| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT COMPILER COMPONENTS -- |
| -- -- |
| -- S E M _ A T T R -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 1992-2003, Free Software Foundation, Inc. -- |
| -- -- |
| -- GNAT is free software; you can redistribute it and/or modify it under -- |
| -- terms of the GNU General Public License as published by the Free Soft- -- |
| -- ware Foundation; either version 2, or (at your option) any later ver- -- |
| -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- |
| -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- |
| -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- |
| -- for more details. You should have received a copy of the GNU General -- |
| -- Public License distributed with GNAT; see file COPYING. If not, write -- |
| -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- |
| -- MA 02111-1307, USA. -- |
| -- -- |
| -- GNAT was originally developed by the GNAT team at New York University. -- |
| -- Extensive contributions were provided by Ada Core Technologies Inc. -- |
| -- -- |
| ------------------------------------------------------------------------------ |
| |
| -- Attribute handling is isolated in a separate package to ease the addition |
| -- of implementation defined attributes. Logically this processing belongs |
| -- in chapter 4. See Sem_Ch4 for a description of the relation of the |
| -- Analyze and Resolve routines for expression components. |
| |
| -- This spec also documents all GNAT implementation defined pragmas |
| |
| with Snames; use Snames; |
| with Types; use Types; |
| |
| package Sem_Attr is |
| |
| type Attribute_Class_Array is array (Attribute_Id) of Boolean; |
| -- Type used to build attribute classification flag arrays |
| |
| ----------------------------------------- |
| -- Implementation Dependent Attributes -- |
| ----------------------------------------- |
| |
| -- This section describes the implementation dependent attributes |
| -- provided in GNAT, as well as constructing an array of flags |
| -- indicating which attributes these are. |
| |
| Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'( |
| |
| ------------------ |
| -- Abort_Signal -- |
| ------------------ |
| |
| Attribute_Abort_Signal => True, |
| -- |
| -- Standard'Abort_Signal (Standard is the only allowed prefix) |
| -- provides the entity for the special exception used to signal |
| -- task abort or asynchronous transfer of control. Normally this |
| -- attribute should only be used in the tasking runtime (it is |
| -- highly peculiar, and completely outside the normal semantics |
| -- of Ada, for a user program to intercept the abort exception). |
| |
| ------------------ |
| -- Address_Size -- |
| ------------------ |
| |
| Attribute_Address_Size => True, |
| -- |
| -- Standard'Address_Size (Standard is the only allowed prefix) is |
| -- a static constant giving the number of bits in an Address. It |
| -- is used primarily for constructing the definition of Memory_Size |
| -- in package Standard, but may be freely used in user programs. |
| -- This is a static attribute. |
| |
| --------------- |
| -- Asm_Input -- |
| --------------- |
| |
| Attribute_Asm_Input => True, |
| -- |
| -- Used only in conjunction with the Asm and Asm_Volatile subprograms |
| -- in package Machine_Code to construct machine instructions. See |
| -- documentation in package Machine_Code in file s-maccod.ads. |
| |
| ---------------- |
| -- Asm_Output -- |
| ---------------- |
| |
| Attribute_Asm_Output => True, |
| -- |
| -- Used only in conjunction with the Asm and Asm_Volatile subprograms |
| -- in package Machine_Code to construct machine instructions. See |
| -- documentation in package Machine_Code in file s-maccod.ads. |
| |
| --------------- |
| -- AST_Entry -- |
| --------------- |
| |
| Attribute_AST_Entry => True, |
| -- |
| -- E'Ast_Entry, where E is a task entry, yields a value of the |
| -- predefined type System.DEC.AST_Handler, that enables the given |
| -- entry to be called when an AST occurs. If the name to which the |
| -- attribute applies has not been specified with the pragma AST_Entry, |
| -- the attribute returns the value No_Ast_Handler, and no AST occurs. |
| -- If the entry is for a task that is not callable (T'Callable False), |
| -- the exception program error is raised. If an AST occurs for an |
| -- entry of a task that is terminated, the program is erroneous. |
| -- |
| -- The attribute AST_Entry is supported only in OpenVMS versions |
| -- of GNAT. It will be rejected as illegal in other GNAT versions. |
| |
| --------- |
| -- Bit -- |
| --------- |
| |
| Attribute_Bit => True, |
| -- |
| -- Obj'Bit, where Obj is any object, yields the bit offset within |
| -- the storage unit (byte) that contains the first bit of storage |
| -- allocated for the object. The value of this attribute is of the |
| -- type Universal_Integer, and is always a non-negative number not |
| -- exceeding the value of System.Storage_Unit. |
| -- |
| -- For an object that is a variable or a constant allocated in a |
| -- register, the value is zero. (The use of this attribute does not |
| -- force the allocation of a variable to memory). |
| -- |
| -- For an object that is a formal parameter, this attribute applies |
| -- to either the matching actual parameter or to a copy of the |
| -- matching actual parameter. |
| -- |
| -- For an access object the value is zero. Note that Obj.all'Bit is |
| -- subject to an Access_Check for the designated object. Similarly |
| -- for a record component X.C'Bit is subject to a discriminant check |
| -- and X(I).Bit and X(I1..I2)'Bit are subject to index checks. |
| -- |
| -- This attribute is designed to be compatible with the DEC Ada |
| -- definition and implementation of the Bit attribute. |
| |
| ------------------ |
| -- Code_Address -- |
| ------------------ |
| |
| Attribute_Code_Address => True, |
| -- |
| -- subp'Code_Address, where subp is a subprogram entity, gives the |
| -- address of the first generated instruction for a subprogram. This |
| -- is often, but not always the same as the 'Address value, which is |
| -- the address to be used in a call. The differences occur in the case |
| -- of a nested procedure (where Address yields the address of the |
| -- trampoline code used to load the static link), and on some systems |
| -- which use procedure descriptors (in which case Address yields the |
| -- address of the descriptor). |
| |
| ----------------------- |
| -- Default_Bit_Order -- |
| ----------------------- |
| |
| Attribute_Default_Bit_Order => True, |
| -- |
| -- Standard'Default_Bit_Order (Standard is the only permissible prefix), |
| -- provides the value System.Default_Bit_Order as a Pos value (0 for |
| -- High_Order_First, 1 for Low_Order_First). This is used to construct |
| -- the definition of Default_Bit_Order in package System. This is a |
| -- static attribute. |
| |
| --------------- |
| -- Elab_Body -- |
| --------------- |
| |
| Attribute_Elab_Body => True, |
| -- |
| -- This attribute can only be applied to a program unit name. It |
| -- returns the entity for the corresponding elaboration procedure |
| -- for elaborating the body of the referenced unit. This is used |
| -- in the main generated elaboration procedure by the binder, and |
| -- is not normally used in any other context, but there may be |
| -- specialized situations in which it is useful to be able to |
| -- call this elaboration procedure from Ada code, e.g. if it |
| -- is necessary to do selective reelaboration to fix some error. |
| |
| --------------- |
| -- Elab_Spec -- |
| --------------- |
| |
| Attribute_Elab_Spec => True, |
| -- |
| -- This attribute can only be applied to a program unit name. It |
| -- returns the entity for the corresponding elaboration procedure |
| -- for elaborating the spec of the referenced unit. This is used |
| -- in the main generated elaboration procedure by the binder, and |
| -- is not normally used in any other context, but there may be |
| -- specialized situations in which it is useful to be able to |
| -- call this elaboration procedure from Ada code, e.g. if it |
| -- is necessary to do selective reelaboration to fix some error. |
| |
| ---------------- |
| -- Elaborated -- |
| ---------------- |
| |
| Attribute_Elaborated => True, |
| -- |
| -- Lunit'Elaborated, where Lunit is a library unit, yields a boolean |
| -- value indicating whether or not the body of the designated library |
| -- unit has been elaborated yet. |
| |
| -------------- |
| -- Enum_Rep -- |
| -------------- |
| |
| Attribute_Enum_Rep => True, |
| -- |
| -- For every enumeration subtype S, S'Enum_Rep denotes a function |
| -- with the following specification: |
| -- |
| -- function S'Enum_Rep (Arg : S'Base) return universal_integer; |
| -- |
| -- The function returns the representation value for the given |
| -- enumeration value. This will be equal to the 'Pos value in the |
| -- absence of an enumeration representation clause. This is a static |
| -- attribute (i.e. the result is static if the argument is static). |
| |
| ----------------- |
| -- Fixed_Value -- |
| ----------------- |
| |
| Attribute_Fixed_Value => True, |
| -- |
| -- For every fixed-point type S, S'Fixed_Value denotes a function |
| -- with the following specification: |
| -- |
| -- function S'Fixed_Value (Arg : universal_integer) return S; |
| -- |
| -- The value returned is the fixed-point value V such that |
| -- |
| -- V = Arg * S'Small |
| -- |
| -- The effect is thus equivalent to first converting the argument |
| -- to the integer type used to represent S, and then doing an |
| -- unchecked conversion to the fixed-point type. This attribute is |
| -- primarily intended for use in implementation of the input-output |
| -- functions for fixed-point values. |
| |
| ----------------------- |
| -- Has_Discriminants -- |
| ----------------------- |
| |
| Attribute_Has_Discriminants => True, |
| -- |
| -- Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields |
| -- a Boolean value indicating whether or not the actual instantiation |
| -- type has discriminants. |
| |
| --------- |
| -- Img -- |
| --------- |
| |
| Attribute_Img => True, |
| -- |
| -- The 'Img function is defined for any prefix, P, that denotes an |
| -- object of scalar type T. P'Img is equivalent to T'Image (P). This |
| -- is convenient for debugging. For example: |
| -- |
| -- Put_Line ("X = " & X'Img); |
| -- |
| -- has the same meaning as the more verbose: |
| -- |
| -- Put_Line ("X = " & Temperature_Type'Image (X)); |
| -- |
| -- where Temperature_Type is the subtype of the object X. |
| |
| ------------------- |
| -- Integer_Value -- |
| ------------------- |
| |
| Attribute_Integer_Value => True, |
| -- |
| -- For every integer type S, S'Integer_Value denotes a function |
| -- with the following specification: |
| -- |
| -- function S'Integer_Value (Arg : universal_fixed) return S; |
| -- |
| -- The value returned is the integer value V, such that |
| -- |
| -- Arg = V * fixed-type'Small |
| -- |
| -- The effect is thus equivalent to first doing an unchecked convert |
| -- from the fixed-point type to its corresponding implementation type, |
| -- and then converting the result to the target integer type. This |
| -- attribute is primarily intended for use in implementation of the |
| -- standard input-output functions for fixed-point values. |
| |
| ------------------ |
| -- Machine_Size -- |
| ------------------ |
| |
| Attribute_Machine_Size => True, |
| -- |
| -- This attribute is identical to the Object_Size attribute. It is |
| -- provided for compatibility with the DEC attribute of this name. |
| |
| ----------------------- |
| -- Maximum_Alignment -- |
| ----------------------- |
| |
| Attribute_Maximum_Alignment => True, |
| -- |
| -- Standard'Maximum_Alignment (Standard is the only permissible prefix) |
| -- provides the maximum useful alignment value for the target. This |
| -- is a static value that can be used to specify the alignment for an |
| -- object, guaranteeing that it is properly aligned in all cases. The |
| -- time this is useful is when an external object is imported and its |
| -- alignment requirements are unknown. This is a static attribute. |
| |
| -------------------- |
| -- Mechanism_Code -- |
| -------------------- |
| |
| Attribute_Mechanism_Code => True, |
| -- |
| -- function'Mechanism_Code yeilds an integer code for the mechanism |
| -- used for the result of function, and subprogram'Mechanism_Code (n) |
| -- yields the mechanism used for formal parameter number n (a static |
| -- integer value, 1 = first parameter). The code returned is: |
| -- |
| -- 1 = by copy (value) |
| -- 2 = by reference |
| -- 3 = by descriptor (default descriptor type) |
| -- 4 = by descriptor (UBS unaligned bit string) |
| -- 5 = by descriptor (UBSB aligned bit string with arbitrary bounds) |
| -- 6 = by descriptor (UBA unaligned bit array) |
| -- 7 = by descriptor (S string, also scalar access type parameter) |
| -- 8 = by descriptor (SB string with arbitrary bounds) |
| -- 9 = by descriptor (A contiguous array) |
| -- 10 = by descriptor (NCA non-contiguous array) |
| |
| -------------------- |
| -- Null_Parameter -- |
| -------------------- |
| |
| Attribute_Null_Parameter => True, |
| -- |
| -- A reference T'Null_Parameter denotes an (imaginary) object of |
| -- type or subtype T allocated at (machine) address zero. The |
| -- attribute is allowed only as the default expression of a formal |
| -- parameter, or as an actual expression of a subporgram call. In |
| -- either case, the subprogram must be imported. |
| -- |
| -- The identity of the object is represented by the address zero |
| -- in the argument list, independent of the passing mechanism |
| -- (explicit or default). |
| -- |
| -- The reason that this capability is needed is that for a record |
| -- or other composite object passed by reference, there is no other |
| -- way of specifying that a zero address should be passed. |
| |
| ----------------- |
| -- Object_Size -- |
| ----------------- |
| |
| Attribute_Object_Size => True, |
| -- |
| -- Type'Object_Size is the same as Type'Size for all types except |
| -- fixed-point types and discrete types. For fixed-point types and |
| -- discrete types, this attribute gives the size used for default |
| -- allocation of objects and components of the size. See section |
| -- in Einfo ("Handling of type'Size values") for further details. |
| |
| ------------------------- |
| -- Passed_By_Reference -- |
| ------------------------- |
| |
| Attribute_Passed_By_Reference => True, |
| -- |
| -- T'Passed_By_Reference for any subtype T returns a boolean value |
| -- that is true if the type is normally passed by reference and |
| -- false if the type is normally passed by copy in calls. For scalar |
| -- types, the result is always False and is static. For non-scalar |
| -- types, the result is non-static (since it is computed by Gigi). |
| |
| ------------------ |
| -- Range_Length -- |
| ------------------ |
| |
| Attribute_Range_Length => True, |
| -- |
| -- T'Range_Length for any discrete type T yields the number of |
| -- values represented by the subtype (zero for a null range). The |
| -- result is static for static subtypes. Note that Range_Length |
| -- applied to the index subtype of a one dimensional array always |
| -- gives the same result as Range applied to the array itself. |
| -- The result is of type universal integer. |
| |
| ------------------ |
| -- Storage_Unit -- |
| ------------------ |
| |
| Attribute_Storage_Unit => True, |
| -- |
| -- Standard'Storage_Unit (Standard is the only permissible prefix) |
| -- provides the value System.Storage_Unit, and is intended primarily |
| -- for constructing this definition in package System (see note above |
| -- in Default_Bit_Order description). The is a static attribute. |
| |
| ----------------- |
| -- Target_Name -- |
| ----------------- |
| |
| Attribute_Target_Name => True, |
| -- |
| -- Standard'Target_Name yields the string identifying the target |
| -- for the compilation, taken from Sdefault.Target_Name. |
| |
| ---------------- |
| -- To_Address -- |
| ---------------- |
| |
| Attribute_To_Address => True, |
| -- |
| -- System'To_Address (Address is the only permissible prefix) |
| -- is a function that takes any integer value, and converts it into |
| -- an address value. The semantics is to first convert the integer |
| -- value to type Integer_Address according to normal conversion |
| -- rules, and then to convert this to an address using the same |
| -- semantics as the System.Storage_Elements.To_Address function. |
| -- The important difference is that this is a static attribute |
| -- so it can be used in initializations in preealborate packages. |
| |
| ---------------- |
| -- Type_Class -- |
| ---------------- |
| |
| Attribute_Type_Class => True, |
| -- |
| -- T'Type_Class for any type or subtype T yields the value of the |
| -- type class for the full type of T. If T is a generic formal type, |
| -- then the value is the value for the corresponding actual subtype. |
| -- The value of this attribute is of type System.Aux_DEC.Type_Class, |
| -- which has the following definition: |
| -- |
| -- type Type_Class is |
| -- (Type_Class_Enumeration, |
| -- Type_Class_Integer, |
| -- Type_Class_Fixed_Point, |
| -- Type_Class_Floating_Point, |
| -- Type_Class_Array, |
| -- Type_Class_Record, |
| -- Type_Class_Access, |
| -- Type_Class_Task, |
| -- Type_Class_Address); |
| -- |
| -- Protected types yield the value Type_Class_Task, which thus |
| -- applies to all concurrent types. This attribute is designed to |
| -- be compatible with the DEC Ada attribute of the same name. |
| -- |
| -- Note: if pragma Extend_System is used to merge the definitions of |
| -- Aux_DEC into System, then the type Type_Class can be referenced |
| -- as an entity within System, as can its enumeration literals. |
| |
| ----------------- |
| -- UET_Address -- |
| ----------------- |
| |
| Attribute_UET_Address => True, |
| -- |
| -- Unit'UET_Address, where Unit is a program unit, yields the address |
| -- of the unit exception table for the specified unit. This is only |
| -- used in the internal implementation of exception handling. See the |
| -- implementation of unit Ada.Exceptions for details on its use. |
| |
| ------------------------------ |
| -- Universal_Literal_String -- |
| ------------------------------ |
| |
| Attribute_Universal_Literal_String => True, |
| -- |
| -- The prefix of 'Universal_Literal_String must be a named number. |
| -- The static result is the string consisting of the characters of |
| -- the number as defined in the original source. This allows the |
| -- user program to access the actual text of named numbers without |
| -- intermediate conversions and without the need to enclose the |
| -- strings in quotes (which would preclude their use as numbers). |
| -- This is used internally for the construction of values of the |
| -- floating-point attributes from the file ttypef.ads, but may |
| -- also be used by user programs. |
| |
| ------------------------- |
| -- Unrestricted_Access -- |
| ------------------------- |
| |
| Attribute_Unrestricted_Access => True, |
| -- |
| -- The Unrestricted_Access attribute is similar to Access except that |
| -- all accessibility and aliased view checks are omitted. This is very |
| -- much a user-beware attribute. Basically its status is very similar |
| -- to Address, for which it is a desirable replacement where the value |
| -- desired is an access type. In other words, its effect is identical |
| -- to first taking 'Address and then doing an unchecked conversion to |
| -- a desired access type. Note that in GNAT, but not necessarily in |
| -- other implementations, the use of static chains for inner level |
| -- subprograms means that Unrestricted_Access applied to a subprogram |
| -- yields a value that can be called as long as the subprogram is in |
| -- scope (normal Ada 95 accessibility rules restrict this usage). |
| |
| --------------- |
| -- VADS_Size -- |
| --------------- |
| |
| Attribute_VADS_Size => True, |
| -- |
| -- Typ'VADS_Size yields the Size value typically yielded by some |
| -- Ada 83 compilers. The differences between VADS_Size and Size |
| -- is that for scalar types for which no Size has been specified, |
| -- VADS_Size yields the Object_Size rather than the Value_Size. |
| -- For example, while Natural'Size is typically 31, the value of |
| -- Natural'VADS_Size is 32. For all other types, Size and VADS_Size |
| -- yield the same value. |
| |
| ---------------- |
| -- Value_Size -- |
| ---------------- |
| |
| Attribute_Value_Size => True, |
| -- |
| -- Type'Value_Size is the number of bits required to represent a |
| -- value of the given subtype. It is the same as Type'Size, but, |
| -- unlike Size, may be set for non-first subtypes. See section |
| -- in Einfo ("Handling of type'Size values") for further details. |
| |
| --------------- |
| -- Word_Size -- |
| --------------- |
| |
| Attribute_Word_Size => True, |
| -- |
| -- Standard'Word_Size (Standard is the only permissible prefix) |
| -- provides the value System.Word_Size, and is intended primarily |
| -- for constructing this definition in package System (see note above |
| -- in Default_Bit_Order description). This is a static attribute. |
| |
| others => False); |
| |
| ----------------- |
| -- Subprograms -- |
| ----------------- |
| |
| procedure Analyze_Attribute (N : Node_Id); |
| -- Performs bottom up semantic analysis of an attribute. Note that the |
| -- parser has already checked that type returning attributes appear only |
| -- in appropriate contexts (i.e. in subtype marks, or as prefixes for |
| -- other attributes). |
| |
| procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id); |
| -- Performs type resolution of attribute. If the attribute yields |
| -- a universal value, mark its type as that of the context. On |
| -- the other hand, if the context itself is universal (as in |
| -- T'Val (T'Pos (X)), mark the type as being the largest type of |
| -- that class that can be used at run-time. This is correct since |
| -- either the value gets folded (in which case it doesn't matter |
| -- what type of the class we give if, since the folding uses universal |
| -- arithmetic anyway) or it doesn't get folded (in which case it is |
| -- going to be dealt with at runtime, and the largest type is right). |
| |
| end Sem_Attr; |
