1 /*
   2  * Copyright (c) 1997, 2010, 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 #ifndef SHARE_VM_OPTO_BLOCK_HPP
  26 #define SHARE_VM_OPTO_BLOCK_HPP
  27 
  28 #include "opto/multnode.hpp"
  29 #include "opto/node.hpp"
  30 #include "opto/phase.hpp"
  31 
  32 // Optimization - Graph Style
  33 
  34 class Block;
  35 class CFGLoop;
  36 class MachCallNode;
  37 class Matcher;
  38 class RootNode;
  39 class VectorSet;
  40 struct Tarjan;
  41 
  42 //------------------------------Block_Array------------------------------------
  43 // Map dense integer indices to Blocks.  Uses classic doubling-array trick.
  44 // Abstractly provides an infinite array of Block*'s, initialized to NULL.
  45 // Note that the constructor just zeros things, and since I use Arena
  46 // allocation I do not need a destructor to reclaim storage.
  47 class Block_Array : public ResourceObj {
  48   uint _size;                   // allocated size, as opposed to formal limit
  49   debug_only(uint _limit;)      // limit to formal domain
  50 protected:
  51   Block **_blocks;
  52   void grow( uint i );          // Grow array node to fit
  53 
  54 public:
  55   Arena *_arena;                // Arena to allocate in
  56 
  57   Block_Array(Arena *a) : _arena(a), _size(OptoBlockListSize) {
  58     debug_only(_limit=0);
  59     _blocks = NEW_ARENA_ARRAY( a, Block *, OptoBlockListSize );
  60     for( int i = 0; i < OptoBlockListSize; i++ ) {
  61       _blocks[i] = NULL;
  62     }
  63   }
  64   Block *lookup( uint i ) const // Lookup, or NULL for not mapped
  65   { return (i<Max()) ? _blocks[i] : (Block*)NULL; }
  66   Block *operator[] ( uint i ) const // Lookup, or assert for not mapped
  67   { assert( i < Max(), "oob" ); return _blocks[i]; }
  68   // Extend the mapping: index i maps to Block *n.
  69   void map( uint i, Block *n ) { if( i>=Max() ) grow(i); _blocks[i] = n; }
  70   uint Max() const { debug_only(return _limit); return _size; }
  71 };
  72 
  73 
  74 class Block_List : public Block_Array {
  75 public:
  76   uint _cnt;
  77   Block_List() : Block_Array(Thread::current()->resource_area()), _cnt(0) {}
  78   void push( Block *b ) { map(_cnt++,b); }
  79   Block *pop() { return _blocks[--_cnt]; }
  80   Block *rpop() { Block *b = _blocks[0]; _blocks[0]=_blocks[--_cnt]; return b;}
  81   void remove( uint i );
  82   void insert( uint i, Block *n );
  83   uint size() const { return _cnt; }
  84   void reset() { _cnt = 0; }
  85   void print();
  86 };
  87 
  88 
  89 class CFGElement : public ResourceObj {
  90  public:
  91   float _freq; // Execution frequency (estimate)
  92 
  93   CFGElement() : _freq(0.0f) {}
  94   virtual bool is_block() { return false; }
  95   virtual bool is_loop()  { return false; }
  96   Block*   as_Block() { assert(is_block(), "must be block"); return (Block*)this; }
  97   CFGLoop* as_CFGLoop()  { assert(is_loop(),  "must be loop");  return (CFGLoop*)this;  }
  98 };
  99 
 100 //------------------------------Block------------------------------------------
 101 // This class defines a Basic Block.
 102 // Basic blocks are used during the output routines, and are not used during
 103 // any optimization pass.  They are created late in the game.
 104 class Block : public CFGElement {
 105  public:
 106   // Nodes in this block, in order
 107   Node_List _nodes;
 108 
 109   // Basic blocks have a Node which defines Control for all Nodes pinned in
 110   // this block.  This Node is a RegionNode.  Exception-causing Nodes
 111   // (division, subroutines) and Phi functions are always pinned.  Later,
 112   // every Node will get pinned to some block.
 113   Node *head() const { return _nodes[0]; }
 114 
 115   // CAUTION: num_preds() is ONE based, so that predecessor numbers match
 116   // input edges to Regions and Phis.
 117   uint num_preds() const { return head()->req(); }
 118   Node *pred(uint i) const { return head()->in(i); }
 119 
 120   // Array of successor blocks, same size as projs array
 121   Block_Array _succs;
 122 
 123   // Basic blocks have some number of Nodes which split control to all
 124   // following blocks.  These Nodes are always Projections.  The field in
 125   // the Projection and the block-ending Node determine which Block follows.
 126   uint _num_succs;
 127 
 128   // Basic blocks also carry all sorts of good old fashioned DFS information
 129   // used to find loops, loop nesting depth, dominators, etc.
 130   uint _pre_order;              // Pre-order DFS number
 131 
 132   // Dominator tree
 133   uint _dom_depth;              // Depth in dominator tree for fast LCA
 134   Block* _idom;                 // Immediate dominator block
 135 
 136   CFGLoop *_loop;               // Loop to which this block belongs
 137   uint _rpo;                    // Number in reverse post order walk
 138 
 139   virtual bool is_block() { return true; }
 140   float succ_prob(uint i);      // return probability of i'th successor
 141   int num_fall_throughs();      // How many fall-through candidate this block has
 142   void update_uncommon_branch(Block* un); // Lower branch prob to uncommon code
 143   bool succ_fall_through(uint i); // Is successor "i" is a fall-through candidate
 144   Block* lone_fall_through();   // Return lone fall-through Block or null
 145 
 146   Block* dom_lca(Block* that);  // Compute LCA in dominator tree.
 147 #ifdef ASSERT
 148   bool dominates(Block* that) {
 149     int dom_diff = this->_dom_depth - that->_dom_depth;
 150     if (dom_diff > 0)  return false;
 151     for (; dom_diff < 0; dom_diff++)  that = that->_idom;
 152     return this == that;
 153   }
 154 #endif
 155 
 156   // Report the alignment required by this block.  Must be a power of 2.
 157   // The previous block will insert nops to get this alignment.
 158   uint code_alignment();
 159   uint compute_loop_alignment();
 160 
 161   // BLOCK_FREQUENCY is a sentinel to mark uses of constant block frequencies.
 162   // It is currently also used to scale such frequencies relative to
 163   // FreqCountInvocations relative to the old value of 1500.
 164 #define BLOCK_FREQUENCY(f) ((f * (float) 1500) / FreqCountInvocations)
 165 
 166   // Register Pressure (estimate) for Splitting heuristic
 167   uint _reg_pressure;
 168   uint _ihrp_index;
 169   uint _freg_pressure;
 170   uint _fhrp_index;
 171 
 172   // Mark and visited bits for an LCA calculation in insert_anti_dependences.
 173   // Since they hold unique node indexes, they do not need reinitialization.
 174   node_idx_t _raise_LCA_mark;
 175   void    set_raise_LCA_mark(node_idx_t x)    { _raise_LCA_mark = x; }
 176   node_idx_t  raise_LCA_mark() const          { return _raise_LCA_mark; }
 177   node_idx_t _raise_LCA_visited;
 178   void    set_raise_LCA_visited(node_idx_t x) { _raise_LCA_visited = x; }
 179   node_idx_t  raise_LCA_visited() const       { return _raise_LCA_visited; }
 180 
 181   // Estimated size in bytes of first instructions in a loop.
 182   uint _first_inst_size;
 183   uint first_inst_size() const     { return _first_inst_size; }
 184   void set_first_inst_size(uint s) { _first_inst_size = s; }
 185 
 186   // Compute the size of first instructions in this block.
 187   uint compute_first_inst_size(uint& sum_size, uint inst_cnt, PhaseRegAlloc* ra);
 188 
 189   // Compute alignment padding if the block needs it.
 190   // Align a loop if loop's padding is less or equal to padding limit
 191   // or the size of first instructions in the loop > padding.
 192   uint alignment_padding(int current_offset) {
 193     int block_alignment = code_alignment();
 194     int max_pad = block_alignment-relocInfo::addr_unit();
 195     if( max_pad > 0 ) {
 196       assert(is_power_of_2(max_pad+relocInfo::addr_unit()), "");
 197       int current_alignment = current_offset & max_pad;
 198       if( current_alignment != 0 ) {
 199         uint padding = (block_alignment-current_alignment) & max_pad;
 200         if( has_loop_alignment() &&
 201             padding > (uint)MaxLoopPad &&
 202             first_inst_size() <= padding ) {
 203           return 0;
 204         }
 205         return padding;
 206       }
 207     }
 208     return 0;
 209   }
 210 
 211   // Connector blocks. Connector blocks are basic blocks devoid of
 212   // instructions, but may have relevant non-instruction Nodes, such as
 213   // Phis or MergeMems. Such blocks are discovered and marked during the
 214   // RemoveEmpty phase, and elided during Output.
 215   bool _connector;
 216   void set_connector() { _connector = true; }
 217   bool is_connector() const { return _connector; };
 218 
 219   // Loop_alignment will be set for blocks which are at the top of loops.
 220   // The block layout pass may rotate loops such that the loop head may not
 221   // be the sequentially first block of the loop encountered in the linear
 222   // list of blocks.  If the layout pass is not run, loop alignment is set
 223   // for each block which is the head of a loop.
 224   uint _loop_alignment;
 225   void set_loop_alignment(Block *loop_top) {
 226     uint new_alignment = loop_top->compute_loop_alignment();
 227     if (new_alignment > _loop_alignment) {
 228       _loop_alignment = new_alignment;
 229     }
 230   }
 231   uint loop_alignment() const { return _loop_alignment; }
 232   bool has_loop_alignment() const { return loop_alignment() > 0; }
 233 
 234   // Create a new Block with given head Node.
 235   // Creates the (empty) predecessor arrays.
 236   Block( Arena *a, Node *headnode )
 237     : CFGElement(),
 238       _nodes(a),
 239       _succs(a),
 240       _num_succs(0),
 241       _pre_order(0),
 242       _idom(0),
 243       _loop(NULL),
 244       _reg_pressure(0),
 245       _ihrp_index(1),
 246       _freg_pressure(0),
 247       _fhrp_index(1),
 248       _raise_LCA_mark(0),
 249       _raise_LCA_visited(0),
 250       _first_inst_size(999999),
 251       _connector(false),
 252       _loop_alignment(0) {
 253     _nodes.push(headnode);
 254   }
 255 
 256   // Index of 'end' Node
 257   uint end_idx() const {
 258     // %%%%% add a proj after every goto
 259     // so (last->is_block_proj() != last) always, then simplify this code
 260     // This will not give correct end_idx for block 0 when it only contains root.
 261     int last_idx = _nodes.size() - 1;
 262     Node *last  = _nodes[last_idx];
 263     assert(last->is_block_proj() == last || last->is_block_proj() == _nodes[last_idx - _num_succs], "");
 264     return (last->is_block_proj() == last) ? last_idx : (last_idx - _num_succs);
 265   }
 266 
 267   // Basic blocks have a Node which ends them.  This Node determines which
 268   // basic block follows this one in the program flow.  This Node is either an
 269   // IfNode, a GotoNode, a JmpNode, or a ReturnNode.
 270   Node *end() const { return _nodes[end_idx()]; }
 271 
 272   // Add an instruction to an existing block.  It must go after the head
 273   // instruction and before the end instruction.
 274   void add_inst( Node *n ) { _nodes.insert(end_idx(),n); }
 275   // Find node in block
 276   uint find_node( const Node *n ) const;
 277   // Find and remove n from block list
 278   void find_remove( const Node *n );
 279 
 280   // Schedule a call next in the block
 281   uint sched_call(Matcher &matcher, Block_Array &bbs, uint node_cnt, Node_List &worklist, int *ready_cnt, MachCallNode *mcall, VectorSet &next_call);
 282 
 283   // Perform basic-block local scheduling
 284   Node *select(PhaseCFG *cfg, Node_List &worklist, int *ready_cnt, VectorSet &next_call, uint sched_slot);
 285   void set_next_call( Node *n, VectorSet &next_call, Block_Array &bbs );
 286   void needed_for_next_call(Node *this_call, VectorSet &next_call, Block_Array &bbs);
 287   bool schedule_local(PhaseCFG *cfg, Matcher &m, int *ready_cnt, VectorSet &next_call);
 288   // Cleanup if any code lands between a Call and his Catch
 289   void call_catch_cleanup(Block_Array &bbs);
 290   // Detect implicit-null-check opportunities.  Basically, find NULL checks
 291   // with suitable memory ops nearby.  Use the memory op to do the NULL check.
 292   // I can generate a memory op if there is not one nearby.
 293   void implicit_null_check(PhaseCFG *cfg, Node *proj, Node *val, int allowed_reasons);
 294 
 295   // Return the empty status of a block
 296   enum { not_empty, empty_with_goto, completely_empty };
 297   int is_Empty() const;
 298 
 299   // Forward through connectors
 300   Block* non_connector() {
 301     Block* s = this;
 302     while (s->is_connector()) {
 303       s = s->_succs[0];
 304     }
 305     return s;
 306   }
 307 
 308   // Return true if b is a successor of this block
 309   bool has_successor(Block* b) const {
 310     for (uint i = 0; i < _num_succs; i++ ) {
 311       if (non_connector_successor(i) == b) {
 312         return true;
 313       }
 314     }
 315     return false;
 316   }
 317 
 318   // Successor block, after forwarding through connectors
 319   Block* non_connector_successor(int i) const {
 320     return _succs[i]->non_connector();
 321   }
 322 
 323   // Examine block's code shape to predict if it is not commonly executed.
 324   bool has_uncommon_code() const;
 325 
 326   // Use frequency calculations and code shape to predict if the block
 327   // is uncommon.
 328   bool is_uncommon( Block_Array &bbs ) const;
 329 
 330 #ifndef PRODUCT
 331   // Debugging print of basic block
 332   void dump_bidx(const Block* orig, outputStream* st = tty) const;
 333   void dump_pred(const Block_Array *bbs, Block* orig, outputStream* st = tty) const;
 334   void dump_head( const Block_Array *bbs, outputStream* st = tty ) const;
 335   void dump() const;
 336   void dump( const Block_Array *bbs ) const;
 337 #endif
 338 };
 339 
 340 
 341 //------------------------------PhaseCFG---------------------------------------
 342 // Build an array of Basic Block pointers, one per Node.
 343 class PhaseCFG : public Phase {
 344  private:
 345   // Build a proper looking cfg.  Return count of basic blocks
 346   uint build_cfg();
 347 
 348   // Perform DFS search.
 349   // Setup 'vertex' as DFS to vertex mapping.
 350   // Setup 'semi' as vertex to DFS mapping.
 351   // Set 'parent' to DFS parent.
 352   uint DFS( Tarjan *tarjan );
 353 
 354   // Helper function to insert a node into a block
 355   void schedule_node_into_block( Node *n, Block *b );
 356 
 357   void replace_block_proj_ctrl( Node *n );
 358 
 359   // Set the basic block for pinned Nodes
 360   void schedule_pinned_nodes( VectorSet &visited );
 361 
 362   // I'll need a few machine-specific GotoNodes.  Clone from this one.
 363   MachNode *_goto;
 364 
 365   Block* insert_anti_dependences(Block* LCA, Node* load, bool verify = false);
 366   void verify_anti_dependences(Block* LCA, Node* load) {
 367     assert(LCA == _bbs[load->_idx], "should already be scheduled");
 368     insert_anti_dependences(LCA, load, true);
 369   }
 370 
 371  public:
 372   PhaseCFG( Arena *a, RootNode *r, Matcher &m );
 373 
 374   uint _num_blocks;             // Count of basic blocks
 375   Block_List _blocks;           // List of basic blocks
 376   RootNode *_root;              // Root of whole program
 377   Block_Array _bbs;             // Map Nodes to owning Basic Block
 378   Block *_broot;                // Basic block of root
 379   uint _rpo_ctr;
 380   CFGLoop* _root_loop;
 381   float _outer_loop_freq;       // Outmost loop frequency
 382 
 383   // Per node latency estimation, valid only during GCM
 384   GrowableArray<uint> *_node_latency;
 385 
 386 #ifndef PRODUCT
 387   bool _trace_opto_pipelining;  // tracing flag
 388 #endif
 389 
 390 #ifdef ASSERT
 391   Unique_Node_List _raw_oops;
 392 #endif
 393 
 394   // Build dominators
 395   void Dominators();
 396 
 397   // Estimate block frequencies based on IfNode probabilities
 398   void Estimate_Block_Frequency();
 399 
 400   // Global Code Motion.  See Click's PLDI95 paper.  Place Nodes in specific
 401   // basic blocks; i.e. _bbs now maps _idx for all Nodes to some Block.
 402   void GlobalCodeMotion( Matcher &m, uint unique, Node_List &proj_list );
 403 
 404   // Compute the (backwards) latency of a node from the uses
 405   void latency_from_uses(Node *n);
 406 
 407   // Compute the (backwards) latency of a node from a single use
 408   int latency_from_use(Node *n, const Node *def, Node *use);
 409 
 410   // Compute the (backwards) latency of a node from the uses of this instruction
 411   void partial_latency_of_defs(Node *n);
 412 
 413   // Schedule Nodes early in their basic blocks.
 414   bool schedule_early(VectorSet &visited, Node_List &roots);
 415 
 416   // For each node, find the latest block it can be scheduled into
 417   // and then select the cheapest block between the latest and earliest
 418   // block to place the node.
 419   void schedule_late(VectorSet &visited, Node_List &stack);
 420 
 421   // Pick a block between early and late that is a cheaper alternative
 422   // to late. Helper for schedule_late.
 423   Block* hoist_to_cheaper_block(Block* LCA, Block* early, Node* self);
 424 
 425   // Compute the instruction global latency with a backwards walk
 426   void ComputeLatenciesBackwards(VectorSet &visited, Node_List &stack);
 427 
 428   // Set loop alignment
 429   void set_loop_alignment();
 430 
 431   // Remove empty basic blocks
 432   void remove_empty();
 433   void fixup_flow();
 434   bool move_to_next(Block* bx, uint b_index);
 435   void move_to_end(Block* bx, uint b_index);
 436   void insert_goto_at(uint block_no, uint succ_no);
 437 
 438   // Check for NeverBranch at block end.  This needs to become a GOTO to the
 439   // true target.  NeverBranch are treated as a conditional branch that always
 440   // goes the same direction for most of the optimizer and are used to give a
 441   // fake exit path to infinite loops.  At this late stage they need to turn
 442   // into Goto's so that when you enter the infinite loop you indeed hang.
 443   void convert_NeverBranch_to_Goto(Block *b);
 444 
 445   CFGLoop* create_loop_tree();
 446 
 447   // Insert a node into a block, and update the _bbs
 448   void insert( Block *b, uint idx, Node *n ) {
 449     b->_nodes.insert( idx, n );
 450     _bbs.map( n->_idx, b );
 451   }
 452 
 453 #ifndef PRODUCT
 454   bool trace_opto_pipelining() const { return _trace_opto_pipelining; }
 455 
 456   // Debugging print of CFG
 457   void dump( ) const;           // CFG only
 458   void _dump_cfg( const Node *end, VectorSet &visited  ) const;
 459   void verify() const;
 460   void dump_headers();
 461 #else
 462   bool trace_opto_pipelining() const { return false; }
 463 #endif
 464 };
 465 
 466 
 467 //------------------------------UnionFind--------------------------------------
 468 // Map Block indices to a block-index for a cfg-cover.
 469 // Array lookup in the optimized case.
 470 class UnionFind : public ResourceObj {
 471   uint _cnt, _max;
 472   uint* _indices;
 473   ReallocMark _nesting;  // assertion check for reallocations
 474 public:
 475   UnionFind( uint max );
 476   void reset( uint max );  // Reset to identity map for [0..max]
 477 
 478   uint lookup( uint nidx ) const {
 479     return _indices[nidx];
 480   }
 481   uint operator[] (uint nidx) const { return lookup(nidx); }
 482 
 483   void map( uint from_idx, uint to_idx ) {
 484     assert( from_idx < _cnt, "oob" );
 485     _indices[from_idx] = to_idx;
 486   }
 487   void extend( uint from_idx, uint to_idx );
 488 
 489   uint Size() const { return _cnt; }
 490 
 491   uint Find( uint idx ) {
 492     assert( idx < 65536, "Must fit into uint");
 493     uint uf_idx = lookup(idx);
 494     return (uf_idx == idx) ? uf_idx : Find_compress(idx);
 495   }
 496   uint Find_compress( uint idx );
 497   uint Find_const( uint idx ) const;
 498   void Union( uint idx1, uint idx2 );
 499 
 500 };
 501 
 502 //----------------------------BlockProbPair---------------------------
 503 // Ordered pair of Node*.
 504 class BlockProbPair VALUE_OBJ_CLASS_SPEC {
 505 protected:
 506   Block* _target;      // block target
 507   float  _prob;        // probability of edge to block
 508 public:
 509   BlockProbPair() : _target(NULL), _prob(0.0) {}
 510   BlockProbPair(Block* b, float p) : _target(b), _prob(p) {}
 511 
 512   Block* get_target() const { return _target; }
 513   float get_prob() const { return _prob; }
 514 };
 515 
 516 //------------------------------CFGLoop-------------------------------------------
 517 class CFGLoop : public CFGElement {
 518   int _id;
 519   int _depth;
 520   CFGLoop *_parent;      // root of loop tree is the method level "pseudo" loop, it's parent is null
 521   CFGLoop *_sibling;     // null terminated list
 522   CFGLoop *_child;       // first child, use child's sibling to visit all immediately nested loops
 523   GrowableArray<CFGElement*> _members; // list of members of loop
 524   GrowableArray<BlockProbPair> _exits; // list of successor blocks and their probabilities
 525   float _exit_prob;       // probability any loop exit is taken on a single loop iteration
 526   void update_succ_freq(Block* b, float freq);
 527 
 528  public:
 529   CFGLoop(int id) :
 530     CFGElement(),
 531     _id(id),
 532     _depth(0),
 533     _parent(NULL),
 534     _sibling(NULL),
 535     _child(NULL),
 536     _exit_prob(1.0f) {}
 537   CFGLoop* parent() { return _parent; }
 538   void push_pred(Block* blk, int i, Block_List& worklist, Block_Array& node_to_blk);
 539   void add_member(CFGElement *s) { _members.push(s); }
 540   void add_nested_loop(CFGLoop* cl);
 541   Block* head() {
 542     assert(_members.at(0)->is_block(), "head must be a block");
 543     Block* hd = _members.at(0)->as_Block();
 544     assert(hd->_loop == this, "just checking");
 545     assert(hd->head()->is_Loop(), "must begin with loop head node");
 546     return hd;
 547   }
 548   Block* backedge_block(); // Return the block on the backedge of the loop (else NULL)
 549   void compute_loop_depth(int depth);
 550   void compute_freq(); // compute frequency with loop assuming head freq 1.0f
 551   void scale_freq();   // scale frequency by loop trip count (including outer loops)
 552   float outer_loop_freq() const; // frequency of outer loop
 553   bool in_loop_nest(Block* b);
 554   float trip_count() const { return 1.0f / _exit_prob; }
 555   virtual bool is_loop()  { return true; }
 556   int id() { return _id; }
 557 
 558 #ifndef PRODUCT
 559   void dump( ) const;
 560   void dump_tree() const;
 561 #endif
 562 };
 563 
 564 
 565 //----------------------------------CFGEdge------------------------------------
 566 // A edge between two basic blocks that will be embodied by a branch or a
 567 // fall-through.
 568 class CFGEdge : public ResourceObj {
 569  private:
 570   Block * _from;        // Source basic block
 571   Block * _to;          // Destination basic block
 572   float _freq;          // Execution frequency (estimate)
 573   int   _state;
 574   bool  _infrequent;
 575   int   _from_pct;
 576   int   _to_pct;
 577 
 578   // Private accessors
 579   int  from_pct() const { return _from_pct; }
 580   int  to_pct()   const { return _to_pct;   }
 581   int  from_infrequent() const { return from_pct() < BlockLayoutMinDiamondPercentage; }
 582   int  to_infrequent()   const { return to_pct()   < BlockLayoutMinDiamondPercentage; }
 583 
 584  public:
 585   enum {
 586     open,               // initial edge state; unprocessed
 587     connected,          // edge used to connect two traces together
 588     interior            // edge is interior to trace (could be backedge)
 589   };
 590 
 591   CFGEdge(Block *from, Block *to, float freq, int from_pct, int to_pct) :
 592     _from(from), _to(to), _freq(freq),
 593     _from_pct(from_pct), _to_pct(to_pct), _state(open) {
 594     _infrequent = from_infrequent() || to_infrequent();
 595   }
 596 
 597   float  freq() const { return _freq; }
 598   Block* from() const { return _from; }
 599   Block* to  () const { return _to;   }
 600   int  infrequent() const { return _infrequent; }
 601   int state() const { return _state; }
 602 
 603   void set_state(int state) { _state = state; }
 604 
 605 #ifndef PRODUCT
 606   void dump( ) const;
 607 #endif
 608 };
 609 
 610 
 611 //-----------------------------------Trace-------------------------------------
 612 // An ordered list of basic blocks.
 613 class Trace : public ResourceObj {
 614  private:
 615   uint _id;             // Unique Trace id (derived from initial block)
 616   Block ** _next_list;  // Array mapping index to next block
 617   Block ** _prev_list;  // Array mapping index to previous block
 618   Block * _first;       // First block in the trace
 619   Block * _last;        // Last block in the trace
 620 
 621   // Return the block that follows "b" in the trace.
 622   Block * next(Block *b) const { return _next_list[b->_pre_order]; }
 623   void set_next(Block *b, Block *n) const { _next_list[b->_pre_order] = n; }
 624 
 625   // Return the block that precedes "b" in the trace.
 626   Block * prev(Block *b) const { return _prev_list[b->_pre_order]; }
 627   void set_prev(Block *b, Block *p) const { _prev_list[b->_pre_order] = p; }
 628 
 629   // We've discovered a loop in this trace. Reset last to be "b", and first as
 630   // the block following "b
 631   void break_loop_after(Block *b) {
 632     _last = b;
 633     _first = next(b);
 634     set_prev(_first, NULL);
 635     set_next(_last, NULL);
 636   }
 637 
 638  public:
 639 
 640   Trace(Block *b, Block **next_list, Block **prev_list) :
 641     _first(b),
 642     _last(b),
 643     _next_list(next_list),
 644     _prev_list(prev_list),
 645     _id(b->_pre_order) {
 646     set_next(b, NULL);
 647     set_prev(b, NULL);
 648   };
 649 
 650   // Return the id number
 651   uint id() const { return _id; }
 652   void set_id(uint id) { _id = id; }
 653 
 654   // Return the first block in the trace
 655   Block * first_block() const { return _first; }
 656 
 657   // Return the last block in the trace
 658   Block * last_block() const { return _last; }
 659 
 660   // Insert a trace in the middle of this one after b
 661   void insert_after(Block *b, Trace *tr) {
 662     set_next(tr->last_block(), next(b));
 663     if (next(b) != NULL) {
 664       set_prev(next(b), tr->last_block());
 665     }
 666 
 667     set_next(b, tr->first_block());
 668     set_prev(tr->first_block(), b);
 669 
 670     if (b == _last) {
 671       _last = tr->last_block();
 672     }
 673   }
 674 
 675   void insert_before(Block *b, Trace *tr) {
 676     Block *p = prev(b);
 677     assert(p != NULL, "use append instead");
 678     insert_after(p, tr);
 679   }
 680 
 681   // Append another trace to this one.
 682   void append(Trace *tr) {
 683     insert_after(_last, tr);
 684   }
 685 
 686   // Append a block at the end of this trace
 687   void append(Block *b) {
 688     set_next(_last, b);
 689     set_prev(b, _last);
 690     _last = b;
 691   }
 692 
 693   // Adjust the the blocks in this trace
 694   void fixup_blocks(PhaseCFG &cfg);
 695   bool backedge(CFGEdge *e);
 696 
 697 #ifndef PRODUCT
 698   void dump( ) const;
 699 #endif
 700 };
 701 
 702 //------------------------------PhaseBlockLayout-------------------------------
 703 // Rearrange blocks into some canonical order, based on edges and their frequencies
 704 class PhaseBlockLayout : public Phase {
 705   PhaseCFG &_cfg;               // Control flow graph
 706 
 707   GrowableArray<CFGEdge *> *edges;
 708   Trace **traces;
 709   Block **next;
 710   Block **prev;
 711   UnionFind *uf;
 712 
 713   // Given a block, find its encompassing Trace
 714   Trace * trace(Block *b) {
 715     return traces[uf->Find_compress(b->_pre_order)];
 716   }
 717  public:
 718   PhaseBlockLayout(PhaseCFG &cfg);
 719 
 720   void find_edges();
 721   void grow_traces();
 722   void merge_traces(bool loose_connections);
 723   void reorder_traces(int count);
 724   void union_traces(Trace* from, Trace* to);
 725 };
 726 
 727 #endif // SHARE_VM_OPTO_BLOCK_HPP