1 /*
   2  * Copyright (c) 1997, 2019, 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_OOPS_GENERATEOOPMAP_HPP
  26 #define SHARE_OOPS_GENERATEOOPMAP_HPP
  27 
  28 #include "interpreter/bytecodeStream.hpp"
  29 #include "memory/allocation.hpp"
  30 #include "oops/method.hpp"
  31 #include "oops/oopsHierarchy.hpp"
  32 #include "runtime/signature.hpp"
  33 #include "utilities/bitMap.hpp"
  34 
  35 // Forward definition
  36 class GenerateOopMap;
  37 class BasicBlock;
  38 class CellTypeState;
  39 class StackMap;
  40 
  41 // These two should be removed. But requires som code to be cleaned up
  42 #define MAXARGSIZE      256      // This should be enough
  43 #define MAX_LOCAL_VARS  65536    // 16-bit entry
  44 
  45 typedef void (*jmpFct_t)(GenerateOopMap *c, int bcpDelta, int* data);
  46 
  47 
  48 //  RetTable
  49 //
  50 // Contains maping between jsr targets and there return addresses. One-to-many mapping
  51 //
  52 class RetTableEntry : public ResourceObj {
  53  private:
  54   static int _init_nof_jsrs;                      // Default size of jsrs list
  55   int _target_bci;                                // Target PC address of jump (bytecode index)
  56   GrowableArray<intptr_t> * _jsrs;                     // List of return addresses  (bytecode index)
  57   RetTableEntry *_next;                           // Link to next entry
  58  public:
  59    RetTableEntry(int target, RetTableEntry *next);
  60 
  61   // Query
  62   int target_bci() const                      { return _target_bci; }
  63   int nof_jsrs() const                        { return _jsrs->length(); }
  64   int jsrs(int i) const                       { assert(i>=0 && i<nof_jsrs(), "Index out of bounds"); return _jsrs->at(i); }
  65 
  66   // Update entry
  67   void add_jsr    (int return_bci)            { _jsrs->append(return_bci); }
  68   void add_delta  (int bci, int delta);
  69   RetTableEntry * next()  const               { return _next; }
  70 };
  71 
  72 
  73 class RetTable {
  74  private:
  75   RetTableEntry *_first;
  76   static int _init_nof_entries;
  77 
  78   void add_jsr(int return_bci, int target_bci);   // Adds entry to list
  79  public:
  80   RetTable()                                                  { _first = NULL; }
  81   void compute_ret_table(const methodHandle& method);
  82   void update_ret_table(int bci, int delta);
  83   RetTableEntry* find_jsrs_for_target(int targBci);
  84 };
  85 
  86 //
  87 // CellTypeState
  88 //
  89 class CellTypeState {
  90  private:
  91   unsigned int _state;
  92 
  93   // Masks for separating the BITS and INFO portions of a CellTypeState
  94   enum { info_mask            = right_n_bits(28),
  95          bits_mask            = (int)(~info_mask) };
  96 
  97   // These constant are used for manipulating the BITS portion of a
  98   // CellTypeState
  99   enum { uninit_bit           = (int)(nth_bit(31)),
 100          ref_bit              = nth_bit(30),
 101          val_bit              = nth_bit(29),
 102          addr_bit             = nth_bit(28),
 103          live_bits_mask       = (int)(bits_mask & ~uninit_bit) };
 104 
 105   // These constants are used for manipulating the INFO portion of a
 106   // CellTypeState
 107   enum { top_info_bit         = nth_bit(27),
 108          not_bottom_info_bit  = nth_bit(26),
 109          info_data_mask       = right_n_bits(26),
 110          info_conflict        = info_mask };
 111 
 112   // Within the INFO data, these values are used to distinguish different
 113   // kinds of references.
 114   enum { ref_not_lock_bit     = nth_bit(25),  // 0 if this reference is locked as a monitor
 115          ref_slot_bit         = nth_bit(24),  // 1 if this reference is a "slot" reference,
 116                                               // 0 if it is a "line" reference.
 117          ref_data_mask        = right_n_bits(24) };
 118 
 119 
 120   // These values are used to initialize commonly used CellTypeState
 121   // constants.
 122   enum { bottom_value         = 0,
 123          uninit_value         = (int)(uninit_bit | info_conflict),
 124          ref_value            = ref_bit,
 125          ref_conflict         = ref_bit | info_conflict,
 126          val_value            = val_bit | info_conflict,
 127          addr_value           = addr_bit,
 128          addr_conflict        = addr_bit | info_conflict };
 129 
 130  public:
 131 
 132   // Since some C++ constructors generate poor code for declarations of the
 133   // form...
 134   //
 135   //   CellTypeState vector[length];
 136   //
 137   // ...we avoid making a constructor for this class.  CellTypeState values
 138   // should be constructed using one of the make_* methods:
 139 
 140   static CellTypeState make_any(int state) {
 141     CellTypeState s;
 142     s._state = state;
 143     // Causes SS10 warning.
 144     // assert(s.is_valid_state(), "check to see if CellTypeState is valid");
 145     return s;
 146   }
 147 
 148   static CellTypeState make_bottom() {
 149     return make_any(0);
 150   }
 151 
 152   static CellTypeState make_top() {
 153     return make_any(AllBits);
 154   }
 155 
 156   static CellTypeState make_addr(int bci) {
 157     assert((bci >= 0) && (bci < info_data_mask), "check to see if ret addr is valid");
 158     return make_any(addr_bit | not_bottom_info_bit | (bci & info_data_mask));
 159   }
 160 
 161   static CellTypeState make_slot_ref(int slot_num) {
 162     assert(slot_num >= 0 && slot_num < ref_data_mask, "slot out of range");
 163     return make_any(ref_bit | not_bottom_info_bit | ref_not_lock_bit | ref_slot_bit |
 164                     (slot_num & ref_data_mask));
 165   }
 166 
 167   static CellTypeState make_line_ref(int bci) {
 168     assert(bci >= 0 && bci < ref_data_mask, "line out of range");
 169     return make_any(ref_bit | not_bottom_info_bit | ref_not_lock_bit |
 170                     (bci & ref_data_mask));
 171   }
 172 
 173   static CellTypeState make_lock_ref(int bci) {
 174     assert(bci >= 0 && bci < ref_data_mask, "line out of range");
 175     return make_any(ref_bit | not_bottom_info_bit | (bci & ref_data_mask));
 176   }
 177 
 178   // Query methods:
 179   bool is_bottom() const                { return _state == 0; }
 180   bool is_live() const                  { return ((_state & live_bits_mask) != 0); }
 181   bool is_valid_state() const {
 182     // Uninitialized and value cells must contain no data in their info field:
 183     if ((can_be_uninit() || can_be_value()) && !is_info_top()) {
 184       return false;
 185     }
 186     // The top bit is only set when all info bits are set:
 187     if (is_info_top() && ((_state & info_mask) != info_mask)) {
 188       return false;
 189     }
 190     // The not_bottom_bit must be set when any other info bit is set:
 191     if (is_info_bottom() && ((_state & info_mask) != 0)) {
 192       return false;
 193     }
 194     return true;
 195   }
 196 
 197   bool is_address() const               { return ((_state & bits_mask) == addr_bit); }
 198   bool is_reference() const             { return ((_state & bits_mask) == ref_bit); }
 199   bool is_value() const                 { return ((_state & bits_mask) == val_bit); }
 200   bool is_uninit() const                { return ((_state & bits_mask) == (uint)uninit_bit); }
 201 
 202   bool can_be_address() const           { return ((_state & addr_bit) != 0); }
 203   bool can_be_reference() const         { return ((_state & ref_bit) != 0); }
 204   bool can_be_value() const             { return ((_state & val_bit) != 0); }
 205   bool can_be_uninit() const            { return ((_state & uninit_bit) != 0); }
 206 
 207   bool is_info_bottom() const           { return ((_state & not_bottom_info_bit) == 0); }
 208   bool is_info_top() const              { return ((_state & top_info_bit) != 0); }
 209   int  get_info() const {
 210     assert((!is_info_top() && !is_info_bottom()),
 211            "check to make sure top/bottom info is not used");
 212     return (_state & info_data_mask);
 213   }
 214 
 215   bool is_good_address() const          { return is_address() && !is_info_top(); }
 216   bool is_lock_reference() const {
 217     return ((_state & (bits_mask | top_info_bit | ref_not_lock_bit)) == ref_bit);
 218   }
 219   bool is_nonlock_reference() const {
 220     return ((_state & (bits_mask | top_info_bit | ref_not_lock_bit)) == (ref_bit | ref_not_lock_bit));
 221   }
 222 
 223   bool equal(CellTypeState a) const     { return _state == a._state; }
 224   bool equal_kind(CellTypeState a) const {
 225     return (_state & bits_mask) == (a._state & bits_mask);
 226   }
 227 
 228   char to_char() const;
 229 
 230   // Merge
 231   CellTypeState merge (CellTypeState cts, int slot) const;
 232 
 233   // Debugging output
 234   void print(outputStream *os);
 235 
 236   // Default values of common values
 237   static CellTypeState bottom;
 238   static CellTypeState uninit;
 239   static CellTypeState ref;
 240   static CellTypeState value;
 241   static CellTypeState refUninit;
 242   static CellTypeState varUninit;
 243   static CellTypeState top;
 244   static CellTypeState addr;
 245 };
 246 
 247 
 248 //
 249 // BasicBlockStruct
 250 //
 251 class BasicBlock: ResourceObj {
 252  private:
 253   bool            _changed;                 // Reached a fixpoint or not
 254  public:
 255   enum Constants {
 256     _dead_basic_block = -2,
 257     _unreached        = -1                  // Alive but not yet reached by analysis
 258     // >=0                                  // Alive and has a merged state
 259   };
 260 
 261   int             _bci;                     // Start of basic block
 262   int             _end_bci;                 // Bci of last instruction in basicblock
 263   int             _max_locals;              // Determines split between vars and stack
 264   int             _max_stack;               // Determines split between stack and monitors
 265   CellTypeState*  _state;                   // State (vars, stack) at entry.
 266   int             _stack_top;               // -1 indicates bottom stack value.
 267   int             _monitor_top;             // -1 indicates bottom monitor stack value.
 268 
 269   CellTypeState* vars()                     { return _state; }
 270   CellTypeState* stack()                    { return _state + _max_locals; }
 271 
 272   bool changed()                            { return _changed; }
 273   void set_changed(bool s)                  { _changed = s; }
 274 
 275   bool is_reachable() const                 { return _stack_top >= 0; }  // Analysis has reached this basicblock
 276 
 277   // All basicblocks that are unreachable are going to have a _stack_top == _dead_basic_block.
 278   // This info. is setup in a pre-parse before the real abstract interpretation starts.
 279   bool is_dead() const                      { return _stack_top == _dead_basic_block; }
 280   bool is_alive() const                     { return _stack_top != _dead_basic_block; }
 281   void mark_as_alive()                      { assert(is_dead(), "must be dead"); _stack_top = _unreached; }
 282 };
 283 
 284 
 285 //
 286 //  GenerateOopMap
 287 //
 288 // Main class used to compute the pointer-maps in a Method
 289 //
 290 class GenerateOopMap {
 291  protected:
 292 
 293   // _monitor_top is set to this constant to indicate that a monitor matching
 294   // problem was encountered prior to this point in control flow.
 295   enum { bad_monitors = -1 };
 296 
 297   // Main variables
 298   methodHandle _method;                     // The method we are examine
 299   RetTable     _rt;                         // Contains the return address mappings
 300   int          _max_locals;                 // Cached value of no. of locals
 301   int          _max_stack;                  // Cached value of max. stack depth
 302   int          _max_monitors;               // Cached value of max. monitor stack depth
 303   int          _has_exceptions;             // True, if exceptions exist for method
 304   bool         _got_error;                  // True, if an error occurred during interpretation.
 305   Handle       _exception;                  // Exception if got_error is true.
 306   bool         _did_rewriting;              // was bytecodes rewritten
 307   bool         _did_relocation;             // was relocation neccessary
 308   bool         _monitor_safe;               // The monitors in this method have been determined
 309                                             // to be safe.
 310 
 311   // Working Cell type state
 312   int            _state_len;                // Size of states
 313   CellTypeState *_state;                    // list of states
 314   char          *_state_vec_buf;            // Buffer used to print a readable version of a state
 315   int            _stack_top;
 316   int            _monitor_top;
 317 
 318   // Timing and statistics
 319   static elapsedTimer _total_oopmap_time;   // Holds cumulative oopmap generation time
 320   static long         _total_byte_count;    // Holds cumulative number of bytes inspected
 321 
 322   // Cell type methods
 323   void            init_state();
 324   void            make_context_uninitialized ();
 325   int             methodsig_to_effect        (Symbol* signature, bool isStatic, CellTypeState* effect);
 326   bool            merge_local_state_vectors  (CellTypeState* cts, CellTypeState* bbts);
 327   bool            merge_monitor_state_vectors(CellTypeState* cts, CellTypeState* bbts);
 328   void            copy_state                 (CellTypeState *dst, CellTypeState *src);
 329   void            merge_state_into_bb        (BasicBlock *bb);
 330   static void     merge_state                (GenerateOopMap *gom, int bcidelta, int* data);
 331   void            set_var                    (int localNo, CellTypeState cts);
 332   CellTypeState   get_var                    (int localNo);
 333   CellTypeState   pop                        ();
 334   void            push                       (CellTypeState cts);
 335   CellTypeState   monitor_pop                ();
 336   void            monitor_push               (CellTypeState cts);
 337   CellTypeState * vars                       ()                                             { return _state; }
 338   CellTypeState * stack                      ()                                             { return _state+_max_locals; }
 339   CellTypeState * monitors                   ()                                             { return _state+_max_locals+_max_stack; }
 340 
 341   void            replace_all_CTS_matches    (CellTypeState match,
 342                                               CellTypeState replace);
 343   void            print_states               (outputStream *os, CellTypeState *vector, int num);
 344   void            print_current_state        (outputStream   *os,
 345                                               BytecodeStream *itr,
 346                                               bool            detailed);
 347   void            report_monitor_mismatch    (const char *msg);
 348 
 349   // Basicblock info
 350   BasicBlock *    _basic_blocks;             // Array of basicblock info
 351   int             _gc_points;
 352   int             _bb_count;
 353   ResourceBitMap  _bb_hdr_bits;
 354 
 355   // Basicblocks methods
 356   void          initialize_bb               ();
 357   void          mark_bbheaders_and_count_gc_points();
 358   bool          is_bb_header                (int bci) const   {
 359     return _bb_hdr_bits.at(bci);
 360   }
 361   int           gc_points                   () const                          { return _gc_points; }
 362   int           bb_count                    () const                          { return _bb_count; }
 363   void          set_bbmark_bit              (int bci);
 364   BasicBlock *  get_basic_block_at          (int bci) const;
 365   BasicBlock *  get_basic_block_containing  (int bci) const;
 366   void          interp_bb                   (BasicBlock *bb);
 367   void          restore_state               (BasicBlock *bb);
 368   int           next_bb_start_pc            (BasicBlock *bb);
 369   void          update_basic_blocks         (int bci, int delta, int new_method_size);
 370   static void   bb_mark_fct                 (GenerateOopMap *c, int deltaBci, int *data);
 371 
 372   // Dead code detection
 373   void          mark_reachable_code();
 374   static void   reachable_basicblock        (GenerateOopMap *c, int deltaBci, int *data);
 375 
 376   // Interpretation methods (primary)
 377   void  do_interpretation                   ();
 378   void  init_basic_blocks                   ();
 379   void  setup_method_entry_state            ();
 380   void  interp_all                          ();
 381 
 382   // Interpretation methods (secondary)
 383   void  interp1                             (BytecodeStream *itr);
 384   void  do_exception_edge                   (BytecodeStream *itr);
 385   void  check_type                          (CellTypeState expected, CellTypeState actual);
 386   void  ppstore                             (CellTypeState *in,  int loc_no);
 387   void  ppload                              (CellTypeState *out, int loc_no);
 388   void  ppush1                              (CellTypeState in);
 389   void  ppush                               (CellTypeState *in);
 390   void  ppop1                               (CellTypeState out);
 391   void  ppop                                (CellTypeState *out);
 392   void  ppop_any                            (int poplen);
 393   void  pp                                  (CellTypeState *in, CellTypeState *out);
 394   void  pp_new_ref                          (CellTypeState *in, int bci);
 395   void  ppdupswap                           (int poplen, const char *out);
 396   void  do_ldc                              (int bci);
 397   void  do_astore                           (int idx);
 398   void  do_jsr                              (int delta);
 399   void  do_field                            (int is_get, int is_static, int idx, int bci);
 400   void  do_method                           (int is_static, int is_interface, int idx, int bci);
 401   void  do_multianewarray                   (int dims, int bci);
 402   void  do_monitorenter                     (int bci);
 403   void  do_monitorexit                      (int bci);
 404   void  do_return_monitor_check             ();
 405   void  do_checkcast                        ();
 406   CellTypeState *sigchar_to_effect          (char sigch, int bci, CellTypeState *out);
 407   int copy_cts                              (CellTypeState *dst, CellTypeState *src);
 408 
 409   // Error handling
 410   void  error_work                          (const char *format, va_list ap) ATTRIBUTE_PRINTF(2, 0);
 411   void  report_error                        (const char *format, ...) ATTRIBUTE_PRINTF(2, 3);
 412   void  verify_error                        (const char *format, ...) ATTRIBUTE_PRINTF(2, 3);
 413   bool  got_error()                         { return _got_error; }
 414 
 415   // Create result set
 416   bool  _report_result;
 417   bool  _report_result_for_send;            // Unfortunatly, stackmaps for sends are special, so we need some extra
 418   BytecodeStream *_itr_send;                // variables to handle them properly.
 419 
 420   void  report_result                       ();
 421 
 422   // Initvars
 423   GrowableArray<intptr_t> * _init_vars;
 424 
 425   void  initialize_vars                     ();
 426   void  add_to_ref_init_set                 (int localNo);
 427 
 428   // Conflicts rewrite logic
 429   bool      _conflict;                      // True, if a conflict occurred during interpretation
 430   int       _nof_refval_conflicts;          // No. of conflicts that require rewrites
 431   int *     _new_var_map;
 432 
 433   void record_refval_conflict               (int varNo);
 434   void rewrite_refval_conflicts             ();
 435   void rewrite_refval_conflict              (int from, int to);
 436   bool rewrite_refval_conflict_inst         (BytecodeStream *i, int from, int to);
 437   bool rewrite_load_or_store                (BytecodeStream *i, Bytecodes::Code bc, Bytecodes::Code bc0, unsigned int varNo);
 438 
 439   void expand_current_instr                 (int bci, int ilen, int newIlen, u_char inst_buffer[]);
 440   bool is_astore                            (BytecodeStream *itr, int *index);
 441   bool is_aload                             (BytecodeStream *itr, int *index);
 442 
 443   // List of bci's where a return address is on top of the stack
 444   GrowableArray<intptr_t> *_ret_adr_tos;
 445 
 446   bool stack_top_holds_ret_addr             (int bci);
 447   void compute_ret_adr_at_TOS               ();
 448   void update_ret_adr_at_TOS                (int bci, int delta);
 449 
 450   int  binsToHold                           (int no)                      { return  ((no+(BitsPerWord-1))/BitsPerWord); }
 451   char *state_vec_to_string                 (CellTypeState* vec, int len);
 452 
 453   // Helper method. Can be used in subclasses to fx. calculate gc_points. If the current instuction
 454   // is a control transfer, then calls the jmpFct all possible destinations.
 455   void  ret_jump_targets_do                 (BytecodeStream *bcs, jmpFct_t jmpFct, int varNo,int *data);
 456   bool  jump_targets_do                     (BytecodeStream *bcs, jmpFct_t jmpFct, int *data);
 457 
 458   friend class RelocCallback;
 459  public:
 460   GenerateOopMap(const methodHandle& method);
 461 
 462   // Compute the map.
 463   void compute_map(TRAPS);
 464   void result_for_basicblock(int bci);    // Do a callback on fill_stackmap_for_opcodes for basicblock containing bci
 465 
 466   // Query
 467   int max_locals() const                           { return _max_locals; }
 468   Method* method() const                           { return _method(); }
 469   methodHandle method_as_handle() const            { return _method; }
 470 
 471   bool did_rewriting()                             { return _did_rewriting; }
 472   bool did_relocation()                            { return _did_relocation; }
 473 
 474   static void print_time();
 475 
 476   // Monitor query
 477   bool monitor_safe()                              { return _monitor_safe; }
 478 
 479   // Specialization methods. Intended use:
 480   // - possible_gc_point must return true for every bci for which the stackmaps must be returned
 481   // - fill_stackmap_prolog is called just before the result is reported. The arguments tells the estimated
 482   //   number of gc points
 483   // - fill_stackmap_for_opcodes is called once for each bytecode index in order (0...code_length-1)
 484   // - fill_stackmap_epilog is called after all results has been reported. Note: Since the algorithm does not report
 485   //   stackmaps for deadcode, fewer gc_points might have been encounted than assumed during the epilog. It is the
 486   //   responsibility of the subclass to count the correct number.
 487   // - fill_init_vars are called once with the result of the init_vars computation
 488   //
 489   // All these methods are used during a call to: compute_map. Note: Non of the return results are valid
 490   // after compute_map returns, since all values are allocated as resource objects.
 491   //
 492   // All virtual method must be implemented in subclasses
 493   virtual bool allow_rewrites             () const                        { return false; }
 494   virtual bool report_results             () const                        { return true;  }
 495   virtual bool report_init_vars           () const                        { return true;  }
 496   virtual bool possible_gc_point          (BytecodeStream *bcs)           { ShouldNotReachHere(); return false; }
 497   virtual void fill_stackmap_prolog       (int nof_gc_points)             { ShouldNotReachHere(); }
 498   virtual void fill_stackmap_epilog       ()                              { ShouldNotReachHere(); }
 499   virtual void fill_stackmap_for_opcodes  (BytecodeStream *bcs,
 500                                            CellTypeState* vars,
 501                                            CellTypeState* stack,
 502                                            int stackTop)                  { ShouldNotReachHere(); }
 503   virtual void fill_init_vars             (GrowableArray<intptr_t> *init_vars) { ShouldNotReachHere();; }
 504 };
 505 
 506 //
 507 // Subclass of the GenerateOopMap Class that just do rewrites of the method, if needed.
 508 // It does not store any oopmaps.
 509 //
 510 class ResolveOopMapConflicts: public GenerateOopMap {
 511  private:
 512 
 513   bool _must_clear_locals;
 514 
 515   virtual bool report_results() const     { return false; }
 516   virtual bool report_init_vars() const   { return true;  }
 517   virtual bool allow_rewrites() const     { return true;  }
 518   virtual bool possible_gc_point          (BytecodeStream *bcs)           { return false; }
 519   virtual void fill_stackmap_prolog       (int nof_gc_points)             {}
 520   virtual void fill_stackmap_epilog       ()                              {}
 521   virtual void fill_stackmap_for_opcodes  (BytecodeStream *bcs,
 522                                            CellTypeState* vars,
 523                                            CellTypeState* stack,
 524                                            int stack_top)                 {}
 525   virtual void fill_init_vars             (GrowableArray<intptr_t> *init_vars) { _must_clear_locals = init_vars->length() > 0; }
 526 
 527 #ifndef PRODUCT
 528   // Statistics
 529   static int _nof_invocations;
 530   static int _nof_rewrites;
 531   static int _nof_relocations;
 532 #endif
 533 
 534  public:
 535   ResolveOopMapConflicts(const methodHandle& method) : GenerateOopMap(method) { _must_clear_locals = false; };
 536 
 537   methodHandle do_potential_rewrite(TRAPS);
 538   bool must_clear_locals() const { return _must_clear_locals; }
 539 };
 540 
 541 
 542 //
 543 // Subclass used by the compiler to generate pairing infomation
 544 //
 545 class GeneratePairingInfo: public GenerateOopMap {
 546  private:
 547 
 548   virtual bool report_results() const     { return false; }
 549   virtual bool report_init_vars() const   { return false; }
 550   virtual bool allow_rewrites() const     { return false;  }
 551   virtual bool possible_gc_point          (BytecodeStream *bcs)           { return false; }
 552   virtual void fill_stackmap_prolog       (int nof_gc_points)             {}
 553   virtual void fill_stackmap_epilog       ()                              {}
 554   virtual void fill_stackmap_for_opcodes  (BytecodeStream *bcs,
 555                                            CellTypeState* vars,
 556                                            CellTypeState* stack,
 557                                            int stack_top)                 {}
 558   virtual void fill_init_vars             (GrowableArray<intptr_t> *init_vars) {}
 559  public:
 560   GeneratePairingInfo(const methodHandle& method) : GenerateOopMap(method)       {};
 561 
 562   // Call compute_map(CHECK) to generate info.
 563 };
 564 
 565 #endif // SHARE_OOPS_GENERATEOOPMAP_HPP