1 /*
   2  * Copyright (c) 2000, 2017, 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 "compiler/compileLog.hpp"
  27 #include "memory/allocation.inline.hpp"
  28 #include "opto/addnode.hpp"
  29 #include "opto/callnode.hpp"
  30 #include "opto/castnode.hpp"
  31 #include "opto/connode.hpp"
  32 #include "opto/convertnode.hpp"
  33 #include "opto/divnode.hpp"
  34 #include "opto/loopnode.hpp"
  35 #include "opto/mulnode.hpp"
  36 #include "opto/movenode.hpp"
  37 #include "opto/opaquenode.hpp"
  38 #include "opto/rootnode.hpp"
  39 #include "opto/runtime.hpp"
  40 #include "opto/subnode.hpp"
  41 #include "opto/superword.hpp"
  42 #include "opto/vectornode.hpp"
  43 
  44 //------------------------------is_loop_exit-----------------------------------
  45 // Given an IfNode, return the loop-exiting projection or NULL if both
  46 // arms remain in the loop.
  47 Node *IdealLoopTree::is_loop_exit(Node *iff) const {
  48   if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests
  49   PhaseIdealLoop *phase = _phase;
  50   // Test is an IfNode, has 2 projections.  If BOTH are in the loop
  51   // we need loop unswitching instead of peeling.
  52   if( !is_member(phase->get_loop( iff->raw_out(0) )) )
  53     return iff->raw_out(0);
  54   if( !is_member(phase->get_loop( iff->raw_out(1) )) )
  55     return iff->raw_out(1);
  56   return NULL;
  57 }
  58 
  59 
  60 //=============================================================================
  61 
  62 
  63 //------------------------------record_for_igvn----------------------------
  64 // Put loop body on igvn work list
  65 void IdealLoopTree::record_for_igvn() {
  66   for( uint i = 0; i < _body.size(); i++ ) {
  67     Node *n = _body.at(i);
  68     _phase->_igvn._worklist.push(n);
  69   }
  70 }
  71 
  72 //------------------------------compute_exact_trip_count-----------------------
  73 // Compute loop trip count if possible. Do not recalculate trip count for
  74 // split loops (pre-main-post) which have their limits and inits behind Opaque node.
  75 void IdealLoopTree::compute_trip_count(PhaseIdealLoop* phase) {
  76   if (!_head->as_Loop()->is_valid_counted_loop()) {
  77     return;
  78   }
  79   CountedLoopNode* cl = _head->as_CountedLoop();
  80   // Trip count may become nonexact for iteration split loops since
  81   // RCE modifies limits. Note, _trip_count value is not reset since
  82   // it is used to limit unrolling of main loop.
  83   cl->set_nonexact_trip_count();
  84 
  85   // Loop's test should be part of loop.
  86   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
  87     return; // Infinite loop
  88 
  89 #ifdef ASSERT
  90   BoolTest::mask bt = cl->loopexit()->test_trip();
  91   assert(bt == BoolTest::lt || bt == BoolTest::gt ||
  92          bt == BoolTest::ne, "canonical test is expected");
  93 #endif
  94 
  95   Node* init_n = cl->init_trip();
  96   Node* limit_n = cl->limit();
  97   if (init_n != NULL && limit_n != NULL) {
  98     // Use longs to avoid integer overflow.
  99     int stride_con = cl->stride_con();
 100     jlong init_con = phase->_igvn.type(init_n)->is_int()->_lo;
 101     jlong limit_con = phase->_igvn.type(limit_n)->is_int()->_hi;
 102     int stride_m   = stride_con - (stride_con > 0 ? 1 : -1);
 103     jlong trip_count = (limit_con - init_con + stride_m)/stride_con;
 104     if (trip_count > 0 && (julong)trip_count < (julong)max_juint) {
 105       if (init_n->is_Con() && limit_n->is_Con()) {
 106         // Set exact trip count.
 107         cl->set_exact_trip_count((uint)trip_count);
 108       } else if (cl->unrolled_count() == 1) {
 109         // Set maximum trip count before unrolling.
 110         cl->set_trip_count((uint)trip_count);
 111       }
 112     }
 113   }
 114 }
 115 
 116 //------------------------------compute_profile_trip_cnt----------------------------
 117 // Compute loop trip count from profile data as
 118 //    (backedge_count + loop_exit_count) / loop_exit_count
 119 void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {
 120   if (!_head->is_CountedLoop()) {
 121     return;
 122   }
 123   CountedLoopNode* head = _head->as_CountedLoop();
 124   if (head->profile_trip_cnt() != COUNT_UNKNOWN) {
 125     return; // Already computed
 126   }
 127   float trip_cnt = (float)max_jint; // default is big
 128 
 129   Node* back = head->in(LoopNode::LoopBackControl);
 130   while (back != head) {
 131     if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
 132         back->in(0) &&
 133         back->in(0)->is_If() &&
 134         back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&
 135         back->in(0)->as_If()->_prob != PROB_UNKNOWN) {
 136       break;
 137     }
 138     back = phase->idom(back);
 139   }
 140   if (back != head) {
 141     assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
 142            back->in(0), "if-projection exists");
 143     IfNode* back_if = back->in(0)->as_If();
 144     float loop_back_cnt = back_if->_fcnt * back_if->_prob;
 145 
 146     // Now compute a loop exit count
 147     float loop_exit_cnt = 0.0f;
 148     for( uint i = 0; i < _body.size(); i++ ) {
 149       Node *n = _body[i];
 150       if( n->is_If() ) {
 151         IfNode *iff = n->as_If();
 152         if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {
 153           Node *exit = is_loop_exit(iff);
 154           if( exit ) {
 155             float exit_prob = iff->_prob;
 156             if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;
 157             if (exit_prob > PROB_MIN) {
 158               float exit_cnt = iff->_fcnt * exit_prob;
 159               loop_exit_cnt += exit_cnt;
 160             }
 161           }
 162         }
 163       }
 164     }
 165     if (loop_exit_cnt > 0.0f) {
 166       trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;
 167     } else {
 168       // No exit count so use
 169       trip_cnt = loop_back_cnt;
 170     }
 171   }
 172 #ifndef PRODUCT
 173   if (TraceProfileTripCount) {
 174     tty->print_cr("compute_profile_trip_cnt  lp: %d cnt: %f\n", head->_idx, trip_cnt);
 175   }
 176 #endif
 177   head->set_profile_trip_cnt(trip_cnt);
 178 }
 179 
 180 //---------------------is_invariant_addition-----------------------------
 181 // Return nonzero index of invariant operand for an Add or Sub
 182 // of (nonconstant) invariant and variant values. Helper for reassociate_invariants.
 183 int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {
 184   int op = n->Opcode();
 185   if (op == Op_AddI || op == Op_SubI) {
 186     bool in1_invar = this->is_invariant(n->in(1));
 187     bool in2_invar = this->is_invariant(n->in(2));
 188     if (in1_invar && !in2_invar) return 1;
 189     if (!in1_invar && in2_invar) return 2;
 190   }
 191   return 0;
 192 }
 193 
 194 //---------------------reassociate_add_sub-----------------------------
 195 // Reassociate invariant add and subtract expressions:
 196 //
 197 // inv1 + (x + inv2)  =>  ( inv1 + inv2) + x
 198 // (x + inv2) + inv1  =>  ( inv1 + inv2) + x
 199 // inv1 + (x - inv2)  =>  ( inv1 - inv2) + x
 200 // inv1 - (inv2 - x)  =>  ( inv1 - inv2) + x
 201 // (x + inv2) - inv1  =>  (-inv1 + inv2) + x
 202 // (x - inv2) + inv1  =>  ( inv1 - inv2) + x
 203 // (x - inv2) - inv1  =>  (-inv1 - inv2) + x
 204 // inv1 + (inv2 - x)  =>  ( inv1 + inv2) - x
 205 // inv1 - (x - inv2)  =>  ( inv1 + inv2) - x
 206 // (inv2 - x) + inv1  =>  ( inv1 + inv2) - x
 207 // (inv2 - x) - inv1  =>  (-inv1 + inv2) - x
 208 // inv1 - (x + inv2)  =>  ( inv1 - inv2) - x
 209 //
 210 Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {
 211   if ((!n1->is_Add() && !n1->is_Sub()) || n1->outcnt() == 0) return NULL;
 212   if (is_invariant(n1)) return NULL;
 213   int inv1_idx = is_invariant_addition(n1, phase);
 214   if (!inv1_idx) return NULL;
 215   // Don't mess with add of constant (igvn moves them to expression tree root.)
 216   if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
 217   Node* inv1 = n1->in(inv1_idx);
 218   Node* n2 = n1->in(3 - inv1_idx);
 219   int inv2_idx = is_invariant_addition(n2, phase);
 220   if (!inv2_idx) return NULL;
 221   Node* x    = n2->in(3 - inv2_idx);
 222   Node* inv2 = n2->in(inv2_idx);
 223 
 224   bool neg_x    = n2->is_Sub() && inv2_idx == 1;
 225   bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
 226   bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;
 227   if (n1->is_Sub() && inv1_idx == 1) {
 228     neg_x    = !neg_x;
 229     neg_inv2 = !neg_inv2;
 230   }
 231   Node* inv1_c = phase->get_ctrl(inv1);
 232   Node* inv2_c = phase->get_ctrl(inv2);
 233   Node* n_inv1;
 234   if (neg_inv1) {
 235     Node *zero = phase->_igvn.intcon(0);
 236     phase->set_ctrl(zero, phase->C->root());
 237     n_inv1 = new SubINode(zero, inv1);
 238     phase->register_new_node(n_inv1, inv1_c);
 239   } else {
 240     n_inv1 = inv1;
 241   }
 242   Node* inv;
 243   if (neg_inv2) {
 244     inv = new SubINode(n_inv1, inv2);
 245   } else {
 246     inv = new AddINode(n_inv1, inv2);
 247   }
 248   phase->register_new_node(inv, phase->get_early_ctrl(inv));
 249 
 250   Node* addx;
 251   if (neg_x) {
 252     addx = new SubINode(inv, x);
 253   } else {
 254     addx = new AddINode(x, inv);
 255   }
 256   phase->register_new_node(addx, phase->get_ctrl(x));
 257   phase->_igvn.replace_node(n1, addx);
 258   assert(phase->get_loop(phase->get_ctrl(n1)) == this, "");
 259   _body.yank(n1);
 260   return addx;
 261 }
 262 
 263 //---------------------reassociate_invariants-----------------------------
 264 // Reassociate invariant expressions:
 265 void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {
 266   for (int i = _body.size() - 1; i >= 0; i--) {
 267     Node *n = _body.at(i);
 268     for (int j = 0; j < 5; j++) {
 269       Node* nn = reassociate_add_sub(n, phase);
 270       if (nn == NULL) break;
 271       n = nn; // again
 272     };
 273   }
 274 }
 275 
 276 //------------------------------policy_peeling---------------------------------
 277 // Return TRUE or FALSE if the loop should be peeled or not.  Peel if we can
 278 // make some loop-invariant test (usually a null-check) happen before the loop.
 279 bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {
 280   Node *test = ((IdealLoopTree*)this)->tail();
 281   int  body_size = ((IdealLoopTree*)this)->_body.size();
 282   // Peeling does loop cloning which can result in O(N^2) node construction
 283   if( body_size > 255 /* Prevent overflow for large body_size */
 284       || (body_size * body_size + phase->C->live_nodes()) > phase->C->max_node_limit() ) {
 285     return false;           // too large to safely clone
 286   }
 287 
 288   // check for vectorized loops, any peeling done was already applied
 289   if (_head->is_CountedLoop() && _head->as_CountedLoop()->do_unroll_only()) return false;
 290 
 291   while( test != _head ) {      // Scan till run off top of loop
 292     if( test->is_If() ) {       // Test?
 293       Node *ctrl = phase->get_ctrl(test->in(1));
 294       if (ctrl->is_top())
 295         return false;           // Found dead test on live IF?  No peeling!
 296       // Standard IF only has one input value to check for loop invariance
 297       assert(test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd || test->Opcode() == Op_RangeCheck, "Check this code when new subtype is added");
 298       // Condition is not a member of this loop?
 299       if( !is_member(phase->get_loop(ctrl)) &&
 300           is_loop_exit(test) )
 301         return true;            // Found reason to peel!
 302     }
 303     // Walk up dominators to loop _head looking for test which is
 304     // executed on every path thru loop.
 305     test = phase->idom(test);
 306   }
 307   return false;
 308 }
 309 
 310 //------------------------------peeled_dom_test_elim---------------------------
 311 // If we got the effect of peeling, either by actually peeling or by making
 312 // a pre-loop which must execute at least once, we can remove all
 313 // loop-invariant dominated tests in the main body.
 314 void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {
 315   bool progress = true;
 316   while( progress ) {
 317     progress = false;           // Reset for next iteration
 318     Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();
 319     Node *test = prev->in(0);
 320     while( test != loop->_head ) { // Scan till run off top of loop
 321 
 322       int p_op = prev->Opcode();
 323       if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&
 324           test->is_If() &&      // Test?
 325           !test->in(1)->is_Con() && // And not already obvious?
 326           // Condition is not a member of this loop?
 327           !loop->is_member(get_loop(get_ctrl(test->in(1))))){
 328         // Walk loop body looking for instances of this test
 329         for( uint i = 0; i < loop->_body.size(); i++ ) {
 330           Node *n = loop->_body.at(i);
 331           if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {
 332             // IfNode was dominated by version in peeled loop body
 333             progress = true;
 334             dominated_by( old_new[prev->_idx], n );
 335           }
 336         }
 337       }
 338       prev = test;
 339       test = idom(test);
 340     } // End of scan tests in loop
 341 
 342   } // End of while( progress )
 343 }
 344 
 345 //------------------------------do_peeling-------------------------------------
 346 // Peel the first iteration of the given loop.
 347 // Step 1: Clone the loop body.  The clone becomes the peeled iteration.
 348 //         The pre-loop illegally has 2 control users (old & new loops).
 349 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
 350 //         Do this by making the old-loop fall-in edges act as if they came
 351 //         around the loopback from the prior iteration (follow the old-loop
 352 //         backedges) and then map to the new peeled iteration.  This leaves
 353 //         the pre-loop with only 1 user (the new peeled iteration), but the
 354 //         peeled-loop backedge has 2 users.
 355 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
 356 //         extra backedge user.
 357 //
 358 //                   orig
 359 //
 360 //                  stmt1
 361 //                    |
 362 //                    v
 363 //              loop predicate
 364 //                    |
 365 //                    v
 366 //                   loop<----+
 367 //                     |      |
 368 //                   stmt2    |
 369 //                     |      |
 370 //                     v      |
 371 //                    if      ^
 372 //                   / \      |
 373 //                  /   \     |
 374 //                 v     v    |
 375 //               false true   |
 376 //               /       \    |
 377 //              /         ----+
 378 //             |
 379 //             v
 380 //           exit
 381 //
 382 //
 383 //            after clone loop
 384 //
 385 //                   stmt1
 386 //                     |
 387 //                     v
 388 //               loop predicate
 389 //                 /       \
 390 //        clone   /         \   orig
 391 //               /           \
 392 //              /             \
 393 //             v               v
 394 //   +---->loop clone          loop<----+
 395 //   |      |                    |      |
 396 //   |    stmt2 clone          stmt2    |
 397 //   |      |                    |      |
 398 //   |      v                    v      |
 399 //   ^      if clone            If      ^
 400 //   |      / \                / \      |
 401 //   |     /   \              /   \     |
 402 //   |    v     v            v     v    |
 403 //   |    true  false      false true   |
 404 //   |    /         \      /       \    |
 405 //   +----           \    /         ----+
 406 //                    \  /
 407 //                    1v v2
 408 //                  region
 409 //                     |
 410 //                     v
 411 //                   exit
 412 //
 413 //
 414 //         after peel and predicate move
 415 //
 416 //                   stmt1
 417 //                    /
 418 //                   /
 419 //        clone     /            orig
 420 //                 /
 421 //                /              +----------+
 422 //               /               |          |
 423 //              /          loop predicate   |
 424 //             /                 |          |
 425 //            v                  v          |
 426 //   TOP-->loop clone          loop<----+   |
 427 //          |                    |      |   |
 428 //        stmt2 clone          stmt2    |   |
 429 //          |                    |      |   ^
 430 //          v                    v      |   |
 431 //          if clone            If      ^   |
 432 //          / \                / \      |   |
 433 //         /   \              /   \     |   |
 434 //        v     v            v     v    |   |
 435 //      true   false      false  true   |   |
 436 //        |         \      /       \    |   |
 437 //        |          \    /         ----+   ^
 438 //        |           \  /                  |
 439 //        |           1v v2                 |
 440 //        v         region                  |
 441 //        |            |                    |
 442 //        |            v                    |
 443 //        |          exit                   |
 444 //        |                                 |
 445 //        +--------------->-----------------+
 446 //
 447 //
 448 //              final graph
 449 //
 450 //                  stmt1
 451 //                    |
 452 //                    v
 453 //                  stmt2 clone
 454 //                    |
 455 //                    v
 456 //                   if clone
 457 //                  / |
 458 //                 /  |
 459 //                v   v
 460 //            false  true
 461 //             |      |
 462 //             |      v
 463 //             | loop predicate
 464 //             |      |
 465 //             |      v
 466 //             |     loop<----+
 467 //             |      |       |
 468 //             |    stmt2     |
 469 //             |      |       |
 470 //             |      v       |
 471 //             v      if      ^
 472 //             |     /  \     |
 473 //             |    /    \    |
 474 //             |   v     v    |
 475 //             | false  true  |
 476 //             |  |        \  |
 477 //             v  v         --+
 478 //            region
 479 //              |
 480 //              v
 481 //             exit
 482 //
 483 void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {
 484 
 485   C->set_major_progress();
 486   // Peeling a 'main' loop in a pre/main/post situation obfuscates the
 487   // 'pre' loop from the main and the 'pre' can no longer have its
 488   // iterations adjusted.  Therefore, we need to declare this loop as
 489   // no longer a 'main' loop; it will need new pre and post loops before
 490   // we can do further RCE.
 491 #ifndef PRODUCT
 492   if (TraceLoopOpts) {
 493     tty->print("Peel         ");
 494     loop->dump_head();
 495   }
 496 #endif
 497   Node* head = loop->_head;
 498   bool counted_loop = head->is_CountedLoop();
 499   if (counted_loop) {
 500     CountedLoopNode *cl = head->as_CountedLoop();
 501     assert(cl->trip_count() > 0, "peeling a fully unrolled loop");
 502     cl->set_trip_count(cl->trip_count() - 1);
 503     if (cl->is_main_loop()) {
 504       cl->set_normal_loop();
 505 #ifndef PRODUCT
 506       if (PrintOpto && VerifyLoopOptimizations) {
 507         tty->print("Peeling a 'main' loop; resetting to 'normal' ");
 508         loop->dump_head();
 509       }
 510 #endif
 511     }
 512   }
 513   Node* entry = head->in(LoopNode::EntryControl);
 514 
 515   // Step 1: Clone the loop body.  The clone becomes the peeled iteration.
 516   //         The pre-loop illegally has 2 control users (old & new loops).
 517   clone_loop( loop, old_new, dom_depth(head) );
 518 
 519   // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
 520   //         Do this by making the old-loop fall-in edges act as if they came
 521   //         around the loopback from the prior iteration (follow the old-loop
 522   //         backedges) and then map to the new peeled iteration.  This leaves
 523   //         the pre-loop with only 1 user (the new peeled iteration), but the
 524   //         peeled-loop backedge has 2 users.
 525   Node* new_entry = old_new[head->in(LoopNode::LoopBackControl)->_idx];
 526   _igvn.hash_delete(head);
 527   head->set_req(LoopNode::EntryControl, new_entry);
 528   for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) {
 529     Node* old = head->fast_out(j);
 530     if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) {
 531       Node* new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
 532       if (!new_exit_value )     // Backedge value is ALSO loop invariant?
 533         // Then loop body backedge value remains the same.
 534         new_exit_value = old->in(LoopNode::LoopBackControl);
 535       _igvn.hash_delete(old);
 536       old->set_req(LoopNode::EntryControl, new_exit_value);
 537     }
 538   }
 539 
 540 
 541   // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
 542   //         extra backedge user.
 543   Node* new_head = old_new[head->_idx];
 544   _igvn.hash_delete(new_head);
 545   new_head->set_req(LoopNode::LoopBackControl, C->top());
 546   for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) {
 547     Node* use = new_head->fast_out(j2);
 548     if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) {
 549       _igvn.hash_delete(use);
 550       use->set_req(LoopNode::LoopBackControl, C->top());
 551     }
 552   }
 553 
 554 
 555   // Step 4: Correct dom-depth info.  Set to loop-head depth.
 556   int dd = dom_depth(head);
 557   set_idom(head, head->in(1), dd);
 558   for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
 559     Node *old = loop->_body.at(j3);
 560     Node *nnn = old_new[old->_idx];
 561     if (!has_ctrl(nnn))
 562       set_idom(nnn, idom(nnn), dd-1);
 563   }
 564 
 565   // Now force out all loop-invariant dominating tests.  The optimizer
 566   // finds some, but we _know_ they are all useless.
 567   peeled_dom_test_elim(loop,old_new);
 568 
 569   loop->record_for_igvn();
 570 }
 571 
 572 #define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop
 573 
 574 //------------------------------policy_maximally_unroll------------------------
 575 // Calculate exact loop trip count and return true if loop can be maximally
 576 // unrolled.
 577 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
 578   CountedLoopNode *cl = _head->as_CountedLoop();
 579   assert(cl->is_normal_loop(), "");
 580   if (!cl->is_valid_counted_loop())
 581     return false; // Malformed counted loop
 582 
 583   if (!cl->has_exact_trip_count()) {
 584     // Trip count is not exact.
 585     return false;
 586   }
 587 
 588   uint trip_count = cl->trip_count();
 589   // Note, max_juint is used to indicate unknown trip count.
 590   assert(trip_count > 1, "one iteration loop should be optimized out already");
 591   assert(trip_count < max_juint, "exact trip_count should be less than max_uint.");
 592 
 593   // Real policy: if we maximally unroll, does it get too big?
 594   // Allow the unrolled mess to get larger than standard loop
 595   // size.  After all, it will no longer be a loop.
 596   uint body_size    = _body.size();
 597   uint unroll_limit = (uint)LoopUnrollLimit * 4;
 598   assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
 599   if (trip_count > unroll_limit || body_size > unroll_limit) {
 600     return false;
 601   }
 602 
 603   // Fully unroll a loop with few iterations regardless next
 604   // conditions since following loop optimizations will split
 605   // such loop anyway (pre-main-post).
 606   if (trip_count <= 3)
 607     return true;
 608 
 609   // Take into account that after unroll conjoined heads and tails will fold,
 610   // otherwise policy_unroll() may allow more unrolling than max unrolling.
 611   uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count;
 612   uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE;
 613   if (body_size != tst_body_size) // Check for int overflow
 614     return false;
 615   if (new_body_size > unroll_limit ||
 616       // Unrolling can result in a large amount of node construction
 617       new_body_size >= phase->C->max_node_limit() - phase->C->live_nodes()) {
 618     return false;
 619   }
 620 
 621   // Do not unroll a loop with String intrinsics code.
 622   // String intrinsics are large and have loops.
 623   for (uint k = 0; k < _body.size(); k++) {
 624     Node* n = _body.at(k);
 625     switch (n->Opcode()) {
 626       case Op_StrComp:
 627       case Op_StrEquals:
 628       case Op_StrIndexOf:
 629       case Op_StrIndexOfChar:
 630       case Op_EncodeISOArray:
 631       case Op_AryEq:
 632       case Op_HasNegatives: {
 633         return false;
 634       }
 635 #if INCLUDE_RTM_OPT
 636       case Op_FastLock:
 637       case Op_FastUnlock: {
 638         // Don't unroll RTM locking code because it is large.
 639         if (UseRTMLocking) {
 640           return false;
 641         }
 642       }
 643 #endif
 644     } // switch
 645   }
 646 
 647   return true; // Do maximally unroll
 648 }
 649 
 650 
 651 //------------------------------policy_unroll----------------------------------
 652 // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if
 653 // the loop is a CountedLoop and the body is small enough.
 654 bool IdealLoopTree::policy_unroll(PhaseIdealLoop *phase) {
 655 
 656   CountedLoopNode *cl = _head->as_CountedLoop();
 657   assert(cl->is_normal_loop() || cl->is_main_loop(), "");
 658 
 659   if (!cl->is_valid_counted_loop())
 660     return false; // Malformed counted loop
 661 
 662   // Protect against over-unrolling.
 663   // After split at least one iteration will be executed in pre-loop.
 664   if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false;
 665 
 666   _local_loop_unroll_limit = LoopUnrollLimit;
 667   _local_loop_unroll_factor = 4;
 668   int future_unroll_ct = cl->unrolled_count() * 2;
 669   if (!cl->do_unroll_only()) {
 670     if (future_unroll_ct > LoopMaxUnroll) return false;
 671   } else {
 672     // obey user constraints on vector mapped loops with additional unrolling applied
 673     int unroll_constraint = (cl->slp_max_unroll()) ? cl->slp_max_unroll() : 1;
 674     if ((future_unroll_ct / unroll_constraint) > LoopMaxUnroll) return false;
 675   }
 676 
 677   // Check for initial stride being a small enough constant
 678   if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;
 679 
 680   // Don't unroll if the next round of unrolling would push us
 681   // over the expected trip count of the loop.  One is subtracted
 682   // from the expected trip count because the pre-loop normally
 683   // executes 1 iteration.
 684   if (UnrollLimitForProfileCheck > 0 &&
 685       cl->profile_trip_cnt() != COUNT_UNKNOWN &&
 686       future_unroll_ct        > UnrollLimitForProfileCheck &&
 687       (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
 688     return false;
 689   }
 690 
 691   // When unroll count is greater than LoopUnrollMin, don't unroll if:
 692   //   the residual iterations are more than 10% of the trip count
 693   //   and rounds of "unroll,optimize" are not making significant progress
 694   //   Progress defined as current size less than 20% larger than previous size.
 695   if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
 696       future_unroll_ct > LoopUnrollMin &&
 697       (future_unroll_ct - 1) * (100 / LoopPercentProfileLimit) > cl->profile_trip_cnt() &&
 698       1.2 * cl->node_count_before_unroll() < (double)_body.size()) {
 699     return false;
 700   }
 701 
 702   Node *init_n = cl->init_trip();
 703   Node *limit_n = cl->limit();
 704   int stride_con = cl->stride_con();
 705   // Non-constant bounds.
 706   // Protect against over-unrolling when init or/and limit are not constant
 707   // (so that trip_count's init value is maxint) but iv range is known.
 708   if (init_n   == NULL || !init_n->is_Con()  ||
 709       limit_n  == NULL || !limit_n->is_Con()) {
 710     Node* phi = cl->phi();
 711     if (phi != NULL) {
 712       assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
 713       const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
 714       int next_stride = stride_con * 2; // stride after this unroll
 715       if (next_stride > 0) {
 716         if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow
 717             iv_type->_lo + next_stride >  iv_type->_hi) {
 718           return false;  // over-unrolling
 719         }
 720       } else if (next_stride < 0) {
 721         if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow
 722             iv_type->_hi + next_stride <  iv_type->_lo) {
 723           return false;  // over-unrolling
 724         }
 725       }
 726     }
 727   }
 728 
 729   // After unroll limit will be adjusted: new_limit = limit-stride.
 730   // Bailout if adjustment overflow.
 731   const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int();
 732   if ((stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi)) ||
 733       (stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo)))
 734     return false;  // overflow
 735 
 736   // Adjust body_size to determine if we unroll or not
 737   uint body_size = _body.size();
 738   // Key test to unroll loop in CRC32 java code
 739   int xors_in_loop = 0;
 740   // Also count ModL, DivL and MulL which expand mightly
 741   for (uint k = 0; k < _body.size(); k++) {
 742     Node* n = _body.at(k);
 743     switch (n->Opcode()) {
 744       case Op_XorI: xors_in_loop++; break; // CRC32 java code
 745       case Op_ModL: body_size += 30; break;
 746       case Op_DivL: body_size += 30; break;
 747       case Op_MulL: body_size += 10; break;
 748       case Op_StrComp:
 749       case Op_StrEquals:
 750       case Op_StrIndexOf:
 751       case Op_StrIndexOfChar:
 752       case Op_EncodeISOArray:
 753       case Op_AryEq:
 754       case Op_HasNegatives: {
 755         // Do not unroll a loop with String intrinsics code.
 756         // String intrinsics are large and have loops.
 757         return false;
 758       }
 759 #if INCLUDE_RTM_OPT
 760       case Op_FastLock:
 761       case Op_FastUnlock: {
 762         // Don't unroll RTM locking code because it is large.
 763         if (UseRTMLocking) {
 764           return false;
 765         }
 766       }
 767 #endif
 768     } // switch
 769   }
 770 
 771   if (UseSuperWord) {
 772     if (!cl->is_reduction_loop()) {
 773       phase->mark_reductions(this);
 774     }
 775 
 776     // Only attempt slp analysis when user controls do not prohibit it
 777     if (LoopMaxUnroll > _local_loop_unroll_factor) {
 778       // Once policy_slp_analysis succeeds, mark the loop with the
 779       // maximal unroll factor so that we minimize analysis passes
 780       if (future_unroll_ct >= _local_loop_unroll_factor) {
 781         policy_unroll_slp_analysis(cl, phase, future_unroll_ct);
 782       }
 783     }
 784   }
 785 
 786   int slp_max_unroll_factor = cl->slp_max_unroll();
 787   if (cl->has_passed_slp()) {
 788     if (slp_max_unroll_factor >= future_unroll_ct) return true;
 789     // Normal case: loop too big
 790     return false;
 791   }
 792 
 793   // Check for being too big
 794   if (body_size > (uint)_local_loop_unroll_limit) {
 795     if (xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;
 796     // Normal case: loop too big
 797     return false;
 798   }
 799 
 800   if (cl->do_unroll_only()) {
 801     if (TraceSuperWordLoopUnrollAnalysis) {
 802       tty->print_cr("policy_unroll passed vector loop(vlen=%d,factor = %d)\n", slp_max_unroll_factor, future_unroll_ct);
 803     }
 804   }
 805 
 806   // Unroll once!  (Each trip will soon do double iterations)
 807   return true;
 808 }
 809 
 810 void IdealLoopTree::policy_unroll_slp_analysis(CountedLoopNode *cl, PhaseIdealLoop *phase, int future_unroll_ct) {
 811   // Enable this functionality target by target as needed
 812   if (SuperWordLoopUnrollAnalysis) {
 813     if (!cl->was_slp_analyzed()) {
 814       SuperWord sw(phase);
 815       sw.transform_loop(this, false);
 816 
 817       // If the loop is slp canonical analyze it
 818       if (sw.early_return() == false) {
 819         sw.unrolling_analysis(_local_loop_unroll_factor);
 820       }
 821     }
 822 
 823     if (cl->has_passed_slp()) {
 824       int slp_max_unroll_factor = cl->slp_max_unroll();
 825       if (slp_max_unroll_factor >= future_unroll_ct) {
 826         int new_limit = cl->node_count_before_unroll() * slp_max_unroll_factor;
 827         if (new_limit > LoopUnrollLimit) {
 828           if (TraceSuperWordLoopUnrollAnalysis) {
 829             tty->print_cr("slp analysis unroll=%d, default limit=%d\n", new_limit, _local_loop_unroll_limit);
 830           }
 831           _local_loop_unroll_limit = new_limit;
 832         }
 833       }
 834     }
 835   }
 836 }
 837 
 838 //------------------------------policy_align-----------------------------------
 839 // Return TRUE or FALSE if the loop should be cache-line aligned.  Gather the
 840 // expression that does the alignment.  Note that only one array base can be
 841 // aligned in a loop (unless the VM guarantees mutual alignment).  Note that
 842 // if we vectorize short memory ops into longer memory ops, we may want to
 843 // increase alignment.
 844 bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {
 845   return false;
 846 }
 847 
 848 //------------------------------policy_range_check-----------------------------
 849 // Return TRUE or FALSE if the loop should be range-check-eliminated.
 850 // Actually we do iteration-splitting, a more powerful form of RCE.
 851 bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {
 852   if (!RangeCheckElimination) return false;
 853 
 854   CountedLoopNode *cl = _head->as_CountedLoop();
 855   // If we unrolled with no intention of doing RCE and we later
 856   // changed our minds, we got no pre-loop.  Either we need to
 857   // make a new pre-loop, or we gotta disallow RCE.
 858   if (cl->is_main_no_pre_loop()) return false; // Disallowed for now.
 859   Node *trip_counter = cl->phi();
 860 
 861   // check for vectorized loops, some opts are no longer needed
 862   if (cl->do_unroll_only()) return false;
 863 
 864   // Check loop body for tests of trip-counter plus loop-invariant vs
 865   // loop-invariant.
 866   for (uint i = 0; i < _body.size(); i++) {
 867     Node *iff = _body[i];
 868     if (iff->Opcode() == Op_If ||
 869         iff->Opcode() == Op_RangeCheck) { // Test?
 870 
 871       // Comparing trip+off vs limit
 872       Node *bol = iff->in(1);
 873       if (bol->req() != 2) continue; // dead constant test
 874       if (!bol->is_Bool()) {
 875         assert(bol->Opcode() == Op_Conv2B, "predicate check only");
 876         continue;
 877       }
 878       if (bol->as_Bool()->_test._test == BoolTest::ne)
 879         continue; // not RC
 880 
 881       Node *cmp = bol->in(1);
 882       Node *rc_exp = cmp->in(1);
 883       Node *limit = cmp->in(2);
 884 
 885       Node *limit_c = phase->get_ctrl(limit);
 886       if( limit_c == phase->C->top() )
 887         return false;           // Found dead test on live IF?  No RCE!
 888       if( is_member(phase->get_loop(limit_c) ) ) {
 889         // Compare might have operands swapped; commute them
 890         rc_exp = cmp->in(2);
 891         limit  = cmp->in(1);
 892         limit_c = phase->get_ctrl(limit);
 893         if( is_member(phase->get_loop(limit_c) ) )
 894           continue;             // Both inputs are loop varying; cannot RCE
 895       }
 896 
 897       if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
 898         continue;
 899       }
 900       // Yeah!  Found a test like 'trip+off vs limit'
 901       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
 902       // we need loop unswitching instead of iteration splitting.
 903       if( is_loop_exit(iff) )
 904         return true;            // Found reason to split iterations
 905     } // End of is IF
 906   }
 907 
 908   return false;
 909 }
 910 
 911 //------------------------------policy_peel_only-------------------------------
 912 // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned.  Useful
 913 // for unrolling loops with NO array accesses.
 914 bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {
 915   // check for vectorized loops, any peeling done was already applied
 916   if (_head->is_CountedLoop() && _head->as_CountedLoop()->do_unroll_only()) return false;
 917 
 918   for( uint i = 0; i < _body.size(); i++ )
 919     if( _body[i]->is_Mem() )
 920       return false;
 921 
 922   // No memory accesses at all!
 923   return true;
 924 }
 925 
 926 //------------------------------clone_up_backedge_goo--------------------------
 927 // If Node n lives in the back_ctrl block and cannot float, we clone a private
 928 // version of n in preheader_ctrl block and return that, otherwise return n.
 929 Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones ) {
 930   if( get_ctrl(n) != back_ctrl ) return n;
 931 
 932   // Only visit once
 933   if (visited.test_set(n->_idx)) {
 934     Node *x = clones.find(n->_idx);
 935     if (x != NULL)
 936       return x;
 937     return n;
 938   }
 939 
 940   Node *x = NULL;               // If required, a clone of 'n'
 941   // Check for 'n' being pinned in the backedge.
 942   if( n->in(0) && n->in(0) == back_ctrl ) {
 943     assert(clones.find(n->_idx) == NULL, "dead loop");
 944     x = n->clone();             // Clone a copy of 'n' to preheader
 945     clones.push(x, n->_idx);
 946     x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
 947   }
 948 
 949   // Recursive fixup any other input edges into x.
 950   // If there are no changes we can just return 'n', otherwise
 951   // we need to clone a private copy and change it.
 952   for( uint i = 1; i < n->req(); i++ ) {
 953     Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i), visited, clones );
 954     if( g != n->in(i) ) {
 955       if( !x ) {
 956         assert(clones.find(n->_idx) == NULL, "dead loop");
 957         x = n->clone();
 958         clones.push(x, n->_idx);
 959       }
 960       x->set_req(i, g);
 961     }
 962   }
 963   if( x ) {                     // x can legally float to pre-header location
 964     register_new_node( x, preheader_ctrl );
 965     return x;
 966   } else {                      // raise n to cover LCA of uses
 967     set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
 968   }
 969   return n;
 970 }
 971 
 972 bool PhaseIdealLoop::cast_incr_before_loop(Node* incr, Node* ctrl, Node* loop) {
 973   Node* castii = new CastIINode(incr, TypeInt::INT, true);
 974   castii->set_req(0, ctrl);
 975   register_new_node(castii, ctrl);
 976   for (DUIterator_Fast imax, i = incr->fast_outs(imax); i < imax; i++) {
 977     Node* n = incr->fast_out(i);
 978     if (n->is_Phi() && n->in(0) == loop) {
 979       int nrep = n->replace_edge(incr, castii);
 980       return true;
 981     }
 982   }
 983   return false;
 984 }
 985 
 986 //------------------------------insert_pre_post_loops--------------------------
 987 // Insert pre and post loops.  If peel_only is set, the pre-loop can not have
 988 // more iterations added.  It acts as a 'peel' only, no lower-bound RCE, no
 989 // alignment.  Useful to unroll loops that do no array accesses.
 990 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
 991 
 992 #ifndef PRODUCT
 993   if (TraceLoopOpts) {
 994     if (peel_only)
 995       tty->print("PeelMainPost ");
 996     else
 997       tty->print("PreMainPost  ");
 998     loop->dump_head();
 999   }
1000 #endif
1001   C->set_major_progress();
1002 
1003   // Find common pieces of the loop being guarded with pre & post loops
1004   CountedLoopNode *main_head = loop->_head->as_CountedLoop();
1005   assert( main_head->is_normal_loop(), "" );
1006   CountedLoopEndNode *main_end = main_head->loopexit();
1007   guarantee(main_end != NULL, "no loop exit node");
1008   assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
1009   uint dd_main_head = dom_depth(main_head);
1010   uint max = main_head->outcnt();
1011 
1012   Node *pre_header= main_head->in(LoopNode::EntryControl);
1013   Node *init      = main_head->init_trip();
1014   Node *incr      = main_end ->incr();
1015   Node *limit     = main_end ->limit();
1016   Node *stride    = main_end ->stride();
1017   Node *cmp       = main_end ->cmp_node();
1018   BoolTest::mask b_test = main_end->test_trip();
1019 
1020   // Need only 1 user of 'bol' because I will be hacking the loop bounds.
1021   Node *bol = main_end->in(CountedLoopEndNode::TestValue);
1022   if( bol->outcnt() != 1 ) {
1023     bol = bol->clone();
1024     register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
1025     _igvn.replace_input_of(main_end, CountedLoopEndNode::TestValue, bol);
1026   }
1027   // Need only 1 user of 'cmp' because I will be hacking the loop bounds.
1028   if( cmp->outcnt() != 1 ) {
1029     cmp = cmp->clone();
1030     register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
1031     _igvn.replace_input_of(bol, 1, cmp);
1032   }
1033 
1034   // Add the post loop
1035   CountedLoopNode *post_head = NULL;
1036   Node *main_exit = insert_post_loop(loop, old_new, main_head, main_end, incr, limit, post_head);
1037 
1038   //------------------------------
1039   // Step B: Create Pre-Loop.
1040 
1041   // Step B1: Clone the loop body.  The clone becomes the pre-loop.  The main
1042   // loop pre-header illegally has 2 control users (old & new loops).
1043   clone_loop( loop, old_new, dd_main_head );
1044   CountedLoopNode*    pre_head = old_new[main_head->_idx]->as_CountedLoop();
1045   CountedLoopEndNode* pre_end  = old_new[main_end ->_idx]->as_CountedLoopEnd();
1046   pre_head->set_pre_loop(main_head);
1047   Node *pre_incr = old_new[incr->_idx];
1048 
1049   // Reduce the pre-loop trip count.
1050   pre_end->_prob = PROB_FAIR;
1051 
1052   // Find the pre-loop normal exit.
1053   Node* pre_exit = pre_end->proj_out(false);
1054   assert( pre_exit->Opcode() == Op_IfFalse, "" );
1055   IfFalseNode *new_pre_exit = new IfFalseNode(pre_end);
1056   _igvn.register_new_node_with_optimizer( new_pre_exit );
1057   set_idom(new_pre_exit, pre_end, dd_main_head);
1058   set_loop(new_pre_exit, loop->_parent);
1059 
1060   // Step B2: Build a zero-trip guard for the main-loop.  After leaving the
1061   // pre-loop, the main-loop may not execute at all.  Later in life this
1062   // zero-trip guard will become the minimum-trip guard when we unroll
1063   // the main-loop.
1064   Node *min_opaq = new Opaque1Node(C, limit);
1065   Node *min_cmp  = new CmpINode( pre_incr, min_opaq );
1066   Node *min_bol  = new BoolNode( min_cmp, b_test );
1067   register_new_node( min_opaq, new_pre_exit );
1068   register_new_node( min_cmp , new_pre_exit );
1069   register_new_node( min_bol , new_pre_exit );
1070 
1071   // Build the IfNode (assume the main-loop is executed always).
1072   IfNode *min_iff = new IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );
1073   _igvn.register_new_node_with_optimizer( min_iff );
1074   set_idom(min_iff, new_pre_exit, dd_main_head);
1075   set_loop(min_iff, loop->_parent);
1076 
1077   // Plug in the false-path, taken if we need to skip main-loop
1078   _igvn.hash_delete( pre_exit );
1079   pre_exit->set_req(0, min_iff);
1080   set_idom(pre_exit, min_iff, dd_main_head);
1081   set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
1082   // Make the true-path, must enter the main loop
1083   Node *min_taken = new IfTrueNode( min_iff );
1084   _igvn.register_new_node_with_optimizer( min_taken );
1085   set_idom(min_taken, min_iff, dd_main_head);
1086   set_loop(min_taken, loop->_parent);
1087   // Plug in the true path
1088   _igvn.hash_delete( main_head );
1089   main_head->set_req(LoopNode::EntryControl, min_taken);
1090   set_idom(main_head, min_taken, dd_main_head);
1091 
1092   Arena *a = Thread::current()->resource_area();
1093   VectorSet visited(a);
1094   Node_Stack clones(a, main_head->back_control()->outcnt());
1095   // Step B3: Make the fall-in values to the main-loop come from the
1096   // fall-out values of the pre-loop.
1097   for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
1098     Node* main_phi = main_head->fast_out(i2);
1099     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
1100       Node *pre_phi = old_new[main_phi->_idx];
1101       Node *fallpre  = clone_up_backedge_goo(pre_head->back_control(),
1102                                              main_head->init_control(),
1103                                              pre_phi->in(LoopNode::LoopBackControl),
1104                                              visited, clones);
1105       _igvn.hash_delete(main_phi);
1106       main_phi->set_req( LoopNode::EntryControl, fallpre );
1107     }
1108   }
1109 
1110   // Nodes inside the loop may be control dependent on a predicate
1111   // that was moved before the preloop. If the back branch of the main
1112   // or post loops becomes dead, those nodes won't be dependent on the
1113   // test that guards that loop nest anymore which could lead to an
1114   // incorrect array access because it executes independently of the
1115   // test that was guarding the loop nest. We add a special CastII on
1116   // the if branch that enters the loop, between the input induction
1117   // variable value and the induction variable Phi to preserve correct
1118   // dependencies.
1119 
1120   // CastII for the main loop:
1121   bool inserted = cast_incr_before_loop( pre_incr, min_taken, main_head );
1122   assert(inserted, "no castII inserted");
1123 
1124   // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
1125   // RCE and alignment may change this later.
1126   Node *cmp_end = pre_end->cmp_node();
1127   assert( cmp_end->in(2) == limit, "" );
1128   Node *pre_limit = new AddINode( init, stride );
1129 
1130   // Save the original loop limit in this Opaque1 node for
1131   // use by range check elimination.
1132   Node *pre_opaq  = new Opaque1Node(C, pre_limit, limit);
1133 
1134   register_new_node( pre_limit, pre_head->in(0) );
1135   register_new_node( pre_opaq , pre_head->in(0) );
1136 
1137   // Since no other users of pre-loop compare, I can hack limit directly
1138   assert( cmp_end->outcnt() == 1, "no other users" );
1139   _igvn.hash_delete(cmp_end);
1140   cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
1141 
1142   // Special case for not-equal loop bounds:
1143   // Change pre loop test, main loop test, and the
1144   // main loop guard test to use lt or gt depending on stride
1145   // direction:
1146   // positive stride use <
1147   // negative stride use >
1148   //
1149   // not-equal test is kept for post loop to handle case
1150   // when init > limit when stride > 0 (and reverse).
1151 
1152   if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
1153 
1154     BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
1155     // Modify pre loop end condition
1156     Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1157     BoolNode* new_bol0 = new BoolNode(pre_bol->in(1), new_test);
1158     register_new_node( new_bol0, pre_head->in(0) );
1159     _igvn.replace_input_of(pre_end, CountedLoopEndNode::TestValue, new_bol0);
1160     // Modify main loop guard condition
1161     assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
1162     BoolNode* new_bol1 = new BoolNode(min_bol->in(1), new_test);
1163     register_new_node( new_bol1, new_pre_exit );
1164     _igvn.hash_delete(min_iff);
1165     min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
1166     // Modify main loop end condition
1167     BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1168     BoolNode* new_bol2 = new BoolNode(main_bol->in(1), new_test);
1169     register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
1170     _igvn.replace_input_of(main_end, CountedLoopEndNode::TestValue, new_bol2);
1171   }
1172 
1173   // Flag main loop
1174   main_head->set_main_loop();
1175   if( peel_only ) main_head->set_main_no_pre_loop();
1176 
1177   // Subtract a trip count for the pre-loop.
1178   main_head->set_trip_count(main_head->trip_count() - 1);
1179 
1180   // It's difficult to be precise about the trip-counts
1181   // for the pre/post loops.  They are usually very short,
1182   // so guess that 4 trips is a reasonable value.
1183   post_head->set_profile_trip_cnt(4.0);
1184   pre_head->set_profile_trip_cnt(4.0);
1185 
1186   // Now force out all loop-invariant dominating tests.  The optimizer
1187   // finds some, but we _know_ they are all useless.
1188   peeled_dom_test_elim(loop,old_new);
1189   loop->record_for_igvn();
1190 }
1191 
1192 //------------------------------insert_vector_post_loop------------------------
1193 // Insert a copy of the atomic unrolled vectorized main loop as a post loop,
1194 // unroll_policy has already informed us that more unrolling is about to happen to
1195 // the main loop.  The resultant post loop will serve as a vectorized drain loop.
1196 void PhaseIdealLoop::insert_vector_post_loop(IdealLoopTree *loop, Node_List &old_new) {
1197   if (!loop->_head->is_CountedLoop()) return;
1198 
1199   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1200 
1201   // only process vectorized main loops
1202   if (!cl->is_vectorized_loop() || !cl->is_main_loop()) return;
1203 
1204   int slp_max_unroll_factor = cl->slp_max_unroll();
1205   int cur_unroll = cl->unrolled_count();
1206 
1207   if (slp_max_unroll_factor == 0) return;
1208 
1209   // only process atomic unroll vector loops (not super unrolled after vectorization)
1210   if (cur_unroll != slp_max_unroll_factor) return;
1211 
1212   // we only ever process this one time
1213   if (cl->has_atomic_post_loop()) return;
1214 
1215 #ifndef PRODUCT
1216   if (TraceLoopOpts) {
1217     tty->print("PostVector  ");
1218     loop->dump_head();
1219   }
1220 #endif
1221   C->set_major_progress();
1222 
1223   // Find common pieces of the loop being guarded with pre & post loops
1224   CountedLoopNode *main_head = loop->_head->as_CountedLoop();
1225   CountedLoopEndNode *main_end = main_head->loopexit();
1226   guarantee(main_end != NULL, "no loop exit node");
1227   // diagnostic to show loop end is not properly formed
1228   assert(main_end->outcnt() == 2, "1 true, 1 false path only");
1229 
1230   // mark this loop as processed
1231   main_head->mark_has_atomic_post_loop();
1232 
1233   Node *incr = main_end->incr();
1234   Node *limit = main_end->limit();
1235 
1236   // In this case we throw away the result as we are not using it to connect anything else.
1237   CountedLoopNode *post_head = NULL;
1238   insert_post_loop(loop, old_new, main_head, main_end, incr, limit, post_head);
1239 
1240   // It's difficult to be precise about the trip-counts
1241   // for post loops.  They are usually very short,
1242   // so guess that unit vector trips is a reasonable value.
1243   post_head->set_profile_trip_cnt(cur_unroll);
1244 
1245   // Now force out all loop-invariant dominating tests.  The optimizer
1246   // finds some, but we _know_ they are all useless.
1247   peeled_dom_test_elim(loop, old_new);
1248   loop->record_for_igvn();
1249 }
1250 
1251 
1252 //-------------------------insert_scalar_rced_post_loop------------------------
1253 // Insert a copy of the rce'd main loop as a post loop,
1254 // We have not unrolled the main loop, so this is the right time to inject this.
1255 // Later we will examine the partner of this post loop pair which still has range checks
1256 // to see inject code which tests at runtime if the range checks are applicable.
1257 void PhaseIdealLoop::insert_scalar_rced_post_loop(IdealLoopTree *loop, Node_List &old_new) {
1258   if (!loop->_head->is_CountedLoop()) return;
1259 
1260   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1261 
1262   // only process RCE'd main loops
1263   if (!cl->is_main_loop() || cl->range_checks_present()) return;
1264 
1265 #ifndef PRODUCT
1266   if (TraceLoopOpts) {
1267     tty->print("PostScalarRce  ");
1268     loop->dump_head();
1269   }
1270 #endif
1271   C->set_major_progress();
1272 
1273   // Find common pieces of the loop being guarded with pre & post loops
1274   CountedLoopNode *main_head = loop->_head->as_CountedLoop();
1275   CountedLoopEndNode *main_end = main_head->loopexit();
1276   guarantee(main_end != NULL, "no loop exit node");
1277   // diagnostic to show loop end is not properly formed
1278   assert(main_end->outcnt() == 2, "1 true, 1 false path only");
1279 
1280   Node *incr = main_end->incr();
1281   Node *limit = main_end->limit();
1282 
1283   // In this case we throw away the result as we are not using it to connect anything else.
1284   CountedLoopNode *post_head = NULL;
1285   insert_post_loop(loop, old_new, main_head, main_end, incr, limit, post_head);
1286 
1287   // It's difficult to be precise about the trip-counts
1288   // for post loops.  They are usually very short,
1289   // so guess that unit vector trips is a reasonable value.
1290   post_head->set_profile_trip_cnt(4.0);
1291   post_head->set_is_rce_post_loop();
1292 
1293   // Now force out all loop-invariant dominating tests.  The optimizer
1294   // finds some, but we _know_ they are all useless.
1295   peeled_dom_test_elim(loop, old_new);
1296   loop->record_for_igvn();
1297 }
1298 
1299 
1300 //------------------------------insert_post_loop-------------------------------
1301 // Insert post loops.  Add a post loop to the given loop passed.
1302 Node *PhaseIdealLoop::insert_post_loop(IdealLoopTree *loop, Node_List &old_new,
1303                                        CountedLoopNode *main_head, CountedLoopEndNode *main_end,
1304                                        Node *incr, Node *limit, CountedLoopNode *&post_head) {
1305 
1306   //------------------------------
1307   // Step A: Create a new post-Loop.
1308   Node* main_exit = main_end->proj_out(false);
1309   assert(main_exit->Opcode() == Op_IfFalse, "");
1310   int dd_main_exit = dom_depth(main_exit);
1311 
1312   // Step A1: Clone the loop body of main. The clone becomes the post-loop.
1313   // The main loop pre-header illegally has 2 control users (old & new loops).
1314   clone_loop(loop, old_new, dd_main_exit);
1315   assert(old_new[main_end->_idx]->Opcode() == Op_CountedLoopEnd, "");
1316   post_head = old_new[main_head->_idx]->as_CountedLoop();
1317   post_head->set_normal_loop();
1318   post_head->set_post_loop(main_head);
1319 
1320   // Reduce the post-loop trip count.
1321   CountedLoopEndNode* post_end = old_new[main_end->_idx]->as_CountedLoopEnd();
1322   post_end->_prob = PROB_FAIR;
1323 
1324   // Build the main-loop normal exit.
1325   IfFalseNode *new_main_exit = new IfFalseNode(main_end);
1326   _igvn.register_new_node_with_optimizer(new_main_exit);
1327   set_idom(new_main_exit, main_end, dd_main_exit);
1328   set_loop(new_main_exit, loop->_parent);
1329 
1330   // Step A2: Build a zero-trip guard for the post-loop.  After leaving the
1331   // main-loop, the post-loop may not execute at all.  We 'opaque' the incr
1332   // (the previous loop trip-counter exit value) because we will be changing
1333   // the exit value (via additional unrolling) so we cannot constant-fold away the zero
1334   // trip guard until all unrolling is done.
1335   Node *zer_opaq = new Opaque1Node(C, incr);
1336   Node *zer_cmp = new CmpINode(zer_opaq, limit);
1337   Node *zer_bol = new BoolNode(zer_cmp, main_end->test_trip());
1338   register_new_node(zer_opaq, new_main_exit);
1339   register_new_node(zer_cmp, new_main_exit);
1340   register_new_node(zer_bol, new_main_exit);
1341 
1342   // Build the IfNode
1343   IfNode *zer_iff = new IfNode(new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN);
1344   _igvn.register_new_node_with_optimizer(zer_iff);
1345   set_idom(zer_iff, new_main_exit, dd_main_exit);
1346   set_loop(zer_iff, loop->_parent);
1347 
1348   // Plug in the false-path, taken if we need to skip this post-loop
1349   _igvn.replace_input_of(main_exit, 0, zer_iff);
1350   set_idom(main_exit, zer_iff, dd_main_exit);
1351   set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
1352   // Make the true-path, must enter this post loop
1353   Node *zer_taken = new IfTrueNode(zer_iff);
1354   _igvn.register_new_node_with_optimizer(zer_taken);
1355   set_idom(zer_taken, zer_iff, dd_main_exit);
1356   set_loop(zer_taken, loop->_parent);
1357   // Plug in the true path
1358   _igvn.hash_delete(post_head);
1359   post_head->set_req(LoopNode::EntryControl, zer_taken);
1360   set_idom(post_head, zer_taken, dd_main_exit);
1361 
1362   Arena *a = Thread::current()->resource_area();
1363   VectorSet visited(a);
1364   Node_Stack clones(a, main_head->back_control()->outcnt());
1365   // Step A3: Make the fall-in values to the post-loop come from the
1366   // fall-out values of the main-loop.
1367   for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
1368     Node* main_phi = main_head->fast_out(i);
1369     if (main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0) {
1370       Node *cur_phi = old_new[main_phi->_idx];
1371       Node *fallnew = clone_up_backedge_goo(main_head->back_control(),
1372                                             post_head->init_control(),
1373                                             main_phi->in(LoopNode::LoopBackControl),
1374                                             visited, clones);
1375       _igvn.hash_delete(cur_phi);
1376       cur_phi->set_req(LoopNode::EntryControl, fallnew);
1377     }
1378   }
1379 
1380   // CastII for the new post loop:
1381   bool inserted = cast_incr_before_loop(zer_opaq->in(1), zer_taken, post_head);
1382   assert(inserted, "no castII inserted");
1383 
1384   return new_main_exit;
1385 }
1386 
1387 //------------------------------is_invariant-----------------------------
1388 // Return true if n is invariant
1389 bool IdealLoopTree::is_invariant(Node* n) const {
1390   Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n;
1391   if (n_c->is_top()) return false;
1392   return !is_member(_phase->get_loop(n_c));
1393 }
1394 
1395 
1396 //------------------------------do_unroll--------------------------------------
1397 // Unroll the loop body one step - make each trip do 2 iterations.
1398 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
1399   assert(LoopUnrollLimit, "");
1400   CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
1401   CountedLoopEndNode *loop_end = loop_head->loopexit();
1402   assert(loop_end, "");
1403 #ifndef PRODUCT
1404   if (PrintOpto && VerifyLoopOptimizations) {
1405     tty->print("Unrolling ");
1406     loop->dump_head();
1407   } else if (TraceLoopOpts) {
1408     if (loop_head->trip_count() < (uint)LoopUnrollLimit) {
1409       tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count());
1410     } else {
1411       tty->print("Unroll %d     ", loop_head->unrolled_count()*2);
1412     }
1413     loop->dump_head();
1414   }
1415 
1416   if (C->do_vector_loop() && (PrintOpto && VerifyLoopOptimizations || TraceLoopOpts)) {
1417     Arena* arena = Thread::current()->resource_area();
1418     Node_Stack stack(arena, C->live_nodes() >> 2);
1419     Node_List rpo_list;
1420     VectorSet visited(arena);
1421     visited.set(loop_head->_idx);
1422     rpo( loop_head, stack, visited, rpo_list );
1423     dump(loop, rpo_list.size(), rpo_list );
1424   }
1425 #endif
1426 
1427   // Remember loop node count before unrolling to detect
1428   // if rounds of unroll,optimize are making progress
1429   loop_head->set_node_count_before_unroll(loop->_body.size());
1430 
1431   Node *ctrl  = loop_head->in(LoopNode::EntryControl);
1432   Node *limit = loop_head->limit();
1433   Node *init  = loop_head->init_trip();
1434   Node *stride = loop_head->stride();
1435 
1436   Node *opaq = NULL;
1437   if (adjust_min_trip) {       // If not maximally unrolling, need adjustment
1438     // Search for zero-trip guard.
1439 
1440     // Check the shape of the graph at the loop entry. If an inappropriate
1441     // graph shape is encountered, the compiler bails out loop unrolling;
1442     // compilation of the method will still succeed.
1443     if (!is_canonical_loop_entry(loop_head)) {
1444       return;
1445     }
1446     opaq = ctrl->in(0)->in(1)->in(1)->in(2);
1447     // Zero-trip test uses an 'opaque' node which is not shared.
1448     assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
1449   }
1450 
1451   C->set_major_progress();
1452 
1453   Node* new_limit = NULL;
1454   int stride_con = stride->get_int();
1455   int stride_p = (stride_con > 0) ? stride_con : -stride_con;
1456   uint old_trip_count = loop_head->trip_count();
1457   // Verify that unroll policy result is still valid.
1458   assert(old_trip_count > 1 &&
1459       (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");
1460 
1461   // Adjust loop limit to keep valid iterations number after unroll.
1462   // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride
1463   // which may overflow.
1464   if (!adjust_min_trip) {
1465     assert(old_trip_count > 1 && (old_trip_count & 1) == 0,
1466         "odd trip count for maximally unroll");
1467     // Don't need to adjust limit for maximally unroll since trip count is even.
1468   } else if (loop_head->has_exact_trip_count() && init->is_Con()) {
1469     // Loop's limit is constant. Loop's init could be constant when pre-loop
1470     // become peeled iteration.
1471     jlong init_con = init->get_int();
1472     // We can keep old loop limit if iterations count stays the same:
1473     //   old_trip_count == new_trip_count * 2
1474     // Note: since old_trip_count >= 2 then new_trip_count >= 1
1475     // so we also don't need to adjust zero trip test.
1476     jlong limit_con  = limit->get_int();
1477     // (stride_con*2) not overflow since stride_con <= 8.
1478     int new_stride_con = stride_con * 2;
1479     int stride_m    = new_stride_con - (stride_con > 0 ? 1 : -1);
1480     jlong trip_count = (limit_con - init_con + stride_m)/new_stride_con;
1481     // New trip count should satisfy next conditions.
1482     assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity");
1483     uint new_trip_count = (uint)trip_count;
1484     adjust_min_trip = (old_trip_count != new_trip_count*2);
1485   }
1486 
1487   if (adjust_min_trip) {
1488     // Step 2: Adjust the trip limit if it is called for.
1489     // The adjustment amount is -stride. Need to make sure if the
1490     // adjustment underflows or overflows, then the main loop is skipped.
1491     Node* cmp = loop_end->cmp_node();
1492     assert(cmp->in(2) == limit, "sanity");
1493     assert(opaq != NULL && opaq->in(1) == limit, "sanity");
1494 
1495     // Verify that policy_unroll result is still valid.
1496     const TypeInt* limit_type = _igvn.type(limit)->is_int();
1497     assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) ||
1498         stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity");
1499 
1500     if (limit->is_Con()) {
1501       // The check in policy_unroll and the assert above guarantee
1502       // no underflow if limit is constant.
1503       new_limit = _igvn.intcon(limit->get_int() - stride_con);
1504       set_ctrl(new_limit, C->root());
1505     } else {
1506       // Limit is not constant.
1507       if (loop_head->unrolled_count() == 1) { // only for first unroll
1508         // Separate limit by Opaque node in case it is an incremented
1509         // variable from previous loop to avoid using pre-incremented
1510         // value which could increase register pressure.
1511         // Otherwise reorg_offsets() optimization will create a separate
1512         // Opaque node for each use of trip-counter and as result
1513         // zero trip guard limit will be different from loop limit.
1514         assert(has_ctrl(opaq), "should have it");
1515         Node* opaq_ctrl = get_ctrl(opaq);
1516         limit = new Opaque2Node( C, limit );
1517         register_new_node( limit, opaq_ctrl );
1518       }
1519       if ((stride_con > 0 && (java_subtract(limit_type->_lo, stride_con) < limit_type->_lo)) ||
1520           (stride_con < 0 && (java_subtract(limit_type->_hi, stride_con) > limit_type->_hi))) {
1521         // No underflow.
1522         new_limit = new SubINode(limit, stride);
1523       } else {
1524         // (limit - stride) may underflow.
1525         // Clamp the adjustment value with MININT or MAXINT:
1526         //
1527         //   new_limit = limit-stride
1528         //   if (stride > 0)
1529         //     new_limit = (limit < new_limit) ? MININT : new_limit;
1530         //   else
1531         //     new_limit = (limit > new_limit) ? MAXINT : new_limit;
1532         //
1533         BoolTest::mask bt = loop_end->test_trip();
1534         assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
1535         Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint);
1536         set_ctrl(adj_max, C->root());
1537         Node* old_limit = NULL;
1538         Node* adj_limit = NULL;
1539         Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL;
1540         if (loop_head->unrolled_count() > 1 &&
1541             limit->is_CMove() && limit->Opcode() == Op_CMoveI &&
1542             limit->in(CMoveNode::IfTrue) == adj_max &&
1543             bol->as_Bool()->_test._test == bt &&
1544             bol->in(1)->Opcode() == Op_CmpI &&
1545             bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) {
1546           // Loop was unrolled before.
1547           // Optimize the limit to avoid nested CMove:
1548           // use original limit as old limit.
1549           old_limit = bol->in(1)->in(1);
1550           // Adjust previous adjusted limit.
1551           adj_limit = limit->in(CMoveNode::IfFalse);
1552           adj_limit = new SubINode(adj_limit, stride);
1553         } else {
1554           old_limit = limit;
1555           adj_limit = new SubINode(limit, stride);
1556         }
1557         assert(old_limit != NULL && adj_limit != NULL, "");
1558         register_new_node( adj_limit, ctrl ); // adjust amount
1559         Node* adj_cmp = new CmpINode(old_limit, adj_limit);
1560         register_new_node( adj_cmp, ctrl );
1561         Node* adj_bool = new BoolNode(adj_cmp, bt);
1562         register_new_node( adj_bool, ctrl );
1563         new_limit = new CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT);
1564       }
1565       register_new_node(new_limit, ctrl);
1566     }
1567     assert(new_limit != NULL, "");
1568     // Replace in loop test.
1569     assert(loop_end->in(1)->in(1) == cmp, "sanity");
1570     if (cmp->outcnt() == 1 && loop_end->in(1)->outcnt() == 1) {
1571       // Don't need to create new test since only one user.
1572       _igvn.hash_delete(cmp);
1573       cmp->set_req(2, new_limit);
1574     } else {
1575       // Create new test since it is shared.
1576       Node* ctrl2 = loop_end->in(0);
1577       Node* cmp2  = cmp->clone();
1578       cmp2->set_req(2, new_limit);
1579       register_new_node(cmp2, ctrl2);
1580       Node* bol2 = loop_end->in(1)->clone();
1581       bol2->set_req(1, cmp2);
1582       register_new_node(bol2, ctrl2);
1583       _igvn.replace_input_of(loop_end, 1, bol2);
1584     }
1585     // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1586     // Make it a 1-trip test (means at least 2 trips).
1587 
1588     // Guard test uses an 'opaque' node which is not shared.  Hence I
1589     // can edit it's inputs directly.  Hammer in the new limit for the
1590     // minimum-trip guard.
1591     assert(opaq->outcnt() == 1, "");
1592     _igvn.replace_input_of(opaq, 1, new_limit);
1593   }
1594 
1595   // Adjust max trip count. The trip count is intentionally rounded
1596   // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1597   // the main, unrolled, part of the loop will never execute as it is protected
1598   // by the min-trip test.  See bug 4834191 for a case where we over-unrolled
1599   // and later determined that part of the unrolled loop was dead.
1600   loop_head->set_trip_count(old_trip_count / 2);
1601 
1602   // Double the count of original iterations in the unrolled loop body.
1603   loop_head->double_unrolled_count();
1604 
1605   // ---------
1606   // Step 4: Clone the loop body.  Move it inside the loop.  This loop body
1607   // represents the odd iterations; since the loop trips an even number of
1608   // times its backedge is never taken.  Kill the backedge.
1609   uint dd = dom_depth(loop_head);
1610   clone_loop( loop, old_new, dd );
1611 
1612   // Make backedges of the clone equal to backedges of the original.
1613   // Make the fall-in from the original come from the fall-out of the clone.
1614   for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
1615     Node* phi = loop_head->fast_out(j);
1616     if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
1617       Node *newphi = old_new[phi->_idx];
1618       _igvn.hash_delete( phi );
1619       _igvn.hash_delete( newphi );
1620 
1621       phi   ->set_req(LoopNode::   EntryControl, newphi->in(LoopNode::LoopBackControl));
1622       newphi->set_req(LoopNode::LoopBackControl, phi   ->in(LoopNode::LoopBackControl));
1623       phi   ->set_req(LoopNode::LoopBackControl, C->top());
1624     }
1625   }
1626   Node *clone_head = old_new[loop_head->_idx];
1627   _igvn.hash_delete( clone_head );
1628   loop_head ->set_req(LoopNode::   EntryControl, clone_head->in(LoopNode::LoopBackControl));
1629   clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
1630   loop_head ->set_req(LoopNode::LoopBackControl, C->top());
1631   loop->_head = clone_head;     // New loop header
1632 
1633   set_idom(loop_head,  loop_head ->in(LoopNode::EntryControl), dd);
1634   set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
1635 
1636   // Kill the clone's backedge
1637   Node *newcle = old_new[loop_end->_idx];
1638   _igvn.hash_delete( newcle );
1639   Node *one = _igvn.intcon(1);
1640   set_ctrl(one, C->root());
1641   newcle->set_req(1, one);
1642   // Force clone into same loop body
1643   uint max = loop->_body.size();
1644   for( uint k = 0; k < max; k++ ) {
1645     Node *old = loop->_body.at(k);
1646     Node *nnn = old_new[old->_idx];
1647     loop->_body.push(nnn);
1648     if (!has_ctrl(old))
1649       set_loop(nnn, loop);
1650   }
1651 
1652   loop->record_for_igvn();
1653 
1654 #ifndef PRODUCT
1655   if (C->do_vector_loop() && (PrintOpto && VerifyLoopOptimizations || TraceLoopOpts)) {
1656     tty->print("\nnew loop after unroll\n");       loop->dump_head();
1657     for (uint i = 0; i < loop->_body.size(); i++) {
1658       loop->_body.at(i)->dump();
1659     }
1660     if(C->clone_map().is_debug()) {
1661       tty->print("\nCloneMap\n");
1662       Dict* dict = C->clone_map().dict();
1663       DictI i(dict);
1664       tty->print_cr("Dict@%p[%d] = ", dict, dict->Size());
1665       for (int ii = 0; i.test(); ++i, ++ii) {
1666         NodeCloneInfo cl((uint64_t)dict->operator[]((void*)i._key));
1667         tty->print("%d->%d:%d,", (int)(intptr_t)i._key, cl.idx(), cl.gen());
1668         if (ii % 10 == 9) {
1669           tty->print_cr(" ");
1670         }
1671       }
1672       tty->print_cr(" ");
1673     }
1674   }
1675 #endif
1676 
1677 }
1678 
1679 //------------------------------do_maximally_unroll----------------------------
1680 
1681 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
1682   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1683   assert(cl->has_exact_trip_count(), "trip count is not exact");
1684   assert(cl->trip_count() > 0, "");
1685 #ifndef PRODUCT
1686   if (TraceLoopOpts) {
1687     tty->print("MaxUnroll  %d ", cl->trip_count());
1688     loop->dump_head();
1689   }
1690 #endif
1691 
1692   // If loop is tripping an odd number of times, peel odd iteration
1693   if ((cl->trip_count() & 1) == 1) {
1694     do_peeling(loop, old_new);
1695   }
1696 
1697   // Now its tripping an even number of times remaining.  Double loop body.
1698   // Do not adjust pre-guards; they are not needed and do not exist.
1699   if (cl->trip_count() > 0) {
1700     assert((cl->trip_count() & 1) == 0, "missed peeling");
1701     do_unroll(loop, old_new, false);
1702   }
1703 }
1704 
1705 void PhaseIdealLoop::mark_reductions(IdealLoopTree *loop) {
1706   if (SuperWordReductions == false) return;
1707 
1708   CountedLoopNode* loop_head = loop->_head->as_CountedLoop();
1709   if (loop_head->unrolled_count() > 1) {
1710     return;
1711   }
1712 
1713   Node* trip_phi = loop_head->phi();
1714   for (DUIterator_Fast imax, i = loop_head->fast_outs(imax); i < imax; i++) {
1715     Node* phi = loop_head->fast_out(i);
1716     if (phi->is_Phi() && phi->outcnt() > 0 && phi != trip_phi) {
1717       // For definitions which are loop inclusive and not tripcounts.
1718       Node* def_node = phi->in(LoopNode::LoopBackControl);
1719 
1720       if (def_node != NULL) {
1721         Node* n_ctrl = get_ctrl(def_node);
1722         if (n_ctrl != NULL && loop->is_member(get_loop(n_ctrl))) {
1723           // Now test it to see if it fits the standard pattern for a reduction operator.
1724           int opc = def_node->Opcode();
1725           if (opc != ReductionNode::opcode(opc, def_node->bottom_type()->basic_type())) {
1726             if (!def_node->is_reduction()) { // Not marked yet
1727               // To be a reduction, the arithmetic node must have the phi as input and provide a def to it
1728               bool ok = false;
1729               for (unsigned j = 1; j < def_node->req(); j++) {
1730                 Node* in = def_node->in(j);
1731                 if (in == phi) {
1732                   ok = true;
1733                   break;
1734                 }
1735               }
1736 
1737               // do nothing if we did not match the initial criteria
1738               if (ok == false) {
1739                 continue;
1740               }
1741 
1742               // The result of the reduction must not be used in the loop
1743               for (DUIterator_Fast imax, i = def_node->fast_outs(imax); i < imax && ok; i++) {
1744                 Node* u = def_node->fast_out(i);
1745                 if (!loop->is_member(get_loop(ctrl_or_self(u)))) {
1746                   continue;
1747                 }
1748                 if (u == phi) {
1749                   continue;
1750                 }
1751                 ok = false;
1752               }
1753 
1754               // iff the uses conform
1755               if (ok) {
1756                 def_node->add_flag(Node::Flag_is_reduction);
1757                 loop_head->mark_has_reductions();
1758               }
1759             }
1760           }
1761         }
1762       }
1763     }
1764   }
1765 }
1766 
1767 //------------------------------adjust_limit-----------------------------------
1768 // Helper function for add_constraint().
1769 Node* PhaseIdealLoop::adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl) {
1770   // Compute "I :: (limit-offset)/scale"
1771   Node *con = new SubINode(rc_limit, offset);
1772   register_new_node(con, pre_ctrl);
1773   Node *X = new DivINode(0, con, scale);
1774   register_new_node(X, pre_ctrl);
1775 
1776   // Adjust loop limit
1777   loop_limit = (stride_con > 0)
1778                ? (Node*)(new MinINode(loop_limit, X))
1779                : (Node*)(new MaxINode(loop_limit, X));
1780   register_new_node(loop_limit, pre_ctrl);
1781   return loop_limit;
1782 }
1783 
1784 //------------------------------add_constraint---------------------------------
1785 // Constrain the main loop iterations so the conditions:
1786 //    low_limit <= scale_con * I + offset  <  upper_limit
1787 // always holds true.  That is, either increase the number of iterations in
1788 // the pre-loop or the post-loop until the condition holds true in the main
1789 // loop.  Stride, scale, offset and limit are all loop invariant.  Further,
1790 // stride and scale are constants (offset and limit often are).
1791 void PhaseIdealLoop::add_constraint( int stride_con, int scale_con, Node *offset, Node *low_limit, Node *upper_limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) {
1792   // For positive stride, the pre-loop limit always uses a MAX function
1793   // and the main loop a MIN function.  For negative stride these are
1794   // reversed.
1795 
1796   // Also for positive stride*scale the affine function is increasing, so the
1797   // pre-loop must check for underflow and the post-loop for overflow.
1798   // Negative stride*scale reverses this; pre-loop checks for overflow and
1799   // post-loop for underflow.
1800 
1801   Node *scale = _igvn.intcon(scale_con);
1802   set_ctrl(scale, C->root());
1803 
1804   if ((stride_con^scale_con) >= 0) { // Use XOR to avoid overflow
1805     // The overflow limit: scale*I+offset < upper_limit
1806     // For main-loop compute
1807     //   ( if (scale > 0) /* and stride > 0 */
1808     //       I < (upper_limit-offset)/scale
1809     //     else /* scale < 0 and stride < 0 */
1810     //       I > (upper_limit-offset)/scale
1811     //   )
1812     //
1813     // (upper_limit-offset) may overflow or underflow.
1814     // But it is fine since main loop will either have
1815     // less iterations or will be skipped in such case.
1816     *main_limit = adjust_limit(stride_con, scale, offset, upper_limit, *main_limit, pre_ctrl);
1817 
1818     // The underflow limit: low_limit <= scale*I+offset.
1819     // For pre-loop compute
1820     //   NOT(scale*I+offset >= low_limit)
1821     //   scale*I+offset < low_limit
1822     //   ( if (scale > 0) /* and stride > 0 */
1823     //       I < (low_limit-offset)/scale
1824     //     else /* scale < 0 and stride < 0 */
1825     //       I > (low_limit-offset)/scale
1826     //   )
1827 
1828     if (low_limit->get_int() == -max_jint) {
1829       // We need this guard when scale*pre_limit+offset >= limit
1830       // due to underflow. So we need execute pre-loop until
1831       // scale*I+offset >= min_int. But (min_int-offset) will
1832       // underflow when offset > 0 and X will be > original_limit
1833       // when stride > 0. To avoid it we replace positive offset with 0.
1834       //
1835       // Also (min_int+1 == -max_int) is used instead of min_int here
1836       // to avoid problem with scale == -1 (min_int/(-1) == min_int).
1837       Node* shift = _igvn.intcon(31);
1838       set_ctrl(shift, C->root());
1839       Node* sign = new RShiftINode(offset, shift);
1840       register_new_node(sign, pre_ctrl);
1841       offset = new AndINode(offset, sign);
1842       register_new_node(offset, pre_ctrl);
1843     } else {
1844       assert(low_limit->get_int() == 0, "wrong low limit for range check");
1845       // The only problem we have here when offset == min_int
1846       // since (0-min_int) == min_int. It may be fine for stride > 0
1847       // but for stride < 0 X will be < original_limit. To avoid it
1848       // max(pre_limit, original_limit) is used in do_range_check().
1849     }
1850     // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
1851     *pre_limit = adjust_limit((-stride_con), scale, offset, low_limit, *pre_limit, pre_ctrl);
1852 
1853   } else { // stride_con*scale_con < 0
1854     // For negative stride*scale pre-loop checks for overflow and
1855     // post-loop for underflow.
1856     //
1857     // The overflow limit: scale*I+offset < upper_limit
1858     // For pre-loop compute
1859     //   NOT(scale*I+offset < upper_limit)
1860     //   scale*I+offset >= upper_limit
1861     //   scale*I+offset+1 > upper_limit
1862     //   ( if (scale < 0) /* and stride > 0 */
1863     //       I < (upper_limit-(offset+1))/scale
1864     //     else /* scale > 0 and stride < 0 */
1865     //       I > (upper_limit-(offset+1))/scale
1866     //   )
1867     //
1868     // (upper_limit-offset-1) may underflow or overflow.
1869     // To avoid it min(pre_limit, original_limit) is used
1870     // in do_range_check() for stride > 0 and max() for < 0.
1871     Node *one  = _igvn.intcon(1);
1872     set_ctrl(one, C->root());
1873 
1874     Node *plus_one = new AddINode(offset, one);
1875     register_new_node( plus_one, pre_ctrl );
1876     // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
1877     *pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl);
1878 
1879     if (low_limit->get_int() == -max_jint) {
1880       // We need this guard when scale*main_limit+offset >= limit
1881       // due to underflow. So we need execute main-loop while
1882       // scale*I+offset+1 > min_int. But (min_int-offset-1) will
1883       // underflow when (offset+1) > 0 and X will be < main_limit
1884       // when scale < 0 (and stride > 0). To avoid it we replace
1885       // positive (offset+1) with 0.
1886       //
1887       // Also (min_int+1 == -max_int) is used instead of min_int here
1888       // to avoid problem with scale == -1 (min_int/(-1) == min_int).
1889       Node* shift = _igvn.intcon(31);
1890       set_ctrl(shift, C->root());
1891       Node* sign = new RShiftINode(plus_one, shift);
1892       register_new_node(sign, pre_ctrl);
1893       plus_one = new AndINode(plus_one, sign);
1894       register_new_node(plus_one, pre_ctrl);
1895     } else {
1896       assert(low_limit->get_int() == 0, "wrong low limit for range check");
1897       // The only problem we have here when offset == max_int
1898       // since (max_int+1) == min_int and (0-min_int) == min_int.
1899       // But it is fine since main loop will either have
1900       // less iterations or will be skipped in such case.
1901     }
1902     // The underflow limit: low_limit <= scale*I+offset.
1903     // For main-loop compute
1904     //   scale*I+offset+1 > low_limit
1905     //   ( if (scale < 0) /* and stride > 0 */
1906     //       I < (low_limit-(offset+1))/scale
1907     //     else /* scale > 0 and stride < 0 */
1908     //       I > (low_limit-(offset+1))/scale
1909     //   )
1910 
1911     *main_limit = adjust_limit(stride_con, scale, plus_one, low_limit, *main_limit, pre_ctrl);
1912   }
1913 }
1914 
1915 
1916 //------------------------------is_scaled_iv---------------------------------
1917 // Return true if exp is a constant times an induction var
1918 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
1919   if (exp == iv) {
1920     if (p_scale != NULL) {
1921       *p_scale = 1;
1922     }
1923     return true;
1924   }
1925   int opc = exp->Opcode();
1926   if (opc == Op_MulI) {
1927     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1928       if (p_scale != NULL) {
1929         *p_scale = exp->in(2)->get_int();
1930       }
1931       return true;
1932     }
1933     if (exp->in(2) == iv && exp->in(1)->is_Con()) {
1934       if (p_scale != NULL) {
1935         *p_scale = exp->in(1)->get_int();
1936       }
1937       return true;
1938     }
1939   } else if (opc == Op_LShiftI) {
1940     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1941       if (p_scale != NULL) {
1942         *p_scale = 1 << exp->in(2)->get_int();
1943       }
1944       return true;
1945     }
1946   }
1947   return false;
1948 }
1949 
1950 //-----------------------------is_scaled_iv_plus_offset------------------------------
1951 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
1952 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
1953   if (is_scaled_iv(exp, iv, p_scale)) {
1954     if (p_offset != NULL) {
1955       Node *zero = _igvn.intcon(0);
1956       set_ctrl(zero, C->root());
1957       *p_offset = zero;
1958     }
1959     return true;
1960   }
1961   int opc = exp->Opcode();
1962   if (opc == Op_AddI) {
1963     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1964       if (p_offset != NULL) {
1965         *p_offset = exp->in(2);
1966       }
1967       return true;
1968     }
1969     if (is_scaled_iv(exp->in(2), iv, p_scale)) {
1970       if (p_offset != NULL) {
1971         *p_offset = exp->in(1);
1972       }
1973       return true;
1974     }
1975     if (exp->in(2)->is_Con()) {
1976       Node* offset2 = NULL;
1977       if (depth < 2 &&
1978           is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
1979                                    p_offset != NULL ? &offset2 : NULL, depth+1)) {
1980         if (p_offset != NULL) {
1981           Node *ctrl_off2 = get_ctrl(offset2);
1982           Node* offset = new AddINode(offset2, exp->in(2));
1983           register_new_node(offset, ctrl_off2);
1984           *p_offset = offset;
1985         }
1986         return true;
1987       }
1988     }
1989   } else if (opc == Op_SubI) {
1990     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1991       if (p_offset != NULL) {
1992         Node *zero = _igvn.intcon(0);
1993         set_ctrl(zero, C->root());
1994         Node *ctrl_off = get_ctrl(exp->in(2));
1995         Node* offset = new SubINode(zero, exp->in(2));
1996         register_new_node(offset, ctrl_off);
1997         *p_offset = offset;
1998       }
1999       return true;
2000     }
2001     if (is_scaled_iv(exp->in(2), iv, p_scale)) {
2002       if (p_offset != NULL) {
2003         *p_scale *= -1;
2004         *p_offset = exp->in(1);
2005       }
2006       return true;
2007     }
2008   }
2009   return false;
2010 }
2011 
2012 //------------------------------do_range_check---------------------------------
2013 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
2014 int PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
2015 #ifndef PRODUCT
2016   if (PrintOpto && VerifyLoopOptimizations) {
2017     tty->print("Range Check Elimination ");
2018     loop->dump_head();
2019   } else if (TraceLoopOpts) {
2020     tty->print("RangeCheck   ");
2021     loop->dump_head();
2022   }
2023 #endif
2024   assert(RangeCheckElimination, "");
2025   CountedLoopNode *cl = loop->_head->as_CountedLoop();
2026   // If we fail before trying to eliminate range checks, set multiversion state
2027   int closed_range_checks = 1;
2028 
2029   // protect against stride not being a constant
2030   if (!cl->stride_is_con())
2031     return closed_range_checks;
2032 
2033   // Find the trip counter; we are iteration splitting based on it
2034   Node *trip_counter = cl->phi();
2035   // Find the main loop limit; we will trim it's iterations
2036   // to not ever trip end tests
2037   Node *main_limit = cl->limit();
2038 
2039   // Check graph shape. Cannot optimize a loop if zero-trip
2040   // Opaque1 node is optimized away and then another round
2041   // of loop opts attempted.
2042   if (!is_canonical_loop_entry(cl)) {
2043     return closed_range_checks;
2044   }
2045 
2046   // Need to find the main-loop zero-trip guard
2047   Node *ctrl  = cl->in(LoopNode::EntryControl);
2048   Node *iffm = ctrl->in(0);
2049   Node *opqzm = iffm->in(1)->in(1)->in(2);
2050   assert(opqzm->in(1) == main_limit, "do not understand situation");
2051 
2052   // Find the pre-loop limit; we will expand its iterations to
2053   // not ever trip low tests.
2054   Node *p_f = iffm->in(0);
2055   // pre loop may have been optimized out
2056   if (p_f->Opcode() != Op_IfFalse) {
2057     return closed_range_checks;
2058   }
2059   CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
2060   assert(pre_end->loopnode()->is_pre_loop(), "");
2061   Node *pre_opaq1 = pre_end->limit();
2062   // Occasionally it's possible for a pre-loop Opaque1 node to be
2063   // optimized away and then another round of loop opts attempted.
2064   // We can not optimize this particular loop in that case.
2065   if (pre_opaq1->Opcode() != Op_Opaque1)
2066     return closed_range_checks;
2067   Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
2068   Node *pre_limit = pre_opaq->in(1);
2069 
2070   // Where do we put new limit calculations
2071   Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
2072 
2073   // Ensure the original loop limit is available from the
2074   // pre-loop Opaque1 node.
2075   Node *orig_limit = pre_opaq->original_loop_limit();
2076   if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP)
2077     return closed_range_checks;
2078 
2079   // Must know if its a count-up or count-down loop
2080 
2081   int stride_con = cl->stride_con();
2082   Node *zero = _igvn.intcon(0);
2083   Node *one  = _igvn.intcon(1);
2084   // Use symmetrical int range [-max_jint,max_jint]
2085   Node *mini = _igvn.intcon(-max_jint);
2086   set_ctrl(zero, C->root());
2087   set_ctrl(one,  C->root());
2088   set_ctrl(mini, C->root());
2089 
2090   // Range checks that do not dominate the loop backedge (ie.
2091   // conditionally executed) can lengthen the pre loop limit beyond
2092   // the original loop limit. To prevent this, the pre limit is
2093   // (for stride > 0) MINed with the original loop limit (MAXed
2094   // stride < 0) when some range_check (rc) is conditionally
2095   // executed.
2096   bool conditional_rc = false;
2097 
2098   // Count number of range checks and reduce by load range limits, if zero,
2099   // the loop is in canonical form to multiversion.
2100   closed_range_checks = 0;
2101 
2102   // Check loop body for tests of trip-counter plus loop-invariant vs loop-variant.
2103   for( uint i = 0; i < loop->_body.size(); i++ ) {
2104     Node *iff = loop->_body[i];
2105     if (iff->Opcode() == Op_If ||
2106         iff->Opcode() == Op_RangeCheck) { // Test?
2107       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
2108       // we need loop unswitching instead of iteration splitting.
2109       closed_range_checks++;
2110       Node *exit = loop->is_loop_exit(iff);
2111       if( !exit ) continue;
2112       int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
2113 
2114       // Get boolean condition to test
2115       Node *i1 = iff->in(1);
2116       if( !i1->is_Bool() ) continue;
2117       BoolNode *bol = i1->as_Bool();
2118       BoolTest b_test = bol->_test;
2119       // Flip sense of test if exit condition is flipped
2120       if( flip )
2121         b_test = b_test.negate();
2122 
2123       // Get compare
2124       Node *cmp = bol->in(1);
2125 
2126       // Look for trip_counter + offset vs limit
2127       Node *rc_exp = cmp->in(1);
2128       Node *limit  = cmp->in(2);
2129       jint scale_con= 1;        // Assume trip counter not scaled
2130 
2131       Node *limit_c = get_ctrl(limit);
2132       if( loop->is_member(get_loop(limit_c) ) ) {
2133         // Compare might have operands swapped; commute them
2134         b_test = b_test.commute();
2135         rc_exp = cmp->in(2);
2136         limit  = cmp->in(1);
2137         limit_c = get_ctrl(limit);
2138         if( loop->is_member(get_loop(limit_c) ) )
2139           continue;             // Both inputs are loop varying; cannot RCE
2140       }
2141       // Here we know 'limit' is loop invariant
2142 
2143       // 'limit' maybe pinned below the zero trip test (probably from a
2144       // previous round of rce), in which case, it can't be used in the
2145       // zero trip test expression which must occur before the zero test's if.
2146       if( limit_c == ctrl ) {
2147         continue;  // Don't rce this check but continue looking for other candidates.
2148       }
2149 
2150       // Check for scaled induction variable plus an offset
2151       Node *offset = NULL;
2152 
2153       if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
2154         continue;
2155       }
2156 
2157       Node *offset_c = get_ctrl(offset);
2158       if( loop->is_member( get_loop(offset_c) ) )
2159         continue;               // Offset is not really loop invariant
2160       // Here we know 'offset' is loop invariant.
2161 
2162       // As above for the 'limit', the 'offset' maybe pinned below the
2163       // zero trip test.
2164       if( offset_c == ctrl ) {
2165         continue; // Don't rce this check but continue looking for other candidates.
2166       }
2167 #ifdef ASSERT
2168       if (TraceRangeLimitCheck) {
2169         tty->print_cr("RC bool node%s", flip ? " flipped:" : ":");
2170         bol->dump(2);
2171       }
2172 #endif
2173       // At this point we have the expression as:
2174       //   scale_con * trip_counter + offset :: limit
2175       // where scale_con, offset and limit are loop invariant.  Trip_counter
2176       // monotonically increases by stride_con, a constant.  Both (or either)
2177       // stride_con and scale_con can be negative which will flip about the
2178       // sense of the test.
2179 
2180       // Adjust pre and main loop limits to guard the correct iteration set
2181       if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
2182         if( b_test._test == BoolTest::lt ) { // Range checks always use lt
2183           // The underflow and overflow limits: 0 <= scale*I+offset < limit
2184           add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );
2185           // (0-offset)/scale could be outside of loop iterations range.
2186           conditional_rc = true;
2187         } else {
2188           if (PrintOpto) {
2189             tty->print_cr("missed RCE opportunity");
2190           }
2191           continue;             // In release mode, ignore it
2192         }
2193       } else {                  // Otherwise work on normal compares
2194         switch( b_test._test ) {
2195         case BoolTest::gt:
2196           // Fall into GE case
2197         case BoolTest::ge:
2198           // Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit
2199           scale_con = -scale_con;
2200           offset = new SubINode( zero, offset );
2201           register_new_node( offset, pre_ctrl );
2202           limit  = new SubINode( zero, limit );
2203           register_new_node( limit, pre_ctrl );
2204           // Fall into LE case
2205         case BoolTest::le:
2206           if (b_test._test != BoolTest::gt) {
2207             // Convert X <= Y to X < Y+1
2208             limit = new AddINode( limit, one );
2209             register_new_node( limit, pre_ctrl );
2210           }
2211           // Fall into LT case
2212         case BoolTest::lt:
2213           // The underflow and overflow limits: MIN_INT <= scale*I+offset < limit
2214           // Note: (MIN_INT+1 == -MAX_INT) is used instead of MIN_INT here
2215           // to avoid problem with scale == -1: MIN_INT/(-1) == MIN_INT.
2216           add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit );
2217           // ((MIN_INT+1)-offset)/scale could be outside of loop iterations range.
2218           // Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could
2219           // still be outside of loop range.
2220           conditional_rc = true;
2221           break;
2222         default:
2223           if (PrintOpto) {
2224             tty->print_cr("missed RCE opportunity");
2225           }
2226           continue;             // Unhandled case
2227         }
2228       }
2229 
2230       // Kill the eliminated test
2231       C->set_major_progress();
2232       Node *kill_con = _igvn.intcon( 1-flip );
2233       set_ctrl(kill_con, C->root());
2234       _igvn.replace_input_of(iff, 1, kill_con);
2235       // Find surviving projection
2236       assert(iff->is_If(), "");
2237       ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
2238       // Find loads off the surviving projection; remove their control edge
2239       for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
2240         Node* cd = dp->fast_out(i); // Control-dependent node
2241         if (cd->is_Load() && cd->depends_only_on_test()) {   // Loads can now float around in the loop
2242           // Allow the load to float around in the loop, or before it
2243           // but NOT before the pre-loop.
2244           _igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL
2245           --i;
2246           --imax;
2247         }
2248       }
2249       if (limit->Opcode() == Op_LoadRange) {
2250         closed_range_checks--;
2251       }
2252 
2253     } // End of is IF
2254 
2255   }
2256 
2257   // Update loop limits
2258   if (conditional_rc) {
2259     pre_limit = (stride_con > 0) ? (Node*)new MinINode(pre_limit, orig_limit)
2260                                  : (Node*)new MaxINode(pre_limit, orig_limit);
2261     register_new_node(pre_limit, pre_ctrl);
2262   }
2263   _igvn.replace_input_of(pre_opaq, 1, pre_limit);
2264 
2265   // Note:: we are making the main loop limit no longer precise;
2266   // need to round up based on stride.
2267   cl->set_nonexact_trip_count();
2268   Node *main_cle = cl->loopexit();
2269   Node *main_bol = main_cle->in(1);
2270   // Hacking loop bounds; need private copies of exit test
2271   if( main_bol->outcnt() > 1 ) {// BoolNode shared?
2272     main_bol = main_bol->clone();// Clone a private BoolNode
2273     register_new_node( main_bol, main_cle->in(0) );
2274     _igvn.replace_input_of(main_cle, 1, main_bol);
2275   }
2276   Node *main_cmp = main_bol->in(1);
2277   if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
2278     main_cmp = main_cmp->clone();// Clone a private CmpNode
2279     register_new_node( main_cmp, main_cle->in(0) );
2280     _igvn.replace_input_of(main_bol, 1, main_cmp);
2281   }
2282   // Hack the now-private loop bounds
2283   _igvn.replace_input_of(main_cmp, 2, main_limit);
2284   // The OpaqueNode is unshared by design
2285   assert( opqzm->outcnt() == 1, "cannot hack shared node" );
2286   _igvn.replace_input_of(opqzm, 1, main_limit);
2287 
2288   return closed_range_checks;
2289 }
2290 
2291 //------------------------------has_range_checks-------------------------------
2292 // Check to see if RCE cleaned the current loop of range-checks.
2293 void PhaseIdealLoop::has_range_checks(IdealLoopTree *loop) {
2294   assert(RangeCheckElimination, "");
2295 
2296   // skip if not a counted loop
2297   if (!loop->is_counted()) return;
2298 
2299   CountedLoopNode *cl = loop->_head->as_CountedLoop();
2300 
2301   // skip this loop if it is already checked
2302   if (cl->has_been_range_checked()) return;
2303 
2304   // Now check for existence of range checks
2305   for (uint i = 0; i < loop->_body.size(); i++) {
2306     Node *iff = loop->_body[i];
2307     int iff_opc = iff->Opcode();
2308     if (iff_opc == Op_If || iff_opc == Op_RangeCheck) {
2309       cl->mark_has_range_checks();
2310       break;
2311     }
2312   }
2313   cl->set_has_been_range_checked();
2314 }
2315 
2316 //-------------------------multi_version_post_loops----------------------------
2317 // Check the range checks that remain, if simple, use the bounds to guard
2318 // which version to a post loop we execute, one with range checks or one without
2319 bool PhaseIdealLoop::multi_version_post_loops(IdealLoopTree *rce_loop, IdealLoopTree *legacy_loop) {
2320   bool multi_version_succeeded = false;
2321   assert(RangeCheckElimination, "");
2322   CountedLoopNode *legacy_cl = legacy_loop->_head->as_CountedLoop();
2323   assert(legacy_cl->is_post_loop(), "");
2324 
2325   // Check for existence of range checks using the unique instance to make a guard with
2326   Unique_Node_List worklist;
2327   for (uint i = 0; i < legacy_loop->_body.size(); i++) {
2328     Node *iff = legacy_loop->_body[i];
2329     int iff_opc = iff->Opcode();
2330     if (iff_opc == Op_If || iff_opc == Op_RangeCheck) {
2331       worklist.push(iff);
2332     }
2333   }
2334 
2335   // Find RCE'd post loop so that we can stage its guard.
2336   if (!is_canonical_loop_entry(legacy_cl)) return multi_version_succeeded;
2337   Node* ctrl = legacy_cl->in(LoopNode::EntryControl);
2338   Node* iffm = ctrl->in(0);
2339 
2340   // Now we test that both the post loops are connected
2341   Node* post_loop_region = iffm->in(0);
2342   if (post_loop_region == NULL) return multi_version_succeeded;
2343   if (!post_loop_region->is_Region()) return multi_version_succeeded;
2344   Node* covering_region = post_loop_region->in(RegionNode::Control+1);
2345   if (covering_region == NULL) return multi_version_succeeded;
2346   if (!covering_region->is_Region()) return multi_version_succeeded;
2347   Node* p_f = covering_region->in(RegionNode::Control);
2348   if (p_f == NULL) return multi_version_succeeded;
2349   if (!p_f->is_IfFalse()) return multi_version_succeeded;
2350   if (!p_f->in(0)->is_CountedLoopEnd()) return multi_version_succeeded;
2351   CountedLoopEndNode* rce_loop_end = p_f->in(0)->as_CountedLoopEnd();
2352   if (rce_loop_end == NULL) return multi_version_succeeded;
2353   CountedLoopNode* rce_cl = rce_loop_end->loopnode();
2354   if (rce_cl == NULL || !rce_cl->is_post_loop()) return multi_version_succeeded;
2355   CountedLoopNode *known_rce_cl = rce_loop->_head->as_CountedLoop();
2356   if (rce_cl != known_rce_cl) return multi_version_succeeded;
2357 
2358   // Then we fetch the cover entry test
2359   ctrl = rce_cl->in(LoopNode::EntryControl);
2360   if (!ctrl->is_IfTrue() && !ctrl->is_IfFalse()) return multi_version_succeeded;
2361 
2362 #ifndef PRODUCT
2363   if (TraceLoopOpts) {
2364     tty->print("PostMultiVersion\n");
2365     rce_loop->dump_head();
2366     legacy_loop->dump_head();
2367   }
2368 #endif
2369 
2370   // Now fetch the limit we want to compare against
2371   Node *limit = rce_cl->limit();
2372   bool first_time = true;
2373 
2374   // If we got this far, we identified the post loop which has been RCE'd and
2375   // we have a work list.  Now we will try to transform the if guard to cause
2376   // the loop pair to be multi version executed with the determination left to runtime
2377   // or the optimizer if full information is known about the given arrays at compile time.
2378   Node *last_min = NULL;
2379   multi_version_succeeded = true;
2380   while (worklist.size()) {
2381     Node* rc_iffm = worklist.pop();
2382     if (rc_iffm->is_If()) {
2383       Node *rc_bolzm = rc_iffm->in(1);
2384       if (rc_bolzm->is_Bool()) {
2385         Node *rc_cmpzm = rc_bolzm->in(1);
2386         if (rc_cmpzm->is_Cmp()) {
2387           Node *rc_left = rc_cmpzm->in(2);
2388           if (rc_left->Opcode() != Op_LoadRange) {
2389             multi_version_succeeded = false;
2390             break;
2391           }
2392           if (first_time) {
2393             last_min = rc_left;
2394             first_time = false;
2395           } else {
2396             Node *cur_min = new MinINode(last_min, rc_left);
2397             last_min = cur_min;
2398             _igvn.register_new_node_with_optimizer(last_min);
2399           }
2400         }
2401       }
2402     }
2403   }
2404 
2405   // All we have to do is update the limit of the rce loop
2406   // with the min of our expression and the current limit.
2407   // We will use this expression to replace the current limit.
2408   if (last_min && multi_version_succeeded) {
2409     Node *cur_min = new MinINode(last_min, limit);
2410     _igvn.register_new_node_with_optimizer(cur_min);
2411     Node *cmp_node = rce_loop_end->cmp_node();
2412     _igvn.replace_input_of(cmp_node, 2, cur_min);
2413     set_idom(cmp_node, cur_min, dom_depth(ctrl));
2414     set_ctrl(cur_min, ctrl);
2415     set_loop(cur_min, rce_loop->_parent);
2416 
2417     legacy_cl->mark_is_multiversioned();
2418     rce_cl->mark_is_multiversioned();
2419     multi_version_succeeded = true;
2420 
2421     C->set_major_progress();
2422   }
2423 
2424   return multi_version_succeeded;
2425 }
2426 
2427 //-------------------------poison_rce_post_loop--------------------------------
2428 // Causes the rce'd post loop to be optimized away if multiversioning fails
2429 void PhaseIdealLoop::poison_rce_post_loop(IdealLoopTree *rce_loop) {
2430   CountedLoopNode *rce_cl = rce_loop->_head->as_CountedLoop();
2431   Node* ctrl = rce_cl->in(LoopNode::EntryControl);
2432   if (ctrl->is_IfTrue() || ctrl->is_IfFalse()) {
2433     Node* iffm = ctrl->in(0);
2434     if (iffm->is_If()) {
2435       Node* cur_bool = iffm->in(1);
2436       if (cur_bool->is_Bool()) {
2437         Node* cur_cmp = cur_bool->in(1);
2438         if (cur_cmp->is_Cmp()) {
2439           BoolTest::mask new_test = BoolTest::gt;
2440           BoolNode *new_bool = new BoolNode(cur_cmp, new_test);
2441           _igvn.replace_node(cur_bool, new_bool);
2442           _igvn._worklist.push(new_bool);
2443           Node* left_op = cur_cmp->in(1);
2444           _igvn.replace_input_of(cur_cmp, 2, left_op);
2445           C->set_major_progress();
2446         }
2447       }
2448     }
2449   }
2450 }
2451 
2452 //------------------------------DCE_loop_body----------------------------------
2453 // Remove simplistic dead code from loop body
2454 void IdealLoopTree::DCE_loop_body() {
2455   for( uint i = 0; i < _body.size(); i++ )
2456     if( _body.at(i)->outcnt() == 0 )
2457       _body.map( i--, _body.pop() );
2458 }
2459 
2460 
2461 //------------------------------adjust_loop_exit_prob--------------------------
2462 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
2463 // Replace with a 1-in-10 exit guess.
2464 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
2465   Node *test = tail();
2466   while( test != _head ) {
2467     uint top = test->Opcode();
2468     if( top == Op_IfTrue || top == Op_IfFalse ) {
2469       int test_con = ((ProjNode*)test)->_con;
2470       assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
2471       IfNode *iff = test->in(0)->as_If();
2472       if( iff->outcnt() == 2 ) {        // Ignore dead tests
2473         Node *bol = iff->in(1);
2474         if( bol && bol->req() > 1 && bol->in(1) &&
2475             ((bol->in(1)->Opcode() == Op_StorePConditional ) ||
2476              (bol->in(1)->Opcode() == Op_StoreIConditional ) ||
2477              (bol->in(1)->Opcode() == Op_StoreLConditional ) ||
2478              (bol->in(1)->Opcode() == Op_CompareAndExchangeB ) ||
2479              (bol->in(1)->Opcode() == Op_CompareAndExchangeS ) ||
2480              (bol->in(1)->Opcode() == Op_CompareAndExchangeI ) ||
2481              (bol->in(1)->Opcode() == Op_CompareAndExchangeL ) ||
2482              (bol->in(1)->Opcode() == Op_CompareAndExchangeP ) ||
2483              (bol->in(1)->Opcode() == Op_CompareAndExchangeN ) ||
2484              (bol->in(1)->Opcode() == Op_WeakCompareAndSwapB ) ||
2485              (bol->in(1)->Opcode() == Op_WeakCompareAndSwapS ) ||
2486              (bol->in(1)->Opcode() == Op_WeakCompareAndSwapI ) ||
2487              (bol->in(1)->Opcode() == Op_WeakCompareAndSwapL ) ||
2488              (bol->in(1)->Opcode() == Op_WeakCompareAndSwapP ) ||
2489              (bol->in(1)->Opcode() == Op_WeakCompareAndSwapN ) ||
2490              (bol->in(1)->Opcode() == Op_CompareAndSwapB ) ||
2491              (bol->in(1)->Opcode() == Op_CompareAndSwapS ) ||
2492              (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
2493              (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
2494              (bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||
2495              (bol->in(1)->Opcode() == Op_CompareAndSwapN )))
2496           return;               // Allocation loops RARELY take backedge
2497         // Find the OTHER exit path from the IF
2498         Node* ex = iff->proj_out(1-test_con);
2499         float p = iff->_prob;
2500         if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
2501           if( top == Op_IfTrue ) {
2502             if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
2503               iff->_prob = PROB_STATIC_FREQUENT;
2504             }
2505           } else {
2506             if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
2507               iff->_prob = PROB_STATIC_INFREQUENT;
2508             }
2509           }
2510         }
2511       }
2512     }
2513     test = phase->idom(test);
2514   }
2515 }
2516 
2517 #ifdef ASSERT
2518 static CountedLoopNode* locate_pre_from_main(CountedLoopNode *cl) {
2519   Node *ctrl  = cl->in(LoopNode::EntryControl);
2520   assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
2521   Node *iffm = ctrl->in(0);
2522   assert(iffm->Opcode() == Op_If, "");
2523   Node *p_f = iffm->in(0);
2524   assert(p_f->Opcode() == Op_IfFalse, "");
2525   CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
2526   assert(pre_end->loopnode()->is_pre_loop(), "");
2527   return pre_end->loopnode();
2528 }
2529 #endif
2530 
2531 // Remove the main and post loops and make the pre loop execute all
2532 // iterations. Useful when the pre loop is found empty.
2533 void IdealLoopTree::remove_main_post_loops(CountedLoopNode *cl, PhaseIdealLoop *phase) {
2534   CountedLoopEndNode* pre_end = cl->loopexit();
2535   Node* pre_cmp = pre_end->cmp_node();
2536   if (pre_cmp->in(2)->Opcode() != Op_Opaque1) {
2537     // Only safe to remove the main loop if the compiler optimized it
2538     // out based on an unknown number of iterations
2539     return;
2540   }
2541 
2542   // Can we find the main loop?
2543   if (_next == NULL) {
2544     return;
2545   }
2546 
2547   Node* next_head = _next->_head;
2548   if (!next_head->is_CountedLoop()) {
2549     return;
2550   }
2551 
2552   CountedLoopNode* main_head = next_head->as_CountedLoop();
2553   if (!main_head->is_main_loop()) {
2554     return;
2555   }
2556 
2557   assert(locate_pre_from_main(main_head) == cl, "bad main loop");
2558   Node* main_iff = main_head->in(LoopNode::EntryControl)->in(0);
2559 
2560   // Remove the Opaque1Node of the pre loop and make it execute all iterations
2561   phase->_igvn.replace_input_of(pre_cmp, 2, pre_cmp->in(2)->in(2));
2562   // Remove the Opaque1Node of the main loop so it can be optimized out
2563   Node* main_cmp = main_iff->in(1)->in(1);
2564   assert(main_cmp->in(2)->Opcode() == Op_Opaque1, "main loop has no opaque node?");
2565   phase->_igvn.replace_input_of(main_cmp, 2, main_cmp->in(2)->in(1));
2566 }
2567 
2568 //------------------------------policy_do_remove_empty_loop--------------------
2569 // Micro-benchmark spamming.  Policy is to always remove empty loops.
2570 // The 'DO' part is to replace the trip counter with the value it will
2571 // have on the last iteration.  This will break the loop.
2572 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
2573   // Minimum size must be empty loop
2574   if (_body.size() > EMPTY_LOOP_SIZE)
2575     return false;
2576 
2577   if (!_head->is_CountedLoop())
2578     return false;     // Dead loop
2579   CountedLoopNode *cl = _head->as_CountedLoop();
2580   if (!cl->is_valid_counted_loop())
2581     return false; // Malformed loop
2582   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
2583     return false;             // Infinite loop
2584 
2585   if (cl->is_pre_loop()) {
2586     // If the loop we are removing is a pre-loop then the main and
2587     // post loop can be removed as well
2588     remove_main_post_loops(cl, phase);
2589   }
2590 
2591 #ifdef ASSERT
2592   // Ensure only one phi which is the iv.
2593   Node* iv = NULL;
2594   for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
2595     Node* n = cl->fast_out(i);
2596     if (n->Opcode() == Op_Phi) {
2597       assert(iv == NULL, "Too many phis" );
2598       iv = n;
2599     }
2600   }
2601   assert(iv == cl->phi(), "Wrong phi" );
2602 #endif
2603 
2604   // main and post loops have explicitly created zero trip guard
2605   bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
2606   if (needs_guard) {
2607     // Skip guard if values not overlap.
2608     const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int();
2609     const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int();
2610     int  stride_con = cl->stride_con();
2611     if (stride_con > 0) {
2612       needs_guard = (init_t->_hi >= limit_t->_lo);
2613     } else {
2614       needs_guard = (init_t->_lo <= limit_t->_hi);
2615     }
2616   }
2617   if (needs_guard) {
2618     // Check for an obvious zero trip guard.
2619     Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));
2620     if (inctrl->Opcode() == Op_IfTrue || inctrl->Opcode() == Op_IfFalse) {
2621       bool maybe_swapped = (inctrl->Opcode() == Op_IfFalse);
2622       // The test should look like just the backedge of a CountedLoop
2623       Node* iff = inctrl->in(0);
2624       if (iff->is_If()) {
2625         Node* bol = iff->in(1);
2626         if (bol->is_Bool()) {
2627           BoolTest test = bol->as_Bool()->_test;
2628           if (maybe_swapped) {
2629             test._test = test.commute();
2630             test._test = test.negate();
2631           }
2632           if (test._test == cl->loopexit()->test_trip()) {
2633             Node* cmp = bol->in(1);
2634             int init_idx = maybe_swapped ? 2 : 1;
2635             int limit_idx = maybe_swapped ? 1 : 2;
2636             if (cmp->is_Cmp() && cmp->in(init_idx) == cl->init_trip() && cmp->in(limit_idx) == cl->limit()) {
2637               needs_guard = false;
2638             }
2639           }
2640         }
2641       }
2642     }
2643   }
2644 
2645 #ifndef PRODUCT
2646   if (PrintOpto) {
2647     tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
2648     this->dump_head();
2649   } else if (TraceLoopOpts) {
2650     tty->print("Empty with%s zero trip guard   ", needs_guard ? "out" : "");
2651     this->dump_head();
2652   }
2653 #endif
2654 
2655   if (needs_guard) {
2656     // Peel the loop to ensure there's a zero trip guard
2657     Node_List old_new;
2658     phase->do_peeling(this, old_new);
2659   }
2660 
2661   // Replace the phi at loop head with the final value of the last
2662   // iteration.  Then the CountedLoopEnd will collapse (backedge never
2663   // taken) and all loop-invariant uses of the exit values will be correct.
2664   Node *phi = cl->phi();
2665   Node *exact_limit = phase->exact_limit(this);
2666   if (exact_limit != cl->limit()) {
2667     // We also need to replace the original limit to collapse loop exit.
2668     Node* cmp = cl->loopexit()->cmp_node();
2669     assert(cl->limit() == cmp->in(2), "sanity");
2670     phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist
2671     phase->_igvn.replace_input_of(cmp, 2, exact_limit); // put cmp on worklist
2672   }
2673   // Note: the final value after increment should not overflow since
2674   // counted loop has limit check predicate.
2675   Node *final = new SubINode( exact_limit, cl->stride() );
2676   phase->register_new_node(final,cl->in(LoopNode::EntryControl));
2677   phase->_igvn.replace_node(phi,final);
2678   phase->C->set_major_progress();
2679   return true;
2680 }
2681 
2682 //------------------------------policy_do_one_iteration_loop-------------------
2683 // Convert one iteration loop into normal code.
2684 bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) {
2685   if (!_head->as_Loop()->is_valid_counted_loop())
2686     return false; // Only for counted loop
2687 
2688   CountedLoopNode *cl = _head->as_CountedLoop();
2689   if (!cl->has_exact_trip_count() || cl->trip_count() != 1) {
2690     return false;
2691   }
2692 
2693 #ifndef PRODUCT
2694   if(TraceLoopOpts) {
2695     tty->print("OneIteration ");
2696     this->dump_head();
2697   }
2698 #endif
2699 
2700   Node *init_n = cl->init_trip();
2701 #ifdef ASSERT
2702   // Loop boundaries should be constant since trip count is exact.
2703   assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration");
2704 #endif
2705   // Replace the phi at loop head with the value of the init_trip.
2706   // Then the CountedLoopEnd will collapse (backedge will not be taken)
2707   // and all loop-invariant uses of the exit values will be correct.
2708   phase->_igvn.replace_node(cl->phi(), cl->init_trip());
2709   phase->C->set_major_progress();
2710   return true;
2711 }
2712 
2713 //=============================================================================
2714 //------------------------------iteration_split_impl---------------------------
2715 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
2716   // Compute loop trip count if possible.
2717   compute_trip_count(phase);
2718 
2719   // Convert one iteration loop into normal code.
2720   if (policy_do_one_iteration_loop(phase))
2721     return true;
2722 
2723   // Check and remove empty loops (spam micro-benchmarks)
2724   if (policy_do_remove_empty_loop(phase))
2725     return true;  // Here we removed an empty loop
2726 
2727   bool should_peel = policy_peeling(phase); // Should we peel?
2728 
2729   bool should_unswitch = policy_unswitching(phase);
2730 
2731   // Non-counted loops may be peeled; exactly 1 iteration is peeled.
2732   // This removes loop-invariant tests (usually null checks).
2733   if (!_head->is_CountedLoop()) { // Non-counted loop
2734     if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
2735       // Partial peel succeeded so terminate this round of loop opts
2736       return false;
2737     }
2738     if (should_peel) {            // Should we peel?
2739       if (PrintOpto) { tty->print_cr("should_peel"); }
2740       phase->do_peeling(this,old_new);
2741     } else if (should_unswitch) {
2742       phase->do_unswitching(this, old_new);
2743     }
2744     return true;
2745   }
2746   CountedLoopNode *cl = _head->as_CountedLoop();
2747 
2748   if (!cl->is_valid_counted_loop()) return true; // Ignore various kinds of broken loops
2749 
2750   // Do nothing special to pre- and post- loops
2751   if (cl->is_pre_loop() || cl->is_post_loop()) return true;
2752 
2753   // Compute loop trip count from profile data
2754   compute_profile_trip_cnt(phase);
2755 
2756   // Before attempting fancy unrolling, RCE or alignment, see if we want
2757   // to completely unroll this loop or do loop unswitching.
2758   if (cl->is_normal_loop()) {
2759     if (should_unswitch) {
2760       phase->do_unswitching(this, old_new);
2761       return true;
2762     }
2763     bool should_maximally_unroll =  policy_maximally_unroll(phase);
2764     if (should_maximally_unroll) {
2765       // Here we did some unrolling and peeling.  Eventually we will
2766       // completely unroll this loop and it will no longer be a loop.
2767       phase->do_maximally_unroll(this,old_new);
2768       return true;
2769     }
2770   }
2771 
2772   // Skip next optimizations if running low on nodes. Note that
2773   // policy_unswitching and policy_maximally_unroll have this check.
2774   int nodes_left = phase->C->max_node_limit() - phase->C->live_nodes();
2775   if ((int)(2 * _body.size()) > nodes_left) {
2776     return true;
2777   }
2778 
2779   // Counted loops may be peeled, may need some iterations run up
2780   // front for RCE, and may want to align loop refs to a cache
2781   // line.  Thus we clone a full loop up front whose trip count is
2782   // at least 1 (if peeling), but may be several more.
2783 
2784   // The main loop will start cache-line aligned with at least 1
2785   // iteration of the unrolled body (zero-trip test required) and
2786   // will have some range checks removed.
2787 
2788   // A post-loop will finish any odd iterations (leftover after
2789   // unrolling), plus any needed for RCE purposes.
2790 
2791   bool should_unroll = policy_unroll(phase);
2792 
2793   bool should_rce = policy_range_check(phase);
2794 
2795   bool should_align = policy_align(phase);
2796 
2797   // If not RCE'ing (iteration splitting) or Aligning, then we do not
2798   // need a pre-loop.  We may still need to peel an initial iteration but
2799   // we will not be needing an unknown number of pre-iterations.
2800   //
2801   // Basically, if may_rce_align reports FALSE first time through,
2802   // we will not be able to later do RCE or Aligning on this loop.
2803   bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
2804 
2805   // If we have any of these conditions (RCE, alignment, unrolling) met, then
2806   // we switch to the pre-/main-/post-loop model.  This model also covers
2807   // peeling.
2808   if (should_rce || should_align || should_unroll) {
2809     if (cl->is_normal_loop())  // Convert to 'pre/main/post' loops
2810       phase->insert_pre_post_loops(this,old_new, !may_rce_align);
2811 
2812     // Adjust the pre- and main-loop limits to let the pre and post loops run
2813     // with full checks, but the main-loop with no checks.  Remove said
2814     // checks from the main body.
2815     if (should_rce) {
2816       if (phase->do_range_check(this, old_new) != 0) {
2817         cl->mark_has_range_checks();
2818       }
2819     } else if (PostLoopMultiversioning) {
2820       phase->has_range_checks(this);
2821     }
2822 
2823     if (should_unroll && !should_peel && PostLoopMultiversioning) {
2824       // Try to setup multiversioning on main loops before they are unrolled
2825       if (cl->is_main_loop() && (cl->unrolled_count() == 1)) {
2826         phase->insert_scalar_rced_post_loop(this, old_new);
2827       }
2828     }
2829 
2830     // Double loop body for unrolling.  Adjust the minimum-trip test (will do
2831     // twice as many iterations as before) and the main body limit (only do
2832     // an even number of trips).  If we are peeling, we might enable some RCE
2833     // and we'd rather unroll the post-RCE'd loop SO... do not unroll if
2834     // peeling.
2835     if (should_unroll && !should_peel) {
2836       if (SuperWordLoopUnrollAnalysis) {
2837         phase->insert_vector_post_loop(this, old_new);
2838       }
2839       phase->do_unroll(this, old_new, true);
2840     }
2841 
2842     // Adjust the pre-loop limits to align the main body
2843     // iterations.
2844     if (should_align)
2845       Unimplemented();
2846 
2847   } else {                      // Else we have an unchanged counted loop
2848     if (should_peel)           // Might want to peel but do nothing else
2849       phase->do_peeling(this,old_new);
2850   }
2851   return true;
2852 }
2853 
2854 
2855 //=============================================================================
2856 //------------------------------iteration_split--------------------------------
2857 bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
2858   // Recursively iteration split nested loops
2859   if (_child && !_child->iteration_split(phase, old_new))
2860     return false;
2861 
2862   // Clean out prior deadwood
2863   DCE_loop_body();
2864 
2865 
2866   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
2867   // Replace with a 1-in-10 exit guess.
2868   if (_parent /*not the root loop*/ &&
2869       !_irreducible &&
2870       // Also ignore the occasional dead backedge
2871       !tail()->is_top()) {
2872     adjust_loop_exit_prob(phase);
2873   }
2874 
2875   // Gate unrolling, RCE and peeling efforts.
2876   if (!_child &&                // If not an inner loop, do not split
2877       !_irreducible &&
2878       _allow_optimizations &&
2879       !tail()->is_top()) {     // Also ignore the occasional dead backedge
2880     if (!_has_call) {
2881         if (!iteration_split_impl(phase, old_new)) {
2882           return false;
2883         }
2884     } else if (policy_unswitching(phase)) {
2885       phase->do_unswitching(this, old_new);
2886     }
2887   }
2888 
2889   // Minor offset re-organization to remove loop-fallout uses of
2890   // trip counter when there was no major reshaping.
2891   phase->reorg_offsets(this);
2892 
2893   if (_next && !_next->iteration_split(phase, old_new))
2894     return false;
2895   return true;
2896 }
2897 
2898 
2899 //=============================================================================
2900 // Process all the loops in the loop tree and replace any fill
2901 // patterns with an intrinsic version.
2902 bool PhaseIdealLoop::do_intrinsify_fill() {
2903   bool changed = false;
2904   for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2905     IdealLoopTree* lpt = iter.current();
2906     changed |= intrinsify_fill(lpt);
2907   }
2908   return changed;
2909 }
2910 
2911 
2912 // Examine an inner loop looking for a a single store of an invariant
2913 // value in a unit stride loop,
2914 bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
2915                                      Node*& shift, Node*& con) {
2916   const char* msg = NULL;
2917   Node* msg_node = NULL;
2918 
2919   store_value = NULL;
2920   con = NULL;
2921   shift = NULL;
2922 
2923   // Process the loop looking for stores.  If there are multiple
2924   // stores or extra control flow give at this point.
2925   CountedLoopNode* head = lpt->_head->as_CountedLoop();
2926   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2927     Node* n = lpt->_body.at(i);
2928     if (n->outcnt() == 0) continue; // Ignore dead
2929     if (n->is_Store()) {
2930       if (store != NULL) {
2931         msg = "multiple stores";
2932         break;
2933       }
2934       int opc = n->Opcode();
2935       if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreNKlass || opc == Op_StoreCM) {
2936         msg = "oop fills not handled";
2937         break;
2938       }
2939       Node* value = n->in(MemNode::ValueIn);
2940       if (!lpt->is_invariant(value)) {
2941         msg  = "variant store value";
2942       } else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) {
2943         msg = "not array address";
2944       }
2945       store = n;
2946       store_value = value;
2947     } else if (n->is_If() && n != head->loopexit()) {
2948       msg = "extra control flow";
2949       msg_node = n;
2950     }
2951   }
2952 
2953   if (store == NULL) {
2954     // No store in loop
2955     return false;
2956   }
2957 
2958   if (msg == NULL && head->stride_con() != 1) {
2959     // could handle negative strides too
2960     if (head->stride_con() < 0) {
2961       msg = "negative stride";
2962     } else {
2963       msg = "non-unit stride";
2964     }
2965   }
2966 
2967   if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) {
2968     msg = "can't handle store address";
2969     msg_node = store->in(MemNode::Address);
2970   }
2971 
2972   if (msg == NULL &&
2973       (!store->in(MemNode::Memory)->is_Phi() ||
2974        store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) {
2975     msg = "store memory isn't proper phi";
2976     msg_node = store->in(MemNode::Memory);
2977   }
2978 
2979   // Make sure there is an appropriate fill routine
2980   BasicType t = store->as_Mem()->memory_type();
2981   const char* fill_name;
2982   if (msg == NULL &&
2983       StubRoutines::select_fill_function(t, false, fill_name) == NULL) {
2984     msg = "unsupported store";
2985     msg_node = store;
2986   }
2987 
2988   if (msg != NULL) {
2989 #ifndef PRODUCT
2990     if (TraceOptimizeFill) {
2991       tty->print_cr("not fill intrinsic candidate: %s", msg);
2992       if (msg_node != NULL) msg_node->dump();
2993     }
2994 #endif
2995     return false;
2996   }
2997 
2998   // Make sure the address expression can be handled.  It should be
2999   // head->phi * elsize + con.  head->phi might have a ConvI2L(CastII()).
3000   Node* elements[4];
3001   Node* cast = NULL;
3002   Node* conv = NULL;
3003   bool found_index = false;
3004   int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements));
3005   for (int e = 0; e < count; e++) {
3006     Node* n = elements[e];
3007     if (n->is_Con() && con == NULL) {
3008       con = n;
3009     } else if (n->Opcode() == Op_LShiftX && shift == NULL) {
3010       Node* value = n->in(1);
3011 #ifdef _LP64
3012       if (value->Opcode() == Op_ConvI2L) {
3013         conv = value;
3014         value = value->in(1);
3015       }
3016       if (value->Opcode() == Op_CastII &&
3017           value->as_CastII()->has_range_check()) {
3018         // Skip range check dependent CastII nodes
3019         cast = value;
3020         value = value->in(1);
3021       }
3022 #endif
3023       if (value != head->phi()) {
3024         msg = "unhandled shift in address";
3025       } else {
3026         if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) {
3027           msg = "scale doesn't match";
3028         } else {
3029           found_index = true;
3030           shift = n;
3031         }
3032       }
3033     } else if (n->Opcode() == Op_ConvI2L && conv == NULL) {
3034       conv = n;
3035       n = n->in(1);
3036       if (n->Opcode() == Op_CastII &&
3037           n->as_CastII()->has_range_check()) {
3038         // Skip range check dependent CastII nodes
3039         cast = n;
3040         n = n->in(1);
3041       }
3042       if (n == head->phi()) {
3043         found_index = true;
3044       } else {
3045         msg = "unhandled input to ConvI2L";
3046       }
3047     } else if (n == head->phi()) {
3048       // no shift, check below for allowed cases
3049       found_index = true;
3050     } else {
3051       msg = "unhandled node in address";
3052       msg_node = n;
3053     }
3054   }
3055 
3056   if (count == -1) {
3057     msg = "malformed address expression";
3058     msg_node = store;
3059   }
3060 
3061   if (!found_index) {
3062     msg = "missing use of index";
3063   }
3064 
3065   // byte sized items won't have a shift
3066   if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) {
3067     msg = "can't find shift";
3068     msg_node = store;
3069   }
3070 
3071   if (msg != NULL) {
3072 #ifndef PRODUCT
3073     if (TraceOptimizeFill) {
3074       tty->print_cr("not fill intrinsic: %s", msg);
3075       if (msg_node != NULL) msg_node->dump();
3076     }
3077 #endif
3078     return false;
3079   }
3080 
3081   // No make sure all the other nodes in the loop can be handled
3082   VectorSet ok(Thread::current()->resource_area());
3083 
3084   // store related values are ok
3085   ok.set(store->_idx);
3086   ok.set(store->in(MemNode::Memory)->_idx);
3087 
3088   CountedLoopEndNode* loop_exit = head->loopexit();
3089   guarantee(loop_exit != NULL, "no loop exit node");
3090 
3091   // Loop structure is ok
3092   ok.set(head->_idx);
3093   ok.set(loop_exit->_idx);
3094   ok.set(head->phi()->_idx);
3095   ok.set(head->incr()->_idx);
3096   ok.set(loop_exit->cmp_node()->_idx);
3097   ok.set(loop_exit->in(1)->_idx);
3098 
3099   // Address elements are ok
3100   if (con)   ok.set(con->_idx);
3101   if (shift) ok.set(shift->_idx);
3102   if (cast)  ok.set(cast->_idx);
3103   if (conv)  ok.set(conv->_idx);
3104 
3105   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
3106     Node* n = lpt->_body.at(i);
3107     if (n->outcnt() == 0) continue; // Ignore dead
3108     if (ok.test(n->_idx)) continue;
3109     // Backedge projection is ok
3110     if (n->is_IfTrue() && n->in(0) == loop_exit) continue;
3111     if (!n->is_AddP()) {
3112       msg = "unhandled node";
3113       msg_node = n;
3114       break;
3115     }
3116   }
3117 
3118   // Make sure no unexpected values are used outside the loop
3119   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
3120     Node* n = lpt->_body.at(i);
3121     // These values can be replaced with other nodes if they are used
3122     // outside the loop.
3123     if (n == store || n == loop_exit || n == head->incr() || n == store->in(MemNode::Memory)) continue;
3124     for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) {
3125       Node* use = iter.get();
3126       if (!lpt->_body.contains(use)) {
3127         msg = "node is used outside loop";
3128         // lpt->_body.dump();
3129         msg_node = n;
3130         break;
3131       }
3132     }
3133   }
3134 
3135 #ifdef ASSERT
3136   if (TraceOptimizeFill) {
3137     if (msg != NULL) {
3138       tty->print_cr("no fill intrinsic: %s", msg);
3139       if (msg_node != NULL) msg_node->dump();
3140     } else {
3141       tty->print_cr("fill intrinsic for:");
3142     }
3143     store->dump();
3144     if (Verbose) {
3145       lpt->_body.dump();
3146     }
3147   }
3148 #endif
3149 
3150   return msg == NULL;
3151 }
3152 
3153 
3154 
3155 bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
3156   // Only for counted inner loops
3157   if (!lpt->is_counted() || !lpt->is_inner()) {
3158     return false;
3159   }
3160 
3161   // Must have constant stride
3162   CountedLoopNode* head = lpt->_head->as_CountedLoop();
3163   if (!head->is_valid_counted_loop() || !head->is_normal_loop()) {
3164     return false;
3165   }
3166 
3167   // Check that the body only contains a store of a loop invariant
3168   // value that is indexed by the loop phi.
3169   Node* store = NULL;
3170   Node* store_value = NULL;
3171   Node* shift = NULL;
3172   Node* offset = NULL;
3173   if (!match_fill_loop(lpt, store, store_value, shift, offset)) {
3174     return false;
3175   }
3176 
3177   Node* exit = head->loopexit()->proj_out(0);
3178   if (exit == NULL) {
3179     return false;
3180   }
3181 
3182 #ifndef PRODUCT
3183   if (TraceLoopOpts) {
3184     tty->print("ArrayFill    ");
3185     lpt->dump_head();
3186   }
3187 #endif
3188 
3189   // Now replace the whole loop body by a call to a fill routine that
3190   // covers the same region as the loop.
3191   Node* base = store->in(MemNode::Address)->as_AddP()->in(AddPNode::Base);
3192 
3193   // Build an expression for the beginning of the copy region
3194   Node* index = head->init_trip();
3195 #ifdef _LP64
3196   index = new ConvI2LNode(index);
3197   _igvn.register_new_node_with_optimizer(index);
3198 #endif
3199   if (shift != NULL) {
3200     // byte arrays don't require a shift but others do.
3201     index = new LShiftXNode(index, shift->in(2));
3202     _igvn.register_new_node_with_optimizer(index);
3203   }
3204   index = new AddPNode(base, base, index);
3205   _igvn.register_new_node_with_optimizer(index);
3206   Node* from = new AddPNode(base, index, offset);
3207   _igvn.register_new_node_with_optimizer(from);
3208   // Compute the number of elements to copy
3209   Node* len = new SubINode(head->limit(), head->init_trip());
3210   _igvn.register_new_node_with_optimizer(len);
3211 
3212   BasicType t = store->as_Mem()->memory_type();
3213   bool aligned = false;
3214   if (offset != NULL && head->init_trip()->is_Con()) {
3215     int element_size = type2aelembytes(t);
3216     aligned = (offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int() * element_size) % HeapWordSize == 0;
3217   }
3218 
3219   // Build a call to the fill routine
3220   const char* fill_name;
3221   address fill = StubRoutines::select_fill_function(t, aligned, fill_name);
3222   assert(fill != NULL, "what?");
3223 
3224   // Convert float/double to int/long for fill routines
3225   if (t == T_FLOAT) {
3226     store_value = new MoveF2INode(store_value);
3227     _igvn.register_new_node_with_optimizer(store_value);
3228   } else if (t == T_DOUBLE) {
3229     store_value = new MoveD2LNode(store_value);
3230     _igvn.register_new_node_with_optimizer(store_value);
3231   }
3232 
3233   Node* mem_phi = store->in(MemNode::Memory);
3234   Node* result_ctrl;
3235   Node* result_mem;
3236   const TypeFunc* call_type = OptoRuntime::array_fill_Type();
3237   CallLeafNode *call = new CallLeafNoFPNode(call_type, fill,
3238                                             fill_name, TypeAryPtr::get_array_body_type(t));
3239   uint cnt = 0;
3240   call->init_req(TypeFunc::Parms + cnt++, from);
3241   call->init_req(TypeFunc::Parms + cnt++, store_value);
3242 #ifdef _LP64
3243   len = new ConvI2LNode(len);
3244   _igvn.register_new_node_with_optimizer(len);
3245 #endif
3246   call->init_req(TypeFunc::Parms + cnt++, len);
3247 #ifdef _LP64
3248   call->init_req(TypeFunc::Parms + cnt++, C->top());
3249 #endif
3250   call->init_req(TypeFunc::Control,   head->init_control());
3251   call->init_req(TypeFunc::I_O,       C->top());       // Does no I/O.
3252   call->init_req(TypeFunc::Memory,    mem_phi->in(LoopNode::EntryControl));
3253   call->init_req(TypeFunc::ReturnAdr, C->start()->proj_out(TypeFunc::ReturnAdr));
3254   call->init_req(TypeFunc::FramePtr,  C->start()->proj_out(TypeFunc::FramePtr));
3255   _igvn.register_new_node_with_optimizer(call);
3256   result_ctrl = new ProjNode(call,TypeFunc::Control);
3257   _igvn.register_new_node_with_optimizer(result_ctrl);
3258   result_mem = new ProjNode(call,TypeFunc::Memory);
3259   _igvn.register_new_node_with_optimizer(result_mem);
3260 
3261 /* Disable following optimization until proper fix (add missing checks).
3262 
3263   // If this fill is tightly coupled to an allocation and overwrites
3264   // the whole body, allow it to take over the zeroing.
3265   AllocateNode* alloc = AllocateNode::Ideal_allocation(base, this);
3266   if (alloc != NULL && alloc->is_AllocateArray()) {
3267     Node* length = alloc->as_AllocateArray()->Ideal_length();
3268     if (head->limit() == length &&
3269         head->init_trip() == _igvn.intcon(0)) {
3270       if (TraceOptimizeFill) {
3271         tty->print_cr("Eliminated zeroing in allocation");
3272       }
3273       alloc->maybe_set_complete(&_igvn);
3274     } else {
3275 #ifdef ASSERT
3276       if (TraceOptimizeFill) {
3277         tty->print_cr("filling array but bounds don't match");
3278         alloc->dump();
3279         head->init_trip()->dump();
3280         head->limit()->dump();
3281         length->dump();
3282       }
3283 #endif
3284     }
3285   }
3286 */
3287 
3288   // Redirect the old control and memory edges that are outside the loop.
3289   // Sometimes the memory phi of the head is used as the outgoing
3290   // state of the loop.  It's safe in this case to replace it with the
3291   // result_mem.
3292   _igvn.replace_node(store->in(MemNode::Memory), result_mem);
3293   lazy_replace(exit, result_ctrl);
3294   _igvn.replace_node(store, result_mem);
3295   // Any uses the increment outside of the loop become the loop limit.
3296   _igvn.replace_node(head->incr(), head->limit());
3297 
3298   // Disconnect the head from the loop.
3299   for (uint i = 0; i < lpt->_body.size(); i++) {
3300     Node* n = lpt->_body.at(i);
3301     _igvn.replace_node(n, C->top());
3302   }
3303 
3304   return true;
3305 }