1 /*
   2  * Copyright (c) 1998, 2018, 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 "gc/shared/barrierSet.hpp"
  29 #include "gc/shared/c2/barrierSetC2.hpp"
  30 #include "libadt/vectset.hpp"
  31 #include "memory/allocation.inline.hpp"
  32 #include "memory/resourceArea.hpp"
  33 #include "opto/addnode.hpp"
  34 #include "opto/callnode.hpp"
  35 #include "opto/connode.hpp"
  36 #include "opto/convertnode.hpp"
  37 #include "opto/divnode.hpp"
  38 #include "opto/idealGraphPrinter.hpp"
  39 #include "opto/loopnode.hpp"
  40 #include "opto/mulnode.hpp"
  41 #include "opto/rootnode.hpp"
  42 #include "opto/superword.hpp"
  43 
  44 //=============================================================================
  45 //------------------------------is_loop_iv-------------------------------------
  46 // Determine if a node is Counted loop induction variable.
  47 // The method is declared in node.hpp.
  48 const Node* Node::is_loop_iv() const {
  49   if (this->is_Phi() && !this->as_Phi()->is_copy() &&
  50       this->as_Phi()->region()->is_CountedLoop() &&
  51       this->as_Phi()->region()->as_CountedLoop()->phi() == this) {
  52     return this;
  53   } else {
  54     return NULL;
  55   }
  56 }
  57 
  58 //=============================================================================
  59 //------------------------------dump_spec--------------------------------------
  60 // Dump special per-node info
  61 #ifndef PRODUCT
  62 void LoopNode::dump_spec(outputStream *st) const {
  63   if (is_inner_loop()) st->print( "inner " );
  64   if (is_partial_peel_loop()) st->print( "partial_peel " );
  65   if (partial_peel_has_failed()) st->print( "partial_peel_failed " );
  66 }
  67 #endif
  68 
  69 //------------------------------is_valid_counted_loop-------------------------
  70 bool LoopNode::is_valid_counted_loop() const {
  71   if (is_CountedLoop()) {
  72     CountedLoopNode*    l  = as_CountedLoop();
  73     CountedLoopEndNode* le = l->loopexit_or_null();
  74     if (le != NULL &&
  75         le->proj_out_or_null(1 /* true */) == l->in(LoopNode::LoopBackControl)) {
  76       Node* phi  = l->phi();
  77       Node* exit = le->proj_out_or_null(0 /* false */);
  78       if (exit != NULL && exit->Opcode() == Op_IfFalse &&
  79           phi != NULL && phi->is_Phi() &&
  80           phi->in(LoopNode::LoopBackControl) == l->incr() &&
  81           le->loopnode() == l && le->stride_is_con()) {
  82         return true;
  83       }
  84     }
  85   }
  86   return false;
  87 }
  88 
  89 //------------------------------get_early_ctrl---------------------------------
  90 // Compute earliest legal control
  91 Node *PhaseIdealLoop::get_early_ctrl( Node *n ) {
  92   assert( !n->is_Phi() && !n->is_CFG(), "this code only handles data nodes" );
  93   uint i;
  94   Node *early;
  95   if (n->in(0) && !n->is_expensive()) {
  96     early = n->in(0);
  97     if (!early->is_CFG()) // Might be a non-CFG multi-def
  98       early = get_ctrl(early);        // So treat input as a straight data input
  99     i = 1;
 100   } else {
 101     early = get_ctrl(n->in(1));
 102     i = 2;
 103   }
 104   uint e_d = dom_depth(early);
 105   assert( early, "" );
 106   for (; i < n->req(); i++) {
 107     Node *cin = get_ctrl(n->in(i));
 108     assert( cin, "" );
 109     // Keep deepest dominator depth
 110     uint c_d = dom_depth(cin);
 111     if (c_d > e_d) {           // Deeper guy?
 112       early = cin;              // Keep deepest found so far
 113       e_d = c_d;
 114     } else if (c_d == e_d &&    // Same depth?
 115                early != cin) { // If not equal, must use slower algorithm
 116       // If same depth but not equal, one _must_ dominate the other
 117       // and we want the deeper (i.e., dominated) guy.
 118       Node *n1 = early;
 119       Node *n2 = cin;
 120       while (1) {
 121         n1 = idom(n1);          // Walk up until break cycle
 122         n2 = idom(n2);
 123         if (n1 == cin ||        // Walked early up to cin
 124             dom_depth(n2) < c_d)
 125           break;                // early is deeper; keep him
 126         if (n2 == early ||      // Walked cin up to early
 127             dom_depth(n1) < c_d) {
 128           early = cin;          // cin is deeper; keep him
 129           break;
 130         }
 131       }
 132       e_d = dom_depth(early);   // Reset depth register cache
 133     }
 134   }
 135 
 136   // Return earliest legal location
 137   assert(early == find_non_split_ctrl(early), "unexpected early control");
 138 
 139   if (n->is_expensive() && !_verify_only && !_verify_me) {
 140     assert(n->in(0), "should have control input");
 141     early = get_early_ctrl_for_expensive(n, early);
 142   }
 143 
 144   return early;
 145 }
 146 
 147 //------------------------------get_early_ctrl_for_expensive---------------------------------
 148 // Move node up the dominator tree as high as legal while still beneficial
 149 Node *PhaseIdealLoop::get_early_ctrl_for_expensive(Node *n, Node* earliest) {
 150   assert(n->in(0) && n->is_expensive(), "expensive node with control input here");
 151   assert(OptimizeExpensiveOps, "optimization off?");
 152 
 153   Node* ctl = n->in(0);
 154   assert(ctl->is_CFG(), "expensive input 0 must be cfg");
 155   uint min_dom_depth = dom_depth(earliest);
 156 #ifdef ASSERT
 157   if (!is_dominator(ctl, earliest) && !is_dominator(earliest, ctl)) {
 158     dump_bad_graph("Bad graph detected in get_early_ctrl_for_expensive", n, earliest, ctl);
 159     assert(false, "Bad graph detected in get_early_ctrl_for_expensive");
 160   }
 161 #endif
 162   if (dom_depth(ctl) < min_dom_depth) {
 163     return earliest;
 164   }
 165 
 166   while (1) {
 167     Node *next = ctl;
 168     // Moving the node out of a loop on the projection of a If
 169     // confuses loop predication. So once we hit a Loop in a If branch
 170     // that doesn't branch to an UNC, we stop. The code that process
 171     // expensive nodes will notice the loop and skip over it to try to
 172     // move the node further up.
 173     if (ctl->is_CountedLoop() && ctl->in(1) != NULL && ctl->in(1)->in(0) != NULL && ctl->in(1)->in(0)->is_If()) {
 174       if (!ctl->in(1)->as_Proj()->is_uncommon_trap_if_pattern(Deoptimization::Reason_none)) {
 175         break;
 176       }
 177       next = idom(ctl->in(1)->in(0));
 178     } else if (ctl->is_Proj()) {
 179       // We only move it up along a projection if the projection is
 180       // the single control projection for its parent: same code path,
 181       // if it's a If with UNC or fallthrough of a call.
 182       Node* parent_ctl = ctl->in(0);
 183       if (parent_ctl == NULL) {
 184         break;
 185       } else if (parent_ctl->is_CountedLoopEnd() && parent_ctl->as_CountedLoopEnd()->loopnode() != NULL) {
 186         next = parent_ctl->as_CountedLoopEnd()->loopnode()->init_control();
 187       } else if (parent_ctl->is_If()) {
 188         if (!ctl->as_Proj()->is_uncommon_trap_if_pattern(Deoptimization::Reason_none)) {
 189           break;
 190         }
 191         assert(idom(ctl) == parent_ctl, "strange");
 192         next = idom(parent_ctl);
 193       } else if (ctl->is_CatchProj()) {
 194         if (ctl->as_Proj()->_con != CatchProjNode::fall_through_index) {
 195           break;
 196         }
 197         assert(parent_ctl->in(0)->in(0)->is_Call(), "strange graph");
 198         next = parent_ctl->in(0)->in(0)->in(0);
 199       } else {
 200         // Check if parent control has a single projection (this
 201         // control is the only possible successor of the parent
 202         // control). If so, we can try to move the node above the
 203         // parent control.
 204         int nb_ctl_proj = 0;
 205         for (DUIterator_Fast imax, i = parent_ctl->fast_outs(imax); i < imax; i++) {
 206           Node *p = parent_ctl->fast_out(i);
 207           if (p->is_Proj() && p->is_CFG()) {
 208             nb_ctl_proj++;
 209             if (nb_ctl_proj > 1) {
 210               break;
 211             }
 212           }
 213         }
 214 
 215         if (nb_ctl_proj > 1) {
 216           break;
 217         }
 218         assert(parent_ctl->is_Start() || parent_ctl->is_MemBar() || parent_ctl->is_Call() ||
 219                BarrierSet::barrier_set()->barrier_set_c2()->is_gc_barrier_node(parent_ctl), "unexpected node");
 220         assert(idom(ctl) == parent_ctl, "strange");
 221         next = idom(parent_ctl);
 222       }
 223     } else {
 224       next = idom(ctl);
 225     }
 226     if (next->is_Root() || next->is_Start() || dom_depth(next) < min_dom_depth) {
 227       break;
 228     }
 229     ctl = next;
 230   }
 231 
 232   if (ctl != n->in(0)) {
 233     _igvn.replace_input_of(n, 0, ctl);
 234     _igvn.hash_insert(n);
 235   }
 236 
 237   return ctl;
 238 }
 239 
 240 
 241 //------------------------------set_early_ctrl---------------------------------
 242 // Set earliest legal control
 243 void PhaseIdealLoop::set_early_ctrl( Node *n ) {
 244   Node *early = get_early_ctrl(n);
 245 
 246   // Record earliest legal location
 247   set_ctrl(n, early);
 248 }
 249 
 250 //------------------------------set_subtree_ctrl-------------------------------
 251 // set missing _ctrl entries on new nodes
 252 void PhaseIdealLoop::set_subtree_ctrl( Node *n ) {
 253   // Already set?  Get out.
 254   if( _nodes[n->_idx] ) return;
 255   // Recursively set _nodes array to indicate where the Node goes
 256   uint i;
 257   for( i = 0; i < n->req(); ++i ) {
 258     Node *m = n->in(i);
 259     if( m && m != C->root() )
 260       set_subtree_ctrl( m );
 261   }
 262 
 263   // Fixup self
 264   set_early_ctrl( n );
 265 }
 266 
 267 // Create a skeleton strip mined outer loop: a Loop head before the
 268 // inner strip mined loop, a safepoint and an exit condition guarded
 269 // by an opaque node after the inner strip mined loop with a backedge
 270 // to the loop head. The inner strip mined loop is left as it is. Only
 271 // once loop optimizations are over, do we adjust the inner loop exit
 272 // condition to limit its number of iterations, set the outer loop
 273 // exit condition and add Phis to the outer loop head. Some loop
 274 // optimizations that operate on the inner strip mined loop need to be
 275 // aware of the outer strip mined loop: loop unswitching needs to
 276 // clone the outer loop as well as the inner, unrolling needs to only
 277 // clone the inner loop etc. No optimizations need to change the outer
 278 // strip mined loop as it is only a skeleton.
 279 IdealLoopTree* PhaseIdealLoop::create_outer_strip_mined_loop(BoolNode *test, Node *cmp, Node *init_control,
 280                                                              IdealLoopTree* loop, float cl_prob, float le_fcnt,
 281                                                              Node*& entry_control, Node*& iffalse) {
 282   Node* outer_test = _igvn.intcon(0);
 283   set_ctrl(outer_test, C->root());
 284   Node *orig = iffalse;
 285   iffalse = iffalse->clone();
 286   _igvn.register_new_node_with_optimizer(iffalse);
 287   set_idom(iffalse, idom(orig), dom_depth(orig));
 288 
 289   IfNode *outer_le = new OuterStripMinedLoopEndNode(iffalse, outer_test, cl_prob, le_fcnt);
 290   Node *outer_ift = new IfTrueNode (outer_le);
 291   Node* outer_iff = orig;
 292   _igvn.replace_input_of(outer_iff, 0, outer_le);
 293 
 294   LoopNode *outer_l = new OuterStripMinedLoopNode(C, init_control, outer_ift);
 295   entry_control = outer_l;
 296 
 297   IdealLoopTree* outer_ilt = new IdealLoopTree(this, outer_l, outer_ift);
 298   IdealLoopTree* parent = loop->_parent;
 299   IdealLoopTree* sibling = parent->_child;
 300   if (sibling == loop) {
 301     parent->_child = outer_ilt;
 302   } else {
 303     while (sibling->_next != loop) {
 304       sibling = sibling->_next;
 305     }
 306     sibling->_next = outer_ilt;
 307   }
 308   outer_ilt->_next = loop->_next;
 309   outer_ilt->_parent = parent;
 310   outer_ilt->_child = loop;
 311   outer_ilt->_nest = loop->_nest;
 312   loop->_parent = outer_ilt;
 313   loop->_next = NULL;
 314   loop->_nest++;
 315 
 316   set_loop(iffalse, outer_ilt);
 317   register_control(outer_le, outer_ilt, iffalse);
 318   register_control(outer_ift, outer_ilt, outer_le);
 319   set_idom(outer_iff, outer_le, dom_depth(outer_le));
 320   _igvn.register_new_node_with_optimizer(outer_l);
 321   set_loop(outer_l, outer_ilt);
 322   set_idom(outer_l, init_control, dom_depth(init_control)+1);
 323 
 324   return outer_ilt;
 325 }
 326 
 327 //------------------------------is_counted_loop--------------------------------
 328 bool PhaseIdealLoop::is_counted_loop(Node* x, IdealLoopTree*& loop) {
 329   PhaseGVN *gvn = &_igvn;
 330 
 331   // Counted loop head must be a good RegionNode with only 3 not NULL
 332   // control input edges: Self, Entry, LoopBack.
 333   if (x->in(LoopNode::Self) == NULL || x->req() != 3 || loop->_irreducible) {
 334     return false;
 335   }
 336   Node *init_control = x->in(LoopNode::EntryControl);
 337   Node *back_control = x->in(LoopNode::LoopBackControl);
 338   if (init_control == NULL || back_control == NULL)    // Partially dead
 339     return false;
 340   // Must also check for TOP when looking for a dead loop
 341   if (init_control->is_top() || back_control->is_top())
 342     return false;
 343 
 344   // Allow funny placement of Safepoint
 345   if (back_control->Opcode() == Op_SafePoint) {
 346     if (LoopStripMiningIter != 0) {
 347       // Leaving the safepoint on the backedge and creating a
 348       // CountedLoop will confuse optimizations. We can't move the
 349       // safepoint around because its jvm state wouldn't match a new
 350       // location. Give up on that loop.
 351       return false;
 352     }
 353     back_control = back_control->in(TypeFunc::Control);
 354   }
 355 
 356   // Controlling test for loop
 357   Node *iftrue = back_control;
 358   uint iftrue_op = iftrue->Opcode();
 359   if (iftrue_op != Op_IfTrue &&
 360       iftrue_op != Op_IfFalse)
 361     // I have a weird back-control.  Probably the loop-exit test is in
 362     // the middle of the loop and I am looking at some trailing control-flow
 363     // merge point.  To fix this I would have to partially peel the loop.
 364     return false; // Obscure back-control
 365 
 366   // Get boolean guarding loop-back test
 367   Node *iff = iftrue->in(0);
 368   if (get_loop(iff) != loop || !iff->in(1)->is_Bool())
 369     return false;
 370   BoolNode *test = iff->in(1)->as_Bool();
 371   BoolTest::mask bt = test->_test._test;
 372   float cl_prob = iff->as_If()->_prob;
 373   if (iftrue_op == Op_IfFalse) {
 374     bt = BoolTest(bt).negate();
 375     cl_prob = 1.0 - cl_prob;
 376   }
 377   // Get backedge compare
 378   Node *cmp = test->in(1);
 379   int cmp_op = cmp->Opcode();
 380   if (cmp_op != Op_CmpI)
 381     return false;                // Avoid pointer & float compares
 382 
 383   // Find the trip-counter increment & limit.  Limit must be loop invariant.
 384   Node *incr  = cmp->in(1);
 385   Node *limit = cmp->in(2);
 386 
 387   // ---------
 388   // need 'loop()' test to tell if limit is loop invariant
 389   // ---------
 390 
 391   if (!is_member(loop, get_ctrl(incr))) { // Swapped trip counter and limit?
 392     Node *tmp = incr;            // Then reverse order into the CmpI
 393     incr = limit;
 394     limit = tmp;
 395     bt = BoolTest(bt).commute(); // And commute the exit test
 396   }
 397   if (is_member(loop, get_ctrl(limit))) // Limit must be loop-invariant
 398     return false;
 399   if (!is_member(loop, get_ctrl(incr))) // Trip counter must be loop-variant
 400     return false;
 401 
 402   Node* phi_incr = NULL;
 403   // Trip-counter increment must be commutative & associative.
 404   if (incr->Opcode() == Op_CastII) {
 405     incr = incr->in(1);
 406   }
 407   if (incr->is_Phi()) {
 408     if (incr->as_Phi()->region() != x || incr->req() != 3)
 409       return false; // Not simple trip counter expression
 410     phi_incr = incr;
 411     incr = phi_incr->in(LoopNode::LoopBackControl); // Assume incr is on backedge of Phi
 412     if (!is_member(loop, get_ctrl(incr))) // Trip counter must be loop-variant
 413       return false;
 414   }
 415 
 416   Node* trunc1 = NULL;
 417   Node* trunc2 = NULL;
 418   const TypeInt* iv_trunc_t = NULL;
 419   Node* orig_incr = incr;
 420   if (!(incr = CountedLoopNode::match_incr_with_optional_truncation(incr, &trunc1, &trunc2, &iv_trunc_t))) {
 421     return false; // Funny increment opcode
 422   }
 423   assert(incr->Opcode() == Op_AddI, "wrong increment code");
 424 
 425   const TypeInt* limit_t = gvn->type(limit)->is_int();
 426   if (trunc1 != NULL) {
 427     // When there is a truncation, we must be sure that after the truncation
 428     // the trip counter will end up higher than the limit, otherwise we are looking
 429     // at an endless loop. Can happen with range checks.
 430 
 431     // Example:
 432     // int i = 0;
 433     // while (true)
 434     //    sum + = array[i];
 435     //    i++;
 436     //    i = i && 0x7fff;
 437     //  }
 438     //
 439     // If the array is shorter than 0x8000 this exits through a AIOOB
 440     //  - Counted loop transformation is ok
 441     // If the array is longer then this is an endless loop
 442     //  - No transformation can be done.
 443 
 444     const TypeInt* incr_t = gvn->type(orig_incr)->is_int();
 445     if (limit_t->_hi > incr_t->_hi) {
 446       // if the limit can have a higher value than the increment (before the phi)
 447       return false;
 448     }
 449   }
 450 
 451   // Get merge point
 452   Node *xphi = incr->in(1);
 453   Node *stride = incr->in(2);
 454   if (!stride->is_Con()) {     // Oops, swap these
 455     if (!xphi->is_Con())       // Is the other guy a constant?
 456       return false;             // Nope, unknown stride, bail out
 457     Node *tmp = xphi;           // 'incr' is commutative, so ok to swap
 458     xphi = stride;
 459     stride = tmp;
 460   }
 461   if (xphi->Opcode() == Op_CastII) {
 462     xphi = xphi->in(1);
 463   }
 464   // Stride must be constant
 465   int stride_con = stride->get_int();
 466   if (stride_con == 0)
 467     return false; // missed some peephole opt
 468 
 469   if (!xphi->is_Phi())
 470     return false; // Too much math on the trip counter
 471   if (phi_incr != NULL && phi_incr != xphi)
 472     return false;
 473   PhiNode *phi = xphi->as_Phi();
 474 
 475   // Phi must be of loop header; backedge must wrap to increment
 476   if (phi->region() != x)
 477     return false;
 478   if ((trunc1 == NULL && phi->in(LoopNode::LoopBackControl) != incr) ||
 479       (trunc1 != NULL && phi->in(LoopNode::LoopBackControl) != trunc1)) {
 480     return false;
 481   }
 482   Node *init_trip = phi->in(LoopNode::EntryControl);
 483 
 484   // If iv trunc type is smaller than int, check for possible wrap.
 485   if (!TypeInt::INT->higher_equal(iv_trunc_t)) {
 486     assert(trunc1 != NULL, "must have found some truncation");
 487 
 488     // Get a better type for the phi (filtered thru if's)
 489     const TypeInt* phi_ft = filtered_type(phi);
 490 
 491     // Can iv take on a value that will wrap?
 492     //
 493     // Ensure iv's limit is not within "stride" of the wrap value.
 494     //
 495     // Example for "short" type
 496     //    Truncation ensures value is in the range -32768..32767 (iv_trunc_t)
 497     //    If the stride is +10, then the last value of the induction
 498     //    variable before the increment (phi_ft->_hi) must be
 499     //    <= 32767 - 10 and (phi_ft->_lo) must be >= -32768 to
 500     //    ensure no truncation occurs after the increment.
 501 
 502     if (stride_con > 0) {
 503       if (iv_trunc_t->_hi - phi_ft->_hi < stride_con ||
 504           iv_trunc_t->_lo > phi_ft->_lo) {
 505         return false;  // truncation may occur
 506       }
 507     } else if (stride_con < 0) {
 508       if (iv_trunc_t->_lo - phi_ft->_lo > stride_con ||
 509           iv_trunc_t->_hi < phi_ft->_hi) {
 510         return false;  // truncation may occur
 511       }
 512     }
 513     // No possibility of wrap so truncation can be discarded
 514     // Promote iv type to Int
 515   } else {
 516     assert(trunc1 == NULL && trunc2 == NULL, "no truncation for int");
 517   }
 518 
 519   // If the condition is inverted and we will be rolling
 520   // through MININT to MAXINT, then bail out.
 521   if (bt == BoolTest::eq || // Bail out, but this loop trips at most twice!
 522       // Odd stride
 523       (bt == BoolTest::ne && stride_con != 1 && stride_con != -1) ||
 524       // Count down loop rolls through MAXINT
 525       ((bt == BoolTest::le || bt == BoolTest::lt) && stride_con < 0) ||
 526       // Count up loop rolls through MININT
 527       ((bt == BoolTest::ge || bt == BoolTest::gt) && stride_con > 0)) {
 528     return false; // Bail out
 529   }
 530 
 531   const TypeInt* init_t = gvn->type(init_trip)->is_int();
 532 
 533   if (stride_con > 0) {
 534     jlong init_p = (jlong)init_t->_lo + stride_con;
 535     if (init_p > (jlong)max_jint || init_p > (jlong)limit_t->_hi)
 536       return false; // cyclic loop or this loop trips only once
 537   } else {
 538     jlong init_p = (jlong)init_t->_hi + stride_con;
 539     if (init_p < (jlong)min_jint || init_p < (jlong)limit_t->_lo)
 540       return false; // cyclic loop or this loop trips only once
 541   }
 542 
 543   if (phi_incr != NULL) {
 544     // check if there is a possiblity of IV overflowing after the first increment
 545     if (stride_con > 0) {
 546       if (init_t->_hi > max_jint - stride_con) {
 547         return false;
 548       }
 549     } else {
 550       if (init_t->_lo < min_jint - stride_con) {
 551         return false;
 552       }
 553     }
 554   }
 555 
 556   // =================================================
 557   // ---- SUCCESS!   Found A Trip-Counted Loop!  -----
 558   //
 559   assert(x->Opcode() == Op_Loop, "regular loops only");
 560   C->print_method(PHASE_BEFORE_CLOOPS, 3);
 561 
 562   Node *hook = new Node(6);
 563 
 564   // ===================================================
 565   // Generate loop limit check to avoid integer overflow
 566   // in cases like next (cyclic loops):
 567   //
 568   // for (i=0; i <= max_jint; i++) {}
 569   // for (i=0; i <  max_jint; i+=2) {}
 570   //
 571   //
 572   // Limit check predicate depends on the loop test:
 573   //
 574   // for(;i != limit; i++)       --> limit <= (max_jint)
 575   // for(;i <  limit; i+=stride) --> limit <= (max_jint - stride + 1)
 576   // for(;i <= limit; i+=stride) --> limit <= (max_jint - stride    )
 577   //
 578 
 579   // Check if limit is excluded to do more precise int overflow check.
 580   bool incl_limit = (bt == BoolTest::le || bt == BoolTest::ge);
 581   int stride_m  = stride_con - (incl_limit ? 0 : (stride_con > 0 ? 1 : -1));
 582 
 583   // If compare points directly to the phi we need to adjust
 584   // the compare so that it points to the incr. Limit have
 585   // to be adjusted to keep trip count the same and the
 586   // adjusted limit should be checked for int overflow.
 587   if (phi_incr != NULL) {
 588     stride_m  += stride_con;
 589   }
 590 
 591   if (limit->is_Con()) {
 592     int limit_con = limit->get_int();
 593     if ((stride_con > 0 && limit_con > (max_jint - stride_m)) ||
 594         (stride_con < 0 && limit_con < (min_jint - stride_m))) {
 595       // Bailout: it could be integer overflow.
 596       return false;
 597     }
 598   } else if ((stride_con > 0 && limit_t->_hi <= (max_jint - stride_m)) ||
 599              (stride_con < 0 && limit_t->_lo >= (min_jint - stride_m))) {
 600       // Limit's type may satisfy the condition, for example,
 601       // when it is an array length.
 602   } else {
 603     // Generate loop's limit check.
 604     // Loop limit check predicate should be near the loop.
 605     ProjNode *limit_check_proj = find_predicate_insertion_point(init_control, Deoptimization::Reason_loop_limit_check);
 606     if (!limit_check_proj) {
 607       // The limit check predicate is not generated if this method trapped here before.
 608 #ifdef ASSERT
 609       if (TraceLoopLimitCheck) {
 610         tty->print("missing loop limit check:");
 611         loop->dump_head();
 612         x->dump(1);
 613       }
 614 #endif
 615       return false;
 616     }
 617 
 618     IfNode* check_iff = limit_check_proj->in(0)->as_If();
 619 
 620     if (!is_dominator(get_ctrl(limit), check_iff->in(0))) {
 621       return false;
 622     }
 623 
 624     Node* cmp_limit;
 625     Node* bol;
 626 
 627     if (stride_con > 0) {
 628       cmp_limit = new CmpINode(limit, _igvn.intcon(max_jint - stride_m));
 629       bol = new BoolNode(cmp_limit, BoolTest::le);
 630     } else {
 631       cmp_limit = new CmpINode(limit, _igvn.intcon(min_jint - stride_m));
 632       bol = new BoolNode(cmp_limit, BoolTest::ge);
 633     }
 634     cmp_limit = _igvn.register_new_node_with_optimizer(cmp_limit);
 635     bol = _igvn.register_new_node_with_optimizer(bol);
 636     set_subtree_ctrl(bol);
 637 
 638     // Replace condition in original predicate but preserve Opaque node
 639     // so that previous predicates could be found.
 640     assert(check_iff->in(1)->Opcode() == Op_Conv2B &&
 641            check_iff->in(1)->in(1)->Opcode() == Op_Opaque1, "");
 642     Node* opq = check_iff->in(1)->in(1);
 643     _igvn.replace_input_of(opq, 1, bol);
 644     // Update ctrl.
 645     set_ctrl(opq, check_iff->in(0));
 646     set_ctrl(check_iff->in(1), check_iff->in(0));
 647 
 648 #ifndef PRODUCT
 649     // report that the loop predication has been actually performed
 650     // for this loop
 651     if (TraceLoopLimitCheck) {
 652       tty->print_cr("Counted Loop Limit Check generated:");
 653       debug_only( bol->dump(2); )
 654     }
 655 #endif
 656   }
 657 
 658   if (phi_incr != NULL) {
 659     // If compare points directly to the phi we need to adjust
 660     // the compare so that it points to the incr. Limit have
 661     // to be adjusted to keep trip count the same and we
 662     // should avoid int overflow.
 663     //
 664     //   i = init; do {} while(i++ < limit);
 665     // is converted to
 666     //   i = init; do {} while(++i < limit+1);
 667     //
 668     limit = gvn->transform(new AddINode(limit, stride));
 669   }
 670 
 671   // Now we need to canonicalize loop condition.
 672   if (bt == BoolTest::ne) {
 673     assert(stride_con == 1 || stride_con == -1, "simple increment only");
 674     // 'ne' can be replaced with 'lt' only when init < limit.
 675     if (stride_con > 0 && init_t->_hi < limit_t->_lo)
 676       bt = BoolTest::lt;
 677     // 'ne' can be replaced with 'gt' only when init > limit.
 678     if (stride_con < 0 && init_t->_lo > limit_t->_hi)
 679       bt = BoolTest::gt;
 680   }
 681 
 682   if (incl_limit) {
 683     // The limit check guaranties that 'limit <= (max_jint - stride)' so
 684     // we can convert 'i <= limit' to 'i < limit+1' since stride != 0.
 685     //
 686     Node* one = (stride_con > 0) ? gvn->intcon( 1) : gvn->intcon(-1);
 687     limit = gvn->transform(new AddINode(limit, one));
 688     if (bt == BoolTest::le)
 689       bt = BoolTest::lt;
 690     else if (bt == BoolTest::ge)
 691       bt = BoolTest::gt;
 692     else
 693       ShouldNotReachHere();
 694   }
 695   set_subtree_ctrl( limit );
 696 
 697   if (LoopStripMiningIter == 0) {
 698     // Check for SafePoint on backedge and remove
 699     Node *sfpt = x->in(LoopNode::LoopBackControl);
 700     if (sfpt->Opcode() == Op_SafePoint && is_deleteable_safept(sfpt)) {
 701       lazy_replace( sfpt, iftrue );
 702       if (loop->_safepts != NULL) {
 703         loop->_safepts->yank(sfpt);
 704       }
 705       loop->_tail = iftrue;
 706     }
 707   }
 708 
 709   // Build a canonical trip test.
 710   // Clone code, as old values may be in use.
 711   incr = incr->clone();
 712   incr->set_req(1,phi);
 713   incr->set_req(2,stride);
 714   incr = _igvn.register_new_node_with_optimizer(incr);
 715   set_early_ctrl( incr );
 716   _igvn.rehash_node_delayed(phi);
 717   phi->set_req_X( LoopNode::LoopBackControl, incr, &_igvn );
 718 
 719   // If phi type is more restrictive than Int, raise to
 720   // Int to prevent (almost) infinite recursion in igvn
 721   // which can only handle integer types for constants or minint..maxint.
 722   if (!TypeInt::INT->higher_equal(phi->bottom_type())) {
 723     Node* nphi = PhiNode::make(phi->in(0), phi->in(LoopNode::EntryControl), TypeInt::INT);
 724     nphi->set_req(LoopNode::LoopBackControl, phi->in(LoopNode::LoopBackControl));
 725     nphi = _igvn.register_new_node_with_optimizer(nphi);
 726     set_ctrl(nphi, get_ctrl(phi));
 727     _igvn.replace_node(phi, nphi);
 728     phi = nphi->as_Phi();
 729   }
 730   cmp = cmp->clone();
 731   cmp->set_req(1,incr);
 732   cmp->set_req(2,limit);
 733   cmp = _igvn.register_new_node_with_optimizer(cmp);
 734   set_ctrl(cmp, iff->in(0));
 735 
 736   test = test->clone()->as_Bool();
 737   (*(BoolTest*)&test->_test)._test = bt;
 738   test->set_req(1,cmp);
 739   _igvn.register_new_node_with_optimizer(test);
 740   set_ctrl(test, iff->in(0));
 741 
 742   // Replace the old IfNode with a new LoopEndNode
 743   Node *lex = _igvn.register_new_node_with_optimizer(new CountedLoopEndNode( iff->in(0), test, cl_prob, iff->as_If()->_fcnt ));
 744   IfNode *le = lex->as_If();
 745   uint dd = dom_depth(iff);
 746   set_idom(le, le->in(0), dd); // Update dominance for loop exit
 747   set_loop(le, loop);
 748 
 749   // Get the loop-exit control
 750   Node *iffalse = iff->as_If()->proj_out(!(iftrue_op == Op_IfTrue));
 751 
 752   // Need to swap loop-exit and loop-back control?
 753   if (iftrue_op == Op_IfFalse) {
 754     Node *ift2=_igvn.register_new_node_with_optimizer(new IfTrueNode (le));
 755     Node *iff2=_igvn.register_new_node_with_optimizer(new IfFalseNode(le));
 756 
 757     loop->_tail = back_control = ift2;
 758     set_loop(ift2, loop);
 759     set_loop(iff2, get_loop(iffalse));
 760 
 761     // Lazy update of 'get_ctrl' mechanism.
 762     lazy_replace(iffalse, iff2);
 763     lazy_replace(iftrue,  ift2);
 764 
 765     // Swap names
 766     iffalse = iff2;
 767     iftrue  = ift2;
 768   } else {
 769     _igvn.rehash_node_delayed(iffalse);
 770     _igvn.rehash_node_delayed(iftrue);
 771     iffalse->set_req_X( 0, le, &_igvn );
 772     iftrue ->set_req_X( 0, le, &_igvn );
 773   }
 774 
 775   set_idom(iftrue,  le, dd+1);
 776   set_idom(iffalse, le, dd+1);
 777   assert(iff->outcnt() == 0, "should be dead now");
 778   lazy_replace( iff, le ); // fix 'get_ctrl'
 779 
 780   Node *sfpt2 = le->in(0);
 781 
 782   Node* entry_control = init_control;
 783   bool strip_mine_loop = LoopStripMiningIter > 1 && loop->_child == NULL &&
 784     sfpt2->Opcode() == Op_SafePoint && !loop->_has_call;
 785   IdealLoopTree* outer_ilt = NULL;
 786   if (strip_mine_loop) {
 787     outer_ilt = create_outer_strip_mined_loop(test, cmp, init_control, loop,
 788                                               cl_prob, le->_fcnt, entry_control,
 789                                               iffalse);
 790   }
 791 
 792   // Now setup a new CountedLoopNode to replace the existing LoopNode
 793   CountedLoopNode *l = new CountedLoopNode(entry_control, back_control);
 794   l->set_unswitch_count(x->as_Loop()->unswitch_count()); // Preserve
 795   // The following assert is approximately true, and defines the intention
 796   // of can_be_counted_loop.  It fails, however, because phase->type
 797   // is not yet initialized for this loop and its parts.
 798   //assert(l->can_be_counted_loop(this), "sanity");
 799   _igvn.register_new_node_with_optimizer(l);
 800   set_loop(l, loop);
 801   loop->_head = l;
 802   // Fix all data nodes placed at the old loop head.
 803   // Uses the lazy-update mechanism of 'get_ctrl'.
 804   lazy_replace( x, l );
 805   set_idom(l, entry_control, dom_depth(entry_control) + 1);
 806 
 807   if (LoopStripMiningIter == 0 || strip_mine_loop) {
 808     // Check for immediately preceding SafePoint and remove
 809     if (sfpt2->Opcode() == Op_SafePoint && (LoopStripMiningIter != 0 || is_deleteable_safept(sfpt2))) {
 810       if (strip_mine_loop) {
 811         Node* outer_le = outer_ilt->_tail->in(0);
 812         Node* sfpt = sfpt2->clone();
 813         sfpt->set_req(0, iffalse);
 814         outer_le->set_req(0, sfpt);
 815         register_control(sfpt, outer_ilt, iffalse);
 816         set_idom(outer_le, sfpt, dom_depth(sfpt));
 817       }
 818       lazy_replace( sfpt2, sfpt2->in(TypeFunc::Control));
 819       if (loop->_safepts != NULL) {
 820         loop->_safepts->yank(sfpt2);
 821       }
 822     }
 823   }
 824 
 825   // Free up intermediate goo
 826   _igvn.remove_dead_node(hook);
 827 
 828 #ifdef ASSERT
 829   assert(l->is_valid_counted_loop(), "counted loop shape is messed up");
 830   assert(l == loop->_head && l->phi() == phi && l->loopexit_or_null() == lex, "" );
 831 #endif
 832 #ifndef PRODUCT
 833   if (TraceLoopOpts) {
 834     tty->print("Counted      ");
 835     loop->dump_head();
 836   }
 837 #endif
 838 
 839   C->print_method(PHASE_AFTER_CLOOPS, 3);
 840 
 841   // Capture bounds of the loop in the induction variable Phi before
 842   // subsequent transformation (iteration splitting) obscures the
 843   // bounds
 844   l->phi()->as_Phi()->set_type(l->phi()->Value(&_igvn));
 845 
 846   if (strip_mine_loop) {
 847     l->mark_strip_mined();
 848     l->verify_strip_mined(1);
 849     outer_ilt->_head->as_Loop()->verify_strip_mined(1);
 850     loop = outer_ilt;
 851   }
 852 
 853   return true;
 854 }
 855 
 856 //----------------------exact_limit-------------------------------------------
 857 Node* PhaseIdealLoop::exact_limit( IdealLoopTree *loop ) {
 858   assert(loop->_head->is_CountedLoop(), "");
 859   CountedLoopNode *cl = loop->_head->as_CountedLoop();
 860   assert(cl->is_valid_counted_loop(), "");
 861 
 862   if (ABS(cl->stride_con()) == 1 ||
 863       cl->limit()->Opcode() == Op_LoopLimit) {
 864     // Old code has exact limit (it could be incorrect in case of int overflow).
 865     // Loop limit is exact with stride == 1. And loop may already have exact limit.
 866     return cl->limit();
 867   }
 868   Node *limit = NULL;
 869 #ifdef ASSERT
 870   BoolTest::mask bt = cl->loopexit()->test_trip();
 871   assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
 872 #endif
 873   if (cl->has_exact_trip_count()) {
 874     // Simple case: loop has constant boundaries.
 875     // Use jlongs to avoid integer overflow.
 876     int stride_con = cl->stride_con();
 877     jlong  init_con = cl->init_trip()->get_int();
 878     jlong limit_con = cl->limit()->get_int();
 879     julong trip_cnt = cl->trip_count();
 880     jlong final_con = init_con + trip_cnt*stride_con;
 881     int final_int = (int)final_con;
 882     // The final value should be in integer range since the loop
 883     // is counted and the limit was checked for overflow.
 884     assert(final_con == (jlong)final_int, "final value should be integer");
 885     limit = _igvn.intcon(final_int);
 886   } else {
 887     // Create new LoopLimit node to get exact limit (final iv value).
 888     limit = new LoopLimitNode(C, cl->init_trip(), cl->limit(), cl->stride());
 889     register_new_node(limit, cl->in(LoopNode::EntryControl));
 890   }
 891   assert(limit != NULL, "sanity");
 892   return limit;
 893 }
 894 
 895 //------------------------------Ideal------------------------------------------
 896 // Return a node which is more "ideal" than the current node.
 897 // Attempt to convert into a counted-loop.
 898 Node *LoopNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 899   if (!can_be_counted_loop(phase) && !is_OuterStripMinedLoop()) {
 900     phase->C->set_major_progress();
 901   }
 902   return RegionNode::Ideal(phase, can_reshape);
 903 }
 904 
 905 void LoopNode::verify_strip_mined(int expect_skeleton) const {
 906 #ifdef ASSERT
 907   const OuterStripMinedLoopNode* outer = NULL;
 908   const CountedLoopNode* inner = NULL;
 909   if (is_strip_mined()) {
 910     assert(is_CountedLoop(), "no Loop should be marked strip mined");
 911     inner = as_CountedLoop();
 912     outer = inner->in(LoopNode::EntryControl)->as_OuterStripMinedLoop();
 913   } else if (is_OuterStripMinedLoop()) {
 914     outer = this->as_OuterStripMinedLoop();
 915     inner = outer->unique_ctrl_out()->as_CountedLoop();
 916     assert(!is_strip_mined(), "outer loop shouldn't be marked strip mined");
 917   }
 918   if (inner != NULL || outer != NULL) {
 919     assert(inner != NULL && outer != NULL, "missing loop in strip mined nest");
 920     Node* outer_tail = outer->in(LoopNode::LoopBackControl);
 921     Node* outer_le = outer_tail->in(0);
 922     assert(outer_le->Opcode() == Op_OuterStripMinedLoopEnd, "tail of outer loop should be an If");
 923     Node* sfpt = outer_le->in(0);
 924     assert(sfpt->Opcode() == Op_SafePoint, "where's the safepoint?");
 925     Node* inner_out = sfpt->in(0);
 926     if (inner_out->outcnt() != 1) {
 927       ResourceMark rm;
 928       Unique_Node_List wq;
 929 
 930       for (DUIterator_Fast imax, i = inner_out->fast_outs(imax); i < imax; i++) {
 931         Node* u = inner_out->fast_out(i);
 932         if (u == sfpt) {
 933           continue;
 934         }
 935         wq.clear();
 936         wq.push(u);
 937         bool found_sfpt = false;
 938         for (uint next = 0; next < wq.size() && !found_sfpt; next++) {
 939           Node *n = wq.at(next);
 940           for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax && !found_sfpt; i++) {
 941             Node* u = n->fast_out(i);
 942             if (u == sfpt) {
 943               found_sfpt = true;
 944             }
 945             if (!u->is_CFG()) {
 946               wq.push(u);
 947             }
 948           }
 949         }
 950         assert(found_sfpt, "no node in loop that's not input to safepoint");
 951       }
 952     }
 953     CountedLoopEndNode* cle = inner_out->in(0)->as_CountedLoopEnd();
 954     assert(cle == inner->loopexit_or_null(), "mismatch");
 955     bool has_skeleton = outer_le->in(1)->bottom_type()->singleton() && outer_le->in(1)->bottom_type()->is_int()->get_con() == 0;
 956     if (has_skeleton) {
 957       assert(expect_skeleton == 1 || expect_skeleton == -1, "unexpected skeleton node");
 958       assert(outer->outcnt() == 2, "only phis");
 959     } else {
 960       assert(expect_skeleton == 0 || expect_skeleton == -1, "no skeleton node?");
 961       uint phis = 0;
 962       for (DUIterator_Fast imax, i = inner->fast_outs(imax); i < imax; i++) {
 963         Node* u = inner->fast_out(i);
 964         if (u->is_Phi()) {
 965           phis++;
 966         }
 967       }
 968       for (DUIterator_Fast imax, i = outer->fast_outs(imax); i < imax; i++) {
 969         Node* u = outer->fast_out(i);
 970         assert(u == outer || u == inner || u->is_Phi(), "nothing between inner and outer loop");
 971       }
 972       uint stores = 0;
 973       for (DUIterator_Fast imax, i = inner_out->fast_outs(imax); i < imax; i++) {
 974         Node* u = inner_out->fast_out(i);
 975         if (u->is_Store()) {
 976           stores++;
 977         }
 978       }
 979       assert(outer->outcnt() >= phis + 2 && outer->outcnt() <= phis + 2 + stores + 1, "only phis");
 980     }
 981     assert(sfpt->outcnt() == 1, "no data node");
 982     assert(outer_tail->outcnt() == 1 || !has_skeleton, "no data node");
 983   }
 984 #endif
 985 }
 986 
 987 //=============================================================================
 988 //------------------------------Ideal------------------------------------------
 989 // Return a node which is more "ideal" than the current node.
 990 // Attempt to convert into a counted-loop.
 991 Node *CountedLoopNode::Ideal(PhaseGVN *phase, bool can_reshape) {
 992   return RegionNode::Ideal(phase, can_reshape);
 993 }
 994 
 995 //------------------------------dump_spec--------------------------------------
 996 // Dump special per-node info
 997 #ifndef PRODUCT
 998 void CountedLoopNode::dump_spec(outputStream *st) const {
 999   LoopNode::dump_spec(st);
1000   if (stride_is_con()) {
1001     st->print("stride: %d ",stride_con());
1002   }
1003   if (is_pre_loop ()) st->print("pre of N%d" , _main_idx);
1004   if (is_main_loop()) st->print("main of N%d", _idx);
1005   if (is_post_loop()) st->print("post of N%d", _main_idx);
1006   if (is_strip_mined()) st->print(" strip mined");
1007 }
1008 #endif
1009 
1010 //=============================================================================
1011 int CountedLoopEndNode::stride_con() const {
1012   return stride()->bottom_type()->is_int()->get_con();
1013 }
1014 
1015 //=============================================================================
1016 //------------------------------Value-----------------------------------------
1017 const Type* LoopLimitNode::Value(PhaseGVN* phase) const {
1018   const Type* init_t   = phase->type(in(Init));
1019   const Type* limit_t  = phase->type(in(Limit));
1020   const Type* stride_t = phase->type(in(Stride));
1021   // Either input is TOP ==> the result is TOP
1022   if (init_t   == Type::TOP) return Type::TOP;
1023   if (limit_t  == Type::TOP) return Type::TOP;
1024   if (stride_t == Type::TOP) return Type::TOP;
1025 
1026   int stride_con = stride_t->is_int()->get_con();
1027   if (stride_con == 1)
1028     return NULL;  // Identity
1029 
1030   if (init_t->is_int()->is_con() && limit_t->is_int()->is_con()) {
1031     // Use jlongs to avoid integer overflow.
1032     jlong init_con   =  init_t->is_int()->get_con();
1033     jlong limit_con  = limit_t->is_int()->get_con();
1034     int  stride_m   = stride_con - (stride_con > 0 ? 1 : -1);
1035     jlong trip_count = (limit_con - init_con + stride_m)/stride_con;
1036     jlong final_con  = init_con + stride_con*trip_count;
1037     int final_int = (int)final_con;
1038     // The final value should be in integer range since the loop
1039     // is counted and the limit was checked for overflow.
1040     assert(final_con == (jlong)final_int, "final value should be integer");
1041     return TypeInt::make(final_int);
1042   }
1043 
1044   return bottom_type(); // TypeInt::INT
1045 }
1046 
1047 //------------------------------Ideal------------------------------------------
1048 // Return a node which is more "ideal" than the current node.
1049 Node *LoopLimitNode::Ideal(PhaseGVN *phase, bool can_reshape) {
1050   if (phase->type(in(Init))   == Type::TOP ||
1051       phase->type(in(Limit))  == Type::TOP ||
1052       phase->type(in(Stride)) == Type::TOP)
1053     return NULL;  // Dead
1054 
1055   int stride_con = phase->type(in(Stride))->is_int()->get_con();
1056   if (stride_con == 1)
1057     return NULL;  // Identity
1058 
1059   if (in(Init)->is_Con() && in(Limit)->is_Con())
1060     return NULL;  // Value
1061 
1062   // Delay following optimizations until all loop optimizations
1063   // done to keep Ideal graph simple.
1064   if (!can_reshape || phase->C->major_progress())
1065     return NULL;
1066 
1067   const TypeInt* init_t  = phase->type(in(Init) )->is_int();
1068   const TypeInt* limit_t = phase->type(in(Limit))->is_int();
1069   int stride_p;
1070   jlong lim, ini;
1071   julong max;
1072   if (stride_con > 0) {
1073     stride_p = stride_con;
1074     lim = limit_t->_hi;
1075     ini = init_t->_lo;
1076     max = (julong)max_jint;
1077   } else {
1078     stride_p = -stride_con;
1079     lim = init_t->_hi;
1080     ini = limit_t->_lo;
1081     max = (julong)min_jint;
1082   }
1083   julong range = lim - ini + stride_p;
1084   if (range <= max) {
1085     // Convert to integer expression if it is not overflow.
1086     Node* stride_m = phase->intcon(stride_con - (stride_con > 0 ? 1 : -1));
1087     Node *range = phase->transform(new SubINode(in(Limit), in(Init)));
1088     Node *bias  = phase->transform(new AddINode(range, stride_m));
1089     Node *trip  = phase->transform(new DivINode(0, bias, in(Stride)));
1090     Node *span  = phase->transform(new MulINode(trip, in(Stride)));
1091     return new AddINode(span, in(Init)); // exact limit
1092   }
1093 
1094   if (is_power_of_2(stride_p) ||                // divisor is 2^n
1095       !Matcher::has_match_rule(Op_LoopLimit)) { // or no specialized Mach node?
1096     // Convert to long expression to avoid integer overflow
1097     // and let igvn optimizer convert this division.
1098     //
1099     Node*   init   = phase->transform( new ConvI2LNode(in(Init)));
1100     Node*  limit   = phase->transform( new ConvI2LNode(in(Limit)));
1101     Node* stride   = phase->longcon(stride_con);
1102     Node* stride_m = phase->longcon(stride_con - (stride_con > 0 ? 1 : -1));
1103 
1104     Node *range = phase->transform(new SubLNode(limit, init));
1105     Node *bias  = phase->transform(new AddLNode(range, stride_m));
1106     Node *span;
1107     if (stride_con > 0 && is_power_of_2(stride_p)) {
1108       // bias >= 0 if stride >0, so if stride is 2^n we can use &(-stride)
1109       // and avoid generating rounding for division. Zero trip guard should
1110       // guarantee that init < limit but sometimes the guard is missing and
1111       // we can get situation when init > limit. Note, for the empty loop
1112       // optimization zero trip guard is generated explicitly which leaves
1113       // only RCE predicate where exact limit is used and the predicate
1114       // will simply fail forcing recompilation.
1115       Node* neg_stride   = phase->longcon(-stride_con);
1116       span = phase->transform(new AndLNode(bias, neg_stride));
1117     } else {
1118       Node *trip  = phase->transform(new DivLNode(0, bias, stride));
1119       span = phase->transform(new MulLNode(trip, stride));
1120     }
1121     // Convert back to int
1122     Node *span_int = phase->transform(new ConvL2INode(span));
1123     return new AddINode(span_int, in(Init)); // exact limit
1124   }
1125 
1126   return NULL;    // No progress
1127 }
1128 
1129 //------------------------------Identity---------------------------------------
1130 // If stride == 1 return limit node.
1131 Node* LoopLimitNode::Identity(PhaseGVN* phase) {
1132   int stride_con = phase->type(in(Stride))->is_int()->get_con();
1133   if (stride_con == 1 || stride_con == -1)
1134     return in(Limit);
1135   return this;
1136 }
1137 
1138 //=============================================================================
1139 //----------------------match_incr_with_optional_truncation--------------------
1140 // Match increment with optional truncation:
1141 // CHAR: (i+1)&0x7fff, BYTE: ((i+1)<<8)>>8, or SHORT: ((i+1)<<16)>>16
1142 // Return NULL for failure. Success returns the increment node.
1143 Node* CountedLoopNode::match_incr_with_optional_truncation(
1144                       Node* expr, Node** trunc1, Node** trunc2, const TypeInt** trunc_type) {
1145   // Quick cutouts:
1146   if (expr == NULL || expr->req() != 3)  return NULL;
1147 
1148   Node *t1 = NULL;
1149   Node *t2 = NULL;
1150   const TypeInt* trunc_t = TypeInt::INT;
1151   Node* n1 = expr;
1152   int   n1op = n1->Opcode();
1153 
1154   // Try to strip (n1 & M) or (n1 << N >> N) from n1.
1155   if (n1op == Op_AndI &&
1156       n1->in(2)->is_Con() &&
1157       n1->in(2)->bottom_type()->is_int()->get_con() == 0x7fff) {
1158     // %%% This check should match any mask of 2**K-1.
1159     t1 = n1;
1160     n1 = t1->in(1);
1161     n1op = n1->Opcode();
1162     trunc_t = TypeInt::CHAR;
1163   } else if (n1op == Op_RShiftI &&
1164              n1->in(1) != NULL &&
1165              n1->in(1)->Opcode() == Op_LShiftI &&
1166              n1->in(2) == n1->in(1)->in(2) &&
1167              n1->in(2)->is_Con()) {
1168     jint shift = n1->in(2)->bottom_type()->is_int()->get_con();
1169     // %%% This check should match any shift in [1..31].
1170     if (shift == 16 || shift == 8) {
1171       t1 = n1;
1172       t2 = t1->in(1);
1173       n1 = t2->in(1);
1174       n1op = n1->Opcode();
1175       if (shift == 16) {
1176         trunc_t = TypeInt::SHORT;
1177       } else if (shift == 8) {
1178         trunc_t = TypeInt::BYTE;
1179       }
1180     }
1181   }
1182 
1183   // If (maybe after stripping) it is an AddI, we won:
1184   if (n1op == Op_AddI) {
1185     *trunc1 = t1;
1186     *trunc2 = t2;
1187     *trunc_type = trunc_t;
1188     return n1;
1189   }
1190 
1191   // failed
1192   return NULL;
1193 }
1194 
1195 LoopNode* CountedLoopNode::skip_strip_mined(int expect_skeleton) {
1196   if (is_strip_mined()) {
1197     verify_strip_mined(expect_skeleton);
1198     return in(EntryControl)->as_Loop();
1199   }
1200   return this;
1201 }
1202 
1203 OuterStripMinedLoopNode* CountedLoopNode::outer_loop() const {
1204   assert(is_strip_mined(), "not a strip mined loop");
1205   Node* c = in(EntryControl);
1206   if (c == NULL || c->is_top() || !c->is_OuterStripMinedLoop()) {
1207     return NULL;
1208   }
1209   return c->as_OuterStripMinedLoop();
1210 }
1211 
1212 IfTrueNode* OuterStripMinedLoopNode::outer_loop_tail() const {
1213   Node* c = in(LoopBackControl);
1214   if (c == NULL || c->is_top()) {
1215     return NULL;
1216   }
1217   return c->as_IfTrue();
1218 }
1219 
1220 IfTrueNode* CountedLoopNode::outer_loop_tail() const {
1221   LoopNode* l = outer_loop();
1222   if (l == NULL) {
1223     return NULL;
1224   }
1225   return l->outer_loop_tail();
1226 }
1227 
1228 OuterStripMinedLoopEndNode* OuterStripMinedLoopNode::outer_loop_end() const {
1229   IfTrueNode* proj = outer_loop_tail();
1230   if (proj == NULL) {
1231     return NULL;
1232   }
1233   Node* c = proj->in(0);
1234   if (c == NULL || c->is_top() || c->outcnt() != 2) {
1235     return NULL;
1236   }
1237   return c->as_OuterStripMinedLoopEnd();
1238 }
1239 
1240 OuterStripMinedLoopEndNode* CountedLoopNode::outer_loop_end() const {
1241   LoopNode* l = outer_loop();
1242   if (l == NULL) {
1243     return NULL;
1244   }
1245   return l->outer_loop_end();
1246 }
1247 
1248 IfFalseNode* OuterStripMinedLoopNode::outer_loop_exit() const {
1249   IfNode* le = outer_loop_end();
1250   if (le == NULL) {
1251     return NULL;
1252   }
1253   Node* c = le->proj_out_or_null(false);
1254   if (c == NULL) {
1255     return NULL;
1256   }
1257   return c->as_IfFalse();
1258 }
1259 
1260 IfFalseNode* CountedLoopNode::outer_loop_exit() const {
1261   LoopNode* l = outer_loop();
1262   if (l == NULL) {
1263     return NULL;
1264   }
1265   return l->outer_loop_exit();
1266 }
1267 
1268 SafePointNode* OuterStripMinedLoopNode::outer_safepoint() const {
1269   IfNode* le = outer_loop_end();
1270   if (le == NULL) {
1271     return NULL;
1272   }
1273   Node* c = le->in(0);
1274   if (c == NULL || c->is_top()) {
1275     return NULL;
1276   }
1277   assert(c->Opcode() == Op_SafePoint, "broken outer loop");
1278   return c->as_SafePoint();
1279 }
1280 
1281 SafePointNode* CountedLoopNode::outer_safepoint() const {
1282   LoopNode* l = outer_loop();
1283   if (l == NULL) {
1284     return NULL;
1285   }
1286   return l->outer_safepoint();
1287 }
1288 
1289 Node* CountedLoopNode::skip_predicates_from_entry(Node* ctrl) {
1290     while (ctrl != NULL && ctrl->is_Proj() && ctrl->in(0)->is_If() &&
1291            ctrl->in(0)->as_If()->proj_out(1-ctrl->as_Proj()->_con)->outcnt() == 1 &&
1292            ctrl->in(0)->as_If()->proj_out(1-ctrl->as_Proj()->_con)->unique_out()->Opcode() == Op_Halt) {
1293       ctrl = ctrl->in(0)->in(0);
1294     }
1295 
1296     return ctrl;
1297   }
1298 
1299 Node* CountedLoopNode::skip_predicates() {
1300   if (is_main_loop()) {
1301     Node* ctrl = skip_strip_mined()->in(LoopNode::EntryControl);
1302 
1303     return skip_predicates_from_entry(ctrl);
1304   }
1305   return in(LoopNode::EntryControl);
1306 }
1307 
1308 void OuterStripMinedLoopNode::adjust_strip_mined_loop(PhaseIterGVN* igvn) {
1309   // Look for the outer & inner strip mined loop, reduce number of
1310   // iterations of the inner loop, set exit condition of outer loop,
1311   // construct required phi nodes for outer loop.
1312   CountedLoopNode* inner_cl = unique_ctrl_out()->as_CountedLoop();
1313   assert(inner_cl->is_strip_mined(), "inner loop should be strip mined");
1314   Node* inner_iv_phi = inner_cl->phi();
1315   if (inner_iv_phi == NULL) {
1316     IfNode* outer_le = outer_loop_end();
1317     Node* iff = igvn->transform(new IfNode(outer_le->in(0), outer_le->in(1), outer_le->_prob, outer_le->_fcnt));
1318     igvn->replace_node(outer_le, iff);
1319     inner_cl->clear_strip_mined();
1320     return;
1321   }
1322   CountedLoopEndNode* inner_cle = inner_cl->loopexit();
1323 
1324   int stride = inner_cl->stride_con();
1325   jlong scaled_iters_long = ((jlong)LoopStripMiningIter) * ABS(stride);
1326   int scaled_iters = (int)scaled_iters_long;
1327   int short_scaled_iters = LoopStripMiningIterShortLoop* ABS(stride);
1328   const TypeInt* inner_iv_t = igvn->type(inner_iv_phi)->is_int();
1329   jlong iter_estimate = (jlong)inner_iv_t->_hi - (jlong)inner_iv_t->_lo;
1330   assert(iter_estimate > 0, "broken");
1331   if ((jlong)scaled_iters != scaled_iters_long || iter_estimate <= short_scaled_iters) {
1332     // Remove outer loop and safepoint (too few iterations)
1333     Node* outer_sfpt = outer_safepoint();
1334     Node* outer_out = outer_loop_exit();
1335     igvn->replace_node(outer_out, outer_sfpt->in(0));
1336     igvn->replace_input_of(outer_sfpt, 0, igvn->C->top());
1337     inner_cl->clear_strip_mined();
1338     return;
1339   }
1340   if (iter_estimate <= scaled_iters_long) {
1341     // We would only go through one iteration of
1342     // the outer loop: drop the outer loop but
1343     // keep the safepoint so we don't run for
1344     // too long without a safepoint
1345     IfNode* outer_le = outer_loop_end();
1346     Node* iff = igvn->transform(new IfNode(outer_le->in(0), outer_le->in(1), outer_le->_prob, outer_le->_fcnt));
1347     igvn->replace_node(outer_le, iff);
1348     inner_cl->clear_strip_mined();
1349     return;
1350   }
1351 
1352   Node* cle_tail = inner_cle->proj_out(true);
1353   ResourceMark rm;
1354   Node_List old_new;
1355   if (cle_tail->outcnt() > 1) {
1356     // Look for nodes on backedge of inner loop and clone them
1357     Unique_Node_List backedge_nodes;
1358     for (DUIterator_Fast imax, i = cle_tail->fast_outs(imax); i < imax; i++) {
1359       Node* u = cle_tail->fast_out(i);
1360       if (u != inner_cl) {
1361         assert(!u->is_CFG(), "control flow on the backedge?");
1362         backedge_nodes.push(u);
1363       }
1364     }
1365     uint last = igvn->C->unique();
1366     for (uint next = 0; next < backedge_nodes.size(); next++) {
1367       Node* n = backedge_nodes.at(next);
1368       old_new.map(n->_idx, n->clone());
1369       for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
1370         Node* u = n->fast_out(i);
1371         assert(!u->is_CFG(), "broken");
1372         if (u->_idx >= last) {
1373           continue;
1374         }
1375         if (!u->is_Phi()) {
1376           backedge_nodes.push(u);
1377         } else {
1378           assert(u->in(0) == inner_cl, "strange phi on the backedge");
1379         }
1380       }
1381     }
1382     // Put the clones on the outer loop backedge
1383     Node* le_tail = outer_loop_tail();
1384     for (uint next = 0; next < backedge_nodes.size(); next++) {
1385       Node *n = old_new[backedge_nodes.at(next)->_idx];
1386       for (uint i = 1; i < n->req(); i++) {
1387         if (n->in(i) != NULL && old_new[n->in(i)->_idx] != NULL) {
1388           n->set_req(i, old_new[n->in(i)->_idx]);
1389         }
1390       }
1391       if (n->in(0) != NULL && n->in(0) == cle_tail) {
1392         n->set_req(0, le_tail);
1393       }
1394       igvn->register_new_node_with_optimizer(n);
1395     }
1396   }
1397 
1398   Node* iv_phi = NULL;
1399   // Make a clone of each phi in the inner loop
1400   // for the outer loop
1401   for (uint i = 0; i < inner_cl->outcnt(); i++) {
1402     Node* u = inner_cl->raw_out(i);
1403     if (u->is_Phi()) {
1404       assert(u->in(0) == inner_cl, "inconsistent");
1405       Node* phi = u->clone();
1406       phi->set_req(0, this);
1407       Node* be = old_new[phi->in(LoopNode::LoopBackControl)->_idx];
1408       if (be != NULL) {
1409         phi->set_req(LoopNode::LoopBackControl, be);
1410       }
1411       phi = igvn->transform(phi);
1412       igvn->replace_input_of(u, LoopNode::EntryControl, phi);
1413       if (u == inner_iv_phi) {
1414         iv_phi = phi;
1415       }
1416     }
1417   }
1418   Node* cle_out = inner_cle->proj_out(false);
1419   if (cle_out->outcnt() > 1) {
1420     // Look for chains of stores that were sunk
1421     // out of the inner loop and are in the outer loop
1422     for (DUIterator_Fast imax, i = cle_out->fast_outs(imax); i < imax; i++) {
1423       Node* u = cle_out->fast_out(i);
1424       if (u->is_Store()) {
1425         Node* first = u;
1426         for(;;) {
1427           Node* next = first->in(MemNode::Memory);
1428           if (!next->is_Store() || next->in(0) != cle_out) {
1429             break;
1430           }
1431           first = next;
1432         }
1433         Node* last = u;
1434         for(;;) {
1435           Node* next = NULL;
1436           for (DUIterator_Fast jmax, j = last->fast_outs(jmax); j < jmax; j++) {
1437             Node* uu = last->fast_out(j);
1438             if (uu->is_Store() && uu->in(0) == cle_out) {
1439               assert(next == NULL, "only one in the outer loop");
1440               next = uu;
1441             }
1442           }
1443           if (next == NULL) {
1444             break;
1445           }
1446           last = next;
1447         }
1448         Node* phi = NULL;
1449         for (DUIterator_Fast jmax, j = fast_outs(jmax); j < jmax; j++) {
1450           Node* uu = fast_out(j);
1451           if (uu->is_Phi()) {
1452             Node* be = uu->in(LoopNode::LoopBackControl);
1453             if (be->is_Store() && old_new[be->_idx] != NULL) {
1454               assert(false, "store on the backedge + sunk stores: unsupported");
1455               // drop outer loop
1456               IfNode* outer_le = outer_loop_end();
1457               Node* iff = igvn->transform(new IfNode(outer_le->in(0), outer_le->in(1), outer_le->_prob, outer_le->_fcnt));
1458               igvn->replace_node(outer_le, iff);
1459               inner_cl->clear_strip_mined();
1460               return;
1461             }
1462             if (be == last || be == first->in(MemNode::Memory)) {
1463               assert(phi == NULL, "only one phi");
1464               phi = uu;
1465             }
1466           }
1467         }
1468 #ifdef ASSERT
1469         for (DUIterator_Fast jmax, j = fast_outs(jmax); j < jmax; j++) {
1470           Node* uu = fast_out(j);
1471           if (uu->is_Phi() && uu->bottom_type() == Type::MEMORY) {
1472             if (uu->adr_type() == igvn->C->get_adr_type(igvn->C->get_alias_index(u->adr_type()))) {
1473               assert(phi == uu, "what's that phi?");
1474             } else if (uu->adr_type() == TypePtr::BOTTOM) {
1475               Node* n = uu->in(LoopNode::LoopBackControl);
1476               uint limit = igvn->C->live_nodes();
1477               uint i = 0;
1478               while (n != uu) {
1479                 i++;
1480                 assert(i < limit, "infinite loop");
1481                 if (n->is_Proj()) {
1482                   n = n->in(0);
1483                 } else if (n->is_SafePoint() || n->is_MemBar()) {
1484                   n = n->in(TypeFunc::Memory);
1485                 } else if (n->is_Phi()) {
1486                   n = n->in(1);
1487                 } else if (n->is_MergeMem()) {
1488                   n = n->as_MergeMem()->memory_at(igvn->C->get_alias_index(u->adr_type()));
1489                 } else if (n->is_Store() || n->is_LoadStore() || n->is_ClearArray()) {
1490                   n = n->in(MemNode::Memory);
1491                 } else {
1492                   n->dump();
1493                   ShouldNotReachHere();
1494                 }
1495               }
1496             }
1497           }
1498         }
1499 #endif
1500         if (phi == NULL) {
1501           // If the an entire chains was sunk, the
1502           // inner loop has no phi for that memory
1503           // slice, create one for the outer loop
1504           phi = PhiNode::make(this, first->in(MemNode::Memory), Type::MEMORY,
1505                               igvn->C->get_adr_type(igvn->C->get_alias_index(u->adr_type())));
1506           phi->set_req(LoopNode::LoopBackControl, last);
1507           phi = igvn->transform(phi);
1508           igvn->replace_input_of(first, MemNode::Memory, phi);
1509         } else {
1510           // Or fix the outer loop fix to include
1511           // that chain of stores.
1512           Node* be = phi->in(LoopNode::LoopBackControl);
1513           assert(!(be->is_Store() && old_new[be->_idx] != NULL), "store on the backedge + sunk stores: unsupported");
1514           if (be == first->in(MemNode::Memory)) {
1515             if (be == phi->in(LoopNode::LoopBackControl)) {
1516               igvn->replace_input_of(phi, LoopNode::LoopBackControl, last);
1517             } else {
1518               igvn->replace_input_of(be, MemNode::Memory, last);
1519             }
1520           } else {
1521 #ifdef ASSERT
1522             if (be == phi->in(LoopNode::LoopBackControl)) {
1523               assert(phi->in(LoopNode::LoopBackControl) == last, "");
1524             } else {
1525               assert(be->in(MemNode::Memory) == last, "");
1526             }
1527 #endif
1528           }
1529         }
1530       }
1531     }
1532   }
1533 
1534   if (iv_phi != NULL) {
1535     // Now adjust the inner loop's exit condition
1536     Node* limit = inner_cl->limit();
1537     Node* sub = NULL;
1538     if (stride > 0) {
1539       sub = igvn->transform(new SubINode(limit, iv_phi));
1540     } else {
1541       sub = igvn->transform(new SubINode(iv_phi, limit));
1542     }
1543     Node* min = igvn->transform(new MinINode(sub, igvn->intcon(scaled_iters)));
1544     Node* new_limit = NULL;
1545     if (stride > 0) {
1546       new_limit = igvn->transform(new AddINode(min, iv_phi));
1547     } else {
1548       new_limit = igvn->transform(new SubINode(iv_phi, min));
1549     }
1550     Node* cmp = inner_cle->cmp_node()->clone();
1551     igvn->replace_input_of(cmp, 2, new_limit);
1552     Node* bol = inner_cle->in(CountedLoopEndNode::TestValue)->clone();
1553     cmp->set_req(2, limit);
1554     bol->set_req(1, igvn->transform(cmp));
1555     igvn->replace_input_of(outer_loop_end(), 1, igvn->transform(bol));
1556   } else {
1557     assert(false, "should be able to adjust outer loop");
1558     IfNode* outer_le = outer_loop_end();
1559     Node* iff = igvn->transform(new IfNode(outer_le->in(0), outer_le->in(1), outer_le->_prob, outer_le->_fcnt));
1560     igvn->replace_node(outer_le, iff);
1561     inner_cl->clear_strip_mined();
1562   }
1563 }
1564 
1565 const Type* OuterStripMinedLoopEndNode::Value(PhaseGVN* phase) const {
1566   if (!in(0)) return Type::TOP;
1567   if (phase->type(in(0)) == Type::TOP)
1568     return Type::TOP;
1569 
1570   return TypeTuple::IFBOTH;
1571 }
1572 
1573 Node *OuterStripMinedLoopEndNode::Ideal(PhaseGVN *phase, bool can_reshape) {
1574   if (remove_dead_region(phase, can_reshape))  return this;
1575 
1576   return NULL;
1577 }
1578 
1579 //------------------------------filtered_type--------------------------------
1580 // Return a type based on condition control flow
1581 // A successful return will be a type that is restricted due
1582 // to a series of dominating if-tests, such as:
1583 //    if (i < 10) {
1584 //       if (i > 0) {
1585 //          here: "i" type is [1..10)
1586 //       }
1587 //    }
1588 // or a control flow merge
1589 //    if (i < 10) {
1590 //       do {
1591 //          phi( , ) -- at top of loop type is [min_int..10)
1592 //         i = ?
1593 //       } while ( i < 10)
1594 //
1595 const TypeInt* PhaseIdealLoop::filtered_type( Node *n, Node* n_ctrl) {
1596   assert(n && n->bottom_type()->is_int(), "must be int");
1597   const TypeInt* filtered_t = NULL;
1598   if (!n->is_Phi()) {
1599     assert(n_ctrl != NULL || n_ctrl == C->top(), "valid control");
1600     filtered_t = filtered_type_from_dominators(n, n_ctrl);
1601 
1602   } else {
1603     Node* phi    = n->as_Phi();
1604     Node* region = phi->in(0);
1605     assert(n_ctrl == NULL || n_ctrl == region, "ctrl parameter must be region");
1606     if (region && region != C->top()) {
1607       for (uint i = 1; i < phi->req(); i++) {
1608         Node* val   = phi->in(i);
1609         Node* use_c = region->in(i);
1610         const TypeInt* val_t = filtered_type_from_dominators(val, use_c);
1611         if (val_t != NULL) {
1612           if (filtered_t == NULL) {
1613             filtered_t = val_t;
1614           } else {
1615             filtered_t = filtered_t->meet(val_t)->is_int();
1616           }
1617         }
1618       }
1619     }
1620   }
1621   const TypeInt* n_t = _igvn.type(n)->is_int();
1622   if (filtered_t != NULL) {
1623     n_t = n_t->join(filtered_t)->is_int();
1624   }
1625   return n_t;
1626 }
1627 
1628 
1629 //------------------------------filtered_type_from_dominators--------------------------------
1630 // Return a possibly more restrictive type for val based on condition control flow of dominators
1631 const TypeInt* PhaseIdealLoop::filtered_type_from_dominators( Node* val, Node *use_ctrl) {
1632   if (val->is_Con()) {
1633      return val->bottom_type()->is_int();
1634   }
1635   uint if_limit = 10; // Max number of dominating if's visited
1636   const TypeInt* rtn_t = NULL;
1637 
1638   if (use_ctrl && use_ctrl != C->top()) {
1639     Node* val_ctrl = get_ctrl(val);
1640     uint val_dom_depth = dom_depth(val_ctrl);
1641     Node* pred = use_ctrl;
1642     uint if_cnt = 0;
1643     while (if_cnt < if_limit) {
1644       if ((pred->Opcode() == Op_IfTrue || pred->Opcode() == Op_IfFalse)) {
1645         if_cnt++;
1646         const TypeInt* if_t = IfNode::filtered_int_type(&_igvn, val, pred);
1647         if (if_t != NULL) {
1648           if (rtn_t == NULL) {
1649             rtn_t = if_t;
1650           } else {
1651             rtn_t = rtn_t->join(if_t)->is_int();
1652           }
1653         }
1654       }
1655       pred = idom(pred);
1656       if (pred == NULL || pred == C->top()) {
1657         break;
1658       }
1659       // Stop if going beyond definition block of val
1660       if (dom_depth(pred) < val_dom_depth) {
1661         break;
1662       }
1663     }
1664   }
1665   return rtn_t;
1666 }
1667 
1668 
1669 //------------------------------dump_spec--------------------------------------
1670 // Dump special per-node info
1671 #ifndef PRODUCT
1672 void CountedLoopEndNode::dump_spec(outputStream *st) const {
1673   if( in(TestValue) != NULL && in(TestValue)->is_Bool() ) {
1674     BoolTest bt( test_trip()); // Added this for g++.
1675 
1676     st->print("[");
1677     bt.dump_on(st);
1678     st->print("]");
1679   }
1680   st->print(" ");
1681   IfNode::dump_spec(st);
1682 }
1683 #endif
1684 
1685 //=============================================================================
1686 //------------------------------is_member--------------------------------------
1687 // Is 'l' a member of 'this'?
1688 bool IdealLoopTree::is_member(const IdealLoopTree *l) const {
1689   while( l->_nest > _nest ) l = l->_parent;
1690   return l == this;
1691 }
1692 
1693 //------------------------------set_nest---------------------------------------
1694 // Set loop tree nesting depth.  Accumulate _has_call bits.
1695 int IdealLoopTree::set_nest( uint depth ) {
1696   _nest = depth;
1697   int bits = _has_call;
1698   if( _child ) bits |= _child->set_nest(depth+1);
1699   if( bits ) _has_call = 1;
1700   if( _next  ) bits |= _next ->set_nest(depth  );
1701   return bits;
1702 }
1703 
1704 //------------------------------split_fall_in----------------------------------
1705 // Split out multiple fall-in edges from the loop header.  Move them to a
1706 // private RegionNode before the loop.  This becomes the loop landing pad.
1707 void IdealLoopTree::split_fall_in( PhaseIdealLoop *phase, int fall_in_cnt ) {
1708   PhaseIterGVN &igvn = phase->_igvn;
1709   uint i;
1710 
1711   // Make a new RegionNode to be the landing pad.
1712   Node *landing_pad = new RegionNode( fall_in_cnt+1 );
1713   phase->set_loop(landing_pad,_parent);
1714   // Gather all the fall-in control paths into the landing pad
1715   uint icnt = fall_in_cnt;
1716   uint oreq = _head->req();
1717   for( i = oreq-1; i>0; i-- )
1718     if( !phase->is_member( this, _head->in(i) ) )
1719       landing_pad->set_req(icnt--,_head->in(i));
1720 
1721   // Peel off PhiNode edges as well
1722   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
1723     Node *oj = _head->fast_out(j);
1724     if( oj->is_Phi() ) {
1725       PhiNode* old_phi = oj->as_Phi();
1726       assert( old_phi->region() == _head, "" );
1727       igvn.hash_delete(old_phi);   // Yank from hash before hacking edges
1728       Node *p = PhiNode::make_blank(landing_pad, old_phi);
1729       uint icnt = fall_in_cnt;
1730       for( i = oreq-1; i>0; i-- ) {
1731         if( !phase->is_member( this, _head->in(i) ) ) {
1732           p->init_req(icnt--, old_phi->in(i));
1733           // Go ahead and clean out old edges from old phi
1734           old_phi->del_req(i);
1735         }
1736       }
1737       // Search for CSE's here, because ZKM.jar does a lot of
1738       // loop hackery and we need to be a little incremental
1739       // with the CSE to avoid O(N^2) node blow-up.
1740       Node *p2 = igvn.hash_find_insert(p); // Look for a CSE
1741       if( p2 ) {                // Found CSE
1742         p->destruct();          // Recover useless new node
1743         p = p2;                 // Use old node
1744       } else {
1745         igvn.register_new_node_with_optimizer(p, old_phi);
1746       }
1747       // Make old Phi refer to new Phi.
1748       old_phi->add_req(p);
1749       // Check for the special case of making the old phi useless and
1750       // disappear it.  In JavaGrande I have a case where this useless
1751       // Phi is the loop limit and prevents recognizing a CountedLoop
1752       // which in turn prevents removing an empty loop.
1753       Node *id_old_phi = igvn.apply_identity(old_phi);
1754       if( id_old_phi != old_phi ) { // Found a simple identity?
1755         // Note that I cannot call 'replace_node' here, because
1756         // that will yank the edge from old_phi to the Region and
1757         // I'm mid-iteration over the Region's uses.
1758         for (DUIterator_Last imin, i = old_phi->last_outs(imin); i >= imin; ) {
1759           Node* use = old_phi->last_out(i);
1760           igvn.rehash_node_delayed(use);
1761           uint uses_found = 0;
1762           for (uint j = 0; j < use->len(); j++) {
1763             if (use->in(j) == old_phi) {
1764               if (j < use->req()) use->set_req (j, id_old_phi);
1765               else                use->set_prec(j, id_old_phi);
1766               uses_found++;
1767             }
1768           }
1769           i -= uses_found;    // we deleted 1 or more copies of this edge
1770         }
1771       }
1772       igvn._worklist.push(old_phi);
1773     }
1774   }
1775   // Finally clean out the fall-in edges from the RegionNode
1776   for( i = oreq-1; i>0; i-- ) {
1777     if( !phase->is_member( this, _head->in(i) ) ) {
1778       _head->del_req(i);
1779     }
1780   }
1781   igvn.rehash_node_delayed(_head);
1782   // Transform landing pad
1783   igvn.register_new_node_with_optimizer(landing_pad, _head);
1784   // Insert landing pad into the header
1785   _head->add_req(landing_pad);
1786 }
1787 
1788 //------------------------------split_outer_loop-------------------------------
1789 // Split out the outermost loop from this shared header.
1790 void IdealLoopTree::split_outer_loop( PhaseIdealLoop *phase ) {
1791   PhaseIterGVN &igvn = phase->_igvn;
1792 
1793   // Find index of outermost loop; it should also be my tail.
1794   uint outer_idx = 1;
1795   while( _head->in(outer_idx) != _tail ) outer_idx++;
1796 
1797   // Make a LoopNode for the outermost loop.
1798   Node *ctl = _head->in(LoopNode::EntryControl);
1799   Node *outer = new LoopNode( ctl, _head->in(outer_idx) );
1800   outer = igvn.register_new_node_with_optimizer(outer, _head);
1801   phase->set_created_loop_node();
1802 
1803   // Outermost loop falls into '_head' loop
1804   _head->set_req(LoopNode::EntryControl, outer);
1805   _head->del_req(outer_idx);
1806   // Split all the Phis up between '_head' loop and 'outer' loop.
1807   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
1808     Node *out = _head->fast_out(j);
1809     if( out->is_Phi() ) {
1810       PhiNode *old_phi = out->as_Phi();
1811       assert( old_phi->region() == _head, "" );
1812       Node *phi = PhiNode::make_blank(outer, old_phi);
1813       phi->init_req(LoopNode::EntryControl,    old_phi->in(LoopNode::EntryControl));
1814       phi->init_req(LoopNode::LoopBackControl, old_phi->in(outer_idx));
1815       phi = igvn.register_new_node_with_optimizer(phi, old_phi);
1816       // Make old Phi point to new Phi on the fall-in path
1817       igvn.replace_input_of(old_phi, LoopNode::EntryControl, phi);
1818       old_phi->del_req(outer_idx);
1819     }
1820   }
1821 
1822   // Use the new loop head instead of the old shared one
1823   _head = outer;
1824   phase->set_loop(_head, this);
1825 }
1826 
1827 //------------------------------fix_parent-------------------------------------
1828 static void fix_parent( IdealLoopTree *loop, IdealLoopTree *parent ) {
1829   loop->_parent = parent;
1830   if( loop->_child ) fix_parent( loop->_child, loop   );
1831   if( loop->_next  ) fix_parent( loop->_next , parent );
1832 }
1833 
1834 //------------------------------estimate_path_freq-----------------------------
1835 static float estimate_path_freq( Node *n ) {
1836   // Try to extract some path frequency info
1837   IfNode *iff;
1838   for( int i = 0; i < 50; i++ ) { // Skip through a bunch of uncommon tests
1839     uint nop = n->Opcode();
1840     if( nop == Op_SafePoint ) {   // Skip any safepoint
1841       n = n->in(0);
1842       continue;
1843     }
1844     if( nop == Op_CatchProj ) {   // Get count from a prior call
1845       // Assume call does not always throw exceptions: means the call-site
1846       // count is also the frequency of the fall-through path.
1847       assert( n->is_CatchProj(), "" );
1848       if( ((CatchProjNode*)n)->_con != CatchProjNode::fall_through_index )
1849         return 0.0f;            // Assume call exception path is rare
1850       Node *call = n->in(0)->in(0)->in(0);
1851       assert( call->is_Call(), "expect a call here" );
1852       const JVMState *jvms = ((CallNode*)call)->jvms();
1853       ciMethodData* methodData = jvms->method()->method_data();
1854       if (!methodData->is_mature())  return 0.0f; // No call-site data
1855       ciProfileData* data = methodData->bci_to_data(jvms->bci());
1856       if ((data == NULL) || !data->is_CounterData()) {
1857         // no call profile available, try call's control input
1858         n = n->in(0);
1859         continue;
1860       }
1861       return data->as_CounterData()->count()/FreqCountInvocations;
1862     }
1863     // See if there's a gating IF test
1864     Node *n_c = n->in(0);
1865     if( !n_c->is_If() ) break;       // No estimate available
1866     iff = n_c->as_If();
1867     if( iff->_fcnt != COUNT_UNKNOWN )   // Have a valid count?
1868       // Compute how much count comes on this path
1869       return ((nop == Op_IfTrue) ? iff->_prob : 1.0f - iff->_prob) * iff->_fcnt;
1870     // Have no count info.  Skip dull uncommon-trap like branches.
1871     if( (nop == Op_IfTrue  && iff->_prob < PROB_LIKELY_MAG(5)) ||
1872         (nop == Op_IfFalse && iff->_prob > PROB_UNLIKELY_MAG(5)) )
1873       break;
1874     // Skip through never-taken branch; look for a real loop exit.
1875     n = iff->in(0);
1876   }
1877   return 0.0f;                  // No estimate available
1878 }
1879 
1880 //------------------------------merge_many_backedges---------------------------
1881 // Merge all the backedges from the shared header into a private Region.
1882 // Feed that region as the one backedge to this loop.
1883 void IdealLoopTree::merge_many_backedges( PhaseIdealLoop *phase ) {
1884   uint i;
1885 
1886   // Scan for the top 2 hottest backedges
1887   float hotcnt = 0.0f;
1888   float warmcnt = 0.0f;
1889   uint hot_idx = 0;
1890   // Loop starts at 2 because slot 1 is the fall-in path
1891   for( i = 2; i < _head->req(); i++ ) {
1892     float cnt = estimate_path_freq(_head->in(i));
1893     if( cnt > hotcnt ) {       // Grab hottest path
1894       warmcnt = hotcnt;
1895       hotcnt = cnt;
1896       hot_idx = i;
1897     } else if( cnt > warmcnt ) { // And 2nd hottest path
1898       warmcnt = cnt;
1899     }
1900   }
1901 
1902   // See if the hottest backedge is worthy of being an inner loop
1903   // by being much hotter than the next hottest backedge.
1904   if( hotcnt <= 0.0001 ||
1905       hotcnt < 2.0*warmcnt ) hot_idx = 0;// No hot backedge
1906 
1907   // Peel out the backedges into a private merge point; peel
1908   // them all except optionally hot_idx.
1909   PhaseIterGVN &igvn = phase->_igvn;
1910 
1911   Node *hot_tail = NULL;
1912   // Make a Region for the merge point
1913   Node *r = new RegionNode(1);
1914   for( i = 2; i < _head->req(); i++ ) {
1915     if( i != hot_idx )
1916       r->add_req( _head->in(i) );
1917     else hot_tail = _head->in(i);
1918   }
1919   igvn.register_new_node_with_optimizer(r, _head);
1920   // Plug region into end of loop _head, followed by hot_tail
1921   while( _head->req() > 3 ) _head->del_req( _head->req()-1 );
1922   igvn.replace_input_of(_head, 2, r);
1923   if( hot_idx ) _head->add_req(hot_tail);
1924 
1925   // Split all the Phis up between '_head' loop and the Region 'r'
1926   for (DUIterator_Fast jmax, j = _head->fast_outs(jmax); j < jmax; j++) {
1927     Node *out = _head->fast_out(j);
1928     if( out->is_Phi() ) {
1929       PhiNode* n = out->as_Phi();
1930       igvn.hash_delete(n);      // Delete from hash before hacking edges
1931       Node *hot_phi = NULL;
1932       Node *phi = new PhiNode(r, n->type(), n->adr_type());
1933       // Check all inputs for the ones to peel out
1934       uint j = 1;
1935       for( uint i = 2; i < n->req(); i++ ) {
1936         if( i != hot_idx )
1937           phi->set_req( j++, n->in(i) );
1938         else hot_phi = n->in(i);
1939       }
1940       // Register the phi but do not transform until whole place transforms
1941       igvn.register_new_node_with_optimizer(phi, n);
1942       // Add the merge phi to the old Phi
1943       while( n->req() > 3 ) n->del_req( n->req()-1 );
1944       igvn.replace_input_of(n, 2, phi);
1945       if( hot_idx ) n->add_req(hot_phi);
1946     }
1947   }
1948 
1949 
1950   // Insert a new IdealLoopTree inserted below me.  Turn it into a clone
1951   // of self loop tree.  Turn self into a loop headed by _head and with
1952   // tail being the new merge point.
1953   IdealLoopTree *ilt = new IdealLoopTree( phase, _head, _tail );
1954   phase->set_loop(_tail,ilt);   // Adjust tail
1955   _tail = r;                    // Self's tail is new merge point
1956   phase->set_loop(r,this);
1957   ilt->_child = _child;         // New guy has my children
1958   _child = ilt;                 // Self has new guy as only child
1959   ilt->_parent = this;          // new guy has self for parent
1960   ilt->_nest = _nest;           // Same nesting depth (for now)
1961 
1962   // Starting with 'ilt', look for child loop trees using the same shared
1963   // header.  Flatten these out; they will no longer be loops in the end.
1964   IdealLoopTree **pilt = &_child;
1965   while( ilt ) {
1966     if( ilt->_head == _head ) {
1967       uint i;
1968       for( i = 2; i < _head->req(); i++ )
1969         if( _head->in(i) == ilt->_tail )
1970           break;                // Still a loop
1971       if( i == _head->req() ) { // No longer a loop
1972         // Flatten ilt.  Hang ilt's "_next" list from the end of
1973         // ilt's '_child' list.  Move the ilt's _child up to replace ilt.
1974         IdealLoopTree **cp = &ilt->_child;
1975         while( *cp ) cp = &(*cp)->_next;   // Find end of child list
1976         *cp = ilt->_next;       // Hang next list at end of child list
1977         *pilt = ilt->_child;    // Move child up to replace ilt
1978         ilt->_head = NULL;      // Flag as a loop UNIONED into parent
1979         ilt = ilt->_child;      // Repeat using new ilt
1980         continue;               // do not advance over ilt->_child
1981       }
1982       assert( ilt->_tail == hot_tail, "expected to only find the hot inner loop here" );
1983       phase->set_loop(_head,ilt);
1984     }
1985     pilt = &ilt->_child;        // Advance to next
1986     ilt = *pilt;
1987   }
1988 
1989   if( _child ) fix_parent( _child, this );
1990 }
1991 
1992 //------------------------------beautify_loops---------------------------------
1993 // Split shared headers and insert loop landing pads.
1994 // Insert a LoopNode to replace the RegionNode.
1995 // Return TRUE if loop tree is structurally changed.
1996 bool IdealLoopTree::beautify_loops( PhaseIdealLoop *phase ) {
1997   bool result = false;
1998   // Cache parts in locals for easy
1999   PhaseIterGVN &igvn = phase->_igvn;
2000 
2001   igvn.hash_delete(_head);      // Yank from hash before hacking edges
2002 
2003   // Check for multiple fall-in paths.  Peel off a landing pad if need be.
2004   int fall_in_cnt = 0;
2005   for( uint i = 1; i < _head->req(); i++ )
2006     if( !phase->is_member( this, _head->in(i) ) )
2007       fall_in_cnt++;
2008   assert( fall_in_cnt, "at least 1 fall-in path" );
2009   if( fall_in_cnt > 1 )         // Need a loop landing pad to merge fall-ins
2010     split_fall_in( phase, fall_in_cnt );
2011 
2012   // Swap inputs to the _head and all Phis to move the fall-in edge to
2013   // the left.
2014   fall_in_cnt = 1;
2015   while( phase->is_member( this, _head->in(fall_in_cnt) ) )
2016     fall_in_cnt++;
2017   if( fall_in_cnt > 1 ) {
2018     // Since I am just swapping inputs I do not need to update def-use info
2019     Node *tmp = _head->in(1);
2020     igvn.rehash_node_delayed(_head);
2021     _head->set_req( 1, _head->in(fall_in_cnt) );
2022     _head->set_req( fall_in_cnt, tmp );
2023     // Swap also all Phis
2024     for (DUIterator_Fast imax, i = _head->fast_outs(imax); i < imax; i++) {
2025       Node* phi = _head->fast_out(i);
2026       if( phi->is_Phi() ) {
2027         igvn.rehash_node_delayed(phi); // Yank from hash before hacking edges
2028         tmp = phi->in(1);
2029         phi->set_req( 1, phi->in(fall_in_cnt) );
2030         phi->set_req( fall_in_cnt, tmp );
2031       }
2032     }
2033   }
2034   assert( !phase->is_member( this, _head->in(1) ), "left edge is fall-in" );
2035   assert(  phase->is_member( this, _head->in(2) ), "right edge is loop" );
2036 
2037   // If I am a shared header (multiple backedges), peel off the many
2038   // backedges into a private merge point and use the merge point as
2039   // the one true backedge.
2040   if( _head->req() > 3 ) {
2041     // Merge the many backedges into a single backedge but leave
2042     // the hottest backedge as separate edge for the following peel.
2043     merge_many_backedges( phase );
2044     result = true;
2045   }
2046 
2047   // If I have one hot backedge, peel off myself loop.
2048   // I better be the outermost loop.
2049   if (_head->req() > 3 && !_irreducible) {
2050     split_outer_loop( phase );
2051     result = true;
2052 
2053   } else if (!_head->is_Loop() && !_irreducible) {
2054     // Make a new LoopNode to replace the old loop head
2055     Node *l = new LoopNode( _head->in(1), _head->in(2) );
2056     l = igvn.register_new_node_with_optimizer(l, _head);
2057     phase->set_created_loop_node();
2058     // Go ahead and replace _head
2059     phase->_igvn.replace_node( _head, l );
2060     _head = l;
2061     phase->set_loop(_head, this);
2062   }
2063 
2064   // Now recursively beautify nested loops
2065   if( _child ) result |= _child->beautify_loops( phase );
2066   if( _next  ) result |= _next ->beautify_loops( phase );
2067   return result;
2068 }
2069 
2070 //------------------------------allpaths_check_safepts----------------------------
2071 // Allpaths backwards scan from loop tail, terminating each path at first safepoint
2072 // encountered.  Helper for check_safepts.
2073 void IdealLoopTree::allpaths_check_safepts(VectorSet &visited, Node_List &stack) {
2074   assert(stack.size() == 0, "empty stack");
2075   stack.push(_tail);
2076   visited.Clear();
2077   visited.set(_tail->_idx);
2078   while (stack.size() > 0) {
2079     Node* n = stack.pop();
2080     if (n->is_Call() && n->as_Call()->guaranteed_safepoint()) {
2081       // Terminate this path
2082     } else if (n->Opcode() == Op_SafePoint) {
2083       if (_phase->get_loop(n) != this) {
2084         if (_required_safept == NULL) _required_safept = new Node_List();
2085         _required_safept->push(n);  // save the one closest to the tail
2086       }
2087       // Terminate this path
2088     } else {
2089       uint start = n->is_Region() ? 1 : 0;
2090       uint end   = n->is_Region() && !n->is_Loop() ? n->req() : start + 1;
2091       for (uint i = start; i < end; i++) {
2092         Node* in = n->in(i);
2093         assert(in->is_CFG(), "must be");
2094         if (!visited.test_set(in->_idx) && is_member(_phase->get_loop(in))) {
2095           stack.push(in);
2096         }
2097       }
2098     }
2099   }
2100 }
2101 
2102 //------------------------------check_safepts----------------------------
2103 // Given dominators, try to find loops with calls that must always be
2104 // executed (call dominates loop tail).  These loops do not need non-call
2105 // safepoints (ncsfpt).
2106 //
2107 // A complication is that a safepoint in a inner loop may be needed
2108 // by an outer loop. In the following, the inner loop sees it has a
2109 // call (block 3) on every path from the head (block 2) to the
2110 // backedge (arc 3->2).  So it deletes the ncsfpt (non-call safepoint)
2111 // in block 2, _but_ this leaves the outer loop without a safepoint.
2112 //
2113 //          entry  0
2114 //                 |
2115 //                 v
2116 // outer 1,2    +->1
2117 //              |  |
2118 //              |  v
2119 //              |  2<---+  ncsfpt in 2
2120 //              |_/|\   |
2121 //                 | v  |
2122 // inner 2,3      /  3  |  call in 3
2123 //               /   |  |
2124 //              v    +--+
2125 //        exit  4
2126 //
2127 //
2128 // This method creates a list (_required_safept) of ncsfpt nodes that must
2129 // be protected is created for each loop. When a ncsfpt maybe deleted, it
2130 // is first looked for in the lists for the outer loops of the current loop.
2131 //
2132 // The insights into the problem:
2133 //  A) counted loops are okay
2134 //  B) innermost loops are okay (only an inner loop can delete
2135 //     a ncsfpt needed by an outer loop)
2136 //  C) a loop is immune from an inner loop deleting a safepoint
2137 //     if the loop has a call on the idom-path
2138 //  D) a loop is also immune if it has a ncsfpt (non-call safepoint) on the
2139 //     idom-path that is not in a nested loop
2140 //  E) otherwise, an ncsfpt on the idom-path that is nested in an inner
2141 //     loop needs to be prevented from deletion by an inner loop
2142 //
2143 // There are two analyses:
2144 //  1) The first, and cheaper one, scans the loop body from
2145 //     tail to head following the idom (immediate dominator)
2146 //     chain, looking for the cases (C,D,E) above.
2147 //     Since inner loops are scanned before outer loops, there is summary
2148 //     information about inner loops.  Inner loops can be skipped over
2149 //     when the tail of an inner loop is encountered.
2150 //
2151 //  2) The second, invoked if the first fails to find a call or ncsfpt on
2152 //     the idom path (which is rare), scans all predecessor control paths
2153 //     from the tail to the head, terminating a path when a call or sfpt
2154 //     is encountered, to find the ncsfpt's that are closest to the tail.
2155 //
2156 void IdealLoopTree::check_safepts(VectorSet &visited, Node_List &stack) {
2157   // Bottom up traversal
2158   IdealLoopTree* ch = _child;
2159   if (_child) _child->check_safepts(visited, stack);
2160   if (_next)  _next ->check_safepts(visited, stack);
2161 
2162   if (!_head->is_CountedLoop() && !_has_sfpt && _parent != NULL && !_irreducible) {
2163     bool  has_call         = false; // call on dom-path
2164     bool  has_local_ncsfpt = false; // ncsfpt on dom-path at this loop depth
2165     Node* nonlocal_ncsfpt  = NULL;  // ncsfpt on dom-path at a deeper depth
2166     // Scan the dom-path nodes from tail to head
2167     for (Node* n = tail(); n != _head; n = _phase->idom(n)) {
2168       if (n->is_Call() && n->as_Call()->guaranteed_safepoint()) {
2169         has_call = true;
2170         _has_sfpt = 1;          // Then no need for a safept!
2171         break;
2172       } else if (n->Opcode() == Op_SafePoint) {
2173         if (_phase->get_loop(n) == this) {
2174           has_local_ncsfpt = true;
2175           break;
2176         }
2177         if (nonlocal_ncsfpt == NULL) {
2178           nonlocal_ncsfpt = n; // save the one closest to the tail
2179         }
2180       } else {
2181         IdealLoopTree* nlpt = _phase->get_loop(n);
2182         if (this != nlpt) {
2183           // If at an inner loop tail, see if the inner loop has already
2184           // recorded seeing a call on the dom-path (and stop.)  If not,
2185           // jump to the head of the inner loop.
2186           assert(is_member(nlpt), "nested loop");
2187           Node* tail = nlpt->_tail;
2188           if (tail->in(0)->is_If()) tail = tail->in(0);
2189           if (n == tail) {
2190             // If inner loop has call on dom-path, so does outer loop
2191             if (nlpt->_has_sfpt) {
2192               has_call = true;
2193               _has_sfpt = 1;
2194               break;
2195             }
2196             // Skip to head of inner loop
2197             assert(_phase->is_dominator(_head, nlpt->_head), "inner head dominated by outer head");
2198             n = nlpt->_head;
2199           }
2200         }
2201       }
2202     }
2203     // Record safept's that this loop needs preserved when an
2204     // inner loop attempts to delete it's safepoints.
2205     if (_child != NULL && !has_call && !has_local_ncsfpt) {
2206       if (nonlocal_ncsfpt != NULL) {
2207         if (_required_safept == NULL) _required_safept = new Node_List();
2208         _required_safept->push(nonlocal_ncsfpt);
2209       } else {
2210         // Failed to find a suitable safept on the dom-path.  Now use
2211         // an all paths walk from tail to head, looking for safepoints to preserve.
2212         allpaths_check_safepts(visited, stack);
2213       }
2214     }
2215   }
2216 }
2217 
2218 //---------------------------is_deleteable_safept----------------------------
2219 // Is safept not required by an outer loop?
2220 bool PhaseIdealLoop::is_deleteable_safept(Node* sfpt) {
2221   assert(sfpt->Opcode() == Op_SafePoint, "");
2222   IdealLoopTree* lp = get_loop(sfpt)->_parent;
2223   while (lp != NULL) {
2224     Node_List* sfpts = lp->_required_safept;
2225     if (sfpts != NULL) {
2226       for (uint i = 0; i < sfpts->size(); i++) {
2227         if (sfpt == sfpts->at(i))
2228           return false;
2229       }
2230     }
2231     lp = lp->_parent;
2232   }
2233   return true;
2234 }
2235 
2236 //---------------------------replace_parallel_iv-------------------------------
2237 // Replace parallel induction variable (parallel to trip counter)
2238 void PhaseIdealLoop::replace_parallel_iv(IdealLoopTree *loop) {
2239   assert(loop->_head->is_CountedLoop(), "");
2240   CountedLoopNode *cl = loop->_head->as_CountedLoop();
2241   if (!cl->is_valid_counted_loop())
2242     return;         // skip malformed counted loop
2243   Node *incr = cl->incr();
2244   if (incr == NULL)
2245     return;         // Dead loop?
2246   Node *init = cl->init_trip();
2247   Node *phi  = cl->phi();
2248   int stride_con = cl->stride_con();
2249 
2250   // Visit all children, looking for Phis
2251   for (DUIterator i = cl->outs(); cl->has_out(i); i++) {
2252     Node *out = cl->out(i);
2253     // Look for other phis (secondary IVs). Skip dead ones
2254     if (!out->is_Phi() || out == phi || !has_node(out))
2255       continue;
2256     PhiNode* phi2 = out->as_Phi();
2257     Node *incr2 = phi2->in( LoopNode::LoopBackControl );
2258     // Look for induction variables of the form:  X += constant
2259     if (phi2->region() != loop->_head ||
2260         incr2->req() != 3 ||
2261         incr2->in(1) != phi2 ||
2262         incr2 == incr ||
2263         incr2->Opcode() != Op_AddI ||
2264         !incr2->in(2)->is_Con())
2265       continue;
2266 
2267     // Check for parallel induction variable (parallel to trip counter)
2268     // via an affine function.  In particular, count-down loops with
2269     // count-up array indices are common. We only RCE references off
2270     // the trip-counter, so we need to convert all these to trip-counter
2271     // expressions.
2272     Node *init2 = phi2->in( LoopNode::EntryControl );
2273     int stride_con2 = incr2->in(2)->get_int();
2274 
2275     // The ratio of the two strides cannot be represented as an int
2276     // if stride_con2 is min_int and stride_con is -1.
2277     if (stride_con2 == min_jint && stride_con == -1) {
2278       continue;
2279     }
2280 
2281     // The general case here gets a little tricky.  We want to find the
2282     // GCD of all possible parallel IV's and make a new IV using this
2283     // GCD for the loop.  Then all possible IVs are simple multiples of
2284     // the GCD.  In practice, this will cover very few extra loops.
2285     // Instead we require 'stride_con2' to be a multiple of 'stride_con',
2286     // where +/-1 is the common case, but other integer multiples are
2287     // also easy to handle.
2288     int ratio_con = stride_con2/stride_con;
2289 
2290     if ((ratio_con * stride_con) == stride_con2) { // Check for exact
2291 #ifndef PRODUCT
2292       if (TraceLoopOpts) {
2293         tty->print("Parallel IV: %d ", phi2->_idx);
2294         loop->dump_head();
2295       }
2296 #endif
2297       // Convert to using the trip counter.  The parallel induction
2298       // variable differs from the trip counter by a loop-invariant
2299       // amount, the difference between their respective initial values.
2300       // It is scaled by the 'ratio_con'.
2301       Node* ratio = _igvn.intcon(ratio_con);
2302       set_ctrl(ratio, C->root());
2303       Node* ratio_init = new MulINode(init, ratio);
2304       _igvn.register_new_node_with_optimizer(ratio_init, init);
2305       set_early_ctrl(ratio_init);
2306       Node* diff = new SubINode(init2, ratio_init);
2307       _igvn.register_new_node_with_optimizer(diff, init2);
2308       set_early_ctrl(diff);
2309       Node* ratio_idx = new MulINode(phi, ratio);
2310       _igvn.register_new_node_with_optimizer(ratio_idx, phi);
2311       set_ctrl(ratio_idx, cl);
2312       Node* add = new AddINode(ratio_idx, diff);
2313       _igvn.register_new_node_with_optimizer(add);
2314       set_ctrl(add, cl);
2315       _igvn.replace_node( phi2, add );
2316       // Sometimes an induction variable is unused
2317       if (add->outcnt() == 0) {
2318         _igvn.remove_dead_node(add);
2319       }
2320       --i; // deleted this phi; rescan starting with next position
2321       continue;
2322     }
2323   }
2324 }
2325 
2326 void IdealLoopTree::remove_safepoints(PhaseIdealLoop* phase, bool keep_one) {
2327   Node* keep = NULL;
2328   if (keep_one) {
2329     // Look for a safepoint on the idom-path.
2330     for (Node* i = tail(); i != _head; i = phase->idom(i)) {
2331       if (i->Opcode() == Op_SafePoint && phase->get_loop(i) == this) {
2332         keep = i;
2333         break; // Found one
2334       }
2335     }
2336   }
2337 
2338   // Don't remove any safepoints if it is requested to keep a single safepoint and
2339   // no safepoint was found on idom-path. It is not safe to remove any safepoint
2340   // in this case since there's no safepoint dominating all paths in the loop body.
2341   bool prune = !keep_one || keep != NULL;
2342 
2343   // Delete other safepoints in this loop.
2344   Node_List* sfpts = _safepts;
2345   if (prune && sfpts != NULL) {
2346     assert(keep == NULL || keep->Opcode() == Op_SafePoint, "not safepoint");
2347     for (uint i = 0; i < sfpts->size(); i++) {
2348       Node* n = sfpts->at(i);
2349       assert(phase->get_loop(n) == this, "");
2350       if (n != keep && phase->is_deleteable_safept(n)) {
2351         phase->lazy_replace(n, n->in(TypeFunc::Control));
2352       }
2353     }
2354   }
2355 }
2356 
2357 //------------------------------counted_loop-----------------------------------
2358 // Convert to counted loops where possible
2359 void IdealLoopTree::counted_loop( PhaseIdealLoop *phase ) {
2360 
2361   // For grins, set the inner-loop flag here
2362   if (!_child) {
2363     if (_head->is_Loop()) _head->as_Loop()->set_inner_loop();
2364   }
2365 
2366   IdealLoopTree* loop = this;
2367   if (_head->is_CountedLoop() ||
2368       phase->is_counted_loop(_head, loop)) {
2369 
2370     if (LoopStripMiningIter == 0 || (LoopStripMiningIter > 1 && _child == NULL)) {
2371       // Indicate we do not need a safepoint here
2372       _has_sfpt = 1;
2373     }
2374 
2375     // Remove safepoints
2376     bool keep_one_sfpt = !(_has_call || _has_sfpt);
2377     remove_safepoints(phase, keep_one_sfpt);
2378 
2379     // Look for induction variables
2380     phase->replace_parallel_iv(this);
2381 
2382   } else if (_parent != NULL && !_irreducible) {
2383     // Not a counted loop. Keep one safepoint.
2384     bool keep_one_sfpt = true;
2385     remove_safepoints(phase, keep_one_sfpt);
2386   }
2387 
2388   // Recursively
2389   assert(loop->_child != this || (loop->_head->as_Loop()->is_OuterStripMinedLoop() && _head->as_CountedLoop()->is_strip_mined()), "what kind of loop was added?");
2390   assert(loop->_child != this || (loop->_child->_child == NULL && loop->_child->_next == NULL), "would miss some loops");
2391   if (loop->_child && loop->_child != this) loop->_child->counted_loop(phase);
2392   if (loop->_next)  loop->_next ->counted_loop(phase);
2393 }
2394 
2395 #ifndef PRODUCT
2396 //------------------------------dump_head--------------------------------------
2397 // Dump 1 liner for loop header info
2398 void IdealLoopTree::dump_head( ) const {
2399   for (uint i=0; i<_nest; i++)
2400     tty->print("  ");
2401   tty->print("Loop: N%d/N%d ",_head->_idx,_tail->_idx);
2402   if (_irreducible) tty->print(" IRREDUCIBLE");
2403   Node* entry = _head->is_Loop() ? _head->as_Loop()->skip_strip_mined(-1)->in(LoopNode::EntryControl) : _head->in(LoopNode::EntryControl);
2404   Node* predicate = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_loop_limit_check);
2405   if (predicate != NULL ) {
2406     tty->print(" limit_check");
2407     entry = entry->in(0)->in(0);
2408   }
2409   if (UseLoopPredicate) {
2410     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_predicate);
2411     if (entry != NULL) {
2412       tty->print(" predicated");
2413       entry = PhaseIdealLoop::skip_loop_predicates(entry);
2414     }
2415   }
2416   if (UseProfiledLoopPredicate) {
2417     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, Deoptimization::Reason_profile_predicate);
2418     if (entry != NULL) {
2419       tty->print(" profile_predicated");
2420     }
2421   }
2422   if (_head->is_CountedLoop()) {
2423     CountedLoopNode *cl = _head->as_CountedLoop();
2424     tty->print(" counted");
2425 
2426     Node* init_n = cl->init_trip();
2427     if (init_n  != NULL &&  init_n->is_Con())
2428       tty->print(" [%d,", cl->init_trip()->get_int());
2429     else
2430       tty->print(" [int,");
2431     Node* limit_n = cl->limit();
2432     if (limit_n  != NULL &&  limit_n->is_Con())
2433       tty->print("%d),", cl->limit()->get_int());
2434     else
2435       tty->print("int),");
2436     int stride_con  = cl->stride_con();
2437     if (stride_con > 0) tty->print("+");
2438     tty->print("%d", stride_con);
2439 
2440     tty->print(" (%0.f iters) ", cl->profile_trip_cnt());
2441 
2442     if (cl->is_pre_loop ()) tty->print(" pre" );
2443     if (cl->is_main_loop()) tty->print(" main");
2444     if (cl->is_post_loop()) tty->print(" post");
2445     if (cl->is_vectorized_loop()) tty->print(" vector");
2446     if (cl->range_checks_present()) tty->print(" rc ");
2447     if (cl->is_multiversioned()) tty->print(" multi ");
2448   }
2449   if (_has_call) tty->print(" has_call");
2450   if (_has_sfpt) tty->print(" has_sfpt");
2451   if (_rce_candidate) tty->print(" rce");
2452   if (_safepts != NULL && _safepts->size() > 0) {
2453     tty->print(" sfpts={"); _safepts->dump_simple(); tty->print(" }");
2454   }
2455   if (_required_safept != NULL && _required_safept->size() > 0) {
2456     tty->print(" req={"); _required_safept->dump_simple(); tty->print(" }");
2457   }
2458   if (Verbose) {
2459     tty->print(" body={"); _body.dump_simple(); tty->print(" }");
2460   }
2461   if (_head->is_Loop() && _head->as_Loop()->is_strip_mined()) {
2462     tty->print(" strip_mined");
2463   }
2464   tty->cr();
2465 }
2466 
2467 //------------------------------dump-------------------------------------------
2468 // Dump loops by loop tree
2469 void IdealLoopTree::dump( ) const {
2470   dump_head();
2471   if (_child) _child->dump();
2472   if (_next)  _next ->dump();
2473 }
2474 
2475 #endif
2476 
2477 static void log_loop_tree(IdealLoopTree* root, IdealLoopTree* loop, CompileLog* log) {
2478   if (loop == root) {
2479     if (loop->_child != NULL) {
2480       log->begin_head("loop_tree");
2481       log->end_head();
2482       if( loop->_child ) log_loop_tree(root, loop->_child, log);
2483       log->tail("loop_tree");
2484       assert(loop->_next == NULL, "what?");
2485     }
2486   } else {
2487     Node* head = loop->_head;
2488     log->begin_head("loop");
2489     log->print(" idx='%d' ", head->_idx);
2490     if (loop->_irreducible) log->print("irreducible='1' ");
2491     if (head->is_Loop()) {
2492       if (head->as_Loop()->is_inner_loop()) log->print("inner_loop='1' ");
2493       if (head->as_Loop()->is_partial_peel_loop()) log->print("partial_peel_loop='1' ");
2494     }
2495     if (head->is_CountedLoop()) {
2496       CountedLoopNode* cl = head->as_CountedLoop();
2497       if (cl->is_pre_loop())  log->print("pre_loop='%d' ",  cl->main_idx());
2498       if (cl->is_main_loop()) log->print("main_loop='%d' ", cl->_idx);
2499       if (cl->is_post_loop()) log->print("post_loop='%d' ",  cl->main_idx());
2500     }
2501     log->end_head();
2502     if( loop->_child ) log_loop_tree(root, loop->_child, log);
2503     log->tail("loop");
2504     if( loop->_next  ) log_loop_tree(root, loop->_next, log);
2505   }
2506 }
2507 
2508 //---------------------collect_potentially_useful_predicates-----------------------
2509 // Helper function to collect potentially useful predicates to prevent them from
2510 // being eliminated by PhaseIdealLoop::eliminate_useless_predicates
2511 void PhaseIdealLoop::collect_potentially_useful_predicates(
2512                          IdealLoopTree * loop, Unique_Node_List &useful_predicates) {
2513   if (loop->_child) { // child
2514     collect_potentially_useful_predicates(loop->_child, useful_predicates);
2515   }
2516 
2517   // self (only loops that we can apply loop predication may use their predicates)
2518   if (loop->_head->is_Loop() &&
2519       !loop->_irreducible    &&
2520       !loop->tail()->is_top()) {
2521     LoopNode* lpn = loop->_head->as_Loop();
2522     Node* entry = lpn->in(LoopNode::EntryControl);
2523     Node* predicate_proj = find_predicate(entry); // loop_limit_check first
2524     if (predicate_proj != NULL ) { // right pattern that can be used by loop predication
2525       assert(entry->in(0)->in(1)->in(1)->Opcode() == Op_Opaque1, "must be");
2526       useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
2527       entry = skip_loop_predicates(entry);
2528     }
2529     predicate_proj = find_predicate(entry); // Predicate
2530     if (predicate_proj != NULL ) {
2531       useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
2532       entry = skip_loop_predicates(entry);
2533     }
2534     if (UseProfiledLoopPredicate) {
2535       predicate_proj = find_predicate(entry); // Predicate
2536       if (predicate_proj != NULL ) {
2537         useful_predicates.push(entry->in(0)->in(1)->in(1)); // good one
2538       }
2539     }
2540   }
2541 
2542   if (loop->_next) { // sibling
2543     collect_potentially_useful_predicates(loop->_next, useful_predicates);
2544   }
2545 }
2546 
2547 //------------------------eliminate_useless_predicates-----------------------------
2548 // Eliminate all inserted predicates if they could not be used by loop predication.
2549 // Note: it will also eliminates loop limits check predicate since it also uses
2550 // Opaque1 node (see Parse::add_predicate()).
2551 void PhaseIdealLoop::eliminate_useless_predicates() {
2552   if (C->predicate_count() == 0)
2553     return; // no predicate left
2554 
2555   Unique_Node_List useful_predicates; // to store useful predicates
2556   if (C->has_loops()) {
2557     collect_potentially_useful_predicates(_ltree_root->_child, useful_predicates);
2558   }
2559 
2560   for (int i = C->predicate_count(); i > 0; i--) {
2561      Node * n = C->predicate_opaque1_node(i-1);
2562      assert(n->Opcode() == Op_Opaque1, "must be");
2563      if (!useful_predicates.member(n)) { // not in the useful list
2564        _igvn.replace_node(n, n->in(1));
2565      }
2566   }
2567 }
2568 
2569 //------------------------process_expensive_nodes-----------------------------
2570 // Expensive nodes have their control input set to prevent the GVN
2571 // from commoning them and as a result forcing the resulting node to
2572 // be in a more frequent path. Use CFG information here, to change the
2573 // control inputs so that some expensive nodes can be commoned while
2574 // not executed more frequently.
2575 bool PhaseIdealLoop::process_expensive_nodes() {
2576   assert(OptimizeExpensiveOps, "optimization off?");
2577 
2578   // Sort nodes to bring similar nodes together
2579   C->sort_expensive_nodes();
2580 
2581   bool progress = false;
2582 
2583   for (int i = 0; i < C->expensive_count(); ) {
2584     Node* n = C->expensive_node(i);
2585     int start = i;
2586     // Find nodes similar to n
2587     i++;
2588     for (; i < C->expensive_count() && Compile::cmp_expensive_nodes(n, C->expensive_node(i)) == 0; i++);
2589     int end = i;
2590     // And compare them two by two
2591     for (int j = start; j < end; j++) {
2592       Node* n1 = C->expensive_node(j);
2593       if (is_node_unreachable(n1)) {
2594         continue;
2595       }
2596       for (int k = j+1; k < end; k++) {
2597         Node* n2 = C->expensive_node(k);
2598         if (is_node_unreachable(n2)) {
2599           continue;
2600         }
2601 
2602         assert(n1 != n2, "should be pair of nodes");
2603 
2604         Node* c1 = n1->in(0);
2605         Node* c2 = n2->in(0);
2606 
2607         Node* parent_c1 = c1;
2608         Node* parent_c2 = c2;
2609 
2610         // The call to get_early_ctrl_for_expensive() moves the
2611         // expensive nodes up but stops at loops that are in a if
2612         // branch. See whether we can exit the loop and move above the
2613         // If.
2614         if (c1->is_Loop()) {
2615           parent_c1 = c1->in(1);
2616         }
2617         if (c2->is_Loop()) {
2618           parent_c2 = c2->in(1);
2619         }
2620 
2621         if (parent_c1 == parent_c2) {
2622           _igvn._worklist.push(n1);
2623           _igvn._worklist.push(n2);
2624           continue;
2625         }
2626 
2627         // Look for identical expensive node up the dominator chain.
2628         if (is_dominator(c1, c2)) {
2629           c2 = c1;
2630         } else if (is_dominator(c2, c1)) {
2631           c1 = c2;
2632         } else if (parent_c1->is_Proj() && parent_c1->in(0)->is_If() &&
2633                    parent_c2->is_Proj() && parent_c1->in(0) == parent_c2->in(0)) {
2634           // Both branches have the same expensive node so move it up
2635           // before the if.
2636           c1 = c2 = idom(parent_c1->in(0));
2637         }
2638         // Do the actual moves
2639         if (n1->in(0) != c1) {
2640           _igvn.hash_delete(n1);
2641           n1->set_req(0, c1);
2642           _igvn.hash_insert(n1);
2643           _igvn._worklist.push(n1);
2644           progress = true;
2645         }
2646         if (n2->in(0) != c2) {
2647           _igvn.hash_delete(n2);
2648           n2->set_req(0, c2);
2649           _igvn.hash_insert(n2);
2650           _igvn._worklist.push(n2);
2651           progress = true;
2652         }
2653       }
2654     }
2655   }
2656 
2657   return progress;
2658 }
2659 
2660 
2661 //=============================================================================
2662 //----------------------------build_and_optimize-------------------------------
2663 // Create a PhaseLoop.  Build the ideal Loop tree.  Map each Ideal Node to
2664 // its corresponding LoopNode.  If 'optimize' is true, do some loop cleanups.
2665 void PhaseIdealLoop::build_and_optimize(LoopOptsMode mode) {
2666   bool do_split_ifs = (mode == LoopOptsDefault || mode == LoopOptsLastRound);
2667   bool skip_loop_opts = (mode == LoopOptsNone);
2668 
2669   ResourceMark rm;
2670 
2671   int old_progress = C->major_progress();
2672   uint orig_worklist_size = _igvn._worklist.size();
2673 
2674   // Reset major-progress flag for the driver's heuristics
2675   C->clear_major_progress();
2676 
2677 #ifndef PRODUCT
2678   // Capture for later assert
2679   uint unique = C->unique();
2680   _loop_invokes++;
2681   _loop_work += unique;
2682 #endif
2683 
2684   // True if the method has at least 1 irreducible loop
2685   _has_irreducible_loops = false;
2686 
2687   _created_loop_node = false;
2688 
2689   Arena *a = Thread::current()->resource_area();
2690   VectorSet visited(a);
2691   // Pre-grow the mapping from Nodes to IdealLoopTrees.
2692   _nodes.map(C->unique(), NULL);
2693   memset(_nodes.adr(), 0, wordSize * C->unique());
2694 
2695   // Pre-build the top-level outermost loop tree entry
2696   _ltree_root = new IdealLoopTree( this, C->root(), C->root() );
2697   // Do not need a safepoint at the top level
2698   _ltree_root->_has_sfpt = 1;
2699 
2700   // Initialize Dominators.
2701   // Checked in clone_loop_predicate() during beautify_loops().
2702   _idom_size = 0;
2703   _idom      = NULL;
2704   _dom_depth = NULL;
2705   _dom_stk   = NULL;
2706 
2707   // Empty pre-order array
2708   allocate_preorders();
2709 
2710   // Build a loop tree on the fly.  Build a mapping from CFG nodes to
2711   // IdealLoopTree entries.  Data nodes are NOT walked.
2712   build_loop_tree();
2713   // Check for bailout, and return
2714   if (C->failing()) {
2715     return;
2716   }
2717 
2718   // No loops after all
2719   if( !_ltree_root->_child && !_verify_only ) C->set_has_loops(false);
2720 
2721   // There should always be an outer loop containing the Root and Return nodes.
2722   // If not, we have a degenerate empty program.  Bail out in this case.
2723   if (!has_node(C->root())) {
2724     if (!_verify_only) {
2725       C->clear_major_progress();
2726       C->record_method_not_compilable("empty program detected during loop optimization");
2727     }
2728     return;
2729   }
2730 
2731   // Nothing to do, so get out
2732   bool stop_early = !C->has_loops() && !skip_loop_opts && !do_split_ifs && !_verify_me && !_verify_only;
2733   bool do_expensive_nodes = C->should_optimize_expensive_nodes(_igvn);
2734   if (stop_early && !do_expensive_nodes) {
2735     _igvn.optimize();           // Cleanup NeverBranches
2736     return;
2737   }
2738 
2739   // Set loop nesting depth
2740   _ltree_root->set_nest( 0 );
2741 
2742   // Split shared headers and insert loop landing pads.
2743   // Do not bother doing this on the Root loop of course.
2744   if( !_verify_me && !_verify_only && _ltree_root->_child ) {
2745     C->print_method(PHASE_BEFORE_BEAUTIFY_LOOPS, 3);
2746     if( _ltree_root->_child->beautify_loops( this ) ) {
2747       // Re-build loop tree!
2748       _ltree_root->_child = NULL;
2749       _nodes.clear();
2750       reallocate_preorders();
2751       build_loop_tree();
2752       // Check for bailout, and return
2753       if (C->failing()) {
2754         return;
2755       }
2756       // Reset loop nesting depth
2757       _ltree_root->set_nest( 0 );
2758 
2759       C->print_method(PHASE_AFTER_BEAUTIFY_LOOPS, 3);
2760     }
2761   }
2762 
2763   // Build Dominators for elision of NULL checks & loop finding.
2764   // Since nodes do not have a slot for immediate dominator, make
2765   // a persistent side array for that info indexed on node->_idx.
2766   _idom_size = C->unique();
2767   _idom      = NEW_RESOURCE_ARRAY( Node*, _idom_size );
2768   _dom_depth = NEW_RESOURCE_ARRAY( uint,  _idom_size );
2769   _dom_stk   = NULL; // Allocated on demand in recompute_dom_depth
2770   memset( _dom_depth, 0, _idom_size * sizeof(uint) );
2771 
2772   Dominators();
2773 
2774   if (!_verify_only) {
2775     // As a side effect, Dominators removed any unreachable CFG paths
2776     // into RegionNodes.  It doesn't do this test against Root, so
2777     // we do it here.
2778     for( uint i = 1; i < C->root()->req(); i++ ) {
2779       if( !_nodes[C->root()->in(i)->_idx] ) {    // Dead path into Root?
2780         _igvn.delete_input_of(C->root(), i);
2781         i--;                      // Rerun same iteration on compressed edges
2782       }
2783     }
2784 
2785     // Given dominators, try to find inner loops with calls that must
2786     // always be executed (call dominates loop tail).  These loops do
2787     // not need a separate safepoint.
2788     Node_List cisstack(a);
2789     _ltree_root->check_safepts(visited, cisstack);
2790   }
2791 
2792   // Walk the DATA nodes and place into loops.  Find earliest control
2793   // node.  For CFG nodes, the _nodes array starts out and remains
2794   // holding the associated IdealLoopTree pointer.  For DATA nodes, the
2795   // _nodes array holds the earliest legal controlling CFG node.
2796 
2797   // Allocate stack with enough space to avoid frequent realloc
2798   int stack_size = (C->live_nodes() >> 1) + 16; // (live_nodes>>1)+16 from Java2D stats
2799   Node_Stack nstack( a, stack_size );
2800 
2801   visited.Clear();
2802   Node_List worklist(a);
2803   // Don't need C->root() on worklist since
2804   // it will be processed among C->top() inputs
2805   worklist.push( C->top() );
2806   visited.set( C->top()->_idx ); // Set C->top() as visited now
2807   build_loop_early( visited, worklist, nstack );
2808 
2809   // Given early legal placement, try finding counted loops.  This placement
2810   // is good enough to discover most loop invariants.
2811   if( !_verify_me && !_verify_only )
2812     _ltree_root->counted_loop( this );
2813 
2814   // Find latest loop placement.  Find ideal loop placement.
2815   visited.Clear();
2816   init_dom_lca_tags();
2817   // Need C->root() on worklist when processing outs
2818   worklist.push( C->root() );
2819   NOT_PRODUCT( C->verify_graph_edges(); )
2820   worklist.push( C->top() );
2821   build_loop_late( visited, worklist, nstack );
2822 
2823   if (_verify_only) {
2824     // restore major progress flag
2825     for (int i = 0; i < old_progress; i++)
2826       C->set_major_progress();
2827     assert(C->unique() == unique, "verification mode made Nodes? ? ?");
2828     assert(_igvn._worklist.size() == orig_worklist_size, "shouldn't push anything");
2829     return;
2830   }
2831 
2832   // clear out the dead code after build_loop_late
2833   while (_deadlist.size()) {
2834     _igvn.remove_globally_dead_node(_deadlist.pop());
2835   }
2836 
2837   if (stop_early) {
2838     assert(do_expensive_nodes, "why are we here?");
2839     if (process_expensive_nodes()) {
2840       // If we made some progress when processing expensive nodes then
2841       // the IGVN may modify the graph in a way that will allow us to
2842       // make some more progress: we need to try processing expensive
2843       // nodes again.
2844       C->set_major_progress();
2845     }
2846     _igvn.optimize();
2847     return;
2848   }
2849 
2850   // Some parser-inserted loop predicates could never be used by loop
2851   // predication or they were moved away from loop during some optimizations.
2852   // For example, peeling. Eliminate them before next loop optimizations.
2853   eliminate_useless_predicates();
2854 
2855 #ifndef PRODUCT
2856   C->verify_graph_edges();
2857   if (_verify_me) {             // Nested verify pass?
2858     // Check to see if the verify mode is broken
2859     assert(C->unique() == unique, "non-optimize mode made Nodes? ? ?");
2860     return;
2861   }
2862   if(VerifyLoopOptimizations) verify();
2863   if(TraceLoopOpts && C->has_loops()) {
2864     _ltree_root->dump();
2865   }
2866 #endif
2867 
2868   if (skip_loop_opts) {
2869     // restore major progress flag
2870     for (int i = 0; i < old_progress; i++) {
2871       C->set_major_progress();
2872     }
2873 
2874     // Cleanup any modified bits
2875     _igvn.optimize();
2876 
2877     if (C->log() != NULL) {
2878       log_loop_tree(_ltree_root, _ltree_root, C->log());
2879     }
2880     return;
2881   }
2882 
2883   if (ReassociateInvariants) {
2884     // Reassociate invariants and prep for split_thru_phi
2885     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2886       IdealLoopTree* lpt = iter.current();
2887       bool is_counted = lpt->is_counted();
2888       if (!is_counted || !lpt->is_inner()) continue;
2889 
2890       // check for vectorized loops, any reassociation of invariants was already done
2891       if (is_counted && lpt->_head->as_CountedLoop()->do_unroll_only()) continue;
2892 
2893       lpt->reassociate_invariants(this);
2894 
2895       // Because RCE opportunities can be masked by split_thru_phi,
2896       // look for RCE candidates and inhibit split_thru_phi
2897       // on just their loop-phi's for this pass of loop opts
2898       if (SplitIfBlocks && do_split_ifs) {
2899         if (lpt->policy_range_check(this)) {
2900           lpt->_rce_candidate = 1; // = true
2901         }
2902       }
2903     }
2904   }
2905 
2906   // Check for aggressive application of split-if and other transforms
2907   // that require basic-block info (like cloning through Phi's)
2908   if( SplitIfBlocks && do_split_ifs ) {
2909     visited.Clear();
2910     split_if_with_blocks( visited, nstack, mode == LoopOptsLastRound );
2911     NOT_PRODUCT( if( VerifyLoopOptimizations ) verify(); );
2912     if (mode == LoopOptsLastRound) {
2913       C->set_major_progress();
2914     }
2915   }
2916 
2917   if (!C->major_progress() && do_expensive_nodes && process_expensive_nodes()) {
2918     C->set_major_progress();
2919   }
2920 
2921   // Perform loop predication before iteration splitting
2922   if (C->has_loops() && !C->major_progress() && (C->predicate_count() > 0)) {
2923     _ltree_root->_child->loop_predication(this);
2924   }
2925 
2926   if (OptimizeFill && UseLoopPredicate && C->has_loops() && !C->major_progress()) {
2927     if (do_intrinsify_fill()) {
2928       C->set_major_progress();
2929     }
2930   }
2931 
2932   // Perform iteration-splitting on inner loops.  Split iterations to avoid
2933   // range checks or one-shot null checks.
2934 
2935   // If split-if's didn't hack the graph too bad (no CFG changes)
2936   // then do loop opts.
2937   if (C->has_loops() && !C->major_progress()) {
2938     memset( worklist.adr(), 0, worklist.Size()*sizeof(Node*) );
2939     _ltree_root->_child->iteration_split( this, worklist );
2940     // No verify after peeling!  GCM has hoisted code out of the loop.
2941     // After peeling, the hoisted code could sink inside the peeled area.
2942     // The peeling code does not try to recompute the best location for
2943     // all the code before the peeled area, so the verify pass will always
2944     // complain about it.
2945   }
2946   // Do verify graph edges in any case
2947   NOT_PRODUCT( C->verify_graph_edges(); );
2948 
2949   if (!do_split_ifs) {
2950     // We saw major progress in Split-If to get here.  We forced a
2951     // pass with unrolling and not split-if, however more split-if's
2952     // might make progress.  If the unrolling didn't make progress
2953     // then the major-progress flag got cleared and we won't try
2954     // another round of Split-If.  In particular the ever-common
2955     // instance-of/check-cast pattern requires at least 2 rounds of
2956     // Split-If to clear out.
2957     C->set_major_progress();
2958   }
2959 
2960   // Repeat loop optimizations if new loops were seen
2961   if (created_loop_node()) {
2962     C->set_major_progress();
2963   }
2964 
2965   // Keep loop predicates and perform optimizations with them
2966   // until no more loop optimizations could be done.
2967   // After that switch predicates off and do more loop optimizations.
2968   if (!C->major_progress() && (C->predicate_count() > 0)) {
2969      C->cleanup_loop_predicates(_igvn);
2970      if (TraceLoopOpts) {
2971        tty->print_cr("PredicatesOff");
2972      }
2973      C->set_major_progress();
2974   }
2975 
2976   // Convert scalar to superword operations at the end of all loop opts.
2977   if (UseSuperWord && C->has_loops() && !C->major_progress()) {
2978     // SuperWord transform
2979     SuperWord sw(this);
2980     for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2981       IdealLoopTree* lpt = iter.current();
2982       if (lpt->is_counted()) {
2983         CountedLoopNode *cl = lpt->_head->as_CountedLoop();
2984 
2985         if (PostLoopMultiversioning && cl->is_rce_post_loop() && !cl->is_vectorized_loop()) {
2986           // Check that the rce'd post loop is encountered first, multiversion after all
2987           // major main loop optimization are concluded
2988           if (!C->major_progress()) {
2989             IdealLoopTree *lpt_next = lpt->_next;
2990             if (lpt_next && lpt_next->is_counted()) {
2991               CountedLoopNode *cl = lpt_next->_head->as_CountedLoop();
2992               has_range_checks(lpt_next);
2993               if (cl->is_post_loop() && cl->range_checks_present()) {
2994                 if (!cl->is_multiversioned()) {
2995                   if (multi_version_post_loops(lpt, lpt_next) == false) {
2996                     // Cause the rce loop to be optimized away if we fail
2997                     cl->mark_is_multiversioned();
2998                     cl->set_slp_max_unroll(0);
2999                     poison_rce_post_loop(lpt);
3000                   }
3001                 }
3002               }
3003             }
3004             sw.transform_loop(lpt, true);
3005           }
3006         } else if (cl->is_main_loop()) {
3007           sw.transform_loop(lpt, true);
3008         }
3009       }
3010     }
3011   }
3012 
3013   // Cleanup any modified bits
3014   _igvn.optimize();
3015 
3016   // disable assert until issue with split_flow_path is resolved (6742111)
3017   // assert(!_has_irreducible_loops || C->parsed_irreducible_loop() || C->is_osr_compilation(),
3018   //        "shouldn't introduce irreducible loops");
3019 
3020   if (C->log() != NULL) {
3021     log_loop_tree(_ltree_root, _ltree_root, C->log());
3022   }
3023 }
3024 
3025 #ifndef PRODUCT
3026 //------------------------------print_statistics-------------------------------
3027 int PhaseIdealLoop::_loop_invokes=0;// Count of PhaseIdealLoop invokes
3028 int PhaseIdealLoop::_loop_work=0; // Sum of PhaseIdealLoop x unique
3029 void PhaseIdealLoop::print_statistics() {
3030   tty->print_cr("PhaseIdealLoop=%d, sum _unique=%d", _loop_invokes, _loop_work);
3031 }
3032 
3033 //------------------------------verify-----------------------------------------
3034 // Build a verify-only PhaseIdealLoop, and see that it agrees with me.
3035 static int fail;                // debug only, so its multi-thread dont care
3036 void PhaseIdealLoop::verify() const {
3037   int old_progress = C->major_progress();
3038   ResourceMark rm;
3039   PhaseIdealLoop loop_verify( _igvn, this );
3040   VectorSet visited(Thread::current()->resource_area());
3041 
3042   fail = 0;
3043   verify_compare( C->root(), &loop_verify, visited );
3044   assert( fail == 0, "verify loops failed" );
3045   // Verify loop structure is the same
3046   _ltree_root->verify_tree(loop_verify._ltree_root, NULL);
3047   // Reset major-progress.  It was cleared by creating a verify version of
3048   // PhaseIdealLoop.
3049   for( int i=0; i<old_progress; i++ )
3050     C->set_major_progress();
3051 }
3052 
3053 //------------------------------verify_compare---------------------------------
3054 // Make sure me and the given PhaseIdealLoop agree on key data structures
3055 void PhaseIdealLoop::verify_compare( Node *n, const PhaseIdealLoop *loop_verify, VectorSet &visited ) const {
3056   if( !n ) return;
3057   if( visited.test_set( n->_idx ) ) return;
3058   if( !_nodes[n->_idx] ) {      // Unreachable
3059     assert( !loop_verify->_nodes[n->_idx], "both should be unreachable" );
3060     return;
3061   }
3062 
3063   uint i;
3064   for( i = 0; i < n->req(); i++ )
3065     verify_compare( n->in(i), loop_verify, visited );
3066 
3067   // Check the '_nodes' block/loop structure
3068   i = n->_idx;
3069   if( has_ctrl(n) ) {           // We have control; verify has loop or ctrl
3070     if( _nodes[i] != loop_verify->_nodes[i] &&
3071         get_ctrl_no_update(n) != loop_verify->get_ctrl_no_update(n) ) {
3072       tty->print("Mismatched control setting for: ");
3073       n->dump();
3074       if( fail++ > 10 ) return;
3075       Node *c = get_ctrl_no_update(n);
3076       tty->print("We have it as: ");
3077       if( c->in(0) ) c->dump();
3078         else tty->print_cr("N%d",c->_idx);
3079       tty->print("Verify thinks: ");
3080       if( loop_verify->has_ctrl(n) )
3081         loop_verify->get_ctrl_no_update(n)->dump();
3082       else
3083         loop_verify->get_loop_idx(n)->dump();
3084       tty->cr();
3085     }
3086   } else {                    // We have a loop
3087     IdealLoopTree *us = get_loop_idx(n);
3088     if( loop_verify->has_ctrl(n) ) {
3089       tty->print("Mismatched loop setting for: ");
3090       n->dump();
3091       if( fail++ > 10 ) return;
3092       tty->print("We have it as: ");
3093       us->dump();
3094       tty->print("Verify thinks: ");
3095       loop_verify->get_ctrl_no_update(n)->dump();
3096       tty->cr();
3097     } else if (!C->major_progress()) {
3098       // Loop selection can be messed up if we did a major progress
3099       // operation, like split-if.  Do not verify in that case.
3100       IdealLoopTree *them = loop_verify->get_loop_idx(n);
3101       if( us->_head != them->_head ||  us->_tail != them->_tail ) {
3102         tty->print("Unequals loops for: ");
3103         n->dump();
3104         if( fail++ > 10 ) return;
3105         tty->print("We have it as: ");
3106         us->dump();
3107         tty->print("Verify thinks: ");
3108         them->dump();
3109         tty->cr();
3110       }
3111     }
3112   }
3113 
3114   // Check for immediate dominators being equal
3115   if( i >= _idom_size ) {
3116     if( !n->is_CFG() ) return;
3117     tty->print("CFG Node with no idom: ");
3118     n->dump();
3119     return;
3120   }
3121   if( !n->is_CFG() ) return;
3122   if( n == C->root() ) return; // No IDOM here
3123 
3124   assert(n->_idx == i, "sanity");
3125   Node *id = idom_no_update(n);
3126   if( id != loop_verify->idom_no_update(n) ) {
3127     tty->print("Unequals idoms for: ");
3128     n->dump();
3129     if( fail++ > 10 ) return;
3130     tty->print("We have it as: ");
3131     id->dump();
3132     tty->print("Verify thinks: ");
3133     loop_verify->idom_no_update(n)->dump();
3134     tty->cr();
3135   }
3136 
3137 }
3138 
3139 //------------------------------verify_tree------------------------------------
3140 // Verify that tree structures match.  Because the CFG can change, siblings
3141 // within the loop tree can be reordered.  We attempt to deal with that by
3142 // reordering the verify's loop tree if possible.
3143 void IdealLoopTree::verify_tree(IdealLoopTree *loop, const IdealLoopTree *parent) const {
3144   assert( _parent == parent, "Badly formed loop tree" );
3145 
3146   // Siblings not in same order?  Attempt to re-order.
3147   if( _head != loop->_head ) {
3148     // Find _next pointer to update
3149     IdealLoopTree **pp = &loop->_parent->_child;
3150     while( *pp != loop )
3151       pp = &((*pp)->_next);
3152     // Find proper sibling to be next
3153     IdealLoopTree **nn = &loop->_next;
3154     while( (*nn) && (*nn)->_head != _head )
3155       nn = &((*nn)->_next);
3156 
3157     // Check for no match.
3158     if( !(*nn) ) {
3159       // Annoyingly, irreducible loops can pick different headers
3160       // after a major_progress operation, so the rest of the loop
3161       // tree cannot be matched.
3162       if (_irreducible && Compile::current()->major_progress())  return;
3163       assert( 0, "failed to match loop tree" );
3164     }
3165 
3166     // Move (*nn) to (*pp)
3167     IdealLoopTree *hit = *nn;
3168     *nn = hit->_next;
3169     hit->_next = loop;
3170     *pp = loop;
3171     loop = hit;
3172     // Now try again to verify
3173   }
3174 
3175   assert( _head  == loop->_head , "mismatched loop head" );
3176   Node *tail = _tail;           // Inline a non-updating version of
3177   while( !tail->in(0) )         // the 'tail()' call.
3178     tail = tail->in(1);
3179   assert( tail == loop->_tail, "mismatched loop tail" );
3180 
3181   // Counted loops that are guarded should be able to find their guards
3182   if( _head->is_CountedLoop() && _head->as_CountedLoop()->is_main_loop() ) {
3183     CountedLoopNode *cl = _head->as_CountedLoop();
3184     Node *init = cl->init_trip();
3185     Node *ctrl = cl->in(LoopNode::EntryControl);
3186     assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
3187     Node *iff  = ctrl->in(0);
3188     assert( iff->Opcode() == Op_If, "" );
3189     Node *bol  = iff->in(1);
3190     assert( bol->Opcode() == Op_Bool, "" );
3191     Node *cmp  = bol->in(1);
3192     assert( cmp->Opcode() == Op_CmpI, "" );
3193     Node *add  = cmp->in(1);
3194     Node *opaq;
3195     if( add->Opcode() == Op_Opaque1 ) {
3196       opaq = add;
3197     } else {
3198       assert( add->Opcode() == Op_AddI || add->Opcode() == Op_ConI , "" );
3199       assert( add == init, "" );
3200       opaq = cmp->in(2);
3201     }
3202     assert( opaq->Opcode() == Op_Opaque1, "" );
3203 
3204   }
3205 
3206   if (_child != NULL)  _child->verify_tree(loop->_child, this);
3207   if (_next  != NULL)  _next ->verify_tree(loop->_next,  parent);
3208   // Innermost loops need to verify loop bodies,
3209   // but only if no 'major_progress'
3210   int fail = 0;
3211   if (!Compile::current()->major_progress() && _child == NULL) {
3212     for( uint i = 0; i < _body.size(); i++ ) {
3213       Node *n = _body.at(i);
3214       if (n->outcnt() == 0)  continue; // Ignore dead
3215       uint j;
3216       for( j = 0; j < loop->_body.size(); j++ )
3217         if( loop->_body.at(j) == n )
3218           break;
3219       if( j == loop->_body.size() ) { // Not found in loop body
3220         // Last ditch effort to avoid assertion: Its possible that we
3221         // have some users (so outcnt not zero) but are still dead.
3222         // Try to find from root.
3223         if (Compile::current()->root()->find(n->_idx)) {
3224           fail++;
3225           tty->print("We have that verify does not: ");
3226           n->dump();
3227         }
3228       }
3229     }
3230     for( uint i2 = 0; i2 < loop->_body.size(); i2++ ) {
3231       Node *n = loop->_body.at(i2);
3232       if (n->outcnt() == 0)  continue; // Ignore dead
3233       uint j;
3234       for( j = 0; j < _body.size(); j++ )
3235         if( _body.at(j) == n )
3236           break;
3237       if( j == _body.size() ) { // Not found in loop body
3238         // Last ditch effort to avoid assertion: Its possible that we
3239         // have some users (so outcnt not zero) but are still dead.
3240         // Try to find from root.
3241         if (Compile::current()->root()->find(n->_idx)) {
3242           fail++;
3243           tty->print("Verify has that we do not: ");
3244           n->dump();
3245         }
3246       }
3247     }
3248     assert( !fail, "loop body mismatch" );
3249   }
3250 }
3251 
3252 #endif
3253 
3254 //------------------------------set_idom---------------------------------------
3255 void PhaseIdealLoop::set_idom(Node* d, Node* n, uint dom_depth) {
3256   uint idx = d->_idx;
3257   if (idx >= _idom_size) {
3258     uint newsize = _idom_size<<1;
3259     while( idx >= newsize ) {
3260       newsize <<= 1;
3261     }
3262     _idom      = REALLOC_RESOURCE_ARRAY( Node*,     _idom,_idom_size,newsize);
3263     _dom_depth = REALLOC_RESOURCE_ARRAY( uint, _dom_depth,_idom_size,newsize);
3264     memset( _dom_depth + _idom_size, 0, (newsize - _idom_size) * sizeof(uint) );
3265     _idom_size = newsize;
3266   }
3267   _idom[idx] = n;
3268   _dom_depth[idx] = dom_depth;
3269 }
3270 
3271 //------------------------------recompute_dom_depth---------------------------------------
3272 // The dominator tree is constructed with only parent pointers.
3273 // This recomputes the depth in the tree by first tagging all
3274 // nodes as "no depth yet" marker.  The next pass then runs up
3275 // the dom tree from each node marked "no depth yet", and computes
3276 // the depth on the way back down.
3277 void PhaseIdealLoop::recompute_dom_depth() {
3278   uint no_depth_marker = C->unique();
3279   uint i;
3280   // Initialize depth to "no depth yet" and realize all lazy updates
3281   for (i = 0; i < _idom_size; i++) {
3282     // Only indices with a _dom_depth has a Node* or NULL (otherwise uninitalized).
3283     if (_dom_depth[i] > 0 && _idom[i] != NULL) {
3284       _dom_depth[i] = no_depth_marker;
3285 
3286       // heal _idom if it has a fwd mapping in _nodes
3287       if (_idom[i]->in(0) == NULL) {
3288         idom(i);
3289       }
3290     }
3291   }
3292   if (_dom_stk == NULL) {
3293     uint init_size = C->live_nodes() / 100; // Guess that 1/100 is a reasonable initial size.
3294     if (init_size < 10) init_size = 10;
3295     _dom_stk = new GrowableArray<uint>(init_size);
3296   }
3297   // Compute new depth for each node.
3298   for (i = 0; i < _idom_size; i++) {
3299     uint j = i;
3300     // Run up the dom tree to find a node with a depth
3301     while (_dom_depth[j] == no_depth_marker) {
3302       _dom_stk->push(j);
3303       j = _idom[j]->_idx;
3304     }
3305     // Compute the depth on the way back down this tree branch
3306     uint dd = _dom_depth[j] + 1;
3307     while (_dom_stk->length() > 0) {
3308       uint j = _dom_stk->pop();
3309       _dom_depth[j] = dd;
3310       dd++;
3311     }
3312   }
3313 }
3314 
3315 //------------------------------sort-------------------------------------------
3316 // Insert 'loop' into the existing loop tree.  'innermost' is a leaf of the
3317 // loop tree, not the root.
3318 IdealLoopTree *PhaseIdealLoop::sort( IdealLoopTree *loop, IdealLoopTree *innermost ) {
3319   if( !innermost ) return loop; // New innermost loop
3320 
3321   int loop_preorder = get_preorder(loop->_head); // Cache pre-order number
3322   assert( loop_preorder, "not yet post-walked loop" );
3323   IdealLoopTree **pp = &innermost;      // Pointer to previous next-pointer
3324   IdealLoopTree *l = *pp;               // Do I go before or after 'l'?
3325 
3326   // Insert at start of list
3327   while( l ) {                  // Insertion sort based on pre-order
3328     if( l == loop ) return innermost; // Already on list!
3329     int l_preorder = get_preorder(l->_head); // Cache pre-order number
3330     assert( l_preorder, "not yet post-walked l" );
3331     // Check header pre-order number to figure proper nesting
3332     if( loop_preorder > l_preorder )
3333       break;                    // End of insertion
3334     // If headers tie (e.g., shared headers) check tail pre-order numbers.
3335     // Since I split shared headers, you'd think this could not happen.
3336     // BUT: I must first do the preorder numbering before I can discover I
3337     // have shared headers, so the split headers all get the same preorder
3338     // number as the RegionNode they split from.
3339     if( loop_preorder == l_preorder &&
3340         get_preorder(loop->_tail) < get_preorder(l->_tail) )
3341       break;                    // Also check for shared headers (same pre#)
3342     pp = &l->_parent;           // Chain up list
3343     l = *pp;
3344   }
3345   // Link into list
3346   // Point predecessor to me
3347   *pp = loop;
3348   // Point me to successor
3349   IdealLoopTree *p = loop->_parent;
3350   loop->_parent = l;            // Point me to successor
3351   if( p ) sort( p, innermost ); // Insert my parents into list as well
3352   return innermost;
3353 }
3354 
3355 //------------------------------build_loop_tree--------------------------------
3356 // I use a modified Vick/Tarjan algorithm.  I need pre- and a post- visit
3357 // bits.  The _nodes[] array is mapped by Node index and holds a NULL for
3358 // not-yet-pre-walked, pre-order # for pre-but-not-post-walked and holds the
3359 // tightest enclosing IdealLoopTree for post-walked.
3360 //
3361 // During my forward walk I do a short 1-layer lookahead to see if I can find
3362 // a loop backedge with that doesn't have any work on the backedge.  This
3363 // helps me construct nested loops with shared headers better.
3364 //
3365 // Once I've done the forward recursion, I do the post-work.  For each child
3366 // I check to see if there is a backedge.  Backedges define a loop!  I
3367 // insert an IdealLoopTree at the target of the backedge.
3368 //
3369 // During the post-work I also check to see if I have several children
3370 // belonging to different loops.  If so, then this Node is a decision point
3371 // where control flow can choose to change loop nests.  It is at this
3372 // decision point where I can figure out how loops are nested.  At this
3373 // time I can properly order the different loop nests from my children.
3374 // Note that there may not be any backedges at the decision point!
3375 //
3376 // Since the decision point can be far removed from the backedges, I can't
3377 // order my loops at the time I discover them.  Thus at the decision point
3378 // I need to inspect loop header pre-order numbers to properly nest my
3379 // loops.  This means I need to sort my childrens' loops by pre-order.
3380 // The sort is of size number-of-control-children, which generally limits
3381 // it to size 2 (i.e., I just choose between my 2 target loops).
3382 void PhaseIdealLoop::build_loop_tree() {
3383   // Allocate stack of size C->live_nodes()/2 to avoid frequent realloc
3384   GrowableArray <Node *> bltstack(C->live_nodes() >> 1);
3385   Node *n = C->root();
3386   bltstack.push(n);
3387   int pre_order = 1;
3388   int stack_size;
3389 
3390   while ( ( stack_size = bltstack.length() ) != 0 ) {
3391     n = bltstack.top(); // Leave node on stack
3392     if ( !is_visited(n) ) {
3393       // ---- Pre-pass Work ----
3394       // Pre-walked but not post-walked nodes need a pre_order number.
3395 
3396       set_preorder_visited( n, pre_order ); // set as visited
3397 
3398       // ---- Scan over children ----
3399       // Scan first over control projections that lead to loop headers.
3400       // This helps us find inner-to-outer loops with shared headers better.
3401 
3402       // Scan children's children for loop headers.
3403       for ( int i = n->outcnt() - 1; i >= 0; --i ) {
3404         Node* m = n->raw_out(i);       // Child
3405         if( m->is_CFG() && !is_visited(m) ) { // Only for CFG children
3406           // Scan over children's children to find loop
3407           for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
3408             Node* l = m->fast_out(j);
3409             if( is_visited(l) &&       // Been visited?
3410                 !is_postvisited(l) &&  // But not post-visited
3411                 get_preorder(l) < pre_order ) { // And smaller pre-order
3412               // Found!  Scan the DFS down this path before doing other paths
3413               bltstack.push(m);
3414               break;
3415             }
3416           }
3417         }
3418       }
3419       pre_order++;
3420     }
3421     else if ( !is_postvisited(n) ) {
3422       // Note: build_loop_tree_impl() adds out edges on rare occasions,
3423       // such as com.sun.rsasign.am::a.
3424       // For non-recursive version, first, process current children.
3425       // On next iteration, check if additional children were added.
3426       for ( int k = n->outcnt() - 1; k >= 0; --k ) {
3427         Node* u = n->raw_out(k);
3428         if ( u->is_CFG() && !is_visited(u) ) {
3429           bltstack.push(u);
3430         }
3431       }
3432       if ( bltstack.length() == stack_size ) {
3433         // There were no additional children, post visit node now
3434         (void)bltstack.pop(); // Remove node from stack
3435         pre_order = build_loop_tree_impl( n, pre_order );
3436         // Check for bailout
3437         if (C->failing()) {
3438           return;
3439         }
3440         // Check to grow _preorders[] array for the case when
3441         // build_loop_tree_impl() adds new nodes.
3442         check_grow_preorders();
3443       }
3444     }
3445     else {
3446       (void)bltstack.pop(); // Remove post-visited node from stack
3447     }
3448   }
3449 }
3450 
3451 //------------------------------build_loop_tree_impl---------------------------
3452 int PhaseIdealLoop::build_loop_tree_impl( Node *n, int pre_order ) {
3453   // ---- Post-pass Work ----
3454   // Pre-walked but not post-walked nodes need a pre_order number.
3455 
3456   // Tightest enclosing loop for this Node
3457   IdealLoopTree *innermost = NULL;
3458 
3459   // For all children, see if any edge is a backedge.  If so, make a loop
3460   // for it.  Then find the tightest enclosing loop for the self Node.
3461   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax; i++) {
3462     Node* m = n->fast_out(i);   // Child
3463     if( n == m ) continue;      // Ignore control self-cycles
3464     if( !m->is_CFG() ) continue;// Ignore non-CFG edges
3465 
3466     IdealLoopTree *l;           // Child's loop
3467     if( !is_postvisited(m) ) {  // Child visited but not post-visited?
3468       // Found a backedge
3469       assert( get_preorder(m) < pre_order, "should be backedge" );
3470       // Check for the RootNode, which is already a LoopNode and is allowed
3471       // to have multiple "backedges".
3472       if( m == C->root()) {     // Found the root?
3473         l = _ltree_root;        // Root is the outermost LoopNode
3474       } else {                  // Else found a nested loop
3475         // Insert a LoopNode to mark this loop.
3476         l = new IdealLoopTree(this, m, n);
3477       } // End of Else found a nested loop
3478       if( !has_loop(m) )        // If 'm' does not already have a loop set
3479         set_loop(m, l);         // Set loop header to loop now
3480 
3481     } else {                    // Else not a nested loop
3482       if( !_nodes[m->_idx] ) continue; // Dead code has no loop
3483       l = get_loop(m);          // Get previously determined loop
3484       // If successor is header of a loop (nest), move up-loop till it
3485       // is a member of some outer enclosing loop.  Since there are no
3486       // shared headers (I've split them already) I only need to go up
3487       // at most 1 level.
3488       while( l && l->_head == m ) // Successor heads loop?
3489         l = l->_parent;         // Move up 1 for me
3490       // If this loop is not properly parented, then this loop
3491       // has no exit path out, i.e. its an infinite loop.
3492       if( !l ) {
3493         // Make loop "reachable" from root so the CFG is reachable.  Basically
3494         // insert a bogus loop exit that is never taken.  'm', the loop head,
3495         // points to 'n', one (of possibly many) fall-in paths.  There may be
3496         // many backedges as well.
3497 
3498         // Here I set the loop to be the root loop.  I could have, after
3499         // inserting a bogus loop exit, restarted the recursion and found my
3500         // new loop exit.  This would make the infinite loop a first-class
3501         // loop and it would then get properly optimized.  What's the use of
3502         // optimizing an infinite loop?
3503         l = _ltree_root;        // Oops, found infinite loop
3504 
3505         if (!_verify_only) {
3506           // Insert the NeverBranch between 'm' and it's control user.
3507           NeverBranchNode *iff = new NeverBranchNode( m );
3508           _igvn.register_new_node_with_optimizer(iff);
3509           set_loop(iff, l);
3510           Node *if_t = new CProjNode( iff, 0 );
3511           _igvn.register_new_node_with_optimizer(if_t);
3512           set_loop(if_t, l);
3513 
3514           Node* cfg = NULL;       // Find the One True Control User of m
3515           for (DUIterator_Fast jmax, j = m->fast_outs(jmax); j < jmax; j++) {
3516             Node* x = m->fast_out(j);
3517             if (x->is_CFG() && x != m && x != iff)
3518               { cfg = x; break; }
3519           }
3520           assert(cfg != NULL, "must find the control user of m");
3521           uint k = 0;             // Probably cfg->in(0)
3522           while( cfg->in(k) != m ) k++; // But check incase cfg is a Region
3523           cfg->set_req( k, if_t ); // Now point to NeverBranch
3524           _igvn._worklist.push(cfg);
3525 
3526           // Now create the never-taken loop exit
3527           Node *if_f = new CProjNode( iff, 1 );
3528           _igvn.register_new_node_with_optimizer(if_f);
3529           set_loop(if_f, l);
3530           // Find frame ptr for Halt.  Relies on the optimizer
3531           // V-N'ing.  Easier and quicker than searching through
3532           // the program structure.
3533           Node *frame = new ParmNode( C->start(), TypeFunc::FramePtr );
3534           _igvn.register_new_node_with_optimizer(frame);
3535           // Halt & Catch Fire
3536           Node *halt = new HaltNode( if_f, frame );
3537           _igvn.register_new_node_with_optimizer(halt);
3538           set_loop(halt, l);
3539           C->root()->add_req(halt);
3540         }
3541         set_loop(C->root(), _ltree_root);
3542       }
3543     }
3544     // Weeny check for irreducible.  This child was already visited (this
3545     // IS the post-work phase).  Is this child's loop header post-visited
3546     // as well?  If so, then I found another entry into the loop.
3547     if (!_verify_only) {
3548       while( is_postvisited(l->_head) ) {
3549         // found irreducible
3550         l->_irreducible = 1; // = true
3551         l = l->_parent;
3552         _has_irreducible_loops = true;
3553         // Check for bad CFG here to prevent crash, and bailout of compile
3554         if (l == NULL) {
3555           C->record_method_not_compilable("unhandled CFG detected during loop optimization");
3556           return pre_order;
3557         }
3558       }
3559       C->set_has_irreducible_loop(_has_irreducible_loops);
3560     }
3561 
3562     // This Node might be a decision point for loops.  It is only if
3563     // it's children belong to several different loops.  The sort call
3564     // does a trivial amount of work if there is only 1 child or all
3565     // children belong to the same loop.  If however, the children
3566     // belong to different loops, the sort call will properly set the
3567     // _parent pointers to show how the loops nest.
3568     //
3569     // In any case, it returns the tightest enclosing loop.
3570     innermost = sort( l, innermost );
3571   }
3572 
3573   // Def-use info will have some dead stuff; dead stuff will have no
3574   // loop decided on.
3575 
3576   // Am I a loop header?  If so fix up my parent's child and next ptrs.
3577   if( innermost && innermost->_head == n ) {
3578     assert( get_loop(n) == innermost, "" );
3579     IdealLoopTree *p = innermost->_parent;
3580     IdealLoopTree *l = innermost;
3581     while( p && l->_head == n ) {
3582       l->_next = p->_child;     // Put self on parents 'next child'
3583       p->_child = l;            // Make self as first child of parent
3584       l = p;                    // Now walk up the parent chain
3585       p = l->_parent;
3586     }
3587   } else {
3588     // Note that it is possible for a LoopNode to reach here, if the
3589     // backedge has been made unreachable (hence the LoopNode no longer
3590     // denotes a Loop, and will eventually be removed).
3591 
3592     // Record tightest enclosing loop for self.  Mark as post-visited.
3593     set_loop(n, innermost);
3594     // Also record has_call flag early on
3595     if( innermost ) {
3596       if( n->is_Call() && !n->is_CallLeaf() && !n->is_macro() ) {
3597         // Do not count uncommon calls
3598         if( !n->is_CallStaticJava() || !n->as_CallStaticJava()->_name ) {
3599           Node *iff = n->in(0)->in(0);
3600           // No any calls for vectorized loops.
3601           if( UseSuperWord || !iff->is_If() ||
3602               (n->in(0)->Opcode() == Op_IfFalse &&
3603                (1.0 - iff->as_If()->_prob) >= 0.01) ||
3604               (iff->as_If()->_prob >= 0.01) )
3605             innermost->_has_call = 1;
3606         }
3607       } else if( n->is_Allocate() && n->as_Allocate()->_is_scalar_replaceable ) {
3608         // Disable loop optimizations if the loop has a scalar replaceable
3609         // allocation. This disabling may cause a potential performance lost
3610         // if the allocation is not eliminated for some reason.
3611         innermost->_allow_optimizations = false;
3612         innermost->_has_call = 1; // = true
3613       } else if (n->Opcode() == Op_SafePoint) {
3614         // Record all safepoints in this loop.
3615         if (innermost->_safepts == NULL) innermost->_safepts = new Node_List();
3616         innermost->_safepts->push(n);
3617       }
3618     }
3619   }
3620 
3621   // Flag as post-visited now
3622   set_postvisited(n);
3623   return pre_order;
3624 }
3625 
3626 
3627 //------------------------------build_loop_early-------------------------------
3628 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
3629 // First pass computes the earliest controlling node possible.  This is the
3630 // controlling input with the deepest dominating depth.
3631 void PhaseIdealLoop::build_loop_early( VectorSet &visited, Node_List &worklist, Node_Stack &nstack ) {
3632   while (worklist.size() != 0) {
3633     // Use local variables nstack_top_n & nstack_top_i to cache values
3634     // on nstack's top.
3635     Node *nstack_top_n = worklist.pop();
3636     uint  nstack_top_i = 0;
3637 //while_nstack_nonempty:
3638     while (true) {
3639       // Get parent node and next input's index from stack's top.
3640       Node  *n = nstack_top_n;
3641       uint   i = nstack_top_i;
3642       uint cnt = n->req(); // Count of inputs
3643       if (i == 0) {        // Pre-process the node.
3644         if( has_node(n) &&            // Have either loop or control already?
3645             !has_ctrl(n) ) {          // Have loop picked out already?
3646           // During "merge_many_backedges" we fold up several nested loops
3647           // into a single loop.  This makes the members of the original
3648           // loop bodies pointing to dead loops; they need to move up
3649           // to the new UNION'd larger loop.  I set the _head field of these
3650           // dead loops to NULL and the _parent field points to the owning
3651           // loop.  Shades of UNION-FIND algorithm.
3652           IdealLoopTree *ilt;
3653           while( !(ilt = get_loop(n))->_head ) {
3654             // Normally I would use a set_loop here.  But in this one special
3655             // case, it is legal (and expected) to change what loop a Node
3656             // belongs to.
3657             _nodes.map(n->_idx, (Node*)(ilt->_parent) );
3658           }
3659           // Remove safepoints ONLY if I've already seen I don't need one.
3660           // (the old code here would yank a 2nd safepoint after seeing a
3661           // first one, even though the 1st did not dominate in the loop body
3662           // and thus could be avoided indefinitely)
3663           if( !_verify_only && !_verify_me && ilt->_has_sfpt && n->Opcode() == Op_SafePoint &&
3664               is_deleteable_safept(n)) {
3665             Node *in = n->in(TypeFunc::Control);
3666             lazy_replace(n,in);       // Pull safepoint now
3667             if (ilt->_safepts != NULL) {
3668               ilt->_safepts->yank(n);
3669             }
3670             // Carry on with the recursion "as if" we are walking
3671             // only the control input
3672             if( !visited.test_set( in->_idx ) ) {
3673               worklist.push(in);      // Visit this guy later, using worklist
3674             }
3675             // Get next node from nstack:
3676             // - skip n's inputs processing by setting i > cnt;
3677             // - we also will not call set_early_ctrl(n) since
3678             //   has_node(n) == true (see the condition above).
3679             i = cnt + 1;
3680           }
3681         }
3682       } // if (i == 0)
3683 
3684       // Visit all inputs
3685       bool done = true;       // Assume all n's inputs will be processed
3686       while (i < cnt) {
3687         Node *in = n->in(i);
3688         ++i;
3689         if (in == NULL) continue;
3690         if (in->pinned() && !in->is_CFG())
3691           set_ctrl(in, in->in(0));
3692         int is_visited = visited.test_set( in->_idx );
3693         if (!has_node(in)) {  // No controlling input yet?
3694           assert( !in->is_CFG(), "CFG Node with no controlling input?" );
3695           assert( !is_visited, "visit only once" );
3696           nstack.push(n, i);  // Save parent node and next input's index.
3697           nstack_top_n = in;  // Process current input now.
3698           nstack_top_i = 0;
3699           done = false;       // Not all n's inputs processed.
3700           break; // continue while_nstack_nonempty;
3701         } else if (!is_visited) {
3702           // This guy has a location picked out for him, but has not yet
3703           // been visited.  Happens to all CFG nodes, for instance.
3704           // Visit him using the worklist instead of recursion, to break
3705           // cycles.  Since he has a location already we do not need to
3706           // find his location before proceeding with the current Node.
3707           worklist.push(in);  // Visit this guy later, using worklist
3708         }
3709       }
3710       if (done) {
3711         // All of n's inputs have been processed, complete post-processing.
3712 
3713         // Compute earliest point this Node can go.
3714         // CFG, Phi, pinned nodes already know their controlling input.
3715         if (!has_node(n)) {
3716           // Record earliest legal location
3717           set_early_ctrl( n );
3718         }
3719         if (nstack.is_empty()) {
3720           // Finished all nodes on stack.
3721           // Process next node on the worklist.
3722           break;
3723         }
3724         // Get saved parent node and next input's index.
3725         nstack_top_n = nstack.node();
3726         nstack_top_i = nstack.index();
3727         nstack.pop();
3728       }
3729     } // while (true)
3730   }
3731 }
3732 
3733 //------------------------------dom_lca_internal--------------------------------
3734 // Pair-wise LCA
3735 Node *PhaseIdealLoop::dom_lca_internal( Node *n1, Node *n2 ) const {
3736   if( !n1 ) return n2;          // Handle NULL original LCA
3737   assert( n1->is_CFG(), "" );
3738   assert( n2->is_CFG(), "" );
3739   // find LCA of all uses
3740   uint d1 = dom_depth(n1);
3741   uint d2 = dom_depth(n2);
3742   while (n1 != n2) {
3743     if (d1 > d2) {
3744       n1 =      idom(n1);
3745       d1 = dom_depth(n1);
3746     } else if (d1 < d2) {
3747       n2 =      idom(n2);
3748       d2 = dom_depth(n2);
3749     } else {
3750       // Here d1 == d2.  Due to edits of the dominator-tree, sections
3751       // of the tree might have the same depth.  These sections have
3752       // to be searched more carefully.
3753 
3754       // Scan up all the n1's with equal depth, looking for n2.
3755       Node *t1 = idom(n1);
3756       while (dom_depth(t1) == d1) {
3757         if (t1 == n2)  return n2;
3758         t1 = idom(t1);
3759       }
3760       // Scan up all the n2's with equal depth, looking for n1.
3761       Node *t2 = idom(n2);
3762       while (dom_depth(t2) == d2) {
3763         if (t2 == n1)  return n1;
3764         t2 = idom(t2);
3765       }
3766       // Move up to a new dominator-depth value as well as up the dom-tree.
3767       n1 = t1;
3768       n2 = t2;
3769       d1 = dom_depth(n1);
3770       d2 = dom_depth(n2);
3771     }
3772   }
3773   return n1;
3774 }
3775 
3776 //------------------------------compute_idom-----------------------------------
3777 // Locally compute IDOM using dom_lca call.  Correct only if the incoming
3778 // IDOMs are correct.
3779 Node *PhaseIdealLoop::compute_idom( Node *region ) const {
3780   assert( region->is_Region(), "" );
3781   Node *LCA = NULL;
3782   for( uint i = 1; i < region->req(); i++ ) {
3783     if( region->in(i) != C->top() )
3784       LCA = dom_lca( LCA, region->in(i) );
3785   }
3786   return LCA;
3787 }
3788 
3789 bool PhaseIdealLoop::verify_dominance(Node* n, Node* use, Node* LCA, Node* early) {
3790   bool had_error = false;
3791 #ifdef ASSERT
3792   if (early != C->root()) {
3793     // Make sure that there's a dominance path from LCA to early
3794     Node* d = LCA;
3795     while (d != early) {
3796       if (d == C->root()) {
3797         dump_bad_graph("Bad graph detected in compute_lca_of_uses", n, early, LCA);
3798         tty->print_cr("*** Use %d isn't dominated by def %d ***", use->_idx, n->_idx);
3799         had_error = true;
3800         break;
3801       }
3802       d = idom(d);
3803     }
3804   }
3805 #endif
3806   return had_error;
3807 }
3808 
3809 
3810 Node* PhaseIdealLoop::compute_lca_of_uses(Node* n, Node* early, bool verify) {
3811   // Compute LCA over list of uses
3812   bool had_error = false;
3813   Node *LCA = NULL;
3814   for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax && LCA != early; i++) {
3815     Node* c = n->fast_out(i);
3816     if (_nodes[c->_idx] == NULL)
3817       continue;                 // Skip the occasional dead node
3818     if( c->is_Phi() ) {         // For Phis, we must land above on the path
3819       for( uint j=1; j<c->req(); j++ ) {// For all inputs
3820         if( c->in(j) == n ) {   // Found matching input?
3821           Node *use = c->in(0)->in(j);
3822           if (_verify_only && use->is_top()) continue;
3823           LCA = dom_lca_for_get_late_ctrl( LCA, use, n );
3824           if (verify) had_error = verify_dominance(n, use, LCA, early) || had_error;
3825         }
3826       }
3827     } else {
3828       // For CFG data-users, use is in the block just prior
3829       Node *use = has_ctrl(c) ? get_ctrl(c) : c->in(0);
3830       LCA = dom_lca_for_get_late_ctrl( LCA, use, n );
3831       if (verify) had_error = verify_dominance(n, use, LCA, early) || had_error;
3832     }
3833   }
3834   assert(!had_error, "bad dominance");
3835   return LCA;
3836 }
3837 
3838 // Check the shape of the graph at the loop entry. In some cases,
3839 // the shape of the graph does not match the shape outlined below.
3840 // That is caused by the Opaque1 node "protecting" the shape of
3841 // the graph being removed by, for example, the IGVN performed
3842 // in PhaseIdealLoop::build_and_optimize().
3843 //
3844 // After the Opaque1 node has been removed, optimizations (e.g., split-if,
3845 // loop unswitching, and IGVN, or a combination of them) can freely change
3846 // the graph's shape. As a result, the graph shape outlined below cannot
3847 // be guaranteed anymore.
3848 bool PhaseIdealLoop::is_canonical_loop_entry(CountedLoopNode* cl) {
3849   if (!cl->is_main_loop() && !cl->is_post_loop()) {
3850     return false;
3851   }
3852   Node* ctrl = cl->skip_predicates();
3853 
3854   if (ctrl == NULL || (!ctrl->is_IfTrue() && !ctrl->is_IfFalse())) {
3855     return false;
3856   }
3857   Node* iffm = ctrl->in(0);
3858   if (iffm == NULL || !iffm->is_If()) {
3859     return false;
3860   }
3861   Node* bolzm = iffm->in(1);
3862   if (bolzm == NULL || !bolzm->is_Bool()) {
3863     return false;
3864   }
3865   Node* cmpzm = bolzm->in(1);
3866   if (cmpzm == NULL || !cmpzm->is_Cmp()) {
3867     return false;
3868   }
3869   // compares can get conditionally flipped
3870   bool found_opaque = false;
3871   for (uint i = 1; i < cmpzm->req(); i++) {
3872     Node* opnd = cmpzm->in(i);
3873     if (opnd && opnd->Opcode() == Op_Opaque1) {
3874       found_opaque = true;
3875       break;
3876     }
3877   }
3878   if (!found_opaque) {
3879     return false;
3880   }
3881   return true;
3882 }
3883 
3884 //------------------------------get_late_ctrl----------------------------------
3885 // Compute latest legal control.
3886 Node *PhaseIdealLoop::get_late_ctrl( Node *n, Node *early ) {
3887   assert(early != NULL, "early control should not be NULL");
3888 
3889   Node* LCA = compute_lca_of_uses(n, early);
3890 #ifdef ASSERT
3891   if (LCA == C->root() && LCA != early) {
3892     // def doesn't dominate uses so print some useful debugging output
3893     compute_lca_of_uses(n, early, true);
3894   }
3895 #endif
3896 
3897   // if this is a load, check for anti-dependent stores
3898   // We use a conservative algorithm to identify potential interfering
3899   // instructions and for rescheduling the load.  The users of the memory
3900   // input of this load are examined.  Any use which is not a load and is
3901   // dominated by early is considered a potentially interfering store.
3902   // This can produce false positives.
3903   if (n->is_Load() && LCA != early) {
3904     Node_List worklist;
3905 
3906     Node *mem = n->in(MemNode::Memory);
3907     for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
3908       Node* s = mem->fast_out(i);
3909       worklist.push(s);
3910     }
3911     while(worklist.size() != 0 && LCA != early) {
3912       Node* s = worklist.pop();
3913       if (s->is_Load() || s->Opcode() == Op_SafePoint) {
3914         continue;
3915       } else if (s->is_MergeMem()) {
3916         for (DUIterator_Fast imax, i = s->fast_outs(imax); i < imax; i++) {
3917           Node* s1 = s->fast_out(i);
3918           worklist.push(s1);
3919         }
3920       } else {
3921         Node *sctrl = has_ctrl(s) ? get_ctrl(s) : s->in(0);
3922         assert(sctrl != NULL || s->outcnt() == 0, "must have control");
3923         if (sctrl != NULL && !sctrl->is_top() && is_dominator(early, sctrl)) {
3924           LCA = dom_lca_for_get_late_ctrl(LCA, sctrl, n);
3925         }
3926       }
3927     }
3928   }
3929 
3930   assert(LCA == find_non_split_ctrl(LCA), "unexpected late control");
3931   return LCA;
3932 }
3933 
3934 // true if CFG node d dominates CFG node n
3935 bool PhaseIdealLoop::is_dominator(Node *d, Node *n) {
3936   if (d == n)
3937     return true;
3938   assert(d->is_CFG() && n->is_CFG(), "must have CFG nodes");
3939   uint dd = dom_depth(d);
3940   while (dom_depth(n) >= dd) {
3941     if (n == d)
3942       return true;
3943     n = idom(n);
3944   }
3945   return false;
3946 }
3947 
3948 //------------------------------dom_lca_for_get_late_ctrl_internal-------------
3949 // Pair-wise LCA with tags.
3950 // Tag each index with the node 'tag' currently being processed
3951 // before advancing up the dominator chain using idom().
3952 // Later calls that find a match to 'tag' know that this path has already
3953 // been considered in the current LCA (which is input 'n1' by convention).
3954 // Since get_late_ctrl() is only called once for each node, the tag array
3955 // does not need to be cleared between calls to get_late_ctrl().
3956 // Algorithm trades a larger constant factor for better asymptotic behavior
3957 //
3958 Node *PhaseIdealLoop::dom_lca_for_get_late_ctrl_internal( Node *n1, Node *n2, Node *tag ) {
3959   uint d1 = dom_depth(n1);
3960   uint d2 = dom_depth(n2);
3961 
3962   do {
3963     if (d1 > d2) {
3964       // current lca is deeper than n2
3965       _dom_lca_tags.map(n1->_idx, tag);
3966       n1 =      idom(n1);
3967       d1 = dom_depth(n1);
3968     } else if (d1 < d2) {
3969       // n2 is deeper than current lca
3970       Node *memo = _dom_lca_tags[n2->_idx];
3971       if( memo == tag ) {
3972         return n1;    // Return the current LCA
3973       }
3974       _dom_lca_tags.map(n2->_idx, tag);
3975       n2 =      idom(n2);
3976       d2 = dom_depth(n2);
3977     } else {
3978       // Here d1 == d2.  Due to edits of the dominator-tree, sections
3979       // of the tree might have the same depth.  These sections have
3980       // to be searched more carefully.
3981 
3982       // Scan up all the n1's with equal depth, looking for n2.
3983       _dom_lca_tags.map(n1->_idx, tag);
3984       Node *t1 = idom(n1);
3985       while (dom_depth(t1) == d1) {
3986         if (t1 == n2)  return n2;
3987         _dom_lca_tags.map(t1->_idx, tag);
3988         t1 = idom(t1);
3989       }
3990       // Scan up all the n2's with equal depth, looking for n1.
3991       _dom_lca_tags.map(n2->_idx, tag);
3992       Node *t2 = idom(n2);
3993       while (dom_depth(t2) == d2) {
3994         if (t2 == n1)  return n1;
3995         _dom_lca_tags.map(t2->_idx, tag);
3996         t2 = idom(t2);
3997       }
3998       // Move up to a new dominator-depth value as well as up the dom-tree.
3999       n1 = t1;
4000       n2 = t2;
4001       d1 = dom_depth(n1);
4002       d2 = dom_depth(n2);
4003     }
4004   } while (n1 != n2);
4005   return n1;
4006 }
4007 
4008 //------------------------------init_dom_lca_tags------------------------------
4009 // Tag could be a node's integer index, 32bits instead of 64bits in some cases
4010 // Intended use does not involve any growth for the array, so it could
4011 // be of fixed size.
4012 void PhaseIdealLoop::init_dom_lca_tags() {
4013   uint limit = C->unique() + 1;
4014   _dom_lca_tags.map( limit, NULL );
4015 #ifdef ASSERT
4016   for( uint i = 0; i < limit; ++i ) {
4017     assert(_dom_lca_tags[i] == NULL, "Must be distinct from each node pointer");
4018   }
4019 #endif // ASSERT
4020 }
4021 
4022 //------------------------------clear_dom_lca_tags------------------------------
4023 // Tag could be a node's integer index, 32bits instead of 64bits in some cases
4024 // Intended use does not involve any growth for the array, so it could
4025 // be of fixed size.
4026 void PhaseIdealLoop::clear_dom_lca_tags() {
4027   uint limit = C->unique() + 1;
4028   _dom_lca_tags.map( limit, NULL );
4029   _dom_lca_tags.clear();
4030 #ifdef ASSERT
4031   for( uint i = 0; i < limit; ++i ) {
4032     assert(_dom_lca_tags[i] == NULL, "Must be distinct from each node pointer");
4033   }
4034 #endif // ASSERT
4035 }
4036 
4037 //------------------------------build_loop_late--------------------------------
4038 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
4039 // Second pass finds latest legal placement, and ideal loop placement.
4040 void PhaseIdealLoop::build_loop_late( VectorSet &visited, Node_List &worklist, Node_Stack &nstack ) {
4041   while (worklist.size() != 0) {
4042     Node *n = worklist.pop();
4043     // Only visit once
4044     if (visited.test_set(n->_idx)) continue;
4045     uint cnt = n->outcnt();
4046     uint   i = 0;
4047     while (true) {
4048       assert( _nodes[n->_idx], "no dead nodes" );
4049       // Visit all children
4050       if (i < cnt) {
4051         Node* use = n->raw_out(i);
4052         ++i;
4053         // Check for dead uses.  Aggressively prune such junk.  It might be
4054         // dead in the global sense, but still have local uses so I cannot
4055         // easily call 'remove_dead_node'.
4056         if( _nodes[use->_idx] != NULL || use->is_top() ) { // Not dead?
4057           // Due to cycles, we might not hit the same fixed point in the verify
4058           // pass as we do in the regular pass.  Instead, visit such phis as
4059           // simple uses of the loop head.
4060           if( use->in(0) && (use->is_CFG() || use->is_Phi()) ) {
4061             if( !visited.test(use->_idx) )
4062               worklist.push(use);
4063           } else if( !visited.test_set(use->_idx) ) {
4064             nstack.push(n, i); // Save parent and next use's index.
4065             n   = use;         // Process all children of current use.
4066             cnt = use->outcnt();
4067             i   = 0;
4068           }
4069         } else {
4070           // Do not visit around the backedge of loops via data edges.
4071           // push dead code onto a worklist
4072           _deadlist.push(use);
4073         }
4074       } else {
4075         // All of n's children have been processed, complete post-processing.
4076         build_loop_late_post(n);
4077         if (nstack.is_empty()) {
4078           // Finished all nodes on stack.
4079           // Process next node on the worklist.
4080           break;
4081         }
4082         // Get saved parent node and next use's index. Visit the rest of uses.
4083         n   = nstack.node();
4084         cnt = n->outcnt();
4085         i   = nstack.index();
4086         nstack.pop();
4087       }
4088     }
4089   }
4090 }
4091 
4092 // Verify that no data node is schedules in the outer loop of a strip
4093 // mined loop.
4094 void PhaseIdealLoop::verify_strip_mined_scheduling(Node *n, Node* least) {
4095 #ifdef ASSERT
4096   if (get_loop(least)->_nest == 0) {
4097     return;
4098   }
4099   IdealLoopTree* loop = get_loop(least);
4100   Node* head = loop->_head;
4101   if (head->is_OuterStripMinedLoop()) {
4102     Node* sfpt = head->as_Loop()->outer_safepoint();
4103     ResourceMark rm;
4104     Unique_Node_List wq;
4105     wq.push(sfpt);
4106     for (uint i = 0; i < wq.size(); i++) {
4107       Node *m = wq.at(i);
4108       for (uint i = 1; i < m->req(); i++) {
4109         Node* nn = m->in(i);
4110         if (nn == n) {
4111           return;
4112         }
4113         if (nn != NULL && has_ctrl(nn) && get_loop(get_ctrl(nn)) == loop) {
4114           wq.push(nn);
4115         }
4116       }
4117     }
4118     ShouldNotReachHere();
4119   }
4120 #endif
4121 }
4122 
4123 
4124 //------------------------------build_loop_late_post---------------------------
4125 // Put Data nodes into some loop nest, by setting the _nodes[]->loop mapping.
4126 // Second pass finds latest legal placement, and ideal loop placement.
4127 void PhaseIdealLoop::build_loop_late_post( Node *n ) {
4128 
4129   if (n->req() == 2 && (n->Opcode() == Op_ConvI2L || n->Opcode() == Op_CastII) && !C->major_progress() && !_verify_only) {
4130     _igvn._worklist.push(n);  // Maybe we'll normalize it, if no more loops.
4131   }
4132 
4133 #ifdef ASSERT
4134   if (_verify_only && !n->is_CFG()) {
4135     // Check def-use domination.
4136     compute_lca_of_uses(n, get_ctrl(n), true /* verify */);
4137   }
4138 #endif
4139 
4140   // CFG and pinned nodes already handled
4141   if( n->in(0) ) {
4142     if( n->in(0)->is_top() ) return; // Dead?
4143 
4144     // We'd like +VerifyLoopOptimizations to not believe that Mod's/Loads
4145     // _must_ be pinned (they have to observe their control edge of course).
4146     // Unlike Stores (which modify an unallocable resource, the memory
4147     // state), Mods/Loads can float around.  So free them up.
4148     bool pinned = true;
4149     switch( n->Opcode() ) {
4150     case Op_DivI:
4151     case Op_DivF:
4152     case Op_DivD:
4153     case Op_ModI:
4154     case Op_ModF:
4155     case Op_ModD:
4156     case Op_LoadB:              // Same with Loads; they can sink
4157     case Op_LoadUB:             // during loop optimizations.
4158     case Op_LoadUS:
4159     case Op_LoadD:
4160     case Op_LoadF:
4161     case Op_LoadI:
4162     case Op_LoadKlass:
4163     case Op_LoadNKlass:
4164     case Op_LoadL:
4165     case Op_LoadS:
4166     case Op_LoadP:
4167     case Op_LoadBarrierSlowReg:
4168     case Op_LoadBarrierWeakSlowReg:
4169     case Op_LoadN:
4170     case Op_LoadRange:
4171     case Op_LoadD_unaligned:
4172     case Op_LoadL_unaligned:
4173     case Op_StrComp:            // Does a bunch of load-like effects
4174     case Op_StrEquals:
4175     case Op_StrIndexOf:
4176     case Op_StrIndexOfChar:
4177     case Op_AryEq:
4178     case Op_HasNegatives:
4179       pinned = false;
4180     }
4181     if( pinned ) {
4182       IdealLoopTree *chosen_loop = get_loop(n->is_CFG() ? n : get_ctrl(n));
4183       if( !chosen_loop->_child )       // Inner loop?
4184         chosen_loop->_body.push(n); // Collect inner loops
4185       return;
4186     }
4187   } else {                      // No slot zero
4188     if( n->is_CFG() ) {         // CFG with no slot 0 is dead
4189       _nodes.map(n->_idx,0);    // No block setting, it's globally dead
4190       return;
4191     }
4192     assert(!n->is_CFG() || n->outcnt() == 0, "");
4193   }
4194 
4195   // Do I have a "safe range" I can select over?
4196   Node *early = get_ctrl(n);// Early location already computed
4197 
4198   // Compute latest point this Node can go
4199   Node *LCA = get_late_ctrl( n, early );
4200   // LCA is NULL due to uses being dead
4201   if( LCA == NULL ) {
4202 #ifdef ASSERT
4203     for (DUIterator i1 = n->outs(); n->has_out(i1); i1++) {
4204       assert( _nodes[n->out(i1)->_idx] == NULL, "all uses must also be dead");
4205     }
4206 #endif
4207     _nodes.map(n->_idx, 0);     // This node is useless
4208     _deadlist.push(n);
4209     return;
4210   }
4211   assert(LCA != NULL && !LCA->is_top(), "no dead nodes");
4212 
4213   Node *legal = LCA;            // Walk 'legal' up the IDOM chain
4214   Node *least = legal;          // Best legal position so far
4215   while( early != legal ) {     // While not at earliest legal
4216 #ifdef ASSERT
4217     if (legal->is_Start() && !early->is_Root()) {
4218       // Bad graph. Print idom path and fail.
4219       dump_bad_graph("Bad graph detected in build_loop_late", n, early, LCA);
4220       assert(false, "Bad graph detected in build_loop_late");
4221     }
4222 #endif
4223     // Find least loop nesting depth
4224     legal = idom(legal);        // Bump up the IDOM tree
4225     // Check for lower nesting depth
4226     if( get_loop(legal)->_nest < get_loop(least)->_nest )
4227       least = legal;
4228   }
4229   assert(early == legal || legal != C->root(), "bad dominance of inputs");
4230 
4231   // Try not to place code on a loop entry projection
4232   // which can inhibit range check elimination.
4233   if (least != early) {
4234     Node* ctrl_out = least->unique_ctrl_out();
4235     if (ctrl_out && ctrl_out->is_Loop() &&
4236         least == ctrl_out->in(LoopNode::EntryControl)) {
4237       // Move the node above predicates as far up as possible so a
4238       // following pass of loop predication doesn't hoist a predicate
4239       // that depends on it above that node.
4240       Node* new_ctrl = least;
4241       for (;;) {
4242         if (!new_ctrl->is_Proj()) {
4243           break;
4244         }
4245         CallStaticJavaNode* call = new_ctrl->as_Proj()->is_uncommon_trap_if_pattern(Deoptimization::Reason_none);
4246         if (call == NULL) {
4247           break;
4248         }
4249         int req = call->uncommon_trap_request();
4250         Deoptimization::DeoptReason trap_reason = Deoptimization::trap_request_reason(req);
4251         if (trap_reason != Deoptimization::Reason_loop_limit_check &&
4252             trap_reason != Deoptimization::Reason_predicate &&
4253             trap_reason != Deoptimization::Reason_profile_predicate) {
4254           break;
4255         }
4256         Node* c = new_ctrl->in(0)->in(0);
4257         if (is_dominator(c, early) && c != early) {
4258           break;
4259         }
4260         new_ctrl = c;
4261       }
4262       least = new_ctrl;
4263     }
4264   }
4265 
4266 #ifdef ASSERT
4267   // If verifying, verify that 'verify_me' has a legal location
4268   // and choose it as our location.
4269   if( _verify_me ) {
4270     Node *v_ctrl = _verify_me->get_ctrl_no_update(n);
4271     Node *legal = LCA;
4272     while( early != legal ) {   // While not at earliest legal
4273       if( legal == v_ctrl ) break;  // Check for prior good location
4274       legal = idom(legal)      ;// Bump up the IDOM tree
4275     }
4276     // Check for prior good location
4277     if( legal == v_ctrl ) least = legal; // Keep prior if found
4278   }
4279 #endif
4280 
4281   // Assign discovered "here or above" point
4282   least = find_non_split_ctrl(least);
4283   verify_strip_mined_scheduling(n, least);
4284   set_ctrl(n, least);
4285 
4286   // Collect inner loop bodies
4287   IdealLoopTree *chosen_loop = get_loop(least);
4288   if( !chosen_loop->_child )   // Inner loop?
4289     chosen_loop->_body.push(n);// Collect inner loops
4290 }
4291 
4292 #ifdef ASSERT
4293 void PhaseIdealLoop::dump_bad_graph(const char* msg, Node* n, Node* early, Node* LCA) {
4294   tty->print_cr("%s", msg);
4295   tty->print("n: "); n->dump();
4296   tty->print("early(n): "); early->dump();
4297   if (n->in(0) != NULL  && !n->in(0)->is_top() &&
4298       n->in(0) != early && !n->in(0)->is_Root()) {
4299     tty->print("n->in(0): "); n->in(0)->dump();
4300   }
4301   for (uint i = 1; i < n->req(); i++) {
4302     Node* in1 = n->in(i);
4303     if (in1 != NULL && in1 != n && !in1->is_top()) {
4304       tty->print("n->in(%d): ", i); in1->dump();
4305       Node* in1_early = get_ctrl(in1);
4306       tty->print("early(n->in(%d)): ", i); in1_early->dump();
4307       if (in1->in(0) != NULL     && !in1->in(0)->is_top() &&
4308           in1->in(0) != in1_early && !in1->in(0)->is_Root()) {
4309         tty->print("n->in(%d)->in(0): ", i); in1->in(0)->dump();
4310       }
4311       for (uint j = 1; j < in1->req(); j++) {
4312         Node* in2 = in1->in(j);
4313         if (in2 != NULL && in2 != n && in2 != in1 && !in2->is_top()) {
4314           tty->print("n->in(%d)->in(%d): ", i, j); in2->dump();
4315           Node* in2_early = get_ctrl(in2);
4316           tty->print("early(n->in(%d)->in(%d)): ", i, j); in2_early->dump();
4317           if (in2->in(0) != NULL     && !in2->in(0)->is_top() &&
4318               in2->in(0) != in2_early && !in2->in(0)->is_Root()) {
4319             tty->print("n->in(%d)->in(%d)->in(0): ", i, j); in2->in(0)->dump();
4320           }
4321         }
4322       }
4323     }
4324   }
4325   tty->cr();
4326   tty->print("LCA(n): "); LCA->dump();
4327   for (uint i = 0; i < n->outcnt(); i++) {
4328     Node* u1 = n->raw_out(i);
4329     if (u1 == n)
4330       continue;
4331     tty->print("n->out(%d): ", i); u1->dump();
4332     if (u1->is_CFG()) {
4333       for (uint j = 0; j < u1->outcnt(); j++) {
4334         Node* u2 = u1->raw_out(j);
4335         if (u2 != u1 && u2 != n && u2->is_CFG()) {
4336           tty->print("n->out(%d)->out(%d): ", i, j); u2->dump();
4337         }
4338       }
4339     } else {
4340       Node* u1_later = get_ctrl(u1);
4341       tty->print("later(n->out(%d)): ", i); u1_later->dump();
4342       if (u1->in(0) != NULL     && !u1->in(0)->is_top() &&
4343           u1->in(0) != u1_later && !u1->in(0)->is_Root()) {
4344         tty->print("n->out(%d)->in(0): ", i); u1->in(0)->dump();
4345       }
4346       for (uint j = 0; j < u1->outcnt(); j++) {
4347         Node* u2 = u1->raw_out(j);
4348         if (u2 == n || u2 == u1)
4349           continue;
4350         tty->print("n->out(%d)->out(%d): ", i, j); u2->dump();
4351         if (!u2->is_CFG()) {
4352           Node* u2_later = get_ctrl(u2);
4353           tty->print("later(n->out(%d)->out(%d)): ", i, j); u2_later->dump();
4354           if (u2->in(0) != NULL     && !u2->in(0)->is_top() &&
4355               u2->in(0) != u2_later && !u2->in(0)->is_Root()) {
4356             tty->print("n->out(%d)->in(0): ", i); u2->in(0)->dump();
4357           }
4358         }
4359       }
4360     }
4361   }
4362   tty->cr();
4363   int ct = 0;
4364   Node *dbg_legal = LCA;
4365   while(!dbg_legal->is_Start() && ct < 100) {
4366     tty->print("idom[%d] ",ct); dbg_legal->dump();
4367     ct++;
4368     dbg_legal = idom(dbg_legal);
4369   }
4370   tty->cr();
4371 }
4372 #endif
4373 
4374 #ifndef PRODUCT
4375 //------------------------------dump-------------------------------------------
4376 void PhaseIdealLoop::dump( ) const {
4377   ResourceMark rm;
4378   Arena* arena = Thread::current()->resource_area();
4379   Node_Stack stack(arena, C->live_nodes() >> 2);
4380   Node_List rpo_list;
4381   VectorSet visited(arena);
4382   visited.set(C->top()->_idx);
4383   rpo( C->root(), stack, visited, rpo_list );
4384   // Dump root loop indexed by last element in PO order
4385   dump( _ltree_root, rpo_list.size(), rpo_list );
4386 }
4387 
4388 void PhaseIdealLoop::dump( IdealLoopTree *loop, uint idx, Node_List &rpo_list ) const {
4389   loop->dump_head();
4390 
4391   // Now scan for CFG nodes in the same loop
4392   for( uint j=idx; j > 0;  j-- ) {
4393     Node *n = rpo_list[j-1];
4394     if( !_nodes[n->_idx] )      // Skip dead nodes
4395       continue;
4396     if( get_loop(n) != loop ) { // Wrong loop nest
4397       if( get_loop(n)->_head == n &&    // Found nested loop?
4398           get_loop(n)->_parent == loop )
4399         dump(get_loop(n),rpo_list.size(),rpo_list);     // Print it nested-ly
4400       continue;
4401     }
4402 
4403     // Dump controlling node
4404     for( uint x = 0; x < loop->_nest; x++ )
4405       tty->print("  ");
4406     tty->print("C");
4407     if( n == C->root() ) {
4408       n->dump();
4409     } else {
4410       Node* cached_idom   = idom_no_update(n);
4411       Node *computed_idom = n->in(0);
4412       if( n->is_Region() ) {
4413         computed_idom = compute_idom(n);
4414         // computed_idom() will return n->in(0) when idom(n) is an IfNode (or
4415         // any MultiBranch ctrl node), so apply a similar transform to
4416         // the cached idom returned from idom_no_update.
4417         cached_idom = find_non_split_ctrl(cached_idom);
4418       }
4419       tty->print(" ID:%d",computed_idom->_idx);
4420       n->dump();
4421       if( cached_idom != computed_idom ) {
4422         tty->print_cr("*** BROKEN IDOM!  Computed as: %d, cached as: %d",
4423                       computed_idom->_idx, cached_idom->_idx);
4424       }
4425     }
4426     // Dump nodes it controls
4427     for( uint k = 0; k < _nodes.Size(); k++ ) {
4428       // (k < C->unique() && get_ctrl(find(k)) == n)
4429       if (k < C->unique() && _nodes[k] == (Node*)((intptr_t)n + 1)) {
4430         Node *m = C->root()->find(k);
4431         if( m && m->outcnt() > 0 ) {
4432           if (!(has_ctrl(m) && get_ctrl_no_update(m) == n)) {
4433             tty->print_cr("*** BROKEN CTRL ACCESSOR!  _nodes[k] is %p, ctrl is %p",
4434                           _nodes[k], has_ctrl(m) ? get_ctrl_no_update(m) : NULL);
4435           }
4436           for( uint j = 0; j < loop->_nest; j++ )
4437             tty->print("  ");
4438           tty->print(" ");
4439           m->dump();
4440         }
4441       }
4442     }
4443   }
4444 }
4445 
4446 // Collect a R-P-O for the whole CFG.
4447 // Result list is in post-order (scan backwards for RPO)
4448 void PhaseIdealLoop::rpo( Node *start, Node_Stack &stk, VectorSet &visited, Node_List &rpo_list ) const {
4449   stk.push(start, 0);
4450   visited.set(start->_idx);
4451 
4452   while (stk.is_nonempty()) {
4453     Node* m   = stk.node();
4454     uint  idx = stk.index();
4455     if (idx < m->outcnt()) {
4456       stk.set_index(idx + 1);
4457       Node* n = m->raw_out(idx);
4458       if (n->is_CFG() && !visited.test_set(n->_idx)) {
4459         stk.push(n, 0);
4460       }
4461     } else {
4462       rpo_list.push(m);
4463       stk.pop();
4464     }
4465   }
4466 }
4467 #endif
4468 
4469 
4470 //=============================================================================
4471 //------------------------------LoopTreeIterator-----------------------------------
4472 
4473 // Advance to next loop tree using a preorder, left-to-right traversal.
4474 void LoopTreeIterator::next() {
4475   assert(!done(), "must not be done.");
4476   if (_curnt->_child != NULL) {
4477     _curnt = _curnt->_child;
4478   } else if (_curnt->_next != NULL) {
4479     _curnt = _curnt->_next;
4480   } else {
4481     while (_curnt != _root && _curnt->_next == NULL) {
4482       _curnt = _curnt->_parent;
4483     }
4484     if (_curnt == _root) {
4485       _curnt = NULL;
4486       assert(done(), "must be done.");
4487     } else {
4488       assert(_curnt->_next != NULL, "must be more to do");
4489       _curnt = _curnt->_next;
4490     }
4491   }
4492 }