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

 /*

  * Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved.

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

  *

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

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

  * published by the Free Software Foundation.

  *

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

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

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

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

  * accompanied this code).

  *

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

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

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

  *

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

  * or visit www.oracle.com if you need additional information or have any

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  */

 #include "precompiled.hpp"

 #include "compiler/oopMap.hpp"

 #include "memory/allocation.inline.hpp"

 #include "opto/addnode.hpp"

 #include "opto/block.hpp"

 #include "opto/callnode.hpp"

 #include "opto/cfgnode.hpp"

 #include "opto/chaitin.hpp"

 #include "opto/coalesce.hpp"

 #include "opto/connode.hpp"

 #include "opto/indexSet.hpp"

 #include "opto/machnode.hpp"

 #include "opto/memnode.hpp"

 #include "opto/opcodes.hpp"

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

 //------------------------------IFG--------------------------------------------

 PhaseIFG::PhaseIFG( Arena *arena ) : Phase(Interference_Graph), _arena(arena) {

 }

 //------------------------------init-------------------------------------------

 void PhaseIFG::init( uint maxlrg ) {

   _maxlrg = maxlrg;

   _yanked = new (_arena) VectorSet(_arena);

   _is_square = false;

   // Make uninitialized adjacency lists

   _adjs = (IndexSet*)_arena->Amalloc(sizeof(IndexSet)*maxlrg);

   // Also make empty live range structures

   _lrgs = (LRG *)_arena->Amalloc( maxlrg * sizeof(LRG) );

   memset(_lrgs,0,sizeof(LRG)*maxlrg);

   // Init all to empty

   for( uint i = 0; i < maxlrg; i++ ) {

     _adjs[i].initialize(maxlrg);

     _lrgs[i].Set_All();

   }

 }

 //------------------------------add--------------------------------------------

 // Add edge between vertices a & b.  These are sorted (triangular matrix),

 // then the smaller number is inserted in the larger numbered array.

 int PhaseIFG::add_edge( uint a, uint b ) {

   lrgs(a).invalid_degree();

   lrgs(b).invalid_degree();

   // Sort a and b, so that a is bigger

   assert( !_is_square, "only on triangular" );

   if( a < b ) { uint tmp = a; a = b; b = tmp; }

   return _adjs[a].insert( b );

 }

 //------------------------------add_vector-------------------------------------

 // Add an edge between 'a' and everything in the vector.

 void PhaseIFG::add_vector( uint a, IndexSet *vec ) {

   // IFG is triangular, so do the inserts where 'a' < 'b'.

   assert( !_is_square, "only on triangular" );

   IndexSet *adjs_a = &_adjs[a];

   if( !vec->count() ) return;

   IndexSetIterator elements(vec);

   uint neighbor;

   while ((neighbor = elements.next()) != 0) {

     add_edge( a, neighbor );

   }

 }

 //------------------------------test-------------------------------------------

 // Is there an edge between a and b?

 int PhaseIFG::test_edge( uint a, uint b ) const {

   // Sort a and b, so that a is larger

   assert( !_is_square, "only on triangular" );

   if( a < b ) { uint tmp = a; a = b; b = tmp; }

   return _adjs[a].member(b);

 }

 //------------------------------SquareUp---------------------------------------

 // Convert triangular matrix to square matrix

 void PhaseIFG::SquareUp() {

   assert( !_is_square, "only on triangular" );

   // Simple transpose

   for( uint i = 0; i < _maxlrg; i++ ) {

     IndexSetIterator elements(&_adjs[i]);

     uint datum;

     while ((datum = elements.next()) != 0) {

       _adjs[datum].insert( i );

     }

   }

   _is_square = true;

 }

 //------------------------------Compute_Effective_Degree-----------------------

 // Compute effective degree in bulk

 void PhaseIFG::Compute_Effective_Degree() {

   assert( _is_square, "only on square" );

   for( uint i = 0; i < _maxlrg; i++ )

     lrgs(i).set_degree(effective_degree(i));

 }

 //------------------------------test_edge_sq-----------------------------------

 int PhaseIFG::test_edge_sq( uint a, uint b ) const {

   assert( _is_square, "only on square" );

   // Swap, so that 'a' has the lesser count.  Then binary search is on

   // the smaller of a's list and b's list.

   if( neighbor_cnt(a) > neighbor_cnt(b) ) { uint tmp = a; a = b; b = tmp; }

   //return _adjs[a].unordered_member(b);

   return _adjs[a].member(b);

 }

 //------------------------------Union------------------------------------------

 // Union edges of B into A

 void PhaseIFG::Union( uint a, uint b ) {

   assert( _is_square, "only on square" );

   IndexSet *A = &_adjs[a];

   IndexSetIterator b_elements(&_adjs[b]);

   uint datum;

   while ((datum = b_elements.next()) != 0) {

     if(A->insert(datum)) {

       _adjs[datum].insert(a);

       lrgs(a).invalid_degree();

       lrgs(datum).invalid_degree();

     }

   }

 }

 //------------------------------remove_node------------------------------------

 // Yank a Node and all connected edges from the IFG.  Return a

 // list of neighbors (edges) yanked.

 IndexSet *PhaseIFG::remove_node( uint a ) {

   assert( _is_square, "only on square" );

   assert( !_yanked->test(a), "" );

   _yanked->set(a);

   // I remove the LRG from all neighbors.

   IndexSetIterator elements(&_adjs[a]);

   LRG &lrg_a = lrgs(a);

   uint datum;

   while ((datum = elements.next()) != 0) {

     _adjs[datum].remove(a);

     lrgs(datum).inc_degree( -lrg_a.compute_degree(lrgs(datum)) );

   }

   return neighbors(a);

 }

 //------------------------------re_insert--------------------------------------

 // Re-insert a yanked Node.

 void PhaseIFG::re_insert( uint a ) {

   assert( _is_square, "only on square" );

   assert( _yanked->test(a), "" );

   (*_yanked) >>= a;

   IndexSetIterator elements(&_adjs[a]);

   uint datum;

   while ((datum = elements.next()) != 0) {

     _adjs[datum].insert(a);

     lrgs(datum).invalid_degree();

   }

 }

 //------------------------------compute_degree---------------------------------

 // Compute the degree between 2 live ranges.  If both live ranges are

 // aligned-adjacent powers-of-2 then we use the MAX size.  If either is

 // mis-aligned (or for Fat-Projections, not-adjacent) then we have to

 // MULTIPLY the sizes.  Inspect Brigg's thesis on register pairs to see why

 // this is so.

 int LRG::compute_degree( LRG &l ) const {

   int tmp;

   int num_regs = _num_regs;

   int nregs = l.num_regs();

   tmp =  (_fat_proj || l._fat_proj)     // either is a fat-proj?

     ? (num_regs * nregs)                // then use product

     : MAX2(num_regs,nregs);             // else use max

   return tmp;

 }

 //------------------------------effective_degree-------------------------------

 // Compute effective degree for this live range.  If both live ranges are

 // aligned-adjacent powers-of-2 then we use the MAX size.  If either is

 // mis-aligned (or for Fat-Projections, not-adjacent) then we have to

 // MULTIPLY the sizes.  Inspect Brigg's thesis on register pairs to see why

 // this is so.

 int PhaseIFG::effective_degree( uint lidx ) const {

   int eff = 0;

   int num_regs = lrgs(lidx).num_regs();

   int fat_proj = lrgs(lidx)._fat_proj;

   IndexSet *s = neighbors(lidx);

   IndexSetIterator elements(s);

   uint nidx;

   while((nidx = elements.next()) != 0) {

     LRG &lrgn = lrgs(nidx);

     int nregs = lrgn.num_regs();

     eff += (fat_proj || lrgn._fat_proj) // either is a fat-proj?

       ? (num_regs * nregs)              // then use product

       : MAX2(num_regs,nregs);           // else use max

   }

   return eff;

 }

 #ifndef PRODUCT

 //------------------------------dump-------------------------------------------

 void PhaseIFG::dump() const {

   tty->print_cr("-- Interference Graph --%s--",

                 _is_square ? "square" : "triangular" );

   if( _is_square ) {

     for( uint i = 0; i < _maxlrg; i++ ) {

       tty->print( (*_yanked)[i] ? "XX " : "  ");

       tty->print("L%d: { ",i);

       IndexSetIterator elements(&_adjs[i]);

       uint datum;

       while ((datum = elements.next()) != 0) {

         tty->print("L%d ", datum);

       }

       tty->print_cr("}");

     }

     return;

   }

   // Triangular

   for( uint i = 0; i < _maxlrg; i++ ) {

     uint j;

     tty->print( (*_yanked)[i] ? "XX " : "  ");

     tty->print("L%d: { ",i);

     for( j = _maxlrg; j > i; j-- )

       if( test_edge(j - 1,i) ) {

         tty->print("L%d ",j - 1);

       }

     tty->print("| ");

     IndexSetIterator elements(&_adjs[i]);

     uint datum;

     while ((datum = elements.next()) != 0) {

       tty->print("L%d ", datum);

     }

     tty->print("}\n");

   }

   tty->print("\n");

 }

 //------------------------------stats------------------------------------------

 void PhaseIFG::stats() const {

   ResourceMark rm;

   int *h_cnt = NEW_RESOURCE_ARRAY(int,_maxlrg*2);

   memset( h_cnt, 0, sizeof(int)*_maxlrg*2 );

   uint i;

   for( i = 0; i < _maxlrg; i++ ) {

     h_cnt[neighbor_cnt(i)]++;

   }

   tty->print_cr("--Histogram of counts--");

   for( i = 0; i < _maxlrg*2; i++ )

     if( h_cnt[i] )

       tty->print("%d/%d ",i,h_cnt[i]);

   tty->print_cr("");

 }

 //------------------------------verify-----------------------------------------

 void PhaseIFG::verify( const PhaseChaitin *pc ) const {

   // IFG is square, sorted and no need for Find

   for( uint i = 0; i < _maxlrg; i++ ) {

     assert(!((*_yanked)[i]) || !neighbor_cnt(i), "Is removed completely" );

     IndexSet *set = &_adjs[i];

     IndexSetIterator elements(set);

     uint idx;

     uint last = 0;

     while ((idx = elements.next()) != 0) {

       assert( idx != i, "Must have empty diagonal");

       assert( pc->Find_const(idx) == idx, "Must not need Find" );

       assert( _adjs[idx].member(i), "IFG not square" );

       assert( !(*_yanked)[idx], "No yanked neighbors" );

       assert( last < idx, "not sorted increasing");

       last = idx;

     }

     assert( !lrgs(i)._degree_valid ||

             effective_degree(i) == lrgs(i).degree(), "degree is valid but wrong" );

   }

 }

 #endif

 //------------------------------interfere_with_live----------------------------

 // Interfere this register with everything currently live.  Use the RegMasks

 // to trim the set of possible interferences. Return a count of register-only

 // interferences as an estimate of register pressure.

 void PhaseChaitin::interfere_with_live( uint r, IndexSet *liveout ) {

   uint retval = 0;

   // Interfere with everything live.

   const RegMask &rm = lrgs(r).mask();

   // Check for interference by checking overlap of regmasks.

   // Only interfere if acceptable register masks overlap.

   IndexSetIterator elements(liveout);

   uint l;

   while( (l = elements.next()) != 0 )

     if( rm.overlap( lrgs(l).mask() ) )

       _ifg->add_edge( r, l );

 }

 //------------------------------build_ifg_virtual------------------------------

 // Actually build the interference graph.  Uses virtual registers only, no

 // physical register masks.  This allows me to be very aggressive when

 // coalescing copies.  Some of this aggressiveness will have to be undone

 // later, but I'd rather get all the copies I can now (since unremoved copies

 // at this point can end up in bad places).  Copies I re-insert later I have

 // more opportunity to insert them in low-frequency locations.

 void PhaseChaitin::build_ifg_virtual( ) {

   // For all blocks (in any order) do...

   for( uint i=0; i<_cfg._num_blocks; i++ ) {

     Block *b = _cfg._blocks[i];

     IndexSet *liveout = _live->live(b);

     // The IFG is built by a single reverse pass over each basic block.

     // Starting with the known live-out set, we remove things that get

     // defined and add things that become live (essentially executing one

     // pass of a standard LIVE analysis). Just before a Node defines a value

     // (and removes it from the live-ness set) that value is certainly live.

     // The defined value interferes with everything currently live.  The

     // value is then removed from the live-ness set and it's inputs are

     // added to the live-ness set.

     for( uint j = b->end_idx() + 1; j > 1; j-- ) {

       Node *n = b->_nodes[j-1];

       // Get value being defined

       uint r = n2lidx(n);

       // Some special values do not allocate

       if( r ) {

         // Remove from live-out set

         liveout->remove(r);

         // Copies do not define a new value and so do not interfere.

         // Remove the copies source from the liveout set before interfering.

         uint idx = n->is_Copy();

         if( idx ) liveout->remove( n2lidx(n->in(idx)) );

         // Interfere with everything live

         interfere_with_live( r, liveout );

       }

       // Make all inputs live

       if( !n->is_Phi() ) {      // Phi function uses come from prior block

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

           liveout->insert( n2lidx(n->in(k)) );

       }

       // 2-address instructions always have the defined value live

       // on entry to the instruction, even though it is being defined

       // by the instruction.  We pretend a virtual copy sits just prior

       // to the instruction and kills the src-def'd register.

       // In other words, for 2-address instructions the defined value

       // interferes with all inputs.

       uint idx;

       if( n->is_Mach() && (idx = n->as_Mach()->two_adr()) ) {

         const MachNode *mach = n->as_Mach();

         // Sometimes my 2-address ADDs are commuted in a bad way.

         // We generally want the USE-DEF register to refer to the

         // loop-varying quantity, to avoid a copy.

         uint op = mach->ideal_Opcode();

         // Check that mach->num_opnds() == 3 to ensure instruction is

         // not subsuming constants, effectively excludes addI_cin_imm

         // Can NOT swap for instructions like addI_cin_imm since it

         // is adding zero to yhi + carry and the second ideal-input

         // points to the result of adding low-halves.

         // Checking req() and num_opnds() does NOT distinguish addI_cout from addI_cout_imm

         if( (op == Op_AddI && mach->req() == 3 && mach->num_opnds() == 3) &&

             n->in(1)->bottom_type()->base() == Type::Int &&

             // See if the ADD is involved in a tight data loop the wrong way

             n->in(2)->is_Phi() &&

             n->in(2)->in(2) == n ) {

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

           n->set_req( 1, n->in(2) );

           n->set_req( 2, tmp );

         }

         // Defined value interferes with all inputs

         uint lidx = n2lidx(n->in(idx));

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

           uint kidx = n2lidx(n->in(k));

           if( kidx != lidx )

             _ifg->add_edge( r, kidx );

         }

       }

     } // End of forall instructions in block

   } // End of forall blocks

 }

 //------------------------------count_int_pressure-----------------------------

 uint PhaseChaitin::count_int_pressure( IndexSet *liveout ) {

   IndexSetIterator elements(liveout);

   uint lidx;

   uint cnt = 0;

   while ((lidx = elements.next()) != 0) {

     if( lrgs(lidx).mask().is_UP() &&

         lrgs(lidx).mask_size() &&

         !lrgs(lidx)._is_float &&

         !lrgs(lidx)._is_vector &&

         lrgs(lidx).mask().overlap(*Matcher::idealreg2regmask[Op_RegI]) )

       cnt += lrgs(lidx).reg_pressure();

   }

   return cnt;

 }

 //------------------------------count_float_pressure---------------------------

 uint PhaseChaitin::count_float_pressure( IndexSet *liveout ) {

   IndexSetIterator elements(liveout);

   uint lidx;

   uint cnt = 0;

   while ((lidx = elements.next()) != 0) {

     if( lrgs(lidx).mask().is_UP() &&

         lrgs(lidx).mask_size() &&

         (lrgs(lidx)._is_float || lrgs(lidx)._is_vector))

       cnt += lrgs(lidx).reg_pressure();

   }

   return cnt;

 }

 //------------------------------lower_pressure---------------------------------

 // Adjust register pressure down by 1.  Capture last hi-to-low transition,

 static void lower_pressure( LRG *lrg, uint where, Block *b, uint *pressure, uint *hrp_index ) {

   if (lrg->mask().is_UP() && lrg->mask_size()) {

     if (lrg->_is_float || lrg->_is_vector) {

       pressure[1] -= lrg->reg_pressure();

       if( pressure[1] == (uint)FLOATPRESSURE ) {

         hrp_index[1] = where;

         if( pressure[1] > b->_freg_pressure )

           b->_freg_pressure = pressure[1]+1;

       }

     } else if( lrg->mask().overlap(*Matcher::idealreg2regmask[Op_RegI]) ) {

       pressure[0] -= lrg->reg_pressure();

       if( pressure[0] == (uint)INTPRESSURE   ) {

         hrp_index[0] = where;

         if( pressure[0] > b->_reg_pressure )

           b->_reg_pressure = pressure[0]+1;

       }

     }

   }

 }

 //------------------------------build_ifg_physical-----------------------------

 // Build the interference graph using physical registers when available.

 // That is, if 2 live ranges are simultaneously alive but in their acceptable

 // register sets do not overlap, then they do not interfere.

 uint PhaseChaitin::build_ifg_physical( ResourceArea *a ) {

   NOT_PRODUCT( Compile::TracePhase t3("buildIFG", &_t_buildIFGphysical, TimeCompiler); )

   uint spill_reg = LRG::SPILL_REG;

   uint must_spill = 0;

   // For all blocks (in any order) do...

   for( uint i = 0; i < _cfg._num_blocks; i++ ) {

     Block *b = _cfg._blocks[i];

     // Clone (rather than smash in place) the liveout info, so it is alive

     // for the "collect_gc_info" phase later.

     IndexSet liveout(_live->live(b));

     uint last_inst = b->end_idx();

     // Compute first nonphi node index

     uint first_inst;

     for( first_inst = 1; first_inst < last_inst; first_inst++ )

       if( !b->_nodes[first_inst]->is_Phi() )

         break;

     // Spills could be inserted before CreateEx node which should be

     // first instruction in block after Phis. Move CreateEx up.

     for( uint insidx = first_inst; insidx < last_inst; insidx++ ) {

       Node *ex = b->_nodes[insidx];

       if( ex->is_SpillCopy() ) continue;

       if( insidx > first_inst && ex->is_Mach() &&

           ex->as_Mach()->ideal_Opcode() == Op_CreateEx ) {

         // If the CreateEx isn't above all the MachSpillCopies

         // then move it to the top.

         b->_nodes.remove(insidx);

         b->_nodes.insert(first_inst, ex);

       }

       // Stop once a CreateEx or any other node is found

       break;

     }

     // Reset block's register pressure values for each ifg construction

     uint pressure[2], hrp_index[2];

     pressure[0] = pressure[1] = 0;

     hrp_index[0] = hrp_index[1] = last_inst+1;

     b->_reg_pressure = b->_freg_pressure = 0;

     // Liveout things are presumed live for the whole block.  We accumulate

     // 'area' accordingly.  If they get killed in the block, we'll subtract

     // the unused part of the block from the area.

     int inst_count = last_inst - first_inst;

     double cost = (inst_count <= 0) ? 0.0 : b->_freq * double(inst_count);

     assert(!(cost < 0.0), "negative spill cost" );

     IndexSetIterator elements(&liveout);

     uint lidx;

     while ((lidx = elements.next()) != 0) {

       LRG &lrg = lrgs(lidx);

       lrg._area += cost;

       // Compute initial register pressure

       if (lrg.mask().is_UP() && lrg.mask_size()) {

         if (lrg._is_float || lrg._is_vector) {   // Count float pressure

           pressure[1] += lrg.reg_pressure();

           if( pressure[1] > b->_freg_pressure )

             b->_freg_pressure = pressure[1];

           // Count int pressure, but do not count the SP, flags

         } else if( lrgs(lidx).mask().overlap(*Matcher::idealreg2regmask[Op_RegI]) ) {

           pressure[0] += lrg.reg_pressure();

           if( pressure[0] > b->_reg_pressure )

             b->_reg_pressure = pressure[0];

         }

       }

     }

     assert( pressure[0] == count_int_pressure  (&liveout), "" );

     assert( pressure[1] == count_float_pressure(&liveout), "" );

     // The IFG is built by a single reverse pass over each basic block.

     // Starting with the known live-out set, we remove things that get

     // defined and add things that become live (essentially executing one

     // pass of a standard LIVE analysis).  Just before a Node defines a value

     // (and removes it from the live-ness set) that value is certainly live.

     // The defined value interferes with everything currently live.  The

     // value is then removed from the live-ness set and it's inputs are added

     // to the live-ness set.

     uint j;

     for( j = last_inst + 1; j > 1; j-- ) {

       Node *n = b->_nodes[j - 1];

       // Get value being defined

       uint r = n2lidx(n);

       // Some special values do not allocate

       if( r ) {

         // A DEF normally costs block frequency; rematerialized values are

         // removed from the DEF sight, so LOWER costs here.

         lrgs(r)._cost += n->rematerialize() ? 0 : b->_freq;

         // If it is not live, then this instruction is dead.  Probably caused

         // by spilling and rematerialization.  Who cares why, yank this baby.

         if( !liveout.member(r) && n->Opcode() != Op_SafePoint ) {

           Node *def = n->in(0);

           if( !n->is_Proj() ||

               // Could also be a flags-projection of a dead ADD or such.

               (n2lidx(def) && !liveout.member(n2lidx(def)) ) ) {

             b->_nodes.remove(j - 1);

             if( lrgs(r)._def == n ) lrgs(r)._def = 0;

             n->disconnect_inputs(NULL, C);

             _cfg._bbs.map(n->_idx,NULL);

             n->replace_by(C->top());

             // Since yanking a Node from block, high pressure moves up one

             hrp_index[0]--;

             hrp_index[1]--;

             continue;

           }

           // Fat-projections kill many registers which cannot be used to

           // hold live ranges.

           if( lrgs(r)._fat_proj ) {

             // Count the int-only registers

             RegMask itmp = lrgs(r).mask();

             itmp.AND(*Matcher::idealreg2regmask[Op_RegI]);

             int iregs = itmp.Size();

             if( pressure[0]+iregs > b->_reg_pressure )

               b->_reg_pressure = pressure[0]+iregs;

             if( pressure[0]       <= (uint)INTPRESSURE &&

                 pressure[0]+iregs >  (uint)INTPRESSURE ) {

               hrp_index[0] = j-1;

             }

             // Count the float-only registers

             RegMask ftmp = lrgs(r).mask();

             ftmp.AND(*Matcher::idealreg2regmask[Op_RegD]);

             int fregs = ftmp.Size();

             if( pressure[1]+fregs > b->_freg_pressure )

               b->_freg_pressure = pressure[1]+fregs;

             if( pressure[1]       <= (uint)FLOATPRESSURE &&

                 pressure[1]+fregs >  (uint)FLOATPRESSURE ) {

               hrp_index[1] = j-1;

             }

           }

         } else {                // Else it is live

           // A DEF also ends 'area' partway through the block.

           lrgs(r)._area -= cost;

           assert(!(lrgs(r)._area < 0.0), "negative spill area" );

           // Insure high score for immediate-use spill copies so they get a color

           if( n->is_SpillCopy()

               && lrgs(r).is_singledef()        // MultiDef live range can still split

               && n->outcnt() == 1              // and use must be in this block

               && _cfg._bbs[n->unique_out()->_idx] == b ) {

             // All single-use MachSpillCopy(s) that immediately precede their

             // use must color early.  If a longer live range steals their

             // color, the spill copy will split and may push another spill copy

             // further away resulting in an infinite spill-split-retry cycle.

             // Assigning a zero area results in a high score() and a good

             // location in the simplify list.

             //

             Node *single_use = n->unique_out();

             assert( b->find_node(single_use) >= j, "Use must be later in block");

             // Use can be earlier in block if it is a Phi, but then I should be a MultiDef

             // Find first non SpillCopy 'm' that follows the current instruction

             // (j - 1) is index for current instruction 'n'

             Node *m = n;

             for( uint i = j; i <= last_inst && m->is_SpillCopy(); ++i ) { m = b->_nodes[i]; }

             if( m == single_use ) {

               lrgs(r)._area = 0.0;

             }

           }

           // Remove from live-out set

           if( liveout.remove(r) ) {

             // Adjust register pressure.

             // Capture last hi-to-lo pressure transition

             lower_pressure( &lrgs(r), j-1, b, pressure, hrp_index );

             assert( pressure[0] == count_int_pressure  (&liveout), "" );

             assert( pressure[1] == count_float_pressure(&liveout), "" );

           }

           // Copies do not define a new value and so do not interfere.

           // Remove the copies source from the liveout set before interfering.

           uint idx = n->is_Copy();

           if( idx ) {

             uint x = n2lidx(n->in(idx));

             if( liveout.remove( x ) ) {

               lrgs(x)._area -= cost;

               // Adjust register pressure.

               lower_pressure( &lrgs(x), j-1, b, pressure, hrp_index );

               assert( pressure[0] == count_int_pressure  (&liveout), "" );

               assert( pressure[1] == count_float_pressure(&liveout), "" );

             }

           }

         } // End of if live or not

         // Interfere with everything live.  If the defined value must

         // go in a particular register, just remove that register from

         // all conflicting parties and avoid the interference.

         // Make exclusions for rematerializable defs.  Since rematerializable

         // DEFs are not bound but the live range is, some uses must be bound.

         // If we spill live range 'r', it can rematerialize at each use site

         // according to its bindings.

         const RegMask &rmask = lrgs(r).mask();

         if( lrgs(r).is_bound() && !(n->rematerialize()) && rmask.is_NotEmpty() ) {

           // Check for common case

           int r_size = lrgs(r).num_regs();

           OptoReg::Name r_reg = (r_size == 1) ? rmask.find_first_elem() : OptoReg::Physical;

           // Smear odd bits

           IndexSetIterator elements(&liveout);

           uint l;

           while ((l = elements.next()) != 0) {

             LRG &lrg = lrgs(l);

             // If 'l' must spill already, do not further hack his bits.

             // He'll get some interferences and be forced to spill later.

             if( lrg._must_spill ) continue;

             // Remove bound register(s) from 'l's choices

             RegMask old = lrg.mask();

             uint old_size = lrg.mask_size();

             // Remove the bits from LRG 'r' from LRG 'l' so 'l' no

             // longer interferes with 'r'.  If 'l' requires aligned

             // adjacent pairs, subtract out bit pairs.

             assert(!lrg._is_vector || !lrg._fat_proj, "sanity");

             if (lrg.num_regs() > 1 && !lrg._fat_proj) {

               RegMask r2mask = rmask;

               // Leave only aligned set of bits.

               r2mask.smear_to_sets(lrg.num_regs());

               // It includes vector case.

               lrg.SUBTRACT( r2mask );

               lrg.compute_set_mask_size();

             } else if( r_size != 1 ) { // fat proj

               lrg.SUBTRACT( rmask );

               lrg.compute_set_mask_size();

             } else {            // Common case: size 1 bound removal

               if( lrg.mask().Member(r_reg) ) {

                 lrg.Remove(r_reg);

                 lrg.set_mask_size(lrg.mask().is_AllStack() ? 65535:old_size-1);

               }

             }

             // If 'l' goes completely dry, it must spill.

             if( lrg.not_free() ) {

               // Give 'l' some kind of reasonable mask, so he picks up

               // interferences (and will spill later).

               lrg.set_mask( old );

               lrg.set_mask_size(old_size);

               must_spill++;

               lrg._must_spill = 1;

               lrg.set_reg(OptoReg::Name(LRG::SPILL_REG));

             }

           }

         } // End of if bound

         // Now interference with everything that is live and has

         // compatible register sets.

         interfere_with_live(r,&liveout);

       } // End of if normal register-allocated value

       // Area remaining in the block

       inst_count--;

       cost = (inst_count <= 0) ? 0.0 : b->_freq * double(inst_count);

       // Make all inputs live

       if( !n->is_Phi() ) {      // Phi function uses come from prior block

         JVMState* jvms = n->jvms();

         uint debug_start = jvms ? jvms->debug_start() : 999999;

         // Start loop at 1 (skip control edge) for most Nodes.

         // SCMemProj's might be the sole use of a StoreLConditional.

         // While StoreLConditionals set memory (the SCMemProj use)

         // they also def flags; if that flag def is unused the

         // allocator sees a flag-setting instruction with no use of

         // the flags and assumes it's dead.  This keeps the (useless)

         // flag-setting behavior alive while also keeping the (useful)

         // memory update effect.

         for( uint k = ((n->Opcode() == Op_SCMemProj) ? 0:1); k < n->req(); k++ ) {

           Node *def = n->in(k);

           uint x = n2lidx(def);

           if( !x ) continue;

           LRG &lrg = lrgs(x);

           // No use-side cost for spilling debug info

           if( k < debug_start )

             // A USE costs twice block frequency (once for the Load, once

             // for a Load-delay).  Rematerialized uses only cost once.

             lrg._cost += (def->rematerialize() ? b->_freq : (b->_freq + b->_freq));

           // It is live now

           if( liveout.insert( x ) ) {

             // Newly live things assumed live from here to top of block

             lrg._area += cost;

             // Adjust register pressure

             if (lrg.mask().is_UP() && lrg.mask_size()) {

               if (lrg._is_float || lrg._is_vector) {

                 pressure[1] += lrg.reg_pressure();

                 if( pressure[1] > b->_freg_pressure )

                   b->_freg_pressure = pressure[1];

               } else if( lrg.mask().overlap(*Matcher::idealreg2regmask[Op_RegI]) ) {

                 pressure[0] += lrg.reg_pressure();

                 if( pressure[0] > b->_reg_pressure )

                   b->_reg_pressure = pressure[0];

               }

             }

             assert( pressure[0] == count_int_pressure  (&liveout), "" );

             assert( pressure[1] == count_float_pressure(&liveout), "" );

           }

           assert(!(lrg._area < 0.0), "negative spill area" );

         }

       }

     } // End of reverse pass over all instructions in block

     // If we run off the top of the block with high pressure and

     // never see a hi-to-low pressure transition, just record that

     // the whole block is high pressure.

     if( pressure[0] > (uint)INTPRESSURE   ) {

       hrp_index[0] = 0;

       if( pressure[0] > b->_reg_pressure )

         b->_reg_pressure = pressure[0];

     }

     if( pressure[1] > (uint)FLOATPRESSURE ) {

       hrp_index[1] = 0;

       if( pressure[1] > b->_freg_pressure )

         b->_freg_pressure = pressure[1];

     }

     // Compute high pressure indice; avoid landing in the middle of projnodes

     j = hrp_index[0];

     if( j < b->_nodes.size() && j < b->end_idx()+1 ) {

       Node *cur = b->_nodes[j];

       while( cur->is_Proj() || (cur->is_MachNullCheck()) || cur->is_Catch() ) {

         j--;

         cur = b->_nodes[j];

       }

     }

     b->_ihrp_index = j;

     j = hrp_index[1];

     if( j < b->_nodes.size() && j < b->end_idx()+1 ) {

       Node *cur = b->_nodes[j];

       while( cur->is_Proj() || (cur->is_MachNullCheck()) || cur->is_Catch() ) {

         j--;

         cur = b->_nodes[j];

       }

     }

     b->_fhrp_index = j;

 #ifndef PRODUCT

     // Gather Register Pressure Statistics

     if( PrintOptoStatistics ) {

       if( b->_reg_pressure > (uint)INTPRESSURE || b->_freg_pressure > (uint)FLOATPRESSURE )

         _high_pressure++;

       else

         _low_pressure++;

     }

 #endif

   } // End of for all blocks

   return must_spill;

 }