1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- F R E E Z E -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2011, 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 26with Types; use Types; 27 28package 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 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. 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 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? 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 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). 158 -- 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. 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_Aggregate 178 (E : Entity_Id; 179 Typ : Entity_Id) return Boolean; 180 181 -- 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. 188 189 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. 196 197 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 209 -- frozen entities. 210 211 procedure Freeze_Before (N : Node_Id; T : Entity_Id); 212 -- Freeze T then Insert the generated Freeze nodes before the node N 213 214 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. 221 222 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. 226 227 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. 241 242end Freeze; 243