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

 /*

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

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

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  * published by the Free Software Foundation.

  *

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  * 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.

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 #include "precompiled.hpp"

 #include "memory/allocation.inline.hpp"

 #include "opto/block.hpp"

 #include "opto/c2compiler.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/matcher.hpp"

 #include "opto/regmask.hpp"

 #ifndef PRODUCT

 void PhaseCoalesce::dump(Node *n) const {

   // Being a const function means I cannot use 'Find'

   uint r = _phc._lrg_map.find(n);

   tty->print("L%d/N%d ",r,n->_idx);

 }

 void PhaseCoalesce::dump() const {

   // I know I have a block layout now, so I can print blocks in a loop

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

     uint j;

     Block* b = _phc._cfg.get_block(i);

     // Print a nice block header

     tty->print("B%d: ",b->_pre_order);

     for( j=1; j<b->num_preds(); j++ )

       tty->print("B%d ", _phc._cfg.get_block_for_node(b->pred(j))->_pre_order);

     tty->print("-> ");

     for( j=0; j<b->_num_succs; j++ )

       tty->print("B%d ",b->_succs[j]->_pre_order);

     tty->print(" IDom: B%d/#%d\n", b->_idom ? b->_idom->_pre_order : 0, b->_dom_depth);

     uint cnt = b->number_of_nodes();

     for( j=0; j<cnt; j++ ) {

       Node *n = b->get_node(j);

       dump( n );

       tty->print("\t%s\t",n->Name());

       // Dump the inputs

       uint k;                   // Exit value of loop

       for( k=0; k<n->req(); k++ ) // For all required inputs

         if( n->in(k) ) dump( n->in(k) );

         else tty->print("_ ");

       int any_prec = 0;

       for( ; k<n->len(); k++ )          // For all precedence inputs

         if( n->in(k) ) {

           if( !any_prec++ ) tty->print(" |");

           dump( n->in(k) );

         }

       // Dump node-specific info

       n->dump_spec(tty);

       tty->print("\n");

     }

     tty->print("\n");

   }

 }

 #endif

 // Combine the live ranges def'd by these 2 Nodes.  N2 is an input to N1.

 void PhaseCoalesce::combine_these_two(Node *n1, Node *n2) {

   uint lr1 = _phc._lrg_map.find(n1);

   uint lr2 = _phc._lrg_map.find(n2);

   if( lr1 != lr2 &&             // Different live ranges already AND

       !_phc._ifg->test_edge_sq( lr1, lr2 ) ) {  // Do not interfere

     LRG *lrg1 = &_phc.lrgs(lr1);

     LRG *lrg2 = &_phc.lrgs(lr2);

     // Not an oop->int cast; oop->oop, int->int, AND int->oop are OK.

     // Now, why is int->oop OK?  We end up declaring a raw-pointer as an oop

     // and in general that's a bad thing.  However, int->oop conversions only

     // happen at GC points, so the lifetime of the misclassified raw-pointer

     // is from the CheckCastPP (that converts it to an oop) backwards up

     // through a merge point and into the slow-path call, and around the

     // diamond up to the heap-top check and back down into the slow-path call.

     // The misclassified raw pointer is NOT live across the slow-path call,

     // and so does not appear in any GC info, so the fact that it is

     // misclassified is OK.

     if( (lrg1->_is_oop || !lrg2->_is_oop) && // not an oop->int cast AND

         // Compatible final mask

         lrg1->mask().overlap( lrg2->mask() ) ) {

       // Merge larger into smaller.

       if( lr1 > lr2 ) {

         uint  tmp =  lr1;  lr1 =  lr2;  lr2 =  tmp;

         Node   *n =   n1;   n1 =   n2;   n2 =    n;

         LRG *ltmp = lrg1; lrg1 = lrg2; lrg2 = ltmp;

       }

       // Union lr2 into lr1

       _phc.Union( n1, n2 );

       if (lrg1->_maxfreq < lrg2->_maxfreq)

         lrg1->_maxfreq = lrg2->_maxfreq;

       // Merge in the IFG

       _phc._ifg->Union( lr1, lr2 );

       // Combine register restrictions

       lrg1->AND(lrg2->mask());

     }

   }

 }

 // Copy coalescing

 void PhaseCoalesce::coalesce_driver() {

   verify();

   // Coalesce from high frequency to low

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

     coalesce(_phc._blks[i]);

   }

 }

 // I am inserting copies to come out of SSA form.  In the general case, I am

 // doing a parallel renaming.  I'm in the Named world now, so I can't do a

 // general parallel renaming.  All the copies now use  "names" (live-ranges)

 // to carry values instead of the explicit use-def chains.  Suppose I need to

 // insert 2 copies into the same block.  They copy L161->L128 and L128->L132.

 // If I insert them in the wrong order then L128 will get clobbered before it

 // can get used by the second copy.  This cannot happen in the SSA model;

 // direct use-def chains get me the right value.  It DOES happen in the named

 // model so I have to handle the reordering of copies.

 //

 // In general, I need to topo-sort the placed copies to avoid conflicts.

 // Its possible to have a closed cycle of copies (e.g., recirculating the same

 // values around a loop).  In this case I need a temp to break the cycle.

 void PhaseAggressiveCoalesce::insert_copy_with_overlap( Block *b, Node *copy, uint dst_name, uint src_name ) {

   // Scan backwards for the locations of the last use of the dst_name.

   // I am about to clobber the dst_name, so the copy must be inserted

   // after the last use.  Last use is really first-use on a backwards scan.

   uint i = b->end_idx()-1;

   while(1) {

     Node *n = b->get_node(i);

     // Check for end of virtual copies; this is also the end of the

     // parallel renaming effort.

     if (n->_idx < _unique) {

       break;

     }

     uint idx = n->is_Copy();

     assert( idx || n->is_Con() || n->is_MachProj(), "Only copies during parallel renaming" );

     if (idx && _phc._lrg_map.find(n->in(idx)) == dst_name) {

       break;

     }

     i--;

   }

   uint last_use_idx = i;

   // Also search for any kill of src_name that exits the block.

   // Since the copy uses src_name, I have to come before any kill.

   uint kill_src_idx = b->end_idx();

   // There can be only 1 kill that exits any block and that is

   // the last kill.  Thus it is the first kill on a backwards scan.

   i = b->end_idx()-1;

   while (1) {

     Node *n = b->get_node(i);

     // Check for end of virtual copies; this is also the end of the

     // parallel renaming effort.

     if (n->_idx < _unique) {

       break;

     }

     assert( n->is_Copy() || n->is_Con() || n->is_MachProj(), "Only copies during parallel renaming" );

     if (_phc._lrg_map.find(n) == src_name) {

       kill_src_idx = i;

       break;

     }

     i--;

   }

   // Need a temp?  Last use of dst comes after the kill of src?

   if (last_use_idx >= kill_src_idx) {

     // Need to break a cycle with a temp

     uint idx = copy->is_Copy();

     Node *tmp = copy->clone();

     uint max_lrg_id = _phc._lrg_map.max_lrg_id();

     _phc.new_lrg(tmp, max_lrg_id);

     _phc._lrg_map.set_max_lrg_id(max_lrg_id + 1);

     // Insert new temp between copy and source

     tmp ->set_req(idx,copy->in(idx));

     copy->set_req(idx,tmp);

     // Save source in temp early, before source is killed

     b->insert_node(tmp, kill_src_idx);

     _phc._cfg.map_node_to_block(tmp, b);

     last_use_idx++;

   }

   // Insert just after last use

   b->insert_node(copy, last_use_idx + 1);

 }

 void PhaseAggressiveCoalesce::insert_copies( Matcher &matcher ) {

   // We do LRGs compressing and fix a liveout data only here since the other

   // place in Split() is guarded by the assert which we never hit.

   _phc._lrg_map.compress_uf_map_for_nodes();

   // Fix block's liveout data for compressed live ranges.

   for (uint lrg = 1; lrg < _phc._lrg_map.max_lrg_id(); lrg++) {

     uint compressed_lrg = _phc._lrg_map.find(lrg);

     if (lrg != compressed_lrg) {

       for (uint bidx = 0; bidx < _phc._cfg.number_of_blocks(); bidx++) {

         IndexSet *liveout = _phc._live->live(_phc._cfg.get_block(bidx));

         if (liveout->member(lrg)) {

           liveout->remove(lrg);

           liveout->insert(compressed_lrg);

         }

       }

     }

   }

   // All new nodes added are actual copies to replace virtual copies.

   // Nodes with index less than '_unique' are original, non-virtual Nodes.

   _unique = C->unique();

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

     C->check_node_count(NodeLimitFudgeFactor, "out of nodes in coalesce");

     if (C->failing()) return;

     Block *b = _phc._cfg.get_block(i);

     uint cnt = b->num_preds();  // Number of inputs to the Phi

     for( uint l = 1; l<b->number_of_nodes(); l++ ) {

       Node *n = b->get_node(l);

       // Do not use removed-copies, use copied value instead

       uint ncnt = n->req();

       for( uint k = 1; k<ncnt; k++ ) {

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

         uint cidx = copy->is_Copy();

         if( cidx ) {

           Node *def = copy->in(cidx);

           if (_phc._lrg_map.find(copy) == _phc._lrg_map.find(def)) {

             n->set_req(k, def);

           }

         }

       }

       // Remove any explicit copies that get coalesced.

       uint cidx = n->is_Copy();

       if( cidx ) {

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

         if (_phc._lrg_map.find(n) == _phc._lrg_map.find(def)) {

           n->replace_by(def);

           n->set_req(cidx,NULL);

           b->remove_node(l);

           l--;

           continue;

         }

       }

       if (n->is_Phi()) {

         // Get the chosen name for the Phi

         uint phi_name = _phc._lrg_map.find(n);

         // Ignore the pre-allocated specials

         if (!phi_name) {

           continue;

         }

         // Check for mismatch inputs to Phi

         for (uint j = 1; j < cnt; j++) {

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

           uint src_name = _phc._lrg_map.find(m);

           if (src_name != phi_name) {

             Block *pred = _phc._cfg.get_block_for_node(b->pred(j));

             Node *copy;

             assert(!m->is_Con() || m->is_Mach(), "all Con must be Mach");

             // Rematerialize constants instead of copying them.

             // We do this only for immediate constants, we avoid constant table loads

             // because that will unsafely extend the live range of the constant table base.

             if (m->is_Mach() && m->as_Mach()->is_Con() && !m->as_Mach()->is_MachConstant() &&

                 m->as_Mach()->rematerialize()) {

               copy = m->clone();

               // Insert the copy in the predecessor basic block

               pred->add_inst(copy);

               // Copy any flags as well

               _phc.clone_projs(pred, pred->end_idx(), m, copy, _phc._lrg_map);

             } else {

               int ireg = m->ideal_reg();

               if (ireg == 0 || ireg == Op_RegFlags) {

                 if (C->subsume_loads()) {

                   C->record_failure(C2Compiler::retry_no_subsuming_loads());

                 } else {

                   assert(false, err_msg("attempted to spill a non-spillable item: %d: %s, ireg = %d",

                                         m->_idx, m->Name(), ireg));

                   C->record_method_not_compilable("attempted to spill a non-spillable item");

                 }

                 return;

               }

               const RegMask *rm = C->matcher()->idealreg2spillmask[ireg];

               copy = new (C) MachSpillCopyNode(m, *rm, *rm);

               // Find a good place to insert.  Kinda tricky, use a subroutine

               insert_copy_with_overlap(pred,copy,phi_name,src_name);

             }

             // Insert the copy in the use-def chain

             n->set_req(j, copy);

             _phc._cfg.map_node_to_block(copy, pred);

             // Extend ("register allocate") the names array for the copy.

             _phc._lrg_map.extend(copy->_idx, phi_name);

           } // End of if Phi names do not match

         } // End of for all inputs to Phi

       } else { // End of if Phi

         // Now check for 2-address instructions

         uint idx;

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

           // Get the chosen name for the Node

           uint name = _phc._lrg_map.find(n);

           assert (name, "no 2-address specials");

           // Check for name mis-match on the 2-address input

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

           if (_phc._lrg_map.find(m) != name) {

             Node *copy;

             assert(!m->is_Con() || m->is_Mach(), "all Con must be Mach");

             // At this point it is unsafe to extend live ranges (6550579).

             // Rematerialize only constants as we do for Phi above.

             if (m->is_Mach() && m->as_Mach()->is_Con() && !m->as_Mach()->is_MachConstant() &&

                 m->as_Mach()->rematerialize()) {

               copy = m->clone();

               // Insert the copy in the basic block, just before us

               b->insert_node(copy, l++);

               l += _phc.clone_projs(b, l, m, copy, _phc._lrg_map);

             } else {

               int ireg = m->ideal_reg();

               if (ireg == 0 || ireg == Op_RegFlags) {

                 assert(false, err_msg("attempted to spill a non-spillable item: %d: %s, ireg = %d",

                                       m->_idx, m->Name(), ireg));

                 C->record_method_not_compilable("attempted to spill a non-spillable item");

                 return;

               }

               const RegMask *rm = C->matcher()->idealreg2spillmask[ireg];

               copy = new (C) MachSpillCopyNode(m, *rm, *rm);

               // Insert the copy in the basic block, just before us

               b->insert_node(copy, l++);

             }

             // Insert the copy in the use-def chain

             n->set_req(idx, copy);

             // Extend ("register allocate") the names array for the copy.

             _phc._lrg_map.extend(copy->_idx, name);

             _phc._cfg.map_node_to_block(copy, b);

           }

         } // End of is two-adr

         // Insert a copy at a debug use for a lrg which has high frequency

         if (b->_freq < OPTO_DEBUG_SPLIT_FREQ || _phc._cfg.is_uncommon(b)) {

           // Walk the debug inputs to the node and check for lrg freq

           JVMState* jvms = n->jvms();

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

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

           for(uint inpidx = debug_start; inpidx < debug_end; inpidx++) {

             // Do not split monitors; they are only needed for debug table

             // entries and need no code.

             if (jvms->is_monitor_use(inpidx)) {

               continue;

             }

             Node *inp = n->in(inpidx);

             uint nidx = _phc._lrg_map.live_range_id(inp);

             LRG &lrg = lrgs(nidx);

             // If this lrg has a high frequency use/def

             if( lrg._maxfreq >= _phc.high_frequency_lrg() ) {

               // If the live range is also live out of this block (like it

               // would be for a fast/slow idiom), the normal spill mechanism

               // does an excellent job.  If it is not live out of this block

               // (like it would be for debug info to uncommon trap) splitting

               // the live range now allows a better allocation in the high

               // frequency blocks.

               //   Build_IFG_virtual has converted the live sets to

               // live-IN info, not live-OUT info.

               uint k;

               for( k=0; k < b->_num_succs; k++ )

                 if( _phc._live->live(b->_succs[k])->member( nidx ) )

                   break;      // Live in to some successor block?

               if( k < b->_num_succs )

                 continue;     // Live out; do not pre-split

               // Split the lrg at this use

               int ireg = inp->ideal_reg();

               if (ireg == 0 || ireg == Op_RegFlags) {

                 assert(false, err_msg("attempted to spill a non-spillable item: %d: %s, ireg = %d",

                                       inp->_idx, inp->Name(), ireg));

                 C->record_method_not_compilable("attempted to spill a non-spillable item");

                 return;

               }

               const RegMask *rm = C->matcher()->idealreg2spillmask[ireg];

               Node *copy = new (C) MachSpillCopyNode( inp, *rm, *rm );

               // Insert the copy in the use-def chain

               n->set_req(inpidx, copy );

               // Insert the copy in the basic block, just before us

               b->insert_node(copy,  l++);

               // Extend ("register allocate") the names array for the copy.

               uint max_lrg_id = _phc._lrg_map.max_lrg_id();

               _phc.new_lrg(copy, max_lrg_id);

               _phc._lrg_map.set_max_lrg_id(max_lrg_id + 1);

               _phc._cfg.map_node_to_block(copy, b);

               //tty->print_cr("Split a debug use in Aggressive Coalesce");

             }  // End of if high frequency use/def

           }  // End of for all debug inputs

         }  // End of if low frequency safepoint

       } // End of if Phi

     } // End of for all instructions

   } // End of for all blocks

 }

 // Aggressive (but pessimistic) copy coalescing of a single block

 // The following coalesce pass represents a single round of aggressive

 // pessimistic coalesce.  "Aggressive" means no attempt to preserve

 // colorability when coalescing.  This occasionally means more spills, but

 // it also means fewer rounds of coalescing for better code - and that means

 // faster compiles.

 // "Pessimistic" means we do not hit the fixed point in one pass (and we are

 // reaching for the least fixed point to boot).  This is typically solved

 // with a few more rounds of coalescing, but the compiler must run fast.  We

 // could optimistically coalescing everything touching PhiNodes together

 // into one big live range, then check for self-interference.  Everywhere

 // the live range interferes with self it would have to be split.  Finding

 // the right split points can be done with some heuristics (based on

 // expected frequency of edges in the live range).  In short, it's a real

 // research problem and the timeline is too short to allow such research.

 // Further thoughts: (1) build the LR in a pass, (2) find self-interference

 // in another pass, (3) per each self-conflict, split, (4) split by finding

 // the low-cost cut (min-cut) of the LR, (5) edges in the LR are weighted

 // according to the GCM algorithm (or just exec freq on CFG edges).

 void PhaseAggressiveCoalesce::coalesce( Block *b ) {

   // Copies are still "virtual" - meaning we have not made them explicitly

   // copies.  Instead, Phi functions of successor blocks have mis-matched

   // live-ranges.  If I fail to coalesce, I'll have to insert a copy to line

   // up the live-ranges.  Check for Phis in successor blocks.

   uint i;

   for( i=0; i<b->_num_succs; i++ ) {

     Block *bs = b->_succs[i];

     // Find index of 'b' in 'bs' predecessors

     uint j=1;

     while (_phc._cfg.get_block_for_node(bs->pred(j)) != b) {

       j++;

     }

     // Visit all the Phis in successor block

     for( uint k = 1; k<bs->number_of_nodes(); k++ ) {

       Node *n = bs->get_node(k);

       if( !n->is_Phi() ) break;

       combine_these_two( n, n->in(j) );

     }

   } // End of for all successor blocks

   // Check _this_ block for 2-address instructions and copies.

   uint cnt = b->end_idx();

   for( i = 1; i<cnt; i++ ) {

     Node *n = b->get_node(i);

     uint idx;

     // 2-address instructions have a virtual Copy matching their input

     // to their output

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

       MachNode *mach = n->as_Mach();

       combine_these_two(mach, mach->in(idx));

     }

   } // End of for all instructions in block

 }

 PhaseConservativeCoalesce::PhaseConservativeCoalesce(PhaseChaitin &chaitin) : PhaseCoalesce(chaitin) {

   _ulr.initialize(_phc._lrg_map.max_lrg_id());

 }

 void PhaseConservativeCoalesce::verify() {

 #ifdef ASSERT

   _phc.set_was_low();

 #endif

 }

 void PhaseConservativeCoalesce::union_helper( Node *lr1_node, Node *lr2_node, uint lr1, uint lr2, Node *src_def, Node *dst_copy, Node *src_copy, Block *b, uint bindex ) {

   // Join live ranges.  Merge larger into smaller.  Union lr2 into lr1 in the

   // union-find tree

   _phc.Union( lr1_node, lr2_node );

   // Single-def live range ONLY if both live ranges are single-def.

   // If both are single def, then src_def powers one live range

   // and def_copy powers the other.  After merging, src_def powers

   // the combined live range.

   lrgs(lr1)._def = (lrgs(lr1).is_multidef() ||

                         lrgs(lr2).is_multidef() )

     ? NodeSentinel : src_def;

   lrgs(lr2)._def = NULL;    // No def for lrg 2

   lrgs(lr2).Clear();        // Force empty mask for LRG 2

   //lrgs(lr2)._size = 0;      // Live-range 2 goes dead

   lrgs(lr1)._is_oop |= lrgs(lr2)._is_oop;

   lrgs(lr2)._is_oop = 0;    // In particular, not an oop for GC info

   if (lrgs(lr1)._maxfreq < lrgs(lr2)._maxfreq)

     lrgs(lr1)._maxfreq = lrgs(lr2)._maxfreq;

   // Copy original value instead.  Intermediate copies go dead, and

   // the dst_copy becomes useless.

   int didx = dst_copy->is_Copy();

   dst_copy->set_req( didx, src_def );

   // Add copy to free list

   // _phc.free_spillcopy(b->_nodes[bindex]);

   assert( b->get_node(bindex) == dst_copy, "" );

   dst_copy->replace_by( dst_copy->in(didx) );

   dst_copy->set_req( didx, NULL);

   b->remove_node(bindex);

   if( bindex < b->_ihrp_index ) b->_ihrp_index--;

   if( bindex < b->_fhrp_index ) b->_fhrp_index--;

   // Stretched lr1; add it to liveness of intermediate blocks

   Block *b2 = _phc._cfg.get_block_for_node(src_copy);

   while( b != b2 ) {

     b = _phc._cfg.get_block_for_node(b->pred(1));

     _phc._live->live(b)->insert(lr1);

   }

 }

 // Factored code from copy_copy that computes extra interferences from

 // lengthening a live range by double-coalescing.

 uint PhaseConservativeCoalesce::compute_separating_interferences(Node *dst_copy, Node *src_copy, Block *b, uint bindex, RegMask &rm, uint reg_degree, uint rm_size, uint lr1, uint lr2 ) {

   assert(!lrgs(lr1)._fat_proj, "cannot coalesce fat_proj");

   assert(!lrgs(lr2)._fat_proj, "cannot coalesce fat_proj");

   Node *prev_copy = dst_copy->in(dst_copy->is_Copy());

   Block *b2 = b;

   uint bindex2 = bindex;

   while( 1 ) {

     // Find previous instruction

     bindex2--;                  // Chain backwards 1 instruction

     while( bindex2 == 0 ) {     // At block start, find prior block

       assert( b2->num_preds() == 2, "cannot double coalesce across c-flow" );

       b2 = _phc._cfg.get_block_for_node(b2->pred(1));

       bindex2 = b2->end_idx()-1;

     }

     // Get prior instruction

     assert(bindex2 < b2->number_of_nodes(), "index out of bounds");

     Node *x = b2->get_node(bindex2);

     if( x == prev_copy ) {      // Previous copy in copy chain?

       if( prev_copy == src_copy)// Found end of chain and all interferences

         break;                  // So break out of loop

       // Else work back one in copy chain

       prev_copy = prev_copy->in(prev_copy->is_Copy());

     } else {                    // Else collect interferences

       uint lidx = _phc._lrg_map.find(x);

       // Found another def of live-range being stretched?

       if(lidx == lr1) {

         return max_juint;

       }

       if(lidx == lr2) {

         return max_juint;

       }

       // If we attempt to coalesce across a bound def

       if( lrgs(lidx).is_bound() ) {

         // Do not let the coalesced LRG expect to get the bound color

         rm.SUBTRACT( lrgs(lidx).mask() );

         // Recompute rm_size

         rm_size = rm.Size();

         //if( rm._flags ) rm_size += 1000000;

         if( reg_degree >= rm_size ) return max_juint;

       }

       if( rm.overlap(lrgs(lidx).mask()) ) {

         // Insert lidx into union LRG; returns TRUE if actually inserted

         if( _ulr.insert(lidx) ) {

           // Infinite-stack neighbors do not alter colorability, as they

           // can always color to some other color.

           if( !lrgs(lidx).mask().is_AllStack() ) {

             // If this coalesce will make any new neighbor uncolorable,

             // do not coalesce.

             if( lrgs(lidx).just_lo_degree() )

               return max_juint;

             // Bump our degree

             if( ++reg_degree >= rm_size )

               return max_juint;

           } // End of if not infinite-stack neighbor

         } // End of if actually inserted

       } // End of if live range overlaps

     } // End of else collect interferences for 1 node

   } // End of while forever, scan back for interferences

   return reg_degree;

 }

 void PhaseConservativeCoalesce::update_ifg(uint lr1, uint lr2, IndexSet *n_lr1, IndexSet *n_lr2) {

   // Some original neighbors of lr1 might have gone away

   // because the constrained register mask prevented them.

   // Remove lr1 from such neighbors.

   IndexSetIterator one(n_lr1);

   uint neighbor;

   LRG &lrg1 = lrgs(lr1);

   while ((neighbor = one.next()) != 0)

     if( !_ulr.member(neighbor) )

       if( _phc._ifg->neighbors(neighbor)->remove(lr1) )

         lrgs(neighbor).inc_degree( -lrg1.compute_degree(lrgs(neighbor)) );

   // lr2 is now called (coalesced into) lr1.

   // Remove lr2 from the IFG.

   IndexSetIterator two(n_lr2);

   LRG &lrg2 = lrgs(lr2);

   while ((neighbor = two.next()) != 0)

     if( _phc._ifg->neighbors(neighbor)->remove(lr2) )

       lrgs(neighbor).inc_degree( -lrg2.compute_degree(lrgs(neighbor)) );

   // Some neighbors of intermediate copies now interfere with the

   // combined live range.

   IndexSetIterator three(&_ulr);

   while ((neighbor = three.next()) != 0)

     if( _phc._ifg->neighbors(neighbor)->insert(lr1) )

       lrgs(neighbor).inc_degree( lrg1.compute_degree(lrgs(neighbor)) );

 }

 static void record_bias( const PhaseIFG *ifg, int lr1, int lr2 ) {

   // Tag copy bias here

   if( !ifg->lrgs(lr1)._copy_bias )

     ifg->lrgs(lr1)._copy_bias = lr2;

   if( !ifg->lrgs(lr2)._copy_bias )

     ifg->lrgs(lr2)._copy_bias = lr1;

 }

 // See if I can coalesce a series of multiple copies together.  I need the

 // final dest copy and the original src copy.  They can be the same Node.

 // Compute the compatible register masks.

 bool PhaseConservativeCoalesce::copy_copy(Node *dst_copy, Node *src_copy, Block *b, uint bindex) {

   if (!dst_copy->is_SpillCopy()) {

     return false;

   }

   if (!src_copy->is_SpillCopy()) {

     return false;

   }

   Node *src_def = src_copy->in(src_copy->is_Copy());

   uint lr1 = _phc._lrg_map.find(dst_copy);

   uint lr2 = _phc._lrg_map.find(src_def);

   // Same live ranges already?

   if (lr1 == lr2) {

     return false;

   }

   // Interfere?

   if (_phc._ifg->test_edge_sq(lr1, lr2)) {

     return false;

   }

   // Not an oop->int cast; oop->oop, int->int, AND int->oop are OK.

   if (!lrgs(lr1)._is_oop && lrgs(lr2)._is_oop) { // not an oop->int cast

     return false;

   }

   // Coalescing between an aligned live range and a mis-aligned live range?

   // No, no!  Alignment changes how we count degree.

   if (lrgs(lr1)._fat_proj != lrgs(lr2)._fat_proj) {

     return false;

   }

   // Sort; use smaller live-range number

   Node *lr1_node = dst_copy;

   Node *lr2_node = src_def;

   if (lr1 > lr2) {

     uint tmp = lr1; lr1 = lr2; lr2 = tmp;

     lr1_node = src_def;  lr2_node = dst_copy;

   }

   // Check for compatibility of the 2 live ranges by

   // intersecting their allowed register sets.

   RegMask rm = lrgs(lr1).mask();

   rm.AND(lrgs(lr2).mask());

   // Number of bits free

   uint rm_size = rm.Size();

   if (UseFPUForSpilling && rm.is_AllStack() ) {

     // Don't coalesce when frequency difference is large

     Block *dst_b = _phc._cfg.get_block_for_node(dst_copy);

     Block *src_def_b = _phc._cfg.get_block_for_node(src_def);

     if (src_def_b->_freq > 10*dst_b->_freq )

       return false;

   }

   // If we can use any stack slot, then effective size is infinite

   if( rm.is_AllStack() ) rm_size += 1000000;

   // Incompatible masks, no way to coalesce

   if( rm_size == 0 ) return false;

   // Another early bail-out test is when we are double-coalescing and the

   // 2 copies are separated by some control flow.

   if( dst_copy != src_copy ) {

     Block *src_b = _phc._cfg.get_block_for_node(src_copy);

     Block *b2 = b;

     while( b2 != src_b ) {

       if( b2->num_preds() > 2 ){// Found merge-point

         _phc._lost_opp_cflow_coalesce++;

         // extra record_bias commented out because Chris believes it is not

         // productive.  Since we can record only 1 bias, we want to choose one

         // that stands a chance of working and this one probably does not.

         //record_bias( _phc._lrgs, lr1, lr2 );

         return false;           // To hard to find all interferences

       }

       b2 = _phc._cfg.get_block_for_node(b2->pred(1));

     }

   }

   // Union the two interference sets together into '_ulr'

   uint reg_degree = _ulr.lrg_union( lr1, lr2, rm_size, _phc._ifg, rm );

   if( reg_degree >= rm_size ) {

     record_bias( _phc._ifg, lr1, lr2 );

     return false;

   }

   // Now I need to compute all the interferences between dst_copy and

   // src_copy.  I'm not willing visit the entire interference graph, so

   // I limit my search to things in dst_copy's block or in a straight

   // line of previous blocks.  I give up at merge points or when I get

   // more interferences than my degree.  I can stop when I find src_copy.

   if( dst_copy != src_copy ) {

     reg_degree = compute_separating_interferences(dst_copy, src_copy, b, bindex, rm, rm_size, reg_degree, lr1, lr2 );

     if( reg_degree == max_juint ) {

       record_bias( _phc._ifg, lr1, lr2 );

       return false;

     }

   } // End of if dst_copy & src_copy are different

   // ---- THE COMBINED LRG IS COLORABLE ----

   // YEAH - Now coalesce this copy away

   assert( lrgs(lr1).num_regs() == lrgs(lr2).num_regs(),   "" );

   IndexSet *n_lr1 = _phc._ifg->neighbors(lr1);

   IndexSet *n_lr2 = _phc._ifg->neighbors(lr2);

   // Update the interference graph

   update_ifg(lr1, lr2, n_lr1, n_lr2);

   _ulr.remove(lr1);

   // Uncomment the following code to trace Coalescing in great detail.

   //

   //if (false) {

   //  tty->cr();

   //  tty->print_cr("#######################################");

   //  tty->print_cr("union %d and %d", lr1, lr2);

   //  n_lr1->dump();

   //  n_lr2->dump();

   //  tty->print_cr("resulting set is");

   //  _ulr.dump();

   //}

   // Replace n_lr1 with the new combined live range.  _ulr will use

   // n_lr1's old memory on the next iteration.  n_lr2 is cleared to

   // send its internal memory to the free list.

   _ulr.swap(n_lr1);

   _ulr.clear();

   n_lr2->clear();

   lrgs(lr1).set_degree( _phc._ifg->effective_degree(lr1) );

   lrgs(lr2).set_degree( 0 );

   // Join live ranges.  Merge larger into smaller.  Union lr2 into lr1 in the

   // union-find tree

   union_helper( lr1_node, lr2_node, lr1, lr2, src_def, dst_copy, src_copy, b, bindex );

   // Combine register restrictions

   lrgs(lr1).set_mask(rm);

   lrgs(lr1).compute_set_mask_size();

   lrgs(lr1)._cost += lrgs(lr2)._cost;

   lrgs(lr1)._area += lrgs(lr2)._area;

   // While its uncommon to successfully coalesce live ranges that started out

   // being not-lo-degree, it can happen.  In any case the combined coalesced

   // live range better Simplify nicely.

   lrgs(lr1)._was_lo = 1;

   // kinda expensive to do all the time

   //tty->print_cr("warning: slow verify happening");

   //_phc._ifg->verify( &_phc );

   return true;

 }

 // Conservative (but pessimistic) copy coalescing of a single block

 void PhaseConservativeCoalesce::coalesce( Block *b ) {

   // Bail out on infrequent blocks

   if (_phc._cfg.is_uncommon(b)) {

     return;

   }

   // Check this block for copies.

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

     // Check for actual copies on inputs.  Coalesce a copy into its

     // input if use and copy's input are compatible.

     Node *copy1 = b->get_node(i);

     uint idx1 = copy1->is_Copy();

     if( !idx1 ) continue;       // Not a copy

     if( copy_copy(copy1,copy1,b,i) ) {

       i--;                      // Retry, same location in block

       PhaseChaitin::_conserv_coalesce++;  // Collect stats on success

       continue;

     }

   }

 }