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.

1 files changed, 2 insertions, 106 deletions

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;