1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2010, 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 3, 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 COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
24 ------------------------------------------------------------------------------
26 with Types; use Types;
30 --------------------------
31 -- Handling of Freezing --
32 --------------------------
34 -- In the formal Ada semantics, freezing of entities occurs at a well
35 -- defined point, described in (RM 13.14). The model in GNAT of freezing
36 -- is that a Freeze_Entity node is generated at the point where an entity
37 -- is frozen, and the entity contains a pointer (Freeze_Node) to this
38 -- generated freeze node.
40 -- The freeze node is processed in the expander to generate associated
41 -- data and subprograms (e.g. an initialization procedure) which must
42 -- be delayed until the type is frozen and its representation can be
43 -- fully determined. Subsequently the freeze node is used by Gigi to
44 -- determine the point at which it should elaborate the corresponding
45 -- entity (this elaboration also requires the representation of the
46 -- entity to be fully determinable). The freeze node is also used to
47 -- provide additional diagnostic information (pinpointing the freeze
48 -- point), when order of freezing errors are detected.
50 -- If we were fully faithful to the Ada model, we would generate freeze
51 -- nodes for all entities, but that is a bit heavy so we optimize (that
52 -- is the nice word) or cut corners (which is a bit more honest). For
53 -- many entities, we do not need to delay the freeze and instead can
54 -- freeze them at the point of declaration. The conditions for this
55 -- early freezing being permissible are as follows:
57 -- There is no associated expander activity that needs to be delayed
59 -- Gigi can fully elaborate the entity at the point of occurrence (or,
60 -- equivalently, no real elaboration is required for the entity).
62 -- In order for these conditions to be met (especially the second), it
63 -- must be the case that all representation characteristics of the entity
64 -- can be determined at declaration time.
66 -- The following indicates how freezing is handled for all entity kinds:
70 -- All declared types have freeze nodes, as well as anonymous base
71 -- types created for type declarations where the defining identifier
72 -- is a first subtype of the anonymous type.
76 -- All first subtypes have freeze nodes. Other subtypes need freeze
77 -- nodes if the corresponding base type has not yet been frozen. If
78 -- the base type has been frozen, then there is no need for a freeze
79 -- node, since no rep clauses can appear for the subtype in any case.
81 -- Implicit types and subtypes
83 -- As noted above, implicit base types always have freeze nodes. Other
84 -- implicit types and subtypes typically do not require freeze nodes,
85 -- because there is no possibility of delaying any information about
86 -- their representation.
90 -- Are frozen at the point of declaration unless one or more of the
91 -- formal types or return type themselves have delayed freezing and
92 -- are not yet frozen. This includes the case of a formal access type
93 -- where the designated type is not frozen. Note that we are talking
94 -- about subprogram specs here (subprogram body entities have no
95 -- relevance), and in any case, subprogram bodies freeze everything.
97 -- Objects with dynamic address clauses
99 -- These have a delayed freeze. Gigi will generate code to evaluate
100 -- the initialization expression if present and store it in a temp.
101 -- The actual object is created at the point of the freeze, and if
102 -- necessary initialized by copying the value of this temporary.
106 -- Are frozen when the associated subprogram is frozen, so there is
107 -- never any need for them to have delayed freezing.
111 -- Are always frozen at the point of declaration
113 -- All Other Entities
115 -- Are always frozen at the point of declaration
117 -- The flag Has_Delayed_Freeze is used for to indicate that delayed
118 -- freezing is required. Usually the associated freeze node is allocated
119 -- at the freezing point. One special exception occurs with anonymous
120 -- base types, where the freeze node is preallocated at the point of
121 -- declaration, so that the First_Subtype_Link field can be set.
123 Freezing_Library_Level_Tagged_Type : Boolean := False;
124 -- Flag used to indicate that we are freezing the primitives of a library
125 -- level tagged types. Used to disable checks on premature freezing.
126 -- More documentation needed??? why is this flag needed? what are these
127 -- checks? why do they need disabling in some cases?
133 function Build_Renamed_Body
135 New_S : Entity_Id) return Node_Id;
136 -- Rewrite renaming declaration as a subprogram body, whose single
137 -- statement is a call to the renamed entity. New_S is the entity that
138 -- appears in the renaming declaration. If this is a Renaming_As_Body,
139 -- then Decl is the original subprogram declaration that is completed
140 -- by the renaming, otherwise it is the renaming declaration itself.
141 -- The caller inserts the body where required. If this call comes
142 -- from a freezing action, the resulting body is analyzed at once.
144 procedure Check_Compile_Time_Size (T : Entity_Id);
145 -- Check to see whether the size of the type T is known at compile time.
146 -- There are three possible cases:
148 -- Size is not known at compile time. In this case, the call has no
149 -- effect. Note that the processing is conservative here, in the sense
150 -- that this routine may decide that the size is not known even if in
151 -- fact Gigi decides it is known, but the opposite situation can never
154 -- Size is known at compile time, but the actual value of the size is
155 -- not known to the front end or is definitely 32 or more. In this case
156 -- Size_Known_At_Compile_Time is set, but the Esize field is left set
157 -- to zero (to be set by Gigi).
159 -- Size is known at compile time, and the actual value of the size is
160 -- known to the front end and is less than 32. In this case, the flag
161 -- Size_Known_At_Compile_Time is set, and in addition Esize is set to
162 -- the required size, allowing for possible front end packing of an
163 -- array using this type as a component type.
165 -- Note: the flag Size_Known_At_Compile_Time is used to determine if the
166 -- secondary stack must be used to return a value of the type, and also
167 -- to determine whether a component clause is allowed for a component
168 -- of the given type.
170 -- Note: this is public because of one dubious use in Sem_Res???
172 -- Note: Check_Compile_Time_Size does not test the case of the size being
173 -- known because a size clause is specifically given. That is because we
174 -- do not allow a size clause if the size would not otherwise be known at
175 -- compile time in any case.
177 function Is_Atomic_Aggregate
179 Typ : Entity_Id) return Boolean;
181 -- If an atomic object is initialized with an aggregate or is assigned an
182 -- aggregate, we have to prevent a piecemeal access or assignment to the
183 -- object, even if the aggregate is to be expanded. We create a temporary
184 -- for the aggregate, and assign the temporary instead, so that the back
185 -- end can generate an atomic move for it. This is only done in the context
186 -- of an object declaration or an assignment. Function is a noop and
187 -- returns false in other contexts.
189 function Freeze_Entity (E : Entity_Id; N : Node_Id) return List_Id;
190 -- Freeze an entity, and return Freeze nodes, to be inserted at the point
191 -- of call. N is a node whose source location corresponds to the freeze
192 -- point. This is used in placing warning messages in the situation where
193 -- it appears that a type has been frozen too early, e.g. when a primitive
194 -- operation is declared after the freezing point of its tagged type.
195 -- Returns No_List if no freeze nodes needed.
197 procedure Freeze_All (From : Entity_Id; After : in out Node_Id);
198 -- Before a non-instance body, or at the end of a declarative part
199 -- freeze all entities therein that are not yet frozen. Calls itself
200 -- recursively to catch types in inner packages that were not frozen
201 -- at the inner level because they were not yet completely defined.
202 -- This routine also analyzes and freezes default parameter expressions
203 -- in subprogram specifications (this has to be delayed until all the
204 -- types are frozen). The resulting freeze nodes are inserted just
205 -- after node After (which is a list node) and analyzed. On return,
206 -- 'After' is updated to point to the last node inserted (or is returned
207 -- unchanged if no nodes were inserted). 'From' is the last entity frozen
208 -- in the scope. It is used to prevent a quadratic traversal over already
211 procedure Freeze_Before (N : Node_Id; T : Entity_Id);
212 -- Freeze T then Insert the generated Freeze nodes before the node N
214 procedure Freeze_Expression (N : Node_Id);
215 -- Freezes the required entities when the Expression N causes freezing.
216 -- The node N here is either a subexpression node (a "real" expression)
217 -- or a subtype mark, or a subtype indication. The latter two cases are
218 -- not really expressions, but they can appear within expressions and
219 -- so need to be similarly treated. Freeze_Expression takes care of
220 -- determining the proper insertion point for generated freeze actions.
222 procedure Freeze_Fixed_Point_Type (Typ : Entity_Id);
223 -- Freeze fixed point type. For fixed-point types, we have to defer
224 -- setting the size and bounds till the freeze point, since they are
225 -- potentially affected by the presence of size and small clauses.
227 procedure Freeze_Itype (T : Entity_Id; N : Node_Id);
228 -- This routine is called when an Itype is created and must be frozen
229 -- immediately at the point of creation (for the sake of the expansion
230 -- activities in Exp_Ch3 (for example, the creation of packed array
231 -- types). We can't just let Freeze_Expression do this job since it
232 -- goes out of its way to make sure that the freeze node occurs at a
233 -- point outside the current construct, e.g. outside the expression or
234 -- outside the initialization procedure. That's normally right, but
235 -- not in this case, since if we create an Itype in an expression it
236 -- may be the case that it is not always elaborated (for example it
237 -- may result from the right operand of a short circuit). In this case
238 -- we want the freeze node to be inserted at the same point as the Itype.
239 -- The node N provides both the location for the freezing and also the
240 -- insertion point for the resulting freeze nodes.
OSDN Git Service
