File: opt.c

package info (click to toggle)
gnu-smalltalk 3.2.4-2.1
  • links: PTS, VCS
  • area: main
  • in suites: jessie, jessie-kfreebsd
  • size: 32,688 kB
  • ctags: 14,104
  • sloc: ansic: 87,424; sh: 22,729; asm: 8,465; perl: 4,513; cpp: 3,548; xml: 1,669; awk: 1,581; yacc: 1,357; makefile: 1,237; lisp: 855; lex: 843; sed: 258; objc: 124
file content (1911 lines) | stat: -rw-r--r-- 52,101 bytes parent folder | download | duplicates (2)
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
/******************************* -*- C -*- ****************************
 *
 *	Functions for byte code optimization & analysis
 *
 *
 ***********************************************************************/

/***********************************************************************
 *
 * Copyright 2000,2001,2002,2003,2006,2008,2009 Free Software Foundation, Inc.
 * Written by Paolo Bonzini.
 *
 * This file is part of GNU Smalltalk.
 *
 * GNU Smalltalk 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.
 *
 * Linking GNU Smalltalk statically or dynamically with other modules is
 * making a combined work based on GNU Smalltalk.  Thus, the terms and
 * conditions of the GNU General Public License cover the whole
 * combination.
 *
 * In addition, as a special exception, the Free Software Foundation
 * give you permission to combine GNU Smalltalk with free software
 * programs or libraries that are released under the GNU LGPL and with
 * independent programs running under the GNU Smalltalk virtual machine.
 *
 * You may copy and distribute such a system following the terms of the
 * GNU GPL for GNU Smalltalk and the licenses of the other code
 * concerned, provided that you include the source code of that other
 * code when and as the GNU GPL requires distribution of source code.
 *
 * Note that people who make modified versions of GNU Smalltalk are not
 * obligated to grant this special exception for their modified
 * versions; it is their choice whether to do so.  The GNU General
 * Public License gives permission to release a modified version without
 * this exception; this exception also makes it possible to release a
 * modified version which carries forward this exception.
 *
 * GNU Smalltalk 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
 * GNU Smalltalk; see the file COPYING.	 If not, write to the Free Software
 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 ***********************************************************************/


#include "gstpriv.h"
#include "match.h"

/* Define this to have verbose messages from the JIT compiler's
   basic-block split phase.  */
/* #define DEBUG_JIT_TRANSLATOR */

/* Define this to have verbose messages from the bytecode verifier.  */
/* #define DEBUG_VERIFIER */

/* Define this to disable the peephole bytecode optimizer.  It works
   well for decreasing the footprint and increasing the speed, so
   there's no reason to do that unless you're debugging the compiler.  */
/* #define NO_OPTIMIZE */

/* Define this to disable superoperators in the peephole bytecode
   optimizer.  Some simple optimizations will still be done, making
   the output suitable for searching superoperator candidates.  */
/* #define NO_SUPEROPERATORS */

/* Define this to disable bytecode verification.  */
/* #define NO_VERIFIER */

/* The JIT compiler prefers optimized bytecodes, because they are
   more regular.  */
#ifdef ENABLE_JIT_TRANSLATION
#undef NO_OPTIMIZE
#endif



/* This structure and the following one are used by the bytecode
   peephole optimizer.
   
   This one, in particular, defines where basic blocks start in the
   non- optimized bytecodes. byte is nothing more than an offset in
   those bytecodes; id is used to pair jump bytecodes with their
   destinations: in the initial scan, when we encounter a jump
   bytecode we fill two block_boundaries -- one has positive id and
   represents the destination of the jump, one has negative id (but
   the same absolute value) and represents the jump bytecode
   itself.  */
typedef struct block_boundary
{
  /* Bytecode at the end of the basic block, -1 if not a jump.  */
  int kind;

  /* Start of the basic block.  */
  int start, end;

  /* Destination IP for the jump at the end of the basic block.  */
  int dest;

  /* Destination basic block for the jump at the end of the basic block.  */
  struct block_boundary *dest_bb;

  /* Size of the optimized basic block.  */
  int opt_length;

  /* Offset of the basic block in the optimized method.  */
  int final_byte;
}
block_boundary;

/* Basic block data structure, common to the JIT and the verifier.  */
typedef struct basic_block_item {
  struct basic_block_item *next;
  struct basic_block_item **bb;
  gst_uchar *bp;
  int sp;

  /* Suspended basic blocks are those for which we know the initial
     instruction pointer, but not the initial stack pointer.  Since
     data-flow analysis should walk them, these are put aside
     momentarily.

     They are generated when there is no basic block for the
     bytecode after a jump or a return.  If they are unreachable
     and they follow a jump, they're supposed to have an initial
     SP = 0, else the initial SP is put to the same as the
     return bytecode's SP (this is to accomodate comp.c's
     behavior when emitting "a ifTrue: [ ^1 ] ifFalse: [ ^2 ]").

     However, the initial SP of a suspended block can always be
     overridden if a jump to the block is found, in which case
     the flag is cleared.  Suspended basic blocks are processed
     FIFO, not LIFO like the normal worklist.  */
  mst_Boolean suspended;
  OOP stack[1];
} basic_block_item;

#define ALLOCA_BASIC_BLOCK(dest, depth, bp_, sp_) \
  do \
    { \
      *(dest) = alloca (sizeof (basic_block_item) + \
		        sizeof (OOP) * ((depth) - 1)); \
      (*(dest))->bb = (dest); \
      (*(dest))->bp = (bp_); \
      (*(dest))->sp = (sp_); \
      (*(dest))->suspended = false; \
    } \
  while (0)

#define INIT_BASIC_BLOCK(bb, temps) \
  do \
    { \
      int i; \
      for (i = 0; i < (temps); i++) \
	(bb)->stack[i] = FROM_INT (VARYING); \
      for (; i < (bb)->sp; i++) \
	(bb)->stack[i] = FROM_INT (UNDEFINED); \
    } \
  while (0)


/* Use the hash table and function in superop1.inl to look for a
   superoperator representing bytecode BC1 with argument ARG, followed
   by bytecode BC2.  */
static inline int search_superop_fixed_arg_1 (int bc1,
					      int arg,
					      int bc2);

/* Use the hash table and function in superop1.inl to look for a
   superoperator representing bytecode BC1 followed by bytecode BC2
   with argument ARG.  */
static inline int search_superop_fixed_arg_2 (int bc1,
					      int bc2,
					      int arg);

/* Scan the bytecodes between FROM and TO, performing a handful of
   peephole optimizations and creating superoperators with
   optimize_superoperators.  The optimized bytecodes are written
   starting at FROM.  */
static int optimize_basic_block (gst_uchar * from,
				 gst_uchar * to);

/* Scan the peephole-optimized bytecodes between FROM and TO.  Generate
   superoperators and rewrite in-place starting at FROM.  Return the
   pointer just past the final byte written. */
static gst_uchar *optimize_superoperators (gst_uchar * from,
					   gst_uchar * to);

/* This compares two block_boundary structures according to their
   ending bytecode position.  */
static int compare_blocks (const PTR a, const PTR b) ATTRIBUTE_PURE;

/* And this compares an int (A) with the starting bytecode of block B.  */
static int search_block (const PTR a, const PTR b) ATTRIBUTE_PURE;

/* Computes the length of a jump at distance OFS.  */
static int compute_jump_length (int ofs) ATTRIBUTE_CONST;

/* This answers how the dirtyness of BLOCKOOP affects
   the block that encloses it.  */
static inline int check_inner_block (OOP blockOOP);

/* This fills a table that says to which bytecodes a jump lands.
   Starting from BP, and for a total of SIZE bytes, bytecodes are
   analyzed and on output DEST[i] is non-zero if and
   only if BP[i] is the destination of a jump. It is positive
   for a forward jump and negative for a backward jump.  The number
   of jumps is returned.  */
static int make_destination_table (gst_uchar * bp,
				   int size,
				   char *dest);

/* Helper function to compute the bytecode verifier's `in'
   sets from the `out' sets.  */
static mst_Boolean merge_stacks (OOP *dest,
				 int dest_sp,
				 OOP *src,
				 int src_sp);


int
_gst_is_simple_return (bc_vector bytecodes)
{
  gst_uchar *bytes;
  int maybe = MTH_NORMAL;
  OOP maybe_object = NULL;
  int i;

  if (bytecodes == NULL)
    return (MTH_NORMAL);

  bytes = bytecodes->base;

  for (i = 1; i <= 3; i++)
    {
      int should_have_been_return = (maybe != MTH_NORMAL);
      if (bytes == bytecodes->ptr)
        return (MTH_NORMAL);

      MATCH_BYTECODES (IS_SIMPLE_RETURN, bytes, (
        PUSH_SELF { maybe = MTH_RETURN_SELF; }
        PUSH_RECEIVER_VARIABLE { maybe = (n << 8) | MTH_RETURN_INSTVAR; }
        PUSH_LIT_CONSTANT { maybe = (n << 8) | MTH_RETURN_LITERAL; }
        PUSH_INTEGER { maybe_object = FROM_INT (n); maybe = MTH_RETURN_LITERAL; }
        PUSH_SPECIAL {
          maybe = MTH_RETURN_LITERAL;
          switch (n)
	    {
	      case NIL_INDEX: maybe_object = _gst_nil_oop; break;
              case TRUE_INDEX: maybe_object = _gst_true_oop; break;
              case FALSE_INDEX: maybe_object = _gst_false_oop; break;
	      default: abort ();
	    }
        }

        LINE_NUMBER_BYTECODE { }
        RETURN_CONTEXT_STACK_TOP {
	  if (maybe_object)
	    _gst_add_forced_object (maybe_object);
	  return maybe;
	}

        STORE_RECEIVER_VARIABLE,
        PUSH_OUTER_TEMP, STORE_OUTER_TEMP,
        JUMP, POP_JUMP_TRUE, POP_JUMP_FALSE,
        PUSH_TEMPORARY_VARIABLE, PUSH_LIT_VARIABLE,
        STORE_TEMPORARY_VARIABLE, STORE_LIT_VARIABLE,
        SEND, POP_INTO_NEW_STACKTOP,
        POP_STACK_TOP, DUP_STACK_TOP,
        SEND_IMMEDIATE, EXIT_INTERPRETER,
        SEND_ARITH, SEND_SPECIAL, MAKE_DIRTY_BLOCK,
        RETURN_METHOD_STACK_TOP { return (MTH_NORMAL); }

        INVALID { abort(); }
      ));

      if (should_have_been_return)
	return (MTH_NORMAL);
    }

  return (MTH_NORMAL);
}

int
_gst_check_kind_of_block (bc_vector bc,
			  OOP * literals)
{
  int status, newStatus;
  gst_uchar *bp, *end;

  status = 0;			/* clean block */
  for (bp = bc->base, end = bc->ptr; bp != end; )
    {
      MATCH_BYTECODES (CHECK_KIND_OF_BLOCK, bp, (
        PUSH_SELF, PUSH_RECEIVER_VARIABLE, 
	STORE_RECEIVER_VARIABLE {
	  if (status == 0)
	    status = 1;
	}

        PUSH_LIT_CONSTANT {
	  newStatus = check_inner_block (literals[n]);
	  if (newStatus > status)
	    {
	      if (newStatus == 31)
		return (31);
	      status = newStatus;
	    }
        }

        PUSH_OUTER_TEMP, STORE_OUTER_TEMP  {
	  if (status < 1 + scopes) status = 1 + scopes;
	  if (status > 31)
	    /* ouch! how deep!! */
	    return (31);
	}

        JUMP,
        POP_JUMP_TRUE,
        POP_JUMP_FALSE,
        PUSH_TEMPORARY_VARIABLE,
        PUSH_LIT_VARIABLE,
        PUSH_SPECIAL,
        PUSH_INTEGER,
        RETURN_CONTEXT_STACK_TOP,
        LINE_NUMBER_BYTECODE,
        STORE_TEMPORARY_VARIABLE,
        STORE_LIT_VARIABLE,
        SEND,
        POP_INTO_NEW_STACKTOP,
        POP_STACK_TOP,
        DUP_STACK_TOP,
        EXIT_INTERPRETER,
        SEND_ARITH,
        SEND_SPECIAL,
        SEND_IMMEDIATE,
	MAKE_DIRTY_BLOCK { }

        RETURN_METHOD_STACK_TOP { return (31); }
        INVALID { abort(); }
      ));
    }
  return (status);
}

int
check_inner_block (OOP blockOOP)
{
  int newStatus;
  gst_compiled_block block;

  if (!IS_CLASS (blockOOP, _gst_compiled_block_class))
    return (0);

  /* Check the cleanness of the inner block and adequately change the status. 
     full block: no way dude -- exit immediately
     clean block: same for us 
     receiver access: same for us
     access to temps in the Xth context: from the perspective of the block
     being checked here, it is like an access to temps in the (X-1)th
     context access to this block's temps: our outerContext can be nil
     either, but for safety we won't be a clean block.  */
  block = (gst_compiled_block) OOP_TO_OBJ (blockOOP);
  newStatus = block->header.clean;
  switch (newStatus)
    {
    case 31:
    case 0:
    case 1:
      return (newStatus);
    default:
      return (newStatus - 1);
    }
}


int
compare_blocks (const PTR a, const PTR b)
{
  const block_boundary *ba = (const block_boundary *) a;
  const block_boundary *bb = (const block_boundary *) b;

  /* Sort by bytecode.  */
  if (ba->end != bb->end)
    return (ba->end - bb->end);

  /* Put first the element representing the jump.  */
  else if (ba->kind != -1 && bb->kind == -1)
    return -1;
  else if (bb->kind != -1 && ba->kind == -1)
    return 1;

  return 0;
}

int
search_block (const PTR a, const PTR b)
{
  const int *ia = (const int *) a;
  const block_boundary *bb = (const block_boundary *) b;

  return (*ia - bb->start);
}

int
compute_jump_length (int ofs)
{
  if (ofs > -256 && ofs < 256)
    return 2;
  else if (ofs > -65536 && ofs < 65536)
    return 4;
  else if (ofs > -16777216 && ofs < 16777216)
    return 6;
  else
    return 8;
}

bc_vector
_gst_optimize_bytecodes (bc_vector bytecodes)
{
#ifdef NO_OPTIMIZE
  return (bytecodes);
#else
  bc_vector old_bytecodes;
  block_boundary *blocks, *block, *last;
  gst_uchar *bp, *end, *first;
  int i;
  mst_Boolean changed;

  bp = bytecodes->base;
  end = bytecodes->ptr;
  blocks = alloca (sizeof (block_boundary) * (end - bp + 1));
  memset (blocks, 0, sizeof (block_boundary) * (end - bp + 1));

  /* 1) Split into basic blocks.  This part cheats so that the final
     fixup also performs jump optimization.  */
  for (last = blocks; bp != end; )
    {
      gst_uchar *dest = bp;
      gst_uchar *dest_ip0;
      mst_Boolean canOptimizeJump, split;
      int kind = 0;
      split = false;

      do
	{
	  dest_ip0 = dest;
	  canOptimizeJump = false;
	  MATCH_BYTECODES (THREAD_JUMPS, dest, (
	    MAKE_DIRTY_BLOCK,
	    SEND_SPECIAL,
	    SEND_ARITH,
	    SEND_IMMEDIATE,
	    PUSH_RECEIVER_VARIABLE,
	    PUSH_TEMPORARY_VARIABLE,
	    PUSH_LIT_CONSTANT,
	    PUSH_LIT_VARIABLE,
	    PUSH_SELF,
	    PUSH_SPECIAL,
	    PUSH_INTEGER,
	    LINE_NUMBER_BYTECODE,
	    STORE_RECEIVER_VARIABLE,
	    STORE_TEMPORARY_VARIABLE,
	    STORE_LIT_VARIABLE,
	    SEND,
	    POP_INTO_NEW_STACKTOP,
	    POP_STACK_TOP,
	    DUP_STACK_TOP,
	    PUSH_OUTER_TEMP,
	    STORE_OUTER_TEMP,
	    EXIT_INTERPRETER { }

	    JUMP {
	      if (ofs == 2
		  && dest[0] == LINE_NUMBER_BYTECODE)
		{
		  /* This could not be optimized to a nop, cause the
		     jump and line number bytecodes lie in different
		     basic blocks! So we rewrite it to a functionally
		     equivalent but optimizable bytecode sequence.  */
		  dest[-2] = dest[0];
		  dest[-1] = dest[1];
		}
	      else if (ofs == 4
		  && IS_PUSH_BYTECODE (dest[0])
		  && dest[2] == POP_STACK_TOP)
		{
		  /* This could not be optimized to a single pop,
		     cause the push and pop bytecodes lie in different
		     basic blocks! Again, rewrite to an optimizable
		     sequence.  */
		  dest[-2] = POP_STACK_TOP;
		  dest[-1] = 0;
		}
	      else
		{
	          /* Don't optimize jumps that have extension bytes.  But if we
		     jump to a return, we can safely optimize: returns are
		     never extended, and the interpreter ignores the extension
		     byte.  TODO: check if this is still true.  */
	          canOptimizeJump = (*IP0 != EXT_BYTE);
		  kind = IP[-2];
	          dest_ip0 = dest = IP0 + ofs;
	          canOptimizeJump |= IS_RETURN_BYTECODE (*dest);
		  split = true;
		}
	    }

	    POP_JUMP_TRUE, POP_JUMP_FALSE {
	      if (ofs == 0)
		{
		  dest[-2] = POP_STACK_TOP;
		  dest[-1] = 0;
		}

	      /* Jumps to CONDITIONAL jumps must not be touched, either because
		 they were unconditional or because they pop the stack top! */
	      else if (dest_ip0 == bp)
		{
		  kind = IP[-2];
		  dest_ip0 = dest = IP0 + ofs;
		  split = true;
		}
	    }

	    RETURN_METHOD_STACK_TOP, RETURN_CONTEXT_STACK_TOP {
	      /* Return bytecodes - patch the original jump to return
	         directly */
	      bp[0] = dest[-2];
	      bp[1] = 0;

	      /* This in fact eliminated the jump, don't split in basic 
	         blocks */
	      split = false;
	    }

	    INVALID { abort (); }
	  ));
	}
      while (canOptimizeJump);

      while (*bp == EXT_BYTE)
	bp += BYTECODE_SIZE;
      bp += BYTECODE_SIZE;

      if (split)
	{
	  assert (bp[-2] == kind);
	  assert (kind == JUMP || kind == JUMP_BACK
	  	  || kind == POP_JUMP_TRUE || kind == POP_JUMP_FALSE);

	  last->dest = -1;
  	  last->end = dest_ip0 - bytecodes->base;
	  last->kind = -1;
	  last++;
	  last->dest = dest_ip0 - bytecodes->base;
	  last->end = bp - bytecodes->base;
	  last->kind = kind;
	  last++;
	}
    }

  last->dest = -1;
  last->end = bp - bytecodes->base;
  last->kind = -1;
  last++;

  /* 2) Get the "real" block boundaries by sorting them according to
     where they happen in the original bytecode; then complete the
     data that was put in BLOCKS by setting the start of the basic
     block, removing the jump bytecode at the end...  */
  qsort (blocks, last - blocks, sizeof (block_boundary), compare_blocks);

  i = 0;
  for (block = blocks; block != last; block++)
    {
      block->start = i;
      if (block->end == i)
	continue;

      i = block->end;
      bp = bytecodes->base + block->end;
      if (bp[-2] == JUMP || bp[-2] == JUMP_BACK
	  || bp[-2] == POP_JUMP_TRUE || bp[-2] == POP_JUMP_FALSE)
	{
	  do
	    block->end -= BYTECODE_SIZE, bp -= BYTECODE_SIZE;
	  while (block->end != block->start && bp[-2] == EXT_BYTE);
	}
    }

  /* ... and computing the destination of the jump as a basic block */
  for (block = blocks; block != last; block++)
    if (block->kind != -1)
      block->dest_bb = bsearch (&block->dest, blocks, last - blocks,
				sizeof (block_boundary), search_block);

  /* Optimize the single basic blocks.  */
  i = 0;
  for (block = blocks; block != last; block++)
    {
      first = bytecodes->base + block->start;
      bp = bytecodes->base + block->end;
      block->opt_length = optimize_basic_block (first, bp);

#ifndef NO_SUPEROPERATORS
      /* Make a superoperator with the last bytecode and the jump.  */
      if (block->kind != -1
          && block->opt_length > 0
	  && !(block->opt_length > 2
	       && first[block->opt_length - 4] == EXT_BYTE))
	{
	  int test = search_superop_fixed_arg_1 (first[block->opt_length - 2],
					         first[block->opt_length - 1],
					         block->kind);
	  if (test != -1)
	    {
	      block->opt_length -= 2;
	      block->kind = test;
	    }
	}
#endif

      block->final_byte = i;
      i += block->opt_length;
    }

  /* Compute the size of the jump bytecodes.  */
  do
    {
      changed = false;
      i = 0;
      for (block = blocks; block != last; block++)
        {
          int jump_length;
          if (block->final_byte != i)
	    {
	      block->final_byte = i;
	      changed = true;
	    }
          if (block->kind != -1)
	    jump_length =
	      compute_jump_length (block->dest_bb->final_byte
				   - (block->final_byte + block->opt_length));
          else
	    jump_length = 0;
          i += block->opt_length + jump_length;
	}
    }
  while (changed);

  /* Put together the whole method.  */
  old_bytecodes = _gst_save_bytecode_array ();
  for (block = blocks; block != last; block++)
    {
      _gst_compile_bytecodes (bytecodes->base + block->start,
			      bytecodes->base + block->start + block->opt_length);
      if (block->kind != -1)
        {
	  int jump_length =
	    compute_jump_length (block->dest_bb->final_byte
				 - (block->final_byte + block->opt_length));
          int ofs = block->dest_bb->final_byte
		    - (block->final_byte + block->opt_length + jump_length);

	  if (ofs < 0)
	    ofs = -ofs;
	  _gst_compile_byte (block->kind, ofs);
	}
    }

  _gst_free_bytecodes (bytecodes);
  bytecodes = _gst_get_bytecodes ();
  _gst_restore_bytecode_array (old_bytecodes);
  return (bytecodes);
#endif
}

static inline int
search_superop_fixed_arg_1(int bc1, int arg, int bc2)
{
  /* ARG is in the range 0..255.  The format of the hash table entries is

     { { BC1, BC2, ARG }, SUPEROP } */

  struct superop_with_fixed_arg_1_type {
    unsigned char bytes[3];
    int superop;
  };

#include "superop1.inl"

  unsigned int key = asso_values[bc1] + asso_values[bc2] + asso_values[arg];

  register const struct superop_with_fixed_arg_1_type *k;

  if (key > MAX_HASH_VALUE)
    return -1;

  k = &keylist[key];
  if (bc1 == k->bytes[0] && bc2 == k->bytes[1] && arg == k->bytes[2])
    return k->superop;
  else
    return -1;
}


static inline int
search_superop_fixed_arg_2(int bc1, int bc2, int arg)
{
  /* ARG is in the range 0..255.  The format of the hash table entries is

     { { BC1, BC2, ARG }, SUPEROP } */

  struct superop_with_fixed_arg_2_type {
    unsigned char bytes[3];
    int superop;
  };

#include "superop2.inl"

  unsigned int key = asso_values[bc1] + asso_values[bc2] + asso_values[arg];

  register const struct superop_with_fixed_arg_2_type *k;

  if (key > MAX_HASH_VALUE)
    return -1;

  k = &keylist[key];
  if (bc1 == k->bytes[0] && bc2 == k->bytes[1] && arg == k->bytes[2])
    return k->superop;
  else
    return -1;
}

int
optimize_basic_block (gst_uchar *from,
		      gst_uchar *to)
{
  /* Points to the optimized bytecodes as they are written.  */
  gst_uchar *opt = from;

  /* Points to the unoptimized bytecodes as they are read.  */
  gst_uchar *bp = from;

  if (from == to)
    return 0;

  do
    {
      /* Perform peephole optimizations.  For simplicity, the optimizations
	 on line number bytecodes don't take into account the possibility
	 that the line number bytecode is extended (>256 lines in
	 a method).  This almost never happens, so we don't bother.  */
      switch (bp[0])
	{
        case PUSH_TEMPORARY_VARIABLE:
        case PUSH_RECEIVER_VARIABLE:
	  /* Leave only the store in store/pop/push sequences.  Don't do this
	     for STORE_LIT_VARIABLE, as it fails if #value: is sent and,
	     for example, self is returned.  */
	  if (opt >= from + 4
	      && (opt == from + 4 || opt[-6] != EXT_BYTE)
	      && opt[-4] == bp[0] + (STORE_TEMPORARY_VARIABLE - PUSH_TEMPORARY_VARIABLE)
	      && opt[-3] == bp[1]
	      && opt[-2] == POP_STACK_TOP
	      && bp[-2] != EXT_BYTE)
	    {
	      opt -= 2;
	      bp += 2;
	      continue;
	    }

	  /* Also rewrite store/pop/line/push to store/line in the middle.  */
	  if (opt >= from + 6
	      && (opt == from + 6 || opt[-8] != EXT_BYTE)
	      && opt[-6] == bp[0] + (STORE_TEMPORARY_VARIABLE - PUSH_TEMPORARY_VARIABLE)
	      && opt[-5] == bp[1]
	      && opt[-4] == POP_STACK_TOP
	      && opt[-2] == LINE_NUMBER_BYTECODE
	      && bp[-2] != EXT_BYTE)
	    {
	      opt[-4] = opt[-2];
	      opt[-3] = opt[-1];
	      opt -= 2;
	      bp += 2;
	      continue;
	    }

	  /* fall through to other pushes.  */

        case PUSH_OUTER_TEMP:
        case PUSH_INTEGER:
        case PUSH_SELF:
        case PUSH_SPECIAL:
        case PUSH_LIT_CONSTANT:
	  /* Remove a push followed by a pop */
          if (bp < to - 2
	      && bp[2] == POP_STACK_TOP)
	    {
	      bp += 4;
	      continue;
	    }

	  /* Remove the pop in a pop/push/return sequence */
          if (opt >= from + 2 && bp < to - 2
	      && bp[2] == RETURN_CONTEXT_STACK_TOP
	      && opt[-2] == POP_STACK_TOP)
	    opt -= 2;

	  /* Rewrite the pop/line number/push sequence to
	     line number/pop/push because this can be better
	     optimized by superoperators (making a superoperator
	     with a nop byte saves on decoding, but not on
	     scheduling the instructions in the interpreter!).  */
	  if (opt >= from + 4
	      && opt[-4] == POP_STACK_TOP
	      && opt[-2] == LINE_NUMBER_BYTECODE)
	    {
	      opt[-4] = LINE_NUMBER_BYTECODE;
	      opt[-3] = opt[-1];
	      opt[-2] = POP_STACK_TOP;
	      opt[-1] = 0;
	    }
	  break;

	case JUMP:
	case JUMP_BACK:
	case POP_JUMP_TRUE:
	case POP_JUMP_FALSE:
	  abort ();

	default:
	  break;
	}

      /* Else, just copy the bytecode to the optimized area.  */
      *opt++ = *bp++;
      *opt++ = *bp++;
    }
  while (bp < to);

#ifndef NO_SUPEROPERATORS
  opt = optimize_superoperators (from, opt);
#endif
  return opt - from;
}

gst_uchar *
optimize_superoperators (gst_uchar * from,
		         gst_uchar * to)
{
  /* Points to the optimized bytecodes that have been written. */
  gst_uchar *opt = from;

  /* Points to the unoptimized bytecodes as they are read.  */
  gst_uchar *bp = from;

  int new_bc;

  if (from == to)
    return from;

  *opt++ = *bp++;
  *opt++ = *bp++;
  while (bp < to)
    {
      /* Copy two bytecodes to the optimized area.  */
      *opt++ = *bp++;
      *opt++ = *bp++;

      do
        {
	  /* Try to match the case when the second argument is fixed.
	     We try this first because
		EXT_BYTE(*), SEND(1)

	     is more beneficial than
		EXT_BYTE(1), SEND(*).  */
	  new_bc = search_superop_fixed_arg_2 (opt[-4], opt[-2], opt[-1]);
	  if (new_bc != -1)
	    {
	      opt[-4] = new_bc;
	      /* opt[-3] is already ok */
	      opt -= 2;

	      /* Look again at the last four bytes.  */
	      continue;
	    }

	  /* If the first bytecode is not extended, try matching it with a
	     fixed argument.  We skip this when the first bytecode is
	     extended because otherwise we might have superoperators like

	       PUSH_OUTER_TEMP(1), SEND(*)

	     Suppose we find

	       EXT_BYTE(1), SUPEROP(2)

	     Now the argument to SEND is 2, but the interpreter receives
	     an argument of 258 and has to decode the argument to extract
	     the real argument of PUSH_OUTER_TEMP (found in the extension
	     byte).  This messes up everything and goes against the very
	     purpose of introducing superoperators.  */
	  if (opt - from == 4 || opt[-6] != EXT_BYTE)
	    {
	      new_bc = search_superop_fixed_arg_1 (opt[-4], opt[-3], opt[-2]);
	      if (new_bc != -1)
		{
		  opt[-4] = new_bc;
		  opt[-3] = opt[-1];
		  opt -= 2;

		  /* Look again at the last four bytes.  */
		  continue;
		}
	    }

	  /* Nothing matched.  Exit. */
	  break;
	}
      while (opt - from >= 4);
    }

  return opt;
}


void
_gst_compute_stack_positions (gst_uchar * bp,
			      int size,
			      PTR * base,
			      PTR ** pos)
{
  basic_block_item **bb_start, *bb_first, *worklist, *susp_head,
	**susp_tail = &susp_head;
  int bc_len;

  bb_start = alloca ((1 + size) * sizeof (basic_block_item *));
  memset (bb_start, 0, (1 + size) * sizeof (basic_block_item *));
  memset (pos, 0, (1 + size) * sizeof (PTR *));

  /* Allocate the first and last basic block specially */
  ALLOCA_BASIC_BLOCK (bb_start, 0, bp, 0);
  ALLOCA_BASIC_BLOCK (bb_start + size, 0, bp + size, 0);
  bb_first = bb_start[0];
  bb_first->next = NULL;

  /* First build the pointers to the basic blocks into BB_START.  Then use
     of a worklist here is only to find a correct order for visiting the
     basic blocks, not because they're visited multiple times.  This
     works transparently when we have a return in the middle of the method.
     Then the basic block is ending, yet it might be that the stack height
     for the next bytecode is already known!!! */
  for (susp_head = NULL, worklist = bb_first; worklist; )
    {
      int curr_sp = worklist->sp;
      bp = worklist->bp;
      bb_start = worklist->bb;
      worklist = worklist->next;

#ifdef DEBUG_JIT_TRANSLATOR
      printf ("Tracing basic block at %d:\n", bb_start - bb_first->bb);
#endif

      do
        {
	  int curr_ip = bb_start - bb_first->bb;
	  int balance;
	  gst_uchar *bp_first = bp;

#ifdef DEBUG_JIT_TRANSLATOR
          printf ("[SP=%3d]%5d:", curr_sp, curr_ip);
          _gst_print_bytecode_name (bp, curr_ip, NULL, "\t");
#endif

	  balance = 0;
	  pos[curr_ip] = base + curr_sp;

	  MATCH_BYTECODES (COMPUTE_STACK_POS, bp, (
	    RETURN_METHOD_STACK_TOP,
	    RETURN_CONTEXT_STACK_TOP {
	      bc_len = bp - bp_first;

	      /* We cannot fill the basic block right now because the
		 stack height might be different.  */
	      if (!bb_start[bc_len])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + bc_len, 0,
				      bp_first + bc_len, curr_sp + balance);
		  bb_start[bc_len]->suspended = true;
		  bb_start[bc_len]->next = NULL;
		  *susp_tail = bb_start[bc_len];
		  susp_tail = &(bb_start[bc_len]->next);
		}
	    }

            POP_INTO_NEW_STACKTOP,
            POP_STACK_TOP { balance--; }

            PUSH_RECEIVER_VARIABLE,
            PUSH_TEMPORARY_VARIABLE,
            PUSH_LIT_CONSTANT,
            PUSH_LIT_VARIABLE,
            PUSH_SELF,
            PUSH_SPECIAL,
            PUSH_INTEGER,
            DUP_STACK_TOP,
            PUSH_OUTER_TEMP { balance++; }

            LINE_NUMBER_BYTECODE,
            STORE_RECEIVER_VARIABLE,
            STORE_TEMPORARY_VARIABLE,
            STORE_LIT_VARIABLE,
            STORE_OUTER_TEMP,
            EXIT_INTERPRETER,
            MAKE_DIRTY_BLOCK { }

            SEND {
	      balance -= super + num_args;
	    }

	    SEND_ARITH {
	      balance -= _gst_builtin_selectors[n].numArgs;
	    }

	    SEND_IMMEDIATE {
	      balance -= super + _gst_builtin_selectors[n].numArgs;
	    }

            SEND_SPECIAL {
	      balance -= _gst_builtin_selectors[n + 16].numArgs;
	    }

            INVALID {
	      abort ();
	    }

            JUMP {
	      bc_len = bp - bp_first;

	      /* We cannot fill the basic block right now because the
		 stack height might be different.  */
	      if (!bb_start[bc_len])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + bc_len, 0,
				      bp_first + bc_len, 0);
		  bb_start[bc_len]->suspended = true;
		  bb_start[bc_len]->next = NULL;
		  *susp_tail = bb_start[bc_len];
		  susp_tail = &(bb_start[bc_len]->next);
		}

	      if (!bb_start[ofs])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + ofs, 0,
				      bp_first + ofs, curr_sp + balance);
		  bb_start[ofs]->next = worklist;
		  worklist = bb_start[ofs];
		}
	      else if (bb_start[ofs]->suspended)
		{
		  bb_start[ofs]->suspended = false;
		  bb_start[ofs]->sp = curr_sp + balance;
		}
	      else if (curr_sp + balance != bb_start[ofs]->sp)
		abort ();
	    }

	    POP_JUMP_TRUE, POP_JUMP_FALSE {
	      balance--;
	      bc_len = bp - bp_first;
	      if (!bb_start[bc_len])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + bc_len, 0,
				      bp_first + bc_len, curr_sp + balance);
		  bb_start[bc_len]->next = worklist;
		  worklist = bb_start[bc_len];
		}
	      else if (bb_start[bc_len]->suspended)
		{
		  bb_start[bc_len]->suspended = false;
		  bb_start[bc_len]->sp = curr_sp + balance;
		}
	      else if (curr_sp + balance != bb_start[bc_len]->sp)
		abort ();

	      if (!bb_start[ofs])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + ofs, 0,
				      bp_first + ofs, curr_sp + balance);
		  bb_start[ofs]->next = worklist;
		  worklist = bb_start[ofs];
		}
              else if (bb_start[ofs]->suspended)
		{
		  bb_start[ofs]->suspended = false;
		  bb_start[ofs]->sp = curr_sp + balance;
		}
	      else if (curr_sp + balance != bb_start[ofs]->sp)
		abort ();
            }
          ));

	  curr_sp += balance;
	  bb_start += bp - bp_first;
	}
      while (!*bb_start);

      if (!worklist && susp_head)
	{
	  worklist = susp_head;
	  susp_head = susp_head->next;
	  worklist->next = NULL;
	  if (!susp_head)
	    susp_tail = &susp_head;
	}
    }
}


void
_gst_analyze_bytecodes (OOP methodOOP,
			 int size,
			 char *dest)
{
  gst_uchar *bp;

  bp = GET_METHOD_BYTECODES (methodOOP);
  make_destination_table (bp, size, dest);

  /* Nothing more for now */
}

int
make_destination_table (gst_uchar * bp,
			int size,
			char *dest)
{
  gst_uchar *end, *bp_first;
  int count;

  memset (dest, 0, sizeof (char) * size);

  for (count = 0, end = bp + size; bp != end;
       dest += bp - bp_first)
    {
      bp_first = bp;
      MATCH_BYTECODES (MAKE_DEST_TABLE, bp, (
        PUSH_RECEIVER_VARIABLE,
        PUSH_TEMPORARY_VARIABLE,
        PUSH_LIT_CONSTANT,
        PUSH_LIT_VARIABLE,
        PUSH_SELF,
        PUSH_SPECIAL,
        PUSH_INTEGER,
        RETURN_METHOD_STACK_TOP,
        RETURN_CONTEXT_STACK_TOP,
        LINE_NUMBER_BYTECODE,
        STORE_RECEIVER_VARIABLE,
        STORE_TEMPORARY_VARIABLE,
        STORE_LIT_VARIABLE,
        SEND,
        POP_INTO_NEW_STACKTOP,
        POP_STACK_TOP,
        DUP_STACK_TOP,
        PUSH_OUTER_TEMP,
        STORE_OUTER_TEMP,
        EXIT_INTERPRETER,
        SEND_ARITH,
        SEND_SPECIAL,
        SEND_IMMEDIATE,
	MAKE_DIRTY_BLOCK { }

        INVALID { abort(); }

        JUMP, POP_JUMP_TRUE, POP_JUMP_FALSE {
          dest[ofs] = ofs > 0 ? 1 : -1;
	  count++;
        }
      ));
    }

  return (count);
}



#define SELF 0
#define VARYING 1
#define UNDEFINED 2

typedef struct partially_constructed_array {
  struct partially_constructed_array *next;
  int sp;
  int size;
} partially_constructed_array;

#define CHECK_LITERAL(n) \
  /* Todo: recurse into BlockClosures! */ \
  last_used_literal = literals[n]; \
  if ((n) >= num_literals) \
    return ("literal out of range");

#define CHECK_TEMP(n) \
  last_used_literal = NULL; \
  if ((n) >= sp - stack) \
    return ("temporary out of range");

#define CHECK_REC_VAR(first, n) \
  last_used_literal = NULL; \
  if ((n) < (first) || (n) >= num_rec_vars) \
    return ("receiver variable out of range");

#define CHECK_LIT_VARIABLE(store, n) \
  CHECK_LITERAL (n); \
  if (IS_INT (literals[(n)]) || \
      !is_a_kind_of (OOP_CLASS (literals[(n)]), _gst_lookup_key_class)) \
    return ("LookupKey expected"); \
  else if (store \
	   && untrusted \
	   && !IS_OOP_UNTRUSTED (literals[(n)])) \
    return ("Invalid global variable access");

#define LIT_VARIABLE_CLASS(n) \
  /* Special case classes because of super and {...} */ \
  (IS_A_CLASS (ASSOCIATION_VALUE (literals[(n)])) \
   ? OOP_CLASS (ASSOCIATION_VALUE (literals[(n)])) \
   : FROM_INT (VARYING))

#define LITERAL_CLASS(n) \
  OOP_INT_CLASS (literals[(n)])

/* Bytecode verification is a dataflow analysis on types.  We perform it
   on basic blocks: `in' is the stack when entering the basic block and
   `out' is the stack upon exit.

   Each member of the stack can be UNDEFINED, a type, or VARYING.  When
   merging two `out' stacks to compute an `in' stack, we have these
   possible situations:
   - the stacks are not the same height, and bytecode verification fails
   - a slot is the same in both stacks, so it has this type in the output too
   - a slot is different in the two stacks, so it is VARYING in the output.

   Bytecode verification proceeds forwards, so the worklist is added all the
   successors of the basic block whenever merging results in a difference.  */

mst_Boolean
merge_stacks (OOP *dest, int dest_sp,
	      OOP *src, int src_sp)
{
  mst_Boolean varied = false;
  assert (dest_sp == src_sp);

  for (; src_sp--; dest++, src++)
    {
      OOP newDest = *src;
      if (newDest != *src)
	{
	  if (*dest != FROM_INT (UNDEFINED))
	    /* If different, mark as overdefined.  */
	    newDest = FROM_INT (VARYING);

	  if (newDest != *dest)
	    {
	      *dest = newDest;
	      varied = true;
	    }
	}
    }

  return (varied);
}

void
_gst_verify_sent_method (OOP methodOOP)
{
  const char *error;
  error = _gst_verify_method (methodOOP, NULL, 0);

  if (error)
    {
      _gst_errorf ("Bytecode verification failed: %s", error);
      if (OOP_CLASS (methodOOP) == _gst_compiled_block_class)
        methodOOP = GET_BLOCK_METHOD (methodOOP);

      _gst_errorf ("Method verification failed for %O>>%O",
                   GET_METHOD_CLASS (methodOOP),
                   GET_METHOD_SELECTOR (methodOOP));

      abort ();
    }
}

const char *
_gst_verify_method (OOP methodOOP, int *num_outer_temps, int depth)
{
#ifndef NO_VERIFIER
  int size, bc_len, num_temps, stack_depth,
    num_literals, num_rec_vars, num_ro_rec_vars;

  mst_Boolean untrusted;
  const char *error;
  gst_uchar *bp;
  OOP *literals, methodClass, last_used_literal;
  basic_block_item **bb_start, *bb_first, *worklist, *susp_head,
    **susp_tail = &susp_head;
  partially_constructed_array *arrays = NULL, *arrays_pool = NULL;

  if (IS_OOP_VERIFIED (methodOOP))
    return (NULL);

  size = NUM_INDEXABLE_FIELDS (methodOOP);
  bp = GET_METHOD_BYTECODES (methodOOP);
  literals = GET_METHOD_LITERALS (methodOOP);
  methodClass = GET_METHOD_CLASS (methodOOP);
  num_literals = NUM_METHOD_LITERALS (methodOOP);
  num_rec_vars = CLASS_FIXED_FIELDS (methodClass);
  untrusted = IS_OOP_UNTRUSTED (methodOOP);

  if (is_a_kind_of (OOP_CLASS (methodOOP), _gst_compiled_method_class))
    {
      method_header header;
      header = GET_METHOD_HEADER (methodOOP);
      num_temps = header.numArgs + header.numTemps;
      stack_depth = header.stack_depth << DEPTH_SCALE;
      switch (header.headerFlag)
        {
	case MTH_NORMAL:
	case MTH_PRIMITIVE:
	case MTH_ANNOTATED:
	case MTH_UNUSED:
	  break;

	case MTH_USER_DEFINED:
	case MTH_RETURN_SELF:
	  methodOOP->flags |= F_VERIFIED;
	  return (NULL);

	case MTH_RETURN_INSTVAR:
	  CHECK_REC_VAR (0, header.primitiveIndex);
	  methodOOP->flags |= F_VERIFIED;
	  return (NULL);

	case MTH_RETURN_LITERAL:
	  CHECK_LITERAL (0);
	  methodOOP->flags |= F_VERIFIED;
	  return (NULL);
        }
    }
  else if (OOP_CLASS (methodOOP) == _gst_compiled_block_class)
    {
      block_header header;
      header = GET_BLOCK_HEADER (methodOOP);

      /* If we're verifying a block but not from a nested call,
	 restart from the top-level method.  */
      if (header.clean != 0 && depth == 0)
	return _gst_verify_method (GET_BLOCK_METHOD (methodOOP), NULL, 0);

      num_temps = header.numArgs + header.numTemps;
      stack_depth = header.depth << DEPTH_SCALE;
    }
  else
    return "invalid class";

  if (untrusted)
    {
       OOP class_oop;
       for (class_oop = methodClass; IS_OOP_UNTRUSTED (class_oop);
            class_oop = SUPERCLASS (class_oop))
         ;

       num_ro_rec_vars = CLASS_FIXED_FIELDS (class_oop);
    }
  else
    num_ro_rec_vars = 0;

#ifdef DEBUG_VERIFIER
  printf ("Verifying %O (max. stack depth = %d):\n", methodOOP, stack_depth);
#endif

  /* Prepare the NUM_OUTER_TEMPS array for the inner blocks.  */
  if (depth)
    {
      int *new_num_outer_temps = alloca (sizeof (int) * (depth + 1));
      memcpy (new_num_outer_temps + 1, num_outer_temps, sizeof (int) * depth);
      new_num_outer_temps[0] = num_temps;
      num_outer_temps = new_num_outer_temps;
    }
  else
    num_outer_temps = &num_temps;

  depth++;

  bb_start = alloca ((1 + size) * sizeof (basic_block_item *));
  memset (bb_start, 0, (1 + size) * sizeof (basic_block_item *));

  /* Allocate the first and last basic block specially */
  ALLOCA_BASIC_BLOCK(bb_start, stack_depth, bp, num_temps);
  ALLOCA_BASIC_BLOCK(bb_start + size, stack_depth, bp + size, num_temps);
  bb_first = bb_start[0];
  bb_first->next = NULL;

  /* First build the pointers to the basic blocks into BB_START.  The use
     of a worklist here is only to find a correct order for visiting the
     basic blocks, not because they're visited multiple times.  This
     works transparently when we have a return in the middle of the method.
     Then the basic block is ending, yet it might be that the stack height
     for the next bytecode is already known!!! */
  for (susp_head = NULL, worklist = bb_first; worklist; )
    {
      int curr_sp = worklist->sp;
      bp = worklist->bp;
      bb_start = worklist->bb;
      worklist = worklist->next;

#ifdef DEBUG_VERIFIER
      printf ("Tracing basic block at %d:\n", bb_start - bb_first->bb);
#endif

      do
        {
	  int curr_ip = bb_start - bb_first->bb;
	  int balance;
	  gst_uchar *bp_first = bp;

#ifdef DEBUG_VERIFIER
          printf ("[SP=%3d]%5d:", curr_sp, curr_ip);
          _gst_print_bytecode_name (bp, curr_ip, literals, "\t");
#endif

	  balance = 0;
	  MATCH_BYTECODES (CREATE_BASIC_BLOCKS, bp, (
	    RETURN_METHOD_STACK_TOP,
	    RETURN_CONTEXT_STACK_TOP {
	      bc_len = bp - bp_first;

	      /* We cannot fill the basic block right now because the
		 stack height might be different.  */
	      if (!bb_start[bc_len])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + bc_len, stack_depth,
				      bp_first + bc_len, curr_sp + balance);
		  bb_start[bc_len]->suspended = true;
		  bb_start[bc_len]->next = NULL;
		  *susp_tail = bb_start[bc_len];
		  susp_tail = &(bb_start[bc_len]->next);
		}
	    }

            POP_STACK_TOP { balance--; }

            PUSH_RECEIVER_VARIABLE,
            PUSH_TEMPORARY_VARIABLE,
            PUSH_LIT_CONSTANT,
            PUSH_LIT_VARIABLE,
            PUSH_SELF,
            PUSH_SPECIAL,
            PUSH_INTEGER,
            PUSH_OUTER_TEMP { balance++; }

            LINE_NUMBER_BYTECODE,
            STORE_RECEIVER_VARIABLE,
            STORE_TEMPORARY_VARIABLE,
            STORE_LIT_VARIABLE,
            STORE_OUTER_TEMP,
            EXIT_INTERPRETER,
            MAKE_DIRTY_BLOCK { }

            SEND {
	      balance -= super + num_args;

	      /* Sends touch the new stack top, so they require an extra slot.  */
	      if (curr_sp + balance < 1)
	        return ("stack underflow");
	    }

	    SEND_ARITH {
	      if (!_gst_builtin_selectors[n].symbol)
		return ("invalid immediate send");

	      balance -= _gst_builtin_selectors[n].numArgs;

	      /* Sends touch the new stack top, so they require an extra slot.  */
	      if (curr_sp + balance < 1)
	        return ("stack underflow");
	    }

            SEND_SPECIAL {
	      if (!_gst_builtin_selectors[n + 16].symbol)
		return ("invalid immediate send");

	      balance -= _gst_builtin_selectors[n + 16].numArgs;

	      /* Sends touch the new stack top, so they require an extra slot.  */
	      if (curr_sp + balance < 1)
	        return ("stack underflow");
	    }

            SEND_IMMEDIATE {
	      if (!_gst_builtin_selectors[n].symbol)
		return ("invalid immediate send");

	      balance -= super + _gst_builtin_selectors[n].numArgs;

	      /* Sends touch the new stack top, so they require an extra slot.  */
	      if (curr_sp + balance < 1)
	        return ("stack underflow");
	    }

            POP_INTO_NEW_STACKTOP {
	      balance--;

	      /* Sends touch the new stack top, so they require an extra slot.  */
	      if (curr_sp + balance < 1)
	        return ("stack underflow");
	    }

            DUP_STACK_TOP {
	      balance++;
	    }

            INVALID {
	      return ("invalid bytecode");
	    }

            JUMP {
	      if (ofs & 1)
		return ("jump to odd offset");

	      if (ofs + curr_ip < 0 || ofs + curr_ip > size)
		return ("jump out of range");

	      if (ofs + curr_ip > 0 && bp_first[ofs - 2] == EXT_BYTE)
		return ("jump skips extension bytecode");

	      bc_len = bp - bp_first;

	      /* We cannot fill the basic block right now because the
		 stack height might be different.  */
	      if (!bb_start[bc_len])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + bc_len, stack_depth,
				      bp_first + bc_len, 0);
		  bb_start[bc_len]->suspended = true;
		  bb_start[bc_len]->next = NULL;
		  *susp_tail = bb_start[bc_len];
		  susp_tail = &(bb_start[bc_len]->next);
		}

	      if (!bb_start[ofs])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + ofs, stack_depth,
				      bp_first + ofs, curr_sp + balance);

		  bb_start[ofs]->next = worklist;
		  worklist = bb_start[ofs];
		  INIT_BASIC_BLOCK (worklist, num_temps);
		}
	      else if (bb_start[ofs]->suspended)
	        {
		  bb_start[ofs]->suspended = false;
		  bb_start[ofs]->sp = curr_sp + balance;
		  INIT_BASIC_BLOCK (bb_start[ofs], num_temps);
		}
	      else if (curr_sp + balance != bb_start[ofs]->sp)
		return ("stack height mismatch");
	    }

	    POP_JUMP_TRUE, POP_JUMP_FALSE {
	      balance--;
	      if (ofs & 1)
		return ("jump to odd offset");

	      if (ofs + curr_ip < 0 || ofs + curr_ip > size)
		return ("jump out of range");

	      if (ofs + curr_ip > 0 && bp_first[ofs - 2] == EXT_BYTE)
		return ("jump skips extension bytecode");

	      bc_len = bp - bp_first;
	      if (!bb_start[bc_len])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + bc_len, stack_depth,
				      bp_first + bc_len, curr_sp + balance);

		  bb_start[bc_len]->next = worklist;
		  worklist = bb_start[bc_len];
		  INIT_BASIC_BLOCK (worklist, num_temps);
		}
              else if (bb_start[bc_len]->suspended)
                {
                  bb_start[bc_len]->suspended = false;
                  bb_start[bc_len]->sp = curr_sp + balance;
		  INIT_BASIC_BLOCK (bb_start[bc_len], num_temps);
                }
	      else if (curr_sp + balance != bb_start[bc_len]->sp)
		return ("stack height mismatch");

	      if (!bb_start[ofs])
		{
		  ALLOCA_BASIC_BLOCK (bb_start + ofs, stack_depth,
				      bp_first + ofs, curr_sp + balance);

		  bb_start[ofs]->next = worklist;
		  worklist = bb_start[ofs];
		  INIT_BASIC_BLOCK (worklist, num_temps);
		}
	      else if (bb_start[ofs]->suspended)
	        {
		  bb_start[ofs]->suspended = false;
		  bb_start[ofs]->sp = curr_sp + balance;
		  INIT_BASIC_BLOCK (bb_start[ofs], num_temps);
		}
	      else if (curr_sp + balance != bb_start[ofs]->sp)
		return ("stack height mismatch");
            }
          ));

	  curr_sp += balance;
	  if (curr_sp >= stack_depth)
	    return ("stack overflow");

	  bb_start += bp - bp_first;
	}
      while (!*bb_start);

      if (!worklist && susp_head)
	{
	  worklist = susp_head;
	  susp_head = susp_head->next;
	  worklist->next = NULL;
	  if (!susp_head)
	    susp_tail = &susp_head;
	}

#ifdef DEBUG_VERIFIER
      printf ("\n");
#endif
    }

  for (worklist = bb_first; worklist; )
    {
      OOP *stack = worklist->stack;
      OOP *sp;

      /* Look for unreachable basic blocks.  */
      if (worklist->sp < 0)
	abort ();

      sp = stack + worklist->sp;
      bp = worklist->bp;
      bb_start = worklist->bb;
      worklist = worklist->next;

#ifdef DEBUG_VERIFIER
      printf ("Executing basic block at %d:\n", bb_start - bb_first->bb);
#endif
      last_used_literal = NULL;

      do
	{
	  gst_uchar *bp_first = bp;

#ifdef DEBUG_VERIFIER
          printf ("[SP=%3d]%5d:", sp - stack, bb_start - bb_first->bb);
          _gst_print_bytecode_name (bp, bb_start - bb_first->bb, literals, "\t");
#endif

	  MATCH_BYTECODES (EXEC_BASIC_BLOCK, bp, (
	    PUSH_RECEIVER_VARIABLE {
	      CHECK_REC_VAR (0, n);
	      *sp++ = FROM_INT (VARYING);
	    }

	    PUSH_TEMPORARY_VARIABLE {
	      CHECK_TEMP (n);
	      *sp++ = stack[n];
	    }

	    PUSH_LIT_CONSTANT {
	      CHECK_LITERAL (n);
	      *sp++ = LITERAL_CLASS (n);
	    }

	    PUSH_LIT_VARIABLE {
	      CHECK_LIT_VARIABLE (false, n);
	      *sp++ = LIT_VARIABLE_CLASS (n);
	    }

	    PUSH_SELF {
	      last_used_literal = NULL;
	      *sp++ = FROM_INT (SELF);
	    }
	    PUSH_SPECIAL {
	      switch (n)
		{
		  case NIL_INDEX: last_used_literal = _gst_nil_oop; break;
	          case TRUE_INDEX: last_used_literal = _gst_true_oop; break;
	          case FALSE_INDEX: last_used_literal = _gst_false_oop; break;
		  default: return "invalid special object index";
		}

	      *sp++ = OOP_CLASS (last_used_literal);
	    }
	    PUSH_INTEGER {
	      last_used_literal = FROM_INT (n);
	      *sp++ = _gst_small_integer_class;
	    }

	    RETURN_METHOD_STACK_TOP {
              block_header header;
	      if (OOP_CLASS (methodOOP) != _gst_compiled_block_class)
		return "invalid return from method";

              header = GET_BLOCK_HEADER (methodOOP);
              if (header.clean != (1 << BLK_CLEAN_BITS) - 1)
		return "invalid return from clean block";

	      break;
	    }
	    RETURN_CONTEXT_STACK_TOP { break; }

	    LINE_NUMBER_BYTECODE { }

	    STORE_RECEIVER_VARIABLE {
	      CHECK_REC_VAR (num_ro_rec_vars, n);
	    }
	    STORE_TEMPORARY_VARIABLE {
	      CHECK_TEMP (n);
	    }
	    STORE_LIT_VARIABLE {
	      CHECK_LIT_VARIABLE (true, n);
	    }

	    SEND {
	      if (super
		  && (!last_used_literal
		      || (!IS_A_CLASS (last_used_literal)
		          && !IS_A_METACLASS (last_used_literal))
		      || !is_a_kind_of (methodClass, last_used_literal)))
		return ("Invalid send to super");

	      last_used_literal = NULL;
	      sp -= super + num_args;
	      if (super && sp[-1] != FROM_INT (SELF))
		return ("Invalid send to super");

	      sp[-1] = FROM_INT (VARYING);
	    }

	    POP_INTO_NEW_STACKTOP {
	      if (sp[-2] != _gst_array_class)
	        return ("Array expected");

	      if (!arrays || &sp[-2] - stack != arrays->sp)
	        return ("Invalid Array constructor");

	      if (n >= arrays->size)
	        return ("Out of bounds Array access");

	      /* Discard arrays whose construction has ended.  */
	      if (n == arrays->size - 1)
	        {
	          partially_constructed_array *next = arrays->next;
	          arrays->next = arrays_pool;
	          arrays_pool = arrays;
	          arrays = next;
	        }

	      last_used_literal = NULL;
	      sp--;
	    }

	    POP_STACK_TOP {
	      last_used_literal = NULL;
	      sp--;
	    }
	    DUP_STACK_TOP {
	      sp++;
	      sp[-1] = sp[-2];
	    }

	    PUSH_OUTER_TEMP {
	      if (scopes == 0 || scopes > depth || n >= num_outer_temps[scopes])
	        return ("temporary out of range");

	      last_used_literal = NULL;
	      *sp++ = FROM_INT (VARYING);
	    }

	    STORE_OUTER_TEMP {
	      if (scopes == 0 || scopes > depth || n >= num_outer_temps[scopes])
	        return ("temporary out of range");
	    }

	    EXIT_INTERPRETER {
	      if (size != 4
		  || IP0 != GET_METHOD_BYTECODES (methodOOP)
		  || *bp != RETURN_CONTEXT_STACK_TOP)
		return ("bad termination method");
	    }

	    JUMP {
	      if (merge_stacks (stack, sp - stack, bb_start[ofs]->stack,
				bb_start[ofs]->sp))
		bb_start[ofs]->next = worklist, worklist = bb_start[ofs];
	    }

	    POP_JUMP_TRUE, POP_JUMP_FALSE {
	      sp--;
	      bc_len = bp - bp_first;
	      if (merge_stacks (stack, sp - stack, bb_start[bc_len]->stack,
				bb_start[bc_len]->sp))
		bb_start[bc_len]->next = worklist, worklist = bb_start[bc_len];

	      if (merge_stacks (stack, sp - stack, bb_start[ofs]->stack,
				bb_start[ofs]->sp))
		bb_start[ofs]->next = worklist, worklist = bb_start[ofs];
	    }

	    SEND_ARITH {
	      sp -= _gst_builtin_selectors[n].numArgs;
	      sp[-1] = FROM_INT (VARYING);
	    }
	    SEND_SPECIAL {
	      sp -= _gst_builtin_selectors[n + 16].numArgs;
	      sp[-1] = FROM_INT (VARYING);
	    }

	    SEND_IMMEDIATE {
	      if (n == NEW_COLON_SPECIAL
		  && IS_INT (last_used_literal)
		  && last_used_literal != FROM_INT (0)
		  && sp[-2] == OOP_CLASS (_gst_array_class))
		{
		  partially_constructed_array *a;
		  sp--;

		  /* If possible, reuse an existing struct, else allocate a new one.  */
		  if (arrays_pool)
		    {
		      a = arrays_pool;
		      arrays_pool = arrays_pool->next;
		    }
		  else
		    a = alloca (sizeof (partially_constructed_array));

		  a->size = TO_INT (last_used_literal);
		  a->sp = &sp[-1] - stack;
		  a->next = arrays;
		  arrays = a;

		  sp[-1] = _gst_array_class;
		}
	      else
	        {
		  if (super
		      && (!last_used_literal
			  || (!IS_A_CLASS (last_used_literal)
			      && !IS_A_METACLASS (last_used_literal))
			  || !is_a_kind_of (methodClass, last_used_literal)))
		    return (_gst_debug (), "Invalid send to super");

		  last_used_literal = NULL;
	          sp -= super + _gst_builtin_selectors[n].numArgs;
	          if (super && sp[-1] != FROM_INT (SELF))
		    return ("Invalid send to super");

	          sp[-1] = FROM_INT (VARYING);
		}
	    }

	    MAKE_DIRTY_BLOCK {
	      if (sp[-1] != _gst_compiled_block_class
		  || !last_used_literal)
		return ("CompiledBlock expected");

	      error = _gst_verify_method (last_used_literal, num_outer_temps, depth);
	      if (error)
	        return (error);
	    }

	    INVALID {
	      abort ();
	    }
	  ));

	  bb_start += bp - bp_first;
	}
      while (!*bb_start);

#ifdef DEBUG_VERIFIER
      printf ("\n");
#endif
    }
#endif /* !NO_VERIFIER */

  methodOOP->flags |= F_VERIFIED;
  return (NULL);
}