1 /*
   2  * Copyright (c) 1999, 2022, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "c1/c1_Canonicalizer.hpp"
  27 #include "c1/c1_Optimizer.hpp"
  28 #include "c1/c1_ValueMap.hpp"
  29 #include "c1/c1_ValueSet.hpp"
  30 #include "c1/c1_ValueStack.hpp"
  31 #include "memory/resourceArea.hpp"
  32 #include "utilities/bitMap.inline.hpp"
  33 #include "compiler/compileLog.hpp"
  34 
  35 typedef GrowableArray<ValueSet*> ValueSetList;
  36 
  37 Optimizer::Optimizer(IR* ir) {
  38   assert(ir->is_valid(), "IR must be valid");
  39   _ir = ir;
  40 }
  41 
  42 class CE_Eliminator: public BlockClosure {
  43  private:
  44   IR* _hir;
  45   int _cee_count;                                // the number of CEs successfully eliminated
  46   int _ifop_count;                               // the number of IfOps successfully simplified
  47   int _has_substitution;
  48 
  49  public:
  50   CE_Eliminator(IR* hir) : _hir(hir), _cee_count(0), _ifop_count(0) {
  51     _has_substitution = false;
  52     _hir->iterate_preorder(this);
  53     if (_has_substitution) {
  54       // substituted some ifops/phis, so resolve the substitution
  55       SubstitutionResolver sr(_hir);
  56     }
  57 
  58     CompileLog* log = _hir->compilation()->log();
  59     if (log != NULL)
  60       log->set_context("optimize name='cee'");
  61   }
  62 
  63   ~CE_Eliminator() {
  64     CompileLog* log = _hir->compilation()->log();
  65     if (log != NULL)
  66       log->clear_context(); // skip marker if nothing was printed
  67   }
  68 
  69   int cee_count() const                          { return _cee_count; }
  70   int ifop_count() const                         { return _ifop_count; }
  71 
  72   void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
  73     int e = sux->number_of_exception_handlers();
  74     for (int i = 0; i < e; i++) {
  75       BlockBegin* xhandler = sux->exception_handler_at(i);
  76       block->add_exception_handler(xhandler);
  77 
  78       assert(xhandler->is_predecessor(sux), "missing predecessor");
  79       if (sux->number_of_preds() == 0) {
  80         // sux is disconnected from graph so disconnect from exception handlers
  81         xhandler->remove_predecessor(sux);
  82       }
  83       if (!xhandler->is_predecessor(block)) {
  84         xhandler->add_predecessor(block);
  85       }
  86     }
  87   }
  88 
  89   virtual void block_do(BlockBegin* block);
  90 
  91  private:
  92   Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
  93 };
  94 
  95 void CE_Eliminator::block_do(BlockBegin* block) {
  96   // 1) find conditional expression
  97   // check if block ends with an If
  98   If* if_ = block->end()->as_If();
  99   if (if_ == NULL) return;
 100 
 101   // check if If works on int or object types
 102   // (we cannot handle If's working on long, float or doubles yet,
 103   // since IfOp doesn't support them - these If's show up if cmp
 104   // operations followed by If's are eliminated)
 105   ValueType* if_type = if_->x()->type();
 106   if (!if_type->is_int() && !if_type->is_object()) return;
 107 
 108   BlockBegin* t_block = if_->tsux();
 109   BlockBegin* f_block = if_->fsux();
 110   Instruction* t_cur = t_block->next();
 111   Instruction* f_cur = f_block->next();
 112 
 113   // one Constant may be present between BlockBegin and BlockEnd
 114   Value t_const = NULL;
 115   Value f_const = NULL;
 116   if (t_cur->as_Constant() != NULL && !t_cur->can_trap()) {
 117     t_const = t_cur;
 118     t_cur = t_cur->next();
 119   }
 120   if (f_cur->as_Constant() != NULL && !f_cur->can_trap()) {
 121     f_const = f_cur;
 122     f_cur = f_cur->next();
 123   }
 124 
 125   // check if both branches end with a goto
 126   Goto* t_goto = t_cur->as_Goto();
 127   if (t_goto == NULL) return;
 128   Goto* f_goto = f_cur->as_Goto();
 129   if (f_goto == NULL) return;
 130 
 131   // check if both gotos merge into the same block
 132   BlockBegin* sux = t_goto->default_sux();
 133   if (sux != f_goto->default_sux()) return;
 134 
 135   // check if at least one word was pushed on sux_state
 136   // inlining depths must match
 137   ValueStack* if_state = if_->state();
 138   ValueStack* sux_state = sux->state();
 139   if (if_state->scope()->level() > sux_state->scope()->level()) {
 140     while (sux_state->scope() != if_state->scope()) {
 141       if_state = if_state->caller_state();
 142       assert(if_state != NULL, "states do not match up");
 143     }
 144   } else if (if_state->scope()->level() < sux_state->scope()->level()) {
 145     while (sux_state->scope() != if_state->scope()) {
 146       sux_state = sux_state->caller_state();
 147       assert(sux_state != NULL, "states do not match up");
 148     }
 149   }
 150 
 151   if (sux_state->stack_size() <= if_state->stack_size()) return;
 152 
 153   // check if phi function is present at end of successor stack and that
 154   // only this phi was pushed on the stack
 155   Value sux_phi = sux_state->stack_at(if_state->stack_size());
 156   if (sux_phi == NULL || sux_phi->as_Phi() == NULL || sux_phi->as_Phi()->block() != sux) return;
 157   if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;
 158 
 159   // get the values that were pushed in the true- and false-branch
 160   Value t_value = t_goto->state()->stack_at(if_state->stack_size());
 161   Value f_value = f_goto->state()->stack_at(if_state->stack_size());
 162 
 163   // backend does not support floats
 164   assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");
 165   if (t_value->type()->is_float_kind()) return;
 166 
 167   // check that successor has no other phi functions but sux_phi
 168   // this can happen when t_block or f_block contained additonal stores to local variables
 169   // that are no longer represented by explicit instructions
 170   for_each_phi_fun(sux, phi,
 171                    if (phi != sux_phi) return;
 172                    );
 173   // true and false blocks can't have phis
 174   for_each_phi_fun(t_block, phi, return; );
 175   for_each_phi_fun(f_block, phi, return; );
 176 
 177   // Only replace safepoint gotos if state_before information is available (if is a safepoint)
 178   bool is_safepoint = if_->is_safepoint();
 179   if (!is_safepoint && (t_goto->is_safepoint() || f_goto->is_safepoint())) {
 180     return;
 181   }
 182 
 183 #ifdef ASSERT
 184 #define DO_DELAYED_VERIFICATION
 185   /*
 186    * We need to verify the internal representation after modifying it.
 187    * Verifying only the blocks that have been tampered with is cheaper than verifying the whole graph, but we must
 188    * capture blocks_to_verify_later before making the changes, since they might not be reachable afterwards.
 189    * DO_DELAYED_VERIFICATION ensures that the code for this is either enabled in full, or not at all.
 190    */
 191 #endif // ASSERT
 192 
 193 #ifdef DO_DELAYED_VERIFICATION
 194   BlockList blocks_to_verify_later;
 195   blocks_to_verify_later.append(block);
 196   blocks_to_verify_later.append(t_block);
 197   blocks_to_verify_later.append(f_block);
 198   blocks_to_verify_later.append(sux);
 199   _hir->expand_with_neighborhood(blocks_to_verify_later);
 200 #endif // DO_DELAYED_VERIFICATION
 201 
 202   // 2) substitute conditional expression
 203   //    with an IfOp followed by a Goto
 204   // cut if_ away and get node before
 205   Instruction* cur_end = if_->prev();
 206 
 207   // append constants of true- and false-block if necessary
 208   // clone constants because original block must not be destroyed
 209   assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
 210   if (t_value == t_const) {
 211     t_value = new Constant(t_const->type());
 212     NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
 213     cur_end = cur_end->set_next(t_value);
 214   }
 215   if (f_value == f_const) {
 216     f_value = new Constant(f_const->type());
 217     NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
 218     cur_end = cur_end->set_next(f_value);
 219   }
 220 
 221   Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
 222   assert(result != NULL, "make_ifop must return a non-null instruction");
 223   if (!result->is_linked() && result->can_be_linked()) {
 224     NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
 225     cur_end = cur_end->set_next(result);
 226   }
 227 
 228   // append Goto to successor
 229   ValueStack* state_before = if_->state_before();
 230   Goto* goto_ = new Goto(sux, state_before, is_safepoint);
 231 
 232   // prepare state for Goto
 233   ValueStack* goto_state = if_state;
 234   goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
 235   goto_state->push(result->type(), result);
 236   assert(goto_state->is_same(sux_state), "states must match now");
 237   goto_->set_state(goto_state);
 238 
 239   cur_end = cur_end->set_next(goto_, goto_state->bci());
 240 
 241   // Adjust control flow graph
 242   BlockBegin::disconnect_edge(block, t_block);
 243   BlockBegin::disconnect_edge(block, f_block);
 244   if (t_block->number_of_preds() == 0) {
 245     BlockBegin::disconnect_edge(t_block, sux);
 246   }
 247   adjust_exception_edges(block, t_block);
 248   if (f_block->number_of_preds() == 0) {
 249     BlockBegin::disconnect_edge(f_block, sux);
 250   }
 251   adjust_exception_edges(block, f_block);
 252 
 253   // update block end
 254   block->set_end(goto_);
 255 
 256   // substitute the phi if possible
 257   if (sux_phi->as_Phi()->operand_count() == 1) {
 258     assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
 259     sux_phi->set_subst(result);
 260     _has_substitution = true;
 261   }
 262 
 263   // 3) successfully eliminated a conditional expression
 264   _cee_count++;
 265   if (PrintCEE) {
 266     tty->print_cr("%d. CEE in B%d (B%d B%d)", cee_count(), block->block_id(), t_block->block_id(), f_block->block_id());
 267     tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
 268   }
 269 
 270 #ifdef DO_DELAYED_VERIFICATION
 271   _hir->verify_local(blocks_to_verify_later);
 272 #endif // DO_DELAYED_VERIFICATION
 273 
 274 }
 275 
 276 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
 277   if (!OptimizeIfOps) {
 278     return new IfOp(x, cond, y, tval, fval);
 279   }
 280 
 281   tval = tval->subst();
 282   fval = fval->subst();
 283   if (tval == fval) {
 284     _ifop_count++;
 285     return tval;
 286   }
 287 
 288   x = x->subst();
 289   y = y->subst();
 290 
 291   Constant* y_const = y->as_Constant();
 292   if (y_const != NULL) {
 293     IfOp* x_ifop = x->as_IfOp();
 294     if (x_ifop != NULL) {                 // x is an ifop, y is a constant
 295       Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
 296       Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
 297 
 298       if (x_tval_const != NULL && x_fval_const != NULL) {
 299         Instruction::Condition x_ifop_cond = x_ifop->cond();
 300 
 301         Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
 302         Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
 303 
 304         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 305         if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
 306           Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
 307           Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
 308 
 309           _ifop_count++;
 310           if (new_tval == new_fval) {
 311             return new_tval;
 312           } else {
 313             return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
 314           }
 315         }
 316       }
 317     } else {
 318       Constant* x_const = x->as_Constant();
 319       if (x_const != NULL) {         // x and y are constants
 320         Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
 321         // not_comparable here is a valid return in case we're comparing unloaded oop constants
 322         if (x_compare_res != Constant::not_comparable) {
 323           _ifop_count++;
 324           return x_compare_res == Constant::cond_true ? tval : fval;
 325         }
 326       }
 327     }
 328   }
 329   return new IfOp(x, cond, y, tval, fval);
 330 }
 331 
 332 void Optimizer::eliminate_conditional_expressions() {
 333   // find conditional expressions & replace them with IfOps
 334   CE_Eliminator ce(ir());
 335 }
 336 
 337 // This removes others' relation to block, but doesnt empty block's lists
 338 void disconnect_from_graph(BlockBegin* block) {
 339   for (int p = 0; p < block->number_of_preds(); p++) {
 340     BlockBegin* pred = block->pred_at(p);
 341     int idx;
 342     while ((idx = pred->end()->find_sux(block)) >= 0) {
 343       pred->end()->remove_sux_at(idx);
 344     }
 345   }
 346   for (int s = 0; s < block->number_of_sux(); s++) {
 347     block->sux_at(s)->remove_predecessor(block);
 348   }
 349 }
 350 
 351 class BlockMerger: public BlockClosure {
 352  private:
 353   IR* _hir;
 354   int _merge_count;              // the number of block pairs successfully merged
 355 
 356  public:
 357   BlockMerger(IR* hir)
 358   : _hir(hir)
 359   , _merge_count(0)
 360   {
 361     _hir->iterate_preorder(this);
 362     CompileLog* log = _hir->compilation()->log();
 363     if (log != NULL)
 364       log->set_context("optimize name='eliminate_blocks'");
 365   }
 366 
 367   ~BlockMerger() {
 368     CompileLog* log = _hir->compilation()->log();
 369     if (log != NULL)
 370       log->clear_context(); // skip marker if nothing was printed
 371   }
 372 
 373   bool try_merge(BlockBegin* block) {
 374     BlockEnd* end = block->end();
 375     if (end->as_Goto() == NULL) return false;
 376 
 377     assert(end->number_of_sux() == 1, "end must have exactly one successor");
 378     // Note: It would be sufficient to check for the number of successors (= 1)
 379     //       in order to decide if this block can be merged potentially. That
 380     //       would then also include switch statements w/ only a default case.
 381     //       However, in that case we would need to make sure the switch tag
 382     //       expression is executed if it can produce observable side effects.
 383     //       We should probably have the canonicalizer simplifying such switch
 384     //       statements and then we are sure we don't miss these merge opportunities
 385     //       here (was bug - gri 7/7/99).
 386     BlockBegin* sux = end->default_sux();
 387     if (sux->number_of_preds() != 1 || sux->is_entry_block() || end->is_safepoint()) return false;
 388     // merge the two blocks
 389 
 390 #ifdef ASSERT
 391     // verify that state at the end of block and at the beginning of sux are equal
 392     // no phi functions must be present at beginning of sux
 393     ValueStack* sux_state = sux->state();
 394     ValueStack* end_state = end->state();
 395 
 396     assert(end_state->scope() == sux_state->scope(), "scopes must match");
 397     assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
 398     assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
 399 
 400     int index;
 401     Value sux_value;
 402     for_each_stack_value(sux_state, index, sux_value) {
 403       assert(sux_value == end_state->stack_at(index), "stack not equal");
 404     }
 405     for_each_local_value(sux_state, index, sux_value) {
 406       Phi* sux_phi = sux_value->as_Phi();
 407       if (sux_phi != NULL && sux_phi->is_illegal()) continue;
 408         assert(sux_value == end_state->local_at(index), "locals not equal");
 409       }
 410     assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
 411 #endif
 412 
 413 #ifdef DO_DELAYED_VERIFICATION
 414     BlockList blocks_to_verify_later;
 415     blocks_to_verify_later.append(block);
 416     _hir->expand_with_neighborhood(blocks_to_verify_later);
 417 #endif // DO_DELAYED_VERIFICATION
 418 
 419     // find instruction before end & append first instruction of sux block
 420     Instruction* prev = end->prev();
 421     Instruction* next = sux->next();
 422     assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
 423     prev->set_next(next);
 424     prev->fixup_block_pointers();
 425 
 426     // disconnect this block from all other blocks
 427     disconnect_from_graph(sux);
 428 #ifdef DO_DELAYED_VERIFICATION
 429     blocks_to_verify_later.remove(sux); // Sux is not part of graph anymore
 430 #endif // DO_DELAYED_VERIFICATION
 431     block->set_end(sux->end());
 432 
 433     // TODO Should this be done in set_end universally?
 434     // add exception handlers of deleted block, if any
 435     for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
 436       BlockBegin* xhandler = sux->exception_handler_at(k);
 437       block->add_exception_handler(xhandler);
 438 
 439       // TODO This should be in disconnect from graph...
 440       // also substitute predecessor of exception handler
 441       assert(xhandler->is_predecessor(sux), "missing predecessor");
 442       xhandler->remove_predecessor(sux);
 443       if (!xhandler->is_predecessor(block)) {
 444         xhandler->add_predecessor(block);
 445       }
 446     }
 447 
 448     // debugging output
 449     _merge_count++;
 450     if (PrintBlockElimination) {
 451       tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
 452                     _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
 453     }
 454 
 455 #ifdef DO_DELAYED_VERIFICATION
 456     _hir->verify_local(blocks_to_verify_later);
 457 #endif // DO_DELAYED_VERIFICATION
 458 
 459     If* if_ = block->end()->as_If();
 460     if (if_) {
 461       IfOp* ifop    = if_->x()->as_IfOp();
 462       Constant* con = if_->y()->as_Constant();
 463       bool swapped = false;
 464       if (!con || !ifop) {
 465         ifop = if_->y()->as_IfOp();
 466         con  = if_->x()->as_Constant();
 467         swapped = true;
 468       }
 469       if (con && ifop) {
 470         Constant* tval = ifop->tval()->as_Constant();
 471         Constant* fval = ifop->fval()->as_Constant();
 472         if (tval && fval) {
 473           // Find the instruction before if_, starting with ifop.
 474           // When if_ and ifop are not in the same block, prev
 475           // becomes NULL In such (rare) cases it is not
 476           // profitable to perform the optimization.
 477           Value prev = ifop;
 478           while (prev != NULL && prev->next() != if_) {
 479             prev = prev->next();
 480           }
 481 
 482           if (prev != NULL) {
 483             Instruction::Condition cond = if_->cond();
 484             BlockBegin* tsux = if_->tsux();
 485             BlockBegin* fsux = if_->fsux();
 486             if (swapped) {
 487               cond = Instruction::mirror(cond);
 488             }
 489 
 490             BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
 491             BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
 492             if (tblock != fblock && !if_->is_safepoint()) {
 493               If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
 494                                  tblock, fblock, if_->state_before(), if_->is_safepoint());
 495               newif->set_state(if_->state()->copy());
 496 
 497               assert(prev->next() == if_, "must be guaranteed by above search");
 498               NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
 499               prev->set_next(newif);
 500               block->set_end(newif);
 501 
 502               _merge_count++;
 503               if (PrintBlockElimination) {
 504                 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
 505               }
 506 
 507 #ifdef DO_DELAYED_VERIFICATION
 508               _hir->verify_local(blocks_to_verify_later);
 509 #endif // DO_DELAYED_VERIFICATION
 510             }
 511           }
 512         }
 513       }
 514     }
 515 
 516     return true;
 517   }
 518 
 519   virtual void block_do(BlockBegin* block) {
 520     // repeat since the same block may merge again
 521     while (try_merge(block)) ;
 522   }
 523 };
 524 
 525 #ifdef ASSERT
 526 #undef DO_DELAYED_VERIFICATION
 527 #endif // ASSERT
 528 
 529 void Optimizer::eliminate_blocks() {
 530   // merge blocks if possible
 531   BlockMerger bm(ir());
 532 }
 533 
 534 
 535 class NullCheckEliminator;
 536 class NullCheckVisitor: public InstructionVisitor {
 537 private:
 538   NullCheckEliminator* _nce;
 539   NullCheckEliminator* nce() { return _nce; }
 540 
 541 public:
 542   NullCheckVisitor() {}
 543 
 544   void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
 545 
 546   void do_Phi            (Phi*             x);
 547   void do_Local          (Local*           x);
 548   void do_Constant       (Constant*        x);
 549   void do_LoadField      (LoadField*       x);
 550   void do_StoreField     (StoreField*      x);
 551   void do_ArrayLength    (ArrayLength*     x);
 552   void do_LoadIndexed    (LoadIndexed*     x);
 553   void do_StoreIndexed   (StoreIndexed*    x);
 554   void do_NegateOp       (NegateOp*        x);
 555   void do_ArithmeticOp   (ArithmeticOp*    x);
 556   void do_ShiftOp        (ShiftOp*         x);
 557   void do_LogicOp        (LogicOp*         x);
 558   void do_CompareOp      (CompareOp*       x);
 559   void do_IfOp           (IfOp*            x);
 560   void do_Convert        (Convert*         x);
 561   void do_NullCheck      (NullCheck*       x);
 562   void do_TypeCast       (TypeCast*        x);
 563   void do_Invoke         (Invoke*          x);
 564   void do_NewInstance    (NewInstance*     x);
 565   void do_NewTypeArray   (NewTypeArray*    x);
 566   void do_NewObjectArray (NewObjectArray*  x);
 567   void do_NewMultiArray  (NewMultiArray*   x);
 568   void do_CheckCast      (CheckCast*       x);
 569   void do_InstanceOf     (InstanceOf*      x);
 570   void do_MonitorEnter   (MonitorEnter*    x);
 571   void do_MonitorExit    (MonitorExit*     x);
 572   void do_Intrinsic      (Intrinsic*       x);
 573   void do_BlockBegin     (BlockBegin*      x);
 574   void do_Goto           (Goto*            x);
 575   void do_If             (If*              x);
 576   void do_TableSwitch    (TableSwitch*     x);
 577   void do_LookupSwitch   (LookupSwitch*    x);
 578   void do_Return         (Return*          x);
 579   void do_Throw          (Throw*           x);
 580   void do_Base           (Base*            x);
 581   void do_OsrEntry       (OsrEntry*        x);
 582   void do_ExceptionObject(ExceptionObject* x);
 583   void do_RoundFP        (RoundFP*         x);
 584   void do_UnsafeGet      (UnsafeGet*       x);
 585   void do_UnsafePut      (UnsafePut*       x);
 586   void do_UnsafeGetAndSet(UnsafeGetAndSet* x);
 587   void do_ProfileCall    (ProfileCall*     x);
 588   void do_ProfileReturnType (ProfileReturnType*  x);
 589   void do_ProfileInvoke  (ProfileInvoke*   x);
 590   void do_RuntimeCall    (RuntimeCall*     x);
 591   void do_MemBar         (MemBar*          x);
 592   void do_RangeCheckPredicate(RangeCheckPredicate* x);
 593 #ifdef ASSERT
 594   void do_Assert         (Assert*          x);
 595 #endif
 596 };
 597 
 598 
 599 // Because of a static contained within (for the purpose of iteration
 600 // over instructions), it is only valid to have one of these active at
 601 // a time
 602 class NullCheckEliminator: public ValueVisitor {
 603  private:
 604   Optimizer*        _opt;
 605 
 606   ValueSet*         _visitable_instructions;        // Visit each instruction only once per basic block
 607   BlockList*        _work_list;                   // Basic blocks to visit
 608 
 609   bool visitable(Value x) {
 610     assert(_visitable_instructions != NULL, "check");
 611     return _visitable_instructions->contains(x);
 612   }
 613   void mark_visited(Value x) {
 614     assert(_visitable_instructions != NULL, "check");
 615     _visitable_instructions->remove(x);
 616   }
 617   void mark_visitable(Value x) {
 618     assert(_visitable_instructions != NULL, "check");
 619     _visitable_instructions->put(x);
 620   }
 621   void clear_visitable_state() {
 622     assert(_visitable_instructions != NULL, "check");
 623     _visitable_instructions->clear();
 624   }
 625 
 626   ValueSet*         _set;                         // current state, propagated to subsequent BlockBegins
 627   ValueSetList      _block_states;                // BlockBegin null-check states for all processed blocks
 628   NullCheckVisitor  _visitor;
 629   NullCheck*        _last_explicit_null_check;
 630 
 631   bool set_contains(Value x)                      { assert(_set != NULL, "check"); return _set->contains(x); }
 632   void set_put     (Value x)                      { assert(_set != NULL, "check"); _set->put(x); }
 633   void set_remove  (Value x)                      { assert(_set != NULL, "check"); _set->remove(x); }
 634 
 635   BlockList* work_list()                          { return _work_list; }
 636 
 637   void iterate_all();
 638   void iterate_one(BlockBegin* block);
 639 
 640   ValueSet* state()                               { return _set; }
 641   void      set_state_from (ValueSet* state)      { _set->set_from(state); }
 642   ValueSet* state_for      (BlockBegin* block)    { return _block_states.at(block->block_id()); }
 643   void      set_state_for  (BlockBegin* block, ValueSet* stack) { _block_states.at_put(block->block_id(), stack); }
 644   // Returns true if caused a change in the block's state.
 645   bool      merge_state_for(BlockBegin* block,
 646                             ValueSet*   incoming_state);
 647 
 648  public:
 649   // constructor
 650   NullCheckEliminator(Optimizer* opt)
 651     : _opt(opt)
 652     , _work_list(new BlockList())
 653     , _set(new ValueSet())
 654     , _block_states(BlockBegin::number_of_blocks(), BlockBegin::number_of_blocks(), NULL)
 655     , _last_explicit_null_check(NULL) {
 656     _visitable_instructions = new ValueSet();
 657     _visitor.set_eliminator(this);
 658     CompileLog* log = _opt->ir()->compilation()->log();
 659     if (log != NULL)
 660       log->set_context("optimize name='null_check_elimination'");
 661   }
 662 
 663   ~NullCheckEliminator() {
 664     CompileLog* log = _opt->ir()->compilation()->log();
 665     if (log != NULL)
 666       log->clear_context(); // skip marker if nothing was printed
 667   }
 668 
 669   Optimizer*  opt()                               { return _opt; }
 670   IR*         ir ()                               { return opt()->ir(); }
 671 
 672   // Process a graph
 673   void iterate(BlockBegin* root);
 674 
 675   void visit(Value* f);
 676 
 677   // In some situations (like NullCheck(x); getfield(x)) the debug
 678   // information from the explicit NullCheck can be used to populate
 679   // the getfield, even if the two instructions are in different
 680   // scopes; this allows implicit null checks to be used but the
 681   // correct exception information to be generated. We must clear the
 682   // last-traversed NullCheck when we reach a potentially-exception-
 683   // throwing instruction, as well as in some other cases.
 684   void        set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
 685   NullCheck*  last_explicit_null_check()                     { return _last_explicit_null_check; }
 686   Value       last_explicit_null_check_obj()                 { return (_last_explicit_null_check
 687                                                                          ? _last_explicit_null_check->obj()
 688                                                                          : NULL); }
 689   NullCheck*  consume_last_explicit_null_check() {
 690     _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
 691     _last_explicit_null_check->set_can_trap(false);
 692     return _last_explicit_null_check;
 693   }
 694   void        clear_last_explicit_null_check()               { _last_explicit_null_check = NULL; }
 695 
 696   // Handlers for relevant instructions
 697   // (separated out from NullCheckVisitor for clarity)
 698 
 699   // The basic contract is that these must leave the instruction in
 700   // the desired state; must not assume anything about the state of
 701   // the instruction. We make multiple passes over some basic blocks
 702   // and the last pass is the only one whose result is valid.
 703   void handle_AccessField     (AccessField* x);
 704   void handle_ArrayLength     (ArrayLength* x);
 705   void handle_LoadIndexed     (LoadIndexed* x);
 706   void handle_StoreIndexed    (StoreIndexed* x);
 707   void handle_NullCheck       (NullCheck* x);
 708   void handle_Invoke          (Invoke* x);
 709   void handle_NewInstance     (NewInstance* x);
 710   void handle_NewArray        (NewArray* x);
 711   void handle_AccessMonitor   (AccessMonitor* x);
 712   void handle_Intrinsic       (Intrinsic* x);
 713   void handle_ExceptionObject (ExceptionObject* x);
 714   void handle_Phi             (Phi* x);
 715   void handle_ProfileCall     (ProfileCall* x);
 716   void handle_ProfileReturnType (ProfileReturnType* x);
 717 };
 718 
 719 
 720 // NEEDS_CLEANUP
 721 // There may be other instructions which need to clear the last
 722 // explicit null check. Anything across which we can not hoist the
 723 // debug information for a NullCheck instruction must clear it. It
 724 // might be safer to pattern match "NullCheck ; {AccessField,
 725 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
 726 // Should test to see performance hit of clearing it for all handlers
 727 // with empty bodies below. If it is negligible then we should leave
 728 // that in for safety, otherwise should think more about it.
 729 void NullCheckVisitor::do_Phi            (Phi*             x) { nce()->handle_Phi(x);      }
 730 void NullCheckVisitor::do_Local          (Local*           x) {}
 731 void NullCheckVisitor::do_Constant       (Constant*        x) { /* FIXME: handle object constants */ }
 732 void NullCheckVisitor::do_LoadField      (LoadField*       x) { nce()->handle_AccessField(x); }
 733 void NullCheckVisitor::do_StoreField     (StoreField*      x) { nce()->handle_AccessField(x); }
 734 void NullCheckVisitor::do_ArrayLength    (ArrayLength*     x) { nce()->handle_ArrayLength(x); }
 735 void NullCheckVisitor::do_LoadIndexed    (LoadIndexed*     x) { nce()->handle_LoadIndexed(x); }
 736 void NullCheckVisitor::do_StoreIndexed   (StoreIndexed*    x) { nce()->handle_StoreIndexed(x); }
 737 void NullCheckVisitor::do_NegateOp       (NegateOp*        x) {}
 738 void NullCheckVisitor::do_ArithmeticOp   (ArithmeticOp*    x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
 739 void NullCheckVisitor::do_ShiftOp        (ShiftOp*         x) {}
 740 void NullCheckVisitor::do_LogicOp        (LogicOp*         x) {}
 741 void NullCheckVisitor::do_CompareOp      (CompareOp*       x) {}
 742 void NullCheckVisitor::do_IfOp           (IfOp*            x) {}
 743 void NullCheckVisitor::do_Convert        (Convert*         x) {}
 744 void NullCheckVisitor::do_NullCheck      (NullCheck*       x) { nce()->handle_NullCheck(x); }
 745 void NullCheckVisitor::do_TypeCast       (TypeCast*        x) {}
 746 void NullCheckVisitor::do_Invoke         (Invoke*          x) { nce()->handle_Invoke(x); }
 747 void NullCheckVisitor::do_NewInstance    (NewInstance*     x) { nce()->handle_NewInstance(x); }
 748 void NullCheckVisitor::do_NewTypeArray   (NewTypeArray*    x) { nce()->handle_NewArray(x); }
 749 void NullCheckVisitor::do_NewObjectArray (NewObjectArray*  x) { nce()->handle_NewArray(x); }
 750 void NullCheckVisitor::do_NewMultiArray  (NewMultiArray*   x) { nce()->handle_NewArray(x); }
 751 void NullCheckVisitor::do_CheckCast      (CheckCast*       x) { nce()->clear_last_explicit_null_check(); }
 752 void NullCheckVisitor::do_InstanceOf     (InstanceOf*      x) {}
 753 void NullCheckVisitor::do_MonitorEnter   (MonitorEnter*    x) { nce()->handle_AccessMonitor(x); }
 754 void NullCheckVisitor::do_MonitorExit    (MonitorExit*     x) { nce()->handle_AccessMonitor(x); }
 755 void NullCheckVisitor::do_Intrinsic      (Intrinsic*       x) { nce()->handle_Intrinsic(x);     }
 756 void NullCheckVisitor::do_BlockBegin     (BlockBegin*      x) {}
 757 void NullCheckVisitor::do_Goto           (Goto*            x) {}
 758 void NullCheckVisitor::do_If             (If*              x) {}
 759 void NullCheckVisitor::do_TableSwitch    (TableSwitch*     x) {}
 760 void NullCheckVisitor::do_LookupSwitch   (LookupSwitch*    x) {}
 761 void NullCheckVisitor::do_Return         (Return*          x) {}
 762 void NullCheckVisitor::do_Throw          (Throw*           x) { nce()->clear_last_explicit_null_check(); }
 763 void NullCheckVisitor::do_Base           (Base*            x) {}
 764 void NullCheckVisitor::do_OsrEntry       (OsrEntry*        x) {}
 765 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
 766 void NullCheckVisitor::do_RoundFP        (RoundFP*         x) {}
 767 void NullCheckVisitor::do_UnsafeGet      (UnsafeGet*       x) {}
 768 void NullCheckVisitor::do_UnsafePut      (UnsafePut*       x) {}
 769 void NullCheckVisitor::do_UnsafeGetAndSet(UnsafeGetAndSet* x) {}
 770 void NullCheckVisitor::do_ProfileCall    (ProfileCall*     x) { nce()->clear_last_explicit_null_check();
 771                                                                 nce()->handle_ProfileCall(x); }
 772 void NullCheckVisitor::do_ProfileReturnType (ProfileReturnType* x) { nce()->handle_ProfileReturnType(x); }
 773 void NullCheckVisitor::do_ProfileInvoke  (ProfileInvoke*   x) {}
 774 void NullCheckVisitor::do_RuntimeCall    (RuntimeCall*     x) {}
 775 void NullCheckVisitor::do_MemBar         (MemBar*          x) {}
 776 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
 777 #ifdef ASSERT
 778 void NullCheckVisitor::do_Assert         (Assert*          x) {}
 779 #endif
 780 
 781 void NullCheckEliminator::visit(Value* p) {
 782   assert(*p != NULL, "should not find NULL instructions");
 783   if (visitable(*p)) {
 784     mark_visited(*p);
 785     (*p)->visit(&_visitor);
 786   }
 787 }
 788 
 789 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
 790   ValueSet* state = state_for(block);
 791   if (state == NULL) {
 792     state = incoming_state->copy();
 793     set_state_for(block, state);
 794     return true;
 795   } else {
 796     bool changed = state->set_intersect(incoming_state);
 797     if (PrintNullCheckElimination && changed) {
 798       tty->print_cr("Block %d's null check state changed", block->block_id());
 799     }
 800     return changed;
 801   }
 802 }
 803 
 804 
 805 void NullCheckEliminator::iterate_all() {
 806   while (work_list()->length() > 0) {
 807     iterate_one(work_list()->pop());
 808   }
 809 }
 810 
 811 
 812 void NullCheckEliminator::iterate_one(BlockBegin* block) {
 813   clear_visitable_state();
 814   // clear out an old explicit null checks
 815   set_last_explicit_null_check(NULL);
 816 
 817   if (PrintNullCheckElimination) {
 818     tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
 819                   block->block_id(),
 820                   ir()->method()->holder()->name()->as_utf8(),
 821                   ir()->method()->name()->as_utf8(),
 822                   ir()->method()->signature()->as_symbol()->as_utf8());
 823   }
 824 
 825   // Create new state if none present (only happens at root)
 826   if (state_for(block) == NULL) {
 827     ValueSet* tmp_state = new ValueSet();
 828     set_state_for(block, tmp_state);
 829     // Initial state is that local 0 (receiver) is non-null for
 830     // non-static methods
 831     ValueStack* stack  = block->state();
 832     IRScope*    scope  = stack->scope();
 833     ciMethod*   method = scope->method();
 834     if (!method->is_static()) {
 835       Local* local0 = stack->local_at(0)->as_Local();
 836       assert(local0 != NULL, "must be");
 837       assert(local0->type() == objectType, "invalid type of receiver");
 838 
 839       if (local0 != NULL) {
 840         // Local 0 is used in this scope
 841         tmp_state->put(local0);
 842         if (PrintNullCheckElimination) {
 843           tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
 844         }
 845       }
 846     }
 847   }
 848 
 849   // Must copy block's state to avoid mutating it during iteration
 850   // through the block -- otherwise "not-null" states can accidentally
 851   // propagate "up" through the block during processing of backward
 852   // branches and algorithm is incorrect (and does not converge)
 853   set_state_from(state_for(block));
 854 
 855   // allow visiting of Phis belonging to this block
 856   for_each_phi_fun(block, phi,
 857                    mark_visitable(phi);
 858                    );
 859 
 860   BlockEnd* e = block->end();
 861   assert(e != NULL, "incomplete graph");
 862   int i;
 863 
 864   // Propagate the state before this block into the exception
 865   // handlers.  They aren't true successors since we aren't guaranteed
 866   // to execute the whole block before executing them.  Also putting
 867   // them on first seems to help reduce the amount of iteration to
 868   // reach a fixed point.
 869   for (i = 0; i < block->number_of_exception_handlers(); i++) {
 870     BlockBegin* next = block->exception_handler_at(i);
 871     if (merge_state_for(next, state())) {
 872       if (!work_list()->contains(next)) {
 873         work_list()->push(next);
 874       }
 875     }
 876   }
 877 
 878   // Iterate through block, updating state.
 879   for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
 880     // Mark instructions in this block as visitable as they are seen
 881     // in the instruction list.  This keeps the iteration from
 882     // visiting instructions which are references in other blocks or
 883     // visiting instructions more than once.
 884     mark_visitable(instr);
 885     if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
 886       mark_visited(instr);
 887       instr->input_values_do(this);
 888       instr->visit(&_visitor);
 889     }
 890   }
 891 
 892   // Propagate state to successors if necessary
 893   for (i = 0; i < e->number_of_sux(); i++) {
 894     BlockBegin* next = e->sux_at(i);
 895     if (merge_state_for(next, state())) {
 896       if (!work_list()->contains(next)) {
 897         work_list()->push(next);
 898       }
 899     }
 900   }
 901 }
 902 
 903 
 904 void NullCheckEliminator::iterate(BlockBegin* block) {
 905   work_list()->push(block);
 906   iterate_all();
 907 }
 908 
 909 void NullCheckEliminator::handle_AccessField(AccessField* x) {
 910   if (x->is_static()) {
 911     if (x->as_LoadField() != NULL) {
 912       // If the field is a non-null static final object field (as is
 913       // often the case for sun.misc.Unsafe), put this LoadField into
 914       // the non-null map
 915       ciField* field = x->field();
 916       if (field->is_constant()) {
 917         ciConstant field_val = field->constant_value();
 918         BasicType field_type = field_val.basic_type();
 919         if (is_reference_type(field_type)) {
 920           ciObject* obj_val = field_val.as_object();
 921           if (!obj_val->is_null_object()) {
 922             if (PrintNullCheckElimination) {
 923               tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
 924                             x->id());
 925             }
 926             set_put(x);
 927           }
 928         }
 929       }
 930     }
 931     // Be conservative
 932     clear_last_explicit_null_check();
 933     return;
 934   }
 935 
 936   Value obj = x->obj();
 937   if (set_contains(obj)) {
 938     // Value is non-null => update AccessField
 939     if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
 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 AccessField %d's null check for value %d",
 944                       x->explicit_null_check()->id(), x->id(), obj->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 AccessField %d's null check for value %d", x->id(), obj->id());
 951       }
 952     }
 953   } else {
 954     set_put(obj);
 955     if (PrintNullCheckElimination) {
 956       tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->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_ArrayLength(ArrayLength* x) {
 967   Value array = x->array();
 968   if (set_contains(array)) {
 969     // Value is non-null => update AccessArray
 970     if (last_explicit_null_check_obj() == array) {
 971       x->set_explicit_null_check(consume_last_explicit_null_check());
 972       x->set_needs_null_check(true);
 973       if (PrintNullCheckElimination) {
 974         tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
 975                       x->explicit_null_check()->id(), x->id(), array->id());
 976       }
 977     } else {
 978       x->set_explicit_null_check(NULL);
 979       x->set_needs_null_check(false);
 980       if (PrintNullCheckElimination) {
 981         tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
 982       }
 983     }
 984   } else {
 985     set_put(array);
 986     if (PrintNullCheckElimination) {
 987       tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
 988     }
 989     // Ensure previous passes do not cause wrong state
 990     x->set_needs_null_check(true);
 991     x->set_explicit_null_check(NULL);
 992   }
 993   clear_last_explicit_null_check();
 994 }
 995 
 996 
 997 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
 998   Value array = x->array();
 999   if (set_contains(array)) {
1000     // Value is non-null => update AccessArray
1001     if (last_explicit_null_check_obj() == array) {
1002       x->set_explicit_null_check(consume_last_explicit_null_check());
1003       x->set_needs_null_check(true);
1004       if (PrintNullCheckElimination) {
1005         tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
1006                       x->explicit_null_check()->id(), x->id(), array->id());
1007       }
1008     } else {
1009       x->set_explicit_null_check(NULL);
1010       x->set_needs_null_check(false);
1011       if (PrintNullCheckElimination) {
1012         tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
1013       }
1014     }
1015   } else {
1016     set_put(array);
1017     if (PrintNullCheckElimination) {
1018       tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
1019     }
1020     // Ensure previous passes do not cause wrong state
1021     x->set_needs_null_check(true);
1022     x->set_explicit_null_check(NULL);
1023   }
1024   clear_last_explicit_null_check();
1025 }
1026 
1027 
1028 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
1029   Value array = x->array();
1030   if (set_contains(array)) {
1031     // Value is non-null => update AccessArray
1032     if (PrintNullCheckElimination) {
1033       tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
1034     }
1035     x->set_needs_null_check(false);
1036   } else {
1037     set_put(array);
1038     if (PrintNullCheckElimination) {
1039       tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
1040     }
1041     // Ensure previous passes do not cause wrong state
1042     x->set_needs_null_check(true);
1043   }
1044   clear_last_explicit_null_check();
1045 }
1046 
1047 
1048 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
1049   Value obj = x->obj();
1050   if (set_contains(obj)) {
1051     // Already proven to be non-null => this NullCheck is useless
1052     if (PrintNullCheckElimination) {
1053       tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
1054     }
1055     // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
1056     // The code generator won't emit LIR for a NullCheck that cannot trap.
1057     x->set_can_trap(false);
1058   } else {
1059     // May be null => add to map and set last explicit NullCheck
1060     x->set_can_trap(true);
1061     // make sure it's pinned if it can trap
1062     x->pin(Instruction::PinExplicitNullCheck);
1063     set_put(obj);
1064     set_last_explicit_null_check(x);
1065     if (PrintNullCheckElimination) {
1066       tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1067     }
1068   }
1069 }
1070 
1071 
1072 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1073   if (!x->has_receiver()) {
1074     // Be conservative
1075     clear_last_explicit_null_check();
1076     return;
1077   }
1078 
1079   Value recv = x->receiver();
1080   if (!set_contains(recv)) {
1081     set_put(recv);
1082     if (PrintNullCheckElimination) {
1083       tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1084     }
1085   }
1086   clear_last_explicit_null_check();
1087 }
1088 
1089 
1090 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1091   set_put(x);
1092   if (PrintNullCheckElimination) {
1093     tty->print_cr("NewInstance %d is non-null", x->id());
1094   }
1095 }
1096 
1097 
1098 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1099   set_put(x);
1100   if (PrintNullCheckElimination) {
1101     tty->print_cr("NewArray %d is non-null", x->id());
1102   }
1103 }
1104 
1105 
1106 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1107   set_put(x);
1108   if (PrintNullCheckElimination) {
1109     tty->print_cr("ExceptionObject %d is non-null", x->id());
1110   }
1111 }
1112 
1113 
1114 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1115   Value obj = x->obj();
1116   if (set_contains(obj)) {
1117     // Value is non-null => update AccessMonitor
1118     if (PrintNullCheckElimination) {
1119       tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1120     }
1121     x->set_needs_null_check(false);
1122   } else {
1123     set_put(obj);
1124     if (PrintNullCheckElimination) {
1125       tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1126     }
1127     // Ensure previous passes do not cause wrong state
1128     x->set_needs_null_check(true);
1129   }
1130   clear_last_explicit_null_check();
1131 }
1132 
1133 
1134 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1135   if (!x->has_receiver()) {
1136     if (x->id() == vmIntrinsics::_arraycopy) {
1137       for (int i = 0; i < x->number_of_arguments(); i++) {
1138         x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1139       }
1140     }
1141 
1142     // Be conservative
1143     clear_last_explicit_null_check();
1144     return;
1145   }
1146 
1147   Value recv = x->receiver();
1148   if (set_contains(recv)) {
1149     // Value is non-null => update Intrinsic
1150     if (PrintNullCheckElimination) {
1151       tty->print_cr("Eliminated Intrinsic %d's null check for value %d", vmIntrinsics::as_int(x->id()), recv->id());
1152     }
1153     x->set_needs_null_check(false);
1154   } else {
1155     set_put(recv);
1156     if (PrintNullCheckElimination) {
1157       tty->print_cr("Intrinsic %d of value %d proves value to be non-null", vmIntrinsics::as_int(x->id()), recv->id());
1158     }
1159     // Ensure previous passes do not cause wrong state
1160     x->set_needs_null_check(true);
1161   }
1162   clear_last_explicit_null_check();
1163 }
1164 
1165 
1166 void NullCheckEliminator::handle_Phi(Phi* x) {
1167   int i;
1168   bool all_non_null = true;
1169   if (x->is_illegal()) {
1170     all_non_null = false;
1171   } else {
1172     for (i = 0; i < x->operand_count(); i++) {
1173       Value input = x->operand_at(i);
1174       if (!set_contains(input)) {
1175         all_non_null = false;
1176       }
1177     }
1178   }
1179 
1180   if (all_non_null) {
1181     // Value is non-null => update Phi
1182     if (PrintNullCheckElimination) {
1183       tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1184     }
1185     x->set_needs_null_check(false);
1186   } else if (set_contains(x)) {
1187     set_remove(x);
1188   }
1189 }
1190 
1191 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1192   for (int i = 0; i < x->nb_profiled_args(); i++) {
1193     x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1194   }
1195 }
1196 
1197 void NullCheckEliminator::handle_ProfileReturnType(ProfileReturnType* x) {
1198   x->set_needs_null_check(!set_contains(x->ret()));
1199 }
1200 
1201 void Optimizer::eliminate_null_checks() {
1202   ResourceMark rm;
1203 
1204   NullCheckEliminator nce(this);
1205 
1206   if (PrintNullCheckElimination) {
1207     tty->print_cr("Starting null check elimination for method %s::%s%s",
1208                   ir()->method()->holder()->name()->as_utf8(),
1209                   ir()->method()->name()->as_utf8(),
1210                   ir()->method()->signature()->as_symbol()->as_utf8());
1211   }
1212 
1213   // Apply to graph
1214   nce.iterate(ir()->start());
1215 
1216   // walk over the graph looking for exception
1217   // handlers and iterate over them as well
1218   int nblocks = BlockBegin::number_of_blocks();
1219   BlockList blocks(nblocks);
1220   boolArray visited_block(nblocks, nblocks, false);
1221 
1222   blocks.push(ir()->start());
1223   visited_block.at_put(ir()->start()->block_id(), true);
1224   for (int i = 0; i < blocks.length(); i++) {
1225     BlockBegin* b = blocks.at(i);
1226     // exception handlers need to be treated as additional roots
1227     for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1228       BlockBegin* excp = b->exception_handler_at(e);
1229       int id = excp->block_id();
1230       if (!visited_block.at(id)) {
1231         blocks.push(excp);
1232         visited_block.at_put(id, true);
1233         nce.iterate(excp);
1234       }
1235     }
1236     // traverse successors
1237     BlockEnd *end = b->end();
1238     for (int s = end->number_of_sux(); s-- > 0; ) {
1239       BlockBegin* next = end->sux_at(s);
1240       int id = next->block_id();
1241       if (!visited_block.at(id)) {
1242         blocks.push(next);
1243         visited_block.at_put(id, true);
1244       }
1245     }
1246   }
1247 
1248 
1249   if (PrintNullCheckElimination) {
1250     tty->print_cr("Done with null check elimination for method %s::%s%s",
1251                   ir()->method()->holder()->name()->as_utf8(),
1252                   ir()->method()->name()->as_utf8(),
1253                   ir()->method()->signature()->as_symbol()->as_utf8());
1254   }
1255 }