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   /* Let `cp_finish_decl' know that this initializer is ok.  */
 396   DECL_INITIAL (decl) = error_mark_node;
 397   decl = pushdecl (decl);
 398
 399   start_decl_1 (decl);
 400   cp_finish_decl (decl, init, NULL_TREE,
 401                   LOOKUP_ONLYCONVERTING|DIRECT_BIND);
 402 }
 403
 404 /* Call this to start a catch block.  DECL is the catch parameter.  */
 405
 406 tree
 407 expand_start_catch_block (tree decl)
 408 {
 409   tree exp;
 410   tree type;
 411
 412   if (! doing_eh (1))
 413     return NULL_TREE;
 414
 415   /* Make sure this declaration is reasonable.  */
 416   if (decl && !complete_ptr_ref_or_void_ptr_p (TREE_TYPE (decl), NULL_TREE))
 417     decl = NULL_TREE;
 418
 419   if (decl)
 420     type = prepare_eh_type (TREE_TYPE (decl));
 421   else
 422     type = NULL_TREE;
 423
 424   if (decl && decl_is_java_type (type, 1))
 425     {
 426       /* Java only passes object via pointer and doesn't require
 427          adjusting.  The java object is immediately before the
 428          generic exception header.  */
 429       exp = build_exc_ptr ();
 430       exp = build1 (NOP_EXPR, build_pointer_type (type), exp);
 431       exp = build2 (MINUS_EXPR, TREE_TYPE (exp), exp,
 432                     TYPE_SIZE_UNIT (TREE_TYPE (exp)));
 433       exp = build_indirect_ref (exp, NULL);
 434       initialize_handler_parm (decl, exp);
 435       return type;
 436     }
 437
 438   /* Call __cxa_end_catch at the end of processing the exception.  */
 439   push_eh_cleanup (type);
 440
 441   /* If there's no decl at all, then all we need to do is make sure
 442      to tell the runtime that we've begun handling the exception.  */
 443   if (decl == NULL)
 444     finish_expr_stmt (do_begin_catch ());
 445
 446   /* If the C++ object needs constructing, we need to do that before
 447      calling __cxa_begin_catch, so that std::uncaught_exception gets
 448      the right value during the copy constructor.  */
 449   else if (TYPE_NEEDS_CONSTRUCTING (TREE_TYPE (decl)))
 450     {
 451       exp = do_get_exception_ptr ();
 452       initialize_handler_parm (decl, exp);
 453       finish_expr_stmt (do_begin_catch ());
 454     }
 455
 456   /* Otherwise the type uses a bitwise copy, and we don't have to worry
 457      about the value of std::uncaught_exception and therefore can do the
 458      copy with the return value of __cxa_end_catch instead.  */
 459   else
 460     {
 461       tree init = do_begin_catch ();
 462       exp = create_temporary_var (ptr_type_node);
 463       DECL_REGISTER (exp) = 1;
 464       cp_finish_decl (exp, init, NULL_TREE, LOOKUP_ONLYCONVERTING);
 465       finish_expr_stmt (build_modify_expr (exp, INIT_EXPR, init));
 466       initialize_handler_parm (decl, exp);
 467     }
 468
 469   return type;
 470 }
 471
 472
 473 /* Call this to end a catch block.  Its responsible for emitting the
 474    code to handle jumping back to the correct place, and for emitting
 475    the label to jump to if this catch block didn't match.  */
 476
 477 void
 478 expand_end_catch_block (void)
 479 {
 480   if (! doing_eh (1))
 481     return;
 482
 483   /* The exception being handled is rethrown if control reaches the end of
 484      a handler of the function-try-block of a constructor or destructor.  */
 485   if (in_function_try_handler
 486       && (DECL_CONSTRUCTOR_P (current_function_decl)
 487           || DECL_DESTRUCTOR_P (current_function_decl)))
 488     finish_expr_stmt (build_throw (NULL_TREE));
 489 }
 490
 491 tree
 492 begin_eh_spec_block (void)
 493 {
 494   tree r = build_stmt (EH_SPEC_BLOCK, NULL_TREE, NULL_TREE);
 495   add_stmt (r);
 496   EH_SPEC_STMTS (r) = push_stmt_list ();
 497   return r;
 498 }
 499
 500 void
 501 finish_eh_spec_block (tree raw_raises, tree eh_spec_block)
 502 {
 503   tree raises;
 504
 505   EH_SPEC_STMTS (eh_spec_block) = pop_stmt_list (EH_SPEC_STMTS (eh_spec_block));
 506
 507   /* Strip cv quals, etc, from the specification types.  */
 508   for (raises = NULL_TREE;
 509        raw_raises && TREE_VALUE (raw_raises);
 510        raw_raises = TREE_CHAIN (raw_raises))
 511     {
 512       tree type = prepare_eh_type (TREE_VALUE (raw_raises));
 513       tree tinfo = eh_type_info (type);
 514
 515       mark_used (tinfo);
 516       raises = tree_cons (NULL_TREE, type, raises);
 517     }
 518
 519   EH_SPEC_RAISES (eh_spec_block) = raises;
 520 }
 521
 522 /* Return a pointer to a buffer for an exception object of type TYPE.  */
 523
 524 static tree
 525 do_allocate_exception (tree type)
 526 {
 527   tree fn;
 528
 529   fn = get_identifier ("__cxa_allocate_exception");
 530   if (!get_global_value_if_present (fn, &fn))
 531     {
 532       /* Declare void *__cxa_allocate_exception(size_t).  */
 533       tree tmp = tree_cons (NULL_TREE, size_type_node, void_list_node);
 534       fn = push_library_fn (fn, build_function_type (ptr_type_node, tmp));
 535     }
 536
 537   return build_function_call (fn, tree_cons (NULL_TREE, size_in_bytes (type),
 538                                              NULL_TREE));
 539 }
 540
 541 /* Call __cxa_free_exception from a cleanup.  This is never invoked
 542    directly, but see the comment for stabilize_throw_expr.  */
 543
 544 static tree
 545 do_free_exception (tree ptr)
 546 {
 547   tree fn;
 548
 549   fn = get_identifier ("__cxa_free_exception");
 550   if (!get_global_value_if_present (fn, &fn))
 551     {
 552       /* Declare void __cxa_free_exception (void *).  */
 553       fn = push_void_library_fn (fn, tree_cons (NULL_TREE, ptr_type_node,
 554                                                 void_list_node));
 555     }
 556
 557   return build_function_call (fn, tree_cons (NULL_TREE, ptr, NULL_TREE));
 558 }
 559
 560 /* Wrap all cleanups for TARGET_EXPRs in MUST_NOT_THROW_EXPR.
 561    Called from build_throw via walk_tree_without_duplicates.  */
 562
 563 static tree
 564 wrap_cleanups_r (tree *tp, int *walk_subtrees ATTRIBUTE_UNUSED,
 565                  void *data ATTRIBUTE_UNUSED)
 566 {
 567   tree exp = *tp;
 568   tree cleanup;
 569
 570   /* Don't walk into types.  */
 571   if (TYPE_P (exp))
 572     {
 573       *walk_subtrees = 0;
 574       return NULL_TREE;
 575     }
 576   if (TREE_CODE (exp) != TARGET_EXPR)
 577     return NULL_TREE;
 578
 579   cleanup = TARGET_EXPR_CLEANUP (exp);
 580   if (cleanup)
 581     {
 582       cleanup = build1 (MUST_NOT_THROW_EXPR, void_type_node, cleanup);
 583       TARGET_EXPR_CLEANUP (exp) = cleanup;
 584     }
 585
 586   /* Keep iterating.  */
 587   return NULL_TREE;
 588 }
 589
 590 /* Build a throw expression.  */
 591
 592 tree
 593 build_throw (tree exp)
 594 {
 595   tree fn;
 596
 597   if (exp == error_mark_node)
 598     return exp;
 599
 600   if (processing_template_decl)
 601     {
 602       current_function_returns_abnormally = 1;
 603       return build_min (THROW_EXPR, void_type_node, exp);
 604     }
 605
 606   if (exp == null_node)
 607     warning (0, "throwing NULL, which has integral, not pointer type");
 608
 609   if (exp != NULL_TREE)
 610     {
 611       if (!is_admissible_throw_operand (exp))
 612         return error_mark_node;
 613     }
 614
 615   if (! doing_eh (1))
 616     return error_mark_node;
 617
 618   if (exp && decl_is_java_type (TREE_TYPE (exp), 1))
 619     {
 620       tree fn = get_identifier ("_Jv_Throw");
 621       if (!get_global_value_if_present (fn, &fn))
 622         {
 623           /* Declare void _Jv_Throw (void *).  */
 624           tree tmp = tree_cons (NULL_TREE, ptr_type_node, void_list_node);
 625           tmp = build_function_type (ptr_type_node, tmp);
 626           fn = push_throw_library_fn (fn, tmp);
 627         }
 628       else if (really_overloaded_fn (fn))
 629         {
 630           error ("%qD should never be overloaded", fn);
 631           return error_mark_node;
 632         }
 633       fn = OVL_CURRENT (fn);
 634       exp = build_function_call (fn, tree_cons (NULL_TREE, exp, NULL_TREE));
 635     }
 636   else if (exp)
 637     {
 638       tree throw_type;
 639       tree cleanup;
 640       tree object, ptr;
 641       tree tmp;
 642       tree temp_expr, allocate_expr;
 643       bool elided;
 644
 645       /* The CLEANUP_TYPE is the internal type of a destructor.  */
 646       if (!cleanup_type)
 647         {
 648           tmp = void_list_node;
 649           tmp = tree_cons (NULL_TREE, ptr_type_node, tmp);
 650           tmp = build_function_type (void_type_node, tmp);
 651           cleanup_type = build_pointer_type (tmp);
 652         }
 653
 654       fn = get_identifier ("__cxa_throw");
 655       if (!get_global_value_if_present (fn, &fn))
 656         {
 657           /* Declare void __cxa_throw (void*, void*, void (*)(void*)).  */
 658           /* ??? Second argument is supposed to be "std::type_info*".  */
 659           tmp = void_list_node;
 660           tmp = tree_cons (NULL_TREE, cleanup_type, tmp);
 661           tmp = tree_cons (NULL_TREE, ptr_type_node, tmp);
 662           tmp = tree_cons (NULL_TREE, ptr_type_node, tmp);
 663           tmp = build_function_type (void_type_node, tmp);
 664           fn = push_throw_library_fn (fn, tmp);
 665         }
 666
 667       /* throw expression */
 668       /* First, decay it.  */
 669       exp = decay_conversion (exp);
 670
 671       /* OK, this is kind of wacky.  The standard says that we call
 672          terminate when the exception handling mechanism, after
 673          completing evaluation of the expression to be thrown but
 674          before the exception is caught (_except.throw_), calls a
 675          user function that exits via an uncaught exception.
 676
 677          So we have to protect the actual initialization of the
 678          exception object with terminate(), but evaluate the
 679          expression first.  Since there could be temps in the
 680          expression, we need to handle that, too.  We also expand
 681          the call to __cxa_allocate_exception first (which doesn't
 682          matter, since it can't throw).  */
 683
 684       /* Allocate the space for the exception.  */
 685       allocate_expr = do_allocate_exception (TREE_TYPE (exp));
 686       allocate_expr = get_target_expr (allocate_expr);
 687       ptr = TARGET_EXPR_SLOT (allocate_expr);
 688       object = build1 (NOP_EXPR, build_pointer_type (TREE_TYPE (exp)), ptr);
 689       object = build_indirect_ref (object, NULL);
 690
 691       elided = (TREE_CODE (exp) == TARGET_EXPR);
 692
 693       /* And initialize the exception object.  */
 694       exp = build_init (object, exp, LOOKUP_ONLYCONVERTING);
 695       if (exp == error_mark_node)
 696         {
 697           error ("  in thrown expression");
 698           return error_mark_node;
 699         }
 700
 701       /* Pre-evaluate the thrown expression first, since if we allocated
 702          the space first we would have to deal with cleaning it up if
 703          evaluating this expression throws.
 704
 705          The case where EXP the initializer is a cast or a function
 706          returning a class is a bit of a grey area in the standard; it's
 707          unclear whether or not it should be allowed to throw.  We used to
 708          say no, as that allowed us to optimize this case without worrying
 709          about deallocating the exception object if it does.  But that
 710          conflicted with expectations (PR 13944) and the EDG compiler; now
 711          we wrap the initialization in a TRY_CATCH_EXPR to call
 712          do_free_exception rather than in a MUST_NOT_THROW_EXPR, for this
 713          case only.
 714
 715          BUT: Issue 475 may do away with this inconsistency by removing the
 716          terminate() in this situation.
 717
 718          Note that we don't check the return value from stabilize_init
 719          because it will only return false in cases where elided is true,
 720          and therefore we don't need to work around the failure to
 721          preevaluate.  */
 722       temp_expr = NULL_TREE;
 723       stabilize_init (exp, &temp_expr);
 724
 725       if (elided)
 726         exp = build2 (TRY_CATCH_EXPR, void_type_node, exp,
 727                       do_free_exception (ptr));
 728       else
 729         exp = build1 (MUST_NOT_THROW_EXPR, void_type_node, exp);
 730
 731       /* Prepend the allocation.  */
 732       exp = build2 (COMPOUND_EXPR, TREE_TYPE (exp), allocate_expr, exp);
 733       if (temp_expr)
 734         {
 735           /* Prepend the calculation of the throw expression.  Also, force
 736              any cleanups from the expression to be evaluated here so that
 737              we don't have to do them during unwinding.  But first wrap
 738              them in MUST_NOT_THROW_EXPR, since they are run after the
 739              exception object is initialized.  */
 740           walk_tree_without_duplicates (&temp_expr, wrap_cleanups_r, 0);
 741           exp = build2 (COMPOUND_EXPR, TREE_TYPE (exp), temp_expr, exp);
 742           exp = build1 (CLEANUP_POINT_EXPR, TREE_TYPE (exp), exp);
 743         }
 744
 745       throw_type = build_eh_type_type (prepare_eh_type (TREE_TYPE (object)));
 746
 747       if (TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (object)))
 748         {
 749           cleanup = lookup_fnfields (TYPE_BINFO (TREE_TYPE (object)),
 750                                      complete_dtor_identifier, 0);
 751           cleanup = BASELINK_FUNCTIONS (cleanup);
 752           mark_used (cleanup);
 753           cxx_mark_addressable (cleanup);
 754           /* Pretend it's a normal function.  */
 755           cleanup = build1 (ADDR_EXPR, cleanup_type, cleanup);
 756         }
 757       else
 758         cleanup = build_int_cst (cleanup_type, 0);
 759
 760       tmp = tree_cons (NULL_TREE, cleanup, NULL_TREE);
 761       tmp = tree_cons (NULL_TREE, throw_type, tmp);
 762       tmp = tree_cons (NULL_TREE, ptr, tmp);
 763       /* ??? Indicate that this function call throws throw_type.  */
 764       tmp = build_function_call (fn, tmp);
 765
 766       /* Tack on the initialization stuff.  */
 767       exp = build2 (COMPOUND_EXPR, TREE_TYPE (tmp), exp, tmp);
 768     }
 769   else
 770     {
 771       /* Rethrow current exception.  */
 772
 773       tree fn = get_identifier ("__cxa_rethrow");
 774       if (!get_global_value_if_present (fn, &fn))
 775         {
 776           /* Declare void __cxa_rethrow (void).  */
 777           fn = push_throw_library_fn
 778             (fn, build_function_type (void_type_node, void_list_node));
 779         }
 780
 781       /* ??? Indicate that this function call allows exceptions of the type
 782          of the enclosing catch block (if known).  */
 783       exp = build_function_call (fn, NULL_TREE);
 784     }
 785
 786   exp = build1 (THROW_EXPR, void_type_node, exp);
 787
 788   return exp;
 789 }
 790
 791 /* Make sure TYPE is complete, pointer to complete, reference to
 792    complete, or pointer to cv void. Issue diagnostic on failure.
 793    Return the zero on failure and nonzero on success. FROM can be
 794    the expr or decl from whence TYPE came, if available.  */
 795
 796 static int
 797 complete_ptr_ref_or_void_ptr_p (tree type, tree from)
 798 {
 799   int is_ptr;
 800
 801   /* Check complete.  */
 802   type = complete_type_or_else (type, from);
 803   if (!type)
 804     return 0;
 805
 806   /* Or a pointer or ref to one, or cv void *.  */
 807   is_ptr = TREE_CODE (type) == POINTER_TYPE;
 808   if (is_ptr || TREE_CODE (type) == REFERENCE_TYPE)
 809     {
 810       tree core = TREE_TYPE (type);
 811
 812       if (is_ptr && VOID_TYPE_P (core))
 813         /* OK */;
 814       else if (!complete_type_or_else (core, from))
 815         return 0;
 816     }
 817   return 1;
 818 }
 819
 820 /* Return truth-value if EXPRESSION is admissible in throw-expression,
 821    i.e. if it is not of incomplete type or a pointer/reference to such
 822    a type or of an abstract class type.  */
 823
 824 static bool
 825 is_admissible_throw_operand (tree expr)
 826 {
 827   tree type = TREE_TYPE (expr);
 828
 829   /* 15.1/4 [...] The type of the throw-expression shall not be an
 830             incomplete type, or a pointer or a reference to an incomplete
 831             type, other than void*, const void*, volatile void*, or
 832             const volatile void*.  Except for these restriction and the
 833             restrictions on type matching mentioned in 15.3, the operand
 834             of throw is treated exactly as a function argument in a call
 835             (5.2.2) or the operand of a return statement.  */
 836   if (!complete_ptr_ref_or_void_ptr_p (type, expr))
 837     return false;
 838
 839   /* 10.4/3 An abstract class shall not be used as a parameter type,
 840             as a function return type or as type of an explicit
 841             conversion.  */
 842   else if (CLASS_TYPE_P (type) && CLASSTYPE_PURE_VIRTUALS (type))
 843     {
 844       error ("expression %qE of abstract class type %qT cannot "
 845              "be used in throw-expression", expr, type);
 846       return false;
 847     }
 848
 849   return true;
 850 }
 851
 852 /* Returns nonzero if FN is a declaration of a standard C library
 853    function which is known not to throw.
 854
 855    [lib.res.on.exception.handling]: None of the functions from the
 856    Standard C library shall report an error by throwing an
 857    exception, unless it calls a program-supplied function that
 858    throws an exception.  */
 859
 860 #include "cfns.h"
 861
 862 int
 863 nothrow_libfn_p (tree fn)
 864 {
 865   tree id;
 866
 867   if (TREE_PUBLIC (fn)
 868       && DECL_EXTERNAL (fn)
 869       && DECL_NAMESPACE_SCOPE_P (fn)
 870       && DECL_EXTERN_C_P (fn))
 871     /* OK */;
 872   else
 873     /* Can't be a C library function.  */
 874     return 0;
 875
 876   /* Being a C library function, DECL_ASSEMBLER_NAME == DECL_NAME
 877      unless the system headers are playing rename tricks, and if
 878      they are, we don't want to be confused by them.  */
 879   id = DECL_NAME (fn);
 880   return !!libc_name_p (IDENTIFIER_POINTER (id), IDENTIFIER_LENGTH (id));
 881 }
 882
 883 /* Returns nonzero if an exception of type FROM will be caught by a
 884    handler for type TO, as per [except.handle].  */
 885
 886 static int
 887 can_convert_eh (tree to, tree from)
 888 {
 889   to = non_reference (to);
 890   from = non_reference (from);
 891
 892   if (TREE_CODE (to) == POINTER_TYPE && TREE_CODE (from) == POINTER_TYPE)
 893     {
 894       to = TREE_TYPE (to);
 895       from = TREE_TYPE (from);
 896
 897       if (! at_least_as_qualified_p (to, from))
 898         return 0;
 899
 900       if (TREE_CODE (to) == VOID_TYPE)
 901         return 1;
 902
 903       /* Else fall through.  */
 904     }
 905
 906   if (CLASS_TYPE_P (to) && CLASS_TYPE_P (from)
 907       && PUBLICLY_UNIQUELY_DERIVED_P (to, from))
 908     return 1;
 909
 910   return 0;
 911 }
 912
 913 /* Check whether any of the handlers in I are shadowed by another handler
 914    accepting TYPE.  Note that the shadowing may not be complete; even if
 915    an exception of type B would be caught by a handler for A, there could
 916    be a derived class C for which A is an ambiguous base but B is not, so
 917    the handler for B would catch an exception of type C.  */
 918
 919 static void
 920 check_handlers_1 (tree master, tree_stmt_iterator i)
 921 {
 922   tree type = TREE_TYPE (master);
 923
 924   for (; !tsi_end_p (i); tsi_next (&i))
 925     {
 926       tree handler = tsi_stmt (i);
 927       if (TREE_TYPE (handler) && can_convert_eh (type, TREE_TYPE (handler)))
 928         {
 929           warning (0, "%Hexception of type %qT will be caught",
 930                    EXPR_LOCUS (handler), TREE_TYPE (handler));
 931           warning (0, "%H   by earlier handler for %qT",
 932                    EXPR_LOCUS (master), type);
 933           break;
 934         }
 935     }
 936 }
 937
 938 /* Given a STATEMENT_LIST of HANDLERs, make sure that they're OK.  */
 939
 940 void
 941 check_handlers (tree handlers)
 942 {
 943   tree_stmt_iterator i;
 944
 945   /* If we don't have a STATEMENT_LIST, then we've just got one
 946      handler, and thus nothing to warn about.  */
 947   if (TREE_CODE (handlers) != STATEMENT_LIST)
 948     return;
 949
 950   i = tsi_start (handlers);
 951   if (!tsi_end_p (i))
 952     while (1)
 953       {
 954         tree handler = tsi_stmt (i);
 955         tsi_next (&i);
 956
 957         /* No more handlers; nothing to shadow.  */
 958         if (tsi_end_p (i))
 959           break;
 960         if (TREE_TYPE (handler) == NULL_TREE)
 961           pedwarn ("%H%<...%> handler must be the last handler for"
 962                    " its try block", EXPR_LOCUS (handler));
 963         else
 964           check_handlers_1 (handler, i);
 965       }
 966 }