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--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                             E X P _ U T I L                              --

--                                                                          --

--                                 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.  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 COPYING3.  If not, go to --

-- http://www.gnu.org/licenses for a complete copy of the license.          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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--  Package containing utility procedures used throughout the expander

with Exp_Tss; use Exp_Tss;

with Namet;   use Namet;

with Rtsfind; use Rtsfind;

with Sinfo;   use Sinfo;

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-circuits (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 Exp_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

   --  Exp_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;

      In_Init_Proc : Boolean := False) 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 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.

   --

   --  If In_Init_Proc is true, the call is part of the initialization of

   --  a component of a composite type, and the enclosing initialization

   --  procedure must be flagged as using the secondary stack. If In_Init_Proc

   --  is false, the call is for a stand-alone object, and the generated

   --  function itself must do its own cleanups.

   function Component_May_Be_Bit_Aligned (Comp : Entity_Id) return Boolean;

   --  This function is in charge of detecting record components that may

   --  cause trouble in the back end if an attempt is made to assign the

   --  component. The back end can handle such assignments with no problem if

   --  the components involved are small (64-bits or less) records or scalar

   --  items (including bit-packed arrays represented with modular types) or

   --  are both aligned on a byte boundary (starting on a byte boundary, and

   --  occupying an integral number of bytes).

   --

   --  However, problems arise for records larger than 64 bits, or for arrays

   --  (other than bit-packed arrays represented with a modular type) if the

   --  component starts on a non-byte boundary, or does not occupy an integral

   --  number of bytes (i.e. there are some bits possibly shared with fields

   --  at the start or beginning of the component). The back end cannot handle

   --  loading and storing such components in a single operation.

   --

   --  This function is used to detect the troublesome situation. it is

   --  conservative in the sense that it produces True unless it knows for

   --  sure that the component is safe (as outlined in the first paragraph

   --  above). The code generation for record and array assignment checks for

   --  trouble using this function, and if so the assignment is generated

   --  component-wise, which the back end is required to handle correctly.

   --

   --  Note that in GNAT 3, the back end will reject such components anyway,

   --  so the hard work in checking for this case is wasted in GNAT 3, but

   --  it is harmless, so it is easier to do it in all cases, rather than

   --  conditionalize it in GNAT 5 or beyond.

   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 Corresponding_Runtime_Package (Typ : Entity_Id) return RTU_Id;

   --  Return the id of the runtime package that will provide support for

   --  concurrent type Typ. Currently only protected types are supported,

   --  and the returned value is one of the following:

   --    System_Tasking_Protected_Objects

   --    System_Tasking_Protected_Objects_Entries

   --    System_Tasking_Protected_Objects_Single_Entry

   function Current_Sem_Unit_Declarations return List_Id;

   --  Return the 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_Subexpr 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 name (e.g. the prefix of an

   --  attribute reference).

   --

   --  Note that if there are any run time checks in Exp, these same checks

   --  will be duplicated in the returned duplicated expression. The two

   --  following functions allow this behavior to be modified.

   function Duplicate_Subexpr_No_Checks

     (Exp      : Node_Id;

      Name_Req : Boolean := False) return Node_Id;

   --  Identical in effect to Duplicate_Subexpr, except that Remove_Checks

   --  is called on the result, so that the duplicated expression does not

   --  include checks. This is appropriate for use when Exp, the original

   --  expression is unconditionally elaborated before the duplicated

   --  expression, so that there is no need to repeat any checks.

   function Duplicate_Subexpr_Move_Checks

     (Exp      : Node_Id;

      Name_Req : Boolean := False) return Node_Id;

   --  Identical in effect to Duplicate_Subexpr, except that Remove_Checks is

   --  called on Exp after the duplication is complete, so that the original

   --  expression does not include checks. In this case the result returned

   --  (the duplicated expression) will retain the original checks. This is

   --  appropriate for use when the duplicated expression is sure to be

   --  elaborated before the original expression Exp, so that there is no need

   --  to repeat the checks.

   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.

   function Entry_Names_OK return Boolean;

   --  Determine whether it is appropriate to dynamically allocate strings

   --  which represent entry [family member] names. These strings are created

   --  by the compiler and used by GDB.

   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_Or_Else 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_Init_Call

     (Var        : Entity_Id;

      Rep_Clause : Node_Id) return Node_Id;

   --  Look for init_proc call for variable Var, either among declarations

   --  between that of Var and a subsequent Rep_Clause applying to Var, or

   --  in the list of freeze actions associated with Var, and if found, return

   --  that call node.

   function Find_Interface_ADT

     (T     : Entity_Id;

      Iface : Entity_Id) return Elmt_Id;

   --  Ada 2005 (AI-251): Given a type T implementing the interface Iface,

   --  return the element of Access_Disp_Table containing the tag of the

   --  interface.

   function Find_Interface_Tag

     (T     : Entity_Id;

      Iface : Entity_Id) return Entity_Id;

   --  Ada 2005 (AI-251): Given a type T implementing the interface Iface,

   --  return the record component containing the tag of Iface.

   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. If T is a class wide type, then the reference is

   --  to an operation of the corresponding root type. Raises Program_Error

   --  exception if no primitive operation is found. This is normally an

   --  internal error, but in some cases is an expected consequence of

   --  illegalities elsewhere.

   function Find_Prim_Op

     (T    : Entity_Id;

      Name : TSS_Name_Type) return Entity_Id;

   --  Find the first primitive operation of type T whose name has the form

   --  indicated by the name parameter (i.e. is a type support subprogram

   --  with the indicated suffix). This function allows use of a primitive

   --  operation which is not directly visible. If T is a class wide type,

   --  then the reference is to an operation of the corresponding root type.

   --  Raises Program_Error exception if no primitive operation is found.

   --  This is normally an internal error, but in some cases is an expected

   --  consequence of illegalities elsewhere.

   function Find_Protection_Object (Scop : Entity_Id) return Entity_Id;

   --  Traverse the scope stack starting from Scop and look for an entry,

   --  entry family, or a subprogram that has a Protection_Object and return

   --  it. Raises Program_Error if no such entity is found since the context

   --  in which this routine is invoked should always have a protection

   --  object.

   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 captures 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.

   procedure Get_Current_Value_Condition

     (Var : Node_Id;

      Op  : out Node_Kind;

      Val : out Node_Id);

   --  This routine processes the Current_Value field of the variable Var. If

   --  the Current_Value field is null or if it represents a known value, then

   --  on return Cond is set to N_Empty, and Val is set to Empty.

   --

   --  The other case is when Current_Value points to an N_If_Statement or an

   --  N_Elsif_Part or a N_Iteration_Scheme node (see description in Einfo for

   --  exact details). In this case, Get_Current_Condition digs out the

   --  condition, and then checks if the condition is known false, known true,

   --  or not known at all. In the first two cases, Get_Current_Condition will

   --  return with Op set to the appropriate conditional operator (inverted if

   --  the condition is known false), and Val set to the constant value. If the

   --  condition is not known, then Op and Val are set for the empty case

   --  (N_Empty and Empty).

   --

   --  The check for whether the condition is true/false unknown depends

   --  on the case:

   --

   --     For an IF, the condition is known true in the THEN part, known false

   --     in any ELSIF or ELSE part, and not known outside the IF statement in

   --     question.

   --

   --     For an ELSIF, the condition is known true in the ELSIF part, known

   --     FALSE in any subsequent ELSIF, or ELSE part, and not known before the

   --     ELSIF, or after the end of the IF statement.

   --

   --  The caller can use this result to determine the value (for the case of

   --  N_Op_Eq), or to determine the result of some other test in other cases

   --  (e.g. no access check required if N_Op_Ne Null).

   function Has_Controlled_Coextensions (Typ : Entity_Id) return Boolean;

   --  Determine whether a record type has anonymous access discriminants with

   --  a controlled designated type.

   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 current 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 determines 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_All_Null_Statements (L : List_Id) return Boolean;

   --  Return True if all the items of the list are N_Null_Statement nodes.

   --  False otherwise. True for an empty list. It is an error to call this

   --  routine with No_List as the argument.

   function Is_Fully_Repped_Tagged_Type (T : Entity_Id) return Boolean;

   --  Tests given type T, and returns True if T is a non-discriminated tagged

   --  type which has a record representation clause that specifies the layout

   --  of all the components, including recursively components in all parent

   --  types. We exclude discriminated types for convenience, it is extremely

   --  unlikely that the special processing associated with the use of this

   --  routine is useful for the case of a discriminated type, and testing for

   --  component overlap would be a pain.

   function Is_Library_Level_Tagged_Type (Typ : Entity_Id) return Boolean;

   --  Return True if Typ is a library level tagged type. Currently we use

   --  this information to build statically allocated dispatch tables.

   function Is_Ref_To_Bit_Packed_Array (N : 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 (N : 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_Possibly_Unaligned_Slice (N : Node_Id) return Boolean;

   --  Determine whether the node P is a slice of an array where the slice

   --  result may cause alignment problems because it has an alignment that

   --  is not compatible with the type. Return True if so.

   function Is_Possibly_Unaligned_Object (N : Node_Id) return Boolean;

   --  Node N is an object reference. This function returns True if it is

   --  possible that the object may not be aligned according to the normal

   --  default alignment requirement for its type (e.g. if it appears in a

   --  packed record, or as part of a component that has a component clause.)

   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.

   function Is_Volatile_Reference (N : Node_Id) return Boolean;

   --  Checks if the node N represents a volatile reference, which can be

   --  either a direct reference to a variable treated as volatile, or an

   --  indexed/selected component where the prefix is treated as volatile,

   --  or has Volatile_Components set. A slice of a volatile variable is

   --  also volatile.

   procedure Kill_Dead_Code (N : Node_Id; Warn : Boolean := False);

   --  N represents a node for a section of code that is known to be dead. Any

   --  exception handler references and warning messages relating to this code

   --  are removed. If Warn is True, a warning will be output at the start of N

   --  indicating the deletion of the code. Note that the tree for the deleted

   --  code is left intact so that e.g. cross-reference data is still valid.

   procedure Kill_Dead_Code (L : List_Id; Warn : Boolean := False);

   --  Like the above procedure, but applies to every element in the given

   --  list. If Warn is True, a warning will be output at the start of N

   --  indicating the deletion of the code.

   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 Known_Non_Null (N : Node_Id) return Boolean;

   --  Given a node N for a subexpression of an access type, determines if

   --  this subexpression yields a value that is known at compile time to

   --  be non-null and returns True if so. Returns False otherwise. It is

   --  an error to call this function if N is not of an access type.

   function Known_Null (N : Node_Id) return Boolean;

   --  Given a node N for a subexpression of an access type, determines if this

   --  subexpression yields a value that is known at compile time to be null

   --  and returns True if so. Returns False otherwise. It is an error to call

   --  this function if N is not of an access type.

   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

   --  expression 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

   --  kind that causes back-end trouble if stack checking is enabled. The

   --  result is True only the size of the type is known at compile time and

   --  large, where large is defined heuristically by the body of this routine.

   --  The purpose of this routine is to help avoid generating troublesome

   --  temporaries that interfere with stack checking mechanism. Note that the

   --  caller has to check whether stack checking is actually enabled in order

   --  to guide the expansion (typically of a function call).

   function Non_Limited_Designated_Type (T : Entity_Id) return Entity_Id;

   --  An anonymous access type may designate a limited view. Check whether

   --  non-limited view is available during expansion, to examine components

   --  or other characteristics of the full type.

   function OK_To_Do_Constant_Replacement (E : Entity_Id) return Boolean;

   --  This function is used when testing whether or not to replace a reference

   --  to entity E by a known constant value. Such replacement must be done

   --  only in a scope known to be safe for such replacements. In particular,

   --  if we are within a subprogram and the entity E is declared outside the

   --  subprogram then we cannot do the replacement, since we do not attempt to

   --  trace subprogram call flow. It is also unsafe to replace statically

   --  allocated values (since they can be modified outside the scope), and we

   --  also inhibit replacement of Volatile or aliased objects since their

   --  address might be captured in a way we do not detect. A value of True is

   --  returned only if the replacement is safe.

   function Possible_Bit_Aligned_Component (N : Node_Id) return Boolean;

   --  This function is used during processing the assignment of a record or

   --  indexed component. The argument N is either the left hand or right hand

   --  side of an assignment, and this function determines if there is a record

   --  component reference where the record may be bit aligned in a manner that

   --  causes trouble for the back end (see Component_May_Be_Bit_Aligned for

   --  further details).

   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 analyzed 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 name. If Variable_Ref is set to

   --  TRUE, a variable is considered as side effect (used in implementing

   --  Force_Evaluation). Note: after call to Remove_Side_Effects, it is safe

   --  to call New_Copy_Tree to obtain a copy of the resulting expression.

   function Represented_As_Scalar (T : Entity_Id) return Boolean;

   --  Returns True iff the implementation of this type in code generation

   --  terms is scalar. This is true for scalars in the Ada sense, and for

   --  packed arrays which are represented by a scalar (modular) type.

   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_Current_Value_Condition (Cnode : Node_Id);

   --  Cnode is N_If_Statement, N_Elsif_Part, or N_Iteration_Scheme (the latter

   --  when a WHILE condition is present). This call checks whether Condition

   --  (Cnode) has embedded expressions of a form that should result in setting

   --  the Current_Value field of one or more entities, and if so sets these

   --  fields to point to Cnode.

   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 Set_Renamed_Subprogram (N : Node_Id; E : Entity_Id);

   --  N is an node which is an entity name that represents the name of a

   --  renamed subprogram. The node is rewritten to be an identifier that

   --  refers directly to the renamed subprogram, given by entity E.

   procedure Silly_Boolean_Array_Not_Test (N : Node_Id; T : Entity_Id);

   --  N is the node for a boolean array NOT operation, and T is the type of

   --  the array. This routine deals with the silly case where the subtype of

   --  the boolean array is False..False or True..True, where it is required

   --  that a Constraint_Error exception be raised (RM 4.5.6(6)).

   procedure Silly_Boolean_Array_Xor_Test (N : Node_Id; T : Entity_Id);

   --  N is the node for a boolean array XOR operation, and T is the type of

   --  the array. This routine deals with the silly case where the subtype of

   --  the boolean array is True..True, where a raise of a Constraint_Error

   --  exception is required (RM 4.5.6(6)).

   function Target_Has_Fixed_Ops

     (Left_Typ   : Entity_Id;

      Right_Typ  : Entity_Id;

      Result_Typ : Entity_Id) return Boolean;

   --  Returns True if and only if the target machine has direct support

   --  for fixed-by-fixed multiplications and divisions for the given

   --  operand and result types. This is called in package Exp_Fixd to

   --  determine whether to expand such operations.

   function Type_May_Have_Bit_Aligned_Components

     (Typ : Entity_Id) return Boolean;

   --  Determines if Typ is a composite type that has within it (looking down

   --  recursively at any subcomponents), a record type which has component

   --  that may be bit aligned (see Possible_Bit_Aligned_Component). The result

   --  is conservative, in that a result of False is decisive. A result of True

   --  means that such a component may or may not be present.

   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 (Duplicate_Subexpr);

   pragma Inline (Force_Evaluation);

   pragma Inline (Is_Library_Level_Tagged_Type);

end Exp_Util;