jdk8-mips64-public/hotspot: src/share/vm/opto/block.cpp@98cb887364d3 (annotated)

src/share/vm/opto/block.cpp@98cb887364d3 (annotated)

src/share/vm/opto/block.cpp

Fri, 27 Feb 2009 13:27:09 -0800

author: twisti
date: Fri, 27 Feb 2009 13:27:09 -0800
changeset 1040: 98cb887364d3
parent 1036: 523ded093c31
child 1063: 7bb995fbd3c0
permissions: -rw-r--r--

6810672: Comment typos
Summary: I have collected some typos I have found while looking at the code.
Reviewed-by: kvn, never

 /*
  * Copyright 1997-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */
 // 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;
 }
 #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 1;                     // no particular alignment
 }
 uint Block::compute_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. 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 = _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 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);
   } else if (has_loop_alignment()) {
     tty->print(" top-of-loop");
   }
   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];
   // 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->_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);
   // Set the frequency of the new block
   block->_freq = freq;
   // 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);
 }
 //------------------------------move_to_next-----------------------------------
 // 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) && (_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;
 }
 //------------------------------move_to_end------------------------------------
 // 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->_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);
 }
 //---------------------------set_loop_alignment--------------------------------
 // Set loop alignment for every block
 void PhaseCFG::set_loop_alignment() {
   uint last = _num_blocks;
   assert( _blocks[0] == _broot, "" );
   for (uint i = 1; i < last; i++ ) {
     Block *b = _blocks[i];
     if (b->head()->is_Loop()) {
       b->set_loop_alignment(b);
     }
   }
 }
 //-----------------------------remove_empty------------------------------------
 // Make empty basic blocks to be "connector" blocks, Move uncommon blocks
 // to the end.
 void PhaseCFG::remove_empty() {
   // Move uncommon blocks to the end
   uint last = _num_blocks;
   assert( _blocks[0] == _broot, "" );
   for (uint i = 1; i < last; i++) {
     Block *b = _blocks[i];
     if (b->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( b->_nodes[b->end_idx()]->Opcode() == Op_NeverBranch )
       convert_NeverBranch_to_Goto(b);
     // Look for uncommon blocks and move to end.
     if (!C->do_freq_based_layout()) {
       if( b->is_uncommon(_bbs) ) {
         move_to_end(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
           move_to_end(b, i);
           last--;
         }
         i--;                      // backup block counter post-increment
       }
     }
   }
   // Move empty blocks to the end
   last = _num_blocks;
   for (uint i = 1; i < last; i++) {
     Block *b = _blocks[i];
     if (b->is_Empty() != Block::not_empty) {
       move_to_end(b, i);
       last--;
       i--;
     }
   } // End of for all blocks
 }
 //-----------------------------fixup_flow--------------------------------------
 // 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 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 (uint 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 (uint 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( !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 = 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 ) {
         // 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 {
 #ifdef ASSERT
   // 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 *def = n->in(k);
         if( def && def != n ) {
           assert( _bbs[def->_idx] || 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( _bbs[def->_idx] == b &&
               !(b->head()->is_Loop() && n->is_Phi()) &&
               // See (+++) comment in reg_split.cpp
               !(n->jvms() != NULL && n->jvms()->is_monitor_use(k)) ) {
             assert( b->find_node(def) < j, "uses must follow definitions" );
           }
           if( def->is_SafePointScalarObject() ) {
             assert(_bbs[def->_idx] == b, "SafePointScalarObject Node should be at the same block as its SafePoint node");
             assert(_bbs[def->_idx] == _bbs[def->in(0)->_idx], "SafePointScalarObject Node should be at the same block as its control edge");
           }
         }
       }
     }
     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
 }
 #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
     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);
 }
 #ifndef PRODUCT
 static void edge_dump(GrowableArray<CFGEdge *> *edges) {
   tty->print_cr("---- Edges ----");
   for (int i = 0; i < edges->length(); i++) {
     CFGEdge *e = edges->at(i);
     if (e != NULL) {
       edges->at(i)->dump();
     }
   }
 }
 static void trace_dump(Trace *traces[], int count) {
   tty->print_cr("---- Traces ----");
   for (int i = 0; i < count; i++) {
     Trace *tr = traces[i];
     if (tr != NULL) {
       tr->dump();
     }
   }
 }
 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
 //=============================================================================
 //------------------------------edge_order-------------------------------------
 // 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;
 }
 //------------------------------trace_frequency_order--------------------------
 // Comparison function for edges
 static 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-------------------------------------
 // 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._num_blocks; i++) {
     Block *b = _cfg._blocks[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._blocks[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._num_blocks; i++) {
     Block *b = _cfg._blocks[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_traces----------------------------------
 // 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;
 }
 //------------------------------grow_traces-------------------------------------
 // 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);
       }
     }
   }
 }
 //------------------------------merge_traces-----------------------------------
 // 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._broot)) {
           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._broot)) {
         e->set_state(CFGEdge::connected);
         src_trace->append(targ_trace);
         union_traces(src_trace, targ_trace);
       }
     }
   }
 }
 //----------------------------reorder_traces-----------------------------------
 // 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._broot);
   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._blocks.reset();
   _cfg._num_blocks = 0;
   for (int i = 0; i < new_count; i++) {
     Trace *tr = new_traces[i];
     if (tr != NULL) {
       tr->fixup_blocks(_cfg);
     }
   }
 }
 //------------------------------PhaseBlockLayout-------------------------------
 // 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._num_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._num_blocks >= (uint) (size - 1), "number of blocks can not shrink");
 }
 //------------------------------backedge---------------------------------------
 // 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;
 }
 //------------------------------fixup_blocks-----------------------------------
 // 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._blocks.push(b);
     cfg._num_blocks++;
     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->_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();
           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->_nodes.map(b->_nodes.size()-2, proj1);
             b->_nodes.map(b->_nodes.size()-1, proj0);
           }
         }
       }
     }
   }
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/opto/block.cpp@98cb887364d3 (annotated)

src/share/vm/opto/block.cpp