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------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- F R E E Z E -- -- -- -- S p e c -- -- -- -- Copyright (C) 1992-2009, Free Software Foundation, Inc. -- -- -- -- GNAT is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 3, or (at your option) any later ver- -- -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- -- or FITNESS FOR A PARTICULAR PURPOSE. -- -- -- -- You should have received a copy of the GNU General Public License along -- -- with this program; see file COPYING3. If not see -- -- <http://www.gnu.org/licenses/>. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ with Types; use Types; package Freeze is -------------------------- -- Handling of Freezing -- -------------------------- -- In the formal Ada semantics, freezing of entities occurs at a well -- defined point, described in (RM 13.14). The model in GNAT of freezing -- is that a Freeze_Entity node is generated at the point where an entity -- is frozen, and the entity contains a pointer (Freeze_Node) to this -- generated freeze node. -- The freeze node is processed in the expander to generate associated -- data and subprograms (e.g. an initialization procedure) which must -- be delayed until the type is frozen and its representation can be -- fully determined. Subsequently the freeze node is used by Gigi to -- determine the point at which it should elaborate the corresponding -- entity (this elaboration also requires the representation of the -- entity to be fully determinable). The freeze node is also used to -- provide additional diagnostic information (pinpointing the freeze -- point), when order of freezing errors are detected. -- If we were fully faithful to the Ada model, we would generate freeze -- nodes for all entities, but that is a bit heavy so we optimize (that -- is the nice word) or cut corners (which is a bit more honest). For -- many entities, we do not need to delay the freeze and instead can -- freeze them at the point of declaration. The conditions for this -- early freezing being permissible are as follows: -- There is no associated expander activity that needs to be delayed -- Gigi can fully elaborate the entity at the point of occurrence (or, -- equivalently, no real elaboration is required for the entity). -- In order for these conditions to be met (especially the second), it -- must be the case that all representation characteristics of the entity -- can be determined at declaration time. -- The following indicates how freezing is handled for all entity kinds: -- Types -- All declared types have freeze nodes, as well as anonymous base -- types created for type declarations where the defining identifier -- is a first subtype of the anonymous type. -- Subtypes -- All first subtypes have freeze nodes. Other subtypes need freeze -- nodes if the corresponding base type has not yet been frozen. If -- the base type has been frozen, then there is no need for a freeze -- node, since no rep clauses can appear for the subtype in any case. -- Implicit types and subtypes -- As noted above, implicit base types always have freeze nodes. Other -- implicit types and subtypes typically do not require freeze nodes, -- because there is no possibility of delaying any information about -- their representation. -- Subprograms -- -- Are frozen at the point of declaration unless one or more of the -- formal types or return type themselves have delayed freezing and -- are not yet frozen. This includes the case of a formal access type -- where the designated type is not frozen. Note that we are talking -- about subprogram specs here (subprogram body entities have no -- relevance), and in any case, subprogram bodies freeze everything. -- Objects with dynamic address clauses -- -- These have a delayed freeze. Gigi will generate code to evaluate -- the initialization expression if present and store it in a temp. -- The actual object is created at the point of the freeze, and if -- necessary initialized by copying the value of this temporary. -- Formal Parameters -- -- Are frozen when the associated subprogram is frozen, so there is -- never any need for them to have delayed freezing. -- Other Objects -- -- Are always frozen at the point of declaration -- All Other Entities -- Are always frozen at the point of declaration -- The flag Has_Delayed_Freeze is used for to indicate that delayed -- freezing is required. Usually the associated freeze node is allocated -- at the freezing point. One special exception occurs with anonymous -- base types, where the freeze node is preallocated at the point of -- declaration, so that the First_Subtype_Link field can be set. Freezing_Library_Level_Tagged_Type : Boolean := False; -- Flag used to indicate that we are freezing the primitives of a library -- level tagged types. Used to disable checks on premature freezing. -- More documentation needed??? why is this flag needed? what are these -- checks? why do they need disabling in some cases? ----------------- -- Subprograms -- ----------------- function Build_Renamed_Body (Decl : Node_Id; New_S : Entity_Id) return Node_Id; -- Rewrite renaming declaration as a subprogram body, whose single -- statement is a call to the renamed entity. New_S is the entity that -- appears in the renaming declaration. If this is a Renaming_As_Body, -- then Decl is the original subprogram declaration that is completed -- by the renaming, otherwise it is the renaming declaration itself. -- The caller inserts the body where required. If this call comes -- from a freezing action, the resulting body is analyzed at once. procedure Check_Compile_Time_Size (T : Entity_Id); -- Check to see whether the size of the type T is known at compile time. -- There are three possible cases: -- -- Size is not known at compile time. In this case, the call has no -- effect. Note that the processing is conservative here, in the sense -- that this routine may decide that the size is not known even if in -- fact Gigi decides it is known, but the opposite situation can never -- occur. -- -- Size is known at compile time, but the actual value of the size is -- not known to the front end or is definitely 32 or more. In this case -- Size_Known_At_Compile_Time is set, but the Esize field is left set -- to zero (to be set by Gigi). -- -- Size is known at compile time, and the actual value of the size is -- known to the front end and is less than 32. In this case, the flag -- Size_Known_At_Compile_Time is set, and in addition Esize is set to -- the required size, allowing for possible front end packing of an -- array using this type as a component type. -- -- Note: the flag Size_Known_At_Compile_Time is used to determine if the -- secondary stack must be used to return a value of the type, and also -- to determine whether a component clause is allowed for a component -- of the given type. -- -- Note: this is public because of one dubious use in Sem_Res??? -- -- Note: Check_Compile_Time_Size does not test the case of the size being -- known because a size clause is specifically given. That is because we -- do not allow a size clause if the size would not otherwise be known at -- compile time in any case. function Is_Atomic_Aggregate (E : Entity_Id; Typ : Entity_Id) return Boolean; -- If an atomic object is initialized with an aggregate or is assigned -- an aggregate, we have to prevent a piecemeal access or assignment -- to the object, even if the aggregate is to be expanded. We create -- a temporary for the aggregate, and assign the temporary instead, -- so that the back end can generate an atomic move for it. This is -- only done in the context of an object declaration or an assignment. -- Function is a noop and returns false in other contexts. function Freeze_Entity (E : Entity_Id; Loc : Source_Ptr) return List_Id; -- Freeze an entity, and return Freeze nodes, to be inserted at the -- point of call. Loc is a source location which corresponds to the -- freeze point. This is used in placing warning messages in the -- situation where it appears that a type has been frozen too early, -- e.g. when a primitive operation is declared after the freezing -- point of its tagged type. Returns No_List if no freeze nodes needed. procedure Freeze_All (From : Entity_Id; After : in out Node_Id); -- Before a non-instance body, or at the end of a declarative part -- freeze all entities therein that are not yet frozen. Calls itself -- recursively to catch types in inner packages that were not frozen -- at the inner level because they were not yet completely defined. -- This routine also analyzes and freezes default parameter expressions -- in subprogram specifications (this has to be delayed until all the -- types are frozen). The resulting freeze nodes are inserted just -- after node After (which is a list node) and analyzed. On return, -- 'After' is updated to point to the last node inserted (or is returned -- unchanged if no nodes were inserted). 'From' is the last entity frozen -- in the scope. It is used to prevent a quadratic traversal over already -- frozen entities. procedure Freeze_Before (N : Node_Id; T : Entity_Id); -- Freeze T then Insert the generated Freeze nodes before the node N procedure Freeze_Expression (N : Node_Id); -- Freezes the required entities when the Expression N causes freezing. -- The node N here is either a subexpression node (a "real" expression) -- or a subtype mark, or a subtype indication. The latter two cases are -- not really expressions, but they can appear within expressions and -- so need to be similarly treated. Freeze_Expression takes care of -- determining the proper insertion point for generated freeze actions. procedure Freeze_Fixed_Point_Type (Typ : Entity_Id); -- Freeze fixed point type. For fixed-point types, we have to defer -- setting the size and bounds till the freeze point, since they are -- potentially affected by the presence of size and small clauses. procedure Freeze_Itype (T : Entity_Id; N : Node_Id); -- This routine is called when an Itype is created and must be frozen -- immediately at the point of creation (for the sake of the expansion -- activities in Exp_Ch3 (for example, the creation of packed array -- types). We can't just let Freeze_Expression do this job since it -- goes out of its way to make sure that the freeze node occurs at a -- point outside the current construct, e.g. outside the expression or -- outside the initialization procedure. That's normally right, but -- not in this case, since if we create an Itype in an expression it -- may be the case that it is not always elaborated (for example it -- may result from the right operand of a short circuit). In this case -- we want the freeze node to be inserted at the same point as the Itype. -- The node N provides both the location for the freezing and also the -- insertion point for the resulting freeze nodes. end Freeze;
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