Add MeetSemiLattice

The upstream version is removed, so we have to vendor the trait in.

src/lattice.rs

@@ -0,0 +1,20 @@
+// Copyright Gary Guo.
+//
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+/// 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;
+}

src/main.rs

@@ -49,6 +49,7 @@ mod ctxt;
 mod atomic_context;
 mod attribute;
 mod infallible_allocation;
+mod lattice;
 mod mir;
 mod monomorphize_collector;
 mod preempt_count;

src/preempt_count/expectation.rs

@@ -9,14 +9,14 @@ use rustc_middle::mir::{self, Body, TerminatorKind};
 use rustc_middle::ty::{
     self, GenericArgs, Instance, PseudoCanonicalInput, Ty, TypingEnv, TypingMode,
 };
-use rustc_mir_dataflow::lattice::MeetSemiLattice;
 use rustc_mir_dataflow::Analysis;
 use rustc_span::DUMMY_SP;
 use rustc_trait_selection::infer::TyCtxtInferExt;
 
 use super::dataflow::AdjustmentComputation;
 use super::{AdjustmentBounds, Error, ExpectationRange, PolyDisplay, UseSite, UseSiteKind};
 use crate::ctxt::AnalysisCtxt;
+use crate::lattice::MeetSemiLattice;
 
 impl<'tcx> AnalysisCtxt<'tcx> {
     pub fn terminator_expectation(

src/preempt_count/mod.rs

@@ -10,10 +10,10 @@ pub mod expectation;
 
 use rustc_errors::ErrorGuaranteed;
 use rustc_middle::ty::{Instance, PseudoCanonicalInput};
-use rustc_mir_dataflow::lattice::MeetSemiLattice;
 use rustc_span::Span;
 
 use self::dataflow::AdjustmentBounds;
+use crate::lattice::MeetSemiLattice;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Encodable, Decodable)]
 pub enum Error {