1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
|
@c Copyright (c) 1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
@c Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@c ---------------------------------------------------------------------
@c Trees
@c ---------------------------------------------------------------------
@node Trees
@chapter Trees: The intermediate representation used by the C and C++ front ends
@cindex Trees
@cindex C/C++ Internal Representation
This chapter documents the internal representation used by GCC to
represent C and C++ source programs. When presented with a C or C++
source program, GCC parses the program, performs semantic analysis
(including the generation of error messages), and then produces the
internal representation described here. This representation contains a
complete representation for the entire translation unit provided as
input to the front end. This representation is then typically processed
by a code-generator in order to produce machine code, but could also be
used in the creation of source browsers, intelligent editors, automatic
documentation generators, interpreters, and any other programs needing
the ability to process C or C++ code.
This chapter explains the internal representation. In particular, it
documents the internal representation for C and C++ source
constructs, and the macros, functions, and variables that can be used to
access these constructs. The C++ representation is largely a superset
of the representation used in the C front end. There is only one
construct used in C that does not appear in the C++ front end and that
is the GNU ``nested function'' extension. Many of the macros documented
here do not apply in C because the corresponding language constructs do
not appear in C@.
If you are developing a ``back end'', be it is a code-generator or some
other tool, that uses this representation, you may occasionally find
that you need to ask questions not easily answered by the functions and
macros available here. If that situation occurs, it is quite likely
that GCC already supports the functionality you desire, but that the
interface is simply not documented here. In that case, you should ask
the GCC maintainers (via mail to @email{gcc@@gcc.gnu.org}) about
documenting the functionality you require. Similarly, if you find
yourself writing functions that do not deal directly with your back end,
but instead might be useful to other people using the GCC front end, you
should submit your patches for inclusion in GCC@.
@menu
* Deficiencies:: Topics net yet covered in this document.
* Tree overview:: All about @code{tree}s.
* Types:: Fundamental and aggregate types.
* Scopes:: Namespaces and classes.
* Functions:: Overloading, function bodies, and linkage.
* Declarations:: Type declarations and variables.
* Attributes:: Declaration and type attributes.
* Expression trees:: From @code{typeid} to @code{throw}.
@end menu
@c ---------------------------------------------------------------------
@c Deficiencies
@c ---------------------------------------------------------------------
@node Deficiencies
@section Deficiencies
There are many places in which this document is incomplet and incorrekt.
It is, as of yet, only @emph{preliminary} documentation.
@c ---------------------------------------------------------------------
@c Overview
@c ---------------------------------------------------------------------
@node Tree overview
@section Overview
@cindex tree
@findex TREE_CODE
The central data structure used by the internal representation is the
@code{tree}. These nodes, while all of the C type @code{tree}, are of
many varieties. A @code{tree} is a pointer type, but the object to
which it points may be of a variety of types. From this point forward,
we will refer to trees in ordinary type, rather than in @code{this
font}, except when talking about the actual C type @code{tree}.
You can tell what kind of node a particular tree is by using the
@code{TREE_CODE} macro. Many, many macros take trees as input and
return trees as output. However, most macros require a certain kind of
tree node as input. In other words, there is a type-system for trees,
but it is not reflected in the C type-system.
For safety, it is useful to configure GCC with @option{--enable-checking}.
Although this results in a significant performance penalty (since all
tree types are checked at run-time), and is therefore inappropriate in a
release version, it is extremely helpful during the development process.
Many macros behave as predicates. Many, although not all, of these
predicates end in @samp{_P}. Do not rely on the result type of these
macros being of any particular type. You may, however, rely on the fact
that the type can be compared to @code{0}, so that statements like
@smallexample
if (TEST_P (t) && !TEST_P (y))
x = 1;
@end smallexample
@noindent
and
@smallexample
int i = (TEST_P (t) != 0);
@end smallexample
@noindent
are legal. Macros that return @code{int} values now may be changed to
return @code{tree} values, or other pointers in the future. Even those
that continue to return @code{int} may return multiple nonzero codes
where previously they returned only zero and one. Therefore, you should
not write code like
@smallexample
if (TEST_P (t) == 1)
@end smallexample
@noindent
as this code is not guaranteed to work correctly in the future.
You should not take the address of values returned by the macros or
functions described here. In particular, no guarantee is given that the
values are lvalues.
In general, the names of macros are all in uppercase, while the names of
functions are entirely in lowercase. There are rare exceptions to this
rule. You should assume that any macro or function whose name is made
up entirely of uppercase letters may evaluate its arguments more than
once. You may assume that a macro or function whose name is made up
entirely of lowercase letters will evaluate its arguments only once.
The @code{error_mark_node} is a special tree. Its tree code is
@code{ERROR_MARK}, but since there is only ever one node with that code,
the usual practice is to compare the tree against
@code{error_mark_node}. (This test is just a test for pointer
equality.) If an error has occurred during front-end processing the
flag @code{errorcount} will be set. If the front end has encountered
code it cannot handle, it will issue a message to the user and set
@code{sorrycount}. When these flags are set, any macro or function
which normally returns a tree of a particular kind may instead return
the @code{error_mark_node}. Thus, if you intend to do any processing of
erroneous code, you must be prepared to deal with the
@code{error_mark_node}.
Occasionally, a particular tree slot (like an operand to an expression,
or a particular field in a declaration) will be referred to as
``reserved for the back end''. These slots are used to store RTL when
the tree is converted to RTL for use by the GCC back end. However, if
that process is not taking place (e.g., if the front end is being hooked
up to an intelligent editor), then those slots may be used by the
back end presently in use.
If you encounter situations that do not match this documentation, such
as tree nodes of types not mentioned here, or macros documented to
return entities of a particular kind that instead return entities of
some different kind, you have found a bug, either in the front end or in
the documentation. Please report these bugs as you would any other
bug.
@menu
* Macros and Functions::Macros and functions that can be used with all trees.
* Identifiers:: The names of things.
* Containers:: Lists and vectors.
@end menu
@c ---------------------------------------------------------------------
@c Trees
@c ---------------------------------------------------------------------
@node Macros and Functions
@subsection Trees
@cindex tree
This section is not here yet.
@c ---------------------------------------------------------------------
@c Identifiers
@c ---------------------------------------------------------------------
@node Identifiers
@subsection Identifiers
@cindex identifier
@cindex name
@tindex IDENTIFIER_NODE
An @code{IDENTIFIER_NODE} represents a slightly more general concept
that the standard C or C++ concept of identifier. In particular, an
@code{IDENTIFIER_NODE} may contain a @samp{$}, or other extraordinary
characters.
There are never two distinct @code{IDENTIFIER_NODE}s representing the
same identifier. Therefore, you may use pointer equality to compare
@code{IDENTIFIER_NODE}s, rather than using a routine like @code{strcmp}.
You can use the following macros to access identifiers:
@ftable @code
@item IDENTIFIER_POINTER
The string represented by the identifier, represented as a
@code{char*}. This string is always @code{NUL}-terminated, and contains
no embedded @code{NUL} characters.
@item IDENTIFIER_LENGTH
The length of the string returned by @code{IDENTIFIER_POINTER}, not
including the trailing @code{NUL}. This value of
@code{IDENTIFIER_LENGTH (x)} is always the same as @code{strlen
(IDENTIFIER_POINTER (x))}.
@item IDENTIFIER_OPNAME_P
This predicate holds if the identifier represents the name of an
overloaded operator. In this case, you should not depend on the
contents of either the @code{IDENTIFIER_POINTER} or the
@code{IDENTIFIER_LENGTH}.
@item IDENTIFIER_TYPENAME_P
This predicate holds if the identifier represents the name of a
user-defined conversion operator. In this case, the @code{TREE_TYPE} of
the @code{IDENTIFIER_NODE} holds the type to which the conversion
operator converts.
@end ftable
@c ---------------------------------------------------------------------
@c Containers
@c ---------------------------------------------------------------------
@node Containers
@subsection Containers
@cindex container
@cindex list
@cindex vector
@tindex TREE_LIST
@tindex TREE_VEC
@findex TREE_PURPOSE
@findex TREE_VALUE
@findex TREE_VEC_LENGTH
@findex TREE_VEC_ELT
Two common container data structures can be represented directly with
tree nodes. A @code{TREE_LIST} is a singly linked list containing two
trees per node. These are the @code{TREE_PURPOSE} and @code{TREE_VALUE}
of each node. (Often, the @code{TREE_PURPOSE} contains some kind of
tag, or additional information, while the @code{TREE_VALUE} contains the
majority of the payload. In other cases, the @code{TREE_PURPOSE} is
simply @code{NULL_TREE}, while in still others both the
@code{TREE_PURPOSE} and @code{TREE_VALUE} are of equal stature.) Given
one @code{TREE_LIST} node, the next node is found by following the
@code{TREE_CHAIN}. If the @code{TREE_CHAIN} is @code{NULL_TREE}, then
you have reached the end of the list.
A @code{TREE_VEC} is a simple vector. The @code{TREE_VEC_LENGTH} is an
integer (not a tree) giving the number of nodes in the vector. The
nodes themselves are accessed using the @code{TREE_VEC_ELT} macro, which
takes two arguments. The first is the @code{TREE_VEC} in question; the
second is an integer indicating which element in the vector is desired.
The elements are indexed from zero.
@c ---------------------------------------------------------------------
@c Types
@c ---------------------------------------------------------------------
@node Types
@section Types
@cindex type
@cindex pointer
@cindex reference
@cindex fundamental type
@cindex array
@tindex VOID_TYPE
@tindex INTEGER_TYPE
@tindex TYPE_MIN_VALUE
@tindex TYPE_MAX_VALUE
@tindex REAL_TYPE
@tindex COMPLEX_TYPE
@tindex ENUMERAL_TYPE
@tindex BOOLEAN_TYPE
@tindex POINTER_TYPE
@tindex REFERENCE_TYPE
@tindex FUNCTION_TYPE
@tindex METHOD_TYPE
@tindex ARRAY_TYPE
@tindex RECORD_TYPE
@tindex UNION_TYPE
@tindex UNKNOWN_TYPE
@tindex OFFSET_TYPE
@tindex TYPENAME_TYPE
@tindex TYPEOF_TYPE
@findex CP_TYPE_QUALS
@findex TYPE_UNQUALIFIED
@findex TYPE_QUAL_CONST
@findex TYPE_QUAL_VOLATILE
@findex TYPE_QUAL_RESTRICT
@findex TYPE_MAIN_VARIANT
@cindex qualified type
@findex TYPE_SIZE
@findex TYPE_ALIGN
@findex TYPE_PRECISION
@findex TYPE_ARG_TYPES
@findex TYPE_METHOD_BASETYPE
@findex TYPE_PTRMEM_P
@findex TYPE_OFFSET_BASETYPE
@findex TREE_TYPE
@findex TYPE_CONTEXT
@findex TYPE_NAME
@findex TYPENAME_TYPE_FULLNAME
@findex TYPE_FIELDS
@findex TYPE_PTROBV_P
All types have corresponding tree nodes. However, you should not assume
that there is exactly one tree node corresponding to each type. There
are often several nodes each of which correspond to the same type.
For the most part, different kinds of types have different tree codes.
(For example, pointer types use a @code{POINTER_TYPE} code while arrays
use an @code{ARRAY_TYPE} code.) However, pointers to member functions
use the @code{RECORD_TYPE} code. Therefore, when writing a
@code{switch} statement that depends on the code associated with a
particular type, you should take care to handle pointers to member
functions under the @code{RECORD_TYPE} case label.
In C++, an array type is not qualified; rather the type of the array
elements is qualified. This situation is reflected in the intermediate
representation. The macros described here will always examine the
qualification of the underlying element type when applied to an array
type. (If the element type is itself an array, then the recursion
continues until a non-array type is found, and the qualification of this
type is examined.) So, for example, @code{CP_TYPE_CONST_P} will hold of
the type @code{const int ()[7]}, denoting an array of seven @code{int}s.
The following functions and macros deal with cv-qualification of types:
@ftable @code
@item CP_TYPE_QUALS
This macro returns the set of type qualifiers applied to this type.
This value is @code{TYPE_UNQUALIFIED} if no qualifiers have been
applied. The @code{TYPE_QUAL_CONST} bit is set if the type is
@code{const}-qualified. The @code{TYPE_QUAL_VOLATILE} bit is set if the
type is @code{volatile}-qualified. The @code{TYPE_QUAL_RESTRICT} bit is
set if the type is @code{restrict}-qualified.
@item CP_TYPE_CONST_P
This macro holds if the type is @code{const}-qualified.
@item CP_TYPE_VOLATILE_P
This macro holds if the type is @code{volatile}-qualified.
@item CP_TYPE_RESTRICT_P
This macro holds if the type is @code{restrict}-qualified.
@item CP_TYPE_CONST_NON_VOLATILE_P
This predicate holds for a type that is @code{const}-qualified, but
@emph{not} @code{volatile}-qualified; other cv-qualifiers are ignored as
well: only the @code{const}-ness is tested.
@item TYPE_MAIN_VARIANT
This macro returns the unqualified version of a type. It may be applied
to an unqualified type, but it is not always the identity function in
that case.
@end ftable
A few other macros and functions are usable with all types:
@ftable @code
@item TYPE_SIZE
The number of bits required to represent the type, represented as an
@code{INTEGER_CST}. For an incomplete type, @code{TYPE_SIZE} will be
@code{NULL_TREE}.
@item TYPE_ALIGN
The alignment of the type, in bits, represented as an @code{int}.
@item TYPE_NAME
This macro returns a declaration (in the form of a @code{TYPE_DECL}) for
the type. (Note this macro does @emph{not} return a
@code{IDENTIFIER_NODE}, as you might expect, given its name!) You can
look at the @code{DECL_NAME} of the @code{TYPE_DECL} to obtain the
actual name of the type. The @code{TYPE_NAME} will be @code{NULL_TREE}
for a type that is not a built-in type, the result of a typedef, or a
named class type.
@item CP_INTEGRAL_TYPE
This predicate holds if the type is an integral type. Notice that in
C++, enumerations are @emph{not} integral types.
@item ARITHMETIC_TYPE_P
This predicate holds if the type is an integral type (in the C++ sense)
or a floating point type.
@item CLASS_TYPE_P
This predicate holds for a class-type.
@item TYPE_BUILT_IN
This predicate holds for a built-in type.
@item TYPE_PTRMEM_P
This predicate holds if the type is a pointer to data member.
@item TYPE_PTR_P
This predicate holds if the type is a pointer type, and the pointee is
not a data member.
@item TYPE_PTRFN_P
This predicate holds for a pointer to function type.
@item TYPE_PTROB_P
This predicate holds for a pointer to object type. Note however that it
does not hold for the generic pointer to object type @code{void *}. You
may use @code{TYPE_PTROBV_P} to test for a pointer to object type as
well as @code{void *}.
@item same_type_p
This predicate takes two types as input, and holds if they are the same
type. For example, if one type is a @code{typedef} for the other, or
both are @code{typedef}s for the same type. This predicate also holds if
the two trees given as input are simply copies of one another; i.e.,
there is no difference between them at the source level, but, for
whatever reason, a duplicate has been made in the representation. You
should never use @code{==} (pointer equality) to compare types; always
use @code{same_type_p} instead.
@end ftable
Detailed below are the various kinds of types, and the macros that can
be used to access them. Although other kinds of types are used
elsewhere in G++, the types described here are the only ones that you
will encounter while examining the intermediate representation.
@table @code
@item VOID_TYPE
Used to represent the @code{void} type.
@item INTEGER_TYPE
Used to represent the various integral types, including @code{char},
@code{short}, @code{int}, @code{long}, and @code{long long}. This code
is not used for enumeration types, nor for the @code{bool} type. Note
that GCC's @code{CHAR_TYPE} node is @emph{not} used to represent
@code{char}. The @code{TYPE_PRECISION} is the number of bits used in
the representation, represented as an @code{unsigned int}. (Note that
in the general case this is not the same value as @code{TYPE_SIZE};
suppose that there were a 24-bit integer type, but that alignment
requirements for the ABI required 32-bit alignment. Then,
@code{TYPE_SIZE} would be an @code{INTEGER_CST} for 32, while
@code{TYPE_PRECISION} would be 24.) The integer type is unsigned if
@code{TYPE_UNSIGNED} holds; otherwise, it is signed.
The @code{TYPE_MIN_VALUE} is an @code{INTEGER_CST} for the smallest
integer that may be represented by this type. Similarly, the
@code{TYPE_MAX_VALUE} is an @code{INTEGER_CST} for the largest integer
that may be represented by this type.
@item REAL_TYPE
Used to represent the @code{float}, @code{double}, and @code{long
double} types. The number of bits in the floating-point representation
is given by @code{TYPE_PRECISION}, as in the @code{INTEGER_TYPE} case.
@item COMPLEX_TYPE
Used to represent GCC built-in @code{__complex__} data types. The
@code{TREE_TYPE} is the type of the real and imaginary parts.
@item ENUMERAL_TYPE
Used to represent an enumeration type. The @code{TYPE_PRECISION} gives
(as an @code{int}), the number of bits used to represent the type. If
there are no negative enumeration constants, @code{TYPE_UNSIGNED} will
hold. The minimum and maximum enumeration constants may be obtained
with @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE}, respectively; each
of these macros returns an @code{INTEGER_CST}.
The actual enumeration constants themselves may be obtained by looking
at the @code{TYPE_VALUES}. This macro will return a @code{TREE_LIST},
containing the constants. The @code{TREE_PURPOSE} of each node will be
an @code{IDENTIFIER_NODE} giving the name of the constant; the
@code{TREE_VALUE} will be an @code{INTEGER_CST} giving the value
assigned to that constant. These constants will appear in the order in
which they were declared. The @code{TREE_TYPE} of each of these
constants will be the type of enumeration type itself.
@item BOOLEAN_TYPE
Used to represent the @code{bool} type.
@item POINTER_TYPE
Used to represent pointer types, and pointer to data member types. The
@code{TREE_TYPE} gives the type to which this type points. If the type
is a pointer to data member type, then @code{TYPE_PTRMEM_P} will hold.
For a pointer to data member type of the form @samp{T X::*},
@code{TYPE_PTRMEM_CLASS_TYPE} will be the type @code{X}, while
@code{TYPE_PTRMEM_POINTED_TO_TYPE} will be the type @code{T}.
@item REFERENCE_TYPE
Used to represent reference types. The @code{TREE_TYPE} gives the type
to which this type refers.
@item FUNCTION_TYPE
Used to represent the type of non-member functions and of static member
functions. The @code{TREE_TYPE} gives the return type of the function.
The @code{TYPE_ARG_TYPES} are a @code{TREE_LIST} of the argument types.
The @code{TREE_VALUE} of each node in this list is the type of the
corresponding argument; the @code{TREE_PURPOSE} is an expression for the
default argument value, if any. If the last node in the list is
@code{void_list_node} (a @code{TREE_LIST} node whose @code{TREE_VALUE}
is the @code{void_type_node}), then functions of this type do not take
variable arguments. Otherwise, they do take a variable number of
arguments.
Note that in C (but not in C++) a function declared like @code{void f()}
is an unprototyped function taking a variable number of arguments; the
@code{TYPE_ARG_TYPES} of such a function will be @code{NULL}.
@item METHOD_TYPE
Used to represent the type of a non-static member function. Like a
@code{FUNCTION_TYPE}, the return type is given by the @code{TREE_TYPE}.
The type of @code{*this}, i.e., the class of which functions of this
type are a member, is given by the @code{TYPE_METHOD_BASETYPE}. The
@code{TYPE_ARG_TYPES} is the parameter list, as for a
@code{FUNCTION_TYPE}, and includes the @code{this} argument.
@item ARRAY_TYPE
Used to represent array types. The @code{TREE_TYPE} gives the type of
the elements in the array. If the array-bound is present in the type,
the @code{TYPE_DOMAIN} is an @code{INTEGER_TYPE} whose
@code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE} will be the lower and
upper bounds of the array, respectively. The @code{TYPE_MIN_VALUE} will
always be an @code{INTEGER_CST} for zero, while the
@code{TYPE_MAX_VALUE} will be one less than the number of elements in
the array, i.e., the highest value which may be used to index an element
in the array.
@item RECORD_TYPE
Used to represent @code{struct} and @code{class} types, as well as
pointers to member functions and similar constructs in other languages.
@code{TYPE_FIELDS} contains the items contained in this type, each of
which can be a @code{FIELD_DECL}, @code{VAR_DECL}, @code{CONST_DECL}, or
@code{TYPE_DECL}. You may not make any assumptions about the ordering
of the fields in the type or whether one or more of them overlap. If
@code{TYPE_PTRMEMFUNC_P} holds, then this type is a pointer-to-member
type. In that case, the @code{TYPE_PTRMEMFUNC_FN_TYPE} is a
@code{POINTER_TYPE} pointing to a @code{METHOD_TYPE}. The
@code{METHOD_TYPE} is the type of a function pointed to by the
pointer-to-member function. If @code{TYPE_PTRMEMFUNC_P} does not hold,
this type is a class type. For more information, see @pxref{Classes}.
@item UNION_TYPE
Used to represent @code{union} types. Similar to @code{RECORD_TYPE}
except that all @code{FIELD_DECL} nodes in @code{TYPE_FIELD} start at
bit position zero.
@item QUAL_UNION_TYPE
Used to represent part of a variant record in Ada. Similar to
@code{UNION_TYPE} except that each @code{FIELD_DECL} has a
@code{DECL_QUALIFIER} field, which contains a boolean expression that
indicates whether the field is present in the object. The type will only
have one field, so each field's @code{DECL_QUALIFIER} is only evaluated
if none of the expressions in the previous fields in @code{TYPE_FIELDS}
are nonzero. Normally these expressions will reference a field in the
outer object using a @code{PLACEHOLDER_EXPR}.
@item UNKNOWN_TYPE
This node is used to represent a type the knowledge of which is
insufficient for a sound processing.
@item OFFSET_TYPE
This node is used to represent a pointer-to-data member. For a data
member @code{X::m} the @code{TYPE_OFFSET_BASETYPE} is @code{X} and the
@code{TREE_TYPE} is the type of @code{m}.
@item TYPENAME_TYPE
Used to represent a construct of the form @code{typename T::A}. The
@code{TYPE_CONTEXT} is @code{T}; the @code{TYPE_NAME} is an
@code{IDENTIFIER_NODE} for @code{A}. If the type is specified via a
template-id, then @code{TYPENAME_TYPE_FULLNAME} yields a
@code{TEMPLATE_ID_EXPR}. The @code{TREE_TYPE} is non-@code{NULL} if the
node is implicitly generated in support for the implicit typename
extension; in which case the @code{TREE_TYPE} is a type node for the
base-class.
@item TYPEOF_TYPE
Used to represent the @code{__typeof__} extension. The
@code{TYPE_FIELDS} is the expression the type of which is being
represented.
@end table
There are variables whose values represent some of the basic types.
These include:
@table @code
@item void_type_node
A node for @code{void}.
@item integer_type_node
A node for @code{int}.
@item unsigned_type_node.
A node for @code{unsigned int}.
@item char_type_node.
A node for @code{char}.
@end table
@noindent
It may sometimes be useful to compare one of these variables with a type
in hand, using @code{same_type_p}.
@c ---------------------------------------------------------------------
@c Scopes
@c ---------------------------------------------------------------------
@node Scopes
@section Scopes
@cindex namespace, class, scope
The root of the entire intermediate representation is the variable
@code{global_namespace}. This is the namespace specified with @code{::}
in C++ source code. All other namespaces, types, variables, functions,
and so forth can be found starting with this namespace.
Besides namespaces, the other high-level scoping construct in C++ is the
class. (Throughout this manual the term @dfn{class} is used to mean the
types referred to in the ANSI/ISO C++ Standard as classes; these include
types defined with the @code{class}, @code{struct}, and @code{union}
keywords.)
@menu
* Namespaces:: Member functions, types, etc.
* Classes:: Members, bases, friends, etc.
@end menu
@c ---------------------------------------------------------------------
@c Namespaces
@c ---------------------------------------------------------------------
@node Namespaces
@subsection Namespaces
@cindex namespace
@tindex NAMESPACE_DECL
A namespace is represented by a @code{NAMESPACE_DECL} node.
However, except for the fact that it is distinguished as the root of the
representation, the global namespace is no different from any other
namespace. Thus, in what follows, we describe namespaces generally,
rather than the global namespace in particular.
The following macros and functions can be used on a @code{NAMESPACE_DECL}:
@ftable @code
@item DECL_NAME
This macro is used to obtain the @code{IDENTIFIER_NODE} corresponding to
the unqualified name of the name of the namespace (@pxref{Identifiers}).
The name of the global namespace is @samp{::}, even though in C++ the
global namespace is unnamed. However, you should use comparison with
@code{global_namespace}, rather than @code{DECL_NAME} to determine
whether or not a namespace is the global one. An unnamed namespace
will have a @code{DECL_NAME} equal to @code{anonymous_namespace_name}.
Within a single translation unit, all unnamed namespaces will have the
same name.
@item DECL_CONTEXT
This macro returns the enclosing namespace. The @code{DECL_CONTEXT} for
the @code{global_namespace} is @code{NULL_TREE}.
@item DECL_NAMESPACE_ALIAS
If this declaration is for a namespace alias, then
@code{DECL_NAMESPACE_ALIAS} is the namespace for which this one is an
alias.
Do not attempt to use @code{cp_namespace_decls} for a namespace which is
an alias. Instead, follow @code{DECL_NAMESPACE_ALIAS} links until you
reach an ordinary, non-alias, namespace, and call
@code{cp_namespace_decls} there.
@item DECL_NAMESPACE_STD_P
This predicate holds if the namespace is the special @code{::std}
namespace.
@item cp_namespace_decls
This function will return the declarations contained in the namespace,
including types, overloaded functions, other namespaces, and so forth.
If there are no declarations, this function will return
@code{NULL_TREE}. The declarations are connected through their
@code{TREE_CHAIN} fields.
Although most entries on this list will be declarations,
@code{TREE_LIST} nodes may also appear. In this case, the
@code{TREE_VALUE} will be an @code{OVERLOAD}. The value of the
@code{TREE_PURPOSE} is unspecified; back ends should ignore this value.
As with the other kinds of declarations returned by
@code{cp_namespace_decls}, the @code{TREE_CHAIN} will point to the next
declaration in this list.
For more information on the kinds of declarations that can occur on this
list, @xref{Declarations}. Some declarations will not appear on this
list. In particular, no @code{FIELD_DECL}, @code{LABEL_DECL}, or
@code{PARM_DECL} nodes will appear here.
This function cannot be used with namespaces that have
@code{DECL_NAMESPACE_ALIAS} set.
@end ftable
@c ---------------------------------------------------------------------
@c Classes
@c ---------------------------------------------------------------------
@node Classes
@subsection Classes
@cindex class
@tindex RECORD_TYPE
@tindex UNION_TYPE
@findex CLASSTYPE_DECLARED_CLASS
@findex TYPE_BINFO
@findex BINFO_TYPE
@findex TYPE_FIELDS
@findex TYPE_VFIELD
@findex TYPE_METHODS
A class type is represented by either a @code{RECORD_TYPE} or a
@code{UNION_TYPE}. A class declared with the @code{union} tag is
represented by a @code{UNION_TYPE}, while classes declared with either
the @code{struct} or the @code{class} tag are represented by
@code{RECORD_TYPE}s. You can use the @code{CLASSTYPE_DECLARED_CLASS}
macro to discern whether or not a particular type is a @code{class} as
opposed to a @code{struct}. This macro will be true only for classes
declared with the @code{class} tag.
Almost all non-function members are available on the @code{TYPE_FIELDS}
list. Given one member, the next can be found by following the
@code{TREE_CHAIN}. You should not depend in any way on the order in
which fields appear on this list. All nodes on this list will be
@samp{DECL} nodes. A @code{FIELD_DECL} is used to represent a non-static
data member, a @code{VAR_DECL} is used to represent a static data
member, and a @code{TYPE_DECL} is used to represent a type. Note that
the @code{CONST_DECL} for an enumeration constant will appear on this
list, if the enumeration type was declared in the class. (Of course,
the @code{TYPE_DECL} for the enumeration type will appear here as well.)
There are no entries for base classes on this list. In particular,
there is no @code{FIELD_DECL} for the ``base-class portion'' of an
object.
The @code{TYPE_VFIELD} is a compiler-generated field used to point to
virtual function tables. It may or may not appear on the
@code{TYPE_FIELDS} list. However, back ends should handle the
@code{TYPE_VFIELD} just like all the entries on the @code{TYPE_FIELDS}
list.
The function members are available on the @code{TYPE_METHODS} list.
Again, subsequent members are found by following the @code{TREE_CHAIN}
field. If a function is overloaded, each of the overloaded functions
appears; no @code{OVERLOAD} nodes appear on the @code{TYPE_METHODS}
list. Implicitly declared functions (including default constructors,
copy constructors, assignment operators, and destructors) will appear on
this list as well.
Every class has an associated @dfn{binfo}, which can be obtained with
@code{TYPE_BINFO}. Binfos are used to represent base-classes. The
binfo given by @code{TYPE_BINFO} is the degenerate case, whereby every
class is considered to be its own base-class. The base binfos for a
particular binfo are held in a vector, whose length is obtained with
@code{BINFO_N_BASE_BINFOS}. The base binfos themselves are obtained
with @code{BINFO_BASE_BINFO} and @code{BINFO_BASE_ITERATE}. To add a
new binfo, use @code{BINFO_BASE_APPEND}. The vector of base binfos can
be obtained with @code{BINFO_BASE_BINFOS}, but normally you do not need
to use that. The class type associated with a binfo is given by
@code{BINFO_TYPE}. It is not always the case that @code{BINFO_TYPE
(TYPE_BINFO (x))}, because of typedefs and qualified types. Neither is
it the case that @code{TYPE_BINFO (BINFO_TYPE (y))} is the same binfo as
@code{y}. The reason is that if @code{y} is a binfo representing a
base-class @code{B} of a derived class @code{D}, then @code{BINFO_TYPE
(y)} will be @code{B}, and @code{TYPE_BINFO (BINFO_TYPE (y))} will be
@code{B} as its own base-class, rather than as a base-class of @code{D}.
The access to a base type can be found with @code{BINFO_BASE_ACCESS}.
This will produce @code{access_public_node}, @code{access_private_node}
or @code{access_protected_node}. If bases are always public,
@code{BINFO_BASE_ACCESSES} may be @code{NULL}.
@code{BINFO_VIRTUAL_P} is used to specify whether the binfo is inherited
virtually or not. The other flags, @code{BINFO_MARKED_P} and
@code{BINFO_FLAG_1} to @code{BINFO_FLAG_6} can be used for language
specific use.
The following macros can be used on a tree node representing a class-type.
@ftable @code
@item LOCAL_CLASS_P
This predicate holds if the class is local class @emph{i.e.}@: declared
inside a function body.
@item TYPE_POLYMORPHIC_P
This predicate holds if the class has at least one virtual function
(declared or inherited).
@item TYPE_HAS_DEFAULT_CONSTRUCTOR
This predicate holds whenever its argument represents a class-type with
default constructor.
@item CLASSTYPE_HAS_MUTABLE
@itemx TYPE_HAS_MUTABLE_P
These predicates hold for a class-type having a mutable data member.
@item CLASSTYPE_NON_POD_P
This predicate holds only for class-types that are not PODs.
@item TYPE_HAS_NEW_OPERATOR
This predicate holds for a class-type that defines
@code{operator new}.
@item TYPE_HAS_ARRAY_NEW_OPERATOR
This predicate holds for a class-type for which
@code{operator new[]} is defined.
@item TYPE_OVERLOADS_CALL_EXPR
This predicate holds for class-type for which the function call
@code{operator()} is overloaded.
@item TYPE_OVERLOADS_ARRAY_REF
This predicate holds for a class-type that overloads
@code{operator[]}
@item TYPE_OVERLOADS_ARROW
This predicate holds for a class-type for which @code{operator->} is
overloaded.
@end ftable
@c ---------------------------------------------------------------------
@c Declarations
@c ---------------------------------------------------------------------
@node Declarations
@section Declarations
@cindex declaration
@cindex variable
@cindex type declaration
@tindex LABEL_DECL
@tindex CONST_DECL
@tindex TYPE_DECL
@tindex VAR_DECL
@tindex PARM_DECL
@tindex FIELD_DECL
@tindex NAMESPACE_DECL
@tindex RESULT_DECL
@tindex TEMPLATE_DECL
@tindex THUNK_DECL
@tindex USING_DECL
@findex THUNK_DELTA
@findex DECL_INITIAL
@findex DECL_SIZE
@findex DECL_ALIGN
@findex DECL_EXTERNAL
This section covers the various kinds of declarations that appear in the
internal representation, except for declarations of functions
(represented by @code{FUNCTION_DECL} nodes), which are described in
@ref{Functions}.
Some macros can be used with any kind of declaration. These include:
@ftable @code
@item DECL_NAME
This macro returns an @code{IDENTIFIER_NODE} giving the name of the
entity.
@item TREE_TYPE
This macro returns the type of the entity declared.
@item TREE_FILENAME
This macro returns the name of the file in which the entity was
declared, as a @code{char*}. For an entity declared implicitly by the
compiler (like @code{__builtin_memcpy}), this will be the string
@code{"<internal>"}.
@item TREE_LINENO
This macro returns the line number at which the entity was declared, as
an @code{int}.
@item DECL_ARTIFICIAL
This predicate holds if the declaration was implicitly generated by the
compiler. For example, this predicate will hold of an implicitly
declared member function, or of the @code{TYPE_DECL} implicitly
generated for a class type. Recall that in C++ code like:
@smallexample
struct S @{@};
@end smallexample
@noindent
is roughly equivalent to C code like:
@smallexample
struct S @{@};
typedef struct S S;
@end smallexample
The implicitly generated @code{typedef} declaration is represented by a
@code{TYPE_DECL} for which @code{DECL_ARTIFICIAL} holds.
@item DECL_NAMESPACE_SCOPE_P
This predicate holds if the entity was declared at a namespace scope.
@item DECL_CLASS_SCOPE_P
This predicate holds if the entity was declared at a class scope.
@item DECL_FUNCTION_SCOPE_P
This predicate holds if the entity was declared inside a function
body.
@end ftable
The various kinds of declarations include:
@table @code
@item LABEL_DECL
These nodes are used to represent labels in function bodies. For more
information, see @ref{Functions}. These nodes only appear in block
scopes.
@item CONST_DECL
These nodes are used to represent enumeration constants. The value of
the constant is given by @code{DECL_INITIAL} which will be an
@code{INTEGER_CST} with the same type as the @code{TREE_TYPE} of the
@code{CONST_DECL}, i.e., an @code{ENUMERAL_TYPE}.
@item RESULT_DECL
These nodes represent the value returned by a function. When a value is
assigned to a @code{RESULT_DECL}, that indicates that the value should
be returned, via bitwise copy, by the function. You can use
@code{DECL_SIZE} and @code{DECL_ALIGN} on a @code{RESULT_DECL}, just as
with a @code{VAR_DECL}.
@item TYPE_DECL
These nodes represent @code{typedef} declarations. The @code{TREE_TYPE}
is the type declared to have the name given by @code{DECL_NAME}. In
some cases, there is no associated name.
@item VAR_DECL
These nodes represent variables with namespace or block scope, as well
as static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} are
analogous to @code{TYPE_SIZE} and @code{TYPE_ALIGN}. For a declaration,
you should always use the @code{DECL_SIZE} and @code{DECL_ALIGN} rather
than the @code{TYPE_SIZE} and @code{TYPE_ALIGN} given by the
@code{TREE_TYPE}, since special attributes may have been applied to the
variable to give it a particular size and alignment. You may use the
predicates @code{DECL_THIS_STATIC} or @code{DECL_THIS_EXTERN} to test
whether the storage class specifiers @code{static} or @code{extern} were
used to declare a variable.
If this variable is initialized (but does not require a constructor),
the @code{DECL_INITIAL} will be an expression for the initializer. The
initializer should be evaluated, and a bitwise copy into the variable
performed. If the @code{DECL_INITIAL} is the @code{error_mark_node},
there is an initializer, but it is given by an explicit statement later
in the code; no bitwise copy is required.
GCC provides an extension that allows either automatic variables, or
global variables, to be placed in particular registers. This extension
is being used for a particular @code{VAR_DECL} if @code{DECL_REGISTER}
holds for the @code{VAR_DECL}, and if @code{DECL_ASSEMBLER_NAME} is not
equal to @code{DECL_NAME}. In that case, @code{DECL_ASSEMBLER_NAME} is
the name of the register into which the variable will be placed.
@item PARM_DECL
Used to represent a parameter to a function. Treat these nodes
similarly to @code{VAR_DECL} nodes. These nodes only appear in the
@code{DECL_ARGUMENTS} for a @code{FUNCTION_DECL}.
The @code{DECL_ARG_TYPE} for a @code{PARM_DECL} is the type that will
actually be used when a value is passed to this function. It may be a
wider type than the @code{TREE_TYPE} of the parameter; for example, the
ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is
@code{int}.
@item FIELD_DECL
These nodes represent non-static data members. The @code{DECL_SIZE} and
@code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes. The
@code{DECL_FIELD_BITPOS} gives the first bit used for this field, as an
@code{INTEGER_CST}. These values are indexed from zero, where zero
indicates the first bit in the object.
If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field.
@item NAMESPACE_DECL
@xref{Namespaces}.
@item TEMPLATE_DECL
These nodes are used to represent class, function, and variable (static
data member) templates. The @code{DECL_TEMPLATE_SPECIALIZATIONS} are a
@code{TREE_LIST}. The @code{TREE_VALUE} of each node in the list is a
@code{TEMPLATE_DECL}s or @code{FUNCTION_DECL}s representing
specializations (including instantiations) of this template. Back ends
can safely ignore @code{TEMPLATE_DECL}s, but should examine
@code{FUNCTION_DECL} nodes on the specializations list just as they
would ordinary @code{FUNCTION_DECL} nodes.
For a class template, the @code{DECL_TEMPLATE_INSTANTIATIONS} list
contains the instantiations. The @code{TREE_VALUE} of each node is an
instantiation of the class. The @code{DECL_TEMPLATE_SPECIALIZATIONS}
contains partial specializations of the class.
@item USING_DECL
Back ends can safely ignore these nodes.
@end table
@c ---------------------------------------------------------------------
@c Functions
@c ---------------------------------------------------------------------
@node Functions
@section Functions
@cindex function
@tindex FUNCTION_DECL
@tindex OVERLOAD
@findex OVL_CURRENT
@findex OVL_NEXT
A function is represented by a @code{FUNCTION_DECL} node. A set of
overloaded functions is sometimes represented by a @code{OVERLOAD} node.
An @code{OVERLOAD} node is not a declaration, so none of the
@samp{DECL_} macros should be used on an @code{OVERLOAD}. An
@code{OVERLOAD} node is similar to a @code{TREE_LIST}. Use
@code{OVL_CURRENT} to get the function associated with an
@code{OVERLOAD} node; use @code{OVL_NEXT} to get the next
@code{OVERLOAD} node in the list of overloaded functions. The macros
@code{OVL_CURRENT} and @code{OVL_NEXT} are actually polymorphic; you can
use them to work with @code{FUNCTION_DECL} nodes as well as with
overloads. In the case of a @code{FUNCTION_DECL}, @code{OVL_CURRENT}
will always return the function itself, and @code{OVL_NEXT} will always
be @code{NULL_TREE}.
To determine the scope of a function, you can use the
@code{DECL_CONTEXT} macro. This macro will return the class
(either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a
@code{NAMESPACE_DECL}) of which the function is a member. For a virtual
function, this macro returns the class in which the function was
actually defined, not the base class in which the virtual declaration
occurred.
If a friend function is defined in a class scope, the
@code{DECL_FRIEND_CONTEXT} macro can be used to determine the class in
which it was defined. For example, in
@smallexample
class C @{ friend void f() @{@} @};
@end smallexample
@noindent
the @code{DECL_CONTEXT} for @code{f} will be the
@code{global_namespace}, but the @code{DECL_FRIEND_CONTEXT} will be the
@code{RECORD_TYPE} for @code{C}.
In C, the @code{DECL_CONTEXT} for a function maybe another function.
This representation indicates that the GNU nested function extension
is in use. For details on the semantics of nested functions, see the
GCC Manual. The nested function can refer to local variables in its
containing function. Such references are not explicitly marked in the
tree structure; back ends must look at the @code{DECL_CONTEXT} for the
referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the
referenced @code{VAR_DECL} is not the same as the function currently
being processed, and neither @code{DECL_EXTERNAL} nor
@code{DECL_STATIC} hold, then the reference is to a local variable in
a containing function, and the back end must take appropriate action.
@menu
* Function Basics:: Function names, linkage, and so forth.
* Function Bodies:: The statements that make up a function body.
@end menu
@c ---------------------------------------------------------------------
@c Function Basics
@c ---------------------------------------------------------------------
@node Function Basics
@subsection Function Basics
@cindex constructor
@cindex destructor
@cindex copy constructor
@cindex assignment operator
@cindex linkage
@findex DECL_NAME
@findex DECL_ASSEMBLER_NAME
@findex TREE_PUBLIC
@findex DECL_LINKONCE_P
@findex DECL_FUNCTION_MEMBER_P
@findex DECL_CONSTRUCTOR_P
@findex DECL_DESTRUCTOR_P
@findex DECL_OVERLOADED_OPERATOR_P
@findex DECL_CONV_FN_P
@findex DECL_ARTIFICIAL
@findex DECL_GLOBAL_CTOR_P
@findex DECL_GLOBAL_DTOR_P
@findex GLOBAL_INIT_PRIORITY
The following macros and functions can be used on a @code{FUNCTION_DECL}:
@ftable @code
@item DECL_MAIN_P
This predicate holds for a function that is the program entry point
@code{::code}.
@item DECL_NAME
This macro returns the unqualified name of the function, as an
@code{IDENTIFIER_NODE}. For an instantiation of a function template,
the @code{DECL_NAME} is the unqualified name of the template, not
something like @code{f<int>}. The value of @code{DECL_NAME} is
undefined when used on a constructor, destructor, overloaded operator,
or type-conversion operator, or any function that is implicitly
generated by the compiler. See below for macros that can be used to
distinguish these cases.
@item DECL_ASSEMBLER_NAME
This macro returns the mangled name of the function, also an
@code{IDENTIFIER_NODE}. This name does not contain leading underscores
on systems that prefix all identifiers with underscores. The mangled
name is computed in the same way on all platforms; if special processing
is required to deal with the object file format used on a particular
platform, it is the responsibility of the back end to perform those
modifications. (Of course, the back end should not modify
@code{DECL_ASSEMBLER_NAME} itself.)
Using @code{DECL_ASSEMBLER_NAME} will cause additional memory to be
allocated (for the mangled name of the entity) so it should be used
only when emitting assembly code. It should not be used within the
optimizers to determine whether or not two declarations are the same,
even though some of the existing optimizers do use it in that way.
These uses will be removed over time.
@item DECL_EXTERNAL
This predicate holds if the function is undefined.
@item TREE_PUBLIC
This predicate holds if the function has external linkage.
@item DECL_LOCAL_FUNCTION_P
This predicate holds if the function was declared at block scope, even
though it has a global scope.
@item DECL_ANTICIPATED
This predicate holds if the function is a built-in function but its
prototype is not yet explicitly declared.
@item DECL_EXTERN_C_FUNCTION_P
This predicate holds if the function is declared as an
`@code{extern "C"}' function.
@item DECL_LINKONCE_P
This macro holds if multiple copies of this function may be emitted in
various translation units. It is the responsibility of the linker to
merge the various copies. Template instantiations are the most common
example of functions for which @code{DECL_LINKONCE_P} holds; G++
instantiates needed templates in all translation units which require them,
and then relies on the linker to remove duplicate instantiations.
FIXME: This macro is not yet implemented.
@item DECL_FUNCTION_MEMBER_P
This macro holds if the function is a member of a class, rather than a
member of a namespace.
@item DECL_STATIC_FUNCTION_P
This predicate holds if the function a static member function.
@item DECL_NONSTATIC_MEMBER_FUNCTION_P
This macro holds for a non-static member function.
@item DECL_CONST_MEMFUNC_P
This predicate holds for a @code{const}-member function.
@item DECL_VOLATILE_MEMFUNC_P
This predicate holds for a @code{volatile}-member function.
@item DECL_CONSTRUCTOR_P
This macro holds if the function is a constructor.
@item DECL_NONCONVERTING_P
This predicate holds if the constructor is a non-converting constructor.
@item DECL_COMPLETE_CONSTRUCTOR_P
This predicate holds for a function which is a constructor for an object
of a complete type.
@item DECL_BASE_CONSTRUCTOR_P
This predicate holds for a function which is a constructor for a base
class sub-object.
@item DECL_COPY_CONSTRUCTOR_P
This predicate holds for a function which is a copy-constructor.
@item DECL_DESTRUCTOR_P
This macro holds if the function is a destructor.
@item DECL_COMPLETE_DESTRUCTOR_P
This predicate holds if the function is the destructor for an object a
complete type.
@item DECL_OVERLOADED_OPERATOR_P
This macro holds if the function is an overloaded operator.
@item DECL_CONV_FN_P
This macro holds if the function is a type-conversion operator.
@item DECL_GLOBAL_CTOR_P
This predicate holds if the function is a file-scope initialization
function.
@item DECL_GLOBAL_DTOR_P
This predicate holds if the function is a file-scope finalization
function.
@item DECL_THUNK_P
This predicate holds if the function is a thunk.
These functions represent stub code that adjusts the @code{this} pointer
and then jumps to another function. When the jumped-to function
returns, control is transferred directly to the caller, without
returning to the thunk. The first parameter to the thunk is always the
@code{this} pointer; the thunk should add @code{THUNK_DELTA} to this
value. (The @code{THUNK_DELTA} is an @code{int}, not an
@code{INTEGER_CST}.)
Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero
the adjusted @code{this} pointer must be adjusted again. The complete
calculation is given by the following pseudo-code:
@smallexample
this += THUNK_DELTA
if (THUNK_VCALL_OFFSET)
this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET]
@end smallexample
Finally, the thunk should jump to the location given
by @code{DECL_INITIAL}; this will always be an expression for the
address of a function.
@item DECL_NON_THUNK_FUNCTION_P
This predicate holds if the function is @emph{not} a thunk function.
@item GLOBAL_INIT_PRIORITY
If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds,
then this gives the initialization priority for the function. The
linker will arrange that all functions for which
@code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority
before @code{main} is called. When the program exits, all functions for
which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order.
@item DECL_ARTIFICIAL
This macro holds if the function was implicitly generated by the
compiler, rather than explicitly declared. In addition to implicitly
generated class member functions, this macro holds for the special
functions created to implement static initialization and destruction, to
compute run-time type information, and so forth.
@item DECL_ARGUMENTS
This macro returns the @code{PARM_DECL} for the first argument to the
function. Subsequent @code{PARM_DECL} nodes can be obtained by
following the @code{TREE_CHAIN} links.
@item DECL_RESULT
This macro returns the @code{RESULT_DECL} for the function.
@item TREE_TYPE
This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for
the function.
@item TYPE_RAISES_EXCEPTIONS
This macro returns the list of exceptions that a (member-)function can
raise. The returned list, if non @code{NULL}, is comprised of nodes
whose @code{TREE_VALUE} represents a type.
@item TYPE_NOTHROW_P
This predicate holds when the exception-specification of its arguments
if of the form `@code{()}'.
@item DECL_ARRAY_DELETE_OPERATOR_P
This predicate holds if the function an overloaded
@code{operator delete[]}.
@end ftable
@c ---------------------------------------------------------------------
@c Function Bodies
@c ---------------------------------------------------------------------
@node Function Bodies
@subsection Function Bodies
@cindex function body
@cindex statements
@tindex BREAK_STMT
@tindex CLEANUP_STMT
@findex CLEANUP_DECL
@findex CLEANUP_EXPR
@tindex CONTINUE_STMT
@tindex DECL_STMT
@findex DECL_STMT_DECL
@tindex DO_STMT
@findex DO_BODY
@findex DO_COND
@tindex EMPTY_CLASS_EXPR
@tindex EXPR_STMT
@findex EXPR_STMT_EXPR
@tindex FOR_STMT
@findex FOR_INIT_STMT
@findex FOR_COND
@findex FOR_EXPR
@findex FOR_BODY
@tindex HANDLER
@tindex IF_STMT
@findex IF_COND
@findex THEN_CLAUSE
@findex ELSE_CLAUSE
@tindex RETURN_INIT
@tindex RETURN_STMT
@findex RETURN_EXPR
@tindex SUBOBJECT
@findex SUBOBJECT_CLEANUP
@tindex SWITCH_STMT
@findex SWITCH_COND
@findex SWITCH_BODY
@tindex TRY_BLOCK
@findex TRY_STMTS
@findex TRY_HANDLERS
@findex HANDLER_PARMS
@findex HANDLER_BODY
@findex USING_STMT
@tindex WHILE_STMT
@findex WHILE_BODY
@findex WHILE_COND
A function that has a definition in the current translation unit will
have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make
use of the particular value given by @code{DECL_INITIAL}.
The @code{DECL_SAVED_TREE} macro will give the complete body of the
function.
@subsubsection Statements
There are tree nodes corresponding to all of the source-level
statement constructs, used within the C and C++ frontends. These are
enumerated here, together with a list of the various macros that can
be used to obtain information about them. There are a few macros that
can be used with all statements:
@ftable @code
@item STMT_IS_FULL_EXPR_P
In C++, statements normally constitute ``full expressions''; temporaries
created during a statement are destroyed when the statement is complete.
However, G++ sometimes represents expressions by statements; these
statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries
created during such statements should be destroyed when the innermost
enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited.
@end ftable
Here is the list of the various statement nodes, and the macros used to
access them. This documentation describes the use of these nodes in
non-template functions (including instantiations of template functions).
In template functions, the same nodes are used, but sometimes in
slightly different ways.
Many of the statements have substatements. For example, a @code{while}
loop will have a body, which is itself a statement. If the substatement
is @code{NULL_TREE}, it is considered equivalent to a statement
consisting of a single @code{;}, i.e., an expression statement in which
the expression has been omitted. A substatement may in fact be a list
of statements, connected via their @code{TREE_CHAIN}s. So, you should
always process the statement tree by looping over substatements, like
this:
@smallexample
void process_stmt (stmt)
tree stmt;
@{
while (stmt)
@{
switch (TREE_CODE (stmt))
@{
case IF_STMT:
process_stmt (THEN_CLAUSE (stmt));
/* More processing here. */
break;
@dots{}
@}
stmt = TREE_CHAIN (stmt);
@}
@}
@end smallexample
In other words, while the @code{then} clause of an @code{if} statement
in C++ can be only one statement (although that one statement may be a
compound statement), the intermediate representation will sometimes use
several statements chained together.
@table @code
@item ASM_EXPR
Used to represent an inline assembly statement. For an inline assembly
statement like:
@smallexample
asm ("mov x, y");
@end smallexample
The @code{ASM_STRING} macro will return a @code{STRING_CST} node for
@code{"mov x, y"}. If the original statement made use of the
extended-assembly syntax, then @code{ASM_OUTPUTS},
@code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs,
and clobbers for the statement, represented as @code{STRING_CST} nodes.
The extended-assembly syntax looks like:
@smallexample
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
@end smallexample
The first string is the @code{ASM_STRING}, containing the instruction
template. The next two strings are the output and inputs, respectively;
this statement has no clobbers. As this example indicates, ``plain''
assembly statements are merely a special case of extended assembly
statements; they have no cv-qualifiers, outputs, inputs, or clobbers.
All of the strings will be @code{NUL}-terminated, and will contain no
embedded @code{NUL}-characters.
If the assembly statement is declared @code{volatile}, or if the
statement was not an extended assembly statement, and is therefore
implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold
of the @code{ASM_EXPR}.
@item BREAK_STMT
Used to represent a @code{break} statement. There are no additional
fields.
@item CASE_LABEL_EXPR
Use to represent a @code{case} label, range of @code{case} labels, or a
@code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a
@code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then
this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is
an expression giving the value of the label. Both @code{CASE_LOW} and
@code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have
the same type as the condition expression in the switch statement.
Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the
statement is a range of case labels. Such statements originate with the
extension that allows users to write things of the form:
@smallexample
case 2 ... 5:
@end smallexample
The first value will be @code{CASE_LOW}, while the second will be
@code{CASE_HIGH}.
@item CLEANUP_STMT
Used to represent an action that should take place upon exit from the
enclosing scope. Typically, these actions are calls to destructors for
local objects, but back ends cannot rely on this fact. If these nodes
are in fact representing such destructors, @code{CLEANUP_DECL} will be
the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be
@code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the
expression to execute. The cleanups executed on exit from a scope
should be run in the reverse order of the order in which the associated
@code{CLEANUP_STMT}s were encountered.
@item CONTINUE_STMT
Used to represent a @code{continue} statement. There are no additional
fields.
@item CTOR_STMT
Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if
@code{CTOR_END_P} holds of the main body of a constructor. See also
@code{SUBOBJECT} for more information on how to use these nodes.
@item DECL_STMT
Used to represent a local declaration. The @code{DECL_STMT_DECL} macro
can be used to obtain the entity declared. This declaration may be a
@code{LABEL_DECL}, indicating that the label declared is a local label.
(As an extension, GCC allows the declaration of labels with scope.) In
C, this declaration may be a @code{FUNCTION_DECL}, indicating the
use of the GCC nested function extension. For more information,
@pxref{Functions}.
@item DO_STMT
Used to represent a @code{do} loop. The body of the loop is given by
@code{DO_BODY} while the termination condition for the loop is given by
@code{DO_COND}. The condition for a @code{do}-statement is always an
expression.
@item EMPTY_CLASS_EXPR
Used to represent a temporary object of a class with no data whose
address is never taken. (All such objects are interchangeable.) The
@code{TREE_TYPE} represents the type of the object.
@item EXPR_STMT
Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to
obtain the expression.
@item FOR_STMT
Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is
the initialization statement for the loop. The @code{FOR_COND} is the
termination condition. The @code{FOR_EXPR} is the expression executed
right before the @code{FOR_COND} on each loop iteration; often, this
expression increments a counter. The body of the loop is given by
@code{FOR_BODY}. Note that @code{FOR_INIT_STMT} and @code{FOR_BODY}
return statements, while @code{FOR_COND} and @code{FOR_EXPR} return
expressions.
@item GOTO_EXPR
Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will
usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension
has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression
indicating the destination. This expression will always have pointer type.
@item HANDLER
Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE}
is the type of exception that will be caught by this handler; it is
equal (by pointer equality) to @code{NULL} if this handler is for all
types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for the catch
parameter, and @code{HANDLER_BODY} is the code for the block itself.
@item IF_STMT
Used to represent an @code{if} statement. The @code{IF_COND} is the
expression.
If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is
a statement (usually a @code{DECL_STMT}). Each time the condition is
evaluated, the statement should be executed. Then, the
@code{TREE_VALUE} should be used as the conditional expression itself.
This representation is used to handle C++ code like this:
@smallexample
if (int i = 7) @dots{}
@end smallexample
where there is a new local variable (or variables) declared within the
condition.
The @code{THEN_CLAUSE} represents the statement given by the @code{then}
condition, while the @code{ELSE_CLAUSE} represents the statement given
by the @code{else} condition.
@item LABEL_EXPR
Used to represent a label. The @code{LABEL_DECL} declared by this
statement can be obtained with the @code{LABEL_EXPR_LABEL} macro. The
@code{IDENTIFIER_NODE} giving the name of the label can be obtained from
the @code{LABEL_DECL} with @code{DECL_NAME}.
@item RETURN_INIT
If the function uses the G++ ``named return value'' extension, meaning
that the function has been defined like:
@smallexample
S f(int) return s @{@dots{}@}
@end smallexample
then there will be a @code{RETURN_INIT}. There is never a named
returned value for a constructor. The first argument to the
@code{RETURN_INIT} is the name of the object returned; the second
argument is the initializer for the object. The object is initialized
when the @code{RETURN_INIT} is encountered. The object referred to is
the actual object returned; this extension is a manual way of doing the
``return-value optimization''. Therefore, the object must actually be
constructed in the place where the object will be returned.
@item RETURN_STMT
Used to represent a @code{return} statement. The @code{RETURN_EXPR} is
the expression returned; it will be @code{NULL_TREE} if the statement
was just
@smallexample
return;
@end smallexample
@item SUBOBJECT
In a constructor, these nodes are used to mark the point at which a
subobject of @code{this} is fully constructed. If, after this point, an
exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set
is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The
cleanups must be executed in the reverse order in which they appear.
@item SWITCH_STMT
Used to represent a @code{switch} statement. The @code{SWITCH_STMT_COND}
is the expression on which the switch is occurring. See the documentation
for an @code{IF_STMT} for more information on the representation used
for the condition. The @code{SWITCH_STMT_BODY} is the body of the switch
statement. The @code{SWITCH_STMT_TYPE} is the original type of switch
expression as given in the source, before any compiler conversions.
@item TRY_BLOCK
Used to represent a @code{try} block. The body of the try block is
given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER}
node. The first handler is given by @code{TRY_HANDLERS}. Subsequent
handlers are obtained by following the @code{TREE_CHAIN} link from one
handler to the next. The body of the handler is given by
@code{HANDLER_BODY}.
If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the
@code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will
be an expression that should be executed if an exception is thrown in
the try block. It must rethrow the exception after executing that code.
And, if an exception is thrown while the expression is executing,
@code{terminate} must be called.
@item USING_STMT
Used to represent a @code{using} directive. The namespace is given by
@code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node
is needed inside template functions, to implement using directives
during instantiation.
@item WHILE_STMT
Used to represent a @code{while} loop. The @code{WHILE_COND} is the
termination condition for the loop. See the documentation for an
@code{IF_STMT} for more information on the representation used for the
condition.
The @code{WHILE_BODY} is the body of the loop.
@end table
@c ---------------------------------------------------------------------
@c Attributes
@c ---------------------------------------------------------------------
@node Attributes
@section Attributes in trees
@cindex attributes
Attributes, as specified using the @code{__attribute__} keyword, are
represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE}
is the name of the attribute, as an @code{IDENTIFIER_NODE}. The
@code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the
attribute, if any, or @code{NULL_TREE} if there are no arguments; the
arguments are stored as the @code{TREE_VALUE} of successive entries in
the list, and may be identifiers or expressions. The @code{TREE_CHAIN}
of the attribute is the next attribute in a list of attributes applying
to the same declaration or type, or @code{NULL_TREE} if there are no
further attributes in the list.
Attributes may be attached to declarations and to types; these
attributes may be accessed with the following macros. All attributes
are stored in this way, and many also cause other changes to the
declaration or type or to other internal compiler data structures.
@deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl})
This macro returns the attributes on the declaration @var{decl}.
@end deftypefn
@deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type})
This macro returns the attributes on the type @var{type}.
@end deftypefn
@c ---------------------------------------------------------------------
@c Expressions
@c ---------------------------------------------------------------------
@node Expression trees
@section Expressions
@cindex expression
@findex TREE_TYPE
@findex TREE_OPERAND
@tindex INTEGER_CST
@findex TREE_INT_CST_HIGH
@findex TREE_INT_CST_LOW
@findex tree_int_cst_lt
@findex tree_int_cst_equal
@tindex REAL_CST
@tindex COMPLEX_CST
@tindex VECTOR_CST
@tindex STRING_CST
@findex TREE_STRING_LENGTH
@findex TREE_STRING_POINTER
@tindex PTRMEM_CST
@findex PTRMEM_CST_CLASS
@findex PTRMEM_CST_MEMBER
@tindex VAR_DECL
@tindex NEGATE_EXPR
@tindex ABS_EXPR
@tindex BIT_NOT_EXPR
@tindex TRUTH_NOT_EXPR
@tindex PREDECREMENT_EXPR
@tindex PREINCREMENT_EXPR
@tindex POSTDECREMENT_EXPR
@tindex POSTINCREMENT_EXPR
@tindex ADDR_EXPR
@tindex INDIRECT_REF
@tindex FIX_TRUNC_EXPR
@tindex FLOAT_EXPR
@tindex COMPLEX_EXPR
@tindex CONJ_EXPR
@tindex REALPART_EXPR
@tindex IMAGPART_EXPR
@tindex NON_LVALUE_EXPR
@tindex NOP_EXPR
@tindex CONVERT_EXPR
@tindex THROW_EXPR
@tindex LSHIFT_EXPR
@tindex RSHIFT_EXPR
@tindex BIT_IOR_EXPR
@tindex BIT_XOR_EXPR
@tindex BIT_AND_EXPR
@tindex TRUTH_ANDIF_EXPR
@tindex TRUTH_ORIF_EXPR
@tindex TRUTH_AND_EXPR
@tindex TRUTH_OR_EXPR
@tindex TRUTH_XOR_EXPR
@tindex PLUS_EXPR
@tindex MINUS_EXPR
@tindex MULT_EXPR
@tindex RDIV_EXPR
@tindex TRUNC_DIV_EXPR
@tindex FLOOR_DIV_EXPR
@tindex CEIL_DIV_EXPR
@tindex ROUND_DIV_EXPR
@tindex TRUNC_MOD_EXPR
@tindex FLOOR_MOD_EXPR
@tindex CEIL_MOD_EXPR
@tindex ROUND_MOD_EXPR
@tindex EXACT_DIV_EXPR
@tindex ARRAY_REF
@tindex ARRAY_RANGE_REF
@tindex LT_EXPR
@tindex LE_EXPR
@tindex GT_EXPR
@tindex GE_EXPR
@tindex EQ_EXPR
@tindex NE_EXPR
@tindex ORDERED_EXPR
@tindex UNORDERED_EXPR
@tindex UNLT_EXPR
@tindex UNLE_EXPR
@tindex UNGT_EXPR
@tindex UNGE_EXPR
@tindex UNEQ_EXPR
@tindex LTGT_EXPR
@tindex MODIFY_EXPR
@tindex INIT_EXPR
@tindex COMPONENT_REF
@tindex COMPOUND_EXPR
@tindex COND_EXPR
@tindex CALL_EXPR
@tindex STMT_EXPR
@tindex BIND_EXPR
@tindex LOOP_EXPR
@tindex EXIT_EXPR
@tindex CLEANUP_POINT_EXPR
@tindex CONSTRUCTOR
@tindex COMPOUND_LITERAL_EXPR
@tindex SAVE_EXPR
@tindex TARGET_EXPR
@tindex AGGR_INIT_EXPR
@tindex VA_ARG_EXPR
The internal representation for expressions is for the most part quite
straightforward. However, there are a few facts that one must bear in
mind. In particular, the expression ``tree'' is actually a directed
acyclic graph. (For example there may be many references to the integer
constant zero throughout the source program; many of these will be
represented by the same expression node.) You should not rely on
certain kinds of node being shared, nor should rely on certain kinds of
nodes being unshared.
The following macros can be used with all expression nodes:
@ftable @code
@item TREE_TYPE
Returns the type of the expression. This value may not be precisely the
same type that would be given the expression in the original program.
@end ftable
In what follows, some nodes that one might expect to always have type
@code{bool} are documented to have either integral or boolean type. At
some point in the future, the C front end may also make use of this same
intermediate representation, and at this point these nodes will
certainly have integral type. The previous sentence is not meant to
imply that the C++ front end does not or will not give these nodes
integral type.
Below, we list the various kinds of expression nodes. Except where
noted otherwise, the operands to an expression are accessed using the
@code{TREE_OPERAND} macro. For example, to access the first operand to
a binary plus expression @code{expr}, use:
@smallexample
TREE_OPERAND (expr, 0)
@end smallexample
@noindent
As this example indicates, the operands are zero-indexed.
The table below begins with constants, moves on to unary expressions,
then proceeds to binary expressions, and concludes with various other
kinds of expressions:
@table @code
@item INTEGER_CST
These nodes represent integer constants. Note that the type of these
constants is obtained with @code{TREE_TYPE}; they are not always of type
@code{int}. In particular, @code{char} constants are represented with
@code{INTEGER_CST} nodes. The value of the integer constant @code{e} is
given by
@smallexample
((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT)
+ TREE_INST_CST_LOW (e))
@end smallexample
@noindent
HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both
@code{TREE_INT_CST_HIGH} and @code{TREE_INT_CST_LOW} return a
@code{HOST_WIDE_INT}. The value of an @code{INTEGER_CST} is interpreted
as a signed or unsigned quantity depending on the type of the constant.
In general, the expression given above will overflow, so it should not
be used to calculate the value of the constant.
The variable @code{integer_zero_node} is an integer constant with value
zero. Similarly, @code{integer_one_node} is an integer constant with
value one. The @code{size_zero_node} and @code{size_one_node} variables
are analogous, but have type @code{size_t} rather than @code{int}.
The function @code{tree_int_cst_lt} is a predicate which holds if its
first argument is less than its second. Both constants are assumed to
have the same signedness (i.e., either both should be signed or both
should be unsigned.) The full width of the constant is used when doing
the comparison; the usual rules about promotions and conversions are
ignored. Similarly, @code{tree_int_cst_equal} holds if the two
constants are equal. The @code{tree_int_cst_sgn} function returns the
sign of a constant. The value is @code{1}, @code{0}, or @code{-1}
according on whether the constant is greater than, equal to, or less
than zero. Again, the signedness of the constant's type is taken into
account; an unsigned constant is never less than zero, no matter what
its bit-pattern.
@item REAL_CST
FIXME: Talk about how to obtain representations of this constant, do
comparisons, and so forth.
@item COMPLEX_CST
These nodes are used to represent complex number constants, that is a
@code{__complex__} whose parts are constant nodes. The
@code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the
imaginary parts respectively.
@item VECTOR_CST
These nodes are used to represent vector constants, whose parts are
constant nodes. Each individual constant node is either an integer or a
double constant node. The first operand is a @code{TREE_LIST} of the
constant nodes and is accessed through @code{TREE_VECTOR_CST_ELTS}.
@item STRING_CST
These nodes represent string-constants. The @code{TREE_STRING_LENGTH}
returns the length of the string, as an @code{int}. The
@code{TREE_STRING_POINTER} is a @code{char*} containing the string
itself. The string may not be @code{NUL}-terminated, and it may contain
embedded @code{NUL} characters. Therefore, the
@code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is
present.
For wide string constants, the @code{TREE_STRING_LENGTH} is the number
of bytes in the string, and the @code{TREE_STRING_POINTER}
points to an array of the bytes of the string, as represented on the
target system (that is, as integers in the target endianness). Wide and
non-wide string constants are distinguished only by the @code{TREE_TYPE}
of the @code{STRING_CST}.
FIXME: The formats of string constants are not well-defined when the
target system bytes are not the same width as host system bytes.
@item PTRMEM_CST
These nodes are used to represent pointer-to-member constants. The
@code{PTRMEM_CST_CLASS} is the class type (either a @code{RECORD_TYPE}
or @code{UNION_TYPE} within which the pointer points), and the
@code{PTRMEM_CST_MEMBER} is the declaration for the pointed to object.
Note that the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is in
general different from the @code{PTRMEM_CST_CLASS}. For example,
given:
@smallexample
struct B @{ int i; @};
struct D : public B @{@};
int D::*dp = &D::i;
@end smallexample
@noindent
The @code{PTRMEM_CST_CLASS} for @code{&D::i} is @code{D}, even though
the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is @code{B},
since @code{B::i} is a member of @code{B}, not @code{D}.
@item VAR_DECL
These nodes represent variables, including static data members. For
more information, @pxref{Declarations}.
@item NEGATE_EXPR
These nodes represent unary negation of the single operand, for both
integer and floating-point types. The type of negation can be
determined by looking at the type of the expression.
The behavior of this operation on signed arithmetic overflow is
controlled by the @code{flag_wrapv} and @code{flag_trapv} variables.
@item ABS_EXPR
These nodes represent the absolute value of the single operand, for
both integer and floating-point types. This is typically used to
implement the @code{abs}, @code{labs} and @code{llabs} builtins for
integer types, and the @code{fabs}, @code{fabsf} and @code{fabsl}
builtins for floating point types. The type of abs operation can
be determined by looking at the type of the expression.
This node is not used for complex types. To represent the modulus
or complex abs of a complex value, use the @code{BUILT_IN_CABS},
@code{BUILT_IN_CABSF} or @code{BUILT_IN_CABSL} builtins, as used
to implement the C99 @code{cabs}, @code{cabsf} and @code{cabsl}
built-in functions.
@item BIT_NOT_EXPR
These nodes represent bitwise complement, and will always have integral
type. The only operand is the value to be complemented.
@item TRUTH_NOT_EXPR
These nodes represent logical negation, and will always have integral
(or boolean) type. The operand is the value being negated. The type
of the operand and that of the result are always of @code{BOOLEAN_TYPE}
or @code{INTEGER_TYPE}.
@item PREDECREMENT_EXPR
@itemx PREINCREMENT_EXPR
@itemx POSTDECREMENT_EXPR
@itemx POSTINCREMENT_EXPR
These nodes represent increment and decrement expressions. The value of
the single operand is computed, and the operand incremented or
decremented. In the case of @code{PREDECREMENT_EXPR} and
@code{PREINCREMENT_EXPR}, the value of the expression is the value
resulting after the increment or decrement; in the case of
@code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value
before the increment or decrement occurs. The type of the operand, like
that of the result, will be either integral, boolean, or floating-point.
@item ADDR_EXPR
These nodes are used to represent the address of an object. (These
expressions will always have pointer or reference type.) The operand may
be another expression, or it may be a declaration.
As an extension, GCC allows users to take the address of a label. In
this case, the operand of the @code{ADDR_EXPR} will be a
@code{LABEL_DECL}. The type of such an expression is @code{void*}.
If the object addressed is not an lvalue, a temporary is created, and
the address of the temporary is used.
@item INDIRECT_REF
These nodes are used to represent the object pointed to by a pointer.
The operand is the pointer being dereferenced; it will always have
pointer or reference type.
@item FIX_TRUNC_EXPR
These nodes represent conversion of a floating-point value to an
integer. The single operand will have a floating-point type, while the
the complete expression will have an integral (or boolean) type. The
operand is rounded towards zero.
@item FLOAT_EXPR
These nodes represent conversion of an integral (or boolean) value to a
floating-point value. The single operand will have integral type, while
the complete expression will have a floating-point type.
FIXME: How is the operand supposed to be rounded? Is this dependent on
@option{-mieee}?
@item COMPLEX_EXPR
These nodes are used to represent complex numbers constructed from two
expressions of the same (integer or real) type. The first operand is the
real part and the second operand is the imaginary part.
@item CONJ_EXPR
These nodes represent the conjugate of their operand.
@item REALPART_EXPR
@itemx IMAGPART_EXPR
These nodes represent respectively the real and the imaginary parts
of complex numbers (their sole argument).
@item NON_LVALUE_EXPR
These nodes indicate that their one and only operand is not an lvalue.
A back end can treat these identically to the single operand.
@item NOP_EXPR
These nodes are used to represent conversions that do not require any
code-generation. For example, conversion of a @code{char*} to an
@code{int*} does not require any code be generated; such a conversion is
represented by a @code{NOP_EXPR}. The single operand is the expression
to be converted. The conversion from a pointer to a reference is also
represented with a @code{NOP_EXPR}.
@item CONVERT_EXPR
These nodes are similar to @code{NOP_EXPR}s, but are used in those
situations where code may need to be generated. For example, if an
@code{int*} is converted to an @code{int} code may need to be generated
on some platforms. These nodes are never used for C++-specific
conversions, like conversions between pointers to different classes in
an inheritance hierarchy. Any adjustments that need to be made in such
cases are always indicated explicitly. Similarly, a user-defined
conversion is never represented by a @code{CONVERT_EXPR}; instead, the
function calls are made explicit.
@item THROW_EXPR
These nodes represent @code{throw} expressions. The single operand is
an expression for the code that should be executed to throw the
exception. However, there is one implicit action not represented in
that expression; namely the call to @code{__throw}. This function takes
no arguments. If @code{setjmp}/@code{longjmp} exceptions are used, the
function @code{__sjthrow} is called instead. The normal GCC back end
uses the function @code{emit_throw} to generate this code; you can
examine this function to see what needs to be done.
@item LSHIFT_EXPR
@itemx RSHIFT_EXPR
These nodes represent left and right shifts, respectively. The first
operand is the value to shift; it will always be of integral type. The
second operand is an expression for the number of bits by which to
shift. Right shift should be treated as arithmetic, i.e., the
high-order bits should be zero-filled when the expression has unsigned
type and filled with the sign bit when the expression has signed type.
Note that the result is undefined if the second operand is larger
than or equal to the first operand's type size.
@item BIT_IOR_EXPR
@itemx BIT_XOR_EXPR
@itemx BIT_AND_EXPR
These nodes represent bitwise inclusive or, bitwise exclusive or, and
bitwise and, respectively. Both operands will always have integral
type.
@item TRUTH_ANDIF_EXPR
@itemx TRUTH_ORIF_EXPR
These nodes represent logical and and logical or, respectively. These
operators are not strict; i.e., the second operand is evaluated only if
the value of the expression is not determined by evaluation of the first
operand. The type of the operands and that of the result are always of
@code{BOOLEAN_TYPE} or @code{INTEGER_TYPE}.
@item TRUTH_AND_EXPR
@itemx TRUTH_OR_EXPR
@itemx TRUTH_XOR_EXPR
These nodes represent logical and, logical or, and logical exclusive or.
They are strict; both arguments are always evaluated. There are no
corresponding operators in C or C++, but the front end will sometimes
generate these expressions anyhow, if it can tell that strictness does
not matter. The type of the operands and that of the result are
always of @code{BOOLEAN_TYPE} or @code{INTEGER_TYPE}.
@itemx PLUS_EXPR
@itemx MINUS_EXPR
@itemx MULT_EXPR
These nodes represent various binary arithmetic operations.
Respectively, these operations are addition, subtraction (of the second
operand from the first) and multiplication. Their operands may have
either integral or floating type, but there will never be case in which
one operand is of floating type and the other is of integral type.
The behavior of these operations on signed arithmetic overflow is
controlled by the @code{flag_wrapv} and @code{flag_trapv} variables.
@item RDIV_EXPR
This node represents a floating point division operation.
@item TRUNC_DIV_EXPR
@itemx FLOOR_DIV_EXPR
@itemx CEIL_DIV_EXPR
@itemx ROUND_DIV_EXPR
These nodes represent integer division operations that return an integer
result. @code{TRUNC_DIV_EXPR} rounds towards zero, @code{FLOOR_DIV_EXPR}
rounds towards negative infinity, @code{CEIL_DIV_EXPR} rounds towards
positive infinity and @code{ROUND_DIV_EXPR} rounds to the closest integer.
Integer division in C and C++ is truncating, i.e.@: @code{TRUNC_DIV_EXPR}.
The behavior of these operations on signed arithmetic overflow, when
dividing the minimum signed integer by minus one, is controlled by the
@code{flag_wrapv} and @code{flag_trapv} variables.
@item TRUNC_MOD_EXPR
@itemx FLOOR_MOD_EXPR
@itemx CEIL_MOD_EXPR
@itemx ROUND_MOD_EXPR
These nodes represent the integer remainder or modulus operation.
The integer modulus of two operands @code{a} and @code{b} is
defined as @code{a - (a/b)*b} where the division calculated using
the corresponding division operator. Hence for @code{TRUNC_MOD_EXPR}
this definition assumes division using truncation towards zero, i.e.@:
@code{TRUNC_DIV_EXPR}. Integer remainder in C and C++ uses truncating
division, i.e.@: @code{TRUNC_MOD_EXPR}.
@item EXACT_DIV_EXPR
The @code{EXACT_DIV_EXPR} code is used to represent integer divisions where
the numerator is known to be an exact multiple of the denominator. This
allows the backend to choose between the faster of @code{TRUNC_DIV_EXPR},
@code{CEIL_DIV_EXPR} and @code{FLOOR_DIV_EXPR} for the current target.
@item ARRAY_REF
These nodes represent array accesses. The first operand is the array;
the second is the index. To calculate the address of the memory
accessed, you must scale the index by the size of the type of the array
elements. The type of these expressions must be the type of a component of
the array. The third and fourth operands are used after gimplification
to represent the lower bound and component size but should not be used
directly; call @code{array_ref_low_bound} and @code{array_ref_element_size}
instead.
@item ARRAY_RANGE_REF
These nodes represent access to a range (or ``slice'') of an array. The
operands are the same as that for @code{ARRAY_REF} and have the same
meanings. The type of these expressions must be an array whose component
type is the same as that of the first operand. The range of that array
type determines the amount of data these expressions access.
@item LT_EXPR
@itemx LE_EXPR
@itemx GT_EXPR
@itemx GE_EXPR
@itemx EQ_EXPR
@itemx NE_EXPR
These nodes represent the less than, less than or equal to, greater
than, greater than or equal to, equal, and not equal comparison
operators. The first and second operand with either be both of integral
type or both of floating type. The result type of these expressions
will always be of integral or boolean type. These operations return
the result type's zero value for false, and the result type's one value
for true.
For floating point comparisons, if we honor IEEE NaNs and either operand
is NaN, then @code{NE_EXPR} always returns true and the remaining operators
always return false. On some targets, comparisons against an IEEE NaN,
other than equality and inequality, may generate a floating point exception.
@item ORDERED_EXPR
@itemx UNORDERED_EXPR
These nodes represent non-trapping ordered and unordered comparison
operators. These operations take two floating point operands and
determine whether they are ordered or unordered relative to each other.
If either operand is an IEEE NaN, their comparison is defined to be
unordered, otherwise the comparison is defined to be ordered. The
result type of these expressions will always be of integral or boolean
type. These operations return the result type's zero value for false,
and the result type's one value for true.
@item UNLT_EXPR
@itemx UNLE_EXPR
@itemx UNGT_EXPR
@itemx UNGE_EXPR
@itemx UNEQ_EXPR
@itemx LTGT_EXPR
These nodes represent the unordered comparison operators.
These operations take two floating point operands and determine whether
the operands are unordered or are less than, less than or equal to,
greater than, greater than or equal to, or equal respectively. For
example, @code{UNLT_EXPR} returns true if either operand is an IEEE
NaN or the first operand is less than the second. With the possible
exception of @code{LTGT_EXPR}, all of these operations are guaranteed
not to generate a floating point exception. The result
type of these expressions will always be of integral or boolean type.
These operations return the result type's zero value for false,
and the result type's one value for true.
@item MODIFY_EXPR
These nodes represent assignment. The left-hand side is the first
operand; the right-hand side is the second operand. The left-hand side
will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or
other lvalue.
These nodes are used to represent not only assignment with @samp{=} but
also compound assignments (like @samp{+=}), by reduction to @samp{=}
assignment. In other words, the representation for @samp{i += 3} looks
just like that for @samp{i = i + 3}.
@item INIT_EXPR
These nodes are just like @code{MODIFY_EXPR}, but are used only when a
variable is initialized, rather than assigned to subsequently.
@item COMPONENT_REF
These nodes represent non-static data member accesses. The first
operand is the object (rather than a pointer to it); the second operand
is the @code{FIELD_DECL} for the data member. The third operand represents
the byte offset of the field, but should not be used directly; call
@code{component_ref_field_offset} instead.
@item COMPOUND_EXPR
These nodes represent comma-expressions. The first operand is an
expression whose value is computed and thrown away prior to the
evaluation of the second operand. The value of the entire expression is
the value of the second operand.
@item COND_EXPR
These nodes represent @code{?:} expressions. The first operand
is of boolean or integral type. If it evaluates to a nonzero value,
the second operand should be evaluated, and returned as the value of the
expression. Otherwise, the third operand is evaluated, and returned as
the value of the expression.
The second operand must have the same type as the entire expression,
unless it unconditionally throws an exception or calls a noreturn
function, in which case it should have void type. The same constraints
apply to the third operand. This allows array bounds checks to be
represented conveniently as @code{(i >= 0 && i < 10) ? i : abort()}.
As a GNU extension, the C language front-ends allow the second
operand of the @code{?:} operator may be omitted in the source.
For example, @code{x ? : 3} is equivalent to @code{x ? x : 3},
assuming that @code{x} is an expression without side-effects.
In the tree representation, however, the second operand is always
present, possibly protected by @code{SAVE_EXPR} if the first
argument does cause side-effects.
@item CALL_EXPR
These nodes are used to represent calls to functions, including
non-static member functions. The first operand is a pointer to the
function to call; it is always an expression whose type is a
@code{POINTER_TYPE}. The second argument is a @code{TREE_LIST}. The
arguments to the call appear left-to-right in the list. The
@code{TREE_VALUE} of each list node contains the expression
corresponding to that argument. (The value of @code{TREE_PURPOSE} for
these nodes is unspecified, and should be ignored.) For non-static
member functions, there will be an operand corresponding to the
@code{this} pointer. There will always be expressions corresponding to
all of the arguments, even if the function is declared with default
arguments and some arguments are not explicitly provided at the call
sites.
@item STMT_EXPR
These nodes are used to represent GCC's statement-expression extension.
The statement-expression extension allows code like this:
@smallexample
int f() @{ return (@{ int j; j = 3; j + 7; @}); @}
@end smallexample
In other words, an sequence of statements may occur where a single
expression would normally appear. The @code{STMT_EXPR} node represents
such an expression. The @code{STMT_EXPR_STMT} gives the statement
contained in the expression. The value of the expression is the value
of the last sub-statement in the body. More precisely, the value is the
value computed by the last statement nested inside @code{BIND_EXPR},
@code{TRY_FINALLY_EXPR}, or @code{TRY_CATCH_EXPR}. For example, in:
@smallexample
(@{ 3; @})
@end smallexample
the value is @code{3} while in:
@smallexample
(@{ if (x) @{ 3; @} @})
@end smallexample
there is no value. If the @code{STMT_EXPR} does not yield a value,
it's type will be @code{void}.
@item BIND_EXPR
These nodes represent local blocks. The first operand is a list of
variables, connected via their @code{TREE_CHAIN} field. These will
never require cleanups. The scope of these variables is just the body
of the @code{BIND_EXPR}. The body of the @code{BIND_EXPR} is the
second operand.
@item LOOP_EXPR
These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY}
represents the body of the loop. It should be executed forever, unless
an @code{EXIT_EXPR} is encountered.
@item EXIT_EXPR
These nodes represent conditional exits from the nearest enclosing
@code{LOOP_EXPR}. The single operand is the condition; if it is
nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only
appear within a @code{LOOP_EXPR}.
@item CLEANUP_POINT_EXPR
These nodes represent full-expressions. The single operand is an
expression to evaluate. Any destructor calls engendered by the creation
of temporaries during the evaluation of that expression should be
performed immediately after the expression is evaluated.
@item CONSTRUCTOR
These nodes represent the brace-enclosed initializers for a structure or
array. The first operand is reserved for use by the back end. The
second operand is a @code{TREE_LIST}. If the @code{TREE_TYPE} of the
@code{CONSTRUCTOR} is a @code{RECORD_TYPE} or @code{UNION_TYPE}, then
the @code{TREE_PURPOSE} of each node in the @code{TREE_LIST} will be a
@code{FIELD_DECL} and the @code{TREE_VALUE} of each node will be the
expression used to initialize that field.
If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an
@code{ARRAY_TYPE}, then the @code{TREE_PURPOSE} of each element in the
@code{TREE_LIST} will be an @code{INTEGER_CST} or a @code{RANGE_EXPR} of
two @code{INTEGER_CST}s. A single @code{INTEGER_CST} indicates which
element of the array (indexed from zero) is being assigned to. A
@code{RANGE_EXPR} indicates an inclusive range of elements to
initialize. In both cases the @code{TREE_VALUE} is the corresponding
initializer. It is re-evaluated for each element of a
@code{RANGE_EXPR}. If the @code{TREE_PURPOSE} is @code{NULL_TREE}, then
the initializer is for the next available array element.
In the front end, you should not depend on the fields appearing in any
particular order. However, in the middle end, fields must appear in
declaration order. You should not assume that all fields will be
represented. Unrepresented fields will be set to zero.
@item COMPOUND_LITERAL_EXPR
@findex COMPOUND_LITERAL_EXPR_DECL_STMT
@findex COMPOUND_LITERAL_EXPR_DECL
These nodes represent ISO C99 compound literals. The
@code{COMPOUND_LITERAL_EXPR_DECL_STMT} is a @code{DECL_STMT}
containing an anonymous @code{VAR_DECL} for
the unnamed object represented by the compound literal; the
@code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR}
representing the brace-enclosed list of initializers in the compound
literal. That anonymous @code{VAR_DECL} can also be accessed directly
by the @code{COMPOUND_LITERAL_EXPR_DECL} macro.
@item SAVE_EXPR
A @code{SAVE_EXPR} represents an expression (possibly involving
side-effects) that is used more than once. The side-effects should
occur only the first time the expression is evaluated. Subsequent uses
should just reuse the computed value. The first operand to the
@code{SAVE_EXPR} is the expression to evaluate. The side-effects should
be executed where the @code{SAVE_EXPR} is first encountered in a
depth-first preorder traversal of the expression tree.
@item TARGET_EXPR
A @code{TARGET_EXPR} represents a temporary object. The first operand
is a @code{VAR_DECL} for the temporary variable. The second operand is
the initializer for the temporary. The initializer is evaluated and,
if non-void, copied (bitwise) into the temporary. If the initializer
is void, that means that it will perform the initialization itself.
Often, a @code{TARGET_EXPR} occurs on the right-hand side of an
assignment, or as the second operand to a comma-expression which is
itself the right-hand side of an assignment, etc. In this case, we say
that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is
``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable
should be treated as an alias for the left-hand side of the assignment,
rather than as a new temporary variable.
The third operand to the @code{TARGET_EXPR}, if present, is a
cleanup-expression (i.e., destructor call) for the temporary. If this
expression is orphaned, then this expression must be executed when the
statement containing this expression is complete. These cleanups must
always be executed in the order opposite to that in which they were
encountered. Note that if a temporary is created on one branch of a
conditional operator (i.e., in the second or third operand to a
@code{COND_EXPR}), the cleanup must be run only if that branch is
actually executed.
See @code{STMT_IS_FULL_EXPR_P} for more information about running these
cleanups.
@item AGGR_INIT_EXPR
An @code{AGGR_INIT_EXPR} represents the initialization as the return
value of a function call, or as the result of a constructor. An
@code{AGGR_INIT_EXPR} will only appear as a full-expression, or as the
second operand of a @code{TARGET_EXPR}. The first operand to the
@code{AGGR_INIT_EXPR} is the address of a function to call, just as in
a @code{CALL_EXPR}. The second operand are the arguments to pass that
function, as a @code{TREE_LIST}, again in a manner similar to that of
a @code{CALL_EXPR}.
If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then
the initialization is via a constructor call. The address of the third
operand of the @code{AGGR_INIT_EXPR}, which is always a @code{VAR_DECL},
is taken, and this value replaces the first argument in the argument
list.
In either case, the expression is void.
@item VA_ARG_EXPR
This node is used to implement support for the C/C++ variable argument-list
mechanism. It represents expressions like @code{va_arg (ap, type)}.
Its @code{TREE_TYPE} yields the tree representation for @code{type} and
its sole argument yields the representation for @code{ap}.
@end table
|