1 /*
   2  * Copyright (c) 1999, 2012, 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 "utilities/bitMap.inline.hpp"
  32 #include "compiler/compileLog.hpp"
  33 
  34 define_array(ValueSetArray, ValueSet*);
  35 define_stack(ValueSetList, ValueSetArray);
  36 
  37 
  38 Optimizer::Optimizer(IR* ir) {
  39   assert(ir->is_valid(), "IR must be valid");
  40   _ir = ir;
  41 }
  42 
  43 class CE_Eliminator: public BlockClosure {
  44  private:
  45   IR* _hir;
  46   int _cee_count;                                // the number of CEs successfully eliminated
  47   int _ifop_count;                               // the number of IfOps successfully simplified
  48   int _has_substitution;
  49 
  50  public:
  51   CE_Eliminator(IR* hir) : _cee_count(0), _ifop_count(0), _hir(hir) {
  52     _has_substitution = false;
  53     _hir->iterate_preorder(this);
  54     if (_has_substitution) {
  55       // substituted some ifops/phis, so resolve the substitution
  56       SubstitutionResolver sr(_hir);
  57     }
  58 
  59     CompileLog* log = _hir->compilation()->log();
  60     if (log != NULL)
  61       log->set_context("optimize name='cee'");
  62   }
  63 
  64   ~CE_Eliminator() {
  65     CompileLog* log = _hir->compilation()->log();
  66     if (log != NULL)
  67       log->clear_context(); // skip marker if nothing was printed
  68   }
  69 
  70   int cee_count() const                          { return _cee_count; }
  71   int ifop_count() const                         { return _ifop_count; }
  72 
  73   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
  74     int e = sux->number_of_exception_handlers();
  75     for (int i = 0; i < e; i++) {
  76       BlockBegin* xhandler = sux->exception_handler_at(i);
  77       block->add_exception_handler(xhandler);
  78 
  79       assert(xhandler->is_predecessor(sux), "missing predecessor");
  80       if (sux->number_of_preds() == 0) {
  81         // sux is disconnected from graph so disconnect from exception handlers
  82         xhandler->remove_predecessor(sux);
  83       }
  84       if (!xhandler->is_predecessor(block)) {
  85         xhandler->add_predecessor(block);
  86       }
  87     }
  88   }
  89 
  90   virtual void block_do(BlockBegin* block);
  91 
  92  private:
  93   Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
  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 
 114   // one Constant may be present between BlockBegin and BlockEnd
 115   Value t_const = NULL;
 116   Value f_const = NULL;
 117   if (t_cur->as_Constant() != NULL && !t_cur->can_trap()) {
 118     t_const = t_cur;
 119     t_cur = t_cur->next();
 120   }
 121   if (f_cur->as_Constant() != NULL && !f_cur->can_trap()) {
 122     f_const = f_cur;
 123     f_cur = f_cur->next();
 124   }
 125 
 126   // check if both branches end with a goto
 127   Goto* t_goto = t_cur->as_Goto();
 128   if (t_goto == NULL) return;
 129   Goto* f_goto = f_cur->as_Goto();
 130   if (f_goto == NULL) return;
 131 
 132   // check if both gotos merge into the same block
 133   BlockBegin* sux = t_goto->default_sux();
 134   if (sux != f_goto->default_sux()) return;
 135 
 136   // check if at least one word was pushed on sux_state
 137   // inlining depths must match
 138   ValueStack* if_state = if_->state();
 139   ValueStack* sux_state = sux->state();
 140   if (if_state->scope()->level() > sux_state->scope()->level()) {
 141     while (sux_state->scope() != if_state->scope()) {
 142       if_state = if_state->caller_state();
 143       assert(if_state != NULL, "states do not match up");
 144     }
 145   } else if (if_state->scope()->level() < sux_state->scope()->level()) {
 146     while (sux_state->scope() != if_state->scope()) {
 147       sux_state = sux_state->caller_state();
 148       assert(sux_state != NULL, "states do not match up");
 149     }
 150   }
 151 
 152   if (sux_state->stack_size() <= if_state->stack_size()) return;
 153 
 154   // check if phi function is present at end of successor stack and that
 155   // only this phi was pushed on the stack
 156   Value sux_phi = sux_state->stack_at(if_state->stack_size());
 157   if (sux_phi == NULL || sux_phi->as_Phi() == NULL || sux_phi->as_Phi()->block() != sux) return;
 158   if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;
 159 
 160   // get the values that were pushed in the true- and false-branch
 161   Value t_value = t_goto->state()->stack_at(if_state->stack_size());
 162   Value f_value = f_goto->state()->stack_at(if_state->stack_size());
 163 
 164   // backend does not support floats
 165   assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");
 166   if (t_value->type()->is_float_kind()) return;
 167 
 168   // check that successor has no other phi functions but sux_phi
 169   // this can happen when t_block or f_block contained additonal stores to local variables
 170   // that are no longer represented by explicit instructions
 171   for_each_phi_fun(sux, phi,
 172                    if (phi != sux_phi) return;
 173                    );
 174   // true and false blocks can't have phis
 175   for_each_phi_fun(t_block, phi, return; );
 176   for_each_phi_fun(f_block, phi, return; );
 177 
 178   // 2) substitute conditional expression
 179   //    with an IfOp followed by a Goto
 180   // cut if_ away and get node before
 181   Instruction* cur_end = if_->prev();
 182 
 183   // append constants of true- and false-block if necessary
 184   // clone constants because original block must not be destroyed
 185   assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
 186   if (t_value == t_const) {
 187     t_value = new Constant(t_const->type());
 188     NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
 189     cur_end = cur_end->set_next(t_value);
 190   }
 191   if (f_value == f_const) {
 192     f_value = new Constant(f_const->type());
 193     NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
 194     cur_end = cur_end->set_next(f_value);
 195   }
 196 
 197   Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
 198   assert(result != NULL, "make_ifop must return a non-null instruction");
 199   if (!result->is_linked() && result->can_be_linked()) {
 200     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
 201     cur_end = cur_end->set_next(result);
 202   }
 203 
 204   // append Goto to successor
 205   ValueStack* state_before = if_->state_before();
 206   Goto* goto_ = new Goto(sux, state_before, if_->is_safepoint() || t_goto->is_safepoint() || f_goto->is_safepoint());
 207 
 208   // prepare state for Goto
 209   ValueStack* goto_state = if_state;
 210   goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
 211   goto_state->push(result->type(), result);
 212   assert(goto_state->is_same(sux_state), "states must match now");
 213   goto_->set_state(goto_state);
 214 
 215   cur_end = cur_end->set_next(goto_, goto_state->bci());
 216 
 217   // Adjust control flow graph
 218   BlockBegin::disconnect_edge(block, t_block);
 219   BlockBegin::disconnect_edge(block, f_block);
 220   if (t_block->number_of_preds() == 0) {
 221     BlockBegin::disconnect_edge(t_block, sux);
 222   }
 223   adjust_exception_edges(block, t_block);
 224   if (f_block->number_of_preds() == 0) {
 225     BlockBegin::disconnect_edge(f_block, sux);
 226   }
 227   adjust_exception_edges(block, f_block);
 228 
 229   // update block end
 230   block->set_end(goto_);
 231 
 232   // substitute the phi if possible
 233   if (sux_phi->as_Phi()->operand_count() == 1) {
 234     assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
 235     sux_phi->set_subst(result);
 236     _has_substitution = true;
 237   }
 238 
 239   // 3) successfully eliminated a conditional expression
 240   _cee_count++;
 241   if (PrintCEE) {
 242     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());
 243     tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
 244   }
 245 
 246   _hir->verify();
 247 }
 248 
 249 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
 250   if (!OptimizeIfOps) {
 251     return new IfOp(x, cond, y, tval, fval);
 252   }
 253 
 254   tval = tval->subst();
 255   fval = fval->subst();
 256   if (tval == fval) {
 257     _ifop_count++;
 258     return tval;
 259   }
 260 
 261   x = x->subst();
 262   y = y->subst();
 263 
 264   Constant* y_const = y->as_Constant();
 265   if (y_const != NULL) {
 266     IfOp* x_ifop = x->as_IfOp();
 267     if (x_ifop != NULL) {                 // x is an ifop, y is a constant
 268       Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
 269       Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
 270 
 271       if (x_tval_const != NULL && x_fval_const != NULL) {
 272         Instruction::Condition x_ifop_cond = x_ifop->cond();
 273 
 274         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
 275         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
 276 
 277         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 278         if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
 279           Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
 280           Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
 281 
 282           _ifop_count++;
 283           if (new_tval == new_fval) {
 284             return new_tval;
 285           } else {
 286             return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
 287           }
 288         }
 289       }
 290     } else {
 291       Constant* x_const = x->as_Constant();
 292       if (x_const != NULL) {         // x and y are constants
 293         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
 294         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 295         if (x_compare_res != Constant::not_comparable) {
 296           _ifop_count++;
 297           return x_compare_res == Constant::cond_true ? tval : fval;
 298         }
 299       }
 300     }
 301   }
 302   return new IfOp(x, cond, y, tval, fval);
 303 }
 304 
 305 void Optimizer::eliminate_conditional_expressions() {
 306   // find conditional expressions & replace them with IfOps
 307   CE_Eliminator ce(ir());
 308 }
 309 
 310 class BlockMerger: public BlockClosure {
 311  private:
 312   IR* _hir;
 313   int _merge_count;              // the number of block pairs successfully merged
 314 
 315  public:
 316   BlockMerger(IR* hir)
 317   : _hir(hir)
 318   , _merge_count(0)
 319   {
 320     _hir->iterate_preorder(this);
 321     CompileLog* log = _hir->compilation()->log();
 322     if (log != NULL)
 323       log->set_context("optimize name='eliminate_blocks'");
 324   }
 325 
 326   ~BlockMerger() {
 327     CompileLog* log = _hir->compilation()->log();
 328     if (log != NULL)
 329       log->clear_context(); // skip marker if nothing was printed
 330   }
 331 
 332   bool try_merge(BlockBegin* block) {
 333     BlockEnd* end = block->end();
 334     if (end->as_Goto() != NULL) {
 335       assert(end->number_of_sux() == 1, "end must have exactly one successor");
 336       // Note: It would be sufficient to check for the number of successors (= 1)
 337       //       in order to decide if this block can be merged potentially. That
 338       //       would then also include switch statements w/ only a default case.
 339       //       However, in that case we would need to make sure the switch tag
 340       //       expression is executed if it can produce observable side effects.
 341       //       We should probably have the canonicalizer simplifying such switch
 342       //       statements and then we are sure we don't miss these merge opportunities
 343       //       here (was bug - gri 7/7/99).
 344       BlockBegin* sux = end->default_sux();
 345       if (sux->number_of_preds() == 1 && !sux->is_entry_block() && !end->is_safepoint()) {
 346         // merge the two blocks
 347 
 348 #ifdef ASSERT
 349         // verify that state at the end of block and at the beginning of sux are equal
 350         // no phi functions must be present at beginning of sux
 351         ValueStack* sux_state = sux->state();
 352         ValueStack* end_state = end->state();
 353 
 354         assert(end_state->scope() == sux_state->scope(), "scopes must match");
 355         assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
 356         assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
 357 
 358         int index;
 359         Value sux_value;
 360         for_each_stack_value(sux_state, index, sux_value) {
 361           assert(sux_value == end_state->stack_at(index), "stack not equal");
 362         }
 363         for_each_local_value(sux_state, index, sux_value) {
 364           assert(sux_value == end_state->local_at(index), "locals not equal");
 365         }
 366         assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
 367 #endif
 368 
 369         // find instruction before end & append first instruction of sux block
 370         Instruction* prev = end->prev();
 371         Instruction* next = sux->next();
 372         assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
 373         prev->set_next(next);
 374         prev->fixup_block_pointers();
 375         sux->disconnect_from_graph();
 376         block->set_end(sux->end());
 377         // add exception handlers of deleted block, if any
 378         for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
 379           BlockBegin* xhandler = sux->exception_handler_at(k);
 380           block->add_exception_handler(xhandler);
 381 
 382           // also substitute predecessor of exception handler
 383           assert(xhandler->is_predecessor(sux), "missing predecessor");
 384           xhandler->remove_predecessor(sux);
 385           if (!xhandler->is_predecessor(block)) {
 386             xhandler->add_predecessor(block);
 387           }
 388         }
 389 
 390         // debugging output
 391         _merge_count++;
 392         if (PrintBlockElimination) {
 393           tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
 394                         _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
 395         }
 396 
 397         _hir->verify();
 398 
 399         If* if_ = block->end()->as_If();
 400         if (if_) {
 401           IfOp* ifop    = if_->x()->as_IfOp();
 402           Constant* con = if_->y()->as_Constant();
 403           bool swapped = false;
 404           if (!con || !ifop) {
 405             ifop = if_->y()->as_IfOp();
 406             con  = if_->x()->as_Constant();
 407             swapped = true;
 408           }
 409           if (con && ifop) {
 410             Constant* tval = ifop->tval()->as_Constant();
 411             Constant* fval = ifop->fval()->as_Constant();
 412             if (tval && fval) {
 413               // Find the instruction before if_, starting with ifop.
 414               // When if_ and ifop are not in the same block, prev
 415               // becomes NULL In such (rare) cases it is not
 416               // profitable to perform the optimization.
 417               Value prev = ifop;
 418               while (prev != NULL && prev->next() != if_) {
 419                 prev = prev->next();
 420               }
 421 
 422               if (prev != NULL) {
 423                 Instruction::Condition cond = if_->cond();
 424                 BlockBegin* tsux = if_->tsux();
 425                 BlockBegin* fsux = if_->fsux();
 426                 if (swapped) {
 427                   cond = Instruction::mirror(cond);
 428                 }
 429 
 430                 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
 431                 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
 432                 if (tblock != fblock && !if_->is_safepoint()) {
 433                   If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
 434                                      tblock, fblock, if_->state_before(), if_->is_safepoint());
 435                   newif->set_state(if_->state()->copy());
 436 
 437                   assert(prev->next() == if_, "must be guaranteed by above search");
 438                   NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
 439                   prev->set_next(newif);
 440                   block->set_end(newif);
 441 
 442                   _merge_count++;
 443                   if (PrintBlockElimination) {
 444                     tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
 445                   }
 446 
 447                   _hir->verify();
 448                 }
 449               }
 450             }
 451           }
 452         }
 453 
 454         return true;
 455       }
 456     }
 457     return false;
 458   }
 459 
 460   virtual void block_do(BlockBegin* block) {
 461     _hir->verify();
 462     // repeat since the same block may merge again
 463     while (try_merge(block)) {
 464       _hir->verify();
 465     }
 466   }
 467 };
 468 
 469 
 470 void Optimizer::eliminate_blocks() {
 471   // merge blocks if possible
 472   BlockMerger bm(ir());
 473 }
 474 
 475 
 476 class NullCheckEliminator;
 477 class NullCheckVisitor: public InstructionVisitor {
 478 private:
 479   NullCheckEliminator* _nce;
 480   NullCheckEliminator* nce() { return _nce; }
 481 
 482 public:
 483   NullCheckVisitor() {}
 484 
 485   void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
 486 
 487   void do_Phi            (Phi*             x);
 488   void do_Local          (Local*           x);
 489   void do_Constant       (Constant*        x);
 490   void do_LoadField      (LoadField*       x);
 491   void do_StoreField     (StoreField*      x);
 492   void do_ArrayLength    (ArrayLength*     x);
 493   void do_LoadIndexed    (LoadIndexed*     x);
 494   void do_StoreIndexed   (StoreIndexed*    x);
 495   void do_NegateOp       (NegateOp*        x);
 496   void do_ArithmeticOp   (ArithmeticOp*    x);
 497   void do_ShiftOp        (ShiftOp*         x);
 498   void do_LogicOp        (LogicOp*         x);
 499   void do_CompareOp      (CompareOp*       x);
 500   void do_IfOp           (IfOp*            x);
 501   void do_Convert        (Convert*         x);
 502   void do_NullCheck      (NullCheck*       x);
 503   void do_TypeCast       (TypeCast*        x);
 504   void do_Invoke         (Invoke*          x);
 505   void do_NewInstance    (NewInstance*     x);
 506   void do_NewTypeArray   (NewTypeArray*    x);
 507   void do_NewObjectArray (NewObjectArray*  x);
 508   void do_NewMultiArray  (NewMultiArray*   x);
 509   void do_CheckCast      (CheckCast*       x);
 510   void do_InstanceOf     (InstanceOf*      x);
 511   void do_MonitorEnter   (MonitorEnter*    x);
 512   void do_MonitorExit    (MonitorExit*     x);
 513   void do_Intrinsic      (Intrinsic*       x);
 514   void do_BlockBegin     (BlockBegin*      x);
 515   void do_Goto           (Goto*            x);
 516   void do_If             (If*              x);
 517   void do_IfInstanceOf   (IfInstanceOf*    x);
 518   void do_TableSwitch    (TableSwitch*     x);
 519   void do_LookupSwitch   (LookupSwitch*    x);
 520   void do_Return         (Return*          x);
 521   void do_Throw          (Throw*           x);
 522   void do_Base           (Base*            x);
 523   void do_OsrEntry       (OsrEntry*        x);
 524   void do_ExceptionObject(ExceptionObject* x);
 525   void do_RoundFP        (RoundFP*         x);
 526   void do_UnsafeGetRaw   (UnsafeGetRaw*    x);
 527   void do_UnsafePutRaw   (UnsafePutRaw*    x);
 528   void do_UnsafeGetObject(UnsafeGetObject* x);
 529   void do_UnsafePutObject(UnsafePutObject* x);
 530   void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);
 531   void do_UnsafePrefetchRead (UnsafePrefetchRead*  x);
 532   void do_UnsafePrefetchWrite(UnsafePrefetchWrite* x);
 533   void do_ProfileCall    (ProfileCall*     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   void do_Assert         (Assert*          x);
 539 };
 540 
 541 
 542 // Because of a static contained within (for the purpose of iteration
 543 // over instructions), it is only valid to have one of these active at
 544 // a time
 545 class NullCheckEliminator: public ValueVisitor {
 546  private:
 547   Optimizer*        _opt;
 548 
 549   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block
 550   BlockList*        _work_list;                   // Basic blocks to visit
 551 
 552   bool visitable(Value x) {
 553     assert(_visitable_instructions != NULL, "check");
 554     return _visitable_instructions->contains(x);
 555   }
 556   void mark_visited(Value x) {
 557     assert(_visitable_instructions != NULL, "check");
 558     _visitable_instructions->remove(x);
 559   }
 560   void mark_visitable(Value x) {
 561     assert(_visitable_instructions != NULL, "check");
 562     _visitable_instructions->put(x);
 563   }
 564   void clear_visitable_state() {
 565     assert(_visitable_instructions != NULL, "check");
 566     _visitable_instructions->clear();
 567   }
 568 
 569   ValueSet*         _set;                         // current state, propagated to subsequent BlockBegins
 570   ValueSetList      _block_states;                // BlockBegin null-check states for all processed blocks
 571   NullCheckVisitor  _visitor;
 572   NullCheck*        _last_explicit_null_check;
 573 
 574   bool set_contains(Value x)                      { assert(_set != NULL, "check"); return _set->contains(x); }
 575   void set_put     (Value x)                      { assert(_set != NULL, "check"); _set->put(x); }
 576   void set_remove  (Value x)                      { assert(_set != NULL, "check"); _set->remove(x); }
 577 
 578   BlockList* work_list()                          { return _work_list; }
 579 
 580   void iterate_all();
 581   void iterate_one(BlockBegin* block);
 582 
 583   ValueSet* state()                               { return _set; }
 584   void      set_state_from (ValueSet* state)      { _set->set_from(state); }
 585   ValueSet* state_for      (BlockBegin* block)    { return _block_states[block->block_id()]; }
 586   void      set_state_for  (BlockBegin* block, ValueSet* stack) { _block_states[block->block_id()] = stack; }
 587   // Returns true if caused a change in the block's state.
 588   bool      merge_state_for(BlockBegin* block,
 589                             ValueSet*   incoming_state);
 590 
 591  public:
 592   // constructor
 593   NullCheckEliminator(Optimizer* opt)
 594     : _opt(opt)
 595     , _set(new ValueSet())
 596     , _last_explicit_null_check(NULL)
 597     , _block_states(BlockBegin::number_of_blocks(), NULL)
 598     , _work_list(new BlockList()) {
 599     _visitable_instructions = new ValueSet();
 600     _visitor.set_eliminator(this);
 601     CompileLog* log = _opt->ir()->compilation()->log();
 602     if (log != NULL)
 603       log->set_context("optimize name='null_check_elimination'");
 604   }
 605 
 606   ~NullCheckEliminator() {
 607     CompileLog* log = _opt->ir()->compilation()->log();
 608     if (log != NULL)
 609       log->clear_context(); // skip marker if nothing was printed
 610   }
 611 
 612   Optimizer*  opt()                               { return _opt; }
 613   IR*         ir ()                               { return opt()->ir(); }
 614 
 615   // Process a graph
 616   void iterate(BlockBegin* root);
 617 
 618   void visit(Value* f);
 619 
 620   // In some situations (like NullCheck(x); getfield(x)) the debug
 621   // information from the explicit NullCheck can be used to populate
 622   // the getfield, even if the two instructions are in different
 623   // scopes; this allows implicit null checks to be used but the
 624   // correct exception information to be generated. We must clear the
 625   // last-traversed NullCheck when we reach a potentially-exception-
 626   // throwing instruction, as well as in some other cases.
 627   void        set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
 628   NullCheck*  last_explicit_null_check()                     { return _last_explicit_null_check; }
 629   Value       last_explicit_null_check_obj()                 { return (_last_explicit_null_check
 630                                                                          ? _last_explicit_null_check->obj()
 631                                                                          : NULL); }
 632   NullCheck*  consume_last_explicit_null_check() {
 633     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
 634     _last_explicit_null_check->set_can_trap(false);
 635     return _last_explicit_null_check;
 636   }
 637   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }
 638 
 639   // Handlers for relevant instructions
 640   // (separated out from NullCheckVisitor for clarity)
 641 
 642   // The basic contract is that these must leave the instruction in
 643   // the desired state; must not assume anything about the state of
 644   // the instruction. We make multiple passes over some basic blocks
 645   // and the last pass is the only one whose result is valid.
 646   void handle_AccessField     (AccessField* x);
 647   void handle_ArrayLength     (ArrayLength* x);
 648   void handle_LoadIndexed     (LoadIndexed* x);
 649   void handle_StoreIndexed    (StoreIndexed* x);
 650   void handle_NullCheck       (NullCheck* x);
 651   void handle_Invoke          (Invoke* x);
 652   void handle_NewInstance     (NewInstance* x);
 653   void handle_NewArray        (NewArray* x);
 654   void handle_AccessMonitor   (AccessMonitor* x);
 655   void handle_Intrinsic       (Intrinsic* x);
 656   void handle_ExceptionObject (ExceptionObject* x);
 657   void handle_Phi             (Phi* x);
 658 };
 659 
 660 
 661 // NEEDS_CLEANUP
 662 // There may be other instructions which need to clear the last
 663 // explicit null check. Anything across which we can not hoist the
 664 // debug information for a NullCheck instruction must clear it. It
 665 // might be safer to pattern match "NullCheck ; {AccessField,
 666 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
 667 // Should test to see performance hit of clearing it for all handlers
 668 // with empty bodies below. If it is negligible then we should leave
 669 // that in for safety, otherwise should think more about it.
 670 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }
 671 void NullCheckVisitor::do_Local          (Local*           x) {}
 672 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }
 673 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }
 674 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }
 675 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }
 676 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }
 677 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }
 678 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}
 679 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
 680 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}
 681 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}
 682 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}
 683 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}
 684 void NullCheckVisitor::do_Convert        (Convert*         x) {}
 685 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }
 686 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}
 687 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }
 688 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }
 689 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }
 690 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }
 691 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }
 692 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }
 693 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}
 694 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }
 695 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }
 696 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }
 697 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}
 698 void NullCheckVisitor::do_Goto           (Goto*            x) {}
 699 void NullCheckVisitor::do_If             (If*              x) {}
 700 void NullCheckVisitor::do_IfInstanceOf   (IfInstanceOf*    x) {}
 701 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}
 702 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}
 703 void NullCheckVisitor::do_Return         (Return*          x) {}
 704 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }
 705 void NullCheckVisitor::do_Base           (Base*            x) {}
 706 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}
 707 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
 708 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}
 709 void NullCheckVisitor::do_UnsafeGetRaw   (UnsafeGetRaw*    x) {}
 710 void NullCheckVisitor::do_UnsafePutRaw   (UnsafePutRaw*    x) {}
 711 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}
 712 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}
 713 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}
 714 void NullCheckVisitor::do_UnsafePrefetchRead (UnsafePrefetchRead*  x) {}
 715 void NullCheckVisitor::do_UnsafePrefetchWrite(UnsafePrefetchWrite* x) {}
 716 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check(); }
 717 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}
 718 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}
 719 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}
 720 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
 721 void NullCheckVisitor::do_Assert         (Assert*          x) {}
 722 
 723 
 724 void NullCheckEliminator::visit(Value* p) {
 725   assert(*p != NULL, "should not find NULL instructions");
 726   if (visitable(*p)) {
 727     mark_visited(*p);
 728     (*p)->visit(&_visitor);
 729   }
 730 }
 731 
 732 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
 733   ValueSet* state = state_for(block);
 734   if (state == NULL) {
 735     state = incoming_state->copy();
 736     set_state_for(block, state);
 737     return true;
 738   } else {
 739     bool changed = state->set_intersect(incoming_state);
 740     if (PrintNullCheckElimination && changed) {
 741       tty->print_cr("Block %d's null check state changed", block->block_id());
 742     }
 743     return changed;
 744   }
 745 }
 746 
 747 
 748 void NullCheckEliminator::iterate_all() {
 749   while (work_list()->length() > 0) {
 750     iterate_one(work_list()->pop());
 751   }
 752 }
 753 
 754 
 755 void NullCheckEliminator::iterate_one(BlockBegin* block) {
 756   clear_visitable_state();
 757   // clear out an old explicit null checks
 758   set_last_explicit_null_check(NULL);
 759 
 760   if (PrintNullCheckElimination) {
 761     tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
 762                   block->block_id(),
 763                   ir()->method()->holder()->name()->as_utf8(),
 764                   ir()->method()->name()->as_utf8(),
 765                   ir()->method()->signature()->as_symbol()->as_utf8());
 766   }
 767 
 768   // Create new state if none present (only happens at root)
 769   if (state_for(block) == NULL) {
 770     ValueSet* tmp_state = new ValueSet();
 771     set_state_for(block, tmp_state);
 772     // Initial state is that local 0 (receiver) is non-null for
 773     // non-static methods
 774     ValueStack* stack  = block->state();
 775     IRScope*    scope  = stack->scope();
 776     ciMethod*   method = scope->method();
 777     if (!method->is_static()) {
 778       Local* local0 = stack->local_at(0)->as_Local();
 779       assert(local0 != NULL, "must be");
 780       assert(local0->type() == objectType, "invalid type of receiver");
 781 
 782       if (local0 != NULL) {
 783         // Local 0 is used in this scope
 784         tmp_state->put(local0);
 785         if (PrintNullCheckElimination) {
 786           tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
 787         }
 788       }
 789     }
 790   }
 791 
 792   // Must copy block's state to avoid mutating it during iteration
 793   // through the block -- otherwise "not-null" states can accidentally
 794   // propagate "up" through the block during processing of backward
 795   // branches and algorithm is incorrect (and does not converge)
 796   set_state_from(state_for(block));
 797 
 798   // allow visiting of Phis belonging to this block
 799   for_each_phi_fun(block, phi,
 800                    mark_visitable(phi);
 801                    );
 802 
 803   BlockEnd* e = block->end();
 804   assert(e != NULL, "incomplete graph");
 805   int i;
 806 
 807   // Propagate the state before this block into the exception
 808   // handlers.  They aren't true successors since we aren't guaranteed
 809   // to execute the whole block before executing them.  Also putting
 810   // them on first seems to help reduce the amount of iteration to
 811   // reach a fixed point.
 812   for (i = 0; i < block->number_of_exception_handlers(); i++) {
 813     BlockBegin* next = block->exception_handler_at(i);
 814     if (merge_state_for(next, state())) {
 815       if (!work_list()->contains(next)) {
 816         work_list()->push(next);
 817       }
 818     }
 819   }
 820 
 821   // Iterate through block, updating state.
 822   for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
 823     // Mark instructions in this block as visitable as they are seen
 824     // in the instruction list.  This keeps the iteration from
 825     // visiting instructions which are references in other blocks or
 826     // visiting instructions more than once.
 827     mark_visitable(instr);
 828     if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
 829       mark_visited(instr);
 830       instr->input_values_do(this);
 831       instr->visit(&_visitor);
 832     }
 833   }
 834 
 835   // Propagate state to successors if necessary
 836   for (i = 0; i < e->number_of_sux(); i++) {
 837     BlockBegin* next = e->sux_at(i);
 838     if (merge_state_for(next, state())) {
 839       if (!work_list()->contains(next)) {
 840         work_list()->push(next);
 841       }
 842     }
 843   }
 844 }
 845 
 846 
 847 void NullCheckEliminator::iterate(BlockBegin* block) {
 848   work_list()->push(block);
 849   iterate_all();
 850 }
 851 
 852 void NullCheckEliminator::handle_AccessField(AccessField* x) {
 853   if (x->is_static()) {
 854     if (x->as_LoadField() != NULL) {
 855       // If the field is a non-null static final object field (as is
 856       // often the case for sun.misc.Unsafe), put this LoadField into
 857       // the non-null map
 858       ciField* field = x->field();
 859       if (field->is_constant()) {
 860         ciConstant field_val = field->constant_value();
 861         BasicType field_type = field_val.basic_type();
 862         if (field_type == T_OBJECT || field_type == T_ARRAY) {
 863           ciObject* obj_val = field_val.as_object();
 864           if (!obj_val->is_null_object()) {
 865             if (PrintNullCheckElimination) {
 866               tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
 867                             x->id());
 868             }
 869             set_put(x);
 870           }
 871         }
 872       }
 873     }
 874     // Be conservative
 875     clear_last_explicit_null_check();
 876     return;
 877   }
 878 
 879   Value obj = x->obj();
 880   if (set_contains(obj)) {
 881     // Value is non-null => update AccessField
 882     if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
 883       x->set_explicit_null_check(consume_last_explicit_null_check());
 884       x->set_needs_null_check(true);
 885       if (PrintNullCheckElimination) {
 886         tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
 887                       x->explicit_null_check()->id(), x->id(), obj->id());
 888       }
 889     } else {
 890       x->set_explicit_null_check(NULL);
 891       x->set_needs_null_check(false);
 892       if (PrintNullCheckElimination) {
 893         tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
 894       }
 895     }
 896   } else {
 897     set_put(obj);
 898     if (PrintNullCheckElimination) {
 899       tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
 900     }
 901     // Ensure previous passes do not cause wrong state
 902     x->set_needs_null_check(true);
 903     x->set_explicit_null_check(NULL);
 904   }
 905   clear_last_explicit_null_check();
 906 }
 907 
 908 
 909 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
 910   Value array = x->array();
 911   if (set_contains(array)) {
 912     // Value is non-null => update AccessArray
 913     if (last_explicit_null_check_obj() == array) {
 914       x->set_explicit_null_check(consume_last_explicit_null_check());
 915       x->set_needs_null_check(true);
 916       if (PrintNullCheckElimination) {
 917         tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
 918                       x->explicit_null_check()->id(), x->id(), array->id());
 919       }
 920     } else {
 921       x->set_explicit_null_check(NULL);
 922       x->set_needs_null_check(false);
 923       if (PrintNullCheckElimination) {
 924         tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
 925       }
 926     }
 927   } else {
 928     set_put(array);
 929     if (PrintNullCheckElimination) {
 930       tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
 931     }
 932     // Ensure previous passes do not cause wrong state
 933     x->set_needs_null_check(true);
 934     x->set_explicit_null_check(NULL);
 935   }
 936   clear_last_explicit_null_check();
 937 }
 938 
 939 
 940 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
 941   Value array = x->array();
 942   if (set_contains(array)) {
 943     // Value is non-null => update AccessArray
 944     if (last_explicit_null_check_obj() == array) {
 945       x->set_explicit_null_check(consume_last_explicit_null_check());
 946       x->set_needs_null_check(true);
 947       if (PrintNullCheckElimination) {
 948         tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
 949                       x->explicit_null_check()->id(), x->id(), array->id());
 950       }
 951     } else {
 952       x->set_explicit_null_check(NULL);
 953       x->set_needs_null_check(false);
 954       if (PrintNullCheckElimination) {
 955         tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
 956       }
 957     }
 958   } else {
 959     set_put(array);
 960     if (PrintNullCheckElimination) {
 961       tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
 962     }
 963     // Ensure previous passes do not cause wrong state
 964     x->set_needs_null_check(true);
 965     x->set_explicit_null_check(NULL);
 966   }
 967   clear_last_explicit_null_check();
 968 }
 969 
 970 
 971 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
 972   Value array = x->array();
 973   if (set_contains(array)) {
 974     // Value is non-null => update AccessArray
 975     if (PrintNullCheckElimination) {
 976       tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
 977     }
 978     x->set_needs_null_check(false);
 979   } else {
 980     set_put(array);
 981     if (PrintNullCheckElimination) {
 982       tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
 983     }
 984     // Ensure previous passes do not cause wrong state
 985     x->set_needs_null_check(true);
 986   }
 987   clear_last_explicit_null_check();
 988 }
 989 
 990 
 991 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
 992   Value obj = x->obj();
 993   if (set_contains(obj)) {
 994     // Already proven to be non-null => this NullCheck is useless
 995     if (PrintNullCheckElimination) {
 996       tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
 997     }
 998     // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
 999     // The code generator won't emit LIR for a NullCheck that cannot trap.
1000     x->set_can_trap(false);
1001   } else {
1002     // May be null => add to map and set last explicit NullCheck
1003     x->set_can_trap(true);
1004     // make sure it's pinned if it can trap
1005     x->pin(Instruction::PinExplicitNullCheck);
1006     set_put(obj);
1007     set_last_explicit_null_check(x);
1008     if (PrintNullCheckElimination) {
1009       tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1010     }
1011   }
1012 }
1013 
1014 
1015 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1016   if (!x->has_receiver()) {
1017     // Be conservative
1018     clear_last_explicit_null_check();
1019     return;
1020   }
1021 
1022   Value recv = x->receiver();
1023   if (!set_contains(recv)) {
1024     set_put(recv);
1025     if (PrintNullCheckElimination) {
1026       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1027     }
1028   }
1029   clear_last_explicit_null_check();
1030 }
1031 
1032 
1033 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1034   set_put(x);
1035   if (PrintNullCheckElimination) {
1036     tty->print_cr("NewInstance %d is non-null", x->id());
1037   }
1038 }
1039 
1040 
1041 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1042   set_put(x);
1043   if (PrintNullCheckElimination) {
1044     tty->print_cr("NewArray %d is non-null", x->id());
1045   }
1046 }
1047 
1048 
1049 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1050   set_put(x);
1051   if (PrintNullCheckElimination) {
1052     tty->print_cr("ExceptionObject %d is non-null", x->id());
1053   }
1054 }
1055 
1056 
1057 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1058   Value obj = x->obj();
1059   if (set_contains(obj)) {
1060     // Value is non-null => update AccessMonitor
1061     if (PrintNullCheckElimination) {
1062       tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1063     }
1064     x->set_needs_null_check(false);
1065   } else {
1066     set_put(obj);
1067     if (PrintNullCheckElimination) {
1068       tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1069     }
1070     // Ensure previous passes do not cause wrong state
1071     x->set_needs_null_check(true);
1072   }
1073   clear_last_explicit_null_check();
1074 }
1075 
1076 
1077 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1078   if (!x->has_receiver()) {
1079     if (x->id() == vmIntrinsics::_arraycopy) {
1080       for (int i = 0; i < x->number_of_arguments(); i++) {
1081         x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1082       }
1083     }
1084 
1085     // Be conservative
1086     clear_last_explicit_null_check();
1087     return;
1088   }
1089 
1090   Value recv = x->receiver();
1091   if (set_contains(recv)) {
1092     // Value is non-null => update Intrinsic
1093     if (PrintNullCheckElimination) {
1094       tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());
1095     }
1096     x->set_needs_null_check(false);
1097   } else {
1098     set_put(recv);
1099     if (PrintNullCheckElimination) {
1100       tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());
1101     }
1102     // Ensure previous passes do not cause wrong state
1103     x->set_needs_null_check(true);
1104   }
1105   clear_last_explicit_null_check();
1106 }
1107 
1108 
1109 void NullCheckEliminator::handle_Phi(Phi* x) {
1110   int i;
1111   bool all_non_null = true;
1112   if (x->is_illegal()) {
1113     all_non_null = false;
1114   } else {
1115     for (i = 0; i < x->operand_count(); i++) {
1116       Value input = x->operand_at(i);
1117       if (!set_contains(input)) {
1118         all_non_null = false;
1119       }
1120     }
1121   }
1122 
1123   if (all_non_null) {
1124     // Value is non-null => update Phi
1125     if (PrintNullCheckElimination) {
1126       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1127     }
1128     x->set_needs_null_check(false);
1129   } else if (set_contains(x)) {
1130     set_remove(x);
1131   }
1132 }
1133 
1134 
1135 void Optimizer::eliminate_null_checks() {
1136   ResourceMark rm;
1137 
1138   NullCheckEliminator nce(this);
1139 
1140   if (PrintNullCheckElimination) {
1141     tty->print_cr("Starting null check elimination for method %s::%s%s",
1142                   ir()->method()->holder()->name()->as_utf8(),
1143                   ir()->method()->name()->as_utf8(),
1144                   ir()->method()->signature()->as_symbol()->as_utf8());
1145   }
1146 
1147   // Apply to graph
1148   nce.iterate(ir()->start());
1149 
1150   // walk over the graph looking for exception
1151   // handlers and iterate over them as well
1152   int nblocks = BlockBegin::number_of_blocks();
1153   BlockList blocks(nblocks);
1154   boolArray visited_block(nblocks, false);
1155 
1156   blocks.push(ir()->start());
1157   visited_block[ir()->start()->block_id()] = true;
1158   for (int i = 0; i < blocks.length(); i++) {
1159     BlockBegin* b = blocks[i];
1160     // exception handlers need to be treated as additional roots
1161     for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1162       BlockBegin* excp = b->exception_handler_at(e);
1163       int id = excp->block_id();
1164       if (!visited_block[id]) {
1165         blocks.push(excp);
1166         visited_block[id] = true;
1167         nce.iterate(excp);
1168       }
1169     }
1170     // traverse successors
1171     BlockEnd *end = b->end();
1172     for (int s = end->number_of_sux(); s-- > 0; ) {
1173       BlockBegin* next = end->sux_at(s);
1174       int id = next->block_id();
1175       if (!visited_block[id]) {
1176         blocks.push(next);
1177         visited_block[id] = true;
1178       }
1179     }
1180   }
1181 
1182 
1183   if (PrintNullCheckElimination) {
1184     tty->print_cr("Done with null check elimination for method %s::%s%s",
1185                   ir()->method()->holder()->name()->as_utf8(),
1186                   ir()->method()->name()->as_utf8(),
1187                   ir()->method()->signature()->as_symbol()->as_utf8());
1188   }
1189 }