gcc/ada/exp_pakd.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             E X P _ P A K D                              --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2002 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 2,  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 COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, USA.                                                      --
  21 --                                                                          --
  22 -- GNAT was originally developed  by the GNAT team at  New York University. --
  23 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  24 --                                                                          --
  25 ------------------------------------------------------------------------------
  26
  27 with Atree;    use Atree;
  28 with Checks;   use Checks;
  29 with Einfo;    use Einfo;
  30 with Exp_Dbug; use Exp_Dbug;
  31 with Exp_Util; use Exp_Util;
  32 with Nlists;   use Nlists;
  33 with Nmake;    use Nmake;
  34 with Opt;      use Opt;
  35 with Rtsfind;  use Rtsfind;
  36 with Sem;      use Sem;
  37 with Sem_Ch8;  use Sem_Ch8;
  38 with Sem_Ch13; use Sem_Ch13;
  39 with Sem_Eval; use Sem_Eval;
  40 with Sem_Res;  use Sem_Res;
  41 with Sem_Util; use Sem_Util;
  42 with Sinfo;    use Sinfo;
  43 with Snames;   use Snames;
  44 with Stand;    use Stand;
  45 with Targparm; use Targparm;
  46 with Tbuild;   use Tbuild;
  47 with Ttypes;   use Ttypes;
  48 with Uintp;    use Uintp;
  49
  50 package body Exp_Pakd is
  51
  52    ---------------------------
  53    -- Endian Considerations --
  54    ---------------------------
  55
  56    --  As described in the specification, bit numbering in a packed array
  57    --  is consistent with bit numbering in a record representation clause,
  58    --  and hence dependent on the endianness of the machine:
  59
  60    --    For little-endian machines, element zero is at the right hand end
  61    --    (low order end) of a bit field.
  62
  63    --    For big-endian machines, element zero is at the left hand end
  64    --    (high order end) of a bit field.
  65
  66    --  The shifts that are used to right justify a field therefore differ
  67    --  in the two cases. For the little-endian case, we can simply use the
  68    --  bit number (i.e. the element number * element size) as the count for
  69    --  a right shift. For the big-endian case, we have to subtract the shift
  70    --  count from an appropriate constant to use in the right shift. We use
  71    --  rotates instead of shifts (which is necessary in the store case to
  72    --  preserve other fields), and we expect that the backend will be able
  73    --  to change the right rotate into a left rotate, avoiding the subtract,
  74    --  if the architecture provides such an instruction.
  75
  76    ----------------------------------------------
  77    -- Entity Tables for Packed Access Routines --
  78    ----------------------------------------------
  79
  80    --  For the cases of component size = 3,5-7,9-15,17-31,33-63 we call
  81    --  library routines. This table is used to obtain the entity for the
  82    --  proper routine.
  83
  84    type E_Array is array (Int range 01 .. 63) of RE_Id;
  85
  86    --  Array of Bits_nn entities. Note that we do not use library routines
  87    --  for the 8-bit and 16-bit cases, but we still fill in the table, using
  88    --  entries from System.Unsigned, because we also use this table for
  89    --  certain special unchecked conversions in the big-endian case.
  90
  91    Bits_Id : constant E_Array :=
  92      (01 => RE_Bits_1,
  93       02 => RE_Bits_2,
  94       03 => RE_Bits_03,
  95       04 => RE_Bits_4,
  96       05 => RE_Bits_05,
  97       06 => RE_Bits_06,
  98       07 => RE_Bits_07,
  99       08 => RE_Unsigned_8,
 100       09 => RE_Bits_09,
 101       10 => RE_Bits_10,
 102       11 => RE_Bits_11,
 103       12 => RE_Bits_12,
 104       13 => RE_Bits_13,
 105       14 => RE_Bits_14,
 106       15 => RE_Bits_15,
 107       16 => RE_Unsigned_16,
 108       17 => RE_Bits_17,
 109       18 => RE_Bits_18,
 110       19 => RE_Bits_19,
 111       20 => RE_Bits_20,
 112       21 => RE_Bits_21,
 113       22 => RE_Bits_22,
 114       23 => RE_Bits_23,
 115       24 => RE_Bits_24,
 116       25 => RE_Bits_25,
 117       26 => RE_Bits_26,
 118       27 => RE_Bits_27,
 119       28 => RE_Bits_28,
 120       29 => RE_Bits_29,
 121       30 => RE_Bits_30,
 122       31 => RE_Bits_31,
 123       32 => RE_Unsigned_32,
 124       33 => RE_Bits_33,
 125       34 => RE_Bits_34,
 126       35 => RE_Bits_35,
 127       36 => RE_Bits_36,
 128       37 => RE_Bits_37,
 129       38 => RE_Bits_38,
 130       39 => RE_Bits_39,
 131       40 => RE_Bits_40,
 132       41 => RE_Bits_41,
 133       42 => RE_Bits_42,
 134       43 => RE_Bits_43,
 135       44 => RE_Bits_44,
 136       45 => RE_Bits_45,
 137       46 => RE_Bits_46,
 138       47 => RE_Bits_47,
 139       48 => RE_Bits_48,
 140       49 => RE_Bits_49,
 141       50 => RE_Bits_50,
 142       51 => RE_Bits_51,
 143       52 => RE_Bits_52,
 144       53 => RE_Bits_53,
 145       54 => RE_Bits_54,
 146       55 => RE_Bits_55,
 147       56 => RE_Bits_56,
 148       57 => RE_Bits_57,
 149       58 => RE_Bits_58,
 150       59 => RE_Bits_59,
 151       60 => RE_Bits_60,
 152       61 => RE_Bits_61,
 153       62 => RE_Bits_62,
 154       63 => RE_Bits_63);
 155
 156    --  Array of Get routine entities. These are used to obtain an element
 157    --  from a packed array. The N'th entry is used to obtain elements from
 158    --  a packed array whose component size is N. RE_Null is used as a null
 159    --  entry, for the cases where a library routine is not used.
 160
 161    Get_Id : constant E_Array :=
 162      (01 => RE_Null,
 163       02 => RE_Null,
 164       03 => RE_Get_03,
 165       04 => RE_Null,
 166       05 => RE_Get_05,
 167       06 => RE_Get_06,
 168       07 => RE_Get_07,
 169       08 => RE_Null,
 170       09 => RE_Get_09,
 171       10 => RE_Get_10,
 172       11 => RE_Get_11,
 173       12 => RE_Get_12,
 174       13 => RE_Get_13,
 175       14 => RE_Get_14,
 176       15 => RE_Get_15,
 177       16 => RE_Null,
 178       17 => RE_Get_17,
 179       18 => RE_Get_18,
 180       19 => RE_Get_19,
 181       20 => RE_Get_20,
 182       21 => RE_Get_21,
 183       22 => RE_Get_22,
 184       23 => RE_Get_23,
 185       24 => RE_Get_24,
 186       25 => RE_Get_25,
 187       26 => RE_Get_26,
 188       27 => RE_Get_27,
 189       28 => RE_Get_28,
 190       29 => RE_Get_29,
 191       30 => RE_Get_30,
 192       31 => RE_Get_31,
 193       32 => RE_Null,
 194       33 => RE_Get_33,
 195       34 => RE_Get_34,
 196       35 => RE_Get_35,
 197       36 => RE_Get_36,
 198       37 => RE_Get_37,
 199       38 => RE_Get_38,
 200       39 => RE_Get_39,
 201       40 => RE_Get_40,
 202       41 => RE_Get_41,
 203       42 => RE_Get_42,
 204       43 => RE_Get_43,
 205       44 => RE_Get_44,
 206       45 => RE_Get_45,
 207       46 => RE_Get_46,
 208       47 => RE_Get_47,
 209       48 => RE_Get_48,
 210       49 => RE_Get_49,
 211       50 => RE_Get_50,
 212       51 => RE_Get_51,
 213       52 => RE_Get_52,
 214       53 => RE_Get_53,
 215       54 => RE_Get_54,
 216       55 => RE_Get_55,
 217       56 => RE_Get_56,
 218       57 => RE_Get_57,
 219       58 => RE_Get_58,
 220       59 => RE_Get_59,
 221       60 => RE_Get_60,
 222       61 => RE_Get_61,
 223       62 => RE_Get_62,
 224       63 => RE_Get_63);
 225
 226    --  Array of Get routine entities to be used in the case where the packed
 227    --  array is itself a component of a packed structure, and therefore may
 228    --  not be fully aligned. This only affects the even sizes, since for the
 229    --  odd sizes, we do not get any fixed alignment in any case.
 230
 231    GetU_Id : constant E_Array :=
 232      (01 => RE_Null,
 233       02 => RE_Null,
 234       03 => RE_Get_03,
 235       04 => RE_Null,
 236       05 => RE_Get_05,
 237       06 => RE_GetU_06,
 238       07 => RE_Get_07,
 239       08 => RE_Null,
 240       09 => RE_Get_09,
 241       10 => RE_GetU_10,
 242       11 => RE_Get_11,
 243       12 => RE_GetU_12,
 244       13 => RE_Get_13,
 245       14 => RE_GetU_14,
 246       15 => RE_Get_15,
 247       16 => RE_Null,
 248       17 => RE_Get_17,
 249       18 => RE_GetU_18,
 250       19 => RE_Get_19,
 251       20 => RE_GetU_20,
 252       21 => RE_Get_21,
 253       22 => RE_GetU_22,
 254       23 => RE_Get_23,
 255       24 => RE_GetU_24,
 256       25 => RE_Get_25,
 257       26 => RE_GetU_26,
 258       27 => RE_Get_27,
 259       28 => RE_GetU_28,
 260       29 => RE_Get_29,
 261       30 => RE_GetU_30,
 262       31 => RE_Get_31,
 263       32 => RE_Null,
 264       33 => RE_Get_33,
 265       34 => RE_GetU_34,
 266       35 => RE_Get_35,
 267       36 => RE_GetU_36,
 268       37 => RE_Get_37,
 269       38 => RE_GetU_38,
 270       39 => RE_Get_39,
 271       40 => RE_GetU_40,
 272       41 => RE_Get_41,
 273       42 => RE_GetU_42,
 274       43 => RE_Get_43,
 275       44 => RE_GetU_44,
 276       45 => RE_Get_45,
 277       46 => RE_GetU_46,
 278       47 => RE_Get_47,
 279       48 => RE_GetU_48,
 280       49 => RE_Get_49,
 281       50 => RE_GetU_50,
 282       51 => RE_Get_51,
 283       52 => RE_GetU_52,
 284       53 => RE_Get_53,
 285       54 => RE_GetU_54,
 286       55 => RE_Get_55,
 287       56 => RE_GetU_56,
 288       57 => RE_Get_57,
 289       58 => RE_GetU_58,
 290       59 => RE_Get_59,
 291       60 => RE_GetU_60,
 292       61 => RE_Get_61,
 293       62 => RE_GetU_62,
 294       63 => RE_Get_63);
 295
 296    --  Array of Set routine entities. These are used to assign an element
 297    --  of a packed array. The N'th entry is used to assign elements for
 298    --  a packed array whose component size is N. RE_Null is used as a null
 299    --  entry, for the cases where a library routine is not used.
 300
 301    Set_Id : E_Array :=
 302      (01 => RE_Null,
 303       02 => RE_Null,
 304       03 => RE_Set_03,
 305       04 => RE_Null,
 306       05 => RE_Set_05,
 307       06 => RE_Set_06,
 308       07 => RE_Set_07,
 309       08 => RE_Null,
 310       09 => RE_Set_09,
 311       10 => RE_Set_10,
 312       11 => RE_Set_11,
 313       12 => RE_Set_12,
 314       13 => RE_Set_13,
 315       14 => RE_Set_14,
 316       15 => RE_Set_15,
 317       16 => RE_Null,
 318       17 => RE_Set_17,
 319       18 => RE_Set_18,
 320       19 => RE_Set_19,
 321       20 => RE_Set_20,
 322       21 => RE_Set_21,
 323       22 => RE_Set_22,
 324       23 => RE_Set_23,
 325       24 => RE_Set_24,
 326       25 => RE_Set_25,
 327       26 => RE_Set_26,
 328       27 => RE_Set_27,
 329       28 => RE_Set_28,
 330       29 => RE_Set_29,
 331       30 => RE_Set_30,
 332       31 => RE_Set_31,
 333       32 => RE_Null,
 334       33 => RE_Set_33,
 335       34 => RE_Set_34,
 336       35 => RE_Set_35,
 337       36 => RE_Set_36,
 338       37 => RE_Set_37,
 339       38 => RE_Set_38,
 340       39 => RE_Set_39,
 341       40 => RE_Set_40,
 342       41 => RE_Set_41,
 343       42 => RE_Set_42,
 344       43 => RE_Set_43,
 345       44 => RE_Set_44,
 346       45 => RE_Set_45,
 347       46 => RE_Set_46,
 348       47 => RE_Set_47,
 349       48 => RE_Set_48,
 350       49 => RE_Set_49,
 351       50 => RE_Set_50,
 352       51 => RE_Set_51,
 353       52 => RE_Set_52,
 354       53 => RE_Set_53,
 355       54 => RE_Set_54,
 356       55 => RE_Set_55,
 357       56 => RE_Set_56,
 358       57 => RE_Set_57,
 359       58 => RE_Set_58,
 360       59 => RE_Set_59,
 361       60 => RE_Set_60,
 362       61 => RE_Set_61,
 363       62 => RE_Set_62,
 364       63 => RE_Set_63);
 365
 366    --  Array of Set routine entities to be used in the case where the packed
 367    --  array is itself a component of a packed structure, and therefore may
 368    --  not be fully aligned. This only affects the even sizes, since for the
 369    --  odd sizes, we do not get any fixed alignment in any case.
 370
 371    SetU_Id : E_Array :=
 372      (01 => RE_Null,
 373       02 => RE_Null,
 374       03 => RE_Set_03,
 375       04 => RE_Null,
 376       05 => RE_Set_05,
 377       06 => RE_SetU_06,
 378       07 => RE_Set_07,
 379       08 => RE_Null,
 380       09 => RE_Set_09,
 381       10 => RE_SetU_10,
 382       11 => RE_Set_11,
 383       12 => RE_SetU_12,
 384       13 => RE_Set_13,
 385       14 => RE_SetU_14,
 386       15 => RE_Set_15,
 387       16 => RE_Null,
 388       17 => RE_Set_17,
 389       18 => RE_SetU_18,
 390       19 => RE_Set_19,
 391       20 => RE_SetU_20,
 392       21 => RE_Set_21,
 393       22 => RE_SetU_22,
 394       23 => RE_Set_23,
 395       24 => RE_SetU_24,
 396       25 => RE_Set_25,
 397       26 => RE_SetU_26,
 398       27 => RE_Set_27,
 399       28 => RE_SetU_28,
 400       29 => RE_Set_29,
 401       30 => RE_SetU_30,
 402       31 => RE_Set_31,
 403       32 => RE_Null,
 404       33 => RE_Set_33,
 405       34 => RE_SetU_34,
 406       35 => RE_Set_35,
 407       36 => RE_SetU_36,
 408       37 => RE_Set_37,
 409       38 => RE_SetU_38,
 410       39 => RE_Set_39,
 411       40 => RE_SetU_40,
 412       41 => RE_Set_41,
 413       42 => RE_SetU_42,
 414       43 => RE_Set_43,
 415       44 => RE_SetU_44,
 416       45 => RE_Set_45,
 417       46 => RE_SetU_46,
 418       47 => RE_Set_47,
 419       48 => RE_SetU_48,
 420       49 => RE_Set_49,
 421       50 => RE_SetU_50,
 422       51 => RE_Set_51,
 423       52 => RE_SetU_52,
 424       53 => RE_Set_53,
 425       54 => RE_SetU_54,
 426       55 => RE_Set_55,
 427       56 => RE_SetU_56,
 428       57 => RE_Set_57,
 429       58 => RE_SetU_58,
 430       59 => RE_Set_59,
 431       60 => RE_SetU_60,
 432       61 => RE_Set_61,
 433       62 => RE_SetU_62,
 434       63 => RE_Set_63);
 435
 436    -----------------------
 437    -- Local Subprograms --
 438    -----------------------
 439
 440    procedure Compute_Linear_Subscript
 441      (Atyp   : Entity_Id;
 442       N      : Node_Id;
 443       Subscr : out Node_Id);
 444    --  Given a constrained array type Atyp, and an indexed component node
 445    --  N referencing an array object of this type, build an expression of
 446    --  type Standard.Integer representing the zero-based linear subscript
 447    --  value. This expression includes any required range checks.
 448
 449    procedure Convert_To_PAT_Type (Aexp : Node_Id);
 450    --  Given an expression of a packed array type, builds a corresponding
 451    --  expression whose type is the implementation type used to represent
 452    --  the packed array. Aexp is analyzed and resolved on entry and on exit.
 453
 454    function Known_Aligned_Enough (Obj : Node_Id; Csiz : Nat) return Boolean;
 455    --  There are two versions of the Set routines, the ones used when the
 456    --  object is known to be sufficiently well aligned given the number of
 457    --  bits, and the ones used when the object is not known to be aligned.
 458    --  This routine is used to determine which set to use. Obj is a reference
 459    --  to the object, and Csiz is the component size of the packed array.
 460    --  True is returned if the alignment of object is known to be sufficient,
 461    --  defined as 1 for odd bit sizes, 4 for bit sizes divisible by 4, and
 462    --  2 otherwise.
 463
 464    function Make_Shift_Left (N : Node_Id; S : Node_Id) return Node_Id;
 465    --  Build a left shift node, checking for the case of a shift count of zero
 466
 467    function Make_Shift_Right (N : Node_Id; S : Node_Id) return Node_Id;
 468    --  Build a right shift node, checking for the case of a shift count of zero
 469
 470    function RJ_Unchecked_Convert_To
 471      (Typ  : Entity_Id;
 472       Expr : Node_Id)
 473       return Node_Id;
 474    --  The packed array code does unchecked conversions which in some cases
 475    --  may involve non-discrete types with differing sizes. The semantics of
 476    --  such conversions is potentially endian dependent, and the effect we
 477    --  want here for such a conversion is to do the conversion in size as
 478    --  though numeric items are involved, and we extend or truncate on the
 479    --  left side. This happens naturally in the little-endian case, but in
 480    --  the big endian case we can get left justification, when what we want
 481    --  is right justification. This routine does the unchecked conversion in
 482    --  a stepwise manner to ensure that it gives the expected result. Hence
 483    --  the name (RJ = Right justified). The parameters Typ and Expr are as
 484    --  for the case of a normal Unchecked_Convert_To call.
 485
 486    procedure Setup_Enumeration_Packed_Array_Reference (N : Node_Id);
 487    --  This routine is called in the Get and Set case for arrays that are
 488    --  packed but not bit-packed, meaning that they have at least one
 489    --  subscript that is of an enumeration type with a non-standard
 490    --  representation. This routine modifies the given node to properly
 491    --  reference the corresponding packed array type.
 492
 493    procedure Setup_Inline_Packed_Array_Reference
 494      (N      : Node_Id;
 495       Atyp   : Entity_Id;
 496       Obj    : in out Node_Id;
 497       Cmask  : out Uint;
 498       Shift  : out Node_Id);
 499    --  This procedure performs common processing on the N_Indexed_Component
 500    --  parameter given as N, whose prefix is a reference to a packed array.
 501    --  This is used for the get and set when the component size is 1,2,4
 502    --  or for other component sizes when the packed array type is a modular
 503    --  type (i.e. the cases that are handled with inline code).
 504    --
 505    --  On entry:
 506    --
 507    --    N is the N_Indexed_Component node for the packed array reference
 508    --
 509    --    Atyp is the constrained array type (the actual subtype has been
 510    --    computed if necessary to obtain the constraints, but this is still
 511    --    the original array type, not the Packed_Array_Type value).
 512    --
 513    --    Obj is the object which is to be indexed. It is always of type Atyp.
 514    --
 515    --  On return:
 516    --
 517    --    Obj is the object containing the desired bit field. It is of type
 518    --    Unsigned or Long_Long_Unsigned, and is either the entire value,
 519    --    for the small static case, or the proper selected byte from the
 520    --    array in the large or dynamic case. This node is analyzed and
 521    --    resolved on return.
 522    --
 523    --    Shift is a node representing the shift count to be used in the
 524    --    rotate right instruction that positions the field for access.
 525    --    This node is analyzed and resolved on return.
 526    --
 527    --    Cmask is a mask corresponding to the width of the component field.
 528    --    Its value is 2 ** Csize - 1 (e.g. 2#1111# for component size of 4).
 529    --
 530    --  Note: in some cases the call to this routine may generate actions
 531    --  (for handling multi-use references and the generation of the packed
 532    --  array type on the fly). Such actions are inserted into the tree
 533    --  directly using Insert_Action.
 534
 535    ------------------------------
 536    -- Compute_Linear_Subcsript --
 537    ------------------------------
 538
 539    procedure Compute_Linear_Subscript
 540      (Atyp   : Entity_Id;
 541       N      : Node_Id;
 542       Subscr : out Node_Id)
 543    is
 544       Loc    : constant Source_Ptr := Sloc (N);
 545       Oldsub : Node_Id;
 546       Newsub : Node_Id;
 547       Indx   : Node_Id;
 548       Styp   : Entity_Id;
 549
 550    begin
 551       Subscr := Empty;
 552
 553       --  Loop through dimensions
 554
 555       Indx   := First_Index (Atyp);
 556       Oldsub := First (Expressions (N));
 557
 558       while Present (Indx) loop
 559          Styp := Etype (Indx);
 560          Newsub := Relocate_Node (Oldsub);
 561
 562          --  Get expression for the subscript value. First, if Do_Range_Check
 563          --  is set on a subscript, then we must do a range check against the
 564          --  original bounds (not the bounds of the packed array type). We do
 565          --  this by introducing a subtype conversion.
 566
 567          if Do_Range_Check (Newsub)
 568            and then Etype (Newsub) /= Styp
 569          then
 570             Newsub := Convert_To (Styp, Newsub);
 571          end if;
 572
 573          --  Now evolve the expression for the subscript. First convert
 574          --  the subscript to be zero based and of an integer type.
 575
 576          --  Case of integer type, where we just subtract to get lower bound
 577
 578          if Is_Integer_Type (Styp) then
 579
 580             --  If length of integer type is smaller than standard integer,
 581             --  then we convert to integer first, then do the subtract
 582
 583             --  Integer (subscript) - Integer (Styp'First)
 584
 585             if Esize (Styp) < Esize (Standard_Integer) then
 586                Newsub :=
 587                  Make_Op_Subtract (Loc,
 588                    Left_Opnd => Convert_To (Standard_Integer, Newsub),
 589                  Right_Opnd =>
 590                    Convert_To (Standard_Integer,
 591                      Make_Attribute_Reference (Loc,
 592                        Prefix         => New_Occurrence_Of (Styp, Loc),
 593                        Attribute_Name => Name_First)));
 594
 595             --  For larger integer types, subtract first, then convert to
 596             --  integer, this deals with strange long long integer bounds.
 597
 598             --    Integer (subscript - Styp'First)
 599
 600             else
 601                Newsub :=
 602                  Convert_To (Standard_Integer,
 603                    Make_Op_Subtract (Loc,
 604                      Left_Opnd => Newsub,
 605                    Right_Opnd =>
 606                      Make_Attribute_Reference (Loc,
 607                        Prefix         => New_Occurrence_Of (Styp, Loc),
 608                        Attribute_Name => Name_First)));
 609             end if;
 610
 611          --  For the enumeration case, we have to use 'Pos to get the value
 612          --  to work with before subtracting the lower bound.
 613
 614          --    Integer (Styp'Pos (subscr)) - Integer (Styp'Pos (Styp'First));
 615
 616          --  This is not quite right for bizarre cases where the size of the
 617          --  enumeration type is > Integer'Size bits due to rep clause ???
 618
 619          else
 620             pragma Assert (Is_Enumeration_Type (Styp));
 621
 622             Newsub :=
 623               Make_Op_Subtract (Loc,
 624                 Left_Opnd => Convert_To (Standard_Integer,
 625                   Make_Attribute_Reference (Loc,
 626                     Prefix         => New_Occurrence_Of (Styp, Loc),
 627                     Attribute_Name => Name_Pos,
 628                     Expressions    => New_List (Newsub))),
 629
 630                 Right_Opnd =>
 631                   Convert_To (Standard_Integer,
 632                     Make_Attribute_Reference (Loc,
 633                       Prefix         => New_Occurrence_Of (Styp, Loc),
 634                       Attribute_Name => Name_Pos,
 635                       Expressions    => New_List (
 636                         Make_Attribute_Reference (Loc,
 637                         Prefix         => New_Occurrence_Of (Styp, Loc),
 638                         Attribute_Name => Name_First)))));
 639          end if;
 640
 641          Set_Paren_Count (Newsub, 1);
 642
 643          --  For the first subscript, we just copy that subscript value
 644
 645          if No (Subscr) then
 646             Subscr := Newsub;
 647
 648          --  Otherwise, we must multiply what we already have by the current
 649          --  stride and then add in the new value to the evolving subscript.
 650
 651          else
 652             Subscr :=
 653               Make_Op_Add (Loc,
 654                 Left_Opnd =>
 655                   Make_Op_Multiply (Loc,
 656                     Left_Opnd  => Subscr,
 657                     Right_Opnd =>
 658                       Make_Attribute_Reference (Loc,
 659                         Attribute_Name => Name_Range_Length,
 660                         Prefix         => New_Occurrence_Of (Styp, Loc))),
 661                 Right_Opnd => Newsub);
 662          end if;
 663
 664          --  Move to next subscript
 665
 666          Next_Index (Indx);
 667          Next (Oldsub);
 668       end loop;
 669    end Compute_Linear_Subscript;
 670
 671    -------------------------
 672    -- Convert_To_PAT_Type --
 673    -------------------------
 674
 675    --  The PAT is always obtained from the actual subtype
 676
 677    procedure Convert_To_PAT_Type (Aexp : Entity_Id) is
 678       Act_ST : Entity_Id;
 679
 680    begin
 681       Convert_To_Actual_Subtype (Aexp);
 682       Act_ST := Underlying_Type (Etype (Aexp));
 683       Create_Packed_Array_Type (Act_ST);
 684
 685       --  Just replace the etype with the packed array type. This works
 686       --  because the expression will not be further analyzed, and Gigi
 687       --  considers the two types equivalent in any case.
 688
 689       Set_Etype (Aexp, Packed_Array_Type (Act_ST));
 690    end Convert_To_PAT_Type;
 691
 692    ------------------------------
 693    -- Create_Packed_Array_Type --
 694    ------------------------------
 695
 696    procedure Create_Packed_Array_Type (Typ : Entity_Id) is
 697       Loc      : constant Source_Ptr := Sloc (Typ);
 698       Ctyp     : constant Entity_Id  := Component_Type (Typ);
 699       Csize    : constant Uint       := Component_Size (Typ);
 700
 701       Ancest   : Entity_Id;
 702       PB_Type  : Entity_Id;
 703       Esiz     : Uint;
 704       Decl     : Node_Id;
 705       PAT      : Entity_Id;
 706       Len_Dim  : Node_Id;
 707       Len_Expr : Node_Id;
 708       Len_Bits : Uint;
 709       Bits_U1  : Node_Id;
 710       PAT_High : Node_Id;
 711       Btyp     : Entity_Id;
 712       Lit      : Node_Id;
 713
 714       procedure Install_PAT;
 715       --  This procedure is called with Decl set to the declaration for the
 716       --  packed array type. It creates the type and installs it as required.
 717
 718       procedure Set_PB_Type;
 719       --  Sets PB_Type to Packed_Bytes{1,2,4} as required by the alignment
 720       --  requirements (see documentation in the spec of this package).
 721
 722       -----------------
 723       -- Install_PAT --
 724       -----------------
 725
 726       procedure Install_PAT is
 727          Pushed_Scope : Boolean := False;
 728
 729       begin
 730          --  We do not want to put the declaration we have created in the tree
 731          --  since it is often hard, and sometimes impossible to find a proper
 732          --  place for it (the impossible case arises for a packed array type
 733          --  with bounds depending on the discriminant, a declaration cannot
 734          --  be put inside the record, and the reference to the discriminant
 735          --  cannot be outside the record).
 736
 737          --  The solution is to analyze the declaration while temporarily
 738          --  attached to the tree at an appropriate point, and then we install
 739          --  the resulting type as an Itype in the packed array type field of
 740          --  the original type, so that no explicit declaration is required.
 741
 742          --  Note: the packed type is created in the scope of its parent
 743          --  type. There are at least some cases where the current scope
 744          --  is deeper, and so when this is the case, we temporarily reset
 745          --  the scope for the definition. This is clearly safe, since the
 746          --  first use of the packed array type will be the implicit
 747          --  reference from the corresponding unpacked type when it is
 748          --  elaborated.
 749
 750          if Is_Itype (Typ) then
 751             Set_Parent (Decl, Associated_Node_For_Itype (Typ));
 752          else
 753             Set_Parent (Decl, Declaration_Node (Typ));
 754          end if;
 755
 756          if Scope (Typ) /= Current_Scope then
 757             New_Scope (Scope (Typ));
 758             Pushed_Scope := True;
 759          end if;
 760
 761          Set_Is_Itype (PAT, True);
 762          Set_Packed_Array_Type (Typ, PAT);
 763          Analyze (Decl, Suppress => All_Checks);
 764
 765          if Pushed_Scope then
 766             Pop_Scope;
 767          end if;
 768
 769          --  Set Esize and RM_Size to the actual size of the packed object
 770          --  Do not reset RM_Size if already set, as happens in the case
 771          --  of a modular type
 772
 773          Set_Esize (PAT, Esiz);
 774
 775          if Unknown_RM_Size (PAT) then
 776             Set_RM_Size (PAT, Esiz);
 777          end if;
 778
 779          --  Set remaining fields of packed array type
 780
 781          Init_Alignment                (PAT);
 782          Set_Parent                    (PAT, Empty);
 783          Set_Associated_Node_For_Itype (PAT, Typ);
 784          Set_Is_Packed_Array_Type      (PAT, True);
 785          Set_Original_Array_Type       (PAT, Typ);
 786
 787          --  We definitely do not want to delay freezing for packed array
 788          --  types. This is of particular importance for the itypes that
 789          --  are generated for record components depending on discriminants
 790          --  where there is no place to put the freeze node.
 791
 792          Set_Has_Delayed_Freeze (PAT, False);
 793          Set_Has_Delayed_Freeze (Etype (PAT), False);
 794       end Install_PAT;
 795
 796       -----------------
 797       -- Set_PB_Type --
 798       -----------------
 799
 800       procedure Set_PB_Type is
 801       begin
 802          --  If the user has specified an explicit alignment for the
 803          --  type or component, take it into account.
 804
 805          if Csize <= 2 or else Csize = 4 or else Csize mod 2 /= 0
 806            or else Alignment (Typ) = 1
 807            or else Component_Alignment (Typ) = Calign_Storage_Unit
 808          then
 809             PB_Type := RTE (RE_Packed_Bytes1);
 810
 811          elsif Csize mod 4 /= 0
 812            or else Alignment (Typ) = 2
 813          then
 814             PB_Type := RTE (RE_Packed_Bytes2);
 815
 816          else
 817             PB_Type := RTE (RE_Packed_Bytes4);
 818          end if;
 819       end Set_PB_Type;
 820
 821    --  Start of processing for Create_Packed_Array_Type
 822
 823    begin
 824       --  If we already have a packed array type, nothing to do
 825
 826       if Present (Packed_Array_Type (Typ)) then
 827          return;
 828       end if;
 829
 830       --  If our immediate ancestor subtype is constrained, and it already
 831       --  has a packed array type, then just share the same type, since the
 832       --  bounds must be the same.
 833
 834       if Ekind (Typ) = E_Array_Subtype then
 835          Ancest := Ancestor_Subtype (Typ);
 836
 837          if Present (Ancest)
 838            and then Is_Constrained (Ancest)
 839            and then Present (Packed_Array_Type (Ancest))
 840          then
 841             Set_Packed_Array_Type (Typ, Packed_Array_Type (Ancest));
 842             return;
 843          end if;
 844       end if;
 845
 846       --  We preset the result type size from the size of the original array
 847       --  type, since this size clearly belongs to the packed array type. The
 848       --  size of the conceptual unpacked type is always set to unknown.
 849
 850       Esiz := Esize (Typ);
 851
 852       --  Case of an array where at least one index is of an enumeration
 853       --  type with a non-standard representation, but the component size
 854       --  is not appropriate for bit packing. This is the case where we
 855       --  have Is_Packed set (we would never be in this unit otherwise),
 856       --  but Is_Bit_Packed_Array is false.
 857
 858       --  Note that if the component size is appropriate for bit packing,
 859       --  then the circuit for the computation of the subscript properly
 860       --  deals with the non-standard enumeration type case by taking the
 861       --  Pos anyway.
 862
 863       if not Is_Bit_Packed_Array (Typ) then
 864
 865          --  Here we build a declaration:
 866
 867          --    type tttP is array (index1, index2, ...) of component_type
 868
 869          --  where index1, index2, are the index types. These are the same
 870          --  as the index types of the original array, except for the non-
 871          --  standard representation enumeration type case, where we have
 872          --  two subcases.
 873
 874          --  For the unconstrained array case, we use
 875
 876          --    Natural range <>
 877
 878          --  For the constrained case, we use
 879
 880          --    Natural range Enum_Type'Pos (Enum_Type'First) ..
 881          --                  Enum_Type'Pos (Enum_Type'Last);
 882
 883          PAT :=
 884            Make_Defining_Identifier (Loc,
 885              Chars => New_External_Name (Chars (Typ), 'P'));
 886
 887          Set_Packed_Array_Type (Typ, PAT);
 888
 889          declare
 890             Indexes   : List_Id := New_List;
 891             Indx      : Node_Id;
 892             Indx_Typ  : Entity_Id;
 893             Enum_Case : Boolean;
 894             Typedef   : Node_Id;
 895
 896          begin
 897             Indx := First_Index (Typ);
 898
 899             while Present (Indx) loop
 900                Indx_Typ := Etype (Indx);
 901
 902                Enum_Case := Is_Enumeration_Type (Indx_Typ)
 903                               and then Has_Non_Standard_Rep (Indx_Typ);
 904
 905                --  Unconstrained case
 906
 907                if not Is_Constrained (Typ) then
 908                   if Enum_Case then
 909                      Indx_Typ := Standard_Natural;
 910                   end if;
 911
 912                   Append_To (Indexes, New_Occurrence_Of (Indx_Typ, Loc));
 913
 914                --  Constrained case
 915
 916                else
 917                   if not Enum_Case then
 918                      Append_To (Indexes, New_Occurrence_Of (Indx_Typ, Loc));
 919
 920                   else
 921                      Append_To (Indexes,
 922                        Make_Subtype_Indication (Loc,
 923                          Subtype_Mark =>
 924                            New_Occurrence_Of (Standard_Natural, Loc),
 925                          Constraint =>
 926                            Make_Range_Constraint (Loc,
 927                              Range_Expression =>
 928                                Make_Range (Loc,
 929                                  Low_Bound =>
 930                                    Make_Attribute_Reference (Loc,
 931                                      Prefix =>
 932                                        New_Occurrence_Of (Indx_Typ, Loc),
 933                                      Attribute_Name => Name_Pos,
 934                                      Expressions => New_List (
 935                                        Make_Attribute_Reference (Loc,
 936                                          Prefix =>
 937                                            New_Occurrence_Of (Indx_Typ, Loc),
 938                                          Attribute_Name => Name_First))),
 939
 940                                  High_Bound =>
 941                                    Make_Attribute_Reference (Loc,
 942                                      Prefix =>
 943                                        New_Occurrence_Of (Indx_Typ, Loc),
 944                                      Attribute_Name => Name_Pos,
 945                                      Expressions => New_List (
 946                                        Make_Attribute_Reference (Loc,
 947                                          Prefix =>
 948                                            New_Occurrence_Of (Indx_Typ, Loc),
 949                                          Attribute_Name => Name_Last)))))));
 950
 951                   end if;
 952                end if;
 953
 954                Next_Index (Indx);
 955             end loop;
 956
 957             if not Is_Constrained (Typ) then
 958                Typedef :=
 959                  Make_Unconstrained_Array_Definition (Loc,
 960                    Subtype_Marks => Indexes,
 961                    Subtype_Indication =>
 962                       New_Occurrence_Of (Ctyp, Loc));
 963
 964             else
 965                Typedef :=
 966                   Make_Constrained_Array_Definition (Loc,
 967                     Discrete_Subtype_Definitions => Indexes,
 968                     Subtype_Indication =>
 969                       New_Occurrence_Of (Ctyp, Loc));
 970             end if;
 971
 972             Decl :=
 973               Make_Full_Type_Declaration (Loc,
 974                 Defining_Identifier => PAT,
 975                 Type_Definition => Typedef);
 976          end;
 977
 978          --  Set type as packed array type and install it
 979
 980          Set_Is_Packed_Array_Type (PAT);
 981          Install_PAT;
 982          return;
 983
 984       --  Case of bit-packing required for unconstrained array. We create
 985       --  a subtype that is equivalent to use Packed_Bytes{1,2,4} as needed.
 986
 987       elsif not Is_Constrained (Typ) then
 988          PAT :=
 989            Make_Defining_Identifier (Loc,
 990              Chars => Make_Packed_Array_Type_Name (Typ, Csize));
 991
 992          Set_Packed_Array_Type (Typ, PAT);
 993          Set_PB_Type;
 994
 995          Decl :=
 996            Make_Subtype_Declaration (Loc,
 997              Defining_Identifier => PAT,
 998                Subtype_Indication => New_Occurrence_Of (PB_Type, Loc));
 999          Install_PAT;
1000          return;
1001
1002       --  Remaining code is for the case of bit-packing for constrained array
1003
1004       --  The name of the packed array subtype is
1005
1006       --    ttt___Xsss
1007
1008       --  where sss is the component size in bits and ttt is the name of
1009       --  the parent packed type.
1010
1011       else
1012          PAT :=
1013            Make_Defining_Identifier (Loc,
1014              Chars => Make_Packed_Array_Type_Name (Typ, Csize));
1015
1016          Set_Packed_Array_Type (Typ, PAT);
1017
1018          --  Build an expression for the length of the array in bits.
1019          --  This is the product of the length of each of the dimensions
1020
1021          declare
1022             J : Nat := 1;
1023
1024          begin
1025             Len_Expr := Empty; -- suppress junk warning
1026
1027             loop
1028                Len_Dim :=
1029                  Make_Attribute_Reference (Loc,
1030                    Attribute_Name => Name_Length,
1031                    Prefix         => New_Occurrence_Of (Typ, Loc),
1032                    Expressions    => New_List (
1033                      Make_Integer_Literal (Loc, J)));
1034
1035                if J = 1 then
1036                   Len_Expr := Len_Dim;
1037
1038                else
1039                   Len_Expr :=
1040                     Make_Op_Multiply (Loc,
1041                       Left_Opnd  => Len_Expr,
1042                       Right_Opnd => Len_Dim);
1043                end if;
1044
1045                J := J + 1;
1046                exit when J > Number_Dimensions (Typ);
1047             end loop;
1048          end;
1049
1050          --  Temporarily attach the length expression to the tree and analyze
1051          --  and resolve it, so that we can test its value. We assume that the
1052          --  total length fits in type Integer.
1053
1054          Set_Parent (Len_Expr, Typ);
1055          Analyze_And_Resolve (Len_Expr, Standard_Integer);
1056
1057          --  Use a modular type if possible. We can do this if we are we
1058          --  have static bounds, and the length is small enough, and the
1059          --  length is not zero. We exclude the zero length case because the
1060          --  size of things is always at least one, and the zero length object
1061          --  would have an anomous size
1062
1063          if Compile_Time_Known_Value (Len_Expr) then
1064             Len_Bits := Expr_Value (Len_Expr) * Csize;
1065
1066             --  We normally consider small enough to mean no larger than the
1067             --  value of System_Max_Binary_Modulus_Power, except that in
1068             --  No_Run_Time mode, we use the Word Size on machines for
1069             --  which double length shifts are not generated in line.
1070
1071             if Len_Bits > 0
1072               and then
1073                 (Len_Bits <= System_Word_Size
1074                    or else (Len_Bits <= System_Max_Binary_Modulus_Power
1075                               and then (not No_Run_Time
1076                                           or else
1077                                         Long_Shifts_Inlined_On_Target)))
1078             then
1079                --  We can use the modular type, it has the form:
1080
1081                --    subtype tttPn is btyp
1082                --      range 0 .. 2 ** (Esize (Typ) * Csize) - 1;
1083
1084                --  Here Siz is 1, 2 or 4, as computed above, and btyp is either
1085                --  Unsigned or Long_Long_Unsigned depending on the length.
1086
1087                if Len_Bits <= Standard_Integer_Size then
1088                   Btyp := RTE (RE_Unsigned);
1089                else
1090                   Btyp := RTE (RE_Long_Long_Unsigned);
1091                end if;
1092
1093                Lit := Make_Integer_Literal (Loc, 2 ** Len_Bits - 1);
1094                Set_Print_In_Hex (Lit);
1095
1096                Decl :=
1097                  Make_Subtype_Declaration (Loc,
1098                    Defining_Identifier => PAT,
1099                      Subtype_Indication =>
1100                        Make_Subtype_Indication (Loc,
1101                          Subtype_Mark => New_Occurrence_Of (Btyp, Loc),
1102
1103                          Constraint =>
1104                            Make_Range_Constraint (Loc,
1105                              Range_Expression =>
1106                                Make_Range (Loc,
1107                                  Low_Bound =>
1108                                    Make_Integer_Literal (Loc, 0),
1109                                  High_Bound => Lit))));
1110
1111                if Esiz = Uint_0 then
1112                   Esiz := Len_Bits;
1113                end if;
1114
1115                Install_PAT;
1116                return;
1117             end if;
1118          end if;
1119
1120          --  Could not use a modular type, for all other cases, we build
1121          --  a packed array subtype:
1122
1123          --    subtype tttPn is
1124          --      System.Packed_Bytes{1,2,4} (0 .. (Bits + 7) / 8 - 1);
1125
1126          --  Bits is the length of the array in bits.
1127
1128          Set_PB_Type;
1129
1130          Bits_U1 :=
1131            Make_Op_Add (Loc,
1132              Left_Opnd =>
1133                Make_Op_Multiply (Loc,
1134                  Left_Opnd  =>
1135                    Make_Integer_Literal (Loc, Csize),
1136                  Right_Opnd => Len_Expr),
1137
1138              Right_Opnd =>
1139                Make_Integer_Literal (Loc, 7));
1140
1141          Set_Paren_Count (Bits_U1, 1);
1142
1143          PAT_High :=
1144            Make_Op_Subtract (Loc,
1145              Left_Opnd =>
1146                Make_Op_Divide (Loc,
1147                  Left_Opnd => Bits_U1,
1148                  Right_Opnd => Make_Integer_Literal (Loc, 8)),
1149              Right_Opnd => Make_Integer_Literal (Loc, 1));
1150
1151          Decl :=
1152            Make_Subtype_Declaration (Loc,
1153              Defining_Identifier => PAT,
1154                Subtype_Indication =>
1155                  Make_Subtype_Indication (Loc,
1156                    Subtype_Mark => New_Occurrence_Of (PB_Type, Loc),
1157                    Constraint =>
1158
1159                      Make_Index_Or_Discriminant_Constraint (Loc,
1160                        Constraints => New_List (
1161                          Make_Range (Loc,
1162                            Low_Bound =>
1163                              Make_Integer_Literal (Loc, 0),
1164                            High_Bound => PAT_High)))));
1165
1166          Install_PAT;
1167       end if;
1168    end Create_Packed_Array_Type;
1169
1170    -----------------------------------
1171    -- Expand_Bit_Packed_Element_Set --
1172    -----------------------------------
1173
1174    procedure Expand_Bit_Packed_Element_Set (N : Node_Id) is
1175       Loc : constant Source_Ptr := Sloc (N);
1176       Lhs : constant Node_Id    := Name (N);
1177
1178       Ass_OK : constant Boolean := Assignment_OK (Lhs);
1179       --  Used to preserve assignment OK status when assignment is rewritten
1180
1181       Rhs : Node_Id := Expression (N);
1182       --  Initially Rhs is the right hand side value, it will be replaced
1183       --  later by an appropriate unchecked conversion for the assignment.
1184
1185       Obj    : Node_Id;
1186       Atyp   : Entity_Id;
1187       PAT    : Entity_Id;
1188       Ctyp   : Entity_Id;
1189       Csiz   : Int;
1190       Shift  : Node_Id;
1191       Cmask  : Uint;
1192
1193       New_Lhs : Node_Id;
1194       New_Rhs : Node_Id;
1195
1196       Rhs_Val_Known : Boolean;
1197       Rhs_Val       : Uint;
1198       --  If the value of the right hand side as an integer constant is
1199       --  known at compile time, Rhs_Val_Known is set True, and Rhs_Val
1200       --  contains the value. Otherwise Rhs_Val_Known is set False, and
1201       --  the Rhs_Val is undefined.
1202
1203    begin
1204       pragma Assert (Is_Bit_Packed_Array (Etype (Prefix (Lhs))));
1205
1206       Obj := Relocate_Node (Prefix (Lhs));
1207       Convert_To_Actual_Subtype (Obj);
1208       Atyp := Etype (Obj);
1209       PAT  := Packed_Array_Type (Atyp);
1210       Ctyp := Component_Type (Atyp);
1211       Csiz := UI_To_Int (Component_Size (Atyp));
1212
1213       --  We convert the right hand side to the proper subtype to ensure
1214       --  that an appropriate range check is made (since the normal range
1215       --  check from assignment will be lost in the transformations). This
1216       --  conversion is analyzed immediately so that subsequent processing
1217       --  can work with an analyzed Rhs (and e.g. look at its Etype)
1218
1219       Rhs := Convert_To (Ctyp, Rhs);
1220       Set_Parent (Rhs, N);
1221       Analyze_And_Resolve (Rhs, Ctyp);
1222
1223       --  Case of component size 1,2,4 or any component size for the modular
1224       --  case. These are the cases for which we can inline the code.
1225
1226       if Csiz = 1 or else Csiz = 2 or else Csiz = 4
1227         or else (Present (PAT) and then Is_Modular_Integer_Type (PAT))
1228       then
1229          Setup_Inline_Packed_Array_Reference (Lhs, Atyp, Obj, Cmask, Shift);
1230
1231          --  The statement to be generated is:
1232
1233          --    Obj := atyp!((Obj and Mask1) or (shift_left (rhs, shift)))
1234
1235          --      where mask1 is obtained by shifting Cmask left Shift bits
1236          --      and then complementing the result.
1237
1238          --      the "and Mask1" is omitted if rhs is constant and all 1 bits
1239
1240          --      the "or ..." is omitted if rhs is constant and all 0 bits
1241
1242          --      rhs is converted to the appropriate type.
1243
1244          --      The result is converted back to the array type, since
1245          --      otherwise we lose knowledge of the packed nature.
1246
1247          --  Determine if right side is all 0 bits or all 1 bits
1248
1249          if Compile_Time_Known_Value (Rhs) then
1250             Rhs_Val       := Expr_Rep_Value (Rhs);
1251             Rhs_Val_Known := True;
1252
1253          --  The following test catches the case of an unchecked conversion
1254          --  of an integer literal. This results from optimizing aggregates
1255          --  of packed types.
1256
1257          elsif Nkind (Rhs) = N_Unchecked_Type_Conversion
1258            and then Compile_Time_Known_Value (Expression (Rhs))
1259          then
1260             Rhs_Val       := Expr_Rep_Value (Expression (Rhs));
1261             Rhs_Val_Known := True;
1262
1263          else
1264             Rhs_Val       := No_Uint;
1265             Rhs_Val_Known := False;
1266          end if;
1267
1268          --  Some special checks for the case where the right hand value
1269          --  is known at compile time. Basically we have to take care of
1270          --  the implicit conversion to the subtype of the component object.
1271
1272          if Rhs_Val_Known then
1273
1274             --  If we have a biased component type then we must manually do
1275             --  the biasing, since we are taking responsibility in this case
1276             --  for constructing the exact bit pattern to be used.
1277
1278             if Has_Biased_Representation (Ctyp) then
1279                Rhs_Val := Rhs_Val - Expr_Rep_Value (Type_Low_Bound (Ctyp));
1280             end if;
1281
1282             --  For a negative value, we manually convert the twos complement
1283             --  value to a corresponding unsigned value, so that the proper
1284             --  field width is maintained. If we did not do this, we would
1285             --  get too many leading sign bits later on.
1286
1287             if Rhs_Val < 0 then
1288                Rhs_Val := 2 ** UI_From_Int (Csiz) + Rhs_Val;
1289             end if;
1290          end if;
1291
1292          New_Lhs := Duplicate_Subexpr (Obj, True);
1293          New_Rhs := Duplicate_Subexpr (Obj);
1294
1295          --  First we deal with the "and"
1296
1297          if not Rhs_Val_Known or else Rhs_Val /= Cmask then
1298             declare
1299                Mask1 : Node_Id;
1300                Lit   : Node_Id;
1301
1302             begin
1303                if Compile_Time_Known_Value (Shift) then
1304                   Mask1 :=
1305                     Make_Integer_Literal (Loc,
1306                       Modulus (Etype (Obj)) - 1 -
1307                                  (Cmask * (2 ** Expr_Value (Shift))));
1308                   Set_Print_In_Hex (Mask1);
1309
1310                else
1311                   Lit := Make_Integer_Literal (Loc, Cmask);
1312                   Set_Print_In_Hex (Lit);
1313                   Mask1 :=
1314                     Make_Op_Not (Loc,
1315                       Right_Opnd => Make_Shift_Left (Lit, Shift));
1316                end if;
1317
1318                New_Rhs :=
1319                  Make_Op_And (Loc,
1320                    Left_Opnd  => New_Rhs,
1321                    Right_Opnd => Mask1);
1322             end;
1323          end if;
1324
1325          --  Then deal with the "or"
1326
1327          if not Rhs_Val_Known or else Rhs_Val /= 0 then
1328             declare
1329                Or_Rhs : Node_Id;
1330
1331                procedure Fixup_Rhs;
1332                --  Adjust Rhs by bias if biased representation for components
1333                --  or remove extraneous high order sign bits if signed.
1334
1335                procedure Fixup_Rhs is
1336                   Etyp : constant Entity_Id := Etype (Rhs);
1337
1338                begin
1339                   --  For biased case, do the required biasing by simply
1340                   --  converting to the biased subtype (the conversion
1341                   --  will generate the required bias).
1342
1343                   if Has_Biased_Representation (Ctyp) then
1344                      Rhs := Convert_To (Ctyp, Rhs);
1345
1346                   --  For a signed integer type that is not biased, generate
1347                   --  a conversion to unsigned to strip high order sign bits.
1348
1349                   elsif Is_Signed_Integer_Type (Ctyp) then
1350                      Rhs := Unchecked_Convert_To (RTE (Bits_Id (Csiz)), Rhs);
1351                   end if;
1352
1353                   --  Set Etype, since it can be referenced before the
1354                   --  node is completely analyzed.
1355
1356                   Set_Etype (Rhs, Etyp);
1357
1358                   --  We now need to do an unchecked conversion of the
1359                   --  result to the target type, but it is important that
1360                   --  this conversion be a right justified conversion and
1361                   --  not a left justified conversion.
1362
1363                   Rhs := RJ_Unchecked_Convert_To (Etype (Obj), Rhs);
1364
1365                end Fixup_Rhs;
1366
1367             begin
1368                if Rhs_Val_Known
1369                  and then Compile_Time_Known_Value (Shift)
1370                then
1371                   Or_Rhs :=
1372                     Make_Integer_Literal (Loc,
1373                       Rhs_Val * (2 ** Expr_Value (Shift)));
1374                   Set_Print_In_Hex (Or_Rhs);
1375
1376                else
1377                   --  We have to convert the right hand side to Etype (Obj).
1378                   --  A special case case arises if what we have now is a Val
1379                   --  attribute reference whose expression type is Etype (Obj).
1380                   --  This happens for assignments of fields from the same
1381                   --  array. In this case we get the required right hand side
1382                   --  by simply removing the inner attribute reference.
1383
1384                   if Nkind (Rhs) = N_Attribute_Reference
1385                     and then Attribute_Name (Rhs) = Name_Val
1386                     and then Etype (First (Expressions (Rhs))) = Etype (Obj)
1387                   then
1388                      Rhs := Relocate_Node (First (Expressions (Rhs)));
1389                      Fixup_Rhs;
1390
1391                   --  If the value of the right hand side is a known integer
1392                   --  value, then just replace it by an untyped constant,
1393                   --  which will be properly retyped when we analyze and
1394                   --  resolve the expression.
1395
1396                   elsif Rhs_Val_Known then
1397
1398                      --  Note that Rhs_Val has already been normalized to
1399                      --  be an unsigned value with the proper number of bits.
1400
1401                      Rhs :=
1402                        Make_Integer_Literal (Loc, Rhs_Val);
1403
1404                   --  Otherwise we need an unchecked conversion
1405
1406                   else
1407                      Fixup_Rhs;
1408                   end if;
1409
1410                   Or_Rhs := Make_Shift_Left (Rhs, Shift);
1411                end if;
1412
1413                if Nkind (New_Rhs) = N_Op_And then
1414                   Set_Paren_Count (New_Rhs, 1);
1415                end if;
1416
1417                New_Rhs :=
1418                  Make_Op_Or (Loc,
1419                    Left_Opnd  => New_Rhs,
1420                    Right_Opnd => Or_Rhs);
1421             end;
1422          end if;
1423
1424          --  Now do the rewrite
1425
1426          Rewrite (N,
1427            Make_Assignment_Statement (Loc,
1428              Name       => New_Lhs,
1429              Expression =>
1430                Unchecked_Convert_To (Etype (New_Lhs), New_Rhs)));
1431          Set_Assignment_OK (Name (N), Ass_OK);
1432
1433       --  All other component sizes for non-modular case
1434
1435       else
1436          --  We generate
1437
1438          --    Set_nn (Arr'address, Subscr, Bits_nn!(Rhs))
1439
1440          --  where Subscr is the computed linear subscript.
1441
1442          declare
1443             Bits_nn : constant Entity_Id := RTE (Bits_Id (Csiz));
1444             Set_nn  : Entity_Id;
1445             Subscr  : Node_Id;
1446             Atyp    : Entity_Id;
1447
1448          begin
1449             --  Acquire proper Set entity. We use the aligned or unaligned
1450             --  case as appropriate.
1451
1452             if Known_Aligned_Enough (Obj, Csiz) then
1453                Set_nn := RTE (Set_Id (Csiz));
1454             else
1455                Set_nn := RTE (SetU_Id (Csiz));
1456             end if;
1457
1458             --  Now generate the set reference
1459
1460             Obj := Relocate_Node (Prefix (Lhs));
1461             Convert_To_Actual_Subtype (Obj);
1462             Atyp := Etype (Obj);
1463             Compute_Linear_Subscript (Atyp, Lhs, Subscr);
1464
1465             Rewrite (N,
1466               Make_Procedure_Call_Statement (Loc,
1467                   Name => New_Occurrence_Of (Set_nn, Loc),
1468                   Parameter_Associations => New_List (
1469                     Make_Byte_Aligned_Attribute_Reference (Loc,
1470                       Attribute_Name => Name_Address,
1471                       Prefix         => Obj),
1472                     Subscr,
1473                     Unchecked_Convert_To (Bits_nn,
1474                       Convert_To (Ctyp, Rhs)))));
1475
1476          end;
1477       end if;
1478
1479       Analyze (N, Suppress => All_Checks);
1480    end Expand_Bit_Packed_Element_Set;
1481
1482    -------------------------------------
1483    -- Expand_Packed_Address_Reference --
1484    -------------------------------------
1485
1486    procedure Expand_Packed_Address_Reference (N : Node_Id) is
1487       Loc    : constant Source_Ptr := Sloc (N);
1488       Ploc   : Source_Ptr;
1489       Pref   : Node_Id;
1490       Expr   : Node_Id;
1491       Term   : Node_Id;
1492       Atyp   : Entity_Id;
1493       Subscr : Node_Id;
1494
1495    begin
1496       Pref := Prefix (N);
1497       Expr := Empty;
1498
1499       --  We build up an expression serially that has the form
1500
1501       --    outer_object'Address
1502       --      + (linear-subscript * component_size  for each array reference
1503       --      +  field'Bit_Position                 for each record field
1504       --      +  ...
1505       --      +  ...) / Storage_Unit;
1506
1507       --  Some additional conversions are required to deal with the addition
1508       --  operation, which is not normally visible to generated code.
1509
1510       loop
1511          Ploc := Sloc (Pref);
1512
1513          if Nkind (Pref) = N_Indexed_Component then
1514             Convert_To_Actual_Subtype (Prefix (Pref));
1515             Atyp := Etype (Prefix (Pref));
1516             Compute_Linear_Subscript (Atyp, Pref, Subscr);
1517
1518             Term :=
1519               Make_Op_Multiply (Ploc,
1520                 Left_Opnd => Subscr,
1521                 Right_Opnd =>
1522                  Make_Attribute_Reference (Ploc,
1523                    Prefix         => New_Occurrence_Of (Atyp, Ploc),
1524                    Attribute_Name => Name_Component_Size));
1525
1526          elsif Nkind (Pref) = N_Selected_Component then
1527             Term :=
1528               Make_Attribute_Reference (Ploc,
1529                 Prefix         => Selector_Name (Pref),
1530                 Attribute_Name => Name_Bit_Position);
1531
1532          else
1533             exit;
1534          end if;
1535
1536          Term := Convert_To (RTE (RE_Integer_Address), Term);
1537
1538          if No (Expr) then
1539             Expr := Term;
1540
1541          else
1542             Expr :=
1543               Make_Op_Add (Ploc,
1544                 Left_Opnd  => Expr,
1545                 Right_Opnd => Term);
1546          end if;
1547
1548          Pref := Prefix (Pref);
1549       end loop;
1550
1551       Rewrite (N,
1552         Unchecked_Convert_To (RTE (RE_Address),
1553           Make_Op_Add (Loc,
1554             Left_Opnd =>
1555               Unchecked_Convert_To (RTE (RE_Integer_Address),
1556                 Make_Attribute_Reference (Loc,
1557                   Prefix         => Pref,
1558                   Attribute_Name => Name_Address)),
1559
1560             Right_Opnd =>
1561               Make_Op_Divide (Loc,
1562                 Left_Opnd => Expr,
1563                 Right_Opnd =>
1564                   Make_Integer_Literal (Loc, System_Storage_Unit)))));
1565
1566       Analyze_And_Resolve (N, RTE (RE_Address));
1567    end Expand_Packed_Address_Reference;
1568
1569    ------------------------------------
1570    -- Expand_Packed_Boolean_Operator --
1571    ------------------------------------
1572
1573    --  This routine expands "a op b" for the packed cases
1574
1575    procedure Expand_Packed_Boolean_Operator (N : Node_Id) is
1576       Loc : constant Source_Ptr := Sloc (N);
1577       Typ : constant Entity_Id  := Etype (N);
1578       L   : constant Node_Id    := Relocate_Node (Left_Opnd  (N));
1579       R   : constant Node_Id    := Relocate_Node (Right_Opnd (N));
1580
1581       Ltyp : Entity_Id;
1582       Rtyp : Entity_Id;
1583       PAT  : Entity_Id;
1584
1585    begin
1586       Convert_To_Actual_Subtype (L);
1587       Convert_To_Actual_Subtype (R);
1588
1589       Ensure_Defined (Etype (L), N);
1590       Ensure_Defined (Etype (R), N);
1591
1592       Apply_Length_Check (R, Etype (L));
1593
1594       Ltyp := Etype (L);
1595       Rtyp := Etype (R);
1596
1597       --  First an odd and silly test. We explicitly check for the XOR
1598       --  case where the component type is True .. True, since this will
1599       --  raise constraint error. A special check is required since CE
1600       --  will not be required other wise (cf Expand_Packed_Not).
1601
1602       --  No such check is required for AND and OR, since for both these
1603       --  cases False op False = False, and True op True = True.
1604
1605       if Nkind (N) = N_Op_Xor then
1606          declare
1607             CT : constant Entity_Id := Component_Type (Rtyp);
1608             BT : constant Entity_Id := Base_Type (CT);
1609
1610          begin
1611             Insert_Action (N,
1612               Make_Raise_Constraint_Error (Loc,
1613                 Condition =>
1614                   Make_Op_And (Loc,
1615                     Left_Opnd =>
1616                       Make_Op_Eq (Loc,
1617                         Left_Opnd =>
1618                           Make_Attribute_Reference (Loc,
1619                             Prefix         => New_Occurrence_Of (CT, Loc),
1620                             Attribute_Name => Name_First),
1621
1622                         Right_Opnd =>
1623                           Convert_To (BT,
1624                             New_Occurrence_Of (Standard_True, Loc))),
1625
1626                     Right_Opnd =>
1627                       Make_Op_Eq (Loc,
1628                         Left_Opnd =>
1629                           Make_Attribute_Reference (Loc,
1630                             Prefix         => New_Occurrence_Of (CT, Loc),
1631                             Attribute_Name => Name_Last),
1632
1633                         Right_Opnd =>
1634                           Convert_To (BT,
1635                             New_Occurrence_Of (Standard_True, Loc)))),
1636                 Reason => CE_Range_Check_Failed));
1637          end;
1638       end if;
1639
1640       --  Now that that silliness is taken care of, get packed array type
1641
1642       Convert_To_PAT_Type (L);
1643       Convert_To_PAT_Type (R);
1644
1645       PAT := Etype (L);
1646
1647       --  For the modular case, we expand a op b into
1648
1649       --    rtyp!(pat!(a) op pat!(b))
1650
1651       --  where rtyp is the Etype of the left operand. Note that we do not
1652       --  convert to the base type, since this would be unconstrained, and
1653       --  hence not have a corresponding packed array type set.
1654
1655       if Is_Modular_Integer_Type (PAT) then
1656          declare
1657             P : Node_Id;
1658
1659          begin
1660             if Nkind (N) = N_Op_And then
1661                P := Make_Op_And (Loc, L, R);
1662
1663             elsif Nkind (N) = N_Op_Or then
1664                P := Make_Op_Or  (Loc, L, R);
1665
1666             else -- Nkind (N) = N_Op_Xor
1667                P := Make_Op_Xor (Loc, L, R);
1668             end if;
1669
1670             Rewrite (N, Unchecked_Convert_To (Rtyp, P));
1671          end;
1672
1673       --  For the array case, we insert the actions
1674
1675       --    Result : Ltype;
1676
1677       --    System.Bitops.Bit_And/Or/Xor
1678       --     (Left'Address,
1679       --      Ltype'Length * Ltype'Component_Size;
1680       --      Right'Address,
1681       --      Rtype'Length * Rtype'Component_Size
1682       --      Result'Address);
1683
1684       --  where Left and Right are the Packed_Bytes{1,2,4} operands and
1685       --  the second argument and fourth arguments are the lengths of the
1686       --  operands in bits. Then we replace the expression by a reference
1687       --  to Result.
1688
1689       else
1690          declare
1691             Result_Ent : constant Entity_Id :=
1692                            Make_Defining_Identifier (Loc,
1693                              Chars => New_Internal_Name ('T'));
1694
1695             E_Id : RE_Id;
1696
1697          begin
1698             if Nkind (N) = N_Op_And then
1699                E_Id := RE_Bit_And;
1700
1701             elsif Nkind (N) = N_Op_Or then
1702                E_Id := RE_Bit_Or;
1703
1704             else -- Nkind (N) = N_Op_Xor
1705                E_Id := RE_Bit_Xor;
1706             end if;
1707
1708             Insert_Actions (N, New_List (
1709
1710               Make_Object_Declaration (Loc,
1711                 Defining_Identifier => Result_Ent,
1712                 Object_Definition => New_Occurrence_Of (Ltyp, Loc)),
1713
1714               Make_Procedure_Call_Statement (Loc,
1715                 Name => New_Occurrence_Of (RTE (E_Id), Loc),
1716                   Parameter_Associations => New_List (
1717
1718                     Make_Byte_Aligned_Attribute_Reference (Loc,
1719                       Attribute_Name => Name_Address,
1720                       Prefix         => L),
1721
1722                     Make_Op_Multiply (Loc,
1723                       Left_Opnd =>
1724                         Make_Attribute_Reference (Loc,
1725                           Prefix =>
1726                             New_Occurrence_Of
1727                               (Etype (First_Index (Ltyp)), Loc),
1728                           Attribute_Name => Name_Range_Length),
1729                       Right_Opnd =>
1730                         Make_Integer_Literal (Loc, Component_Size (Ltyp))),
1731
1732                     Make_Byte_Aligned_Attribute_Reference (Loc,
1733                       Attribute_Name => Name_Address,
1734                       Prefix         => R),
1735
1736                     Make_Op_Multiply (Loc,
1737                       Left_Opnd =>
1738                         Make_Attribute_Reference (Loc,
1739                           Prefix =>
1740                             New_Occurrence_Of
1741                               (Etype (First_Index (Rtyp)), Loc),
1742                           Attribute_Name => Name_Range_Length),
1743                       Right_Opnd =>
1744                         Make_Integer_Literal (Loc, Component_Size (Rtyp))),
1745
1746                     Make_Byte_Aligned_Attribute_Reference (Loc,
1747                       Attribute_Name => Name_Address,
1748                       Prefix => New_Occurrence_Of (Result_Ent, Loc))))));
1749
1750             Rewrite (N,
1751               New_Occurrence_Of (Result_Ent, Loc));
1752          end;
1753       end if;
1754
1755       Analyze_And_Resolve (N, Typ, Suppress => All_Checks);
1756    end Expand_Packed_Boolean_Operator;
1757
1758    -------------------------------------
1759    -- Expand_Packed_Element_Reference --
1760    -------------------------------------
1761
1762    procedure Expand_Packed_Element_Reference (N : Node_Id) is
1763       Loc   : constant Source_Ptr := Sloc (N);
1764       Obj   : Node_Id;
1765       Atyp  : Entity_Id;
1766       PAT   : Entity_Id;
1767       Ctyp  : Entity_Id;
1768       Csiz  : Int;
1769       Shift : Node_Id;
1770       Cmask : Uint;
1771       Lit   : Node_Id;
1772       Arg   : Node_Id;
1773
1774    begin
1775       --  If not bit packed, we have the enumeration case, which is easily
1776       --  dealt with (just adjust the subscripts of the indexed component)
1777
1778       --  Note: this leaves the result as an indexed component, which is
1779       --  still a variable, so can be used in the assignment case, as is
1780       --  required in the enumeration case.
1781
1782       if not Is_Bit_Packed_Array (Etype (Prefix (N))) then
1783          Setup_Enumeration_Packed_Array_Reference (N);
1784          return;
1785       end if;
1786
1787       --  Remaining processing is for the bit-packed case.
1788
1789       Obj := Relocate_Node (Prefix (N));
1790       Convert_To_Actual_Subtype (Obj);
1791       Atyp := Etype (Obj);
1792       PAT  := Packed_Array_Type (Atyp);
1793       Ctyp := Component_Type (Atyp);
1794       Csiz := UI_To_Int (Component_Size (Atyp));
1795
1796       --  Case of component size 1,2,4 or any component size for the modular
1797       --  case. These are the cases for which we can inline the code.
1798
1799       if Csiz = 1 or else Csiz = 2 or else Csiz = 4
1800         or else (Present (PAT) and then Is_Modular_Integer_Type (PAT))
1801       then
1802          Setup_Inline_Packed_Array_Reference (N, Atyp, Obj, Cmask, Shift);
1803          Lit := Make_Integer_Literal (Loc, Cmask);
1804          Set_Print_In_Hex (Lit);
1805
1806          --  We generate a shift right to position the field, followed by a
1807          --  masking operation to extract the bit field, and we finally do an
1808          --  unchecked conversion to convert the result to the required target.
1809
1810          --  Note that the unchecked conversion automatically deals with the
1811          --  bias if we are dealing with a biased representation. What will
1812          --  happen is that we temporarily generate the biased representation,
1813          --  but almost immediately that will be converted to the original
1814          --  unbiased component type, and the bias will disappear.
1815
1816          Arg :=
1817            Make_Op_And (Loc,
1818              Left_Opnd  => Make_Shift_Right (Obj, Shift),
1819              Right_Opnd => Lit);
1820
1821          Analyze_And_Resolve (Arg);
1822
1823          Rewrite (N,
1824            RJ_Unchecked_Convert_To (Ctyp, Arg));
1825
1826       --  All other component sizes for non-modular case
1827
1828       else
1829          --  We generate
1830
1831          --    Component_Type!(Get_nn (Arr'address, Subscr))
1832
1833          --  where Subscr is the computed linear subscript.
1834
1835          declare
1836             Get_nn : Entity_Id;
1837             Subscr : Node_Id;
1838
1839          begin
1840             --  Acquire proper Get entity. We use the aligned or unaligned
1841             --  case as appropriate.
1842
1843             if Known_Aligned_Enough (Obj, Csiz) then
1844                Get_nn := RTE (Get_Id (Csiz));
1845             else
1846                Get_nn := RTE (GetU_Id (Csiz));
1847             end if;
1848
1849             --  Now generate the get reference
1850
1851             Compute_Linear_Subscript (Atyp, N, Subscr);
1852
1853             Rewrite (N,
1854               Unchecked_Convert_To (Ctyp,
1855                 Make_Function_Call (Loc,
1856                   Name => New_Occurrence_Of (Get_nn, Loc),
1857                   Parameter_Associations => New_List (
1858                     Make_Byte_Aligned_Attribute_Reference (Loc,
1859                       Attribute_Name => Name_Address,
1860                       Prefix         => Obj),
1861                     Subscr))));
1862          end;
1863       end if;
1864
1865       Analyze_And_Resolve (N, Ctyp, Suppress => All_Checks);
1866
1867    end Expand_Packed_Element_Reference;
1868
1869    ----------------------
1870    -- Expand_Packed_Eq --
1871    ----------------------
1872
1873    --  Handles expansion of "=" on packed array types
1874
1875    procedure Expand_Packed_Eq (N : Node_Id) is
1876       Loc : constant Source_Ptr := Sloc (N);
1877       L   : constant Node_Id    := Relocate_Node (Left_Opnd  (N));
1878       R   : constant Node_Id    := Relocate_Node (Right_Opnd (N));
1879
1880       LLexpr : Node_Id;
1881       RLexpr : Node_Id;
1882
1883       Ltyp : Entity_Id;
1884       Rtyp : Entity_Id;
1885       PAT  : Entity_Id;
1886
1887    begin
1888       Convert_To_Actual_Subtype (L);
1889       Convert_To_Actual_Subtype (R);
1890       Ltyp := Underlying_Type (Etype (L));
1891       Rtyp := Underlying_Type (Etype (R));
1892
1893       Convert_To_PAT_Type (L);
1894       Convert_To_PAT_Type (R);
1895       PAT := Etype (L);
1896
1897       LLexpr :=
1898         Make_Op_Multiply (Loc,
1899           Left_Opnd =>
1900             Make_Attribute_Reference (Loc,
1901               Attribute_Name => Name_Length,
1902               Prefix         => New_Occurrence_Of (Ltyp, Loc)),
1903           Right_Opnd =>
1904             Make_Integer_Literal (Loc, Component_Size (Ltyp)));
1905
1906       RLexpr :=
1907         Make_Op_Multiply (Loc,
1908           Left_Opnd =>
1909             Make_Attribute_Reference (Loc,
1910               Attribute_Name => Name_Length,
1911               Prefix         => New_Occurrence_Of (Rtyp, Loc)),
1912           Right_Opnd =>
1913             Make_Integer_Literal (Loc, Component_Size (Rtyp)));
1914
1915       --  For the modular case, we transform the comparison to:
1916
1917       --    Ltyp'Length = Rtyp'Length and then PAT!(L) = PAT!(R)
1918
1919       --  where PAT is the packed array type. This works fine, since in the
1920       --  modular case we guarantee that the unused bits are always zeroes.
1921       --  We do have to compare the lengths because we could be comparing
1922       --  two different subtypes of the same base type.
1923
1924       if Is_Modular_Integer_Type (PAT) then
1925          Rewrite (N,
1926            Make_And_Then (Loc,
1927              Left_Opnd =>
1928                Make_Op_Eq (Loc,
1929                  Left_Opnd  => LLexpr,
1930                  Right_Opnd => RLexpr),
1931
1932              Right_Opnd =>
1933                Make_Op_Eq (Loc,
1934                  Left_Opnd => L,
1935                  Right_Opnd => R)));
1936
1937       --  For the non-modular case, we call a runtime routine
1938
1939       --    System.Bit_Ops.Bit_Eq
1940       --      (L'Address, L_Length, R'Address, R_Length)
1941
1942       --  where PAT is the packed array type, and the lengths are the lengths
1943       --  in bits of the original packed arrays. This routine takes care of
1944       --  not comparing the unused bits in the last byte.
1945
1946       else
1947          Rewrite (N,
1948            Make_Function_Call (Loc,
1949              Name => New_Occurrence_Of (RTE (RE_Bit_Eq), Loc),
1950              Parameter_Associations => New_List (
1951                Make_Byte_Aligned_Attribute_Reference (Loc,
1952                  Attribute_Name => Name_Address,
1953                  Prefix         => L),
1954
1955                LLexpr,
1956
1957                Make_Byte_Aligned_Attribute_Reference (Loc,
1958                  Attribute_Name => Name_Address,
1959                  Prefix         => R),
1960
1961                RLexpr)));
1962       end if;
1963
1964       Analyze_And_Resolve (N, Standard_Boolean, Suppress => All_Checks);
1965    end Expand_Packed_Eq;
1966
1967    -----------------------
1968    -- Expand_Packed_Not --
1969    -----------------------
1970
1971    --  Handles expansion of "not" on packed array types
1972
1973    procedure Expand_Packed_Not (N : Node_Id) is
1974       Loc  : constant Source_Ptr := Sloc (N);
1975       Typ  : constant Entity_Id  := Etype (N);
1976       Opnd : constant Node_Id    := Relocate_Node (Right_Opnd (N));
1977
1978       Rtyp : Entity_Id;
1979       PAT  : Entity_Id;
1980       Lit  : Node_Id;
1981
1982    begin
1983       Convert_To_Actual_Subtype (Opnd);
1984       Rtyp := Etype (Opnd);
1985
1986       --  First an odd and silly test. We explicitly check for the case
1987       --  where the 'First of the component type is equal to the 'Last of
1988       --  this component type, and if this is the case, we make sure that
1989       --  constraint error is raised. The reason is that the NOT is bound
1990       --  to cause CE in this case, and we will not otherwise catch it.
1991
1992       --  Believe it or not, this was reported as a bug. Note that nearly
1993       --  always, the test will evaluate statically to False, so the code
1994       --  will be statically removed, and no extra overhead caused.
1995
1996       declare
1997          CT : constant Entity_Id := Component_Type (Rtyp);
1998
1999       begin
2000          Insert_Action (N,
2001            Make_Raise_Constraint_Error (Loc,
2002              Condition =>
2003                Make_Op_Eq (Loc,
2004                  Left_Opnd =>
2005                    Make_Attribute_Reference (Loc,
2006                      Prefix         => New_Occurrence_Of (CT, Loc),
2007                      Attribute_Name => Name_First),
2008
2009                  Right_Opnd =>
2010                    Make_Attribute_Reference (Loc,
2011                      Prefix         => New_Occurrence_Of (CT, Loc),
2012                      Attribute_Name => Name_Last)),
2013              Reason => CE_Range_Check_Failed));
2014       end;
2015
2016       --  Now that that silliness is taken care of, get packed array type
2017
2018       Convert_To_PAT_Type (Opnd);
2019       PAT := Etype (Opnd);
2020
2021       --  For the case where the packed array type is a modular type,
2022       --  not A expands simply into:
2023
2024       --     rtyp!(PAT!(A) xor mask)
2025
2026       --  where PAT is the packed array type, and mask is a mask of all
2027       --  one bits of length equal to the size of this packed type and
2028       --  rtyp is the actual subtype of the operand
2029
2030       Lit := Make_Integer_Literal (Loc, 2 ** Esize (PAT) - 1);
2031       Set_Print_In_Hex (Lit);
2032
2033       if not Is_Array_Type (PAT) then
2034          Rewrite (N,
2035            Unchecked_Convert_To (Rtyp,
2036              Make_Op_Xor (Loc,
2037                Left_Opnd  => Opnd,
2038                Right_Opnd => Lit)));
2039
2040       --  For the array case, we insert the actions
2041
2042       --    Result : Typ;
2043
2044       --    System.Bitops.Bit_Not
2045       --     (Opnd'Address,
2046       --      Typ'Length * Typ'Component_Size;
2047       --      Result'Address);
2048
2049       --  where Opnd is the Packed_Bytes{1,2,4} operand and the second
2050       --  argument is the length of the operand in bits. Then we replace
2051       --  the expression by a reference to Result.
2052
2053       else
2054          declare
2055             Result_Ent : constant Entity_Id :=
2056                            Make_Defining_Identifier (Loc,
2057                              Chars => New_Internal_Name ('T'));
2058
2059          begin
2060             Insert_Actions (N, New_List (
2061
2062               Make_Object_Declaration (Loc,
2063                 Defining_Identifier => Result_Ent,
2064                 Object_Definition => New_Occurrence_Of (Rtyp, Loc)),
2065
2066               Make_Procedure_Call_Statement (Loc,
2067                 Name => New_Occurrence_Of (RTE (RE_Bit_Not), Loc),
2068                   Parameter_Associations => New_List (
2069
2070                     Make_Byte_Aligned_Attribute_Reference (Loc,
2071                       Attribute_Name => Name_Address,
2072                       Prefix         => Opnd),
2073
2074                     Make_Op_Multiply (Loc,
2075                       Left_Opnd =>
2076                         Make_Attribute_Reference (Loc,
2077                           Prefix =>
2078                             New_Occurrence_Of
2079                               (Etype (First_Index (Rtyp)), Loc),
2080                           Attribute_Name => Name_Range_Length),
2081                       Right_Opnd =>
2082                         Make_Integer_Literal (Loc, Component_Size (Rtyp))),
2083
2084                     Make_Byte_Aligned_Attribute_Reference (Loc,
2085                       Attribute_Name => Name_Address,
2086                       Prefix => New_Occurrence_Of (Result_Ent, Loc))))));
2087
2088             Rewrite (N,
2089               New_Occurrence_Of (Result_Ent, Loc));
2090          end;
2091       end if;
2092
2093       Analyze_And_Resolve (N, Typ, Suppress => All_Checks);
2094
2095    end Expand_Packed_Not;
2096
2097    -------------------------------------
2098    -- Involves_Packed_Array_Reference --
2099    -------------------------------------
2100
2101    function Involves_Packed_Array_Reference (N : Node_Id) return Boolean is
2102    begin
2103       if Nkind (N) = N_Indexed_Component
2104         and then Is_Bit_Packed_Array (Etype (Prefix (N)))
2105       then
2106          return True;
2107
2108       elsif Nkind (N) = N_Selected_Component then
2109          return Involves_Packed_Array_Reference (Prefix (N));
2110
2111       else
2112          return False;
2113       end if;
2114    end Involves_Packed_Array_Reference;
2115
2116    --------------------------
2117    -- Known_Aligned_Enough --
2118    --------------------------
2119
2120    function Known_Aligned_Enough (Obj : Node_Id; Csiz : Nat) return Boolean is
2121       Typ : constant Entity_Id := Etype (Obj);
2122
2123       function In_Partially_Packed_Record (Comp : Entity_Id) return Boolean;
2124       --  If the component is in a record that contains previous packed
2125       --  components, consider it unaligned because the back-end might
2126       --  choose to pack the rest of the record. Lead to less efficient code,
2127       --  but safer vis-a-vis of back-end choices.
2128
2129       --------------------------------
2130       -- In_Partially_Packed_Record --
2131       --------------------------------
2132
2133       function In_Partially_Packed_Record (Comp : Entity_Id) return Boolean is
2134          Rec_Type  : constant Entity_Id := Scope (Comp);
2135          Prev_Comp : Entity_Id;
2136
2137       begin
2138          Prev_Comp := First_Entity (Rec_Type);
2139          while Present (Prev_Comp) loop
2140             if Is_Packed (Etype (Prev_Comp)) then
2141                return True;
2142
2143             elsif Prev_Comp = Comp then
2144                return False;
2145             end if;
2146
2147             Next_Entity (Prev_Comp);
2148          end loop;
2149
2150          return False;
2151       end  In_Partially_Packed_Record;
2152
2153    --  Start of processing for Known_Aligned_Enough
2154
2155    begin
2156       --  Odd bit sizes don't need alignment anyway
2157
2158       if Csiz mod 2 = 1 then
2159          return True;
2160
2161       --  If we have a specified alignment, see if it is sufficient, if not
2162       --  then we can't possibly be aligned enough in any case.
2163
2164       elsif Known_Alignment (Etype (Obj)) then
2165          --  Alignment required is 4 if size is a multiple of 4, and
2166          --  2 otherwise (e.g. 12 bits requires 4, 10 bits requires 2)
2167
2168          if Alignment (Etype (Obj)) < 4 - (Csiz mod 4) then
2169             return False;
2170          end if;
2171       end if;
2172
2173       --  OK, alignment should be sufficient, if object is aligned
2174
2175       --  If object is strictly aligned, then it is definitely aligned
2176
2177       if Strict_Alignment (Typ) then
2178          return True;
2179
2180       --  Case of subscripted array reference
2181
2182       elsif Nkind (Obj) = N_Indexed_Component then
2183
2184          --  If we have a pointer to an array, then this is definitely
2185          --  aligned, because pointers always point to aligned versions.
2186
2187          if Is_Access_Type (Etype (Prefix (Obj))) then
2188             return True;
2189
2190          --  Otherwise, go look at the prefix
2191
2192          else
2193             return Known_Aligned_Enough (Prefix (Obj), Csiz);
2194          end if;
2195
2196       --  Case of record field
2197
2198       elsif Nkind (Obj) = N_Selected_Component then
2199
2200          --  What is significant here is whether the record type is packed
2201
2202          if Is_Record_Type (Etype (Prefix (Obj)))
2203            and then Is_Packed (Etype (Prefix (Obj)))
2204          then
2205             return False;
2206
2207          --  Or the component has a component clause which might cause
2208          --  the component to become unaligned (we can't tell if the
2209          --  backend is doing alignment computations).
2210
2211          elsif Present (Component_Clause (Entity (Selector_Name (Obj)))) then
2212             return False;
2213
2214          elsif In_Partially_Packed_Record (Entity (Selector_Name (Obj))) then
2215             return False;
2216
2217          --  In all other cases, go look at prefix
2218
2219          else
2220             return Known_Aligned_Enough (Prefix (Obj), Csiz);
2221          end if;
2222
2223       --  If not selected or indexed component, must be aligned
2224
2225       else
2226          return True;
2227       end if;
2228    end Known_Aligned_Enough;
2229
2230    ---------------------
2231    -- Make_Shift_Left --
2232    ---------------------
2233
2234    function Make_Shift_Left (N : Node_Id; S : Node_Id) return Node_Id is
2235       Nod : Node_Id;
2236
2237    begin
2238       if Compile_Time_Known_Value (S) and then Expr_Value (S) = 0 then
2239          return N;
2240       else
2241          Nod :=
2242            Make_Op_Shift_Left (Sloc (N),
2243              Left_Opnd  => N,
2244              Right_Opnd => S);
2245          Set_Shift_Count_OK (Nod, True);
2246          return Nod;
2247       end if;
2248    end Make_Shift_Left;
2249
2250    ----------------------
2251    -- Make_Shift_Right --
2252    ----------------------
2253
2254    function Make_Shift_Right (N : Node_Id; S : Node_Id) return Node_Id is
2255       Nod : Node_Id;
2256
2257    begin
2258       if Compile_Time_Known_Value (S) and then Expr_Value (S) = 0 then
2259          return N;
2260       else
2261          Nod :=
2262            Make_Op_Shift_Right (Sloc (N),
2263              Left_Opnd  => N,
2264              Right_Opnd => S);
2265          Set_Shift_Count_OK (Nod, True);
2266          return Nod;
2267       end if;
2268    end Make_Shift_Right;
2269
2270    -----------------------------
2271    -- RJ_Unchecked_Convert_To --
2272    -----------------------------
2273
2274    function RJ_Unchecked_Convert_To
2275      (Typ  : Entity_Id;
2276       Expr : Node_Id)
2277       return Node_Id
2278    is
2279       Source_Typ : constant Entity_Id := Etype (Expr);
2280       Target_Typ : constant Entity_Id := Typ;
2281
2282       Src : Node_Id := Expr;
2283
2284       Source_Siz : Nat;
2285       Target_Siz : Nat;
2286
2287    begin
2288       Source_Siz := UI_To_Int (RM_Size (Source_Typ));
2289       Target_Siz := UI_To_Int (RM_Size (Target_Typ));
2290
2291       --  In the big endian case, if the lengths of the two types differ,
2292       --  then we must worry about possible left justification in the
2293       --  conversion, and avoiding that is what this is all about.
2294
2295       if Bytes_Big_Endian and then Source_Siz /= Target_Siz then
2296
2297          --  First step, if the source type is not a discrete type, then we
2298          --  first convert to a modular type of the source length, since
2299          --  otherwise, on a big-endian machine, we get left-justification.
2300
2301          if not Is_Discrete_Type (Source_Typ) then
2302             Src := Unchecked_Convert_To (RTE (Bits_Id (Source_Siz)), Src);
2303          end if;
2304
2305          --  Next step. If the target is not a discrete type, then we first
2306          --  convert to a modular type of the target length, since
2307          --  otherwise, on a big-endian machine, we get left-justification.
2308
2309          if not Is_Discrete_Type (Target_Typ) then
2310             Src := Unchecked_Convert_To (RTE (Bits_Id (Target_Siz)), Src);
2311          end if;
2312       end if;
2313
2314       --  And now we can do the final conversion to the target type
2315
2316       return Unchecked_Convert_To (Target_Typ, Src);
2317    end RJ_Unchecked_Convert_To;
2318
2319    ----------------------------------------------
2320    -- Setup_Enumeration_Packed_Array_Reference --
2321    ----------------------------------------------
2322
2323    --  All we have to do here is to find the subscripts that correspond
2324    --  to the index positions that have non-standard enumeration types
2325    --  and insert a Pos attribute to get the proper subscript value.
2326
2327    --  Finally the prefix must be uncheck converted to the corresponding
2328    --  packed array type.
2329
2330    --  Note that the component type is unchanged, so we do not need to
2331    --  fiddle with the types (Gigi always automatically takes the packed
2332    --  array type if it is set, as it will be in this case).
2333
2334    procedure Setup_Enumeration_Packed_Array_Reference (N : Node_Id) is
2335       Pfx   : constant Node_Id   := Prefix (N);
2336       Typ   : constant Entity_Id := Etype (N);
2337       Exprs : constant List_Id   := Expressions (N);
2338       Expr  : Node_Id;
2339
2340    begin
2341       --  If the array is unconstrained, then we replace the array
2342       --  reference with its actual subtype. This actual subtype will
2343       --  have a packed array type with appropriate bounds.
2344
2345       if not Is_Constrained (Packed_Array_Type (Etype (Pfx))) then
2346          Convert_To_Actual_Subtype (Pfx);
2347       end if;
2348
2349       Expr := First (Exprs);
2350       while Present (Expr) loop
2351          declare
2352             Loc      : constant Source_Ptr := Sloc (Expr);
2353             Expr_Typ : constant Entity_Id := Etype (Expr);
2354
2355          begin
2356             if Is_Enumeration_Type (Expr_Typ)
2357               and then Has_Non_Standard_Rep (Expr_Typ)
2358             then
2359                Rewrite (Expr,
2360                  Make_Attribute_Reference (Loc,
2361                    Prefix         => New_Occurrence_Of (Expr_Typ, Loc),
2362                    Attribute_Name => Name_Pos,
2363                    Expressions    => New_List (Relocate_Node (Expr))));
2364                Analyze_And_Resolve (Expr, Standard_Natural);
2365             end if;
2366          end;
2367
2368          Next (Expr);
2369       end loop;
2370
2371       Rewrite (N,
2372         Make_Indexed_Component (Sloc (N),
2373           Prefix      =>
2374             Unchecked_Convert_To (Packed_Array_Type (Etype (Pfx)), Pfx),
2375           Expressions => Exprs));
2376
2377       Analyze_And_Resolve (N, Typ);
2378
2379    end Setup_Enumeration_Packed_Array_Reference;
2380
2381    -----------------------------------------
2382    -- Setup_Inline_Packed_Array_Reference --
2383    -----------------------------------------
2384
2385    procedure Setup_Inline_Packed_Array_Reference
2386      (N      : Node_Id;
2387       Atyp   : Entity_Id;
2388       Obj    : in out Node_Id;
2389       Cmask  : out Uint;
2390       Shift  : out Node_Id)
2391    is
2392       Loc    : constant Source_Ptr := Sloc (N);
2393       Ctyp   : Entity_Id;
2394       PAT    : Entity_Id;
2395       Otyp   : Entity_Id;
2396       Csiz   : Uint;
2397       Osiz   : Uint;
2398
2399    begin
2400       Ctyp := Component_Type (Atyp);
2401       Csiz := Component_Size (Atyp);
2402
2403       Convert_To_PAT_Type (Obj);
2404       PAT  := Etype (Obj);
2405
2406       Cmask := 2 ** Csiz - 1;
2407
2408       if Is_Array_Type (PAT) then
2409          Otyp := Component_Type (PAT);
2410          Osiz := Esize (Otyp);
2411
2412       else
2413          Otyp := PAT;
2414
2415          --  In the case where the PAT is a modular type, we want the actual
2416          --  size in bits of the modular value we use. This is neither the
2417          --  Object_Size nor the Value_Size, either of which may have been
2418          --  reset to strange values, but rather the minimum size. Note that
2419          --  since this is a modular type with full range, the issue of
2420          --  biased representation does not arise.
2421
2422          Osiz := UI_From_Int (Minimum_Size (Otyp));
2423       end if;
2424
2425       Compute_Linear_Subscript (Atyp, N, Shift);
2426
2427       --  If the component size is not 1, then the subscript must be
2428       --  multiplied by the component size to get the shift count.
2429
2430       if Csiz /= 1 then
2431          Shift :=
2432            Make_Op_Multiply (Loc,
2433              Left_Opnd => Make_Integer_Literal (Loc, Csiz),
2434              Right_Opnd => Shift);
2435       end if;
2436
2437       --  If we have the array case, then this shift count must be broken
2438       --  down into a byte subscript, and a shift within the byte.
2439
2440       if Is_Array_Type (PAT) then
2441
2442          declare
2443             New_Shift : Node_Id;
2444
2445          begin
2446             --  We must analyze shift, since we will duplicate it
2447
2448             Set_Parent (Shift, N);
2449             Analyze_And_Resolve
2450               (Shift, Standard_Integer, Suppress => All_Checks);
2451
2452             --  The shift count within the word is
2453             --    shift mod Osiz
2454
2455             New_Shift :=
2456               Make_Op_Mod (Loc,
2457                 Left_Opnd  => Duplicate_Subexpr (Shift),
2458                 Right_Opnd => Make_Integer_Literal (Loc, Osiz));
2459
2460             --  The subscript to be used on the PAT array is
2461             --    shift / Osiz
2462
2463             Obj :=
2464               Make_Indexed_Component (Loc,
2465                 Prefix => Obj,
2466                 Expressions => New_List (
2467                   Make_Op_Divide (Loc,
2468                     Left_Opnd => Duplicate_Subexpr (Shift),
2469                     Right_Opnd => Make_Integer_Literal (Loc, Osiz))));
2470
2471             Shift := New_Shift;
2472          end;
2473
2474       --  For the modular integer case, the object to be manipulated is
2475       --  the entire array, so Obj is unchanged. Note that we will reset
2476       --  its type to PAT before returning to the caller.
2477
2478       else
2479          null;
2480       end if;
2481
2482       --  The one remaining step is to modify the shift count for the
2483       --  big-endian case. Consider the following example in a byte:
2484
2485       --     xxxxxxxx  bits of byte
2486       --     vvvvvvvv  bits of value
2487       --     33221100  little-endian numbering
2488       --     00112233  big-endian numbering
2489
2490       --  Here we have the case of 2-bit fields
2491
2492       --  For the little-endian case, we already have the proper shift
2493       --  count set, e.g. for element 2, the shift count is 2*2 = 4.
2494
2495       --  For the big endian case, we have to adjust the shift count,
2496       --  computing it as (N - F) - shift, where N is the number of bits
2497       --  in an element of the array used to implement the packed array,
2498       --  F is the number of bits in a source level array element, and
2499       --  shift is the count so far computed.
2500
2501       if Bytes_Big_Endian then
2502          Shift :=
2503            Make_Op_Subtract (Loc,
2504              Left_Opnd  => Make_Integer_Literal (Loc, Osiz - Csiz),
2505              Right_Opnd => Shift);
2506       end if;
2507
2508       Set_Parent (Shift, N);
2509       Set_Parent (Obj, N);
2510       Analyze_And_Resolve (Obj,   Otyp,             Suppress => All_Checks);
2511       Analyze_And_Resolve (Shift, Standard_Integer, Suppress => All_Checks);
2512
2513       --  Make sure final type of object is the appropriate packed type
2514
2515       Set_Etype (Obj, Otyp);
2516
2517    end Setup_Inline_Packed_Array_Reference;
2518
2519 end Exp_Pakd;