[Ada] Switch from __sync to __atomic builtins for Lock_Free_Try_Write

[Pierre-Marie de Rodat <derodat@adacore.com>]

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Routine Lock_Free_Try_Write was using deprecated __sync GCC builtins.
Now it uses __atomic builtins, which are recommended for new code.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* libgnat/s-atopri.ads (Atomic_Compare_Exchange): Replaces
	deprecated Sync_Compare_And_Swap.
	* libgnat/s-atopri.adb (Lock_Free_Try_Write): Switch from __sync
	to __atomic builtins.

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diff --git a/gcc/ada/libgnat/s-atopri.adb b/gcc/ada/libgnat/s-atopri.adb
--- a/gcc/ada/libgnat/s-atopri.adb
+++ b/gcc/ada/libgnat/s-atopri.adb
@@ -55,23 +55,16 @@ package body System.Atomic_Primitives is
        Expected : in out Atomic_Type;
        Desired  : Atomic_Type) return Boolean
    is
-      function My_Sync_Compare_And_Swap is
-        new Sync_Compare_And_Swap (Atomic_Type);
-
-      Actual : Atomic_Type;
+      function My_Atomic_Compare_Exchange is
+        new Atomic_Compare_Exchange (Atomic_Type);
 
    begin
       if Expected /= Desired then
          if Atomic_Type'Atomic_Always_Lock_Free then
-            Actual := My_Sync_Compare_And_Swap (Ptr, Expected, Desired);
+            return My_Atomic_Compare_Exchange (Ptr, Expected'Address, Desired);
          else
             raise Program_Error;
          end if;
-
-         if Actual /= Expected then
-            Expected := Actual;
-            return False;
-         end if;
       end if;
 
       return True;


diff --git a/gcc/ada/libgnat/s-atopri.ads b/gcc/ada/libgnat/s-atopri.ads
--- a/gcc/ada/libgnat/s-atopri.ads
+++ b/gcc/ada/libgnat/s-atopri.ads
@@ -80,17 +80,20 @@ package System.Atomic_Primitives is
 
    generic
       type Atomic_Type is mod <>;
-   function Sync_Compare_And_Swap
-     (Ptr      : Address;
-      Expected : Atomic_Type;
-      Desired  : Atomic_Type) return Atomic_Type;
+   function Atomic_Compare_Exchange
+     (Ptr           : Address;
+      Expected      : Address;
+      Desired       : Atomic_Type;
+      Weak          : Boolean   := False;
+      Success_Model : Mem_Model := Seq_Cst;
+      Failure_Model : Mem_Model := Seq_Cst) return Boolean;
    pragma Import
-     (Intrinsic, Sync_Compare_And_Swap, "__sync_val_compare_and_swap");
+     (Intrinsic, Atomic_Compare_Exchange, "__atomic_compare_exchange_n");
 
-   function Sync_Compare_And_Swap_8  is new Sync_Compare_And_Swap (uint8);
-   function Sync_Compare_And_Swap_16 is new Sync_Compare_And_Swap (uint16);
-   function Sync_Compare_And_Swap_32 is new Sync_Compare_And_Swap (uint32);
-   function Sync_Compare_And_Swap_64 is new Sync_Compare_And_Swap (uint64);
+   function Atomic_Compare_Exchange_8  is new Atomic_Compare_Exchange (uint8);
+   function Atomic_Compare_Exchange_16 is new Atomic_Compare_Exchange (uint16);
+   function Atomic_Compare_Exchange_32 is new Atomic_Compare_Exchange (uint32);
+   function Atomic_Compare_Exchange_64 is new Atomic_Compare_Exchange (uint64);
 
    function Atomic_Test_And_Set
      (Ptr   : System.Address;