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
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>LLVM Programmer's Manual</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
</head>
<body>
<div class="doc_title">
LLVM Programmer's Manual
</div>
<ol>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#general">General Information</a>
<ul>
<li><a href="#stl">The C++ Standard Template Library</a></li>
<!--
<li>The <tt>-time-passes</tt> option</li>
<li>How to use the LLVM Makefile system</li>
<li>How to write a regression test</li>
-->
</ul>
</li>
<li><a href="#apis">Important and useful LLVM APIs</a>
<ul>
<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
and <tt>dyn_cast<></tt> templates</a> </li>
<li><a href="#DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt>
option</a>
<ul>
<li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
and the <tt>-debug-only</tt> option</a> </li>
</ul>
</li>
<li><a href="#Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
option</a></li>
<!--
<li>The <tt>InstVisitor</tt> template
<li>The general graph API
-->
</ul>
</li>
<li><a href="#common">Helpful Hints for Common Operations</a>
<ul>
<li><a href="#inspection">Basic Inspection and Traversal Routines</a>
<ul>
<li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
in a <tt>Function</tt></a> </li>
<li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
in a <tt>BasicBlock</tt></a> </li>
<li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
in a <tt>Function</tt></a> </li>
<li><a href="#iterate_convert">Turning an iterator into a
class pointer</a> </li>
<li><a href="#iterate_complex">Finding call sites: a more
complex example</a> </li>
<li><a href="#calls_and_invokes">Treating calls and invokes
the same way</a> </li>
<li><a href="#iterate_chains">Iterating over def-use &
use-def chains</a> </li>
</ul>
</li>
<li><a href="#simplechanges">Making simple changes</a>
<ul>
<li><a href="#schanges_creating">Creating and inserting new
<tt>Instruction</tt>s</a> </li>
<li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
<li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
with another <tt>Value</tt></a> </li>
</ul>
</li>
<!--
<li>Working with the Control Flow Graph
<ul>
<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
<li>
<li>
</ul>
-->
</ul>
</li>
<li><a href="#advanced">Advanced Topics</a>
<ul>
<li><a href="#TypeResolve">LLVM Type Resolution</a>
<ul>
<li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
<li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
<li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
<li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
</ul></li>
<li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
</ul></li>
<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
<ul>
<li><a href="#Value">The <tt>Value</tt> class</a>
<ul>
<li><a href="#User">The <tt>User</tt> class</a>
<ul>
<li><a href="#Instruction">The <tt>Instruction</tt> class</a>
<ul>
<li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt> class</a></li>
</ul>
</li>
<li><a href="#Module">The <tt>Module</tt> class</a></li>
<li><a href="#Constant">The <tt>Constant</tt> class</a>
<ul>
<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
<ul>
<li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
<li><a href="#Function">The <tt>Function</tt> class</a></li>
<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<li><a href="#Type">The <tt>Type</tt> class</a> </li>
<li><a href="#Argument">The <tt>Argument</tt> class</a></li>
</ul>
</li>
</ul>
</li>
</ol>
<div class="doc_author">
<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
<a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
<a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="introduction">Introduction </a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This document is meant to highlight some of the important classes and
interfaces available in the LLVM source-base. This manual is not
intended to explain what LLVM is, how it works, and what LLVM code looks
like. It assumes that you know the basics of LLVM and are interested
in writing transformations or otherwise analyzing or manipulating the
code.</p>
<p>This document should get you oriented so that you can find your
way in the continuously growing source code that makes up the LLVM
infrastructure. Note that this manual is not intended to serve as a
replacement for reading the source code, so if you think there should be
a method in one of these classes to do something, but it's not listed,
check the source. Links to the <a href="/doxygen/">doxygen</a> sources
are provided to make this as easy as possible.</p>
<p>The first section of this document describes general information that is
useful to know when working in the LLVM infrastructure, and the second describes
the Core LLVM classes. In the future this manual will be extended with
information describing how to use extension libraries, such as dominator
information, CFG traversal routines, and useful utilities like the <tt><a
href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="general">General Information</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This section contains general information that is useful if you are working
in the LLVM source-base, but that isn't specific to any particular API.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="stl">The C++ Standard Template Library</a>
</div>
<div class="doc_text">
<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
perhaps much more than you are used to, or have seen before. Because of
this, you might want to do a little background reading in the
techniques used and capabilities of the library. There are many good
pages that discuss the STL, and several books on the subject that you
can get, so it will not be discussed in this document.</p>
<p>Here are some useful links:</p>
<ol>
<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
reference</a> - an excellent reference for the STL and other parts of the
standard C++ library.</li>
<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
O'Reilly book in the making. It has a decent
Standard Library
Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
published.</li>
<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
Questions</a></li>
<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
Contains a useful <a
href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
STL</a>.</li>
<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
Page</a></li>
<li><a href="http://64.78.49.204/">
Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
the book).</a></li>
</ol>
<p>You are also encouraged to take a look at the <a
href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
to write maintainable code more than where to put your curly braces.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="stl">Other useful references</a>
</div>
<div class="doc_text">
<ol>
<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Branch and Tag Primer</a></li>
<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
static and shared libraries across platforms</a></li>
</ol>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="apis">Important and useful LLVM APIs</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>Here we highlight some LLVM APIs that are generally useful and good to
know about when writing transformations.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="isa">The isa<>, cast<> and dyn_cast<> templates</a>
</div>
<div class="doc_text">
<p>The LLVM source-base makes extensive use of a custom form of RTTI.
These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
operator, but they don't have some drawbacks (primarily stemming from
the fact that <tt>dynamic_cast<></tt> only works on classes that
have a v-table). Because they are used so often, you must know what they
do and how they work. All of these templates are defined in the <a
href="/doxygen/Casting_8h-source.html"><tt>Support/Casting.h</tt></a>
file (note that you very rarely have to include this file directly).</p>
<dl>
<dt><tt>isa<></tt>: </dt>
<dd>The <tt>isa<></tt> operator works exactly like the Java
"<tt>instanceof</tt>" operator. It returns true or false depending on whether
a reference or pointer points to an instance of the specified class. This can
be very useful for constraint checking of various sorts (example below).</dd>
<dt><tt>cast<></tt>: </dt>
<dd>The <tt>cast<></tt> operator is a "checked cast" operation. It
converts a pointer or reference from a base class to a derived cast, causing
an assertion failure if it is not really an instance of the right type. This
should be used in cases where you have some information that makes you believe
that something is of the right type. An example of the <tt>isa<></tt>
and <tt>cast<></tt> template is:
<pre>
static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
if (isa<<a href="#Constant">Constant</a>>(V) || isa<<a href="#Argument">Argument</a>>(V) || isa<<a href="#GlobalValue">GlobalValue</a>>(V))
return true;
<i>// Otherwise, it must be an instruction...</i>
return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
}
</pre>
<p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
operator.</p>
</dd>
<dt><tt>dyn_cast<></tt>:</dt>
<dd>The <tt>dyn_cast<></tt> operator is a "checking cast" operation. It
checks to see if the operand is of the specified type, and if so, returns a
pointer to it (this operator does not work with references). If the operand is
not of the correct type, a null pointer is returned. Thus, this works very
much like the <tt>dynamic_cast</tt> operator in C++, and should be used in the
same circumstances. Typically, the <tt>dyn_cast<></tt> operator is used
in an <tt>if</tt> statement or some other flow control statement like this:
<pre>
if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
...
}
</pre>
<p> This form of the <tt>if</tt> statement effectively combines together a
call to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
statement, which is very convenient.</p>
<p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
<tt>dynamic_cast</tt> or Java's <tt>instanceof</tt> operator, can be abused.
In particular you should not use big chained <tt>if/then/else</tt> blocks to
check for lots of different variants of classes. If you find yourself
wanting to do this, it is much cleaner and more efficient to use the
<tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
</dd>
<dt><tt>cast_or_null<></tt>: </dt>
<dd>The <tt>cast_or_null<></tt> operator works just like the
<tt>cast<></tt> operator, except that it allows for a null pointer as
an argument (which it then propagates). This can sometimes be useful,
allowing you to combine several null checks into one.</dd>
<dt><tt>dyn_cast_or_null<></tt>: </dt>
<dd>The <tt>dyn_cast_or_null<></tt> operator works just like the
<tt>dyn_cast<></tt> operator, except that it allows for a null pointer
as an argument (which it then propagates). This can sometimes be useful,
allowing you to combine several null checks into one.</dd>
</dl>
<p>These five templates can be used with any classes, whether they have a
v-table or not. To add support for these templates, you simply need to add
<tt>classof</tt> static methods to the class you are interested casting
to. Describing this is currently outside the scope of this document, but there
are lots of examples in the LLVM source base.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
</div>
<div class="doc_text">
<p>Often when working on your pass you will put a bunch of debugging printouts
and other code into your pass. After you get it working, you want to remove
it... but you may need it again in the future (to work out new bugs that you run
across).</p>
<p> Naturally, because of this, you don't want to delete the debug printouts,
but you don't want them to always be noisy. A standard compromise is to comment
them out, allowing you to enable them if you need them in the future.</p>
<p>The "<tt><a href="/doxygen/Debug_8h-source.html">Support/Debug.h</a></tt>"
file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
this problem. Basically, you can put arbitrary code into the argument of the
<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
tool) is run with the '<tt>-debug</tt>' command line argument:</p>
<pre> ... <br> DEBUG(std::cerr << "I am here!\n");<br> ...<br></pre>
<p>Then you can run your pass like this:</p>
<pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> I am here!<br> $<br></pre>
<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
to not have to create "yet another" command line option for the debug output for
your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
so they do not cause a performance impact at all (for the same reason, they
should also not contain side-effects!).</p>
<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
program hasn't been started yet, you can always just run it with
<tt>-debug</tt>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE()</tt> and
the <tt>-debug-only</tt> option</a>
</div>
<div class="doc_text">
<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
just turns on <b>too much</b> information (such as when working on the code
generator). If you want to enable debug information with more fine-grained
control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
option as follows:</p>
<pre> ...<br> DEBUG(std::cerr << "No debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE "foo"<br> DEBUG(std::cerr << "'foo' debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE "bar"<br> DEBUG(std::cerr << "'bar' debug type\n");<br> #undef DEBUG_TYPE<br> #define DEBUG_TYPE ""<br> DEBUG(std::cerr << "No debug type (2)\n");<br> ...<br></pre>
<p>Then you can run your pass like this:</p>
<pre> $ opt < a.bc > /dev/null -mypass<br> <no output><br> $ opt < a.bc > /dev/null -mypass -debug<br> No debug type<br> 'foo' debug type<br> 'bar' debug type<br> No debug type (2)<br> $ opt < a.bc > /dev/null -mypass -debug-only=foo<br> 'foo' debug type<br> $ opt < a.bc > /dev/null -mypass -debug-only=bar<br> 'bar' debug type<br> $<br></pre>
<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
a file, to specify the debug type for the entire module (if you do this before
you <tt>#include "Support/Debug.h"</tt>, you don't have to insert the ugly
<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
"bar", because there is no system in place to ensure that names do not
conflict. If two different modules use the same string, they will all be turned
on when the name is specified. This allows, for example, all debug information
for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
even if the source lives in multiple files.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
option</a>
</div>
<div class="doc_text">
<p>The "<tt><a
href="/doxygen/Statistic_8h-source.html">Support/Statistic.h</a></tt>" file
provides a template named <tt>Statistic</tt> that is used as a unified way to
keep track of what the LLVM compiler is doing and how effective various
optimizations are. It is useful to see what optimizations are contributing to
making a particular program run faster.</p>
<p>Often you may run your pass on some big program, and you're interested to see
how many times it makes a certain transformation. Although you can do this with
hand inspection, or some ad-hoc method, this is a real pain and not very useful
for big programs. Using the <tt>Statistic</tt> template makes it very easy to
keep track of this information, and the calculated information is presented in a
uniform manner with the rest of the passes being executed.</p>
<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
it are as follows:</p>
<ol>
<li>Define your statistic like this:
<pre>static Statistic<> NumXForms("mypassname", "The # of times I did stuff");<br></pre>
<p>The <tt>Statistic</tt> template can emulate just about any data-type,
but if you do not specify a template argument, it defaults to acting like
an unsigned int counter (this is usually what you want).</p></li>
<li>Whenever you make a transformation, bump the counter:
<pre> ++NumXForms; // I did stuff<br></pre>
</li>
</ol>
<p>That's all you have to do. To get '<tt>opt</tt>' to print out the
statistics gathered, use the '<tt>-stats</tt>' option:</p>
<pre> $ opt -stats -mypassname < program.bc > /dev/null<br> ... statistic output ...<br></pre>
<p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
suite, it gives a report that looks like this:</p>
<pre> 7646 bytecodewriter - Number of normal instructions<br> 725 bytecodewriter - Number of oversized instructions<br> 129996 bytecodewriter - Number of bytecode bytes written<br> 2817 raise - Number of insts DCEd or constprop'd<br> 3213 raise - Number of cast-of-self removed<br> 5046 raise - Number of expression trees converted<br> 75 raise - Number of other getelementptr's formed<br> 138 raise - Number of load/store peepholes<br> 42 deadtypeelim - Number of unused typenames removed from symtab<br> 392 funcresolve - Number of varargs functions resolved<br> 27 globaldce - Number of global variables removed<br> 2 adce - Number of basic blocks removed<br> 134 cee - Number of branches revectored<br> 49 cee - Number of setcc instruction eliminated<br> 532 gcse - Number of loads removed<br> 2919 gcse - Number of instructions removed<br> 86 indvars - Number of canonical indvars added<br> 87 indvars - Number of aux indvars removed<br> 25 instcombine - Number of dead inst eliminate<br> 434 instcombine - Number of insts combined<br> 248 licm - Number of load insts hoisted<br> 1298 licm - Number of insts hoisted to a loop pre-header<br> 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)<br> 75 mem2reg - Number of alloca's promoted<br> 1444 cfgsimplify - Number of blocks simplified<br></pre>
<p>Obviously, with so many optimizations, having a unified framework for this
stuff is very nice. Making your pass fit well into the framework makes it more
maintainable and useful.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="common">Helpful Hints for Common Operations</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This section describes how to perform some very simple transformations of
LLVM code. This is meant to give examples of common idioms used, showing the
practical side of LLVM transformations. <p> Because this is a "how-to" section,
you should also read about the main classes that you will be working with. The
<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
and descriptions of the main classes that you should know about.</p>
</div>
<!-- NOTE: this section should be heavy on example code -->
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="inspection">Basic Inspection and Traversal Routines</a>
</div>
<div class="doc_text">
<p>The LLVM compiler infrastructure have many different data structures that may
be traversed. Following the example of the C++ standard template library, the
techniques used to traverse these various data structures are all basically the
same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
function returns an iterator pointing to one past the last valid element of the
sequence, and there is some <tt>XXXiterator</tt> data type that is common
between the two operations.</p>
<p>Because the pattern for iteration is common across many different aspects of
the program representation, the standard template library algorithms may be used
on them, and it is easier to remember how to iterate. First we show a few common
examples of the data structures that need to be traversed. Other data
structures are traversed in very similar ways.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="iterate_function">Iterating over the </a><a
href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
href="#Function"><tt>Function</tt></a>
</div>
<div class="doc_text">
<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
transform in some way; in particular, you'd like to manipulate its
<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
an example that prints the name of a <tt>BasicBlock</tt> and the number of
<tt>Instruction</tt>s it contains:</p>
<pre> // func is a pointer to a Function instance<br> for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i) {<br><br> // print out the name of the basic block if it has one, and then the<br> // number of instructions that it contains<br><br> cerr << "Basic block (name=" << i->getName() << ") has " <br> << i->size() << " instructions.\n";<br> }<br></pre>
<p>Note that i can be used as if it were a pointer for the purposes of
invoking member functions of the <tt>Instruction</tt> class. This is
because the indirection operator is overloaded for the iterator
classes. In the above code, the expression <tt>i->size()</tt> is
exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="iterate_basicblock">Iterating over the </a><a
href="#Instruction"><tt>Instruction</tt></a>s in a <a
href="#BasicBlock"><tt>BasicBlock</tt></a>
</div>
<div class="doc_text">
<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
easy to iterate over the individual instructions that make up
<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
a <tt>BasicBlock</tt>:</p>
<pre>
// blk is a pointer to a BasicBlock instance
for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
// the next statement works since operator<<(ostream&,...)
// is overloaded for Instruction&
std::cerr << *i << "\n";
</pre>
<p>However, this isn't really the best way to print out the contents of a
<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
anything you'll care about, you could have just invoked the print routine on the
basic block itself: <tt>std::cerr << *blk << "\n";</tt>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="iterate_institer">Iterating over the </a><a
href="#Instruction"><tt>Instruction</tt></a>s in a <a
href="#Function"><tt>Function</tt></a>
</div>
<div class="doc_text">
<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
<tt>InstIterator</tt> should be used instead. You'll need to include <a
href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
small example that shows how to dump all instructions in a function to the standard error stream:<p>
<pre>#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"<br>...<br>// Suppose F is a ptr to a function<br>for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)<br> cerr << *i << "\n";<br></pre>
Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
worklist with its initial contents. For example, if you wanted to
initialize a worklist to contain all instructions in a <tt>Function</tt>
F, all you would need to do is something like:
<pre>std::set<Instruction*> worklist;<br>worklist.insert(inst_begin(F), inst_end(F));<br></pre>
<p>The STL set <tt>worklist</tt> would now contain all instructions in the
<tt>Function</tt> pointed to by F.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="iterate_convert">Turning an iterator into a class pointer (and
vice-versa)</a>
</div>
<div class="doc_text">
<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
instance when all you've got at hand is an iterator. Well, extracting
a reference or a pointer from an iterator is very straight-forward.
Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
is a <tt>BasicBlock::const_iterator</tt>:</p>
<pre> Instruction& inst = *i; // grab reference to instruction reference<br> Instruction* pinst = &*i; // grab pointer to instruction reference<br> const Instruction& inst = *j;<br></pre>
<p>However, the iterators you'll be working with in the LLVM framework are
special: they will automatically convert to a ptr-to-instance type whenever they
need to. Instead of dereferencing the iterator and then taking the address of
the result, you can simply assign the iterator to the proper pointer type and
you get the dereference and address-of operation as a result of the assignment
(behind the scenes, this is a result of overloading casting mechanisms). Thus
the last line of the last example,</p>
<pre>Instruction* pinst = &*i;</pre>
<p>is semantically equivalent to</p>
<pre>Instruction* pinst = i;</pre>
<p>It's also possible to turn a class pointer into the corresponding iterator,
and this is a constant time operation (very efficient). The following code
snippet illustrates use of the conversion constructors provided by LLVM
iterators. By using these, you can explicitly grab the iterator of something
without actually obtaining it via iteration over some structure:</p>
<pre>void printNextInstruction(Instruction* inst) {<br> BasicBlock::iterator it(inst);<br> ++it; // after this line, it refers to the instruction after *inst.<br> if (it != inst->getParent()->end()) cerr << *it << "\n";<br>}<br></pre>
</div>
<!--_______________________________________________________________________-->
<div class="doc_subsubsection">
<a name="iterate_complex">Finding call sites: a slightly more complex
example</a>
</div>
<div class="doc_text">
<p>Say that you're writing a FunctionPass and would like to count all the
locations in the entire module (that is, across every <tt>Function</tt>) where a
certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
much more straight-forward manner, but this example will allow us to explore how
you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
is what we want to do:</p>
<pre>initialize callCounter to zero<br>for each Function f in the Module<br> for each BasicBlock b in f<br> for each Instruction i in b<br> if (i is a CallInst and calls the given function)<br> increment callCounter<br></pre>
<p>And the actual code is (remember, since we're writing a
<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
override the <tt>runOnFunction</tt> method...):</p>
<pre>Function* targetFunc = ...;<br><br>class OurFunctionPass : public FunctionPass {<br> public:<br> OurFunctionPass(): callCounter(0) { }<br><br> virtual runOnFunction(Function& F) {<br> for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {<br> for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {<br> if (<a
href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
href="#CallInst">CallInst</a>>(&*i)) {<br> // we know we've encountered a call instruction, so we<br> // need to determine if it's a call to the<br> // function pointed to by m_func or not.<br> <br> if (callInst->getCalledFunction() == targetFunc)<br> ++callCounter;<br> }<br> }<br> }<br> <br> private:<br> unsigned callCounter;<br>};<br></pre>
</div>
<!--_______________________________________________________________________-->
<div class="doc_subsubsection">
<a name="calls_and_invokes">Treating calls and invokes the same way</a>
</div>
<div class="doc_text">
<p>You may have noticed that the previous example was a bit oversimplified in
that it did not deal with call sites generated by 'invoke' instructions. In
this, and in other situations, you may find that you want to treat
<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
most-specific common base class is <tt>Instruction</tt>, which includes lots of
less closely-related things. For these cases, LLVM provides a handy wrapper
class called <a
href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
methods that provide functionality common to <tt>CallInst</tt>s and
<tt>InvokeInst</tt>s.</p>
<p>This class has "value semantics": it should be passed by value, not by
reference and it should not be dynamically allocated or deallocated using
<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
assignable and constructable, with costs equivalents to that of a bare pointer.
If you look at its definition, it has only a single pointer member.</p>
</div>
<!--_______________________________________________________________________-->
<div class="doc_subsubsection">
<a name="iterate_chains">Iterating over def-use & use-def chains</a>
</div>
<div class="doc_text">
<p>Frequently, we might have an instance of the <a
href="/doxygen/structllvm_1_1Value.html">Value Class</a> and we want to
determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
particular function <tt>foo</tt>. Finding all of the instructions that
<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
of <tt>F</tt>:</p>
<pre>Function* F = ...;<br><br>for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i) {<br> if (Instruction *Inst = dyn_cast<Instruction>(*i)) {<br> cerr << "F is used in instruction:\n";<br> cerr << *Inst << "\n";<br> }<br>}<br></pre>
<p>Alternately, it's common to have an instance of the <a
href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
all of the values that a particular instruction uses (that is, the operands of
the particular <tt>Instruction</tt>):</p>
<pre>Instruction* pi = ...;<br><br>for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {<br> Value* v = *i;<br> ...<br>}<br></pre>
<!--
def-use chains ("finding all users of"): Value::use_begin/use_end
use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
-->
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="simplechanges">Making simple changes</a>
</div>
<div class="doc_text">
<p>There are some primitive transformation operations present in the LLVM
infrastructure that are worth knowing about. When performing
transformations, it's fairly common to manipulate the contents of basic
blocks. This section describes some of the common methods for doing so
and gives example code.</p>
</div>
<!--_______________________________________________________________________-->
<div class="doc_subsubsection">
<a name="schanges_creating">Creating and inserting new
<tt>Instruction</tt>s</a>
</div>
<div class="doc_text">
<p><i>Instantiating Instructions</i></p>
<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
constructor for the kind of instruction to instantiate and provide the necessary
parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
(const-ptr-to) <tt>Type</tt>. Thus:</p>
<pre>AllocaInst* ai = new AllocaInst(Type::IntTy);</pre>
<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
subclass is likely to have varying default parameters which change the semantics
of the instruction, so refer to the <a
href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Instruction</a> that you're interested in instantiating.</p>
<p><i>Naming values</i></p>
<p>It is very useful to name the values of instructions when you're able to, as
this facilitates the debugging of your transformations. If you end up looking
at generated LLVM machine code, you definitely want to have logical names
associated with the results of instructions! By supplying a value for the
<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
associate a logical name with the result of the instruction's execution at
runtime. For example, say that I'm writing a transformation that dynamically
allocates space for an integer on the stack, and that integer is going to be
used as some kind of index by some other code. To accomplish this, I place an
<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
<tt>Function</tt>, and I'm intending to use it within the same
<tt>Function</tt>. I might do:</p>
<pre>AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");</pre>
<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
execution value, which is a pointer to an integer on the runtime stack.</p>
<p><i>Inserting instructions</i></p>
<p>There are essentially two ways to insert an <tt>Instruction</tt>
into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
<ul>
<li>Insertion into an explicit instruction list
<p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
before <tt>*pi</tt>, we do the following: </p>
<pre> BasicBlock *pb = ...;<br> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().insert(pi, newInst); // inserts newInst before pi in pb<br></pre>
<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
classes provide constructors which take a pointer to a
<tt>BasicBlock</tt> to be appended to. For example code that
looked like: </p>
<pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(...);<br> pb->getInstList().push_back(newInst); // appends newInst to pb<br></pre>
<p>becomes: </p>
<pre> BasicBlock *pb = ...;<br> Instruction *newInst = new Instruction(..., pb);<br></pre>
<p>which is much cleaner, especially if you are creating
long instruction streams.</p></li>
<li>Insertion into an implicit instruction list
<p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
are implicitly associated with an existing instruction list: the instruction
list of the enclosing basic block. Thus, we could have accomplished the same
thing as the above code without being given a <tt>BasicBlock</tt> by doing:
</p>
<pre> Instruction *pi = ...;<br> Instruction *newInst = new Instruction(...);<br> pi->getParent()->getInstList().insert(pi, newInst);<br></pre>
<p>In fact, this sequence of steps occurs so frequently that the
<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
constructors which take (as a default parameter) a pointer to an
<tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
precede. That is, <tt>Instruction</tt> constructors are capable of
inserting the newly-created instance into the <tt>BasicBlock</tt> of a
provided instruction, immediately before that instruction. Using an
<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
parameter, the above code becomes:</p>
<pre>Instruction* pi = ...;<br>Instruction* newInst = new Instruction(..., pi);<br></pre>
<p>which is much cleaner, especially if you're creating a lot of
instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
</ul>
</div>
<!--_______________________________________________________________________-->
<div class="doc_subsubsection">
<a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
</div>
<div class="doc_text">
<p>Deleting an instruction from an existing sequence of instructions that form a
<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
you must have a pointer to the instruction that you wish to delete. Second, you
need to obtain the pointer to that instruction's basic block. You use the
pointer to the basic block to get its list of instructions and then use the
erase function to remove your instruction. For example:</p>
<pre> <a href="#Instruction">Instruction</a> *I = .. ;<br> <a
href="#BasicBlock">BasicBlock</a> *BB = I->getParent();<br> BB->getInstList().erase(I);<br></pre>
</div>
<!--_______________________________________________________________________-->
<div class="doc_subsubsection">
<a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
<tt>Value</tt></a>
</div>
<div class="doc_text">
<p><i>Replacing individual instructions</i></p>
<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
and <tt>ReplaceInstWithInst</tt>.</p>
<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
<ul>
<li><tt>ReplaceInstWithValue</tt>
<p>This function replaces all uses (within a basic block) of a given
instruction with a value, and then removes the original instruction. The
following example illustrates the replacement of the result of a particular
<tt>AllocaInst</tt> that allocates memory for a single integer with a null
pointer to an integer.</p>
<pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,<br> Constant::getNullValue(PointerType::get(Type::IntTy)));<br></pre></li>
<li><tt>ReplaceInstWithInst</tt>
<p>This function replaces a particular instruction with another
instruction. The following example illustrates the replacement of one
<tt>AllocaInst</tt> with another.</p>
<pre>AllocaInst* instToReplace = ...;<br>BasicBlock::iterator ii(instToReplace);<br>ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,<br> new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));<br></pre></li>
</ul>
<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
<p>You can use <tt>Value::replaceAllUsesWith</tt> and
<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
doxygen documentation for the <a href="/doxygen/structllvm_1_1Value.html">Value Class</a>
and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
information.</p>
<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
ReplaceInstWithValue, ReplaceInstWithInst -->
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="advanced">Advanced Topics</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>
This section describes some of the advanced or obscure API's that most clients
do not need to be aware of. These API's tend manage the inner workings of the
LLVM system, and only need to be accessed in unusual circumstances.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="TypeResolve">LLVM Type Resolution</a>
</div>
<div class="doc_text">
<p>
The LLVM type system has a very simple goal: allow clients to compare types for
structural equality with a simple pointer comparison (aka a shallow compare).
This goal makes clients much simpler and faster, and is used throughout the LLVM
system.
</p>
<p>
Unfortunately achieving this goal is not a simple matter. In particular,
recursive types and late resolution of opaque types makes the situation very
difficult to handle. Fortunately, for the most part, our implementation makes
most clients able to be completely unaware of the nasty internal details. The
primary case where clients are exposed to the inner workings of it are when
building a recursive type. In addition to this case, the LLVM bytecode reader,
assembly parser, and linker also have to be aware of the inner workings of this
system.
</p>
<p>
For our purposes below, we need three concepts. First, an "Opaque Type" is
exactly as defined in the <a href="LangRef.html#t_opaque">language
reference</a>. Second an "Abstract Type" is any type which includes an
opaque type as part of its type graph (for example "<tt>{ opaque, int }</tt>").
Third, a concrete type is a type that is not an abstract type (e.g. "<tt>[ int,
float }</tt>").
</p>
</div>
<!-- ______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="BuildRecType">Basic Recursive Type Construction</a>
</div>
<div class="doc_text">
<p>
Because the most common question is "how do I build a recursive type with LLVM",
we answer it now and explain it as we go. Here we include enough to cause this
to be emitted to an output .ll file:
</p>
<pre>
%mylist = type { %mylist*, int }
</pre>
<p>
To build this, use the following LLVM APIs:
</p>
<pre>
//<i> Create the initial outer struct.</i>
<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
std::vector<const Type*> Elts;
Elts.push_back(PointerType::get(StructTy));
Elts.push_back(Type::IntTy);
StructType *NewSTy = StructType::get(Elts);
//<i> At this point, NewSTy = "{ opaque*, int }". Tell VMCore that</i>
//<i> the struct and the opaque type are actually the same.</i>
cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
// <i>kept up-to-date.</i>
NewSTy = cast<StructType>(StructTy.get());
// <i>Add a name for the type to the module symbol table (optional).</i>
MyModule->addTypeName("mylist", NewSTy);
</pre>
<p>
This code shows the basic approach used to build recursive types: build a
non-recursive type using 'opaque', then use type unification to close the cycle.
The type unification step is performed by the <tt><a
ref="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
described next. After that, we describe the <a
href="#PATypeHolder">PATypeHolder class</a>.
</p>
</div>
<!-- ______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
</div>
<div class="doc_text">
<p>
The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
While this method is actually a member of the DerivedType class, it is most
often used on OpaqueType instances. Type unification is actually a recursive
process. After unification, types can become structurally isomorphic to
existing types, and all duplicates are deleted (to preserve pointer equality).
</p>
<p>
In the example above, the OpaqueType object is definitely deleted.
Additionally, if there is an "{ \2*, int}" type already created in the system,
the pointer and struct type created are <b>also</b> deleted. Obviously whenever
a type is deleted, any "Type*" pointers in the program are invalidated. As
such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
types can never move or be deleted). To deal with this, the <a
href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
reference to a possibly refined type, and the <a
href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
complex datastructures.
</p>
</div>
<!-- ______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="PATypeHolder">The PATypeHolder Class</a>
</div>
<div class="doc_text">
<p>
PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
happily goes about nuking types that become isomorphic to existing types, it
automatically updates all PATypeHolder objects to point to the new type. In the
example above, this allows the code to maintain a pointer to the resultant
resolved recursive type, even though the Type*'s are potentially invalidated.
</p>
<p>
PATypeHolder is an extremely light-weight object that uses a lazy union-find
implementation to update pointers. For example the pointer from a Value to its
Type is maintained by PATypeHolder objects.
</p>
</div>
<!-- ______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="AbstractTypeUser">The AbstractTypeUser Class</a>
</div>
<div class="doc_text">
<p>
Some data structures need more to perform more complex updates when types get
resolved. The <a href="#SymbolTable">SymbolTable</a> class, for example, needs
move and potentially merge type planes in its representation when a pointer
changes.</p>
<p>
To support this, a class can derive from the AbstractTypeUser class. This class
allows it to get callbacks when certain types are resolved. To register to get
callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
methods can be called on a type. Note that these methods only work for <i>
abstract</i> types. Concrete types (those that do not include an opaque objects
somewhere) can never be refined.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
</div>
<div class="doc_text">
<p>This class provides a symbol table that the <a
href="#Function"><tt>Function</tt></a> and <a href="#Module">
<tt>Module</tt></a> classes use for naming definitions. The symbol table can
provide a name for any <a href="#Value"><tt>Value</tt></a> or <a
href="#Type"><tt>Type</tt></a>. <tt>SymbolTable</tt> is an abstract data
type. It hides the data it contains and provides access to it through a
controlled interface.</p>
<p>Note that the symbol table class is should not be directly accessed by most
clients. It should only be used when iteration over the symbol table names
themselves are required, which is very special purpose. Note that not all LLVM
<a href="#Value">Value</a>s have names, and those without names (i.e. they have
an empty name) do not exist in the symbol table.
</p>
<p>To use the <tt>SymbolTable</tt> well, you need to understand the
structure of the information it holds. The class contains two
<tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
<tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
The second, <tt>tmap</tt>, is a map of names to <tt>Type*</tt>. Thus, Values
are stored in two-dimensions and accessed by <tt>Type</tt> and name. Types,
however, are stored in a single dimension and accessed only by name.</p>
<p>The interface of this class provides three basic types of operations:
<ol>
<li><em>Accessors</em>. Accessors provide read-only access to information
such as finding a value for a name with the
<a href="#SymbolTable_lookup">lookup</a> method.</li>
<li><em>Mutators</em>. Mutators allow the user to add information to the
<tt>SymbolTable</tt> with methods like
<a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
<li><em>Iterators</em>. Iterators allow the user to traverse the content
of the symbol table in well defined ways, such as the method
<a href="#SymbolTable_type_begin"><tt>type_begin</tt></a>.</li>
</ol>
<h3>Accessors</h3>
<dl>
<dt><tt>Value* lookup(const Type* Ty, const std::string& name) const</tt>:
</dt>
<dd>The <tt>lookup</tt> method searches the type plane given by the
<tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
If a suitable <tt>Value</tt> is not found, null is returned.</dd>
<dt><tt>Type* lookupType( const std::string& name) const</tt>:</dt>
<dd>The <tt>lookupType</tt> method searches through the types for a
<tt>Type</tt> with the provided <tt>name</tt>. If a suitable <tt>Type</tt>
is not found, null is returned.</dd>
<dt><tt>bool hasTypes() const</tt>:</dt>
<dd>This function returns true if an entry has been made into the type
map.</dd>
<dt><tt>bool isEmpty() const</tt>:</dt>
<dd>This function returns true if both the value and types maps are
empty</dd>
</dl>
<h3>Mutators</h3>
<dl>
<dt><tt>void insert(Value *Val)</tt>:</dt>
<dd>This method adds the provided value to the symbol table. The Value must
have both a name and a type which are extracted and used to place the value
in the correct type plane under the value's name.</dd>
<dt><tt>void insert(const std::string& Name, Value *Val)</tt>:</dt>
<dd> Inserts a constant or type into the symbol table with the specified
name. There can be a many to one mapping between names and constants
or types.</dd>
<dt><tt>void insert(const std::string& Name, Type *Typ)</tt>:</dt>
<dd> Inserts a type into the symbol table with the specified name. There
can be a many-to-one mapping between names and types. This method
allows a type with an existing entry in the symbol table to get
a new name.</dd>
<dt><tt>void remove(Value* Val)</tt>:</dt>
<dd> This method removes a named value from the symbol table. The
type and name of the Value are extracted from \p N and used to
lookup the Value in the correct type plane. If the Value is
not in the symbol table, this method silently ignores the
request.</dd>
<dt><tt>void remove(Type* Typ)</tt>:</dt>
<dd> This method removes a named type from the symbol table. The
name of the type is extracted from \P T and used to look up
the Type in the type map. If the Type is not in the symbol
table, this method silently ignores the request.</dd>
<dt><tt>Value* remove(const std::string& Name, Value *Val)</tt>:</dt>
<dd> Remove a constant or type with the specified name from the
symbol table.</dd>
<dt><tt>Type* remove(const std::string& Name, Type* T)</tt>:</dt>
<dd> Remove a type with the specified name from the symbol table.
Returns the removed Type.</dd>
<dt><tt>Value *value_remove(const value_iterator& It)</tt>:</dt>
<dd> Removes a specific value from the symbol table.
Returns the removed value.</dd>
<dt><tt>bool strip()</tt>:</dt>
<dd> This method will strip the symbol table of its names leaving
the type and values. </dd>
<dt><tt>void clear()</tt>:</dt>
<dd>Empty the symbol table completely.</dd>
</dl>
<h3>Iteration</h3>
<p>The following functions describe three types of iterators you can obtain
the beginning or end of the sequence for both const and non-const. It is
important to keep track of the different kinds of iterators. There are
three idioms worth pointing out:</p>
<table>
<tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
<tr>
<td align="left">Planes Of name/Value maps</td><td>PI</td>
<td align="left"><pre><tt>
for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
PE = ST.plane_end(); PI != PE; ++PI ) {
PI->first // This is the Type* of the plane
PI->second // This is the SymbolTable::ValueMap of name/Value pairs
</tt></pre></td>
</tr>
<tr>
<td align="left">All name/Type Pairs</td><td>TI</td>
<td align="left"><pre><tt>
for (SymbolTable::type_const_iterator TI = ST.type_begin(),
TE = ST.type_end(); TI != TE; ++TI )
TI->first // This is the name of the type
TI->second // This is the Type* value associated with the name
</tt></pre></td>
</tr>
<tr>
<td align="left">name/Value pairs in a plane</td><td>VI</td>
<td align="left"><pre><tt>
for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
VE = ST.value_end(SomeType); VI != VE; ++VI )
VI->first // This is the name of the Value
VI->second // This is the Value* value associated with the name
</tt></pre></td>
</tr>
</table>
<p>Using the recommended iterator names and idioms will help you avoid
making mistakes. Of particular note, make sure that whenever you use
value_begin(SomeType) that you always compare the resulting iterator
with value_end(SomeType) not value_end(SomeOtherType) or else you
will loop infinitely.</p>
<dl>
<dt><tt>plane_iterator plane_begin()</tt>:</dt>
<dd>Get an iterator that starts at the beginning of the type planes.
The iterator will iterate over the Type/ValueMap pairs in the
type planes. </dd>
<dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
<dd>Get a const_iterator that starts at the beginning of the type
planes. The iterator will iterate over the Type/ValueMap pairs
in the type planes. </dd>
<dt><tt>plane_iterator plane_end()</tt>:</dt>
<dd>Get an iterator at the end of the type planes. This serves as
the marker for end of iteration over the type planes.</dd>
<dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
<dd>Get a const_iterator at the end of the type planes. This serves as
the marker for end of iteration over the type planes.</dd>
<dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
<dd>Get an iterator that starts at the beginning of a type plane.
The iterator will iterate over the name/value pairs in the type plane.
Note: The type plane must already exist before using this.</dd>
<dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
<dd>Get a const_iterator that starts at the beginning of a type plane.
The iterator will iterate over the name/value pairs in the type plane.
Note: The type plane must already exist before using this.</dd>
<dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
<dd>Get an iterator to the end of a type plane. This serves as the marker
for end of iteration of the type plane.
Note: The type plane must already exist before using this.</dd>
<dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
<dd>Get a const_iterator to the end of a type plane. This serves as the
marker for end of iteration of the type plane.
Note: the type plane must already exist before using this.</dd>
<dt><tt>type_iterator type_begin()</tt>:</dt>
<dd>Get an iterator to the start of the name/Type map.</dd>
<dt><tt>type_const_iterator type_begin() cons</tt>:</dt>
<dd> Get a const_iterator to the start of the name/Type map.</dd>
<dt><tt>type_iterator type_end()</tt>:</dt>
<dd>Get an iterator to the end of the name/Type map. This serves as the
marker for end of iteration of the types.</dd>
<dt><tt>type_const_iterator type_end() const</tt>:</dt>
<dd>Get a const-iterator to the end of the name/Type map. This serves
as the marker for end of iteration of the types.</dd>
<dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
<dd>This method returns a plane_const_iterator for iteration over
the type planes starting at a specific plane, given by \p Ty.</dd>
<dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
<dd>This method returns a plane_iterator for iteration over the
type planes starting at a specific plane, given by \p Ty.</dd>
</dl>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>The Core LLVM classes are the primary means of representing the program
being inspected or transformed. The core LLVM classes are defined in
header files in the <tt>include/llvm/</tt> directory, and implemented in
the <tt>lib/VMCore</tt> directory.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Value">The <tt>Value</tt> class</a>
</div>
<div>
<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
<br>
doxygen info: <a href="/doxygen/structllvm_1_1Value.html">Value Class</a></p>
<p>The <tt>Value</tt> class is the most important class in the LLVM Source
base. It represents a typed value that may be used (among other things) as an
operand to an instruction. There are many different types of <tt>Value</tt>s,
such as <a href="#Constant"><tt>Constant</tt></a>s,<a
href="#Argument"><tt>Argument</tt></a>s. Even <a
href="#Instruction"><tt>Instruction</tt></a>s and <a
href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
for a program. For example, an incoming argument to a function (represented
with an instance of the <a href="#Argument">Argument</a> class) is "used" by
every instruction in the function that references the argument. To keep track
of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
href="#User"><tt>User</tt></a>s that is using it (the <a
href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
def-use information in the program, and is accessible through the <tt>use_</tt>*
methods, shown below.</p>
<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
method. In addition, all LLVM values can be named. The "name" of the
<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
<pre> %<b>foo</b> = add int 1, 2<br></pre>
<p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
that the name of any value may be missing (an empty string), so names should
<b>ONLY</b> be used for debugging (making the source code easier to read,
debugging printouts), they should not be used to keep track of values or map
between them. For this purpose, use a <tt>std::map</tt> of pointers to the
<tt>Value</tt> itself instead.</p>
<p>One important aspect of LLVM is that there is no distinction between an SSA
variable and the operation that produces it. Because of this, any reference to
the value produced by an instruction (or the value available as an incoming
argument, for example) is represented as a direct pointer to the instance of
the class that
represents this value. Although this may take some getting used to, it
simplifies the representation and makes it easier to manipulate.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
</div>
<div class="doc_text">
<ul>
<li><tt>Value::use_iterator</tt> - Typedef for iterator over the
use-list<br>
<tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
the use-list<br>
<tt>unsigned use_size()</tt> - Returns the number of users of the
value.<br>
<tt>bool use_empty()</tt> - Returns true if there are no users.<br>
<tt>use_iterator use_begin()</tt> - Get an iterator to the start of
the use-list.<br>
<tt>use_iterator use_end()</tt> - Get an iterator to the end of the
use-list.<br>
<tt><a href="#User">User</a> *use_back()</tt> - Returns the last
element in the list.
<p> These methods are the interface to access the def-use
information in LLVM. As with all other iterators in LLVM, the naming
conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
</li>
<li><tt><a href="#Type">Type</a> *getType() const</tt>
<p>This method returns the Type of the Value.</p>
</li>
<li><tt>bool hasName() const</tt><br>
<tt>std::string getName() const</tt><br>
<tt>void setName(const std::string &Name)</tt>
<p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
be aware of the <a href="#nameWarning">precaution above</a>.</p>
</li>
<li><tt>void replaceAllUsesWith(Value *V)</tt>
<p>This method traverses the use list of a <tt>Value</tt> changing all <a
href="#User"><tt>User</tt>s</a> of the current value to refer to
"<tt>V</tt>" instead. For example, if you detect that an instruction always
produces a constant value (for example through constant folding), you can
replace all uses of the instruction with the constant like this:</p>
<pre> Inst->replaceAllUsesWith(ConstVal);<br></pre>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="User">The <tt>User</tt> class</a>
</div>
<div class="doc_text">
<p>
<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Superclass: <a href="#Value"><tt>Value</tt></a></p>
<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
referring to. The <tt>User</tt> class itself is a subclass of
<tt>Value</tt>.</p>
<p>The operands of a <tt>User</tt> point directly to the LLVM <a
href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
Single Assignment (SSA) form, there can only be one definition referred to,
allowing this direct connection. This connection provides the use-def
information in LLVM.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_User">Important Public Members of the <tt>User</tt> class</a>
</div>
<div class="doc_text">
<p>The <tt>User</tt> class exposes the operand list in two ways: through
an index access interface and through an iterator based interface.</p>
<ul>
<li><tt>Value *getOperand(unsigned i)</tt><br>
<tt>unsigned getNumOperands()</tt>
<p> These two methods expose the operands of the <tt>User</tt> in a
convenient form for direct access.</p></li>
<li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
list<br>
<tt>op_iterator op_begin()</tt> - Get an iterator to the start of
the operand list.<br>
<tt>op_iterator op_end()</tt> - Get an iterator to the end of the
operand list.
<p> Together, these methods make up the iterator based interface to
the operands of a <tt>User</tt>.</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Instruction">The <tt>Instruction</tt> class</a>
</div>
<div class="doc_text">
<p><tt>#include "</tt><tt><a
href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Superclasses: <a href="#User"><tt>User</tt></a>, <a
href="#Value"><tt>Value</tt></a></p>
<p>The <tt>Instruction</tt> class is the common base class for all LLVM
instructions. It provides only a few methods, but is a very commonly used
class. The primary data tracked by the <tt>Instruction</tt> class itself is the
opcode (instruction type) and the parent <a
href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
into. To represent a specific type of instruction, one of many subclasses of
<tt>Instruction</tt> are used.</p>
<p> Because the <tt>Instruction</tt> class subclasses the <a
href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
way as for other <a href="#User"><tt>User</tt></a>s (with the
<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
file contains some meta-data about the various different types of instructions
in LLVM. It describes the enum values that are used as opcodes (for example
<tt>Instruction::Add</tt> and <tt>Instruction::SetLE</tt>), as well as the
concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
href="#SetCondInst">SetCondInst</a></tt>). Unfortunately, the use of macros in
this file confuses doxygen, so these enum values don't show up correctly in the
<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
class</a>
</div>
<div class="doc_text">
<ul>
<li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
<p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
this <tt>Instruction</tt> is embedded into.</p></li>
<li><tt>bool mayWriteToMemory()</tt>
<p>Returns true if the instruction writes to memory, i.e. it is a
<tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
<li><tt>unsigned getOpcode()</tt>
<p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
<li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
<p>Returns another instance of the specified instruction, identical
in all ways to the original except that the instruction has no parent
(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
and it has no name</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
</div>
<div class="doc_text">
<p><tt>#include "<a
href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
Class</a><br>
Superclass: <a href="#Value"><tt>Value</tt></a></p>
<p>This class represents a single entry multiple exit section of the code,
commonly known as a basic block by the compiler community. The
<tt>BasicBlock</tt> class maintains a list of <a
href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
Matching the language definition, the last element of this list of instructions
is always a terminator instruction (a subclass of the <a
href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
<p>In addition to tracking the list of instructions that make up the block, the
<tt>BasicBlock</tt> class also keeps track of the <a
href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
<p>Note that <tt>BasicBlock</tt>s themselves are <a
href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
<tt>label</tt>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
class</a>
</div>
<div class="doc_text">
<ul>
<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
href="#Function">Function</a> *Parent = 0)</tt>
<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
insertion into a function. The constructor optionally takes a name for the new
block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
automatically inserted at the end of the specified <a
href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
<tt>size()</tt>, <tt>empty()</tt>
STL-style functions for accessing the instruction list.
<p>These methods and typedefs are forwarding functions that have the same
semantics as the standard library methods of the same names. These methods
expose the underlying instruction list of a basic block in a way that is easy to
manipulate. To get the full complement of container operations (including
operations to update the list), you must use the <tt>getInstList()</tt>
method.</p></li>
<li><tt>BasicBlock::InstListType &getInstList()</tt>
<p>This method is used to get access to the underlying container that actually
holds the Instructions. This method must be used when there isn't a forwarding
function in the <tt>BasicBlock</tt> class for the operation that you would like
to perform. Because there are no forwarding functions for "updating"
operations, you need to use this if you want to update the contents of a
<tt>BasicBlock</tt>.</p></li>
<li><tt><a href="#Function">Function</a> *getParent()</tt>
<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
embedded into, or a null pointer if it is homeless.</p></li>
<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
<p> Returns a pointer to the terminator instruction that appears at the end of
the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
instruction in the block is not a terminator, then a null pointer is
returned.</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
</div>
<div class="doc_text">
<p><tt>#include "<a
href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
Class</a><br>
Superclasses: <a href="#User"><tt>User</tt></a>, <a
href="#Value"><tt>Value</tt></a></p>
<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
Because they are visible at global scope, they are also subject to linking with
other globals defined in different translation units. To control the linking
process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
defined by the <tt>LinkageTypes</tt> enumeration.</p>
<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
<tt>static</tt> in C), it is not visible to code outside the current translation
unit, and does not participate in linking. If it has external linkage, it is
visible to external code, and does participate in linking. In addition to
linkage information, <tt>GlobalValue</tt>s keep track of which <a
href="#Module"><tt>Module</tt></a> they are currently part of.</p>
<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
global is always a pointer to its contents. It is important to remember this
when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
int]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
the address of the first element of this array and the value of the
<tt>GlobalVariable</tt> are the same, they have different types. The
<tt>GlobalVariable</tt>'s type is <tt>[24 x int]</tt>. The first element's type
is <tt>int.</tt> Because of this, accessing a global value requires you to
dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
Language Reference Manual</a>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
class</a>
</div>
<div class="doc_text">
<ul>
<li><tt>bool hasInternalLinkage() const</tt><br>
<tt>bool hasExternalLinkage() const</tt><br>
<tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
<p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
<p> </p>
</li>
<li><tt><a href="#Module">Module</a> *getParent()</tt>
<p> This returns the <a href="#Module"><tt>Module</tt></a> that the
GlobalValue is currently embedded into.</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Function">The <tt>Function</tt> class</a>
</div>
<div class="doc_text">
<p><tt>#include "<a
href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
actually one of the more complex classes in the LLVM heirarchy because it must
keep track of a large amount of data. The <tt>Function</tt> class keeps track
of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal <a
href="#Argument"><tt>Argument</tt></a>s, and a <a
href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
commonly used part of <tt>Function</tt> objects. The list imposes an implicit
ordering of the blocks in the function, which indicate how the code will be
layed out by the backend. Additionally, the first <a
href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
block. There are no implicit exit nodes, and in fact there may be multiple exit
nodes from a single <tt>Function</tt>. If the <a
href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
the <tt>Function</tt> is actually a function declaration: the actual body of the
function hasn't been linked in yet.</p>
<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
<tt>Function</tt> class also keeps track of the list of formal <a
href="#Argument"><tt>Argument</tt></a>s that the function receives. This
container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
LLVM feature that is only used when you have to look up a value by name. Aside
from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
internally to make sure that there are not conflicts between the names of <a
href="#Instruction"><tt>Instruction</tt></a>s, <a
href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
and therefore also a <a href="#Constant">Constant</a>. The value of the function
is its address (after linking) which is guaranteed to be constant.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Function">Important Public Members of the <tt>Function</tt>
class</a>
</div>
<div class="doc_text">
<ul>
<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
*Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)</tt>
<p>Constructor used when you need to create new <tt>Function</tt>s to add
the the program. The constructor must specify the type of the function to
create and what type of linkage the function should have. The <a
href="#FunctionType"><tt>FunctionType</tt></a> argument
specifies the formal arguments and return value for the function. The same
<a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
create multiple functions. The <tt>Parent</tt> argument specifies the Module
in which the function is defined. If this argument is provided, the function
will automatically be inserted into that module's list of
functions.</p></li>
<li><tt>bool isExternal()</tt>
<p>Return whether or not the <tt>Function</tt> has a body defined. If the
function is "external", it does not have a body, and thus must be resolved
by linking with a function defined in a different translation unit.</p></li>
<li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
<tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
<tt>begin()</tt>, <tt>end()</tt>
<tt>size()</tt>, <tt>empty()</tt>
<p>These are forwarding methods that make it easy to access the contents of
a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
list.</p></li>
<li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
<p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
is necessary to use when you need to update the list or perform a complex
action that doesn't have a forwarding method.</p></li>
<li><tt>Function::arg_iterator</tt> - Typedef for the argument list
iterator<br>
<tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
<tt>arg_begin()</tt>, <tt>arg_end()</tt>
<tt>arg_size()</tt>, <tt>arg_empty()</tt>
<p>These are forwarding methods that make it easy to access the contents of
a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
list.</p></li>
<li><tt>Function::ArgumentListType &getArgumentList()</tt>
<p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
necessary to use when you need to update the list or perform a complex
action that doesn't have a forwarding method.</p></li>
<li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
<p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
function. Because the entry block for the function is always the first
block, this returns the first block of the <tt>Function</tt>.</p></li>
<li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
<tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
<p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
<tt>Function</tt> and returns the return type of the function, or the <a
href="#FunctionType"><tt>FunctionType</tt></a> of the actual
function.</p></li>
<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
<p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
for this <tt>Function</tt>.</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
</div>
<div class="doc_text">
<p><tt>#include "<a
href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
<br>
doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Class</a><br> Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>, <a
href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
<p>Global variables are represented with the (suprise suprise)
<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
always referenced by their address (global values must live in memory, so their
"name" refers to their address). See <a
href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global variables
may have an initial value (which must be a <a
href="#Constant"><tt>Constant</tt></a>), and if they have an initializer, they
may be marked as "constant" themselves (indicating that their contents never
change at runtime).</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_GlobalVariable">Important Public Members of the
<tt>GlobalVariable</tt> class</a>
</div>
<div class="doc_text">
<ul>
<li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
*Initializer = 0, const std::string &Name = "", Module* Parent = 0)</tt>
<p>Create a new global variable of the specified type. If
<tt>isConstant</tt> is true then the global variable will be marked as
unchanging for the program. The Linkage parameter specifies the type of
linkage (internal, external, weak, linkonce, appending) for the variable. If
the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then
the resultant global variable will have internal linkage. AppendingLinkage
concatenates together all instances (in different translation units) of the
variable into a single variable but is only applicable to arrays. See
the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
further details on linkage types. Optionally an initializer, a name, and the
module to put the variable into may be specified for the global variable as
well.</p></li>
<li><tt>bool isConstant() const</tt>
<p>Returns true if this is a global variable that is known not to
be modified at runtime.</p></li>
<li><tt>bool hasInitializer()</tt>
<p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
<li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
<p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
to call this method if there is no initializer.</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Module">The <tt>Module</tt> class</a>
</div>
<div class="doc_text">
<p><tt>#include "<a
href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
<p>The <tt>Module</tt> class represents the top level structure present in LLVM
programs. An LLVM module is effectively either a translation unit of the
original program or a combination of several translation units merged by the
linker. The <tt>Module</tt> class keeps track of a list of <a
href="#Function"><tt>Function</tt></a>s, a list of <a
href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
helpful member functions that try to make common operations easy.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
</div>
<div class="doc_text">
<ul>
<li><tt>Module::Module(std::string name = "")</tt></li>
</ul>
<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
provide a name for it (probably based on the name of the translation unit).</p>
<ul>
<li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
<tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
<tt>begin()</tt>, <tt>end()</tt>
<tt>size()</tt>, <tt>empty()</tt>
<p>These are forwarding methods that make it easy to access the contents of
a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
list.</p></li>
<li><tt>Module::FunctionListType &getFunctionList()</tt>
<p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
necessary to use when you need to update the list or perform a complex
action that doesn't have a forwarding method.</p>
<p><!-- Global Variable --></p></li>
</ul>
<hr>
<ul>
<li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
<tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
<tt>global_begin()</tt>, <tt>global_end()</tt>
<tt>global_size()</tt>, <tt>global_empty()</tt>
<p> These are forwarding methods that make it easy to access the contents of
a <tt>Module</tt> object's <a
href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
<li><tt>Module::GlobalListType &getGlobalList()</tt>
<p>Returns the list of <a
href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
use when you need to update the list or perform a complex action that
doesn't have a forwarding method.</p>
<p><!-- Symbol table stuff --> </p></li>
</ul>
<hr>
<ul>
<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
<p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
for this <tt>Module</tt>.</p>
<p><!-- Convenience methods --></p></li>
</ul>
<hr>
<ul>
<li><tt><a href="#Function">Function</a> *getFunction(const std::string
&Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
<p>Look up the specified function in the <tt>Module</tt> <a
href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
<tt>null</tt>.</p></li>
<li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
<p>Look up the specified function in the <tt>Module</tt> <a
href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
external declaration for the function and return it.</p></li>
<li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
<p>If there is at least one entry in the <a
href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
string.</p></li>
<li><tt>bool addTypeName(const std::string &Name, const <a
href="#Type">Type</a> *Ty)</tt>
<p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
name, true is returned and the <a
href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Constant">The <tt>Constant</tt> class and subclasses</a>
</div>
<div class="doc_text">
<p>Constant represents a base class for different types of constants. It
is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt,
ConstantArray etc for representing the various types of Constants.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Constant">Important Public Methods</a>
</div>
<div class="doc_text">
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">Important Subclasses of Constant </div>
<div class="doc_text">
<ul>
<li>ConstantSInt : This subclass of Constant represents a signed integer
constant.
<ul>
<li><tt>int64_t getValue() const</tt>: Returns the underlying value of
this constant. </li>
</ul>
</li>
<li>ConstantUInt : This class represents an unsigned integer.
<ul>
<li><tt>uint64_t getValue() const</tt>: Returns the underlying value of
this constant. </li>
</ul>
</li>
<li>ConstantFP : This class represents a floating point constant.
<ul>
<li><tt>double getValue() const</tt>: Returns the underlying value of
this constant. </li>
</ul>
</li>
<li>ConstantBool : This represents a boolean constant.
<ul>
<li><tt>bool getValue() const</tt>: Returns the underlying value of this
constant. </li>
</ul>
</li>
<li>ConstantArray : This represents a constant array.
<ul>
<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
a vector of component constants that makeup this array. </li>
</ul>
</li>
<li>ConstantStruct : This represents a constant struct.
<ul>
<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
a vector of component constants that makeup this array. </li>
</ul>
</li>
<li>GlobalValue : This represents either a global variable or a function. In
either case, the value is a constant fixed address (after linking).
</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Type">The <tt>Type</tt> class and Derived Types</a>
</div>
<div class="doc_text">
<p>Type as noted earlier is also a subclass of a Value class. Any primitive
type (like int, short etc) in LLVM is an instance of Type Class. All other
types are instances of subclasses of type like FunctionType, ArrayType
etc. DerivedType is the interface for all such dervied types including
FunctionType, ArrayType, PointerType, StructType. Types can have names. They can
be recursive (StructType). There exists exactly one instance of any type
structure at a time. This allows using pointer equality of Type *s for comparing
types.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Value">Important Public Methods</a>
</div>
<div class="doc_text">
<ul>
<li><tt>bool isSigned() const</tt>: Returns whether an integral numeric type
is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is
not true for Float and Double. </li>
<li><tt>bool isUnsigned() const</tt>: Returns whether a numeric type is
unsigned. This is not quite the complement of isSigned... nonnumeric types
return false as they do with isSigned. This returns true for UByteTy,
UShortTy, UIntTy, and ULongTy. </li>
<li><tt>bool isInteger() const</tt>: Equivalent to isSigned() || isUnsigned().</li>
<li><tt>bool isIntegral() const</tt>: Returns true if this is an integral
type, which is either Bool type or one of the Integer types.</li>
<li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
floating point types.</li>
<li><tt>isLosslesslyConvertableTo (const Type *Ty) const</tt>: Return true if
this type can be converted to 'Ty' without any reinterpretation of bits. For
example, uint to int or one pointer type to another.</li>
</ul>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="m_Value">Important Derived Types</a>
</div>
<div class="doc_text">
<ul>
<li>SequentialType : This is subclassed by ArrayType and PointerType
<ul>
<li><tt>const Type * getElementType() const</tt>: Returns the type of each
of the elements in the sequential type. </li>
</ul>
</li>
<li>ArrayType : This is a subclass of SequentialType and defines interface for
array types.
<ul>
<li><tt>unsigned getNumElements() const</tt>: Returns the number of
elements in the array. </li>
</ul>
</li>
<li>PointerType : Subclass of SequentialType for pointer types. </li>
<li>StructType : subclass of DerivedTypes for struct types </li>
<li>FunctionType : subclass of DerivedTypes for function types.
<ul>
<li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
function</li>
<li><tt> const Type * getReturnType() const</tt>: Returns the
return type of the function.</li>
<li><tt>const Type * getParamType (unsigned i)</tt>: Returns
the type of the ith parameter.</li>
<li><tt> const unsigned getNumParams() const</tt>: Returns the
number of formal parameters.</li>
</ul>
</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="Argument">The <tt>Argument</tt> class</a>
</div>
<div class="doc_text">
<p>This subclass of Value defines the interface for incoming formal
arguments to a function. A Function maintains a list of its formal
arguments. An argument has a pointer to the parent Function.</p>
</div>
<!-- *********************************************************************** -->
<hr>
<address>
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
<a href="http://validator.w3.org/check/referer"><img
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
</body>
</html>
<!-- vim: sw=2 noai
-->
|