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

 /*

  * Copyright 1999-2008 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

  * have any questions.

  *

  */

 #include "incls/_precompiled.incl"

 #include "incls/_loopopts.cpp.incl"

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

 //------------------------------split_thru_phi---------------------------------

 // Split Node 'n' through merge point if there is enough win.

 Node *PhaseIdealLoop::split_thru_phi( Node *n, Node *region, int policy ) {

   if (n->Opcode() == Op_ConvI2L && n->bottom_type() != TypeLong::LONG) {

     // ConvI2L may have type information on it which is unsafe to push up

     // so disable this for now

     return NULL;

   }

   int wins = 0;

   assert( !n->is_CFG(), "" );

   assert( region->is_Region(), "" );

   const Type* type = n->bottom_type();

   const TypeOopPtr *t_oop = _igvn.type(n)->isa_oopptr();

   Node *phi;

   if( t_oop != NULL && t_oop->is_known_instance_field() ) {

     int iid    = t_oop->instance_id();

     int index  = C->get_alias_index(t_oop);

     int offset = t_oop->offset();

     phi = new (C,region->req()) PhiNode(region, type, NULL, iid, index, offset);

   } else {

     phi = new (C,region->req()) PhiNode(region, type);

   }

   uint old_unique = C->unique();

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

     Node *x;

     Node* the_clone = NULL;

     if( region->in(i) == C->top() ) {

       x = C->top();             // Dead path?  Use a dead data op

     } else {

       x = n->clone();           // Else clone up the data op

       the_clone = x;            // Remember for possible deletion.

       // Alter data node to use pre-phi inputs

       if( n->in(0) == region )

         x->set_req( 0, region->in(i) );

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

         Node *in = n->in(j);

         if( in->is_Phi() && in->in(0) == region )

           x->set_req( j, in->in(i) ); // Use pre-Phi input for the clone

       }

     }

     // Check for a 'win' on some paths

     const Type *t = x->Value(&_igvn);

     bool singleton = t->singleton();

     // A TOP singleton indicates that there are no possible values incoming

     // along a particular edge. In most cases, this is OK, and the Phi will

     // be eliminated later in an Ideal call. However, we can't allow this to

     // happen if the singleton occurs on loop entry, as the elimination of

     // the PhiNode may cause the resulting node to migrate back to a previous

     // loop iteration.

     if( singleton && t == Type::TOP ) {

       // Is_Loop() == false does not confirm the absence of a loop (e.g., an

       // irreducible loop may not be indicated by an affirmative is_Loop());

       // therefore, the only top we can split thru a phi is on a backedge of

       // a loop.

       singleton &= region->is_Loop() && (i != LoopNode::EntryControl);

     }

     if( singleton ) {

       wins++;

       x = ((PhaseGVN&)_igvn).makecon(t);

     } else {

       // We now call Identity to try to simplify the cloned node.

       // Note that some Identity methods call phase->type(this).

       // Make sure that the type array is big enough for

       // our new node, even though we may throw the node away.

       // (Note: This tweaking with igvn only works because x is a new node.)

       _igvn.set_type(x, t);

       // If x is a TypeNode, capture any more-precise type permanently into Node

       // otherwise it will be not updated during igvn->transform since

       // igvn->type(x) is set to x->Value() already.

       x->raise_bottom_type(t);

       Node *y = x->Identity(&_igvn);

       if( y != x ) {

         wins++;

         x = y;

       } else {

         y = _igvn.hash_find(x);

         if( y ) {

           wins++;

           x = y;

         } else {

           // Else x is a new node we are keeping

           // We do not need register_new_node_with_optimizer

           // because set_type has already been called.

           _igvn._worklist.push(x);

         }

       }

     }

     if (x != the_clone && the_clone != NULL)

       _igvn.remove_dead_node(the_clone);

     phi->set_req( i, x );

   }

   // Too few wins?

   if( wins <= policy ) {

     _igvn.remove_dead_node(phi);

     return NULL;

   }

   // Record Phi

   register_new_node( phi, region );

   for( uint i2 = 1; i2 < phi->req(); i2++ ) {

     Node *x = phi->in(i2);

     // If we commoned up the cloned 'x' with another existing Node,

     // the existing Node picks up a new use.  We need to make the

     // existing Node occur higher up so it dominates its uses.

     Node *old_ctrl;

     IdealLoopTree *old_loop;

     // The occasional new node

     if( x->_idx >= old_unique ) {   // Found a new, unplaced node?

       old_ctrl = x->is_Con() ? C->root() : NULL;

       old_loop = NULL;              // Not in any prior loop

     } else {

       old_ctrl = x->is_Con() ? C->root() : get_ctrl(x);

       old_loop = get_loop(old_ctrl); // Get prior loop

     }

     // New late point must dominate new use

     Node *new_ctrl = dom_lca( old_ctrl, region->in(i2) );

     // Set new location

     set_ctrl(x, new_ctrl);

     IdealLoopTree *new_loop = get_loop( new_ctrl );

     // If changing loop bodies, see if we need to collect into new body

     if( old_loop != new_loop ) {

       if( old_loop && !old_loop->_child )

         old_loop->_body.yank(x);

       if( !new_loop->_child )

         new_loop->_body.push(x);  // Collect body info

     }

   }

   return phi;

 }

 //------------------------------dominated_by------------------------------------

 // Replace the dominated test with an obvious true or false.  Place it on the

 // IGVN worklist for later cleanup.  Move control-dependent data Nodes on the

 // live path up to the dominating control.

 void PhaseIdealLoop::dominated_by( Node *prevdom, Node *iff ) {

 #ifndef PRODUCT

   if( VerifyLoopOptimizations && PrintOpto ) tty->print_cr("dominating test");

 #endif

   // prevdom is the dominating projection of the dominating test.

   assert( iff->is_If(), "" );

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

   int pop = prevdom->Opcode();

   assert( pop == Op_IfFalse || pop == Op_IfTrue, "" );

   // 'con' is set to true or false to kill the dominated test.

   Node *con = _igvn.makecon(pop == Op_IfTrue ? TypeInt::ONE : TypeInt::ZERO);

   set_ctrl(con, C->root()); // Constant gets a new use

   // Hack the dominated test

   _igvn.hash_delete(iff);

   iff->set_req(1, con);

   _igvn._worklist.push(iff);

   // If I dont have a reachable TRUE and FALSE path following the IfNode then

   // I can assume this path reaches an infinite loop.  In this case it's not

   // important to optimize the data Nodes - either the whole compilation will

   // be tossed or this path (and all data Nodes) will go dead.

   if( iff->outcnt() != 2 ) return;

   // Make control-dependent data Nodes on the live path (path that will remain

   // once the dominated IF is removed) become control-dependent on the

   // dominating projection.

   Node* dp = ((IfNode*)iff)->proj_out(pop == Op_IfTrue);

   IdealLoopTree *old_loop = get_loop(dp);

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

     Node* cd = dp->fast_out(i); // Control-dependent node

     if( cd->depends_only_on_test() ) {

       assert( cd->in(0) == dp, "" );

       _igvn.hash_delete( cd );

       cd->set_req(0, prevdom);

       set_early_ctrl( cd );

       _igvn._worklist.push(cd);

       IdealLoopTree *new_loop = get_loop(get_ctrl(cd));

       if( old_loop != new_loop ) {

         if( !old_loop->_child ) old_loop->_body.yank(cd);

         if( !new_loop->_child ) new_loop->_body.push(cd);

       }

       --i;

       --imax;

     }

   }

 }

 //------------------------------has_local_phi_input----------------------------

 // Return TRUE if 'n' has Phi inputs from its local block and no other

 // block-local inputs (all non-local-phi inputs come from earlier blocks)

 Node *PhaseIdealLoop::has_local_phi_input( Node *n ) {

   Node *n_ctrl = get_ctrl(n);

   // See if some inputs come from a Phi in this block, or from before

   // this block.

   uint i;

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

     Node *phi = n->in(i);

     if( phi->is_Phi() && phi->in(0) == n_ctrl )

       break;

   }

   if( i >= n->req() )

     return NULL;                // No Phi inputs; nowhere to clone thru

   // Check for inputs created between 'n' and the Phi input.  These

   // must split as well; they have already been given the chance

   // (courtesy of a post-order visit) and since they did not we must

   // recover the 'cost' of splitting them by being very profitable

   // when splitting 'n'.  Since this is unlikely we simply give up.

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

     Node *m = n->in(i);

     if( get_ctrl(m) == n_ctrl && !m->is_Phi() ) {

       // We allow the special case of AddP's with no local inputs.

       // This allows us to split-up address expressions.

       if (m->is_AddP() &&

           get_ctrl(m->in(2)) != n_ctrl &&

           get_ctrl(m->in(3)) != n_ctrl) {

         // Move the AddP up to dominating point

         set_ctrl_and_loop(m, find_non_split_ctrl(idom(n_ctrl)));

         continue;

       }

       return NULL;

     }

   }

   return n_ctrl;

 }

 //------------------------------remix_address_expressions----------------------

 // Rework addressing expressions to get the most loop-invariant stuff

 // moved out.  We'd like to do all associative operators, but it's especially

 // important (common) to do address expressions.

 Node *PhaseIdealLoop::remix_address_expressions( Node *n ) {

   if (!has_ctrl(n))  return NULL;

   Node *n_ctrl = get_ctrl(n);

   IdealLoopTree *n_loop = get_loop(n_ctrl);

   // See if 'n' mixes loop-varying and loop-invariant inputs and

   // itself is loop-varying.

   // Only interested in binary ops (and AddP)

   if( n->req() < 3 || n->req() > 4 ) return NULL;

   Node *n1_ctrl = get_ctrl(n->in(                    1));

   Node *n2_ctrl = get_ctrl(n->in(                    2));

   Node *n3_ctrl = get_ctrl(n->in(n->req() == 3 ? 2 : 3));

   IdealLoopTree *n1_loop = get_loop( n1_ctrl );

   IdealLoopTree *n2_loop = get_loop( n2_ctrl );

   IdealLoopTree *n3_loop = get_loop( n3_ctrl );

   // Does one of my inputs spin in a tighter loop than self?

   if( (n_loop->is_member( n1_loop ) && n_loop != n1_loop) ||

       (n_loop->is_member( n2_loop ) && n_loop != n2_loop) ||

       (n_loop->is_member( n3_loop ) && n_loop != n3_loop) )

     return NULL;                // Leave well enough alone

   // Is at least one of my inputs loop-invariant?

   if( n1_loop == n_loop &&

       n2_loop == n_loop &&

       n3_loop == n_loop )

     return NULL;                // No loop-invariant inputs

   int n_op = n->Opcode();

   // Replace expressions like ((V+I) << 2) with (V<<2 + I<<2).

   if( n_op == Op_LShiftI ) {

     // Scale is loop invariant

     Node *scale = n->in(2);

     Node *scale_ctrl = get_ctrl(scale);

     IdealLoopTree *scale_loop = get_loop(scale_ctrl );

     if( n_loop == scale_loop || !scale_loop->is_member( n_loop ) )

       return NULL;

     const TypeInt *scale_t = scale->bottom_type()->isa_int();

     if( scale_t && scale_t->is_con() && scale_t->get_con() >= 16 )

       return NULL;              // Dont bother with byte/short masking

     // Add must vary with loop (else shift would be loop-invariant)

     Node *add = n->in(1);

     Node *add_ctrl = get_ctrl(add);

     IdealLoopTree *add_loop = get_loop(add_ctrl);

     //assert( n_loop == add_loop, "" );

     if( n_loop != add_loop ) return NULL;  // happens w/ evil ZKM loops

     // Convert I-V into I+ (0-V); same for V-I

     if( add->Opcode() == Op_SubI &&

         _igvn.type( add->in(1) ) != TypeInt::ZERO ) {

       Node *zero = _igvn.intcon(0);

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

       Node *neg = new (C, 3) SubINode( _igvn.intcon(0), add->in(2) );

       register_new_node( neg, get_ctrl(add->in(2) ) );

       add = new (C, 3) AddINode( add->in(1), neg );

       register_new_node( add, add_ctrl );

     }

     if( add->Opcode() != Op_AddI ) return NULL;

     // See if one add input is loop invariant

     Node *add_var = add->in(1);

     Node *add_var_ctrl = get_ctrl(add_var);

     IdealLoopTree *add_var_loop = get_loop(add_var_ctrl );

     Node *add_invar = add->in(2);

     Node *add_invar_ctrl = get_ctrl(add_invar);

     IdealLoopTree *add_invar_loop = get_loop(add_invar_ctrl );

     if( add_var_loop == n_loop ) {

     } else if( add_invar_loop == n_loop ) {

       // Swap to find the invariant part

       add_invar = add_var;

       add_invar_ctrl = add_var_ctrl;

       add_invar_loop = add_var_loop;

       add_var = add->in(2);

       Node *add_var_ctrl = get_ctrl(add_var);

       IdealLoopTree *add_var_loop = get_loop(add_var_ctrl );

     } else                      // Else neither input is loop invariant

       return NULL;

     if( n_loop == add_invar_loop || !add_invar_loop->is_member( n_loop ) )

       return NULL;              // No invariant part of the add?

     // Yes!  Reshape address expression!

     Node *inv_scale = new (C, 3) LShiftINode( add_invar, scale );

     register_new_node( inv_scale, add_invar_ctrl );

     Node *var_scale = new (C, 3) LShiftINode( add_var, scale );

     register_new_node( var_scale, n_ctrl );

     Node *var_add = new (C, 3) AddINode( var_scale, inv_scale );

     register_new_node( var_add, n_ctrl );

     _igvn.hash_delete( n );

     _igvn.subsume_node( n, var_add );

     return var_add;

   }

   // Replace (I+V) with (V+I)

   if( n_op == Op_AddI ||

       n_op == Op_AddL ||

       n_op == Op_AddF ||

       n_op == Op_AddD ||

       n_op == Op_MulI ||

       n_op == Op_MulL ||

       n_op == Op_MulF ||

       n_op == Op_MulD ) {

     if( n2_loop == n_loop ) {

       assert( n1_loop != n_loop, "" );

       n->swap_edges(1, 2);

     }

   }

   // Replace ((I1 +p V) +p I2) with ((I1 +p I2) +p V),

   // but not if I2 is a constant.

   if( n_op == Op_AddP ) {

     if( n2_loop == n_loop && n3_loop != n_loop ) {

       if( n->in(2)->Opcode() == Op_AddP && !n->in(3)->is_Con() ) {

         Node *n22_ctrl = get_ctrl(n->in(2)->in(2));

         Node *n23_ctrl = get_ctrl(n->in(2)->in(3));

         IdealLoopTree *n22loop = get_loop( n22_ctrl );

         IdealLoopTree *n23_loop = get_loop( n23_ctrl );

         if( n22loop != n_loop && n22loop->is_member(n_loop) &&

             n23_loop == n_loop ) {

           Node *add1 = new (C, 4) AddPNode( n->in(1), n->in(2)->in(2), n->in(3) );

           // Stuff new AddP in the loop preheader

           register_new_node( add1, n_loop->_head->in(LoopNode::EntryControl) );

           Node *add2 = new (C, 4) AddPNode( n->in(1), add1, n->in(2)->in(3) );

           register_new_node( add2, n_ctrl );

           _igvn.hash_delete( n );

           _igvn.subsume_node( n, add2 );

           return add2;

         }

       }

     }

     // Replace (I1 +p (I2 + V)) with ((I1 +p I2) +p V)

     if( n2_loop != n_loop && n3_loop == n_loop ) {

       if( n->in(3)->Opcode() == Op_AddI ) {

         Node *V = n->in(3)->in(1);

         Node *I = n->in(3)->in(2);

         if( is_member(n_loop,get_ctrl(V)) ) {

         } else {

           Node *tmp = V; V = I; I = tmp;

         }

         if( !is_member(n_loop,get_ctrl(I)) ) {

           Node *add1 = new (C, 4) AddPNode( n->in(1), n->in(2), I );

           // Stuff new AddP in the loop preheader

           register_new_node( add1, n_loop->_head->in(LoopNode::EntryControl) );

           Node *add2 = new (C, 4) AddPNode( n->in(1), add1, V );

           register_new_node( add2, n_ctrl );

           _igvn.hash_delete( n );

           _igvn.subsume_node( n, add2 );

           return add2;

         }

       }

     }

   }

   return NULL;

 }

 //------------------------------conditional_move-------------------------------

 // Attempt to replace a Phi with a conditional move.  We have some pretty

 // strict profitability requirements.  All Phis at the merge point must

 // be converted, so we can remove the control flow.  We need to limit the

 // number of c-moves to a small handful.  All code that was in the side-arms

 // of the CFG diamond is now speculatively executed.  This code has to be

 // "cheap enough".  We are pretty much limited to CFG diamonds that merge

 // 1 or 2 items with a total of 1 or 2 ops executed speculatively.

 Node *PhaseIdealLoop::conditional_move( Node *region ) {

   assert( region->is_Region(), "sanity check" );

   if( region->req() != 3 ) return NULL;

   // Check for CFG diamond

   Node *lp = region->in(1);

   Node *rp = region->in(2);

   if( !lp || !rp ) return NULL;

   Node *lp_c = lp->in(0);

   if( lp_c == NULL || lp_c != rp->in(0) || !lp_c->is_If() ) return NULL;

   IfNode *iff = lp_c->as_If();

   // Check for highly predictable branch.  No point in CMOV'ing if

   // we are going to predict accurately all the time.

   // %%% This hides patterns produced by utility methods like Math.min.

   if( iff->_prob < PROB_UNLIKELY_MAG(3) ||

       iff->_prob > PROB_LIKELY_MAG(3) )

     return NULL;

   // Check for ops pinned in an arm of the diamond.

   // Can't remove the control flow in this case

   if( lp->outcnt() > 1 ) return NULL;

   if( rp->outcnt() > 1 ) return NULL;

   // Check profitability

   int cost = 0;

   int phis = 0;

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

     Node *out = region->fast_out(i);

     if( !out->is_Phi() ) continue; // Ignore other control edges, etc

     phis++;

     PhiNode* phi = out->as_Phi();

     switch (phi->type()->basic_type()) {

     case T_LONG:

       cost++;                   // Probably encodes as 2 CMOV's

     case T_INT:                 // These all CMOV fine

     case T_FLOAT:

     case T_DOUBLE:

     case T_ADDRESS:             // (RawPtr)

       cost++;

       break;

     case T_NARROWOOP: // Fall through

     case T_OBJECT: {            // Base oops are OK, but not derived oops

       const TypeOopPtr *tp = phi->type()->make_ptr()->isa_oopptr();

       // Derived pointers are Bad (tm): what's the Base (for GC purposes) of a

       // CMOVE'd derived pointer?  It's a CMOVE'd derived base.  Thus

       // CMOVE'ing a derived pointer requires we also CMOVE the base.  If we

       // have a Phi for the base here that we convert to a CMOVE all is well

       // and good.  But if the base is dead, we'll not make a CMOVE.  Later

       // the allocator will have to produce a base by creating a CMOVE of the

       // relevant bases.  This puts the allocator in the business of

       // manufacturing expensive instructions, generally a bad plan.

       // Just Say No to Conditionally-Moved Derived Pointers.

       if( tp && tp->offset() != 0 )

         return NULL;

       cost++;

       break;

     }

     default:

       return NULL;              // In particular, can't do memory or I/O

     }

     // Add in cost any speculative ops

     for( uint j = 1; j < region->req(); j++ ) {

       Node *proj = region->in(j);

       Node *inp = phi->in(j);

       if (get_ctrl(inp) == proj) { // Found local op

         cost++;

         // Check for a chain of dependent ops; these will all become

         // speculative in a CMOV.

         for( uint k = 1; k < inp->req(); k++ )

           if (get_ctrl(inp->in(k)) == proj)

             return NULL;        // Too much speculative goo

       }

     }

     // See if the Phi is used by a Cmp or Narrow oop Decode/Encode.

     // This will likely Split-If, a higher-payoff operation.

     for (DUIterator_Fast kmax, k = phi->fast_outs(kmax); k < kmax; k++) {

       Node* use = phi->fast_out(k);

       if( use->is_Cmp() || use->is_DecodeN() || use->is_EncodeP() )

         return NULL;

     }

   }

   if( cost >= ConditionalMoveLimit ) return NULL; // Too much goo

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

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

   int cmp_op = bol->in(1)->Opcode();

   // It is expensive to generate flags from a float compare.

   // Avoid duplicated float compare.

   if( phis > 1 && (cmp_op == Op_CmpF || cmp_op == Op_CmpD)) return NULL;

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

   // Now replace all Phis with CMOV's

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

   uint flip = (lp->Opcode() == Op_IfTrue);

   while( 1 ) {

     PhiNode* phi = NULL;

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

       Node *out = region->fast_out(i);

       if (out->is_Phi()) {

         phi = out->as_Phi();

         break;

       }

     }

     if (phi == NULL)  break;

 #ifndef PRODUCT

     if( PrintOpto && VerifyLoopOptimizations ) tty->print_cr("CMOV");

 #endif

     // Move speculative ops

     for( uint j = 1; j < region->req(); j++ ) {

       Node *proj = region->in(j);

       Node *inp = phi->in(j);

       if (get_ctrl(inp) == proj) { // Found local op

 #ifndef PRODUCT

         if( PrintOpto && VerifyLoopOptimizations ) {

           tty->print("  speculate: ");

           inp->dump();

         }

 #endif

         set_ctrl(inp, cmov_ctrl);

       }

     }

     Node *cmov = CMoveNode::make( C, cmov_ctrl, iff->in(1), phi->in(1+flip), phi->in(2-flip), _igvn.type(phi) );

     register_new_node( cmov, cmov_ctrl );

     _igvn.hash_delete(phi);

     _igvn.subsume_node( phi, cmov );

 #ifndef PRODUCT

     if( VerifyLoopOptimizations ) verify();

 #endif

   }

   // The useless CFG diamond will fold up later; see the optimization in

   // RegionNode::Ideal.

   _igvn._worklist.push(region);

   return iff->in(1);

 }

 //------------------------------split_if_with_blocks_pre-----------------------

 // Do the real work in a non-recursive function.  Data nodes want to be

 // cloned in the pre-order so they can feed each other nicely.

 Node *PhaseIdealLoop::split_if_with_blocks_pre( Node *n ) {

   // Cloning these guys is unlikely to win

   int n_op = n->Opcode();

   if( n_op == Op_MergeMem ) return n;

   if( n->is_Proj() ) return n;

   // Do not clone-up CmpFXXX variations, as these are always

   // followed by a CmpI

   if( n->is_Cmp() ) return n;

   // Attempt to use a conditional move instead of a phi/branch

   if( ConditionalMoveLimit > 0 && n_op == Op_Region ) {

     Node *cmov = conditional_move( n );

     if( cmov ) return cmov;

   }

   if( n->is_CFG() || n->is_LoadStore() )

     return n;

   if( n_op == Op_Opaque1 ||     // Opaque nodes cannot be mod'd

       n_op == Op_Opaque2 ) {

     if( !C->major_progress() )   // If chance of no more loop opts...

       _igvn._worklist.push(n);  // maybe we'll remove them

     return n;

   }

   if( n->is_Con() ) return n;   // No cloning for Con nodes

   Node *n_ctrl = get_ctrl(n);

   if( !n_ctrl ) return n;       // Dead node

   // Attempt to remix address expressions for loop invariants

   Node *m = remix_address_expressions( n );

   if( m ) return m;

   // Determine if the Node has inputs from some local Phi.

   // Returns the block to clone thru.

   Node *n_blk = has_local_phi_input( n );

   if( !n_blk ) return n;

   // Do not clone the trip counter through on a CountedLoop

   // (messes up the canonical shape).

   if( n_blk->is_CountedLoop() && n->Opcode() == Op_AddI ) return n;

   // Check for having no control input; not pinned.  Allow

   // dominating control.

   if( n->in(0) ) {

     Node *dom = idom(n_blk);

     if( dom_lca( n->in(0), dom ) != n->in(0) )

       return n;

   }

   // Policy: when is it profitable.  You must get more wins than

   // policy before it is considered profitable.  Policy is usually 0,

   // so 1 win is considered profitable.  Big merges will require big

   // cloning, so get a larger policy.

   int policy = n_blk->req() >> 2;

   // If the loop is a candidate for range check elimination,

   // delay splitting through it's phi until a later loop optimization

   if (n_blk->is_CountedLoop()) {

     IdealLoopTree *lp = get_loop(n_blk);

     if (lp && lp->_rce_candidate) {

       return n;

     }

   }

   // Use same limit as split_if_with_blocks_post

   if( C->unique() > 35000 ) return n; // Method too big

   // Split 'n' through the merge point if it is profitable

   Node *phi = split_thru_phi( n, n_blk, policy );

   if( !phi ) return n;

   // Found a Phi to split thru!

   // Replace 'n' with the new phi

   _igvn.hash_delete(n);

   _igvn.subsume_node( n, phi );

   // Moved a load around the loop, 'en-registering' something.

   if( n_blk->Opcode() == Op_Loop && n->is_Load() &&

       !phi->in(LoopNode::LoopBackControl)->is_Load() )

     C->set_major_progress();

   return phi;

 }

 static bool merge_point_too_heavy(Compile* C, Node* region) {

   // Bail out if the region and its phis have too many users.

   int weight = 0;

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

     weight += region->fast_out(i)->outcnt();

   }

   int nodes_left = MaxNodeLimit - C->unique();

   if (weight * 8 > nodes_left) {

 #ifndef PRODUCT

     if (PrintOpto)

       tty->print_cr("*** Split-if bails out:  %d nodes, region weight %d", C->unique(), weight);

 #endif

     return true;

   } else {

     return false;

   }

 }

 #ifdef _LP64

 static bool merge_point_safe(Node* region) {

   // 4799512: Stop split_if_with_blocks from splitting a block with a ConvI2LNode

   // having a PhiNode input. This sidesteps the dangerous case where the split

   // ConvI2LNode may become TOP if the input Value() does not

   // overlap the ConvI2L range, leaving a node which may not dominate its

   // uses.

   // A better fix for this problem can be found in the BugTraq entry, but

   // expediency for Mantis demands this hack.

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

     Node* n = region->fast_out(i);

     if (n->is_Phi()) {

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

         Node* m = n->fast_out(j);

         if (m->Opcode() == Op_ConvI2L) {

           return false;

         }

       }

     }

   }

   return true;

 }

 #endif

 //------------------------------place_near_use---------------------------------

 // Place some computation next to use but not inside inner loops.

 // For inner loop uses move it to the preheader area.

 Node *PhaseIdealLoop::place_near_use( Node *useblock ) const {

   IdealLoopTree *u_loop = get_loop( useblock );

   return (u_loop->_irreducible || u_loop->_child)

     ? useblock

     : u_loop->_head->in(LoopNode::EntryControl);

 }

 //------------------------------split_if_with_blocks_post----------------------

 // Do the real work in a non-recursive function.  CFG hackery wants to be

 // in the post-order, so it can dirty the I-DOM info and not use the dirtied

 // info.

 void PhaseIdealLoop::split_if_with_blocks_post( Node *n ) {

   // Cloning Cmp through Phi's involves the split-if transform.

   // FastLock is not used by an If

   if( n->is_Cmp() && !n->is_FastLock() ) {

     if( C->unique() > 35000 ) return; // Method too big

     // Do not do 'split-if' if irreducible loops are present.

     if( _has_irreducible_loops )

       return;

     Node *n_ctrl = get_ctrl(n);

     // Determine if the Node has inputs from some local Phi.

     // Returns the block to clone thru.

     Node *n_blk = has_local_phi_input( n );

     if( n_blk != n_ctrl ) return;

     if( merge_point_too_heavy(C, n_ctrl) )

       return;

     if( n->outcnt() != 1 ) return; // Multiple bool's from 1 compare?

     Node *bol = n->unique_out();

     assert( bol->is_Bool(), "expect a bool here" );

     if( bol->outcnt() != 1 ) return;// Multiple branches from 1 compare?

     Node *iff = bol->unique_out();

     // Check some safety conditions

     if( iff->is_If() ) {        // Classic split-if?

       if( iff->in(0) != n_ctrl ) return; // Compare must be in same blk as if

     } else if (iff->is_CMove()) { // Trying to split-up a CMOVE

       if( get_ctrl(iff->in(2)) == n_ctrl ||

           get_ctrl(iff->in(3)) == n_ctrl )

         return;                 // Inputs not yet split-up

       if ( get_loop(n_ctrl) != get_loop(get_ctrl(iff)) ) {

         return;                 // Loop-invar test gates loop-varying CMOVE

       }

     } else {

       return;  // some other kind of node, such as an Allocate

     }

     // Do not do 'split-if' if some paths are dead.  First do dead code

     // elimination and then see if its still profitable.

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

       if( n_ctrl->in(i) == C->top() )

         return;

     // When is split-if profitable?  Every 'win' on means some control flow

     // goes dead, so it's almost always a win.

     int policy = 0;

     // If trying to do a 'Split-If' at the loop head, it is only

     // profitable if the cmp folds up on BOTH paths.  Otherwise we

     // risk peeling a loop forever.

     // CNC - Disabled for now.  Requires careful handling of loop

     // body selection for the cloned code.  Also, make sure we check

     // for any input path not being in the same loop as n_ctrl.  For

     // irreducible loops we cannot check for 'n_ctrl->is_Loop()'

     // because the alternative loop entry points won't be converted

     // into LoopNodes.

     IdealLoopTree *n_loop = get_loop(n_ctrl);

     for( uint j = 1; j < n_ctrl->req(); j++ )

       if( get_loop(n_ctrl->in(j)) != n_loop )

         return;

 #ifdef _LP64

     // Check for safety of the merge point.

     if( !merge_point_safe(n_ctrl) ) {

       return;

     }

 #endif

     // Split compare 'n' through the merge point if it is profitable

     Node *phi = split_thru_phi( n, n_ctrl, policy );

     if( !phi ) return;

     // Found a Phi to split thru!

     // Replace 'n' with the new phi

     _igvn.hash_delete(n);

     _igvn.subsume_node( n, phi );

     // Now split the bool up thru the phi

     Node *bolphi = split_thru_phi( bol, n_ctrl, -1 );

     _igvn.hash_delete(bol);

     _igvn.subsume_node( bol, bolphi );

     assert( iff->in(1) == bolphi, "" );

     if( bolphi->Value(&_igvn)->singleton() )

       return;

     // Conditional-move?  Must split up now

     if( !iff->is_If() ) {

       Node *cmovphi = split_thru_phi( iff, n_ctrl, -1 );

       _igvn.hash_delete(iff);

       _igvn.subsume_node( iff, cmovphi );

       return;

     }

     // Now split the IF

     do_split_if( iff );

     return;

   }

   // Check for an IF ready to split; one that has its

   // condition codes input coming from a Phi at the block start.

   int n_op = n->Opcode();

   // Check for an IF being dominated by another IF same test

   if( n_op == Op_If ) {

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

     uint max = bol->outcnt();

     // Check for same test used more than once?

     if( n_op == Op_If && max > 1 && bol->is_Bool() ) {

       // Search up IDOMs to see if this IF is dominated.

       Node *cutoff = get_ctrl(bol);

       // Now search up IDOMs till cutoff, looking for a dominating test

       Node *prevdom = n;

       Node *dom = idom(prevdom);

       while( dom != cutoff ) {

         if( dom->req() > 1 && dom->in(1) == bol && prevdom->in(0) == dom ) {

           // Replace the dominated test with an obvious true or false.

           // Place it on the IGVN worklist for later cleanup.

           C->set_major_progress();

           dominated_by( prevdom, n );

 #ifndef PRODUCT

           if( VerifyLoopOptimizations ) verify();

 #endif

           return;

         }

         prevdom = dom;

         dom = idom(prevdom);

       }

     }

   }

   // See if a shared loop-varying computation has no loop-varying uses.

   // Happens if something is only used for JVM state in uncommon trap exits,

   // like various versions of induction variable+offset.  Clone the

   // computation per usage to allow it to sink out of the loop.

   if (has_ctrl(n) && !n->in(0)) {// n not dead and has no control edge (can float about)

     Node *n_ctrl = get_ctrl(n);

     IdealLoopTree *n_loop = get_loop(n_ctrl);

     if( n_loop != _ltree_root ) {

       DUIterator_Fast imax, i = n->fast_outs(imax);

       for (; i < imax; i++) {

         Node* u = n->fast_out(i);

         if( !has_ctrl(u) )     break; // Found control user

         IdealLoopTree *u_loop = get_loop(get_ctrl(u));

         if( u_loop == n_loop ) break; // Found loop-varying use

         if( n_loop->is_member( u_loop ) ) break; // Found use in inner loop

         if( u->Opcode() == Op_Opaque1 ) break; // Found loop limit, bugfix for 4677003

       }

       bool did_break = (i < imax);  // Did we break out of the previous loop?

       if (!did_break && n->outcnt() > 1) { // All uses in outer loops!

         Node *late_load_ctrl;

         if (n->is_Load()) {

           // If n is a load, get and save the result from get_late_ctrl(),

           // to be later used in calculating the control for n's clones.

           clear_dom_lca_tags();

           late_load_ctrl = get_late_ctrl(n, n_ctrl);

         }

         // If n is a load, and the late control is the same as the current

         // control, then the cloning of n is a pointless exercise, because

         // GVN will ensure that we end up where we started.

         if (!n->is_Load() || late_load_ctrl != n_ctrl) {

           for (DUIterator_Last jmin, j = n->last_outs(jmin); j >= jmin; ) {

             Node *u = n->last_out(j); // Clone private computation per use

             _igvn.hash_delete(u);

             _igvn._worklist.push(u);

             Node *x = n->clone(); // Clone computation

             Node *x_ctrl = NULL;

             if( u->is_Phi() ) {

               // Replace all uses of normal nodes.  Replace Phi uses

               // individually, so the separate Nodes can sink down

               // different paths.

               uint k = 1;

               while( u->in(k) != n ) k++;

               u->set_req( k, x );

               // x goes next to Phi input path

               x_ctrl = u->in(0)->in(k);

               --j;

             } else {              // Normal use

               // Replace all uses

               for( uint k = 0; k < u->req(); k++ ) {

                 if( u->in(k) == n ) {

                   u->set_req( k, x );

                   --j;

                 }

               }

               x_ctrl = get_ctrl(u);

             }

             // Find control for 'x' next to use but not inside inner loops.

             // For inner loop uses get the preheader area.

             x_ctrl = place_near_use(x_ctrl);

             if (n->is_Load()) {

               // For loads, add a control edge to a CFG node outside of the loop

               // to force them to not combine and return back inside the loop

               // during GVN optimization (4641526).

               //

               // Because we are setting the actual control input, factor in

               // the result from get_late_ctrl() so we respect any

               // anti-dependences. (6233005).

               x_ctrl = dom_lca(late_load_ctrl, x_ctrl);

               // Don't allow the control input to be a CFG splitting node.

               // Such nodes should only have ProjNodes as outs, e.g. IfNode

               // should only have IfTrueNode and IfFalseNode (4985384).

               x_ctrl = find_non_split_ctrl(x_ctrl);

               assert(dom_depth(n_ctrl) <= dom_depth(x_ctrl), "n is later than its clone");

               x->set_req(0, x_ctrl);

             }

             register_new_node(x, x_ctrl);

             // Some institutional knowledge is needed here: 'x' is

             // yanked because if the optimizer runs GVN on it all the

             // cloned x's will common up and undo this optimization and

             // be forced back in the loop.  This is annoying because it

             // makes +VerifyOpto report false-positives on progress.  I

             // tried setting control edges on the x's to force them to

             // not combine, but the matching gets worried when it tries

             // to fold a StoreP and an AddP together (as part of an

             // address expression) and the AddP and StoreP have

             // different controls.

             if( !x->is_Load() && !x->is_DecodeN() ) _igvn._worklist.yank(x);

           }

           _igvn.remove_dead_node(n);

         }

       }

     }

   }

   // Check for Opaque2's who's loop has disappeared - who's input is in the

   // same loop nest as their output.  Remove 'em, they are no longer useful.

   if( n_op == Op_Opaque2 &&

       n->in(1) != NULL &&

       get_loop(get_ctrl(n)) == get_loop(get_ctrl(n->in(1))) ) {

     _igvn.add_users_to_worklist(n);

     _igvn.hash_delete(n);

     _igvn.subsume_node( n, n->in(1) );

   }

 }

 //------------------------------split_if_with_blocks---------------------------

 // Check for aggressive application of 'split-if' optimization,

 // using basic block level info.

 void PhaseIdealLoop::split_if_with_blocks( VectorSet &visited, Node_Stack &nstack ) {

   Node *n = C->root();

   visited.set(n->_idx); // first, mark node as visited

   // Do pre-visit work for root

   n = split_if_with_blocks_pre( n );

   uint cnt = n->outcnt();

   uint i   = 0;

   while (true) {

     // Visit all children

     if (i < cnt) {

       Node* use = n->raw_out(i);

       ++i;

       if (use->outcnt() != 0 && !visited.test_set(use->_idx)) {

         // Now do pre-visit work for this use

         use = split_if_with_blocks_pre( use );

         nstack.push(n, i); // Save parent and next use's index.

         n   = use;         // Process all children of current use.

         cnt = use->outcnt();

         i   = 0;

       }

     }

     else {

       // All of n's children have been processed, complete post-processing.

       if (cnt != 0 && !n->is_Con()) {

         assert(has_node(n), "no dead nodes");

         split_if_with_blocks_post( n );

       }

       if (nstack.is_empty()) {

         // Finished all nodes on stack.

         break;

       }

       // Get saved parent node and next use's index. Visit the rest of uses.

       n   = nstack.node();

       cnt = n->outcnt();

       i   = nstack.index();

       nstack.pop();

     }

   }

 }

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

 //

 //                   C L O N E   A   L O O P   B O D Y

 //

 //------------------------------clone_iff--------------------------------------

 // Passed in a Phi merging (recursively) some nearly equivalent Bool/Cmps.

 // "Nearly" because all Nodes have been cloned from the original in the loop,

 // but the fall-in edges to the Cmp are different.  Clone bool/Cmp pairs

 // through the Phi recursively, and return a Bool.

 BoolNode *PhaseIdealLoop::clone_iff( PhiNode *phi, IdealLoopTree *loop ) {

   // Convert this Phi into a Phi merging Bools

   uint i;

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

     Node *b = phi->in(i);

     if( b->is_Phi() ) {

       _igvn.hash_delete(phi);

       _igvn._worklist.push(phi);

       phi->set_req(i, clone_iff( b->as_Phi(), loop ));

     } else {

       assert( b->is_Bool(), "" );

     }

   }

   Node *sample_bool = phi->in(1);

   Node *sample_cmp  = sample_bool->in(1);

   // Make Phis to merge the Cmp's inputs.

   int size = phi->in(0)->req();

   PhiNode *phi1 = new (C, size) PhiNode( phi->in(0), Type::TOP );

   PhiNode *phi2 = new (C, size) PhiNode( phi->in(0), Type::TOP );

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

     Node *n1 = phi->in(i)->in(1)->in(1);

     Node *n2 = phi->in(i)->in(1)->in(2);

     phi1->set_req( i, n1 );

     phi2->set_req( i, n2 );

     phi1->set_type( phi1->type()->meet(n1->bottom_type()) );

     phi2->set_type( phi2->type()->meet(n2->bottom_type()) );

   }

   // See if these Phis have been made before.

   // Register with optimizer

   Node *hit1 = _igvn.hash_find_insert(phi1);

   if( hit1 ) {                  // Hit, toss just made Phi

     _igvn.remove_dead_node(phi1); // Remove new phi

     assert( hit1->is_Phi(), "" );

     phi1 = (PhiNode*)hit1;      // Use existing phi

   } else {                      // Miss

     _igvn.register_new_node_with_optimizer(phi1);

   }

   Node *hit2 = _igvn.hash_find_insert(phi2);

   if( hit2 ) {                  // Hit, toss just made Phi

     _igvn.remove_dead_node(phi2); // Remove new phi

     assert( hit2->is_Phi(), "" );

     phi2 = (PhiNode*)hit2;      // Use existing phi

   } else {                      // Miss

     _igvn.register_new_node_with_optimizer(phi2);

   }

   // Register Phis with loop/block info

   set_ctrl(phi1, phi->in(0));

   set_ctrl(phi2, phi->in(0));

   // Make a new Cmp

   Node *cmp = sample_cmp->clone();

   cmp->set_req( 1, phi1 );

   cmp->set_req( 2, phi2 );

   _igvn.register_new_node_with_optimizer(cmp);

   set_ctrl(cmp, phi->in(0));

   // Make a new Bool

   Node *b = sample_bool->clone();

   b->set_req(1,cmp);

   _igvn.register_new_node_with_optimizer(b);

   set_ctrl(b, phi->in(0));

   assert( b->is_Bool(), "" );

   return (BoolNode*)b;

 }

 //------------------------------clone_bool-------------------------------------

 // Passed in a Phi merging (recursively) some nearly equivalent Bool/Cmps.

 // "Nearly" because all Nodes have been cloned from the original in the loop,

 // but the fall-in edges to the Cmp are different.  Clone bool/Cmp pairs

 // through the Phi recursively, and return a Bool.

 CmpNode *PhaseIdealLoop::clone_bool( PhiNode *phi, IdealLoopTree *loop ) {

   uint i;

   // Convert this Phi into a Phi merging Bools

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

     Node *b = phi->in(i);

     if( b->is_Phi() ) {

       _igvn.hash_delete(phi);

       _igvn._worklist.push(phi);

       phi->set_req(i, clone_bool( b->as_Phi(), loop ));

     } else {

       assert( b->is_Cmp() || b->is_top(), "inputs are all Cmp or TOP" );

     }

   }

   Node *sample_cmp = phi->in(1);

   // Make Phis to merge the Cmp's inputs.

   int size = phi->in(0)->req();

   PhiNode *phi1 = new (C, size) PhiNode( phi->in(0), Type::TOP );

   PhiNode *phi2 = new (C, size) PhiNode( phi->in(0), Type::TOP );

   for( uint j = 1; j < phi->req(); j++ ) {

     Node *cmp_top = phi->in(j); // Inputs are all Cmp or TOP

     Node *n1, *n2;

     if( cmp_top->is_Cmp() ) {

       n1 = cmp_top->in(1);

       n2 = cmp_top->in(2);

     } else {

       n1 = n2 = cmp_top;

     }

     phi1->set_req( j, n1 );

     phi2->set_req( j, n2 );

     phi1->set_type( phi1->type()->meet(n1->bottom_type()) );

     phi2->set_type( phi2->type()->meet(n2->bottom_type()) );

   }

   // See if these Phis have been made before.

   // Register with optimizer

   Node *hit1 = _igvn.hash_find_insert(phi1);

   if( hit1 ) {                  // Hit, toss just made Phi

     _igvn.remove_dead_node(phi1); // Remove new phi

     assert( hit1->is_Phi(), "" );

     phi1 = (PhiNode*)hit1;      // Use existing phi

   } else {                      // Miss

     _igvn.register_new_node_with_optimizer(phi1);

   }

   Node *hit2 = _igvn.hash_find_insert(phi2);

   if( hit2 ) {                  // Hit, toss just made Phi

     _igvn.remove_dead_node(phi2); // Remove new phi

     assert( hit2->is_Phi(), "" );

     phi2 = (PhiNode*)hit2;      // Use existing phi

   } else {                      // Miss

     _igvn.register_new_node_with_optimizer(phi2);

   }

   // Register Phis with loop/block info

   set_ctrl(phi1, phi->in(0));

   set_ctrl(phi2, phi->in(0));

   // Make a new Cmp

   Node *cmp = sample_cmp->clone();

   cmp->set_req( 1, phi1 );

   cmp->set_req( 2, phi2 );

   _igvn.register_new_node_with_optimizer(cmp);

   set_ctrl(cmp, phi->in(0));

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

   return (CmpNode*)cmp;

 }

 //------------------------------sink_use---------------------------------------

 // If 'use' was in the loop-exit block, it now needs to be sunk

 // below the post-loop merge point.

 void PhaseIdealLoop::sink_use( Node *use, Node *post_loop ) {

   if (!use->is_CFG() && get_ctrl(use) == post_loop->in(2)) {

     set_ctrl(use, post_loop);

     for (DUIterator j = use->outs(); use->has_out(j); j++)

       sink_use(use->out(j), post_loop);

   }

 }

 //------------------------------clone_loop-------------------------------------

 //

 //                   C L O N E   A   L O O P   B O D Y

 //

 // This is the basic building block of the loop optimizations.  It clones an

 // entire loop body.  It makes an old_new loop body mapping; with this mapping

 // you can find the new-loop equivalent to an old-loop node.  All new-loop

 // nodes are exactly equal to their old-loop counterparts, all edges are the

 // same.  All exits from the old-loop now have a RegionNode that merges the

 // equivalent new-loop path.  This is true even for the normal "loop-exit"

 // condition.  All uses of loop-invariant old-loop values now come from (one

 // or more) Phis that merge their new-loop equivalents.

 //

 // This operation leaves the graph in an illegal state: there are two valid

 // control edges coming from the loop pre-header to both loop bodies.  I'll

 // definitely have to hack the graph after running this transform.

 //

 // From this building block I will further edit edges to perform loop peeling

 // or loop unrolling or iteration splitting (Range-Check-Elimination), etc.

 //

 // Parameter side_by_size_idom:

 //   When side_by_size_idom is NULL, the dominator tree is constructed for

 //      the clone loop to dominate the original.  Used in construction of

 //      pre-main-post loop sequence.

 //   When nonnull, the clone and original are side-by-side, both are

 //      dominated by the side_by_side_idom node.  Used in construction of

 //      unswitched loops.

 void PhaseIdealLoop::clone_loop( IdealLoopTree *loop, Node_List &old_new, int dd,

                                  Node* side_by_side_idom) {

   // Step 1: Clone the loop body.  Make the old->new mapping.

   uint i;

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

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

     Node *nnn = old->clone();

     old_new.map( old->_idx, nnn );

     _igvn.register_new_node_with_optimizer(nnn);

   }

   // Step 2: Fix the edges in the new body.  If the old input is outside the

   // loop use it.  If the old input is INside the loop, use the corresponding

   // new node instead.

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

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

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

     // Fix CFG/Loop controlling the new node

     if (has_ctrl(old)) {

       set_ctrl(nnn, old_new[get_ctrl(old)->_idx]);

     } else {

       set_loop(nnn, loop->_parent);

       if (old->outcnt() > 0) {

         set_idom( nnn, old_new[idom(old)->_idx], dd );

       }

     }

     // Correct edges to the new node

     for( uint j = 0; j < nnn->req(); j++ ) {

         Node *n = nnn->in(j);

         if( n ) {

           IdealLoopTree *old_in_loop = get_loop( has_ctrl(n) ? get_ctrl(n) : n );

           if( loop->is_member( old_in_loop ) )

             nnn->set_req(j, old_new[n->_idx]);

         }

     }

     _igvn.hash_find_insert(nnn);

   }

   Node *newhead = old_new[loop->_head->_idx];

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

   // Step 3: Now fix control uses.  Loop varying control uses have already

   // been fixed up (as part of all input edges in Step 2).  Loop invariant

   // control uses must be either an IfFalse or an IfTrue.  Make a merge

   // point to merge the old and new IfFalse/IfTrue nodes; make the use

   // refer to this.

   ResourceArea *area = Thread::current()->resource_area();

   Node_List worklist(area);

   uint new_counter = C->unique();

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

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

     if( !old->is_CFG() ) continue;

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

     // Copy uses to a worklist, so I can munge the def-use info

     // with impunity.

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

       worklist.push(old->fast_out(j));

     while( worklist.size() ) {  // Visit all uses

       Node *use = worklist.pop();

       if (!has_node(use))  continue; // Ignore dead nodes

       IdealLoopTree *use_loop = get_loop( has_ctrl(use) ? get_ctrl(use) : use );

       if( !loop->is_member( use_loop ) && use->is_CFG() ) {

         // Both OLD and USE are CFG nodes here.

         assert( use->is_Proj(), "" );

         // Clone the loop exit control projection

         Node *newuse = use->clone();

         newuse->set_req(0,nnn);

         _igvn.register_new_node_with_optimizer(newuse);

         set_loop(newuse, use_loop);

         set_idom(newuse, nnn, dom_depth(nnn) + 1 );

         // We need a Region to merge the exit from the peeled body and the

         // exit from the old loop body.

         RegionNode *r = new (C, 3) RegionNode(3);

         // Map the old use to the new merge point

         old_new.map( use->_idx, r );

         uint dd_r = MIN2(dom_depth(newuse),dom_depth(use));

         assert( dd_r >= dom_depth(dom_lca(newuse,use)), "" );

         // The original user of 'use' uses 'r' instead.

         for (DUIterator_Last lmin, l = use->last_outs(lmin); l >= lmin;) {

           Node* useuse = use->last_out(l);

           _igvn.hash_delete(useuse);

           _igvn._worklist.push(useuse);

           uint uses_found = 0;

           if( useuse->in(0) == use ) {

             useuse->set_req(0, r);

             uses_found++;

             if( useuse->is_CFG() ) {

               assert( dom_depth(useuse) > dd_r, "" );

               set_idom(useuse, r, dom_depth(useuse));

             }

           }

           for( uint k = 1; k < useuse->req(); k++ ) {

             if( useuse->in(k) == use ) {

               useuse->set_req(k, r);

               uses_found++;

             }

           }

           l -= uses_found;    // we deleted 1 or more copies of this edge

         }

         // Now finish up 'r'

         r->set_req( 1, newuse );

         r->set_req( 2,    use );

         _igvn.register_new_node_with_optimizer(r);

         set_loop(r, use_loop);

         set_idom(r, !side_by_side_idom ? newuse->in(0) : side_by_side_idom, dd_r);

       } // End of if a loop-exit test

     }

   }

   // Step 4: If loop-invariant use is not control, it must be dominated by a

   // loop exit IfFalse/IfTrue.  Find "proper" loop exit.  Make a Region

   // there if needed.  Make a Phi there merging old and new used values.

   Node_List *split_if_set = NULL;

   Node_List *split_bool_set = NULL;

   Node_List *split_cex_set = NULL;

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

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

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

     // Copy uses to a worklist, so I can munge the def-use info

     // with impunity.

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

       worklist.push(old->fast_out(j));

     while( worklist.size() ) {

       Node *use = worklist.pop();

       if (!has_node(use))  continue; // Ignore dead nodes

       if (use->in(0) == C->top())  continue;

       IdealLoopTree *use_loop = get_loop( has_ctrl(use) ? get_ctrl(use) : use );

       // Check for data-use outside of loop - at least one of OLD or USE

       // must not be a CFG node.

       if( !loop->is_member( use_loop ) && (!old->is_CFG() || !use->is_CFG())) {

         // If the Data use is an IF, that means we have an IF outside of the

         // loop that is switching on a condition that is set inside of the

         // loop.  Happens if people set a loop-exit flag; then test the flag

         // in the loop to break the loop, then test is again outside of the

         // loop to determine which way the loop exited.

         if( use->is_If() || use->is_CMove() ) {

           // Since this code is highly unlikely, we lazily build the worklist

           // of such Nodes to go split.

           if( !split_if_set )

             split_if_set = new Node_List(area);

           split_if_set->push(use);

         }

         if( use->is_Bool() ) {

           if( !split_bool_set )

             split_bool_set = new Node_List(area);

           split_bool_set->push(use);

         }

         if( use->Opcode() == Op_CreateEx ) {

           if( !split_cex_set )

             split_cex_set = new Node_List(area);

           split_cex_set->push(use);

         }

         // Get "block" use is in

         uint idx = 0;

         while( use->in(idx) != old ) idx++;

         Node *prev = use->is_CFG() ? use : get_ctrl(use);

         assert( !loop->is_member( get_loop( prev ) ), "" );

         Node *cfg = prev->_idx >= new_counter

           ? prev->in(2)

           : idom(prev);

         if( use->is_Phi() )     // Phi use is in prior block

           cfg = prev->in(idx);  // NOT in block of Phi itself

         if (cfg->is_top()) {    // Use is dead?

           _igvn.hash_delete(use);

           _igvn._worklist.push(use);

           use->set_req(idx, C->top());

           continue;

         }

         while( !loop->is_member( get_loop( cfg ) ) ) {

           prev = cfg;

           cfg = cfg->_idx >= new_counter ? cfg->in(2) : idom(cfg);

         }

         // If the use occurs after merging several exits from the loop, then

         // old value must have dominated all those exits.  Since the same old

         // value was used on all those exits we did not need a Phi at this

         // merge point.  NOW we do need a Phi here.  Each loop exit value

         // is now merged with the peeled body exit; each exit gets its own

         // private Phi and those Phis need to be merged here.

         Node *phi;

         if( prev->is_Region() ) {

           if( idx == 0 ) {      // Updating control edge?

             phi = prev;         // Just use existing control

           } else {              // Else need a new Phi

             phi = PhiNode::make( prev, old );

             // Now recursively fix up the new uses of old!

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

               worklist.push(phi); // Onto worklist once for each 'old' input

             }

           }

         } else {

           // Get new RegionNode merging old and new loop exits

           prev = old_new[prev->_idx];

           assert( prev, "just made this in step 7" );

           if( idx == 0 ) {      // Updating control edge?

             phi = prev;         // Just use existing control

           } else {              // Else need a new Phi

             // Make a new Phi merging data values properly

             phi = PhiNode::make( prev, old );

             phi->set_req( 1, nnn );

           }

         }

         // If inserting a new Phi, check for prior hits

         if( idx != 0 ) {

           Node *hit = _igvn.hash_find_insert(phi);

           if( hit == NULL ) {

            _igvn.register_new_node_with_optimizer(phi); // Register new phi

           } else {                                      // or

             // Remove the new phi from the graph and use the hit

             _igvn.remove_dead_node(phi);

             phi = hit;                                  // Use existing phi

           }

           set_ctrl(phi, prev);

         }

         // Make 'use' use the Phi instead of the old loop body exit value

         _igvn.hash_delete(use);

         _igvn._worklist.push(use);

         use->set_req(idx, phi);

         if( use->_idx >= new_counter ) { // If updating new phis

           // Not needed for correctness, but prevents a weak assert

           // in AddPNode from tripping (when we end up with different

           // base & derived Phis that will become the same after

           // IGVN does CSE).

           Node *hit = _igvn.hash_find_insert(use);

           if( hit )             // Go ahead and re-hash for hits.

             _igvn.subsume_node( use, hit );

         }

         // If 'use' was in the loop-exit block, it now needs to be sunk

         // below the post-loop merge point.

         sink_use( use, prev );

       }

     }

   }

   // Check for IFs that need splitting/cloning.  Happens if an IF outside of

   // the loop uses a condition set in the loop.  The original IF probably

   // takes control from one or more OLD Regions (which in turn get from NEW

   // Regions).  In any case, there will be a set of Phis for each merge point

   // from the IF up to where the original BOOL def exists the loop.

   if( split_if_set ) {

     while( split_if_set->size() ) {

       Node *iff = split_if_set->pop();

       if( iff->in(1)->is_Phi() ) {

         BoolNode *b = clone_iff( iff->in(1)->as_Phi(), loop );

         _igvn.hash_delete(iff);

         _igvn._worklist.push(iff);

         iff->set_req(1, b);

       }

     }

   }

   if( split_bool_set ) {

     while( split_bool_set->size() ) {

       Node *b = split_bool_set->pop();

       Node *phi = b->in(1);

       assert( phi->is_Phi(), "" );

       CmpNode *cmp = clone_bool( (PhiNode*)phi, loop );

       _igvn.hash_delete(b);

       _igvn._worklist.push(b);

       b->set_req(1, cmp);

     }

   }

   if( split_cex_set ) {

     while( split_cex_set->size() ) {

       Node *b = split_cex_set->pop();

       assert( b->in(0)->is_Region(), "" );

       assert( b->in(1)->is_Phi(), "" );

       assert( b->in(0)->in(0) == b->in(1)->in(0), "" );

       split_up( b, b->in(0), NULL );

     }

   }

 }

 //---------------------- stride_of_possible_iv -------------------------------------

 // Looks for an iff/bool/comp with one operand of the compare

 // being a cycle involving an add and a phi,

 // with an optional truncation (left-shift followed by a right-shift)

 // of the add. Returns zero if not an iv.

 int PhaseIdealLoop::stride_of_possible_iv(Node* iff) {

   Node* trunc1 = NULL;

   Node* trunc2 = NULL;

   const TypeInt* ttype = NULL;

   if (!iff->is_If() || iff->in(1) == NULL || !iff->in(1)->is_Bool()) {

     return 0;

   }

   BoolNode* bl = iff->in(1)->as_Bool();

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

   if (!cmp || cmp->Opcode() != Op_CmpI && cmp->Opcode() != Op_CmpU) {

     return 0;

   }

   // Must have an invariant operand

   if (is_member(get_loop(iff), get_ctrl(cmp->in(2)))) {

     return 0;

   }

   Node* add2 = NULL;

   Node* cmp1 = cmp->in(1);

   if (cmp1->is_Phi()) {

     // (If (Bool (CmpX phi:(Phi ...(Optional-trunc(AddI phi add2))) )))

     Node* phi = cmp1;

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

       Node* in = phi->in(i);

       Node* add = CountedLoopNode::match_incr_with_optional_truncation(in,

                                 &trunc1, &trunc2, &ttype);

       if (add && add->in(1) == phi) {

         add2 = add->in(2);

         break;

       }

     }

   } else {

     // (If (Bool (CmpX addtrunc:(Optional-trunc((AddI (Phi ...addtrunc...) add2)) )))

     Node* addtrunc = cmp1;

     Node* add = CountedLoopNode::match_incr_with_optional_truncation(addtrunc,

                                 &trunc1, &trunc2, &ttype);

     if (add && add->in(1)->is_Phi()) {

       Node* phi = add->in(1);

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

         if (phi->in(i) == addtrunc) {

           add2 = add->in(2);

           break;

         }

       }

     }

   }

   if (add2 != NULL) {

     const TypeInt* add2t = _igvn.type(add2)->is_int();

     if (add2t->is_con()) {

       return add2t->get_con();

     }

   }

   return 0;

 }

 //---------------------- stay_in_loop -------------------------------------

 // Return the (unique) control output node that's in the loop (if it exists.)

 Node* PhaseIdealLoop::stay_in_loop( Node* n, IdealLoopTree *loop) {

   Node* unique = NULL;

   if (!n) return NULL;

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

     Node* use = n->fast_out(i);

     if (!has_ctrl(use) && loop->is_member(get_loop(use))) {

       if (unique != NULL) {

         return NULL;

       }

       unique = use;

     }

   }

   return unique;

 }

 //------------------------------ register_node -------------------------------------

 // Utility to register node "n" with PhaseIdealLoop

 void PhaseIdealLoop::register_node(Node* n, IdealLoopTree *loop, Node* pred, int ddepth) {

   _igvn.register_new_node_with_optimizer(n);

   loop->_body.push(n);

   if (n->is_CFG()) {

     set_loop(n, loop);

     set_idom(n, pred, ddepth);

   } else {

     set_ctrl(n, pred);

   }

 }

 //------------------------------ proj_clone -------------------------------------

 // Utility to create an if-projection

 ProjNode* PhaseIdealLoop::proj_clone(ProjNode* p, IfNode* iff) {

   ProjNode* c = p->clone()->as_Proj();

   c->set_req(0, iff);

   return c;

 }

 //------------------------------ short_circuit_if -------------------------------------

 // Force the iff control output to be the live_proj

 Node* PhaseIdealLoop::short_circuit_if(IfNode* iff, ProjNode* live_proj) {

   int proj_con = live_proj->_con;

   assert(proj_con == 0 || proj_con == 1, "false or true projection");

   Node *con = _igvn.intcon(proj_con);

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

   if (iff) {

     iff->set_req(1, con);

   }

   return con;

 }

 //------------------------------ insert_if_before_proj -------------------------------------

 // Insert a new if before an if projection (* - new node)

 //

 // before

 //           if(test)

 //           /     \

 //          v       v

 //    other-proj   proj (arg)

 //

 // after

 //           if(test)

 //           /     \

 //          /       v

 //         |      * proj-clone

 //         v          |

 //    other-proj      v

 //                * new_if(relop(cmp[IU](left,right)))

 //                  /  \

 //                 v    v

 //         * new-proj  proj

 //         (returned)

 //

 ProjNode* PhaseIdealLoop::insert_if_before_proj(Node* left, bool Signed, BoolTest::mask relop, Node* right, ProjNode* proj) {

   IfNode* iff = proj->in(0)->as_If();

   IdealLoopTree *loop = get_loop(proj);

   ProjNode *other_proj = iff->proj_out(!proj->is_IfTrue())->as_Proj();

   int ddepth = dom_depth(proj);

   _igvn.hash_delete(iff);

   _igvn._worklist.push(iff);

   _igvn.hash_delete(proj);

   _igvn._worklist.push(proj);

   proj->set_req(0, NULL);  // temporary disconnect

   ProjNode* proj2 = proj_clone(proj, iff);

   register_node(proj2, loop, iff, ddepth);

   Node* cmp = Signed ? (Node*) new (C,3)CmpINode(left, right) : (Node*) new (C,3)CmpUNode(left, right);

   register_node(cmp, loop, proj2, ddepth);

   BoolNode* bol = new (C,2)BoolNode(cmp, relop);

   register_node(bol, loop, proj2, ddepth);

   IfNode* new_if = new (C,2)IfNode(proj2, bol, iff->_prob, iff->_fcnt);

   register_node(new_if, loop, proj2, ddepth);

   proj->set_req(0, new_if); // reattach

   set_idom(proj, new_if, ddepth);

   ProjNode* new_exit = proj_clone(other_proj, new_if)->as_Proj();

   register_node(new_exit, get_loop(other_proj), new_if, ddepth);

   return new_exit;

 }

 //------------------------------ insert_region_before_proj -------------------------------------

 // Insert a region before an if projection (* - new node)

 //

 // before

 //           if(test)

 //          /      |

 //         v       |

 //       proj      v

 //               other-proj

 //

 // after

 //           if(test)

 //          /      |

 //         v       |

 // * proj-clone    v

 //         |     other-proj

 //         v

 // * new-region

 //         |

 //         v

 // *      dum_if

 //       /     \

 //      v       \

 // * dum-proj    v

 //              proj

 //

 RegionNode* PhaseIdealLoop::insert_region_before_proj(ProjNode* proj) {

   IfNode* iff = proj->in(0)->as_If();

   IdealLoopTree *loop = get_loop(proj);

   ProjNode *other_proj = iff->proj_out(!proj->is_IfTrue())->as_Proj();

   int ddepth = dom_depth(proj);

   _igvn.hash_delete(iff);

   _igvn._worklist.push(iff);

   _igvn.hash_delete(proj);

   _igvn._worklist.push(proj);

   proj->set_req(0, NULL);  // temporary disconnect

   ProjNode* proj2 = proj_clone(proj, iff);

   register_node(proj2, loop, iff, ddepth);

   RegionNode* reg = new (C,2)RegionNode(2);

   reg->set_req(1, proj2);

   register_node(reg, loop, iff, ddepth);

   IfNode* dum_if = new (C,2)IfNode(reg, short_circuit_if(NULL, proj), iff->_prob, iff->_fcnt);

   register_node(dum_if, loop, reg, ddepth);

   proj->set_req(0, dum_if); // reattach

   set_idom(proj, dum_if, ddepth);

   ProjNode* dum_proj = proj_clone(other_proj, dum_if);

   register_node(dum_proj, loop, dum_if, ddepth);

   return reg;

 }

 //------------------------------ insert_cmpi_loop_exit -------------------------------------

 // Clone a signed compare loop exit from an unsigned compare and

 // insert it before the unsigned cmp on the stay-in-loop path.

 // All new nodes inserted in the dominator tree between the original

 // if and it's projections.  The original if test is replaced with

 // a constant to force the stay-in-loop path.

 //

 // This is done to make sure that the original if and it's projections

 // still dominate the same set of control nodes, that the ctrl() relation

 // from data nodes to them is preserved, and that their loop nesting is

 // preserved.

 //

 // before

 //          if(i <u limit)    unsigned compare loop exit

 //         /       |

 //        v        v

 //   exit-proj   stay-in-loop-proj

 //

 // after

 //          if(stay-in-loop-const)  original if

 //         /       |

 //        /        v

 //       /  if(i <  limit)    new signed test

 //      /  /       |

 //     /  /        v

 //    /  /  if(i <u limit)    new cloned unsigned test

 //   /  /   /      |

 //   v  v  v       |

 //    region       |

 //        |        |

 //      dum-if     |

 //     /  |        |

 // ether  |        |

 //        v        v

 //   exit-proj   stay-in-loop-proj

 //

 IfNode* PhaseIdealLoop::insert_cmpi_loop_exit(IfNode* if_cmpu, IdealLoopTree *loop) {

   const bool Signed   = true;

   const bool Unsigned = false;

   BoolNode* bol = if_cmpu->in(1)->as_Bool();

   if (bol->_test._test != BoolTest::lt) return NULL;

   CmpNode* cmpu = bol->in(1)->as_Cmp();

   if (cmpu->Opcode() != Op_CmpU) return NULL;

   int stride = stride_of_possible_iv(if_cmpu);

   if (stride == 0) return NULL;

   ProjNode* lp_continue = stay_in_loop(if_cmpu, loop)->as_Proj();

   ProjNode* lp_exit     = if_cmpu->proj_out(!lp_continue->is_IfTrue())->as_Proj();

   Node* limit = NULL;

   if (stride > 0) {

     limit = cmpu->in(2);

   } else {

     limit = _igvn.makecon(TypeInt::ZERO);

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

   }

   // Create a new region on the exit path

   RegionNode* reg = insert_region_before_proj(lp_exit);

   // Clone the if-cmpu-true-false using a signed compare

   BoolTest::mask rel_i = stride > 0 ? bol->_test._test : BoolTest::ge;

   ProjNode* cmpi_exit = insert_if_before_proj(cmpu->in(1), Signed, rel_i, limit, lp_continue);

   reg->add_req(cmpi_exit);

   // Clone the if-cmpu-true-false

   BoolTest::mask rel_u = bol->_test._test;

   ProjNode* cmpu_exit = insert_if_before_proj(cmpu->in(1), Unsigned, rel_u, cmpu->in(2), lp_continue);

   reg->add_req(cmpu_exit);

   // Force original if to stay in loop.

   short_circuit_if(if_cmpu, lp_continue);

   return cmpi_exit->in(0)->as_If();

 }

 //------------------------------ remove_cmpi_loop_exit -------------------------------------

 // Remove a previously inserted signed compare loop exit.

 void PhaseIdealLoop::remove_cmpi_loop_exit(IfNode* if_cmp, IdealLoopTree *loop) {

   Node* lp_proj = stay_in_loop(if_cmp, loop);

   assert(if_cmp->in(1)->in(1)->Opcode() == Op_CmpI &&

          stay_in_loop(lp_proj, loop)->is_If() &&

          stay_in_loop(lp_proj, loop)->in(1)->in(1)->Opcode() == Op_CmpU, "inserted cmpi before cmpu");

   Node *con = _igvn.makecon(lp_proj->is_IfTrue() ? TypeInt::ONE : TypeInt::ZERO);

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

   if_cmp->set_req(1, con);

 }

 //------------------------------ scheduled_nodelist -------------------------------------

 // Create a post order schedule of nodes that are in the

 // "member" set.  The list is returned in "sched".

 // The first node in "sched" is the loop head, followed by

 // nodes which have no inputs in the "member" set, and then

 // followed by the nodes that have an immediate input dependence

 // on a node in "sched".

 void PhaseIdealLoop::scheduled_nodelist( IdealLoopTree *loop, VectorSet& member, Node_List &sched ) {

   assert(member.test(loop->_head->_idx), "loop head must be in member set");

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

   VectorSet visited(a);

   Node_Stack nstack(a, loop->_body.size());

   Node* n  = loop->_head;  // top of stack is cached in "n"

   uint idx = 0;

   visited.set(n->_idx);

   // Initially push all with no inputs from within member set

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

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

     if (member.test(elt->_idx)) {

       bool found = false;

       for (uint j = 0; j < elt->req(); j++) {

         Node* def = elt->in(j);

         if (def && member.test(def->_idx) && def != elt) {

           found = true;

           break;

         }

       }

       if (!found && elt != loop->_head) {

         nstack.push(n, idx);

         n = elt;

         assert(!visited.test(n->_idx), "not seen yet");

         visited.set(n->_idx);

       }

     }

   }

   // traverse out's that are in the member set

   while (true) {

     if (idx < n->outcnt()) {

       Node* use = n->raw_out(idx);

       idx++;

       if (!visited.test_set(use->_idx)) {

         if (member.test(use->_idx)) {

           nstack.push(n, idx);

           n = use;

           idx = 0;

         }

       }

     } else {

       // All outputs processed

       sched.push(n);

       if (nstack.is_empty()) break;

       n   = nstack.node();

       idx = nstack.index();

       nstack.pop();

     }

   }

 }

 //------------------------------ has_use_in_set -------------------------------------

 // Has a use in the vector set

 bool PhaseIdealLoop::has_use_in_set( Node* n, VectorSet& vset ) {

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

     Node* use = n->fast_out(j);

     if (vset.test(use->_idx)) {

       return true;

     }

   }

   return false;

 }

 //------------------------------ has_use_internal_to_set -------------------------------------

 // Has use internal to the vector set (ie. not in a phi at the loop head)

 bool PhaseIdealLoop::has_use_internal_to_set( Node* n, VectorSet& vset, IdealLoopTree *loop ) {

   Node* head  = loop->_head;

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

     Node* use = n->fast_out(j);

     if (vset.test(use->_idx) && !(use->is_Phi() && use->in(0) == head)) {

       return true;

     }

   }

   return false;

 }

 //------------------------------ clone_for_use_outside_loop -------------------------------------

 // clone "n" for uses that are outside of loop

 void PhaseIdealLoop::clone_for_use_outside_loop( IdealLoopTree *loop, Node* n, Node_List& worklist ) {

   assert(worklist.size() == 0, "should be empty");

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

     Node* use = n->fast_out(j);

     if( !loop->is_member(get_loop(has_ctrl(use) ? get_ctrl(use) : use)) ) {

       worklist.push(use);

     }

   }

   while( worklist.size() ) {

     Node *use = worklist.pop();

     if (!has_node(use) || use->in(0) == C->top()) continue;

     uint j;

     for (j = 0; j < use->req(); j++) {

       if (use->in(j) == n) break;

     }

     assert(j < use->req(), "must be there");

     // clone "n" and insert it between the inputs of "n" and the use outside the loop

     Node* n_clone = n->clone();

     _igvn.hash_delete(use);

     use->set_req(j, n_clone);

     _igvn._worklist.push(use);

     Node* use_c;

     if (!use->is_Phi()) {

       use_c = has_ctrl(use) ? get_ctrl(use) : use->in(0);

     } else {

       // Use in a phi is considered a use in the associated predecessor block

       use_c = use->in(0)->in(j);

     }

     set_ctrl(n_clone, use_c);

     assert(!loop->is_member(get_loop(use_c)), "should be outside loop");

     get_loop(use_c)->_body.push(n_clone);

     _igvn.register_new_node_with_optimizer(n_clone);

 #if !defined(PRODUCT)

     if (TracePartialPeeling) {

       tty->print_cr("loop exit cloning old: %d new: %d newbb: %d", n->_idx, n_clone->_idx, get_ctrl(n_clone)->_idx);

     }

 #endif

   }

 }

 //------------------------------ clone_for_special_use_inside_loop -------------------------------------

 // clone "n" for special uses that are in the not_peeled region.

 // If these def-uses occur in separate blocks, the code generator

 // marks the method as not compilable.  For example, if a "BoolNode"

 // is in a different basic block than the "IfNode" that uses it, then

 // the compilation is aborted in the code generator.

 void PhaseIdealLoop::clone_for_special_use_inside_loop( IdealLoopTree *loop, Node* n,

                                                         VectorSet& not_peel, Node_List& sink_list, Node_List& worklist ) {

   if (n->is_Phi() || n->is_Load()) {

     return;

   }

   assert(worklist.size() == 0, "should be empty");

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

     Node* use = n->fast_out(j);

     if ( not_peel.test(use->_idx) &&

          (use->is_If() || use->is_CMove() || use->is_Bool()) &&

          use->in(1) == n)  {

       worklist.push(use);

     }

   }

   if (worklist.size() > 0) {

     // clone "n" and insert it between inputs of "n" and the use

     Node* n_clone = n->clone();

     loop->_body.push(n_clone);

     _igvn.register_new_node_with_optimizer(n_clone);

     set_ctrl(n_clone, get_ctrl(n));

     sink_list.push(n_clone);

     not_peel <<= n_clone->_idx;  // add n_clone to not_peel set.

 #if !defined(PRODUCT)

     if (TracePartialPeeling) {

       tty->print_cr("special not_peeled cloning old: %d new: %d", n->_idx, n_clone->_idx);

     }

 #endif

     while( worklist.size() ) {

       Node *use = worklist.pop();

       _igvn.hash_delete(use);

       _igvn._worklist.push(use);

       for (uint j = 1; j < use->req(); j++) {

         if (use->in(j) == n) {

           use->set_req(j, n_clone);

         }

       }

     }

   }

 }

 //------------------------------ insert_phi_for_loop -------------------------------------

 // Insert phi(lp_entry_val, back_edge_val) at use->in(idx) for loop lp if phi does not already exist

 void PhaseIdealLoop::insert_phi_for_loop( Node* use, uint idx, Node* lp_entry_val, Node* back_edge_val, LoopNode* lp ) {

   Node *phi = PhiNode::make(lp, back_edge_val);

   phi->set_req(LoopNode::EntryControl, lp_entry_val);

   // Use existing phi if it already exists

   Node *hit = _igvn.hash_find_insert(phi);

   if( hit == NULL ) {

     _igvn.register_new_node_with_optimizer(phi);

     set_ctrl(phi, lp);

   } else {

     // Remove the new phi from the graph and use the hit

     _igvn.remove_dead_node(phi);

     phi = hit;

   }

   _igvn.hash_delete(use);

   _igvn._worklist.push(use);

   use->set_req(idx, phi);

 }

 #ifdef ASSERT

 //------------------------------ is_valid_loop_partition -------------------------------------

 // Validate the loop partition sets: peel and not_peel

 bool PhaseIdealLoop::is_valid_loop_partition( IdealLoopTree *loop, VectorSet& peel, Node_List& peel_list,

                                               VectorSet& not_peel ) {

   uint i;

   // Check that peel_list entries are in the peel set

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

     if (!peel.test(peel_list.at(i)->_idx)) {

       return false;

     }

   }

   // Check at loop members are in one of peel set or not_peel set

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

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

     uint di = def->_idx;

     // Check that peel set elements are in peel_list

     if (peel.test(di)) {

       if (not_peel.test(di)) {

         return false;

       }

       // Must be in peel_list also

       bool found = false;

       for (uint j = 0; j < peel_list.size(); j++) {

         if (peel_list.at(j)->_idx == di) {

           found = true;

           break;

         }

       }

       if (!found) {

         return false;

       }

     } else if (not_peel.test(di)) {

       if (peel.test(di)) {

         return false;

       }

     } else {

       return false;

     }

   }

   return true;

 }

 //------------------------------ is_valid_clone_loop_exit_use -------------------------------------

 // Ensure a use outside of loop is of the right form

 bool PhaseIdealLoop::is_valid_clone_loop_exit_use( IdealLoopTree *loop, Node* use, uint exit_idx) {

   Node *use_c = has_ctrl(use) ? get_ctrl(use) : use;

   return (use->is_Phi() &&

           use_c->is_Region() && use_c->req() == 3 &&

           (use_c->in(exit_idx)->Opcode() == Op_IfTrue ||

            use_c->in(exit_idx)->Opcode() == Op_IfFalse ||

            use_c->in(exit_idx)->Opcode() == Op_JumpProj) &&

           loop->is_member( get_loop( use_c->in(exit_idx)->in(0) ) ) );

 }

 //------------------------------ is_valid_clone_loop_form -------------------------------------

 // Ensure that all uses outside of loop are of the right form

 bool PhaseIdealLoop::is_valid_clone_loop_form( IdealLoopTree *loop, Node_List& peel_list,

                                                uint orig_exit_idx, uint clone_exit_idx) {

   uint len = peel_list.size();

   for (uint i = 0; i < len; i++) {

     Node *def = peel_list.at(i);

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

       Node *use = def->fast_out(j);

       Node *use_c = has_ctrl(use) ? get_ctrl(use) : use;

       if (!loop->is_member(get_loop(use_c))) {

         // use is not in the loop, check for correct structure

         if (use->in(0) == def) {

           // Okay

         } else if (!is_valid_clone_loop_exit_use(loop, use, orig_exit_idx)) {

           return false;

         }

       }

     }

   }

   return true;

 }

 #endif

 //------------------------------ partial_peel -------------------------------------

 // Partially peel (aka loop rotation) the top portion of a loop (called

 // the peel section below) by cloning it and placing one copy just before

 // the new loop head and the other copy at the bottom of the new loop.

 //

 //    before                       after                where it came from

 //

 //    stmt1                        stmt1

 //  loop:                          stmt2                     clone

 //    stmt2                        if condA goto exitA       clone

 //    if condA goto exitA        new_loop:                   new

 //    stmt3                        stmt3                     clone

 //    if !condB goto loop          if condB goto exitB       clone

 //  exitB:                         stmt2                     orig

 //    stmt4                        if !condA goto new_loop   orig

 //  exitA:                         goto exitA

 //                               exitB:

 //                                 stmt4

 //                               exitA:

 //

 // Step 1: find the cut point: an exit test on probable

 //         induction variable.

 // Step 2: schedule (with cloning) operations in the peel

 //         section that can be executed after the cut into

 //         the section that is not peeled.  This may need

 //         to clone operations into exit blocks.  For

 //         instance, a reference to A[i] in the not-peel

 //         section and a reference to B[i] in an exit block

 //         may cause a left-shift of i by 2 to be placed

 //         in the peel block.  This step will clone the left

 //         shift into the exit block and sink the left shift

 //         from the peel to the not-peel section.

 // Step 3: clone the loop, retarget the control, and insert

 //         phis for values that are live across the new loop

 //         head.  This is very dependent on the graph structure

 //         from clone_loop.  It creates region nodes for

 //         exit control and associated phi nodes for values

 //         flow out of the loop through that exit.  The region

 //         node is dominated by the clone's control projection.

 //         So the clone's peel section is placed before the

 //         new loop head, and the clone's not-peel section is

 //         forms the top part of the new loop.  The original

 //         peel section forms the tail of the new loop.

 // Step 4: update the dominator tree and recompute the

 //         dominator depth.

 //

 //                   orig

 //

 //                  stmt1

 //                    |

 //                    v

 //                   loop<----+

 //                     |      |

 //                   stmt2    |

 //                     |      |

 //                     v      |

 //                    ifA     |

 //                   / |      |

 //                  v  v      |

 //               false true   ^  <-- last_peel

 //               /     |      |

 //              /   ===|==cut |

 //             /     stmt3    |  <-- first_not_peel

 //            /        |      |

 //            |        v      |

 //            v       ifB     |

 //          exitA:   / \      |

 //                  /   \     |

 //                 v     v    |

 //               false true   |

 //               /       \    |

 //              /         ----+

 //             |

 //             v

 //           exitB:

 //           stmt4

 //

 //

 //            after clone loop

 //

 //                   stmt1

 //                 /       \

 //        clone   /         \   orig

 //               /           \

 //              /             \

 //             v               v

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

 //   |      |                    |      |

 //   |    stmt2                stmt2    |

 //   |      |                    |      |

 //   |      v                    v      |

 //   |      ifA                 ifA     |

 //   |      | \                / |      |

 //   |      v  v              v  v      |

 //   ^    true  false      false true   ^  <-- last_peel

 //   |      |   ^   \       /    |      |

 //   | cut==|==  \   \     /  ===|==cut |

 //   |    stmt3   \   \   /    stmt3    |  <-- first_not_peel

 //   |      |    dom   | |       |      |

 //   |      v      \  1v v2      v      |

 //   |      ifB     regionA     ifB     |

 //   |      / \        |       / \      |

 //   |     /   \       v      /   \     |

 //   |    v     v    exitA:  v     v    |

 //   |    true  false      false true   |

 //   |    /     ^   \      /       \    |

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

 //               dom  \  /

 //                 \  1v v2

 //                  regionB

 //                     |

 //                     v

 //                   exitB:

 //                   stmt4

 //

 //

 //           after partial peel

 //

 //                  stmt1

 //                 /

 //        clone   /             orig

 //               /          TOP

 //              /             \

 //             v               v

 //    TOP->region             region----+

 //          |                    |      |

 //        stmt2                stmt2    |

 //          |                    |      |

 //          v                    v      |

 //          ifA                 ifA     |

 //          | \                / |      |

 //          v  v              v  v      |

 //        true  false      false true   |     <-- last_peel

 //          |   ^   \       /    +------|---+

 //  +->newloop   \   \     /  === ==cut |   |

 //  |     stmt3   \   \   /     TOP     |   |

 //  |       |    dom   | |      stmt3   |   | <-- first_not_peel

 //  |       v      \  1v v2      v      |   |

 //  |       ifB     regionA     ifB     ^   v

 //  |       / \        |       / \      |   |

 //  |      /   \       v      /   \     |   |

 //  |     v     v    exitA:  v     v    |   |

 //  |     true  false      false true   |   |

 //  |     /     ^   \      /       \    |   |

 //  |    |       \   \    /         v   |   |

 //  |    |       dom  \  /         TOP  |   |

 //  |    |         \  1v v2             |   |

 //  ^    v          regionB             |   |

 //  |    |             |                |   |

 //  |    |             v                ^   v

 //  |    |           exitB:             |   |

 //  |    |           stmt4              |   |

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

 //  |                                       |

 //  +-----------------<---------------------+

 //

 //

 //              final graph

 //

 //                  stmt1

 //                    |

 //                    v

 //         ........> ifA clone

 //         :        / |

 //        dom      /  |

 //         :      v   v

 //         :  false   true

 //         :  |       |

 //         :  |     stmt2 clone

 //         :  |       |

 //         :  |       v

 //         :  |    newloop<-----+

 //         :  |        |        |

 //         :  |     stmt3 clone |

 //         :  |        |        |

 //         :  |        v        |

 //         :  |       ifB       |

 //         :  |      / \        |

 //         :  |     v   v       |

 //         :  |  false true     |

 //         :  |   |     |       |

 //         :  |   v    stmt2    |

 //         :  | exitB:  |       |

 //         :  | stmt4   v       |

 //         :  |       ifA orig  |

 //         :  |      /  \       |

 //         :  |     /    \      |

 //         :  |    v     v      |

 //         :  |  false  true    |

 //         :  |  /        \     |

 //         :  v  v         -----+

 //          RegionA

 //             |

 //             v

 //           exitA

 //

 bool PhaseIdealLoop::partial_peel( IdealLoopTree *loop, Node_List &old_new ) {

   if (!loop->_head->is_Loop()) {

     return false;  }

   LoopNode *head  = loop->_head->as_Loop();

   if (head->is_partial_peel_loop() || head->partial_peel_has_failed()) {

     return false;

   }

   // Check for complex exit control

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

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

     int opc = n->Opcode();

     if (n->is_Call()        ||

         opc == Op_Catch     ||

         opc == Op_CatchProj ||

         opc == Op_Jump      ||

         opc == Op_JumpProj) {

 #if !defined(PRODUCT)

       if (TracePartialPeeling) {

         tty->print_cr("\nExit control too complex: lp: %d", head->_idx);

       }

 #endif

       return false;

     }

   }

   int dd = dom_depth(head);

   // Step 1: find cut point

   // Walk up dominators to loop head looking for first loop exit

   // which is executed on every path thru loop.

   IfNode *peel_if = NULL;

   IfNode *peel_if_cmpu = NULL;

   Node *iff = loop->tail();

   while( iff != head ) {

     if( iff->is_If() ) {

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

       if (ctrl->is_top()) return false; // Dead test on live IF.

       // If loop-varying exit-test, check for induction variable

       if( loop->is_member(get_loop(ctrl)) &&

           loop->is_loop_exit(iff) &&

           is_possible_iv_test(iff)) {

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

         if (cmp->Opcode() == Op_CmpI) {

           peel_if = iff->as_If();

         } else {

           assert(cmp->Opcode() == Op_CmpU, "must be CmpI or CmpU");

           peel_if_cmpu = iff->as_If();

         }

       }

     }

     iff = idom(iff);

   }

   // Prefer signed compare over unsigned compare.

   IfNode* new_peel_if = NULL;

   if (peel_if == NULL) {

     if (!PartialPeelAtUnsignedTests || peel_if_cmpu == NULL) {

       return false;   // No peel point found

     }

     new_peel_if = insert_cmpi_loop_exit(peel_if_cmpu, loop);

     if (new_peel_if == NULL) {

       return false;   // No peel point found

     }

     peel_if = new_peel_if;

   }

   Node* last_peel        = stay_in_loop(peel_if, loop);

   Node* first_not_peeled = stay_in_loop(last_peel, loop);

   if (first_not_peeled == NULL || first_not_peeled == head) {

     return false;

   }

 #if !defined(PRODUCT)

   if (TracePartialPeeling) {

     tty->print_cr("before partial peel one iteration");

     Node_List wl;

     Node* t = head->in(2);

     while (true) {

       wl.push(t);

       if (t == head) break;

       t = idom(t);

     }

     while (wl.size() > 0) {

       Node* tt = wl.pop();

       tt->dump();

       if (tt == last_peel) tty->print_cr("-- cut --");

     }

   }

 #endif

   ResourceArea *area = Thread::current()->resource_area();

   VectorSet peel(area);

   VectorSet not_peel(area);

   Node_List peel_list(area);

   Node_List worklist(area);

   Node_List sink_list(area);

   // Set of cfg nodes to peel are those that are executable from

   // the head through last_peel.

   assert(worklist.size() == 0, "should be empty");

   worklist.push(head);

   peel.set(head->_idx);

   while (worklist.size() > 0) {

     Node *n = worklist.pop();

     if (n != last_peel) {

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

         Node* use = n->fast_out(j);

         if (use->is_CFG() &&

             loop->is_member(get_loop(use)) &&

             !peel.test_set(use->_idx)) {

           worklist.push(use);

         }

       }

     }

   }

   // Set of non-cfg nodes to peel are those that are control

   // dependent on the cfg nodes.

   uint i;

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

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

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

     if (peel.test(n_c->_idx)) {

       peel.set(n->_idx);

     } else {

       not_peel.set(n->_idx);

     }

   }

   // Step 2: move operations from the peeled section down into the

   //         not-peeled section

   // Get a post order schedule of nodes in the peel region

   // Result in right-most operand.

   scheduled_nodelist(loop, peel, peel_list );

   assert(is_valid_loop_partition(loop, peel, peel_list, not_peel), "bad partition");

   // For future check for too many new phis

   uint old_phi_cnt = 0;

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

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

     if (use->is_Phi()) old_phi_cnt++;

   }

 #if !defined(PRODUCT)

   if (TracePartialPeeling) {

     tty->print_cr("\npeeled list");

   }

 #endif

   // Evacuate nodes in peel region into the not_peeled region if possible

   uint new_phi_cnt = 0;

   for (i = 0; i < peel_list.size();) {

     Node* n = peel_list.at(i);

 #if !defined(PRODUCT)

   if (TracePartialPeeling) n->dump();

 #endif

     bool incr = true;

     if ( !n->is_CFG() ) {

       if ( has_use_in_set(n, not_peel) ) {

         // If not used internal to the peeled region,

         // move "n" from peeled to not_peeled region.

         if ( !has_use_internal_to_set(n, peel, loop) ) {

           // if not pinned and not a load (which maybe anti-dependent on a store)

           // and not a CMove (Matcher expects only bool->cmove).

           if ( n->in(0) == NULL && !n->is_Load() && !n->is_CMove() ) {

             clone_for_use_outside_loop( loop, n, worklist );

             sink_list.push(n);

             peel     >>= n->_idx; // delete n from peel set.

             not_peel <<= n->_idx; // add n to not_peel set.

             peel_list.remove(i);

             incr = false;

 #if !defined(PRODUCT)

             if (TracePartialPeeling) {

               tty->print_cr("sink to not_peeled region: %d newbb: %d",

                             n->_idx, get_ctrl(n)->_idx);

             }

 #endif

           }

         } else {

           // Otherwise check for special def-use cases that span

           // the peel/not_peel boundary such as bool->if

           clone_for_special_use_inside_loop( loop, n, not_peel, sink_list, worklist );

           new_phi_cnt++;

         }

       }

     }

     if (incr) i++;

   }

   if (new_phi_cnt > old_phi_cnt + PartialPeelNewPhiDelta) {

 #if !defined(PRODUCT)

     if (TracePartialPeeling) {

       tty->print_cr("\nToo many new phis: %d  old %d new cmpi: %c",

                     new_phi_cnt, old_phi_cnt, new_peel_if != NULL?'T':'F');

     }

 #endif

     if (new_peel_if != NULL) {

       remove_cmpi_loop_exit(new_peel_if, loop);

     }

     // Inhibit more partial peeling on this loop

     assert(!head->is_partial_peel_loop(), "not partial peeled");

     head->mark_partial_peel_failed();

     return false;

   }

   // Step 3: clone loop, retarget control, and insert new phis

   // Create new loop head for new phis and to hang

   // the nodes being moved (sinked) from the peel region.

   LoopNode* new_head = new (C, 3) LoopNode(last_peel, last_peel);

   _igvn.register_new_node_with_optimizer(new_head);

   assert(first_not_peeled->in(0) == last_peel, "last_peel <- first_not_peeled");

   first_not_peeled->set_req(0, new_head);

   set_loop(new_head, loop);

   loop->_body.push(new_head);

   not_peel.set(new_head->_idx);

   set_idom(new_head, last_peel, dom_depth(first_not_peeled));

   set_idom(first_not_peeled, new_head, dom_depth(first_not_peeled));

   while (sink_list.size() > 0) {

     Node* n = sink_list.pop();

     set_ctrl(n, new_head);

   }

   assert(is_valid_loop_partition(loop, peel, peel_list, not_peel), "bad partition");

   clone_loop( loop, old_new, dd );

   const uint clone_exit_idx = 1;

   const uint orig_exit_idx  = 2;

   assert(is_valid_clone_loop_form( loop, peel_list, orig_exit_idx, clone_exit_idx ), "bad clone loop");

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

   LoopNode* new_head_clone     = old_new[new_head->_idx]->as_Loop();

   Node* orig_tail_clone        = head_clone->in(2);

   // Add phi if "def" node is in peel set and "use" is not

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

     Node *def  = peel_list.at(i);

     if (!def->is_CFG()) {

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

         Node *use = def->fast_out(j);

         if (has_node(use) && use->in(0) != C->top() &&

             (!peel.test(use->_idx) ||

              (use->is_Phi() && use->in(0) == head)) ) {

           worklist.push(use);

         }

       }

       while( worklist.size() ) {

         Node *use = worklist.pop();

         for (uint j = 1; j < use->req(); j++) {

           Node* n = use->in(j);

           if (n == def) {

             // "def" is in peel set, "use" is not in peel set

             // or "use" is in the entry boundary (a phi) of the peel set

             Node* use_c = has_ctrl(use) ? get_ctrl(use) : use;

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

               // use is in loop

               if (old_new[use->_idx] != NULL) { // null for dead code

                 Node* use_clone = old_new[use->_idx];

                 _igvn.hash_delete(use);

                 use->set_req(j, C->top());

                 _igvn._worklist.push(use);

                 insert_phi_for_loop( use_clone, j, old_new[def->_idx], def, new_head_clone );

               }

             } else {

               assert(is_valid_clone_loop_exit_use(loop, use, orig_exit_idx), "clone loop format");

               // use is not in the loop, check if the live range includes the cut

               Node* lp_if = use_c->in(orig_exit_idx)->in(0);

               if (not_peel.test(lp_if->_idx)) {

                 assert(j == orig_exit_idx, "use from original loop");

                 insert_phi_for_loop( use, clone_exit_idx, old_new[def->_idx], def, new_head_clone );

               }

             }

           }

         }

       }

     }

   }

   // Step 3b: retarget control

   // Redirect control to the new loop head if a cloned node in

   // the not_peeled region has control that points into the peeled region.

   // This necessary because the cloned peeled region will be outside

   // the loop.

   //                            from    to

   //          cloned-peeled    <---+

   //    new_head_clone:            |    <--+

   //          cloned-not_peeled  in(0)    in(0)

   //          orig-peeled

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

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

     if (!n->is_CFG()           && n->in(0) != NULL        &&

         not_peel.test(n->_idx) && peel.test(n->in(0)->_idx)) {

       Node* n_clone = old_new[n->_idx];

       _igvn.hash_delete(n_clone);

       n_clone->set_req(0, new_head_clone);

       _igvn._worklist.push(n_clone);

     }

   }

   // Backedge of the surviving new_head (the clone) is original last_peel

   _igvn.hash_delete(new_head_clone);

   new_head_clone->set_req(LoopNode::LoopBackControl, last_peel);

   _igvn._worklist.push(new_head_clone);

   // Cut first node in original not_peel set

   _igvn.hash_delete(new_head);

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

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

   _igvn._worklist.push(new_head);

   // Copy head_clone back-branch info to original head

   // and remove original head's loop entry and

   // clone head's back-branch

   _igvn.hash_delete(head);

   _igvn.hash_delete(head_clone);

   head->set_req(LoopNode::EntryControl, head_clone->in(LoopNode::LoopBackControl));

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

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

   _igvn._worklist.push(head);

   _igvn._worklist.push(head_clone);

   // Similarly modify the phis

   for (DUIterator_Fast kmax, k = head->fast_outs(kmax); k < kmax; k++) {

     Node* use = head->fast_out(k);

     if (use->is_Phi() && use->outcnt() > 0) {

       Node* use_clone = old_new[use->_idx];

       _igvn.hash_delete(use);

       _igvn.hash_delete(use_clone);

       use->set_req(LoopNode::EntryControl, use_clone->in(LoopNode::LoopBackControl));

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

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

       _igvn._worklist.push(use);

       _igvn._worklist.push(use_clone);

     }

   }

   // Step 4: update dominator tree and dominator depth

   set_idom(head, orig_tail_clone, dd);

   recompute_dom_depth();

   // Inhibit more partial peeling on this loop

   new_head_clone->set_partial_peel_loop();

   C->set_major_progress();

 #if !defined(PRODUCT)

   if (TracePartialPeeling) {

     tty->print_cr("\nafter partial peel one iteration");

     Node_List wl(area);

     Node* t = last_peel;

     while (true) {

       wl.push(t);

       if (t == head_clone) break;

       t = idom(t);

     }

     while (wl.size() > 0) {

       Node* tt = wl.pop();

       if (tt == head) tty->print_cr("orig head");

       else if (tt == new_head_clone) tty->print_cr("new head");

       else if (tt == head_clone) tty->print_cr("clone head");

       tt->dump();

     }

   }

 #endif

   return true;