[Ada] A new utility routine for detecting attribute 'Old

Add a utility routine for detecting attribute 'Old. It will be
immediately reused in the GNATprove backend.

2019-09-17  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* sem_util.ads, sem_util.adb (Is_Attribute_Old): New utility
	routine.

From-SVN: r275780

gcc/ada/ChangeLog

+2019-09-17  Piotr Trojanek  <trojanek@adacore.com>
+
+	* sem_util.ads, sem_util.adb (Is_Attribute_Old): New utility
+	routine.
+
 2019-09-17  Yannick Moy  <moy@adacore.com>
 
 	* inline.adb (Can_Be_Inlined_In_GNATprove_Mode): Add handling

gcc/ada/sem_util.adb

@@ -13559,6 +13559,16 @@ package body Sem_Util is
                              Is_Volatile_Full_Access (Etype (Entity (N)))));
    end Is_Atomic_Or_VFA_Object;
 
+   ----------------------
+   -- Is_Attribute_Old --
+   ----------------------
+
+   function Is_Attribute_Old (N : Node_Id) return Boolean is
+   begin
+      return Nkind (N) = N_Attribute_Reference
+        and then Attribute_Name (N) = Name_Old;
+   end Is_Attribute_Old;
+
    -------------------------
    -- Is_Attribute_Result --
    -------------------------

gcc/ada/sem_util.ads

@@ -1549,6 +1549,9 @@ package Sem_Util is
    --  Determine whether arbitrary node N denotes a reference to an object
    --  which is either atomic or Volatile_Full_Access.
 
+   function Is_Attribute_Old (N : Node_Id) return Boolean;
+   --  Determine whether node N denotes attribute 'Old
+
    function Is_Attribute_Result (N : Node_Id) return Boolean;
    --  Determine whether node N denotes attribute 'Result