Rvalue in rustc_middle::mir::syntax - Rust
Description: The various kinds of rvalues that can appear in MIR.

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## Rvalue

# Enum Rvalue

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    pub enum Rvalue<'tcx> {
        Use(Operand<'tcx>),
        Repeat(Operand<'tcx>, Const<'tcx>),
        Ref(Region<'tcx>, BorrowKind, Place<'tcx>),
        ThreadLocalRef(DefId),
        RawPtr(RawPtrKind, Place<'tcx>),
        Cast(CastKind, Operand<'tcx>, Ty<'tcx>),
        BinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),
        UnaryOp(UnOp, Operand<'tcx>),
        Discriminant(Place<'tcx>),
        Aggregate(Box<AggregateKind<'tcx>>, IndexVec<FieldIdx, Operand<'tcx>>),
        CopyForDeref(Place<'tcx>),
        WrapUnsafeBinder(Operand<'tcx>, Ty<'tcx>),
    }

Expand description

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.

## Variants§

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### Use(Operand<'tcx>)

Yields the operand unchanged

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### Repeat(Operand<'tcx>, Const<'tcx>)

Creates an array where each element is the value of the operand.

Corresponds to source code like `[x; 32]`.

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### Ref(Region<'tcx>, BorrowKind, Place<'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.

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### ThreadLocalRef(DefId)

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?

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### RawPtr(RawPtrKind, Place<'tcx>)

Creates a raw pointer with the indicated mutability to the place.

This is generated by pointer casts like `&v as *const _` or raw borrow expressions like `&raw const v`.

Like with references, the semantics of this operation are heavily dependent on the aliasing model.

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### Cast(CastKind, Operand<'tcx>, Ty<'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.

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### BinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>)

- `Offset` has the same semantics as `offset`, except that the second parameter may be a `usize` as well.
- The comparison operations accept `bool`s, `char`s, signed or unsigned integers, floats, raw pointers, or function pointers and return a `bool`. The types of the operands must be matching, up to the usual caveat of the lifetimes in function pointers.
- Left and right shift operations accept signed or unsigned integers not necessarily of the same type and return a value of the same type as their LHS. Like in Rust, the RHS is truncated as needed.
- The `Bit*` operations accept signed integers, unsigned integers, or bools with matching types and return a value of that type.
- The `FooWithOverflow` are like the `Foo`, but returning `(T, bool)` instead of just `T`, where the `bool` is true if the result is not equal to the infinite-precision result.
- The remaining operations accept signed integers, unsigned integers, or floats with matching types and return a value of that type.

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### UnaryOp(UnOp, Operand<'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.

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### Discriminant(Place<'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.

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### Aggregate(Box<AggregateKind<'tcx>>, IndexVec<FieldIdx, Operand<'tcx>>)

Creates an aggregate value, like a tuple or struct.

This is needed because dataflow analysis needs to distinguish `dest = Foo { x: ..., y: ... }` from `dest.x = ...; dest.y = ...;` in the case that `Foo` has a destructor.

Disallowed after deaggregation for all aggregate kinds except `Array` and `Coroutine`. After coroutine lowering, `Coroutine` aggregate kinds are disallowed too.

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### CopyForDeref(Place<'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 returned value is written into a `DerefTemp` local and that its only use 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.

Disallowed in runtime MIR and is replaced by normal copies.

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### WrapUnsafeBinder(Operand<'tcx>, Ty<'tcx>)

Wraps a value in an unsafe binder.

## Implementations§

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### impl<'tcx> Rvalue<'tcx>

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#### pub fn is_safe_to_remove(&self) -> bool

Returns true if rvalue can be safely removed when the result is unused.

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#### pub fn ty<D>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> Ty<'tcx>
where D: ?Sized + HasLocalDecls<'tcx>,

## Trait Implementations§

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### impl<'tcx> Clone for Rvalue<'tcx>

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#### fn clone(&self) -> Rvalue<'tcx>

Returns a duplicate of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl<'tcx> Debug for Rvalue<'tcx>

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#### fn fmt(&self, fmt: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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### impl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for Rvalue<'tcx>

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#### fn decode(__decoder: &mut __D) -> Self

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### impl<'tcx, __E: TyEncoder<'tcx>> Encodable<__E> for Rvalue<'tcx>

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#### fn encode(&self, __encoder: &mut __E)

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### impl<'tcx> Hash for Rvalue<'tcx>

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#### fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given `Hasher`. Read more
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#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for Rvalue<'tcx>

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#### fn hash_stable( &self, __hcx: &mut StableHashingContext<'__ctx>, __hasher: &mut StableHasher, )

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### impl<'tcx> PartialEq for Rvalue<'tcx>

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#### fn eq(&self, other: &Rvalue<'tcx>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Rvalue<'tcx>

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#### fn try_fold_with<__F: FallibleTypeFolder<TyCtxt<'tcx>>>( self, __folder: &mut __F, ) -> Result<Self, __F::Error>

The entry point for folding. To fold a value `t` with a folder `f` call: `t.try_fold_with(f)`. Read more
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#### fn fold_with<__F: TypeFolder<TyCtxt<'tcx>>>(self, __folder: &mut __F) -> Self

The entry point for folding. To fold a value `t` with a folder `f` call: `t.fold_with(f)`. Read more
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### impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Rvalue<'tcx>

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#### fn visit_with<__V: TypeVisitor<TyCtxt<'tcx>>>( &self, __visitor: &mut __V, ) -> __V::Result

The entry point for visiting. To visit a value `t` with a visitor `v` call: `t.visit_with(v)`. Read more
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### impl<'tcx> StructuralPartialEq for Rvalue<'tcx>

## Auto Trait Implementations§

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### impl<'tcx> DynSend for Rvalue<'tcx>

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### impl<'tcx> DynSync for Rvalue<'tcx>

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### impl<'tcx> Freeze for Rvalue<'tcx>

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### impl<'tcx> !RefUnwindSafe for Rvalue<'tcx>

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### impl<'tcx> Send for Rvalue<'tcx>

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### impl<'tcx> Sync for Rvalue<'tcx>

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### impl<'tcx> Unpin for Rvalue<'tcx>

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### impl<'tcx> UnsafeUnpin for Rvalue<'tcx>

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### impl<'tcx> !UnwindSafe for Rvalue<'tcx>

## Blanket Implementations§

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### impl<T> Aligned for T

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#### const ALIGN: Alignment

Alignment of `Self`.
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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> AnyEq for T
where T: Any + PartialEq,

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#### fn equals(&self, other: &(dyn Any + 'static)) -> bool

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#### fn as_any(&self) -> &(dyn Any + 'static)

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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T, R> CollectAndApply<T, R> for T

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#### fn collect_and_apply<I, F>(iter: I, f: F) -> R
where I: Iterator<Item = T>, F: FnOnce(&[T]) -> R,

Equivalent to `f(&iter.collect::<Vec<_>>())`.

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#### type Output = R

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### impl<'tcx, T> DepNodeKey<'tcx> for T
where T: for<'a> HashStable<StableHashingContext<'a>> + Debug,

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#### default fn key_fingerprint_style() -> KeyFingerprintStyle

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#### default fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint

This method turns a query key into an opaque `Fingerprint` to be used in `DepNode`.
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#### default fn try_recover_key(_: TyCtxt<'tcx>, _: &DepNode) -> Option<T>

This method tries to recover the query key from the given `DepNode`, something which is needed when forcing `DepNode`s during red-green evaluation. The query system will only call this method if `fingerprint_style()` is not `FingerprintStyle::Opaque`. It is always valid to return `None` here, in which case incremental compilation will treat the query as having changed instead of forcing it.
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### impl<T> DynClone for T
where T: Clone,

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#### fn __clone_box(&self, _: Private) -> *mut ()

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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T> Instrument for T

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#### fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided `Span`, returning an `Instrumented` wrapper. Read more
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#### fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current `Span`, returning an `Instrumented` wrapper. Read more
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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> IntoEither for T

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#### fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left` is `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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#### fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left(&self)` returns `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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### impl<K> IntoQueryKey<K> for K

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#### fn into_query_key(self) -> K

Argument conversion from `Self` to `K`. This should always be a very cheap conversion, e.g. `LocalDefId::to_def_id`.
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### impl<'tcx, T> IsSuggestable<'tcx> for T
where T: TypeVisitable<TyCtxt<'tcx>> + TypeFoldable<TyCtxt<'tcx>>,

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#### fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool

Whether this makes sense to suggest in a diagnostic. Read more
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#### fn make_suggestable( self, tcx: TyCtxt<'tcx>, infer_suggestable: bool, placeholder: Option<Ty<'tcx>>, ) -> Option<T>

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### impl<T> MaybeResult<T> for T

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#### type Error = !

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#### fn from(_: Result<T, <T as MaybeResult<T>>::Error>) -> T

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#### fn to_result(self) -> Result<T, <T as MaybeResult<T>>::Error>

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### impl<T> Pointable for T

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#### const ALIGN: usize

The alignment of pointer.
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#### type Init = T

The type for initializers.
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#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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### impl<T> Same for T

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#### type Output = T

Should always be `Self`
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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### impl<I, T> TypeVisitableExt<I> for T
where I: Interner, T: TypeVisitable<I>,

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#### fn has_type_flags(&self, flags: TypeFlags) -> bool

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#### fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool

Returns `true` if `self` has any late-bound regions that are either bound by `binder` or bound by some binder outside of `binder`. If `binder` is `ty::INNERMOST`, this indicates whether there are any late-bound regions that appear free.
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#### fn error_reported(&self) -> Result<(), <I as Interner>::ErrorGuaranteed>

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#### fn non_region_error_reported( &self, ) -> Result<(), <I as Interner>::ErrorGuaranteed>

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#### fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool

Returns `true` if this type has any regions that escape `binder` (and hence are not bound by it).
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#### fn has_escaping_bound_vars(&self) -> bool

Return `true` if this type has regions that are not a part of the type. For example, `for<'a> fn(&'a i32)` return `false`, while `fn(&'a i32)` would return `true`. The latter can occur when traversing through the former. Read more
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#### fn has_aliases(&self) -> bool

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#### fn has_opaque_types(&self) -> bool

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#### fn has_coroutines(&self) -> bool

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#### fn references_error(&self) -> bool

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#### fn has_non_region_param(&self) -> bool

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#### fn has_infer_regions(&self) -> bool

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#### fn has_infer_types(&self) -> bool

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#### fn has_non_region_infer(&self) -> bool

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#### fn has_infer(&self) -> bool

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#### fn has_placeholders(&self) -> bool

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#### fn has_non_region_placeholders(&self) -> bool

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#### fn has_param(&self) -> bool

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#### fn has_free_regions(&self) -> bool

“Free” regions in this context means that it has any region that is not (a) erased or (b) late-bound.
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#### fn has_erased_regions(&self) -> bool

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#### fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.
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#### fn is_global(&self) -> bool

Indicates whether this value references only ‘global’ generic parameters that are the same regardless of what fn we are in. This is used for caching.
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#### fn has_bound_regions(&self) -> bool

True if there are any late-bound regions
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#### fn has_non_region_bound_vars(&self) -> bool

True if there are any late-bound non-region variables
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#### fn has_bound_vars(&self) -> bool

True if there are any bound variables
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#### fn still_further_specializable(&self) -> bool

Indicates whether this value still has parameters/placeholders/inference variables which could be replaced later, in a way that would change the results of `impl` specialization.
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#### fn has_non_region_error(&self) -> bool

True if a type or const error is reachable
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### impl<I, T, U> Upcast<I, U> for T
where U: UpcastFrom<I, T>,

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#### fn upcast(self, interner: I) -> U

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### impl<I, T> UpcastFrom<I, T> for T

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#### fn upcast_from(from: T, _tcx: I) -> T

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### impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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#### fn vzip(self) -> V

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### impl<T> WithSubscriber for T

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#### fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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#### fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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### impl<T> ErasedDestructor for T
where T: 'static,

## Layout§

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain `repr(...)` attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 40 bytes

Size for each variant:

- `Use`: 31 bytes
- `Repeat`: 39 bytes
- `Ref`: 31 bytes
- `ThreadLocalRef`: 11 bytes
- `RawPtr`: 23 bytes
- `Cast`: 39 bytes
- `BinaryOp`: 15 bytes
- `UnaryOp`: 31 bytes
- `Discriminant`: 23 bytes
- `Aggregate`: 39 bytes
- `CopyForDeref`: 23 bytes
- `WrapUnsafeBinder`: 39 bytes