gcc/cp/except.c

   1 /* Handle exceptional things in C++.
   2    Copyright (C) 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
   3    2000, 2001, 2002, 2003, 2004, 2005  Free Software Foundation, Inc.
   4    Contributed by Michael Tiemann <tiemann@cygnus.com>
   5    Rewritten by Mike Stump <mrs@cygnus.com>, based upon an
   6    initial re-implementation courtesy Tad Hunt.
   7
   8 This file is part of GCC.
   9
  10 GCC is free software; you can redistribute it and/or modify
  11 it under the terms of the GNU General Public License as published by
  12 the Free Software Foundation; either version 2, or (at your option)
  13 any later version.
  14
  15 GCC is distributed in the hope that it will be useful,
  16 but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 GNU General Public License for more details.
  19
  20 You should have received a copy of the GNU General Public License
  21 along with GCC; see the file COPYING.  If not, write to
  22 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  23 Boston, MA 02110-1301, USA.  */
  24
  25
  26 #include "config.h"
  27 #include "system.h"
  28 #include "coretypes.h"
  29 #include "tm.h"
  30 #include "tree.h"
  31 #include "rtl.h"
  32 #include "expr.h"
  33 #include "libfuncs.h"
  34 #include "cp-tree.h"
  35 #include "flags.h"
  36 #include "output.h"
  37 #include "except.h"
  38 #include "toplev.h"
  39 #include "tree-inline.h"
  40 #include "tree-iterator.h"
  41 #include "target.h"
  42
  43 static void push_eh_cleanup (tree);
  44 static tree prepare_eh_type (tree);
  45 static tree build_eh_type_type (tree);
  46 static tree do_begin_catch (void);
  47 static int dtor_nothrow (tree);
  48 static tree do_end_catch (tree);
  49 static bool decl_is_java_type (tree decl, int err);
  50 static void initialize_handler_parm (tree, tree);
  51 static tree do_allocate_exception (tree);
  52 static tree wrap_cleanups_r (tree *, int *, void *);
  53 static int complete_ptr_ref_or_void_ptr_p (tree, tree);
  54 static bool is_admissible_throw_operand (tree);
  55 static int can_convert_eh (tree, tree);
  56 static tree cp_protect_cleanup_actions (void);
  57
  58 /* Sets up all the global eh stuff that needs to be initialized at the
  59    start of compilation.  */
  60
  61 void
  62 init_exception_processing (void)
  63 {
  64   tree tmp;
  65
  66   /* void std::terminate (); */
  67   push_namespace (std_identifier);
  68   tmp = build_function_type (void_type_node, void_list_node);
  69   terminate_node = build_cp_library_fn_ptr ("terminate", tmp);
  70   TREE_THIS_VOLATILE (terminate_node) = 1;
  71   TREE_NOTHROW (terminate_node) = 1;
  72   pop_namespace ();
  73
  74   /* void __cxa_call_unexpected(void *); */
  75   tmp = tree_cons (NULL_TREE, ptr_type_node, void_list_node);
  76   tmp = build_function_type (void_type_node, tmp);
  77   call_unexpected_node
  78     = push_throw_library_fn (get_identifier ("__cxa_call_unexpected"), tmp);
  79
  80   eh_personality_libfunc = init_one_libfunc (USING_SJLJ_EXCEPTIONS
  81                                              ? "__gxx_personality_sj0"
  82                                              : "__gxx_personality_v0");
  83   if (targetm.arm_eabi_unwinder)
  84     unwind_resume_libfunc = init_one_libfunc ("__cxa_end_cleanup");
  85   else
  86     default_init_unwind_resume_libfunc ();
  87
  88   lang_eh_runtime_type = build_eh_type_type;
  89   lang_protect_cleanup_actions = &cp_protect_cleanup_actions;
  90 }
  91
  92 /* Returns an expression to be executed if an unhandled exception is
  93    propagated out of a cleanup region.  */
  94
  95 static tree
  96 cp_protect_cleanup_actions (void)
  97 {
  98   /* [except.terminate]
  99
 100      When the destruction of an object during stack unwinding exits
 101      using an exception ... void terminate(); is called.  */
 102   return build_call (terminate_node, NULL_TREE);
 103 }
 104
 105 static tree
 106 prepare_eh_type (tree type)
 107 {
 108   if (type == NULL_TREE)
 109     return type;
 110   if (type == error_mark_node)
 111     return error_mark_node;
 112
 113   /* peel back references, so they match.  */
 114   type = non_reference (type);
 115
 116   /* Peel off cv qualifiers.  */
 117   type = TYPE_MAIN_VARIANT (type);
 118
 119   return type;
 120 }
 121
 122 /* Return the type info for TYPE as used by EH machinery.  */
 123 tree
 124 eh_type_info (tree type)
 125 {
 126   tree exp;
 127
 128   if (type == NULL_TREE || type == error_mark_node)
 129     return type;
 130
 131   if (decl_is_java_type (type, 0))
 132     exp = build_java_class_ref (TREE_TYPE (type));
 133   else
 134     exp = get_tinfo_decl (type);
 135
 136   return exp;
 137 }
 138
 139 /* Build the address of a typeinfo decl for use in the runtime
 140    matching field of the exception model.  */
 141
 142 static tree
 143 build_eh_type_type (tree type)
 144 {
 145   tree exp = eh_type_info (type);
 146
 147   if (!exp)
 148     return NULL;
 149
 150   mark_used (exp);
 151
 152   return convert (ptr_type_node, build_address (exp));
 153 }
 154
 155 tree
 156 build_exc_ptr (void)
 157 {
 158   return build0 (EXC_PTR_EXPR, ptr_type_node);
 159 }
 160
 161 /* Build up a call to __cxa_get_exception_ptr so that we can build a
 162    copy constructor for the thrown object.  */
 163
 164 static tree
 165 do_get_exception_ptr (void)
 166 {
 167   tree fn;
 168
 169   fn = get_identifier ("__cxa_get_exception_ptr");
 170   if (!get_global_value_if_present (fn, &fn))
 171     {
 172       /* Declare void* __cxa_get_exception_ptr (void *).  */
 173       tree tmp = tree_cons (NULL_TREE, ptr_type_node, void_list_node);
 174       fn = push_library_fn (fn, build_function_type (ptr_type_node, tmp));
 175     }
 176
 177   return build_function_call (fn, tree_cons (NULL_TREE, build_exc_ptr (),
 178                                              NULL_TREE));
 179 }
 180
 181 /* Build up a call to __cxa_begin_catch, to tell the runtime that the
 182    exception has been handled.  */
 183
 184 static tree
 185 do_begin_catch (void)
 186 {
 187   tree fn;
 188
 189   fn = get_identifier ("__cxa_begin_catch");
 190   if (!get_global_value_if_present (fn, &fn))
 191     {
 192       /* Declare void* __cxa_begin_catch (void *).  */
 193       tree tmp = tree_cons (NULL_TREE, ptr_type_node, void_list_node);
 194       fn = push_library_fn (fn, build_function_type (ptr_type_node, tmp));
 195     }
 196
 197   return build_function_call (fn, tree_cons (NULL_TREE, build_exc_ptr (),
 198                                              NULL_TREE));
 199 }
 200
 201 /* Returns nonzero if cleaning up an exception of type TYPE (which can be
 202    NULL_TREE for a ... handler) will not throw an exception.  */
 203
 204 static int
 205 dtor_nothrow (tree type)
 206 {
 207   if (type == NULL_TREE)
 208     return 0;
 209
 210   if (!CLASS_TYPE_P (type))
 211     return 1;
 212
 213   if (CLASSTYPE_LAZY_DESTRUCTOR (type))
 214     lazily_declare_fn (sfk_destructor, type);
 215
 216   return TREE_NOTHROW (CLASSTYPE_DESTRUCTORS (type));
 217 }
 218
 219 /* Build up a call to __cxa_end_catch, to destroy the exception object
 220    for the current catch block if no others are currently using it.  */
 221
 222 static tree
 223 do_end_catch (tree type)
 224 {
 225   tree fn, cleanup;
 226
 227   fn = get_identifier ("__cxa_end_catch");
 228   if (!get_global_value_if_present (fn, &fn))
 229     {
 230       /* Declare void __cxa_end_catch ().  */
 231       fn = push_void_library_fn (fn, void_list_node);
 232       /* This can throw if the destructor for the exception throws.  */
 233       TREE_NOTHROW (fn) = 0;
 234     }
 235
 236   cleanup = build_function_call (fn, NULL_TREE);
 237   TREE_NOTHROW (cleanup) = dtor_nothrow (type);
 238
 239   return cleanup;
 240 }
 241
 242 /* This routine creates the cleanup for the current exception.  */
 243
 244 static void
 245 push_eh_cleanup (tree type)
 246 {
 247   finish_decl_cleanup (NULL_TREE, do_end_catch (type));
 248 }
 249
 250 /* Return nonzero value if DECL is a Java type suitable for catch or
 251    throw.  */
 252
 253 static bool
 254 decl_is_java_type (tree decl, int err)
 255 {
 256   bool r = (TREE_CODE (decl) == POINTER_TYPE
 257             && TREE_CODE (TREE_TYPE (decl)) == RECORD_TYPE
 258             && TYPE_FOR_JAVA (TREE_TYPE (decl)));
 259
 260   if (err)
 261     {
 262       if (TREE_CODE (decl) == REFERENCE_TYPE
 263           && TREE_CODE (TREE_TYPE (decl)) == RECORD_TYPE
 264           && TYPE_FOR_JAVA (TREE_TYPE (decl)))
 265         {
 266           /* Can't throw a reference.  */
 267           error ("type %qT is disallowed in Java %<throw%> or %<catch%>",
 268                  decl);
 269         }
 270
 271       if (r)
 272         {
 273           tree jthrow_node
 274             = IDENTIFIER_GLOBAL_VALUE (get_identifier ("jthrowable"));
 275
 276           if (jthrow_node == NULL_TREE)
 277             fatal_error
 278               ("call to Java %<catch%> or %<throw%> with %<jthrowable%> undefined");
 279
 280           jthrow_node = TREE_TYPE (TREE_TYPE (jthrow_node));
 281
 282           if (! DERIVED_FROM_P (jthrow_node, TREE_TYPE (decl)))
 283             {
 284               /* Thrown object must be a Throwable.  */
 285               error ("type %qT is not derived from %<java::lang::Throwable%>",
 286                      TREE_TYPE (decl));
 287             }
 288         }
 289     }
 290
 291   return r;
 292 }
 293
 294 /* Select the personality routine to be used for exception handling,
 295    or issue an error if we need two different ones in the same
 296    translation unit.
 297    ??? At present eh_personality_libfunc is set to
 298    __gxx_personality_(sj|v)0 in init_exception_processing - should it
 299    be done here instead?  */
 300 void
 301 choose_personality_routine (enum languages lang)
 302 {
 303   static enum {
 304     chose_none,
 305     chose_cpp,
 306     chose_java,
 307     gave_error
 308   } state;
 309
 310   switch (state)
 311     {
 312     case gave_error:
 313       return;
 314
 315     case chose_cpp:
 316       if (lang != lang_cplusplus)
 317         goto give_error;
 318       return;
 319
 320     case chose_java:
 321       if (lang != lang_java)
 322         goto give_error;
 323       return;
 324
 325     case chose_none:
 326       ; /* Proceed to language selection.  */
 327     }
 328
 329   switch (lang)
 330     {
 331     case lang_cplusplus:
 332       state = chose_cpp;
 333       break;
 334
 335     case lang_java:
 336       state = chose_java;
 337       eh_personality_libfunc = init_one_libfunc (USING_SJLJ_EXCEPTIONS
 338                                                  ? "__gcj_personality_sj0"
 339                                                  : "__gcj_personality_v0");
 340       break;
 341
 342     default:
 343       gcc_unreachable ();
 344     }
 345   return;
 346
 347  give_error:
 348   error ("mixing C++ and Java catches in a single translation unit");
 349   state = gave_error;
 350 }
 351
 352 /* Initialize the catch parameter DECL.  */
 353
 354 static void
 355 initialize_handler_parm (tree decl, tree exp)
 356 {
 357   tree init;
 358   tree init_type;
 359
 360   /* Make sure we mark the catch param as used, otherwise we'll get a
 361      warning about an unused ((anonymous)).  */
 362   TREE_USED (decl) = 1;
 363
 364   /* Figure out the type that the initializer is.  Pointers are returned
 365      adjusted by value from __cxa_begin_catch.  Others are returned by
 366      reference.  */
 367   init_type = TREE_TYPE (decl);
 368   if (!POINTER_TYPE_P (init_type))
 369     init_type = build_reference_type (init_type);
 370
 371   choose_personality_routine (decl_is_java_type (init_type, 0)
 372                               ? lang_java : lang_cplusplus);
 373
 374   /* Since pointers are passed by value, initialize a reference to
 375      pointer catch parm with the address of the temporary.  */
 376   if (TREE_CODE (init_type) == REFERENCE_TYPE
 377       && TYPE_PTR_P (TREE_TYPE (init_type)))
 378     exp = build_unary_op (ADDR_EXPR, exp, 1);
 379
 380   exp = ocp_convert (init_type, exp, CONV_IMPLICIT|CONV_FORCE_TEMP, 0);
 381
 382   init = convert_from_reference (exp);
 383
 384   /* If the constructor for the catch parm exits via an exception, we
 385      must call terminate.  See eh23.C.  */
 386   if (TYPE_NEEDS_CONSTRUCTING (TREE_TYPE (decl)))
 387     {
 388       /* Generate the copy constructor call directly so we can wrap it.
 389          See also expand_default_init.  */
 390       init = ocp_convert (TREE_TYPE (decl), init,
 391                           CONV_IMPLICIT|CONV_FORCE_TEMP, 0);
 392       init = build1 (MUST_NOT_THROW_EXPR, TREE_TYPE (init), init);
 393     }
 394
 395   decl = pushdecl (decl);
 396
 397   start_decl_1 (decl, true);
 398   cp_finish_decl (decl, init, /*init_const_expr_p=*/false, NULL_TREE,
 399                   LOOKUP_ONLYCONVERTING|DIRECT_BIND);
 400 }
 401
 402 /* Call this to start a catch block.  DECL is the catch parameter.  */
 403
 404 tree
 405 expand_start_catch_block (tree decl)
 406 {
 407   tree exp;
 408   tree type;
 409
 410   if (! doing_eh (1))
 411     return NULL_TREE;
 412
 413   /* Make sure this declaration is reasonable.  */
 414   if (decl && !complete_ptr_ref_or_void_ptr_p (TREE_TYPE (decl), NULL_TREE))
 415     decl = error_mark_node;
 416
 417   if (decl)
 418     type = prepare_eh_type (TREE_TYPE (decl));
 419   else
 420     type = NULL_TREE;
 421
 422   if (decl && decl_is_java_type (type, 1))
 423     {
 424       /* Java only passes object via pointer and doesn't require
 425          adjusting.  The java object is immediately before the
 426          generic exception header.  */
 427       exp = build_exc_ptr ();
 428       exp = build1 (NOP_EXPR, build_pointer_type (type), exp);
 429       exp = build2 (MINUS_EXPR, TREE_TYPE (exp), exp,
 430                     TYPE_SIZE_UNIT (TREE_TYPE (exp)));
 431       exp = build_indirect_ref (exp, NULL);
 432       initialize_handler_parm (decl, exp);
 433       return type;
 434     }
 435
 436   /* Call __cxa_end_catch at the end of processing the exception.  */
 437   push_eh_cleanup (type);
 438
 439   /* If there's no decl at all, then all we need to do is make sure
 440      to tell the runtime that we've begun handling the exception.  */
 441   if (decl == NULL || decl == error_mark_node)
 442     finish_expr_stmt (do_begin_catch ());
 443
 444   /* If the C++ object needs constructing, we need to do that before
 445      calling __cxa_begin_catch, so that std::uncaught_exception gets
 446      the right value during the copy constructor.  */
 447   else if (flag_use_cxa_get_exception_ptr
 448            && TYPE_NEEDS_CONSTRUCTING (TREE_TYPE (decl)))
 449     {
 450       exp = do_get_exception_ptr ();
 451       initialize_handler_parm (decl, exp);
 452       finish_expr_stmt (do_begin_catch ());
 453     }
 454
 455   /* Otherwise the type uses a bitwise copy, and we don't have to worry
 456      about the value of std::uncaught_exception and therefore can do the
 457      copy with the return value of __cxa_end_catch instead.  */
 458   else
 459     {
 460       tree init = do_begin_catch ();
 461       tree init_type = type;
 462
 463       /* Pointers are passed by values, everything else by reference.  */
 464       if (!TYPE_PTR_P (type))
 465         init_type = build_pointer_type (type);
 466       if (init_type != TREE_TYPE (init))
 467         init = build1 (NOP_EXPR, init_type, init);
 468       exp = create_temporary_var (init_type);
 469       DECL_REGISTER (exp) = 1;
 470       cp_finish_decl (exp, init, /*init_const_expr=*/false,
 471                       NULL_TREE, LOOKUP_ONLYCONVERTING);
 472       initialize_handler_parm (decl, exp);
 473     }
 474
 475   return type;
 476 }
 477
 478
 479 /* Call this to end a catch block.  Its responsible for emitting the
 480    code to handle jumping back to the correct place, and for emitting
 481    the label to jump to if this catch block didn't match.  */
 482
 483 void
 484 expand_end_catch_block (void)
 485 {
 486   if (! doing_eh (1))
 487     return;
 488
 489   /* The exception being handled is rethrown if control reaches the end of
 490      a handler of the function-try-block of a constructor or destructor.  */
 491   if (in_function_try_handler
 492       && (DECL_CONSTRUCTOR_P (current_function_decl)
 493           || DECL_DESTRUCTOR_P (current_function_decl)))
 494     finish_expr_stmt (build_throw (NULL_TREE));
 495 }
 496
 497 tree
 498 begin_eh_spec_block (void)
 499 {
 500   tree r = build_stmt (EH_SPEC_BLOCK, NULL_TREE, NULL_TREE);
 501   add_stmt (r);
 502   EH_SPEC_STMTS (r) = push_stmt_list ();
 503   return r;
 504 }
 505
 506 void
 507 finish_eh_spec_block (tree raw_raises, tree eh_spec_block)
 508 {
 509   tree raises;
 510
 511   EH_SPEC_STMTS (eh_spec_block) = pop_stmt_list (EH_SPEC_STMTS (eh_spec_block));
 512
 513   /* Strip cv quals, etc, from the specification types.  */
 514   for (raises = NULL_TREE;
 515        raw_raises && TREE_VALUE (raw_raises);
 516        raw_raises = TREE_CHAIN (raw_raises))
 517     {
 518       tree type = prepare_eh_type (TREE_VALUE (raw_raises));
 519       tree tinfo = eh_type_info (type);
 520
 521       mark_used (tinfo);
 522       raises = tree_cons (NULL_TREE, type, raises);
 523     }
 524
 525   EH_SPEC_RAISES (eh_spec_block) = raises;
 526 }
 527
 528 /* Return a pointer to a buffer for an exception object of type TYPE.  */
 529
 530 static tree
 531 do_allocate_exception (tree type)
 532 {
 533   tree fn;
 534
 535   fn = get_identifier ("__cxa_allocate_exception");
 536   if (!get_global_value_if_present (fn, &fn))
 537     {
 538       /* Declare void *__cxa_allocate_exception(size_t).  */
 539       tree tmp = tree_cons (NULL_TREE, size_type_node, void_list_node);
 540       fn = push_library_fn (fn, build_function_type (ptr_type_node, tmp));
 541     }
 542
 543   return build_function_call (fn, tree_cons (NULL_TREE, size_in_bytes (type),
 544                                              NULL_TREE));
 545 }
 546
 547 /* Call __cxa_free_exception from a cleanup.  This is never invoked
 548    directly, but see the comment for stabilize_throw_expr.  */
 549
 550 static tree
 551 do_free_exception (tree ptr)
 552 {
 553   tree fn;
 554
 555   fn = get_identifier ("__cxa_free_exception");
 556   if (!get_global_value_if_present (fn, &fn))
 557     {
 558       /* Declare void __cxa_free_exception (void *).  */
 559       fn = push_void_library_fn (fn, tree_cons (NULL_TREE, ptr_type_node,
 560                                                 void_list_node));
 561     }
 562
 563   return build_function_call (fn, tree_cons (NULL_TREE, ptr, NULL_TREE));
 564 }
 565
 566 /* Wrap all cleanups for TARGET_EXPRs in MUST_NOT_THROW_EXPR.
 567    Called from build_throw via walk_tree_without_duplicates.  */
 568
 569 static tree
 570 wrap_cleanups_r (tree *tp, int *walk_subtrees ATTRIBUTE_UNUSED,
 571                  void *data ATTRIBUTE_UNUSED)
 572 {
 573   tree exp = *tp;
 574   tree cleanup;
 575
 576   /* Don't walk into types.  */
 577   if (TYPE_P (exp))
 578     {
 579       *walk_subtrees = 0;
 580       return NULL_TREE;
 581     }
 582   if (TREE_CODE (exp) != TARGET_EXPR)
 583     return NULL_TREE;
 584
 585   cleanup = TARGET_EXPR_CLEANUP (exp);
 586   if (cleanup)
 587     {
 588       cleanup = build1 (MUST_NOT_THROW_EXPR, void_type_node, cleanup);
 589       TARGET_EXPR_CLEANUP (exp) = cleanup;
 590     }
 591
 592   /* Keep iterating.  */
 593   return NULL_TREE;
 594 }
 595
 596 /* Build a throw expression.  */
 597
 598 tree
 599 build_throw (tree exp)
 600 {
 601   tree fn;
 602
 603   if (exp == error_mark_node)
 604     return exp;
 605
 606   if (processing_template_decl)
 607     {
 608       if (cfun)
 609         current_function_returns_abnormally = 1;
 610       return build_min (THROW_EXPR, void_type_node, exp);
 611     }
 612
 613   if (exp == null_node)
 614     warning (0, "throwing NULL, which has integral, not pointer type");
 615
 616   if (exp != NULL_TREE)
 617     {
 618       if (!is_admissible_throw_operand (exp))
 619         return error_mark_node;
 620     }
 621
 622   if (! doing_eh (1))
 623     return error_mark_node;
 624
 625   if (exp && decl_is_java_type (TREE_TYPE (exp), 1))
 626     {
 627       tree fn = get_identifier ("_Jv_Throw");
 628       if (!get_global_value_if_present (fn, &fn))
 629         {
 630           /* Declare void _Jv_Throw (void *).  */
 631           tree tmp = tree_cons (NULL_TREE, ptr_type_node, void_list_node);
 632           tmp = build_function_type (ptr_type_node, tmp);
 633           fn = push_throw_library_fn (fn, tmp);
 634         }
 635       else if (really_overloaded_fn (fn))
 636         {
 637           error ("%qD should never be overloaded", fn);
 638           return error_mark_node;
 639         }
 640       fn = OVL_CURRENT (fn);
 641       exp = build_function_call (fn, tree_cons (NULL_TREE, exp, NULL_TREE));
 642     }
 643   else if (exp)
 644     {
 645       tree throw_type;
 646       tree temp_type;
 647       tree cleanup;
 648       tree object, ptr;
 649       tree tmp;
 650       tree temp_expr, allocate_expr;
 651       bool elided;
 652
 653       /* The CLEANUP_TYPE is the internal type of a destructor.  */
 654       if (!cleanup_type)
 655         {
 656           tmp = void_list_node;
 657           tmp = tree_cons (NULL_TREE, ptr_type_node, tmp);
 658           tmp = build_function_type (void_type_node, tmp);
 659           cleanup_type = build_pointer_type (tmp);
 660         }
 661
 662       fn = get_identifier ("__cxa_throw");
 663       if (!get_global_value_if_present (fn, &fn))
 664         {
 665           /* Declare void __cxa_throw (void*, void*, void (*)(void*)).  */
 666           /* ??? Second argument is supposed to be "std::type_info*".  */
 667           tmp = void_list_node;
 668           tmp = tree_cons (NULL_TREE, cleanup_type, tmp);
 669           tmp = tree_cons (NULL_TREE, ptr_type_node, tmp);
 670           tmp = tree_cons (NULL_TREE, ptr_type_node, tmp);
 671           tmp = build_function_type (void_type_node, tmp);
 672           fn = push_throw_library_fn (fn, tmp);
 673         }
 674
 675       /* [except.throw]
 676
 677          A throw-expression initializes a temporary object, the type
 678          of which is determined by removing any top-level
 679          cv-qualifiers from the static type of the operand of throw
 680          and adjusting the type from "array of T" or "function return
 681          T" to "pointer to T" or "pointer to function returning T"
 682          respectively.  */
 683       temp_type = is_bitfield_expr_with_lowered_type (exp);
 684       if (!temp_type)
 685         temp_type = type_decays_to (TYPE_MAIN_VARIANT (TREE_TYPE (exp)));
 686
 687       /* OK, this is kind of wacky.  The standard says that we call
 688          terminate when the exception handling mechanism, after
 689          completing evaluation of the expression to be thrown but
 690          before the exception is caught (_except.throw_), calls a
 691          user function that exits via an uncaught exception.
 692
 693          So we have to protect the actual initialization of the
 694          exception object with terminate(), but evaluate the
 695          expression first.  Since there could be temps in the
 696          expression, we need to handle that, too.  We also expand
 697          the call to __cxa_allocate_exception first (which doesn't
 698          matter, since it can't throw).  */
 699
 700       /* Allocate the space for the exception.  */
 701       allocate_expr = do_allocate_exception (temp_type);
 702       allocate_expr = get_target_expr (allocate_expr);
 703       ptr = TARGET_EXPR_SLOT (allocate_expr);
 704       object = build_nop (build_pointer_type (temp_type), ptr);
 705       object = build_indirect_ref (object, NULL);
 706
 707       elided = (TREE_CODE (exp) == TARGET_EXPR);
 708
 709       /* And initialize the exception object.  */
 710       if (CLASS_TYPE_P (temp_type))
 711         {
 712           /* Call the copy constructor.  */
 713           exp = (build_special_member_call
 714                  (object, complete_ctor_identifier,
 715                   build_tree_list (NULL_TREE, exp),
 716                   TREE_TYPE (object),
 717                   LOOKUP_NORMAL | LOOKUP_ONLYCONVERTING));
 718           if (exp == error_mark_node)
 719             {
 720               error ("  in thrown expression");
 721               return error_mark_node;
 722             }
 723         }
 724       else
 725         exp = build2 (INIT_EXPR, temp_type, object,
 726                       decay_conversion (exp));
 727
 728       /* Pre-evaluate the thrown expression first, since if we allocated
 729          the space first we would have to deal with cleaning it up if
 730          evaluating this expression throws.
 731
 732          The case where EXP the initializer is a cast or a function
 733          returning a class is a bit of a grey area in the standard; it's
 734          unclear whether or not it should be allowed to throw.  We used to
 735          say no, as that allowed us to optimize this case without worrying
 736          about deallocating the exception object if it does.  But that
 737          conflicted with expectations (PR 13944) and the EDG compiler; now
 738          we wrap the initialization in a TRY_CATCH_EXPR to call
 739          do_free_exception rather than in a MUST_NOT_THROW_EXPR, for this
 740          case only.
 741
 742          BUT: Issue 475 may do away with this inconsistency by removing the
 743          terminate() in this situation.
 744
 745          Note that we don't check the return value from stabilize_init
 746          because it will only return false in cases where elided is true,
 747          and therefore we don't need to work around the failure to
 748          preevaluate.  */
 749       temp_expr = NULL_TREE;
 750       stabilize_init (exp, &temp_expr);
 751
 752       /* Wrap the initialization in a CLEANUP_POINT_EXPR so that cleanups
 753          for temporaries within the initialization are run before the one
 754          for the exception object, preserving LIFO order.  */
 755       exp = build1 (CLEANUP_POINT_EXPR, void_type_node, exp);
 756
 757       if (elided)
 758         exp = build2 (TRY_CATCH_EXPR, void_type_node, exp,
 759                       do_free_exception (ptr));
 760       else
 761         exp = build1 (MUST_NOT_THROW_EXPR, void_type_node, exp);
 762
 763       /* Prepend the allocation.  */
 764       exp = build2 (COMPOUND_EXPR, TREE_TYPE (exp), allocate_expr, exp);
 765       if (temp_expr)
 766         {
 767           /* Prepend the calculation of the throw expression.  Also, force
 768              any cleanups from the expression to be evaluated here so that
 769              we don't have to do them during unwinding.  But first wrap
 770              them in MUST_NOT_THROW_EXPR, since they are run after the
 771              exception object is initialized.  */
 772           walk_tree_without_duplicates (&temp_expr, wrap_cleanups_r, 0);
 773           exp = build2 (COMPOUND_EXPR, TREE_TYPE (exp), temp_expr, exp);
 774           exp = build1 (CLEANUP_POINT_EXPR, TREE_TYPE (exp), exp);
 775         }
 776
 777       throw_type = build_eh_type_type (prepare_eh_type (TREE_TYPE (object)));
 778
 779       if (TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (object)))
 780         {
 781           cleanup = lookup_fnfields (TYPE_BINFO (TREE_TYPE (object)),
 782                                      complete_dtor_identifier, 0);
 783           cleanup = BASELINK_FUNCTIONS (cleanup);
 784           mark_used (cleanup);
 785           cxx_mark_addressable (cleanup);
 786           /* Pretend it's a normal function.  */
 787           cleanup = build1 (ADDR_EXPR, cleanup_type, cleanup);
 788         }
 789       else
 790         cleanup = build_int_cst (cleanup_type, 0);
 791
 792       tmp = tree_cons (NULL_TREE, cleanup, NULL_TREE);
 793       tmp = tree_cons (NULL_TREE, throw_type, tmp);
 794       tmp = tree_cons (NULL_TREE, ptr, tmp);
 795       /* ??? Indicate that this function call throws throw_type.  */
 796       tmp = build_function_call (fn, tmp);
 797
 798       /* Tack on the initialization stuff.  */
 799       exp = build2 (COMPOUND_EXPR, TREE_TYPE (tmp), exp, tmp);
 800     }
 801   else
 802     {
 803       /* Rethrow current exception.  */
 804
 805       tree fn = get_identifier ("__cxa_rethrow");
 806       if (!get_global_value_if_present (fn, &fn))
 807         {
 808           /* Declare void __cxa_rethrow (void).  */
 809           fn = push_throw_library_fn
 810             (fn, build_function_type (void_type_node, void_list_node));
 811         }
 812
 813       /* ??? Indicate that this function call allows exceptions of the type
 814          of the enclosing catch block (if known).  */
 815       exp = build_function_call (fn, NULL_TREE);
 816     }
 817
 818   exp = build1 (THROW_EXPR, void_type_node, exp);
 819
 820   return exp;
 821 }
 822
 823 /* Make sure TYPE is complete, pointer to complete, reference to
 824    complete, or pointer to cv void. Issue diagnostic on failure.
 825    Return the zero on failure and nonzero on success. FROM can be
 826    the expr or decl from whence TYPE came, if available.  */
 827
 828 static int
 829 complete_ptr_ref_or_void_ptr_p (tree type, tree from)
 830 {
 831   int is_ptr;
 832
 833   /* Check complete.  */
 834   type = complete_type_or_else (type, from);
 835   if (!type)
 836     return 0;
 837
 838   /* Or a pointer or ref to one, or cv void *.  */
 839   is_ptr = TREE_CODE (type) == POINTER_TYPE;
 840   if (is_ptr || TREE_CODE (type) == REFERENCE_TYPE)
 841     {
 842       tree core = TREE_TYPE (type);
 843
 844       if (is_ptr && VOID_TYPE_P (core))
 845         /* OK */;
 846       else if (!complete_type_or_else (core, from))
 847         return 0;
 848     }
 849   return 1;
 850 }
 851
 852 /* Return truth-value if EXPRESSION is admissible in throw-expression,
 853    i.e. if it is not of incomplete type or a pointer/reference to such
 854    a type or of an abstract class type.  */
 855
 856 static bool
 857 is_admissible_throw_operand (tree expr)
 858 {
 859   tree type = TREE_TYPE (expr);
 860
 861   /* 15.1/4 [...] The type of the throw-expression shall not be an
 862             incomplete type, or a pointer or a reference to an incomplete
 863             type, other than void*, const void*, volatile void*, or
 864             const volatile void*.  Except for these restriction and the
 865             restrictions on type matching mentioned in 15.3, the operand
 866             of throw is treated exactly as a function argument in a call
 867             (5.2.2) or the operand of a return statement.  */
 868   if (!complete_ptr_ref_or_void_ptr_p (type, expr))
 869     return false;
 870
 871   /* 10.4/3 An abstract class shall not be used as a parameter type,
 872             as a function return type or as type of an explicit
 873             conversion.  */
 874   else if (CLASS_TYPE_P (type) && CLASSTYPE_PURE_VIRTUALS (type))
 875     {
 876       error ("expression %qE of abstract class type %qT cannot "
 877              "be used in throw-expression", expr, type);
 878       return false;
 879     }
 880
 881   return true;
 882 }
 883
 884 /* Returns nonzero if FN is a declaration of a standard C library
 885    function which is known not to throw.
 886
 887    [lib.res.on.exception.handling]: None of the functions from the
 888    Standard C library shall report an error by throwing an
 889    exception, unless it calls a program-supplied function that
 890    throws an exception.  */
 891
 892 #include "cfns.h"
 893
 894 int
 895 nothrow_libfn_p (tree fn)
 896 {
 897   tree id;
 898
 899   if (TREE_PUBLIC (fn)
 900       && DECL_EXTERNAL (fn)
 901       && DECL_NAMESPACE_SCOPE_P (fn)
 902       && DECL_EXTERN_C_P (fn))
 903     /* OK */;
 904   else
 905     /* Can't be a C library function.  */
 906     return 0;
 907
 908   /* Being a C library function, DECL_ASSEMBLER_NAME == DECL_NAME
 909      unless the system headers are playing rename tricks, and if
 910      they are, we don't want to be confused by them.  */
 911   id = DECL_NAME (fn);
 912   return !!libc_name_p (IDENTIFIER_POINTER (id), IDENTIFIER_LENGTH (id));
 913 }
 914
 915 /* Returns nonzero if an exception of type FROM will be caught by a
 916    handler for type TO, as per [except.handle].  */
 917
 918 static int
 919 can_convert_eh (tree to, tree from)
 920 {
 921   to = non_reference (to);
 922   from = non_reference (from);
 923
 924   if (TREE_CODE (to) == POINTER_TYPE && TREE_CODE (from) == POINTER_TYPE)
 925     {
 926       to = TREE_TYPE (to);
 927       from = TREE_TYPE (from);
 928
 929       if (! at_least_as_qualified_p (to, from))
 930         return 0;
 931
 932       if (TREE_CODE (to) == VOID_TYPE)
 933         return 1;
 934
 935       /* Else fall through.  */
 936     }
 937
 938   if (CLASS_TYPE_P (to) && CLASS_TYPE_P (from)
 939       && PUBLICLY_UNIQUELY_DERIVED_P (to, from))
 940     return 1;
 941
 942   return 0;
 943 }
 944
 945 /* Check whether any of the handlers in I are shadowed by another handler
 946    accepting TYPE.  Note that the shadowing may not be complete; even if
 947    an exception of type B would be caught by a handler for A, there could
 948    be a derived class C for which A is an ambiguous base but B is not, so
 949    the handler for B would catch an exception of type C.  */
 950
 951 static void
 952 check_handlers_1 (tree master, tree_stmt_iterator i)
 953 {
 954   tree type = TREE_TYPE (master);
 955
 956   for (; !tsi_end_p (i); tsi_next (&i))
 957     {
 958       tree handler = tsi_stmt (i);
 959       if (TREE_TYPE (handler) && can_convert_eh (type, TREE_TYPE (handler)))
 960         {
 961           warning (0, "%Hexception of type %qT will be caught",
 962                    EXPR_LOCUS (handler), TREE_TYPE (handler));
 963           warning (0, "%H   by earlier handler for %qT",
 964                    EXPR_LOCUS (master), type);
 965           break;
 966         }
 967     }
 968 }
 969
 970 /* Given a STATEMENT_LIST of HANDLERs, make sure that they're OK.  */
 971
 972 void
 973 check_handlers (tree handlers)
 974 {
 975   tree_stmt_iterator i;
 976
 977   /* If we don't have a STATEMENT_LIST, then we've just got one
 978      handler, and thus nothing to warn about.  */
 979   if (TREE_CODE (handlers) != STATEMENT_LIST)
 980     return;
 981
 982   i = tsi_start (handlers);
 983   if (!tsi_end_p (i))
 984     while (1)
 985       {
 986         tree handler = tsi_stmt (i);
 987         tsi_next (&i);
 988
 989         /* No more handlers; nothing to shadow.  */
 990         if (tsi_end_p (i))
 991           break;
 992         if (TREE_TYPE (handler) == NULL_TREE)
 993           pedwarn ("%H%<...%> handler must be the last handler for"
 994                    " its try block", EXPR_LOCUS (handler));
 995         else
 996           check_handlers_1 (handler, i);
 997       }
 998 }