------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- E X P _ U T I L -- -- -- -- S p e c -- -- -- -- $Revision: 1.112 $ -- -- -- Copyright (C) 1992-2001 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 2, 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. See the GNU General Public License -- -- for more details. You should have received a copy of the GNU General -- -- Public License distributed with GNAT; see file COPYING. If not, write -- -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- -- MA 02111-1307, USA. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). -- -- -- ------------------------------------------------------------------------------ -- Package containing utility procedures used throughout the expander with Snames; use Snames; with Rtsfind; use Rtsfind; with Types; use Types; package Exp_Util is ----------------------------------------------- -- Handling of Actions Associated with Nodes -- ----------------------------------------------- -- The evaluation of certain expression nodes involves the elaboration -- of associated types and other declarations, and the execution of -- statement sequences. Expansion routines generating such actions must -- find an appropriate place in the tree to hang the actions so that -- they will be evaluated at the appropriate point. -- Some cases are simple: -- For an expression occurring in a simple statement that is in a list -- of statements, the actions are simply inserted into the list before -- the associated statement. -- For an expression occurring in a declaration (declarations always -- appear in lists), the actions are similarly inserted into the list -- just before the associated declaration. -- The following special cases arise: -- For actions associated with the right operand of a short circuit -- form, the actions are first stored in the short circuit form node -- in the Actions field. The expansion of these forms subsequently -- expands the short circuit forms into if statements which can then -- be moved as described above. -- For actions appearing in the Condition expression of a while loop, -- or an elsif clause, the actions are similarly temporarily stored in -- in the node (N_Elsif_Part or N_Iteration_Scheme) associated with -- the expression using the Condition_Actions field. Subsequently, the -- expansion of these nodes rewrites the control structures involved to -- reposition the actions in normal statement sequence. -- For actions appearing in the then or else expression of a conditional -- expression, these actions are similarly placed in the node, using the -- Then_Actions or Else_Actions field as appropriate. Once again the -- expansion of the N_Conditional_Expression node rewrites the node so -- that the actions can be normally positioned. -- Basically what we do is to climb up to the tree looking for the -- proper insertion point, as described by one of the above cases, -- and then insert the appropriate action or actions. -- Note if more than one insert call is made specifying the same -- Assoc_Node, then the actions are elaborated in the order of the -- calls, and this guarantee is preserved for the special cases above. procedure Insert_Action (Assoc_Node : Node_Id; Ins_Action : Node_Id); -- Insert the action Ins_Action at the appropriate point as described -- above. The action is analyzed using the default checks after it is -- inserted. Assoc_Node is the node with which the action is associated. procedure Insert_Action (Assoc_Node : Node_Id; Ins_Action : Node_Id; Suppress : Check_Id); -- Insert the action Ins_Action at the appropriate point as described -- above. The action is analyzed using the default checks as modified -- by the given Suppress argument after it is inserted. Assoc_Node is -- the node with which the action is associated. procedure Insert_Actions (Assoc_Node : Node_Id; Ins_Actions : List_Id); -- Insert the list of action Ins_Actions at the appropriate point as -- described above. The actions are analyzed using the default checks -- after they are inserted. Assoc_Node is the node with which the actions -- are associated. Ins_Actions may be No_List, in which case the call has -- no effect. procedure Insert_Actions (Assoc_Node : Node_Id; Ins_Actions : List_Id; Suppress : Check_Id); -- Insert the list of action Ins_Actions at the appropriate point as -- described above. The actions are analyzed using the default checks -- as modified by the given Suppress argument after they are inserted. -- Assoc_Node is the node with which the actions are associated. -- Ins_Actions may be No_List, in which case the call has no effect. procedure Insert_Actions_After (Assoc_Node : Node_Id; Ins_Actions : List_Id); -- Assoc_Node must be a node in a list. Same as Insert_Actions but -- actions will be inserted after N in a manner that is compatible with -- the transient scope mechanism. This procedure must be used instead -- of Insert_List_After if Assoc_Node may be in a transient scope. -- -- Implementation limitation: Assoc_Node must be a statement. We can -- generalize to expressions if there is a need but this is tricky to -- implement because of short-ciruits (among other things).??? procedure Insert_Library_Level_Action (N : Node_Id); -- This procedure inserts and analyzes the node N as an action at the -- library level for the current unit (i.e. it is attached to the -- Actions field of the N_Compilation_Aux node for the main unit). procedure Insert_Library_Level_Actions (L : List_Id); -- Similar, but inserts a list of actions. ----------------------- -- Other Subprograms -- ----------------------- procedure Adjust_Condition (N : Node_Id); -- The node N is an expression whose root-type is Boolean, and which -- represents a boolean value used as a condition (i.e. a True/False -- value). This routine handles the case of C and Fortran convention -- boolean types, which have zero/non-zero semantics rather than the -- normal 0/1 semantics, and also the case of an enumeration rep -- clause that specifies a non-standard representation. On return, -- node N always has the type Standard.Boolean, with a value that -- is a standard Boolean values of 0/1 for False/True. This procedure -- is used in two situations. First, the processing for a condition -- field always calls Adjust_Condition, so that the boolean value -- presented to the backend is a standard value. Second, for the -- code for boolean operations such as AND, Adjust_Condition is -- called on both operands, and then the operation is done in the -- domain of Standard_Boolean, then Adjust_Result_Type is called -- on the result to possibly reset the original type. This procedure -- also takes care of validity checking if Validity_Checks = Tests. procedure Adjust_Result_Type (N : Node_Id; T : Entity_Id); -- The processing of boolean operations like AND uses the procedure -- Adjust_Condition so that it can operate on Standard.Boolean, which -- is the only boolean type on which the backend needs to be able to -- implement such operators. This means that the result is also of -- type Standard.Boolean. In general the type must be reset back to -- the original type to get proper semantics, and that is the purpose -- of this procedure. N is the node (of type Standard.Boolean), and -- T is the desired type. As an optimization, this procedure leaves -- the type as Standard.Boolean in contexts where this is permissible -- (in particular for Condition fields, and for operands of other -- logical operations higher up the tree). The call to this procedure -- is completely ignored if the argument N is not of type Boolean. procedure Append_Freeze_Action (T : Entity_Id; N : Node_Id); -- Add a new freeze action for the given type. The freeze action is -- attached to the freeze node for the type. Actions will be elaborated -- in the order in which they are added. Note that the added node is not -- analyzed. The analyze call is found in Sem_Ch13.Expand_N_Freeze_Entity. procedure Append_Freeze_Actions (T : Entity_Id; L : List_Id); -- Adds the given list of freeze actions (declarations or statements) -- for the given type. The freeze actions are attached to the freeze -- node for the type. Actions will be elaborated in the order in which -- they are added, and the actions within the list will be elaborated in -- list order. Note that the added nodes are not analyzed. The analyze -- call is found in Sem_Ch13.Expand_N_Freeze_Entity. function Build_Runtime_Call (Loc : Source_Ptr; RE : RE_Id) return Node_Id; -- Build an N_Procedure_Call_Statement calling the given runtime entity. -- The call has no parameters. The first argument provides the location -- information for the tree and for error messages. The call node is not -- analyzed on return, the caller is responsible for analyzing it. function Build_Task_Image_Decls (Loc : Source_Ptr; Id_Ref : Node_Id; A_Type : Entity_Id) return List_Id; -- Build declaration for a variable that holds an identifying string -- to be used as a task name. Id_Ref is an identifier if the task is -- a variable, and a selected or indexed component if the task is a -- component of an object. If it is an indexed component, A_Type is -- the corresponding array type. Its index types are used to build the -- string as an image of the index values. For composite types, the -- result includes two declarations: one for a generated function that -- computes the image without using concatenation, and one for the -- variable that holds the result. procedure Convert_To_Actual_Subtype (Exp : Node_Id); -- The Etype of an expression is the nominal type of the expression, -- not the actual subtype. Often these are the same, but not always. -- For example, a reference to a formal of unconstrained type has the -- unconstrained type as its Etype, but the actual subtype is obtained -- by applying the actual bounds. This routine is given an expression, -- Exp, and (if necessary), replaces it using Rewrite, with a conversion -- to the actual subtype, building the actual subtype if necessary. If -- the expression is already of the requested type, then it is unchanged. function Current_Sem_Unit_Declarations return List_Id; -- Return the a place where it is fine to insert declarations for the -- current semantic unit. If the unit is a package body, return the -- visible declarations of the corresponding spec. For RCI stubs, this -- is necessary because the point at which they are generated may not -- be the earliest point at which they are used. function Duplicate_Subexpr (Exp : Node_Id; Name_Req : Boolean := False) return Node_Id; -- Given the node for a subexpression, this function makes a logical -- copy of the subexpression, and returns it. This is intended for use -- when the expansion of an expression needs to repeat part of it. For -- example, replacing a**2 by a*a requires two references to a which -- may be a complex subexpression. Duplicate_Subexpression guarantees -- not to duplicate side effects. If necessary, it generates actions -- to save the expression value in a temporary, inserting these actions -- into the tree using Insert_Actions with Exp as the insertion location. -- The original expression and the returned result then become references -- to this saved value. Exp must be analyzed on entry. On return, Exp -- is analyzed, but the caller is responsible for analyzing the returned -- copy after it is attached to the tree. The Name_Req flag is set to -- ensure that the result is suitable for use in a context requiring a -- name (e.g. the prefix of an attribute reference). procedure Ensure_Defined (Typ : Entity_Id; N : Node_Id); -- This procedure ensures that type referenced by Typ is defined. For the -- case of a type other than an Itype, nothing needs to be done, since -- all such types have declaration nodes. For Itypes, an N_Itype_Reference -- node is generated and inserted at the given node N. This is typically -- used to ensure that an Itype is properly defined outside a conditional -- construct when it is referenced in more than one branch. procedure Evolve_And_Then (Cond : in out Node_Id; Cond1 : Node_Id); -- Rewrites Cond with the expression: Cond and then Cond1. If Cond is -- Empty, then simply returns Cond1 (this allows the use of Empty to -- initialize a series of checks evolved by this routine, with a final -- result of Empty indicating that no checks were required). The Sloc -- field of the constructed N_And_Then node is copied from Cond1. procedure Evolve_Or_Else (Cond : in out Node_Id; Cond1 : Node_Id); -- Rewrites Cond with the expression: Cond or else Cond1. If Cond is -- Empty, then simply returns Cond1 (this allows the use of Empty to -- initialize a series of checks evolved by this routine, with a final -- result of Empty indicating that no checks were required). The Sloc -- field of the constructed N_And_Then node is copied from Cond1. procedure Expand_Subtype_From_Expr (N : Node_Id; Unc_Type : Entity_Id; Subtype_Indic : Node_Id; Exp : Node_Id); -- Build a constrained subtype from the initial value in object -- declarations and/or allocations when the type is indefinite (including -- class-wide). function Find_Prim_Op (T : Entity_Id; Name : Name_Id) return Entity_Id; -- Find the first primitive operation of type T whose name is 'Name'. -- this function allows the use of a primitive operation which is not -- directly visible procedure Force_Evaluation (Exp : Node_Id; Name_Req : Boolean := False); -- Force the evaluation of the expression right away. Similar behavior -- to Remove_Side_Effects when Variable_Ref is set to TRUE. That is to -- say, it removes the side-effects and capture the values of the -- variables. Remove_Side_effects guarantees that multiple evaluations -- of the same expression won't generate multiple side effects, whereas -- Force_Evaluation further guarantees that all evaluations will yield -- the same result. procedure Generate_Poll_Call (N : Node_Id); -- If polling is active, then a call to the Poll routine is built, -- and then inserted before the given node N and analyzed. function Homonym_Number (Subp : Entity_Id) return Nat; -- Here subp is the entity for a subprogram. This routine returns the -- homonym number used to disambiguate overloaded subprograms in the -- same scope (the number is used as part of constructed names to make -- sure that they are unique). The number is the ordinal position on -- the Homonym chain, counting only entries in the curren scope. If -- an entity is not overloaded, the returned number will be one. function Inside_Init_Proc return Boolean; -- Returns True if current scope is within an Init_Proc function In_Unconditional_Context (Node : Node_Id) return Boolean; -- Node is the node for a statement or a component of a statement. -- This function deteermines if the statement appears in a context -- that is unconditionally executed, i.e. it is not within a loop -- or a conditional or a case statement etc. function Is_Ref_To_Bit_Packed_Array (P : Node_Id) return Boolean; -- Determine whether the node P is a reference to a bit packed -- array, i.e. whether the designated object is a component of -- a bit packed array, or a subcomponent of such a component. -- If so, then all subscripts in P are evaluated with a call -- to Force_Evaluation, and True is returned. Otherwise False -- is returned, and P is not affected. function Is_Ref_To_Bit_Packed_Slice (P : Node_Id) return Boolean; -- Determine whether the node P is a reference to a bit packed -- slice, i.e. whether the designated object is bit packed slice -- or a component of a bit packed slice. Return True if so. function Is_Renamed_Object (N : Node_Id) return Boolean; -- Returns True if the node N is a renamed object. An expression -- is considered to be a renamed object if either it is the Name -- of an object renaming declaration, or is the prefix of a name -- which is a renamed object. For example, in: -- -- x : r renames a (1 .. 2) (1); -- -- We consider that a (1 .. 2) is a renamed object since it is the -- prefix of the name in the renaming declaration. function Is_Untagged_Derivation (T : Entity_Id) return Boolean; -- Returns true if type T is not tagged and is a derived type, -- or is a private type whose completion is such a type. procedure Kill_Dead_Code (N : Node_Id); -- N represents a node for a section of code that is known to be -- dead. The node is deleted, and any exception handler references -- and warning messages relating to this code are removed. procedure Kill_Dead_Code (L : List_Id); -- Like the above procedure, but applies to every element in the given -- list. Each of the entries is removed from the list before killing it. function Known_Non_Negative (Opnd : Node_Id) return Boolean; -- Given a node for a subexpression, determines if it represents a value -- that cannot possibly be negative, and if so returns True. A value of -- False means that it is not known if the value is positive or negative. function Make_Subtype_From_Expr (E : Node_Id; Unc_Typ : Entity_Id) return Node_Id; -- Returns a subtype indication corresponding to the actual type of an -- expresion E. Unc_Typ is an unconstrained array or record, or -- a classwide type. function May_Generate_Large_Temp (Typ : Entity_Id) return Boolean; -- Determines if the given type, Typ, may require a large temporary -- of the type that causes trouble if stack checking is enabled. The -- result is True only if stack checking is enabled and the size of -- the type is known at compile time and large, where large is defined -- hueristically by the body of this routine. The purpose of this -- routine is to help avoid generating troublesome temporaries that -- intefere with the stack checking mechanism. function Must_Be_Aligned (Obj : Node_Id) return Boolean; -- Given an object reference, determines whether or not the object -- is required to be aligned according to its type'alignment value. -- Normally, objects are required to be aligned, and the result will -- be True. The situation in which this is not the case is if the -- object reference involves a component of a packed array, where -- the type of the component is not required to have strict alignment. -- In this case, false will be returned. procedure Remove_Side_Effects (Exp : Node_Id; Name_Req : Boolean := False; Variable_Ref : Boolean := False); -- Given the node for a subexpression, this function replaces the node -- if necessary by an equivalent subexpression that is guaranteed to be -- side effect free. This is done by extracting any actions that could -- cause side effects, and inserting them using Insert_Actions into the -- tree to which Exp is attached. Exp must be analayzed and resolved -- before the call and is analyzed and resolved on return. The Name_Req -- may only be set to True if Exp has the form of a name, and the -- effect is to guarantee that any replacement maintains the form of a -- name. If Variable_Ref is set to TRUE, a variable is considered as a -- side effect (used in implementing Force_Evaluation). Note: after a -- call to Remove_Side_Effects, it is safe to use a call to -- New_Copy_Tree to obtain a copy of the resulting expression. function Safe_Unchecked_Type_Conversion (Exp : Node_Id) return Boolean; -- Given the node for an N_Unchecked_Type_Conversion, return True -- if this is an unchecked conversion that Gigi can handle directly. -- Otherwise return False if it is one for which the front end must -- provide a temporary. Note that the node need not be analyzed, and -- thus the Etype field may not be set, but in that case it must be -- the case that the Subtype_Mark field of the node is set/analyzed. procedure Set_Elaboration_Flag (N : Node_Id; Spec_Id : Entity_Id); -- N is the node for a subprogram or generic body, and Spec_Id -- is the entity for the corresponding spec. If an elaboration -- entity is defined, then this procedure generates an assignment -- statement to set it True, immediately after the body is elaborated. -- However, no assignment is generated in the case of library level -- procedures, since the setting of the flag in this case is generated -- in the binder. We do that so that we can detect cases where this is -- the only elaboration action that is required. procedure Wrap_Cleanup_Procedure (N : Node_Id); -- Given an N_Subprogram_Body node, this procedure adds an Abort_Defer -- call at the start of the statement sequence, and an Abort_Undefer call -- at the end of the statement sequence. All cleanup routines (i.e. those -- that are called from "at end" handlers) must defer abort on entry and -- undefer abort on exit. Note that it is assumed that the code for the -- procedure does not contain any return statements which would allow the -- flow of control to escape doing the undefer call. private pragma Inline (Force_Evaluation); pragma Inline (Duplicate_Subexpr); end Exp_Util;