1 /*
   2  * Copyright (c) 1999, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "c1/c1_Canonicalizer.hpp"
  27 #include "c1/c1_Optimizer.hpp"
  28 #include "c1/c1_ValueMap.hpp"
  29 #include "c1/c1_ValueSet.hpp"
  30 #include "c1/c1_ValueStack.hpp"
  31 #include "memory/resourceArea.hpp"
  32 #include "utilities/bitMap.inline.hpp"
  33 #include "compiler/compileLog.hpp"
  34 
  35 define_array(ValueSetArray, ValueSet*);
  36 define_stack(ValueSetList, ValueSetArray);
  37 
  38 
  39 Optimizer::Optimizer(IR* ir) {
  40   assert(ir->is_valid(), "IR must be valid");
  41   _ir = ir;
  42 }
  43 
  44 class CE_Eliminator: public BlockClosure {
  45  private:
  46   IR* _hir;
  47   int _cee_count;                                // the number of CEs successfully eliminated
  48   int _ifop_count;                               // the number of IfOps successfully simplified
  49   int _has_substitution;
  50 
  51  public:
  52   CE_Eliminator(IR* hir) : _cee_count(0), _ifop_count(0), _hir(hir) {
  53     _has_substitution = false;
  54     _hir->iterate_preorder(this);
  55     if (_has_substitution) {
  56       // substituted some ifops/phis, so resolve the substitution
  57       SubstitutionResolver sr(_hir);
  58     }
  59 
  60     CompileLog* log = _hir->compilation()->log();
  61     if (log != NULL)
  62       log->set_context("optimize name='cee'");
  63   }
  64 
  65   ~CE_Eliminator() {
  66     CompileLog* log = _hir->compilation()->log();
  67     if (log != NULL)
  68       log->clear_context(); // skip marker if nothing was printed
  69   }
  70 
  71   int cee_count() const                          { return _cee_count; }
  72   int ifop_count() const                         { return _ifop_count; }
  73 
  74   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
  75     int e = sux->number_of_exception_handlers();
  76     for (int i = 0; i < e; i++) {
  77       BlockBegin* xhandler = sux->exception_handler_at(i);
  78       block->add_exception_handler(xhandler);
  79 
  80       assert(xhandler->is_predecessor(sux), "missing predecessor");
  81       if (sux->number_of_preds() == 0) {
  82         // sux is disconnected from graph so disconnect from exception handlers
  83         xhandler->remove_predecessor(sux);
  84       }
  85       if (!xhandler->is_predecessor(block)) {
  86         xhandler->add_predecessor(block);
  87       }
  88     }
  89   }
  90 
  91   virtual void block_do(BlockBegin* block);
  92 
  93  private:
  94   Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
  95 };
  96 
  97 void CE_Eliminator::block_do(BlockBegin* block) {
  98   // 1) find conditional expression
  99   // check if block ends with an If
 100   If* if_ = block->end()->as_If();
 101   if (if_ == NULL) return;
 102 
 103   // check if If works on int or object types
 104   // (we cannot handle If's working on long, float or doubles yet,
 105   // since IfOp doesn't support them - these If's show up if cmp
 106   // operations followed by If's are eliminated)
 107   ValueType* if_type = if_->x()->type();
 108   if (!if_type->is_int() && !if_type->is_object()) return;
 109 
 110   BlockBegin* t_block = if_->tsux();
 111   BlockBegin* f_block = if_->fsux();
 112   Instruction* t_cur = t_block->next();
 113   Instruction* f_cur = f_block->next();
 114 
 115   // one Constant may be present between BlockBegin and BlockEnd
 116   Value t_const = NULL;
 117   Value f_const = NULL;
 118   if (t_cur->as_Constant() != NULL && !t_cur->can_trap()) {
 119     t_const = t_cur;
 120     t_cur = t_cur->next();
 121   }
 122   if (f_cur->as_Constant() != NULL && !f_cur->can_trap()) {
 123     f_const = f_cur;
 124     f_cur = f_cur->next();
 125   }
 126 
 127   // check if both branches end with a goto
 128   Goto* t_goto = t_cur->as_Goto();
 129   if (t_goto == NULL) return;
 130   Goto* f_goto = f_cur->as_Goto();
 131   if (f_goto == NULL) return;
 132 
 133   // check if both gotos merge into the same block
 134   BlockBegin* sux = t_goto->default_sux();
 135   if (sux != f_goto->default_sux()) return;
 136 
 137   // check if at least one word was pushed on sux_state
 138   // inlining depths must match
 139   ValueStack* if_state = if_->state();
 140   ValueStack* sux_state = sux->state();
 141   if (if_state->scope()->level() > sux_state->scope()->level()) {
 142     while (sux_state->scope() != if_state->scope()) {
 143       if_state = if_state->caller_state();
 144       assert(if_state != NULL, "states do not match up");
 145     }
 146   } else if (if_state->scope()->level() < sux_state->scope()->level()) {
 147     while (sux_state->scope() != if_state->scope()) {
 148       sux_state = sux_state->caller_state();
 149       assert(sux_state != NULL, "states do not match up");
 150     }
 151   }
 152 
 153   if (sux_state->stack_size() <= if_state->stack_size()) return;
 154 
 155   // check if phi function is present at end of successor stack and that
 156   // only this phi was pushed on the stack
 157   Value sux_phi = sux_state->stack_at(if_state->stack_size());
 158   if (sux_phi == NULL || sux_phi->as_Phi() == NULL || sux_phi->as_Phi()->block() != sux) return;
 159   if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;
 160 
 161   // get the values that were pushed in the true- and false-branch
 162   Value t_value = t_goto->state()->stack_at(if_state->stack_size());
 163   Value f_value = f_goto->state()->stack_at(if_state->stack_size());
 164 
 165   // backend does not support floats
 166   assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");
 167   if (t_value->type()->is_float_kind()) return;
 168 
 169   // check that successor has no other phi functions but sux_phi
 170   // this can happen when t_block or f_block contained additonal stores to local variables
 171   // that are no longer represented by explicit instructions
 172   for_each_phi_fun(sux, phi,
 173                    if (phi != sux_phi) return;
 174                    );
 175   // true and false blocks can't have phis
 176   for_each_phi_fun(t_block, phi, return; );
 177   for_each_phi_fun(f_block, phi, return; );
 178 
 179   // 2) substitute conditional expression
 180   //    with an IfOp followed by a Goto
 181   // cut if_ away and get node before
 182   Instruction* cur_end = if_->prev();
 183 
 184   // append constants of true- and false-block if necessary
 185   // clone constants because original block must not be destroyed
 186   assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
 187   if (t_value == t_const) {
 188     t_value = new Constant(t_const->type());
 189     NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
 190     cur_end = cur_end->set_next(t_value);
 191   }
 192   if (f_value == f_const) {
 193     f_value = new Constant(f_const->type());
 194     NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
 195     cur_end = cur_end->set_next(f_value);
 196   }
 197 
 198   Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
 199   assert(result != NULL, "make_ifop must return a non-null instruction");
 200   if (!result->is_linked() && result->can_be_linked()) {
 201     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
 202     cur_end = cur_end->set_next(result);
 203   }
 204 
 205   // append Goto to successor
 206   ValueStack* state_before = if_->state_before();
 207   Goto* goto_ = new Goto(sux, state_before, if_->is_safepoint() || t_goto->is_safepoint() || f_goto->is_safepoint());
 208 
 209   // prepare state for Goto
 210   ValueStack* goto_state = if_state;
 211   goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
 212   goto_state->push(result->type(), result);
 213   assert(goto_state->is_same(sux_state), "states must match now");
 214   goto_->set_state(goto_state);
 215 
 216   cur_end = cur_end->set_next(goto_, goto_state->bci());
 217 
 218   // Adjust control flow graph
 219   BlockBegin::disconnect_edge(block, t_block);
 220   BlockBegin::disconnect_edge(block, f_block);
 221   if (t_block->number_of_preds() == 0) {
 222     BlockBegin::disconnect_edge(t_block, sux);
 223   }
 224   adjust_exception_edges(block, t_block);
 225   if (f_block->number_of_preds() == 0) {
 226     BlockBegin::disconnect_edge(f_block, sux);
 227   }
 228   adjust_exception_edges(block, f_block);
 229 
 230   // update block end
 231   block->set_end(goto_);
 232 
 233   // substitute the phi if possible
 234   if (sux_phi->as_Phi()->operand_count() == 1) {
 235     assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
 236     sux_phi->set_subst(result);
 237     _has_substitution = true;
 238   }
 239 
 240   // 3) successfully eliminated a conditional expression
 241   _cee_count++;
 242   if (PrintCEE) {
 243     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());
 244     tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
 245   }
 246 
 247   _hir->verify();
 248 }
 249 
 250 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
 251   if (!OptimizeIfOps) {
 252     return new IfOp(x, cond, y, tval, fval);
 253   }
 254 
 255   tval = tval->subst();
 256   fval = fval->subst();
 257   if (tval == fval) {
 258     _ifop_count++;
 259     return tval;
 260   }
 261 
 262   x = x->subst();
 263   y = y->subst();
 264 
 265   Constant* y_const = y->as_Constant();
 266   if (y_const != NULL) {
 267     IfOp* x_ifop = x->as_IfOp();
 268     if (x_ifop != NULL) {                 // x is an ifop, y is a constant
 269       Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
 270       Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
 271 
 272       if (x_tval_const != NULL && x_fval_const != NULL) {
 273         Instruction::Condition x_ifop_cond = x_ifop->cond();
 274 
 275         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
 276         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
 277 
 278         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 279         if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
 280           Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
 281           Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
 282 
 283           _ifop_count++;
 284           if (new_tval == new_fval) {
 285             return new_tval;
 286           } else {
 287             return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
 288           }
 289         }
 290       }
 291     } else {
 292       Constant* x_const = x->as_Constant();
 293       if (x_const != NULL) {         // x and y are constants
 294         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
 295         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 296         if (x_compare_res != Constant::not_comparable) {
 297           _ifop_count++;
 298           return x_compare_res == Constant::cond_true ? tval : fval;
 299         }
 300       }
 301     }
 302   }
 303   return new IfOp(x, cond, y, tval, fval);
 304 }
 305 
 306 void Optimizer::eliminate_conditional_expressions() {
 307   // find conditional expressions & replace them with IfOps
 308   CE_Eliminator ce(ir());
 309 }
 310 
 311 class BlockMerger: public BlockClosure {
 312  private:
 313   IR* _hir;
 314   int _merge_count;              // the number of block pairs successfully merged
 315 
 316  public:
 317   BlockMerger(IR* hir)
 318   : _hir(hir)
 319   , _merge_count(0)
 320   {
 321     _hir->iterate_preorder(this);
 322     CompileLog* log = _hir->compilation()->log();
 323     if (log != NULL)
 324       log->set_context("optimize name='eliminate_blocks'");
 325   }
 326 
 327   ~BlockMerger() {
 328     CompileLog* log = _hir->compilation()->log();
 329     if (log != NULL)
 330       log->clear_context(); // skip marker if nothing was printed
 331   }
 332 
 333   bool try_merge(BlockBegin* block) {
 334     BlockEnd* end = block->end();
 335     if (end->as_Goto() != NULL) {
 336       assert(end->number_of_sux() == 1, "end must have exactly one successor");
 337       // Note: It would be sufficient to check for the number of successors (= 1)
 338       //       in order to decide if this block can be merged potentially. That
 339       //       would then also include switch statements w/ only a default case.
 340       //       However, in that case we would need to make sure the switch tag
 341       //       expression is executed if it can produce observable side effects.
 342       //       We should probably have the canonicalizer simplifying such switch
 343       //       statements and then we are sure we don't miss these merge opportunities
 344       //       here (was bug - gri 7/7/99).
 345       BlockBegin* sux = end->default_sux();
 346       if (sux->number_of_preds() == 1 && !sux->is_entry_block() && !end->is_safepoint()) {
 347         // merge the two blocks
 348 
 349 #ifdef ASSERT
 350         // verify that state at the end of block and at the beginning of sux are equal
 351         // no phi functions must be present at beginning of sux
 352         ValueStack* sux_state = sux->state();
 353         ValueStack* end_state = end->state();
 354 
 355         assert(end_state->scope() == sux_state->scope(), "scopes must match");
 356         assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
 357         assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
 358 
 359         int index;
 360         Value sux_value;
 361         for_each_stack_value(sux_state, index, sux_value) {
 362           assert(sux_value == end_state->stack_at(index), "stack not equal");
 363         }
 364         for_each_local_value(sux_state, index, sux_value) {
 365           assert(sux_value == end_state->local_at(index), "locals not equal");
 366         }
 367         assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
 368 #endif
 369 
 370         // find instruction before end & append first instruction of sux block
 371         Instruction* prev = end->prev();
 372         Instruction* next = sux->next();
 373         assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
 374         prev->set_next(next);
 375         prev->fixup_block_pointers();
 376         sux->disconnect_from_graph();
 377         block->set_end(sux->end());
 378         // add exception handlers of deleted block, if any
 379         for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
 380           BlockBegin* xhandler = sux->exception_handler_at(k);
 381           block->add_exception_handler(xhandler);
 382 
 383           // also substitute predecessor of exception handler
 384           assert(xhandler->is_predecessor(sux), "missing predecessor");
 385           xhandler->remove_predecessor(sux);
 386           if (!xhandler->is_predecessor(block)) {
 387             xhandler->add_predecessor(block);
 388           }
 389         }
 390 
 391         // debugging output
 392         _merge_count++;
 393         if (PrintBlockElimination) {
 394           tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
 395                         _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
 396         }
 397 
 398         _hir->verify();
 399 
 400         If* if_ = block->end()->as_If();
 401         if (if_) {
 402           IfOp* ifop    = if_->x()->as_IfOp();
 403           Constant* con = if_->y()->as_Constant();
 404           bool swapped = false;
 405           if (!con || !ifop) {
 406             ifop = if_->y()->as_IfOp();
 407             con  = if_->x()->as_Constant();
 408             swapped = true;
 409           }
 410           if (con && ifop) {
 411             Constant* tval = ifop->tval()->as_Constant();
 412             Constant* fval = ifop->fval()->as_Constant();
 413             if (tval && fval) {
 414               // Find the instruction before if_, starting with ifop.
 415               // When if_ and ifop are not in the same block, prev
 416               // becomes NULL In such (rare) cases it is not
 417               // profitable to perform the optimization.
 418               Value prev = ifop;
 419               while (prev != NULL && prev->next() != if_) {
 420                 prev = prev->next();
 421               }
 422 
 423               if (prev != NULL) {
 424                 Instruction::Condition cond = if_->cond();
 425                 BlockBegin* tsux = if_->tsux();
 426                 BlockBegin* fsux = if_->fsux();
 427                 if (swapped) {
 428                   cond = Instruction::mirror(cond);
 429                 }
 430 
 431                 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
 432                 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
 433                 if (tblock != fblock && !if_->is_safepoint()) {
 434                   If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
 435                                      tblock, fblock, if_->state_before(), if_->is_safepoint());
 436                   newif->set_state(if_->state()->copy());
 437 
 438                   assert(prev->next() == if_, "must be guaranteed by above search");
 439                   NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
 440                   prev->set_next(newif);
 441                   block->set_end(newif);
 442 
 443                   _merge_count++;
 444                   if (PrintBlockElimination) {
 445                     tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
 446                   }
 447 
 448                   _hir->verify();
 449                 }
 450               }
 451             }
 452           }
 453         }
 454 
 455         return true;
 456       }
 457     }
 458     return false;
 459   }
 460 
 461   virtual void block_do(BlockBegin* block) {
 462     _hir->verify();
 463     // repeat since the same block may merge again
 464     while (try_merge(block)) {
 465       _hir->verify();
 466     }
 467   }
 468 };
 469 
 470 
 471 void Optimizer::eliminate_blocks() {
 472   // merge blocks if possible
 473   BlockMerger bm(ir());
 474 }
 475 
 476 
 477 class NullCheckEliminator;
 478 class NullCheckVisitor: public InstructionVisitor {
 479 private:
 480   NullCheckEliminator* _nce;
 481   NullCheckEliminator* nce() { return _nce; }
 482 
 483 public:
 484   NullCheckVisitor() {}
 485 
 486   void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
 487 
 488   void do_Phi            (Phi*             x);
 489   void do_Local          (Local*           x);
 490   void do_Constant       (Constant*        x);
 491   void do_LoadField      (LoadField*       x);
 492   void do_StoreField     (StoreField*      x);
 493   void do_ArrayLength    (ArrayLength*     x);
 494   void do_LoadIndexed    (LoadIndexed*     x);
 495   void do_StoreIndexed   (StoreIndexed*    x);
 496   void do_NegateOp       (NegateOp*        x);
 497   void do_ArithmeticOp   (ArithmeticOp*    x);
 498   void do_ShiftOp        (ShiftOp*         x);
 499   void do_LogicOp        (LogicOp*         x);
 500   void do_CompareOp      (CompareOp*       x);
 501   void do_IfOp           (IfOp*            x);
 502   void do_Convert        (Convert*         x);
 503   void do_NullCheck      (NullCheck*       x);
 504   void do_TypeCast       (TypeCast*        x);
 505   void do_Invoke         (Invoke*          x);
 506   void do_NewInstance    (NewInstance*     x);
 507   void do_NewTypeArray   (NewTypeArray*    x);
 508   void do_NewObjectArray (NewObjectArray*  x);
 509   void do_NewMultiArray  (NewMultiArray*   x);
 510   void do_CheckCast      (CheckCast*       x);
 511   void do_InstanceOf     (InstanceOf*      x);
 512   void do_MonitorEnter   (MonitorEnter*    x);
 513   void do_MonitorExit    (MonitorExit*     x);
 514   void do_Intrinsic      (Intrinsic*       x);
 515   void do_BlockBegin     (BlockBegin*      x);
 516   void do_Goto           (Goto*            x);
 517   void do_If             (If*              x);
 518   void do_IfInstanceOf   (IfInstanceOf*    x);
 519   void do_TableSwitch    (TableSwitch*     x);
 520   void do_LookupSwitch   (LookupSwitch*    x);
 521   void do_Return         (Return*          x);
 522   void do_Throw          (Throw*           x);
 523   void do_Base           (Base*            x);
 524   void do_OsrEntry       (OsrEntry*        x);
 525   void do_ExceptionObject(ExceptionObject* x);
 526   void do_RoundFP        (RoundFP*         x);
 527   void do_UnsafeGetRaw   (UnsafeGetRaw*    x);
 528   void do_UnsafePutRaw   (UnsafePutRaw*    x);
 529   void do_UnsafeGetObject(UnsafeGetObject* x);
 530   void do_UnsafePutObject(UnsafePutObject* x);
 531   void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);
 532   void do_ProfileCall    (ProfileCall*     x);
 533   void do_ProfileReturnType (ProfileReturnType*  x);
 534   void do_ProfileInvoke  (ProfileInvoke*   x);
 535   void do_RuntimeCall    (RuntimeCall*     x);
 536   void do_MemBar         (MemBar*          x);
 537   void do_RangeCheckPredicate(RangeCheckPredicate* x);
 538 #ifdef ASSERT
 539   void do_Assert         (Assert*          x);
 540 #endif
 541 };
 542 
 543 
 544 // Because of a static contained within (for the purpose of iteration
 545 // over instructions), it is only valid to have one of these active at
 546 // a time
 547 class NullCheckEliminator: public ValueVisitor {
 548  private:
 549   Optimizer*        _opt;
 550 
 551   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block
 552   BlockList*        _work_list;                   // Basic blocks to visit
 553 
 554   bool visitable(Value x) {
 555     assert(_visitable_instructions != NULL, "check");
 556     return _visitable_instructions->contains(x);
 557   }
 558   void mark_visited(Value x) {
 559     assert(_visitable_instructions != NULL, "check");
 560     _visitable_instructions->remove(x);
 561   }
 562   void mark_visitable(Value x) {
 563     assert(_visitable_instructions != NULL, "check");
 564     _visitable_instructions->put(x);
 565   }
 566   void clear_visitable_state() {
 567     assert(_visitable_instructions != NULL, "check");
 568     _visitable_instructions->clear();
 569   }
 570 
 571   ValueSet*         _set;                         // current state, propagated to subsequent BlockBegins
 572   ValueSetList      _block_states;                // BlockBegin null-check states for all processed blocks
 573   NullCheckVisitor  _visitor;
 574   NullCheck*        _last_explicit_null_check;
 575 
 576   bool set_contains(Value x)                      { assert(_set != NULL, "check"); return _set->contains(x); }
 577   void set_put     (Value x)                      { assert(_set != NULL, "check"); _set->put(x); }
 578   void set_remove  (Value x)                      { assert(_set != NULL, "check"); _set->remove(x); }
 579 
 580   BlockList* work_list()                          { return _work_list; }
 581 
 582   void iterate_all();
 583   void iterate_one(BlockBegin* block);
 584 
 585   ValueSet* state()                               { return _set; }
 586   void      set_state_from (ValueSet* state)      { _set->set_from(state); }
 587   ValueSet* state_for      (BlockBegin* block)    { return _block_states[block->block_id()]; }
 588   void      set_state_for  (BlockBegin* block, ValueSet* stack) { _block_states[block->block_id()] = stack; }
 589   // Returns true if caused a change in the block's state.
 590   bool      merge_state_for(BlockBegin* block,
 591                             ValueSet*   incoming_state);
 592 
 593  public:
 594   // constructor
 595   NullCheckEliminator(Optimizer* opt)
 596     : _opt(opt)
 597     , _set(new ValueSet())
 598     , _last_explicit_null_check(NULL)
 599     , _block_states(BlockBegin::number_of_blocks(), NULL)
 600     , _work_list(new BlockList()) {
 601     _visitable_instructions = new ValueSet();
 602     _visitor.set_eliminator(this);
 603     CompileLog* log = _opt->ir()->compilation()->log();
 604     if (log != NULL)
 605       log->set_context("optimize name='null_check_elimination'");
 606   }
 607 
 608   ~NullCheckEliminator() {
 609     CompileLog* log = _opt->ir()->compilation()->log();
 610     if (log != NULL)
 611       log->clear_context(); // skip marker if nothing was printed
 612   }
 613 
 614   Optimizer*  opt()                               { return _opt; }
 615   IR*         ir ()                               { return opt()->ir(); }
 616 
 617   // Process a graph
 618   void iterate(BlockBegin* root);
 619 
 620   void visit(Value* f);
 621 
 622   // In some situations (like NullCheck(x); getfield(x)) the debug
 623   // information from the explicit NullCheck can be used to populate
 624   // the getfield, even if the two instructions are in different
 625   // scopes; this allows implicit null checks to be used but the
 626   // correct exception information to be generated. We must clear the
 627   // last-traversed NullCheck when we reach a potentially-exception-
 628   // throwing instruction, as well as in some other cases.
 629   void        set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
 630   NullCheck*  last_explicit_null_check()                     { return _last_explicit_null_check; }
 631   Value       last_explicit_null_check_obj()                 { return (_last_explicit_null_check
 632                                                                          ? _last_explicit_null_check->obj()
 633                                                                          : NULL); }
 634   NullCheck*  consume_last_explicit_null_check() {
 635     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
 636     _last_explicit_null_check->set_can_trap(false);
 637     return _last_explicit_null_check;
 638   }
 639   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }
 640 
 641   // Handlers for relevant instructions
 642   // (separated out from NullCheckVisitor for clarity)
 643 
 644   // The basic contract is that these must leave the instruction in
 645   // the desired state; must not assume anything about the state of
 646   // the instruction. We make multiple passes over some basic blocks
 647   // and the last pass is the only one whose result is valid.
 648   void handle_AccessField     (AccessField* x);
 649   void handle_ArrayLength     (ArrayLength* x);
 650   void handle_LoadIndexed     (LoadIndexed* x);
 651   void handle_StoreIndexed    (StoreIndexed* x);
 652   void handle_NullCheck       (NullCheck* x);
 653   void handle_Invoke          (Invoke* x);
 654   void handle_NewInstance     (NewInstance* x);
 655   void handle_NewArray        (NewArray* x);
 656   void handle_AccessMonitor   (AccessMonitor* x);
 657   void handle_Intrinsic       (Intrinsic* x);
 658   void handle_ExceptionObject (ExceptionObject* x);
 659   void handle_Phi             (Phi* x);
 660   void handle_ProfileCall     (ProfileCall* x);
 661   void handle_ProfileReturnType (ProfileReturnType* x);
 662 };
 663 
 664 
 665 // NEEDS_CLEANUP
 666 // There may be other instructions which need to clear the last
 667 // explicit null check. Anything across which we can not hoist the
 668 // debug information for a NullCheck instruction must clear it. It
 669 // might be safer to pattern match "NullCheck ; {AccessField,
 670 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
 671 // Should test to see performance hit of clearing it for all handlers
 672 // with empty bodies below. If it is negligible then we should leave
 673 // that in for safety, otherwise should think more about it.
 674 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }
 675 void NullCheckVisitor::do_Local          (Local*           x) {}
 676 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }
 677 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }
 678 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }
 679 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }
 680 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }
 681 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }
 682 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}
 683 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
 684 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}
 685 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}
 686 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}
 687 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}
 688 void NullCheckVisitor::do_Convert        (Convert*         x) {}
 689 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }
 690 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}
 691 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }
 692 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }
 693 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }
 694 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }
 695 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }
 696 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }
 697 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}
 698 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }
 699 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }
 700 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }
 701 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}
 702 void NullCheckVisitor::do_Goto           (Goto*            x) {}
 703 void NullCheckVisitor::do_If             (If*              x) {}
 704 void NullCheckVisitor::do_IfInstanceOf   (IfInstanceOf*    x) {}
 705 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}
 706 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}
 707 void NullCheckVisitor::do_Return         (Return*          x) {}
 708 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }
 709 void NullCheckVisitor::do_Base           (Base*            x) {}
 710 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}
 711 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
 712 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}
 713 void NullCheckVisitor::do_UnsafeGetRaw   (UnsafeGetRaw*    x) {}
 714 void NullCheckVisitor::do_UnsafePutRaw   (UnsafePutRaw*    x) {}
 715 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}
 716 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}
 717 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}
 718 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check();
 719                                                                 nce()->handle_ProfileCall(x); }
 720 void NullCheckVisitor::do_ProfileReturnType (ProfileReturnType* x) { nce()->handle_ProfileReturnType(x); }
 721 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}
 722 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}
 723 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}
 724 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
 725 #ifdef ASSERT
 726 void NullCheckVisitor::do_Assert         (Assert*          x) {}
 727 #endif
 728 
 729 void NullCheckEliminator::visit(Value* p) {
 730   assert(*p != NULL, "should not find NULL instructions");
 731   if (visitable(*p)) {
 732     mark_visited(*p);
 733     (*p)->visit(&_visitor);
 734   }
 735 }
 736 
 737 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
 738   ValueSet* state = state_for(block);
 739   if (state == NULL) {
 740     state = incoming_state->copy();
 741     set_state_for(block, state);
 742     return true;
 743   } else {
 744     bool changed = state->set_intersect(incoming_state);
 745     if (PrintNullCheckElimination && changed) {
 746       tty->print_cr("Block %d's null check state changed", block->block_id());
 747     }
 748     return changed;
 749   }
 750 }
 751 
 752 
 753 void NullCheckEliminator::iterate_all() {
 754   while (work_list()->length() > 0) {
 755     iterate_one(work_list()->pop());
 756   }
 757 }
 758 
 759 
 760 void NullCheckEliminator::iterate_one(BlockBegin* block) {
 761   clear_visitable_state();
 762   // clear out an old explicit null checks
 763   set_last_explicit_null_check(NULL);
 764 
 765   if (PrintNullCheckElimination) {
 766     tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
 767                   block->block_id(),
 768                   ir()->method()->holder()->name()->as_utf8(),
 769                   ir()->method()->name()->as_utf8(),
 770                   ir()->method()->signature()->as_symbol()->as_utf8());
 771   }
 772 
 773   // Create new state if none present (only happens at root)
 774   if (state_for(block) == NULL) {
 775     ValueSet* tmp_state = new ValueSet();
 776     set_state_for(block, tmp_state);
 777     // Initial state is that local 0 (receiver) is non-null for
 778     // non-static methods
 779     ValueStack* stack  = block->state();
 780     IRScope*    scope  = stack->scope();
 781     ciMethod*   method = scope->method();
 782     if (!method->is_static()) {
 783       Local* local0 = stack->local_at(0)->as_Local();
 784       assert(local0 != NULL, "must be");
 785       assert(local0->type() == objectType, "invalid type of receiver");
 786 
 787       if (local0 != NULL) {
 788         // Local 0 is used in this scope
 789         tmp_state->put(local0);
 790         if (PrintNullCheckElimination) {
 791           tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
 792         }
 793       }
 794     }
 795   }
 796 
 797   // Must copy block's state to avoid mutating it during iteration
 798   // through the block -- otherwise "not-null" states can accidentally
 799   // propagate "up" through the block during processing of backward
 800   // branches and algorithm is incorrect (and does not converge)
 801   set_state_from(state_for(block));
 802 
 803   // allow visiting of Phis belonging to this block
 804   for_each_phi_fun(block, phi,
 805                    mark_visitable(phi);
 806                    );
 807 
 808   BlockEnd* e = block->end();
 809   assert(e != NULL, "incomplete graph");
 810   int i;
 811 
 812   // Propagate the state before this block into the exception
 813   // handlers.  They aren't true successors since we aren't guaranteed
 814   // to execute the whole block before executing them.  Also putting
 815   // them on first seems to help reduce the amount of iteration to
 816   // reach a fixed point.
 817   for (i = 0; i < block->number_of_exception_handlers(); i++) {
 818     BlockBegin* next = block->exception_handler_at(i);
 819     if (merge_state_for(next, state())) {
 820       if (!work_list()->contains(next)) {
 821         work_list()->push(next);
 822       }
 823     }
 824   }
 825 
 826   // Iterate through block, updating state.
 827   for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
 828     // Mark instructions in this block as visitable as they are seen
 829     // in the instruction list.  This keeps the iteration from
 830     // visiting instructions which are references in other blocks or
 831     // visiting instructions more than once.
 832     mark_visitable(instr);
 833     if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
 834       mark_visited(instr);
 835       instr->input_values_do(this);
 836       instr->visit(&_visitor);
 837     }
 838   }
 839 
 840   // Propagate state to successors if necessary
 841   for (i = 0; i < e->number_of_sux(); i++) {
 842     BlockBegin* next = e->sux_at(i);
 843     if (merge_state_for(next, state())) {
 844       if (!work_list()->contains(next)) {
 845         work_list()->push(next);
 846       }
 847     }
 848   }
 849 }
 850 
 851 
 852 void NullCheckEliminator::iterate(BlockBegin* block) {
 853   work_list()->push(block);
 854   iterate_all();
 855 }
 856 
 857 void NullCheckEliminator::handle_AccessField(AccessField* x) {
 858   if (x->is_static()) {
 859     if (x->as_LoadField() != NULL) {
 860       // If the field is a non-null static final object field (as is
 861       // often the case for sun.misc.Unsafe), put this LoadField into
 862       // the non-null map
 863       ciField* field = x->field();
 864       if (field->is_constant()) {
 865         ciConstant field_val = field->constant_value();
 866         BasicType field_type = field_val.basic_type();
 867         if (field_type == T_OBJECT || field_type == T_ARRAY) {
 868           ciObject* obj_val = field_val.as_object();
 869           if (!obj_val->is_null_object()) {
 870             if (PrintNullCheckElimination) {
 871               tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
 872                             x->id());
 873             }
 874             set_put(x);
 875           }
 876         }
 877       }
 878     }
 879     // Be conservative
 880     clear_last_explicit_null_check();
 881     return;
 882   }
 883 
 884   Value obj = x->obj();
 885   if (set_contains(obj)) {
 886     // Value is non-null => update AccessField
 887     if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
 888       x->set_explicit_null_check(consume_last_explicit_null_check());
 889       x->set_needs_null_check(true);
 890       if (PrintNullCheckElimination) {
 891         tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
 892                       x->explicit_null_check()->id(), x->id(), obj->id());
 893       }
 894     } else {
 895       x->set_explicit_null_check(NULL);
 896       x->set_needs_null_check(false);
 897       if (PrintNullCheckElimination) {
 898         tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
 899       }
 900     }
 901   } else {
 902     set_put(obj);
 903     if (PrintNullCheckElimination) {
 904       tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
 905     }
 906     // Ensure previous passes do not cause wrong state
 907     x->set_needs_null_check(true);
 908     x->set_explicit_null_check(NULL);
 909   }
 910   clear_last_explicit_null_check();
 911 }
 912 
 913 
 914 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
 915   Value array = x->array();
 916   if (set_contains(array)) {
 917     // Value is non-null => update AccessArray
 918     if (last_explicit_null_check_obj() == array) {
 919       x->set_explicit_null_check(consume_last_explicit_null_check());
 920       x->set_needs_null_check(true);
 921       if (PrintNullCheckElimination) {
 922         tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
 923                       x->explicit_null_check()->id(), x->id(), array->id());
 924       }
 925     } else {
 926       x->set_explicit_null_check(NULL);
 927       x->set_needs_null_check(false);
 928       if (PrintNullCheckElimination) {
 929         tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
 930       }
 931     }
 932   } else {
 933     set_put(array);
 934     if (PrintNullCheckElimination) {
 935       tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
 936     }
 937     // Ensure previous passes do not cause wrong state
 938     x->set_needs_null_check(true);
 939     x->set_explicit_null_check(NULL);
 940   }
 941   clear_last_explicit_null_check();
 942 }
 943 
 944 
 945 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
 946   Value array = x->array();
 947   if (set_contains(array)) {
 948     // Value is non-null => update AccessArray
 949     if (last_explicit_null_check_obj() == array) {
 950       x->set_explicit_null_check(consume_last_explicit_null_check());
 951       x->set_needs_null_check(true);
 952       if (PrintNullCheckElimination) {
 953         tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
 954                       x->explicit_null_check()->id(), x->id(), array->id());
 955       }
 956     } else {
 957       x->set_explicit_null_check(NULL);
 958       x->set_needs_null_check(false);
 959       if (PrintNullCheckElimination) {
 960         tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
 961       }
 962     }
 963   } else {
 964     set_put(array);
 965     if (PrintNullCheckElimination) {
 966       tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
 967     }
 968     // Ensure previous passes do not cause wrong state
 969     x->set_needs_null_check(true);
 970     x->set_explicit_null_check(NULL);
 971   }
 972   clear_last_explicit_null_check();
 973 }
 974 
 975 
 976 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
 977   Value array = x->array();
 978   if (set_contains(array)) {
 979     // Value is non-null => update AccessArray
 980     if (PrintNullCheckElimination) {
 981       tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
 982     }
 983     x->set_needs_null_check(false);
 984   } else {
 985     set_put(array);
 986     if (PrintNullCheckElimination) {
 987       tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
 988     }
 989     // Ensure previous passes do not cause wrong state
 990     x->set_needs_null_check(true);
 991   }
 992   clear_last_explicit_null_check();
 993 }
 994 
 995 
 996 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
 997   Value obj = x->obj();
 998   if (set_contains(obj)) {
 999     // Already proven to be non-null => this NullCheck is useless
1000     if (PrintNullCheckElimination) {
1001       tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
1002     }
1003     // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
1004     // The code generator won't emit LIR for a NullCheck that cannot trap.
1005     x->set_can_trap(false);
1006   } else {
1007     // May be null => add to map and set last explicit NullCheck
1008     x->set_can_trap(true);
1009     // make sure it's pinned if it can trap
1010     x->pin(Instruction::PinExplicitNullCheck);
1011     set_put(obj);
1012     set_last_explicit_null_check(x);
1013     if (PrintNullCheckElimination) {
1014       tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1015     }
1016   }
1017 }
1018 
1019 
1020 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1021   if (!x->has_receiver()) {
1022     // Be conservative
1023     clear_last_explicit_null_check();
1024     return;
1025   }
1026 
1027   Value recv = x->receiver();
1028   if (!set_contains(recv)) {
1029     set_put(recv);
1030     if (PrintNullCheckElimination) {
1031       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1032     }
1033   }
1034   clear_last_explicit_null_check();
1035 }
1036 
1037 
1038 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1039   set_put(x);
1040   if (PrintNullCheckElimination) {
1041     tty->print_cr("NewInstance %d is non-null", x->id());
1042   }
1043 }
1044 
1045 
1046 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1047   set_put(x);
1048   if (PrintNullCheckElimination) {
1049     tty->print_cr("NewArray %d is non-null", x->id());
1050   }
1051 }
1052 
1053 
1054 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1055   set_put(x);
1056   if (PrintNullCheckElimination) {
1057     tty->print_cr("ExceptionObject %d is non-null", x->id());
1058   }
1059 }
1060 
1061 
1062 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1063   Value obj = x->obj();
1064   if (set_contains(obj)) {
1065     // Value is non-null => update AccessMonitor
1066     if (PrintNullCheckElimination) {
1067       tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1068     }
1069     x->set_needs_null_check(false);
1070   } else {
1071     set_put(obj);
1072     if (PrintNullCheckElimination) {
1073       tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1074     }
1075     // Ensure previous passes do not cause wrong state
1076     x->set_needs_null_check(true);
1077   }
1078   clear_last_explicit_null_check();
1079 }
1080 
1081 
1082 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1083   if (!x->has_receiver()) {
1084     if (x->id() == vmIntrinsics::_arraycopy) {
1085       for (int i = 0; i < x->number_of_arguments(); i++) {
1086         x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1087       }
1088     }
1089 
1090     // Be conservative
1091     clear_last_explicit_null_check();
1092     return;
1093   }
1094 
1095   Value recv = x->receiver();
1096   if (set_contains(recv)) {
1097     // Value is non-null => update Intrinsic
1098     if (PrintNullCheckElimination) {
1099       tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());
1100     }
1101     x->set_needs_null_check(false);
1102   } else {
1103     set_put(recv);
1104     if (PrintNullCheckElimination) {
1105       tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());
1106     }
1107     // Ensure previous passes do not cause wrong state
1108     x->set_needs_null_check(true);
1109   }
1110   clear_last_explicit_null_check();
1111 }
1112 
1113 
1114 void NullCheckEliminator::handle_Phi(Phi* x) {
1115   int i;
1116   bool all_non_null = true;
1117   if (x->is_illegal()) {
1118     all_non_null = false;
1119   } else {
1120     for (i = 0; i < x->operand_count(); i++) {
1121       Value input = x->operand_at(i);
1122       if (!set_contains(input)) {
1123         all_non_null = false;
1124       }
1125     }
1126   }
1127 
1128   if (all_non_null) {
1129     // Value is non-null => update Phi
1130     if (PrintNullCheckElimination) {
1131       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1132     }
1133     x->set_needs_null_check(false);
1134   } else if (set_contains(x)) {
1135     set_remove(x);
1136   }
1137 }
1138 
1139 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1140   for (int i = 0; i < x->nb_profiled_args(); i++) {
1141     x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1142   }
1143 }
1144 
1145 void NullCheckEliminator::handle_ProfileReturnType(ProfileReturnType* x) {
1146   x->set_needs_null_check(!set_contains(x->ret()));
1147 }
1148 
1149 void Optimizer::eliminate_null_checks() {
1150   ResourceMark rm;
1151 
1152   NullCheckEliminator nce(this);
1153 
1154   if (PrintNullCheckElimination) {
1155     tty->print_cr("Starting null check elimination for method %s::%s%s",
1156                   ir()->method()->holder()->name()->as_utf8(),
1157                   ir()->method()->name()->as_utf8(),
1158                   ir()->method()->signature()->as_symbol()->as_utf8());
1159   }
1160 
1161   // Apply to graph
1162   nce.iterate(ir()->start());
1163 
1164   // walk over the graph looking for exception
1165   // handlers and iterate over them as well
1166   int nblocks = BlockBegin::number_of_blocks();
1167   BlockList blocks(nblocks);
1168   boolArray visited_block(nblocks, false);
1169 
1170   blocks.push(ir()->start());
1171   visited_block[ir()->start()->block_id()] = true;
1172   for (int i = 0; i < blocks.length(); i++) {
1173     BlockBegin* b = blocks[i];
1174     // exception handlers need to be treated as additional roots
1175     for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1176       BlockBegin* excp = b->exception_handler_at(e);
1177       int id = excp->block_id();
1178       if (!visited_block[id]) {
1179         blocks.push(excp);
1180         visited_block[id] = true;
1181         nce.iterate(excp);
1182       }
1183     }
1184     // traverse successors
1185     BlockEnd *end = b->end();
1186     for (int s = end->number_of_sux(); s-- > 0; ) {
1187       BlockBegin* next = end->sux_at(s);
1188       int id = next->block_id();
1189       if (!visited_block[id]) {
1190         blocks.push(next);
1191         visited_block[id] = true;
1192       }
1193     }
1194   }
1195 
1196 
1197   if (PrintNullCheckElimination) {
1198     tty->print_cr("Done with null check elimination for method %s::%s%s",
1199                   ir()->method()->holder()->name()->as_utf8(),
1200                   ir()->method()->name()->as_utf8(),
1201                   ir()->method()->signature()->as_symbol()->as_utf8());
1202   }
1203 }