------------------------------------------------------------------------------ -- -- -- 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;