1 /*
   2  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "libadt/vectset.hpp"
  27 #include "memory/allocation.inline.hpp"
  28 #include "opto/block.hpp"
  29 #include "opto/cfgnode.hpp"
  30 #include "opto/chaitin.hpp"
  31 #include "opto/loopnode.hpp"
  32 #include "opto/machnode.hpp"
  33 #include "opto/matcher.hpp"
  34 #include "opto/opcodes.hpp"
  35 #include "opto/rootnode.hpp"
  36 #include "utilities/copy.hpp"
  37 
  38 // Optimization - Graph Style
  39 
  40 
  41 //-----------------------------------------------------------------------------
  42 void Block_Array::grow( uint i ) {
  43   assert(i >= Max(), "must be an overflow");
  44   debug_only(_limit = i+1);
  45   if( i < _size )  return;
  46   if( !_size ) {
  47     _size = 1;
  48     _blocks = (Block**)_arena->Amalloc( _size * sizeof(Block*) );
  49     _blocks[0] = NULL;
  50   }
  51   uint old = _size;
  52   while( i >= _size ) _size <<= 1;      // Double to fit
  53   _blocks = (Block**)_arena->Arealloc( _blocks, old*sizeof(Block*),_size*sizeof(Block*));
  54   Copy::zero_to_bytes( &_blocks[old], (_size-old)*sizeof(Block*) );
  55 }
  56 
  57 //=============================================================================
  58 void Block_List::remove(uint i) {
  59   assert(i < _cnt, "index out of bounds");
  60   Copy::conjoint_words_to_lower((HeapWord*)&_blocks[i+1], (HeapWord*)&_blocks[i], ((_cnt-i-1)*sizeof(Block*)));
  61   pop(); // shrink list by one block
  62 }
  63 
  64 void Block_List::insert(uint i, Block *b) {
  65   push(b); // grow list by one block
  66   Copy::conjoint_words_to_higher((HeapWord*)&_blocks[i], (HeapWord*)&_blocks[i+1], ((_cnt-i-1)*sizeof(Block*)));
  67   _blocks[i] = b;
  68 }
  69 
  70 #ifndef PRODUCT
  71 void Block_List::print() {
  72   for (uint i=0; i < size(); i++) {
  73     tty->print("B%d ", _blocks[i]->_pre_order);
  74   }
  75   tty->print("size = %d\n", size());
  76 }
  77 #endif
  78 
  79 //=============================================================================
  80 
  81 uint Block::code_alignment() {
  82   // Check for Root block
  83   if (_pre_order == 0) return CodeEntryAlignment;
  84   // Check for Start block
  85   if (_pre_order == 1) return InteriorEntryAlignment;
  86   // Check for loop alignment
  87   if (has_loop_alignment()) return loop_alignment();
  88 
  89   return relocInfo::addr_unit(); // no particular alignment
  90 }
  91 
  92 uint Block::compute_loop_alignment() {
  93   Node *h = head();
  94   int unit_sz = relocInfo::addr_unit();
  95   if (h->is_Loop() && h->as_Loop()->is_inner_loop())  {
  96     // Pre- and post-loops have low trip count so do not bother with
  97     // NOPs for align loop head.  The constants are hidden from tuning
  98     // but only because my "divide by 4" heuristic surely gets nearly
  99     // all possible gain (a "do not align at all" heuristic has a
 100     // chance of getting a really tiny gain).
 101     if (h->is_CountedLoop() && (h->as_CountedLoop()->is_pre_loop() ||
 102                                 h->as_CountedLoop()->is_post_loop())) {
 103       return (OptoLoopAlignment > 4*unit_sz) ? (OptoLoopAlignment>>2) : unit_sz;
 104     }
 105     // Loops with low backedge frequency should not be aligned.
 106     Node *n = h->in(LoopNode::LoopBackControl)->in(0);
 107     if (n->is_MachIf() && n->as_MachIf()->_prob < 0.01) {
 108       return unit_sz; // Loop does not loop, more often than not!
 109     }
 110     return OptoLoopAlignment; // Otherwise align loop head
 111   }
 112 
 113   return unit_sz; // no particular alignment
 114 }
 115 
 116 //-----------------------------------------------------------------------------
 117 // Compute the size of first 'inst_cnt' instructions in this block.
 118 // Return the number of instructions left to compute if the block has
 119 // less then 'inst_cnt' instructions. Stop, and return 0 if sum_size
 120 // exceeds OptoLoopAlignment.
 121 uint Block::compute_first_inst_size(uint& sum_size, uint inst_cnt,
 122                                     PhaseRegAlloc* ra) {
 123   uint last_inst = _nodes.size();
 124   for( uint j = 0; j < last_inst && inst_cnt > 0; j++ ) {
 125     uint inst_size = _nodes[j]->size(ra);
 126     if( inst_size > 0 ) {
 127       inst_cnt--;
 128       uint sz = sum_size + inst_size;
 129       if( sz <= (uint)OptoLoopAlignment ) {
 130         // Compute size of instructions which fit into fetch buffer only
 131         // since all inst_cnt instructions will not fit even if we align them.
 132         sum_size = sz;
 133       } else {
 134         return 0;
 135       }
 136     }
 137   }
 138   return inst_cnt;
 139 }
 140 
 141 //-----------------------------------------------------------------------------
 142 uint Block::find_node( const Node *n ) const {
 143   for( uint i = 0; i < _nodes.size(); i++ ) {
 144     if( _nodes[i] == n )
 145       return i;
 146   }
 147   ShouldNotReachHere();
 148   return 0;
 149 }
 150 
 151 // Find and remove n from block list
 152 void Block::find_remove( const Node *n ) {
 153   _nodes.remove(find_node(n));
 154 }
 155 
 156 //------------------------------is_Empty---------------------------------------
 157 // Return empty status of a block.  Empty blocks contain only the head, other
 158 // ideal nodes, and an optional trailing goto.
 159 int Block::is_Empty() const {
 160 
 161   // Root or start block is not considered empty
 162   if (head()->is_Root() || head()->is_Start()) {
 163     return not_empty;
 164   }
 165 
 166   int success_result = completely_empty;
 167   int end_idx = _nodes.size()-1;
 168 
 169   // Check for ending goto
 170   if ((end_idx > 0) && (_nodes[end_idx]->is_MachGoto())) {
 171     success_result = empty_with_goto;
 172     end_idx--;
 173   }
 174 
 175   // Unreachable blocks are considered empty
 176   if (num_preds() <= 1) {
 177     return success_result;
 178   }
 179 
 180   // Ideal nodes are allowable in empty blocks: skip them  Only MachNodes
 181   // turn directly into code, because only MachNodes have non-trivial
 182   // emit() functions.
 183   while ((end_idx > 0) && !_nodes[end_idx]->is_Mach()) {
 184     end_idx--;
 185   }
 186 
 187   // No room for any interesting instructions?
 188   if (end_idx == 0) {
 189     return success_result;
 190   }
 191 
 192   return not_empty;
 193 }
 194 
 195 //------------------------------has_uncommon_code------------------------------
 196 // Return true if the block's code implies that it is likely to be
 197 // executed infrequently.  Check to see if the block ends in a Halt or
 198 // a low probability call.
 199 bool Block::has_uncommon_code() const {
 200   Node* en = end();
 201 
 202   if (en->is_MachGoto())
 203     en = en->in(0);
 204   if (en->is_Catch())
 205     en = en->in(0);
 206   if (en->is_MachProj() && en->in(0)->is_MachCall()) {
 207     MachCallNode* call = en->in(0)->as_MachCall();
 208     if (call->cnt() != COUNT_UNKNOWN && call->cnt() <= PROB_UNLIKELY_MAG(4)) {
 209       // This is true for slow-path stubs like new_{instance,array},
 210       // slow_arraycopy, complete_monitor_locking, uncommon_trap.
 211       // The magic number corresponds to the probability of an uncommon_trap,
 212       // even though it is a count not a probability.
 213       return true;
 214     }
 215   }
 216 
 217   int op = en->is_Mach() ? en->as_Mach()->ideal_Opcode() : en->Opcode();
 218   return op == Op_Halt;
 219 }
 220 
 221 //------------------------------is_uncommon------------------------------------
 222 // True if block is low enough frequency or guarded by a test which
 223 // mostly does not go here.
 224 bool Block::is_uncommon( Block_Array &bbs ) const {
 225   // Initial blocks must never be moved, so are never uncommon.
 226   if (head()->is_Root() || head()->is_Start())  return false;
 227 
 228   // Check for way-low freq
 229   if( _freq < BLOCK_FREQUENCY(0.00001f) ) return true;
 230 
 231   // Look for code shape indicating uncommon_trap or slow path
 232   if (has_uncommon_code()) return true;
 233 
 234   const float epsilon = 0.05f;
 235   const float guard_factor = PROB_UNLIKELY_MAG(4) / (1.f - epsilon);
 236   uint uncommon_preds = 0;
 237   uint freq_preds = 0;
 238   uint uncommon_for_freq_preds = 0;
 239 
 240   for( uint i=1; i<num_preds(); i++ ) {
 241     Block* guard = bbs[pred(i)->_idx];
 242     // Check to see if this block follows its guard 1 time out of 10000
 243     // or less.
 244     //
 245     // See list of magnitude-4 unlikely probabilities in cfgnode.hpp which
 246     // we intend to be "uncommon", such as slow-path TLE allocation,
 247     // predicted call failure, and uncommon trap triggers.
 248     //
 249     // Use an epsilon value of 5% to allow for variability in frequency
 250     // predictions and floating point calculations. The net effect is
 251     // that guard_factor is set to 9500.
 252     //
 253     // Ignore low-frequency blocks.
 254     // The next check is (guard->_freq < 1.e-5 * 9500.).
 255     if(guard->_freq*BLOCK_FREQUENCY(guard_factor) < BLOCK_FREQUENCY(0.00001f)) {
 256       uncommon_preds++;
 257     } else {
 258       freq_preds++;
 259       if( _freq < guard->_freq * guard_factor ) {
 260         uncommon_for_freq_preds++;
 261       }
 262     }
 263   }
 264   if( num_preds() > 1 &&
 265       // The block is uncommon if all preds are uncommon or
 266       (uncommon_preds == (num_preds()-1) ||
 267       // it is uncommon for all frequent preds.
 268        uncommon_for_freq_preds == freq_preds) ) {
 269     return true;
 270   }
 271   return false;
 272 }
 273 
 274 //------------------------------dump-------------------------------------------
 275 #ifndef PRODUCT
 276 void Block::dump_bidx(const Block* orig, outputStream* st) const {
 277   if (_pre_order) st->print("B%d",_pre_order);
 278   else st->print("N%d", head()->_idx);
 279 
 280   if (Verbose && orig != this) {
 281     // Dump the original block's idx
 282     st->print(" (");
 283     orig->dump_bidx(orig, st);
 284     st->print(")");
 285   }
 286 }
 287 
 288 void Block::dump_pred(const Block_Array *bbs, Block* orig, outputStream* st) const {
 289   if (is_connector()) {
 290     for (uint i=1; i<num_preds(); i++) {
 291       Block *p = ((*bbs)[pred(i)->_idx]);
 292       p->dump_pred(bbs, orig, st);
 293     }
 294   } else {
 295     dump_bidx(orig, st);
 296     st->print(" ");
 297   }
 298 }
 299 
 300 void Block::dump_head( const Block_Array *bbs, outputStream* st ) const {
 301   // Print the basic block
 302   dump_bidx(this, st);
 303   st->print(": #\t");
 304 
 305   // Print the incoming CFG edges and the outgoing CFG edges
 306   for( uint i=0; i<_num_succs; i++ ) {
 307     non_connector_successor(i)->dump_bidx(_succs[i], st);
 308     st->print(" ");
 309   }
 310   st->print("<- ");
 311   if( head()->is_block_start() ) {
 312     for (uint i=1; i<num_preds(); i++) {
 313       Node *s = pred(i);
 314       if (bbs) {
 315         Block *p = (*bbs)[s->_idx];
 316         p->dump_pred(bbs, p, st);
 317       } else {
 318         while (!s->is_block_start())
 319           s = s->in(0);
 320         st->print("N%d ", s->_idx );
 321       }
 322     }
 323   } else
 324     st->print("BLOCK HEAD IS JUNK  ");
 325 
 326   // Print loop, if any
 327   const Block *bhead = this;    // Head of self-loop
 328   Node *bh = bhead->head();
 329   if( bbs && bh->is_Loop() && !head()->is_Root() ) {
 330     LoopNode *loop = bh->as_Loop();
 331     const Block *bx = (*bbs)[loop->in(LoopNode::LoopBackControl)->_idx];
 332     while (bx->is_connector()) {
 333       bx = (*bbs)[bx->pred(1)->_idx];
 334     }
 335     st->print("\tLoop: B%d-B%d ", bhead->_pre_order, bx->_pre_order);
 336     // Dump any loop-specific bits, especially for CountedLoops.
 337     loop->dump_spec(st);
 338   } else if (has_loop_alignment()) {
 339     st->print(" top-of-loop");
 340   }
 341   st->print(" Freq: %g",_freq);
 342   if( Verbose || WizardMode ) {
 343     st->print(" IDom: %d/#%d", _idom ? _idom->_pre_order : 0, _dom_depth);
 344     st->print(" RegPressure: %d",_reg_pressure);
 345     st->print(" IHRP Index: %d",_ihrp_index);
 346     st->print(" FRegPressure: %d",_freg_pressure);
 347     st->print(" FHRP Index: %d",_fhrp_index);
 348   }
 349   st->print_cr("");
 350 }
 351 
 352 void Block::dump() const { dump(NULL); }
 353 
 354 void Block::dump( const Block_Array *bbs ) const {
 355   dump_head(bbs);
 356   uint cnt = _nodes.size();
 357   for( uint i=0; i<cnt; i++ )
 358     _nodes[i]->dump();
 359   tty->print("\n");
 360 }
 361 #endif
 362 
 363 //=============================================================================
 364 //------------------------------PhaseCFG---------------------------------------
 365 PhaseCFG::PhaseCFG( Arena *a, RootNode *r, Matcher &m ) :
 366   Phase(CFG),
 367   _bbs(a),
 368   _root(r),
 369   _node_latency(NULL)
 370 #ifndef PRODUCT
 371   , _trace_opto_pipelining(TraceOptoPipelining || C->method_has_option("TraceOptoPipelining"))
 372 #endif
 373 #ifdef ASSERT
 374   , _raw_oops(a)
 375 #endif
 376 {
 377   ResourceMark rm;
 378   // I'll need a few machine-specific GotoNodes.  Make an Ideal GotoNode,
 379   // then Match it into a machine-specific Node.  Then clone the machine
 380   // Node on demand.
 381   Node *x = new (C) GotoNode(NULL);
 382   x->init_req(0, x);
 383   _goto = m.match_tree(x);
 384   assert(_goto != NULL, "");
 385   _goto->set_req(0,_goto);
 386 
 387   // Build the CFG in Reverse Post Order
 388   _num_blocks = build_cfg();
 389   _broot = _bbs[_root->_idx];
 390 }
 391 
 392 //------------------------------build_cfg--------------------------------------
 393 // Build a proper looking CFG.  Make every block begin with either a StartNode
 394 // or a RegionNode.  Make every block end with either a Goto, If or Return.
 395 // The RootNode both starts and ends it's own block.  Do this with a recursive
 396 // backwards walk over the control edges.
 397 uint PhaseCFG::build_cfg() {
 398   Arena *a = Thread::current()->resource_area();
 399   VectorSet visited(a);
 400 
 401   // Allocate stack with enough space to avoid frequent realloc
 402   Node_Stack nstack(a, C->unique() >> 1);
 403   nstack.push(_root, 0);
 404   uint sum = 0;                 // Counter for blocks
 405 
 406   while (nstack.is_nonempty()) {
 407     // node and in's index from stack's top
 408     // 'np' is _root (see above) or RegionNode, StartNode: we push on stack
 409     // only nodes which point to the start of basic block (see below).
 410     Node *np = nstack.node();
 411     // idx > 0, except for the first node (_root) pushed on stack
 412     // at the beginning when idx == 0.
 413     // We will use the condition (idx == 0) later to end the build.
 414     uint idx = nstack.index();
 415     Node *proj = np->in(idx);
 416     const Node *x = proj->is_block_proj();
 417     // Does the block end with a proper block-ending Node?  One of Return,
 418     // If or Goto? (This check should be done for visited nodes also).
 419     if (x == NULL) {                    // Does not end right...
 420       Node *g = _goto->clone(); // Force it to end in a Goto
 421       g->set_req(0, proj);
 422       np->set_req(idx, g);
 423       x = proj = g;
 424     }
 425     if (!visited.test_set(x->_idx)) { // Visit this block once
 426       // Skip any control-pinned middle'in stuff
 427       Node *p = proj;
 428       do {
 429         proj = p;                   // Update pointer to last Control
 430         p = p->in(0);               // Move control forward
 431       } while( !p->is_block_proj() &&
 432                !p->is_block_start() );
 433       // Make the block begin with one of Region or StartNode.
 434       if( !p->is_block_start() ) {
 435         RegionNode *r = new (C) RegionNode( 2 );
 436         r->init_req(1, p);         // Insert RegionNode in the way
 437         proj->set_req(0, r);        // Insert RegionNode in the way
 438         p = r;
 439       }
 440       // 'p' now points to the start of this basic block
 441 
 442       // Put self in array of basic blocks
 443       Block *bb = new (_bbs._arena) Block(_bbs._arena,p);
 444       _bbs.map(p->_idx,bb);
 445       _bbs.map(x->_idx,bb);
 446       if( x != p ) {                // Only for root is x == p
 447         bb->_nodes.push((Node*)x);
 448       }
 449       // Now handle predecessors
 450       ++sum;                        // Count 1 for self block
 451       uint cnt = bb->num_preds();
 452       for (int i = (cnt - 1); i > 0; i-- ) { // For all predecessors
 453         Node *prevproj = p->in(i);  // Get prior input
 454         assert( !prevproj->is_Con(), "dead input not removed" );
 455         // Check to see if p->in(i) is a "control-dependent" CFG edge -
 456         // i.e., it splits at the source (via an IF or SWITCH) and merges
 457         // at the destination (via a many-input Region).
 458         // This breaks critical edges.  The RegionNode to start the block
 459         // will be added when <p,i> is pulled off the node stack
 460         if ( cnt > 2 ) {             // Merging many things?
 461           assert( prevproj== bb->pred(i),"");
 462           if(prevproj->is_block_proj() != prevproj) { // Control-dependent edge?
 463             // Force a block on the control-dependent edge
 464             Node *g = _goto->clone();       // Force it to end in a Goto
 465             g->set_req(0,prevproj);
 466             p->set_req(i,g);
 467           }
 468         }
 469         nstack.push(p, i);  // 'p' is RegionNode or StartNode
 470       }
 471     } else { // Post-processing visited nodes
 472       nstack.pop();                 // remove node from stack
 473       // Check if it the fist node pushed on stack at the beginning.
 474       if (idx == 0) break;          // end of the build
 475       // Find predecessor basic block
 476       Block *pb = _bbs[x->_idx];
 477       // Insert into nodes array, if not already there
 478       if( !_bbs.lookup(proj->_idx) ) {
 479         assert( x != proj, "" );
 480         // Map basic block of projection
 481         _bbs.map(proj->_idx,pb);
 482         pb->_nodes.push(proj);
 483       }
 484       // Insert self as a child of my predecessor block
 485       pb->_succs.map(pb->_num_succs++, _bbs[np->_idx]);
 486       assert( pb->_nodes[ pb->_nodes.size() - pb->_num_succs ]->is_block_proj(),
 487               "too many control users, not a CFG?" );
 488     }
 489   }
 490   // Return number of basic blocks for all children and self
 491   return sum;
 492 }
 493 
 494 //------------------------------insert_goto_at---------------------------------
 495 // Inserts a goto & corresponding basic block between
 496 // block[block_no] and its succ_no'th successor block
 497 void PhaseCFG::insert_goto_at(uint block_no, uint succ_no) {
 498   // get block with block_no
 499   assert(block_no < _num_blocks, "illegal block number");
 500   Block* in  = _blocks[block_no];
 501   // get successor block succ_no
 502   assert(succ_no < in->_num_succs, "illegal successor number");
 503   Block* out = in->_succs[succ_no];
 504   // Compute frequency of the new block. Do this before inserting
 505   // new block in case succ_prob() needs to infer the probability from
 506   // surrounding blocks.
 507   float freq = in->_freq * in->succ_prob(succ_no);
 508   // get ProjNode corresponding to the succ_no'th successor of the in block
 509   ProjNode* proj = in->_nodes[in->_nodes.size() - in->_num_succs + succ_no]->as_Proj();
 510   // create region for basic block
 511   RegionNode* region = new (C) RegionNode(2);
 512   region->init_req(1, proj);
 513   // setup corresponding basic block
 514   Block* block = new (_bbs._arena) Block(_bbs._arena, region);
 515   _bbs.map(region->_idx, block);
 516   C->regalloc()->set_bad(region->_idx);
 517   // add a goto node
 518   Node* gto = _goto->clone(); // get a new goto node
 519   gto->set_req(0, region);
 520   // add it to the basic block
 521   block->_nodes.push(gto);
 522   _bbs.map(gto->_idx, block);
 523   C->regalloc()->set_bad(gto->_idx);
 524   // hook up successor block
 525   block->_succs.map(block->_num_succs++, out);
 526   // remap successor's predecessors if necessary
 527   for (uint i = 1; i < out->num_preds(); i++) {
 528     if (out->pred(i) == proj) out->head()->set_req(i, gto);
 529   }
 530   // remap predecessor's successor to new block
 531   in->_succs.map(succ_no, block);
 532   // Set the frequency of the new block
 533   block->_freq = freq;
 534   // add new basic block to basic block list
 535   _blocks.insert(block_no + 1, block);
 536   _num_blocks++;
 537 }
 538 
 539 //------------------------------no_flip_branch---------------------------------
 540 // Does this block end in a multiway branch that cannot have the default case
 541 // flipped for another case?
 542 static bool no_flip_branch( Block *b ) {
 543   int branch_idx = b->_nodes.size() - b->_num_succs-1;
 544   if( branch_idx < 1 ) return false;
 545   Node *bra = b->_nodes[branch_idx];
 546   if( bra->is_Catch() )
 547     return true;
 548   if( bra->is_Mach() ) {
 549     if( bra->is_MachNullCheck() )
 550       return true;
 551     int iop = bra->as_Mach()->ideal_Opcode();
 552     if( iop == Op_FastLock || iop == Op_FastUnlock )
 553       return true;
 554   }
 555   return false;
 556 }
 557 
 558 //------------------------------convert_NeverBranch_to_Goto--------------------
 559 // Check for NeverBranch at block end.  This needs to become a GOTO to the
 560 // true target.  NeverBranch are treated as a conditional branch that always
 561 // goes the same direction for most of the optimizer and are used to give a
 562 // fake exit path to infinite loops.  At this late stage they need to turn
 563 // into Goto's so that when you enter the infinite loop you indeed hang.
 564 void PhaseCFG::convert_NeverBranch_to_Goto(Block *b) {
 565   // Find true target
 566   int end_idx = b->end_idx();
 567   int idx = b->_nodes[end_idx+1]->as_Proj()->_con;
 568   Block *succ = b->_succs[idx];
 569   Node* gto = _goto->clone(); // get a new goto node
 570   gto->set_req(0, b->head());
 571   Node *bp = b->_nodes[end_idx];
 572   b->_nodes.map(end_idx,gto); // Slam over NeverBranch
 573   _bbs.map(gto->_idx, b);
 574   C->regalloc()->set_bad(gto->_idx);
 575   b->_nodes.pop();              // Yank projections
 576   b->_nodes.pop();              // Yank projections
 577   b->_succs.map(0,succ);        // Map only successor
 578   b->_num_succs = 1;
 579   // remap successor's predecessors if necessary
 580   uint j;
 581   for( j = 1; j < succ->num_preds(); j++)
 582     if( succ->pred(j)->in(0) == bp )
 583       succ->head()->set_req(j, gto);
 584   // Kill alternate exit path
 585   Block *dead = b->_succs[1-idx];
 586   for( j = 1; j < dead->num_preds(); j++)
 587     if( dead->pred(j)->in(0) == bp )
 588       break;
 589   // Scan through block, yanking dead path from
 590   // all regions and phis.
 591   dead->head()->del_req(j);
 592   for( int k = 1; dead->_nodes[k]->is_Phi(); k++ )
 593     dead->_nodes[k]->del_req(j);
 594 }
 595 
 596 //------------------------------move_to_next-----------------------------------
 597 // Helper function to move block bx to the slot following b_index. Return
 598 // true if the move is successful, otherwise false
 599 bool PhaseCFG::move_to_next(Block* bx, uint b_index) {
 600   if (bx == NULL) return false;
 601 
 602   // Return false if bx is already scheduled.
 603   uint bx_index = bx->_pre_order;
 604   if ((bx_index <= b_index) && (_blocks[bx_index] == bx)) {
 605     return false;
 606   }
 607 
 608   // Find the current index of block bx on the block list
 609   bx_index = b_index + 1;
 610   while( bx_index < _num_blocks && _blocks[bx_index] != bx ) bx_index++;
 611   assert(_blocks[bx_index] == bx, "block not found");
 612 
 613   // If the previous block conditionally falls into bx, return false,
 614   // because moving bx will create an extra jump.
 615   for(uint k = 1; k < bx->num_preds(); k++ ) {
 616     Block* pred = _bbs[bx->pred(k)->_idx];
 617     if (pred == _blocks[bx_index-1]) {
 618       if (pred->_num_succs != 1) {
 619         return false;
 620       }
 621     }
 622   }
 623 
 624   // Reinsert bx just past block 'b'
 625   _blocks.remove(bx_index);
 626   _blocks.insert(b_index + 1, bx);
 627   return true;
 628 }
 629 
 630 //------------------------------move_to_end------------------------------------
 631 // Move empty and uncommon blocks to the end.
 632 void PhaseCFG::move_to_end(Block *b, uint i) {
 633   int e = b->is_Empty();
 634   if (e != Block::not_empty) {
 635     if (e == Block::empty_with_goto) {
 636       // Remove the goto, but leave the block.
 637       b->_nodes.pop();
 638     }
 639     // Mark this block as a connector block, which will cause it to be
 640     // ignored in certain functions such as non_connector_successor().
 641     b->set_connector();
 642   }
 643   // Move the empty block to the end, and don't recheck.
 644   _blocks.remove(i);
 645   _blocks.push(b);
 646 }
 647 
 648 //---------------------------set_loop_alignment--------------------------------
 649 // Set loop alignment for every block
 650 void PhaseCFG::set_loop_alignment() {
 651   uint last = _num_blocks;
 652   assert( _blocks[0] == _broot, "" );
 653 
 654   for (uint i = 1; i < last; i++ ) {
 655     Block *b = _blocks[i];
 656     if (b->head()->is_Loop()) {
 657       b->set_loop_alignment(b);
 658     }
 659   }
 660 }
 661 
 662 //-----------------------------remove_empty------------------------------------
 663 // Make empty basic blocks to be "connector" blocks, Move uncommon blocks
 664 // to the end.
 665 void PhaseCFG::remove_empty() {
 666   // Move uncommon blocks to the end
 667   uint last = _num_blocks;
 668   assert( _blocks[0] == _broot, "" );
 669 
 670   for (uint i = 1; i < last; i++) {
 671     Block *b = _blocks[i];
 672     if (b->is_connector()) break;
 673 
 674     // Check for NeverBranch at block end.  This needs to become a GOTO to the
 675     // true target.  NeverBranch are treated as a conditional branch that
 676     // always goes the same direction for most of the optimizer and are used
 677     // to give a fake exit path to infinite loops.  At this late stage they
 678     // need to turn into Goto's so that when you enter the infinite loop you
 679     // indeed hang.
 680     if( b->_nodes[b->end_idx()]->Opcode() == Op_NeverBranch )
 681       convert_NeverBranch_to_Goto(b);
 682 
 683     // Look for uncommon blocks and move to end.
 684     if (!C->do_freq_based_layout()) {
 685       if( b->is_uncommon(_bbs) ) {
 686         move_to_end(b, i);
 687         last--;                   // No longer check for being uncommon!
 688         if( no_flip_branch(b) ) { // Fall-thru case must follow?
 689           b = _blocks[i];         // Find the fall-thru block
 690           move_to_end(b, i);
 691           last--;
 692         }
 693         i--;                      // backup block counter post-increment
 694       }
 695     }
 696   }
 697 
 698   // Move empty blocks to the end
 699   last = _num_blocks;
 700   for (uint i = 1; i < last; i++) {
 701     Block *b = _blocks[i];
 702     if (b->is_Empty() != Block::not_empty) {
 703       move_to_end(b, i);
 704       last--;
 705       i--;
 706     }
 707   } // End of for all blocks
 708 }
 709 
 710 //-----------------------------fixup_flow--------------------------------------
 711 // Fix up the final control flow for basic blocks.
 712 void PhaseCFG::fixup_flow() {
 713   // Fixup final control flow for the blocks.  Remove jump-to-next
 714   // block.  If neither arm of a IF follows the conditional branch, we
 715   // have to add a second jump after the conditional.  We place the
 716   // TRUE branch target in succs[0] for both GOTOs and IFs.
 717   for (uint i=0; i < _num_blocks; i++) {
 718     Block *b = _blocks[i];
 719     b->_pre_order = i;          // turn pre-order into block-index
 720 
 721     // Connector blocks need no further processing.
 722     if (b->is_connector()) {
 723       assert((i+1) == _num_blocks || _blocks[i+1]->is_connector(),
 724              "All connector blocks should sink to the end");
 725       continue;
 726     }
 727     assert(b->is_Empty() != Block::completely_empty,
 728            "Empty blocks should be connectors");
 729 
 730     Block *bnext = (i < _num_blocks-1) ? _blocks[i+1] : NULL;
 731     Block *bs0 = b->non_connector_successor(0);
 732 
 733     // Check for multi-way branches where I cannot negate the test to
 734     // exchange the true and false targets.
 735     if( no_flip_branch( b ) ) {
 736       // Find fall through case - if must fall into its target
 737       int branch_idx = b->_nodes.size() - b->_num_succs;
 738       for (uint j2 = 0; j2 < b->_num_succs; j2++) {
 739         const ProjNode* p = b->_nodes[branch_idx + j2]->as_Proj();
 740         if (p->_con == 0) {
 741           // successor j2 is fall through case
 742           if (b->non_connector_successor(j2) != bnext) {
 743             // but it is not the next block => insert a goto
 744             insert_goto_at(i, j2);
 745           }
 746           // Put taken branch in slot 0
 747           if( j2 == 0 && b->_num_succs == 2) {
 748             // Flip targets in succs map
 749             Block *tbs0 = b->_succs[0];
 750             Block *tbs1 = b->_succs[1];
 751             b->_succs.map( 0, tbs1 );
 752             b->_succs.map( 1, tbs0 );
 753           }
 754           break;
 755         }
 756       }
 757       // Remove all CatchProjs
 758       for (uint j1 = 0; j1 < b->_num_succs; j1++) b->_nodes.pop();
 759 
 760     } else if (b->_num_succs == 1) {
 761       // Block ends in a Goto?
 762       if (bnext == bs0) {
 763         // We fall into next block; remove the Goto
 764         b->_nodes.pop();
 765       }
 766 
 767     } else if( b->_num_succs == 2 ) { // Block ends in a If?
 768       // Get opcode of 1st projection (matches _succs[0])
 769       // Note: Since this basic block has 2 exits, the last 2 nodes must
 770       //       be projections (in any order), the 3rd last node must be
 771       //       the IfNode (we have excluded other 2-way exits such as
 772       //       CatchNodes already).
 773       MachNode *iff   = b->_nodes[b->_nodes.size()-3]->as_Mach();
 774       ProjNode *proj0 = b->_nodes[b->_nodes.size()-2]->as_Proj();
 775       ProjNode *proj1 = b->_nodes[b->_nodes.size()-1]->as_Proj();
 776 
 777       // Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].
 778       assert(proj0->raw_out(0) == b->_succs[0]->head(), "Mismatch successor 0");
 779       assert(proj1->raw_out(0) == b->_succs[1]->head(), "Mismatch successor 1");
 780 
 781       Block *bs1 = b->non_connector_successor(1);
 782 
 783       // Check for neither successor block following the current
 784       // block ending in a conditional. If so, move one of the
 785       // successors after the current one, provided that the
 786       // successor was previously unscheduled, but moveable
 787       // (i.e., all paths to it involve a branch).
 788       if( !C->do_freq_based_layout() && bnext != bs0 && bnext != bs1 ) {
 789         // Choose the more common successor based on the probability
 790         // of the conditional branch.
 791         Block *bx = bs0;
 792         Block *by = bs1;
 793 
 794         // _prob is the probability of taking the true path. Make
 795         // p the probability of taking successor #1.
 796         float p = iff->as_MachIf()->_prob;
 797         if( proj0->Opcode() == Op_IfTrue ) {
 798           p = 1.0 - p;
 799         }
 800 
 801         // Prefer successor #1 if p > 0.5
 802         if (p > PROB_FAIR) {
 803           bx = bs1;
 804           by = bs0;
 805         }
 806 
 807         // Attempt the more common successor first
 808         if (move_to_next(bx, i)) {
 809           bnext = bx;
 810         } else if (move_to_next(by, i)) {
 811           bnext = by;
 812         }
 813       }
 814 
 815       // Check for conditional branching the wrong way.  Negate
 816       // conditional, if needed, so it falls into the following block
 817       // and branches to the not-following block.
 818 
 819       // Check for the next block being in succs[0].  We are going to branch
 820       // to succs[0], so we want the fall-thru case as the next block in
 821       // succs[1].
 822       if (bnext == bs0) {
 823         // Fall-thru case in succs[0], so flip targets in succs map
 824         Block *tbs0 = b->_succs[0];
 825         Block *tbs1 = b->_succs[1];
 826         b->_succs.map( 0, tbs1 );
 827         b->_succs.map( 1, tbs0 );
 828         // Flip projection for each target
 829         { ProjNode *tmp = proj0; proj0 = proj1; proj1 = tmp; }
 830 
 831       } else if( bnext != bs1 ) {
 832         // Need a double-branch
 833         // The existing conditional branch need not change.
 834         // Add a unconditional branch to the false target.
 835         // Alas, it must appear in its own block and adding a
 836         // block this late in the game is complicated.  Sigh.
 837         insert_goto_at(i, 1);
 838       }
 839 
 840       // Make sure we TRUE branch to the target
 841       if( proj0->Opcode() == Op_IfFalse ) {
 842         iff->as_MachIf()->negate();
 843       }
 844 
 845       b->_nodes.pop();          // Remove IfFalse & IfTrue projections
 846       b->_nodes.pop();
 847 
 848     } else {
 849       // Multi-exit block, e.g. a switch statement
 850       // But we don't need to do anything here
 851     }
 852   } // End of for all blocks
 853 }
 854 
 855 
 856 //------------------------------dump-------------------------------------------
 857 #ifndef PRODUCT
 858 void PhaseCFG::_dump_cfg( const Node *end, VectorSet &visited  ) const {
 859   const Node *x = end->is_block_proj();
 860   assert( x, "not a CFG" );
 861 
 862   // Do not visit this block again
 863   if( visited.test_set(x->_idx) ) return;
 864 
 865   // Skip through this block
 866   const Node *p = x;
 867   do {
 868     p = p->in(0);               // Move control forward
 869     assert( !p->is_block_proj() || p->is_Root(), "not a CFG" );
 870   } while( !p->is_block_start() );
 871 
 872   // Recursively visit
 873   for( uint i=1; i<p->req(); i++ )
 874     _dump_cfg(p->in(i),visited);
 875 
 876   // Dump the block
 877   _bbs[p->_idx]->dump(&_bbs);
 878 }
 879 
 880 void PhaseCFG::dump( ) const {
 881   tty->print("\n--- CFG --- %d BBs\n",_num_blocks);
 882   if( _blocks.size() ) {        // Did we do basic-block layout?
 883     for( uint i=0; i<_num_blocks; i++ )
 884       _blocks[i]->dump(&_bbs);
 885   } else {                      // Else do it with a DFS
 886     VectorSet visited(_bbs._arena);
 887     _dump_cfg(_root,visited);
 888   }
 889 }
 890 
 891 void PhaseCFG::dump_headers() {
 892   for( uint i = 0; i < _num_blocks; i++ ) {
 893     if( _blocks[i] == NULL ) continue;
 894     _blocks[i]->dump_head(&_bbs);
 895   }
 896 }
 897 
 898 void PhaseCFG::verify( ) const {
 899 #ifdef ASSERT
 900   // Verify sane CFG
 901   for (uint i = 0; i < _num_blocks; i++) {
 902     Block *b = _blocks[i];
 903     uint cnt = b->_nodes.size();
 904     uint j;
 905     for (j = 0; j < cnt; j++)  {
 906       Node *n = b->_nodes[j];
 907       assert( _bbs[n->_idx] == b, "" );
 908       if (j >= 1 && n->is_Mach() &&
 909           n->as_Mach()->ideal_Opcode() == Op_CreateEx) {
 910         assert(j == 1 || b->_nodes[j-1]->is_Phi(),
 911                "CreateEx must be first instruction in block");
 912       }
 913       for (uint k = 0; k < n->req(); k++) {
 914         Node *def = n->in(k);
 915         if (def && def != n) {
 916           assert(_bbs[def->_idx] || def->is_Con(),
 917                  "must have block; constants for debug info ok");
 918           // Verify that instructions in the block is in correct order.
 919           // Uses must follow their definition if they are at the same block.
 920           // Mostly done to check that MachSpillCopy nodes are placed correctly
 921           // when CreateEx node is moved in build_ifg_physical().
 922           if (_bbs[def->_idx] == b &&
 923               !(b->head()->is_Loop() && n->is_Phi()) &&
 924               // See (+++) comment in reg_split.cpp
 925               !(n->jvms() != NULL && n->jvms()->is_monitor_use(k))) {
 926             bool is_loop = false;
 927             if (n->is_Phi()) {
 928               for (uint l = 1; l < def->req(); l++) {
 929                 if (n == def->in(l)) {
 930                   is_loop = true;
 931                   break; // Some kind of loop
 932                 }
 933               }
 934             }
 935             assert(is_loop || b->find_node(def) < j, "uses must follow definitions");
 936           }
 937         }
 938       }
 939     }
 940 
 941     j = b->end_idx();
 942     Node *bp = (Node*)b->_nodes[b->_nodes.size()-1]->is_block_proj();
 943     assert( bp, "last instruction must be a block proj" );
 944     assert( bp == b->_nodes[j], "wrong number of successors for this block" );
 945     if (bp->is_Catch()) {
 946       while (b->_nodes[--j]->is_MachProj()) ;
 947       assert(b->_nodes[j]->is_MachCall(), "CatchProj must follow call");
 948     } else if (bp->is_Mach() && bp->as_Mach()->ideal_Opcode() == Op_If) {
 949       assert(b->_num_succs == 2, "Conditional branch must have two targets");
 950     }
 951   }
 952 #endif
 953 }
 954 #endif
 955 
 956 //=============================================================================
 957 //------------------------------UnionFind--------------------------------------
 958 UnionFind::UnionFind( uint max ) : _cnt(max), _max(max), _indices(NEW_RESOURCE_ARRAY(uint,max)) {
 959   Copy::zero_to_bytes( _indices, sizeof(uint)*max );
 960 }
 961 
 962 void UnionFind::extend( uint from_idx, uint to_idx ) {
 963   _nesting.check();
 964   if( from_idx >= _max ) {
 965     uint size = 16;
 966     while( size <= from_idx ) size <<=1;
 967     _indices = REALLOC_RESOURCE_ARRAY( uint, _indices, _max, size );
 968     _max = size;
 969   }
 970   while( _cnt <= from_idx ) _indices[_cnt++] = 0;
 971   _indices[from_idx] = to_idx;
 972 }
 973 
 974 void UnionFind::reset( uint max ) {
 975   assert( max <= max_uint, "Must fit within uint" );
 976   // Force the Union-Find mapping to be at least this large
 977   extend(max,0);
 978   // Initialize to be the ID mapping.
 979   for( uint i=0; i<max; i++ ) map(i,i);
 980 }
 981 
 982 //------------------------------Find_compress----------------------------------
 983 // Straight out of Tarjan's union-find algorithm
 984 uint UnionFind::Find_compress( uint idx ) {
 985   uint cur  = idx;
 986   uint next = lookup(cur);
 987   while( next != cur ) {        // Scan chain of equivalences
 988     assert( next < cur, "always union smaller" );
 989     cur = next;                 // until find a fixed-point
 990     next = lookup(cur);
 991   }
 992   // Core of union-find algorithm: update chain of
 993   // equivalences to be equal to the root.
 994   while( idx != next ) {
 995     uint tmp = lookup(idx);
 996     map(idx, next);
 997     idx = tmp;
 998   }
 999   return idx;
1000 }
1001 
1002 //------------------------------Find_const-------------------------------------
1003 // Like Find above, but no path compress, so bad asymptotic behavior
1004 uint UnionFind::Find_const( uint idx ) const {
1005   if( idx == 0 ) return idx;    // Ignore the zero idx
1006   // Off the end?  This can happen during debugging dumps
1007   // when data structures have not finished being updated.
1008   if( idx >= _max ) return idx;
1009   uint next = lookup(idx);
1010   while( next != idx ) {        // Scan chain of equivalences
1011     idx = next;                 // until find a fixed-point
1012     next = lookup(idx);
1013   }
1014   return next;
1015 }
1016 
1017 //------------------------------Union------------------------------------------
1018 // union 2 sets together.
1019 void UnionFind::Union( uint idx1, uint idx2 ) {
1020   uint src = Find(idx1);
1021   uint dst = Find(idx2);
1022   assert( src, "" );
1023   assert( dst, "" );
1024   assert( src < _max, "oob" );
1025   assert( dst < _max, "oob" );
1026   assert( src < dst, "always union smaller" );
1027   map(dst,src);
1028 }
1029 
1030 #ifndef PRODUCT
1031 static void edge_dump(GrowableArray<CFGEdge *> *edges) {
1032   tty->print_cr("---- Edges ----");
1033   for (int i = 0; i < edges->length(); i++) {
1034     CFGEdge *e = edges->at(i);
1035     if (e != NULL) {
1036       edges->at(i)->dump();
1037     }
1038   }
1039 }
1040 
1041 static void trace_dump(Trace *traces[], int count) {
1042   tty->print_cr("---- Traces ----");
1043   for (int i = 0; i < count; i++) {
1044     Trace *tr = traces[i];
1045     if (tr != NULL) {
1046       tr->dump();
1047     }
1048   }
1049 }
1050 
1051 void Trace::dump( ) const {
1052   tty->print_cr("Trace (freq %f)", first_block()->_freq);
1053   for (Block *b = first_block(); b != NULL; b = next(b)) {
1054     tty->print("  B%d", b->_pre_order);
1055     if (b->head()->is_Loop()) {
1056       tty->print(" (L%d)", b->compute_loop_alignment());
1057     }
1058     if (b->has_loop_alignment()) {
1059       tty->print(" (T%d)", b->code_alignment());
1060     }
1061   }
1062   tty->cr();
1063 }
1064 
1065 void CFGEdge::dump( ) const {
1066   tty->print(" B%d  -->  B%d  Freq: %f  out:%3d%%  in:%3d%%  State: ",
1067              from()->_pre_order, to()->_pre_order, freq(), _from_pct, _to_pct);
1068   switch(state()) {
1069   case connected:
1070     tty->print("connected");
1071     break;
1072   case open:
1073     tty->print("open");
1074     break;
1075   case interior:
1076     tty->print("interior");
1077     break;
1078   }
1079   if (infrequent()) {
1080     tty->print("  infrequent");
1081   }
1082   tty->cr();
1083 }
1084 #endif
1085 
1086 //=============================================================================
1087 
1088 //------------------------------edge_order-------------------------------------
1089 // Comparison function for edges
1090 static int edge_order(CFGEdge **e0, CFGEdge **e1) {
1091   float freq0 = (*e0)->freq();
1092   float freq1 = (*e1)->freq();
1093   if (freq0 != freq1) {
1094     return freq0 > freq1 ? -1 : 1;
1095   }
1096 
1097   int dist0 = (*e0)->to()->_rpo - (*e0)->from()->_rpo;
1098   int dist1 = (*e1)->to()->_rpo - (*e1)->from()->_rpo;
1099 
1100   return dist1 - dist0;
1101 }
1102 
1103 //------------------------------trace_frequency_order--------------------------
1104 // Comparison function for edges
1105 extern "C" int trace_frequency_order(const void *p0, const void *p1) {
1106   Trace *tr0 = *(Trace **) p0;
1107   Trace *tr1 = *(Trace **) p1;
1108   Block *b0 = tr0->first_block();
1109   Block *b1 = tr1->first_block();
1110 
1111   // The trace of connector blocks goes at the end;
1112   // we only expect one such trace
1113   if (b0->is_connector() != b1->is_connector()) {
1114     return b1->is_connector() ? -1 : 1;
1115   }
1116 
1117   // Pull more frequently executed blocks to the beginning
1118   float freq0 = b0->_freq;
1119   float freq1 = b1->_freq;
1120   if (freq0 != freq1) {
1121     return freq0 > freq1 ? -1 : 1;
1122   }
1123 
1124   int diff = tr0->first_block()->_rpo - tr1->first_block()->_rpo;
1125 
1126   return diff;
1127 }
1128 
1129 //------------------------------find_edges-------------------------------------
1130 // Find edges of interest, i.e, those which can fall through. Presumes that
1131 // edges which don't fall through are of low frequency and can be generally
1132 // ignored.  Initialize the list of traces.
1133 void PhaseBlockLayout::find_edges()
1134 {
1135   // Walk the blocks, creating edges and Traces
1136   uint i;
1137   Trace *tr = NULL;
1138   for (i = 0; i < _cfg._num_blocks; i++) {
1139     Block *b = _cfg._blocks[i];
1140     tr = new Trace(b, next, prev);
1141     traces[tr->id()] = tr;
1142 
1143     // All connector blocks should be at the end of the list
1144     if (b->is_connector()) break;
1145 
1146     // If this block and the next one have a one-to-one successor
1147     // predecessor relationship, simply append the next block
1148     int nfallthru = b->num_fall_throughs();
1149     while (nfallthru == 1 &&
1150            b->succ_fall_through(0)) {
1151       Block *n = b->_succs[0];
1152 
1153       // Skip over single-entry connector blocks, we don't want to
1154       // add them to the trace.
1155       while (n->is_connector() && n->num_preds() == 1) {
1156         n = n->_succs[0];
1157       }
1158 
1159       // We see a merge point, so stop search for the next block
1160       if (n->num_preds() != 1) break;
1161 
1162       i++;
1163       assert(n = _cfg._blocks[i], "expecting next block");
1164       tr->append(n);
1165       uf->map(n->_pre_order, tr->id());
1166       traces[n->_pre_order] = NULL;
1167       nfallthru = b->num_fall_throughs();
1168       b = n;
1169     }
1170 
1171     if (nfallthru > 0) {
1172       // Create a CFGEdge for each outgoing
1173       // edge that could be a fall-through.
1174       for (uint j = 0; j < b->_num_succs; j++ ) {
1175         if (b->succ_fall_through(j)) {
1176           Block *target = b->non_connector_successor(j);
1177           float freq = b->_freq * b->succ_prob(j);
1178           int from_pct = (int) ((100 * freq) / b->_freq);
1179           int to_pct = (int) ((100 * freq) / target->_freq);
1180           edges->append(new CFGEdge(b, target, freq, from_pct, to_pct));
1181         }
1182       }
1183     }
1184   }
1185 
1186   // Group connector blocks into one trace
1187   for (i++; i < _cfg._num_blocks; i++) {
1188     Block *b = _cfg._blocks[i];
1189     assert(b->is_connector(), "connector blocks at the end");
1190     tr->append(b);
1191     uf->map(b->_pre_order, tr->id());
1192     traces[b->_pre_order] = NULL;
1193   }
1194 }
1195 
1196 //------------------------------union_traces----------------------------------
1197 // Union two traces together in uf, and null out the trace in the list
1198 void PhaseBlockLayout::union_traces(Trace* updated_trace, Trace* old_trace)
1199 {
1200   uint old_id = old_trace->id();
1201   uint updated_id = updated_trace->id();
1202 
1203   uint lo_id = updated_id;
1204   uint hi_id = old_id;
1205 
1206   // If from is greater than to, swap values to meet
1207   // UnionFind guarantee.
1208   if (updated_id > old_id) {
1209     lo_id = old_id;
1210     hi_id = updated_id;
1211 
1212     // Fix up the trace ids
1213     traces[lo_id] = traces[updated_id];
1214     updated_trace->set_id(lo_id);
1215   }
1216 
1217   // Union the lower with the higher and remove the pointer
1218   // to the higher.
1219   uf->Union(lo_id, hi_id);
1220   traces[hi_id] = NULL;
1221 }
1222 
1223 //------------------------------grow_traces-------------------------------------
1224 // Append traces together via the most frequently executed edges
1225 void PhaseBlockLayout::grow_traces()
1226 {
1227   // Order the edges, and drive the growth of Traces via the most
1228   // frequently executed edges.
1229   edges->sort(edge_order);
1230   for (int i = 0; i < edges->length(); i++) {
1231     CFGEdge *e = edges->at(i);
1232 
1233     if (e->state() != CFGEdge::open) continue;
1234 
1235     Block *src_block = e->from();
1236     Block *targ_block = e->to();
1237 
1238     // Don't grow traces along backedges?
1239     if (!BlockLayoutRotateLoops) {
1240       if (targ_block->_rpo <= src_block->_rpo) {
1241         targ_block->set_loop_alignment(targ_block);
1242         continue;
1243       }
1244     }
1245 
1246     Trace *src_trace = trace(src_block);
1247     Trace *targ_trace = trace(targ_block);
1248 
1249     // If the edge in question can join two traces at their ends,
1250     // append one trace to the other.
1251    if (src_trace->last_block() == src_block) {
1252       if (src_trace == targ_trace) {
1253         e->set_state(CFGEdge::interior);
1254         if (targ_trace->backedge(e)) {
1255           // Reset i to catch any newly eligible edge
1256           // (Or we could remember the first "open" edge, and reset there)
1257           i = 0;
1258         }
1259       } else if (targ_trace->first_block() == targ_block) {
1260         e->set_state(CFGEdge::connected);
1261         src_trace->append(targ_trace);
1262         union_traces(src_trace, targ_trace);
1263       }
1264     }
1265   }
1266 }
1267 
1268 //------------------------------merge_traces-----------------------------------
1269 // Embed one trace into another, if the fork or join points are sufficiently
1270 // balanced.
1271 void PhaseBlockLayout::merge_traces(bool fall_thru_only)
1272 {
1273   // Walk the edge list a another time, looking at unprocessed edges.
1274   // Fold in diamonds
1275   for (int i = 0; i < edges->length(); i++) {
1276     CFGEdge *e = edges->at(i);
1277 
1278     if (e->state() != CFGEdge::open) continue;
1279     if (fall_thru_only) {
1280       if (e->infrequent()) continue;
1281     }
1282 
1283     Block *src_block = e->from();
1284     Trace *src_trace = trace(src_block);
1285     bool src_at_tail = src_trace->last_block() == src_block;
1286 
1287     Block *targ_block  = e->to();
1288     Trace *targ_trace  = trace(targ_block);
1289     bool targ_at_start = targ_trace->first_block() == targ_block;
1290 
1291     if (src_trace == targ_trace) {
1292       // This may be a loop, but we can't do much about it.
1293       e->set_state(CFGEdge::interior);
1294       continue;
1295     }
1296 
1297     if (fall_thru_only) {
1298       // If the edge links the middle of two traces, we can't do anything.
1299       // Mark the edge and continue.
1300       if (!src_at_tail & !targ_at_start) {
1301         continue;
1302       }
1303 
1304       // Don't grow traces along backedges?
1305       if (!BlockLayoutRotateLoops && (targ_block->_rpo <= src_block->_rpo)) {
1306           continue;
1307       }
1308 
1309       // If both ends of the edge are available, why didn't we handle it earlier?
1310       assert(src_at_tail ^ targ_at_start, "Should have caught this edge earlier.");
1311 
1312       if (targ_at_start) {
1313         // Insert the "targ" trace in the "src" trace if the insertion point
1314         // is a two way branch.
1315         // Better profitability check possible, but may not be worth it.
1316         // Someday, see if the this "fork" has an associated "join";
1317         // then make a policy on merging this trace at the fork or join.
1318         // For example, other things being equal, it may be better to place this
1319         // trace at the join point if the "src" trace ends in a two-way, but
1320         // the insertion point is one-way.
1321         assert(src_block->num_fall_throughs() == 2, "unexpected diamond");
1322         e->set_state(CFGEdge::connected);
1323         src_trace->insert_after(src_block, targ_trace);
1324         union_traces(src_trace, targ_trace);
1325       } else if (src_at_tail) {
1326         if (src_trace != trace(_cfg._broot)) {
1327           e->set_state(CFGEdge::connected);
1328           targ_trace->insert_before(targ_block, src_trace);
1329           union_traces(targ_trace, src_trace);
1330         }
1331       }
1332     } else if (e->state() == CFGEdge::open) {
1333       // Append traces, even without a fall-thru connection.
1334       // But leave root entry at the beginning of the block list.
1335       if (targ_trace != trace(_cfg._broot)) {
1336         e->set_state(CFGEdge::connected);
1337         src_trace->append(targ_trace);
1338         union_traces(src_trace, targ_trace);
1339       }
1340     }
1341   }
1342 }
1343 
1344 //----------------------------reorder_traces-----------------------------------
1345 // Order the sequence of the traces in some desirable way, and fixup the
1346 // jumps at the end of each block.
1347 void PhaseBlockLayout::reorder_traces(int count)
1348 {
1349   ResourceArea *area = Thread::current()->resource_area();
1350   Trace ** new_traces = NEW_ARENA_ARRAY(area, Trace *, count);
1351   Block_List worklist;
1352   int new_count = 0;
1353 
1354   // Compact the traces.
1355   for (int i = 0; i < count; i++) {
1356     Trace *tr = traces[i];
1357     if (tr != NULL) {
1358       new_traces[new_count++] = tr;
1359     }
1360   }
1361 
1362   // The entry block should be first on the new trace list.
1363   Trace *tr = trace(_cfg._broot);
1364   assert(tr == new_traces[0], "entry trace misplaced");
1365 
1366   // Sort the new trace list by frequency
1367   qsort(new_traces + 1, new_count - 1, sizeof(new_traces[0]), trace_frequency_order);
1368 
1369   // Patch up the successor blocks
1370   _cfg._blocks.reset();
1371   _cfg._num_blocks = 0;
1372   for (int i = 0; i < new_count; i++) {
1373     Trace *tr = new_traces[i];
1374     if (tr != NULL) {
1375       tr->fixup_blocks(_cfg);
1376     }
1377   }
1378 }
1379 
1380 //------------------------------PhaseBlockLayout-------------------------------
1381 // Order basic blocks based on frequency
1382 PhaseBlockLayout::PhaseBlockLayout(PhaseCFG &cfg) :
1383   Phase(BlockLayout),
1384   _cfg(cfg)
1385 {
1386   ResourceMark rm;
1387   ResourceArea *area = Thread::current()->resource_area();
1388 
1389   // List of traces
1390   int size = _cfg._num_blocks + 1;
1391   traces = NEW_ARENA_ARRAY(area, Trace *, size);
1392   memset(traces, 0, size*sizeof(Trace*));
1393   next = NEW_ARENA_ARRAY(area, Block *, size);
1394   memset(next,   0, size*sizeof(Block *));
1395   prev = NEW_ARENA_ARRAY(area, Block *, size);
1396   memset(prev  , 0, size*sizeof(Block *));
1397 
1398   // List of edges
1399   edges = new GrowableArray<CFGEdge*>;
1400 
1401   // Mapping block index --> block_trace
1402   uf = new UnionFind(size);
1403   uf->reset(size);
1404 
1405   // Find edges and create traces.
1406   find_edges();
1407 
1408   // Grow traces at their ends via most frequent edges.
1409   grow_traces();
1410 
1411   // Merge one trace into another, but only at fall-through points.
1412   // This may make diamonds and other related shapes in a trace.
1413   merge_traces(true);
1414 
1415   // Run merge again, allowing two traces to be catenated, even if
1416   // one does not fall through into the other. This appends loosely
1417   // related traces to be near each other.
1418   merge_traces(false);
1419 
1420   // Re-order all the remaining traces by frequency
1421   reorder_traces(size);
1422 
1423   assert(_cfg._num_blocks >= (uint) (size - 1), "number of blocks can not shrink");
1424 }
1425 
1426 
1427 //------------------------------backedge---------------------------------------
1428 // Edge e completes a loop in a trace. If the target block is head of the
1429 // loop, rotate the loop block so that the loop ends in a conditional branch.
1430 bool Trace::backedge(CFGEdge *e) {
1431   bool loop_rotated = false;
1432   Block *src_block  = e->from();
1433   Block *targ_block    = e->to();
1434 
1435   assert(last_block() == src_block, "loop discovery at back branch");
1436   if (first_block() == targ_block) {
1437     if (BlockLayoutRotateLoops && last_block()->num_fall_throughs() < 2) {
1438       // Find the last block in the trace that has a conditional
1439       // branch.
1440       Block *b;
1441       for (b = last_block(); b != NULL; b = prev(b)) {
1442         if (b->num_fall_throughs() == 2) {
1443           break;
1444         }
1445       }
1446 
1447       if (b != last_block() && b != NULL) {
1448         loop_rotated = true;
1449 
1450         // Rotate the loop by doing two-part linked-list surgery.
1451         append(first_block());
1452         break_loop_after(b);
1453       }
1454     }
1455 
1456     // Backbranch to the top of a trace
1457     // Scroll forward through the trace from the targ_block. If we find
1458     // a loop head before another loop top, use the the loop head alignment.
1459     for (Block *b = targ_block; b != NULL; b = next(b)) {
1460       if (b->has_loop_alignment()) {
1461         break;
1462       }
1463       if (b->head()->is_Loop()) {
1464         targ_block = b;
1465         break;
1466       }
1467     }
1468 
1469     first_block()->set_loop_alignment(targ_block);
1470 
1471   } else {
1472     // Backbranch into the middle of a trace
1473     targ_block->set_loop_alignment(targ_block);
1474   }
1475 
1476   return loop_rotated;
1477 }
1478 
1479 //------------------------------fixup_blocks-----------------------------------
1480 // push blocks onto the CFG list
1481 // ensure that blocks have the correct two-way branch sense
1482 void Trace::fixup_blocks(PhaseCFG &cfg) {
1483   Block *last = last_block();
1484   for (Block *b = first_block(); b != NULL; b = next(b)) {
1485     cfg._blocks.push(b);
1486     cfg._num_blocks++;
1487     if (!b->is_connector()) {
1488       int nfallthru = b->num_fall_throughs();
1489       if (b != last) {
1490         if (nfallthru == 2) {
1491           // Ensure that the sense of the branch is correct
1492           Block *bnext = next(b);
1493           Block *bs0 = b->non_connector_successor(0);
1494 
1495           MachNode *iff = b->_nodes[b->_nodes.size()-3]->as_Mach();
1496           ProjNode *proj0 = b->_nodes[b->_nodes.size()-2]->as_Proj();
1497           ProjNode *proj1 = b->_nodes[b->_nodes.size()-1]->as_Proj();
1498 
1499           if (bnext == bs0) {
1500             // Fall-thru case in succs[0], should be in succs[1]
1501 
1502             // Flip targets in _succs map
1503             Block *tbs0 = b->_succs[0];
1504             Block *tbs1 = b->_succs[1];
1505             b->_succs.map( 0, tbs1 );
1506             b->_succs.map( 1, tbs0 );
1507 
1508             // Flip projections to match targets
1509             b->_nodes.map(b->_nodes.size()-2, proj1);
1510             b->_nodes.map(b->_nodes.size()-1, proj0);
1511           }
1512         }
1513       }
1514     }
1515   }
1516 }