hotspot/src/share/vm/oops/methodDataOop.hpp

/*
 * Copyright 2000-2007 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 */

class BytecodeStream;

// The MethodData object collects counts and other profile information
// during zeroth-tier (interpretive) and first-tier execution.
// The profile is used later by compilation heuristics.  Some heuristics
// enable use of aggressive (or "heroic") optimizations.  An aggressive
// optimization often has a down-side, a corner case that it handles
// poorly, but which is thought to be rare.  The profile provides
// evidence of this rarity for a given method or even BCI.  It allows
// the compiler to back out of the optimization at places where it
// has historically been a poor choice.  Other heuristics try to use
// specific information gathered about types observed at a given site.
//
// All data in the profile is approximate.  It is expected to be accurate
// on the whole, but the system expects occasional inaccuraces, due to
// counter overflow, multiprocessor races during data collection, space
// limitations, missing MDO blocks, etc.  Bad or missing data will degrade
// optimization quality but will not affect correctness.  Also, each MDO
// is marked with its birth-date ("creation_mileage") which can be used
// to assess the quality ("maturity") of its data.
//
// Short (<32-bit) counters are designed to overflow to a known "saturated"
// state.  Also, certain recorded per-BCI events are given one-bit counters
// which overflow to a saturated state which applied to all counters at
// that BCI.  In other words, there is a small lattice which approximates
// the ideal of an infinite-precision counter for each event at each BCI,
// and the lattice quickly "bottoms out" in a state where all counters
// are taken to be indefinitely large.
//
// The reader will find many data races in profile gathering code, starting
// with invocation counter incrementation.  None of these races harm correct
// execution of the compiled code.

// DataLayout
//
// Overlay for generic profiling data.
class DataLayout VALUE_OBJ_CLASS_SPEC {
private:
  // Every data layout begins with a header.  This header
  // contains a tag, which is used to indicate the size/layout
  // of the data, 4 bits of flags, which can be used in any way,
  // 4 bits of trap history (none/one reason/many reasons),
  // and a bci, which is used to tie this piece of data to a
  // specific bci in the bytecodes.
  union {
    intptr_t _bits;
    struct {
      u1 _tag;
      u1 _flags;
      u2 _bci;
    } _struct;
  } _header;

  // The data layout has an arbitrary number of cells, each sized
  // to accomodate a pointer or an integer.
  intptr_t _cells[1];

  // Some types of data layouts need a length field.
  static bool needs_array_len(u1 tag);

public:
  enum {
    counter_increment = 1
  };

  enum {
    cell_size = sizeof(intptr_t)
  };

  // Tag values
  enum {
    no_tag,
    bit_data_tag,
    counter_data_tag,
    jump_data_tag,
    receiver_type_data_tag,
    virtual_call_data_tag,
    ret_data_tag,
    branch_data_tag,
    multi_branch_data_tag
  };

  enum {
    // The _struct._flags word is formatted as [trap_state:4 | flags:4].
    // The trap state breaks down further as [recompile:1 | reason:3].
    // This further breakdown is defined in deoptimization.cpp.
    // See Deoptimization::trap_state_reason for an assert that
    // trap_bits is big enough to hold reasons < Reason_RECORDED_LIMIT.
    //
    // The trap_state is collected only if ProfileTraps is true.
    trap_bits = 1+3,  // 3: enough to distinguish [0..Reason_RECORDED_LIMIT].
    trap_shift = BitsPerByte - trap_bits,
    trap_mask = right_n_bits(trap_bits),
    trap_mask_in_place = (trap_mask << trap_shift),
    flag_limit = trap_shift,
    flag_mask = right_n_bits(flag_limit),
    first_flag = 0
  };

  // Size computation
  static int header_size_in_bytes() {
    return cell_size;
  }
  static int header_size_in_cells() {
    return 1;
  }

  static int compute_size_in_bytes(int cell_count) {
    return header_size_in_bytes() + cell_count * cell_size;
  }

  // Initialization
  void initialize(u1 tag, u2 bci, int cell_count);

  // Accessors
  u1 tag() {
    return _header._struct._tag;
  }

  // Return a few bits of trap state.  Range is [0..trap_mask].
  // The state tells if traps with zero, one, or many reasons have occurred.
  // It also tells whether zero or many recompilations have occurred.
  // The associated trap histogram in the MDO itself tells whether
  // traps are common or not.  If a BCI shows that a trap X has
  // occurred, and the MDO shows N occurrences of X, we make the
  // simplifying assumption that all N occurrences can be blamed
  // on that BCI.
  int trap_state() {
    return ((_header._struct._flags >> trap_shift) & trap_mask);
  }

  void set_trap_state(int new_state) {
    assert(ProfileTraps, "used only under +ProfileTraps");
    uint old_flags = (_header._struct._flags & flag_mask);
    _header._struct._flags = (new_state << trap_shift) | old_flags;
    assert(trap_state() == new_state, "sanity");
  }

  u1 flags() {
    return _header._struct._flags;
  }

  u2 bci() {
    return _header._struct._bci;
  }

  void set_header(intptr_t value) {
    _header._bits = value;
  }
  void release_set_header(intptr_t value) {
    OrderAccess::release_store_ptr(&_header._bits, value);
  }
  intptr_t header() {
    return _header._bits;
  }
  void set_cell_at(int index, intptr_t value) {
    _cells[index] = value;
  }
  void release_set_cell_at(int index, intptr_t value) {
    OrderAccess::release_store_ptr(&_cells[index], value);
  }
  intptr_t cell_at(int index) {
    return _cells[index];
  }
  intptr_t* adr_cell_at(int index) {
    return &_cells[index];
  }
  oop* adr_oop_at(int index) {
    return (oop*)&(_cells[index]);
  }

  void set_flag_at(int flag_number) {
    assert(flag_number < flag_limit, "oob");
    _header._struct._flags |= (0x1 << flag_number);
  }
  bool flag_at(int flag_number) {
    assert(flag_number < flag_limit, "oob");
    return (_header._struct._flags & (0x1 << flag_number)) != 0;
  }

  // Low-level support for code generation.
  static ByteSize header_offset() {
    return byte_offset_of(DataLayout, _header);
  }
  static ByteSize tag_offset() {
    return byte_offset_of(DataLayout, _header._struct._tag);
  }
  static ByteSize flags_offset() {
    return byte_offset_of(DataLayout, _header._struct._flags);
  }
  static ByteSize bci_offset() {
    return byte_offset_of(DataLayout, _header._struct._bci);
  }
  static ByteSize cell_offset(int index) {
    return byte_offset_of(DataLayout, _cells[index]);
  }
  // Return a value which, when or-ed as a byte into _flags, sets the flag.
  static int flag_number_to_byte_constant(int flag_number) {
    assert(0 <= flag_number && flag_number < flag_limit, "oob");
    DataLayout temp; temp.set_header(0);
    temp.set_flag_at(flag_number);
    return temp._header._struct._flags;
  }
  // Return a value which, when or-ed as a word into _header, sets the flag.
  static intptr_t flag_mask_to_header_mask(int byte_constant) {
    DataLayout temp; temp.set_header(0);
    temp._header._struct._flags = byte_constant;
    return temp._header._bits;
  }
};


// ProfileData class hierarchy
class ProfileData;
class   BitData;
class     CounterData;
class       ReceiverTypeData;
class         VirtualCallData;
class       RetData;
class   JumpData;
class     BranchData;
class   ArrayData;
class     MultiBranchData;


// ProfileData
//
// A ProfileData object is created to refer to a section of profiling
// data in a structured way.
class ProfileData : public ResourceObj {
private:
#ifndef PRODUCT
  enum {
    tab_width_one = 16,
    tab_width_two = 36
  };
#endif // !PRODUCT

  // This is a pointer to a section of profiling data.
  DataLayout* _data;

protected:
  DataLayout* data() { return _data; }

  enum {
    cell_size = DataLayout::cell_size
  };

public:
  // How many cells are in this?
  virtual int cell_count() {
    ShouldNotReachHere();
    return -1;
  }

  // Return the size of this data.
  int size_in_bytes() {
    return DataLayout::compute_size_in_bytes(cell_count());
  }

protected:
  // Low-level accessors for underlying data
  void set_intptr_at(int index, intptr_t value) {
    assert(0 <= index && index < cell_count(), "oob");
    data()->set_cell_at(index, value);
  }
  void release_set_intptr_at(int index, intptr_t value) {
    assert(0 <= index && index < cell_count(), "oob");
    data()->release_set_cell_at(index, value);
  }
  intptr_t intptr_at(int index) {
    assert(0 <= index && index < cell_count(), "oob");
    return data()->cell_at(index);
  }
  void set_uint_at(int index, uint value) {
    set_intptr_at(index, (intptr_t) value);
  }
  void release_set_uint_at(int index, uint value) {
    release_set_intptr_at(index, (intptr_t) value);
  }
  uint uint_at(int index) {
    return (uint)intptr_at(index);
  }
  void set_int_at(int index, int value) {
    set_intptr_at(index, (intptr_t) value);
  }
  void release_set_int_at(int index, int value) {
    release_set_intptr_at(index, (intptr_t) value);
  }
  int int_at(int index) {
    return (int)intptr_at(index);
  }
  int int_at_unchecked(int index) {
    return (int)data()->cell_at(index);
  }
  void set_oop_at(int index, oop value) {
    set_intptr_at(index, (intptr_t) value);
  }
  oop oop_at(int index) {
    return (oop)intptr_at(index);
  }
  oop* adr_oop_at(int index) {
    assert(0 <= index && index < cell_count(), "oob");
    return data()->adr_oop_at(index);
  }

  void set_flag_at(int flag_number) {
    data()->set_flag_at(flag_number);
  }
  bool flag_at(int flag_number) {
    return data()->flag_at(flag_number);
  }

  // two convenient imports for use by subclasses:
  static ByteSize cell_offset(int index) {
    return DataLayout::cell_offset(index);
  }
  static int flag_number_to_byte_constant(int flag_number) {
    return DataLayout::flag_number_to_byte_constant(flag_number);
  }

  ProfileData(DataLayout* data) {
    _data = data;
  }

public:
  // Constructor for invalid ProfileData.
  ProfileData();

  u2 bci() {
    return data()->bci();
  }

  address dp() {
    return (address)_data;
  }

  int trap_state() {
    return data()->trap_state();
  }
  void set_trap_state(int new_state) {
    data()->set_trap_state(new_state);
  }

  // Type checking
  virtual bool is_BitData()         { return false; }
  virtual bool is_CounterData()     { return false; }
  virtual bool is_JumpData()        { return false; }
  virtual bool is_ReceiverTypeData(){ return false; }
  virtual bool is_VirtualCallData() { return false; }
  virtual bool is_RetData()         { return false; }
  virtual bool is_BranchData()      { return false; }
  virtual bool is_ArrayData()       { return false; }
  virtual bool is_MultiBranchData() { return false; }

  BitData* as_BitData() {
    assert(is_BitData(), "wrong type");
    return is_BitData()         ? (BitData*)        this : NULL;
  }
  CounterData* as_CounterData() {
    assert(is_CounterData(), "wrong type");
    return is_CounterData()     ? (CounterData*)    this : NULL;
  }
  JumpData* as_JumpData() {
    assert(is_JumpData(), "wrong type");
    return is_JumpData()        ? (JumpData*)       this : NULL;
  }
  ReceiverTypeData* as_ReceiverTypeData() {
    assert(is_ReceiverTypeData(), "wrong type");
    return is_ReceiverTypeData() ? (ReceiverTypeData*)this : NULL;
  }
  VirtualCallData* as_VirtualCallData() {
    assert(is_VirtualCallData(), "wrong type");
    return is_VirtualCallData() ? (VirtualCallData*)this : NULL;
  }
  RetData* as_RetData() {
    assert(is_RetData(), "wrong type");
    return is_RetData()         ? (RetData*)        this : NULL;
  }
  BranchData* as_BranchData() {
    assert(is_BranchData(), "wrong type");
    return is_BranchData()      ? (BranchData*)     this : NULL;
  }
  ArrayData* as_ArrayData() {
    assert(is_ArrayData(), "wrong type");
    return is_ArrayData()       ? (ArrayData*)      this : NULL;
  }
  MultiBranchData* as_MultiBranchData() {
    assert(is_MultiBranchData(), "wrong type");
    return is_MultiBranchData() ? (MultiBranchData*)this : NULL;
  }


  // Subclass specific initialization
  virtual void post_initialize(BytecodeStream* stream, methodDataOop mdo) {}

  // GC support
  virtual void follow_contents() {}
  virtual void oop_iterate(OopClosure* blk) {}
  virtual void oop_iterate_m(OopClosure* blk, MemRegion mr) {}
  virtual void adjust_pointers() {}

#ifndef SERIALGC
  // Parallel old support
  virtual void follow_contents(ParCompactionManager* cm) {}
  virtual void update_pointers() {}
  virtual void update_pointers(HeapWord* beg_addr, HeapWord* end_addr) {}
#endif // SERIALGC

  // CI translation: ProfileData can represent both MethodDataOop data
  // as well as CIMethodData data. This function is provided for translating
  // an oop in a ProfileData to the ci equivalent. Generally speaking,
  // most ProfileData don't require any translation, so we provide the null
  // translation here, and the required translators are in the ci subclasses.
  virtual void translate_from(ProfileData* data) {}

  virtual void print_data_on(outputStream* st) {
    ShouldNotReachHere();
  }

#ifndef PRODUCT
  void print_shared(outputStream* st, const char* name);
  void tab(outputStream* st);
#endif
};

// BitData
//
// A BitData holds a flag or two in its header.
class BitData : public ProfileData {
protected:
  enum {
    // null_seen:
    //  saw a null operand (cast/aastore/instanceof)
    null_seen_flag              = DataLayout::first_flag + 0
  };
  enum { bit_cell_count = 0 };  // no additional data fields needed.
public:
  BitData(DataLayout* layout) : ProfileData(layout) {
  }

  virtual bool is_BitData() { return true; }

  static int static_cell_count() {
    return bit_cell_count;
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  // Accessor

  // The null_seen flag bit is specially known to the interpreter.
  // Consulting it allows the compiler to avoid setting up null_check traps.
  bool null_seen()     { return flag_at(null_seen_flag); }
  void set_null_seen()    { set_flag_at(null_seen_flag); }


  // Code generation support
  static int null_seen_byte_constant() {
    return flag_number_to_byte_constant(null_seen_flag);
  }

  static ByteSize bit_data_size() {
    return cell_offset(bit_cell_count);
  }

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// CounterData
//
// A CounterData corresponds to a simple counter.
class CounterData : public BitData {
protected:
  enum {
    count_off,
    counter_cell_count
  };
public:
  CounterData(DataLayout* layout) : BitData(layout) {}

  virtual bool is_CounterData() { return true; }

  static int static_cell_count() {
    return counter_cell_count;
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  // Direct accessor
  uint count() {
    return uint_at(count_off);
  }

  // Code generation support
  static ByteSize count_offset() {
    return cell_offset(count_off);
  }
  static ByteSize counter_data_size() {
    return cell_offset(counter_cell_count);
  }

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// JumpData
//
// A JumpData is used to access profiling information for a direct
// branch.  It is a counter, used for counting the number of branches,
// plus a data displacement, used for realigning the data pointer to
// the corresponding target bci.
class JumpData : public ProfileData {
protected:
  enum {
    taken_off_set,
    displacement_off_set,
    jump_cell_count
  };

  void set_displacement(int displacement) {
    set_int_at(displacement_off_set, displacement);
  }

public:
  JumpData(DataLayout* layout) : ProfileData(layout) {
    assert(layout->tag() == DataLayout::jump_data_tag ||
      layout->tag() == DataLayout::branch_data_tag, "wrong type");
  }

  virtual bool is_JumpData() { return true; }

  static int static_cell_count() {
    return jump_cell_count;
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  // Direct accessor
  uint taken() {
    return uint_at(taken_off_set);
  }
  // Saturating counter
  uint inc_taken() {
    uint cnt = taken() + 1;
    // Did we wrap? Will compiler screw us??
    if (cnt == 0) cnt--;
    set_uint_at(taken_off_set, cnt);
    return cnt;
  }

  int displacement() {
    return int_at(displacement_off_set);
  }

  // Code generation support
  static ByteSize taken_offset() {
    return cell_offset(taken_off_set);
  }

  static ByteSize displacement_offset() {
    return cell_offset(displacement_off_set);
  }

  // Specific initialization.
  void post_initialize(BytecodeStream* stream, methodDataOop mdo);

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// ReceiverTypeData
//
// A ReceiverTypeData is used to access profiling information about a
// dynamic type check.  It consists of a counter which counts the total times
// that the check is reached, and a series of (klassOop, count) pairs
// which are used to store a type profile for the receiver of the check.
class ReceiverTypeData : public CounterData {
protected:
  enum {
    receiver0_offset = counter_cell_count,
    count0_offset,
    receiver_type_row_cell_count = (count0_offset + 1) - receiver0_offset
  };

public:
  ReceiverTypeData(DataLayout* layout) : CounterData(layout) {
    assert(layout->tag() == DataLayout::receiver_type_data_tag ||
           layout->tag() == DataLayout::virtual_call_data_tag, "wrong type");
  }

  virtual bool is_ReceiverTypeData() { return true; }

  static int static_cell_count() {
    return counter_cell_count + (uint) TypeProfileWidth * receiver_type_row_cell_count;
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  // Direct accessors
  static uint row_limit() {
    return TypeProfileWidth;
  }
  static int receiver_cell_index(uint row) {
    return receiver0_offset + row * receiver_type_row_cell_count;
  }
  static int receiver_count_cell_index(uint row) {
    return count0_offset + row * receiver_type_row_cell_count;
  }

  // Get the receiver at row.  The 'unchecked' version is needed by parallel old
  // gc; it does not assert the receiver is a klass.  During compaction of the
  // perm gen, the klass may already have moved, so the is_klass() predicate
  // would fail.  The 'normal' version should be used whenever possible.
  klassOop receiver_unchecked(uint row) {
    assert(row < row_limit(), "oob");
    oop recv = oop_at(receiver_cell_index(row));
    return (klassOop)recv;
  }

  klassOop receiver(uint row) {
    klassOop recv = receiver_unchecked(row);
    assert(recv == NULL || ((oop)recv)->is_klass(), "wrong type");
    return recv;
  }

  uint receiver_count(uint row) {
    assert(row < row_limit(), "oob");
    return uint_at(receiver_count_cell_index(row));
  }

  // Code generation support
  static ByteSize receiver_offset(uint row) {
    return cell_offset(receiver_cell_index(row));
  }
  static ByteSize receiver_count_offset(uint row) {
    return cell_offset(receiver_count_cell_index(row));
  }
  static ByteSize receiver_type_data_size() {
    return cell_offset(static_cell_count());
  }

  // GC support
  virtual void follow_contents();
  virtual void oop_iterate(OopClosure* blk);
  virtual void oop_iterate_m(OopClosure* blk, MemRegion mr);
  virtual void adjust_pointers();

#ifndef SERIALGC
  // Parallel old support
  virtual void follow_contents(ParCompactionManager* cm);
  virtual void update_pointers();
  virtual void update_pointers(HeapWord* beg_addr, HeapWord* end_addr);
#endif // SERIALGC

  oop* adr_receiver(uint row) {
    return adr_oop_at(receiver_cell_index(row));
  }

#ifndef PRODUCT
  void print_receiver_data_on(outputStream* st);
  void print_data_on(outputStream* st);
#endif
};

// VirtualCallData
//
// A VirtualCallData is used to access profiling information about a
// virtual call.  For now, it has nothing more than a ReceiverTypeData.
class VirtualCallData : public ReceiverTypeData {
public:
  VirtualCallData(DataLayout* layout) : ReceiverTypeData(layout) {
    assert(layout->tag() == DataLayout::virtual_call_data_tag, "wrong type");
  }

  virtual bool is_VirtualCallData() { return true; }

  static int static_cell_count() {
    // At this point we could add more profile state, e.g., for arguments.
    // But for now it's the same size as the base record type.
    return ReceiverTypeData::static_cell_count();
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  // Direct accessors
  static ByteSize virtual_call_data_size() {
    return cell_offset(static_cell_count());
  }

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// RetData
//
// A RetData is used to access profiling information for a ret bytecode.
// It is composed of a count of the number of times that the ret has
// been executed, followed by a series of triples of the form
// (bci, count, di) which count the number of times that some bci was the
// target of the ret and cache a corresponding data displacement.
class RetData : public CounterData {
protected:
  enum {
    bci0_offset = counter_cell_count,
    count0_offset,
    displacement0_offset,
    ret_row_cell_count = (displacement0_offset + 1) - bci0_offset
  };

  void set_bci(uint row, int bci) {
    assert((uint)row < row_limit(), "oob");
    set_int_at(bci0_offset + row * ret_row_cell_count, bci);
  }
  void release_set_bci(uint row, int bci) {
    assert((uint)row < row_limit(), "oob");
    // 'release' when setting the bci acts as a valid flag for other
    // threads wrt bci_count and bci_displacement.
    release_set_int_at(bci0_offset + row * ret_row_cell_count, bci);
  }
  void set_bci_count(uint row, uint count) {
    assert((uint)row < row_limit(), "oob");
    set_uint_at(count0_offset + row * ret_row_cell_count, count);
  }
  void set_bci_displacement(uint row, int disp) {
    set_int_at(displacement0_offset + row * ret_row_cell_count, disp);
  }

public:
  RetData(DataLayout* layout) : CounterData(layout) {
    assert(layout->tag() == DataLayout::ret_data_tag, "wrong type");
  }

  virtual bool is_RetData() { return true; }

  enum {
    no_bci = -1 // value of bci when bci1/2 are not in use.
  };

  static int static_cell_count() {
    return counter_cell_count + (uint) BciProfileWidth * ret_row_cell_count;
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  static uint row_limit() {
    return BciProfileWidth;
  }
  static int bci_cell_index(uint row) {
    return bci0_offset + row * ret_row_cell_count;
  }
  static int bci_count_cell_index(uint row) {
    return count0_offset + row * ret_row_cell_count;
  }
  static int bci_displacement_cell_index(uint row) {
    return displacement0_offset + row * ret_row_cell_count;
  }

  // Direct accessors
  int bci(uint row) {
    return int_at(bci_cell_index(row));
  }
  uint bci_count(uint row) {
    return uint_at(bci_count_cell_index(row));
  }
  int bci_displacement(uint row) {
    return int_at(bci_displacement_cell_index(row));
  }

  // Interpreter Runtime support
  address fixup_ret(int return_bci, methodDataHandle mdo);

  // Code generation support
  static ByteSize bci_offset(uint row) {
    return cell_offset(bci_cell_index(row));
  }
  static ByteSize bci_count_offset(uint row) {
    return cell_offset(bci_count_cell_index(row));
  }
  static ByteSize bci_displacement_offset(uint row) {
    return cell_offset(bci_displacement_cell_index(row));
  }

  // Specific initialization.
  void post_initialize(BytecodeStream* stream, methodDataOop mdo);

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// BranchData
//
// A BranchData is used to access profiling data for a two-way branch.
// It consists of taken and not_taken counts as well as a data displacement
// for the taken case.
class BranchData : public JumpData {
protected:
  enum {
    not_taken_off_set = jump_cell_count,
    branch_cell_count
  };

  void set_displacement(int displacement) {
    set_int_at(displacement_off_set, displacement);
  }

public:
  BranchData(DataLayout* layout) : JumpData(layout) {
    assert(layout->tag() == DataLayout::branch_data_tag, "wrong type");
  }

  virtual bool is_BranchData() { return true; }

  static int static_cell_count() {
    return branch_cell_count;
  }

  virtual int cell_count() {
    return static_cell_count();
  }

  // Direct accessor
  uint not_taken() {
    return uint_at(not_taken_off_set);
  }

  uint inc_not_taken() {
    uint cnt = not_taken() + 1;
    // Did we wrap? Will compiler screw us??
    if (cnt == 0) cnt--;
    set_uint_at(not_taken_off_set, cnt);
    return cnt;
  }

  // Code generation support
  static ByteSize not_taken_offset() {
    return cell_offset(not_taken_off_set);
  }
  static ByteSize branch_data_size() {
    return cell_offset(branch_cell_count);
  }

  // Specific initialization.
  void post_initialize(BytecodeStream* stream, methodDataOop mdo);

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// ArrayData
//
// A ArrayData is a base class for accessing profiling data which does
// not have a statically known size.  It consists of an array length
// and an array start.
class ArrayData : public ProfileData {
protected:
  friend class DataLayout;

  enum {
    array_len_off_set,
    array_start_off_set
  };

  uint array_uint_at(int index) {
    int aindex = index + array_start_off_set;
    return uint_at(aindex);
  }
  int array_int_at(int index) {
    int aindex = index + array_start_off_set;
    return int_at(aindex);
  }
  oop array_oop_at(int index) {
    int aindex = index + array_start_off_set;
    return oop_at(aindex);
  }
  void array_set_int_at(int index, int value) {
    int aindex = index + array_start_off_set;
    set_int_at(aindex, value);
  }

  // Code generation support for subclasses.
  static ByteSize array_element_offset(int index) {
    return cell_offset(array_start_off_set + index);
  }

public:
  ArrayData(DataLayout* layout) : ProfileData(layout) {}

  virtual bool is_ArrayData() { return true; }

  static int static_cell_count() {
    return -1;
  }

  int array_len() {
    return int_at_unchecked(array_len_off_set);
  }

  virtual int cell_count() {
    return array_len() + 1;
  }

  // Code generation support
  static ByteSize array_len_offset() {
    return cell_offset(array_len_off_set);
  }
  static ByteSize array_start_offset() {
    return cell_offset(array_start_off_set);
  }
};

// MultiBranchData
//
// A MultiBranchData is used to access profiling information for
// a multi-way branch (*switch bytecodes).  It consists of a series
// of (count, displacement) pairs, which count the number of times each
// case was taken and specify the data displacment for each branch target.
class MultiBranchData : public ArrayData {
protected:
  enum {
    default_count_off_set,
    default_disaplacement_off_set,
    case_array_start
  };
  enum {
    relative_count_off_set,
    relative_displacement_off_set,
    per_case_cell_count
  };

  void set_default_displacement(int displacement) {
    array_set_int_at(default_disaplacement_off_set, displacement);
  }
  void set_displacement_at(int index, int displacement) {
    array_set_int_at(case_array_start +
                     index * per_case_cell_count +
                     relative_displacement_off_set,
                     displacement);
  }

public:
  MultiBranchData(DataLayout* layout) : ArrayData(layout) {
    assert(layout->tag() == DataLayout::multi_branch_data_tag, "wrong type");
  }

  virtual bool is_MultiBranchData() { return true; }

  static int compute_cell_count(BytecodeStream* stream);

  int number_of_cases() {
    int alen = array_len() - 2; // get rid of default case here.
    assert(alen % per_case_cell_count == 0, "must be even");
    return (alen / per_case_cell_count);
  }

  uint default_count() {
    return array_uint_at(default_count_off_set);
  }
  int default_displacement() {
    return array_int_at(default_disaplacement_off_set);
  }

  uint count_at(int index) {
    return array_uint_at(case_array_start +
                         index * per_case_cell_count +
                         relative_count_off_set);
  }
  int displacement_at(int index) {
    return array_int_at(case_array_start +
                        index * per_case_cell_count +
                        relative_displacement_off_set);
  }

  // Code generation support
  static ByteSize default_count_offset() {
    return array_element_offset(default_count_off_set);
  }
  static ByteSize default_displacement_offset() {
    return array_element_offset(default_disaplacement_off_set);
  }
  static ByteSize case_count_offset(int index) {
    return case_array_offset() +
           (per_case_size() * index) +
           relative_count_offset();
  }
  static ByteSize case_array_offset() {
    return array_element_offset(case_array_start);
  }
  static ByteSize per_case_size() {
    return in_ByteSize(per_case_cell_count) * cell_size;
  }
  static ByteSize relative_count_offset() {
    return in_ByteSize(relative_count_off_set) * cell_size;
  }
  static ByteSize relative_displacement_offset() {
    return in_ByteSize(relative_displacement_off_set) * cell_size;
  }

  // Specific initialization.
  void post_initialize(BytecodeStream* stream, methodDataOop mdo);

#ifndef PRODUCT
  void print_data_on(outputStream* st);
#endif
};

// methodDataOop
//
// A methodDataOop holds information which has been collected about
// a method.  Its layout looks like this:
//
// -----------------------------
// | header                    |
// | klass                     |
// -----------------------------
// | method                    |
// | size of the methodDataOop |
// -----------------------------
// | Data entries...           |
// |   (variable size)         |
// |                           |
// .                           .
// .                           .
// .                           .
// |                           |
// -----------------------------
//
// The data entry area is a heterogeneous array of DataLayouts. Each
// DataLayout in the array corresponds to a specific bytecode in the
// method.  The entries in the array are sorted by the corresponding
// bytecode.  Access to the data is via resource-allocated ProfileData,
// which point to the underlying blocks of DataLayout structures.
//
// During interpretation, if profiling in enabled, the interpreter
// maintains a method data pointer (mdp), which points at the entry
// in the array corresponding to the current bci.  In the course of
// intepretation, when a bytecode is encountered that has profile data
// associated with it, the entry pointed to by mdp is updated, then the
// mdp is adjusted to point to the next appropriate DataLayout.  If mdp
// is NULL to begin with, the interpreter assumes that the current method
// is not (yet) being profiled.
//
// In methodDataOop parlance, "dp" is a "data pointer", the actual address
// of a DataLayout element.  A "di" is a "data index", the offset in bytes
// from the base of the data entry array.  A "displacement" is the byte offset
// in certain ProfileData objects that indicate the amount the mdp must be
// adjusted in the event of a change in control flow.
//

class methodDataOopDesc : public oopDesc {
  friend class VMStructs;
private:
  friend class ProfileData;

  // Back pointer to the methodOop
  methodOop _method;

  // Size of this oop in bytes
  int _size;

  // Cached hint for bci_to_dp and bci_to_data
  int _hint_di;

  // Whole-method sticky bits and flags
public:
  enum {
    _trap_hist_limit    = 16,   // decoupled from Deoptimization::Reason_LIMIT
    _trap_hist_mask     = max_jubyte,
    _extra_data_count   = 4     // extra DataLayout headers, for trap history
  }; // Public flag values
private:
  uint _nof_decompiles;             // count of all nmethod removals
  uint _nof_overflow_recompiles;    // recompile count, excluding recomp. bits
  uint _nof_overflow_traps;         // trap count, excluding _trap_hist
  union {
    intptr_t _align;
    u1 _array[_trap_hist_limit];
  } _trap_hist;

  // Support for interprocedural escape analysis, from Thomas Kotzmann.
  intx              _eflags;          // flags on escape information
  intx              _arg_local;       // bit set of non-escaping arguments
  intx              _arg_stack;       // bit set of stack-allocatable arguments
  intx              _arg_returned;    // bit set of returned arguments

  int _creation_mileage;            // method mileage at MDO creation

  // Size of _data array in bytes.  (Excludes header and extra_data fields.)
  int _data_size;

  // Beginning of the data entries
  intptr_t _data[1];

  // Helper for size computation
  static int compute_data_size(BytecodeStream* stream);
  static int bytecode_cell_count(Bytecodes::Code code);
  enum { no_profile_data = -1, variable_cell_count = -2 };

  // Helper for initialization
  DataLayout* data_layout_at(int data_index) {
    assert(data_index % sizeof(intptr_t) == 0, "unaligned");
    return (DataLayout*) (((address)_data) + data_index);
  }

  // Initialize an individual data segment.  Returns the size of
  // the segment in bytes.
  int initialize_data(BytecodeStream* stream, int data_index);

  // Helper for data_at
  DataLayout* limit_data_position() {
    return (DataLayout*)((address)data_base() + _data_size);
  }
  bool out_of_bounds(int data_index) {
    return data_index >= data_size();
  }

  // Give each of the data entries a chance to perform specific
  // data initialization.
  void post_initialize(BytecodeStream* stream);

  // hint accessors
  int      hint_di() const  { return _hint_di; }
  void set_hint_di(int di)  {
    assert(!out_of_bounds(di), "hint_di out of bounds");
    _hint_di = di;
  }
  ProfileData* data_before(int bci) {
    // avoid SEGV on this edge case
    if (data_size() == 0)
      return NULL;
    int hint = hint_di();
    if (data_layout_at(hint)->bci() <= bci)
      return data_at(hint);
    return first_data();
  }

  // What is the index of the first data entry?
  int first_di() { return 0; }

  // Find or create an extra ProfileData:
  ProfileData* bci_to_extra_data(int bci, bool create_if_missing);

public:
  static int header_size() {
    return sizeof(methodDataOopDesc)/wordSize;
  }

  // Compute the size of a methodDataOop before it is created.
  static int compute_allocation_size_in_bytes(methodHandle method);
  static int compute_allocation_size_in_words(methodHandle method);
  static int compute_extra_data_count(int data_size, int empty_bc_count);

  // Determine if a given bytecode can have profile information.
  static bool bytecode_has_profile(Bytecodes::Code code) {
    return bytecode_cell_count(code) != no_profile_data;
  }

  // Perform initialization of a new methodDataOop
  void initialize(methodHandle method);

  // My size
  int object_size_in_bytes() { return _size; }
  int object_size() {
    return align_object_size(align_size_up(_size, BytesPerWord)/BytesPerWord);
  }

  int      creation_mileage() const  { return _creation_mileage; }
  void set_creation_mileage(int x)   { _creation_mileage = x; }
  bool is_mature() const;  // consult mileage and ProfileMaturityPercentage
  static int mileage_of(methodOop m);

  // Support for interprocedural escape analysis, from Thomas Kotzmann.
  enum EscapeFlag {
    estimated    = 1 << 0,
    return_local = 1 << 1
  };

  intx eflags()                                  { return _eflags; }
  intx arg_local()                               { return _arg_local; }
  intx arg_stack()                               { return _arg_stack; }
  intx arg_returned()                            { return _arg_returned; }

  void set_eflags(intx v)                        { _eflags = v; }
  void set_arg_local(intx v)                     { _arg_local = v; }
  void set_arg_stack(intx v)                     { _arg_stack = v; }
  void set_arg_returned(intx v)                  { _arg_returned = v; }

  void clear_escape_info()                       { _eflags = _arg_local = _arg_stack = _arg_returned = 0; }

  // Location and size of data area
  address data_base() const {
    return (address) _data;
  }
  int data_size() {
    return _data_size;
  }

  // Accessors
  methodOop method() { return _method; }

  // Get the data at an arbitrary (sort of) data index.
  ProfileData* data_at(int data_index);

  // Walk through the data in order.
  ProfileData* first_data() { return data_at(first_di()); }
  ProfileData* next_data(ProfileData* current);
  bool is_valid(ProfileData* current) { return current != NULL; }

  // Convert a dp (data pointer) to a di (data index).
  int dp_to_di(address dp) {
    return dp - ((address)_data);
  }

  address di_to_dp(int di) {
    return (address)data_layout_at(di);
  }

  // bci to di/dp conversion.
  address bci_to_dp(int bci);
  int bci_to_di(int bci) {
    return dp_to_di(bci_to_dp(bci));
  }

  // Get the data at an arbitrary bci, or NULL if there is none.
  ProfileData* bci_to_data(int bci);

  // Same, but try to create an extra_data record if one is needed:
  ProfileData* allocate_bci_to_data(int bci) {
    ProfileData* data = bci_to_data(bci);
    return (data != NULL) ? data : bci_to_extra_data(bci, true);
  }

  // Add a handful of extra data records, for trap tracking.
  DataLayout* extra_data_base() { return limit_data_position(); }
  DataLayout* extra_data_limit() { return (DataLayout*)((address)this + object_size_in_bytes()); }
  int extra_data_size() { return (address)extra_data_limit()
                               - (address)extra_data_base(); }
  static DataLayout* next_extra(DataLayout* dp) { return (DataLayout*)((address)dp + in_bytes(DataLayout::cell_offset(0))); }

  // Return (uint)-1 for overflow.
  uint trap_count(int reason) const {
    assert((uint)reason < _trap_hist_limit, "oob");
    return (int)((_trap_hist._array[reason]+1) & _trap_hist_mask) - 1;
  }
  // For loops:
  static uint trap_reason_limit() { return _trap_hist_limit; }
  static uint trap_count_limit()  { return _trap_hist_mask; }
  uint inc_trap_count(int reason) {
    // Count another trap, anywhere in this method.
    assert(reason >= 0, "must be single trap");
    if ((uint)reason < _trap_hist_limit) {
      uint cnt1 = 1 + _trap_hist._array[reason];
      if ((cnt1 & _trap_hist_mask) != 0) {  // if no counter overflow...
        _trap_hist._array[reason] = cnt1;
        return cnt1;
      } else {
        return _trap_hist_mask + (++_nof_overflow_traps);
      }
    } else {
      // Could not represent the count in the histogram.
      return (++_nof_overflow_traps);
    }
  }

  uint overflow_trap_count() const {
    return _nof_overflow_traps;
  }
  uint overflow_recompile_count() const {
    return _nof_overflow_recompiles;
  }
  void inc_overflow_recompile_count() {
    _nof_overflow_recompiles += 1;
  }
  uint decompile_count() const {
    return _nof_decompiles;
  }
  void inc_decompile_count() {
    _nof_decompiles += 1;
  }

  // Support for code generation
  static ByteSize data_offset() {
    return byte_offset_of(methodDataOopDesc, _data[0]);
  }

  // GC support
  oop* adr_method() const { return (oop*)&_method; }
  bool object_is_parsable() const { return _size != 0; }
  void set_object_is_parsable(int object_size_in_bytes) { _size = object_size_in_bytes; }

#ifndef PRODUCT
  // printing support for method data
  void print_data_on(outputStream* st);
#endif

  // verification
  void verify_data_on(outputStream* st);
};