8352075: Perf regression accessing fields

Reviewed-by: coleenp, iklam, jsjolen

src/hotspot/share/classfile/classFileParser.cpp

@@ -3740,6 +3740,7 @@ void ClassFileParser::apply_parsed_class_metadata(
   _cp->set_pool_holder(this_klass);
   this_klass->set_constants(_cp);
   this_klass->set_fieldinfo_stream(_fieldinfo_stream);
+  this_klass->set_fieldinfo_search_table(_fieldinfo_search_table);
   this_klass->set_fields_status(_fields_status);
   this_klass->set_methods(_methods);
   this_klass->set_inner_classes(_inner_classes);
@@ -3749,6 +3750,8 @@ void ClassFileParser::apply_parsed_class_metadata(
   this_klass->set_permitted_subclasses(_permitted_subclasses);
   this_klass->set_record_components(_record_components);
 
+  DEBUG_ONLY(FieldInfoStream::validate_search_table(_cp, _fieldinfo_stream, _fieldinfo_search_table));
+
   // Delay the setting of _local_interfaces and _transitive_interfaces until after
   // initialize_supers() in fill_instance_klass(). It is because the _local_interfaces could
   // be shared with _transitive_interfaces and _transitive_interfaces may be shared with
@@ -5056,6 +5059,7 @@ void ClassFileParser::fill_instance_klass(InstanceKlass* ik,
   // note that is not safe to use the fields in the parser from this point on
   assert(nullptr == _cp, "invariant");
   assert(nullptr == _fieldinfo_stream, "invariant");
+  assert(nullptr == _fieldinfo_search_table, "invariant");
   assert(nullptr == _fields_status, "invariant");
   assert(nullptr == _methods, "invariant");
   assert(nullptr == _inner_classes, "invariant");
@@ -5276,6 +5280,7 @@ ClassFileParser::ClassFileParser(ClassFileStream* stream,
   _super_klass(),
   _cp(nullptr),
   _fieldinfo_stream(nullptr),
+  _fieldinfo_search_table(nullptr),
   _fields_status(nullptr),
   _methods(nullptr),
   _inner_classes(nullptr),
@@ -5352,6 +5357,7 @@ void ClassFileParser::clear_class_metadata() {
   // deallocated if classfile parsing returns an error.
   _cp = nullptr;
   _fieldinfo_stream = nullptr;
+  _fieldinfo_search_table = nullptr;
   _fields_status = nullptr;
   _methods = nullptr;
   _inner_classes = nullptr;
@@ -5374,6 +5380,7 @@ ClassFileParser::~ClassFileParser() {
   if (_fieldinfo_stream != nullptr) {
     MetadataFactory::free_array<u1>(_loader_data, _fieldinfo_stream);
   }
+  MetadataFactory::free_array<u1>(_loader_data, _fieldinfo_search_table);
 
   if (_fields_status != nullptr) {
     MetadataFactory::free_array<FieldStatus>(_loader_data, _fields_status);
@@ -5774,6 +5781,7 @@ void ClassFileParser::post_process_parsed_stream(const ClassFileStream* const st
   _fieldinfo_stream =
     FieldInfoStream::create_FieldInfoStream(_temp_field_info, _java_fields_count,
                                             injected_fields_count, loader_data(), CHECK);
+  _fieldinfo_search_table = FieldInfoStream::create_search_table(_cp, _fieldinfo_stream, _loader_data, CHECK);
   _fields_status =
     MetadataFactory::new_array<FieldStatus>(_loader_data, _temp_field_info->length(),
                                             FieldStatus(0), CHECK);

src/hotspot/share/classfile/classFileParser.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2025, 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
@@ -123,6 +123,7 @@ class ClassFileParser {
   const InstanceKlass* _super_klass;
   ConstantPool* _cp;
   Array<u1>* _fieldinfo_stream;
+  Array<u1>* _fieldinfo_search_table;
   Array<FieldStatus>* _fields_status;
   Array<Method*>* _methods;
   Array<u2>* _inner_classes;

src/hotspot/share/classfile/fieldLayoutBuilder.cpp

@@ -301,7 +301,7 @@ void FieldLayout::reconstruct_layout(const InstanceKlass* ik, bool& has_instance
   BasicType last_type;
   int last_offset = -1;
   while (ik != nullptr) {
-    for (AllFieldStream fs(ik->fieldinfo_stream(), ik->constants()); !fs.done(); fs.next()) {
+    for (AllFieldStream fs(ik); !fs.done(); fs.next()) {
       BasicType type = Signature::basic_type(fs.signature());
       // distinction between static and non-static fields is missing
       if (fs.access_flags().is_static()) continue;
@@ -461,7 +461,7 @@ void FieldLayout::print(outputStream* output, bool is_static, const InstanceKlas
         bool found = false;
         const InstanceKlass* ik = super;
         while (!found && ik != nullptr) {
-          for (AllFieldStream fs(ik->fieldinfo_stream(), ik->constants()); !fs.done(); fs.next()) {
+          for (AllFieldStream fs(ik); !fs.done(); fs.next()) {
             if (fs.offset() == b->offset()) {
               output->print_cr(" @%d \"%s\" %s %d/%d %s",
                   b->offset(),

src/hotspot/share/classfile/javaClasses.cpp

@@ -967,6 +967,13 @@ void java_lang_Class::fixup_mirror(Klass* k, TRAPS) {
       Array<u1>* new_fis = FieldInfoStream::create_FieldInfoStream(fields, java_fields, injected_fields, k->class_loader_data(), CHECK);
       ik->set_fieldinfo_stream(new_fis);
       MetadataFactory::free_array<u1>(k->class_loader_data(), old_stream);
+
+      Array<u1>* old_table = ik->fieldinfo_search_table();
+      Array<u1>* search_table = FieldInfoStream::create_search_table(ik->constants(), new_fis, k->class_loader_data(), CHECK);
+      ik->set_fieldinfo_search_table(search_table);
+      MetadataFactory::free_array<u1>(k->class_loader_data(), old_table);
+
+      DEBUG_ONLY(FieldInfoStream::validate_search_table(ik->constants(), new_fis, search_table));
     }
   }
 

src/hotspot/share/oops/fieldInfo.cpp

@@ -22,8 +22,11 @@
  *
  */
 
+#include "memory/resourceArea.hpp"
+#include "cds/cdsConfig.hpp"
 #include "oops/fieldInfo.inline.hpp"
 #include "runtime/atomic.hpp"
+#include "utilities/packedTable.hpp"
 
 void FieldInfo::print(outputStream* os, ConstantPool* cp) {
   os->print_cr("index=%d name_index=%d name=%s signature_index=%d signature=%s offset=%d "
@@ -37,8 +40,10 @@ void FieldInfo::print(outputStream* os, ConstantPool* cp) {
                 field_flags().as_uint(),
                 initializer_index(),
                 generic_signature_index(),
-                _field_flags.is_injected() ? lookup_symbol(generic_signature_index())->as_utf8() : cp->symbol_at(generic_signature_index())->as_utf8(),
+                _field_flags.is_generic() ? (_field_flags.is_injected() ?
-                contended_group());
+                  lookup_symbol(generic_signature_index())->as_utf8() : cp->symbol_at(generic_signature_index())->as_utf8()
+                  ) : "",
+                is_contended() ? contended_group() : 0);
 }
 
 void FieldInfo::print_from_growable_array(outputStream* os, GrowableArray<FieldInfo>* array, ConstantPool* cp) {
@@ -62,13 +67,17 @@ Array<u1>* FieldInfoStream::create_FieldInfoStream(GrowableArray<FieldInfo>* fie
   StreamSizer s;
   StreamFieldSizer sizer(&s);
 
+  assert(fields->length() == java_fields + injected_fields, "must be");
+
   sizer.consumer()->accept_uint(java_fields);
   sizer.consumer()->accept_uint(injected_fields);
   for (int i = 0; i < fields->length(); i++) {
     FieldInfo* fi = fields->adr_at(i);
     sizer.map_field_info(*fi);
   }
-  int storage_size = sizer.consumer()->position() + 1;
+  // Originally there was an extra byte with 0 terminating the reading;
+  // now we check limits instead.
+  int storage_size = sizer.consumer()->position();
   Array<u1>* const fis = MetadataFactory::new_array<u1>(loader_data, storage_size, CHECK_NULL);
 
   using StreamWriter = UNSIGNED5::Writer<Array<u1>*, int, ArrayHelper<Array<u1>*, int>>;
@@ -79,15 +88,14 @@ Array<u1>* FieldInfoStream::create_FieldInfoStream(GrowableArray<FieldInfo>* fie
   writer.consumer()->accept_uint(java_fields);
   writer.consumer()->accept_uint(injected_fields);
   for (int i = 0; i < fields->length(); i++) {
-    FieldInfo* fi = fields->adr_at(i);
+    writer.map_field_info(fields->at(i));
-    writer.map_field_info(*fi);
   }
 
 #ifdef ASSERT
   FieldInfoReader r(fis);
-  int jfc = r.next_uint();
+  int jfc, ifc;
+  r.read_field_counts(&jfc, &ifc);
   assert(jfc == java_fields, "Must be");
-  int ifc = r.next_uint();
   assert(ifc == injected_fields, "Must be");
   for (int i = 0; i < jfc + ifc; i++) {
     FieldInfo fi;
@@ -113,30 +121,221 @@ Array<u1>* FieldInfoStream::create_FieldInfoStream(GrowableArray<FieldInfo>* fie
   return fis;
 }
 
-GrowableArray<FieldInfo>* FieldInfoStream::create_FieldInfoArray(const Array<u1>* fis, int* java_fields_count, int* injected_fields_count) {
+int FieldInfoStream::compare_name_and_sig(const Symbol* n1, const Symbol* s1, const Symbol* n2, const Symbol* s2) {
-  int length = FieldInfoStream::num_total_fields(fis);
+  int cmp = n1->fast_compare(n2);
-  GrowableArray<FieldInfo>* array = new GrowableArray<FieldInfo>(length);
+  return cmp != 0 ? cmp : s1->fast_compare(s2);
+}
+
+
+// We use both name and signature during the comparison; while JLS require unique
+// names for fields, JVMS requires only unique name + signature combination.
+struct field_pos {
+  Symbol* _name;
+  Symbol* _signature;
+  int _index;
+  int _position;
+};
+
+class FieldInfoSupplier: public PackedTableBuilder::Supplier {
+  const field_pos* _positions;
+  size_t _elements;
+
+public:
+  FieldInfoSupplier(const field_pos* positions, size_t elements): _positions(positions), _elements(elements) {}
+
+  bool next(uint32_t* key, uint32_t* value) override {
+    if (_elements == 0) {
+      return false;
+    }
+    *key = _positions->_position;
+    *value = _positions->_index;
+    ++_positions;
+    --_elements;
+    return true;
+  }
+};
+
+Array<u1>* FieldInfoStream::create_search_table(ConstantPool* cp, const Array<u1>* fis, ClassLoaderData* loader_data, TRAPS) {
+  if (CDSConfig::is_dumping_dynamic_archive()) {
+    // We cannot use search table; in case of dynamic archives it should be sorted by "requested" addresses,
+    // but Symbol* addresses are coming from _constants, which has "buffered" addresses.
+    // For background, see new comments inside allocate_node_impl in symbolTable.cpp
+    return nullptr;
+  }
+
   FieldInfoReader r(fis);
-  *java_fields_count = r.next_uint();
+  int java_fields;
-  *injected_fields_count = r.next_uint();
+  int injected_fields;
+  r.read_field_counts(&java_fields, &injected_fields);
+  assert(java_fields >= 0, "must be");
+  if (java_fields == 0 || fis->length() == 0 || static_cast<uint>(java_fields) < BinarySearchThreshold) {
+    return nullptr;
+  }
+
+  ResourceMark rm;
+  field_pos* positions = NEW_RESOURCE_ARRAY(field_pos, java_fields);
+  for (int i = 0; i < java_fields; ++i) {
+    assert(r.has_next(), "number of fields must match");
+
+    positions[i]._position = r.position();
+    FieldInfo fi;
+    r.read_field_info(fi);
+
+    positions[i]._name = fi.name(cp);
+    positions[i]._signature = fi.signature(cp);
+    positions[i]._index = i;
+  }
+  auto compare_pair = [](const void* v1, const void* v2) {
+    const field_pos* p1 = reinterpret_cast<const field_pos*>(v1);
+    const field_pos* p2 = reinterpret_cast<const field_pos*>(v2);
+    return compare_name_and_sig(p1->_name, p1->_signature, p2->_name, p2->_signature);
+  };
+  qsort(positions, java_fields, sizeof(field_pos), compare_pair);
+
+  PackedTableBuilder builder(fis->length() - 1, java_fields - 1);
+  Array<u1>* table = MetadataFactory::new_array<u1>(loader_data, java_fields * builder.element_bytes(), CHECK_NULL);
+  FieldInfoSupplier supplier(positions, java_fields);
+  builder.fill(table->data(), static_cast<size_t>(table->length()), supplier);
+  return table;
+}
+
+GrowableArray<FieldInfo>* FieldInfoStream::create_FieldInfoArray(const Array<u1>* fis, int* java_fields_count, int* injected_fields_count) {
+  FieldInfoReader r(fis);
+  r.read_field_counts(java_fields_count, injected_fields_count);
+  int length = *java_fields_count + *injected_fields_count;
+
+  GrowableArray<FieldInfo>* array = new GrowableArray<FieldInfo>(length);
   while (r.has_next()) {
     FieldInfo fi;
     r.read_field_info(fi);
     array->append(fi);
   }
   assert(array->length() == length, "Must be");
-  assert(array->length() == *java_fields_count + *injected_fields_count, "Must be");
   return array;
 }
 
 void FieldInfoStream::print_from_fieldinfo_stream(Array<u1>* fis, outputStream* os, ConstantPool* cp) {
-  int length = FieldInfoStream::num_total_fields(fis);
   FieldInfoReader r(fis);
-  int java_field_count = r.next_uint();
+  int java_fields_count;
-  int injected_fields_count = r.next_uint();
+  int injected_fields_count;
+  r.read_field_counts(&java_fields_count, &injected_fields_count);
   while (r.has_next()) {
     FieldInfo fi;
     r.read_field_info(fi);
     fi.print(os, cp);
   }
 }
+
+class FieldInfoComparator: public PackedTableLookup::Comparator {
+  const FieldInfoReader* _reader;
+  ConstantPool* _cp;
+  const Symbol* _name;
+  const Symbol* _signature;
+
+public:
+  FieldInfoComparator(const FieldInfoReader* reader, ConstantPool* cp, const Symbol* name, const Symbol* signature):
+    _reader(reader), _cp(cp), _name(name), _signature(signature) {}
+
+  int compare_to(uint32_t position) override {
+    FieldInfoReader r2(*_reader);
+    r2.set_position_and_next_index(position, -1);
+    u2 name_index, sig_index;
+    r2.read_name_and_signature(&name_index, &sig_index);
+    Symbol* mid_name = _cp->symbol_at(name_index);
+    Symbol* mid_sig = _cp->symbol_at(sig_index);
+
+    return FieldInfoStream::compare_name_and_sig(_name, _signature, mid_name, mid_sig);
+  }
+
+#ifdef ASSERT
+  void reset(uint32_t position) override {
+    FieldInfoReader r2(*_reader);
+    r2.set_position_and_next_index(position, -1);
+    u2 name_index, signature_index;
+    r2.read_name_and_signature(&name_index, &signature_index);
+    _name = _cp->symbol_at(name_index);
+    _signature = _cp->symbol_at(signature_index);
+  }
+#endif // ASSERT
+};
+
+#ifdef ASSERT
+void FieldInfoStream::validate_search_table(ConstantPool* cp, const Array<u1>* fis, const Array<u1>* search_table) {
+  if (search_table == nullptr) {
+    return;
+  }
+  FieldInfoReader reader(fis);
+  int java_fields, injected_fields;
+  reader.read_field_counts(&java_fields, &injected_fields);
+  assert(java_fields > 0, "must be");
+
+  PackedTableLookup lookup(fis->length() - 1, java_fields - 1, search_table);
+  assert(lookup.element_bytes() * java_fields == static_cast<unsigned int>(search_table->length()), "size does not match");
+
+  FieldInfoComparator comparator(&reader, cp, nullptr, nullptr);
+  // Check 1: assert that elements have the correct order based on the comparison function
+  lookup.validate_order(comparator);
+
+  // Check 2: Iterate through the original stream (not just search_table) and try if lookup works as expected
+  reader.set_position_and_next_index(0, 0);
+  reader.read_field_counts(&java_fields, &injected_fields);
+  while (reader.has_next()) {
+    int field_start = reader.position();
+    FieldInfo fi;
+    reader.read_field_info(fi);
+    if (fi.field_flags().is_injected()) {
+      // checking only java fields that precede injected ones
+      break;
+    }
+
+    FieldInfoReader r2(fis);
+    int index = r2.search_table_lookup(search_table, fi.name(cp), fi.signature(cp), cp, java_fields);
+    assert(index == static_cast<int>(fi.index()), "wrong index: %d != %u", index, fi.index());
+    assert(index == r2.next_index(), "index should match");
+    assert(field_start == r2.position(), "must find the same position");
+  }
+}
+#endif // ASSERT
+
+void FieldInfoStream::print_search_table(outputStream* st, ConstantPool* cp, const Array<u1>* fis, const Array<u1>* search_table) {
+  if (search_table == nullptr) {
+    return;
+  }
+  FieldInfoReader reader(fis);
+  int java_fields, injected_fields;
+  reader.read_field_counts(&java_fields, &injected_fields);
+  assert(java_fields > 0, "must be");
+  PackedTableLookup lookup(fis->length() - 1, java_fields - 1, search_table);
+  auto printer = [&] (size_t offset, uint32_t position, uint32_t index) {
+    reader.set_position_and_next_index(position, -1);
+    u2 name_index, sig_index;
+    reader.read_name_and_signature(&name_index, &sig_index);
+    Symbol* name = cp->symbol_at(name_index);
+    Symbol* sig = cp->symbol_at(sig_index);
+    st->print("   [%zu] #%d,#%d = ", offset, name_index, sig_index);
+    name->print_symbol_on(st);
+    st->print(":");
+    sig->print_symbol_on(st);
+    st->print(" @ %p,%p", name, sig);
+    st->cr();
+  };
+
+  lookup.iterate(printer);
+}
+
+int FieldInfoReader::search_table_lookup(const Array<u1>* search_table, const Symbol* name, const Symbol* signature, ConstantPool* cp, int java_fields) {
+  assert(java_fields >= 0, "must be");
+  if (java_fields == 0) {
+    return -1;
+  }
+  FieldInfoComparator comp(this, cp, name, signature);
+  PackedTableLookup lookup(_r.limit() - 1, java_fields - 1, search_table);
+  uint32_t position;
+  static_assert(sizeof(uint32_t) == sizeof(_next_index), "field size assert");
+  if (lookup.search(comp, &position, reinterpret_cast<uint32_t*>(&_next_index))) {
+    _r.set_position(static_cast<int>(position));
+    return _next_index;
+  } else {
+    return -1;
+  }
+}

src/hotspot/share/oops/fieldInfo.hpp

@@ -222,29 +222,28 @@ public:
   void map_field_info(const FieldInfo& fi);
 };
 
-
 // Gadget for decoding and reading the stream of field records.
 class FieldInfoReader {
-  friend class FieldInfoStream;
-  friend class ClassFileParser;
-  friend class FieldStreamBase;
-  friend class FieldInfo;
-
   UNSIGNED5::Reader<const u1*, int> _r;
   int _next_index;
 
-  public:
+public:
   FieldInfoReader(const Array<u1>* fi);
 
-  private:
+private:
-  uint32_t next_uint() { return _r.next_uint(); }
+  inline uint32_t next_uint() { return _r.next_uint(); }
   void skip(int n) { int s = _r.try_skip(n); assert(s == n,""); }
 
 public:
-  int has_next() { return _r.has_next(); }
+  void read_field_counts(int* java_fields, int* injected_fields);
-  int position() { return _r.position(); }
+  int has_next() const { return _r.position() < _r.limit(); }
-  int next_index() { return _next_index; }
+  int position() const { return _r.position(); }
+  int next_index() const { return _next_index; }
+  void read_name_and_signature(u2* name_index, u2* signature_index);
   void read_field_info(FieldInfo& fi);
+
+  int search_table_lookup(const Array<u1>* search_table, const Symbol* name, const Symbol* signature, ConstantPool* cp, int java_fields);
+
   // skip a whole field record, both required and optional bits
   FieldInfoReader&  skip_field_info();
 
@@ -271,6 +270,11 @@ class FieldInfoStream : AllStatic {
   friend class JavaFieldStream;
   friend class FieldStreamBase;
   friend class ClassFileParser;
+  friend class FieldInfoReader;
+  friend class FieldInfoComparator;
+
+ private:
+  static int compare_name_and_sig(const Symbol* n1, const Symbol* s1, const Symbol* n2, const Symbol* s2);
 
  public:
   static int num_java_fields(const Array<u1>* fis);
@@ -278,9 +282,14 @@ class FieldInfoStream : AllStatic {
   static int num_total_fields(const Array<u1>* fis);
 
   static Array<u1>* create_FieldInfoStream(GrowableArray<FieldInfo>* fields, int java_fields, int injected_fields,
-                                                          ClassLoaderData* loader_data, TRAPS);
+                                           ClassLoaderData* loader_data, TRAPS);
+  static Array<u1>* create_search_table(ConstantPool* cp, const Array<u1>* fis, ClassLoaderData* loader_data, TRAPS);
   static GrowableArray<FieldInfo>* create_FieldInfoArray(const Array<u1>* fis, int* java_fields_count, int* injected_fields_count);
   static void print_from_fieldinfo_stream(Array<u1>* fis, outputStream* os, ConstantPool* cp);
+
+  DEBUG_ONLY(static void validate_search_table(ConstantPool* cp, const Array<u1>* fis, const Array<u1>* search_table);)
+
+  static void print_search_table(outputStream* st, ConstantPool* cp, const Array<u1>* fis, const Array<u1>* search_table);
 };
 
 class FieldStatus {

src/hotspot/share/oops/fieldInfo.inline.hpp

@@ -56,16 +56,27 @@ inline Symbol* FieldInfo::lookup_symbol(int symbol_index) const {
 
 inline int FieldInfoStream::num_injected_java_fields(const Array<u1>* fis) {
   FieldInfoReader fir(fis);
-  fir.skip(1);
+  int java_fields_count;
-  return fir.next_uint();
+  int injected_fields_count;
+  fir.read_field_counts(&java_fields_count, &injected_fields_count);
+  return injected_fields_count;
 }
 
 inline int FieldInfoStream::num_total_fields(const Array<u1>* fis) {
   FieldInfoReader fir(fis);
-  return fir.next_uint() + fir.next_uint();
+  int java_fields_count;
+  int injected_fields_count;
+  fir.read_field_counts(&java_fields_count, &injected_fields_count);
+  return java_fields_count + injected_fields_count;
 }
 
-inline int FieldInfoStream::num_java_fields(const Array<u1>* fis) { return FieldInfoReader(fis).next_uint(); }
+inline int FieldInfoStream::num_java_fields(const Array<u1>* fis) {
+  FieldInfoReader fir(fis);
+  int java_fields_count;
+  int injected_fields_count;
+  fir.read_field_counts(&java_fields_count, &injected_fields_count);
+  return java_fields_count;
+}
 
 template<typename CON>
 inline void Mapper<CON>::map_field_info(const FieldInfo& fi) {
@@ -94,13 +105,22 @@ inline void Mapper<CON>::map_field_info(const FieldInfo& fi) {
 
 
 inline FieldInfoReader::FieldInfoReader(const Array<u1>* fi)
-  : _r(fi->data(), 0),
+  : _r(fi->data(), fi->length()),
     _next_index(0) { }
 
+inline void FieldInfoReader::read_field_counts(int* java_fields, int* injected_fields) {
+  *java_fields = next_uint();
+  *injected_fields = next_uint();
+}
+
+inline void FieldInfoReader::read_name_and_signature(u2* name_index, u2* signature_index) {
+  *name_index = checked_cast<u2>(next_uint());
+  *signature_index = checked_cast<u2>(next_uint());
+}
+
 inline void FieldInfoReader::read_field_info(FieldInfo& fi) {
   fi._index = _next_index++;
-  fi._name_index = checked_cast<u2>(next_uint());
+  read_name_and_signature(&fi._name_index, &fi._signature_index);
-  fi._signature_index = checked_cast<u2>(next_uint());
   fi._offset = next_uint();
   fi._access_flags = AccessFlags(checked_cast<u2>(next_uint()));
   fi._field_flags = FieldInfo::FieldFlags(next_uint());

src/hotspot/share/oops/fieldStreams.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2025, 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
@@ -56,17 +56,23 @@ class FieldStreamBase : public StackObj {
 
   inline FieldStreamBase(const Array<u1>* fieldinfo_stream, ConstantPool* constants, int start, int limit);
 
-  inline FieldStreamBase(Array<u1>* fieldinfo_stream, ConstantPool* constants);
+  inline FieldStreamBase(const Array<u1>* fieldinfo_stream, ConstantPool* constants);
 
-  private:
+ private:
    void initialize() {
-    int java_fields_count = _reader.next_uint();
+    int java_fields_count;
-    int injected_fields_count = _reader.next_uint();
+    int injected_fields_count;
-    assert( _limit <= java_fields_count + injected_fields_count, "Safety check");
+    _reader.read_field_counts(&java_fields_count, &injected_fields_count);
+    if (_limit < _index) {
+      _limit = java_fields_count + injected_fields_count;
+    } else {
+      assert( _limit <= java_fields_count + injected_fields_count, "Safety check");
+    }
     if (_limit != 0) {
       _reader.read_field_info(_fi_buf);
     }
    }
+
  public:
   inline FieldStreamBase(InstanceKlass* klass);
 
@@ -138,8 +144,11 @@ class FieldStreamBase : public StackObj {
 
 // Iterate over only the Java fields
 class JavaFieldStream : public FieldStreamBase {
+  Array<u1>* _search_table;
+
  public:
-  JavaFieldStream(const InstanceKlass* k): FieldStreamBase(k->fieldinfo_stream(), k->constants(), 0, k->java_fields_count()) {}
+  JavaFieldStream(const InstanceKlass* k): FieldStreamBase(k->fieldinfo_stream(), k->constants(), 0, k->java_fields_count()),
+    _search_table(k->fieldinfo_search_table()) {}
 
   u2 name_index() const {
     assert(!field()->field_flags().is_injected(), "regular only");
@@ -149,7 +158,6 @@ class JavaFieldStream : public FieldStreamBase {
   u2 signature_index() const {
     assert(!field()->field_flags().is_injected(), "regular only");
     return field()->signature_index();
-    return -1;
   }
 
   u2 generic_signature_index() const {
@@ -164,6 +172,10 @@ class JavaFieldStream : public FieldStreamBase {
     assert(!field()->field_flags().is_injected(), "regular only");
     return field()->initializer_index();
   }
+
+  // Performs either a linear search or binary search through the stream
+  // looking for a matching name/signature combo
+  bool lookup(const Symbol* name, const Symbol* signature);
 };
 
 
@@ -176,7 +188,6 @@ class InternalFieldStream : public FieldStreamBase {
 
 class AllFieldStream : public FieldStreamBase {
  public:
-  AllFieldStream(Array<u1>* fieldinfo, ConstantPool* constants): FieldStreamBase(fieldinfo, constants) {}
   AllFieldStream(const InstanceKlass* k):      FieldStreamBase(k->fieldinfo_stream(), k->constants()) {}
 };
 

src/hotspot/share/oops/fieldStreams.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2025, 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
@@ -33,22 +33,18 @@
 FieldStreamBase::FieldStreamBase(const Array<u1>* fieldinfo_stream, ConstantPool* constants, int start, int limit) :
          _fieldinfo_stream(fieldinfo_stream),
          _reader(FieldInfoReader(_fieldinfo_stream)),
-         _constants(constantPoolHandle(Thread::current(), constants)), _index(start) {
+         _constants(constantPoolHandle(Thread::current(), constants)),
-  _index = start;
+         _index(start),
-  if (limit < start) {
+         _limit(limit) {
-    _limit = FieldInfoStream::num_total_fields(_fieldinfo_stream);
-  } else {
-    _limit = limit;
-  }
   initialize();
 }
 
-FieldStreamBase::FieldStreamBase(Array<u1>* fieldinfo_stream, ConstantPool* constants) :
+FieldStreamBase::FieldStreamBase(const Array<u1>* fieldinfo_stream, ConstantPool* constants) :
         _fieldinfo_stream(fieldinfo_stream),
         _reader(FieldInfoReader(_fieldinfo_stream)),
         _constants(constantPoolHandle(Thread::current(), constants)),
         _index(0),
-        _limit(FieldInfoStream::num_total_fields(_fieldinfo_stream)) {
+        _limit(-1) {
   initialize();
 }
 
@@ -57,9 +53,28 @@ FieldStreamBase::FieldStreamBase(InstanceKlass* klass) :
          _reader(FieldInfoReader(_fieldinfo_stream)),
          _constants(constantPoolHandle(Thread::current(), klass->constants())),
          _index(0),
-         _limit(FieldInfoStream::num_total_fields(_fieldinfo_stream)) {
+         _limit(-1) {
   assert(klass == field_holder(), "");
   initialize();
 }
 
+inline bool JavaFieldStream::lookup(const Symbol* name, const Symbol* signature) {
+  if (_search_table != nullptr) {
+    int index = _reader.search_table_lookup(_search_table, name, signature, _constants(), _limit);
+    if (index >= 0) {
+      assert(index < _limit, "must be");
+      _index = index;
+      _reader.read_field_info(_fi_buf);
+      return true;
+    }
+  } else {
+    for (; !done(); next()) {
+      if (this->name() == name && this->signature() == signature) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 #endif // SHARE_OOPS_FIELDSTREAMS_INLINE_HPP

src/hotspot/share/oops/instanceKlass.cpp

@@ -686,6 +686,11 @@ void InstanceKlass::deallocate_contents(ClassLoaderData* loader_data) {
   }
   set_fieldinfo_stream(nullptr);
 
+  if (fieldinfo_search_table() != nullptr && !fieldinfo_search_table()->is_shared()) {
+    MetadataFactory::free_array<u1>(loader_data, fieldinfo_search_table());
+  }
+  set_fieldinfo_search_table(nullptr);
+
   if (fields_status() != nullptr && !fields_status()->is_shared()) {
     MetadataFactory::free_array<FieldStatus>(loader_data, fields_status());
   }
@@ -1786,13 +1791,12 @@ FieldInfo InstanceKlass::field(int index) const {
 }
 
 bool InstanceKlass::find_local_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const {
-  for (JavaFieldStream fs(this); !fs.done(); fs.next()) {
+  JavaFieldStream fs(this);
-    Symbol* f_name = fs.name();
+  if (fs.lookup(name, sig)) {
-    Symbol* f_sig  = fs.signature();
+    assert(fs.name() == name, "name must match");
-    if (f_name == name && f_sig == sig) {
+    assert(fs.signature() == sig, "signature must match");
-      fd->reinitialize(const_cast<InstanceKlass*>(this), fs.to_FieldInfo());
+    fd->reinitialize(const_cast<InstanceKlass*>(this), fs.to_FieldInfo());
-      return true;
+    return true;
-    }
   }
   return false;
 }
@@ -2610,6 +2614,7 @@ void InstanceKlass::metaspace_pointers_do(MetaspaceClosure* it) {
   }
 
   it->push(&_fieldinfo_stream);
+  it->push(&_fieldinfo_search_table);
   // _fields_status might be written into by Rewriter::scan_method() -> fd.set_has_initialized_final_update()
   it->push(&_fields_status, MetaspaceClosure::_writable);
 
@@ -2710,6 +2715,8 @@ void InstanceKlass::remove_unshareable_info() {
   DEBUG_ONLY(_shared_class_load_count = 0);
 
   remove_unshareable_flags();
+
+  DEBUG_ONLY(FieldInfoStream::validate_search_table(_constants, _fieldinfo_stream, _fieldinfo_search_table));
 }
 
 void InstanceKlass::remove_unshareable_flags() {
@@ -2816,6 +2823,8 @@ void InstanceKlass::restore_unshareable_info(ClassLoaderData* loader_data, Handl
   if (DiagnoseSyncOnValueBasedClasses && has_value_based_class_annotation() && !is_value_based()) {
     set_is_value_based();
   }
+
+  DEBUG_ONLY(FieldInfoStream::validate_search_table(_constants, _fieldinfo_stream, _fieldinfo_search_table));
 }
 
 // Check if a class or any of its supertypes has a version older than 50.
@@ -3760,6 +3769,11 @@ void InstanceKlass::print_on(outputStream* st) const {
     map++;
   }
   st->cr();
+
+  if (fieldinfo_search_table() != nullptr) {
+    st->print_cr(BULLET"---- field info search table:");
+    FieldInfoStream::print_search_table(st, _constants, _fieldinfo_stream, _fieldinfo_search_table);
+  }
 }
 
 void InstanceKlass::print_value_on(outputStream* st) const {

src/hotspot/share/oops/instanceKlass.hpp

@@ -276,6 +276,7 @@ class InstanceKlass: public Klass {
 
   // Fields information is stored in an UNSIGNED5 encoded stream (see fieldInfo.hpp)
   Array<u1>*          _fieldinfo_stream;
+  Array<u1>*          _fieldinfo_search_table;
   Array<FieldStatus>* _fields_status;
 
   // embedded Java vtable follows here
@@ -398,6 +399,9 @@ class InstanceKlass: public Klass {
   Array<u1>* fieldinfo_stream() const { return _fieldinfo_stream; }
   void set_fieldinfo_stream(Array<u1>* fis) { _fieldinfo_stream = fis; }
 
+  Array<u1>* fieldinfo_search_table() const { return _fieldinfo_search_table; }
+  void set_fieldinfo_search_table(Array<u1>* table) { _fieldinfo_search_table = table; }
+
   Array<FieldStatus>* fields_status() const {return _fields_status; }
   void set_fields_status(Array<FieldStatus>* array) { _fields_status = array; }
 

src/hotspot/share/prims/jvmtiRedefineClasses.cpp

@@ -3550,6 +3550,13 @@ void VM_RedefineClasses::set_new_constant_pool(
     Array<u1>* new_fis = FieldInfoStream::create_FieldInfoStream(fields, java_fields, injected_fields, scratch_class->class_loader_data(), CHECK);
     scratch_class->set_fieldinfo_stream(new_fis);
     MetadataFactory::free_array<u1>(scratch_class->class_loader_data(), old_stream);
+
+    Array<u1>* old_table = scratch_class->fieldinfo_search_table();
+    Array<u1>* search_table = FieldInfoStream::create_search_table(scratch_class->constants(), new_fis, scratch_class->class_loader_data(), CHECK);
+    scratch_class->set_fieldinfo_search_table(search_table);
+    MetadataFactory::free_array<u1>(scratch_class->class_loader_data(), old_table);
+
+    DEBUG_ONLY(FieldInfoStream::validate_search_table(scratch_class->constants(), new_fis, search_table));
   }
 
   // Update constant pool indices in the inner classes info to use

src/hotspot/share/runtime/globals.hpp

@@ -2005,6 +2005,10 @@ const int ObjectAlignmentInBytes = 8;
   product(bool, UseThreadsLockThrottleLock, true, DIAGNOSTIC,               \
           "Use an extra lock during Thread start and exit to alleviate"     \
           "contention on Threads_lock.")                                    \
+                                                                            \
+  develop(uint, BinarySearchThreshold, 16,                                  \
+          "Minimal number of elements in a sorted collection to prefer"     \
+          "binary search over simple linear search." )                      \
 
 // end of RUNTIME_FLAGS
 

src/hotspot/share/utilities/packedTable.cpp

@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 2025, 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+#include <cstring>
+
+#include "utilities/align.hpp"
+#include "utilities/count_leading_zeros.hpp"
+#include "utilities/packedTable.hpp"
+
+// The thresholds are inclusive, and in practice the limits are rounded
+// to the nearest power-of-two - 1.
+// Based on the max_key and max_value we figure out the number of bits required to store
+// key and value; imagine that only as bits (not aligned to byte boundary... yet).
+// Then we concatenate the bits for key and value, and 'add' 1-7 padding zeroes
+// (high-order bits) to align on bytes.
+// In the end we have each element in the table consuming 1-8 bytes (case with 0 bits for key
+// is ruled out).
+PackedTableBase::PackedTableBase(uint32_t max_key, uint32_t max_value) {
+  unsigned int key_bits = max_key == 0 ? 0 : 32 - count_leading_zeros(max_key);
+  unsigned int value_bits = max_value == 0 ? 0 : 32 - count_leading_zeros(max_value);
+  _element_bytes = align_up(key_bits + value_bits, 8) / 8;
+  // shifting left by 32 is undefined behaviour, and in practice returns 1
+  _key_mask = key_bits >= 32 ? -1 : (1U << key_bits) - 1;
+  _value_shift = key_bits;
+  _value_mask = value_bits >= 32 ? -1 : (1U << value_bits) - 1;
+  guarantee(_element_bytes > 0, "wouldn't work");
+  assert(_element_bytes <= sizeof(uint64_t), "shouldn't happen");
+}
+
+// Note: we require the supplier to provide the elements in the final order as we can't easily sort
+// within this method - qsort() accepts only pure function as comparator.
+void PackedTableBuilder::fill(u1* table, size_t table_length, Supplier &supplier) const {
+  uint32_t key, value;
+  size_t offset = 0;
+  for (; offset <= table_length && supplier.next(&key, &value); offset += _element_bytes) {
+    assert((key & ~_key_mask) == 0, "key out of bounds");
+    assert((value & ~_value_mask) == 0, "value out of bounds: %x vs. %x (%x)", value, _value_mask, ~_value_mask);
+    uint64_t element = static_cast<uint64_t>(key) | (static_cast<uint64_t>(value) << _value_shift);
+    for (unsigned int i = 0; i < _element_bytes; ++i) {
+      table[offset + i] = static_cast<u1>(0xFF & element);
+      element >>= 8;
+    }
+  }
+
+  assert(offset == table_length, "Did not fill whole array");
+  assert(!supplier.next(&key, &value), "Supplier has more elements");
+}
+
+uint64_t PackedTableLookup::read_element(size_t offset) const {
+  uint64_t element = 0;
+  for (unsigned int i = 0; i < _element_bytes; ++i) {
+    element |= static_cast<uint64_t>(_table[offset + i]) << (8 * i);
+  }
+  assert((element & ~((uint64_t) _key_mask | ((uint64_t) _value_mask << _value_shift))) == 0, "read too much");
+  return element;
+}
+
+bool PackedTableLookup::search(Comparator& comparator, uint32_t* found_key, uint32_t* found_value) const {
+  unsigned int low = 0, high = checked_cast<unsigned int>(_table_length / _element_bytes);
+  assert(low < high, "must be");
+  while (low < high) {
+    unsigned int mid = low + (high - low) / 2;
+    assert(mid >= low && mid < high, "integer overflow?");
+    uint64_t element = read_element(_element_bytes * mid);
+    // Ignoring high 32 bits in element on purpose
+    uint32_t key = static_cast<uint32_t>(element) & _key_mask;
+    int cmp = comparator.compare_to(key);
+    if (cmp == 0) {
+      *found_key = key;
+      // Since __builtin_memcpy in read_element does not copy bits outside the element
+      // anything above _value_mask << _value_shift should be zero.
+      *found_value = checked_cast<uint32_t>(element >> _value_shift) & _value_mask;
+      return true;
+    } else if (cmp < 0) {
+      high = mid;
+    } else {
+      low = mid + 1;
+    }
+  }
+  return false;
+}
+
+#ifdef ASSERT
+void PackedTableLookup::validate_order(Comparator &comparator) const {
+  auto validator = [&] (size_t offset, uint32_t key, uint32_t value) {
+    if (offset != 0) {
+      assert(comparator.compare_to(key) < 0, "not sorted");
+    }
+    comparator.reset(key);
+  };
+  iterate(validator);
+}
+#endif

src/hotspot/share/utilities/packedTable.hpp

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2025, 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "oops/array.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+// Base for space-optimized structure supporting binary search. Each element
+// consists of up to 32-bit key, and up to 32-bit value; these are packed
+// into a bit-record with 1-byte alignment.
+// The keys are ordered according to a custom comparator.
+class PackedTableBase {
+protected:
+  unsigned int _element_bytes;
+  uint32_t _key_mask;
+  unsigned int _value_shift;
+  uint32_t _value_mask;
+
+public:
+  PackedTableBase(uint32_t max_key, uint32_t max_value);
+
+  // Returns number of bytes each element will occupy.
+  inline unsigned int element_bytes(void) const { return _element_bytes; }
+};
+
+// Helper class for constructing a packed table in the provided array.
+class PackedTableBuilder: public PackedTableBase {
+public:
+  class Supplier {
+  public:
+    // Returns elements with already ordered keys.
+    // This function should return true when the key and value was set,
+    // and false when there's no more elements.
+    // Packed table does NOT support duplicate keys.
+    virtual bool next(uint32_t* key, uint32_t* value) = 0;
+  };
+
+  // The thresholds are inclusive, and in practice the limits are rounded
+  // to the nearest power-of-two - 1.
+  // See PackedTableBase constructor for details.
+  PackedTableBuilder(uint32_t max_key, uint32_t max_value): PackedTableBase(max_key, max_value) {}
+
+  // Constructs a packed table in the provided array, filling it with elements
+  // from the supplier. Note that no comparator is requied by this method -
+  // the supplier must return elements with already ordered keys.
+  // The table_length (in bytes) should match number of elements provided
+  // by the supplier (when Supplier::next() returns false the whole array should
+  // be filled).
+  void fill(u1* table, size_t table_length, Supplier &supplier) const;
+};
+
+// Helper class for lookup in a packed table.
+class PackedTableLookup: public PackedTableBase {
+  const u1* const _table;
+  const size_t _table_length;
+
+  uint64_t read_element(size_t offset) const;
+
+public:
+
+  // The comparator implementation does not have to store a key (uint32_t);
+  // the idea is that key can point into a different structure that hosts data
+  // suitable for the actual comparison. That's why PackedTableLookup::search(...)
+  // returns the key it found as well as the value.
+  class Comparator {
+  public:
+    // Returns negative/0/positive if the target referred to by this comparator
+    // is lower/equal/higher than the target referred to by the key.
+    virtual int compare_to(uint32_t key) = 0;
+    // Changes the target this comparator refers to.
+    DEBUG_ONLY(virtual void reset(uint32_t key) = 0);
+  };
+
+  // The thresholds are inclusive, and in practice the limits are rounded
+  // to the nearest power-of-two - 1.
+  // See PackedTableBase constructor for details.
+  PackedTableLookup(uint32_t max_key, uint32_t max_value, const u1 *table, size_t table_length):
+    PackedTableBase(max_key, max_value), _table(table), _table_length(table_length) {}
+
+  PackedTableLookup(uint32_t max_key, uint32_t max_value, const Array<u1> *table):
+    PackedTableLookup(max_key, max_value, table->data(), static_cast<size_t>(table->length())) {}
+
+  // Performs a binary search in the packed table, looking for an element with key
+  // referring to a target equal according to the comparator.
+  // When the element is found, found_key and found_value are updated from the element
+  // and the function returns true.
+  // When the element is not found, found_key and found_value are not changed and
+  // the function returns false.
+  bool search(Comparator& comparator, uint32_t* found_key, uint32_t* found_value) const;
+
+  // Asserts that elements in the packed table follow the order defined by the comparator.
+  DEBUG_ONLY(void validate_order(Comparator &comparator) const);
+
+  template<typename Function>
+  void iterate(Function func) const {
+    for (size_t offset = 0; offset < _table_length; offset += _element_bytes) {
+      uint64_t element = read_element(offset);
+      uint32_t key = static_cast<uint32_t>(element) & _key_mask;
+      uint32_t value = checked_cast<uint32_t>(element >> _value_shift) & _value_mask;
+      func(offset, key, value);
+    }
+  }
+};

src/hotspot/share/utilities/unsigned5.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2025, 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
@@ -261,7 +261,7 @@ class UNSIGNED5 : AllStatic {
     ARR _array;
     OFF _limit;
     OFF _position;
-    int next_length() {
+    int next_length() const {
       return UNSIGNED5::check_length(_array, _position, _limit, GET());
     }
   public:
@@ -270,7 +270,7 @@ class UNSIGNED5 : AllStatic {
     uint32_t next_uint() {
       return UNSIGNED5::read_uint(_array, _position, _limit, GET());
     }
-    bool has_next() {
+    bool has_next() const {
       return next_length() != 0;
     }
     // tries to skip count logical entries; returns actual number skipped
@@ -284,8 +284,9 @@ class UNSIGNED5 : AllStatic {
       return actual;
     }
     ARR array() { return _array; }
-    OFF limit() { return _limit; }
+    OFF limit() const { return _limit; }
-    OFF position() { return _position; }
+    OFF position() const { return _position; }
+    void set_limit(OFF limit) { _limit = limit; }
     void set_position(OFF position) { _position = position; }
 
     // For debugging, even in product builds (see debug.cpp).

test/hotspot/gtest/utilities/test_packedTable.cpp

@@ -0,0 +1,158 @@
+/*
+ * Copyright (c) 2025, 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+#include "utilities/packedTable.hpp"
+#include "unittest.hpp"
+
+class Supplier: public PackedTableBuilder::Supplier {
+  uint32_t* _keys;
+  uint32_t* _values;
+  size_t _num_keys;
+
+public:
+  Supplier(uint32_t* keys, uint32_t* values, size_t num_keys):
+    _keys(keys), _values(values), _num_keys(num_keys) {}
+
+  bool next(uint32_t* key, uint32_t* value) override {
+    if (_num_keys == 0) {
+      return false;
+    }
+    *key = *_keys;
+    ++_keys;
+    if (_values != nullptr) {
+      *value = *_values;
+      ++_values;
+    } else {
+      *value = 0;
+    }
+    --_num_keys;
+    return true;
+  }
+};
+
+class Comparator: public PackedTableLookup::Comparator {
+  uint32_t _current;
+
+public:
+  int compare_to(uint32_t key) override {
+    return _current < key ? -1 : (_current > key ? 1 : 0);
+  }
+
+  void reset(uint32_t key) DEBUG_ONLY(override) {
+    _current = key;
+  }
+};
+
+static void test(uint32_t max_key, uint32_t max_value, unsigned int length) {
+  if (length > max_key + 1) {
+    // can't generate more keys, as keys must be unique
+    return;
+  }
+  PackedTableBuilder builder(max_key, max_value);
+  size_t table_length = length * builder.element_bytes();
+  u1* table = new u1[table_length];
+
+  uint32_t* keys = new uint32_t[length];
+  uint32_t* values = max_value != 0 ? new uint32_t[length] : nullptr;
+  for (unsigned int i = 0; i < length; ++i) {
+    keys[i] = i;
+    if (values != nullptr) {
+      values[i] = i % max_value;
+    }
+  }
+  Supplier sup(keys, values, length);
+  builder.fill(table, table_length, sup);
+
+  Comparator comparator;
+  PackedTableLookup lookup(max_key, max_value, table, table_length);
+#ifdef ASSERT
+  lookup.validate_order(comparator);
+#endif
+
+  for (unsigned int i = 0; i < length; ++i) {
+    uint32_t key, value;
+    comparator.reset(keys[i]);
+    EXPECT_TRUE(lookup.search(comparator, &key, &value));
+    EXPECT_EQ(key, keys[i]);
+    if (values != nullptr) {
+      EXPECT_EQ(value, values[i]);
+    } else {
+      EXPECT_EQ(value, 0U);
+    }
+  }
+
+  delete[] keys;
+  delete[] values;
+}
+
+static void test_with_bits(uint32_t max_key, uint32_t max_value) {
+  // Some small sizes
+  for (unsigned int i = 0; i <= 100; ++i) {
+    test(max_key, max_value, i);
+  }
+  test(max_key, max_value, 10000);
+}
+
+TEST(PackedTableLookup, lookup) {
+  for (int key_bits = 1; key_bits <= 32; ++key_bits) {
+    for (int value_bits = 0; value_bits <= 32; ++value_bits) {
+      test_with_bits(static_cast<uint32_t>((1ULL << key_bits) - 1),
+                     static_cast<uint32_t>((1ULL << value_bits) - 1));
+    }
+  }
+}
+
+TEST(PackedTableBase, element_bytes) {
+  {
+    PackedTableBuilder builder(1, 0);
+    EXPECT_EQ(builder.element_bytes(), 1U);
+  }
+  {
+    PackedTableBuilder builder(15, 15);
+    EXPECT_EQ(builder.element_bytes(), 1U);
+  }
+  {
+    PackedTableBuilder builder(15, 16);
+    EXPECT_EQ(builder.element_bytes(), 2U);
+  }
+  {
+    PackedTableBuilder builder(31, 7);
+    EXPECT_EQ(builder.element_bytes(), 1U);
+  }
+  {
+    PackedTableBuilder builder(32, 7);
+    EXPECT_EQ(builder.element_bytes(), 2U);
+  }
+  {
+    PackedTableBuilder builder(-1, 0);
+    EXPECT_EQ(builder.element_bytes(), 4U);
+  }
+  {
+    PackedTableBuilder builder(-1, 1);
+    EXPECT_EQ(builder.element_bytes(), 5U);
+  }
+  {
+    PackedTableBuilder builder(-1, -1);
+    EXPECT_EQ(builder.element_bytes(), 8U);
+  }
+}

test/hotspot/jtreg/runtime/FieldStream/LocalFieldLookupTest.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright (c) 2025, 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+import static org.objectweb.asm.ClassWriter.COMPUTE_FRAMES;
+import static org.objectweb.asm.ClassWriter.COMPUTE_MAXS;
+import static org.objectweb.asm.Opcodes.*;
+
+/*
+ * @test id=defaults
+ * @bug 8352075
+ * @library /test/lib
+ * @library /testlibrary/asm
+ * @run main/othervm LocalFieldLookupTest
+ */
+/*
+ * @test id=custom-threshold
+ * @bug 8352075
+ * @library /test/lib
+ * @library /testlibrary/asm
+ * @requires vm.debug == true
+ * @run main/othervm LocalFieldLookupTest
+ * @run main/othervm -XX:BinarySearchThreshold=0 LocalFieldLookupTest
+ * @run main/othervm -XX:BinarySearchThreshold=1 LocalFieldLookupTest
+ * @run main/othervm -XX:BinarySearchThreshold=15 LocalFieldLookupTest
+ * @run main/othervm -XX:BinarySearchThreshold=100000 LocalFieldLookupTest
+ */
+public class LocalFieldLookupTest {
+    private static final String TEST_CLASS_NAME = "Test";
+    private static final int MAX_FIELDS_IN_METHOD = 10000;
+
+    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
+        // Test small classes, covering the tested thresholds
+        for (int i = 0; i <= 33; ++i) {
+            makeClass(i).newInstance();
+        }
+        // Test classes around 256 fields (index encoding 1/2 bytes) to check off-by-one errors
+        for (int i = 254; i <= 259; ++i) {
+            makeClass(255).newInstance();
+        }
+        // We would like to test #fields that create have the stream about 65536 bytes long;
+        // this value is not exposed, though, so these are rather experimentally found values,
+        // hence fragile. Moreover, since the stream length is incremented by about 8 bytes
+        // for each field we cannot test for off-by-one errors reliably.
+        for (int i = 8433; i <= 8437; ++i) {
+            makeClass(i).newInstance();
+        }
+        // The largest class we can create - this one has 65533 entries in the constant pool
+        makeClass(26205).newInstance();
+    }
+
+    public static Class<?> makeClass(int fields) throws ClassNotFoundException {
+        ClassWriter writer = new ClassWriter(COMPUTE_MAXS | COMPUTE_FRAMES);
+        writer.visit(49, Opcodes.ACC_PUBLIC + Opcodes.ACC_SUPER, TEST_CLASS_NAME,null, "java/lang/Object", null);
+
+        for (int i = 0; i < fields; i += 2) {
+            writer.visitField(ACC_PUBLIC, "f" + i, "I",  null, null);
+            // Let's use duplicate names to confirm search takes signatures into account
+            if (i + 1 < fields) {
+                writer.visitField(ACC_PUBLIC, "f" + i, "J",  null, null);
+            }
+        }
+        // We initialize fields in multiple methods to avoid running into bytecode limit per method
+        MethodVisitor fi = null;
+        for (int i = 0; i < fields; i+= 2) {
+            if (fi == null) {
+                fi = writer.visitMethod(ACC_PRIVATE, "init" + i, "()V", null, null);
+                fi.visitCode();
+            }
+            fi.visitVarInsn(Opcodes.ALOAD, 0);
+            fi.visitInsn(Opcodes.ICONST_2);
+            fi.visitFieldInsn(PUTFIELD, TEST_CLASS_NAME, "f" + i, "I");
+            if (i + 1 < fields) {
+                fi.visitVarInsn(Opcodes.ALOAD, 0);
+                fi.visitInsn(Opcodes.LCONST_1);
+                fi.visitFieldInsn(PUTFIELD, TEST_CLASS_NAME, "f" + i, "J");
+            }
+            if (i % MAX_FIELDS_IN_METHOD == MAX_FIELDS_IN_METHOD - 2) {
+                fi.visitInsn(Opcodes.RETURN);
+                fi.visitMaxs(0, 0);
+                fi.visitEnd();
+                fi = null;
+            }
+        }
+        if (fi != null) {
+            fi.visitInsn(Opcodes.RETURN);
+            fi.visitMaxs(0, 0);
+            fi.visitEnd();
+        }
+        {
+            MethodVisitor mv = writer.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
+            mv.visitCode();
+            mv.visitVarInsn(ALOAD, 0);
+            mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
+            for (int i = 0; i < fields; i += MAX_FIELDS_IN_METHOD) {
+                mv.visitVarInsn(ALOAD, 0);
+                mv.visitMethodInsn(INVOKESPECIAL, TEST_CLASS_NAME, "init" + i, "()V", false);
+            }
+            mv.visitInsn(RETURN);
+            mv.visitMaxs(0, 0);
+            mv.visitEnd();
+        }
+        writer.visitEnd();
+
+        byte[] bytecode = writer.toByteArray();
+        ClassLoader cl = new ClassLoader() {
+            @Override
+            protected Class<?> findClass(String name) throws ClassNotFoundException {
+                if (!TEST_CLASS_NAME.equals(name)) {
+                    throw new ClassNotFoundException();
+                }
+                return defineClass(TEST_CLASS_NAME, bytecode, 0, bytecode.length);
+            }
+        };
+        return cl.loadClass(TEST_CLASS_NAME);
+    }
+}