[Ada] Fix incorrect stub generation for types in instances

This fixes a fallout of a recent change clearing the
Is_Generic_Actual_Type on the implicit full view of a private actual
type in an instance.  This flag is used to help disambiguating formal
types instantiated on the same actual type within an instance, but it
should be cleared outside the instance to let the usual disambiguation
rules apply again to these types outside the instance.

This in particular means that Exp_Dist cannot rely on it to detect
subtypes representing generic actual types, hence the need for the new
predicate.

2019-08-19  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* exp_dist.adb (Is_Generic_Actual_Subtype): New predicate.
	(Build_From_Any_Call, Build_To_Any_Call, Build_TypeCode_Call):
	Use it instead of Is_Generic_Actual_Type flag to detect subtypes
	representing generic actual types.

From-SVN: r274650

gcc/ada/ChangeLog

+2019-08-19  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* exp_dist.adb (Is_Generic_Actual_Subtype): New predicate.
+	(Build_From_Any_Call, Build_To_Any_Call, Build_TypeCode_Call):
+	Use it instead of Is_Generic_Actual_Type flag to detect subtypes
+	representing generic actual types.
+
 2019-08-19  Ed Schonberg  <schonberg@adacore.com>
 
 	* sem_warn.adb (Check_References, Generic_Body_Formal): When a

gcc/ada/exp_dist.adb

@@ -8201,6 +8201,12 @@ package body Exp_Dist is
          --  type from Interfaces, or the smallest floating point type from
          --  Standard whose range encompasses that of Typ.
 
+         function Is_Generic_Actual_Subtype (Typ : Entity_Id) return Boolean;
+         --  Return true if Typ is a subtype representing a generic formal type
+         --  as a subtype of the actual type in an instance. This is needed to
+         --  recognize these subtypes because the Is_Generic_Actual_Type flag
+         --  can only be relied upon within the instance.
+
          function Make_Helper_Function_Name
            (Loc : Source_Ptr;
             Typ : Entity_Id;
@@ -8453,7 +8459,7 @@ package body Exp_Dist is
             --  For the subtype representing a generic actual type, go to the
             --  actual type.
 
-            if Is_Generic_Actual_Type (U_Type) then
+            if Is_Generic_Actual_Subtype (U_Type) then
                U_Type := Underlying_Type (Base_Type (U_Type));
             end if;
 
@@ -9262,7 +9268,7 @@ package body Exp_Dist is
             --  For the subtype representing a generic actual type, go to the
             --  actual type.
 
-            if Is_Generic_Actual_Type (U_Type) then
+            if Is_Generic_Actual_Subtype (U_Type) then
                U_Type := Underlying_Type (Base_Type (U_Type));
             end if;
 
@@ -10116,7 +10122,7 @@ package body Exp_Dist is
             --  For the subtype representing a generic actual type, go to the
             --  actual type.
 
-            if Is_Generic_Actual_Type (U_Type) then
+            if Is_Generic_Actual_Subtype (U_Type) then
                U_Type := Underlying_Type (Base_Type (U_Type));
             end if;
 
@@ -10901,6 +10907,30 @@ package body Exp_Dist is
 
          end Find_Numeric_Representation;
 
+         ---------------------------------
+         --  Is_Generic_Actual_Subtype  --
+         ---------------------------------
+
+         function Is_Generic_Actual_Subtype (Typ : Entity_Id) return Boolean is
+         begin
+            if Is_Itype (Typ)
+              and then Present (Associated_Node_For_Itype (Typ))
+            then
+               declare
+                  N : constant Node_Id := Associated_Node_For_Itype (Typ);
+               begin
+                  if Nkind (N) = N_Subtype_Declaration
+                    and then Nkind (Parent (N)) = N_Package_Specification
+                    and then Is_Generic_Instance (Scope_Of_Spec (Parent (N)))
+                  then
+                     return True;
+                  end if;
+               end;
+            end if;
+
+            return False;
+         end Is_Generic_Actual_Subtype;
+
          ---------------------------
          -- Append_Array_Traversal --
          ---------------------------