1 /*
   2  * Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "compiler/compileLog.hpp"
  27 #include "memory/allocation.inline.hpp"
  28 #include "opto/addnode.hpp"
  29 #include "opto/callnode.hpp"
  30 #include "opto/connode.hpp"
  31 #include "opto/divnode.hpp"
  32 #include "opto/loopnode.hpp"
  33 #include "opto/mulnode.hpp"
  34 #include "opto/rootnode.hpp"
  35 #include "opto/runtime.hpp"
  36 #include "opto/subnode.hpp"
  37 
  38 //------------------------------is_loop_exit-----------------------------------
  39 // Given an IfNode, return the loop-exiting projection or NULL if both
  40 // arms remain in the loop.
  41 Node *IdealLoopTree::is_loop_exit(Node *iff) const {
  42   if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests
  43   PhaseIdealLoop *phase = _phase;
  44   // Test is an IfNode, has 2 projections.  If BOTH are in the loop
  45   // we need loop unswitching instead of peeling.
  46   if( !is_member(phase->get_loop( iff->raw_out(0) )) )
  47     return iff->raw_out(0);
  48   if( !is_member(phase->get_loop( iff->raw_out(1) )) )
  49     return iff->raw_out(1);
  50   return NULL;
  51 }
  52 
  53 
  54 //=============================================================================
  55 
  56 
  57 //------------------------------record_for_igvn----------------------------
  58 // Put loop body on igvn work list
  59 void IdealLoopTree::record_for_igvn() {
  60   for( uint i = 0; i < _body.size(); i++ ) {
  61     Node *n = _body.at(i);
  62     _phase->_igvn._worklist.push(n);
  63   }
  64 }
  65 
  66 //------------------------------compute_exact_trip_count-----------------------
  67 // Compute loop exact trip count if possible. Do not recalculate trip count for
  68 // split loops (pre-main-post) which have their limits and inits behind Opaque node.
  69 void IdealLoopTree::compute_exact_trip_count( PhaseIdealLoop *phase ) {
  70   if (!_head->as_Loop()->is_valid_counted_loop()) {
  71     return;
  72   }
  73   CountedLoopNode* cl = _head->as_CountedLoop();
  74   // Trip count may become nonexact for iteration split loops since
  75   // RCE modifies limits. Note, _trip_count value is not reset since
  76   // it is used to limit unrolling of main loop.
  77   cl->set_nonexact_trip_count();
  78 
  79   // Loop's test should be part of loop.
  80   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
  81     return; // Infinite loop
  82 
  83 #ifdef ASSERT
  84   BoolTest::mask bt = cl->loopexit()->test_trip();
  85   assert(bt == BoolTest::lt || bt == BoolTest::gt ||
  86          bt == BoolTest::ne, "canonical test is expected");
  87 #endif
  88 
  89   Node* init_n = cl->init_trip();
  90   Node* limit_n = cl->limit();
  91   if (init_n  != NULL &&  init_n->is_Con() &&
  92       limit_n != NULL && limit_n->is_Con()) {
  93     // Use longs to avoid integer overflow.
  94     int stride_con  = cl->stride_con();
  95     jlong init_con   = cl->init_trip()->get_int();
  96     jlong limit_con  = cl->limit()->get_int();
  97     int stride_m    = stride_con - (stride_con > 0 ? 1 : -1);
  98     jlong trip_count = (limit_con - init_con + stride_m)/stride_con;
  99     if (trip_count > 0 && (julong)trip_count < (julong)max_juint) {
 100       // Set exact trip count.
 101       cl->set_exact_trip_count((uint)trip_count);
 102     }
 103   }
 104 }
 105 
 106 //------------------------------compute_profile_trip_cnt----------------------------
 107 // Compute loop trip count from profile data as
 108 //    (backedge_count + loop_exit_count) / loop_exit_count
 109 void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {
 110   if (!_head->is_CountedLoop()) {
 111     return;
 112   }
 113   CountedLoopNode* head = _head->as_CountedLoop();
 114   if (head->profile_trip_cnt() != COUNT_UNKNOWN) {
 115     return; // Already computed
 116   }
 117   float trip_cnt = (float)max_jint; // default is big
 118 
 119   Node* back = head->in(LoopNode::LoopBackControl);
 120   while (back != head) {
 121     if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
 122         back->in(0) &&
 123         back->in(0)->is_If() &&
 124         back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&
 125         back->in(0)->as_If()->_prob != PROB_UNKNOWN) {
 126       break;
 127     }
 128     back = phase->idom(back);
 129   }
 130   if (back != head) {
 131     assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&
 132            back->in(0), "if-projection exists");
 133     IfNode* back_if = back->in(0)->as_If();
 134     float loop_back_cnt = back_if->_fcnt * back_if->_prob;
 135 
 136     // Now compute a loop exit count
 137     float loop_exit_cnt = 0.0f;
 138     for( uint i = 0; i < _body.size(); i++ ) {
 139       Node *n = _body[i];
 140       if( n->is_If() ) {
 141         IfNode *iff = n->as_If();
 142         if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {
 143           Node *exit = is_loop_exit(iff);
 144           if( exit ) {
 145             float exit_prob = iff->_prob;
 146             if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;
 147             if (exit_prob > PROB_MIN) {
 148               float exit_cnt = iff->_fcnt * exit_prob;
 149               loop_exit_cnt += exit_cnt;
 150             }
 151           }
 152         }
 153       }
 154     }
 155     if (loop_exit_cnt > 0.0f) {
 156       trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;
 157     } else {
 158       // No exit count so use
 159       trip_cnt = loop_back_cnt;
 160     }
 161   }
 162 #ifndef PRODUCT
 163   if (TraceProfileTripCount) {
 164     tty->print_cr("compute_profile_trip_cnt  lp: %d cnt: %f\n", head->_idx, trip_cnt);
 165   }
 166 #endif
 167   head->set_profile_trip_cnt(trip_cnt);
 168 }
 169 
 170 //---------------------is_invariant_addition-----------------------------
 171 // Return nonzero index of invariant operand for an Add or Sub
 172 // of (nonconstant) invariant and variant values. Helper for reassociate_invariants.
 173 int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {
 174   int op = n->Opcode();
 175   if (op == Op_AddI || op == Op_SubI) {
 176     bool in1_invar = this->is_invariant(n->in(1));
 177     bool in2_invar = this->is_invariant(n->in(2));
 178     if (in1_invar && !in2_invar) return 1;
 179     if (!in1_invar && in2_invar) return 2;
 180   }
 181   return 0;
 182 }
 183 
 184 //---------------------reassociate_add_sub-----------------------------
 185 // Reassociate invariant add and subtract expressions:
 186 //
 187 // inv1 + (x + inv2)  =>  ( inv1 + inv2) + x
 188 // (x + inv2) + inv1  =>  ( inv1 + inv2) + x
 189 // inv1 + (x - inv2)  =>  ( inv1 - inv2) + x
 190 // inv1 - (inv2 - x)  =>  ( inv1 - inv2) + x
 191 // (x + inv2) - inv1  =>  (-inv1 + inv2) + x
 192 // (x - inv2) + inv1  =>  ( inv1 - inv2) + x
 193 // (x - inv2) - inv1  =>  (-inv1 - inv2) + x
 194 // inv1 + (inv2 - x)  =>  ( inv1 + inv2) - x
 195 // inv1 - (x - inv2)  =>  ( inv1 + inv2) - x
 196 // (inv2 - x) + inv1  =>  ( inv1 + inv2) - x
 197 // (inv2 - x) - inv1  =>  (-inv1 + inv2) - x
 198 // inv1 - (x + inv2)  =>  ( inv1 - inv2) - x
 199 //
 200 Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {
 201   if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL;
 202   if (is_invariant(n1)) return NULL;
 203   int inv1_idx = is_invariant_addition(n1, phase);
 204   if (!inv1_idx) return NULL;
 205   // Don't mess with add of constant (igvn moves them to expression tree root.)
 206   if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;
 207   Node* inv1 = n1->in(inv1_idx);
 208   Node* n2 = n1->in(3 - inv1_idx);
 209   int inv2_idx = is_invariant_addition(n2, phase);
 210   if (!inv2_idx) return NULL;
 211   Node* x    = n2->in(3 - inv2_idx);
 212   Node* inv2 = n2->in(inv2_idx);
 213 
 214   bool neg_x    = n2->is_Sub() && inv2_idx == 1;
 215   bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;
 216   bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;
 217   if (n1->is_Sub() && inv1_idx == 1) {
 218     neg_x    = !neg_x;
 219     neg_inv2 = !neg_inv2;
 220   }
 221   Node* inv1_c = phase->get_ctrl(inv1);
 222   Node* inv2_c = phase->get_ctrl(inv2);
 223   Node* n_inv1;
 224   if (neg_inv1) {
 225     Node *zero = phase->_igvn.intcon(0);
 226     phase->set_ctrl(zero, phase->C->root());
 227     n_inv1 = new (phase->C) SubINode(zero, inv1);
 228     phase->register_new_node(n_inv1, inv1_c);
 229   } else {
 230     n_inv1 = inv1;
 231   }
 232   Node* inv;
 233   if (neg_inv2) {
 234     inv = new (phase->C) SubINode(n_inv1, inv2);
 235   } else {
 236     inv = new (phase->C) AddINode(n_inv1, inv2);
 237   }
 238   phase->register_new_node(inv, phase->get_early_ctrl(inv));
 239 
 240   Node* addx;
 241   if (neg_x) {
 242     addx = new (phase->C) SubINode(inv, x);
 243   } else {
 244     addx = new (phase->C) AddINode(x, inv);
 245   }
 246   phase->register_new_node(addx, phase->get_ctrl(x));
 247   phase->_igvn.replace_node(n1, addx);
 248   assert(phase->get_loop(phase->get_ctrl(n1)) == this, "");
 249   _body.yank(n1);
 250   return addx;
 251 }
 252 
 253 //---------------------reassociate_invariants-----------------------------
 254 // Reassociate invariant expressions:
 255 void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {
 256   for (int i = _body.size() - 1; i >= 0; i--) {
 257     Node *n = _body.at(i);
 258     for (int j = 0; j < 5; j++) {
 259       Node* nn = reassociate_add_sub(n, phase);
 260       if (nn == NULL) break;
 261       n = nn; // again
 262     };
 263   }
 264 }
 265 
 266 //------------------------------policy_peeling---------------------------------
 267 // Return TRUE or FALSE if the loop should be peeled or not.  Peel if we can
 268 // make some loop-invariant test (usually a null-check) happen before the loop.
 269 bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {
 270   Node *test = ((IdealLoopTree*)this)->tail();
 271   int  body_size = ((IdealLoopTree*)this)->_body.size();
 272   int  live_node_count = phase->C->live_nodes();
 273   // Peeling does loop cloning which can result in O(N^2) node construction
 274   if( body_size > 255 /* Prevent overflow for large body_size */
 275       || (body_size * body_size + live_node_count > MaxNodeLimit) ) {
 276     return false;           // too large to safely clone
 277   }
 278   while( test != _head ) {      // Scan till run off top of loop
 279     if( test->is_If() ) {       // Test?
 280       Node *ctrl = phase->get_ctrl(test->in(1));
 281       if (ctrl->is_top())
 282         return false;           // Found dead test on live IF?  No peeling!
 283       // Standard IF only has one input value to check for loop invariance
 284       assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "Check this code when new subtype is added");
 285       // Condition is not a member of this loop?
 286       if( !is_member(phase->get_loop(ctrl)) &&
 287           is_loop_exit(test) )
 288         return true;            // Found reason to peel!
 289     }
 290     // Walk up dominators to loop _head looking for test which is
 291     // executed on every path thru loop.
 292     test = phase->idom(test);
 293   }
 294   return false;
 295 }
 296 
 297 //------------------------------peeled_dom_test_elim---------------------------
 298 // If we got the effect of peeling, either by actually peeling or by making
 299 // a pre-loop which must execute at least once, we can remove all
 300 // loop-invariant dominated tests in the main body.
 301 void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {
 302   bool progress = true;
 303   while( progress ) {
 304     progress = false;           // Reset for next iteration
 305     Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();
 306     Node *test = prev->in(0);
 307     while( test != loop->_head ) { // Scan till run off top of loop
 308 
 309       int p_op = prev->Opcode();
 310       if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&
 311           test->is_If() &&      // Test?
 312           !test->in(1)->is_Con() && // And not already obvious?
 313           // Condition is not a member of this loop?
 314           !loop->is_member(get_loop(get_ctrl(test->in(1))))){
 315         // Walk loop body looking for instances of this test
 316         for( uint i = 0; i < loop->_body.size(); i++ ) {
 317           Node *n = loop->_body.at(i);
 318           if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {
 319             // IfNode was dominated by version in peeled loop body
 320             progress = true;
 321             dominated_by( old_new[prev->_idx], n );
 322           }
 323         }
 324       }
 325       prev = test;
 326       test = idom(test);
 327     } // End of scan tests in loop
 328 
 329   } // End of while( progress )
 330 }
 331 
 332 //------------------------------do_peeling-------------------------------------
 333 // Peel the first iteration of the given loop.
 334 // Step 1: Clone the loop body.  The clone becomes the peeled iteration.
 335 //         The pre-loop illegally has 2 control users (old & new loops).
 336 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
 337 //         Do this by making the old-loop fall-in edges act as if they came
 338 //         around the loopback from the prior iteration (follow the old-loop
 339 //         backedges) and then map to the new peeled iteration.  This leaves
 340 //         the pre-loop with only 1 user (the new peeled iteration), but the
 341 //         peeled-loop backedge has 2 users.
 342 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
 343 //         extra backedge user.
 344 //
 345 //                   orig
 346 //
 347 //                  stmt1
 348 //                    |
 349 //                    v
 350 //              loop predicate
 351 //                    |
 352 //                    v
 353 //                   loop<----+
 354 //                     |      |
 355 //                   stmt2    |
 356 //                     |      |
 357 //                     v      |
 358 //                    if      ^
 359 //                   / \      |
 360 //                  /   \     |
 361 //                 v     v    |
 362 //               false true   |
 363 //               /       \    |
 364 //              /         ----+
 365 //             |
 366 //             v
 367 //           exit
 368 //
 369 //
 370 //            after clone loop
 371 //
 372 //                   stmt1
 373 //                     |
 374 //                     v
 375 //               loop predicate
 376 //                 /       \
 377 //        clone   /         \   orig
 378 //               /           \
 379 //              /             \
 380 //             v               v
 381 //   +---->loop clone          loop<----+
 382 //   |      |                    |      |
 383 //   |    stmt2 clone          stmt2    |
 384 //   |      |                    |      |
 385 //   |      v                    v      |
 386 //   ^      if clone            If      ^
 387 //   |      / \                / \      |
 388 //   |     /   \              /   \     |
 389 //   |    v     v            v     v    |
 390 //   |    true  false      false true   |
 391 //   |    /         \      /       \    |
 392 //   +----           \    /         ----+
 393 //                    \  /
 394 //                    1v v2
 395 //                  region
 396 //                     |
 397 //                     v
 398 //                   exit
 399 //
 400 //
 401 //         after peel and predicate move
 402 //
 403 //                   stmt1
 404 //                    /
 405 //                   /
 406 //        clone     /            orig
 407 //                 /
 408 //                /              +----------+
 409 //               /               |          |
 410 //              /          loop predicate   |
 411 //             /                 |          |
 412 //            v                  v          |
 413 //   TOP-->loop clone          loop<----+   |
 414 //          |                    |      |   |
 415 //        stmt2 clone          stmt2    |   |
 416 //          |                    |      |   ^
 417 //          v                    v      |   |
 418 //          if clone            If      ^   |
 419 //          / \                / \      |   |
 420 //         /   \              /   \     |   |
 421 //        v     v            v     v    |   |
 422 //      true   false      false  true   |   |
 423 //        |         \      /       \    |   |
 424 //        |          \    /         ----+   ^
 425 //        |           \  /                  |
 426 //        |           1v v2                 |
 427 //        v         region                  |
 428 //        |            |                    |
 429 //        |            v                    |
 430 //        |          exit                   |
 431 //        |                                 |
 432 //        +--------------->-----------------+
 433 //
 434 //
 435 //              final graph
 436 //
 437 //                  stmt1
 438 //                    |
 439 //                    v
 440 //                  stmt2 clone
 441 //                    |
 442 //                    v
 443 //                   if clone
 444 //                  / |
 445 //                 /  |
 446 //                v   v
 447 //            false  true
 448 //             |      |
 449 //             |      v
 450 //             | loop predicate
 451 //             |      |
 452 //             |      v
 453 //             |     loop<----+
 454 //             |      |       |
 455 //             |    stmt2     |
 456 //             |      |       |
 457 //             |      v       |
 458 //             v      if      ^
 459 //             |     /  \     |
 460 //             |    /    \    |
 461 //             |   v     v    |
 462 //             | false  true  |
 463 //             |  |        \  |
 464 //             v  v         --+
 465 //            region
 466 //              |
 467 //              v
 468 //             exit
 469 //
 470 void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {
 471 
 472   C->set_major_progress();
 473   // Peeling a 'main' loop in a pre/main/post situation obfuscates the
 474   // 'pre' loop from the main and the 'pre' can no longer have it's
 475   // iterations adjusted.  Therefore, we need to declare this loop as
 476   // no longer a 'main' loop; it will need new pre and post loops before
 477   // we can do further RCE.
 478 #ifndef PRODUCT
 479   if (TraceLoopOpts) {
 480     tty->print("Peel         ");
 481     loop->dump_head();
 482   }
 483 #endif
 484   Node* head = loop->_head;
 485   bool counted_loop = head->is_CountedLoop();
 486   if (counted_loop) {
 487     CountedLoopNode *cl = head->as_CountedLoop();
 488     assert(cl->trip_count() > 0, "peeling a fully unrolled loop");
 489     cl->set_trip_count(cl->trip_count() - 1);
 490     if (cl->is_main_loop()) {
 491       cl->set_normal_loop();
 492 #ifndef PRODUCT
 493       if (PrintOpto && VerifyLoopOptimizations) {
 494         tty->print("Peeling a 'main' loop; resetting to 'normal' ");
 495         loop->dump_head();
 496       }
 497 #endif
 498     }
 499   }
 500   Node* entry = head->in(LoopNode::EntryControl);
 501 
 502   // Step 1: Clone the loop body.  The clone becomes the peeled iteration.
 503   //         The pre-loop illegally has 2 control users (old & new loops).
 504   clone_loop( loop, old_new, dom_depth(head) );
 505 
 506   // Step 2: Make the old-loop fall-in edges point to the peeled iteration.
 507   //         Do this by making the old-loop fall-in edges act as if they came
 508   //         around the loopback from the prior iteration (follow the old-loop
 509   //         backedges) and then map to the new peeled iteration.  This leaves
 510   //         the pre-loop with only 1 user (the new peeled iteration), but the
 511   //         peeled-loop backedge has 2 users.
 512   Node* new_entry = old_new[head->in(LoopNode::LoopBackControl)->_idx];
 513   _igvn.hash_delete(head);
 514   head->set_req(LoopNode::EntryControl, new_entry);
 515   for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) {
 516     Node* old = head->fast_out(j);
 517     if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) {
 518       Node* new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
 519       if (!new_exit_value )     // Backedge value is ALSO loop invariant?
 520         // Then loop body backedge value remains the same.
 521         new_exit_value = old->in(LoopNode::LoopBackControl);
 522       _igvn.hash_delete(old);
 523       old->set_req(LoopNode::EntryControl, new_exit_value);
 524     }
 525   }
 526 
 527 
 528   // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
 529   //         extra backedge user.
 530   Node* new_head = old_new[head->_idx];
 531   _igvn.hash_delete(new_head);
 532   new_head->set_req(LoopNode::LoopBackControl, C->top());
 533   for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) {
 534     Node* use = new_head->fast_out(j2);
 535     if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) {
 536       _igvn.hash_delete(use);
 537       use->set_req(LoopNode::LoopBackControl, C->top());
 538     }
 539   }
 540 
 541 
 542   // Step 4: Correct dom-depth info.  Set to loop-head depth.
 543   int dd = dom_depth(head);
 544   set_idom(head, head->in(1), dd);
 545   for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
 546     Node *old = loop->_body.at(j3);
 547     Node *nnn = old_new[old->_idx];
 548     if (!has_ctrl(nnn))
 549       set_idom(nnn, idom(nnn), dd-1);
 550   }
 551 
 552   // Now force out all loop-invariant dominating tests.  The optimizer
 553   // finds some, but we _know_ they are all useless.
 554   peeled_dom_test_elim(loop,old_new);
 555 
 556   loop->record_for_igvn();
 557 }
 558 
 559 #define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop
 560 
 561 //------------------------------policy_maximally_unroll------------------------
 562 // Calculate exact loop trip count and return true if loop can be maximally
 563 // unrolled.
 564 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
 565   CountedLoopNode *cl = _head->as_CountedLoop();
 566   assert(cl->is_normal_loop(), "");
 567   if (!cl->is_valid_counted_loop())
 568     return false; // Malformed counted loop
 569 
 570   if (!cl->has_exact_trip_count()) {
 571     // Trip count is not exact.
 572     return false;
 573   }
 574 
 575   uint trip_count = cl->trip_count();
 576   // Note, max_juint is used to indicate unknown trip count.
 577   assert(trip_count > 1, "one iteration loop should be optimized out already");
 578   assert(trip_count < max_juint, "exact trip_count should be less than max_uint.");
 579 
 580   // Real policy: if we maximally unroll, does it get too big?
 581   // Allow the unrolled mess to get larger than standard loop
 582   // size.  After all, it will no longer be a loop.
 583   uint body_size    = _body.size();
 584   uint unroll_limit = (uint)LoopUnrollLimit * 4;
 585   assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
 586   if (trip_count > unroll_limit || body_size > unroll_limit) {
 587     return false;
 588   }
 589 
 590   // Fully unroll a loop with few iterations regardless next
 591   // conditions since following loop optimizations will split
 592   // such loop anyway (pre-main-post).
 593   if (trip_count <= 3)
 594     return true;
 595 
 596   // Take into account that after unroll conjoined heads and tails will fold,
 597   // otherwise policy_unroll() may allow more unrolling than max unrolling.
 598   uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count;
 599   uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE;
 600   if (body_size != tst_body_size) // Check for int overflow
 601     return false;
 602   if (new_body_size > unroll_limit ||
 603       // Unrolling can result in a large amount of node construction
 604       new_body_size >= MaxNodeLimit - (uint) phase->C->live_nodes()) {
 605     return false;
 606   }
 607 
 608   // Do not unroll a loop with String intrinsics code.
 609   // String intrinsics are large and have loops.
 610   for (uint k = 0; k < _body.size(); k++) {
 611     Node* n = _body.at(k);
 612     switch (n->Opcode()) {
 613       case Op_StrComp:
 614       case Op_StrEquals:
 615       case Op_StrIndexOf:
 616       case Op_EncodeISOArray:
 617       case Op_AryEq: {
 618         return false;
 619       }
 620     } // switch
 621   }
 622 
 623   return true; // Do maximally unroll
 624 }
 625 
 626 
 627 //------------------------------policy_unroll----------------------------------
 628 // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if
 629 // the loop is a CountedLoop and the body is small enough.
 630 bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const {
 631 
 632   CountedLoopNode *cl = _head->as_CountedLoop();
 633   assert(cl->is_normal_loop() || cl->is_main_loop(), "");
 634 
 635   if (!cl->is_valid_counted_loop())
 636     return false; // Malformed counted loop
 637 
 638   // Protect against over-unrolling.
 639   // After split at least one iteration will be executed in pre-loop.
 640   if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false;
 641 
 642   int future_unroll_ct = cl->unrolled_count() * 2;
 643   if (future_unroll_ct > LoopMaxUnroll) return false;
 644 
 645   // Check for initial stride being a small enough constant
 646   if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;
 647 
 648   // Don't unroll if the next round of unrolling would push us
 649   // over the expected trip count of the loop.  One is subtracted
 650   // from the expected trip count because the pre-loop normally
 651   // executes 1 iteration.
 652   if (UnrollLimitForProfileCheck > 0 &&
 653       cl->profile_trip_cnt() != COUNT_UNKNOWN &&
 654       future_unroll_ct        > UnrollLimitForProfileCheck &&
 655       (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
 656     return false;
 657   }
 658 
 659   // When unroll count is greater than LoopUnrollMin, don't unroll if:
 660   //   the residual iterations are more than 10% of the trip count
 661   //   and rounds of "unroll,optimize" are not making significant progress
 662   //   Progress defined as current size less than 20% larger than previous size.
 663   if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
 664       future_unroll_ct > LoopUnrollMin &&
 665       (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() &&
 666       1.2 * cl->node_count_before_unroll() < (double)_body.size()) {
 667     return false;
 668   }
 669 
 670   Node *init_n = cl->init_trip();
 671   Node *limit_n = cl->limit();
 672   int stride_con = cl->stride_con();
 673   // Non-constant bounds.
 674   // Protect against over-unrolling when init or/and limit are not constant
 675   // (so that trip_count's init value is maxint) but iv range is known.
 676   if (init_n   == NULL || !init_n->is_Con()  ||
 677       limit_n  == NULL || !limit_n->is_Con()) {
 678     Node* phi = cl->phi();
 679     if (phi != NULL) {
 680       assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
 681       const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
 682       int next_stride = stride_con * 2; // stride after this unroll
 683       if (next_stride > 0) {
 684         if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow
 685             iv_type->_lo + next_stride >  iv_type->_hi) {
 686           return false;  // over-unrolling
 687         }
 688       } else if (next_stride < 0) {
 689         if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow
 690             iv_type->_hi + next_stride <  iv_type->_lo) {
 691           return false;  // over-unrolling
 692         }
 693       }
 694     }
 695   }
 696 
 697   // After unroll limit will be adjusted: new_limit = limit-stride.
 698   // Bailout if adjustment overflow.
 699   const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int();
 700   if (stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi) ||
 701       stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo))
 702     return false;  // overflow
 703 
 704   // Adjust body_size to determine if we unroll or not
 705   uint body_size = _body.size();
 706   // Key test to unroll loop in CRC32 java code
 707   int xors_in_loop = 0;
 708   // Also count ModL, DivL and MulL which expand mightly
 709   for (uint k = 0; k < _body.size(); k++) {
 710     Node* n = _body.at(k);
 711     switch (n->Opcode()) {
 712       case Op_XorI: xors_in_loop++; break; // CRC32 java code
 713       case Op_ModL: body_size += 30; break;
 714       case Op_DivL: body_size += 30; break;
 715       case Op_MulL: body_size += 10; break;
 716       case Op_FlagsProj:
 717         // Can't handle unrolling of loops containing
 718         // nodes that generate a FlagsProj at the moment
 719         return false;
 720       case Op_StrComp:
 721       case Op_StrEquals:
 722       case Op_StrIndexOf:
 723       case Op_EncodeISOArray:
 724       case Op_AryEq: {
 725         // Do not unroll a loop with String intrinsics code.
 726         // String intrinsics are large and have loops.
 727         return false;
 728       }
 729     } // switch
 730   }
 731 
 732   // Check for being too big
 733   if (body_size > (uint)LoopUnrollLimit) {
 734     if (xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;
 735     // Normal case: loop too big
 736     return false;
 737   }
 738 
 739   // Unroll once!  (Each trip will soon do double iterations)
 740   return true;
 741 }
 742 
 743 //------------------------------policy_align-----------------------------------
 744 // Return TRUE or FALSE if the loop should be cache-line aligned.  Gather the
 745 // expression that does the alignment.  Note that only one array base can be
 746 // aligned in a loop (unless the VM guarantees mutual alignment).  Note that
 747 // if we vectorize short memory ops into longer memory ops, we may want to
 748 // increase alignment.
 749 bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {
 750   return false;
 751 }
 752 
 753 //------------------------------policy_range_check-----------------------------
 754 // Return TRUE or FALSE if the loop should be range-check-eliminated.
 755 // Actually we do iteration-splitting, a more powerful form of RCE.
 756 bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {
 757   if (!RangeCheckElimination) return false;
 758 
 759   CountedLoopNode *cl = _head->as_CountedLoop();
 760   // If we unrolled with no intention of doing RCE and we later
 761   // changed our minds, we got no pre-loop.  Either we need to
 762   // make a new pre-loop, or we gotta disallow RCE.
 763   if (cl->is_main_no_pre_loop()) return false; // Disallowed for now.
 764   Node *trip_counter = cl->phi();
 765 
 766   // Check loop body for tests of trip-counter plus loop-invariant vs
 767   // loop-invariant.
 768   for (uint i = 0; i < _body.size(); i++) {
 769     Node *iff = _body[i];
 770     if (iff->Opcode() == Op_If) { // Test?
 771 
 772       // Comparing trip+off vs limit
 773       Node *bol = iff->in(1);
 774       if (bol->req() != 2) continue; // dead constant test
 775       if (!bol->is_Bool()) {
 776         assert(UseLoopPredicate && bol->Opcode() == Op_Conv2B, "predicate check only");
 777         continue;
 778       }
 779       if (bol->as_Bool()->_test._test == BoolTest::ne)
 780         continue; // not RC
 781 
 782       Node *cmp = bol->in(1);
 783       if (cmp->is_FlagsProj()) {
 784         continue;
 785       }
 786 
 787       Node *rc_exp = cmp->in(1);
 788       Node *limit = cmp->in(2);
 789 
 790       Node *limit_c = phase->get_ctrl(limit);
 791       if( limit_c == phase->C->top() )
 792         return false;           // Found dead test on live IF?  No RCE!
 793       if( is_member(phase->get_loop(limit_c) ) ) {
 794         // Compare might have operands swapped; commute them
 795         rc_exp = cmp->in(2);
 796         limit  = cmp->in(1);
 797         limit_c = phase->get_ctrl(limit);
 798         if( is_member(phase->get_loop(limit_c) ) )
 799           continue;             // Both inputs are loop varying; cannot RCE
 800       }
 801 
 802       if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {
 803         continue;
 804       }
 805       // Yeah!  Found a test like 'trip+off vs limit'
 806       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
 807       // we need loop unswitching instead of iteration splitting.
 808       if( is_loop_exit(iff) )
 809         return true;            // Found reason to split iterations
 810     } // End of is IF
 811   }
 812 
 813   return false;
 814 }
 815 
 816 //------------------------------policy_peel_only-------------------------------
 817 // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned.  Useful
 818 // for unrolling loops with NO array accesses.
 819 bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {
 820 
 821   for( uint i = 0; i < _body.size(); i++ )
 822     if( _body[i]->is_Mem() )
 823       return false;
 824 
 825   // No memory accesses at all!
 826   return true;
 827 }
 828 
 829 //------------------------------clone_up_backedge_goo--------------------------
 830 // If Node n lives in the back_ctrl block and cannot float, we clone a private
 831 // version of n in preheader_ctrl block and return that, otherwise return n.
 832 Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones ) {
 833   if( get_ctrl(n) != back_ctrl ) return n;
 834 
 835   // Only visit once
 836   if (visited.test_set(n->_idx)) {
 837     Node *x = clones.find(n->_idx);
 838     if (x != NULL)
 839       return x;
 840     return n;
 841   }
 842 
 843   Node *x = NULL;               // If required, a clone of 'n'
 844   // Check for 'n' being pinned in the backedge.
 845   if( n->in(0) && n->in(0) == back_ctrl ) {
 846     assert(clones.find(n->_idx) == NULL, "dead loop");
 847     x = n->clone();             // Clone a copy of 'n' to preheader
 848     clones.push(x, n->_idx);
 849     x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
 850   }
 851 
 852   // Recursive fixup any other input edges into x.
 853   // If there are no changes we can just return 'n', otherwise
 854   // we need to clone a private copy and change it.
 855   for( uint i = 1; i < n->req(); i++ ) {
 856     Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i), visited, clones );
 857     if( g != n->in(i) ) {
 858       if( !x ) {
 859         assert(clones.find(n->_idx) == NULL, "dead loop");
 860         x = n->clone();
 861         clones.push(x, n->_idx);
 862       }
 863       x->set_req(i, g);
 864     }
 865   }
 866   if( x ) {                     // x can legally float to pre-header location
 867     register_new_node( x, preheader_ctrl );
 868     return x;
 869   } else {                      // raise n to cover LCA of uses
 870     set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
 871   }
 872   return n;
 873 }
 874 
 875 //------------------------------insert_pre_post_loops--------------------------
 876 // Insert pre and post loops.  If peel_only is set, the pre-loop can not have
 877 // more iterations added.  It acts as a 'peel' only, no lower-bound RCE, no
 878 // alignment.  Useful to unroll loops that do no array accesses.
 879 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
 880 
 881 #ifndef PRODUCT
 882   if (TraceLoopOpts) {
 883     if (peel_only)
 884       tty->print("PeelMainPost ");
 885     else
 886       tty->print("PreMainPost  ");
 887     loop->dump_head();
 888   }
 889 #endif
 890   C->set_major_progress();
 891 
 892   // Find common pieces of the loop being guarded with pre & post loops
 893   CountedLoopNode *main_head = loop->_head->as_CountedLoop();
 894   assert( main_head->is_normal_loop(), "" );
 895   CountedLoopEndNode *main_end = main_head->loopexit();
 896   guarantee(main_end != NULL, "no loop exit node");
 897   assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
 898   uint dd_main_head = dom_depth(main_head);
 899   uint max = main_head->outcnt();
 900 
 901   Node *pre_header= main_head->in(LoopNode::EntryControl);
 902   Node *init      = main_head->init_trip();
 903   Node *incr      = main_end ->incr();
 904   Node *limit     = main_end ->limit();
 905   Node *stride    = main_end ->stride();
 906   Node *cmp       = main_end ->cmp_node();
 907   BoolTest::mask b_test = main_end->test_trip();
 908 
 909   // Need only 1 user of 'bol' because I will be hacking the loop bounds.
 910   Node *bol = main_end->in(CountedLoopEndNode::TestValue);
 911   if( bol->outcnt() != 1 ) {
 912     bol = bol->clone();
 913     register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
 914     _igvn.hash_delete(main_end);
 915     main_end->set_req(CountedLoopEndNode::TestValue, bol);
 916   }
 917   // Need only 1 user of 'cmp' because I will be hacking the loop bounds.
 918   if( cmp->outcnt() != 1 ) {
 919     cmp = cmp->clone();
 920     register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
 921     _igvn.hash_delete(bol);
 922     bol->set_req(1, cmp);
 923   }
 924 
 925   //------------------------------
 926   // Step A: Create Post-Loop.
 927   Node* main_exit = main_end->proj_out(false);
 928   assert( main_exit->Opcode() == Op_IfFalse, "" );
 929   int dd_main_exit = dom_depth(main_exit);
 930 
 931   // Step A1: Clone the loop body.  The clone becomes the post-loop.  The main
 932   // loop pre-header illegally has 2 control users (old & new loops).
 933   clone_loop( loop, old_new, dd_main_exit );
 934   assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" );
 935   CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop();
 936   post_head->set_post_loop(main_head);
 937 
 938   // Reduce the post-loop trip count.
 939   CountedLoopEndNode* post_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
 940   post_end->_prob = PROB_FAIR;
 941 
 942   // Build the main-loop normal exit.
 943   IfFalseNode *new_main_exit = new (C) IfFalseNode(main_end);
 944   _igvn.register_new_node_with_optimizer( new_main_exit );
 945   set_idom(new_main_exit, main_end, dd_main_exit );
 946   set_loop(new_main_exit, loop->_parent);
 947 
 948   // Step A2: Build a zero-trip guard for the post-loop.  After leaving the
 949   // main-loop, the post-loop may not execute at all.  We 'opaque' the incr
 950   // (the main-loop trip-counter exit value) because we will be changing
 951   // the exit value (via unrolling) so we cannot constant-fold away the zero
 952   // trip guard until all unrolling is done.
 953   Node *zer_opaq = new (C) Opaque1Node(C, incr);
 954   Node *zer_cmp  = new (C) CmpINode( zer_opaq, limit );
 955   Node *zer_bol  = new (C) BoolNode( zer_cmp, b_test );
 956   register_new_node( zer_opaq, new_main_exit );
 957   register_new_node( zer_cmp , new_main_exit );
 958   register_new_node( zer_bol , new_main_exit );
 959 
 960   // Build the IfNode
 961   IfNode *zer_iff = new (C) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN );
 962   _igvn.register_new_node_with_optimizer( zer_iff );
 963   set_idom(zer_iff, new_main_exit, dd_main_exit);
 964   set_loop(zer_iff, loop->_parent);
 965 
 966   // Plug in the false-path, taken if we need to skip post-loop
 967   _igvn.replace_input_of(main_exit, 0, zer_iff);
 968   set_idom(main_exit, zer_iff, dd_main_exit);
 969   set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
 970   // Make the true-path, must enter the post loop
 971   Node *zer_taken = new (C) IfTrueNode( zer_iff );
 972   _igvn.register_new_node_with_optimizer( zer_taken );
 973   set_idom(zer_taken, zer_iff, dd_main_exit);
 974   set_loop(zer_taken, loop->_parent);
 975   // Plug in the true path
 976   _igvn.hash_delete( post_head );
 977   post_head->set_req(LoopNode::EntryControl, zer_taken);
 978   set_idom(post_head, zer_taken, dd_main_exit);
 979 
 980   Arena *a = Thread::current()->resource_area();
 981   VectorSet visited(a);
 982   Node_Stack clones(a, main_head->back_control()->outcnt());
 983   // Step A3: Make the fall-in values to the post-loop come from the
 984   // fall-out values of the main-loop.
 985   for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
 986     Node* main_phi = main_head->fast_out(i);
 987     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) {
 988       Node *post_phi = old_new[main_phi->_idx];
 989       Node *fallmain  = clone_up_backedge_goo(main_head->back_control(),
 990                                               post_head->init_control(),
 991                                               main_phi->in(LoopNode::LoopBackControl),
 992                                               visited, clones);
 993       _igvn.hash_delete(post_phi);
 994       post_phi->set_req( LoopNode::EntryControl, fallmain );
 995     }
 996   }
 997 
 998   // Update local caches for next stanza
 999   main_exit = new_main_exit;
1000 
1001 
1002   //------------------------------
1003   // Step B: Create Pre-Loop.
1004 
1005   // Step B1: Clone the loop body.  The clone becomes the pre-loop.  The main
1006   // loop pre-header illegally has 2 control users (old & new loops).
1007   clone_loop( loop, old_new, dd_main_head );
1008   CountedLoopNode*    pre_head = old_new[main_head->_idx]->as_CountedLoop();
1009   CountedLoopEndNode* pre_end  = old_new[main_end ->_idx]->as_CountedLoopEnd();
1010   pre_head->set_pre_loop(main_head);
1011   Node *pre_incr = old_new[incr->_idx];
1012 
1013   // Reduce the pre-loop trip count.
1014   pre_end->_prob = PROB_FAIR;
1015 
1016   // Find the pre-loop normal exit.
1017   Node* pre_exit = pre_end->proj_out(false);
1018   assert( pre_exit->Opcode() == Op_IfFalse, "" );
1019   IfFalseNode *new_pre_exit = new (C) IfFalseNode(pre_end);
1020   _igvn.register_new_node_with_optimizer( new_pre_exit );
1021   set_idom(new_pre_exit, pre_end, dd_main_head);
1022   set_loop(new_pre_exit, loop->_parent);
1023 
1024   // Step B2: Build a zero-trip guard for the main-loop.  After leaving the
1025   // pre-loop, the main-loop may not execute at all.  Later in life this
1026   // zero-trip guard will become the minimum-trip guard when we unroll
1027   // the main-loop.
1028   Node *min_opaq = new (C) Opaque1Node(C, limit);
1029   Node *min_cmp  = new (C) CmpINode( pre_incr, min_opaq );
1030   Node *min_bol  = new (C) BoolNode( min_cmp, b_test );
1031   register_new_node( min_opaq, new_pre_exit );
1032   register_new_node( min_cmp , new_pre_exit );
1033   register_new_node( min_bol , new_pre_exit );
1034 
1035   // Build the IfNode (assume the main-loop is executed always).
1036   IfNode *min_iff = new (C) IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );
1037   _igvn.register_new_node_with_optimizer( min_iff );
1038   set_idom(min_iff, new_pre_exit, dd_main_head);
1039   set_loop(min_iff, loop->_parent);
1040 
1041   // Plug in the false-path, taken if we need to skip main-loop
1042   _igvn.hash_delete( pre_exit );
1043   pre_exit->set_req(0, min_iff);
1044   set_idom(pre_exit, min_iff, dd_main_head);
1045   set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
1046   // Make the true-path, must enter the main loop
1047   Node *min_taken = new (C) IfTrueNode( min_iff );
1048   _igvn.register_new_node_with_optimizer( min_taken );
1049   set_idom(min_taken, min_iff, dd_main_head);
1050   set_loop(min_taken, loop->_parent);
1051   // Plug in the true path
1052   _igvn.hash_delete( main_head );
1053   main_head->set_req(LoopNode::EntryControl, min_taken);
1054   set_idom(main_head, min_taken, dd_main_head);
1055 
1056   visited.Clear();
1057   clones.clear();
1058   // Step B3: Make the fall-in values to the main-loop come from the
1059   // fall-out values of the pre-loop.
1060   for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
1061     Node* main_phi = main_head->fast_out(i2);
1062     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
1063       Node *pre_phi = old_new[main_phi->_idx];
1064       Node *fallpre  = clone_up_backedge_goo(pre_head->back_control(),
1065                                              main_head->init_control(),
1066                                              pre_phi->in(LoopNode::LoopBackControl),
1067                                              visited, clones);
1068       _igvn.hash_delete(main_phi);
1069       main_phi->set_req( LoopNode::EntryControl, fallpre );
1070     }
1071   }
1072 
1073   // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
1074   // RCE and alignment may change this later.
1075   Node *cmp_end = pre_end->cmp_node();
1076   assert( cmp_end->in(2) == limit, "" );
1077   Node *pre_limit = new (C) AddINode( init, stride );
1078 
1079   // Save the original loop limit in this Opaque1 node for
1080   // use by range check elimination.
1081   Node *pre_opaq  = new (C) Opaque1Node(C, pre_limit, limit);
1082 
1083   register_new_node( pre_limit, pre_head->in(0) );
1084   register_new_node( pre_opaq , pre_head->in(0) );
1085 
1086   // Since no other users of pre-loop compare, I can hack limit directly
1087   assert( cmp_end->outcnt() == 1, "no other users" );
1088   _igvn.hash_delete(cmp_end);
1089   cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
1090 
1091   // Special case for not-equal loop bounds:
1092   // Change pre loop test, main loop test, and the
1093   // main loop guard test to use lt or gt depending on stride
1094   // direction:
1095   // positive stride use <
1096   // negative stride use >
1097   //
1098   // not-equal test is kept for post loop to handle case
1099   // when init > limit when stride > 0 (and reverse).
1100 
1101   if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
1102 
1103     BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
1104     // Modify pre loop end condition
1105     Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1106     BoolNode* new_bol0 = new (C) BoolNode(pre_bol->in(1), new_test);
1107     register_new_node( new_bol0, pre_head->in(0) );
1108     _igvn.hash_delete(pre_end);
1109     pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0);
1110     // Modify main loop guard condition
1111     assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
1112     BoolNode* new_bol1 = new (C) BoolNode(min_bol->in(1), new_test);
1113     register_new_node( new_bol1, new_pre_exit );
1114     _igvn.hash_delete(min_iff);
1115     min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
1116     // Modify main loop end condition
1117     BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1118     BoolNode* new_bol2 = new (C) BoolNode(main_bol->in(1), new_test);
1119     register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
1120     _igvn.hash_delete(main_end);
1121     main_end->set_req(CountedLoopEndNode::TestValue, new_bol2);
1122   }
1123 
1124   // Flag main loop
1125   main_head->set_main_loop();
1126   if( peel_only ) main_head->set_main_no_pre_loop();
1127 
1128   // Subtract a trip count for the pre-loop.
1129   main_head->set_trip_count(main_head->trip_count() - 1);
1130 
1131   // It's difficult to be precise about the trip-counts
1132   // for the pre/post loops.  They are usually very short,
1133   // so guess that 4 trips is a reasonable value.
1134   post_head->set_profile_trip_cnt(4.0);
1135   pre_head->set_profile_trip_cnt(4.0);
1136 
1137   // Now force out all loop-invariant dominating tests.  The optimizer
1138   // finds some, but we _know_ they are all useless.
1139   peeled_dom_test_elim(loop,old_new);
1140 }
1141 
1142 //------------------------------is_invariant-----------------------------
1143 // Return true if n is invariant
1144 bool IdealLoopTree::is_invariant(Node* n) const {
1145   Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n;
1146   if (n_c->is_top()) return false;
1147   return !is_member(_phase->get_loop(n_c));
1148 }
1149 
1150 
1151 //------------------------------do_unroll--------------------------------------
1152 // Unroll the loop body one step - make each trip do 2 iterations.
1153 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
1154   assert(LoopUnrollLimit, "");
1155   CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
1156   CountedLoopEndNode *loop_end = loop_head->loopexit();
1157   assert(loop_end, "");
1158 #ifndef PRODUCT
1159   if (PrintOpto && VerifyLoopOptimizations) {
1160     tty->print("Unrolling ");
1161     loop->dump_head();
1162   } else if (TraceLoopOpts) {
1163     if (loop_head->trip_count() < (uint)LoopUnrollLimit) {
1164       tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count());
1165     } else {
1166       tty->print("Unroll %d     ", loop_head->unrolled_count()*2);
1167     }
1168     loop->dump_head();
1169   }
1170 #endif
1171 
1172   // Remember loop node count before unrolling to detect
1173   // if rounds of unroll,optimize are making progress
1174   loop_head->set_node_count_before_unroll(loop->_body.size());
1175 
1176   Node *ctrl  = loop_head->in(LoopNode::EntryControl);
1177   Node *limit = loop_head->limit();
1178   Node *init  = loop_head->init_trip();
1179   Node *stride = loop_head->stride();
1180 
1181   Node *opaq = NULL;
1182   if (adjust_min_trip) {       // If not maximally unrolling, need adjustment
1183     // Search for zero-trip guard.
1184     assert( loop_head->is_main_loop(), "" );
1185     assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
1186     Node *iff = ctrl->in(0);
1187     assert( iff->Opcode() == Op_If, "" );
1188     Node *bol = iff->in(1);
1189     assert( bol->Opcode() == Op_Bool, "" );
1190     Node *cmp = bol->in(1);
1191     assert( cmp->Opcode() == Op_CmpI, "" );
1192     opaq = cmp->in(2);
1193     // Occasionally it's possible for a zero-trip guard Opaque1 node to be
1194     // optimized away and then another round of loop opts attempted.
1195     // We can not optimize this particular loop in that case.
1196     if (opaq->Opcode() != Op_Opaque1)
1197       return; // Cannot find zero-trip guard!  Bail out!
1198     // Zero-trip test uses an 'opaque' node which is not shared.
1199     assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
1200   }
1201 
1202   C->set_major_progress();
1203 
1204   Node* new_limit = NULL;
1205   if (UnrollLimitCheck) {
1206     int stride_con = stride->get_int();
1207     int stride_p = (stride_con > 0) ? stride_con : -stride_con;
1208     uint old_trip_count = loop_head->trip_count();
1209     // Verify that unroll policy result is still valid.
1210     assert(old_trip_count > 1 &&
1211            (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");
1212 
1213     // Adjust loop limit to keep valid iterations number after unroll.
1214     // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride
1215     // which may overflow.
1216     if (!adjust_min_trip) {
1217       assert(old_trip_count > 1 && (old_trip_count & 1) == 0,
1218              "odd trip count for maximally unroll");
1219       // Don't need to adjust limit for maximally unroll since trip count is even.
1220     } else if (loop_head->has_exact_trip_count() && init->is_Con()) {
1221       // Loop's limit is constant. Loop's init could be constant when pre-loop
1222       // become peeled iteration.
1223       jlong init_con = init->get_int();
1224       // We can keep old loop limit if iterations count stays the same:
1225       //   old_trip_count == new_trip_count * 2
1226       // Note: since old_trip_count >= 2 then new_trip_count >= 1
1227       // so we also don't need to adjust zero trip test.
1228       jlong limit_con  = limit->get_int();
1229       // (stride_con*2) not overflow since stride_con <= 8.
1230       int new_stride_con = stride_con * 2;
1231       int stride_m    = new_stride_con - (stride_con > 0 ? 1 : -1);
1232       jlong trip_count = (limit_con - init_con + stride_m)/new_stride_con;
1233       // New trip count should satisfy next conditions.
1234       assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity");
1235       uint new_trip_count = (uint)trip_count;
1236       adjust_min_trip = (old_trip_count != new_trip_count*2);
1237     }
1238 
1239     if (adjust_min_trip) {
1240       // Step 2: Adjust the trip limit if it is called for.
1241       // The adjustment amount is -stride. Need to make sure if the
1242       // adjustment underflows or overflows, then the main loop is skipped.
1243       Node* cmp = loop_end->cmp_node();
1244       assert(cmp->in(2) == limit, "sanity");
1245       assert(opaq != NULL && opaq->in(1) == limit, "sanity");
1246 
1247       // Verify that policy_unroll result is still valid.
1248       const TypeInt* limit_type = _igvn.type(limit)->is_int();
1249       assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) ||
1250              stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity");
1251 
1252       if (limit->is_Con()) {
1253         // The check in policy_unroll and the assert above guarantee
1254         // no underflow if limit is constant.
1255         new_limit = _igvn.intcon(limit->get_int() - stride_con);
1256         set_ctrl(new_limit, C->root());
1257       } else {
1258         // Limit is not constant.
1259         if (loop_head->unrolled_count() == 1) { // only for first unroll
1260           // Separate limit by Opaque node in case it is an incremented
1261           // variable from previous loop to avoid using pre-incremented
1262           // value which could increase register pressure.
1263           // Otherwise reorg_offsets() optimization will create a separate
1264           // Opaque node for each use of trip-counter and as result
1265           // zero trip guard limit will be different from loop limit.
1266           assert(has_ctrl(opaq), "should have it");
1267           Node* opaq_ctrl = get_ctrl(opaq);
1268           limit = new (C) Opaque2Node( C, limit );
1269           register_new_node( limit, opaq_ctrl );
1270         }
1271         if (stride_con > 0 && ((limit_type->_lo - stride_con) < limit_type->_lo) ||
1272                    stride_con < 0 && ((limit_type->_hi - stride_con) > limit_type->_hi)) {
1273           // No underflow.
1274           new_limit = new (C) SubINode(limit, stride);
1275         } else {
1276           // (limit - stride) may underflow.
1277           // Clamp the adjustment value with MININT or MAXINT:
1278           //
1279           //   new_limit = limit-stride
1280           //   if (stride > 0)
1281           //     new_limit = (limit < new_limit) ? MININT : new_limit;
1282           //   else
1283           //     new_limit = (limit > new_limit) ? MAXINT : new_limit;
1284           //
1285           BoolTest::mask bt = loop_end->test_trip();
1286           assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
1287           Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint);
1288           set_ctrl(adj_max, C->root());
1289           Node* old_limit = NULL;
1290           Node* adj_limit = NULL;
1291           Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL;
1292           if (loop_head->unrolled_count() > 1 &&
1293               limit->is_CMove() && limit->Opcode() == Op_CMoveI &&
1294               limit->in(CMoveNode::IfTrue) == adj_max &&
1295               bol->as_Bool()->_test._test == bt &&
1296               bol->in(1)->Opcode() == Op_CmpI &&
1297               bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) {
1298             // Loop was unrolled before.
1299             // Optimize the limit to avoid nested CMove:
1300             // use original limit as old limit.
1301             old_limit = bol->in(1)->in(1);
1302             // Adjust previous adjusted limit.
1303             adj_limit = limit->in(CMoveNode::IfFalse);
1304             adj_limit = new (C) SubINode(adj_limit, stride);
1305           } else {
1306             old_limit = limit;
1307             adj_limit = new (C) SubINode(limit, stride);
1308           }
1309           assert(old_limit != NULL && adj_limit != NULL, "");
1310           register_new_node( adj_limit, ctrl ); // adjust amount
1311           Node* adj_cmp = new (C) CmpINode(old_limit, adj_limit);
1312           register_new_node( adj_cmp, ctrl );
1313           Node* adj_bool = new (C) BoolNode(adj_cmp, bt);
1314           register_new_node( adj_bool, ctrl );
1315           new_limit = new (C) CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT);
1316         }
1317         register_new_node(new_limit, ctrl);
1318       }
1319       assert(new_limit != NULL, "");
1320       // Replace in loop test.
1321       assert(loop_end->in(1)->in(1) == cmp, "sanity");
1322       if (cmp->outcnt() == 1 && loop_end->in(1)->outcnt() == 1) {
1323         // Don't need to create new test since only one user.
1324         _igvn.hash_delete(cmp);
1325         cmp->set_req(2, new_limit);
1326       } else {
1327         // Create new test since it is shared.
1328         Node* ctrl2 = loop_end->in(0);
1329         Node* cmp2  = cmp->clone();
1330         cmp2->set_req(2, new_limit);
1331         register_new_node(cmp2, ctrl2);
1332         Node* bol2 = loop_end->in(1)->clone();
1333         bol2->set_req(1, cmp2);
1334         register_new_node(bol2, ctrl2);
1335         _igvn.hash_delete(loop_end);
1336         loop_end->set_req(1, bol2);
1337       }
1338       // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1339       // Make it a 1-trip test (means at least 2 trips).
1340 
1341       // Guard test uses an 'opaque' node which is not shared.  Hence I
1342       // can edit it's inputs directly.  Hammer in the new limit for the
1343       // minimum-trip guard.
1344       assert(opaq->outcnt() == 1, "");
1345       _igvn.hash_delete(opaq);
1346       opaq->set_req(1, new_limit);
1347     }
1348 
1349     // Adjust max trip count. The trip count is intentionally rounded
1350     // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1351     // the main, unrolled, part of the loop will never execute as it is protected
1352     // by the min-trip test.  See bug 4834191 for a case where we over-unrolled
1353     // and later determined that part of the unrolled loop was dead.
1354     loop_head->set_trip_count(old_trip_count / 2);
1355 
1356     // Double the count of original iterations in the unrolled loop body.
1357     loop_head->double_unrolled_count();
1358 
1359   } else { // LoopLimitCheck
1360 
1361     // Adjust max trip count. The trip count is intentionally rounded
1362     // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1363     // the main, unrolled, part of the loop will never execute as it is protected
1364     // by the min-trip test.  See bug 4834191 for a case where we over-unrolled
1365     // and later determined that part of the unrolled loop was dead.
1366     loop_head->set_trip_count(loop_head->trip_count() / 2);
1367 
1368     // Double the count of original iterations in the unrolled loop body.
1369     loop_head->double_unrolled_count();
1370 
1371     // -----------
1372     // Step 2: Cut back the trip counter for an unroll amount of 2.
1373     // Loop will normally trip (limit - init)/stride_con.  Since it's a
1374     // CountedLoop this is exact (stride divides limit-init exactly).
1375     // We are going to double the loop body, so we want to knock off any
1376     // odd iteration: (trip_cnt & ~1).  Then back compute a new limit.
1377     Node *span = new (C) SubINode( limit, init );
1378     register_new_node( span, ctrl );
1379     Node *trip = new (C) DivINode( 0, span, stride );
1380     register_new_node( trip, ctrl );
1381     Node *mtwo = _igvn.intcon(-2);
1382     set_ctrl(mtwo, C->root());
1383     Node *rond = new (C) AndINode( trip, mtwo );
1384     register_new_node( rond, ctrl );
1385     Node *spn2 = new (C) MulINode( rond, stride );
1386     register_new_node( spn2, ctrl );
1387     new_limit = new (C) AddINode( spn2, init );
1388     register_new_node( new_limit, ctrl );
1389 
1390     // Hammer in the new limit
1391     Node *ctrl2 = loop_end->in(0);
1392     Node *cmp2 = new (C) CmpINode( loop_head->incr(), new_limit );
1393     register_new_node( cmp2, ctrl2 );
1394     Node *bol2 = new (C) BoolNode( cmp2, loop_end->test_trip() );
1395     register_new_node( bol2, ctrl2 );
1396     _igvn.hash_delete(loop_end);
1397     loop_end->set_req(CountedLoopEndNode::TestValue, bol2);
1398 
1399     // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1400     // Make it a 1-trip test (means at least 2 trips).
1401     if( adjust_min_trip ) {
1402       assert( new_limit != NULL, "" );
1403       // Guard test uses an 'opaque' node which is not shared.  Hence I
1404       // can edit it's inputs directly.  Hammer in the new limit for the
1405       // minimum-trip guard.
1406       assert( opaq->outcnt() == 1, "" );
1407       _igvn.hash_delete(opaq);
1408       opaq->set_req(1, new_limit);
1409     }
1410   } // LoopLimitCheck
1411 
1412   // ---------
1413   // Step 4: Clone the loop body.  Move it inside the loop.  This loop body
1414   // represents the odd iterations; since the loop trips an even number of
1415   // times its backedge is never taken.  Kill the backedge.
1416   uint dd = dom_depth(loop_head);
1417   clone_loop( loop, old_new, dd );
1418 
1419   // Make backedges of the clone equal to backedges of the original.
1420   // Make the fall-in from the original come from the fall-out of the clone.
1421   for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
1422     Node* phi = loop_head->fast_out(j);
1423     if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
1424       Node *newphi = old_new[phi->_idx];
1425       _igvn.hash_delete( phi );
1426       _igvn.hash_delete( newphi );
1427 
1428       phi   ->set_req(LoopNode::   EntryControl, newphi->in(LoopNode::LoopBackControl));
1429       newphi->set_req(LoopNode::LoopBackControl, phi   ->in(LoopNode::LoopBackControl));
1430       phi   ->set_req(LoopNode::LoopBackControl, C->top());
1431     }
1432   }
1433   Node *clone_head = old_new[loop_head->_idx];
1434   _igvn.hash_delete( clone_head );
1435   loop_head ->set_req(LoopNode::   EntryControl, clone_head->in(LoopNode::LoopBackControl));
1436   clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
1437   loop_head ->set_req(LoopNode::LoopBackControl, C->top());
1438   loop->_head = clone_head;     // New loop header
1439 
1440   set_idom(loop_head,  loop_head ->in(LoopNode::EntryControl), dd);
1441   set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
1442 
1443   // Kill the clone's backedge
1444   Node *newcle = old_new[loop_end->_idx];
1445   _igvn.hash_delete( newcle );
1446   Node *one = _igvn.intcon(1);
1447   set_ctrl(one, C->root());
1448   newcle->set_req(1, one);
1449   // Force clone into same loop body
1450   uint max = loop->_body.size();
1451   for( uint k = 0; k < max; k++ ) {
1452     Node *old = loop->_body.at(k);
1453     Node *nnn = old_new[old->_idx];
1454     loop->_body.push(nnn);
1455     if (!has_ctrl(old))
1456       set_loop(nnn, loop);
1457   }
1458 
1459   loop->record_for_igvn();
1460 }
1461 
1462 //------------------------------do_maximally_unroll----------------------------
1463 
1464 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
1465   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1466   assert(cl->has_exact_trip_count(), "trip count is not exact");
1467   assert(cl->trip_count() > 0, "");
1468 #ifndef PRODUCT
1469   if (TraceLoopOpts) {
1470     tty->print("MaxUnroll  %d ", cl->trip_count());
1471     loop->dump_head();
1472   }
1473 #endif
1474 
1475   // If loop is tripping an odd number of times, peel odd iteration
1476   if ((cl->trip_count() & 1) == 1) {
1477     do_peeling(loop, old_new);
1478   }
1479 
1480   // Now its tripping an even number of times remaining.  Double loop body.
1481   // Do not adjust pre-guards; they are not needed and do not exist.
1482   if (cl->trip_count() > 0) {
1483     assert((cl->trip_count() & 1) == 0, "missed peeling");
1484     do_unroll(loop, old_new, false);
1485   }
1486 }
1487 
1488 //------------------------------dominates_backedge---------------------------------
1489 // Returns true if ctrl is executed on every complete iteration
1490 bool IdealLoopTree::dominates_backedge(Node* ctrl) {
1491   assert(ctrl->is_CFG(), "must be control");
1492   Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl);
1493   return _phase->dom_lca_internal(ctrl, backedge) == ctrl;
1494 }
1495 
1496 //------------------------------adjust_limit-----------------------------------
1497 // Helper function for add_constraint().
1498 Node* PhaseIdealLoop::adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl) {
1499   // Compute "I :: (limit-offset)/scale"
1500   Node *con = new (C) SubINode(rc_limit, offset);
1501   register_new_node(con, pre_ctrl);
1502   Node *X = new (C) DivINode(0, con, scale);
1503   register_new_node(X, pre_ctrl);
1504 
1505   // Adjust loop limit
1506   loop_limit = (stride_con > 0)
1507                ? (Node*)(new (C) MinINode(loop_limit, X))
1508                : (Node*)(new (C) MaxINode(loop_limit, X));
1509   register_new_node(loop_limit, pre_ctrl);
1510   return loop_limit;
1511 }
1512 
1513 //------------------------------add_constraint---------------------------------
1514 // Constrain the main loop iterations so the conditions:
1515 //    low_limit <= scale_con * I + offset  <  upper_limit
1516 // always holds true.  That is, either increase the number of iterations in
1517 // the pre-loop or the post-loop until the condition holds true in the main
1518 // loop.  Stride, scale, offset and limit are all loop invariant.  Further,
1519 // stride and scale are constants (offset and limit often are).
1520 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 ) {
1521   // For positive stride, the pre-loop limit always uses a MAX function
1522   // and the main loop a MIN function.  For negative stride these are
1523   // reversed.
1524 
1525   // Also for positive stride*scale the affine function is increasing, so the
1526   // pre-loop must check for underflow and the post-loop for overflow.
1527   // Negative stride*scale reverses this; pre-loop checks for overflow and
1528   // post-loop for underflow.
1529 
1530   Node *scale = _igvn.intcon(scale_con);
1531   set_ctrl(scale, C->root());
1532 
1533   if ((stride_con^scale_con) >= 0) { // Use XOR to avoid overflow
1534     // The overflow limit: scale*I+offset < upper_limit
1535     // For main-loop compute
1536     //   ( if (scale > 0) /* and stride > 0 */
1537     //       I < (upper_limit-offset)/scale
1538     //     else /* scale < 0 and stride < 0 */
1539     //       I > (upper_limit-offset)/scale
1540     //   )
1541     //
1542     // (upper_limit-offset) may overflow or underflow.
1543     // But it is fine since main loop will either have
1544     // less iterations or will be skipped in such case.
1545     *main_limit = adjust_limit(stride_con, scale, offset, upper_limit, *main_limit, pre_ctrl);
1546 
1547     // The underflow limit: low_limit <= scale*I+offset.
1548     // For pre-loop compute
1549     //   NOT(scale*I+offset >= low_limit)
1550     //   scale*I+offset < low_limit
1551     //   ( if (scale > 0) /* and stride > 0 */
1552     //       I < (low_limit-offset)/scale
1553     //     else /* scale < 0 and stride < 0 */
1554     //       I > (low_limit-offset)/scale
1555     //   )
1556 
1557     if (low_limit->get_int() == -max_jint) {
1558       if (!RangeLimitCheck) return;
1559       // We need this guard when scale*pre_limit+offset >= limit
1560       // due to underflow. So we need execute pre-loop until
1561       // scale*I+offset >= min_int. But (min_int-offset) will
1562       // underflow when offset > 0 and X will be > original_limit
1563       // when stride > 0. To avoid it we replace positive offset with 0.
1564       //
1565       // Also (min_int+1 == -max_int) is used instead of min_int here
1566       // to avoid problem with scale == -1 (min_int/(-1) == min_int).
1567       Node* shift = _igvn.intcon(31);
1568       set_ctrl(shift, C->root());
1569       Node* sign = new (C) RShiftINode(offset, shift);
1570       register_new_node(sign, pre_ctrl);
1571       offset = new (C) AndINode(offset, sign);
1572       register_new_node(offset, pre_ctrl);
1573     } else {
1574       assert(low_limit->get_int() == 0, "wrong low limit for range check");
1575       // The only problem we have here when offset == min_int
1576       // since (0-min_int) == min_int. It may be fine for stride > 0
1577       // but for stride < 0 X will be < original_limit. To avoid it
1578       // max(pre_limit, original_limit) is used in do_range_check().
1579     }
1580     // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
1581     *pre_limit = adjust_limit((-stride_con), scale, offset, low_limit, *pre_limit, pre_ctrl);
1582 
1583   } else { // stride_con*scale_con < 0
1584     // For negative stride*scale pre-loop checks for overflow and
1585     // post-loop for underflow.
1586     //
1587     // The overflow limit: scale*I+offset < upper_limit
1588     // For pre-loop compute
1589     //   NOT(scale*I+offset < upper_limit)
1590     //   scale*I+offset >= upper_limit
1591     //   scale*I+offset+1 > upper_limit
1592     //   ( if (scale < 0) /* and stride > 0 */
1593     //       I < (upper_limit-(offset+1))/scale
1594     //     else /* scale > 0 and stride < 0 */
1595     //       I > (upper_limit-(offset+1))/scale
1596     //   )
1597     //
1598     // (upper_limit-offset-1) may underflow or overflow.
1599     // To avoid it min(pre_limit, original_limit) is used
1600     // in do_range_check() for stride > 0 and max() for < 0.
1601     Node *one  = _igvn.intcon(1);
1602     set_ctrl(one, C->root());
1603 
1604     Node *plus_one = new (C) AddINode(offset, one);
1605     register_new_node( plus_one, pre_ctrl );
1606     // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);
1607     *pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl);
1608 
1609     if (low_limit->get_int() == -max_jint) {
1610       if (!RangeLimitCheck) return;
1611       // We need this guard when scale*main_limit+offset >= limit
1612       // due to underflow. So we need execute main-loop while
1613       // scale*I+offset+1 > min_int. But (min_int-offset-1) will
1614       // underflow when (offset+1) > 0 and X will be < main_limit
1615       // when scale < 0 (and stride > 0). To avoid it we replace
1616       // positive (offset+1) with 0.
1617       //
1618       // Also (min_int+1 == -max_int) is used instead of min_int here
1619       // to avoid problem with scale == -1 (min_int/(-1) == min_int).
1620       Node* shift = _igvn.intcon(31);
1621       set_ctrl(shift, C->root());
1622       Node* sign = new (C) RShiftINode(plus_one, shift);
1623       register_new_node(sign, pre_ctrl);
1624       plus_one = new (C) AndINode(plus_one, sign);
1625       register_new_node(plus_one, pre_ctrl);
1626     } else {
1627       assert(low_limit->get_int() == 0, "wrong low limit for range check");
1628       // The only problem we have here when offset == max_int
1629       // since (max_int+1) == min_int and (0-min_int) == min_int.
1630       // But it is fine since main loop will either have
1631       // less iterations or will be skipped in such case.
1632     }
1633     // The underflow limit: low_limit <= scale*I+offset.
1634     // For main-loop compute
1635     //   scale*I+offset+1 > low_limit
1636     //   ( if (scale < 0) /* and stride > 0 */
1637     //       I < (low_limit-(offset+1))/scale
1638     //     else /* scale > 0 and stride < 0 */
1639     //       I > (low_limit-(offset+1))/scale
1640     //   )
1641 
1642     *main_limit = adjust_limit(stride_con, scale, plus_one, low_limit, *main_limit, pre_ctrl);
1643   }
1644 }
1645 
1646 
1647 //------------------------------is_scaled_iv---------------------------------
1648 // Return true if exp is a constant times an induction var
1649 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
1650   if (exp == iv) {
1651     if (p_scale != NULL) {
1652       *p_scale = 1;
1653     }
1654     return true;
1655   }
1656   int opc = exp->Opcode();
1657   if (opc == Op_MulI) {
1658     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1659       if (p_scale != NULL) {
1660         *p_scale = exp->in(2)->get_int();
1661       }
1662       return true;
1663     }
1664     if (exp->in(2) == iv && exp->in(1)->is_Con()) {
1665       if (p_scale != NULL) {
1666         *p_scale = exp->in(1)->get_int();
1667       }
1668       return true;
1669     }
1670   } else if (opc == Op_LShiftI) {
1671     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1672       if (p_scale != NULL) {
1673         *p_scale = 1 << exp->in(2)->get_int();
1674       }
1675       return true;
1676     }
1677   }
1678   return false;
1679 }
1680 
1681 //-----------------------------is_scaled_iv_plus_offset------------------------------
1682 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
1683 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
1684   if (is_scaled_iv(exp, iv, p_scale)) {
1685     if (p_offset != NULL) {
1686       Node *zero = _igvn.intcon(0);
1687       set_ctrl(zero, C->root());
1688       *p_offset = zero;
1689     }
1690     return true;
1691   }
1692   int opc = exp->Opcode();
1693   if (opc == Op_AddI) {
1694     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1695       if (p_offset != NULL) {
1696         *p_offset = exp->in(2);
1697       }
1698       return true;
1699     }
1700     if (exp->in(2)->is_Con()) {
1701       Node* offset2 = NULL;
1702       if (depth < 2 &&
1703           is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
1704                                    p_offset != NULL ? &offset2 : NULL, depth+1)) {
1705         if (p_offset != NULL) {
1706           Node *ctrl_off2 = get_ctrl(offset2);
1707           Node* offset = new (C) AddINode(offset2, exp->in(2));
1708           register_new_node(offset, ctrl_off2);
1709           *p_offset = offset;
1710         }
1711         return true;
1712       }
1713     }
1714   } else if (opc == Op_SubI) {
1715     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1716       if (p_offset != NULL) {
1717         Node *zero = _igvn.intcon(0);
1718         set_ctrl(zero, C->root());
1719         Node *ctrl_off = get_ctrl(exp->in(2));
1720         Node* offset = new (C) SubINode(zero, exp->in(2));
1721         register_new_node(offset, ctrl_off);
1722         *p_offset = offset;
1723       }
1724       return true;
1725     }
1726     if (is_scaled_iv(exp->in(2), iv, p_scale)) {
1727       if (p_offset != NULL) {
1728         *p_scale *= -1;
1729         *p_offset = exp->in(1);
1730       }
1731       return true;
1732     }
1733   }
1734   return false;
1735 }
1736 
1737 //------------------------------do_range_check---------------------------------
1738 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
1739 void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
1740 #ifndef PRODUCT
1741   if (PrintOpto && VerifyLoopOptimizations) {
1742     tty->print("Range Check Elimination ");
1743     loop->dump_head();
1744   } else if (TraceLoopOpts) {
1745     tty->print("RangeCheck   ");
1746     loop->dump_head();
1747   }
1748 #endif
1749   assert(RangeCheckElimination, "");
1750   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1751   assert(cl->is_main_loop(), "");
1752 
1753   // protect against stride not being a constant
1754   if (!cl->stride_is_con())
1755     return;
1756 
1757   // Find the trip counter; we are iteration splitting based on it
1758   Node *trip_counter = cl->phi();
1759   // Find the main loop limit; we will trim it's iterations
1760   // to not ever trip end tests
1761   Node *main_limit = cl->limit();
1762 
1763   // Need to find the main-loop zero-trip guard
1764   Node *ctrl  = cl->in(LoopNode::EntryControl);
1765   assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
1766   Node *iffm = ctrl->in(0);
1767   assert(iffm->Opcode() == Op_If, "");
1768   Node *bolzm = iffm->in(1);
1769   assert(bolzm->Opcode() == Op_Bool, "");
1770   Node *cmpzm = bolzm->in(1);
1771   assert(cmpzm->is_Cmp(), "");
1772   Node *opqzm = cmpzm->in(2);
1773   // Can not optimize a loop if zero-trip Opaque1 node is optimized
1774   // away and then another round of loop opts attempted.
1775   if (opqzm->Opcode() != Op_Opaque1)
1776     return;
1777   assert(opqzm->in(1) == main_limit, "do not understand situation");
1778 
1779   // Find the pre-loop limit; we will expand it's iterations to
1780   // not ever trip low tests.
1781   Node *p_f = iffm->in(0);
1782   assert(p_f->Opcode() == Op_IfFalse, "");
1783   CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
1784   assert(pre_end->loopnode()->is_pre_loop(), "");
1785   Node *pre_opaq1 = pre_end->limit();
1786   // Occasionally it's possible for a pre-loop Opaque1 node to be
1787   // optimized away and then another round of loop opts attempted.
1788   // We can not optimize this particular loop in that case.
1789   if (pre_opaq1->Opcode() != Op_Opaque1)
1790     return;
1791   Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
1792   Node *pre_limit = pre_opaq->in(1);
1793 
1794   // Where do we put new limit calculations
1795   Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
1796 
1797   // Ensure the original loop limit is available from the
1798   // pre-loop Opaque1 node.
1799   Node *orig_limit = pre_opaq->original_loop_limit();
1800   if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP)
1801     return;
1802 
1803   // Must know if its a count-up or count-down loop
1804 
1805   int stride_con = cl->stride_con();
1806   Node *zero = _igvn.intcon(0);
1807   Node *one  = _igvn.intcon(1);
1808   // Use symmetrical int range [-max_jint,max_jint]
1809   Node *mini = _igvn.intcon(-max_jint);
1810   set_ctrl(zero, C->root());
1811   set_ctrl(one,  C->root());
1812   set_ctrl(mini, C->root());
1813 
1814   // Range checks that do not dominate the loop backedge (ie.
1815   // conditionally executed) can lengthen the pre loop limit beyond
1816   // the original loop limit. To prevent this, the pre limit is
1817   // (for stride > 0) MINed with the original loop limit (MAXed
1818   // stride < 0) when some range_check (rc) is conditionally
1819   // executed.
1820   bool conditional_rc = false;
1821 
1822   // Check loop body for tests of trip-counter plus loop-invariant vs
1823   // loop-invariant.
1824   for( uint i = 0; i < loop->_body.size(); i++ ) {
1825     Node *iff = loop->_body[i];
1826     if( iff->Opcode() == Op_If ) { // Test?
1827 
1828       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
1829       // we need loop unswitching instead of iteration splitting.
1830       Node *exit = loop->is_loop_exit(iff);
1831       if( !exit ) continue;
1832       int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
1833 
1834       // Get boolean condition to test
1835       Node *i1 = iff->in(1);
1836       if( !i1->is_Bool() ) continue;
1837       BoolNode *bol = i1->as_Bool();
1838       BoolTest b_test = bol->_test;
1839       // Flip sense of test if exit condition is flipped
1840       if( flip )
1841         b_test = b_test.negate();
1842 
1843       // Get compare
1844       Node *cmp = bol->in(1);
1845 
1846       // Look for trip_counter + offset vs limit
1847       Node *rc_exp = cmp->in(1);
1848       Node *limit  = cmp->in(2);
1849       jint scale_con= 1;        // Assume trip counter not scaled
1850 
1851       Node *limit_c = get_ctrl(limit);
1852       if( loop->is_member(get_loop(limit_c) ) ) {
1853         // Compare might have operands swapped; commute them
1854         b_test = b_test.commute();
1855         rc_exp = cmp->in(2);
1856         limit  = cmp->in(1);
1857         limit_c = get_ctrl(limit);
1858         if( loop->is_member(get_loop(limit_c) ) )
1859           continue;             // Both inputs are loop varying; cannot RCE
1860       }
1861       // Here we know 'limit' is loop invariant
1862 
1863       // 'limit' maybe pinned below the zero trip test (probably from a
1864       // previous round of rce), in which case, it can't be used in the
1865       // zero trip test expression which must occur before the zero test's if.
1866       if( limit_c == ctrl ) {
1867         continue;  // Don't rce this check but continue looking for other candidates.
1868       }
1869 
1870       // Check for scaled induction variable plus an offset
1871       Node *offset = NULL;
1872 
1873       if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
1874         continue;
1875       }
1876 
1877       Node *offset_c = get_ctrl(offset);
1878       if( loop->is_member( get_loop(offset_c) ) )
1879         continue;               // Offset is not really loop invariant
1880       // Here we know 'offset' is loop invariant.
1881 
1882       // As above for the 'limit', the 'offset' maybe pinned below the
1883       // zero trip test.
1884       if( offset_c == ctrl ) {
1885         continue; // Don't rce this check but continue looking for other candidates.
1886       }
1887 #ifdef ASSERT
1888       if (TraceRangeLimitCheck) {
1889         tty->print_cr("RC bool node%s", flip ? " flipped:" : ":");
1890         bol->dump(2);
1891       }
1892 #endif
1893       // At this point we have the expression as:
1894       //   scale_con * trip_counter + offset :: limit
1895       // where scale_con, offset and limit are loop invariant.  Trip_counter
1896       // monotonically increases by stride_con, a constant.  Both (or either)
1897       // stride_con and scale_con can be negative which will flip about the
1898       // sense of the test.
1899 
1900       // Adjust pre and main loop limits to guard the correct iteration set
1901       if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
1902         if( b_test._test == BoolTest::lt ) { // Range checks always use lt
1903           // The underflow and overflow limits: 0 <= scale*I+offset < limit
1904           add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );
1905           if (!conditional_rc) {
1906             // (0-offset)/scale could be outside of loop iterations range.
1907             conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;
1908           }
1909         } else {
1910 #ifndef PRODUCT
1911           if( PrintOpto )
1912             tty->print_cr("missed RCE opportunity");
1913 #endif
1914           continue;             // In release mode, ignore it
1915         }
1916       } else {                  // Otherwise work on normal compares
1917         switch( b_test._test ) {
1918         case BoolTest::gt:
1919           // Fall into GE case
1920         case BoolTest::ge:
1921           // Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit
1922           scale_con = -scale_con;
1923           offset = new (C) SubINode( zero, offset );
1924           register_new_node( offset, pre_ctrl );
1925           limit  = new (C) SubINode( zero, limit  );
1926           register_new_node( limit, pre_ctrl );
1927           // Fall into LE case
1928         case BoolTest::le:
1929           if (b_test._test != BoolTest::gt) {
1930             // Convert X <= Y to X < Y+1
1931             limit = new (C) AddINode( limit, one );
1932             register_new_node( limit, pre_ctrl );
1933           }
1934           // Fall into LT case
1935         case BoolTest::lt:
1936           // The underflow and overflow limits: MIN_INT <= scale*I+offset < limit
1937           // Note: (MIN_INT+1 == -MAX_INT) is used instead of MIN_INT here
1938           // to avoid problem with scale == -1: MIN_INT/(-1) == MIN_INT.
1939           add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit );
1940           if (!conditional_rc) {
1941             // ((MIN_INT+1)-offset)/scale could be outside of loop iterations range.
1942             // Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could
1943             // still be outside of loop range.
1944             conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;
1945           }
1946           break;
1947         default:
1948 #ifndef PRODUCT
1949           if( PrintOpto )
1950             tty->print_cr("missed RCE opportunity");
1951 #endif
1952           continue;             // Unhandled case
1953         }
1954       }
1955 
1956       // Kill the eliminated test
1957       C->set_major_progress();
1958       Node *kill_con = _igvn.intcon( 1-flip );
1959       set_ctrl(kill_con, C->root());
1960       _igvn.replace_input_of(iff, 1, kill_con);
1961       // Find surviving projection
1962       assert(iff->is_If(), "");
1963       ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
1964       // Find loads off the surviving projection; remove their control edge
1965       for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
1966         Node* cd = dp->fast_out(i); // Control-dependent node
1967         if (cd->is_Load() && cd->depends_only_on_test()) {   // Loads can now float around in the loop
1968           // Allow the load to float around in the loop, or before it
1969           // but NOT before the pre-loop.
1970           _igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL
1971           --i;
1972           --imax;
1973         }
1974       }
1975 
1976     } // End of is IF
1977 
1978   }
1979 
1980   // Update loop limits
1981   if (conditional_rc) {
1982     pre_limit = (stride_con > 0) ? (Node*)new (C) MinINode(pre_limit, orig_limit)
1983                                  : (Node*)new (C) MaxINode(pre_limit, orig_limit);
1984     register_new_node(pre_limit, pre_ctrl);
1985   }
1986   _igvn.hash_delete(pre_opaq);
1987   pre_opaq->set_req(1, pre_limit);
1988 
1989   // Note:: we are making the main loop limit no longer precise;
1990   // need to round up based on stride.
1991   cl->set_nonexact_trip_count();
1992   if (!LoopLimitCheck && stride_con != 1 && stride_con != -1) { // Cutout for common case
1993     // "Standard" round-up logic:  ([main_limit-init+(y-1)]/y)*y+init
1994     // Hopefully, compiler will optimize for powers of 2.
1995     Node *ctrl = get_ctrl(main_limit);
1996     Node *stride = cl->stride();
1997     Node *init = cl->init_trip();
1998     Node *span = new (C) SubINode(main_limit,init);
1999     register_new_node(span,ctrl);
2000     Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));
2001     Node *add = new (C) AddINode(span,rndup);
2002     register_new_node(add,ctrl);
2003     Node *div = new (C) DivINode(0,add,stride);
2004     register_new_node(div,ctrl);
2005     Node *mul = new (C) MulINode(div,stride);
2006     register_new_node(mul,ctrl);
2007     Node *newlim = new (C) AddINode(mul,init);
2008     register_new_node(newlim,ctrl);
2009     main_limit = newlim;
2010   }
2011 
2012   Node *main_cle = cl->loopexit();
2013   Node *main_bol = main_cle->in(1);
2014   // Hacking loop bounds; need private copies of exit test
2015   if( main_bol->outcnt() > 1 ) {// BoolNode shared?
2016     _igvn.hash_delete(main_cle);
2017     main_bol = main_bol->clone();// Clone a private BoolNode
2018     register_new_node( main_bol, main_cle->in(0) );
2019     main_cle->set_req(1,main_bol);
2020   }
2021   Node *main_cmp = main_bol->in(1);
2022   if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
2023     _igvn.hash_delete(main_bol);
2024     main_cmp = main_cmp->clone();// Clone a private CmpNode
2025     register_new_node( main_cmp, main_cle->in(0) );
2026     main_bol->set_req(1,main_cmp);
2027   }
2028   // Hack the now-private loop bounds
2029   _igvn.replace_input_of(main_cmp, 2, main_limit);
2030   // The OpaqueNode is unshared by design
2031   assert( opqzm->outcnt() == 1, "cannot hack shared node" );
2032   _igvn.replace_input_of(opqzm, 1, main_limit);
2033 }
2034 
2035 //------------------------------DCE_loop_body----------------------------------
2036 // Remove simplistic dead code from loop body
2037 void IdealLoopTree::DCE_loop_body() {
2038   for( uint i = 0; i < _body.size(); i++ )
2039     if( _body.at(i)->outcnt() == 0 )
2040       _body.map( i--, _body.pop() );
2041 }
2042 
2043 
2044 //------------------------------adjust_loop_exit_prob--------------------------
2045 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
2046 // Replace with a 1-in-10 exit guess.
2047 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
2048   Node *test = tail();
2049   while( test != _head ) {
2050     uint top = test->Opcode();
2051     if( top == Op_IfTrue || top == Op_IfFalse ) {
2052       int test_con = ((ProjNode*)test)->_con;
2053       assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
2054       IfNode *iff = test->in(0)->as_If();
2055       if( iff->outcnt() == 2 ) {        // Ignore dead tests
2056         Node *bol = iff->in(1);
2057         if( bol && bol->req() > 1 && bol->in(1) &&
2058             ((bol->in(1)->Opcode() == Op_StorePConditional ) ||
2059              (bol->in(1)->Opcode() == Op_StoreIConditional ) ||
2060              (bol->in(1)->Opcode() == Op_StoreLConditional ) ||
2061              (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
2062              (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
2063              (bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||
2064              (bol->in(1)->Opcode() == Op_CompareAndSwapN )))
2065           return;               // Allocation loops RARELY take backedge
2066         // Find the OTHER exit path from the IF
2067         Node* ex = iff->proj_out(1-test_con);
2068         float p = iff->_prob;
2069         if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
2070           if( top == Op_IfTrue ) {
2071             if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
2072               iff->_prob = PROB_STATIC_FREQUENT;
2073             }
2074           } else {
2075             if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
2076               iff->_prob = PROB_STATIC_INFREQUENT;
2077             }
2078           }
2079         }
2080       }
2081     }
2082     test = phase->idom(test);
2083   }
2084 }
2085 
2086 
2087 //------------------------------policy_do_remove_empty_loop--------------------
2088 // Micro-benchmark spamming.  Policy is to always remove empty loops.
2089 // The 'DO' part is to replace the trip counter with the value it will
2090 // have on the last iteration.  This will break the loop.
2091 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
2092   // Minimum size must be empty loop
2093   if (_body.size() > EMPTY_LOOP_SIZE)
2094     return false;
2095 
2096   if (!_head->is_CountedLoop())
2097     return false;     // Dead loop
2098   CountedLoopNode *cl = _head->as_CountedLoop();
2099   if (!cl->is_valid_counted_loop())
2100     return false; // Malformed loop
2101   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
2102     return false;             // Infinite loop
2103 
2104 #ifdef ASSERT
2105   // Ensure only one phi which is the iv.
2106   Node* iv = NULL;
2107   for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
2108     Node* n = cl->fast_out(i);
2109     if (n->Opcode() == Op_Phi) {
2110       assert(iv == NULL, "Too many phis" );
2111       iv = n;
2112     }
2113   }
2114   assert(iv == cl->phi(), "Wrong phi" );
2115 #endif
2116 
2117   // main and post loops have explicitly created zero trip guard
2118   bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
2119   if (needs_guard) {
2120     // Skip guard if values not overlap.
2121     const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int();
2122     const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int();
2123     int  stride_con = cl->stride_con();
2124     if (stride_con > 0) {
2125       needs_guard = (init_t->_hi >= limit_t->_lo);
2126     } else {
2127       needs_guard = (init_t->_lo <= limit_t->_hi);
2128     }
2129   }
2130   if (needs_guard) {
2131     // Check for an obvious zero trip guard.
2132     Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));
2133     if (inctrl->Opcode() == Op_IfTrue) {
2134       // The test should look like just the backedge of a CountedLoop
2135       Node* iff = inctrl->in(0);
2136       if (iff->is_If()) {
2137         Node* bol = iff->in(1);
2138         if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) {
2139           Node* cmp = bol->in(1);
2140           if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) {
2141             needs_guard = false;
2142           }
2143         }
2144       }
2145     }
2146   }
2147 
2148 #ifndef PRODUCT
2149   if (PrintOpto) {
2150     tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
2151     this->dump_head();
2152   } else if (TraceLoopOpts) {
2153     tty->print("Empty with%s zero trip guard   ", needs_guard ? "out" : "");
2154     this->dump_head();
2155   }
2156 #endif
2157 
2158   if (needs_guard) {
2159     // Peel the loop to ensure there's a zero trip guard
2160     Node_List old_new;
2161     phase->do_peeling(this, old_new);
2162   }
2163 
2164   // Replace the phi at loop head with the final value of the last
2165   // iteration.  Then the CountedLoopEnd will collapse (backedge never
2166   // taken) and all loop-invariant uses of the exit values will be correct.
2167   Node *phi = cl->phi();
2168   Node *exact_limit = phase->exact_limit(this);
2169   if (exact_limit != cl->limit()) {
2170     // We also need to replace the original limit to collapse loop exit.
2171     Node* cmp = cl->loopexit()->cmp_node();
2172     assert(cl->limit() == cmp->in(2), "sanity");
2173     phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist
2174     phase->_igvn.replace_input_of(cmp, 2, exact_limit); // put cmp on worklist
2175   }
2176   // Note: the final value after increment should not overflow since
2177   // counted loop has limit check predicate.
2178   Node *final = new (phase->C) SubINode( exact_limit, cl->stride() );
2179   phase->register_new_node(final,cl->in(LoopNode::EntryControl));
2180   phase->_igvn.replace_node(phi,final);
2181   phase->C->set_major_progress();
2182   return true;
2183 }
2184 
2185 //------------------------------policy_do_one_iteration_loop-------------------
2186 // Convert one iteration loop into normal code.
2187 bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) {
2188   if (!_head->as_Loop()->is_valid_counted_loop())
2189     return false; // Only for counted loop
2190 
2191   CountedLoopNode *cl = _head->as_CountedLoop();
2192   if (!cl->has_exact_trip_count() || cl->trip_count() != 1) {
2193     return false;
2194   }
2195 
2196 #ifndef PRODUCT
2197   if(TraceLoopOpts) {
2198     tty->print("OneIteration ");
2199     this->dump_head();
2200   }
2201 #endif
2202 
2203   Node *init_n = cl->init_trip();
2204 #ifdef ASSERT
2205   // Loop boundaries should be constant since trip count is exact.
2206   assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration");
2207 #endif
2208   // Replace the phi at loop head with the value of the init_trip.
2209   // Then the CountedLoopEnd will collapse (backedge will not be taken)
2210   // and all loop-invariant uses of the exit values will be correct.
2211   phase->_igvn.replace_node(cl->phi(), cl->init_trip());
2212   phase->C->set_major_progress();
2213   return true;
2214 }
2215 
2216 //=============================================================================
2217 //------------------------------iteration_split_impl---------------------------
2218 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
2219   // Compute exact loop trip count if possible.
2220   compute_exact_trip_count(phase);
2221 
2222   // Convert one iteration loop into normal code.
2223   if (policy_do_one_iteration_loop(phase))
2224     return true;
2225 
2226   // Check and remove empty loops (spam micro-benchmarks)
2227   if (policy_do_remove_empty_loop(phase))
2228     return true;  // Here we removed an empty loop
2229 
2230   bool should_peel = policy_peeling(phase); // Should we peel?
2231 
2232   bool should_unswitch = policy_unswitching(phase);
2233 
2234   // Non-counted loops may be peeled; exactly 1 iteration is peeled.
2235   // This removes loop-invariant tests (usually null checks).
2236   if (!_head->is_CountedLoop()) { // Non-counted loop
2237     if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
2238       // Partial peel succeeded so terminate this round of loop opts
2239       return false;
2240     }
2241     if (should_peel) {            // Should we peel?
2242 #ifndef PRODUCT
2243       if (PrintOpto) tty->print_cr("should_peel");
2244 #endif
2245       phase->do_peeling(this,old_new);
2246     } else if (should_unswitch) {
2247       phase->do_unswitching(this, old_new);
2248     }
2249     return true;
2250   }
2251   CountedLoopNode *cl = _head->as_CountedLoop();
2252 
2253   if (!cl->is_valid_counted_loop()) return true; // Ignore various kinds of broken loops
2254 
2255   // Do nothing special to pre- and post- loops
2256   if (cl->is_pre_loop() || cl->is_post_loop()) return true;
2257 
2258   // Compute loop trip count from profile data
2259   compute_profile_trip_cnt(phase);
2260 
2261   // Before attempting fancy unrolling, RCE or alignment, see if we want
2262   // to completely unroll this loop or do loop unswitching.
2263   if (cl->is_normal_loop()) {
2264     if (should_unswitch) {
2265       phase->do_unswitching(this, old_new);
2266       return true;
2267     }
2268     bool should_maximally_unroll =  policy_maximally_unroll(phase);
2269     if (should_maximally_unroll) {
2270       // Here we did some unrolling and peeling.  Eventually we will
2271       // completely unroll this loop and it will no longer be a loop.
2272       phase->do_maximally_unroll(this,old_new);
2273       return true;
2274     }
2275   }
2276 
2277   // Skip next optimizations if running low on nodes. Note that
2278   // policy_unswitching and policy_maximally_unroll have this check.
2279   uint nodes_left = MaxNodeLimit - (uint) phase->C->live_nodes();
2280   if ((2 * _body.size()) > nodes_left) {
2281     return true;
2282   }
2283 
2284   // Counted loops may be peeled, may need some iterations run up
2285   // front for RCE, and may want to align loop refs to a cache
2286   // line.  Thus we clone a full loop up front whose trip count is
2287   // at least 1 (if peeling), but may be several more.
2288 
2289   // The main loop will start cache-line aligned with at least 1
2290   // iteration of the unrolled body (zero-trip test required) and
2291   // will have some range checks removed.
2292 
2293   // A post-loop will finish any odd iterations (leftover after
2294   // unrolling), plus any needed for RCE purposes.
2295 
2296   bool should_unroll = policy_unroll(phase);
2297 
2298   bool should_rce = policy_range_check(phase);
2299 
2300   bool should_align = policy_align(phase);
2301 
2302   // If not RCE'ing (iteration splitting) or Aligning, then we do not
2303   // need a pre-loop.  We may still need to peel an initial iteration but
2304   // we will not be needing an unknown number of pre-iterations.
2305   //
2306   // Basically, if may_rce_align reports FALSE first time through,
2307   // we will not be able to later do RCE or Aligning on this loop.
2308   bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
2309 
2310   // If we have any of these conditions (RCE, alignment, unrolling) met, then
2311   // we switch to the pre-/main-/post-loop model.  This model also covers
2312   // peeling.
2313   if (should_rce || should_align || should_unroll) {
2314     if (cl->is_normal_loop())  // Convert to 'pre/main/post' loops
2315       phase->insert_pre_post_loops(this,old_new, !may_rce_align);
2316 
2317     // Adjust the pre- and main-loop limits to let the pre and post loops run
2318     // with full checks, but the main-loop with no checks.  Remove said
2319     // checks from the main body.
2320     if (should_rce)
2321       phase->do_range_check(this,old_new);
2322 
2323     // Double loop body for unrolling.  Adjust the minimum-trip test (will do
2324     // twice as many iterations as before) and the main body limit (only do
2325     // an even number of trips).  If we are peeling, we might enable some RCE
2326     // and we'd rather unroll the post-RCE'd loop SO... do not unroll if
2327     // peeling.
2328     if (should_unroll && !should_peel)
2329       phase->do_unroll(this,old_new, true);
2330 
2331     // Adjust the pre-loop limits to align the main body
2332     // iterations.
2333     if (should_align)
2334       Unimplemented();
2335 
2336   } else {                      // Else we have an unchanged counted loop
2337     if (should_peel)           // Might want to peel but do nothing else
2338       phase->do_peeling(this,old_new);
2339   }
2340   return true;
2341 }
2342 
2343 
2344 //=============================================================================
2345 //------------------------------iteration_split--------------------------------
2346 bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
2347   // Recursively iteration split nested loops
2348   if (_child && !_child->iteration_split(phase, old_new))
2349     return false;
2350 
2351   // Clean out prior deadwood
2352   DCE_loop_body();
2353 
2354 
2355   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
2356   // Replace with a 1-in-10 exit guess.
2357   if (_parent /*not the root loop*/ &&
2358       !_irreducible &&
2359       // Also ignore the occasional dead backedge
2360       !tail()->is_top()) {
2361     adjust_loop_exit_prob(phase);
2362   }
2363 
2364   // Gate unrolling, RCE and peeling efforts.
2365   if (!_child &&                // If not an inner loop, do not split
2366       !_irreducible &&
2367       _allow_optimizations &&
2368       !tail()->is_top()) {     // Also ignore the occasional dead backedge
2369     if (!_has_call) {
2370         if (!iteration_split_impl(phase, old_new)) {
2371           return false;
2372         }
2373     } else if (policy_unswitching(phase)) {
2374       phase->do_unswitching(this, old_new);
2375     }
2376   }
2377 
2378   // Minor offset re-organization to remove loop-fallout uses of
2379   // trip counter when there was no major reshaping.
2380   phase->reorg_offsets(this);
2381 
2382   if (_next && !_next->iteration_split(phase, old_new))
2383     return false;
2384   return true;
2385 }
2386 
2387 
2388 //=============================================================================
2389 // Process all the loops in the loop tree and replace any fill
2390 // patterns with an intrisc version.
2391 bool PhaseIdealLoop::do_intrinsify_fill() {
2392   bool changed = false;
2393   for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2394     IdealLoopTree* lpt = iter.current();
2395     changed |= intrinsify_fill(lpt);
2396   }
2397   return changed;
2398 }
2399 
2400 
2401 // Examine an inner loop looking for a a single store of an invariant
2402 // value in a unit stride loop,
2403 bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
2404                                      Node*& shift, Node*& con) {
2405   const char* msg = NULL;
2406   Node* msg_node = NULL;
2407 
2408   store_value = NULL;
2409   con = NULL;
2410   shift = NULL;
2411 
2412   // Process the loop looking for stores.  If there are multiple
2413   // stores or extra control flow give at this point.
2414   CountedLoopNode* head = lpt->_head->as_CountedLoop();
2415   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2416     Node* n = lpt->_body.at(i);
2417     if (n->outcnt() == 0) continue; // Ignore dead
2418     if (n->is_Store()) {
2419       if (store != NULL) {
2420         msg = "multiple stores";
2421         break;
2422       }
2423       int opc = n->Opcode();
2424       if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreNKlass || opc == Op_StoreCM) {
2425         msg = "oop fills not handled";
2426         break;
2427       }
2428       Node* value = n->in(MemNode::ValueIn);
2429       if (!lpt->is_invariant(value)) {
2430         msg  = "variant store value";
2431       } else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) {
2432         msg = "not array address";
2433       }
2434       store = n;
2435       store_value = value;
2436     } else if (n->is_If() && n != head->loopexit()) {
2437       msg = "extra control flow";
2438       msg_node = n;
2439     }
2440   }
2441 
2442   if (store == NULL) {
2443     // No store in loop
2444     return false;
2445   }
2446 
2447   if (msg == NULL && head->stride_con() != 1) {
2448     // could handle negative strides too
2449     if (head->stride_con() < 0) {
2450       msg = "negative stride";
2451     } else {
2452       msg = "non-unit stride";
2453     }
2454   }
2455 
2456   if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) {
2457     msg = "can't handle store address";
2458     msg_node = store->in(MemNode::Address);
2459   }
2460 
2461   if (msg == NULL &&
2462       (!store->in(MemNode::Memory)->is_Phi() ||
2463        store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) {
2464     msg = "store memory isn't proper phi";
2465     msg_node = store->in(MemNode::Memory);
2466   }
2467 
2468   // Make sure there is an appropriate fill routine
2469   BasicType t = store->as_Mem()->memory_type();
2470   const char* fill_name;
2471   if (msg == NULL &&
2472       StubRoutines::select_fill_function(t, false, fill_name) == NULL) {
2473     msg = "unsupported store";
2474     msg_node = store;
2475   }
2476 
2477   if (msg != NULL) {
2478 #ifndef PRODUCT
2479     if (TraceOptimizeFill) {
2480       tty->print_cr("not fill intrinsic candidate: %s", msg);
2481       if (msg_node != NULL) msg_node->dump();
2482     }
2483 #endif
2484     return false;
2485   }
2486 
2487   // Make sure the address expression can be handled.  It should be
2488   // head->phi * elsize + con.  head->phi might have a ConvI2L.
2489   Node* elements[4];
2490   Node* conv = NULL;
2491   bool found_index = false;
2492   int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements));
2493   for (int e = 0; e < count; e++) {
2494     Node* n = elements[e];
2495     if (n->is_Con() && con == NULL) {
2496       con = n;
2497     } else if (n->Opcode() == Op_LShiftX && shift == NULL) {
2498       Node* value = n->in(1);
2499 #ifdef _LP64
2500       if (value->Opcode() == Op_ConvI2L) {
2501         conv = value;
2502         value = value->in(1);
2503       }
2504 #endif
2505       if (value != head->phi()) {
2506         msg = "unhandled shift in address";
2507       } else {
2508         if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) {
2509           msg = "scale doesn't match";
2510         } else {
2511           found_index = true;
2512           shift = n;
2513         }
2514       }
2515     } else if (n->Opcode() == Op_ConvI2L && conv == NULL) {
2516       if (n->in(1) == head->phi()) {
2517         found_index = true;
2518         conv = n;
2519       } else {
2520         msg = "unhandled input to ConvI2L";
2521       }
2522     } else if (n == head->phi()) {
2523       // no shift, check below for allowed cases
2524       found_index = true;
2525     } else {
2526       msg = "unhandled node in address";
2527       msg_node = n;
2528     }
2529   }
2530 
2531   if (count == -1) {
2532     msg = "malformed address expression";
2533     msg_node = store;
2534   }
2535 
2536   if (!found_index) {
2537     msg = "missing use of index";
2538   }
2539 
2540   // byte sized items won't have a shift
2541   if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) {
2542     msg = "can't find shift";
2543     msg_node = store;
2544   }
2545 
2546   if (msg != NULL) {
2547 #ifndef PRODUCT
2548     if (TraceOptimizeFill) {
2549       tty->print_cr("not fill intrinsic: %s", msg);
2550       if (msg_node != NULL) msg_node->dump();
2551     }
2552 #endif
2553     return false;
2554   }
2555 
2556   // No make sure all the other nodes in the loop can be handled
2557   VectorSet ok(Thread::current()->resource_area());
2558 
2559   // store related values are ok
2560   ok.set(store->_idx);
2561   ok.set(store->in(MemNode::Memory)->_idx);
2562 
2563   CountedLoopEndNode* loop_exit = head->loopexit();
2564   guarantee(loop_exit != NULL, "no loop exit node");
2565 
2566   // Loop structure is ok
2567   ok.set(head->_idx);
2568   ok.set(loop_exit->_idx);
2569   ok.set(head->phi()->_idx);
2570   ok.set(head->incr()->_idx);
2571   ok.set(loop_exit->cmp_node()->_idx);
2572   ok.set(loop_exit->in(1)->_idx);
2573 
2574   // Address elements are ok
2575   if (con)   ok.set(con->_idx);
2576   if (shift) ok.set(shift->_idx);
2577   if (conv)  ok.set(conv->_idx);
2578 
2579   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2580     Node* n = lpt->_body.at(i);
2581     if (n->outcnt() == 0) continue; // Ignore dead
2582     if (ok.test(n->_idx)) continue;
2583     // Backedge projection is ok
2584     if (n->is_IfTrue() && n->in(0) == loop_exit) continue;
2585     if (!n->is_AddP()) {
2586       msg = "unhandled node";
2587       msg_node = n;
2588       break;
2589     }
2590   }
2591 
2592   // Make sure no unexpected values are used outside the loop
2593   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2594     Node* n = lpt->_body.at(i);
2595     // These values can be replaced with other nodes if they are used
2596     // outside the loop.
2597     if (n == store || n == loop_exit || n == head->incr() || n == store->in(MemNode::Memory)) continue;
2598     for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) {
2599       Node* use = iter.get();
2600       if (!lpt->_body.contains(use)) {
2601         msg = "node is used outside loop";
2602         // lpt->_body.dump();
2603         msg_node = n;
2604         break;
2605       }
2606     }
2607   }
2608 
2609 #ifdef ASSERT
2610   if (TraceOptimizeFill) {
2611     if (msg != NULL) {
2612       tty->print_cr("no fill intrinsic: %s", msg);
2613       if (msg_node != NULL) msg_node->dump();
2614     } else {
2615       tty->print_cr("fill intrinsic for:");
2616     }
2617     store->dump();
2618     if (Verbose) {
2619       lpt->_body.dump();
2620     }
2621   }
2622 #endif
2623 
2624   return msg == NULL;
2625 }
2626 
2627 
2628 
2629 bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
2630   // Only for counted inner loops
2631   if (!lpt->is_counted() || !lpt->is_inner()) {
2632     return false;
2633   }
2634 
2635   // Must have constant stride
2636   CountedLoopNode* head = lpt->_head->as_CountedLoop();
2637   if (!head->is_valid_counted_loop() || !head->is_normal_loop()) {
2638     return false;
2639   }
2640 
2641   // Check that the body only contains a store of a loop invariant
2642   // value that is indexed by the loop phi.
2643   Node* store = NULL;
2644   Node* store_value = NULL;
2645   Node* shift = NULL;
2646   Node* offset = NULL;
2647   if (!match_fill_loop(lpt, store, store_value, shift, offset)) {
2648     return false;
2649   }
2650 
2651 #ifndef PRODUCT
2652   if (TraceLoopOpts) {
2653     tty->print("ArrayFill    ");
2654     lpt->dump_head();
2655   }
2656 #endif
2657 
2658   // Now replace the whole loop body by a call to a fill routine that
2659   // covers the same region as the loop.
2660   Node* base = store->in(MemNode::Address)->as_AddP()->in(AddPNode::Base);
2661 
2662   // Build an expression for the beginning of the copy region
2663   Node* index = head->init_trip();
2664 #ifdef _LP64
2665   index = new (C) ConvI2LNode(index);
2666   _igvn.register_new_node_with_optimizer(index);
2667 #endif
2668   if (shift != NULL) {
2669     // byte arrays don't require a shift but others do.
2670     index = new (C) LShiftXNode(index, shift->in(2));
2671     _igvn.register_new_node_with_optimizer(index);
2672   }
2673   index = new (C) AddPNode(base, base, index);
2674   _igvn.register_new_node_with_optimizer(index);
2675   Node* from = new (C) AddPNode(base, index, offset);
2676   _igvn.register_new_node_with_optimizer(from);
2677   // Compute the number of elements to copy
2678   Node* len = new (C) SubINode(head->limit(), head->init_trip());
2679   _igvn.register_new_node_with_optimizer(len);
2680 
2681   BasicType t = store->as_Mem()->memory_type();
2682   bool aligned = false;
2683   if (offset != NULL && head->init_trip()->is_Con()) {
2684     int element_size = type2aelembytes(t);
2685     aligned = (offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int() * element_size) % HeapWordSize == 0;
2686   }
2687 
2688   // Build a call to the fill routine
2689   const char* fill_name;
2690   address fill = StubRoutines::select_fill_function(t, aligned, fill_name);
2691   assert(fill != NULL, "what?");
2692 
2693   // Convert float/double to int/long for fill routines
2694   if (t == T_FLOAT) {
2695     store_value = new (C) MoveF2INode(store_value);
2696     _igvn.register_new_node_with_optimizer(store_value);
2697   } else if (t == T_DOUBLE) {
2698     store_value = new (C) MoveD2LNode(store_value);
2699     _igvn.register_new_node_with_optimizer(store_value);
2700   }
2701 
2702   Node* mem_phi = store->in(MemNode::Memory);
2703   Node* result_ctrl;
2704   Node* result_mem;
2705   const TypeFunc* call_type = OptoRuntime::array_fill_Type();
2706   CallLeafNode *call = new (C) CallLeafNoFPNode(call_type, fill,
2707                                                 fill_name, TypeAryPtr::get_array_body_type(t));
2708   call->init_req(TypeFunc::Parms+0, from);
2709   call->init_req(TypeFunc::Parms+1, store_value);
2710 #ifdef _LP64
2711   len = new (C) ConvI2LNode(len);
2712   _igvn.register_new_node_with_optimizer(len);
2713 #endif
2714   call->init_req(TypeFunc::Parms+2, len);
2715 #ifdef _LP64
2716   call->init_req(TypeFunc::Parms+3, C->top());
2717 #endif
2718   call->init_req( TypeFunc::Control, head->init_control());
2719   call->init_req( TypeFunc::I_O    , C->top() )        ;   // does no i/o
2720   call->init_req( TypeFunc::Memory ,  mem_phi->in(LoopNode::EntryControl) );
2721   call->init_req( TypeFunc::ReturnAdr, C->start()->proj_out(TypeFunc::ReturnAdr) );
2722   call->init_req( TypeFunc::FramePtr, C->start()->proj_out(TypeFunc::FramePtr) );
2723   _igvn.register_new_node_with_optimizer(call);
2724   result_ctrl = new (C) ProjNode(call,TypeFunc::Control);
2725   _igvn.register_new_node_with_optimizer(result_ctrl);
2726   result_mem = new (C) ProjNode(call,TypeFunc::Memory);
2727   _igvn.register_new_node_with_optimizer(result_mem);
2728 
2729 /* Disable following optimization until proper fix (add missing checks).
2730 
2731   // If this fill is tightly coupled to an allocation and overwrites
2732   // the whole body, allow it to take over the zeroing.
2733   AllocateNode* alloc = AllocateNode::Ideal_allocation(base, this);
2734   if (alloc != NULL && alloc->is_AllocateArray()) {
2735     Node* length = alloc->as_AllocateArray()->Ideal_length();
2736     if (head->limit() == length &&
2737         head->init_trip() == _igvn.intcon(0)) {
2738       if (TraceOptimizeFill) {
2739         tty->print_cr("Eliminated zeroing in allocation");
2740       }
2741       alloc->maybe_set_complete(&_igvn);
2742     } else {
2743 #ifdef ASSERT
2744       if (TraceOptimizeFill) {
2745         tty->print_cr("filling array but bounds don't match");
2746         alloc->dump();
2747         head->init_trip()->dump();
2748         head->limit()->dump();
2749         length->dump();
2750       }
2751 #endif
2752     }
2753   }
2754 */
2755 
2756   // Redirect the old control and memory edges that are outside the loop.
2757   Node* exit = head->loopexit()->proj_out(0);
2758   // Sometimes the memory phi of the head is used as the outgoing
2759   // state of the loop.  It's safe in this case to replace it with the
2760   // result_mem.
2761   _igvn.replace_node(store->in(MemNode::Memory), result_mem);
2762   _igvn.replace_node(exit, result_ctrl);
2763   _igvn.replace_node(store, result_mem);
2764   // Any uses the increment outside of the loop become the loop limit.
2765   _igvn.replace_node(head->incr(), head->limit());
2766 
2767   // Disconnect the head from the loop.
2768   for (uint i = 0; i < lpt->_body.size(); i++) {
2769     Node* n = lpt->_body.at(i);
2770     _igvn.replace_node(n, C->top());
2771   }
2772 
2773   return true;
2774 }