gcc/ada/exp_ch8.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                              E X P _ C H 8                               --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2012, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT; see file COPYING3.  If not, go to --
  19 -- http://www.gnu.org/licenses for a complete copy of the license.          --
  20 --                                                                          --
  21 -- GNAT was originally developed  by the GNAT team at  New York University. --
  22 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  23 --                                                                          --
  24 ------------------------------------------------------------------------------
  25
  26 with Atree;    use Atree;
  27 with Einfo;    use Einfo;
  28 with Exp_Ch4;  use Exp_Ch4;
  29 with Exp_Ch6;  use Exp_Ch6;
  30 with Exp_Dbug; use Exp_Dbug;
  31 with Exp_Util; use Exp_Util;
  32 with Freeze;   use Freeze;
  33 with Namet;    use Namet;
  34 with Nmake;    use Nmake;
  35 with Nlists;   use Nlists;
  36 with Opt;      use Opt;
  37 with Sem;      use Sem;
  38 with Sem_Ch8;  use Sem_Ch8;
  39 with Sem_Util; use Sem_Util;
  40 with Sinfo;    use Sinfo;
  41 with Snames;   use Snames;
  42 with Stand;    use Stand;
  43 with Tbuild;   use Tbuild;
  44
  45 package body Exp_Ch8 is
  46
  47    ---------------------------------------------
  48    -- Expand_N_Exception_Renaming_Declaration --
  49    ---------------------------------------------
  50
  51    procedure Expand_N_Exception_Renaming_Declaration (N : Node_Id) is
  52       Decl : constant Node_Id := Debug_Renaming_Declaration (N);
  53    begin
  54       if Present (Decl) then
  55          Insert_Action (N, Decl);
  56       end if;
  57    end Expand_N_Exception_Renaming_Declaration;
  58
  59    ------------------------------------------
  60    -- Expand_N_Object_Renaming_Declaration --
  61    ------------------------------------------
  62
  63    --  Most object renaming cases can be done by just capturing the address
  64    --  of the renamed object. The cases in which this is not true are when
  65    --  this address is not computable, since it involves extraction of a
  66    --  packed array element, or of a record component to which a component
  67    --  clause applies (that can specify an arbitrary bit boundary), or where
  68    --  the enclosing record itself has a non-standard representation.
  69
  70    --  In these two cases, we pre-evaluate the renaming expression, by
  71    --  extracting and freezing the values of any subscripts, and then we
  72    --  set the flag Is_Renaming_Of_Object which means that any reference
  73    --  to the object will be handled by macro substitution in the front
  74    --  end, and the back end will know to ignore the renaming declaration.
  75
  76    --  An additional odd case that requires processing by expansion is
  77    --  the renaming of a discriminant of a mutable record type. The object
  78    --  is a constant because it renames something that cannot be assigned to,
  79    --  but in fact the underlying value can change and must be reevaluated
  80    --  at each reference. Gigi does have a notion of a "constant view" of
  81    --  an object, and therefore the front-end must perform the expansion.
  82    --  For simplicity, and to bypass some obscure code-generation problem,
  83    --  we use macro substitution for all renamed discriminants, whether the
  84    --  enclosing type is constrained or not.
  85
  86    --  The other special processing required is for the case of renaming
  87    --  of an object of a class wide type, where it is necessary to build
  88    --  the appropriate subtype for the renamed object.
  89    --  More comments needed for this para ???
  90
  91    procedure Expand_N_Object_Renaming_Declaration (N : Node_Id) is
  92       Nam  : constant Node_Id := Name (N);
  93       Decl : Node_Id;
  94       T    : Entity_Id;
  95
  96       function Evaluation_Required (Nam : Node_Id) return Boolean;
  97       --  Determines whether it is necessary to do static name evaluation for
  98       --  renaming of Nam. It is considered necessary if evaluating the name
  99       --  involves indexing a packed array, or extracting a component of a
 100       --  record to which a component clause applies. Note that we are only
 101       --  interested in these operations if they occur as part of the name
 102       --  itself, subscripts are just values that are computed as part of the
 103       --  evaluation, so their form is unimportant.
 104
 105       -------------------------
 106       -- Evaluation_Required --
 107       -------------------------
 108
 109       function Evaluation_Required (Nam : Node_Id) return Boolean is
 110       begin
 111          if Nkind_In (Nam, N_Indexed_Component, N_Slice) then
 112             if Is_Packed (Etype (Prefix (Nam))) then
 113                return True;
 114             else
 115                return Evaluation_Required (Prefix (Nam));
 116             end if;
 117
 118          elsif Nkind (Nam) = N_Selected_Component then
 119             declare
 120                Rec_Type : constant Entity_Id := Etype (Prefix (Nam));
 121
 122             begin
 123                if Present (Component_Clause (Entity (Selector_Name (Nam))))
 124                  or else Has_Non_Standard_Rep (Rec_Type)
 125                then
 126                   return True;
 127
 128                elsif Ekind (Entity (Selector_Name (Nam))) = E_Discriminant
 129                  and then Is_Record_Type (Rec_Type)
 130                  and then not Is_Concurrent_Record_Type (Rec_Type)
 131                then
 132                   return True;
 133
 134                else
 135                   return Evaluation_Required (Prefix (Nam));
 136                end if;
 137             end;
 138
 139          else
 140             return False;
 141          end if;
 142       end Evaluation_Required;
 143
 144    --  Start of processing for Expand_N_Object_Renaming_Declaration
 145
 146    begin
 147       --  Perform name evaluation if required
 148
 149       if Evaluation_Required (Nam) then
 150          Evaluate_Name (Nam);
 151          Set_Is_Renaming_Of_Object (Defining_Identifier (N));
 152       end if;
 153
 154       --  Deal with construction of subtype in class-wide case
 155
 156       T := Etype (Defining_Identifier (N));
 157
 158       if Is_Class_Wide_Type (T) then
 159          Expand_Subtype_From_Expr (N, T, Subtype_Mark (N), Name (N));
 160          Find_Type (Subtype_Mark (N));
 161          Set_Etype (Defining_Identifier (N), Entity (Subtype_Mark (N)));
 162
 163          --  Freeze the class-wide subtype here to ensure that the subtype
 164          --  and equivalent type are frozen before the renaming.
 165
 166          Freeze_Before (N, Entity (Subtype_Mark (N)));
 167       end if;
 168
 169       --  Ada 2005 (AI-318-02): If the renamed object is a call to a build-in-
 170       --  place function, then a temporary return object needs to be created
 171       --  and access to it must be passed to the function. Currently we limit
 172       --  such functions to those with inherently limited result subtypes, but
 173       --  eventually we plan to expand the functions that are treated as
 174       --  build-in-place to include other composite result types.
 175
 176       if Ada_Version >= Ada_2005
 177         and then Is_Build_In_Place_Function_Call (Nam)
 178       then
 179          Make_Build_In_Place_Call_In_Anonymous_Context (Nam);
 180       end if;
 181
 182       --  Create renaming entry for debug information
 183
 184       Decl := Debug_Renaming_Declaration (N);
 185
 186       if Present (Decl) then
 187          Insert_Action (N, Decl);
 188       end if;
 189    end Expand_N_Object_Renaming_Declaration;
 190
 191    -------------------------------------------
 192    -- Expand_N_Package_Renaming_Declaration --
 193    -------------------------------------------
 194
 195    procedure Expand_N_Package_Renaming_Declaration (N : Node_Id) is
 196       Decl : constant Node_Id := Debug_Renaming_Declaration (N);
 197
 198    begin
 199       if Present (Decl) then
 200
 201          --  If we are in a compilation unit, then this is an outer
 202          --  level declaration, and must have a scope of Standard
 203
 204          if Nkind (Parent (N)) = N_Compilation_Unit then
 205             declare
 206                Aux : constant Node_Id := Aux_Decls_Node (Parent (N));
 207
 208             begin
 209                Push_Scope (Standard_Standard);
 210
 211                if No (Actions (Aux)) then
 212                   Set_Actions (Aux, New_List (Decl));
 213                else
 214                   Append (Decl, Actions (Aux));
 215                end if;
 216
 217                Analyze (Decl);
 218
 219                --  Enter the debug variable in the qualification list, which
 220                --  must be done at this point because auxiliary declarations
 221                --  occur at the library level and aren't associated with a
 222                --  normal scope.
 223
 224                Qualify_Entity_Names (Decl);
 225
 226                Pop_Scope;
 227             end;
 228
 229          --  Otherwise, just insert after the package declaration
 230
 231          else
 232             Insert_Action (N, Decl);
 233          end if;
 234       end if;
 235    end Expand_N_Package_Renaming_Declaration;
 236
 237    ----------------------------------------------
 238    -- Expand_N_Subprogram_Renaming_Declaration --
 239    ----------------------------------------------
 240
 241    procedure Expand_N_Subprogram_Renaming_Declaration (N : Node_Id) is
 242       Loc : constant Source_Ptr := Sloc (N);
 243       Id  : constant Entity_Id  := Defining_Entity (N);
 244
 245       function Build_Body_For_Renaming return Node_Id;
 246       --  Build and return the body for the renaming declaration of an equality
 247       --  or inequality operator.
 248
 249       -----------------------------
 250       -- Build_Body_For_Renaming --
 251       -----------------------------
 252
 253       function Build_Body_For_Renaming return Node_Id is
 254          Body_Id : Entity_Id;
 255          Decl    : Node_Id;
 256
 257       begin
 258          Set_Alias (Id, Empty);
 259          Set_Has_Completion (Id, False);
 260          Rewrite (N,
 261            Make_Subprogram_Declaration (Sloc (N),
 262              Specification => Specification (N)));
 263          Set_Has_Delayed_Freeze (Id);
 264
 265          Body_Id := Make_Defining_Identifier (Sloc (N), Chars (Id));
 266          Set_Debug_Info_Needed (Body_Id);
 267
 268          Decl :=
 269            Make_Subprogram_Body (Loc,
 270              Specification              =>
 271                Make_Function_Specification (Loc,
 272                  Defining_Unit_Name       => Body_Id,
 273                  Parameter_Specifications => Copy_Parameter_List (Id),
 274                  Result_Definition        =>
 275                    New_Occurrence_Of (Standard_Boolean, Loc)),
 276              Declarations               => Empty_List,
 277              Handled_Statement_Sequence => Empty);
 278
 279          return Decl;
 280       end Build_Body_For_Renaming;
 281
 282       --  Local variables
 283
 284       Nam : constant Node_Id := Name (N);
 285
 286    --  Start of processing for Expand_N_Subprogram_Renaming_Declaration
 287
 288    begin
 289       --  When the prefix of the name is a function call, we must force the
 290       --  call to be made by removing side effects from the call, since we
 291       --  must only call the function once.
 292
 293       if Nkind (Nam) = N_Selected_Component
 294         and then Nkind (Prefix (Nam)) = N_Function_Call
 295       then
 296          Remove_Side_Effects (Prefix (Nam));
 297
 298       --  For an explicit dereference, the prefix must be captured to prevent
 299       --  reevaluation on calls through the renaming, which could result in
 300       --  calling the wrong subprogram if the access value were to be changed.
 301
 302       elsif Nkind (Nam) = N_Explicit_Dereference then
 303          Force_Evaluation (Prefix (Nam));
 304       end if;
 305
 306       --  Handle cases where we build a body for a renamed equality
 307
 308       if Is_Entity_Name (Nam)
 309         and then Chars (Entity (Nam)) = Name_Op_Eq
 310         and then Scope (Entity (Nam)) = Standard_Standard
 311       then
 312          declare
 313             Left  : constant Entity_Id := First_Formal (Id);
 314             Right : constant Entity_Id := Next_Formal (Left);
 315             Typ   : constant Entity_Id := Etype (Left);
 316             Decl  : Node_Id;
 317
 318          begin
 319             --  Check whether this is a renaming of a predefined equality on an
 320             --  untagged record type (AI05-0123).
 321
 322             if Ada_Version >= Ada_2012
 323               and then Is_Record_Type (Typ)
 324               and then not Is_Tagged_Type (Typ)
 325               and then not Is_Frozen (Typ)
 326             then
 327                --  Build body for renamed equality, to capture its current
 328                --  meaning. It may be redefined later, but the renaming is
 329                --  elaborated where it occurs. This is technically known as
 330                --  Squirreling semantics. Renaming is rewritten as a subprogram
 331                --  declaration, and the body is inserted at the end of the
 332                --  current declaration list to prevent premature freezing.
 333
 334                Decl := Build_Body_For_Renaming;
 335
 336                Set_Handled_Statement_Sequence (Decl,
 337                  Make_Handled_Sequence_Of_Statements (Loc,
 338                    Statements => New_List (
 339                      Make_Simple_Return_Statement (Loc,
 340                        Expression =>
 341                          Expand_Record_Equality
 342                            (Id,
 343                             Typ    => Typ,
 344                             Lhs    => Make_Identifier (Loc, Chars (Left)),
 345                             Rhs    => Make_Identifier (Loc, Chars (Right)),
 346                             Bodies => Declarations (Decl))))));
 347
 348                Append (Decl, List_Containing (N));
 349             end if;
 350          end;
 351       end if;
 352    end Expand_N_Subprogram_Renaming_Declaration;
 353
 354 end Exp_Ch8;