+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT COMPILER COMPONENTS --
--- --
--- S E M _ A T T R --
--- --
--- S p e c --
--- --
--- $Revision: 1.1.16.1 $
--- --
--- Copyright (C) 1992-1999, 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.
-
- ----------------------------
- -- Max_Interrupt_Priority --
- ----------------------------
-
- Attribute_Max_Interrupt_Priority => True,
- --
- -- Standard'Max_Interrupt_Priority (Standard is the only permissible
- -- prefix), provides the value System.Max_Interrupt_Priority, and is
- -- intended primarily for constructing this definition in package
- -- System (see note above in Default_Bit_Order description}. This
- -- is a static attribute.
-
- ------------------
- -- Max_Priority --
- ------------------
-
- Attribute_Max_Priority => True,
- --
- -- Standard'Max_Priority (Standard is the only permissible prefix)
- -- provides the value System.Max_Priority, and is intended primarily
- -- for constructing this definition in package System (see note above
- -- in Default_Bit_Order description). This is a static attribute.
-
- -----------------------
- -- 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.
-
- ----------
- -- Tick --
- ----------
-
- Attribute_Tick => True,
- --
- -- Standard'Tick (Standard is the only permissible prefix) provides
- -- the value System.Tick, and is intended primarily for constructing
- -- this definition in package System (see note above in description
- -- of Default_Bit_Order). This is a static attribute.
-
- ----------------
- -- 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;
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