Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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  */

 #include "precompiled.hpp"

 #include "compiler/compileLog.hpp"

 #include "memory/allocation.inline.hpp"

 #include "opto/addnode.hpp"

 #include "opto/callnode.hpp"

 #include "opto/connode.hpp"

 #include "opto/divnode.hpp"

 #include "opto/loopnode.hpp"

 #include "opto/mulnode.hpp"

 #include "opto/rootnode.hpp"

 #include "opto/runtime.hpp"

 #include "opto/subnode.hpp"

 //------------------------------is_loop_exit-----------------------------------

 // Given an IfNode, return the loop-exiting projection or NULL if both

 // arms remain in the loop.

 Node *IdealLoopTree::is_loop_exit(Node *iff) const {

   if( iff->outcnt() != 2 ) return NULL; // Ignore partially dead tests

   PhaseIdealLoop *phase = _phase;

   // Test is an IfNode, has 2 projections.  If BOTH are in the loop

   // we need loop unswitching instead of peeling.

   if( !is_member(phase->get_loop( iff->raw_out(0) )) )

     return iff->raw_out(0);

   if( !is_member(phase->get_loop( iff->raw_out(1) )) )

     return iff->raw_out(1);

   return NULL;

 }

 //=============================================================================

 //------------------------------record_for_igvn----------------------------

 // Put loop body on igvn work list

 void IdealLoopTree::record_for_igvn() {

   for( uint i = 0; i < _body.size(); i++ ) {

     Node *n = _body.at(i);

     _phase->_igvn._worklist.push(n);

   }

 }

 //------------------------------compute_exact_trip_count-----------------------

 // Compute loop exact trip count if possible. Do not recalculate trip count for

 // split loops (pre-main-post) which have their limits and inits behind Opaque node.

 void IdealLoopTree::compute_exact_trip_count( PhaseIdealLoop *phase ) {

   if (!_head->as_Loop()->is_valid_counted_loop()) {

     return;

   }

   CountedLoopNode* cl = _head->as_CountedLoop();

   // Trip count may become nonexact for iteration split loops since

   // RCE modifies limits. Note, _trip_count value is not reset since

   // it is used to limit unrolling of main loop.

   cl->set_nonexact_trip_count();

   // Loop's test should be part of loop.

   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))

     return; // Infinite loop

 #ifdef ASSERT

   BoolTest::mask bt = cl->loopexit()->test_trip();

   assert(bt == BoolTest::lt || bt == BoolTest::gt ||

          bt == BoolTest::ne, "canonical test is expected");

 #endif

   Node* init_n = cl->init_trip();

   Node* limit_n = cl->limit();

   if (init_n  != NULL &&  init_n->is_Con() &&

       limit_n != NULL && limit_n->is_Con()) {

     // Use longs to avoid integer overflow.

     int stride_con  = cl->stride_con();

     jlong init_con   = cl->init_trip()->get_int();

     jlong limit_con  = cl->limit()->get_int();

     int stride_m    = stride_con - (stride_con > 0 ? 1 : -1);

     jlong trip_count = (limit_con - init_con + stride_m)/stride_con;

     if (trip_count > 0 && (julong)trip_count < (julong)max_juint) {

       // Set exact trip count.

       cl->set_exact_trip_count((uint)trip_count);

     }

   }

 }

 //------------------------------compute_profile_trip_cnt----------------------------

 // Compute loop trip count from profile data as

 //    (backedge_count + loop_exit_count) / loop_exit_count

 void IdealLoopTree::compute_profile_trip_cnt( PhaseIdealLoop *phase ) {

   if (!_head->is_CountedLoop()) {

     return;

   }

   CountedLoopNode* head = _head->as_CountedLoop();

   if (head->profile_trip_cnt() != COUNT_UNKNOWN) {

     return; // Already computed

   }

   float trip_cnt = (float)max_jint; // default is big

   Node* back = head->in(LoopNode::LoopBackControl);

   while (back != head) {

     if ((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&

         back->in(0) &&

         back->in(0)->is_If() &&

         back->in(0)->as_If()->_fcnt != COUNT_UNKNOWN &&

         back->in(0)->as_If()->_prob != PROB_UNKNOWN) {

       break;

     }

     back = phase->idom(back);

   }

   if (back != head) {

     assert((back->Opcode() == Op_IfTrue || back->Opcode() == Op_IfFalse) &&

            back->in(0), "if-projection exists");

     IfNode* back_if = back->in(0)->as_If();

     float loop_back_cnt = back_if->_fcnt * back_if->_prob;

     // Now compute a loop exit count

     float loop_exit_cnt = 0.0f;

     for( uint i = 0; i < _body.size(); i++ ) {

       Node *n = _body[i];

       if( n->is_If() ) {

         IfNode *iff = n->as_If();

         if( iff->_fcnt != COUNT_UNKNOWN && iff->_prob != PROB_UNKNOWN ) {

           Node *exit = is_loop_exit(iff);

           if( exit ) {

             float exit_prob = iff->_prob;

             if (exit->Opcode() == Op_IfFalse) exit_prob = 1.0 - exit_prob;

             if (exit_prob > PROB_MIN) {

               float exit_cnt = iff->_fcnt * exit_prob;

               loop_exit_cnt += exit_cnt;

             }

           }

         }

       }

     }

     if (loop_exit_cnt > 0.0f) {

       trip_cnt = (loop_back_cnt + loop_exit_cnt) / loop_exit_cnt;

     } else {

       // No exit count so use

       trip_cnt = loop_back_cnt;

     }

   }

 #ifndef PRODUCT

   if (TraceProfileTripCount) {

     tty->print_cr("compute_profile_trip_cnt  lp: %d cnt: %f\n", head->_idx, trip_cnt);

   }

 #endif

   head->set_profile_trip_cnt(trip_cnt);

 }

 //---------------------is_invariant_addition-----------------------------

 // Return nonzero index of invariant operand for an Add or Sub

 // of (nonconstant) invariant and variant values. Helper for reassociate_invariants.

 int IdealLoopTree::is_invariant_addition(Node* n, PhaseIdealLoop *phase) {

   int op = n->Opcode();

   if (op == Op_AddI || op == Op_SubI) {

     bool in1_invar = this->is_invariant(n->in(1));

     bool in2_invar = this->is_invariant(n->in(2));

     if (in1_invar && !in2_invar) return 1;

     if (!in1_invar && in2_invar) return 2;

   }

   return 0;

 }

 //---------------------reassociate_add_sub-----------------------------

 // Reassociate invariant add and subtract expressions:

 //

 // inv1 + (x + inv2)  =>  ( inv1 + inv2) + x

 // (x + inv2) + inv1  =>  ( inv1 + inv2) + x

 // inv1 + (x - inv2)  =>  ( inv1 - inv2) + x

 // inv1 - (inv2 - x)  =>  ( inv1 - inv2) + x

 // (x + inv2) - inv1  =>  (-inv1 + inv2) + x

 // (x - inv2) + inv1  =>  ( inv1 - inv2) + x

 // (x - inv2) - inv1  =>  (-inv1 - inv2) + x

 // inv1 + (inv2 - x)  =>  ( inv1 + inv2) - x

 // inv1 - (x - inv2)  =>  ( inv1 + inv2) - x

 // (inv2 - x) + inv1  =>  ( inv1 + inv2) - x

 // (inv2 - x) - inv1  =>  (-inv1 + inv2) - x

 // inv1 - (x + inv2)  =>  ( inv1 - inv2) - x

 //

 Node* IdealLoopTree::reassociate_add_sub(Node* n1, PhaseIdealLoop *phase) {

   if (!n1->is_Add() && !n1->is_Sub() || n1->outcnt() == 0) return NULL;

   if (is_invariant(n1)) return NULL;

   int inv1_idx = is_invariant_addition(n1, phase);

   if (!inv1_idx) return NULL;

   // Don't mess with add of constant (igvn moves them to expression tree root.)

   if (n1->is_Add() && n1->in(2)->is_Con()) return NULL;

   Node* inv1 = n1->in(inv1_idx);

   Node* n2 = n1->in(3 - inv1_idx);

   int inv2_idx = is_invariant_addition(n2, phase);

   if (!inv2_idx) return NULL;

   Node* x    = n2->in(3 - inv2_idx);

   Node* inv2 = n2->in(inv2_idx);

   bool neg_x    = n2->is_Sub() && inv2_idx == 1;

   bool neg_inv2 = n2->is_Sub() && inv2_idx == 2;

   bool neg_inv1 = n1->is_Sub() && inv1_idx == 2;

   if (n1->is_Sub() && inv1_idx == 1) {

     neg_x    = !neg_x;

     neg_inv2 = !neg_inv2;

   }

   Node* inv1_c = phase->get_ctrl(inv1);

   Node* inv2_c = phase->get_ctrl(inv2);

   Node* n_inv1;

   if (neg_inv1) {

     Node *zero = phase->_igvn.intcon(0);

     phase->set_ctrl(zero, phase->C->root());

     n_inv1 = new (phase->C) SubINode(zero, inv1);

     phase->register_new_node(n_inv1, inv1_c);

   } else {

     n_inv1 = inv1;

   }

   Node* inv;

   if (neg_inv2) {

     inv = new (phase->C) SubINode(n_inv1, inv2);

   } else {

     inv = new (phase->C) AddINode(n_inv1, inv2);

   }

   phase->register_new_node(inv, phase->get_early_ctrl(inv));

   Node* addx;

   if (neg_x) {

     addx = new (phase->C) SubINode(inv, x);

   } else {

     addx = new (phase->C) AddINode(x, inv);

   }

   phase->register_new_node(addx, phase->get_ctrl(x));

   phase->_igvn.replace_node(n1, addx);

   assert(phase->get_loop(phase->get_ctrl(n1)) == this, "");

   _body.yank(n1);

   return addx;

 }

 //---------------------reassociate_invariants-----------------------------

 // Reassociate invariant expressions:

 void IdealLoopTree::reassociate_invariants(PhaseIdealLoop *phase) {

   for (int i = _body.size() - 1; i >= 0; i--) {

     Node *n = _body.at(i);

     for (int j = 0; j < 5; j++) {

       Node* nn = reassociate_add_sub(n, phase);

       if (nn == NULL) break;

       n = nn; // again

     };

   }

 }

 //------------------------------policy_peeling---------------------------------

 // Return TRUE or FALSE if the loop should be peeled or not.  Peel if we can

 // make some loop-invariant test (usually a null-check) happen before the loop.

 bool IdealLoopTree::policy_peeling( PhaseIdealLoop *phase ) const {

   Node *test = ((IdealLoopTree*)this)->tail();

   int  body_size = ((IdealLoopTree*)this)->_body.size();

   int  live_node_count = phase->C->live_nodes();

   // Peeling does loop cloning which can result in O(N^2) node construction

   if( body_size > 255 /* Prevent overflow for large body_size */

       || (body_size * body_size + live_node_count > MaxNodeLimit) ) {

     return false;           // too large to safely clone

   }

   while( test != _head ) {      // Scan till run off top of loop

     if( test->is_If() ) {       // Test?

       Node *ctrl = phase->get_ctrl(test->in(1));

       if (ctrl->is_top())

         return false;           // Found dead test on live IF?  No peeling!

       // Standard IF only has one input value to check for loop invariance

       assert( test->Opcode() == Op_If || test->Opcode() == Op_CountedLoopEnd, "Check this code when new subtype is added");

       // Condition is not a member of this loop?

       if( !is_member(phase->get_loop(ctrl)) &&

           is_loop_exit(test) )

         return true;            // Found reason to peel!

     }

     // Walk up dominators to loop _head looking for test which is

     // executed on every path thru loop.

     test = phase->idom(test);

   }

   return false;

 }

 //------------------------------peeled_dom_test_elim---------------------------

 // If we got the effect of peeling, either by actually peeling or by making

 // a pre-loop which must execute at least once, we can remove all

 // loop-invariant dominated tests in the main body.

 void PhaseIdealLoop::peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new ) {

   bool progress = true;

   while( progress ) {

     progress = false;           // Reset for next iteration

     Node *prev = loop->_head->in(LoopNode::LoopBackControl);//loop->tail();

     Node *test = prev->in(0);

     while( test != loop->_head ) { // Scan till run off top of loop

       int p_op = prev->Opcode();

       if( (p_op == Op_IfFalse || p_op == Op_IfTrue) &&

           test->is_If() &&      // Test?

           !test->in(1)->is_Con() && // And not already obvious?

           // Condition is not a member of this loop?

           !loop->is_member(get_loop(get_ctrl(test->in(1))))){

         // Walk loop body looking for instances of this test

         for( uint i = 0; i < loop->_body.size(); i++ ) {

           Node *n = loop->_body.at(i);

           if( n->is_If() && n->in(1) == test->in(1) /*&& n != loop->tail()->in(0)*/ ) {

             // IfNode was dominated by version in peeled loop body

             progress = true;

             dominated_by( old_new[prev->_idx], n );

           }

         }

       }

       prev = test;

       test = idom(test);

     } // End of scan tests in loop

   } // End of while( progress )

 }

 //------------------------------do_peeling-------------------------------------

 // Peel the first iteration of the given loop.

 // Step 1: Clone the loop body.  The clone becomes the peeled iteration.

 //         The pre-loop illegally has 2 control users (old & new loops).

 // Step 2: Make the old-loop fall-in edges point to the peeled iteration.

 //         Do this by making the old-loop fall-in edges act as if they came

 //         around the loopback from the prior iteration (follow the old-loop

 //         backedges) and then map to the new peeled iteration.  This leaves

 //         the pre-loop with only 1 user (the new peeled iteration), but the

 //         peeled-loop backedge has 2 users.

 // Step 3: Cut the backedge on the clone (so its not a loop) and remove the

 //         extra backedge user.

 //

 //                   orig

 //

 //                  stmt1

 //                    |

 //                    v

 //              loop predicate

 //                    |

 //                    v

 //                   loop<----+

 //                     |      |

 //                   stmt2    |

 //                     |      |

 //                     v      |

 //                    if      ^

 //                   / \      |

 //                  /   \     |

 //                 v     v    |

 //               false true   |

 //               /       \    |

 //              /         ----+

 //             |

 //             v

 //           exit

 //

 //

 //            after clone loop

 //

 //                   stmt1

 //                     |

 //                     v

 //               loop predicate

 //                 /       \

 //        clone   /         \   orig

 //               /           \

 //              /             \

 //             v               v

 //   +---->loop clone          loop<----+

 //   |      |                    |      |

 //   |    stmt2 clone          stmt2    |

 //   |      |                    |      |

 //   |      v                    v      |

 //   ^      if clone            If      ^

 //   |      / \                / \      |

 //   |     /   \              /   \     |

 //   |    v     v            v     v    |

 //   |    true  false      false true   |

 //   |    /         \      /       \    |

 //   +----           \    /         ----+

 //                    \  /

 //                    1v v2

 //                  region

 //                     |

 //                     v

 //                   exit

 //

 //

 //         after peel and predicate move

 //

 //                   stmt1

 //                    /

 //                   /

 //        clone     /            orig

 //                 /

 //                /              +----------+

 //               /               |          |

 //              /          loop predicate   |

 //             /                 |          |

 //            v                  v          |

 //   TOP-->loop clone          loop<----+   |

 //          |                    |      |   |

 //        stmt2 clone          stmt2    |   |

 //          |                    |      |   ^

 //          v                    v      |   |

 //          if clone            If      ^   |

 //          / \                / \      |   |

 //         /   \              /   \     |   |

 //        v     v            v     v    |   |

 //      true   false      false  true   |   |

 //        |         \      /       \    |   |

 //        |          \    /         ----+   ^

 //        |           \  /                  |

 //        |           1v v2                 |

 //        v         region                  |

 //        |            |                    |

 //        |            v                    |

 //        |          exit                   |

 //        |                                 |

 //        +--------------->-----------------+

 //

 //

 //              final graph

 //

 //                  stmt1

 //                    |

 //                    v

 //                  stmt2 clone

 //                    |

 //                    v

 //                   if clone

 //                  / |

 //                 /  |

 //                v   v

 //            false  true

 //             |      |

 //             |      v

 //             | loop predicate

 //             |      |

 //             |      v

 //             |     loop<----+

 //             |      |       |

 //             |    stmt2     |

 //             |      |       |

 //             |      v       |

 //             v      if      ^

 //             |     /  \     |

 //             |    /    \    |

 //             |   v     v    |

 //             | false  true  |

 //             |  |        \  |

 //             v  v         --+

 //            region

 //              |

 //              v

 //             exit

 //

 void PhaseIdealLoop::do_peeling( IdealLoopTree *loop, Node_List &old_new ) {

   C->set_major_progress();

   // Peeling a 'main' loop in a pre/main/post situation obfuscates the

   // 'pre' loop from the main and the 'pre' can no longer have it's

   // iterations adjusted.  Therefore, we need to declare this loop as

   // no longer a 'main' loop; it will need new pre and post loops before

   // we can do further RCE.

 #ifndef PRODUCT

   if (TraceLoopOpts) {

     tty->print("Peel         ");

     loop->dump_head();

   }

 #endif

   Node* head = loop->_head;

   bool counted_loop = head->is_CountedLoop();

   if (counted_loop) {

     CountedLoopNode *cl = head->as_CountedLoop();

     assert(cl->trip_count() > 0, "peeling a fully unrolled loop");

     cl->set_trip_count(cl->trip_count() - 1);

     if (cl->is_main_loop()) {

       cl->set_normal_loop();

 #ifndef PRODUCT

       if (PrintOpto && VerifyLoopOptimizations) {

         tty->print("Peeling a 'main' loop; resetting to 'normal' ");

         loop->dump_head();

       }

 #endif

     }

   }

   Node* entry = head->in(LoopNode::EntryControl);

   // Step 1: Clone the loop body.  The clone becomes the peeled iteration.

   //         The pre-loop illegally has 2 control users (old & new loops).

   clone_loop( loop, old_new, dom_depth(head) );

   // Step 2: Make the old-loop fall-in edges point to the peeled iteration.

   //         Do this by making the old-loop fall-in edges act as if they came

   //         around the loopback from the prior iteration (follow the old-loop

   //         backedges) and then map to the new peeled iteration.  This leaves

   //         the pre-loop with only 1 user (the new peeled iteration), but the

   //         peeled-loop backedge has 2 users.

   Node* new_entry = old_new[head->in(LoopNode::LoopBackControl)->_idx];

   _igvn.hash_delete(head);

   head->set_req(LoopNode::EntryControl, new_entry);

   for (DUIterator_Fast jmax, j = head->fast_outs(jmax); j < jmax; j++) {

     Node* old = head->fast_out(j);

     if (old->in(0) == loop->_head && old->req() == 3 && old->is_Phi()) {

       Node* new_exit_value = old_new[old->in(LoopNode::LoopBackControl)->_idx];

       if (!new_exit_value )     // Backedge value is ALSO loop invariant?

         // Then loop body backedge value remains the same.

         new_exit_value = old->in(LoopNode::LoopBackControl);

       _igvn.hash_delete(old);

       old->set_req(LoopNode::EntryControl, new_exit_value);

     }

   }

   // Step 3: Cut the backedge on the clone (so its not a loop) and remove the

   //         extra backedge user.

   Node* new_head = old_new[head->_idx];

   _igvn.hash_delete(new_head);

   new_head->set_req(LoopNode::LoopBackControl, C->top());

   for (DUIterator_Fast j2max, j2 = new_head->fast_outs(j2max); j2 < j2max; j2++) {

     Node* use = new_head->fast_out(j2);

     if (use->in(0) == new_head && use->req() == 3 && use->is_Phi()) {

       _igvn.hash_delete(use);

       use->set_req(LoopNode::LoopBackControl, C->top());

     }

   }

   // Step 4: Correct dom-depth info.  Set to loop-head depth.

   int dd = dom_depth(head);

   set_idom(head, head->in(1), dd);

   for (uint j3 = 0; j3 < loop->_body.size(); j3++) {

     Node *old = loop->_body.at(j3);

     Node *nnn = old_new[old->_idx];

     if (!has_ctrl(nnn))

       set_idom(nnn, idom(nnn), dd-1);

   }

   // Now force out all loop-invariant dominating tests.  The optimizer

   // finds some, but we _know_ they are all useless.

   peeled_dom_test_elim(loop,old_new);

   loop->record_for_igvn();

 }

 #define EMPTY_LOOP_SIZE 7 // number of nodes in an empty loop

 //------------------------------policy_maximally_unroll------------------------

 // Calculate exact loop trip count and return true if loop can be maximally

 // unrolled.

 bool IdealLoopTree::policy_maximally_unroll( PhaseIdealLoop *phase ) const {

   CountedLoopNode *cl = _head->as_CountedLoop();

   assert(cl->is_normal_loop(), "");

   if (!cl->is_valid_counted_loop())

     return false; // Malformed counted loop

   if (!cl->has_exact_trip_count()) {

     // Trip count is not exact.

     return false;

   }

   uint trip_count = cl->trip_count();

   // Note, max_juint is used to indicate unknown trip count.

   assert(trip_count > 1, "one iteration loop should be optimized out already");

   assert(trip_count < max_juint, "exact trip_count should be less than max_uint.");

   // Real policy: if we maximally unroll, does it get too big?

   // Allow the unrolled mess to get larger than standard loop

   // size.  After all, it will no longer be a loop.

   uint body_size    = _body.size();

   uint unroll_limit = (uint)LoopUnrollLimit * 4;

   assert( (intx)unroll_limit == LoopUnrollLimit * 4, "LoopUnrollLimit must fit in 32bits");

   if (trip_count > unroll_limit || body_size > unroll_limit) {

     return false;

   }

   // Fully unroll a loop with few iterations regardless next

   // conditions since following loop optimizations will split

   // such loop anyway (pre-main-post).

   if (trip_count <= 3)

     return true;

   // Take into account that after unroll conjoined heads and tails will fold,

   // otherwise policy_unroll() may allow more unrolling than max unrolling.

   uint new_body_size = EMPTY_LOOP_SIZE + (body_size - EMPTY_LOOP_SIZE) * trip_count;

   uint tst_body_size = (new_body_size - EMPTY_LOOP_SIZE) / trip_count + EMPTY_LOOP_SIZE;

   if (body_size != tst_body_size) // Check for int overflow

     return false;

   if (new_body_size > unroll_limit ||

       // Unrolling can result in a large amount of node construction

       new_body_size >= MaxNodeLimit - (uint) phase->C->live_nodes()) {

     return false;

   }

   // Do not unroll a loop with String intrinsics code.

   // String intrinsics are large and have loops.

   for (uint k = 0; k < _body.size(); k++) {

     Node* n = _body.at(k);

     switch (n->Opcode()) {

       case Op_StrComp:

       case Op_StrEquals:

       case Op_StrIndexOf:

       case Op_EncodeISOArray:

       case Op_AryEq: {

         return false;

       }

 #if INCLUDE_RTM_OPT

       case Op_FastLock:

       case Op_FastUnlock: {

         // Don't unroll RTM locking code because it is large.

         if (UseRTMLocking) {

           return false;

         }

       }

 #endif

     } // switch

   }

   return true; // Do maximally unroll

 }

 //------------------------------policy_unroll----------------------------------

 // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if

 // the loop is a CountedLoop and the body is small enough.

 bool IdealLoopTree::policy_unroll( PhaseIdealLoop *phase ) const {

   CountedLoopNode *cl = _head->as_CountedLoop();

   assert(cl->is_normal_loop() || cl->is_main_loop(), "");

   if (!cl->is_valid_counted_loop())

     return false; // Malformed counted loop

   // Protect against over-unrolling.

   // After split at least one iteration will be executed in pre-loop.

   if (cl->trip_count() <= (uint)(cl->is_normal_loop() ? 2 : 1)) return false;

   int future_unroll_ct = cl->unrolled_count() * 2;

   if (future_unroll_ct > LoopMaxUnroll) return false;

   // Check for initial stride being a small enough constant

   if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;

   // Don't unroll if the next round of unrolling would push us

   // over the expected trip count of the loop.  One is subtracted

   // from the expected trip count because the pre-loop normally

   // executes 1 iteration.

   if (UnrollLimitForProfileCheck > 0 &&

       cl->profile_trip_cnt() != COUNT_UNKNOWN &&

       future_unroll_ct        > UnrollLimitForProfileCheck &&

       (float)future_unroll_ct > cl->profile_trip_cnt() - 1.0) {

     return false;

   }

   // When unroll count is greater than LoopUnrollMin, don't unroll if:

   //   the residual iterations are more than 10% of the trip count

   //   and rounds of "unroll,optimize" are not making significant progress

   //   Progress defined as current size less than 20% larger than previous size.

   if (UseSuperWord && cl->node_count_before_unroll() > 0 &&

       future_unroll_ct > LoopUnrollMin &&

       (future_unroll_ct - 1) * 10.0 > cl->profile_trip_cnt() &&

       1.2 * cl->node_count_before_unroll() < (double)_body.size()) {

     return false;

   }

   Node *init_n = cl->init_trip();

   Node *limit_n = cl->limit();

   int stride_con = cl->stride_con();

   // Non-constant bounds.

   // Protect against over-unrolling when init or/and limit are not constant

   // (so that trip_count's init value is maxint) but iv range is known.

   if (init_n   == NULL || !init_n->is_Con()  ||

       limit_n  == NULL || !limit_n->is_Con()) {

     Node* phi = cl->phi();

     if (phi != NULL) {

       assert(phi->is_Phi() && phi->in(0) == _head, "Counted loop should have iv phi.");

       const TypeInt* iv_type = phase->_igvn.type(phi)->is_int();

       int next_stride = stride_con * 2; // stride after this unroll

       if (next_stride > 0) {

         if (iv_type->_lo + next_stride <= iv_type->_lo || // overflow

             iv_type->_lo + next_stride >  iv_type->_hi) {

           return false;  // over-unrolling

         }

       } else if (next_stride < 0) {

         if (iv_type->_hi + next_stride >= iv_type->_hi || // overflow

             iv_type->_hi + next_stride <  iv_type->_lo) {

           return false;  // over-unrolling

         }

       }

     }

   }

   // After unroll limit will be adjusted: new_limit = limit-stride.

   // Bailout if adjustment overflow.

   const TypeInt* limit_type = phase->_igvn.type(limit_n)->is_int();

   if (stride_con > 0 && ((limit_type->_hi - stride_con) >= limit_type->_hi) ||

       stride_con < 0 && ((limit_type->_lo - stride_con) <= limit_type->_lo))

     return false;  // overflow

   // Adjust body_size to determine if we unroll or not

   uint body_size = _body.size();

   // Key test to unroll loop in CRC32 java code

   int xors_in_loop = 0;

   // Also count ModL, DivL and MulL which expand mightly

   for (uint k = 0; k < _body.size(); k++) {

     Node* n = _body.at(k);

     switch (n->Opcode()) {

       case Op_XorI: xors_in_loop++; break; // CRC32 java code

       case Op_ModL: body_size += 30; break;

       case Op_DivL: body_size += 30; break;

       case Op_MulL: body_size += 10; break;

       case Op_StrComp:

       case Op_StrEquals:

       case Op_StrIndexOf:

       case Op_EncodeISOArray:

       case Op_AryEq: {

         // Do not unroll a loop with String intrinsics code.

         // String intrinsics are large and have loops.

         return false;

       }

 #if INCLUDE_RTM_OPT

       case Op_FastLock:

       case Op_FastUnlock: {

         // Don't unroll RTM locking code because it is large.

         if (UseRTMLocking) {

           return false;

         }

       }

 #endif

     } // switch

   }

   // Check for being too big

   if (body_size > (uint)LoopUnrollLimit) {

     if (xors_in_loop >= 4 && body_size < (uint)LoopUnrollLimit*4) return true;

     // Normal case: loop too big

     return false;

   }

   // Unroll once!  (Each trip will soon do double iterations)

   return true;

 }

 //------------------------------policy_align-----------------------------------

 // Return TRUE or FALSE if the loop should be cache-line aligned.  Gather the

 // expression that does the alignment.  Note that only one array base can be

 // aligned in a loop (unless the VM guarantees mutual alignment).  Note that

 // if we vectorize short memory ops into longer memory ops, we may want to

 // increase alignment.

 bool IdealLoopTree::policy_align( PhaseIdealLoop *phase ) const {

   return false;

 }

 //------------------------------policy_range_check-----------------------------

 // Return TRUE or FALSE if the loop should be range-check-eliminated.

 // Actually we do iteration-splitting, a more powerful form of RCE.

 bool IdealLoopTree::policy_range_check( PhaseIdealLoop *phase ) const {

   if (!RangeCheckElimination) return false;

   CountedLoopNode *cl = _head->as_CountedLoop();

   // If we unrolled with no intention of doing RCE and we later

   // changed our minds, we got no pre-loop.  Either we need to

   // make a new pre-loop, or we gotta disallow RCE.

   if (cl->is_main_no_pre_loop()) return false; // Disallowed for now.

   Node *trip_counter = cl->phi();

   // Check loop body for tests of trip-counter plus loop-invariant vs

   // loop-invariant.

   for (uint i = 0; i < _body.size(); i++) {

     Node *iff = _body[i];

     if (iff->Opcode() == Op_If) { // Test?

       // Comparing trip+off vs limit

       Node *bol = iff->in(1);

       if (bol->req() != 2) continue; // dead constant test

       if (!bol->is_Bool()) {

         assert(UseLoopPredicate && bol->Opcode() == Op_Conv2B, "predicate check only");

         continue;

       }

       if (bol->as_Bool()->_test._test == BoolTest::ne)

         continue; // not RC

       Node *cmp = bol->in(1);

       Node *rc_exp = cmp->in(1);

       Node *limit = cmp->in(2);

       Node *limit_c = phase->get_ctrl(limit);

       if( limit_c == phase->C->top() )

         return false;           // Found dead test on live IF?  No RCE!

       if( is_member(phase->get_loop(limit_c) ) ) {

         // Compare might have operands swapped; commute them

         rc_exp = cmp->in(2);

         limit  = cmp->in(1);

         limit_c = phase->get_ctrl(limit);

         if( is_member(phase->get_loop(limit_c) ) )

           continue;             // Both inputs are loop varying; cannot RCE

       }

       if (!phase->is_scaled_iv_plus_offset(rc_exp, trip_counter, NULL, NULL)) {

         continue;

       }

       // Yeah!  Found a test like 'trip+off vs limit'

       // Test is an IfNode, has 2 projections.  If BOTH are in the loop

       // we need loop unswitching instead of iteration splitting.

       if( is_loop_exit(iff) )

         return true;            // Found reason to split iterations

     } // End of is IF

   }

   return false;

 }

 //------------------------------policy_peel_only-------------------------------

 // Return TRUE or FALSE if the loop should NEVER be RCE'd or aligned.  Useful

 // for unrolling loops with NO array accesses.

 bool IdealLoopTree::policy_peel_only( PhaseIdealLoop *phase ) const {

   for( uint i = 0; i < _body.size(); i++ )

     if( _body[i]->is_Mem() )

       return false;

   // No memory accesses at all!

   return true;

 }

 //------------------------------clone_up_backedge_goo--------------------------

 // If Node n lives in the back_ctrl block and cannot float, we clone a private

 // version of n in preheader_ctrl block and return that, otherwise return n.

 Node *PhaseIdealLoop::clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones ) {

   if( get_ctrl(n) != back_ctrl ) return n;

   // Only visit once

   if (visited.test_set(n->_idx)) {

     Node *x = clones.find(n->_idx);

     if (x != NULL)

       return x;

     return n;

   }

   Node *x = NULL;               // If required, a clone of 'n'

   // Check for 'n' being pinned in the backedge.

   if( n->in(0) && n->in(0) == back_ctrl ) {

     assert(clones.find(n->_idx) == NULL, "dead loop");

     x = n->clone();             // Clone a copy of 'n' to preheader

     clones.push(x, n->_idx);

     x->set_req( 0, preheader_ctrl ); // Fix x's control input to preheader

   }

   // Recursive fixup any other input edges into x.

   // If there are no changes we can just return 'n', otherwise

   // we need to clone a private copy and change it.

   for( uint i = 1; i < n->req(); i++ ) {

     Node *g = clone_up_backedge_goo( back_ctrl, preheader_ctrl, n->in(i), visited, clones );

     if( g != n->in(i) ) {

       if( !x ) {

         assert(clones.find(n->_idx) == NULL, "dead loop");

         x = n->clone();

         clones.push(x, n->_idx);

       }

       x->set_req(i, g);

     }

   }

   if( x ) {                     // x can legally float to pre-header location

     register_new_node( x, preheader_ctrl );

     return x;

   } else {                      // raise n to cover LCA of uses

     set_ctrl( n, find_non_split_ctrl(back_ctrl->in(0)) );

   }

   return n;

 }

 //------------------------------insert_pre_post_loops--------------------------

 // Insert pre and post loops.  If peel_only is set, the pre-loop can not have

 // more iterations added.  It acts as a 'peel' only, no lower-bound RCE, no

 // alignment.  Useful to unroll loops that do no array accesses.

 void PhaseIdealLoop::insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only ) {

 #ifndef PRODUCT

   if (TraceLoopOpts) {

     if (peel_only)

       tty->print("PeelMainPost ");

     else

       tty->print("PreMainPost  ");

     loop->dump_head();

   }

 #endif

   C->set_major_progress();

   // Find common pieces of the loop being guarded with pre & post loops

   CountedLoopNode *main_head = loop->_head->as_CountedLoop();

   assert( main_head->is_normal_loop(), "" );

   CountedLoopEndNode *main_end = main_head->loopexit();

   guarantee(main_end != NULL, "no loop exit node");

   assert( main_end->outcnt() == 2, "1 true, 1 false path only" );

   uint dd_main_head = dom_depth(main_head);

   uint max = main_head->outcnt();

   Node *pre_header= main_head->in(LoopNode::EntryControl);

   Node *init      = main_head->init_trip();

   Node *incr      = main_end ->incr();

   Node *limit     = main_end ->limit();

   Node *stride    = main_end ->stride();

   Node *cmp       = main_end ->cmp_node();

   BoolTest::mask b_test = main_end->test_trip();

   // Need only 1 user of 'bol' because I will be hacking the loop bounds.

   Node *bol = main_end->in(CountedLoopEndNode::TestValue);

   if( bol->outcnt() != 1 ) {

     bol = bol->clone();

     register_new_node(bol,main_end->in(CountedLoopEndNode::TestControl));

     _igvn.hash_delete(main_end);

     main_end->set_req(CountedLoopEndNode::TestValue, bol);

   }

   // Need only 1 user of 'cmp' because I will be hacking the loop bounds.

   if( cmp->outcnt() != 1 ) {

     cmp = cmp->clone();

     register_new_node(cmp,main_end->in(CountedLoopEndNode::TestControl));

     _igvn.hash_delete(bol);

     bol->set_req(1, cmp);

   }

   //------------------------------

   // Step A: Create Post-Loop.

   Node* main_exit = main_end->proj_out(false);

   assert( main_exit->Opcode() == Op_IfFalse, "" );

   int dd_main_exit = dom_depth(main_exit);

   // Step A1: Clone the loop body.  The clone becomes the post-loop.  The main

   // loop pre-header illegally has 2 control users (old & new loops).

   clone_loop( loop, old_new, dd_main_exit );

   assert( old_new[main_end ->_idx]->Opcode() == Op_CountedLoopEnd, "" );

   CountedLoopNode *post_head = old_new[main_head->_idx]->as_CountedLoop();

   post_head->set_post_loop(main_head);

   // Reduce the post-loop trip count.

   CountedLoopEndNode* post_end = old_new[main_end ->_idx]->as_CountedLoopEnd();

   post_end->_prob = PROB_FAIR;

   // Build the main-loop normal exit.

   IfFalseNode *new_main_exit = new (C) IfFalseNode(main_end);

   _igvn.register_new_node_with_optimizer( new_main_exit );

   set_idom(new_main_exit, main_end, dd_main_exit );

   set_loop(new_main_exit, loop->_parent);

   // Step A2: Build a zero-trip guard for the post-loop.  After leaving the

   // main-loop, the post-loop may not execute at all.  We 'opaque' the incr

   // (the main-loop trip-counter exit value) because we will be changing

   // the exit value (via unrolling) so we cannot constant-fold away the zero

   // trip guard until all unrolling is done.

   Node *zer_opaq = new (C) Opaque1Node(C, incr);

   Node *zer_cmp  = new (C) CmpINode( zer_opaq, limit );

   Node *zer_bol  = new (C) BoolNode( zer_cmp, b_test );

   register_new_node( zer_opaq, new_main_exit );

   register_new_node( zer_cmp , new_main_exit );

   register_new_node( zer_bol , new_main_exit );

   // Build the IfNode

   IfNode *zer_iff = new (C) IfNode( new_main_exit, zer_bol, PROB_FAIR, COUNT_UNKNOWN );

   _igvn.register_new_node_with_optimizer( zer_iff );

   set_idom(zer_iff, new_main_exit, dd_main_exit);

   set_loop(zer_iff, loop->_parent);

   // Plug in the false-path, taken if we need to skip post-loop

   _igvn.replace_input_of(main_exit, 0, zer_iff);

   set_idom(main_exit, zer_iff, dd_main_exit);

   set_idom(main_exit->unique_out(), zer_iff, dd_main_exit);

   // Make the true-path, must enter the post loop

   Node *zer_taken = new (C) IfTrueNode( zer_iff );

   _igvn.register_new_node_with_optimizer( zer_taken );

   set_idom(zer_taken, zer_iff, dd_main_exit);

   set_loop(zer_taken, loop->_parent);

   // Plug in the true path

   _igvn.hash_delete( post_head );

   post_head->set_req(LoopNode::EntryControl, zer_taken);

   set_idom(post_head, zer_taken, dd_main_exit);

   Arena *a = Thread::current()->resource_area();

   VectorSet visited(a);

   Node_Stack clones(a, main_head->back_control()->outcnt());

   // Step A3: Make the fall-in values to the post-loop come from the

   // fall-out values of the main-loop.

   for (DUIterator_Fast imax, i = main_head->fast_outs(imax); i < imax; i++) {

     Node* main_phi = main_head->fast_out(i);

     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() >0 ) {

       Node *post_phi = old_new[main_phi->_idx];

       Node *fallmain  = clone_up_backedge_goo(main_head->back_control(),

                                               post_head->init_control(),

                                               main_phi->in(LoopNode::LoopBackControl),

                                               visited, clones);

       _igvn.hash_delete(post_phi);

       post_phi->set_req( LoopNode::EntryControl, fallmain );

     }

   }

   // Update local caches for next stanza

   main_exit = new_main_exit;

   //------------------------------

   // Step B: Create Pre-Loop.

   // Step B1: Clone the loop body.  The clone becomes the pre-loop.  The main

   // loop pre-header illegally has 2 control users (old & new loops).

   clone_loop( loop, old_new, dd_main_head );

   CountedLoopNode*    pre_head = old_new[main_head->_idx]->as_CountedLoop();

   CountedLoopEndNode* pre_end  = old_new[main_end ->_idx]->as_CountedLoopEnd();

   pre_head->set_pre_loop(main_head);

   Node *pre_incr = old_new[incr->_idx];

   // Reduce the pre-loop trip count.

   pre_end->_prob = PROB_FAIR;

   // Find the pre-loop normal exit.

   Node* pre_exit = pre_end->proj_out(false);

   assert( pre_exit->Opcode() == Op_IfFalse, "" );

   IfFalseNode *new_pre_exit = new (C) IfFalseNode(pre_end);

   _igvn.register_new_node_with_optimizer( new_pre_exit );

   set_idom(new_pre_exit, pre_end, dd_main_head);

   set_loop(new_pre_exit, loop->_parent);

   // Step B2: Build a zero-trip guard for the main-loop.  After leaving the

   // pre-loop, the main-loop may not execute at all.  Later in life this

   // zero-trip guard will become the minimum-trip guard when we unroll

   // the main-loop.

   Node *min_opaq = new (C) Opaque1Node(C, limit);

   Node *min_cmp  = new (C) CmpINode( pre_incr, min_opaq );

   Node *min_bol  = new (C) BoolNode( min_cmp, b_test );

   register_new_node( min_opaq, new_pre_exit );

   register_new_node( min_cmp , new_pre_exit );

   register_new_node( min_bol , new_pre_exit );

   // Build the IfNode (assume the main-loop is executed always).

   IfNode *min_iff = new (C) IfNode( new_pre_exit, min_bol, PROB_ALWAYS, COUNT_UNKNOWN );

   _igvn.register_new_node_with_optimizer( min_iff );

   set_idom(min_iff, new_pre_exit, dd_main_head);

   set_loop(min_iff, loop->_parent);

   // Plug in the false-path, taken if we need to skip main-loop

   _igvn.hash_delete( pre_exit );

   pre_exit->set_req(0, min_iff);

   set_idom(pre_exit, min_iff, dd_main_head);

   set_idom(pre_exit->unique_out(), min_iff, dd_main_head);

   // Make the true-path, must enter the main loop

   Node *min_taken = new (C) IfTrueNode( min_iff );

   _igvn.register_new_node_with_optimizer( min_taken );

   set_idom(min_taken, min_iff, dd_main_head);

   set_loop(min_taken, loop->_parent);

   // Plug in the true path

   _igvn.hash_delete( main_head );

   main_head->set_req(LoopNode::EntryControl, min_taken);

   set_idom(main_head, min_taken, dd_main_head);

   visited.Clear();

   clones.clear();

   // Step B3: Make the fall-in values to the main-loop come from the

   // fall-out values of the pre-loop.

   for (DUIterator_Fast i2max, i2 = main_head->fast_outs(i2max); i2 < i2max; i2++) {

     Node* main_phi = main_head->fast_out(i2);

     if( main_phi->is_Phi() && main_phi->in(0) == main_head && main_phi->outcnt() > 0 ) {

       Node *pre_phi = old_new[main_phi->_idx];

       Node *fallpre  = clone_up_backedge_goo(pre_head->back_control(),

                                              main_head->init_control(),

                                              pre_phi->in(LoopNode::LoopBackControl),

                                              visited, clones);

       _igvn.hash_delete(main_phi);

       main_phi->set_req( LoopNode::EntryControl, fallpre );

     }

   }

   // Step B4: Shorten the pre-loop to run only 1 iteration (for now).

   // RCE and alignment may change this later.

   Node *cmp_end = pre_end->cmp_node();

   assert( cmp_end->in(2) == limit, "" );

   Node *pre_limit = new (C) AddINode( init, stride );

   // Save the original loop limit in this Opaque1 node for

   // use by range check elimination.

   Node *pre_opaq  = new (C) Opaque1Node(C, pre_limit, limit);

   register_new_node( pre_limit, pre_head->in(0) );

   register_new_node( pre_opaq , pre_head->in(0) );

   // Since no other users of pre-loop compare, I can hack limit directly

   assert( cmp_end->outcnt() == 1, "no other users" );

   _igvn.hash_delete(cmp_end);

   cmp_end->set_req(2, peel_only ? pre_limit : pre_opaq);

   // Special case for not-equal loop bounds:

   // Change pre loop test, main loop test, and the

   // main loop guard test to use lt or gt depending on stride

   // direction:

   // positive stride use <

   // negative stride use >

   //

   // not-equal test is kept for post loop to handle case

   // when init > limit when stride > 0 (and reverse).

   if (pre_end->in(CountedLoopEndNode::TestValue)->as_Bool()->_test._test == BoolTest::ne) {

     BoolTest::mask new_test = (main_end->stride_con() > 0) ? BoolTest::lt : BoolTest::gt;

     // Modify pre loop end condition

     Node* pre_bol = pre_end->in(CountedLoopEndNode::TestValue)->as_Bool();

     BoolNode* new_bol0 = new (C) BoolNode(pre_bol->in(1), new_test);

     register_new_node( new_bol0, pre_head->in(0) );

     _igvn.hash_delete(pre_end);

     pre_end->set_req(CountedLoopEndNode::TestValue, new_bol0);

     // Modify main loop guard condition

     assert(min_iff->in(CountedLoopEndNode::TestValue) == min_bol, "guard okay");

     BoolNode* new_bol1 = new (C) BoolNode(min_bol->in(1), new_test);

     register_new_node( new_bol1, new_pre_exit );

     _igvn.hash_delete(min_iff);

     min_iff->set_req(CountedLoopEndNode::TestValue, new_bol1);

     // Modify main loop end condition

     BoolNode* main_bol = main_end->in(CountedLoopEndNode::TestValue)->as_Bool();

     BoolNode* new_bol2 = new (C) BoolNode(main_bol->in(1), new_test);

     register_new_node( new_bol2, main_end->in(CountedLoopEndNode::TestControl) );

     _igvn.hash_delete(main_end);

     main_end->set_req(CountedLoopEndNode::TestValue, new_bol2);

   }

   // Flag main loop

   main_head->set_main_loop();

   if( peel_only ) main_head->set_main_no_pre_loop();

   // Subtract a trip count for the pre-loop.

   main_head->set_trip_count(main_head->trip_count() - 1);

   // It's difficult to be precise about the trip-counts

   // for the pre/post loops.  They are usually very short,

   // so guess that 4 trips is a reasonable value.

   post_head->set_profile_trip_cnt(4.0);

   pre_head->set_profile_trip_cnt(4.0);

   // Now force out all loop-invariant dominating tests.  The optimizer

   // finds some, but we _know_ they are all useless.

   peeled_dom_test_elim(loop,old_new);

   loop->record_for_igvn();

 }

 //------------------------------is_invariant-----------------------------

 // Return true if n is invariant

 bool IdealLoopTree::is_invariant(Node* n) const {

   Node *n_c = _phase->has_ctrl(n) ? _phase->get_ctrl(n) : n;

   if (n_c->is_top()) return false;

   return !is_member(_phase->get_loop(n_c));

 }

 //------------------------------do_unroll--------------------------------------

 // Unroll the loop body one step - make each trip do 2 iterations.

 void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip ) {

   assert(LoopUnrollLimit, "");

   CountedLoopNode *loop_head = loop->_head->as_CountedLoop();

   CountedLoopEndNode *loop_end = loop_head->loopexit();

   assert(loop_end, "");

 #ifndef PRODUCT

   if (PrintOpto && VerifyLoopOptimizations) {

     tty->print("Unrolling ");

     loop->dump_head();

   } else if (TraceLoopOpts) {

     if (loop_head->trip_count() < (uint)LoopUnrollLimit) {

       tty->print("Unroll %d(%2d) ", loop_head->unrolled_count()*2, loop_head->trip_count());

     } else {

       tty->print("Unroll %d     ", loop_head->unrolled_count()*2);

     }

     loop->dump_head();

   }

 #endif

   // Remember loop node count before unrolling to detect

   // if rounds of unroll,optimize are making progress

   loop_head->set_node_count_before_unroll(loop->_body.size());

   Node *ctrl  = loop_head->in(LoopNode::EntryControl);

   Node *limit = loop_head->limit();

   Node *init  = loop_head->init_trip();

   Node *stride = loop_head->stride();

   Node *opaq = NULL;

   if (adjust_min_trip) {       // If not maximally unrolling, need adjustment

     // Search for zero-trip guard.

     assert( loop_head->is_main_loop(), "" );

     assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );

     Node *iff = ctrl->in(0);

     assert( iff->Opcode() == Op_If, "" );

     Node *bol = iff->in(1);

     assert( bol->Opcode() == Op_Bool, "" );

     Node *cmp = bol->in(1);

     assert( cmp->Opcode() == Op_CmpI, "" );

     opaq = cmp->in(2);

     // Occasionally it's possible for a zero-trip guard Opaque1 node to be

     // optimized away and then another round of loop opts attempted.

     // We can not optimize this particular loop in that case.

     if (opaq->Opcode() != Op_Opaque1)

       return; // Cannot find zero-trip guard!  Bail out!

     // Zero-trip test uses an 'opaque' node which is not shared.

     assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");

   }

   C->set_major_progress();

   Node* new_limit = NULL;

   if (UnrollLimitCheck) {

     int stride_con = stride->get_int();

     int stride_p = (stride_con > 0) ? stride_con : -stride_con;

     uint old_trip_count = loop_head->trip_count();

     // Verify that unroll policy result is still valid.

     assert(old_trip_count > 1 &&

            (!adjust_min_trip || stride_p <= (1<<3)*loop_head->unrolled_count()), "sanity");

     // Adjust loop limit to keep valid iterations number after unroll.

     // Use (limit - stride) instead of (((limit - init)/stride) & (-2))*stride

     // which may overflow.

     if (!adjust_min_trip) {

       assert(old_trip_count > 1 && (old_trip_count & 1) == 0,

              "odd trip count for maximally unroll");

       // Don't need to adjust limit for maximally unroll since trip count is even.

     } else if (loop_head->has_exact_trip_count() && init->is_Con()) {

       // Loop's limit is constant. Loop's init could be constant when pre-loop

       // become peeled iteration.

       jlong init_con = init->get_int();

       // We can keep old loop limit if iterations count stays the same:

       //   old_trip_count == new_trip_count * 2

       // Note: since old_trip_count >= 2 then new_trip_count >= 1

       // so we also don't need to adjust zero trip test.

       jlong limit_con  = limit->get_int();

       // (stride_con*2) not overflow since stride_con <= 8.

       int new_stride_con = stride_con * 2;

       int stride_m    = new_stride_con - (stride_con > 0 ? 1 : -1);

       jlong trip_count = (limit_con - init_con + stride_m)/new_stride_con;

       // New trip count should satisfy next conditions.

       assert(trip_count > 0 && (julong)trip_count < (julong)max_juint/2, "sanity");

       uint new_trip_count = (uint)trip_count;

       adjust_min_trip = (old_trip_count != new_trip_count*2);

     }

     if (adjust_min_trip) {

       // Step 2: Adjust the trip limit if it is called for.

       // The adjustment amount is -stride. Need to make sure if the

       // adjustment underflows or overflows, then the main loop is skipped.

       Node* cmp = loop_end->cmp_node();

       assert(cmp->in(2) == limit, "sanity");

       assert(opaq != NULL && opaq->in(1) == limit, "sanity");

       // Verify that policy_unroll result is still valid.

       const TypeInt* limit_type = _igvn.type(limit)->is_int();

       assert(stride_con > 0 && ((limit_type->_hi - stride_con) < limit_type->_hi) ||

              stride_con < 0 && ((limit_type->_lo - stride_con) > limit_type->_lo), "sanity");

       if (limit->is_Con()) {

         // The check in policy_unroll and the assert above guarantee

         // no underflow if limit is constant.

         new_limit = _igvn.intcon(limit->get_int() - stride_con);

         set_ctrl(new_limit, C->root());

       } else {

         // Limit is not constant.

         if (loop_head->unrolled_count() == 1) { // only for first unroll

           // Separate limit by Opaque node in case it is an incremented

           // variable from previous loop to avoid using pre-incremented

           // value which could increase register pressure.

           // Otherwise reorg_offsets() optimization will create a separate

           // Opaque node for each use of trip-counter and as result

           // zero trip guard limit will be different from loop limit.

           assert(has_ctrl(opaq), "should have it");

           Node* opaq_ctrl = get_ctrl(opaq);

           limit = new (C) Opaque2Node( C, limit );

           register_new_node( limit, opaq_ctrl );

         }

         if (stride_con > 0 && ((limit_type->_lo - stride_con) < limit_type->_lo) ||

                    stride_con < 0 && ((limit_type->_hi - stride_con) > limit_type->_hi)) {

           // No underflow.

           new_limit = new (C) SubINode(limit, stride);

         } else {

           // (limit - stride) may underflow.

           // Clamp the adjustment value with MININT or MAXINT:

           //

           //   new_limit = limit-stride

           //   if (stride > 0)

           //     new_limit = (limit < new_limit) ? MININT : new_limit;

           //   else

           //     new_limit = (limit > new_limit) ? MAXINT : new_limit;

           //

           BoolTest::mask bt = loop_end->test_trip();

           assert(bt == BoolTest::lt || bt == BoolTest::gt, "canonical test is expected");

           Node* adj_max = _igvn.intcon((stride_con > 0) ? min_jint : max_jint);

           set_ctrl(adj_max, C->root());

           Node* old_limit = NULL;

           Node* adj_limit = NULL;

           Node* bol = limit->is_CMove() ? limit->in(CMoveNode::Condition) : NULL;

           if (loop_head->unrolled_count() > 1 &&

               limit->is_CMove() && limit->Opcode() == Op_CMoveI &&

               limit->in(CMoveNode::IfTrue) == adj_max &&

               bol->as_Bool()->_test._test == bt &&

               bol->in(1)->Opcode() == Op_CmpI &&

               bol->in(1)->in(2) == limit->in(CMoveNode::IfFalse)) {

             // Loop was unrolled before.

             // Optimize the limit to avoid nested CMove:

             // use original limit as old limit.

             old_limit = bol->in(1)->in(1);

             // Adjust previous adjusted limit.

             adj_limit = limit->in(CMoveNode::IfFalse);

             adj_limit = new (C) SubINode(adj_limit, stride);

           } else {

             old_limit = limit;

             adj_limit = new (C) SubINode(limit, stride);

           }

           assert(old_limit != NULL && adj_limit != NULL, "");

           register_new_node( adj_limit, ctrl ); // adjust amount

           Node* adj_cmp = new (C) CmpINode(old_limit, adj_limit);

           register_new_node( adj_cmp, ctrl );

           Node* adj_bool = new (C) BoolNode(adj_cmp, bt);

           register_new_node( adj_bool, ctrl );

           new_limit = new (C) CMoveINode(adj_bool, adj_limit, adj_max, TypeInt::INT);

         }

         register_new_node(new_limit, ctrl);

       }

       assert(new_limit != NULL, "");

       // Replace in loop test.

       assert(loop_end->in(1)->in(1) == cmp, "sanity");

       if (cmp->outcnt() == 1 && loop_end->in(1)->outcnt() == 1) {

         // Don't need to create new test since only one user.

         _igvn.hash_delete(cmp);

         cmp->set_req(2, new_limit);

       } else {

         // Create new test since it is shared.

         Node* ctrl2 = loop_end->in(0);

         Node* cmp2  = cmp->clone();

         cmp2->set_req(2, new_limit);

         register_new_node(cmp2, ctrl2);

         Node* bol2 = loop_end->in(1)->clone();

         bol2->set_req(1, cmp2);

         register_new_node(bol2, ctrl2);

         _igvn.hash_delete(loop_end);

         loop_end->set_req(1, bol2);

       }

       // Step 3: Find the min-trip test guaranteed before a 'main' loop.

       // Make it a 1-trip test (means at least 2 trips).

       // Guard test uses an 'opaque' node which is not shared.  Hence I

       // can edit it's inputs directly.  Hammer in the new limit for the

       // minimum-trip guard.

       assert(opaq->outcnt() == 1, "");

       _igvn.hash_delete(opaq);

       opaq->set_req(1, new_limit);

     }

     // Adjust max trip count. The trip count is intentionally rounded

     // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,

     // the main, unrolled, part of the loop will never execute as it is protected

     // by the min-trip test.  See bug 4834191 for a case where we over-unrolled

     // and later determined that part of the unrolled loop was dead.

     loop_head->set_trip_count(old_trip_count / 2);

     // Double the count of original iterations in the unrolled loop body.

     loop_head->double_unrolled_count();

   } else { // LoopLimitCheck

     // Adjust max trip count. The trip count is intentionally rounded

     // down here (e.g. 15-> 7-> 3-> 1) because if we unwittingly over-unroll,

     // the main, unrolled, part of the loop will never execute as it is protected

     // by the min-trip test.  See bug 4834191 for a case where we over-unrolled

     // and later determined that part of the unrolled loop was dead.

     loop_head->set_trip_count(loop_head->trip_count() / 2);

     // Double the count of original iterations in the unrolled loop body.

     loop_head->double_unrolled_count();

     // -----------

     // Step 2: Cut back the trip counter for an unroll amount of 2.

     // Loop will normally trip (limit - init)/stride_con.  Since it's a

     // CountedLoop this is exact (stride divides limit-init exactly).

     // We are going to double the loop body, so we want to knock off any

     // odd iteration: (trip_cnt & ~1).  Then back compute a new limit.

     Node *span = new (C) SubINode( limit, init );

     register_new_node( span, ctrl );

     Node *trip = new (C) DivINode( 0, span, stride );

     register_new_node( trip, ctrl );

     Node *mtwo = _igvn.intcon(-2);

     set_ctrl(mtwo, C->root());

     Node *rond = new (C) AndINode( trip, mtwo );

     register_new_node( rond, ctrl );

     Node *spn2 = new (C) MulINode( rond, stride );

     register_new_node( spn2, ctrl );

     new_limit = new (C) AddINode( spn2, init );

     register_new_node( new_limit, ctrl );

     // Hammer in the new limit

     Node *ctrl2 = loop_end->in(0);

     Node *cmp2 = new (C) CmpINode( loop_head->incr(), new_limit );

     register_new_node( cmp2, ctrl2 );

     Node *bol2 = new (C) BoolNode( cmp2, loop_end->test_trip() );

     register_new_node( bol2, ctrl2 );

     _igvn.hash_delete(loop_end);

     loop_end->set_req(CountedLoopEndNode::TestValue, bol2);

     // Step 3: Find the min-trip test guaranteed before a 'main' loop.

     // Make it a 1-trip test (means at least 2 trips).

     if( adjust_min_trip ) {

       assert( new_limit != NULL, "" );

       // Guard test uses an 'opaque' node which is not shared.  Hence I

       // can edit it's inputs directly.  Hammer in the new limit for the

       // minimum-trip guard.

       assert( opaq->outcnt() == 1, "" );

       _igvn.hash_delete(opaq);

       opaq->set_req(1, new_limit);

     }

   } // LoopLimitCheck

   // ---------

   // Step 4: Clone the loop body.  Move it inside the loop.  This loop body

   // represents the odd iterations; since the loop trips an even number of

   // times its backedge is never taken.  Kill the backedge.

   uint dd = dom_depth(loop_head);

   clone_loop( loop, old_new, dd );

   // Make backedges of the clone equal to backedges of the original.

   // Make the fall-in from the original come from the fall-out of the clone.

   for (DUIterator_Fast jmax, j = loop_head->fast_outs(jmax); j < jmax; j++) {

     Node* phi = loop_head->fast_out(j);

     if( phi->is_Phi() && phi->in(0) == loop_head && phi->outcnt() > 0 ) {

       Node *newphi = old_new[phi->_idx];

       _igvn.hash_delete( phi );

       _igvn.hash_delete( newphi );

       phi   ->set_req(LoopNode::   EntryControl, newphi->in(LoopNode::LoopBackControl));

       newphi->set_req(LoopNode::LoopBackControl, phi   ->in(LoopNode::LoopBackControl));

       phi   ->set_req(LoopNode::LoopBackControl, C->top());

     }

   }

   Node *clone_head = old_new[loop_head->_idx];

   _igvn.hash_delete( clone_head );

   loop_head ->set_req(LoopNode::   EntryControl, clone_head->in(LoopNode::LoopBackControl));

   clone_head->set_req(LoopNode::LoopBackControl, loop_head ->in(LoopNode::LoopBackControl));

   loop_head ->set_req(LoopNode::LoopBackControl, C->top());

   loop->_head = clone_head;     // New loop header

   set_idom(loop_head,  loop_head ->in(LoopNode::EntryControl), dd);

   set_idom(clone_head, clone_head->in(LoopNode::EntryControl), dd);

   // Kill the clone's backedge

   Node *newcle = old_new[loop_end->_idx];

   _igvn.hash_delete( newcle );

   Node *one = _igvn.intcon(1);

   set_ctrl(one, C->root());

   newcle->set_req(1, one);

   // Force clone into same loop body

   uint max = loop->_body.size();

   for( uint k = 0; k < max; k++ ) {

     Node *old = loop->_body.at(k);

     Node *nnn = old_new[old->_idx];

     loop->_body.push(nnn);

     if (!has_ctrl(old))

       set_loop(nnn, loop);

   }

   loop->record_for_igvn();

 }

 //------------------------------do_maximally_unroll----------------------------

 void PhaseIdealLoop::do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new ) {

   CountedLoopNode *cl = loop->_head->as_CountedLoop();

   assert(cl->has_exact_trip_count(), "trip count is not exact");

   assert(cl->trip_count() > 0, "");

 #ifndef PRODUCT

   if (TraceLoopOpts) {

     tty->print("MaxUnroll  %d ", cl->trip_count());

     loop->dump_head();

   }

 #endif

   // If loop is tripping an odd number of times, peel odd iteration

   if ((cl->trip_count() & 1) == 1) {

     do_peeling(loop, old_new);

   }

   // Now its tripping an even number of times remaining.  Double loop body.

   // Do not adjust pre-guards; they are not needed and do not exist.

   if (cl->trip_count() > 0) {

     assert((cl->trip_count() & 1) == 0, "missed peeling");

     do_unroll(loop, old_new, false);

   }

 }

 //------------------------------dominates_backedge---------------------------------

 // Returns true if ctrl is executed on every complete iteration

 bool IdealLoopTree::dominates_backedge(Node* ctrl) {

   assert(ctrl->is_CFG(), "must be control");

   Node* backedge = _head->as_Loop()->in(LoopNode::LoopBackControl);

   return _phase->dom_lca_internal(ctrl, backedge) == ctrl;

 }

 //------------------------------adjust_limit-----------------------------------

 // Helper function for add_constraint().

 Node* PhaseIdealLoop::adjust_limit(int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl) {

   // Compute "I :: (limit-offset)/scale"

   Node *con = new (C) SubINode(rc_limit, offset);

   register_new_node(con, pre_ctrl);

   Node *X = new (C) DivINode(0, con, scale);

   register_new_node(X, pre_ctrl);

   // Adjust loop limit

   loop_limit = (stride_con > 0)

                ? (Node*)(new (C) MinINode(loop_limit, X))

                : (Node*)(new (C) MaxINode(loop_limit, X));

   register_new_node(loop_limit, pre_ctrl);

   return loop_limit;

 }

 //------------------------------add_constraint---------------------------------

 // Constrain the main loop iterations so the conditions:

 //    low_limit <= scale_con * I + offset  <  upper_limit

 // always holds true.  That is, either increase the number of iterations in

 // the pre-loop or the post-loop until the condition holds true in the main

 // loop.  Stride, scale, offset and limit are all loop invariant.  Further,

 // stride and scale are constants (offset and limit often are).

 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 ) {

   // For positive stride, the pre-loop limit always uses a MAX function

   // and the main loop a MIN function.  For negative stride these are

   // reversed.

   // Also for positive stride*scale the affine function is increasing, so the

   // pre-loop must check for underflow and the post-loop for overflow.

   // Negative stride*scale reverses this; pre-loop checks for overflow and

   // post-loop for underflow.

   Node *scale = _igvn.intcon(scale_con);

   set_ctrl(scale, C->root());

   if ((stride_con^scale_con) >= 0) { // Use XOR to avoid overflow

     // The overflow limit: scale*I+offset < upper_limit

     // For main-loop compute

     //   ( if (scale > 0) /* and stride > 0 */

     //       I < (upper_limit-offset)/scale

     //     else /* scale < 0 and stride < 0 */

     //       I > (upper_limit-offset)/scale

     //   )

     //

     // (upper_limit-offset) may overflow or underflow.

     // But it is fine since main loop will either have

     // less iterations or will be skipped in such case.

     *main_limit = adjust_limit(stride_con, scale, offset, upper_limit, *main_limit, pre_ctrl);

     // The underflow limit: low_limit <= scale*I+offset.

     // For pre-loop compute

     //   NOT(scale*I+offset >= low_limit)

     //   scale*I+offset < low_limit

     //   ( if (scale > 0) /* and stride > 0 */

     //       I < (low_limit-offset)/scale

     //     else /* scale < 0 and stride < 0 */

     //       I > (low_limit-offset)/scale

     //   )

     if (low_limit->get_int() == -max_jint) {

       if (!RangeLimitCheck) return;

       // We need this guard when scale*pre_limit+offset >= limit

       // due to underflow. So we need execute pre-loop until

       // scale*I+offset >= min_int. But (min_int-offset) will

       // underflow when offset > 0 and X will be > original_limit

       // when stride > 0. To avoid it we replace positive offset with 0.

       //

       // Also (min_int+1 == -max_int) is used instead of min_int here

       // to avoid problem with scale == -1 (min_int/(-1) == min_int).

       Node* shift = _igvn.intcon(31);

       set_ctrl(shift, C->root());

       Node* sign = new (C) RShiftINode(offset, shift);

       register_new_node(sign, pre_ctrl);

       offset = new (C) AndINode(offset, sign);

       register_new_node(offset, pre_ctrl);

     } else {

       assert(low_limit->get_int() == 0, "wrong low limit for range check");

       // The only problem we have here when offset == min_int

       // since (0-min_int) == min_int. It may be fine for stride > 0

       // but for stride < 0 X will be < original_limit. To avoid it

       // max(pre_limit, original_limit) is used in do_range_check().

     }

     // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);

     *pre_limit = adjust_limit((-stride_con), scale, offset, low_limit, *pre_limit, pre_ctrl);

   } else { // stride_con*scale_con < 0

     // For negative stride*scale pre-loop checks for overflow and

     // post-loop for underflow.

     //

     // The overflow limit: scale*I+offset < upper_limit

     // For pre-loop compute

     //   NOT(scale*I+offset < upper_limit)

     //   scale*I+offset >= upper_limit

     //   scale*I+offset+1 > upper_limit

     //   ( if (scale < 0) /* and stride > 0 */

     //       I < (upper_limit-(offset+1))/scale

     //     else /* scale > 0 and stride < 0 */

     //       I > (upper_limit-(offset+1))/scale

     //   )

     //

     // (upper_limit-offset-1) may underflow or overflow.

     // To avoid it min(pre_limit, original_limit) is used

     // in do_range_check() for stride > 0 and max() for < 0.

     Node *one  = _igvn.intcon(1);

     set_ctrl(one, C->root());

     Node *plus_one = new (C) AddINode(offset, one);

     register_new_node( plus_one, pre_ctrl );

     // Pass (-stride) to indicate pre_loop_cond = NOT(main_loop_cond);

     *pre_limit = adjust_limit((-stride_con), scale, plus_one, upper_limit, *pre_limit, pre_ctrl);

     if (low_limit->get_int() == -max_jint) {

       if (!RangeLimitCheck) return;

       // We need this guard when scale*main_limit+offset >= limit

       // due to underflow. So we need execute main-loop while

       // scale*I+offset+1 > min_int. But (min_int-offset-1) will

       // underflow when (offset+1) > 0 and X will be < main_limit

       // when scale < 0 (and stride > 0). To avoid it we replace

       // positive (offset+1) with 0.

       //

       // Also (min_int+1 == -max_int) is used instead of min_int here

       // to avoid problem with scale == -1 (min_int/(-1) == min_int).

       Node* shift = _igvn.intcon(31);

       set_ctrl(shift, C->root());

       Node* sign = new (C) RShiftINode(plus_one, shift);

       register_new_node(sign, pre_ctrl);

       plus_one = new (C) AndINode(plus_one, sign);

       register_new_node(plus_one, pre_ctrl);

     } else {

       assert(low_limit->get_int() == 0, "wrong low limit for range check");

       // The only problem we have here when offset == max_int

       // since (max_int+1) == min_int and (0-min_int) == min_int.

       // But it is fine since main loop will either have

       // less iterations or will be skipped in such case.

     }

     // The underflow limit: low_limit <= scale*I+offset.

     // For main-loop compute

     //   scale*I+offset+1 > low_limit

     //   ( if (scale < 0) /* and stride > 0 */

     //       I < (low_limit-(offset+1))/scale

     //     else /* scale > 0 and stride < 0 */

     //       I > (low_limit-(offset+1))/scale

     //   )

     *main_limit = adjust_limit(stride_con, scale, plus_one, low_limit, *main_limit, pre_ctrl);

   }

 }

 //------------------------------is_scaled_iv---------------------------------

 // Return true if exp is a constant times an induction var

 bool PhaseIdealLoop::is_scaled_iv(Node* exp, Node* iv, int* p_scale) {

   if (exp == iv) {

     if (p_scale != NULL) {

       *p_scale = 1;

     }

     return true;

   }

   int opc = exp->Opcode();

   if (opc == Op_MulI) {

     if (exp->in(1) == iv && exp->in(2)->is_Con()) {

       if (p_scale != NULL) {

         *p_scale = exp->in(2)->get_int();

       }

       return true;

     }

     if (exp->in(2) == iv && exp->in(1)->is_Con()) {

       if (p_scale != NULL) {

         *p_scale = exp->in(1)->get_int();

       }

       return true;

     }

   } else if (opc == Op_LShiftI) {

     if (exp->in(1) == iv && exp->in(2)->is_Con()) {

       if (p_scale != NULL) {

         *p_scale = 1 << exp->in(2)->get_int();

       }

       return true;

     }

   }

   return false;

 }

 //-----------------------------is_scaled_iv_plus_offset------------------------------

 // Return true if exp is a simple induction variable expression: k1*iv + (invar + k2)

 bool PhaseIdealLoop::is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth) {

   if (is_scaled_iv(exp, iv, p_scale)) {

     if (p_offset != NULL) {

       Node *zero = _igvn.intcon(0);

       set_ctrl(zero, C->root());

       *p_offset = zero;

     }

     return true;

   }

   int opc = exp->Opcode();

   if (opc == Op_AddI) {

     if (is_scaled_iv(exp->in(1), iv, p_scale)) {

       if (p_offset != NULL) {

         *p_offset = exp->in(2);

       }

       return true;

     }

     if (exp->in(2)->is_Con()) {

       Node* offset2 = NULL;

       if (depth < 2 &&

           is_scaled_iv_plus_offset(exp->in(1), iv, p_scale,

                                    p_offset != NULL ? &offset2 : NULL, depth+1)) {

         if (p_offset != NULL) {

           Node *ctrl_off2 = get_ctrl(offset2);

           Node* offset = new (C) AddINode(offset2, exp->in(2));

           register_new_node(offset, ctrl_off2);

           *p_offset = offset;

         }

         return true;

       }

     }

   } else if (opc == Op_SubI) {

     if (is_scaled_iv(exp->in(1), iv, p_scale)) {

       if (p_offset != NULL) {

         Node *zero = _igvn.intcon(0);

         set_ctrl(zero, C->root());

         Node *ctrl_off = get_ctrl(exp->in(2));

         Node* offset = new (C) SubINode(zero, exp->in(2));

         register_new_node(offset, ctrl_off);

         *p_offset = offset;

       }

       return true;

     }

     if (is_scaled_iv(exp->in(2), iv, p_scale)) {

       if (p_offset != NULL) {

         *p_scale *= -1;

         *p_offset = exp->in(1);

       }

       return true;

     }

   }

   return false;

 }

 //------------------------------do_range_check---------------------------------

 // Eliminate range-checks and other trip-counter vs loop-invariant tests.

 void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {

 #ifndef PRODUCT

   if (PrintOpto && VerifyLoopOptimizations) {

     tty->print("Range Check Elimination ");

     loop->dump_head();

   } else if (TraceLoopOpts) {

     tty->print("RangeCheck   ");

     loop->dump_head();

   }

 #endif

   assert(RangeCheckElimination, "");

   CountedLoopNode *cl = loop->_head->as_CountedLoop();

   assert(cl->is_main_loop(), "");

   // protect against stride not being a constant

   if (!cl->stride_is_con())

     return;

   // Find the trip counter; we are iteration splitting based on it

   Node *trip_counter = cl->phi();

   // Find the main loop limit; we will trim it's iterations

   // to not ever trip end tests

   Node *main_limit = cl->limit();

   // Need to find the main-loop zero-trip guard

   Node *ctrl  = cl->in(LoopNode::EntryControl);

   assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");

   Node *iffm = ctrl->in(0);

   assert(iffm->Opcode() == Op_If, "");

   Node *bolzm = iffm->in(1);

   assert(bolzm->Opcode() == Op_Bool, "");

   Node *cmpzm = bolzm->in(1);

   assert(cmpzm->is_Cmp(), "");

   Node *opqzm = cmpzm->in(2);

   // Can not optimize a loop if zero-trip Opaque1 node is optimized

   // away and then another round of loop opts attempted.

   if (opqzm->Opcode() != Op_Opaque1)

     return;

   assert(opqzm->in(1) == main_limit, "do not understand situation");

   // Find the pre-loop limit; we will expand it's iterations to

   // not ever trip low tests.

   Node *p_f = iffm->in(0);

   assert(p_f->Opcode() == Op_IfFalse, "");

   CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();

   assert(pre_end->loopnode()->is_pre_loop(), "");

   Node *pre_opaq1 = pre_end->limit();

   // Occasionally it's possible for a pre-loop Opaque1 node to be

   // optimized away and then another round of loop opts attempted.

   // We can not optimize this particular loop in that case.

   if (pre_opaq1->Opcode() != Op_Opaque1)

     return;

   Opaque1Node *pre_opaq = (Opaque1Node*)pre_opaq1;

   Node *pre_limit = pre_opaq->in(1);

   // Where do we put new limit calculations

   Node *pre_ctrl = pre_end->loopnode()->in(LoopNode::EntryControl);

   // Ensure the original loop limit is available from the

   // pre-loop Opaque1 node.

   Node *orig_limit = pre_opaq->original_loop_limit();

   if (orig_limit == NULL || _igvn.type(orig_limit) == Type::TOP)

     return;

   // Must know if its a count-up or count-down loop

   int stride_con = cl->stride_con();

   Node *zero = _igvn.intcon(0);

   Node *one  = _igvn.intcon(1);

   // Use symmetrical int range [-max_jint,max_jint]

   Node *mini = _igvn.intcon(-max_jint);

   set_ctrl(zero, C->root());

   set_ctrl(one,  C->root());

   set_ctrl(mini, C->root());

   // Range checks that do not dominate the loop backedge (ie.

   // conditionally executed) can lengthen the pre loop limit beyond

   // the original loop limit. To prevent this, the pre limit is

   // (for stride > 0) MINed with the original loop limit (MAXed

   // stride < 0) when some range_check (rc) is conditionally

   // executed.

   bool conditional_rc = false;

   // Check loop body for tests of trip-counter plus loop-invariant vs

   // loop-invariant.

   for( uint i = 0; i < loop->_body.size(); i++ ) {

     Node *iff = loop->_body[i];

     if( iff->Opcode() == Op_If ) { // Test?

       // Test is an IfNode, has 2 projections.  If BOTH are in the loop

       // we need loop unswitching instead of iteration splitting.

       Node *exit = loop->is_loop_exit(iff);

       if( !exit ) continue;

       int flip = (exit->Opcode() == Op_IfTrue) ? 1 : 0;

       // Get boolean condition to test

       Node *i1 = iff->in(1);

       if( !i1->is_Bool() ) continue;

       BoolNode *bol = i1->as_Bool();

       BoolTest b_test = bol->_test;

       // Flip sense of test if exit condition is flipped

       if( flip )

         b_test = b_test.negate();

       // Get compare

       Node *cmp = bol->in(1);

       // Look for trip_counter + offset vs limit

       Node *rc_exp = cmp->in(1);

       Node *limit  = cmp->in(2);

       jint scale_con= 1;        // Assume trip counter not scaled

       Node *limit_c = get_ctrl(limit);

       if( loop->is_member(get_loop(limit_c) ) ) {

         // Compare might have operands swapped; commute them

         b_test = b_test.commute();

         rc_exp = cmp->in(2);

         limit  = cmp->in(1);

         limit_c = get_ctrl(limit);

         if( loop->is_member(get_loop(limit_c) ) )

           continue;             // Both inputs are loop varying; cannot RCE

       }

       // Here we know 'limit' is loop invariant

       // 'limit' maybe pinned below the zero trip test (probably from a

       // previous round of rce), in which case, it can't be used in the

       // zero trip test expression which must occur before the zero test's if.

       if( limit_c == ctrl ) {

         continue;  // Don't rce this check but continue looking for other candidates.

       }

       // Check for scaled induction variable plus an offset

       Node *offset = NULL;

       if (!is_scaled_iv_plus_offset(rc_exp, trip_counter, &scale_con, &offset)) {

         continue;

       }

       Node *offset_c = get_ctrl(offset);

       if( loop->is_member( get_loop(offset_c) ) )

         continue;               // Offset is not really loop invariant

       // Here we know 'offset' is loop invariant.

       // As above for the 'limit', the 'offset' maybe pinned below the

       // zero trip test.

       if( offset_c == ctrl ) {

         continue; // Don't rce this check but continue looking for other candidates.

       }

 #ifdef ASSERT

       if (TraceRangeLimitCheck) {

         tty->print_cr("RC bool node%s", flip ? " flipped:" : ":");

         bol->dump(2);

       }

 #endif

       // At this point we have the expression as:

       //   scale_con * trip_counter + offset :: limit

       // where scale_con, offset and limit are loop invariant.  Trip_counter

       // monotonically increases by stride_con, a constant.  Both (or either)

       // stride_con and scale_con can be negative which will flip about the

       // sense of the test.

       // Adjust pre and main loop limits to guard the correct iteration set

       if( cmp->Opcode() == Op_CmpU ) {// Unsigned compare is really 2 tests

         if( b_test._test == BoolTest::lt ) { // Range checks always use lt

           // The underflow and overflow limits: 0 <= scale*I+offset < limit

           add_constraint( stride_con, scale_con, offset, zero, limit, pre_ctrl, &pre_limit, &main_limit );

           if (!conditional_rc) {

             // (0-offset)/scale could be outside of loop iterations range.

             conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;

           }

         } else {

 #ifndef PRODUCT

           if( PrintOpto )

             tty->print_cr("missed RCE opportunity");

 #endif

           continue;             // In release mode, ignore it

         }

       } else {                  // Otherwise work on normal compares

         switch( b_test._test ) {

         case BoolTest::gt:

           // Fall into GE case

         case BoolTest::ge:

           // Convert (I*scale+offset) >= Limit to (I*(-scale)+(-offset)) <= -Limit

           scale_con = -scale_con;

           offset = new (C) SubINode( zero, offset );

           register_new_node( offset, pre_ctrl );

           limit  = new (C) SubINode( zero, limit  );

           register_new_node( limit, pre_ctrl );

           // Fall into LE case

         case BoolTest::le:

           if (b_test._test != BoolTest::gt) {

             // Convert X <= Y to X < Y+1

             limit = new (C) AddINode( limit, one );

             register_new_node( limit, pre_ctrl );

           }

           // Fall into LT case

         case BoolTest::lt:

           // The underflow and overflow limits: MIN_INT <= scale*I+offset < limit

           // Note: (MIN_INT+1 == -MAX_INT) is used instead of MIN_INT here

           // to avoid problem with scale == -1: MIN_INT/(-1) == MIN_INT.

           add_constraint( stride_con, scale_con, offset, mini, limit, pre_ctrl, &pre_limit, &main_limit );

           if (!conditional_rc) {

             // ((MIN_INT+1)-offset)/scale could be outside of loop iterations range.

             // Note: negative offset is replaced with 0 but (MIN_INT+1)/scale could

             // still be outside of loop range.

             conditional_rc = !loop->dominates_backedge(iff) || RangeLimitCheck;

           }

           break;

         default:

 #ifndef PRODUCT

           if( PrintOpto )

             tty->print_cr("missed RCE opportunity");

 #endif

           continue;             // Unhandled case

         }

       }

       // Kill the eliminated test

       C->set_major_progress();

       Node *kill_con = _igvn.intcon( 1-flip );

       set_ctrl(kill_con, C->root());

       _igvn.replace_input_of(iff, 1, kill_con);

       // Find surviving projection

       assert(iff->is_If(), "");

       ProjNode* dp = ((IfNode*)iff)->proj_out(1-flip);

       // Find loads off the surviving projection; remove their control edge

       for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {

         Node* cd = dp->fast_out(i); // Control-dependent node

         if (cd->is_Load() && cd->depends_only_on_test()) {   // Loads can now float around in the loop

           // Allow the load to float around in the loop, or before it

           // but NOT before the pre-loop.

           _igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL

           --i;

           --imax;

         }

       }

     } // End of is IF

   }

   // Update loop limits

   if (conditional_rc) {

     pre_limit = (stride_con > 0) ? (Node*)new (C) MinINode(pre_limit, orig_limit)

                                  : (Node*)new (C) MaxINode(pre_limit, orig_limit);

     register_new_node(pre_limit, pre_ctrl);

   }

   _igvn.hash_delete(pre_opaq);

   pre_opaq->set_req(1, pre_limit);

   // Note:: we are making the main loop limit no longer precise;

   // need to round up based on stride.

   cl->set_nonexact_trip_count();

   if (!LoopLimitCheck && stride_con != 1 && stride_con != -1) { // Cutout for common case

     // "Standard" round-up logic:  ([main_limit-init+(y-1)]/y)*y+init

     // Hopefully, compiler will optimize for powers of 2.

     Node *ctrl = get_ctrl(main_limit);

     Node *stride = cl->stride();

     Node *init = cl->init_trip();

     Node *span = new (C) SubINode(main_limit,init);

     register_new_node(span,ctrl);

     Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));

     Node *add = new (C) AddINode(span,rndup);

     register_new_node(add,ctrl);

     Node *div = new (C) DivINode(0,add,stride);

     register_new_node(div,ctrl);

     Node *mul = new (C) MulINode(div,stride);

     register_new_node(mul,ctrl);

     Node *newlim = new (C) AddINode(mul,init);

     register_new_node(newlim,ctrl);

     main_limit = newlim;

   }

   Node *main_cle = cl->loopexit();

   Node *main_bol = main_cle->in(1);

   // Hacking loop bounds; need private copies of exit test

   if( main_bol->outcnt() > 1 ) {// BoolNode shared?

     _igvn.hash_delete(main_cle);

     main_bol = main_bol->clone();// Clone a private BoolNode

     register_new_node( main_bol, main_cle->in(0) );

     main_cle->set_req(1,main_bol);

   }

   Node *main_cmp = main_bol->in(1);

   if( main_cmp->outcnt() > 1 ) { // CmpNode shared?

     _igvn.hash_delete(main_bol);

     main_cmp = main_cmp->clone();// Clone a private CmpNode

     register_new_node( main_cmp, main_cle->in(0) );

     main_bol->set_req(1,main_cmp);

   }

   // Hack the now-private loop bounds

   _igvn.replace_input_of(main_cmp, 2, main_limit);

   // The OpaqueNode is unshared by design

   assert( opqzm->outcnt() == 1, "cannot hack shared node" );

   _igvn.replace_input_of(opqzm, 1, main_limit);

 }

 //------------------------------DCE_loop_body----------------------------------

 // Remove simplistic dead code from loop body

 void IdealLoopTree::DCE_loop_body() {

   for( uint i = 0; i < _body.size(); i++ )

     if( _body.at(i)->outcnt() == 0 )

       _body.map( i--, _body.pop() );

 }

 //------------------------------adjust_loop_exit_prob--------------------------

 // Look for loop-exit tests with the 50/50 (or worse) guesses from the parsing stage.

 // Replace with a 1-in-10 exit guess.

 void IdealLoopTree::adjust_loop_exit_prob( PhaseIdealLoop *phase ) {

   Node *test = tail();

   while( test != _head ) {

     uint top = test->Opcode();

     if( top == Op_IfTrue || top == Op_IfFalse ) {

       int test_con = ((ProjNode*)test)->_con;

       assert(top == (uint)(test_con? Op_IfTrue: Op_IfFalse), "sanity");

       IfNode *iff = test->in(0)->as_If();

       if( iff->outcnt() == 2 ) {        // Ignore dead tests

         Node *bol = iff->in(1);

         if( bol && bol->req() > 1 && bol->in(1) &&

             ((bol->in(1)->Opcode() == Op_StorePConditional ) ||

              (bol->in(1)->Opcode() == Op_StoreIConditional ) ||

              (bol->in(1)->Opcode() == Op_StoreLConditional ) ||

              (bol->in(1)->Opcode() == Op_CompareAndSwapI ) ||

              (bol->in(1)->Opcode() == Op_CompareAndSwapL ) ||

              (bol->in(1)->Opcode() == Op_CompareAndSwapP ) ||

              (bol->in(1)->Opcode() == Op_CompareAndSwapN )))

           return;               // Allocation loops RARELY take backedge

         // Find the OTHER exit path from the IF

         Node* ex = iff->proj_out(1-test_con);

         float p = iff->_prob;

         if( !phase->is_member( this, ex ) && iff->_fcnt == COUNT_UNKNOWN ) {

           if( top == Op_IfTrue ) {

             if( p < (PROB_FAIR + PROB_UNLIKELY_MAG(3))) {

               iff->_prob = PROB_STATIC_FREQUENT;

             }

           } else {

             if( p > (PROB_FAIR - PROB_UNLIKELY_MAG(3))) {

               iff->_prob = PROB_STATIC_INFREQUENT;

             }

           }

         }

       }

     }

     test = phase->idom(test);

   }

 }

 //------------------------------policy_do_remove_empty_loop--------------------

 // Micro-benchmark spamming.  Policy is to always remove empty loops.

 // The 'DO' part is to replace the trip counter with the value it will

 // have on the last iteration.  This will break the loop.

 bool IdealLoopTree::policy_do_remove_empty_loop( PhaseIdealLoop *phase ) {

   // Minimum size must be empty loop

   if (_body.size() > EMPTY_LOOP_SIZE)

     return false;

   if (!_head->is_CountedLoop())

     return false;     // Dead loop

   CountedLoopNode *cl = _head->as_CountedLoop();

   if (!cl->is_valid_counted_loop())

     return false; // Malformed loop

   if (!phase->is_member(this, phase->get_ctrl(cl->loopexit()->in(CountedLoopEndNode::TestValue))))

     return false;             // Infinite loop

 #ifdef ASSERT

   // Ensure only one phi which is the iv.

   Node* iv = NULL;

   for (DUIterator_Fast imax, i = cl->fast_outs(imax); i < imax; i++) {

     Node* n = cl->fast_out(i);

     if (n->Opcode() == Op_Phi) {

       assert(iv == NULL, "Too many phis" );

       iv = n;

     }

   }

   assert(iv == cl->phi(), "Wrong phi" );

 #endif

   // main and post loops have explicitly created zero trip guard

   bool needs_guard = !cl->is_main_loop() && !cl->is_post_loop();

   if (needs_guard) {

     // Skip guard if values not overlap.

     const TypeInt* init_t = phase->_igvn.type(cl->init_trip())->is_int();

     const TypeInt* limit_t = phase->_igvn.type(cl->limit())->is_int();

     int  stride_con = cl->stride_con();

     if (stride_con > 0) {

       needs_guard = (init_t->_hi >= limit_t->_lo);

     } else {

       needs_guard = (init_t->_lo <= limit_t->_hi);

     }

   }

   if (needs_guard) {

     // Check for an obvious zero trip guard.

     Node* inctrl = PhaseIdealLoop::skip_loop_predicates(cl->in(LoopNode::EntryControl));

     if (inctrl->Opcode() == Op_IfTrue) {

       // The test should look like just the backedge of a CountedLoop

       Node* iff = inctrl->in(0);

       if (iff->is_If()) {

         Node* bol = iff->in(1);

         if (bol->is_Bool() && bol->as_Bool()->_test._test == cl->loopexit()->test_trip()) {

           Node* cmp = bol->in(1);

           if (cmp->is_Cmp() && cmp->in(1) == cl->init_trip() && cmp->in(2) == cl->limit()) {

             needs_guard = false;

           }

         }

       }

     }

   }

 #ifndef PRODUCT

   if (PrintOpto) {

     tty->print("Removing empty loop with%s zero trip guard", needs_guard ? "out" : "");

     this->dump_head();

   } else if (TraceLoopOpts) {

     tty->print("Empty with%s zero trip guard   ", needs_guard ? "out" : "");

     this->dump_head();

   }

 #endif

   if (needs_guard) {

     // Peel the loop to ensure there's a zero trip guard

     Node_List old_new;

     phase->do_peeling(this, old_new);

   }

   // Replace the phi at loop head with the final value of the last

   // iteration.  Then the CountedLoopEnd will collapse (backedge never

   // taken) and all loop-invariant uses of the exit values will be correct.

   Node *phi = cl->phi();

   Node *exact_limit = phase->exact_limit(this);

   if (exact_limit != cl->limit()) {

     // We also need to replace the original limit to collapse loop exit.

     Node* cmp = cl->loopexit()->cmp_node();

     assert(cl->limit() == cmp->in(2), "sanity");

     phase->_igvn._worklist.push(cmp->in(2)); // put limit on worklist

     phase->_igvn.replace_input_of(cmp, 2, exact_limit); // put cmp on worklist

   }

   // Note: the final value after increment should not overflow since

   // counted loop has limit check predicate.

   Node *final = new (phase->C) SubINode( exact_limit, cl->stride() );

   phase->register_new_node(final,cl->in(LoopNode::EntryControl));

   phase->_igvn.replace_node(phi,final);

   phase->C->set_major_progress();

   return true;

 }

 //------------------------------policy_do_one_iteration_loop-------------------

 // Convert one iteration loop into normal code.

 bool IdealLoopTree::policy_do_one_iteration_loop( PhaseIdealLoop *phase ) {

   if (!_head->as_Loop()->is_valid_counted_loop())

     return false; // Only for counted loop

   CountedLoopNode *cl = _head->as_CountedLoop();

   if (!cl->has_exact_trip_count() || cl->trip_count() != 1) {

     return false;

   }

 #ifndef PRODUCT

   if(TraceLoopOpts) {

     tty->print("OneIteration ");

     this->dump_head();

   }

 #endif

   Node *init_n = cl->init_trip();

 #ifdef ASSERT

   // Loop boundaries should be constant since trip count is exact.

   assert(init_n->get_int() + cl->stride_con() >= cl->limit()->get_int(), "should be one iteration");

 #endif

   // Replace the phi at loop head with the value of the init_trip.

   // Then the CountedLoopEnd will collapse (backedge will not be taken)

   // and all loop-invariant uses of the exit values will be correct.

   phase->_igvn.replace_node(cl->phi(), cl->init_trip());

   phase->C->set_major_progress();

   return true;

 }

 //=============================================================================

 //------------------------------iteration_split_impl---------------------------

 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {

   // Compute exact loop trip count if possible.

   compute_exact_trip_count(phase);

   // Convert one iteration loop into normal code.

   if (policy_do_one_iteration_loop(phase))

     return true;

   // Check and remove empty loops (spam micro-benchmarks)

   if (policy_do_remove_empty_loop(phase))

     return true;  // Here we removed an empty loop

   bool should_peel = policy_peeling(phase); // Should we peel?

   bool should_unswitch = policy_unswitching(phase);

   // Non-counted loops may be peeled; exactly 1 iteration is peeled.

   // This removes loop-invariant tests (usually null checks).

   if (!_head->is_CountedLoop()) { // Non-counted loop

     if (PartialPeelLoop && phase->partial_peel(this, old_new)) {

       // Partial peel succeeded so terminate this round of loop opts

       return false;

     }

     if (should_peel) {            // Should we peel?

 #ifndef PRODUCT

       if (PrintOpto) tty->print_cr("should_peel");

 #endif

       phase->do_peeling(this,old_new);

     } else if (should_unswitch) {

       phase->do_unswitching(this, old_new);

     }

     return true;

   }

   CountedLoopNode *cl = _head->as_CountedLoop();

   if (!cl->is_valid_counted_loop()) return true; // Ignore various kinds of broken loops

   // Do nothing special to pre- and post- loops

   if (cl->is_pre_loop() || cl->is_post_loop()) return true;

   // Compute loop trip count from profile data

   compute_profile_trip_cnt(phase);

   // Before attempting fancy unrolling, RCE or alignment, see if we want

   // to completely unroll this loop or do loop unswitching.

   if (cl->is_normal_loop()) {

     if (should_unswitch) {

       phase->do_unswitching(this, old_new);

       return true;

     }

     bool should_maximally_unroll =  policy_maximally_unroll(phase);

     if (should_maximally_unroll) {

       // Here we did some unrolling and peeling.  Eventually we will

       // completely unroll this loop and it will no longer be a loop.

       phase->do_maximally_unroll(this,old_new);

       return true;

     }

   }

   // Skip next optimizations if running low on nodes. Note that

   // policy_unswitching and policy_maximally_unroll have this check.

   uint nodes_left = MaxNodeLimit - (uint) phase->C->live_nodes();

   if ((2 * _body.size()) > nodes_left) {

     return true;

   }

   // Counted loops may be peeled, may need some iterations run up

   // front for RCE, and may want to align loop refs to a cache

   // line.  Thus we clone a full loop up front whose trip count is

   // at least 1 (if peeling), but may be several more.

   // The main loop will start cache-line aligned with at least 1

   // iteration of the unrolled body (zero-trip test required) and

   // will have some range checks removed.

   // A post-loop will finish any odd iterations (leftover after

   // unrolling), plus any needed for RCE purposes.

   bool should_unroll = policy_unroll(phase);

   bool should_rce = policy_range_check(phase);

   bool should_align = policy_align(phase);

   // If not RCE'ing (iteration splitting) or Aligning, then we do not

   // need a pre-loop.  We may still need to peel an initial iteration but

   // we will not be needing an unknown number of pre-iterations.

   //

   // Basically, if may_rce_align reports FALSE first time through,

   // we will not be able to later do RCE or Aligning on this loop.

   bool may_rce_align = !policy_peel_only(phase) || should_rce || should_align;

   // If we have any of these conditions (RCE, alignment, unrolling) met, then

   // we switch to the pre-/main-/post-loop model.  This model also covers

   // peeling.

   if (should_rce || should_align || should_unroll) {

     if (cl->is_normal_loop())  // Convert to 'pre/main/post' loops

       phase->insert_pre_post_loops(this,old_new, !may_rce_align);

     // Adjust the pre- and main-loop limits to let the pre and post loops run

     // with full checks, but the main-loop with no checks.  Remove said

     // checks from the main body.

     if (should_rce)

       phase->do_range_check(this,old_new);

     // Double loop body for unrolling.  Adjust the minimum-trip test (will do

     // twice as many iterations as before) and the main body limit (only do

     // an even number of trips).  If we are peeling, we might enable some RCE

     // and we'd rather unroll the post-RCE'd loop SO... do not unroll if

     // peeling.

     if (should_unroll && !should_peel)

       phase->do_unroll(this,old_new, true);

     // Adjust the pre-loop limits to align the main body

     // iterations.

     if (should_align)

       Unimplemented();

   } else {                      // Else we have an unchanged counted loop

     if (should_peel)           // Might want to peel but do nothing else

       phase->do_peeling(this,old_new);

   }

   return true;

 }

 //=============================================================================

 //------------------------------iteration_split--------------------------------

 bool IdealLoopTree::iteration_split( PhaseIdealLoop *phase, Node_List &old_new ) {

   // Recursively iteration split nested loops

   if (_child && !_child->iteration_split(phase, old_new))

     return false;

   // Clean out prior deadwood

   DCE_loop_body();

   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.

   // Replace with a 1-in-10 exit guess.

   if (_parent /*not the root loop*/ &&

       !_irreducible &&

       // Also ignore the occasional dead backedge

       !tail()->is_top()) {

     adjust_loop_exit_prob(phase);

   }

   // Gate unrolling, RCE and peeling efforts.

   if (!_child &&                // If not an inner loop, do not split

       !_irreducible &&

       _allow_optimizations &&

       !tail()->is_top()) {     // Also ignore the occasional dead backedge

     if (!_has_call) {

         if (!iteration_split_impl(phase, old_new)) {

           return false;

         }

     } else if (policy_unswitching(phase)) {

       phase->do_unswitching(this, old_new);

     }

   }

   // Minor offset re-organization to remove loop-fallout uses of

   // trip counter when there was no major reshaping.

   phase->reorg_offsets(this);

   if (_next && !_next->iteration_split(phase, old_new))

     return false;

   return true;

 }

 //=============================================================================

 // Process all the loops in the loop tree and replace any fill

 // patterns with an intrisc version.

 bool PhaseIdealLoop::do_intrinsify_fill() {

   bool changed = false;

   for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {

     IdealLoopTree* lpt = iter.current();

     changed |= intrinsify_fill(lpt);

   }

   return changed;

 }

 // Examine an inner loop looking for a a single store of an invariant

 // value in a unit stride loop,

 bool PhaseIdealLoop::match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,

                                      Node*& shift, Node*& con) {

   const char* msg = NULL;

   Node* msg_node = NULL;

   store_value = NULL;

   con = NULL;

   shift = NULL;

   // Process the loop looking for stores.  If there are multiple

   // stores or extra control flow give at this point.

   CountedLoopNode* head = lpt->_head->as_CountedLoop();

   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {

     Node* n = lpt->_body.at(i);

     if (n->outcnt() == 0) continue; // Ignore dead

     if (n->is_Store()) {

       if (store != NULL) {

         msg = "multiple stores";

         break;

       }

       int opc = n->Opcode();

       if (opc == Op_StoreP || opc == Op_StoreN || opc == Op_StoreNKlass || opc == Op_StoreCM) {

         msg = "oop fills not handled";

         break;

       }

       Node* value = n->in(MemNode::ValueIn);

       if (!lpt->is_invariant(value)) {

         msg  = "variant store value";

       } else if (!_igvn.type(n->in(MemNode::Address))->isa_aryptr()) {

         msg = "not array address";

       }

       store = n;

       store_value = value;

     } else if (n->is_If() && n != head->loopexit()) {

       msg = "extra control flow";

       msg_node = n;

     }

   }

   if (store == NULL) {

     // No store in loop

     return false;

   }

   if (msg == NULL && head->stride_con() != 1) {

     // could handle negative strides too

     if (head->stride_con() < 0) {

       msg = "negative stride";

     } else {

       msg = "non-unit stride";

     }

   }

   if (msg == NULL && !store->in(MemNode::Address)->is_AddP()) {

     msg = "can't handle store address";

     msg_node = store->in(MemNode::Address);

   }

   if (msg == NULL &&

       (!store->in(MemNode::Memory)->is_Phi() ||

        store->in(MemNode::Memory)->in(LoopNode::LoopBackControl) != store)) {

     msg = "store memory isn't proper phi";

     msg_node = store->in(MemNode::Memory);

   }

   // Make sure there is an appropriate fill routine

   BasicType t = store->as_Mem()->memory_type();

   const char* fill_name;

   if (msg == NULL &&

       StubRoutines::select_fill_function(t, false, fill_name) == NULL) {

     msg = "unsupported store";

     msg_node = store;

   }

   if (msg != NULL) {

 #ifndef PRODUCT

     if (TraceOptimizeFill) {

       tty->print_cr("not fill intrinsic candidate: %s", msg);

       if (msg_node != NULL) msg_node->dump();

     }

 #endif

     return false;

   }

   // Make sure the address expression can be handled.  It should be

   // head->phi * elsize + con.  head->phi might have a ConvI2L.

   Node* elements[4];

   Node* conv = NULL;

   bool found_index = false;

   int count = store->in(MemNode::Address)->as_AddP()->unpack_offsets(elements, ARRAY_SIZE(elements));

   for (int e = 0; e < count; e++) {

     Node* n = elements[e];

     if (n->is_Con() && con == NULL) {

       con = n;

     } else if (n->Opcode() == Op_LShiftX && shift == NULL) {

       Node* value = n->in(1);

 #ifdef _LP64

       if (value->Opcode() == Op_ConvI2L) {

         conv = value;

         value = value->in(1);

       }

 #endif

       if (value != head->phi()) {

         msg = "unhandled shift in address";

       } else {

         if (type2aelembytes(store->as_Mem()->memory_type(), true) != (1 << n->in(2)->get_int())) {

           msg = "scale doesn't match";

         } else {

           found_index = true;

           shift = n;

         }

       }

     } else if (n->Opcode() == Op_ConvI2L && conv == NULL) {

       if (n->in(1) == head->phi()) {

         found_index = true;

         conv = n;

       } else {

         msg = "unhandled input to ConvI2L";

       }

     } else if (n == head->phi()) {

       // no shift, check below for allowed cases

       found_index = true;

     } else {

       msg = "unhandled node in address";

       msg_node = n;

     }

   }

   if (count == -1) {

     msg = "malformed address expression";

     msg_node = store;

   }

   if (!found_index) {

     msg = "missing use of index";

   }

   // byte sized items won't have a shift

   if (msg == NULL && shift == NULL && t != T_BYTE && t != T_BOOLEAN) {

     msg = "can't find shift";

     msg_node = store;

   }

   if (msg != NULL) {

 #ifndef PRODUCT

     if (TraceOptimizeFill) {

       tty->print_cr("not fill intrinsic: %s", msg);

       if (msg_node != NULL) msg_node->dump();

     }

 #endif

     return false;

   }

   // No make sure all the other nodes in the loop can be handled

   VectorSet ok(Thread::current()->resource_area());

   // store related values are ok

   ok.set(store->_idx);

   ok.set(store->in(MemNode::Memory)->_idx);

   CountedLoopEndNode* loop_exit = head->loopexit();

   guarantee(loop_exit != NULL, "no loop exit node");

   // Loop structure is ok

   ok.set(head->_idx);

   ok.set(loop_exit->_idx);

   ok.set(head->phi()->_idx);

   ok.set(head->incr()->_idx);

   ok.set(loop_exit->cmp_node()->_idx);

   ok.set(loop_exit->in(1)->_idx);

   // Address elements are ok

   if (con)   ok.set(con->_idx);

   if (shift) ok.set(shift->_idx);

   if (conv)  ok.set(conv->_idx);

   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {

     Node* n = lpt->_body.at(i);

     if (n->outcnt() == 0) continue; // Ignore dead

     if (ok.test(n->_idx)) continue;

     // Backedge projection is ok

     if (n->is_IfTrue() && n->in(0) == loop_exit) continue;

     if (!n->is_AddP()) {

       msg = "unhandled node";

       msg_node = n;

       break;

     }

   }

   // Make sure no unexpected values are used outside the loop

   for (uint i = 0; msg == NULL && i < lpt->_body.size(); i++) {

     Node* n = lpt->_body.at(i);

     // These values can be replaced with other nodes if they are used

     // outside the loop.

     if (n == store || n == loop_exit || n == head->incr() || n == store->in(MemNode::Memory)) continue;

     for (SimpleDUIterator iter(n); iter.has_next(); iter.next()) {

       Node* use = iter.get();

       if (!lpt->_body.contains(use)) {

         msg = "node is used outside loop";

         // lpt->_body.dump();

         msg_node = n;

         break;

       }

     }

   }

 #ifdef ASSERT

   if (TraceOptimizeFill) {

     if (msg != NULL) {

       tty->print_cr("no fill intrinsic: %s", msg);

       if (msg_node != NULL) msg_node->dump();

     } else {

       tty->print_cr("fill intrinsic for:");

     }

     store->dump();

     if (Verbose) {

       lpt->_body.dump();

     }

   }

 #endif

   return msg == NULL;

 }

 bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {

   // Only for counted inner loops

   if (!lpt->is_counted() || !lpt->is_inner()) {

     return false;

   }