1 /*
   2  * Copyright (c) 1997, 2017, 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_OOPS_GENERATEOOPMAP_HPP
  26 #define SHARE_VM_OOPS_GENERATEOOPMAP_HPP
  27 
  28 #include "interpreter/bytecodeStream.hpp"
  29 #include "memory/allocation.inline.hpp"
  30 #include "memory/universe.inline.hpp"
  31 #include "oops/method.hpp"
  32 #include "oops/oopsHierarchy.hpp"
  33 #include "runtime/signature.hpp"
  34 #include "utilities/bitMap.hpp"
  35 
  36 // Forward definition
  37 class GenerateOopMap;
  38 class BasicBlock;
  39 class CellTypeState;
  40 class StackMap;
  41 
  42 // These two should be removed. But requires som code to be cleaned up
  43 #define MAXARGSIZE      256      // This should be enough
  44 #define MAX_LOCAL_VARS  65536    // 16-bit entry
  45 
  46 typedef void (*jmpFct_t)(GenerateOopMap *c, int bcpDelta, int* data);
  47 
  48 
  49 //  RetTable
  50 //
  51 // Contains maping between jsr targets and there return addresses. One-to-many mapping
  52 //
  53 class RetTableEntry : public ResourceObj {
  54  private:
  55   static int _init_nof_jsrs;                      // Default size of jsrs list
  56   int _target_bci;                                // Target PC address of jump (bytecode index)
  57   GrowableArray<intptr_t> * _jsrs;                     // List of return addresses  (bytecode index)
  58   RetTableEntry *_next;                           // Link to next entry
  59  public:
  60    RetTableEntry(int target, RetTableEntry *next)  { _target_bci=target; _jsrs = new GrowableArray<intptr_t>(_init_nof_jsrs); _next = next;  }
  61 
  62   // Query
  63   int target_bci() const                      { return _target_bci; }
  64   int nof_jsrs() const                        { return _jsrs->length(); }
  65   int jsrs(int i) const                       { assert(i>=0 && i<nof_jsrs(), "Index out of bounds"); return _jsrs->at(i); }
  66 
  67   // Update entry
  68   void add_jsr    (int return_bci)            { _jsrs->append(return_bci); }
  69   void add_delta  (int bci, int delta);
  70   RetTableEntry * next()  const               { return _next; }
  71 };
  72 
  73 
  74 class RetTable VALUE_OBJ_CLASS_SPEC {
  75  private:
  76   RetTableEntry *_first;
  77   static int _init_nof_entries;
  78 
  79   void add_jsr(int return_bci, int target_bci);   // Adds entry to list
  80  public:
  81   RetTable()                                                  { _first = NULL; }
  82   void compute_ret_table(const methodHandle& method);
  83   void update_ret_table(int bci, int delta);
  84   RetTableEntry* find_jsrs_for_target(int targBci);
  85 };
  86 
  87 //
  88 // CellTypeState
  89 //
  90 class CellTypeState VALUE_OBJ_CLASS_SPEC {
  91  private:
  92   unsigned int _state;
  93 
  94   // Masks for separating the BITS and INFO portions of a CellTypeState
  95   enum { info_mask            = right_n_bits(28),
  96          bits_mask            = (int)(~info_mask) };
  97 
  98   // These constant are used for manipulating the BITS portion of a
  99   // CellTypeState
 100   enum { uninit_bit           = (int)(nth_bit(31)),
 101          ref_bit              = nth_bit(30),
 102          val_bit              = nth_bit(29),
 103          addr_bit             = nth_bit(28),
 104          live_bits_mask       = (int)(bits_mask & ~uninit_bit) };
 105 
 106   // These constants are used for manipulating the INFO portion of a
 107   // CellTypeState
 108   enum { top_info_bit         = nth_bit(27),
 109          not_bottom_info_bit  = nth_bit(26),
 110          info_data_mask       = right_n_bits(26),
 111          info_conflict        = info_mask };
 112 
 113   // Within the INFO data, these values are used to distinguish different
 114   // kinds of references.
 115   enum { ref_not_lock_bit     = nth_bit(25),  // 0 if this reference is locked as a monitor
 116          ref_slot_bit         = nth_bit(24),  // 1 if this reference is a "slot" reference,
 117                                               // 0 if it is a "line" reference.
 118          ref_data_mask        = right_n_bits(24) };
 119 
 120 
 121   // These values are used to initialize commonly used CellTypeState
 122   // constants.
 123   enum { bottom_value         = 0,
 124          uninit_value         = (int)(uninit_bit | info_conflict),
 125          ref_value            = ref_bit,
 126          ref_conflict         = ref_bit | info_conflict,
 127          val_value            = val_bit | info_conflict,
 128          addr_value           = addr_bit,
 129          addr_conflict        = addr_bit | info_conflict };
 130 
 131  public:
 132 
 133   // Since some C++ constructors generate poor code for declarations of the
 134   // form...
 135   //
 136   //   CellTypeState vector[length];
 137   //
 138   // ...we avoid making a constructor for this class.  CellTypeState values
 139   // should be constructed using one of the make_* methods:
 140 
 141   static CellTypeState make_any(int state) {
 142     CellTypeState s;
 143     s._state = state;
 144     // Causes SS10 warning.
 145     // assert(s.is_valid_state(), "check to see if CellTypeState is valid");
 146     return s;
 147   }
 148 
 149   static CellTypeState make_bottom() {
 150     return make_any(0);
 151   }
 152 
 153   static CellTypeState make_top() {
 154     return make_any(AllBits);
 155   }
 156 
 157   static CellTypeState make_addr(int bci) {
 158     assert((bci >= 0) && (bci < info_data_mask), "check to see if ret addr is valid");
 159     return make_any(addr_bit | not_bottom_info_bit | (bci & info_data_mask));
 160   }
 161 
 162   static CellTypeState make_slot_ref(int slot_num) {
 163     assert(slot_num >= 0 && slot_num < ref_data_mask, "slot out of range");
 164     return make_any(ref_bit | not_bottom_info_bit | ref_not_lock_bit | ref_slot_bit |
 165                     (slot_num & ref_data_mask));
 166   }
 167 
 168   static CellTypeState make_line_ref(int bci) {
 169     assert(bci >= 0 && bci < ref_data_mask, "line out of range");
 170     return make_any(ref_bit | not_bottom_info_bit | ref_not_lock_bit |
 171                     (bci & ref_data_mask));
 172   }
 173 
 174   static CellTypeState make_lock_ref(int bci) {
 175     assert(bci >= 0 && bci < ref_data_mask, "line out of range");
 176     return make_any(ref_bit | not_bottom_info_bit | (bci & ref_data_mask));
 177   }
 178 
 179   // Query methods:
 180   bool is_bottom() const                { return _state == 0; }
 181   bool is_live() const                  { return ((_state & live_bits_mask) != 0); }
 182   bool is_valid_state() const {
 183     // Uninitialized and value cells must contain no data in their info field:
 184     if ((can_be_uninit() || can_be_value()) && !is_info_top()) {
 185       return false;
 186     }
 187     // The top bit is only set when all info bits are set:
 188     if (is_info_top() && ((_state & info_mask) != info_mask)) {
 189       return false;
 190     }
 191     // The not_bottom_bit must be set when any other info bit is set:
 192     if (is_info_bottom() && ((_state & info_mask) != 0)) {
 193       return false;
 194     }
 195     return true;
 196   }
 197 
 198   bool is_address() const               { return ((_state & bits_mask) == addr_bit); }
 199   bool is_reference() const             { return ((_state & bits_mask) == ref_bit); }
 200   bool is_value() const                 { return ((_state & bits_mask) == val_bit); }
 201   bool is_uninit() const                { return ((_state & bits_mask) == (uint)uninit_bit); }
 202 
 203   bool can_be_address() const           { return ((_state & addr_bit) != 0); }
 204   bool can_be_reference() const         { return ((_state & ref_bit) != 0); }
 205   bool can_be_value() const             { return ((_state & val_bit) != 0); }
 206   bool can_be_uninit() const            { return ((_state & uninit_bit) != 0); }
 207 
 208   bool is_info_bottom() const           { return ((_state & not_bottom_info_bit) == 0); }
 209   bool is_info_top() const              { return ((_state & top_info_bit) != 0); }
 210   int  get_info() const {
 211     assert((!is_info_top() && !is_info_bottom()),
 212            "check to make sure top/bottom info is not used");
 213     return (_state & info_data_mask);
 214   }
 215 
 216   bool is_good_address() const          { return is_address() && !is_info_top(); }
 217   bool is_lock_reference() const {
 218     return ((_state & (bits_mask | top_info_bit | ref_not_lock_bit)) == ref_bit);
 219   }
 220   bool is_nonlock_reference() const {
 221     return ((_state & (bits_mask | top_info_bit | ref_not_lock_bit)) == (ref_bit | ref_not_lock_bit));
 222   }
 223 
 224   bool equal(CellTypeState a) const     { return _state == a._state; }
 225   bool equal_kind(CellTypeState a) const {
 226     return (_state & bits_mask) == (a._state & bits_mask);
 227   }
 228 
 229   char to_char() const;
 230 
 231   // Merge
 232   CellTypeState merge (CellTypeState cts, int slot) const;
 233 
 234   // Debugging output
 235   void print(outputStream *os);
 236 
 237   // Default values of common values
 238   static CellTypeState bottom;
 239   static CellTypeState uninit;
 240   static CellTypeState ref;
 241   static CellTypeState value;
 242   static CellTypeState refUninit;
 243   static CellTypeState varUninit;
 244   static CellTypeState top;
 245   static CellTypeState addr;
 246 };
 247 
 248 
 249 //
 250 // BasicBlockStruct
 251 //
 252 class BasicBlock: ResourceObj {
 253  private:
 254   bool            _changed;                 // Reached a fixpoint or not
 255  public:
 256   enum Constants {
 257     _dead_basic_block = -2,
 258     _unreached        = -1                  // Alive but not yet reached by analysis
 259     // >=0                                  // Alive and has a merged state
 260   };
 261 
 262   int             _bci;                     // Start of basic block
 263   int             _end_bci;                 // Bci of last instruction in basicblock
 264   int             _max_locals;              // Determines split between vars and stack
 265   int             _max_stack;               // Determines split between stack and monitors
 266   CellTypeState*  _state;                   // State (vars, stack) at entry.
 267   int             _stack_top;               // -1 indicates bottom stack value.
 268   int             _monitor_top;             // -1 indicates bottom monitor stack value.
 269 
 270   CellTypeState* vars()                     { return _state; }
 271   CellTypeState* stack()                    { return _state + _max_locals; }
 272 
 273   bool changed()                            { return _changed; }
 274   void set_changed(bool s)                  { _changed = s; }
 275 
 276   bool is_reachable() const                 { return _stack_top >= 0; }  // Analysis has reached this basicblock
 277 
 278   // All basicblocks that are unreachable are going to have a _stack_top == _dead_basic_block.
 279   // This info. is setup in a pre-parse before the real abstract interpretation starts.
 280   bool is_dead() const                      { return _stack_top == _dead_basic_block; }
 281   bool is_alive() const                     { return _stack_top != _dead_basic_block; }
 282   void mark_as_alive()                      { assert(is_dead(), "must be dead"); _stack_top = _unreached; }
 283 };
 284 
 285 
 286 //
 287 //  GenerateOopMap
 288 //
 289 // Main class used to compute the pointer-maps in a Method
 290 //
 291 class GenerateOopMap VALUE_OBJ_CLASS_SPEC {
 292  protected:
 293 
 294   // _monitor_top is set to this constant to indicate that a monitor matching
 295   // problem was encountered prior to this point in control flow.
 296   enum { bad_monitors = -1 };
 297 
 298   // Main variables
 299   methodHandle _method;                     // The method we are examine
 300   RetTable     _rt;                         // Contains the return address mappings
 301   int          _max_locals;                 // Cached value of no. of locals
 302   int          _max_stack;                  // Cached value of max. stack depth
 303   int          _max_monitors;               // Cached value of max. monitor stack depth
 304   int          _has_exceptions;             // True, if exceptions exist for method
 305   bool         _got_error;                  // True, if an error occurred during interpretation.
 306   Handle       _exception;                  // Exception if got_error is true.
 307   bool         _did_rewriting;              // was bytecodes rewritten
 308   bool         _did_relocation;             // was relocation neccessary
 309   bool         _monitor_safe;               // The monitors in this method have been determined
 310                                             // to be safe.
 311 
 312   // Working Cell type state
 313   int            _state_len;                // Size of states
 314   CellTypeState *_state;                    // list of states
 315   char          *_state_vec_buf;            // Buffer used to print a readable version of a state
 316   int            _stack_top;
 317   int            _monitor_top;
 318 
 319   // Timing and statistics
 320   static elapsedTimer _total_oopmap_time;   // Holds cumulative oopmap generation time
 321   static long         _total_byte_count;    // Holds cumulative number of bytes inspected
 322 
 323   // Cell type methods
 324   void            init_state();
 325   void            make_context_uninitialized ();
 326   int             methodsig_to_effect        (Symbol* signature, bool isStatic, CellTypeState* effect);
 327   bool            merge_local_state_vectors  (CellTypeState* cts, CellTypeState* bbts);
 328   bool            merge_monitor_state_vectors(CellTypeState* cts, CellTypeState* bbts);
 329   void            copy_state                 (CellTypeState *dst, CellTypeState *src);
 330   void            merge_state_into_bb        (BasicBlock *bb);
 331   static void     merge_state                (GenerateOopMap *gom, int bcidelta, int* data);
 332   void            set_var                    (int localNo, CellTypeState cts);
 333   CellTypeState   get_var                    (int localNo);
 334   CellTypeState   pop                        ();
 335   void            push                       (CellTypeState cts);
 336   CellTypeState   monitor_pop                ();
 337   void            monitor_push               (CellTypeState cts);
 338   CellTypeState * vars                       ()                                             { return _state; }
 339   CellTypeState * stack                      ()                                             { return _state+_max_locals; }
 340   CellTypeState * monitors                   ()                                             { return _state+_max_locals+_max_stack; }
 341 
 342   void            replace_all_CTS_matches    (CellTypeState match,
 343                                               CellTypeState replace);
 344   void            print_states               (outputStream *os, CellTypeState *vector, int num);
 345   void            print_current_state        (outputStream   *os,
 346                                               BytecodeStream *itr,
 347                                               bool            detailed);
 348   void            report_monitor_mismatch    (const char *msg);
 349 
 350   // Basicblock info
 351   BasicBlock *    _basic_blocks;             // Array of basicblock info
 352   int             _gc_points;
 353   int             _bb_count;
 354   ResourceBitMap  _bb_hdr_bits;
 355 
 356   // Basicblocks methods
 357   void          initialize_bb               ();
 358   void          mark_bbheaders_and_count_gc_points();
 359   bool          is_bb_header                (int bci) const   {
 360     return _bb_hdr_bits.at(bci);
 361   }
 362   int           gc_points                   () const                          { return _gc_points; }
 363   int           bb_count                    () const                          { return _bb_count; }
 364   inline void   set_bbmark_bit              (int bci);
 365   void          clear_bbmark_bit            (int bci) {
 366     _bb_hdr_bits.at_put(bci, false);
 367   }
 368   BasicBlock *  get_basic_block_at          (int bci) const;
 369   BasicBlock *  get_basic_block_containing  (int bci) const;
 370   void          interp_bb                   (BasicBlock *bb);
 371   void          restore_state               (BasicBlock *bb);
 372   int           next_bb_start_pc            (BasicBlock *bb);
 373   void          update_basic_blocks         (int bci, int delta, int new_method_size);
 374   static void   bb_mark_fct                 (GenerateOopMap *c, int deltaBci, int *data);
 375 
 376   // Dead code detection
 377   void          mark_reachable_code();
 378   static void   reachable_basicblock        (GenerateOopMap *c, int deltaBci, int *data);
 379 
 380   // Interpretation methods (primary)
 381   void  do_interpretation                   ();
 382   void  init_basic_blocks                   ();
 383   void  setup_method_entry_state            ();
 384   void  interp_all                          ();
 385 
 386   // Interpretation methods (secondary)
 387   void  interp1                             (BytecodeStream *itr);
 388   void  do_exception_edge                   (BytecodeStream *itr);
 389   void  check_type                          (CellTypeState expected, CellTypeState actual);
 390   void  ppstore                             (CellTypeState *in,  int loc_no);
 391   void  ppload                              (CellTypeState *out, int loc_no);
 392   void  ppush1                              (CellTypeState in);
 393   void  ppush                               (CellTypeState *in);
 394   void  ppop1                               (CellTypeState out);
 395   void  ppop                                (CellTypeState *out);
 396   void  ppop_any                            (int poplen);
 397   void  pp                                  (CellTypeState *in, CellTypeState *out);
 398   void  pp_new_ref                          (CellTypeState *in, int bci);
 399   void  ppdupswap                           (int poplen, const char *out);
 400   void  do_ldc                              (int bci);
 401   void  do_astore                           (int idx);
 402   void  do_jsr                              (int delta);
 403   void  do_field                            (int is_get, int is_static, int idx, int bci);
 404   void  do_method                           (int is_static, int is_interface, int idx, int bci);
 405   void  do_multianewarray                   (int dims, int bci);
 406   void  do_monitorenter                     (int bci);
 407   void  do_monitorexit                      (int bci);
 408   void  do_return_monitor_check             ();
 409   void  do_checkcast                        ();
 410   CellTypeState *sigchar_to_effect          (char sigch, int bci, CellTypeState *out);
 411   int copy_cts                              (CellTypeState *dst, CellTypeState *src);
 412 
 413   // Error handling
 414   void  error_work                          (const char *format, va_list ap) ATTRIBUTE_PRINTF(2, 0);
 415   void  report_error                        (const char *format, ...) ATTRIBUTE_PRINTF(2, 3);
 416   void  verify_error                        (const char *format, ...) ATTRIBUTE_PRINTF(2, 3);
 417   bool  got_error()                         { return _got_error; }
 418 
 419   // Create result set
 420   bool  _report_result;
 421   bool  _report_result_for_send;            // Unfortunatly, stackmaps for sends are special, so we need some extra
 422   BytecodeStream *_itr_send;                // variables to handle them properly.
 423 
 424   void  report_result                       ();
 425 
 426   // Initvars
 427   GrowableArray<intptr_t> * _init_vars;
 428 
 429   void  initialize_vars                     ();
 430   void  add_to_ref_init_set                 (int localNo);
 431 
 432   // Conflicts rewrite logic
 433   bool      _conflict;                      // True, if a conflict occurred during interpretation
 434   int       _nof_refval_conflicts;          // No. of conflicts that require rewrites
 435   int *     _new_var_map;
 436 
 437   void record_refval_conflict               (int varNo);
 438   void rewrite_refval_conflicts             ();
 439   void rewrite_refval_conflict              (int from, int to);
 440   bool rewrite_refval_conflict_inst         (BytecodeStream *i, int from, int to);
 441   bool rewrite_load_or_store                (BytecodeStream *i, Bytecodes::Code bc, Bytecodes::Code bc0, unsigned int varNo);
 442 
 443   void expand_current_instr                 (int bci, int ilen, int newIlen, u_char inst_buffer[]);
 444   bool is_astore                            (BytecodeStream *itr, int *index);
 445   bool is_aload                             (BytecodeStream *itr, int *index);
 446 
 447   // List of bci's where a return address is on top of the stack
 448   GrowableArray<intptr_t> *_ret_adr_tos;
 449 
 450   bool stack_top_holds_ret_addr             (int bci);
 451   void compute_ret_adr_at_TOS               ();
 452   void update_ret_adr_at_TOS                (int bci, int delta);
 453 
 454   int  binsToHold                           (int no)                      { return  ((no+(BitsPerWord-1))/BitsPerWord); }
 455   char *state_vec_to_string                 (CellTypeState* vec, int len);
 456 
 457   // Helper method. Can be used in subclasses to fx. calculate gc_points. If the current instuction
 458   // is a control transfer, then calls the jmpFct all possible destinations.
 459   void  ret_jump_targets_do                 (BytecodeStream *bcs, jmpFct_t jmpFct, int varNo,int *data);
 460   bool  jump_targets_do                     (BytecodeStream *bcs, jmpFct_t jmpFct, int *data);
 461 
 462   friend class RelocCallback;
 463  public:
 464   GenerateOopMap(const methodHandle& method);
 465 
 466   // Compute the map.
 467   void compute_map(TRAPS);
 468   void result_for_basicblock(int bci);    // Do a callback on fill_stackmap_for_opcodes for basicblock containing bci
 469 
 470   // Query
 471   int max_locals() const                           { return _max_locals; }
 472   Method* method() const                           { return _method(); }
 473   methodHandle method_as_handle() const            { return _method; }
 474 
 475   bool did_rewriting()                             { return _did_rewriting; }
 476   bool did_relocation()                            { return _did_relocation; }
 477 
 478   static void print_time();
 479 
 480   // Monitor query
 481   bool monitor_safe()                              { return _monitor_safe; }
 482 
 483   // Specialization methods. Intended use:
 484   // - possible_gc_point must return true for every bci for which the stackmaps must be returned
 485   // - fill_stackmap_prolog is called just before the result is reported. The arguments tells the estimated
 486   //   number of gc points
 487   // - fill_stackmap_for_opcodes is called once for each bytecode index in order (0...code_length-1)
 488   // - fill_stackmap_epilog is called after all results has been reported. Note: Since the algorithm does not report
 489   //   stackmaps for deadcode, fewer gc_points might have been encounted than assumed during the epilog. It is the
 490   //   responsibility of the subclass to count the correct number.
 491   // - fill_init_vars are called once with the result of the init_vars computation
 492   //
 493   // All these methods are used during a call to: compute_map. Note: Non of the return results are valid
 494   // after compute_map returns, since all values are allocated as resource objects.
 495   //
 496   // All virtual method must be implemented in subclasses
 497   virtual bool allow_rewrites             () const                        { return false; }
 498   virtual bool report_results             () const                        { return true;  }
 499   virtual bool report_init_vars           () const                        { return true;  }
 500   virtual bool possible_gc_point          (BytecodeStream *bcs)           { ShouldNotReachHere(); return false; }
 501   virtual void fill_stackmap_prolog       (int nof_gc_points)             { ShouldNotReachHere(); }
 502   virtual void fill_stackmap_epilog       ()                              { ShouldNotReachHere(); }
 503   virtual void fill_stackmap_for_opcodes  (BytecodeStream *bcs,
 504                                            CellTypeState* vars,
 505                                            CellTypeState* stack,
 506                                            int stackTop)                  { ShouldNotReachHere(); }
 507   virtual void fill_init_vars             (GrowableArray<intptr_t> *init_vars) { ShouldNotReachHere();; }
 508 };
 509 
 510 //
 511 // Subclass of the GenerateOopMap Class that just do rewrites of the method, if needed.
 512 // It does not store any oopmaps.
 513 //
 514 class ResolveOopMapConflicts: public GenerateOopMap {
 515  private:
 516 
 517   bool _must_clear_locals;
 518 
 519   virtual bool report_results() const     { return false; }
 520   virtual bool report_init_vars() const   { return true;  }
 521   virtual bool allow_rewrites() const     { return true;  }
 522   virtual bool possible_gc_point          (BytecodeStream *bcs)           { return false; }
 523   virtual void fill_stackmap_prolog       (int nof_gc_points)             {}
 524   virtual void fill_stackmap_epilog       ()                              {}
 525   virtual void fill_stackmap_for_opcodes  (BytecodeStream *bcs,
 526                                            CellTypeState* vars,
 527                                            CellTypeState* stack,
 528                                            int stack_top)                 {}
 529   virtual void fill_init_vars             (GrowableArray<intptr_t> *init_vars) { _must_clear_locals = init_vars->length() > 0; }
 530 
 531 #ifndef PRODUCT
 532   // Statistics
 533   static int _nof_invocations;
 534   static int _nof_rewrites;
 535   static int _nof_relocations;
 536 #endif
 537 
 538  public:
 539   ResolveOopMapConflicts(const methodHandle& method) : GenerateOopMap(method) { _must_clear_locals = false; };
 540 
 541   methodHandle do_potential_rewrite(TRAPS);
 542   bool must_clear_locals() const { return _must_clear_locals; }
 543 };
 544 
 545 
 546 //
 547 // Subclass used by the compiler to generate pairing infomation
 548 //
 549 class GeneratePairingInfo: public GenerateOopMap {
 550  private:
 551 
 552   virtual bool report_results() const     { return false; }
 553   virtual bool report_init_vars() const   { return false; }
 554   virtual bool allow_rewrites() const     { return false;  }
 555   virtual bool possible_gc_point          (BytecodeStream *bcs)           { return false; }
 556   virtual void fill_stackmap_prolog       (int nof_gc_points)             {}
 557   virtual void fill_stackmap_epilog       ()                              {}
 558   virtual void fill_stackmap_for_opcodes  (BytecodeStream *bcs,
 559                                            CellTypeState* vars,
 560                                            CellTypeState* stack,
 561                                            int stack_top)                 {}
 562   virtual void fill_init_vars             (GrowableArray<intptr_t> *init_vars) {}
 563  public:
 564   GeneratePairingInfo(const methodHandle& method) : GenerateOopMap(method)       {};
 565 
 566   // Call compute_map(CHECK) to generate info.
 567 };
 568 
 569 #endif // SHARE_VM_OOPS_GENERATEOOPMAP_HPP