path: root/gcc/ada/exp_ch8.adb

------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                              E X P _ C H 8                               --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 1992-2015, 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.      --
--                                                                          --
------------------------------------------------------------------------------

with Atree;    use Atree;
with Einfo;    use Einfo;
with Exp_Ch4;  use Exp_Ch4;
with Exp_Ch6;  use Exp_Ch6;
with Exp_Dbug; use Exp_Dbug;
with Exp_Util; use Exp_Util;
with Freeze;   use Freeze;
with Ghost;    use Ghost;
with Namet;    use Namet;
with Nmake;    use Nmake;
with Nlists;   use Nlists;
with Opt;      use Opt;
with Sem;      use Sem;
with Sem_Ch8;  use Sem_Ch8;
with Sem_Util; use Sem_Util;
with Sinfo;    use Sinfo;
with Snames;   use Snames;
with Stand;    use Stand;
with Tbuild;   use Tbuild;

package body Exp_Ch8 is

   ---------------------------------------------
   -- Expand_N_Exception_Renaming_Declaration --
   ---------------------------------------------

   procedure Expand_N_Exception_Renaming_Declaration (N : Node_Id) is
      Save_Ghost_Mode : constant Ghost_Mode_Type := Ghost_Mode;

      Decl : Node_Id;

   begin
      --  The exception renaming declaration is Ghost when it is subject to
      --  pragma Ghost or renames a Ghost entity. To accomodate both cases, set
      --  the mode now to ensure that any nodes generated during expansion are
      --  properly marked as Ghost.

      Set_Ghost_Mode (N);

      Decl := Debug_Renaming_Declaration (N);

      if Present (Decl) then
         Insert_Action (N, Decl);
      end if;

      Ghost_Mode := Save_Ghost_Mode;
   end Expand_N_Exception_Renaming_Declaration;

   ------------------------------------------
   -- Expand_N_Object_Renaming_Declaration --
   ------------------------------------------

   --  Most object renaming cases can be done by just capturing the address
   --  of the renamed object. The cases in which this is not true are when
   --  this address is not computable, since it involves extraction of a
   --  packed array element, or of a record component to which a component
   --  clause applies (that can specify an arbitrary bit boundary), or where
   --  the enclosing record itself has a non-standard representation.

   --  In these two cases, we pre-evaluate the renaming expression, by
   --  extracting and freezing the values of any subscripts, and then we
   --  set the flag Is_Renaming_Of_Object which means that any reference
   --  to the object will be handled by macro substitution in the front
   --  end, and the back end will know to ignore the renaming declaration.

   --  An additional odd case that requires processing by expansion is
   --  the renaming of a discriminant of a mutable record type. The object
   --  is a constant because it renames something that cannot be assigned to,
   --  but in fact the underlying value can change and must be reevaluated
   --  at each reference. Gigi does have a notion of a "constant view" of
   --  an object, and therefore the front-end must perform the expansion.
   --  For simplicity, and to bypass some obscure code-generation problem,
   --  we use macro substitution for all renamed discriminants, whether the
   --  enclosing type is constrained or not.

   --  The other special processing required is for the case of renaming
   --  of an object of a class wide type, where it is necessary to build
   --  the appropriate subtype for the renamed object.
   --  More comments needed for this para ???

   procedure Expand_N_Object_Renaming_Declaration (N : Node_Id) is
      Nam  : constant Node_Id := Name (N);
      Decl : Node_Id;
      T    : Entity_Id;

      function Evaluation_Required (Nam : Node_Id) return Boolean;
      --  Determines whether it is necessary to do static name evaluation for
      --  renaming of Nam. It is considered necessary if evaluating the name
      --  involves indexing a packed array, or extracting a component of a
      --  record to which a component clause applies. Note that we are only
      --  interested in these operations if they occur as part of the name
      --  itself, subscripts are just values that are computed as part of the
      --  evaluation, so their form is unimportant.

      -------------------------
      -- Evaluation_Required --
      -------------------------

      function Evaluation_Required (Nam : Node_Id) return Boolean is
      begin
         if Nkind_In (Nam, N_Indexed_Component, N_Slice) then
            if Is_Packed (Etype (Prefix (Nam))) then
               return True;
            else
               return Evaluation_Required (Prefix (Nam));
            end if;

         elsif Nkind (Nam) = N_Selected_Component then
            declare
               Rec_Type : constant Entity_Id := Etype (Prefix (Nam));

            begin
               if Present (Component_Clause (Entity (Selector_Name (Nam))))
                 or else Has_Non_Standard_Rep (Rec_Type)
               then
                  return True;

               elsif Ekind (Entity (Selector_Name (Nam))) = E_Discriminant
                 and then Is_Record_Type (Rec_Type)
                 and then not Is_Concurrent_Record_Type (Rec_Type)
               then
                  return True;

               else
                  return Evaluation_Required (Prefix (Nam));
               end if;
            end;

         else
            return False;
         end if;
      end Evaluation_Required;

      --  Local variables

      Save_Ghost_Mode : constant Ghost_Mode_Type := Ghost_Mode;

   --  Start of processing for Expand_N_Object_Renaming_Declaration

   begin
      --  The object renaming declaration is Ghost when it is subject to pragma
      --  Ghost or renames a Ghost entity. To accomodate both cases, set the
      --  mode now to ensure that any nodes generated during expansion are
      --  properly marked as Ghost.

      Set_Ghost_Mode (N);

      --  Perform name evaluation if required

      if Evaluation_Required (Nam) then
         Evaluate_Name (Nam);
         Set_Is_Renaming_Of_Object (Defining_Identifier (N));
      end if;

      --  Deal with construction of subtype in class-wide case

      T := Etype (Defining_Identifier (N));

      if Is_Class_Wide_Type (T) then
         Expand_Subtype_From_Expr (N, T, Subtype_Mark (N), Name (N));
         Find_Type (Subtype_Mark (N));
         Set_Etype (Defining_Identifier (N), Entity (Subtype_Mark (N)));

         --  Freeze the class-wide subtype here to ensure that the subtype
         --  and equivalent type are frozen before the renaming.

         Freeze_Before (N, Entity (Subtype_Mark (N)));
      end if;

      --  Ada 2005 (AI-318-02): If the renamed object is a call to a build-in-
      --  place function, then a temporary return object needs to be created
      --  and access to it must be passed to the function. Currently we limit
      --  such functions to those with inherently limited result subtypes, but
      --  eventually we plan to expand the functions that are treated as
      --  build-in-place to include other composite result types.

      if Ada_Version >= Ada_2005
        and then Is_Build_In_Place_Function_Call (Nam)
      then
         Make_Build_In_Place_Call_In_Anonymous_Context (Nam);
      end if;

      --  Create renaming entry for debug information

      Decl := Debug_Renaming_Declaration (N);

      if Present (Decl) then
         Insert_Action (N, Decl);
      end if;

      Ghost_Mode := Save_Ghost_Mode;
   end Expand_N_Object_Renaming_Declaration;

   -------------------------------------------
   -- Expand_N_Package_Renaming_Declaration --
   -------------------------------------------

   procedure Expand_N_Package_Renaming_Declaration (N : Node_Id) is
      Save_Ghost_Mode : constant Ghost_Mode_Type := Ghost_Mode;

      Decl : Node_Id;

   begin
      --  The package renaming declaration is Ghost when it is subject to
      --  pragma Ghost or renames a Ghost entity. To accomodate both cases,
      --  set the mode now to ensure that any nodes generated during expansion
      --  are properly marked as Ghost.

      Set_Ghost_Mode (N);

      Decl := Debug_Renaming_Declaration (N);

      if Present (Decl) then

         --  If we are in a compilation unit, then this is an outer
         --  level declaration, and must have a scope of Standard

         if Nkind (Parent (N)) = N_Compilation_Unit then
            declare
               Aux : constant Node_Id := Aux_Decls_Node (Parent (N));

            begin
               Push_Scope (Standard_Standard);

               if No (Actions (Aux)) then
                  Set_Actions (Aux, New_List (Decl));
               else
                  Append (Decl, Actions (Aux));
               end if;

               Analyze (Decl);

               --  Enter the debug variable in the qualification list, which
               --  must be done at this point because auxiliary declarations
               --  occur at the library level and aren't associated with a
               --  normal scope.

               Qualify_Entity_Names (Decl);

               Pop_Scope;
            end;

         --  Otherwise, just insert after the package declaration

         else
            Insert_Action (N, Decl);
         end if;
      end if;

      Ghost_Mode := Save_Ghost_Mode;
   end Expand_N_Package_Renaming_Declaration;

   ----------------------------------------------
   -- Expand_N_Subprogram_Renaming_Declaration --
   ----------------------------------------------

   procedure Expand_N_Subprogram_Renaming_Declaration (N : Node_Id) is
      Loc : constant Source_Ptr := Sloc (N);
      Id  : constant Entity_Id  := Defining_Entity (N);

      function Build_Body_For_Renaming return Node_Id;
      --  Build and return the body for the renaming declaration of an equality
      --  or inequality operator.

      -----------------------------
      -- Build_Body_For_Renaming --
      -----------------------------

      function Build_Body_For_Renaming return Node_Id is
         Body_Id : Entity_Id;
         Decl    : Node_Id;

      begin
         Set_Alias (Id, Empty);
         Set_Has_Completion (Id, False);
         Rewrite (N,
           Make_Subprogram_Declaration (Sloc (N),
             Specification => Specification (N)));
         Set_Has_Delayed_Freeze (Id);

         Body_Id := Make_Defining_Identifier (Sloc (N), Chars (Id));
         Set_Debug_Info_Needed (Body_Id);

         Decl :=
           Make_Subprogram_Body (Loc,
             Specification              =>
               Make_Function_Specification (Loc,
                 Defining_Unit_Name       => Body_Id,
                 Parameter_Specifications => Copy_Parameter_List (Id),
                 Result_Definition        =>
                   New_Occurrence_Of (Standard_Boolean, Loc)),
             Declarations               => Empty_List,
             Handled_Statement_Sequence => Empty);

         return Decl;
      end Build_Body_For_Renaming;

      --  Local variables

      Nam             : constant Node_Id         := Name (N);
      Save_Ghost_Mode : constant Ghost_Mode_Type := Ghost_Mode;

   --  Start of processing for Expand_N_Subprogram_Renaming_Declaration

   begin
      --  The subprogram renaming declaration is Ghost when it is subject to
      --  pragma Ghost or renames a Ghost entity. To accomodate both cases, set
      --  the mode now to ensure that any nodes created during expansion are
      --  properly flagged as ignored Ghost.

      Set_Ghost_Mode (N);

      --  When the prefix of the name is a function call, we must force the
      --  call to be made by removing side effects from the call, since we
      --  must only call the function once.

      if Nkind (Nam) = N_Selected_Component
        and then Nkind (Prefix (Nam)) = N_Function_Call
      then
         Remove_Side_Effects (Prefix (Nam));

      --  For an explicit dereference, the prefix must be captured to prevent
      --  reevaluation on calls through the renaming, which could result in
      --  calling the wrong subprogram if the access value were to be changed.

      elsif Nkind (Nam) = N_Explicit_Dereference then
         Force_Evaluation (Prefix (Nam));
      end if;

      --  Handle cases where we build a body for a renamed equality

      if Is_Entity_Name (Nam)
        and then Chars (Entity (Nam)) = Name_Op_Eq
        and then Scope (Entity (Nam)) = Standard_Standard
      then
         declare
            Left  : constant Entity_Id := First_Formal (Id);
            Right : constant Entity_Id := Next_Formal (Left);
            Typ   : constant Entity_Id := Etype (Left);
            Decl  : Node_Id;

         begin
            --  Check whether this is a renaming of a predefined equality on an
            --  untagged record type (AI05-0123).

            if Ada_Version >= Ada_2012
              and then Is_Record_Type (Typ)
              and then not Is_Tagged_Type (Typ)
              and then not Is_Frozen (Typ)
            then
               --  Build body for renamed equality, to capture its current
               --  meaning. It may be redefined later, but the renaming is
               --  elaborated where it occurs. This is technically known as
               --  Squirreling semantics. Renaming is rewritten as a subprogram
               --  declaration, and the generated  body is inserted into the
               --  freeze actions for the subprogram.

               Decl := Build_Body_For_Renaming;

               Set_Handled_Statement_Sequence (Decl,
                 Make_Handled_Sequence_Of_Statements (Loc,
                   Statements => New_List (
                     Make_Simple_Return_Statement (Loc,
                       Expression =>
                         Expand_Record_Equality
                           (Id,
                            Typ    => Typ,
                            Lhs    => Make_Identifier (Loc, Chars (Left)),
                            Rhs    => Make_Identifier (Loc, Chars (Right)),
                            Bodies => Declarations (Decl))))));

               Append_Freeze_Action (Id, Decl);
            end if;
         end;
      end if;

      Ghost_Mode := Save_Ghost_Mode;
   end Expand_N_Subprogram_Renaming_Declaration;

end Exp_Ch8;