//! 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 super::{BasicBlock, Const, Local, UserTypeProjection}; use crate::mir::coverage::{CodeRegion, CoverageKind}; use crate::traits::Reveal; use crate::ty::adjustment::PointerCoercion; use crate::ty::GenericArgsRef; use crate::ty::{self, List, Ty}; use crate::ty::{Region, UserTypeAnnotationIndex}; use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece}; use rustc_hir::def_id::DefId; use rustc_hir::{self as hir}; use rustc_hir::{self, GeneratorKind}; use rustc_index::IndexVec; use rustc_target::abi::{FieldIdx, VariantIdx}; use rustc_ast::Mutability; use rustc_span::def_id::LocalDefId; use rustc_span::symbol::Symbol; use rustc_span::Span; use rustc_target::asm::InlineAsmRegOrRegClass; use smallvec::SmallVec; /// 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}`). /// - Generator bodies: In analysis MIR, locals may actually be behind a pointer that user code has /// access to. This occurs in generator 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 generator 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 reveal(&self) -> Reveal { match *self { MirPhase::Built | MirPhase::Analysis(_) => Reveal::UserFacing, MirPhase::Runtime(_) => Reveal::All, } } } /// 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`] /// * [`Rvalue::Ref`] with `BorrowKind::Fake` /// /// 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::GeneratorDrop`] /// * [`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, /// 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 prevent `if let None = x { ... }`, for example, because the /// mutating `(*x as Some).0` can't affect the discriminant of `x`. /// We can also report errors with this kind of borrow differently. Fake, /// 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, } /////////////////////////////////////////////////////////////////////////// // 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 generators 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>, variant_index: VariantIdx }, /// Deinitializes the place. /// /// This writes `uninit` bytes to the entire place. Deinit(Box>), /// `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. 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 is UB. However, for an /// unallocated local an additional `StorageDead` all is simply 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 /// 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>), /// 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. It is UB if the place is not pointing to live memory. PlaceMention(Box>), /// 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), /// Marks the start of a "coverage region", injected with '-Cinstrument-coverage'. A /// `Coverage` statement carries metadata about the coverage region, used to inject a coverage /// map into the binary. If `Coverage::kind` is a `Counter`, the statement also generates /// executable code, to increment a counter variable at runtime, each time the code region is /// executed. Coverage(Box), /// 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>), /// 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::()` 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), /// 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 = ;` /// /// is that `` is evaluated into a temporary and then this temporary is /// into the pattern. /// /// However, if we see the simple pattern `let var = `, we optimize this to /// evaluate `` 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), /// 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 Coverage { pub kind: CoverageKind, pub code_region: Option, } #[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 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 ) 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) } } /////////////////////////////////////////////////////////////////////////// // 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 generator body, this has slightly different semantics; it instead causes a /// `GeneratorState::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. args: Vec>, /// 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, /// 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, }, /// 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>, target: BasicBlock, unwind: UnwindAction, }, /// Marks a suspend point. /// /// Like `Return` terminators in generator bodies, this computes `value` and then a /// `GeneratorState::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 generator is dropped before then, the `drop` basic block is invoked. /// /// Not permitted in bodies that are not generator bodies, or after generator 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 generator is dropped at this suspend point. drop: Option, }, /// Indicates the end of dropping a generator. /// /// Semantically just a `return` (from the generators drop glue). Only permitted in the same situations /// as `yield`. /// /// **Needs clarification**: Is that even correct? The generator 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? GeneratorDrop, /// 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 { /// The template for the inline assembly, with placeholders. template: &'tcx [InlineAsmTemplatePiece], /// The operands for the inline assembly, as `Operand`s or `Place`s. operands: Vec>, /// 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], /// Destination block after the inline assembly returns, unless it is /// diverging (InlineAsmOptions::NORETURN). destination: Option, /// 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::Assert { .. } => "Assert", TerminatorKind::Yield { .. } => "Yield", TerminatorKind::GeneratorDrop => "GeneratorDrop", 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<[u128; 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 // 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 { BoundsCheck { len: O, index: O }, Overflow(BinOp, O, O), OverflowNeg(O), DivisionByZero(O), RemainderByZero(O), ResumedAfterReturn(GeneratorKind), ResumedAfterPanic(GeneratorKind), 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>, }, InOut { reg: InlineAsmRegOrRegClass, late: bool, in_value: Operand<'tcx>, out_place: Option>, }, Const { value: Box>, }, SymFn { value: Box>, }, SymStatic { def_id: DefId, }, } /// Type for MIR `Assert` terminator error messages. pub type AssertMessage<'tcx> = AssertKind>; /////////////////////////////////////////////////////////////////////////// // 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 on a place with its variant /// index already set is not well-formed. /// - [`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 generators. If the ADT or /// generator 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. /// /// Computing a place may cause UB. One possibility is that the pointer used for a `Deref` may not /// be suitably aligned. Another possibility is that the place is not in bounds, meaning it does not /// point to an actual allocation. /// /// However, if this is actually UB and when the UB kicks in is undecided. This is being discussed /// in [UCG#319]. The options include that every place must obey those rules, that only some places /// must obey them, or that places impose no rules of their own. /// /// [UCG#319]: https://github.com/rust-lang/unsafe-code-guidelines/issues/319 /// /// Rust currently requires that every place obey those two rules. This is checked by MIRI and taken /// advantage of by codegen (via `gep inbounds`). That is possibly subject to change. #[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>, } #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)] #[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)] pub enum ProjectionElem { 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. 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 generator. /// /// The included Symbol is the name of the variant, used for printing MIR. Downcast(Option, 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>; /////////////////////////////////////////////////////////////////////////// // 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>), } #[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::>`, 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, 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 pointer with the indicated mutability to the place. /// /// This is generated by pointer casts like `&v as *const _` or raw address of expressions like /// `&raw v` or `addr_of!(v)`. /// /// Like with references, the semantics of this operation are heavily dependent on the aliasing /// model. AddressOf(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. 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. Figure out why /// `ArrayToPointer` and `MutToConstPointer` are special. 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 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>)>), /// Same as `BinaryOp`, but yields `(T, bool)` with a `bool` indicating an error condition. /// /// For addition, subtraction, and multiplication on integers the error condition is set when /// the infinite precision result would not be equal to the actual result. /// /// Other combinations of types and operators are unsupported. CheckedBinaryOp(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 `Generator`. After /// generator lowering, `Generator` aggregate kinds are disallowed too. Aggregate(Box>, IndexVec>), /// Transmutes a `*mut u8` into shallow-initialized `Box`. /// /// 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_addr` for more details. PointerExposeAddress, /// An address-to-pointer cast that picks up an exposed provenance. /// See the docs on `from_exposed_addr` for more details. PointerFromExposedAddress, /// 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. PointerCoercion(PointerCoercion), /// Cast into a dyn* object. DynStar, 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, } #[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, Option), Closure(DefId, GenericArgsRef<'tcx>), Generator(DefId, GenericArgsRef<'tcx>, hir::Movability), } #[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), } #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)] #[derive(HashStable, TyEncodable, TyDecodable, TypeFoldable, TypeVisitable)] pub enum UnOp { /// The `!` operator for logical inversion Not, /// The `-` operator for negation Neg, } #[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Ord, 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, /// The `-` operator (subtraction) Sub, /// Like `Sub`, but with UB on overflow. (Integers only.) SubUnchecked, /// The `*` operator (multiplication) Mul, /// Like `Mul`, but with UB on overflow. (Integers only.) MulUnchecked, /// 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 truncated to the size of the first operand before shifting. Shl, /// Like `Shl`, but is UB if the RHS >= LHS::BITS ShlUnchecked, /// The `>>` operator (shift right) /// /// The offset is truncated to the size of the first operand before shifting. /// /// 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 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 `ptr.offset` operator Offset, } // Some nodes are used a lot. Make sure they don't unintentionally get bigger. #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))] mod size_asserts { 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); // tidy-alphabetical-end }