1 /*
   2  * Copyright (c) 2000, 2011, 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 && !LoopLimitCheck), "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     long init_con   = cl->init_trip()->get_int();
  96     long limit_con  = cl->limit()->get_int();
  97     int stride_m    = stride_con - (stride_con > 0 ? 1 : -1);
  98     long 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, 3) 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, 3) SubINode(n_inv1, inv2);
 235   } else {
 236     inv = new (phase->C, 3) 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, 3) SubINode(inv, x);
 243   } else {
 244     addx = new (phase->C, 3) 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  uniq      = phase->C->unique();
 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 + uniq > 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_exit_value = old_new[head->in(LoopNode::LoopBackControl)->_idx];
 513   new_exit_value = move_loop_predicates(entry, new_exit_value, !counted_loop);
 514   _igvn.hash_delete(head);
 515   head->set_req(LoopNode::EntryControl, new_exit_value);
 516   for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) {
 517     Node* old = head->fast_out(j);
 518     if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) {
 519       new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];
 520       if (!new_exit_value )     // Backedge value is ALSO loop invariant?
 521         // Then loop body backedge value remains the same.
 522         new_exit_value = old->in(LoopNode::LoopBackControl);
 523       _igvn.hash_delete(old);
 524       old->set_req(LoopNode::EntryControl, new_exit_value);
 525     }
 526   }
 527 
 528 
 529   // Step 3: Cut the backedge on the clone (so its not a loop) and remove the
 530   //         extra backedge user.
 531   Node* new_head = old_new[head->_idx];
 532   _igvn.hash_delete(new_head);
 533   new_head->set_req(LoopNode::LoopBackControl, C->top());
 534   for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) {
 535     Node* use = new_head->fast_out(j2);
 536     if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) {
 537       _igvn.hash_delete(use);
 538       use->set_req(LoopNode::LoopBackControl, C->top());
 539     }
 540   }
 541 
 542 
 543   // Step 4: Correct dom-depth info.  Set to loop-head depth.
 544   int dd = dom_depth(head);
 545   set_idom(head, head->in(1), dd);
 546   for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
 547     Node *old = loop->_body.at(j3);
 548     Node *nnn = old_new[old->_idx];
 549     if (!has_ctrl(nnn))
 550       set_idom(nnn, idom(nnn), dd-1);
 551     // While we're at it, remove any SafePoints from the peeled code
 552     if (old->Opcode() == Op_SafePoint) {
 553       Node *nnn = old_new[old->_idx];
 554       lazy_replace(nnn,nnn->in(TypeFunc::Control));
 555     }
 556   }
 557 
 558   // Now force out all loop-invariant dominating tests.  The optimizer
 559   // finds some, but we _know_ they are all useless.
 560   peeled_dom_test_elim(loop,old_new);
 561 
 562   loop->record_for_igvn();
 563 }
 564 
 565 #define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop
 566 
 567 //------------------------------policy_maximally_unroll------------------------
 568 // Calculate exact loop trip count and return true if loop can be maximally
 569 // unrolled.
 570 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {
 571   CountedLoopNode *cl = _head->as_CountedLoop();
 572   assert(cl->is_normal_loop(), "");
 573   if (!cl->is_valid_counted_loop())
 574     return false; // Malformed counted loop
 575 
 576   if (!cl->has_exact_trip_count()) {
 577     // Trip count is not exact.
 578     return false;
 579   }
 580 
 581   uint trip_count = cl->trip_count();
 582   // Note, max_juint is used to indicate unknown trip count.
 583   assert(trip_count > 1, "one iteration loop should be optimized out already");
 584   assert(trip_count < max_juint, "exact trip_count should be less than max_uint.");
 585 
 586   // Real policy: if we maximally unroll, does it get too big?
 587   // Allow the unrolled mess to get larger than standard loop
 588   // size.  After all, it will no longer be a loop.
 589   uint body_size    = _body.size();
 590   uint unroll_limit = (uint)LoopUnrollLimit * 4;
 591   assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");
 592   if (trip_count > unroll_limit || body_size > unroll_limit) {
 593     return false;
 594   }
 595 
 596   // Fully unroll a loop with few iterations regardless next
 597   // conditions since following loop optimizations will split
 598   // such loop anyway (pre-main-post).
 599   if (trip_count <= 3)
 600     return true;
 601 
 602   // Take into account that after unroll conjoined heads and tails will fold,
 603   // otherwise policy_unroll() may allow more unrolling than max unrolling.
 604   uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count;
 605   uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE;
 606   if (body_size != tst_body_size) // Check for int overflow
 607     return false;
 608   if (new_body_size > unroll_limit ||
 609       // Unrolling can result in a large amount of node construction
 610       new_body_size >= MaxNodeLimit - phase->C->unique()) {
 611     return false;
 612   }
 613 
 614   // Do not unroll a loop with String intrinsics code.
 615   // String intrinsics are large and have loops.
 616   for (uint k = 0; k < _body.size(); k++) {
 617     Node* n = _body.at(k);
 618     switch (n->Opcode()) {
 619       case Op_StrComp:
 620       case Op_StrEquals:
 621       case Op_StrIndexOf:
 622       case Op_AryEq: {
 623         return false;
 624       }
 625     } // switch
 626   }
 627 
 628   return true; // Do maximally unroll
 629 }
 630 
 631 
 632 #define MAX_UNROLL 16 // maximum number of unrolls for main loop
 633 
 634 //------------------------------policy_unroll----------------------------------
 635 // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if
 636 // the loop is a CountedLoop and the body is small enough.
 637 bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const {
 638 
 639   CountedLoopNode *cl = _head->as_CountedLoop();
 640   assert(cl->is_normal_loop() || cl->is_main_loop(), "");
 641 
 642   if (!cl->is_valid_counted_loop())
 643     return false; // Malformed counted loop
 644 
 645   // Protect against over-unrolling.
 646   // After split at least one iteration will be executed in pre-loop.
 647   if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false;
 648 
 649   int future_unroll_ct = cl->unrolled_count() * 2;
 650   if (future_unroll_ct > MAX_UNROLL) return false;
 651 
 652   // Check for initial stride being a small enough constant
 653   if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;
 654 
 655   // Don't unroll if the next round of unrolling would push us
 656   // over the expected trip count of the loop.  One is subtracted
 657   // from the expected trip count because the pre-loop normally
 658   // executes 1 iteration.
 659   if (UnrollLimitForProfileCheck > 0 &&
 660       cl->profile_trip_cnt() != COUNT_UNKNOWN &&
 661       future_unroll_ct        > UnrollLimitForProfileCheck &&
 662       (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {
 663     return false;
 664   }
 665 
 666   // When unroll count is greater than LoopUnrollMin, don't unroll if:
 667   //   the residual iterations are more than 10% of the trip count
 668   //   and rounds of "unroll,optimize" are not making significant progress
 669   //   Progress defined as current size less than 20% larger than previous size.
 670   if (UseSuperWord && cl->node_count_before_unroll() > 0 &&
 671       future_unroll_ct > LoopUnrollMin &&
 672       (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() &&
 673       1.2 * cl->node_count_before_unroll() < (double)_body.size()) {
 674     return false;
 675   }
 676 
 677   Node *init_n = cl->init_trip();
 678   Node *limit_n = cl->limit();
 679   int stride_con = cl->stride_con();
 680   // Non-constant bounds.
 681   // Protect against over-unrolling when init or/and limit are not constant
 682   // (so that trip_count's init value is maxint) but iv range is known.
 683   if (init_n   == NULL || !init_n->is_Con()  ||
 684       limit_n  == NULL || !limit_n->is_Con()) {
 685     Node* phi = cl->phi();
 686     if (phi != NULL) {
 687       assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");
 688       const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();
 689       int next_stride = stride_con * 2; // stride after this unroll
 690       if (next_stride > 0) {
 691         if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow
 692             iv_type->_lo + next_stride >  iv_type->_hi) {
 693           return false;  // over-unrolling
 694         }
 695       } else if (next_stride < 0) {
 696         if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow
 697             iv_type->_hi + next_stride <  iv_type->_lo) {
 698           return false;  // over-unrolling
 699         }
 700       }
 701     }
 702   }
 703 
 704   // After unroll limit will be adjusted: new_limit = limit-stride.
 705   // Bailout if adjustment overflow.
 706   const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int();
 707   if (stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi) ||
 708       stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo))
 709     return false;  // overflow
 710 
 711   // Adjust body_size to determine if we unroll or not
 712   uint body_size = _body.size();
 713   // Also count ModL, DivL and MulL which expand mightly
 714   for (uint k = 0; k < _body.size(); k++) {
 715     Node* n = _body.at(k);
 716     switch (n->Opcode()) {
 717       case Op_ModL: body_size += 30; break;
 718       case Op_DivL: body_size += 30; break;
 719       case Op_MulL: body_size += 10; break;
 720       case Op_StrComp:
 721       case Op_StrEquals:
 722       case Op_StrIndexOf:
 723       case Op_AryEq: {
 724         // Do not unroll a loop with String intrinsics code.
 725         // String intrinsics are large and have loops.
 726         return false;
 727       }
 728     } // switch
 729   }
 730 
 731   // Check for being too big
 732   if (body_size > (uint)LoopUnrollLimit) {
 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 ) {
 828   if( get_ctrl(n) != back_ctrl ) return n;
 829 
 830   Node *x = NULL;               // If required, a clone of 'n'
 831   // Check for 'n' being pinned in the backedge.
 832   if( n->in(0) && n->in(0) == back_ctrl ) {
 833     x = n->clone();             // Clone a copy of 'n' to preheader
 834     x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader
 835   }
 836 
 837   // Recursive fixup any other input edges into x.
 838   // If there are no changes we can just return 'n', otherwise
 839   // we need to clone a private copy and change it.
 840   for( uint i = 1; i < n->req(); i++ ) {
 841     Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i) );
 842     if( g != n->in(i) ) {
 843       if( !x )
 844         x = n->clone();
 845       x->set_req(i, g);
 846     }
 847   }
 848   if( x ) {                     // x can legally float to pre-header location
 849     register_new_node( x, preheader_ctrl );
 850     return x;
 851   } else {                      // raise n to cover LCA of uses
 852     set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );
 853   }
 854   return n;
 855 }
 856 
 857 //------------------------------insert_pre_post_loops--------------------------
 858 // Insert pre and post loops.  If peel_only is set, the pre-loop can not have
 859 // more iterations added.  It acts as a 'peel' only, no lower-bound RCE, no
 860 // alignment.  Useful to unroll loops that do no array accesses.
 861 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {
 862 
 863 #ifndef PRODUCT
 864   if (TraceLoopOpts) {
 865     if (peel_only)
 866       tty->print("PeelMainPost ");
 867     else
 868       tty->print("PreMainPost  ");
 869     loop->dump_head();
 870   }
 871 #endif
 872   C->set_major_progress();
 873 
 874   // Find common pieces of the loop being guarded with pre & post loops
 875   CountedLoopNode *main_head = loop->_head->as_CountedLoop();
 876   assert( main_head->is_normal_loop(), "" );
 877   CountedLoopEndNode *main_end = main_head->loopexit();
 878   assert( main_end->outcnt() == 2, "1 true, 1 false path only" );
 879   uint dd_main_head = dom_depth(main_head);
 880   uint max = main_head->outcnt();
 881 
 882   Node *pre_header= main_head->in(LoopNode::EntryControl);
 883   Node *init      = main_head->init_trip();
 884   Node *incr      = main_end ->incr();
 885   Node *limit     = main_end ->limit();
 886   Node *stride    = main_end ->stride();
 887   Node *cmp       = main_end ->cmp_node();
 888   BoolTest::mask b_test = main_end->test_trip();
 889 
 890   // Need only 1 user of 'bol' because I will be hacking the loop bounds.
 891   Node *bol = main_end->in(CountedLoopEndNode::TestValue);
 892   if( bol->outcnt() != 1 ) {
 893     bol = bol->clone();
 894     register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));
 895     _igvn.hash_delete(main_end);
 896     main_end->set_req(CountedLoopEndNode::TestValue, bol);
 897   }
 898   // Need only 1 user of 'cmp' because I will be hacking the loop bounds.
 899   if( cmp->outcnt() != 1 ) {
 900     cmp = cmp->clone();
 901     register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));
 902     _igvn.hash_delete(bol);
 903     bol->set_req(1, cmp);
 904   }
 905 
 906   //------------------------------
 907   // Step A: Create Post-Loop.
 908   Node* main_exit = main_end->proj_out(false);
 909   assert( main_exit->Opcode() == Op_IfFalse, "" );
 910   int dd_main_exit = dom_depth(main_exit);
 911 
 912   // Step A1: Clone the loop body.  The clone becomes the post-loop.  The main
 913   // loop pre-header illegally has 2 control users (old & new loops).
 914   clone_loop( loop, old_new, dd_main_exit );
 915   assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" );
 916   CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop();
 917   post_head->set_post_loop(main_head);
 918 
 919   // Reduce the post-loop trip count.
 920   CountedLoopEndNode* post_end = old_new[main_end ->_idx]->as_CountedLoopEnd();
 921   post_end->_prob = PROB_FAIR;
 922 
 923   // Build the main-loop normal exit.
 924   IfFalseNode *new_main_exit = new (C, 1) IfFalseNode(main_end);
 925   _igvn.register_new_node_with_optimizer( new_main_exit );
 926   set_idom(new_main_exit, main_end, dd_main_exit );
 927   set_loop(new_main_exit, loop->_parent);
 928 
 929   // Step A2: Build a zero-trip guard for the post-loop.  After leaving the
 930   // main-loop, the post-loop may not execute at all.  We 'opaque' the incr
 931   // (the main-loop trip-counter exit value) because we will be changing
 932   // the exit value (via unrolling) so we cannot constant-fold away the zero
 933   // trip guard until all unrolling is done.
 934   Node *zer_opaq = new (C, 2) Opaque1Node(C, incr);
 935   Node *zer_cmp  = new (C, 3) CmpINode( zer_opaq, limit );
 936   Node *zer_bol  = new (C, 2) BoolNode( zer_cmp, b_test );
 937   register_new_node( zer_opaq, new_main_exit );
 938   register_new_node( zer_cmp , new_main_exit );
 939   register_new_node( zer_bol , new_main_exit );
 940 
 941   // Build the IfNode
 942   IfNode *zer_iff = new (C, 2) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN );
 943   _igvn.register_new_node_with_optimizer( zer_iff );
 944   set_idom(zer_iff, new_main_exit, dd_main_exit);
 945   set_loop(zer_iff, loop->_parent);
 946 
 947   // Plug in the false-path, taken if we need to skip post-loop
 948   _igvn.hash_delete( main_exit );
 949   main_exit->set_req(0, zer_iff);
 950   _igvn._worklist.push(main_exit);
 951   set_idom(main_exit, zer_iff, dd_main_exit);
 952   set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);
 953   // Make the true-path, must enter the post loop
 954   Node *zer_taken = new (C, 1) IfTrueNode( zer_iff );
 955   _igvn.register_new_node_with_optimizer( zer_taken );
 956   set_idom(zer_taken, zer_iff, dd_main_exit);
 957   set_loop(zer_taken, loop->_parent);
 958   // Plug in the true path
 959   _igvn.hash_delete( post_head );
 960   post_head->set_req(LoopNode::EntryControl, zer_taken);
 961   set_idom(post_head, zer_taken, dd_main_exit);
 962 
 963   // Step A3: Make the fall-in values to the post-loop come from the
 964   // fall-out values of the main-loop.
 965   for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {
 966     Node* main_phi = main_head->fast_out(i);
 967     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) {
 968       Node *post_phi = old_new[main_phi->_idx];
 969       Node *fallmain  = clone_up_backedge_goo(main_head->back_control(),
 970                                               post_head->init_control(),
 971                                               main_phi->in(LoopNode::LoopBackControl));
 972       _igvn.hash_delete(post_phi);
 973       post_phi->set_req( LoopNode::EntryControl, fallmain );
 974     }
 975   }
 976 
 977   // Update local caches for next stanza
 978   main_exit = new_main_exit;
 979 
 980 
 981   //------------------------------
 982   // Step B: Create Pre-Loop.
 983 
 984   // Step B1: Clone the loop body.  The clone becomes the pre-loop.  The main
 985   // loop pre-header illegally has 2 control users (old & new loops).
 986   clone_loop( loop, old_new, dd_main_head );
 987   CountedLoopNode*    pre_head = old_new[main_head->_idx]->as_CountedLoop();
 988   CountedLoopEndNode* pre_end  = old_new[main_end ->_idx]->as_CountedLoopEnd();
 989   pre_head->set_pre_loop(main_head);
 990   Node *pre_incr = old_new[incr->_idx];
 991 
 992   // Reduce the pre-loop trip count.
 993   pre_end->_prob = PROB_FAIR;
 994 
 995   // Find the pre-loop normal exit.
 996   Node* pre_exit = pre_end->proj_out(false);
 997   assert( pre_exit->Opcode() == Op_IfFalse, "" );
 998   IfFalseNode *new_pre_exit = new (C, 1) IfFalseNode(pre_end);
 999   _igvn.register_new_node_with_optimizer( new_pre_exit );
1000   set_idom(new_pre_exit, pre_end, dd_main_head);
1001   set_loop(new_pre_exit, loop->_parent);
1002 
1003   // Step B2: Build a zero-trip guard for the main-loop.  After leaving the
1004   // pre-loop, the main-loop may not execute at all.  Later in life this
1005   // zero-trip guard will become the minimum-trip guard when we unroll
1006   // the main-loop.
1007   Node *min_opaq = new (C, 2) Opaque1Node(C, limit);
1008   Node *min_cmp  = new (C, 3) CmpINode( pre_incr, min_opaq );
1009   Node *min_bol  = new (C, 2) BoolNode( min_cmp, b_test );
1010   register_new_node( min_opaq, new_pre_exit );
1011   register_new_node( min_cmp , new_pre_exit );
1012   register_new_node( min_bol , new_pre_exit );
1013 
1014   // Build the IfNode (assume the main-loop is executed always).
1015   IfNode *min_iff = new (C, 2) IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );
1016   _igvn.register_new_node_with_optimizer( min_iff );
1017   set_idom(min_iff, new_pre_exit, dd_main_head);
1018   set_loop(min_iff, loop->_parent);
1019 
1020   // Plug in the false-path, taken if we need to skip main-loop
1021   _igvn.hash_delete( pre_exit );
1022   pre_exit->set_req(0, min_iff);
1023   set_idom(pre_exit, min_iff, dd_main_head);
1024   set_idom(pre_exit->unique_out(), min_iff, dd_main_head);
1025   // Make the true-path, must enter the main loop
1026   Node *min_taken = new (C, 1) IfTrueNode( min_iff );
1027   _igvn.register_new_node_with_optimizer( min_taken );
1028   set_idom(min_taken, min_iff, dd_main_head);
1029   set_loop(min_taken, loop->_parent);
1030   // Plug in the true path
1031   _igvn.hash_delete( main_head );
1032   main_head->set_req(LoopNode::EntryControl, min_taken);
1033   set_idom(main_head, min_taken, dd_main_head);
1034 
1035   // Step B3: Make the fall-in values to the main-loop come from the
1036   // fall-out values of the pre-loop.
1037   for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {
1038     Node* main_phi = main_head->fast_out(i2);
1039     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {
1040       Node *pre_phi = old_new[main_phi->_idx];
1041       Node *fallpre  = clone_up_backedge_goo(pre_head->back_control(),
1042                                              main_head->init_control(),
1043                                              pre_phi->in(LoopNode::LoopBackControl));
1044       _igvn.hash_delete(main_phi);
1045       main_phi->set_req( LoopNode::EntryControl, fallpre );
1046     }
1047   }
1048 
1049   // Step B4: Shorten the pre-loop to run only 1 iteration (for now).
1050   // RCE and alignment may change this later.
1051   Node *cmp_end = pre_end->cmp_node();
1052   assert( cmp_end->in(2) == limit, "" );
1053   Node *pre_limit = new (C, 3) AddINode( init, stride );
1054 
1055   // Save the original loop limit in this Opaque1 node for
1056   // use by range check elimination.
1057   Node *pre_opaq  = new (C, 3) Opaque1Node(C, pre_limit, limit);
1058 
1059   register_new_node( pre_limit, pre_head->in(0) );
1060   register_new_node( pre_opaq , pre_head->in(0) );
1061 
1062   // Since no other users of pre-loop compare, I can hack limit directly
1063   assert( cmp_end->outcnt() == 1, "no other users" );
1064   _igvn.hash_delete(cmp_end);
1065   cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);
1066 
1067   // Special case for not-equal loop bounds:
1068   // Change pre loop test, main loop test, and the
1069   // main loop guard test to use lt or gt depending on stride
1070   // direction:
1071   // positive stride use <
1072   // negative stride use >
1073 
1074   if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {
1075     assert(!LoopLimitCheck, "only canonical tests (lt or gt) are expected");
1076 
1077     BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;
1078     // Modify pre loop end condition
1079     Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1080     BoolNode* new_bol0 = new (C, 2) BoolNode(pre_bol->in(1), new_test);
1081     register_new_node( new_bol0, pre_head->in(0) );
1082     _igvn.hash_delete(pre_end);
1083     pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0);
1084     // Modify main loop guard condition
1085     assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");
1086     BoolNode* new_bol1 = new (C, 2) BoolNode(min_bol->in(1), new_test);
1087     register_new_node( new_bol1, new_pre_exit );
1088     _igvn.hash_delete(min_iff);
1089     min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);
1090     // Modify main loop end condition
1091     BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();
1092     BoolNode* new_bol2 = new (C, 2) BoolNode(main_bol->in(1), new_test);
1093     register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );
1094     _igvn.hash_delete(main_end);
1095     main_end->set_req(CountedLoopEndNode::TestValue, new_bol2);
1096   }
1097 
1098   // Flag main loop
1099   main_head->set_main_loop();
1100   if( peel_only ) main_head->set_main_no_pre_loop();
1101 
1102   // Subtract a trip count for the pre-loop.
1103   main_head->set_trip_count(main_head->trip_count() - 1);
1104 
1105   // It's difficult to be precise about the trip-counts
1106   // for the pre/post loops.  They are usually very short,
1107   // so guess that 4 trips is a reasonable value.
1108   post_head->set_profile_trip_cnt(4.0);
1109   pre_head->set_profile_trip_cnt(4.0);
1110 
1111   // Now force out all loop-invariant dominating tests.  The optimizer
1112   // finds some, but we _know_ they are all useless.
1113   peeled_dom_test_elim(loop,old_new);
1114 }
1115 
1116 //------------------------------is_invariant-----------------------------
1117 // Return true if n is invariant
1118 bool IdealLoopTree::is_invariant(Node* n) const {
1119   Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n;
1120   if (n_c->is_top()) return false;
1121   return !is_member(_phase->get_loop(n_c));
1122 }
1123 
1124 
1125 //------------------------------do_unroll--------------------------------------
1126 // Unroll the loop body one step - make each trip do 2 iterations.
1127 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {
1128   assert(LoopUnrollLimit, "");
1129   CountedLoopNode *loop_head = loop->_head->as_CountedLoop();
1130   CountedLoopEndNode *loop_end = loop_head->loopexit();
1131   assert(loop_end, "");
1132 #ifndef PRODUCT
1133   if (PrintOpto && VerifyLoopOptimizations) {
1134     tty->print("Unrolling ");
1135     loop->dump_head();
1136   } else if (TraceLoopOpts) {
1137     if (loop_head->trip_count() < (uint)LoopUnrollLimit) {
1138       tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count());
1139     } else {
1140       tty->print("Unroll %d     ", loop_head->unrolled_count()*2);
1141     }
1142     loop->dump_head();
1143   }
1144 #endif
1145 
1146   // Remember loop node count before unrolling to detect
1147   // if rounds of unroll,optimize are making progress
1148   loop_head->set_node_count_before_unroll(loop->_body.size());
1149 
1150   Node *ctrl  = loop_head->in(LoopNode::EntryControl);
1151   Node *limit = loop_head->limit();
1152   Node *init  = loop_head->init_trip();
1153   Node *stride = loop_head->stride();
1154 
1155   Node *opaq = NULL;
1156   if (adjust_min_trip) {       // If not maximally unrolling, need adjustment
1157     // Search for zero-trip guard.
1158     assert( loop_head->is_main_loop(), "" );
1159     assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
1160     Node *iff = ctrl->in(0);
1161     assert( iff->Opcode() == Op_If, "" );
1162     Node *bol = iff->in(1);
1163     assert( bol->Opcode() == Op_Bool, "" );
1164     Node *cmp = bol->in(1);
1165     assert( cmp->Opcode() == Op_CmpI, "" );
1166     opaq = cmp->in(2);
1167     // Occasionally it's possible for a zero-trip guard Opaque1 node to be
1168     // optimized away and then another round of loop opts attempted.
1169     // We can not optimize this particular loop in that case.
1170     if (opaq->Opcode() != Op_Opaque1)
1171       return; // Cannot find zero-trip guard!  Bail out!
1172     // Zero-trip test uses an 'opaque' node which is not shared.
1173     assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
1174   }
1175 
1176   C->set_major_progress();
1177 
1178   Node* new_limit = NULL;
1179   if (UnrollLimitCheck) {
1180     int stride_con = stride->get_int();
1181     int stride_p = (stride_con > 0) ? stride_con : -stride_con;
1182     uint old_trip_count = loop_head->trip_count();
1183     // Verify that unroll policy result is still valid.
1184     assert(old_trip_count > 1 &&
1185            (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");
1186 
1187     // Adjust loop limit to keep valid iterations number after unroll.
1188     // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride
1189     // which may overflow.
1190     if (!adjust_min_trip) {
1191       assert(old_trip_count > 1 && (old_trip_count & 1) == 0,
1192              "odd trip count for maximally unroll");
1193       // Don't need to adjust limit for maximally unroll since trip count is even.
1194     } else if (loop_head->has_exact_trip_count() && init->is_Con()) {
1195       // Loop's limit is constant. Loop's init could be constant when pre-loop
1196       // become peeled iteration.
1197       long init_con = init->get_int();
1198       // We can keep old loop limit if iterations count stays the same:
1199       //   old_trip_count == new_trip_count * 2
1200       // Note: since old_trip_count >= 2 then new_trip_count >= 1
1201       // so we also don't need to adjust zero trip test.
1202       long limit_con  = limit->get_int();
1203       // (stride_con*2) not overflow since stride_con <= 8.
1204       int new_stride_con = stride_con * 2;
1205       int stride_m    = new_stride_con - (stride_con > 0 ? 1 : -1);
1206       long trip_count = (limit_con - init_con + stride_m)/new_stride_con;
1207       // New trip count should satisfy next conditions.
1208       assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity");
1209       uint new_trip_count = (uint)trip_count;
1210       adjust_min_trip = (old_trip_count != new_trip_count*2);
1211     }
1212 
1213     if (adjust_min_trip) {
1214       // Step 2: Adjust the trip limit if it is called for.
1215       // The adjustment amount is -stride. Need to make sure if the
1216       // adjustment underflows or overflows, then the main loop is skipped.
1217       Node* cmp = loop_end->cmp_node();
1218       assert(cmp->in(2) == limit, "sanity");
1219       assert(opaq != NULL && opaq->in(1) == limit, "sanity");
1220 
1221       // Verify that policy_unroll result is still valid.
1222       const TypeInt* limit_type = _igvn.type(limit)->is_int();
1223       assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) ||
1224              stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity");
1225 
1226       if (limit->is_Con()) {
1227         // The check in policy_unroll and the assert above guarantee
1228         // no underflow if limit is constant.
1229         new_limit = _igvn.intcon(limit->get_int() - stride_con);
1230         set_ctrl(new_limit, C->root());
1231       } else {
1232         if (stride_con > 0 && ((limit_type->_lo - stride_con) < limit_type->_lo) ||
1233                    stride_con < 0 && ((limit_type->_hi - stride_con) > limit_type->_hi)) {
1234           // No underflow.
1235           new_limit = new (C, 3) SubINode(limit, stride);
1236         } else {
1237           // (limit - stride) may underflow.
1238           // Clamp the adjustment value with MININT or MAXINT:
1239           //
1240           //   new_limit = limit-stride
1241           //   if (stride > 0)
1242           //     new_limit = (limit < new_limit) ? MININT : new_limit;
1243           //   else
1244           //     new_limit = (limit > new_limit) ? MAXINT : new_limit;
1245           //
1246           BoolTest::mask bt = loop_end->test_trip();
1247           assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");
1248           Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint);
1249           set_ctrl(adj_max, C->root());
1250           Node* old_limit = NULL;
1251           Node* adj_limit = NULL;
1252           Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL;
1253           if (loop_head->unrolled_count() > 1 &&
1254               limit->is_CMove() && limit->Opcode() == Op_CMoveI &&
1255               limit->in(CMoveNode::IfTrue) == adj_max &&
1256               bol->as_Bool()->_test._test == bt &&
1257               bol->in(1)->Opcode() == Op_CmpI &&
1258               bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) {
1259             // Loop was unrolled before.
1260             // Optimize the limit to avoid nested CMove:
1261             // use original limit as old limit.
1262             old_limit = bol->in(1)->in(1);
1263             // Adjust previous adjusted limit.
1264             adj_limit = limit->in(CMoveNode::IfFalse);
1265             adj_limit = new (C, 3) SubINode(adj_limit, stride);
1266           } else {
1267             old_limit = limit;
1268             adj_limit = new (C, 3) SubINode(limit, stride);
1269           }
1270           assert(old_limit != NULL && adj_limit != NULL, "");
1271           register_new_node( adj_limit, ctrl ); // adjust amount
1272           Node* adj_cmp = new (C, 3) CmpINode(old_limit, adj_limit);
1273           register_new_node( adj_cmp, ctrl );
1274           Node* adj_bool = new (C, 2) BoolNode(adj_cmp, bt);
1275           register_new_node( adj_bool, ctrl );
1276           new_limit = new (C, 4) CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT);
1277         }
1278         register_new_node(new_limit, ctrl);
1279       }
1280       assert(new_limit != NULL, "");
1281       if (limit->outcnt() == 2) {
1282         // Replace old limit if it is used only in loop tests.
1283         _igvn.replace_node(limit, new_limit);
1284       } else {
1285         // Replace in loop test.
1286         _igvn.hash_delete(cmp);
1287         cmp->set_req(2, new_limit);
1288 
1289         // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1290         // Make it a 1-trip test (means at least 2 trips).
1291 
1292         // Guard test uses an 'opaque' node which is not shared.  Hence I
1293         // can edit it's inputs directly.  Hammer in the new limit for the
1294         // minimum-trip guard.
1295         assert(opaq->outcnt() == 1, "");
1296         _igvn.hash_delete(opaq);
1297         opaq->set_req(1, new_limit);
1298       }
1299     }
1300 
1301     // Adjust max trip count. The trip count is intentionally rounded
1302     // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1303     // the main, unrolled, part of the loop will never execute as it is protected
1304     // by the min-trip test.  See bug 4834191 for a case where we over-unrolled
1305     // and later determined that part of the unrolled loop was dead.
1306     loop_head->set_trip_count(old_trip_count / 2);
1307 
1308     // Double the count of original iterations in the unrolled loop body.
1309     loop_head->double_unrolled_count();
1310 
1311   } else { // LoopLimitCheck
1312 
1313     // Adjust max trip count. The trip count is intentionally rounded
1314     // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,
1315     // the main, unrolled, part of the loop will never execute as it is protected
1316     // by the min-trip test.  See bug 4834191 for a case where we over-unrolled
1317     // and later determined that part of the unrolled loop was dead.
1318     loop_head->set_trip_count(loop_head->trip_count() / 2);
1319 
1320     // Double the count of original iterations in the unrolled loop body.
1321     loop_head->double_unrolled_count();
1322 
1323     // -----------
1324     // Step 2: Cut back the trip counter for an unroll amount of 2.
1325     // Loop will normally trip (limit - init)/stride_con.  Since it's a
1326     // CountedLoop this is exact (stride divides limit-init exactly).
1327     // We are going to double the loop body, so we want to knock off any
1328     // odd iteration: (trip_cnt & ~1).  Then back compute a new limit.
1329     Node *span = new (C, 3) SubINode( limit, init );
1330     register_new_node( span, ctrl );
1331     Node *trip = new (C, 3) DivINode( 0, span, stride );
1332     register_new_node( trip, ctrl );
1333     Node *mtwo = _igvn.intcon(-2);
1334     set_ctrl(mtwo, C->root());
1335     Node *rond = new (C, 3) AndINode( trip, mtwo );
1336     register_new_node( rond, ctrl );
1337     Node *spn2 = new (C, 3) MulINode( rond, stride );
1338     register_new_node( spn2, ctrl );
1339     new_limit = new (C, 3) AddINode( spn2, init );
1340     register_new_node( new_limit, ctrl );
1341 
1342     // Hammer in the new limit
1343     Node *ctrl2 = loop_end->in(0);
1344     Node *cmp2 = new (C, 3) CmpINode( loop_head->incr(), new_limit );
1345     register_new_node( cmp2, ctrl2 );
1346     Node *bol2 = new (C, 2) BoolNode( cmp2, loop_end->test_trip() );
1347     register_new_node( bol2, ctrl2 );
1348     _igvn.hash_delete(loop_end);
1349     loop_end->set_req(CountedLoopEndNode::TestValue, bol2);
1350 
1351     // Step 3: Find the min-trip test guaranteed before a 'main' loop.
1352     // Make it a 1-trip test (means at least 2 trips).
1353     if( adjust_min_trip ) {
1354       assert( new_limit != NULL, "" );
1355       // Guard test uses an 'opaque' node which is not shared.  Hence I
1356       // can edit it's inputs directly.  Hammer in the new limit for the
1357       // minimum-trip guard.
1358       assert( opaq->outcnt() == 1, "" );
1359       _igvn.hash_delete(opaq);
1360       opaq->set_req(1, new_limit);
1361     }
1362   } // LoopLimitCheck
1363 
1364   // ---------
1365   // Step 4: Clone the loop body.  Move it inside the loop.  This loop body
1366   // represents the odd iterations; since the loop trips an even number of
1367   // times its backedge is never taken.  Kill the backedge.
1368   uint dd = dom_depth(loop_head);
1369   clone_loop( loop, old_new, dd );
1370 
1371   // Make backedges of the clone equal to backedges of the original.
1372   // Make the fall-in from the original come from the fall-out of the clone.
1373   for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {
1374     Node* phi = loop_head->fast_out(j);
1375     if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {
1376       Node *newphi = old_new[phi->_idx];
1377       _igvn.hash_delete( phi );
1378       _igvn.hash_delete( newphi );
1379 
1380       phi   ->set_req(LoopNode::   EntryControl, newphi->in(LoopNode::LoopBackControl));
1381       newphi->set_req(LoopNode::LoopBackControl, phi   ->in(LoopNode::LoopBackControl));
1382       phi   ->set_req(LoopNode::LoopBackControl, C->top());
1383     }
1384   }
1385   Node *clone_head = old_new[loop_head->_idx];
1386   _igvn.hash_delete( clone_head );
1387   loop_head ->set_req(LoopNode::   EntryControl, clone_head->in(LoopNode::LoopBackControl));
1388   clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));
1389   loop_head ->set_req(LoopNode::LoopBackControl, C->top());
1390   loop->_head = clone_head;     // New loop header
1391 
1392   set_idom(loop_head,  loop_head ->in(LoopNode::EntryControl), dd);
1393   set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);
1394 
1395   // Kill the clone's backedge
1396   Node *newcle = old_new[loop_end->_idx];
1397   _igvn.hash_delete( newcle );
1398   Node *one = _igvn.intcon(1);
1399   set_ctrl(one, C->root());
1400   newcle->set_req(1, one);
1401   // Force clone into same loop body
1402   uint max = loop->_body.size();
1403   for( uint k = 0; k < max; k++ ) {
1404     Node *old = loop->_body.at(k);
1405     Node *nnn = old_new[old->_idx];
1406     loop->_body.push(nnn);
1407     if (!has_ctrl(old))
1408       set_loop(nnn, loop);
1409   }
1410 
1411   loop->record_for_igvn();
1412 }
1413 
1414 //------------------------------do_maximally_unroll----------------------------
1415 
1416 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {
1417   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1418   assert(cl->has_exact_trip_count(), "trip count is not exact");
1419   assert(cl->trip_count() > 0, "");
1420 #ifndef PRODUCT
1421   if (TraceLoopOpts) {
1422     tty->print("MaxUnroll  %d ", cl->trip_count());
1423     loop->dump_head();
1424   }
1425 #endif
1426 
1427   // If loop is tripping an odd number of times, peel odd iteration
1428   if ((cl->trip_count() & 1) == 1) {
1429     do_peeling(loop, old_new);
1430   }
1431 
1432   // Now its tripping an even number of times remaining.  Double loop body.
1433   // Do not adjust pre-guards; they are not needed and do not exist.
1434   if (cl->trip_count() > 0) {
1435     assert((cl->trip_count() & 1) == 0, "missed peeling");
1436     do_unroll(loop, old_new, false);
1437   }
1438 }
1439 
1440 //------------------------------dominates_backedge---------------------------------
1441 // Returns true if ctrl is executed on every complete iteration
1442 bool IdealLoopTree::dominates_backedge(Node* ctrl) {
1443   assert(ctrl->is_CFG(), "must be control");
1444   Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl);
1445   return _phase->dom_lca_internal(ctrl, backedge) == ctrl;
1446 }
1447 
1448 //------------------------------add_constraint---------------------------------
1449 // Constrain the main loop iterations so the conditions:
1450 //    low_limit <= scale_con * I + offset  <  upper_limit
1451 // always holds true.  That is, either increase the number of iterations in
1452 // the pre-loop or the post-loop until the condition holds true in the main
1453 // loop.  Stride, scale, offset and limit are all loop invariant.  Further,
1454 // stride and scale are constants (offset and limit often are).
1455 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 ) {
1456   // For positive stride, the pre-loop limit always uses a MAX function
1457   // and the main loop a MIN function.  For negative stride these are
1458   // reversed.
1459 
1460   // Also for positive stride*scale the affine function is increasing, so the
1461   // pre-loop must check for underflow and the post-loop for overflow.
1462   // Negative stride*scale reverses this; pre-loop checks for overflow and
1463   // post-loop for underflow.
1464   if (stride_con*scale_con > 0) {
1465     // The overflow limit: scale*I+offset < upper_limit
1466     // For main-loop compute
1467     //   ( if (scale > 0) /* and stride > 0 */
1468     //       I < (upper_limit-offset)/scale
1469     //     else /* scale < 0 and stride < 0 */
1470     //       I > (upper_limit-offset)/scale
1471     //   )
1472     //
1473     // (upper_limit-offset) may overflow when offset < 0.
1474     // But it is fine since main loop will either have
1475     // less iterations or will be skipped in such case.
1476     Node *con = new (C, 3) SubINode(upper_limit, offset);
1477     register_new_node(con, pre_ctrl);
1478     Node *scale = _igvn.intcon(scale_con);
1479     set_ctrl(scale, C->root());
1480     Node *X = new (C, 3) DivINode(0, con, scale);
1481     register_new_node(X, pre_ctrl);
1482 
1483     // Adjust main-loop last iteration
1484     Node *loop_limit = *main_limit;
1485     loop_limit = (stride_con > 0) // scale > 0
1486       ? (Node*)(new (C, 3) MinINode(loop_limit, X))
1487       : (Node*)(new (C, 3) MaxINode(loop_limit, X));
1488     register_new_node(loop_limit, pre_ctrl);
1489     *main_limit = loop_limit;
1490 
1491     // The underflow limit: low_limit <= scale*I+offset.
1492     // For pre-loop compute
1493     //   NOT(scale*I+offset >= low_limit)
1494     //   scale*I+offset < low_limit
1495     //   ( if (scale > 0) /* and stride > 0 */
1496     //       I < (low_limit-offset)/scale
1497     //     else /* scale < 0 and stride < 0 */
1498     //       I > (low_limit-offset)/scale
1499     //   )
1500 
1501     if (low_limit->get_int() == -max_jint) {
1502       if (!RangeLimitCheck) return;
1503       // We need this guard when scale*pre_limit+offset >= limit
1504       // due to underflow so we need execute pre-loop until
1505       // scale*I+offset >= min_int. But (low_limit-offset) will
1506       // underflow when offset > 0 and X will be > original_limit.
1507       // To avoid it we replace offset = offset > 0 ? 0 : offset
1508       // and add min(pre_limit, original_limit).
1509       Node* shift = _igvn.intcon(31);
1510       set_ctrl(shift, C->root());
1511       Node *neg_off = new (C, 3) RShiftINode(offset, shift);
1512       register_new_node(neg_off, pre_ctrl);
1513       offset = new (C, 3) AndINode(offset, neg_off);
1514       register_new_node(offset, pre_ctrl);
1515     } else {
1516       assert(low_limit->get_int() == 0, "wrong low limit for range check");
1517       // The only problem we have here when offset == min_int
1518       // since (0-min_int) == min_int. It may be fine for scale > 0
1519       // but for scale < 0 X will be < original_limit.
1520     }
1521     con = new (C, 3) SubINode(low_limit, offset);
1522     register_new_node(con, pre_ctrl);
1523     scale = _igvn.intcon(scale_con);
1524     set_ctrl(scale, C->root());
1525     X = new (C, 3) DivINode(0, con, scale);
1526     register_new_node(X, pre_ctrl);
1527 
1528     // Adjust pre-loop last iteration
1529     loop_limit = *pre_limit;
1530     loop_limit = (stride_con > 0) // scale > 0
1531       ? (Node*)(new (C, 3) MaxINode(loop_limit, X))
1532       : (Node*)(new (C, 3) MinINode(loop_limit, X));
1533     register_new_node( loop_limit, pre_ctrl );
1534     *pre_limit = loop_limit;
1535 
1536   } else { // stride_con*scale_con < 0
1537     // For negative stride*scale pre-loop checks for overflow and
1538     // post-loop for underflow.
1539     //
1540     // The underflow limit: low_limit <= scale*I+offset.
1541     // For main-loop compute
1542     //   scale*I+offset+1 > low_limit
1543     //   ( if (scale < 0) /* and stride > 0 */
1544     //       I < (low_limit-(offset+1))/scale
1545     //     else /* scale < 0 and stride < 0 */
1546     //       I > (low_limit-(offset+1))/scale
1547     //   )
1548 
1549     if (low_limit->get_int() == -max_jint) {
1550       if (!RangeLimitCheck) return;
1551     } else {
1552       assert(low_limit->get_int() == 0, "wrong low limit for range check");
1553     }
1554 
1555     Node *one  = _igvn.intcon(1);
1556     set_ctrl(one, C->root());
1557     Node *plus_one = new (C, 3) AddINode(offset, one);
1558     register_new_node( plus_one, pre_ctrl );
1559     Node *con = new (C, 3) SubINode(low_limit, plus_one);
1560     register_new_node(con, pre_ctrl);
1561     Node *scale = _igvn.intcon(scale_con);
1562     set_ctrl(scale, C->root());
1563     Node *X = new (C, 3) DivINode(0, con, scale);
1564     register_new_node(X, pre_ctrl);
1565 
1566     // Adjust main-loop last iteration
1567     Node *loop_limit = *main_limit;
1568     loop_limit = (stride_con > 0) // scale < 0
1569       ? (Node*)(new (C, 3) MinINode(loop_limit, X))
1570       : (Node*)(new (C, 3) MaxINode(loop_limit, X));
1571     register_new_node(loop_limit, pre_ctrl);
1572     *main_limit = loop_limit;
1573 
1574     // The overflow limit: scale*I+offset < upper_limit
1575     // For pre-loop compute
1576     //   NOT(scale*I+offset < upper_limit)
1577     //   scale*I+offset >= upper_limit
1578     //   scale*I+offset+1 > upper_limit
1579     //   ( if (scale < 0) /* and stride > 0 */
1580     //       I < (upper_limit-(offset+1))/scale
1581     //     else /* scale < 0 and stride < 0 */
1582     //       I > (upper_limit-(offset+1))/scale
1583     //   )
1584     plus_one = new (C, 3) AddINode(offset, one);
1585     register_new_node( plus_one, pre_ctrl );
1586     con = new (C, 3) SubINode(upper_limit, plus_one);
1587     register_new_node(con, pre_ctrl);
1588     scale = _igvn.intcon(scale_con);
1589     set_ctrl(scale, C->root());
1590     X = new (C, 3) DivINode(0, con, scale);
1591     register_new_node(X, pre_ctrl);
1592 
1593     // Adjust pre-loop last iteration
1594     loop_limit = *pre_limit;
1595     loop_limit = (stride_con > 0) // scale < 0
1596       ? (Node*)(new (C, 3) MaxINode(loop_limit, X))
1597       : (Node*)(new (C, 3) MinINode(loop_limit, X));
1598     register_new_node( loop_limit, pre_ctrl );
1599     *pre_limit = loop_limit;
1600 
1601   }
1602 }
1603 
1604 
1605 //------------------------------is_scaled_iv---------------------------------
1606 // Return true if exp is a constant times an induction var
1607 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {
1608   if (exp == iv) {
1609     if (p_scale != NULL) {
1610       *p_scale = 1;
1611     }
1612     return true;
1613   }
1614   int opc = exp->Opcode();
1615   if (opc == Op_MulI) {
1616     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1617       if (p_scale != NULL) {
1618         *p_scale = exp->in(2)->get_int();
1619       }
1620       return true;
1621     }
1622     if (exp->in(2) == iv && exp->in(1)->is_Con()) {
1623       if (p_scale != NULL) {
1624         *p_scale = exp->in(1)->get_int();
1625       }
1626       return true;
1627     }
1628   } else if (opc == Op_LShiftI) {
1629     if (exp->in(1) == iv && exp->in(2)->is_Con()) {
1630       if (p_scale != NULL) {
1631         *p_scale = 1 << exp->in(2)->get_int();
1632       }
1633       return true;
1634     }
1635   }
1636   return false;
1637 }
1638 
1639 //-----------------------------is_scaled_iv_plus_offset------------------------------
1640 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)
1641 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {
1642   if (is_scaled_iv(exp, iv, p_scale)) {
1643     if (p_offset != NULL) {
1644       Node *zero = _igvn.intcon(0);
1645       set_ctrl(zero, C->root());
1646       *p_offset = zero;
1647     }
1648     return true;
1649   }
1650   int opc = exp->Opcode();
1651   if (opc == Op_AddI) {
1652     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1653       if (p_offset != NULL) {
1654         *p_offset = exp->in(2);
1655       }
1656       return true;
1657     }
1658     if (exp->in(2)->is_Con()) {
1659       Node* offset2 = NULL;
1660       if (depth < 2 &&
1661           is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,
1662                                    p_offset != NULL ? &offset2 : NULL, depth+1)) {
1663         if (p_offset != NULL) {
1664           Node *ctrl_off2 = get_ctrl(offset2);
1665           Node* offset = new (C, 3) AddINode(offset2, exp->in(2));
1666           register_new_node(offset, ctrl_off2);
1667           *p_offset = offset;
1668         }
1669         return true;
1670       }
1671     }
1672   } else if (opc == Op_SubI) {
1673     if (is_scaled_iv(exp->in(1), iv, p_scale)) {
1674       if (p_offset != NULL) {
1675         Node *zero = _igvn.intcon(0);
1676         set_ctrl(zero, C->root());
1677         Node *ctrl_off = get_ctrl(exp->in(2));
1678         Node* offset = new (C, 3) SubINode(zero, exp->in(2));
1679         register_new_node(offset, ctrl_off);
1680         *p_offset = offset;
1681       }
1682       return true;
1683     }
1684     if (is_scaled_iv(exp->in(2), iv, p_scale)) {
1685       if (p_offset != NULL) {
1686         *p_scale *= -1;
1687         *p_offset = exp->in(1);
1688       }
1689       return true;
1690     }
1691   }
1692   return false;
1693 }
1694 
1695 //------------------------------do_range_check---------------------------------
1696 // Eliminate range-checks and other trip-counter vs loop-invariant tests.
1697 void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
1698 #ifndef PRODUCT
1699   if (PrintOpto && VerifyLoopOptimizations) {
1700     tty->print("Range Check Elimination ");
1701     loop->dump_head();
1702   } else if (TraceLoopOpts) {
1703     tty->print("RangeCheck   ");
1704     loop->dump_head();
1705   }
1706 #endif
1707   assert(RangeCheckElimination, "");
1708   CountedLoopNode *cl = loop->_head->as_CountedLoop();
1709   assert(cl->is_main_loop(), "");
1710 
1711   // protect against stride not being a constant
1712   if (!cl->stride_is_con())
1713     return;
1714 
1715   // Find the trip counter; we are iteration splitting based on it
1716   Node *trip_counter = cl->phi();
1717   // Find the main loop limit; we will trim it's iterations
1718   // to not ever trip end tests
1719   Node *main_limit = cl->limit();
1720 
1721   // Need to find the main-loop zero-trip guard
1722   Node *ctrl  = cl->in(LoopNode::EntryControl);
1723   assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
1724   Node *iffm = ctrl->in(0);
1725   assert(iffm->Opcode() == Op_If, "");
1726   Node *bolzm = iffm->in(1);
1727   assert(bolzm->Opcode() == Op_Bool, "");
1728   Node *cmpzm = bolzm->in(1);
1729   assert(cmpzm->is_Cmp(), "");
1730   Node *opqzm = cmpzm->in(2);
1731   // Can not optimize a loop if zero-trip Opaque1 node is optimized
1732   // away and then another round of loop opts attempted.
1733   if (opqzm->Opcode() != Op_Opaque1)
1734     return;
1735   assert(opqzm->in(1) == main_limit, "do not understand situation");
1736 
1737   // Find the pre-loop limit; we will expand it's iterations to
1738   // not ever trip low tests.
1739   Node *p_f = iffm->in(0);
1740   assert(p_f->Opcode() == Op_IfFalse, "");
1741   CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
1742   assert(pre_end->loopnode()->is_pre_loop(), "");
1743   Node *pre_opaq1 = pre_end->limit();
1744   // Occasionally it's possible for a pre-loop Opaque1 node to be
1745   // optimized away and then another round of loop opts attempted.
1746   // We can not optimize this particular loop in that case.
1747   if (pre_opaq1->Opcode() != Op_Opaque1)
1748     return;
1749   Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;
1750   Node *pre_limit = pre_opaq->in(1);
1751 
1752   // Where do we put new limit calculations
1753   Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);
1754 
1755   // Ensure the original loop limit is available from the
1756   // pre-loop Opaque1 node.
1757   Node *orig_limit = pre_opaq->original_loop_limit();
1758   if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP)
1759     return;
1760 
1761   // Must know if its a count-up or count-down loop
1762 
1763   int stride_con = cl->stride_con();
1764   Node *zero = _igvn.intcon(0);
1765   Node *one  = _igvn.intcon(1);
1766   // Use symmetrical int range [-max_jint,max_jint]
1767   Node *mini = _igvn.intcon(-max_jint);
1768   set_ctrl(zero, C->root());
1769   set_ctrl(one,  C->root());
1770   set_ctrl(mini, C->root());
1771 
1772   // Range checks that do not dominate the loop backedge (ie.
1773   // conditionally executed) can lengthen the pre loop limit beyond
1774   // the original loop limit. To prevent this, the pre limit is
1775   // (for stride > 0) MINed with the original loop limit (MAXed
1776   // stride < 0) when some range_check (rc) is conditionally
1777   // executed.
1778   bool conditional_rc = false;
1779 
1780   // Check loop body for tests of trip-counter plus loop-invariant vs
1781   // loop-invariant.
1782   for( uint i = 0; i < loop->_body.size(); i++ ) {
1783     Node *iff = loop->_body[i];
1784     if( iff->Opcode() == Op_If ) { // Test?
1785 
1786       // Test is an IfNode, has 2 projections.  If BOTH are in the loop
1787       // we need loop unswitching instead of iteration splitting.
1788       Node *exit = loop->is_loop_exit(iff);
1789       if( !exit ) continue;
1790       int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;
1791 
1792       // Get boolean condition to test
1793       Node *i1 = iff->in(1);
1794       if( !i1->is_Bool() ) continue;
1795       BoolNode *bol = i1->as_Bool();
1796       BoolTest b_test = bol->_test;
1797       // Flip sense of test if exit condition is flipped
1798       if( flip )
1799         b_test = b_test.negate();
1800 
1801       // Get compare
1802       Node *cmp = bol->in(1);
1803 
1804       // Look for trip_counter + offset vs limit
1805       Node *rc_exp = cmp->in(1);
1806       Node *limit  = cmp->in(2);
1807       jint scale_con= 1;        // Assume trip counter not scaled
1808 
1809       Node *limit_c = get_ctrl(limit);
1810       if( loop->is_member(get_loop(limit_c) ) ) {
1811         // Compare might have operands swapped; commute them
1812         b_test = b_test.commute();
1813         rc_exp = cmp->in(2);
1814         limit  = cmp->in(1);
1815         limit_c = get_ctrl(limit);
1816         if( loop->is_member(get_loop(limit_c) ) )
1817           continue;             // Both inputs are loop varying; cannot RCE
1818       }
1819       // Here we know 'limit' is loop invariant
1820 
1821       // 'limit' maybe pinned below the zero trip test (probably from a
1822       // previous round of rce), in which case, it can't be used in the
1823       // zero trip test expression which must occur before the zero test's if.
1824       if( limit_c == ctrl ) {
1825         continue;  // Don't rce this check but continue looking for other candidates.
1826       }
1827 
1828       // Check for scaled induction variable plus an offset
1829       Node *offset = NULL;
1830 
1831       if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {
1832         continue;
1833       }
1834 
1835       Node *offset_c = get_ctrl(offset);
1836       if( loop->is_member( get_loop(offset_c) ) )
1837         continue;               // Offset is not really loop invariant
1838       // Here we know 'offset' is loop invariant.
1839 
1840       // As above for the 'limit', the 'offset' maybe pinned below the
1841       // zero trip test.
1842       if( offset_c == ctrl ) {
1843         continue; // Don't rce this check but continue looking for other candidates.
1844       }
1845 #ifdef ASSERT
1846       if (TraceRangeLimitCheck) {
1847         tty->print_cr("RC bool node%s", flip ? " flipped:" : ":");
1848         bol->dump(2);
1849       }
1850 #endif
1851       // At this point we have the expression as:
1852       //   scale_con * trip_counter + offset :: limit
1853       // where scale_con, offset and limit are loop invariant.  Trip_counter
1854       // monotonically increases by stride_con, a constant.  Both (or either)
1855       // stride_con and scale_con can be negative which will flip about the
1856       // sense of the test.
1857 
1858       // Adjust pre and main loop limits to guard the correct iteration set
1859       if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests
1860         if( b_test._test == BoolTest::lt ) { // Range checks always use lt
1861           // The underflow and overflow limits: 0 <= scale*I+offset < limit
1862           add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );
1863           if (!conditional_rc) {
1864             conditional_rc = !loop->dominates_backedge(iff);
1865             // It is also needed if offset->_lo == min_int since
1866             // (0-min_int) == min_int. It may be fine for stride > 0
1867             // but for stride < 0 pre_limit will be < original_limit.
1868             const TypeInt* offset_t = _igvn.type(offset)->is_int();
1869             conditional_rc |= RangeLimitCheck && (offset_t->_lo == min_jint) &&
1870                               (scale_con<0) && (stride_con<0);
1871           }
1872         } else {
1873 #ifndef PRODUCT
1874           if( PrintOpto )
1875             tty->print_cr("missed RCE opportunity");
1876 #endif
1877           continue;             // In release mode, ignore it
1878         }
1879       } else {                  // Otherwise work on normal compares
1880         switch( b_test._test ) {
1881         case BoolTest::gt:
1882           // Fall into GE case
1883         case BoolTest::ge:
1884           // Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit
1885           scale_con = -scale_con;
1886           offset = new (C, 3) SubINode( zero, offset );
1887           register_new_node( offset, pre_ctrl );
1888           limit  = new (C, 3) SubINode( zero, limit  );
1889           register_new_node( limit, pre_ctrl );
1890           // Fall into LE case
1891         case BoolTest::le:
1892           if (b_test._test != BoolTest::gt) {
1893             // Convert X <= Y to X < Y+1
1894             limit = new (C, 3) AddINode( limit, one );
1895             register_new_node( limit, pre_ctrl );
1896           }
1897           // Fall into LT case
1898         case BoolTest::lt:
1899           // The underflow and overflow limits: MIN_INT <= scale*I+offset < limit
1900           add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit );
1901           if (!conditional_rc) {
1902             conditional_rc = !loop->dominates_backedge(iff);
1903             // It is also needed if scale*pre_limit+offset >= limit
1904             // due to underflow so we need execute pre-loop until
1905             // scale*I+offset >= min_int. But (low_limit-offset) will
1906             // underflow when offset > 0 and X will be > original_limit.
1907             const TypeInt* offset_t = _igvn.type(offset)->is_int();
1908             conditional_rc |= RangeLimitCheck && (offset_t->_hi > 0) &&
1909                               (scale_con>0) && (stride_con>0);
1910           }
1911           break;
1912         default:
1913 #ifndef PRODUCT
1914           if( PrintOpto )
1915             tty->print_cr("missed RCE opportunity");
1916 #endif
1917           continue;             // Unhandled case
1918         }
1919       }
1920 
1921       // Kill the eliminated test
1922       C->set_major_progress();
1923       Node *kill_con = _igvn.intcon( 1-flip );
1924       set_ctrl(kill_con, C->root());
1925       _igvn.hash_delete(iff);
1926       iff->set_req(1, kill_con);
1927       _igvn._worklist.push(iff);
1928       // Find surviving projection
1929       assert(iff->is_If(), "");
1930       ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);
1931       // Find loads off the surviving projection; remove their control edge
1932       for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
1933         Node* cd = dp->fast_out(i); // Control-dependent node
1934         if( cd->is_Load() ) {   // Loads can now float around in the loop
1935           _igvn.hash_delete(cd);
1936           // Allow the load to float around in the loop, or before it
1937           // but NOT before the pre-loop.
1938           cd->set_req(0, ctrl);   // ctrl, not NULL
1939           _igvn._worklist.push(cd);
1940           --i;
1941           --imax;
1942         }
1943       }
1944 
1945     } // End of is IF
1946 
1947   }
1948 
1949   // Update loop limits
1950   if (conditional_rc) {
1951     pre_limit = (stride_con > 0) ? (Node*)new (C,3) MinINode(pre_limit, orig_limit)
1952                                  : (Node*)new (C,3) MaxINode(pre_limit, orig_limit);
1953     register_new_node(pre_limit, pre_ctrl);
1954   }
1955   _igvn.hash_delete(pre_opaq);
1956   pre_opaq->set_req(1, pre_limit);
1957 
1958   // Note:: we are making the main loop limit no longer precise;
1959   // need to round up based on stride.
1960   cl->set_nonexact_trip_count();
1961   if (!LoopLimitCheck && stride_con != 1 && stride_con != -1) { // Cutout for common case
1962     // "Standard" round-up logic:  ([main_limit-init+(y-1)]/y)*y+init
1963     // Hopefully, compiler will optimize for powers of 2.
1964     Node *ctrl = get_ctrl(main_limit);
1965     Node *stride = cl->stride();
1966     Node *init = cl->init_trip();
1967     Node *span = new (C, 3) SubINode(main_limit,init);
1968     register_new_node(span,ctrl);
1969     Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));
1970     Node *add = new (C, 3) AddINode(span,rndup);
1971     register_new_node(add,ctrl);
1972     Node *div = new (C, 3) DivINode(0,add,stride);
1973     register_new_node(div,ctrl);
1974     Node *mul = new (C, 3) MulINode(div,stride);
1975     register_new_node(mul,ctrl);
1976     Node *newlim = new (C, 3) AddINode(mul,init);
1977     register_new_node(newlim,ctrl);
1978     main_limit = newlim;
1979   }
1980 
1981   Node *main_cle = cl->loopexit();
1982   Node *main_bol = main_cle->in(1);
1983   // Hacking loop bounds; need private copies of exit test
1984   if( main_bol->outcnt() > 1 ) {// BoolNode shared?
1985     _igvn.hash_delete(main_cle);
1986     main_bol = main_bol->clone();// Clone a private BoolNode
1987     register_new_node( main_bol, main_cle->in(0) );
1988     main_cle->set_req(1,main_bol);
1989   }
1990   Node *main_cmp = main_bol->in(1);
1991   if( main_cmp->outcnt() > 1 ) { // CmpNode shared?
1992     _igvn.hash_delete(main_bol);
1993     main_cmp = main_cmp->clone();// Clone a private CmpNode
1994     register_new_node( main_cmp, main_cle->in(0) );
1995     main_bol->set_req(1,main_cmp);
1996   }
1997   // Hack the now-private loop bounds
1998   _igvn.hash_delete(main_cmp);
1999   main_cmp->set_req(2, main_limit);
2000   _igvn._worklist.push(main_cmp);
2001   // The OpaqueNode is unshared by design
2002   _igvn.hash_delete(opqzm);
2003   assert( opqzm->outcnt() == 1, "cannot hack shared node" );
2004   opqzm->set_req(1,main_limit);
2005   _igvn._worklist.push(opqzm);
2006 }
2007 
2008 //------------------------------DCE_loop_body----------------------------------
2009 // Remove simplistic dead code from loop body
2010 void IdealLoopTree::DCE_loop_body() {
2011   for( uint i = 0; i < _body.size(); i++ )
2012     if( _body.at(i)->outcnt() == 0 )
2013       _body.map( i--, _body.pop() );
2014 }
2015 
2016 
2017 //------------------------------adjust_loop_exit_prob--------------------------
2018 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.
2019 // Replace with a 1-in-10 exit guess.
2020 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {
2021   Node *test = tail();
2022   while( test != _head ) {
2023     uint top = test->Opcode();
2024     if( top == Op_IfTrue || top == Op_IfFalse ) {
2025       int test_con = ((ProjNode*)test)->_con;
2026       assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");
2027       IfNode *iff = test->in(0)->as_If();
2028       if( iff->outcnt() == 2 ) {        // Ignore dead tests
2029         Node *bol = iff->in(1);
2030         if( bol && bol->req() > 1 && bol->in(1) &&
2031             ((bol->in(1)->Opcode() == Op_StorePConditional ) ||
2032              (bol->in(1)->Opcode() == Op_StoreIConditional ) ||
2033              (bol->in(1)->Opcode() == Op_StoreLConditional ) ||
2034              (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||
2035              (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||
2036              (bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||
2037              (bol->in(1)->Opcode() == Op_CompareAndSwapN )))
2038           return;               // Allocation loops RARELY take backedge
2039         // Find the OTHER exit path from the IF
2040         Node* ex = iff->proj_out(1-test_con);
2041         float p = iff->_prob;
2042         if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {
2043           if( top == Op_IfTrue ) {
2044             if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {
2045               iff->_prob = PROB_STATIC_FREQUENT;
2046             }
2047           } else {
2048             if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {
2049               iff->_prob = PROB_STATIC_INFREQUENT;
2050             }
2051           }
2052         }
2053       }
2054     }
2055     test = phase->idom(test);
2056   }
2057 }
2058 
2059 
2060 //------------------------------policy_do_remove_empty_loop--------------------
2061 // Micro-benchmark spamming.  Policy is to always remove empty loops.
2062 // The 'DO' part is to replace the trip counter with the value it will
2063 // have on the last iteration.  This will break the loop.
2064 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {
2065   // Minimum size must be empty loop
2066   if (_body.size() > EMPTY_LOOP_SIZE)
2067     return false;
2068 
2069   if (!_head->is_CountedLoop())
2070     return false;     // Dead loop
2071   CountedLoopNode *cl = _head->as_CountedLoop();
2072   if (!cl->loopexit())
2073     return false; // Malformed loop
2074   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))
2075     return false;             // Infinite loop
2076 
2077 #ifdef ASSERT
2078   // Ensure only one phi which is the iv.
2079   Node* iv = NULL;
2080   for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {
2081     Node* n = cl->fast_out(i);
2082     if (n->Opcode() == Op_Phi) {
2083       assert(iv == NULL, "Too many phis" );
2084       iv = n;
2085     }
2086   }
2087   assert(iv == cl->phi(), "Wrong phi" );
2088 #endif
2089 
2090   // main and post loops have explicitly created zero trip guard
2091   bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();
2092   if (needs_guard) {
2093     // Skip guard if values not overlap.
2094     const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int();
2095     const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int();
2096     int  stride_con = cl->stride_con();
2097     if (stride_con > 0) {
2098       needs_guard = (init_t->_hi >= limit_t->_lo);
2099     } else {
2100       needs_guard = (init_t->_lo <= limit_t->_hi);
2101     }
2102   }
2103   if (needs_guard) {
2104     // Check for an obvious zero trip guard.
2105     Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));
2106     if (inctrl->Opcode() == Op_IfTrue) {
2107       // The test should look like just the backedge of a CountedLoop
2108       Node* iff = inctrl->in(0);
2109       if (iff->is_If()) {
2110         Node* bol = iff->in(1);
2111         if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) {
2112           Node* cmp = bol->in(1);
2113           if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) {
2114             needs_guard = false;
2115           }
2116         }
2117       }
2118     }
2119   }
2120 
2121 #ifndef PRODUCT
2122   if (PrintOpto) {
2123     tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");
2124     this->dump_head();
2125   } else if (TraceLoopOpts) {
2126     tty->print("Empty with%s zero trip guard   ", needs_guard ? "out" : "");
2127     this->dump_head();
2128   }
2129 #endif
2130 
2131   if (needs_guard) {
2132     // Peel the loop to ensure there's a zero trip guard
2133     Node_List old_new;
2134     phase->do_peeling(this, old_new);
2135   }
2136 
2137   // Replace the phi at loop head with the final value of the last
2138   // iteration.  Then the CountedLoopEnd will collapse (backedge never
2139   // taken) and all loop-invariant uses of the exit values will be correct.
2140   Node *phi = cl->phi();
2141   Node *exact_limit = phase->exact_limit(this);
2142   if (exact_limit != cl->limit()) {
2143     // We also need to replace the original limit to collapse loop exit.
2144     Node* cmp = cl->loopexit()->cmp_node();
2145     assert(cl->limit() == cmp->in(2), "sanity");
2146     phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist
2147     phase->_igvn.hash_delete(cmp);
2148     cmp->set_req(2, exact_limit);
2149     phase->_igvn._worklist.push(cmp);        // put cmp on worklist
2150   }
2151   // Note: the final value after increment should not overflow since
2152   // counted loop has limit check predicate.
2153   Node *final = new (phase->C, 3) SubINode( exact_limit, cl->stride() );
2154   phase->register_new_node(final,cl->in(LoopNode::EntryControl));
2155   phase->_igvn.replace_node(phi,final);
2156   phase->C->set_major_progress();
2157   return true;
2158 }
2159 
2160 //------------------------------policy_do_one_iteration_loop-------------------
2161 // Convert one iteration loop into normal code.
2162 bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) {
2163   if (!_head->as_Loop()->is_valid_counted_loop())
2164     return false; // Only for counted loop
2165 
2166   CountedLoopNode *cl = _head->as_CountedLoop();
2167   if (!cl->has_exact_trip_count() || cl->trip_count() != 1) {
2168     return false;
2169   }
2170 
2171 #ifndef PRODUCT
2172   if(TraceLoopOpts) {
2173     tty->print("OneIteration ");
2174     this->dump_head();
2175   }
2176 #endif
2177 
2178   Node *init_n = cl->init_trip();
2179 #ifdef ASSERT
2180   // Loop boundaries should be constant since trip count is exact.
2181   assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration");
2182 #endif
2183   // Replace the phi at loop head with the value of the init_trip.
2184   // Then the CountedLoopEnd will collapse (backedge will not be taken)
2185   // and all loop-invariant uses of the exit values will be correct.
2186   phase->_igvn.replace_node(cl->phi(), cl->init_trip());
2187   phase->C->set_major_progress();
2188   return true;
2189 }
2190 
2191 //=============================================================================
2192 //------------------------------iteration_split_impl---------------------------
2193 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {
2194   // Compute exact loop trip count if possible.
2195   compute_exact_trip_count(phase);
2196 
2197   // Convert one iteration loop into normal code.
2198   if (policy_do_one_iteration_loop(phase))
2199     return true;
2200 
2201   // Check and remove empty loops (spam micro-benchmarks)
2202   if (policy_do_remove_empty_loop(phase))
2203     return true;  // Here we removed an empty loop
2204 
2205   bool should_peel = policy_peeling(phase); // Should we peel?
2206 
2207   bool should_unswitch = policy_unswitching(phase);
2208 
2209   // Non-counted loops may be peeled; exactly 1 iteration is peeled.
2210   // This removes loop-invariant tests (usually null checks).
2211   if (!_head->is_CountedLoop()) { // Non-counted loop
2212     if (PartialPeelLoop && phase->partial_peel(this, old_new)) {
2213       // Partial peel succeeded so terminate this round of loop opts
2214       return false;
2215     }
2216     if (should_peel) {            // Should we peel?
2217 #ifndef PRODUCT
2218       if (PrintOpto) tty->print_cr("should_peel");
2219 #endif
2220       phase->do_peeling(this,old_new);
2221     } else if (should_unswitch) {
2222       phase->do_unswitching(this, old_new);
2223     }
2224     return true;
2225   }
2226   CountedLoopNode *cl = _head->as_CountedLoop();
2227 
2228   if (!cl->loopexit()) return true; // Ignore various kinds of broken loops
2229 
2230   // Do nothing special to pre- and post- loops
2231   if (cl->is_pre_loop() || cl->is_post_loop()) return true;
2232 
2233   // Compute loop trip count from profile data
2234   compute_profile_trip_cnt(phase);
2235 
2236   // Before attempting fancy unrolling, RCE or alignment, see if we want
2237   // to completely unroll this loop or do loop unswitching.
2238   if (cl->is_normal_loop()) {
2239     if (should_unswitch) {
2240       phase->do_unswitching(this, old_new);
2241       return true;
2242     }
2243     bool should_maximally_unroll =  policy_maximally_unroll(phase);
2244     if (should_maximally_unroll) {
2245       // Here we did some unrolling and peeling.  Eventually we will
2246       // completely unroll this loop and it will no longer be a loop.
2247       phase->do_maximally_unroll(this,old_new);
2248       return true;
2249     }
2250   }
2251 
2252   // Skip next optimizations if running low on nodes. Note that
2253   // policy_unswitching and policy_maximally_unroll have this check.
2254   uint nodes_left = MaxNodeLimit - phase->C->unique();
2255   if ((2 * _body.size()) > nodes_left) {
2256     return true;
2257   }
2258 
2259   // Counted loops may be peeled, may need some iterations run up
2260   // front for RCE, and may want to align loop refs to a cache
2261   // line.  Thus we clone a full loop up front whose trip count is
2262   // at least 1 (if peeling), but may be several more.
2263 
2264   // The main loop will start cache-line aligned with at least 1
2265   // iteration of the unrolled body (zero-trip test required) and
2266   // will have some range checks removed.
2267 
2268   // A post-loop will finish any odd iterations (leftover after
2269   // unrolling), plus any needed for RCE purposes.
2270 
2271   bool should_unroll = policy_unroll(phase);
2272 
2273   bool should_rce = policy_range_check(phase);
2274 
2275   bool should_align = policy_align(phase);
2276 
2277   // If not RCE'ing (iteration splitting) or Aligning, then we do not
2278   // need a pre-loop.  We may still need to peel an initial iteration but
2279   // we will not be needing an unknown number of pre-iterations.
2280   //
2281   // Basically, if may_rce_align reports FALSE first time through,
2282   // we will not be able to later do RCE or Aligning on this loop.
2283   bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;
2284 
2285   // If we have any of these conditions (RCE, alignment, unrolling) met, then
2286   // we switch to the pre-/main-/post-loop model.  This model also covers
2287   // peeling.
2288   if (should_rce || should_align || should_unroll) {
2289     if (cl->is_normal_loop())  // Convert to 'pre/main/post' loops
2290       phase->insert_pre_post_loops(this,old_new, !may_rce_align);
2291 
2292     // Adjust the pre- and main-loop limits to let the pre and post loops run
2293     // with full checks, but the main-loop with no checks.  Remove said
2294     // checks from the main body.
2295     if (should_rce)
2296       phase->do_range_check(this,old_new);
2297 
2298     // Double loop body for unrolling.  Adjust the minimum-trip test (will do
2299     // twice as many iterations as before) and the main body limit (only do
2300     // an even number of trips).  If we are peeling, we might enable some RCE
2301     // and we'd rather unroll the post-RCE'd loop SO... do not unroll if
2302     // peeling.
2303     if (should_unroll && !should_peel)
2304       phase->do_unroll(this,old_new, true);
2305 
2306     // Adjust the pre-loop limits to align the main body
2307     // iterations.
2308     if (should_align)
2309       Unimplemented();
2310 
2311   } else {                      // Else we have an unchanged counted loop
2312     if (should_peel)           // Might want to peel but do nothing else
2313       phase->do_peeling(this,old_new);
2314   }
2315   return true;
2316 }
2317 
2318 
2319 //=============================================================================
2320 //------------------------------iteration_split--------------------------------
2321 bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {
2322   // Recursively iteration split nested loops
2323   if (_child && !_child->iteration_split(phase, old_new))
2324     return false;
2325 
2326   // Clean out prior deadwood
2327   DCE_loop_body();
2328 
2329 
2330   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
2331   // Replace with a 1-in-10 exit guess.
2332   if (_parent /*not the root loop*/ &&
2333       !_irreducible &&
2334       // Also ignore the occasional dead backedge
2335       !tail()->is_top()) {
2336     adjust_loop_exit_prob(phase);
2337   }
2338 
2339   // Gate unrolling, RCE and peeling efforts.
2340   if (!_child &&                // If not an inner loop, do not split
2341       !_irreducible &&
2342       _allow_optimizations &&
2343       !tail()->is_top()) {     // Also ignore the occasional dead backedge
2344     if (!_has_call) {
2345         if (!iteration_split_impl(phase, old_new)) {
2346           return false;
2347         }
2348     } else if (policy_unswitching(phase)) {
2349       phase->do_unswitching(this, old_new);
2350     }
2351   }
2352 
2353   // Minor offset re-organization to remove loop-fallout uses of
2354   // trip counter when there was no major reshaping.
2355   phase->reorg_offsets(this);
2356 
2357   if (_next && !_next->iteration_split(phase, old_new))
2358     return false;
2359   return true;
2360 }
2361 
2362 
2363 //=============================================================================
2364 // Process all the loops in the loop tree and replace any fill
2365 // patterns with an intrisc version.
2366 bool PhaseIdealLoop::do_intrinsify_fill() {
2367   bool changed = false;
2368   for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
2369     IdealLoopTree* lpt = iter.current();
2370     changed |= intrinsify_fill(lpt);
2371   }
2372   return changed;
2373 }
2374 
2375 
2376 // Examine an inner loop looking for a a single store of an invariant
2377 // value in a unit stride loop,
2378 bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
2379                                      Node*& shift, Node*& con) {
2380   const char* msg = NULL;
2381   Node* msg_node = NULL;
2382 
2383   store_value = NULL;
2384   con = NULL;
2385   shift = NULL;
2386 
2387   // Process the loop looking for stores.  If there are multiple
2388   // stores or extra control flow give at this point.
2389   CountedLoopNode* head = lpt->_head->as_CountedLoop();
2390   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2391     Node* n = lpt->_body.at(i);
2392     if (n->outcnt() == 0) continue; // Ignore dead
2393     if (n->is_Store()) {
2394       if (store != NULL) {
2395         msg = "multiple stores";
2396         break;
2397       }
2398       int opc = n->Opcode();
2399       if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreCM) {
2400         msg = "oop fills not handled";
2401         break;
2402       }
2403       Node* value = n->in(MemNode::ValueIn);
2404       if (!lpt->is_invariant(value)) {
2405         msg  = "variant store value";
2406       } else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) {
2407         msg = "not array address";
2408       }
2409       store = n;
2410       store_value = value;
2411     } else if (n->is_If() && n != head->loopexit()) {
2412       msg = "extra control flow";
2413       msg_node = n;
2414     }
2415   }
2416 
2417   if (store == NULL) {
2418     // No store in loop
2419     return false;
2420   }
2421 
2422   if (msg == NULL && head->stride_con() != 1) {
2423     // could handle negative strides too
2424     if (head->stride_con() < 0) {
2425       msg = "negative stride";
2426     } else {
2427       msg = "non-unit stride";
2428     }
2429   }
2430 
2431   if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) {
2432     msg = "can't handle store address";
2433     msg_node = store->in(MemNode::Address);
2434   }
2435 
2436   if (msg == NULL &&
2437       (!store->in(MemNode::Memory)->is_Phi() ||
2438        store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) {
2439     msg = "store memory isn't proper phi";
2440     msg_node = store->in(MemNode::Memory);
2441   }
2442 
2443   // Make sure there is an appropriate fill routine
2444   BasicType t = store->as_Mem()->memory_type();
2445   const char* fill_name;
2446   if (msg == NULL &&
2447       StubRoutines::select_fill_function(t, false, fill_name) == NULL) {
2448     msg = "unsupported store";
2449     msg_node = store;
2450   }
2451 
2452   if (msg != NULL) {
2453 #ifndef PRODUCT
2454     if (TraceOptimizeFill) {
2455       tty->print_cr("not fill intrinsic candidate: %s", msg);
2456       if (msg_node != NULL) msg_node->dump();
2457     }
2458 #endif
2459     return false;
2460   }
2461 
2462   // Make sure the address expression can be handled.  It should be
2463   // head->phi * elsize + con.  head->phi might have a ConvI2L.
2464   Node* elements[4];
2465   Node* conv = NULL;
2466   bool found_index = false;
2467   int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements));
2468   for (int e = 0; e < count; e++) {
2469     Node* n = elements[e];
2470     if (n->is_Con() && con == NULL) {
2471       con = n;
2472     } else if (n->Opcode() == Op_LShiftX && shift == NULL) {
2473       Node* value = n->in(1);
2474 #ifdef _LP64
2475       if (value->Opcode() == Op_ConvI2L) {
2476         conv = value;
2477         value = value->in(1);
2478       }
2479 #endif
2480       if (value != head->phi()) {
2481         msg = "unhandled shift in address";
2482       } else {
2483         if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) {
2484           msg = "scale doesn't match";
2485         } else {
2486           found_index = true;
2487           shift = n;
2488         }
2489       }
2490     } else if (n->Opcode() == Op_ConvI2L && conv == NULL) {
2491       if (n->in(1) == head->phi()) {
2492         found_index = true;
2493         conv = n;
2494       } else {
2495         msg = "unhandled input to ConvI2L";
2496       }
2497     } else if (n == head->phi()) {
2498       // no shift, check below for allowed cases
2499       found_index = true;
2500     } else {
2501       msg = "unhandled node in address";
2502       msg_node = n;
2503     }
2504   }
2505 
2506   if (count == -1) {
2507     msg = "malformed address expression";
2508     msg_node = store;
2509   }
2510 
2511   if (!found_index) {
2512     msg = "missing use of index";
2513   }
2514 
2515   // byte sized items won't have a shift
2516   if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) {
2517     msg = "can't find shift";
2518     msg_node = store;
2519   }
2520 
2521   if (msg != NULL) {
2522 #ifndef PRODUCT
2523     if (TraceOptimizeFill) {
2524       tty->print_cr("not fill intrinsic: %s", msg);
2525       if (msg_node != NULL) msg_node->dump();
2526     }
2527 #endif
2528     return false;
2529   }
2530 
2531   // No make sure all the other nodes in the loop can be handled
2532   VectorSet ok(Thread::current()->resource_area());
2533 
2534   // store related values are ok
2535   ok.set(store->_idx);
2536   ok.set(store->in(MemNode::Memory)->_idx);
2537 
2538   // Loop structure is ok
2539   ok.set(head->_idx);
2540   ok.set(head->loopexit()->_idx);
2541   ok.set(head->phi()->_idx);
2542   ok.set(head->incr()->_idx);
2543   ok.set(head->loopexit()->cmp_node()->_idx);
2544   ok.set(head->loopexit()->in(1)->_idx);
2545 
2546   // Address elements are ok
2547   if (con)   ok.set(con->_idx);
2548   if (shift) ok.set(shift->_idx);
2549   if (conv)  ok.set(conv->_idx);
2550 
2551   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2552     Node* n = lpt->_body.at(i);
2553     if (n->outcnt() == 0) continue; // Ignore dead
2554     if (ok.test(n->_idx)) continue;
2555     // Backedge projection is ok
2556     if (n->is_IfTrue() && n->in(0) == head->loopexit()) continue;
2557     if (!n->is_AddP()) {
2558       msg = "unhandled node";
2559       msg_node = n;
2560       break;
2561     }
2562   }
2563 
2564   // Make sure no unexpected values are used outside the loop
2565   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {
2566     Node* n = lpt->_body.at(i);
2567     // These values can be replaced with other nodes if they are used
2568     // outside the loop.
2569     if (n == store || n == head->loopexit() || n == head->incr() || n == store->in(MemNode::Memory)) continue;
2570     for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) {
2571       Node* use = iter.get();
2572       if (!lpt->_body.contains(use)) {
2573         msg = "node is used outside loop";
2574         // lpt->_body.dump();
2575         msg_node = n;
2576         break;
2577       }
2578     }
2579   }
2580 
2581 #ifdef ASSERT
2582   if (TraceOptimizeFill) {
2583     if (msg != NULL) {
2584       tty->print_cr("no fill intrinsic: %s", msg);
2585       if (msg_node != NULL) msg_node->dump();
2586     } else {
2587       tty->print_cr("fill intrinsic for:");
2588     }
2589     store->dump();
2590     if (Verbose) {
2591       lpt->_body.dump();
2592     }
2593   }
2594 #endif
2595 
2596   return msg == NULL;
2597 }
2598 
2599 
2600 
2601 bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
2602   // Only for counted inner loops
2603   if (!lpt->is_counted() || !lpt->is_inner()) {
2604     return false;
2605   }
2606 
2607   // Must have constant stride
2608   CountedLoopNode* head = lpt->_head->as_CountedLoop();
2609   if (!head->stride_is_con() || !head->is_normal_loop()) {
2610     return false;
2611   }
2612 
2613   // Check that the body only contains a store of a loop invariant
2614   // value that is indexed by the loop phi.
2615   Node* store = NULL;
2616   Node* store_value = NULL;
2617   Node* shift = NULL;
2618   Node* offset = NULL;
2619   if (!match_fill_loop(lpt, store, store_value, shift, offset)) {
2620     return false;
2621   }
2622 
2623 #ifndef PRODUCT
2624   if (TraceLoopOpts) {
2625     tty->print("ArrayFill    ");
2626     lpt->dump_head();
2627   }
2628 #endif
2629 
2630   // Now replace the whole loop body by a call to a fill routine that
2631   // covers the same region as the loop.
2632   Node* base = store->in(MemNode::Address)->as_AddP()->in(AddPNode::Base);
2633 
2634   // Build an expression for the beginning of the copy region
2635   Node* index = head->init_trip();
2636 #ifdef _LP64
2637   index = new (C, 2) ConvI2LNode(index);
2638   _igvn.register_new_node_with_optimizer(index);
2639 #endif
2640   if (shift != NULL) {
2641     // byte arrays don't require a shift but others do.
2642     index = new (C, 3) LShiftXNode(index, shift->in(2));
2643     _igvn.register_new_node_with_optimizer(index);
2644   }
2645   index = new (C, 4) AddPNode(base, base, index);
2646   _igvn.register_new_node_with_optimizer(index);
2647   Node* from = new (C, 4) AddPNode(base, index, offset);
2648   _igvn.register_new_node_with_optimizer(from);
2649   // Compute the number of elements to copy
2650   Node* len = new (C, 3) SubINode(head->limit(), head->init_trip());
2651   _igvn.register_new_node_with_optimizer(len);
2652 
2653   BasicType t = store->as_Mem()->memory_type();
2654   bool aligned = false;
2655   if (offset != NULL && head->init_trip()->is_Con()) {
2656     int element_size = type2aelembytes(t);
2657     aligned = (offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int() * element_size) % HeapWordSize == 0;
2658   }
2659 
2660   // Build a call to the fill routine
2661   const char* fill_name;
2662   address fill = StubRoutines::select_fill_function(t, aligned, fill_name);
2663   assert(fill != NULL, "what?");
2664 
2665   // Convert float/double to int/long for fill routines
2666   if (t == T_FLOAT) {
2667     store_value = new (C, 2) MoveF2INode(store_value);
2668     _igvn.register_new_node_with_optimizer(store_value);
2669   } else if (t == T_DOUBLE) {
2670     store_value = new (C, 2) MoveD2LNode(store_value);
2671     _igvn.register_new_node_with_optimizer(store_value);
2672   }
2673 
2674   Node* mem_phi = store->in(MemNode::Memory);
2675   Node* result_ctrl;
2676   Node* result_mem;
2677   const TypeFunc* call_type = OptoRuntime::array_fill_Type();
2678   int size = call_type->domain()->cnt();
2679   CallLeafNode *call = new (C, size) CallLeafNoFPNode(call_type, fill,
2680                                                       fill_name, TypeAryPtr::get_array_body_type(t));
2681   call->init_req(TypeFunc::Parms+0, from);
2682   call->init_req(TypeFunc::Parms+1, store_value);
2683 #ifdef _LP64
2684   len = new (C, 2) ConvI2LNode(len);
2685   _igvn.register_new_node_with_optimizer(len);
2686 #endif
2687   call->init_req(TypeFunc::Parms+2, len);
2688 #ifdef _LP64
2689   call->init_req(TypeFunc::Parms+3, C->top());
2690 #endif
2691   call->init_req( TypeFunc::Control, head->init_control());
2692   call->init_req( TypeFunc::I_O    , C->top() )        ;   // does no i/o
2693   call->init_req( TypeFunc::Memory ,  mem_phi->in(LoopNode::EntryControl) );
2694   call->init_req( TypeFunc::ReturnAdr, C->start()->proj_out(TypeFunc::ReturnAdr) );
2695   call->init_req( TypeFunc::FramePtr, C->start()->proj_out(TypeFunc::FramePtr) );
2696   _igvn.register_new_node_with_optimizer(call);
2697   result_ctrl = new (C, 1) ProjNode(call,TypeFunc::Control);
2698   _igvn.register_new_node_with_optimizer(result_ctrl);
2699   result_mem = new (C, 1) ProjNode(call,TypeFunc::Memory);
2700   _igvn.register_new_node_with_optimizer(result_mem);
2701 
2702   // If this fill is tightly coupled to an allocation and overwrites
2703   // the whole body, allow it to take over the zeroing.
2704   AllocateNode* alloc = AllocateNode::Ideal_allocation(base, this);
2705   if (alloc != NULL && alloc->is_AllocateArray()) {
2706     Node* length = alloc->as_AllocateArray()->Ideal_length();
2707     if (head->limit() == length &&
2708         head->init_trip() == _igvn.intcon(0)) {
2709       if (TraceOptimizeFill) {
2710         tty->print_cr("Eliminated zeroing in allocation");
2711       }
2712       alloc->maybe_set_complete(&_igvn);
2713     } else {
2714 #ifdef ASSERT
2715       if (TraceOptimizeFill) {
2716         tty->print_cr("filling array but bounds don't match");
2717         alloc->dump();
2718         head->init_trip()->dump();
2719         head->limit()->dump();
2720         length->dump();
2721       }
2722 #endif
2723     }
2724   }
2725 
2726   // Redirect the old control and memory edges that are outside the loop.
2727   Node* exit = head->loopexit()->proj_out(0);
2728   // Sometimes the memory phi of the head is used as the outgoing
2729   // state of the loop.  It's safe in this case to replace it with the
2730   // result_mem.
2731   _igvn.replace_node(store->in(MemNode::Memory), result_mem);
2732   _igvn.replace_node(exit, result_ctrl);
2733   _igvn.replace_node(store, result_mem);
2734   // Any uses the increment outside of the loop become the loop limit.
2735   _igvn.replace_node(head->incr(), head->limit());
2736 
2737   // Disconnect the head from the loop.
2738   for (uint i = 0; i < lpt->_body.size(); i++) {
2739     Node* n = lpt->_body.at(i);
2740     _igvn.replace_node(n, C->top());
2741   }
2742 
2743   return true;
2744 }