pub struct EarlyOtherwiseBranch;
Expand description

This pass optimizes something like

let x: Option<()>;
let y: Option<()>;
match (x,y) {
    (Some(_), Some(_)) => {0},
    _ => {1}
}

into something like

let x: Option<()>;
let y: Option<()>;
let discriminant_x = std::mem::discriminant(x);
let discriminant_y = std::mem::discriminant(y);
if discriminant_x == discriminant_y {
    match x {
        Some(_) => 0,
        _ => 1, // <----
    } //               | Actually the same bb
} else { //            |
    1 // <--------------
}

Specifically, it looks for instances of control flow like this:


    =================
    |      BB1      |
    |---------------|                  ============================
    |     ...       |         /------> |            BBC           |
    |---------------|         |        |--------------------------|
    |  switchInt(Q) |         |        |   _cl = discriminant(P)  |
    |       c       | --------/        |--------------------------|
    |       d       | -------\         |       switchInt(_cl)     |
    |      ...      |        |         |            c             | ---> BBC.2
    |    otherwise  | --\    |    /--- |         otherwise        |
    =================   |    |    |    ============================
                        |    |    |
    =================   |    |    |
    |      BBU      | <-|    |    |    ============================
    |---------------|   |    \-------> |            BBD           |
    |---------------|   |         |    |--------------------------|
    |  unreachable  |   |         |    |   _dl = discriminant(P)  |
    =================   |         |    |--------------------------|
                        |         |    |       switchInt(_dl)     |
    =================   |         |    |            d             | ---> BBD.2
    |      BB9      | <--------------- |         otherwise        |
    |---------------|                  ============================
    |      ...      |
    =================

Where the otherwise branch on BB1 is permitted to either go to BBU or to BB9. In the code:

  • BB1 is parent and BBC, BBD are children
  • P is child_place
  • child_ty is the type of _cl.
  • Q is parent_op.
  • parent_ty is the type of Q.
  • BB9 is destination All this is then transformed into:

    =======================
    |          BB1        |
    |---------------------|                  ============================
    |          ...        |         /------> |           BBEq           |
    | _s = discriminant(P)|         |        |--------------------------|
    | _t = Ne(Q, _s)      |         |        |--------------------------|
    |---------------------|         |        |       switchInt(Q)       |
    |     switchInt(_t)   |         |        |            c             | ---> BBC.2
    |        false        | --------/        |            d             | ---> BBD.2
    |       otherwise     | ---------------- |         otherwise        |
    =======================       |          ============================
                                  |
    =================             |
    |      BB9      | <-----------/
    |---------------|
    |      ...      |
    =================

This is only correct for some P, since P is now computed outside the original switchInt. The filter on which P are allowed (together with discussion of its correctness) is found in may_hoist.

Trait Implementations§

source§

impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch

source§

fn is_enabled(&self, sess: &Session) -> bool

Returns true if this pass is enabled with the current combination of compiler flags.
source§

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>)

source§

fn name(&self) -> &'static str

source§

fn profiler_name(&self) -> &'static str

source§

fn is_mir_dump_enabled(&self) -> bool

Auto Trait Implementations§

Blanket Implementations§

source§

impl<T> Aligned for T

source§

const ALIGN: Alignment = _

Alignment of Self.
source§

impl<T> Any for T
where T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

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

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

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

Mutably borrows from an owned value. Read more
source§

impl<T, R> CollectAndApply<T, R> for T

source§

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<_>>()).

§

type Output = R

source§

impl<T> Filterable for T

source§

fn filterable( self, filter_name: &'static str ) -> RequestFilterDataProvider<T, fn(_: DataRequest<'_>) -> bool>

Creates a filterable data provider with the given name for debugging. Read more
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T> Instrument for T

source§

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

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
source§

fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
source§

impl<T, U> Into<U> for T
where U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

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

source§

impl<P> IntoQueryParam<P> for P

source§

impl<T> MaybeResult<T> for T

§

type Error = !

source§

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

source§

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

source§

impl<T> Pointable for T

source§

const ALIGN: usize = _

The alignment of pointer.
§

type Init = T

The type for initializers.
source§

unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
source§

unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
source§

unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
source§

unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
source§

impl<T> Same for T

§

type Output = T

Should always be Self
source§

impl<'tcx, T> ToPredicate<'tcx, T> for T

source§

fn to_predicate(self, _tcx: TyCtxt<'tcx>) -> T

source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

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

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
source§

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

source§

fn vzip(self) -> V

source§

impl<Tcx, T> Value<Tcx> for T
where Tcx: DepContext,

source§

default fn from_cycle_error( tcx: Tcx, cycle_error: &CycleError, _guar: ErrorGuaranteed ) -> T

source§

impl<T> WithSubscriber for T

source§

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
source§

fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
source§

impl<'a, T> Captures<'a> for T
where T: ?Sized,

source§

impl<'a, T> Captures<'a> for T
where T: ?Sized,

source§

impl<T> ErasedDestructor for T
where T: 'static,

source§

impl<T> MaybeSendSync for T
where T: Send + Sync,

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: 0 bytes