diff --git a/storage/innobase/sync/srw_lock.cc b/storage/innobase/sync/srw_lock.cc
index 926787c0052..c443bd61905 100644
--- a/storage/innobase/sync/srw_lock.cc
+++ b/storage/innobase/sync/srw_lock.cc
@@ -294,10 +294,16 @@ void srw_mutex_impl<true>::wait_and_lock()
     DBUG_ASSERT(~HOLDER & lk);
     if (lk & HOLDER)
       lk= lock.load(std::memory_order_relaxed);
+#if defined _WIN32 || defined __i386__ || defined __x86_64__
     else if (lock.compare_exchange_weak(lk, lk | HOLDER,
                                         std::memory_order_acquire,
                                         std::memory_order_relaxed))
       return;
+#else
+    else if (!((lk= lock.fetch_or(HOLDER, std::memory_order_relaxed)) &
+               HOLDER))
+      goto acquired;
+#endif
     else
       srw_pause(delay);
     if (!--spin)
@@ -312,10 +318,21 @@ void srw_mutex_impl<true>::wait_and_lock()
       wait(lk);
       lk= lock.load(std::memory_order_relaxed);
     }
+#if defined _WIN32 || defined __i386__ || defined __x86_64__
     else if (lock.compare_exchange_weak(lk, lk | HOLDER,
                                         std::memory_order_acquire,
                                         std::memory_order_relaxed))
       return;
+#else
+    else if (!((lk= lock.fetch_or(HOLDER, std::memory_order_relaxed)) &
+               HOLDER))
+    {
+acquired:
+      DBUG_ASSERT(lk);
+      std::atomic_thread_fence(std::memory_order_acquire);
+      return;
+    }
+#endif
   }
 }
 
@@ -330,10 +347,20 @@ void srw_mutex_impl<false>::wait_and_lock()
       wait(lk);
       lk= lock.load(std::memory_order_relaxed);
     }
+#if defined _WIN32 || defined __i386__ || defined __x86_64__
     else if (lock.compare_exchange_weak(lk, lk | HOLDER,
                                         std::memory_order_acquire,
                                         std::memory_order_relaxed))
       return;
+#else
+    else if (!((lk= lock.fetch_or(HOLDER, std::memory_order_relaxed)) &
+               HOLDER))
+    {
+      DBUG_ASSERT(lk);
+      std::atomic_thread_fence(std::memory_order_acquire);
+      return;
+    }
+#endif
   }
 }