Enum rustc_middle::mir::MirPhase

pub enum MirPhase {
    Built,
    Const,
    ConstsPromoted,
    Derefered,
    DropsLowered,
    Deaggregated,
    GeneratorsLowered,
    Optimized,
}

The various “big phases” that MIR goes through.

These phases all describe dialects of MIR. Since all MIR uses the same datastructures, the dialects forbid certain variants or values in certain phases. The sections below summarize the changes, but do not document them thoroughly. The full documentation is found in the appropriate documentation for the thing the change is affecting.

Warning: ordering of variants is significant.

Variants

Built

The dialect of MIR used during all phases before DropsLowered is the same. This is also the MIR that analysis such as borrowck uses.

One important thing to remember about the behavior of this section of MIR is that drop terminators (including drop and replace) are conditional. The elaborate drops pass will then replace each instance of a drop terminator with a nop, an unconditional drop, or a drop conditioned on a drop flag. Of course, this means that it is important that the drop elaboration can accurately recognize when things are initialized and when things are de-initialized. That means any code running on this version of MIR must be sure to produce output that drop elaboration can reason about. See the section on the drop terminatorss for more details.

Const

ConstsPromoted

This phase checks the MIR for promotable elements and takes them out of the main MIR body by creating a new MIR body per promoted element. After this phase (and thus the termination of the mir_promoted query), these promoted elements are available in the promoted_mir query.

Derefered

After this projections may only contain deref projections as the first element.

DropsLowered

Beginning with this phase, the following variants are disallowed:

• TerminatorKind::DropAndReplace
• TerminatorKind::FalseUnwind
• TerminatorKind::FalseEdge
• StatementKind::FakeRead
• StatementKind::AscribeUserType
• Rvalue::Ref with BorrowKind::Shallow

And the following variant is allowed:

• StatementKind::Retag

Furthermore, Drop now uses explicit drop flags visible in the MIR and reaching a Drop terminator means that the auto-generated drop glue will be invoked. Also, Copy operands are allowed for non-Copy types.

Deaggregated

Beginning with this phase, the following variant is disallowed:

• Rvalue::Aggregate for any AggregateKind except Array

And the following variant is allowed:

• StatementKind::SetDiscriminant

GeneratorsLowered

Before this phase, generators are in the “source code” form, featuring yield statements and such. With this phase change, they are transformed into a proper state machine. Running optimizations before this change can be potentially dangerous because the source code is to some extent a “lie.” In particular, yield terminators effectively make the value of all locals visible to the caller. This means that dead store elimination before them, or code motion across them, is not correct in general. This is also exasperated by type checking having pre-computed a list of the types that it thinks are ok to be live across a yield point - this is necessary to decide eg whether autotraits are implemented. Introducing new types across a yield point will lead to ICEs becaues of this.

Beginning with this phase, the following variants are disallowed:

• TerminatorKind::Yield
• TerminatorKind::GeneratorDrop
• ProjectionElem::Deref of Box

Optimized

Implementations

impl MirPhase

pub fn phase_index(&self) -> usize

Gets the index of the current MirPhase within the set of all MirPhases.

Trait Implementations

impl Clone for MirPhase

fn clone(&self) -> MirPhase

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MirPhase

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

Formats the value using the given formatter.

impl<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for MirPhase

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

impl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for MirPhase

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

impl<'__ctx> HashStable<StableHashingContext<'__ctx>> for MirPhase

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

impl<'tcx> Lift<'tcx> for MirPhase

type Lifted = MirPhase

fn lift_to_tcx(self, _: TyCtxt<'tcx>) -> Option<Self>

impl Ord for MirPhase

fn cmp(&self, other: &MirPhase) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl PartialEq<MirPhase> for MirPhase

fn eq(&self, other: &MirPhase) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl PartialOrd<MirPhase> for MirPhase

fn partial_cmp(&self, other: &MirPhase) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<'tcx> TypeFoldable<'tcx> for MirPhase

fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
    self,
    _: &mut F
) -> Result<MirPhase, F::Error>

The entry point for folding. To fold a value t with a folder f call: t.try_fold_with(f).

fn fold_with<F: TypeFolder<'tcx>>(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.

impl<'tcx> TypeVisitable<'tcx> for MirPhase

fn visit_with<F: TypeVisitor<'tcx>>(&self, _: &mut F) -> ControlFlow<F::BreakTy>

The entry point for visiting. To visit a value t with a visitor v call: t.visit_with(v).

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.

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).

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

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.

fn has_erased_regions(&self) -> bool

fn has_erasable_regions(&self) -> bool

True if there are any un-erased free regions.

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.

fn has_late_bound_regions(&self) -> bool

True if there are any late-bound regions

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.

impl Copy for MirPhase

impl Eq for MirPhase

impl StructuralEq for MirPhase

impl StructuralPartialEq for MirPhase

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: 1 byte

Size for each variant:

• Built: 0 bytes
• Const: 0 bytes
• ConstsPromoted: 0 bytes
• Derefered: 0 bytes
• DropsLowered: 0 bytes
• Deaggregated: 0 bytes
• GeneratorsLowered: 0 bytes
• Optimized: 0 bytes