rustc_middle/mir/syntax.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
//! This defines the syntax of MIR, i.e., the set of available MIR operations, and other definitions
//! closely related to MIR semantics.
//! This is in a dedicated file so that changes to this file can be reviewed more carefully.
//! The intention is that this file only contains datatype declarations, no code.
use rustc_abi::{FieldIdx, VariantIdx};
use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece, Mutability};
use rustc_data_structures::packed::Pu128;
use rustc_hir::CoroutineKind;
use rustc_hir::def_id::DefId;
use rustc_index::IndexVec;
use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
use rustc_span::Span;
use rustc_span::def_id::LocalDefId;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::Symbol;
use rustc_target::asm::InlineAsmRegOrRegClass;
use smallvec::SmallVec;
use super::{BasicBlock, Const, Local, UserTypeProjection};
use crate::mir::coverage::CoverageKind;
use crate::ty::adjustment::PointerCoercion;
use crate::ty::{self, GenericArgsRef, List, Region, Ty, TyCtxt, UserTypeAnnotationIndex};
/// Represents the "flavors" of MIR.
///
/// All flavors of MIR use the same data structure, but there are some important differences. These
/// differences come in two forms: Dialects and phases.
///
/// Dialects represent a stronger distinction than phases. This is because the transitions between
/// dialects are semantic changes, and therefore technically *lowerings* between distinct IRs. In
/// other words, the same [`Body`](crate::mir::Body) might be well-formed for multiple dialects, but
/// have different semantic meaning and different behavior at runtime.
///
/// Each dialect additionally has a number of phases. However, phase changes never involve semantic
/// changes. If some MIR is well-formed both before and after a phase change, it is also guaranteed
/// that it has the same semantic meaning. In this sense, phase changes can only add additional
/// restrictions on what MIR is well-formed.
///
/// When adding phases, remember to update [`MirPhase::phase_index`].
#[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
#[derive(HashStable)]
pub enum MirPhase {
/// The MIR that is generated by MIR building.
///
/// The only things that operate on this dialect are unsafeck, the various MIR lints, and const
/// qualifs.
///
/// This has no distinct phases.
Built,
/// The MIR used for most analysis.
///
/// The only semantic change between analysis and built MIR is constant promotion. In built MIR,
/// sequences of statements that would generally be subject to constant promotion are
/// semantically constants, while in analysis MIR all constants are explicit.
///
/// The result of const promotion is available from the `mir_promoted` and `promoted_mir` queries.
///
/// This is the version of MIR used by borrowck and friends.
Analysis(AnalysisPhase),
/// The MIR used for CTFE, optimizations, and codegen.
///
/// The semantic changes that occur in the lowering from analysis to runtime MIR are as follows:
///
/// - Drops: In analysis MIR, `Drop` terminators represent *conditional* drops; roughly speaking,
/// if dataflow analysis determines that the place being dropped is uninitialized, the drop will
/// not be executed. The exact semantics of this aren't written down anywhere, which means they
/// are essentially "what drop elaboration does." In runtime MIR, the drops are unconditional;
/// when a `Drop` terminator is reached, if the type has drop glue that drop glue is always
/// executed. This may be UB if the underlying place is not initialized.
/// - Packed drops: Places might in general be misaligned - in most cases this is UB, the exception
/// is fields of packed structs. In analysis MIR, `Drop(P)` for a `P` that might be misaligned
/// for this reason implicitly moves `P` to a temporary before dropping. Runtime MIR has no such
/// rules, and dropping a misaligned place is simply UB.
/// - Unwinding: in analysis MIR, unwinding from a function which may not unwind aborts. In runtime
/// MIR, this is UB.
/// - Retags: If `-Zmir-emit-retag` is enabled, analysis MIR has "implicit" retags in the same way
/// that Rust itself has them. Where exactly these are is generally subject to change, and so we
/// don't document this here. Runtime MIR has most retags explicit (though implicit retags
/// can still occur at `Rvalue::{Ref,AddrOf}`).
/// - Coroutine bodies: In analysis MIR, locals may actually be behind a pointer that user code has
/// access to. This occurs in coroutine bodies. Such locals do not behave like other locals,
/// because they eg may be aliased in surprising ways. Runtime MIR has no such special locals -
/// all coroutine bodies are lowered and so all places that look like locals really are locals.
///
/// Also note that the lint pass which reports eg `200_u8 + 200_u8` as an error is run as a part
/// of analysis to runtime MIR lowering. To ensure lints are reported reliably, this means that
/// transformations which may suppress such errors should not run on analysis MIR.
Runtime(RuntimePhase),
}
impl MirPhase {
pub fn name(&self) -> &'static str {
match *self {
MirPhase::Built => "built",
MirPhase::Analysis(AnalysisPhase::Initial) => "analysis",
MirPhase::Analysis(AnalysisPhase::PostCleanup) => "analysis-post-cleanup",
MirPhase::Runtime(RuntimePhase::Initial) => "runtime",
MirPhase::Runtime(RuntimePhase::PostCleanup) => "runtime-post-cleanup",
MirPhase::Runtime(RuntimePhase::Optimized) => "runtime-optimized",
}
}
pub fn param_env<'tcx>(&self, tcx: TyCtxt<'tcx>, body_def_id: DefId) -> ty::ParamEnv<'tcx> {
match self {
MirPhase::Built | MirPhase::Analysis(_) => tcx.param_env(body_def_id),
MirPhase::Runtime(_) => tcx.param_env_reveal_all_normalized(body_def_id),
}
}
}
/// See [`MirPhase::Analysis`].
#[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
#[derive(HashStable)]
pub enum AnalysisPhase {
Initial = 0,
/// Beginning in this phase, the following variants are disallowed:
/// * [`TerminatorKind::FalseUnwind`]
/// * [`TerminatorKind::FalseEdge`]
/// * [`StatementKind::FakeRead`]
/// * [`StatementKind::AscribeUserType`]
/// * [`StatementKind::Coverage`] with [`CoverageKind::BlockMarker`] or [`CoverageKind::SpanMarker`]
/// * [`Rvalue::Ref`] with `BorrowKind::Fake`
/// * [`CastKind::PointerCoercion`] with any of the following:
/// * [`PointerCoercion::ArrayToPointer`]
/// * [`PointerCoercion::MutToConstPointer`]
///
/// Furthermore, `Deref` projections must be the first projection within any place (if they
/// appear at all)
PostCleanup = 1,
}
/// See [`MirPhase::Runtime`].
#[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
#[derive(HashStable)]
pub enum RuntimePhase {
/// In addition to the semantic changes, beginning with this phase, the following variants are
/// disallowed:
/// * [`TerminatorKind::Yield`]
/// * [`TerminatorKind::CoroutineDrop`]
/// * [`Rvalue::Aggregate`] for any `AggregateKind` except `Array`
/// * [`PlaceElem::OpaqueCast`]
///
/// And the following variants are allowed:
/// * [`StatementKind::Retag`]
/// * [`StatementKind::SetDiscriminant`]
/// * [`StatementKind::Deinit`]
///
/// Furthermore, `Copy` operands are allowed for non-`Copy` types.
Initial = 0,
/// Beginning with this phase, the following variant is disallowed:
/// * [`ProjectionElem::Deref`] of `Box`
PostCleanup = 1,
Optimized = 2,
}
///////////////////////////////////////////////////////////////////////////
// Borrow kinds
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, TyEncodable, TyDecodable)]
#[derive(Hash, HashStable)]
pub enum BorrowKind {
/// Data must be immutable and is aliasable.
Shared,
/// An immutable, aliasable borrow that is discarded after borrow-checking. Can behave either
/// like a normal shared borrow or like a special shallow borrow (see [`FakeBorrowKind`]).
///
/// This is used when lowering index expressions and matches. This is used to prevent code like
/// the following from compiling:
/// ```compile_fail,E0510
/// let mut x: &[_] = &[[0, 1]];
/// let y: &[_] = &[];
/// let _ = x[0][{x = y; 1}];
/// ```
/// ```compile_fail,E0510
/// let mut x = &Some(0);
/// match *x {
/// None => (),
/// Some(_) if { x = &None; false } => (),
/// Some(_) => (),
/// }
/// ```
/// We can also report errors with this kind of borrow differently.
Fake(FakeBorrowKind),
/// Data is mutable and not aliasable.
Mut { kind: MutBorrowKind },
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, TyEncodable, TyDecodable)]
#[derive(Hash, HashStable)]
pub enum MutBorrowKind {
Default,
/// This borrow arose from method-call auto-ref. (i.e., `adjustment::Adjust::Borrow`)
TwoPhaseBorrow,
/// Data must be immutable but not aliasable. This kind of borrow
/// cannot currently be expressed by the user and is used only in
/// implicit closure bindings. It is needed when the closure is
/// borrowing or mutating a mutable referent, e.g.:
/// ```
/// let mut z = 3;
/// let x: &mut isize = &mut z;
/// let y = || *x += 5;
/// ```
/// If we were to try to translate this closure into a more explicit
/// form, we'd encounter an error with the code as written:
/// ```compile_fail,E0594
/// struct Env<'a> { x: &'a &'a mut isize }
/// let mut z = 3;
/// let x: &mut isize = &mut z;
/// let y = (&mut Env { x: &x }, fn_ptr); // Closure is pair of env and fn
/// fn fn_ptr(env: &mut Env) { **env.x += 5; }
/// ```
/// This is then illegal because you cannot mutate an `&mut` found
/// in an aliasable location. To solve, you'd have to translate with
/// an `&mut` borrow:
/// ```compile_fail,E0596
/// struct Env<'a> { x: &'a mut &'a mut isize }
/// let mut z = 3;
/// let x: &mut isize = &mut z;
/// let y = (&mut Env { x: &mut x }, fn_ptr); // changed from &x to &mut x
/// fn fn_ptr(env: &mut Env) { **env.x += 5; }
/// ```
/// Now the assignment to `**env.x` is legal, but creating a
/// mutable pointer to `x` is not because `x` is not mutable. We
/// could fix this by declaring `x` as `let mut x`. This is ok in
/// user code, if awkward, but extra weird for closures, since the
/// borrow is hidden.
///
/// So we introduce a `ClosureCapture` borrow -- user will not have to mark the variable
/// containing the mutable reference as `mut`, as they didn't ever
/// intend to mutate the mutable reference itself. We still mutable capture it in order to
/// mutate the pointed value through it (but not mutating the reference itself).
///
/// This solves the problem. For simplicity, we don't give users the way to express this
/// borrow, it's just used when translating closures.
ClosureCapture,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, TyEncodable, TyDecodable)]
#[derive(Hash, HashStable)]
pub enum FakeBorrowKind {
/// A shared shallow borrow. The immediately borrowed place must be immutable, but projections
/// from it don't need to be. For example, a shallow borrow of `a.b` doesn't conflict with a
/// mutable borrow of `a.b.c`.
///
/// This is used when lowering matches: when matching on a place we want to ensure that place
/// have the same value from the start of the match until an arm is selected. This prevents this
/// code from compiling:
/// ```compile_fail,E0510
/// let mut x = &Some(0);
/// match *x {
/// None => (),
/// Some(_) if { x = &None; false } => (),
/// Some(_) => (),
/// }
/// ```
/// This can't be a shared borrow because mutably borrowing `(*x as Some).0` should not checking
/// the discriminant or accessing other variants, because the mutating `(*x as Some).0` can't
/// affect the discriminant of `x`. E.g. the following is allowed:
/// ```rust
/// let mut x = Some(0);
/// match x {
/// Some(_)
/// if {
/// if let Some(ref mut y) = x {
/// *y += 1;
/// };
/// true
/// } => {}
/// _ => {}
/// }
/// ```
Shallow,
/// A shared (deep) borrow. Data must be immutable and is aliasable.
///
/// This is used when lowering deref patterns, where shallow borrows wouldn't prevent something
/// like:
// ```compile_fail
// let mut b = Box::new(false);
// match b {
// deref!(true) => {} // not reached because `*b == false`
// _ if { *b = true; false } => {} // not reached because the guard is `false`
// deref!(false) => {} // not reached because the guard changed it
// // UB because we reached the unreachable.
// }
// ```
Deep,
}
///////////////////////////////////////////////////////////////////////////
// Statements
/// The various kinds of statements that can appear in MIR.
///
/// Not all of these are allowed at every [`MirPhase`]. Check the documentation there to see which
/// ones you do not have to worry about. The MIR validator will generally enforce such restrictions,
/// causing an ICE if they are violated.
#[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum StatementKind<'tcx> {
/// Assign statements roughly correspond to an assignment in Rust proper (`x = ...`) except
/// without the possibility of dropping the previous value (that must be done separately, if at
/// all). The *exact* way this works is undecided. It probably does something like evaluating
/// the LHS to a place and the RHS to a value, and then storing the value to the place. Various
/// parts of this may do type specific things that are more complicated than simply copying
/// bytes.
///
/// **Needs clarification**: The implication of the above idea would be that assignment implies
/// that the resulting value is initialized. I believe we could commit to this separately from
/// committing to whatever part of the memory model we would need to decide on to make the above
/// paragraph precise. Do we want to?
///
/// Assignments in which the types of the place and rvalue differ are not well-formed.
///
/// **Needs clarification**: Do we ever want to worry about non-free (in the body) lifetimes for
/// the typing requirement in post drop-elaboration MIR? I think probably not - I'm not sure we
/// could meaningfully require this anyway. How about free lifetimes? Is ignoring this
/// interesting for optimizations? Do we want to allow such optimizations?
///
/// **Needs clarification**: We currently require that the LHS place not overlap with any place
/// read as part of computation of the RHS for some rvalues (generally those not producing
/// primitives). This requirement is under discussion in [#68364]. As a part of this discussion,
/// it is also unclear in what order the components are evaluated.
///
/// [#68364]: https://github.com/rust-lang/rust/issues/68364
///
/// See [`Rvalue`] documentation for details on each of those.
Assign(Box<(Place<'tcx>, Rvalue<'tcx>)>),
/// This represents all the reading that a pattern match may do (e.g., inspecting constants and
/// discriminant values), and the kind of pattern it comes from. This is in order to adapt
/// potential error messages to these specific patterns.
///
/// Note that this also is emitted for regular `let` bindings to ensure that locals that are
/// never accessed still get some sanity checks for, e.g., `let x: ! = ..;`
///
/// When executed at runtime this is a nop.
///
/// Disallowed after drop elaboration.
FakeRead(Box<(FakeReadCause, Place<'tcx>)>),
/// Write the discriminant for a variant to the enum Place.
///
/// This is permitted for both coroutines and ADTs. This does not necessarily write to the
/// entire place; instead, it writes to the minimum set of bytes as required by the layout for
/// the type.
SetDiscriminant { place: Box<Place<'tcx>>, variant_index: VariantIdx },
/// Deinitializes the place.
///
/// This writes `uninit` bytes to the entire place.
Deinit(Box<Place<'tcx>>),
/// `StorageLive` and `StorageDead` statements mark the live range of a local.
///
/// At any point during the execution of a function, each local is either allocated or
/// unallocated. Except as noted below, all locals except function parameters are initially
/// unallocated. `StorageLive` statements cause memory to be allocated for the local while
/// `StorageDead` statements cause the memory to be freed. In other words,
/// `StorageLive`/`StorageDead` act like the heap operations `allocate`/`deallocate`, but for
/// stack-allocated local variables. Using a local in any way (not only reading/writing from it)
/// while it is unallocated is UB.
///
/// Some locals have no `StorageLive` or `StorageDead` statements within the entire MIR body.
/// These locals are implicitly allocated for the full duration of the function. There is a
/// convenience method at `rustc_mir_dataflow::storage::always_storage_live_locals` for
/// computing these locals.
///
/// If the local is already allocated, calling `StorageLive` again will implicitly free the
/// local and then allocate fresh uninitilized memory. If a local is already deallocated,
/// calling `StorageDead` again is a NOP.
StorageLive(Local),
/// See `StorageLive` above.
StorageDead(Local),
/// Retag references in the given place, ensuring they got fresh tags.
///
/// This is part of the Stacked Borrows model. These statements are currently only interpreted
/// by miri and only generated when `-Z mir-emit-retag` is passed. See
/// <https://internals.rust-lang.org/t/stacked-borrows-an-aliasing-model-for-rust/8153/> for
/// more details.
///
/// For code that is not specific to stacked borrows, you should consider retags to read and
/// modify the place in an opaque way.
///
/// Only `RetagKind::Default` and `RetagKind::FnEntry` are permitted.
Retag(RetagKind, Box<Place<'tcx>>),
/// This statement exists to preserve a trace of a scrutinee matched against a wildcard binding.
/// This is especially useful for `let _ = PLACE;` bindings that desugar to a single
/// `PlaceMention(PLACE)`.
///
/// When executed at runtime, this computes the given place, but then discards
/// it without doing a load. `let _ = *ptr;` is fine even if the pointer is dangling.
PlaceMention(Box<Place<'tcx>>),
/// Encodes a user's type ascription. These need to be preserved
/// intact so that NLL can respect them. For example:
/// ```ignore (illustrative)
/// let a: T = y;
/// ```
/// The effect of this annotation is to relate the type `T_y` of the place `y`
/// to the user-given type `T`. The effect depends on the specified variance:
///
/// - `Covariant` -- requires that `T_y <: T`
/// - `Contravariant` -- requires that `T_y :> T`
/// - `Invariant` -- requires that `T_y == T`
/// - `Bivariant` -- no effect
///
/// When executed at runtime this is a nop.
///
/// Disallowed after drop elaboration.
AscribeUserType(Box<(Place<'tcx>, UserTypeProjection)>, ty::Variance),
/// Carries control-flow-sensitive information injected by `-Cinstrument-coverage`,
/// such as where to generate physical coverage-counter-increments during codegen.
///
/// Coverage statements are used in conjunction with the coverage mappings and other
/// information stored in the function's
/// [`mir::Body::function_coverage_info`](crate::mir::Body::function_coverage_info).
/// (For inlined MIR, take care to look up the *original function's* coverage info.)
///
/// Interpreters and codegen backends that don't support coverage instrumentation
/// can usually treat this as a no-op.
Coverage(CoverageKind),
/// Denotes a call to an intrinsic that does not require an unwind path and always returns.
/// This avoids adding a new block and a terminator for simple intrinsics.
Intrinsic(Box<NonDivergingIntrinsic<'tcx>>),
/// Instructs the const eval interpreter to increment a counter; this counter is used to track
/// how many steps the interpreter has taken. It is used to prevent the user from writing const
/// code that runs for too long or infinitely. Other than in the const eval interpreter, this
/// is a no-op.
ConstEvalCounter,
/// No-op. Useful for deleting instructions without affecting statement indices.
Nop,
}
impl StatementKind<'_> {
/// Returns a simple string representation of a `StatementKind` variant, independent of any
/// values it might hold (e.g. `StatementKind::Assign` always returns `"Assign"`).
pub const fn name(&self) -> &'static str {
match self {
StatementKind::Assign(..) => "Assign",
StatementKind::FakeRead(..) => "FakeRead",
StatementKind::SetDiscriminant { .. } => "SetDiscriminant",
StatementKind::Deinit(..) => "Deinit",
StatementKind::StorageLive(..) => "StorageLive",
StatementKind::StorageDead(..) => "StorageDead",
StatementKind::Retag(..) => "Retag",
StatementKind::PlaceMention(..) => "PlaceMention",
StatementKind::AscribeUserType(..) => "AscribeUserType",
StatementKind::Coverage(..) => "Coverage",
StatementKind::Intrinsic(..) => "Intrinsic",
StatementKind::ConstEvalCounter => "ConstEvalCounter",
StatementKind::Nop => "Nop",
}
}
}
#[derive(
Clone,
TyEncodable,
TyDecodable,
Debug,
PartialEq,
Hash,
HashStable,
TypeFoldable,
TypeVisitable
)]
pub enum NonDivergingIntrinsic<'tcx> {
/// Denotes a call to the intrinsic function `assume`.
///
/// The operand must be a boolean. Optimizers may use the value of the boolean to backtrack its
/// computation to infer information about other variables. So if the boolean came from a
/// `x < y` operation, subsequent operations on `x` and `y` could elide various bound checks.
/// If the argument is `false`, this operation is equivalent to `TerminatorKind::Unreachable`.
Assume(Operand<'tcx>),
/// Denotes a call to the intrinsic function `copy_nonoverlapping`.
///
/// First, all three operands are evaluated. `src` and `dest` must each be a reference, pointer,
/// or `Box` pointing to the same type `T`. `count` must evaluate to a `usize`. Then, `src` and
/// `dest` are dereferenced, and `count * size_of::<T>()` bytes beginning with the first byte of
/// the `src` place are copied to the contiguous range of bytes beginning with the first byte
/// of `dest`.
///
/// **Needs clarification**: In what order are operands computed and dereferenced? It should
/// probably match the order for assignment, but that is also undecided.
///
/// **Needs clarification**: Is this typed or not, ie is there a typed load and store involved?
/// I vaguely remember Ralf saying somewhere that he thought it should not be.
CopyNonOverlapping(CopyNonOverlapping<'tcx>),
}
/// Describes what kind of retag is to be performed.
#[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, Hash, HashStable)]
#[rustc_pass_by_value]
pub enum RetagKind {
/// The initial retag of arguments when entering a function.
FnEntry,
/// Retag preparing for a two-phase borrow.
TwoPhase,
/// Retagging raw pointers.
Raw,
/// A "normal" retag.
Default,
}
/// The `FakeReadCause` describes the type of pattern why a FakeRead statement exists.
#[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, Hash, HashStable, PartialEq)]
pub enum FakeReadCause {
/// Inject a fake read of the borrowed input at the end of each guards
/// code.
///
/// This should ensure that you cannot change the variant for an enum while
/// you are in the midst of matching on it.
ForMatchGuard,
/// `let x: !; match x {}` doesn't generate any read of x so we need to
/// generate a read of x to check that it is initialized and safe.
///
/// If a closure pattern matches a Place starting with an Upvar, then we introduce a
/// FakeRead for that Place outside the closure, in such a case this option would be
/// Some(closure_def_id).
/// Otherwise, the value of the optional LocalDefId will be None.
//
// We can use LocalDefId here since fake read statements are removed
// before codegen in the `CleanupNonCodegenStatements` pass.
ForMatchedPlace(Option<LocalDefId>),
/// A fake read of the RefWithinGuard version of a bind-by-value variable
/// in a match guard to ensure that its value hasn't change by the time
/// we create the OutsideGuard version.
ForGuardBinding,
/// Officially, the semantics of
///
/// `let pattern = <expr>;`
///
/// is that `<expr>` is evaluated into a temporary and then this temporary is
/// into the pattern.
///
/// However, if we see the simple pattern `let var = <expr>`, we optimize this to
/// evaluate `<expr>` directly into the variable `var`. This is mostly unobservable,
/// but in some cases it can affect the borrow checker, as in #53695.
/// Therefore, we insert a "fake read" here to ensure that we get
/// appropriate errors.
///
/// If a closure pattern matches a Place starting with an Upvar, then we introduce a
/// FakeRead for that Place outside the closure, in such a case this option would be
/// Some(closure_def_id).
/// Otherwise, the value of the optional DefId will be None.
ForLet(Option<LocalDefId>),
/// If we have an index expression like
///
/// (*x)[1][{ x = y; 4}]
///
/// then the first bounds check is invalidated when we evaluate the second
/// index expression. Thus we create a fake borrow of `x` across the second
/// indexer, which will cause a borrow check error.
ForIndex,
}
#[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub struct CopyNonOverlapping<'tcx> {
pub src: Operand<'tcx>,
pub dst: Operand<'tcx>,
/// Number of elements to copy from src to dest, not bytes.
pub count: Operand<'tcx>,
}
/// Represents how a [`TerminatorKind::Call`] was constructed.
/// Used only for diagnostics.
#[derive(Clone, Copy, TyEncodable, TyDecodable, Debug, PartialEq, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum CallSource {
/// This came from something such as `a > b` or `a + b`. In THIR, if `from_hir_call`
/// is false then this is the desugaring.
OverloadedOperator,
/// This was from comparison generated by a match, used by const-eval for better errors
/// when the comparison cannot be done in compile time.
///
/// (see <https://github.com/rust-lang/rust/issues/90237>)
MatchCmp,
/// Other types of desugaring that did not come from the HIR, but we don't care about
/// for diagnostics (yet).
Misc,
/// Normal function call, no special source
Normal,
}
impl CallSource {
pub fn from_hir_call(self) -> bool {
matches!(self, CallSource::Normal)
}
}
#[derive(Clone, Copy, Debug, TyEncodable, TyDecodable, Hash, HashStable, PartialEq)]
#[derive(TypeFoldable, TypeVisitable)]
/// The macro that an inline assembly block was created by
pub enum InlineAsmMacro {
/// The `asm!` macro
Asm,
/// The `naked_asm!` macro
NakedAsm,
}
impl InlineAsmMacro {
pub const fn diverges(self, options: InlineAsmOptions) -> bool {
match self {
InlineAsmMacro::Asm => options.contains(InlineAsmOptions::NORETURN),
InlineAsmMacro::NakedAsm => true,
}
}
}
///////////////////////////////////////////////////////////////////////////
// Terminators
/// The various kinds of terminators, representing ways of exiting from a basic block.
///
/// A note on unwinding: Panics may occur during the execution of some terminators. Depending on the
/// `-C panic` flag, this may either cause the program to abort or the call stack to unwind. Such
/// terminators have a `unwind: UnwindAction` field on them. If stack unwinding occurs, then
/// once the current function is reached, an action will be taken based on the `unwind` field.
/// If the action is `Cleanup`, then the execution continues at the given basic block. If the
/// action is `Continue` then no cleanup is performed, and the stack continues unwinding.
///
/// The basic block pointed to by a `Cleanup` unwind action must have its `cleanup` flag set.
/// `cleanup` basic blocks have a couple restrictions:
/// 1. All `unwind` fields in them must be `UnwindAction::Terminate` or `UnwindAction::Unreachable`.
/// 2. `Return` terminators are not allowed in them. `Terminate` and `Resume` terminators are.
/// 3. All other basic blocks (in the current body) that are reachable from `cleanup` basic blocks
/// must also be `cleanup`. This is a part of the type system and checked statically, so it is
/// still an error to have such an edge in the CFG even if it's known that it won't be taken at
/// runtime.
/// 4. The control flow between cleanup blocks must look like an upside down tree. Roughly
/// speaking, this means that control flow that looks like a V is allowed, while control flow
/// that looks like a W is not. This is necessary to ensure that landing pad information can be
/// correctly codegened on MSVC. More precisely:
///
/// Begin with the standard control flow graph `G`. Modify `G` as follows: for any two cleanup
/// vertices `u` and `v` such that `u` dominates `v`, contract `u` and `v` into a single vertex,
/// deleting self edges and duplicate edges in the process. Now remove all vertices from `G`
/// that are not cleanup vertices or are not reachable. The resulting graph must be an inverted
/// tree, that is each vertex may have at most one successor and there may be no cycles.
#[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, TypeFoldable, TypeVisitable)]
pub enum TerminatorKind<'tcx> {
/// Block has one successor; we continue execution there.
Goto { target: BasicBlock },
/// Switches based on the computed value.
///
/// First, evaluates the `discr` operand. The type of the operand must be a signed or unsigned
/// integer, char, or bool, and must match the given type. Then, if the list of switch targets
/// contains the computed value, continues execution at the associated basic block. Otherwise,
/// continues execution at the "otherwise" basic block.
///
/// Target values may not appear more than once.
SwitchInt {
/// The discriminant value being tested.
discr: Operand<'tcx>,
targets: SwitchTargets,
},
/// Indicates that the landing pad is finished and that the process should continue unwinding.
///
/// Like a return, this marks the end of this invocation of the function.
///
/// Only permitted in cleanup blocks. `Resume` is not permitted with `-C unwind=abort` after
/// deaggregation runs.
UnwindResume,
/// Indicates that the landing pad is finished and that the process should terminate.
///
/// Used to prevent unwinding for foreign items or with `-C unwind=abort`. Only permitted in
/// cleanup blocks.
UnwindTerminate(UnwindTerminateReason),
/// Returns from the function.
///
/// Like function calls, the exact semantics of returns in Rust are unclear. Returning very
/// likely at least assigns the value currently in the return place (`_0`) to the place
/// specified in the associated `Call` terminator in the calling function, as if assigned via
/// `dest = move _0`. It might additionally do other things, like have side-effects in the
/// aliasing model.
///
/// If the body is a coroutine body, this has slightly different semantics; it instead causes a
/// `CoroutineState::Returned(_0)` to be created (as if by an `Aggregate` rvalue) and assigned
/// to the return place.
Return,
/// Indicates a terminator that can never be reached.
///
/// Executing this terminator is UB.
Unreachable,
/// The behavior of this statement differs significantly before and after drop elaboration.
///
/// After drop elaboration: `Drop` terminators are a complete nop for types that have no drop
/// glue. For other types, `Drop` terminators behave exactly like a call to
/// `core::mem::drop_in_place` with a pointer to the given place.
///
/// `Drop` before drop elaboration is a *conditional* execution of the drop glue. Specifically,
/// the `Drop` will be executed if...
///
/// **Needs clarification**: End of that sentence. This in effect should document the exact
/// behavior of drop elaboration. The following sounds vaguely right, but I'm not quite sure:
///
/// > The drop glue is executed if, among all statements executed within this `Body`, an assignment to
/// > the place or one of its "parents" occurred more recently than a move out of it. This does not
/// > consider indirect assignments.
///
/// The `replace` flag indicates whether this terminator was created as part of an assignment.
/// This should only be used for diagnostic purposes, and does not have any operational
/// meaning.
Drop { place: Place<'tcx>, target: BasicBlock, unwind: UnwindAction, replace: bool },
/// Roughly speaking, evaluates the `func` operand and the arguments, and starts execution of
/// the referred to function. The operand types must match the argument types of the function.
/// The return place type must match the return type. The type of the `func` operand must be
/// callable, meaning either a function pointer, a function type, or a closure type.
///
/// **Needs clarification**: The exact semantics of this. Current backends rely on `move`
/// operands not aliasing the return place. It is unclear how this is justified in MIR, see
/// [#71117].
///
/// [#71117]: https://github.com/rust-lang/rust/issues/71117
Call {
/// The function that’s being called.
func: Operand<'tcx>,
/// Arguments the function is called with.
/// These are owned by the callee, which is free to modify them.
/// This allows the memory occupied by "by-value" arguments to be
/// reused across function calls without duplicating the contents.
/// The span for each arg is also included
/// (e.g. `a` and `b` in `x.foo(a, b)`).
args: Box<[Spanned<Operand<'tcx>>]>,
/// Where the returned value will be written
destination: Place<'tcx>,
/// Where to go after this call returns. If none, the call necessarily diverges.
target: Option<BasicBlock>,
/// Action to be taken if the call unwinds.
unwind: UnwindAction,
/// Where this call came from in HIR/THIR.
call_source: CallSource,
/// This `Span` is the span of the function, without the dot and receiver
/// e.g. `foo(a, b)` in `x.foo(a, b)`
fn_span: Span,
},
/// Tail call.
///
/// Roughly speaking this is a chimera of [`Call`] and [`Return`], with some caveats.
/// Semantically tail calls consists of two actions:
/// - pop of the current stack frame
/// - a call to the `func`, with the return address of the **current** caller
/// - so that a `return` inside `func` returns to the caller of the caller
/// of the function that is currently being executed
///
/// Note that in difference with [`Call`] this is missing
/// - `destination` (because it's always the return place)
/// - `target` (because it's always taken from the current stack frame)
/// - `unwind` (because it's always taken from the current stack frame)
///
/// [`Call`]: TerminatorKind::Call
/// [`Return`]: TerminatorKind::Return
TailCall {
/// The function that’s being called.
func: Operand<'tcx>,
/// Arguments the function is called with.
/// These are owned by the callee, which is free to modify them.
/// This allows the memory occupied by "by-value" arguments to be
/// reused across function calls without duplicating the contents.
args: Box<[Spanned<Operand<'tcx>>]>,
// FIXME(explicit_tail_calls): should we have the span for `become`? is this span accurate? do we need it?
/// This `Span` is the span of the function, without the dot and receiver
/// (e.g. `foo(a, b)` in `x.foo(a, b)`
fn_span: Span,
},
/// Evaluates the operand, which must have type `bool`. If it is not equal to `expected`,
/// initiates a panic. Initiating a panic corresponds to a `Call` terminator with some
/// unspecified constant as the function to call, all the operands stored in the `AssertMessage`
/// as parameters, and `None` for the destination. Keep in mind that the `cleanup` path is not
/// necessarily executed even in the case of a panic, for example in `-C panic=abort`. If the
/// assertion does not fail, execution continues at the specified basic block.
///
/// When overflow checking is disabled and this is run-time MIR (as opposed to compile-time MIR
/// that is used for CTFE), the following variants of this terminator behave as `goto target`:
/// - `OverflowNeg(..)`,
/// - `Overflow(op, ..)` if op is add, sub, mul, shl, shr, but NOT div or rem.
Assert {
cond: Operand<'tcx>,
expected: bool,
msg: Box<AssertMessage<'tcx>>,
target: BasicBlock,
unwind: UnwindAction,
},
/// Marks a suspend point.
///
/// Like `Return` terminators in coroutine bodies, this computes `value` and then a
/// `CoroutineState::Yielded(value)` as if by `Aggregate` rvalue. That value is then assigned to
/// the return place of the function calling this one, and execution continues in the calling
/// function. When next invoked with the same first argument, execution of this function
/// continues at the `resume` basic block, with the second argument written to the `resume_arg`
/// place. If the coroutine is dropped before then, the `drop` basic block is invoked.
///
/// Not permitted in bodies that are not coroutine bodies, or after coroutine lowering.
///
/// **Needs clarification**: What about the evaluation order of the `resume_arg` and `value`?
Yield {
/// The value to return.
value: Operand<'tcx>,
/// Where to resume to.
resume: BasicBlock,
/// The place to store the resume argument in.
resume_arg: Place<'tcx>,
/// Cleanup to be done if the coroutine is dropped at this suspend point.
drop: Option<BasicBlock>,
},
/// Indicates the end of dropping a coroutine.
///
/// Semantically just a `return` (from the coroutines drop glue). Only permitted in the same situations
/// as `yield`.
///
/// **Needs clarification**: Is that even correct? The coroutine drop code is always confusing
/// to me, because it's not even really in the current body.
///
/// **Needs clarification**: Are there type system constraints on these terminators? Should
/// there be a "block type" like `cleanup` blocks for them?
CoroutineDrop,
/// A block where control flow only ever takes one real path, but borrowck needs to be more
/// conservative.
///
/// At runtime this is semantically just a goto.
///
/// Disallowed after drop elaboration.
FalseEdge {
/// The target normal control flow will take.
real_target: BasicBlock,
/// A block control flow could conceptually jump to, but won't in
/// practice.
imaginary_target: BasicBlock,
},
/// A terminator for blocks that only take one path in reality, but where we reserve the right
/// to unwind in borrowck, even if it won't happen in practice. This can arise in infinite loops
/// with no function calls for example.
///
/// At runtime this is semantically just a goto.
///
/// Disallowed after drop elaboration.
FalseUnwind {
/// The target normal control flow will take.
real_target: BasicBlock,
/// The imaginary cleanup block link. This particular path will never be taken
/// in practice, but in order to avoid fragility we want to always
/// consider it in borrowck. We don't want to accept programs which
/// pass borrowck only when `panic=abort` or some assertions are disabled
/// due to release vs. debug mode builds.
unwind: UnwindAction,
},
/// Block ends with an inline assembly block. This is a terminator since
/// inline assembly is allowed to diverge.
InlineAsm {
/// Macro used to create this inline asm: one of `asm!` or `naked_asm!`
asm_macro: InlineAsmMacro,
/// The template for the inline assembly, with placeholders.
template: &'tcx [InlineAsmTemplatePiece],
/// The operands for the inline assembly, as `Operand`s or `Place`s.
operands: Box<[InlineAsmOperand<'tcx>]>,
/// Miscellaneous options for the inline assembly.
options: InlineAsmOptions,
/// Source spans for each line of the inline assembly code. These are
/// used to map assembler errors back to the line in the source code.
line_spans: &'tcx [Span],
/// Valid targets for the inline assembly.
/// The first element is the fallthrough destination, unless
/// asm_macro == InlineAsmMacro::NakedAsm or InlineAsmOptions::NORETURN is set.
targets: Box<[BasicBlock]>,
/// Action to be taken if the inline assembly unwinds. This is present
/// if and only if InlineAsmOptions::MAY_UNWIND is set.
unwind: UnwindAction,
},
}
impl TerminatorKind<'_> {
/// Returns a simple string representation of a `TerminatorKind` variant, independent of any
/// values it might hold (e.g. `TerminatorKind::Call` always returns `"Call"`).
pub const fn name(&self) -> &'static str {
match self {
TerminatorKind::Goto { .. } => "Goto",
TerminatorKind::SwitchInt { .. } => "SwitchInt",
TerminatorKind::UnwindResume => "UnwindResume",
TerminatorKind::UnwindTerminate(_) => "UnwindTerminate",
TerminatorKind::Return => "Return",
TerminatorKind::Unreachable => "Unreachable",
TerminatorKind::Drop { .. } => "Drop",
TerminatorKind::Call { .. } => "Call",
TerminatorKind::TailCall { .. } => "TailCall",
TerminatorKind::Assert { .. } => "Assert",
TerminatorKind::Yield { .. } => "Yield",
TerminatorKind::CoroutineDrop => "CoroutineDrop",
TerminatorKind::FalseEdge { .. } => "FalseEdge",
TerminatorKind::FalseUnwind { .. } => "FalseUnwind",
TerminatorKind::InlineAsm { .. } => "InlineAsm",
}
}
}
#[derive(Debug, Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq)]
pub struct SwitchTargets {
/// Possible values. The locations to branch to in each case
/// are found in the corresponding indices from the `targets` vector.
pub(super) values: SmallVec<[Pu128; 1]>,
/// Possible branch sites. The last element of this vector is used
/// for the otherwise branch, so targets.len() == values.len() + 1
/// should hold.
//
// This invariant is quite non-obvious and also could be improved.
// One way to make this invariant is to have something like this instead:
//
// branches: Vec<(ConstInt, BasicBlock)>,
// otherwise: Option<BasicBlock> // exhaustive if None
//
// However we’ve decided to keep this as-is until we figure a case
// where some other approach seems to be strictly better than other.
pub(super) targets: SmallVec<[BasicBlock; 2]>,
}
/// Action to be taken when a stack unwind happens.
#[derive(Copy, Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum UnwindAction {
/// No action is to be taken. Continue unwinding.
///
/// This is similar to `Cleanup(bb)` where `bb` does nothing but `Resume`, but they are not
/// equivalent, as presence of `Cleanup(_)` will make a frame non-POF.
Continue,
/// Triggers undefined behavior if unwind happens.
Unreachable,
/// Terminates the execution if unwind happens.
///
/// Depending on the platform and situation this may cause a non-unwindable panic or abort.
Terminate(UnwindTerminateReason),
/// Cleanups to be done.
Cleanup(BasicBlock),
}
/// The reason we are terminating the process during unwinding.
#[derive(Copy, Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum UnwindTerminateReason {
/// Unwinding is just not possible given the ABI of this function.
Abi,
/// We were already cleaning up for an ongoing unwind, and a *second*, *nested* unwind was
/// triggered by the drop glue.
InCleanup,
}
/// Information about an assertion failure.
#[derive(Clone, Hash, HashStable, PartialEq, Debug)]
#[derive(TyEncodable, TyDecodable, TypeFoldable, TypeVisitable)]
pub enum AssertKind<O> {
BoundsCheck { len: O, index: O },
Overflow(BinOp, O, O),
OverflowNeg(O),
DivisionByZero(O),
RemainderByZero(O),
ResumedAfterReturn(CoroutineKind),
ResumedAfterPanic(CoroutineKind),
MisalignedPointerDereference { required: O, found: O },
}
#[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum InlineAsmOperand<'tcx> {
In {
reg: InlineAsmRegOrRegClass,
value: Operand<'tcx>,
},
Out {
reg: InlineAsmRegOrRegClass,
late: bool,
place: Option<Place<'tcx>>,
},
InOut {
reg: InlineAsmRegOrRegClass,
late: bool,
in_value: Operand<'tcx>,
out_place: Option<Place<'tcx>>,
},
Const {
value: Box<ConstOperand<'tcx>>,
},
SymFn {
value: Box<ConstOperand<'tcx>>,
},
SymStatic {
def_id: DefId,
},
Label {
/// This represents the index into the `targets` array in `TerminatorKind::InlineAsm`.
target_index: usize,
},
}
/// Type for MIR `Assert` terminator error messages.
pub type AssertMessage<'tcx> = AssertKind<Operand<'tcx>>;
///////////////////////////////////////////////////////////////////////////
// Places
/// Places roughly correspond to a "location in memory." Places in MIR are the same mathematical
/// object as places in Rust. This of course means that what exactly they are is undecided and part
/// of the Rust memory model. However, they will likely contain at least the following pieces of
/// information in some form:
///
/// 1. The address in memory that the place refers to.
/// 2. The provenance with which the place is being accessed.
/// 3. The type of the place and an optional variant index. See [`PlaceTy`][super::tcx::PlaceTy].
/// 4. Optionally, some metadata. This exists if and only if the type of the place is not `Sized`.
///
/// We'll give a description below of how all pieces of the place except for the provenance are
/// calculated. We cannot give a description of the provenance, because that is part of the
/// undecided aliasing model - we only include it here at all to acknowledge its existence.
///
/// Each local naturally corresponds to the place `Place { local, projection: [] }`. This place has
/// the address of the local's allocation and the type of the local.
///
/// **Needs clarification:** Unsized locals seem to present a bit of an issue. Their allocation
/// can't actually be created on `StorageLive`, because it's unclear how big to make the allocation.
/// Furthermore, MIR produces assignments to unsized locals, although that is not permitted under
/// `#![feature(unsized_locals)]` in Rust. Besides just putting "unsized locals are special and
/// different" in a bunch of places, I (JakobDegen) don't know how to incorporate this behavior into
/// the current MIR semantics in a clean way - possibly this needs some design work first.
///
/// For places that are not locals, ie they have a non-empty list of projections, we define the
/// values as a function of the parent place, that is the place with its last [`ProjectionElem`]
/// stripped. The way this is computed of course depends on the kind of that last projection
/// element:
///
/// - [`Downcast`](ProjectionElem::Downcast): This projection sets the place's variant index to the
/// given one, and makes no other changes. A `Downcast` projection must always be followed
/// immediately by a `Field` projection.
/// - [`Field`](ProjectionElem::Field): `Field` projections take their parent place and create a
/// place referring to one of the fields of the type. The resulting address is the parent
/// address, plus the offset of the field. The type becomes the type of the field. If the parent
/// was unsized and so had metadata associated with it, then the metadata is retained if the
/// field is unsized and thrown out if it is sized.
///
/// These projections are only legal for tuples, ADTs, closures, and coroutines. If the ADT or
/// coroutine has more than one variant, the parent place's variant index must be set, indicating
/// which variant is being used. If it has just one variant, the variant index may or may not be
/// included - the single possible variant is inferred if it is not included.
/// - [`OpaqueCast`](ProjectionElem::OpaqueCast): This projection changes the place's type to the
/// given one, and makes no other changes. A `OpaqueCast` projection on any type other than an
/// opaque type from the current crate is not well-formed.
/// - [`ConstantIndex`](ProjectionElem::ConstantIndex): Computes an offset in units of `T` into the
/// place as described in the documentation for the `ProjectionElem`. The resulting address is
/// the parent's address plus that offset, and the type is `T`. This is only legal if the parent
/// place has type `[T; N]` or `[T]` (*not* `&[T]`). Since such a `T` is always sized, any
/// resulting metadata is thrown out.
/// - [`Subslice`](ProjectionElem::Subslice): This projection calculates an offset and a new
/// address in a similar manner as `ConstantIndex`. It is also only legal on `[T; N]` and `[T]`.
/// However, this yields a `Place` of type `[T]`, and additionally sets the metadata to be the
/// length of the subslice.
/// - [`Index`](ProjectionElem::Index): Like `ConstantIndex`, only legal on `[T; N]` or `[T]`.
/// However, `Index` additionally takes a local from which the value of the index is computed at
/// runtime. Computing the value of the index involves interpreting the `Local` as a
/// `Place { local, projection: [] }`, and then computing its value as if done via
/// [`Operand::Copy`]. The array/slice is then indexed with the resulting value. The local must
/// have type `usize`.
/// - [`Deref`](ProjectionElem::Deref): Derefs are the last type of projection, and the most
/// complicated. They are only legal on parent places that are references, pointers, or `Box`. A
/// `Deref` projection begins by loading a value from the parent place, as if by
/// [`Operand::Copy`]. It then dereferences the resulting pointer, creating a place of the
/// pointee's type. The resulting address is the address that was stored in the pointer. If the
/// pointee type is unsized, the pointer additionally stored the value of the metadata.
///
/// The "validity invariant" of places is the same as that of raw pointers, meaning that e.g.
/// `*ptr` on a dangling or unaligned pointer is never UB. (Later doing a load/store on that place
/// or turning it into a reference can be UB though!) The only ways for a place computation can
/// cause UB are:
/// - On a `Deref` projection, we do an actual load of the inner place, with all the usual
/// consequences (the inner place must be based on an aligned pointer, it must point to allocated
/// memory, the aliasig model must allow reads, this must not be a data race).
/// - For the projections that perform pointer arithmetic, the offset must in-bounds of an
/// allocation (i.e., the preconditions of `ptr::offset` must be met).
#[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, HashStable, TypeFoldable, TypeVisitable)]
pub struct Place<'tcx> {
pub local: Local,
/// projection out of a place (access a field, deref a pointer, etc)
pub projection: &'tcx List<PlaceElem<'tcx>>,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
pub enum ProjectionElem<V, T> {
Deref,
/// A field (e.g., `f` in `_1.f`) is one variant of [`ProjectionElem`]. Conceptually,
/// rustc can identify that a field projection refers to either two different regions of memory
/// or the same one between the base and the 'projection element'.
/// Read more about projections in the [rustc-dev-guide][mir-datatypes]
///
/// [mir-datatypes]: https://rustc-dev-guide.rust-lang.org/mir/index.html#mir-data-types
Field(FieldIdx, T),
/// Index into a slice/array.
///
/// Note that this does not also dereference, and so it does not exactly correspond to slice
/// indexing in Rust. In other words, in the below Rust code:
///
/// ```rust
/// let x = &[1, 2, 3, 4];
/// let i = 2;
/// x[i];
/// ```
///
/// The `x[i]` is turned into a `Deref` followed by an `Index`, not just an `Index`. The same
/// thing is true of the `ConstantIndex` and `Subslice` projections below.
Index(V),
/// These indices are generated by slice patterns. Easiest to explain
/// by example:
///
/// ```ignore (illustrative)
/// [X, _, .._, _, _] => { offset: 0, min_length: 4, from_end: false },
/// [_, X, .._, _, _] => { offset: 1, min_length: 4, from_end: false },
/// [_, _, .._, X, _] => { offset: 2, min_length: 4, from_end: true },
/// [_, _, .._, _, X] => { offset: 1, min_length: 4, from_end: true },
/// ```
ConstantIndex {
/// index or -index (in Python terms), depending on from_end
offset: u64,
/// The thing being indexed must be at least this long -- otherwise, the
/// projection is UB.
///
/// For arrays this is always the exact length.
min_length: u64,
/// Counting backwards from end? This is always false when indexing an
/// array.
from_end: bool,
},
/// These indices are generated by slice patterns.
///
/// If `from_end` is true `slice[from..slice.len() - to]`.
/// Otherwise `array[from..to]`.
Subslice {
from: u64,
to: u64,
/// Whether `to` counts from the start or end of the array/slice.
/// For `PlaceElem`s this is `true` if and only if the base is a slice.
/// For `ProjectionKind`, this can also be `true` for arrays.
from_end: bool,
},
/// "Downcast" to a variant of an enum or a coroutine.
///
/// The included Symbol is the name of the variant, used for printing MIR.
///
/// This operation itself is never UB, all it does is change the type of the place.
Downcast(Option<Symbol>, VariantIdx),
/// Like an explicit cast from an opaque type to a concrete type, but without
/// requiring an intermediate variable.
OpaqueCast(T),
/// A `Subtype(T)` projection is applied to any `StatementKind::Assign` where
/// type of lvalue doesn't match the type of rvalue, the primary goal is making subtyping
/// explicit during optimizations and codegen.
///
/// This projection doesn't impact the runtime behavior of the program except for potentially changing
/// some type metadata of the interpreter or codegen backend.
///
/// This goal is achieved with mir_transform pass `Subtyper`, which runs right after
/// borrowchecker, as we only care about subtyping that can affect trait selection and
/// `TypeId`.
Subtype(T),
}
/// Alias for projections as they appear in places, where the base is a place
/// and the index is a local.
pub type PlaceElem<'tcx> = ProjectionElem<Local, Ty<'tcx>>;
///////////////////////////////////////////////////////////////////////////
// Operands
/// An operand in MIR represents a "value" in Rust, the definition of which is undecided and part of
/// the memory model. One proposal for a definition of values can be found [on UCG][value-def].
///
/// [value-def]: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/value-domain.md
///
/// The most common way to create values is via loading a place. Loading a place is an operation
/// which reads the memory of the place and converts it to a value. This is a fundamentally *typed*
/// operation. The nature of the value produced depends on the type of the conversion. Furthermore,
/// there may be other effects: if the type has a validity constraint loading the place might be UB
/// if the validity constraint is not met.
///
/// **Needs clarification:** Is loading a place that has its variant index set well-formed? Miri
/// currently implements it, but it seems like this may be something to check against in the
/// validator.
#[derive(Clone, PartialEq, TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
pub enum Operand<'tcx> {
/// Creates a value by loading the given place.
///
/// Before drop elaboration, the type of the place must be `Copy`. After drop elaboration there
/// is no such requirement.
Copy(Place<'tcx>),
/// Creates a value by performing loading the place, just like the `Copy` operand.
///
/// This *may* additionally overwrite the place with `uninit` bytes, depending on how we decide
/// in [UCG#188]. You should not emit MIR that may attempt a subsequent second load of this
/// place without first re-initializing it.
///
/// **Needs clarification:** The operational impact of `Move` is unclear. Currently (both in
/// Miri and codegen) it has no effect at all unless it appears in an argument to `Call`; for
/// `Call` it allows the argument to be passed to the callee "in-place", i.e. the callee might
/// just get a reference to this place instead of a full copy. Miri implements this with a
/// combination of aliasing model "protectors" and putting `uninit` into the place. Ralf
/// proposes that we don't want these semantics for `Move` in regular assignments, because
/// loading a place should not have side-effects, and the aliasing model "protectors" are
/// inherently tied to a function call. Are these the semantics we want for MIR? Is this
/// something we can even decide without knowing more about Rust's memory model?
///
/// [UCG#188]: https://github.com/rust-lang/unsafe-code-guidelines/issues/188
Move(Place<'tcx>),
/// Constants are already semantically values, and remain unchanged.
Constant(Box<ConstOperand<'tcx>>),
}
#[derive(Clone, Copy, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub struct ConstOperand<'tcx> {
pub span: Span,
/// Optional user-given type: for something like
/// `collect::<Vec<_>>`, this would be present and would
/// indicate that `Vec<_>` was explicitly specified.
///
/// Needed for NLL to impose user-given type constraints.
pub user_ty: Option<UserTypeAnnotationIndex>,
pub const_: Const<'tcx>,
}
///////////////////////////////////////////////////////////////////////////
// Rvalues
/// The various kinds of rvalues that can appear in MIR.
///
/// Not all of these are allowed at every [`MirPhase`] - when this is the case, it's stated below.
///
/// Computing any rvalue begins by evaluating the places and operands in some order (**Needs
/// clarification**: Which order?). These are then used to produce a "value" - the same kind of
/// value that an [`Operand`] produces.
#[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, TypeFoldable, TypeVisitable)]
pub enum Rvalue<'tcx> {
/// Yields the operand unchanged
Use(Operand<'tcx>),
/// Creates an array where each element is the value of the operand.
///
/// This is the cause of a bug in the case where the repetition count is zero because the value
/// is not dropped, see [#74836].
///
/// Corresponds to source code like `[x; 32]`.
///
/// [#74836]: https://github.com/rust-lang/rust/issues/74836
Repeat(Operand<'tcx>, ty::Const<'tcx>),
/// Creates a reference of the indicated kind to the place.
///
/// There is not much to document here, because besides the obvious parts the semantics of this
/// are essentially entirely a part of the aliasing model. There are many UCG issues discussing
/// exactly what the behavior of this operation should be.
///
/// `Shallow` borrows are disallowed after drop lowering.
Ref(Region<'tcx>, BorrowKind, Place<'tcx>),
/// Creates a pointer/reference to the given thread local.
///
/// The yielded type is a `*mut T` if the static is mutable, otherwise if the static is extern a
/// `*const T`, and if neither of those apply a `&T`.
///
/// **Note:** This is a runtime operation that actually executes code and is in this sense more
/// like a function call. Also, eliminating dead stores of this rvalue causes `fn main() {}` to
/// SIGILL for some reason that I (JakobDegen) never got a chance to look into.
///
/// **Needs clarification**: Are there weird additional semantics here related to the runtime
/// nature of this operation?
ThreadLocalRef(DefId),
/// Creates a raw pointer with the indicated mutability to the place.
///
/// This is generated by pointer casts like `&v as *const _` or raw borrow expressions like
/// `&raw const v`.
///
/// Like with references, the semantics of this operation are heavily dependent on the aliasing
/// model.
RawPtr(Mutability, Place<'tcx>),
/// Yields the length of the place, as a `usize`.
///
/// If the type of the place is an array, this is the array length. For slices (`[T]`, not
/// `&[T]`) this accesses the place's metadata to determine the length. This rvalue is
/// ill-formed for places of other types.
///
/// This cannot be a `UnOp(PtrMetadata, _)` because that expects a value, and we only
/// have a place, and `UnOp(PtrMetadata, RawPtr(place))` is not a thing.
Len(Place<'tcx>),
/// Performs essentially all of the casts that can be performed via `as`.
///
/// This allows for casts from/to a variety of types.
///
/// **FIXME**: Document exactly which `CastKind`s allow which types of casts.
Cast(CastKind, Operand<'tcx>, Ty<'tcx>),
/// * `Offset` has the same semantics as [`offset`](pointer::offset), except that the second
/// parameter may be a `usize` as well.
/// * The comparison operations accept `bool`s, `char`s, signed or unsigned integers, floats,
/// raw pointers, or function pointers and return a `bool`. The types of the operands must be
/// matching, up to the usual caveat of the lifetimes in function pointers.
/// * Left and right shift operations accept signed or unsigned integers not necessarily of the
/// same type and return a value of the same type as their LHS. Like in Rust, the RHS is
/// truncated as needed.
/// * The `Bit*` operations accept signed integers, unsigned integers, or bools with matching
/// types and return a value of that type.
/// * The `FooWithOverflow` are like the `Foo`, but returning `(T, bool)` instead of just `T`,
/// where the `bool` is true if the result is not equal to the infinite-precision result.
/// * The remaining operations accept signed integers, unsigned integers, or floats with
/// matching types and return a value of that type.
BinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),
/// Computes a value as described by the operation.
NullaryOp(NullOp<'tcx>, Ty<'tcx>),
/// Exactly like `BinaryOp`, but less operands.
///
/// Also does two's-complement arithmetic. Negation requires a signed integer or a float;
/// bitwise not requires a signed integer, unsigned integer, or bool. Both operation kinds
/// return a value with the same type as their operand.
UnaryOp(UnOp, Operand<'tcx>),
/// Computes the discriminant of the place, returning it as an integer of type
/// [`discriminant_ty`]. Returns zero for types without discriminant.
///
/// The validity requirements for the underlying value are undecided for this rvalue, see
/// [#91095]. Note too that the value of the discriminant is not the same thing as the
/// variant index; use [`discriminant_for_variant`] to convert.
///
/// [`discriminant_ty`]: crate::ty::Ty::discriminant_ty
/// [#91095]: https://github.com/rust-lang/rust/issues/91095
/// [`discriminant_for_variant`]: crate::ty::Ty::discriminant_for_variant
Discriminant(Place<'tcx>),
/// Creates an aggregate value, like a tuple or struct.
///
/// This is needed because dataflow analysis needs to distinguish
/// `dest = Foo { x: ..., y: ... }` from `dest.x = ...; dest.y = ...;` in the case that `Foo`
/// has a destructor.
///
/// Disallowed after deaggregation for all aggregate kinds except `Array` and `Coroutine`. After
/// coroutine lowering, `Coroutine` aggregate kinds are disallowed too.
Aggregate(Box<AggregateKind<'tcx>>, IndexVec<FieldIdx, Operand<'tcx>>),
/// Transmutes a `*mut u8` into shallow-initialized `Box<T>`.
///
/// This is different from a normal transmute because dataflow analysis will treat the box as
/// initialized but its content as uninitialized. Like other pointer casts, this in general
/// affects alias analysis.
ShallowInitBox(Operand<'tcx>, Ty<'tcx>),
/// A CopyForDeref is equivalent to a read from a place at the
/// codegen level, but is treated specially by drop elaboration. When such a read happens, it
/// is guaranteed (via nature of the mir_opt `Derefer` in rustc_mir_transform/src/deref_separator)
/// that the only use of the returned value is a deref operation, immediately
/// followed by one or more projections. Drop elaboration treats this rvalue as if the
/// read never happened and just projects further. This allows simplifying various MIR
/// optimizations and codegen backends that previously had to handle deref operations anywhere
/// in a place.
CopyForDeref(Place<'tcx>),
}
#[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
pub enum CastKind {
/// An exposing pointer to address cast. A cast between a pointer and an integer type, or
/// between a function pointer and an integer type.
/// See the docs on `expose_provenance` for more details.
PointerExposeProvenance,
/// An address-to-pointer cast that picks up an exposed provenance.
/// See the docs on `with_exposed_provenance` for more details.
PointerWithExposedProvenance,
/// Pointer related casts that are done by coercions. Note that reference-to-raw-ptr casts are
/// translated into `&raw mut/const *r`, i.e., they are not actually casts.
///
/// The following are allowed in [`AnalysisPhase::Initial`] as they're needed for borrowck,
/// but after that are forbidden (including in all phases of runtime MIR):
/// * [`PointerCoercion::ArrayToPointer`]
/// * [`PointerCoercion::MutToConstPointer`]
///
/// Both are runtime nops, so should be [`CastKind::PtrToPtr`] instead in runtime MIR.
PointerCoercion(PointerCoercion, CoercionSource),
IntToInt,
FloatToInt,
FloatToFloat,
IntToFloat,
PtrToPtr,
FnPtrToPtr,
/// Reinterpret the bits of the input as a different type.
///
/// MIR is well-formed if the input and output types have different sizes,
/// but running a transmute between differently-sized types is UB.
///
/// Allowed only in [`MirPhase::Runtime`]; Earlier it's a [`TerminatorKind::Call`].
Transmute,
}
/// Represents how a [`CastKind::PointerCoercion`] was constructed.
/// Used only for diagnostics.
#[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
pub enum CoercionSource {
/// The coercion was manually written by the user with an `as` cast.
AsCast,
/// The coercion was automatically inserted by the compiler.
Implicit,
}
#[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum AggregateKind<'tcx> {
/// The type is of the element
Array(Ty<'tcx>),
Tuple,
/// The second field is the variant index. It's equal to 0 for struct
/// and union expressions. The last field is the
/// active field number and is present only for union expressions
/// -- e.g., for a union expression `SomeUnion { c: .. }`, the
/// active field index would identity the field `c`
Adt(DefId, VariantIdx, GenericArgsRef<'tcx>, Option<UserTypeAnnotationIndex>, Option<FieldIdx>),
Closure(DefId, GenericArgsRef<'tcx>),
Coroutine(DefId, GenericArgsRef<'tcx>),
CoroutineClosure(DefId, GenericArgsRef<'tcx>),
/// Construct a raw pointer from the data pointer and metadata.
///
/// The `Ty` here is the type of the *pointee*, not the pointer itself.
/// The `Mutability` indicates whether this produces a `*const` or `*mut`.
///
/// The [`Rvalue::Aggregate`] operands for thus must be
///
/// 0. A raw pointer of matching mutability with any [`core::ptr::Thin`] pointee
/// 1. A value of the appropriate [`core::ptr::Pointee::Metadata`] type
///
/// *Both* operands must always be included, even the unit value if this is
/// creating a thin pointer. If you're just converting between thin pointers,
/// you may want an [`Rvalue::Cast`] with [`CastKind::PtrToPtr`] instead.
RawPtr(Ty<'tcx>, Mutability),
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
pub enum NullOp<'tcx> {
/// Returns the size of a value of that type
SizeOf,
/// Returns the minimum alignment of a type
AlignOf,
/// Returns the offset of a field
OffsetOf(&'tcx List<(VariantIdx, FieldIdx)>),
/// Returns whether we should perform some UB-checking at runtime.
/// See the `ub_checks` intrinsic docs for details.
UbChecks,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[derive(HashStable, TyEncodable, TyDecodable, TypeFoldable, TypeVisitable)]
pub enum UnOp {
/// The `!` operator for logical inversion
Not,
/// The `-` operator for negation
Neg,
/// Gets the metadata `M` from a `*const`/`*mut`/`&`/`&mut` to
/// `impl Pointee<Metadata = M>`.
///
/// For example, this will give a `()` from `*const i32`, a `usize` from
/// `&mut [u8]`, or a `ptr::DynMetadata<dyn Foo>` (internally a pointer)
/// from a `*mut dyn Foo`.
///
/// Allowed only in [`MirPhase::Runtime`]; earlier it's an intrinsic.
PtrMetadata,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
pub enum BinOp {
/// The `+` operator (addition)
Add,
/// Like `Add`, but with UB on overflow. (Integers only.)
AddUnchecked,
/// Like `Add`, but returns `(T, bool)` of both the wrapped result
/// and a bool indicating whether it overflowed.
AddWithOverflow,
/// The `-` operator (subtraction)
Sub,
/// Like `Sub`, but with UB on overflow. (Integers only.)
SubUnchecked,
/// Like `Sub`, but returns `(T, bool)` of both the wrapped result
/// and a bool indicating whether it overflowed.
SubWithOverflow,
/// The `*` operator (multiplication)
Mul,
/// Like `Mul`, but with UB on overflow. (Integers only.)
MulUnchecked,
/// Like `Mul`, but returns `(T, bool)` of both the wrapped result
/// and a bool indicating whether it overflowed.
MulWithOverflow,
/// The `/` operator (division)
///
/// For integer types, division by zero is UB, as is `MIN / -1` for signed.
/// The compiler should have inserted checks prior to this.
///
/// Floating-point division by zero is safe, and does not need guards.
Div,
/// The `%` operator (modulus)
///
/// For integer types, using zero as the modulus (second operand) is UB,
/// as is `MIN % -1` for signed.
/// The compiler should have inserted checks prior to this.
///
/// Floating-point remainder by zero is safe, and does not need guards.
Rem,
/// The `^` operator (bitwise xor)
BitXor,
/// The `&` operator (bitwise and)
BitAnd,
/// The `|` operator (bitwise or)
BitOr,
/// The `<<` operator (shift left)
///
/// The offset is given by `RHS.rem_euclid(LHS::BITS)`.
/// In other words, it is (uniquely) determined as follows:
/// - it is "equal modulo LHS::BITS" to the RHS
/// - it is in the range `0..LHS::BITS`
Shl,
/// Like `Shl`, but is UB if the RHS >= LHS::BITS or RHS < 0
ShlUnchecked,
/// The `>>` operator (shift right)
///
/// The offset is given by `RHS.rem_euclid(LHS::BITS)`.
/// In other words, it is (uniquely) determined as follows:
/// - it is "equal modulo LHS::BITS" to the RHS
/// - it is in the range `0..LHS::BITS`
///
/// This is an arithmetic shift if the LHS is signed
/// and a logical shift if the LHS is unsigned.
Shr,
/// Like `Shl`, but is UB if the RHS >= LHS::BITS or RHS < 0
ShrUnchecked,
/// The `==` operator (equality)
Eq,
/// The `<` operator (less than)
Lt,
/// The `<=` operator (less than or equal to)
Le,
/// The `!=` operator (not equal to)
Ne,
/// The `>=` operator (greater than or equal to)
Ge,
/// The `>` operator (greater than)
Gt,
/// The `<=>` operator (three-way comparison, like `Ord::cmp`)
///
/// This is supported only on the integer types and `char`, always returning
/// [`rustc_hir::LangItem::OrderingEnum`] (aka [`std::cmp::Ordering`]).
///
/// [`Rvalue::BinaryOp`]`(BinOp::Cmp, A, B)` returns
/// - `Ordering::Less` (`-1_i8`, as a Scalar) if `A < B`
/// - `Ordering::Equal` (`0_i8`, as a Scalar) if `A == B`
/// - `Ordering::Greater` (`+1_i8`, as a Scalar) if `A > B`
Cmp,
/// The `ptr.offset` operator
Offset,
}
// Some nodes are used a lot. Make sure they don't unintentionally get bigger.
#[cfg(target_pointer_width = "64")]
mod size_asserts {
use rustc_data_structures::static_assert_size;
use super::*;
// tidy-alphabetical-start
static_assert_size!(AggregateKind<'_>, 32);
static_assert_size!(Operand<'_>, 24);
static_assert_size!(Place<'_>, 16);
static_assert_size!(PlaceElem<'_>, 24);
static_assert_size!(Rvalue<'_>, 40);
static_assert_size!(StatementKind<'_>, 16);
static_assert_size!(TerminatorKind<'_>, 80);
// tidy-alphabetical-end
}