1 //! This defines the syntax of MIR, i.e., the set of available MIR operations, and other definitions
2 //! closely related to MIR semantics.
3 //! This is in a dedicated file so that changes to this file can be reviewed more carefully.
4 //! The intention is that this file only contains datatype declarations, no code.
6 use super::{BasicBlock, Constant, Field, Local, SwitchTargets, UserTypeProjection};
8 use crate::mir::coverage::{CodeRegion, CoverageKind};
9 use crate::ty::adjustment::PointerCast;
10 use crate::ty::subst::SubstsRef;
11 use crate::ty::{self, List, Ty};
12 use crate::ty::{Region, UserTypeAnnotationIndex};
14 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
15 use rustc_hir::def_id::DefId;
16 use rustc_hir::{self as hir};
17 use rustc_hir::{self, GeneratorKind};
18 use rustc_target::abi::VariantIdx;
20 use rustc_ast::Mutability;
21 use rustc_span::def_id::LocalDefId;
22 use rustc_span::symbol::Symbol;
24 use rustc_target::asm::InlineAsmRegOrRegClass;
26 /// Represents the "flavors" of MIR.
28 /// All flavors of MIR use the same data structure, but there are some important differences. These
29 /// differences come in two forms: Dialects and phases.
31 /// Dialects represent a stronger distinction than phases. This is because the transitions between
32 /// dialects are semantic changes, and therefore technically *lowerings* between distinct IRs. In
33 /// other words, the same [`Body`](crate::mir::Body) might be well-formed for multiple dialects, but
34 /// have different semantic meaning and different behavior at runtime.
36 /// Each dialect additionally has a number of phases. However, phase changes never involve semantic
37 /// changes. If some MIR is well-formed both before and after a phase change, it is also guaranteed
38 /// that it has the same semantic meaning. In this sense, phase changes can only add additional
39 /// restrictions on what MIR is well-formed.
41 /// When adding phases, remember to update [`MirPhase::phase_index`].
42 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
45 /// The MIR that is generated by MIR building.
47 /// The only things that operate on this dialect are unsafeck, the various MIR lints, and const
50 /// This has no distinct phases.
52 /// The MIR used for most analysis.
54 /// The only semantic change between analysis and built MIR is constant promotion. In built MIR,
55 /// sequences of statements that would generally be subject to constant promotion are
56 /// semantically constants, while in analysis MIR all constants are explicit.
58 /// The result of const promotion is available from the `mir_promoted` and `promoted_mir` queries.
60 /// This is the version of MIR used by borrowck and friends.
61 Analysis(AnalysisPhase),
62 /// The MIR used for CTFE, optimizations, and codegen.
64 /// The semantic changes that occur in the lowering from analysis to runtime MIR are as follows:
66 /// - Drops: In analysis MIR, `Drop` terminators represent *conditional* drops; roughly speaking,
67 /// if dataflow analysis determines that the place being dropped is uninitialized, the drop will
68 /// not be executed. The exact semantics of this aren't written down anywhere, which means they
69 /// are essentially "what drop elaboration does." In runtime MIR, the drops are unconditional;
70 /// when a `Drop` terminator is reached, if the type has drop glue that drop glue is always
71 /// executed. This may be UB if the underlying place is not initialized.
72 /// - Packed drops: Places might in general be misaligned - in most cases this is UB, the exception
73 /// is fields of packed structs. In analysis MIR, `Drop(P)` for a `P` that might be misaligned
74 /// for this reason implicitly moves `P` to a temporary before dropping. Runtime MIR has no such
75 /// rules, and dropping a misaligned place is simply UB.
76 /// - Unwinding: in analysis MIR, unwinding from a function which may not unwind aborts. In runtime
78 /// - Retags: If `-Zmir-emit-retag` is enabled, analysis MIR has "implicit" retags in the same way
79 /// that Rust itself has them. Where exactly these are is generally subject to change, and so we
80 /// don't document this here. Runtime MIR has all retags explicit.
81 /// - Generator bodies: In analysis MIR, locals may actually be behind a pointer that user code has
82 /// access to. This occurs in generator bodies. Such locals do not behave like other locals,
83 /// because they eg may be aliased in surprising ways. Runtime MIR has no such special locals -
84 /// all generator bodies are lowered and so all places that look like locals really are locals.
86 /// Also note that the lint pass which reports eg `200_u8 + 200_u8` as an error is run as a part
87 /// of analysis to runtime MIR lowering. To ensure lints are reported reliably, this means that
88 /// transformations which may suppress such errors should not run on analysis MIR.
89 Runtime(RuntimePhase),
93 pub fn name(&self) -> &'static str {
95 MirPhase::Built => "built",
96 MirPhase::Analysis(AnalysisPhase::Initial) => "analysis",
97 MirPhase::Analysis(AnalysisPhase::PostCleanup) => "analysis-post-cleanup",
98 MirPhase::Runtime(RuntimePhase::Initial) => "runtime",
99 MirPhase::Runtime(RuntimePhase::PostCleanup) => "runtime-post-cleanup",
100 MirPhase::Runtime(RuntimePhase::Optimized) => "runtime-optimized",
105 /// See [`MirPhase::Analysis`].
106 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
107 #[derive(HashStable)]
108 pub enum AnalysisPhase {
110 /// Beginning in this phase, the following variants are disallowed:
111 /// * [`TerminatorKind::FalseUnwind`]
112 /// * [`TerminatorKind::FalseEdge`]
113 /// * [`StatementKind::FakeRead`]
114 /// * [`StatementKind::AscribeUserType`]
115 /// * [`Rvalue::Ref`] with `BorrowKind::Shallow`
117 /// Furthermore, `Deref` projections must be the first projection within any place (if they
122 /// See [`MirPhase::Runtime`].
123 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
124 #[derive(HashStable)]
125 pub enum RuntimePhase {
126 /// In addition to the semantic changes, beginning with this phase, the following variants are
128 /// * [`TerminatorKind::DropAndReplace`]
129 /// * [`TerminatorKind::Yield`]
130 /// * [`TerminatorKind::GeneratorDrop`]
131 /// * [`Rvalue::Aggregate`] for any `AggregateKind` except `Array`
133 /// And the following variants are allowed:
134 /// * [`StatementKind::Retag`]
135 /// * [`StatementKind::SetDiscriminant`]
136 /// * [`StatementKind::Deinit`]
138 /// Furthermore, `Copy` operands are allowed for non-`Copy` types.
140 /// Beginning with this phase, the following variant is disallowed:
141 /// * [`ProjectionElem::Deref`] of `Box`
146 ///////////////////////////////////////////////////////////////////////////
149 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, TyEncodable, TyDecodable)]
150 #[derive(Hash, HashStable)]
151 pub enum BorrowKind {
152 /// Data must be immutable and is aliasable.
155 /// The immediately borrowed place must be immutable, but projections from
156 /// it don't need to be. For example, a shallow borrow of `a.b` doesn't
157 /// conflict with a mutable borrow of `a.b.c`.
159 /// This is used when lowering matches: when matching on a place we want to
160 /// ensure that place have the same value from the start of the match until
161 /// an arm is selected. This prevents this code from compiling:
162 /// ```compile_fail,E0510
163 /// let mut x = &Some(0);
166 /// Some(_) if { x = &None; false } => (),
170 /// This can't be a shared borrow because mutably borrowing (*x as Some).0
171 /// should not prevent `if let None = x { ... }`, for example, because the
172 /// mutating `(*x as Some).0` can't affect the discriminant of `x`.
173 /// We can also report errors with this kind of borrow differently.
176 /// Data must be immutable but not aliasable. This kind of borrow
177 /// cannot currently be expressed by the user and is used only in
178 /// implicit closure bindings. It is needed when the closure is
179 /// borrowing or mutating a mutable referent, e.g.:
182 /// let x: &mut isize = &mut z;
183 /// let y = || *x += 5;
185 /// If we were to try to translate this closure into a more explicit
186 /// form, we'd encounter an error with the code as written:
187 /// ```compile_fail,E0594
188 /// struct Env<'a> { x: &'a &'a mut isize }
190 /// let x: &mut isize = &mut z;
191 /// let y = (&mut Env { x: &x }, fn_ptr); // Closure is pair of env and fn
192 /// fn fn_ptr(env: &mut Env) { **env.x += 5; }
194 /// This is then illegal because you cannot mutate an `&mut` found
195 /// in an aliasable location. To solve, you'd have to translate with
196 /// an `&mut` borrow:
197 /// ```compile_fail,E0596
198 /// struct Env<'a> { x: &'a mut &'a mut isize }
200 /// let x: &mut isize = &mut z;
201 /// let y = (&mut Env { x: &mut x }, fn_ptr); // changed from &x to &mut x
202 /// fn fn_ptr(env: &mut Env) { **env.x += 5; }
204 /// Now the assignment to `**env.x` is legal, but creating a
205 /// mutable pointer to `x` is not because `x` is not mutable. We
206 /// could fix this by declaring `x` as `let mut x`. This is ok in
207 /// user code, if awkward, but extra weird for closures, since the
208 /// borrow is hidden.
210 /// So we introduce a "unique imm" borrow -- the referent is
211 /// immutable, but not aliasable. This solves the problem. For
212 /// simplicity, we don't give users the way to express this
213 /// borrow, it's just used when translating closures.
216 /// Data is mutable and not aliasable.
218 /// `true` if this borrow arose from method-call auto-ref
219 /// (i.e., `adjustment::Adjust::Borrow`).
220 allow_two_phase_borrow: bool,
224 ///////////////////////////////////////////////////////////////////////////
227 /// The various kinds of statements that can appear in MIR.
229 /// Not all of these are allowed at every [`MirPhase`]. Check the documentation there to see which
230 /// ones you do not have to worry about. The MIR validator will generally enforce such restrictions,
231 /// causing an ICE if they are violated.
232 #[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
233 #[derive(TypeFoldable, TypeVisitable)]
234 pub enum StatementKind<'tcx> {
235 /// Assign statements roughly correspond to an assignment in Rust proper (`x = ...`) except
236 /// without the possibility of dropping the previous value (that must be done separately, if at
237 /// all). The *exact* way this works is undecided. It probably does something like evaluating
238 /// the LHS to a place and the RHS to a value, and then storing the value to the place. Various
239 /// parts of this may do type specific things that are more complicated than simply copying
242 /// **Needs clarification**: The implication of the above idea would be that assignment implies
243 /// that the resulting value is initialized. I believe we could commit to this separately from
244 /// committing to whatever part of the memory model we would need to decide on to make the above
245 /// paragragh precise. Do we want to?
247 /// Assignments in which the types of the place and rvalue differ are not well-formed.
249 /// **Needs clarification**: Do we ever want to worry about non-free (in the body) lifetimes for
250 /// the typing requirement in post drop-elaboration MIR? I think probably not - I'm not sure we
251 /// could meaningfully require this anyway. How about free lifetimes? Is ignoring this
252 /// interesting for optimizations? Do we want to allow such optimizations?
254 /// **Needs clarification**: We currently require that the LHS place not overlap with any place
255 /// read as part of computation of the RHS for some rvalues (generally those not producing
256 /// primitives). This requirement is under discussion in [#68364]. As a part of this discussion,
257 /// it is also unclear in what order the components are evaluated.
259 /// [#68364]: https://github.com/rust-lang/rust/issues/68364
261 /// See [`Rvalue`] documentation for details on each of those.
262 Assign(Box<(Place<'tcx>, Rvalue<'tcx>)>),
264 /// This represents all the reading that a pattern match may do (e.g., inspecting constants and
265 /// discriminant values), and the kind of pattern it comes from. This is in order to adapt
266 /// potential error messages to these specific patterns.
268 /// Note that this also is emitted for regular `let` bindings to ensure that locals that are
269 /// never accessed still get some sanity checks for, e.g., `let x: ! = ..;`
271 /// When executed at runtime this is a nop.
273 /// Disallowed after drop elaboration.
274 FakeRead(Box<(FakeReadCause, Place<'tcx>)>),
276 /// Write the discriminant for a variant to the enum Place.
278 /// This is permitted for both generators and ADTs. This does not necessarily write to the
279 /// entire place; instead, it writes to the minimum set of bytes as required by the layout for
281 SetDiscriminant { place: Box<Place<'tcx>>, variant_index: VariantIdx },
283 /// Deinitializes the place.
285 /// This writes `uninit` bytes to the entire place.
286 Deinit(Box<Place<'tcx>>),
288 /// `StorageLive` and `StorageDead` statements mark the live range of a local.
290 /// At any point during the execution of a function, each local is either allocated or
291 /// unallocated. Except as noted below, all locals except function parameters are initially
292 /// unallocated. `StorageLive` statements cause memory to be allocated for the local while
293 /// `StorageDead` statements cause the memory to be freed. Using a local in any way (not only
294 /// reading/writing from it) while it is unallocated is UB.
296 /// Some locals have no `StorageLive` or `StorageDead` statements within the entire MIR body.
297 /// These locals are implicitly allocated for the full duration of the function. There is a
298 /// convenience method at `rustc_mir_dataflow::storage::always_storage_live_locals` for
299 /// computing these locals.
301 /// If the local is already allocated, calling `StorageLive` again is UB. However, for an
302 /// unallocated local an additional `StorageDead` all is simply a nop.
305 /// See `StorageLive` above.
308 /// Retag references in the given place, ensuring they got fresh tags.
310 /// This is part of the Stacked Borrows model. These statements are currently only interpreted
311 /// by miri and only generated when `-Z mir-emit-retag` is passed. See
312 /// <https://internals.rust-lang.org/t/stacked-borrows-an-aliasing-model-for-rust/8153/> for
315 /// For code that is not specific to stacked borrows, you should consider retags to read
316 /// and modify the place in an opaque way.
317 Retag(RetagKind, Box<Place<'tcx>>),
319 /// Encodes a user's type ascription. These need to be preserved
320 /// intact so that NLL can respect them. For example:
321 /// ```ignore (illustrative)
324 /// The effect of this annotation is to relate the type `T_y` of the place `y`
325 /// to the user-given type `T`. The effect depends on the specified variance:
327 /// - `Covariant` -- requires that `T_y <: T`
328 /// - `Contravariant` -- requires that `T_y :> T`
329 /// - `Invariant` -- requires that `T_y == T`
330 /// - `Bivariant` -- no effect
332 /// When executed at runtime this is a nop.
334 /// Disallowed after drop elaboration.
335 AscribeUserType(Box<(Place<'tcx>, UserTypeProjection)>, ty::Variance),
337 /// Marks the start of a "coverage region", injected with '-Cinstrument-coverage'. A
338 /// `Coverage` statement carries metadata about the coverage region, used to inject a coverage
339 /// map into the binary. If `Coverage::kind` is a `Counter`, the statement also generates
340 /// executable code, to increment a counter variable at runtime, each time the code region is
342 Coverage(Box<Coverage>),
344 /// Denotes a call to an intrinsic that does not require an unwind path and always returns.
345 /// This avoids adding a new block and a terminator for simple intrinsics.
346 Intrinsic(Box<NonDivergingIntrinsic<'tcx>>),
348 /// No-op. Useful for deleting instructions without affecting statement indices.
363 pub enum NonDivergingIntrinsic<'tcx> {
364 /// Denotes a call to the intrinsic function `assume`.
366 /// The operand must be a boolean. Optimizers may use the value of the boolean to backtrack its
367 /// computation to infer information about other variables. So if the boolean came from a
368 /// `x < y` operation, subsequent operations on `x` and `y` could elide various bound checks.
369 /// If the argument is `false`, this operation is equivalent to `TerminatorKind::Unreachable`.
370 Assume(Operand<'tcx>),
372 /// Denotes a call to the intrinsic function `copy_nonoverlapping`.
374 /// First, all three operands are evaluated. `src` and `dest` must each be a reference, pointer,
375 /// or `Box` pointing to the same type `T`. `count` must evaluate to a `usize`. Then, `src` and
376 /// `dest` are dereferenced, and `count * size_of::<T>()` bytes beginning with the first byte of
377 /// the `src` place are copied to the contiguous range of bytes beginning with the first byte
380 /// **Needs clarification**: In what order are operands computed and dereferenced? It should
381 /// probably match the order for assignment, but that is also undecided.
383 /// **Needs clarification**: Is this typed or not, ie is there a typed load and store involved?
384 /// I vaguely remember Ralf saying somewhere that he thought it should not be.
385 CopyNonOverlapping(CopyNonOverlapping<'tcx>),
388 impl std::fmt::Display for NonDivergingIntrinsic<'_> {
389 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
391 Self::Assume(op) => write!(f, "assume({op:?})"),
392 Self::CopyNonOverlapping(CopyNonOverlapping { src, dst, count }) => {
393 write!(f, "copy_nonoverlapping(dst = {dst:?}, src = {src:?}, count = {count:?})")
399 /// Describes what kind of retag is to be performed.
400 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, PartialEq, Eq, Hash, HashStable)]
401 #[rustc_pass_by_value]
403 /// The initial retag when entering a function.
405 /// Retag preparing for a two-phase borrow.
407 /// Retagging raw pointers.
409 /// A "normal" retag.
413 /// The `FakeReadCause` describes the type of pattern why a FakeRead statement exists.
414 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, Hash, HashStable, PartialEq)]
415 pub enum FakeReadCause {
416 /// Inject a fake read of the borrowed input at the end of each guards
419 /// This should ensure that you cannot change the variant for an enum while
420 /// you are in the midst of matching on it.
423 /// `let x: !; match x {}` doesn't generate any read of x so we need to
424 /// generate a read of x to check that it is initialized and safe.
426 /// If a closure pattern matches a Place starting with an Upvar, then we introduce a
427 /// FakeRead for that Place outside the closure, in such a case this option would be
428 /// Some(closure_def_id).
429 /// Otherwise, the value of the optional LocalDefId will be None.
431 // We can use LocalDefId here since fake read statements are removed
432 // before codegen in the `CleanupNonCodegenStatements` pass.
433 ForMatchedPlace(Option<LocalDefId>),
435 /// A fake read of the RefWithinGuard version of a bind-by-value variable
436 /// in a match guard to ensure that its value hasn't change by the time
437 /// we create the OutsideGuard version.
440 /// Officially, the semantics of
442 /// `let pattern = <expr>;`
444 /// is that `<expr>` is evaluated into a temporary and then this temporary is
445 /// into the pattern.
447 /// However, if we see the simple pattern `let var = <expr>`, we optimize this to
448 /// evaluate `<expr>` directly into the variable `var`. This is mostly unobservable,
449 /// but in some cases it can affect the borrow checker, as in #53695.
450 /// Therefore, we insert a "fake read" here to ensure that we get
451 /// appropriate errors.
453 /// If a closure pattern matches a Place starting with an Upvar, then we introduce a
454 /// FakeRead for that Place outside the closure, in such a case this option would be
455 /// Some(closure_def_id).
456 /// Otherwise, the value of the optional DefId will be None.
457 ForLet(Option<LocalDefId>),
459 /// If we have an index expression like
461 /// (*x)[1][{ x = y; 4}]
463 /// then the first bounds check is invalidated when we evaluate the second
464 /// index expression. Thus we create a fake borrow of `x` across the second
465 /// indexer, which will cause a borrow check error.
469 #[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
470 #[derive(TypeFoldable, TypeVisitable)]
471 pub struct Coverage {
472 pub kind: CoverageKind,
473 pub code_region: Option<CodeRegion>,
476 #[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
477 #[derive(TypeFoldable, TypeVisitable)]
478 pub struct CopyNonOverlapping<'tcx> {
479 pub src: Operand<'tcx>,
480 pub dst: Operand<'tcx>,
481 /// Number of elements to copy from src to dest, not bytes.
482 pub count: Operand<'tcx>,
485 ///////////////////////////////////////////////////////////////////////////
488 /// The various kinds of terminators, representing ways of exiting from a basic block.
490 /// A note on unwinding: Panics may occur during the execution of some terminators. Depending on the
491 /// `-C panic` flag, this may either cause the program to abort or the call stack to unwind. Such
492 /// terminators have a `cleanup: Option<BasicBlock>` field on them. If stack unwinding occurs, then
493 /// once the current function is reached, execution continues at the given basic block, if any. If
494 /// `cleanup` is `None` then no cleanup is performed, and the stack continues unwinding. This is
495 /// equivalent to the execution of a `Resume` terminator.
497 /// The basic block pointed to by a `cleanup` field must have its `cleanup` flag set. `cleanup`
498 /// basic blocks have a couple restrictions:
499 /// 1. All `cleanup` fields in them must be `None`.
500 /// 2. `Return` terminators are not allowed in them. `Abort` and `Unwind` terminators are.
501 /// 3. All other basic blocks (in the current body) that are reachable from `cleanup` basic blocks
502 /// must also be `cleanup`. This is a part of the type system and checked statically, so it is
503 /// still an error to have such an edge in the CFG even if it's known that it won't be taken at
505 #[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, TypeFoldable, TypeVisitable)]
506 pub enum TerminatorKind<'tcx> {
507 /// Block has one successor; we continue execution there.
508 Goto { target: BasicBlock },
510 /// Switches based on the computed value.
512 /// First, evaluates the `discr` operand. The type of the operand must be a signed or unsigned
513 /// integer, char, or bool, and must match the given type. Then, if the list of switch targets
514 /// contains the computed value, continues execution at the associated basic block. Otherwise,
515 /// continues execution at the "otherwise" basic block.
517 /// Target values may not appear more than once.
519 /// The discriminant value being tested.
520 discr: Operand<'tcx>,
522 /// The type of value being tested.
523 /// This is always the same as the type of `discr`.
524 /// FIXME: remove this redundant information. Currently, it is relied on by pretty-printing.
527 targets: SwitchTargets,
530 /// Indicates that the landing pad is finished and that the process should continue unwinding.
532 /// Like a return, this marks the end of this invocation of the function.
534 /// Only permitted in cleanup blocks. `Resume` is not permitted with `-C unwind=abort` after
535 /// deaggregation runs.
538 /// Indicates that the landing pad is finished and that the process should abort.
540 /// Used to prevent unwinding for foreign items or with `-C unwind=abort`. Only permitted in
544 /// Returns from the function.
546 /// Like function calls, the exact semantics of returns in Rust are unclear. Returning very
547 /// likely at least assigns the value currently in the return place (`_0`) to the place
548 /// specified in the associated `Call` terminator in the calling function, as if assigned via
549 /// `dest = move _0`. It might additionally do other things, like have side-effects in the
552 /// If the body is a generator body, this has slightly different semantics; it instead causes a
553 /// `GeneratorState::Returned(_0)` to be created (as if by an `Aggregate` rvalue) and assigned
554 /// to the return place.
557 /// Indicates a terminator that can never be reached.
559 /// Executing this terminator is UB.
562 /// The behavior of this statement differs significantly before and after drop elaboration.
563 /// After drop elaboration, `Drop` executes the drop glue for the specified place, after which
564 /// it continues execution/unwinds at the given basic blocks. It is possible that executing drop
565 /// glue is special - this would be part of Rust's memory model. (**FIXME**: due we have an
566 /// issue tracking if drop glue has any interesting semantics in addition to those of a function
569 /// `Drop` before drop elaboration is a *conditional* execution of the drop glue. Specifically, the
570 /// `Drop` will be executed if...
572 /// **Needs clarification**: End of that sentence. This in effect should document the exact
573 /// behavior of drop elaboration. The following sounds vaguely right, but I'm not quite sure:
575 /// > The drop glue is executed if, among all statements executed within this `Body`, an assignment to
576 /// > the place or one of its "parents" occurred more recently than a move out of it. This does not
577 /// > consider indirect assignments.
578 Drop { place: Place<'tcx>, target: BasicBlock, unwind: Option<BasicBlock> },
580 /// Drops the place and assigns a new value to it.
582 /// This first performs the exact same operation as the pre drop-elaboration `Drop` terminator;
583 /// it then additionally assigns the `value` to the `place` as if by an assignment statement.
584 /// This assignment occurs both in the unwind and the regular code paths. The semantics are best
585 /// explained by the elaboration:
589 /// DropAndReplace(P <- V, goto BB1, unwind BB2)
597 /// Drop(P, goto BB1, unwind BB2)
600 /// // P is now uninitialized
604 /// // P is now uninitialized -- its dtor panicked
609 /// Disallowed after drop elaboration.
612 value: Operand<'tcx>,
614 unwind: Option<BasicBlock>,
617 /// Roughly speaking, evaluates the `func` operand and the arguments, and starts execution of
618 /// the referred to function. The operand types must match the argument types of the function.
619 /// The return place type must match the return type. The type of the `func` operand must be
620 /// callable, meaning either a function pointer, a function type, or a closure type.
622 /// **Needs clarification**: The exact semantics of this. Current backends rely on `move`
623 /// operands not aliasing the return place. It is unclear how this is justified in MIR, see
626 /// [#71117]: https://github.com/rust-lang/rust/issues/71117
628 /// The function that’s being called.
630 /// Arguments the function is called with.
631 /// These are owned by the callee, which is free to modify them.
632 /// This allows the memory occupied by "by-value" arguments to be
633 /// reused across function calls without duplicating the contents.
634 args: Vec<Operand<'tcx>>,
635 /// Where the returned value will be written
636 destination: Place<'tcx>,
637 /// Where to go after this call returns. If none, the call necessarily diverges.
638 target: Option<BasicBlock>,
639 /// Cleanups to be done if the call unwinds.
640 cleanup: Option<BasicBlock>,
641 /// `true` if this is from a call in HIR rather than from an overloaded
642 /// operator. True for overloaded function call.
644 /// This `Span` is the span of the function, without the dot and receiver
645 /// (e.g. `foo(a, b)` in `x.foo(a, b)`
649 /// Evaluates the operand, which must have type `bool`. If it is not equal to `expected`,
650 /// initiates a panic. Initiating a panic corresponds to a `Call` terminator with some
651 /// unspecified constant as the function to call, all the operands stored in the `AssertMessage`
652 /// as parameters, and `None` for the destination. Keep in mind that the `cleanup` path is not
653 /// necessarily executed even in the case of a panic, for example in `-C panic=abort`. If the
654 /// assertion does not fail, execution continues at the specified basic block.
658 msg: AssertMessage<'tcx>,
660 cleanup: Option<BasicBlock>,
663 /// Marks a suspend point.
665 /// Like `Return` terminators in generator bodies, this computes `value` and then a
666 /// `GeneratorState::Yielded(value)` as if by `Aggregate` rvalue. That value is then assigned to
667 /// the return place of the function calling this one, and execution continues in the calling
668 /// function. When next invoked with the same first argument, execution of this function
669 /// continues at the `resume` basic block, with the second argument written to the `resume_arg`
670 /// place. If the generator is dropped before then, the `drop` basic block is invoked.
672 /// Not permitted in bodies that are not generator bodies, or after generator lowering.
674 /// **Needs clarification**: What about the evaluation order of the `resume_arg` and `value`?
676 /// The value to return.
677 value: Operand<'tcx>,
678 /// Where to resume to.
680 /// The place to store the resume argument in.
681 resume_arg: Place<'tcx>,
682 /// Cleanup to be done if the generator is dropped at this suspend point.
683 drop: Option<BasicBlock>,
686 /// Indicates the end of dropping a generator.
688 /// Semantically just a `return` (from the generators drop glue). Only permitted in the same situations
691 /// **Needs clarification**: Is that even correct? The generator drop code is always confusing
692 /// to me, because it's not even really in the current body.
694 /// **Needs clarification**: Are there type system constraints on these terminators? Should
695 /// there be a "block type" like `cleanup` blocks for them?
698 /// A block where control flow only ever takes one real path, but borrowck needs to be more
701 /// At runtime this is semantically just a goto.
703 /// Disallowed after drop elaboration.
705 /// The target normal control flow will take.
706 real_target: BasicBlock,
707 /// A block control flow could conceptually jump to, but won't in
709 imaginary_target: BasicBlock,
712 /// A terminator for blocks that only take one path in reality, but where we reserve the right
713 /// to unwind in borrowck, even if it won't happen in practice. This can arise in infinite loops
714 /// with no function calls for example.
716 /// At runtime this is semantically just a goto.
718 /// Disallowed after drop elaboration.
720 /// The target normal control flow will take.
721 real_target: BasicBlock,
722 /// The imaginary cleanup block link. This particular path will never be taken
723 /// in practice, but in order to avoid fragility we want to always
724 /// consider it in borrowck. We don't want to accept programs which
725 /// pass borrowck only when `panic=abort` or some assertions are disabled
726 /// due to release vs. debug mode builds. This needs to be an `Option` because
727 /// of the `remove_noop_landing_pads` and `abort_unwinding_calls` passes.
728 unwind: Option<BasicBlock>,
731 /// Block ends with an inline assembly block. This is a terminator since
732 /// inline assembly is allowed to diverge.
734 /// The template for the inline assembly, with placeholders.
735 template: &'tcx [InlineAsmTemplatePiece],
737 /// The operands for the inline assembly, as `Operand`s or `Place`s.
738 operands: Vec<InlineAsmOperand<'tcx>>,
740 /// Miscellaneous options for the inline assembly.
741 options: InlineAsmOptions,
743 /// Source spans for each line of the inline assembly code. These are
744 /// used to map assembler errors back to the line in the source code.
745 line_spans: &'tcx [Span],
747 /// Destination block after the inline assembly returns, unless it is
748 /// diverging (InlineAsmOptions::NORETURN).
749 destination: Option<BasicBlock>,
751 /// Cleanup to be done if the inline assembly unwinds. This is present
752 /// if and only if InlineAsmOptions::MAY_UNWIND is set.
753 cleanup: Option<BasicBlock>,
757 /// Information about an assertion failure.
758 #[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, TypeFoldable, TypeVisitable)]
759 pub enum AssertKind<O> {
760 BoundsCheck { len: O, index: O },
761 Overflow(BinOp, O, O),
765 ResumedAfterReturn(GeneratorKind),
766 ResumedAfterPanic(GeneratorKind),
769 #[derive(Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
770 #[derive(TypeFoldable, TypeVisitable)]
771 pub enum InlineAsmOperand<'tcx> {
773 reg: InlineAsmRegOrRegClass,
774 value: Operand<'tcx>,
777 reg: InlineAsmRegOrRegClass,
779 place: Option<Place<'tcx>>,
782 reg: InlineAsmRegOrRegClass,
784 in_value: Operand<'tcx>,
785 out_place: Option<Place<'tcx>>,
788 value: Box<Constant<'tcx>>,
791 value: Box<Constant<'tcx>>,
798 /// Type for MIR `Assert` terminator error messages.
799 pub type AssertMessage<'tcx> = AssertKind<Operand<'tcx>>;
801 ///////////////////////////////////////////////////////////////////////////
804 /// Places roughly correspond to a "location in memory." Places in MIR are the same mathematical
805 /// object as places in Rust. This of course means that what exactly they are is undecided and part
806 /// of the Rust memory model. However, they will likely contain at least the following pieces of
807 /// information in some form:
809 /// 1. The address in memory that the place refers to.
810 /// 2. The provenance with which the place is being accessed.
811 /// 3. The type of the place and an optional variant index. See [`PlaceTy`][super::tcx::PlaceTy].
812 /// 4. Optionally, some metadata. This exists if and only if the type of the place is not `Sized`.
814 /// We'll give a description below of how all pieces of the place except for the provenance are
815 /// calculated. We cannot give a description of the provenance, because that is part of the
816 /// undecided aliasing model - we only include it here at all to acknowledge its existence.
818 /// Each local naturally corresponds to the place `Place { local, projection: [] }`. This place has
819 /// the address of the local's allocation and the type of the local.
821 /// **Needs clarification:** Unsized locals seem to present a bit of an issue. Their allocation
822 /// can't actually be created on `StorageLive`, because it's unclear how big to make the allocation.
823 /// Furthermore, MIR produces assignments to unsized locals, although that is not permitted under
824 /// `#![feature(unsized_locals)]` in Rust. Besides just putting "unsized locals are special and
825 /// different" in a bunch of places, I (JakobDegen) don't know how to incorporate this behavior into
826 /// the current MIR semantics in a clean way - possibly this needs some design work first.
828 /// For places that are not locals, ie they have a non-empty list of projections, we define the
829 /// values as a function of the parent place, that is the place with its last [`ProjectionElem`]
830 /// stripped. The way this is computed of course depends on the kind of that last projection
833 /// - [`Downcast`](ProjectionElem::Downcast): This projection sets the place's variant index to the
834 /// given one, and makes no other changes. A `Downcast` projection on a place with its variant
835 /// index already set is not well-formed.
836 /// - [`Field`](ProjectionElem::Field): `Field` projections take their parent place and create a
837 /// place referring to one of the fields of the type. The resulting address is the parent
838 /// address, plus the offset of the field. The type becomes the type of the field. If the parent
839 /// was unsized and so had metadata associated with it, then the metadata is retained if the
840 /// field is unsized and thrown out if it is sized.
842 /// These projections are only legal for tuples, ADTs, closures, and generators. If the ADT or
843 /// generator has more than one variant, the parent place's variant index must be set, indicating
844 /// which variant is being used. If it has just one variant, the variant index may or may not be
845 /// included - the single possible variant is inferred if it is not included.
846 /// - [`OpaqueCast`](ProjectionElem::OpaqueCast): This projection changes the place's type to the
847 /// given one, and makes no other changes. A `OpaqueCast` projection on any type other than an
848 /// opaque type from the current crate is not well-formed.
849 /// - [`ConstantIndex`](ProjectionElem::ConstantIndex): Computes an offset in units of `T` into the
850 /// place as described in the documentation for the `ProjectionElem`. The resulting address is
851 /// the parent's address plus that offset, and the type is `T`. This is only legal if the parent
852 /// place has type `[T; N]` or `[T]` (*not* `&[T]`). Since such a `T` is always sized, any
853 /// resulting metadata is thrown out.
854 /// - [`Subslice`](ProjectionElem::Subslice): This projection calculates an offset and a new
855 /// address in a similar manner as `ConstantIndex`. It is also only legal on `[T; N]` and `[T]`.
856 /// However, this yields a `Place` of type `[T]`, and additionally sets the metadata to be the
857 /// length of the subslice.
858 /// - [`Index`](ProjectionElem::Index): Like `ConstantIndex`, only legal on `[T; N]` or `[T]`.
859 /// However, `Index` additionally takes a local from which the value of the index is computed at
860 /// runtime. Computing the value of the index involves interpreting the `Local` as a
861 /// `Place { local, projection: [] }`, and then computing its value as if done via
862 /// [`Operand::Copy`]. The array/slice is then indexed with the resulting value. The local must
863 /// have type `usize`.
864 /// - [`Deref`](ProjectionElem::Deref): Derefs are the last type of projection, and the most
865 /// complicated. They are only legal on parent places that are references, pointers, or `Box`. A
866 /// `Deref` projection begins by loading a value from the parent place, as if by
867 /// [`Operand::Copy`]. It then dereferences the resulting pointer, creating a place of the
868 /// pointee's type. The resulting address is the address that was stored in the pointer. If the
869 /// pointee type is unsized, the pointer additionally stored the value of the metadata.
871 /// Computing a place may cause UB. One possibility is that the pointer used for a `Deref` may not
872 /// be suitably aligned. Another possibility is that the place is not in bounds, meaning it does not
873 /// point to an actual allocation.
875 /// However, if this is actually UB and when the UB kicks in is undecided. This is being discussed
876 /// in [UCG#319]. The options include that every place must obey those rules, that only some places
877 /// must obey them, or that places impose no rules of their own.
879 /// [UCG#319]: https://github.com/rust-lang/unsafe-code-guidelines/issues/319
881 /// Rust currently requires that every place obey those two rules. This is checked by MIRI and taken
882 /// advantage of by codegen (via `gep inbounds`). That is possibly subject to change.
883 #[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, HashStable, TypeFoldable, TypeVisitable)]
884 pub struct Place<'tcx> {
887 /// projection out of a place (access a field, deref a pointer, etc)
888 pub projection: &'tcx List<PlaceElem<'tcx>>,
891 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
892 #[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
893 pub enum ProjectionElem<V, T> {
896 /// Index into a slice/array.
898 /// Note that this does not also dereference, and so it does not exactly correspond to slice
899 /// indexing in Rust. In other words, in the below Rust code:
902 /// let x = &[1, 2, 3, 4];
907 /// The `x[i]` is turned into a `Deref` followed by an `Index`, not just an `Index`. The same
908 /// thing is true of the `ConstantIndex` and `Subslice` projections below.
911 /// These indices are generated by slice patterns. Easiest to explain
914 /// ```ignore (illustrative)
915 /// [X, _, .._, _, _] => { offset: 0, min_length: 4, from_end: false },
916 /// [_, X, .._, _, _] => { offset: 1, min_length: 4, from_end: false },
917 /// [_, _, .._, X, _] => { offset: 2, min_length: 4, from_end: true },
918 /// [_, _, .._, _, X] => { offset: 1, min_length: 4, from_end: true },
921 /// index or -index (in Python terms), depending on from_end
923 /// The thing being indexed must be at least this long. For arrays this
924 /// is always the exact length.
926 /// Counting backwards from end? This is always false when indexing an
931 /// These indices are generated by slice patterns.
933 /// If `from_end` is true `slice[from..slice.len() - to]`.
934 /// Otherwise `array[from..to]`.
938 /// Whether `to` counts from the start or end of the array/slice.
939 /// For `PlaceElem`s this is `true` if and only if the base is a slice.
940 /// For `ProjectionKind`, this can also be `true` for arrays.
944 /// "Downcast" to a variant of an enum or a generator.
946 /// The included Symbol is the name of the variant, used for printing MIR.
947 Downcast(Option<Symbol>, VariantIdx),
949 /// Like an explicit cast from an opaque type to a concrete type, but without
950 /// requiring an intermediate variable.
954 /// Alias for projections as they appear in places, where the base is a place
955 /// and the index is a local.
956 pub type PlaceElem<'tcx> = ProjectionElem<Local, Ty<'tcx>>;
958 ///////////////////////////////////////////////////////////////////////////
961 /// An operand in MIR represents a "value" in Rust, the definition of which is undecided and part of
962 /// the memory model. One proposal for a definition of values can be found [on UCG][value-def].
964 /// [value-def]: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/value-domain.md
966 /// The most common way to create values is via loading a place. Loading a place is an operation
967 /// which reads the memory of the place and converts it to a value. This is a fundamentally *typed*
968 /// operation. The nature of the value produced depends on the type of the conversion. Furthermore,
969 /// there may be other effects: if the type has a validity constraint loading the place might be UB
970 /// if the validity constraint is not met.
972 /// **Needs clarification:** Ralf proposes that loading a place not have side-effects.
973 /// This is what is implemented in miri today. Are these the semantics we want for MIR? Is this
974 /// something we can even decide without knowing more about Rust's memory model?
976 /// **Needs clarifiation:** Is loading a place that has its variant index set well-formed? Miri
977 /// currently implements it, but it seems like this may be something to check against in the
979 #[derive(Clone, PartialEq, TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
980 pub enum Operand<'tcx> {
981 /// Creates a value by loading the given place.
983 /// Before drop elaboration, the type of the place must be `Copy`. After drop elaboration there
984 /// is no such requirement.
987 /// Creates a value by performing loading the place, just like the `Copy` operand.
989 /// This *may* additionally overwrite the place with `uninit` bytes, depending on how we decide
990 /// in [UCG#188]. You should not emit MIR that may attempt a subsequent second load of this
991 /// place without first re-initializing it.
993 /// [UCG#188]: https://github.com/rust-lang/unsafe-code-guidelines/issues/188
996 /// Constants are already semantically values, and remain unchanged.
997 Constant(Box<Constant<'tcx>>),
1000 ///////////////////////////////////////////////////////////////////////////
1003 /// The various kinds of rvalues that can appear in MIR.
1005 /// Not all of these are allowed at every [`MirPhase`] - when this is the case, it's stated below.
1007 /// Computing any rvalue begins by evaluating the places and operands in some order (**Needs
1008 /// clarification**: Which order?). These are then used to produce a "value" - the same kind of
1009 /// value that an [`Operand`] produces.
1010 #[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, TypeFoldable, TypeVisitable)]
1011 pub enum Rvalue<'tcx> {
1012 /// Yields the operand unchanged
1015 /// Creates an array where each element is the value of the operand.
1017 /// This is the cause of a bug in the case where the repetition count is zero because the value
1018 /// is not dropped, see [#74836].
1020 /// Corresponds to source code like `[x; 32]`.
1022 /// [#74836]: https://github.com/rust-lang/rust/issues/74836
1023 Repeat(Operand<'tcx>, ty::Const<'tcx>),
1025 /// Creates a reference of the indicated kind to the place.
1027 /// There is not much to document here, because besides the obvious parts the semantics of this
1028 /// are essentially entirely a part of the aliasing model. There are many UCG issues discussing
1029 /// exactly what the behavior of this operation should be.
1031 /// `Shallow` borrows are disallowed after drop lowering.
1032 Ref(Region<'tcx>, BorrowKind, Place<'tcx>),
1034 /// Creates a pointer/reference to the given thread local.
1036 /// The yielded type is a `*mut T` if the static is mutable, otherwise if the static is extern a
1037 /// `*const T`, and if neither of those apply a `&T`.
1039 /// **Note:** This is a runtime operation that actually executes code and is in this sense more
1040 /// like a function call. Also, eliminating dead stores of this rvalue causes `fn main() {}` to
1041 /// SIGILL for some reason that I (JakobDegen) never got a chance to look into.
1043 /// **Needs clarification**: Are there weird additional semantics here related to the runtime
1044 /// nature of this operation?
1045 ThreadLocalRef(DefId),
1047 /// Creates a pointer with the indicated mutability to the place.
1049 /// This is generated by pointer casts like `&v as *const _` or raw address of expressions like
1050 /// `&raw v` or `addr_of!(v)`.
1052 /// Like with references, the semantics of this operation are heavily dependent on the aliasing
1054 AddressOf(Mutability, Place<'tcx>),
1056 /// Yields the length of the place, as a `usize`.
1058 /// If the type of the place is an array, this is the array length. For slices (`[T]`, not
1059 /// `&[T]`) this accesses the place's metadata to determine the length. This rvalue is
1060 /// ill-formed for places of other types.
1063 /// Performs essentially all of the casts that can be performed via `as`.
1065 /// This allows for casts from/to a variety of types.
1067 /// **FIXME**: Document exactly which `CastKind`s allow which types of casts. Figure out why
1068 /// `ArrayToPointer` and `MutToConstPointer` are special.
1069 Cast(CastKind, Operand<'tcx>, Ty<'tcx>),
1071 /// * `Offset` has the same semantics as [`offset`](pointer::offset), except that the second
1072 /// parameter may be a `usize` as well.
1073 /// * The comparison operations accept `bool`s, `char`s, signed or unsigned integers, floats,
1074 /// raw pointers, or function pointers and return a `bool`. The types of the operands must be
1075 /// matching, up to the usual caveat of the lifetimes in function pointers.
1076 /// * Left and right shift operations accept signed or unsigned integers not necessarily of the
1077 /// same type and return a value of the same type as their LHS. Like in Rust, the RHS is
1078 /// truncated as needed.
1079 /// * The `Bit*` operations accept signed integers, unsigned integers, or bools with matching
1080 /// types and return a value of that type.
1081 /// * The remaining operations accept signed integers, unsigned integers, or floats with
1082 /// matching types and return a value of that type.
1083 BinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),
1085 /// Same as `BinaryOp`, but yields `(T, bool)` with a `bool` indicating an error condition.
1087 /// When overflow checking is disabled and we are generating run-time code, the error condition
1088 /// is false. Otherwise, and always during CTFE, the error condition is determined as described
1091 /// For addition, subtraction, and multiplication on integers the error condition is set when
1092 /// the infinite precision result would be unequal to the actual result.
1094 /// For shift operations on integers the error condition is set when the value of right-hand
1095 /// side is greater than or equal to the number of bits in the type of the left-hand side, or
1096 /// when the value of right-hand side is negative.
1098 /// Other combinations of types and operators are unsupported.
1099 CheckedBinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),
1101 /// Computes a value as described by the operation.
1102 NullaryOp(NullOp, Ty<'tcx>),
1104 /// Exactly like `BinaryOp`, but less operands.
1106 /// Also does two's-complement arithmetic. Negation requires a signed integer or a float;
1107 /// bitwise not requires a signed integer, unsigned integer, or bool. Both operation kinds
1108 /// return a value with the same type as their operand.
1109 UnaryOp(UnOp, Operand<'tcx>),
1111 /// Computes the discriminant of the place, returning it as an integer of type
1112 /// [`discriminant_ty`]. Returns zero for types without discriminant.
1114 /// The validity requirements for the underlying value are undecided for this rvalue, see
1115 /// [#91095]. Note too that the value of the discriminant is not the same thing as the
1116 /// variant index; use [`discriminant_for_variant`] to convert.
1118 /// [`discriminant_ty`]: crate::ty::Ty::discriminant_ty
1119 /// [#91095]: https://github.com/rust-lang/rust/issues/91095
1120 /// [`discriminant_for_variant`]: crate::ty::Ty::discriminant_for_variant
1121 Discriminant(Place<'tcx>),
1123 /// Creates an aggregate value, like a tuple or struct.
1125 /// This is needed because dataflow analysis needs to distinguish
1126 /// `dest = Foo { x: ..., y: ... }` from `dest.x = ...; dest.y = ...;` in the case that `Foo`
1127 /// has a destructor.
1129 /// Disallowed after deaggregation for all aggregate kinds except `Array` and `Generator`. After
1130 /// generator lowering, `Generator` aggregate kinds are disallowed too.
1131 Aggregate(Box<AggregateKind<'tcx>>, Vec<Operand<'tcx>>),
1133 /// Transmutes a `*mut u8` into shallow-initialized `Box<T>`.
1135 /// This is different from a normal transmute because dataflow analysis will treat the box as
1136 /// initialized but its content as uninitialized. Like other pointer casts, this in general
1137 /// affects alias analysis.
1138 ShallowInitBox(Operand<'tcx>, Ty<'tcx>),
1140 /// A CopyForDeref is equivalent to a read from a place at the
1141 /// codegen level, but is treated specially by drop elaboration. When such a read happens, it
1142 /// is guaranteed (via nature of the mir_opt `Derefer` in rustc_mir_transform/src/deref_separator)
1143 /// that the only use of the returned value is a deref operation, immediately
1144 /// followed by one or more projections. Drop elaboration treats this rvalue as if the
1145 /// read never happened and just projects further. This allows simplifying various MIR
1146 /// optimizations and codegen backends that previously had to handle deref operations anywhere
1148 CopyForDeref(Place<'tcx>),
1151 #[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
1153 /// An exposing pointer to address cast. A cast between a pointer and an integer type, or
1154 /// between a function pointer and an integer type.
1155 /// See the docs on `expose_addr` for more details.
1156 PointerExposeAddress,
1157 /// An address-to-pointer cast that picks up an exposed provenance.
1158 /// See the docs on `from_exposed_addr` for more details.
1159 PointerFromExposedAddress,
1160 /// All sorts of pointer-to-pointer casts. Note that reference-to-raw-ptr casts are
1161 /// translated into `&raw mut/const *r`, i.e., they are not actually casts.
1162 Pointer(PointerCast),
1163 /// Cast into a dyn* object.
1173 #[derive(Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
1174 #[derive(TypeFoldable, TypeVisitable)]
1175 pub enum AggregateKind<'tcx> {
1176 /// The type is of the element
1180 /// The second field is the variant index. It's equal to 0 for struct
1181 /// and union expressions. The fourth field is
1182 /// active field number and is present only for union expressions
1183 /// -- e.g., for a union expression `SomeUnion { c: .. }`, the
1184 /// active field index would identity the field `c`
1185 Adt(DefId, VariantIdx, SubstsRef<'tcx>, Option<UserTypeAnnotationIndex>, Option<usize>),
1187 // Note: We can use LocalDefId since closures and generators a deaggregated
1189 Closure(LocalDefId, SubstsRef<'tcx>),
1190 Generator(LocalDefId, SubstsRef<'tcx>, hir::Movability),
1193 #[derive(Copy, Clone, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
1195 /// Returns the size of a value of that type
1197 /// Returns the minimum alignment of a type
1201 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
1202 #[derive(HashStable, TyEncodable, TyDecodable, TypeFoldable, TypeVisitable)]
1204 /// The `!` operator for logical inversion
1206 /// The `-` operator for negation
1210 #[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Ord, Eq, Hash)]
1211 #[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
1213 /// The `+` operator (addition)
1215 /// The `-` operator (subtraction)
1217 /// The `*` operator (multiplication)
1219 /// The `/` operator (division)
1221 /// Division by zero is UB, because the compiler should have inserted checks
1224 /// The `%` operator (modulus)
1226 /// Using zero as the modulus (second operand) is UB, because the compiler
1227 /// should have inserted checks prior to this.
1229 /// The `^` operator (bitwise xor)
1231 /// The `&` operator (bitwise and)
1233 /// The `|` operator (bitwise or)
1235 /// The `<<` operator (shift left)
1237 /// The offset is truncated to the size of the first operand before shifting.
1239 /// The `>>` operator (shift right)
1241 /// The offset is truncated to the size of the first operand before shifting.
1243 /// The `==` operator (equality)
1245 /// The `<` operator (less than)
1247 /// The `<=` operator (less than or equal to)
1249 /// The `!=` operator (not equal to)
1251 /// The `>=` operator (greater than or equal to)
1253 /// The `>` operator (greater than)
1255 /// The `ptr.offset` operator
1259 // Some nodes are used a lot. Make sure they don't unintentionally get bigger.
1260 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
1263 // tidy-alphabetical-start
1264 static_assert_size!(AggregateKind<'_>, 40);
1265 static_assert_size!(Operand<'_>, 24);
1266 static_assert_size!(Place<'_>, 16);
1267 static_assert_size!(PlaceElem<'_>, 24);
1268 static_assert_size!(Rvalue<'_>, 40);
1269 // tidy-alphabetical-end