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) 1992-2009, 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_Ch6;  use Exp_Ch6;
  29 with Exp_Dbug; use Exp_Dbug;
  30 with Exp_Util; use Exp_Util;
  31 with Freeze;   use Freeze;
  32 with Nlists;   use Nlists;
  33 with Opt;      use Opt;
  34 with Sem;      use Sem;
  35 with Sem_Ch8;  use Sem_Ch8;
  36 with Sinfo;    use Sinfo;
  37 with Stand;    use Stand;
  38
  39 package body Exp_Ch8 is
  40
  41    ---------------------------------------------
  42    -- Expand_N_Exception_Renaming_Declaration --
  43    ---------------------------------------------
  44
  45    procedure Expand_N_Exception_Renaming_Declaration (N : Node_Id) is
  46       Decl : constant Node_Id := Debug_Renaming_Declaration (N);
  47
  48    begin
  49       if Present (Decl) then
  50          Insert_Action (N, Decl);
  51       end if;
  52    end Expand_N_Exception_Renaming_Declaration;
  53
  54    ------------------------------------------
  55    -- Expand_N_Object_Renaming_Declaration --
  56    ------------------------------------------
  57
  58    --  Most object renaming cases can be done by just capturing the address
  59    --  of the renamed object. The cases in which this is not true are when
  60    --  this address is not computable, since it involves extraction of a
  61    --  packed array element, or of a record component to which a component
  62    --  clause applies (that can specify an arbitrary bit boundary), or where
  63    --  the enclosing record itself has a non-standard representation.
  64
  65    --  In these two cases, we pre-evaluate the renaming expression, by
  66    --  extracting and freezing the values of any subscripts, and then we
  67    --  set the flag Is_Renaming_Of_Object which means that any reference
  68    --  to the object will be handled by macro substitution in the front
  69    --  end, and the back end will know to ignore the renaming declaration.
  70
  71    --  An additional odd case that requires processing by expansion is
  72    --  the renaming of a discriminant of a mutable record type. The object
  73    --  is a constant because it renames something that cannot be assigned to,
  74    --  but in fact the underlying value can change and must be reevaluated
  75    --  at each reference. Gigi does have a notion of a "constant view" of
  76    --  an object, and therefore the front-end must perform the expansion.
  77    --  For simplicity, and to bypass some obscure code-generation problem,
  78    --  we use macro substitution for all renamed discriminants, whether the
  79    --  enclosing type is constrained or not.
  80
  81    --  The other special processing required is for the case of renaming
  82    --  of an object of a class wide type, where it is necessary to build
  83    --  the appropriate subtype for the renamed object.
  84    --  More comments needed for this para ???
  85
  86    procedure Expand_N_Object_Renaming_Declaration (N : Node_Id) is
  87       Nam  : constant Node_Id := Name (N);
  88       T    : Entity_Id;
  89       Decl : Node_Id;
  90
  91       procedure Evaluate_Name (Fname : Node_Id);
  92       --  A recursive procedure used to freeze a name in the sense described
  93       --  above, i.e. any variable references or function calls are removed.
  94       --  Of course the outer level variable reference must not be removed.
  95       --  For example in A(J,F(K)), A is left as is, but J and F(K) are
  96       --  evaluated and removed.
  97
  98       function Evaluation_Required (Nam : Node_Id) return Boolean;
  99       --  Determines whether it is necessary to do static name evaluation
 100       --  for renaming of Nam. It is considered necessary if evaluating the
 101       --  name involves indexing a packed array, or extracting a component
 102       --  of a record to which a component clause applies. Note that we are
 103       --  only interested in these operations if they occur as part of the
 104       --  name itself, subscripts are just values that are computed as part
 105       --  of the evaluation, so their form is unimportant.
 106
 107       -------------------
 108       -- Evaluate_Name --
 109       -------------------
 110
 111       procedure Evaluate_Name (Fname : Node_Id) is
 112          K : constant Node_Kind := Nkind (Fname);
 113          E : Node_Id;
 114
 115       begin
 116          --  For an explicit dereference, we simply force the evaluation
 117          --  of the name expression. The dereference provides a value that
 118          --  is the address for the renamed object, and it is precisely
 119          --  this value that we want to preserve.
 120
 121          if K = N_Explicit_Dereference then
 122             Force_Evaluation (Prefix (Fname));
 123
 124          --  For a selected component, we simply evaluate the prefix
 125
 126          elsif K = N_Selected_Component then
 127             Evaluate_Name (Prefix (Fname));
 128
 129          --  For an indexed component, or an attribute reference, we evaluate
 130          --  the prefix, which is itself a name, recursively, and then force
 131          --  the evaluation of all the subscripts (or attribute expressions).
 132
 133          elsif Nkind_In (K, N_Indexed_Component, N_Attribute_Reference) then
 134             Evaluate_Name (Prefix (Fname));
 135
 136             E := First (Expressions (Fname));
 137             while Present (E) loop
 138                Force_Evaluation (E);
 139
 140                if Original_Node (E) /= E then
 141                   Set_Do_Range_Check (E, Do_Range_Check (Original_Node (E)));
 142                end if;
 143
 144                Next (E);
 145             end loop;
 146
 147          --  For a slice, we evaluate the prefix, as for the indexed component
 148          --  case and then, if there is a range present, either directly or
 149          --  as the constraint of a discrete subtype indication, we evaluate
 150          --  the two bounds of this range.
 151
 152          elsif K = N_Slice then
 153             Evaluate_Name (Prefix (Fname));
 154
 155             declare
 156                DR     : constant Node_Id := Discrete_Range (Fname);
 157                Constr : Node_Id;
 158                Rexpr  : Node_Id;
 159
 160             begin
 161                if Nkind (DR) = N_Range then
 162                   Force_Evaluation (Low_Bound (DR));
 163                   Force_Evaluation (High_Bound (DR));
 164
 165                elsif Nkind (DR) = N_Subtype_Indication then
 166                   Constr := Constraint (DR);
 167
 168                   if Nkind (Constr) = N_Range_Constraint then
 169                      Rexpr := Range_Expression (Constr);
 170
 171                      Force_Evaluation (Low_Bound (Rexpr));
 172                      Force_Evaluation (High_Bound (Rexpr));
 173                   end if;
 174                end if;
 175             end;
 176
 177          --  For a type conversion, the expression of the conversion must be
 178          --  the name of an object, and we simply need to evaluate this name.
 179
 180          elsif K = N_Type_Conversion then
 181             Evaluate_Name (Expression (Fname));
 182
 183          --  For a function call, we evaluate the call
 184
 185          elsif K = N_Function_Call then
 186             Force_Evaluation (Fname);
 187
 188          --  The remaining cases are direct name, operator symbol and
 189          --  character literal. In all these cases, we do nothing, since
 190          --  we want to reevaluate each time the renamed object is used.
 191
 192          else
 193             return;
 194          end if;
 195       end Evaluate_Name;
 196
 197       -------------------------
 198       -- Evaluation_Required --
 199       -------------------------
 200
 201       function Evaluation_Required (Nam : Node_Id) return Boolean is
 202       begin
 203          if Nkind_In (Nam, N_Indexed_Component, N_Slice) then
 204             if Is_Packed (Etype (Prefix (Nam))) then
 205                return True;
 206             else
 207                return Evaluation_Required (Prefix (Nam));
 208             end if;
 209
 210          elsif Nkind (Nam) = N_Selected_Component then
 211             declare
 212                Rec_Type : constant Entity_Id := Etype (Prefix (Nam));
 213
 214             begin
 215                if Present (Component_Clause (Entity (Selector_Name (Nam))))
 216                  or else Has_Non_Standard_Rep (Rec_Type)
 217                then
 218                   return True;
 219
 220                elsif Ekind (Entity (Selector_Name (Nam))) = E_Discriminant
 221                  and then Is_Record_Type (Rec_Type)
 222                  and then not Is_Concurrent_Record_Type (Rec_Type)
 223                then
 224                   return True;
 225
 226                else
 227                   return Evaluation_Required (Prefix (Nam));
 228                end if;
 229             end;
 230
 231          else
 232             return False;
 233          end if;
 234       end Evaluation_Required;
 235
 236    --  Start of processing for Expand_N_Object_Renaming_Declaration
 237
 238    begin
 239       --  Perform name evaluation if required
 240
 241       if Evaluation_Required (Nam) then
 242          Evaluate_Name (Nam);
 243          Set_Is_Renaming_Of_Object (Defining_Identifier (N));
 244       end if;
 245
 246       --  Deal with construction of subtype in class-wide case
 247
 248       T := Etype (Defining_Identifier (N));
 249
 250       if Is_Class_Wide_Type (T) then
 251          Expand_Subtype_From_Expr (N, T, Subtype_Mark (N), Name (N));
 252          Find_Type (Subtype_Mark (N));
 253          Set_Etype (Defining_Identifier (N), Entity (Subtype_Mark (N)));
 254
 255          --  Freeze the class-wide subtype here to ensure that the subtype
 256          --  and equivalent type are frozen before the renaming.
 257
 258          Freeze_Before (N, Entity (Subtype_Mark (N)));
 259       end if;
 260
 261       --  Ada 2005 (AI-318-02): If the renamed object is a call to a build-in-
 262       --  place function, then a temporary return object needs to be created
 263       --  and access to it must be passed to the function. Currently we limit
 264       --  such functions to those with inherently limited result subtypes, but
 265       --  eventually we plan to expand the functions that are treated as
 266       --  build-in-place to include other composite result types.
 267
 268       if Ada_Version >= Ada_05
 269         and then Is_Build_In_Place_Function_Call (Nam)
 270       then
 271          Make_Build_In_Place_Call_In_Anonymous_Context (Nam);
 272       end if;
 273
 274       --  Create renaming entry for debug information
 275
 276       Decl := Debug_Renaming_Declaration (N);
 277
 278       if Present (Decl) then
 279          Insert_Action (N, Decl);
 280       end if;
 281    end Expand_N_Object_Renaming_Declaration;
 282
 283    -------------------------------------------
 284    -- Expand_N_Package_Renaming_Declaration --
 285    -------------------------------------------
 286
 287    procedure Expand_N_Package_Renaming_Declaration (N : Node_Id) is
 288       Decl : constant Node_Id := Debug_Renaming_Declaration (N);
 289
 290    begin
 291       if Present (Decl) then
 292
 293          --  If we are in a compilation unit, then this is an outer
 294          --  level declaration, and must have a scope of Standard
 295
 296          if Nkind (Parent (N)) = N_Compilation_Unit then
 297             declare
 298                Aux : constant Node_Id := Aux_Decls_Node (Parent (N));
 299
 300             begin
 301                Push_Scope (Standard_Standard);
 302
 303                if No (Actions (Aux)) then
 304                   Set_Actions (Aux, New_List (Decl));
 305                else
 306                   Append (Decl, Actions (Aux));
 307                end if;
 308
 309                Analyze (Decl);
 310
 311                --  Enter the debug variable in the qualification list, which
 312                --  must be done at this point because auxiliary declarations
 313                --  occur at the library level and aren't associated with a
 314                --  normal scope.
 315
 316                Qualify_Entity_Names (Decl);
 317
 318                Pop_Scope;
 319             end;
 320
 321          --  Otherwise, just insert after the package declaration
 322
 323          else
 324             Insert_Action (N, Decl);
 325          end if;
 326       end if;
 327    end Expand_N_Package_Renaming_Declaration;
 328
 329    ----------------------------------------------
 330    -- Expand_N_Subprogram_Renaming_Declaration --
 331    ----------------------------------------------
 332
 333    procedure Expand_N_Subprogram_Renaming_Declaration (N : Node_Id) is
 334       Nam : constant Node_Id := Name (N);
 335
 336    begin
 337       --  When the prefix of the name is a function call, we must force the
 338       --  call to be made by removing side effects from the call, since we
 339       --  must only call the function once.
 340
 341       if Nkind (Nam) = N_Selected_Component
 342         and then Nkind (Prefix (Nam)) = N_Function_Call
 343       then
 344          Remove_Side_Effects (Prefix (Nam));
 345
 346       --  For an explicit dereference, the prefix must be captured to prevent
 347       --  reevaluation on calls through the renaming, which could result in
 348       --  calling the wrong subprogram if the access value were to be changed.
 349
 350       elsif Nkind (Nam) = N_Explicit_Dereference then
 351          Force_Evaluation (Prefix (Nam));
 352       end if;
 353    end Expand_N_Subprogram_Renaming_Declaration;
 354
 355 end Exp_Ch8;