1 /*
   2  * Copyright (c) 2011, 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 "opto/loopnode.hpp"
  27 #include "opto/addnode.hpp"
  28 #include "opto/callnode.hpp"
  29 #include "opto/connode.hpp"
  30 #include "opto/loopnode.hpp"
  31 #include "opto/mulnode.hpp"
  32 #include "opto/rootnode.hpp"
  33 #include "opto/subnode.hpp"
  34 
  35 /*
  36  * The general idea of Loop Predication is to insert a predicate on the entry
  37  * path to a loop, and raise a uncommon trap if the check of the condition fails.
  38  * The condition checks are promoted from inside the loop body, and thus
  39  * the checks inside the loop could be eliminated. Currently, loop predication
  40  * optimization has been applied to remove array range check and loop invariant
  41  * checks (such as null checks).
  42 */
  43 
  44 //-------------------------------is_uncommon_trap_proj----------------------------
  45 // Return true if proj is the form of "proj->[region->..]call_uct"
  46 bool PhaseIdealLoop::is_uncommon_trap_proj(ProjNode* proj, Deoptimization::DeoptReason reason) {
  47   int path_limit = 10;
  48   assert(proj, "invalid argument");
  49   Node* out = proj;
  50   for (int ct = 0; ct < path_limit; ct++) {
  51     out = out->unique_ctrl_out();
  52     if (out == NULL)
  53       return false;
  54     if (out->is_CallStaticJava()) {
  55       int req = out->as_CallStaticJava()->uncommon_trap_request();
  56       if (req != 0) {
  57         Deoptimization::DeoptReason trap_reason = Deoptimization::trap_request_reason(req);
  58         if (trap_reason == reason || reason == Deoptimization::Reason_none) {
  59            return true;
  60         }
  61       }
  62       return false; // don't do further after call
  63     }
  64     if (out->Opcode() != Op_Region)
  65       return false;
  66   }
  67   return false;
  68 }
  69 
  70 //-------------------------------is_uncommon_trap_if_pattern-------------------------
  71 // Return true  for "if(test)-> proj -> ...
  72 //                          |
  73 //                          V
  74 //                      other_proj->[region->..]call_uct"
  75 //
  76 // "must_reason_predicate" means the uct reason must be Reason_predicate
  77 bool PhaseIdealLoop::is_uncommon_trap_if_pattern(ProjNode *proj, Deoptimization::DeoptReason reason) {
  78   Node *in0 = proj->in(0);
  79   if (!in0->is_If()) return false;
  80   // Variation of a dead If node.
  81   if (in0->outcnt() < 2)  return false;
  82   IfNode* iff = in0->as_If();
  83 
  84   // we need "If(Conv2B(Opaque1(...)))" pattern for reason_predicate
  85   if (reason != Deoptimization::Reason_none) {
  86     if (iff->in(1)->Opcode() != Op_Conv2B ||
  87        iff->in(1)->in(1)->Opcode() != Op_Opaque1) {
  88       return false;
  89     }
  90   }
  91 
  92   ProjNode* other_proj = iff->proj_out(1-proj->_con)->as_Proj();
  93   if (is_uncommon_trap_proj(other_proj, reason)) {
  94     assert(reason == Deoptimization::Reason_none ||
  95            Compile::current()->is_predicate_opaq(iff->in(1)->in(1)), "should be on the list");
  96     return true;
  97   }
  98   return false;
  99 }
 100 
 101 //-------------------------------register_control-------------------------
 102 void PhaseIdealLoop::register_control(Node* n, IdealLoopTree *loop, Node* pred) {
 103   assert(n->is_CFG(), "must be control node");
 104   _igvn.register_new_node_with_optimizer(n);
 105   loop->_body.push(n);
 106   set_loop(n, loop);
 107   // When called from beautify_loops() idom is not constructed yet.
 108   if (_idom != NULL) {
 109     set_idom(n, pred, dom_depth(pred));
 110   }
 111 }
 112 
 113 //------------------------------create_new_if_for_predicate------------------------
 114 // create a new if above the uct_if_pattern for the predicate to be promoted.
 115 //
 116 //          before                                after
 117 //        ----------                           ----------
 118 //           ctrl                                 ctrl
 119 //            |                                     |
 120 //            |                                     |
 121 //            v                                     v
 122 //           iff                                 new_iff
 123 //          /    \                                /      \
 124 //         /      \                              /        \
 125 //        v        v                            v          v
 126 //  uncommon_proj cont_proj                   if_uct     if_cont
 127 // \      |        |                           |          |
 128 //  \     |        |                           |          |
 129 //   v    v        v                           |          v
 130 //     rgn       loop                          |         iff
 131 //      |                                      |        /     \
 132 //      |                                      |       /       \
 133 //      v                                      |      v         v
 134 // uncommon_trap                               | uncommon_proj cont_proj
 135 //                                           \  \    |           |
 136 //                                            \  \   |           |
 137 //                                             v  v  v           v
 138 //                                               rgn           loop
 139 //                                                |
 140 //                                                |
 141 //                                                v
 142 //                                           uncommon_trap
 143 //
 144 //
 145 // We will create a region to guard the uct call if there is no one there.
 146 // The true projecttion (if_cont) of the new_iff is returned.
 147 // This code is also used to clone predicates to clonned loops.
 148 ProjNode* PhaseIdealLoop::create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
 149                                                       Deoptimization::DeoptReason reason) {
 150   assert(is_uncommon_trap_if_pattern(cont_proj, reason), "must be a uct if pattern!");
 151   IfNode* iff = cont_proj->in(0)->as_If();
 152 
 153   ProjNode *uncommon_proj = iff->proj_out(1 - cont_proj->_con);
 154   Node     *rgn   = uncommon_proj->unique_ctrl_out();
 155   assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
 156 
 157   uint proj_index = 1; // region's edge corresponding to uncommon_proj
 158   if (!rgn->is_Region()) { // create a region to guard the call
 159     assert(rgn->is_Call(), "must be call uct");
 160     CallNode* call = rgn->as_Call();
 161     IdealLoopTree* loop = get_loop(call);
 162     rgn = new (C) RegionNode(1);
 163     rgn->add_req(uncommon_proj);
 164     register_control(rgn, loop, uncommon_proj);
 165     _igvn.hash_delete(call);
 166     call->set_req(0, rgn);
 167     // When called from beautify_loops() idom is not constructed yet.
 168     if (_idom != NULL) {
 169       set_idom(call, rgn, dom_depth(rgn));
 170     }
 171   } else {
 172     // Find region's edge corresponding to uncommon_proj
 173     for (; proj_index < rgn->req(); proj_index++)
 174       if (rgn->in(proj_index) == uncommon_proj) break;
 175     assert(proj_index < rgn->req(), "sanity");
 176   }
 177 
 178   Node* entry = iff->in(0);
 179   if (new_entry != NULL) {
 180     // Clonning the predicate to new location.
 181     entry = new_entry;
 182   }
 183   // Create new_iff
 184   IdealLoopTree* lp = get_loop(entry);
 185   IfNode *new_iff = iff->clone()->as_If();
 186   new_iff->set_req(0, entry);
 187   register_control(new_iff, lp, entry);
 188   Node *if_cont = new (C) IfTrueNode(new_iff);
 189   Node *if_uct  = new (C) IfFalseNode(new_iff);
 190   if (cont_proj->is_IfFalse()) {
 191     // Swap
 192     Node* tmp = if_uct; if_uct = if_cont; if_cont = tmp;
 193   }
 194   register_control(if_cont, lp, new_iff);
 195   register_control(if_uct, get_loop(rgn), new_iff);
 196 
 197   // if_uct to rgn
 198   _igvn.hash_delete(rgn);
 199   rgn->add_req(if_uct);
 200   // When called from beautify_loops() idom is not constructed yet.
 201   if (_idom != NULL) {
 202     Node* ridom = idom(rgn);
 203     Node* nrdom = dom_lca(ridom, new_iff);
 204     set_idom(rgn, nrdom, dom_depth(rgn));
 205   }
 206 
 207   // If rgn has phis add new edges which has the same
 208   // value as on original uncommon_proj pass.
 209   assert(rgn->in(rgn->req() -1) == if_uct, "new edge should be last");
 210   bool has_phi = false;
 211   for (DUIterator_Fast imax, i = rgn->fast_outs(imax); i < imax; i++) {
 212     Node* use = rgn->fast_out(i);
 213     if (use->is_Phi() && use->outcnt() > 0) {
 214       assert(use->in(0) == rgn, "");
 215       _igvn.rehash_node_delayed(use);
 216       use->add_req(use->in(proj_index));
 217       has_phi = true;
 218     }
 219   }
 220   assert(!has_phi || rgn->req() > 3, "no phis when region is created");
 221 
 222   if (new_entry == NULL) {
 223     // Attach if_cont to iff
 224     _igvn.hash_delete(iff);
 225     iff->set_req(0, if_cont);
 226     if (_idom != NULL) {
 227       set_idom(iff, if_cont, dom_depth(iff));
 228     }
 229   }
 230   return if_cont->as_Proj();
 231 }
 232 
 233 //------------------------------create_new_if_for_predicate------------------------
 234 // Create a new if below new_entry for the predicate to be cloned (IGVN optimization)
 235 ProjNode* PhaseIterGVN::create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
 236                                                     Deoptimization::DeoptReason reason) {
 237   assert(new_entry != 0, "only used for clone predicate");
 238   assert(PhaseIdealLoop::is_uncommon_trap_if_pattern(cont_proj, reason), "must be a uct if pattern!");
 239   IfNode* iff = cont_proj->in(0)->as_If();
 240 
 241   ProjNode *uncommon_proj = iff->proj_out(1 - cont_proj->_con);
 242   Node     *rgn   = uncommon_proj->unique_ctrl_out();
 243   assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
 244 
 245   uint proj_index = 1; // region's edge corresponding to uncommon_proj
 246   if (!rgn->is_Region()) { // create a region to guard the call
 247     assert(rgn->is_Call(), "must be call uct");
 248     CallNode* call = rgn->as_Call();
 249     rgn = new (C) RegionNode(1);
 250     register_new_node_with_optimizer(rgn);
 251     rgn->add_req(uncommon_proj);
 252     hash_delete(call);
 253     call->set_req(0, rgn);
 254   } else {
 255     // Find region's edge corresponding to uncommon_proj
 256     for (; proj_index < rgn->req(); proj_index++)
 257       if (rgn->in(proj_index) == uncommon_proj) break;
 258     assert(proj_index < rgn->req(), "sanity");
 259   }
 260 
 261   // Create new_iff in new location.
 262   IfNode *new_iff = iff->clone()->as_If();
 263   new_iff->set_req(0, new_entry);
 264 
 265   register_new_node_with_optimizer(new_iff);
 266   Node *if_cont = new (C) IfTrueNode(new_iff);
 267   Node *if_uct  = new (C) IfFalseNode(new_iff);
 268   if (cont_proj->is_IfFalse()) {
 269     // Swap
 270     Node* tmp = if_uct; if_uct = if_cont; if_cont = tmp;
 271   }
 272   register_new_node_with_optimizer(if_cont);
 273   register_new_node_with_optimizer(if_uct);
 274 
 275   // if_uct to rgn
 276   hash_delete(rgn);
 277   rgn->add_req(if_uct);
 278 
 279   // If rgn has phis add corresponding new edges which has the same
 280   // value as on original uncommon_proj pass.
 281   assert(rgn->in(rgn->req() -1) == if_uct, "new edge should be last");
 282   bool has_phi = false;
 283   for (DUIterator_Fast imax, i = rgn->fast_outs(imax); i < imax; i++) {
 284     Node* use = rgn->fast_out(i);
 285     if (use->is_Phi() && use->outcnt() > 0) {
 286       rehash_node_delayed(use);
 287       use->add_req(use->in(proj_index));
 288       has_phi = true;
 289     }
 290   }
 291   assert(!has_phi || rgn->req() > 3, "no phis when region is created");
 292 
 293   return if_cont->as_Proj();
 294 }
 295 
 296 //--------------------------clone_predicate-----------------------
 297 ProjNode* PhaseIdealLoop::clone_predicate(ProjNode* predicate_proj, Node* new_entry,
 298                                           Deoptimization::DeoptReason reason,
 299                                           PhaseIdealLoop* loop_phase,
 300                                           PhaseIterGVN* igvn) {
 301   ProjNode* new_predicate_proj;
 302   if (loop_phase != NULL) {
 303     new_predicate_proj = loop_phase->create_new_if_for_predicate(predicate_proj, new_entry, reason);
 304   } else {
 305     new_predicate_proj =       igvn->create_new_if_for_predicate(predicate_proj, new_entry, reason);
 306   }
 307   IfNode* iff = new_predicate_proj->in(0)->as_If();
 308   Node* ctrl  = iff->in(0);
 309 
 310   // Match original condition since predicate's projections could be swapped.
 311   assert(predicate_proj->in(0)->in(1)->in(1)->Opcode()==Op_Opaque1, "must be");
 312   Node* opq = new (igvn->C) Opaque1Node(igvn->C, predicate_proj->in(0)->in(1)->in(1)->in(1));
 313   igvn->C->add_predicate_opaq(opq);
 314 
 315   Node* bol = new (igvn->C) Conv2BNode(opq);
 316   if (loop_phase != NULL) {
 317     loop_phase->register_new_node(opq, ctrl);
 318     loop_phase->register_new_node(bol, ctrl);
 319   } else {
 320     igvn->register_new_node_with_optimizer(opq);
 321     igvn->register_new_node_with_optimizer(bol);
 322   }
 323   igvn->hash_delete(iff);
 324   iff->set_req(1, bol);
 325   return new_predicate_proj;
 326 }
 327 
 328 
 329 //--------------------------clone_loop_predicates-----------------------
 330 // Interface from IGVN
 331 Node* PhaseIterGVN::clone_loop_predicates(Node* old_entry, Node* new_entry, bool clone_limit_check) {
 332   return PhaseIdealLoop::clone_loop_predicates(old_entry, new_entry, clone_limit_check, NULL, this);
 333 }
 334 
 335 // Interface from PhaseIdealLoop
 336 Node* PhaseIdealLoop::clone_loop_predicates(Node* old_entry, Node* new_entry, bool clone_limit_check) {
 337   return clone_loop_predicates(old_entry, new_entry, clone_limit_check, this, &this->_igvn);
 338 }
 339 
 340 // Clone loop predicates to cloned loops (peeled, unswitched, split_if).
 341 Node* PhaseIdealLoop::clone_loop_predicates(Node* old_entry, Node* new_entry,
 342                                                 bool clone_limit_check,
 343                                                 PhaseIdealLoop* loop_phase,
 344                                                 PhaseIterGVN* igvn) {
 345 #ifdef ASSERT
 346   if (new_entry == NULL || !(new_entry->is_Proj() || new_entry->is_Region() || new_entry->is_SafePoint())) {
 347     if (new_entry != NULL)
 348       new_entry->dump();
 349     assert(false, "not IfTrue, IfFalse, Region or SafePoint");
 350   }
 351 #endif
 352   // Search original predicates
 353   Node* entry = old_entry;
 354   ProjNode* limit_check_proj = NULL;
 355   if (LoopLimitCheck) {
 356     limit_check_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 357     if (limit_check_proj != NULL) {
 358       entry = entry->in(0)->in(0);
 359     }
 360   }
 361   if (UseLoopPredicate) {
 362     ProjNode* predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 363     if (predicate_proj != NULL) { // right pattern that can be used by loop predication
 364       // clone predicate
 365       new_entry = clone_predicate(predicate_proj, new_entry,
 366                                   Deoptimization::Reason_predicate,
 367                                   loop_phase, igvn);
 368       assert(new_entry != NULL && new_entry->is_Proj(), "IfTrue or IfFalse after clone predicate");
 369       if (TraceLoopPredicate) {
 370         tty->print("Loop Predicate cloned: ");
 371         debug_only( new_entry->in(0)->dump(); )
 372       }
 373     }
 374   }
 375   if (limit_check_proj != NULL && clone_limit_check) {
 376     // Clone loop limit check last to insert it before loop.
 377     // Don't clone a limit check which was already finalized
 378     // for this counted loop (only one limit check is needed).
 379     new_entry = clone_predicate(limit_check_proj, new_entry,
 380                                 Deoptimization::Reason_loop_limit_check,
 381                                 loop_phase, igvn);
 382     assert(new_entry != NULL && new_entry->is_Proj(), "IfTrue or IfFalse after clone limit check");
 383     if (TraceLoopLimitCheck) {
 384       tty->print("Loop Limit Check cloned: ");
 385       debug_only( new_entry->in(0)->dump(); )
 386     }
 387   }
 388   return new_entry;
 389 }
 390 
 391 //--------------------------skip_loop_predicates------------------------------
 392 // Skip related predicates.
 393 Node* PhaseIdealLoop::skip_loop_predicates(Node* entry) {
 394   Node* predicate = NULL;
 395   if (LoopLimitCheck) {
 396     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 397     if (predicate != NULL) {
 398       entry = entry->in(0)->in(0);
 399     }
 400   }
 401   if (UseLoopPredicate) {
 402     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 403     if (predicate != NULL) { // right pattern that can be used by loop predication
 404       IfNode* iff = entry->in(0)->as_If();
 405       ProjNode* uncommon_proj = iff->proj_out(1 - entry->as_Proj()->_con);
 406       Node* rgn = uncommon_proj->unique_ctrl_out();
 407       assert(rgn->is_Region() || rgn->is_Call(), "must be a region or call uct");
 408       entry = entry->in(0)->in(0);
 409       while (entry != NULL && entry->is_Proj() && entry->in(0)->is_If()) {
 410         uncommon_proj = entry->in(0)->as_If()->proj_out(1 - entry->as_Proj()->_con);
 411         if (uncommon_proj->unique_ctrl_out() != rgn)
 412           break;
 413         entry = entry->in(0)->in(0);
 414       }
 415     }
 416   }
 417   return entry;
 418 }
 419 
 420 //--------------------------find_predicate_insertion_point-------------------
 421 // Find a good location to insert a predicate
 422 ProjNode* PhaseIdealLoop::find_predicate_insertion_point(Node* start_c, Deoptimization::DeoptReason reason) {
 423   if (start_c == NULL || !start_c->is_Proj())
 424     return NULL;
 425   if (is_uncommon_trap_if_pattern(start_c->as_Proj(), reason)) {
 426     return start_c->as_Proj();
 427   }
 428   return NULL;
 429 }
 430 
 431 //--------------------------find_predicate------------------------------------
 432 // Find a predicate
 433 Node* PhaseIdealLoop::find_predicate(Node* entry) {
 434   Node* predicate = NULL;
 435   if (LoopLimitCheck) {
 436     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 437     if (predicate != NULL) { // right pattern that can be used by loop predication
 438       return entry;
 439     }
 440   }
 441   if (UseLoopPredicate) {
 442     predicate = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 443     if (predicate != NULL) { // right pattern that can be used by loop predication
 444       return entry;
 445     }
 446   }
 447   return NULL;
 448 }
 449 
 450 //------------------------------Invariance-----------------------------------
 451 // Helper class for loop_predication_impl to compute invariance on the fly and
 452 // clone invariants.
 453 class Invariance : public StackObj {
 454   VectorSet _visited, _invariant;
 455   Node_Stack _stack;
 456   VectorSet _clone_visited;
 457   Node_List _old_new; // map of old to new (clone)
 458   IdealLoopTree* _lpt;
 459   PhaseIdealLoop* _phase;
 460 
 461   // Helper function to set up the invariance for invariance computation
 462   // If n is a known invariant, set up directly. Otherwise, look up the
 463   // the possibility to push n onto the stack for further processing.
 464   void visit(Node* use, Node* n) {
 465     if (_lpt->is_invariant(n)) { // known invariant
 466       _invariant.set(n->_idx);
 467     } else if (!n->is_CFG()) {
 468       Node *n_ctrl = _phase->ctrl_or_self(n);
 469       Node *u_ctrl = _phase->ctrl_or_self(use); // self if use is a CFG
 470       if (_phase->is_dominator(n_ctrl, u_ctrl)) {
 471         _stack.push(n, n->in(0) == NULL ? 1 : 0);
 472       }
 473     }
 474   }
 475 
 476   // Compute invariance for "the_node" and (possibly) all its inputs recursively
 477   // on the fly
 478   void compute_invariance(Node* n) {
 479     assert(_visited.test(n->_idx), "must be");
 480     visit(n, n);
 481     while (_stack.is_nonempty()) {
 482       Node*  n = _stack.node();
 483       uint idx = _stack.index();
 484       if (idx == n->req()) { // all inputs are processed
 485         _stack.pop();
 486         // n is invariant if it's inputs are all invariant
 487         bool all_inputs_invariant = true;
 488         for (uint i = 0; i < n->req(); i++) {
 489           Node* in = n->in(i);
 490           if (in == NULL) continue;
 491           assert(_visited.test(in->_idx), "must have visited input");
 492           if (!_invariant.test(in->_idx)) { // bad guy
 493             all_inputs_invariant = false;
 494             break;
 495           }
 496         }
 497         if (all_inputs_invariant) {
 498           _invariant.set(n->_idx); // I am a invariant too
 499         }
 500       } else { // process next input
 501         _stack.set_index(idx + 1);
 502         Node* m = n->in(idx);
 503         if (m != NULL && !_visited.test_set(m->_idx)) {
 504           visit(n, m);
 505         }
 506       }
 507     }
 508   }
 509 
 510   // Helper function to set up _old_new map for clone_nodes.
 511   // If n is a known invariant, set up directly ("clone" of n == n).
 512   // Otherwise, push n onto the stack for real cloning.
 513   void clone_visit(Node* n) {
 514     assert(_invariant.test(n->_idx), "must be invariant");
 515     if (_lpt->is_invariant(n)) { // known invariant
 516       _old_new.map(n->_idx, n);
 517     } else { // to be cloned
 518       assert(!n->is_CFG(), "should not see CFG here");
 519       _stack.push(n, n->in(0) == NULL ? 1 : 0);
 520     }
 521   }
 522 
 523   // Clone "n" and (possibly) all its inputs recursively
 524   void clone_nodes(Node* n, Node* ctrl) {
 525     clone_visit(n);
 526     while (_stack.is_nonempty()) {
 527       Node*  n = _stack.node();
 528       uint idx = _stack.index();
 529       if (idx == n->req()) { // all inputs processed, clone n!
 530         _stack.pop();
 531         // clone invariant node
 532         Node* n_cl = n->clone();
 533         _old_new.map(n->_idx, n_cl);
 534         _phase->register_new_node(n_cl, ctrl);
 535         for (uint i = 0; i < n->req(); i++) {
 536           Node* in = n_cl->in(i);
 537           if (in == NULL) continue;
 538           n_cl->set_req(i, _old_new[in->_idx]);
 539         }
 540       } else { // process next input
 541         _stack.set_index(idx + 1);
 542         Node* m = n->in(idx);
 543         if (m != NULL && !_clone_visited.test_set(m->_idx)) {
 544           clone_visit(m); // visit the input
 545         }
 546       }
 547     }
 548   }
 549 
 550  public:
 551   Invariance(Arena* area, IdealLoopTree* lpt) :
 552     _lpt(lpt), _phase(lpt->_phase),
 553     _visited(area), _invariant(area), _stack(area, 10 /* guess */),
 554     _clone_visited(area), _old_new(area)
 555   {}
 556 
 557   // Map old to n for invariance computation and clone
 558   void map_ctrl(Node* old, Node* n) {
 559     assert(old->is_CFG() && n->is_CFG(), "must be");
 560     _old_new.map(old->_idx, n); // "clone" of old is n
 561     _invariant.set(old->_idx);  // old is invariant
 562     _clone_visited.set(old->_idx);
 563   }
 564 
 565   // Driver function to compute invariance
 566   bool is_invariant(Node* n) {
 567     if (!_visited.test_set(n->_idx))
 568       compute_invariance(n);
 569     return (_invariant.test(n->_idx) != 0);
 570   }
 571 
 572   // Driver function to clone invariant
 573   Node* clone(Node* n, Node* ctrl) {
 574     assert(ctrl->is_CFG(), "must be");
 575     assert(_invariant.test(n->_idx), "must be an invariant");
 576     if (!_clone_visited.test(n->_idx))
 577       clone_nodes(n, ctrl);
 578     return _old_new[n->_idx];
 579   }
 580 };
 581 
 582 //------------------------------is_range_check_if -----------------------------------
 583 // Returns true if the predicate of iff is in "scale*iv + offset u< load_range(ptr)" format
 584 // Note: this function is particularly designed for loop predication. We require load_range
 585 //       and offset to be loop invariant computed on the fly by "invar"
 586 bool IdealLoopTree::is_range_check_if(IfNode *iff, PhaseIdealLoop *phase, Invariance& invar) const {
 587   if (!is_loop_exit(iff)) {
 588     return false;
 589   }
 590   if (!iff->in(1)->is_Bool()) {
 591     return false;
 592   }
 593   const BoolNode *bol = iff->in(1)->as_Bool();
 594   if (bol->_test._test != BoolTest::lt) {
 595     return false;
 596   }
 597   if (!bol->in(1)->is_Cmp()) {
 598     return false;
 599   }
 600   const CmpNode *cmp = bol->in(1)->as_Cmp();
 601   if (cmp->Opcode() != Op_CmpU) {
 602     return false;
 603   }
 604   Node* range = cmp->in(2);
 605   if (range->Opcode() != Op_LoadRange) {
 606     const TypeInt* tint = phase->_igvn.type(range)->isa_int();
 607     if (tint == NULL || tint->empty() || tint->_lo < 0) {
 608       // Allow predication on positive values that aren't LoadRanges.
 609       // This allows optimization of loops where the length of the
 610       // array is a known value and doesn't need to be loaded back
 611       // from the array.
 612       return false;
 613     }
 614   }
 615   if (!invar.is_invariant(range)) {
 616     return false;
 617   }
 618   Node *iv     = _head->as_CountedLoop()->phi();
 619   int   scale  = 0;
 620   Node *offset = NULL;
 621   if (!phase->is_scaled_iv_plus_offset(cmp->in(1), iv, &scale, &offset)) {
 622     return false;
 623   }
 624   if (offset && !invar.is_invariant(offset)) { // offset must be invariant
 625     return false;
 626   }
 627   return true;
 628 }
 629 
 630 //------------------------------rc_predicate-----------------------------------
 631 // Create a range check predicate
 632 //
 633 // for (i = init; i < limit; i += stride) {
 634 //    a[scale*i+offset]
 635 // }
 636 //
 637 // Compute max(scale*i + offset) for init <= i < limit and build the predicate
 638 // as "max(scale*i + offset) u< a.length".
 639 //
 640 // There are two cases for max(scale*i + offset):
 641 // (1) stride*scale > 0
 642 //   max(scale*i + offset) = scale*(limit-stride) + offset
 643 // (2) stride*scale < 0
 644 //   max(scale*i + offset) = scale*init + offset
 645 BoolNode* PhaseIdealLoop::rc_predicate(IdealLoopTree *loop, Node* ctrl,
 646                                        int scale, Node* offset,
 647                                        Node* init, Node* limit, Node* stride,
 648                                        Node* range, bool upper) {
 649   stringStream* predString = NULL;
 650   if (TraceLoopPredicate) {
 651     predString = new stringStream();
 652     predString->print("rc_predicate ");
 653   }
 654 
 655   Node* max_idx_expr  = init;
 656   int stride_con = stride->get_int();
 657   if ((stride_con > 0) == (scale > 0) == upper) {
 658     if (LoopLimitCheck) {
 659       // With LoopLimitCheck limit is not exact.
 660       // Calculate exact limit here.
 661       // Note, counted loop's test is '<' or '>'.
 662       limit = exact_limit(loop);
 663       max_idx_expr = new (C) SubINode(limit, stride);
 664       register_new_node(max_idx_expr, ctrl);
 665       if (TraceLoopPredicate) predString->print("(limit - stride) ");
 666     } else {
 667       max_idx_expr = new (C) SubINode(limit, stride);
 668       register_new_node(max_idx_expr, ctrl);
 669       if (TraceLoopPredicate) predString->print("(limit - stride) ");
 670     }
 671   } else {
 672     if (TraceLoopPredicate) predString->print("init ");
 673   }
 674 
 675   if (scale != 1) {
 676     ConNode* con_scale = _igvn.intcon(scale);
 677     max_idx_expr = new (C) MulINode(max_idx_expr, con_scale);
 678     register_new_node(max_idx_expr, ctrl);
 679     if (TraceLoopPredicate) predString->print("* %d ", scale);
 680   }
 681 
 682   if (offset && (!offset->is_Con() || offset->get_int() != 0)){
 683     max_idx_expr = new (C) AddINode(max_idx_expr, offset);
 684     register_new_node(max_idx_expr, ctrl);
 685     if (TraceLoopPredicate)
 686       if (offset->is_Con()) predString->print("+ %d ", offset->get_int());
 687       else predString->print("+ offset ");
 688   }
 689 
 690   CmpUNode* cmp = new (C) CmpUNode(max_idx_expr, range);
 691   register_new_node(cmp, ctrl);
 692   BoolNode* bol = new (C) BoolNode(cmp, BoolTest::lt);
 693   register_new_node(bol, ctrl);
 694 
 695   if (TraceLoopPredicate) {
 696     predString->print_cr("<u range");
 697     tty->print(predString->as_string());
 698   }
 699   return bol;
 700 }
 701 
 702 //------------------------------ loop_predication_impl--------------------------
 703 // Insert loop predicates for null checks and range checks
 704 bool PhaseIdealLoop::loop_predication_impl(IdealLoopTree *loop) {
 705   if (!UseLoopPredicate) return false;
 706 
 707   if (!loop->_head->is_Loop()) {
 708     // Could be a simple region when irreducible loops are present.
 709     return false;
 710   }
 711   LoopNode* head = loop->_head->as_Loop();
 712 
 713   if (head->unique_ctrl_out()->Opcode() == Op_NeverBranch) {
 714     // do nothing for infinite loops
 715     return false;
 716   }
 717 
 718   CountedLoopNode *cl = NULL;
 719   if (head->is_valid_counted_loop()) {
 720     cl = head->as_CountedLoop();
 721     // do nothing for iteration-splitted loops
 722     if (!cl->is_normal_loop()) return false;
 723     // Avoid RCE if Counted loop's test is '!='.
 724     BoolTest::mask bt = cl->loopexit()->test_trip();
 725     if (bt != BoolTest::lt && bt != BoolTest::gt)
 726       cl = NULL;
 727   }
 728 
 729   Node* entry = head->in(LoopNode::EntryControl);
 730   ProjNode *predicate_proj = NULL;
 731   // Loop limit check predicate should be near the loop.
 732   if (LoopLimitCheck) {
 733     predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
 734     if (predicate_proj != NULL)
 735       entry = predicate_proj->in(0)->in(0);
 736   }
 737 
 738   predicate_proj = find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
 739   if (!predicate_proj) {
 740 #ifndef PRODUCT
 741     if (TraceLoopPredicate) {
 742       tty->print("missing predicate:");
 743       loop->dump_head();
 744       head->dump(1);
 745     }
 746 #endif
 747     return false;
 748   }
 749   ConNode* zero = _igvn.intcon(0);
 750   set_ctrl(zero, C->root());
 751 
 752   ResourceArea *area = Thread::current()->resource_area();
 753   Invariance invar(area, loop);
 754 
 755   // Create list of if-projs such that a newer proj dominates all older
 756   // projs in the list, and they all dominate loop->tail()
 757   Node_List if_proj_list(area);
 758   Node *current_proj = loop->tail(); //start from tail
 759   while (current_proj != head) {
 760     if (loop == get_loop(current_proj) && // still in the loop ?
 761         current_proj->is_Proj()        && // is a projection  ?
 762         current_proj->in(0)->Opcode() == Op_If) { // is a if projection ?
 763       if_proj_list.push(current_proj);
 764     }
 765     current_proj = idom(current_proj);
 766   }
 767 
 768   bool hoisted = false; // true if at least one proj is promoted
 769   while (if_proj_list.size() > 0) {
 770     // Following are changed to nonnull when a predicate can be hoisted
 771     ProjNode* new_predicate_proj = NULL;
 772 
 773     ProjNode* proj = if_proj_list.pop()->as_Proj();
 774     IfNode*   iff  = proj->in(0)->as_If();
 775 
 776     if (!is_uncommon_trap_if_pattern(proj, Deoptimization::Reason_none)) {
 777       if (loop->is_loop_exit(iff)) {
 778         // stop processing the remaining projs in the list because the execution of them
 779         // depends on the condition of "iff" (iff->in(1)).
 780         break;
 781       } else {
 782         // Both arms are inside the loop. There are two cases:
 783         // (1) there is one backward branch. In this case, any remaining proj
 784         //     in the if_proj list post-dominates "iff". So, the condition of "iff"
 785         //     does not determine the execution the remining projs directly, and we
 786         //     can safely continue.
 787         // (2) both arms are forwarded, i.e. a diamond shape. In this case, "proj"
 788         //     does not dominate loop->tail(), so it can not be in the if_proj list.
 789         continue;
 790       }
 791     }
 792 
 793     Node*     test = iff->in(1);
 794     if (!test->is_Bool()){ //Conv2B, ...
 795       continue;
 796     }
 797     BoolNode* bol = test->as_Bool();
 798     if (invar.is_invariant(bol)) {
 799       // Invariant test
 800       new_predicate_proj = create_new_if_for_predicate(predicate_proj, NULL,
 801                                                        Deoptimization::Reason_predicate);
 802       Node* ctrl = new_predicate_proj->in(0)->as_If()->in(0);
 803       BoolNode* new_predicate_bol = invar.clone(bol, ctrl)->as_Bool();
 804 
 805       // Negate test if necessary
 806       bool negated = false;
 807       if (proj->_con != predicate_proj->_con) {
 808         new_predicate_bol = new (C) BoolNode(new_predicate_bol->in(1), new_predicate_bol->_test.negate());
 809         register_new_node(new_predicate_bol, ctrl);
 810         negated = true;
 811       }
 812       IfNode* new_predicate_iff = new_predicate_proj->in(0)->as_If();
 813       _igvn.hash_delete(new_predicate_iff);
 814       new_predicate_iff->set_req(1, new_predicate_bol);
 815 #ifndef PRODUCT
 816       if (TraceLoopPredicate) {
 817         tty->print("Predicate invariant if%s: %d ", negated ? " negated" : "", new_predicate_iff->_idx);
 818         loop->dump_head();
 819       } else if (TraceLoopOpts) {
 820         tty->print("Predicate IC ");
 821         loop->dump_head();
 822       }
 823 #endif
 824     } else if (cl != NULL && loop->is_range_check_if(iff, this, invar)) {
 825       assert(proj->_con == predicate_proj->_con, "must match");
 826 
 827       // Range check for counted loops
 828       const Node*    cmp    = bol->in(1)->as_Cmp();
 829       Node*          idx    = cmp->in(1);
 830       assert(!invar.is_invariant(idx), "index is variant");
 831       Node* rng = cmp->in(2);
 832       assert(rng->Opcode() == Op_LoadRange || _igvn.type(rng)->is_int() >= 0, "must be");
 833       assert(invar.is_invariant(rng), "range must be invariant");
 834       int scale    = 1;
 835       Node* offset = zero;
 836       bool ok = is_scaled_iv_plus_offset(idx, cl->phi(), &scale, &offset);
 837       assert(ok, "must be index expression");
 838 
 839       Node* init    = cl->init_trip();
 840       Node* limit   = cl->limit();
 841       Node* stride  = cl->stride();
 842 
 843       // Build if's for the upper and lower bound tests.  The
 844       // lower_bound test will dominate the upper bound test and all
 845       // cloned or created nodes will use the lower bound test as
 846       // their declared control.
 847       ProjNode* lower_bound_proj = create_new_if_for_predicate(predicate_proj, NULL, Deoptimization::Reason_predicate);
 848       ProjNode* upper_bound_proj = create_new_if_for_predicate(predicate_proj, NULL, Deoptimization::Reason_predicate);
 849       assert(upper_bound_proj->in(0)->as_If()->in(0) == lower_bound_proj, "should dominate");
 850       Node *ctrl = lower_bound_proj->in(0)->as_If()->in(0);
 851 
 852       // Perform cloning to keep Invariance state correct since the
 853       // late schedule will place invariant things in the loop.
 854       rng = invar.clone(rng, ctrl);
 855       if (offset && offset != zero) {
 856         assert(invar.is_invariant(offset), "offset must be loop invariant");
 857         offset = invar.clone(offset, ctrl);
 858       }
 859 
 860       // Test the lower bound
 861       Node*  lower_bound_bol = rc_predicate(loop, ctrl, scale, offset, init, limit, stride, rng, false);
 862       IfNode* lower_bound_iff = lower_bound_proj->in(0)->as_If();
 863       _igvn.hash_delete(lower_bound_iff);
 864       lower_bound_iff->set_req(1, lower_bound_bol);
 865       if (TraceLoopPredicate) tty->print_cr("lower bound check if: %d", lower_bound_iff->_idx);
 866 
 867       // Test the upper bound
 868       Node* upper_bound_bol = rc_predicate(loop, lower_bound_proj, scale, offset, init, limit, stride, rng, true);
 869       IfNode* upper_bound_iff = upper_bound_proj->in(0)->as_If();
 870       _igvn.hash_delete(upper_bound_iff);
 871       upper_bound_iff->set_req(1, upper_bound_bol);
 872       if (TraceLoopPredicate) tty->print_cr("upper bound check if: %d", lower_bound_iff->_idx);
 873 
 874       // Fall through into rest of the clean up code which will move
 875       // any dependent nodes onto the upper bound test.
 876       new_predicate_proj = upper_bound_proj;
 877 
 878 #ifndef PRODUCT
 879       if (TraceLoopOpts && !TraceLoopPredicate) {
 880         tty->print("Predicate RC ");
 881         loop->dump_head();
 882       }
 883 #endif
 884     } else {
 885       // Loop variant check (for example, range check in non-counted loop)
 886       // with uncommon trap.
 887       continue;
 888     }
 889     assert(new_predicate_proj != NULL, "sanity");
 890     // Success - attach condition (new_predicate_bol) to predicate if
 891     invar.map_ctrl(proj, new_predicate_proj); // so that invariance test can be appropriate
 892 
 893     // Eliminate the old If in the loop body
 894     dominated_by( new_predicate_proj, iff, proj->_con != new_predicate_proj->_con );
 895 
 896     hoisted = true;
 897     C->set_major_progress();
 898   } // end while
 899 
 900 #ifndef PRODUCT
 901   // report that the loop predication has been actually performed
 902   // for this loop
 903   if (TraceLoopPredicate && hoisted) {
 904     tty->print("Loop Predication Performed:");
 905     loop->dump_head();
 906   }
 907 #endif
 908 
 909   return hoisted;
 910 }
 911 
 912 //------------------------------loop_predication--------------------------------
 913 // driver routine for loop predication optimization
 914 bool IdealLoopTree::loop_predication( PhaseIdealLoop *phase) {
 915   bool hoisted = false;
 916   // Recursively promote predicates
 917   if (_child) {
 918     hoisted = _child->loop_predication( phase);
 919   }
 920 
 921   // self
 922   if (!_irreducible && !tail()->is_top()) {
 923     hoisted |= phase->loop_predication_impl(this);
 924   }
 925 
 926   if (_next) { //sibling
 927     hoisted |= _next->loop_predication( phase);
 928   }
 929 
 930   return hoisted;
 931 }