1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- F R E E Z E -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2003, 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 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. -- 21-- -- 22-- GNAT was originally developed by the GNAT team at New York University. -- 23-- Extensive contributions were provided by Ada Core Technologies Inc. -- 24-- -- 25------------------------------------------------------------------------------ 26 27with Types; use Types; 28 29package Freeze is 30 31 -------------------------- 32 -- Handling of Freezing -- 33 -------------------------- 34 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. 40 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. 50 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: 57 58 -- There is no associated expander activity that needs to be delayed 59 60 -- Gigi can fully elaborate the entity at the point of occurrence (or, 61 -- equivalently, no real elaboration is required for the entity). 62 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. 66 67 -- The following indicates how freezing is handled for all entity kinds: 68 69 -- Types 70 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. 74 75 -- Subtypes 76 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. 81 82 -- Implicit types and subtypes 83 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. 88 89 -- Subprograms 90 -- 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. 97 98 -- Objects with dynamic address clauses 99 -- 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. 104 105 -- Formal Parameters 106 -- 107 -- Are frozen when the associated subprogram is frozen, so there is 108 -- never any need for them to have delayed freezing. 109 110 -- Other Objects 111 -- 112 -- Are always frozen at the point of declaration 113 114 -- All Other Entities 115 116 -- Are always frozen at the point of declaration 117 118 -- 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. 123 124 ----------------- 125 -- Subprograms -- 126 ----------------- 127 128 function Build_Renamed_Body 129 (Decl : Node_Id; 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. 138 139 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: 142 -- 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 147 -- occur. 148 -- 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). 153 -- 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. 159 -- 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. 164 -- 165 -- Note: this is public because of one dubious use in Sem_Res??? 166 -- 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. 171 172 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. 178 179 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. 186 187 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 199 -- frozen entities. 200 201 procedure Freeze_Before (N : Node_Id; T : Entity_Id); 202 -- Freeze T then Insert the generated Freeze nodes before the node N. 203 204 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. 211 212 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. 216 217 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. 231 232end Freeze; 233