rustc_codegen_ssa/back/
write.rs

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
use std::any::Any;
use std::assert_matches::assert_matches;
use std::marker::PhantomData;
use std::path::{Path, PathBuf};
use std::sync::Arc;
use std::sync::mpsc::{Receiver, Sender, channel};
use std::{fs, io, mem, str, thread};

use rustc_ast::attr;
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_data_structures::jobserver::{self, Acquired};
use rustc_data_structures::memmap::Mmap;
use rustc_data_structures::profiling::{SelfProfilerRef, VerboseTimingGuard};
use rustc_errors::emitter::Emitter;
use rustc_errors::translation::Translate;
use rustc_errors::{
    Diag, DiagArgMap, DiagCtxt, DiagMessage, ErrCode, FatalError, FluentBundle, Level, MultiSpan,
    Style, Suggestions,
};
use rustc_fs_util::link_or_copy;
use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
use rustc_incremental::{
    copy_cgu_workproduct_to_incr_comp_cache_dir, in_incr_comp_dir, in_incr_comp_dir_sess,
};
use rustc_metadata::EncodedMetadata;
use rustc_metadata::fs::copy_to_stdout;
use rustc_middle::bug;
use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
use rustc_middle::middle::exported_symbols::SymbolExportInfo;
use rustc_middle::ty::TyCtxt;
use rustc_session::Session;
use rustc_session::config::{
    self, CrateType, Lto, OutFileName, OutputFilenames, OutputType, Passes, SwitchWithOptPath,
};
use rustc_span::source_map::SourceMap;
use rustc_span::{FileName, InnerSpan, Span, SpanData, sym};
use rustc_target::spec::{MergeFunctions, SanitizerSet};
use tracing::debug;

use super::link::{self, ensure_removed};
use super::lto::{self, SerializedModule};
use super::symbol_export::symbol_name_for_instance_in_crate;
use crate::errors::ErrorCreatingRemarkDir;
use crate::traits::*;
use crate::{
    CachedModuleCodegen, CodegenResults, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind,
    errors,
};

const PRE_LTO_BC_EXT: &str = "pre-lto.bc";

/// What kind of object file to emit.
#[derive(Clone, Copy, PartialEq)]
pub enum EmitObj {
    // No object file.
    None,

    // Just uncompressed llvm bitcode. Provides easy compatibility with
    // emscripten's ecc compiler, when used as the linker.
    Bitcode,

    // Object code, possibly augmented with a bitcode section.
    ObjectCode(BitcodeSection),
}

/// What kind of llvm bitcode section to embed in an object file.
#[derive(Clone, Copy, PartialEq)]
pub enum BitcodeSection {
    // No bitcode section.
    None,

    // A full, uncompressed bitcode section.
    Full,
}

/// Module-specific configuration for `optimize_and_codegen`.
pub struct ModuleConfig {
    /// Names of additional optimization passes to run.
    pub passes: Vec<String>,
    /// Some(level) to optimize at a certain level, or None to run
    /// absolutely no optimizations (used for the metadata module).
    pub opt_level: Option<config::OptLevel>,

    /// Some(level) to optimize binary size, or None to not affect program size.
    pub opt_size: Option<config::OptLevel>,

    pub pgo_gen: SwitchWithOptPath,
    pub pgo_use: Option<PathBuf>,
    pub pgo_sample_use: Option<PathBuf>,
    pub debug_info_for_profiling: bool,
    pub instrument_coverage: bool,

    pub sanitizer: SanitizerSet,
    pub sanitizer_recover: SanitizerSet,
    pub sanitizer_dataflow_abilist: Vec<String>,
    pub sanitizer_memory_track_origins: usize,

    // Flags indicating which outputs to produce.
    pub emit_pre_lto_bc: bool,
    pub emit_no_opt_bc: bool,
    pub emit_bc: bool,
    pub emit_ir: bool,
    pub emit_asm: bool,
    pub emit_obj: EmitObj,
    pub emit_thin_lto: bool,
    pub emit_thin_lto_summary: bool,
    pub bc_cmdline: String,

    // Miscellaneous flags. These are mostly copied from command-line
    // options.
    pub verify_llvm_ir: bool,
    pub lint_llvm_ir: bool,
    pub no_prepopulate_passes: bool,
    pub no_builtins: bool,
    pub time_module: bool,
    pub vectorize_loop: bool,
    pub vectorize_slp: bool,
    pub merge_functions: bool,
    pub emit_lifetime_markers: bool,
    pub llvm_plugins: Vec<String>,
}

impl ModuleConfig {
    fn new(kind: ModuleKind, tcx: TyCtxt<'_>, no_builtins: bool) -> ModuleConfig {
        // If it's a regular module, use `$regular`, otherwise use `$other`.
        // `$regular` and `$other` are evaluated lazily.
        macro_rules! if_regular {
            ($regular: expr, $other: expr) => {
                if let ModuleKind::Regular = kind { $regular } else { $other }
            };
        }

        let sess = tcx.sess;
        let opt_level_and_size = if_regular!(Some(sess.opts.optimize), None);

        let save_temps = sess.opts.cg.save_temps;

        let should_emit_obj = sess.opts.output_types.contains_key(&OutputType::Exe)
            || match kind {
                ModuleKind::Regular => sess.opts.output_types.contains_key(&OutputType::Object),
                ModuleKind::Allocator => false,
                ModuleKind::Metadata => sess.opts.output_types.contains_key(&OutputType::Metadata),
            };

        let emit_obj = if !should_emit_obj {
            EmitObj::None
        } else if sess.target.obj_is_bitcode
            || (sess.opts.cg.linker_plugin_lto.enabled() && !no_builtins)
        {
            // This case is selected if the target uses objects as bitcode, or
            // if linker plugin LTO is enabled. In the linker plugin LTO case
            // the assumption is that the final link-step will read the bitcode
            // and convert it to object code. This may be done by either the
            // native linker or rustc itself.
            //
            // Note, however, that the linker-plugin-lto requested here is
            // explicitly ignored for `#![no_builtins]` crates. These crates are
            // specifically ignored by rustc's LTO passes and wouldn't work if
            // loaded into the linker. These crates define symbols that LLVM
            // lowers intrinsics to, and these symbol dependencies aren't known
            // until after codegen. As a result any crate marked
            // `#![no_builtins]` is assumed to not participate in LTO and
            // instead goes on to generate object code.
            EmitObj::Bitcode
        } else if need_bitcode_in_object(tcx) {
            EmitObj::ObjectCode(BitcodeSection::Full)
        } else {
            EmitObj::ObjectCode(BitcodeSection::None)
        };

        ModuleConfig {
            passes: if_regular!(sess.opts.cg.passes.clone(), vec![]),

            opt_level: opt_level_and_size,
            opt_size: opt_level_and_size,

            pgo_gen: if_regular!(
                sess.opts.cg.profile_generate.clone(),
                SwitchWithOptPath::Disabled
            ),
            pgo_use: if_regular!(sess.opts.cg.profile_use.clone(), None),
            pgo_sample_use: if_regular!(sess.opts.unstable_opts.profile_sample_use.clone(), None),
            debug_info_for_profiling: sess.opts.unstable_opts.debug_info_for_profiling,
            instrument_coverage: if_regular!(sess.instrument_coverage(), false),

            sanitizer: if_regular!(sess.opts.unstable_opts.sanitizer, SanitizerSet::empty()),
            sanitizer_dataflow_abilist: if_regular!(
                sess.opts.unstable_opts.sanitizer_dataflow_abilist.clone(),
                Vec::new()
            ),
            sanitizer_recover: if_regular!(
                sess.opts.unstable_opts.sanitizer_recover,
                SanitizerSet::empty()
            ),
            sanitizer_memory_track_origins: if_regular!(
                sess.opts.unstable_opts.sanitizer_memory_track_origins,
                0
            ),

            emit_pre_lto_bc: if_regular!(
                save_temps || need_pre_lto_bitcode_for_incr_comp(sess),
                false
            ),
            emit_no_opt_bc: if_regular!(save_temps, false),
            emit_bc: if_regular!(
                save_temps || sess.opts.output_types.contains_key(&OutputType::Bitcode),
                save_temps
            ),
            emit_ir: if_regular!(
                sess.opts.output_types.contains_key(&OutputType::LlvmAssembly),
                false
            ),
            emit_asm: if_regular!(
                sess.opts.output_types.contains_key(&OutputType::Assembly),
                false
            ),
            emit_obj,
            emit_thin_lto: sess.opts.unstable_opts.emit_thin_lto,
            emit_thin_lto_summary: if_regular!(
                sess.opts.output_types.contains_key(&OutputType::ThinLinkBitcode),
                false
            ),
            bc_cmdline: sess.target.bitcode_llvm_cmdline.to_string(),

            verify_llvm_ir: sess.verify_llvm_ir(),
            lint_llvm_ir: sess.opts.unstable_opts.lint_llvm_ir,
            no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes,
            no_builtins: no_builtins || sess.target.no_builtins,

            // Exclude metadata and allocator modules from time_passes output,
            // since they throw off the "LLVM passes" measurement.
            time_module: if_regular!(true, false),

            // Copy what clang does by turning on loop vectorization at O2 and
            // slp vectorization at O3.
            vectorize_loop: !sess.opts.cg.no_vectorize_loops
                && (sess.opts.optimize == config::OptLevel::Default
                    || sess.opts.optimize == config::OptLevel::Aggressive),
            vectorize_slp: !sess.opts.cg.no_vectorize_slp
                && sess.opts.optimize == config::OptLevel::Aggressive,

            // Some targets (namely, NVPTX) interact badly with the
            // MergeFunctions pass. This is because MergeFunctions can generate
            // new function calls which may interfere with the target calling
            // convention; e.g. for the NVPTX target, PTX kernels should not
            // call other PTX kernels. MergeFunctions can also be configured to
            // generate aliases instead, but aliases are not supported by some
            // backends (again, NVPTX). Therefore, allow targets to opt out of
            // the MergeFunctions pass, but otherwise keep the pass enabled (at
            // O2 and O3) since it can be useful for reducing code size.
            merge_functions: match sess
                .opts
                .unstable_opts
                .merge_functions
                .unwrap_or(sess.target.merge_functions)
            {
                MergeFunctions::Disabled => false,
                MergeFunctions::Trampolines | MergeFunctions::Aliases => {
                    use config::OptLevel::*;
                    match sess.opts.optimize {
                        Aggressive | Default | SizeMin | Size => true,
                        Less | No => false,
                    }
                }
            },

            emit_lifetime_markers: sess.emit_lifetime_markers(),
            llvm_plugins: if_regular!(sess.opts.unstable_opts.llvm_plugins.clone(), vec![]),
        }
    }

    pub fn bitcode_needed(&self) -> bool {
        self.emit_bc
            || self.emit_thin_lto_summary
            || self.emit_obj == EmitObj::Bitcode
            || self.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full)
    }
}

/// Configuration passed to the function returned by the `target_machine_factory`.
pub struct TargetMachineFactoryConfig {
    /// Split DWARF is enabled in LLVM by checking that `TM.MCOptions.SplitDwarfFile` isn't empty,
    /// so the path to the dwarf object has to be provided when we create the target machine.
    /// This can be ignored by backends which do not need it for their Split DWARF support.
    pub split_dwarf_file: Option<PathBuf>,

    /// The name of the output object file. Used for setting OutputFilenames in target options
    /// so that LLVM can emit the CodeView S_OBJNAME record in pdb files
    pub output_obj_file: Option<PathBuf>,
}

impl TargetMachineFactoryConfig {
    pub fn new(
        cgcx: &CodegenContext<impl WriteBackendMethods>,
        module_name: &str,
    ) -> TargetMachineFactoryConfig {
        let split_dwarf_file = if cgcx.target_can_use_split_dwarf {
            cgcx.output_filenames.split_dwarf_path(
                cgcx.split_debuginfo,
                cgcx.split_dwarf_kind,
                Some(module_name),
            )
        } else {
            None
        };

        let output_obj_file =
            Some(cgcx.output_filenames.temp_path(OutputType::Object, Some(module_name)));
        TargetMachineFactoryConfig { split_dwarf_file, output_obj_file }
    }
}

pub type TargetMachineFactoryFn<B> = Arc<
    dyn Fn(
            TargetMachineFactoryConfig,
        ) -> Result<
            <B as WriteBackendMethods>::TargetMachine,
            <B as WriteBackendMethods>::TargetMachineError,
        > + Send
        + Sync,
>;

type ExportedSymbols = FxHashMap<CrateNum, Arc<Vec<(String, SymbolExportInfo)>>>;

/// Additional resources used by optimize_and_codegen (not module specific)
#[derive(Clone)]
pub struct CodegenContext<B: WriteBackendMethods> {
    // Resources needed when running LTO
    pub prof: SelfProfilerRef,
    pub lto: Lto,
    pub save_temps: bool,
    pub fewer_names: bool,
    pub time_trace: bool,
    pub exported_symbols: Option<Arc<ExportedSymbols>>,
    pub opts: Arc<config::Options>,
    pub crate_types: Vec<CrateType>,
    pub each_linked_rlib_for_lto: Vec<(CrateNum, PathBuf)>,
    pub output_filenames: Arc<OutputFilenames>,
    pub regular_module_config: Arc<ModuleConfig>,
    pub metadata_module_config: Arc<ModuleConfig>,
    pub allocator_module_config: Arc<ModuleConfig>,
    pub tm_factory: TargetMachineFactoryFn<B>,
    pub msvc_imps_needed: bool,
    pub is_pe_coff: bool,
    pub target_can_use_split_dwarf: bool,
    pub target_arch: String,
    pub target_is_like_osx: bool,
    pub target_is_like_aix: bool,
    pub split_debuginfo: rustc_target::spec::SplitDebuginfo,
    pub split_dwarf_kind: rustc_session::config::SplitDwarfKind,

    /// All commandline args used to invoke the compiler, with @file args fully expanded.
    /// This will only be used within debug info, e.g. in the pdb file on windows
    /// This is mainly useful for other tools that reads that debuginfo to figure out
    /// how to call the compiler with the same arguments.
    pub expanded_args: Vec<String>,

    /// Emitter to use for diagnostics produced during codegen.
    pub diag_emitter: SharedEmitter,
    /// LLVM optimizations for which we want to print remarks.
    pub remark: Passes,
    /// Directory into which should the LLVM optimization remarks be written.
    /// If `None`, they will be written to stderr.
    pub remark_dir: Option<PathBuf>,
    /// The incremental compilation session directory, or None if we are not
    /// compiling incrementally
    pub incr_comp_session_dir: Option<PathBuf>,
    /// Channel back to the main control thread to send messages to
    pub coordinator_send: Sender<Box<dyn Any + Send>>,
    /// `true` if the codegen should be run in parallel.
    ///
    /// Depends on [`CodegenBackend::supports_parallel()`] and `-Zno_parallel_backend`.
    pub parallel: bool,
}

impl<B: WriteBackendMethods> CodegenContext<B> {
    pub fn create_dcx(&self) -> DiagCtxt {
        DiagCtxt::new(Box::new(self.diag_emitter.clone()))
    }

    pub fn config(&self, kind: ModuleKind) -> &ModuleConfig {
        match kind {
            ModuleKind::Regular => &self.regular_module_config,
            ModuleKind::Metadata => &self.metadata_module_config,
            ModuleKind::Allocator => &self.allocator_module_config,
        }
    }
}

fn generate_lto_work<B: ExtraBackendMethods>(
    cgcx: &CodegenContext<B>,
    needs_fat_lto: Vec<FatLtoInput<B>>,
    needs_thin_lto: Vec<(String, B::ThinBuffer)>,
    import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
) -> Vec<(WorkItem<B>, u64)> {
    let _prof_timer = cgcx.prof.generic_activity("codegen_generate_lto_work");

    if !needs_fat_lto.is_empty() {
        assert!(needs_thin_lto.is_empty());
        let module =
            B::run_fat_lto(cgcx, needs_fat_lto, import_only_modules).unwrap_or_else(|e| e.raise());
        // We are adding a single work item, so the cost doesn't matter.
        vec![(WorkItem::LTO(module), 0)]
    } else {
        assert!(needs_fat_lto.is_empty());
        let (lto_modules, copy_jobs) = B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules)
            .unwrap_or_else(|e| e.raise());
        lto_modules
            .into_iter()
            .map(|module| {
                let cost = module.cost();
                (WorkItem::LTO(module), cost)
            })
            .chain(copy_jobs.into_iter().map(|wp| {
                (
                    WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen {
                        name: wp.cgu_name.clone(),
                        source: wp,
                    }),
                    0, // copying is very cheap
                )
            }))
            .collect()
    }
}

struct CompiledModules {
    modules: Vec<CompiledModule>,
    allocator_module: Option<CompiledModule>,
}

fn need_bitcode_in_object(tcx: TyCtxt<'_>) -> bool {
    let sess = tcx.sess;
    sess.opts.cg.embed_bitcode
        && tcx.crate_types().contains(&CrateType::Rlib)
        && sess.opts.output_types.contains_key(&OutputType::Exe)
}

fn need_pre_lto_bitcode_for_incr_comp(sess: &Session) -> bool {
    if sess.opts.incremental.is_none() {
        return false;
    }

    match sess.lto() {
        Lto::No => false,
        Lto::Fat | Lto::Thin | Lto::ThinLocal => true,
    }
}

pub(crate) fn start_async_codegen<B: ExtraBackendMethods>(
    backend: B,
    tcx: TyCtxt<'_>,
    target_cpu: String,
    metadata: EncodedMetadata,
    metadata_module: Option<CompiledModule>,
) -> OngoingCodegen<B> {
    let (coordinator_send, coordinator_receive) = channel();

    let crate_attrs = tcx.hir().attrs(rustc_hir::CRATE_HIR_ID);
    let no_builtins = attr::contains_name(crate_attrs, sym::no_builtins);

    let crate_info = CrateInfo::new(tcx, target_cpu);

    let regular_config = ModuleConfig::new(ModuleKind::Regular, tcx, no_builtins);
    let metadata_config = ModuleConfig::new(ModuleKind::Metadata, tcx, no_builtins);
    let allocator_config = ModuleConfig::new(ModuleKind::Allocator, tcx, no_builtins);

    let (shared_emitter, shared_emitter_main) = SharedEmitter::new();
    let (codegen_worker_send, codegen_worker_receive) = channel();

    let coordinator_thread = start_executing_work(
        backend.clone(),
        tcx,
        &crate_info,
        shared_emitter,
        codegen_worker_send,
        coordinator_receive,
        Arc::new(regular_config),
        Arc::new(metadata_config),
        Arc::new(allocator_config),
        coordinator_send.clone(),
    );

    OngoingCodegen {
        backend,
        metadata,
        metadata_module,
        crate_info,

        codegen_worker_receive,
        shared_emitter_main,
        coordinator: Coordinator {
            sender: coordinator_send,
            future: Some(coordinator_thread),
            phantom: PhantomData,
        },
        output_filenames: Arc::clone(tcx.output_filenames(())),
    }
}

fn copy_all_cgu_workproducts_to_incr_comp_cache_dir(
    sess: &Session,
    compiled_modules: &CompiledModules,
) -> FxIndexMap<WorkProductId, WorkProduct> {
    let mut work_products = FxIndexMap::default();

    if sess.opts.incremental.is_none() {
        return work_products;
    }

    let _timer = sess.timer("copy_all_cgu_workproducts_to_incr_comp_cache_dir");

    for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) {
        let mut files = Vec::new();
        if let Some(object_file_path) = &module.object {
            files.push((OutputType::Object.extension(), object_file_path.as_path()));
        }
        if let Some(dwarf_object_file_path) = &module.dwarf_object {
            files.push(("dwo", dwarf_object_file_path.as_path()));
        }
        if let Some(path) = &module.assembly {
            files.push((OutputType::Assembly.extension(), path.as_path()));
        }
        if let Some(path) = &module.llvm_ir {
            files.push((OutputType::LlvmAssembly.extension(), path.as_path()));
        }
        if let Some(path) = &module.bytecode {
            files.push((OutputType::Bitcode.extension(), path.as_path()));
        }
        if let Some((id, product)) =
            copy_cgu_workproduct_to_incr_comp_cache_dir(sess, &module.name, files.as_slice())
        {
            work_products.insert(id, product);
        }
    }

    work_products
}

fn produce_final_output_artifacts(
    sess: &Session,
    compiled_modules: &CompiledModules,
    crate_output: &OutputFilenames,
) {
    let mut user_wants_bitcode = false;
    let mut user_wants_objects = false;

    // Produce final compile outputs.
    let copy_gracefully = |from: &Path, to: &OutFileName| match to {
        OutFileName::Stdout => {
            if let Err(e) = copy_to_stdout(from) {
                sess.dcx().emit_err(errors::CopyPath::new(from, to.as_path(), e));
            }
        }
        OutFileName::Real(path) => {
            if let Err(e) = fs::copy(from, path) {
                sess.dcx().emit_err(errors::CopyPath::new(from, path, e));
            }
        }
    };

    let copy_if_one_unit = |output_type: OutputType, keep_numbered: bool| {
        if compiled_modules.modules.len() == 1 {
            // 1) Only one codegen unit. In this case it's no difficulty
            //    to copy `foo.0.x` to `foo.x`.
            let module_name = Some(&compiled_modules.modules[0].name[..]);
            let path = crate_output.temp_path(output_type, module_name);
            let output = crate_output.path(output_type);
            if !output_type.is_text_output() && output.is_tty() {
                sess.dcx()
                    .emit_err(errors::BinaryOutputToTty { shorthand: output_type.shorthand() });
            } else {
                copy_gracefully(&path, &output);
            }
            if !sess.opts.cg.save_temps && !keep_numbered {
                // The user just wants `foo.x`, not `foo.#module-name#.x`.
                ensure_removed(sess.dcx(), &path);
            }
        } else {
            let extension = crate_output
                .temp_path(output_type, None)
                .extension()
                .unwrap()
                .to_str()
                .unwrap()
                .to_owned();

            if crate_output.outputs.contains_explicit_name(&output_type) {
                // 2) Multiple codegen units, with `--emit foo=some_name`. We have
                //    no good solution for this case, so warn the user.
                sess.dcx().emit_warn(errors::IgnoringEmitPath { extension });
            } else if crate_output.single_output_file.is_some() {
                // 3) Multiple codegen units, with `-o some_name`. We have
                //    no good solution for this case, so warn the user.
                sess.dcx().emit_warn(errors::IgnoringOutput { extension });
            } else {
                // 4) Multiple codegen units, but no explicit name. We
                //    just leave the `foo.0.x` files in place.
                // (We don't have to do any work in this case.)
            }
        }
    };

    // Flag to indicate whether the user explicitly requested bitcode.
    // Otherwise, we produced it only as a temporary output, and will need
    // to get rid of it.
    for output_type in crate_output.outputs.keys() {
        match *output_type {
            OutputType::Bitcode => {
                user_wants_bitcode = true;
                // Copy to .bc, but always keep the .0.bc. There is a later
                // check to figure out if we should delete .0.bc files, or keep
                // them for making an rlib.
                copy_if_one_unit(OutputType::Bitcode, true);
            }
            OutputType::ThinLinkBitcode => {
                copy_if_one_unit(OutputType::ThinLinkBitcode, false);
            }
            OutputType::LlvmAssembly => {
                copy_if_one_unit(OutputType::LlvmAssembly, false);
            }
            OutputType::Assembly => {
                copy_if_one_unit(OutputType::Assembly, false);
            }
            OutputType::Object => {
                user_wants_objects = true;
                copy_if_one_unit(OutputType::Object, true);
            }
            OutputType::Mir | OutputType::Metadata | OutputType::Exe | OutputType::DepInfo => {}
        }
    }

    // Clean up unwanted temporary files.

    // We create the following files by default:
    //  - #crate#.#module-name#.bc
    //  - #crate#.#module-name#.o
    //  - #crate#.crate.metadata.bc
    //  - #crate#.crate.metadata.o
    //  - #crate#.o (linked from crate.##.o)
    //  - #crate#.bc (copied from crate.##.bc)
    // We may create additional files if requested by the user (through
    // `-C save-temps` or `--emit=` flags).

    if !sess.opts.cg.save_temps {
        // Remove the temporary .#module-name#.o objects. If the user didn't
        // explicitly request bitcode (with --emit=bc), and the bitcode is not
        // needed for building an rlib, then we must remove .#module-name#.bc as
        // well.

        // Specific rules for keeping .#module-name#.bc:
        //  - If the user requested bitcode (`user_wants_bitcode`), and
        //    codegen_units > 1, then keep it.
        //  - If the user requested bitcode but codegen_units == 1, then we
        //    can toss .#module-name#.bc because we copied it to .bc earlier.
        //  - If we're not building an rlib and the user didn't request
        //    bitcode, then delete .#module-name#.bc.
        // If you change how this works, also update back::link::link_rlib,
        // where .#module-name#.bc files are (maybe) deleted after making an
        // rlib.
        let needs_crate_object = crate_output.outputs.contains_key(&OutputType::Exe);

        let keep_numbered_bitcode = user_wants_bitcode && sess.codegen_units().as_usize() > 1;

        let keep_numbered_objects =
            needs_crate_object || (user_wants_objects && sess.codegen_units().as_usize() > 1);

        for module in compiled_modules.modules.iter() {
            if let Some(ref path) = module.object {
                if !keep_numbered_objects {
                    ensure_removed(sess.dcx(), path);
                }
            }

            if let Some(ref path) = module.dwarf_object {
                if !keep_numbered_objects {
                    ensure_removed(sess.dcx(), path);
                }
            }

            if let Some(ref path) = module.bytecode {
                if !keep_numbered_bitcode {
                    ensure_removed(sess.dcx(), path);
                }
            }
        }

        if !user_wants_bitcode {
            if let Some(ref allocator_module) = compiled_modules.allocator_module {
                if let Some(ref path) = allocator_module.bytecode {
                    ensure_removed(sess.dcx(), path);
                }
            }
        }
    }

    if sess.opts.json_artifact_notifications {
        if compiled_modules.modules.len() == 1 {
            compiled_modules.modules[0].for_each_output(|_path, ty| {
                if sess.opts.output_types.contains_key(&ty) {
                    let descr = ty.shorthand();
                    // for single cgu file is renamed to drop cgu specific suffix
                    // so we regenerate it the same way
                    let path = crate_output.path(ty);
                    sess.dcx().emit_artifact_notification(path.as_path(), descr);
                }
            });
        } else {
            for module in &compiled_modules.modules {
                module.for_each_output(|path, ty| {
                    if sess.opts.output_types.contains_key(&ty) {
                        let descr = ty.shorthand();
                        sess.dcx().emit_artifact_notification(&path, descr);
                    }
                });
            }
        }
    }

    // We leave the following files around by default:
    //  - #crate#.o
    //  - #crate#.crate.metadata.o
    //  - #crate#.bc
    // These are used in linking steps and will be cleaned up afterward.
}

pub(crate) enum WorkItem<B: WriteBackendMethods> {
    /// Optimize a newly codegened, totally unoptimized module.
    Optimize(ModuleCodegen<B::Module>),
    /// Copy the post-LTO artifacts from the incremental cache to the output
    /// directory.
    CopyPostLtoArtifacts(CachedModuleCodegen),
    /// Performs (Thin)LTO on the given module.
    LTO(lto::LtoModuleCodegen<B>),
}

impl<B: WriteBackendMethods> WorkItem<B> {
    fn module_kind(&self) -> ModuleKind {
        match *self {
            WorkItem::Optimize(ref m) => m.kind,
            WorkItem::CopyPostLtoArtifacts(_) | WorkItem::LTO(_) => ModuleKind::Regular,
        }
    }

    /// Generate a short description of this work item suitable for use as a thread name.
    fn short_description(&self) -> String {
        // `pthread_setname()` on *nix ignores anything beyond the first 15
        // bytes. Use short descriptions to maximize the space available for
        // the module name.
        #[cfg(not(windows))]
        fn desc(short: &str, _long: &str, name: &str) -> String {
            // The short label is three bytes, and is followed by a space. That
            // leaves 11 bytes for the CGU name. How we obtain those 11 bytes
            // depends on the CGU name form.
            //
            // - Non-incremental, e.g. `regex.f10ba03eb5ec7975-cgu.0`: the part
            //   before the `-cgu.0` is the same for every CGU, so use the
            //   `cgu.0` part. The number suffix will be different for each
            //   CGU.
            //
            // - Incremental (normal), e.g. `2i52vvl2hco29us0`: use the whole
            //   name because each CGU will have a unique ASCII hash, and the
            //   first 11 bytes will be enough to identify it.
            //
            // - Incremental (with `-Zhuman-readable-cgu-names`), e.g.
            //   `regex.f10ba03eb5ec7975-re_builder.volatile`: use the whole
            //   name. The first 11 bytes won't be enough to uniquely identify
            //   it, but no obvious substring will, and this is a rarely used
            //   option so it doesn't matter much.
            //
            assert_eq!(short.len(), 3);
            let name = if let Some(index) = name.find("-cgu.") {
                &name[index + 1..] // +1 skips the leading '-'.
            } else {
                name
            };
            format!("{short} {name}")
        }

        // Windows has no thread name length limit, so use more descriptive names.
        #[cfg(windows)]
        fn desc(_short: &str, long: &str, name: &str) -> String {
            format!("{long} {name}")
        }

        match self {
            WorkItem::Optimize(m) => desc("opt", "optimize module", &m.name),
            WorkItem::CopyPostLtoArtifacts(m) => desc("cpy", "copy LTO artifacts for", &m.name),
            WorkItem::LTO(m) => desc("lto", "LTO module", m.name()),
        }
    }
}

/// A result produced by the backend.
pub(crate) enum WorkItemResult<B: WriteBackendMethods> {
    /// The backend has finished compiling a CGU, nothing more required.
    Finished(CompiledModule),

    /// The backend has finished compiling a CGU, which now needs linking
    /// because `-Zcombine-cgu` was specified.
    NeedsLink(ModuleCodegen<B::Module>),

    /// The backend has finished compiling a CGU, which now needs to go through
    /// fat LTO.
    NeedsFatLto(FatLtoInput<B>),

    /// The backend has finished compiling a CGU, which now needs to go through
    /// thin LTO.
    NeedsThinLto(String, B::ThinBuffer),
}

pub enum FatLtoInput<B: WriteBackendMethods> {
    Serialized { name: String, buffer: B::ModuleBuffer },
    InMemory(ModuleCodegen<B::Module>),
}

/// Actual LTO type we end up choosing based on multiple factors.
pub(crate) enum ComputedLtoType {
    No,
    Thin,
    Fat,
}

pub(crate) fn compute_per_cgu_lto_type(
    sess_lto: &Lto,
    opts: &config::Options,
    sess_crate_types: &[CrateType],
    module_kind: ModuleKind,
) -> ComputedLtoType {
    // Metadata modules never participate in LTO regardless of the lto
    // settings.
    if module_kind == ModuleKind::Metadata {
        return ComputedLtoType::No;
    }

    // If the linker does LTO, we don't have to do it. Note that we
    // keep doing full LTO, if it is requested, as not to break the
    // assumption that the output will be a single module.
    let linker_does_lto = opts.cg.linker_plugin_lto.enabled();

    // When we're automatically doing ThinLTO for multi-codegen-unit
    // builds we don't actually want to LTO the allocator modules if
    // it shows up. This is due to various linker shenanigans that
    // we'll encounter later.
    let is_allocator = module_kind == ModuleKind::Allocator;

    // We ignore a request for full crate graph LTO if the crate type
    // is only an rlib, as there is no full crate graph to process,
    // that'll happen later.
    //
    // This use case currently comes up primarily for targets that
    // require LTO so the request for LTO is always unconditionally
    // passed down to the backend, but we don't actually want to do
    // anything about it yet until we've got a final product.
    let is_rlib = sess_crate_types.len() == 1 && sess_crate_types[0] == CrateType::Rlib;

    match sess_lto {
        Lto::ThinLocal if !linker_does_lto && !is_allocator => ComputedLtoType::Thin,
        Lto::Thin if !linker_does_lto && !is_rlib => ComputedLtoType::Thin,
        Lto::Fat if !is_rlib => ComputedLtoType::Fat,
        _ => ComputedLtoType::No,
    }
}

fn execute_optimize_work_item<B: ExtraBackendMethods>(
    cgcx: &CodegenContext<B>,
    module: ModuleCodegen<B::Module>,
    module_config: &ModuleConfig,
) -> Result<WorkItemResult<B>, FatalError> {
    let dcx = cgcx.create_dcx();
    let dcx = dcx.handle();

    unsafe {
        B::optimize(cgcx, dcx, &module, module_config)?;
    }

    // After we've done the initial round of optimizations we need to
    // decide whether to synchronously codegen this module or ship it
    // back to the coordinator thread for further LTO processing (which
    // has to wait for all the initial modules to be optimized).

    let lto_type = compute_per_cgu_lto_type(&cgcx.lto, &cgcx.opts, &cgcx.crate_types, module.kind);

    // If we're doing some form of incremental LTO then we need to be sure to
    // save our module to disk first.
    let bitcode = if cgcx.config(module.kind).emit_pre_lto_bc {
        let filename = pre_lto_bitcode_filename(&module.name);
        cgcx.incr_comp_session_dir.as_ref().map(|path| path.join(&filename))
    } else {
        None
    };

    match lto_type {
        ComputedLtoType::No => finish_intra_module_work(cgcx, module, module_config),
        ComputedLtoType::Thin => {
            let (name, thin_buffer) = B::prepare_thin(module, false);
            if let Some(path) = bitcode {
                fs::write(&path, thin_buffer.data()).unwrap_or_else(|e| {
                    panic!("Error writing pre-lto-bitcode file `{}`: {}", path.display(), e);
                });
            }
            Ok(WorkItemResult::NeedsThinLto(name, thin_buffer))
        }
        ComputedLtoType::Fat => match bitcode {
            Some(path) => {
                let (name, buffer) = B::serialize_module(module);
                fs::write(&path, buffer.data()).unwrap_or_else(|e| {
                    panic!("Error writing pre-lto-bitcode file `{}`: {}", path.display(), e);
                });
                Ok(WorkItemResult::NeedsFatLto(FatLtoInput::Serialized { name, buffer }))
            }
            None => Ok(WorkItemResult::NeedsFatLto(FatLtoInput::InMemory(module))),
        },
    }
}

fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
    cgcx: &CodegenContext<B>,
    module: CachedModuleCodegen,
    module_config: &ModuleConfig,
) -> WorkItemResult<B> {
    let incr_comp_session_dir = cgcx.incr_comp_session_dir.as_ref().unwrap();

    let load_from_incr_comp_dir = |output_path: PathBuf, saved_path: &str| {
        let source_file = in_incr_comp_dir(incr_comp_session_dir, saved_path);
        debug!(
            "copying preexisting module `{}` from {:?} to {}",
            module.name,
            source_file,
            output_path.display()
        );
        match link_or_copy(&source_file, &output_path) {
            Ok(_) => Some(output_path),
            Err(error) => {
                cgcx.create_dcx().handle().emit_err(errors::CopyPathBuf {
                    source_file,
                    output_path,
                    error,
                });
                None
            }
        }
    };

    let dwarf_object =
        module.source.saved_files.get("dwo").as_ref().and_then(|saved_dwarf_object_file| {
            let dwarf_obj_out = cgcx
                .output_filenames
                .split_dwarf_path(cgcx.split_debuginfo, cgcx.split_dwarf_kind, Some(&module.name))
                .expect(
                    "saved dwarf object in work product but `split_dwarf_path` returned `None`",
                );
            load_from_incr_comp_dir(dwarf_obj_out, saved_dwarf_object_file)
        });

    let load_from_incr_cache = |perform, output_type: OutputType| {
        if perform {
            let saved_file = module.source.saved_files.get(output_type.extension())?;
            let output_path = cgcx.output_filenames.temp_path(output_type, Some(&module.name));
            load_from_incr_comp_dir(output_path, &saved_file)
        } else {
            None
        }
    };

    let should_emit_obj = module_config.emit_obj != EmitObj::None;
    let assembly = load_from_incr_cache(module_config.emit_asm, OutputType::Assembly);
    let llvm_ir = load_from_incr_cache(module_config.emit_ir, OutputType::LlvmAssembly);
    let bytecode = load_from_incr_cache(module_config.emit_bc, OutputType::Bitcode);
    let object = load_from_incr_cache(should_emit_obj, OutputType::Object);
    if should_emit_obj && object.is_none() {
        cgcx.create_dcx().handle().emit_fatal(errors::NoSavedObjectFile { cgu_name: &module.name })
    }

    WorkItemResult::Finished(CompiledModule {
        name: module.name,
        kind: ModuleKind::Regular,
        object,
        dwarf_object,
        bytecode,
        assembly,
        llvm_ir,
    })
}

fn execute_lto_work_item<B: ExtraBackendMethods>(
    cgcx: &CodegenContext<B>,
    module: lto::LtoModuleCodegen<B>,
    module_config: &ModuleConfig,
) -> Result<WorkItemResult<B>, FatalError> {
    let module = unsafe { module.optimize(cgcx)? };
    finish_intra_module_work(cgcx, module, module_config)
}

fn finish_intra_module_work<B: ExtraBackendMethods>(
    cgcx: &CodegenContext<B>,
    module: ModuleCodegen<B::Module>,
    module_config: &ModuleConfig,
) -> Result<WorkItemResult<B>, FatalError> {
    let dcx = cgcx.create_dcx();
    let dcx = dcx.handle();

    if !cgcx.opts.unstable_opts.combine_cgu
        || module.kind == ModuleKind::Metadata
        || module.kind == ModuleKind::Allocator
    {
        let module = unsafe { B::codegen(cgcx, dcx, module, module_config)? };
        Ok(WorkItemResult::Finished(module))
    } else {
        Ok(WorkItemResult::NeedsLink(module))
    }
}

/// Messages sent to the coordinator.
pub(crate) enum Message<B: WriteBackendMethods> {
    /// A jobserver token has become available. Sent from the jobserver helper
    /// thread.
    Token(io::Result<Acquired>),

    /// The backend has finished processing a work item for a codegen unit.
    /// Sent from a backend worker thread.
    WorkItem { result: Result<WorkItemResult<B>, Option<WorkerFatalError>>, worker_id: usize },

    /// The frontend has finished generating something (backend IR or a
    /// post-LTO artifact) for a codegen unit, and it should be passed to the
    /// backend. Sent from the main thread.
    CodegenDone { llvm_work_item: WorkItem<B>, cost: u64 },

    /// Similar to `CodegenDone`, but for reusing a pre-LTO artifact
    /// Sent from the main thread.
    AddImportOnlyModule {
        module_data: SerializedModule<B::ModuleBuffer>,
        work_product: WorkProduct,
    },

    /// The frontend has finished generating everything for all codegen units.
    /// Sent from the main thread.
    CodegenComplete,

    /// Some normal-ish compiler error occurred, and codegen should be wound
    /// down. Sent from the main thread.
    CodegenAborted,
}

/// A message sent from the coordinator thread to the main thread telling it to
/// process another codegen unit.
pub struct CguMessage;

// A cut-down version of `rustc_errors::DiagInner` that impls `Send`, which
// can be used to send diagnostics from codegen threads to the main thread.
// It's missing the following fields from `rustc_errors::DiagInner`.
// - `span`: it doesn't impl `Send`.
// - `suggestions`: it doesn't impl `Send`, and isn't used for codegen
//   diagnostics.
// - `sort_span`: it doesn't impl `Send`.
// - `is_lint`: lints aren't relevant during codegen.
// - `emitted_at`: not used for codegen diagnostics.
struct Diagnostic {
    level: Level,
    messages: Vec<(DiagMessage, Style)>,
    code: Option<ErrCode>,
    children: Vec<Subdiagnostic>,
    args: DiagArgMap,
}

// A cut-down version of `rustc_errors::Subdiag` that impls `Send`. It's
// missing the following fields from `rustc_errors::Subdiag`.
// - `span`: it doesn't impl `Send`.
pub(crate) struct Subdiagnostic {
    level: Level,
    messages: Vec<(DiagMessage, Style)>,
}

#[derive(PartialEq, Clone, Copy, Debug)]
enum MainThreadState {
    /// Doing nothing.
    Idle,

    /// Doing codegen, i.e. MIR-to-LLVM-IR conversion.
    Codegenning,

    /// Idle, but lending the compiler process's Token to an LLVM thread so it can do useful work.
    Lending,
}

fn start_executing_work<B: ExtraBackendMethods>(
    backend: B,
    tcx: TyCtxt<'_>,
    crate_info: &CrateInfo,
    shared_emitter: SharedEmitter,
    codegen_worker_send: Sender<CguMessage>,
    coordinator_receive: Receiver<Box<dyn Any + Send>>,
    regular_config: Arc<ModuleConfig>,
    metadata_config: Arc<ModuleConfig>,
    allocator_config: Arc<ModuleConfig>,
    tx_to_llvm_workers: Sender<Box<dyn Any + Send>>,
) -> thread::JoinHandle<Result<CompiledModules, ()>> {
    let coordinator_send = tx_to_llvm_workers;
    let sess = tcx.sess;

    let mut each_linked_rlib_for_lto = Vec::new();
    drop(link::each_linked_rlib(crate_info, None, &mut |cnum, path| {
        if link::ignored_for_lto(sess, crate_info, cnum) {
            return;
        }
        each_linked_rlib_for_lto.push((cnum, path.to_path_buf()));
    }));

    // Compute the set of symbols we need to retain when doing LTO (if we need to)
    let exported_symbols = {
        let mut exported_symbols = FxHashMap::default();

        let copy_symbols = |cnum| {
            let symbols = tcx
                .exported_symbols(cnum)
                .iter()
                .map(|&(s, lvl)| (symbol_name_for_instance_in_crate(tcx, s, cnum), lvl))
                .collect();
            Arc::new(symbols)
        };

        match sess.lto() {
            Lto::No => None,
            Lto::ThinLocal => {
                exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
                Some(Arc::new(exported_symbols))
            }
            Lto::Fat | Lto::Thin => {
                exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
                for &(cnum, ref _path) in &each_linked_rlib_for_lto {
                    exported_symbols.insert(cnum, copy_symbols(cnum));
                }
                Some(Arc::new(exported_symbols))
            }
        }
    };

    // First up, convert our jobserver into a helper thread so we can use normal
    // mpsc channels to manage our messages and such.
    // After we've requested tokens then we'll, when we can,
    // get tokens on `coordinator_receive` which will
    // get managed in the main loop below.
    let coordinator_send2 = coordinator_send.clone();
    let helper = jobserver::client()
        .into_helper_thread(move |token| {
            drop(coordinator_send2.send(Box::new(Message::Token::<B>(token))));
        })
        .expect("failed to spawn helper thread");

    let ol =
        if tcx.sess.opts.unstable_opts.no_codegen || !tcx.sess.opts.output_types.should_codegen() {
            // If we know that we won’t be doing codegen, create target machines without optimisation.
            config::OptLevel::No
        } else {
            tcx.backend_optimization_level(())
        };
    let backend_features = tcx.global_backend_features(());

    let remark_dir = if let Some(ref dir) = sess.opts.unstable_opts.remark_dir {
        let result = fs::create_dir_all(dir).and_then(|_| dir.canonicalize());
        match result {
            Ok(dir) => Some(dir),
            Err(error) => sess.dcx().emit_fatal(ErrorCreatingRemarkDir { error }),
        }
    } else {
        None
    };

    let cgcx = CodegenContext::<B> {
        crate_types: tcx.crate_types().to_vec(),
        each_linked_rlib_for_lto,
        lto: sess.lto(),
        fewer_names: sess.fewer_names(),
        save_temps: sess.opts.cg.save_temps,
        time_trace: sess.opts.unstable_opts.llvm_time_trace,
        opts: Arc::new(sess.opts.clone()),
        prof: sess.prof.clone(),
        exported_symbols,
        remark: sess.opts.cg.remark.clone(),
        remark_dir,
        incr_comp_session_dir: sess.incr_comp_session_dir_opt().map(|r| r.clone()),
        coordinator_send,
        expanded_args: tcx.sess.expanded_args.clone(),
        diag_emitter: shared_emitter.clone(),
        output_filenames: Arc::clone(tcx.output_filenames(())),
        regular_module_config: regular_config,
        metadata_module_config: metadata_config,
        allocator_module_config: allocator_config,
        tm_factory: backend.target_machine_factory(tcx.sess, ol, backend_features),
        msvc_imps_needed: msvc_imps_needed(tcx),
        is_pe_coff: tcx.sess.target.is_like_windows,
        target_can_use_split_dwarf: tcx.sess.target_can_use_split_dwarf(),
        target_arch: tcx.sess.target.arch.to_string(),
        target_is_like_osx: tcx.sess.target.is_like_osx,
        target_is_like_aix: tcx.sess.target.is_like_aix,
        split_debuginfo: tcx.sess.split_debuginfo(),
        split_dwarf_kind: tcx.sess.opts.unstable_opts.split_dwarf_kind,
        parallel: backend.supports_parallel() && !sess.opts.unstable_opts.no_parallel_backend,
    };

    // This is the "main loop" of parallel work happening for parallel codegen.
    // It's here that we manage parallelism, schedule work, and work with
    // messages coming from clients.
    //
    // There are a few environmental pre-conditions that shape how the system
    // is set up:
    //
    // - Error reporting can only happen on the main thread because that's the
    //   only place where we have access to the compiler `Session`.
    // - LLVM work can be done on any thread.
    // - Codegen can only happen on the main thread.
    // - Each thread doing substantial work must be in possession of a `Token`
    //   from the `Jobserver`.
    // - The compiler process always holds one `Token`. Any additional `Tokens`
    //   have to be requested from the `Jobserver`.
    //
    // Error Reporting
    // ===============
    // The error reporting restriction is handled separately from the rest: We
    // set up a `SharedEmitter` that holds an open channel to the main thread.
    // When an error occurs on any thread, the shared emitter will send the
    // error message to the receiver main thread (`SharedEmitterMain`). The
    // main thread will periodically query this error message queue and emit
    // any error messages it has received. It might even abort compilation if
    // it has received a fatal error. In this case we rely on all other threads
    // being torn down automatically with the main thread.
    // Since the main thread will often be busy doing codegen work, error
    // reporting will be somewhat delayed, since the message queue can only be
    // checked in between two work packages.
    //
    // Work Processing Infrastructure
    // ==============================
    // The work processing infrastructure knows three major actors:
    //
    // - the coordinator thread,
    // - the main thread, and
    // - LLVM worker threads
    //
    // The coordinator thread is running a message loop. It instructs the main
    // thread about what work to do when, and it will spawn off LLVM worker
    // threads as open LLVM WorkItems become available.
    //
    // The job of the main thread is to codegen CGUs into LLVM work packages
    // (since the main thread is the only thread that can do this). The main
    // thread will block until it receives a message from the coordinator, upon
    // which it will codegen one CGU, send it to the coordinator and block
    // again. This way the coordinator can control what the main thread is
    // doing.
    //
    // The coordinator keeps a queue of LLVM WorkItems, and when a `Token` is
    // available, it will spawn off a new LLVM worker thread and let it process
    // a WorkItem. When a LLVM worker thread is done with its WorkItem,
    // it will just shut down, which also frees all resources associated with
    // the given LLVM module, and sends a message to the coordinator that the
    // WorkItem has been completed.
    //
    // Work Scheduling
    // ===============
    // The scheduler's goal is to minimize the time it takes to complete all
    // work there is, however, we also want to keep memory consumption low
    // if possible. These two goals are at odds with each other: If memory
    // consumption were not an issue, we could just let the main thread produce
    // LLVM WorkItems at full speed, assuring maximal utilization of
    // Tokens/LLVM worker threads. However, since codegen is usually faster
    // than LLVM processing, the queue of LLVM WorkItems would fill up and each
    // WorkItem potentially holds on to a substantial amount of memory.
    //
    // So the actual goal is to always produce just enough LLVM WorkItems as
    // not to starve our LLVM worker threads. That means, once we have enough
    // WorkItems in our queue, we can block the main thread, so it does not
    // produce more until we need them.
    //
    // Doing LLVM Work on the Main Thread
    // ----------------------------------
    // Since the main thread owns the compiler process's implicit `Token`, it is
    // wasteful to keep it blocked without doing any work. Therefore, what we do
    // in this case is: We spawn off an additional LLVM worker thread that helps
    // reduce the queue. The work it is doing corresponds to the implicit
    // `Token`. The coordinator will mark the main thread as being busy with
    // LLVM work. (The actual work happens on another OS thread but we just care
    // about `Tokens`, not actual threads).
    //
    // When any LLVM worker thread finishes while the main thread is marked as
    // "busy with LLVM work", we can do a little switcheroo: We give the Token
    // of the just finished thread to the LLVM worker thread that is working on
    // behalf of the main thread's implicit Token, thus freeing up the main
    // thread again. The coordinator can then again decide what the main thread
    // should do. This allows the coordinator to make decisions at more points
    // in time.
    //
    // Striking a Balance between Throughput and Memory Consumption
    // ------------------------------------------------------------
    // Since our two goals, (1) use as many Tokens as possible and (2) keep
    // memory consumption as low as possible, are in conflict with each other,
    // we have to find a trade off between them. Right now, the goal is to keep
    // all workers busy, which means that no worker should find the queue empty
    // when it is ready to start.
    // How do we do achieve this? Good question :) We actually never know how
    // many `Tokens` are potentially available so it's hard to say how much to
    // fill up the queue before switching the main thread to LLVM work. Also we
    // currently don't have a means to estimate how long a running LLVM worker
    // will still be busy with it's current WorkItem. However, we know the
    // maximal count of available Tokens that makes sense (=the number of CPU
    // cores), so we can take a conservative guess. The heuristic we use here
    // is implemented in the `queue_full_enough()` function.
    //
    // Some Background on Jobservers
    // -----------------------------
    // It's worth also touching on the management of parallelism here. We don't
    // want to just spawn a thread per work item because while that's optimal
    // parallelism it may overload a system with too many threads or violate our
    // configuration for the maximum amount of cpu to use for this process. To
    // manage this we use the `jobserver` crate.
    //
    // Job servers are an artifact of GNU make and are used to manage
    // parallelism between processes. A jobserver is a glorified IPC semaphore
    // basically. Whenever we want to run some work we acquire the semaphore,
    // and whenever we're done with that work we release the semaphore. In this
    // manner we can ensure that the maximum number of parallel workers is
    // capped at any one point in time.
    //
    // LTO and the coordinator thread
    // ------------------------------
    //
    // The final job the coordinator thread is responsible for is managing LTO
    // and how that works. When LTO is requested what we'll do is collect all
    // optimized LLVM modules into a local vector on the coordinator. Once all
    // modules have been codegened and optimized we hand this to the `lto`
    // module for further optimization. The `lto` module will return back a list
    // of more modules to work on, which the coordinator will continue to spawn
    // work for.
    //
    // Each LLVM module is automatically sent back to the coordinator for LTO if
    // necessary. There's already optimizations in place to avoid sending work
    // back to the coordinator if LTO isn't requested.
    return B::spawn_named_thread(cgcx.time_trace, "coordinator".to_string(), move || {
        let mut worker_id_counter = 0;
        let mut free_worker_ids = Vec::new();
        let mut get_worker_id = |free_worker_ids: &mut Vec<usize>| {
            if let Some(id) = free_worker_ids.pop() {
                id
            } else {
                let id = worker_id_counter;
                worker_id_counter += 1;
                id
            }
        };

        // This is where we collect codegen units that have gone all the way
        // through codegen and LLVM.
        let mut compiled_modules = vec![];
        let mut compiled_allocator_module = None;
        let mut needs_link = Vec::new();
        let mut needs_fat_lto = Vec::new();
        let mut needs_thin_lto = Vec::new();
        let mut lto_import_only_modules = Vec::new();
        let mut started_lto = false;

        /// Possible state transitions:
        /// - Ongoing -> Completed
        /// - Ongoing -> Aborted
        /// - Completed -> Aborted
        #[derive(Debug, PartialEq)]
        enum CodegenState {
            Ongoing,
            Completed,
            Aborted,
        }
        use CodegenState::*;
        let mut codegen_state = Ongoing;

        // This is the queue of LLVM work items that still need processing.
        let mut work_items = Vec::<(WorkItem<B>, u64)>::new();

        // This are the Jobserver Tokens we currently hold. Does not include
        // the implicit Token the compiler process owns no matter what.
        let mut tokens = Vec::new();

        let mut main_thread_state = MainThreadState::Idle;

        // How many LLVM worker threads are running while holding a Token. This
        // *excludes* any that the main thread is lending a Token to.
        let mut running_with_own_token = 0;

        // How many LLVM worker threads are running in total. This *includes*
        // any that the main thread is lending a Token to.
        let running_with_any_token = |main_thread_state, running_with_own_token| {
            running_with_own_token
                + if main_thread_state == MainThreadState::Lending { 1 } else { 0 }
        };

        let mut llvm_start_time: Option<VerboseTimingGuard<'_>> = None;

        // Run the message loop while there's still anything that needs message
        // processing. Note that as soon as codegen is aborted we simply want to
        // wait for all existing work to finish, so many of the conditions here
        // only apply if codegen hasn't been aborted as they represent pending
        // work to be done.
        loop {
            // While there are still CGUs to be codegened, the coordinator has
            // to decide how to utilize the compiler processes implicit Token:
            // For codegenning more CGU or for running them through LLVM.
            if codegen_state == Ongoing {
                if main_thread_state == MainThreadState::Idle {
                    // Compute the number of workers that will be running once we've taken as many
                    // items from the work queue as we can, plus one for the main thread. It's not
                    // critically important that we use this instead of just
                    // `running_with_own_token`, but it prevents the `queue_full_enough` heuristic
                    // from fluctuating just because a worker finished up and we decreased the
                    // `running_with_own_token` count, even though we're just going to increase it
                    // right after this when we put a new worker to work.
                    let extra_tokens = tokens.len().checked_sub(running_with_own_token).unwrap();
                    let additional_running = std::cmp::min(extra_tokens, work_items.len());
                    let anticipated_running = running_with_own_token + additional_running + 1;

                    if !queue_full_enough(work_items.len(), anticipated_running) {
                        // The queue is not full enough, process more codegen units:
                        if codegen_worker_send.send(CguMessage).is_err() {
                            panic!("Could not send CguMessage to main thread")
                        }
                        main_thread_state = MainThreadState::Codegenning;
                    } else {
                        // The queue is full enough to not let the worker
                        // threads starve. Use the implicit Token to do some
                        // LLVM work too.
                        let (item, _) =
                            work_items.pop().expect("queue empty - queue_full_enough() broken?");
                        main_thread_state = MainThreadState::Lending;
                        spawn_work(
                            &cgcx,
                            &mut llvm_start_time,
                            get_worker_id(&mut free_worker_ids),
                            item,
                        );
                    }
                }
            } else if codegen_state == Completed {
                if running_with_any_token(main_thread_state, running_with_own_token) == 0
                    && work_items.is_empty()
                {
                    // All codegen work is done. Do we have LTO work to do?
                    if needs_fat_lto.is_empty()
                        && needs_thin_lto.is_empty()
                        && lto_import_only_modules.is_empty()
                    {
                        // Nothing more to do!
                        break;
                    }

                    // We have LTO work to do. Perform the serial work here of
                    // figuring out what we're going to LTO and then push a
                    // bunch of work items onto our queue to do LTO. This all
                    // happens on the coordinator thread but it's very quick so
                    // we don't worry about tokens.
                    assert!(!started_lto);
                    started_lto = true;

                    let needs_fat_lto = mem::take(&mut needs_fat_lto);
                    let needs_thin_lto = mem::take(&mut needs_thin_lto);
                    let import_only_modules = mem::take(&mut lto_import_only_modules);

                    for (work, cost) in
                        generate_lto_work(&cgcx, needs_fat_lto, needs_thin_lto, import_only_modules)
                    {
                        let insertion_index = work_items
                            .binary_search_by_key(&cost, |&(_, cost)| cost)
                            .unwrap_or_else(|e| e);
                        work_items.insert(insertion_index, (work, cost));
                        if cgcx.parallel {
                            helper.request_token();
                        }
                    }
                }

                // In this branch, we know that everything has been codegened,
                // so it's just a matter of determining whether the implicit
                // Token is free to use for LLVM work.
                match main_thread_state {
                    MainThreadState::Idle => {
                        if let Some((item, _)) = work_items.pop() {
                            main_thread_state = MainThreadState::Lending;
                            spawn_work(
                                &cgcx,
                                &mut llvm_start_time,
                                get_worker_id(&mut free_worker_ids),
                                item,
                            );
                        } else {
                            // There is no unstarted work, so let the main thread
                            // take over for a running worker. Otherwise the
                            // implicit token would just go to waste.
                            // We reduce the `running` counter by one. The
                            // `tokens.truncate()` below will take care of
                            // giving the Token back.
                            assert!(running_with_own_token > 0);
                            running_with_own_token -= 1;
                            main_thread_state = MainThreadState::Lending;
                        }
                    }
                    MainThreadState::Codegenning => bug!(
                        "codegen worker should not be codegenning after \
                              codegen was already completed"
                    ),
                    MainThreadState::Lending => {
                        // Already making good use of that token
                    }
                }
            } else {
                // Don't queue up any more work if codegen was aborted, we're
                // just waiting for our existing children to finish.
                assert!(codegen_state == Aborted);
                if running_with_any_token(main_thread_state, running_with_own_token) == 0 {
                    break;
                }
            }

            // Spin up what work we can, only doing this while we've got available
            // parallelism slots and work left to spawn.
            if codegen_state != Aborted {
                while !work_items.is_empty() && running_with_own_token < tokens.len() {
                    let (item, _) = work_items.pop().unwrap();
                    spawn_work(
                        &cgcx,
                        &mut llvm_start_time,
                        get_worker_id(&mut free_worker_ids),
                        item,
                    );
                    running_with_own_token += 1;
                }
            }

            // Relinquish accidentally acquired extra tokens.
            tokens.truncate(running_with_own_token);

            // If a thread exits successfully then we drop a token associated
            // with that worker and update our `running_with_own_token` count.
            // We may later re-acquire a token to continue running more work.
            // We may also not actually drop a token here if the worker was
            // running with an "ephemeral token".
            let mut free_worker = |worker_id| {
                if main_thread_state == MainThreadState::Lending {
                    main_thread_state = MainThreadState::Idle;
                } else {
                    running_with_own_token -= 1;
                }

                free_worker_ids.push(worker_id);
            };

            let msg = coordinator_receive.recv().unwrap();
            match *msg.downcast::<Message<B>>().ok().unwrap() {
                // Save the token locally and the next turn of the loop will use
                // this to spawn a new unit of work, or it may get dropped
                // immediately if we have no more work to spawn.
                Message::Token(token) => {
                    match token {
                        Ok(token) => {
                            tokens.push(token);

                            if main_thread_state == MainThreadState::Lending {
                                // If the main thread token is used for LLVM work
                                // at the moment, we turn that thread into a regular
                                // LLVM worker thread, so the main thread is free
                                // to react to codegen demand.
                                main_thread_state = MainThreadState::Idle;
                                running_with_own_token += 1;
                            }
                        }
                        Err(e) => {
                            let msg = &format!("failed to acquire jobserver token: {e}");
                            shared_emitter.fatal(msg);
                            codegen_state = Aborted;
                        }
                    }
                }

                Message::CodegenDone { llvm_work_item, cost } => {
                    // We keep the queue sorted by estimated processing cost,
                    // so that more expensive items are processed earlier. This
                    // is good for throughput as it gives the main thread more
                    // time to fill up the queue and it avoids scheduling
                    // expensive items to the end.
                    // Note, however, that this is not ideal for memory
                    // consumption, as LLVM module sizes are not evenly
                    // distributed.
                    let insertion_index = work_items.binary_search_by_key(&cost, |&(_, cost)| cost);
                    let insertion_index = match insertion_index {
                        Ok(idx) | Err(idx) => idx,
                    };
                    work_items.insert(insertion_index, (llvm_work_item, cost));

                    if cgcx.parallel {
                        helper.request_token();
                    }
                    assert_eq!(main_thread_state, MainThreadState::Codegenning);
                    main_thread_state = MainThreadState::Idle;
                }

                Message::CodegenComplete => {
                    if codegen_state != Aborted {
                        codegen_state = Completed;
                    }
                    assert_eq!(main_thread_state, MainThreadState::Codegenning);
                    main_thread_state = MainThreadState::Idle;
                }

                // If codegen is aborted that means translation was aborted due
                // to some normal-ish compiler error. In this situation we want
                // to exit as soon as possible, but we want to make sure all
                // existing work has finished. Flag codegen as being done, and
                // then conditions above will ensure no more work is spawned but
                // we'll keep executing this loop until `running_with_own_token`
                // hits 0.
                Message::CodegenAborted => {
                    codegen_state = Aborted;
                }

                Message::WorkItem { result, worker_id } => {
                    free_worker(worker_id);

                    match result {
                        Ok(WorkItemResult::Finished(compiled_module)) => {
                            match compiled_module.kind {
                                ModuleKind::Regular => {
                                    assert!(needs_link.is_empty());
                                    compiled_modules.push(compiled_module);
                                }
                                ModuleKind::Allocator => {
                                    assert!(compiled_allocator_module.is_none());
                                    compiled_allocator_module = Some(compiled_module);
                                }
                                ModuleKind::Metadata => bug!("Should be handled separately"),
                            }
                        }
                        Ok(WorkItemResult::NeedsLink(module)) => {
                            assert!(compiled_modules.is_empty());
                            needs_link.push(module);
                        }
                        Ok(WorkItemResult::NeedsFatLto(fat_lto_input)) => {
                            assert!(!started_lto);
                            assert!(needs_thin_lto.is_empty());
                            needs_fat_lto.push(fat_lto_input);
                        }
                        Ok(WorkItemResult::NeedsThinLto(name, thin_buffer)) => {
                            assert!(!started_lto);
                            assert!(needs_fat_lto.is_empty());
                            needs_thin_lto.push((name, thin_buffer));
                        }
                        Err(Some(WorkerFatalError)) => {
                            // Like `CodegenAborted`, wait for remaining work to finish.
                            codegen_state = Aborted;
                        }
                        Err(None) => {
                            // If the thread failed that means it panicked, so
                            // we abort immediately.
                            bug!("worker thread panicked");
                        }
                    }
                }

                Message::AddImportOnlyModule { module_data, work_product } => {
                    assert!(!started_lto);
                    assert_eq!(codegen_state, Ongoing);
                    assert_eq!(main_thread_state, MainThreadState::Codegenning);
                    lto_import_only_modules.push((module_data, work_product));
                    main_thread_state = MainThreadState::Idle;
                }
            }
        }

        if codegen_state == Aborted {
            return Err(());
        }

        let needs_link = mem::take(&mut needs_link);
        if !needs_link.is_empty() {
            assert!(compiled_modules.is_empty());
            let dcx = cgcx.create_dcx();
            let dcx = dcx.handle();
            let module = B::run_link(&cgcx, dcx, needs_link).map_err(|_| ())?;
            let module = unsafe {
                B::codegen(&cgcx, dcx, module, cgcx.config(ModuleKind::Regular)).map_err(|_| ())?
            };
            compiled_modules.push(module);
        }

        // Drop to print timings
        drop(llvm_start_time);

        // Regardless of what order these modules completed in, report them to
        // the backend in the same order every time to ensure that we're handing
        // out deterministic results.
        compiled_modules.sort_by(|a, b| a.name.cmp(&b.name));

        Ok(CompiledModules {
            modules: compiled_modules,
            allocator_module: compiled_allocator_module,
        })
    })
    .expect("failed to spawn coordinator thread");

    // A heuristic that determines if we have enough LLVM WorkItems in the
    // queue so that the main thread can do LLVM work instead of codegen
    fn queue_full_enough(items_in_queue: usize, workers_running: usize) -> bool {
        // This heuristic scales ahead-of-time codegen according to available
        // concurrency, as measured by `workers_running`. The idea is that the
        // more concurrency we have available, the more demand there will be for
        // work items, and the fuller the queue should be kept to meet demand.
        // An important property of this approach is that we codegen ahead of
        // time only as much as necessary, so as to keep fewer LLVM modules in
        // memory at once, thereby reducing memory consumption.
        //
        // When the number of workers running is less than the max concurrency
        // available to us, this heuristic can cause us to instruct the main
        // thread to work on an LLVM item (that is, tell it to "LLVM") instead
        // of codegen, even though it seems like it *should* be codegenning so
        // that we can create more work items and spawn more LLVM workers.
        //
        // But this is not a problem. When the main thread is told to LLVM,
        // according to this heuristic and how work is scheduled, there is
        // always at least one item in the queue, and therefore at least one
        // pending jobserver token request. If there *is* more concurrency
        // available, we will immediately receive a token, which will upgrade
        // the main thread's LLVM worker to a real one (conceptually), and free
        // up the main thread to codegen if necessary. On the other hand, if
        // there isn't more concurrency, then the main thread working on an LLVM
        // item is appropriate, as long as the queue is full enough for demand.
        //
        // Speaking of which, how full should we keep the queue? Probably less
        // full than you'd think. A lot has to go wrong for the queue not to be
        // full enough and for that to have a negative effect on compile times.
        //
        // Workers are unlikely to finish at exactly the same time, so when one
        // finishes and takes another work item off the queue, we often have
        // ample time to codegen at that point before the next worker finishes.
        // But suppose that codegen takes so long that the workers exhaust the
        // queue, and we have one or more workers that have nothing to work on.
        // Well, it might not be so bad. Of all the LLVM modules we create and
        // optimize, one has to finish last. It's not necessarily the case that
        // by losing some concurrency for a moment, we delay the point at which
        // that last LLVM module is finished and the rest of compilation can
        // proceed. Also, when we can't take advantage of some concurrency, we
        // give tokens back to the job server. That enables some other rustc to
        // potentially make use of the available concurrency. That could even
        // *decrease* overall compile time if we're lucky. But yes, if no other
        // rustc can make use of the concurrency, then we've squandered it.
        //
        // However, keeping the queue full is also beneficial when we have a
        // surge in available concurrency. Then items can be taken from the
        // queue immediately, without having to wait for codegen.
        //
        // So, the heuristic below tries to keep one item in the queue for every
        // four running workers. Based on limited benchmarking, this appears to
        // be more than sufficient to avoid increasing compilation times.
        let quarter_of_workers = workers_running - 3 * workers_running / 4;
        items_in_queue > 0 && items_in_queue >= quarter_of_workers
    }
}

/// `FatalError` is explicitly not `Send`.
#[must_use]
pub(crate) struct WorkerFatalError;

fn spawn_work<'a, B: ExtraBackendMethods>(
    cgcx: &'a CodegenContext<B>,
    llvm_start_time: &mut Option<VerboseTimingGuard<'a>>,
    worker_id: usize,
    work: WorkItem<B>,
) {
    if cgcx.config(work.module_kind()).time_module && llvm_start_time.is_none() {
        *llvm_start_time = Some(cgcx.prof.verbose_generic_activity("LLVM_passes"));
    }

    let cgcx = cgcx.clone();

    B::spawn_named_thread(cgcx.time_trace, work.short_description(), move || {
        // Set up a destructor which will fire off a message that we're done as
        // we exit.
        struct Bomb<B: ExtraBackendMethods> {
            coordinator_send: Sender<Box<dyn Any + Send>>,
            result: Option<Result<WorkItemResult<B>, FatalError>>,
            worker_id: usize,
        }
        impl<B: ExtraBackendMethods> Drop for Bomb<B> {
            fn drop(&mut self) {
                let worker_id = self.worker_id;
                let msg = match self.result.take() {
                    Some(Ok(result)) => Message::WorkItem::<B> { result: Ok(result), worker_id },
                    Some(Err(FatalError)) => {
                        Message::WorkItem::<B> { result: Err(Some(WorkerFatalError)), worker_id }
                    }
                    None => Message::WorkItem::<B> { result: Err(None), worker_id },
                };
                drop(self.coordinator_send.send(Box::new(msg)));
            }
        }

        let mut bomb =
            Bomb::<B> { coordinator_send: cgcx.coordinator_send.clone(), result: None, worker_id };

        // Execute the work itself, and if it finishes successfully then flag
        // ourselves as a success as well.
        //
        // Note that we ignore any `FatalError` coming out of `execute_work_item`,
        // as a diagnostic was already sent off to the main thread - just
        // surface that there was an error in this worker.
        bomb.result = {
            let module_config = cgcx.config(work.module_kind());

            Some(match work {
                WorkItem::Optimize(m) => {
                    let _timer =
                        cgcx.prof.generic_activity_with_arg("codegen_module_optimize", &*m.name);
                    execute_optimize_work_item(&cgcx, m, module_config)
                }
                WorkItem::CopyPostLtoArtifacts(m) => {
                    let _timer = cgcx.prof.generic_activity_with_arg(
                        "codegen_copy_artifacts_from_incr_cache",
                        &*m.name,
                    );
                    Ok(execute_copy_from_cache_work_item(&cgcx, m, module_config))
                }
                WorkItem::LTO(m) => {
                    let _timer =
                        cgcx.prof.generic_activity_with_arg("codegen_module_perform_lto", m.name());
                    execute_lto_work_item(&cgcx, m, module_config)
                }
            })
        };
    })
    .expect("failed to spawn work thread");
}

enum SharedEmitterMessage {
    Diagnostic(Diagnostic),
    InlineAsmError(SpanData, String, Level, Option<(String, Vec<InnerSpan>)>),
    Fatal(String),
}

#[derive(Clone)]
pub struct SharedEmitter {
    sender: Sender<SharedEmitterMessage>,
}

pub struct SharedEmitterMain {
    receiver: Receiver<SharedEmitterMessage>,
}

impl SharedEmitter {
    fn new() -> (SharedEmitter, SharedEmitterMain) {
        let (sender, receiver) = channel();

        (SharedEmitter { sender }, SharedEmitterMain { receiver })
    }

    pub fn inline_asm_error(
        &self,
        span: SpanData,
        msg: String,
        level: Level,
        source: Option<(String, Vec<InnerSpan>)>,
    ) {
        drop(self.sender.send(SharedEmitterMessage::InlineAsmError(span, msg, level, source)));
    }

    fn fatal(&self, msg: &str) {
        drop(self.sender.send(SharedEmitterMessage::Fatal(msg.to_string())));
    }
}

impl Translate for SharedEmitter {
    fn fluent_bundle(&self) -> Option<&FluentBundle> {
        None
    }

    fn fallback_fluent_bundle(&self) -> &FluentBundle {
        panic!("shared emitter attempted to translate a diagnostic");
    }
}

impl Emitter for SharedEmitter {
    fn emit_diagnostic(
        &mut self,
        mut diag: rustc_errors::DiagInner,
        _registry: &rustc_errors::registry::Registry,
    ) {
        // Check that we aren't missing anything interesting when converting to
        // the cut-down local `DiagInner`.
        assert_eq!(diag.span, MultiSpan::new());
        assert_eq!(diag.suggestions, Suggestions::Enabled(vec![]));
        assert_eq!(diag.sort_span, rustc_span::DUMMY_SP);
        assert_eq!(diag.is_lint, None);
        // No sensible check for `diag.emitted_at`.

        let args = mem::replace(&mut diag.args, DiagArgMap::default());
        drop(
            self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic {
                level: diag.level(),
                messages: diag.messages,
                code: diag.code,
                children: diag
                    .children
                    .into_iter()
                    .map(|child| Subdiagnostic { level: child.level, messages: child.messages })
                    .collect(),
                args,
            })),
        );
    }

    fn source_map(&self) -> Option<&SourceMap> {
        None
    }
}

impl SharedEmitterMain {
    fn check(&self, sess: &Session, blocking: bool) {
        loop {
            let message = if blocking {
                match self.receiver.recv() {
                    Ok(message) => Ok(message),
                    Err(_) => Err(()),
                }
            } else {
                match self.receiver.try_recv() {
                    Ok(message) => Ok(message),
                    Err(_) => Err(()),
                }
            };

            match message {
                Ok(SharedEmitterMessage::Diagnostic(diag)) => {
                    // The diagnostic has been received on the main thread.
                    // Convert it back to a full `Diagnostic` and emit.
                    let dcx = sess.dcx();
                    let mut d =
                        rustc_errors::DiagInner::new_with_messages(diag.level, diag.messages);
                    d.code = diag.code; // may be `None`, that's ok
                    d.children = diag
                        .children
                        .into_iter()
                        .map(|sub| rustc_errors::Subdiag {
                            level: sub.level,
                            messages: sub.messages,
                            span: MultiSpan::new(),
                        })
                        .collect();
                    d.args = diag.args;
                    dcx.emit_diagnostic(d);
                    sess.dcx().abort_if_errors();
                }
                Ok(SharedEmitterMessage::InlineAsmError(span, msg, level, source)) => {
                    assert_matches!(level, Level::Error | Level::Warning | Level::Note);
                    let mut err = Diag::<()>::new(sess.dcx(), level, msg);
                    if !span.is_dummy() {
                        err.span(span.span());
                    }

                    // Point to the generated assembly if it is available.
                    if let Some((buffer, spans)) = source {
                        let source = sess
                            .source_map()
                            .new_source_file(FileName::inline_asm_source_code(&buffer), buffer);
                        let spans: Vec<_> = spans
                            .iter()
                            .map(|sp| {
                                Span::with_root_ctxt(
                                    source.normalized_byte_pos(sp.start as u32),
                                    source.normalized_byte_pos(sp.end as u32),
                                )
                            })
                            .collect();
                        err.span_note(spans, "instantiated into assembly here");
                    }

                    err.emit();
                }
                Ok(SharedEmitterMessage::Fatal(msg)) => {
                    sess.dcx().fatal(msg);
                }
                Err(_) => {
                    break;
                }
            }
        }
    }
}

pub struct Coordinator<B: ExtraBackendMethods> {
    pub sender: Sender<Box<dyn Any + Send>>,
    future: Option<thread::JoinHandle<Result<CompiledModules, ()>>>,
    // Only used for the Message type.
    phantom: PhantomData<B>,
}

impl<B: ExtraBackendMethods> Coordinator<B> {
    fn join(mut self) -> std::thread::Result<Result<CompiledModules, ()>> {
        self.future.take().unwrap().join()
    }
}

impl<B: ExtraBackendMethods> Drop for Coordinator<B> {
    fn drop(&mut self) {
        if let Some(future) = self.future.take() {
            // If we haven't joined yet, signal to the coordinator that it should spawn no more
            // work, and wait for worker threads to finish.
            drop(self.sender.send(Box::new(Message::CodegenAborted::<B>)));
            drop(future.join());
        }
    }
}

pub struct OngoingCodegen<B: ExtraBackendMethods> {
    pub backend: B,
    pub metadata: EncodedMetadata,
    pub metadata_module: Option<CompiledModule>,
    pub crate_info: CrateInfo,
    pub codegen_worker_receive: Receiver<CguMessage>,
    pub shared_emitter_main: SharedEmitterMain,
    pub output_filenames: Arc<OutputFilenames>,
    pub coordinator: Coordinator<B>,
}

impl<B: ExtraBackendMethods> OngoingCodegen<B> {
    pub fn join(self, sess: &Session) -> (CodegenResults, FxIndexMap<WorkProductId, WorkProduct>) {
        self.shared_emitter_main.check(sess, true);
        let compiled_modules = sess.time("join_worker_thread", || match self.coordinator.join() {
            Ok(Ok(compiled_modules)) => compiled_modules,
            Ok(Err(())) => {
                sess.dcx().abort_if_errors();
                panic!("expected abort due to worker thread errors")
            }
            Err(_) => {
                bug!("panic during codegen/LLVM phase");
            }
        });

        sess.dcx().abort_if_errors();

        let work_products =
            copy_all_cgu_workproducts_to_incr_comp_cache_dir(sess, &compiled_modules);
        produce_final_output_artifacts(sess, &compiled_modules, &self.output_filenames);

        // FIXME: time_llvm_passes support - does this use a global context or
        // something?
        if sess.codegen_units().as_usize() == 1 && sess.opts.unstable_opts.time_llvm_passes {
            self.backend.print_pass_timings()
        }

        if sess.print_llvm_stats() {
            self.backend.print_statistics()
        }

        (
            CodegenResults {
                metadata: self.metadata,
                crate_info: self.crate_info,

                modules: compiled_modules.modules,
                allocator_module: compiled_modules.allocator_module,
                metadata_module: self.metadata_module,
            },
            work_products,
        )
    }

    pub(crate) fn codegen_finished(&self, tcx: TyCtxt<'_>) {
        self.wait_for_signal_to_codegen_item();
        self.check_for_errors(tcx.sess);
        drop(self.coordinator.sender.send(Box::new(Message::CodegenComplete::<B>)));
    }

    pub(crate) fn check_for_errors(&self, sess: &Session) {
        self.shared_emitter_main.check(sess, false);
    }

    pub(crate) fn wait_for_signal_to_codegen_item(&self) {
        match self.codegen_worker_receive.recv() {
            Ok(CguMessage) => {
                // Ok to proceed.
            }
            Err(_) => {
                // One of the LLVM threads must have panicked, fall through so
                // error handling can be reached.
            }
        }
    }
}

pub(crate) fn submit_codegened_module_to_llvm<B: ExtraBackendMethods>(
    _backend: &B,
    tx_to_llvm_workers: &Sender<Box<dyn Any + Send>>,
    module: ModuleCodegen<B::Module>,
    cost: u64,
) {
    let llvm_work_item = WorkItem::Optimize(module);
    drop(tx_to_llvm_workers.send(Box::new(Message::CodegenDone::<B> { llvm_work_item, cost })));
}

pub(crate) fn submit_post_lto_module_to_llvm<B: ExtraBackendMethods>(
    _backend: &B,
    tx_to_llvm_workers: &Sender<Box<dyn Any + Send>>,
    module: CachedModuleCodegen,
) {
    let llvm_work_item = WorkItem::CopyPostLtoArtifacts(module);
    drop(tx_to_llvm_workers.send(Box::new(Message::CodegenDone::<B> { llvm_work_item, cost: 0 })));
}

pub(crate) fn submit_pre_lto_module_to_llvm<B: ExtraBackendMethods>(
    _backend: &B,
    tcx: TyCtxt<'_>,
    tx_to_llvm_workers: &Sender<Box<dyn Any + Send>>,
    module: CachedModuleCodegen,
) {
    let filename = pre_lto_bitcode_filename(&module.name);
    let bc_path = in_incr_comp_dir_sess(tcx.sess, &filename);
    let file = fs::File::open(&bc_path)
        .unwrap_or_else(|e| panic!("failed to open bitcode file `{}`: {}", bc_path.display(), e));

    let mmap = unsafe {
        Mmap::map(file).unwrap_or_else(|e| {
            panic!("failed to mmap bitcode file `{}`: {}", bc_path.display(), e)
        })
    };
    // Schedule the module to be loaded
    drop(tx_to_llvm_workers.send(Box::new(Message::AddImportOnlyModule::<B> {
        module_data: SerializedModule::FromUncompressedFile(mmap),
        work_product: module.source,
    })));
}

fn pre_lto_bitcode_filename(module_name: &str) -> String {
    format!("{module_name}.{PRE_LTO_BC_EXT}")
}

fn msvc_imps_needed(tcx: TyCtxt<'_>) -> bool {
    // This should never be true (because it's not supported). If it is true,
    // something is wrong with commandline arg validation.
    assert!(
        !(tcx.sess.opts.cg.linker_plugin_lto.enabled()
            && tcx.sess.target.is_like_windows
            && tcx.sess.opts.cg.prefer_dynamic)
    );

    // We need to generate _imp__ symbol if we are generating an rlib or we include one
    // indirectly from ThinLTO. In theory these are not needed as ThinLTO could resolve
    // these, but it currently does not do so.
    let can_have_static_objects =
        tcx.sess.lto() == Lto::Thin || tcx.crate_types().iter().any(|ct| *ct == CrateType::Rlib);

    tcx.sess.target.is_like_windows &&
    can_have_static_objects   &&
    // ThinLTO can't handle this workaround in all cases, so we don't
    // emit the `__imp_` symbols. Instead we make them unnecessary by disallowing
    // dynamic linking when linker plugin LTO is enabled.
    !tcx.sess.opts.cg.linker_plugin_lto.enabled()
}