[Ada] Reuse Package_Specification in Is_Incomplete_Or_Private_Type

gcc/ada/

	* sem_aux.adb (Package_Specification): Add assertions to confirm
	the kind of the of parameter and returned node.
	* sem_ch12.adb (Remove_Parent): Reorder conditions; this change
	appears to be semantically neutral, but is enough to avoid the
	problematic call to Package_Specification.
	* sem_util.adb (Is_Incomplete_Or_Private_Type): Replace loop
	with a call to Package_Specification.

gcc/ada/sem_aux.adb

@@ -1421,12 +1421,16 @@ package body Sem_Aux is
       N : Node_Id;
 
    begin
+      pragma Assert (Is_Package_Or_Generic_Package (E));
+
       N := Parent (E);
 
       if Nkind (N) = N_Defining_Program_Unit_Name then
          N := Parent (N);
       end if;
 
+      pragma Assert (Nkind (N) = N_Package_Specification);
+
       return N;
    end Package_Specification;
 

gcc/ada/sem_ch12.adb

@@ -15222,14 +15222,15 @@ package body Sem_Ch12 is
             --  subunit of a generic contains an instance of a child unit of
             --  its generic parent unit.
 
-            elsif S = Current_Scope and then Is_Generic_Instance (S) then
+            elsif S = Current_Scope and then Is_Generic_Instance (S)
+              and then (In_Package_Body (S) or else In_Private_Part (S))
+            then
                declare
                   Par : constant Entity_Id :=
                           Generic_Parent (Package_Specification (S));
                begin
                   if Present (Par)
                     and then P = Scope (Par)
-                    and then (In_Package_Body (S) or else In_Private_Part (S))
                   then
                      Set_In_Private_Part (P);
                      Install_Private_Declarations (P);

gcc/ada/sem_util.adb

@@ -14751,17 +14751,11 @@ package body Sem_Util is
 
       --  Private or Taft amendment type case
 
-      declare
-         Pkg_Decl : Node_Id;
-
-      begin
-         if Present (S) and then Is_Package_Or_Generic_Package (S) then
-            Pkg_Decl := S;
-
-            while Nkind (Pkg_Decl) /= N_Package_Specification loop
-               Pkg_Decl := Parent (Pkg_Decl);
-            end loop;
+      if Present (S) and then Is_Package_Or_Generic_Package (S) then
+         declare
+            Pkg_Decl : constant Node_Id := Package_Specification (S);
 
+         begin
             --  It is knows that Typ has a private view, look for it in the
             --  visible declarations of the enclosing scope. A special case
             --  of this is when the two views have been exchanged - the full
@@ -14785,8 +14779,8 @@ package body Sem_Util is
             elsif In_Package_Body (S) then
                return Inspect_Decls (Private_Declarations (Pkg_Decl), True);
             end if;
-         end if;
-      end;
+         end;
+      end if;
 
       --  The type has no incomplete or private view