1 /*
   2  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "jvm.h"
  27 #include "classfile/classFileParser.hpp"
  28 #include "classfile/fieldLayoutBuilder.hpp"
  29 #include "memory/resourceArea.hpp"
  30 #include "oops/array.hpp"
  31 #include "oops/fieldStreams.inline.hpp"
  32 #include "oops/instanceMirrorKlass.hpp"
  33 #include "oops/klass.inline.hpp"
  34 #include "runtime/fieldDescriptor.inline.hpp"
  35 
  36 
  37 LayoutRawBlock::LayoutRawBlock(Kind kind, int size) :
  38   _next_block(NULL),
  39   _prev_block(NULL),
  40   _kind(kind),
  41   _offset(-1),
  42   _alignment(1),
  43   _size(size),
  44   _field_index(-1),
  45   _is_reference(false) {
  46   assert(kind == EMPTY || kind == RESERVED || kind == PADDING || kind == INHERITED,
  47          "Otherwise, should use the constructor with a field index argument");
  48   assert(size > 0, "Sanity check");
  49 }
  50 
  51 
  52 LayoutRawBlock::LayoutRawBlock(int index, Kind kind, int size, int alignment, bool is_reference) :
  53  _next_block(NULL),
  54  _prev_block(NULL),
  55  _kind(kind),
  56  _offset(-1),
  57  _alignment(alignment),
  58  _size(size),
  59  _field_index(index),
  60  _is_reference(is_reference) {
  61   assert(kind == REGULAR || kind == FLATTENED || kind == INHERITED,
  62          "Other kind do not have a field index");
  63   assert(size > 0, "Sanity check");
  64   assert(alignment > 0, "Sanity check");
  65 }
  66 
  67 bool LayoutRawBlock::fit(int size, int alignment) {
  68   int adjustment = 0;
  69   if ((_offset % alignment) != 0) {
  70     adjustment = alignment - (_offset % alignment);
  71   }
  72   return _size >= size + adjustment;
  73 }
  74 
  75 FieldGroup::FieldGroup(int contended_group) :
  76   _next(NULL),
  77   _primitive_fields(NULL),
  78   _oop_fields(NULL),
  79   _contended_group(contended_group),  // -1 means no contended group, 0 means default contended group
  80   _oop_count(0) {}
  81 
  82 void FieldGroup::add_primitive_field(AllFieldStream fs, BasicType type) {
  83   int size = type2aelembytes(type);
  84   LayoutRawBlock* block = new LayoutRawBlock(fs.index(), LayoutRawBlock::REGULAR, size, size /* alignment == size for primitive types */, false);
  85   if (_primitive_fields == NULL) {
  86     _primitive_fields = new(ResourceObj::RESOURCE_AREA, mtInternal) GrowableArray<LayoutRawBlock*>(INITIAL_LIST_SIZE);
  87   }
  88   _primitive_fields->append(block);
  89 }
  90 
  91 void FieldGroup::add_oop_field(AllFieldStream fs) {
  92   int size = type2aelembytes(T_OBJECT);
  93   LayoutRawBlock* block = new LayoutRawBlock(fs.index(), LayoutRawBlock::REGULAR, size, size /* alignment == size for oops */, true);
  94   if (_oop_fields == NULL) {
  95     _oop_fields = new(ResourceObj::RESOURCE_AREA, mtInternal) GrowableArray<LayoutRawBlock*>(INITIAL_LIST_SIZE);
  96   }
  97   _oop_fields->append(block);
  98   _oop_count++;
  99 }
 100 
 101 void FieldGroup::sort_by_size() {
 102   if (_primitive_fields != NULL) {
 103     _primitive_fields->sort(LayoutRawBlock::compare_size_inverted);
 104   }
 105 }
 106 
 107 FieldLayout::FieldLayout(Array<u2>* fields, ConstantPool* cp) :
 108   _fields(fields),
 109   _cp(cp),
 110   _blocks(NULL),
 111   _start(_blocks),
 112   _last(_blocks) {}
 113 
 114 void FieldLayout::initialize_static_layout() {
 115   _blocks = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
 116   _blocks->set_offset(0);
 117   _last = _blocks;
 118   _start = _blocks;
 119   // Note: at this stage, InstanceMirrorKlass::offset_of_static_fields() could be zero, because
 120   // during bootstrapping, the size of the java.lang.Class is still not known when layout
 121   // of static field is computed. Field offsets are fixed later when the size is known
 122   // (see java_lang_Class::fixup_mirror())
 123   if (InstanceMirrorKlass::offset_of_static_fields() > 0) {
 124     insert(first_empty_block(), new LayoutRawBlock(LayoutRawBlock::RESERVED, InstanceMirrorKlass::offset_of_static_fields()));
 125     _blocks->set_offset(0);
 126   }
 127 }
 128 
 129 void FieldLayout::initialize_instance_layout(const InstanceKlass* super_klass) {
 130   if (super_klass == NULL) {
 131     _blocks = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
 132     _blocks->set_offset(0);
 133     _last = _blocks;
 134     _start = _blocks;
 135     insert(first_empty_block(), new LayoutRawBlock(LayoutRawBlock::RESERVED, instanceOopDesc::base_offset_in_bytes()));
 136   } else {
 137     bool has_fields = reconstruct_layout(super_klass);
 138     fill_holes(super_klass);
 139     if ((UseEmptySlotsInSupers && !super_klass->has_contended_annotations()) || !has_fields) {
 140       _start = _blocks;  // start allocating fields from the first empty block
 141     } else {
 142       _start = _last;    // append fields at the end of the reconstructed layout
 143     }
 144   }
 145 }
 146 
 147 LayoutRawBlock* FieldLayout::first_field_block() {
 148   LayoutRawBlock* block = _start;
 149   while (block->kind() != LayoutRawBlock::INHERITED && block->kind() != LayoutRawBlock::REGULAR
 150       && block->kind() != LayoutRawBlock::FLATTENED && block->kind() != LayoutRawBlock::PADDING) {
 151     block = block->next_block();
 152   }
 153   return block;
 154 }
 155 
 156 
 157 // Insert a set of fields into a layout using a best-fit strategy.
 158 // For each field, search for the smallest empty slot able to fit the field
 159 // (satisfying both size and alignment requirements), if none is found,
 160 // add the field at the end of the layout.
 161 // Fields cannot be inserted before the block specified in the "start" argument
 162 void FieldLayout::add(GrowableArray<LayoutRawBlock*>* list, LayoutRawBlock* start) {
 163   if (list == NULL) return;
 164   if (start == NULL) start = this->_start;
 165   bool last_search_success = false;
 166   int last_size = 0;
 167   int last_alignment = 0;
 168   for (int i = 0; i < list->length(); i ++) {
 169     LayoutRawBlock* b = list->at(i);
 170     LayoutRawBlock* cursor = NULL;
 171     LayoutRawBlock* candidate = NULL;
 172 
 173     // if start is the last block, just append the field
 174     if (start == last_block()) {
 175       candidate = last_block();
 176     }
 177     // Before iterating over the layout to find an empty slot fitting the field's requirements,
 178     // check if the previous field had the same requirements and if the search for a fitting slot
 179     // was successful. If the requirements were the same but the search failed, a new search will
 180     // fail the same way, so just append the field at the of the layout.
 181     else  if (b->size() == last_size && b->alignment() == last_alignment && !last_search_success) {
 182       candidate = last_block();
 183     } else {
 184       // Iterate over the layout to find an empty slot fitting the field's requirements
 185       last_size = b->size();
 186       last_alignment = b->alignment();
 187       cursor = last_block()->prev_block();
 188       assert(cursor != NULL, "Sanity check");
 189       last_search_success = true;
 190       while (cursor != start) {
 191         if (cursor->kind() == LayoutRawBlock::EMPTY && cursor->fit(b->size(), b->alignment())) {
 192           if (candidate == NULL || cursor->size() < candidate->size()) {
 193             candidate = cursor;
 194           }
 195         }
 196         cursor = cursor->prev_block();
 197       }
 198       if (candidate == NULL) {
 199         candidate = last_block();
 200         last_search_success = false;
 201       }
 202       assert(candidate != NULL, "Candidate must not be null");
 203       assert(candidate->kind() == LayoutRawBlock::EMPTY, "Candidate must be an empty block");
 204       assert(candidate->fit(b->size(), b->alignment()), "Candidate must be able to store the block");
 205     }
 206 
 207     insert_field_block(candidate, b);
 208   }
 209 }
 210 
 211 // Used for classes with hard coded field offsets, insert a field at the specified offset */
 212 void FieldLayout::add_field_at_offset(LayoutRawBlock* block, int offset, LayoutRawBlock* start) {
 213   assert(block != NULL, "Sanity check");
 214   block->set_offset(offset);
 215   if (start == NULL) {
 216     start = this->_start;
 217   }
 218   LayoutRawBlock* slot = start;
 219   while (slot != NULL) {
 220     if ((slot->offset() <= block->offset() && (slot->offset() + slot->size()) > block->offset()) ||
 221         slot == _last){
 222       assert(slot->kind() == LayoutRawBlock::EMPTY, "Matching slot must be an empty slot");
 223       assert(slot->size() >= block->offset() + block->size() ,"Matching slot must be big enough");
 224       if (slot->offset() < block->offset()) {
 225         int adjustment = block->offset() - slot->offset();
 226         LayoutRawBlock* adj = new LayoutRawBlock(LayoutRawBlock::EMPTY, adjustment);
 227         insert(slot, adj);
 228       }
 229       insert(slot, block);
 230       if (slot->size() == 0) {
 231         remove(slot);
 232       }
 233       FieldInfo::from_field_array(_fields, block->field_index())->set_offset(block->offset());
 234       return;
 235     }
 236     slot = slot->next_block();
 237   }
 238   fatal("Should have found a matching slot above, corrupted layout or invalid offset");
 239 }
 240 
 241 // The allocation logic uses a best fit strategy: the set of fields is allocated
 242 // in the first empty slot big enough to contain the whole set ((including padding
 243 // to fit alignment constraints).
 244 void FieldLayout::add_contiguously(GrowableArray<LayoutRawBlock*>* list, LayoutRawBlock* start) {
 245   if (list == NULL) return;
 246   if (start == NULL) {
 247     start = _start;
 248   }
 249   // This code assumes that if the first block is well aligned, the following
 250   // blocks would naturally be well aligned (no need for adjustment)
 251   int size = 0;
 252   for (int i = 0; i < list->length(); i++) {
 253     size += list->at(i)->size();
 254   }
 255 
 256   LayoutRawBlock* candidate = NULL;
 257   if (start == last_block()) {
 258     candidate = last_block();
 259   } else {
 260     LayoutRawBlock* first = list->at(0);
 261     candidate = last_block()->prev_block();
 262     while (candidate->kind() != LayoutRawBlock::EMPTY || !candidate->fit(size, first->alignment())) {
 263       if (candidate == start) {
 264         candidate = last_block();
 265         break;
 266       }
 267       candidate = candidate->prev_block();
 268     }
 269     assert(candidate != NULL, "Candidate must not be null");
 270     assert(candidate->kind() == LayoutRawBlock::EMPTY, "Candidate must be an empty block");
 271     assert(candidate->fit(size, first->alignment()), "Candidate must be able to store the whole contiguous block");
 272   }
 273 
 274   for (int i = 0; i < list->length(); i++) {
 275     LayoutRawBlock* b = list->at(i);
 276     insert_field_block(candidate, b);
 277     assert((candidate->offset() % b->alignment() == 0), "Contiguous blocks must be naturally well aligned");
 278   }
 279 }
 280 
 281 LayoutRawBlock* FieldLayout::insert_field_block(LayoutRawBlock* slot, LayoutRawBlock* block) {
 282   assert(slot->kind() == LayoutRawBlock::EMPTY, "Blocks can only be inserted in empty blocks");
 283   if (slot->offset() % block->alignment() != 0) {
 284     int adjustment = block->alignment() - (slot->offset() % block->alignment());
 285     LayoutRawBlock* adj = new LayoutRawBlock(LayoutRawBlock::EMPTY, adjustment);
 286     insert(slot, adj);
 287   }
 288   insert(slot, block);
 289   if (slot->size() == 0) {
 290     remove(slot);
 291   }
 292   FieldInfo::from_field_array(_fields, block->field_index())->set_offset(block->offset());
 293   return block;
 294 }
 295 
 296 bool FieldLayout::reconstruct_layout(const InstanceKlass* ik) {
 297   bool has_instance_fields = false;
 298   GrowableArray<LayoutRawBlock*>* all_fields = new GrowableArray<LayoutRawBlock*>(32);
 299   while (ik != NULL) {
 300     for (AllFieldStream fs(ik->fields(), ik->constants()); !fs.done(); fs.next()) {
 301       BasicType type = Signature::basic_type(fs.signature());
 302       // distinction between static and non-static fields is missing
 303       if (fs.access_flags().is_static()) continue;
 304       has_instance_fields = true;
 305       int size = type2aelembytes(type);
 306       // INHERITED blocks are marked as non-reference because oop_maps are handled by their holder class
 307       LayoutRawBlock* block = new LayoutRawBlock(fs.index(), LayoutRawBlock::INHERITED, size, size, false);
 308       block->set_offset(fs.offset());
 309       all_fields->append(block);
 310     }
 311     ik = ik->super() == NULL ? NULL : InstanceKlass::cast(ik->super());
 312   }
 313 
 314   all_fields->sort(LayoutRawBlock::compare_offset);
 315   _blocks = new LayoutRawBlock(LayoutRawBlock::RESERVED, instanceOopDesc::base_offset_in_bytes());
 316   _blocks->set_offset(0);
 317   _last = _blocks;
 318 
 319   for(int i = 0; i < all_fields->length(); i++) {
 320     LayoutRawBlock* b = all_fields->at(i);
 321     _last->set_next_block(b);
 322     b->set_prev_block(_last);
 323     _last = b;
 324   }
 325   _start = _blocks;
 326   return has_instance_fields;
 327 }
 328 
 329 // Called during the reconstruction of a layout, after fields from super
 330 // classes have been inserted. It fills unused slots between inserted fields
 331 // with EMPTY blocks, so the regular field insertion methods would work.
 332 // This method handles classes with @Contended annotations differently
 333 // by inserting PADDING blocks instead of EMPTY block to prevent subclasses'
 334 // fields to interfere with contended fields/classes.
 335 void FieldLayout::fill_holes(const InstanceKlass* super_klass) {
 336   assert(_blocks != NULL, "Sanity check");
 337   assert(_blocks->offset() == 0, "first block must be at offset zero");
 338   LayoutRawBlock::Kind filling_type = super_klass->has_contended_annotations() ? LayoutRawBlock::PADDING: LayoutRawBlock::EMPTY;
 339   LayoutRawBlock* b = _blocks;
 340   while (b->next_block() != NULL) {
 341     if (b->next_block()->offset() > (b->offset() + b->size())) {
 342       int size = b->next_block()->offset() - (b->offset() + b->size());
 343       LayoutRawBlock* empty = new LayoutRawBlock(filling_type, size);
 344       empty->set_offset(b->offset() + b->size());
 345       empty->set_next_block(b->next_block());
 346       b->next_block()->set_prev_block(empty);
 347       b->set_next_block(empty);
 348       empty->set_prev_block(b);
 349     }
 350     b = b->next_block();
 351   }
 352   assert(b->next_block() == NULL, "Invariant at this point");
 353   assert(b->kind() != LayoutRawBlock::EMPTY, "Sanity check");
 354 
 355   // If the super class has @Contended annotation, a padding block is
 356   // inserted at the end to ensure that fields from the subclasses won't share
 357   // the cache line of the last field of the contended class
 358   if (super_klass->has_contended_annotations() && ContendedPaddingWidth > 0) {
 359     LayoutRawBlock* p = new LayoutRawBlock(LayoutRawBlock::PADDING, ContendedPaddingWidth);
 360     p->set_offset(b->offset() + b->size());
 361     b->set_next_block(p);
 362     p->set_prev_block(b);
 363     b = p;
 364   }
 365 
 366   if (!UseEmptySlotsInSupers) {
 367     // Add an empty slots to align fields of the subclass on a heapOopSize boundary
 368     // in order to emulate the behavior of the previous algorithm
 369     int align = (b->offset() + b->size()) % heapOopSize;
 370     if (align != 0) {
 371       int sz = heapOopSize - align;
 372       LayoutRawBlock* p = new LayoutRawBlock(LayoutRawBlock::EMPTY, sz);
 373       p->set_offset(b->offset() + b->size());
 374       b->set_next_block(p);
 375       p->set_prev_block(b);
 376       b = p;
 377     }
 378   }
 379 
 380   LayoutRawBlock* last = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
 381   last->set_offset(b->offset() + b->size());
 382   assert(last->offset() > 0, "Sanity check");
 383   b->set_next_block(last);
 384   last->set_prev_block(b);
 385   _last = last;
 386 }
 387 
 388 LayoutRawBlock* FieldLayout::insert(LayoutRawBlock* slot, LayoutRawBlock* block) {
 389   assert(slot->kind() == LayoutRawBlock::EMPTY, "Blocks can only be inserted in empty blocks");
 390   assert(slot->offset() % block->alignment() == 0, "Incompatible alignment");
 391   block->set_offset(slot->offset());
 392   slot->set_offset(slot->offset() + block->size());
 393   assert((slot->size() - block->size()) < slot->size(), "underflow checking");
 394   assert(slot->size() - block->size() >= 0, "no negative size allowed");
 395   slot->set_size(slot->size() - block->size());
 396   block->set_prev_block(slot->prev_block());
 397   block->set_next_block(slot);
 398   slot->set_prev_block(block);
 399   if (block->prev_block() != NULL) {
 400     block->prev_block()->set_next_block(block);
 401   }
 402   if (_blocks == slot) {
 403     _blocks = block;
 404   }
 405   return block;
 406 }
 407 
 408 void FieldLayout::remove(LayoutRawBlock* block) {
 409   assert(block != NULL, "Sanity check");
 410   assert(block != _last, "Sanity check");
 411   if (_blocks == block) {
 412     _blocks = block->next_block();
 413     if (_blocks != NULL) {
 414       _blocks->set_prev_block(NULL);
 415     }
 416   } else {
 417     assert(block->prev_block() != NULL, "_prev should be set for non-head blocks");
 418     block->prev_block()->set_next_block(block->next_block());
 419     block->next_block()->set_prev_block(block->prev_block());
 420   }
 421   if (block == _start) {
 422     _start = block->prev_block();
 423   }
 424 }
 425 
 426 void FieldLayout::print(outputStream* output, bool is_static, const InstanceKlass* super) {
 427   ResourceMark rm;
 428   LayoutRawBlock* b = _blocks;
 429   while(b != _last) {
 430     switch(b->kind()) {
 431       case LayoutRawBlock::REGULAR: {
 432         FieldInfo* fi = FieldInfo::from_field_array(_fields, b->field_index());
 433         output->print_cr(" @%d \"%s\" %s %d/%d %s",
 434                          b->offset(),
 435                          fi->name(_cp)->as_C_string(),
 436                          fi->signature(_cp)->as_C_string(),
 437                          b->size(),
 438                          b->alignment(),
 439                          "REGULAR");
 440         break;
 441       }
 442       case LayoutRawBlock::FLATTENED: {
 443         FieldInfo* fi = FieldInfo::from_field_array(_fields, b->field_index());
 444         output->print_cr(" @%d \"%s\" %s %d/%d %s",
 445                          b->offset(),
 446                          fi->name(_cp)->as_C_string(),
 447                          fi->signature(_cp)->as_C_string(),
 448                          b->size(),
 449                          b->alignment(),
 450                          "FLATTENED");
 451         break;
 452       }
 453       case LayoutRawBlock::RESERVED: {
 454         output->print_cr(" @%d %d/- %s",
 455                          b->offset(),
 456                          b->size(),
 457                          "RESERVED");
 458         break;
 459       }
 460       case LayoutRawBlock::INHERITED: {
 461         assert(!is_static, "Static fields are not inherited in layouts");
 462         assert(super != NULL, "super klass must be provided to retrieve inherited fields info");
 463         bool found = false;
 464         const InstanceKlass* ik = super;
 465         while (!found && ik != NULL) {
 466           for (AllFieldStream fs(ik->fields(), ik->constants()); !fs.done(); fs.next()) {
 467             if (fs.offset() == b->offset()) {
 468               output->print_cr(" @%d \"%s\" %s %d/%d %s",
 469                   b->offset(),
 470                   fs.name()->as_C_string(),
 471                   fs.signature()->as_C_string(),
 472                   b->size(),
 473                   b->size(), // so far, alignment constraint == size, will change with Valhalla
 474                   "INHERITED");
 475               found = true;
 476               break;
 477             }
 478           }
 479           ik = ik->java_super();
 480         }
 481         break;
 482       }
 483       case LayoutRawBlock::EMPTY:
 484         output->print_cr(" @%d %d/1 %s",
 485                          b->offset(),
 486                          b->size(),
 487                         "EMPTY");
 488         break;
 489       case LayoutRawBlock::PADDING:
 490         output->print_cr(" @%d %d/1 %s",
 491                          b->offset(),
 492                          b->size(),
 493                         "PADDING");
 494         break;
 495     }
 496     b = b->next_block();
 497   }
 498 }
 499 
 500 FieldLayoutBuilder::FieldLayoutBuilder(const Symbol* classname, const InstanceKlass* super_klass, ConstantPool* constant_pool,
 501       Array<u2>* fields, bool is_contended, FieldLayoutInfo* info) :
 502   _classname(classname),
 503   _super_klass(super_klass),
 504   _constant_pool(constant_pool),
 505   _fields(fields),
 506   _info(info),
 507   _root_group(NULL),
 508   _contended_groups(GrowableArray<FieldGroup*>(8)),
 509   _static_fields(NULL),
 510   _layout(NULL),
 511   _static_layout(NULL),
 512   _nonstatic_oopmap_count(0),
 513   _alignment(-1),
 514   _has_nonstatic_fields(false),
 515   _is_contended(is_contended) {}
 516 
 517 
 518 FieldGroup* FieldLayoutBuilder::get_or_create_contended_group(int g) {
 519   assert(g > 0, "must only be called for named contended groups");
 520   FieldGroup* fg = NULL;
 521   for (int i = 0; i < _contended_groups.length(); i++) {
 522     fg = _contended_groups.at(i);
 523     if (fg->contended_group() == g) return fg;
 524   }
 525   fg = new FieldGroup(g);
 526   _contended_groups.append(fg);
 527   return fg;
 528 }
 529 
 530 void FieldLayoutBuilder::prologue() {
 531   _layout = new FieldLayout(_fields, _constant_pool);
 532   const InstanceKlass* super_klass = _super_klass;
 533   _layout->initialize_instance_layout(super_klass);
 534   if (super_klass != NULL) {
 535     _has_nonstatic_fields = super_klass->has_nonstatic_fields();
 536   }
 537   _static_layout = new FieldLayout(_fields, _constant_pool);
 538   _static_layout->initialize_static_layout();
 539   _static_fields = new FieldGroup();
 540   _root_group = new FieldGroup();
 541 }
 542 
 543 // Field sorting for regular classes:
 544 //   - fields are sorted in static and non-static fields
 545 //   - non-static fields are also sorted according to their contention group
 546 //     (support of the @Contended annotation)
 547 //   - @Contended annotation is ignored for static fields
 548 void FieldLayoutBuilder::regular_field_sorting() {
 549   for (AllFieldStream fs(_fields, _constant_pool); !fs.done(); fs.next()) {
 550     FieldGroup* group = NULL;
 551     if (fs.access_flags().is_static()) {
 552       group = _static_fields;
 553     } else {
 554       _has_nonstatic_fields = true;
 555       if (fs.is_contended()) {
 556         int g = fs.contended_group();
 557         if (g == 0) {
 558           group = new FieldGroup(true);
 559           _contended_groups.append(group);
 560         } else {
 561           group = get_or_create_contended_group(g);
 562         }
 563       } else {
 564         group = _root_group;
 565       }
 566     }
 567     assert(group != NULL, "invariant");
 568     BasicType type = Signature::basic_type(fs.signature());
 569     switch(type) {
 570       case T_BYTE:
 571       case T_CHAR:
 572       case T_DOUBLE:
 573       case T_FLOAT:
 574       case T_INT:
 575       case T_LONG:
 576       case T_SHORT:
 577       case T_BOOLEAN:
 578         group->add_primitive_field(fs, type);
 579         break;
 580       case T_OBJECT:
 581       case T_ARRAY:
 582         if (group != _static_fields) _nonstatic_oopmap_count++;
 583         group->add_oop_field(fs);
 584         break;
 585       default:
 586         fatal("Something wrong?");
 587     }
 588   }
 589   _root_group->sort_by_size();
 590   _static_fields->sort_by_size();
 591   if (!_contended_groups.is_empty()) {
 592     for (int i = 0; i < _contended_groups.length(); i++) {
 593       _contended_groups.at(i)->sort_by_size();
 594     }
 595   }
 596 }
 597 
 598 void FieldLayoutBuilder::insert_contended_padding(LayoutRawBlock* slot) {
 599   if (ContendedPaddingWidth > 0) {
 600     LayoutRawBlock* padding = new LayoutRawBlock(LayoutRawBlock::PADDING, ContendedPaddingWidth);
 601     _layout->insert(slot, padding);
 602   }
 603 }
 604 
 605 // Computation of regular classes layout is an evolution of the previous default layout
 606 // (FieldAllocationStyle 1):
 607 //   - primitive fields are allocated first (from the biggest to the smallest)
 608 //   - then oop fields are allocated, either in existing gaps or at the end of
 609 //     the layout
 610 void FieldLayoutBuilder::compute_regular_layout() {
 611   bool need_tail_padding = false;
 612   prologue();
 613   regular_field_sorting();
 614 
 615   if (_is_contended) {
 616     _layout->set_start(_layout->last_block());
 617     // insertion is currently easy because the current strategy doesn't try to fill holes
 618     // in super classes layouts => the _start block is by consequence the _last_block
 619     insert_contended_padding(_layout->start());
 620     need_tail_padding = true;
 621   }
 622   _layout->add(_root_group->primitive_fields());
 623   _layout->add(_root_group->oop_fields());
 624 
 625   if (!_contended_groups.is_empty()) {
 626     for (int i = 0; i < _contended_groups.length(); i++) {
 627       FieldGroup* cg = _contended_groups.at(i);
 628       LayoutRawBlock* start = _layout->last_block();
 629       insert_contended_padding(start);
 630       _layout->add(cg->primitive_fields(), start);
 631       _layout->add(cg->oop_fields(), start);
 632       need_tail_padding = true;
 633     }
 634   }
 635 
 636   if (need_tail_padding) {
 637     insert_contended_padding(_layout->last_block());
 638   }
 639 
 640   _static_layout->add_contiguously(this->_static_fields->oop_fields());
 641   _static_layout->add(this->_static_fields->primitive_fields());
 642 
 643   epilogue();
 644 }
 645 
 646 // Compute layout of the java/lang/ref/Reference class according
 647 // to the hard coded offsets of its fields
 648 void FieldLayoutBuilder::compute_java_lang_ref_Reference_layout() {
 649   prologue();
 650   regular_field_sorting();
 651 
 652   assert(_contended_groups.is_empty(), "java.lang.Reference has no @Contended annotations");
 653   assert(_root_group->primitive_fields() == NULL, "java.lang.Reference has no nonstatic primitive fields");
 654   int field_count = 0;
 655   int offset = -1;
 656   for (int i = 0; i < _root_group->oop_fields()->length(); i++) {
 657     LayoutRawBlock* b = _root_group->oop_fields()->at(i);
 658     FieldInfo* fi = FieldInfo::from_field_array(_fields, b->field_index());
 659     if (fi->name(_constant_pool)->equals("referent")) {
 660       offset = java_lang_ref_Reference::referent_offset;
 661     } else if (fi->name(_constant_pool)->equals("queue")) {
 662       offset = java_lang_ref_Reference::queue_offset;
 663     } else if (fi->name(_constant_pool)->equals("next")) {
 664       offset = java_lang_ref_Reference::next_offset;
 665     } else if (fi->name(_constant_pool)->equals("discovered")) {
 666       offset = java_lang_ref_Reference::discovered_offset;
 667     }
 668     assert(offset != -1, "Unknown field");
 669     _layout->add_field_at_offset(b, offset);
 670     field_count++;
 671   }
 672   assert(field_count == 4, "Wrong number of fields in java.lang.ref.Reference");
 673 
 674   _static_layout->add_contiguously(this->_static_fields->oop_fields());
 675   _static_layout->add(this->_static_fields->primitive_fields());
 676 
 677   epilogue();
 678 }
 679 
 680 // Compute layout of the boxing class according
 681 // to the hard coded offsets of their fields
 682 void FieldLayoutBuilder::compute_boxing_class_layout() {
 683   prologue();
 684   regular_field_sorting();
 685 
 686   assert(_contended_groups.is_empty(), "Boxing classes have no @Contended annotations");
 687   assert(_root_group->oop_fields() == NULL, "Boxing classes have no nonstatic oops fields");
 688   int field_count = 0;
 689   int offset = -1;
 690 
 691   for (int i = 0; i < _root_group->primitive_fields()->length(); i++) {
 692     LayoutRawBlock* b = _root_group->primitive_fields()->at(i);
 693     FieldInfo* fi = FieldInfo::from_field_array(_fields, b->field_index());
 694     assert(fi->name(_constant_pool)->equals("value"), "Boxing classes have a single nonstatic field named 'value'");
 695     BasicType type = Signature::basic_type(fi->signature(_constant_pool));
 696     offset = java_lang_boxing_object::value_offset_in_bytes(type);
 697     assert(offset != -1, "Unknown field");
 698     _layout->add_field_at_offset(b, offset);
 699     field_count++;
 700   }
 701   assert(field_count == 1, "Wrong number of fields for a boxing class");
 702 
 703   _static_layout->add_contiguously(this->_static_fields->oop_fields());
 704   _static_layout->add(this->_static_fields->primitive_fields());
 705 
 706   epilogue();
 707 }
 708 
 709 void FieldLayoutBuilder::epilogue() {
 710   // Computing oopmaps
 711   int super_oop_map_count = (_super_klass == NULL) ? 0 :_super_klass->nonstatic_oop_map_count();
 712   int max_oop_map_count = super_oop_map_count + _nonstatic_oopmap_count;
 713 
 714   OopMapBlocksBuilder* nonstatic_oop_maps =
 715       new OopMapBlocksBuilder(max_oop_map_count);
 716   if (super_oop_map_count > 0) {
 717     nonstatic_oop_maps->initialize_inherited_blocks(_super_klass->start_of_nonstatic_oop_maps(),
 718     _super_klass->nonstatic_oop_map_count());
 719   }
 720 
 721   if (_root_group->oop_fields() != NULL) {
 722     for (int i = 0; i < _root_group->oop_fields()->length(); i++) {
 723       LayoutRawBlock* b = _root_group->oop_fields()->at(i);
 724       nonstatic_oop_maps->add(b->offset(), 1);
 725     }
 726   }
 727 
 728   if (!_contended_groups.is_empty()) {
 729     for (int i = 0; i < _contended_groups.length(); i++) {
 730       FieldGroup* cg = _contended_groups.at(i);
 731       if (cg->oop_count() > 0) {
 732         assert(cg->oop_fields() != NULL && cg->oop_fields()->at(0) != NULL, "oop_count > 0 but no oop fields found");
 733         nonstatic_oop_maps->add(cg->oop_fields()->at(0)->offset(), cg->oop_count());
 734       }
 735     }
 736   }
 737 
 738   nonstatic_oop_maps->compact();
 739 
 740   int instance_end = align_up(_layout->last_block()->offset(), wordSize);
 741   int static_fields_end = align_up(_static_layout->last_block()->offset(), wordSize);
 742   int static_fields_size = (static_fields_end -
 743       InstanceMirrorKlass::offset_of_static_fields()) / wordSize;
 744   int nonstatic_field_end = align_up(_layout->last_block()->offset(), heapOopSize);
 745 
 746   // Pass back information needed for InstanceKlass creation
 747 
 748   _info->oop_map_blocks = nonstatic_oop_maps;
 749   _info->_instance_size = align_object_size(instance_end / wordSize);
 750   _info->_static_field_size = static_fields_size;
 751   _info->_nonstatic_field_size = (nonstatic_field_end - instanceOopDesc::base_offset_in_bytes()) / heapOopSize;
 752   _info->_has_nonstatic_fields = _has_nonstatic_fields;
 753 
 754   if (PrintFieldLayout) {
 755     ResourceMark rm;
 756     tty->print_cr("Layout of class %s", _classname->as_C_string());
 757     tty->print_cr("Instance fields:");
 758     _layout->print(tty, false, _super_klass);
 759     tty->print_cr("Static fields:");
 760     _static_layout->print(tty, true, NULL);
 761     tty->print_cr("Instance size = %d bytes", _info->_instance_size * wordSize);
 762     tty->print_cr("---");
 763   }
 764 }
 765 
 766 void FieldLayoutBuilder::build_layout() {
 767   if (_classname == vmSymbols::java_lang_ref_Reference()) {
 768     compute_java_lang_ref_Reference_layout();
 769   } else if (_classname == vmSymbols::java_lang_Boolean() ||
 770              _classname == vmSymbols::java_lang_Character() ||
 771              _classname == vmSymbols::java_lang_Float() ||
 772              _classname == vmSymbols::java_lang_Double() ||
 773              _classname == vmSymbols::java_lang_Byte() ||
 774              _classname == vmSymbols::java_lang_Short() ||
 775              _classname == vmSymbols::java_lang_Integer() ||
 776              _classname == vmSymbols::java_lang_Long()) {
 777     compute_boxing_class_layout();
 778   } else {
 779     compute_regular_layout();
 780   }
 781 }
 782