gcc/cp/cvt.c

   1 /* Language-level data type conversion for GNU C++.
   2    Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   3    1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
   4    Hacked by Michael Tiemann (tiemann@cygnus.com)
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU General Public License as published by
  10 the Free Software Foundation; either version 2, or (at your option)
  11 any later version.
  12
  13 GCC is distributed in the hope that it will be useful,
  14 but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 GNU General Public License for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GCC; see the file COPYING.  If not, write to
  20 the Free Software Foundation, 59 Temple Place - Suite 330,
  21 Boston, MA 02111-1307, USA.  */
  22
  23
  24 /* This file contains the functions for converting C++ expressions
  25    to different data types.  The only entry point is `convert'.
  26    Every language front end must have a `convert' function
  27    but what kind of conversions it does will depend on the language.  */
  28
  29 #include "config.h"
  30 #include "system.h"
  31 #include "coretypes.h"
  32 #include "tm.h"
  33 #include "tree.h"
  34 #include "flags.h"
  35 #include "cp-tree.h"
  36 #include "convert.h"
  37 #include "toplev.h"
  38 #include "decl.h"
  39
  40 static tree cp_convert_to_pointer (tree, tree, bool);
  41 static tree convert_to_pointer_force (tree, tree);
  42 static tree build_up_reference (tree, tree, int, tree);
  43 static void warn_ref_binding (tree, tree, tree);
  44
  45 /* Change of width--truncation and extension of integers or reals--
  46    is represented with NOP_EXPR.  Proper functioning of many things
  47    assumes that no other conversions can be NOP_EXPRs.
  48
  49    Conversion between integer and pointer is represented with CONVERT_EXPR.
  50    Converting integer to real uses FLOAT_EXPR
  51    and real to integer uses FIX_TRUNC_EXPR.
  52
  53    Here is a list of all the functions that assume that widening and
  54    narrowing is always done with a NOP_EXPR:
  55      In convert.c, convert_to_integer.
  56      In c-typeck.c, build_binary_op_nodefault (boolean ops),
  57         and c_common_truthvalue_conversion.
  58      In expr.c: expand_expr, for operands of a MULT_EXPR.
  59      In fold-const.c: fold.
  60      In tree.c: get_narrower and get_unwidened.
  61
  62    C++: in multiple-inheritance, converting between pointers may involve
  63    adjusting them by a delta stored within the class definition.  */
  64 \f
  65 /* Subroutines of `convert'.  */
  66
  67 /* if converting pointer to pointer
  68      if dealing with classes, check for derived->base or vice versa
  69      else if dealing with method pointers, delegate
  70      else convert blindly
  71    else if converting class, pass off to build_type_conversion
  72    else try C-style pointer conversion.  If FORCE is true then allow
  73    conversions via virtual bases (these are permitted by reinterpret_cast,
  74    but not static_cast).  */
  75
  76 static tree
  77 cp_convert_to_pointer (tree type, tree expr, bool force)
  78 {
  79   tree intype = TREE_TYPE (expr);
  80   enum tree_code form;
  81   tree rval;
  82
  83   if (IS_AGGR_TYPE (intype))
  84     {
  85       intype = complete_type (intype);
  86       if (!COMPLETE_TYPE_P (intype))
  87         {
  88           error ("can't convert from incomplete type `%T' to `%T'",
  89                     intype, type);
  90           return error_mark_node;
  91         }
  92
  93       rval = build_type_conversion (type, expr);
  94       if (rval)
  95         {
  96           if (rval == error_mark_node)
  97             error ("conversion of `%E' from `%T' to `%T' is ambiguous",
  98                       expr, intype, type);
  99           return rval;
 100         }
 101     }
 102
 103   /* Handle anachronistic conversions from (::*)() to cv void* or (*)().  */
 104   if (TREE_CODE (type) == POINTER_TYPE
 105       && (TREE_CODE (TREE_TYPE (type)) == FUNCTION_TYPE
 106           || VOID_TYPE_P (TREE_TYPE (type))))
 107     {
 108       /* Allow an implicit this pointer for pointer to member
 109          functions.  */
 110       if (TYPE_PTRMEMFUNC_P (intype))
 111         {
 112           if (pedantic || warn_pmf2ptr)
 113             pedwarn ("converting from `%T' to `%T'", intype, type);
 114           if (TREE_CODE (expr) == PTRMEM_CST)
 115             expr = build_address (PTRMEM_CST_MEMBER (expr));
 116           else
 117             {
 118               tree decl = maybe_dummy_object (TYPE_PTRMEM_CLASS_TYPE (intype),
 119                                               0);
 120               decl = build_address (decl);
 121               expr = get_member_function_from_ptrfunc (&decl, expr);
 122             }
 123         }
 124       else if (TREE_CODE (TREE_TYPE (expr)) == METHOD_TYPE)
 125         {
 126           if (pedantic || warn_pmf2ptr)
 127             pedwarn ("converting from `%T' to `%T'", intype, type);
 128           expr = build_addr_func (expr);
 129         }
 130       if (TREE_CODE (TREE_TYPE (expr)) == POINTER_TYPE)
 131         return build_nop (type, expr);
 132       intype = TREE_TYPE (expr);
 133     }
 134
 135   if (expr == error_mark_node)
 136     return error_mark_node;
 137
 138   form = TREE_CODE (intype);
 139
 140   if (POINTER_TYPE_P (intype))
 141     {
 142       intype = TYPE_MAIN_VARIANT (intype);
 143
 144       if (TYPE_MAIN_VARIANT (type) != intype
 145           && TREE_CODE (type) == POINTER_TYPE
 146           && TREE_CODE (TREE_TYPE (type)) == RECORD_TYPE
 147           && IS_AGGR_TYPE (TREE_TYPE (type))
 148           && IS_AGGR_TYPE (TREE_TYPE (intype))
 149           && TREE_CODE (TREE_TYPE (intype)) == RECORD_TYPE)
 150         {
 151           enum tree_code code = PLUS_EXPR;
 152           tree binfo;
 153           tree intype_class;
 154           tree type_class;
 155           bool same_p;
 156
 157           intype_class = TREE_TYPE (intype);
 158           type_class = TREE_TYPE (type);
 159
 160           same_p = same_type_p (TYPE_MAIN_VARIANT (intype_class),
 161                                 TYPE_MAIN_VARIANT (type_class));
 162           binfo = NULL_TREE;
 163           /* Try derived to base conversion.  */
 164           if (!same_p)
 165             binfo = lookup_base (intype_class, type_class, ba_check, NULL);
 166           if (!same_p && !binfo)
 167             {
 168               /* Try base to derived conversion.  */
 169               binfo = lookup_base (type_class, intype_class, ba_check, NULL);
 170               code = MINUS_EXPR;
 171             }
 172           if (binfo == error_mark_node)
 173             return error_mark_node;
 174           if (binfo || same_p)
 175             {
 176               if (binfo)
 177                 expr = build_base_path (code, expr, binfo, 0);
 178               /* Add any qualifier conversions.  */
 179               return build_nop (type, expr);
 180             }
 181         }
 182
 183       if (TYPE_PTRMEMFUNC_P (type))
 184         {
 185           error ("cannot convert `%E' from type `%T' to type `%T'",
 186                     expr, intype, type);
 187           return error_mark_node;
 188         }
 189
 190       return build_nop (type, expr);
 191     }
 192   else if (TYPE_PTRMEM_P (type) && TYPE_PTRMEM_P (intype))
 193     {
 194       tree b1;
 195       tree b2;
 196       tree binfo;
 197       enum tree_code code = PLUS_EXPR;
 198       base_kind bk;
 199
 200       b1 = TYPE_PTRMEM_CLASS_TYPE (type);
 201       b2 = TYPE_PTRMEM_CLASS_TYPE (intype);
 202       binfo = lookup_base (b1, b2, ba_check, &bk);
 203       if (!binfo)
 204         {
 205           binfo = lookup_base (b2, b1, ba_check, &bk);
 206           code = MINUS_EXPR;
 207         }
 208       if (binfo == error_mark_node)
 209         return error_mark_node;
 210
 211       if (bk == bk_via_virtual)
 212         {
 213           if (force)
 214             warning ("pointer to member cast from `%T' to `%T' is via virtual base",
 215                      intype, type);
 216           else
 217             {
 218               error ("pointer to member cast from `%T' to `%T' is via virtual base",
 219                      intype, type);
 220               return error_mark_node;
 221             }
 222           /* This is a reinterpret cast, whose result is unspecified.
 223              We choose to do nothing.  */
 224           return build1 (NOP_EXPR, type, expr);
 225         }
 226
 227       if (TREE_CODE (expr) == PTRMEM_CST)
 228         expr = cplus_expand_constant (expr);
 229
 230       if (binfo && !integer_zerop (BINFO_OFFSET (binfo)))
 231         expr = size_binop (code,
 232                            build_nop (sizetype, expr),
 233                            BINFO_OFFSET (binfo));
 234       return build_nop (type, expr);
 235     }
 236   else if (TYPE_PTRMEMFUNC_P (type) && TYPE_PTRMEMFUNC_P (intype))
 237     return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), expr, 0);
 238   else if (TYPE_PTRMEMFUNC_P (intype))
 239     {
 240       if (!warn_pmf2ptr)
 241         {
 242           if (TREE_CODE (expr) == PTRMEM_CST)
 243             return cp_convert_to_pointer (type,
 244                                           PTRMEM_CST_MEMBER (expr),
 245                                           force);
 246           else if (TREE_CODE (expr) == OFFSET_REF)
 247             {
 248               tree object = TREE_OPERAND (expr, 0);
 249               return get_member_function_from_ptrfunc (&object,
 250                                                        TREE_OPERAND (expr, 1));
 251             }
 252         }
 253       error ("cannot convert `%E' from type `%T' to type `%T'",
 254                 expr, intype, type);
 255       return error_mark_node;
 256     }
 257
 258   if (integer_zerop (expr))
 259     {
 260       if (TYPE_PTRMEMFUNC_P (type))
 261         return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), expr, 0);
 262
 263       if (TYPE_PTRMEM_P (type))
 264         /* A NULL pointer-to-member is represented by -1, not by
 265            zero.  */
 266         expr = build_int_2 (-1, -1);
 267       else
 268         expr = build_int_2 (0, 0);
 269       TREE_TYPE (expr) = type;
 270       /* Fix up the representation of -1 if appropriate.  */
 271       force_fit_type (expr, 0);
 272       return expr;
 273     }
 274   else if (TYPE_PTR_TO_MEMBER_P (type) && INTEGRAL_CODE_P (form))
 275     {
 276       error ("invalid conversion from '%T' to '%T'", intype, type);
 277       return error_mark_node;
 278     }
 279
 280   if (INTEGRAL_CODE_P (form))
 281     {
 282       if (TYPE_PRECISION (intype) == POINTER_SIZE)
 283         return build1 (CONVERT_EXPR, type, expr);
 284       expr = cp_convert (c_common_type_for_size (POINTER_SIZE, 0), expr);
 285       /* Modes may be different but sizes should be the same.  */
 286       if (GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (expr)))
 287           != GET_MODE_SIZE (TYPE_MODE (type)))
 288         /* There is supposed to be some integral type
 289            that is the same width as a pointer.  */
 290         abort ();
 291       return convert_to_pointer (type, expr);
 292     }
 293
 294   if (type_unknown_p (expr))
 295     return instantiate_type (type, expr, tf_error | tf_warning);
 296
 297   error ("cannot convert `%E' from type `%T' to type `%T'",
 298             expr, intype, type);
 299   return error_mark_node;
 300 }
 301
 302 /* Like convert, except permit conversions to take place which
 303    are not normally allowed due to access restrictions
 304    (such as conversion from sub-type to private super-type).  */
 305
 306 static tree
 307 convert_to_pointer_force (tree type, tree expr)
 308 {
 309   tree intype = TREE_TYPE (expr);
 310   enum tree_code form = TREE_CODE (intype);
 311
 312   if (form == POINTER_TYPE)
 313     {
 314       intype = TYPE_MAIN_VARIANT (intype);
 315
 316       if (TYPE_MAIN_VARIANT (type) != intype
 317           && TREE_CODE (TREE_TYPE (type)) == RECORD_TYPE
 318           && IS_AGGR_TYPE (TREE_TYPE (type))
 319           && IS_AGGR_TYPE (TREE_TYPE (intype))
 320           && TREE_CODE (TREE_TYPE (intype)) == RECORD_TYPE)
 321         {
 322           enum tree_code code = PLUS_EXPR;
 323           tree binfo;
 324
 325           binfo = lookup_base (TREE_TYPE (intype), TREE_TYPE (type),
 326                                ba_ignore, NULL);
 327           if (!binfo)
 328             {
 329               binfo = lookup_base (TREE_TYPE (type), TREE_TYPE (intype),
 330                                    ba_ignore, NULL);
 331               code = MINUS_EXPR;
 332             }
 333           if (binfo == error_mark_node)
 334             return error_mark_node;
 335           if (binfo)
 336             {
 337               expr = build_base_path (code, expr, binfo, 0);
 338               if (expr == error_mark_node)
 339                  return error_mark_node;
 340               /* Add any qualifier conversions.  */
 341               if (!same_type_p (TREE_TYPE (TREE_TYPE (expr)),
 342                                 TREE_TYPE (type)))
 343                 expr = build_nop (type, expr);
 344               return expr;
 345             }
 346         }
 347     }
 348
 349   return cp_convert_to_pointer (type, expr, true);
 350 }
 351
 352 /* We are passing something to a function which requires a reference.
 353    The type we are interested in is in TYPE. The initial
 354    value we have to begin with is in ARG.
 355
 356    FLAGS controls how we manage access checking.
 357    DIRECT_BIND in FLAGS controls how any temporaries are generated.
 358      If DIRECT_BIND is set, DECL is the reference we're binding to.  */
 359
 360 static tree
 361 build_up_reference (tree type, tree arg, int flags, tree decl)
 362 {
 363   tree rval;
 364   tree argtype = TREE_TYPE (arg);
 365   tree target_type = TREE_TYPE (type);
 366
 367   my_friendly_assert (TREE_CODE (type) == REFERENCE_TYPE, 187);
 368
 369   if ((flags & DIRECT_BIND) && ! real_lvalue_p (arg))
 370     {
 371       /* Create a new temporary variable.  We can't just use a TARGET_EXPR
 372          here because it needs to live as long as DECL.  */
 373       tree targ = arg;
 374
 375       arg = make_temporary_var_for_ref_to_temp (decl, TREE_TYPE (arg));
 376
 377       /* Process the initializer for the declaration.  */
 378       DECL_INITIAL (arg) = targ;
 379       cp_finish_decl (arg, targ, NULL_TREE,
 380                       LOOKUP_ONLYCONVERTING|DIRECT_BIND);
 381     }
 382   else if (!(flags & DIRECT_BIND) && ! lvalue_p (arg))
 383     return get_target_expr (arg);
 384
 385   /* If we had a way to wrap this up, and say, if we ever needed its
 386      address, transform all occurrences of the register, into a memory
 387      reference we could win better.  */
 388   rval = build_unary_op (ADDR_EXPR, arg, 1);
 389   if (rval == error_mark_node)
 390     return error_mark_node;
 391
 392   if ((flags & LOOKUP_PROTECT)
 393       && TYPE_MAIN_VARIANT (argtype) != TYPE_MAIN_VARIANT (target_type)
 394       && IS_AGGR_TYPE (argtype)
 395       && IS_AGGR_TYPE (target_type))
 396     {
 397       /* We go through lookup_base for the access control.  */
 398       tree binfo = lookup_base (argtype, target_type, ba_check, NULL);
 399       if (binfo == error_mark_node)
 400         return error_mark_node;
 401       if (binfo == NULL_TREE)
 402         return error_not_base_type (target_type, argtype);
 403       rval = build_base_path (PLUS_EXPR, rval, binfo, 1);
 404     }
 405   else
 406     rval
 407       = convert_to_pointer_force (build_pointer_type (target_type), rval);
 408   return build_nop (type, rval);
 409 }
 410
 411 /* Subroutine of convert_to_reference. REFTYPE is the target reference type.
 412    INTYPE is the original rvalue type and DECL is an optional _DECL node
 413    for diagnostics.
 414
 415    [dcl.init.ref] says that if an rvalue is used to
 416    initialize a reference, then the reference must be to a
 417    non-volatile const type.  */
 418
 419 static void
 420 warn_ref_binding (tree reftype, tree intype, tree decl)
 421 {
 422   tree ttl = TREE_TYPE (reftype);
 423
 424   if (!CP_TYPE_CONST_NON_VOLATILE_P (ttl))
 425     {
 426       const char *msg;
 427
 428       if (CP_TYPE_VOLATILE_P (ttl) && decl)
 429           msg = "initialization of volatile reference type `%#T' from rvalue of type `%T'";
 430       else if (CP_TYPE_VOLATILE_P (ttl))
 431           msg = "conversion to volatile reference type `%#T' from rvalue of type `%T'";
 432       else if (decl)
 433           msg = "initialization of non-const reference type `%#T' from rvalue of type `%T'";
 434       else
 435           msg = "conversion to non-const reference type `%#T' from rvalue of type `%T'";
 436
 437       pedwarn (msg, reftype, intype);
 438     }
 439 }
 440
 441 /* For C++: Only need to do one-level references, but cannot
 442    get tripped up on signed/unsigned differences.
 443
 444    DECL is either NULL_TREE or the _DECL node for a reference that is being
 445    initialized.  It can be error_mark_node if we don't know the _DECL but
 446    we know it's an initialization.  */
 447
 448 tree
 449 convert_to_reference (tree reftype, tree expr, int convtype,
 450                       int flags, tree decl)
 451 {
 452   tree type = TYPE_MAIN_VARIANT (TREE_TYPE (reftype));
 453   tree intype;
 454   tree rval = NULL_TREE;
 455   tree rval_as_conversion = NULL_TREE;
 456   bool can_convert_intype_to_type;
 457
 458   if (TREE_CODE (type) == FUNCTION_TYPE
 459       && TREE_TYPE (expr) == unknown_type_node)
 460     expr = instantiate_type (type, expr,
 461                              (flags & LOOKUP_COMPLAIN)
 462                              ? tf_error | tf_warning : tf_none);
 463   else
 464     expr = convert_from_reference (expr);
 465
 466   if (expr == error_mark_node)
 467     return error_mark_node;
 468
 469   intype = TREE_TYPE (expr);
 470
 471   my_friendly_assert (TREE_CODE (intype) != REFERENCE_TYPE, 364);
 472
 473   intype = TYPE_MAIN_VARIANT (intype);
 474
 475   can_convert_intype_to_type = can_convert (type, intype);
 476   if (!can_convert_intype_to_type
 477       && (convtype & CONV_IMPLICIT) && IS_AGGR_TYPE (intype)
 478       && ! (flags & LOOKUP_NO_CONVERSION))
 479     {
 480       /* Look for a user-defined conversion to lvalue that we can use.  */
 481
 482       rval_as_conversion
 483         = build_type_conversion (reftype, expr);
 484
 485       if (rval_as_conversion && rval_as_conversion != error_mark_node
 486           && real_lvalue_p (rval_as_conversion))
 487         {
 488           expr = rval_as_conversion;
 489           rval_as_conversion = NULL_TREE;
 490           intype = type;
 491           can_convert_intype_to_type = 1;
 492         }
 493     }
 494
 495   if (((convtype & CONV_STATIC) && can_convert (intype, type))
 496       || ((convtype & CONV_IMPLICIT) && can_convert_intype_to_type))
 497     {
 498       if (flags & LOOKUP_COMPLAIN)
 499         {
 500           tree ttl = TREE_TYPE (reftype);
 501           tree ttr = lvalue_type (expr);
 502
 503           if (! real_lvalue_p (expr))
 504             warn_ref_binding (reftype, intype, decl);
 505
 506           if (! (convtype & CONV_CONST)
 507                    && !at_least_as_qualified_p (ttl, ttr))
 508             pedwarn ("conversion from `%T' to `%T' discards qualifiers",
 509                         ttr, reftype);
 510         }
 511
 512       return build_up_reference (reftype, expr, flags, decl);
 513     }
 514   else if ((convtype & CONV_REINTERPRET) && lvalue_p (expr))
 515     {
 516       /* When casting an lvalue to a reference type, just convert into
 517          a pointer to the new type and deference it.  This is allowed
 518          by San Diego WP section 5.2.9 paragraph 12, though perhaps it
 519          should be done directly (jason).  (int &)ri ---> *(int*)&ri */
 520
 521       /* B* bp; A& ar = (A&)bp; is valid, but it's probably not what they
 522          meant.  */
 523       if (TREE_CODE (intype) == POINTER_TYPE
 524           && (comptypes (TREE_TYPE (intype), type,
 525                          COMPARE_BASE | COMPARE_DERIVED)))
 526         warning ("casting `%T' to `%T' does not dereference pointer",
 527                  intype, reftype);
 528
 529       rval = build_unary_op (ADDR_EXPR, expr, 0);
 530       if (rval != error_mark_node)
 531         rval = convert_force (build_pointer_type (TREE_TYPE (reftype)),
 532                               rval, 0);
 533       if (rval != error_mark_node)
 534         rval = build1 (NOP_EXPR, reftype, rval);
 535     }
 536   else
 537     {
 538       rval = convert_for_initialization (NULL_TREE, type, expr, flags,
 539                                          "converting", 0, 0);
 540       if (rval == NULL_TREE || rval == error_mark_node)
 541         return rval;
 542       warn_ref_binding (reftype, intype, decl);
 543       rval = build_up_reference (reftype, rval, flags, decl);
 544     }
 545
 546   if (rval)
 547     {
 548       /* If we found a way to convert earlier, then use it.  */
 549       return rval;
 550     }
 551
 552   if (flags & LOOKUP_COMPLAIN)
 553     error ("cannot convert type `%T' to type `%T'", intype, reftype);
 554
 555   return error_mark_node;
 556 }
 557
 558 /* We are using a reference VAL for its value. Bash that reference all the
 559    way down to its lowest form.  */
 560
 561 tree
 562 convert_from_reference (tree val)
 563 {
 564   if (TREE_CODE (TREE_TYPE (val)) == REFERENCE_TYPE)
 565     return build_indirect_ref (val, NULL);
 566   return val;
 567 }
 568
 569 /* Implicitly convert the lvalue EXPR to another lvalue of type TOTYPE,
 570    preserving cv-qualification.  */
 571
 572 tree
 573 convert_lvalue (tree totype, tree expr)
 574 {
 575   totype = cp_build_qualified_type (totype, TYPE_QUALS (TREE_TYPE (expr)));
 576   totype = build_reference_type (totype);
 577   expr = convert_to_reference (totype, expr, CONV_IMPLICIT, LOOKUP_NORMAL,
 578                                NULL_TREE);
 579   return convert_from_reference (expr);
 580 }
 581
 582 /* Really perform an lvalue-to-rvalue conversion, including copying an
 583    argument of class type into a temporary.  */
 584
 585 tree
 586 force_rvalue (tree expr)
 587 {
 588   if (IS_AGGR_TYPE (TREE_TYPE (expr)) && TREE_CODE (expr) != TARGET_EXPR)
 589     expr = ocp_convert (TREE_TYPE (expr), expr,
 590                         CONV_IMPLICIT|CONV_FORCE_TEMP, LOOKUP_NORMAL);
 591   else
 592     expr = decay_conversion (expr);
 593
 594   return expr;
 595 }
 596 \f
 597 /* C++ conversions, preference to static cast conversions.  */
 598
 599 tree
 600 cp_convert (tree type, tree expr)
 601 {
 602   return ocp_convert (type, expr, CONV_OLD_CONVERT, LOOKUP_NORMAL);
 603 }
 604
 605 /* Conversion...
 606
 607    FLAGS indicates how we should behave.  */
 608
 609 tree
 610 ocp_convert (tree type, tree expr, int convtype, int flags)
 611 {
 612   tree e = expr;
 613   enum tree_code code = TREE_CODE (type);
 614
 615   if (error_operand_p (e) || type == error_mark_node)
 616     return error_mark_node;
 617
 618   complete_type (type);
 619   complete_type (TREE_TYPE (expr));
 620
 621   e = decl_constant_value (e);
 622
 623   if (IS_AGGR_TYPE (type) && (convtype & CONV_FORCE_TEMP)
 624       /* Some internal structures (vtable_entry_type, sigtbl_ptr_type)
 625          don't go through finish_struct, so they don't have the synthesized
 626          constructors.  So don't force a temporary.  */
 627       && TYPE_HAS_CONSTRUCTOR (type))
 628     /* We need a new temporary; don't take this shortcut.  */;
 629   else if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (e)))
 630     {
 631       if (same_type_p (type, TREE_TYPE (e)))
 632         /* The call to fold will not always remove the NOP_EXPR as
 633            might be expected, since if one of the types is a typedef;
 634            the comparison in fold is just equality of pointers, not a
 635            call to comptypes.  We don't call fold in this case because
 636            that can result in infinite recursion; fold will call
 637            convert, which will call ocp_convert, etc.  */
 638         return e;
 639       /* For complex data types, we need to perform componentwise
 640          conversion.  */
 641       else if (TREE_CODE (type) == COMPLEX_TYPE)
 642         return fold (convert_to_complex (type, e));
 643       else if (TREE_CODE (e) == TARGET_EXPR)
 644         {
 645           /* Don't build a NOP_EXPR of class type.  Instead, change the
 646              type of the temporary.  Only allow this for cv-qual changes,
 647              though.  */
 648           if (!same_type_p (TYPE_MAIN_VARIANT (TREE_TYPE (e)),
 649                             TYPE_MAIN_VARIANT (type)))
 650             abort ();
 651           TREE_TYPE (e) = TREE_TYPE (TARGET_EXPR_SLOT (e)) = type;
 652           return e;
 653         }
 654       else if (TREE_ADDRESSABLE (type))
 655         /* We shouldn't be treating objects of ADDRESSABLE type as rvalues.  */
 656         abort ();
 657       else
 658         return fold (build1 (NOP_EXPR, type, e));
 659     }
 660
 661   if (code == VOID_TYPE && (convtype & CONV_STATIC))
 662     {
 663       e = convert_to_void (e, /*implicit=*/NULL);
 664       return e;
 665     }
 666
 667   if (INTEGRAL_CODE_P (code))
 668     {
 669       tree intype = TREE_TYPE (e);
 670       /* enum = enum, enum = int, enum = float, (enum)pointer are all
 671          errors.  */
 672       if (TREE_CODE (type) == ENUMERAL_TYPE
 673           && ((ARITHMETIC_TYPE_P (intype) && ! (convtype & CONV_STATIC))
 674               || (TREE_CODE (intype) == POINTER_TYPE)))
 675         {
 676           pedwarn ("conversion from `%#T' to `%#T'", intype, type);
 677
 678           if (flag_pedantic_errors)
 679             return error_mark_node;
 680         }
 681       if (IS_AGGR_TYPE (intype))
 682         {
 683           tree rval;
 684           rval = build_type_conversion (type, e);
 685           if (rval)
 686             return rval;
 687           if (flags & LOOKUP_COMPLAIN)
 688             error ("`%#T' used where a `%T' was expected", intype, type);
 689           return error_mark_node;
 690         }
 691       if (code == BOOLEAN_TYPE)
 692         return cp_truthvalue_conversion (e);
 693
 694       return fold (convert_to_integer (type, e));
 695     }
 696   if (POINTER_TYPE_P (type) || TYPE_PTR_TO_MEMBER_P (type))
 697     return fold (cp_convert_to_pointer (type, e, false));
 698   if (code == VECTOR_TYPE)
 699     return fold (convert_to_vector (type, e));
 700   if (code == REAL_TYPE || code == COMPLEX_TYPE)
 701     {
 702       if (IS_AGGR_TYPE (TREE_TYPE (e)))
 703         {
 704           tree rval;
 705           rval = build_type_conversion (type, e);
 706           if (rval)
 707             return rval;
 708           else
 709             if (flags & LOOKUP_COMPLAIN)
 710               error ("`%#T' used where a floating point value was expected",
 711                         TREE_TYPE (e));
 712         }
 713       if (code == REAL_TYPE)
 714         return fold (convert_to_real (type, e));
 715       else if (code == COMPLEX_TYPE)
 716         return fold (convert_to_complex (type, e));
 717     }
 718
 719   /* New C++ semantics:  since assignment is now based on
 720      memberwise copying,  if the rhs type is derived from the
 721      lhs type, then we may still do a conversion.  */
 722   if (IS_AGGR_TYPE_CODE (code))
 723     {
 724       tree dtype = TREE_TYPE (e);
 725       tree ctor = NULL_TREE;
 726
 727       dtype = TYPE_MAIN_VARIANT (dtype);
 728
 729       /* Conversion between aggregate types.  New C++ semantics allow
 730          objects of derived type to be cast to objects of base type.
 731          Old semantics only allowed this between pointers.
 732
 733          There may be some ambiguity between using a constructor
 734          vs. using a type conversion operator when both apply.  */
 735
 736       ctor = e;
 737
 738       if (abstract_virtuals_error (NULL_TREE, type))
 739         return error_mark_node;
 740
 741       if ((flags & LOOKUP_ONLYCONVERTING)
 742           && ! (IS_AGGR_TYPE (dtype) && DERIVED_FROM_P (type, dtype)))
 743         /* For copy-initialization, first we create a temp of the proper type
 744            with a user-defined conversion sequence, then we direct-initialize
 745            the target with the temp (see [dcl.init]).  */
 746         ctor = build_user_type_conversion (type, ctor, flags);
 747       else
 748         ctor = build_special_member_call (NULL_TREE,
 749                                           complete_ctor_identifier,
 750                                           build_tree_list (NULL_TREE, ctor),
 751                                           TYPE_BINFO (type), flags);
 752       if (ctor)
 753         return build_cplus_new (type, ctor);
 754     }
 755
 756   if (flags & LOOKUP_COMPLAIN)
 757     error ("conversion from `%T' to non-scalar type `%T' requested",
 758               TREE_TYPE (expr), type);
 759   return error_mark_node;
 760 }
 761
 762 /* When an expression is used in a void context, its value is discarded and
 763    no lvalue-rvalue and similar conversions happen [expr.static.cast/4,
 764    stmt.expr/1, expr.comma/1].  This permits dereferencing an incomplete type
 765    in a void context. The C++ standard does not define what an `access' to an
 766    object is, but there is reason to believe that it is the lvalue to rvalue
 767    conversion -- if it were not, `*&*p = 1' would violate [expr]/4 in that it
 768    accesses `*p' not to calculate the value to be stored. But, dcl.type.cv/8
 769    indicates that volatile semantics should be the same between C and C++
 770    where ever possible. C leaves it implementation defined as to what
 771    constitutes an access to a volatile. So, we interpret `*vp' as a read of
 772    the volatile object `vp' points to, unless that is an incomplete type. For
 773    volatile references we do not do this interpretation, because that would
 774    make it impossible to ignore the reference return value from functions. We
 775    issue warnings in the confusing cases.
 776
 777    IMPLICIT is tells us the context of an implicit void conversion.  */
 778
 779 tree
 780 convert_to_void (tree expr, const char *implicit)
 781 {
 782   if (expr == error_mark_node
 783       || TREE_TYPE (expr) == error_mark_node)
 784     return error_mark_node;
 785   if (!TREE_TYPE (expr))
 786     return expr;
 787   if (VOID_TYPE_P (TREE_TYPE (expr)))
 788     return expr;
 789   switch (TREE_CODE (expr))
 790     {
 791     case COND_EXPR:
 792       {
 793         /* The two parts of a cond expr might be separate lvalues.  */
 794         tree op1 = TREE_OPERAND (expr,1);
 795         tree op2 = TREE_OPERAND (expr,2);
 796         tree new_op1 = convert_to_void
 797           (op1, (implicit && !TREE_SIDE_EFFECTS (op2)
 798                  ? "second operand of conditional" : NULL));
 799         tree new_op2 = convert_to_void
 800           (op2, (implicit && !TREE_SIDE_EFFECTS (op1)
 801                  ? "third operand of conditional" : NULL));
 802
 803         expr = build (COND_EXPR, TREE_TYPE (new_op1),
 804                       TREE_OPERAND (expr, 0), new_op1, new_op2);
 805         break;
 806       }
 807
 808     case COMPOUND_EXPR:
 809       {
 810         /* The second part of a compound expr contains the value.  */
 811         tree op1 = TREE_OPERAND (expr,1);
 812         tree new_op1 = convert_to_void
 813           (op1, (implicit && !TREE_NO_WARNING (expr)
 814                  ? "right-hand operand of comma" : NULL));
 815
 816         if (new_op1 != op1)
 817           {
 818             tree t = build (COMPOUND_EXPR, TREE_TYPE (new_op1),
 819                             TREE_OPERAND (expr, 0), new_op1);
 820             expr = t;
 821           }
 822
 823         break;
 824       }
 825
 826     case NON_LVALUE_EXPR:
 827     case NOP_EXPR:
 828       /* These have already decayed to rvalue.  */
 829       break;
 830
 831     case CALL_EXPR:   /* We have a special meaning for volatile void fn().  */
 832       break;
 833
 834     case INDIRECT_REF:
 835       {
 836         tree type = TREE_TYPE (expr);
 837         int is_reference = TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0)))
 838                            == REFERENCE_TYPE;
 839         int is_volatile = TYPE_VOLATILE (type);
 840         int is_complete = COMPLETE_TYPE_P (complete_type (type));
 841
 842         if (is_volatile && !is_complete)
 843           warning ("object of incomplete type `%T' will not be accessed in %s",
 844                       type, implicit ? implicit : "void context");
 845         else if (is_reference && is_volatile)
 846           warning ("object of type `%T' will not be accessed in %s",
 847                       TREE_TYPE (TREE_OPERAND (expr, 0)),
 848                       implicit ? implicit : "void context");
 849         if (is_reference || !is_volatile || !is_complete)
 850           expr = TREE_OPERAND (expr, 0);
 851
 852         break;
 853       }
 854
 855     case VAR_DECL:
 856       {
 857         /* External variables might be incomplete.  */
 858         tree type = TREE_TYPE (expr);
 859         int is_complete = COMPLETE_TYPE_P (complete_type (type));
 860
 861         if (TYPE_VOLATILE (type) && !is_complete)
 862           warning ("object `%E' of incomplete type `%T' will not be accessed in %s",
 863                       expr, type, implicit ? implicit : "void context");
 864         break;
 865       }
 866
 867     default:;
 868     }
 869   {
 870     tree probe = expr;
 871
 872     if (TREE_CODE (probe) == ADDR_EXPR)
 873       probe = TREE_OPERAND (expr, 0);
 874     if (type_unknown_p (probe))
 875       {
 876         /* [over.over] enumerates the places where we can take the address
 877            of an overloaded function, and this is not one of them.  */
 878         pedwarn ("%s cannot resolve address of overloaded function",
 879                     implicit ? implicit : "void cast");
 880         expr = void_zero_node;
 881       }
 882     else if (implicit && probe == expr && is_overloaded_fn (probe))
 883       /* Only warn when there is no &.  */
 884       warning ("%s is a reference, not call, to function `%E'",
 885                   implicit, expr);
 886   }
 887
 888   if (expr != error_mark_node && !VOID_TYPE_P (TREE_TYPE (expr)))
 889     {
 890       if (implicit && warn_unused_value
 891           && !TREE_SIDE_EFFECTS (expr) && !TREE_NO_WARNING (expr))
 892         warning ("%s has no effect", implicit);
 893       expr = build1 (CONVERT_EXPR, void_type_node, expr);
 894     }
 895   return expr;
 896 }
 897
 898 /* Create an expression whose value is that of EXPR,
 899    converted to type TYPE.  The TREE_TYPE of the value
 900    is always TYPE.  This function implements all reasonable
 901    conversions; callers should filter out those that are
 902    not permitted by the language being compiled.
 903
 904    Most of this routine is from build_reinterpret_cast.
 905
 906    The backend cannot call cp_convert (what was convert) because
 907    conversions to/from basetypes may involve memory references
 908    (vbases) and adding or subtracting small values (multiple
 909    inheritance), but it calls convert from the constant folding code
 910    on subtrees of already built trees after it has ripped them apart.
 911
 912    Also, if we ever support range variables, we'll probably also have to
 913    do a little bit more work.  */
 914
 915 tree
 916 convert (tree type, tree expr)
 917 {
 918   tree intype;
 919
 920   if (type == error_mark_node || expr == error_mark_node)
 921     return error_mark_node;
 922
 923   intype = TREE_TYPE (expr);
 924
 925   if (POINTER_TYPE_P (type) && POINTER_TYPE_P (intype))
 926     {
 927       expr = decl_constant_value (expr);
 928       return fold (build1 (NOP_EXPR, type, expr));
 929     }
 930
 931   return ocp_convert (type, expr, CONV_OLD_CONVERT,
 932                       LOOKUP_NORMAL|LOOKUP_NO_CONVERSION);
 933 }
 934
 935 /* Like cp_convert, except permit conversions to take place which
 936    are not normally allowed due to access restrictions
 937    (such as conversion from sub-type to private super-type).  */
 938
 939 tree
 940 convert_force (tree type, tree expr, int convtype)
 941 {
 942   tree e = expr;
 943   enum tree_code code = TREE_CODE (type);
 944
 945   if (code == REFERENCE_TYPE)
 946     return fold (convert_to_reference (type, e, CONV_C_CAST, LOOKUP_COMPLAIN,
 947                                        NULL_TREE));
 948   else if (TREE_CODE (TREE_TYPE (e)) == REFERENCE_TYPE)
 949     e = convert_from_reference (e);
 950
 951   if (code == POINTER_TYPE)
 952     return fold (convert_to_pointer_force (type, e));
 953
 954   /* From typeck.c convert_for_assignment */
 955   if (((TREE_CODE (TREE_TYPE (e)) == POINTER_TYPE && TREE_CODE (e) == ADDR_EXPR
 956         && TREE_CODE (TREE_TYPE (e)) == POINTER_TYPE
 957         && TREE_CODE (TREE_TYPE (TREE_TYPE (e))) == METHOD_TYPE)
 958        || integer_zerop (e)
 959        || TYPE_PTRMEMFUNC_P (TREE_TYPE (e)))
 960       && TYPE_PTRMEMFUNC_P (type))
 961     {
 962       /* compatible pointer to member functions.  */
 963       return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), e, 1);
 964     }
 965
 966   return ocp_convert (type, e, CONV_C_CAST|convtype, LOOKUP_NORMAL);
 967 }
 968
 969 /* Convert an aggregate EXPR to type XTYPE.  If a conversion
 970    exists, return the attempted conversion.  This may
 971    return ERROR_MARK_NODE if the conversion is not
 972    allowed (references private members, etc).
 973    If no conversion exists, NULL_TREE is returned.
 974
 975    FIXME: Ambiguity checking is wrong.  Should choose one by the implicit
 976    object parameter, or by the second standard conversion sequence if
 977    that doesn't do it.  This will probably wait for an overloading rewrite.
 978    (jason 8/9/95)  */
 979
 980 tree
 981 build_type_conversion (tree xtype, tree expr)
 982 {
 983   /* C++: check to see if we can convert this aggregate type
 984      into the required type.  */
 985   return build_user_type_conversion (xtype, expr, LOOKUP_NORMAL);
 986 }
 987
 988 /* Convert the given EXPR to one of a group of types suitable for use in an
 989    expression.  DESIRES is a combination of various WANT_* flags (q.v.)
 990    which indicates which types are suitable.  If COMPLAIN is true, complain
 991    about ambiguity; otherwise, the caller will deal with it.  */
 992
 993 tree
 994 build_expr_type_conversion (int desires, tree expr, bool complain)
 995 {
 996   tree basetype = TREE_TYPE (expr);
 997   tree conv = NULL_TREE;
 998   tree winner = NULL_TREE;
 999
1000   if (expr == null_node
1001       && (desires & WANT_INT)
1002       && !(desires & WANT_NULL))
1003     warning ("converting NULL to non-pointer type");
1004
1005   expr = convert_from_reference (expr);
1006   basetype = TREE_TYPE (expr);
1007
1008   if (basetype == error_mark_node)
1009     return error_mark_node;
1010
1011   if (! IS_AGGR_TYPE (basetype))
1012     switch (TREE_CODE (basetype))
1013       {
1014       case INTEGER_TYPE:
1015         if ((desires & WANT_NULL) && null_ptr_cst_p (expr))
1016           return expr;
1017         /* else fall through...  */
1018
1019       case BOOLEAN_TYPE:
1020         return (desires & WANT_INT) ? expr : NULL_TREE;
1021       case ENUMERAL_TYPE:
1022         return (desires & WANT_ENUM) ? expr : NULL_TREE;
1023       case REAL_TYPE:
1024         return (desires & WANT_FLOAT) ? expr : NULL_TREE;
1025       case POINTER_TYPE:
1026         return (desires & WANT_POINTER) ? expr : NULL_TREE;
1027
1028       case FUNCTION_TYPE:
1029       case ARRAY_TYPE:
1030         return (desires & WANT_POINTER) ? decay_conversion (expr)
1031                                         : NULL_TREE;
1032       default:
1033         return NULL_TREE;
1034       }
1035
1036   /* The code for conversions from class type is currently only used for
1037      delete expressions.  Other expressions are handled by build_new_op.  */
1038   if (!complete_type_or_else (basetype, expr))
1039     return error_mark_node;
1040   if (!TYPE_HAS_CONVERSION (basetype))
1041     return NULL_TREE;
1042
1043   for (conv = lookup_conversions (basetype); conv; conv = TREE_CHAIN (conv))
1044     {
1045       int win = 0;
1046       tree candidate;
1047       tree cand = TREE_VALUE (conv);
1048
1049       if (winner && winner == cand)
1050         continue;
1051
1052       candidate = non_reference (TREE_TYPE (TREE_TYPE (cand)));
1053
1054       switch (TREE_CODE (candidate))
1055         {
1056         case BOOLEAN_TYPE:
1057         case INTEGER_TYPE:
1058           win = (desires & WANT_INT); break;
1059         case ENUMERAL_TYPE:
1060           win = (desires & WANT_ENUM); break;
1061         case REAL_TYPE:
1062           win = (desires & WANT_FLOAT); break;
1063         case POINTER_TYPE:
1064           win = (desires & WANT_POINTER); break;
1065
1066         default:
1067           break;
1068         }
1069
1070       if (win)
1071         {
1072           if (winner)
1073             {
1074               if (complain)
1075                 {
1076                   error ("ambiguous default type conversion from `%T'",
1077                             basetype);
1078                   error ("  candidate conversions include `%D' and `%D'",
1079                             winner, cand);
1080                 }
1081               return error_mark_node;
1082             }
1083           else
1084             winner = cand;
1085         }
1086     }
1087
1088   if (winner)
1089     {
1090       tree type = non_reference (TREE_TYPE (TREE_TYPE (winner)));
1091       return build_user_type_conversion (type, expr, LOOKUP_NORMAL);
1092     }
1093
1094   return NULL_TREE;
1095 }
1096
1097 /* Implements integral promotion (4.1) and float->double promotion.  */
1098
1099 tree
1100 type_promotes_to (tree type)
1101 {
1102   if (type == error_mark_node)
1103     return error_mark_node;
1104
1105   type = TYPE_MAIN_VARIANT (type);
1106
1107   /* bool always promotes to int (not unsigned), even if it's the same
1108      size.  */
1109   if (type == boolean_type_node)
1110     type = integer_type_node;
1111
1112   /* Normally convert enums to int, but convert wide enums to something
1113      wider.  */
1114   else if (TREE_CODE (type) == ENUMERAL_TYPE
1115            || type == wchar_type_node)
1116     {
1117       int precision = MAX (TYPE_PRECISION (type),
1118                            TYPE_PRECISION (integer_type_node));
1119       tree totype = c_common_type_for_size (precision, 0);
1120       if (TYPE_UNSIGNED (type)
1121           && ! int_fits_type_p (TYPE_MAX_VALUE (type), totype))
1122         type = c_common_type_for_size (precision, 1);
1123       else
1124         type = totype;
1125     }
1126   else if (c_promoting_integer_type_p (type))
1127     {
1128       /* Retain unsignedness if really not getting bigger.  */
1129       if (TYPE_UNSIGNED (type)
1130           && TYPE_PRECISION (type) == TYPE_PRECISION (integer_type_node))
1131         type = unsigned_type_node;
1132       else
1133         type = integer_type_node;
1134     }
1135   else if (type == float_type_node)
1136     type = double_type_node;
1137
1138   return type;
1139 }
1140
1141 /* The routines below this point are carefully written to conform to
1142    the standard.  They use the same terminology, and follow the rules
1143    closely.  Although they are used only in pt.c at the moment, they
1144    should presumably be used everywhere in the future.  */
1145
1146 /* Attempt to perform qualification conversions on EXPR to convert it
1147    to TYPE.  Return the resulting expression, or error_mark_node if
1148    the conversion was impossible.  */
1149
1150 tree
1151 perform_qualification_conversions (tree type, tree expr)
1152 {
1153   tree expr_type;
1154
1155   expr_type = TREE_TYPE (expr);
1156
1157   if (TYPE_PTR_P (type) && TYPE_PTR_P (expr_type)
1158       && comp_ptr_ttypes (TREE_TYPE (type), TREE_TYPE (expr_type)))
1159     return build_nop (type, expr);
1160   else if (TYPE_PTR_TO_MEMBER_P (type)
1161            && TYPE_PTR_TO_MEMBER_P (expr_type)
1162            && same_type_p (TYPE_PTRMEM_CLASS_TYPE (type),
1163                            TYPE_PTRMEM_CLASS_TYPE (expr_type))
1164            && comp_ptr_ttypes (TYPE_PTRMEM_POINTED_TO_TYPE (type),
1165                                TYPE_PTRMEM_POINTED_TO_TYPE (expr_type)))
1166     return build_nop (type, expr);
1167   else
1168     return error_mark_node;
1169 }