Struct rustc_middle::mir::syntax::Place
source · Expand description
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:
- The address in memory that the place refers to.
- The provenance with which the place is being accessed.
- The type of the place and an optional variant index. See
PlaceTy
. - 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
: This projection sets the place’s variant index to the given one, and makes no other changes. ADowncast
projection on a place with its variant index already set is not well-formed. -
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.
-
ConstantIndex
: Computes an offset in units ofT
into the place as described in the documentation for theProjectionElem
. The resulting address is the parent’s address plus that offset, and the type isT
. This is only legal if the parent place has type[T; N]
or[T]
(not&[T]
). Since such aT
is always sized, any resulting metadata is thrown out. -
Subslice
: This projection calculates an offset and a new address in a similar manner asConstantIndex
. It is also only legal on[T; N]
and[T]
. However, this yields aPlace
of type[T]
, and additionally sets the metadata to be the length of the subslice. -
Index
: LikeConstantIndex
, 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 theLocal
as aPlace { local, projection: [] }
, and then computing its value as if done viaOperand::Copy
. The array/slice is then indexed with the resulting value. The local must have typeusize
. -
Deref
: Derefs are the last type of projection, and the most complicated. They are only legal on parent places that are references, pointers, orBox
. ADeref
projection begins by loading a value from the parent place, as if byOperand::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.
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.
Fields
local: Local
projection: &'tcx List<PlaceElem<'tcx>>
projection out of a place (access a field, deref a pointer, etc)
Implementations
sourceimpl<'tcx> Place<'tcx>
impl<'tcx> Place<'tcx>
pub fn return_place() -> Place<'tcx>
sourcepub fn is_indirect(&self) -> bool
pub fn is_indirect(&self) -> bool
Returns true
if this Place
contains a Deref
projection.
If Place::is_indirect
returns false, the caller knows that the Place
refers to the
same region of memory as its base.
sourcepub fn has_deref(&self) -> bool
pub fn has_deref(&self) -> bool
If MirPhase >= Derefered and if projection contains Deref, It’s guaranteed to be in the first place
sourcepub fn local_or_deref_local(&self) -> Option<Local>
pub fn local_or_deref_local(&self) -> Option<Local>
Finds the innermost Local
from this Place
, if it is either a local itself or
a single deref of a local.
sourcepub fn as_local(&self) -> Option<Local>
pub fn as_local(&self) -> Option<Local>
If this place represents a local variable like _X
with no
projections, return Some(_X)
.
pub fn as_ref(&self) -> PlaceRef<'tcx>
sourcepub fn iter_projections(
self
) -> impl Iterator<Item = (PlaceRef<'tcx>, PlaceElem<'tcx>)> + DoubleEndedIterator
pub fn iter_projections(
self
) -> impl Iterator<Item = (PlaceRef<'tcx>, PlaceElem<'tcx>)> + DoubleEndedIterator
Iterate over the projections in evaluation order, i.e., the first element is the base with its projection and then subsequently more projections are added. As a concrete example, given the place a.b.c, this would yield:
- (a, .b)
- (a.b, .c)
Given a place without projections, the iterator is empty.
sourcepub fn project_deeper(
self,
more_projections: &[PlaceElem<'tcx>],
tcx: TyCtxt<'tcx>
) -> Self
pub fn project_deeper(
self,
more_projections: &[PlaceElem<'tcx>],
tcx: TyCtxt<'tcx>
) -> Self
Generates a new place by appending more_projections
to the existing ones
and interning the result.
Trait Implementations
sourceimpl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for Place<'tcx>
impl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for Place<'tcx>
fn hash_stable(
&self,
__hcx: &mut StableHashingContext<'__ctx>,
__hasher: &mut StableHasher
)
sourceimpl<'tcx> PartialEq<Place<'tcx>> for Place<'tcx>
impl<'tcx> PartialEq<Place<'tcx>> for Place<'tcx>
sourceimpl<'tcx> TypeFoldable<'tcx> for Place<'tcx>
impl<'tcx> TypeFoldable<'tcx> for Place<'tcx>
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>
sourcefn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self
fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
. Read moresourceimpl<'tcx> TypeVisitable<'tcx> for Place<'tcx>
impl<'tcx> TypeVisitable<'tcx> for Place<'tcx>
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>
sourcefn 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. Read moresourcefn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
true
if this self
has any regions that escape binder
(and
hence are not bound by it). Read morefn 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
fn has_erased_regions(&self) -> bool
sourcefn has_erasable_regions(&self) -> bool
fn has_erasable_regions(&self) -> bool
sourcefn is_global(&self) -> bool
fn is_global(&self) -> bool
sourcefn has_late_bound_regions(&self) -> bool
fn has_late_bound_regions(&self) -> bool
sourcefn still_further_specializable(&self) -> bool
fn still_further_specializable(&self) -> bool
impl
specialization. Read moreimpl<'tcx> Copy for Place<'tcx>
impl<'tcx> Eq for Place<'tcx>
impl<'tcx> StructuralEq for Place<'tcx>
impl<'tcx> StructuralPartialEq for Place<'tcx>
Auto Trait Implementations
impl<'tcx> !RefUnwindSafe for Place<'tcx>
impl<'tcx> Send for Place<'tcx>
impl<'tcx> Sync for Place<'tcx>
impl<'tcx> Unpin for Place<'tcx>
impl<'tcx> !UnwindSafe for Place<'tcx>
Blanket Implementations
sourceimpl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for Twhere
T: Copy,
impl<'tcx, T> ArenaAllocatable<'tcx, IsCopy> for Twhere
T: Copy,
fn allocate_on(self, arena: &'a Arena<'tcx>) -> &'a mut T
fn allocate_from_iter(
arena: &'a Arena<'tcx>,
iter: impl IntoIterator<Item = T>
) -> &'a mut [T]ⓘNotable traits for &[u8]impl Read for &[u8]impl Write for &mut [u8]
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
sourceimpl<Ctxt, T> DepNodeParams<Ctxt> for Twhere
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Ctxt, T> DepNodeParams<Ctxt> for Twhere
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
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>
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 moresourceimpl<T, R> InternIteratorElement<T, R> for T
impl<T, R> InternIteratorElement<T, R> for T
type Output = R
fn intern_with<I, F>(iter: I, f: F) -> <T as InternIteratorElement<T, R>>::Outputwhere
I: Iterator<Item = T>,
F: FnOnce(&[T]) -> R,
sourceimpl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
sourceimpl<CTX, T> Value<CTX> for Twhere
CTX: DepContext,
impl<CTX, T> Value<CTX> for Twhere
CTX: DepContext,
default fn from_cycle_error(tcx: CTX) -> T
impl<'a, T> Captures<'a> for Twhere
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