path: root/gcc/ada/exp_disp.ads

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--                         GNAT COMPILER COMPONENTS                         --
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------------------------------------------------------------------------------

--  This package contains routines involved in tagged types and dynamic
--  dispatching expansion.

with Types; use Types;
with Uintp; use Uintp;

package Exp_Disp is

   -------------------------------------
   -- Predefined primitive operations --
   -------------------------------------

   --  The predefined primitive operations (PPOs) are subprograms generated
   --  by GNAT for a particular tagged type. Their role is to provide support
   --  for different Ada language features such as the attribute 'Size or
   --  handling of dispatching triggers in select statements. PPOs are created
   --  when a tagged type is expanded or frozen. These subprograms are later
   --  collected and inserted into the dispatch table of a tagged type at
   --  fixed positions. Some of the PPOs that manipulate data in tagged objects
   --  require the generation of thunks.

   --  List of predefined primitive operations

   --    Leading underscores designate reserved names. Bracketed numerical
   --    values represent dispatch table slot numbers.

   --      _Size (1) - implementation of the attribute 'Size for any tagged
   --      type. Constructs of the form Prefix'Size are converted into
   --      Prefix._Size.

   --      TSS_Stream_Read (2) - implementation of the stream attribute Read
   --      for any tagged type.

   --      TSS_Stream_Write (3) - implementation of the stream attribute Write
   --      for any tagged type.

   --      TSS_Stream_Input (4) - implementation of the stream attribute Input
   --      for any tagged type.

   --      TSS_Stream_Output (5) - implementation of the stream attribute
   --      Output for any tagged type.

   --      Op_Eq (6) - implementation of the equality operator for any non-
   --      limited tagged type.

   --      _Assign (7) - implementation of the assignment operator for any
   --      non-limited tagged type.

   --      TSS_Deep_Adjust (8) - implementation of the finalization operation
   --      Adjust for any non-limited tagged type.

   --      TSS_Deep_Finalize (9) - implementation of the finalization
   --      operation Finalize for any non-limited tagged type.

   --      _Disp_Asynchronous_Select (10) - used in the expansion of ATC with
   --      dispatching triggers. Null implementation for limited interfaces,
   --      full body generation for types that implement limited interfaces,
   --      not generated for the rest of the cases. See Expand_N_Asynchronous_
   --      Select in Exp_Ch9 for more information.

   --      _Disp_Conditional_Select (11) - used in the expansion of conditional
   --      selects with dispatching triggers. Null implementation for limited
   --      interfaces, full body generation for types that implement limited
   --      interfaces, not generated for the rest of the cases. See Expand_N_
   --      Conditional_Entry_Call in Exp_Ch9 for more information.

   --      _Disp_Get_Prim_Op_Kind (12) - helper routine used in the expansion
   --      of ATC with dispatching triggers. Null implementation for limited
   --      interfaces, full body generation for types that implement limited
   --      interfaces, not generated for the rest of the cases.

   --      _Disp_Get_Task_Id (13) - helper routine used in the expansion of
   --      Abort, attributes 'Callable and 'Terminated for task interface
   --      class-wide types. Full body generation for task types, null
   --      implementation for limited interfaces, not generated for the rest
   --      of the cases. See Expand_N_Attribute_Reference in Exp_Attr and
   --      Expand_N_Abort_Statement in Exp_Ch9 for more information.

   --      _Disp_Requeue (14) - used in the expansion of dispatching requeue
   --      statements. Null implementation is provided for protected, task
   --      and synchronized interfaces. Protected and task types implementing
   --      concurrent interfaces receive full bodies. See Expand_N_Requeue_
   --      Statement in Exp_Ch9 for more information.

   --      _Disp_Timed_Select (15) - used in the expansion of timed selects
   --      with dispatching triggers. Null implementation for limited
   --      interfaces, full body generation for types that implement limited
   --      interfaces, not generated for the rest of the cases. See Expand_N_
   --      Timed_Entry_Call for more information.

   --  Life cycle of predefined primitive operations

   --      The specifications and bodies of the PPOs are created by
   --      Make_Predefined_Primitive_Specs and Predefined_Primitive_Bodies
   --      in Exp_Ch3. The generated specifications are immediately analyzed,
   --      while the bodies are left as freeze actions to the tagged type for
   --      which they are created.

   --      PPOs are collected and added to the Primitive_Operations list of
   --      a type by the regular analysis mechanism.

   --      PPOs are frozen by Exp_Ch3.Predefined_Primitive_Freeze

   --      Thunks for PPOs are created by Make_DT

   --      Dispatch table positions of PPOs are set by Set_All_DT_Position

   --      Calls to PPOs proceed as regular dispatching calls. If the PPO
   --      has a thunk, a call proceeds as a regular dispatching call with
   --      a thunk.

   --  Guidelines for addition of new predefined primitive operations

   --      Update the value of constant Max_Predef_Prims in a-tags.ads to
   --      indicate the new number of PPOs.

   --      Introduce a new predefined name for the new PPO in Snames.ads and
   --      Snames.adb.

   --      Categorize the new PPO name as predefined by adding an entry in
   --      Is_Predefined_Dispatching_Operation in Exp_Disp.

   --      Generate the specification of the new PPO in Make_Predefined_
   --      Primitive_Spec in Exp_Ch3.adb. The Is_Internal flag of the defining
   --      identifier of the specification must be set to True.

   --      Generate the body of the new PPO in Predefined_Primitive_Bodies in
   --      Exp_Ch3.adb. The Is_Internal flag of the defining identifier of the
   --      specification must be set to True.

   --      If the new PPO requires a thunk, add an entry in Freeze_Subprogram
   --      in Exp_Ch6.adb.

   --      When generating calls to a PPO, use Find_Prim_Op from Exp_Util.ads
   --      to retrieve the entity of the operation directly.

   --  Number of predefined primitive operations added by the Expander
   --  for a tagged type. If more predefined primitive operations are
   --  added, the following items must be changed:

   --    Ada.Tags.Max_Predef_Prims         - indirect use
   --    Exp_Disp.Default_Prim_Op_Position - indirect use
   --    Exp_Disp.Set_All_DT_Position      - direct   use

   procedure Apply_Tag_Checks (Call_Node : Node_Id);
   --  Generate checks required on dispatching calls

   function Building_Static_DT (Typ : Entity_Id) return Boolean;
   pragma Inline (Building_Static_DT);
   --  Returns true when building statically allocated dispatch tables

   procedure Build_Static_Dispatch_Tables (N : Node_Id);
   --  N is a library level package declaration or package body. Build the
   --  static dispatch table of the tagged types defined at library level. In
   --  case of package declarations with private part the generated nodes are
   --  added at the end of the list of private declarations. Otherwise they are
   --  added to the end of the list of public declarations. In case of package
   --  bodies they are added to the end of the list of declarations of the
   --  package body.

   function Convert_Tag_To_Interface
     (Typ : Entity_Id; Expr : Node_Id) return Node_Id;
   pragma Inline (Convert_Tag_To_Interface);
   --  This function is used in class-wide interface conversions; the expanded
   --  code generated to convert a tagged object to a class-wide interface type
   --  involves referencing the tag component containing the secondary dispatch
   --  table associated with the interface. Given the expression Expr that
   --  references a tag component, we cannot generate an unchecked conversion
   --  to leave the expression decorated with the class-wide interface type Typ
   --  because an unchecked conversion cannot be seen as a no-op. An unchecked
   --  conversion is conceptually a function call and therefore the RM allows
   --  the backend to obtain a copy of the value of the actual object and store
   --  it in some other place (like a register); in such case the interface
   --  conversion is not equivalent to a displacement of the pointer to the
   --  interface and any further displacement fails. Although the functionality
   --  of this function is simple and could be done directly, the purpose of
   --  this routine is to leave well documented in the sources these
   --  occurrences.

   --  If Expr is an N_Selected_Component that references a tag generate:
   --     type ityp is non null access Typ;
   --     ityp!(Expr'Address).all

   --  if Expr is an N_Function_Call to Ada.Tags.Displace then generate:
   --     type ityp is non null access Typ;
   --     ityp!(Expr).all

   function CPP_Num_Prims (Typ : Entity_Id) return Nat;
   --  Return the number of primitives of the C++ part of the dispatch table.
   --  For types that are not derivations of CPP types return 0.

   procedure Expand_Dispatching_Call (Call_Node : Node_Id);
   --  Expand the call to the operation through the dispatch table and perform
   --  the required tag checks when appropriate. For CPP types tag checks are
   --  not relevant.

   procedure Expand_Interface_Actuals (Call_Node : Node_Id);
   --  Ada 2005 (AI-251): Displace all the actuals corresponding to class-wide
   --  interfaces to reference the interface tag of the actual object

   procedure Expand_Interface_Conversion (N : Node_Id);
   --  Ada 2005 (AI-251): N is a type-conversion node. Displace the pointer
   --  to the object to give access to the interface tag associated with the
   --  dispatch table of the target type.

   procedure Expand_Interface_Thunk
     (Prim       : Node_Id;
      Thunk_Id   : out Entity_Id;
      Thunk_Code : out Node_Id);
   --  Ada 2005 (AI-251): When a tagged type implements abstract interfaces we
   --  generate additional subprograms (thunks) associated with each primitive
   --  Prim to have a layout compatible with the C++ ABI. The thunk displaces
   --  the pointers to the actuals that depend on the controlling type before
   --  transferring control to the target subprogram. If there is no need to
   --  generate the thunk then Thunk_Id and Thunk_Code are set to Empty.
   --  Otherwise they are set to the defining identifier and the subprogram
   --  body of the generated thunk.

   function Has_CPP_Constructors (Typ : Entity_Id) return Boolean;
   --  Returns true if the type has CPP constructors

   function Is_Expanded_Dispatching_Call (N : Node_Id) return Boolean;
   --  Returns true if N is the expanded code of a dispatching call

   function Is_Predefined_Dispatching_Operation (E : Entity_Id) return Boolean;
   --  Ada 2005 (AI-251): Determines if E is a predefined primitive operation

   function Is_Predefined_Internal_Operation (E : Entity_Id) return Boolean;
   --  Similar to the previous one, but excludes stream operations, because
   --  these may be overridden, and need extra formals, like user-defined
   --  operations.

   function Is_Predefined_Interface_Primitive (E : Entity_Id) return Boolean;
   --  Ada 2005 (AI-345): Returns True if E is one of the predefined primitives
   --  required to implement interfaces.

   function Make_DT (Typ : Entity_Id; N : Node_Id := Empty) return List_Id;
   --  Expand the declarations for the Dispatch Table. The node N is the
   --  declaration that forces the generation of the table. It is used to place
   --  error messages when the declaration leads to the freezing of a given
   --  primitive operation that has an incomplete non- tagged formal.

   function Make_Disp_Asynchronous_Select_Body
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the body of the primitive operation of type
   --  Typ used for dispatching in asynchronous selects. Generate a null body
   --  if Typ is an interface type.

   function Make_Disp_Asynchronous_Select_Spec
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the specification of the primitive operation
   --  of type Typ used for dispatching in asynchronous selects.

   function Make_Disp_Conditional_Select_Body
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the body of the primitive operation of type
   --  Typ used for dispatching in conditional selects. Generate a null body
   --  if Typ is an interface type.

   function Make_Disp_Conditional_Select_Spec
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the specification of the primitive operation
   --  of type Typ used for dispatching in conditional selects.

   function Make_Disp_Get_Prim_Op_Kind_Body
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the body of the primitive operation of type
   --  Typ used for retrieving the callable entity kind during dispatching in
   --  asynchronous selects. Generate a null body if Typ is an interface type.

   function Make_Disp_Get_Prim_Op_Kind_Spec
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the specification of the primitive operation
   --  of the type Typ use for retrieving the callable entity kind during
   --  dispatching in asynchronous selects.

   function Make_Disp_Get_Task_Id_Body
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate body of the primitive operation of type Typ
   --  used for retrieving the _task_id field of a task interface class- wide
   --  type. Generate a null body if Typ is an interface or a non-task type.

   function Make_Disp_Get_Task_Id_Spec
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the specification of the primitive operation
   --  of type Typ used for retrieving the _task_id field of a task interface
   --  class-wide type.

   function Make_Disp_Requeue_Body
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI05-0030): Generate the body of the primitive operation of
   --  type Typ used for dispatching on requeue statements. Generate a body
   --  containing a single null-statement if Typ is an interface type.

   function Make_Disp_Requeue_Spec
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI05-0030): Generate the specification of the primitive
   --  operation of type Typ used for dispatching requeue statements.

   function Make_Disp_Timed_Select_Body
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the body of the primitive operation of type
   --  Typ used for dispatching in timed selects. Generate a body containing
   --  a single null-statement if Typ is an interface type.

   function Make_Disp_Timed_Select_Spec
     (Typ : Entity_Id) return Node_Id;
   --  Ada 2005 (AI-345): Generate the specification of the primitive operation
   --  of type Typ used for dispatching in timed selects.

   function Make_Select_Specific_Data_Table
     (Typ : Entity_Id) return List_Id;
   --  Ada 2005 (AI-345): Create and populate the auxiliary table in the TSD
   --  of Typ used for dispatching in asynchronous, conditional and timed
   --  selects. Generate code to set the primitive operation kinds and entry
   --  indexes of primitive operations and primitive wrappers.

   function Make_Tags (Typ : Entity_Id) return List_Id;
   --  Generate the entities associated with the primary and secondary tags of
   --  Typ and fill the contents of Access_Disp_Table. In case of library level
   --  tagged types this routine imports the forward declaration of the tag
   --  entity, that will be declared and exported by Make_DT.

   function Register_Primitive
     (Loc     : Source_Ptr;
      Prim    : Entity_Id) return List_Id;
   --  Build code to register Prim in the primary or secondary dispatch table.
   --  If Prim is associated with a secondary dispatch table then generate also
   --  its thunk and register it in the associated secondary dispatch table.
   --  In general the dispatch tables are always generated by Make_DT and
   --  Make_Secondary_DT; this routine is only used in two corner cases:
   --
   --    1) To construct the dispatch table of a tagged type whose parent
   --       is a CPP_Class (see Build_Init_Procedure).
   --    2) To handle late overriding of dispatching operations (see
   --       Check_Dispatching_Operation and Make_DT).
   --
   --  The caller is responsible for inserting the generated code in the
   --  proper place.

   procedure Set_All_DT_Position (Typ : Entity_Id);
   --  Set the DT_Position field for each primitive operation. In the CPP
   --  Class case check that no pragma CPP_Virtual is missing and that the
   --  DT_Position are coherent

   procedure Set_CPP_Constructors (Typ : Entity_Id);
   --  Typ is a CPP_Class type. Create the Init procedures of that type
   --  required to handle its default and non-default constructors. The
   --  functions to which pragma CPP_Constructor is applied in the sources
   --  are functions returning this type, and having an implicit access to the
   --  target object in its first argument; such implicit argument is explicit
   --  in the IP procedures built here.

   procedure Set_DT_Position_Value (Prim  : Entity_Id; Value : Uint);
   --  Set the position of a dispatching primitive its dispatch table. For
   --  subprogram wrappers propagate the value to the wrapped subprogram.

   procedure Set_DTC_Entity_Value (Tagged_Type : Entity_Id; Prim : Entity_Id);
   --  Set the definite value of the DTC_Entity value associated with a given
   --  primitive of a tagged type. For subprogram wrappers, propagate the value
   --  to the wrapped subprogram.

   procedure Write_DT (Typ : Entity_Id);
   pragma Export (Ada, Write_DT);
   --  Debugging procedure (to be called within gdb)

end Exp_Disp;