2006-10-31 Robert Dewar <dewar@adacore.com>

[pf3gnuchains/gcc-fork.git] / gcc / ada / sem_util.ads

------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                             S E M _ U T I L                              --
--                                                                          --
--                                 S p e c                                  --
--                                                                          --
--          Copyright (C) 1992-2006, 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- --
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-- 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 --
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-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
-- Boston, MA 02110-1301, USA.                                              --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

--  Package containing utility procedures used throughout the semantics

with Einfo;  use Einfo;
with Types;  use Types;
with Uintp;  use Uintp;
with Urealp; use Urealp;

package Sem_Util is

   procedure Add_Access_Type_To_Process (E : Entity_Id; A : Entity_Id);
   --  Add A to the list of access types to process when expanding the
   --  freeze node of E.

   function Alignment_In_Bits (E : Entity_Id) return Uint;
   --  If the alignment of the type or object E is currently known to the
   --  compiler, then this function returns the alignment value in bits.
   --  Otherwise Uint_0 is returned, indicating that the alignment of the
   --  entity is not yet known to the compiler.

   procedure Apply_Compile_Time_Constraint_Error
     (N      : Node_Id;
      Msg    : String;
      Reason : RT_Exception_Code;
      Ent    : Entity_Id  := Empty;
      Typ    : Entity_Id  := Empty;
      Loc    : Source_Ptr := No_Location;
      Rep    : Boolean    := True;
      Warn   : Boolean    := False);
   --  N is a subexpression which will raise constraint error when evaluated
   --  at runtime. Msg is a message that explains the reason for raising the
   --  exception. The last character is ? if the message is always a warning,
   --  even in Ada 95, and is not a ? if the message represents an illegality
   --  (because of violation of static expression rules) in Ada 95 (but not
   --  in Ada 83). Typically this routine posts all messages at the Sloc of
   --  node N. However, if Loc /= No_Location, Loc is the Sloc used to output
   --  the message. After posting the appropriate message, and if the flag
   --  Rep is set, this routine replaces the expression with an appropriate
   --  N_Raise_Constraint_Error node using the given Reason code. This node
   --  is then marked as being static if the original node is static, but
   --  sets the flag Raises_Constraint_Error, preventing further evaluation.
   --  The error message may contain a } or & insertion character. This
   --  normally references Etype (N), unless the Ent argument is given
   --  explicitly, in which case it is used instead. The type of the raise
   --  node that is built is normally Etype (N), but if the Typ parameter
   --  is present, this is used instead. Warn is normally False. If it is
   --  True then the message is treated as a warning even though it does
   --  not end with a ? (this is used when the caller wants to parametrize
   --  whether an error or warning is given.

   function Build_Actual_Subtype
     (T : Entity_Id;
      N : Node_Or_Entity_Id) return Node_Id;
   --  Build an anonymous subtype for an entity or expression, using the
   --  bounds of the entity or the discriminants of the enclosing record.
   --  T is the type for which the actual subtype is required, and N is either
   --  a defining identifier, or any subexpression.

   function Build_Actual_Subtype_Of_Component
     (T : Entity_Id;
      N : Node_Id) return Node_Id;
   --  Determine whether a selected component has a type that depends on
   --  discriminants, and build actual subtype for it if so.

   function Build_Default_Subtype
     (T : Entity_Id;
      N : Node_Id) return Entity_Id;
   --  If T is an unconstrained type with defaulted discriminants, build a
   --  subtype constrained by the default values, insert the subtype
   --  declaration in the tree before N, and return the entity of that
   --  subtype. Otherwise, simply return T.

   function Build_Discriminal_Subtype_Of_Component
     (T : Entity_Id) return Node_Id;
   --  Determine whether a record component has a type that depends on
   --  discriminants, and build actual subtype for it if so.

   procedure Build_Elaboration_Entity (N : Node_Id; Spec_Id : Entity_Id);
   --  Given a compilation unit node N, allocate an elaboration boolean for
   --  the compilation unit, and install it in the Elaboration_Entity field
   --  of Spec_Id, the entity for the compilation unit.

   function Cannot_Raise_Constraint_Error (Expr : Node_Id) return Boolean;
   --  Returns True if the expression cannot possibly raise Constraint_Error.
   --  The response is conservative in the sense that a result of False does
   --  not necessarily mean that CE could be raised, but a response of True
   --  means that for sure CE cannot be raised.

   procedure Check_Fully_Declared (T : Entity_Id; N : Node_Id);
   --  Verify that the full declaration of type T has been seen. If not,
   --  place error message on node N. Used in  object declarations, type
   --  conversions, qualified expressions.

   procedure Check_Potentially_Blocking_Operation (N : Node_Id);
   --  N is one of the statement forms that is a potentially blocking
   --  operation. If it appears within a protected action, emit warning.

   procedure Check_VMS (Construct : Node_Id);
   --  Check that this the target is OpenVMS, and if so, return with
   --  no effect, otherwise post an error noting this can only be used
   --  with OpenVMS ports. The argument is the construct in question
   --  and is used to post the error message.

   procedure Collect_Abstract_Interfaces
     (T                         : Entity_Id;
      Ifaces_List               : out Elist_Id;
      Exclude_Parent_Interfaces : Boolean := False);
   --  Ada 2005 (AI-251): Collect whole list of abstract interfaces that are
   --  directly or indirectly implemented by T. Exclude_Parent_Interfaces is
   --  used to avoid addition of inherited interfaces to the generated list.

   function Collect_Primitive_Operations (T : Entity_Id) return Elist_Id;
   --  Called upon type derivation and extension. We scan the declarative
   --  part in  which the type appears, and collect subprograms that have
   --  one subsidiary subtype of the type. These subprograms can only
   --  appear after the type itself.

   procedure Collect_Synchronized_Interfaces
     (Typ         : Entity_Id;
      Ifaces_List : out Elist_Id);
   --  Similar to Collect_Abstract_Interfaces, but tailored to task and
   --  protected types.

   function Compile_Time_Constraint_Error
     (N    : Node_Id;
      Msg  : String;
      Ent  : Entity_Id  := Empty;
      Loc  : Source_Ptr := No_Location;
      Warn : Boolean    := False) return Node_Id;
   --  This is similar to Apply_Compile_Time_Constraint_Error in that it
   --  generates a warning (or error) message in the same manner, but it does
   --  not replace any nodes. For convenience, the function always returns its
   --  first argument. The message is a warning if the message ends with ?, or
   --  we are operating in Ada 83 mode, or if the Warn parameter is set to
   --  True.

   procedure Conditional_Delay (New_Ent, Old_Ent : Entity_Id);
   --  Sets the Has_Delayed_Freeze flag of New if the Delayed_Freeze flag
   --  of Old is set and Old has no yet been Frozen (i.e. Is_Frozen is false);

   function Current_Entity (N : Node_Id) return Entity_Id;
   --  Find the currently visible definition for a given identifier, that is to
   --  say the first entry in the visibility chain for the Chars of N.

   function Current_Entity_In_Scope (N : Node_Id) return Entity_Id;
   --  Find whether there is a previous definition for identifier N in the
   --  current scope. Because declarations for a scope are not necessarily
   --  contiguous (e.g. for packages) the first entry on the visibility chain
   --  for N is not necessarily in the current scope.

   function Current_Scope return Entity_Id;
   --  Get entity representing current scope

   function Current_Subprogram return Entity_Id;
   --  Returns current enclosing subprogram. If Current_Scope is a subprogram,
   --  then that is what is returned, otherwise the Enclosing_Subprogram of
   --  the Current_Scope is returned. The returned value is Empty if this
   --  is called from a library package which is not within any subprogram.

   function Defining_Entity (N : Node_Id) return Entity_Id;
   --  Given a declaration N, returns the associated defining entity. If
   --  the declaration has a specification, the entity is obtained from
   --  the specification. If the declaration has a defining unit name,
   --  then the defining entity is obtained from the defining unit name
   --  ignoring any child unit prefixes.

   function Denotes_Discriminant
     (N                : Node_Id;
      Check_Concurrent : Boolean := False) return Boolean;
   --  Returns True if node N is an Entity_Name node for a discriminant.
   --  If the flag Check_Concurrent is true, function also returns true
   --  when N denotes the discriminal of the discriminant of a concurrent
   --  type. This is necessary to disable some optimizations on private
   --  components of protected types, and constraint checks on entry
   --  families constrained by discriminants.

   function Depends_On_Discriminant (N : Node_Id) return Boolean;
   --  Returns True if N denotes a discriminant or if N is a range, a subtype
   --  indication or a scalar subtype where one of the bounds is a
   --  discriminant.

   function Designate_Same_Unit
     (Name1 : Node_Id;
      Name2 : Node_Id) return  Boolean;
   --  Return true if Name1 and Name2 designate the same unit name;
   --  each of these names is supposed to be a selected component name,
   --  an expanded name, a defining program unit name or an identifier

   function Enclosing_Generic_Body
     (N : Node_Id) return Node_Id;
   --  Returns the Node_Id associated with the innermost enclosing
   --  generic body, if any. If none, then returns Empty.

   function Enclosing_Generic_Unit
     (N : Node_Id) return Node_Id;
   --  Returns the Node_Id associated with the innermost enclosing
   --  generic unit, if any. If none, then returns Empty.

   function Enclosing_Lib_Unit_Entity return Entity_Id;
   --  Returns the entity of enclosing N_Compilation_Unit Node which is the
   --  root of the current scope (which must not be Standard_Standard, and
   --  the caller is responsible for ensuring this condition).

   function Enclosing_Lib_Unit_Node (N : Node_Id) return Node_Id;
   --  Returns the enclosing N_Compilation_Unit Node that is the root
   --  of a subtree containing N.

   function Enclosing_Subprogram (E : Entity_Id) return Entity_Id;
   --  Utility function to return the Ada entity of the subprogram enclosing
   --  the entity E, if any. Returns Empty if no enclosing subprogram.

   procedure Ensure_Freeze_Node (E : Entity_Id);
   --  Make sure a freeze node is allocated for entity E. If necessary,
   --  build and initialize a new freeze node and set Has_Delayed_Freeze
   --  true for entity E.

   procedure Enter_Name (Def_Id : Entity_Id);
   --  Insert new name in symbol table of current scope with check for
   --  duplications (error message is issued if a conflict is found)
   --  Note: Enter_Name is not used for overloadable entities, instead
   --  these are entered using Sem_Ch6.Enter_Overloadable_Entity.

   procedure Explain_Limited_Type (T : Entity_Id; N : Node_Id);
   --  This procedure is called after issuing a message complaining
   --  about an inappropriate use of limited type T. If useful, it
   --  adds additional continuation lines to the message explaining
   --  why type T is limited. Messages are placed at node N.

   function Find_Corresponding_Discriminant
     (Id   : Node_Id;
      Typ  : Entity_Id) return Entity_Id;
   --  Because discriminants may have different names in a generic unit
   --  and in an instance, they are resolved positionally when possible.
   --  A reference to a discriminant carries the discriminant that it
   --  denotes when analyzed. Subsequent uses of this id on a different
   --  type denote the discriminant at the same position in this new type.

   function First_Actual (Node : Node_Id) return Node_Id;
   --  Node is an N_Function_Call or N_Procedure_Call_Statement node. The
   --  result returned is the first actual parameter in declaration order
   --  (not the order of parameters as they appeared in the source, which
   --  can be quite different as a result of the use of named parameters).
   --  Empty is returned for a call with no parameters. The procedure for
   --  iterating through the actuals in declaration order is to use this
   --  function to find the first actual, and then use Next_Actual to obtain
   --  the next actual in declaration order. Note that the value returned
   --  is always the expression (not the N_Parameter_Association nodes
   --  even if named association is used).

   function Full_Qualified_Name (E : Entity_Id) return String_Id;
   --  Generates the string literal corresponding to the E's full qualified
   --  name in upper case. An ASCII.NUL is appended as the last character.
   --  The names in the string are generated by Namet.Get_Decoded_Name_String.

   function Find_Static_Alternative (N : Node_Id) return Node_Id;
   --  N is a case statement whose expression is a compile-time value.
   --  Determine the alternative chosen, so that the code of non-selected
   --  alternatives, and the warnings that may apply to them, are removed.

   procedure Gather_Components
     (Typ           : Entity_Id;
      Comp_List     : Node_Id;
      Governed_By   : List_Id;
      Into          : Elist_Id;
      Report_Errors : out Boolean);
   --  The purpose of this procedure is to gather the valid components in a
   --  record type according to the values of its discriminants, in order to
   --  validate the components of a record aggregate.
   --
   --    Typ is the type of the aggregate when its constrained discriminants
   --      need to be collected, otherwise it is Empty.
   --
   --    Comp_List is an N_Component_List node.
   --
   --    Governed_By is a list of N_Component_Association nodes, where each
   --     choice list contains the name of a discriminant and the expression
   --     field gives its value. The values of the discriminants governing
   --     the (possibly nested) variant parts in Comp_List are found in this
   --     Component_Association List.
   --
   --    Into is the list where the valid components are appended. Note that
   --     Into need not be an Empty list. If it's not, components are attached
   --     to its tail.
   --
   --    Report_Errors is set to True if the values of the discriminants are
   --     non-static.
   --
   --  This procedure is also used when building a record subtype. If the
   --  discriminant constraint of the subtype is static, the components of the
   --  subtype are only those of the variants selected by the values of the
   --  discriminants. Otherwise all components of the parent must be included
   --  in the subtype for semantic analysis.

   function Get_Actual_Subtype (N : Node_Id) return Entity_Id;
   --  Given a node for an expression, obtain the actual subtype of the
   --  expression. In the case of a parameter where the formal is an
   --  unconstrained array or discriminated type, this will be the
   --  previously constructed subtype of the actual. Note that this is
   --  not quite the "Actual Subtype" of the RM, since it is always
   --  a constrained type, i.e. it is the subtype of the value of the
   --  actual. The actual subtype is also returned in other cases where
   --  it has already been constructed for an object. Otherwise the
   --  expression type is returned unchanged, except for the case of an
   --  unconstrained array type, where an actual subtype is created, using
   --  Insert_Actions if necessary to insert any associated actions.

   function Get_Actual_Subtype_If_Available (N : Node_Id) return Entity_Id;
   --  This is like Get_Actual_Subtype, except that it never constructs an
   --  actual subtype. If an actual subtype is already available, i.e. the
   --  Actual_Subtype field of the corresponding entity is set, then it is
   --  returned. Otherwise the Etype of the node is returned.

   function Get_Default_External_Name (E : Node_Or_Entity_Id) return Node_Id;
   --  This is used to construct the string literal node representing a
   --  default external name, i.e. one that is constructed from the name
   --  of an entity, or (in the case of extended DEC import/export pragmas,
   --  an identifier provided as the external name. Letters in the name are
   --  according to the setting of Opt.External_Name_Default_Casing.

   function Get_Generic_Entity (N : Node_Id) return Entity_Id;
   --  Returns the true generic entity in an instantiation. If the name in
   --  the instantiation is a renaming, the function returns the renamed
   --  generic.

   procedure Get_Index_Bounds (N : Node_Id; L, H : out Node_Id);
   --  This procedure assigns to L and H respectively the values of the
   --  low and high bounds of node N, which must be a range, subtype
   --  indication, or the name of a scalar subtype. The result in L, H
   --  may be set to Error if there was an earlier error in the range.

   function Get_Enum_Lit_From_Pos
     (T   : Entity_Id;
      Pos : Uint;
      Loc : Source_Ptr) return Entity_Id;
   --  This function obtains the E_Enumeration_Literal entity for the
   --  specified value from the enumneration type or subtype T. The
   --  second argument is the Pos value, which is assumed to be in range.
   --  The third argument supplies a source location for constructed
   --  nodes returned by this function.

   procedure Get_Library_Unit_Name_String (Decl_Node : Node_Id);
   --  Retrieve the fully expanded name of the library unit declared by
   --  Decl_Node into the name buffer.

   function Get_Name_Entity_Id (Id : Name_Id) return Entity_Id;
   --  An entity value is associated with each name in the name table. The
   --  Get_Name_Entity_Id function fetches the Entity_Id of this entity,
   --  which is the innermost visible entity with the given name. See the
   --  body of Sem_Ch8 for further details on handling of entity visibility.

   function Get_Subprogram_Entity (Nod : Node_Id) return Entity_Id;
   --  Nod is either a procedure call statement, or a function call, or
   --  an accept statement node. This procedure finds the Entity_Id of the
   --  related subprogram or entry and returns it, or if no subprogram can
   --  be found, returns Empty.

   function Get_Referenced_Object (N : Node_Id) return Node_Id;
   --  Given a node, return the renamed object if the node represents
   --  a renamed object, otherwise return the node unchanged. The node
   --  may represent an arbitrary expression.

   function Get_Subprogram_Body (E : Entity_Id) return Node_Id;
   --  Given the entity for a subprogram (E_Function or E_Procedure),
   --  return the corresponding N_Subprogram_Body node. If the corresponding
   --  body of the declaration is missing (as for an imported subprogram)
   --  return Empty.

   function Get_Task_Body_Procedure (E : Entity_Id) return Node_Id;
   pragma Inline (Get_Task_Body_Procedure);
   --  Given an entity for a task type or subtype, retrieves the
   --  Task_Body_Procedure field from the corresponding task type
   --  declaration.

   function Has_Access_Values (T : Entity_Id) return Boolean;
   --  Returns true if type or subtype T is an access type, or has a
   --  component (at any recursive level) that is an access type. This
   --  is a conservative predicate, if it is not known whether or not
   --  T contains access values (happens for generic formals in some
   --  cases), then False is returned.

   type Alignment_Result is (Known_Compatible, Unknown, Known_Incompatible);
   --  Result of Has_Compatible_Alignment test, description found below. Note
   --  that the values are arranged in increasing order of problematicness.

   function Has_Abstract_Interfaces (Tagged_Type : Entity_Id) return Boolean;
   --  Returns true if Tagged_Type implements some abstract interface

   function Has_Compatible_Alignment
     (Obj  : Entity_Id;
      Expr : Node_Id) return Alignment_Result;
   --  Obj is an object entity, and expr is a node for an object reference. If
   --  the alignment of the object referenced by Expr is known to be compatible
   --  with the alignment of Obj (i.e. is larger or the same), then the result
   --  is Known_Compatible. If the alignment of the object referenced by Expr
   --  is known to be less than the alignment of Obj, then Known_Incompatible
   --  is returned. If neither condition can be reliably established at compile
   --  time, then Unknown is returned. This is used to determine if alignment
   --  checks are required for address clauses, and also whether copies must
   --  be made when objects are passed by reference.
   --
   --  Note: Known_Incompatible does not mean that at run time the alignment
   --  of Expr is known to be wrong for Obj, just that it can be determined
   --  that alignments have been explicitly or implicitly specified which
   --  are incompatible (whereas Unknown means that even this is not known).
   --  The appropriate reaction of a caller to Known_Incompatible is to treat
   --  it as Unknown, but issue a warning that there may be an alignment error.

   function Has_Declarations (N : Node_Id) return Boolean;
   --  Determines if the node can have declarations

   function Has_Discriminant_Dependent_Constraint
     (Comp : Entity_Id) return Boolean;
   --  Returns True if and only if Comp has a constrained subtype
   --  that depends on a discriminant.

   function Has_Infinities (E : Entity_Id) return Boolean;
   --  Determines if the range of the floating-point type E includes
   --  infinities. Returns False if E is not a floating-point type.

   function Has_Null_Exclusion (N : Node_Id) return Boolean;
   --  Determine whether node N has a null exclusion

   function Has_Preelaborable_Initialization (E : Entity_Id) return Boolean;
   --  Return True iff type E has preelaborable initialiation as defined in
   --  Ada 2005 (see AI-161 for details of the definition of this attribute).

   function Has_Private_Component (Type_Id : Entity_Id) return Boolean;
   --  Check if a type has a (sub)component of a private type that has not
   --  yet received a full declaration.

   function Has_Stream (T : Entity_Id) return Boolean;
   --  Tests if type T is derived from Ada.Streams.Root_Stream_Type, or
   --  in the case of a composite type, has a component for which this
   --  predicate is True, and if so returns True. Otherwise a result of
   --  False means that there is no Stream type in sight. For a private
   --  type, the test is applied to the underlying type (or returns False
   --  if there is no underlying type).

   function Has_Tagged_Component (Typ : Entity_Id) return Boolean;
   --  Typ must be a composite type (array or record). This function is used
   --  to check if '=' has to be expanded into a bunch component comparaisons.

   function In_Instance return Boolean;
   --  Returns True if the current scope is within a generic instance

   function In_Instance_Body return Boolean;
   --  Returns True if current scope is within the body of an instance, where
   --  several semantic checks (e.g. accessibility checks) are relaxed.

   function In_Instance_Not_Visible return Boolean;
   --  Returns True if current scope is with the private part or the body of
   --  an instance. Other semantic checks are suppressed in this context.

   function In_Instance_Visible_Part return Boolean;
   --  Returns True if current scope is within the visible part of a package
   --  instance, where several additional semantic checks apply.

   function In_Package_Body return Boolean;
   --  Returns True if current scope is within a package body

   function In_Subprogram_Or_Concurrent_Unit return Boolean;
   --  Determines if the current scope is within a subprogram compilation
   --  unit (inside a subprogram declaration, subprogram body, or generic
   --  subprogram declaration) or within a task or protected body. The test
   --  is for appearing anywhere within such a construct (that is it does not
   --  need to be directly within).

   function In_Visible_Part (Scope_Id : Entity_Id) return Boolean;
   --  Determine whether a declaration occurs within the visible part of a
   --  package specification. The package must be on the scope stack, and the
   --  corresponding private part must not.

   procedure Insert_Explicit_Dereference (N : Node_Id);
   --  In a context that requires a composite or subprogram type and
   --  where a prefix is an access type, rewrite the access type node
   --  N (which is the prefix, e.g. of an indexed component) as an
   --  explicit dereference.

   function Is_AAMP_Float (E : Entity_Id) return Boolean;
   --  Defined for all type entities. Returns True only for the base type
   --  of float types with AAMP format. The particular format is determined
   --  by the Digits_Value value which is 6 for the 32-bit floating point type,
   --  or 9 for the 48-bit type. This is not an attribute function (like
   --  VAX_Float) in order to not use up an extra flag and to prevent
   --  the dependency of Einfo on Targparm which would be required for a
   --  synthesized attribute.

   function Is_Actual_Parameter (N : Node_Id) return Boolean;
   --  Determines if N is an actual parameter in a subprogram call

   function Is_Aliased_View (Obj : Node_Id) return Boolean;
   --  Determine if Obj is an aliased view, i.e. the name of an
   --  object to which 'Access or 'Unchecked_Access can apply.

   function Is_Ancestor_Package
     (E1 : Entity_Id;
      E2 : Entity_Id) return Boolean;
   --  Determine whether package E1 is an ancestor of E2

   function Is_Atomic_Object (N : Node_Id) return Boolean;
   --  Determines if the given node denotes an atomic object in the sense
   --  of the legality checks described in RM C.6(12).

   function Is_Controlling_Limited_Procedure
     (Proc_Nam : Entity_Id) return Boolean;
   --  Ada 2005 (AI-345): Determine whether Proc_Nam is a primitive procedure
   --  of a limited interface with a controlling first parameter.

   function Is_Dependent_Component_Of_Mutable_Object
     (Object : Node_Id) return Boolean;
   --  Returns True if Object is the name of a subcomponent that
   --  depends on discriminants of a variable whose nominal subtype
   --  is unconstrained and not indefinite, and the variable is
   --  not aliased. Otherwise returns False. The nodes passed
   --  to this function are assumed to denote objects.

   function Is_Dereferenced (N : Node_Id) return Boolean;
   --  N is a subexpression node of an access type. This function returns
   --  true if N appears as the prefix of a node that does a dereference
   --  of the access value (selected/indexed component, explicit dereference
   --  or a slice), and false otherwise.

   function Is_Descendent_Of (T1 : Entity_Id; T2 : Entity_Id) return Boolean;
   --  Returns True if type T1 is a descendent of type T2, and false otherwise.
   --  This is the RM definition, a type is a descendent of another type if it
   --  is the same type or is derived from a descendent of the other type.

   function Is_Descendent_Of_Address (T1 : Entity_Id) return Boolean;
   --  Returns True if type T1 is a descendent of Address or its base type.
   --  Similar to calling Is_Descendent_Of with Base_Type (RTE (RE_Address))
   --  except that it avoids creating an unconditional dependency on System.

   function Is_False (U : Uint) return Boolean;
   --  The argument is a Uint value which is the Boolean'Pos value of a
   --  Boolean operand (i.e. is either 0 for False, or 1 for True). This
   --  function simply tests if it is False (i.e. zero)

   function Is_Fixed_Model_Number (U : Ureal; T : Entity_Id) return Boolean;
   --  Returns True iff the number U is a model number of the fixed-
   --  point type T, i.e. if it is an exact multiple of Small.

   function Is_Fully_Initialized_Type (Typ : Entity_Id) return Boolean;
   --  Typ is a type entity. This function returns true if this type is
   --  fully initialized, meaning that an object of the type is fully
   --  initialized. Note that initialization resulting from the use of
   --  pragma Normalized_Scalars does not count. Note that this is only
   --  used for the purpose of issuing warnings for objects that are
   --  potentially referenced uninitialized. This means that the result
   --  returned is not crucial, but probably should err on the side of
   --  thinking things are fully initialized if it does not know.

   function Is_Inherited_Operation (E : Entity_Id) return Boolean;
   --  E is a subprogram. Return True is E is an implicit operation inherited
   --  by a derived type declarations.

   function Is_Library_Level_Entity (E : Entity_Id) return Boolean;
   --  A library-level declaration is one that is accessible from Standard,
   --  i.e. a library unit or an entity declared in a library package.

   function Is_Local_Variable_Reference (Expr : Node_Id) return Boolean;
   --  Determines whether Expr is a refeference to a variable or IN OUT
   --  mode parameter of the current enclosing subprogram.
   --  Why are OUT parameters not considered here ???

   function Is_Object_Reference (N : Node_Id) return Boolean;
   --  Determines if the tree referenced by N represents an object. Both
   --  variable and constant objects return True (compare Is_Variable).

   function Is_OK_Variable_For_Out_Formal (AV : Node_Id) return Boolean;
   --  Used to test if AV is an acceptable formal for an OUT or IN OUT
   --  formal. Note that the Is_Variable function is not quite the right
   --  test because this is a case in which conversions whose expression
   --  is a variable (in the Is_Variable sense) with a non-tagged type
   --  target are considered view conversions and hence variables.

   function Is_Partially_Initialized_Type (Typ : Entity_Id) return Boolean;
   --  Typ is a type entity. This function returns true if this type is
   --  partly initialized, meaning that an object of the type is at least
   --  partly initialized (in particular in the record case, that at least
   --  one field has an initialization expression). Note that initialization
   --  resulting from the use of pragma Normalized_Scalars does not count.

   function Is_Potentially_Persistent_Type (T : Entity_Id) return Boolean;
   --  Determines if type T is a potentially persistent type. A potentially
   --  persistent type is defined (recursively) as a scalar type, a non-tagged
   --  record whose components are all of a potentially persistent type, or an
   --  array with all static constraints whose component type is potentially
   --  persistent. A private type is potentially persistent if the full type
   --  is potentially persistent.

   function Is_RCI_Pkg_Spec_Or_Body (Cunit : Node_Id) return Boolean;
   --  Return True if a compilation unit is the specification or the
   --  body of a remote call interface package.

   function Is_Remote_Access_To_Class_Wide_Type (E : Entity_Id) return Boolean;
   --  Return True if E is a remote access-to-class-wide-limited_private type

   function Is_Remote_Access_To_Subprogram_Type (E : Entity_Id) return Boolean;
   --  Return True if E is a remote access to subprogram type

   function Is_Remote_Call (N : Node_Id) return Boolean;
   --  Return True if N denotes a potentially remote call

   function Is_Renamed_Entry (Proc_Nam : Entity_Id) return Boolean;
   --  Return True if Proc_Nam is a procedure renaming of an entry

   function Is_Selector_Name (N : Node_Id) return Boolean;
   --  Given an N_Identifier node N, determines if it is a Selector_Name.
   --  As described in Sinfo, Selector_Names are special because they
   --  represent use of the N_Identifier node for a true identifer, when
   --  normally such nodes represent a direct name.

   function Is_Statement (N : Node_Id) return Boolean;
   --  Check if the node N is a statement node. Note that this includes
   --  the case of procedure call statements (unlike the direct use of
   --  the N_Statement_Other_Than_Procedure_Call subtype from Sinfo).
   --  Note that a label is *not* a statement, and will return False.

   function Is_Transfer (N : Node_Id) return Boolean;
   --  Returns True if the node N is a statement which is known to cause
   --  an unconditional transfer of control at runtime, i.e. the following
   --  statement definitely will not be executed.

   function Is_True (U : Uint) return Boolean;
   --  The argument is a Uint value which is the Boolean'Pos value of a
   --  Boolean operand (i.e. is either 0 for False, or 1 for True). This
   --  function simply tests if it is True (i.e. non-zero)

   function Is_Variable (N : Node_Id) return Boolean;
   --  Determines if the tree referenced by N represents a variable, i.e.
   --  can appear on the left side of an assignment. There is one situation,
   --  namely formal parameters, in which non-tagged type conversions are
   --  also considered variables, but Is_Variable returns False for such
   --  cases, since it has no knowledge of the context. Note that this is
   --  the point at which Assignment_OK is checked, and True is returned
   --  for any tree thus marked.

   function Is_Volatile_Object (N : Node_Id) return Boolean;
   --  Determines if the given node denotes an volatile object in the sense
   --  of the legality checks described in RM C.6(12). Note that the test
   --  here is for something actually declared as volatile, not for an object
   --  that gets treated as volatile (see Einfo.Treat_As_Volatile).

   procedure Kill_Current_Values;
   --  This procedure is called to clear all constant indications from all
   --  entities in the current scope and in any parent scopes if the current
   --  scope is a block or a package (and that recursion continues to the
   --  top scope that is not a block or a package). This is used when the
   --  sequential flow-of-control assumption is violated (occurence of a
   --  label, head of a loop, or start of an exception handler). The effect
   --  of the call is to clear the Constant_Value field (but we do not need
   --  to clear the Is_True_Constant flag, since that only gets reset if
   --  there really is an assignment somewhere in the entity scope). This
   --  procedure also calls Kill_All_Checks, since this is a special case
   --  of needing to forget saved values. This procedure also clears any
   --  Is_Known_Non_Null flags in variables, constants or parameters
   --  since these are also not known to be valid.

   procedure Kill_Current_Values (Ent : Entity_Id);
   --  This performs the same processing as described above for the form with
   --  no argument, but for the specific entity given. The call has no effect
   --  if the entity Ent is not for an object.

   procedure Kill_Size_Check_Code (E : Entity_Id);
   --  Called when an address clause or pragma Import is applied to an
   --  entity. If the entity is a variable or a constant, and size check
   --  code is present, this size check code is killed, since the object
   --  will not be allocated by the program.

   function Known_To_Be_Assigned (N : Node_Id) return Boolean;
   --  The node N is an entity reference. This function determines whether the
   --  reference is for sure an assignment of the entity, returning True if
   --  so. This differs from May_Be_Lvalue in that it defaults in the other
   --  direction. Cases which may possibly be assignments but are not known to
   --  be may return True from May_Be_Lvalue, but False from this function.

   function May_Be_Lvalue (N : Node_Id) return Boolean;
   --  Determines if N could be an lvalue (e.g. an assignment left hand side).
   --  An lvalue is defined as any expression which appears in a context where
   --  a name is required by the syntax, and the identity, rather than merely
   --  the value of the node is needed (for example, the prefix of an Access
   --  attribute is in this category). Note that, as implied by the name, this
   --  test is conservative. If it cannot be sure that N is NOT an lvalue, then
   --  it returns True. It tries hard to get the answer right, but it is hard
   --  to guarantee this in all cases. Note that it is more possible to give
   --  correct answer if the tree is fully analyzed.

   function New_External_Entity
     (Kind         : Entity_Kind;
      Scope_Id     : Entity_Id;
      Sloc_Value   : Source_Ptr;
      Related_Id   : Entity_Id;
      Suffix       : Character;
      Suffix_Index : Nat := 0;
      Prefix       : Character := ' ') return Entity_Id;
   --  This function creates an N_Defining_Identifier node for an internal
   --  created entity, such as an implicit type or subtype, or a record
   --  initialization procedure. The entity name is constructed with a call
   --  to New_External_Name (Related_Id, Suffix, Suffix_Index, Prefix), so
   --  that the generated name may be referenced as a public entry, and the
   --  Is_Public flag is set if needed (using Set_Public_Status). If the
   --  entity is for a type or subtype, the size/align fields are initialized
   --  to unknown (Uint_0).

   function New_Internal_Entity
     (Kind       : Entity_Kind;
      Scope_Id   : Entity_Id;
      Sloc_Value : Source_Ptr;
      Id_Char    : Character) return Entity_Id;
   --  This function is similar to New_External_Entity, except that the
   --  name is constructed by New_Internal_Name (Id_Char). This is used
   --  when the resulting entity does not have to be referenced as a
   --  public entity (and in this case Is_Public is not set).

   procedure Next_Actual (Actual_Id : in out Node_Id);
   pragma Inline (Next_Actual);
   --  Next_Actual (N) is equivalent to N := Next_Actual (N)

   function Next_Actual (Actual_Id : Node_Id) return Node_Id;
   --  Find next actual parameter in declaration order. As described for
   --  First_Actual, this is the next actual in the declaration order, not
   --  the call order, so this does not correspond to simply taking the
   --  next entry of the Parameter_Associations list. The argument is an
   --  actual previously returned by a call to First_Actual or Next_Actual.
   --  Note that the result produced is always an expression, not a parameter
   --  assciation node, even if named notation was used.

   procedure Normalize_Actuals
     (N       : Node_Id;
      S       : Entity_Id;
      Report  : Boolean;
      Success : out Boolean);
   --  Reorders lists of actuals according to names of formals, value returned
   --  in Success indicates sucess of reordering. For more details, see body.
   --  Errors are reported only if Report is set to True.

   procedure Note_Possible_Modification (N : Node_Id);
   --  This routine is called if the sub-expression N maybe the target of
   --  an assignment (e.g. it is the left side of an assignment, used as
   --  an out parameters, or used as prefixes of access attributes). It
   --  sets May_Be_Modified in the associated entity if there is one,
   --  taking into account the rule that in the case of renamed objects,
   --  it is the flag in the renamed object that must be set.

   function Object_Access_Level (Obj : Node_Id) return Uint;
   --  Return the accessibility level of the view of the object Obj.
   --  For convenience, qualified expressions applied to object names
   --  are also allowed as actuals for this function.

   function Overrides_Synchronized_Primitive
     (Def_Id      : Entity_Id;
      First_Hom   : Entity_Id;
      Ifaces_List : Elist_Id;
      In_Scope    : Boolean := True) return Entity_Id;
   --  Determine whether entry or subprogram Def_Id overrides a primitive
   --  operation that belongs to one of the interfaces in Ifaces_List. A
   --  specific homonym chain can be specified by setting First_Hom. Flag
   --  In_Scope is used to designate whether the entry or subprogram was
   --  declared inside the scope of the synchronized type or after. Return
   --  the overriden entity or Empty.

   function Private_Component (Type_Id : Entity_Id) return Entity_Id;
   --  Returns some private component (if any) of the given Type_Id.
   --  Used to enforce the rules on visibility of operations on composite
   --  types, that depend on the full view of the component type. For a
   --  record type there may be several such components, we just return
   --  the first one.

   procedure Process_End_Label
     (N   : Node_Id;
      Typ : Character;
      Ent : Entity_Id);
   --  N is a node whose End_Label is to be processed, generating all
   --  appropriate cross-reference entries, and performing style checks
   --  for any identifier references in the end label. Typ is either
   --  'e' or 't indicating the type of the cross-reference entity
   --  (e for spec, t for body, see Lib.Xref spec for details). The
   --  parameter Ent gives the entity to which the End_Label refers,
   --  and to which cross-references are to be generated.

   function Real_Convert (S : String) return Node_Id;
   --  S is a possibly signed syntactically valid real literal. The result
   --  returned is an N_Real_Literal node representing the literal value.

   function Rep_To_Pos_Flag (E : Entity_Id; Loc : Source_Ptr) return Node_Id;
   --  This is used to construct the second argument in a call to Rep_To_Pos
   --  which is Standard_True if range checks are enabled (E is an entity to
   --  which the Range_Checks_Suppressed test is applied), and Standard_False
   --  if range checks are suppressed. Loc is the location for the node that
   --  is returned (which is a New_Occurrence of the appropriate entity).
   --
   --  Note: one might think that it would be fine to always use True and
   --  to ignore the suppress in this case, but it is generally better to
   --  believe a request to suppress exceptions if possible, and further
   --  more there is at least one case in the generated code (the code for
   --  array assignment in a loop) that depends on this suppression.

   procedure Require_Entity (N : Node_Id);
   --  N is a node which should have an entity value if it is an entity name.
   --  If not, then check if there were previous errors. If so, just fill
   --  in with Any_Id and ignore. Otherwise signal a program error exception.
   --  This is used as a defense mechanism against ill-formed trees caused by
   --  previous errors (particularly in -gnatq mode).

   function Requires_Transient_Scope (Id : Entity_Id) return Boolean;
   --  E is a type entity. The result is True when temporaries of this
   --  type need to be wrapped in a transient scope to be reclaimed
   --  properly when a secondary stack is in use. Examples of types
   --  requiring such wrapping are controlled types and variable-sized
   --  types including unconstrained arrays

   procedure Reset_Analyzed_Flags (N : Node_Id);
   --  Reset the Analyzed flags in all nodes of the tree whose root is N

   function Safe_To_Capture_Value
     (N    : Node_Id;
      Ent  : Entity_Id;
      Cond : Boolean := False) return Boolean;
   --  The caller is interested in capturing a value (either the current value,
   --  or an indication that the value is non-null) for the given entity Ent.
   --  This value can only be captured if sequential execution semantics can be
   --  properly guaranteed so that a subsequent reference will indeed be sure
   --  that this current value indication is correct. The node N is the
   --  construct which resulted in the possible capture of the value (this
   --  is used to check if we are in a conditional).
   --
   --  Cond is used to skip the test for being inside a conditional. It is used
   --  in the case of capturing values from if/while tests, which already do a
   --  proper job of handling scoping issues without this help.
   --
   --  The only entities whose values can be captured are OUT and IN OUT formal
   --  parameters, and variables unless Cond is True, in which case we also
   --  allow IN formals, loop parameters and constants, where we cannot ever
   --  capture actual value information, but we can capture conditional tests.

   function Same_Name (N1, N2 : Node_Id) return Boolean;
   --  Determine if two (possibly expanded) names are the same name

   function Same_Type (T1, T2 : Entity_Id) return Boolean;
   --  Determines if T1 and T2 represent exactly the same type. Two types
   --  are the same if they are identical, or if one is an unconstrained
   --  subtype of the other, or they are both common subtypes of the same
   --  type with identical constraints. The result returned is conservative.
   --  It is True if the types are known to be the same, but a result of
   --  False is indecisive (e.g. the compiler may not be able to tell that
   --  two constraints are identical).

   function Scope_Within_Or_Same (Scope1, Scope2 : Entity_Id) return Boolean;
   --  Determines if the entity Scope1 is the same as Scope2, or if it is
   --  inside it, where both entities represent scopes. Note that scopes
   --  are only partially ordered, so Scope_Within_Or_Same (A,B) and
   --  Scope_Within_Or_Same (B,A) can both be False for a given pair A,B.

   function Scope_Within (Scope1, Scope2 : Entity_Id) return Boolean;
   --  Like Scope_Within_Or_Same, except that this function returns
   --  False in the case where Scope1 and Scope2 are the same scope.

   procedure Set_Current_Entity (E : Entity_Id);
   --  Establish the entity E as the currently visible definition of its
   --  associated name (i.e. the Node_Id associated with its name)

   procedure Set_Entity_With_Style_Check (N : Node_Id; Val : Entity_Id);
   --  This procedure has the same calling sequence as Set_Entity, but
   --  if Style_Check is set, then it calls a style checking routine which
   --  can check identifier spelling style.

   procedure Set_Name_Entity_Id (Id : Name_Id; Val : Entity_Id);
   --  Sets the Entity_Id value associated with the given name, which is the
   --  Id of the innermost visible entity with the given name. See the body
   --  of package Sem_Ch8 for further details on the handling of visibility.

   procedure Set_Next_Actual (Ass1_Id : Node_Id; Ass2_Id : Node_Id);
   --  The arguments may be parameter associations, whose descendants
   --  are the optional formal name and the actual parameter. Positional
   --  parameters are already members of a list, and do not need to be
   --  chained separately. See also First_Actual and Next_Actual.

   procedure Set_Public_Status (Id : Entity_Id);
   --  If an entity (visible or otherwise) is defined in a library
   --  package, or a package that is itself public, then this subprogram
   --  labels the entity public as well.

   procedure Set_Scope_Is_Transient (V : Boolean := True);
   --  Set the flag Is_Transient of the current scope

   procedure Set_Size_Info (T1, T2 : Entity_Id);
   --  Copies the Esize field and Has_Biased_Representation flag from sub(type)
   --  entity T2 to (sub)type entity T1. Also copies the Is_Unsigned_Type flag
   --  in the fixed-point and discrete cases, and also copies the alignment
   --  value from T2 to T1. It does NOT copy the RM_Size field, which must be
   --  separately set if this is required to be copied also.

   function Scope_Is_Transient  return Boolean;
   --  True if the current scope is transient

   function Static_Integer (N : Node_Id) return Uint;
   --  This function analyzes the given expression node and then resolves it
   --  as any integer type. If the result is static, then the value of the
   --  universal expression is returned, otherwise an error message is output
   --  and a value of No_Uint is returned.

   function Statically_Different (E1, E2 : Node_Id) return Boolean;
   --  Return True if it can be statically determined that the Expressions
   --  E1 and E2 refer to different objects

   function Subprogram_Access_Level (Subp : Entity_Id) return Uint;
   --  Return the accessibility level of the view denoted by Subp

   procedure Trace_Scope (N : Node_Id; E : Entity_Id; Msg : String);
   --  Print debugging information on entry to each unit being analyzed

   procedure Transfer_Entities (From : Entity_Id; To : Entity_Id);
   --  Move a list of entities from one scope to another, and recompute
   --  Is_Public based upon the new scope.

   function Type_Access_Level (Typ : Entity_Id) return Uint;
   --  Return the accessibility level of Typ

   function Unit_Declaration_Node (Unit_Id : Entity_Id) return Node_Id;
   --  Unit_Id is the simple name of a program unit, this function returns the
   --  corresponding xxx_Declaration node for the entity. Also applies to the
   --  body entities for subprograms, tasks and protected units, in which case
   --  it returns the subprogram, task or protected body node for it. The unit
   --  may be a child unit with any number of ancestors.

   function Universal_Interpretation (Opnd : Node_Id) return Entity_Id;
   --  Yields universal_Integer or Universal_Real if this is a candidate

   function Unqualify (Expr : Node_Id) return Node_Id;
   --  Removes any qualifications from Expr. For example, for T1'(T2'(X)),
   --  this returns X. If Expr is not a qualified expression, returns Expr.

   function Within_Init_Proc return Boolean;
   --  Determines if Current_Scope is within an init proc

   procedure Wrong_Type (Expr : Node_Id; Expected_Type : Entity_Id);
   --  Output error message for incorrectly typed expression. Expr is the
   --  node for the incorrectly typed construct (Etype (Expr) is the type
   --  found), and Expected_Type is the entity for the expected type. Note
   --  that Expr does not have to be a subexpression, anything with an
   --  Etype field may be used.

private
   pragma Inline (Current_Entity);
   pragma Inline (Get_Name_Entity_Id);
   pragma Inline (Is_False);
   pragma Inline (Is_Statement);
   pragma Inline (Is_True);
   pragma Inline (Set_Current_Entity);
   pragma Inline (Set_Name_Entity_Id);
   pragma Inline (Set_Size_Info);
   pragma Inline (Unqualify);

end Sem_Util;