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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. --
-- --
------------------------------------------------------------------------------
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;
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