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--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                               F R E E Z E                                --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1992-2010, 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.  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 COPYING3.  If not, go to --

-- http://www.gnu.org/licenses for a complete copy of the license.          --

--                                                                          --

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

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

--                                                                          --

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with Types; use Types;

package Freeze is

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

   -- Handling of Freezing --

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

   --  In the formal Ada semantics, freezing of entities occurs at a well

   --  defined point, described in (RM 13.14). The model in GNAT of freezing

   --  is that a Freeze_Entity node is generated at the point where an entity

   --  is frozen, and the entity contains a pointer (Freeze_Node) to this

   --  generated freeze node.

   --  The freeze node is processed in the expander to generate associated

   --  data and subprograms (e.g. an initialization procedure) which must

   --  be delayed until the type is frozen and its representation can be

   --  fully determined. Subsequently the freeze node is used by Gigi to

   --  determine the point at which it should elaborate the corresponding

   --  entity (this elaboration also requires the representation of the

   --  entity to be fully determinable). The freeze node is also used to

   --  provide additional diagnostic information (pinpointing the freeze

   --  point), when order of freezing errors are detected.

   --  If we were fully faithful to the Ada model, we would generate freeze

   --  nodes for all entities, but that is a bit heavy so we optimize (that

   --  is the nice word) or cut corners (which is a bit more honest). For

   --  many entities, we do not need to delay the freeze and instead can

   --  freeze them at the point of declaration. The conditions for this

   --  early freezing being permissible are as follows:

   --    There is no associated expander activity that needs to be delayed

   --    Gigi can fully elaborate the entity at the point of occurrence (or,

   --    equivalently, no real elaboration is required for the entity).

   --  In order for these conditions to be met (especially the second), it

   --  must be the case that all representation characteristics of the entity

   --  can be determined at declaration time.

   --  The following indicates how freezing is handled for all entity kinds:

   --    Types

   --      All declared types have freeze nodes, as well as anonymous base

   --      types created for type declarations where the defining identifier

   --      is a first subtype of the anonymous type.

   --    Subtypes

   --      All first subtypes have freeze nodes. Other subtypes need freeze

   --      nodes if the corresponding base type has not yet been frozen. If

   --      the base type has been frozen, then there is no need for a freeze

   --      node, since no rep clauses can appear for the subtype in any case.

   --    Implicit types and subtypes

   --      As noted above, implicit base types always have freeze nodes. Other

   --      implicit types and subtypes typically do not require freeze nodes,

   --      because there is no possibility of delaying any information about

   --      their representation.

   --    Subprograms

   --

   --      Are frozen at the point of declaration unless one or more of the

   --      formal types or return type themselves have delayed freezing and

   --      are not yet frozen. This includes the case of a formal access type

   --      where the designated type is not frozen. Note that we are talking

   --      about subprogram specs here (subprogram body entities have no

   --      relevance), and in any case, subprogram bodies freeze everything.

   --    Objects with dynamic address clauses

   --

   --      These have a delayed freeze. Gigi will generate code to evaluate

   --      the initialization expression if present and store it in a temp.

   --      The actual object is created at the point of the freeze, and if

   --      necessary initialized by copying the value of this temporary.

   --    Formal Parameters

   --

   --      Are frozen when the associated subprogram is frozen, so there is

   --      never any need for them to have delayed freezing.

   --    Other Objects

   --

   --      Are always frozen at the point of declaration

   --    All Other Entities

   --      Are always frozen at the point of declaration

   --  The flag Has_Delayed_Freeze is used for to indicate that delayed

   --  freezing is required. Usually the associated freeze node is allocated

   --  at the freezing point. One special exception occurs with anonymous

   --  base types, where the freeze node is preallocated at the point of

   --  declaration, so that the First_Subtype_Link field can be set.

   Freezing_Library_Level_Tagged_Type : Boolean := False;

   --  Flag used to indicate that we are freezing the primitives of a library

   --  level tagged types. Used to disable checks on premature freezing.

   --  More documentation needed??? why is this flag needed? what are these

   --  checks? why do they need disabling in some cases?

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

   -- Subprograms --

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

   function Build_Renamed_Body

     (Decl  : Node_Id;

      New_S : Entity_Id) return Node_Id;

   --  Rewrite renaming declaration as a subprogram body, whose single

   --  statement is a call to the renamed entity. New_S is the entity that

   --  appears in the renaming declaration. If this is a Renaming_As_Body,

   --  then Decl is the original subprogram declaration that is completed

   --  by the renaming, otherwise it is the renaming declaration itself.

   --  The caller inserts the body where required. If this call comes

   --  from a freezing action, the resulting body is analyzed at once.

   procedure Check_Compile_Time_Size (T : Entity_Id);

   --  Check to see whether the size of the type T is known at compile time.

   --  There are three possible cases:

   --

   --    Size is not known at compile time. In this case, the call has no

   --    effect. Note that the processing is conservative here, in the sense

   --    that this routine may decide that the size is not known even if in

   --    fact Gigi decides it is known, but the opposite situation can never

   --    occur.

   --

   --    Size is known at compile time, but the actual value of the size is

   --    not known to the front end or is definitely 32 or more. In this case

   --    Size_Known_At_Compile_Time is set, but the Esize field is left set

   --    to zero (to be set by Gigi).

   --

   --    Size is known at compile time, and the actual value of the size is

   --    known to the front end and is less than 32. In this case, the flag

   --    Size_Known_At_Compile_Time is set, and in addition Esize is set to

   --    the required size, allowing for possible front end packing of an

   --    array using this type as a component type.

   --

   --  Note: the flag Size_Known_At_Compile_Time is used to determine if the

   --  secondary stack must be used to return a value of the type, and also

   --  to determine whether a component clause is allowed for a component

   --  of the given type.

   --

   --  Note: this is public because of one dubious use in Sem_Res???

   --

   --  Note: Check_Compile_Time_Size does not test the case of the size being

   --  known because a size clause is specifically given. That is because we

   --  do not allow a size clause if the size would not otherwise be known at

   --  compile time in any case.

   function Is_Atomic_Aggregate

     (E   : Entity_Id;

      Typ : Entity_Id) return Boolean;

   --  If an atomic object is initialized with an aggregate or is assigned an

   --  aggregate, we have to prevent a piecemeal access or assignment to the

   --  object, even if the aggregate is to be expanded. We create a temporary

   --  for the aggregate, and assign the temporary instead, so that the back

   --  end can generate an atomic move for it. This is only done in the context

   --  of an object declaration or an assignment. Function is a noop and

   --  returns false in other contexts.

   function Freeze_Entity (E : Entity_Id; N : Node_Id) return List_Id;

   --  Freeze an entity, and return Freeze nodes, to be inserted at the point

   --  of call. N is a node whose source location corresponds to the freeze

   --  point. This is used in placing warning messages in the situation where

   --  it appears that a type has been frozen too early, e.g. when a primitive

   --  operation is declared after the freezing point of its tagged type.

   --  Returns No_List if no freeze nodes needed.

   procedure Freeze_All (From : Entity_Id; After : in out Node_Id);

   --  Before a non-instance body, or at the end of a declarative part

   --  freeze all entities therein that are not yet frozen. Calls itself

   --  recursively to catch types in inner packages that were not frozen

   --  at the inner level because they were not yet completely defined.

   --  This routine also analyzes and freezes default parameter expressions

   --  in subprogram specifications (this has to be delayed until all the

   --  types are frozen). The resulting freeze nodes are inserted just

   --  after node After (which is a list node) and analyzed. On return,

   --  'After' is updated to point to the last node inserted (or is returned

   --  unchanged if no nodes were inserted). 'From' is the last entity frozen

   --  in the scope. It is used to prevent a quadratic traversal over already

   --  frozen entities.

   procedure Freeze_Before (N : Node_Id; T : Entity_Id);

   --  Freeze T then Insert the generated Freeze nodes before the node N

   procedure Freeze_Expression (N : Node_Id);

   --  Freezes the required entities when the Expression N causes freezing.

   --  The node N here is either a subexpression node (a "real" expression)

   --  or a subtype mark, or a subtype indication. The latter two cases are

   --  not really expressions, but they can appear within expressions and

   --  so need to be similarly treated. Freeze_Expression takes care of

   --  determining the proper insertion point for generated freeze actions.

   procedure Freeze_Fixed_Point_Type (Typ : Entity_Id);

   --  Freeze fixed point type. For fixed-point types, we have to defer

   --  setting the size and bounds till the freeze point, since they are

   --  potentially affected by the presence of size and small clauses.

   procedure Freeze_Itype (T : Entity_Id; N : Node_Id);

   --  This routine is called when an Itype is created and must be frozen

   --  immediately at the point of creation (for the sake of the expansion

   --  activities in Exp_Ch3 (for example, the creation of packed array

   --  types). We can't just let Freeze_Expression do this job since it

   --  goes out of its way to make sure that the freeze node occurs at a

   --  point outside the current construct, e.g. outside the expression or

   --  outside the initialization procedure. That's normally right, but

   --  not in this case, since if we create an Itype in an expression it

   --  may be the case that it is not always elaborated (for example it

   --  may result from the right operand of a short circuit). In this case

   --  we want the freeze node to be inserted at the same point as the Itype.

   --  The node N provides both the location for the freezing and also the

   --  insertion point for the resulting freeze nodes.

end Freeze;