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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                               E L I S T S                                --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1992-2009, 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 3,  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.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

--  This package provides facilities for manipulating lists of nodes (see

--  package Atree for format and implementation of tree nodes). Separate list

--  elements are allocated to represent elements of these lists, so it is

--  possible for a given node to be on more than one element list at a time.

--  See also package Nlists, which provides another form that is threaded

--  through the nodes themselves (using the Link field), which is more time

--  and space efficient, but a node can be only one such list.

with Types;  use Types;

with System;

package Elists is

   --  An element list is represented by a header that is allocated in the

   --  Elist header table. This header contains pointers to the first and

   --  last elements in the list, or to No_Elmt if the list is empty.

   --  The elements in the list each contain a pointer to the next element

   --  and a pointer to the referenced node. Putting a node into an element

   --  list causes no change at all to the node itself, so a node may be

   --  included in multiple element lists, and the nodes thus included may

   --  or may not be elements of node lists (see package Nlists).

   procedure Initialize;

   --  Initialize allocation of element list tables. Called at the start of

   --  compiling each new main source file. Note that Initialize must not be

   --  called if Tree_Read is used.

   procedure Lock;

   --  Lock tables used for element lists before calling backend

   procedure Unlock;

   --  Unlock list tables, in cases where the back end needs to modify them

   procedure Tree_Read;

   --  Initializes internal tables from current tree file using the relevant

   --  Table.Tree_Read routines. Note that Initialize should not be called if

   --  Tree_Read is used. Tree_Read includes all necessary initialization.

   procedure Tree_Write;

   --  Writes out internal tables to current tree file using the relevant

   --  Table.Tree_Write routines.

   function Last_Elist_Id return Elist_Id;

   --  Returns Id of last allocated element list header

   function Elists_Address return System.Address;

   --  Return address of Elists table (used in Back_End for Gigi call)

   function Num_Elists return Nat;

   --  Number of currently allocated element lists

   function Last_Elmt_Id return Elmt_Id;

   --  Returns Id of last allocated list element

   function Elmts_Address return System.Address;

   --  Return address of Elmts table (used in Back_End for Gigi call)

   function Node (Elmt : Elmt_Id) return Node_Or_Entity_Id;

   pragma Inline (Node);

   --  Returns the value of a given list element. Returns Empty if Elmt

   --  is set to No_Elmt.

   function New_Elmt_List return Elist_Id;

   --  Creates a new empty element list. Typically this is used to initialize

   --  a field in some other node which points to an element list where the

   --  list is then subsequently filled in using Append calls.

   function First_Elmt (List : Elist_Id) return Elmt_Id;

   pragma Inline (First_Elmt);

   --  Obtains the first element of the given element list or, if the list has

   --  no items, then No_Elmt is returned.

   function Last_Elmt (List : Elist_Id) return Elmt_Id;

   pragma Inline (Last_Elmt);

   --  Obtains the last element of the given element list or, if the list has

   --  no items, then No_Elmt is returned.

   function Next_Elmt (Elmt : Elmt_Id) return Elmt_Id;

   pragma Inline (Next_Elmt);

   --  This function returns the next element on an element list. The argument

   --  must be a list element other than No_Elmt. Returns No_Elmt if the given

   --  element is the last element of the list.

   procedure Next_Elmt (Elmt : in out Elmt_Id);

   pragma Inline (Next_Elmt);

   --  Next_Elmt (Elmt) is equivalent to Elmt := Next_Elmt (Elmt)

   function Is_Empty_Elmt_List (List : Elist_Id) return Boolean;

   pragma Inline (Is_Empty_Elmt_List);

   --  This function determines if a given tree id references an element list

   --  that contains no items.

   procedure Append_Elmt (N : Node_Or_Entity_Id; To : Elist_Id);

   --  Appends N at the end of To, allocating a new element. N must be a

   --  non-empty node or entity Id, and To must be an Elist (not No_Elist).

   procedure Append_Unique_Elmt (N : Node_Or_Entity_Id; To : Elist_Id);

   --  Like Append_Elmt, except that a check is made to see if To already

   --  contains N and if so the call has no effect.

   procedure Prepend_Elmt (N : Node_Or_Entity_Id; To : Elist_Id);

   --  Appends N at the beginning of To, allocating a new element

   procedure Insert_Elmt_After (N : Node_Or_Entity_Id; Elmt : Elmt_Id);

   --  Add a new element (N) right after the pre-existing element Elmt

   --  It is invalid to call this subprogram with Elmt = No_Elmt.

   procedure Replace_Elmt (Elmt : Elmt_Id; New_Node : Node_Or_Entity_Id);

   pragma Inline (Replace_Elmt);

   --  Causes the given element of the list to refer to New_Node, the node

   --  which was previously referred to by Elmt is effectively removed from

   --  the list and replaced by New_Node.

   procedure Remove_Elmt (List : Elist_Id; Elmt : Elmt_Id);

   --  Removes Elmt from the given list. The node itself is not affected,

   --  but the space used by the list element may be (but is not required

   --  to be) freed for reuse in a subsequent Append_Elmt call.

   procedure Remove_Last_Elmt (List : Elist_Id);

   --  Removes the last element of the given list. The node itself is not

   --  affected, but the space used by the list element may be (but is not

   --  required to be) freed for reuse in a subsequent Append_Elmt call.

   function No (List : Elist_Id) return Boolean;

   pragma Inline (No);

   --  Tests given Id for equality with No_Elist. This allows notations like

   --  "if No (Statements)" as opposed to "if Statements = No_Elist".

   function Present (List : Elist_Id) return Boolean;

   pragma Inline (Present);

   --  Tests given Id for inequality with No_Elist. This allows notations like

   --  "if Present (Statements)" as opposed to "if Statements /= No_Elist".

   function No (Elmt : Elmt_Id) return Boolean;

   pragma Inline (No);

   --  Tests given Id for equality with No_Elmt. This allows notations like

   --  "if No (Operation)" as opposed to "if Operation = No_Elmt".

   function Present (Elmt : Elmt_Id) return Boolean;

   pragma Inline (Present);

   --  Tests given Id for inequality with No_Elmt. This allows notations like

   --  "if Present (Operation)" as opposed to "if Operation /= No_Elmt".

end Elists;