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 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   if (flags & LOOKUP_SPECULATIVELY)
 556     return NULL_TREE;
 557
 558   return error_mark_node;
 559 }
 560
 561 /* We are using a reference VAL for its value. Bash that reference all the
 562    way down to its lowest form.  */
 563
 564 tree
 565 convert_from_reference (tree val)
 566 {
 567   if (TREE_CODE (TREE_TYPE (val)) == REFERENCE_TYPE)
 568     return build_indirect_ref (val, NULL);
 569   return val;
 570 }
 571
 572 /* Implicitly convert the lvalue EXPR to another lvalue of type TOTYPE,
 573    preserving cv-qualification.  */
 574
 575 tree
 576 convert_lvalue (tree totype, tree expr)
 577 {
 578   totype = cp_build_qualified_type (totype, TYPE_QUALS (TREE_TYPE (expr)));
 579   totype = build_reference_type (totype);
 580   expr = convert_to_reference (totype, expr, CONV_IMPLICIT, LOOKUP_NORMAL,
 581                                NULL_TREE);
 582   return convert_from_reference (expr);
 583 }
 584
 585 /* Really perform an lvalue-to-rvalue conversion, including copying an
 586    argument of class type into a temporary.  */
 587
 588 tree
 589 force_rvalue (tree expr)
 590 {
 591   if (IS_AGGR_TYPE (TREE_TYPE (expr)) && TREE_CODE (expr) != TARGET_EXPR)
 592     expr = ocp_convert (TREE_TYPE (expr), expr,
 593                         CONV_IMPLICIT|CONV_FORCE_TEMP, LOOKUP_NORMAL);
 594   else
 595     expr = decay_conversion (expr);
 596
 597   return expr;
 598 }
 599 \f
 600 /* C++ conversions, preference to static cast conversions.  */
 601
 602 tree
 603 cp_convert (tree type, tree expr)
 604 {
 605   return ocp_convert (type, expr, CONV_OLD_CONVERT, LOOKUP_NORMAL);
 606 }
 607
 608 /* Conversion...
 609
 610    FLAGS indicates how we should behave.  */
 611
 612 tree
 613 ocp_convert (tree type, tree expr, int convtype, int flags)
 614 {
 615   tree e = expr;
 616   enum tree_code code = TREE_CODE (type);
 617
 618   if (error_operand_p (e) || type == error_mark_node)
 619     return error_mark_node;
 620
 621   complete_type (type);
 622   complete_type (TREE_TYPE (expr));
 623
 624   e = decl_constant_value (e);
 625
 626   if (IS_AGGR_TYPE (type) && (convtype & CONV_FORCE_TEMP)
 627       /* Some internal structures (vtable_entry_type, sigtbl_ptr_type)
 628          don't go through finish_struct, so they don't have the synthesized
 629          constructors.  So don't force a temporary.  */
 630       && TYPE_HAS_CONSTRUCTOR (type))
 631     /* We need a new temporary; don't take this shortcut.  */;
 632   else if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (e)))
 633     {
 634       if (same_type_p (type, TREE_TYPE (e)))
 635         /* The call to fold will not always remove the NOP_EXPR as
 636            might be expected, since if one of the types is a typedef;
 637            the comparison in fold is just equality of pointers, not a
 638            call to comptypes.  We don't call fold in this case because
 639            that can result in infinite recursion; fold will call
 640            convert, which will call ocp_convert, etc.  */
 641         return e;
 642       /* For complex data types, we need to perform componentwise
 643          conversion.  */
 644       else if (TREE_CODE (type) == COMPLEX_TYPE)
 645         return fold (convert_to_complex (type, e));
 646       else if (TREE_CODE (e) == TARGET_EXPR)
 647         {
 648           /* Don't build a NOP_EXPR of class type.  Instead, change the
 649              type of the temporary.  Only allow this for cv-qual changes,
 650              though.  */
 651           if (!same_type_p (TYPE_MAIN_VARIANT (TREE_TYPE (e)),
 652                             TYPE_MAIN_VARIANT (type)))
 653             abort ();
 654           TREE_TYPE (e) = TREE_TYPE (TARGET_EXPR_SLOT (e)) = type;
 655           return e;
 656         }
 657       else if (TREE_ADDRESSABLE (type))
 658         /* We shouldn't be treating objects of ADDRESSABLE type as rvalues.  */
 659         abort ();
 660       else
 661         return fold (build1 (NOP_EXPR, type, e));
 662     }
 663
 664   if (code == VOID_TYPE && (convtype & CONV_STATIC))
 665     {
 666       e = convert_to_void (e, /*implicit=*/NULL);
 667       return e;
 668     }
 669
 670   if (INTEGRAL_CODE_P (code))
 671     {
 672       tree intype = TREE_TYPE (e);
 673       /* enum = enum, enum = int, enum = float, (enum)pointer are all
 674          errors.  */
 675       if (TREE_CODE (type) == ENUMERAL_TYPE
 676           && ((ARITHMETIC_TYPE_P (intype) && ! (convtype & CONV_STATIC))
 677               || (TREE_CODE (intype) == POINTER_TYPE)))
 678         {
 679           pedwarn ("conversion from `%#T' to `%#T'", intype, type);
 680
 681           if (flag_pedantic_errors)
 682             return error_mark_node;
 683         }
 684       if (IS_AGGR_TYPE (intype))
 685         {
 686           tree rval;
 687           rval = build_type_conversion (type, e);
 688           if (rval)
 689             return rval;
 690           if (flags & LOOKUP_COMPLAIN)
 691             error ("`%#T' used where a `%T' was expected", intype, type);
 692           if (flags & LOOKUP_SPECULATIVELY)
 693             return NULL_TREE;
 694           return error_mark_node;
 695         }
 696       if (code == BOOLEAN_TYPE)
 697         return cp_truthvalue_conversion (e);
 698
 699       return fold (convert_to_integer (type, e));
 700     }
 701   if (POINTER_TYPE_P (type) || TYPE_PTR_TO_MEMBER_P (type))
 702     return fold (cp_convert_to_pointer (type, e, false));
 703   if (code == VECTOR_TYPE)
 704     return fold (convert_to_vector (type, e));
 705   if (code == REAL_TYPE || code == COMPLEX_TYPE)
 706     {
 707       if (IS_AGGR_TYPE (TREE_TYPE (e)))
 708         {
 709           tree rval;
 710           rval = build_type_conversion (type, e);
 711           if (rval)
 712             return rval;
 713           else
 714             if (flags & LOOKUP_COMPLAIN)
 715               error ("`%#T' used where a floating point value was expected",
 716                         TREE_TYPE (e));
 717         }
 718       if (code == REAL_TYPE)
 719         return fold (convert_to_real (type, e));
 720       else if (code == COMPLEX_TYPE)
 721         return fold (convert_to_complex (type, e));
 722     }
 723
 724   /* New C++ semantics:  since assignment is now based on
 725      memberwise copying,  if the rhs type is derived from the
 726      lhs type, then we may still do a conversion.  */
 727   if (IS_AGGR_TYPE_CODE (code))
 728     {
 729       tree dtype = TREE_TYPE (e);
 730       tree ctor = NULL_TREE;
 731
 732       dtype = TYPE_MAIN_VARIANT (dtype);
 733
 734       /* Conversion between aggregate types.  New C++ semantics allow
 735          objects of derived type to be cast to objects of base type.
 736          Old semantics only allowed this between pointers.
 737
 738          There may be some ambiguity between using a constructor
 739          vs. using a type conversion operator when both apply.  */
 740
 741       ctor = e;
 742
 743       if (abstract_virtuals_error (NULL_TREE, type))
 744         return error_mark_node;
 745
 746       if ((flags & LOOKUP_ONLYCONVERTING)
 747           && ! (IS_AGGR_TYPE (dtype) && DERIVED_FROM_P (type, dtype)))
 748         /* For copy-initialization, first we create a temp of the proper type
 749            with a user-defined conversion sequence, then we direct-initialize
 750            the target with the temp (see [dcl.init]).  */
 751         ctor = build_user_type_conversion (type, ctor, flags);
 752       else
 753         ctor = build_special_member_call (NULL_TREE,
 754                                           complete_ctor_identifier,
 755                                           build_tree_list (NULL_TREE, ctor),
 756                                           TYPE_BINFO (type), flags);
 757       if (ctor)
 758         return build_cplus_new (type, ctor);
 759     }
 760
 761   if (flags & LOOKUP_COMPLAIN)
 762     error ("conversion from `%T' to non-scalar type `%T' requested",
 763               TREE_TYPE (expr), type);
 764   if (flags & LOOKUP_SPECULATIVELY)
 765     return NULL_TREE;
 766   return error_mark_node;
 767 }
 768
 769 /* When an expression is used in a void context, its value is discarded and
 770    no lvalue-rvalue and similar conversions happen [expr.static.cast/4,
 771    stmt.expr/1, expr.comma/1].  This permits dereferencing an incomplete type
 772    in a void context. The C++ standard does not define what an `access' to an
 773    object is, but there is reason to believe that it is the lvalue to rvalue
 774    conversion -- if it were not, `*&*p = 1' would violate [expr]/4 in that it
 775    accesses `*p' not to calculate the value to be stored. But, dcl.type.cv/8
 776    indicates that volatile semantics should be the same between C and C++
 777    where ever possible. C leaves it implementation defined as to what
 778    constitutes an access to a volatile. So, we interpret `*vp' as a read of
 779    the volatile object `vp' points to, unless that is an incomplete type. For
 780    volatile references we do not do this interpretation, because that would
 781    make it impossible to ignore the reference return value from functions. We
 782    issue warnings in the confusing cases.
 783
 784    IMPLICIT is tells us the context of an implicit void conversion.  */
 785
 786 tree
 787 convert_to_void (tree expr, const char *implicit)
 788 {
 789   if (expr == error_mark_node
 790       || TREE_TYPE (expr) == error_mark_node)
 791     return error_mark_node;
 792   if (!TREE_TYPE (expr))
 793     return expr;
 794   if (VOID_TYPE_P (TREE_TYPE (expr)))
 795     return expr;
 796   switch (TREE_CODE (expr))
 797     {
 798     case COND_EXPR:
 799       {
 800         /* The two parts of a cond expr might be separate lvalues.  */
 801         tree op1 = TREE_OPERAND (expr,1);
 802         tree op2 = TREE_OPERAND (expr,2);
 803         tree new_op1 = convert_to_void
 804           (op1, (implicit && !TREE_SIDE_EFFECTS (op2)
 805                  ? "second operand of conditional" : NULL));
 806         tree new_op2 = convert_to_void
 807           (op2, (implicit && !TREE_SIDE_EFFECTS (op1)
 808                  ? "third operand of conditional" : NULL));
 809
 810         expr = build (COND_EXPR, TREE_TYPE (new_op1),
 811                       TREE_OPERAND (expr, 0), new_op1, new_op2);
 812         break;
 813       }
 814
 815     case COMPOUND_EXPR:
 816       {
 817         /* The second part of a compound expr contains the value.  */
 818         tree op1 = TREE_OPERAND (expr,1);
 819         tree new_op1 = convert_to_void
 820           (op1, (implicit && !TREE_NO_UNUSED_WARNING (expr)
 821                  ? "right-hand operand of comma" : NULL));
 822
 823         if (new_op1 != op1)
 824           {
 825             tree t = build (COMPOUND_EXPR, TREE_TYPE (new_op1),
 826                             TREE_OPERAND (expr, 0), new_op1);
 827             expr = t;
 828           }
 829
 830         break;
 831       }
 832
 833     case NON_LVALUE_EXPR:
 834     case NOP_EXPR:
 835       /* These have already decayed to rvalue.  */
 836       break;
 837
 838     case CALL_EXPR:   /* We have a special meaning for volatile void fn().  */
 839       break;
 840
 841     case INDIRECT_REF:
 842       {
 843         tree type = TREE_TYPE (expr);
 844         int is_reference = TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0)))
 845                            == REFERENCE_TYPE;
 846         int is_volatile = TYPE_VOLATILE (type);
 847         int is_complete = COMPLETE_TYPE_P (complete_type (type));
 848
 849         if (is_volatile && !is_complete)
 850           warning ("object of incomplete type `%T' will not be accessed in %s",
 851                       type, implicit ? implicit : "void context");
 852         else if (is_reference && is_volatile)
 853           warning ("object of type `%T' will not be accessed in %s",
 854                       TREE_TYPE (TREE_OPERAND (expr, 0)),
 855                       implicit ? implicit : "void context");
 856         if (is_reference || !is_volatile || !is_complete)
 857           expr = TREE_OPERAND (expr, 0);
 858
 859         break;
 860       }
 861
 862     case VAR_DECL:
 863       {
 864         /* External variables might be incomplete.  */
 865         tree type = TREE_TYPE (expr);
 866         int is_complete = COMPLETE_TYPE_P (complete_type (type));
 867
 868         if (TYPE_VOLATILE (type) && !is_complete)
 869           warning ("object `%E' of incomplete type `%T' will not be accessed in %s",
 870                       expr, type, implicit ? implicit : "void context");
 871         break;
 872       }
 873
 874     default:;
 875     }
 876   {
 877     tree probe = expr;
 878
 879     if (TREE_CODE (probe) == ADDR_EXPR)
 880       probe = TREE_OPERAND (expr, 0);
 881     if (type_unknown_p (probe))
 882       {
 883         /* [over.over] enumerates the places where we can take the address
 884            of an overloaded function, and this is not one of them.  */
 885         pedwarn ("%s cannot resolve address of overloaded function",
 886                     implicit ? implicit : "void cast");
 887         expr = void_zero_node;
 888       }
 889     else if (implicit && probe == expr && is_overloaded_fn (probe))
 890       /* Only warn when there is no &.  */
 891       warning ("%s is a reference, not call, to function `%E'",
 892                   implicit, expr);
 893   }
 894
 895   if (expr != error_mark_node && !VOID_TYPE_P (TREE_TYPE (expr)))
 896     {
 897       if (implicit && !TREE_SIDE_EFFECTS (expr) && warn_unused_value)
 898         warning ("%s has no effect", implicit);
 899       expr = build1 (CONVERT_EXPR, void_type_node, expr);
 900     }
 901   return expr;
 902 }
 903
 904 /* Create an expression whose value is that of EXPR,
 905    converted to type TYPE.  The TREE_TYPE of the value
 906    is always TYPE.  This function implements all reasonable
 907    conversions; callers should filter out those that are
 908    not permitted by the language being compiled.
 909
 910    Most of this routine is from build_reinterpret_cast.
 911
 912    The backend cannot call cp_convert (what was convert) because
 913    conversions to/from basetypes may involve memory references
 914    (vbases) and adding or subtracting small values (multiple
 915    inheritance), but it calls convert from the constant folding code
 916    on subtrees of already built trees after it has ripped them apart.
 917
 918    Also, if we ever support range variables, we'll probably also have to
 919    do a little bit more work.  */
 920
 921 tree
 922 convert (tree type, tree expr)
 923 {
 924   tree intype;
 925
 926   if (type == error_mark_node || expr == error_mark_node)
 927     return error_mark_node;
 928
 929   intype = TREE_TYPE (expr);
 930
 931   if (POINTER_TYPE_P (type) && POINTER_TYPE_P (intype))
 932     {
 933       expr = decl_constant_value (expr);
 934       return fold (build1 (NOP_EXPR, type, expr));
 935     }
 936
 937   return ocp_convert (type, expr, CONV_OLD_CONVERT,
 938                       LOOKUP_NORMAL|LOOKUP_NO_CONVERSION);
 939 }
 940
 941 /* Like cp_convert, except permit conversions to take place which
 942    are not normally allowed due to access restrictions
 943    (such as conversion from sub-type to private super-type).  */
 944
 945 tree
 946 convert_force (tree type, tree expr, int convtype)
 947 {
 948   tree e = expr;
 949   enum tree_code code = TREE_CODE (type);
 950
 951   if (code == REFERENCE_TYPE)
 952     return fold (convert_to_reference (type, e, CONV_C_CAST, LOOKUP_COMPLAIN,
 953                                        NULL_TREE));
 954   else if (TREE_CODE (TREE_TYPE (e)) == REFERENCE_TYPE)
 955     e = convert_from_reference (e);
 956
 957   if (code == POINTER_TYPE)
 958     return fold (convert_to_pointer_force (type, e));
 959
 960   /* From typeck.c convert_for_assignment */
 961   if (((TREE_CODE (TREE_TYPE (e)) == POINTER_TYPE && TREE_CODE (e) == ADDR_EXPR
 962         && TREE_CODE (TREE_TYPE (e)) == POINTER_TYPE
 963         && TREE_CODE (TREE_TYPE (TREE_TYPE (e))) == METHOD_TYPE)
 964        || integer_zerop (e)
 965        || TYPE_PTRMEMFUNC_P (TREE_TYPE (e)))
 966       && TYPE_PTRMEMFUNC_P (type))
 967     {
 968       /* compatible pointer to member functions.  */
 969       return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), e, 1);
 970     }
 971
 972   return ocp_convert (type, e, CONV_C_CAST|convtype, LOOKUP_NORMAL);
 973 }
 974
 975 /* Convert an aggregate EXPR to type XTYPE.  If a conversion
 976    exists, return the attempted conversion.  This may
 977    return ERROR_MARK_NODE if the conversion is not
 978    allowed (references private members, etc).
 979    If no conversion exists, NULL_TREE is returned.
 980
 981    FIXME: Ambiguity checking is wrong.  Should choose one by the implicit
 982    object parameter, or by the second standard conversion sequence if
 983    that doesn't do it.  This will probably wait for an overloading rewrite.
 984    (jason 8/9/95)  */
 985
 986 tree
 987 build_type_conversion (tree xtype, tree expr)
 988 {
 989   /* C++: check to see if we can convert this aggregate type
 990      into the required type.  */
 991   return build_user_type_conversion (xtype, expr, LOOKUP_NORMAL);
 992 }
 993
 994 /* Convert the given EXPR to one of a group of types suitable for use in an
 995    expression.  DESIRES is a combination of various WANT_* flags (q.v.)
 996    which indicates which types are suitable.  If COMPLAIN is true, complain
 997    about ambiguity; otherwise, the caller will deal with it.  */
 998
 999 tree
1000 build_expr_type_conversion (int desires, tree expr, bool complain)
1001 {
1002   tree basetype = TREE_TYPE (expr);
1003   tree conv = NULL_TREE;
1004   tree winner = NULL_TREE;
1005
1006   if (expr == null_node
1007       && (desires & WANT_INT)
1008       && !(desires & WANT_NULL))
1009     warning ("converting NULL to non-pointer type");
1010
1011   expr = convert_from_reference (expr);
1012   basetype = TREE_TYPE (expr);
1013
1014   if (basetype == error_mark_node)
1015     return error_mark_node;
1016
1017   if (! IS_AGGR_TYPE (basetype))
1018     switch (TREE_CODE (basetype))
1019       {
1020       case INTEGER_TYPE:
1021         if ((desires & WANT_NULL) && null_ptr_cst_p (expr))
1022           return expr;
1023         /* else fall through...  */
1024
1025       case BOOLEAN_TYPE:
1026         return (desires & WANT_INT) ? expr : NULL_TREE;
1027       case ENUMERAL_TYPE:
1028         return (desires & WANT_ENUM) ? expr : NULL_TREE;
1029       case REAL_TYPE:
1030         return (desires & WANT_FLOAT) ? expr : NULL_TREE;
1031       case POINTER_TYPE:
1032         return (desires & WANT_POINTER) ? expr : NULL_TREE;
1033
1034       case FUNCTION_TYPE:
1035       case ARRAY_TYPE:
1036         return (desires & WANT_POINTER) ? decay_conversion (expr)
1037                                         : NULL_TREE;
1038       default:
1039         return NULL_TREE;
1040       }
1041
1042   /* The code for conversions from class type is currently only used for
1043      delete expressions.  Other expressions are handled by build_new_op.  */
1044
1045   if (! TYPE_HAS_CONVERSION (basetype))
1046     return NULL_TREE;
1047
1048   for (conv = lookup_conversions (basetype); conv; conv = TREE_CHAIN (conv))
1049     {
1050       int win = 0;
1051       tree candidate;
1052       tree cand = TREE_VALUE (conv);
1053
1054       if (winner && winner == cand)
1055         continue;
1056
1057       candidate = non_reference (TREE_TYPE (TREE_TYPE (cand)));
1058
1059       switch (TREE_CODE (candidate))
1060         {
1061         case BOOLEAN_TYPE:
1062         case INTEGER_TYPE:
1063           win = (desires & WANT_INT); break;
1064         case ENUMERAL_TYPE:
1065           win = (desires & WANT_ENUM); break;
1066         case REAL_TYPE:
1067           win = (desires & WANT_FLOAT); break;
1068         case POINTER_TYPE:
1069           win = (desires & WANT_POINTER); break;
1070
1071         default:
1072           break;
1073         }
1074
1075       if (win)
1076         {
1077           if (winner)
1078             {
1079               if (complain)
1080                 {
1081                   error ("ambiguous default type conversion from `%T'",
1082                             basetype);
1083                   error ("  candidate conversions include `%D' and `%D'",
1084                             winner, cand);
1085                 }
1086               return error_mark_node;
1087             }
1088           else
1089             winner = cand;
1090         }
1091     }
1092
1093   if (winner)
1094     {
1095       tree type = non_reference (TREE_TYPE (TREE_TYPE (winner)));
1096       return build_user_type_conversion (type, expr, LOOKUP_NORMAL);
1097     }
1098
1099   return NULL_TREE;
1100 }
1101
1102 /* Implements integral promotion (4.1) and float->double promotion.  */
1103
1104 tree
1105 type_promotes_to (tree type)
1106 {
1107   if (type == error_mark_node)
1108     return error_mark_node;
1109
1110   type = TYPE_MAIN_VARIANT (type);
1111
1112   /* bool always promotes to int (not unsigned), even if it's the same
1113      size.  */
1114   if (type == boolean_type_node)
1115     type = integer_type_node;
1116
1117   /* Normally convert enums to int, but convert wide enums to something
1118      wider.  */
1119   else if (TREE_CODE (type) == ENUMERAL_TYPE
1120            || type == wchar_type_node)
1121     {
1122       int precision = MAX (TYPE_PRECISION (type),
1123                            TYPE_PRECISION (integer_type_node));
1124       tree totype = c_common_type_for_size (precision, 0);
1125       if (TREE_UNSIGNED (type)
1126           && ! int_fits_type_p (TYPE_MAX_VALUE (type), totype))
1127         type = c_common_type_for_size (precision, 1);
1128       else
1129         type = totype;
1130     }
1131   else if (c_promoting_integer_type_p (type))
1132     {
1133       /* Retain unsignedness if really not getting bigger.  */
1134       if (TREE_UNSIGNED (type)
1135           && TYPE_PRECISION (type) == TYPE_PRECISION (integer_type_node))
1136         type = unsigned_type_node;
1137       else
1138         type = integer_type_node;
1139     }
1140   else if (type == float_type_node)
1141     type = double_type_node;
1142
1143   return type;
1144 }
1145
1146 /* The routines below this point are carefully written to conform to
1147    the standard.  They use the same terminology, and follow the rules
1148    closely.  Although they are used only in pt.c at the moment, they
1149    should presumably be used everywhere in the future.  */
1150
1151 /* Attempt to perform qualification conversions on EXPR to convert it
1152    to TYPE.  Return the resulting expression, or error_mark_node if
1153    the conversion was impossible.  */
1154
1155 tree
1156 perform_qualification_conversions (tree type, tree expr)
1157 {
1158   tree expr_type;
1159
1160   expr_type = TREE_TYPE (expr);
1161
1162   if (TYPE_PTR_P (type) && TYPE_PTR_P (expr_type)
1163       && comp_ptr_ttypes (TREE_TYPE (type), TREE_TYPE (expr_type)))
1164     return build_nop (type, expr);
1165   else if (TYPE_PTR_TO_MEMBER_P (type)
1166            && TYPE_PTR_TO_MEMBER_P (expr_type)
1167            && same_type_p (TYPE_PTRMEM_CLASS_TYPE (type),
1168                            TYPE_PTRMEM_CLASS_TYPE (expr_type))
1169            && comp_ptr_ttypes (TYPE_PTRMEM_POINTED_TO_TYPE (type),
1170                                TYPE_PTRMEM_POINTED_TO_TYPE (expr_type)))
1171     return build_nop (type, expr);
1172   else
1173     return error_mark_node;
1174 }