Remove the `DefinitelyInitializedPlaces` analysis.

Its only use is in the `tests/ui/mir-dataflow/def_inits-1.rs` where it
is tested via `rustc_peek_definite_init`.

Also, it's probably buggy. It's supposed to be the inverse of
`MaybeUninitializedPlaces`, and it mostly is, except that
`apply_terminator_effect` is a little different, and
`apply_switch_int_edge_effects` is missing. Unlike
`MaybeUninitializedPlaces`, which is used extensively in borrow
checking, any bugs in `DefinitelyInitializedPlaces` are easy to overlook
because it is only used in one small test.

This commit removes the analysis. It also removes
`rustc_peek_definite_init`, `Dual` and `MeetSemiLattice`, all of which
are no longer needed.

7 files changed, 13 insertions, 279 deletions

diff --git a/compiler/rustc_mir_dataflow/src/framework/fmt.rs b/compiler/rustc_mir_dataflow/src/framework/fmt.rs
index ed540cd148c..c177d98106f 100644
--- a/compiler/rustc_mir_dataflow/src/framework/fmt.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/fmt.rs
@@ -230,16 +230,3 @@ where
         write!(f, "{}", ctxt.move_data().move_paths[*self])
     }
 }
-
-impl<T, C> DebugWithContext<C> for crate::lattice::Dual<T>
-where
-    T: DebugWithContext<C>,
-{
-    fn fmt_with(&self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        (self.0).fmt_with(ctxt, f)
-    }
-
-    fn fmt_diff_with(&self, old: &Self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        (self.0).fmt_diff_with(&old.0, ctxt, f)
-    }
-}
diff --git a/compiler/rustc_mir_dataflow/src/framework/lattice.rs b/compiler/rustc_mir_dataflow/src/framework/lattice.rs
index 4d03ee53b7c..6d2a7a099a0 100644
--- a/compiler/rustc_mir_dataflow/src/framework/lattice.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/lattice.rs
@@ -25,8 +25,8 @@
 //!
 //! ## `PartialOrd`
 //!
-//! Given that they represent partially ordered sets, you may be surprised that [`JoinSemiLattice`]
-//! and [`MeetSemiLattice`] do not have [`PartialOrd`] as a supertrait. This
+//! Given that it represents a partially ordered set, you may be surprised that [`JoinSemiLattice`]
+//! does not have [`PartialOrd`] as a supertrait. This
 //! is because most standard library types use lexicographic ordering instead of set inclusion for
 //! their `PartialOrd` impl. Since we do not actually need to compare lattice elements to run a
 //! dataflow analysis, there's no need for a newtype wrapper with a custom `PartialOrd` impl. The
@@ -58,23 +58,6 @@ pub trait JoinSemiLattice: Eq {
     fn join(&mut self, other: &Self) -> bool;
 }
 
-/// A [partially ordered set][poset] that has a [greatest lower bound][glb] for any pair of
-/// elements in the set.
-///
-/// Dataflow analyses only require that their domains implement [`JoinSemiLattice`], not
-/// `MeetSemiLattice`. However, types that will be used as dataflow domains should implement both
-/// so that they can be used with [`Dual`].
-///
-/// [glb]: https://en.wikipedia.org/wiki/Infimum_and_supremum
-/// [poset]: https://en.wikipedia.org/wiki/Partially_ordered_set
-pub trait MeetSemiLattice: Eq {
-    /// Computes the greatest lower bound of two elements, storing the result in `self` and
-    /// returning `true` if `self` has changed.
-    ///
-    /// The lattice meet operator is abbreviated as `∧`.
-    fn meet(&mut self, other: &Self) -> bool;
-}
-
 /// A set that has a "bottom" element, which is less than or equal to any other element.
 pub trait HasBottom {
     const BOTTOM: Self;
@@ -105,17 +88,6 @@ impl JoinSemiLattice for bool {
     }
 }
 
-impl MeetSemiLattice for bool {
-    fn meet(&mut self, other: &Self) -> bool {
-        if let (true, false) = (*self, *other) {
-            *self = false;
-            return true;
-        }
-
-        false
-    }
-}
-
 impl HasBottom for bool {
     const BOTTOM: Self = false;
 
@@ -145,18 +117,6 @@ impl<I: Idx, T: JoinSemiLattice> JoinSemiLattice for IndexVec<I, T> {
     }
 }
 
-impl<I: Idx, T: MeetSemiLattice> MeetSemiLattice for IndexVec<I, T> {
-    fn meet(&mut self, other: &Self) -> bool {
-        assert_eq!(self.len(), other.len());
-
-        let mut changed = false;
-        for (a, b) in iter::zip(self, other) {
-            changed |= a.meet(b);
-        }
-        changed
-    }
-}
-
 /// A `BitSet` represents the lattice formed by the powerset of all possible values of
 /// the index type `T` ordered by inclusion. Equivalently, it is a tuple of "two-point" lattices,
 /// one for each possible value of `T`.
@@ -166,60 +126,12 @@ impl<T: Idx> JoinSemiLattice for BitSet<T> {
     }
 }
 
-impl<T: Idx> MeetSemiLattice for BitSet<T> {
-    fn meet(&mut self, other: &Self) -> bool {
-        self.intersect(other)
-    }
-}
-
 impl<T: Idx> JoinSemiLattice for ChunkedBitSet<T> {
     fn join(&mut self, other: &Self) -> bool {
         self.union(other)
     }
 }
 
-impl<T: Idx> MeetSemiLattice for ChunkedBitSet<T> {
-    fn meet(&mut self, other: &Self) -> bool {
-        self.intersect(other)
-    }
-}
-
-/// The counterpart of a given semilattice `T` using the [inverse order].
-///
-/// The dual of a join-semilattice is a meet-semilattice and vice versa. For example, the dual of a
-/// powerset has the empty set as its top element and the full set as its bottom element and uses
-/// set *intersection* as its join operator.
-///
-/// [inverse order]: https://en.wikipedia.org/wiki/Duality_(order_theory)
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub struct Dual<T>(pub T);
-
-impl<T: Idx> BitSetExt<T> for Dual<BitSet<T>> {
-    fn contains(&self, elem: T) -> bool {
-        self.0.contains(elem)
-    }
-
-    fn union(&mut self, other: &HybridBitSet<T>) {
-        self.0.union(other);
-    }
-
-    fn subtract(&mut self, other: &HybridBitSet<T>) {
-        self.0.subtract(other);
-    }
-}
-
-impl<T: MeetSemiLattice> JoinSemiLattice for Dual<T> {
-    fn join(&mut self, other: &Self) -> bool {
-        self.0.meet(&other.0)
-    }
-}
-
-impl<T: JoinSemiLattice> MeetSemiLattice for Dual<T> {
-    fn meet(&mut self, other: &Self) -> bool {
-        self.0.join(&other.0)
-    }
-}
-
 /// Extends a type `T` with top and bottom elements to make it a partially ordered set in which no
 /// value of `T` is comparable with any other.
 ///
@@ -257,22 +169,6 @@ impl<T: Clone + Eq> JoinSemiLattice for FlatSet<T> {
     }
 }
 
-impl<T: Clone + Eq> MeetSemiLattice for FlatSet<T> {
-    fn meet(&mut self, other: &Self) -> bool {
-        let result = match (&*self, other) {
-            (Self::Bottom, _) | (_, Self::Top) => return false,
-            (Self::Elem(ref a), Self::Elem(ref b)) if a == b => return false,
-
-            (Self::Top, Self::Elem(ref x)) => Self::Elem(x.clone()),
-
-            _ => Self::Bottom,
-        };
-
-        *self = result;
-        true
-    }
-}
-
 impl<T> HasBottom for FlatSet<T> {
     const BOTTOM: Self = Self::Bottom;
 
diff --git a/compiler/rustc_mir_dataflow/src/framework/mod.rs b/compiler/rustc_mir_dataflow/src/framework/mod.rs
index 244dfe26ad3..359d9280c52 100644
--- a/compiler/rustc_mir_dataflow/src/framework/mod.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/mod.rs
@@ -378,16 +378,6 @@ impl<T, S: GenKill<T>> GenKill<T> for MaybeReachable<S> {
     }
 }
 
-impl<T: Idx> GenKill<T> for lattice::Dual<BitSet<T>> {
-    fn gen_(&mut self, elem: T) {
-        self.0.insert(elem);
-    }
-
-    fn kill(&mut self, elem: T) {
-        self.0.remove(elem);
-    }
-}
-
 // NOTE: DO NOT CHANGE VARIANT ORDER. The derived `Ord` impls rely on the current order.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 enum Effect {
diff --git a/compiler/rustc_mir_dataflow/src/impls/initialized.rs b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
index 9bb50d1e056..2c10d4b1cd3 100644
--- a/compiler/rustc_mir_dataflow/src/impls/initialized.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
@@ -12,7 +12,7 @@ use crate::framework::SwitchIntEdgeEffects;
 use crate::move_paths::{HasMoveData, InitIndex, InitKind, LookupResult, MoveData, MovePathIndex};
 use crate::{
     Analysis, GenKill, MaybeReachable, drop_flag_effects, drop_flag_effects_for_function_entry,
-    drop_flag_effects_for_location, lattice, on_all_children_bits, on_lookup_result_bits,
+    drop_flag_effects_for_location, on_all_children_bits, on_lookup_result_bits,
 };
 
 /// `MaybeInitializedPlaces` tracks all places that might be
@@ -42,10 +42,10 @@ use crate::{
 /// }
 /// ```
 ///
-/// To determine whether a place *must* be initialized at a
-/// particular control-flow point, one can take the set-difference
-/// between this data and the data from `MaybeUninitializedPlaces` at the
-/// corresponding control-flow point.
+/// To determine whether a place is *definitely* initialized at a
+/// particular control-flow point, one can take the set-complement
+/// of the data from `MaybeUninitializedPlaces` at the corresponding
+/// control-flow point.
 ///
 /// Similarly, at a given `drop` statement, the set-intersection
 /// between this data and `MaybeUninitializedPlaces` yields the set of
@@ -117,10 +117,10 @@ impl<'a, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'a, 'tcx> {
 /// }
 /// ```
 ///
-/// To determine whether a place *must* be uninitialized at a
-/// particular control-flow point, one can take the set-difference
-/// between this data and the data from `MaybeInitializedPlaces` at the
-/// corresponding control-flow point.
+/// To determine whether a place is *definitely* uninitialized at a
+/// particular control-flow point, one can take the set-complement
+/// of the data from `MaybeInitializedPlaces` at the corresponding
+/// control-flow point.
 ///
 /// Similarly, at a given `drop` statement, the set-intersection
 /// between this data and `MaybeInitializedPlaces` yields the set of
@@ -170,57 +170,6 @@ impl<'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
     }
 }
 
-/// `DefinitelyInitializedPlaces` tracks all places that are definitely
-/// initialized upon reaching a particular point in the control flow
-/// for a function.
-///
-/// For example, in code like the following, we have corresponding
-/// dataflow information shown in the right-hand comments.
-///
-/// ```rust
-/// struct S;
-/// fn foo(pred: bool) {                        // definite-init:
-///                                             // {          }
-///     let a = S; let mut b = S; let c; let d; // {a, b      }
-///
-///     if pred {
-///         drop(a);                            // {   b,     }
-///         b = S;                              // {   b,     }
-///
-///     } else {
-///         drop(b);                            // {a,        }
-///         d = S;                              // {a,       d}
-///
-///     }                                       // {          }
-///
-///     c = S;                                  // {       c  }
-/// }
-/// ```
-///
-/// To determine whether a place *may* be uninitialized at a
-/// particular control-flow point, one can take the set-complement
-/// of this data.
-///
-/// Similarly, at a given `drop` statement, the set-difference between
-/// this data and `MaybeInitializedPlaces` yields the set of places
-/// that would require a dynamic drop-flag at that statement.
-pub struct DefinitelyInitializedPlaces<'a, 'tcx> {
-    body: &'a Body<'tcx>,
-    move_data: &'a MoveData<'tcx>,
-}
-
-impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
-    pub fn new(body: &'a Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
-        DefinitelyInitializedPlaces { body, move_data }
-    }
-}
-
-impl<'a, 'tcx> HasMoveData<'tcx> for DefinitelyInitializedPlaces<'a, 'tcx> {
-    fn move_data(&self) -> &MoveData<'tcx> {
-        self.move_data
-    }
-}
-
 /// `EverInitializedPlaces` tracks all places that might have ever been
 /// initialized upon reaching a particular point in the control flow
 /// for a function, without an intervening `StorageDead`.
@@ -293,19 +242,6 @@ impl<'tcx> MaybeUninitializedPlaces<'_, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
-    fn update_bits(
-        trans: &mut <Self as Analysis<'tcx>>::Domain,
-        path: MovePathIndex,
-        state: DropFlagState,
-    ) {
-        match state {
-            DropFlagState::Absent => trans.kill(path),
-            DropFlagState::Present => trans.gen_(path),
-        }
-    }
-}
-
 impl<'tcx> Analysis<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
     /// There can be many more `MovePathIndex` than there are locals in a MIR body.
     /// We use a chunked bitset to avoid paying too high a memory footprint.
@@ -554,70 +490,6 @@ impl<'tcx> Analysis<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Analysis<'tcx> for DefinitelyInitializedPlaces<'a, 'tcx> {
-    /// Use set intersection as the join operator.
-    type Domain = lattice::Dual<BitSet<MovePathIndex>>;
-
-    const NAME: &'static str = "definite_init";
-
-    fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
-        // bottom = initialized (start_block_effect counters this at outset)
-        lattice::Dual(BitSet::new_filled(self.move_data().move_paths.len()))
-    }
-
-    // sets on_entry bits for Arg places
-    fn initialize_start_block(&self, _: &mir::Body<'tcx>, state: &mut Self::Domain) {
-        state.0.clear();
-
-        drop_flag_effects_for_function_entry(self.body, self.move_data, |path, s| {
-            assert!(s == DropFlagState::Present);
-            state.0.insert(path);
-        });
-    }
-
-    fn apply_statement_effect(
-        &mut self,
-        trans: &mut Self::Domain,
-        _statement: &mir::Statement<'tcx>,
-        location: Location,
-    ) {
-        drop_flag_effects_for_location(self.body, self.move_data, location, |path, s| {
-            Self::update_bits(trans, path, s)
-        })
-    }
-
-    fn apply_terminator_effect<'mir>(
-        &mut self,
-        trans: &mut Self::Domain,
-        terminator: &'mir mir::Terminator<'tcx>,
-        location: Location,
-    ) -> TerminatorEdges<'mir, 'tcx> {
-        drop_flag_effects_for_location(self.body, self.move_data, location, |path, s| {
-            Self::update_bits(trans, path, s)
-        });
-        terminator.edges()
-    }
-
-    fn apply_call_return_effect(
-        &mut self,
-        trans: &mut Self::Domain,
-        _block: mir::BasicBlock,
-        return_places: CallReturnPlaces<'_, 'tcx>,
-    ) {
-        return_places.for_each(|place| {
-            // when a call returns successfully, that means we need to set
-            // the bits for that dest_place to 1 (initialized).
-            on_lookup_result_bits(
-                self.move_data(),
-                self.move_data().rev_lookup.find(place.as_ref()),
-                |mpi| {
-                    trans.gen_(mpi);
-                },
-            );
-        });
-    }
-}
-
 impl<'tcx> Analysis<'tcx> for EverInitializedPlaces<'_, 'tcx> {
     /// There can be many more `InitIndex` than there are locals in a MIR body.
     /// We use a chunked bitset to avoid paying too high a memory footprint.
diff --git a/compiler/rustc_mir_dataflow/src/impls/mod.rs b/compiler/rustc_mir_dataflow/src/impls/mod.rs
index 9b5bfa9bfa0..57ded63c9ba 100644
--- a/compiler/rustc_mir_dataflow/src/impls/mod.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/mod.rs
@@ -9,8 +9,7 @@ mod storage_liveness;
 
 pub use self::borrowed_locals::{MaybeBorrowedLocals, borrowed_locals};
 pub use self::initialized::{
-    DefinitelyInitializedPlaces, EverInitializedPlaces, MaybeInitializedPlaces,
-    MaybeUninitializedPlaces,
+    EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
 };
 pub use self::liveness::{
     MaybeLiveLocals, MaybeTransitiveLiveLocals, TransferFunction as LivenessTransferFunction,
diff --git a/compiler/rustc_mir_dataflow/src/rustc_peek.rs b/compiler/rustc_mir_dataflow/src/rustc_peek.rs
index 99d0ccde105..34ef8afdde3 100644
--- a/compiler/rustc_mir_dataflow/src/rustc_peek.rs
+++ b/compiler/rustc_mir_dataflow/src/rustc_peek.rs
@@ -12,9 +12,7 @@ use crate::errors::{
     PeekMustBePlaceOrRefPlace, StopAfterDataFlowEndedCompilation,
 };
 use crate::framework::BitSetExt;
-use crate::impls::{
-    DefinitelyInitializedPlaces, MaybeInitializedPlaces, MaybeLiveLocals, MaybeUninitializedPlaces,
-};
+use crate::impls::{MaybeInitializedPlaces, MaybeLiveLocals, MaybeUninitializedPlaces};
 use crate::move_paths::{HasMoveData, LookupResult, MoveData, MovePathIndex};
 use crate::{Analysis, JoinSemiLattice, ResultsCursor};
 
@@ -56,13 +54,6 @@ pub fn sanity_check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
         sanity_check_via_rustc_peek(tcx, flow_uninits.into_results_cursor(body));
     }
 
-    if has_rustc_mir_with(tcx, def_id, sym::rustc_peek_definite_init).is_some() {
-        let flow_def_inits =
-            DefinitelyInitializedPlaces::new(body, &move_data).iterate_to_fixpoint(tcx, body, None);
-
-        sanity_check_via_rustc_peek(tcx, flow_def_inits.into_results_cursor(body));
-    }
-
     if has_rustc_mir_with(tcx, def_id, sym::rustc_peek_liveness).is_some() {
         let flow_liveness = MaybeLiveLocals.iterate_to_fixpoint(tcx, body, None);
 
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index a2d9859645f..20dd41bb56c 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1725,7 +1725,6 @@ symbols! {
         rustc_partition_reused,
         rustc_pass_by_value,
         rustc_peek,
-        rustc_peek_definite_init,
         rustc_peek_liveness,
         rustc_peek_maybe_init,
         rustc_peek_maybe_uninit,