Enum rustc_middle::mir::StatementKind
source · [−]pub enum StatementKind<'tcx> {
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>>),
AscribeUserType(Box<(Place<'tcx>, UserTypeProjection)>, Variance),
Coverage(Box<Coverage>),
CopyNonOverlapping(Box<CopyNonOverlapping<'tcx>>),
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 paragragh 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.
Using a local before a StorageLive
or after a StorageDead
is not well-formed. These
statements are not required. If the entire MIR body contains no StorageLive
/StorageDead
statements for a particular local, the local is always considered live.
More precisely, the MIR validator currently does a MaybeStorageLiveLocals
analysis to
check validity of each use of a local. I believe this is equivalent to requiring for every
use of a local, there exist at least one path from the root to that use that contains a
StorageLive
more recently than a StorageDead
.
Needs clarification: Is it permitted to have two StorageLive
s without an intervening
StorageDead
? Two StorageDead
s without an intervening StorageLive
? LLVM says poison,
yes. If the answer to any of these is “no,” is breaking that rule UB or is it an error to
have a path in the CFG that might do this?
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.
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.
CopyNonOverlapping(Box<CopyNonOverlapping<'tcx>>)
Denotes a call to the intrinsic function copy_nonoverlapping
.
First, all three operands are evaluated. src
and dest
must each be a reference, pointer,
or Box
pointing to the same type T
. count
must evaluate to a usize
. Then, src
and
dest
are dereferenced, and count * size_of::<T>()
bytes beginning with the first byte of
the src
place are copied to the continguous 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.
Nop
No-op. Useful for deleting instructions without affecting statement indices.
Implementations
Trait Implementations
sourceimpl<'tcx> Clone for StatementKind<'tcx>
impl<'tcx> Clone for StatementKind<'tcx>
sourcefn clone(&self) -> StatementKind<'tcx>
fn clone(&self) -> StatementKind<'tcx>
Returns a copy of the value. Read more
1.0.0 · sourcefn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
sourceimpl<'tcx> Debug for StatementKind<'tcx>
impl<'tcx> Debug for StatementKind<'tcx>
sourceimpl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for StatementKind<'tcx>
impl<'tcx, __D: TyDecoder<'tcx>> Decodable<__D> for StatementKind<'tcx>
sourceimpl<'tcx, __E: TyEncoder<'tcx>> Encodable<__E> for StatementKind<'tcx>
impl<'tcx, __E: TyEncoder<'tcx>> Encodable<__E> for StatementKind<'tcx>
sourceimpl<'tcx> Hash for StatementKind<'tcx>
impl<'tcx> Hash for StatementKind<'tcx>
sourceimpl<'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
)
sourceimpl<'tcx> PartialEq<StatementKind<'tcx>> for StatementKind<'tcx>
impl<'tcx> PartialEq<StatementKind<'tcx>> for StatementKind<'tcx>
sourcefn eq(&self, other: &StatementKind<'tcx>) -> bool
fn eq(&self, other: &StatementKind<'tcx>) -> bool
This method tests for self
and other
values to be equal, and is used
by ==
. Read more
sourcefn ne(&self, other: &StatementKind<'tcx>) -> bool
fn ne(&self, other: &StatementKind<'tcx>) -> bool
This method tests for !=
.
sourceimpl<'tcx> TypeFoldable<'tcx> for StatementKind<'tcx>
impl<'tcx> TypeFoldable<'tcx> for StatementKind<'tcx>
sourcefn try_super_fold_with<__F: FallibleTypeFolder<'tcx>>(
self,
__folder: &mut __F
) -> Result<Self, __F::Error>
fn try_super_fold_with<__F: FallibleTypeFolder<'tcx>>(
self,
__folder: &mut __F
) -> Result<Self, __F::Error>
Traverses the type in question, typically by calling try_fold_with
on
each field/element. This is true even for types of interest such as
Ty
. This should only be called within TypeFolder
methods, when
non-custom traversals are desired for types of interest. Read more
sourcefn super_visit_with<__F: TypeVisitor<'tcx>>(
&self,
__folder: &mut __F
) -> ControlFlow<__F::BreakTy>
fn super_visit_with<__F: TypeVisitor<'tcx>>(
&self,
__folder: &mut __F
) -> ControlFlow<__F::BreakTy>
Traverses the type in question, typically by calling visit_with
on
each field/element. This is true even for types of interest such as
Ty
. This should only be called within TypeVisitor
methods, when
non-custom traversals are desired for types of interest. Read more
sourcefn try_fold_with<F: FallibleTypeFolder<'tcx>>(
self,
folder: &mut F
) -> Result<Self, F::Error>
fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
self,
folder: &mut F
) -> Result<Self, F::Error>
The main entry point for folding. To fold a value t
with a folder f
call: t.try_fold_with(f)
. Read more
sourcefn fold_with<F: TypeFolder<'tcx, Error = !>>(self, folder: &mut F) -> Self
fn fold_with<F: TypeFolder<'tcx, Error = !>>(self, folder: &mut F) -> Self
A convenient alternative to try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
. Read more
sourcefn super_fold_with<F: TypeFolder<'tcx, Error = !>>(self, folder: &mut F) -> Self
fn super_fold_with<F: TypeFolder<'tcx, Error = !>>(self, folder: &mut F) -> Self
A convenient alternative to try_super_fold_with
for use with
infallible folders. Do not override this method, to ensure coherence
with try_super_fold_with
. Read more
sourcefn visit_with<V: TypeVisitor<'tcx>>(
&self,
visitor: &mut V
) -> ControlFlow<V::BreakTy>
fn visit_with<V: TypeVisitor<'tcx>>(
&self,
visitor: &mut V
) -> ControlFlow<V::BreakTy>
The entry point for visiting. To visit a value t
with a visitor v
call: t.visit_with(v)
. Read more
sourcefn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
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. Read more
sourcefn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
Returns true
if this self
has any regions that escape binder
(and
hence are not bound by it). Read more
fn has_escaping_bound_vars(&self) -> bool
fn has_type_flags(&self, flags: TypeFlags) -> bool
fn has_projections(&self) -> bool
fn has_opaque_types(&self) -> bool
fn references_error(&self) -> bool
fn error_reported(&self) -> Option<ErrorGuaranteed>
fn has_param_types_or_consts(&self) -> bool
fn has_infer_regions(&self) -> bool
fn has_infer_types(&self) -> bool
fn has_infer_types_or_consts(&self) -> bool
fn needs_infer(&self) -> bool
fn has_placeholders(&self) -> bool
fn needs_subst(&self) -> bool
sourcefn has_free_regions(&self) -> bool
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. Read more
fn has_erased_regions(&self) -> bool
sourcefn has_erasable_regions(&self) -> bool
fn has_erasable_regions(&self) -> bool
True if there are any un-erased free regions.
sourcefn is_global(&self) -> bool
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. Read more
sourcefn has_late_bound_regions(&self) -> bool
fn has_late_bound_regions(&self) -> bool
True if there are any late-bound regions
sourcefn still_further_specializable(&self) -> bool
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. Read more
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
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<Ctxt, T> DepNodeParams<Ctxt> for T where
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Ctxt, T> DepNodeParams<Ctxt> for T where
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
default fn fingerprint_style() -> FingerprintStyle
sourcedefault fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint
default fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint
This method turns the parameters of a DepNodeConstructor into an opaque Fingerprint to be used in DepNode. Not all DepNodeParams support being turned into a Fingerprint (they don’t need to if the corresponding DepNode is anonymous). Read more
default fn to_debug_str(&self, Ctxt) -> String
sourcedefault fn recover(Ctxt, &DepNode<<Ctxt as DepContext>::DepKind>) -> Option<T>
default fn recover(Ctxt, &DepNode<<Ctxt as DepContext>::DepKind>) -> 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. Read more
sourceimpl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
toowned_clone_into
)Uses borrowed data to replace owned data, usually by cloning. Read more
impl<'a, T> Captures<'a> for T where
T: ?Sized,
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 bytesAscribeUserType
: 15 bytesCoverage
: 15 bytesCopyNonOverlapping
: 15 bytesNop
: 0 bytes