diff src/share/vm/opto/block.cpp @ 0:a61af66fc99e

Initial load
author duke
date Sat, 01 Dec 2007 00:00:00 +0000
parents
children 756b58154237
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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/opto/block.cpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,952 @@
+/*
+ * Copyright 1997-2006 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+// Optimization - Graph Style
+
+#include "incls/_precompiled.incl"
+#include "incls/_block.cpp.incl"
+
+
+//-----------------------------------------------------------------------------
+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;
+}
+
+
+//=============================================================================
+
+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
+  Node *h = head();
+  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) ? (OptoLoopAlignment>>2) : 1;
+    // 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 1;             // Loop does not loop, more often than not!
+    }
+    return OptoLoopAlignment; // Otherwise align loop head
+  }
+  return 1;                     // 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.
+uint Block::compute_first_inst_size(uint& sum_size, uint inst_cnt,
+                                    PhaseRegAlloc* ra) {
+  uint last_inst = _nodes.size();
+  for( uint j = 0; j < last_inst && inst_cnt > 0; j++ ) {
+    uint inst_size = _nodes[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 < _nodes.size(); i++ ) {
+    if( _nodes[i] == n )
+      return i;
+  }
+  ShouldNotReachHere();
+  return 0;
+}
+
+// Find and remove n from block list
+void Block::find_remove( const Node *n ) {
+  _nodes.remove(find_node(n));
+}
+
+//------------------------------is_Empty---------------------------------------
+// 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 = _nodes.size()-1;
+
+  // Check for ending goto
+  if ((end_idx > 0) && (_nodes[end_idx]->is_Goto())) {
+    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) && !_nodes[end_idx]->is_Mach()) {
+    end_idx--;
+  }
+
+  // No room for any interesting instructions?
+  if (end_idx == 0) {
+    return success_result;
+  }
+
+  return not_empty;
+}
+
+//------------------------------has_uncommon_code------------------------------
+// Return true if the block's code implies that it is not 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_Goto())
+    en = en->in(0);
+  if (en->is_Catch())
+    en = en->in(0);
+  if (en->is_Proj() && 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;
+}
+
+//------------------------------is_uncommon------------------------------------
+// True if block is low enough frequency or guarded by a test which
+// mostly does not go here.
+bool Block::is_uncommon( Block_Array &bbs ) const {
+  // Initial blocks must never be moved, so are never uncommon.
+  if (head()->is_Root() || head()->is_Start())  return false;
+
+  // Check for way-low freq
+  if( _freq < BLOCK_FREQUENCY(0.00001f) ) return true;
+
+  // Look for code shape indicating uncommon_trap or slow path
+  if (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<num_preds(); i++ ) {
+    Block* guard = bbs[pred(i)->_idx];
+    // 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( _freq < guard->_freq * guard_factor ) {
+        uncommon_for_freq_preds++;
+      }
+    }
+  }
+  if( num_preds() > 1 &&
+      // The block is uncommon if all preds are uncommon or
+      (uncommon_preds == (num_preds()-1) ||
+      // it is uncommon for all frequent preds.
+       uncommon_for_freq_preds == freq_preds) ) {
+    return true;
+  }
+  return false;
+}
+
+//------------------------------dump-------------------------------------------
+#ifndef PRODUCT
+void Block::dump_bidx(const Block* orig) const {
+  if (_pre_order) tty->print("B%d",_pre_order);
+  else tty->print("N%d", head()->_idx);
+
+  if (Verbose && orig != this) {
+    // Dump the original block's idx
+    tty->print(" (");
+    orig->dump_bidx(orig);
+    tty->print(")");
+  }
+}
+
+void Block::dump_pred(const Block_Array *bbs, Block* orig) const {
+  if (is_connector()) {
+    for (uint i=1; i<num_preds(); i++) {
+      Block *p = ((*bbs)[pred(i)->_idx]);
+      p->dump_pred(bbs, orig);
+    }
+  } else {
+    dump_bidx(orig);
+    tty->print(" ");
+  }
+}
+
+void Block::dump_head( const Block_Array *bbs ) const {
+  // Print the basic block
+  dump_bidx(this);
+  tty->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]);
+    tty->print(" ");
+  }
+  tty->print("<- ");
+  if( head()->is_block_start() ) {
+    for (uint i=1; i<num_preds(); i++) {
+      Node *s = pred(i);
+      if (bbs) {
+        Block *p = (*bbs)[s->_idx];
+        p->dump_pred(bbs, p);
+      } else {
+        while (!s->is_block_start())
+          s = s->in(0);
+        tty->print("N%d ", s->_idx );
+      }
+    }
+  } else
+    tty->print("BLOCK HEAD IS JUNK  ");
+
+  // Print loop, if any
+  const Block *bhead = this;    // Head of self-loop
+  Node *bh = bhead->head();
+  if( bbs && bh->is_Loop() && !head()->is_Root() ) {
+    LoopNode *loop = bh->as_Loop();
+    const Block *bx = (*bbs)[loop->in(LoopNode::LoopBackControl)->_idx];
+    while (bx->is_connector()) {
+      bx = (*bbs)[bx->pred(1)->_idx];
+    }
+    tty->print("\tLoop: B%d-B%d ", bhead->_pre_order, bx->_pre_order);
+    // Dump any loop-specific bits, especially for CountedLoops.
+    loop->dump_spec(tty);
+  }
+  tty->print(" Freq: %g",_freq);
+  if( Verbose || WizardMode ) {
+    tty->print(" IDom: %d/#%d", _idom ? _idom->_pre_order : 0, _dom_depth);
+    tty->print(" RegPressure: %d",_reg_pressure);
+    tty->print(" IHRP Index: %d",_ihrp_index);
+    tty->print(" FRegPressure: %d",_freg_pressure);
+    tty->print(" FHRP Index: %d",_fhrp_index);
+  }
+  tty->print_cr("");
+}
+
+void Block::dump() const { dump(0); }
+
+void Block::dump( const Block_Array *bbs ) const {
+  dump_head(bbs);
+  uint cnt = _nodes.size();
+  for( uint i=0; i<cnt; i++ )
+    _nodes[i]->dump();
+  tty->print("\n");
+}
+#endif
+
+//=============================================================================
+//------------------------------PhaseCFG---------------------------------------
+PhaseCFG::PhaseCFG( Arena *a, RootNode *r, Matcher &m ) :
+  Phase(CFG),
+  _bbs(a),
+  _root(r)
+#ifndef PRODUCT
+  , _trace_opto_pipelining(TraceOptoPipelining || C->method_has_option("TraceOptoPipelining"))
+#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, 1) GotoNode(NULL);
+  x->init_req(0, x);
+  _goto = m.match_tree(x);
+  assert(_goto != NULL, "");
+  _goto->set_req(0,_goto);
+
+  // Build the CFG in Reverse Post Order
+  _num_blocks = build_cfg();
+  _broot = _bbs[_root->_idx];
+}
+
+//------------------------------build_cfg--------------------------------------
+// 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, 2) 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 (_bbs._arena) Block(_bbs._arena,p);
+      _bbs.map(p->_idx,bb);
+      _bbs.map(x->_idx,bb);
+      if( x != p )                  // Only for root is x == p
+        bb->_nodes.push((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 = _bbs[x->_idx];
+      // Insert into nodes array, if not already there
+      if( !_bbs.lookup(proj->_idx) ) {
+        assert( x != proj, "" );
+        // Map basic block of projection
+        _bbs.map(proj->_idx,pb);
+        pb->_nodes.push(proj);
+      }
+      // Insert self as a child of my predecessor block
+      pb->_succs.map(pb->_num_succs++, _bbs[np->_idx]);
+      assert( pb->_nodes[ pb->_nodes.size() - 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;
+}
+
+//------------------------------insert_goto_at---------------------------------
+// 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 < _num_blocks, "illegal block number");
+  Block* in  = _blocks[block_no];
+  // get successor block succ_no
+  assert(succ_no < in->_num_succs, "illegal successor number");
+  Block* out = in->_succs[succ_no];
+  // get ProjNode corresponding to the succ_no'th successor of the in block
+  ProjNode* proj = in->_nodes[in->_nodes.size() - in->_num_succs + succ_no]->as_Proj();
+  // create region for basic block
+  RegionNode* region = new (C, 2) RegionNode(2);
+  region->init_req(1, proj);
+  // setup corresponding basic block
+  Block* block = new (_bbs._arena) Block(_bbs._arena, region);
+  _bbs.map(region->_idx, 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->_nodes.push(gto);
+  _bbs.map(gto->_idx, 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);
+  // add new basic block to basic block list
+  _blocks.insert(block_no + 1, block);
+  _num_blocks++;
+}
+
+//------------------------------no_flip_branch---------------------------------
+// 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->_nodes.size() - b->_num_succs-1;
+  if( branch_idx < 1 ) return false;
+  Node *bra = b->_nodes[branch_idx];
+  if( bra->is_Catch() ) return true;
+  if( bra->is_Mach() ) {
+    if( bra->is_MachNullCheck() ) return true;
+    int iop = bra->as_Mach()->ideal_Opcode();
+    if( iop == Op_FastLock || iop == Op_FastUnlock )
+      return true;
+  }
+  return false;
+}
+
+//------------------------------convert_NeverBranch_to_Goto--------------------
+// 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->_nodes[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->_nodes[end_idx];
+  b->_nodes.map(end_idx,gto); // Slam over NeverBranch
+  _bbs.map(gto->_idx, b);
+  C->regalloc()->set_bad(gto->_idx);
+  b->_nodes.pop();              // Yank projections
+  b->_nodes.pop();              // 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->_nodes[k]->is_Phi(); k++ )
+    dead->_nodes[k]->del_req(j);
+}
+
+//------------------------------MoveToNext-------------------------------------
+// Helper function to move block bx to the slot following b_index. Return
+// true if the move is successful, otherwise false
+bool PhaseCFG::MoveToNext(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) && (_blocks[bx_index] == bx)) {
+    return false;
+  }
+
+  // Find the current index of block bx on the block list
+  bx_index = b_index + 1;
+  while( bx_index < _num_blocks && _blocks[bx_index] != bx ) bx_index++;
+  assert(_blocks[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 = _bbs[bx->pred(k)->_idx];
+    if (pred == _blocks[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;
+}
+
+//------------------------------MoveToEnd--------------------------------------
+// Move empty and uncommon blocks to the end.
+void PhaseCFG::MoveToEnd(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->_nodes.pop();
+    }
+    // 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);
+}
+
+//------------------------------RemoveEmpty------------------------------------
+// Remove empty basic blocks and useless branches.
+void PhaseCFG::RemoveEmpty() {
+  // Move uncommon blocks to the end
+  uint last = _num_blocks;
+  uint i;
+  assert( _blocks[0] == _broot, "" );
+  for( i = 1; i < last; i++ ) {
+    Block *b = _blocks[i];
+
+    // 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( b->_nodes[b->end_idx()]->Opcode() == Op_NeverBranch )
+      convert_NeverBranch_to_Goto(b);
+
+    // Look for uncommon blocks and move to end.
+    if( b->is_uncommon(_bbs) ) {
+      MoveToEnd(b, i);
+      last--;                   // No longer check for being uncommon!
+      if( no_flip_branch(b) ) { // Fall-thru case must follow?
+        b = _blocks[i];         // Find the fall-thru block
+        MoveToEnd(b, i);
+        last--;
+      }
+      i--;                      // backup block counter post-increment
+    }
+  }
+
+  // Remove empty blocks
+  uint j1;
+  last = _num_blocks;
+  for( i=0; i < last; i++ ) {
+    Block *b = _blocks[i];
+    if (i > 0) {
+      if (b->is_Empty() != Block::not_empty) {
+        MoveToEnd(b, i);
+        last--;
+        i--;
+      }
+    }
+  } // End of for all blocks
+
+  // Fixup final control flow for the blocks.  Remove jump-to-next
+  // block.  If neither arm of a 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( i=0; i < _num_blocks; i++ ) {
+    Block *b = _blocks[i];
+    b->_pre_order = i;          // turn pre-order into block-index
+
+    // Connector blocks need no further processing.
+    if (b->is_connector()) {
+      assert((i+1) == _num_blocks || _blocks[i+1]->is_connector(),
+             "All connector blocks should sink to the end");
+      continue;
+    }
+    assert(b->is_Empty() != Block::completely_empty,
+           "Empty blocks should be connectors");
+
+    Block *bnext = (i < _num_blocks-1) ? _blocks[i+1] : NULL;
+    Block *bs0 = b->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( b ) ) {
+      // Find fall through case - if must fall into its target
+      int branch_idx = b->_nodes.size() - b->_num_succs;
+      for (uint j2 = 0; j2 < b->_num_succs; j2++) {
+        const ProjNode* p = b->_nodes[branch_idx + j2]->as_Proj();
+        if (p->_con == 0) {
+          // successor j2 is fall through case
+          if (b->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 && b->_num_succs == 2) {
+            // 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 );
+          }
+          break;
+        }
+      }
+      // Remove all CatchProjs
+      for (j1 = 0; j1 < b->_num_succs; j1++) b->_nodes.pop();
+
+    } else if (b->_num_succs == 1) {
+      // Block ends in a Goto?
+      if (bnext == bs0) {
+        // We fall into next block; remove the Goto
+        b->_nodes.pop();
+      }
+
+    } else if( b->_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   = b->_nodes[b->_nodes.size()-3]->as_Mach();
+      ProjNode *proj0 = b->_nodes[b->_nodes.size()-2]->as_Proj();
+      ProjNode *proj1 = b->_nodes[b->_nodes.size()-1]->as_Proj();
+
+      // Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].
+      assert(proj0->raw_out(0) == b->_succs[0]->head(), "Mismatch successor 0");
+      assert(proj1->raw_out(0) == b->_succs[1]->head(), "Mismatch successor 1");
+
+      Block *bs1 = b->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( 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 (MoveToNext(bx, i)) {
+          bnext = bx;
+        } else if (MoveToNext(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 = b->_succs[0];
+        Block *tbs1 = b->_succs[1];
+        b->_succs.map( 0, tbs1 );
+        b->_succs.map( 1, tbs0 );
+        // Flip projection for each target
+        { ProjNode *tmp = proj0; proj0 = proj1; proj1 = tmp; }
+
+      } else if( bnext == bs1 ) { // Fall-thru is already in succs[1]
+
+      } else {                  // Else 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->negate();
+
+      b->_nodes.pop();          // Remove IfFalse & IfTrue projections
+      b->_nodes.pop();
+
+    } else {
+      // Multi-exit block, e.g. a switch statement
+      // But we don't need to do anything here
+    }
+
+  } // End of for all blocks
+
+}
+
+
+//------------------------------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
+  _bbs[p->_idx]->dump(&_bbs);
+}
+
+void PhaseCFG::dump( ) const {
+  tty->print("\n--- CFG --- %d BBs\n",_num_blocks);
+  if( _blocks.size() ) {        // Did we do basic-block layout?
+    for( uint i=0; i<_num_blocks; i++ )
+      _blocks[i]->dump(&_bbs);
+  } else {                      // Else do it with a DFS
+    VectorSet visited(_bbs._arena);
+    _dump_cfg(_root,visited);
+  }
+}
+
+void PhaseCFG::dump_headers() {
+  for( uint i = 0; i < _num_blocks; i++ ) {
+    if( _blocks[i] == NULL ) continue;
+    _blocks[i]->dump_head(&_bbs);
+  }
+}
+
+void PhaseCFG::verify( ) const {
+  // Verify sane CFG
+  for( uint i = 0; i < _num_blocks; i++ ) {
+    Block *b = _blocks[i];
+    uint cnt = b->_nodes.size();
+    uint j;
+    for( j = 0; j < cnt; j++ ) {
+      Node *n = b->_nodes[j];
+      assert( _bbs[n->_idx] == b, "" );
+      if( j >= 1 && n->is_Mach() &&
+          n->as_Mach()->ideal_Opcode() == Op_CreateEx ) {
+        assert( j == 1 || b->_nodes[j-1]->is_Phi(),
+                "CreateEx must be first instruction in block" );
+      }
+      for( uint k = 0; k < n->req(); k++ ) {
+        Node *use = n->in(k);
+        if( use && use != n ) {
+          assert( _bbs[use->_idx] || use->is_Con(),
+                  "must have block; constants for debug info ok" );
+        }
+      }
+    }
+
+    j = b->end_idx();
+    Node *bp = (Node*)b->_nodes[b->_nodes.size()-1]->is_block_proj();
+    assert( bp, "last instruction must be a block proj" );
+    assert( bp == b->_nodes[j], "wrong number of successors for this block" );
+    if( bp->is_Catch() ) {
+      while( b->_nodes[--j]->Opcode() == Op_MachProj ) ;
+      assert( b->_nodes[j]->is_Call(), "CatchProj must follow call" );
+    }
+    else if( bp->is_Mach() && bp->as_Mach()->ideal_Opcode() == Op_If ) {
+      assert( b->_num_succs == 2, "Conditional branch must have two targets");
+    }
+  }
+}
+#endif
+
+//=============================================================================
+//------------------------------UnionFind--------------------------------------
+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);
+}
+
+//------------------------------Find_compress----------------------------------
+// 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;
+}
+
+//------------------------------Find_const-------------------------------------
+// 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
+    assert( next < idx, "always union smaller" );
+    idx = next;                 // until find a fixed-point
+    next = lookup(idx);
+  }
+  return next;
+}
+
+//------------------------------Union------------------------------------------
+// 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);
+}