1 /*
  2  * Copyright (c) 2020, 2025, 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 "classfile/classFileParser.hpp"
 26 #include "classfile/fieldLayoutBuilder.hpp"
 27 #include "jvm.h"
 28 #include "memory/resourceArea.hpp"
 29 #include "oops/array.hpp"
 30 #include "oops/fieldStreams.inline.hpp"
 31 #include "oops/instanceMirrorKlass.hpp"
 32 #include "oops/instanceKlass.inline.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(nullptr),
 39   _prev_block(nullptr),
 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(nullptr),
 54  _prev_block(nullptr),
 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(nullptr),
 77   _primitive_fields(nullptr),
 78   _oop_fields(nullptr),
 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(int idx, BasicType type) {
 83   int size = type2aelembytes(type);
 84   LayoutRawBlock* block = new LayoutRawBlock(idx, LayoutRawBlock::REGULAR, size, size /* alignment == size for primitive types */, false);
 85   if (_primitive_fields == nullptr) {
 86     _primitive_fields = new GrowableArray<LayoutRawBlock*>(INITIAL_LIST_SIZE);
 87   }
 88   _primitive_fields->append(block);
 89 }
 90 
 91 void FieldGroup::add_oop_field(int idx) {
 92   int size = type2aelembytes(T_OBJECT);
 93   LayoutRawBlock* block = new LayoutRawBlock(idx, LayoutRawBlock::REGULAR, size, size /* alignment == size for oops */, true);
 94   if (_oop_fields == nullptr) {
 95     _oop_fields = new 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 != nullptr) {
103     _primitive_fields->sort(LayoutRawBlock::compare_size_inverted);
104   }
105 }
106 
107 FieldLayout::FieldLayout(GrowableArray<FieldInfo>* field_info, ConstantPool* cp) :
108   _field_info(field_info),
109   _cp(cp),
110   _blocks(nullptr),
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 == nullptr) {
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 (!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 == nullptr) return;
164   if (start == nullptr) 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 = nullptr;
171     LayoutRawBlock* candidate = nullptr;
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 != nullptr, "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 == nullptr || cursor->size() < candidate->size()) {
193             candidate = cursor;
194           }
195         }
196         cursor = cursor->prev_block();
197       }
198       if (candidate == nullptr) {
199         candidate = last_block();
200         last_search_success = false;
201       }
202       assert(candidate != nullptr, "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 != nullptr, "Sanity check");
214   block->set_offset(offset);
215   if (start == nullptr) {
216     start = this->_start;
217   }
218   LayoutRawBlock* slot = start;
219   while (slot != nullptr) {
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       _field_info->adr_at(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 == nullptr) return;
246   if (start == nullptr) {
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 = nullptr;
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 != nullptr, "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   _field_info->adr_at(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 != nullptr) {
300     for (AllFieldStream fs(ik->fieldinfo_stream(), 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() == nullptr ? nullptr : 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 != nullptr, "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() != nullptr) {
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() == nullptr, "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   LayoutRawBlock* last = new LayoutRawBlock(LayoutRawBlock::EMPTY, INT_MAX);
367   last->set_offset(b->offset() + b->size());
368   assert(last->offset() > 0, "Sanity check");
369   b->set_next_block(last);
370   last->set_prev_block(b);
371   _last = last;
372 }
373 
374 LayoutRawBlock* FieldLayout::insert(LayoutRawBlock* slot, LayoutRawBlock* block) {
375   assert(slot->kind() == LayoutRawBlock::EMPTY, "Blocks can only be inserted in empty blocks");
376   assert(slot->offset() % block->alignment() == 0, "Incompatible alignment");
377   block->set_offset(slot->offset());
378   slot->set_offset(slot->offset() + block->size());
379   assert((slot->size() - block->size()) < slot->size(), "underflow checking");
380   assert(slot->size() - block->size() >= 0, "no negative size allowed");
381   slot->set_size(slot->size() - block->size());
382   block->set_prev_block(slot->prev_block());
383   block->set_next_block(slot);
384   slot->set_prev_block(block);
385   if (block->prev_block() != nullptr) {
386     block->prev_block()->set_next_block(block);
387   }
388   if (_blocks == slot) {
389     _blocks = block;
390   }
391   return block;
392 }
393 
394 void FieldLayout::remove(LayoutRawBlock* block) {
395   assert(block != nullptr, "Sanity check");
396   assert(block != _last, "Sanity check");
397   if (_blocks == block) {
398     _blocks = block->next_block();
399     if (_blocks != nullptr) {
400       _blocks->set_prev_block(nullptr);
401     }
402   } else {
403     assert(block->prev_block() != nullptr, "_prev should be set for non-head blocks");
404     block->prev_block()->set_next_block(block->next_block());
405     block->next_block()->set_prev_block(block->prev_block());
406   }
407   if (block == _start) {
408     _start = block->prev_block();
409   }
410 }
411 
412 void FieldLayout::print(outputStream* output, bool is_static, const InstanceKlass* super) {
413   ResourceMark rm;
414   LayoutRawBlock* b = _blocks;
415   while(b != _last) {
416     switch(b->kind()) {
417       case LayoutRawBlock::REGULAR: {
418         FieldInfo* fi = _field_info->adr_at(b->field_index());
419         output->print_cr(" @%d \"%s\" %s %d/%d %s",
420                          b->offset(),
421                          fi->name(_cp)->as_C_string(),
422                          fi->signature(_cp)->as_C_string(),
423                          b->size(),
424                          b->alignment(),
425                          "REGULAR");
426         break;
427       }
428       case LayoutRawBlock::FLATTENED: {
429         FieldInfo* fi = _field_info->adr_at(b->field_index());
430         output->print_cr(" @%d \"%s\" %s %d/%d %s",
431                          b->offset(),
432                          fi->name(_cp)->as_C_string(),
433                          fi->signature(_cp)->as_C_string(),
434                          b->size(),
435                          b->alignment(),
436                          "FLATTENED");
437         break;
438       }
439       case LayoutRawBlock::RESERVED: {
440         output->print_cr(" @%d %d/- %s",
441                          b->offset(),
442                          b->size(),
443                          "RESERVED");
444         break;
445       }
446       case LayoutRawBlock::INHERITED: {
447         assert(!is_static, "Static fields are not inherited in layouts");
448         assert(super != nullptr, "super klass must be provided to retrieve inherited fields info");
449         bool found = false;
450         const InstanceKlass* ik = super;
451         while (!found && ik != nullptr) {
452           for (AllFieldStream fs(ik->fieldinfo_stream(), ik->constants()); !fs.done(); fs.next()) {
453             if (fs.offset() == b->offset()) {
454               output->print_cr(" @%d \"%s\" %s %d/%d %s",
455                   b->offset(),
456                   fs.name()->as_C_string(),
457                   fs.signature()->as_C_string(),
458                   b->size(),
459                   b->size(), // so far, alignment constraint == size, will change with Valhalla
460                   "INHERITED");
461               found = true;
462               break;
463             }
464           }
465           ik = ik->java_super();
466         }
467         break;
468       }
469       case LayoutRawBlock::EMPTY:
470         output->print_cr(" @%d %d/1 %s",
471                          b->offset(),
472                          b->size(),
473                         "EMPTY");
474         break;
475       case LayoutRawBlock::PADDING:
476         output->print_cr(" @%d %d/1 %s",
477                          b->offset(),
478                          b->size(),
479                         "PADDING");
480         break;
481     }
482     b = b->next_block();
483   }
484 }
485 
486 FieldLayoutBuilder::FieldLayoutBuilder(const Symbol* classname, const InstanceKlass* super_klass, ConstantPool* constant_pool,
487       GrowableArray<FieldInfo>* field_info, bool is_contended, FieldLayoutInfo* info) :
488   _classname(classname),
489   _super_klass(super_klass),
490   _constant_pool(constant_pool),
491   _field_info(field_info),
492   _info(info),
493   _root_group(nullptr),
494   _contended_groups(GrowableArray<FieldGroup*>(8)),
495   _static_fields(nullptr),
496   _layout(nullptr),
497   _static_layout(nullptr),
498   _nonstatic_oopmap_count(0),
499   _alignment(-1),
500   _has_nonstatic_fields(false),
501   _is_contended(is_contended) {}
502 
503 
504 FieldGroup* FieldLayoutBuilder::get_or_create_contended_group(int g) {
505   assert(g > 0, "must only be called for named contended groups");
506   FieldGroup* fg = nullptr;
507   for (int i = 0; i < _contended_groups.length(); i++) {
508     fg = _contended_groups.at(i);
509     if (fg->contended_group() == g) return fg;
510   }
511   fg = new FieldGroup(g);
512   _contended_groups.append(fg);
513   return fg;
514 }
515 
516 void FieldLayoutBuilder::prologue() {
517   _layout = new FieldLayout(_field_info, _constant_pool);
518   const InstanceKlass* super_klass = _super_klass;
519   _layout->initialize_instance_layout(super_klass);
520   if (super_klass != nullptr) {
521     _has_nonstatic_fields = super_klass->has_nonstatic_fields();
522   }
523   _static_layout = new FieldLayout(_field_info, _constant_pool);
524   _static_layout->initialize_static_layout();
525   _static_fields = new FieldGroup();
526   _root_group = new FieldGroup();
527 }
528 
529 // Field sorting for regular classes:
530 //   - fields are sorted in static and non-static fields
531 //   - non-static fields are also sorted according to their contention group
532 //     (support of the @Contended annotation)
533 //   - @Contended annotation is ignored for static fields
534 void FieldLayoutBuilder::regular_field_sorting() {
535   int idx = 0;
536   for (GrowableArrayIterator<FieldInfo> it = _field_info->begin(); it != _field_info->end(); ++it, ++idx) {
537     FieldInfo ctrl = _field_info->at(0);
538     FieldGroup* group = nullptr;
539     FieldInfo fieldinfo = *it;
540     if (fieldinfo.access_flags().is_static()) {
541       group = _static_fields;
542     } else {
543       _has_nonstatic_fields = true;
544       if (fieldinfo.field_flags().is_contended()) {
545         int g = fieldinfo.contended_group();
546         if (g == 0) {
547           group = new FieldGroup(true);
548           _contended_groups.append(group);
549         } else {
550           group = get_or_create_contended_group(g);
551         }
552       } else {
553         group = _root_group;
554       }
555     }
556     assert(group != nullptr, "invariant");
557     BasicType type = Signature::basic_type(fieldinfo.signature(_constant_pool));
558     switch(type) {
559       case T_BYTE:
560       case T_CHAR:
561       case T_DOUBLE:
562       case T_FLOAT:
563       case T_INT:
564       case T_LONG:
565       case T_SHORT:
566       case T_BOOLEAN:
567         group->add_primitive_field(idx, type);
568         break;
569       case T_OBJECT:
570       case T_ARRAY:
571         if (group != _static_fields) _nonstatic_oopmap_count++;
572         group->add_oop_field(idx);
573         break;
574       default:
575         fatal("Something wrong?");
576     }
577   }
578   _root_group->sort_by_size();
579   _static_fields->sort_by_size();
580   if (!_contended_groups.is_empty()) {
581     for (int i = 0; i < _contended_groups.length(); i++) {
582       _contended_groups.at(i)->sort_by_size();
583     }
584   }
585 }
586 
587 void FieldLayoutBuilder::insert_contended_padding(LayoutRawBlock* slot) {
588   if (ContendedPaddingWidth > 0) {
589     LayoutRawBlock* padding = new LayoutRawBlock(LayoutRawBlock::PADDING, ContendedPaddingWidth);
590     _layout->insert(slot, padding);
591   }
592 }
593 
594 // Computation of regular classes layout is an evolution of the previous default layout
595 // (FieldAllocationStyle 1):
596 //   - primitive fields are allocated first (from the biggest to the smallest)
597 //   - then oop fields are allocated, either in existing gaps or at the end of
598 //     the layout
599 void FieldLayoutBuilder::compute_regular_layout() {
600   bool need_tail_padding = false;
601   prologue();
602   regular_field_sorting();
603 
604   if (_is_contended) {
605     _layout->set_start(_layout->last_block());
606     // insertion is currently easy because the current strategy doesn't try to fill holes
607     // in super classes layouts => the _start block is by consequence the _last_block
608     insert_contended_padding(_layout->start());
609     need_tail_padding = true;
610   }
611   _layout->add(_root_group->primitive_fields());
612   _layout->add(_root_group->oop_fields());
613 
614   if (!_contended_groups.is_empty()) {
615     for (int i = 0; i < _contended_groups.length(); i++) {
616       FieldGroup* cg = _contended_groups.at(i);
617       LayoutRawBlock* start = _layout->last_block();
618       insert_contended_padding(start);
619       _layout->add(cg->primitive_fields(), start);
620       _layout->add(cg->oop_fields(), start);
621       need_tail_padding = true;
622     }
623   }
624 
625   if (need_tail_padding) {
626     insert_contended_padding(_layout->last_block());
627   }
628 
629   _static_layout->add_contiguously(this->_static_fields->oop_fields());
630   _static_layout->add(this->_static_fields->primitive_fields());
631 
632   epilogue();
633 }
634 
635 void FieldLayoutBuilder::epilogue() {
636   // Computing oopmaps
637   int super_oop_map_count = (_super_klass == nullptr) ? 0 :_super_klass->nonstatic_oop_map_count();
638   int max_oop_map_count = super_oop_map_count + _nonstatic_oopmap_count;
639 
640   OopMapBlocksBuilder* nonstatic_oop_maps =
641       new OopMapBlocksBuilder(max_oop_map_count);
642   if (super_oop_map_count > 0) {
643     nonstatic_oop_maps->initialize_inherited_blocks(_super_klass->start_of_nonstatic_oop_maps(),
644     _super_klass->nonstatic_oop_map_count());
645   }
646 
647   if (_root_group->oop_fields() != nullptr) {
648     for (int i = 0; i < _root_group->oop_fields()->length(); i++) {
649       LayoutRawBlock* b = _root_group->oop_fields()->at(i);
650       nonstatic_oop_maps->add(b->offset(), 1);
651     }
652   }
653 
654   if (!_contended_groups.is_empty()) {
655     for (int i = 0; i < _contended_groups.length(); i++) {
656       FieldGroup* cg = _contended_groups.at(i);
657       if (cg->oop_count() > 0) {
658         assert(cg->oop_fields() != nullptr && cg->oop_fields()->at(0) != nullptr, "oop_count > 0 but no oop fields found");
659         nonstatic_oop_maps->add(cg->oop_fields()->at(0)->offset(), cg->oop_count());
660       }
661     }
662   }
663 
664   nonstatic_oop_maps->compact();
665 
666   int instance_end = align_up(_layout->last_block()->offset(), wordSize);
667   int static_fields_end = align_up(_static_layout->last_block()->offset(), wordSize);
668   int static_fields_size = (static_fields_end -
669       InstanceMirrorKlass::offset_of_static_fields()) / wordSize;
670   int nonstatic_field_end = align_up(_layout->last_block()->offset(), heapOopSize);
671 
672   // Pass back information needed for InstanceKlass creation
673 
674   _info->oop_map_blocks = nonstatic_oop_maps;
675   _info->_instance_size = align_object_size(instance_end / wordSize);
676   _info->_static_field_size = static_fields_size;
677   _info->_nonstatic_field_size = (nonstatic_field_end - instanceOopDesc::base_offset_in_bytes()) / heapOopSize;
678   _info->_has_nonstatic_fields = _has_nonstatic_fields;
679 
680   if (PrintFieldLayout) {
681     ResourceMark rm;
682     tty->print_cr("Layout of class %s", _classname->as_C_string());
683     tty->print_cr("Instance fields:");
684     _layout->print(tty, false, _super_klass);
685     tty->print_cr("Static fields:");
686     _static_layout->print(tty, true, nullptr);
687     tty->print_cr("Instance size = %d bytes", _info->_instance_size * wordSize);
688     tty->print_cr("---");
689   }
690 }
691 
692 void FieldLayoutBuilder::build_layout() {
693   compute_regular_layout();
694 }