1 /*
   2  * Copyright (c) 1998, 2020, 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 "ci/ciMethodData.hpp"
  27 #include "compiler/compileLog.hpp"
  28 #include "libadt/vectset.hpp"
  29 #include "memory/allocation.inline.hpp"
  30 #include "opto/addnode.hpp"
  31 #include "opto/callnode.hpp"
  32 #include "opto/connode.hpp"
  33 #include "opto/divnode.hpp"
  34 #include "opto/idealGraphPrinter.hpp"
  35 #include "opto/loopnode.hpp"
  36 #include "opto/mulnode.hpp"
  37 #include "opto/rootnode.hpp"
  38 #include "opto/superword.hpp"
  39 
  40 //=============================================================================
  41 //------------------------------is_loop_iv-------------------------------------
  42 // Determine if a node is Counted loop induction variable.
  43 // The method is declared in node.hpp.
  44 const Node* Node::is_loop_iv() const {
  45   if (this->is_Phi() && !this->as_Phi()->is_copy() &&
  46       this->as_Phi()->region()->is_CountedLoop() &&
  47       this->as_Phi()->region()->as_CountedLoop()->phi() == this) {
  48     return this;
  49   } else {
  50     return NULL;
  51   }
  52 }
  53 
  54 //=============================================================================
  55 //------------------------------dump_spec--------------------------------------
  56 // Dump special per-node info
  57 #ifndef PRODUCT
  58 void LoopNode::dump_spec(outputStream *st) const {
  59   if (is_inner_loop()) st->print( "inner " );
  60   if (is_partial_peel_loop()) st->print( "partial_peel " );
  61   if (partial_peel_has_failed()) st->print( "partial_peel_failed " );
  62 }
  63 #endif
  64 
  65 //------------------------------is_valid_counted_loop-------------------------
  66 bool LoopNode::is_valid_counted_loop() const {
  67   if (is_CountedLoop()) {
  68     CountedLoopNode*    l  = as_CountedLoop();
  69     CountedLoopEndNode* le = l->loopexit();
  70     if (le != NULL &&
  71         le->proj_out(1 /* true */) == l->in(LoopNode::LoopBackControl)) {
  72       Node* phi  = l->phi();
  73       Node* exit = le->proj_out(0 /* false */);
  74       if (exit != NULL && exit->Opcode() == Op_IfFalse &&
  75           phi != NULL && phi->is_Phi() &&
  76           phi->in(LoopNode::LoopBackControl) == l->incr() &&
  77           le->loopnode() == l && le->stride_is_con()) {
  78         return true;
  79       }
  80     }
  81   }
  82   return false;
  83 }
  84 
  85 //------------------------------get_early_ctrl---------------------------------
  86 // Compute earliest legal control
  87 Node *PhaseIdealLoop::get_early_ctrl( Node *n ) {
  88   assert( !n->is_Phi() && !n->is_CFG(), "this code only handles data nodes" );
  89   uint i;
  90   Node *early;
  91   if (n->in(0) && !n->is_expensive()) {
  92     early = n->in(0);
  93     if (!early->is_CFG()) // Might be a non-CFG multi-def
  94       early = get_ctrl(early);        // So treat input as a straight data input
  95     i = 1;
  96   } else {
  97     early = get_ctrl(n->in(1));
  98     i = 2;
  99   }
 100   uint e_d = dom_depth(early);
 101   assert( early, "" );
 102   for (; i < n->req(); i++) {
 103     Node *cin = get_ctrl(n->in(i));
 104     assert( cin, "" );
 105     // Keep deepest dominator depth
 106     uint c_d = dom_depth(cin);
 107     if (c_d > e_d) {           // Deeper guy?
 108       early = cin;              // Keep deepest found so far
 109       e_d = c_d;
 110     } else if (c_d == e_d &&    // Same depth?
 111                early != cin) { // If not equal, must use slower algorithm
 112       // If same depth but not equal, one _must_ dominate the other
 113       // and we want the deeper (i.e., dominated) guy.
 114       Node *n1 = early;
 115       Node *n2 = cin;
 116       while (1) {
 117         n1 = idom(n1);          // Walk up until break cycle
 118         n2 = idom(n2);
 119         if (n1 == cin ||        // Walked early up to cin
 120             dom_depth(n2) < c_d)
 121           break;                // early is deeper; keep him
 122         if (n2 == early ||      // Walked cin up to early
 123             dom_depth(n1) < c_d) {
 124           early = cin;          // cin is deeper; keep him
 125           break;
 126         }
 127       }
 128       e_d = dom_depth(early);   // Reset depth register cache
 129     }
 130   }
 131 
 132   // Return earliest legal location
 133   assert(early == find_non_split_ctrl(early), "unexpected early control");
 134 
 135   if (n->is_expensive()) {
 136     assert(n->in(0), "should have control input");
 137     early = get_early_ctrl_for_expensive(n, early);
 138   }
 139 
 140   return early;
 141 }
 142 
 143 //------------------------------get_early_ctrl_for_expensive---------------------------------
 144 // Move node up the dominator tree as high as legal while still beneficial
 145 Node *PhaseIdealLoop::get_early_ctrl_for_expensive(Node *n, Node* earliest) {
 146   assert(n->in(0) && n->is_expensive(), "expensive node with control input here");
 147   assert(OptimizeExpensiveOps, "optimization off?");
 148 
 149   Node* ctl = n->in(0);
 150   assert(ctl->is_CFG(), "expensive input 0 must be cfg");
 151   uint min_dom_depth = dom_depth(earliest);
 152 #ifdef ASSERT
 153   if (!is_dominator(ctl, earliest) && !is_dominator(earliest, ctl)) {
 154     dump_bad_graph("Bad graph detected in get_early_ctrl_for_expensive", n, earliest, ctl);
 155     assert(false, "Bad graph detected in get_early_ctrl_for_expensive");
 156   }
 157 #endif
 158   if (dom_depth(ctl) < min_dom_depth) {
 159     return earliest;
 160   }
 161 
 162   while (1) {
 163     Node *next = ctl;
 164     // Moving the node out of a loop on the projection of a If
 165     // confuses loop predication. So once we hit a Loop in a If branch
 166     // that doesn't branch to an UNC, we stop. The code that process
 167     // expensive nodes will notice the loop and skip over it to try to
 168     // move the node further up.
 169     if (ctl->is_CountedLoop() && ctl->in(1) != NULL && ctl->in(1)->in(0) != NULL && ctl->in(1)->in(0)->is_If()) {
 170       if (!ctl->in(1)->as_Proj()->is_uncommon_trap_if_pattern(Deoptimization::Reason_none)) {
 171         break;
 172       }
 173       next = idom(ctl->in(1)->in(0));
 174     } else if (ctl->is_Proj()) {
 175       // We only move it up along a projection if the projection is
 176       // the single control projection for its parent: same code path,
 177       // if it's a If with UNC or fallthrough of a call.
 178       Node* parent_ctl = ctl->in(0);
 179       if (parent_ctl == NULL) {
 180         break;
 181       } else if (parent_ctl->is_CountedLoopEnd() && parent_ctl->as_CountedLoopEnd()->loopnode() != NULL) {
 182         next = parent_ctl->as_CountedLoopEnd()->loopnode()->init_control();
 183       } else if (parent_ctl->is_If()) {
 184         if (!ctl->as_Proj()->is_uncommon_trap_if_pattern(Deoptimization::Reason_none)) {
 185           break;
 186         }
 187         assert(idom(ctl) == parent_ctl, "strange");
 188         next = idom(parent_ctl);
 189       } else if (ctl->is_CatchProj()) {
 190         if (ctl->as_Proj()->_con != CatchProjNode::fall_through_index) {
 191           break;
 192         }
 193         assert(parent_ctl->in(0)->in(0)->is_Call(), "strange graph");
 194         next = parent_ctl->in(0)->in(0)->in(0);
 195       } else {
 196         // Check if parent control has a single projection (this
 197         // control is the only possible successor of the parent
 198         // control). If so, we can try to move the node above the
 199         // parent control.
 200         int nb_ctl_proj = 0;
 201         for (DUIterator_Fast imax, i = parent_ctl->fast_outs(imax); i < imax; i++) {
 202           Node *p = parent_ctl->fast_out(i);
 203           if (p->is_Proj() && p->is_CFG()) {
 204             nb_ctl_proj++;
 205             if (nb_ctl_proj > 1) {
 206               break;
 207             }
 208           }
 209         }
 210 
 211         if (nb_ctl_proj > 1) {
 212           break;
 213         }
 214         assert(parent_ctl->is_Start() || parent_ctl->is_MemBar() || parent_ctl->is_Call(), "unexpected node");
 215         assert(idom(ctl) == parent_ctl, "strange");
 216         next = idom(parent_ctl);
 217       }
 218     } else {
 219       next = idom(ctl);
 220     }
 221     if (next->is_Root() || next->is_Start() || dom_depth(next) < min_dom_depth) {
 222       break;
 223     }
 224     ctl = next;
 225   }
 226 
 227   if (ctl != n->in(0)) {
 228     _igvn.hash_delete(n);
 229     n->set_req(0, ctl);
 230     _igvn.hash_insert(n);
 231   }
 232 
 233   return ctl;
 234 }
 235 
 236 
 237 //------------------------------set_early_ctrl---------------------------------
 238 // Set earliest legal control
 239 void PhaseIdealLoop::set_early_ctrl( Node *n ) {
 240   Node *early = get_early_ctrl(n);
 241 
 242   // Record earliest legal location
 243   set_ctrl(n, early);
 244 }
 245 
 246 //------------------------------set_subtree_ctrl-------------------------------
 247 // set missing _ctrl entries on new nodes
 248 void PhaseIdealLoop::set_subtree_ctrl( Node *n ) {
 249   // Already set?  Get out.
 250   if( _nodes[n->_idx] ) return;
 251   // Recursively set _nodes array to indicate where the Node goes
 252   uint i;
 253   for( i = 0; i < n->req(); ++i ) {
 254     Node *m = n->in(i);
 255     if( m && m != C->root() )
 256       set_subtree_ctrl( m );
 257   }
 258 
 259   // Fixup self
 260   set_early_ctrl( n );
 261 }
 262 
 263 //------------------------------is_counted_loop--------------------------------
 264 bool PhaseIdealLoop::is_counted_loop( Node *x, IdealLoopTree *loop ) {
 265   PhaseGVN *gvn = &_igvn;
 266 
 267   // Counted loop head must be a good RegionNode with only 3 not NULL
 268   // control input edges: Self, Entry, LoopBack.
 269   if (x->in(LoopNode::Self) == NULL || x->req() != 3 || loop->_irreducible) {
 270     return false;
 271   }
 272   Node *init_control = x->in(LoopNode::EntryControl);
 273   Node *back_control = x->in(LoopNode::LoopBackControl);
 274   if (init_control == NULL || back_control == NULL)    // Partially dead
 275     return false;
 276   // Must also check for TOP when looking for a dead loop
 277   if (init_control->is_top() || back_control->is_top())
 278     return false;
 279 
 280   // Allow funny placement of Safepoint
 281   if (back_control->Opcode() == Op_SafePoint) {
 282     if (UseCountedLoopSafepoints) {
 283       // Leaving the safepoint on the backedge and creating a
 284       // CountedLoop will confuse optimizations. We can't move the
 285       // safepoint around because its jvm state wouldn't match a new
 286       // location. Give up on that loop.
 287       return false;
 288     }
 289     back_control = back_control->in(TypeFunc::Control);
 290   }
 291 
 292   // Controlling test for loop
 293   Node *iftrue = back_control;
 294   uint iftrue_op = iftrue->Opcode();
 295   if (iftrue_op != Op_IfTrue &&
 296       iftrue_op != Op_IfFalse)
 297     // I have a weird back-control.  Probably the loop-exit test is in
 298     // the middle of the loop and I am looking at some trailing control-flow
 299     // merge point.  To fix this I would have to partially peel the loop.
 300     return false; // Obscure back-control
 301 
 302   // Get boolean guarding loop-back test
 303   Node *iff = iftrue->in(0);
 304   if (get_loop(iff) != loop || !iff->in(1)->is_Bool())
 305     return false;
 306   BoolNode *test = iff->in(1)->as_Bool();
 307   BoolTest::mask bt = test->_test._test;
 308   float cl_prob = iff->as_If()->_prob;
 309   if (iftrue_op == Op_IfFalse) {
 310     bt = BoolTest(bt).negate();
 311     cl_prob = 1.0 - cl_prob;
 312   }
 313   // Get backedge compare
 314   Node *cmp = test->in(1);
 315   int cmp_op = cmp->Opcode();
 316   if (cmp_op != Op_CmpI)
 317     return false;                // Avoid pointer & float compares
 318 
 319   // Find the trip-counter increment & limit.  Limit must be loop invariant.
 320   Node *incr  = cmp->in(1);
 321   Node *limit = cmp->in(2);
 322 
 323   // ---------
 324   // need 'loop()' test to tell if limit is loop invariant
 325   // ---------
 326 
 327   if (!is_member(loop, get_ctrl(incr))) { // Swapped trip counter and limit?
 328     Node *tmp = incr;            // Then reverse order into the CmpI
 329     incr = limit;
 330     limit = tmp;
 331     bt = BoolTest(bt).commute(); // And commute the exit test
 332   }
 333   if (is_member(loop, get_ctrl(limit))) // Limit must be loop-invariant
 334     return false;
 335   if (!is_member(loop, get_ctrl(incr))) // Trip counter must be loop-variant
 336     return false;
 337 
 338   Node* phi_incr = NULL;
 339   // Trip-counter increment must be commutative & associative.
 340   if (incr->is_Phi()) {
 341     if (incr->as_Phi()->region() != x || incr->req() != 3)
 342       return false; // Not simple trip counter expression
 343     phi_incr = incr;
 344     incr = phi_incr->in(LoopNode::LoopBackControl); // Assume incr is on backedge of Phi
 345     if (!is_member(loop, get_ctrl(incr))) // Trip counter must be loop-variant
 346       return false;
 347   }
 348 
 349   Node* trunc1 = NULL;
 350   Node* trunc2 = NULL;
 351   const TypeInt* iv_trunc_t = NULL;
 352   if (!(incr = CountedLoopNode::match_incr_with_optional_truncation(incr, &trunc1, &trunc2, &iv_trunc_t))) {
 353     return false; // Funny increment opcode
 354   }
 355   assert(incr->Opcode() == Op_AddI, "wrong increment code");
 356 
 357   // Get merge point
 358   Node *xphi = incr->in(1);
 359   Node *stride = incr->in(2);
 360   if (!stride->is_Con()) {     // Oops, swap these
 361     if (!xphi->is_Con())       // Is the other guy a constant?
 362       return false;             // Nope, unknown stride, bail out
 363     Node *tmp = xphi;           // 'incr' is commutative, so ok to swap
 364     xphi = stride;
 365     stride = tmp;
 366   }
 367   // Stride must be constant
 368   int stride_con = stride->get_int();
 369   if (stride_con == 0)
 370     return false; // missed some peephole opt
 371 
 372   if (!xphi->is_Phi())
 373     return false; // Too much math on the trip counter
 374   if (phi_incr != NULL && phi_incr != xphi)
 375     return false;
 376   PhiNode *phi = xphi->as_Phi();
 377 
 378   // Phi must be of loop header; backedge must wrap to increment
 379   if (phi->region() != x)
 380     return false;
 381   if (trunc1 == NULL && phi->in(LoopNode::LoopBackControl) != incr ||
 382       trunc1 != NULL && phi->in(LoopNode::LoopBackControl) != trunc1) {
 383     return false;
 384   }
 385   Node *init_trip = phi->in(LoopNode::EntryControl);
 386 
 387   // If iv trunc type is smaller than int, check for possible wrap.
 388   if (!TypeInt::INT->higher_equal(iv_trunc_t)) {
 389     assert(trunc1 != NULL, "must have found some truncation");
 390 
 391     // Get a better type for the phi (filtered thru if's)
 392     const TypeInt* phi_ft = filtered_type(phi);
 393 
 394     // Can iv take on a value that will wrap?
 395     //
 396     // Ensure iv's limit is not within "stride" of the wrap value.
 397     //
 398     // Example for "short" type
 399     //    Truncation ensures value is in the range -32768..32767 (iv_trunc_t)
 400     //    If the stride is +10, then the last value of the induction
 401     //    variable before the increment (phi_ft->_hi) must be
 402     //    <= 32767 - 10 and (phi_ft->_lo) must be >= -32768 to
 403     //    ensure no truncation occurs after the increment.
 404 
 405     if (stride_con > 0) {
 406       if (iv_trunc_t->_hi - phi_ft->_hi < stride_con ||
 407           iv_trunc_t->_lo > phi_ft->_lo) {
 408         return false;  // truncation may occur
 409       }
 410     } else if (stride_con < 0) {
 411       if (iv_trunc_t->_lo - phi_ft->_lo > stride_con ||
 412           iv_trunc_t->_hi < phi_ft->_hi) {
 413         return false;  // truncation may occur
 414       }
 415     }
 416     // No possibility of wrap so truncation can be discarded
 417     // Promote iv type to Int
 418   } else {
 419     assert(trunc1 == NULL && trunc2 == NULL, "no truncation for int");
 420   }
 421 
 422   // If the condition is inverted and we will be rolling
 423   // through MININT to MAXINT, then bail out.
 424   if (bt == BoolTest::eq || // Bail out, but this loop trips at most twice!
 425       // Odd stride
 426       bt == BoolTest::ne && stride_con != 1 && stride_con != -1 ||
 427       // Count down loop rolls through MAXINT
 428       (bt == BoolTest::le || bt == BoolTest::lt) && stride_con < 0 ||
 429       // Count up loop rolls through MININT
 430       (bt == BoolTest::ge || bt == BoolTest::gt) && stride_con > 0) {
 431     return false; // Bail out
 432   }
 433 
 434   const TypeInt* init_t = gvn->type(init_trip)->is_int();
 435   const TypeInt* limit_t = gvn->type(limit)->is_int();
 436 
 437   if (stride_con > 0) {
 438     jlong init_p = (jlong)init_t->_lo + stride_con;
 439     if (init_p > (jlong)max_jint || init_p > (jlong)limit_t->_hi)
 440       return false; // cyclic loop or this loop trips only once
 441   } else {
 442     jlong init_p = (jlong)init_t->_hi + stride_con;
 443     if (init_p < (jlong)min_jint || init_p < (jlong)limit_t->_lo)
 444       return false; // cyclic loop or this loop trips only once
 445   }
 446 
 447   if (phi_incr != NULL) {
 448     // check if there is a possiblity of IV overflowing after the first increment
 449     if (stride_con > 0) {
 450       if (init_t->_hi > max_jint - stride_con) {
 451         return false;
 452       }
 453     } else {
 454       if (init_t->_lo < min_jint - stride_con) {
 455         return false;
 456       }
 457     }
 458   }
 459 
 460   // =================================================
 461   // ---- SUCCESS!   Found A Trip-Counted Loop!  -----
 462   //
 463   assert(x->Opcode() == Op_Loop, "regular loops only");
 464   C->print_method(PHASE_BEFORE_CLOOPS, 3);
 465 
 466   Node *hook = new (C) Node(6);
 467 
 468   if (LoopLimitCheck) {
 469 
 470   // ===================================================
 471   // Generate loop limit check to avoid integer overflow
 472   // in cases like next (cyclic loops):
 473   //
 474   // for (i=0; i <= max_jint; i++) {}
 475   // for (i=0; i <  max_jint; i+=2) {}
 476   //
 477   //
 478   // Limit check predicate depends on the loop test:
 479   //
 480   // for(;i != limit; i++)       --> limit <= (max_jint)
 481   // for(;i <  limit; i+=stride) --> limit <= (max_jint - stride + 1)
 482   // for(;i <= limit; i+=stride) --> limit <= (max_jint - stride    )
 483   //
 484 
 485   // Check if limit is excluded to do more precise int overflow check.
 486   bool incl_limit = (bt == BoolTest::le || bt == BoolTest::ge);
 487   int stride_m  = stride_con - (incl_limit ? 0 : (stride_con > 0 ? 1 : -1));
 488 
 489   // If compare points directly to the phi we need to adjust
 490   // the compare so that it points to the incr. Limit have
 491   // to be adjusted to keep trip count the same and the
 492   // adjusted limit should be checked for int overflow.
 493   if (phi_incr != NULL) {
 494     stride_m  += stride_con;
 495   }
 496 
 497   if (limit->is_Con()) {
 498     int limit_con = limit->get_int();
 499     if ((stride_con > 0 && limit_con > (max_jint - stride_m)) ||
 500         (stride_con < 0 && limit_con < (min_jint - stride_m))) {
 501       // Bailout: it could be integer overflow.
 502       return false;
 503     }
 504   } else if ((stride_con > 0 && limit_t->_hi <= (max_jint - stride_m)) ||
 505              (stride_con < 0 && limit_t->_lo >= (min_jint - stride_m))) {
 506       // Limit's type may satisfy the condition, for example,
 507       // when it is an array length.
 508   } else {
 509     // Generate loop's limit check.
 510     // Loop limit check predicate should be near the loop.
 511     ProjNode *limit_check_proj = find_predicate_insertion_point(init_control, Deoptimization::Reason_loop_limit_check);
 512     if (!limit_check_proj) {
 513       // The limit check predicate is not generated if this method trapped here before.
 514 #ifdef ASSERT
 515       if (TraceLoopLimitCheck) {
 516         tty->print("missing loop limit check:");
 517         loop->dump_head();
 518         x->dump(1);
 519       }
 520 #endif
 521       return false;
 522     }
 523 
 524     IfNode* check_iff = limit_check_proj->in(0)->as_If();
 525     Node* cmp_limit;
 526     Node* bol;
 527 
 528     if (stride_con > 0) {
 529       cmp_limit = new (C) CmpINode(limit, _igvn.intcon(max_jint - stride_m));
 530       bol = new (C) BoolNode(cmp_limit, BoolTest::le);
 531     } else {
 532       cmp_limit = new (C) CmpINode(limit, _igvn.intcon(min_jint - stride_m));
 533       bol = new (C) BoolNode(cmp_limit, BoolTest::ge);
 534     }
 535     cmp_limit = _igvn.register_new_node_with_optimizer(cmp_limit);
 536     bol = _igvn.register_new_node_with_optimizer(bol);
 537     set_subtree_ctrl(bol);
 538 
 539     // Replace condition in original predicate but preserve Opaque node
 540     // so that previous predicates could be found.
 541     assert(check_iff->in(1)->Opcode() == Op_Conv2B &&
 542            check_iff->in(1)->in(1)->Opcode() == Op_Opaque1, "");
 543     Node* opq = check_iff->in(1)->in(1);
 544     _igvn.hash_delete(opq);
 545     opq->set_req(1, bol);
 546     // Update ctrl.
 547     set_ctrl(opq, check_iff->in(0));
 548     set_ctrl(check_iff->in(1), check_iff->in(0));
 549 
 550 #ifndef PRODUCT
 551     // report that the loop predication has been actually performed
 552     // for this loop
 553     if (TraceLoopLimitCheck) {
 554       tty->print_cr("Counted Loop Limit Check generated:");
 555       debug_only( bol->dump(2); )
 556     }
 557 #endif
 558   }
 559 
 560   if (phi_incr != NULL) {
 561     // If compare points directly to the phi we need to adjust
 562     // the compare so that it points to the incr. Limit have
 563     // to be adjusted to keep trip count the same and we
 564     // should avoid int overflow.
 565     //
 566     //   i = init; do {} while(i++ < limit);
 567     // is converted to
 568     //   i = init; do {} while(++i < limit+1);
 569     //
 570     limit = gvn->transform(new (C) AddINode(limit, stride));
 571   }
 572 
 573   // Now we need to canonicalize loop condition.
 574   if (bt == BoolTest::ne) {
 575     assert(stride_con == 1 || stride_con == -1, "simple increment only");
 576     // 'ne' can be replaced with 'lt' only when init < limit.
 577     if (stride_con > 0 && init_t->_hi < limit_t->_lo)
 578       bt = BoolTest::lt;
 579     // 'ne' can be replaced with 'gt' only when init > limit.
 580     if (stride_con < 0 && init_t->_lo > limit_t->_hi)
 581       bt = BoolTest::gt;
 582   }
 583 
 584   if (incl_limit) {
 585     // The limit check guaranties that 'limit <= (max_jint - stride)' so
 586     // we can convert 'i <= limit' to 'i < limit+1' since stride != 0.
 587     //
 588     Node* one = (stride_con > 0) ? gvn->intcon( 1) : gvn->intcon(-1);
 589     limit = gvn->transform(new (C) AddINode(limit, one));
 590     if (bt == BoolTest::le)
 591       bt = BoolTest::lt;
 592     else if (bt == BoolTest::ge)
 593       bt = BoolTest::gt;
 594     else
 595       ShouldNotReachHere();
 596   }
 597   set_subtree_ctrl( limit );
 598 
 599   } else { // LoopLimitCheck
 600 
 601   // If compare points to incr, we are ok.  Otherwise the compare
 602   // can directly point to the phi; in this case adjust the compare so that
 603   // it points to the incr by adjusting the limit.
 604   if (cmp->in(1) == phi || cmp->in(2) == phi)
 605     limit = gvn->transform(new (C) AddINode(limit,stride));
 606 
 607   // trip-count for +-tive stride should be: (limit - init_trip + stride - 1)/stride.
 608   // Final value for iterator should be: trip_count * stride + init_trip.
 609   Node *one_p = gvn->intcon( 1);
 610   Node *one_m = gvn->intcon(-1);
 611 
 612   Node *trip_count = NULL;
 613   switch( bt ) {
 614   case BoolTest::eq:
 615     ShouldNotReachHere();
 616   case BoolTest::ne:            // Ahh, the case we desire
 617     if (stride_con == 1)
 618       trip_count = gvn->transform(new (C) SubINode(limit,init_trip));
 619     else if (stride_con == -1)
 620       trip_count = gvn->transform(new (C) SubINode(init_trip,limit));
 621     else
 622       ShouldNotReachHere();
 623     set_subtree_ctrl(trip_count);
 624     //_loop.map(trip_count->_idx,loop(limit));
 625     break;
 626   case BoolTest::le:            // Maybe convert to '<' case
 627     limit = gvn->transform(new (C) AddINode(limit,one_p));
 628     set_subtree_ctrl( limit );
 629     hook->init_req(4, limit);
 630 
 631     bt = BoolTest::lt;
 632     // Make the new limit be in the same loop nest as the old limit
 633     //_loop.map(limit->_idx,limit_loop);
 634     // Fall into next case
 635   case BoolTest::lt: {          // Maybe convert to '!=' case
 636     if (stride_con < 0) // Count down loop rolls through MAXINT
 637       ShouldNotReachHere();
 638     Node *range = gvn->transform(new (C) SubINode(limit,init_trip));
 639     set_subtree_ctrl( range );
 640     hook->init_req(0, range);
 641 
 642     Node *bias  = gvn->transform(new (C) AddINode(range,stride));
 643     set_subtree_ctrl( bias );
 644     hook->init_req(1, bias);
 645 
 646     Node *bias1 = gvn->transform(new (C) AddINode(bias,one_m));
 647     set_subtree_ctrl( bias1 );
 648     hook->init_req(2, bias1);
 649 
 650     trip_count  = gvn->transform(new (C) DivINode(0,bias1,stride));
 651     set_subtree_ctrl( trip_count );
 652     hook->init_req(3, trip_count);
 653     break;
 654   }
 655 
 656   case BoolTest::ge:            // Maybe convert to '>' case
 657     limit = gvn->transform(new (C) AddINode(limit,one_m));
 658     set_subtree_ctrl( limit );
 659     hook->init_req(4 ,limit);
 660 
 661     bt = BoolTest::gt;
 662     // Make the new limit be in the same loop nest as the old limit
 663     //_loop.map(limit->_idx,limit_loop);
 664     // Fall into next case
 665   case BoolTest::gt: {          // Maybe convert to '!=' case
 666     if (stride_con > 0) // count up loop rolls through MININT
 667       ShouldNotReachHere();
 668     Node *range = gvn->transform(new (C) SubINode(limit,init_trip));
 669     set_subtree_ctrl( range );
 670     hook->init_req(0, range);
 671 
 672     Node *bias  = gvn->transform(new (C) AddINode(range,stride));
 673     set_subtree_ctrl( bias );
 674     hook->init_req(1, bias);
 675 
 676     Node *bias1 = gvn->transform(new (C) AddINode(bias,one_p));
 677     set_subtree_ctrl( bias1 );
 678     hook->init_req(2, bias1);
 679 
 680     trip_count  = gvn->transform(new (C) DivINode(0,bias1,stride));
 681     set_subtree_ctrl( trip_count );
 682     hook->init_req(3, trip_count);
 683     break;
 684   }
 685   } // switch( bt )
 686 
 687   Node *span = gvn->transform(new (C) MulINode(trip_count,stride));
 688   set_subtree_ctrl( span );
 689   hook->init_req(5, span);
 690 
 691   limit = gvn->transform(new (C) AddINode(span,init_trip));
 692   set_subtree_ctrl( limit );
 693 
 694   } // LoopLimitCheck
 695 
 696   if (!UseCountedLoopSafepoints) {
 697     // Check for SafePoint on backedge and remove
 698     Node *sfpt = x->in(LoopNode::LoopBackControl);
 699     if (sfpt->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt)) {
 700       lazy_replace( sfpt, iftrue );
 701       if (loop->_safepts != NULL) {
 702         loop->_safepts->yank(sfpt);
 703       }
 704       loop->_tail = iftrue;
 705     }
 706   }
 707 
 708   // Build a canonical trip test.
 709   // Clone code, as old values may be in use.
 710   incr = incr->clone();
 711   incr->set_req(1,phi);
 712   incr->set_req(2,stride);
 713   incr = _igvn.register_new_node_with_optimizer(incr);
 714   set_early_ctrl( incr );
 715   _igvn.hash_delete(phi);
 716   phi->set_req_X( LoopNode::LoopBackControl, incr, &_igvn );
 717 
 718   // If phi type is more restrictive than Int, raise to
 719   // Int to prevent (almost) infinite recursion in igvn
 720   // which can only handle integer types for constants or minint..maxint.
 721   if (!TypeInt::INT->higher_equal(phi->bottom_type())) {
 722     Node* nphi = PhiNode::make(phi->in(0), phi->in(LoopNode::EntryControl), TypeInt::INT);
 723     nphi->set_req(LoopNode::LoopBackControl, phi->in(LoopNode::LoopBackControl));
 724     nphi = _igvn.register_new_node_with_optimizer(nphi);
 725     set_ctrl(nphi, get_ctrl(phi));
 726     _igvn.replace_node(phi, nphi);
 727     phi = nphi->as_Phi();
 728   }
 729   cmp = cmp->clone();
 730   cmp->set_req(1,incr);
 731   cmp->set_req(2,limit);
 732   cmp = _igvn.register_new_node_with_optimizer(cmp);
 733   set_ctrl(cmp, iff->in(0));
 734 
 735   test = test->clone()->as_Bool();
 736   (*(BoolTest*)&test->_test)._test = bt;
 737   test->set_req(1,cmp);
 738   _igvn.register_new_node_with_optimizer(test);
 739   set_ctrl(test, iff->in(0));
 740 
 741   // Replace the old IfNode with a new LoopEndNode
 742   Node *lex = _igvn.register_new_node_with_optimizer(new (C) CountedLoopEndNode( iff->in(0), test, cl_prob, iff->as_If()->_fcnt ));
 743   IfNode *le = lex->as_If();
 744   uint dd = dom_depth(iff);
 745   set_idom(le, le->in(0), dd); // Update dominance for loop exit
 746   set_loop(le, loop);
 747 
 748   // Get the loop-exit control
 749   Node *iffalse = iff->as_If()->proj_out(!(iftrue_op == Op_IfTrue));
 750 
 751   // Need to swap loop-exit and loop-back control?
 752   if (iftrue_op == Op_IfFalse) {
 753     Node *ift2=_igvn.register_new_node_with_optimizer(new (C) IfTrueNode (le));
 754     Node *iff2=_igvn.register_new_node_with_optimizer(new (C) IfFalseNode(le));
 755 
 756     loop->_tail = back_control = ift2;
 757     set_loop(ift2, loop);
 758     set_loop(iff2, get_loop(iffalse));
 759 
 760     // Lazy update of 'get_ctrl' mechanism.
 761     lazy_replace(iffalse, iff2);
 762     lazy_replace(iftrue,  ift2);
 763 
 764     // Swap names
 765     iffalse = iff2;
 766     iftrue  = ift2;
 767   } else {
 768     _igvn.hash_delete(iffalse);
 769     _igvn.hash_delete(iftrue);
 770     iffalse->set_req_X( 0, le, &_igvn );
 771     iftrue ->set_req_X( 0, le, &_igvn );
 772   }
 773 
 774   set_idom(iftrue,  le, dd+1);
 775   set_idom(iffalse, le, dd+1);
 776   assert(iff->outcnt() == 0, "should be dead now");
 777   lazy_replace( iff, le ); // fix 'get_ctrl'
 778 
 779   // Now setup a new CountedLoopNode to replace the existing LoopNode
 780   CountedLoopNode *l = new (C) CountedLoopNode(init_control, back_control);
 781   l->set_unswitch_count(x->as_Loop()->unswitch_count()); // Preserve
 782   // The following assert is approximately true, and defines the intention
 783   // of can_be_counted_loop.  It fails, however, because phase->type
 784   // is not yet initialized for this loop and its parts.
 785   //assert(l->can_be_counted_loop(this), "sanity");
 786   _igvn.register_new_node_with_optimizer(l);
 787   set_loop(l, loop);
 788   loop->_head = l;
 789   // Fix all data nodes placed at the old loop head.
 790   // Uses the lazy-update mechanism of 'get_ctrl'.
 791   lazy_replace( x, l );
 792   set_idom(l, init_control, dom_depth(x));
 793 
 794   if (!UseCountedLoopSafepoints) {
 795     // Check for immediately preceding SafePoint and remove
 796     Node *sfpt2 = le->in(0);
 797     if (sfpt2->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt2)) {
 798       lazy_replace( sfpt2, sfpt2->in(TypeFunc::Control));
 799       if (loop->_safepts != NULL) {
 800         loop->_safepts->yank(sfpt2);
 801       }
 802     }
 803   }
 804 
 805   // Free up intermediate goo
 806   _igvn.remove_dead_node(hook);
 807 
 808 #ifdef ASSERT
 809   assert(l->is_valid_counted_loop(), "counted loop shape is messed up");
 810   assert(l == loop->_head && l->phi() == phi && l->loopexit() == lex, "" );
 811 #endif
 812 #ifndef PRODUCT
 813   if (TraceLoopOpts) {
 814     tty->print("Counted      ");
 815     loop->dump_head();
 816   }
 817 #endif
 818 
 819   C->print_method(PHASE_AFTER_CLOOPS, 3);
 820 
 821   return true;
 822 }
 823 
 824 //----------------------exact_limit-------------------------------------------
 825 Node* PhaseIdealLoop::exact_limit( IdealLoopTree *loop ) {
 826   assert(loop->_head->is_CountedLoop(), "");
 827   CountedLoopNode *cl = loop->_head->as_CountedLoop();
 828   assert(cl->is_valid_counted_loop(), "");
 829 
 830   if (!LoopLimitCheck || ABS(cl->stride_con()) == 1 ||
 831       cl->limit()->Opcode() == Op_LoopLimit) {
 832     // Old code has exact limit (it could be incorrect in case of int overflow).
 833     // Loop limit is exact with stride == 1. And loop may already have exact limit.
 834     return cl->limit();
 835   }
 836   Node *limit = NULL;
 837 #ifdef ASSERT
 838   BoolTest::mask bt = cl->loopexit()->test_trip();
 839   assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
 840 #endif
 841   if (cl->has_exact_trip_count()) {
 842     // Simple case: loop has constant boundaries.
 843     // Use jlongs to avoid integer overflow.
 844     int stride_con = cl->stride_con();
 845     jlong  init_con = cl->init_trip()->get_int();
 846     jlong limit_con = cl->limit()->get_int();
 847     julong trip_cnt = cl->trip_count();
 848     jlong final_con = init_con + trip_cnt*stride_con;
 849     int final_int = (int)final_con;
 850     // The final value should be in integer range since the loop
 851     // is counted and the limit was checked for overflow.
 852     assert(final_con == (jlong)final_int, "final value should be integer");
 853     limit = _igvn.intcon(final_int);
 854   } else {
 855     // Create new LoopLimit node to get exact limit (final iv value).
 856     limit = new (C) LoopLimitNode(C, cl->init_trip(), cl->limit(), cl->stride());
 857     register_new_node(limit, cl->in(LoopNode::EntryControl));
 858   }
 859   assert(limit != NULL, "sanity");
 860   return limit;
 861 }
 862 
 863 //------------------------------Ideal------------------------------------------
 864 // Return a node which is more "ideal" than the current node.
 865 // Attempt to convert into a counted-loop.
 866 Node *LoopNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 867   if (!can_be_counted_loop(phase)) {
 868     phase->C->set_major_progress();
 869   }
 870   return RegionNode::Ideal(phase, can_reshape);
 871 }
 872 
 873 
 874 //=============================================================================
 875 //------------------------------Ideal------------------------------------------
 876 // Return a node which is more "ideal" than the current node.
 877 // Attempt to convert into a counted-loop.
 878 Node *CountedLoopNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 879   return RegionNode::Ideal(phase, can_reshape);
 880 }
 881 
 882 //------------------------------dump_spec--------------------------------------
 883 // Dump special per-node info
 884 #ifndef PRODUCT
 885 void CountedLoopNode::dump_spec(outputStream *st) const {
 886   LoopNode::dump_spec(st);
 887   if (stride_is_con()) {
 888     st->print("stride: %d ",stride_con());
 889   }
 890   if (is_pre_loop ()) st->print("pre of N%d" , _main_idx);
 891   if (is_main_loop()) st->print("main of N%d", _idx);
 892   if (is_post_loop()) st->print("post of N%d", _main_idx);
 893 }
 894 #endif
 895 
 896 //=============================================================================
 897 int CountedLoopEndNode::stride_con() const {
 898   return stride()->bottom_type()->is_int()->get_con();
 899 }
 900 
 901 //=============================================================================
 902 //------------------------------Value-----------------------------------------
 903 const Type *LoopLimitNode::Value( PhaseTransform *phase ) const {
 904   const Type* init_t   = phase->type(in(Init));
 905   const Type* limit_t  = phase->type(in(Limit));
 906   const Type* stride_t = phase->type(in(Stride));
 907   // Either input is TOP ==> the result is TOP
 908   if (init_t   == Type::TOP) return Type::TOP;
 909   if (limit_t  == Type::TOP) return Type::TOP;
 910   if (stride_t == Type::TOP) return Type::TOP;
 911 
 912   int stride_con = stride_t->is_int()->get_con();
 913   if (stride_con == 1)
 914     return NULL;  // Identity
 915 
 916   if (init_t->is_int()->is_con() && limit_t->is_int()->is_con()) {
 917     // Use jlongs to avoid integer overflow.
 918     jlong init_con   =  init_t->is_int()->get_con();
 919     jlong limit_con  = limit_t->is_int()->get_con();
 920     int  stride_m   = stride_con - (stride_con > 0 ? 1 : -1);
 921     jlong trip_count = (limit_con - init_con + stride_m)/stride_con;
 922     jlong final_con  = init_con + stride_con*trip_count;
 923     int final_int = (int)final_con;
 924     // The final value should be in integer range since the loop
 925     // is counted and the limit was checked for overflow.
 926     assert(final_con == (jlong)final_int, "final value should be integer");
 927     return TypeInt::make(final_int);
 928   }
 929 
 930   return bottom_type(); // TypeInt::INT
 931 }
 932 
 933 //------------------------------Ideal------------------------------------------
 934 // Return a node which is more "ideal" than the current node.
 935 Node *LoopLimitNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 936   if (phase->type(in(Init))   == Type::TOP ||
 937       phase->type(in(Limit))  == Type::TOP ||
 938       phase->type(in(Stride)) == Type::TOP)
 939     return NULL;  // Dead
 940 
 941   int stride_con = phase->type(in(Stride))->is_int()->get_con();
 942   if (stride_con == 1)
 943     return NULL;  // Identity
 944 
 945   if (in(Init)->is_Con() && in(Limit)->is_Con())
 946     return NULL;  // Value
 947 
 948   // Delay following optimizations until all loop optimizations
 949   // done to keep Ideal graph simple.
 950   if (!can_reshape || phase->C->major_progress())
 951     return NULL;
 952 
 953   const TypeInt* init_t  = phase->type(in(Init) )->is_int();
 954   const TypeInt* limit_t = phase->type(in(Limit))->is_int();
 955   int stride_p;
 956   jlong lim, ini;
 957   julong max;
 958   if (stride_con > 0) {
 959     stride_p = stride_con;
 960     lim = limit_t->_hi;
 961     ini = init_t->_lo;
 962     max = (julong)max_jint;
 963   } else {
 964     stride_p = -stride_con;
 965     lim = init_t->_hi;
 966     ini = limit_t->_lo;
 967     max = (julong)min_jint;
 968   }
 969   julong range = lim - ini + stride_p;
 970   if (range <= max) {
 971     // Convert to integer expression if it is not overflow.
 972     Node* stride_m = phase->intcon(stride_con - (stride_con > 0 ? 1 : -1));
 973     Node *range = phase->transform(new (phase->C) SubINode(in(Limit), in(Init)));
 974     Node *bias  = phase->transform(new (phase->C) AddINode(range, stride_m));
 975     Node *trip  = phase->transform(new (phase->C) DivINode(0, bias, in(Stride)));
 976     Node *span  = phase->transform(new (phase->C) MulINode(trip, in(Stride)));
 977     return new (phase->C) AddINode(span, in(Init)); // exact limit
 978   }
 979 
 980   if (is_power_of_2(stride_p) ||                // divisor is 2^n
 981       !Matcher::has_match_rule(Op_LoopLimit)) { // or no specialized Mach node?
 982     // Convert to long expression to avoid integer overflow
 983     // and let igvn optimizer convert this division.
 984     //
 985     Node*   init   = phase->transform( new (phase->C) ConvI2LNode(in(Init)));
 986     Node*  limit   = phase->transform( new (phase->C) ConvI2LNode(in(Limit)));
 987     Node* stride   = phase->longcon(stride_con);
 988     Node* stride_m = phase->longcon(stride_con - (stride_con > 0 ? 1 : -1));
 989 
 990     Node *range = phase->transform(new (phase->C) SubLNode(limit, init));
 991     Node *bias  = phase->transform(new (phase->C) AddLNode(range, stride_m));
 992     Node *span;
 993     if (stride_con > 0 && is_power_of_2(stride_p)) {
 994       // bias >= 0 if stride >0, so if stride is 2^n we can use &(-stride)
 995       // and avoid generating rounding for division. Zero trip guard should
 996       // guarantee that init < limit but sometimes the guard is missing and
 997       // we can get situation when init > limit. Note, for the empty loop
 998       // optimization zero trip guard is generated explicitly which leaves
 999       // only RCE predicate where exact limit is used and the predicate
1000       // will simply fail forcing recompilation.
1001       Node* neg_stride   = phase->longcon(-stride_con);
1002       span = phase->transform(new (phase->C) AndLNode(bias, neg_stride));
1003     } else {
1004       Node *trip  = phase->transform(new (phase->C) DivLNode(0, bias, stride));
1005       span = phase->transform(new (phase->C) MulLNode(trip, stride));
1006     }
1007     // Convert back to int
1008     Node *span_int = phase->transform(new (phase->C) ConvL2INode(span));
1009     return new (phase->C) AddINode(span_int, in(Init)); // exact limit
1010   }
1011 
1012   return NULL;    // No progress
1013 }
1014 
1015 //------------------------------Identity---------------------------------------
1016 // If stride == 1 return limit node.
1017 Node *LoopLimitNode::Identity( PhaseTransform *phase ) {
1018   int stride_con = phase->type(in(Stride))->is_int()->get_con();
1019   if (stride_con == 1 || stride_con == -1)
1020     return in(Limit);
1021   return this;
1022 }
1023 
1024 //=============================================================================
1025 //----------------------match_incr_with_optional_truncation--------------------
1026 // Match increment with optional truncation:
1027 // CHAR: (i+1)&0x7fff, BYTE: ((i+1)<<8)>>8, or SHORT: ((i+1)<<16)>>16
1028 // Return NULL for failure. Success returns the increment node.
1029 Node* CountedLoopNode::match_incr_with_optional_truncation(
1030                       Node* expr, Node** trunc1, Node** trunc2, const TypeInt** trunc_type) {
1031   // Quick cutouts:
1032   if (expr == NULL || expr->req() != 3)  return NULL;
1033 
1034   Node *t1 = NULL;
1035   Node *t2 = NULL;
1036   const TypeInt* trunc_t = TypeInt::INT;
1037   Node* n1 = expr;
1038   int   n1op = n1->Opcode();
1039 
1040   // Try to strip (n1 & M) or (n1 << N >> N) from n1.
1041   if (n1op == Op_AndI &&
1042       n1->in(2)->is_Con() &&
1043       n1->in(2)->bottom_type()->is_int()->get_con() == 0x7fff) {
1044     // %%% This check should match any mask of 2**K-1.
1045     t1 = n1;
1046     n1 = t1->in(1);
1047     n1op = n1->Opcode();
1048     trunc_t = TypeInt::CHAR;
1049   } else if (n1op == Op_RShiftI &&
1050              n1->in(1) != NULL &&
1051              n1->in(1)->Opcode() == Op_LShiftI &&
1052              n1->in(2) == n1->in(1)->in(2) &&
1053              n1->in(2)->is_Con()) {
1054     jint shift = n1->in(2)->bottom_type()->is_int()->get_con();
1055     // %%% This check should match any shift in [1..31].
1056     if (shift == 16 || shift == 8) {
1057       t1 = n1;
1058       t2 = t1->in(1);
1059       n1 = t2->in(1);
1060       n1op = n1->Opcode();
1061       if (shift == 16) {
1062         trunc_t = TypeInt::SHORT;
1063       } else if (shift == 8) {
1064         trunc_t = TypeInt::BYTE;
1065       }
1066     }
1067   }
1068 
1069   // If (maybe after stripping) it is an AddI, we won:
1070   if (n1op == Op_AddI) {
1071     *trunc1 = t1;
1072     *trunc2 = t2;
1073     *trunc_type = trunc_t;
1074     return n1;
1075   }
1076 
1077   // failed
1078   return NULL;
1079 }
1080 
1081 
1082 //------------------------------filtered_type--------------------------------
1083 // Return a type based on condition control flow
1084 // A successful return will be a type that is restricted due
1085 // to a series of dominating if-tests, such as:
1086 //    if (i < 10) {
1087 //       if (i > 0) {
1088 //          here: "i" type is [1..10)
1089 //       }
1090 //    }
1091 // or a control flow merge
1092 //    if (i < 10) {
1093 //       do {
1094 //          phi( , ) -- at top of loop type is [min_int..10)
1095 //         i = ?
1096 //       } while ( i < 10)
1097 //
1098 const TypeInt* PhaseIdealLoop::filtered_type( Node *n, Node* n_ctrl) {
1099   assert(n && n->bottom_type()->is_int(), "must be int");
1100   const TypeInt* filtered_t = NULL;
1101   if (!n->is_Phi()) {
1102     assert(n_ctrl != NULL || n_ctrl == C->top(), "valid control");
1103     filtered_t = filtered_type_from_dominators(n, n_ctrl);
1104 
1105   } else {
1106     Node* phi    = n->as_Phi();
1107     Node* region = phi->in(0);
1108     assert(n_ctrl == NULL || n_ctrl == region, "ctrl parameter must be region");
1109     if (region && region != C->top()) {
1110       for (uint i = 1; i < phi->req(); i++) {
1111         Node* val   = phi->in(i);
1112         Node* use_c = region->in(i);
1113         const TypeInt* val_t = filtered_type_from_dominators(val, use_c);
1114         if (val_t != NULL) {
1115           if (filtered_t == NULL) {
1116             filtered_t = val_t;
1117           } else {
1118             filtered_t = filtered_t->meet(val_t)->is_int();
1119           }
1120         }
1121       }
1122     }
1123   }
1124   const TypeInt* n_t = _igvn.type(n)->is_int();
1125   if (filtered_t != NULL) {
1126     n_t = n_t->join(filtered_t)->is_int();
1127   }
1128   return n_t;
1129 }
1130 
1131 
1132 //------------------------------filtered_type_from_dominators--------------------------------
1133 // Return a possibly more restrictive type for val based on condition control flow of dominators
1134 const TypeInt* PhaseIdealLoop::filtered_type_from_dominators( Node* val, Node *use_ctrl) {
1135   if (val->is_Con()) {
1136      return val->bottom_type()->is_int();
1137   }
1138   uint if_limit = 10; // Max number of dominating if's visited
1139   const TypeInt* rtn_t = NULL;
1140 
1141   if (use_ctrl && use_ctrl != C->top()) {
1142     Node* val_ctrl = get_ctrl(val);
1143     uint val_dom_depth = dom_depth(val_ctrl);
1144     Node* pred = use_ctrl;
1145     uint if_cnt = 0;
1146     while (if_cnt < if_limit) {
1147       if ((pred->Opcode() == Op_IfTrue || pred->Opcode() == Op_IfFalse)) {
1148         if_cnt++;
1149         const TypeInt* if_t = IfNode::filtered_int_type(&_igvn, val, pred);
1150         if (if_t != NULL) {
1151           if (rtn_t == NULL) {
1152             rtn_t = if_t;
1153           } else {
1154             rtn_t = rtn_t->join(if_t)->is_int();
1155           }
1156         }
1157       }
1158       pred = idom(pred);
1159       if (pred == NULL || pred == C->top()) {
1160         break;
1161       }
1162       // Stop if going beyond definition block of val
1163       if (dom_depth(pred) < val_dom_depth) {
1164         break;
1165       }
1166     }
1167   }
1168   return rtn_t;
1169 }
1170 
1171 
1172 //------------------------------dump_spec--------------------------------------
1173 // Dump special per-node info
1174 #ifndef PRODUCT
1175 void CountedLoopEndNode::dump_spec(outputStream *st) const {
1176   if( in(TestValue)->is_Bool() ) {
1177     BoolTest bt( test_trip()); // Added this for g++.
1178 
1179     st->print("[");
1180     bt.dump_on(st);
1181     st->print("]");
1182   }
1183   st->print(" ");
1184   IfNode::dump_spec(st);
1185 }
1186 #endif
1187 
1188 //=============================================================================
1189 //------------------------------is_member--------------------------------------
1190 // Is 'l' a member of 'this'?
1191 int IdealLoopTree::is_member( const IdealLoopTree *l ) const {
1192   while( l->_nest > _nest ) l = l->_parent;
1193   return l == this;
1194 }
1195 
1196 //------------------------------set_nest---------------------------------------
1197 // Set loop tree nesting depth.  Accumulate _has_call bits.
1198 int IdealLoopTree::set_nest( uint depth ) {
1199   _nest = depth;
1200   int bits = _has_call;
1201   if( _child ) bits |= _child->set_nest(depth+1);
1202   if( bits ) _has_call = 1;
1203   if( _next  ) bits |= _next ->set_nest(depth  );
1204   return bits;
1205 }
1206 
1207 //------------------------------split_fall_in----------------------------------
1208 // Split out multiple fall-in edges from the loop header.  Move them to a
1209 // private RegionNode before the loop.  This becomes the loop landing pad.
1210 void IdealLoopTree::split_fall_in( PhaseIdealLoop *phase, int fall_in_cnt ) {
1211   PhaseIterGVN &igvn = phase->_igvn;
1212   uint i;
1213 
1214   // Make a new RegionNode to be the landing pad.
1215   Node *landing_pad = new (phase->C) RegionNode( fall_in_cnt+1 );
1216   phase->set_loop(landing_pad,_parent);
1217   // Gather all the fall-in control paths into the landing pad
1218   uint icnt = fall_in_cnt;
1219   uint oreq = _head->req();
1220   for( i = oreq-1; i>0; i-- )
1221     if( !phase->is_member( this, _head->in(i) ) )
1222       landing_pad->set_req(icnt--,_head->in(i));
1223 
1224   // Peel off PhiNode edges as well
1225   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
1226     Node *oj = _head->fast_out(j);
1227     if( oj->is_Phi() ) {
1228       PhiNode* old_phi = oj->as_Phi();
1229       assert( old_phi->region() == _head, "" );
1230       igvn.hash_delete(old_phi);   // Yank from hash before hacking edges
1231       Node *p = PhiNode::make_blank(landing_pad, old_phi);
1232       uint icnt = fall_in_cnt;
1233       for( i = oreq-1; i>0; i-- ) {
1234         if( !phase->is_member( this, _head->in(i) ) ) {
1235           p->init_req(icnt--, old_phi->in(i));
1236           // Go ahead and clean out old edges from old phi
1237           old_phi->del_req(i);
1238         }
1239       }
1240       // Search for CSE's here, because ZKM.jar does a lot of
1241       // loop hackery and we need to be a little incremental
1242       // with the CSE to avoid O(N^2) node blow-up.
1243       Node *p2 = igvn.hash_find_insert(p); // Look for a CSE
1244       if( p2 ) {                // Found CSE
1245         p->destruct();          // Recover useless new node
1246         p = p2;                 // Use old node
1247       } else {
1248         igvn.register_new_node_with_optimizer(p, old_phi);
1249       }
1250       // Make old Phi refer to new Phi.
1251       old_phi->add_req(p);
1252       // Check for the special case of making the old phi useless and
1253       // disappear it.  In JavaGrande I have a case where this useless
1254       // Phi is the loop limit and prevents recognizing a CountedLoop
1255       // which in turn prevents removing an empty loop.
1256       Node *id_old_phi = old_phi->Identity( &igvn );
1257       if( id_old_phi != old_phi ) { // Found a simple identity?
1258         // Note that I cannot call 'replace_node' here, because
1259         // that will yank the edge from old_phi to the Region and
1260         // I'm mid-iteration over the Region's uses.
1261         for (DUIterator_Last imin, i = old_phi->last_outs(imin); i >= imin; ) {
1262           Node* use = old_phi->last_out(i);
1263           igvn.rehash_node_delayed(use);
1264           uint uses_found = 0;
1265           for (uint j = 0; j < use->len(); j++) {
1266             if (use->in(j) == old_phi) {
1267               if (j < use->req()) use->set_req (j, id_old_phi);
1268               else                use->set_prec(j, id_old_phi);
1269               uses_found++;
1270             }
1271           }
1272           i -= uses_found;    // we deleted 1 or more copies of this edge
1273         }
1274       }
1275       igvn._worklist.push(old_phi);
1276     }
1277   }
1278   // Finally clean out the fall-in edges from the RegionNode
1279   for( i = oreq-1; i>0; i-- ) {
1280     if( !phase->is_member( this, _head->in(i) ) ) {
1281       _head->del_req(i);
1282     }
1283   }
1284   // Transform landing pad
1285   igvn.register_new_node_with_optimizer(landing_pad, _head);
1286   // Insert landing pad into the header
1287   _head->add_req(landing_pad);
1288 }
1289 
1290 //------------------------------split_outer_loop-------------------------------
1291 // Split out the outermost loop from this shared header.
1292 void IdealLoopTree::split_outer_loop( PhaseIdealLoop *phase ) {
1293   PhaseIterGVN &igvn = phase->_igvn;
1294 
1295   // Find index of outermost loop; it should also be my tail.
1296   uint outer_idx = 1;
1297   while( _head->in(outer_idx) != _tail ) outer_idx++;
1298 
1299   // Make a LoopNode for the outermost loop.
1300   Node *ctl = _head->in(LoopNode::EntryControl);
1301   Node *outer = new (phase->C) LoopNode( ctl, _head->in(outer_idx) );
1302   outer = igvn.register_new_node_with_optimizer(outer, _head);
1303   phase->set_created_loop_node();
1304 
1305   // Outermost loop falls into '_head' loop
1306   _head->set_req(LoopNode::EntryControl, outer);
1307   _head->del_req(outer_idx);
1308   // Split all the Phis up between '_head' loop and 'outer' loop.
1309   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
1310     Node *out = _head->fast_out(j);
1311     if( out->is_Phi() ) {
1312       PhiNode *old_phi = out->as_Phi();
1313       assert( old_phi->region() == _head, "" );
1314       Node *phi = PhiNode::make_blank(outer, old_phi);
1315       phi->init_req(LoopNode::EntryControl,    old_phi->in(LoopNode::EntryControl));
1316       phi->init_req(LoopNode::LoopBackControl, old_phi->in(outer_idx));
1317       phi = igvn.register_new_node_with_optimizer(phi, old_phi);
1318       // Make old Phi point to new Phi on the fall-in path
1319       igvn.replace_input_of(old_phi, LoopNode::EntryControl, phi);
1320       old_phi->del_req(outer_idx);
1321     }
1322   }
1323 
1324   // Use the new loop head instead of the old shared one
1325   _head = outer;
1326   phase->set_loop(_head, this);
1327 }
1328 
1329 //------------------------------fix_parent-------------------------------------
1330 static void fix_parent( IdealLoopTree *loop, IdealLoopTree *parent ) {
1331   loop->_parent = parent;
1332   if( loop->_child ) fix_parent( loop->_child, loop   );
1333   if( loop->_next  ) fix_parent( loop->_next , parent );
1334 }
1335 
1336 //------------------------------estimate_path_freq-----------------------------
1337 static float estimate_path_freq( Node *n ) {
1338   // Try to extract some path frequency info
1339   IfNode *iff;
1340   for( int i = 0; i < 50; i++ ) { // Skip through a bunch of uncommon tests
1341     uint nop = n->Opcode();
1342     if( nop == Op_SafePoint ) {   // Skip any safepoint
1343       n = n->in(0);
1344       continue;
1345     }
1346     if( nop == Op_CatchProj ) {   // Get count from a prior call
1347       // Assume call does not always throw exceptions: means the call-site
1348       // count is also the frequency of the fall-through path.
1349       assert( n->is_CatchProj(), "" );
1350       if( ((CatchProjNode*)n)->_con != CatchProjNode::fall_through_index )
1351         return 0.0f;            // Assume call exception path is rare
1352       Node *call = n->in(0)->in(0)->in(0);
1353       assert( call->is_Call(), "expect a call here" );
1354       const JVMState *jvms = ((CallNode*)call)->jvms();
1355       ciMethodData* methodData = jvms->method()->method_data();
1356       if (!methodData->is_mature())  return 0.0f; // No call-site data
1357       ciProfileData* data = methodData->bci_to_data(jvms->bci());
1358       if ((data == NULL) || !data->is_CounterData()) {
1359         // no call profile available, try call's control input
1360         n = n->in(0);
1361         continue;
1362       }
1363       return data->as_CounterData()->count()/FreqCountInvocations;
1364     }
1365     // See if there's a gating IF test
1366     Node *n_c = n->in(0);
1367     if( !n_c->is_If() ) break;       // No estimate available
1368     iff = n_c->as_If();
1369     if( iff->_fcnt != COUNT_UNKNOWN )   // Have a valid count?
1370       // Compute how much count comes on this path
1371       return ((nop == Op_IfTrue) ? iff->_prob : 1.0f - iff->_prob) * iff->_fcnt;
1372     // Have no count info.  Skip dull uncommon-trap like branches.
1373     if( (nop == Op_IfTrue  && iff->_prob < PROB_LIKELY_MAG(5)) ||
1374         (nop == Op_IfFalse && iff->_prob > PROB_UNLIKELY_MAG(5)) )
1375       break;
1376     // Skip through never-taken branch; look for a real loop exit.
1377     n = iff->in(0);
1378   }
1379   return 0.0f;                  // No estimate available
1380 }
1381 
1382 //------------------------------merge_many_backedges---------------------------
1383 // Merge all the backedges from the shared header into a private Region.
1384 // Feed that region as the one backedge to this loop.
1385 void IdealLoopTree::merge_many_backedges( PhaseIdealLoop *phase ) {
1386   uint i;
1387 
1388   // Scan for the top 2 hottest backedges
1389   float hotcnt = 0.0f;
1390   float warmcnt = 0.0f;
1391   uint hot_idx = 0;
1392   // Loop starts at 2 because slot 1 is the fall-in path
1393   for( i = 2; i < _head->req(); i++ ) {
1394     float cnt = estimate_path_freq(_head->in(i));
1395     if( cnt > hotcnt ) {       // Grab hottest path
1396       warmcnt = hotcnt;
1397       hotcnt = cnt;
1398       hot_idx = i;
1399     } else if( cnt > warmcnt ) { // And 2nd hottest path
1400       warmcnt = cnt;
1401     }
1402   }
1403 
1404   // See if the hottest backedge is worthy of being an inner loop
1405   // by being much hotter than the next hottest backedge.
1406   if( hotcnt <= 0.0001 ||
1407       hotcnt < 2.0*warmcnt ) hot_idx = 0;// No hot backedge
1408 
1409   // Peel out the backedges into a private merge point; peel
1410   // them all except optionally hot_idx.
1411   PhaseIterGVN &igvn = phase->_igvn;
1412 
1413   Node *hot_tail = NULL;
1414   // Make a Region for the merge point
1415   Node *r = new (phase->C) RegionNode(1);
1416   for( i = 2; i < _head->req(); i++ ) {
1417     if( i != hot_idx )
1418       r->add_req( _head->in(i) );
1419     else hot_tail = _head->in(i);
1420   }
1421   igvn.register_new_node_with_optimizer(r, _head);
1422   // Plug region into end of loop _head, followed by hot_tail
1423   while( _head->req() > 3 ) _head->del_req( _head->req()-1 );
1424   _head->set_req(2, r);
1425   if( hot_idx ) _head->add_req(hot_tail);
1426 
1427   // Split all the Phis up between '_head' loop and the Region 'r'
1428   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
1429     Node *out = _head->fast_out(j);
1430     if( out->is_Phi() ) {
1431       PhiNode* n = out->as_Phi();
1432       igvn.hash_delete(n);      // Delete from hash before hacking edges
1433       Node *hot_phi = NULL;
1434       Node *phi = new (phase->C) PhiNode(r, n->type(), n->adr_type());
1435       // Check all inputs for the ones to peel out
1436       uint j = 1;
1437       for( uint i = 2; i < n->req(); i++ ) {
1438         if( i != hot_idx )
1439           phi->set_req( j++, n->in(i) );
1440         else hot_phi = n->in(i);
1441       }
1442       // Register the phi but do not transform until whole place transforms
1443       igvn.register_new_node_with_optimizer(phi, n);
1444       // Add the merge phi to the old Phi
1445       while( n->req() > 3 ) n->del_req( n->req()-1 );
1446       n->set_req(2, phi);
1447       if( hot_idx ) n->add_req(hot_phi);
1448     }
1449   }
1450 
1451 
1452   // Insert a new IdealLoopTree inserted below me.  Turn it into a clone
1453   // of self loop tree.  Turn self into a loop headed by _head and with
1454   // tail being the new merge point.
1455   IdealLoopTree *ilt = new IdealLoopTree( phase, _head, _tail );
1456   phase->set_loop(_tail,ilt);   // Adjust tail
1457   _tail = r;                    // Self's tail is new merge point
1458   phase->set_loop(r,this);
1459   ilt->_child = _child;         // New guy has my children
1460   _child = ilt;                 // Self has new guy as only child
1461   ilt->_parent = this;          // new guy has self for parent
1462   ilt->_nest = _nest;           // Same nesting depth (for now)
1463 
1464   // Starting with 'ilt', look for child loop trees using the same shared
1465   // header.  Flatten these out; they will no longer be loops in the end.
1466   IdealLoopTree **pilt = &_child;
1467   while( ilt ) {
1468     if( ilt->_head == _head ) {
1469       uint i;
1470       for( i = 2; i < _head->req(); i++ )
1471         if( _head->in(i) == ilt->_tail )
1472           break;                // Still a loop
1473       if( i == _head->req() ) { // No longer a loop
1474         // Flatten ilt.  Hang ilt's "_next" list from the end of
1475         // ilt's '_child' list.  Move the ilt's _child up to replace ilt.
1476         IdealLoopTree **cp = &ilt->_child;
1477         while( *cp ) cp = &(*cp)->_next;   // Find end of child list
1478         *cp = ilt->_next;       // Hang next list at end of child list
1479         *pilt = ilt->_child;    // Move child up to replace ilt
1480         ilt->_head = NULL;      // Flag as a loop UNIONED into parent
1481         ilt = ilt->_child;      // Repeat using new ilt
1482         continue;               // do not advance over ilt->_child
1483       }
1484       assert( ilt->_tail == hot_tail, "expected to only find the hot inner loop here" );
1485       phase->set_loop(_head,ilt);
1486     }
1487     pilt = &ilt->_child;        // Advance to next
1488     ilt = *pilt;
1489   }
1490 
1491   if( _child ) fix_parent( _child, this );
1492 }
1493 
1494 //------------------------------beautify_loops---------------------------------
1495 // Split shared headers and insert loop landing pads.
1496 // Insert a LoopNode to replace the RegionNode.
1497 // Return TRUE if loop tree is structurally changed.
1498 bool IdealLoopTree::beautify_loops( PhaseIdealLoop *phase ) {
1499   bool result = false;
1500   // Cache parts in locals for easy
1501   PhaseIterGVN &igvn = phase->_igvn;
1502 
1503   igvn.hash_delete(_head);      // Yank from hash before hacking edges
1504 
1505   // Check for multiple fall-in paths.  Peel off a landing pad if need be.
1506   int fall_in_cnt = 0;
1507   for( uint i = 1; i < _head->req(); i++ )
1508     if( !phase->is_member( this, _head->in(i) ) )
1509       fall_in_cnt++;
1510   assert( fall_in_cnt, "at least 1 fall-in path" );
1511   if( fall_in_cnt > 1 )         // Need a loop landing pad to merge fall-ins
1512     split_fall_in( phase, fall_in_cnt );
1513 
1514   // Swap inputs to the _head and all Phis to move the fall-in edge to
1515   // the left.
1516   fall_in_cnt = 1;
1517   while( phase->is_member( this, _head->in(fall_in_cnt) ) )
1518     fall_in_cnt++;
1519   if( fall_in_cnt > 1 ) {
1520     // Since I am just swapping inputs I do not need to update def-use info
1521     Node *tmp = _head->in(1);
1522     _head->set_req( 1, _head->in(fall_in_cnt) );
1523     _head->set_req( fall_in_cnt, tmp );
1524     // Swap also all Phis
1525     for (DUIterator_Fast imax, i = _head->fast_outs(imax); i < imax; i++) {
1526       Node* phi = _head->fast_out(i);
1527       if( phi->is_Phi() ) {
1528         igvn.hash_delete(phi); // Yank from hash before hacking edges
1529         tmp = phi->in(1);
1530         phi->set_req( 1, phi->in(fall_in_cnt) );
1531         phi->set_req( fall_in_cnt, tmp );
1532       }
1533     }
1534   }
1535   assert( !phase->is_member( this, _head->in(1) ), "left edge is fall-in" );
1536   assert(  phase->is_member( this, _head->in(2) ), "right edge is loop" );
1537 
1538   // If I am a shared header (multiple backedges), peel off the many
1539   // backedges into a private merge point and use the merge point as
1540   // the one true backedge.
1541   if (_head->req() > 3) {
1542     // Merge the many backedges into a single backedge but leave
1543     // the hottest backedge as separate edge for the following peel.
1544     if (!_irreducible) {
1545       merge_many_backedges( phase );
1546     }
1547 
1548     // When recursively beautify my children, split_fall_in can change
1549     // loop tree structure when I am an irreducible loop. Then the head
1550     // of my children has a req() not bigger than 3. Here we need to set
1551     // result to true to catch that case in order to tell the caller to
1552     // rebuild loop tree. See issue JDK-8244407 for details.
1553     result = true;
1554   }
1555 
1556   // If I have one hot backedge, peel off myself loop.
1557   // I better be the outermost loop.
1558   if (_head->req() > 3 && !_irreducible) {
1559     split_outer_loop( phase );
1560     result = true;
1561 
1562   } else if (!_head->is_Loop() && !_irreducible) {
1563     // Make a new LoopNode to replace the old loop head
1564     Node *l = new (phase->C) LoopNode( _head->in(1), _head->in(2) );
1565     l = igvn.register_new_node_with_optimizer(l, _head);
1566     phase->set_created_loop_node();
1567     // Go ahead and replace _head
1568     phase->_igvn.replace_node( _head, l );
1569     _head = l;
1570     phase->set_loop(_head, this);
1571   }
1572 
1573   // Now recursively beautify nested loops
1574   if( _child ) result |= _child->beautify_loops( phase );
1575   if( _next  ) result |= _next ->beautify_loops( phase );
1576   return result;
1577 }
1578 
1579 //------------------------------allpaths_check_safepts----------------------------
1580 // Allpaths backwards scan from loop tail, terminating each path at first safepoint
1581 // encountered.  Helper for check_safepts.
1582 void IdealLoopTree::allpaths_check_safepts(VectorSet &visited, Node_List &stack) {
1583   assert(stack.size() == 0, "empty stack");
1584   stack.push(_tail);
1585   visited.Clear();
1586   visited.set(_tail->_idx);
1587   while (stack.size() > 0) {
1588     Node* n = stack.pop();
1589     if (n->is_Call() && n->as_Call()->guaranteed_safepoint()) {
1590       // Terminate this path
1591     } else if (n->Opcode() == Op_SafePoint) {
1592       if (_phase->get_loop(n) != this) {
1593         if (_required_safept == NULL) _required_safept = new Node_List();
1594         _required_safept->push(n);  // save the one closest to the tail
1595       }
1596       // Terminate this path
1597     } else {
1598       uint start = n->is_Region() ? 1 : 0;
1599       uint end   = n->is_Region() && !n->is_Loop() ? n->req() : start + 1;
1600       for (uint i = start; i < end; i++) {
1601         Node* in = n->in(i);
1602         assert(in->is_CFG(), "must be");
1603         if (!visited.test_set(in->_idx) && is_member(_phase->get_loop(in))) {
1604           stack.push(in);
1605         }
1606       }
1607     }
1608   }
1609 }
1610 
1611 //------------------------------check_safepts----------------------------
1612 // Given dominators, try to find loops with calls that must always be
1613 // executed (call dominates loop tail).  These loops do not need non-call
1614 // safepoints (ncsfpt).
1615 //
1616 // A complication is that a safepoint in a inner loop may be needed
1617 // by an outer loop. In the following, the inner loop sees it has a
1618 // call (block 3) on every path from the head (block 2) to the
1619 // backedge (arc 3->2).  So it deletes the ncsfpt (non-call safepoint)
1620 // in block 2, _but_ this leaves the outer loop without a safepoint.
1621 //
1622 //          entry  0
1623 //                 |
1624 //                 v
1625 // outer 1,2    +->1
1626 //              |  |
1627 //              |  v
1628 //              |  2<---+  ncsfpt in 2
1629 //              |_/|\   |
1630 //                 | v  |
1631 // inner 2,3      /  3  |  call in 3
1632 //               /   |  |
1633 //              v    +--+
1634 //        exit  4
1635 //
1636 //
1637 // This method creates a list (_required_safept) of ncsfpt nodes that must
1638 // be protected is created for each loop. When a ncsfpt maybe deleted, it
1639 // is first looked for in the lists for the outer loops of the current loop.
1640 //
1641 // The insights into the problem:
1642 //  A) counted loops are okay
1643 //  B) innermost loops are okay (only an inner loop can delete
1644 //     a ncsfpt needed by an outer loop)
1645 //  C) a loop is immune from an inner loop deleting a safepoint
1646 //     if the loop has a call on the idom-path
1647 //  D) a loop is also immune if it has a ncsfpt (non-call safepoint) on the
1648 //     idom-path that is not in a nested loop
1649 //  E) otherwise, an ncsfpt on the idom-path that is nested in an inner
1650 //     loop needs to be prevented from deletion by an inner loop
1651 //
1652 // There are two analyses:
1653 //  1) The first, and cheaper one, scans the loop body from
1654 //     tail to head following the idom (immediate dominator)
1655 //     chain, looking for the cases (C,D,E) above.
1656 //     Since inner loops are scanned before outer loops, there is summary
1657 //     information about inner loops.  Inner loops can be skipped over
1658 //     when the tail of an inner loop is encountered.
1659 //
1660 //  2) The second, invoked if the first fails to find a call or ncsfpt on
1661 //     the idom path (which is rare), scans all predecessor control paths
1662 //     from the tail to the head, terminating a path when a call or sfpt
1663 //     is encountered, to find the ncsfpt's that are closest to the tail.
1664 //
1665 void IdealLoopTree::check_safepts(VectorSet &visited, Node_List &stack) {
1666   // Bottom up traversal
1667   IdealLoopTree* ch = _child;
1668   if (_child) _child->check_safepts(visited, stack);
1669   if (_next)  _next ->check_safepts(visited, stack);
1670 
1671   if (!_head->is_CountedLoop() && !_has_sfpt && _parent != NULL && !_irreducible) {
1672     bool  has_call         = false; // call on dom-path
1673     bool  has_local_ncsfpt = false; // ncsfpt on dom-path at this loop depth
1674     Node* nonlocal_ncsfpt  = NULL;  // ncsfpt on dom-path at a deeper depth
1675     // Scan the dom-path nodes from tail to head
1676     for (Node* n = tail(); n != _head; n = _phase->idom(n)) {
1677       if (n->is_Call() && n->as_Call()->guaranteed_safepoint()) {
1678         has_call = true;
1679         _has_sfpt = 1;          // Then no need for a safept!
1680         break;
1681       } else if (n->Opcode() == Op_SafePoint) {
1682         if (_phase->get_loop(n) == this) {
1683           has_local_ncsfpt = true;
1684           break;
1685         }
1686         if (nonlocal_ncsfpt == NULL) {
1687           nonlocal_ncsfpt = n; // save the one closest to the tail
1688         }
1689       } else {
1690         IdealLoopTree* nlpt = _phase->get_loop(n);
1691         if (this != nlpt) {
1692           // If at an inner loop tail, see if the inner loop has already
1693           // recorded seeing a call on the dom-path (and stop.)  If not,
1694           // jump to the head of the inner loop.
1695           assert(is_member(nlpt), "nested loop");
1696           Node* tail = nlpt->_tail;
1697           if (tail->in(0)->is_If()) tail = tail->in(0);
1698           if (n == tail) {
1699             // If inner loop has call on dom-path, so does outer loop
1700             if (nlpt->_has_sfpt) {
1701               has_call = true;
1702               _has_sfpt = 1;
1703               break;
1704             }
1705             // Skip to head of inner loop
1706             assert(_phase->is_dominator(_head, nlpt->_head), "inner head dominated by outer head");
1707             n = nlpt->_head;
1708           }
1709         }
1710       }
1711     }
1712     // Record safept's that this loop needs preserved when an
1713     // inner loop attempts to delete it's safepoints.
1714     if (_child != NULL && !has_call && !has_local_ncsfpt) {
1715       if (nonlocal_ncsfpt != NULL) {
1716         if (_required_safept == NULL) _required_safept = new Node_List();
1717         _required_safept->push(nonlocal_ncsfpt);
1718       } else {
1719         // Failed to find a suitable safept on the dom-path.  Now use
1720         // an all paths walk from tail to head, looking for safepoints to preserve.
1721         allpaths_check_safepts(visited, stack);
1722       }
1723     }
1724   }
1725 }
1726 
1727 //---------------------------is_deleteable_safept----------------------------
1728 // Is safept not required by an outer loop?
1729 bool PhaseIdealLoop::is_deleteable_safept(Node* sfpt) {
1730   assert(sfpt->Opcode() == Op_SafePoint, "");
1731   IdealLoopTree* lp = get_loop(sfpt)->_parent;
1732   while (lp != NULL) {
1733     Node_List* sfpts = lp->_required_safept;
1734     if (sfpts != NULL) {
1735       for (uint i = 0; i < sfpts->size(); i++) {
1736         if (sfpt == sfpts->at(i))
1737           return false;
1738       }
1739     }
1740     lp = lp->_parent;
1741   }
1742   return true;
1743 }
1744 
1745 //---------------------------replace_parallel_iv-------------------------------
1746 // Replace parallel induction variable (parallel to trip counter)
1747 void PhaseIdealLoop::replace_parallel_iv(IdealLoopTree *loop) {
1748   assert(loop->_head->is_CountedLoop(), "");
1749   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1750   if (!cl->is_valid_counted_loop())
1751     return;         // skip malformed counted loop
1752   Node *incr = cl->incr();
1753   if (incr == NULL)
1754     return;         // Dead loop?
1755   Node *init = cl->init_trip();
1756   Node *phi  = cl->phi();
1757   int stride_con = cl->stride_con();
1758 
1759   // Visit all children, looking for Phis
1760   for (DUIterator i = cl->outs(); cl->has_out(i); i++) {
1761     Node *out = cl->out(i);
1762     // Look for other phis (secondary IVs). Skip dead ones
1763     if (!out->is_Phi() || out == phi || !has_node(out))
1764       continue;
1765     PhiNode* phi2 = out->as_Phi();
1766     Node *incr2 = phi2->in( LoopNode::LoopBackControl );
1767     // Look for induction variables of the form:  X += constant
1768     if (phi2->region() != loop->_head ||
1769         incr2->req() != 3 ||
1770         incr2->in(1) != phi2 ||
1771         incr2 == incr ||
1772         incr2->Opcode() != Op_AddI ||
1773         !incr2->in(2)->is_Con())
1774       continue;
1775 
1776     // Check for parallel induction variable (parallel to trip counter)
1777     // via an affine function.  In particular, count-down loops with
1778     // count-up array indices are common. We only RCE references off
1779     // the trip-counter, so we need to convert all these to trip-counter
1780     // expressions.
1781     Node *init2 = phi2->in( LoopNode::EntryControl );
1782     int stride_con2 = incr2->in(2)->get_int();
1783 
1784     // The ratio of the two strides cannot be represented as an int
1785     // if stride_con2 is min_int and stride_con is -1.
1786     if (stride_con2 == min_jint && stride_con == -1) {
1787       continue;
1788     }
1789 
1790     // The general case here gets a little tricky.  We want to find the
1791     // GCD of all possible parallel IV's and make a new IV using this
1792     // GCD for the loop.  Then all possible IVs are simple multiples of
1793     // the GCD.  In practice, this will cover very few extra loops.
1794     // Instead we require 'stride_con2' to be a multiple of 'stride_con',
1795     // where +/-1 is the common case, but other integer multiples are
1796     // also easy to handle.
1797     int ratio_con = stride_con2/stride_con;
1798 
1799     if ((ratio_con * stride_con) == stride_con2) { // Check for exact
1800 #ifndef PRODUCT
1801       if (TraceLoopOpts) {
1802         tty->print("Parallel IV: %d ", phi2->_idx);
1803         loop->dump_head();
1804       }
1805 #endif
1806       // Convert to using the trip counter.  The parallel induction
1807       // variable differs from the trip counter by a loop-invariant
1808       // amount, the difference between their respective initial values.
1809       // It is scaled by the 'ratio_con'.
1810       Node* ratio = _igvn.intcon(ratio_con);
1811       set_ctrl(ratio, C->root());
1812       Node* ratio_init = new (C) MulINode(init, ratio);
1813       _igvn.register_new_node_with_optimizer(ratio_init, init);
1814       set_early_ctrl(ratio_init);
1815       Node* diff = new (C) SubINode(init2, ratio_init);
1816       _igvn.register_new_node_with_optimizer(diff, init2);
1817       set_early_ctrl(diff);
1818       Node* ratio_idx = new (C) MulINode(phi, ratio);
1819       _igvn.register_new_node_with_optimizer(ratio_idx, phi);
1820       set_ctrl(ratio_idx, cl);
1821       Node* add = new (C) AddINode(ratio_idx, diff);
1822       _igvn.register_new_node_with_optimizer(add);
1823       set_ctrl(add, cl);
1824       _igvn.replace_node( phi2, add );
1825       // Sometimes an induction variable is unused
1826       if (add->outcnt() == 0) {
1827         _igvn.remove_dead_node(add);
1828       }
1829       --i; // deleted this phi; rescan starting with next position
1830       continue;
1831     }
1832   }
1833 }
1834 
1835 void IdealLoopTree::remove_safepoints(PhaseIdealLoop* phase, bool keep_one) {
1836   Node* keep = NULL;
1837   if (keep_one) {
1838     // Look for a safepoint on the idom-path.
1839     for (Node* i = tail(); i != _head; i = phase->idom(i)) {
1840       if (i->Opcode() == Op_SafePoint && phase->get_loop(i) == this) {
1841         keep = i;
1842         break; // Found one
1843       }
1844     }
1845   }
1846 
1847   // Don't remove any safepoints if it is requested to keep a single safepoint and
1848   // no safepoint was found on idom-path. It is not safe to remove any safepoint
1849   // in this case since there's no safepoint dominating all paths in the loop body.
1850   bool prune = !keep_one || keep != NULL;
1851 
1852   // Delete other safepoints in this loop.
1853   Node_List* sfpts = _safepts;
1854   if (prune && sfpts != NULL) {
1855     assert(keep == NULL || keep->Opcode() == Op_SafePoint, "not safepoint");
1856     for (uint i = 0; i < sfpts->size(); i++) {
1857       Node* n = sfpts->at(i);
1858       assert(phase->get_loop(n) == this, "");
1859       if (n != keep && phase->is_deleteable_safept(n)) {
1860         phase->lazy_replace(n, n->in(TypeFunc::Control));
1861       }
1862     }
1863   }
1864 }
1865 
1866 //------------------------------counted_loop-----------------------------------
1867 // Convert to counted loops where possible
1868 void IdealLoopTree::counted_loop( PhaseIdealLoop *phase ) {
1869 
1870   // For grins, set the inner-loop flag here
1871   if (!_child) {
1872     if (_head->is_Loop()) _head->as_Loop()->set_inner_loop();
1873   }
1874 
1875   if (_head->is_CountedLoop() ||
1876       phase->is_counted_loop(_head, this)) {
1877 
1878     if (!UseCountedLoopSafepoints) {
1879       // Indicate we do not need a safepoint here
1880       _has_sfpt = 1;
1881     }
1882 
1883     // Remove safepoints
1884     bool keep_one_sfpt = !(_has_call || _has_sfpt);
1885     remove_safepoints(phase, keep_one_sfpt);
1886 
1887     // Look for induction variables
1888     phase->replace_parallel_iv(this);
1889 
1890   } else if (_parent != NULL && !_irreducible) {
1891     // Not a counted loop. Keep one safepoint.
1892     bool keep_one_sfpt = true;
1893     remove_safepoints(phase, keep_one_sfpt);
1894   }
1895 
1896   // Recursively
1897   if (_child) _child->counted_loop( phase );
1898   if (_next)  _next ->counted_loop( phase );
1899 }
1900 
1901 #ifndef PRODUCT
1902 //------------------------------dump_head--------------------------------------
1903 // Dump 1 liner for loop header info
1904 void IdealLoopTree::dump_head( ) const {
1905   for (uint i=0; i<_nest; i++)
1906     tty->print("  ");
1907   tty->print("Loop: N%d/N%d ",_head->_idx,_tail->_idx);
1908   if (_irreducible) tty->print(" IRREDUCIBLE");
1909   Node* entry = _head->in(LoopNode::EntryControl);
1910   if (LoopLimitCheck) {
1911     Node* predicate = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
1912     if (predicate != NULL ) {
1913       tty->print(" limit_check");
1914       entry = entry->in(0)->in(0);
1915     }
1916   }
1917   if (UseLoopPredicate) {
1918     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
1919     if (entry != NULL) {
1920       tty->print(" predicated");
1921     }
1922   }
1923   if (_head->is_CountedLoop()) {
1924     CountedLoopNode *cl = _head->as_CountedLoop();
1925     tty->print(" counted");
1926 
1927     Node* init_n = cl->init_trip();
1928     if (init_n  != NULL &&  init_n->is_Con())
1929       tty->print(" [%d,", cl->init_trip()->get_int());
1930     else
1931       tty->print(" [int,");
1932     Node* limit_n = cl->limit();
1933     if (limit_n  != NULL &&  limit_n->is_Con())
1934       tty->print("%d),", cl->limit()->get_int());
1935     else
1936       tty->print("int),");
1937     int stride_con  = cl->stride_con();
1938     if (stride_con > 0) tty->print("+");
1939     tty->print("%d", stride_con);
1940 
1941     tty->print(" (%d iters) ", (int)cl->profile_trip_cnt());
1942 
1943     if (cl->is_pre_loop ()) tty->print(" pre" );
1944     if (cl->is_main_loop()) tty->print(" main");
1945     if (cl->is_post_loop()) tty->print(" post");
1946   }
1947   if (_has_call) tty->print(" has_call");
1948   if (_has_sfpt) tty->print(" has_sfpt");
1949   if (_rce_candidate) tty->print(" rce");
1950   if (_safepts != NULL && _safepts->size() > 0) {
1951     tty->print(" sfpts={"); _safepts->dump_simple(); tty->print(" }");
1952   }
1953   if (_required_safept != NULL && _required_safept->size() > 0) {
1954     tty->print(" req={"); _required_safept->dump_simple(); tty->print(" }");
1955   }
1956   tty->cr();
1957 }
1958 
1959 //------------------------------dump-------------------------------------------
1960 // Dump loops by loop tree
1961 void IdealLoopTree::dump( ) const {
1962   dump_head();
1963   if (_child) _child->dump();
1964   if (_next)  _next ->dump();
1965 }
1966 
1967 #endif
1968 
1969 static void log_loop_tree(IdealLoopTree* root, IdealLoopTree* loop, CompileLog* log) {
1970   if (loop == root) {
1971     if (loop->_child != NULL) {
1972       log->begin_head("loop_tree");
1973       log->end_head();
1974       if( loop->_child ) log_loop_tree(root, loop->_child, log);
1975       log->tail("loop_tree");
1976       assert(loop->_next == NULL, "what?");
1977     }
1978   } else {
1979     Node* head = loop->_head;
1980     log->begin_head("loop");
1981     log->print(" idx='%d' ", head->_idx);
1982     if (loop->_irreducible) log->print("irreducible='1' ");
1983     if (head->is_Loop()) {
1984       if (head->as_Loop()->is_inner_loop()) log->print("inner_loop='1' ");
1985       if (head->as_Loop()->is_partial_peel_loop()) log->print("partial_peel_loop='1' ");
1986     }
1987     if (head->is_CountedLoop()) {
1988       CountedLoopNode* cl = head->as_CountedLoop();
1989       if (cl->is_pre_loop())  log->print("pre_loop='%d' ",  cl->main_idx());
1990       if (cl->is_main_loop()) log->print("main_loop='%d' ", cl->_idx);
1991       if (cl->is_post_loop()) log->print("post_loop='%d' ",  cl->main_idx());
1992     }
1993     log->end_head();
1994     if( loop->_child ) log_loop_tree(root, loop->_child, log);
1995     log->tail("loop");
1996     if( loop->_next  ) log_loop_tree(root, loop->_next, log);
1997   }
1998 }
1999 
2000 //---------------------collect_potentially_useful_predicates-----------------------
2001 // Helper function to collect potentially useful predicates to prevent them from
2002 // being eliminated by PhaseIdealLoop::eliminate_useless_predicates
2003 void PhaseIdealLoop::collect_potentially_useful_predicates(
2004                          IdealLoopTree * loop, Unique_Node_List &useful_predicates) {
2005   if (loop->_child) { // child
2006     collect_potentially_useful_predicates(loop->_child, useful_predicates);
2007   }
2008 
2009   // self (only loops that we can apply loop predication may use their predicates)
2010   if (loop->_head->is_Loop() &&
2011       !loop->_irreducible    &&
2012       !loop->tail()->is_top()) {
2013     LoopNode* lpn = loop->_head->as_Loop();
2014     Node* entry = lpn->in(LoopNode::EntryControl);
2015     Node* predicate_proj = find_predicate(entry); // loop_limit_check first
2016     if (predicate_proj != NULL ) { // right pattern that can be used by loop predication
2017       assert(entry->in(0)->in(1)->in(1)->Opcode() == Op_Opaque1, "must be");
2018       useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
2019       entry = entry->in(0)->in(0);
2020     }
2021     predicate_proj = find_predicate(entry); // Predicate
2022     if (predicate_proj != NULL ) {
2023       useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
2024     }
2025   }
2026 
2027   if (loop->_next) { // sibling
2028     collect_potentially_useful_predicates(loop->_next, useful_predicates);
2029   }
2030 }
2031 
2032 //------------------------eliminate_useless_predicates-----------------------------
2033 // Eliminate all inserted predicates if they could not be used by loop predication.
2034 // Note: it will also eliminates loop limits check predicate since it also uses
2035 // Opaque1 node (see Parse::add_predicate()).
2036 void PhaseIdealLoop::eliminate_useless_predicates() {
2037   if (C->predicate_count() == 0)
2038     return; // no predicate left
2039 
2040   Unique_Node_List useful_predicates; // to store useful predicates
2041   if (C->has_loops()) {
2042     collect_potentially_useful_predicates(_ltree_root->_child, useful_predicates);
2043   }
2044 
2045   for (int i = C->predicate_count(); i > 0; i--) {
2046      Node * n = C->predicate_opaque1_node(i-1);
2047      assert(n->Opcode() == Op_Opaque1, "must be");
2048      if (!useful_predicates.member(n)) { // not in the useful list
2049        _igvn.replace_node(n, n->in(1));
2050      }
2051   }
2052 }
2053 
2054 //------------------------process_expensive_nodes-----------------------------
2055 // Expensive nodes have their control input set to prevent the GVN
2056 // from commoning them and as a result forcing the resulting node to
2057 // be in a more frequent path. Use CFG information here, to change the
2058 // control inputs so that some expensive nodes can be commoned while
2059 // not executed more frequently.
2060 bool PhaseIdealLoop::process_expensive_nodes() {
2061   assert(OptimizeExpensiveOps, "optimization off?");
2062 
2063   // Sort nodes to bring similar nodes together
2064   C->sort_expensive_nodes();
2065 
2066   bool progress = false;
2067 
2068   for (int i = 0; i < C->expensive_count(); ) {
2069     Node* n = C->expensive_node(i);
2070     int start = i;
2071     // Find nodes similar to n
2072     i++;
2073     for (; i < C->expensive_count() && Compile::cmp_expensive_nodes(n, C->expensive_node(i)) == 0; i++);
2074     int end = i;
2075     // And compare them two by two
2076     for (int j = start; j < end; j++) {
2077       Node* n1 = C->expensive_node(j);
2078       if (is_node_unreachable(n1)) {
2079         continue;
2080       }
2081       for (int k = j+1; k < end; k++) {
2082         Node* n2 = C->expensive_node(k);
2083         if (is_node_unreachable(n2)) {
2084           continue;
2085         }
2086 
2087         assert(n1 != n2, "should be pair of nodes");
2088 
2089         Node* c1 = n1->in(0);
2090         Node* c2 = n2->in(0);
2091 
2092         Node* parent_c1 = c1;
2093         Node* parent_c2 = c2;
2094 
2095         // The call to get_early_ctrl_for_expensive() moves the
2096         // expensive nodes up but stops at loops that are in a if
2097         // branch. See whether we can exit the loop and move above the
2098         // If.
2099         if (c1->is_Loop()) {
2100           parent_c1 = c1->in(1);
2101         }
2102         if (c2->is_Loop()) {
2103           parent_c2 = c2->in(1);
2104         }
2105 
2106         if (parent_c1 == parent_c2) {
2107           _igvn._worklist.push(n1);
2108           _igvn._worklist.push(n2);
2109           continue;
2110         }
2111 
2112         // Look for identical expensive node up the dominator chain.
2113         if (is_dominator(c1, c2)) {
2114           c2 = c1;
2115         } else if (is_dominator(c2, c1)) {
2116           c1 = c2;
2117         } else if (parent_c1->is_Proj() && parent_c1->in(0)->is_If() &&
2118                    parent_c2->is_Proj() && parent_c1->in(0) == parent_c2->in(0)) {
2119           // Both branches have the same expensive node so move it up
2120           // before the if.
2121           c1 = c2 = idom(parent_c1->in(0));
2122         }
2123         // Do the actual moves
2124         if (n1->in(0) != c1) {
2125           _igvn.hash_delete(n1);
2126           n1->set_req(0, c1);
2127           _igvn.hash_insert(n1);
2128           _igvn._worklist.push(n1);
2129           progress = true;
2130         }
2131         if (n2->in(0) != c2) {
2132           _igvn.hash_delete(n2);
2133           n2->set_req(0, c2);
2134           _igvn.hash_insert(n2);
2135           _igvn._worklist.push(n2);
2136           progress = true;
2137         }
2138       }
2139     }
2140   }
2141 
2142   return progress;
2143 }
2144 
2145 
2146 //=============================================================================
2147 //----------------------------build_and_optimize-------------------------------
2148 // Create a PhaseLoop.  Build the ideal Loop tree.  Map each Ideal Node to
2149 // its corresponding LoopNode.  If 'optimize' is true, do some loop cleanups.
2150 void PhaseIdealLoop::build_and_optimize(bool do_split_ifs, bool skip_loop_opts) {
2151   ResourceMark rm;
2152 
2153   int old_progress = C->major_progress();
2154   uint orig_worklist_size = _igvn._worklist.size();
2155 
2156   // Reset major-progress flag for the driver's heuristics
2157   C->clear_major_progress();
2158 
2159 #ifndef PRODUCT
2160   // Capture for later assert
2161   uint unique = C->unique();
2162   _loop_invokes++;
2163   _loop_work += unique;
2164 #endif
2165 
2166   // True if the method has at least 1 irreducible loop
2167   _has_irreducible_loops = false;
2168 
2169   _created_loop_node = false;
2170 
2171   Arena *a = Thread::current()->resource_area();
2172   VectorSet visited(a);
2173   // Pre-grow the mapping from Nodes to IdealLoopTrees.
2174   _nodes.map(C->unique(), NULL);
2175   memset(_nodes.adr(), 0, wordSize * C->unique());
2176 
2177   // Pre-build the top-level outermost loop tree entry
2178   _ltree_root = new IdealLoopTree( this, C->root(), C->root() );
2179   // Do not need a safepoint at the top level
2180   _ltree_root->_has_sfpt = 1;
2181 
2182   // Initialize Dominators.
2183   // Checked in clone_loop_predicate() during beautify_loops().
2184   _idom_size = 0;
2185   _idom      = NULL;
2186   _dom_depth = NULL;
2187   _dom_stk   = NULL;
2188 
2189   // Empty pre-order array
2190   allocate_preorders();
2191 
2192   // Build a loop tree on the fly.  Build a mapping from CFG nodes to
2193   // IdealLoopTree entries.  Data nodes are NOT walked.
2194   build_loop_tree();
2195   // Check for bailout, and return
2196   if (C->failing()) {
2197     return;
2198   }
2199 
2200   // No loops after all
2201   if( !_ltree_root->_child && !_verify_only ) C->set_has_loops(false);
2202 
2203   // There should always be an outer loop containing the Root and Return nodes.
2204   // If not, we have a degenerate empty program.  Bail out in this case.
2205   if (!has_node(C->root())) {
2206     if (!_verify_only) {
2207       C->clear_major_progress();
2208       C->record_method_not_compilable("empty program detected during loop optimization");
2209     }
2210     return;
2211   }
2212 
2213   // Nothing to do, so get out
2214   bool stop_early = !C->has_loops() && !skip_loop_opts && !do_split_ifs && !_verify_me && !_verify_only;
2215   bool do_expensive_nodes = C->should_optimize_expensive_nodes(_igvn);
2216   if (stop_early && !do_expensive_nodes) {
2217     _igvn.optimize();           // Cleanup NeverBranches
2218     return;
2219   }
2220 
2221   // Set loop nesting depth
2222   _ltree_root->set_nest( 0 );
2223 
2224   // Split shared headers and insert loop landing pads.
2225   // Do not bother doing this on the Root loop of course.
2226   if( !_verify_me && !_verify_only && _ltree_root->_child ) {
2227     C->print_method(PHASE_BEFORE_BEAUTIFY_LOOPS, 3);
2228     if( _ltree_root->_child->beautify_loops( this ) ) {
2229       // Re-build loop tree!
2230       _ltree_root->_child = NULL;
2231       _nodes.clear();
2232       reallocate_preorders();
2233       build_loop_tree();
2234       // Check for bailout, and return
2235       if (C->failing()) {
2236         return;
2237       }
2238       // Reset loop nesting depth
2239       _ltree_root->set_nest( 0 );
2240 
2241       C->print_method(PHASE_AFTER_BEAUTIFY_LOOPS, 3);
2242     }
2243   }
2244 
2245   // Build Dominators for elision of NULL checks & loop finding.
2246   // Since nodes do not have a slot for immediate dominator, make
2247   // a persistent side array for that info indexed on node->_idx.
2248   _idom_size = C->unique();
2249   _idom      = NEW_RESOURCE_ARRAY( Node*, _idom_size );
2250   _dom_depth = NEW_RESOURCE_ARRAY( uint,  _idom_size );
2251   _dom_stk   = NULL; // Allocated on demand in recompute_dom_depth
2252   memset( _dom_depth, 0, _idom_size * sizeof(uint) );
2253 
2254   Dominators();
2255 
2256   if (!_verify_only) {
2257     // As a side effect, Dominators removed any unreachable CFG paths
2258     // into RegionNodes.  It doesn't do this test against Root, so
2259     // we do it here.
2260     for( uint i = 1; i < C->root()->req(); i++ ) {
2261       if( !_nodes[C->root()->in(i)->_idx] ) {    // Dead path into Root?
2262         _igvn.delete_input_of(C->root(), i);
2263         i--;                      // Rerun same iteration on compressed edges
2264       }
2265     }
2266 
2267     // Given dominators, try to find inner loops with calls that must
2268     // always be executed (call dominates loop tail).  These loops do
2269     // not need a separate safepoint.
2270     Node_List cisstack(a);
2271     _ltree_root->check_safepts(visited, cisstack);
2272   }
2273 
2274   // Walk the DATA nodes and place into loops.  Find earliest control
2275   // node.  For CFG nodes, the _nodes array starts out and remains
2276   // holding the associated IdealLoopTree pointer.  For DATA nodes, the
2277   // _nodes array holds the earliest legal controlling CFG node.
2278 
2279   // Allocate stack with enough space to avoid frequent realloc
2280   int stack_size = (C->live_nodes() >> 1) + 16; // (live_nodes>>1)+16 from Java2D stats
2281   Node_Stack nstack( a, stack_size );
2282 
2283   visited.Clear();
2284   Node_List worklist(a);
2285   // Don't need C->root() on worklist since
2286   // it will be processed among C->top() inputs
2287   worklist.push( C->top() );
2288   visited.set( C->top()->_idx ); // Set C->top() as visited now
2289   build_loop_early( visited, worklist, nstack );
2290 
2291   // Given early legal placement, try finding counted loops.  This placement
2292   // is good enough to discover most loop invariants.
2293   if( !_verify_me && !_verify_only )
2294     _ltree_root->counted_loop( this );
2295 
2296   // Find latest loop placement.  Find ideal loop placement.
2297   visited.Clear();
2298   init_dom_lca_tags();
2299   // Need C->root() on worklist when processing outs
2300   worklist.push( C->root() );
2301   NOT_PRODUCT( C->verify_graph_edges(); )
2302   worklist.push( C->top() );
2303   build_loop_late( visited, worklist, nstack );
2304 
2305   if (_verify_only) {
2306     // restore major progress flag
2307     for (int i = 0; i < old_progress; i++)
2308       C->set_major_progress();
2309     assert(C->unique() == unique, "verification mode made Nodes? ? ?");
2310     assert(_igvn._worklist.size() == orig_worklist_size, "shouldn't push anything");
2311     return;
2312   }
2313 
2314   // clear out the dead code after build_loop_late
2315   while (_deadlist.size()) {
2316     _igvn.remove_globally_dead_node(_deadlist.pop());
2317   }
2318 
2319   if (stop_early) {
2320     assert(do_expensive_nodes, "why are we here?");
2321     if (process_expensive_nodes()) {
2322       // If we made some progress when processing expensive nodes then
2323       // the IGVN may modify the graph in a way that will allow us to
2324       // make some more progress: we need to try processing expensive
2325       // nodes again.
2326       C->set_major_progress();
2327     }
2328     _igvn.optimize();
2329     return;
2330   }
2331 
2332   // Some parser-inserted loop predicates could never be used by loop
2333   // predication or they were moved away from loop during some optimizations.
2334   // For example, peeling. Eliminate them before next loop optimizations.
2335   if (UseLoopPredicate || LoopLimitCheck) {
2336     eliminate_useless_predicates();
2337   }
2338 
2339 #ifndef PRODUCT
2340   C->verify_graph_edges();
2341   if (_verify_me) {             // Nested verify pass?
2342     // Check to see if the verify mode is broken
2343     assert(C->unique() == unique, "non-optimize mode made Nodes? ? ?");
2344     return;
2345   }
2346   if(VerifyLoopOptimizations) verify();
2347   if(TraceLoopOpts && C->has_loops()) {
2348     _ltree_root->dump();
2349   }
2350 #endif
2351 
2352   if (skip_loop_opts) {
2353     // restore major progress flag
2354     for (int i = 0; i < old_progress; i++) {
2355       C->set_major_progress();
2356     }
2357 
2358     // Cleanup any modified bits
2359     _igvn.optimize();
2360 
2361     if (C->log() != NULL) {
2362       log_loop_tree(_ltree_root, _ltree_root, C->log());
2363     }
2364     return;
2365   }
2366 
2367   if (ReassociateInvariants) {
2368     // Reassociate invariants and prep for split_thru_phi
2369     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2370       IdealLoopTree* lpt = iter.current();
2371       if (!lpt->is_counted() || !lpt->is_inner()) continue;
2372 
2373       lpt->reassociate_invariants(this);
2374 
2375       // Because RCE opportunities can be masked by split_thru_phi,
2376       // look for RCE candidates and inhibit split_thru_phi
2377       // on just their loop-phi's for this pass of loop opts
2378       if (SplitIfBlocks && do_split_ifs) {
2379         if (lpt->policy_range_check(this)) {
2380           lpt->_rce_candidate = 1; // = true
2381         }
2382       }
2383     }
2384   }
2385 
2386   // Check for aggressive application of split-if and other transforms
2387   // that require basic-block info (like cloning through Phi's)
2388   if( SplitIfBlocks && do_split_ifs ) {
2389     visited.Clear();
2390     split_if_with_blocks( visited, nstack );
2391     NOT_PRODUCT( if( VerifyLoopOptimizations ) verify(); );
2392   }
2393 
2394   if (!C->major_progress() && do_expensive_nodes && process_expensive_nodes()) {
2395     C->set_major_progress();
2396   }
2397 
2398   // Perform loop predication before iteration splitting
2399   if (C->has_loops() && !C->major_progress() && (C->predicate_count() > 0)) {
2400     _ltree_root->_child->loop_predication(this);
2401   }
2402 
2403   if (OptimizeFill && UseLoopPredicate && C->has_loops() && !C->major_progress()) {
2404     if (do_intrinsify_fill()) {
2405       C->set_major_progress();
2406     }
2407   }
2408 
2409   // Perform iteration-splitting on inner loops.  Split iterations to avoid
2410   // range checks or one-shot null checks.
2411 
2412   // If split-if's didn't hack the graph too bad (no CFG changes)
2413   // then do loop opts.
2414   if (C->has_loops() && !C->major_progress()) {
2415     memset( worklist.adr(), 0, worklist.Size()*sizeof(Node*) );
2416     _ltree_root->_child->iteration_split( this, worklist );
2417     // No verify after peeling!  GCM has hoisted code out of the loop.
2418     // After peeling, the hoisted code could sink inside the peeled area.
2419     // The peeling code does not try to recompute the best location for
2420     // all the code before the peeled area, so the verify pass will always
2421     // complain about it.
2422   }
2423   // Do verify graph edges in any case
2424   NOT_PRODUCT( C->verify_graph_edges(); );
2425 
2426   if (!do_split_ifs) {
2427     // We saw major progress in Split-If to get here.  We forced a
2428     // pass with unrolling and not split-if, however more split-if's
2429     // might make progress.  If the unrolling didn't make progress
2430     // then the major-progress flag got cleared and we won't try
2431     // another round of Split-If.  In particular the ever-common
2432     // instance-of/check-cast pattern requires at least 2 rounds of
2433     // Split-If to clear out.
2434     C->set_major_progress();
2435   }
2436 
2437   // Repeat loop optimizations if new loops were seen
2438   if (created_loop_node()) {
2439     C->set_major_progress();
2440   }
2441 
2442   // Keep loop predicates and perform optimizations with them
2443   // until no more loop optimizations could be done.
2444   // After that switch predicates off and do more loop optimizations.
2445   if (!C->major_progress() && (C->predicate_count() > 0)) {
2446      C->cleanup_loop_predicates(_igvn);
2447 #ifndef PRODUCT
2448      if (TraceLoopOpts) {
2449        tty->print_cr("PredicatesOff");
2450      }
2451 #endif
2452      C->set_major_progress();
2453   }
2454 
2455   // Convert scalar to superword operations at the end of all loop opts.
2456   if (UseSuperWord && C->has_loops() && !C->major_progress()) {
2457     // SuperWord transform
2458     SuperWord sw(this);
2459     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2460       IdealLoopTree* lpt = iter.current();
2461       if (lpt->is_counted()) {
2462         sw.transform_loop(lpt);
2463       }
2464     }
2465   }
2466 
2467   // Cleanup any modified bits
2468   _igvn.optimize();
2469 
2470   // disable assert until issue with split_flow_path is resolved (6742111)
2471   // assert(!_has_irreducible_loops || C->parsed_irreducible_loop() || C->is_osr_compilation(),
2472   //        "shouldn't introduce irreducible loops");
2473 
2474   if (C->log() != NULL) {
2475     log_loop_tree(_ltree_root, _ltree_root, C->log());
2476   }
2477 }
2478 
2479 #ifndef PRODUCT
2480 //------------------------------print_statistics-------------------------------
2481 int PhaseIdealLoop::_loop_invokes=0;// Count of PhaseIdealLoop invokes
2482 int PhaseIdealLoop::_loop_work=0; // Sum of PhaseIdealLoop x unique
2483 void PhaseIdealLoop::print_statistics() {
2484   tty->print_cr("PhaseIdealLoop=%d, sum _unique=%d", _loop_invokes, _loop_work);
2485 }
2486 
2487 //------------------------------verify-----------------------------------------
2488 // Build a verify-only PhaseIdealLoop, and see that it agrees with me.
2489 static int fail;                // debug only, so its multi-thread dont care
2490 void PhaseIdealLoop::verify() const {
2491   int old_progress = C->major_progress();
2492   ResourceMark rm;
2493   PhaseIdealLoop loop_verify( _igvn, this );
2494   VectorSet visited(Thread::current()->resource_area());
2495 
2496   fail = 0;
2497   verify_compare( C->root(), &loop_verify, visited );
2498   assert( fail == 0, "verify loops failed" );
2499   // Verify loop structure is the same
2500   _ltree_root->verify_tree(loop_verify._ltree_root, NULL);
2501   // Reset major-progress.  It was cleared by creating a verify version of
2502   // PhaseIdealLoop.
2503   for( int i=0; i<old_progress; i++ )
2504     C->set_major_progress();
2505 }
2506 
2507 //------------------------------verify_compare---------------------------------
2508 // Make sure me and the given PhaseIdealLoop agree on key data structures
2509 void PhaseIdealLoop::verify_compare( Node *n, const PhaseIdealLoop *loop_verify, VectorSet &visited ) const {
2510   if( !n ) return;
2511   if( visited.test_set( n->_idx ) ) return;
2512   if( !_nodes[n->_idx] ) {      // Unreachable
2513     assert( !loop_verify->_nodes[n->_idx], "both should be unreachable" );
2514     return;
2515   }
2516 
2517   uint i;
2518   for( i = 0; i < n->req(); i++ )
2519     verify_compare( n->in(i), loop_verify, visited );
2520 
2521   // Check the '_nodes' block/loop structure
2522   i = n->_idx;
2523   if( has_ctrl(n) ) {           // We have control; verify has loop or ctrl
2524     if( _nodes[i] != loop_verify->_nodes[i] &&
2525         get_ctrl_no_update(n) != loop_verify->get_ctrl_no_update(n) ) {
2526       tty->print("Mismatched control setting for: ");
2527       n->dump();
2528       if( fail++ > 10 ) return;
2529       Node *c = get_ctrl_no_update(n);
2530       tty->print("We have it as: ");
2531       if( c->in(0) ) c->dump();
2532         else tty->print_cr("N%d",c->_idx);
2533       tty->print("Verify thinks: ");
2534       if( loop_verify->has_ctrl(n) )
2535         loop_verify->get_ctrl_no_update(n)->dump();
2536       else
2537         loop_verify->get_loop_idx(n)->dump();
2538       tty->cr();
2539     }
2540   } else {                    // We have a loop
2541     IdealLoopTree *us = get_loop_idx(n);
2542     if( loop_verify->has_ctrl(n) ) {
2543       tty->print("Mismatched loop setting for: ");
2544       n->dump();
2545       if( fail++ > 10 ) return;
2546       tty->print("We have it as: ");
2547       us->dump();
2548       tty->print("Verify thinks: ");
2549       loop_verify->get_ctrl_no_update(n)->dump();
2550       tty->cr();
2551     } else if (!C->major_progress()) {
2552       // Loop selection can be messed up if we did a major progress
2553       // operation, like split-if.  Do not verify in that case.
2554       IdealLoopTree *them = loop_verify->get_loop_idx(n);
2555       if( us->_head != them->_head ||  us->_tail != them->_tail ) {
2556         tty->print("Unequals loops for: ");
2557         n->dump();
2558         if( fail++ > 10 ) return;
2559         tty->print("We have it as: ");
2560         us->dump();
2561         tty->print("Verify thinks: ");
2562         them->dump();
2563         tty->cr();
2564       }
2565     }
2566   }
2567 
2568   // Check for immediate dominators being equal
2569   if( i >= _idom_size ) {
2570     if( !n->is_CFG() ) return;
2571     tty->print("CFG Node with no idom: ");
2572     n->dump();
2573     return;
2574   }
2575   if( !n->is_CFG() ) return;
2576   if( n == C->root() ) return; // No IDOM here
2577 
2578   assert(n->_idx == i, "sanity");
2579   Node *id = idom_no_update(n);
2580   if( id != loop_verify->idom_no_update(n) ) {
2581     tty->print("Unequals idoms for: ");
2582     n->dump();
2583     if( fail++ > 10 ) return;
2584     tty->print("We have it as: ");
2585     id->dump();
2586     tty->print("Verify thinks: ");
2587     loop_verify->idom_no_update(n)->dump();
2588     tty->cr();
2589   }
2590 
2591 }
2592 
2593 //------------------------------verify_tree------------------------------------
2594 // Verify that tree structures match.  Because the CFG can change, siblings
2595 // within the loop tree can be reordered.  We attempt to deal with that by
2596 // reordering the verify's loop tree if possible.
2597 void IdealLoopTree::verify_tree(IdealLoopTree *loop, const IdealLoopTree *parent) const {
2598   assert( _parent == parent, "Badly formed loop tree" );
2599 
2600   // Siblings not in same order?  Attempt to re-order.
2601   if( _head != loop->_head ) {
2602     // Find _next pointer to update
2603     IdealLoopTree **pp = &loop->_parent->_child;
2604     while( *pp != loop )
2605       pp = &((*pp)->_next);
2606     // Find proper sibling to be next
2607     IdealLoopTree **nn = &loop->_next;
2608     while( (*nn) && (*nn)->_head != _head )
2609       nn = &((*nn)->_next);
2610 
2611     // Check for no match.
2612     if( !(*nn) ) {
2613       // Annoyingly, irreducible loops can pick different headers
2614       // after a major_progress operation, so the rest of the loop
2615       // tree cannot be matched.
2616       if (_irreducible && Compile::current()->major_progress())  return;
2617       assert( 0, "failed to match loop tree" );
2618     }
2619 
2620     // Move (*nn) to (*pp)
2621     IdealLoopTree *hit = *nn;
2622     *nn = hit->_next;
2623     hit->_next = loop;
2624     *pp = loop;
2625     loop = hit;
2626     // Now try again to verify
2627   }
2628 
2629   assert( _head  == loop->_head , "mismatched loop head" );
2630   Node *tail = _tail;           // Inline a non-updating version of
2631   while( !tail->in(0) )         // the 'tail()' call.
2632     tail = tail->in(1);
2633   assert( tail == loop->_tail, "mismatched loop tail" );
2634 
2635   // Counted loops that are guarded should be able to find their guards
2636   if( _head->is_CountedLoop() && _head->as_CountedLoop()->is_main_loop() ) {
2637     CountedLoopNode *cl = _head->as_CountedLoop();
2638     Node *init = cl->init_trip();
2639     Node *ctrl = cl->in(LoopNode::EntryControl);
2640     assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
2641     Node *iff  = ctrl->in(0);
2642     assert( iff->Opcode() == Op_If, "" );
2643     Node *bol  = iff->in(1);
2644     assert( bol->Opcode() == Op_Bool, "" );
2645     Node *cmp  = bol->in(1);
2646     assert( cmp->Opcode() == Op_CmpI, "" );
2647     Node *add  = cmp->in(1);
2648     Node *opaq;
2649     if( add->Opcode() == Op_Opaque1 ) {
2650       opaq = add;
2651     } else {
2652       assert( add->Opcode() == Op_AddI || add->Opcode() == Op_ConI , "" );
2653       assert( add == init, "" );
2654       opaq = cmp->in(2);
2655     }
2656     assert( opaq->Opcode() == Op_Opaque1, "" );
2657 
2658   }
2659 
2660   if (_child != NULL)  _child->verify_tree(loop->_child, this);
2661   if (_next  != NULL)  _next ->verify_tree(loop->_next,  parent);
2662   // Innermost loops need to verify loop bodies,
2663   // but only if no 'major_progress'
2664   int fail = 0;
2665   if (!Compile::current()->major_progress() && _child == NULL) {
2666     for( uint i = 0; i < _body.size(); i++ ) {
2667       Node *n = _body.at(i);
2668       if (n->outcnt() == 0)  continue; // Ignore dead
2669       uint j;
2670       for( j = 0; j < loop->_body.size(); j++ )
2671         if( loop->_body.at(j) == n )
2672           break;
2673       if( j == loop->_body.size() ) { // Not found in loop body
2674         // Last ditch effort to avoid assertion: Its possible that we
2675         // have some users (so outcnt not zero) but are still dead.
2676         // Try to find from root.
2677         if (Compile::current()->root()->find(n->_idx)) {
2678           fail++;
2679           tty->print("We have that verify does not: ");
2680           n->dump();
2681         }
2682       }
2683     }
2684     for( uint i2 = 0; i2 < loop->_body.size(); i2++ ) {
2685       Node *n = loop->_body.at(i2);
2686       if (n->outcnt() == 0)  continue; // Ignore dead
2687       uint j;
2688       for( j = 0; j < _body.size(); j++ )
2689         if( _body.at(j) == n )
2690           break;
2691       if( j == _body.size() ) { // Not found in loop body
2692         // Last ditch effort to avoid assertion: Its possible that we
2693         // have some users (so outcnt not zero) but are still dead.
2694         // Try to find from root.
2695         if (Compile::current()->root()->find(n->_idx)) {
2696           fail++;
2697           tty->print("Verify has that we do not: ");
2698           n->dump();
2699         }
2700       }
2701     }
2702     assert( !fail, "loop body mismatch" );
2703   }
2704 }
2705 
2706 #endif
2707 
2708 //------------------------------set_idom---------------------------------------
2709 void PhaseIdealLoop::set_idom(Node* d, Node* n, uint dom_depth) {
2710   uint idx = d->_idx;
2711   if (idx >= _idom_size) {
2712     uint newsize = _idom_size<<1;
2713     while( idx >= newsize ) {
2714       newsize <<= 1;
2715     }
2716     _idom      = REALLOC_RESOURCE_ARRAY( Node*,     _idom,_idom_size,newsize);
2717     _dom_depth = REALLOC_RESOURCE_ARRAY( uint, _dom_depth,_idom_size,newsize);
2718     memset( _dom_depth + _idom_size, 0, (newsize - _idom_size) * sizeof(uint) );
2719     _idom_size = newsize;
2720   }
2721   _idom[idx] = n;
2722   _dom_depth[idx] = dom_depth;
2723 }
2724 
2725 //------------------------------recompute_dom_depth---------------------------------------
2726 // The dominator tree is constructed with only parent pointers.
2727 // This recomputes the depth in the tree by first tagging all
2728 // nodes as "no depth yet" marker.  The next pass then runs up
2729 // the dom tree from each node marked "no depth yet", and computes
2730 // the depth on the way back down.
2731 void PhaseIdealLoop::recompute_dom_depth() {
2732   uint no_depth_marker = C->unique();
2733   uint i;
2734   // Initialize depth to "no depth yet"
2735   for (i = 0; i < _idom_size; i++) {
2736     if (_dom_depth[i] > 0 && _idom[i] != NULL) {
2737      _dom_depth[i] = no_depth_marker;
2738     }
2739   }
2740   if (_dom_stk == NULL) {
2741     uint init_size = C->live_nodes() / 100; // Guess that 1/100 is a reasonable initial size.
2742     if (init_size < 10) init_size = 10;
2743     _dom_stk = new GrowableArray<uint>(init_size);
2744   }
2745   // Compute new depth for each node.
2746   for (i = 0; i < _idom_size; i++) {
2747     uint j = i;
2748     // Run up the dom tree to find a node with a depth
2749     while (_dom_depth[j] == no_depth_marker) {
2750       _dom_stk->push(j);
2751       j = _idom[j]->_idx;
2752     }
2753     // Compute the depth on the way back down this tree branch
2754     uint dd = _dom_depth[j] + 1;
2755     while (_dom_stk->length() > 0) {
2756       uint j = _dom_stk->pop();
2757       _dom_depth[j] = dd;
2758       dd++;
2759     }
2760   }
2761 }
2762 
2763 //------------------------------sort-------------------------------------------
2764 // Insert 'loop' into the existing loop tree.  'innermost' is a leaf of the
2765 // loop tree, not the root.
2766 IdealLoopTree *PhaseIdealLoop::sort( IdealLoopTree *loop, IdealLoopTree *innermost ) {
2767   if( !innermost ) return loop; // New innermost loop
2768 
2769   int loop_preorder = get_preorder(loop->_head); // Cache pre-order number
2770   assert( loop_preorder, "not yet post-walked loop" );
2771   IdealLoopTree **pp = &innermost;      // Pointer to previous next-pointer
2772   IdealLoopTree *l = *pp;               // Do I go before or after 'l'?
2773 
2774   // Insert at start of list
2775   while( l ) {                  // Insertion sort based on pre-order
2776     if( l == loop ) return innermost; // Already on list!
2777     int l_preorder = get_preorder(l->_head); // Cache pre-order number
2778     assert( l_preorder, "not yet post-walked l" );
2779     // Check header pre-order number to figure proper nesting
2780     if( loop_preorder > l_preorder )
2781       break;                    // End of insertion
2782     // If headers tie (e.g., shared headers) check tail pre-order numbers.
2783     // Since I split shared headers, you'd think this could not happen.
2784     // BUT: I must first do the preorder numbering before I can discover I
2785     // have shared headers, so the split headers all get the same preorder
2786     // number as the RegionNode they split from.
2787     if( loop_preorder == l_preorder &&
2788         get_preorder(loop->_tail) < get_preorder(l->_tail) )
2789       break;                    // Also check for shared headers (same pre#)
2790     pp = &l->_parent;           // Chain up list
2791     l = *pp;
2792   }
2793   // Link into list
2794   // Point predecessor to me
2795   *pp = loop;
2796   // Point me to successor
2797   IdealLoopTree *p = loop->_parent;
2798   loop->_parent = l;            // Point me to successor
2799   if( p ) sort( p, innermost ); // Insert my parents into list as well
2800   return innermost;
2801 }
2802 
2803 //------------------------------build_loop_tree--------------------------------
2804 // I use a modified Vick/Tarjan algorithm.  I need pre- and a post- visit
2805 // bits.  The _nodes[] array is mapped by Node index and holds a NULL for
2806 // not-yet-pre-walked, pre-order # for pre-but-not-post-walked and holds the
2807 // tightest enclosing IdealLoopTree for post-walked.
2808 //
2809 // During my forward walk I do a short 1-layer lookahead to see if I can find
2810 // a loop backedge with that doesn't have any work on the backedge.  This
2811 // helps me construct nested loops with shared headers better.
2812 //
2813 // Once I've done the forward recursion, I do the post-work.  For each child
2814 // I check to see if there is a backedge.  Backedges define a loop!  I
2815 // insert an IdealLoopTree at the target of the backedge.
2816 //
2817 // During the post-work I also check to see if I have several children
2818 // belonging to different loops.  If so, then this Node is a decision point
2819 // where control flow can choose to change loop nests.  It is at this
2820 // decision point where I can figure out how loops are nested.  At this
2821 // time I can properly order the different loop nests from my children.
2822 // Note that there may not be any backedges at the decision point!
2823 //
2824 // Since the decision point can be far removed from the backedges, I can't
2825 // order my loops at the time I discover them.  Thus at the decision point
2826 // I need to inspect loop header pre-order numbers to properly nest my
2827 // loops.  This means I need to sort my childrens' loops by pre-order.
2828 // The sort is of size number-of-control-children, which generally limits
2829 // it to size 2 (i.e., I just choose between my 2 target loops).
2830 void PhaseIdealLoop::build_loop_tree() {
2831   // Allocate stack of size C->live_nodes()/2 to avoid frequent realloc
2832   GrowableArray <Node *> bltstack(C->live_nodes() >> 1);
2833   Node *n = C->root();
2834   bltstack.push(n);
2835   int pre_order = 1;
2836   int stack_size;
2837 
2838   while ( ( stack_size = bltstack.length() ) != 0 ) {
2839     n = bltstack.top(); // Leave node on stack
2840     if ( !is_visited(n) ) {
2841       // ---- Pre-pass Work ----
2842       // Pre-walked but not post-walked nodes need a pre_order number.
2843 
2844       set_preorder_visited( n, pre_order ); // set as visited
2845 
2846       // ---- Scan over children ----
2847       // Scan first over control projections that lead to loop headers.
2848       // This helps us find inner-to-outer loops with shared headers better.
2849 
2850       // Scan children's children for loop headers.
2851       for ( int i = n->outcnt() - 1; i >= 0; --i ) {
2852         Node* m = n->raw_out(i);       // Child
2853         if( m->is_CFG() && !is_visited(m) ) { // Only for CFG children
2854           // Scan over children's children to find loop
2855           for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
2856             Node* l = m->fast_out(j);
2857             if( is_visited(l) &&       // Been visited?
2858                 !is_postvisited(l) &&  // But not post-visited
2859                 get_preorder(l) < pre_order ) { // And smaller pre-order
2860               // Found!  Scan the DFS down this path before doing other paths
2861               bltstack.push(m);
2862               break;
2863             }
2864           }
2865         }
2866       }
2867       pre_order++;
2868     }
2869     else if ( !is_postvisited(n) ) {
2870       // Note: build_loop_tree_impl() adds out edges on rare occasions,
2871       // such as com.sun.rsasign.am::a.
2872       // For non-recursive version, first, process current children.
2873       // On next iteration, check if additional children were added.
2874       for ( int k = n->outcnt() - 1; k >= 0; --k ) {
2875         Node* u = n->raw_out(k);
2876         if ( u->is_CFG() && !is_visited(u) ) {
2877           bltstack.push(u);
2878         }
2879       }
2880       if ( bltstack.length() == stack_size ) {
2881         // There were no additional children, post visit node now
2882         (void)bltstack.pop(); // Remove node from stack
2883         pre_order = build_loop_tree_impl( n, pre_order );
2884         // Check for bailout
2885         if (C->failing()) {
2886           return;
2887         }
2888         // Check to grow _preorders[] array for the case when
2889         // build_loop_tree_impl() adds new nodes.
2890         check_grow_preorders();
2891       }
2892     }
2893     else {
2894       (void)bltstack.pop(); // Remove post-visited node from stack
2895     }
2896   }
2897 }
2898 
2899 //------------------------------build_loop_tree_impl---------------------------
2900 int PhaseIdealLoop::build_loop_tree_impl( Node *n, int pre_order ) {
2901   // ---- Post-pass Work ----
2902   // Pre-walked but not post-walked nodes need a pre_order number.
2903 
2904   // Tightest enclosing loop for this Node
2905   IdealLoopTree *innermost = NULL;
2906 
2907   // For all children, see if any edge is a backedge.  If so, make a loop
2908   // for it.  Then find the tightest enclosing loop for the self Node.
2909   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
2910     Node* m = n->fast_out(i);   // Child
2911     if( n == m ) continue;      // Ignore control self-cycles
2912     if( !m->is_CFG() ) continue;// Ignore non-CFG edges
2913 
2914     IdealLoopTree *l;           // Child's loop
2915     if( !is_postvisited(m) ) {  // Child visited but not post-visited?
2916       // Found a backedge
2917       assert( get_preorder(m) < pre_order, "should be backedge" );
2918       // Check for the RootNode, which is already a LoopNode and is allowed
2919       // to have multiple "backedges".
2920       if( m == C->root()) {     // Found the root?
2921         l = _ltree_root;        // Root is the outermost LoopNode
2922       } else {                  // Else found a nested loop
2923         // Insert a LoopNode to mark this loop.
2924         l = new IdealLoopTree(this, m, n);
2925       } // End of Else found a nested loop
2926       if( !has_loop(m) )        // If 'm' does not already have a loop set
2927         set_loop(m, l);         // Set loop header to loop now
2928 
2929     } else {                    // Else not a nested loop
2930       if( !_nodes[m->_idx] ) continue; // Dead code has no loop
2931       l = get_loop(m);          // Get previously determined loop
2932       // If successor is header of a loop (nest), move up-loop till it
2933       // is a member of some outer enclosing loop.  Since there are no
2934       // shared headers (I've split them already) I only need to go up
2935       // at most 1 level.
2936       while( l && l->_head == m ) // Successor heads loop?
2937         l = l->_parent;         // Move up 1 for me
2938       // If this loop is not properly parented, then this loop
2939       // has no exit path out, i.e. its an infinite loop.
2940       if( !l ) {
2941         // Make loop "reachable" from root so the CFG is reachable.  Basically
2942         // insert a bogus loop exit that is never taken.  'm', the loop head,
2943         // points to 'n', one (of possibly many) fall-in paths.  There may be
2944         // many backedges as well.
2945 
2946         // Here I set the loop to be the root loop.  I could have, after
2947         // inserting a bogus loop exit, restarted the recursion and found my
2948         // new loop exit.  This would make the infinite loop a first-class
2949         // loop and it would then get properly optimized.  What's the use of
2950         // optimizing an infinite loop?
2951         l = _ltree_root;        // Oops, found infinite loop
2952 
2953         if (!_verify_only) {
2954           // Insert the NeverBranch between 'm' and it's control user.
2955           NeverBranchNode *iff = new (C) NeverBranchNode( m );
2956           _igvn.register_new_node_with_optimizer(iff);
2957           set_loop(iff, l);
2958           Node *if_t = new (C) CProjNode( iff, 0 );
2959           _igvn.register_new_node_with_optimizer(if_t);
2960           set_loop(if_t, l);
2961 
2962           Node* cfg = NULL;       // Find the One True Control User of m
2963           for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
2964             Node* x = m->fast_out(j);
2965             if (x->is_CFG() && x != m && x != iff)
2966               { cfg = x; break; }
2967           }
2968           assert(cfg != NULL, "must find the control user of m");
2969           uint k = 0;             // Probably cfg->in(0)
2970           while( cfg->in(k) != m ) k++; // But check incase cfg is a Region
2971           cfg->set_req( k, if_t ); // Now point to NeverBranch
2972 
2973           // Now create the never-taken loop exit
2974           Node *if_f = new (C) CProjNode( iff, 1 );
2975           _igvn.register_new_node_with_optimizer(if_f);
2976           set_loop(if_f, l);
2977           // Find frame ptr for Halt.  Relies on the optimizer
2978           // V-N'ing.  Easier and quicker than searching through
2979           // the program structure.
2980           Node *frame = new (C) ParmNode( C->start(), TypeFunc::FramePtr );
2981           _igvn.register_new_node_with_optimizer(frame);
2982           // Halt & Catch Fire
2983           Node *halt = new (C) HaltNode( if_f, frame );
2984           _igvn.register_new_node_with_optimizer(halt);
2985           set_loop(halt, l);
2986           C->root()->add_req(halt);
2987         }
2988         set_loop(C->root(), _ltree_root);
2989       }
2990     }
2991     // Weeny check for irreducible.  This child was already visited (this
2992     // IS the post-work phase).  Is this child's loop header post-visited
2993     // as well?  If so, then I found another entry into the loop.
2994     if (!_verify_only) {
2995       while( is_postvisited(l->_head) ) {
2996         // found irreducible
2997         l->_irreducible = 1; // = true
2998         l = l->_parent;
2999         _has_irreducible_loops = true;
3000         // Check for bad CFG here to prevent crash, and bailout of compile
3001         if (l == NULL) {
3002           C->record_method_not_compilable("unhandled CFG detected during loop optimization");
3003           return pre_order;
3004         }
3005       }
3006       C->set_has_irreducible_loop(_has_irreducible_loops);
3007     }
3008 
3009     // This Node might be a decision point for loops.  It is only if
3010     // it's children belong to several different loops.  The sort call
3011     // does a trivial amount of work if there is only 1 child or all
3012     // children belong to the same loop.  If however, the children
3013     // belong to different loops, the sort call will properly set the
3014     // _parent pointers to show how the loops nest.
3015     //
3016     // In any case, it returns the tightest enclosing loop.
3017     innermost = sort( l, innermost );
3018   }
3019 
3020   // Def-use info will have some dead stuff; dead stuff will have no
3021   // loop decided on.
3022 
3023   // Am I a loop header?  If so fix up my parent's child and next ptrs.
3024   if( innermost && innermost->_head == n ) {
3025     assert( get_loop(n) == innermost, "" );
3026     IdealLoopTree *p = innermost->_parent;
3027     IdealLoopTree *l = innermost;
3028     while( p && l->_head == n ) {
3029       l->_next = p->_child;     // Put self on parents 'next child'
3030       p->_child = l;            // Make self as first child of parent
3031       l = p;                    // Now walk up the parent chain
3032       p = l->_parent;
3033     }
3034   } else {
3035     // Note that it is possible for a LoopNode to reach here, if the
3036     // backedge has been made unreachable (hence the LoopNode no longer
3037     // denotes a Loop, and will eventually be removed).
3038 
3039     // Record tightest enclosing loop for self.  Mark as post-visited.
3040     set_loop(n, innermost);
3041     // Also record has_call flag early on
3042     if( innermost ) {
3043       if( n->is_Call() && !n->is_CallLeaf() && !n->is_macro() ) {
3044         // Do not count uncommon calls
3045         if( !n->is_CallStaticJava() || !n->as_CallStaticJava()->_name ) {
3046           Node *iff = n->in(0)->in(0);
3047           // No any calls for vectorized loops.
3048           if( UseSuperWord || !iff->is_If() ||
3049               (n->in(0)->Opcode() == Op_IfFalse &&
3050                (1.0 - iff->as_If()->_prob) >= 0.01) ||
3051               (iff->as_If()->_prob >= 0.01) )
3052             innermost->_has_call = 1;
3053         }
3054       } else if( n->is_Allocate() && n->as_Allocate()->_is_scalar_replaceable ) {
3055         // Disable loop optimizations if the loop has a scalar replaceable
3056         // allocation. This disabling may cause a potential performance lost
3057         // if the allocation is not eliminated for some reason.
3058         innermost->_allow_optimizations = false;
3059         innermost->_has_call = 1; // = true
3060       } else if (n->Opcode() == Op_SafePoint) {
3061         // Record all safepoints in this loop.
3062         if (innermost->_safepts == NULL) innermost->_safepts = new Node_List();
3063         innermost->_safepts->push(n);
3064       }
3065     }
3066   }
3067 
3068   // Flag as post-visited now
3069   set_postvisited(n);
3070   return pre_order;
3071 }
3072 
3073 
3074 //------------------------------build_loop_early-------------------------------
3075 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
3076 // First pass computes the earliest controlling node possible.  This is the
3077 // controlling input with the deepest dominating depth.
3078 void PhaseIdealLoop::build_loop_early( VectorSet &visited, Node_List &worklist, Node_Stack &nstack ) {
3079   while (worklist.size() != 0) {
3080     // Use local variables nstack_top_n & nstack_top_i to cache values
3081     // on nstack's top.
3082     Node *nstack_top_n = worklist.pop();
3083     uint  nstack_top_i = 0;
3084 //while_nstack_nonempty:
3085     while (true) {
3086       // Get parent node and next input's index from stack's top.
3087       Node  *n = nstack_top_n;
3088       uint   i = nstack_top_i;
3089       uint cnt = n->req(); // Count of inputs
3090       if (i == 0) {        // Pre-process the node.
3091         if( has_node(n) &&            // Have either loop or control already?
3092             !has_ctrl(n) ) {          // Have loop picked out already?
3093           // During "merge_many_backedges" we fold up several nested loops
3094           // into a single loop.  This makes the members of the original
3095           // loop bodies pointing to dead loops; they need to move up
3096           // to the new UNION'd larger loop.  I set the _head field of these
3097           // dead loops to NULL and the _parent field points to the owning
3098           // loop.  Shades of UNION-FIND algorithm.
3099           IdealLoopTree *ilt;
3100           while( !(ilt = get_loop(n))->_head ) {
3101             // Normally I would use a set_loop here.  But in this one special
3102             // case, it is legal (and expected) to change what loop a Node
3103             // belongs to.
3104             _nodes.map(n->_idx, (Node*)(ilt->_parent) );
3105           }
3106           // Remove safepoints ONLY if I've already seen I don't need one.
3107           // (the old code here would yank a 2nd safepoint after seeing a
3108           // first one, even though the 1st did not dominate in the loop body
3109           // and thus could be avoided indefinitely)
3110           if( !_verify_only && !_verify_me && ilt->_has_sfpt && n->Opcode() == Op_SafePoint &&
3111               is_deleteable_safept(n)) {
3112             Node *in = n->in(TypeFunc::Control);
3113             lazy_replace(n,in);       // Pull safepoint now
3114             if (ilt->_safepts != NULL) {
3115               ilt->_safepts->yank(n);
3116             }
3117             // Carry on with the recursion "as if" we are walking
3118             // only the control input
3119             if( !visited.test_set( in->_idx ) ) {
3120               worklist.push(in);      // Visit this guy later, using worklist
3121             }
3122             // Get next node from nstack:
3123             // - skip n's inputs processing by setting i > cnt;
3124             // - we also will not call set_early_ctrl(n) since
3125             //   has_node(n) == true (see the condition above).
3126             i = cnt + 1;
3127           }
3128         }
3129       } // if (i == 0)
3130 
3131       // Visit all inputs
3132       bool done = true;       // Assume all n's inputs will be processed
3133       while (i < cnt) {
3134         Node *in = n->in(i);
3135         ++i;
3136         if (in == NULL) continue;
3137         if (in->pinned() && !in->is_CFG())
3138           set_ctrl(in, in->in(0));
3139         int is_visited = visited.test_set( in->_idx );
3140         if (!has_node(in)) {  // No controlling input yet?
3141           assert( !in->is_CFG(), "CFG Node with no controlling input?" );
3142           assert( !is_visited, "visit only once" );
3143           nstack.push(n, i);  // Save parent node and next input's index.
3144           nstack_top_n = in;  // Process current input now.
3145           nstack_top_i = 0;
3146           done = false;       // Not all n's inputs processed.
3147           break; // continue while_nstack_nonempty;
3148         } else if (!is_visited) {
3149           // This guy has a location picked out for him, but has not yet
3150           // been visited.  Happens to all CFG nodes, for instance.
3151           // Visit him using the worklist instead of recursion, to break
3152           // cycles.  Since he has a location already we do not need to
3153           // find his location before proceeding with the current Node.
3154           worklist.push(in);  // Visit this guy later, using worklist
3155         }
3156       }
3157       if (done) {
3158         // All of n's inputs have been processed, complete post-processing.
3159 
3160         // Compute earliest point this Node can go.
3161         // CFG, Phi, pinned nodes already know their controlling input.
3162         if (!has_node(n)) {
3163           // Record earliest legal location
3164           set_early_ctrl( n );
3165         }
3166         if (nstack.is_empty()) {
3167           // Finished all nodes on stack.
3168           // Process next node on the worklist.
3169           break;
3170         }
3171         // Get saved parent node and next input's index.
3172         nstack_top_n = nstack.node();
3173         nstack_top_i = nstack.index();
3174         nstack.pop();
3175       }
3176     } // while (true)
3177   }
3178 }
3179 
3180 //------------------------------dom_lca_internal--------------------------------
3181 // Pair-wise LCA
3182 Node *PhaseIdealLoop::dom_lca_internal( Node *n1, Node *n2 ) const {
3183   if( !n1 ) return n2;          // Handle NULL original LCA
3184   assert( n1->is_CFG(), "" );
3185   assert( n2->is_CFG(), "" );
3186   // find LCA of all uses
3187   uint d1 = dom_depth(n1);
3188   uint d2 = dom_depth(n2);
3189   while (n1 != n2) {
3190     if (d1 > d2) {
3191       n1 =      idom(n1);
3192       d1 = dom_depth(n1);
3193     } else if (d1 < d2) {
3194       n2 =      idom(n2);
3195       d2 = dom_depth(n2);
3196     } else {
3197       // Here d1 == d2.  Due to edits of the dominator-tree, sections
3198       // of the tree might have the same depth.  These sections have
3199       // to be searched more carefully.
3200 
3201       // Scan up all the n1's with equal depth, looking for n2.
3202       Node *t1 = idom(n1);
3203       while (dom_depth(t1) == d1) {
3204         if (t1 == n2)  return n2;
3205         t1 = idom(t1);
3206       }
3207       // Scan up all the n2's with equal depth, looking for n1.
3208       Node *t2 = idom(n2);
3209       while (dom_depth(t2) == d2) {
3210         if (t2 == n1)  return n1;
3211         t2 = idom(t2);
3212       }
3213       // Move up to a new dominator-depth value as well as up the dom-tree.
3214       n1 = t1;
3215       n2 = t2;
3216       d1 = dom_depth(n1);
3217       d2 = dom_depth(n2);
3218     }
3219   }
3220   return n1;
3221 }
3222 
3223 //------------------------------compute_idom-----------------------------------
3224 // Locally compute IDOM using dom_lca call.  Correct only if the incoming
3225 // IDOMs are correct.
3226 Node *PhaseIdealLoop::compute_idom( Node *region ) const {
3227   assert( region->is_Region(), "" );
3228   Node *LCA = NULL;
3229   for( uint i = 1; i < region->req(); i++ ) {
3230     if( region->in(i) != C->top() )
3231       LCA = dom_lca( LCA, region->in(i) );
3232   }
3233   return LCA;
3234 }
3235 
3236 bool PhaseIdealLoop::verify_dominance(Node* n, Node* use, Node* LCA, Node* early) {
3237   bool had_error = false;
3238 #ifdef ASSERT
3239   if (early != C->root()) {
3240     // Make sure that there's a dominance path from LCA to early
3241     Node* d = LCA;
3242     while (d != early) {
3243       if (d == C->root()) {
3244         dump_bad_graph("Bad graph detected in compute_lca_of_uses", n, early, LCA);
3245         tty->print_cr("*** Use %d isn't dominated by def %d ***", use->_idx, n->_idx);
3246         had_error = true;
3247         break;
3248       }
3249       d = idom(d);
3250     }
3251   }
3252 #endif
3253   return had_error;
3254 }
3255 
3256 
3257 Node* PhaseIdealLoop::compute_lca_of_uses(Node* n, Node* early, bool verify) {
3258   // Compute LCA over list of uses
3259   bool had_error = false;
3260   Node *LCA = NULL;
3261   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax && LCA != early; i++) {
3262     Node* c = n->fast_out(i);
3263     if (_nodes[c->_idx] == NULL)
3264       continue;                 // Skip the occasional dead node
3265     if( c->is_Phi() ) {         // For Phis, we must land above on the path
3266       for( uint j=1; j<c->req(); j++ ) {// For all inputs
3267         if( c->in(j) == n ) {   // Found matching input?
3268           Node *use = c->in(0)->in(j);
3269           if (_verify_only && use->is_top()) continue;
3270           LCA = dom_lca_for_get_late_ctrl( LCA, use, n );
3271           if (verify) had_error = verify_dominance(n, use, LCA, early) || had_error;
3272         }
3273       }
3274     } else {
3275       // For CFG data-users, use is in the block just prior
3276       Node *use = has_ctrl(c) ? get_ctrl(c) : c->in(0);
3277       LCA = dom_lca_for_get_late_ctrl( LCA, use, n );
3278       if (verify) had_error = verify_dominance(n, use, LCA, early) || had_error;
3279     }
3280   }
3281   assert(!had_error, "bad dominance");
3282   return LCA;
3283 }
3284 
3285 // Check the shape of the graph at the loop entry. In some cases,
3286 // the shape of the graph does not match the shape outlined below.
3287 // That is caused by the Opaque1 node "protecting" the shape of
3288 // the graph being removed by, for example, the IGVN performed
3289 // in PhaseIdealLoop::build_and_optimize().
3290 //
3291 // After the Opaque1 node has been removed, optimizations (e.g., split-if,
3292 // loop unswitching, and IGVN, or a combination of them) can freely change
3293 // the graph's shape. As a result, the graph shape outlined below cannot
3294 // be guaranteed anymore.
3295 bool PhaseIdealLoop::is_canonical_main_loop_entry(CountedLoopNode* cl) {
3296   assert(cl->is_main_loop(), "check should be applied to main loops");
3297   Node* ctrl = cl->in(LoopNode::EntryControl);
3298   if (ctrl == NULL || (!ctrl->is_IfTrue() && !ctrl->is_IfFalse())) {
3299     return false;
3300   }
3301   Node* iffm = ctrl->in(0);
3302   if (iffm == NULL || !iffm->is_If()) {
3303     return false;
3304   }
3305   Node* bolzm = iffm->in(1);
3306   if (bolzm == NULL || !bolzm->is_Bool()) {
3307     return false;
3308   }
3309   Node* cmpzm = bolzm->in(1);
3310   if (cmpzm == NULL || !cmpzm->is_Cmp()) {
3311     return false;
3312   }
3313   Node* opqzm = cmpzm->in(2);
3314   if (opqzm == NULL || opqzm->Opcode() != Op_Opaque1) {
3315     return false;
3316   }
3317   return true;
3318 }
3319 
3320 //------------------------------get_late_ctrl----------------------------------
3321 // Compute latest legal control.
3322 Node *PhaseIdealLoop::get_late_ctrl( Node *n, Node *early ) {
3323   assert(early != NULL, "early control should not be NULL");
3324 
3325   Node* LCA = compute_lca_of_uses(n, early);
3326 #ifdef ASSERT
3327   if (LCA == C->root() && LCA != early) {
3328     // def doesn't dominate uses so print some useful debugging output
3329     compute_lca_of_uses(n, early, true);
3330   }
3331 #endif
3332 
3333   // if this is a load, check for anti-dependent stores
3334   // We use a conservative algorithm to identify potential interfering
3335   // instructions and for rescheduling the load.  The users of the memory
3336   // input of this load are examined.  Any use which is not a load and is
3337   // dominated by early is considered a potentially interfering store.
3338   // This can produce false positives.
3339   if (n->is_Load() && LCA != early) {
3340     Node_List worklist;
3341 
3342     Node *mem = n->in(MemNode::Memory);
3343     for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
3344       Node* s = mem->fast_out(i);
3345       worklist.push(s);
3346     }
3347     while(worklist.size() != 0 && LCA != early) {
3348       Node* s = worklist.pop();
3349       if (s->is_Load()) {
3350         continue;
3351       } else if (s->is_MergeMem()) {
3352         for (DUIterator_Fast imax, i = s->fast_outs(imax); i < imax; i++) {
3353           Node* s1 = s->fast_out(i);
3354           worklist.push(s1);
3355         }
3356       } else {
3357         Node *sctrl = has_ctrl(s) ? get_ctrl(s) : s->in(0);
3358         assert(sctrl != NULL || s->outcnt() == 0, "must have control");
3359         if (sctrl != NULL && !sctrl->is_top() && is_dominator(early, sctrl)) {
3360           LCA = dom_lca_for_get_late_ctrl(LCA, sctrl, n);
3361         }
3362       }
3363     }
3364   }
3365 
3366   assert(LCA == find_non_split_ctrl(LCA), "unexpected late control");
3367   return LCA;
3368 }
3369 
3370 // true if CFG node d dominates CFG node n
3371 bool PhaseIdealLoop::is_dominator(Node *d, Node *n) {
3372   if (d == n)
3373     return true;
3374   assert(d->is_CFG() && n->is_CFG(), "must have CFG nodes");
3375   uint dd = dom_depth(d);
3376   while (dom_depth(n) >= dd) {
3377     if (n == d)
3378       return true;
3379     n = idom(n);
3380   }
3381   return false;
3382 }
3383 
3384 //------------------------------dom_lca_for_get_late_ctrl_internal-------------
3385 // Pair-wise LCA with tags.
3386 // Tag each index with the node 'tag' currently being processed
3387 // before advancing up the dominator chain using idom().
3388 // Later calls that find a match to 'tag' know that this path has already
3389 // been considered in the current LCA (which is input 'n1' by convention).
3390 // Since get_late_ctrl() is only called once for each node, the tag array
3391 // does not need to be cleared between calls to get_late_ctrl().
3392 // Algorithm trades a larger constant factor for better asymptotic behavior
3393 //
3394 Node *PhaseIdealLoop::dom_lca_for_get_late_ctrl_internal( Node *n1, Node *n2, Node *tag ) {
3395   uint d1 = dom_depth(n1);
3396   uint d2 = dom_depth(n2);
3397 
3398   do {
3399     if (d1 > d2) {
3400       // current lca is deeper than n2
3401       _dom_lca_tags.map(n1->_idx, tag);
3402       n1 =      idom(n1);
3403       d1 = dom_depth(n1);
3404     } else if (d1 < d2) {
3405       // n2 is deeper than current lca
3406       Node *memo = _dom_lca_tags[n2->_idx];
3407       if( memo == tag ) {
3408         return n1;    // Return the current LCA
3409       }
3410       _dom_lca_tags.map(n2->_idx, tag);
3411       n2 =      idom(n2);
3412       d2 = dom_depth(n2);
3413     } else {
3414       // Here d1 == d2.  Due to edits of the dominator-tree, sections
3415       // of the tree might have the same depth.  These sections have
3416       // to be searched more carefully.
3417 
3418       // Scan up all the n1's with equal depth, looking for n2.
3419       _dom_lca_tags.map(n1->_idx, tag);
3420       Node *t1 = idom(n1);
3421       while (dom_depth(t1) == d1) {
3422         if (t1 == n2)  return n2;
3423         _dom_lca_tags.map(t1->_idx, tag);
3424         t1 = idom(t1);
3425       }
3426       // Scan up all the n2's with equal depth, looking for n1.
3427       _dom_lca_tags.map(n2->_idx, tag);
3428       Node *t2 = idom(n2);
3429       while (dom_depth(t2) == d2) {
3430         if (t2 == n1)  return n1;
3431         _dom_lca_tags.map(t2->_idx, tag);
3432         t2 = idom(t2);
3433       }
3434       // Move up to a new dominator-depth value as well as up the dom-tree.
3435       n1 = t1;
3436       n2 = t2;
3437       d1 = dom_depth(n1);
3438       d2 = dom_depth(n2);
3439     }
3440   } while (n1 != n2);
3441   return n1;
3442 }
3443 
3444 //------------------------------init_dom_lca_tags------------------------------
3445 // Tag could be a node's integer index, 32bits instead of 64bits in some cases
3446 // Intended use does not involve any growth for the array, so it could
3447 // be of fixed size.
3448 void PhaseIdealLoop::init_dom_lca_tags() {
3449   uint limit = C->unique() + 1;
3450   _dom_lca_tags.map( limit, NULL );
3451 #ifdef ASSERT
3452   for( uint i = 0; i < limit; ++i ) {
3453     assert(_dom_lca_tags[i] == NULL, "Must be distinct from each node pointer");
3454   }
3455 #endif // ASSERT
3456 }
3457 
3458 //------------------------------clear_dom_lca_tags------------------------------
3459 // Tag could be a node's integer index, 32bits instead of 64bits in some cases
3460 // Intended use does not involve any growth for the array, so it could
3461 // be of fixed size.
3462 void PhaseIdealLoop::clear_dom_lca_tags() {
3463   uint limit = C->unique() + 1;
3464   _dom_lca_tags.map( limit, NULL );
3465   _dom_lca_tags.clear();
3466 #ifdef ASSERT
3467   for( uint i = 0; i < limit; ++i ) {
3468     assert(_dom_lca_tags[i] == NULL, "Must be distinct from each node pointer");
3469   }
3470 #endif // ASSERT
3471 }
3472 
3473 //------------------------------build_loop_late--------------------------------
3474 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
3475 // Second pass finds latest legal placement, and ideal loop placement.
3476 void PhaseIdealLoop::build_loop_late( VectorSet &visited, Node_List &worklist, Node_Stack &nstack ) {
3477   while (worklist.size() != 0) {
3478     Node *n = worklist.pop();
3479     // Only visit once
3480     if (visited.test_set(n->_idx)) continue;
3481     uint cnt = n->outcnt();
3482     uint   i = 0;
3483     while (true) {
3484       assert( _nodes[n->_idx], "no dead nodes" );
3485       // Visit all children
3486       if (i < cnt) {
3487         Node* use = n->raw_out(i);
3488         ++i;
3489         // Check for dead uses.  Aggressively prune such junk.  It might be
3490         // dead in the global sense, but still have local uses so I cannot
3491         // easily call 'remove_dead_node'.
3492         if( _nodes[use->_idx] != NULL || use->is_top() ) { // Not dead?
3493           // Due to cycles, we might not hit the same fixed point in the verify
3494           // pass as we do in the regular pass.  Instead, visit such phis as
3495           // simple uses of the loop head.
3496           if( use->in(0) && (use->is_CFG() || use->is_Phi()) ) {
3497             if( !visited.test(use->_idx) )
3498               worklist.push(use);
3499           } else if( !visited.test_set(use->_idx) ) {
3500             nstack.push(n, i); // Save parent and next use's index.
3501             n   = use;         // Process all children of current use.
3502             cnt = use->outcnt();
3503             i   = 0;
3504           }
3505         } else {
3506           // Do not visit around the backedge of loops via data edges.
3507           // push dead code onto a worklist
3508           _deadlist.push(use);
3509         }
3510       } else {
3511         // All of n's children have been processed, complete post-processing.
3512         build_loop_late_post(n);
3513         if (nstack.is_empty()) {
3514           // Finished all nodes on stack.
3515           // Process next node on the worklist.
3516           break;
3517         }
3518         // Get saved parent node and next use's index. Visit the rest of uses.
3519         n   = nstack.node();
3520         cnt = n->outcnt();
3521         i   = nstack.index();
3522         nstack.pop();
3523       }
3524     }
3525   }
3526 }
3527 
3528 //------------------------------build_loop_late_post---------------------------
3529 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
3530 // Second pass finds latest legal placement, and ideal loop placement.
3531 void PhaseIdealLoop::build_loop_late_post( Node *n ) {
3532 
3533   if (n->req() == 2 && n->Opcode() == Op_ConvI2L && !C->major_progress() && !_verify_only) {
3534     _igvn._worklist.push(n);  // Maybe we'll normalize it, if no more loops.
3535   }
3536 
3537 #ifdef ASSERT
3538   if (_verify_only && !n->is_CFG()) {
3539     // Check def-use domination.
3540     compute_lca_of_uses(n, get_ctrl(n), true /* verify */);
3541   }
3542 #endif
3543 
3544   // CFG and pinned nodes already handled
3545   if( n->in(0) ) {
3546     if( n->in(0)->is_top() ) return; // Dead?
3547 
3548     // We'd like +VerifyLoopOptimizations to not believe that Mod's/Loads
3549     // _must_ be pinned (they have to observe their control edge of course).
3550     // Unlike Stores (which modify an unallocable resource, the memory
3551     // state), Mods/Loads can float around.  So free them up.
3552     bool pinned = true;
3553     switch( n->Opcode() ) {
3554     case Op_DivI:
3555     case Op_DivF:
3556     case Op_DivD:
3557     case Op_ModI:
3558     case Op_ModF:
3559     case Op_ModD:
3560     case Op_LoadB:              // Same with Loads; they can sink
3561     case Op_LoadUB:             // during loop optimizations.
3562     case Op_LoadUS:
3563     case Op_LoadD:
3564     case Op_LoadF:
3565     case Op_LoadI:
3566     case Op_LoadKlass:
3567     case Op_LoadNKlass:
3568     case Op_LoadL:
3569     case Op_LoadS:
3570     case Op_LoadP:
3571     case Op_LoadN:
3572     case Op_LoadRange:
3573     case Op_LoadD_unaligned:
3574     case Op_LoadL_unaligned:
3575     case Op_StrComp:            // Does a bunch of load-like effects
3576     case Op_StrEquals:
3577     case Op_StrIndexOf:
3578     case Op_AryEq:
3579       pinned = false;
3580     }
3581     if( pinned ) {
3582       IdealLoopTree *chosen_loop = get_loop(n->is_CFG() ? n : get_ctrl(n));
3583       if( !chosen_loop->_child )       // Inner loop?
3584         chosen_loop->_body.push(n); // Collect inner loops
3585       return;
3586     }
3587   } else {                      // No slot zero
3588     if( n->is_CFG() ) {         // CFG with no slot 0 is dead
3589       _nodes.map(n->_idx,0);    // No block setting, it's globally dead
3590       return;
3591     }
3592     assert(!n->is_CFG() || n->outcnt() == 0, "");
3593   }
3594 
3595   // Do I have a "safe range" I can select over?
3596   Node *early = get_ctrl(n);// Early location already computed
3597 
3598   // Compute latest point this Node can go
3599   Node *LCA = get_late_ctrl( n, early );
3600   // LCA is NULL due to uses being dead
3601   if( LCA == NULL ) {
3602 #ifdef ASSERT
3603     for (DUIterator i1 = n->outs(); n->has_out(i1); i1++) {
3604       assert( _nodes[n->out(i1)->_idx] == NULL, "all uses must also be dead");
3605     }
3606 #endif
3607     _nodes.map(n->_idx, 0);     // This node is useless
3608     _deadlist.push(n);
3609     return;
3610   }
3611   assert(LCA != NULL && !LCA->is_top(), "no dead nodes");
3612 
3613   Node *legal = LCA;            // Walk 'legal' up the IDOM chain
3614   Node *least = legal;          // Best legal position so far
3615   while( early != legal ) {     // While not at earliest legal
3616 #ifdef ASSERT
3617     if (legal->is_Start() && !early->is_Root()) {
3618       // Bad graph. Print idom path and fail.
3619       dump_bad_graph("Bad graph detected in build_loop_late", n, early, LCA);
3620       assert(false, "Bad graph detected in build_loop_late");
3621     }
3622 #endif
3623     // Find least loop nesting depth
3624     legal = idom(legal);        // Bump up the IDOM tree
3625     // Check for lower nesting depth
3626     if( get_loop(legal)->_nest < get_loop(least)->_nest )
3627       least = legal;
3628   }
3629   assert(early == legal || legal != C->root(), "bad dominance of inputs");
3630 
3631   // Try not to place code on a loop entry projection
3632   // which can inhibit range check elimination.
3633   if (least != early) {
3634     Node* ctrl_out = least->unique_ctrl_out();
3635     if (ctrl_out && ctrl_out->is_CountedLoop() &&
3636         least == ctrl_out->in(LoopNode::EntryControl)) {
3637       Node* least_dom = idom(least);
3638       if (get_loop(least_dom)->is_member(get_loop(least))) {
3639         least = least_dom;
3640       }
3641     }
3642   }
3643 
3644 #ifdef ASSERT
3645   // If verifying, verify that 'verify_me' has a legal location
3646   // and choose it as our location.
3647   if( _verify_me ) {
3648     Node *v_ctrl = _verify_me->get_ctrl_no_update(n);
3649     Node *legal = LCA;
3650     while( early != legal ) {   // While not at earliest legal
3651       if( legal == v_ctrl ) break;  // Check for prior good location
3652       legal = idom(legal)      ;// Bump up the IDOM tree
3653     }
3654     // Check for prior good location
3655     if( legal == v_ctrl ) least = legal; // Keep prior if found
3656   }
3657 #endif
3658 
3659   // Assign discovered "here or above" point
3660   least = find_non_split_ctrl(least);
3661   set_ctrl(n, least);
3662 
3663   // Collect inner loop bodies
3664   IdealLoopTree *chosen_loop = get_loop(least);
3665   if( !chosen_loop->_child )   // Inner loop?
3666     chosen_loop->_body.push(n);// Collect inner loops
3667 }
3668 
3669 #ifdef ASSERT
3670 void PhaseIdealLoop::dump_bad_graph(const char* msg, Node* n, Node* early, Node* LCA) {
3671   tty->print_cr("%s", msg);
3672   tty->print("n: "); n->dump();
3673   tty->print("early(n): "); early->dump();
3674   if (n->in(0) != NULL  && !n->in(0)->is_top() &&
3675       n->in(0) != early && !n->in(0)->is_Root()) {
3676     tty->print("n->in(0): "); n->in(0)->dump();
3677   }
3678   for (uint i = 1; i < n->req(); i++) {
3679     Node* in1 = n->in(i);
3680     if (in1 != NULL && in1 != n && !in1->is_top()) {
3681       tty->print("n->in(%d): ", i); in1->dump();
3682       Node* in1_early = get_ctrl(in1);
3683       tty->print("early(n->in(%d)): ", i); in1_early->dump();
3684       if (in1->in(0) != NULL     && !in1->in(0)->is_top() &&
3685           in1->in(0) != in1_early && !in1->in(0)->is_Root()) {
3686         tty->print("n->in(%d)->in(0): ", i); in1->in(0)->dump();
3687       }
3688       for (uint j = 1; j < in1->req(); j++) {
3689         Node* in2 = in1->in(j);
3690         if (in2 != NULL && in2 != n && in2 != in1 && !in2->is_top()) {
3691           tty->print("n->in(%d)->in(%d): ", i, j); in2->dump();
3692           Node* in2_early = get_ctrl(in2);
3693           tty->print("early(n->in(%d)->in(%d)): ", i, j); in2_early->dump();
3694           if (in2->in(0) != NULL     && !in2->in(0)->is_top() &&
3695               in2->in(0) != in2_early && !in2->in(0)->is_Root()) {
3696             tty->print("n->in(%d)->in(%d)->in(0): ", i, j); in2->in(0)->dump();
3697           }
3698         }
3699       }
3700     }
3701   }
3702   tty->cr();
3703   tty->print("LCA(n): "); LCA->dump();
3704   for (uint i = 0; i < n->outcnt(); i++) {
3705     Node* u1 = n->raw_out(i);
3706     if (u1 == n)
3707       continue;
3708     tty->print("n->out(%d): ", i); u1->dump();
3709     if (u1->is_CFG()) {
3710       for (uint j = 0; j < u1->outcnt(); j++) {
3711         Node* u2 = u1->raw_out(j);
3712         if (u2 != u1 && u2 != n && u2->is_CFG()) {
3713           tty->print("n->out(%d)->out(%d): ", i, j); u2->dump();
3714         }
3715       }
3716     } else {
3717       Node* u1_later = get_ctrl(u1);
3718       tty->print("later(n->out(%d)): ", i); u1_later->dump();
3719       if (u1->in(0) != NULL     && !u1->in(0)->is_top() &&
3720           u1->in(0) != u1_later && !u1->in(0)->is_Root()) {
3721         tty->print("n->out(%d)->in(0): ", i); u1->in(0)->dump();
3722       }
3723       for (uint j = 0; j < u1->outcnt(); j++) {
3724         Node* u2 = u1->raw_out(j);
3725         if (u2 == n || u2 == u1)
3726           continue;
3727         tty->print("n->out(%d)->out(%d): ", i, j); u2->dump();
3728         if (!u2->is_CFG()) {
3729           Node* u2_later = get_ctrl(u2);
3730           tty->print("later(n->out(%d)->out(%d)): ", i, j); u2_later->dump();
3731           if (u2->in(0) != NULL     && !u2->in(0)->is_top() &&
3732               u2->in(0) != u2_later && !u2->in(0)->is_Root()) {
3733             tty->print("n->out(%d)->in(0): ", i); u2->in(0)->dump();
3734           }
3735         }
3736       }
3737     }
3738   }
3739   tty->cr();
3740   int ct = 0;
3741   Node *dbg_legal = LCA;
3742   while(!dbg_legal->is_Start() && ct < 100) {
3743     tty->print("idom[%d] ",ct); dbg_legal->dump();
3744     ct++;
3745     dbg_legal = idom(dbg_legal);
3746   }
3747   tty->cr();
3748 }
3749 #endif
3750 
3751 #ifndef PRODUCT
3752 //------------------------------dump-------------------------------------------
3753 void PhaseIdealLoop::dump( ) const {
3754   ResourceMark rm;
3755   Arena* arena = Thread::current()->resource_area();
3756   Node_Stack stack(arena, C->live_nodes() >> 2);
3757   Node_List rpo_list;
3758   VectorSet visited(arena);
3759   visited.set(C->top()->_idx);
3760   rpo( C->root(), stack, visited, rpo_list );
3761   // Dump root loop indexed by last element in PO order
3762   dump( _ltree_root, rpo_list.size(), rpo_list );
3763 }
3764 
3765 void PhaseIdealLoop::dump( IdealLoopTree *loop, uint idx, Node_List &rpo_list ) const {
3766   loop->dump_head();
3767 
3768   // Now scan for CFG nodes in the same loop
3769   for( uint j=idx; j > 0;  j-- ) {
3770     Node *n = rpo_list[j-1];
3771     if( !_nodes[n->_idx] )      // Skip dead nodes
3772       continue;
3773     if( get_loop(n) != loop ) { // Wrong loop nest
3774       if( get_loop(n)->_head == n &&    // Found nested loop?
3775           get_loop(n)->_parent == loop )
3776         dump(get_loop(n),rpo_list.size(),rpo_list);     // Print it nested-ly
3777       continue;
3778     }
3779 
3780     // Dump controlling node
3781     for( uint x = 0; x < loop->_nest; x++ )
3782       tty->print("  ");
3783     tty->print("C");
3784     if( n == C->root() ) {
3785       n->dump();
3786     } else {
3787       Node* cached_idom   = idom_no_update(n);
3788       Node *computed_idom = n->in(0);
3789       if( n->is_Region() ) {
3790         computed_idom = compute_idom(n);
3791         // computed_idom() will return n->in(0) when idom(n) is an IfNode (or
3792         // any MultiBranch ctrl node), so apply a similar transform to
3793         // the cached idom returned from idom_no_update.
3794         cached_idom = find_non_split_ctrl(cached_idom);
3795       }
3796       tty->print(" ID:%d",computed_idom->_idx);
3797       n->dump();
3798       if( cached_idom != computed_idom ) {
3799         tty->print_cr("*** BROKEN IDOM!  Computed as: %d, cached as: %d",
3800                       computed_idom->_idx, cached_idom->_idx);
3801       }
3802     }
3803     // Dump nodes it controls
3804     for( uint k = 0; k < _nodes.Size(); k++ ) {
3805       // (k < C->unique() && get_ctrl(find(k)) == n)
3806       if (k < C->unique() && _nodes[k] == (Node*)((intptr_t)n + 1)) {
3807         Node *m = C->root()->find(k);
3808         if( m && m->outcnt() > 0 ) {
3809           if (!(has_ctrl(m) && get_ctrl_no_update(m) == n)) {
3810             tty->print_cr("*** BROKEN CTRL ACCESSOR!  _nodes[k] is %p, ctrl is %p",
3811                           _nodes[k], has_ctrl(m) ? get_ctrl_no_update(m) : NULL);
3812           }
3813           for( uint j = 0; j < loop->_nest; j++ )
3814             tty->print("  ");
3815           tty->print(" ");
3816           m->dump();
3817         }
3818       }
3819     }
3820   }
3821 }
3822 
3823 // Collect a R-P-O for the whole CFG.
3824 // Result list is in post-order (scan backwards for RPO)
3825 void PhaseIdealLoop::rpo( Node *start, Node_Stack &stk, VectorSet &visited, Node_List &rpo_list ) const {
3826   stk.push(start, 0);
3827   visited.set(start->_idx);
3828 
3829   while (stk.is_nonempty()) {
3830     Node* m   = stk.node();
3831     uint  idx = stk.index();
3832     if (idx < m->outcnt()) {
3833       stk.set_index(idx + 1);
3834       Node* n = m->raw_out(idx);
3835       if (n->is_CFG() && !visited.test_set(n->_idx)) {
3836         stk.push(n, 0);
3837       }
3838     } else {
3839       rpo_list.push(m);
3840       stk.pop();
3841     }
3842   }
3843 }
3844 #endif
3845 
3846 
3847 //=============================================================================
3848 //------------------------------LoopTreeIterator-----------------------------------
3849 
3850 // Advance to next loop tree using a preorder, left-to-right traversal.
3851 void LoopTreeIterator::next() {
3852   assert(!done(), "must not be done.");
3853   if (_curnt->_child != NULL) {
3854     _curnt = _curnt->_child;
3855   } else if (_curnt->_next != NULL) {
3856     _curnt = _curnt->_next;
3857   } else {
3858     while (_curnt != _root && _curnt->_next == NULL) {
3859       _curnt = _curnt->_parent;
3860     }
3861     if (_curnt == _root) {
3862       _curnt = NULL;
3863       assert(done(), "must be done.");
3864     } else {
3865       assert(_curnt->_next != NULL, "must be more to do");
3866       _curnt = _curnt->_next;
3867     }
3868   }
3869 }