summaryrefslogtreecommitdiff
path: root/compiler/GHC/Core.hs
blob: 613aef8f95734dd778519a0f3a89bd27274e7ad0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-}

{-# LANGUAGE CPP, DeriveDataTypeable, FlexibleContexts #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -Wno-incomplete-uni-patterns   #-}
{-# OPTIONS_GHC -Wno-incomplete-record-updates #-}

-- | GHC.Core holds all the main data types for use by for the Glasgow Haskell Compiler midsection
module GHC.Core (
        -- * Main data types
        Expr(..), Alt, Bind(..), AltCon(..), Arg,
        Tickish(..), TickishScoping(..), TickishPlacement(..),
        CoreProgram, CoreExpr, CoreAlt, CoreBind, CoreArg, CoreBndr,
        TaggedExpr, TaggedAlt, TaggedBind, TaggedArg, TaggedBndr(..), deTagExpr,

        -- * In/Out type synonyms
        InId, InBind, InExpr, InAlt, InArg, InType, InKind,
               InBndr, InVar, InCoercion, InTyVar, InCoVar,
        OutId, OutBind, OutExpr, OutAlt, OutArg, OutType, OutKind,
               OutBndr, OutVar, OutCoercion, OutTyVar, OutCoVar, MOutCoercion,

        -- ** 'Expr' construction
        mkLet, mkLets, mkLetNonRec, mkLetRec, mkLams,
        mkApps, mkTyApps, mkCoApps, mkVarApps, mkTyArg,

        mkIntLit, mkIntLitInt,
        mkWordLit, mkWordLitWord,
        mkWord64LitWord64, mkInt64LitInt64,
        mkCharLit, mkStringLit,
        mkFloatLit, mkFloatLitFloat,
        mkDoubleLit, mkDoubleLitDouble,

        mkConApp, mkConApp2, mkTyBind, mkCoBind,
        varToCoreExpr, varsToCoreExprs,

        isId, cmpAltCon, cmpAlt, ltAlt,

        -- ** Simple 'Expr' access functions and predicates
        bindersOf, bindersOfBinds, rhssOfBind, rhssOfAlts,
        collectBinders, collectTyBinders, collectTyAndValBinders,
        collectNBinders,
        collectArgs, stripNArgs, collectArgsTicks, flattenBinds,

        exprToType, exprToCoercion_maybe,
        applyTypeToArg,

        isValArg, isTypeArg, isCoArg, isTyCoArg, valArgCount, valBndrCount,
        isRuntimeArg, isRuntimeVar,

        -- * Tick-related functions
        tickishCounts, tickishScoped, tickishScopesLike, tickishFloatable,
        tickishCanSplit, mkNoCount, mkNoScope,
        tickishIsCode, tickishPlace,
        tickishContains,

        -- * Unfolding data types
        Unfolding(..),  UnfoldingGuidance(..), UnfoldingSource(..),

        -- ** Constructing 'Unfolding's
        noUnfolding, bootUnfolding, evaldUnfolding, mkOtherCon,
        unSaturatedOk, needSaturated, boringCxtOk, boringCxtNotOk,

        -- ** Predicates and deconstruction on 'Unfolding'
        unfoldingTemplate, expandUnfolding_maybe,
        maybeUnfoldingTemplate, otherCons,
        isValueUnfolding, isEvaldUnfolding, isCheapUnfolding,
        isExpandableUnfolding, isConLikeUnfolding, isCompulsoryUnfolding,
        isStableUnfolding, hasCoreUnfolding, hasSomeUnfolding,
        isBootUnfolding,
        canUnfold, neverUnfoldGuidance, isStableSource,

        -- * Annotated expression data types
        AnnExpr, AnnExpr'(..), AnnBind(..), AnnAlt,

        -- ** Operations on annotated expressions
        collectAnnArgs, collectAnnArgsTicks,

        -- ** Operations on annotations
        deAnnotate, deAnnotate', deAnnAlt, deAnnBind,
        collectAnnBndrs, collectNAnnBndrs,

        -- * Orphanhood
        IsOrphan(..), isOrphan, notOrphan, chooseOrphanAnchor,

        -- * Core rule data types
        CoreRule(..), RuleBase,
        RuleName, RuleFun, IdUnfoldingFun, InScopeEnv,
        RuleEnv(..), RuleOpts(..), mkRuleEnv, emptyRuleEnv,

        -- ** Operations on 'CoreRule's
        ruleArity, ruleName, ruleIdName, ruleActivation,
        setRuleIdName, ruleModule,
        isBuiltinRule, isLocalRule, isAutoRule,
    ) where

#include "HsVersions.h"

import GHC.Prelude
import GHC.Platform

import GHC.Types.CostCentre
import GHC.Types.Var.Env( InScopeSet )
import GHC.Types.Var
import GHC.Core.Type
import GHC.Core.Coercion
import GHC.Types.Name
import GHC.Types.Name.Set
import GHC.Types.Name.Env( NameEnv, emptyNameEnv )
import GHC.Types.Literal
import GHC.Core.DataCon
import GHC.Unit.Module
import GHC.Types.Basic
import GHC.Utils.Outputable
import GHC.Utils.Misc
import GHC.Types.Unique.Set
import GHC.Types.SrcLoc ( RealSrcSpan, containsSpan )
import GHC.Utils.Binary

import Data.Data hiding (TyCon)
import Data.Int
import Data.Word

infixl 4 `mkApps`, `mkTyApps`, `mkVarApps`, `App`, `mkCoApps`
-- Left associative, so that we can say (f `mkTyApps` xs `mkVarApps` ys)

{-
************************************************************************
*                                                                      *
\subsection{The main data types}
*                                                                      *
************************************************************************

These data types are the heart of the compiler
-}

-- | This is the data type that represents GHCs core intermediate language. Currently
-- GHC uses System FC <https://www.microsoft.com/en-us/research/publication/system-f-with-type-equality-coercions/> for this purpose,
-- which is closely related to the simpler and better known System F <http://en.wikipedia.org/wiki/System_F>.
--
-- We get from Haskell source to this Core language in a number of stages:
--
-- 1. The source code is parsed into an abstract syntax tree, which is represented
--    by the data type 'GHC.Hs.Expr.HsExpr' with the names being 'GHC.Types.Name.Reader.RdrNames'
--
-- 2. This syntax tree is /renamed/, which attaches a 'GHC.Types.Unique.Unique' to every 'GHC.Types.Name.Reader.RdrName'
--    (yielding a 'GHC.Types.Name.Name') to disambiguate identifiers which are lexically identical.
--    For example, this program:
--
-- @
--      f x = let f x = x + 1
--            in f (x - 2)
-- @
--
--    Would be renamed by having 'Unique's attached so it looked something like this:
--
-- @
--      f_1 x_2 = let f_3 x_4 = x_4 + 1
--                in f_3 (x_2 - 2)
-- @
--    But see Note [Shadowing] below.
--
-- 3. The resulting syntax tree undergoes type checking (which also deals with instantiating
--    type class arguments) to yield a 'GHC.Hs.Expr.HsExpr' type that has 'GHC.Types.Id.Id' as it's names.
--
-- 4. Finally the syntax tree is /desugared/ from the expressive 'GHC.Hs.Expr.HsExpr' type into
--    this 'Expr' type, which has far fewer constructors and hence is easier to perform
--    optimization, analysis and code generation on.
--
-- The type parameter @b@ is for the type of binders in the expression tree.
--
-- The language consists of the following elements:
--
-- *  Variables
--    See Note [Variable occurrences in Core]
--
-- *  Primitive literals
--
-- *  Applications: note that the argument may be a 'Type'.
--    See Note [Core let/app invariant]
--    See Note [Levity polymorphism invariants]
--
-- *  Lambda abstraction
--    See Note [Levity polymorphism invariants]
--
-- *  Recursive and non recursive @let@s. Operationally
--    this corresponds to allocating a thunk for the things
--    bound and then executing the sub-expression.
--
--    See Note [Core letrec invariant]
--    See Note [Core let/app invariant]
--    See Note [Levity polymorphism invariants]
--    See Note [Core type and coercion invariant]
--
-- *  Case expression. Operationally this corresponds to evaluating
--    the scrutinee (expression examined) to weak head normal form
--    and then examining at most one level of resulting constructor (i.e. you
--    cannot do nested pattern matching directly with this).
--
--    The binder gets bound to the value of the scrutinee,
--    and the 'Type' must be that of all the case alternatives
--
--    IMPORTANT: see Note [Case expression invariants]
--
-- *  Cast an expression to a particular type.
--    This is used to implement @newtype@s (a @newtype@ constructor or
--    destructor just becomes a 'Cast' in Core) and GADTs.
--
-- *  Notes. These allow general information to be added to expressions
--    in the syntax tree
--
-- *  A type: this should only show up at the top level of an Arg
--
-- *  A coercion

{- Note [Why does Case have a 'Type' field?]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The obvious alternative is
   exprType (Case scrut bndr alts)
     | (_,_,rhs1):_ <- alts
     = exprType rhs1

But caching the type in the Case constructor
  exprType (Case scrut bndr ty alts) = ty
is better for at least three reasons:

* It works when there are no alternatives (see case invariant 1 above)

* It might be faster in deeply-nested situations.

* It might not be quite the same as (exprType rhs) for one
  of the RHSs in alts. Consider a phantom type synonym
       type S a = Int
   and we want to form the case expression
        case x of { K (a::*) -> (e :: S a) }
   Then exprType of the RHS is (S a), but we cannot make that be
   the 'ty' in the Case constructor because 'a' is simply not in
   scope there. Instead we must expand the synonym to Int before
   putting it in the Case constructor.  See GHC.Core.Utils.mkSingleAltCase.

   So we'd have to do synonym expansion in exprType which would
   be inefficient.

* The type stored in the case is checked with lintInTy. This checks
  (among other things) that it does not mention any variables that are
  not in scope. If we did not have the type there, it would be a bit
  harder for Core Lint to reject case blah of Ex x -> x where
      data Ex = forall a. Ex a.
-}

-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
data Expr b
  = Var   Id
  | Lit   Literal
  | App   (Expr b) (Arg b)
  | Lam   b (Expr b)
  | Let   (Bind b) (Expr b)
  | Case  (Expr b) b Type [Alt b]   -- See Note [Case expression invariants]
                                    -- and Note [Why does Case have a 'Type' field?]
  | Cast  (Expr b) Coercion
  | Tick  (Tickish Id) (Expr b)
  | Type  Type
  | Coercion Coercion
  deriving Data

-- | Type synonym for expressions that occur in function argument positions.
-- Only 'Arg' should contain a 'Type' at top level, general 'Expr' should not
type Arg b = Expr b

-- | A case split alternative. Consists of the constructor leading to the alternative,
-- the variables bound from the constructor, and the expression to be executed given that binding.
-- The default alternative is @(DEFAULT, [], rhs)@

-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
type Alt b = (AltCon, [b], Expr b)

-- | A case alternative constructor (i.e. pattern match)

-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
data AltCon
  = DataAlt DataCon   --  ^ A plain data constructor: @case e of { Foo x -> ... }@.
                      -- Invariant: the 'DataCon' is always from a @data@ type, and never from a @newtype@

  | LitAlt  Literal   -- ^ A literal: @case e of { 1 -> ... }@
                      -- Invariant: always an *unlifted* literal
                      -- See Note [Literal alternatives]

  | DEFAULT           -- ^ Trivial alternative: @case e of { _ -> ... }@
   deriving (Eq, Data)

-- This instance is a bit shady. It can only be used to compare AltCons for
-- a single type constructor. Fortunately, it seems quite unlikely that we'll
-- ever need to compare AltCons for different type constructors.
-- The instance adheres to the order described in [Core case invariants]
instance Ord AltCon where
  compare (DataAlt con1) (DataAlt con2) =
    ASSERT( dataConTyCon con1 == dataConTyCon con2 )
    compare (dataConTag con1) (dataConTag con2)
  compare (DataAlt _) _ = GT
  compare _ (DataAlt _) = LT
  compare (LitAlt l1) (LitAlt l2) = compare l1 l2
  compare (LitAlt _) DEFAULT = GT
  compare DEFAULT DEFAULT = EQ
  compare DEFAULT _ = LT

-- | Binding, used for top level bindings in a module and local bindings in a @let@.

-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
data Bind b = NonRec b (Expr b)
            | Rec [(b, (Expr b))]
  deriving Data

{-
Note [Shadowing]
~~~~~~~~~~~~~~~~
While various passes attempt to rename on-the-fly in a manner that
avoids "shadowing" (thereby simplifying downstream optimizations),
neither the simplifier nor any other pass GUARANTEES that shadowing is
avoided. Thus, all passes SHOULD work fine even in the presence of
arbitrary shadowing in their inputs.

In particular, scrutinee variables `x` in expressions of the form
`Case e x t` are often renamed to variables with a prefix
"wild_". These "wild" variables may appear in the body of the
case-expression, and further, may be shadowed within the body.

So the Unique in a Var is not really unique at all.  Still, it's very
useful to give a constant-time equality/ordering for Vars, and to give
a key that can be used to make sets of Vars (VarSet), or mappings from
Vars to other things (VarEnv).   Moreover, if you do want to eliminate
shadowing, you can give a new Unique to an Id without changing its
printable name, which makes debugging easier.

Note [Literal alternatives]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Literal alternatives (LitAlt lit) are always for *un-lifted* literals.
We have one literal, a literal Integer, that is lifted, and we don't
allow in a LitAlt, because LitAlt cases don't do any evaluation. Also
(see #5603) if you say
    case 3 of
      IS x -> ...
      IP _ -> ...
      IN _ -> ...
(where IS, IP, IN are the constructors for Integer) we don't want the
simplifier calling findAlt with argument (LitAlt 3).  No no.  Integer
literals are an opaque encoding of an algebraic data type, not of
an unlifted literal, like all the others.

Also, we do not permit case analysis with literal patterns on floating-point
types. See #9238 and Note [Rules for floating-point comparisons] in
GHC.Core.Opt.ConstantFold for the rationale for this restriction.

-------------------------- GHC.Core INVARIANTS ---------------------------

Note [Variable occurrences in Core]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Variable /occurrences/ are never CoVars, though /bindings/ can be.
All CoVars appear in Coercions.

For example
  \(c :: Age~#Int) (d::Int). d |> (sym c)
Here 'c' is a CoVar, which is lambda-bound, but it /occurs/ in
a Coercion, (sym c).

Note [Core letrec invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The right hand sides of all top-level and recursive @let@s
/must/ be of lifted type (see "Type#type_classification" for
the meaning of /lifted/ vs. /unlifted/).

There is one exception to this rule, top-level @let@s are
allowed to bind primitive string literals: see
Note [Core top-level string literals].

Note [Core top-level string literals]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As an exception to the usual rule that top-level binders must be lifted,
we allow binding primitive string literals (of type Addr#) of type Addr# at the
top level. This allows us to share string literals earlier in the pipeline and
crucially allows other optimizations in the Core2Core pipeline to fire.
Consider,

  f n = let a::Addr# = "foo"#
        in \x -> blah

In order to be able to inline `f`, we would like to float `a` to the top.
Another option would be to inline `a`, but that would lead to duplicating string
literals, which we want to avoid. See #8472.

The solution is simply to allow top-level unlifted binders. We can't allow
arbitrary unlifted expression at the top-level though, unlifted binders cannot
be thunks, so we just allow string literals.

We allow the top-level primitive string literals to be wrapped in Ticks
in the same way they can be wrapped when nested in an expression.
CoreToSTG currently discards Ticks around top-level primitive string literals.
See #14779.

Also see Note [Compilation plan for top-level string literals].

Note [Compilation plan for top-level string literals]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is a summary on how top-level string literals are handled by various
parts of the compilation pipeline.

* In the source language, there is no way to bind a primitive string literal
  at the top level.

* In Core, we have a special rule that permits top-level Addr# bindings. See
  Note [Core top-level string literals]. Core-to-core passes may introduce
  new top-level string literals.

* In STG, top-level string literals are explicitly represented in the syntax
  tree.

* A top-level string literal may end up exported from a module. In this case,
  in the object file, the content of the exported literal is given a label with
  the _bytes suffix.

Note [Core let/app invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The let/app invariant
     the right hand side of a non-recursive 'Let', and
     the argument of an 'App',
    /may/ be of unlifted type, but only if
    the expression is ok-for-speculation
    or the 'Let' is for a join point.

This means that the let can be floated around
without difficulty. For example, this is OK:

   y::Int# = x +# 1#

But this is not, as it may affect termination if the
expression is floated out:

   y::Int# = fac 4#

In this situation you should use @case@ rather than a @let@. The function
'GHC.Core.Utils.needsCaseBinding' can help you determine which to generate, or
alternatively use 'GHC.Core.Make.mkCoreLet' rather than this constructor directly,
which will generate a @case@ if necessary

The let/app invariant is initially enforced by mkCoreLet and mkCoreApp in
GHC.Core.Make.

For discussion of some implications of the let/app invariant primops see
Note [Checking versus non-checking primops] in GHC.Builtin.PrimOps.

Note [Case expression invariants]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Case expressions are one of the more complicated elements of the Core
language, and come with a number of invariants.  All of them should be
checked by Core Lint.

1. The list of alternatives may be empty;
   See Note [Empty case alternatives]

2. The 'DEFAULT' case alternative must be first in the list,
   if it occurs at all.  Checked in GHC.Core.Lint.checkCaseAlts.

3. The remaining cases are in order of (strictly) increasing
     tag  (for 'DataAlts') or
     lit  (for 'LitAlts').
   This makes finding the relevant constructor easy, and makes
   comparison easier too.   Checked in GHC.Core.Lint.checkCaseAlts.

4. The list of alternatives must be exhaustive. An /exhaustive/ case
   does not necessarily mention all constructors:

   @
        data Foo = Red | Green | Blue
        ... case x of
              Red   -> True
              other -> f (case x of
                              Green -> ...
                              Blue  -> ... ) ...
   @

   The inner case does not need a @Red@ alternative, because @x@
   can't be @Red@ at that program point.

   This is not checked by Core Lint -- it's very hard to do so.
   E.g. suppose that inner case was floated out, thus:
         let a = case x of
                   Green -> ...
                   Blue  -> ... )
         case x of
           Red   -> True
           other -> f a
   Now it's really hard to see that the Green/Blue case is
   exhaustive.  But it is.

   If you have a case-expression that really /isn't/ exhaustive,
   we may generate seg-faults.  Consider the Green/Blue case
   above.  Since there are only two branches we may generate
   code that tests for Green, and if not Green simply /assumes/
   Blue (since, if the case is exhaustive, that's all that
   remains).  Of course, if it's not Blue and we start fetching
   fields that should be in a Blue constructor, we may die
   horribly. See also Note [Core Lint guarantee] in GHC.Core.Lint.

5. Floating-point values must not be scrutinised against literals.
   See #9238 and Note [Rules for floating-point comparisons]
   in GHC.Core.Opt.ConstantFold for rationale.  Checked in lintCaseExpr;
   see the call to isFloatingTy.

6. The 'ty' field of (Case scrut bndr ty alts) is the type of the
   /entire/ case expression.  Checked in lintAltExpr.
   See also Note [Why does Case have a 'Type' field?].

7. The type of the scrutinee must be the same as the type
   of the case binder, obviously.  Checked in lintCaseExpr.

8. The multiplicity of the binders in constructor patterns must be the
   multiplicity of the corresponding field /scaled by the multiplicity of the
   case binder/. Checked in lintCoreAlt.

Note [Core type and coercion invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We allow a /non-recursive/, /non-top-level/ let to bind type and
coercion variables.  These can be very convenient for postponing type
substitutions until the next run of the simplifier.

* A type variable binding must have a RHS of (Type ty)

* A coercion variable binding must have a RHS of (Coercion co)

  It is possible to have terms that return a coercion, but we use
  case-binding for those; e.g.
     case (eq_sel d) of (co :: a ~# b) -> blah
  where eq_sel :: (a~b) -> (a~#b)

  Or even even
      case (df @Int) of (co :: a ~# b) -> blah
  Which is very exotic, and I think never encountered; but see
  Note [Equality superclasses in quantified constraints]
  in GHC.Tc.Solver.Canonical

Note [Core case invariants]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
See Note [Case expression invariants]

Note [Levity polymorphism invariants]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The levity-polymorphism invariants are these (as per "Levity Polymorphism",
PLDI '17):

* The type of a term-binder must not be levity-polymorphic,
  unless it is a let(rec)-bound join point
     (see Note [Invariants on join points])

* The type of the argument of an App must not be levity-polymorphic.

A type (t::TYPE r) is "levity polymorphic" if 'r' has any free variables.

For example
  \(r::RuntimeRep). \(a::TYPE r). \(x::a). e
is illegal because x's type has kind (TYPE r), which has 'r' free.

See Note [Levity polymorphism checking] in GHC.HsToCore.Monad to see where these
invariants are established for user-written code.

Note [Core let goal]
~~~~~~~~~~~~~~~~~~~~
* The simplifier tries to ensure that if the RHS of a let is a constructor
  application, its arguments are trivial, so that the constructor can be
  inlined vigorously.

Note [Type let]
~~~~~~~~~~~~~~~
See #type_let#

Note [Empty case alternatives]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The alternatives of a case expression should be exhaustive.  But
this exhaustive list can be empty!

* A case expression can have empty alternatives if (and only if) the
  scrutinee is bound to raise an exception or diverge. When do we know
  this?  See Note [Bottoming expressions] in GHC.Core.Utils.

* The possibility of empty alternatives is one reason we need a type on
  the case expression: if the alternatives are empty we can't get the
  type from the alternatives!

* In the case of empty types (see Note [Bottoming expressions]), say
    data T
  we do NOT want to replace
    case (x::T) of Bool {}   -->   error Bool "Inaccessible case"
  because x might raise an exception, and *that*'s what we want to see!
  (#6067 is an example.) To preserve semantics we'd have to say
     x `seq` error Bool "Inaccessible case"
  but the 'seq' is just such a case, so we are back to square 1.

* We can use the empty-alternative construct to coerce error values from
  one type to another.  For example

    f :: Int -> Int
    f n = error "urk"

    g :: Int -> (# Char, Bool #)
    g x = case f x of { 0 -> ..., n -> ... }

  Then if we inline f in g's RHS we get
    case (error Int "urk") of (# Char, Bool #) { ... }
  and we can discard the alternatives since the scrutinee is bottom to give
    case (error Int "urk") of (# Char, Bool #) {}

  This is nicer than using an unsafe coerce between Int ~ (# Char,Bool #),
  if for no other reason that we don't need to instantiate the (~) at an
  unboxed type.

* We treat a case expression with empty alternatives as trivial iff
  its scrutinee is (see GHC.Core.Utils.exprIsTrivial).  This is actually
  important; see Note [Empty case is trivial] in GHC.Core.Utils

* An empty case is replaced by its scrutinee during the CoreToStg
  conversion; remember STG is un-typed, so there is no need for
  the empty case to do the type conversion.

Note [Join points]
~~~~~~~~~~~~~~~~~~
In Core, a *join point* is a specially tagged function whose only occurrences
are saturated tail calls. A tail call can appear in these places:

  1. In the branches (not the scrutinee) of a case
  2. Underneath a let (value or join point)
  3. Inside another join point

We write a join-point declaration as
  join j @a @b x y = e1 in e2,
like a let binding but with "join" instead (or "join rec" for "let rec"). Note
that we put the parameters before the = rather than using lambdas; this is
because it's relevant how many parameters the join point takes *as a join
point.* This number is called the *join arity,* distinct from arity because it
counts types as well as values. Note that a join point may return a lambda! So
  join j x = x + 1
is different from
  join j = \x -> x + 1
The former has join arity 1, while the latter has join arity 0.

The identifier for a join point is called a join id or a *label.* An invocation
is called a *jump.* We write a jump using the jump keyword:

  jump j 3

The words *label* and *jump* are evocative of assembly code (or Cmm) for a
reason: join points are indeed compiled as labeled blocks, and jumps become
actual jumps (plus argument passing and stack adjustment). There is no closure
allocated and only a fraction of the function-call overhead. Hence we would
like as many functions as possible to become join points (see OccurAnal) and
the type rules for join points ensure we preserve the properties that make them
efficient.

In the actual AST, a join point is indicated by the IdDetails of the binder: a
local value binding gets 'VanillaId' but a join point gets a 'JoinId' with its
join arity.

For more details, see the paper:

  Luke Maurer, Paul Downen, Zena Ariola, and Simon Peyton Jones. "Compiling
  without continuations." Submitted to PLDI'17.

  https://www.microsoft.com/en-us/research/publication/compiling-without-continuations/

Note [Invariants on join points]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Join points must follow these invariants:

  1. All occurrences must be tail calls. Each of these tail calls must pass the
     same number of arguments, counting both types and values; we call this the
     "join arity" (to distinguish from regular arity, which only counts values).

     See Note [Join points are less general than the paper]

  2. For join arity n, the right-hand side must begin with at least n lambdas.
     No ticks, no casts, just lambdas!  C.f. GHC.Core.Utils.joinRhsArity.

     2a. Moreover, this same constraint applies to any unfolding of
         the binder.  Reason: if we want to push a continuation into
         the RHS we must push it into the unfolding as well.

     2b. The Arity (in the IdInfo) of a join point is the number of value
         binders in the top n lambdas, where n is the join arity.

         So arity <= join arity; the former counts only value binders
         while the latter counts all binders.
         e.g. Suppose $j has join arity 1
               let j = \x y. e in case x of { A -> j 1; B -> j 2 }
         Then its ordinary arity is also 1, not 2.

         The arity of a join point isn't very important; but short of setting
         it to zero, it is helpful to have an invariant.  E.g. #17294.

  3. If the binding is recursive, then all other bindings in the recursive group
     must also be join points.

  4. The binding's type must not be polymorphic in its return type (as defined
     in Note [The polymorphism rule of join points]).

However, join points have simpler invariants in other ways

  5. A join point can have an unboxed type without the RHS being
     ok-for-speculation (i.e. drop the let/app invariant)
     e.g.  let j :: Int# = factorial x in ...

  6. A join point can have a levity-polymorphic RHS
     e.g.  let j :: r :: TYPE l = fail void# in ...
     This happened in an intermediate program #13394

Examples:

  join j1  x = 1 + x in jump j (jump j x)  -- Fails 1: non-tail call
  join j1' x = 1 + x in if even a
                          then jump j1 a
                          else jump j1 a b -- Fails 1: inconsistent calls
  join j2  x = flip (+) x in j2 1 2        -- Fails 2: not enough lambdas
  join j2' x = \y -> x + y in j3 1         -- Passes: extra lams ok
  join j @a (x :: a) = x                   -- Fails 4: polymorphic in ret type

Invariant 1 applies to left-hand sides of rewrite rules, so a rule for a join
point must have an exact call as its LHS.

Strictly speaking, invariant 3 is redundant, since a call from inside a lazy
binding isn't a tail call. Since a let-bound value can't invoke a free join
point, then, they can't be mutually recursive. (A Core binding group *can*
include spurious extra bindings if the occurrence analyser hasn't run, so
invariant 3 does still need to be checked.) For the rigorous definition of
"tail call", see Section 3 of the paper (Note [Join points]).

Invariant 4 is subtle; see Note [The polymorphism rule of join points].

Invariant 6 is to enable code like this:

  f = \(r :: RuntimeRep) (a :: TYPE r) (x :: T).
      join j :: a
           j = error @r @a "bloop"
      in case x of
           A -> j
           B -> j
           C -> error @r @a "blurp"

Core Lint will check these invariants, anticipating that any binder whose
OccInfo is marked AlwaysTailCalled will become a join point as soon as the
simplifier (or simpleOptPgm) runs.

Note [Join points are less general than the paper]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the paper "Compiling without continuations", this expression is
perfectly valid:

    join { j = \_ -> e }
    in (case blah of       )
       (  True  -> j void# ) arg
       (  False -> blah    )

assuming 'j' has arity 1.   Here the call to 'j' does not look like a
tail call, but actually everything is fine. See Section 3, "Managing \Delta"
in the paper.

In GHC, however, we adopt a slightly more restrictive subset, in which
join point calls must be tail calls.  I think we /could/ loosen it up, but
in fact the simplifier ensures that we always get tail calls, and it makes
the back end a bit easier I think.  Generally, just less to think about;
nothing deeper than that.

Note [The type of a join point]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A join point has the same type it would have as a function. That is, if it takes
an Int and a Bool and its body produces a String, its type is `Int -> Bool ->
String`. Natural as this may seem, it can be awkward. A join point shouldn't be
thought to "return" in the same sense a function does---a jump is one-way. This
is crucial for understanding how case-of-case interacts with join points:

  case (join
          j :: Int -> Bool -> String
          j x y = ...
        in
          jump j z w) of
    "" -> True
    _  -> False

The simplifier will pull the case into the join point (see Note [Join points
and case-of-case] in GHC.Core.Opt.Simplify):

  join
    j :: Int -> Bool -> Bool -- changed!
    j x y = case ... of "" -> True
                        _  -> False
  in
    jump j z w

The body of the join point now returns a Bool, so the label `j` has to have its
type updated accordingly. Inconvenient though this may be, it has the advantage
that 'GHC.Core.Utils.exprType' can still return a type for any expression, including
a jump.

This differs from the paper (see Note [Invariants on join points]). In the
paper, we instead give j the type `Int -> Bool -> forall a. a`. Then each jump
carries the "return type" as a parameter, exactly the way other non-returning
functions like `error` work:

  case (join
          j :: Int -> Bool -> forall a. a
          j x y = ...
        in
          jump j z w @String) of
    "" -> True
    _  -> False

Now we can move the case inward and we only have to change the jump:

  join
    j :: Int -> Bool -> forall a. a
    j x y = case ... of "" -> True
                        _  -> False
  in
    jump j z w @Bool

(Core Lint would still check that the body of the join point has the right type;
that type would simply not be reflected in the join id.)

Note [The polymorphism rule of join points]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Invariant 4 of Note [Invariants on join points] forbids a join point to be
polymorphic in its return type. That is, if its type is

  forall a1 ... ak. t1 -> ... -> tn -> r

where its join arity is k+n, none of the type parameters ai may occur free in r.

In some way, this falls out of the fact that given

  join
     j @a1 ... @ak x1 ... xn = e1
  in e2

then all calls to `j` are in tail-call positions of `e`, and expressions in
tail-call positions in `e` have the same type as `e`.
Therefore the type of `e1` -- the return type of the join point -- must be the
same as the type of e2.
Since the type variables aren't bound in `e2`, its type can't include them, and
thus neither can the type of `e1`.

This unfortunately prevents the `go` in the following code from being a
join-point:

  iter :: forall a. Int -> (a -> a) -> a -> a
  iter @a n f x = go @a n f x
    where
      go :: forall a. Int -> (a -> a) -> a -> a
      go @a 0 _ x = x
      go @a n f x = go @a (n-1) f (f x)

In this case, a static argument transformation would fix that (see
ticket #14620):

  iter :: forall a. Int -> (a -> a) -> a -> a
  iter @a n f x = go' @a n f x
    where
      go' :: Int -> (a -> a) -> a -> a
      go' 0 _ x = x
      go' n f x = go' (n-1) f (f x)

In general, loopification could be employed to do that (see #14068.)

Can we simply drop the requirement, and allow `go` to be a join-point? We
could, and it would work. But we could not longer apply the case-of-join-point
transformation universally. This transformation would do:

  case (join go @a n f x = case n of 0 -> x
                                     n -> go @a (n-1) f (f x)
        in go @Bool n neg True) of
    True -> e1; False -> e2

 ===>

  join go @a n f x = case n of 0 -> case x of True -> e1; False -> e2
                               n -> go @a (n-1) f (f x)
  in go @Bool n neg True

but that is ill-typed, as `x` is type `a`, not `Bool`.


This also justifies why we do not consider the `e` in `e |> co` to be in
tail position: A cast changes the type, but the type must be the same. But
operationally, casts are vacuous, so this is a bit unfortunate! See #14610 for
ideas how to fix this.

************************************************************************
*                                                                      *
            In/Out type synonyms
*                                                                      *
********************************************************************* -}

{- Many passes apply a substitution, and it's very handy to have type
   synonyms to remind us whether or not the substitution has been applied -}

-- Pre-cloning or substitution
type InBndr     = CoreBndr
type InType     = Type
type InKind     = Kind
type InBind     = CoreBind
type InExpr     = CoreExpr
type InAlt      = CoreAlt
type InArg      = CoreArg
type InCoercion = Coercion

-- Post-cloning or substitution
type OutBndr     = CoreBndr
type OutType     = Type
type OutKind     = Kind
type OutCoercion = Coercion
type OutBind     = CoreBind
type OutExpr     = CoreExpr
type OutAlt      = CoreAlt
type OutArg      = CoreArg
type MOutCoercion = MCoercion


{- *********************************************************************
*                                                                      *
              Ticks
*                                                                      *
************************************************************************
-}

-- | Allows attaching extra information to points in expressions

-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
data Tickish id =
    -- | An @{-# SCC #-}@ profiling annotation, either automatically
    -- added by the desugarer as a result of -auto-all, or added by
    -- the user.
    ProfNote {
      profNoteCC    :: CostCentre, -- ^ the cost centre
      profNoteCount :: !Bool,      -- ^ bump the entry count?
      profNoteScope :: !Bool       -- ^ scopes over the enclosed expression
                                   -- (i.e. not just a tick)
    }

  -- | A "tick" used by HPC to track the execution of each
  -- subexpression in the original source code.
  | HpcTick {
      tickModule :: Module,
      tickId     :: !Int
    }

  -- | A breakpoint for the GHCi debugger.  This behaves like an HPC
  -- tick, but has a list of free variables which will be available
  -- for inspection in GHCi when the program stops at the breakpoint.
  --
  -- NB. we must take account of these Ids when (a) counting free variables,
  -- and (b) substituting (don't substitute for them)
  | Breakpoint
    { breakpointId     :: !Int
    , breakpointFVs    :: [id]  -- ^ the order of this list is important:
                                -- it matches the order of the lists in the
                                -- appropriate entry in 'GHC.Driver.Types.ModBreaks'.
                                --
                                -- Careful about substitution!  See
                                -- Note [substTickish] in "GHC.Core.Subst".
    }

  -- | A source note.
  --
  -- Source notes are pure annotations: Their presence should neither
  -- influence compilation nor execution. The semantics are given by
  -- causality: The presence of a source note means that a local
  -- change in the referenced source code span will possibly provoke
  -- the generated code to change. On the flip-side, the functionality
  -- of annotated code *must* be invariant against changes to all
  -- source code *except* the spans referenced in the source notes
  -- (see "Causality of optimized Haskell" paper for details).
  --
  -- Therefore extending the scope of any given source note is always
  -- valid. Note that it is still undesirable though, as this reduces
  -- their usefulness for debugging and profiling. Therefore we will
  -- generally try only to make use of this property where it is
  -- necessary to enable optimizations.
  | SourceNote
    { sourceSpan :: RealSrcSpan -- ^ Source covered
    , sourceName :: String      -- ^ Name for source location
                                --   (uses same names as CCs)
    }

  deriving (Eq, Ord, Data)

-- | A "counting tick" (where tickishCounts is True) is one that
-- counts evaluations in some way.  We cannot discard a counting tick,
-- and the compiler should preserve the number of counting ticks as
-- far as possible.
--
-- However, we still allow the simplifier to increase or decrease
-- sharing, so in practice the actual number of ticks may vary, except
-- that we never change the value from zero to non-zero or vice versa.
tickishCounts :: Tickish id -> Bool
tickishCounts n@ProfNote{} = profNoteCount n
tickishCounts HpcTick{}    = True
tickishCounts Breakpoint{} = True
tickishCounts _            = False


-- | Specifies the scoping behaviour of ticks. This governs the
-- behaviour of ticks that care about the covered code and the cost
-- associated with it. Important for ticks relating to profiling.
data TickishScoping =
    -- | No scoping: The tick does not care about what code it
    -- covers. Transformations can freely move code inside as well as
    -- outside without any additional annotation obligations
    NoScope

    -- | Soft scoping: We want all code that is covered to stay
    -- covered.  Note that this scope type does not forbid
    -- transformations from happening, as long as all results of
    -- the transformations are still covered by this tick or a copy of
    -- it. For example
    --
    --   let x = tick<...> (let y = foo in bar) in baz
    --     ===>
    --   let x = tick<...> bar; y = tick<...> foo in baz
    --
    -- Is a valid transformation as far as "bar" and "foo" is
    -- concerned, because both still are scoped over by the tick.
    --
    -- Note though that one might object to the "let" not being
    -- covered by the tick any more. However, we are generally lax
    -- with this - constant costs don't matter too much, and given
    -- that the "let" was effectively merged we can view it as having
    -- lost its identity anyway.
    --
    -- Also note that this scoping behaviour allows floating a tick
    -- "upwards" in pretty much any situation. For example:
    --
    --   case foo of x -> tick<...> bar
    --     ==>
    --   tick<...> case foo of x -> bar
    --
    -- While this is always legal, we want to make a best effort to
    -- only make us of this where it exposes transformation
    -- opportunities.
  | SoftScope

    -- | Cost centre scoping: We don't want any costs to move to other
    -- cost-centre stacks. This means we not only want no code or cost
    -- to get moved out of their cost centres, but we also object to
    -- code getting associated with new cost-centre ticks - or
    -- changing the order in which they get applied.
    --
    -- A rule of thumb is that we don't want any code to gain new
    -- annotations. However, there are notable exceptions, for
    -- example:
    --
    --   let f = \y -> foo in tick<...> ... (f x) ...
    --     ==>
    --   tick<...> ... foo[x/y] ...
    --
    -- In-lining lambdas like this is always legal, because inlining a
    -- function does not change the cost-centre stack when the
    -- function is called.
  | CostCentreScope

  deriving (Eq)

-- | Returns the intended scoping rule for a Tickish
tickishScoped :: Tickish id -> TickishScoping
tickishScoped n@ProfNote{}
  | profNoteScope n        = CostCentreScope
  | otherwise              = NoScope
tickishScoped HpcTick{}    = NoScope
tickishScoped Breakpoint{} = CostCentreScope
   -- Breakpoints are scoped: eventually we're going to do call
   -- stacks, but also this helps prevent the simplifier from moving
   -- breakpoints around and changing their result type (see #1531).
tickishScoped SourceNote{} = SoftScope

-- | Returns whether the tick scoping rule is at least as permissive
-- as the given scoping rule.
tickishScopesLike :: Tickish id -> TickishScoping -> Bool
tickishScopesLike t scope = tickishScoped t `like` scope
  where NoScope         `like` _               = True
        _               `like` NoScope         = False
        SoftScope       `like` _               = True
        _               `like` SoftScope       = False
        CostCentreScope `like` _               = True

-- | Returns @True@ for ticks that can be floated upwards easily even
-- where it might change execution counts, such as:
--
--   Just (tick<...> foo)
--     ==>
--   tick<...> (Just foo)
--
-- This is a combination of @tickishSoftScope@ and
-- @tickishCounts@. Note that in principle splittable ticks can become
-- floatable using @mkNoTick@ -- even though there's currently no
-- tickish for which that is the case.
tickishFloatable :: Tickish id -> Bool
tickishFloatable t = t `tickishScopesLike` SoftScope && not (tickishCounts t)

-- | Returns @True@ for a tick that is both counting /and/ scoping and
-- can be split into its (tick, scope) parts using 'mkNoScope' and
-- 'mkNoTick' respectively.
tickishCanSplit :: Tickish id -> Bool
tickishCanSplit ProfNote{profNoteScope = True, profNoteCount = True}
                   = True
tickishCanSplit _  = False

mkNoCount :: Tickish id -> Tickish id
mkNoCount n | not (tickishCounts n)   = n
            | not (tickishCanSplit n) = panic "mkNoCount: Cannot split!"
mkNoCount n@ProfNote{}                = n {profNoteCount = False}
mkNoCount _                           = panic "mkNoCount: Undefined split!"

mkNoScope :: Tickish id -> Tickish id
mkNoScope n | tickishScoped n == NoScope  = n
            | not (tickishCanSplit n)     = panic "mkNoScope: Cannot split!"
mkNoScope n@ProfNote{}                    = n {profNoteScope = False}
mkNoScope _                               = panic "mkNoScope: Undefined split!"

-- | Return @True@ if this source annotation compiles to some backend
-- code. Without this flag, the tickish is seen as a simple annotation
-- that does not have any associated evaluation code.
--
-- What this means that we are allowed to disregard the tick if doing
-- so means that we can skip generating any code in the first place. A
-- typical example is top-level bindings:
--
--   foo = tick<...> \y -> ...
--     ==>
--   foo = \y -> tick<...> ...
--
-- Here there is just no operational difference between the first and
-- the second version. Therefore code generation should simply
-- translate the code as if it found the latter.
tickishIsCode :: Tickish id -> Bool
tickishIsCode SourceNote{} = False
tickishIsCode _tickish     = True  -- all the rest for now


-- | Governs the kind of expression that the tick gets placed on when
-- annotating for example using @mkTick@. If we find that we want to
-- put a tickish on an expression ruled out here, we try to float it
-- inwards until we find a suitable expression.
data TickishPlacement =

    -- | Place ticks exactly on run-time expressions. We can still
    -- move the tick through pure compile-time constructs such as
    -- other ticks, casts or type lambdas. This is the most
    -- restrictive placement rule for ticks, as all tickishs have in
    -- common that they want to track runtime processes. The only
    -- legal placement rule for counting ticks.
    PlaceRuntime

    -- | As @PlaceRuntime@, but we float the tick through all
    -- lambdas. This makes sense where there is little difference
    -- between annotating the lambda and annotating the lambda's code.
  | PlaceNonLam

    -- | In addition to floating through lambdas, cost-centre style
    -- tickishs can also be moved from constructors, non-function
    -- variables and literals. For example:
    --
    --   let x = scc<...> C (scc<...> y) (scc<...> 3) in ...
    --
    -- Neither the constructor application, the variable or the
    -- literal are likely to have any cost worth mentioning. And even
    -- if y names a thunk, the call would not care about the
    -- evaluation context. Therefore removing all annotations in the
    -- above example is safe.
  | PlaceCostCentre

  deriving (Eq)

-- | Placement behaviour we want for the ticks
tickishPlace :: Tickish id -> TickishPlacement
tickishPlace n@ProfNote{}
  | profNoteCount n        = PlaceRuntime
  | otherwise              = PlaceCostCentre
tickishPlace HpcTick{}     = PlaceRuntime
tickishPlace Breakpoint{}  = PlaceRuntime
tickishPlace SourceNote{}  = PlaceNonLam

-- | Returns whether one tick "contains" the other one, therefore
-- making the second tick redundant.
tickishContains :: Eq b => Tickish b -> Tickish b -> Bool
tickishContains (SourceNote sp1 n1) (SourceNote sp2 n2)
  = containsSpan sp1 sp2 && n1 == n2
    -- compare the String last
tickishContains t1 t2
  = t1 == t2

{-
************************************************************************
*                                                                      *
                Orphans
*                                                                      *
************************************************************************
-}

-- | Is this instance an orphan?  If it is not an orphan, contains an 'OccName'
-- witnessing the instance's non-orphanhood.
-- See Note [Orphans]
data IsOrphan
  = IsOrphan
  | NotOrphan OccName -- The OccName 'n' witnesses the instance's non-orphanhood
                      -- In that case, the instance is fingerprinted as part
                      -- of the definition of 'n's definition
    deriving Data

-- | Returns true if 'IsOrphan' is orphan.
isOrphan :: IsOrphan -> Bool
isOrphan IsOrphan = True
isOrphan _ = False

-- | Returns true if 'IsOrphan' is not an orphan.
notOrphan :: IsOrphan -> Bool
notOrphan NotOrphan{} = True
notOrphan _ = False

chooseOrphanAnchor :: NameSet -> IsOrphan
-- Something (rule, instance) is relate to all the Names in this
-- list. Choose one of them to be an "anchor" for the orphan.  We make
-- the choice deterministic to avoid gratuitous changes in the ABI
-- hash (#4012).  Specifically, use lexicographic comparison of
-- OccName rather than comparing Uniques
--
-- NB: 'minimum' use Ord, and (Ord OccName) works lexicographically
--
chooseOrphanAnchor local_names
  | isEmptyNameSet local_names = IsOrphan
  | otherwise                  = NotOrphan (minimum occs)
  where
    occs = map nameOccName $ nonDetEltsUniqSet local_names
    -- It's OK to use nonDetEltsUFM here, see comments above

instance Binary IsOrphan where
    put_ bh IsOrphan = putByte bh 0
    put_ bh (NotOrphan n) = do
        putByte bh 1
        put_ bh n
    get bh = do
        h <- getByte bh
        case h of
            0 -> return IsOrphan
            _ -> do
                n <- get bh
                return $ NotOrphan n

{-
Note [Orphans]
~~~~~~~~~~~~~~
Class instances, rules, and family instances are divided into orphans
and non-orphans.  Roughly speaking, an instance/rule is an orphan if
its left hand side mentions nothing defined in this module.  Orphan-hood
has two major consequences

 * A module that contains orphans is called an "orphan module".  If
   the module being compiled depends (transitively) on an orphan
   module M, then M.hi is read in regardless of whether M is otherwise
   needed. This is to ensure that we don't miss any instance decls in
   M.  But it's painful, because it means we need to keep track of all
   the orphan modules below us.

 * A non-orphan is not finger-printed separately.  Instead, for
   fingerprinting purposes it is treated as part of the entity it
   mentions on the LHS.  For example
      data T = T1 | T2
      instance Eq T where ....
   The instance (Eq T) is incorporated as part of T's fingerprint.

   In contrast, orphans are all fingerprinted together in the
   mi_orph_hash field of the ModIface.

   See GHC.Iface.Recomp.addFingerprints.

Orphan-hood is computed
  * For class instances:
      when we make a ClsInst
    (because it is needed during instance lookup)

  * For rules and family instances:
       when we generate an IfaceRule (GHC.Iface.Make.coreRuleToIfaceRule)
                     or IfaceFamInst (GHC.Iface.Make.instanceToIfaceInst)
-}

{-
************************************************************************
*                                                                      *
\subsection{Rewrite rules}
*                                                                      *
************************************************************************

The CoreRule type and its friends are dealt with mainly in GHC.Core.Rules, but
GHC.Core.FVs, GHC.Core.Subst, GHC.Core.Ppr, GHC.Core.Tidy also inspect the
representation.
-}

-- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
type RuleBase = NameEnv [CoreRule]
        -- The rules are unordered;
        -- we sort out any overlaps on lookup

-- | A full rule environment which we can apply rules from.  Like a 'RuleBase',
-- but it also includes the set of visible orphans we use to filter out orphan
-- rules which are not visible (even though we can see them...)
data RuleEnv
    = RuleEnv { re_base          :: RuleBase
              , re_visible_orphs :: ModuleSet
              }

mkRuleEnv :: RuleBase -> [Module] -> RuleEnv
mkRuleEnv rules vis_orphs = RuleEnv rules (mkModuleSet vis_orphs)

emptyRuleEnv :: RuleEnv
emptyRuleEnv = RuleEnv emptyNameEnv emptyModuleSet

-- | A 'CoreRule' is:
--
-- * \"Local\" if the function it is a rule for is defined in the
--   same module as the rule itself.
--
-- * \"Orphan\" if nothing on the LHS is defined in the same module
--   as the rule itself
data CoreRule
  = Rule {
        ru_name :: RuleName,            -- ^ Name of the rule, for communication with the user
        ru_act  :: Activation,          -- ^ When the rule is active

        -- Rough-matching stuff
        -- see comments with InstEnv.ClsInst( is_cls, is_rough )
        ru_fn    :: Name,               -- ^ Name of the 'GHC.Types.Id.Id' at the head of this rule
        ru_rough :: [Maybe Name],       -- ^ Name at the head of each argument to the left hand side

        -- Proper-matching stuff
        -- see comments with InstEnv.ClsInst( is_tvs, is_tys )
        ru_bndrs :: [CoreBndr],         -- ^ Variables quantified over
        ru_args  :: [CoreExpr],         -- ^ Left hand side arguments

        -- And the right-hand side
        ru_rhs   :: CoreExpr,           -- ^ Right hand side of the rule
                                        -- Occurrence info is guaranteed correct
                                        -- See Note [OccInfo in unfoldings and rules]

        -- Locality
        ru_auto :: Bool,   -- ^ @True@  <=> this rule is auto-generated
                           --               (notably by Specialise or SpecConstr)
                           --   @False@ <=> generated at the user's behest
                           -- See Note [Trimming auto-rules] in "GHC.Iface.Tidy"
                           -- for the sole purpose of this field.

        ru_origin :: !Module,   -- ^ 'Module' the rule was defined in, used
                                -- to test if we should see an orphan rule.

        ru_orphan :: !IsOrphan, -- ^ Whether or not the rule is an orphan.

        ru_local :: Bool        -- ^ @True@ iff the fn at the head of the rule is
                                -- defined in the same module as the rule
                                -- and is not an implicit 'Id' (like a record selector,
                                -- class operation, or data constructor).  This
                                -- is different from 'ru_orphan', where a rule
                                -- can avoid being an orphan if *any* Name in
                                -- LHS of the rule was defined in the same
                                -- module as the rule.
    }

  -- | Built-in rules are used for constant folding
  -- and suchlike.  They have no free variables.
  -- A built-in rule is always visible (there is no such thing as
  -- an orphan built-in rule.)
  | BuiltinRule {
        ru_name  :: RuleName,   -- ^ As above
        ru_fn    :: Name,       -- ^ As above
        ru_nargs :: Int,        -- ^ Number of arguments that 'ru_try' consumes,
                                -- if it fires, including type arguments
        ru_try   :: RuleFun
                -- ^ This function does the rewrite.  It given too many
                -- arguments, it simply discards them; the returned 'CoreExpr'
                -- is just the rewrite of 'ru_fn' applied to the first 'ru_nargs' args
    }
                -- See Note [Extra args in rule matching] in GHC.Core.Rules

-- | Rule options
data RuleOpts = RuleOpts
   { roPlatform                :: !Platform -- ^ Target platform
   , roNumConstantFolding      :: !Bool     -- ^ Enable more advanced numeric constant folding
   , roExcessRationalPrecision :: !Bool     -- ^ Cut down precision of Rational values to that of Float/Double if disabled
   }

type RuleFun = RuleOpts -> InScopeEnv -> Id -> [CoreExpr] -> Maybe CoreExpr
type InScopeEnv = (InScopeSet, IdUnfoldingFun)

type IdUnfoldingFun = Id -> Unfolding
-- A function that embodies how to unfold an Id if you need
-- to do that in the Rule.  The reason we need to pass this info in
-- is that whether an Id is unfoldable depends on the simplifier phase

isBuiltinRule :: CoreRule -> Bool
isBuiltinRule (BuiltinRule {}) = True
isBuiltinRule _                = False

isAutoRule :: CoreRule -> Bool
isAutoRule (BuiltinRule {}) = False
isAutoRule (Rule { ru_auto = is_auto }) = is_auto

-- | The number of arguments the 'ru_fn' must be applied
-- to before the rule can match on it
ruleArity :: CoreRule -> Int
ruleArity (BuiltinRule {ru_nargs = n}) = n
ruleArity (Rule {ru_args = args})      = length args

ruleName :: CoreRule -> RuleName
ruleName = ru_name

ruleModule :: CoreRule -> Maybe Module
ruleModule Rule { ru_origin } = Just ru_origin
ruleModule BuiltinRule {} = Nothing

ruleActivation :: CoreRule -> Activation
ruleActivation (BuiltinRule { })       = AlwaysActive
ruleActivation (Rule { ru_act = act }) = act

-- | The 'Name' of the 'GHC.Types.Id.Id' at the head of the rule left hand side
ruleIdName :: CoreRule -> Name
ruleIdName = ru_fn

isLocalRule :: CoreRule -> Bool
isLocalRule = ru_local

-- | Set the 'Name' of the 'GHC.Types.Id.Id' at the head of the rule left hand side
setRuleIdName :: Name -> CoreRule -> CoreRule
setRuleIdName nm ru = ru { ru_fn = nm }

{-
************************************************************************
*                                                                      *
                Unfoldings
*                                                                      *
************************************************************************

The @Unfolding@ type is declared here to avoid numerous loops
-}

-- | Records the /unfolding/ of an identifier, which is approximately the form the
-- identifier would have if we substituted its definition in for the identifier.
-- This type should be treated as abstract everywhere except in "GHC.Core.Unfold"
data Unfolding
  = NoUnfolding        -- ^ We have no information about the unfolding.

  | BootUnfolding      -- ^ We have no information about the unfolding, because
                       -- this 'Id' came from an @hi-boot@ file.
                       -- See Note [Inlining and hs-boot files] in "GHC.CoreToIface"
                       -- for what this is used for.

  | OtherCon [AltCon]  -- ^ It ain't one of these constructors.
                       -- @OtherCon xs@ also indicates that something has been evaluated
                       -- and hence there's no point in re-evaluating it.
                       -- @OtherCon []@ is used even for non-data-type values
                       -- to indicated evaluated-ness.  Notably:
                       --
                       -- > data C = C !(Int -> Int)
                       -- > case x of { C f -> ... }
                       --
                       -- Here, @f@ gets an @OtherCon []@ unfolding.

  | DFunUnfolding {     -- The Unfolding of a DFunId
                        -- See Note [DFun unfoldings]
                        --     df = /\a1..am. \d1..dn. MkD t1 .. tk
                        --                                 (op1 a1..am d1..dn)
                        --                                 (op2 a1..am d1..dn)
        df_bndrs :: [Var],      -- The bound variables [a1..m],[d1..dn]
        df_con   :: DataCon,    -- The dictionary data constructor (never a newtype datacon)
        df_args  :: [CoreExpr]  -- Args of the data con: types, superclasses and methods,
    }                           -- in positional order

  | CoreUnfolding {             -- An unfolding for an Id with no pragma,
                                -- or perhaps a NOINLINE pragma
                                -- (For NOINLINE, the phase, if any, is in the
                                -- InlinePragInfo for this Id.)
        uf_tmpl       :: CoreExpr,        -- Template; occurrence info is correct
        uf_src        :: UnfoldingSource, -- Where the unfolding came from
        uf_is_top     :: Bool,          -- True <=> top level binding
        uf_is_value   :: Bool,          -- exprIsHNF template (cached); it is ok to discard
                                        --      a `seq` on this variable
        uf_is_conlike :: Bool,          -- True <=> applicn of constructor or CONLIKE function
                                        --      Cached version of exprIsConLike
        uf_is_work_free :: Bool,                -- True <=> doesn't waste (much) work to expand
                                        --          inside an inlining
                                        --      Cached version of exprIsCheap
        uf_expandable :: Bool,          -- True <=> can expand in RULE matching
                                        --      Cached version of exprIsExpandable
        uf_guidance   :: UnfoldingGuidance      -- Tells about the *size* of the template.
    }
  -- ^ An unfolding with redundant cached information. Parameters:
  --
  --  uf_tmpl: Template used to perform unfolding;
  --           NB: Occurrence info is guaranteed correct:
  --               see Note [OccInfo in unfoldings and rules]
  --
  --  uf_is_top: Is this a top level binding?
  --
  --  uf_is_value: 'exprIsHNF' template (cached); it is ok to discard a 'seq' on
  --     this variable
  --
  --  uf_is_work_free:  Does this waste only a little work if we expand it inside an inlining?
  --     Basically this is a cached version of 'exprIsWorkFree'
  --
  --  uf_guidance:  Tells us about the /size/ of the unfolding template


------------------------------------------------
data UnfoldingSource
  = -- See also Note [Historical note: unfoldings for wrappers]

    InlineRhs          -- The current rhs of the function
                       -- Replace uf_tmpl each time around

  | InlineStable       -- From an INLINE or INLINABLE pragma
                       --   INLINE     if guidance is UnfWhen
                       --   INLINABLE  if guidance is UnfIfGoodArgs/UnfoldNever
                       -- (well, technically an INLINABLE might be made
                       -- UnfWhen if it was small enough, and then
                       -- it will behave like INLINE outside the current
                       -- module, but that is the way automatic unfoldings
                       -- work so it is consistent with the intended
                       -- meaning of INLINABLE).
                       --
                       -- uf_tmpl may change, but only as a result of
                       -- gentle simplification, it doesn't get updated
                       -- to the current RHS during compilation as with
                       -- InlineRhs.
                       --
                       -- See Note [InlineStable]

  | InlineCompulsory   -- Something that *has* no binding, so you *must* inline it
                       -- Only a few primop-like things have this property
                       -- (see "GHC.Types.Id.Make", calls to mkCompulsoryUnfolding).
                       -- Inline absolutely always, however boring the context.



-- | 'UnfoldingGuidance' says when unfolding should take place
data UnfoldingGuidance
  = UnfWhen {   -- Inline without thinking about the *size* of the uf_tmpl
                -- Used (a) for small *and* cheap unfoldings
                --      (b) for INLINE functions
                -- See Note [INLINE for small functions] in GHC.Core.Unfold
      ug_arity    :: Arity,     -- Number of value arguments expected

      ug_unsat_ok  :: Bool,     -- True <=> ok to inline even if unsaturated
      ug_boring_ok :: Bool      -- True <=> ok to inline even if the context is boring
                -- So True,True means "always"
    }

  | UnfIfGoodArgs {     -- Arose from a normal Id; the info here is the
                        -- result of a simple analysis of the RHS

      ug_args ::  [Int],  -- Discount if the argument is evaluated.
                          -- (i.e., a simplification will definitely
                          -- be possible).  One elt of the list per *value* arg.

      ug_size :: Int,     -- The "size" of the unfolding.

      ug_res :: Int       -- Scrutinee discount: the discount to subtract if the thing is in
    }                     -- a context (case (thing args) of ...),
                          -- (where there are the right number of arguments.)

  | UnfNever        -- The RHS is big, so don't inline it
  deriving (Eq)

{-
Note [Historical note: unfoldings for wrappers]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We used to have a nice clever scheme in interface files for
wrappers. A wrapper's unfolding can be reconstructed from its worker's
id and its strictness. This decreased .hi file size (sometimes
significantly, for modules like GHC.Classes with many high-arity w/w
splits) and had a slight corresponding effect on compile times.

However, when we added the second demand analysis, this scheme lead to
some Core lint errors. The second analysis could change the strictness
signatures, which sometimes resulted in a wrapper's regenerated
unfolding applying the wrapper to too many arguments.

Instead of repairing the clever .hi scheme, we abandoned it in favor
of simplicity. The .hi sizes are usually insignificant (excluding the
+1M for base libraries), and compile time barely increases (~+1% for
nofib). The nicer upshot is that the UnfoldingSource no longer mentions
an Id, so, eg, substitutions need not traverse them.


Note [DFun unfoldings]
~~~~~~~~~~~~~~~~~~~~~~
The Arity in a DFunUnfolding is total number of args (type and value)
that the DFun needs to produce a dictionary.  That's not necessarily
related to the ordinary arity of the dfun Id, esp if the class has
one method, so the dictionary is represented by a newtype.  Example

     class C a where { op :: a -> Int }
     instance C a -> C [a] where op xs = op (head xs)

The instance translates to

     $dfCList :: forall a. C a => C [a]  -- Arity 2!
     $dfCList = /\a.\d. $copList {a} d |> co

     $copList :: forall a. C a => [a] -> Int  -- Arity 2!
     $copList = /\a.\d.\xs. op {a} d (head xs)

Now we might encounter (op (dfCList {ty} d) a1 a2)
and we want the (op (dfList {ty} d)) rule to fire, because $dfCList
has all its arguments, even though its (value) arity is 2.  That's
why we record the number of expected arguments in the DFunUnfolding.

Note that although it's an Arity, it's most convenient for it to give
the *total* number of arguments, both type and value.  See the use
site in exprIsConApp_maybe.
-}

-- Constants for the UnfWhen constructor
needSaturated, unSaturatedOk :: Bool
needSaturated = False
unSaturatedOk = True

boringCxtNotOk, boringCxtOk :: Bool
boringCxtOk    = True
boringCxtNotOk = False

------------------------------------------------
noUnfolding :: Unfolding
-- ^ There is no known 'Unfolding'
evaldUnfolding :: Unfolding
-- ^ This unfolding marks the associated thing as being evaluated

noUnfolding    = NoUnfolding
evaldUnfolding = OtherCon []

-- | There is no known 'Unfolding', because this came from an
-- hi-boot file.
bootUnfolding :: Unfolding
bootUnfolding = BootUnfolding

mkOtherCon :: [AltCon] -> Unfolding
mkOtherCon = OtherCon

isStableSource :: UnfoldingSource -> Bool
-- Keep the unfolding template
isStableSource InlineCompulsory   = True
isStableSource InlineStable       = True
isStableSource InlineRhs          = False

-- | Retrieves the template of an unfolding: panics if none is known
unfoldingTemplate :: Unfolding -> CoreExpr
unfoldingTemplate = uf_tmpl

-- | Retrieves the template of an unfolding if possible
-- maybeUnfoldingTemplate is used mainly wnen specialising, and we do
-- want to specialise DFuns, so it's important to return a template
-- for DFunUnfoldings
maybeUnfoldingTemplate :: Unfolding -> Maybe CoreExpr
maybeUnfoldingTemplate (CoreUnfolding { uf_tmpl = expr })
  = Just expr
maybeUnfoldingTemplate (DFunUnfolding { df_bndrs = bndrs, df_con = con, df_args = args })
  = Just (mkLams bndrs (mkApps (Var (dataConWorkId con)) args))
maybeUnfoldingTemplate _
  = Nothing

-- | The constructors that the unfolding could never be:
-- returns @[]@ if no information is available
otherCons :: Unfolding -> [AltCon]
otherCons (OtherCon cons) = cons
otherCons _               = []

-- | Determines if it is certainly the case that the unfolding will
-- yield a value (something in HNF): returns @False@ if unsure
isValueUnfolding :: Unfolding -> Bool
        -- Returns False for OtherCon
isValueUnfolding (CoreUnfolding { uf_is_value = is_evald }) = is_evald
isValueUnfolding _                                          = False

-- | Determines if it possibly the case that the unfolding will
-- yield a value. Unlike 'isValueUnfolding' it returns @True@
-- for 'OtherCon'
isEvaldUnfolding :: Unfolding -> Bool
        -- Returns True for OtherCon
isEvaldUnfolding (OtherCon _)                               = True
isEvaldUnfolding (CoreUnfolding { uf_is_value = is_evald }) = is_evald
isEvaldUnfolding _                                          = False

-- | @True@ if the unfolding is a constructor application, the application
-- of a CONLIKE function or 'OtherCon'
isConLikeUnfolding :: Unfolding -> Bool
isConLikeUnfolding (OtherCon _)                             = True
isConLikeUnfolding (CoreUnfolding { uf_is_conlike = con })  = con
isConLikeUnfolding _                                        = False

-- | Is the thing we will unfold into certainly cheap?
isCheapUnfolding :: Unfolding -> Bool
isCheapUnfolding (CoreUnfolding { uf_is_work_free = is_wf }) = is_wf
isCheapUnfolding _                                           = False

isExpandableUnfolding :: Unfolding -> Bool
isExpandableUnfolding (CoreUnfolding { uf_expandable = is_expable }) = is_expable
isExpandableUnfolding _                                              = False

expandUnfolding_maybe :: Unfolding -> Maybe CoreExpr
-- Expand an expandable unfolding; this is used in rule matching
--   See Note [Expanding variables] in GHC.Core.Rules
-- The key point here is that CONLIKE things can be expanded
expandUnfolding_maybe (CoreUnfolding { uf_expandable = True, uf_tmpl = rhs }) = Just rhs
expandUnfolding_maybe _                                                       = Nothing

isCompulsoryUnfolding :: Unfolding -> Bool
isCompulsoryUnfolding (CoreUnfolding { uf_src = InlineCompulsory }) = True
isCompulsoryUnfolding _                                             = False

isStableUnfolding :: Unfolding -> Bool
-- True of unfoldings that should not be overwritten
-- by a CoreUnfolding for the RHS of a let-binding
isStableUnfolding (CoreUnfolding { uf_src = src }) = isStableSource src
isStableUnfolding (DFunUnfolding {})               = True
isStableUnfolding _                                = False

-- | Only returns False if there is no unfolding information available at all
hasSomeUnfolding :: Unfolding -> Bool
hasSomeUnfolding NoUnfolding   = False
hasSomeUnfolding BootUnfolding = False
hasSomeUnfolding _             = True

isBootUnfolding :: Unfolding -> Bool
isBootUnfolding BootUnfolding = True
isBootUnfolding _             = False

neverUnfoldGuidance :: UnfoldingGuidance -> Bool
neverUnfoldGuidance UnfNever = True
neverUnfoldGuidance _        = False

hasCoreUnfolding :: Unfolding -> Bool
-- An unfolding "has Core" if it contains a Core expression, which
-- may mention free variables. See Note [Fragile unfoldings]
hasCoreUnfolding (CoreUnfolding {}) = True
hasCoreUnfolding (DFunUnfolding {}) = True
hasCoreUnfolding _                  = False
  -- NoUnfolding, BootUnfolding, OtherCon have no Core

canUnfold :: Unfolding -> Bool
canUnfold (CoreUnfolding { uf_guidance = g }) = not (neverUnfoldGuidance g)
canUnfold _                                   = False

{- Note [Fragile unfoldings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
An unfolding is "fragile" if it mentions free variables (and hence would
need substitution) or might be affected by optimisation.  The non-fragile
ones are

   NoUnfolding, BootUnfolding

   OtherCon {}    If we know this binder (say a lambda binder) will be
                  bound to an evaluated thing, we want to retain that
                  info in simpleOptExpr; see #13077.

We consider even a StableUnfolding as fragile, because it needs substitution.

Note [InlineStable]
~~~~~~~~~~~~~~~~~
When you say
      {-# INLINE f #-}
      f x = <rhs>
you intend that calls (f e) are replaced by <rhs>[e/x] So we
should capture (\x.<rhs>) in the Unfolding of 'f', and never meddle
with it.  Meanwhile, we can optimise <rhs> to our heart's content,
leaving the original unfolding intact in Unfolding of 'f'. For example
        all xs = foldr (&&) True xs
        any p = all . map p  {-# INLINE any #-}
We optimise any's RHS fully, but leave the InlineRule saying "all . map p",
which deforests well at the call site.

So INLINE pragma gives rise to an InlineRule, which captures the original RHS.

Moreover, it's only used when 'f' is applied to the
specified number of arguments; that is, the number of argument on
the LHS of the '=' sign in the original source definition.
For example, (.) is now defined in the libraries like this
   {-# INLINE (.) #-}
   (.) f g = \x -> f (g x)
so that it'll inline when applied to two arguments. If 'x' appeared
on the left, thus
   (.) f g x = f (g x)
it'd only inline when applied to three arguments.  This slightly-experimental
change was requested by Roman, but it seems to make sense.

See also Note [Inlining an InlineRule] in GHC.Core.Unfold.


Note [OccInfo in unfoldings and rules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In unfoldings and rules, we guarantee that the template is occ-analysed,
so that the occurrence info on the binders is correct.  This is important,
because the Simplifier does not re-analyse the template when using it. If
the occurrence info is wrong
  - We may get more simplifier iterations than necessary, because
    once-occ info isn't there
  - More seriously, we may get an infinite loop if there's a Rec
    without a loop breaker marked


************************************************************************
*                                                                      *
                  AltCon
*                                                                      *
************************************************************************
-}

-- The Ord is needed for the FiniteMap used in the lookForConstructor
-- in GHC.Core.Opt.Simplify.Env.  If you declared that lookForConstructor
-- *ignores* constructor-applications with LitArg args, then you could get rid
-- of this Ord.

instance Outputable AltCon where
  ppr (DataAlt dc) = ppr dc
  ppr (LitAlt lit) = ppr lit
  ppr DEFAULT      = text "__DEFAULT"

cmpAlt :: (AltCon, a, b) -> (AltCon, a, b) -> Ordering
cmpAlt (con1, _, _) (con2, _, _) = con1 `cmpAltCon` con2

ltAlt :: (AltCon, a, b) -> (AltCon, a, b) -> Bool
ltAlt a1 a2 = (a1 `cmpAlt` a2) == LT

cmpAltCon :: AltCon -> AltCon -> Ordering
-- ^ Compares 'AltCon's within a single list of alternatives
-- DEFAULT comes out smallest, so that sorting by AltCon puts
-- alternatives in the order required: see Note [Case expression invariants]
cmpAltCon DEFAULT      DEFAULT     = EQ
cmpAltCon DEFAULT      _           = LT

cmpAltCon (DataAlt d1) (DataAlt d2) = dataConTag d1 `compare` dataConTag d2
cmpAltCon (DataAlt _)  DEFAULT      = GT
cmpAltCon (LitAlt  l1) (LitAlt  l2) = l1 `compare` l2
cmpAltCon (LitAlt _)   DEFAULT      = GT

cmpAltCon con1 con2 = WARN( True, text "Comparing incomparable AltCons" <+>
                                  ppr con1 <+> ppr con2 )
                      LT

{-
************************************************************************
*                                                                      *
\subsection{Useful synonyms}
*                                                                      *
************************************************************************

Note [CoreProgram]
~~~~~~~~~~~~~~~~~~
The top level bindings of a program, a CoreProgram, are represented as
a list of CoreBind

 * Later bindings in the list can refer to earlier ones, but not vice
   versa.  So this is OK
      NonRec { x = 4 }
      Rec { p = ...q...x...
          ; q = ...p...x }
      Rec { f = ...p..x..f.. }
      NonRec { g = ..f..q...x.. }
   But it would NOT be ok for 'f' to refer to 'g'.

 * The occurrence analyser does strongly-connected component analysis
   on each Rec binding, and splits it into a sequence of smaller
   bindings where possible.  So the program typically starts life as a
   single giant Rec, which is then dependency-analysed into smaller
   chunks.
-}

-- If you edit this type, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
type CoreProgram = [CoreBind]   -- See Note [CoreProgram]

-- | The common case for the type of binders and variables when
-- we are manipulating the Core language within GHC
type CoreBndr = Var
-- | Expressions where binders are 'CoreBndr's
type CoreExpr = Expr CoreBndr
-- | Argument expressions where binders are 'CoreBndr's
type CoreArg  = Arg  CoreBndr
-- | Binding groups where binders are 'CoreBndr's
type CoreBind = Bind CoreBndr
-- | Case alternatives where binders are 'CoreBndr's
type CoreAlt  = Alt  CoreBndr

{-
************************************************************************
*                                                                      *
\subsection{Tagging}
*                                                                      *
************************************************************************
-}

-- | Binders are /tagged/ with a t
data TaggedBndr t = TB CoreBndr t       -- TB for "tagged binder"

type TaggedBind t = Bind (TaggedBndr t)
type TaggedExpr t = Expr (TaggedBndr t)
type TaggedArg  t = Arg  (TaggedBndr t)
type TaggedAlt  t = Alt  (TaggedBndr t)

instance Outputable b => Outputable (TaggedBndr b) where
  ppr (TB b l) = char '<' <> ppr b <> comma <> ppr l <> char '>'

deTagExpr :: TaggedExpr t -> CoreExpr
deTagExpr (Var v)                   = Var v
deTagExpr (Lit l)                   = Lit l
deTagExpr (Type ty)                 = Type ty
deTagExpr (Coercion co)             = Coercion co
deTagExpr (App e1 e2)               = App (deTagExpr e1) (deTagExpr e2)
deTagExpr (Lam (TB b _) e)          = Lam b (deTagExpr e)
deTagExpr (Let bind body)           = Let (deTagBind bind) (deTagExpr body)
deTagExpr (Case e (TB b _) ty alts) = Case (deTagExpr e) b ty (map deTagAlt alts)
deTagExpr (Tick t e)                = Tick t (deTagExpr e)
deTagExpr (Cast e co)               = Cast (deTagExpr e) co

deTagBind :: TaggedBind t -> CoreBind
deTagBind (NonRec (TB b _) rhs) = NonRec b (deTagExpr rhs)
deTagBind (Rec prs)             = Rec [(b, deTagExpr rhs) | (TB b _, rhs) <- prs]

deTagAlt :: TaggedAlt t -> CoreAlt
deTagAlt (con, bndrs, rhs) = (con, [b | TB b _ <- bndrs], deTagExpr rhs)

{-
************************************************************************
*                                                                      *
\subsection{Core-constructing functions with checking}
*                                                                      *
************************************************************************
-}

-- | Apply a list of argument expressions to a function expression in a nested fashion. Prefer to
-- use 'GHC.Core.Make.mkCoreApps' if possible
mkApps    :: Expr b -> [Arg b]  -> Expr b
-- | Apply a list of type argument expressions to a function expression in a nested fashion
mkTyApps  :: Expr b -> [Type]   -> Expr b
-- | Apply a list of coercion argument expressions to a function expression in a nested fashion
mkCoApps  :: Expr b -> [Coercion] -> Expr b
-- | Apply a list of type or value variables to a function expression in a nested fashion
mkVarApps :: Expr b -> [Var] -> Expr b
-- | Apply a list of argument expressions to a data constructor in a nested fashion. Prefer to
-- use 'GHC.Core.Make.mkCoreConApps' if possible
mkConApp      :: DataCon -> [Arg b] -> Expr b

mkApps    f args = foldl' App                       f args
mkCoApps  f args = foldl' (\ e a -> App e (Coercion a)) f args
mkVarApps f vars = foldl' (\ e a -> App e (varToCoreExpr a)) f vars
mkConApp con args = mkApps (Var (dataConWorkId con)) args

mkTyApps  f args = foldl' (\ e a -> App e (mkTyArg a)) f args

mkConApp2 :: DataCon -> [Type] -> [Var] -> Expr b
mkConApp2 con tys arg_ids = Var (dataConWorkId con)
                            `mkApps` map Type tys
                            `mkApps` map varToCoreExpr arg_ids

mkTyArg :: Type -> Expr b
mkTyArg ty
  | Just co <- isCoercionTy_maybe ty = Coercion co
  | otherwise                        = Type ty

-- | Create a machine integer literal expression of type @Int#@ from an @Integer@.
-- If you want an expression of type @Int@ use 'GHC.Core.Make.mkIntExpr'
mkIntLit      :: Platform -> Integer -> Expr b
-- | Create a machine integer literal expression of type @Int#@ from an @Int@.
-- If you want an expression of type @Int@ use 'GHC.Core.Make.mkIntExpr'
mkIntLitInt   :: Platform -> Int     -> Expr b

mkIntLit    platform n = Lit (mkLitInt platform n)
mkIntLitInt platform n = Lit (mkLitInt platform (toInteger n))

-- | Create a machine word literal expression of type  @Word#@ from an @Integer@.
-- If you want an expression of type @Word@ use 'GHC.Core.Make.mkWordExpr'
mkWordLit     :: Platform -> Integer -> Expr b
-- | Create a machine word literal expression of type  @Word#@ from a @Word@.
-- If you want an expression of type @Word@ use 'GHC.Core.Make.mkWordExpr'
mkWordLitWord :: Platform -> Word -> Expr b

mkWordLit     platform w = Lit (mkLitWord platform w)
mkWordLitWord platform w = Lit (mkLitWord platform (toInteger w))

mkWord64LitWord64 :: Word64 -> Expr b
mkWord64LitWord64 w = Lit (mkLitWord64 (toInteger w))

mkInt64LitInt64 :: Int64 -> Expr b
mkInt64LitInt64 w = Lit (mkLitInt64 (toInteger w))

-- | Create a machine character literal expression of type @Char#@.
-- If you want an expression of type @Char@ use 'GHC.Core.Make.mkCharExpr'
mkCharLit :: Char -> Expr b
-- | Create a machine string literal expression of type @Addr#@.
-- If you want an expression of type @String@ use 'GHC.Core.Make.mkStringExpr'
mkStringLit :: String -> Expr b

mkCharLit   c = Lit (mkLitChar c)
mkStringLit s = Lit (mkLitString s)

-- | Create a machine single precision literal expression of type @Float#@ from a @Rational@.
-- If you want an expression of type @Float@ use 'GHC.Core.Make.mkFloatExpr'
mkFloatLit :: Rational -> Expr b
-- | Create a machine single precision literal expression of type @Float#@ from a @Float@.
-- If you want an expression of type @Float@ use 'GHC.Core.Make.mkFloatExpr'
mkFloatLitFloat :: Float -> Expr b

mkFloatLit      f = Lit (mkLitFloat f)
mkFloatLitFloat f = Lit (mkLitFloat (toRational f))

-- | Create a machine double precision literal expression of type @Double#@ from a @Rational@.
-- If you want an expression of type @Double@ use 'GHC.Core.Make.mkDoubleExpr'
mkDoubleLit :: Rational -> Expr b
-- | Create a machine double precision literal expression of type @Double#@ from a @Double@.
-- If you want an expression of type @Double@ use 'GHC.Core.Make.mkDoubleExpr'
mkDoubleLitDouble :: Double -> Expr b

mkDoubleLit       d = Lit (mkLitDouble d)
mkDoubleLitDouble d = Lit (mkLitDouble (toRational d))

-- | Bind all supplied binding groups over an expression in a nested let expression. Assumes
-- that the rhs satisfies the let/app invariant.  Prefer to use 'GHC.Core.Make.mkCoreLets' if
-- possible, which does guarantee the invariant
mkLets        :: [Bind b] -> Expr b -> Expr b
-- | Bind all supplied binders over an expression in a nested lambda expression. Prefer to
-- use 'GHC.Core.Make.mkCoreLams' if possible
mkLams        :: [b] -> Expr b -> Expr b

mkLams binders body = foldr Lam body binders
mkLets binds body   = foldr mkLet body binds

mkLet :: Bind b -> Expr b -> Expr b
-- The desugarer sometimes generates an empty Rec group
-- which Lint rejects, so we kill it off right away
mkLet (Rec []) body = body
mkLet bind     body = Let bind body

-- | @mkLetNonRec bndr rhs body@ wraps @body@ in a @let@ binding @bndr@.
mkLetNonRec :: b -> Expr b -> Expr b -> Expr b
mkLetNonRec b rhs body = Let (NonRec b rhs) body

-- | @mkLetRec binds body@ wraps @body@ in a @let rec@ with the given set of
-- @binds@ if binds is non-empty.
mkLetRec :: [(b, Expr b)] -> Expr b -> Expr b
mkLetRec [] body = body
mkLetRec bs body = Let (Rec bs) body

-- | Create a binding group where a type variable is bound to a type. Per "GHC.Core#type_let",
-- this can only be used to bind something in a non-recursive @let@ expression
mkTyBind :: TyVar -> Type -> CoreBind
mkTyBind tv ty      = NonRec tv (Type ty)

-- | Create a binding group where a type variable is bound to a type. Per "GHC.Core#type_let",
-- this can only be used to bind something in a non-recursive @let@ expression
mkCoBind :: CoVar -> Coercion -> CoreBind
mkCoBind cv co      = NonRec cv (Coercion co)

-- | Convert a binder into either a 'Var' or 'Type' 'Expr' appropriately
varToCoreExpr :: CoreBndr -> Expr b
varToCoreExpr v | isTyVar v = Type (mkTyVarTy v)
                | isCoVar v = Coercion (mkCoVarCo v)
                | otherwise = ASSERT( isId v ) Var v

varsToCoreExprs :: [CoreBndr] -> [Expr b]
varsToCoreExprs vs = map varToCoreExpr vs

{-
************************************************************************
*                                                                      *
   Getting a result type
*                                                                      *
************************************************************************

These are defined here to avoid a module loop between GHC.Core.Utils and GHC.Core.FVs

-}

applyTypeToArg :: Type -> CoreExpr -> Type
-- ^ Determines the type resulting from applying an expression with given type
-- to a given argument expression
applyTypeToArg fun_ty arg = piResultTy fun_ty (exprToType arg)

-- | If the expression is a 'Type', converts. Otherwise,
-- panics. NB: This does /not/ convert 'Coercion' to 'CoercionTy'.
exprToType :: CoreExpr -> Type
exprToType (Type ty)     = ty
exprToType _bad          = pprPanic "exprToType" empty

-- | If the expression is a 'Coercion', converts.
exprToCoercion_maybe :: CoreExpr -> Maybe Coercion
exprToCoercion_maybe (Coercion co) = Just co
exprToCoercion_maybe _             = Nothing

{-
************************************************************************
*                                                                      *
\subsection{Simple access functions}
*                                                                      *
************************************************************************
-}

-- | Extract every variable by this group
bindersOf  :: Bind b -> [b]
-- If you edit this function, you may need to update the GHC formalism
-- See Note [GHC Formalism] in GHC.Core.Lint
bindersOf (NonRec binder _) = [binder]
bindersOf (Rec pairs)       = [binder | (binder, _) <- pairs]

-- | 'bindersOf' applied to a list of binding groups
bindersOfBinds :: [Bind b] -> [b]
bindersOfBinds binds = foldr ((++) . bindersOf) [] binds

rhssOfBind :: Bind b -> [Expr b]
rhssOfBind (NonRec _ rhs) = [rhs]
rhssOfBind (Rec pairs)    = [rhs | (_,rhs) <- pairs]

rhssOfAlts :: [Alt b] -> [Expr b]
rhssOfAlts alts = [e | (_,_,e) <- alts]

-- | Collapse all the bindings in the supplied groups into a single
-- list of lhs\/rhs pairs suitable for binding in a 'Rec' binding group
flattenBinds :: [Bind b] -> [(b, Expr b)]
flattenBinds (NonRec b r : binds) = (b,r) : flattenBinds binds
flattenBinds (Rec prs1   : binds) = prs1 ++ flattenBinds binds
flattenBinds []                   = []

-- | We often want to strip off leading lambdas before getting down to
-- business. Variants are 'collectTyBinders', 'collectValBinders',
-- and 'collectTyAndValBinders'
collectBinders         :: Expr b   -> ([b],     Expr b)
collectTyBinders       :: CoreExpr -> ([TyVar], CoreExpr)
collectValBinders      :: CoreExpr -> ([Id],    CoreExpr)
collectTyAndValBinders :: CoreExpr -> ([TyVar], [Id], CoreExpr)
-- | Strip off exactly N leading lambdas (type or value). Good for use with
-- join points.
collectNBinders        :: Int -> Expr b -> ([b], Expr b)

collectBinders expr
  = go [] expr
  where
    go bs (Lam b e) = go (b:bs) e
    go bs e          = (reverse bs, e)

collectTyBinders expr
  = go [] expr
  where
    go tvs (Lam b e) | isTyVar b = go (b:tvs) e
    go tvs e                     = (reverse tvs, e)

collectValBinders expr
  = go [] expr
  where
    go ids (Lam b e) | isId b = go (b:ids) e
    go ids body               = (reverse ids, body)

collectTyAndValBinders expr
  = (tvs, ids, body)
  where
    (tvs, body1) = collectTyBinders expr
    (ids, body)  = collectValBinders body1

collectNBinders orig_n orig_expr
  = go orig_n [] orig_expr
  where
    go 0 bs expr      = (reverse bs, expr)
    go n bs (Lam b e) = go (n-1) (b:bs) e
    go _ _  _         = pprPanic "collectNBinders" $ int orig_n

-- | Takes a nested application expression and returns the function
-- being applied and the arguments to which it is applied
collectArgs :: Expr b -> (Expr b, [Arg b])
collectArgs expr
  = go expr []
  where
    go (App f a) as = go f (a:as)
    go e         as = (e, as)

-- | Attempt to remove the last N arguments of a function call.
-- Strip off any ticks or coercions encountered along the way and any
-- at the end.
stripNArgs :: Word -> Expr a -> Maybe (Expr a)
stripNArgs !n (Tick _ e) = stripNArgs n e
stripNArgs n (Cast f _) = stripNArgs n f
stripNArgs 0 e = Just e
stripNArgs n (App f _) = stripNArgs (n - 1) f
stripNArgs _ _ = Nothing

-- | Like @collectArgs@, but also collects looks through floatable
-- ticks if it means that we can find more arguments.
collectArgsTicks :: (Tickish Id -> Bool) -> Expr b
                 -> (Expr b, [Arg b], [Tickish Id])
collectArgsTicks skipTick expr
  = go expr [] []
  where
    go (App f a)  as ts = go f (a:as) ts
    go (Tick t e) as ts
      | skipTick t      = go e as (t:ts)
    go e          as ts = (e, as, reverse ts)


{-
************************************************************************
*                                                                      *
\subsection{Predicates}
*                                                                      *
************************************************************************

At one time we optionally carried type arguments through to runtime.
@isRuntimeVar v@ returns if (Lam v _) really becomes a lambda at runtime,
i.e. if type applications are actual lambdas because types are kept around
at runtime.  Similarly isRuntimeArg.
-}

-- | Will this variable exist at runtime?
isRuntimeVar :: Var -> Bool
isRuntimeVar = isId

-- | Will this argument expression exist at runtime?
isRuntimeArg :: CoreExpr -> Bool
isRuntimeArg = isValArg

-- | Returns @True@ for value arguments, false for type args
-- NB: coercions are value arguments (zero width, to be sure,
-- like State#, but still value args).
isValArg :: Expr b -> Bool
isValArg e = not (isTypeArg e)

-- | Returns @True@ iff the expression is a 'Type' or 'Coercion'
-- expression at its top level
isTyCoArg :: Expr b -> Bool
isTyCoArg (Type {})     = True
isTyCoArg (Coercion {}) = True
isTyCoArg _             = False

-- | Returns @True@ iff the expression is a 'Coercion'
-- expression at its top level
isCoArg :: Expr b -> Bool
isCoArg (Coercion {}) = True
isCoArg _             = False

-- | Returns @True@ iff the expression is a 'Type' expression at its
-- top level.  Note this does NOT include 'Coercion's.
isTypeArg :: Expr b -> Bool
isTypeArg (Type {}) = True
isTypeArg _         = False

-- | The number of binders that bind values rather than types
valBndrCount :: [CoreBndr] -> Int
valBndrCount = count isId

-- | The number of argument expressions that are values rather than types at their top level
valArgCount :: [Arg b] -> Int
valArgCount = count isValArg

{-
************************************************************************
*                                                                      *
\subsection{Annotated core}
*                                                                      *
************************************************************************
-}

-- | Annotated core: allows annotation at every node in the tree
type AnnExpr bndr annot = (annot, AnnExpr' bndr annot)

-- | A clone of the 'Expr' type but allowing annotation at every tree node
data AnnExpr' bndr annot
  = AnnVar      Id
  | AnnLit      Literal
  | AnnLam      bndr (AnnExpr bndr annot)
  | AnnApp      (AnnExpr bndr annot) (AnnExpr bndr annot)
  | AnnCase     (AnnExpr bndr annot) bndr Type [AnnAlt bndr annot]
  | AnnLet      (AnnBind bndr annot) (AnnExpr bndr annot)
  | AnnCast     (AnnExpr bndr annot) (annot, Coercion)
                   -- Put an annotation on the (root of) the coercion
  | AnnTick     (Tickish Id) (AnnExpr bndr annot)
  | AnnType     Type
  | AnnCoercion Coercion

-- | A clone of the 'Alt' type but allowing annotation at every tree node
type AnnAlt bndr annot = (AltCon, [bndr], AnnExpr bndr annot)

-- | A clone of the 'Bind' type but allowing annotation at every tree node
data AnnBind bndr annot
  = AnnNonRec bndr (AnnExpr bndr annot)
  | AnnRec    [(bndr, AnnExpr bndr annot)]

-- | Takes a nested application expression and returns the function
-- being applied and the arguments to which it is applied
collectAnnArgs :: AnnExpr b a -> (AnnExpr b a, [AnnExpr b a])
collectAnnArgs expr
  = go expr []
  where
    go (_, AnnApp f a) as = go f (a:as)
    go e               as = (e, as)

collectAnnArgsTicks :: (Tickish Var -> Bool) -> AnnExpr b a
                       -> (AnnExpr b a, [AnnExpr b a], [Tickish Var])
collectAnnArgsTicks tickishOk expr
  = go expr [] []
  where
    go (_, AnnApp f a)  as ts = go f (a:as) ts
    go (_, AnnTick t e) as ts | tickishOk t
                              = go e as (t:ts)
    go e                as ts = (e, as, reverse ts)

deAnnotate :: AnnExpr bndr annot -> Expr bndr
deAnnotate (_, e) = deAnnotate' e

deAnnotate' :: AnnExpr' bndr annot -> Expr bndr
deAnnotate' (AnnType t)           = Type t
deAnnotate' (AnnCoercion co)      = Coercion co
deAnnotate' (AnnVar  v)           = Var v
deAnnotate' (AnnLit  lit)         = Lit lit
deAnnotate' (AnnLam  binder body) = Lam binder (deAnnotate body)
deAnnotate' (AnnApp  fun arg)     = App (deAnnotate fun) (deAnnotate arg)
deAnnotate' (AnnCast e (_,co))    = Cast (deAnnotate e) co
deAnnotate' (AnnTick tick body)   = Tick tick (deAnnotate body)

deAnnotate' (AnnLet bind body)
  = Let (deAnnBind bind) (deAnnotate body)
deAnnotate' (AnnCase scrut v t alts)
  = Case (deAnnotate scrut) v t (map deAnnAlt alts)

deAnnAlt :: AnnAlt bndr annot -> Alt bndr
deAnnAlt (con,args,rhs) = (con,args,deAnnotate rhs)

deAnnBind  :: AnnBind b annot -> Bind b
deAnnBind (AnnNonRec var rhs) = NonRec var (deAnnotate rhs)
deAnnBind (AnnRec pairs) = Rec [(v,deAnnotate rhs) | (v,rhs) <- pairs]

-- | As 'collectBinders' but for 'AnnExpr' rather than 'Expr'
collectAnnBndrs :: AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
collectAnnBndrs e
  = collect [] e
  where
    collect bs (_, AnnLam b body) = collect (b:bs) body
    collect bs body               = (reverse bs, body)

-- | As 'collectNBinders' but for 'AnnExpr' rather than 'Expr'
collectNAnnBndrs :: Int -> AnnExpr bndr annot -> ([bndr], AnnExpr bndr annot)
collectNAnnBndrs orig_n e
  = collect orig_n [] e
  where
    collect 0 bs body               = (reverse bs, body)
    collect n bs (_, AnnLam b body) = collect (n-1) (b:bs) body
    collect _ _  _                  = pprPanic "collectNBinders" $ int orig_n