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src/hotspot/share/classfile/fieldLayoutBuilder.cpp

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@@ -1,7 +1,7 @@
  /*
-  * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+  * Copyright (c) 2020, 2024, 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.

@@ -23,45 +23,53 @@
   */
  
  #include "precompiled.hpp"
  #include "classfile/classFileParser.hpp"
  #include "classfile/fieldLayoutBuilder.hpp"
+ #include "classfile/systemDictionary.hpp"
+ #include "classfile/vmSymbols.hpp"
  #include "jvm.h"
  #include "memory/resourceArea.hpp"
  #include "oops/array.hpp"
  #include "oops/fieldStreams.inline.hpp"
  #include "oops/instanceMirrorKlass.hpp"
  #include "oops/instanceKlass.inline.hpp"
  #include "oops/klass.inline.hpp"
+ #include "oops/inlineKlass.inline.hpp"
  #include "runtime/fieldDescriptor.inline.hpp"
  
- 
  LayoutRawBlock::LayoutRawBlock(Kind kind, int size) :
    _next_block(nullptr),
    _prev_block(nullptr),
+   _inline_klass(nullptr),
    _kind(kind),
    _offset(-1),
    _alignment(1),
    _size(size),
    _field_index(-1),
-   _is_reference(false) {
-   assert(kind == EMPTY || kind == RESERVED || kind == PADDING || kind == INHERITED,
+   _null_marker_offset(-1),
+   _is_reference(false),
+   _needs_null_marker(false) {
+   assert(kind == EMPTY || kind == RESERVED || kind == PADDING || kind == INHERITED || kind == NULL_MARKER,
           "Otherwise, should use the constructor with a field index argument");
    assert(size > 0, "Sanity check");
  }
  
  
  LayoutRawBlock::LayoutRawBlock(int index, Kind kind, int size, int alignment, bool is_reference) :
   _next_block(nullptr),
   _prev_block(nullptr),
+  _inline_klass(nullptr),
   _kind(kind),
   _offset(-1),
   _alignment(alignment),
   _size(size),
   _field_index(index),
-  _is_reference(is_reference) {
-   assert(kind == REGULAR || kind == FLATTENED || kind == INHERITED,
+  _null_marker_offset(-1),
+  _is_reference(is_reference),
+  _needs_null_marker(false) {
+   assert(kind == REGULAR || kind == FLAT || kind == INHERITED || kind == INHERITED_NULL_MARKER,
           "Other kind do not have a field index");
    assert(size > 0, "Sanity check");
    assert(alignment > 0, "Sanity check");
  }
  

@@ -73,22 +81,24 @@
    return _size >= size + adjustment;
  }
  
  FieldGroup::FieldGroup(int contended_group) :
    _next(nullptr),
-   _primitive_fields(nullptr),
+   _small_primitive_fields(nullptr),
+   _big_primitive_fields(nullptr),
    _oop_fields(nullptr),
    _contended_group(contended_group),  // -1 means no contended group, 0 means default contended group
    _oop_count(0) {}
  
  void FieldGroup::add_primitive_field(int idx, BasicType type) {
    int size = type2aelembytes(type);
    LayoutRawBlock* block = new LayoutRawBlock(idx, LayoutRawBlock::REGULAR, size, size /* alignment == size for primitive types */, false);
-   if (_primitive_fields == nullptr) {
-     _primitive_fields = new GrowableArray<LayoutRawBlock*>(INITIAL_LIST_SIZE);
+   if (size >= oopSize) {
+     add_to_big_primitive_list(block);
+   } else {
+     add_to_small_primitive_list(block);
    }
-   _primitive_fields->append(block);
  }
  
  void FieldGroup::add_oop_field(int idx) {
    int size = type2aelembytes(T_OBJECT);
    LayoutRawBlock* block = new LayoutRawBlock(idx, LayoutRawBlock::REGULAR, size, size /* alignment == size for oops */, true);

@@ -97,22 +107,55 @@
    }
    _oop_fields->append(block);
    _oop_count++;
  }
  
+ void FieldGroup::add_flat_field(int idx, InlineKlass* vk, bool needs_null_marker) {
+   LayoutRawBlock* block = new LayoutRawBlock(idx, LayoutRawBlock::FLAT, vk->get_payload_size_in_bytes(), vk->get_alignment(), false);
+   block->set_inline_klass(vk);
+   if (needs_null_marker) block->set_needs_null_marker();
+   if (block->size() >= oopSize) {
+     add_to_big_primitive_list(block);
+   } else {
+     add_to_small_primitive_list(block);
+   }
+ }
+ 
  void FieldGroup::sort_by_size() {
-   if (_primitive_fields != nullptr) {
-     _primitive_fields->sort(LayoutRawBlock::compare_size_inverted);
+   if (_small_primitive_fields != nullptr) {
+     _small_primitive_fields->sort(LayoutRawBlock::compare_size_inverted);
+   }
+   if (_big_primitive_fields != nullptr) {
+     _big_primitive_fields->sort(LayoutRawBlock::compare_size_inverted);
+   }
+ }
+ 
+ void FieldGroup::add_to_small_primitive_list(LayoutRawBlock* block) {
+   if (_small_primitive_fields == nullptr) {
+     _small_primitive_fields = new GrowableArray<LayoutRawBlock*>(INITIAL_LIST_SIZE);
+   }
+   _small_primitive_fields->append(block);
+ }
+ 
+ void FieldGroup::add_to_big_primitive_list(LayoutRawBlock* block) {
+   if (_big_primitive_fields == nullptr) {
+     _big_primitive_fields = new GrowableArray<LayoutRawBlock*>(INITIAL_LIST_SIZE);
    }
+   _big_primitive_fields->append(block);
  }
  
  FieldLayout::FieldLayout(GrowableArray<FieldInfo>* field_info, ConstantPool* cp) :
    _field_info(field_info),
    _cp(cp),
    _blocks(nullptr),
    _start(_blocks),
-   _last(_blocks) {}
+   _last(_blocks),
+   _super_first_field_offset(-1),
+   _super_alignment(-1),
+   _super_min_align_required(-1),
+   _super_has_fields(false),
+   _has_missing_null_markers(false) {}
  
  void FieldLayout::initialize_static_layout() {
    _blocks = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
    _blocks->set_offset(0);
    _last = _blocks;

@@ -133,32 +176,34 @@
      _blocks->set_offset(0);
      _last = _blocks;
      _start = _blocks;
      insert(first_empty_block(), new LayoutRawBlock(LayoutRawBlock::RESERVED, instanceOopDesc::base_offset_in_bytes()));
    } else {
-     bool has_fields = reconstruct_layout(super_klass);
+     _super_has_fields = reconstruct_layout(super_klass);
      fill_holes(super_klass);
-     if ((UseEmptySlotsInSupers && !super_klass->has_contended_annotations()) || !has_fields) {
-       _start = _blocks;  // start allocating fields from the first empty block
+     if ((UseEmptySlotsInSupers && !super_klass->has_contended_annotations()) || !_super_has_fields) {
+       _start = _blocks; // Setting _start to _blocks instead of _last would allow subclasses
+       // to allocate fields in empty slots of their super classes
      } else {
        _start = _last;    // append fields at the end of the reconstructed layout
      }
    }
  }
  
  LayoutRawBlock* FieldLayout::first_field_block() {
-   LayoutRawBlock* block = _start;
-   while (block->kind() != LayoutRawBlock::INHERITED && block->kind() != LayoutRawBlock::REGULAR
-       && block->kind() != LayoutRawBlock::FLATTENED && block->kind() != LayoutRawBlock::PADDING) {
+   LayoutRawBlock* block = _blocks;
+   while (block != nullptr
+          && block->kind() != LayoutRawBlock::INHERITED
+          && block->kind() != LayoutRawBlock::REGULAR
+          && block->kind() != LayoutRawBlock::FLAT) {
      block = block->next_block();
    }
    return block;
  }
  
- 
- // Insert a set of fields into a layout using a best-fit strategy.
- // For each field, search for the smallest empty slot able to fit the field
+ // Insert a set of fields into a layout.
+ // For each field, search for an empty slot able to fit the field
  // (satisfying both size and alignment requirements), if none is found,
  // add the field at the end of the layout.
  // Fields cannot be inserted before the block specified in the "start" argument
  void FieldLayout::add(GrowableArray<LayoutRawBlock*>* list, LayoutRawBlock* start) {
    if (list == nullptr) return;

@@ -168,11 +213,10 @@
    int last_alignment = 0;
    for (int i = 0; i < list->length(); i ++) {
      LayoutRawBlock* b = list->at(i);
      LayoutRawBlock* cursor = nullptr;
      LayoutRawBlock* candidate = nullptr;
- 
      // if start is the last block, just append the field
      if (start == last_block()) {
        candidate = last_block();
      }
      // Before iterating over the layout to find an empty slot fitting the field's requirements,

@@ -186,10 +230,11 @@
        last_size = b->size();
        last_alignment = b->alignment();
        cursor = last_block()->prev_block();
        assert(cursor != nullptr, "Sanity check");
        last_search_success = true;
+ 
        while (cursor != start) {
          if (cursor->kind() == LayoutRawBlock::EMPTY && cursor->fit(b->size(), b->alignment())) {
            if (candidate == nullptr || cursor->size() < candidate->size()) {
              candidate = cursor;
            }

@@ -202,11 +247,10 @@
        }
        assert(candidate != nullptr, "Candidate must not be null");
        assert(candidate->kind() == LayoutRawBlock::EMPTY, "Candidate must be an empty block");
        assert(candidate->fit(b->size(), b->alignment()), "Candidate must be able to store the block");
      }
- 
      insert_field_block(candidate, b);
    }
  }
  
  // Used for classes with hard coded field offsets, insert a field at the specified offset */

@@ -219,21 +263,23 @@
    LayoutRawBlock* slot = start;
    while (slot != nullptr) {
      if ((slot->offset() <= block->offset() && (slot->offset() + slot->size()) > block->offset()) ||
          slot == _last){
        assert(slot->kind() == LayoutRawBlock::EMPTY, "Matching slot must be an empty slot");
-       assert(slot->size() >= block->offset() + block->size() ,"Matching slot must be big enough");
+       assert(slot->size() >= block->offset() - slot->offset() + block->size() ,"Matching slot must be big enough");
        if (slot->offset() < block->offset()) {
          int adjustment = block->offset() - slot->offset();
          LayoutRawBlock* adj = new LayoutRawBlock(LayoutRawBlock::EMPTY, adjustment);
          insert(slot, adj);
        }
        insert(slot, block);
        if (slot->size() == 0) {
          remove(slot);
        }
-       _field_info->adr_at(block->field_index())->set_offset(block->offset());
+       if (block->kind() == LayoutRawBlock::REGULAR || block->kind() == LayoutRawBlock::FLAT) {
+         _field_info->adr_at(block->field_index())->set_offset(block->offset());
+       }
        return;
      }
      slot = slot->next_block();
    }
    fatal("Should have found a matching slot above, corrupted layout or invalid offset");

@@ -284,41 +330,70 @@
    if (slot->offset() % block->alignment() != 0) {
      int adjustment = block->alignment() - (slot->offset() % block->alignment());
      LayoutRawBlock* adj = new LayoutRawBlock(LayoutRawBlock::EMPTY, adjustment);
      insert(slot, adj);
    }
+   assert(block->size() >= block->size(), "Enough space must remain afte adjustment");
    insert(slot, block);
+   if (block->needs_null_marker()) {
+     _has_missing_null_markers = true;
+   }
    if (slot->size() == 0) {
      remove(slot);
    }
-   _field_info->adr_at(block->field_index())->set_offset(block->offset());
+   // NULL_MARKER blocks have a field index pointing to the field that needs a null marker,
+   // so the field_info at this index must not be updated with the null marker's offset
+   if (block->kind() != LayoutRawBlock::NULL_MARKER) {
+     _field_info->adr_at(block->field_index())->set_offset(block->offset());
+   }
    return block;
  }
  
  bool FieldLayout::reconstruct_layout(const InstanceKlass* ik) {
    bool has_instance_fields = false;
+   if (ik->is_abstract() && !ik->is_identity_class()) {
+     _super_alignment = type2aelembytes(BasicType::T_LONG);
+   }
    GrowableArray<LayoutRawBlock*>* all_fields = new GrowableArray<LayoutRawBlock*>(32);
    while (ik != nullptr) {
      for (AllFieldStream fs(ik->fieldinfo_stream(), ik->constants()); !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;
        has_instance_fields = true;
-       int size = type2aelembytes(type);
-       // INHERITED blocks are marked as non-reference because oop_maps are handled by their holder class
-       LayoutRawBlock* block = new LayoutRawBlock(fs.index(), LayoutRawBlock::INHERITED, size, size, false);
+       if (_super_first_field_offset == -1 || fs.offset() < _super_first_field_offset) _super_first_field_offset = fs.offset();
+       LayoutRawBlock* block;
+       if (fs.is_flat()) {
+         InlineKlass* vk = InlineKlass::cast(ik->get_inline_type_field_klass(fs.index()));
+         block = new LayoutRawBlock(fs.index(), LayoutRawBlock::INHERITED, vk->get_payload_size_in_bytes(),
+                                    vk->get_alignment(), false);
+         assert(_super_alignment == -1 || _super_alignment >=  vk->get_alignment(), "Invalid value alignment");
+         _super_min_align_required = _super_min_align_required > vk->get_alignment() ? _super_min_align_required : vk->get_alignment();
+         if (!fs.field_flags().is_null_free_inline_type()) {
+           assert(fs.field_flags().has_null_marker(), "Nullable flat fields must have a null marker");
+           LayoutRawBlock* marker = new LayoutRawBlock(fs.index(), LayoutRawBlock::INHERITED_NULL_MARKER, 1 /* current NULL_MARKER block are one byte */,
+                                     1, false);
+           marker->set_offset(fs.null_marker_offset());
+           all_fields->append(marker);
+         }
+       } else {
+         int size = type2aelembytes(type);
+         // INHERITED blocks are marked as non-reference because oop_maps are handled by their holder class
+         block = new LayoutRawBlock(fs.index(), LayoutRawBlock::INHERITED, size, size, false);
+         // For primitive types, the alignment is equal to the size
+         assert(_super_alignment == -1 || _super_alignment >=  size, "Invalid value alignment");
+         _super_min_align_required = _super_min_align_required > size ? _super_min_align_required : size;
+       }
        block->set_offset(fs.offset());
        all_fields->append(block);
      }
      ik = ik->super() == nullptr ? nullptr : InstanceKlass::cast(ik->super());
    }
- 
    all_fields->sort(LayoutRawBlock::compare_offset);
    _blocks = new LayoutRawBlock(LayoutRawBlock::RESERVED, instanceOopDesc::base_offset_in_bytes());
    _blocks->set_offset(0);
    _last = _blocks;
- 
    for(int i = 0; i < all_fields->length(); i++) {
      LayoutRawBlock* b = all_fields->at(i);
      _last->set_next_block(b);
      b->set_prev_block(_last);
      _last = b;

@@ -350,22 +425,20 @@
      }
      b = b->next_block();
    }
    assert(b->next_block() == nullptr, "Invariant at this point");
    assert(b->kind() != LayoutRawBlock::EMPTY, "Sanity check");
- 
    // If the super class has @Contended annotation, a padding block is
    // inserted at the end to ensure that fields from the subclasses won't share
    // the cache line of the last field of the contended class
    if (super_klass->has_contended_annotations() && ContendedPaddingWidth > 0) {
      LayoutRawBlock* p = new LayoutRawBlock(LayoutRawBlock::PADDING, ContendedPaddingWidth);
      p->set_offset(b->offset() + b->size());
      b->set_next_block(p);
      p->set_prev_block(b);
      b = p;
    }
- 
    if (!UseEmptySlotsInSupers) {
      // Add an empty slots to align fields of the subclass on a heapOopSize boundary
      // in order to emulate the behavior of the previous algorithm
      int align = (b->offset() + b->size()) % heapOopSize;
      if (align != 0) {

@@ -375,11 +448,10 @@
        b->set_next_block(p);
        p->set_prev_block(b);
        b = p;
      }
    }
- 
    LayoutRawBlock* last = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
    last->set_offset(b->offset() + b->size());
    assert(last->offset() > 0, "Sanity check");
    b->set_next_block(last);
    last->set_prev_block(b);

@@ -401,10 +473,13 @@
      block->prev_block()->set_next_block(block);
    }
    if (_blocks == slot) {
      _blocks = block;
    }
+   if (_start == slot) {
+     _start = block;
+   }
    return block;
  }
  
  void FieldLayout::remove(LayoutRawBlock* block) {
    assert(block != nullptr, "Sanity check");

@@ -422,101 +497,143 @@
    if (block == _start) {
      _start = block->prev_block();
    }
  }
  
- void FieldLayout::print(outputStream* output, bool is_static, const InstanceKlass* super) {
+ void FieldLayout::print(outputStream* output, bool is_static, const InstanceKlass* super, Array<InlineKlass*>* inline_fields) {
    ResourceMark rm;
    LayoutRawBlock* b = _blocks;
    while(b != _last) {
      switch(b->kind()) {
        case LayoutRawBlock::REGULAR: {
          FieldInfo* fi = _field_info->adr_at(b->field_index());
-         output->print_cr(" @%d \"%s\" %s %d/%d %s",
+         output->print_cr(" @%d %s %d/%d \"%s\" %s",
                           b->offset(),
-                          fi->name(_cp)->as_C_string(),
-                          fi->signature(_cp)->as_C_string(),
+                          "REGULAR",
                           b->size(),
                           b->alignment(),
-                          "REGULAR");
+                          fi->name(_cp)->as_C_string(),
+                          fi->signature(_cp)->as_C_string());
          break;
        }
-       case LayoutRawBlock::FLATTENED: {
+       case LayoutRawBlock::FLAT: {
          FieldInfo* fi = _field_info->adr_at(b->field_index());
-         output->print_cr(" @%d \"%s\" %s %d/%d %s",
+         InlineKlass* ik = inline_fields->at(fi->index());
+         assert(ik != nullptr, "");
+         output->print(" @%d %s %d/%d \"%s\" %s %s@%p",
                           b->offset(),
-                          fi->name(_cp)->as_C_string(),
-                          fi->signature(_cp)->as_C_string(),
+                          "FLAT",
                           b->size(),
                           b->alignment(),
-                          "FLATTENED");
+                          fi->name(_cp)->as_C_string(),
+                          fi->signature(_cp)->as_C_string(),
+                          ik->name()->as_C_string(),
+                          ik->class_loader_data());
+         if (fi->field_flags().has_null_marker()) {
+           output->print_cr(" null marker offset %d %s", fi->null_marker_offset(),
+                            fi->field_flags().is_null_marker_internal() ? "(internal)" : "");
+         } else {
+           output->print_cr("");
+         }
          break;
        }
        case LayoutRawBlock::RESERVED: {
-         output->print_cr(" @%d %d/- %s",
+         output->print_cr(" @%d %s %d/-",
                           b->offset(),
-                          b->size(),
-                          "RESERVED");
+                          "RESERVED",
+                          b->size());
          break;
        }
        case LayoutRawBlock::INHERITED: {
          assert(!is_static, "Static fields are not inherited in layouts");
          assert(super != nullptr, "super klass must be provided to retrieve inherited fields info");
          bool found = false;
          const InstanceKlass* ik = super;
          while (!found && ik != nullptr) {
            for (AllFieldStream fs(ik->fieldinfo_stream(), ik->constants()); !fs.done(); fs.next()) {
-             if (fs.offset() == b->offset()) {
-               output->print_cr(" @%d \"%s\" %s %d/%d %s",
+             if (fs.offset() == b->offset() && fs.access_flags().is_static() == is_static) {
+               output->print_cr(" @%d %s %d/%d \"%s\" %s",
                    b->offset(),
-                   fs.name()->as_C_string(),
-                   fs.signature()->as_C_string(),
+                   "INHERITED",
                    b->size(),
-                   b->size(), // so far, alignment constraint == size, will change with Valhalla
-                   "INHERITED");
+                   b->size(), // so far, alignment constraint == size, will change with Valhalla => FIXME
+                   fs.name()->as_C_string(),
+                   fs.signature()->as_C_string());
                found = true;
                break;
              }
-           }
-           ik = ik->java_super();
          }
-         break;
+         ik = ik->java_super();
        }
-       case LayoutRawBlock::EMPTY:
-         output->print_cr(" @%d %d/1 %s",
-                          b->offset(),
-                          b->size(),
-                         "EMPTY");
-         break;
-       case LayoutRawBlock::PADDING:
-         output->print_cr(" @%d %d/1 %s",
-                          b->offset(),
-                          b->size(),
-                         "PADDING");
-         break;
+       break;
+     }
+     case LayoutRawBlock::INHERITED_NULL_MARKER :
+       output->print_cr(" @%d %s %d/1",
+                        b->offset(),
+                       "INHERITED_NULL_MARKER",
+                        b->size());
+       break;
+     case LayoutRawBlock::EMPTY:
+       output->print_cr(" @%d %s %d/1",
+                        b->offset(),
+                       "EMPTY",
+                        b->size());
+       break;
+     case LayoutRawBlock::PADDING:
+       output->print_cr(" @%d %s %d/1",
+                       b->offset(),
+                       "PADDING",
+                       b->size());
+       break;
+     case LayoutRawBlock::NULL_MARKER:
+     {
+       FieldInfo* fi = _field_info->adr_at(b->field_index());
+       output->print_cr(" @%d %s %d/1 null marker for field at offset %d",
+                       b->offset(),
+                       "NULL_MARKER",
+                       b->size(),
+                       fi->offset());
+       break;
+     }
+     default:
+       fatal("Unknown block type");
      }
      b = b->next_block();
    }
  }
  
- FieldLayoutBuilder::FieldLayoutBuilder(const Symbol* classname, const InstanceKlass* super_klass, ConstantPool* constant_pool,
-       GrowableArray<FieldInfo>* field_info, bool is_contended, FieldLayoutInfo* info) :
+ FieldLayoutBuilder::FieldLayoutBuilder(const Symbol* classname, ClassLoaderData* loader_data, const InstanceKlass* super_klass, ConstantPool* constant_pool,
+                                        GrowableArray<FieldInfo>* field_info, bool is_contended, bool is_inline_type,bool is_abstract_value,
+                                        FieldLayoutInfo* info, Array<InlineKlass*>* inline_type_field_klasses) :
    _classname(classname),
+   _loader_data(loader_data),
    _super_klass(super_klass),
    _constant_pool(constant_pool),
    _field_info(field_info),
    _info(info),
+   _inline_type_field_klasses(inline_type_field_klasses),
    _root_group(nullptr),
    _contended_groups(GrowableArray<FieldGroup*>(8)),
    _static_fields(nullptr),
    _layout(nullptr),
    _static_layout(nullptr),
    _nonstatic_oopmap_count(0),
    _alignment(-1),
+   _first_field_offset(-1),
+   _internal_null_marker_offset(-1),
+   _payload_size_in_bytes(-1),
+   _atomic_field_count(0),
+   _fields_size_sum(0),
    _has_nonstatic_fields(false),
-   _is_contended(is_contended) {}
- 
+   _has_inline_type_fields(false),
+   _is_contended(is_contended),
+   _is_inline_type(is_inline_type),
+   _is_abstract_value(is_abstract_value),
+   _has_flattening_information(is_inline_type),
+   _has_nonatomic_values(false),
+   _nullable_atomic_flat_candidate(false),
+   _has_null_markers(false) {}
  
  FieldGroup* FieldLayoutBuilder::get_or_create_contended_group(int g) {
    assert(g > 0, "must only be called for named contended groups");
    FieldGroup* fg = nullptr;
    for (int i = 0; i < _contended_groups.length(); i++) {

@@ -539,25 +656,26 @@
    _static_layout->initialize_static_layout();
    _static_fields = new FieldGroup();
    _root_group = new FieldGroup();
  }
  
- // Field sorting for regular classes:
+ // Field sorting for regular (non-inline) classes:
  //   - fields are sorted in static and non-static fields
  //   - non-static fields are also sorted according to their contention group
  //     (support of the @Contended annotation)
  //   - @Contended annotation is ignored for static fields
+ //   - field flattening decisions are taken in this method
  void FieldLayoutBuilder::regular_field_sorting() {
    int idx = 0;
    for (GrowableArrayIterator<FieldInfo> it = _field_info->begin(); it != _field_info->end(); ++it, ++idx) {
-     FieldInfo ctrl = _field_info->at(0);
      FieldGroup* group = nullptr;
      FieldInfo fieldinfo = *it;
      if (fieldinfo.access_flags().is_static()) {
        group = _static_fields;
      } else {
        _has_nonstatic_fields = true;
+       _atomic_field_count++;  // we might decrement this
        if (fieldinfo.field_flags().is_contended()) {
          int g = fieldinfo.contended_group();
          if (g == 0) {
            group = new FieldGroup(true);
            _contended_groups.append(group);

@@ -569,27 +687,76 @@
        }
      }
      assert(group != nullptr, "invariant");
      BasicType type = Signature::basic_type(fieldinfo.signature(_constant_pool));
      switch(type) {
-       case T_BYTE:
-       case T_CHAR:
-       case T_DOUBLE:
-       case T_FLOAT:
-       case T_INT:
-       case T_LONG:
-       case T_SHORT:
-       case T_BOOLEAN:
-         group->add_primitive_field(idx, type);
-         break;
-       case T_OBJECT:
-       case T_ARRAY:
+     case T_BYTE:
+     case T_CHAR:
+     case T_DOUBLE:
+     case T_FLOAT:
+     case T_INT:
+     case T_LONG:
+     case T_SHORT:
+     case T_BOOLEAN:
+       group->add_primitive_field(idx, type);
+       break;
+     case T_OBJECT:
+     case T_ARRAY:
+     {
+       bool field_is_known_value_class =  !fieldinfo.field_flags().is_injected() && _inline_type_field_klasses != nullptr && _inline_type_field_klasses->at(fieldinfo.index()) != nullptr;
+       bool value_has_oops = field_is_known_value_class ? _inline_type_field_klasses->at(fieldinfo.index())->nonstatic_oop_count() > 0 : true;
+       bool is_candidate_for_flattening = fieldinfo.field_flags().is_null_free_inline_type() || (EnableNullableFieldFlattening && field_is_known_value_class && !value_has_oops);
+       // if (!fieldinfo.field_flags().is_null_free_inline_type()) {
+       if (!is_candidate_for_flattening) {
          if (group != _static_fields) _nonstatic_oopmap_count++;
          group->add_oop_field(idx);
-         break;
-       default:
-         fatal("Something wrong?");
+       } else {
+         assert(type != T_ARRAY, "null free ptr to array not supported");
+         _has_inline_type_fields = true;
+         if (group == _static_fields) {
+           // static fields are never flat
+           group->add_oop_field(idx);
+         } else {
+           // Check below is performed for non-static fields, it should be performed for static fields too but at this stage,
+           // it is not guaranteed that the klass of the static field has been loaded, so the test for static fields is delayed
+           // until the linking phase
+           Klass* klass =  _inline_type_field_klasses->at(idx);
+           assert(klass != nullptr, "Sanity check");
+           InlineKlass* vk = InlineKlass::cast(klass);
+           assert(!fieldinfo.field_flags().is_null_free_inline_type() || vk->is_implicitly_constructible(), "must be, should have been checked in post_process_parsed_stream()");
+           _has_flattening_information = true;
+           // Flattening decision to be taken here
+           // This code assumes all verification already have been performed
+           // (field's type has been loaded and it is an inline klass)
+           bool too_big_to_flatten = (InlineFieldMaxFlatSize >= 0 &&
+                                     (vk->size_helper() * HeapWordSize) > InlineFieldMaxFlatSize);
+           bool too_atomic_to_flatten = vk->must_be_atomic() || AlwaysAtomicAccesses;
+           bool too_volatile_to_flatten = fieldinfo.access_flags().is_volatile();
+           if (vk->is_naturally_atomic()) {
+             too_atomic_to_flatten = false;
+             //too_volatile_to_flatten = false; //FIXME
+             // Currently, volatile fields are never flat, this could change in the future
+           }
+           if (!(too_big_to_flatten | too_atomic_to_flatten | too_volatile_to_flatten)) {
+             group->add_flat_field(idx, vk, !fieldinfo.field_flags().is_null_free_inline_type());
+             _nonstatic_oopmap_count += vk->nonstatic_oop_map_count();
+             _field_info->adr_at(idx)->field_flags_addr()->update_flat(true);
+             if (!vk->is_atomic()) {  // flat and non-atomic: take note
+               _has_nonatomic_values = true;
+               _atomic_field_count--;  // every other field is atomic but this one
+             }
+             if (!fieldinfo.field_flags().is_null_free_inline_type()) _has_null_markers = true;
+           } else {
+             _nonstatic_oopmap_count++;
+             group->add_oop_field(idx);
+           }
+         }
+       }
+       break;
+     }
+     default:
+       fatal("Something wrong?");
      }
    }
    _root_group->sort_by_size();
    _static_fields->sort_by_size();
    if (!_contended_groups.is_empty()) {

@@ -597,87 +764,378 @@
        _contended_groups.at(i)->sort_by_size();
      }
    }
  }
  
+ /* Field sorting for inline classes:
+  *   - because inline classes are immutable, the @Contended annotation is ignored
+  *     when computing their layout (with only read operation, there's no false
+  *     sharing issue)
+  *   - this method also records the alignment of the field with the most
+  *     constraining alignment, this value is then used as the alignment
+  *     constraint when flattening this inline type into another container
+  *   - field flattening decisions are taken in this method (those decisions are
+  *     currently only based in the size of the fields to be flattened, the size
+  *     of the resulting instance is not considered)
+  */
+ void FieldLayoutBuilder::inline_class_field_sorting() {
+   assert(_is_inline_type || _is_abstract_value, "Should only be used for inline classes");
+   int alignment = -1;
+   for (GrowableArrayIterator<FieldInfo> it = _field_info->begin(); it != _field_info->end(); ++it) {
+     FieldGroup* group = nullptr;
+     FieldInfo fieldinfo = *it;
+     int field_alignment = 1;
+     if (fieldinfo.access_flags().is_static()) {
+       group = _static_fields;
+     } else {
+       _has_nonstatic_fields = true;
+       _atomic_field_count++;  // we might decrement this
+       group = _root_group;
+     }
+     assert(group != nullptr, "invariant");
+     BasicType type = Signature::basic_type(fieldinfo.signature(_constant_pool));
+     switch(type) {
+     case T_BYTE:
+     case T_CHAR:
+     case T_DOUBLE:
+     case T_FLOAT:
+     case T_INT:
+     case T_LONG:
+     case T_SHORT:
+     case T_BOOLEAN:
+       if (group != _static_fields) {
+         field_alignment = type2aelembytes(type); // alignment == size for primitive types
+       }
+       group->add_primitive_field(fieldinfo.index(), type);
+       break;
+     case T_OBJECT:
+     case T_ARRAY:
+     {
+       bool field_is_known_value_class =  !fieldinfo.field_flags().is_injected() && _inline_type_field_klasses != nullptr && _inline_type_field_klasses->at(fieldinfo.index()) != nullptr;
+       bool value_has_oops = field_is_known_value_class ? _inline_type_field_klasses->at(fieldinfo.index())->nonstatic_oop_count() > 0 : true;
+       bool is_candidate_for_flattening = fieldinfo.field_flags().is_null_free_inline_type() || (EnableNullableFieldFlattening && field_is_known_value_class && !value_has_oops);
+       // if (!fieldinfo.field_flags().is_null_free_inline_type()) {
+       if (!is_candidate_for_flattening) {
+         if (group != _static_fields) {
+           _nonstatic_oopmap_count++;
+           field_alignment = type2aelembytes(type); // alignment == size for oops
+         }
+         group->add_oop_field(fieldinfo.index());
+       } else {
+         assert(type != T_ARRAY, "null free ptr to array not supported");
+         _has_inline_type_fields = true;
+         if (group == _static_fields) {
+           // static fields are never flat
+           group->add_oop_field(fieldinfo.index());
+         } else {
+           // Check below is performed for non-static fields, it should be performed for static fields too but at this stage,
+           // it is not guaranteed that the klass of the static field has been loaded, so the test for static fields is delayed
+           // until the linking phase
+           Klass* klass =  _inline_type_field_klasses->at(fieldinfo.index());
+           assert(klass != nullptr, "Sanity check");
+           InlineKlass* vk = InlineKlass::cast(klass);
+           assert(vk->is_implicitly_constructible(), "must be, should have been checked in post_process_parsed_stream()");
+           // Flattening decision to be taken here
+           // This code assumes all verifications have already been performed
+           // (field's type has been loaded and it is an inline klass)
+           bool too_big_to_flatten = (InlineFieldMaxFlatSize >= 0 &&
+                                     (vk->size_helper() * HeapWordSize) > InlineFieldMaxFlatSize);
+           bool too_atomic_to_flatten = vk->must_be_atomic() || AlwaysAtomicAccesses;
+           bool too_volatile_to_flatten = fieldinfo.access_flags().is_volatile();
+           if (vk->is_naturally_atomic()) {
+             too_atomic_to_flatten = false;
+             //too_volatile_to_flatten = false; //FIXME
+             // Currently, volatile fields are never flat, this could change in the future
+           }
+           if (!(too_big_to_flatten | too_atomic_to_flatten | too_volatile_to_flatten)) {
+             group->add_flat_field(fieldinfo.index(), vk, !fieldinfo.field_flags().is_null_free_inline_type());
+             _nonstatic_oopmap_count += vk->nonstatic_oop_map_count();
+             field_alignment = vk->get_alignment();
+             _field_info->adr_at(fieldinfo.index())->field_flags_addr()->update_flat(true);
+             if (!vk->is_atomic()) {  // flat and non-atomic: take note
+               _has_nonatomic_values = true;
+               _atomic_field_count--;  // every other field is atomic but this one
+             }
+             if (!fieldinfo.field_flags().is_null_free_inline_type()) _has_null_markers = true;
+           } else {
+             _nonstatic_oopmap_count++;
+             field_alignment = type2aelembytes(T_OBJECT);
+             group->add_oop_field(fieldinfo.index());
+           }
+         }
+       }
+       break;
+     }
+     default:
+       fatal("Unexpected BasicType");
+     }
+     if (!fieldinfo.access_flags().is_static() && field_alignment > alignment) alignment = field_alignment;
+   }
+   _alignment = alignment;
+   assert(_has_nonstatic_fields || _is_abstract_value, "Concrete value types do not support zero instance size yet");
+ }
+ 
  void FieldLayoutBuilder::insert_contended_padding(LayoutRawBlock* slot) {
    if (ContendedPaddingWidth > 0) {
      LayoutRawBlock* padding = new LayoutRawBlock(LayoutRawBlock::PADDING, ContendedPaddingWidth);
      _layout->insert(slot, padding);
    }
  }
  
- // Computation of regular classes layout is an evolution of the previous default layout
- // (FieldAllocationStyle 1):
- //   - primitive fields are allocated first (from the biggest to the smallest)
- //   - then oop fields are allocated, either in existing gaps or at the end of
- //     the layout
+ /* Computation of regular classes layout is an evolution of the previous default layout
+  * (FieldAllocationStyle 1):
+  *   - primitive fields (both primitive types and flat inline types) are allocated
+  *     first, from the biggest to the smallest
+  *   - then oop fields are allocated (to increase chances to have contiguous oops and
+  *     a simpler oopmap).
+  */
  void FieldLayoutBuilder::compute_regular_layout() {
    bool need_tail_padding = false;
    prologue();
    regular_field_sorting();
- 
    if (_is_contended) {
      _layout->set_start(_layout->last_block());
      // insertion is currently easy because the current strategy doesn't try to fill holes
      // in super classes layouts => the _start block is by consequence the _last_block
      insert_contended_padding(_layout->start());
      need_tail_padding = true;
    }
-   _layout->add(_root_group->primitive_fields());
+   _layout->add(_root_group->big_primitive_fields());
+   _layout->add(_root_group->small_primitive_fields());
    _layout->add(_root_group->oop_fields());
  
    if (!_contended_groups.is_empty()) {
      for (int i = 0; i < _contended_groups.length(); i++) {
        FieldGroup* cg = _contended_groups.at(i);
        LayoutRawBlock* start = _layout->last_block();
        insert_contended_padding(start);
-       _layout->add(cg->primitive_fields(), start);
+       _layout->add(cg->big_primitive_fields());
+       _layout->add(cg->small_primitive_fields(), start);
        _layout->add(cg->oop_fields(), start);
        need_tail_padding = true;
      }
    }
  
    if (need_tail_padding) {
      insert_contended_padding(_layout->last_block());
    }
  
-   _static_layout->add_contiguously(this->_static_fields->oop_fields());
-   _static_layout->add(this->_static_fields->primitive_fields());
+   if (EnableNullableFieldFlattening && _layout->has_missing_null_markers()) {
+     insert_null_markers();
+   }
+ 
+   // Warning: IntanceMirrorKlass expects static oops to be allocated first
+   _static_layout->add_contiguously(_static_fields->oop_fields());
+   _static_layout->add(_static_fields->big_primitive_fields());
+   _static_layout->add(_static_fields->small_primitive_fields());
+ 
+   epilogue();
+ }
+ 
+ void FieldLayoutBuilder::insert_null_markers() {
+   if (!EnableNullableFieldFlattening || !_layout->has_missing_null_markers()) return;
+   GrowableArray<LayoutRawBlock*>* list = new GrowableArray<LayoutRawBlock*>(10);
+   for (LayoutRawBlock* block = _layout->first_field_block(); block != _layout->last_block(); block = block->next_block()) {
+     if (block->needs_null_marker()) {
+       assert(block->kind() == LayoutRawBlock::FLAT, "Only flat fields might need null markers");
+       if (block->inline_klass()->has_internal_null_marker_offset()) {
+         // The inline klass has an internal null marker slot, let's use it
+         // The inline klass has the internal null marker offset from the begining of the object,
+         // compute the offset relative to begining of payload
+         int internal_null_marker_offset = block->inline_klass()->get_internal_null_marker_offset() - block->inline_klass()->first_field_offset();
+         block->set_null_marker_offset(block->offset() + internal_null_marker_offset);
+         _field_info->adr_at(block->field_index())->set_null_marker_offset(block->null_marker_offset());
+         _field_info->adr_at(block->field_index())->field_flags_addr()->update_null_marker(true);
+         _field_info->adr_at(block->field_index())->field_flags_addr()->update_internal_null_marker(true);
+       } else {
+         // No internal null marker, need a external slot in the container
+         LayoutRawBlock* marker = new LayoutRawBlock(LayoutRawBlock::NULL_MARKER, 1);
+         marker->set_field_index(block->field_index());
+         list->append(marker);
+       }
+     }
+   }
+   _layout->add(list);
+   for (GrowableArrayIterator<LayoutRawBlock*> it = list->begin(); it != list->end(); ++it) {
+     LayoutRawBlock* block = *it;
+     assert(block->offset() != -1, "Must be set");
+     assert(!block->needs_null_marker(), "Must have been set");
+     _field_info->adr_at(block->field_index())->set_null_marker_offset(block->offset());
+     _field_info->adr_at(block->field_index())->field_flags_addr()->update_null_marker(true);
+   }
+ }
+ 
+ /* Computation of inline classes has a slightly different strategy than for
+  * regular classes. Regular classes have their oop fields allocated at the end
+  * of the layout to increase GC performances. Unfortunately, this strategy
+  * increases the number of empty slots inside an instance. Because the purpose
+  * of inline classes is to be embedded into other containers, it is critical
+  * to keep their size as small as possible. For this reason, the allocation
+  * strategy is:
+  *   - big primitive fields (primitive types and flat inline type smaller
+  *     than an oop) are allocated first (from the biggest to the smallest)
+  *   - then oop fields
+  *   - then small primitive fields (from the biggest to the smallest)
+  */
+ void FieldLayoutBuilder::compute_inline_class_layout() {
+   prologue();
+   inline_class_field_sorting();
+ 
+   assert(_layout->start()->kind() == LayoutRawBlock::RESERVED, "Unexpected");
+ 
+   if (_layout->super_has_fields() && !_is_abstract_value) {  // non-static field layout
+     if (!_has_nonstatic_fields) {
+       assert(_is_abstract_value, "Concrete value types have at least one field");
+       // Nothing to do
+     } else {
+       // decide which alignment to use, then set first allowed field offset
+ 
+       assert(_layout->super_alignment() >= _alignment, "Incompatible alignment");
+       assert(_layout->super_alignment() % _alignment == 0, "Incompatible alignment");
+ 
+       if (_alignment < _layout->super_alignment()) {
+         int new_alignment = _alignment > _layout->super_min_align_required() ? _alignment : _layout->super_min_align_required();
+         assert(new_alignment % _alignment == 0, "Must be");
+         assert(new_alignment % _layout->super_min_align_required() == 0, "Must be");
+         _alignment = new_alignment;
+       }
+       if (_layout->first_empty_block()->offset() < _layout->first_field_block()->offset()) {
+         LayoutRawBlock* first_empty = _layout->start()->next_block();
+         if (first_empty->offset() % _alignment != 0) {
+           int size =  _alignment - (first_empty->offset() % _alignment);
+           LayoutRawBlock* padding = new LayoutRawBlock(LayoutRawBlock::PADDING, size);
+           _layout->insert(first_empty, padding);
+           _layout->set_start(padding);
+         } else {
+           _layout->set_start( _layout->start());
+         }
+       } else {
+         _layout->set_start(_layout->first_field_block());
+       }
+     }
+   } else {
+     if (_is_abstract_value && _has_nonstatic_fields) {
+       _alignment = type2aelembytes(BasicType::T_LONG);
+     }
+     assert(_layout->start()->next_block()->kind() == LayoutRawBlock::EMPTY || !UseCompressedClassPointers, "Unexpected");
+     LayoutRawBlock* first_empty = _layout->start()->next_block();
+     if (first_empty->offset() % _alignment != 0) {
+       LayoutRawBlock* padding = new LayoutRawBlock(LayoutRawBlock::PADDING, _alignment - (first_empty->offset() % _alignment));
+       _layout->insert(first_empty, padding);
+       if (first_empty->size() == 0) {
+         _layout->remove(first_empty);
+       }
+       _layout->set_start(padding);
+     }
+   }
+ 
+   _layout->add(_root_group->big_primitive_fields());
+   _layout->add(_root_group->oop_fields());
+   _layout->add(_root_group->small_primitive_fields());
+ 
+   if (EnableNullableFieldFlattening && _layout->has_missing_null_markers()) {
+     insert_null_markers();
+   }
+ 
+   LayoutRawBlock* first_field = _layout->first_field_block();
+   if (first_field != nullptr) {
+     _first_field_offset = _layout->first_field_block()->offset();
+     _payload_size_in_bytes = _layout->last_block()->offset() - _layout->first_field_block()->offset();
+   } else {
+     // special case for empty value types
+     _first_field_offset = _layout->blocks()->size();
+     _payload_size_in_bytes = 0;
+   }
+   if (_layout->first_field_block() == nullptr) {
+     assert(_is_abstract_value, "Concrete inline types must have at least one field");
+     _payload_size_in_bytes = 0;
+   } else {
+     _payload_size_in_bytes = _layout->last_block()->offset() - _layout->first_field_block()->offset();
+   }
+ 
+   // Looking if there's an empty slot inside the layout that could be used to store a null marker
+   LayoutRawBlock* b = _layout->first_field_block();
+   if (b != nullptr) {
+     while (b != _layout->last_block()) {
+       if (b->kind() == LayoutRawBlock::EMPTY) {
+         break;
+       }
+       b = b->next_block();
+     }
+     if (b != _layout->last_block()) {
+       // found an empty slot, register its offset from the beginning of the payload
+       _internal_null_marker_offset = b->offset();
+     }
+   } else {
+     assert(_is_abstract_value, "Only abstract value can have no fields");
+   }
+ 
+   // Warning:: InstanceMirrorKlass expects static oops to be allocated first
+   _static_layout->add_contiguously(_static_fields->oop_fields());
+   _static_layout->add(_static_fields->big_primitive_fields());
+   _static_layout->add(_static_fields->small_primitive_fields());
  
    epilogue();
  }
  
+ void FieldLayoutBuilder::add_flat_field_oopmap(OopMapBlocksBuilder* nonstatic_oop_maps,
+                 InlineKlass* vklass, int offset) {
+   int diff = offset - vklass->first_field_offset();
+   const OopMapBlock* map = vklass->start_of_nonstatic_oop_maps();
+   const OopMapBlock* last_map = map + vklass->nonstatic_oop_map_count();
+   while (map < last_map) {
+     nonstatic_oop_maps->add(map->offset() + diff, map->count());
+     map++;
+   }
+ }
+ 
+ void FieldLayoutBuilder::register_embedded_oops_from_list(OopMapBlocksBuilder* nonstatic_oop_maps, GrowableArray<LayoutRawBlock*>* list) {
+   if (list != nullptr) {
+     for (int i = 0; i < list->length(); i++) {
+       LayoutRawBlock* f = list->at(i);
+       if (f->kind() == LayoutRawBlock::FLAT) {
+         InlineKlass* vk = f->inline_klass();
+         assert(vk != nullptr, "Should have been initialized");
+         if (vk->contains_oops()) {
+           add_flat_field_oopmap(nonstatic_oop_maps, vk, f->offset());
+         }
+       }
+     }
+   }
+ }
+ 
+ void FieldLayoutBuilder::register_embedded_oops(OopMapBlocksBuilder* nonstatic_oop_maps, FieldGroup* group) {
+   if (group->oop_fields() != nullptr) {
+     for (int i = 0; i < group->oop_fields()->length(); i++) {
+       LayoutRawBlock* b = group->oop_fields()->at(i);
+       nonstatic_oop_maps->add(b->offset(), 1);
+     }
+   }
+   register_embedded_oops_from_list(nonstatic_oop_maps, group->big_primitive_fields());
+   register_embedded_oops_from_list(nonstatic_oop_maps, group->small_primitive_fields());
+ }
+ 
  void FieldLayoutBuilder::epilogue() {
    // Computing oopmaps
    int super_oop_map_count = (_super_klass == nullptr) ? 0 :_super_klass->nonstatic_oop_map_count();
    int max_oop_map_count = super_oop_map_count + _nonstatic_oopmap_count;
- 
    OopMapBlocksBuilder* nonstatic_oop_maps =
        new OopMapBlocksBuilder(max_oop_map_count);
    if (super_oop_map_count > 0) {
      nonstatic_oop_maps->initialize_inherited_blocks(_super_klass->start_of_nonstatic_oop_maps(),
      _super_klass->nonstatic_oop_map_count());
    }
- 
-   if (_root_group->oop_fields() != nullptr) {
-     for (int i = 0; i < _root_group->oop_fields()->length(); i++) {
-       LayoutRawBlock* b = _root_group->oop_fields()->at(i);
-       nonstatic_oop_maps->add(b->offset(), 1);
-     }
-   }
- 
+   register_embedded_oops(nonstatic_oop_maps, _root_group);
    if (!_contended_groups.is_empty()) {
      for (int i = 0; i < _contended_groups.length(); i++) {
        FieldGroup* cg = _contended_groups.at(i);
        if (cg->oop_count() > 0) {
          assert(cg->oop_fields() != nullptr && cg->oop_fields()->at(0) != nullptr, "oop_count > 0 but no oop fields found");
-         nonstatic_oop_maps->add(cg->oop_fields()->at(0)->offset(), cg->oop_count());
+         register_embedded_oops(nonstatic_oop_maps, cg);
        }
      }
    }
- 
    nonstatic_oop_maps->compact();
  
    int instance_end = align_up(_layout->last_block()->offset(), wordSize);
    int static_fields_end = align_up(_static_layout->last_block()->offset(), wordSize);
    int static_fields_size = (static_fields_end -

@@ -689,21 +1147,84 @@
    _info->oop_map_blocks = nonstatic_oop_maps;
    _info->_instance_size = align_object_size(instance_end / wordSize);
    _info->_static_field_size = static_fields_size;
    _info->_nonstatic_field_size = (nonstatic_field_end - instanceOopDesc::base_offset_in_bytes()) / heapOopSize;
    _info->_has_nonstatic_fields = _has_nonstatic_fields;
+   _info->_has_inline_fields = _has_inline_type_fields;
+   _info->_has_null_marker_offsets = _has_null_markers;
+ 
+   // An inline type is naturally atomic if it has just one field, and
+   // that field is simple enough.
+   _info->_is_naturally_atomic = (_is_inline_type &&
+                                  (_atomic_field_count <= 1) &&
+                                  !_has_nonatomic_values &&
+                                  _contended_groups.is_empty());
+   // This may be too restrictive, since if all the fields fit in 64
+   // bits we could make the decision to align instances of this class
+   // to 64-bit boundaries, and load and store them as single words.
+   // And on machines which supported larger atomics we could similarly
+   // allow larger values to be atomic, if properly aligned.
+ 
+ #ifdef ASSERT
+   // Tests verifying integrity of field layouts are using the output of -XX:+PrintFieldLayout
+   // which prints the details of LayoutRawBlocks used to compute the layout.
+   // The code below checks that offsets in the _field_info meta-data match offsets
+   // in the LayoutRawBlocks
+   LayoutRawBlock* b = _layout->blocks();
+   while(b != _layout->last_block()) {
+     if (b->kind() == LayoutRawBlock::REGULAR || b->kind() == LayoutRawBlock::FLAT) {
+       assert(_field_info->adr_at(b->field_index())->offset() == (u4)b->offset()," Must match");
+     }
+     b = b->next_block();
+   }
+   b = _static_layout->blocks();
+   while(b != _static_layout->last_block()) {
+     if (b->kind() == LayoutRawBlock::REGULAR || b->kind() == LayoutRawBlock::FLAT) {
+       assert(_field_info->adr_at(b->field_index())->offset() == (u4)b->offset()," Must match");
+     }
+     b = b->next_block();
+   }
+ #endif // ASSERT
+ 
+   static bool first_layout_print = true;
  
-   if (PrintFieldLayout) {
+ 
+   if (PrintFieldLayout || (PrintInlineLayout && _has_flattening_information)) {
      ResourceMark rm;
-     tty->print_cr("Layout of class %s", _classname->as_C_string());
-     tty->print_cr("Instance fields:");
-     _layout->print(tty, false, _super_klass);
-     tty->print_cr("Static fields:");
-     _static_layout->print(tty, true, nullptr);
-     tty->print_cr("Instance size = %d bytes", _info->_instance_size * wordSize);
-     tty->print_cr("---");
+     stringStream st;
+     if (first_layout_print) {
+       st.print_cr("Field layout log format: @offset size/alignment [name] [signature] [comment]");
+       st.print_cr("Heap oop size = %d", heapOopSize);
+       first_layout_print = false;
+     }
+     if (_super_klass != nullptr) {
+       st.print_cr("Layout of class %s@%p extends %s@%p", _classname->as_C_string(),
+                     _loader_data, _super_klass->name()->as_C_string(), _super_klass->class_loader_data());
+     } else {
+       st.print_cr("Layout of class %s@%p", _classname->as_C_string(), _loader_data);
+     }
+     st.print_cr("Instance fields:");
+     _layout->print(&st, false, _super_klass, _inline_type_field_klasses);
+     st.print_cr("Static fields:");
+     _static_layout->print(&st, true, nullptr, _inline_type_field_klasses);
+     st.print_cr("Instance size = %d bytes", _info->_instance_size * wordSize);
+     if (_is_inline_type) {
+       st.print_cr("First field offset = %d", _first_field_offset);
+       st.print_cr("Alignment = %d bytes", _alignment);
+       st.print_cr("Exact size = %d bytes", _payload_size_in_bytes);
+       if (_internal_null_marker_offset != -1) {
+         st.print_cr("Null marker offset = %d", _internal_null_marker_offset);
+       }
+     }
+     st.print_cr("---");
+     // Print output all together.
+     tty->print_raw(st.as_string());
    }
  }
  
  void FieldLayoutBuilder::build_layout() {
-   compute_regular_layout();
+   if (_is_inline_type || _is_abstract_value) {
+     compute_inline_class_layout();
+   } else {
+     compute_regular_layout();
+   }
  }
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