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src/hotspot/share/c1/c1_Optimizer.cpp

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  72   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
  73     int e = sux->number_of_exception_handlers();
  74     for (int i = 0; i < e; i++) {
  75       BlockBegin* xhandler = sux->exception_handler_at(i);
  76       block->add_exception_handler(xhandler);
  77 
  78       assert(xhandler->is_predecessor(sux), "missing predecessor");
  79       if (sux->number_of_preds() == 0) {
  80         // sux is disconnected from graph so disconnect from exception handlers
  81         xhandler->remove_predecessor(sux);
  82       }
  83       if (!xhandler->is_predecessor(block)) {
  84         xhandler->add_predecessor(block);
  85       }
  86     }
  87   }
  88 
  89   virtual void block_do(BlockBegin* block);
  90 
  91  private:
  92   Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);

  93 };
  94 
  95 void CE_Eliminator::block_do(BlockBegin* block) {
  96   // 1) find conditional expression
  97   // check if block ends with an If
  98   If* if_ = block->end()->as_If();
  99   if (if_ == NULL) return;
 100 
 101   // check if If works on int or object types
 102   // (we cannot handle If's working on long, float or doubles yet,
 103   // since IfOp doesn't support them - these If's show up if cmp
 104   // operations followed by If's are eliminated)
 105   ValueType* if_type = if_->x()->type();
 106   if (!if_type->is_int() && !if_type->is_object()) return;
 107 
 108   BlockBegin* t_block = if_->tsux();
 109   BlockBegin* f_block = if_->fsux();
 110   Instruction* t_cur = t_block->next();
 111   Instruction* f_cur = f_block->next();
 112 

 201 
 202   // 2) substitute conditional expression
 203   //    with an IfOp followed by a Goto
 204   // cut if_ away and get node before
 205   Instruction* cur_end = if_->prev();
 206 
 207   // append constants of true- and false-block if necessary
 208   // clone constants because original block must not be destroyed
 209   assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
 210   if (t_value == t_const) {
 211     t_value = new Constant(t_const->type());
 212     NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
 213     cur_end = cur_end->set_next(t_value);
 214   }
 215   if (f_value == f_const) {
 216     f_value = new Constant(f_const->type());
 217     NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
 218     cur_end = cur_end->set_next(f_value);
 219   }
 220 
 221   Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);

 222   assert(result != NULL, "make_ifop must return a non-null instruction");
 223   if (!result->is_linked() && result->can_be_linked()) {
 224     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
 225     cur_end = cur_end->set_next(result);
 226   }
 227 
 228   // append Goto to successor
 229   ValueStack* state_before = if_->state_before();
 230   Goto* goto_ = new Goto(sux, state_before, is_safepoint);
 231 
 232   // prepare state for Goto
 233   ValueStack* goto_state = if_state;
 234   goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
 235   goto_state->push(result->type(), result);
 236   assert(goto_state->is_same(sux_state), "states must match now");
 237   goto_->set_state(goto_state);
 238 
 239   cur_end = cur_end->set_next(goto_, goto_state->bci());
 240 
 241   // Adjust control flow graph

 256   // substitute the phi if possible
 257   if (sux_phi->as_Phi()->operand_count() == 1) {
 258     assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
 259     sux_phi->set_subst(result);
 260     _has_substitution = true;
 261   }
 262 
 263   // 3) successfully eliminated a conditional expression
 264   _cee_count++;
 265   if (PrintCEE) {
 266     tty->print_cr("%d. CEE in B%d (B%d B%d)", cee_count(), block->block_id(), t_block->block_id(), f_block->block_id());
 267     tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
 268   }
 269 
 270 #ifdef DO_DELAYED_VERIFICATION
 271   _hir->verify_local(blocks_to_verify_later);
 272 #endif // DO_DELAYED_VERIFICATION
 273 
 274 }
 275 
 276 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {

 277   if (!OptimizeIfOps) {
 278     return new IfOp(x, cond, y, tval, fval);
 279   }
 280 
 281   tval = tval->subst();
 282   fval = fval->subst();
 283   if (tval == fval) {
 284     _ifop_count++;
 285     return tval;
 286   }
 287 
 288   x = x->subst();
 289   y = y->subst();
 290 
 291   Constant* y_const = y->as_Constant();
 292   if (y_const != NULL) {
 293     IfOp* x_ifop = x->as_IfOp();
 294     if (x_ifop != NULL) {                 // x is an ifop, y is a constant
 295       Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
 296       Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
 297 
 298       if (x_tval_const != NULL && x_fval_const != NULL) {
 299         Instruction::Condition x_ifop_cond = x_ifop->cond();
 300 
 301         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
 302         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
 303 
 304         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 305         if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
 306           Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
 307           Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
 308 
 309           _ifop_count++;
 310           if (new_tval == new_fval) {
 311             return new_tval;
 312           } else {
 313             return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
 314           }
 315         }
 316       }
 317     } else {
 318       Constant* x_const = x->as_Constant();
 319       if (x_const != NULL) {         // x and y are constants
 320         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
 321         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 322         if (x_compare_res != Constant::not_comparable) {
 323           _ifop_count++;
 324           return x_compare_res == Constant::cond_true ? tval : fval;
 325         }
 326       }
 327     }
 328   }
 329   return new IfOp(x, cond, y, tval, fval);
 330 }
 331 
 332 void Optimizer::eliminate_conditional_expressions() {
 333   // find conditional expressions & replace them with IfOps
 334   CE_Eliminator ce(ir());
 335 }
 336 
 337 // This removes others' relation to block, but doesnt empty block's lists
 338 void disconnect_from_graph(BlockBegin* block) {
 339   for (int p = 0; p < block->number_of_preds(); p++) {
 340     BlockBegin* pred = block->pred_at(p);
 341     int idx;
 342     while ((idx = pred->end()->find_sux(block)) >= 0) {
 343       pred->end()->remove_sux_at(idx);
 344     }
 345   }
 346   for (int s = 0; s < block->number_of_sux(); s++) {
 347     block->sux_at(s)->remove_predecessor(block);
 348   }
 349 }

 449     _merge_count++;
 450     if (PrintBlockElimination) {
 451       tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
 452                     _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
 453     }
 454 
 455 #ifdef DO_DELAYED_VERIFICATION
 456     _hir->verify_local(blocks_to_verify_later);
 457 #endif // DO_DELAYED_VERIFICATION
 458 
 459     If* if_ = block->end()->as_If();
 460     if (if_) {
 461       IfOp* ifop    = if_->x()->as_IfOp();
 462       Constant* con = if_->y()->as_Constant();
 463       bool swapped = false;
 464       if (!con || !ifop) {
 465         ifop = if_->y()->as_IfOp();
 466         con  = if_->x()->as_Constant();
 467         swapped = true;
 468       }
 469       if (con && ifop) {
 470         Constant* tval = ifop->tval()->as_Constant();
 471         Constant* fval = ifop->fval()->as_Constant();
 472         if (tval && fval) {
 473           // Find the instruction before if_, starting with ifop.
 474           // When if_ and ifop are not in the same block, prev
 475           // becomes NULL In such (rare) cases it is not
 476           // profitable to perform the optimization.
 477           Value prev = ifop;
 478           while (prev != NULL && prev->next() != if_) {
 479             prev = prev->next();
 480           }
 481 
 482           if (prev != NULL) {
 483             Instruction::Condition cond = if_->cond();
 484             BlockBegin* tsux = if_->tsux();
 485             BlockBegin* fsux = if_->fsux();
 486             if (swapped) {
 487               cond = Instruction::mirror(cond);
 488             }
 489 
 490             BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
 491             BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
 492             if (tblock != fblock && !if_->is_safepoint()) {
 493               If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
 494                                  tblock, fblock, if_->state_before(), if_->is_safepoint());
 495               newif->set_state(if_->state()->copy());
 496 
 497               assert(prev->next() == if_, "must be guaranteed by above search");
 498               NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
 499               prev->set_next(newif);
 500               block->set_end(newif);
 501 
 502               _merge_count++;
 503               if (PrintBlockElimination) {
 504                 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
 505               }
 506 
 507 #ifdef DO_DELAYED_VERIFICATION
 508               _hir->verify_local(blocks_to_verify_later);
 509 #endif // DO_DELAYED_VERIFICATION
 510             }
 511           }
 512         }
 513       }
 514     }

 545 
 546   void do_Phi            (Phi*             x);
 547   void do_Local          (Local*           x);
 548   void do_Constant       (Constant*        x);
 549   void do_LoadField      (LoadField*       x);
 550   void do_StoreField     (StoreField*      x);
 551   void do_ArrayLength    (ArrayLength*     x);
 552   void do_LoadIndexed    (LoadIndexed*     x);
 553   void do_StoreIndexed   (StoreIndexed*    x);
 554   void do_NegateOp       (NegateOp*        x);
 555   void do_ArithmeticOp   (ArithmeticOp*    x);
 556   void do_ShiftOp        (ShiftOp*         x);
 557   void do_LogicOp        (LogicOp*         x);
 558   void do_CompareOp      (CompareOp*       x);
 559   void do_IfOp           (IfOp*            x);
 560   void do_Convert        (Convert*         x);
 561   void do_NullCheck      (NullCheck*       x);
 562   void do_TypeCast       (TypeCast*        x);
 563   void do_Invoke         (Invoke*          x);
 564   void do_NewInstance    (NewInstance*     x);

 565   void do_NewTypeArray   (NewTypeArray*    x);
 566   void do_NewObjectArray (NewObjectArray*  x);
 567   void do_NewMultiArray  (NewMultiArray*   x);

 568   void do_CheckCast      (CheckCast*       x);
 569   void do_InstanceOf     (InstanceOf*      x);
 570   void do_MonitorEnter   (MonitorEnter*    x);
 571   void do_MonitorExit    (MonitorExit*     x);
 572   void do_Intrinsic      (Intrinsic*       x);
 573   void do_BlockBegin     (BlockBegin*      x);
 574   void do_Goto           (Goto*            x);
 575   void do_If             (If*              x);
 576   void do_TableSwitch    (TableSwitch*     x);
 577   void do_LookupSwitch   (LookupSwitch*    x);
 578   void do_Return         (Return*          x);
 579   void do_Throw          (Throw*           x);
 580   void do_Base           (Base*            x);
 581   void do_OsrEntry       (OsrEntry*        x);
 582   void do_ExceptionObject(ExceptionObject* x);
 583   void do_RoundFP        (RoundFP*         x);
 584   void do_UnsafeGet      (UnsafeGet*       x);
 585   void do_UnsafePut      (UnsafePut*       x);
 586   void do_UnsafeGetAndSet(UnsafeGetAndSet* x);
 587   void do_ProfileCall    (ProfileCall*     x);
 588   void do_ProfileReturnType (ProfileReturnType*  x);

 589   void do_ProfileInvoke  (ProfileInvoke*   x);
 590   void do_RuntimeCall    (RuntimeCall*     x);
 591   void do_MemBar         (MemBar*          x);
 592   void do_RangeCheckPredicate(RangeCheckPredicate* x);
 593 #ifdef ASSERT
 594   void do_Assert         (Assert*          x);
 595 #endif
 596 };
 597 
 598 
 599 // Because of a static contained within (for the purpose of iteration
 600 // over instructions), it is only valid to have one of these active at
 601 // a time
 602 class NullCheckEliminator: public ValueVisitor {
 603  private:
 604   Optimizer*        _opt;
 605 
 606   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block
 607   BlockList*        _work_list;                   // Basic blocks to visit
 608 

 690     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
 691     _last_explicit_null_check->set_can_trap(false);
 692     return _last_explicit_null_check;
 693   }
 694   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }
 695 
 696   // Handlers for relevant instructions
 697   // (separated out from NullCheckVisitor for clarity)
 698 
 699   // The basic contract is that these must leave the instruction in
 700   // the desired state; must not assume anything about the state of
 701   // the instruction. We make multiple passes over some basic blocks
 702   // and the last pass is the only one whose result is valid.
 703   void handle_AccessField     (AccessField* x);
 704   void handle_ArrayLength     (ArrayLength* x);
 705   void handle_LoadIndexed     (LoadIndexed* x);
 706   void handle_StoreIndexed    (StoreIndexed* x);
 707   void handle_NullCheck       (NullCheck* x);
 708   void handle_Invoke          (Invoke* x);
 709   void handle_NewInstance     (NewInstance* x);

 710   void handle_NewArray        (NewArray* x);
 711   void handle_AccessMonitor   (AccessMonitor* x);
 712   void handle_Intrinsic       (Intrinsic* x);
 713   void handle_ExceptionObject (ExceptionObject* x);
 714   void handle_Phi             (Phi* x);
 715   void handle_ProfileCall     (ProfileCall* x);
 716   void handle_ProfileReturnType (ProfileReturnType* x);

 717 };
 718 
 719 
 720 // NEEDS_CLEANUP
 721 // There may be other instructions which need to clear the last
 722 // explicit null check. Anything across which we can not hoist the
 723 // debug information for a NullCheck instruction must clear it. It
 724 // might be safer to pattern match "NullCheck ; {AccessField,
 725 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
 726 // Should test to see performance hit of clearing it for all handlers
 727 // with empty bodies below. If it is negligible then we should leave
 728 // that in for safety, otherwise should think more about it.
 729 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }
 730 void NullCheckVisitor::do_Local          (Local*           x) {}
 731 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }
 732 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }
 733 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }
 734 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }
 735 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }
 736 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }
 737 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}
 738 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
 739 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}
 740 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}
 741 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}
 742 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}
 743 void NullCheckVisitor::do_Convert        (Convert*         x) {}
 744 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }
 745 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}
 746 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }
 747 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }

 748 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }
 749 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }
 750 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }

 751 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }
 752 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}
 753 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }
 754 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }
 755 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }
 756 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}
 757 void NullCheckVisitor::do_Goto           (Goto*            x) {}
 758 void NullCheckVisitor::do_If             (If*              x) {}
 759 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}
 760 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}
 761 void NullCheckVisitor::do_Return         (Return*          x) {}
 762 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }
 763 void NullCheckVisitor::do_Base           (Base*            x) {}
 764 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}
 765 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
 766 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}
 767 void NullCheckVisitor::do_UnsafeGet      (UnsafeGet*       x) {}
 768 void NullCheckVisitor::do_UnsafePut      (UnsafePut*       x) {}
 769 void NullCheckVisitor::do_UnsafeGetAndSet(UnsafeGetAndSet* x) {}
 770 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check();
 771                                                                 nce()->handle_ProfileCall(x); }
 772 void NullCheckVisitor::do_ProfileReturnType (ProfileReturnType* x) { nce()->handle_ProfileReturnType(x); }
 773 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}

 774 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}
 775 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}
 776 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
 777 #ifdef ASSERT
 778 void NullCheckVisitor::do_Assert         (Assert*          x) {}
 779 #endif
 780 
 781 void NullCheckEliminator::visit(Value* p) {
 782   assert(*p != NULL, "should not find NULL instructions");
 783   if (visitable(*p)) {
 784     mark_visited(*p);
 785     (*p)->visit(&_visitor);
 786   }
 787 }
 788 
 789 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
 790   ValueSet* state = state_for(block);
 791   if (state == NULL) {
 792     state = incoming_state->copy();
 793     set_state_for(block, state);

1077   }
1078 
1079   Value recv = x->receiver();
1080   if (!set_contains(recv)) {
1081     set_put(recv);
1082     if (PrintNullCheckElimination) {
1083       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1084     }
1085   }
1086   clear_last_explicit_null_check();
1087 }
1088 
1089 
1090 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1091   set_put(x);
1092   if (PrintNullCheckElimination) {
1093     tty->print_cr("NewInstance %d is non-null", x->id());
1094   }
1095 }
1096 







1097 
1098 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1099   set_put(x);
1100   if (PrintNullCheckElimination) {
1101     tty->print_cr("NewArray %d is non-null", x->id());
1102   }
1103 }
1104 
1105 
1106 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1107   set_put(x);
1108   if (PrintNullCheckElimination) {
1109     tty->print_cr("ExceptionObject %d is non-null", x->id());
1110   }
1111 }
1112 
1113 
1114 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1115   Value obj = x->obj();
1116   if (set_contains(obj)) {

1181     // Value is non-null => update Phi
1182     if (PrintNullCheckElimination) {
1183       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1184     }
1185     x->set_needs_null_check(false);
1186   } else if (set_contains(x)) {
1187     set_remove(x);
1188   }
1189 }
1190 
1191 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1192   for (int i = 0; i < x->nb_profiled_args(); i++) {
1193     x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1194   }
1195 }
1196 
1197 void NullCheckEliminator::handle_ProfileReturnType(ProfileReturnType* x) {
1198   x->set_needs_null_check(!set_contains(x->ret()));
1199 }
1200 





1201 void Optimizer::eliminate_null_checks() {
1202   ResourceMark rm;
1203 
1204   NullCheckEliminator nce(this);
1205 
1206   if (PrintNullCheckElimination) {
1207     tty->print_cr("Starting null check elimination for method %s::%s%s",
1208                   ir()->method()->holder()->name()->as_utf8(),
1209                   ir()->method()->name()->as_utf8(),
1210                   ir()->method()->signature()->as_symbol()->as_utf8());
1211   }
1212 
1213   // Apply to graph
1214   nce.iterate(ir()->start());
1215 
1216   // walk over the graph looking for exception
1217   // handlers and iterate over them as well
1218   int nblocks = BlockBegin::number_of_blocks();
1219   BlockList blocks(nblocks);
1220   boolArray visited_block(nblocks, nblocks, false);

  72   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
  73     int e = sux->number_of_exception_handlers();
  74     for (int i = 0; i < e; i++) {
  75       BlockBegin* xhandler = sux->exception_handler_at(i);
  76       block->add_exception_handler(xhandler);
  77 
  78       assert(xhandler->is_predecessor(sux), "missing predecessor");
  79       if (sux->number_of_preds() == 0) {
  80         // sux is disconnected from graph so disconnect from exception handlers
  81         xhandler->remove_predecessor(sux);
  82       }
  83       if (!xhandler->is_predecessor(block)) {
  84         xhandler->add_predecessor(block);
  85       }
  86     }
  87   }
  88 
  89   virtual void block_do(BlockBegin* block);
  90 
  91  private:
  92   Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval,
  93                   ValueStack* state_before, bool substitutability_check);
  94 };
  95 
  96 void CE_Eliminator::block_do(BlockBegin* block) {
  97   // 1) find conditional expression
  98   // check if block ends with an If
  99   If* if_ = block->end()->as_If();
 100   if (if_ == NULL) return;
 101 
 102   // check if If works on int or object types
 103   // (we cannot handle If's working on long, float or doubles yet,
 104   // since IfOp doesn't support them - these If's show up if cmp
 105   // operations followed by If's are eliminated)
 106   ValueType* if_type = if_->x()->type();
 107   if (!if_type->is_int() && !if_type->is_object()) return;
 108 
 109   BlockBegin* t_block = if_->tsux();
 110   BlockBegin* f_block = if_->fsux();
 111   Instruction* t_cur = t_block->next();
 112   Instruction* f_cur = f_block->next();
 113 

 202 
 203   // 2) substitute conditional expression
 204   //    with an IfOp followed by a Goto
 205   // cut if_ away and get node before
 206   Instruction* cur_end = if_->prev();
 207 
 208   // append constants of true- and false-block if necessary
 209   // clone constants because original block must not be destroyed
 210   assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
 211   if (t_value == t_const) {
 212     t_value = new Constant(t_const->type());
 213     NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
 214     cur_end = cur_end->set_next(t_value);
 215   }
 216   if (f_value == f_const) {
 217     f_value = new Constant(f_const->type());
 218     NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
 219     cur_end = cur_end->set_next(f_value);
 220   }
 221 
 222   Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value,
 223                            if_->state_before(), if_->substitutability_check());
 224   assert(result != NULL, "make_ifop must return a non-null instruction");
 225   if (!result->is_linked() && result->can_be_linked()) {
 226     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
 227     cur_end = cur_end->set_next(result);
 228   }
 229 
 230   // append Goto to successor
 231   ValueStack* state_before = if_->state_before();
 232   Goto* goto_ = new Goto(sux, state_before, is_safepoint);
 233 
 234   // prepare state for Goto
 235   ValueStack* goto_state = if_state;
 236   goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
 237   goto_state->push(result->type(), result);
 238   assert(goto_state->is_same(sux_state), "states must match now");
 239   goto_->set_state(goto_state);
 240 
 241   cur_end = cur_end->set_next(goto_, goto_state->bci());
 242 
 243   // Adjust control flow graph

 258   // substitute the phi if possible
 259   if (sux_phi->as_Phi()->operand_count() == 1) {
 260     assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
 261     sux_phi->set_subst(result);
 262     _has_substitution = true;
 263   }
 264 
 265   // 3) successfully eliminated a conditional expression
 266   _cee_count++;
 267   if (PrintCEE) {
 268     tty->print_cr("%d. CEE in B%d (B%d B%d)", cee_count(), block->block_id(), t_block->block_id(), f_block->block_id());
 269     tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
 270   }
 271 
 272 #ifdef DO_DELAYED_VERIFICATION
 273   _hir->verify_local(blocks_to_verify_later);
 274 #endif // DO_DELAYED_VERIFICATION
 275 
 276 }
 277 
 278 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval,
 279                                ValueStack* state_before, bool substitutability_check) {
 280   if (!OptimizeIfOps) {
 281     return new IfOp(x, cond, y, tval, fval, state_before, substitutability_check);
 282   }
 283 
 284   tval = tval->subst();
 285   fval = fval->subst();
 286   if (tval == fval) {
 287     _ifop_count++;
 288     return tval;
 289   }
 290 
 291   x = x->subst();
 292   y = y->subst();
 293 
 294   Constant* y_const = y->as_Constant();
 295   if (y_const != NULL) {
 296     IfOp* x_ifop = x->as_IfOp();
 297     if (x_ifop != NULL) {                 // x is an ifop, y is a constant
 298       Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
 299       Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
 300 
 301       if (x_tval_const != NULL && x_fval_const != NULL) {
 302         Instruction::Condition x_ifop_cond = x_ifop->cond();
 303 
 304         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
 305         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
 306 
 307         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 308         if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
 309           Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
 310           Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
 311 
 312           _ifop_count++;
 313           if (new_tval == new_fval) {
 314             return new_tval;
 315           } else {
 316             return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval, state_before, substitutability_check);
 317           }
 318         }
 319       }
 320     } else {
 321       Constant* x_const = x->as_Constant();
 322       if (x_const != NULL) {         // x and y are constants
 323         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
 324         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 325         if (x_compare_res != Constant::not_comparable) {
 326           _ifop_count++;
 327           return x_compare_res == Constant::cond_true ? tval : fval;
 328         }
 329       }
 330     }
 331   }
 332   return new IfOp(x, cond, y, tval, fval, state_before, substitutability_check);
 333 }
 334 
 335 void Optimizer::eliminate_conditional_expressions() {
 336   // find conditional expressions & replace them with IfOps
 337   CE_Eliminator ce(ir());
 338 }
 339 
 340 // This removes others' relation to block, but doesnt empty block's lists
 341 void disconnect_from_graph(BlockBegin* block) {
 342   for (int p = 0; p < block->number_of_preds(); p++) {
 343     BlockBegin* pred = block->pred_at(p);
 344     int idx;
 345     while ((idx = pred->end()->find_sux(block)) >= 0) {
 346       pred->end()->remove_sux_at(idx);
 347     }
 348   }
 349   for (int s = 0; s < block->number_of_sux(); s++) {
 350     block->sux_at(s)->remove_predecessor(block);
 351   }
 352 }

 452     _merge_count++;
 453     if (PrintBlockElimination) {
 454       tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
 455                     _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
 456     }
 457 
 458 #ifdef DO_DELAYED_VERIFICATION
 459     _hir->verify_local(blocks_to_verify_later);
 460 #endif // DO_DELAYED_VERIFICATION
 461 
 462     If* if_ = block->end()->as_If();
 463     if (if_) {
 464       IfOp* ifop    = if_->x()->as_IfOp();
 465       Constant* con = if_->y()->as_Constant();
 466       bool swapped = false;
 467       if (!con || !ifop) {
 468         ifop = if_->y()->as_IfOp();
 469         con  = if_->x()->as_Constant();
 470         swapped = true;
 471       }
 472       if (con && ifop && !ifop->substitutability_check()) {
 473         Constant* tval = ifop->tval()->as_Constant();
 474         Constant* fval = ifop->fval()->as_Constant();
 475         if (tval && fval) {
 476           // Find the instruction before if_, starting with ifop.
 477           // When if_ and ifop are not in the same block, prev
 478           // becomes NULL In such (rare) cases it is not
 479           // profitable to perform the optimization.
 480           Value prev = ifop;
 481           while (prev != NULL && prev->next() != if_) {
 482             prev = prev->next();
 483           }
 484 
 485           if (prev != NULL) {
 486             Instruction::Condition cond = if_->cond();
 487             BlockBegin* tsux = if_->tsux();
 488             BlockBegin* fsux = if_->fsux();
 489             if (swapped) {
 490               cond = Instruction::mirror(cond);
 491             }
 492 
 493             BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
 494             BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
 495             if (tblock != fblock && !if_->is_safepoint()) {
 496               If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
 497                                  tblock, fblock, if_->state_before(), if_->is_safepoint(), ifop->substitutability_check());
 498               newif->set_state(if_->state()->copy());
 499 
 500               assert(prev->next() == if_, "must be guaranteed by above search");
 501               NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
 502               prev->set_next(newif);
 503               block->set_end(newif);
 504 
 505               _merge_count++;
 506               if (PrintBlockElimination) {
 507                 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
 508               }
 509 
 510 #ifdef DO_DELAYED_VERIFICATION
 511               _hir->verify_local(blocks_to_verify_later);
 512 #endif // DO_DELAYED_VERIFICATION
 513             }
 514           }
 515         }
 516       }
 517     }

 548 
 549   void do_Phi            (Phi*             x);
 550   void do_Local          (Local*           x);
 551   void do_Constant       (Constant*        x);
 552   void do_LoadField      (LoadField*       x);
 553   void do_StoreField     (StoreField*      x);
 554   void do_ArrayLength    (ArrayLength*     x);
 555   void do_LoadIndexed    (LoadIndexed*     x);
 556   void do_StoreIndexed   (StoreIndexed*    x);
 557   void do_NegateOp       (NegateOp*        x);
 558   void do_ArithmeticOp   (ArithmeticOp*    x);
 559   void do_ShiftOp        (ShiftOp*         x);
 560   void do_LogicOp        (LogicOp*         x);
 561   void do_CompareOp      (CompareOp*       x);
 562   void do_IfOp           (IfOp*            x);
 563   void do_Convert        (Convert*         x);
 564   void do_NullCheck      (NullCheck*       x);
 565   void do_TypeCast       (TypeCast*        x);
 566   void do_Invoke         (Invoke*          x);
 567   void do_NewInstance    (NewInstance*     x);
 568   void do_NewInlineTypeInstance(NewInlineTypeInstance* x);
 569   void do_NewTypeArray   (NewTypeArray*    x);
 570   void do_NewObjectArray (NewObjectArray*  x);
 571   void do_NewMultiArray  (NewMultiArray*   x);
 572   void do_Deoptimize     (Deoptimize*      x);
 573   void do_CheckCast      (CheckCast*       x);
 574   void do_InstanceOf     (InstanceOf*      x);
 575   void do_MonitorEnter   (MonitorEnter*    x);
 576   void do_MonitorExit    (MonitorExit*     x);
 577   void do_Intrinsic      (Intrinsic*       x);
 578   void do_BlockBegin     (BlockBegin*      x);
 579   void do_Goto           (Goto*            x);
 580   void do_If             (If*              x);
 581   void do_TableSwitch    (TableSwitch*     x);
 582   void do_LookupSwitch   (LookupSwitch*    x);
 583   void do_Return         (Return*          x);
 584   void do_Throw          (Throw*           x);
 585   void do_Base           (Base*            x);
 586   void do_OsrEntry       (OsrEntry*        x);
 587   void do_ExceptionObject(ExceptionObject* x);
 588   void do_RoundFP        (RoundFP*         x);
 589   void do_UnsafeGet      (UnsafeGet*       x);
 590   void do_UnsafePut      (UnsafePut*       x);
 591   void do_UnsafeGetAndSet(UnsafeGetAndSet* x);
 592   void do_ProfileCall    (ProfileCall*     x);
 593   void do_ProfileReturnType (ProfileReturnType*  x);
 594   void do_ProfileACmpTypes(ProfileACmpTypes*  x);
 595   void do_ProfileInvoke  (ProfileInvoke*   x);
 596   void do_RuntimeCall    (RuntimeCall*     x);
 597   void do_MemBar         (MemBar*          x);
 598   void do_RangeCheckPredicate(RangeCheckPredicate* x);
 599 #ifdef ASSERT
 600   void do_Assert         (Assert*          x);
 601 #endif
 602 };
 603 
 604 
 605 // Because of a static contained within (for the purpose of iteration
 606 // over instructions), it is only valid to have one of these active at
 607 // a time
 608 class NullCheckEliminator: public ValueVisitor {
 609  private:
 610   Optimizer*        _opt;
 611 
 612   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block
 613   BlockList*        _work_list;                   // Basic blocks to visit
 614 

 696     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
 697     _last_explicit_null_check->set_can_trap(false);
 698     return _last_explicit_null_check;
 699   }
 700   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }
 701 
 702   // Handlers for relevant instructions
 703   // (separated out from NullCheckVisitor for clarity)
 704 
 705   // The basic contract is that these must leave the instruction in
 706   // the desired state; must not assume anything about the state of
 707   // the instruction. We make multiple passes over some basic blocks
 708   // and the last pass is the only one whose result is valid.
 709   void handle_AccessField     (AccessField* x);
 710   void handle_ArrayLength     (ArrayLength* x);
 711   void handle_LoadIndexed     (LoadIndexed* x);
 712   void handle_StoreIndexed    (StoreIndexed* x);
 713   void handle_NullCheck       (NullCheck* x);
 714   void handle_Invoke          (Invoke* x);
 715   void handle_NewInstance     (NewInstance* x);
 716   void handle_NewInlineTypeInstance(NewInlineTypeInstance* x);
 717   void handle_NewArray        (NewArray* x);
 718   void handle_AccessMonitor   (AccessMonitor* x);
 719   void handle_Intrinsic       (Intrinsic* x);
 720   void handle_ExceptionObject (ExceptionObject* x);
 721   void handle_Phi             (Phi* x);
 722   void handle_ProfileCall     (ProfileCall* x);
 723   void handle_ProfileReturnType (ProfileReturnType* x);
 724   void handle_ProfileACmpTypes(ProfileACmpTypes* x);
 725 };
 726 
 727 
 728 // NEEDS_CLEANUP
 729 // There may be other instructions which need to clear the last
 730 // explicit null check. Anything across which we can not hoist the
 731 // debug information for a NullCheck instruction must clear it. It
 732 // might be safer to pattern match "NullCheck ; {AccessField,
 733 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
 734 // Should test to see performance hit of clearing it for all handlers
 735 // with empty bodies below. If it is negligible then we should leave
 736 // that in for safety, otherwise should think more about it.
 737 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }
 738 void NullCheckVisitor::do_Local          (Local*           x) {}
 739 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }
 740 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }
 741 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }
 742 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }
 743 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }
 744 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }
 745 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}
 746 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
 747 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}
 748 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}
 749 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}
 750 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}
 751 void NullCheckVisitor::do_Convert        (Convert*         x) {}
 752 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }
 753 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}
 754 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }
 755 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }
 756 void NullCheckVisitor::do_NewInlineTypeInstance(NewInlineTypeInstance* x) { nce()->handle_NewInlineTypeInstance(x); }
 757 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }
 758 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }
 759 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }
 760 void NullCheckVisitor::do_Deoptimize     (Deoptimize*      x) {}
 761 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }
 762 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}
 763 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }
 764 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }
 765 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }
 766 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}
 767 void NullCheckVisitor::do_Goto           (Goto*            x) {}
 768 void NullCheckVisitor::do_If             (If*              x) {}
 769 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}
 770 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}
 771 void NullCheckVisitor::do_Return         (Return*          x) {}
 772 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }
 773 void NullCheckVisitor::do_Base           (Base*            x) {}
 774 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}
 775 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
 776 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}
 777 void NullCheckVisitor::do_UnsafeGet      (UnsafeGet*       x) {}
 778 void NullCheckVisitor::do_UnsafePut      (UnsafePut*       x) {}
 779 void NullCheckVisitor::do_UnsafeGetAndSet(UnsafeGetAndSet* x) {}
 780 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check();
 781                                                                 nce()->handle_ProfileCall(x); }
 782 void NullCheckVisitor::do_ProfileReturnType (ProfileReturnType* x) { nce()->handle_ProfileReturnType(x); }
 783 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}
 784 void NullCheckVisitor::do_ProfileACmpTypes(ProfileACmpTypes* x) { nce()->handle_ProfileACmpTypes(x); }
 785 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}
 786 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}
 787 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
 788 #ifdef ASSERT
 789 void NullCheckVisitor::do_Assert         (Assert*          x) {}
 790 #endif
 791 
 792 void NullCheckEliminator::visit(Value* p) {
 793   assert(*p != NULL, "should not find NULL instructions");
 794   if (visitable(*p)) {
 795     mark_visited(*p);
 796     (*p)->visit(&_visitor);
 797   }
 798 }
 799 
 800 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
 801   ValueSet* state = state_for(block);
 802   if (state == NULL) {
 803     state = incoming_state->copy();
 804     set_state_for(block, state);

1088   }
1089 
1090   Value recv = x->receiver();
1091   if (!set_contains(recv)) {
1092     set_put(recv);
1093     if (PrintNullCheckElimination) {
1094       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1095     }
1096   }
1097   clear_last_explicit_null_check();
1098 }
1099 
1100 
1101 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1102   set_put(x);
1103   if (PrintNullCheckElimination) {
1104     tty->print_cr("NewInstance %d is non-null", x->id());
1105   }
1106 }
1107 
1108 void NullCheckEliminator::handle_NewInlineTypeInstance(NewInlineTypeInstance* x) {
1109   set_put(x);
1110   if (PrintNullCheckElimination) {
1111     tty->print_cr("NewInlineTypeInstance %d is non-null", x->id());
1112   }
1113 }
1114 
1115 
1116 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1117   set_put(x);
1118   if (PrintNullCheckElimination) {
1119     tty->print_cr("NewArray %d is non-null", x->id());
1120   }
1121 }
1122 
1123 
1124 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1125   set_put(x);
1126   if (PrintNullCheckElimination) {
1127     tty->print_cr("ExceptionObject %d is non-null", x->id());
1128   }
1129 }
1130 
1131 
1132 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1133   Value obj = x->obj();
1134   if (set_contains(obj)) {

1199     // Value is non-null => update Phi
1200     if (PrintNullCheckElimination) {
1201       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1202     }
1203     x->set_needs_null_check(false);
1204   } else if (set_contains(x)) {
1205     set_remove(x);
1206   }
1207 }
1208 
1209 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1210   for (int i = 0; i < x->nb_profiled_args(); i++) {
1211     x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1212   }
1213 }
1214 
1215 void NullCheckEliminator::handle_ProfileReturnType(ProfileReturnType* x) {
1216   x->set_needs_null_check(!set_contains(x->ret()));
1217 }
1218 
1219 void NullCheckEliminator::handle_ProfileACmpTypes(ProfileACmpTypes* x) {
1220   x->set_left_maybe_null(!set_contains(x->left()));
1221   x->set_right_maybe_null(!set_contains(x->right()));
1222 }
1223 
1224 void Optimizer::eliminate_null_checks() {
1225   ResourceMark rm;
1226 
1227   NullCheckEliminator nce(this);
1228 
1229   if (PrintNullCheckElimination) {
1230     tty->print_cr("Starting null check elimination for method %s::%s%s",
1231                   ir()->method()->holder()->name()->as_utf8(),
1232                   ir()->method()->name()->as_utf8(),
1233                   ir()->method()->signature()->as_symbol()->as_utf8());
1234   }
1235 
1236   // Apply to graph
1237   nce.iterate(ir()->start());
1238 
1239   // walk over the graph looking for exception
1240   // handlers and iterate over them as well
1241   int nblocks = BlockBegin::number_of_blocks();
1242   BlockList blocks(nblocks);
1243   boolArray visited_block(nblocks, nblocks, false);
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