[Ada] Remove obsolete Is_For_Access_Subtype machinery

This change removes the Is_For_Access_Subtype machinery from the
compiler.  This machinery was devised a long time ago to deal with a
peculiarity of the freezing for access-to-record subtypes but has been
degenerate for quite some time now and does not seem to serve any useful
purpose at this point.

Morever it has an annoying side effect whereby it causes Underlying_Type
to return the (unconstrained) base record type when invoked on the
designated record subtype, which is very problematic for GNATprove.

There should be no functional changes.

2019-07-22  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* einfo.ads (Is_For_Access_Subtype): Delete.
	(Set_Is_For_Access_Subtype): Likewise.
	* einfo.adb (Is_For_Access_Subtype): Likewise.
	(Set_Is_For_Access_Subtype): Likewise.
	(Write_Entity_Flags): Do not write Is_For_Access_Subtype.
	* exp_ch4.adb (Expand_N_Selected_Component): Do not deal with
	it.
	* exp_spark.adb (Expand_SPARK_N_Selected_Component): Likewise.
	* sem_ch4.adb (Analyze_Explicit_Dereference): Likewise.
	* sem_ch3.adb (Build_Discriminated_Subtype): Do not build a
	special private subtype for access-to-record subtypes.

From-SVN: r273682

gcc/ada/ChangeLog

 2019-07-22  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* einfo.ads (Is_For_Access_Subtype): Delete.
+	(Set_Is_For_Access_Subtype): Likewise.
+	* einfo.adb (Is_For_Access_Subtype): Likewise.
+	(Set_Is_For_Access_Subtype): Likewise.
+	(Write_Entity_Flags): Do not write Is_For_Access_Subtype.
+	* exp_ch4.adb (Expand_N_Selected_Component): Do not deal with
+	it.
+	* exp_spark.adb (Expand_SPARK_N_Selected_Component): Likewise.
+	* sem_ch4.adb (Analyze_Explicit_Dereference): Likewise.
+	* sem_ch3.adb (Build_Discriminated_Subtype): Do not build a
+	special private subtype for access-to-record subtypes.
+
+2019-07-22  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* sem_ch3.adb (Complete_Private_Subtype): Rework the setting of
 	the Etype of the full view for full base types that cannot
 	contain any discriminant.  Remove code and comment about it in

gcc/ada/einfo.adb

@@ -421,7 +421,6 @@ package body Einfo is
    --    Never_Set_In_Source             Flag115
    --    Is_Visible_Lib_Unit             Flag116
    --    Is_Unchecked_Union              Flag117
-   --    Is_For_Access_Subtype           Flag118
    --    Has_Convention_Pragma           Flag119
    --    Has_Primitive_Operations        Flag120
 
@@ -2303,12 +2302,6 @@ package body Einfo is
       return Flag70 (Id);
    end Is_First_Subtype;
 
-   function Is_For_Access_Subtype (Id : E) return B is
-   begin
-      pragma Assert (Ekind_In (Id, E_Record_Subtype, E_Private_Subtype));
-      return Flag118 (Id);
-   end Is_For_Access_Subtype;
-
    function Is_Formal_Subprogram (Id : E) return B is
    begin
       return Flag111 (Id);
@@ -5526,12 +5519,6 @@ package body Einfo is
       Set_Flag70 (Id, V);
    end Set_Is_First_Subtype;
 
-   procedure Set_Is_For_Access_Subtype (Id : E; V : B := True) is
-   begin
-      pragma Assert (Ekind_In (Id, E_Record_Subtype, E_Private_Subtype));
-      Set_Flag118 (Id, V);
-   end Set_Is_For_Access_Subtype;
-
    procedure Set_Is_Formal_Subprogram (Id : E; V : B := True) is
    begin
       Set_Flag111 (Id, V);
@@ -9826,7 +9813,6 @@ package body Einfo is
       W ("Is_Exported",                     Flag99  (Id));
       W ("Is_Finalized_Transient",          Flag252 (Id));
       W ("Is_First_Subtype",                Flag70  (Id));
-      W ("Is_For_Access_Subtype",           Flag118 (Id));
       W ("Is_Formal_Subprogram",            Flag111 (Id));
       W ("Is_Frozen",                       Flag4   (Id));
       W ("Is_Generic_Actual_Subprogram",    Flag274 (Id));

gcc/ada/einfo.ads

@@ -2608,12 +2608,6 @@ package Einfo is
 --    Is_Formal_Subprogram (Flag111)
 --       Defined in all entities. Set for generic formal subprograms.
 
---    Is_For_Access_Subtype (Flag118)
---       Defined in E_Private_Subtype and E_Record_Subtype entities. Means the
---       sole purpose of the type is to be designated by an Access_Subtype and
---       hence should not be expanded into components because the type may not
---       have been found or frozen yet.
-
 --    Is_Frozen (Flag4)
 --       Defined in all type and subtype entities. Set if type or subtype has
 --       been frozen.
@@ -6458,7 +6452,6 @@ package Einfo is
    --    Stored_Constraint                   (Elist23)
    --    Has_Completion                      (Flag26)
    --    Is_Controlled_Active                (Flag42)   (base type only)
-   --    Is_For_Access_Subtype               (Flag118)  (subtype only)
    --    (plus type attributes)
 
    --  E_Procedure
@@ -7311,7 +7304,6 @@ package Einfo is
    function Is_Exported                         (Id : E) return B;
    function Is_Finalized_Transient              (Id : E) return B;
    function Is_First_Subtype                    (Id : E) return B;
-   function Is_For_Access_Subtype               (Id : E) return B;
    function Is_Frozen                           (Id : E) return B;
    function Is_Generic_Instance                 (Id : E) return B;
    function Is_Hidden                           (Id : E) return B;
@@ -8012,7 +8004,6 @@ package Einfo is
    procedure Set_Is_Exported                     (Id : E; V : B := True);
    procedure Set_Is_Finalized_Transient          (Id : E; V : B := True);
    procedure Set_Is_First_Subtype                (Id : E; V : B := True);
-   procedure Set_Is_For_Access_Subtype           (Id : E; V : B := True);
    procedure Set_Is_Formal_Subprogram            (Id : E; V : B := True);
    procedure Set_Is_Frozen                       (Id : E; V : B := True);
    procedure Set_Is_Generic_Actual_Subprogram    (Id : E; V : B := True);
@@ -8859,7 +8850,6 @@ package Einfo is
    pragma Inline (Is_First_Subtype);
    pragma Inline (Is_Fixed_Point_Type);
    pragma Inline (Is_Floating_Point_Type);
-   pragma Inline (Is_For_Access_Subtype);
    pragma Inline (Is_Formal);
    pragma Inline (Is_Formal_Object);
    pragma Inline (Is_Formal_Subprogram);
@@ -9376,7 +9366,6 @@ package Einfo is
    pragma Inline (Set_Is_Exported);
    pragma Inline (Set_Is_Finalized_Transient);
    pragma Inline (Set_Is_First_Subtype);
-   pragma Inline (Set_Is_For_Access_Subtype);
    pragma Inline (Set_Is_Formal_Subprogram);
    pragma Inline (Set_Is_Frozen);
    pragma Inline (Set_Is_Generic_Actual_Subprogram);

gcc/ada/exp_ch4.adb

@@ -10330,12 +10330,6 @@ package body Exp_Ch4 is
          Insert_Explicit_Dereference (P);
          Analyze_And_Resolve (P, Designated_Type (Ptyp));
 
-         if Ekind (Etype (P)) = E_Private_Subtype
-           and then Is_For_Access_Subtype (Etype (P))
-         then
-            Set_Etype (P, Base_Type (Etype (P)));
-         end if;
-
          Ptyp := Etype (P);
       end if;
 

gcc/ada/exp_spark.adb

@@ -522,12 +522,6 @@ package body Exp_SPARK is
 
          Insert_Explicit_Dereference (Pref);
          Analyze_And_Resolve (Pref, Designated_Type (Typ));
-
-         if Ekind (Etype (Pref)) = E_Private_Subtype
-           and then Is_For_Access_Subtype (Etype (Pref))
-         then
-            Set_Etype (Pref, Base_Type (Etype (Pref)));
-         end if;
       end if;
    end Expand_SPARK_N_Selected_Component;
 

gcc/ada/sem_ch3.adb

@@ -221,9 +221,7 @@ package body Sem_Ch3 is
    --  T has discriminants but there are no discriminant constraints). The
    --  Related_Nod is the same as Decl_Node in Create_Constrained_Components.
    --  The For_Access says whether or not this subtype is really constraining
-   --  an access type. That is its sole purpose is the designated type of an
-   --  access type -- in which case a Private_Subtype Is_For_Access_Subtype
-   --  is built to avoid freezing T when the access subtype is frozen.
+   --  an access type.
 
    function Build_Scalar_Bound
      (Bound : Node_Id;
@@ -10236,12 +10234,7 @@ package body Sem_Ch3 is
 
    begin
       if Ekind (T) = E_Record_Type then
-         if For_Access then
-            Set_Ekind (Def_Id, E_Private_Subtype);
-            Set_Is_For_Access_Subtype (Def_Id, True);
-         else
-            Set_Ekind (Def_Id, E_Record_Subtype);
-         end if;
+         Set_Ekind (Def_Id, E_Record_Subtype);
 
          --  Inherit preelaboration flag from base, for types for which it
          --  may have been set: records, private types, protected types.
@@ -10372,7 +10365,7 @@ package body Sem_Ch3 is
          then
             Create_Constrained_Components (Def_Id, Related_Nod, T, Elist);
 
-         elsif not For_Access then
+         else
             Set_Cloned_Subtype (Def_Id, T);
          end if;
       end if;

gcc/ada/sem_ch4.adb

@@ -2101,21 +2101,12 @@ package body Sem_Ch4 is
       if not Is_Overloaded (P) then
          if Is_Access_Type (Etype (P)) then
 
-            --  Set the Etype. We need to go through Is_For_Access_Subtypes to
-            --  avoid other problems caused by the Private_Subtype and it is
-            --  safe to go to the Base_Type because this is the same as
-            --  converting the access value to its Base_Type.
+            --  Set the Etype
 
             declare
-               DT : Entity_Id := Designated_Type (Etype (P));
+               DT : constant Entity_Id := Designated_Type (Etype (P));
 
             begin
-               if Ekind (DT) = E_Private_Subtype
-                 and then Is_For_Access_Subtype (DT)
-               then
-                  DT := Base_Type (DT);
-               end if;
-
                --  An explicit dereference is a legal occurrence of an
                --  incomplete type imported through a limited_with clause, if
                --  the full view is visible, or if we are within an instance