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

 /*

  * Copyright 2000-2008 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

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  */

 #include "incls/_precompiled.incl"

 #include "incls/_loopTransform.cpp.incl"

 //------------------------------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_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, 3) SubINode(zero, inv1);

     phase->register_new_node(n_inv1, inv1_c);

   } else {

     n_inv1 = inv1;

   }

   Node* inv;

   if (neg_inv2) {

     inv = new (phase->C, 3) SubINode(n_inv1, inv2);

   } else {

     inv = new (phase->C, 3) AddINode(n_inv1, inv2);

   }

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

   Node* addx;

   if (neg_x) {

     addx = new (phase->C, 3) SubINode(inv, x);

   } else {

     addx = new (phase->C, 3) AddINode(x, inv);

   }

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

   phase->_igvn.hash_delete(n1);

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

   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  uniq      = phase->C->unique();

   // 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 + uniq > 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.

 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.

   Node *h = loop->_head;

   if( h->is_CountedLoop() ) {

     CountedLoopNode *cl = h->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

     }

   }

   // 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(loop->_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.

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

     Node* old = loop->_head->fast_out(j);

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

         (old->is_Loop() || 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 *nnn = old_new[loop->_head->_idx];

   _igvn.hash_delete(nnn);

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

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

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

     if( use->in(0) == nnn && 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(loop->_head);

   set_idom(loop->_head, loop->_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);

     // While we're at it, remove any SafePoints from the peeled code

     if( old->Opcode() == Op_SafePoint ) {

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

       lazy_replace(nnn,nnn->in(TypeFunc::Control));

     }

   }

   // 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();

 }

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

 // Return exact loop trip count, or 0 if not maximally unrolling

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

   CountedLoopNode *cl = _head->as_CountedLoop();

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

   Node *init_n = cl->init_trip();

   Node *limit_n = cl->limit();

   // Non-constant bounds

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

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

       // protect against stride not being a constant

       !cl->stride_is_con() ) {

     return false;

   }

   int init   = init_n->get_int();

   int limit  = limit_n->get_int();

   int span   = limit - init;

   int stride = cl->stride_con();

   if (init >= limit || stride > span) {

     // return a false (no maximally unroll) and the regular unroll/peel

     // route will make a small mess which CCP will fold away.

     return false;

   }

   uint trip_count = span/stride;   // trip_count can be greater than 2 Gig.

   assert( (int)trip_count*stride == span, "must divide evenly" );

   // 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");

   cl->set_trip_count(trip_count);

   if( trip_count <= unroll_limit && body_size <= unroll_limit ) {

     uint new_body_size = body_size * trip_count;

     if (new_body_size <= unroll_limit &&

         body_size == new_body_size / trip_count &&

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

         new_body_size < MaxNodeLimit - phase->C->unique()) {

       return true;    // maximally unroll

     }

   }

   return false;               // Do not 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(), "" );

   // protect against stride not being a constant

   if( !cl->stride_is_con() ) return false;

   // protect against over-unrolling

   if( cl->trip_count() <= 1 ) return false;

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

   // 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();

   // 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 = cl->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

         }

       }

     }

   }

   // Adjust body_size to determine if we unroll or not

   uint body_size = _body.size();

   // Key test to unroll CaffeineMark's Logic test

   int xors_in_loop = 0;

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

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

     switch( _body.at(k)->Opcode() ) {

     case Op_XorI: xors_in_loop++; break; // CaffeineMark's Logic test

     case Op_ModL: body_size += 30; break;

     case Op_DivL: body_size += 30; break;

     case Op_MulL: body_size += 10; break;

     }

   }

   // 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;

   }

   // Check for stride being a small enough constant

   if( abs(cl->stride_con()) > (1<<3) ) 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

       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 ) {

   if( get_ctrl(n) != back_ctrl ) 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 ) {

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

     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) );

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

       if( !x )

         x = n->clone();

       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 ) {

   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();

   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, 1) 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, 2) Opaque1Node(C, incr);

   Node *zer_cmp  = new (C, 3) CmpINode( zer_opaq, limit );

   Node *zer_bol  = new (C, 2) 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, 2) 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.hash_delete( main_exit );

   main_exit->set_req(0, zer_iff);

   _igvn._worklist.push(main_exit);

   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, 1) 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);

   // 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));

       _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, 1) 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, 2) Opaque1Node(C, limit);

   Node *min_cmp  = new (C, 3) CmpINode( pre_incr, min_opaq );

   Node *min_bol  = new (C, 2) 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, 2) 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, 1) 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);

   // 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));

       _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, 3) AddINode( init, stride );

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

   // use by range check elimination.

   Node *pre_opaq  = new (C, 3) 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 >

   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, 2) 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, 2) 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, 2) 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();

   // 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);

 }

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

 // Return true if n is invariant

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

   Node *n_c = _phase->get_ctrl(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, "" );

 #ifndef PRODUCT

   if( PrintOpto && VerifyLoopOptimizations ) {

     tty->print("Unrolling ");

     loop->dump_head();

   }

 #endif

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

   CountedLoopEndNode *loop_end = loop_head->loopexit();

   assert( loop_end, "" );

   // 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 *strid = loop_head->stride();

   Node *opaq = NULL;

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

     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 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( opaq->Opcode() != Op_Opaque1 )

       return;                   // Cannot find pre-loop!  Bail out!

   }

   C->set_major_progress();

   // 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, 3) SubINode( limit, init );

   register_new_node( span, ctrl );

   Node *trip = new (C, 3) DivINode( 0, span, strid );

   register_new_node( trip, ctrl );

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

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

   Node *rond = new (C, 3) AndINode( trip, mtwo );

   register_new_node( rond, ctrl );

   Node *spn2 = new (C, 3) MulINode( rond, strid );

   register_new_node( spn2, ctrl );

   Node *lim2 = new (C, 3) AddINode( spn2, init );

   register_new_node( lim2, ctrl );

   // Hammer in the new limit

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

   Node *cmp2 = new (C, 3) CmpINode( loop_head->incr(), lim2 );

   register_new_node( cmp2, ctrl2 );

   Node *bol2 = new (C, 2) 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 ) {

     // 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, lim2);

   }

   // ---------

   // 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->trip_count() > 0, "");

   // 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 ) {

     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;

 }

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

 // Constrain the main loop iterations so the condition:

 //    scale_con * I + offset  <  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 *limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit ) {

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

   Node *con = new (C, 3) SubINode( limit, offset );

   register_new_node( con, pre_ctrl );

   Node *scale = _igvn.intcon(scale_con);

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

   Node *X = new (C, 3) DivINode( 0, con, scale );

   register_new_node( X, pre_ctrl );

   // 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.

   if( stride_con*scale_con > 0 ) {

     // Compute I < (limit-offset)/scale_con

     // Adjust main-loop last iteration to be MIN/MAX(main_loop,X)

     *main_limit = (stride_con > 0)

       ? (Node*)(new (C, 3) MinINode( *main_limit, X ))

       : (Node*)(new (C, 3) MaxINode( *main_limit, X ));

     register_new_node( *main_limit, pre_ctrl );

   } else {

     // Compute (limit-offset)/scale_con + SGN(-scale_con) <= I

     // Add the negation of the main-loop constraint to the pre-loop.

     // See footnote [++] below for a derivation of the limit expression.

     Node *incr = _igvn.intcon(scale_con > 0 ? -1 : 1);

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

     Node *adj = new (C, 3) AddINode( X, incr );

     register_new_node( adj, pre_ctrl );

     *pre_limit = (scale_con > 0)

       ? (Node*)new (C, 3) MinINode( *pre_limit, adj )

       : (Node*)new (C, 3) MaxINode( *pre_limit, adj );

     register_new_node( *pre_limit, pre_ctrl );

 //   [++] Here's the algebra that justifies the pre-loop limit expression:

 //

 //   NOT( scale_con * I + offset  <  limit )

 //      ==

 //   scale_con * I + offset  >=  limit

 //      ==

 //   SGN(scale_con) * I  >=  (limit-offset)/|scale_con|

 //      ==

 //   (limit-offset)/|scale_con|   <=  I * SGN(scale_con)

 //      ==

 //   (limit-offset)/|scale_con|-1  <  I * SGN(scale_con)

 //      ==

 //   ( if (scale_con > 0) /*common case*/

 //       (limit-offset)/scale_con - 1  <  I

 //     else

 //       (limit-offset)/scale_con + 1  >  I

 //    )

 //   ( if (scale_con > 0) /*common case*/

 //       (limit-offset)/scale_con + SGN(-scale_con)  <  I

 //     else

 //       (limit-offset)/scale_con + SGN(-scale_con)  >  I

   }

 }

 //------------------------------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, 3) 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, 3) 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();

   }

 #endif

   assert( RangeCheckElimination, "" );

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

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

   // 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();

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

   // not ever trip low tests.

   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 *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;

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

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

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

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

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

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

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

     return;

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

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

   // protect against stride not being a constant

   if ( !cl->stride_is_con() ) {

     return;

   }

   int stride_con = cl->stride_con();

   Node *zero = _igvn.intcon(0);

   Node *one  = _igvn.intcon(1);

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

   set_ctrl(one,  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.

       }

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

           add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit );

           // The underflow limit: 0 <= scale*I+offset.

           // Some math yields: -scale*I-(offset+1) < 0

           Node *plus_one = new (C, 3) AddINode( offset, one );

           register_new_node( plus_one, pre_ctrl );

           Node *neg_offset = new (C, 3) SubINode( zero, plus_one );

           register_new_node( neg_offset, pre_ctrl );

           add_constraint( stride_con, -scale_con, neg_offset, zero, pre_ctrl, &pre_limit, &main_limit );

           if (!conditional_rc) {

             conditional_rc = !loop->dominates_backedge(iff);

           }

         } 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::ge:      // Convert X >= Y to -X <= -Y

           scale_con = -scale_con;

           offset = new (C, 3) SubINode( zero, offset );

           register_new_node( offset, pre_ctrl );

           limit  = new (C, 3) SubINode( zero, limit  );

           register_new_node( limit, pre_ctrl );

           // Fall into LE case

         case BoolTest::le:      // Convert X <= Y to X < Y+1

           limit = new (C, 3) AddINode( limit, one );

           register_new_node( limit, pre_ctrl );

           // Fall into LT case

         case BoolTest::lt:

           add_constraint( stride_con, scale_con, offset, limit, pre_ctrl, &pre_limit, &main_limit );

           if (!conditional_rc) {

             conditional_rc = !loop->dominates_backedge(iff);

           }

           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.hash_delete(iff);

       iff->set_req(1, kill_con);

       _igvn._worklist.push(iff);

       // 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() ) {   // Loads can now float around in the loop

           _igvn.hash_delete(cd);

           // Allow the load to float around in the loop, or before it

           // but NOT before the pre-loop.

           cd->set_req(0, ctrl);   // ctrl, not NULL

           _igvn._worklist.push(cd);

           --i;

           --imax;

         }

       }

     } // End of is IF

   }

   // Update loop limits

   if (conditional_rc) {

     pre_limit = (stride_con > 0) ? (Node*)new (C,3) MinINode(pre_limit, orig_limit)

                                  : (Node*)new (C,3) 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.

   if( 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, 3) SubINode(main_limit,init);

     register_new_node(span,ctrl);

     Node *rndup = _igvn.intcon(stride_con + ((stride_con>0)?-1:1));

     Node *add = new (C, 3) AddINode(span,rndup);

     register_new_node(add,ctrl);

     Node *div = new (C, 3) DivINode(0,add,stride);

     register_new_node(div,ctrl);

     Node *mul = new (C, 3) MulINode(div,stride);

     register_new_node(mul,ctrl);

     Node *newlim = new (C, 3) 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.hash_delete(main_cmp);

   main_cmp->set_req(2, main_limit);

   _igvn._worklist.push(main_cmp);

   // The OpaqueNode is unshared by design

   _igvn.hash_delete(opqzm);

   assert( opqzm->outcnt() == 1, "cannot hack shared node" );

   opqzm->set_req(1,main_limit);

   _igvn._worklist.push(opqzm);

 }

 //------------------------------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() > 7/*number of nodes in an empty loop*/ ) return false;

   if( !_head->is_CountedLoop() ) return false;     // Dead loop

   CountedLoopNode *cl = _head->as_CountedLoop();

   if( !cl->loopexit() ) return false; // Malformed loop

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

     return false;             // Infinite loop

 #ifndef PRODUCT

   if( PrintOpto )

     tty->print_cr("Removing empty loop");

 #endif

 #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

   // 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 *final = new (phase->C, 3) SubINode( cl->limit(), cl->stride() );

   phase->register_new_node(final,cl->in(LoopNode::EntryControl));

   phase->_igvn.hash_delete(phi);

   phase->_igvn.subsume_node(phi,final);

   phase->C->set_major_progress();

   return true;

 }

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

 //------------------------------iteration_split_impl---------------------------

 bool IdealLoopTree::iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new ) {

   // 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->loopexit() ) 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() ) {

     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;

     }

     if (should_unswitch) {

       phase->do_unswitching(this, old_new);

       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.

   if( _head->is_CountedLoop() ) phase->reorg_offsets( this );

   if( _next && !_next->iteration_split( phase, old_new ))

     return false;

   return true;

 }