gcc/ada/sem_disp.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ D I S P                              --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2008, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
  19 -- http://www.gnu.org/licenses for a complete copy of the license.          --
  20 --                                                                          --
  21 -- GNAT was originally developed  by the GNAT team at  New York University. --
  22 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  23 --                                                                          --
  24 ------------------------------------------------------------------------------
  25
  26 with Atree;    use Atree;
  27 with Debug;    use Debug;
  28 with Elists;   use Elists;
  29 with Einfo;    use Einfo;
  30 with Exp_Disp; use Exp_Disp;
  31 with Exp_Ch7;  use Exp_Ch7;
  32 with Exp_Tss;  use Exp_Tss;
  33 with Errout;   use Errout;
  34 with Lib.Xref; use Lib.Xref;
  35 with Namet;    use Namet;
  36 with Nlists;   use Nlists;
  37 with Nmake;    use Nmake;
  38 with Opt;      use Opt;
  39 with Output;   use Output;
  40 with Restrict; use Restrict;
  41 with Rident;   use Rident;
  42 with Sem;      use Sem;
  43 with Sem_Ch6;  use Sem_Ch6;
  44 with Sem_Eval; use Sem_Eval;
  45 with Sem_Type; use Sem_Type;
  46 with Sem_Util; use Sem_Util;
  47 with Snames;   use Snames;
  48 with Stand;    use Stand;
  49 with Sinfo;    use Sinfo;
  50 with Targparm; use Targparm;
  51 with Tbuild;   use Tbuild;
  52 with Uintp;    use Uintp;
  53
  54 package body Sem_Disp is
  55
  56    -----------------------
  57    -- Local Subprograms --
  58    -----------------------
  59
  60    procedure Add_Dispatching_Operation
  61      (Tagged_Type : Entity_Id;
  62       New_Op      : Entity_Id);
  63    --  Add New_Op in the list of primitive operations of Tagged_Type
  64
  65    function Check_Controlling_Type
  66      (T    : Entity_Id;
  67       Subp : Entity_Id) return Entity_Id;
  68    --  T is the tagged type of a formal parameter or the result of Subp.
  69    --  If the subprogram has a controlling parameter or result that matches
  70    --  the type, then returns the tagged type of that parameter or result
  71    --  (returning the designated tagged type in the case of an access
  72    --  parameter); otherwise returns empty.
  73
  74    -------------------------------
  75    -- Add_Dispatching_Operation --
  76    -------------------------------
  77
  78    procedure Add_Dispatching_Operation
  79      (Tagged_Type : Entity_Id;
  80       New_Op      : Entity_Id)
  81    is
  82       List : constant Elist_Id := Primitive_Operations (Tagged_Type);
  83
  84    begin
  85       --  The dispatching operation may already be on the list, if it the
  86       --  wrapper for an inherited function of a null extension (see exp_ch3
  87       --  for the construction of function wrappers). The list of primitive
  88       --  operations must not contain duplicates.
  89
  90       Append_Unique_Elmt (New_Op, List);
  91    end Add_Dispatching_Operation;
  92
  93    -------------------------------
  94    -- Check_Controlling_Formals --
  95    -------------------------------
  96
  97    procedure Check_Controlling_Formals
  98      (Typ  : Entity_Id;
  99       Subp : Entity_Id)
 100    is
 101       Formal    : Entity_Id;
 102       Ctrl_Type : Entity_Id;
 103
 104    begin
 105       Formal := First_Formal (Subp);
 106
 107       while Present (Formal) loop
 108          Ctrl_Type := Check_Controlling_Type (Etype (Formal), Subp);
 109
 110          if Present (Ctrl_Type) then
 111
 112             --  When the controlling type is concurrent and declared within a
 113             --  generic or inside an instance, use its corresponding record
 114             --  type.
 115
 116             if Is_Concurrent_Type (Ctrl_Type)
 117               and then Present (Corresponding_Record_Type (Ctrl_Type))
 118             then
 119                Ctrl_Type := Corresponding_Record_Type (Ctrl_Type);
 120             end if;
 121
 122             if Ctrl_Type = Typ then
 123                Set_Is_Controlling_Formal (Formal);
 124
 125                --  Ada 2005 (AI-231): Anonymous access types used in
 126                --  controlling parameters exclude null because it is necessary
 127                --  to read the tag to dispatch, and null has no tag.
 128
 129                if Ekind (Etype (Formal)) = E_Anonymous_Access_Type then
 130                   Set_Can_Never_Be_Null (Etype (Formal));
 131                   Set_Is_Known_Non_Null (Etype (Formal));
 132                end if;
 133
 134                --  Check that the parameter's nominal subtype statically
 135                --  matches the first subtype.
 136
 137                if Ekind (Etype (Formal)) = E_Anonymous_Access_Type then
 138                   if not Subtypes_Statically_Match
 139                            (Typ, Designated_Type (Etype (Formal)))
 140                   then
 141                      Error_Msg_N
 142                        ("parameter subtype does not match controlling type",
 143                         Formal);
 144                   end if;
 145
 146                elsif not Subtypes_Statically_Match (Typ, Etype (Formal)) then
 147                   Error_Msg_N
 148                     ("parameter subtype does not match controlling type",
 149                      Formal);
 150                end if;
 151
 152                if Present (Default_Value (Formal)) then
 153
 154                   --  In Ada 2005, access parameters can have defaults
 155
 156                   if Ekind (Etype (Formal)) = E_Anonymous_Access_Type
 157                     and then Ada_Version < Ada_05
 158                   then
 159                      Error_Msg_N
 160                        ("default not allowed for controlling access parameter",
 161                         Default_Value (Formal));
 162
 163                   elsif not Is_Tag_Indeterminate (Default_Value (Formal)) then
 164                      Error_Msg_N
 165                        ("default expression must be a tag indeterminate" &
 166                         " function call", Default_Value (Formal));
 167                   end if;
 168                end if;
 169
 170             elsif Comes_From_Source (Subp) then
 171                Error_Msg_N
 172                  ("operation can be dispatching in only one type", Subp);
 173             end if;
 174          end if;
 175
 176          Next_Formal (Formal);
 177       end loop;
 178
 179       if Present (Etype (Subp)) then
 180          Ctrl_Type := Check_Controlling_Type (Etype (Subp), Subp);
 181
 182          if Present (Ctrl_Type) then
 183             if Ctrl_Type = Typ then
 184                Set_Has_Controlling_Result (Subp);
 185
 186                --  Check that result subtype statically matches first subtype
 187                --  (Ada 2005) : Subp may have a controlling access result.
 188
 189                if Subtypes_Statically_Match (Typ, Etype (Subp))
 190                  or else (Ekind (Etype (Subp)) = E_Anonymous_Access_Type
 191                             and then
 192                               Subtypes_Statically_Match
 193                                 (Typ, Designated_Type (Etype (Subp))))
 194                then
 195                   null;
 196
 197                else
 198                   Error_Msg_N
 199                     ("result subtype does not match controlling type", Subp);
 200                end if;
 201
 202             elsif Comes_From_Source (Subp) then
 203                Error_Msg_N
 204                  ("operation can be dispatching in only one type", Subp);
 205             end if;
 206          end if;
 207       end if;
 208    end Check_Controlling_Formals;
 209
 210    ----------------------------
 211    -- Check_Controlling_Type --
 212    ----------------------------
 213
 214    function Check_Controlling_Type
 215      (T    : Entity_Id;
 216       Subp : Entity_Id) return Entity_Id
 217    is
 218       Tagged_Type : Entity_Id := Empty;
 219
 220    begin
 221       if Is_Tagged_Type (T) then
 222          if Is_First_Subtype (T) then
 223             Tagged_Type := T;
 224          else
 225             Tagged_Type := Base_Type (T);
 226          end if;
 227
 228       elsif Ekind (T) = E_Anonymous_Access_Type
 229         and then Is_Tagged_Type (Designated_Type (T))
 230       then
 231          if Ekind (Designated_Type (T)) /= E_Incomplete_Type then
 232             if Is_First_Subtype (Designated_Type (T)) then
 233                Tagged_Type := Designated_Type (T);
 234             else
 235                Tagged_Type := Base_Type (Designated_Type (T));
 236             end if;
 237
 238          --  Ada 2005 : an incomplete type can be tagged. An operation with
 239          --  an access parameter of the type is dispatching.
 240
 241          elsif Scope (Designated_Type (T)) = Current_Scope then
 242             Tagged_Type := Designated_Type (T);
 243
 244          --  Ada 2005 (AI-50217)
 245
 246          elsif From_With_Type (Designated_Type (T))
 247            and then Present (Non_Limited_View (Designated_Type (T)))
 248          then
 249             if Is_First_Subtype (Non_Limited_View (Designated_Type (T))) then
 250                Tagged_Type := Non_Limited_View (Designated_Type (T));
 251             else
 252                Tagged_Type := Base_Type (Non_Limited_View
 253                                          (Designated_Type (T)));
 254             end if;
 255          end if;
 256       end if;
 257
 258       if No (Tagged_Type)
 259         or else Is_Class_Wide_Type (Tagged_Type)
 260       then
 261          return Empty;
 262
 263       --  The dispatching type and the primitive operation must be defined
 264       --  in the same scope, except in the case of internal operations and
 265       --  formal abstract subprograms.
 266
 267       elsif ((Scope (Subp) = Scope (Tagged_Type) or else Is_Internal (Subp))
 268                and then (not Is_Generic_Type (Tagged_Type)
 269                           or else not Comes_From_Source (Subp)))
 270         or else
 271           (Is_Formal_Subprogram (Subp) and then Is_Abstract_Subprogram (Subp))
 272         or else
 273           (Nkind (Parent (Parent (Subp))) = N_Subprogram_Renaming_Declaration
 274             and then
 275               Present (Corresponding_Formal_Spec (Parent (Parent (Subp))))
 276             and then
 277               Is_Abstract_Subprogram (Subp))
 278       then
 279          return Tagged_Type;
 280
 281       else
 282          return Empty;
 283       end if;
 284    end Check_Controlling_Type;
 285
 286    ----------------------------
 287    -- Check_Dispatching_Call --
 288    ----------------------------
 289
 290    procedure Check_Dispatching_Call (N : Node_Id) is
 291       Loc                    : constant Source_Ptr := Sloc (N);
 292       Actual                 : Node_Id;
 293       Formal                 : Entity_Id;
 294       Control                : Node_Id := Empty;
 295       Func                   : Entity_Id;
 296       Subp_Entity            : Entity_Id;
 297       Indeterm_Ancestor_Call : Boolean := False;
 298       Indeterm_Ctrl_Type     : Entity_Id;
 299
 300       Static_Tag : Node_Id := Empty;
 301       --  If a controlling formal has a statically tagged actual, the tag of
 302       --  this actual is to be used for any tag-indeterminate actual
 303
 304       procedure Check_Dispatching_Context;
 305       --  If the call is tag-indeterminate and the entity being called is
 306       --  abstract, verify that the context is a call that will eventually
 307       --  provide a tag for dispatching, or has provided one already.
 308
 309       -------------------------------
 310       -- Check_Dispatching_Context --
 311       -------------------------------
 312
 313       procedure Check_Dispatching_Context is
 314          Subp : constant Entity_Id := Entity (Name (N));
 315          Par  : Node_Id;
 316
 317       begin
 318          if Is_Abstract_Subprogram (Subp)
 319            and then No (Controlling_Argument (N))
 320          then
 321             if Present (Alias (Subp))
 322               and then not Is_Abstract_Subprogram (Alias (Subp))
 323               and then No (DTC_Entity (Subp))
 324             then
 325                --  Private overriding of inherited abstract operation,
 326                --  call is legal.
 327
 328                Set_Entity (Name (N), Alias (Subp));
 329                return;
 330
 331             else
 332                Par := Parent (N);
 333
 334                while Present (Par) loop
 335
 336                   if (Nkind (Par) = N_Function_Call            or else
 337                       Nkind (Par) = N_Procedure_Call_Statement or else
 338                       Nkind (Par) = N_Assignment_Statement     or else
 339                       Nkind (Par) = N_Op_Eq                    or else
 340                       Nkind (Par) = N_Op_Ne)
 341                     and then Is_Tagged_Type (Etype (Subp))
 342                   then
 343                      return;
 344
 345                   elsif Nkind (Par) = N_Qualified_Expression
 346                     or else Nkind (Par) = N_Unchecked_Type_Conversion
 347                   then
 348                      Par := Parent (Par);
 349
 350                   else
 351                      if Ekind (Subp) = E_Function then
 352                         Error_Msg_N
 353                           ("call to abstract function must be dispatching", N);
 354
 355                      --  This error can occur for a procedure in the case of a
 356                      --  call to an abstract formal procedure with a statically
 357                      --  tagged operand.
 358
 359                      else
 360                         Error_Msg_N
 361                           ("call to abstract procedure must be dispatching",
 362                            N);
 363                      end if;
 364
 365                      return;
 366                   end if;
 367                end loop;
 368             end if;
 369          end if;
 370       end Check_Dispatching_Context;
 371
 372    --  Start of processing for Check_Dispatching_Call
 373
 374    begin
 375       --  Find a controlling argument, if any
 376
 377       if Present (Parameter_Associations (N)) then
 378          Actual := First_Actual (N);
 379
 380          Subp_Entity := Entity (Name (N));
 381          Formal := First_Formal (Subp_Entity);
 382
 383          while Present (Actual) loop
 384             Control := Find_Controlling_Arg (Actual);
 385             exit when Present (Control);
 386
 387             --  Check for the case where the actual is a tag-indeterminate call
 388             --  whose result type is different than the tagged type associated
 389             --  with the containing call, but is an ancestor of the type.
 390
 391             if Is_Controlling_Formal (Formal)
 392               and then Is_Tag_Indeterminate (Actual)
 393               and then Base_Type (Etype (Actual)) /= Base_Type (Etype (Formal))
 394               and then Is_Ancestor (Etype (Actual), Etype (Formal))
 395             then
 396                Indeterm_Ancestor_Call := True;
 397                Indeterm_Ctrl_Type     := Etype (Formal);
 398
 399             --  If the formal is controlling but the actual is not, the type
 400             --  of the actual is statically known, and may be used as the
 401             --  controlling tag for some other-indeterminate actual.
 402
 403             elsif Is_Controlling_Formal (Formal)
 404               and then Is_Entity_Name (Actual)
 405               and then Is_Tagged_Type (Etype (Actual))
 406             then
 407                Static_Tag := Actual;
 408             end if;
 409
 410             Next_Actual (Actual);
 411             Next_Formal (Formal);
 412          end loop;
 413
 414          --  If the call doesn't have a controlling actual but does have
 415          --  an indeterminate actual that requires dispatching treatment,
 416          --  then an object is needed that will serve as the controlling
 417          --  argument for a dispatching call on the indeterminate actual.
 418          --  This can only occur in the unusual situation of a default
 419          --  actual given by a tag-indeterminate call and where the type
 420          --  of the call is an ancestor of the type associated with a
 421          --  containing call to an inherited operation (see AI-239).
 422          --  Rather than create an object of the tagged type, which would
 423          --  be problematic for various reasons (default initialization,
 424          --  discriminants), the tag of the containing call's associated
 425          --  tagged type is directly used to control the dispatching.
 426
 427          if No (Control)
 428            and then Indeterm_Ancestor_Call
 429            and then No (Static_Tag)
 430          then
 431             Control :=
 432               Make_Attribute_Reference (Loc,
 433                 Prefix         => New_Occurrence_Of (Indeterm_Ctrl_Type, Loc),
 434                 Attribute_Name => Name_Tag);
 435
 436             Analyze (Control);
 437          end if;
 438
 439          if Present (Control) then
 440
 441             --  Verify that no controlling arguments are statically tagged
 442
 443             if Debug_Flag_E then
 444                Write_Str ("Found Dispatching call");
 445                Write_Int (Int (N));
 446                Write_Eol;
 447             end if;
 448
 449             Actual := First_Actual (N);
 450
 451             while Present (Actual) loop
 452                if Actual /= Control then
 453
 454                   if not Is_Controlling_Actual (Actual) then
 455                      null; -- Can be anything
 456
 457                   elsif Is_Dynamically_Tagged (Actual) then
 458                      null; -- Valid parameter
 459
 460                   elsif Is_Tag_Indeterminate (Actual) then
 461
 462                      --  The tag is inherited from the enclosing call (the
 463                      --  node we are currently analyzing). Explicitly expand
 464                      --  the actual, since the previous call to Expand
 465                      --  (from Resolve_Call) had no way of knowing about
 466                      --  the required dispatching.
 467
 468                      Propagate_Tag (Control, Actual);
 469
 470                   else
 471                      Error_Msg_N
 472                        ("controlling argument is not dynamically tagged",
 473                         Actual);
 474                      return;
 475                   end if;
 476                end if;
 477
 478                Next_Actual (Actual);
 479             end loop;
 480
 481             --  Mark call as a dispatching call
 482
 483             Set_Controlling_Argument (N, Control);
 484             Check_Restriction (No_Dispatching_Calls, N);
 485
 486          --  If there is a statically tagged actual and a tag-indeterminate
 487          --  call to a function of the ancestor (such as that provided by a
 488          --  default), then treat this as a dispatching call and propagate
 489          --  the tag to the tag-indeterminate call(s).
 490
 491          elsif Present (Static_Tag) and then Indeterm_Ancestor_Call then
 492             Control :=
 493               Make_Attribute_Reference (Loc,
 494                 Prefix         =>
 495                   New_Occurrence_Of (Etype (Static_Tag), Loc),
 496                 Attribute_Name => Name_Tag);
 497
 498             Analyze (Control);
 499
 500             Actual := First_Actual (N);
 501             Formal := First_Formal (Subp_Entity);
 502             while Present (Actual) loop
 503                if Is_Tag_Indeterminate (Actual)
 504                  and then Is_Controlling_Formal (Formal)
 505                then
 506                   Propagate_Tag (Control, Actual);
 507                end if;
 508
 509                Next_Actual (Actual);
 510                Next_Formal (Formal);
 511             end loop;
 512
 513             Check_Dispatching_Context;
 514
 515          else
 516             --  The call is not dispatching, so check that there aren't any
 517             --  tag-indeterminate abstract calls left.
 518
 519             Actual := First_Actual (N);
 520             while Present (Actual) loop
 521                if Is_Tag_Indeterminate (Actual) then
 522
 523                   --  Function call case
 524
 525                   if Nkind (Original_Node (Actual)) = N_Function_Call then
 526                      Func := Entity (Name (Original_Node (Actual)));
 527
 528                   --  If the actual is an attribute then it can't be abstract
 529                   --  (the only current case of a tag-indeterminate attribute
 530                   --  is the stream Input attribute).
 531
 532                   elsif
 533                     Nkind (Original_Node (Actual)) = N_Attribute_Reference
 534                   then
 535                      Func := Empty;
 536
 537                   --  Only other possibility is a qualified expression whose
 538                   --  constituent expression is itself a call.
 539
 540                   else
 541                      Func :=
 542                        Entity (Name
 543                          (Original_Node
 544                            (Expression (Original_Node (Actual)))));
 545                   end if;
 546
 547                   if Present (Func) and then Is_Abstract_Subprogram (Func) then
 548                      Error_Msg_N (
 549                        "call to abstract function must be dispatching", N);
 550                   end if;
 551                end if;
 552
 553                Next_Actual (Actual);
 554             end loop;
 555
 556             Check_Dispatching_Context;
 557          end if;
 558
 559       else
 560          --  If dispatching on result, the enclosing call, if any, will
 561          --  determine the controlling argument. Otherwise this is the
 562          --  primitive operation of the root type.
 563
 564          Check_Dispatching_Context;
 565       end if;
 566    end Check_Dispatching_Call;
 567
 568    ---------------------------------
 569    -- Check_Dispatching_Operation --
 570    ---------------------------------
 571
 572    procedure Check_Dispatching_Operation (Subp, Old_Subp : Entity_Id) is
 573       Tagged_Type            : Entity_Id;
 574       Has_Dispatching_Parent : Boolean := False;
 575       Body_Is_Last_Primitive : Boolean := False;
 576
 577       function Is_Visibly_Controlled (T : Entity_Id) return Boolean;
 578       --  Check whether T is derived from a visibly controlled type.
 579       --  This is true if the root type is declared in Ada.Finalization.
 580       --  If T is derived instead from a private type whose full view
 581       --  is controlled, an explicit Initialize/Adjust/Finalize subprogram
 582       --  does not override the inherited one.
 583
 584       ---------------------------
 585       -- Is_Visibly_Controlled --
 586       ---------------------------
 587
 588       function Is_Visibly_Controlled (T : Entity_Id) return Boolean is
 589          Root : constant Entity_Id := Root_Type (T);
 590       begin
 591          return Chars (Scope (Root)) = Name_Finalization
 592            and then Chars (Scope (Scope (Root))) = Name_Ada
 593            and then Scope (Scope (Scope (Root))) = Standard_Standard;
 594       end Is_Visibly_Controlled;
 595
 596    --  Start of processing for Check_Dispatching_Operation
 597
 598    begin
 599       if Ekind (Subp) /= E_Procedure and then Ekind (Subp) /= E_Function then
 600          return;
 601       end if;
 602
 603       Set_Is_Dispatching_Operation (Subp, False);
 604       Tagged_Type := Find_Dispatching_Type (Subp);
 605
 606       --  Ada 2005 (AI-345)
 607
 608       if Ada_Version = Ada_05
 609         and then Present (Tagged_Type)
 610         and then Is_Concurrent_Type (Tagged_Type)
 611       then
 612          --  Protect the frontend against previously detected errors
 613
 614          if No (Corresponding_Record_Type (Tagged_Type)) then
 615             return;
 616          end if;
 617
 618          Tagged_Type := Corresponding_Record_Type (Tagged_Type);
 619       end if;
 620
 621       --  If Subp is derived from a dispatching operation then it should
 622       --  always be treated as dispatching. In this case various checks
 623       --  below will be bypassed. Makes sure that late declarations for
 624       --  inherited private subprograms are treated as dispatching, even
 625       --  if the associated tagged type is already frozen.
 626
 627       Has_Dispatching_Parent :=
 628          Present (Alias (Subp))
 629            and then Is_Dispatching_Operation (Alias (Subp));
 630
 631       if No (Tagged_Type) then
 632
 633          --  Ada 2005 (AI-251): Check that Subp is not a primitive associated
 634          --  with an abstract interface type unless the interface acts as a
 635          --  parent type in a derivation. If the interface type is a formal
 636          --  type then the operation is not primitive and therefore legal.
 637
 638          declare
 639             E   : Entity_Id;
 640             Typ : Entity_Id;
 641
 642          begin
 643             E := First_Entity (Subp);
 644             while Present (E) loop
 645
 646                --  For an access parameter, check designated type.
 647
 648                if Ekind (Etype (E)) = E_Anonymous_Access_Type then
 649                   Typ := Designated_Type (Etype (E));
 650                else
 651                   Typ := Etype (E);
 652                end if;
 653
 654                if Comes_From_Source (Subp)
 655                  and then Is_Interface (Typ)
 656                  and then not Is_Class_Wide_Type (Typ)
 657                  and then not Is_Derived_Type (Typ)
 658                  and then not Is_Generic_Type (Typ)
 659                  and then not In_Instance
 660                then
 661                   Error_Msg_N ("?declaration of& is too late!", Subp);
 662                   Error_Msg_NE
 663                     ("\spec should appear immediately after declaration of &!",
 664                      Subp, Typ);
 665                   exit;
 666                end if;
 667
 668                Next_Entity (E);
 669             end loop;
 670
 671             --  In case of functions check also the result type
 672
 673             if Ekind (Subp) = E_Function then
 674                if Is_Access_Type (Etype (Subp)) then
 675                   Typ := Designated_Type (Etype (Subp));
 676                else
 677                   Typ := Etype (Subp);
 678                end if;
 679
 680                if not Is_Class_Wide_Type (Typ)
 681                  and then Is_Interface (Typ)
 682                  and then not Is_Derived_Type (Typ)
 683                then
 684                   Error_Msg_N ("?declaration of& is too late!", Subp);
 685                   Error_Msg_NE
 686                     ("\spec should appear immediately after declaration of &!",
 687                      Subp, Typ);
 688                end if;
 689             end if;
 690          end;
 691
 692          return;
 693
 694       --  The subprograms build internally after the freezing point (such as
 695       --  the Init procedure) are not primitives
 696
 697       elsif Is_Frozen (Tagged_Type)
 698         and then not Comes_From_Source (Subp)
 699         and then not Has_Dispatching_Parent
 700       then
 701          return;
 702
 703       --  The operation may be a child unit, whose scope is the defining
 704       --  package, but which is not a primitive operation of the type.
 705
 706       elsif Is_Child_Unit (Subp) then
 707          return;
 708
 709       --  If the subprogram is not defined in a package spec, the only case
 710       --  where it can be a dispatching op is when it overrides an operation
 711       --  before the freezing point of the type.
 712
 713       elsif ((not Is_Package_Or_Generic_Package (Scope (Subp)))
 714                or else In_Package_Body (Scope (Subp)))
 715         and then not Has_Dispatching_Parent
 716       then
 717          if not Comes_From_Source (Subp)
 718            or else (Present (Old_Subp) and then not Is_Frozen (Tagged_Type))
 719          then
 720             null;
 721
 722          --  If the type is already frozen, the overriding is not allowed
 723          --  except when Old_Subp is not a dispatching operation (which
 724          --  can occur when Old_Subp was inherited by an untagged type).
 725          --  However, a body with no previous spec freezes the type "after"
 726          --  its declaration, and therefore is a legal overriding (unless
 727          --  the type has already been frozen). Only the first such body
 728          --  is legal.
 729
 730          elsif Present (Old_Subp)
 731            and then Is_Dispatching_Operation (Old_Subp)
 732          then
 733             if Comes_From_Source (Subp)
 734               and then
 735                 (Nkind (Unit_Declaration_Node (Subp)) = N_Subprogram_Body
 736                   or else Nkind (Unit_Declaration_Node (Subp)) in N_Body_Stub)
 737             then
 738                declare
 739                   Subp_Body : constant Node_Id := Unit_Declaration_Node (Subp);
 740                   Decl_Item : Node_Id          := Next (Parent (Tagged_Type));
 741
 742                begin
 743                   --  ??? The checks here for whether the type has been
 744                   --  frozen prior to the new body are not complete. It's
 745                   --  not simple to check frozenness at this point since
 746                   --  the body has already caused the type to be prematurely
 747                   --  frozen in Analyze_Declarations, but we're forced to
 748                   --  recheck this here because of the odd rule interpretation
 749                   --  that allows the overriding if the type wasn't frozen
 750                   --  prior to the body. The freezing action should probably
 751                   --  be delayed until after the spec is seen, but that's
 752                   --  a tricky change to the delicate freezing code.
 753
 754                   --  Look at each declaration following the type up
 755                   --  until the new subprogram body. If any of the
 756                   --  declarations is a body then the type has been
 757                   --  frozen already so the overriding primitive is
 758                   --  illegal.
 759
 760                   while Present (Decl_Item)
 761                     and then (Decl_Item /= Subp_Body)
 762                   loop
 763                      if Comes_From_Source (Decl_Item)
 764                        and then (Nkind (Decl_Item) in N_Proper_Body
 765                                   or else Nkind (Decl_Item) in N_Body_Stub)
 766                      then
 767                         Error_Msg_N ("overriding of& is too late!", Subp);
 768                         Error_Msg_N
 769                           ("\spec should appear immediately after the type!",
 770                            Subp);
 771                         exit;
 772                      end if;
 773
 774                      Next (Decl_Item);
 775                   end loop;
 776
 777                   --  If the subprogram doesn't follow in the list of
 778                   --  declarations including the type then the type
 779                   --  has definitely been frozen already and the body
 780                   --  is illegal.
 781
 782                   if No (Decl_Item) then
 783                      Error_Msg_N ("overriding of& is too late!", Subp);
 784                      Error_Msg_N
 785                        ("\spec should appear immediately after the type!",
 786                         Subp);
 787
 788                   elsif Is_Frozen (Subp) then
 789
 790                      --  The subprogram body declares a primitive operation.
 791                      --  if the subprogram is already frozen, we must update
 792                      --  its dispatching information explicitly here. The
 793                      --  information is taken from the overridden subprogram.
 794                      --  We must also generate a cross-reference entry because
 795                      --  references to other primitives were already created
 796                      --  when type was frozen.
 797
 798                      Body_Is_Last_Primitive := True;
 799
 800                      if Present (DTC_Entity (Old_Subp)) then
 801                         Set_DTC_Entity (Subp, DTC_Entity (Old_Subp));
 802                         Set_DT_Position (Subp, DT_Position (Old_Subp));
 803
 804                         if not Restriction_Active (No_Dispatching_Calls) then
 805                            if Building_Static_DT (Tagged_Type) then
 806
 807                               --  If the static dispatch table has not been
 808                               --  built then there is nothing else to do now;
 809                               --  otherwise we notify that we cannot build the
 810                               --  static dispatch table.
 811
 812                               if Has_Dispatch_Table (Tagged_Type) then
 813                                  Error_Msg_N
 814                                    ("overriding of& is too late for building" &
 815                                     " static dispatch tables!", Subp);
 816                                  Error_Msg_N
 817                                    ("\spec should appear immediately after" &
 818                                     " the type!", Subp);
 819                               end if;
 820
 821                            else
 822                               Register_Primitive (Sloc (Subp_Body),
 823                                 Prim    => Subp,
 824                                 Ins_Nod => Subp_Body);
 825                            end if;
 826
 827                            Generate_Reference (Tagged_Type, Subp, 'p', False);
 828                         end if;
 829                      end if;
 830                   end if;
 831                end;
 832
 833             else
 834                Error_Msg_N ("overriding of& is too late!", Subp);
 835                Error_Msg_N
 836                  ("\subprogram spec should appear immediately after the type!",
 837                   Subp);
 838             end if;
 839
 840          --  If the type is not frozen yet and we are not in the overriding
 841          --  case it looks suspiciously like an attempt to define a primitive
 842          --  operation.
 843
 844          elsif not Is_Frozen (Tagged_Type) then
 845             Error_Msg_N
 846               ("?not dispatching (must be defined in a package spec)", Subp);
 847             return;
 848
 849          --  When the type is frozen, it is legitimate to define a new
 850          --  non-primitive operation.
 851
 852          else
 853             return;
 854          end if;
 855
 856       --  Now, we are sure that the scope is a package spec. If the subprogram
 857       --  is declared after the freezing point of the type that's an error
 858
 859       elsif Is_Frozen (Tagged_Type) and then not Has_Dispatching_Parent then
 860          Error_Msg_N ("this primitive operation is declared too late", Subp);
 861          Error_Msg_NE
 862            ("?no primitive operations for& after this line",
 863             Freeze_Node (Tagged_Type),
 864             Tagged_Type);
 865          return;
 866       end if;
 867
 868       Check_Controlling_Formals (Tagged_Type, Subp);
 869
 870       --  Now it should be a correct primitive operation, put it in the list
 871
 872       if Present (Old_Subp) then
 873          Check_Subtype_Conformant (Subp, Old_Subp);
 874
 875          if (Chars (Subp) = Name_Initialize
 876            or else Chars (Subp) = Name_Adjust
 877            or else Chars (Subp) = Name_Finalize)
 878            and then Is_Controlled (Tagged_Type)
 879            and then not Is_Visibly_Controlled (Tagged_Type)
 880          then
 881             Set_Is_Overriding_Operation (Subp, False);
 882             Error_Msg_NE
 883               ("operation does not override inherited&?", Subp, Subp);
 884          else
 885             Override_Dispatching_Operation (Tagged_Type, Old_Subp, Subp);
 886             Set_Is_Overriding_Operation (Subp);
 887
 888             --  Ada 2005 (AI-251): In case of late overriding of a primitive
 889             --  that covers abstract interface subprograms we must register it
 890             --  in all the secondary dispatch tables associated with abstract
 891             --  interfaces.
 892
 893             if Body_Is_Last_Primitive then
 894                declare
 895                   Subp_Body : constant Node_Id := Unit_Declaration_Node (Subp);
 896                   Elmt      : Elmt_Id;
 897                   Prim      : Node_Id;
 898
 899                begin
 900                   Elmt := First_Elmt (Primitive_Operations (Tagged_Type));
 901                   while Present (Elmt) loop
 902                      Prim := Node (Elmt);
 903
 904                      if Present (Alias (Prim))
 905                        and then Present (Abstract_Interface_Alias (Prim))
 906                        and then Alias (Prim) = Subp
 907                      then
 908                         Register_Primitive (Sloc (Prim),
 909                           Prim    => Prim,
 910                           Ins_Nod => Subp_Body);
 911                      end if;
 912
 913                      Next_Elmt (Elmt);
 914                   end loop;
 915
 916                   --  Redisplay the contents of the updated dispatch table
 917
 918                   if Debug_Flag_ZZ then
 919                      Write_Str ("Late overriding: ");
 920                      Write_DT (Tagged_Type);
 921                   end if;
 922                end;
 923             end if;
 924          end if;
 925
 926       --  If no old subprogram, then we add this as a dispatching operation,
 927       --  but we avoid doing this if an error was posted, to prevent annoying
 928       --  cascaded errors.
 929
 930       elsif not Error_Posted (Subp) then
 931          Add_Dispatching_Operation (Tagged_Type, Subp);
 932       end if;
 933
 934       Set_Is_Dispatching_Operation (Subp, True);
 935
 936       if not Body_Is_Last_Primitive then
 937          Set_DT_Position (Subp, No_Uint);
 938
 939       elsif Has_Controlled_Component (Tagged_Type)
 940         and then
 941          (Chars (Subp) = Name_Initialize
 942            or else Chars (Subp) = Name_Adjust
 943            or else Chars (Subp) = Name_Finalize)
 944       then
 945          declare
 946             F_Node   : constant Node_Id := Freeze_Node (Tagged_Type);
 947             Decl     : Node_Id;
 948             Old_P    : Entity_Id;
 949             Old_Bod  : Node_Id;
 950             Old_Spec : Entity_Id;
 951
 952             C_Names : constant array (1 .. 3) of Name_Id :=
 953                         (Name_Initialize,
 954                          Name_Adjust,
 955                          Name_Finalize);
 956
 957             D_Names : constant array (1 .. 3) of TSS_Name_Type :=
 958                         (TSS_Deep_Initialize,
 959                          TSS_Deep_Adjust,
 960                          TSS_Deep_Finalize);
 961
 962          begin
 963             --  Remove previous controlled function, which was constructed
 964             --  and analyzed when the type was frozen. This requires
 965             --  removing the body of the redefined primitive, as well as
 966             --  its specification if needed (there is no spec created for
 967             --  Deep_Initialize, see exp_ch3.adb). We must also dismantle
 968             --  the exception information that may have been generated for
 969             --  it when front end zero-cost tables are enabled.
 970
 971             for J in D_Names'Range loop
 972                Old_P := TSS (Tagged_Type, D_Names (J));
 973
 974                if Present (Old_P)
 975                 and then Chars (Subp) = C_Names (J)
 976                then
 977                   Old_Bod := Unit_Declaration_Node (Old_P);
 978                   Remove (Old_Bod);
 979                   Set_Is_Eliminated (Old_P);
 980                   Set_Scope (Old_P,  Scope (Current_Scope));
 981
 982                   if Nkind (Old_Bod) = N_Subprogram_Body
 983                     and then Present (Corresponding_Spec (Old_Bod))
 984                   then
 985                      Old_Spec := Corresponding_Spec (Old_Bod);
 986                      Set_Has_Completion             (Old_Spec, False);
 987                   end if;
 988                end if;
 989             end loop;
 990
 991             Build_Late_Proc (Tagged_Type, Chars (Subp));
 992
 993             --  The new operation is added to the actions of the freeze
 994             --  node for the type, but this node has already been analyzed,
 995             --  so we must retrieve and analyze explicitly the new body.
 996
 997             if Present (F_Node)
 998               and then Present (Actions (F_Node))
 999             then
1000                Decl := Last (Actions (F_Node));
1001                Analyze (Decl);
1002             end if;
1003          end;
1004       end if;
1005    end Check_Dispatching_Operation;
1006
1007    ------------------------------------------
1008    -- Check_Operation_From_Incomplete_Type --
1009    ------------------------------------------
1010
1011    procedure Check_Operation_From_Incomplete_Type
1012      (Subp : Entity_Id;
1013       Typ  : Entity_Id)
1014    is
1015       Full       : constant Entity_Id := Full_View (Typ);
1016       Parent_Typ : constant Entity_Id := Etype (Full);
1017       Old_Prim   : constant Elist_Id  := Primitive_Operations (Parent_Typ);
1018       New_Prim   : constant Elist_Id  := Primitive_Operations (Full);
1019       Op1, Op2   : Elmt_Id;
1020       Prev       : Elmt_Id := No_Elmt;
1021
1022       function Derives_From (Proc : Entity_Id) return Boolean;
1023       --  Check that Subp has the signature of an operation derived from Proc.
1024       --  Subp has an access parameter that designates Typ.
1025
1026       ------------------
1027       -- Derives_From --
1028       ------------------
1029
1030       function Derives_From (Proc : Entity_Id) return Boolean is
1031          F1, F2 : Entity_Id;
1032
1033       begin
1034          if Chars (Proc) /= Chars (Subp) then
1035             return False;
1036          end if;
1037
1038          F1 := First_Formal (Proc);
1039          F2 := First_Formal (Subp);
1040
1041          while Present (F1) and then Present (F2) loop
1042
1043             if Ekind (Etype (F1)) = E_Anonymous_Access_Type then
1044
1045                if Ekind (Etype (F2)) /= E_Anonymous_Access_Type then
1046                   return False;
1047
1048                elsif Designated_Type (Etype (F1)) = Parent_Typ
1049                  and then Designated_Type (Etype (F2)) /= Full
1050                then
1051                   return False;
1052                end if;
1053
1054             elsif Ekind (Etype (F2)) = E_Anonymous_Access_Type then
1055                return False;
1056
1057             elsif Etype (F1) /= Etype (F2) then
1058                return False;
1059             end if;
1060
1061             Next_Formal (F1);
1062             Next_Formal (F2);
1063          end loop;
1064
1065          return No (F1) and then No (F2);
1066       end Derives_From;
1067
1068    --  Start of processing for Check_Operation_From_Incomplete_Type
1069
1070    begin
1071       --  The operation may override an inherited one, or may be a new one
1072       --  altogether. The inherited operation will have been hidden by the
1073       --  current one at the point of the type derivation, so it does not
1074       --  appear in the list of primitive operations of the type. We have to
1075       --  find the proper place of insertion in the list of primitive opera-
1076       --  tions by iterating over the list for the parent type.
1077
1078       Op1 := First_Elmt (Old_Prim);
1079       Op2 := First_Elmt (New_Prim);
1080
1081       while Present (Op1) and then Present (Op2) loop
1082
1083          if Derives_From (Node (Op1)) then
1084
1085             if No (Prev) then
1086                Prepend_Elmt (Subp, New_Prim);
1087             else
1088                Insert_Elmt_After (Subp, Prev);
1089             end if;
1090
1091             return;
1092          end if;
1093
1094          Prev := Op2;
1095          Next_Elmt (Op1);
1096          Next_Elmt (Op2);
1097       end loop;
1098
1099       --  Operation is a new primitive
1100
1101       Append_Elmt (Subp, New_Prim);
1102    end Check_Operation_From_Incomplete_Type;
1103
1104    ---------------------------------------
1105    -- Check_Operation_From_Private_View --
1106    ---------------------------------------
1107
1108    procedure Check_Operation_From_Private_View (Subp, Old_Subp : Entity_Id) is
1109       Tagged_Type : Entity_Id;
1110
1111    begin
1112       if Is_Dispatching_Operation (Alias (Subp)) then
1113          Set_Scope (Subp, Current_Scope);
1114          Tagged_Type := Find_Dispatching_Type (Subp);
1115
1116          --  Add Old_Subp to primitive operations if not already present.
1117
1118          if Present (Tagged_Type) and then Is_Tagged_Type (Tagged_Type) then
1119             Append_Unique_Elmt (Old_Subp, Primitive_Operations (Tagged_Type));
1120
1121             --  If Old_Subp isn't already marked as dispatching then
1122             --  this is the case of an operation of an untagged private
1123             --  type fulfilled by a tagged type that overrides an
1124             --  inherited dispatching operation, so we set the necessary
1125             --  dispatching attributes here.
1126
1127             if not Is_Dispatching_Operation (Old_Subp) then
1128
1129                --  If the untagged type has no discriminants, and the full
1130                --  view is constrained, there will be a spurious mismatch
1131                --  of subtypes on the controlling arguments, because the tagged
1132                --  type is the internal base type introduced in the derivation.
1133                --  Use the original type to verify conformance, rather than the
1134                --  base type.
1135
1136                if not Comes_From_Source (Tagged_Type)
1137                  and then Has_Discriminants (Tagged_Type)
1138                then
1139                   declare
1140                      Formal : Entity_Id;
1141                   begin
1142                      Formal := First_Formal (Old_Subp);
1143                      while Present (Formal) loop
1144                         if Tagged_Type = Base_Type (Etype (Formal)) then
1145                            Tagged_Type := Etype (Formal);
1146                         end if;
1147
1148                         Next_Formal (Formal);
1149                      end loop;
1150                   end;
1151
1152                   if Tagged_Type = Base_Type (Etype (Old_Subp)) then
1153                      Tagged_Type := Etype (Old_Subp);
1154                   end if;
1155                end if;
1156
1157                Check_Controlling_Formals (Tagged_Type, Old_Subp);
1158                Set_Is_Dispatching_Operation (Old_Subp, True);
1159                Set_DT_Position (Old_Subp, No_Uint);
1160             end if;
1161
1162             --  If the old subprogram is an explicit renaming of some other
1163             --  entity, it is not overridden by the inherited subprogram.
1164             --  Otherwise, update its alias and other attributes.
1165
1166             if Present (Alias (Old_Subp))
1167               and then Nkind (Unit_Declaration_Node (Old_Subp))
1168                 /= N_Subprogram_Renaming_Declaration
1169             then
1170                Set_Alias (Old_Subp, Alias (Subp));
1171
1172                --  The derived subprogram should inherit the abstractness
1173                --  of the parent subprogram (except in the case of a function
1174                --  returning the type). This sets the abstractness properly
1175                --  for cases where a private extension may have inherited
1176                --  an abstract operation, but the full type is derived from
1177                --  a descendant type and inherits a nonabstract version.
1178
1179                if Etype (Subp) /= Tagged_Type then
1180                   Set_Is_Abstract_Subprogram
1181                     (Old_Subp, Is_Abstract_Subprogram (Alias (Subp)));
1182                end if;
1183             end if;
1184          end if;
1185       end if;
1186    end Check_Operation_From_Private_View;
1187
1188    --------------------------
1189    -- Find_Controlling_Arg --
1190    --------------------------
1191
1192    function Find_Controlling_Arg (N : Node_Id) return Node_Id is
1193       Orig_Node : constant Node_Id := Original_Node (N);
1194       Typ       : Entity_Id;
1195
1196    begin
1197       if Nkind (Orig_Node) = N_Qualified_Expression then
1198          return Find_Controlling_Arg (Expression (Orig_Node));
1199       end if;
1200
1201       --  Dispatching on result case. If expansion is disabled, the node still
1202       --  has the structure of a function call. However, if the function name
1203       --  is an operator and the call was given in infix form, the original
1204       --  node has no controlling result and we must examine the current node.
1205
1206       if Nkind (N) = N_Function_Call
1207         and then Present (Controlling_Argument (N))
1208         and then Has_Controlling_Result (Entity (Name (N)))
1209       then
1210          return Controlling_Argument (N);
1211
1212       --  If expansion is enabled, the call may have been transformed into
1213       --  an indirect call, and we need to recover the original node.
1214
1215       elsif Nkind (Orig_Node) = N_Function_Call
1216         and then Present (Controlling_Argument (Orig_Node))
1217         and then Has_Controlling_Result (Entity (Name (Orig_Node)))
1218       then
1219          return Controlling_Argument (Orig_Node);
1220
1221       --  Normal case
1222
1223       elsif Is_Controlling_Actual (N)
1224         or else
1225          (Nkind (Parent (N)) = N_Qualified_Expression
1226            and then Is_Controlling_Actual (Parent (N)))
1227       then
1228          Typ := Etype (N);
1229
1230          if Is_Access_Type (Typ) then
1231             --  In the case of an Access attribute, use the type of
1232             --  the prefix, since in the case of an actual for an
1233             --  access parameter, the attribute's type may be of a
1234             --  specific designated type, even though the prefix
1235             --  type is class-wide.
1236
1237             if Nkind (N) = N_Attribute_Reference then
1238                Typ := Etype (Prefix (N));
1239
1240             --  An allocator is dispatching if the type of qualified
1241             --  expression is class_wide, in which case this is the
1242             --  controlling type.
1243
1244             elsif Nkind (Orig_Node) = N_Allocator
1245                and then Nkind (Expression (Orig_Node)) = N_Qualified_Expression
1246             then
1247                Typ := Etype (Expression (Orig_Node));
1248
1249             else
1250                Typ := Designated_Type (Typ);
1251             end if;
1252          end if;
1253
1254          if Is_Class_Wide_Type (Typ)
1255            or else
1256              (Nkind (Parent (N)) = N_Qualified_Expression
1257                and then Is_Access_Type (Etype (N))
1258                and then Is_Class_Wide_Type (Designated_Type (Etype (N))))
1259          then
1260             return N;
1261          end if;
1262       end if;
1263
1264       return Empty;
1265    end Find_Controlling_Arg;
1266
1267    ---------------------------
1268    -- Find_Dispatching_Type --
1269    ---------------------------
1270
1271    function Find_Dispatching_Type (Subp : Entity_Id) return Entity_Id is
1272       Formal    : Entity_Id;
1273       Ctrl_Type : Entity_Id;
1274
1275    begin
1276       if Present (DTC_Entity (Subp)) then
1277          return Scope (DTC_Entity (Subp));
1278
1279       else
1280          Formal := First_Formal (Subp);
1281          while Present (Formal) loop
1282             Ctrl_Type := Check_Controlling_Type (Etype (Formal), Subp);
1283
1284             if Present (Ctrl_Type) then
1285                return Ctrl_Type;
1286             end if;
1287
1288             Next_Formal (Formal);
1289          end loop;
1290
1291       --  The subprogram may also be dispatching on result
1292
1293          if Present (Etype (Subp)) then
1294             Ctrl_Type := Check_Controlling_Type (Etype (Subp), Subp);
1295
1296             if Present (Ctrl_Type) then
1297                return Ctrl_Type;
1298             end if;
1299          end if;
1300       end if;
1301
1302       return Empty;
1303    end Find_Dispatching_Type;
1304
1305    ---------------------------
1306    -- Is_Dynamically_Tagged --
1307    ---------------------------
1308
1309    function Is_Dynamically_Tagged (N : Node_Id) return Boolean is
1310    begin
1311       if Nkind (N) = N_Error then
1312          return False;
1313       else
1314          return Find_Controlling_Arg (N) /= Empty;
1315       end if;
1316    end Is_Dynamically_Tagged;
1317
1318    --------------------------
1319    -- Is_Tag_Indeterminate --
1320    --------------------------
1321
1322    function Is_Tag_Indeterminate (N : Node_Id) return Boolean is
1323       Nam       : Entity_Id;
1324       Actual    : Node_Id;
1325       Orig_Node : constant Node_Id := Original_Node (N);
1326
1327    begin
1328       if Nkind (Orig_Node) = N_Function_Call
1329         and then Is_Entity_Name (Name (Orig_Node))
1330       then
1331          Nam := Entity (Name (Orig_Node));
1332
1333          if not Has_Controlling_Result (Nam) then
1334             return False;
1335
1336          --  An explicit dereference means that the call has already been
1337          --  expanded and there is no tag to propagate.
1338
1339          elsif Nkind (N) = N_Explicit_Dereference then
1340             return False;
1341
1342          --  If there are no actuals, the call is tag-indeterminate
1343
1344          elsif No (Parameter_Associations (Orig_Node)) then
1345             return True;
1346
1347          else
1348             Actual := First_Actual (Orig_Node);
1349             while Present (Actual) loop
1350                if Is_Controlling_Actual (Actual)
1351                  and then not Is_Tag_Indeterminate (Actual)
1352                then
1353                   return False; -- one operand is dispatching
1354                end if;
1355
1356                Next_Actual (Actual);
1357             end loop;
1358
1359             return True;
1360          end if;
1361
1362       elsif Nkind (Orig_Node) = N_Qualified_Expression then
1363          return Is_Tag_Indeterminate (Expression (Orig_Node));
1364
1365       --  Case of a call to the Input attribute (possibly rewritten), which is
1366       --  always tag-indeterminate except when its prefix is a Class attribute.
1367
1368       elsif Nkind (Orig_Node) = N_Attribute_Reference
1369         and then
1370           Get_Attribute_Id (Attribute_Name (Orig_Node)) = Attribute_Input
1371         and then
1372           Nkind (Prefix (Orig_Node)) /= N_Attribute_Reference
1373       then
1374          return True;
1375
1376       --  In Ada 2005 a function that returns an anonymous access type can
1377       --  dispatching, and the dereference of a call to such a function
1378       --  is also tag-indeterminate.
1379
1380       elsif Nkind (Orig_Node) = N_Explicit_Dereference
1381         and then Ada_Version >= Ada_05
1382       then
1383          return Is_Tag_Indeterminate (Prefix (Orig_Node));
1384
1385       else
1386          return False;
1387       end if;
1388    end Is_Tag_Indeterminate;
1389
1390    ------------------------------------
1391    -- Override_Dispatching_Operation --
1392    ------------------------------------
1393
1394    procedure Override_Dispatching_Operation
1395      (Tagged_Type : Entity_Id;
1396       Prev_Op     : Entity_Id;
1397       New_Op      : Entity_Id)
1398    is
1399       Elmt : Elmt_Id;
1400       Prim : Node_Id;
1401
1402    begin
1403       --  Diagnose failure to match No_Return in parent (Ada-2005, AI-414, but
1404       --  we do it unconditionally in Ada 95 now, since this is our pragma!)
1405
1406       if No_Return (Prev_Op) and then not No_Return (New_Op) then
1407          Error_Msg_N ("procedure & must have No_Return pragma", New_Op);
1408          Error_Msg_N ("\since overridden procedure has No_Return", New_Op);
1409       end if;
1410
1411       --  If there is no previous operation to override, the type declaration
1412       --  was malformed, and an error must have been emitted already.
1413
1414       Elmt := First_Elmt (Primitive_Operations (Tagged_Type));
1415       while Present (Elmt)
1416         and then Node (Elmt) /= Prev_Op
1417       loop
1418          Next_Elmt (Elmt);
1419       end loop;
1420
1421       if No (Elmt) then
1422          return;
1423       end if;
1424
1425       Replace_Elmt (Elmt, New_Op);
1426
1427       if Ada_Version >= Ada_05
1428         and then Has_Abstract_Interfaces (Tagged_Type)
1429       then
1430          --  Ada 2005 (AI-251): Update the attribute alias of all the aliased
1431          --  entities of the overridden primitive to reference New_Op, and also
1432          --  propagate the proper value of Is_Abstract_Subprogram. Verify
1433          --  that the new operation is subtype conformant with the interface
1434          --  operations that it implements (for operations inherited from the
1435          --  parent itself, this check is made when building the derived type).
1436
1437          Elmt := First_Elmt (Primitive_Operations (Tagged_Type));
1438          while Present (Elmt) loop
1439             Prim := Node (Elmt);
1440
1441             if Prim = New_Op then
1442                null;
1443
1444             --  Note: The check on Is_Subprogram protects the frontend against
1445             --  reading attributes in entities that are not yet fully decorated
1446
1447             elsif Is_Subprogram (Prim)
1448               and then Present (Abstract_Interface_Alias (Prim))
1449               and then Alias (Prim) = Prev_Op
1450               and then Present (Etype (New_Op))
1451             then
1452                Set_Alias (Prim, New_Op);
1453                Check_Subtype_Conformant (New_Op, Prim);
1454                Set_Is_Abstract_Subprogram
1455                  (Prim, Is_Abstract_Subprogram (New_Op));
1456
1457                --  Ensure that this entity will be expanded to fill the
1458                --  corresponding entry in its dispatch table.
1459
1460                if not Is_Abstract_Subprogram (Prim) then
1461                   Set_Has_Delayed_Freeze (Prim);
1462                end if;
1463             end if;
1464
1465             Next_Elmt (Elmt);
1466          end loop;
1467       end if;
1468
1469       if (not Is_Package_Or_Generic_Package (Current_Scope))
1470         or else not In_Private_Part (Current_Scope)
1471       then
1472          --  Not a private primitive
1473
1474          null;
1475
1476       else pragma Assert (Is_Inherited_Operation (Prev_Op));
1477
1478          --  Make the overriding operation into an alias of the implicit one.
1479          --  In this fashion a call from outside ends up calling the new body
1480          --  even if non-dispatching, and a call from inside calls the
1481          --  overriding operation because it hides the implicit one. To
1482          --  indicate that the body of Prev_Op is never called, set its
1483          --  dispatch table entity to Empty.
1484
1485          Set_Alias (Prev_Op, New_Op);
1486          Set_DTC_Entity (Prev_Op, Empty);
1487          return;
1488       end if;
1489    end Override_Dispatching_Operation;
1490
1491    -------------------
1492    -- Propagate_Tag --
1493    -------------------
1494
1495    procedure Propagate_Tag (Control : Node_Id; Actual : Node_Id) is
1496       Call_Node : Node_Id;
1497       Arg       : Node_Id;
1498
1499    begin
1500       if Nkind (Actual) = N_Function_Call then
1501          Call_Node := Actual;
1502
1503       elsif Nkind (Actual) = N_Identifier
1504         and then Nkind (Original_Node (Actual)) = N_Function_Call
1505       then
1506          --  Call rewritten as object declaration when stack-checking
1507          --  is enabled. Propagate tag to expression in declaration, which
1508          --  is original call.
1509
1510          Call_Node := Expression (Parent (Entity (Actual)));
1511
1512       --  Ada 2005: If this is a dereference of a call to a function with a
1513       --  dispatching access-result, the tag is propagated when the dereference
1514       --  itself is expanded (see exp_ch6.adb) and there is nothing else to do.
1515
1516       elsif Nkind (Actual) = N_Explicit_Dereference
1517         and then Nkind (Original_Node (Prefix (Actual))) = N_Function_Call
1518       then
1519          return;
1520
1521       --  Only other possibilities are parenthesized or qualified expression,
1522       --  or an expander-generated unchecked conversion of a function call to
1523       --  a stream Input attribute.
1524
1525       else
1526          Call_Node := Expression (Actual);
1527       end if;
1528
1529       --  Do not set the Controlling_Argument if already set. This happens
1530       --  in the special case of _Input (see Exp_Attr, case Input).
1531
1532       if No (Controlling_Argument (Call_Node)) then
1533          Set_Controlling_Argument (Call_Node, Control);
1534       end if;
1535
1536       Arg := First_Actual (Call_Node);
1537
1538       while Present (Arg) loop
1539          if Is_Tag_Indeterminate (Arg) then
1540             Propagate_Tag (Control,  Arg);
1541          end if;
1542
1543          Next_Actual (Arg);
1544       end loop;
1545
1546       --  Expansion of dispatching calls is suppressed when VM_Target, because
1547       --  the VM back-ends directly handle the generation of dispatching
1548       --  calls and would have to undo any expansion to an indirect call.
1549
1550       if VM_Target = No_VM then
1551          Expand_Dispatching_Call (Call_Node);
1552
1553       --  Expansion of a dispatching call results in an indirect call, which in
1554       --  turn causes current values to be killed (see Resolve_Call), so on VM
1555       --  targets we do the call here to ensure consistent warnings between VM
1556       --  and non-VM targets.
1557
1558       else
1559          Kill_Current_Values;
1560       end if;
1561    end Propagate_Tag;
1562
1563 end Sem_Disp;