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(block);
 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_->is_safepoint() ? if_->state_before() : NULL;
 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(block);
 371         Instruction* next = sux->next();
 372         assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
 373         prev->set_next(next);
 374         sux->disconnect_from_graph();
 375         block->set_end(sux->end());
 376         // add exception handlers of deleted block, if any
 377         for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
 378           BlockBegin* xhandler = sux->exception_handler_at(k);
 379           block->add_exception_handler(xhandler);
 380 
 381           // also substitute predecessor of exception handler
 382           assert(xhandler->is_predecessor(sux), "missing predecessor");
 383           xhandler->remove_predecessor(sux);
 384           if (!xhandler->is_predecessor(block)) {
 385             xhandler->add_predecessor(block);
 386           }
 387         }
 388 
 389         // debugging output
 390         _merge_count++;
 391         if (PrintBlockElimination) {
 392           tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
 393                         _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
 394         }
 395 
 396         _hir->verify();
 397 
 398         If* if_ = block->end()->as_If();
 399         if (if_) {
 400           IfOp* ifop    = if_->x()->as_IfOp();
 401           Constant* con = if_->y()->as_Constant();
 402           bool swapped = false;
 403           if (!con || !ifop) {
 404             ifop = if_->y()->as_IfOp();
 405             con  = if_->x()->as_Constant();
 406             swapped = true;
 407           }
 408           if (con && ifop) {
 409             Constant* tval = ifop->tval()->as_Constant();
 410             Constant* fval = ifop->fval()->as_Constant();
 411             if (tval && fval) {
 412               // Find the instruction before if_, starting with ifop.
 413               // When if_ and ifop are not in the same block, prev
 414               // becomes NULL In such (rare) cases it is not
 415               // profitable to perform the optimization.
 416               Value prev = ifop;
 417               while (prev != NULL && prev->next() != if_) {
 418                 prev = prev->next();
 419               }
 420 
 421               if (prev != NULL) {
 422                 Instruction::Condition cond = if_->cond();
 423                 BlockBegin* tsux = if_->tsux();
 424                 BlockBegin* fsux = if_->fsux();
 425                 if (swapped) {
 426                   cond = Instruction::mirror(cond);
 427                 }
 428 
 429                 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
 430                 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
 431                 if (tblock != fblock && !if_->is_safepoint()) {
 432                   If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
 433                                      tblock, fblock, if_->state_before(), if_->is_safepoint());
 434                   newif->set_state(if_->state()->copy());
 435 
 436                   assert(prev->next() == if_, "must be guaranteed by above search");
 437                   NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
 438                   prev->set_next(newif);
 439                   block->set_end(newif);
 440 
 441                   _merge_count++;
 442                   if (PrintBlockElimination) {
 443                     tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
 444                   }
 445 
 446                   _hir->verify();
 447                 }
 448               }
 449             }
 450           }
 451         }
 452 
 453         return true;
 454       }
 455     }
 456     return false;
 457   }
 458 
 459   virtual void block_do(BlockBegin* block) {
 460     _hir->verify();
 461     // repeat since the same block may merge again
 462     while (try_merge(block)) {
 463       _hir->verify();
 464     }
 465   }
 466 };
 467 
 468 
 469 void Optimizer::eliminate_blocks() {
 470   // merge blocks if possible
 471   BlockMerger bm(ir());
 472 }
 473 
 474 
 475 class NullCheckEliminator;
 476 class NullCheckVisitor: public InstructionVisitor {
 477 private:
 478   NullCheckEliminator* _nce;
 479   NullCheckEliminator* nce() { return _nce; }
 480 
 481 public:
 482   NullCheckVisitor() {}
 483 
 484   void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
 485 
 486   void do_Phi            (Phi*             x);
 487   void do_Local          (Local*           x);
 488   void do_Constant       (Constant*        x);
 489   void do_LoadField      (LoadField*       x);
 490   void do_StoreField     (StoreField*      x);
 491   void do_ArrayLength    (ArrayLength*     x);
 492   void do_LoadIndexed    (LoadIndexed*     x);
 493   void do_StoreIndexed   (StoreIndexed*    x);
 494   void do_NegateOp       (NegateOp*        x);
 495   void do_ArithmeticOp   (ArithmeticOp*    x);
 496   void do_ShiftOp        (ShiftOp*         x);
 497   void do_LogicOp        (LogicOp*         x);
 498   void do_CompareOp      (CompareOp*       x);
 499   void do_IfOp           (IfOp*            x);
 500   void do_Convert        (Convert*         x);
 501   void do_NullCheck      (NullCheck*       x);
 502   void do_TypeCast       (TypeCast*        x);
 503   void do_Invoke         (Invoke*          x);
 504   void do_NewInstance    (NewInstance*     x);
 505   void do_NewTypeArray   (NewTypeArray*    x);
 506   void do_NewObjectArray (NewObjectArray*  x);
 507   void do_NewMultiArray  (NewMultiArray*   x);
 508   void do_CheckCast      (CheckCast*       x);
 509   void do_InstanceOf     (InstanceOf*      x);
 510   void do_MonitorEnter   (MonitorEnter*    x);
 511   void do_MonitorExit    (MonitorExit*     x);
 512   void do_Intrinsic      (Intrinsic*       x);
 513   void do_BlockBegin     (BlockBegin*      x);
 514   void do_Goto           (Goto*            x);
 515   void do_If             (If*              x);
 516   void do_IfInstanceOf   (IfInstanceOf*    x);
 517   void do_TableSwitch    (TableSwitch*     x);
 518   void do_LookupSwitch   (LookupSwitch*    x);
 519   void do_Return         (Return*          x);
 520   void do_Throw          (Throw*           x);
 521   void do_Base           (Base*            x);
 522   void do_OsrEntry       (OsrEntry*        x);
 523   void do_ExceptionObject(ExceptionObject* x);
 524   void do_RoundFP        (RoundFP*         x);
 525   void do_UnsafeGetRaw   (UnsafeGetRaw*    x);
 526   void do_UnsafePutRaw   (UnsafePutRaw*    x);
 527   void do_UnsafeGetObject(UnsafeGetObject* x);
 528   void do_UnsafePutObject(UnsafePutObject* x);
 529   void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);
 530   void do_UnsafePrefetchRead (UnsafePrefetchRead*  x);
 531   void do_UnsafePrefetchWrite(UnsafePrefetchWrite* x);
 532   void do_ProfileCall    (ProfileCall*     x);
 533   void do_ProfileInvoke  (ProfileInvoke*   x);
 534   void do_RuntimeCall    (RuntimeCall*     x);
 535   void do_MemBar         (MemBar*          x);
 536 };
 537 
 538 
 539 // Because of a static contained within (for the purpose of iteration
 540 // over instructions), it is only valid to have one of these active at
 541 // a time
 542 class NullCheckEliminator: public ValueVisitor {
 543  private:
 544   Optimizer*        _opt;
 545 
 546   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block
 547   BlockList*        _work_list;                   // Basic blocks to visit
 548 
 549   bool visitable(Value x) {
 550     assert(_visitable_instructions != NULL, "check");
 551     return _visitable_instructions->contains(x);
 552   }
 553   void mark_visited(Value x) {
 554     assert(_visitable_instructions != NULL, "check");
 555     _visitable_instructions->remove(x);
 556   }
 557   void mark_visitable(Value x) {
 558     assert(_visitable_instructions != NULL, "check");
 559     _visitable_instructions->put(x);
 560   }
 561   void clear_visitable_state() {
 562     assert(_visitable_instructions != NULL, "check");
 563     _visitable_instructions->clear();
 564   }
 565 
 566   ValueSet*         _set;                         // current state, propagated to subsequent BlockBegins
 567   ValueSetList      _block_states;                // BlockBegin null-check states for all processed blocks
 568   NullCheckVisitor  _visitor;
 569   NullCheck*        _last_explicit_null_check;
 570 
 571   bool set_contains(Value x)                      { assert(_set != NULL, "check"); return _set->contains(x); }
 572   void set_put     (Value x)                      { assert(_set != NULL, "check"); _set->put(x); }
 573   void set_remove  (Value x)                      { assert(_set != NULL, "check"); _set->remove(x); }
 574 
 575   BlockList* work_list()                          { return _work_list; }
 576 
 577   void iterate_all();
 578   void iterate_one(BlockBegin* block);
 579 
 580   ValueSet* state()                               { return _set; }
 581   void      set_state_from (ValueSet* state)      { _set->set_from(state); }
 582   ValueSet* state_for      (BlockBegin* block)    { return _block_states[block->block_id()]; }
 583   void      set_state_for  (BlockBegin* block, ValueSet* stack) { _block_states[block->block_id()] = stack; }
 584   // Returns true if caused a change in the block's state.
 585   bool      merge_state_for(BlockBegin* block,
 586                             ValueSet*   incoming_state);
 587 
 588  public:
 589   // constructor
 590   NullCheckEliminator(Optimizer* opt)
 591     : _opt(opt)
 592     , _set(new ValueSet())
 593     , _last_explicit_null_check(NULL)
 594     , _block_states(BlockBegin::number_of_blocks(), NULL)
 595     , _work_list(new BlockList()) {
 596     _visitable_instructions = new ValueSet();
 597     _visitor.set_eliminator(this);
 598     CompileLog* log = _opt->ir()->compilation()->log();
 599     if (log != NULL)
 600       log->set_context("optimize name='null_check_elimination'");
 601   }
 602 
 603   ~NullCheckEliminator() {
 604     CompileLog* log = _opt->ir()->compilation()->log();
 605     if (log != NULL)
 606       log->clear_context(); // skip marker if nothing was printed
 607   }
 608 
 609   Optimizer*  opt()                               { return _opt; }
 610   IR*         ir ()                               { return opt()->ir(); }
 611 
 612   // Process a graph
 613   void iterate(BlockBegin* root);
 614 
 615   void visit(Value* f);
 616 
 617   // In some situations (like NullCheck(x); getfield(x)) the debug
 618   // information from the explicit NullCheck can be used to populate
 619   // the getfield, even if the two instructions are in different
 620   // scopes; this allows implicit null checks to be used but the
 621   // correct exception information to be generated. We must clear the
 622   // last-traversed NullCheck when we reach a potentially-exception-
 623   // throwing instruction, as well as in some other cases.
 624   void        set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
 625   NullCheck*  last_explicit_null_check()                     { return _last_explicit_null_check; }
 626   Value       last_explicit_null_check_obj()                 { return (_last_explicit_null_check
 627                                                                          ? _last_explicit_null_check->obj()
 628                                                                          : NULL); }
 629   NullCheck*  consume_last_explicit_null_check() {
 630     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
 631     _last_explicit_null_check->set_can_trap(false);
 632     return _last_explicit_null_check;
 633   }
 634   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }
 635 
 636   // Handlers for relevant instructions
 637   // (separated out from NullCheckVisitor for clarity)
 638 
 639   // The basic contract is that these must leave the instruction in
 640   // the desired state; must not assume anything about the state of
 641   // the instruction. We make multiple passes over some basic blocks
 642   // and the last pass is the only one whose result is valid.
 643   void handle_AccessField     (AccessField* x);
 644   void handle_ArrayLength     (ArrayLength* x);
 645   void handle_LoadIndexed     (LoadIndexed* x);
 646   void handle_StoreIndexed    (StoreIndexed* x);
 647   void handle_NullCheck       (NullCheck* x);
 648   void handle_Invoke          (Invoke* x);
 649   void handle_NewInstance     (NewInstance* x);
 650   void handle_NewArray        (NewArray* x);
 651   void handle_AccessMonitor   (AccessMonitor* x);
 652   void handle_Intrinsic       (Intrinsic* x);
 653   void handle_ExceptionObject (ExceptionObject* x);
 654   void handle_Phi             (Phi* x);
 655 };
 656 
 657 
 658 // NEEDS_CLEANUP
 659 // There may be other instructions which need to clear the last
 660 // explicit null check. Anything across which we can not hoist the
 661 // debug information for a NullCheck instruction must clear it. It
 662 // might be safer to pattern match "NullCheck ; {AccessField,
 663 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
 664 // Should test to see performance hit of clearing it for all handlers
 665 // with empty bodies below. If it is negligible then we should leave
 666 // that in for safety, otherwise should think more about it.
 667 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }
 668 void NullCheckVisitor::do_Local          (Local*           x) {}
 669 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }
 670 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }
 671 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }
 672 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }
 673 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }
 674 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }
 675 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}
 676 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
 677 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}
 678 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}
 679 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}
 680 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}
 681 void NullCheckVisitor::do_Convert        (Convert*         x) {}
 682 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }
 683 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}
 684 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }
 685 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }
 686 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }
 687 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }
 688 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }
 689 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }
 690 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}
 691 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }
 692 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }
 693 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }
 694 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}
 695 void NullCheckVisitor::do_Goto           (Goto*            x) {}
 696 void NullCheckVisitor::do_If             (If*              x) {}
 697 void NullCheckVisitor::do_IfInstanceOf   (IfInstanceOf*    x) {}
 698 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}
 699 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}
 700 void NullCheckVisitor::do_Return         (Return*          x) {}
 701 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }
 702 void NullCheckVisitor::do_Base           (Base*            x) {}
 703 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}
 704 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
 705 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}
 706 void NullCheckVisitor::do_UnsafeGetRaw   (UnsafeGetRaw*    x) {}
 707 void NullCheckVisitor::do_UnsafePutRaw   (UnsafePutRaw*    x) {}
 708 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}
 709 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}
 710 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}
 711 void NullCheckVisitor::do_UnsafePrefetchRead (UnsafePrefetchRead*  x) {}
 712 void NullCheckVisitor::do_UnsafePrefetchWrite(UnsafePrefetchWrite* x) {}
 713 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check(); }
 714 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}
 715 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}
 716 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}
 717 
 718 
 719 void NullCheckEliminator::visit(Value* p) {
 720   assert(*p != NULL, "should not find NULL instructions");
 721   if (visitable(*p)) {
 722     mark_visited(*p);
 723     (*p)->visit(&_visitor);
 724   }
 725 }
 726 
 727 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
 728   ValueSet* state = state_for(block);
 729   if (state == NULL) {
 730     state = incoming_state->copy();
 731     set_state_for(block, state);
 732     return true;
 733   } else {
 734     bool changed = state->set_intersect(incoming_state);
 735     if (PrintNullCheckElimination && changed) {
 736       tty->print_cr("Block %d's null check state changed", block->block_id());
 737     }
 738     return changed;
 739   }
 740 }
 741 
 742 
 743 void NullCheckEliminator::iterate_all() {
 744   while (work_list()->length() > 0) {
 745     iterate_one(work_list()->pop());
 746   }
 747 }
 748 
 749 
 750 void NullCheckEliminator::iterate_one(BlockBegin* block) {
 751   clear_visitable_state();
 752   // clear out an old explicit null checks
 753   set_last_explicit_null_check(NULL);
 754 
 755   if (PrintNullCheckElimination) {
 756     tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
 757                   block->block_id(),
 758                   ir()->method()->holder()->name()->as_utf8(),
 759                   ir()->method()->name()->as_utf8(),
 760                   ir()->method()->signature()->as_symbol()->as_utf8());
 761   }
 762 
 763   // Create new state if none present (only happens at root)
 764   if (state_for(block) == NULL) {
 765     ValueSet* tmp_state = new ValueSet();
 766     set_state_for(block, tmp_state);
 767     // Initial state is that local 0 (receiver) is non-null for
 768     // non-static methods
 769     ValueStack* stack  = block->state();
 770     IRScope*    scope  = stack->scope();
 771     ciMethod*   method = scope->method();
 772     if (!method->is_static()) {
 773       Local* local0 = stack->local_at(0)->as_Local();
 774       assert(local0 != NULL, "must be");
 775       assert(local0->type() == objectType, "invalid type of receiver");
 776 
 777       if (local0 != NULL) {
 778         // Local 0 is used in this scope
 779         tmp_state->put(local0);
 780         if (PrintNullCheckElimination) {
 781           tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
 782         }
 783       }
 784     }
 785   }
 786 
 787   // Must copy block's state to avoid mutating it during iteration
 788   // through the block -- otherwise "not-null" states can accidentally
 789   // propagate "up" through the block during processing of backward
 790   // branches and algorithm is incorrect (and does not converge)
 791   set_state_from(state_for(block));
 792 
 793   // allow visiting of Phis belonging to this block
 794   for_each_phi_fun(block, phi,
 795                    mark_visitable(phi);
 796                    );
 797 
 798   BlockEnd* e = block->end();
 799   assert(e != NULL, "incomplete graph");
 800   int i;
 801 
 802   // Propagate the state before this block into the exception
 803   // handlers.  They aren't true successors since we aren't guaranteed
 804   // to execute the whole block before executing them.  Also putting
 805   // them on first seems to help reduce the amount of iteration to
 806   // reach a fixed point.
 807   for (i = 0; i < block->number_of_exception_handlers(); i++) {
 808     BlockBegin* next = block->exception_handler_at(i);
 809     if (merge_state_for(next, state())) {
 810       if (!work_list()->contains(next)) {
 811         work_list()->push(next);
 812       }
 813     }
 814   }
 815 
 816   // Iterate through block, updating state.
 817   for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
 818     // Mark instructions in this block as visitable as they are seen
 819     // in the instruction list.  This keeps the iteration from
 820     // visiting instructions which are references in other blocks or
 821     // visiting instructions more than once.
 822     mark_visitable(instr);
 823     if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
 824       mark_visited(instr);
 825       instr->input_values_do(this);
 826       instr->visit(&_visitor);
 827     }
 828   }
 829 
 830   // Propagate state to successors if necessary
 831   for (i = 0; i < e->number_of_sux(); i++) {
 832     BlockBegin* next = e->sux_at(i);
 833     if (merge_state_for(next, state())) {
 834       if (!work_list()->contains(next)) {
 835         work_list()->push(next);
 836       }
 837     }
 838   }
 839 }
 840 
 841 
 842 void NullCheckEliminator::iterate(BlockBegin* block) {
 843   work_list()->push(block);
 844   iterate_all();
 845 }
 846 
 847 void NullCheckEliminator::handle_AccessField(AccessField* x) {
 848   if (x->is_static()) {
 849     if (x->as_LoadField() != NULL) {
 850       // If the field is a non-null static final object field (as is
 851       // often the case for sun.misc.Unsafe), put this LoadField into
 852       // the non-null map
 853       ciField* field = x->field();
 854       if (field->is_constant()) {
 855         ciConstant field_val = field->constant_value();
 856         BasicType field_type = field_val.basic_type();
 857         if (field_type == T_OBJECT || field_type == T_ARRAY) {
 858           ciObject* obj_val = field_val.as_object();
 859           if (!obj_val->is_null_object()) {
 860             if (PrintNullCheckElimination) {
 861               tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
 862                             x->id());
 863             }
 864             set_put(x);
 865           }
 866         }
 867       }
 868     }
 869     // Be conservative
 870     clear_last_explicit_null_check();
 871     return;
 872   }
 873 
 874   Value obj = x->obj();
 875   if (set_contains(obj)) {
 876     // Value is non-null => update AccessField
 877     if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
 878       x->set_explicit_null_check(consume_last_explicit_null_check());
 879       x->set_needs_null_check(true);
 880       if (PrintNullCheckElimination) {
 881         tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
 882                       x->explicit_null_check()->id(), x->id(), obj->id());
 883       }
 884     } else {
 885       x->set_explicit_null_check(NULL);
 886       x->set_needs_null_check(false);
 887       if (PrintNullCheckElimination) {
 888         tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
 889       }
 890     }
 891   } else {
 892     set_put(obj);
 893     if (PrintNullCheckElimination) {
 894       tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
 895     }
 896     // Ensure previous passes do not cause wrong state
 897     x->set_needs_null_check(true);
 898     x->set_explicit_null_check(NULL);
 899   }
 900   clear_last_explicit_null_check();
 901 }
 902 
 903 
 904 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
 905   Value array = x->array();
 906   if (set_contains(array)) {
 907     // Value is non-null => update AccessArray
 908     if (last_explicit_null_check_obj() == array) {
 909       x->set_explicit_null_check(consume_last_explicit_null_check());
 910       x->set_needs_null_check(true);
 911       if (PrintNullCheckElimination) {
 912         tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
 913                       x->explicit_null_check()->id(), x->id(), array->id());
 914       }
 915     } else {
 916       x->set_explicit_null_check(NULL);
 917       x->set_needs_null_check(false);
 918       if (PrintNullCheckElimination) {
 919         tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
 920       }
 921     }
 922   } else {
 923     set_put(array);
 924     if (PrintNullCheckElimination) {
 925       tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
 926     }
 927     // Ensure previous passes do not cause wrong state
 928     x->set_needs_null_check(true);
 929     x->set_explicit_null_check(NULL);
 930   }
 931   clear_last_explicit_null_check();
 932 }
 933 
 934 
 935 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
 936   Value array = x->array();
 937   if (set_contains(array)) {
 938     // Value is non-null => update AccessArray
 939     if (last_explicit_null_check_obj() == array) {
 940       x->set_explicit_null_check(consume_last_explicit_null_check());
 941       x->set_needs_null_check(true);
 942       if (PrintNullCheckElimination) {
 943         tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
 944                       x->explicit_null_check()->id(), x->id(), array->id());
 945       }
 946     } else {
 947       x->set_explicit_null_check(NULL);
 948       x->set_needs_null_check(false);
 949       if (PrintNullCheckElimination) {
 950         tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
 951       }
 952     }
 953   } else {
 954     set_put(array);
 955     if (PrintNullCheckElimination) {
 956       tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
 957     }
 958     // Ensure previous passes do not cause wrong state
 959     x->set_needs_null_check(true);
 960     x->set_explicit_null_check(NULL);
 961   }
 962   clear_last_explicit_null_check();
 963 }
 964 
 965 
 966 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
 967   Value array = x->array();
 968   if (set_contains(array)) {
 969     // Value is non-null => update AccessArray
 970     if (PrintNullCheckElimination) {
 971       tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
 972     }
 973     x->set_needs_null_check(false);
 974   } else {
 975     set_put(array);
 976     if (PrintNullCheckElimination) {
 977       tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
 978     }
 979     // Ensure previous passes do not cause wrong state
 980     x->set_needs_null_check(true);
 981   }
 982   clear_last_explicit_null_check();
 983 }
 984 
 985 
 986 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
 987   Value obj = x->obj();
 988   if (set_contains(obj)) {
 989     // Already proven to be non-null => this NullCheck is useless
 990     if (PrintNullCheckElimination) {
 991       tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
 992     }
 993     // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
 994     // The code generator won't emit LIR for a NullCheck that cannot trap.
 995     x->set_can_trap(false);
 996   } else {
 997     // May be null => add to map and set last explicit NullCheck
 998     x->set_can_trap(true);
 999     // make sure it's pinned if it can trap
1000     x->pin(Instruction::PinExplicitNullCheck);
1001     set_put(obj);
1002     set_last_explicit_null_check(x);
1003     if (PrintNullCheckElimination) {
1004       tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1005     }
1006   }
1007 }
1008 
1009 
1010 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1011   if (!x->has_receiver()) {
1012     // Be conservative
1013     clear_last_explicit_null_check();
1014     return;
1015   }
1016 
1017   Value recv = x->receiver();
1018   if (!set_contains(recv)) {
1019     set_put(recv);
1020     if (PrintNullCheckElimination) {
1021       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1022     }
1023   }
1024   clear_last_explicit_null_check();
1025 }
1026 
1027 
1028 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1029   set_put(x);
1030   if (PrintNullCheckElimination) {
1031     tty->print_cr("NewInstance %d is non-null", x->id());
1032   }
1033 }
1034 
1035 
1036 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1037   set_put(x);
1038   if (PrintNullCheckElimination) {
1039     tty->print_cr("NewArray %d is non-null", x->id());
1040   }
1041 }
1042 
1043 
1044 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1045   set_put(x);
1046   if (PrintNullCheckElimination) {
1047     tty->print_cr("ExceptionObject %d is non-null", x->id());
1048   }
1049 }
1050 
1051 
1052 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1053   Value obj = x->obj();
1054   if (set_contains(obj)) {
1055     // Value is non-null => update AccessMonitor
1056     if (PrintNullCheckElimination) {
1057       tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1058     }
1059     x->set_needs_null_check(false);
1060   } else {
1061     set_put(obj);
1062     if (PrintNullCheckElimination) {
1063       tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1064     }
1065     // Ensure previous passes do not cause wrong state
1066     x->set_needs_null_check(true);
1067   }
1068   clear_last_explicit_null_check();
1069 }
1070 
1071 
1072 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1073   if (!x->has_receiver()) {
1074     if (x->id() == vmIntrinsics::_arraycopy) {
1075       for (int i = 0; i < x->number_of_arguments(); i++) {
1076         x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1077       }
1078     }
1079 
1080     // Be conservative
1081     clear_last_explicit_null_check();
1082     return;
1083   }
1084 
1085   Value recv = x->receiver();
1086   if (set_contains(recv)) {
1087     // Value is non-null => update Intrinsic
1088     if (PrintNullCheckElimination) {
1089       tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());
1090     }
1091     x->set_needs_null_check(false);
1092   } else {
1093     set_put(recv);
1094     if (PrintNullCheckElimination) {
1095       tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());
1096     }
1097     // Ensure previous passes do not cause wrong state
1098     x->set_needs_null_check(true);
1099   }
1100   clear_last_explicit_null_check();
1101 }
1102 
1103 
1104 void NullCheckEliminator::handle_Phi(Phi* x) {
1105   int i;
1106   bool all_non_null = true;
1107   if (x->is_illegal()) {
1108     all_non_null = false;
1109   } else {
1110     for (i = 0; i < x->operand_count(); i++) {
1111       Value input = x->operand_at(i);
1112       if (!set_contains(input)) {
1113         all_non_null = false;
1114       }
1115     }
1116   }
1117 
1118   if (all_non_null) {
1119     // Value is non-null => update Phi
1120     if (PrintNullCheckElimination) {
1121       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1122     }
1123     x->set_needs_null_check(false);
1124   } else if (set_contains(x)) {
1125     set_remove(x);
1126   }
1127 }
1128 
1129 
1130 void Optimizer::eliminate_null_checks() {
1131   ResourceMark rm;
1132 
1133   NullCheckEliminator nce(this);
1134 
1135   if (PrintNullCheckElimination) {
1136     tty->print_cr("Starting null check elimination for method %s::%s%s",
1137                   ir()->method()->holder()->name()->as_utf8(),
1138                   ir()->method()->name()->as_utf8(),
1139                   ir()->method()->signature()->as_symbol()->as_utf8());
1140   }
1141 
1142   // Apply to graph
1143   nce.iterate(ir()->start());
1144 
1145   // walk over the graph looking for exception
1146   // handlers and iterate over them as well
1147   int nblocks = BlockBegin::number_of_blocks();
1148   BlockList blocks(nblocks);
1149   boolArray visited_block(nblocks, false);
1150 
1151   blocks.push(ir()->start());
1152   visited_block[ir()->start()->block_id()] = true;
1153   for (int i = 0; i < blocks.length(); i++) {
1154     BlockBegin* b = blocks[i];
1155     // exception handlers need to be treated as additional roots
1156     for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1157       BlockBegin* excp = b->exception_handler_at(e);
1158       int id = excp->block_id();
1159       if (!visited_block[id]) {
1160         blocks.push(excp);
1161         visited_block[id] = true;
1162         nce.iterate(excp);
1163       }
1164     }
1165     // traverse successors
1166     BlockEnd *end = b->end();
1167     for (int s = end->number_of_sux(); s-- > 0; ) {
1168       BlockBegin* next = end->sux_at(s);
1169       int id = next->block_id();
1170       if (!visited_block[id]) {
1171         blocks.push(next);
1172         visited_block[id] = true;
1173       }
1174     }
1175   }
1176 
1177 
1178   if (PrintNullCheckElimination) {
1179     tty->print_cr("Done with null check elimination for method %s::%s%s",
1180                   ir()->method()->holder()->name()->as_utf8(),
1181                   ir()->method()->name()->as_utf8(),
1182                   ir()->method()->signature()->as_symbol()->as_utf8());
1183   }
1184 }