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