1 /*
   2  * Copyright (c) 1997, 2016, 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 "memory/resourceArea.hpp"
  29 #include "compiler/compilerDirectives.hpp"
  30 #include "opto/block.hpp"
  31 #include "opto/cfgnode.hpp"
  32 #include "opto/chaitin.hpp"
  33 #include "opto/loopnode.hpp"
  34 #include "opto/machnode.hpp"
  35 #include "opto/matcher.hpp"
  36 #include "opto/opcodes.hpp"
  37 #include "opto/rootnode.hpp"
  38 #include "utilities/copy.hpp"
  39 
  40 void Block_Array::grow( uint i ) {
  41   assert(i >= Max(), "must be an overflow");
  42   debug_only(_limit = i+1);
  43   if( i < _size )  return;
  44   if( !_size ) {
  45     _size = 1;
  46     _blocks = (Block**)_arena->Amalloc( _size * sizeof(Block*) );
  47     _blocks[0] = NULL;
  48   }
  49   uint old = _size;
  50   while( i >= _size ) _size <<= 1;      // Double to fit
  51   _blocks = (Block**)_arena->Arealloc( _blocks, old*sizeof(Block*),_size*sizeof(Block*));
  52   Copy::zero_to_bytes( &_blocks[old], (_size-old)*sizeof(Block*) );
  53 }
  54 
  55 void Block_List::remove(uint i) {
  56   assert(i < _cnt, "index out of bounds");
  57   Copy::conjoint_words_to_lower((HeapWord*)&_blocks[i+1], (HeapWord*)&_blocks[i], ((_cnt-i-1)*sizeof(Block*)));
  58   pop(); // shrink list by one block
  59 }
  60 
  61 void Block_List::insert(uint i, Block *b) {
  62   push(b); // grow list by one block
  63   Copy::conjoint_words_to_higher((HeapWord*)&_blocks[i], (HeapWord*)&_blocks[i+1], ((_cnt-i-1)*sizeof(Block*)));
  64   _blocks[i] = b;
  65 }
  66 
  67 #ifndef PRODUCT
  68 void Block_List::print() {
  69   for (uint i=0; i < size(); i++) {
  70     tty->print("B%d ", _blocks[i]->_pre_order);
  71   }
  72   tty->print("size = %d\n", size());
  73 }
  74 #endif
  75 
  76 uint Block::code_alignment() const {
  77   // Check for Root block
  78   if (_pre_order == 0) return CodeEntryAlignment;
  79   // Check for Start block
  80   if (_pre_order == 1) return InteriorEntryAlignment;
  81   // Check for loop alignment
  82   if (has_loop_alignment()) return loop_alignment();
  83 
  84   return relocInfo::addr_unit(); // no particular alignment
  85 }
  86 
  87 uint Block::compute_loop_alignment() {
  88   Node *h = head();
  89   int unit_sz = relocInfo::addr_unit();
  90   if (h->is_Loop() && h->as_Loop()->is_inner_loop())  {
  91     // Pre- and post-loops have low trip count so do not bother with
  92     // NOPs for align loop head.  The constants are hidden from tuning
  93     // but only because my "divide by 4" heuristic surely gets nearly
  94     // all possible gain (a "do not align at all" heuristic has a
  95     // chance of getting a really tiny gain).
  96     if (h->is_CountedLoop() && (h->as_CountedLoop()->is_pre_loop() ||
  97                                 h->as_CountedLoop()->is_post_loop())) {
  98       return (OptoLoopAlignment > 4*unit_sz) ? (OptoLoopAlignment>>2) : unit_sz;
  99     }
 100     // Loops with low backedge frequency should not be aligned.
 101     Node *n = h->in(LoopNode::LoopBackControl)->in(0);
 102     if (n->is_MachIf() && n->as_MachIf()->_prob < 0.01) {
 103       return unit_sz; // Loop does not loop, more often than not!
 104     }
 105     return OptoLoopAlignment; // Otherwise align loop head
 106   }
 107 
 108   return unit_sz; // no particular alignment
 109 }
 110 
 111 // Compute the size of first 'inst_cnt' instructions in this block.
 112 // Return the number of instructions left to compute if the block has
 113 // less then 'inst_cnt' instructions. Stop, and return 0 if sum_size
 114 // exceeds OptoLoopAlignment.
 115 uint Block::compute_first_inst_size(uint& sum_size, uint inst_cnt,
 116                                     PhaseRegAlloc* ra) {
 117   uint last_inst = number_of_nodes();
 118   for( uint j = 0; j < last_inst && inst_cnt > 0; j++ ) {
 119     uint inst_size = get_node(j)->size(ra);
 120     if( inst_size > 0 ) {
 121       inst_cnt--;
 122       uint sz = sum_size + inst_size;
 123       if( sz <= (uint)OptoLoopAlignment ) {
 124         // Compute size of instructions which fit into fetch buffer only
 125         // since all inst_cnt instructions will not fit even if we align them.
 126         sum_size = sz;
 127       } else {
 128         return 0;
 129       }
 130     }
 131   }
 132   return inst_cnt;
 133 }
 134 
 135 uint Block::find_node( const Node *n ) const {
 136   for( uint i = 0; i < number_of_nodes(); i++ ) {
 137     if( get_node(i) == n )
 138       return i;
 139   }
 140   ShouldNotReachHere();
 141   return 0;
 142 }
 143 
 144 // Find and remove n from block list
 145 void Block::find_remove( const Node *n ) {
 146   remove_node(find_node(n));
 147 }
 148 
 149 bool Block::contains(const Node *n) const {
 150   return _nodes.contains(n);
 151 }
 152 
 153 // Return empty status of a block.  Empty blocks contain only the head, other
 154 // ideal nodes, and an optional trailing goto.
 155 int Block::is_Empty() const {
 156 
 157   // Root or start block is not considered empty
 158   if (head()->is_Root() || head()->is_Start()) {
 159     return not_empty;
 160   }
 161 
 162   int success_result = completely_empty;
 163   int end_idx = number_of_nodes() - 1;
 164 
 165   // Check for ending goto
 166   if ((end_idx > 0) && (get_node(end_idx)->is_MachGoto())) {
 167     success_result = empty_with_goto;
 168     end_idx--;
 169   }
 170 
 171   // Unreachable blocks are considered empty
 172   if (num_preds() <= 1) {
 173     return success_result;
 174   }
 175 
 176   // Ideal nodes are allowable in empty blocks: skip them  Only MachNodes
 177   // turn directly into code, because only MachNodes have non-trivial
 178   // emit() functions.
 179   while ((end_idx > 0) && !get_node(end_idx)->is_Mach()) {
 180     end_idx--;
 181   }
 182 
 183   // No room for any interesting instructions?
 184   if (end_idx == 0) {
 185     return success_result;
 186   }
 187 
 188   return not_empty;
 189 }
 190 
 191 // Return true if the block's code implies that it is likely to be
 192 // executed infrequently.  Check to see if the block ends in a Halt or
 193 // a low probability call.
 194 bool Block::has_uncommon_code() const {
 195   Node* en = end();
 196 
 197   if (en->is_MachGoto())
 198     en = en->in(0);
 199   if (en->is_Catch())
 200     en = en->in(0);
 201   if (en->is_MachProj() && en->in(0)->is_MachCall()) {
 202     MachCallNode* call = en->in(0)->as_MachCall();
 203     if (call->cnt() != COUNT_UNKNOWN && call->cnt() <= PROB_UNLIKELY_MAG(4)) {
 204       // This is true for slow-path stubs like new_{instance,array},
 205       // slow_arraycopy, complete_monitor_locking, uncommon_trap.
 206       // The magic number corresponds to the probability of an uncommon_trap,
 207       // even though it is a count not a probability.
 208       return true;
 209     }
 210   }
 211 
 212   int op = en->is_Mach() ? en->as_Mach()->ideal_Opcode() : en->Opcode();
 213   return op == Op_Halt;
 214 }
 215 
 216 // True if block is low enough frequency or guarded by a test which
 217 // mostly does not go here.
 218 bool PhaseCFG::is_uncommon(const Block* block) {
 219   // Initial blocks must never be moved, so are never uncommon.
 220   if (block->head()->is_Root() || block->head()->is_Start())  return false;
 221 
 222   // Check for way-low freq
 223   if(block->_freq < BLOCK_FREQUENCY(0.00001f) ) return true;
 224 
 225   // Look for code shape indicating uncommon_trap or slow path
 226   if (block->has_uncommon_code()) return true;
 227 
 228   const float epsilon = 0.05f;
 229   const float guard_factor = PROB_UNLIKELY_MAG(4) / (1.f - epsilon);
 230   uint uncommon_preds = 0;
 231   uint freq_preds = 0;
 232   uint uncommon_for_freq_preds = 0;
 233 
 234   for( uint i=1; i< block->num_preds(); i++ ) {
 235     Block* guard = get_block_for_node(block->pred(i));
 236     // Check to see if this block follows its guard 1 time out of 10000
 237     // or less.
 238     //
 239     // See list of magnitude-4 unlikely probabilities in cfgnode.hpp which
 240     // we intend to be "uncommon", such as slow-path TLE allocation,
 241     // predicted call failure, and uncommon trap triggers.
 242     //
 243     // Use an epsilon value of 5% to allow for variability in frequency
 244     // predictions and floating point calculations. The net effect is
 245     // that guard_factor is set to 9500.
 246     //
 247     // Ignore low-frequency blocks.
 248     // The next check is (guard->_freq < 1.e-5 * 9500.).
 249     if(guard->_freq*BLOCK_FREQUENCY(guard_factor) < BLOCK_FREQUENCY(0.00001f)) {
 250       uncommon_preds++;
 251     } else {
 252       freq_preds++;
 253       if(block->_freq < guard->_freq * guard_factor ) {
 254         uncommon_for_freq_preds++;
 255       }
 256     }
 257   }
 258   if( block->num_preds() > 1 &&
 259       // The block is uncommon if all preds are uncommon or
 260       (uncommon_preds == (block->num_preds()-1) ||
 261       // it is uncommon for all frequent preds.
 262        uncommon_for_freq_preds == freq_preds) ) {
 263     return true;
 264   }
 265   return false;
 266 }
 267 
 268 #ifndef PRODUCT
 269 void Block::dump_bidx(const Block* orig, outputStream* st) const {
 270   if (_pre_order) st->print("B%d",_pre_order);
 271   else st->print("N%d", head()->_idx);
 272 
 273   if (Verbose && orig != this) {
 274     // Dump the original block's idx
 275     st->print(" (");
 276     orig->dump_bidx(orig, st);
 277     st->print(")");
 278   }
 279 }
 280 
 281 void Block::dump_pred(const PhaseCFG* cfg, Block* orig, outputStream* st) const {
 282   if (is_connector()) {
 283     for (uint i=1; i<num_preds(); i++) {
 284       Block *p = cfg->get_block_for_node(pred(i));
 285       p->dump_pred(cfg, orig, st);
 286     }
 287   } else {
 288     dump_bidx(orig, st);
 289     st->print(" ");
 290   }
 291 }
 292 
 293 void Block::dump_head(const PhaseCFG* cfg, outputStream* st) const {
 294   // Print the basic block
 295   dump_bidx(this, st);
 296   st->print(": #\t");
 297 
 298   // Print the incoming CFG edges and the outgoing CFG edges
 299   for( uint i=0; i<_num_succs; i++ ) {
 300     non_connector_successor(i)->dump_bidx(_succs[i], st);
 301     st->print(" ");
 302   }
 303   st->print("<- ");
 304   if( head()->is_block_start() ) {
 305     for (uint i=1; i<num_preds(); i++) {
 306       Node *s = pred(i);
 307       if (cfg != NULL) {
 308         Block *p = cfg->get_block_for_node(s);
 309         p->dump_pred(cfg, p, st);
 310       } else {
 311         while (!s->is_block_start())
 312           s = s->in(0);
 313         st->print("N%d ", s->_idx );
 314       }
 315     }
 316   } else {
 317     st->print("BLOCK HEAD IS JUNK  ");
 318   }
 319 
 320   // Print loop, if any
 321   const Block *bhead = this;    // Head of self-loop
 322   Node *bh = bhead->head();
 323 
 324   if ((cfg != NULL) && bh->is_Loop() && !head()->is_Root()) {
 325     LoopNode *loop = bh->as_Loop();
 326     const Block *bx = cfg->get_block_for_node(loop->in(LoopNode::LoopBackControl));
 327     while (bx->is_connector()) {
 328       bx = cfg->get_block_for_node(bx->pred(1));
 329     }
 330     st->print("\tLoop: B%d-B%d ", bhead->_pre_order, bx->_pre_order);
 331     // Dump any loop-specific bits, especially for CountedLoops.
 332     loop->dump_spec(st);
 333   } else if (has_loop_alignment()) {
 334     st->print(" top-of-loop");
 335   }
 336   st->print(" Freq: %g",_freq);
 337   if( Verbose || WizardMode ) {
 338     st->print(" IDom: %d/#%d", _idom ? _idom->_pre_order : 0, _dom_depth);
 339     st->print(" RegPressure: %d",_reg_pressure);
 340     st->print(" IHRP Index: %d",_ihrp_index);
 341     st->print(" FRegPressure: %d",_freg_pressure);
 342     st->print(" FHRP Index: %d",_fhrp_index);
 343   }
 344   st->cr();
 345 }
 346 
 347 void Block::dump() const {
 348   dump(NULL);
 349 }
 350 
 351 void Block::dump(const PhaseCFG* cfg) const {
 352   dump_head(cfg);
 353   for (uint i=0; i< number_of_nodes(); i++) {
 354     get_node(i)->dump();
 355   }
 356   tty->print("\n");
 357 }
 358 #endif
 359 
 360 PhaseCFG::PhaseCFG(Arena* arena, RootNode* root, Matcher& matcher)
 361 : Phase(CFG)
 362 , _block_arena(arena)
 363 , _regalloc(NULL)
 364 , _scheduling_for_pressure(false)
 365 , _root(root)
 366 , _matcher(matcher)
 367 , _node_to_block_mapping(arena)
 368 , _node_latency(NULL)
 369 #ifndef PRODUCT
 370 , _trace_opto_pipelining(C->directive()->TraceOptoPipeliningOption)
 371 #endif
 372 #ifdef ASSERT
 373 , _raw_oops(arena)
 374 #endif
 375 {
 376   ResourceMark rm;
 377   // I'll need a few machine-specific GotoNodes.  Make an Ideal GotoNode,
 378   // then Match it into a machine-specific Node.  Then clone the machine
 379   // Node on demand.
 380   Node *x = new GotoNode(NULL);
 381   x->init_req(0, x);
 382   _goto = matcher.match_tree(x);
 383   assert(_goto != NULL, "");
 384   _goto->set_req(0,_goto);
 385 
 386   // Build the CFG in Reverse Post Order
 387   _number_of_blocks = build_cfg();
 388   _root_block = get_block_for_node(_root);
 389 }
 390 
 391 // Build a proper looking CFG.  Make every block begin with either a StartNode
 392 // or a RegionNode.  Make every block end with either a Goto, If or Return.
 393 // The RootNode both starts and ends it's own block.  Do this with a recursive
 394 // backwards walk over the control edges.
 395 uint PhaseCFG::build_cfg() {
 396   Arena *a = Thread::current()->resource_area();
 397   VectorSet visited(a);
 398 
 399   // Allocate stack with enough space to avoid frequent realloc
 400   Node_Stack nstack(a, C->live_nodes() >> 1);
 401   nstack.push(_root, 0);
 402   uint sum = 0;                 // Counter for blocks
 403 
 404   while (nstack.is_nonempty()) {
 405     // node and in's index from stack's top
 406     // 'np' is _root (see above) or RegionNode, StartNode: we push on stack
 407     // only nodes which point to the start of basic block (see below).
 408     Node *np = nstack.node();
 409     // idx > 0, except for the first node (_root) pushed on stack
 410     // at the beginning when idx == 0.
 411     // We will use the condition (idx == 0) later to end the build.
 412     uint idx = nstack.index();
 413     Node *proj = np->in(idx);
 414     const Node *x = proj->is_block_proj();
 415     // Does the block end with a proper block-ending Node?  One of Return,
 416     // If or Goto? (This check should be done for visited nodes also).
 417     if (x == NULL) {                    // Does not end right...
 418       Node *g = _goto->clone(); // Force it to end in a Goto
 419       g->set_req(0, proj);
 420       np->set_req(idx, g);
 421       x = proj = g;
 422     }
 423     if (!visited.test_set(x->_idx)) { // Visit this block once
 424       // Skip any control-pinned middle'in stuff
 425       Node *p = proj;
 426       do {
 427         proj = p;                   // Update pointer to last Control
 428         p = p->in(0);               // Move control forward
 429       } while( !p->is_block_proj() &&
 430                !p->is_block_start() );
 431       // Make the block begin with one of Region or StartNode.
 432       if( !p->is_block_start() ) {
 433         RegionNode *r = new RegionNode( 2 );
 434         r->init_req(1, p);         // Insert RegionNode in the way
 435         proj->set_req(0, r);        // Insert RegionNode in the way
 436         p = r;
 437       }
 438       // 'p' now points to the start of this basic block
 439 
 440       // Put self in array of basic blocks
 441       Block *bb = new (_block_arena) Block(_block_arena, p);
 442       map_node_to_block(p, bb);
 443       map_node_to_block(x, bb);
 444       if( x != p ) {                // Only for root is x == p
 445         bb->push_node((Node*)x);
 446       }
 447       // Now handle predecessors
 448       ++sum;                        // Count 1 for self block
 449       uint cnt = bb->num_preds();
 450       for (int i = (cnt - 1); i > 0; i-- ) { // For all predecessors
 451         Node *prevproj = p->in(i);  // Get prior input
 452         assert( !prevproj->is_Con(), "dead input not removed" );
 453         // Check to see if p->in(i) is a "control-dependent" CFG edge -
 454         // i.e., it splits at the source (via an IF or SWITCH) and merges
 455         // at the destination (via a many-input Region).
 456         // This breaks critical edges.  The RegionNode to start the block
 457         // will be added when <p,i> is pulled off the node stack
 458         if ( cnt > 2 ) {             // Merging many things?
 459           assert( prevproj== bb->pred(i),"");
 460           if(prevproj->is_block_proj() != prevproj) { // Control-dependent edge?
 461             // Force a block on the control-dependent edge
 462             Node *g = _goto->clone();       // Force it to end in a Goto
 463             g->set_req(0,prevproj);
 464             p->set_req(i,g);
 465           }
 466         }
 467         nstack.push(p, i);  // 'p' is RegionNode or StartNode
 468       }
 469     } else { // Post-processing visited nodes
 470       nstack.pop();                 // remove node from stack
 471       // Check if it the fist node pushed on stack at the beginning.
 472       if (idx == 0) break;          // end of the build
 473       // Find predecessor basic block
 474       Block *pb = get_block_for_node(x);
 475       // Insert into nodes array, if not already there
 476       if (!has_block(proj)) {
 477         assert( x != proj, "" );
 478         // Map basic block of projection
 479         map_node_to_block(proj, pb);
 480         pb->push_node(proj);
 481       }
 482       // Insert self as a child of my predecessor block
 483       pb->_succs.map(pb->_num_succs++, get_block_for_node(np));
 484       assert( pb->get_node(pb->number_of_nodes() - pb->_num_succs)->is_block_proj(),
 485               "too many control users, not a CFG?" );
 486     }
 487   }
 488   // Return number of basic blocks for all children and self
 489   return sum;
 490 }
 491 
 492 // Inserts a goto & corresponding basic block between
 493 // block[block_no] and its succ_no'th successor block
 494 void PhaseCFG::insert_goto_at(uint block_no, uint succ_no) {
 495   // get block with block_no
 496   assert(block_no < number_of_blocks(), "illegal block number");
 497   Block* in  = get_block(block_no);
 498   // get successor block succ_no
 499   assert(succ_no < in->_num_succs, "illegal successor number");
 500   Block* out = in->_succs[succ_no];
 501   // Compute frequency of the new block. Do this before inserting
 502   // new block in case succ_prob() needs to infer the probability from
 503   // surrounding blocks.
 504   float freq = in->_freq * in->succ_prob(succ_no);
 505   // get ProjNode corresponding to the succ_no'th successor of the in block
 506   ProjNode* proj = in->get_node(in->number_of_nodes() - in->_num_succs + succ_no)->as_Proj();
 507   // create region for basic block
 508   RegionNode* region = new RegionNode(2);
 509   region->init_req(1, proj);
 510   // setup corresponding basic block
 511   Block* block = new (_block_arena) Block(_block_arena, region);
 512   map_node_to_block(region, block);
 513   C->regalloc()->set_bad(region->_idx);
 514   // add a goto node
 515   Node* gto = _goto->clone(); // get a new goto node
 516   gto->set_req(0, region);
 517   // add it to the basic block
 518   block->push_node(gto);
 519   map_node_to_block(gto, block);
 520   C->regalloc()->set_bad(gto->_idx);
 521   // hook up successor block
 522   block->_succs.map(block->_num_succs++, out);
 523   // remap successor's predecessors if necessary
 524   for (uint i = 1; i < out->num_preds(); i++) {
 525     if (out->pred(i) == proj) out->head()->set_req(i, gto);
 526   }
 527   // remap predecessor's successor to new block
 528   in->_succs.map(succ_no, block);
 529   // Set the frequency of the new block
 530   block->_freq = freq;
 531   // add new basic block to basic block list
 532   add_block_at(block_no + 1, block);
 533 }
 534 
 535 // Does this block end in a multiway branch that cannot have the default case
 536 // flipped for another case?
 537 static bool no_flip_branch(Block *b) {
 538   int branch_idx = b->number_of_nodes() - b->_num_succs-1;
 539   if (branch_idx < 1) {
 540     return false;
 541   }
 542   Node *branch = b->get_node(branch_idx);
 543   if (branch->is_Catch()) {
 544     return true;
 545   }
 546   if (branch->is_Mach()) {
 547     if (branch->is_MachNullCheck()) {
 548       return true;
 549     }
 550     int iop = branch->as_Mach()->ideal_Opcode();
 551     if (iop == Op_FastLock || iop == Op_FastUnlock) {
 552       return true;
 553     }
 554     // Don't flip if branch has an implicit check.
 555     if (branch->as_Mach()->is_TrapBasedCheckNode()) {
 556       return true;
 557     }
 558   }
 559   return false;
 560 }
 561 
 562 // Check for NeverBranch at block end.  This needs to become a GOTO to the
 563 // true target.  NeverBranch are treated as a conditional branch that always
 564 // goes the same direction for most of the optimizer and are used to give a
 565 // fake exit path to infinite loops.  At this late stage they need to turn
 566 // into Goto's so that when you enter the infinite loop you indeed hang.
 567 void PhaseCFG::convert_NeverBranch_to_Goto(Block *b) {
 568   // Find true target
 569   int end_idx = b->end_idx();
 570   int idx = b->get_node(end_idx+1)->as_Proj()->_con;
 571   Block *succ = b->_succs[idx];
 572   Node* gto = _goto->clone(); // get a new goto node
 573   gto->set_req(0, b->head());
 574   Node *bp = b->get_node(end_idx);
 575   b->map_node(gto, end_idx); // Slam over NeverBranch
 576   map_node_to_block(gto, b);
 577   C->regalloc()->set_bad(gto->_idx);
 578   b->pop_node();              // Yank projections
 579   b->pop_node();              // Yank projections
 580   b->_succs.map(0,succ);        // Map only successor
 581   b->_num_succs = 1;
 582   // remap successor's predecessors if necessary
 583   uint j;
 584   for( j = 1; j < succ->num_preds(); j++)
 585     if( succ->pred(j)->in(0) == bp )
 586       succ->head()->set_req(j, gto);
 587   // Kill alternate exit path
 588   Block *dead = b->_succs[1-idx];
 589   for( j = 1; j < dead->num_preds(); j++)
 590     if( dead->pred(j)->in(0) == bp )
 591       break;
 592   // Scan through block, yanking dead path from
 593   // all regions and phis.
 594   dead->head()->del_req(j);
 595   for( int k = 1; dead->get_node(k)->is_Phi(); k++ )
 596     dead->get_node(k)->del_req(j);
 597 }
 598 
 599 // Helper function to move block bx to the slot following b_index. Return
 600 // true if the move is successful, otherwise false
 601 bool PhaseCFG::move_to_next(Block* bx, uint b_index) {
 602   if (bx == NULL) return false;
 603 
 604   // Return false if bx is already scheduled.
 605   uint bx_index = bx->_pre_order;
 606   if ((bx_index <= b_index) && (get_block(bx_index) == bx)) {
 607     return false;
 608   }
 609 
 610   // Find the current index of block bx on the block list
 611   bx_index = b_index + 1;
 612   while (bx_index < number_of_blocks() && get_block(bx_index) != bx) {
 613     bx_index++;
 614   }
 615   assert(get_block(bx_index) == bx, "block not found");
 616 
 617   // If the previous block conditionally falls into bx, return false,
 618   // because moving bx will create an extra jump.
 619   for(uint k = 1; k < bx->num_preds(); k++ ) {
 620     Block* pred = get_block_for_node(bx->pred(k));
 621     if (pred == get_block(bx_index - 1)) {
 622       if (pred->_num_succs != 1) {
 623         return false;
 624       }
 625     }
 626   }
 627 
 628   // Reinsert bx just past block 'b'
 629   _blocks.remove(bx_index);
 630   _blocks.insert(b_index + 1, bx);
 631   return true;
 632 }
 633 
 634 // Move empty and uncommon blocks to the end.
 635 void PhaseCFG::move_to_end(Block *b, uint i) {
 636   int e = b->is_Empty();
 637   if (e != Block::not_empty) {
 638     if (e == Block::empty_with_goto) {
 639       // Remove the goto, but leave the block.
 640       b->pop_node();
 641     }
 642     // Mark this block as a connector block, which will cause it to be
 643     // ignored in certain functions such as non_connector_successor().
 644     b->set_connector();
 645   }
 646   // Move the empty block to the end, and don't recheck.
 647   _blocks.remove(i);
 648   _blocks.push(b);
 649 }
 650 
 651 // Set loop alignment for every block
 652 void PhaseCFG::set_loop_alignment() {
 653   uint last = number_of_blocks();
 654   assert(get_block(0) == get_root_block(), "");
 655 
 656   for (uint i = 1; i < last; i++) {
 657     Block* block = get_block(i);
 658     if (block->head()->is_Loop()) {
 659       block->set_loop_alignment(block);
 660     }
 661   }
 662 }
 663 
 664 // Make empty basic blocks to be "connector" blocks, Move uncommon blocks
 665 // to the end.
 666 void PhaseCFG::remove_empty_blocks() {
 667   // Move uncommon blocks to the end
 668   uint last = number_of_blocks();
 669   assert(get_block(0) == get_root_block(), "");
 670 
 671   for (uint i = 1; i < last; i++) {
 672     Block* block = get_block(i);
 673     if (block->is_connector()) {
 674       break;
 675     }
 676 
 677     // Check for NeverBranch at block end.  This needs to become a GOTO to the
 678     // true target.  NeverBranch are treated as a conditional branch that
 679     // always goes the same direction for most of the optimizer and are used
 680     // to give a fake exit path to infinite loops.  At this late stage they
 681     // need to turn into Goto's so that when you enter the infinite loop you
 682     // indeed hang.
 683     if (block->get_node(block->end_idx())->Opcode() == Op_NeverBranch) {
 684       convert_NeverBranch_to_Goto(block);
 685     }
 686 
 687     // Look for uncommon blocks and move to end.
 688     if (!C->do_freq_based_layout()) {
 689       if (is_uncommon(block)) {
 690         move_to_end(block, i);
 691         last--;                   // No longer check for being uncommon!
 692         if (no_flip_branch(block)) { // Fall-thru case must follow?
 693           // Find the fall-thru block
 694           block = get_block(i);
 695           move_to_end(block, i);
 696           last--;
 697         }
 698         // backup block counter post-increment
 699         i--;
 700       }
 701     }
 702   }
 703 
 704   // Move empty blocks to the end
 705   last = number_of_blocks();
 706   for (uint i = 1; i < last; i++) {
 707     Block* block = get_block(i);
 708     if (block->is_Empty() != Block::not_empty) {
 709       move_to_end(block, i);
 710       last--;
 711       i--;
 712     }
 713   } // End of for all blocks
 714 }
 715 
 716 Block *PhaseCFG::fixup_trap_based_check(Node *branch, Block *block, int block_pos, Block *bnext) {
 717   // Trap based checks must fall through to the successor with
 718   // PROB_ALWAYS.
 719   // They should be an If with 2 successors.
 720   assert(branch->is_MachIf(),   "must be If");
 721   assert(block->_num_succs == 2, "must have 2 successors");
 722 
 723   // Get the If node and the projection for the first successor.
 724   MachIfNode *iff   = block->get_node(block->number_of_nodes()-3)->as_MachIf();
 725   ProjNode   *proj0 = block->get_node(block->number_of_nodes()-2)->as_Proj();
 726   ProjNode   *proj1 = block->get_node(block->number_of_nodes()-1)->as_Proj();
 727   ProjNode   *projt = (proj0->Opcode() == Op_IfTrue)  ? proj0 : proj1;
 728   ProjNode   *projf = (proj0->Opcode() == Op_IfFalse) ? proj0 : proj1;
 729 
 730   // Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].
 731   assert(proj0->raw_out(0) == block->_succs[0]->head(), "Mismatch successor 0");
 732   assert(proj1->raw_out(0) == block->_succs[1]->head(), "Mismatch successor 1");
 733 
 734   ProjNode *proj_always;
 735   ProjNode *proj_never;
 736   // We must negate the branch if the implicit check doesn't follow
 737   // the branch's TRUE path. Then, the new TRUE branch target will
 738   // be the old FALSE branch target.
 739   if (iff->_prob <= 2*PROB_NEVER) {   // There are small rounding errors.
 740     proj_never  = projt;
 741     proj_always = projf;
 742   } else {
 743     // We must negate the branch if the trap doesn't follow the
 744     // branch's TRUE path. Then, the new TRUE branch target will
 745     // be the old FALSE branch target.
 746     proj_never  = projf;
 747     proj_always = projt;
 748     iff->negate();
 749   }
 750   assert(iff->_prob <= 2*PROB_NEVER, "Trap based checks are expected to trap never!");
 751   // Map the successors properly
 752   block->_succs.map(0, get_block_for_node(proj_never ->raw_out(0)));   // The target of the trap.
 753   block->_succs.map(1, get_block_for_node(proj_always->raw_out(0)));   // The fall through target.
 754 
 755   if (block->get_node(block->number_of_nodes() - block->_num_succs + 1) != proj_always) {
 756     block->map_node(proj_never,  block->number_of_nodes() - block->_num_succs + 0);
 757     block->map_node(proj_always, block->number_of_nodes() - block->_num_succs + 1);
 758   }
 759 
 760   // Place the fall through block after this block.
 761   Block *bs1 = block->non_connector_successor(1);
 762   if (bs1 != bnext && move_to_next(bs1, block_pos)) {
 763     bnext = bs1;
 764   }
 765   // If the fall through block still is not the next block, insert a goto.
 766   if (bs1 != bnext) {
 767     insert_goto_at(block_pos, 1);
 768   }
 769   return bnext;
 770 }
 771 
 772 // Fix up the final control flow for basic blocks.
 773 void PhaseCFG::fixup_flow() {
 774   // Fixup final control flow for the blocks.  Remove jump-to-next
 775   // block. If neither arm of an IF follows the conditional branch, we
 776   // have to add a second jump after the conditional.  We place the
 777   // TRUE branch target in succs[0] for both GOTOs and IFs.
 778   for (uint i = 0; i < number_of_blocks(); i++) {
 779     Block* block = get_block(i);
 780     block->_pre_order = i;          // turn pre-order into block-index
 781 
 782     // Connector blocks need no further processing.
 783     if (block->is_connector()) {
 784       assert((i+1) == number_of_blocks() || get_block(i + 1)->is_connector(), "All connector blocks should sink to the end");
 785       continue;
 786     }
 787     assert(block->is_Empty() != Block::completely_empty, "Empty blocks should be connectors");
 788 
 789     Block* bnext = (i < number_of_blocks() - 1) ? get_block(i + 1) : NULL;
 790     Block* bs0 = block->non_connector_successor(0);
 791 
 792     // Check for multi-way branches where I cannot negate the test to
 793     // exchange the true and false targets.
 794     if (no_flip_branch(block)) {
 795       // Find fall through case - if must fall into its target.
 796       // Get the index of the branch's first successor.
 797       int branch_idx = block->number_of_nodes() - block->_num_succs;
 798 
 799       // The branch is 1 before the branch's first successor.
 800       Node *branch = block->get_node(branch_idx-1);
 801 
 802       // Handle no-flip branches which have implicit checks and which require
 803       // special block ordering and individual semantics of the 'fall through
 804       // case'.
 805       if ((TrapBasedNullChecks || TrapBasedRangeChecks) &&
 806           branch->is_Mach() && branch->as_Mach()->is_TrapBasedCheckNode()) {
 807         bnext = fixup_trap_based_check(branch, block, i, bnext);
 808       } else {
 809         // Else, default handling for no-flip branches
 810         for (uint j2 = 0; j2 < block->_num_succs; j2++) {
 811           const ProjNode* p = block->get_node(branch_idx + j2)->as_Proj();
 812           if (p->_con == 0) {
 813             // successor j2 is fall through case
 814             if (block->non_connector_successor(j2) != bnext) {
 815               // but it is not the next block => insert a goto
 816               insert_goto_at(i, j2);
 817             }
 818             // Put taken branch in slot 0
 819             if (j2 == 0 && block->_num_succs == 2) {
 820               // Flip targets in succs map
 821               Block *tbs0 = block->_succs[0];
 822               Block *tbs1 = block->_succs[1];
 823               block->_succs.map(0, tbs1);
 824               block->_succs.map(1, tbs0);
 825             }
 826             break;
 827           }
 828         }
 829       }
 830 
 831       // Remove all CatchProjs
 832       for (uint j = 0; j < block->_num_succs; j++) {
 833         block->pop_node();
 834       }
 835 
 836     } else if (block->_num_succs == 1) {
 837       // Block ends in a Goto?
 838       if (bnext == bs0) {
 839         // We fall into next block; remove the Goto
 840         block->pop_node();
 841       }
 842 
 843     } else if(block->_num_succs == 2) { // Block ends in a If?
 844       // Get opcode of 1st projection (matches _succs[0])
 845       // Note: Since this basic block has 2 exits, the last 2 nodes must
 846       //       be projections (in any order), the 3rd last node must be
 847       //       the IfNode (we have excluded other 2-way exits such as
 848       //       CatchNodes already).
 849       MachNode* iff   = block->get_node(block->number_of_nodes() - 3)->as_Mach();
 850       ProjNode* proj0 = block->get_node(block->number_of_nodes() - 2)->as_Proj();
 851       ProjNode* proj1 = block->get_node(block->number_of_nodes() - 1)->as_Proj();
 852 
 853       // Assert that proj0 and succs[0] match up. Similarly for proj1 and succs[1].
 854       assert(proj0->raw_out(0) == block->_succs[0]->head(), "Mismatch successor 0");
 855       assert(proj1->raw_out(0) == block->_succs[1]->head(), "Mismatch successor 1");
 856 
 857       Block* bs1 = block->non_connector_successor(1);
 858 
 859       // Check for neither successor block following the current
 860       // block ending in a conditional. If so, move one of the
 861       // successors after the current one, provided that the
 862       // successor was previously unscheduled, but moveable
 863       // (i.e., all paths to it involve a branch).
 864       if (!C->do_freq_based_layout() && bnext != bs0 && bnext != bs1) {
 865         // Choose the more common successor based on the probability
 866         // of the conditional branch.
 867         Block* bx = bs0;
 868         Block* by = bs1;
 869 
 870         // _prob is the probability of taking the true path. Make
 871         // p the probability of taking successor #1.
 872         float p = iff->as_MachIf()->_prob;
 873         if (proj0->Opcode() == Op_IfTrue) {
 874           p = 1.0 - p;
 875         }
 876 
 877         // Prefer successor #1 if p > 0.5
 878         if (p > PROB_FAIR) {
 879           bx = bs1;
 880           by = bs0;
 881         }
 882 
 883         // Attempt the more common successor first
 884         if (move_to_next(bx, i)) {
 885           bnext = bx;
 886         } else if (move_to_next(by, i)) {
 887           bnext = by;
 888         }
 889       }
 890 
 891       // Check for conditional branching the wrong way.  Negate
 892       // conditional, if needed, so it falls into the following block
 893       // and branches to the not-following block.
 894 
 895       // Check for the next block being in succs[0].  We are going to branch
 896       // to succs[0], so we want the fall-thru case as the next block in
 897       // succs[1].
 898       if (bnext == bs0) {
 899         // Fall-thru case in succs[0], so flip targets in succs map
 900         Block* tbs0 = block->_succs[0];
 901         Block* tbs1 = block->_succs[1];
 902         block->_succs.map(0, tbs1);
 903         block->_succs.map(1, tbs0);
 904         // Flip projection for each target
 905         ProjNode* tmp = proj0;
 906         proj0 = proj1;
 907         proj1 = tmp;
 908 
 909       } else if(bnext != bs1) {
 910         // Need a double-branch
 911         // The existing conditional branch need not change.
 912         // Add a unconditional branch to the false target.
 913         // Alas, it must appear in its own block and adding a
 914         // block this late in the game is complicated.  Sigh.
 915         insert_goto_at(i, 1);
 916       }
 917 
 918       // Make sure we TRUE branch to the target
 919       if (proj0->Opcode() == Op_IfFalse) {
 920         iff->as_MachIf()->negate();
 921       }
 922 
 923       block->pop_node();          // Remove IfFalse & IfTrue projections
 924       block->pop_node();
 925 
 926     } else {
 927       // Multi-exit block, e.g. a switch statement
 928       // But we don't need to do anything here
 929     }
 930   } // End of for all blocks
 931 }
 932 
 933 
 934 // postalloc_expand: Expand nodes after register allocation.
 935 //
 936 // postalloc_expand has to be called after register allocation, just
 937 // before output (i.e. scheduling). It only gets called if
 938 // Matcher::require_postalloc_expand is true.
 939 //
 940 // Background:
 941 //
 942 // Nodes that are expandend (one compound node requiring several
 943 // assembler instructions to be implemented split into two or more
 944 // non-compound nodes) after register allocation are not as nice as
 945 // the ones expanded before register allocation - they don't
 946 // participate in optimizations as global code motion. But after
 947 // register allocation we can expand nodes that use registers which
 948 // are not spillable or registers that are not allocated, because the
 949 // old compound node is simply replaced (in its location in the basic
 950 // block) by a new subgraph which does not contain compound nodes any
 951 // more. The scheduler called during output can later on process these
 952 // non-compound nodes.
 953 //
 954 // Implementation:
 955 //
 956 // Nodes requiring postalloc expand are specified in the ad file by using
 957 // a postalloc_expand statement instead of ins_encode. A postalloc_expand
 958 // contains a single call to an encoding, as does an ins_encode
 959 // statement. Instead of an emit() function a postalloc_expand() function
 960 // is generated that doesn't emit assembler but creates a new
 961 // subgraph. The code below calls this postalloc_expand function for each
 962 // node with the appropriate attribute. This function returns the new
 963 // nodes generated in an array passed in the call. The old node,
 964 // potential MachTemps before and potential Projs after it then get
 965 // disconnected and replaced by the new nodes. The instruction
 966 // generating the result has to be the last one in the array. In
 967 // general it is assumed that Projs after the node expanded are
 968 // kills. These kills are not required any more after expanding as
 969 // there are now explicitly visible def-use chains and the Projs are
 970 // removed. This does not hold for calls: They do not only have
 971 // kill-Projs but also Projs defining values. Therefore Projs after
 972 // the node expanded are removed for all but for calls. If a node is
 973 // to be reused, it must be added to the nodes list returned, and it
 974 // will be added again.
 975 //
 976 // Implementing the postalloc_expand function for a node in an enc_class
 977 // is rather tedious. It requires knowledge about many node details, as
 978 // the nodes and the subgraph must be hand crafted. To simplify this,
 979 // adlc generates some utility variables into the postalloc_expand function,
 980 // e.g., holding the operands as specified by the postalloc_expand encoding
 981 // specification, e.g.:
 982 //  * unsigned idx_<par_name>  holding the index of the node in the ins
 983 //  * Node *n_<par_name>       holding the node loaded from the ins
 984 //  * MachOpnd *op_<par_name>  holding the corresponding operand
 985 //
 986 // The ordering of operands can not be determined by looking at a
 987 // rule. Especially if a match rule matches several different trees,
 988 // several nodes are generated from one instruct specification with
 989 // different operand orderings. In this case the adlc generated
 990 // variables are the only way to access the ins and operands
 991 // deterministically.
 992 //
 993 // If assigning a register to a node that contains an oop, don't
 994 // forget to call ra_->set_oop() for the node.
 995 void PhaseCFG::postalloc_expand(PhaseRegAlloc* _ra) {
 996   GrowableArray <Node *> new_nodes(32); // Array with new nodes filled by postalloc_expand function of node.
 997   GrowableArray <Node *> remove(32);
 998   GrowableArray <Node *> succs(32);
 999   unsigned int max_idx = C->unique();   // Remember to distinguish new from old nodes.
1000   DEBUG_ONLY(bool foundNode = false);
1001 
1002   // for all blocks
1003   for (uint i = 0; i < number_of_blocks(); i++) {
1004     Block *b = _blocks[i];
1005     // For all instructions in the current block.
1006     for (uint j = 0; j < b->number_of_nodes(); j++) {
1007       Node *n = b->get_node(j);
1008       if (n->is_Mach() && n->as_Mach()->requires_postalloc_expand()) {
1009 #ifdef ASSERT
1010         if (TracePostallocExpand) {
1011           if (!foundNode) {
1012             foundNode = true;
1013             tty->print("POSTALLOC EXPANDING %d %s\n", C->compile_id(),
1014                        C->method() ? C->method()->name()->as_utf8() : C->stub_name());
1015           }
1016           tty->print("  postalloc expanding "); n->dump();
1017           if (Verbose) {
1018             tty->print("    with ins:\n");
1019             for (uint k = 0; k < n->len(); ++k) {
1020               if (n->in(k)) { tty->print("        "); n->in(k)->dump(); }
1021             }
1022           }
1023         }
1024 #endif
1025         new_nodes.clear();
1026         // Collect nodes that have to be removed from the block later on.
1027         uint req = n->req();
1028         remove.clear();
1029         for (uint k = 0; k < req; ++k) {
1030           if (n->in(k) && n->in(k)->is_MachTemp()) {
1031             remove.push(n->in(k)); // MachTemps which are inputs to the old node have to be removed.
1032             n->in(k)->del_req(0);
1033             j--;
1034           }
1035         }
1036 
1037         // Check whether we can allocate enough nodes. We set a fix limit for
1038         // the size of postalloc expands with this.
1039         uint unique_limit = C->unique() + 40;
1040         if (unique_limit >= _ra->node_regs_max_index()) {
1041           Compile::current()->record_failure("out of nodes in postalloc expand");
1042           return;
1043         }
1044 
1045         // Emit (i.e. generate new nodes).
1046         n->as_Mach()->postalloc_expand(&new_nodes, _ra);
1047 
1048         assert(C->unique() < unique_limit, "You allocated too many nodes in your postalloc expand.");
1049 
1050         // Disconnect the inputs of the old node.
1051         //
1052         // We reuse MachSpillCopy nodes. If we need to expand them, there
1053         // are many, so reusing pays off. If reused, the node already
1054         // has the new ins. n must be the last node on new_nodes list.
1055         if (!n->is_MachSpillCopy()) {
1056           for (int k = req - 1; k >= 0; --k) {
1057             n->del_req(k);
1058           }
1059         }
1060 
1061 #ifdef ASSERT
1062         // Check that all nodes have proper operands.
1063         for (int k = 0; k < new_nodes.length(); ++k) {
1064           if (new_nodes.at(k)->_idx < max_idx || !new_nodes.at(k)->is_Mach()) continue; // old node, Proj ...
1065           MachNode *m = new_nodes.at(k)->as_Mach();
1066           for (unsigned int l = 0; l < m->num_opnds(); ++l) {
1067             if (MachOper::notAnOper(m->_opnds[l])) {
1068               outputStream *os = tty;
1069               os->print("Node %s ", m->Name());
1070               os->print("has invalid opnd %d: %p\n", l, m->_opnds[l]);
1071               assert(0, "Invalid operands, see inline trace in hs_err_pid file.");
1072             }
1073           }
1074         }
1075 #endif
1076 
1077         // Collect succs of old node in remove (for projections) and in succs (for
1078         // all other nodes) do _not_ collect projections in remove (but in succs)
1079         // in case the node is a call. We need the projections for calls as they are
1080         // associated with registes (i.e. they are defs).
1081         succs.clear();
1082         for (DUIterator k = n->outs(); n->has_out(k); k++) {
1083           if (n->out(k)->is_Proj() && !n->is_MachCall() && !n->is_MachBranch()) {
1084             remove.push(n->out(k));
1085           } else {
1086             succs.push(n->out(k));
1087           }
1088         }
1089         // Replace old node n as input of its succs by last of the new nodes.
1090         for (int k = 0; k < succs.length(); ++k) {
1091           Node *succ = succs.at(k);
1092           for (uint l = 0; l < succ->req(); ++l) {
1093             if (succ->in(l) == n) {
1094               succ->set_req(l, new_nodes.at(new_nodes.length() - 1));
1095             }
1096           }
1097           for (uint l = succ->req(); l < succ->len(); ++l) {
1098             if (succ->in(l) == n) {
1099               succ->set_prec(l, new_nodes.at(new_nodes.length() - 1));
1100             }
1101           }
1102         }
1103 
1104         // Index of old node in block.
1105         uint index = b->find_node(n);
1106         // Insert new nodes into block and map them in nodes->blocks array
1107         // and remember last node in n2.
1108         Node *n2 = NULL;
1109         for (int k = 0; k < new_nodes.length(); ++k) {
1110           n2 = new_nodes.at(k);
1111           b->insert_node(n2, ++index);
1112           map_node_to_block(n2, b);
1113         }
1114 
1115         // Add old node n to remove and remove them all from block.
1116         remove.push(n);
1117         j--;
1118 #ifdef ASSERT
1119         if (TracePostallocExpand && Verbose) {
1120           tty->print("    removing:\n");
1121           for (int k = 0; k < remove.length(); ++k) {
1122             tty->print("        "); remove.at(k)->dump();
1123           }
1124           tty->print("    inserting:\n");
1125           for (int k = 0; k < new_nodes.length(); ++k) {
1126             tty->print("        "); new_nodes.at(k)->dump();
1127           }
1128         }
1129 #endif
1130         for (int k = 0; k < remove.length(); ++k) {
1131           if (b->contains(remove.at(k))) {
1132             b->find_remove(remove.at(k));
1133           } else {
1134             assert(remove.at(k)->is_Proj() && (remove.at(k)->in(0)->is_MachBranch()), "");
1135           }
1136         }
1137         // If anything has been inserted (n2 != NULL), continue after last node inserted.
1138         // This does not always work. Some postalloc expands don't insert any nodes, if they
1139         // do optimizations (e.g., max(x,x)). In this case we decrement j accordingly.
1140         j = n2 ? b->find_node(n2) : j;
1141       }
1142     }
1143   }
1144 
1145 #ifdef ASSERT
1146   if (foundNode) {
1147     tty->print("FINISHED %d %s\n", C->compile_id(),
1148                C->method() ? C->method()->name()->as_utf8() : C->stub_name());
1149     tty->flush();
1150   }
1151 #endif
1152 }
1153 
1154 
1155 //------------------------------dump-------------------------------------------
1156 #ifndef PRODUCT
1157 void PhaseCFG::_dump_cfg( const Node *end, VectorSet &visited  ) const {
1158   const Node *x = end->is_block_proj();
1159   assert( x, "not a CFG" );
1160 
1161   // Do not visit this block again
1162   if( visited.test_set(x->_idx) ) return;
1163 
1164   // Skip through this block
1165   const Node *p = x;
1166   do {
1167     p = p->in(0);               // Move control forward
1168     assert( !p->is_block_proj() || p->is_Root(), "not a CFG" );
1169   } while( !p->is_block_start() );
1170 
1171   // Recursively visit
1172   for (uint i = 1; i < p->req(); i++) {
1173     _dump_cfg(p->in(i), visited);
1174   }
1175 
1176   // Dump the block
1177   get_block_for_node(p)->dump(this);
1178 }
1179 
1180 void PhaseCFG::dump( ) const {
1181   tty->print("\n--- CFG --- %d BBs\n", number_of_blocks());
1182   if (_blocks.size()) {        // Did we do basic-block layout?
1183     for (uint i = 0; i < number_of_blocks(); i++) {
1184       const Block* block = get_block(i);
1185       block->dump(this);
1186     }
1187   } else {                      // Else do it with a DFS
1188     VectorSet visited(_block_arena);
1189     _dump_cfg(_root,visited);
1190   }
1191 }
1192 
1193 void PhaseCFG::dump_headers() {
1194   for (uint i = 0; i < number_of_blocks(); i++) {
1195     Block* block = get_block(i);
1196     if (block != NULL) {
1197       block->dump_head(this);
1198     }
1199   }
1200 }
1201 
1202 void PhaseCFG::verify() const {
1203 #ifdef ASSERT
1204   // Verify sane CFG
1205   for (uint i = 0; i < number_of_blocks(); i++) {
1206     Block* block = get_block(i);
1207     uint cnt = block->number_of_nodes();
1208     uint j;
1209     for (j = 0; j < cnt; j++)  {
1210       Node *n = block->get_node(j);
1211       assert(get_block_for_node(n) == block, "");
1212       if (j >= 1 && n->is_Mach() && n->as_Mach()->ideal_Opcode() == Op_CreateEx) {
1213         assert(j == 1 || block->get_node(j-1)->is_Phi(), "CreateEx must be first instruction in block");
1214       }
1215       for (uint k = 0; k < n->req(); k++) {
1216         Node *def = n->in(k);
1217         if (def && def != n) {
1218           assert(get_block_for_node(def) || def->is_Con(), "must have block; constants for debug info ok");
1219           // Verify that instructions in the block is in correct order.
1220           // Uses must follow their definition if they are at the same block.
1221           // Mostly done to check that MachSpillCopy nodes are placed correctly
1222           // when CreateEx node is moved in build_ifg_physical().
1223           if (get_block_for_node(def) == block && !(block->head()->is_Loop() && n->is_Phi()) &&
1224               // See (+++) comment in reg_split.cpp
1225               !(n->jvms() != NULL && n->jvms()->is_monitor_use(k))) {
1226             bool is_loop = false;
1227             if (n->is_Phi()) {
1228               for (uint l = 1; l < def->req(); l++) {
1229                 if (n == def->in(l)) {
1230                   is_loop = true;
1231                   break; // Some kind of loop
1232                 }
1233               }
1234             }
1235             assert(is_loop || block->find_node(def) < j, "uses must follow definitions");
1236           }
1237         }
1238       }
1239     }
1240 
1241     j = block->end_idx();
1242     Node* bp = (Node*)block->get_node(block->number_of_nodes() - 1)->is_block_proj();
1243     assert(bp, "last instruction must be a block proj");
1244     assert(bp == block->get_node(j), "wrong number of successors for this block");
1245     if (bp->is_Catch()) {
1246       while (block->get_node(--j)->is_MachProj()) {
1247         ;
1248       }
1249       assert(block->get_node(j)->is_MachCall(), "CatchProj must follow call");
1250     } else if (bp->is_Mach() && bp->as_Mach()->ideal_Opcode() == Op_If) {
1251       assert(block->_num_succs == 2, "Conditional branch must have two targets");
1252     }
1253   }
1254 #endif
1255 }
1256 #endif
1257 
1258 UnionFind::UnionFind( uint max ) : _cnt(max), _max(max), _indices(NEW_RESOURCE_ARRAY(uint,max)) {
1259   Copy::zero_to_bytes( _indices, sizeof(uint)*max );
1260 }
1261 
1262 void UnionFind::extend( uint from_idx, uint to_idx ) {
1263   _nesting.check();
1264   if( from_idx >= _max ) {
1265     uint size = 16;
1266     while( size <= from_idx ) size <<=1;
1267     _indices = REALLOC_RESOURCE_ARRAY( uint, _indices, _max, size );
1268     _max = size;
1269   }
1270   while( _cnt <= from_idx ) _indices[_cnt++] = 0;
1271   _indices[from_idx] = to_idx;
1272 }
1273 
1274 void UnionFind::reset( uint max ) {
1275   // Force the Union-Find mapping to be at least this large
1276   extend(max,0);
1277   // Initialize to be the ID mapping.
1278   for( uint i=0; i<max; i++ ) map(i,i);
1279 }
1280 
1281 // Straight out of Tarjan's union-find algorithm
1282 uint UnionFind::Find_compress( uint idx ) {
1283   uint cur  = idx;
1284   uint next = lookup(cur);
1285   while( next != cur ) {        // Scan chain of equivalences
1286     assert( next < cur, "always union smaller" );
1287     cur = next;                 // until find a fixed-point
1288     next = lookup(cur);
1289   }
1290   // Core of union-find algorithm: update chain of
1291   // equivalences to be equal to the root.
1292   while( idx != next ) {
1293     uint tmp = lookup(idx);
1294     map(idx, next);
1295     idx = tmp;
1296   }
1297   return idx;
1298 }
1299 
1300 // Like Find above, but no path compress, so bad asymptotic behavior
1301 uint UnionFind::Find_const( uint idx ) const {
1302   if( idx == 0 ) return idx;    // Ignore the zero idx
1303   // Off the end?  This can happen during debugging dumps
1304   // when data structures have not finished being updated.
1305   if( idx >= _max ) return idx;
1306   uint next = lookup(idx);
1307   while( next != idx ) {        // Scan chain of equivalences
1308     idx = next;                 // until find a fixed-point
1309     next = lookup(idx);
1310   }
1311   return next;
1312 }
1313 
1314 // union 2 sets together.
1315 void UnionFind::Union( uint idx1, uint idx2 ) {
1316   uint src = Find(idx1);
1317   uint dst = Find(idx2);
1318   assert( src, "" );
1319   assert( dst, "" );
1320   assert( src < _max, "oob" );
1321   assert( dst < _max, "oob" );
1322   assert( src < dst, "always union smaller" );
1323   map(dst,src);
1324 }
1325 
1326 #ifndef PRODUCT
1327 void Trace::dump( ) const {
1328   tty->print_cr("Trace (freq %f)", first_block()->_freq);
1329   for (Block *b = first_block(); b != NULL; b = next(b)) {
1330     tty->print("  B%d", b->_pre_order);
1331     if (b->head()->is_Loop()) {
1332       tty->print(" (L%d)", b->compute_loop_alignment());
1333     }
1334     if (b->has_loop_alignment()) {
1335       tty->print(" (T%d)", b->code_alignment());
1336     }
1337   }
1338   tty->cr();
1339 }
1340 
1341 void CFGEdge::dump( ) const {
1342   tty->print(" B%d  -->  B%d  Freq: %f  out:%3d%%  in:%3d%%  State: ",
1343              from()->_pre_order, to()->_pre_order, freq(), _from_pct, _to_pct);
1344   switch(state()) {
1345   case connected:
1346     tty->print("connected");
1347     break;
1348   case open:
1349     tty->print("open");
1350     break;
1351   case interior:
1352     tty->print("interior");
1353     break;
1354   }
1355   if (infrequent()) {
1356     tty->print("  infrequent");
1357   }
1358   tty->cr();
1359 }
1360 #endif
1361 
1362 // Comparison function for edges
1363 static int edge_order(CFGEdge **e0, CFGEdge **e1) {
1364   float freq0 = (*e0)->freq();
1365   float freq1 = (*e1)->freq();
1366   if (freq0 != freq1) {
1367     return freq0 > freq1 ? -1 : 1;
1368   }
1369 
1370   int dist0 = (*e0)->to()->_rpo - (*e0)->from()->_rpo;
1371   int dist1 = (*e1)->to()->_rpo - (*e1)->from()->_rpo;
1372 
1373   return dist1 - dist0;
1374 }
1375 
1376 // Comparison function for edges
1377 extern "C" int trace_frequency_order(const void *p0, const void *p1) {
1378   Trace *tr0 = *(Trace **) p0;
1379   Trace *tr1 = *(Trace **) p1;
1380   Block *b0 = tr0->first_block();
1381   Block *b1 = tr1->first_block();
1382 
1383   // The trace of connector blocks goes at the end;
1384   // we only expect one such trace
1385   if (b0->is_connector() != b1->is_connector()) {
1386     return b1->is_connector() ? -1 : 1;
1387   }
1388 
1389   // Pull more frequently executed blocks to the beginning
1390   float freq0 = b0->_freq;
1391   float freq1 = b1->_freq;
1392   if (freq0 != freq1) {
1393     return freq0 > freq1 ? -1 : 1;
1394   }
1395 
1396   int diff = tr0->first_block()->_rpo - tr1->first_block()->_rpo;
1397 
1398   return diff;
1399 }
1400 
1401 // Find edges of interest, i.e, those which can fall through. Presumes that
1402 // edges which don't fall through are of low frequency and can be generally
1403 // ignored.  Initialize the list of traces.
1404 void PhaseBlockLayout::find_edges() {
1405   // Walk the blocks, creating edges and Traces
1406   uint i;
1407   Trace *tr = NULL;
1408   for (i = 0; i < _cfg.number_of_blocks(); i++) {
1409     Block* b = _cfg.get_block(i);
1410     tr = new Trace(b, next, prev);
1411     traces[tr->id()] = tr;
1412 
1413     // All connector blocks should be at the end of the list
1414     if (b->is_connector()) break;
1415 
1416     // If this block and the next one have a one-to-one successor
1417     // predecessor relationship, simply append the next block
1418     int nfallthru = b->num_fall_throughs();
1419     while (nfallthru == 1 &&
1420            b->succ_fall_through(0)) {
1421       Block *n = b->_succs[0];
1422 
1423       // Skip over single-entry connector blocks, we don't want to
1424       // add them to the trace.
1425       while (n->is_connector() && n->num_preds() == 1) {
1426         n = n->_succs[0];
1427       }
1428 
1429       // We see a merge point, so stop search for the next block
1430       if (n->num_preds() != 1) break;
1431 
1432       i++;
1433       assert(n = _cfg.get_block(i), "expecting next block");
1434       tr->append(n);
1435       uf->map(n->_pre_order, tr->id());
1436       traces[n->_pre_order] = NULL;
1437       nfallthru = b->num_fall_throughs();
1438       b = n;
1439     }
1440 
1441     if (nfallthru > 0) {
1442       // Create a CFGEdge for each outgoing
1443       // edge that could be a fall-through.
1444       for (uint j = 0; j < b->_num_succs; j++ ) {
1445         if (b->succ_fall_through(j)) {
1446           Block *target = b->non_connector_successor(j);
1447           float freq = b->_freq * b->succ_prob(j);
1448           int from_pct = (int) ((100 * freq) / b->_freq);
1449           int to_pct = (int) ((100 * freq) / target->_freq);
1450           edges->append(new CFGEdge(b, target, freq, from_pct, to_pct));
1451         }
1452       }
1453     }
1454   }
1455 
1456   // Group connector blocks into one trace
1457   for (i++; i < _cfg.number_of_blocks(); i++) {
1458     Block *b = _cfg.get_block(i);
1459     assert(b->is_connector(), "connector blocks at the end");
1460     tr->append(b);
1461     uf->map(b->_pre_order, tr->id());
1462     traces[b->_pre_order] = NULL;
1463   }
1464 }
1465 
1466 // Union two traces together in uf, and null out the trace in the list
1467 void PhaseBlockLayout::union_traces(Trace* updated_trace, Trace* old_trace) {
1468   uint old_id = old_trace->id();
1469   uint updated_id = updated_trace->id();
1470 
1471   uint lo_id = updated_id;
1472   uint hi_id = old_id;
1473 
1474   // If from is greater than to, swap values to meet
1475   // UnionFind guarantee.
1476   if (updated_id > old_id) {
1477     lo_id = old_id;
1478     hi_id = updated_id;
1479 
1480     // Fix up the trace ids
1481     traces[lo_id] = traces[updated_id];
1482     updated_trace->set_id(lo_id);
1483   }
1484 
1485   // Union the lower with the higher and remove the pointer
1486   // to the higher.
1487   uf->Union(lo_id, hi_id);
1488   traces[hi_id] = NULL;
1489 }
1490 
1491 // Append traces together via the most frequently executed edges
1492 void PhaseBlockLayout::grow_traces() {
1493   // Order the edges, and drive the growth of Traces via the most
1494   // frequently executed edges.
1495   edges->sort(edge_order);
1496   for (int i = 0; i < edges->length(); i++) {
1497     CFGEdge *e = edges->at(i);
1498 
1499     if (e->state() != CFGEdge::open) continue;
1500 
1501     Block *src_block = e->from();
1502     Block *targ_block = e->to();
1503 
1504     // Don't grow traces along backedges?
1505     if (!BlockLayoutRotateLoops) {
1506       if (targ_block->_rpo <= src_block->_rpo) {
1507         targ_block->set_loop_alignment(targ_block);
1508         continue;
1509       }
1510     }
1511 
1512     Trace *src_trace = trace(src_block);
1513     Trace *targ_trace = trace(targ_block);
1514 
1515     // If the edge in question can join two traces at their ends,
1516     // append one trace to the other.
1517    if (src_trace->last_block() == src_block) {
1518       if (src_trace == targ_trace) {
1519         e->set_state(CFGEdge::interior);
1520         if (targ_trace->backedge(e)) {
1521           // Reset i to catch any newly eligible edge
1522           // (Or we could remember the first "open" edge, and reset there)
1523           i = 0;
1524         }
1525       } else if (targ_trace->first_block() == targ_block) {
1526         e->set_state(CFGEdge::connected);
1527         src_trace->append(targ_trace);
1528         union_traces(src_trace, targ_trace);
1529       }
1530     }
1531   }
1532 }
1533 
1534 // Embed one trace into another, if the fork or join points are sufficiently
1535 // balanced.
1536 void PhaseBlockLayout::merge_traces(bool fall_thru_only) {
1537   // Walk the edge list a another time, looking at unprocessed edges.
1538   // Fold in diamonds
1539   for (int i = 0; i < edges->length(); i++) {
1540     CFGEdge *e = edges->at(i);
1541 
1542     if (e->state() != CFGEdge::open) continue;
1543     if (fall_thru_only) {
1544       if (e->infrequent()) continue;
1545     }
1546 
1547     Block *src_block = e->from();
1548     Trace *src_trace = trace(src_block);
1549     bool src_at_tail = src_trace->last_block() == src_block;
1550 
1551     Block *targ_block  = e->to();
1552     Trace *targ_trace  = trace(targ_block);
1553     bool targ_at_start = targ_trace->first_block() == targ_block;
1554 
1555     if (src_trace == targ_trace) {
1556       // This may be a loop, but we can't do much about it.
1557       e->set_state(CFGEdge::interior);
1558       continue;
1559     }
1560 
1561     if (fall_thru_only) {
1562       // If the edge links the middle of two traces, we can't do anything.
1563       // Mark the edge and continue.
1564       if (!src_at_tail & !targ_at_start) {
1565         continue;
1566       }
1567 
1568       // Don't grow traces along backedges?
1569       if (!BlockLayoutRotateLoops && (targ_block->_rpo <= src_block->_rpo)) {
1570           continue;
1571       }
1572 
1573       // If both ends of the edge are available, why didn't we handle it earlier?
1574       assert(src_at_tail ^ targ_at_start, "Should have caught this edge earlier.");
1575 
1576       if (targ_at_start) {
1577         // Insert the "targ" trace in the "src" trace if the insertion point
1578         // is a two way branch.
1579         // Better profitability check possible, but may not be worth it.
1580         // Someday, see if the this "fork" has an associated "join";
1581         // then make a policy on merging this trace at the fork or join.
1582         // For example, other things being equal, it may be better to place this
1583         // trace at the join point if the "src" trace ends in a two-way, but
1584         // the insertion point is one-way.
1585         assert(src_block->num_fall_throughs() == 2, "unexpected diamond");
1586         e->set_state(CFGEdge::connected);
1587         src_trace->insert_after(src_block, targ_trace);
1588         union_traces(src_trace, targ_trace);
1589       } else if (src_at_tail) {
1590         if (src_trace != trace(_cfg.get_root_block())) {
1591           e->set_state(CFGEdge::connected);
1592           targ_trace->insert_before(targ_block, src_trace);
1593           union_traces(targ_trace, src_trace);
1594         }
1595       }
1596     } else if (e->state() == CFGEdge::open) {
1597       // Append traces, even without a fall-thru connection.
1598       // But leave root entry at the beginning of the block list.
1599       if (targ_trace != trace(_cfg.get_root_block())) {
1600         e->set_state(CFGEdge::connected);
1601         src_trace->append(targ_trace);
1602         union_traces(src_trace, targ_trace);
1603       }
1604     }
1605   }
1606 }
1607 
1608 // Order the sequence of the traces in some desirable way, and fixup the
1609 // jumps at the end of each block.
1610 void PhaseBlockLayout::reorder_traces(int count) {
1611   ResourceArea *area = Thread::current()->resource_area();
1612   Trace ** new_traces = NEW_ARENA_ARRAY(area, Trace *, count);
1613   Block_List worklist;
1614   int new_count = 0;
1615 
1616   // Compact the traces.
1617   for (int i = 0; i < count; i++) {
1618     Trace *tr = traces[i];
1619     if (tr != NULL) {
1620       new_traces[new_count++] = tr;
1621     }
1622   }
1623 
1624   // The entry block should be first on the new trace list.
1625   Trace *tr = trace(_cfg.get_root_block());
1626   assert(tr == new_traces[0], "entry trace misplaced");
1627 
1628   // Sort the new trace list by frequency
1629   qsort(new_traces + 1, new_count - 1, sizeof(new_traces[0]), trace_frequency_order);
1630 
1631   // Patch up the successor blocks
1632   _cfg.clear_blocks();
1633   for (int i = 0; i < new_count; i++) {
1634     Trace *tr = new_traces[i];
1635     if (tr != NULL) {
1636       tr->fixup_blocks(_cfg);
1637     }
1638   }
1639 }
1640 
1641 // Order basic blocks based on frequency
1642 PhaseBlockLayout::PhaseBlockLayout(PhaseCFG &cfg)
1643 : Phase(BlockLayout)
1644 , _cfg(cfg) {
1645   ResourceMark rm;
1646   ResourceArea *area = Thread::current()->resource_area();
1647 
1648   // List of traces
1649   int size = _cfg.number_of_blocks() + 1;
1650   traces = NEW_ARENA_ARRAY(area, Trace *, size);
1651   memset(traces, 0, size*sizeof(Trace*));
1652   next = NEW_ARENA_ARRAY(area, Block *, size);
1653   memset(next,   0, size*sizeof(Block *));
1654   prev = NEW_ARENA_ARRAY(area, Block *, size);
1655   memset(prev  , 0, size*sizeof(Block *));
1656 
1657   // List of edges
1658   edges = new GrowableArray<CFGEdge*>;
1659 
1660   // Mapping block index --> block_trace
1661   uf = new UnionFind(size);
1662   uf->reset(size);
1663 
1664   // Find edges and create traces.
1665   find_edges();
1666 
1667   // Grow traces at their ends via most frequent edges.
1668   grow_traces();
1669 
1670   // Merge one trace into another, but only at fall-through points.
1671   // This may make diamonds and other related shapes in a trace.
1672   merge_traces(true);
1673 
1674   // Run merge again, allowing two traces to be catenated, even if
1675   // one does not fall through into the other. This appends loosely
1676   // related traces to be near each other.
1677   merge_traces(false);
1678 
1679   // Re-order all the remaining traces by frequency
1680   reorder_traces(size);
1681 
1682   assert(_cfg.number_of_blocks() >= (uint) (size - 1), "number of blocks can not shrink");
1683 }
1684 
1685 
1686 // Edge e completes a loop in a trace. If the target block is head of the
1687 // loop, rotate the loop block so that the loop ends in a conditional branch.
1688 bool Trace::backedge(CFGEdge *e) {
1689   bool loop_rotated = false;
1690   Block *src_block  = e->from();
1691   Block *targ_block    = e->to();
1692 
1693   assert(last_block() == src_block, "loop discovery at back branch");
1694   if (first_block() == targ_block) {
1695     if (BlockLayoutRotateLoops && last_block()->num_fall_throughs() < 2) {
1696       // Find the last block in the trace that has a conditional
1697       // branch.
1698       Block *b;
1699       for (b = last_block(); b != NULL; b = prev(b)) {
1700         if (b->num_fall_throughs() == 2) {
1701           break;
1702         }
1703       }
1704 
1705       if (b != last_block() && b != NULL) {
1706         loop_rotated = true;
1707 
1708         // Rotate the loop by doing two-part linked-list surgery.
1709         append(first_block());
1710         break_loop_after(b);
1711       }
1712     }
1713 
1714     // Backbranch to the top of a trace
1715     // Scroll forward through the trace from the targ_block. If we find
1716     // a loop head before another loop top, use the the loop head alignment.
1717     for (Block *b = targ_block; b != NULL; b = next(b)) {
1718       if (b->has_loop_alignment()) {
1719         break;
1720       }
1721       if (b->head()->is_Loop()) {
1722         targ_block = b;
1723         break;
1724       }
1725     }
1726 
1727     first_block()->set_loop_alignment(targ_block);
1728 
1729   } else {
1730     // That loop may already have a loop top (we're reaching it again
1731     // through the backedge of an outer loop)
1732     Block* b = prev(targ_block);
1733     bool has_top = targ_block->head()->is_Loop() && b->has_loop_alignment() && !b->head()->is_Loop();
1734     if (!has_top) {
1735       // Backbranch into the middle of a trace
1736       targ_block->set_loop_alignment(targ_block);
1737     }
1738   }
1739 
1740   return loop_rotated;
1741 }
1742 
1743 // push blocks onto the CFG list
1744 // ensure that blocks have the correct two-way branch sense
1745 void Trace::fixup_blocks(PhaseCFG &cfg) {
1746   Block *last = last_block();
1747   for (Block *b = first_block(); b != NULL; b = next(b)) {
1748     cfg.add_block(b);
1749     if (!b->is_connector()) {
1750       int nfallthru = b->num_fall_throughs();
1751       if (b != last) {
1752         if (nfallthru == 2) {
1753           // Ensure that the sense of the branch is correct
1754           Block *bnext = next(b);
1755           Block *bs0 = b->non_connector_successor(0);
1756 
1757           MachNode *iff = b->get_node(b->number_of_nodes() - 3)->as_Mach();
1758           ProjNode *proj0 = b->get_node(b->number_of_nodes() - 2)->as_Proj();
1759           ProjNode *proj1 = b->get_node(b->number_of_nodes() - 1)->as_Proj();
1760 
1761           if (bnext == bs0) {
1762             // Fall-thru case in succs[0], should be in succs[1]
1763 
1764             // Flip targets in _succs map
1765             Block *tbs0 = b->_succs[0];
1766             Block *tbs1 = b->_succs[1];
1767             b->_succs.map( 0, tbs1 );
1768             b->_succs.map( 1, tbs0 );
1769 
1770             // Flip projections to match targets
1771             b->map_node(proj1, b->number_of_nodes() - 2);
1772             b->map_node(proj0, b->number_of_nodes() - 1);
1773           }
1774         }
1775       }
1776     }
1777   }
1778 }