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