1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2003, Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
25 ------------------------------------------------------------------------------
27 with Types; use Types;
31 --------------------------
32 -- Handling of Freezing --
33 --------------------------
35 -- In the formal Ada semantics, freezing of entities occurs at a well
36 -- defined point, described in (RM 13.14). The model in GNAT of freezing
37 -- is that a Freeze_Entity node is generated at the point where an entity
38 -- is frozen, and the entity contains a pointer (Freeze_Node) to this
39 -- generated freeze node.
41 -- The freeze node is processed in the expander to generate associated
42 -- data and subprograms (e.g. an initialization procedure) which must
43 -- be delayed until the type is frozen and its representation can be
44 -- fully determined. Subsequently the freeze node is used by Gigi to
45 -- determine the point at which it should elaborate the corresponding
46 -- entity (this elaboration also requires the representation of the
47 -- entity to be fully determinable). The freeze node is also used to
48 -- provide additional diagnostic information (pinpointing the freeze
49 -- point), when order of freezing errors are detected.
51 -- If we were fully faithful to the Ada model, we would generate freeze
52 -- nodes for all entities, but that is a bit heavy so we optimize (that
53 -- is the nice word) or cut corners (which is a bit more honest). For
54 -- many entities, we do not need to delay the freeze and instead can
55 -- freeze them at the point of declaration. The conditions for this
56 -- early freezing being permissible are as follows:
58 -- There is no associated expander activity that needs to be delayed
60 -- Gigi can fully elaborate the entity at the point of occurrence (or,
61 -- equivalently, no real elaboration is required for the entity).
63 -- In order for these conditions to be met (especially the second), it
64 -- must be the case that all representation characteristics of the entity
65 -- can be determined at declaration time.
67 -- The following indicates how freezing is handled for all entity kinds:
71 -- All declared types have freeze nodes, as well as anonymous base
72 -- types created for type declarations where the defining identifier
73 -- is a first subtype of the anonymous type.
77 -- All first subtypes have freeze nodes. Other subtypes need freeze
78 -- nodes if the corresponding base type has not yet been frozen. If
79 -- the base type has been frozen, then there is no need for a freeze
80 -- node, since no rep clauses can appear for the subtype in any case.
82 -- Implicit types and subtypes
84 -- As noted above, implicit base types always have freeze nodes. Other
85 -- implicit types and subtypes typically do not require freeze nodes,
86 -- because there is no possibility of delaying any information about
87 -- their representation.
91 -- Are frozen at the point of declaration unless one or more of the
92 -- formal types or return type themselves have delayed freezing and
93 -- are not yet frozen. This includes the case of a formal access type
94 -- where the designated type is not frozen. Note that we are talking
95 -- about subprogram specs here (subprogram body entities have no
96 -- relevance), and in any case, subprogram bodies freeze everything.
98 -- Objects with dynamic address clauses
100 -- These have a delayed freeze. Gigi will generate code to evaluate
101 -- the initialization expression if present and store it in a temp.
102 -- The actual object is created at the point of the freeze, and if
103 -- necessary initialized by copying the value of this temporary.
107 -- Are frozen when the associated subprogram is frozen, so there is
108 -- never any need for them to have delayed freezing.
112 -- Are always frozen at the point of declaration
114 -- All Other Entities
116 -- Are always frozen at the point of declaration
118 -- The flag Has_Delayed_Freeze is used for to indicate that delayed
119 -- freezing is required. Usually the associated freeze node is allocated
120 -- at the freezing point. One special exception occurs with anonymous
121 -- base types, where the freeze node is preallocated at the point of
122 -- declaration, so that the First_Subtype_Link field can be set.
128 function Build_Renamed_Body
130 New_S : Entity_Id) return Node_Id;
131 -- Rewrite renaming declaration as a subprogram body, whose single
132 -- statement is a call to the renamed entity. New_S is the entity that
133 -- appears in the renaming declaration. If this is a Renaming_As_Body,
134 -- then Decl is the original subprogram declaration that is completed
135 -- by the renaming, otherwise it is the renaming declaration itself.
136 -- The caller inserts the body where required. If this call comes
137 -- from a freezing action, the resulting body is analyzed at once.
139 procedure Check_Compile_Time_Size (T : Entity_Id);
140 -- Check to see whether the size of the type T is known at compile time.
141 -- There are three possible cases:
143 -- Size is not known at compile time. In this case, the call has no
144 -- effect. Note that the processing is conservative here, in the sense
145 -- that this routine may decide that the size is not known even if in
146 -- fact Gigi decides it is known, but the opposite situation can never
149 -- Size is known at compile time, but the actual value of the size is
150 -- not known to the front end or is definitely 32 or more. In this case
151 -- Size_Known_At_Compile_Time is set, but the Esize field is left set
152 -- to zero (to be set by Gigi).
154 -- Size is known at compile time, and the actual value of the size is
155 -- known to the front end and is less than 32. In this case, the flag
156 -- Size_Known_At_Compile_Time is set, and in addition Esize is set to
157 -- the required size, allowing for possible front end packing of an
158 -- array using this type as a component type.
160 -- Note: the flag Size_Known_At_Compile_Time is used to determine if the
161 -- secondary stack must be used to return a value of the type, and also
162 -- to determine whether a component clause is allowed for a component
163 -- of the given type.
165 -- Note: this is public because of one dubious use in Sem_Res???
167 -- Note: Check_Compile_Time_Size does not test the case of the size being
168 -- known because a size clause is specifically given. That is because we
169 -- do not allow a size clause if the size would not otherwise be known at
170 -- compile time in any case.
172 procedure Expand_Atomic_Aggregate (E : Entity_Id; Typ : Entity_Id);
173 -- If an atomic object is initialized with an aggregate or is assigned
174 -- an aggregate, we have to prevent a piecemeal access or assignment
175 -- to the object, even if the aggregate is to be expanded. we create
176 -- a temporary for the aggregate, and assign the temporary instead,
177 -- so that the back end can generate an atomic move for it.
179 function Freeze_Entity (E : Entity_Id; Loc : Source_Ptr) return List_Id;
180 -- Freeze an entity, and return Freeze nodes, to be inserted at the
181 -- point of call. Loc is a source location which corresponds to the
182 -- freeze point. This is used in placing warning messages in the
183 -- situation where it appears that a type has been frozen too early,
184 -- e.g. when a primitive operation is declared after the freezing
185 -- point of its tagged type. Returns No_List if no freeze nodes needed.
187 procedure Freeze_All (From : Entity_Id; After : in out Node_Id);
188 -- Before a non-instance body, or at the end of a declarative part
189 -- freeze all entities therein that are not yet frozen. Calls itself
190 -- recursively to catch types in inner packages that were not frozen
191 -- at the inner level because they were not yet completely defined.
192 -- This routine also analyzes and freezes default parameter expressions
193 -- in subprogram specifications (this has to be delayed until all the
194 -- types are frozen). The resulting freeze nodes are inserted just
195 -- after node After (which is a list node) and analyzed. On return,
196 -- 'After' is updated to point to the last node inserted (or is returned
197 -- unchanged if no nodes were inserted). 'From' is the last entity frozen
198 -- in the scope. It is used to prevent a quadratic traversal over already
201 procedure Freeze_Before (N : Node_Id; T : Entity_Id);
202 -- Freeze T then Insert the generated Freeze nodes before the node N.
204 procedure Freeze_Expression (N : Node_Id);
205 -- Freezes the required entities when the Expression N causes freezing.
206 -- The node N here is either a subexpression node (a "real" expression)
207 -- or a subtype mark, or a subtype indication. The latter two cases are
208 -- not really expressions, but they can appear within expressions and
209 -- so need to be similarly treated. Freeze_Expression takes care of
210 -- determining the proper insertion point for generated freeze actions.
212 procedure Freeze_Fixed_Point_Type (Typ : Entity_Id);
213 -- Freeze fixed point type. For fixed-point types, we have to defer
214 -- setting the size and bounds till the freeze point, since they are
215 -- potentially affected by the presence of size and small clauses.
217 procedure Freeze_Itype (T : Entity_Id; N : Node_Id);
218 -- This routine is called when an Itype is created and must be frozen
219 -- immediately at the point of creation (for the sake of the expansion
220 -- activities in Exp_Ch3 (for example, the creation of packed array
221 -- types). We can't just let Freeze_Expression do this job since it
222 -- goes out of its way to make sure that the freeze node occurs at a
223 -- point outside the current construct, e.g. outside the expression or
224 -- outside the initialization procedure. That's normally right, but
225 -- not in this case, since if we create an Itype in an expression it
226 -- may be the case that it is not always elaborated (for example it
227 -- may result from the right operand of a short circuit). In this case
228 -- we want the freeze node to be inserted at the same point as the Itype.
229 -- The node N provides both the location for the freezing and also the
230 -- insertion point for the resulting freeze nodes.
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