1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2012, Free Software Foundation, Inc. --
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. --
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/>. --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
25 ------------------------------------------------------------------------------
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.
32 -- This spec also documents all GNAT implementation defined pragmas
34 with Exp_Tss; use Exp_Tss;
35 with Namet; use Namet;
36 with Snames; use Snames;
37 with Types; use Types;
41 -----------------------------------------
42 -- Implementation Dependent Attributes --
43 -----------------------------------------
45 -- This section describes the implementation dependent attributes
46 -- provided in GNAT, as well as constructing an array of flags
47 -- indicating which attributes these are.
49 Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'(
55 Attribute_Abort_Signal => True,
56 -- Standard'Abort_Signal (Standard is the only allowed prefix) provides
57 -- the entity for the special exception used to signal task abort or
58 -- asynchronous transfer of control. Normally this attribute should only
59 -- be used in the tasking runtime (it is highly peculiar, and completely
60 -- outside the normal semantics of Ada, for a user program to intercept
61 -- the abort exception).
67 Attribute_Address_Size => True,
68 -- Standard'Address_Size (Standard is the only allowed prefix) is
69 -- a static constant giving the number of bits in an Address. It
70 -- is used primarily for constructing the definition of Memory_Size
71 -- in package Standard, but may be freely used in user programs.
72 -- This is a static attribute.
78 Attribute_Asm_Input => True,
79 -- Used only in conjunction with the Asm subprograms in package
80 -- Machine_Code to construct machine instructions. See documentation
81 -- in package Machine_Code in file s-maccod.ads.
87 Attribute_Asm_Output => True,
88 -- Used only in conjunction with the Asm subprograms in package
89 -- Machine_Code to construct machine instructions. See documentation
90 -- in package Machine_Code in file s-maccod.ads.
96 Attribute_AST_Entry => True,
97 -- E'Ast_Entry, where E is a task entry, yields a value of the
98 -- predefined type System.DEC.AST_Handler, that enables the given
99 -- entry to be called when an AST occurs. If the name to which the
100 -- attribute applies has not been specified with the pragma AST_Entry,
101 -- the attribute returns the value No_Ast_Handler, and no AST occurs.
102 -- If the entry is for a task that is not callable (T'Callable False),
103 -- the exception program error is raised. If an AST occurs for an
104 -- entry of a task that is terminated, the program is erroneous.
106 -- The attribute AST_Entry is supported only in OpenVMS versions
107 -- of GNAT. It will be rejected as illegal in other GNAT versions.
113 Attribute_Bit => True,
114 -- Obj'Bit, where Obj is any object, yields the bit offset within the
115 -- storage unit (byte) that contains the first bit of storage allocated
116 -- for the object. The attribute value is of type Universal_Integer,
117 -- and is always a non-negative number not exceeding the value of
118 -- System.Storage_Unit.
120 -- For an object that is a variable or a constant allocated in a
121 -- register, the value is zero. (The use of this attribute does not
122 -- force the allocation of a variable to memory).
124 -- For an object that is a formal parameter, this attribute applies to
125 -- either the matching actual parameter or to a copy of the matching
128 -- For an access object the value is zero. Note that Obj.all'Bit is
129 -- subject to an Access_Check for the designated object. Similarly
130 -- for a record component X.C'Bit is subject to a discriminant check
131 -- and X(I).Bit and X(I1..I2)'Bit are subject to index checks.
133 -- This attribute is designed to be compatible with the DEC Ada
134 -- definition and implementation of the Bit attribute.
140 Attribute_Code_Address => True,
141 -- The reference subp'Code_Address, where subp is a subprogram entity,
142 -- gives the address of the first generated instruction for the sub-
143 -- program. This is often, but not always the same as the 'Address
144 -- value, which is the address to be used in a call. The differences
145 -- occur in the case of a nested procedure (where Address yields the
146 -- address of the trampoline code used to load the static link), and on
147 -- some systems which use procedure descriptors (in which case Address
148 -- yields the address of the descriptor).
150 -----------------------
151 -- Default_Bit_Order --
152 -----------------------
154 Attribute_Default_Bit_Order => True,
155 -- Standard'Default_Bit_Order (Standard is the only permissible prefix),
156 -- provides the value System.Default_Bit_Order as a Pos value (0 for
157 -- High_Order_First, 1 for Low_Order_First). This is used to construct
158 -- the definition of Default_Bit_Order in package System. This is a
165 Attribute_Elab_Body => True,
166 -- This attribute can only be applied to a program unit name. It returns
167 -- the entity for the corresponding elaboration procedure for elabor-
168 -- ating the body of the referenced unit. This is used in the main
169 -- generated elaboration procedure by the binder, and is not normally
170 -- used in any other context, but there may be specialized situations in
171 -- which it is useful to be able to call this elaboration procedure from
172 -- Ada code, e.g. if it is necessary to do selective reelaboration to
179 Attribute_Elab_Subp_Body => True,
180 -- This attribute can only be applied to a library level subprogram
181 -- name and is only relevant in CodePeer mode. It returns the entity
182 -- for the corresponding elaboration procedure for elaborating the body
183 -- of the referenced subprogram unit. This is used in the main generated
184 -- elaboration procedure by the binder in CodePeer mode only.
190 Attribute_Elab_Spec => True,
191 -- This attribute can only be applied to a program unit name. It
192 -- returns the entity for the corresponding elaboration procedure
193 -- for elaborating the spec of the referenced unit. This is used
194 -- in the main generated elaboration procedure by the binder, and
195 -- is not normally used in any other context, but there may be
196 -- specialized situations in which it is useful to be able to
197 -- call this elaboration procedure from Ada code, e.g. if it
198 -- is necessary to do selective reelaboration to fix some error.
204 Attribute_Elaborated => True,
205 -- Lunit'Elaborated, where Lunit is a library unit, yields a boolean
206 -- value indicating whether or not the body of the designated library
207 -- unit has been elaborated yet.
213 Attribute_Enum_Rep => True,
214 -- For every enumeration subtype S, S'Enum_Rep denotes a function
215 -- with the following specification:
217 -- function S'Enum_Rep (Arg : S'Base) return universal_integer;
219 -- The function returns the representation value for the given
220 -- enumeration value. This will be equal to the 'Pos value in the
221 -- absence of an enumeration representation clause. This is a static
222 -- attribute (i.e. the result is static if the argument is static).
228 Attribute_Enum_Val => True,
229 -- For every enumeration subtype S, S'Enum_Val denotes a function
230 -- with the following specification:
232 -- function S'Enum_Val (Arg : universal_integer) return S'Base;
234 -- This function performs the inverse transformation to Enum_Rep. Given
235 -- a representation value for the type, it returns the corresponding
236 -- enumeration value. Constraint_Error is raised if no value of the
237 -- enumeration type corresponds to the given integer value.
243 Attribute_Fixed_Value => True,
244 -- For every fixed-point type S, S'Fixed_Value denotes a function
245 -- with the following specification:
247 -- function S'Fixed_Value (Arg : universal_integer) return S;
249 -- The value returned is the fixed-point value V such that
253 -- The effect is thus equivalent to first converting the argument to
254 -- the integer type used to represent S, and then doing an unchecked
255 -- conversion to the fixed-point type. This attribute is primarily
256 -- intended for use in implementation of the input-output functions for
257 -- fixed-point values.
259 -----------------------
260 -- Has_Discriminants --
261 -----------------------
263 Attribute_Has_Discriminants => True,
264 -- Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields
265 -- a Boolean value indicating whether or not the actual instantiation
266 -- type has discriminants.
272 Attribute_Img => True,
273 -- The 'Img function is defined for any prefix, P, that denotes an
274 -- object of scalar type T. P'Img is equivalent to T'Image (P). This
275 -- is convenient for debugging. For example:
277 -- Put_Line ("X = " & X'Img);
279 -- has the same meaning as the more verbose:
281 -- Put_Line ("X = " & Temperature_Type'Image (X));
283 -- where Temperature_Type is the subtype of the object X.
289 Attribute_Integer_Value => True,
290 -- For every integer type S, S'Integer_Value denotes a function
291 -- with the following specification:
293 -- function S'Integer_Value (Arg : universal_fixed) return S;
295 -- The value returned is the integer value V, such that
297 -- Arg = V * fixed-type'Small
299 -- The effect is thus equivalent to first doing an unchecked convert
300 -- from the fixed-point type to its corresponding implementation type,
301 -- and then converting the result to the target integer type. This
302 -- attribute is primarily intended for use in implementation of the
303 -- standard input-output functions for fixed-point values.
305 Attribute_Invalid_Value => True,
306 -- For every scalar type, S'Invalid_Value designates an undefined value
307 -- of the type. If possible this value is an invalid value, and in fact
308 -- is identical to the value that would be set if Initialize_Scalars
309 -- mode were in effect (including the behavior of its value on
310 -- environment variables or binder switches). The intended use is
311 -- to set a value where initialization is required (e.g. as a result of
312 -- the coding standards in use), but logically no initialization is
313 -- needed, and the value should never be accessed.
315 Attribute_Loop_Entry => True,
316 -- For every object of a non-limited type, S'Loop_Entry [(Loop_Name)]
317 -- denotes the constant value of prefix S at the point of entry into the
318 -- related loop. The type of the attribute is the type of the prefix.
324 Attribute_Machine_Size => True,
325 -- This attribute is identical to the Object_Size attribute. It is
326 -- provided for compatibility with the DEC attribute of this name.
328 -----------------------
329 -- Maximum_Alignment --
330 -----------------------
332 Attribute_Maximum_Alignment => True,
333 -- Standard'Maximum_Alignment (Standard is the only permissible prefix)
334 -- provides the maximum useful alignment value for the target. This
335 -- is a static value that can be used to specify the alignment for an
336 -- object, guaranteeing that it is properly aligned in all cases. The
337 -- time this is useful is when an external object is imported and its
338 -- alignment requirements are unknown. This is a static attribute.
344 Attribute_Mechanism_Code => True,
345 -- function'Mechanism_Code yields an integer code for the mechanism
346 -- used for the result of function, and subprogram'Mechanism_Code (n)
347 -- yields the mechanism used for formal parameter number n (a static
348 -- integer value, 1 = first parameter). The code returned is:
350 -- 1 = by copy (value)
352 -- 3 = by descriptor (default descriptor type)
353 -- 4 = by descriptor (UBS unaligned bit string)
354 -- 5 = by descriptor (UBSB aligned bit string with arbitrary bounds)
355 -- 6 = by descriptor (UBA unaligned bit array)
356 -- 7 = by descriptor (S string, also scalar access type parameter)
357 -- 8 = by descriptor (SB string with arbitrary bounds)
358 -- 9 = by descriptor (A contiguous array)
359 -- 10 = by descriptor (NCA non-contiguous array)
365 Attribute_Null_Parameter => True,
366 -- A reference T'Null_Parameter denotes an (imaginary) object of type or
367 -- subtype T allocated at (machine) address zero. The attribute is
368 -- allowed only as the default expression of a formal parameter, or as
369 -- an actual expression of a subprogram call. In either case, the
370 -- subprogram must be imported.
372 -- The identity of the object is represented by the address zero in the
373 -- argument list, independent of the passing mechanism (explicit or
376 -- The reason that this capability is needed is that for a record or
377 -- other composite object passed by reference, there is no other way of
378 -- specifying that a zero address should be passed.
384 Attribute_Object_Size => True,
385 -- Type'Object_Size is the same as Type'Size for all types except
386 -- fixed-point types and discrete types. For fixed-point types and
387 -- discrete types, this attribute gives the size used for default
388 -- allocation of objects and components of the size. See section in
389 -- Einfo ("Handling of type'Size values") for further details.
391 -------------------------
392 -- Passed_By_Reference --
393 -------------------------
395 Attribute_Passed_By_Reference => True,
396 -- T'Passed_By_Reference for any subtype T returns a boolean value that
397 -- is true if the type is normally passed by reference and false if the
398 -- type is normally passed by copy in calls. For scalar types, the
399 -- result is always False and is static. For non-scalar types, the
400 -- result is non-static (since it is computed by Gigi).
406 Attribute_Range_Length => True,
407 -- T'Range_Length for any discrete type T yields the number of values
408 -- represented by the subtype (zero for a null range). The result is
409 -- static for static subtypes. Note that Range_Length applied to the
410 -- index subtype of a one dimensional array always gives the same result
411 -- as Range applied to the array itself. The result is of type universal
418 Attribute_Ref => True,
419 -- System.Address'Ref (Address is the only permissible prefix) is
420 -- equivalent to System'To_Address, provided for compatibility with
427 Attribute_Storage_Unit => True,
428 -- Standard'Storage_Unit (Standard is the only permissible prefix)
429 -- provides the value System.Storage_Unit, and is intended primarily
430 -- for constructing this definition in package System (see note above
431 -- in Default_Bit_Order description). The is a static attribute.
437 Attribute_Stub_Type => True,
438 -- The GNAT implementation of remote access-to-classwide types is
439 -- organised as described in AARM E.4(20.t): a value of an RACW type
440 -- (designating a remote object) is represented as a normal access
441 -- value, pointing to a "stub" object which in turn contains the
442 -- necessary information to contact the designated remote object. A
443 -- call on any dispatching operation of such a stub object does the
444 -- remote call, if necessary, using the information in the stub object
445 -- to locate the target partition, etc.
447 -- For a prefix T that denotes a remote access-to-classwide type,
448 -- T'Stub_Type denotes the type of the corresponding stub objects.
450 -- By construction, the layout of T'Stub_Type is identical to that of
451 -- System.Partition_Interface.RACW_Stub_Type (see implementation notes
452 -- in body of Exp_Dist).
458 Attribute_Target_Name => True,
459 -- Standard'Target_Name yields the string identifying the target for the
460 -- compilation, taken from Sdefault.Target_Name.
466 Attribute_To_Address => True,
467 -- System'To_Address (System is the only permissible prefix) is a
468 -- function that takes any integer value, and converts it into an
469 -- address value. The semantics is to first convert the integer value to
470 -- type Integer_Address according to normal conversion rules, and then
471 -- to convert this to an address using the same semantics as the
472 -- System.Storage_Elements.To_Address function. The important difference
473 -- is that this is a static attribute so it can be used in
474 -- initializations in preelaborate packages.
480 Attribute_Type_Class => True,
481 -- T'Type_Class for any type or subtype T yields the value of the type
482 -- class for the full type of T. If T is a generic formal type, then the
483 -- value is the value for the corresponding actual subtype. The value of
484 -- this attribute is of type System.Aux_DEC.Type_Class, which has the
485 -- following definition:
487 -- type Type_Class is
488 -- (Type_Class_Enumeration,
489 -- Type_Class_Integer,
490 -- Type_Class_Fixed_Point,
491 -- Type_Class_Floating_Point,
493 -- Type_Class_Record,
494 -- Type_Class_Access,
496 -- Type_Class_Address);
498 -- Protected types yield the value Type_Class_Task, which thus applies
499 -- to all concurrent types. This attribute is designed to be compatible
500 -- with the DEC Ada attribute of the same name.
502 -- Note: if pragma Extend_System is used to merge the definitions of
503 -- Aux_DEC into System, then the type Type_Class can be referenced
504 -- as an entity within System, as can its enumeration literals.
510 Attribute_UET_Address => True,
511 -- Unit'UET_Address, where Unit is a program unit, yields the address
512 -- of the unit exception table for the specified unit. This is only
513 -- used in the internal implementation of exception handling. See the
514 -- implementation of unit Ada.Exceptions for details on its use.
516 ------------------------------
517 -- Universal_Literal_String --
518 ------------------------------
520 Attribute_Universal_Literal_String => True,
521 -- The prefix of 'Universal_Literal_String must be a named number.
522 -- The static result is the string consisting of the characters of
523 -- the number as defined in the original source. This allows the
524 -- user program to access the actual text of named numbers without
525 -- intermediate conversions and without the need to enclose the
526 -- strings in quotes (which would preclude their use as numbers).
528 -------------------------
529 -- Unrestricted_Access --
530 -------------------------
532 Attribute_Unrestricted_Access => True,
533 -- The Unrestricted_Access attribute is similar to Access except that
534 -- all accessibility and aliased view checks are omitted. This is very
535 -- much a user-beware attribute. Basically its status is very similar
536 -- to Address, for which it is a desirable replacement where the value
537 -- desired is an access type. In other words, its effect is identical
538 -- to first taking 'Address and then doing an unchecked conversion to
539 -- a desired access type. Note that in GNAT, but not necessarily in
540 -- other implementations, the use of static chains for inner level
541 -- subprograms means that Unrestricted_Access applied to a subprogram
542 -- yields a value that can be called as long as the subprogram is in
543 -- scope (normal Ada 95 accessibility rules restrict this usage).
549 Attribute_VADS_Size => True,
550 -- Typ'VADS_Size yields the Size value typically yielded by some Ada 83
551 -- compilers. The differences between VADS_Size and Size is that for
552 -- scalar types for which no Size has been specified, VADS_Size yields
553 -- the Object_Size rather than the Value_Size. For example, while
554 -- Natural'Size is typically 31, the value of Natural'VADS_Size is 32.
555 -- For all other types, Size and VADS_Size yield the same value.
561 Attribute_Valid_Scalars => True,
562 -- Obj'Valid_Scalars can be applied to any object. The result depends
563 -- on the type of the object:
565 -- For a scalar type, the result is the same as obj'Valid
567 -- For an array object, the result is True if the result of applying
568 -- Valid_Scalars to every component is True. For an empty array the
571 -- For a record object, the result is True if the result of applying
572 -- Valid_Scalars to every component is True. For class-wide types,
573 -- only the components of the base type are checked. For variant
574 -- records, only the components actually present are checked. The
575 -- discriminants, if any, are also checked. If there are no components
576 -- or discriminants, the result is True.
578 -- For any other type that has discriminants, the result is True if
579 -- the result of applying Valid_Scalars to each discriminant is True.
581 -- For all other types, the result is always True
583 -- A warning is given for a trivially True result, when the attribute
584 -- is applied to an object that is not of scalar, array, or record
585 -- type, or in the composite case if no scalar subcomponents exist. For
586 -- a variant record, the warning is given only if none of the variants
587 -- have scalar subcomponents. In addition, the warning is suppressed
588 -- for private types, or generic formal types in an instance.
594 Attribute_Value_Size => True,
595 -- Type'Value_Size is the number of bits required to represent value of
596 -- the given subtype. It is the same as Type'Size, but, unlike Size, may
597 -- be set for non-first subtypes. See section in Einfo ("Handling of
598 -- type'Size values") for further details.
604 Attribute_Word_Size => True,
605 -- Standard'Word_Size (Standard is the only permissible prefix)
606 -- provides the value System.Word_Size, and is intended primarily
607 -- for constructing this definition in package System (see note above
608 -- in Default_Bit_Order description). This is a static attribute.
616 procedure Analyze_Attribute (N : Node_Id);
617 -- Performs bottom up semantic analysis of an attribute. Note that the
618 -- parser has already checked that type returning attributes appear only
619 -- in appropriate contexts (i.e. in subtype marks, or as prefixes for
620 -- other attributes).
622 function Name_Implies_Lvalue_Prefix (Nam : Name_Id) return Boolean;
623 -- Determine whether the name of an attribute reference categorizes its
624 -- prefix as an lvalue. The following attributes fall under this bracket
625 -- by directly or indirectly modifying their prefixes.
631 -- Unrestricted_Access
633 procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id);
634 -- Performs type resolution of attribute. If the attribute yields a
635 -- universal value, mark its type as that of the context. On the other
636 -- hand, if the context itself is universal (as in T'Val (T'Pos (X)), mark
637 -- the type as being the largest type of that class that can be used at
638 -- run-time. This is correct since either the value gets folded (in which
639 -- case it doesn't matter what type of the class we give if, since the
640 -- folding uses universal arithmetic anyway) or it doesn't get folded (in
641 -- which case it is going to be dealt with at runtime, and the largest type
644 function Stream_Attribute_Available
647 Partial_View : Entity_Id := Empty) return Boolean;
648 -- For a limited type Typ, return True if and only if the given attribute
649 -- is available. For Ada 2005, availability is defined by 13.13.2(36/1).
650 -- For Ada 95, an attribute is considered to be available if it has been
651 -- specified using an attribute definition clause for the type, or for its
652 -- full view, or for an ancestor of either. Parameter Partial_View is used
653 -- only internally, when checking for an attribute definition clause that
654 -- is not visible (Ada 95 only).
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