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

 /*

  * Copyright (c) 1997, 2014, 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

  * questions.

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  */

 #include "precompiled.hpp"

 #include "libadt/vectset.hpp"

 #include "memory/allocation.inline.hpp"

 #include "opto/block.hpp"

 #include "opto/cfgnode.hpp"

 #include "opto/chaitin.hpp"

 #include "opto/loopnode.hpp"

 #include "opto/machnode.hpp"

 #include "opto/matcher.hpp"

 #include "opto/opcodes.hpp"

 #include "opto/rootnode.hpp"

 #include "utilities/copy.hpp"

 void Block_Array::grow( uint i ) {

   assert(i >= Max(), "must be an overflow");

   debug_only(_limit = i+1);

   if( i < _size )  return;

   if( !_size ) {

     _size = 1;

     _blocks = (Block**)_arena->Amalloc( _size * sizeof(Block*) );

     _blocks[0] = NULL;

   }

   uint old = _size;

   while( i >= _size ) _size <<= 1;      // Double to fit

   _blocks = (Block**)_arena->Arealloc( _blocks, old*sizeof(Block*),_size*sizeof(Block*));

   Copy::zero_to_bytes( &_blocks[old], (_size-old)*sizeof(Block*) );

 }

 void Block_List::remove(uint i) {

   assert(i < _cnt, "index out of bounds");

   Copy::conjoint_words_to_lower((HeapWord*)&_blocks[i+1], (HeapWord*)&_blocks[i], ((_cnt-i-1)*sizeof(Block*)));

   pop(); // shrink list by one block

 }

 void Block_List::insert(uint i, Block *b) {

   push(b); // grow list by one block

   Copy::conjoint_words_to_higher((HeapWord*)&_blocks[i], (HeapWord*)&_blocks[i+1], ((_cnt-i-1)*sizeof(Block*)));

   _blocks[i] = b;

 }

 #ifndef PRODUCT

 void Block_List::print() {

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

     tty->print("B%d ", _blocks[i]->_pre_order);

   }

   tty->print("size = %d\n", size());

 }

 #endif

 uint Block::code_alignment() {

   // Check for Root block

   if (_pre_order == 0) return CodeEntryAlignment;

   // Check for Start block

   if (_pre_order == 1) return InteriorEntryAlignment;

   // Check for loop alignment

   if (has_loop_alignment()) return loop_alignment();

   return relocInfo::addr_unit(); // no particular alignment

 }

 uint Block::compute_loop_alignment() {

   Node *h = head();

   int unit_sz = relocInfo::addr_unit();

   if (h->is_Loop() && h->as_Loop()->is_inner_loop())  {

     // Pre- and post-loops have low trip count so do not bother with

     // NOPs for align loop head.  The constants are hidden from tuning

     // but only because my "divide by 4" heuristic surely gets nearly

     // all possible gain (a "do not align at all" heuristic has a

     // chance of getting a really tiny gain).

     if (h->is_CountedLoop() && (h->as_CountedLoop()->is_pre_loop() ||

                                 h->as_CountedLoop()->is_post_loop())) {

       return (OptoLoopAlignment > 4*unit_sz) ? (OptoLoopAlignment>>2) : unit_sz;

     }

     // Loops with low backedge frequency should not be aligned.

     Node *n = h->in(LoopNode::LoopBackControl)->in(0);

     if (n->is_MachIf() && n->as_MachIf()->_prob < 0.01) {

       return unit_sz; // Loop does not loop, more often than not!

     }

     return OptoLoopAlignment; // Otherwise align loop head

   }

   return unit_sz; // no particular alignment

 }

 // Compute the size of first 'inst_cnt' instructions in this block.

 // Return the number of instructions left to compute if the block has

 // less then 'inst_cnt' instructions. Stop, and return 0 if sum_size

 // exceeds OptoLoopAlignment.

 uint Block::compute_first_inst_size(uint& sum_size, uint inst_cnt,

                                     PhaseRegAlloc* ra) {

   uint last_inst = number_of_nodes();

   for( uint j = 0; j < last_inst && inst_cnt > 0; j++ ) {

     uint inst_size = get_node(j)->size(ra);

     if( inst_size > 0 ) {

       inst_cnt--;

       uint sz = sum_size + inst_size;

       if( sz <= (uint)OptoLoopAlignment ) {

         // Compute size of instructions which fit into fetch buffer only

         // since all inst_cnt instructions will not fit even if we align them.

         sum_size = sz;

       } else {

         return 0;

       }

     }

   }

   return inst_cnt;

 }

 uint Block::find_node( const Node *n ) const {

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

     if( get_node(i) == n )

       return i;

   }

   ShouldNotReachHere();

   return 0;

 }

 // Find and remove n from block list

 void Block::find_remove( const Node *n ) {

   remove_node(find_node(n));

 }

 bool Block::contains(const Node *n) const {

   return _nodes.contains(n);

 }

 // Return empty status of a block.  Empty blocks contain only the head, other

 // ideal nodes, and an optional trailing goto.

 int Block::is_Empty() const {

   // Root or start block is not considered empty

   if (head()->is_Root() || head()->is_Start()) {

     return not_empty;

   }

   int success_result = completely_empty;

   int end_idx = number_of_nodes() - 1;

   // Check for ending goto

   if ((end_idx > 0) && (get_node(end_idx)->is_MachGoto())) {

     success_result = empty_with_goto;

     end_idx--;

   }

   // Unreachable blocks are considered empty

   if (num_preds() <= 1) {

     return success_result;

   }

   // Ideal nodes are allowable in empty blocks: skip them  Only MachNodes

   // turn directly into code, because only MachNodes have non-trivial

   // emit() functions.

   while ((end_idx > 0) && !get_node(end_idx)->is_Mach()) {

     end_idx--;

   }

   // No room for any interesting instructions?

   if (end_idx == 0) {

     return success_result;

   }

   return not_empty;

 }

 // Return true if the block's code implies that it is likely to be

 // executed infrequently.  Check to see if the block ends in a Halt or

 // a low probability call.

 bool Block::has_uncommon_code() const {

   Node* en = end();

   if (en->is_MachGoto())

     en = en->in(0);

   if (en->is_Catch())

     en = en->in(0);

   if (en->is_MachProj() && en->in(0)->is_MachCall()) {

     MachCallNode* call = en->in(0)->as_MachCall();

     if (call->cnt() != COUNT_UNKNOWN && call->cnt() <= PROB_UNLIKELY_MAG(4)) {

       // This is true for slow-path stubs like new_{instance,array},

       // slow_arraycopy, complete_monitor_locking, uncommon_trap.

       // The magic number corresponds to the probability of an uncommon_trap,

       // even though it is a count not a probability.

       return true;

     }

   }

   int op = en->is_Mach() ? en->as_Mach()->ideal_Opcode() : en->Opcode();

   return op == Op_Halt;

 }

 // True if block is low enough frequency or guarded by a test which

 // mostly does not go here.

 bool PhaseCFG::is_uncommon(const Block* block) {

   // Initial blocks must never be moved, so are never uncommon.

   if (block->head()->is_Root() || block->head()->is_Start())  return false;

   // Check for way-low freq

   if(block->_freq < BLOCK_FREQUENCY(0.00001f) ) return true;

   // Look for code shape indicating uncommon_trap or slow path

   if (block->has_uncommon_code()) return true;

   const float epsilon = 0.05f;

   const float guard_factor = PROB_UNLIKELY_MAG(4) / (1.f - epsilon);

   uint uncommon_preds = 0;

   uint freq_preds = 0;

   uint uncommon_for_freq_preds = 0;

   for( uint i=1; i< block->num_preds(); i++ ) {

     Block* guard = get_block_for_node(block->pred(i));

     // Check to see if this block follows its guard 1 time out of 10000

     // or less.

     //

     // See list of magnitude-4 unlikely probabilities in cfgnode.hpp which

     // we intend to be "uncommon", such as slow-path TLE allocation,

     // predicted call failure, and uncommon trap triggers.

     //

     // Use an epsilon value of 5% to allow for variability in frequency

     // predictions and floating point calculations. The net effect is

     // that guard_factor is set to 9500.

     //

     // Ignore low-frequency blocks.

     // The next check is (guard->_freq < 1.e-5 * 9500.).

     if(guard->_freq*BLOCK_FREQUENCY(guard_factor) < BLOCK_FREQUENCY(0.00001f)) {

       uncommon_preds++;

     } else {

       freq_preds++;

       if(block->_freq < guard->_freq * guard_factor ) {

         uncommon_for_freq_preds++;

       }

     }

   }

   if( block->num_preds() > 1 &&

       // The block is uncommon if all preds are uncommon or

       (uncommon_preds == (block->num_preds()-1) ||

       // it is uncommon for all frequent preds.

        uncommon_for_freq_preds == freq_preds) ) {

     return true;

   }

   return false;

 }

 #ifndef PRODUCT

 void Block::dump_bidx(const Block* orig, outputStream* st) const {

   if (_pre_order) st->print("B%d",_pre_order);

   else st->print("N%d", head()->_idx);

   if (Verbose && orig != this) {

     // Dump the original block's idx

     st->print(" (");

     orig->dump_bidx(orig, st);

     st->print(")");

   }

 }

 void Block::dump_pred(const PhaseCFG* cfg, Block* orig, outputStream* st) const {

   if (is_connector()) {

     for (uint i=1; i<num_preds(); i++) {

       Block *p = cfg->get_block_for_node(pred(i));

       p->dump_pred(cfg, orig, st);

     }

   } else {

     dump_bidx(orig, st);

     st->print(" ");

   }

 }

 void Block::dump_head(const PhaseCFG* cfg, outputStream* st) const {

   // Print the basic block

   dump_bidx(this, st);

   st->print(": #\t");

   // Print the incoming CFG edges and the outgoing CFG edges

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

     non_connector_successor(i)->dump_bidx(_succs[i], st);

     st->print(" ");

   }

   st->print("<- ");

   if( head()->is_block_start() ) {

     for (uint i=1; i<num_preds(); i++) {

       Node *s = pred(i);

       if (cfg != NULL) {

         Block *p = cfg->get_block_for_node(s);

         p->dump_pred(cfg, p, st);

       } else {

         while (!s->is_block_start())

           s = s->in(0);

         st->print("N%d ", s->_idx );

       }

     }

   } else {

     st->print("BLOCK HEAD IS JUNK  ");

   }

   // Print loop, if any

   const Block *bhead = this;    // Head of self-loop

   Node *bh = bhead->head();

   if ((cfg != NULL) && bh->is_Loop() && !head()->is_Root()) {

     LoopNode *loop = bh->as_Loop();

     const Block *bx = cfg->get_block_for_node(loop->in(LoopNode::LoopBackControl));

     while (bx->is_connector()) {

       bx = cfg->get_block_for_node(bx->pred(1));

     }

     st->print("\tLoop: B%d-B%d ", bhead->_pre_order, bx->_pre_order);

     // Dump any loop-specific bits, especially for CountedLoops.

     loop->dump_spec(st);

   } else if (has_loop_alignment()) {

     st->print(" top-of-loop");

   }

   st->print(" Freq: %g",_freq);

   if( Verbose || WizardMode ) {

     st->print(" IDom: %d/#%d", _idom ? _idom->_pre_order : 0, _dom_depth);

     st->print(" RegPressure: %d",_reg_pressure);

     st->print(" IHRP Index: %d",_ihrp_index);

     st->print(" FRegPressure: %d",_freg_pressure);

     st->print(" FHRP Index: %d",_fhrp_index);

   }

   st->cr();

 }

 void Block::dump() const {

   dump(NULL);

 }

 void Block::dump(const PhaseCFG* cfg) const {

   dump_head(cfg);

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

     get_node(i)->dump();

   }

   tty->print("\n");

 }

 #endif

 PhaseCFG::PhaseCFG(Arena* arena, RootNode* root, Matcher& matcher)

 : Phase(CFG)

 , _block_arena(arena)

 , _root(root)

 , _matcher(matcher)

 , _node_to_block_mapping(arena)

 , _node_latency(NULL)

 #ifndef PRODUCT

 , _trace_opto_pipelining(TraceOptoPipelining || C->method_has_option("TraceOptoPipelining"))

 #endif

 #ifdef ASSERT

 , _raw_oops(arena)

 #endif

 {

   ResourceMark rm;

   // I'll need a few machine-specific GotoNodes.  Make an Ideal GotoNode,

   // then Match it into a machine-specific Node.  Then clone the machine

   // Node on demand.

   Node *x = new (C) GotoNode(NULL);

   x->init_req(0, x);

   _goto = matcher.match_tree(x);

   assert(_goto != NULL, "");

   _goto->set_req(0,_goto);

   // Build the CFG in Reverse Post Order

   _number_of_blocks = build_cfg();

   _root_block = get_block_for_node(_root);

 }

 // Build a proper looking CFG.  Make every block begin with either a StartNode

 // or a RegionNode.  Make every block end with either a Goto, If or Return.

 // The RootNode both starts and ends it's own block.  Do this with a recursive

 // backwards walk over the control edges.

 uint PhaseCFG::build_cfg() {

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

   VectorSet visited(a);

   // Allocate stack with enough space to avoid frequent realloc

   Node_Stack nstack(a, C->unique() >> 1);

   nstack.push(_root, 0);

   uint sum = 0;                 // Counter for blocks

   while (nstack.is_nonempty()) {

     // node and in's index from stack's top

     // 'np' is _root (see above) or RegionNode, StartNode: we push on stack

     // only nodes which point to the start of basic block (see below).

     Node *np = nstack.node();

     // idx > 0, except for the first node (_root) pushed on stack

     // at the beginning when idx == 0.

     // We will use the condition (idx == 0) later to end the build.

     uint idx = nstack.index();

     Node *proj = np->in(idx);

     const Node *x = proj->is_block_proj();

     // Does the block end with a proper block-ending Node?  One of Return,

     // If or Goto? (This check should be done for visited nodes also).

     if (x == NULL) {                    // Does not end right...

       Node *g = _goto->clone(); // Force it to end in a Goto

       g->set_req(0, proj);

       np->set_req(idx, g);

       x = proj = g;

     }

     if (!visited.test_set(x->_idx)) { // Visit this block once

       // Skip any control-pinned middle'in stuff

       Node *p = proj;

       do {

         proj = p;                   // Update pointer to last Control

         p = p->in(0);               // Move control forward

       } while( !p->is_block_proj() &&

                !p->is_block_start() );

       // Make the block begin with one of Region or StartNode.

       if( !p->is_block_start() ) {

         RegionNode *r = new (C) RegionNode( 2 );

         r->init_req(1, p);         // Insert RegionNode in the way

         proj->set_req(0, r);        // Insert RegionNode in the way

         p = r;

       }

       // 'p' now points to the start of this basic block

       // Put self in array of basic blocks

       Block *bb = new (_block_arena) Block(_block_arena, p);

       map_node_to_block(p, bb);

       map_node_to_block(x, bb);

       if( x != p ) {                // Only for root is x == p

         bb->push_node((Node*)x);

       }

       // Now handle predecessors

       ++sum;                        // Count 1 for self block

       uint cnt = bb->num_preds();

       for (int i = (cnt - 1); i > 0; i-- ) { // For all predecessors

         Node *prevproj = p->in(i);  // Get prior input

         assert( !prevproj->is_Con(), "dead input not removed" );

         // Check to see if p->in(i) is a "control-dependent" CFG edge -

         // i.e., it splits at the source (via an IF or SWITCH) and merges

         // at the destination (via a many-input Region).

         // This breaks critical edges.  The RegionNode to start the block

         // will be added when <p,i> is pulled off the node stack

         if ( cnt > 2 ) {             // Merging many things?

           assert( prevproj== bb->pred(i),"");

           if(prevproj->is_block_proj() != prevproj) { // Control-dependent edge?

             // Force a block on the control-dependent edge

             Node *g = _goto->clone();       // Force it to end in a Goto

             g->set_req(0,prevproj);

             p->set_req(i,g);

           }

         }

         nstack.push(p, i);  // 'p' is RegionNode or StartNode

       }

     } else { // Post-processing visited nodes

       nstack.pop();                 // remove node from stack

       // Check if it the fist node pushed on stack at the beginning.

       if (idx == 0) break;          // end of the build

       // Find predecessor basic block

       Block *pb = get_block_for_node(x);

       // Insert into nodes array, if not already there

       if (!has_block(proj)) {

         assert( x != proj, "" );

         // Map basic block of projection

         map_node_to_block(proj, pb);

         pb->push_node(proj);

       }

       // Insert self as a child of my predecessor block

       pb->_succs.map(pb->_num_succs++, get_block_for_node(np));

       assert( pb->get_node(pb->number_of_nodes() - pb->_num_succs)->is_block_proj(),

               "too many control users, not a CFG?" );

     }

   }

   // Return number of basic blocks for all children and self

   return sum;

 }

 // Inserts a goto & corresponding basic block between

 // block[block_no] and its succ_no'th successor block

 void PhaseCFG::insert_goto_at(uint block_no, uint succ_no) {

   // get block with block_no

   assert(block_no < number_of_blocks(), "illegal block number");

   Block* in  = get_block(block_no);

   // get successor block succ_no

   assert(succ_no < in->_num_succs, "illegal successor number");

   Block* out = in->_succs[succ_no];

   // Compute frequency of the new block. Do this before inserting

   // new block in case succ_prob() needs to infer the probability from

   // surrounding blocks.

   float freq = in->_freq * in->succ_prob(succ_no);

   // get ProjNode corresponding to the succ_no'th successor of the in block

   ProjNode* proj = in->get_node(in->number_of_nodes() - in->_num_succs + succ_no)->as_Proj();

   // create region for basic block

   RegionNode* region = new (C) RegionNode(2);

   region->init_req(1, proj);

   // setup corresponding basic block

   Block* block = new (_block_arena) Block(_block_arena, region);

   map_node_to_block(region, block);

   C->regalloc()->set_bad(region->_idx);

   // add a goto node

   Node* gto = _goto->clone(); // get a new goto node

   gto->set_req(0, region);

   // add it to the basic block

   block->push_node(gto);

   map_node_to_block(gto, block);

   C->regalloc()->set_bad(gto->_idx);

   // hook up successor block

   block->_succs.map(block->_num_succs++, out);

   // remap successor's predecessors if necessary

   for (uint i = 1; i < out->num_preds(); i++) {

     if (out->pred(i) == proj) out->head()->set_req(i, gto);

   }

   // remap predecessor's successor to new block

   in->_succs.map(succ_no, block);

   // Set the frequency of the new block

   block->_freq = freq;

   // add new basic block to basic block list

   add_block_at(block_no + 1, block);

 }

 // Does this block end in a multiway branch that cannot have the default case

 // flipped for another case?

 static bool no_flip_branch(Block *b) {

   int branch_idx = b->number_of_nodes() - b->_num_succs-1;

   if (branch_idx < 1) {

     return false;

   }

   Node *branch = b->get_node(branch_idx);

   if (branch->is_Catch()) {

     return true;

   }

   if (branch->is_Mach()) {

     if (branch->is_MachNullCheck()) {

       return true;

     }

     int iop = branch->as_Mach()->ideal_Opcode();

     if (iop == Op_FastLock || iop == Op_FastUnlock) {

       return true;

     }

     // Don't flip if branch has an implicit check.

     if (branch->as_Mach()->is_TrapBasedCheckNode()) {

       return true;

     }

   }

   return false;

 }

 // Check for NeverBranch at block end.  This needs to become a GOTO to the

 // true target.  NeverBranch are treated as a conditional branch that always

 // goes the same direction for most of the optimizer and are used to give a

 // fake exit path to infinite loops.  At this late stage they need to turn

 // into Goto's so that when you enter the infinite loop you indeed hang.

 void PhaseCFG::convert_NeverBranch_to_Goto(Block *b) {

   // Find true target

   int end_idx = b->end_idx();

   int idx = b->get_node(end_idx+1)->as_Proj()->_con;

   Block *succ = b->_succs[idx];

   Node* gto = _goto->clone(); // get a new goto node

   gto->set_req(0, b->head());

   Node *bp = b->get_node(end_idx);

   b->map_node(gto, end_idx); // Slam over NeverBranch

   map_node_to_block(gto, b);

   C->regalloc()->set_bad(gto->_idx);

   b->pop_node();              // Yank projections

   b->pop_node();              // Yank projections

   b->_succs.map(0,succ);        // Map only successor

   b->_num_succs = 1;

   // remap successor's predecessors if necessary

   uint j;

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

     if( succ->pred(j)->in(0) == bp )

       succ->head()->set_req(j, gto);

   // Kill alternate exit path

   Block *dead = b->_succs[1-idx];

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

     if( dead->pred(j)->in(0) == bp )

       break;

   // Scan through block, yanking dead path from

   // all regions and phis.

   dead->head()->del_req(j);

   for( int k = 1; dead->get_node(k)->is_Phi(); k++ )

     dead->get_node(k)->del_req(j);

 }

 // Helper function to move block bx to the slot following b_index. Return

 // true if the move is successful, otherwise false

 bool PhaseCFG::move_to_next(Block* bx, uint b_index) {

   if (bx == NULL) return false;

   // Return false if bx is already scheduled.

   uint bx_index = bx->_pre_order;

   if ((bx_index <= b_index) && (get_block(bx_index) == bx)) {

     return false;

   }

   // Find the current index of block bx on the block list

   bx_index = b_index + 1;

   while (bx_index < number_of_blocks() && get_block(bx_index) != bx) {

     bx_index++;

   }

   assert(get_block(bx_index) == bx, "block not found");

   // If the previous block conditionally falls into bx, return false,

   // because moving bx will create an extra jump.

   for(uint k = 1; k < bx->num_preds(); k++ ) {

     Block* pred = get_block_for_node(bx->pred(k));

     if (pred == get_block(bx_index - 1)) {

       if (pred->_num_succs != 1) {

         return false;

       }

     }

   }

   // Reinsert bx just past block 'b'

   _blocks.remove(bx_index);

   _blocks.insert(b_index + 1, bx);

   return true;

 }

 // Move empty and uncommon blocks to the end.

 void PhaseCFG::move_to_end(Block *b, uint i) {

   int e = b->is_Empty();

   if (e != Block::not_empty) {

     if (e == Block::empty_with_goto) {

       // Remove the goto, but leave the block.

       b->pop_node();

     }

     // Mark this block as a connector block, which will cause it to be

     // ignored in certain functions such as non_connector_successor().

     b->set_connector();

   }

   // Move the empty block to the end, and don't recheck.

   _blocks.remove(i);

   _blocks.push(b);

 }

 // Set loop alignment for every block

 void PhaseCFG::set_loop_alignment() {

   uint last = number_of_blocks();

   assert(get_block(0) == get_root_block(), "");

   for (uint i = 1; i < last; i++) {

     Block* block = get_block(i);

     if (block->head()->is_Loop()) {

       block->set_loop_alignment(block);

     }

   }

 }

 // Make empty basic blocks to be "connector" blocks, Move uncommon blocks

 // to the end.

 void PhaseCFG::remove_empty_blocks() {

   // Move uncommon blocks to the end

   uint last = number_of_blocks();

   assert(get_block(0) == get_root_block(), "");

   for (uint i = 1; i < last; i++) {

     Block* block = get_block(i);

     if (block->is_connector()) {

       break;

     }

     // Check for NeverBranch at block end.  This needs to become a GOTO to the

     // true target.  NeverBranch are treated as a conditional branch that

     // always goes the same direction for most of the optimizer and are used

     // to give a fake exit path to infinite loops.  At this late stage they

     // need to turn into Goto's so that when you enter the infinite loop you

     // indeed hang.

     if (block->get_node(block->end_idx())->Opcode() == Op_NeverBranch) {

       convert_NeverBranch_to_Goto(block);

     }

     // Look for uncommon blocks and move to end.

     if (!C->do_freq_based_layout()) {

       if (is_uncommon(block)) {

         move_to_end(block, i);

         last--;                   // No longer check for being uncommon!

         if (no_flip_branch(block)) { // Fall-thru case must follow?

           // Find the fall-thru block

           block = get_block(i);

           move_to_end(block, i);

           last--;

         }

         // backup block counter post-increment

         i--;

       }

     }

   }

   // Move empty blocks to the end

   last = number_of_blocks();

   for (uint i = 1; i < last; i++) {

     Block* block = get_block(i);

     if (block->is_Empty() != Block::not_empty) {

       move_to_end(block, i);

       last--;

       i--;

     }

   } // End of for all blocks

 }

 Block *PhaseCFG::fixup_trap_based_check(Node *branch, Block *block, int block_pos, Block *bnext) {

   // Trap based checks must fall through to the successor with

   // PROB_ALWAYS.

   // They should be an If with 2 successors.

   assert(branch->is_MachIf(),   "must be If");

   assert(block->_num_succs == 2, "must have 2 successors");

   // Get the If node and the projection for the first successor.

   MachIfNode *iff   = block->get_node(block->number_of_nodes()-3)->as_MachIf();

   ProjNode   *proj0 = block->get_node(block->number_of_nodes()-2)->as_Proj();

   ProjNode   *proj1 = block->get_node(block->number_of_nodes()-1)->as_Proj();

   ProjNode   *projt = (proj0->Opcode() == Op_IfTrue)  ? proj0 : proj1;

   ProjNode   *projf = (proj0->Opcode() == Op_IfFalse) ? proj0 : proj1;

   // Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].

   assert(proj0->raw_out(0) == block->_succs[0]->head(), "Mismatch successor 0");

   assert(proj1->raw_out(0) == block->_succs[1]->head(), "Mismatch successor 1");

   ProjNode *proj_always;

   ProjNode *proj_never;

   // We must negate the branch if the implicit check doesn't follow

   // the branch's TRUE path. Then, the new TRUE branch target will

   // be the old FALSE branch target.

   if (iff->_prob <= 2*PROB_NEVER) {   // There are small rounding errors.

     proj_never  = projt;

     proj_always = projf;

   } else {

     // We must negate the branch if the trap doesn't follow the

     // branch's TRUE path. Then, the new TRUE branch target will

     // be the old FALSE branch target.

     proj_never  = projf;

     proj_always = projt;

     iff->negate();

   }

   assert(iff->_prob <= 2*PROB_NEVER, "Trap based checks are expected to trap never!");

   // Map the successors properly

   block->_succs.map(0, get_block_for_node(proj_never ->raw_out(0)));   // The target of the trap.

   block->_succs.map(1, get_block_for_node(proj_always->raw_out(0)));   // The fall through target.

   if (block->get_node(block->number_of_nodes() - block->_num_succs + 1) != proj_always) {

     block->map_node(proj_never,  block->number_of_nodes() - block->_num_succs + 0);

     block->map_node(proj_always, block->number_of_nodes() - block->_num_succs + 1);

   }

   // Place the fall through block after this block.

   Block *bs1 = block->non_connector_successor(1);

   if (bs1 != bnext && move_to_next(bs1, block_pos)) {

     bnext = bs1;

   }

   // If the fall through block still is not the next block, insert a goto.

   if (bs1 != bnext) {

     insert_goto_at(block_pos, 1);

   }

   return bnext;

 }

 // Fix up the final control flow for basic blocks.

 void PhaseCFG::fixup_flow() {

   // Fixup final control flow for the blocks.  Remove jump-to-next

   // block. If neither arm of an IF follows the conditional branch, we

   // have to add a second jump after the conditional.  We place the

   // TRUE branch target in succs[0] for both GOTOs and IFs.

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

     Block* block = get_block(i);

     block->_pre_order = i;          // turn pre-order into block-index

     // Connector blocks need no further processing.

     if (block->is_connector()) {

       assert((i+1) == number_of_blocks() || get_block(i + 1)->is_connector(), "All connector blocks should sink to the end");

       continue;

     }

     assert(block->is_Empty() != Block::completely_empty, "Empty blocks should be connectors");

     Block* bnext = (i < number_of_blocks() - 1) ? get_block(i + 1) : NULL;

     Block* bs0 = block->non_connector_successor(0);

     // Check for multi-way branches where I cannot negate the test to

     // exchange the true and false targets.

     if (no_flip_branch(block)) {

       // Find fall through case - if must fall into its target.

       // Get the index of the branch's first successor.

       int branch_idx = block->number_of_nodes() - block->_num_succs;

       // The branch is 1 before the branch's first successor.

       Node *branch = block->get_node(branch_idx-1);

       // Handle no-flip branches which have implicit checks and which require

       // special block ordering and individual semantics of the 'fall through

       // case'.

       if ((TrapBasedNullChecks || TrapBasedRangeChecks) &&

           branch->is_Mach() && branch->as_Mach()->is_TrapBasedCheckNode()) {

         bnext = fixup_trap_based_check(branch, block, i, bnext);

       } else {

         // Else, default handling for no-flip branches

         for (uint j2 = 0; j2 < block->_num_succs; j2++) {

           const ProjNode* p = block->get_node(branch_idx + j2)->as_Proj();

           if (p->_con == 0) {

             // successor j2 is fall through case

             if (block->non_connector_successor(j2) != bnext) {

               // but it is not the next block => insert a goto

               insert_goto_at(i, j2);

             }

             // Put taken branch in slot 0

             if (j2 == 0 && block->_num_succs == 2) {

               // Flip targets in succs map

               Block *tbs0 = block->_succs[0];

               Block *tbs1 = block->_succs[1];

               block->_succs.map(0, tbs1);

               block->_succs.map(1, tbs0);

             }

             break;

           }

         }

       }

       // Remove all CatchProjs

       for (uint j = 0; j < block->_num_succs; j++) {

         block->pop_node();

       }

     } else if (block->_num_succs == 1) {

       // Block ends in a Goto?

       if (bnext == bs0) {

         // We fall into next block; remove the Goto

         block->pop_node();

       }

     } else if(block->_num_succs == 2) { // Block ends in a If?

       // Get opcode of 1st projection (matches _succs[0])

       // Note: Since this basic block has 2 exits, the last 2 nodes must

       //       be projections (in any order), the 3rd last node must be

       //       the IfNode (we have excluded other 2-way exits such as

       //       CatchNodes already).

       MachNode* iff   = block->get_node(block->number_of_nodes() - 3)->as_Mach();

       ProjNode* proj0 = block->get_node(block->number_of_nodes() - 2)->as_Proj();

       ProjNode* proj1 = block->get_node(block->number_of_nodes() - 1)->as_Proj();

       // Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].

       assert(proj0->raw_out(0) == block->_succs[0]->head(), "Mismatch successor 0");

       assert(proj1->raw_out(0) == block->_succs[1]->head(), "Mismatch successor 1");

       Block* bs1 = block->non_connector_successor(1);

       // Check for neither successor block following the current

       // block ending in a conditional. If so, move one of the

       // successors after the current one, provided that the

       // successor was previously unscheduled, but moveable

       // (i.e., all paths to it involve a branch).

       if (!C->do_freq_based_layout() && bnext != bs0 && bnext != bs1) {

         // Choose the more common successor based on the probability

         // of the conditional branch.

         Block* bx = bs0;

         Block* by = bs1;

         // _prob is the probability of taking the true path. Make

         // p the probability of taking successor #1.

         float p = iff->as_MachIf()->_prob;

         if (proj0->Opcode() == Op_IfTrue) {

           p = 1.0 - p;

         }

         // Prefer successor #1 if p > 0.5

         if (p > PROB_FAIR) {

           bx = bs1;

           by = bs0;

         }

         // Attempt the more common successor first

         if (move_to_next(bx, i)) {

           bnext = bx;

         } else if (move_to_next(by, i)) {

           bnext = by;

         }

       }

       // Check for conditional branching the wrong way.  Negate

       // conditional, if needed, so it falls into the following block

       // and branches to the not-following block.

       // Check for the next block being in succs[0].  We are going to branch

       // to succs[0], so we want the fall-thru case as the next block in

       // succs[1].

       if (bnext == bs0) {

         // Fall-thru case in succs[0], so flip targets in succs map

         Block* tbs0 = block->_succs[0];

         Block* tbs1 = block->_succs[1];

         block->_succs.map(0, tbs1);

         block->_succs.map(1, tbs0);

         // Flip projection for each target

         ProjNode* tmp = proj0;

         proj0 = proj1;

         proj1 = tmp;

       } else if(bnext != bs1) {

         // Need a double-branch

         // The existing conditional branch need not change.

         // Add a unconditional branch to the false target.

         // Alas, it must appear in its own block and adding a

         // block this late in the game is complicated.  Sigh.

         insert_goto_at(i, 1);

       }

       // Make sure we TRUE branch to the target

       if (proj0->Opcode() == Op_IfFalse) {

         iff->as_MachIf()->negate();

       }

       block->pop_node();          // Remove IfFalse & IfTrue projections

       block->pop_node();

     } else {

       // Multi-exit block, e.g. a switch statement

       // But we don't need to do anything here

     }

   } // End of for all blocks

 }

 // postalloc_expand: Expand nodes after register allocation.

 //

 // postalloc_expand has to be called after register allocation, just

 // before output (i.e. scheduling). It only gets called if

 // Matcher::require_postalloc_expand is true.

 //

 // Background:

 //

 // Nodes that are expandend (one compound node requiring several

 // assembler instructions to be implemented split into two or more

 // non-compound nodes) after register allocation are not as nice as

 // the ones expanded before register allocation - they don't

 // participate in optimizations as global code motion. But after

 // register allocation we can expand nodes that use registers which

 // are not spillable or registers that are not allocated, because the

 // old compound node is simply replaced (in its location in the basic

 // block) by a new subgraph which does not contain compound nodes any

 // more. The scheduler called during output can later on process these

 // non-compound nodes.

 //

 // Implementation:

 //

 // Nodes requiring postalloc expand are specified in the ad file by using

 // a postalloc_expand statement instead of ins_encode. A postalloc_expand

 // contains a single call to an encoding, as does an ins_encode

 // statement. Instead of an emit() function a postalloc_expand() function

 // is generated that doesn't emit assembler but creates a new

 // subgraph. The code below calls this postalloc_expand function for each

 // node with the appropriate attribute. This function returns the new

 // nodes generated in an array passed in the call. The old node,

 // potential MachTemps before and potential Projs after it then get

 // disconnected and replaced by the new nodes. The instruction

 // generating the result has to be the last one in the array. In

 // general it is assumed that Projs after the node expanded are

 // kills. These kills are not required any more after expanding as

 // there are now explicitly visible def-use chains and the Projs are

 // removed. This does not hold for calls: They do not only have

 // kill-Projs but also Projs defining values. Therefore Projs after

 // the node expanded are removed for all but for calls. If a node is

 // to be reused, it must be added to the nodes list returned, and it

 // will be added again.

 //

 // Implementing the postalloc_expand function for a node in an enc_class

 // is rather tedious. It requires knowledge about many node details, as

 // the nodes and the subgraph must be hand crafted. To simplify this,

 // adlc generates some utility variables into the postalloc_expand function,

 // e.g., holding the operands as specified by the postalloc_expand encoding

 // specification, e.g.:

 //  * unsigned idx_<par_name>  holding the index of the node in the ins

 //  * Node *n_<par_name>       holding the node loaded from the ins

 //  * MachOpnd *op_<par_name>  holding the corresponding operand

 //

 // The ordering of operands can not be determined by looking at a

 // rule. Especially if a match rule matches several different trees,

 // several nodes are generated from one instruct specification with

 // different operand orderings. In this case the adlc generated

 // variables are the only way to access the ins and operands

 // deterministically.

 //

 // If assigning a register to a node that contains an oop, don't

 // forget to call ra_->set_oop() for the node.

 void PhaseCFG::postalloc_expand(PhaseRegAlloc* _ra) {

   GrowableArray <Node *> new_nodes(32); // Array with new nodes filled by postalloc_expand function of node.

   GrowableArray <Node *> remove(32);

   GrowableArray <Node *> succs(32);

   unsigned int max_idx = C->unique();   // Remember to distinguish new from old nodes.

   DEBUG_ONLY(bool foundNode = false);

   // for all blocks

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

     Block *b = _blocks[i];

     // For all instructions in the current block.

     for (uint j = 0; j < b->number_of_nodes(); j++) {

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

       if (n->is_Mach() && n->as_Mach()->requires_postalloc_expand()) {

 #ifdef ASSERT

         if (TracePostallocExpand) {

           if (!foundNode) {

             foundNode = true;

             tty->print("POSTALLOC EXPANDING %d %s\n", C->compile_id(),

                        C->method() ? C->method()->name()->as_utf8() : C->stub_name());

           }

           tty->print("  postalloc expanding "); n->dump();

           if (Verbose) {

             tty->print("    with ins:\n");

             for (uint k = 0; k < n->len(); ++k) {

               if (n->in(k)) { tty->print("        "); n->in(k)->dump(); }

             }

           }

         }

 #endif

         new_nodes.clear();

         // Collect nodes that have to be removed from the block later on.

         uint req = n->req();

         remove.clear();

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

           if (n->in(k) && n->in(k)->is_MachTemp()) {

             remove.push(n->in(k)); // MachTemps which are inputs to the old node have to be removed.

             n->in(k)->del_req(0);

             j--;

           }

         }

         // Check whether we can allocate enough nodes. We set a fix limit for

         // the size of postalloc expands with this.

         uint unique_limit = C->unique() + 40;

         if (unique_limit >= _ra->node_regs_max_index()) {

           Compile::current()->record_failure("out of nodes in postalloc expand");

           return;

         }

         // Emit (i.e. generate new nodes).

         n->as_Mach()->postalloc_expand(&new_nodes, _ra);

         assert(C->unique() < unique_limit, "You allocated too many nodes in your postalloc expand.");

         // Disconnect the inputs of the old node.

         //

         // We reuse MachSpillCopy nodes. If we need to expand them, there

         // are many, so reusing pays off. If reused, the node already

         // has the new ins. n must be the last node on new_nodes list.

         if (!n->is_MachSpillCopy()) {

           for (int k = req - 1; k >= 0; --k) {

             n->del_req(k);

           }

         }

 #ifdef ASSERT

         // Check that all nodes have proper operands.

         for (int k = 0; k < new_nodes.length(); ++k) {

           if (new_nodes.at(k)->_idx < max_idx || !new_nodes.at(k)->is_Mach()) continue; // old node, Proj ...

           MachNode *m = new_nodes.at(k)->as_Mach();

           for (unsigned int l = 0; l < m->num_opnds(); ++l) {

             if (MachOper::notAnOper(m->_opnds[l])) {

               outputStream *os = tty;

               os->print("Node %s ", m->Name());

               os->print("has invalid opnd %d: %p\n", l, m->_opnds[l]);

               assert(0, "Invalid operands, see inline trace in hs_err_pid file.");

             }

           }

         }

 #endif

         // Collect succs of old node in remove (for projections) and in succs (for

         // all other nodes) do _not_ collect projections in remove (but in succs)

         // in case the node is a call. We need the projections for calls as they are

         // associated with registes (i.e. they are defs).

         succs.clear();

         for (DUIterator k = n->outs(); n->has_out(k); k++) {

           if (n->out(k)->is_Proj() && !n->is_MachCall() && !n->is_MachBranch()) {

             remove.push(n->out(k));

           } else {

             succs.push(n->out(k));

           }

         }

         // Replace old node n as input of its succs by last of the new nodes.

         for (int k = 0; k < succs.length(); ++k) {

           Node *succ = succs.at(k);

           for (uint l = 0; l < succ->req(); ++l) {

             if (succ->in(l) == n) {

               succ->set_req(l, new_nodes.at(new_nodes.length() - 1));

             }

           }

           for (uint l = succ->req(); l < succ->len(); ++l) {

             if (succ->in(l) == n) {

               succ->set_prec(l, new_nodes.at(new_nodes.length() - 1));

             }

           }

         }

         // Index of old node in block.

         uint index = b->find_node(n);

         // Insert new nodes into block and map them in nodes->blocks array

         // and remember last node in n2.

         Node *n2 = NULL;

         for (int k = 0; k < new_nodes.length(); ++k) {

           n2 = new_nodes.at(k);

           b->insert_node(n2, ++index);

           map_node_to_block(n2, b);

         }

         // Add old node n to remove and remove them all from block.

         remove.push(n);

         j--;

 #ifdef ASSERT

         if (TracePostallocExpand && Verbose) {

           tty->print("    removing:\n");

           for (int k = 0; k < remove.length(); ++k) {

             tty->print("        "); remove.at(k)->dump();

           }

           tty->print("    inserting:\n");

           for (int k = 0; k < new_nodes.length(); ++k) {

             tty->print("        "); new_nodes.at(k)->dump();

           }

         }

 #endif

         for (int k = 0; k < remove.length(); ++k) {

           if (b->contains(remove.at(k))) {

             b->find_remove(remove.at(k));

           } else {

             assert(remove.at(k)->is_Proj() && (remove.at(k)->in(0)->is_MachBranch()), "");

           }

         }

         // If anything has been inserted (n2 != NULL), continue after last node inserted.

         // This does not always work. Some postalloc expands don't insert any nodes, if they

         // do optimizations (e.g., max(x,x)). In this case we decrement j accordingly.

         j = n2 ? b->find_node(n2) : j;

       }

     }

   }

 #ifdef ASSERT

   if (foundNode) {

     tty->print("FINISHED %d %s\n", C->compile_id(),

                C->method() ? C->method()->name()->as_utf8() : C->stub_name());

     tty->flush();

   }

 #endif

 }

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

 #ifndef PRODUCT

 void PhaseCFG::_dump_cfg( const Node *end, VectorSet &visited  ) const {

   const Node *x = end->is_block_proj();

   assert( x, "not a CFG" );

   // Do not visit this block again

   if( visited.test_set(x->_idx) ) return;

   // Skip through this block

   const Node *p = x;

   do {

     p = p->in(0);               // Move control forward

     assert( !p->is_block_proj() || p->is_Root(), "not a CFG" );

   } while( !p->is_block_start() );

   // Recursively visit

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

     _dump_cfg(p->in(i), visited);

   }

   // Dump the block

   get_block_for_node(p)->dump(this);

 }

 void PhaseCFG::dump( ) const {

   tty->print("\n--- CFG --- %d BBs\n", number_of_blocks());

   if (_blocks.size()) {        // Did we do basic-block layout?

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

       const Block* block = get_block(i);

       block->dump(this);

     }

   } else {                      // Else do it with a DFS

     VectorSet visited(_block_arena);

     _dump_cfg(_root,visited);

   }

 }

 void PhaseCFG::dump_headers() {

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

     Block* block = get_block(i);

     if (block != NULL) {

       block->dump_head(this);

     }

   }

 }

 void PhaseCFG::verify() const {

 #ifdef ASSERT

   // Verify sane CFG

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

     Block* block = get_block(i);

     uint cnt = block->number_of_nodes();

     uint j;

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

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

       assert(get_block_for_node(n) == block, "");

       if (j >= 1 && n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_CreateEx) {

         assert(j == 1 || block->get_node(j-1)->is_Phi(), "CreateEx must be first instruction in block");

       }

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

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

         if (def && def != n) {

           assert(get_block_for_node(def) || def->is_Con(), "must have block; constants for debug info ok");

           // Verify that instructions in the block is in correct order.

           // Uses must follow their definition if they are at the same block.

           // Mostly done to check that MachSpillCopy nodes are placed correctly

           // when CreateEx node is moved in build_ifg_physical().

           if (get_block_for_node(def) == block && !(block->head()->is_Loop() && n->is_Phi()) &&

               // See (+++) comment in reg_split.cpp

               !(n->jvms() != NULL && n->jvms()->is_monitor_use(k))) {

             bool is_loop = false;

             if (n->is_Phi()) {

               for (uint l = 1; l < def->req(); l++) {

                 if (n == def->in(l)) {

                   is_loop = true;

                   break; // Some kind of loop

                 }

               }

             }

             assert(is_loop || block->find_node(def) < j, "uses must follow definitions");

           }

         }

       }

     }

     j = block->end_idx();

     Node* bp = (Node*)block->get_node(block->number_of_nodes() - 1)->is_block_proj();

     assert(bp, "last instruction must be a block proj");

     assert(bp == block->get_node(j), "wrong number of successors for this block");

     if (bp->is_Catch()) {

       while (block->get_node(--j)->is_MachProj()) {

         ;

       }

       assert(block->get_node(j)->is_MachCall(), "CatchProj must follow call");

     } else if (bp->is_Mach() && bp->as_Mach()->ideal_Opcode() == Op_If) {

       assert(block->_num_succs == 2, "Conditional branch must have two targets");

     }

   }

 #endif

 }

 #endif

 UnionFind::UnionFind( uint max ) : _cnt(max), _max(max), _indices(NEW_RESOURCE_ARRAY(uint,max)) {

   Copy::zero_to_bytes( _indices, sizeof(uint)*max );

 }

 void UnionFind::extend( uint from_idx, uint to_idx ) {

   _nesting.check();

   if( from_idx >= _max ) {

     uint size = 16;

     while( size <= from_idx ) size <<=1;

     _indices = REALLOC_RESOURCE_ARRAY( uint, _indices, _max, size );

     _max = size;

   }

   while( _cnt <= from_idx ) _indices[_cnt++] = 0;

   _indices[from_idx] = to_idx;

 }

 void UnionFind::reset( uint max ) {

   assert( max <= max_uint, "Must fit within uint" );

   // Force the Union-Find mapping to be at least this large

   extend(max,0);

   // Initialize to be the ID mapping.

   for( uint i=0; i<max; i++ ) map(i,i);

 }

 // Straight out of Tarjan's union-find algorithm

 uint UnionFind::Find_compress( uint idx ) {

   uint cur  = idx;

   uint next = lookup(cur);

   while( next != cur ) {        // Scan chain of equivalences

     assert( next < cur, "always union smaller" );

     cur = next;                 // until find a fixed-point

     next = lookup(cur);

   }

   // Core of union-find algorithm: update chain of

   // equivalences to be equal to the root.

   while( idx != next ) {

     uint tmp = lookup(idx);

     map(idx, next);

     idx = tmp;

   }

   return idx;

 }

 // Like Find above, but no path compress, so bad asymptotic behavior

 uint UnionFind::Find_const( uint idx ) const {

   if( idx == 0 ) return idx;    // Ignore the zero idx

   // Off the end?  This can happen during debugging dumps

   // when data structures have not finished being updated.

   if( idx >= _max ) return idx;

   uint next = lookup(idx);

   while( next != idx ) {        // Scan chain of equivalences

     idx = next;                 // until find a fixed-point

     next = lookup(idx);

   }

   return next;

 }

 // union 2 sets together.

 void UnionFind::Union( uint idx1, uint idx2 ) {

   uint src = Find(idx1);

   uint dst = Find(idx2);

   assert( src, "" );

   assert( dst, "" );

   assert( src < _max, "oob" );

   assert( dst < _max, "oob" );

   assert( src < dst, "always union smaller" );

   map(dst,src);

 }

 #ifndef PRODUCT

 void Trace::dump( ) const {

   tty->print_cr("Trace (freq %f)", first_block()->_freq);

   for (Block *b = first_block(); b != NULL; b = next(b)) {

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

     if (b->head()->is_Loop()) {

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

     }

     if (b->has_loop_alignment()) {

       tty->print(" (T%d)", b->code_alignment());

     }

   }

   tty->cr();

 }

 void CFGEdge::dump( ) const {

   tty->print(" B%d  -->  B%d  Freq: %f  out:%3d%%  in:%3d%%  State: ",

              from()->_pre_order, to()->_pre_order, freq(), _from_pct, _to_pct);

   switch(state()) {

   case connected:

     tty->print("connected");

     break;

   case open:

     tty->print("open");

     break;

   case interior:

     tty->print("interior");

     break;

   }

   if (infrequent()) {

     tty->print("  infrequent");

   }

   tty->cr();

 }

 #endif

 // Comparison function for edges

 static int edge_order(CFGEdge **e0, CFGEdge **e1) {

   float freq0 = (*e0)->freq();

   float freq1 = (*e1)->freq();

   if (freq0 != freq1) {

     return freq0 > freq1 ? -1 : 1;

   }

   int dist0 = (*e0)->to()->_rpo - (*e0)->from()->_rpo;

   int dist1 = (*e1)->to()->_rpo - (*e1)->from()->_rpo;

   return dist1 - dist0;

 }

 // Comparison function for edges

 extern "C" int trace_frequency_order(const void *p0, const void *p1) {

   Trace *tr0 = *(Trace **) p0;

   Trace *tr1 = *(Trace **) p1;

   Block *b0 = tr0->first_block();

   Block *b1 = tr1->first_block();

   // The trace of connector blocks goes at the end;

   // we only expect one such trace

   if (b0->is_connector() != b1->is_connector()) {

     return b1->is_connector() ? -1 : 1;

   }

   // Pull more frequently executed blocks to the beginning

   float freq0 = b0->_freq;

   float freq1 = b1->_freq;

   if (freq0 != freq1) {

     return freq0 > freq1 ? -1 : 1;

   }

   int diff = tr0->first_block()->_rpo - tr1->first_block()->_rpo;

   return diff;

 }

 // Find edges of interest, i.e, those which can fall through. Presumes that

 // edges which don't fall through are of low frequency and can be generally

 // ignored.  Initialize the list of traces.

 void PhaseBlockLayout::find_edges() {

   // Walk the blocks, creating edges and Traces

   uint i;

   Trace *tr = NULL;

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

     Block* b = _cfg.get_block(i);

     tr = new Trace(b, next, prev);

     traces[tr->id()] = tr;

     // All connector blocks should be at the end of the list

     if (b->is_connector()) break;

     // If this block and the next one have a one-to-one successor

     // predecessor relationship, simply append the next block

     int nfallthru = b->num_fall_throughs();

     while (nfallthru == 1 &&

            b->succ_fall_through(0)) {

       Block *n = b->_succs[0];

       // Skip over single-entry connector blocks, we don't want to

       // add them to the trace.

       while (n->is_connector() && n->num_preds() == 1) {

         n = n->_succs[0];

       }

       // We see a merge point, so stop search for the next block

       if (n->num_preds() != 1) break;

       i++;

       assert(n = _cfg.get_block(i), "expecting next block");

       tr->append(n);

       uf->map(n->_pre_order, tr->id());

       traces[n->_pre_order] = NULL;

       nfallthru = b->num_fall_throughs();

       b = n;

     }

     if (nfallthru > 0) {

       // Create a CFGEdge for each outgoing

       // edge that could be a fall-through.

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

         if (b->succ_fall_through(j)) {

           Block *target = b->non_connector_successor(j);

           float freq = b->_freq * b->succ_prob(j);

           int from_pct = (int) ((100 * freq) / b->_freq);

           int to_pct = (int) ((100 * freq) / target->_freq);

           edges->append(new CFGEdge(b, target, freq, from_pct, to_pct));

         }

       }

     }

   }

   // Group connector blocks into one trace

   for (i++; i < _cfg.number_of_blocks(); i++) {

     Block *b = _cfg.get_block(i);

     assert(b->is_connector(), "connector blocks at the end");

     tr->append(b);

     uf->map(b->_pre_order, tr->id());

     traces[b->_pre_order] = NULL;

   }

 }

 // Union two traces together in uf, and null out the trace in the list

 void PhaseBlockLayout::union_traces(Trace* updated_trace, Trace* old_trace) {

   uint old_id = old_trace->id();

   uint updated_id = updated_trace->id();

   uint lo_id = updated_id;

   uint hi_id = old_id;

   // If from is greater than to, swap values to meet

   // UnionFind guarantee.

   if (updated_id > old_id) {

     lo_id = old_id;

     hi_id = updated_id;

     // Fix up the trace ids

     traces[lo_id] = traces[updated_id];

     updated_trace->set_id(lo_id);

   }

   // Union the lower with the higher and remove the pointer

   // to the higher.

   uf->Union(lo_id, hi_id);

   traces[hi_id] = NULL;

 }

 // Append traces together via the most frequently executed edges

 void PhaseBlockLayout::grow_traces() {

   // Order the edges, and drive the growth of Traces via the most

   // frequently executed edges.

   edges->sort(edge_order);

   for (int i = 0; i < edges->length(); i++) {

     CFGEdge *e = edges->at(i);

     if (e->state() != CFGEdge::open) continue;

     Block *src_block = e->from();

     Block *targ_block = e->to();

     // Don't grow traces along backedges?

     if (!BlockLayoutRotateLoops) {

       if (targ_block->_rpo <= src_block->_rpo) {

         targ_block->set_loop_alignment(targ_block);

         continue;

       }

     }

     Trace *src_trace = trace(src_block);

     Trace *targ_trace = trace(targ_block);

     // If the edge in question can join two traces at their ends,

     // append one trace to the other.

    if (src_trace->last_block() == src_block) {

       if (src_trace == targ_trace) {

         e->set_state(CFGEdge::interior);

         if (targ_trace->backedge(e)) {

           // Reset i to catch any newly eligible edge

           // (Or we could remember the first "open" edge, and reset there)

           i = 0;

         }

       } else if (targ_trace->first_block() == targ_block) {

         e->set_state(CFGEdge::connected);

         src_trace->append(targ_trace);

         union_traces(src_trace, targ_trace);

       }

     }

   }

 }

 // Embed one trace into another, if the fork or join points are sufficiently

 // balanced.

 void PhaseBlockLayout::merge_traces(bool fall_thru_only) {

   // Walk the edge list a another time, looking at unprocessed edges.

   // Fold in diamonds

   for (int i = 0; i < edges->length(); i++) {

     CFGEdge *e = edges->at(i);

     if (e->state() != CFGEdge::open) continue;

     if (fall_thru_only) {

       if (e->infrequent()) continue;

     }

     Block *src_block = e->from();

     Trace *src_trace = trace(src_block);

     bool src_at_tail = src_trace->last_block() == src_block;

     Block *targ_block  = e->to();

     Trace *targ_trace  = trace(targ_block);

     bool targ_at_start = targ_trace->first_block() == targ_block;

     if (src_trace == targ_trace) {

       // This may be a loop, but we can't do much about it.

       e->set_state(CFGEdge::interior);

       continue;

     }

     if (fall_thru_only) {

       // If the edge links the middle of two traces, we can't do anything.

       // Mark the edge and continue.

       if (!src_at_tail & !targ_at_start) {

         continue;

       }

       // Don't grow traces along backedges?

       if (!BlockLayoutRotateLoops && (targ_block->_rpo <= src_block->_rpo)) {

           continue;

       }

       // If both ends of the edge are available, why didn't we handle it earlier?

       assert(src_at_tail ^ targ_at_start, "Should have caught this edge earlier.");

       if (targ_at_start) {

         // Insert the "targ" trace in the "src" trace if the insertion point

         // is a two way branch.

         // Better profitability check possible, but may not be worth it.

         // Someday, see if the this "fork" has an associated "join";

         // then make a policy on merging this trace at the fork or join.

         // For example, other things being equal, it may be better to place this

         // trace at the join point if the "src" trace ends in a two-way, but

         // the insertion point is one-way.

         assert(src_block->num_fall_throughs() == 2, "unexpected diamond");

         e->set_state(CFGEdge::connected);

         src_trace->insert_after(src_block, targ_trace);

         union_traces(src_trace, targ_trace);

       } else if (src_at_tail) {

         if (src_trace != trace(_cfg.get_root_block())) {

           e->set_state(CFGEdge::connected);

           targ_trace->insert_before(targ_block, src_trace);

           union_traces(targ_trace, src_trace);

         }

       }

     } else if (e->state() == CFGEdge::open) {

       // Append traces, even without a fall-thru connection.

       // But leave root entry at the beginning of the block list.

       if (targ_trace != trace(_cfg.get_root_block())) {

         e->set_state(CFGEdge::connected);

         src_trace->append(targ_trace);

         union_traces(src_trace, targ_trace);

       }

     }

   }

 }

 // Order the sequence of the traces in some desirable way, and fixup the

 // jumps at the end of each block.

 void PhaseBlockLayout::reorder_traces(int count) {

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

   Trace ** new_traces = NEW_ARENA_ARRAY(area, Trace *, count);

   Block_List worklist;

   int new_count = 0;

   // Compact the traces.

   for (int i = 0; i < count; i++) {

     Trace *tr = traces[i];

     if (tr != NULL) {

       new_traces[new_count++] = tr;

     }

   }

   // The entry block should be first on the new trace list.

   Trace *tr = trace(_cfg.get_root_block());

   assert(tr == new_traces[0], "entry trace misplaced");

   // Sort the new trace list by frequency

   qsort(new_traces + 1, new_count - 1, sizeof(new_traces[0]), trace_frequency_order);

   // Patch up the successor blocks

   _cfg.clear_blocks();

   for (int i = 0; i < new_count; i++) {

     Trace *tr = new_traces[i];

     if (tr != NULL) {

       tr->fixup_blocks(_cfg);

     }

   }

 }

 // Order basic blocks based on frequency

 PhaseBlockLayout::PhaseBlockLayout(PhaseCFG &cfg)

 : Phase(BlockLayout)

 , _cfg(cfg) {

   ResourceMark rm;

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

   // List of traces

   int size = _cfg.number_of_blocks() + 1;

   traces = NEW_ARENA_ARRAY(area, Trace *, size);

   memset(traces, 0, size*sizeof(Trace*));

   next = NEW_ARENA_ARRAY(area, Block *, size);

   memset(next,   0, size*sizeof(Block *));

   prev = NEW_ARENA_ARRAY(area, Block *, size);

   memset(prev  , 0, size*sizeof(Block *));

   // List of edges

   edges = new GrowableArray<CFGEdge*>;

   // Mapping block index --> block_trace

   uf = new UnionFind(size);

   uf->reset(size);

   // Find edges and create traces.

   find_edges();

   // Grow traces at their ends via most frequent edges.

   grow_traces();

   // Merge one trace into another, but only at fall-through points.

   // This may make diamonds and other related shapes in a trace.

   merge_traces(true);

   // Run merge again, allowing two traces to be catenated, even if

   // one does not fall through into the other. This appends loosely

   // related traces to be near each other.

   merge_traces(false);

   // Re-order all the remaining traces by frequency

   reorder_traces(size);

   assert(_cfg.number_of_blocks() >= (uint) (size - 1), "number of blocks can not shrink");

 }

 // Edge e completes a loop in a trace. If the target block is head of the

 // loop, rotate the loop block so that the loop ends in a conditional branch.

 bool Trace::backedge(CFGEdge *e) {

   bool loop_rotated = false;

   Block *src_block  = e->from();

   Block *targ_block    = e->to();

   assert(last_block() == src_block, "loop discovery at back branch");

   if (first_block() == targ_block) {

     if (BlockLayoutRotateLoops && last_block()->num_fall_throughs() < 2) {

       // Find the last block in the trace that has a conditional

       // branch.

       Block *b;

       for (b = last_block(); b != NULL; b = prev(b)) {

         if (b->num_fall_throughs() == 2) {

           break;

         }

       }

       if (b != last_block() && b != NULL) {

         loop_rotated = true;

         // Rotate the loop by doing two-part linked-list surgery.

         append(first_block());

         break_loop_after(b);

       }

     }

     // Backbranch to the top of a trace

     // Scroll forward through the trace from the targ_block. If we find

     // a loop head before another loop top, use the the loop head alignment.

     for (Block *b = targ_block; b != NULL; b = next(b)) {

       if (b->has_loop_alignment()) {

         break;

       }

       if (b->head()->is_Loop()) {

         targ_block = b;

         break;

       }

     }

     first_block()->set_loop_alignment(targ_block);

   } else {

     // Backbranch into the middle of a trace

     targ_block->set_loop_alignment(targ_block);

   }

   return loop_rotated;

 }

 // push blocks onto the CFG list

 // ensure that blocks have the correct two-way branch sense

 void Trace::fixup_blocks(PhaseCFG &cfg) {

   Block *last = last_block();

   for (Block *b = first_block(); b != NULL; b = next(b)) {

     cfg.add_block(b);

     if (!b->is_connector()) {

       int nfallthru = b->num_fall_throughs();

       if (b != last) {

         if (nfallthru == 2) {

           // Ensure that the sense of the branch is correct

           Block *bnext = next(b);

           Block *bs0 = b->non_connector_successor(0);

           MachNode *iff = b->get_node(b->number_of_nodes() - 3)->as_Mach();

           ProjNode *proj0 = b->get_node(b->number_of_nodes() - 2)->as_Proj();

           ProjNode *proj1 = b->get_node(b->number_of_nodes() - 1)->as_Proj();

           if (bnext == bs0) {

             // Fall-thru case in succs[0], should be in succs[1]

             // Flip targets in _succs map

             Block *tbs0 = b->_succs[0];

             Block *tbs1 = b->_succs[1];

             b->_succs.map( 0, tbs1 );

             b->_succs.map( 1, tbs0 );

             // Flip projections to match targets

             b->map_node(proj1, b->number_of_nodes() - 2);

             b->map_node(proj0, b->number_of_nodes() - 1);

           }

         }

       }

     }

   }

 }