gcc/ada/sem_attr.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ A T T R                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2016, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- You should have received a copy of the GNU General Public License along  --
  19 -- with this program; see file COPYING3.  If not see                        --
  20 -- <http://www.gnu.org/licenses/>.                                          --
  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 --  Attribute handling is isolated in a separate package to ease the addition
  28 --  of implementation defined attributes. Logically this processing belongs
  29 --  in chapter 4. See Sem_Ch4 for a description of the relation of the
  30 --  Analyze and Resolve routines for expression components.
  31
  32 --  This spec also documents all GNAT implementation defined pragmas
  33
  34 with Exp_Tss; use Exp_Tss;
  35 with Namet;   use Namet;
  36 with Snames;  use Snames;
  37 with Types;   use Types;
  38
  39 package Sem_Attr is
  40
  41    -----------------------------------------
  42    -- Implementation Dependent Attributes --
  43    -----------------------------------------
  44
  45    --  This section describes the implementation dependent attributes provided
  46    --  in GNAT, as well as constructing an array of flags indicating which
  47    --  attributes these are.
  48
  49    Attribute_Impl_Def : constant Attribute_Class_Array :=
  50      Attribute_Class_Array'(
  51
  52       ------------------
  53       -- Abort_Signal --
  54       ------------------
  55
  56       Attribute_Abort_Signal => True,
  57       --  Standard'Abort_Signal (Standard is the only allowed prefix) provides
  58       --  the entity for the special exception used to signal task abort or
  59       --  asynchronous transfer of control. Normally this attribute should only
  60       --  be used in the tasking runtime (it is highly peculiar, and completely
  61       --  outside the normal semantics of Ada, for a user program to intercept
  62       --  the abort exception).
  63
  64       ------------------
  65       -- Address_Size --
  66       ------------------
  67
  68       Attribute_Address_Size => True,
  69       --  Standard'Address_Size (Standard is the only allowed prefix) is
  70       --  a static constant giving the number of bits in an Address. It
  71       --  is used primarily for constructing the definition of Memory_Size
  72       --  in package Standard, but may be freely used in user programs.
  73       --  This is a static attribute.
  74
  75       ---------------
  76       -- Asm_Input --
  77       ---------------
  78
  79       Attribute_Asm_Input => True,
  80       --  Used only in conjunction with the Asm subprograms in package
  81       --  Machine_Code to construct machine instructions. See documentation
  82       --  in package Machine_Code in file s-maccod.ads.
  83
  84       ----------------
  85       -- Asm_Output --
  86       ----------------
  87
  88       Attribute_Asm_Output => True,
  89       --  Used only in conjunction with the Asm subprograms in package
  90       --  Machine_Code to construct machine instructions. See documentation
  91       --  in package Machine_Code in file s-maccod.ads.
  92
  93       ---------
  94       -- Bit --
  95       ---------
  96
  97       Attribute_Bit => True,
  98       --  Obj'Bit, where Obj is any object, yields the bit offset within the
  99       --  storage unit (byte) that contains the first bit of storage allocated
 100       --  for the object. The attribute value is of type Universal_Integer,
 101       --  and is always a non-negative number not exceeding the value of
 102       --  System.Storage_Unit.
 103       --
 104       --  For an object that is a variable or a constant allocated in a
 105       --  register, the value is zero. (The use of this attribute does not
 106       --  force the allocation of a variable to memory).
 107       --
 108       --  For an object that is a formal parameter, this attribute applies to
 109       --  either the matching actual parameter or to a copy of the matching
 110       --  actual parameter.
 111       --
 112       --  For an access object the value is zero. Note that Obj.all'Bit is
 113       --  subject to an Access_Check for the designated object. Similarly
 114       --  for a record component X.C'Bit is subject to a discriminant check
 115       --  and X(I).Bit and X(I1..I2)'Bit are subject to index checks.
 116       --
 117       --  This attribute is designed to be compatible with the DEC Ada
 118       --  definition and implementation of the Bit attribute.
 119
 120       ------------------
 121       -- Code_Address --
 122       ------------------
 123
 124       Attribute_Code_Address => True,
 125       --  The reference subp'Code_Address, where subp is a subprogram entity,
 126       --  gives the address of the first generated instruction for the sub-
 127       --  program. This is often, but not always the same as the 'Address
 128       --  value, which is the address to be used in a call. The differences
 129       --  occur in the case of a nested procedure (where Address yields the
 130       --  address of the trampoline code used to load the static link), and on
 131       --  some systems which use procedure descriptors (in which case Address
 132       --  yields the address of the descriptor).
 133
 134       -----------------------
 135       -- Default_Bit_Order --
 136       -----------------------
 137
 138       Attribute_Default_Bit_Order => True,
 139       --  Standard'Default_Bit_Order (Standard is the only permissible prefix)
 140       --  provides the value System.Default_Bit_Order as a Pos value (0 for
 141       --  High_Order_First, 1 for Low_Order_First). This is used to construct
 142       --  the definition of Default_Bit_Order in package System. This is a
 143       --  static attribute.
 144
 145       ----------------------------------
 146       -- Default_Scalar_Storage_Order --
 147       ----------------------------------
 148
 149       Attribute_Default_Scalar_Storage_Order => True,
 150       --  Standard'Default_Scalar_Storage_Order (Standard is the
 151       --  only permissible prefix) provides the current value of the
 152       --  default scalar storage order (as specified using pragma
 153       --  Default_Scalar_Storage_Order, or equal to Default_Bit_Order if
 154       --  unspecified) as a System.Bit_Order value. This is a static attribute.
 155
 156       -----------
 157       -- Deref --
 158       -----------
 159
 160       Attribute_Deref => True,
 161       --  typ'Deref (expr) is valid only if expr is of type System'Address.
 162       --  The result is an object of type typ that is obtained by treating the
 163       --  address as an access-to-typ value that points to the result. It is
 164       --  basically equivalent to (atyp!expr).all where atyp is an access type
 165       --  for the type.
 166
 167       ---------------
 168       -- Elab_Body --
 169       ---------------
 170
 171       Attribute_Elab_Body => True,
 172       --  This attribute can only be applied to a program unit name. It
 173       --  returns the entity for the corresponding elaboration procedure for
 174       --  elaborating the body of the referenced unit. This is used in the main
 175       --  generated elaboration procedure by the binder, and is not normally
 176       --  used in any other context, but there may be specialized situations in
 177       --  which it is useful to be able to call this elaboration procedure from
 178       --  Ada code, e.g. if it is necessary to do selective reelaboration to
 179       --  fix some error.
 180
 181       --------------------
 182       -- Elab_Subp_Body --
 183       --------------------
 184
 185       Attribute_Elab_Subp_Body => True,
 186       --  This attribute can only be applied to a library level subprogram
 187       --  name and is only relevant in CodePeer mode. It returns the entity
 188       --  for the corresponding elaboration procedure for elaborating the body
 189       --  of the referenced subprogram unit. This is used in the main generated
 190       --  elaboration procedure by the binder in CodePeer mode only.
 191
 192       ---------------
 193       -- Elab_Spec --
 194       ---------------
 195
 196       Attribute_Elab_Spec => True,
 197       --  This attribute can only be applied to a program unit name. It
 198       --  returns the entity for the corresponding elaboration procedure for
 199       --  elaborating the spec of the referenced unit. This is used in the main
 200       --  generated elaboration procedure by the binder, and is not normally
 201       --  used in any other context, but there may be specialized situations in
 202       --  which it is useful to be able to call this elaboration procedure from
 203       --  Ada code, e.g. if it is necessary to do selective reelaboration to
 204       --  fix some error.
 205
 206       ----------------
 207       -- Elaborated --
 208       ----------------
 209
 210       Attribute_Elaborated => True,
 211       --  Lunit'Elaborated, where Lunit is a library unit, yields a boolean
 212       --  value indicating whether or not the body of the designated library
 213       --  unit has been elaborated yet.
 214
 215       --------------
 216       -- Enum_Rep --
 217       --------------
 218
 219       Attribute_Enum_Rep => True,
 220       --  For every enumeration subtype S, S'Enum_Rep denotes a function
 221       --  with the following specification:
 222       --
 223       --    function S'Enum_Rep (Arg : S'Base) return universal_integer;
 224       --
 225       --  The function returns the representation value for the given
 226       --  enumeration value. This will be equal to the 'Pos value in the
 227       --  absence of an enumeration representation clause. This is a static
 228       --  attribute (i.e. the result is static if the argument is static).
 229
 230       --------------
 231       -- Enum_Val --
 232       --------------
 233
 234       Attribute_Enum_Val => True,
 235       --  For every enumeration subtype S, S'Enum_Val denotes a function with
 236       --  the following specification:
 237       --
 238       --    function S'Enum_Val (Arg : universal_integer) return S'Base;
 239       --
 240       --  This function performs the inverse transformation to Enum_Rep. Given
 241       --  a representation value for the type, it returns the corresponding
 242       --  enumeration value. Constraint_Error is raised if no value of the
 243       --  enumeration type corresponds to the given integer value.
 244
 245       -----------------------
 246       -- Finalization_Size --
 247       -----------------------
 248
 249       Attribute_Finalization_Size => True,
 250       --  For every object or non-class-wide-type, Finalization_Size returns
 251       --  the size of the hidden header used for finalization purposes as if
 252       --  the object or type was allocated on the heap. The size of the header
 253       --  does take into account any extra padding due to alignment issues.
 254
 255       -----------------
 256       -- Fixed_Value --
 257       -----------------
 258
 259       Attribute_Fixed_Value => True,
 260       --  For every fixed-point type S, S'Fixed_Value denotes a function
 261       --  with the following specification:
 262       --
 263       --    function S'Fixed_Value (Arg : universal_integer) return S;
 264       --
 265       --  The value returned is the fixed-point value V such that
 266       --
 267       --    V = Arg * S'Small
 268       --
 269       --  The effect is thus equivalent to first converting the argument to
 270       --  the integer type used to represent S, and then doing an unchecked
 271       --  conversion to the fixed-point type. This attribute is primarily
 272       --  intended for use in implementation of the input-output functions
 273       --  for fixed-point values.
 274
 275       -----------------------
 276       -- Has_Discriminants --
 277       -----------------------
 278
 279       Attribute_Has_Discriminants => True,
 280       --  Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields
 281       --  a Boolean value indicating whether or not the actual instantiation
 282       --  type has discriminants.
 283
 284       ---------
 285       -- Img --
 286       ---------
 287
 288       Attribute_Img => True,
 289       --  The 'Img function is defined for any prefix, P, that denotes an
 290       --  object of scalar type T. P'Img is equivalent to T'Image (P). This
 291       --  is convenient for debugging. For example:
 292       --
 293       --     Put_Line ("X = " & X'Img);
 294       --
 295       --  has the same meaning as the more verbose:
 296       --
 297       --     Put_Line ("X = " & Temperature_Type'Image (X));
 298       --
 299       --  where Temperature_Type is the subtype of the object X.
 300
 301       -------------------
 302       -- Integer_Value --
 303       -------------------
 304
 305       Attribute_Integer_Value => True,
 306       --  For every integer type S, S'Integer_Value denotes a function
 307       --  with the following specification:
 308       --
 309       --    function S'Integer_Value (Arg : universal_fixed) return S;
 310       --
 311       --  The value returned is the integer value V, such that
 312       --
 313       --    Arg = V * fixed-type'Small
 314       --
 315       --  The effect is thus equivalent to first doing an unchecked convert
 316       --  from the fixed-point type to its corresponding implementation type,
 317       --  and then converting the result to the target integer type. This
 318       --  attribute is primarily intended for use in implementation of the
 319       --  standard input-output functions for fixed-point values.
 320
 321       Attribute_Invalid_Value => True,
 322       --  For every scalar type, S'Invalid_Value designates an undefined value
 323       --  of the type. If possible this value is an invalid value, and in fact
 324       --  is identical to the value that would be set if Initialize_Scalars
 325       --  mode were in effect (including the behavior of its value on
 326       --  environment variables or binder switches). The intended use is to
 327       --  set a value where initialization is required (e.g. as a result of the
 328       --  coding standards in use), but logically no initialization is needed,
 329       --  and the value should never be accessed.
 330
 331       Attribute_Loop_Entry => True,
 332       --  For every object of a non-limited type, S'Loop_Entry [(Loop_Name)]
 333       --  denotes the constant value of prefix S at the point of entry into the
 334       --  related loop. The type of the attribute is the type of the prefix.
 335
 336       ------------------
 337       -- Machine_Size --
 338       ------------------
 339
 340       Attribute_Machine_Size => True,
 341       --  This attribute is identical to the Object_Size attribute. It is
 342       --  provided for compatibility with the DEC attribute of this name.
 343
 344       -----------------------
 345       -- Maximum_Alignment --
 346       -----------------------
 347
 348       Attribute_Maximum_Alignment => True,
 349       --  Standard'Maximum_Alignment (Standard is the only permissible prefix)
 350       --  provides the maximum useful alignment value for the target. This is a
 351       --  static value that can be used to specify the alignment for an object,
 352       --  guaranteeing that it is properly aligned in all cases. The time this
 353       --  is useful is when an external object is imported and its alignment
 354       --  requirements are unknown. This is a static attribute.
 355
 356       --------------------
 357       -- Mechanism_Code --
 358       --------------------
 359
 360       Attribute_Mechanism_Code => True,
 361       --  function'Mechanism_Code yields an integer code for the mechanism
 362       --  used for the result of function, and subprogram'Mechanism_Code (n)
 363       --  yields the mechanism used for formal parameter number n (a static
 364       --  integer value, 1 = first parameter). The code returned is:
 365       --
 366       --     1 = by copy (value)
 367       --     2 = by reference
 368       --     3 = by descriptor (default descriptor type)
 369       --     4 = by descriptor (UBS  unaligned bit string)
 370       --     5 = by descriptor (UBSB aligned bit string with arbitrary bounds)
 371       --     6 = by descriptor (UBA  unaligned bit array)
 372       --     7 = by descriptor (S    string, also scalar access type parameter)
 373       --     8 = by descriptor (SB   string with arbitrary bounds)
 374       --     9 = by descriptor (A    contiguous array)
 375       --    10 = by descriptor (NCA  non-contiguous array)
 376
 377       --------------------
 378       -- Null_Parameter --
 379       --------------------
 380
 381       Attribute_Null_Parameter => True,
 382       --  A reference T'Null_Parameter denotes an (imaginary) object of type
 383       --  or subtype T allocated at (machine) address zero. The attribute is
 384       --  allowed only as the default expression of a formal parameter, or
 385       --  as an actual expression of a subprogram call. In either case, the
 386       --  subprogram must be imported.
 387       --
 388       --  The identity of the object is represented by the address zero in
 389       --  the argument list, independent of the passing mechanism (explicit
 390       --  or default).
 391       --
 392       --  The reason that this capability is needed is that for a record or
 393       --  other composite object passed by reference, there is no other way
 394       --  of specifying that a zero address should be passed.
 395
 396       -----------------
 397       -- Object_Size --
 398       -----------------
 399
 400       Attribute_Object_Size => True,
 401       --  Type'Object_Size is the same as Type'Size for all types except
 402       --  fixed-point types and discrete types. For fixed-point types and
 403       --  discrete types, this attribute gives the size used for default
 404       --  allocation of objects and components of the size. See section in
 405       --  Einfo ("Handling of Type'Size values") for further details.
 406
 407       -------------------------
 408       -- Passed_By_Reference --
 409       -------------------------
 410
 411       Attribute_Passed_By_Reference => True,
 412       --  T'Passed_By_Reference for any subtype T returns a boolean value that
 413       --  is true if the type is normally passed by reference and false if the
 414       --  type is normally passed by copy in calls. For scalar types, the
 415       --  result is always False and is static. For non-scalar types, the
 416       --  result is non-static (since it is computed by Gigi).
 417
 418       ------------------
 419       -- Range_Length --
 420       ------------------
 421
 422       Attribute_Range_Length => True,
 423       --  T'Range_Length for any discrete type T yields the number of values
 424       --  represented by the subtype (zero for a null range). The result is
 425       --  static for static subtypes. Note that Range_Length applied to the
 426       --  index subtype of a one dimensional array always gives the same result
 427       --  as Range applied to the array itself. The result is of type universal
 428       --  integer.
 429
 430       ---------
 431       -- Ref --
 432       ---------
 433
 434       Attribute_Ref => True,
 435       --  System.Address'Ref (Address is the only permissible prefix) is
 436       --  equivalent to System'To_Address, provided for compatibility with
 437       --  other compilers.
 438
 439       ------------------
 440       -- Storage_Unit --
 441       ------------------
 442
 443       Attribute_Storage_Unit => True,
 444       --  Standard'Storage_Unit (Standard is the only permissible prefix)
 445       --  provides the value System.Storage_Unit, and is intended primarily
 446       --  for constructing this definition in package System (see note above
 447       --  in Default_Bit_Order description). The is a static attribute.
 448
 449       ---------------
 450       -- Stub_Type --
 451       ---------------
 452
 453       Attribute_Stub_Type => True,
 454       --  The GNAT implementation of remote access-to-classwide types is
 455       --  organised as described in AARM E.4(20.t): a value of an RACW type
 456       --  (designating a remote object) is represented as a normal access
 457       --  value, pointing to a "stub" object which in turn contains the
 458       --  necessary information to contact the designated remote object. A
 459       --  call on any dispatching operation of such a stub object does the
 460       --  remote call, if necessary, using the information in the stub object
 461       --  to locate the target partition, etc.
 462       --
 463       --  For a prefix T that denotes a remote access-to-classwide type,
 464       --  T'Stub_Type denotes the type of the corresponding stub objects.
 465       --
 466       --  By construction, the layout of T'Stub_Type is identical to that of
 467       --  System.Partition_Interface.RACW_Stub_Type (see implementation notes
 468       --  in body of Exp_Dist).
 469
 470       -----------------
 471       -- Target_Name --
 472       -----------------
 473
 474       Attribute_Target_Name => True,
 475       --  Standard'Target_Name yields the string identifying the target for the
 476       --  compilation, taken from Sdefault.Target_Name.
 477
 478       ----------------
 479       -- To_Address --
 480       ----------------
 481
 482       Attribute_To_Address => True,
 483       --  System'To_Address (System is the only permissible prefix) is a
 484       --  function that takes any integer value, and converts it into an
 485       --  address value. The semantics is to first convert the integer value to
 486       --  type Integer_Address according to normal conversion rules, and then
 487       --  to convert this to an address using the same semantics as the
 488       --  System.Storage_Elements.To_Address function. The important difference
 489       --  is that this is a static attribute so it can be used in
 490       --  initializations in preelaborate packages.
 491
 492       ----------------
 493       -- Type_Class --
 494       ----------------
 495
 496       Attribute_Type_Class => True,
 497       --  T'Type_Class for any type or subtype T yields the value of the type
 498       --  class for the full type of T. If T is a generic formal type, then the
 499       --  value is the value for the corresponding actual subtype. The value of
 500       --  this attribute is of type System.Aux_DEC.Type_Class, which has the
 501       --  following definition:
 502       --
 503       --    type Type_Class is
 504       --      (Type_Class_Enumeration,
 505       --       Type_Class_Integer,
 506       --       Type_Class_Fixed_Point,
 507       --       Type_Class_Floating_Point,
 508       --       Type_Class_Array,
 509       --       Type_Class_Record,
 510       --       Type_Class_Access,
 511       --       Type_Class_Task,
 512       --       Type_Class_Address);
 513       --
 514       --  Protected types yield the value Type_Class_Task, which thus applies
 515       --  to all concurrent types. This attribute is designed to be compatible
 516       --  with the DEC Ada attribute of the same name.
 517       --
 518       --  Note: if pragma Extend_System is used to merge the definitions of
 519       --  Aux_DEC into System, then the type Type_Class can be referenced
 520       --  as an entity within System, as can its enumeration literals.
 521
 522       ------------------------------
 523       -- Universal_Literal_String --
 524       ------------------------------
 525
 526       Attribute_Universal_Literal_String => True,
 527       --  The prefix of 'Universal_Literal_String must be a named number.
 528       --  The static result is the string consisting of the characters of
 529       --  the number as defined in the original source. This allows the
 530       --  user program to access the actual text of named numbers without
 531       --  intermediate conversions and without the need to enclose the
 532       --  strings in quotes (which would preclude their use as numbers).
 533
 534       -------------------------
 535       -- Unrestricted_Access --
 536       -------------------------
 537
 538       Attribute_Unrestricted_Access => True,
 539       --  The Unrestricted_Access attribute is similar to Access except that
 540       --  all accessibility and aliased view checks are omitted. This is very
 541       --  much a user-beware attribute. Basically its status is very similar
 542       --  to Address, for which it is a desirable replacement where the value
 543       --  desired is an access type. In other words, its effect is identical
 544       --  to first taking 'Address and then doing an unchecked conversion to
 545       --  a desired access type. Note that in GNAT, but not necessarily in
 546       --  other implementations, the use of static chains for inner level
 547       --  subprograms means that Unrestricted_Access applied to a subprogram
 548       --  yields a value that can be called as long as the subprogram is in
 549       --  scope (normal Ada 95 accessibility rules restrict this usage).
 550
 551       ---------------
 552       -- VADS_Size --
 553       ---------------
 554
 555       Attribute_VADS_Size => True,
 556       --  Typ'VADS_Size yields the Size value typically yielded by some Ada 83
 557       --  compilers. The differences between VADS_Size and Size is that for
 558       --  scalar types for which no Size has been specified, VADS_Size yields
 559       --  the Object_Size rather than the Value_Size. For example, while
 560       --  Natural'Size is typically 31, the value of Natural'VADS_Size is 32.
 561       --  For all other types, Size and VADS_Size yield the same value.
 562
 563       -------------------
 564       -- Valid_Scalars --
 565       -------------------
 566
 567       Attribute_Valid_Scalars => True,
 568       --  Obj'Valid_Scalars can be applied to any object. The result depends
 569       --  on the type of the object:
 570       --
 571       --    For a scalar type, the result is the same as obj'Valid
 572       --
 573       --    For an array object, the result is True if the result of applying
 574       --    Valid_Scalars to every component is True. For an empty array the
 575       --    result is True.
 576       --
 577       --    For a record object, the result is True if the result of applying
 578       --    Valid_Scalars to every component is True. For class-wide types,
 579       --    only the components of the base type are checked. For variant
 580       --    records, only the components actually present are checked. The
 581       --    discriminants, if any, are also checked. If there are no components
 582       --    or discriminants, the result is True.
 583       --
 584       --    For any other type that has discriminants, the result is True if
 585       --    the result of applying Valid_Scalars to each discriminant is True.
 586       --
 587       --    For all other types, the result is always True
 588       --
 589       --  A warning is given for a trivially True result, when the attribute
 590       --  is applied to an object that is not of scalar, array, or record
 591       --  type, or in the composite case if no scalar subcomponents exist. For
 592       --  a variant record, the warning is given only if none of the variants
 593       --  have scalar subcomponents. In addition, the warning is suppressed
 594       --  for private types, or generic formal types in an instance.
 595
 596       ----------------
 597       -- Value_Size --
 598       ----------------
 599
 600       Attribute_Value_Size => True,
 601       --  Type'Value_Size is the number of bits required to represent value of
 602       --  the given subtype. It is the same as Type'Size, but, unlike Size, may
 603       --  be set for non-first subtypes. See section in Einfo ("Handling of
 604       --  type'Size values") for further details.
 605
 606       ---------------
 607       -- Word_Size --
 608       ---------------
 609
 610       Attribute_Word_Size => True,
 611       --  Standard'Word_Size (Standard is the only permissible prefix)
 612       --  provides the value System.Word_Size, and is intended primarily
 613       --  for constructing this definition in package System (see note above
 614       --  in Default_Bit_Order description). This is a static attribute.
 615
 616       others => False);
 617
 618    --  The following table lists all attributes that yield a result of a
 619    --  universal type.
 620
 621    Universal_Type_Attribute : constant array (Attribute_Id) of Boolean :=
 622      (Attribute_Aft                          => True,
 623       Attribute_Alignment                    => True,
 624       Attribute_Component_Size               => True,
 625       Attribute_Count                        => True,
 626       Attribute_Delta                        => True,
 627       Attribute_Digits                       => True,
 628       Attribute_Exponent                     => True,
 629       Attribute_First_Bit                    => True,
 630       Attribute_Fore                         => True,
 631       Attribute_Last_Bit                     => True,
 632       Attribute_Length                       => True,
 633       Attribute_Machine_Emax                 => True,
 634       Attribute_Machine_Emin                 => True,
 635       Attribute_Machine_Mantissa             => True,
 636       Attribute_Machine_Radix                => True,
 637       Attribute_Max_Alignment_For_Allocation => True,
 638       Attribute_Max_Size_In_Storage_Elements => True,
 639       Attribute_Model_Emin                   => True,
 640       Attribute_Model_Epsilon                => True,
 641       Attribute_Model_Mantissa               => True,
 642       Attribute_Model_Small                  => True,
 643       Attribute_Modulus                      => True,
 644       Attribute_Pos                          => True,
 645       Attribute_Position                     => True,
 646       Attribute_Safe_First                   => True,
 647       Attribute_Safe_Last                    => True,
 648       Attribute_Scale                        => True,
 649       Attribute_Size                         => True,
 650       Attribute_Small                        => True,
 651       Attribute_Wide_Wide_Width              => True,
 652       Attribute_Wide_Width                   => True,
 653       Attribute_Width                        => True,
 654       others                                 => False);
 655
 656    -----------------
 657    -- Subprograms --
 658    -----------------
 659
 660    procedure Analyze_Attribute (N : Node_Id);
 661    --  Performs bottom up semantic analysis of an attribute. Note that the
 662    --  parser has already checked that type returning attributes appear only
 663    --  in appropriate contexts (i.e. in subtype marks, or as prefixes for
 664    --  other attributes).
 665
 666    function Name_Implies_Lvalue_Prefix (Nam : Name_Id) return Boolean;
 667    --  Determine whether the name of an attribute reference categorizes its
 668    --  prefix as an lvalue. The following attributes fall under this bracket
 669    --  by directly or indirectly modifying their prefixes.
 670    --     Access
 671    --     Address
 672    --     Input
 673    --     Read
 674    --     Unchecked_Access
 675    --     Unrestricted_Access
 676
 677    procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id);
 678    --  Performs type resolution of attribute. If the attribute yields a
 679    --  universal value, mark its type as that of the context. On the other
 680    --  hand, if the context itself is universal (as in T'Val (T'Pos (X)), mark
 681    --  the type as being the largest type of that class that can be used at
 682    --  run-time. This is correct since either the value gets folded (in which
 683    --  case it doesn't matter what type of the class we give if, since the
 684    --  folding uses universal arithmetic anyway) or it doesn't get folded (in
 685    --  which case it is going to be dealt with at runtime, and the largest type
 686    --  is right).
 687
 688    function Stream_Attribute_Available
 689      (Typ          : Entity_Id;
 690       Nam          : TSS_Name_Type;
 691       Partial_View : Entity_Id := Empty) return Boolean;
 692    --  For a limited type Typ, return True if and only if the given attribute
 693    --  is available. For Ada 2005, availability is defined by 13.13.2(36/1).
 694    --  For Ada 95, an attribute is considered to be available if it has been
 695    --  specified using an attribute definition clause for the type, or for its
 696    --  full view, or for an ancestor of either. Parameter Partial_View is used
 697    --  only internally, when checking for an attribute definition clause that
 698    --  is not visible (Ada 95 only).
 699
 700 end Sem_Attr;