/*

 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

#include "oops/generateOopMap.hpp"

#include "runtime/mutex.hpp"

// A Cache for storing (method, bci) -> oopMap.

// The memory management system uses the cache when locating object

// references in an interpreted frame.

//

// OopMapCache's are allocated lazily per InstanceKlass.

// The oopMap (InterpreterOopMap) is stored as a bit mask. If the

// bit_mask can fit into two words it is stored in

// the _bit_mask array, otherwise it is allocated on the heap.

// For OopMapCacheEntry the bit_mask is allocated in the C heap

// because these entries persist between garbage collections.

// For InterpreterOopMap the bit_mask is allocated in

// a resource area for better performance.  InterpreterOopMap

// should only be created and deleted during same garbage collection.

//

// If ENABBLE_ZAP_DEAD_LOCALS is defined, two bits are used

// per entry instead of one. In all cases,

// the first bit is set to indicate oops as opposed to other

// values. If the second bit is available,

// it is set for dead values. We get the following encoding:

//

// 00 live value

// 01 live oop

// 10 dead value

// 11 <unused>                                   (we cannot distinguish between dead oops or values with the current oop map generator)

class OffsetClosure  {

 public:

  virtual void offset_do(int offset) = 0;

};

class OopMapCacheEntry;

class InterpreterOopMap: ResourceObj {

  friend class OopMapCache;

 public:

  enum {

    N                = 4,                // the number of words reserved

                                         // for inlined mask storage

    small_mask_limit = N * BitsPerWord,  // the maximum number of bits

                                         // available for small masks,

                                         // small_mask_limit can be set to 0

                                         // for testing bit_mask allocation

    bits_per_entry   = 2,

    dead_bit_number  = 1,

    oop_bit_number   = 0

  };

 private:

  Method*        _method;         // the method for which the mask is valid

  unsigned short _bci;            // the bci    for which the mask is valid

  int            _mask_size;      // the mask size in bits

  int            _expression_stack_size; // the size of the expression stack in slots

 protected:

  intptr_t       _bit_mask[N];    // the bit mask if

                                  // mask_size <= small_mask_limit,

                                  // ptr to bit mask otherwise

                                  // "protected" so that sub classes can

                                  // access it without using trickery in

                                  // methd bit_mask().

#ifdef ASSERT

  bool _resource_allocate_bit_mask;

#endif

  // access methods

  Method*        method() const                  { return _method; }

  void           set_method(Method* v)           { _method = v; }

  int            bci() const                     { return _bci; }

  void           set_bci(int v)                  { _bci = v; }

  int            mask_size() const               { return _mask_size; }

  void           set_mask_size(int v)            { _mask_size = v; }

  // Test bit mask size and return either the in-line bit mask or allocated

  // bit mask.

  uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }

  // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT

  size_t mask_word_size() const {

    return (mask_size() + BitsPerWord - 1) / BitsPerWord;

  }

  uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }

  void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }

  // Lookup

  bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }

  bool is_empty() const;

  // Initialization

  void initialize();

 public:

  InterpreterOopMap();

  ~InterpreterOopMap();

  // Copy the OopMapCacheEntry in parameter "from" into this

  // InterpreterOopMap.  If the _bit_mask[0] in "from" points to

  // allocated space (i.e., the bit mask was to large to hold

  // in-line), allocate the space from a Resource area.

  void resource_copy(OopMapCacheEntry* from);

  void iterate_oop(OffsetClosure* oop_closure) const;

  void print() const;

  int number_of_entries() const                  { return mask_size() / bits_per_entry; }

  bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }

  bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }

  int expression_stack_size() const              { return _expression_stack_size; }

};

class OopMapCache : public CHeapObj<mtClass> {

 static OopMapCacheEntry* volatile _old_entries;

 private:

  enum { _size        = 32,     // Use fixed size for now

         _probe_depth = 3       // probe depth in case of collisions

  };

  OopMapCacheEntry* volatile * _array;

  unsigned int hash_value_for(const methodHandle& method, int bci) const;

  OopMapCacheEntry* entry_at(int i) const;

  bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);

  static void enqueue_for_cleanup(OopMapCacheEntry* entry);

  void flush();

 public:

  OopMapCache();

  ~OopMapCache();                                // free up memory

  // flush cache entry is occupied by an obsolete method

  void flush_obsolete_entries();

  // Returns the oopMap for (method, bci) in parameter "entry".

  // Returns false if an oop map was not found.

  void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry);

  // Compute an oop map without updating the cache or grabbing any locks (for debugging)

  static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);

  static void cleanup_old_entries();

};