Enum rustc_middle::mir::syntax::StatementKind
source · pub enum StatementKind<'tcx> {
Show 13 variants
Assign(Box<(Place<'tcx>, Rvalue<'tcx>)>),
FakeRead(Box<(FakeReadCause, Place<'tcx>)>),
SetDiscriminant {
place: Box<Place<'tcx>>,
variant_index: VariantIdx,
},
Deinit(Box<Place<'tcx>>),
StorageLive(Local),
StorageDead(Local),
Retag(RetagKind, Box<Place<'tcx>>),
PlaceMention(Box<Place<'tcx>>),
AscribeUserType(Box<(Place<'tcx>, UserTypeProjection)>, Variance),
Coverage(Box<Coverage>),
Intrinsic(Box<NonDivergingIntrinsic<'tcx>>),
ConstEvalCounter,
Nop,
}
Expand description
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.
Variants§
Assign(Box<(Place<'tcx>, Rvalue<'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.
See Rvalue
documentation for details on each of those.
FakeRead(Box<(FakeReadCause, Place<'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.
SetDiscriminant
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.
Deinit(Box<Place<'tcx>>)
Deinitializes the place.
This writes uninit
bytes to the entire place.
StorageLive(Local)
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.
StorageDead(Local)
See StorageLive
above.
Retag(RetagKind, Box<Place<'tcx>>)
Retag references in the given place, ensuring they got fresh tags.
This is part of the Stacked Borrows model. These statements are currently only interpreted
by miri and only generated when -Z mir-emit-retag
is passed. See
https://internals.rust-lang.org/t/stacked-borrows-an-aliasing-model-for-rust/8153/ for
more details.
For code that is not specific to stacked borrows, you should consider retags to read and modify the place in an opaque way.
Only RetagKind::Default
and RetagKind::FnEntry
are permitted.
PlaceMention(Box<Place<'tcx>>)
This statement exists to preserve a trace of a scrutinee matched against a wildcard binding.
This is especially useful for let _ = PLACE;
bindings that desugar to a single
PlaceMention(PLACE)
.
When executed at runtime, this computes the given place, but then discards it without doing a load. It is UB if the place is not pointing to live memory.
AscribeUserType(Box<(Place<'tcx>, UserTypeProjection)>, Variance)
Encodes a user’s type ascription. These need to be preserved intact so that NLL can respect them. For example:
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 thatT_y <: T
Contravariant
– requires thatT_y :> T
Invariant
– requires thatT_y == T
Bivariant
– no effect
When executed at runtime this is a nop.
Disallowed after drop elaboration.
Coverage(Box<Coverage>)
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.
Intrinsic(Box<NonDivergingIntrinsic<'tcx>>)
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.
ConstEvalCounter
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.
Nop
No-op. Useful for deleting instructions without affecting statement indices.
Implementations§
source§impl<'tcx> StatementKind<'tcx>
impl<'tcx> StatementKind<'tcx>
Trait Implementations§
source§impl<'tcx> Clone for StatementKind<'tcx>
impl<'tcx> Clone for StatementKind<'tcx>
source§fn clone(&self) -> StatementKind<'tcx>
fn clone(&self) -> StatementKind<'tcx>
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl<'tcx> Debug for StatementKind<'tcx>
impl<'tcx> Debug for StatementKind<'tcx>
source§impl<'tcx> Hash for StatementKind<'tcx>
impl<'tcx> Hash for StatementKind<'tcx>
source§impl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for StatementKind<'tcx>
impl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for StatementKind<'tcx>
fn hash_stable( &self, __hcx: &mut StableHashingContext<'__ctx>, __hasher: &mut StableHasher )
source§impl<'tcx> PartialEq<StatementKind<'tcx>> for StatementKind<'tcx>
impl<'tcx> PartialEq<StatementKind<'tcx>> for StatementKind<'tcx>
source§fn eq(&self, other: &StatementKind<'tcx>) -> bool
fn eq(&self, other: &StatementKind<'tcx>) -> bool
self
and other
values to be equal, and is used
by ==
.source§impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for StatementKind<'tcx>
impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for StatementKind<'tcx>
source§fn try_fold_with<__F: FallibleTypeFolder<TyCtxt<'tcx>>>(
self,
__folder: &mut __F
) -> Result<Self, __F::Error>
fn try_fold_with<__F: FallibleTypeFolder<TyCtxt<'tcx>>>( self, __folder: &mut __F ) -> Result<Self, __F::Error>
source§fn fold_with<F>(self, folder: &mut F) -> Selfwhere
F: TypeFolder<I>,
fn fold_with<F>(self, folder: &mut F) -> Selfwhere F: TypeFolder<I>,
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
.source§impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for StatementKind<'tcx>
impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for StatementKind<'tcx>
source§fn visit_with<__V: TypeVisitor<TyCtxt<'tcx>>>(
&self,
__visitor: &mut __V
) -> ControlFlow<__V::BreakTy>
fn visit_with<__V: TypeVisitor<TyCtxt<'tcx>>>( &self, __visitor: &mut __V ) -> ControlFlow<__V::BreakTy>
impl<'tcx> StructuralPartialEq for StatementKind<'tcx>
Auto Trait Implementations§
impl<'tcx> !RefUnwindSafe for StatementKind<'tcx>
impl<'tcx> !Send for StatementKind<'tcx>
impl<'tcx> !Sync for StatementKind<'tcx>
impl<'tcx> Unpin for StatementKind<'tcx>
impl<'tcx> !UnwindSafe for StatementKind<'tcx>
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T, R> CollectAndApply<T, R> for T
impl<T, R> CollectAndApply<T, R> for T
source§impl<Tcx, T> DepNodeParams<Tcx> for Twhere
Tcx: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Tcx, T> DepNodeParams<Tcx> for Twhere Tcx: DepContext, T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
default fn fingerprint_style() -> FingerprintStyle
source§default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint
default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint
default fn to_debug_str(&self, _: Tcx) -> String
source§default fn recover(_: Tcx, _: &DepNode) -> Option<T>
default fn recover(_: Tcx, _: &DepNode) -> Option<T>
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
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impl<P> IntoQueryParam<P> for P
fn into_query_param(self) -> P
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source§fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
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.source§fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
true
if this type has any regions that escape binder
(and
hence are not bound by it).source§fn has_escaping_bound_vars(&self) -> bool
fn has_escaping_bound_vars(&self) -> bool
true
if this type has regions that are not a part of the type.
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return false
, while fn(&'a i32)
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former. Read morefn has_type_flags(&self, flags: TypeFlags) -> bool
fn has_projections(&self) -> bool
fn has_inherent_projections(&self) -> bool
fn has_opaque_types(&self) -> bool
fn has_generators(&self) -> bool
fn references_error(&self) -> bool
fn error_reported(&self) -> Result<(), ErrorGuaranteed>
fn has_non_region_param(&self) -> bool
fn has_infer_regions(&self) -> bool
fn has_infer_types(&self) -> bool
fn has_non_region_infer(&self) -> bool
fn has_infer(&self) -> bool
fn has_placeholders(&self) -> bool
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source§fn has_free_regions(&self) -> bool
fn has_free_regions(&self) -> bool
fn has_erased_regions(&self) -> bool
source§fn has_erasable_regions(&self) -> bool
fn has_erasable_regions(&self) -> bool
source§fn is_global(&self) -> bool
fn is_global(&self) -> bool
source§fn has_late_bound_regions(&self) -> bool
fn has_late_bound_regions(&self) -> bool
source§fn has_non_region_late_bound(&self) -> bool
fn has_non_region_late_bound(&self) -> bool
source§fn has_late_bound_vars(&self) -> bool
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source§fn still_further_specializable(&self) -> bool
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specialization.source§impl<Tcx, T> Value<Tcx> for Twhere
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default fn from_cycle_error( tcx: Tcx, cycle: &[QueryInfo], _guar: ErrorGuaranteed ) -> T
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: 16 bytes
Size for each variant:
Assign
: 15 bytesFakeRead
: 15 bytesSetDiscriminant
: 15 bytesDeinit
: 15 bytesStorageLive
: 7 bytesStorageDead
: 7 bytesRetag
: 15 bytesPlaceMention
: 15 bytesAscribeUserType
: 15 bytesCoverage
: 15 bytesIntrinsic
: 15 bytesConstEvalCounter
: 0 bytesNop
: 0 bytes