1 /*
   2  * Copyright (c) 2011, 2014, 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 "opto/loopnode.hpp"
  27 #include "opto/addnode.hpp"
  28 #include "opto/callnode.hpp"
  29 #include "opto/connode.hpp"
  30 #include "opto/convertnode.hpp"
  31 #include "opto/loopnode.hpp"
  32 #include "opto/mulnode.hpp"
  33 #include "opto/opaquenode.hpp"
  34 #include "opto/rootnode.hpp"
  35 #include "opto/subnode.hpp"
  36 
  37 /*
  38  * The general idea of Loop Predication is to insert a predicate on the entry
  39  * path to a loop, and raise a uncommon trap if the check of the condition fails.
  40  * The condition checks are promoted from inside the loop body, and thus
  41  * the checks inside the loop could be eliminated. Currently, loop predication
  42  * optimization has been applied to remove array range check and loop invariant
  43  * checks (such as null checks).
  44 */
  45 
  46 //-------------------------------register_control-------------------------
  47 void PhaseIdealLoop::register_control(Node* n, IdealLoopTree *loop, Node* pred) {
  48   assert(n->is_CFG(), "must be control node");
  49   _igvn.register_new_node_with_optimizer(n);
  50   loop->_body.push(n);
  51   set_loop(n, loop);
  52   // When called from beautify_loops() idom is not constructed yet.
  53   if (_idom != NULL) {
  54     set_idom(n, pred, dom_depth(pred));
  55   }
  56 }
  57 
  58 //------------------------------create_new_if_for_predicate------------------------
  59 // create a new if above the uct_if_pattern for the predicate to be promoted.
  60 //
  61 //          before                                after
  62 //        ----------                           ----------
  63 //           ctrl                                 ctrl
  64 //            |                                     |
  65 //            |                                     |
  66 //            v                                     v
  67 //           iff                                 new_iff
  68 //          /    \                                /      \
  69 //         /      \                              /        \
  70 //        v        v                            v          v
  71 //  uncommon_proj cont_proj                   if_uct     if_cont
  72 // \      |        |                           |          |
  73 //  \     |        |                           |          |
  74 //   v    v        v                           |          v
  75 //     rgn       loop                          |         iff
  76 //      |                                      |        /     \
  77 //      |                                      |       /       \
  78 //      v                                      |      v         v
  79 // uncommon_trap                               | uncommon_proj cont_proj
  80 //                                           \  \    |           |
  81 //                                            \  \   |           |
  82 //                                             v  v  v           v
  83 //                                               rgn           loop
  84 //                                                |
  85 //                                                |
  86 //                                                v
  87 //                                           uncommon_trap
  88 //
  89 //
  90 // We will create a region to guard the uct call if there is no one there.
  91 // The true projecttion (if_cont) of the new_iff is returned.
  92 // This code is also used to clone predicates to cloned loops.
  93 ProjNode* PhaseIdealLoop::create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
  94                                                       Deoptimization::DeoptReason reason) {
  95   assert(cont_proj->is_uncommon_trap_if_pattern(reason), "must be a uct if pattern!");
  96   IfNode* iff = cont_proj->in(0)->as_If();
  97 
  98   ProjNode *uncommon_proj = iff->proj_out(1 - cont_proj->_con);
  99   Node     *rgn   = uncommon_proj->unique_ctrl_out();
 100   assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
 101 
 102   uint proj_index = 1; // region's edge corresponding to uncommon_proj
 103   if (!rgn->is_Region()) { // create a region to guard the call
 104     assert(rgn->is_Call(), "must be call uct");
 105     CallNode* call = rgn->as_Call();
 106     IdealLoopTree* loop = get_loop(call);
 107     rgn = new RegionNode(1);
 108     rgn->add_req(uncommon_proj);
 109     register_control(rgn, loop, uncommon_proj);
 110     _igvn.replace_input_of(call, 0, rgn);
 111     // When called from beautify_loops() idom is not constructed yet.
 112     if (_idom != NULL) {
 113       set_idom(call, rgn, dom_depth(rgn));
 114     }
 115   } else {
 116     // Find region's edge corresponding to uncommon_proj
 117     for (; proj_index < rgn->req(); proj_index++)
 118       if (rgn->in(proj_index) == uncommon_proj) break;
 119     assert(proj_index < rgn->req(), "sanity");
 120   }
 121 
 122   Node* entry = iff->in(0);
 123   if (new_entry != NULL) {
 124     // Clonning the predicate to new location.
 125     entry = new_entry;
 126   }
 127   // Create new_iff
 128   IdealLoopTree* lp = get_loop(entry);
 129   IfNode *new_iff = iff->clone()->as_If();
 130   new_iff->set_req(0, entry);
 131   register_control(new_iff, lp, entry);
 132   Node *if_cont = new IfTrueNode(new_iff);
 133   Node *if_uct  = new IfFalseNode(new_iff);
 134   if (cont_proj->is_IfFalse()) {
 135     // Swap
 136     Node* tmp = if_uct; if_uct = if_cont; if_cont = tmp;
 137   }
 138   register_control(if_cont, lp, new_iff);
 139   register_control(if_uct, get_loop(rgn), new_iff);
 140 
 141   // if_uct to rgn
 142   _igvn.hash_delete(rgn);
 143   rgn->add_req(if_uct);
 144   // When called from beautify_loops() idom is not constructed yet.
 145   if (_idom != NULL) {
 146     Node* ridom = idom(rgn);
 147     Node* nrdom = dom_lca(ridom, new_iff);
 148     set_idom(rgn, nrdom, dom_depth(rgn));
 149   }
 150 
 151   // If rgn has phis add new edges which has the same
 152   // value as on original uncommon_proj pass.
 153   assert(rgn->in(rgn->req() -1) == if_uct, "new edge should be last");
 154   bool has_phi = false;
 155   for (DUIterator_Fast imax, i = rgn->fast_outs(imax); i < imax; i++) {
 156     Node* use = rgn->fast_out(i);
 157     if (use->is_Phi() && use->outcnt() > 0) {
 158       assert(use->in(0) == rgn, "");
 159       _igvn.rehash_node_delayed(use);
 160       use->add_req(use->in(proj_index));
 161       has_phi = true;
 162     }
 163   }
 164   assert(!has_phi || rgn->req() > 3, "no phis when region is created");
 165 
 166   if (new_entry == NULL) {
 167     // Attach if_cont to iff
 168     _igvn.replace_input_of(iff, 0, if_cont);
 169     if (_idom != NULL) {
 170       set_idom(iff, if_cont, dom_depth(iff));
 171     }
 172   }
 173   return if_cont->as_Proj();
 174 }
 175 
 176 //------------------------------create_new_if_for_predicate------------------------
 177 // Create a new if below new_entry for the predicate to be cloned (IGVN optimization)
 178 ProjNode* PhaseIterGVN::create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
 179                                                     Deoptimization::DeoptReason reason) {
 180   assert(new_entry != 0, "only used for clone predicate");
 181   assert(cont_proj->is_uncommon_trap_if_pattern(reason), "must be a uct if pattern!");
 182   IfNode* iff = cont_proj->in(0)->as_If();
 183 
 184   ProjNode *uncommon_proj = iff->proj_out(1 - cont_proj->_con);
 185   Node     *rgn   = uncommon_proj->unique_ctrl_out();
 186   assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
 187 
 188   uint proj_index = 1; // region's edge corresponding to uncommon_proj
 189   if (!rgn->is_Region()) { // create a region to guard the call
 190     assert(rgn->is_Call(), "must be call uct");
 191     CallNode* call = rgn->as_Call();
 192     rgn = new RegionNode(1);
 193     register_new_node_with_optimizer(rgn);
 194     rgn->add_req(uncommon_proj);
 195     replace_input_of(call, 0, rgn);
 196   } else {
 197     // Find region's edge corresponding to uncommon_proj
 198     for (; proj_index < rgn->req(); proj_index++)
 199       if (rgn->in(proj_index) == uncommon_proj) break;
 200     assert(proj_index < rgn->req(), "sanity");
 201   }
 202 
 203   // Create new_iff in new location.
 204   IfNode *new_iff = iff->clone()->as_If();
 205   new_iff->set_req(0, new_entry);
 206 
 207   register_new_node_with_optimizer(new_iff);
 208   Node *if_cont = new IfTrueNode(new_iff);
 209   Node *if_uct  = new IfFalseNode(new_iff);
 210   if (cont_proj->is_IfFalse()) {
 211     // Swap
 212     Node* tmp = if_uct; if_uct = if_cont; if_cont = tmp;
 213   }
 214   register_new_node_with_optimizer(if_cont);
 215   register_new_node_with_optimizer(if_uct);
 216 
 217   // if_uct to rgn
 218   hash_delete(rgn);
 219   rgn->add_req(if_uct);
 220 
 221   // If rgn has phis add corresponding new edges which has the same
 222   // value as on original uncommon_proj pass.
 223   assert(rgn->in(rgn->req() -1) == if_uct, "new edge should be last");
 224   bool has_phi = false;
 225   for (DUIterator_Fast imax, i = rgn->fast_outs(imax); i < imax; i++) {
 226     Node* use = rgn->fast_out(i);
 227     if (use->is_Phi() && use->outcnt() > 0) {
 228       rehash_node_delayed(use);
 229       use->add_req(use->in(proj_index));
 230       has_phi = true;
 231     }
 232   }
 233   assert(!has_phi || rgn->req() > 3, "no phis when region is created");
 234 
 235   return if_cont->as_Proj();
 236 }
 237 
 238 //--------------------------clone_predicate-----------------------
 239 ProjNode* PhaseIdealLoop::clone_predicate(ProjNode* predicate_proj, Node* new_entry,
 240                                           Deoptimization::DeoptReason reason,
 241                                           PhaseIdealLoop* loop_phase,
 242                                           PhaseIterGVN* igvn) {
 243   ProjNode* new_predicate_proj;
 244   if (loop_phase != NULL) {
 245     new_predicate_proj = loop_phase->create_new_if_for_predicate(predicate_proj, new_entry, reason);
 246   } else {
 247     new_predicate_proj =       igvn->create_new_if_for_predicate(predicate_proj, new_entry, reason);
 248   }
 249   IfNode* iff = new_predicate_proj->in(0)->as_If();
 250   Node* ctrl  = iff->in(0);
 251 
 252   // Match original condition since predicate's projections could be swapped.
 253   assert(predicate_proj->in(0)->in(1)->in(1)->Opcode()==Op_Opaque1, "must be");
 254   Node* opq = new Opaque1Node(igvn->C, predicate_proj->in(0)->in(1)->in(1)->in(1));
 255   igvn->C->add_predicate_opaq(opq);
 256 
 257   Node* bol = new Conv2BNode(opq);
 258   if (loop_phase != NULL) {
 259     loop_phase->register_new_node(opq, ctrl);
 260     loop_phase->register_new_node(bol, ctrl);
 261   } else {
 262     igvn->register_new_node_with_optimizer(opq);
 263     igvn->register_new_node_with_optimizer(bol);
 264   }
 265   igvn->hash_delete(iff);
 266   iff->set_req(1, bol);
 267   return new_predicate_proj;
 268 }
 269 
 270 
 271 //--------------------------clone_loop_predicates-----------------------
 272 // Interface from IGVN
 273 Node* PhaseIterGVN::clone_loop_predicates(Node* old_entry, Node* new_entry, bool clone_limit_check) {
 274   return PhaseIdealLoop::clone_loop_predicates(old_entry, new_entry, clone_limit_check, NULL, this);
 275 }
 276 
 277 // Interface from PhaseIdealLoop
 278 Node* PhaseIdealLoop::clone_loop_predicates(Node* old_entry, Node* new_entry, bool clone_limit_check) {
 279   return clone_loop_predicates(old_entry, new_entry, clone_limit_check, this, &this->_igvn);
 280 }
 281 
 282 // Clone loop predicates to cloned loops (peeled, unswitched, split_if).
 283 Node* PhaseIdealLoop::clone_loop_predicates(Node* old_entry, Node* new_entry,
 284                                                 bool clone_limit_check,
 285                                                 PhaseIdealLoop* loop_phase,
 286                                                 PhaseIterGVN* igvn) {
 287 #ifdef ASSERT
 288   if (new_entry == NULL || !(new_entry->is_Proj() || new_entry->is_Region() || new_entry->is_SafePoint())) {
 289     if (new_entry != NULL)
 290       new_entry->dump();
 291     assert(false, "not IfTrue, IfFalse, Region or SafePoint");
 292   }
 293 #endif
 294   // Search original predicates
 295   Node* entry = old_entry;
 296   ProjNode* limit_check_proj = NULL;
 297   if (LoopLimitCheck) {
 298     limit_check_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 299     if (limit_check_proj != NULL) {
 300       entry = entry->in(0)->in(0);
 301     }
 302   }
 303   if (UseLoopPredicate) {
 304     ProjNode* predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 305     if (predicate_proj != NULL) { // right pattern that can be used by loop predication
 306       // clone predicate
 307       new_entry = clone_predicate(predicate_proj, new_entry,
 308                                   Deoptimization::Reason_predicate,
 309                                   loop_phase, igvn);
 310       assert(new_entry != NULL && new_entry->is_Proj(), "IfTrue or IfFalse after clone predicate");
 311       if (TraceLoopPredicate) {
 312         tty->print("Loop Predicate cloned: ");
 313         debug_only( new_entry->in(0)->dump(); )
 314       }
 315     }
 316   }
 317   if (limit_check_proj != NULL && clone_limit_check) {
 318     // Clone loop limit check last to insert it before loop.
 319     // Don't clone a limit check which was already finalized
 320     // for this counted loop (only one limit check is needed).
 321     new_entry = clone_predicate(limit_check_proj, new_entry,
 322                                 Deoptimization::Reason_loop_limit_check,
 323                                 loop_phase, igvn);
 324     assert(new_entry != NULL && new_entry->is_Proj(), "IfTrue or IfFalse after clone limit check");
 325     if (TraceLoopLimitCheck) {
 326       tty->print("Loop Limit Check cloned: ");
 327       debug_only( new_entry->in(0)->dump(); )
 328     }
 329   }
 330   return new_entry;
 331 }
 332 
 333 //--------------------------skip_loop_predicates------------------------------
 334 // Skip related predicates.
 335 Node* PhaseIdealLoop::skip_loop_predicates(Node* entry) {
 336   Node* predicate = NULL;
 337   if (LoopLimitCheck) {
 338     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 339     if (predicate != NULL) {
 340       entry = entry->in(0)->in(0);
 341     }
 342   }
 343   if (UseLoopPredicate) {
 344     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 345     if (predicate != NULL) { // right pattern that can be used by loop predication
 346       IfNode* iff = entry->in(0)->as_If();
 347       ProjNode* uncommon_proj = iff->proj_out(1 - entry->as_Proj()->_con);
 348       Node* rgn = uncommon_proj->unique_ctrl_out();
 349       assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
 350       entry = entry->in(0)->in(0);
 351       while (entry != NULL && entry->is_Proj() && entry->in(0)->is_If()) {
 352         uncommon_proj = entry->in(0)->as_If()->proj_out(1 - entry->as_Proj()->_con);
 353         if (uncommon_proj->unique_ctrl_out() != rgn)
 354           break;
 355         entry = entry->in(0)->in(0);
 356       }
 357     }
 358   }
 359   return entry;
 360 }
 361 
 362 //--------------------------find_predicate_insertion_point-------------------
 363 // Find a good location to insert a predicate
 364 ProjNode* PhaseIdealLoop::find_predicate_insertion_point(Node* start_c, Deoptimization::DeoptReason reason) {
 365   if (start_c == NULL || !start_c->is_Proj())
 366     return NULL;
 367   if (start_c->as_Proj()->is_uncommon_trap_if_pattern(reason)) {
 368     return start_c->as_Proj();
 369   }
 370   return NULL;
 371 }
 372 
 373 //--------------------------find_predicate------------------------------------
 374 // Find a predicate
 375 Node* PhaseIdealLoop::find_predicate(Node* entry) {
 376   Node* predicate = NULL;
 377   if (LoopLimitCheck) {
 378     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 379     if (predicate != NULL) { // right pattern that can be used by loop predication
 380       return entry;
 381     }
 382   }
 383   if (UseLoopPredicate) {
 384     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 385     if (predicate != NULL) { // right pattern that can be used by loop predication
 386       return entry;
 387     }
 388   }
 389   return NULL;
 390 }
 391 
 392 //------------------------------Invariance-----------------------------------
 393 // Helper class for loop_predication_impl to compute invariance on the fly and
 394 // clone invariants.
 395 class Invariance : public StackObj {
 396   VectorSet _visited, _invariant;
 397   Node_Stack _stack;
 398   VectorSet _clone_visited;
 399   Node_List _old_new; // map of old to new (clone)
 400   IdealLoopTree* _lpt;
 401   PhaseIdealLoop* _phase;
 402 
 403   // Helper function to set up the invariance for invariance computation
 404   // If n is a known invariant, set up directly. Otherwise, look up the
 405   // the possibility to push n onto the stack for further processing.
 406   void visit(Node* use, Node* n) {
 407     if (_lpt->is_invariant(n)) { // known invariant
 408       _invariant.set(n->_idx);
 409     } else if (!n->is_CFG()) {
 410       Node *n_ctrl = _phase->ctrl_or_self(n);
 411       Node *u_ctrl = _phase->ctrl_or_self(use); // self if use is a CFG
 412       if (_phase->is_dominator(n_ctrl, u_ctrl)) {
 413         _stack.push(n, n->in(0) == NULL ? 1 : 0);
 414       }
 415     }
 416   }
 417 
 418   // Compute invariance for "the_node" and (possibly) all its inputs recursively
 419   // on the fly
 420   void compute_invariance(Node* n) {
 421     assert(_visited.test(n->_idx), "must be");
 422     visit(n, n);
 423     while (_stack.is_nonempty()) {
 424       Node*  n = _stack.node();
 425       uint idx = _stack.index();
 426       if (idx == n->req()) { // all inputs are processed
 427         _stack.pop();
 428         // n is invariant if it's inputs are all invariant
 429         bool all_inputs_invariant = true;
 430         for (uint i = 0; i < n->req(); i++) {
 431           Node* in = n->in(i);
 432           if (in == NULL) continue;
 433           assert(_visited.test(in->_idx), "must have visited input");
 434           if (!_invariant.test(in->_idx)) { // bad guy
 435             all_inputs_invariant = false;
 436             break;
 437           }
 438         }
 439         if (all_inputs_invariant) {
 440           _invariant.set(n->_idx); // I am a invariant too
 441         }
 442       } else { // process next input
 443         _stack.set_index(idx + 1);
 444         Node* m = n->in(idx);
 445         if (m != NULL && !_visited.test_set(m->_idx)) {
 446           visit(n, m);
 447         }
 448       }
 449     }
 450   }
 451 
 452   // Helper function to set up _old_new map for clone_nodes.
 453   // If n is a known invariant, set up directly ("clone" of n == n).
 454   // Otherwise, push n onto the stack for real cloning.
 455   void clone_visit(Node* n) {
 456     assert(_invariant.test(n->_idx), "must be invariant");
 457     if (_lpt->is_invariant(n)) { // known invariant
 458       _old_new.map(n->_idx, n);
 459     } else { // to be cloned
 460       assert(!n->is_CFG(), "should not see CFG here");
 461       _stack.push(n, n->in(0) == NULL ? 1 : 0);
 462     }
 463   }
 464 
 465   // Clone "n" and (possibly) all its inputs recursively
 466   void clone_nodes(Node* n, Node* ctrl) {
 467     clone_visit(n);
 468     while (_stack.is_nonempty()) {
 469       Node*  n = _stack.node();
 470       uint idx = _stack.index();
 471       if (idx == n->req()) { // all inputs processed, clone n!
 472         _stack.pop();
 473         // clone invariant node
 474         Node* n_cl = n->clone();
 475         _old_new.map(n->_idx, n_cl);
 476         _phase->register_new_node(n_cl, ctrl);
 477         for (uint i = 0; i < n->req(); i++) {
 478           Node* in = n_cl->in(i);
 479           if (in == NULL) continue;
 480           n_cl->set_req(i, _old_new[in->_idx]);
 481         }
 482       } else { // process next input
 483         _stack.set_index(idx + 1);
 484         Node* m = n->in(idx);
 485         if (m != NULL && !_clone_visited.test_set(m->_idx)) {
 486           clone_visit(m); // visit the input
 487         }
 488       }
 489     }
 490   }
 491 
 492  public:
 493   Invariance(Arena* area, IdealLoopTree* lpt) :
 494     _lpt(lpt), _phase(lpt->_phase),
 495     _visited(area), _invariant(area), _stack(area, 10 /* guess */),
 496     _clone_visited(area), _old_new(area)
 497   {}
 498 
 499   // Map old to n for invariance computation and clone
 500   void map_ctrl(Node* old, Node* n) {
 501     assert(old->is_CFG() && n->is_CFG(), "must be");
 502     _old_new.map(old->_idx, n); // "clone" of old is n
 503     _invariant.set(old->_idx);  // old is invariant
 504     _clone_visited.set(old->_idx);
 505   }
 506 
 507   // Driver function to compute invariance
 508   bool is_invariant(Node* n) {
 509     if (!_visited.test_set(n->_idx))
 510       compute_invariance(n);
 511     return (_invariant.test(n->_idx) != 0);
 512   }
 513 
 514   // Driver function to clone invariant
 515   Node* clone(Node* n, Node* ctrl) {
 516     assert(ctrl->is_CFG(), "must be");
 517     assert(_invariant.test(n->_idx), "must be an invariant");
 518     if (!_clone_visited.test(n->_idx))
 519       clone_nodes(n, ctrl);
 520     return _old_new[n->_idx];
 521   }
 522 };
 523 
 524 //------------------------------is_range_check_if -----------------------------------
 525 // Returns true if the predicate of iff is in "scale*iv + offset u< load_range(ptr)" format
 526 // Note: this function is particularly designed for loop predication. We require load_range
 527 //       and offset to be loop invariant computed on the fly by "invar"
 528 bool IdealLoopTree::is_range_check_if(IfNode *iff, PhaseIdealLoop *phase, Invariance& invar) const {
 529   if (!is_loop_exit(iff)) {
 530     return false;
 531   }
 532   if (!iff->in(1)->is_Bool()) {
 533     return false;
 534   }
 535   const BoolNode *bol = iff->in(1)->as_Bool();
 536   if (bol->_test._test != BoolTest::lt) {
 537     return false;
 538   }
 539   if (!bol->in(1)->is_Cmp()) {
 540     return false;
 541   }
 542   const CmpNode *cmp = bol->in(1)->as_Cmp();
 543   if (cmp->Opcode() != Op_CmpU) {
 544     return false;
 545   }
 546   Node* range = cmp->in(2);
 547   if (range->Opcode() != Op_LoadRange) {
 548     const TypeInt* tint = phase->_igvn.type(range)->isa_int();
 549     if (tint == NULL || tint->empty() || tint->_lo < 0) {
 550       // Allow predication on positive values that aren't LoadRanges.
 551       // This allows optimization of loops where the length of the
 552       // array is a known value and doesn't need to be loaded back
 553       // from the array.
 554       return false;
 555     }
 556   }
 557   if (!invar.is_invariant(range)) {
 558     return false;
 559   }
 560   Node *iv     = _head->as_CountedLoop()->phi();
 561   int   scale  = 0;
 562   Node *offset = NULL;
 563   if (!phase->is_scaled_iv_plus_offset(cmp->in(1), iv, &scale, &offset)) {
 564     return false;
 565   }
 566   if (offset && !invar.is_invariant(offset)) { // offset must be invariant
 567     return false;
 568   }
 569   return true;
 570 }
 571 
 572 //------------------------------rc_predicate-----------------------------------
 573 // Create a range check predicate
 574 //
 575 // for (i = init; i < limit; i += stride) {
 576 //    a[scale*i+offset]
 577 // }
 578 //
 579 // Compute max(scale*i + offset) for init <= i < limit and build the predicate
 580 // as "max(scale*i + offset) u< a.length".
 581 //
 582 // There are two cases for max(scale*i + offset):
 583 // (1) stride*scale > 0
 584 //   max(scale*i + offset) = scale*(limit-stride) + offset
 585 // (2) stride*scale < 0
 586 //   max(scale*i + offset) = scale*init + offset
 587 BoolNode* PhaseIdealLoop::rc_predicate(IdealLoopTree *loop, Node* ctrl,
 588                                        int scale, Node* offset,
 589                                        Node* init, Node* limit, Node* stride,
 590                                        Node* range, bool upper) {
 591   stringStream* predString = NULL;
 592   if (TraceLoopPredicate) {
 593     predString = new stringStream();
 594     predString->print("rc_predicate ");
 595   }
 596 
 597   Node* max_idx_expr  = init;
 598   int stride_con = stride->get_int();
 599   if ((stride_con > 0) == (scale > 0) == upper) {
 600     if (LoopLimitCheck) {
 601       // With LoopLimitCheck limit is not exact.
 602       // Calculate exact limit here.
 603       // Note, counted loop's test is '<' or '>'.
 604       limit = exact_limit(loop);
 605       max_idx_expr = new SubINode(limit, stride);
 606       register_new_node(max_idx_expr, ctrl);
 607       if (TraceLoopPredicate) predString->print("(limit - stride) ");
 608     } else {
 609       max_idx_expr = new SubINode(limit, stride);
 610       register_new_node(max_idx_expr, ctrl);
 611       if (TraceLoopPredicate) predString->print("(limit - stride) ");
 612     }
 613   } else {
 614     if (TraceLoopPredicate) predString->print("init ");
 615   }
 616 
 617   if (scale != 1) {
 618     ConNode* con_scale = _igvn.intcon(scale);
 619     max_idx_expr = new MulINode(max_idx_expr, con_scale);
 620     register_new_node(max_idx_expr, ctrl);
 621     if (TraceLoopPredicate) predString->print("* %d ", scale);
 622   }
 623 
 624   if (offset && (!offset->is_Con() || offset->get_int() != 0)){
 625     max_idx_expr = new AddINode(max_idx_expr, offset);
 626     register_new_node(max_idx_expr, ctrl);
 627     if (TraceLoopPredicate)
 628       if (offset->is_Con()) predString->print("+ %d ", offset->get_int());
 629       else predString->print("+ offset ");
 630   }
 631 
 632   CmpUNode* cmp = new CmpUNode(max_idx_expr, range);
 633   register_new_node(cmp, ctrl);
 634   BoolNode* bol = new BoolNode(cmp, BoolTest::lt);
 635   register_new_node(bol, ctrl);
 636 
 637   if (TraceLoopPredicate) {
 638     predString->print_cr("<u range");
 639     tty->print("%s", predString->as_string());
 640   }
 641   return bol;
 642 }
 643 
 644 //------------------------------ loop_predication_impl--------------------------
 645 // Insert loop predicates for null checks and range checks
 646 bool PhaseIdealLoop::loop_predication_impl(IdealLoopTree *loop) {
 647   if (!UseLoopPredicate) return false;
 648 
 649   if (!loop->_head->is_Loop()) {
 650     // Could be a simple region when irreducible loops are present.
 651     return false;
 652   }
 653   LoopNode* head = loop->_head->as_Loop();
 654 
 655   if (head->unique_ctrl_out()->Opcode() == Op_NeverBranch) {
 656     // do nothing for infinite loops
 657     return false;
 658   }
 659 
 660   CountedLoopNode *cl = NULL;
 661   if (head->is_valid_counted_loop()) {
 662     cl = head->as_CountedLoop();
 663     // do nothing for iteration-splitted loops
 664     if (!cl->is_normal_loop()) return false;
 665     // Avoid RCE if Counted loop's test is '!='.
 666     BoolTest::mask bt = cl->loopexit()->test_trip();
 667     if (bt != BoolTest::lt && bt != BoolTest::gt)
 668       cl = NULL;
 669   }
 670 
 671   Node* entry = head->in(LoopNode::EntryControl);
 672   ProjNode *predicate_proj = NULL;
 673   // Loop limit check predicate should be near the loop.
 674   if (LoopLimitCheck) {
 675     predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 676     if (predicate_proj != NULL)
 677       entry = predicate_proj->in(0)->in(0);
 678   }
 679 
 680   predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 681   if (!predicate_proj) {
 682 #ifndef PRODUCT
 683     if (TraceLoopPredicate) {
 684       tty->print("missing predicate:");
 685       loop->dump_head();
 686       head->dump(1);
 687     }
 688 #endif
 689     return false;
 690   }
 691   ConNode* zero = _igvn.intcon(0);
 692   set_ctrl(zero, C->root());
 693 
 694   ResourceArea *area = Thread::current()->resource_area();
 695   Invariance invar(area, loop);
 696 
 697   // Create list of if-projs such that a newer proj dominates all older
 698   // projs in the list, and they all dominate loop->tail()
 699   Node_List if_proj_list(area);
 700   Node *current_proj = loop->tail(); //start from tail
 701   while (current_proj != head) {
 702     if (loop == get_loop(current_proj) && // still in the loop ?
 703         current_proj->is_Proj()        && // is a projection  ?
 704         current_proj->in(0)->Opcode() == Op_If) { // is a if projection ?
 705       if_proj_list.push(current_proj);
 706     }
 707     current_proj = idom(current_proj);
 708   }
 709 
 710   bool hoisted = false; // true if at least one proj is promoted
 711   while (if_proj_list.size() > 0) {
 712     // Following are changed to nonnull when a predicate can be hoisted
 713     ProjNode* new_predicate_proj = NULL;
 714 
 715     ProjNode* proj = if_proj_list.pop()->as_Proj();
 716     IfNode*   iff  = proj->in(0)->as_If();
 717 
 718     if (!proj->is_uncommon_trap_if_pattern(Deoptimization::Reason_none)) {
 719       if (loop->is_loop_exit(iff)) {
 720         // stop processing the remaining projs in the list because the execution of them
 721         // depends on the condition of "iff" (iff->in(1)).
 722         break;
 723       } else {
 724         // Both arms are inside the loop. There are two cases:
 725         // (1) there is one backward branch. In this case, any remaining proj
 726         //     in the if_proj list post-dominates "iff". So, the condition of "iff"
 727         //     does not determine the execution the remining projs directly, and we
 728         //     can safely continue.
 729         // (2) both arms are forwarded, i.e. a diamond shape. In this case, "proj"
 730         //     does not dominate loop->tail(), so it can not be in the if_proj list.
 731         continue;
 732       }
 733     }
 734 
 735     Node*     test = iff->in(1);
 736     if (!test->is_Bool()){ //Conv2B, ...
 737       continue;
 738     }
 739     BoolNode* bol = test->as_Bool();
 740     if (invar.is_invariant(bol)) {
 741       // Invariant test
 742       new_predicate_proj = create_new_if_for_predicate(predicate_proj, NULL,
 743                                                        Deoptimization::Reason_predicate);
 744       Node* ctrl = new_predicate_proj->in(0)->as_If()->in(0);
 745       BoolNode* new_predicate_bol = invar.clone(bol, ctrl)->as_Bool();
 746 
 747       // Negate test if necessary
 748       bool negated = false;
 749       if (proj->_con != predicate_proj->_con) {
 750         new_predicate_bol = new BoolNode(new_predicate_bol->in(1), new_predicate_bol->_test.negate());
 751         register_new_node(new_predicate_bol, ctrl);
 752         negated = true;
 753       }
 754       IfNode* new_predicate_iff = new_predicate_proj->in(0)->as_If();
 755       _igvn.hash_delete(new_predicate_iff);
 756       new_predicate_iff->set_req(1, new_predicate_bol);
 757 #ifndef PRODUCT
 758       if (TraceLoopPredicate) {
 759         tty->print("Predicate invariant if%s: %d ", negated ? " negated" : "", new_predicate_iff->_idx);
 760         loop->dump_head();
 761       } else if (TraceLoopOpts) {
 762         tty->print("Predicate IC ");
 763         loop->dump_head();
 764       }
 765 #endif
 766     } else if (cl != NULL && loop->is_range_check_if(iff, this, invar)) {
 767       // Range check for counted loops
 768       const Node*    cmp    = bol->in(1)->as_Cmp();
 769       Node*          idx    = cmp->in(1);
 770       assert(!invar.is_invariant(idx), "index is variant");
 771       Node* rng = cmp->in(2);
 772       assert(rng->Opcode() == Op_LoadRange || _igvn.type(rng)->is_int() >= 0, "must be");
 773       assert(invar.is_invariant(rng), "range must be invariant");
 774       int scale    = 1;
 775       Node* offset = zero;
 776       bool ok = is_scaled_iv_plus_offset(idx, cl->phi(), &scale, &offset);
 777       assert(ok, "must be index expression");
 778 
 779       Node* init    = cl->init_trip();
 780       Node* limit   = cl->limit();
 781       Node* stride  = cl->stride();
 782 
 783       // Build if's for the upper and lower bound tests.  The
 784       // lower_bound test will dominate the upper bound test and all
 785       // cloned or created nodes will use the lower bound test as
 786       // their declared control.
 787       ProjNode* lower_bound_proj = create_new_if_for_predicate(predicate_proj, NULL, Deoptimization::Reason_predicate);
 788       ProjNode* upper_bound_proj = create_new_if_for_predicate(predicate_proj, NULL, Deoptimization::Reason_predicate);
 789       assert(upper_bound_proj->in(0)->as_If()->in(0) == lower_bound_proj, "should dominate");
 790       Node *ctrl = lower_bound_proj->in(0)->as_If()->in(0);
 791 
 792       // Perform cloning to keep Invariance state correct since the
 793       // late schedule will place invariant things in the loop.
 794       rng = invar.clone(rng, ctrl);
 795       if (offset && offset != zero) {
 796         assert(invar.is_invariant(offset), "offset must be loop invariant");
 797         offset = invar.clone(offset, ctrl);
 798       }
 799 
 800       // Test the lower bound
 801       BoolNode*  lower_bound_bol = rc_predicate(loop, ctrl, scale, offset, init, limit, stride, rng, false);
 802       // Negate test if necessary
 803       bool negated = false;
 804       if (proj->_con != predicate_proj->_con) {
 805         lower_bound_bol = new BoolNode(lower_bound_bol->in(1), lower_bound_bol->_test.negate());
 806         register_new_node(lower_bound_bol, ctrl);
 807         negated = true;
 808       }
 809       IfNode* lower_bound_iff = lower_bound_proj->in(0)->as_If();
 810       _igvn.hash_delete(lower_bound_iff);
 811       lower_bound_iff->set_req(1, lower_bound_bol);
 812       if (TraceLoopPredicate) tty->print_cr("lower bound check if: %s %d ", negated ? " negated" : "", lower_bound_iff->_idx);
 813 
 814       // Test the upper bound
 815       BoolNode* upper_bound_bol = rc_predicate(loop, lower_bound_proj, scale, offset, init, limit, stride, rng, true);
 816       negated = false;
 817       if (proj->_con != predicate_proj->_con) {
 818         upper_bound_bol = new BoolNode(upper_bound_bol->in(1), upper_bound_bol->_test.negate());
 819         register_new_node(upper_bound_bol, ctrl);
 820         negated = true;
 821       }
 822       IfNode* upper_bound_iff = upper_bound_proj->in(0)->as_If();
 823       _igvn.hash_delete(upper_bound_iff);
 824       upper_bound_iff->set_req(1, upper_bound_bol);
 825       if (TraceLoopPredicate) tty->print_cr("upper bound check if: %s %d ", negated ? " negated" : "", lower_bound_iff->_idx);
 826 
 827       // Fall through into rest of the clean up code which will move
 828       // any dependent nodes onto the upper bound test.
 829       new_predicate_proj = upper_bound_proj;
 830 
 831 #ifndef PRODUCT
 832       if (TraceLoopOpts && !TraceLoopPredicate) {
 833         tty->print("Predicate RC ");
 834         loop->dump_head();
 835       }
 836 #endif
 837     } else {
 838       // Loop variant check (for example, range check in non-counted loop)
 839       // with uncommon trap.
 840       continue;
 841     }
 842     assert(new_predicate_proj != NULL, "sanity");
 843     // Success - attach condition (new_predicate_bol) to predicate if
 844     invar.map_ctrl(proj, new_predicate_proj); // so that invariance test can be appropriate
 845 
 846     // Eliminate the old If in the loop body
 847     dominated_by( new_predicate_proj, iff, proj->_con != new_predicate_proj->_con );
 848 
 849     hoisted = true;
 850     C->set_major_progress();
 851   } // end while
 852 
 853 #ifndef PRODUCT
 854   // report that the loop predication has been actually performed
 855   // for this loop
 856   if (TraceLoopPredicate && hoisted) {
 857     tty->print("Loop Predication Performed:");
 858     loop->dump_head();
 859   }
 860 #endif
 861 
 862   return hoisted;
 863 }
 864 
 865 //------------------------------loop_predication--------------------------------
 866 // driver routine for loop predication optimization
 867 bool IdealLoopTree::loop_predication( PhaseIdealLoop *phase) {
 868   bool hoisted = false;
 869   // Recursively promote predicates
 870   if (_child) {
 871     hoisted = _child->loop_predication( phase);
 872   }
 873 
 874   // self
 875   if (!_irreducible && !tail()->is_top()) {
 876     hoisted |= phase->loop_predication_impl(this);
 877   }
 878 
 879   if (_next) { //sibling
 880     hoisted |= _next->loop_predication( phase);
 881   }
 882 
 883   return hoisted;
 884 }