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1 706 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT COMPILER COMPONENTS                         --
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--                                                                          --
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--                             S E M _ C H 1 3                              --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--          Copyright (C) 1992-2010, Free Software Foundation, Inc.         --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
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-- for  more details.  You should have  received  a copy of the GNU General --
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-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
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-- http://www.gnu.org/licenses for a complete copy of the license.          --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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with Table;
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with Types; use Types;
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with Uintp; use Uintp;
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package Sem_Ch13 is
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   procedure Analyze_At_Clause                          (N : Node_Id);
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   procedure Analyze_Attribute_Definition_Clause        (N : Node_Id);
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   procedure Analyze_Enumeration_Representation_Clause  (N : Node_Id);
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   procedure Analyze_Free_Statement                     (N : Node_Id);
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   procedure Analyze_Freeze_Entity                      (N : Node_Id);
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   procedure Analyze_Record_Representation_Clause       (N : Node_Id);
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   procedure Analyze_Code_Statement                     (N : Node_Id);
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   procedure Analyze_Aspect_Specifications (N : Node_Id; E : Entity_Id);
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   --  This procedure is called to analyze aspect specifications for node N. E
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   --  is the corresponding entity declared by the declaration node N. Callers
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   --  should check that Has_Aspects (N) is True before calling this routine.
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   procedure Adjust_Record_For_Reverse_Bit_Order (R : Entity_Id);
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   --  Called from Freeze where R is a record entity for which reverse bit
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   --  order is specified and there is at least one component clause. Adjusts
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   --  component positions according to either Ada 95 or Ada 2005 (AI-133).
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   procedure Build_Invariant_Procedure (Typ : Entity_Id; N : Node_Id);
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   --  Typ is a private type with invariants (indicated by Has_Invariants being
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   --  set for Typ, indicating the presence of pragma Invariant entries on the
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   --  rep chain, note that Invariant aspects have already been converted to
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   --  pragma Invariant), then this procedure builds the spec and body for the
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   --  corresponding Invariant procedure, inserting them at appropriate points
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   --  in the package specification N. Invariant_Procedure is set for Typ. Note
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   --  that this procedure is called at the end of processing the declarations
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   --  in the visible part (i.e. the right point for visibility analysis of
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   --  the invariant expression).
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   procedure Check_Record_Representation_Clause (N : Node_Id);
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   --  This procedure completes the analysis of a record representation clause
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   --  N. It is called at freeze time after adjustment of component clause bit
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   --  positions for possible non-standard bit order. In the case of Ada 2005
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   --  (machine scalar) mode, this adjustment can make substantial changes, so
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   --  some checks, in particular for component overlaps cannot be done at the
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   --  time the record representation clause is first seen, but must be delayed
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   --  till freeze time, and in particular is called after calling the above
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   --  procedure for adjusting record bit positions for reverse bit order.
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70
   procedure Initialize;
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   --  Initialize internal tables for new compilation
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   procedure Set_Enum_Esize (T : Entity_Id);
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   --  This routine sets the Esize field for an enumeration type T, based
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   --  on the current representation information available for T. Note that
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   --  the setting of the RM_Size field is not affected. This routine also
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   --  initializes the alignment field to zero.
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   function Minimum_Size
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     (T      : Entity_Id;
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      Biased : Boolean := False) return Nat;
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   --  Given an elementary type, determines the minimum number of bits required
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   --  to represent all values of the type. This function may not be called
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   --  with any other types. If the flag Biased is set True, then the minimum
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   --  size calculation that biased representation is used in the case of a
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   --  discrete type, e.g. the range 7..8 gives a minimum size of 4 with
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   --  Biased set to False, and 1 with Biased set to True. Note that the
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   --  biased parameter only has an effect if the type is not biased, it
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   --  causes Minimum_Size to indicate the minimum size of an object with
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   --  the given type, of the size the type would have if it were biased. If
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   --  the type is already biased, then Minimum_Size returns the biased size,
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   --  regardless of the setting of Biased. Also, fixed-point types are never
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   --  biased in the current implementation. If the size is not known at
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   --  compile time, this function returns 0.
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   procedure Check_Constant_Address_Clause (Expr : Node_Id; U_Ent : Entity_Id);
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   --  Expr is an expression for an address clause. This procedure checks
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   --  that the expression is constant, in the limited sense that it is safe
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   --  to evaluate it at the point the object U_Ent is declared, rather than
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   --  at the point of the address clause. The condition for this to be true
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   --  is that the expression has no variables, no constants declared after
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   --  U_Ent, and no calls to non-pure functions. If this condition is not
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   --  met, then an appropriate error message is posted. This check is applied
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   --  at the point an object with an address clause is frozen, as well as for
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   --  address clauses for tasks and entries.
106
 
107
   procedure Check_Size
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     (N      : Node_Id;
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      T      : Entity_Id;
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      Siz    : Uint;
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      Biased : out Boolean);
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   --  Called when size Siz is specified for subtype T. This subprogram checks
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   --  that the size is appropriate, posting errors on node N as required.
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   --  This check is effective for elementary types and bit-packed arrays.
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   --  For other non-elementary types, a check is only made if an explicit
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   --  size has been given for the type (and the specified size must match).
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   --  The parameter Biased is set False if the size specified did not require
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   --  the use of biased representation, and True if biased representation
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   --  was required to meet the size requirement. Note that Biased is only
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   --  set if the type is not currently biased, but biasing it is the only
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   --  way to meet the requirement. If the type is currently biased, then
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   --  this biased size is used in the initial check, and Biased is False.
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   --  If the size is too small, and an error message is given, then both
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   --  Esize and RM_Size are reset to the allowed minimum value in T.
125
 
126
   function Rep_Item_Too_Early (T : Entity_Id; N : Node_Id) return Boolean;
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   --  Called at the start of processing a representation clause or a
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   --  representation pragma. Used to check that the representation item
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   --  is not being applied to an incomplete type or to a generic formal
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   --  type or a type derived from a generic formal type. Returns False if
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   --  no such error occurs. If this error does occur, appropriate error
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   --  messages are posted on node N, and True is returned.
133
 
134
   function Rep_Item_Too_Late
135
     (T     : Entity_Id;
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      N     : Node_Id;
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      FOnly : Boolean := False) return Boolean;
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   --  Called at the start of processing a representation clause or a
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   --  representation pragma. Used to check that a representation item
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   --  for entity T does not appear too late (according to the rules in
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   --  RM 13.1(9) and RM 13.1(10)). N is the associated node, which in
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   --  the pragma case is the pragma or representation clause itself, used
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   --  for placing error messages if the item is too late.
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   --
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   --  Fonly is a flag that causes only the freezing rule (para 9) to be
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   --  applied, and the tests of para 10 are skipped. This is appropriate
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   --  for both subtype related attributes (Alignment and Size) and for
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   --  stream attributes, which, although certainly not subtype related
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   --  attributes, clearly should not be subject to the para 10 restrictions
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   --  (see AI95-00137). Similarly, we also skip the para 10 restrictions for
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   --  the Storage_Size case where they also clearly do not apply, and for
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   --  Stream_Convert which is in the same category as the stream attributes.
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   --
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   --  If the rep item is too late, an appropriate message is output and
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   --  True is returned, which is a signal that the caller should abandon
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   --  processing for the item. If the item is not too late, then False
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   --  is returned, and the caller can continue processing the item.
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   --
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   --  If no error is detected, this call also as a side effect links the
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   --  representation item onto the head of the representation item chain
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   --  (referenced by the First_Rep_Item field of the entity).
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   --
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   --  Note: Rep_Item_Too_Late must be called with the underlying type in
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   --  the case of a private or incomplete type. The protocol is to first
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   --  check for Rep_Item_Too_Early using the initial entity, then take the
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   --  underlying type, then call Rep_Item_Too_Late on the result.
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   --
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   --  Note: Calls to Rep_Item_Too_Late are ignored for the case of attribute
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   --  definition clauses which have From_Aspect_Specification set. This is
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   --  because such clauses are linked on to the Rep_Item chain in procedure
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   --  Sem_Ch13.Analyze_Aspect_Specifications. See that procedure for details.
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   function Same_Representation (Typ1, Typ2 : Entity_Id) return Boolean;
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   --  Given two types, where the two types are related by possible derivation,
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   --  determines if the two types have the same representation, or different
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   --  representations, requiring the special processing for representation
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   --  change. A False result is possible only for array, enumeration or
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   --  record types.
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   procedure Validate_Unchecked_Conversion
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     (N        : Node_Id;
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      Act_Unit : Entity_Id);
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   --  Validate a call to unchecked conversion. N is the node for the actual
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   --  instantiation, which is used only for error messages. Act_Unit is the
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   --  entity for the instantiation, from which the actual types etc. for this
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   --  instantiation can be determined. This procedure makes an entry in a
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   --  table and/or generates an N_Validate_Unchecked_Conversion node. The
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   --  actual checking is done in Validate_Unchecked_Conversions or in the
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   --  back end as required.
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   procedure Validate_Unchecked_Conversions;
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   --  This routine is called after calling the backend to validate unchecked
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   --  conversions for size and alignment appropriateness. The reason it is
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   --  called that late is to take advantage of any back-annotation of size
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   --  and alignment performed by the backend.
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   procedure Validate_Address_Clauses;
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   --  This is called after the back end has been called (and thus after the
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   --  alignments of objects have been back annotated). It goes through the
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   --  table of saved address clauses checking for suspicious alignments and
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   --  if necessary issuing warnings.
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   procedure Validate_Independence;
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   --  This is called after the back end has been called (and thus after the
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   --  layout of components has been back annotated). It goes through the
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   --  table of saved pragma Independent[_Component] entries, checking that
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   --  independence can be achieved, and if necessary issuing error messages.
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   -------------------------------------
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   -- Table for Validate_Independence --
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   -------------------------------------
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   --  If a legal pragma Independent or Independent_Components is given for
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   --  an entity, then an entry is made in this table, to be checked by a
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   --  call to Validate_Independence after back annotation of layout is done.
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   type Independence_Check_Record is record
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      N : Node_Id;
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      --  The pragma Independent or Independent_Components
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      E : Entity_Id;
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      --  The entity to which it applies
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   end record;
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   package Independence_Checks is new Table.Table (
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     Table_Component_Type => Independence_Check_Record,
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     Table_Index_Type     => Int,
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     Table_Low_Bound      => 1,
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     Table_Initial        => 20,
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     Table_Increment      => 200,
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     Table_Name           => "Independence_Checks");
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   -----------------------------------
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   -- Handling of Aspect Visibility --
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   -----------------------------------
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   --  The visibility of aspects is tricky. First, the visibility is delayed
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   --  to the freeze point. This is not too complicated, what we do is simply
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   --  to leave the aspect "laying in wait" for the freeze point, and at that
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   --  point materialize and analye the corresponding attribute definition
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   --  clause or pragma. There is some special processing for preconditions
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   --  and postonditions, where the pragmas themselves deal with the required
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   --  delay, but basically the approach is the same, delay analysis of the
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   --  expression to the freeze point.
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   --  Much harder is the requirement for diagnosing cases in which an early
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   --  freeze causes a change in visibility. Consider:
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   --    package AspectVis is
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   --       R_Size : constant Integer := 32;
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   --
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   --       package Inner is
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   --          type R is new Integer with
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   --            Size => R_Size;
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   --          F : R; -- freezes
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   --          R_Size : constant Integer := 64;
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   --          S : constant Integer := R'Size; -- 32 not 64
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   --       end Inner;
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   --    end AspectVis;
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   --  Here the 32 not 64 shows what would be expected if this program were
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   --  legal, since the evaluation of R_Size has to be done at the freeze
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   --  point and gets the outer definition not the inner one.
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   --  But the language rule requires this program to be diagnosed as illegal
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   --  because the visibility changes between the freeze point and the end of
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   --  the declarative region.
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   --  To meet this requirement, we first note that the Expression field of the
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   --  N_Aspect_Specification node holds the raw unanalyzed expression, which
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   --  will get used in processing the aspect. At the time of analyzing the
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   --  N_Aspect_Specification node, we create a complete copy of the expression
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   --  and store it in the entity field of the Identifier (an odd usage, but
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   --  the identifier is not used except to identify the aspect, so its Entity
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   --  field is otherwise unused, and we are short of room in the node).
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   --  This copy stays unanalyzed up to the freeze point, where we analyze the
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   --  resulting pragma or attribute definition clause, except that in the
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   --  case of invariants and predicates, we mark occurrences of the subtype
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   --  name as having the entity of the subprogram parameter, so that they
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   --  will not cause trouble in the following steps.
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   --  Then at the freeze point, we create another copy of this unanalyzed
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   --  expression. By this time we no longer need the Expression field for
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   --  other purposes, so we can store it there. Now we have two copies of
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   --  the original unanalyzed expression. One of them gets preanalyzed at
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   --  the freeze point to capture the visibility at the freeze point.
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   --  Now when we hit the freeze all at the end of the declarative part, if
290
   --  we come across a frozen entity with delayed aspects, we still have one
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   --  copy of the unanalyzed expression available in the node, and we again
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   --  do a preanalysis using that copy and the visibility at the end of the
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   --  declarative part. Now we have two preanalyzed expression (preanalysis
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   --  is good enough, since we are only interested in referenced entities).
295
   --  One captures the visibility at the freeze point, the other captures the
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   --  visibility at the end of the declarative part. We see if the entities
297
   --  in these two expressions are the same, by seeing if the two expressions
298
   --  are fully conformant, and if not, issue appropriate error messages.
299
 
300
   --  Quite an awkward procedure, but this is an awkard requirement!
301
 
302
   procedure Check_Aspect_At_Freeze_Point (ASN : Node_Id);
303
   --  Performs the processing described above at the freeze point, ASN is the
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   --  N_Aspect_Specification node for the aspect.
305
 
306
   procedure Check_Aspect_At_End_Of_Declarations (ASN : Node_Id);
307
   --  Performs the processing described above at the freeze all point, and
308
   --  issues appropriate error messages if the visibility has indeed changed.
309
   --  Again, ASN is the N_Aspect_Specification node for the aspect.
310
end Sem_Ch13;

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