aboutsummaryrefslogtreecommitdiff
path: root/gcc/ggc-page.c
blob: e0dfb1610d404fc26d734486d7623b16daaab0b9 (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
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
/* "Bag-of-pages" garbage collector for the GNU compiler.
   Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004
   Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
#include "toplev.h"
#include "flags.h"
#include "ggc.h"
#include "timevar.h"
#include "params.h"
#include "tree-flow.h"
#ifdef ENABLE_VALGRIND_CHECKING
# ifdef HAVE_VALGRIND_MEMCHECK_H
#  include <valgrind/memcheck.h>
# elif defined HAVE_MEMCHECK_H
#  include <memcheck.h>
# else
#  include <valgrind.h>
# endif
#else
/* Avoid #ifdef:s when we can help it.  */
#define VALGRIND_DISCARD(x)
#endif

/* Prefer MAP_ANON(YMOUS) to /dev/zero, since we don't need to keep a
   file open.  Prefer either to valloc.  */
#ifdef HAVE_MMAP_ANON
# undef HAVE_MMAP_DEV_ZERO

# include <sys/mman.h>
# ifndef MAP_FAILED
#  define MAP_FAILED -1
# endif
# if !defined (MAP_ANONYMOUS) && defined (MAP_ANON)
#  define MAP_ANONYMOUS MAP_ANON
# endif
# define USING_MMAP

#endif

#ifdef HAVE_MMAP_DEV_ZERO

# include <sys/mman.h>
# ifndef MAP_FAILED
#  define MAP_FAILED -1
# endif
# define USING_MMAP

#endif

#ifndef USING_MMAP
#define USING_MALLOC_PAGE_GROUPS
#endif

/* Stategy:

   This garbage-collecting allocator allocates objects on one of a set
   of pages.  Each page can allocate objects of a single size only;
   available sizes are powers of two starting at four bytes.  The size
   of an allocation request is rounded up to the next power of two
   (`order'), and satisfied from the appropriate page.

   Each page is recorded in a page-entry, which also maintains an
   in-use bitmap of object positions on the page.  This allows the
   allocation state of a particular object to be flipped without
   touching the page itself.

   Each page-entry also has a context depth, which is used to track
   pushing and popping of allocation contexts.  Only objects allocated
   in the current (highest-numbered) context may be collected.

   Page entries are arranged in an array of singly-linked lists.  The
   array is indexed by the allocation size, in bits, of the pages on
   it; i.e. all pages on a list allocate objects of the same size.
   Pages are ordered on the list such that all non-full pages precede
   all full pages, with non-full pages arranged in order of decreasing
   context depth.

   Empty pages (of all orders) are kept on a single page cache list,
   and are considered first when new pages are required; they are
   deallocated at the start of the next collection if they haven't
   been recycled by then.  */

/* Define GGC_DEBUG_LEVEL to print debugging information.
     0: No debugging output.
     1: GC statistics only.
     2: Page-entry allocations/deallocations as well.
     3: Object allocations as well.
     4: Object marks as well.  */
#define GGC_DEBUG_LEVEL (0)

#ifndef HOST_BITS_PER_PTR
#define HOST_BITS_PER_PTR  HOST_BITS_PER_LONG
#endif


/* A two-level tree is used to look up the page-entry for a given
   pointer.  Two chunks of the pointer's bits are extracted to index
   the first and second levels of the tree, as follows:

				   HOST_PAGE_SIZE_BITS
			   32		|      |
       msb +----------------+----+------+------+ lsb
			    |    |      |
			 PAGE_L1_BITS   |
				 |      |
			       PAGE_L2_BITS

   The bottommost HOST_PAGE_SIZE_BITS are ignored, since page-entry
   pages are aligned on system page boundaries.  The next most
   significant PAGE_L2_BITS and PAGE_L1_BITS are the second and first
   index values in the lookup table, respectively.

   For 32-bit architectures and the settings below, there are no
   leftover bits.  For architectures with wider pointers, the lookup
   tree points to a list of pages, which must be scanned to find the
   correct one.  */

#define PAGE_L1_BITS	(8)
#define PAGE_L2_BITS	(32 - PAGE_L1_BITS - G.lg_pagesize)
#define PAGE_L1_SIZE	((size_t) 1 << PAGE_L1_BITS)
#define PAGE_L2_SIZE	((size_t) 1 << PAGE_L2_BITS)

#define LOOKUP_L1(p) \
  (((size_t) (p) >> (32 - PAGE_L1_BITS)) & ((1 << PAGE_L1_BITS) - 1))

#define LOOKUP_L2(p) \
  (((size_t) (p) >> G.lg_pagesize) & ((1 << PAGE_L2_BITS) - 1))

/* The number of objects per allocation page, for objects on a page of
   the indicated ORDER.  */
#define OBJECTS_PER_PAGE(ORDER) objects_per_page_table[ORDER]

/* The number of objects in P.  */
#define OBJECTS_IN_PAGE(P) ((P)->bytes / OBJECT_SIZE ((P)->order))

/* The size of an object on a page of the indicated ORDER.  */
#define OBJECT_SIZE(ORDER) object_size_table[ORDER]

/* For speed, we avoid doing a general integer divide to locate the
   offset in the allocation bitmap, by precalculating numbers M, S
   such that (O * M) >> S == O / Z (modulo 2^32), for any offset O
   within the page which is evenly divisible by the object size Z.  */
#define DIV_MULT(ORDER) inverse_table[ORDER].mult
#define DIV_SHIFT(ORDER) inverse_table[ORDER].shift
#define OFFSET_TO_BIT(OFFSET, ORDER) \
  (((OFFSET) * DIV_MULT (ORDER)) >> DIV_SHIFT (ORDER))

/* The number of extra orders, not corresponding to power-of-two sized
   objects.  */

#define NUM_EXTRA_ORDERS ARRAY_SIZE (extra_order_size_table)

#define RTL_SIZE(NSLOTS) \
  (RTX_HDR_SIZE + (NSLOTS) * sizeof (rtunion))

#define TREE_EXP_SIZE(OPS) \
  (sizeof (struct tree_exp) + ((OPS) - 1) * sizeof (tree))

/* The Ith entry is the maximum size of an object to be stored in the
   Ith extra order.  Adding a new entry to this array is the *only*
   thing you need to do to add a new special allocation size.  */

static const size_t extra_order_size_table[] = {
  sizeof (struct stmt_ann_d),
  sizeof (struct tree_decl),
  sizeof (struct tree_list),
  TREE_EXP_SIZE (2),
  RTL_SIZE (2),			/* MEM, PLUS, etc.  */
  RTL_SIZE (9),			/* INSN */
};

/* The total number of orders.  */

#define NUM_ORDERS (HOST_BITS_PER_PTR + NUM_EXTRA_ORDERS)

/* We use this structure to determine the alignment required for
   allocations.  For power-of-two sized allocations, that's not a
   problem, but it does matter for odd-sized allocations.  */

struct max_alignment {
  char c;
  union {
    HOST_WIDEST_INT i;
    long double d;
  } u;
};

/* The biggest alignment required.  */

#define MAX_ALIGNMENT (offsetof (struct max_alignment, u))

/* Compute the smallest nonnegative number which when added to X gives
   a multiple of F.  */

#define ROUND_UP_VALUE(x, f) ((f) - 1 - ((f) - 1 + (x)) % (f))

/* Compute the smallest multiple of F that is >= X.  */

#define ROUND_UP(x, f) (CEIL (x, f) * (f))

/* The Ith entry is the number of objects on a page or order I.  */

static unsigned objects_per_page_table[NUM_ORDERS];

/* The Ith entry is the size of an object on a page of order I.  */

static size_t object_size_table[NUM_ORDERS];

/* The Ith entry is a pair of numbers (mult, shift) such that
   ((k * mult) >> shift) mod 2^32 == (k / OBJECT_SIZE(I)) mod 2^32,
   for all k evenly divisible by OBJECT_SIZE(I).  */

static struct
{
  size_t mult;
  unsigned int shift;
}
inverse_table[NUM_ORDERS];

/* A page_entry records the status of an allocation page.  This
   structure is dynamically sized to fit the bitmap in_use_p.  */
typedef struct page_entry
{
  /* The next page-entry with objects of the same size, or NULL if
     this is the last page-entry.  */
  struct page_entry *next;

  /* The previous page-entry with objects of the same size, or NULL if
     this is the first page-entry.   The PREV pointer exists solely to
     keep the cost of ggc_free manageable.  */
  struct page_entry *prev;

  /* The number of bytes allocated.  (This will always be a multiple
     of the host system page size.)  */
  size_t bytes;

  /* The address at which the memory is allocated.  */
  char *page;

#ifdef USING_MALLOC_PAGE_GROUPS
  /* Back pointer to the page group this page came from.  */
  struct page_group *group;
#endif

  /* This is the index in the by_depth varray where this page table
     can be found.  */
  unsigned long index_by_depth;

  /* Context depth of this page.  */
  unsigned short context_depth;

  /* The number of free objects remaining on this page.  */
  unsigned short num_free_objects;

  /* A likely candidate for the bit position of a free object for the
     next allocation from this page.  */
  unsigned short next_bit_hint;

  /* The lg of size of objects allocated from this page.  */
  unsigned char order;

  /* A bit vector indicating whether or not objects are in use.  The
     Nth bit is one if the Nth object on this page is allocated.  This
     array is dynamically sized.  */
  unsigned long in_use_p[1];
} page_entry;

#ifdef USING_MALLOC_PAGE_GROUPS
/* A page_group describes a large allocation from malloc, from which
   we parcel out aligned pages.  */
typedef struct page_group
{
  /* A linked list of all extant page groups.  */
  struct page_group *next;

  /* The address we received from malloc.  */
  char *allocation;

  /* The size of the block.  */
  size_t alloc_size;

  /* A bitmask of pages in use.  */
  unsigned int in_use;
} page_group;
#endif

#if HOST_BITS_PER_PTR <= 32

/* On 32-bit hosts, we use a two level page table, as pictured above.  */
typedef page_entry **page_table[PAGE_L1_SIZE];

#else

/* On 64-bit hosts, we use the same two level page tables plus a linked
   list that disambiguates the top 32-bits.  There will almost always be
   exactly one entry in the list.  */
typedef struct page_table_chain
{
  struct page_table_chain *next;
  size_t high_bits;
  page_entry **table[PAGE_L1_SIZE];
} *page_table;

#endif

/* The rest of the global variables.  */
static struct globals
{
  /* The Nth element in this array is a page with objects of size 2^N.
     If there are any pages with free objects, they will be at the
     head of the list.  NULL if there are no page-entries for this
     object size.  */
  page_entry *pages[NUM_ORDERS];

  /* The Nth element in this array is the last page with objects of
     size 2^N.  NULL if there are no page-entries for this object
     size.  */
  page_entry *page_tails[NUM_ORDERS];

  /* Lookup table for associating allocation pages with object addresses.  */
  page_table lookup;

  /* The system's page size.  */
  size_t pagesize;
  size_t lg_pagesize;

  /* Bytes currently allocated.  */
  size_t allocated;

  /* Bytes currently allocated at the end of the last collection.  */
  size_t allocated_last_gc;

  /* Total amount of memory mapped.  */
  size_t bytes_mapped;

  /* Bit N set if any allocations have been done at context depth N.  */
  unsigned long context_depth_allocations;

  /* Bit N set if any collections have been done at context depth N.  */
  unsigned long context_depth_collections;

  /* The current depth in the context stack.  */
  unsigned short context_depth;

  /* A file descriptor open to /dev/zero for reading.  */
#if defined (HAVE_MMAP_DEV_ZERO)
  int dev_zero_fd;
#endif

  /* A cache of free system pages.  */
  page_entry *free_pages;

#ifdef USING_MALLOC_PAGE_GROUPS
  page_group *page_groups;
#endif

  /* The file descriptor for debugging output.  */
  FILE *debug_file;

  /* Current number of elements in use in depth below.  */
  unsigned int depth_in_use;

  /* Maximum number of elements that can be used before resizing.  */
  unsigned int depth_max;

  /* Each element of this arry is an index in by_depth where the given
     depth starts.  This structure is indexed by that given depth we
     are interested in.  */
  unsigned int *depth;

  /* Current number of elements in use in by_depth below.  */
  unsigned int by_depth_in_use;

  /* Maximum number of elements that can be used before resizing.  */
  unsigned int by_depth_max;

  /* Each element of this array is a pointer to a page_entry, all
     page_entries can be found in here by increasing depth.
     index_by_depth in the page_entry is the index into this data
     structure where that page_entry can be found.  This is used to
     speed up finding all page_entries at a particular depth.  */
  page_entry **by_depth;

  /* Each element is a pointer to the saved in_use_p bits, if any,
     zero otherwise.  We allocate them all together, to enable a
     better runtime data access pattern.  */
  unsigned long **save_in_use;

#ifdef ENABLE_GC_ALWAYS_COLLECT
  /* List of free objects to be verified as actually free on the
     next collection.  */
  struct free_object
  {
    void *object;
    struct free_object *next;
  } *free_object_list;
#endif

#ifdef GATHER_STATISTICS
  struct
  {
    /* Total memory allocated with ggc_alloc.  */
    unsigned long long total_allocated;
    /* Total overhead for memory to be allocated with ggc_alloc.  */
    unsigned long long total_overhead;

    /* Total allocations and overhead for sizes less than 32, 64 and 128.
       These sizes are interesting because they are typical cache line
       sizes.  */
   
    unsigned long long total_allocated_under32;
    unsigned long long total_overhead_under32;
  
    unsigned long long total_allocated_under64;
    unsigned long long total_overhead_under64;
  
    unsigned long long total_allocated_under128;
    unsigned long long total_overhead_under128;
  
    /* The allocations for each of the allocation orders.  */
    unsigned long long total_allocated_per_order[NUM_ORDERS];

    /* The overhead for each of the allocation orders.  */
    unsigned long long total_overhead_per_order[NUM_ORDERS];
  } stats;
#endif
} G;

/* The size in bytes required to maintain a bitmap for the objects
   on a page-entry.  */
#define BITMAP_SIZE(Num_objects) \
  (CEIL ((Num_objects), HOST_BITS_PER_LONG) * sizeof(long))

/* Allocate pages in chunks of this size, to throttle calls to memory
   allocation routines.  The first page is used, the rest go onto the
   free list.  This cannot be larger than HOST_BITS_PER_INT for the
   in_use bitmask for page_group.  Hosts that need a different value
   can override this by defining GGC_QUIRE_SIZE explicitly.  */
#ifndef GGC_QUIRE_SIZE
# ifdef USING_MMAP
#  define GGC_QUIRE_SIZE 256
# else
#  define GGC_QUIRE_SIZE 16
# endif
#endif

/* Initial guess as to how many page table entries we might need.  */
#define INITIAL_PTE_COUNT 128

static int ggc_allocated_p (const void *);
static page_entry *lookup_page_table_entry (const void *);
static void set_page_table_entry (void *, page_entry *);
#ifdef USING_MMAP
static char *alloc_anon (char *, size_t);
#endif
#ifdef USING_MALLOC_PAGE_GROUPS
static size_t page_group_index (char *, char *);
static void set_page_group_in_use (page_group *, char *);
static void clear_page_group_in_use (page_group *, char *);
#endif
static struct page_entry * alloc_page (unsigned);
static void free_page (struct page_entry *);
static void release_pages (void);
static void clear_marks (void);
static void sweep_pages (void);
static void ggc_recalculate_in_use_p (page_entry *);
static void compute_inverse (unsigned);
static inline void adjust_depth (void);
static void move_ptes_to_front (int, int);

void debug_print_page_list (int);
static void push_depth (unsigned int);
static void push_by_depth (page_entry *, unsigned long *);
struct alloc_zone *rtl_zone = NULL;
struct alloc_zone *tree_zone = NULL;
struct alloc_zone *garbage_zone = NULL;

/* Push an entry onto G.depth.  */

inline static void
push_depth (unsigned int i)
{
  if (G.depth_in_use >= G.depth_max)
    {
      G.depth_max *= 2;
      G.depth = xrealloc (G.depth, G.depth_max * sizeof (unsigned int));
    }
  G.depth[G.depth_in_use++] = i;
}

/* Push an entry onto G.by_depth and G.save_in_use.  */

inline static void
push_by_depth (page_entry *p, unsigned long *s)
{
  if (G.by_depth_in_use >= G.by_depth_max)
    {
      G.by_depth_max *= 2;
      G.by_depth = xrealloc (G.by_depth,
			     G.by_depth_max * sizeof (page_entry *));
      G.save_in_use = xrealloc (G.save_in_use,
				G.by_depth_max * sizeof (unsigned long *));
    }
  G.by_depth[G.by_depth_in_use] = p;
  G.save_in_use[G.by_depth_in_use++] = s;
}

#if (GCC_VERSION < 3001)
#define prefetch(X) ((void) X)
#else
#define prefetch(X) __builtin_prefetch (X)
#endif

#define save_in_use_p_i(__i) \
  (G.save_in_use[__i])
#define save_in_use_p(__p) \
  (save_in_use_p_i (__p->index_by_depth))

/* Returns nonzero if P was allocated in GC'able memory.  */

static inline int
ggc_allocated_p (const void *p)
{
  page_entry ***base;
  size_t L1, L2;

#if HOST_BITS_PER_PTR <= 32
  base = &G.lookup[0];
#else
  page_table table = G.lookup;
  size_t high_bits = (size_t) p & ~ (size_t) 0xffffffff;
  while (1)
    {
      if (table == NULL)
	return 0;
      if (table->high_bits == high_bits)
	break;
      table = table->next;
    }
  base = &table->table[0];
#endif

  /* Extract the level 1 and 2 indices.  */
  L1 = LOOKUP_L1 (p);
  L2 = LOOKUP_L2 (p);

  return base[L1] && base[L1][L2];
}

/* Traverse the page table and find the entry for a page.
   Die (probably) if the object wasn't allocated via GC.  */

static inline page_entry *
lookup_page_table_entry (const void *p)
{
  page_entry ***base;
  size_t L1, L2;

#if HOST_BITS_PER_PTR <= 32
  base = &G.lookup[0];
#else
  page_table table = G.lookup;
  size_t high_bits = (size_t) p & ~ (size_t) 0xffffffff;
  while (table->high_bits != high_bits)
    table = table->next;
  base = &table->table[0];
#endif

  /* Extract the level 1 and 2 indices.  */
  L1 = LOOKUP_L1 (p);
  L2 = LOOKUP_L2 (p);

  return base[L1][L2];
}

/* Set the page table entry for a page.  */

static void
set_page_table_entry (void *p, page_entry *entry)
{
  page_entry ***base;
  size_t L1, L2;

#if HOST_BITS_PER_PTR <= 32
  base = &G.lookup[0];
#else
  page_table table;
  size_t high_bits = (size_t) p & ~ (size_t) 0xffffffff;
  for (table = G.lookup; table; table = table->next)
    if (table->high_bits == high_bits)
      goto found;

  /* Not found -- allocate a new table.  */
  table = xcalloc (1, sizeof(*table));
  table->next = G.lookup;
  table->high_bits = high_bits;
  G.lookup = table;
found:
  base = &table->table[0];
#endif

  /* Extract the level 1 and 2 indices.  */
  L1 = LOOKUP_L1 (p);
  L2 = LOOKUP_L2 (p);

  if (base[L1] == NULL)
    base[L1] = xcalloc (PAGE_L2_SIZE, sizeof (page_entry *));

  base[L1][L2] = entry;
}

/* Prints the page-entry for object size ORDER, for debugging.  */

void
debug_print_page_list (int order)
{
  page_entry *p;
  printf ("Head=%p, Tail=%p:\n", (void *) G.pages[order],
	  (void *) G.page_tails[order]);
  p = G.pages[order];
  while (p != NULL)
    {
      printf ("%p(%1d|%3d) -> ", (void *) p, p->context_depth,
	      p->num_free_objects);
      p = p->next;
    }
  printf ("NULL\n");
  fflush (stdout);
}

#ifdef USING_MMAP
/* Allocate SIZE bytes of anonymous memory, preferably near PREF,
   (if non-null).  The ifdef structure here is intended to cause a
   compile error unless exactly one of the HAVE_* is defined.  */

static inline char *
alloc_anon (char *pref ATTRIBUTE_UNUSED, size_t size)
{
#ifdef HAVE_MMAP_ANON
  char *page = mmap (pref, size, PROT_READ | PROT_WRITE,
		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
#endif
#ifdef HAVE_MMAP_DEV_ZERO
  char *page = mmap (pref, size, PROT_READ | PROT_WRITE,
		     MAP_PRIVATE, G.dev_zero_fd, 0);
#endif

  if (page == (char *) MAP_FAILED)
    {
      perror ("virtual memory exhausted");
      exit (FATAL_EXIT_CODE);
    }

  /* Remember that we allocated this memory.  */
  G.bytes_mapped += size;

  /* Pretend we don't have access to the allocated pages.  We'll enable
     access to smaller pieces of the area in ggc_alloc.  Discard the
     handle to avoid handle leak.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_NOACCESS (page, size));

  return page;
}
#endif
#ifdef USING_MALLOC_PAGE_GROUPS
/* Compute the index for this page into the page group.  */

static inline size_t
page_group_index (char *allocation, char *page)
{
  return (size_t) (page - allocation) >> G.lg_pagesize;
}

/* Set and clear the in_use bit for this page in the page group.  */

static inline void
set_page_group_in_use (page_group *group, char *page)
{
  group->in_use |= 1 << page_group_index (group->allocation, page);
}

static inline void
clear_page_group_in_use (page_group *group, char *page)
{
  group->in_use &= ~(1 << page_group_index (group->allocation, page));
}
#endif

/* Allocate a new page for allocating objects of size 2^ORDER,
   and return an entry for it.  The entry is not added to the
   appropriate page_table list.  */

static inline struct page_entry *
alloc_page (unsigned order)
{
  struct page_entry *entry, *p, **pp;
  char *page;
  size_t num_objects;
  size_t bitmap_size;
  size_t page_entry_size;
  size_t entry_size;
#ifdef USING_MALLOC_PAGE_GROUPS
  page_group *group;
#endif

  num_objects = OBJECTS_PER_PAGE (order);
  bitmap_size = BITMAP_SIZE (num_objects + 1);
  page_entry_size = sizeof (page_entry) - sizeof (long) + bitmap_size;
  entry_size = num_objects * OBJECT_SIZE (order);
  if (entry_size < G.pagesize)
    entry_size = G.pagesize;

  entry = NULL;
  page = NULL;

  /* Check the list of free pages for one we can use.  */
  for (pp = &G.free_pages, p = *pp; p; pp = &p->next, p = *pp)
    if (p->bytes == entry_size)
      break;

  if (p != NULL)
    {
      /* Recycle the allocated memory from this page ...  */
      *pp = p->next;
      page = p->page;

#ifdef USING_MALLOC_PAGE_GROUPS
      group = p->group;
#endif

      /* ... and, if possible, the page entry itself.  */
      if (p->order == order)
	{
	  entry = p;
	  memset (entry, 0, page_entry_size);
	}
      else
	free (p);
    }
#ifdef USING_MMAP
  else if (entry_size == G.pagesize)
    {
      /* We want just one page.  Allocate a bunch of them and put the
	 extras on the freelist.  (Can only do this optimization with
	 mmap for backing store.)  */
      struct page_entry *e, *f = G.free_pages;
      int i;

      page = alloc_anon (NULL, G.pagesize * GGC_QUIRE_SIZE);

      /* This loop counts down so that the chain will be in ascending
	 memory order.  */
      for (i = GGC_QUIRE_SIZE - 1; i >= 1; i--)
	{
	  e = xcalloc (1, page_entry_size);
	  e->order = order;
	  e->bytes = G.pagesize;
	  e->page = page + (i << G.lg_pagesize);
	  e->next = f;
	  f = e;
	}

      G.free_pages = f;
    }
  else
    page = alloc_anon (NULL, entry_size);
#endif
#ifdef USING_MALLOC_PAGE_GROUPS
  else
    {
      /* Allocate a large block of memory and serve out the aligned
	 pages therein.  This results in much less memory wastage
	 than the traditional implementation of valloc.  */

      char *allocation, *a, *enda;
      size_t alloc_size, head_slop, tail_slop;
      int multiple_pages = (entry_size == G.pagesize);

      if (multiple_pages)
	alloc_size = GGC_QUIRE_SIZE * G.pagesize;
      else
	alloc_size = entry_size + G.pagesize - 1;
      allocation = xmalloc (alloc_size);

      page = (char *) (((size_t) allocation + G.pagesize - 1) & -G.pagesize);
      head_slop = page - allocation;
      if (multiple_pages)
	tail_slop = ((size_t) allocation + alloc_size) & (G.pagesize - 1);
      else
	tail_slop = alloc_size - entry_size - head_slop;
      enda = allocation + alloc_size - tail_slop;

      /* We allocated N pages, which are likely not aligned, leaving
	 us with N-1 usable pages.  We plan to place the page_group
	 structure somewhere in the slop.  */
      if (head_slop >= sizeof (page_group))
	group = (page_group *)page - 1;
      else
	{
	  /* We magically got an aligned allocation.  Too bad, we have
	     to waste a page anyway.  */
	  if (tail_slop == 0)
	    {
	      enda -= G.pagesize;
	      tail_slop += G.pagesize;
	    }
	  gcc_assert (tail_slop >= sizeof (page_group));
	  group = (page_group *)enda;
	  tail_slop -= sizeof (page_group);
	}

      /* Remember that we allocated this memory.  */
      group->next = G.page_groups;
      group->allocation = allocation;
      group->alloc_size = alloc_size;
      group->in_use = 0;
      G.page_groups = group;
      G.bytes_mapped += alloc_size;

      /* If we allocated multiple pages, put the rest on the free list.  */
      if (multiple_pages)
	{
	  struct page_entry *e, *f = G.free_pages;
	  for (a = enda - G.pagesize; a != page; a -= G.pagesize)
	    {
	      e = xcalloc (1, page_entry_size);
	      e->order = order;
	      e->bytes = G.pagesize;
	      e->page = a;
	      e->group = group;
	      e->next = f;
	      f = e;
	    }
	  G.free_pages = f;
	}
    }
#endif

  if (entry == NULL)
    entry = xcalloc (1, page_entry_size);

  entry->bytes = entry_size;
  entry->page = page;
  entry->context_depth = G.context_depth;
  entry->order = order;
  entry->num_free_objects = num_objects;
  entry->next_bit_hint = 1;

  G.context_depth_allocations |= (unsigned long)1 << G.context_depth;

#ifdef USING_MALLOC_PAGE_GROUPS
  entry->group = group;
  set_page_group_in_use (group, page);
#endif

  /* Set the one-past-the-end in-use bit.  This acts as a sentry as we
     increment the hint.  */
  entry->in_use_p[num_objects / HOST_BITS_PER_LONG]
    = (unsigned long) 1 << (num_objects % HOST_BITS_PER_LONG);

  set_page_table_entry (page, entry);

  if (GGC_DEBUG_LEVEL >= 2)
    fprintf (G.debug_file,
	     "Allocating page at %p, object size=%lu, data %p-%p\n",
	     (void *) entry, (unsigned long) OBJECT_SIZE (order), page,
	     page + entry_size - 1);

  return entry;
}

/* Adjust the size of G.depth so that no index greater than the one
   used by the top of the G.by_depth is used.  */

static inline void
adjust_depth (void)
{
  page_entry *top;

  if (G.by_depth_in_use)
    {
      top = G.by_depth[G.by_depth_in_use-1];

      /* Peel back indices in depth that index into by_depth, so that
	 as new elements are added to by_depth, we note the indices
	 of those elements, if they are for new context depths.  */
      while (G.depth_in_use > (size_t)top->context_depth+1)
	--G.depth_in_use;
    }
}

/* For a page that is no longer needed, put it on the free page list.  */

static void
free_page (page_entry *entry)
{
  if (GGC_DEBUG_LEVEL >= 2)
    fprintf (G.debug_file,
	     "Deallocating page at %p, data %p-%p\n", (void *) entry,
	     entry->page, entry->page + entry->bytes - 1);

  /* Mark the page as inaccessible.  Discard the handle to avoid handle
     leak.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_NOACCESS (entry->page, entry->bytes));

  set_page_table_entry (entry->page, NULL);

#ifdef USING_MALLOC_PAGE_GROUPS
  clear_page_group_in_use (entry->group, entry->page);
#endif

  if (G.by_depth_in_use > 1)
    {
      page_entry *top = G.by_depth[G.by_depth_in_use-1];
      int i = entry->index_by_depth;

      /* We cannot free a page from a context deeper than the current
	 one.  */
      gcc_assert (entry->context_depth == top->context_depth);
      
      /* Put top element into freed slot.  */
      G.by_depth[i] = top;
      G.save_in_use[i] = G.save_in_use[G.by_depth_in_use-1];
      top->index_by_depth = i;
    }
  --G.by_depth_in_use;

  adjust_depth ();

  entry->next = G.free_pages;
  G.free_pages = entry;
}

/* Release the free page cache to the system.  */

static void
release_pages (void)
{
#ifdef USING_MMAP
  page_entry *p, *next;
  char *start;
  size_t len;

  /* Gather up adjacent pages so they are unmapped together.  */
  p = G.free_pages;

  while (p)
    {
      start = p->page;
      next = p->next;
      len = p->bytes;
      free (p);
      p = next;

      while (p && p->page == start + len)
	{
	  next = p->next;
	  len += p->bytes;
	  free (p);
	  p = next;
	}

      munmap (start, len);
      G.bytes_mapped -= len;
    }

  G.free_pages = NULL;
#endif
#ifdef USING_MALLOC_PAGE_GROUPS
  page_entry **pp, *p;
  page_group **gp, *g;

  /* Remove all pages from free page groups from the list.  */
  pp = &G.free_pages;
  while ((p = *pp) != NULL)
    if (p->group->in_use == 0)
      {
	*pp = p->next;
	free (p);
      }
    else
      pp = &p->next;

  /* Remove all free page groups, and release the storage.  */
  gp = &G.page_groups;
  while ((g = *gp) != NULL)
    if (g->in_use == 0)
      {
	*gp = g->next;
	G.bytes_mapped -= g->alloc_size;
	free (g->allocation);
      }
    else
      gp = &g->next;
#endif
}

/* This table provides a fast way to determine ceil(log_2(size)) for
   allocation requests.  The minimum allocation size is eight bytes.  */

static unsigned char size_lookup[257] =
{
  3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4,
  4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
  5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
  6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
  6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
  7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
  8
};

/* Typed allocation function.  Does nothing special in this collector.  */

void *
ggc_alloc_typed_stat (enum gt_types_enum type ATTRIBUTE_UNUSED, size_t size
		      MEM_STAT_DECL)
{
  return ggc_alloc_stat (size PASS_MEM_STAT);
}

/* Zone allocation function.  Does nothing special in this collector.  */

void *
ggc_alloc_zone_stat (size_t size, struct alloc_zone *zone ATTRIBUTE_UNUSED
		     MEM_STAT_DECL)
{
  return ggc_alloc_stat (size PASS_MEM_STAT);
}

/* Allocate a chunk of memory of SIZE bytes.  Its contents are undefined.  */

void *
ggc_alloc_stat (size_t size MEM_STAT_DECL)
{
  size_t order, word, bit, object_offset, object_size;
  struct page_entry *entry;
  void *result;

  if (size <= 256)
    {
      order = size_lookup[size];
      object_size = OBJECT_SIZE (order);
    }
  else
    {
      order = 9;
      while (size > (object_size = OBJECT_SIZE (order)))
	order++;
    }

  /* If there are non-full pages for this size allocation, they are at
     the head of the list.  */
  entry = G.pages[order];

  /* If there is no page for this object size, or all pages in this
     context are full, allocate a new page.  */
  if (entry == NULL || entry->num_free_objects == 0)
    {
      struct page_entry *new_entry;
      new_entry = alloc_page (order);

      new_entry->index_by_depth = G.by_depth_in_use;
      push_by_depth (new_entry, 0);

      /* We can skip context depths, if we do, make sure we go all the
	 way to the new depth.  */
      while (new_entry->context_depth >= G.depth_in_use)
	push_depth (G.by_depth_in_use-1);

      /* If this is the only entry, it's also the tail.  If it is not
	 the only entry, then we must update the PREV pointer of the
	 ENTRY (G.pages[order]) to point to our new page entry.  */
      if (entry == NULL)
	G.page_tails[order] = new_entry;
      else
	entry->prev = new_entry;

      /* Put new pages at the head of the page list.  By definition the
	 entry at the head of the list always has a NULL pointer.  */
      new_entry->next = entry;
      new_entry->prev = NULL;
      entry = new_entry;
      G.pages[order] = new_entry;

      /* For a new page, we know the word and bit positions (in the
	 in_use bitmap) of the first available object -- they're zero.  */
      new_entry->next_bit_hint = 1;
      word = 0;
      bit = 0;
      object_offset = 0;
    }
  else
    {
      /* First try to use the hint left from the previous allocation
	 to locate a clear bit in the in-use bitmap.  We've made sure
	 that the one-past-the-end bit is always set, so if the hint
	 has run over, this test will fail.  */
      unsigned hint = entry->next_bit_hint;
      word = hint / HOST_BITS_PER_LONG;
      bit = hint % HOST_BITS_PER_LONG;

      /* If the hint didn't work, scan the bitmap from the beginning.  */
      if ((entry->in_use_p[word] >> bit) & 1)
	{
	  word = bit = 0;
	  while (~entry->in_use_p[word] == 0)
	    ++word;
	  while ((entry->in_use_p[word] >> bit) & 1)
	    ++bit;
	  hint = word * HOST_BITS_PER_LONG + bit;
	}

      /* Next time, try the next bit.  */
      entry->next_bit_hint = hint + 1;

      object_offset = hint * object_size;
    }

  /* Set the in-use bit.  */
  entry->in_use_p[word] |= ((unsigned long) 1 << bit);

  /* Keep a running total of the number of free objects.  If this page
     fills up, we may have to move it to the end of the list if the
     next page isn't full.  If the next page is full, all subsequent
     pages are full, so there's no need to move it.  */
  if (--entry->num_free_objects == 0
      && entry->next != NULL
      && entry->next->num_free_objects > 0)
    {
      /* We have a new head for the list.  */
      G.pages[order] = entry->next;

      /* We are moving ENTRY to the end of the page table list.
	 The new page at the head of the list will have NULL in
	 its PREV field and ENTRY will have NULL in its NEXT field.  */
      entry->next->prev = NULL;
      entry->next = NULL;

      /* Append ENTRY to the tail of the list.  */
      entry->prev = G.page_tails[order];
      G.page_tails[order]->next = entry;
      G.page_tails[order] = entry;
    }

  /* Calculate the object's address.  */
  result = entry->page + object_offset;
#ifdef GATHER_STATISTICS
  ggc_record_overhead (OBJECT_SIZE (order), OBJECT_SIZE (order) - size,
		       result PASS_MEM_STAT);
#endif

#ifdef ENABLE_GC_CHECKING
  /* Keep poisoning-by-writing-0xaf the object, in an attempt to keep the
     exact same semantics in presence of memory bugs, regardless of
     ENABLE_VALGRIND_CHECKING.  We override this request below.  Drop the
     handle to avoid handle leak.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_WRITABLE (result, object_size));

  /* `Poison' the entire allocated object, including any padding at
     the end.  */
  memset (result, 0xaf, object_size);

  /* Make the bytes after the end of the object unaccessible.  Discard the
     handle to avoid handle leak.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_NOACCESS ((char *) result + size,
					    object_size - size));
#endif

  /* Tell Valgrind that the memory is there, but its content isn't
     defined.  The bytes at the end of the object are still marked
     unaccessible.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_WRITABLE (result, size));

  /* Keep track of how many bytes are being allocated.  This
     information is used in deciding when to collect.  */
  G.allocated += object_size;

#ifdef GATHER_STATISTICS
  {
    size_t overhead = object_size - size;

    G.stats.total_overhead += overhead;
    G.stats.total_allocated += object_size;
    G.stats.total_overhead_per_order[order] += overhead;
    G.stats.total_allocated_per_order[order] += object_size;

    if (size <= 32)
      {
	G.stats.total_overhead_under32 += overhead;
	G.stats.total_allocated_under32 += object_size;
      }
    if (size <= 64)
      {
	G.stats.total_overhead_under64 += overhead;
	G.stats.total_allocated_under64 += object_size;
      }
    if (size <= 128)
      {
	G.stats.total_overhead_under128 += overhead;
	G.stats.total_allocated_under128 += object_size;
      }
  }
#endif

  if (GGC_DEBUG_LEVEL >= 3)
    fprintf (G.debug_file,
	     "Allocating object, requested size=%lu, actual=%lu at %p on %p\n",
	     (unsigned long) size, (unsigned long) object_size, result,
	     (void *) entry);

  return result;
}

/* If P is not marked, marks it and return false.  Otherwise return true.
   P must have been allocated by the GC allocator; it mustn't point to
   static objects, stack variables, or memory allocated with malloc.  */

int
ggc_set_mark (const void *p)
{
  page_entry *entry;
  unsigned bit, word;
  unsigned long mask;

  /* Look up the page on which the object is alloced.  If the object
     wasn't allocated by the collector, we'll probably die.  */
  entry = lookup_page_table_entry (p);
  gcc_assert (entry);

  /* Calculate the index of the object on the page; this is its bit
     position in the in_use_p bitmap.  */
  bit = OFFSET_TO_BIT (((const char *) p) - entry->page, entry->order);
  word = bit / HOST_BITS_PER_LONG;
  mask = (unsigned long) 1 << (bit % HOST_BITS_PER_LONG);

  /* If the bit was previously set, skip it.  */
  if (entry->in_use_p[word] & mask)
    return 1;

  /* Otherwise set it, and decrement the free object count.  */
  entry->in_use_p[word] |= mask;
  entry->num_free_objects -= 1;

  if (GGC_DEBUG_LEVEL >= 4)
    fprintf (G.debug_file, "Marking %p\n", p);

  return 0;
}

/* Return 1 if P has been marked, zero otherwise.
   P must have been allocated by the GC allocator; it mustn't point to
   static objects, stack variables, or memory allocated with malloc.  */

int
ggc_marked_p (const void *p)
{
  page_entry *entry;
  unsigned bit, word;
  unsigned long mask;

  /* Look up the page on which the object is alloced.  If the object
     wasn't allocated by the collector, we'll probably die.  */
  entry = lookup_page_table_entry (p);
  gcc_assert (entry);

  /* Calculate the index of the object on the page; this is its bit
     position in the in_use_p bitmap.  */
  bit = OFFSET_TO_BIT (((const char *) p) - entry->page, entry->order);
  word = bit / HOST_BITS_PER_LONG;
  mask = (unsigned long) 1 << (bit % HOST_BITS_PER_LONG);

  return (entry->in_use_p[word] & mask) != 0;
}

/* Return the size of the gc-able object P.  */

size_t
ggc_get_size (const void *p)
{
  page_entry *pe = lookup_page_table_entry (p);
  return OBJECT_SIZE (pe->order);
}

/* Release the memory for object P.  */

void
ggc_free (void *p)
{
  page_entry *pe = lookup_page_table_entry (p);
  size_t order = pe->order;
  size_t size = OBJECT_SIZE (order);

#ifdef GATHER_STATISTICS
  ggc_free_overhead (p);
#endif

  if (GGC_DEBUG_LEVEL >= 3)
    fprintf (G.debug_file,
	     "Freeing object, actual size=%lu, at %p on %p\n",
	     (unsigned long) size, p, (void *) pe);

#ifdef ENABLE_GC_CHECKING
  /* Poison the data, to indicate the data is garbage.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_WRITABLE (p, size));
  memset (p, 0xa5, size);
#endif
  /* Let valgrind know the object is free.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_NOACCESS (p, size));

#ifdef ENABLE_GC_ALWAYS_COLLECT
  /* In the completely-anal-checking mode, we do *not* immediately free
     the data, but instead verify that the data is *actually* not 
     reachable the next time we collect.  */
  {
    struct free_object *fo = xmalloc (sizeof (struct free_object));
    fo->object = p;
    fo->next = G.free_object_list;
    G.free_object_list = fo;
  }
#else
  {
    unsigned int bit_offset, word, bit;

    G.allocated -= size;

    /* Mark the object not-in-use.  */
    bit_offset = OFFSET_TO_BIT (((const char *) p) - pe->page, order);
    word = bit_offset / HOST_BITS_PER_LONG;
    bit = bit_offset % HOST_BITS_PER_LONG;
    pe->in_use_p[word] &= ~(1UL << bit);

    if (pe->num_free_objects++ == 0)
      {
	page_entry *p, *q;

	/* If the page is completely full, then it's supposed to
	   be after all pages that aren't.  Since we've freed one
	   object from a page that was full, we need to move the
	   page to the head of the list. 

	   PE is the node we want to move.  Q is the previous node
	   and P is the next node in the list.  */
	q = pe->prev;
	if (q && q->num_free_objects == 0)
	  {
	    p = pe->next;

	    q->next = p;

	    /* If PE was at the end of the list, then Q becomes the
	       new end of the list.  If PE was not the end of the
	       list, then we need to update the PREV field for P.  */
	    if (!p)
	      G.page_tails[order] = q;
	    else
	      p->prev = q;

	    /* Move PE to the head of the list.  */
	    pe->next = G.pages[order];
	    pe->prev = NULL;
	    G.pages[order]->prev = pe;
	    G.pages[order] = pe;
	  }

	/* Reset the hint bit to point to the only free object.  */
	pe->next_bit_hint = bit_offset;
      }
  }
#endif
}

/* Subroutine of init_ggc which computes the pair of numbers used to
   perform division by OBJECT_SIZE (order) and fills in inverse_table[].

   This algorithm is taken from Granlund and Montgomery's paper
   "Division by Invariant Integers using Multiplication"
   (Proc. SIGPLAN PLDI, 1994), section 9 (Exact division by
   constants).  */

static void
compute_inverse (unsigned order)
{
  size_t size, inv; 
  unsigned int e;

  size = OBJECT_SIZE (order);
  e = 0;
  while (size % 2 == 0)
    {
      e++;
      size >>= 1;
    }

  inv = size;
  while (inv * size != 1)
    inv = inv * (2 - inv*size);

  DIV_MULT (order) = inv;
  DIV_SHIFT (order) = e;
}

/* Initialize the ggc-mmap allocator.  */
void
init_ggc (void)
{
  unsigned order;

  G.pagesize = getpagesize();
  G.lg_pagesize = exact_log2 (G.pagesize);

#ifdef HAVE_MMAP_DEV_ZERO
  G.dev_zero_fd = open ("/dev/zero", O_RDONLY);
  if (G.dev_zero_fd == -1)
    internal_error ("open /dev/zero: %m");
#endif

#if 0
  G.debug_file = fopen ("ggc-mmap.debug", "w");
#else
  G.debug_file = stdout;
#endif

#ifdef USING_MMAP
  /* StunOS has an amazing off-by-one error for the first mmap allocation
     after fiddling with RLIMIT_STACK.  The result, as hard as it is to
     believe, is an unaligned page allocation, which would cause us to
     hork badly if we tried to use it.  */
  {
    char *p = alloc_anon (NULL, G.pagesize);
    struct page_entry *e;
    if ((size_t)p & (G.pagesize - 1))
      {
	/* How losing.  Discard this one and try another.  If we still
	   can't get something useful, give up.  */

	p = alloc_anon (NULL, G.pagesize);
	gcc_assert (!((size_t)p & (G.pagesize - 1)));
      }

    /* We have a good page, might as well hold onto it...  */
    e = xcalloc (1, sizeof (struct page_entry));
    e->bytes = G.pagesize;
    e->page = p;
    e->next = G.free_pages;
    G.free_pages = e;
  }
#endif

  /* Initialize the object size table.  */
  for (order = 0; order < HOST_BITS_PER_PTR; ++order)
    object_size_table[order] = (size_t) 1 << order;
  for (order = HOST_BITS_PER_PTR; order < NUM_ORDERS; ++order)
    {
      size_t s = extra_order_size_table[order - HOST_BITS_PER_PTR];

      /* If S is not a multiple of the MAX_ALIGNMENT, then round it up
	 so that we're sure of getting aligned memory.  */
      s = ROUND_UP (s, MAX_ALIGNMENT);
      object_size_table[order] = s;
    }

  /* Initialize the objects-per-page and inverse tables.  */
  for (order = 0; order < NUM_ORDERS; ++order)
    {
      objects_per_page_table[order] = G.pagesize / OBJECT_SIZE (order);
      if (objects_per_page_table[order] == 0)
	objects_per_page_table[order] = 1;
      compute_inverse (order);
    }

  /* Reset the size_lookup array to put appropriately sized objects in
     the special orders.  All objects bigger than the previous power
     of two, but no greater than the special size, should go in the
     new order.  */
  for (order = HOST_BITS_PER_PTR; order < NUM_ORDERS; ++order)
    {
      int o;
      int i;

      o = size_lookup[OBJECT_SIZE (order)];
      for (i = OBJECT_SIZE (order); size_lookup [i] == o; --i)
	size_lookup[i] = order;
    }

  G.depth_in_use = 0;
  G.depth_max = 10;
  G.depth = xmalloc (G.depth_max * sizeof (unsigned int));

  G.by_depth_in_use = 0;
  G.by_depth_max = INITIAL_PTE_COUNT;
  G.by_depth = xmalloc (G.by_depth_max * sizeof (page_entry *));
  G.save_in_use = xmalloc (G.by_depth_max * sizeof (unsigned long *));
}

/* Start a new GGC zone.  */

struct alloc_zone *
new_ggc_zone (const char *name ATTRIBUTE_UNUSED)
{
  return NULL;
}

/* Destroy a GGC zone.  */
void
destroy_ggc_zone (struct alloc_zone *zone ATTRIBUTE_UNUSED)
{
}

/* Increment the `GC context'.  Objects allocated in an outer context
   are never freed, eliminating the need to register their roots.  */

void
ggc_push_context (void)
{
  ++G.context_depth;

  /* Die on wrap.  */
  gcc_assert (G.context_depth < HOST_BITS_PER_LONG);
}

/* Merge the SAVE_IN_USE_P and IN_USE_P arrays in P so that IN_USE_P
   reflects reality.  Recalculate NUM_FREE_OBJECTS as well.  */

static void
ggc_recalculate_in_use_p (page_entry *p)
{
  unsigned int i;
  size_t num_objects;

  /* Because the past-the-end bit in in_use_p is always set, we
     pretend there is one additional object.  */
  num_objects = OBJECTS_IN_PAGE (p) + 1;

  /* Reset the free object count.  */
  p->num_free_objects = num_objects;

  /* Combine the IN_USE_P and SAVE_IN_USE_P arrays.  */
  for (i = 0;
       i < CEIL (BITMAP_SIZE (num_objects),
		 sizeof (*p->in_use_p));
       ++i)
    {
      unsigned long j;

      /* Something is in use if it is marked, or if it was in use in a
	 context further down the context stack.  */
      p->in_use_p[i] |= save_in_use_p (p)[i];

      /* Decrement the free object count for every object allocated.  */
      for (j = p->in_use_p[i]; j; j >>= 1)
	p->num_free_objects -= (j & 1);
    }

  gcc_assert (p->num_free_objects < num_objects);
}

/* Decrement the `GC context'.  All objects allocated since the
   previous ggc_push_context are migrated to the outer context.  */

void
ggc_pop_context (void)
{
  unsigned long omask;
  unsigned int depth, i, e;
#ifdef ENABLE_CHECKING
  unsigned int order;
#endif

  depth = --G.context_depth;
  omask = (unsigned long)1 << (depth + 1);

  if (!((G.context_depth_allocations | G.context_depth_collections) & omask))
    return;

  G.context_depth_allocations |= (G.context_depth_allocations & omask) >> 1;
  G.context_depth_allocations &= omask - 1;
  G.context_depth_collections &= omask - 1;

  /* The G.depth array is shortened so that the last index is the
     context_depth of the top element of by_depth.  */
  if (depth+1 < G.depth_in_use)
    e = G.depth[depth+1];
  else
    e = G.by_depth_in_use;

  /* We might not have any PTEs of depth depth.  */
  if (depth < G.depth_in_use)
    {

      /* First we go through all the pages at depth depth to
	 recalculate the in use bits.  */
      for (i = G.depth[depth]; i < e; ++i)
	{
	  page_entry *p = G.by_depth[i];

	  /* Check that all of the pages really are at the depth that
	     we expect.  */
	  gcc_assert (p->context_depth == depth);
	  gcc_assert (p->index_by_depth == i);

	  prefetch (&save_in_use_p_i (i+8));
	  prefetch (&save_in_use_p_i (i+16));
	  if (save_in_use_p_i (i))
	    {
	      p = G.by_depth[i];
	      ggc_recalculate_in_use_p (p);
	      free (save_in_use_p_i (i));
	      save_in_use_p_i (i) = 0;
	    }
	}
    }

  /* Then, we reset all page_entries with a depth greater than depth
     to be at depth.  */
  for (i = e; i < G.by_depth_in_use; ++i)
    {
      page_entry *p = G.by_depth[i];

      /* Check that all of the pages really are at the depth we
	 expect.  */
      gcc_assert (p->context_depth > depth);
      gcc_assert (p->index_by_depth == i);
      p->context_depth = depth;
    }

  adjust_depth ();

#ifdef ENABLE_CHECKING
  for (order = 2; order < NUM_ORDERS; order++)
    {
      page_entry *p;

      for (p = G.pages[order]; p != NULL; p = p->next)
	gcc_assert (p->context_depth < depth ||
		    (p->context_depth == depth && !save_in_use_p (p)));
    }
#endif
}

/* Unmark all objects.  */

static void
clear_marks (void)
{
  unsigned order;

  for (order = 2; order < NUM_ORDERS; order++)
    {
      page_entry *p;

      for (p = G.pages[order]; p != NULL; p = p->next)
	{
	  size_t num_objects = OBJECTS_IN_PAGE (p);
	  size_t bitmap_size = BITMAP_SIZE (num_objects + 1);

	  /* The data should be page-aligned.  */
	  gcc_assert (!((size_t) p->page & (G.pagesize - 1)));

	  /* Pages that aren't in the topmost context are not collected;
	     nevertheless, we need their in-use bit vectors to store GC
	     marks.  So, back them up first.  */
	  if (p->context_depth < G.context_depth)
	    {
	      if (! save_in_use_p (p))
		save_in_use_p (p) = xmalloc (bitmap_size);
	      memcpy (save_in_use_p (p), p->in_use_p, bitmap_size);
	    }

	  /* Reset reset the number of free objects and clear the
             in-use bits.  These will be adjusted by mark_obj.  */
	  p->num_free_objects = num_objects;
	  memset (p->in_use_p, 0, bitmap_size);

	  /* Make sure the one-past-the-end bit is always set.  */
	  p->in_use_p[num_objects / HOST_BITS_PER_LONG]
	    = ((unsigned long) 1 << (num_objects % HOST_BITS_PER_LONG));
	}
    }
}

/* Free all empty pages.  Partially empty pages need no attention
   because the `mark' bit doubles as an `unused' bit.  */

static void
sweep_pages (void)
{
  unsigned order;

  for (order = 2; order < NUM_ORDERS; order++)
    {
      /* The last page-entry to consider, regardless of entries
	 placed at the end of the list.  */
      page_entry * const last = G.page_tails[order];

      size_t num_objects;
      size_t live_objects;
      page_entry *p, *previous;
      int done;

      p = G.pages[order];
      if (p == NULL)
	continue;

      previous = NULL;
      do
	{
	  page_entry *next = p->next;

	  /* Loop until all entries have been examined.  */
	  done = (p == last);

	  num_objects = OBJECTS_IN_PAGE (p);

	  /* Add all live objects on this page to the count of
             allocated memory.  */
	  live_objects = num_objects - p->num_free_objects;

	  G.allocated += OBJECT_SIZE (order) * live_objects;

	  /* Only objects on pages in the topmost context should get
	     collected.  */
	  if (p->context_depth < G.context_depth)
	    ;

	  /* Remove the page if it's empty.  */
	  else if (live_objects == 0)
	    {
	      /* If P was the first page in the list, then NEXT
		 becomes the new first page in the list, otherwise
		 splice P out of the forward pointers.  */
	      if (! previous)
		G.pages[order] = next;
	      else
		previous->next = next;
	    
	      /* Splice P out of the back pointers too.  */
	      if (next)
		next->prev = previous;

	      /* Are we removing the last element?  */
	      if (p == G.page_tails[order])
		G.page_tails[order] = previous;
	      free_page (p);
	      p = previous;
	    }

	  /* If the page is full, move it to the end.  */
	  else if (p->num_free_objects == 0)
	    {
	      /* Don't move it if it's already at the end.  */
	      if (p != G.page_tails[order])
		{
		  /* Move p to the end of the list.  */
		  p->next = NULL;
		  p->prev = G.page_tails[order];
		  G.page_tails[order]->next = p;

		  /* Update the tail pointer...  */
		  G.page_tails[order] = p;

		  /* ... and the head pointer, if necessary.  */
		  if (! previous)
		    G.pages[order] = next;
		  else
		    previous->next = next;

		  /* And update the backpointer in NEXT if necessary.  */
		  if (next)
		    next->prev = previous;

		  p = previous;
		}
	    }

	  /* If we've fallen through to here, it's a page in the
	     topmost context that is neither full nor empty.  Such a
	     page must precede pages at lesser context depth in the
	     list, so move it to the head.  */
	  else if (p != G.pages[order])
	    {
	      previous->next = p->next;

	      /* Update the backchain in the next node if it exists.  */
	      if (p->next)
		p->next->prev = previous;

	      /* Move P to the head of the list.  */
	      p->next = G.pages[order];
	      p->prev = NULL;
	      G.pages[order]->prev = p;

	      /* Update the head pointer.  */
	      G.pages[order] = p;

	      /* Are we moving the last element?  */
	      if (G.page_tails[order] == p)
	        G.page_tails[order] = previous;
	      p = previous;
	    }

	  previous = p;
	  p = next;
	}
      while (! done);

      /* Now, restore the in_use_p vectors for any pages from contexts
         other than the current one.  */
      for (p = G.pages[order]; p; p = p->next)
	if (p->context_depth != G.context_depth)
	  ggc_recalculate_in_use_p (p);
    }
}

#ifdef ENABLE_GC_CHECKING
/* Clobber all free objects.  */

static void
poison_pages (void)
{
  unsigned order;

  for (order = 2; order < NUM_ORDERS; order++)
    {
      size_t size = OBJECT_SIZE (order);
      page_entry *p;

      for (p = G.pages[order]; p != NULL; p = p->next)
	{
	  size_t num_objects;
	  size_t i;

	  if (p->context_depth != G.context_depth)
	    /* Since we don't do any collection for pages in pushed
	       contexts, there's no need to do any poisoning.  And
	       besides, the IN_USE_P array isn't valid until we pop
	       contexts.  */
	    continue;

	  num_objects = OBJECTS_IN_PAGE (p);
	  for (i = 0; i < num_objects; i++)
	    {
	      size_t word, bit;
	      word = i / HOST_BITS_PER_LONG;
	      bit = i % HOST_BITS_PER_LONG;
	      if (((p->in_use_p[word] >> bit) & 1) == 0)
		{
		  char *object = p->page + i * size;

		  /* Keep poison-by-write when we expect to use Valgrind,
		     so the exact same memory semantics is kept, in case
		     there are memory errors.  We override this request
		     below.  */
		  VALGRIND_DISCARD (VALGRIND_MAKE_WRITABLE (object, size));
		  memset (object, 0xa5, size);

		  /* Drop the handle to avoid handle leak.  */
		  VALGRIND_DISCARD (VALGRIND_MAKE_NOACCESS (object, size));
		}
	    }
	}
    }
}
#else
#define poison_pages()
#endif

#ifdef ENABLE_GC_ALWAYS_COLLECT
/* Validate that the reportedly free objects actually are.  */

static void
validate_free_objects (void)
{
  struct free_object *f, *next, *still_free = NULL;

  for (f = G.free_object_list; f ; f = next)
    {
      page_entry *pe = lookup_page_table_entry (f->object);
      size_t bit, word;

      bit = OFFSET_TO_BIT ((char *)f->object - pe->page, pe->order);
      word = bit / HOST_BITS_PER_LONG;
      bit = bit % HOST_BITS_PER_LONG;
      next = f->next;

      /* Make certain it isn't visible from any root.  Notice that we
	 do this check before sweep_pages merges save_in_use_p.  */
      gcc_assert (!(pe->in_use_p[word] & (1UL << bit)));

      /* If the object comes from an outer context, then retain the
	 free_object entry, so that we can verify that the address
	 isn't live on the stack in some outer context.  */
      if (pe->context_depth != G.context_depth)
	{
	  f->next = still_free;
	  still_free = f;
	}
      else
	free (f);
    }

  G.free_object_list = still_free;
}
#else
#define validate_free_objects()
#endif

/* Top level mark-and-sweep routine.  */

void
ggc_collect (void)
{
  /* Avoid frequent unnecessary work by skipping collection if the
     total allocations haven't expanded much since the last
     collection.  */
  float allocated_last_gc =
    MAX (G.allocated_last_gc, (size_t)PARAM_VALUE (GGC_MIN_HEAPSIZE) * 1024);

  float min_expand = allocated_last_gc * PARAM_VALUE (GGC_MIN_EXPAND) / 100;

  if (G.allocated < allocated_last_gc + min_expand && !ggc_force_collect)
    return;

  timevar_push (TV_GC);
  if (!quiet_flag)
    fprintf (stderr, " {GC %luk -> ", (unsigned long) G.allocated / 1024);
  if (GGC_DEBUG_LEVEL >= 2)
    fprintf (G.debug_file, "BEGIN COLLECTING\n");

  /* Zero the total allocated bytes.  This will be recalculated in the
     sweep phase.  */
  G.allocated = 0;

  /* Release the pages we freed the last time we collected, but didn't
     reuse in the interim.  */
  release_pages ();

  /* Indicate that we've seen collections at this context depth.  */
  G.context_depth_collections = ((unsigned long)1 << (G.context_depth + 1)) - 1;

  clear_marks ();
  ggc_mark_roots ();
#ifdef GATHER_STATISTICS
  ggc_prune_overhead_list ();
#endif
  poison_pages ();
  validate_free_objects ();
  sweep_pages ();

  G.allocated_last_gc = G.allocated;

  timevar_pop (TV_GC);

  if (!quiet_flag)
    fprintf (stderr, "%luk}", (unsigned long) G.allocated / 1024);
  if (GGC_DEBUG_LEVEL >= 2)
    fprintf (G.debug_file, "END COLLECTING\n");
}

/* Print allocation statistics.  */
#define SCALE(x) ((unsigned long) ((x) < 1024*10 \
		  ? (x) \
		  : ((x) < 1024*1024*10 \
		     ? (x) / 1024 \
		     : (x) / (1024*1024))))
#define STAT_LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))

void
ggc_print_statistics (void)
{
  struct ggc_statistics stats;
  unsigned int i;
  size_t total_overhead = 0;

  /* Clear the statistics.  */
  memset (&stats, 0, sizeof (stats));

  /* Make sure collection will really occur.  */
  G.allocated_last_gc = 0;

  /* Collect and print the statistics common across collectors.  */
  ggc_print_common_statistics (stderr, &stats);

  /* Release free pages so that we will not count the bytes allocated
     there as part of the total allocated memory.  */
  release_pages ();

  /* Collect some information about the various sizes of
     allocation.  */
  fprintf (stderr,
           "Memory still allocated at the end of the compilation process\n");
  fprintf (stderr, "%-5s %10s  %10s  %10s\n",
	   "Size", "Allocated", "Used", "Overhead");
  for (i = 0; i < NUM_ORDERS; ++i)
    {
      page_entry *p;
      size_t allocated;
      size_t in_use;
      size_t overhead;

      /* Skip empty entries.  */
      if (!G.pages[i])
	continue;

      overhead = allocated = in_use = 0;

      /* Figure out the total number of bytes allocated for objects of
	 this size, and how many of them are actually in use.  Also figure
	 out how much memory the page table is using.  */
      for (p = G.pages[i]; p; p = p->next)
	{
	  allocated += p->bytes;
	  in_use +=
	    (OBJECTS_IN_PAGE (p) - p->num_free_objects) * OBJECT_SIZE (i);

	  overhead += (sizeof (page_entry) - sizeof (long)
		       + BITMAP_SIZE (OBJECTS_IN_PAGE (p) + 1));
	}
      fprintf (stderr, "%-5lu %10lu%c %10lu%c %10lu%c\n",
	       (unsigned long) OBJECT_SIZE (i),
	       SCALE (allocated), STAT_LABEL (allocated),
	       SCALE (in_use), STAT_LABEL (in_use),
	       SCALE (overhead), STAT_LABEL (overhead));
      total_overhead += overhead;
    }
  fprintf (stderr, "%-5s %10lu%c %10lu%c %10lu%c\n", "Total",
	   SCALE (G.bytes_mapped), STAT_LABEL (G.bytes_mapped),
	   SCALE (G.allocated), STAT_LABEL(G.allocated),
	   SCALE (total_overhead), STAT_LABEL (total_overhead));

#ifdef GATHER_STATISTICS  
  {
    fprintf (stderr, "\nTotal allocations and overheads during the compilation process\n");

    fprintf (stderr, "Total Overhead:                        %10lld\n",
             G.stats.total_overhead);
    fprintf (stderr, "Total Allocated:                       %10lld\n",
             G.stats.total_allocated);

    fprintf (stderr, "Total Overhead  under  32B:            %10lld\n",
             G.stats.total_overhead_under32);
    fprintf (stderr, "Total Allocated under  32B:            %10lld\n",
             G.stats.total_allocated_under32);
    fprintf (stderr, "Total Overhead  under  64B:            %10lld\n",
             G.stats.total_overhead_under64);
    fprintf (stderr, "Total Allocated under  64B:            %10lld\n",
             G.stats.total_allocated_under64);
    fprintf (stderr, "Total Overhead  under 128B:            %10lld\n",
             G.stats.total_overhead_under128);
    fprintf (stderr, "Total Allocated under 128B:            %10lld\n",
             G.stats.total_allocated_under128);
   
    for (i = 0; i < NUM_ORDERS; i++)
      if (G.stats.total_allocated_per_order[i])
        {
          fprintf (stderr, "Total Overhead  page size %7d:     %10lld\n",
                   OBJECT_SIZE (i), G.stats.total_overhead_per_order[i]);
          fprintf (stderr, "Total Allocated page size %7d:     %10lld\n",
                   OBJECT_SIZE (i), G.stats.total_allocated_per_order[i]);
        }
  }
#endif
}

struct ggc_pch_data
{
  struct ggc_pch_ondisk
  {
    unsigned totals[NUM_ORDERS];
  } d;
  size_t base[NUM_ORDERS];
  size_t written[NUM_ORDERS];
};

struct ggc_pch_data *
init_ggc_pch (void)
{
  return xcalloc (sizeof (struct ggc_pch_data), 1);
}

void
ggc_pch_count_object (struct ggc_pch_data *d, void *x ATTRIBUTE_UNUSED,
		      size_t size, bool is_string ATTRIBUTE_UNUSED)
{
  unsigned order;

  if (size <= 256)
    order = size_lookup[size];
  else
    {
      order = 9;
      while (size > OBJECT_SIZE (order))
	order++;
    }

  d->d.totals[order]++;
}

size_t
ggc_pch_total_size (struct ggc_pch_data *d)
{
  size_t a = 0;
  unsigned i;

  for (i = 0; i < NUM_ORDERS; i++)
    a += ROUND_UP (d->d.totals[i] * OBJECT_SIZE (i), G.pagesize);
  return a;
}

void
ggc_pch_this_base (struct ggc_pch_data *d, void *base)
{
  size_t a = (size_t) base;
  unsigned i;

  for (i = 0; i < NUM_ORDERS; i++)
    {
      d->base[i] = a;
      a += ROUND_UP (d->d.totals[i] * OBJECT_SIZE (i), G.pagesize);
    }
}


char *
ggc_pch_alloc_object (struct ggc_pch_data *d, void *x ATTRIBUTE_UNUSED,
		      size_t size, bool is_string ATTRIBUTE_UNUSED)
{
  unsigned order;
  char *result;

  if (size <= 256)
    order = size_lookup[size];
  else
    {
      order = 9;
      while (size > OBJECT_SIZE (order))
	order++;
    }

  result = (char *) d->base[order];
  d->base[order] += OBJECT_SIZE (order);
  return result;
}

void
ggc_pch_prepare_write (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
		       FILE *f ATTRIBUTE_UNUSED)
{
  /* Nothing to do.  */
}

void
ggc_pch_write_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
		      FILE *f, void *x, void *newx ATTRIBUTE_UNUSED,
		      size_t size, bool is_string ATTRIBUTE_UNUSED)
{
  unsigned order;
  static const char emptyBytes[256];

  if (size <= 256)
    order = size_lookup[size];
  else
    {
      order = 9;
      while (size > OBJECT_SIZE (order))
	order++;
    }

  if (fwrite (x, size, 1, f) != 1)
    fatal_error ("can't write PCH file: %m");

  /* If SIZE is not the same as OBJECT_SIZE(order), then we need to pad the
     object out to OBJECT_SIZE(order).  This happens for strings.  */

  if (size != OBJECT_SIZE (order))
    {
      unsigned padding = OBJECT_SIZE(order) - size;

      /* To speed small writes, we use a nulled-out array that's larger
         than most padding requests as the source for our null bytes.  This
         permits us to do the padding with fwrite() rather than fseek(), and
         limits the chance the the OS may try to flush any outstanding
         writes.  */
      if (padding <= sizeof(emptyBytes))
        {
          if (fwrite (emptyBytes, 1, padding, f) != padding)
            fatal_error ("can't write PCH file");
        }
      else
        {
          /* Larger than our buffer?  Just default to fseek.  */
          if (fseek (f, padding, SEEK_CUR) != 0)
            fatal_error ("can't write PCH file");
        }
    }

  d->written[order]++;
  if (d->written[order] == d->d.totals[order]
      && fseek (f, ROUND_UP_VALUE (d->d.totals[order] * OBJECT_SIZE (order),
				   G.pagesize),
		SEEK_CUR) != 0)
    fatal_error ("can't write PCH file: %m");
}

void
ggc_pch_finish (struct ggc_pch_data *d, FILE *f)
{
  if (fwrite (&d->d, sizeof (d->d), 1, f) != 1)
    fatal_error ("can't write PCH file: %m");
  free (d);
}

/* Move the PCH PTE entries just added to the end of by_depth, to the
   front.  */

static void
move_ptes_to_front (int count_old_page_tables, int count_new_page_tables)
{
  unsigned i;

  /* First, we swap the new entries to the front of the varrays.  */
  page_entry **new_by_depth;
  unsigned long **new_save_in_use;

  new_by_depth = xmalloc (G.by_depth_max * sizeof (page_entry *));
  new_save_in_use = xmalloc (G.by_depth_max * sizeof (unsigned long *));

  memcpy (&new_by_depth[0],
	  &G.by_depth[count_old_page_tables],
	  count_new_page_tables * sizeof (void *));
  memcpy (&new_by_depth[count_new_page_tables],
	  &G.by_depth[0],
	  count_old_page_tables * sizeof (void *));
  memcpy (&new_save_in_use[0],
	  &G.save_in_use[count_old_page_tables],
	  count_new_page_tables * sizeof (void *));
  memcpy (&new_save_in_use[count_new_page_tables],
	  &G.save_in_use[0],
	  count_old_page_tables * sizeof (void *));

  free (G.by_depth);
  free (G.save_in_use);

  G.by_depth = new_by_depth;
  G.save_in_use = new_save_in_use;

  /* Now update all the index_by_depth fields.  */
  for (i = G.by_depth_in_use; i > 0; --i)
    {
      page_entry *p = G.by_depth[i-1];
      p->index_by_depth = i-1;
    }

  /* And last, we update the depth pointers in G.depth.  The first
     entry is already 0, and context 0 entries always start at index
     0, so there is nothing to update in the first slot.  We need a
     second slot, only if we have old ptes, and if we do, they start
     at index count_new_page_tables.  */
  if (count_old_page_tables)
    push_depth (count_new_page_tables);
}

void
ggc_pch_read (FILE *f, void *addr)
{
  struct ggc_pch_ondisk d;
  unsigned i;
  char *offs = addr;
  unsigned long count_old_page_tables;
  unsigned long count_new_page_tables;

  count_old_page_tables = G.by_depth_in_use;

  /* We've just read in a PCH file.  So, every object that used to be
     allocated is now free.  */
  clear_marks ();
#ifdef ENABLE_GC_CHECKING
  poison_pages ();
#endif

  /* No object read from a PCH file should ever be freed.  So, set the
     context depth to 1, and set the depth of all the currently-allocated
     pages to be 1 too.  PCH pages will have depth 0.  */
  gcc_assert (!G.context_depth);
  G.context_depth = 1;
  for (i = 0; i < NUM_ORDERS; i++)
    {
      page_entry *p;
      for (p = G.pages[i]; p != NULL; p = p->next)
	p->context_depth = G.context_depth;
    }

  /* Allocate the appropriate page-table entries for the pages read from
     the PCH file.  */
  if (fread (&d, sizeof (d), 1, f) != 1)
    fatal_error ("can't read PCH file: %m");

  for (i = 0; i < NUM_ORDERS; i++)
    {
      struct page_entry *entry;
      char *pte;
      size_t bytes;
      size_t num_objs;
      size_t j;

      if (d.totals[i] == 0)
	continue;

      bytes = ROUND_UP (d.totals[i] * OBJECT_SIZE (i), G.pagesize);
      num_objs = bytes / OBJECT_SIZE (i);
      entry = xcalloc (1, (sizeof (struct page_entry)
			   - sizeof (long)
			   + BITMAP_SIZE (num_objs + 1)));
      entry->bytes = bytes;
      entry->page = offs;
      entry->context_depth = 0;
      offs += bytes;
      entry->num_free_objects = 0;
      entry->order = i;

      for (j = 0;
	   j + HOST_BITS_PER_LONG <= num_objs + 1;
	   j += HOST_BITS_PER_LONG)
	entry->in_use_p[j / HOST_BITS_PER_LONG] = -1;
      for (; j < num_objs + 1; j++)
	entry->in_use_p[j / HOST_BITS_PER_LONG]
	  |= 1L << (j % HOST_BITS_PER_LONG);

      for (pte = entry->page;
	   pte < entry->page + entry->bytes;
	   pte += G.pagesize)
	set_page_table_entry (pte, entry);

      if (G.page_tails[i] != NULL)
	G.page_tails[i]->next = entry;
      else
	G.pages[i] = entry;
      G.page_tails[i] = entry;

      /* We start off by just adding all the new information to the
	 end of the varrays, later, we will move the new information
	 to the front of the varrays, as the PCH page tables are at
	 context 0.  */
      push_by_depth (entry, 0);
    }

  /* Now, we update the various data structures that speed page table
     handling.  */
  count_new_page_tables = G.by_depth_in_use - count_old_page_tables;

  move_ptes_to_front (count_old_page_tables, count_new_page_tables);

  /* Update the statistics.  */
  G.allocated = G.allocated_last_gc = offs - (char *)addr;
}