constantPool.hpp

/*
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 * 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.
 *
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 * 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).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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#ifndef SHARE_VM_OOPS_CONSTANTPOOLOOP_HPP
#define SHARE_VM_OOPS_CONSTANTPOOLOOP_HPP

#include "oops/arrayOop.hpp"
#include "oops/cpCache.hpp"
#include "oops/objArrayOop.hpp"
#include "oops/symbol.hpp"
#include "oops/typeArrayOop.hpp"
#include "runtime/handles.hpp"
#include "utilities/constantTag.hpp"
#ifdef TARGET_ARCH_x86
# include "bytes_x86.hpp"
#endif
#ifdef TARGET_ARCH_sparc
# include "bytes_sparc.hpp"
#endif
#ifdef TARGET_ARCH_zero
# include "bytes_zero.hpp"
#endif
#ifdef TARGET_ARCH_arm
# include "bytes_arm.hpp"
#endif
#ifdef TARGET_ARCH_ppc
# include "bytes_ppc.hpp"
#endif

// A constantPool is an array containing class constants as described in the
// class file.
//
// Most of the constant pool entries are written during class parsing, which
// is safe.  For klass types, the constant pool entry is
// modified when the entry is resolved.  If a klass constant pool
// entry is read without a lock, only the resolved state guarantees that
// the entry in the constant pool is a klass object and not a Symbol*.

class SymbolHashMap;

class CPSlot VALUE_OBJ_CLASS_SPEC {
  intptr_t _ptr;
 public:
  CPSlot(intptr_t ptr): _ptr(ptr) {}
  CPSlot(Klass* ptr): _ptr((intptr_t)ptr) {}
  CPSlot(Symbol* ptr): _ptr((intptr_t)ptr | 1) {}

  intptr_t value()   { return _ptr; }
  bool is_resolved()   { return (_ptr & 1) == 0; }
  bool is_unresolved() { return (_ptr & 1) == 1; }

  Symbol* get_symbol() {
    assert(is_unresolved(), "bad call");
    return (Symbol*)(_ptr & ~1);
  }
  Klass* get_klass() {
    assert(is_resolved(), "bad call");
    return (Klass*)_ptr;
  }
};

class ConstantPool : public Metadata {
  friend class VMStructs;
  friend class BytecodeInterpreter;  // Directly extracts an oop in the pool for fast instanceof/checkcast
  friend class Universe;             // For null constructor
 private:
  Array<u1>*           _tags;        // the tag array describing the constant pool's contents
  ConstantPoolCache*   _cache;       // the cache holding interpreter runtime information
  InstanceKlass*       _pool_holder; // the corresponding class
  Array<u2>*           _operands;    // for variable-sized (InvokeDynamic) nodes, usually empty

  // Array of resolved objects from the constant pool and map from resolved
  // object index to original constant pool index
  jobject              _resolved_references;
  Array<u2>*           _reference_map;

  int                  _flags;         // a few header bits to describe contents for GC
  int                  _length; // number of elements in the array

  bool                 _on_stack;     // Redefined method still executing refers to this constant pool.

  union {
    // set for CDS to restore resolved references
    int                _resolved_reference_length;
    // keeps version number for redefined classes (used in backtrace)
    int                _version;
  } _saved;

  Monitor*             _lock;

  void set_tags(Array<u1>* tags)               { _tags = tags; }
  void tag_at_put(int which, jbyte t)          { tags()->at_put(which, t); }
  void release_tag_at_put(int which, jbyte t)  { tags()->release_at_put(which, t); }

  void set_operands(Array<u2>* operands)       { _operands = operands; }

  enum FlagBit {
    FB_has_invokedynamic = 1,
    FB_has_pseudo_string = 2,
    FB_has_preresolution = 3
  };

  int flags() const                         { return _flags; }
  void set_flags(int f)                     { _flags = f; }
  bool flag_at(FlagBit fb) const            { return (_flags & (1 << (int)fb)) != 0; }
  void set_flag_at(FlagBit fb);
  // no clear_flag_at function; they only increase

 private:
  intptr_t* base() const { return (intptr_t*) (((char*) this) + sizeof(ConstantPool)); }

  CPSlot slot_at(int which) {
    assert(is_within_bounds(which), "index out of bounds");
    // Uses volatile because the klass slot changes without a lock.
    volatile intptr_t adr = (intptr_t)OrderAccess::load_ptr_acquire(obj_at_addr_raw(which));
    assert(adr != 0 || which == 0, "cp entry for klass should not be zero");
    return CPSlot(adr);
  }

  void slot_at_put(int which, CPSlot s) const {
    assert(is_within_bounds(which), "index out of bounds");
    assert(s.value() != 0, "Caught something");
    *(intptr_t*)&base()[which] = s.value();
  }
  intptr_t* obj_at_addr_raw(int which) const {
    assert(is_within_bounds(which), "index out of bounds");
    return (intptr_t*) &base()[which];
  }

  jint* int_at_addr(int which) const {
    assert(is_within_bounds(which), "index out of bounds");
    return (jint*) &base()[which];
  }

  jlong* long_at_addr(int which) const {
    assert(is_within_bounds(which), "index out of bounds");
    return (jlong*) &base()[which];
  }

  jfloat* float_at_addr(int which) const {
    assert(is_within_bounds(which), "index out of bounds");
    return (jfloat*) &base()[which];
  }

  jdouble* double_at_addr(int which) const {
    assert(is_within_bounds(which), "index out of bounds");
    return (jdouble*) &base()[which];
  }

  ConstantPool(Array<u1>* tags);
  ConstantPool() { assert(DumpSharedSpaces || UseSharedSpaces, "only for CDS"); }
 public:
  static ConstantPool* allocate(ClassLoaderData* loader_data, int length, TRAPS);

  bool is_constantPool() const volatile     { return true; }

  Array<u1>* tags() const                   { return _tags; }
  Array<u2>* operands() const               { return _operands; }

  bool has_pseudo_string() const            { return flag_at(FB_has_pseudo_string); }
  bool has_invokedynamic() const            { return flag_at(FB_has_invokedynamic); }
  bool has_preresolution() const            { return flag_at(FB_has_preresolution); }
  void set_pseudo_string()                  {    set_flag_at(FB_has_pseudo_string); }
  void set_invokedynamic()                  {    set_flag_at(FB_has_invokedynamic); }
  void set_preresolution()                  {    set_flag_at(FB_has_preresolution); }

  // Redefine classes support.  If a method refering to this constant pool
  // is on the executing stack, or as a handle in vm code, this constant pool
  // can't be removed from the set of previous versions saved in the instance
  // class.
  bool on_stack() const                     { return _on_stack; }
  void set_on_stack(const bool value);

  // Klass holding pool
  InstanceKlass* pool_holder() const      { return _pool_holder; }
  void set_pool_holder(InstanceKlass* k)  { _pool_holder = k; }
  InstanceKlass** pool_holder_addr()      { return &_pool_holder; }

  // Interpreter runtime support
  ConstantPoolCache* cache() const        { return _cache; }
  void set_cache(ConstantPoolCache* cache){ _cache = cache; }

  // Create object cache in the constant pool
  void initialize_resolved_references(ClassLoaderData* loader_data,
                                      intStack reference_map,
                                      int constant_pool_map_length,
                                      TRAPS);

  // resolved strings, methodHandles and callsite objects from the constant pool
  objArrayOop resolved_references()  const;
  // mapping resolved object array indexes to cp indexes and back.
  int object_to_cp_index(int index)         { return _reference_map->at(index); }
  int cp_to_object_index(int index);

  // Invokedynamic indexes.
  // They must look completely different from normal indexes.
  // The main reason is that byte swapping is sometimes done on normal indexes.
  // Finally, it is helpful for debugging to tell the two apart.
  static bool is_invokedynamic_index(int i) { return (i < 0); }
  static int  decode_invokedynamic_index(int i) { assert(is_invokedynamic_index(i),  ""); return ~i; }
  static int  encode_invokedynamic_index(int i) { assert(!is_invokedynamic_index(i), ""); return ~i; }


  // The invokedynamic points at a CP cache entry.  This entry points back
  // at the original CP entry (CONSTANT_InvokeDynamic) and also (via f2) at an entry
  // in the resolved_references array (which provides the appendix argument).
  int invokedynamic_cp_cache_index(int index) const {
    assert (is_invokedynamic_index(index), "should be a invokedynamic index");
    int cache_index = decode_invokedynamic_index(index);
    return cache_index;
  }
  ConstantPoolCacheEntry* invokedynamic_cp_cache_entry_at(int index) const {
    // decode index that invokedynamic points to.
    int cp_cache_index = invokedynamic_cp_cache_index(index);
    return cache()->entry_at(cp_cache_index);
  }

  // Assembly code support
  static int tags_offset_in_bytes()         { return offset_of(ConstantPool, _tags); }
  static int cache_offset_in_bytes()        { return offset_of(ConstantPool, _cache); }
  static int pool_holder_offset_in_bytes()  { return offset_of(ConstantPool, _pool_holder); }
  static int resolved_references_offset_in_bytes() { return offset_of(ConstantPool, _resolved_references); }
  static int reference_map_offset_in_bytes() { return offset_of(ConstantPool, _reference_map); }

  // Storing constants

  void klass_at_put(int which, Klass* k) {
    assert(k != NULL, "resolved class shouldn't be null");
    assert(is_within_bounds(which), "index out of bounds");
    OrderAccess::release_store_ptr((Klass* volatile *)obj_at_addr_raw(which), k);
    // The interpreter assumes when the tag is stored, the klass is resolved
    // and the Klass* is a klass rather than a Symbol*, so we need
    // hardware store ordering here.
    release_tag_at_put(which, JVM_CONSTANT_Class);
  }

  // For temporary use while constructing constant pool
  void klass_index_at_put(int which, int name_index) {
    tag_at_put(which, JVM_CONSTANT_ClassIndex);
    *int_at_addr(which) = name_index;
  }

  // Temporary until actual use
  void unresolved_klass_at_put(int which, Symbol* s) {
    release_tag_at_put(which, JVM_CONSTANT_UnresolvedClass);
    slot_at_put(which, s);
  }

  void method_handle_index_at_put(int which, int ref_kind, int ref_index) {
    tag_at_put(which, JVM_CONSTANT_MethodHandle);
    *int_at_addr(which) = ((jint) ref_index<<16) | ref_kind;
  }

  void method_type_index_at_put(int which, int ref_index) {
    tag_at_put(which, JVM_CONSTANT_MethodType);
    *int_at_addr(which) = ref_index;
  }

  void invoke_dynamic_at_put(int which, int bootstrap_specifier_index, int name_and_type_index) {
    tag_at_put(which, JVM_CONSTANT_InvokeDynamic);
    *int_at_addr(which) = ((jint) name_and_type_index<<16) | bootstrap_specifier_index;
  }

  void unresolved_string_at_put(int which, Symbol* s) {
    release_tag_at_put(which, JVM_CONSTANT_String);
    *symbol_at_addr(which) = s;
  }

  void int_at_put(int which, jint i) {
    tag_at_put(which, JVM_CONSTANT_Integer);
    *int_at_addr(which) = i;
  }

  void long_at_put(int which, jlong l) {
    tag_at_put(which, JVM_CONSTANT_Long);
    // *long_at_addr(which) = l;
    Bytes::put_native_u8((address)long_at_addr(which), *((u8*) &l));
  }

  void float_at_put(int which, jfloat f) {
    tag_at_put(which, JVM_CONSTANT_Float);
    *float_at_addr(which) = f;
  }

  void double_at_put(int which, jdouble d) {
    tag_at_put(which, JVM_CONSTANT_Double);
    // *double_at_addr(which) = d;
    // u8 temp = *(u8*) &d;
    Bytes::put_native_u8((address) double_at_addr(which), *((u8*) &d));
  }

  Symbol** symbol_at_addr(int which) const {
    assert(is_within_bounds(which), "index out of bounds");
    return (Symbol**) &base()[which];
  }

  void symbol_at_put(int which, Symbol* s) {
    assert(s->refcount() != 0, "should have nonzero refcount");
    tag_at_put(which, JVM_CONSTANT_Utf8);
    *symbol_at_addr(which) = s;
  }

  void string_at_put(int which, int obj_index, oop str) {
    resolved_references()->obj_at_put(obj_index, str);
  }

  void set_object_tag_at(int which) {
    release_tag_at_put(which, JVM_CONSTANT_Object);
    }

  void object_at_put(int which, oop obj) {
    resolved_references()->obj_at_put(cp_to_object_index(which), obj);
  }

  // For temporary use while constructing constant pool
  void string_index_at_put(int which, int string_index) {
    tag_at_put(which, JVM_CONSTANT_StringIndex);
    *int_at_addr(which) = string_index;
  }

  void field_at_put(int which, int class_index, int name_and_type_index) {
    tag_at_put(which, JVM_CONSTANT_Fieldref);
    *int_at_addr(which) = ((jint) name_and_type_index<<16) | class_index;
  }

  void method_at_put(int which, int class_index, int name_and_type_index) {
    tag_at_put(which, JVM_CONSTANT_Methodref);
    *int_at_addr(which) = ((jint) name_and_type_index<<16) | class_index;
  }

  void interface_method_at_put(int which, int class_index, int name_and_type_index) {
    tag_at_put(which, JVM_CONSTANT_InterfaceMethodref);
    *int_at_addr(which) = ((jint) name_and_type_index<<16) | class_index;  // Not so nice
  }

  void name_and_type_at_put(int which, int name_index, int signature_index) {
    tag_at_put(which, JVM_CONSTANT_NameAndType);
    *int_at_addr(which) = ((jint) signature_index<<16) | name_index;  // Not so nice
  }

  // Tag query

  constantTag tag_at(int which) const { return (constantTag)tags()->at_acquire(which); }

  // Fetching constants

  Klass* klass_at(int which, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    return klass_at_impl(h_this, which, CHECK_NULL);
  }

  Symbol* klass_name_at(int which);  // Returns the name, w/o resolving.

  Klass* resolved_klass_at(int which) {  // Used by Compiler
    guarantee(tag_at(which).is_klass(), "Corrupted constant pool");
    // Must do an acquire here in case another thread resolved the klass
    // behind our back, lest we later load stale values thru the oop.
    return CPSlot((Klass*)OrderAccess::load_ptr_acquire(obj_at_addr_raw(which))).get_klass();
  }

  // This method should only be used with a cpool lock or during parsing or gc
  Symbol* unresolved_klass_at(int which) {     // Temporary until actual use
    Symbol* s = CPSlot((Symbol*)OrderAccess::load_ptr_acquire(obj_at_addr_raw(which))).get_symbol();
    // check that the klass is still unresolved.
    assert(tag_at(which).is_unresolved_klass(), "Corrupted constant pool");
    return s;
  }

  // RedefineClasses() API support:
  Symbol* klass_at_noresolve(int which) { return klass_name_at(which); }

  jint int_at(int which) {
    assert(tag_at(which).is_int(), "Corrupted constant pool");
    return *int_at_addr(which);
  }

  jlong long_at(int which) {
    assert(tag_at(which).is_long(), "Corrupted constant pool");
    // return *long_at_addr(which);
    u8 tmp = Bytes::get_native_u8((address)&base()[which]);
    return *((jlong*)&tmp);
  }

  jfloat float_at(int which) {
    assert(tag_at(which).is_float(), "Corrupted constant pool");
    return *float_at_addr(which);
  }

  jdouble double_at(int which) {
    assert(tag_at(which).is_double(), "Corrupted constant pool");
    u8 tmp = Bytes::get_native_u8((address)&base()[which]);
    return *((jdouble*)&tmp);
  }

  Symbol* symbol_at(int which) {
    assert(tag_at(which).is_utf8(), "Corrupted constant pool");
    return *symbol_at_addr(which);
  }

  oop string_at(int which, int obj_index, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    return string_at_impl(h_this, which, obj_index, THREAD);
  }
  oop string_at(int which, TRAPS) {
    int obj_index = cp_to_object_index(which);
    return string_at(which, obj_index, THREAD);
  }

  // Version that can be used before string oop array is created.
  oop uncached_string_at(int which, TRAPS);

  oop object_at(int which) {
    assert(tag_at(which).is_object(), "Corrupted constant pool");
    int obj_index = cp_to_object_index(which);
    return resolved_references()->obj_at(obj_index);
  }

  // A "pseudo-string" is an non-string oop that has found is way into
  // a String entry.
  // Under EnableInvokeDynamic this can happen if the user patches a live
  // object into a CONSTANT_String entry of an anonymous class.
  // Method oops internally created for method handles may also
  // use pseudo-strings to link themselves to related metaobjects.

  bool is_pseudo_string_at(int which) {
    // A pseudo string is a string that doesn't have a symbol in the cpSlot
    return unresolved_string_at(which) == NULL;
  }

  oop pseudo_string_at(int which, int obj_index) {
    assert(tag_at(which).is_string(), "Corrupted constant pool");
    assert(unresolved_string_at(which) == NULL, "shouldn't have symbol");
    oop s = resolved_references()->obj_at(obj_index);
    return s;
  }

  void pseudo_string_at_put(int which, int obj_index, oop x) {
    assert(EnableInvokeDynamic, "");
    set_pseudo_string();        // mark header
    assert(tag_at(which).is_string(), "Corrupted constant pool");
    string_at_put(which, obj_index, x);    // this works just fine
  }

  // only called when we are sure a string entry is already resolved (via an
  // earlier string_at call.
  oop resolved_string_at(int which) {
    assert(tag_at(which).is_string(), "Corrupted constant pool");
    // Must do an acquire here in case another thread resolved the klass
    // behind our back, lest we later load stale values thru the oop.
    // we might want a volatile_obj_at in ObjArrayKlass.
    int obj_index = cp_to_object_index(which);
    return resolved_references()->obj_at(obj_index);
  }

  Symbol* unresolved_string_at(int which) {
    assert(tag_at(which).is_string(), "Corrupted constant pool");
    Symbol* s = *symbol_at_addr(which);
    return s;
  }

  // Returns an UTF8 for a CONSTANT_String entry at a given index.
  // UTF8 char* representation was chosen to avoid conversion of
  // java_lang_Strings at resolved entries into Symbol*s
  // or vice versa.
  // Caller is responsible for checking for pseudo-strings.
  char* string_at_noresolve(int which);

  jint name_and_type_at(int which) {
    assert(tag_at(which).is_name_and_type(), "Corrupted constant pool");
    return *int_at_addr(which);
  }

  int method_handle_ref_kind_at(int which) {
    assert(tag_at(which).is_method_handle(), "Corrupted constant pool");
    return extract_low_short_from_int(*int_at_addr(which));  // mask out unwanted ref_index bits
  }
  int method_handle_index_at(int which) {
    assert(tag_at(which).is_method_handle(), "Corrupted constant pool");
    return extract_high_short_from_int(*int_at_addr(which));  // shift out unwanted ref_kind bits
  }
  int method_type_index_at(int which) {
    assert(tag_at(which).is_method_type(), "Corrupted constant pool");
    return *int_at_addr(which);
  }
  // Derived queries:
  Symbol* method_handle_name_ref_at(int which) {
    int member = method_handle_index_at(which);
    return impl_name_ref_at(member, true);
  }
  Symbol* method_handle_signature_ref_at(int which) {
    int member = method_handle_index_at(which);
    return impl_signature_ref_at(member, true);
  }
  int method_handle_klass_index_at(int which) {
    int member = method_handle_index_at(which);
    return impl_klass_ref_index_at(member, true);
  }
  Symbol* method_type_signature_at(int which) {
    int sym = method_type_index_at(which);
    return symbol_at(sym);
  }

  int invoke_dynamic_name_and_type_ref_index_at(int which) {
    assert(tag_at(which).is_invoke_dynamic(), "Corrupted constant pool");
    return extract_high_short_from_int(*int_at_addr(which));
  }
  int invoke_dynamic_bootstrap_specifier_index(int which) {
    assert(tag_at(which).value() == JVM_CONSTANT_InvokeDynamic, "Corrupted constant pool");
    return extract_low_short_from_int(*int_at_addr(which));
  }
  int invoke_dynamic_operand_base(int which) {
    int bootstrap_specifier_index = invoke_dynamic_bootstrap_specifier_index(which);
    return operand_offset_at(operands(), bootstrap_specifier_index);
  }
  // The first part of the operands array consists of an index into the second part.
  // Extract a 32-bit index value from the first part.
  static int operand_offset_at(Array<u2>* operands, int bootstrap_specifier_index) {
    int n = (bootstrap_specifier_index * 2);
    assert(n >= 0 && n+2 <= operands->length(), "oob");
    // The first 32-bit index points to the beginning of the second part
    // of the operands array.  Make sure this index is in the first part.
    DEBUG_ONLY(int second_part = build_int_from_shorts(operands->at(0),
                                                       operands->at(1)));
    assert(second_part == 0 || n+2 <= second_part, "oob (2)");
    int offset = build_int_from_shorts(operands->at(n+0),
                                       operands->at(n+1));
    // The offset itself must point into the second part of the array.
    assert(offset == 0 || offset >= second_part && offset <= operands->length(), "oob (3)");
    return offset;
  }
  static void operand_offset_at_put(Array<u2>* operands, int bootstrap_specifier_index, int offset) {
    int n = bootstrap_specifier_index * 2;
    assert(n >= 0 && n+2 <= operands->length(), "oob");
    operands->at_put(n+0, extract_low_short_from_int(offset));
    operands->at_put(n+1, extract_high_short_from_int(offset));
  }
  static int operand_array_length(Array<u2>* operands) {
    if (operands == NULL || operands->length() == 0)  return 0;
    int second_part = operand_offset_at(operands, 0);
    return (second_part / 2);
  }

#ifdef ASSERT
  // operand tuples fit together exactly, end to end
  static int operand_limit_at(Array<u2>* operands, int bootstrap_specifier_index) {
    int nextidx = bootstrap_specifier_index + 1;
    if (nextidx == operand_array_length(operands))
      return operands->length();
    else
      return operand_offset_at(operands, nextidx);
  }
  int invoke_dynamic_operand_limit(int which) {
    int bootstrap_specifier_index = invoke_dynamic_bootstrap_specifier_index(which);
    return operand_limit_at(operands(), bootstrap_specifier_index);
  }
#endif //ASSERT

  // layout of InvokeDynamic bootstrap method specifier (in second part of operands array):
  enum {
         _indy_bsm_offset  = 0,  // CONSTANT_MethodHandle bsm
         _indy_argc_offset = 1,  // u2 argc
         _indy_argv_offset = 2   // u2 argv[argc]
  };
  int invoke_dynamic_bootstrap_method_ref_index_at(int which) {
    assert(tag_at(which).is_invoke_dynamic(), "Corrupted constant pool");
    int op_base = invoke_dynamic_operand_base(which);
    return operands()->at(op_base + _indy_bsm_offset);
  }
  int invoke_dynamic_argument_count_at(int which) {
    assert(tag_at(which).is_invoke_dynamic(), "Corrupted constant pool");
    int op_base = invoke_dynamic_operand_base(which);
    int argc = operands()->at(op_base + _indy_argc_offset);
    DEBUG_ONLY(int end_offset = op_base + _indy_argv_offset + argc;
               int next_offset = invoke_dynamic_operand_limit(which));
    assert(end_offset == next_offset, "matched ending");
    return argc;
  }
  int invoke_dynamic_argument_index_at(int which, int j) {
    int op_base = invoke_dynamic_operand_base(which);
    DEBUG_ONLY(int argc = operands()->at(op_base + _indy_argc_offset));
    assert((uint)j < (uint)argc, "oob");
    return operands()->at(op_base + _indy_argv_offset + j);
  }

  // The following methods (name/signature/klass_ref_at, klass_ref_at_noresolve,
  // name_and_type_ref_index_at) all expect to be passed indices obtained
  // directly from the bytecode.
  // If the indices are meant to refer to fields or methods, they are
  // actually rewritten constant pool cache indices.
  // The routine remap_instruction_operand_from_cache manages the adjustment
  // of these values back to constant pool indices.

  // There are also "uncached" versions which do not adjust the operand index; see below.

  // FIXME: Consider renaming these with a prefix "cached_" to make the distinction clear.
  // In a few cases (the verifier) there are uses before a cpcache has been built,
  // which are handled by a dynamic check in remap_instruction_operand_from_cache.
  // FIXME: Remove the dynamic check, and adjust all callers to specify the correct mode.

  // Lookup for entries consisting of (klass_index, name_and_type index)
  Klass* klass_ref_at(int which, TRAPS);
  Symbol* klass_ref_at_noresolve(int which);
  Symbol* name_ref_at(int which)                { return impl_name_ref_at(which, false); }
  Symbol* signature_ref_at(int which)           { return impl_signature_ref_at(which, false); }

  int klass_ref_index_at(int which)               { return impl_klass_ref_index_at(which, false); }
  int name_and_type_ref_index_at(int which)       { return impl_name_and_type_ref_index_at(which, false); }

  // Lookup for entries consisting of (name_index, signature_index)
  int name_ref_index_at(int which_nt);            // ==  low-order jshort of name_and_type_at(which_nt)
  int signature_ref_index_at(int which_nt);       // == high-order jshort of name_and_type_at(which_nt)

  BasicType basic_type_for_signature_at(int which);

  // Resolve string constants (to prevent allocation during compilation)
  void resolve_string_constants(TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    resolve_string_constants_impl(h_this, CHECK);
  }

  // CDS support
  void remove_unshareable_info();
  void restore_unshareable_info(TRAPS);
  bool resolve_class_constants(TRAPS);
  // The ConstantPool vtable is restored by this call when the ConstantPool is
  // in the shared archive.  See patch_klass_vtables() in metaspaceShared.cpp for
  // all the gory details.  SA, dtrace and pstack helpers distinguish metadata
  // by their vtable.
  void restore_vtable() { guarantee(is_constantPool(), "vtable restored by this call"); }

 private:
  enum { _no_index_sentinel = -1, _possible_index_sentinel = -2 };
 public:

  // Resolve late bound constants.
  oop resolve_constant_at(int index, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    return resolve_constant_at_impl(h_this, index, _no_index_sentinel, THREAD);
  }

  oop resolve_cached_constant_at(int cache_index, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    return resolve_constant_at_impl(h_this, _no_index_sentinel, cache_index, THREAD);
  }

  oop resolve_possibly_cached_constant_at(int pool_index, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    return resolve_constant_at_impl(h_this, pool_index, _possible_index_sentinel, THREAD);
  }

  oop resolve_bootstrap_specifier_at(int index, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    return resolve_bootstrap_specifier_at_impl(h_this, index, THREAD);
  }

  // Klass name matches name at offset
  bool klass_name_at_matches(instanceKlassHandle k, int which);

  // Sizing
  int length() const                   { return _length; }
  void set_length(int length)          { _length = length; }

  // Tells whether index is within bounds.
  bool is_within_bounds(int index) const {
    return 0 <= index && index < length();
  }

  static int header_size()             { return sizeof(ConstantPool)/HeapWordSize; }
  static int size(int length)          { return align_object_size(header_size() + length); }
  int size() const                     { return size(length()); }

  friend class ClassFileParser;
  friend class SystemDictionary;

  // Used by compiler to prevent classloading.
  static Method*          method_at_if_loaded      (constantPoolHandle this_oop, int which);
  static bool       has_appendix_at_if_loaded      (constantPoolHandle this_oop, int which);
  static oop            appendix_at_if_loaded      (constantPoolHandle this_oop, int which);
  static bool    has_method_type_at_if_loaded      (constantPoolHandle this_oop, int which);
  static oop         method_type_at_if_loaded      (constantPoolHandle this_oop, int which);
  static Klass*            klass_at_if_loaded      (constantPoolHandle this_oop, int which);
  static Klass*        klass_ref_at_if_loaded      (constantPoolHandle this_oop, int which);
  // Same as above - but does LinkResolving.
  static Klass*        klass_ref_at_if_loaded_check(constantPoolHandle this_oop, int which, TRAPS);

  // Routines currently used for annotations (only called by jvm.cpp) but which might be used in the
  // future by other Java code. These take constant pool indices rather than
  // constant pool cache indices as do the peer methods above.
  Symbol* uncached_klass_ref_at_noresolve(int which);
  Symbol* uncached_name_ref_at(int which)                 { return impl_name_ref_at(which, true); }
  Symbol* uncached_signature_ref_at(int which)            { return impl_signature_ref_at(which, true); }
  int       uncached_klass_ref_index_at(int which)          { return impl_klass_ref_index_at(which, true); }
  int       uncached_name_and_type_ref_index_at(int which)  { return impl_name_and_type_ref_index_at(which, true); }

  // Sharing
  int pre_resolve_shared_klasses(TRAPS);

  // Debugging
  const char* printable_name_at(int which) PRODUCT_RETURN0;

#ifdef ASSERT
  enum { CPCACHE_INDEX_TAG = 0x10000 };  // helps keep CP cache indices distinct from CP indices
#else
  enum { CPCACHE_INDEX_TAG = 0 };        // in product mode, this zero value is a no-op
#endif //ASSERT

  static int decode_cpcache_index(int raw_index, bool invokedynamic_ok = false) {
    if (invokedynamic_ok && is_invokedynamic_index(raw_index))
      return decode_invokedynamic_index(raw_index);
    else
      return raw_index - CPCACHE_INDEX_TAG;
  }

 private:

  void set_resolved_references(jobject s) { _resolved_references = s; }
  Array<u2>* reference_map() const        { return _reference_map; }
  void set_reference_map(Array<u2>* o)    { _reference_map = o; }

  // patch JSR 292 resolved references after the class is linked.
  void patch_resolved_references(GrowableArray<Handle>* cp_patches);

  Symbol* impl_name_ref_at(int which, bool uncached);
  Symbol* impl_signature_ref_at(int which, bool uncached);
  int       impl_klass_ref_index_at(int which, bool uncached);
  int       impl_name_and_type_ref_index_at(int which, bool uncached);

  int remap_instruction_operand_from_cache(int operand);  // operand must be biased by CPCACHE_INDEX_TAG

  // Used while constructing constant pool (only by ClassFileParser)
  jint klass_index_at(int which) {
    assert(tag_at(which).is_klass_index(), "Corrupted constant pool");
    return *int_at_addr(which);
  }

  jint string_index_at(int which) {
    assert(tag_at(which).is_string_index(), "Corrupted constant pool");
    return *int_at_addr(which);
  }

  // Performs the LinkResolver checks
  static void verify_constant_pool_resolve(constantPoolHandle this_oop, KlassHandle klass, TRAPS);

  // Implementation of methods that needs an exposed 'this' pointer, in order to
  // handle GC while executing the method
  static Klass* klass_at_impl(constantPoolHandle this_oop, int which, TRAPS);
  static oop string_at_impl(constantPoolHandle this_oop, int which, int obj_index, TRAPS);

  // Resolve string constants (to prevent allocation during compilation)
  static void resolve_string_constants_impl(constantPoolHandle this_oop, TRAPS);

  static oop resolve_constant_at_impl(constantPoolHandle this_oop, int index, int cache_index, TRAPS);
  static void save_and_throw_exception(constantPoolHandle this_oop, int which, int tag_value, TRAPS);
  static oop resolve_bootstrap_specifier_at_impl(constantPoolHandle this_oop, int index, TRAPS);

 public:
  // Merging ConstantPool* support:
  bool compare_entry_to(int index1, constantPoolHandle cp2, int index2, TRAPS);
  void copy_cp_to(int start_i, int end_i, constantPoolHandle to_cp, int to_i, TRAPS) {
    constantPoolHandle h_this(THREAD, this);
    copy_cp_to_impl(h_this, start_i, end_i, to_cp, to_i, THREAD);
  }
  static void copy_cp_to_impl(constantPoolHandle from_cp, int start_i, int end_i, constantPoolHandle to_cp, int to_i, TRAPS);
  static void copy_entry_to(constantPoolHandle from_cp, int from_i, constantPoolHandle to_cp, int to_i, TRAPS);
  int  find_matching_entry(int pattern_i, constantPoolHandle search_cp, TRAPS);
  int  version() const                    { return _saved._version; }
  void set_version(int version)           { _saved._version = version; }
  void increment_and_save_version(int version) {
    _saved._version = version >= 0 ? version++ : version;  // keep overflow
  }

  void set_resolved_reference_length(int length) { _saved._resolved_reference_length = length; }
  int  resolved_reference_length() const  { return _saved._resolved_reference_length; }
  void set_lock(Monitor* lock)            { _lock = lock; }
  Monitor* lock()                         { return _lock; }

  // Decrease ref counts of symbols that are in the constant pool
  // when the holder class is unloaded
  void unreference_symbols();

  // Deallocate constant pool for RedefineClasses
  void deallocate_contents(ClassLoaderData* loader_data);
  void release_C_heap_structures();

  // JVMTI accesss - GetConstantPool, RetransformClasses, ...
  friend class JvmtiConstantPoolReconstituter;

 private:
  jint cpool_entry_size(jint idx);
  jint hash_entries_to(SymbolHashMap *symmap, SymbolHashMap *classmap);

  // Copy cpool bytes into byte array.
  // Returns:
  //  int > 0, count of the raw cpool bytes that have been copied
  //        0, OutOfMemory error
  //       -1, Internal error
  int  copy_cpool_bytes(int cpool_size,
                        SymbolHashMap* tbl,
                        unsigned char *bytes);

 public:
  // Verify
  void verify_on(outputStream* st);

  // Printing
  void print_on(outputStream* st) const;
  void print_value_on(outputStream* st) const;
  void print_entry_on(int index, outputStream* st);

  const char* internal_name() const { return "{constant pool}"; }

#ifndef PRODUCT
  // Compile the world support
  static void preload_and_initialize_all_classes(ConstantPool* constant_pool, TRAPS);
#endif
};

class SymbolHashMapEntry : public CHeapObj<mtSymbol> {
 private:
  unsigned int        _hash;   // 32-bit hash for item
  SymbolHashMapEntry* _next;   // Next element in the linked list for this bucket
  Symbol*             _symbol; // 1-st part of the mapping: symbol => value
  u2                  _value;  // 2-nd part of the mapping: symbol => value

 public:
  unsigned   int hash() const             { return _hash;   }
  void       set_hash(unsigned int hash)  { _hash = hash;   }

  SymbolHashMapEntry* next() const        { return _next;   }
  void set_next(SymbolHashMapEntry* next) { _next = next;   }

  Symbol*    symbol() const               { return _symbol; }
  void       set_symbol(Symbol* sym)      { _symbol = sym;  }

  u2         value() const                {  return _value; }
  void       set_value(u2 value)          { _value = value; }

  SymbolHashMapEntry(unsigned int hash, Symbol* symbol, u2 value)
    : _hash(hash), _symbol(symbol), _value(value), _next(NULL) {}

}; // End SymbolHashMapEntry class


class SymbolHashMapBucket : public CHeapObj<mtSymbol> {

private:
  SymbolHashMapEntry*    _entry;

public:
  SymbolHashMapEntry* entry() const         {  return _entry; }
  void set_entry(SymbolHashMapEntry* entry) { _entry = entry; }
  void clear()                              { _entry = NULL;  }

}; // End SymbolHashMapBucket class


class SymbolHashMap: public CHeapObj<mtSymbol> {

 private:
  // Default number of entries in the table
  enum SymbolHashMap_Constants {
    _Def_HashMap_Size = 256
  };

  int                   _table_size;
  SymbolHashMapBucket*  _buckets;

  void initialize_table(int table_size) {
    _table_size = table_size;
    _buckets = NEW_C_HEAP_ARRAY(SymbolHashMapBucket, table_size, mtSymbol);
    for (int index = 0; index < table_size; index++) {
      _buckets[index].clear();
    }
  }

 public:

  int table_size() const        { return _table_size; }

  SymbolHashMap()               { initialize_table(_Def_HashMap_Size); }
  SymbolHashMap(int table_size) { initialize_table(table_size); }

  // hash P(31) from Kernighan & Ritchie
  static unsigned int compute_hash(const char* str, int len) {
    unsigned int hash = 0;
    while (len-- > 0) {
      hash = 31*hash + (unsigned) *str;
      str++;
    }
    return hash;
  }

  SymbolHashMapEntry* bucket(int i) {
    return _buckets[i].entry();
  }

  void add_entry(Symbol* sym, u2 value);
  SymbolHashMapEntry* find_entry(Symbol* sym);

  u2 symbol_to_value(Symbol* sym) {
    SymbolHashMapEntry *entry = find_entry(sym);
    return (entry == NULL) ? 0 : entry->value();
  }

  ~SymbolHashMap() {
    SymbolHashMapEntry* next;
    for (int i = 0; i < _table_size; i++) {
      for (SymbolHashMapEntry* cur = bucket(i); cur != NULL; cur = next) {
        next = cur->next();
        delete(cur);
      }
    }
    delete _buckets;
  }
}; // End SymbolHashMap class

#endif // SHARE_VM_OOPS_CONSTANTPOOLOOP_HPP