Mercurial > hg > CbC > CbC_gcc
comparison gcc/ada/freeze.ads @ 111:04ced10e8804
gcc 7
author | kono |
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date | Fri, 27 Oct 2017 22:46:09 +0900 |
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children | 84e7813d76e9 |
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1 ------------------------------------------------------------------------------ | |
2 -- -- | |
3 -- GNAT COMPILER COMPONENTS -- | |
4 -- -- | |
5 -- F R E E Z E -- | |
6 -- -- | |
7 -- S p e c -- | |
8 -- -- | |
9 -- Copyright (C) 1992-2017, Free Software Foundation, Inc. -- | |
10 -- -- | |
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. -- | |
20 -- -- | |
21 -- GNAT was originally developed by the GNAT team at New York University. -- | |
22 -- Extensive contributions were provided by Ada Core Technologies Inc. -- | |
23 -- -- | |
24 ------------------------------------------------------------------------------ | |
25 | |
26 with Types; use Types; | |
27 | |
28 package Freeze is | |
29 | |
30 -------------------------- | |
31 -- Handling of Freezing -- | |
32 -------------------------- | |
33 | |
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. | |
39 | |
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. | |
49 | |
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: | |
56 | |
57 -- There is no associated expander activity that needs to be delayed | |
58 | |
59 -- Gigi can fully elaborate the entity at the point of occurrence (or, | |
60 -- equivalently, no real elaboration is required for the entity). | |
61 | |
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. | |
65 | |
66 -- The following indicates how freezing is handled for all entity kinds: | |
67 | |
68 -- Types | |
69 | |
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. | |
73 | |
74 -- Subtypes | |
75 | |
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. | |
80 | |
81 -- Implicit types and subtypes | |
82 | |
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. | |
87 | |
88 -- Subprograms | |
89 -- | |
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. | |
96 | |
97 -- Objects with dynamic address clauses | |
98 -- | |
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. | |
103 | |
104 -- Formal Parameters | |
105 -- | |
106 -- Are frozen when the associated subprogram is frozen, so there is | |
107 -- never any need for them to have delayed freezing. | |
108 | |
109 -- Other Objects | |
110 -- | |
111 -- Are always frozen at the point of declaration | |
112 | |
113 -- All Other Entities | |
114 | |
115 -- Are always frozen at the point of declaration | |
116 | |
117 -- The flag Has_Delayed_Freeze is used to indicate that delayed freezing | |
118 -- is required. Usually the associated freeze node is allocated at the | |
119 -- freezing point. One special exception occurs with anonymous base types, | |
120 -- where the freeze node is preallocated at the point of declaration, so | |
121 -- that the First_Subtype_Link field can be set. | |
122 | |
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 type. 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? | |
128 | |
129 ----------------- | |
130 -- Subprograms -- | |
131 ----------------- | |
132 | |
133 function Build_Renamed_Body | |
134 (Decl : Node_Id; | |
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. | |
143 | |
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: | |
147 -- | |
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 | |
152 -- occur. | |
153 -- | |
154 -- Size is known at compile time, but the actual value of the size is not | |
155 -- known to the front end or is definitely greater than 64. In this case, | |
156 -- Size_Known_At_Compile_Time is set, but the RM_Size field is left set | |
157 -- to zero (to be set by Gigi). | |
158 -- | |
159 -- Size is known at compile time, and the actual value of the size is | |
160 -- known to the front end and is not greater than 64. In this case, the | |
161 -- flag Size_Known_At_Compile_Time is set, and in addition RM_Size is set | |
162 -- to the required size, allowing for possible front end packing of an | |
163 -- array using this type as a component type. | |
164 -- | |
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. | |
169 -- | |
170 -- Note: this is public because of one dubious use in Sem_Res??? | |
171 -- | |
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. | |
176 | |
177 function Is_Atomic_VFA_Aggregate (N : Node_Id) return Boolean; | |
178 -- If an atomic/VFA object is initialized with an aggregate or is assigned | |
179 -- an aggregate, we have to prevent a piecemeal access or assignment to the | |
180 -- object, even if the aggregate is to be expanded. We create a temporary | |
181 -- for the aggregate, and assign the temporary instead, so that the back | |
182 -- end can generate an atomic move for it. This is only done in the context | |
183 -- of an object declaration or an assignment. Function is a noop and | |
184 -- returns false in other contexts. | |
185 | |
186 procedure Explode_Initialization_Compound_Statement (E : Entity_Id); | |
187 -- If Initialization_Statements (E) is an N_Compound_Statement, insert its | |
188 -- actions in the enclosing list and reset the attribute. | |
189 | |
190 function Freeze_Entity | |
191 (E : Entity_Id; | |
192 N : Node_Id; | |
193 Do_Freeze_Profile : Boolean := True) return List_Id; | |
194 -- Freeze an entity, and return Freeze nodes, to be inserted at the point | |
195 -- of call. N is a node whose source location corresponds to the freeze | |
196 -- point. This is used in placing warning messages in the situation where | |
197 -- it appears that a type has been frozen too early, e.g. when a primitive | |
198 -- operation is declared after the freezing point of its tagged type. | |
199 -- Returns No_List if no freeze nodes needed. Parameter Do_Freeze_Profile | |
200 -- is used when E is a subprogram, and determines whether the profile of | |
201 -- the subprogram should be frozen as well. | |
202 | |
203 procedure Freeze_All (From : Entity_Id; After : in out Node_Id); | |
204 -- Before a non-instance body, or at the end of a declarative part, | |
205 -- freeze all entities therein that are not yet frozen. Calls itself | |
206 -- recursively to catch types in inner packages that were not frozen | |
207 -- at the inner level because they were not yet completely defined. | |
208 -- This routine also analyzes and freezes default parameter expressions | |
209 -- in subprogram specifications (this has to be delayed until all the | |
210 -- types are frozen). The resulting freeze nodes are inserted just | |
211 -- after node After (which is a list node) and analyzed. On return, | |
212 -- 'After' is updated to point to the last node inserted (or is returned | |
213 -- unchanged if no nodes were inserted). 'From' is the last entity frozen | |
214 -- in the scope. It is used to prevent a quadratic traversal over already | |
215 -- frozen entities. | |
216 | |
217 procedure Freeze_Before | |
218 (N : Node_Id; | |
219 T : Entity_Id; | |
220 Do_Freeze_Profile : Boolean := True); | |
221 -- Freeze T then Insert the generated Freeze nodes before the node N. Flag | |
222 -- Do_Freeze_Profile is used when T is an overloadable entity and indicates | |
223 -- whether its profile should be frozen at the same time. | |
224 | |
225 procedure Freeze_Expression (N : Node_Id); | |
226 -- Freezes the required entities when the Expression N causes freezing. | |
227 -- The node N here is either a subexpression node (a "real" expression) | |
228 -- or a subtype mark, or a subtype indication. The latter two cases are | |
229 -- not really expressions, but they can appear within expressions and | |
230 -- so need to be similarly treated. Freeze_Expression takes care of | |
231 -- determining the proper insertion point for generated freeze actions. | |
232 | |
233 procedure Freeze_Fixed_Point_Type (Typ : Entity_Id); | |
234 -- Freeze fixed point type. For fixed-point types, we have to defer | |
235 -- setting the size and bounds till the freeze point, since they are | |
236 -- potentially affected by the presence of size and small clauses. | |
237 | |
238 procedure Freeze_Itype (T : Entity_Id; N : Node_Id); | |
239 -- This routine is called when an Itype is created and must be frozen | |
240 -- immediately at the point of creation (for the sake of the expansion | |
241 -- activities in Exp_Ch3 (for example, the creation of packed array | |
242 -- types). We can't just let Freeze_Expression do this job since it | |
243 -- goes out of its way to make sure that the freeze node occurs at a | |
244 -- point outside the current construct, e.g. outside the expression or | |
245 -- outside the initialization procedure. That's normally right, but | |
246 -- not in this case, since if we create an Itype in an expression it | |
247 -- may be the case that it is not always elaborated (for example it | |
248 -- may result from the right operand of a short circuit). In this case | |
249 -- we want the freeze node to be inserted at the same point as the Itype. | |
250 -- The node N provides both the location for the freezing and also the | |
251 -- insertion point for the resulting freeze nodes. | |
252 | |
253 end Freeze; |