1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   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.
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  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).
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_OPTO_LOOPNODE_HPP
  26 #define SHARE_VM_OPTO_LOOPNODE_HPP
  27 
  28 #include "opto/cfgnode.hpp"
  29 #include "opto/multnode.hpp"
  30 #include "opto/phaseX.hpp"
  31 #include "opto/subnode.hpp"
  32 #include "opto/type.hpp"
  33 
  34 class CmpNode;
  35 class CountedLoopEndNode;
  36 class CountedLoopNode;
  37 class IdealLoopTree;
  38 class LoopNode;
  39 class Node;
  40 class PhaseIdealLoop;
  41 class VectorSet;
  42 class Invariance;
  43 struct small_cache;
  44 
  45 //
  46 //                  I D E A L I Z E D   L O O P S
  47 //
  48 // Idealized loops are the set of loops I perform more interesting
  49 // transformations on, beyond simple hoisting.
  50 
  51 //------------------------------LoopNode---------------------------------------
  52 // Simple loop header.  Fall in path on left, loop-back path on right.
  53 class LoopNode : public RegionNode {
  54   // Size is bigger to hold the flags.  However, the flags do not change
  55   // the semantics so it does not appear in the hash & cmp functions.
  56   virtual uint size_of() const { return sizeof(*this); }
  57 protected:
  58   short _loop_flags;
  59   // Names for flag bitfields
  60   enum { Normal=0, Pre=1, Main=2, Post=3, PreMainPostFlagsMask=3,
  61          MainHasNoPreLoop=4,
  62          HasExactTripCount=8,
  63          InnerLoop=16,
  64          PartialPeelLoop=32,
  65          PartialPeelFailed=64 };
  66   char _unswitch_count;
  67   enum { _unswitch_max=3 };
  68 
  69 public:
  70   // Names for edge indices
  71   enum { Self=0, EntryControl, LoopBackControl };
  72 
  73   int is_inner_loop() const { return _loop_flags & InnerLoop; }
  74   void set_inner_loop() { _loop_flags |= InnerLoop; }
  75 
  76   int is_partial_peel_loop() const { return _loop_flags & PartialPeelLoop; }
  77   void set_partial_peel_loop() { _loop_flags |= PartialPeelLoop; }
  78   int partial_peel_has_failed() const { return _loop_flags & PartialPeelFailed; }
  79   void mark_partial_peel_failed() { _loop_flags |= PartialPeelFailed; }
  80 
  81   int unswitch_max() { return _unswitch_max; }
  82   int unswitch_count() { return _unswitch_count; }
  83   void set_unswitch_count(int val) {
  84     assert (val <= unswitch_max(), "too many unswitches");
  85     _unswitch_count = val;
  86   }
  87 
  88   LoopNode( Node *entry, Node *backedge ) : RegionNode(3), _loop_flags(0), _unswitch_count(0) {
  89     init_class_id(Class_Loop);
  90     init_req(EntryControl, entry);
  91     init_req(LoopBackControl, backedge);
  92   }
  93 
  94   virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
  95   virtual int Opcode() const;
  96   bool can_be_counted_loop(PhaseTransform* phase) const {
  97     return req() == 3 && in(0) != NULL &&
  98       in(1) != NULL && phase->type(in(1)) != Type::TOP &&
  99       in(2) != NULL && phase->type(in(2)) != Type::TOP;
 100   }
 101   bool is_valid_counted_loop() const;
 102 #ifndef PRODUCT
 103   virtual void dump_spec(outputStream *st) const;
 104 #endif
 105 };
 106 
 107 //------------------------------Counted Loops----------------------------------
 108 // Counted loops are all trip-counted loops, with exactly 1 trip-counter exit
 109 // path (and maybe some other exit paths).  The trip-counter exit is always
 110 // last in the loop.  The trip-counter have to stride by a constant;
 111 // the exit value is also loop invariant.
 112 
 113 // CountedLoopNodes and CountedLoopEndNodes come in matched pairs.  The
 114 // CountedLoopNode has the incoming loop control and the loop-back-control
 115 // which is always the IfTrue before the matching CountedLoopEndNode.  The
 116 // CountedLoopEndNode has an incoming control (possibly not the
 117 // CountedLoopNode if there is control flow in the loop), the post-increment
 118 // trip-counter value, and the limit.  The trip-counter value is always of
 119 // the form (Op old-trip-counter stride).  The old-trip-counter is produced
 120 // by a Phi connected to the CountedLoopNode.  The stride is constant.
 121 // The Op is any commutable opcode, including Add, Mul, Xor.  The
 122 // CountedLoopEndNode also takes in the loop-invariant limit value.
 123 
 124 // From a CountedLoopNode I can reach the matching CountedLoopEndNode via the
 125 // loop-back control.  From CountedLoopEndNodes I can reach CountedLoopNodes
 126 // via the old-trip-counter from the Op node.
 127 
 128 //------------------------------CountedLoopNode--------------------------------
 129 // CountedLoopNodes head simple counted loops.  CountedLoopNodes have as
 130 // inputs the incoming loop-start control and the loop-back control, so they
 131 // act like RegionNodes.  They also take in the initial trip counter, the
 132 // loop-invariant stride and the loop-invariant limit value.  CountedLoopNodes
 133 // produce a loop-body control and the trip counter value.  Since
 134 // CountedLoopNodes behave like RegionNodes I still have a standard CFG model.
 135 
 136 class CountedLoopNode : public LoopNode {
 137   // Size is bigger to hold _main_idx.  However, _main_idx does not change
 138   // the semantics so it does not appear in the hash & cmp functions.
 139   virtual uint size_of() const { return sizeof(*this); }
 140 
 141   // For Pre- and Post-loops during debugging ONLY, this holds the index of
 142   // the Main CountedLoop.  Used to assert that we understand the graph shape.
 143   node_idx_t _main_idx;
 144 
 145   // Known trip count calculated by compute_exact_trip_count()
 146   uint  _trip_count;
 147 
 148   // Expected trip count from profile data
 149   float _profile_trip_cnt;
 150 
 151   // Log2 of original loop bodies in unrolled loop
 152   int _unrolled_count_log2;
 153 
 154   // Node count prior to last unrolling - used to decide if
 155   // unroll,optimize,unroll,optimize,... is making progress
 156   int _node_count_before_unroll;
 157 
 158 public:
 159   CountedLoopNode( Node *entry, Node *backedge )
 160     : LoopNode(entry, backedge), _main_idx(0), _trip_count(max_juint),
 161       _profile_trip_cnt(COUNT_UNKNOWN), _unrolled_count_log2(0),
 162       _node_count_before_unroll(0) {
 163     init_class_id(Class_CountedLoop);
 164     // Initialize _trip_count to the largest possible value.
 165     // Will be reset (lower) if the loop's trip count is known.
 166   }
 167 
 168   virtual int Opcode() const;
 169   virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
 170 
 171   Node *init_control() const { return in(EntryControl); }
 172   Node *back_control() const { return in(LoopBackControl); }
 173   CountedLoopEndNode *loopexit() const;
 174   Node *init_trip() const;
 175   Node *stride() const;
 176   int   stride_con() const;
 177   bool  stride_is_con() const;
 178   Node *limit() const;
 179   Node *incr() const;
 180   Node *phi() const;
 181 
 182   // Match increment with optional truncation
 183   static Node* match_incr_with_optional_truncation(Node* expr, Node** trunc1, Node** trunc2, const TypeInt** trunc_type);
 184 
 185   // A 'main' loop has a pre-loop and a post-loop.  The 'main' loop
 186   // can run short a few iterations and may start a few iterations in.
 187   // It will be RCE'd and unrolled and aligned.
 188 
 189   // A following 'post' loop will run any remaining iterations.  Used
 190   // during Range Check Elimination, the 'post' loop will do any final
 191   // iterations with full checks.  Also used by Loop Unrolling, where
 192   // the 'post' loop will do any epilog iterations needed.  Basically,
 193   // a 'post' loop can not profitably be further unrolled or RCE'd.
 194 
 195   // A preceding 'pre' loop will run at least 1 iteration (to do peeling),
 196   // it may do under-flow checks for RCE and may do alignment iterations
 197   // so the following main loop 'knows' that it is striding down cache
 198   // lines.
 199 
 200   // A 'main' loop that is ONLY unrolled or peeled, never RCE'd or
 201   // Aligned, may be missing it's pre-loop.
 202   int is_normal_loop() const { return (_loop_flags&PreMainPostFlagsMask) == Normal; }
 203   int is_pre_loop   () const { return (_loop_flags&PreMainPostFlagsMask) == Pre;    }
 204   int is_main_loop  () const { return (_loop_flags&PreMainPostFlagsMask) == Main;   }
 205   int is_post_loop  () const { return (_loop_flags&PreMainPostFlagsMask) == Post;   }
 206   int is_main_no_pre_loop() const { return _loop_flags & MainHasNoPreLoop; }
 207   void set_main_no_pre_loop() { _loop_flags |= MainHasNoPreLoop; }
 208 
 209   int main_idx() const { return _main_idx; }
 210 
 211 
 212   void set_pre_loop  (CountedLoopNode *main) { assert(is_normal_loop(),""); _loop_flags |= Pre ; _main_idx = main->_idx; }
 213   void set_main_loop (                     ) { assert(is_normal_loop(),""); _loop_flags |= Main;                         }
 214   void set_post_loop (CountedLoopNode *main) { assert(is_normal_loop(),""); _loop_flags |= Post; _main_idx = main->_idx; }
 215   void set_normal_loop(                    ) { _loop_flags &= ~PreMainPostFlagsMask; }
 216 
 217   void set_trip_count(uint tc) { _trip_count = tc; }
 218   uint trip_count()            { return _trip_count; }
 219 
 220   bool has_exact_trip_count() const { return (_loop_flags & HasExactTripCount) != 0; }
 221   void set_exact_trip_count(uint tc) {
 222     _trip_count = tc;
 223     _loop_flags |= HasExactTripCount;
 224   }
 225   void set_nonexact_trip_count() {
 226     _loop_flags &= ~HasExactTripCount;
 227   }
 228 
 229   void set_profile_trip_cnt(float ptc) { _profile_trip_cnt = ptc; }
 230   float profile_trip_cnt()             { return _profile_trip_cnt; }
 231 
 232   void double_unrolled_count() { _unrolled_count_log2++; }
 233   int  unrolled_count()        { return 1 << MIN2(_unrolled_count_log2, BitsPerInt-3); }
 234 
 235   void set_node_count_before_unroll(int ct) { _node_count_before_unroll = ct; }
 236   int  node_count_before_unroll()           { return _node_count_before_unroll; }
 237 
 238 #ifndef PRODUCT
 239   virtual void dump_spec(outputStream *st) const;
 240 #endif
 241 };
 242 
 243 //------------------------------CountedLoopEndNode-----------------------------
 244 // CountedLoopEndNodes end simple trip counted loops.  They act much like
 245 // IfNodes.
 246 class CountedLoopEndNode : public IfNode {
 247 public:
 248   enum { TestControl, TestValue };
 249 
 250   CountedLoopEndNode( Node *control, Node *test, float prob, float cnt )
 251     : IfNode( control, test, prob, cnt) {
 252     init_class_id(Class_CountedLoopEnd);
 253   }
 254   virtual int Opcode() const;
 255 
 256   Node *cmp_node() const            { return (in(TestValue)->req() >=2) ? in(TestValue)->in(1) : NULL; }
 257   Node *incr() const                { Node *tmp = cmp_node(); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }
 258   Node *limit() const               { Node *tmp = cmp_node(); return (tmp && tmp->req()==3) ? tmp->in(2) : NULL; }
 259   Node *stride() const              { Node *tmp = incr    (); return (tmp && tmp->req()==3) ? tmp->in(2) : NULL; }
 260   Node *init_trip() const           { Node *tmp = phi     (); return (tmp && tmp->req()==3) ? tmp->in(1) : NULL; }
 261   int stride_con() const;
 262   bool stride_is_con() const        { Node *tmp = stride  (); return (tmp != NULL && tmp->is_Con()); }
 263   BoolTest::mask test_trip() const  { return in(TestValue)->as_Bool()->_test._test; }
 264   PhiNode *phi() const {
 265     Node *tmp = incr();
 266     if (tmp && tmp->req() == 3) {
 267       Node* phi = tmp->in(1);
 268       if (phi->is_Phi()) {
 269         return phi->as_Phi();
 270       }
 271     }
 272     return NULL;
 273   }
 274   CountedLoopNode *loopnode() const {
 275     // The CountedLoopNode that goes with this CountedLoopEndNode may
 276     // have been optimized out by the IGVN so be cautious with the
 277     // pattern matching on the graph
 278     PhiNode* iv_phi = phi();
 279     if (iv_phi == NULL) {
 280       return NULL;
 281     }
 282     Node *ln = iv_phi->in(0);
 283     if (ln->is_CountedLoop() && ln->as_CountedLoop()->loopexit() == this) {
 284       return (CountedLoopNode*)ln;
 285     }
 286     return NULL;
 287   }
 288 
 289 #ifndef PRODUCT
 290   virtual void dump_spec(outputStream *st) const;
 291 #endif
 292 };
 293 
 294 
 295 inline CountedLoopEndNode *CountedLoopNode::loopexit() const {
 296   Node *bc = back_control();
 297   if( bc == NULL ) return NULL;
 298   Node *le = bc->in(0);
 299   if( le->Opcode() != Op_CountedLoopEnd )
 300     return NULL;
 301   return (CountedLoopEndNode*)le;
 302 }
 303 inline Node *CountedLoopNode::init_trip() const { return loopexit() ? loopexit()->init_trip() : NULL; }
 304 inline Node *CountedLoopNode::stride() const { return loopexit() ? loopexit()->stride() : NULL; }
 305 inline int CountedLoopNode::stride_con() const { return loopexit() ? loopexit()->stride_con() : 0; }
 306 inline bool CountedLoopNode::stride_is_con() const { return loopexit() && loopexit()->stride_is_con(); }
 307 inline Node *CountedLoopNode::limit() const { return loopexit() ? loopexit()->limit() : NULL; }
 308 inline Node *CountedLoopNode::incr() const { return loopexit() ? loopexit()->incr() : NULL; }
 309 inline Node *CountedLoopNode::phi() const { return loopexit() ? loopexit()->phi() : NULL; }
 310 
 311 //------------------------------LoopLimitNode-----------------------------
 312 // Counted Loop limit node which represents exact final iterator value:
 313 // trip_count = (limit - init_trip + stride - 1)/stride
 314 // final_value= trip_count * stride + init_trip.
 315 // Use HW instructions to calculate it when it can overflow in integer.
 316 // Note, final_value should fit into integer since counted loop has
 317 // limit check: limit <= max_int-stride.
 318 class LoopLimitNode : public Node {
 319   enum { Init=1, Limit=2, Stride=3 };
 320  public:
 321   LoopLimitNode( Compile* C, Node *init, Node *limit, Node *stride ) : Node(0,init,limit,stride) {
 322     // Put it on the Macro nodes list to optimize during macro nodes expansion.
 323     init_flags(Flag_is_macro);
 324     C->add_macro_node(this);
 325   }
 326   virtual int Opcode() const;
 327   virtual const Type *bottom_type() const { return TypeInt::INT; }
 328   virtual uint ideal_reg() const { return Op_RegI; }
 329   virtual const Type *Value( PhaseTransform *phase ) const;
 330   virtual Node *Ideal(PhaseGVN *phase, bool can_reshape);
 331   virtual Node *Identity( PhaseTransform *phase );
 332 };
 333 
 334 // -----------------------------IdealLoopTree----------------------------------
 335 class IdealLoopTree : public ResourceObj {
 336 public:
 337   IdealLoopTree *_parent;       // Parent in loop tree
 338   IdealLoopTree *_next;         // Next sibling in loop tree
 339   IdealLoopTree *_child;        // First child in loop tree
 340 
 341   // The head-tail backedge defines the loop.
 342   // If tail is NULL then this loop has multiple backedges as part of the
 343   // same loop.  During cleanup I'll peel off the multiple backedges; merge
 344   // them at the loop bottom and flow 1 real backedge into the loop.
 345   Node *_head;                  // Head of loop
 346   Node *_tail;                  // Tail of loop
 347   inline Node *tail();          // Handle lazy update of _tail field
 348   PhaseIdealLoop* _phase;
 349 
 350   Node_List _body;              // Loop body for inner loops
 351 
 352   uint8 _nest;                  // Nesting depth
 353   uint8 _irreducible:1,         // True if irreducible
 354         _has_call:1,            // True if has call safepoint
 355         _has_sfpt:1,            // True if has non-call safepoint
 356         _rce_candidate:1;       // True if candidate for range check elimination
 357 
 358   Node_List* _safepts;          // List of safepoints in this loop
 359   Node_List* _required_safept;  // A inner loop cannot delete these safepts;
 360   bool  _allow_optimizations;   // Allow loop optimizations
 361 
 362   IdealLoopTree( PhaseIdealLoop* phase, Node *head, Node *tail )
 363     : _parent(0), _next(0), _child(0),
 364       _head(head), _tail(tail),
 365       _phase(phase),
 366       _safepts(NULL),
 367       _required_safept(NULL),
 368       _allow_optimizations(true),
 369       _nest(0), _irreducible(0), _has_call(0), _has_sfpt(0), _rce_candidate(0)
 370   { }
 371 
 372   // Is 'l' a member of 'this'?
 373   int is_member( const IdealLoopTree *l ) const; // Test for nested membership
 374 
 375   // Set loop nesting depth.  Accumulate has_call bits.
 376   int set_nest( uint depth );
 377 
 378   // Split out multiple fall-in edges from the loop header.  Move them to a
 379   // private RegionNode before the loop.  This becomes the loop landing pad.
 380   void split_fall_in( PhaseIdealLoop *phase, int fall_in_cnt );
 381 
 382   // Split out the outermost loop from this shared header.
 383   void split_outer_loop( PhaseIdealLoop *phase );
 384 
 385   // Merge all the backedges from the shared header into a private Region.
 386   // Feed that region as the one backedge to this loop.
 387   void merge_many_backedges( PhaseIdealLoop *phase );
 388 
 389   // Split shared headers and insert loop landing pads.
 390   // Insert a LoopNode to replace the RegionNode.
 391   // Returns TRUE if loop tree is structurally changed.
 392   bool beautify_loops( PhaseIdealLoop *phase );
 393 
 394   // Perform optimization to use the loop predicates for null checks and range checks.
 395   // Applies to any loop level (not just the innermost one)
 396   bool loop_predication( PhaseIdealLoop *phase);
 397 
 398   // Perform iteration-splitting on inner loops.  Split iterations to
 399   // avoid range checks or one-shot null checks.  Returns false if the
 400   // current round of loop opts should stop.
 401   bool iteration_split( PhaseIdealLoop *phase, Node_List &old_new );
 402 
 403   // Driver for various flavors of iteration splitting.  Returns false
 404   // if the current round of loop opts should stop.
 405   bool iteration_split_impl( PhaseIdealLoop *phase, Node_List &old_new );
 406 
 407   // Given dominators, try to find loops with calls that must always be
 408   // executed (call dominates loop tail).  These loops do not need non-call
 409   // safepoints (ncsfpt).
 410   void check_safepts(VectorSet &visited, Node_List &stack);
 411 
 412   // Allpaths backwards scan from loop tail, terminating each path at first safepoint
 413   // encountered.
 414   void allpaths_check_safepts(VectorSet &visited, Node_List &stack);
 415 
 416   // Remove safepoints from loop. Optionally keeping one.
 417   void remove_safepoints(PhaseIdealLoop* phase, bool keep_one);
 418 
 419   // Convert to counted loops where possible
 420   void counted_loop( PhaseIdealLoop *phase );
 421 
 422   // Check for Node being a loop-breaking test
 423   Node *is_loop_exit(Node *iff) const;
 424 
 425   // Returns true if ctrl is executed on every complete iteration
 426   bool dominates_backedge(Node* ctrl);
 427 
 428   // Remove simplistic dead code from loop body
 429   void DCE_loop_body();
 430 
 431   // Look for loop-exit tests with my 50/50 guesses from the Parsing stage.
 432   // Replace with a 1-in-10 exit guess.
 433   void adjust_loop_exit_prob( PhaseIdealLoop *phase );
 434 
 435   // Return TRUE or FALSE if the loop should never be RCE'd or aligned.
 436   // Useful for unrolling loops with NO array accesses.
 437   bool policy_peel_only( PhaseIdealLoop *phase ) const;
 438 
 439   // Return TRUE or FALSE if the loop should be unswitched -- clone
 440   // loop with an invariant test
 441   bool policy_unswitching( PhaseIdealLoop *phase ) const;
 442 
 443   // Micro-benchmark spamming.  Remove empty loops.
 444   bool policy_do_remove_empty_loop( PhaseIdealLoop *phase );
 445 
 446   // Convert one iteration loop into normal code.
 447   bool policy_do_one_iteration_loop( PhaseIdealLoop *phase );
 448 
 449   // Return TRUE or FALSE if the loop should be peeled or not.  Peel if we can
 450   // make some loop-invariant test (usually a null-check) happen before the
 451   // loop.
 452   bool policy_peeling( PhaseIdealLoop *phase ) const;
 453 
 454   // Return TRUE or FALSE if the loop should be maximally unrolled. Stash any
 455   // known trip count in the counted loop node.
 456   bool policy_maximally_unroll( PhaseIdealLoop *phase ) const;
 457 
 458   // Return TRUE or FALSE if the loop should be unrolled or not.  Unroll if
 459   // the loop is a CountedLoop and the body is small enough.
 460   bool policy_unroll( PhaseIdealLoop *phase ) const;
 461 
 462   // Return TRUE or FALSE if the loop should be range-check-eliminated.
 463   // Gather a list of IF tests that are dominated by iteration splitting;
 464   // also gather the end of the first split and the start of the 2nd split.
 465   bool policy_range_check( PhaseIdealLoop *phase ) const;
 466 
 467   // Return TRUE or FALSE if the loop should be cache-line aligned.
 468   // Gather the expression that does the alignment.  Note that only
 469   // one array base can be aligned in a loop (unless the VM guarantees
 470   // mutual alignment).  Note that if we vectorize short memory ops
 471   // into longer memory ops, we may want to increase alignment.
 472   bool policy_align( PhaseIdealLoop *phase ) const;
 473 
 474   // Return TRUE if "iff" is a range check.
 475   bool is_range_check_if(IfNode *iff, PhaseIdealLoop *phase, Invariance& invar) const;
 476 
 477   // Compute loop exact trip count if possible
 478   void compute_exact_trip_count( PhaseIdealLoop *phase );
 479 
 480   // Compute loop trip count from profile data
 481   void compute_profile_trip_cnt( PhaseIdealLoop *phase );
 482 
 483   // Reassociate invariant expressions.
 484   void reassociate_invariants(PhaseIdealLoop *phase);
 485   // Reassociate invariant add and subtract expressions.
 486   Node* reassociate_add_sub(Node* n1, PhaseIdealLoop *phase);
 487   // Return nonzero index of invariant operand if invariant and variant
 488   // are combined with an Add or Sub. Helper for reassociate_invariants.
 489   int is_invariant_addition(Node* n, PhaseIdealLoop *phase);
 490 
 491   // Return true if n is invariant
 492   bool is_invariant(Node* n) const;
 493 
 494   // Put loop body on igvn work list
 495   void record_for_igvn();
 496 
 497   bool is_loop()    { return !_irreducible && _tail && !_tail->is_top(); }
 498   bool is_inner()   { return is_loop() && _child == NULL; }
 499   bool is_counted() { return is_loop() && _head != NULL && _head->is_CountedLoop(); }
 500 
 501 #ifndef PRODUCT
 502   void dump_head( ) const;      // Dump loop head only
 503   void dump() const;            // Dump this loop recursively
 504   void verify_tree(IdealLoopTree *loop, const IdealLoopTree *parent) const;
 505 #endif
 506 
 507 };
 508 
 509 // -----------------------------PhaseIdealLoop---------------------------------
 510 // Computes the mapping from Nodes to IdealLoopTrees.  Organizes IdealLoopTrees into a
 511 // loop tree.  Drives the loop-based transformations on the ideal graph.
 512 class PhaseIdealLoop : public PhaseTransform {
 513   friend class IdealLoopTree;
 514   friend class SuperWord;
 515   // Pre-computed def-use info
 516   PhaseIterGVN &_igvn;
 517 
 518   // Head of loop tree
 519   IdealLoopTree *_ltree_root;
 520 
 521   // Array of pre-order numbers, plus post-visited bit.
 522   // ZERO for not pre-visited.  EVEN for pre-visited but not post-visited.
 523   // ODD for post-visited.  Other bits are the pre-order number.
 524   uint *_preorders;
 525   uint _max_preorder;
 526 
 527   const PhaseIdealLoop* _verify_me;
 528   bool _verify_only;
 529 
 530   // Allocate _preorders[] array
 531   void allocate_preorders() {
 532     _max_preorder = C->unique()+8;
 533     _preorders = NEW_RESOURCE_ARRAY(uint, _max_preorder);
 534     memset(_preorders, 0, sizeof(uint) * _max_preorder);
 535   }
 536 
 537   // Allocate _preorders[] array
 538   void reallocate_preorders() {
 539     if ( _max_preorder < C->unique() ) {
 540       _preorders = REALLOC_RESOURCE_ARRAY(uint, _preorders, _max_preorder, C->unique());
 541       _max_preorder = C->unique();
 542     }
 543     memset(_preorders, 0, sizeof(uint) * _max_preorder);
 544   }
 545 
 546   // Check to grow _preorders[] array for the case when build_loop_tree_impl()
 547   // adds new nodes.
 548   void check_grow_preorders( ) {
 549     if ( _max_preorder < C->unique() ) {
 550       uint newsize = _max_preorder<<1;  // double size of array
 551       _preorders = REALLOC_RESOURCE_ARRAY(uint, _preorders, _max_preorder, newsize);
 552       memset(&_preorders[_max_preorder],0,sizeof(uint)*(newsize-_max_preorder));
 553       _max_preorder = newsize;
 554     }
 555   }
 556   // Check for pre-visited.  Zero for NOT visited; non-zero for visited.
 557   int is_visited( Node *n ) const { return _preorders[n->_idx]; }
 558   // Pre-order numbers are written to the Nodes array as low-bit-set values.
 559   void set_preorder_visited( Node *n, int pre_order ) {
 560     assert( !is_visited( n ), "already set" );
 561     _preorders[n->_idx] = (pre_order<<1);
 562   };
 563   // Return pre-order number.
 564   int get_preorder( Node *n ) const { assert( is_visited(n), "" ); return _preorders[n->_idx]>>1; }
 565 
 566   // Check for being post-visited.
 567   // Should be previsited already (checked with assert(is_visited(n))).
 568   int is_postvisited( Node *n ) const { assert( is_visited(n), "" ); return _preorders[n->_idx]&1; }
 569 
 570   // Mark as post visited
 571   void set_postvisited( Node *n ) { assert( !is_postvisited( n ), "" ); _preorders[n->_idx] |= 1; }
 572 
 573   // Set/get control node out.  Set lower bit to distinguish from IdealLoopTree
 574   // Returns true if "n" is a data node, false if it's a control node.
 575   bool has_ctrl( Node *n ) const { return ((intptr_t)_nodes[n->_idx]) & 1; }
 576 
 577   // clear out dead code after build_loop_late
 578   Node_List _deadlist;
 579 
 580   // Support for faster execution of get_late_ctrl()/dom_lca()
 581   // when a node has many uses and dominator depth is deep.
 582   Node_Array _dom_lca_tags;
 583   void   init_dom_lca_tags();
 584   void   clear_dom_lca_tags();
 585 
 586   // Helper for debugging bad dominance relationships
 587   bool verify_dominance(Node* n, Node* use, Node* LCA, Node* early);
 588 
 589   Node* compute_lca_of_uses(Node* n, Node* early, bool verify = false);
 590 
 591   // Inline wrapper for frequent cases:
 592   // 1) only one use
 593   // 2) a use is the same as the current LCA passed as 'n1'
 594   Node *dom_lca_for_get_late_ctrl( Node *lca, Node *n, Node *tag ) {
 595     assert( n->is_CFG(), "" );
 596     // Fast-path NULL lca
 597     if( lca != NULL && lca != n ) {
 598       assert( lca->is_CFG(), "" );
 599       // find LCA of all uses
 600       n = dom_lca_for_get_late_ctrl_internal( lca, n, tag );
 601     }
 602     return find_non_split_ctrl(n);
 603   }
 604   Node *dom_lca_for_get_late_ctrl_internal( Node *lca, Node *n, Node *tag );
 605 
 606   // Helper function for directing control inputs away from CFG split
 607   // points.
 608   Node *find_non_split_ctrl( Node *ctrl ) const {
 609     if (ctrl != NULL) {
 610       if (ctrl->is_MultiBranch()) {
 611         ctrl = ctrl->in(0);
 612       }
 613       assert(ctrl->is_CFG(), "CFG");
 614     }
 615     return ctrl;
 616   }
 617 
 618   bool cast_incr_before_loop(Node* incr, Node* ctrl, Node* loop);
 619 
 620 public:
 621   bool has_node( Node* n ) const {
 622     guarantee(n != NULL, "No Node.");
 623     return _nodes[n->_idx] != NULL;
 624   }
 625   // check if transform created new nodes that need _ctrl recorded
 626   Node *get_late_ctrl( Node *n, Node *early );
 627   Node *get_early_ctrl( Node *n );
 628   Node *get_early_ctrl_for_expensive(Node *n, Node* earliest);
 629   void set_early_ctrl( Node *n );
 630   void set_subtree_ctrl( Node *root );
 631   void set_ctrl( Node *n, Node *ctrl ) {
 632     assert( !has_node(n) || has_ctrl(n), "" );
 633     assert( ctrl->in(0), "cannot set dead control node" );
 634     assert( ctrl == find_non_split_ctrl(ctrl), "must set legal crtl" );
 635     _nodes.map( n->_idx, (Node*)((intptr_t)ctrl + 1) );
 636   }
 637   // Set control and update loop membership
 638   void set_ctrl_and_loop(Node* n, Node* ctrl) {
 639     IdealLoopTree* old_loop = get_loop(get_ctrl(n));
 640     IdealLoopTree* new_loop = get_loop(ctrl);
 641     if (old_loop != new_loop) {
 642       if (old_loop->_child == NULL) old_loop->_body.yank(n);
 643       if (new_loop->_child == NULL) new_loop->_body.push(n);
 644     }
 645     set_ctrl(n, ctrl);
 646   }
 647   // Control nodes can be replaced or subsumed.  During this pass they
 648   // get their replacement Node in slot 1.  Instead of updating the block
 649   // location of all Nodes in the subsumed block, we lazily do it.  As we
 650   // pull such a subsumed block out of the array, we write back the final
 651   // correct block.
 652   Node *get_ctrl( Node *i ) {
 653     assert(has_node(i), "");
 654     Node *n = get_ctrl_no_update(i);
 655     _nodes.map( i->_idx, (Node*)((intptr_t)n + 1) );
 656     assert(has_node(i) && has_ctrl(i), "");
 657     assert(n == find_non_split_ctrl(n), "must return legal ctrl" );
 658     return n;
 659   }
 660   // true if CFG node d dominates CFG node n
 661   bool is_dominator(Node *d, Node *n);
 662   // return get_ctrl for a data node and self(n) for a CFG node
 663   Node* ctrl_or_self(Node* n) {
 664     if (has_ctrl(n))
 665       return get_ctrl(n);
 666     else {
 667       assert (n->is_CFG(), "must be a CFG node");
 668       return n;
 669     }
 670   }
 671 
 672 private:
 673   Node *get_ctrl_no_update_helper(Node *i) const {
 674     assert(has_ctrl(i), "should be control, not loop");
 675     return (Node*)(((intptr_t)_nodes[i->_idx]) & ~1);
 676   }
 677 
 678   Node *get_ctrl_no_update(Node *i) const {
 679     assert( has_ctrl(i), "" );
 680     Node *n = get_ctrl_no_update_helper(i);
 681     if (!n->in(0)) {
 682       // Skip dead CFG nodes
 683       do {
 684         n = get_ctrl_no_update_helper(n);
 685       } while (!n->in(0));
 686       n = find_non_split_ctrl(n);
 687     }
 688     return n;
 689   }
 690 
 691   // Check for loop being set
 692   // "n" must be a control node. Returns true if "n" is known to be in a loop.
 693   bool has_loop( Node *n ) const {
 694     assert(!has_node(n) || !has_ctrl(n), "");
 695     return has_node(n);
 696   }
 697   // Set loop
 698   void set_loop( Node *n, IdealLoopTree *loop ) {
 699     _nodes.map(n->_idx, (Node*)loop);
 700   }
 701   // Lazy-dazy update of 'get_ctrl' and 'idom_at' mechanisms.  Replace
 702   // the 'old_node' with 'new_node'.  Kill old-node.  Add a reference
 703   // from old_node to new_node to support the lazy update.  Reference
 704   // replaces loop reference, since that is not needed for dead node.
 705 public:
 706   void lazy_update(Node *old_node, Node *new_node) {
 707     assert(old_node != new_node, "no cycles please");
 708     // Re-use the side array slot for this node to provide the
 709     // forwarding pointer.
 710     _nodes.map(old_node->_idx, (Node*)((intptr_t)new_node + 1));
 711   }
 712   void lazy_replace(Node *old_node, Node *new_node) {
 713     _igvn.replace_node(old_node, new_node);
 714     lazy_update(old_node, new_node);
 715   }
 716 
 717 private:
 718 
 719   // Place 'n' in some loop nest, where 'n' is a CFG node
 720   void build_loop_tree();
 721   int build_loop_tree_impl( Node *n, int pre_order );
 722   // Insert loop into the existing loop tree.  'innermost' is a leaf of the
 723   // loop tree, not the root.
 724   IdealLoopTree *sort( IdealLoopTree *loop, IdealLoopTree *innermost );
 725 
 726   // Place Data nodes in some loop nest
 727   void build_loop_early( VectorSet &visited, Node_List &worklist, Node_Stack &nstack );
 728   void build_loop_late ( VectorSet &visited, Node_List &worklist, Node_Stack &nstack );
 729   void build_loop_late_post ( Node* n );
 730 
 731   // Array of immediate dominance info for each CFG node indexed by node idx
 732 private:
 733   uint _idom_size;
 734   Node **_idom;                 // Array of immediate dominators
 735   uint *_dom_depth;           // Used for fast LCA test
 736   GrowableArray<uint>* _dom_stk; // For recomputation of dom depth
 737 
 738   Node* idom_no_update(Node* d) const {
 739     assert(d->_idx < _idom_size, "oob");
 740     Node* n = _idom[d->_idx];
 741     assert(n != NULL,"Bad immediate dominator info.");
 742     while (n->in(0) == NULL) {  // Skip dead CFG nodes
 743       //n = n->in(1);
 744       n = (Node*)(((intptr_t)_nodes[n->_idx]) & ~1);
 745       assert(n != NULL,"Bad immediate dominator info.");
 746     }
 747     return n;
 748   }
 749   Node *idom(Node* d) const {
 750     uint didx = d->_idx;
 751     Node *n = idom_no_update(d);
 752     _idom[didx] = n;            // Lazily remove dead CFG nodes from table.
 753     return n;
 754   }
 755   uint dom_depth(Node* d) const {
 756     guarantee(d != NULL, "Null dominator info.");
 757     guarantee(d->_idx < _idom_size, "");
 758     return _dom_depth[d->_idx];
 759   }
 760   void set_idom(Node* d, Node* n, uint dom_depth);
 761   // Locally compute IDOM using dom_lca call
 762   Node *compute_idom( Node *region ) const;
 763   // Recompute dom_depth
 764   void recompute_dom_depth();
 765 
 766   // Is safept not required by an outer loop?
 767   bool is_deleteable_safept(Node* sfpt);
 768 
 769   // Replace parallel induction variable (parallel to trip counter)
 770   void replace_parallel_iv(IdealLoopTree *loop);
 771 
 772   // Perform verification that the graph is valid.
 773   PhaseIdealLoop( PhaseIterGVN &igvn) :
 774     PhaseTransform(Ideal_Loop),
 775     _igvn(igvn),
 776     _dom_lca_tags(arena()), // Thread::resource_area
 777     _verify_me(NULL),
 778     _verify_only(true) {
 779     build_and_optimize(false, false);
 780   }
 781 
 782   // build the loop tree and perform any requested optimizations
 783   void build_and_optimize(bool do_split_if, bool skip_loop_opts);
 784 
 785 public:
 786   // Dominators for the sea of nodes
 787   void Dominators();
 788   Node *dom_lca( Node *n1, Node *n2 ) const {
 789     return find_non_split_ctrl(dom_lca_internal(n1, n2));
 790   }
 791   Node *dom_lca_internal( Node *n1, Node *n2 ) const;
 792 
 793   // Compute the Ideal Node to Loop mapping
 794   PhaseIdealLoop( PhaseIterGVN &igvn, bool do_split_ifs, bool skip_loop_opts = false) :
 795     PhaseTransform(Ideal_Loop),
 796     _igvn(igvn),
 797     _dom_lca_tags(arena()), // Thread::resource_area
 798     _verify_me(NULL),
 799     _verify_only(false) {
 800     build_and_optimize(do_split_ifs, skip_loop_opts);
 801   }
 802 
 803   // Verify that verify_me made the same decisions as a fresh run.
 804   PhaseIdealLoop( PhaseIterGVN &igvn, const PhaseIdealLoop *verify_me) :
 805     PhaseTransform(Ideal_Loop),
 806     _igvn(igvn),
 807     _dom_lca_tags(arena()), // Thread::resource_area
 808     _verify_me(verify_me),
 809     _verify_only(false) {
 810     build_and_optimize(false, false);
 811   }
 812 
 813   // Build and verify the loop tree without modifying the graph.  This
 814   // is useful to verify that all inputs properly dominate their uses.
 815   static void verify(PhaseIterGVN& igvn) {
 816 #ifdef ASSERT
 817     PhaseIdealLoop v(igvn);
 818 #endif
 819   }
 820 
 821   // True if the method has at least 1 irreducible loop
 822   bool _has_irreducible_loops;
 823 
 824   // Per-Node transform
 825   virtual Node *transform( Node *a_node ) { return 0; }
 826 
 827   bool is_counted_loop( Node *x, IdealLoopTree *loop );
 828 
 829   Node* exact_limit( IdealLoopTree *loop );
 830 
 831   // Return a post-walked LoopNode
 832   IdealLoopTree *get_loop( Node *n ) const {
 833     // Dead nodes have no loop, so return the top level loop instead
 834     if (!has_node(n))  return _ltree_root;
 835     assert(!has_ctrl(n), "");
 836     return (IdealLoopTree*)_nodes[n->_idx];
 837   }
 838 
 839   // Is 'n' a (nested) member of 'loop'?
 840   int is_member( const IdealLoopTree *loop, Node *n ) const {
 841     return loop->is_member(get_loop(n)); }
 842 
 843   // This is the basic building block of the loop optimizations.  It clones an
 844   // entire loop body.  It makes an old_new loop body mapping; with this
 845   // mapping you can find the new-loop equivalent to an old-loop node.  All
 846   // new-loop nodes are exactly equal to their old-loop counterparts, all
 847   // edges are the same.  All exits from the old-loop now have a RegionNode
 848   // that merges the equivalent new-loop path.  This is true even for the
 849   // normal "loop-exit" condition.  All uses of loop-invariant old-loop values
 850   // now come from (one or more) Phis that merge their new-loop equivalents.
 851   // Parameter side_by_side_idom:
 852   //   When side_by_size_idom is NULL, the dominator tree is constructed for
 853   //      the clone loop to dominate the original.  Used in construction of
 854   //      pre-main-post loop sequence.
 855   //   When nonnull, the clone and original are side-by-side, both are
 856   //      dominated by the passed in side_by_side_idom node.  Used in
 857   //      construction of unswitched loops.
 858   void clone_loop( IdealLoopTree *loop, Node_List &old_new, int dom_depth,
 859                    Node* side_by_side_idom = NULL);
 860 
 861   // If we got the effect of peeling, either by actually peeling or by
 862   // making a pre-loop which must execute at least once, we can remove
 863   // all loop-invariant dominated tests in the main body.
 864   void peeled_dom_test_elim( IdealLoopTree *loop, Node_List &old_new );
 865 
 866   // Generate code to do a loop peel for the given loop (and body).
 867   // old_new is a temp array.
 868   void do_peeling( IdealLoopTree *loop, Node_List &old_new );
 869 
 870   // Add pre and post loops around the given loop.  These loops are used
 871   // during RCE, unrolling and aligning loops.
 872   void insert_pre_post_loops( IdealLoopTree *loop, Node_List &old_new, bool peel_only );
 873   // If Node n lives in the back_ctrl block, we clone a private version of n
 874   // in preheader_ctrl block and return that, otherwise return n.
 875   Node *clone_up_backedge_goo( Node *back_ctrl, Node *preheader_ctrl, Node *n, VectorSet &visited, Node_Stack &clones );
 876 
 877   // Take steps to maximally unroll the loop.  Peel any odd iterations, then
 878   // unroll to do double iterations.  The next round of major loop transforms
 879   // will repeat till the doubled loop body does all remaining iterations in 1
 880   // pass.
 881   void do_maximally_unroll( IdealLoopTree *loop, Node_List &old_new );
 882 
 883   // Unroll the loop body one step - make each trip do 2 iterations.
 884   void do_unroll( IdealLoopTree *loop, Node_List &old_new, bool adjust_min_trip );
 885 
 886   // Return true if exp is a constant times an induction var
 887   bool is_scaled_iv(Node* exp, Node* iv, int* p_scale);
 888 
 889   // Return true if exp is a scaled induction var plus (or minus) constant
 890   bool is_scaled_iv_plus_offset(Node* exp, Node* iv, int* p_scale, Node** p_offset, int depth = 0);
 891 
 892   // Create a new if above the uncommon_trap_if_pattern for the predicate to be promoted
 893   ProjNode* create_new_if_for_predicate(ProjNode* cont_proj, Node* new_entry,
 894                                         Deoptimization::DeoptReason reason);
 895   void register_control(Node* n, IdealLoopTree *loop, Node* pred);
 896 
 897   // Clone loop predicates to cloned loops (peeled, unswitched)
 898   static ProjNode* clone_predicate(ProjNode* predicate_proj, Node* new_entry,
 899                                    Deoptimization::DeoptReason reason,
 900                                    PhaseIdealLoop* loop_phase,
 901                                    PhaseIterGVN* igvn);
 902 
 903   static Node* clone_loop_predicates(Node* old_entry, Node* new_entry,
 904                                          bool clone_limit_check,
 905                                          PhaseIdealLoop* loop_phase,
 906                                          PhaseIterGVN* igvn);
 907   Node* clone_loop_predicates(Node* old_entry, Node* new_entry, bool clone_limit_check);
 908 
 909   static Node* skip_loop_predicates(Node* entry);
 910 
 911   // Find a good location to insert a predicate
 912   static ProjNode* find_predicate_insertion_point(Node* start_c, Deoptimization::DeoptReason reason);
 913   // Find a predicate
 914   static Node* find_predicate(Node* entry);
 915   // Construct a range check for a predicate if
 916   BoolNode* rc_predicate(IdealLoopTree *loop, Node* ctrl,
 917                          int scale, Node* offset,
 918                          Node* init, Node* limit, jint stride,
 919                          Node* range, bool upper, bool &overflow);
 920 
 921   // Implementation of the loop predication to promote checks outside the loop
 922   bool loop_predication_impl(IdealLoopTree *loop);
 923 
 924   // Helper function to collect predicate for eliminating the useless ones
 925   void collect_potentially_useful_predicates(IdealLoopTree *loop, Unique_Node_List &predicate_opaque1);
 926   void eliminate_useless_predicates();
 927 
 928   // Change the control input of expensive nodes to allow commoning by
 929   // IGVN when it is guaranteed to not result in a more frequent
 930   // execution of the expensive node. Return true if progress.
 931   bool process_expensive_nodes();
 932 
 933   // Check whether node has become unreachable
 934   bool is_node_unreachable(Node *n) const {
 935     return !has_node(n) || n->is_unreachable(_igvn);
 936   }
 937 
 938   // Eliminate range-checks and other trip-counter vs loop-invariant tests.
 939   void do_range_check( IdealLoopTree *loop, Node_List &old_new );
 940 
 941   // Create a slow version of the loop by cloning the loop
 942   // and inserting an if to select fast-slow versions.
 943   ProjNode* create_slow_version_of_loop(IdealLoopTree *loop,
 944                                         Node_List &old_new);
 945 
 946   // Clone loop with an invariant test (that does not exit) and
 947   // insert a clone of the test that selects which version to
 948   // execute.
 949   void do_unswitching (IdealLoopTree *loop, Node_List &old_new);
 950 
 951   // Find candidate "if" for unswitching
 952   IfNode* find_unswitching_candidate(const IdealLoopTree *loop) const;
 953 
 954   // Range Check Elimination uses this function!
 955   // Constrain the main loop iterations so the affine function:
 956   //    low_limit <= scale_con * I + offset  <  upper_limit
 957   // always holds true.  That is, either increase the number of iterations in
 958   // the pre-loop or the post-loop until the condition holds true in the main
 959   // loop.  Scale_con, offset and limit are all loop invariant.
 960   void add_constraint( int stride_con, int scale_con, Node *offset, Node *low_limit, Node *upper_limit, Node *pre_ctrl, Node **pre_limit, Node **main_limit );
 961   // Helper function for add_constraint().
 962   Node* adjust_limit( int stride_con, Node * scale, Node *offset, Node *rc_limit, Node *loop_limit, Node *pre_ctrl );
 963 
 964   // Partially peel loop up through last_peel node.
 965   bool partial_peel( IdealLoopTree *loop, Node_List &old_new );
 966 
 967   // Create a scheduled list of nodes control dependent on ctrl set.
 968   void scheduled_nodelist( IdealLoopTree *loop, VectorSet& ctrl, Node_List &sched );
 969   // Has a use in the vector set
 970   bool has_use_in_set( Node* n, VectorSet& vset );
 971   // Has use internal to the vector set (ie. not in a phi at the loop head)
 972   bool has_use_internal_to_set( Node* n, VectorSet& vset, IdealLoopTree *loop );
 973   // clone "n" for uses that are outside of loop
 974   int  clone_for_use_outside_loop( IdealLoopTree *loop, Node* n, Node_List& worklist );
 975   // clone "n" for special uses that are in the not_peeled region
 976   void clone_for_special_use_inside_loop( IdealLoopTree *loop, Node* n,
 977                                           VectorSet& not_peel, Node_List& sink_list, Node_List& worklist );
 978   // Insert phi(lp_entry_val, back_edge_val) at use->in(idx) for loop lp if phi does not already exist
 979   void insert_phi_for_loop( Node* use, uint idx, Node* lp_entry_val, Node* back_edge_val, LoopNode* lp );
 980 #ifdef ASSERT
 981   // Validate the loop partition sets: peel and not_peel
 982   bool is_valid_loop_partition( IdealLoopTree *loop, VectorSet& peel, Node_List& peel_list, VectorSet& not_peel );
 983   // Ensure that uses outside of loop are of the right form
 984   bool is_valid_clone_loop_form( IdealLoopTree *loop, Node_List& peel_list,
 985                                  uint orig_exit_idx, uint clone_exit_idx);
 986   bool is_valid_clone_loop_exit_use( IdealLoopTree *loop, Node* use, uint exit_idx);
 987 #endif
 988 
 989   // Returns nonzero constant stride if-node is a possible iv test (otherwise returns zero.)
 990   int stride_of_possible_iv( Node* iff );
 991   bool is_possible_iv_test( Node* iff ) { return stride_of_possible_iv(iff) != 0; }
 992   // Return the (unique) control output node that's in the loop (if it exists.)
 993   Node* stay_in_loop( Node* n, IdealLoopTree *loop);
 994   // Insert a signed compare loop exit cloned from an unsigned compare.
 995   IfNode* insert_cmpi_loop_exit(IfNode* if_cmpu, IdealLoopTree *loop);
 996   void remove_cmpi_loop_exit(IfNode* if_cmp, IdealLoopTree *loop);
 997   // Utility to register node "n" with PhaseIdealLoop
 998   void register_node(Node* n, IdealLoopTree *loop, Node* pred, int ddepth);
 999   // Utility to create an if-projection
1000   ProjNode* proj_clone(ProjNode* p, IfNode* iff);
1001   // Force the iff control output to be the live_proj
1002   Node* short_circuit_if(IfNode* iff, ProjNode* live_proj);
1003   // Insert a region before an if projection
1004   RegionNode* insert_region_before_proj(ProjNode* proj);
1005   // Insert a new if before an if projection
1006   ProjNode* insert_if_before_proj(Node* left, bool Signed, BoolTest::mask relop, Node* right, ProjNode* proj);
1007 
1008   // Passed in a Phi merging (recursively) some nearly equivalent Bool/Cmps.
1009   // "Nearly" because all Nodes have been cloned from the original in the loop,
1010   // but the fall-in edges to the Cmp are different.  Clone bool/Cmp pairs
1011   // through the Phi recursively, and return a Bool.
1012   BoolNode *clone_iff( PhiNode *phi, IdealLoopTree *loop );
1013   CmpNode *clone_bool( PhiNode *phi, IdealLoopTree *loop );
1014 
1015 
1016   // Rework addressing expressions to get the most loop-invariant stuff
1017   // moved out.  We'd like to do all associative operators, but it's especially
1018   // important (common) to do address expressions.
1019   Node *remix_address_expressions( Node *n );
1020 
1021   // Attempt to use a conditional move instead of a phi/branch
1022   Node *conditional_move( Node *n );
1023 
1024   // Reorganize offset computations to lower register pressure.
1025   // Mostly prevent loop-fallout uses of the pre-incremented trip counter
1026   // (which are then alive with the post-incremented trip counter
1027   // forcing an extra register move)
1028   void reorg_offsets( IdealLoopTree *loop );
1029 
1030   // Check for aggressive application of 'split-if' optimization,
1031   // using basic block level info.
1032   void  split_if_with_blocks     ( VectorSet &visited, Node_Stack &nstack );
1033   Node *split_if_with_blocks_pre ( Node *n );
1034   void  split_if_with_blocks_post( Node *n );
1035   Node *has_local_phi_input( Node *n );
1036   // Mark an IfNode as being dominated by a prior test,
1037   // without actually altering the CFG (and hence IDOM info).
1038   void dominated_by( Node *prevdom, Node *iff, bool flip = false, bool exclude_loop_predicate = false );
1039 
1040   // Split Node 'n' through merge point
1041   Node *split_thru_region( Node *n, Node *region );
1042   // Split Node 'n' through merge point if there is enough win.
1043   Node *split_thru_phi( Node *n, Node *region, int policy );
1044   // Found an If getting its condition-code input from a Phi in the
1045   // same block.  Split thru the Region.
1046   void do_split_if( Node *iff );
1047 
1048   // Conversion of fill/copy patterns into intrisic versions
1049   bool do_intrinsify_fill();
1050   bool intrinsify_fill(IdealLoopTree* lpt);
1051   bool match_fill_loop(IdealLoopTree* lpt, Node*& store, Node*& store_value,
1052                        Node*& shift, Node*& offset);
1053 
1054 private:
1055   // Return a type based on condition control flow
1056   const TypeInt* filtered_type( Node *n, Node* n_ctrl);
1057   const TypeInt* filtered_type( Node *n ) { return filtered_type(n, NULL); }
1058  // Helpers for filtered type
1059   const TypeInt* filtered_type_from_dominators( Node* val, Node *val_ctrl);
1060 
1061   // Helper functions
1062   Node *spinup( Node *iff, Node *new_false, Node *new_true, Node *region, Node *phi, small_cache *cache );
1063   Node *find_use_block( Node *use, Node *def, Node *old_false, Node *new_false, Node *old_true, Node *new_true );
1064   void handle_use( Node *use, Node *def, small_cache *cache, Node *region_dom, Node *new_false, Node *new_true, Node *old_false, Node *old_true );
1065   bool split_up( Node *n, Node *blk1, Node *blk2 );
1066   void sink_use( Node *use, Node *post_loop );
1067   Node *place_near_use( Node *useblock ) const;
1068 
1069   bool _created_loop_node;
1070 public:
1071   void set_created_loop_node() { _created_loop_node = true; }
1072   bool created_loop_node()     { return _created_loop_node; }
1073   void register_new_node( Node *n, Node *blk );
1074 
1075 #ifdef ASSERT
1076   void dump_bad_graph(const char* msg, Node* n, Node* early, Node* LCA);
1077 #endif
1078 
1079 #ifndef PRODUCT
1080   void dump( ) const;
1081   void dump( IdealLoopTree *loop, uint rpo_idx, Node_List &rpo_list ) const;
1082   void rpo( Node *start, Node_Stack &stk, VectorSet &visited, Node_List &rpo_list ) const;
1083   void verify() const;          // Major slow  :-)
1084   void verify_compare( Node *n, const PhaseIdealLoop *loop_verify, VectorSet &visited ) const;
1085   IdealLoopTree *get_loop_idx(Node* n) const {
1086     // Dead nodes have no loop, so return the top level loop instead
1087     return _nodes[n->_idx] ? (IdealLoopTree*)_nodes[n->_idx] : _ltree_root;
1088   }
1089   // Print some stats
1090   static void print_statistics();
1091   static int _loop_invokes;     // Count of PhaseIdealLoop invokes
1092   static int _loop_work;        // Sum of PhaseIdealLoop x _unique
1093 #endif
1094 };
1095 
1096 inline Node* IdealLoopTree::tail() {
1097 // Handle lazy update of _tail field
1098   Node *n = _tail;
1099   //while( !n->in(0) )  // Skip dead CFG nodes
1100     //n = n->in(1);
1101   if (n->in(0) == NULL)
1102     n = _phase->get_ctrl(n);
1103   _tail = n;
1104   return n;
1105 }
1106 
1107 
1108 // Iterate over the loop tree using a preorder, left-to-right traversal.
1109 //
1110 // Example that visits all counted loops from within PhaseIdealLoop
1111 //
1112 //  for (LoopTreeIterator iter(_ltree_root); !iter.done(); iter.next()) {
1113 //   IdealLoopTree* lpt = iter.current();
1114 //   if (!lpt->is_counted()) continue;
1115 //   ...
1116 class LoopTreeIterator : public StackObj {
1117 private:
1118   IdealLoopTree* _root;
1119   IdealLoopTree* _curnt;
1120 
1121 public:
1122   LoopTreeIterator(IdealLoopTree* root) : _root(root), _curnt(root) {}
1123 
1124   bool done() { return _curnt == NULL; }       // Finished iterating?
1125 
1126   void next();                                 // Advance to next loop tree
1127 
1128   IdealLoopTree* current() { return _curnt; }  // Return current value of iterator.
1129 };
1130 
1131 #endif // SHARE_VM_OPTO_LOOPNODE_HPP