summaryrefslogtreecommitdiff
path: root/js/src/vm/Shape.h
blob: 85bc044a55262694892f7db6142b659ffc2f7932 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef vm_Shape_h
#define vm_Shape_h

#include "mozilla/Attributes.h"
#include "mozilla/GuardObjects.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Maybe.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/TemplateLib.h"

#include "jsapi.h"
#include "jsfriendapi.h"
#include "jspropertytree.h"
#include "jstypes.h"
#include "NamespaceImports.h"

#include "gc/Barrier.h"
#include "gc/Heap.h"
#include "gc/Marking.h"
#include "gc/Rooting.h"
#include "js/HashTable.h"
#include "js/MemoryMetrics.h"
#include "js/RootingAPI.h"
#include "js/UbiNode.h"
#include "vm/ObjectGroup.h"
#include "vm/String.h"
#include "vm/Symbol.h"

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4800)
#pragma warning(push)
#pragma warning(disable:4100) /* Silence unreferenced formal parameter warnings */
#endif

/*
 * In isolation, a Shape represents a property that exists in one or more
 * objects; it has an id, flags, etc. (But it doesn't represent the property's
 * value.)  However, Shapes are always stored in linked linear sequence of
 * Shapes, called "shape lineages". Each shape lineage represents the layout of
 * an entire object.
 *
 * Every JSObject has a pointer, |shape_|, accessible via lastProperty(), to
 * the last Shape in a shape lineage, which identifies the property most
 * recently added to the object.  This pointer permits fast object layout
 * tests. The shape lineage order also dictates the enumeration order for the
 * object; ECMA requires no particular order but this implementation has
 * promised and delivered property definition order.
 *
 * Shape lineages occur in two kinds of data structure.
 *
 * 1. N-ary property trees. Each path from a non-root node to the root node in
 *    a property tree is a shape lineage. Property trees permit full (or
 *    partial) sharing of Shapes between objects that have fully (or partly)
 *    identical layouts. The root is an EmptyShape whose identity is determined
 *    by the object's class, compartment and prototype. These Shapes are shared
 *    and immutable.
 *
 * 2. Dictionary mode lists. Shapes in such lists are said to be "in
 *    dictionary mode", as are objects that point to such Shapes. These Shapes
 *    are unshared, private to a single object, and immutable except for their
 *    links in the dictionary list.
 *
 * All shape lineages are bi-directionally linked, via the |parent| and
 * |kids|/|listp| members.
 *
 * Shape lineages start out life in the property tree. They can be converted
 * (by copying) to dictionary mode lists in the following circumstances.
 *
 * 1. The shape lineage's size reaches MAX_HEIGHT. This reasonable limit avoids
 *    potential worst cases involving shape lineage mutations.
 *
 * 2. A property represented by a non-last Shape in a shape lineage is removed
 *    from an object. (In the last Shape case, obj->shape_ can be easily
 *    adjusted to point to obj->shape_->parent.)  We originally tried lazy
 *    forking of the property tree, but this blows up for delete/add
 *    repetitions.
 *
 * 3. A property represented by a non-last Shape in a shape lineage has its
 *    attributes modified.
 *
 * To find the Shape for a particular property of an object initially requires
 * a linear search. But if the number of searches starting at any particular
 * Shape in the property tree exceeds LINEAR_SEARCHES_MAX and the Shape's
 * lineage has (excluding the EmptyShape) at least MIN_ENTRIES, we create an
 * auxiliary hash table -- the ShapeTable -- that allows faster lookup.
 * Furthermore, a ShapeTable is always created for dictionary mode lists,
 * and it is attached to the last Shape in the lineage. Shape tables for
 * property tree Shapes never change, but shape tables for dictionary mode
 * Shapes can grow and shrink.
 *
 * To save memory, shape tables can be discarded on GC and recreated when
 * needed. AutoKeepShapeTables can be used to avoid discarding shape tables
 * for a particular zone. Methods operating on ShapeTables take either an
 * AutoCheckCannotGC or AutoKeepShapeTables argument, to help ensure tables
 * are not purged while we're using them.
 *
 * There used to be a long, math-heavy comment here explaining why property
 * trees are more space-efficient than alternatives.  This was removed in bug
 * 631138; see that bug for the full details.
 *
 * For getters/setters, an AccessorShape is allocated. This is a slightly fatter
 * type with extra fields for the getter/setter data.
 *
 * Because many Shapes have similar data, there is actually a secondary type
 * called a BaseShape that holds some of a Shape's data.  Many shapes can share
 * a single BaseShape.
 */

#define JSSLOT_FREE(clasp)  JSCLASS_RESERVED_SLOTS(clasp)

namespace js {

class TenuringTracer;

typedef JSGetterOp GetterOp;
typedef JSSetterOp SetterOp;

/* Limit on the number of slotful properties in an object. */
static const uint32_t SHAPE_INVALID_SLOT = JS_BIT(24) - 1;
static const uint32_t SHAPE_MAXIMUM_SLOT = JS_BIT(24) - 2;

enum class MaybeAdding { Adding = true, NotAdding = false };

class AutoKeepShapeTables;

/*
 * Shapes use multiplicative hashing, but specialized to
 * minimize footprint.
 */
class ShapeTable {
  public:
    friend class NativeObject;
    friend class BaseShape;
    static const uint32_t MIN_ENTRIES   = 11;

    class Entry {
        // js::Shape pointer tag bit indicating a collision.
        static const uintptr_t SHAPE_COLLISION = 1;
        static Shape* const SHAPE_REMOVED; // = SHAPE_COLLISION

        Shape* shape_;

        Entry() = delete;
        Entry(const Entry&) = delete;
        Entry& operator=(const Entry&) = delete;

      public:
        bool isFree() const { return shape_ == nullptr; }
        bool isRemoved() const { return shape_ == SHAPE_REMOVED; }
        bool isLive() const { return !isFree() && !isRemoved(); }
        bool hadCollision() const { return uintptr_t(shape_) & SHAPE_COLLISION; }

        void setFree() { shape_ = nullptr; }
        void setRemoved() { shape_ = SHAPE_REMOVED; }

        Shape* shape() const {
            return reinterpret_cast<Shape*>(uintptr_t(shape_) & ~SHAPE_COLLISION);
        }

        void setShape(Shape* shape) {
            MOZ_ASSERT(isFree());
            MOZ_ASSERT(shape);
            MOZ_ASSERT(shape != SHAPE_REMOVED);
            shape_ = shape;
            MOZ_ASSERT(!hadCollision());
        }

        void flagCollision() {
            shape_ = reinterpret_cast<Shape*>(uintptr_t(shape_) | SHAPE_COLLISION);
        }
        void setPreservingCollision(Shape* shape) {
            shape_ = reinterpret_cast<Shape*>(uintptr_t(shape) | uintptr_t(hadCollision()));
        }
    };

  private:
    static const uint32_t HASH_BITS     = mozilla::tl::BitSize<HashNumber>::value;

    // This value is low because it's common for a ShapeTable to be created
    // with an entryCount of zero.
    static const uint32_t MIN_SIZE_LOG2 = 2;
    static const uint32_t MIN_SIZE      = JS_BIT(MIN_SIZE_LOG2);

    uint32_t        hashShift_;         /* multiplicative hash shift */

    uint32_t        entryCount_;        /* number of entries in table */
    uint32_t        removedCount_;      /* removed entry sentinels in table */

    uint32_t        freeList_;          /* SHAPE_INVALID_SLOT or head of slot
                                           freelist in owning dictionary-mode
                                           object */

    Entry*          entries_;          /* table of ptrs to shared tree nodes */

    template<MaybeAdding Adding>
    Entry& searchUnchecked(jsid id);

  public:
    explicit ShapeTable(uint32_t nentries)
      : hashShift_(HASH_BITS - MIN_SIZE_LOG2),
        entryCount_(nentries),
        removedCount_(0),
        freeList_(SHAPE_INVALID_SLOT),
        entries_(nullptr)
    {
        /* NB: entries is set by init, which must be called. */
    }

    ~ShapeTable() {
        js_free(entries_);
    }

    uint32_t entryCount() const { return entryCount_; }

    uint32_t freeList() const { return freeList_; }
    void setFreeList(uint32_t slot) { freeList_ = slot; }

    /*
     * This counts the ShapeTable object itself (which must be
     * heap-allocated) and its |entries| array.
     */
    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return mallocSizeOf(this) + mallocSizeOf(entries_);
    }

    // init() is fallible and reports OOM to the context.
    bool init(ExclusiveContext* cx, Shape* lastProp);

    // change() is fallible but does not report OOM.
    bool change(ExclusiveContext* cx, int log2Delta);

    template<MaybeAdding Adding>
    MOZ_ALWAYS_INLINE Entry& search(jsid id, const AutoKeepShapeTables&) {
        return searchUnchecked<Adding>(id);
    }

    template<MaybeAdding Adding>
    MOZ_ALWAYS_INLINE Entry& search(jsid id, const JS::AutoCheckCannotGC&) {
        return searchUnchecked<Adding>(id);
    }

    void trace(JSTracer* trc);
#ifdef JSGC_HASH_TABLE_CHECKS
    void checkAfterMovingGC();
#endif

  private:
    Entry& getEntry(uint32_t i) const {
        MOZ_ASSERT(i < capacity());
        return entries_[i];
    }
    void decEntryCount() {
        MOZ_ASSERT(entryCount_ > 0);
        entryCount_--;
    }
    void incEntryCount() {
        entryCount_++;
        MOZ_ASSERT(entryCount_ + removedCount_ <= capacity());
    }
    void incRemovedCount() {
        removedCount_++;
        MOZ_ASSERT(entryCount_ + removedCount_ <= capacity());
    }

    /* By definition, hashShift = HASH_BITS - log2(capacity). */
    uint32_t capacity() const { return JS_BIT(HASH_BITS - hashShift_); }

    /* Whether we need to grow.  We want to do this if the load factor is >= 0.75 */
    bool needsToGrow() const {
        uint32_t size = capacity();
        return entryCount_ + removedCount_ >= size - (size >> 2);
    }

    /*
     * Try to grow the table.  On failure, reports out of memory on cx
     * and returns false.  This will make any extant pointers into the
     * table invalid.  Don't call this unless needsToGrow() is true.
     */
    bool grow(ExclusiveContext* cx);
};

// Ensures no shape tables are purged in the current zone.
class MOZ_RAII AutoKeepShapeTables
{
    ExclusiveContext* cx_;
    bool prev_;

    AutoKeepShapeTables(const AutoKeepShapeTables&) = delete;
    void operator=(const AutoKeepShapeTables&) = delete;

  public:
    explicit inline AutoKeepShapeTables(ExclusiveContext* cx);
    inline ~AutoKeepShapeTables();
};

/*
 * Use the reserved attribute bit to mean shadowability.
 */
#define JSPROP_SHADOWABLE       JSPROP_INTERNAL_USE_BIT

/*
 * Shapes encode information about both a property lineage *and* a particular
 * property. This information is split across the Shape and the BaseShape
 * at shape->base(). Both Shape and BaseShape can be either owned or unowned
 * by, respectively, the Object or Shape referring to them.
 *
 * Owned Shapes are used in dictionary objects, and form a doubly linked list
 * whose entries are all owned by that dictionary. Unowned Shapes are all in
 * the property tree.
 *
 * Owned BaseShapes are used for shapes which have shape tables, including the
 * last properties in all dictionaries. Unowned BaseShapes compactly store
 * information common to many shapes. In a given zone there is a single
 * BaseShape for each combination of BaseShape information. This information is
 * cloned in owned BaseShapes so that information can be quickly looked up for a
 * given object or shape without regard to whether the base shape is owned or
 * not.
 *
 * All combinations of owned/unowned Shapes/BaseShapes are possible:
 *
 * Owned Shape, Owned BaseShape:
 *
 *     Last property in a dictionary object. The BaseShape is transferred from
 *     property to property as the object's last property changes.
 *
 * Owned Shape, Unowned BaseShape:
 *
 *     Property in a dictionary object other than the last one.
 *
 * Unowned Shape, Owned BaseShape:
 *
 *     Property in the property tree which has a shape table.
 *
 * Unowned Shape, Unowned BaseShape:
 *
 *     Property in the property tree which does not have a shape table.
 *
 * BaseShapes additionally encode some information about the referring object
 * itself. This includes the object's class and various flags that may be set
 * for the object. Except for the class, this information is mutable and may
 * change when the object has an established property lineage. On such changes
 * the entire property lineage is not updated, but rather only the last property
 * (and its base shape). This works because only the object's last property is
 * used to query information about the object. Care must be taken to call
 * JSObject::canRemoveLastProperty when unwinding an object to an earlier
 * property, however.
 */

class AccessorShape;
class Shape;
class UnownedBaseShape;
struct StackBaseShape;

class BaseShape : public gc::TenuredCell
{
  public:
    friend class Shape;
    friend struct StackBaseShape;
    friend struct StackShape;
    friend void gc::MergeCompartments(JSCompartment* source, JSCompartment* target);

    enum Flag {
        /* Owned by the referring shape. */
        OWNED_SHAPE        = 0x1,

        /* (0x2 and 0x4 are unused) */

        /*
         * Flags set which describe the referring object. Once set these cannot
         * be unset (except during object densification of sparse indexes), and
         * are transferred from shape to shape as the object's last property
         * changes.
         *
         * If you add a new flag here, please add appropriate code to
         * JSObject::dump to dump it as part of object representation.
         */

        DELEGATE            =    0x8,
        NOT_EXTENSIBLE      =   0x10,
        INDEXED             =   0x20,
        /* (0x40 is unused) */
        HAD_ELEMENTS_ACCESS =   0x80,
        /* (0x100 is unused) */
        ITERATED_SINGLETON  =  0x200,
        NEW_GROUP_UNKNOWN   =  0x400,
        UNCACHEABLE_PROTO   =  0x800,
        IMMUTABLE_PROTOTYPE = 0x1000,

        // See JSObject::isQualifiedVarObj().
        QUALIFIED_VAROBJ    = 0x2000,

        // 0x4000 is unused.

        // For a function used as an interpreted constructor, whether a 'new'
        // type had constructor information cleared.
        NEW_SCRIPT_CLEARED  = 0x8000,

        OBJECT_FLAG_MASK    = 0xfff8
    };

  private:
    const Class*        clasp_;        /* Class of referring object. */
    uint32_t            flags;          /* Vector of above flags. */
    uint32_t            slotSpan_;      /* Object slot span for BaseShapes at
                                         * dictionary last properties. */

    /* For owned BaseShapes, the canonical unowned BaseShape. */
    GCPtrUnownedBaseShape unowned_;

    /* For owned BaseShapes, the shape's shape table. */
    ShapeTable*      table_;

#if JS_BITS_PER_WORD == 32
    // Ensure sizeof(BaseShape) is a multiple of gc::CellSize.
    uint32_t padding_;
#endif

    BaseShape(const BaseShape& base) = delete;
    BaseShape& operator=(const BaseShape& other) = delete;

  public:
    void finalize(FreeOp* fop);

    explicit inline BaseShape(const StackBaseShape& base);

    /* Not defined: BaseShapes must not be stack allocated. */
    ~BaseShape();

    const Class* clasp() const { return clasp_; }

    bool isOwned() const { return !!(flags & OWNED_SHAPE); }

    static void copyFromUnowned(BaseShape& dest, UnownedBaseShape& src);
    inline void adoptUnowned(UnownedBaseShape* other);

    void setOwned(UnownedBaseShape* unowned) {
        flags |= OWNED_SHAPE;
        unowned_ = unowned;
    }

    uint32_t getObjectFlags() const { return flags & OBJECT_FLAG_MASK; }

    bool hasTable() const { MOZ_ASSERT_IF(table_, isOwned()); return table_ != nullptr; }
    void setTable(ShapeTable* table) { MOZ_ASSERT(isOwned()); table_ = table; }

    ShapeTable* maybeTable(const AutoKeepShapeTables&) const {
        MOZ_ASSERT_IF(table_, isOwned());
        return table_;
    }
    ShapeTable* maybeTable(const JS::AutoCheckCannotGC&) const {
        MOZ_ASSERT_IF(table_, isOwned());
        return table_;
    }
    void maybePurgeTable() {
        if (table_ && table_->freeList() == SHAPE_INVALID_SLOT) {
            js_delete(table_);
            table_ = nullptr;
        }
    }

    uint32_t slotSpan() const { MOZ_ASSERT(isOwned()); return slotSpan_; }
    void setSlotSpan(uint32_t slotSpan) { MOZ_ASSERT(isOwned()); slotSpan_ = slotSpan; }

    /*
     * Lookup base shapes from the zone's baseShapes table, adding if not
     * already found.
     */
    static UnownedBaseShape* getUnowned(ExclusiveContext* cx, StackBaseShape& base);

    /* Get the canonical base shape. */
    inline UnownedBaseShape* unowned();

    /* Get the canonical base shape for an owned one. */
    inline UnownedBaseShape* baseUnowned();

    /* Get the canonical base shape for an unowned one (i.e. identity). */
    inline UnownedBaseShape* toUnowned();

    /* Check that an owned base shape is consistent with its unowned base. */
    void assertConsistency();

    /* For JIT usage */
    static inline size_t offsetOfFlags() { return offsetof(BaseShape, flags); }

    static const JS::TraceKind TraceKind = JS::TraceKind::BaseShape;

    void traceChildren(JSTracer* trc);
    void traceChildrenSkipShapeTable(JSTracer* trc);

#ifdef DEBUG
    bool canSkipMarkingShapeTable(Shape* lastShape);
#endif

  private:
    static void staticAsserts() {
        JS_STATIC_ASSERT(offsetof(BaseShape, clasp_) == offsetof(js::shadow::BaseShape, clasp_));
        static_assert(sizeof(BaseShape) % gc::CellSize == 0,
                      "Things inheriting from gc::Cell must have a size that's "
                      "a multiple of gc::CellSize");
    }

    void traceShapeTable(JSTracer* trc);
};

class UnownedBaseShape : public BaseShape {};

UnownedBaseShape*
BaseShape::unowned()
{
    return isOwned() ? baseUnowned() : toUnowned();
}

UnownedBaseShape*
BaseShape::toUnowned()
{
    MOZ_ASSERT(!isOwned() && !unowned_);
    return static_cast<UnownedBaseShape*>(this);
}

UnownedBaseShape*
BaseShape::baseUnowned()
{
    MOZ_ASSERT(isOwned() && unowned_);
    return unowned_;
}

/* Entries for the per-zone baseShapes set of unowned base shapes. */
struct StackBaseShape : public DefaultHasher<ReadBarriered<UnownedBaseShape*>>
{
    uint32_t flags;
    const Class* clasp;

    explicit StackBaseShape(BaseShape* base)
      : flags(base->flags & BaseShape::OBJECT_FLAG_MASK),
        clasp(base->clasp_)
    {}

    inline StackBaseShape(ExclusiveContext* cx, const Class* clasp, uint32_t objectFlags);
    explicit inline StackBaseShape(Shape* shape);

    struct Lookup
    {
        uint32_t flags;
        const Class* clasp;

        MOZ_IMPLICIT Lookup(const StackBaseShape& base)
          : flags(base.flags), clasp(base.clasp)
        {}

        MOZ_IMPLICIT Lookup(UnownedBaseShape* base)
          : flags(base->getObjectFlags()), clasp(base->clasp())
        {
            MOZ_ASSERT(!base->isOwned());
        }
    };

    static inline HashNumber hash(const Lookup& lookup);
    static inline bool match(ReadBarriered<UnownedBaseShape*> key, const Lookup& lookup);
};

static MOZ_ALWAYS_INLINE js::HashNumber
HashId(jsid id)
{
    // HashGeneric alone would work, but bits of atom and symbol addresses
    // could then be recovered from the hash code. See bug 1330769.
    if (MOZ_LIKELY(JSID_IS_ATOM(id)))
        return JSID_TO_ATOM(id)->hash();
    if (JSID_IS_SYMBOL(id))
        return JSID_TO_SYMBOL(id)->hash();
    return mozilla::HashGeneric(JSID_BITS(id));
}

template <>
struct DefaultHasher<jsid>
{
    typedef jsid Lookup;
    static HashNumber hash(jsid id) {
        return HashId(id);
    }
    static bool match(jsid id1, jsid id2) {
        return id1 == id2;
    }
};

using BaseShapeSet = JS::GCHashSet<ReadBarriered<UnownedBaseShape*>,
                                   StackBaseShape,
                                   SystemAllocPolicy>;

class Shape : public gc::TenuredCell
{
    friend class ::JSObject;
    friend class ::JSFunction;
    friend class NativeObject;
    friend class PropertyTree;
    friend class TenuringTracer;
    friend struct StackBaseShape;
    friend struct StackShape;
    friend class JS::ubi::Concrete<Shape>;
    friend class js::gc::RelocationOverlay;

  protected:
    GCPtrBaseShape base_;
    PreBarrieredId propid_;

    enum SlotInfo : uint32_t
    {
        /* Number of fixed slots in objects with this shape. */
        // FIXED_SLOTS_MAX is the biggest count of fixed slots a Shape can store
        FIXED_SLOTS_MAX        = 0x1f,
        FIXED_SLOTS_SHIFT      = 27,
        FIXED_SLOTS_MASK       = uint32_t(FIXED_SLOTS_MAX << FIXED_SLOTS_SHIFT),

        /*
         * numLinearSearches starts at zero and is incremented initially on
         * search() calls. Once numLinearSearches reaches LINEAR_SEARCHES_MAX,
         * the table is created on the next search() call. The table can also
         * be created when hashifying for dictionary mode.
         */
        LINEAR_SEARCHES_MAX    = 0x7,
        LINEAR_SEARCHES_SHIFT  = 24,
        LINEAR_SEARCHES_MASK   = LINEAR_SEARCHES_MAX << LINEAR_SEARCHES_SHIFT,

        /*
         * Mask to get the index in object slots for shapes which hasSlot().
         * For !hasSlot() shapes in the property tree with a parent, stores the
         * parent's slot index (which may be invalid), and invalid for all
         * other shapes.
         */
        SLOT_MASK              = JS_BIT(24) - 1
    };

    uint32_t            slotInfo;       /* mask of above info */
    uint8_t             attrs;          /* attributes, see jsapi.h JSPROP_* */
    uint8_t             flags;          /* flags, see below for defines */

    GCPtrShape   parent;          /* parent node, reverse for..in order */
    /* kids is valid when !inDictionary(), listp is valid when inDictionary(). */
    union {
        KidsPointer kids;         /* null, single child, or a tagged ptr
                                     to many-kids data structure */
        GCPtrShape* listp;        /* dictionary list starting at shape_
                                     has a double-indirect back pointer,
                                     either to the next shape's parent if not
                                     last, else to obj->shape_ */
    };

    template<MaybeAdding Adding = MaybeAdding::NotAdding>
    static inline Shape* search(ExclusiveContext* cx, Shape* start, jsid id);

    template<MaybeAdding Adding = MaybeAdding::NotAdding>
    static inline MOZ_MUST_USE bool search(ExclusiveContext* cx, Shape* start, jsid id,
                                           const AutoKeepShapeTables&,
                                           Shape** pshape, ShapeTable::Entry** pentry);

    static inline Shape* searchNoHashify(Shape* start, jsid id);

    void removeFromDictionary(NativeObject* obj);
    void insertIntoDictionary(GCPtrShape* dictp);

    inline void initDictionaryShape(const StackShape& child, uint32_t nfixed,
                                    GCPtrShape* dictp);

    /* Replace the base shape of the last shape in a non-dictionary lineage with base. */
    static Shape* replaceLastProperty(ExclusiveContext* cx, StackBaseShape& base,
                                      TaggedProto proto, HandleShape shape);

    /*
     * This function is thread safe if every shape in the lineage of |shape|
     * is thread local, which is the case when we clone the entire shape
     * lineage in preparation for converting an object to dictionary mode.
     */
    static bool hashify(ExclusiveContext* cx, Shape* shape);
    void handoffTableTo(Shape* newShape);

    void setParent(Shape* p) {
        MOZ_ASSERT_IF(p && !p->hasMissingSlot() && !inDictionary(),
                      p->maybeSlot() <= maybeSlot());
        MOZ_ASSERT_IF(p && !inDictionary(),
                      hasSlot() == (p->maybeSlot() != maybeSlot()));
        parent = p;
    }

    bool ensureOwnBaseShape(ExclusiveContext* cx) {
        if (base()->isOwned())
            return true;
        return makeOwnBaseShape(cx);
    }

    bool makeOwnBaseShape(ExclusiveContext* cx);

    MOZ_ALWAYS_INLINE MOZ_MUST_USE bool maybeCreateTableForLookup(ExclusiveContext* cx);

  public:
    bool hasTable() const { return base()->hasTable(); }

    ShapeTable* maybeTable(const AutoKeepShapeTables& keep) const {
        return base()->maybeTable(keep);
    }
    ShapeTable* maybeTable(const JS::AutoCheckCannotGC& check) const {
        return base()->maybeTable(check);
    }

    template <typename T>
    MOZ_MUST_USE ShapeTable* ensureTableForDictionary(ExclusiveContext* cx, const T& nogc) {
        MOZ_ASSERT(inDictionary());
        if (ShapeTable* table = maybeTable(nogc))
            return table;
        if (!hashify(cx, this))
            return nullptr;
        ShapeTable* table = maybeTable(nogc);
        MOZ_ASSERT(table);
        return table;
    }

    void addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf,
                                JS::ShapeInfo* info) const
    {
        JS::AutoCheckCannotGC nogc;
        if (ShapeTable* table = maybeTable(nogc)) {
            if (inDictionary())
                info->shapesMallocHeapDictTables += table->sizeOfIncludingThis(mallocSizeOf);
            else
                info->shapesMallocHeapTreeTables += table->sizeOfIncludingThis(mallocSizeOf);
        }

        if (!inDictionary() && kids.isHash())
            info->shapesMallocHeapTreeKids += kids.toHash()->sizeOfIncludingThis(mallocSizeOf);
    }

    bool isAccessorShape() const {
        MOZ_ASSERT_IF(flags & ACCESSOR_SHAPE, getAllocKind() == gc::AllocKind::ACCESSOR_SHAPE);
        return flags & ACCESSOR_SHAPE;
    }
    AccessorShape& asAccessorShape() const {
        MOZ_ASSERT(isAccessorShape());
        return *(AccessorShape*)this;
    }

    const GCPtrShape& previous() const { return parent; }

    template <AllowGC allowGC>
    class Range {
      protected:
        friend class Shape;

        typename MaybeRooted<Shape*, allowGC>::RootType cursor;

      public:
        Range(ExclusiveContext* cx, Shape* shape) : cursor(cx, shape) {
            JS_STATIC_ASSERT(allowGC == CanGC);
        }

        explicit Range(Shape* shape) : cursor((ExclusiveContext*) nullptr, shape) {
            JS_STATIC_ASSERT(allowGC == NoGC);
        }

        bool empty() const {
            return !cursor || cursor->isEmptyShape();
        }

        Shape& front() const {
            MOZ_ASSERT(!empty());
            return *cursor;
        }

        void popFront() {
            MOZ_ASSERT(!empty());
            cursor = cursor->parent;
        }
    };

    const Class* getObjectClass() const {
        return base()->clasp_;
    }

    static Shape* setObjectFlags(ExclusiveContext* cx,
                                 BaseShape::Flag flag, TaggedProto proto, Shape* last);

    uint32_t getObjectFlags() const { return base()->getObjectFlags(); }
    bool hasAllObjectFlags(BaseShape::Flag flags) const {
        MOZ_ASSERT(flags);
        MOZ_ASSERT(!(flags & ~BaseShape::OBJECT_FLAG_MASK));
        return (base()->flags & flags) == flags;
    }

  protected:
    /*
     * Implementation-private bits stored in shape->flags. See public: enum {}
     * flags further below, which were allocated FCFS over time, so interleave
     * with these bits.
     */
    enum {
        /* Property stored in per-object dictionary, not shared property tree. */
        IN_DICTIONARY   = 0x01,

        /*
         * Slotful property was stored to more than once. This is used as a
         * hint for type inference.
         */
        OVERWRITTEN     = 0x02,

        /*
         * This shape is an AccessorShape, a fat Shape that can store
         * getter/setter information.
         */
        ACCESSOR_SHAPE  = 0x04,

        /* Flags used to speed up isBigEnoughForAShapeTable(). */
        HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE = 0x08,
        CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE = 0x10,
    };

    /* Get a shape identical to this one, without parent/kids information. */
    inline Shape(const StackShape& other, uint32_t nfixed);

    /* Used by EmptyShape (see jsscopeinlines.h). */
    inline Shape(UnownedBaseShape* base, uint32_t nfixed);

    /* Copy constructor disabled, to avoid misuse of the above form. */
    Shape(const Shape& other) = delete;

    /* Allocate a new shape based on the given StackShape. */
    static inline Shape* new_(ExclusiveContext* cx, Handle<StackShape> other, uint32_t nfixed);

    /*
     * Whether this shape has a valid slot value. This may be true even if
     * !hasSlot() (see SlotInfo comment above), and may be false even if
     * hasSlot() if the shape is being constructed and has not had a slot
     * assigned yet. After construction, hasSlot() implies !hasMissingSlot().
     */
    bool hasMissingSlot() const { return maybeSlot() == SHAPE_INVALID_SLOT; }

  public:
    bool inDictionary() const {
        return (flags & IN_DICTIONARY) != 0;
    }

    inline GetterOp getter() const;
    bool hasDefaultGetter() const { return !getter(); }
    GetterOp getterOp() const { MOZ_ASSERT(!hasGetterValue()); return getter(); }
    inline JSObject* getterObject() const;
    bool hasGetterObject() const { return hasGetterValue() && getterObject(); }

    // Per ES5, decode null getterObj as the undefined value, which encodes as null.
    Value getterValue() const {
        MOZ_ASSERT(hasGetterValue());
        if (JSObject* getterObj = getterObject())
            return ObjectValue(*getterObj);
        return UndefinedValue();
    }

    Value getterOrUndefined() const {
        return hasGetterValue() ? getterValue() : UndefinedValue();
    }

    inline SetterOp setter() const;
    bool hasDefaultSetter() const { return !setter(); }
    SetterOp setterOp() const { MOZ_ASSERT(!hasSetterValue()); return setter(); }
    inline JSObject* setterObject() const;
    bool hasSetterObject() const { return hasSetterValue() && setterObject(); }

    // Per ES5, decode null setterObj as the undefined value, which encodes as null.
    Value setterValue() const {
        MOZ_ASSERT(hasSetterValue());
        if (JSObject* setterObj = setterObject())
            return ObjectValue(*setterObj);
        return UndefinedValue();
    }

    Value setterOrUndefined() const {
        return hasSetterValue() ? setterValue() : UndefinedValue();
    }

    void setOverwritten() {
        flags |= OVERWRITTEN;
    }
    bool hadOverwrite() const {
        return flags & OVERWRITTEN;
    }

    void update(GetterOp getter, SetterOp setter, uint8_t attrs);

    bool matches(const Shape* other) const {
        return propid_.get() == other->propid_.get() &&
               matchesParamsAfterId(other->base(), other->maybeSlot(), other->attrs, other->flags,
                                    other->getter(), other->setter());
    }

    inline bool matches(const StackShape& other) const;

    bool matchesParamsAfterId(BaseShape* base, uint32_t aslot, unsigned aattrs, unsigned aflags,
                              GetterOp rawGetter, SetterOp rawSetter) const
    {
        return base->unowned() == this->base()->unowned() &&
               maybeSlot() == aslot &&
               attrs == aattrs &&
               getter() == rawGetter &&
               setter() == rawSetter;
    }

    BaseShape* base() const { return base_.get(); }

    bool hasSlot() const {
        return (attrs & JSPROP_SHARED) == 0;
    }
    uint32_t slot() const { MOZ_ASSERT(hasSlot() && !hasMissingSlot()); return maybeSlot(); }
    uint32_t maybeSlot() const {
        return slotInfo & SLOT_MASK;
    }

    bool isEmptyShape() const {
        MOZ_ASSERT_IF(JSID_IS_EMPTY(propid_), hasMissingSlot());
        return JSID_IS_EMPTY(propid_);
    }

    uint32_t slotSpan(const Class* clasp) const {
        MOZ_ASSERT(!inDictionary());
        uint32_t free = JSSLOT_FREE(clasp);
        return hasMissingSlot() ? free : Max(free, maybeSlot() + 1);
    }

    uint32_t slotSpan() const {
        return slotSpan(getObjectClass());
    }

    void setSlot(uint32_t slot) {
        MOZ_ASSERT(slot <= SHAPE_INVALID_SLOT);
        slotInfo = slotInfo & ~Shape::SLOT_MASK;
        slotInfo = slotInfo | slot;
    }

    uint32_t numFixedSlots() const {
        return slotInfo >> FIXED_SLOTS_SHIFT;
    }

    void setNumFixedSlots(uint32_t nfixed) {
        MOZ_ASSERT(nfixed < FIXED_SLOTS_MAX);
        slotInfo = slotInfo & ~FIXED_SLOTS_MASK;
        slotInfo = slotInfo | (nfixed << FIXED_SLOTS_SHIFT);
    }

    uint32_t numLinearSearches() const {
        return (slotInfo & LINEAR_SEARCHES_MASK) >> LINEAR_SEARCHES_SHIFT;
    }

    void incrementNumLinearSearches() {
        uint32_t count = numLinearSearches();
        MOZ_ASSERT(count < LINEAR_SEARCHES_MAX);
        slotInfo = slotInfo & ~LINEAR_SEARCHES_MASK;
        slotInfo = slotInfo | ((count + 1) << LINEAR_SEARCHES_SHIFT);
    }

    const PreBarrieredId& propid() const {
        MOZ_ASSERT(!isEmptyShape());
        MOZ_ASSERT(!JSID_IS_VOID(propid_));
        return propid_;
    }
    PreBarrieredId& propidRef() { MOZ_ASSERT(!JSID_IS_VOID(propid_)); return propid_; }
    jsid propidRaw() const {
        // Return the actual jsid, not an internal reference.
        return propid();
    }

    uint8_t attributes() const { return attrs; }
    bool configurable() const { return (attrs & JSPROP_PERMANENT) == 0; }
    bool enumerable() const { return (attrs & JSPROP_ENUMERATE) != 0; }
    bool writable() const {
        return (attrs & JSPROP_READONLY) == 0;
    }
    bool hasGetterValue() const { return attrs & JSPROP_GETTER; }
    bool hasSetterValue() const { return attrs & JSPROP_SETTER; }

    bool isDataDescriptor() const {
        return (attrs & (JSPROP_SETTER | JSPROP_GETTER)) == 0;
    }
    bool isAccessorDescriptor() const {
        return (attrs & (JSPROP_SETTER | JSPROP_GETTER)) != 0;
    }

    bool hasShadowable() const { return attrs & JSPROP_SHADOWABLE; }

    uint32_t entryCount() {
        JS::AutoCheckCannotGC nogc;
        if (ShapeTable* table = maybeTable(nogc))
            return table->entryCount();
        uint32_t count = 0;
        for (Shape::Range<NoGC> r(this); !r.empty(); r.popFront())
            ++count;
        return count;
    }

  private:
    bool isBigEnoughForAShapeTableSlow() {
        uint32_t count = 0;
        for (Shape::Range<NoGC> r(this); !r.empty(); r.popFront()) {
            ++count;
            if (count >= ShapeTable::MIN_ENTRIES)
                return true;
        }
        return false;
    }
    void clearCachedBigEnoughForShapeTable() {
        flags &= ~(HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE | CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE);
    }

  public:
    bool isBigEnoughForAShapeTable() {
        MOZ_ASSERT(!hasTable());

        // isBigEnoughForAShapeTableSlow is pretty inefficient so we only call
        // it once and cache the result.

        if (flags & HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE) {
            bool res = flags & CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE;
            MOZ_ASSERT(res == isBigEnoughForAShapeTableSlow());
            return res;
        }

        MOZ_ASSERT(!(flags & CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE));

        bool res = isBigEnoughForAShapeTableSlow();
        if (res)
            flags |= CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE;
        flags |= HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE;
        return res;
    }

#ifdef DEBUG
    void dump(FILE* fp) const;
    void dumpSubtree(int level, FILE* fp) const;
#endif

    void sweep();
    void finalize(FreeOp* fop);
    void removeChild(Shape* child);

    static const JS::TraceKind TraceKind = JS::TraceKind::Shape;

    void traceChildren(JSTracer* trc);

    inline Shape* search(ExclusiveContext* cx, jsid id);
    MOZ_ALWAYS_INLINE Shape* searchLinear(jsid id);

    void fixupAfterMovingGC();
    void fixupGetterSetterForBarrier(JSTracer* trc);
    void updateBaseShapeAfterMovingGC();

    /* For JIT usage */
    static inline size_t offsetOfBase() { return offsetof(Shape, base_); }
    static inline size_t offsetOfSlotInfo() { return offsetof(Shape, slotInfo); }
    static inline uint32_t fixedSlotsMask() { return FIXED_SLOTS_MASK; }

  private:
    void fixupDictionaryShapeAfterMovingGC();
    void fixupShapeTreeAfterMovingGC();

    static void staticAsserts() {
        JS_STATIC_ASSERT(offsetof(Shape, base_) == offsetof(js::shadow::Shape, base));
        JS_STATIC_ASSERT(offsetof(Shape, slotInfo) == offsetof(js::shadow::Shape, slotInfo));
        JS_STATIC_ASSERT(FIXED_SLOTS_SHIFT == js::shadow::Shape::FIXED_SLOTS_SHIFT);
    }
};

/* Fat Shape used for accessor properties. */
class AccessorShape : public Shape
{
    friend class Shape;
    friend class NativeObject;

    union {
        GetterOp rawGetter;     /* getter hook for shape */
        JSObject* getterObj;    /* user-defined callable "get" object or
                                   null if shape->hasGetterValue() */
    };
    union {
        SetterOp rawSetter;     /* setter hook for shape */
        JSObject* setterObj;    /* user-defined callable "set" object or
                                   null if shape->hasSetterValue() */
    };

  public:
    /* Get a shape identical to this one, without parent/kids information. */
    inline AccessorShape(const StackShape& other, uint32_t nfixed);
};

inline
StackBaseShape::StackBaseShape(Shape* shape)
  : flags(shape->getObjectFlags()),
    clasp(shape->getObjectClass())
{}

class MOZ_RAII AutoRooterGetterSetter
{
    class Inner final : private JS::CustomAutoRooter
    {
      public:
        inline Inner(ExclusiveContext* cx, uint8_t attrs, GetterOp* pgetter_, SetterOp* psetter_);

      private:
        virtual void trace(JSTracer* trc);

        uint8_t attrs;
        GetterOp* pgetter;
        SetterOp* psetter;
    };

  public:
    inline AutoRooterGetterSetter(ExclusiveContext* cx, uint8_t attrs,
                                  GetterOp* pgetter, SetterOp* psetter
                                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
    inline AutoRooterGetterSetter(ExclusiveContext* cx, uint8_t attrs,
                                  JSNative* pgetter, JSNative* psetter
                                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM);

  private:
    mozilla::Maybe<Inner> inner;
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

struct EmptyShape : public js::Shape
{
    EmptyShape(UnownedBaseShape* base, uint32_t nfixed)
      : js::Shape(base, nfixed)
    { }

    static Shape* new_(ExclusiveContext* cx, Handle<UnownedBaseShape*> base, uint32_t nfixed);

    /*
     * Lookup an initial shape matching the given parameters, creating an empty
     * shape if none was found.
     */
    static Shape* getInitialShape(ExclusiveContext* cx, const Class* clasp,
                                  TaggedProto proto, size_t nfixed, uint32_t objectFlags = 0);
    static Shape* getInitialShape(ExclusiveContext* cx, const Class* clasp,
                                  TaggedProto proto, gc::AllocKind kind, uint32_t objectFlags = 0);

    /*
     * Reinsert an alternate initial shape, to be returned by future
     * getInitialShape calls, until the new shape becomes unreachable in a GC
     * and the table entry is purged.
     */
    static void insertInitialShape(ExclusiveContext* cx, HandleShape shape, HandleObject proto);

    /*
     * Some object subclasses are allocated with a built-in set of properties.
     * The first time such an object is created, these built-in properties must
     * be set manually, to compute an initial shape.  Afterward, that initial
     * shape can be reused for newly-created objects that use the subclass's
     * standard prototype.  This method should be used in a post-allocation
     * init method, to ensure that objects of such subclasses compute and cache
     * the initial shape, if it hasn't already been computed.
     */
    template<class ObjectSubclass>
    static inline bool
    ensureInitialCustomShape(ExclusiveContext* cx, Handle<ObjectSubclass*> obj);
};

// InitialShapeProto stores either:
//
// * A TaggedProto (or ReadBarriered<TaggedProto>).
//
// * A JSProtoKey. This is used instead of the TaggedProto if the proto is one
//   of the global's builtin prototypes. For instance, if the proto is the
//   initial Object.prototype, we use key_ = JSProto_Object, proto_ = nullptr.
//
// Using the JSProtoKey here is an optimization that lets us share more shapes
// across compartments within a zone.
template <typename PtrType>
class InitialShapeProto
{
    template <typename T> friend class InitialShapeProto;

    JSProtoKey key_;
    PtrType proto_;

  public:
    InitialShapeProto()
      : key_(JSProto_LIMIT), proto_()
    {}

    InitialShapeProto(JSProtoKey key, TaggedProto proto)
      : key_(key), proto_(proto)
    {}

    template <typename T>
    explicit InitialShapeProto(const InitialShapeProto<T>& other)
      : key_(other.key()), proto_(other.proto_)
    {}

    explicit InitialShapeProto(TaggedProto proto)
      : key_(JSProto_LIMIT), proto_(proto)
    {}
    explicit InitialShapeProto(JSProtoKey key)
      : key_(key), proto_(nullptr)
    {
        MOZ_ASSERT(key < JSProto_LIMIT);
    }

    HashNumber hashCode() const {
        return proto_.hashCode() ^ HashNumber(key_);
    }
    template <typename T>
    bool match(const InitialShapeProto<T>& other) const {
        return key_ == other.key_ &&
               proto_.uniqueId() == other.proto_.unbarrieredGet().uniqueId();
    }

    JSProtoKey key() const {
        return key_;
    }
    const PtrType& proto() const {
        return proto_;
    }
    void setProto(TaggedProto proto) {
        proto_ = proto;
    }
};

/*
 * Entries for the per-zone initialShapes set indexing initial shapes for
 * objects in the zone and the associated types.
 */
struct InitialShapeEntry
{
    /*
     * Initial shape to give to the object. This is an empty shape, except for
     * certain classes (e.g. String, RegExp) which may add certain baked-in
     * properties.
     */
    ReadBarriered<Shape*> shape;

    /*
     * Matching prototype for the entry. The shape of an object determines its
     * prototype, but the prototype cannot be determined from the shape itself.
     */
    using ShapeProto = InitialShapeProto<ReadBarriered<TaggedProto>>;
    ShapeProto proto;

    /* State used to determine a match on an initial shape. */
    struct Lookup {
        using ShapeProto = InitialShapeProto<TaggedProto>;
        const Class* clasp;
        ShapeProto proto;
        uint32_t nfixed;
        uint32_t baseFlags;

        Lookup(const Class* clasp, ShapeProto proto, uint32_t nfixed, uint32_t baseFlags)
          : clasp(clasp), proto(proto), nfixed(nfixed), baseFlags(baseFlags)
        {}
    };

    inline InitialShapeEntry();
    inline InitialShapeEntry(Shape* shape, const Lookup::ShapeProto& proto);

    static inline HashNumber hash(const Lookup& lookup);
    static inline bool match(const InitialShapeEntry& key, const Lookup& lookup);
    static void rekey(InitialShapeEntry& k, const InitialShapeEntry& newKey) { k = newKey; }

    bool needsSweep() {
        Shape* ushape = shape.unbarrieredGet();
        JSObject* protoObj = proto.proto().raw();
        return (gc::IsAboutToBeFinalizedUnbarriered(&ushape) ||
                (proto.proto().isObject() && gc::IsAboutToBeFinalizedUnbarriered(&protoObj)));
    }
};

using InitialShapeSet = JS::GCHashSet<InitialShapeEntry, InitialShapeEntry, SystemAllocPolicy>;

struct StackShape
{
    /* For performance, StackShape only roots when absolutely necessary. */
    UnownedBaseShape* base;
    jsid propid;
    GetterOp rawGetter;
    SetterOp rawSetter;
    uint32_t slot_;
    uint8_t attrs;
    uint8_t flags;

    explicit StackShape(UnownedBaseShape* base, jsid propid, uint32_t slot,
                        unsigned attrs, unsigned flags)
      : base(base),
        propid(propid),
        rawGetter(nullptr),
        rawSetter(nullptr),
        slot_(slot),
        attrs(uint8_t(attrs)),
        flags(uint8_t(flags))
    {
        MOZ_ASSERT(base);
        MOZ_ASSERT(!JSID_IS_VOID(propid));
        MOZ_ASSERT(slot <= SHAPE_INVALID_SLOT);
        MOZ_ASSERT_IF(attrs & (JSPROP_GETTER | JSPROP_SETTER), attrs & JSPROP_SHARED);
    }

    explicit StackShape(Shape* shape)
      : base(shape->base()->unowned()),
        propid(shape->propidRef()),
        rawGetter(shape->getter()),
        rawSetter(shape->setter()),
        slot_(shape->maybeSlot()),
        attrs(shape->attrs),
        flags(shape->flags)
    {}

    void updateGetterSetter(GetterOp rawGetter, SetterOp rawSetter) {
        if (rawGetter || rawSetter || (attrs & (JSPROP_GETTER|JSPROP_SETTER)))
            flags |= Shape::ACCESSOR_SHAPE;
        else
            flags &= ~Shape::ACCESSOR_SHAPE;

        this->rawGetter = rawGetter;
        this->rawSetter = rawSetter;
    }

    bool hasSlot() const { return (attrs & JSPROP_SHARED) == 0; }
    bool hasMissingSlot() const { return maybeSlot() == SHAPE_INVALID_SLOT; }

    uint32_t slot() const { MOZ_ASSERT(hasSlot() && !hasMissingSlot()); return slot_; }
    uint32_t maybeSlot() const { return slot_; }

    uint32_t slotSpan() const {
        uint32_t free = JSSLOT_FREE(base->clasp_);
        return hasMissingSlot() ? free : (maybeSlot() + 1);
    }

    void setSlot(uint32_t slot) {
        MOZ_ASSERT(slot <= SHAPE_INVALID_SLOT);
        slot_ = slot;
    }

    bool isAccessorShape() const {
        return flags & Shape::ACCESSOR_SHAPE;
    }

    HashNumber hash() const {
        HashNumber hash = uintptr_t(base);

        /* Accumulate from least to most random so the low bits are most random. */
        hash = mozilla::RotateLeft(hash, 4) ^ attrs;
        hash = mozilla::RotateLeft(hash, 4) ^ slot_;
        hash = mozilla::RotateLeft(hash, 4) ^ HashId(propid);
        hash = mozilla::RotateLeft(hash, 4) ^ uintptr_t(rawGetter);
        hash = mozilla::RotateLeft(hash, 4) ^ uintptr_t(rawSetter);
        return hash;
    }

    // Traceable implementation.
    static void trace(StackShape* stackShape, JSTracer* trc) { stackShape->trace(trc); }
    void trace(JSTracer* trc);
};

template <typename Outer>
class StackShapeOperations {
    const StackShape& ss() const { return static_cast<const Outer*>(this)->get(); }

  public:
    bool hasSlot() const { return ss().hasSlot(); }
    bool hasMissingSlot() const { return ss().hasMissingSlot(); }
    uint32_t slot() const { return ss().slot(); }
    uint32_t maybeSlot() const { return ss().maybeSlot(); }
    uint32_t slotSpan() const { return ss().slotSpan(); }
    bool isAccessorShape() const { return ss().isAccessorShape(); }
    uint8_t attrs() const { return ss().attrs; }
};

template <typename Outer>
class MutableStackShapeOperations : public StackShapeOperations<Outer> {
    StackShape& ss() { return static_cast<Outer*>(this)->get(); }

  public:
    void updateGetterSetter(GetterOp rawGetter, SetterOp rawSetter) {
        ss().updateGetterSetter(rawGetter, rawSetter);
    }
    void setSlot(uint32_t slot) { ss().setSlot(slot); }
    void setBase(UnownedBaseShape* base) { ss().base = base; }
    void setAttrs(uint8_t attrs) { ss().attrs = attrs; }
};

template <>
class RootedBase<StackShape> : public MutableStackShapeOperations<JS::Rooted<StackShape>>
{};

template <>
class HandleBase<StackShape> : public StackShapeOperations<JS::Handle<StackShape>>
{};

template <>
class MutableHandleBase<StackShape>
  : public MutableStackShapeOperations<JS::MutableHandle<StackShape>>
{};

inline
Shape::Shape(const StackShape& other, uint32_t nfixed)
  : base_(other.base),
    propid_(other.propid),
    slotInfo(other.maybeSlot() | (nfixed << FIXED_SLOTS_SHIFT)),
    attrs(other.attrs),
    flags(other.flags),
    parent(nullptr)
{
#ifdef DEBUG
    gc::AllocKind allocKind = getAllocKind();
    MOZ_ASSERT_IF(other.isAccessorShape(), allocKind == gc::AllocKind::ACCESSOR_SHAPE);
    MOZ_ASSERT_IF(allocKind == gc::AllocKind::SHAPE, !other.isAccessorShape());
#endif

    MOZ_ASSERT_IF(attrs & (JSPROP_GETTER | JSPROP_SETTER), attrs & JSPROP_SHARED);
    kids.setNull();
}

// This class is used to add a post barrier on the AccessorShape's getter/setter
// objects. It updates the pointers and the shape's entry in the parent's
// KidsHash table.
class ShapeGetterSetterRef : public gc::BufferableRef
{
    AccessorShape* shape_;

  public:
    explicit ShapeGetterSetterRef(AccessorShape* shape) : shape_(shape) {}
    void trace(JSTracer* trc) override { shape_->fixupGetterSetterForBarrier(trc); }
};

static inline void
GetterSetterWriteBarrierPost(AccessorShape* shape)
{
    MOZ_ASSERT(shape);
    if (shape->hasGetterObject()) {
        gc::StoreBuffer* sb = reinterpret_cast<gc::Cell*>(shape->getterObject())->storeBuffer();
        if (sb) {
            sb->putGeneric(ShapeGetterSetterRef(shape));
            return;
        }
    }
    if (shape->hasSetterObject()) {
        gc::StoreBuffer* sb = reinterpret_cast<gc::Cell*>(shape->setterObject())->storeBuffer();
        if (sb) {
            sb->putGeneric(ShapeGetterSetterRef(shape));
            return;
        }
    }
}

inline
AccessorShape::AccessorShape(const StackShape& other, uint32_t nfixed)
  : Shape(other, nfixed),
    rawGetter(other.rawGetter),
    rawSetter(other.rawSetter)
{
    MOZ_ASSERT(getAllocKind() == gc::AllocKind::ACCESSOR_SHAPE);
    GetterSetterWriteBarrierPost(this);
}

inline
Shape::Shape(UnownedBaseShape* base, uint32_t nfixed)
  : base_(base),
    propid_(JSID_EMPTY),
    slotInfo(SHAPE_INVALID_SLOT | (nfixed << FIXED_SLOTS_SHIFT)),
    attrs(JSPROP_SHARED),
    flags(0),
    parent(nullptr)
{
    MOZ_ASSERT(base);
    kids.setNull();
}

inline GetterOp
Shape::getter() const
{
    return isAccessorShape() ? asAccessorShape().rawGetter : nullptr;
}

inline SetterOp
Shape::setter() const
{
    return isAccessorShape() ? asAccessorShape().rawSetter : nullptr;
}

inline JSObject*
Shape::getterObject() const
{
    MOZ_ASSERT(hasGetterValue());
    return asAccessorShape().getterObj;
}

inline JSObject*
Shape::setterObject() const
{
    MOZ_ASSERT(hasSetterValue());
    return asAccessorShape().setterObj;
}

inline void
Shape::initDictionaryShape(const StackShape& child, uint32_t nfixed, GCPtrShape* dictp)
{
    if (child.isAccessorShape())
        new (this) AccessorShape(child, nfixed);
    else
        new (this) Shape(child, nfixed);
    this->flags |= IN_DICTIONARY;

    this->listp = nullptr;
    if (dictp)
        insertIntoDictionary(dictp);
}

inline Shape*
Shape::searchLinear(jsid id)
{
    for (Shape* shape = this; shape; ) {
        if (shape->propidRef() == id)
            return shape;
        shape = shape->parent;
    }

    return nullptr;
}

/*
 * Keep this function in sync with search. It neither hashifies the start
 * shape nor increments linear search count.
 */
inline Shape*
Shape::searchNoHashify(Shape* start, jsid id)
{
    /*
     * If we have a table, search in the shape table, else do a linear
     * search. We never hashify into a table in parallel.
     */
    JS::AutoCheckCannotGC nogc;
    if (ShapeTable* table = start->maybeTable(nogc)) {
        ShapeTable::Entry& entry = table->search<MaybeAdding::NotAdding>(id, nogc);
        return entry.shape();
    }

    return start->searchLinear(id);
}

inline bool
Shape::matches(const StackShape& other) const
{
    return propid_.get() == other.propid &&
           matchesParamsAfterId(other.base, other.slot_, other.attrs, other.flags,
                                other.rawGetter, other.rawSetter);
}

// Property lookup hooks on objects are required to return a non-nullptr shape
// to signify that the property has been found. For cases where the property is
// not actually represented by a Shape, use a dummy value. This includes all
// properties of non-native objects, and dense elements for native objects.
// Use separate APIs for these two cases.

template <AllowGC allowGC>
static inline void
MarkNonNativePropertyFound(typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
{
    propp.set(reinterpret_cast<Shape*>(1));
}

template <AllowGC allowGC>
static inline void
MarkDenseOrTypedArrayElementFound(typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
{
    propp.set(reinterpret_cast<Shape*>(1));
}

static inline bool
IsImplicitDenseOrTypedArrayElement(Shape* prop)
{
    return prop == reinterpret_cast<Shape*>(1);
}

static inline bool
IsImplicitNonNativeProperty(Shape* prop)
{
    return prop == reinterpret_cast<Shape*>(1);
}

Shape*
ReshapeForAllocKind(JSContext* cx, Shape* shape, TaggedProto proto,
                    gc::AllocKind allocKind);

} // namespace js

#ifdef _MSC_VER
#pragma warning(pop)
#pragma warning(pop)
#endif

// JS::ubi::Nodes can point to Shapes and BaseShapes; they're js::gc::Cell
// instances that occupy a compartment.
namespace JS {
namespace ubi {

template<>
class Concrete<js::Shape> : TracerConcrete<js::Shape> {
  protected:
    explicit Concrete(js::Shape *ptr) : TracerConcrete<js::Shape>(ptr) { }

  public:
    static void construct(void *storage, js::Shape *ptr) { new (storage) Concrete(ptr); }

    Size size(mozilla::MallocSizeOf mallocSizeOf) const override;

    const char16_t* typeName() const override { return concreteTypeName; }
    static const char16_t concreteTypeName[];
};

template<>
class Concrete<js::BaseShape> : TracerConcrete<js::BaseShape> {
  protected:
    explicit Concrete(js::BaseShape *ptr) : TracerConcrete<js::BaseShape>(ptr) { }

  public:
    static void construct(void *storage, js::BaseShape *ptr) { new (storage) Concrete(ptr); }

    Size size(mozilla::MallocSizeOf mallocSizeOf) const override;

    const char16_t* typeName() const override { return concreteTypeName; }
    static const char16_t concreteTypeName[];
};

} // namespace ubi
} // namespace JS

#endif /* vm_Shape_h */