Merging upstream version 1.73.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 778 insertions, 0 deletions

diff --git a/compiler/rustc_mir_dataflow/src/impls/initialized.rs b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
new file mode 100644
index 000000000..e6d383d62
--- /dev/null
+++ b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
@@ -0,0 +1,778 @@
+use rustc_index::bit_set::{BitSet, ChunkedBitSet};
+use rustc_index::Idx;
+use rustc_middle::mir::{self, Body, CallReturnPlaces, Location, TerminatorEdges};
+use rustc_middle::ty::{self, TyCtxt};
+
+use crate::drop_flag_effects_for_function_entry;
+use crate::drop_flag_effects_for_location;
+use crate::elaborate_drops::DropFlagState;
+use crate::framework::SwitchIntEdgeEffects;
+use crate::move_paths::{HasMoveData, InitIndex, InitKind, LookupResult, MoveData, MovePathIndex};
+use crate::on_lookup_result_bits;
+use crate::MoveDataParamEnv;
+use crate::{drop_flag_effects, on_all_children_bits, on_all_drop_children_bits};
+use crate::{lattice, AnalysisDomain, GenKill, GenKillAnalysis, MaybeReachable};
+
+/// `MaybeInitializedPlaces` tracks all places that might be
+/// 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) {                        // maybe-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}
+///
+///     }                                       // {a, b,    d}
+///
+///     c = S;                                  // {a, b, c, d}
+/// }
+/// ```
+///
+/// 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.
+///
+/// Similarly, at a given `drop` statement, the set-intersection
+/// between this data and `MaybeUninitializedPlaces` yields the set of
+/// places that would require a dynamic drop-flag at that statement.
+pub struct MaybeInitializedPlaces<'a, 'tcx> {
+    tcx: TyCtxt<'tcx>,
+    body: &'a Body<'tcx>,
+    mdpe: &'a MoveDataParamEnv<'tcx>,
+    skip_unreachable_unwind: bool,
+}
+
+impl<'a, 'tcx> MaybeInitializedPlaces<'a, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, mdpe: &'a MoveDataParamEnv<'tcx>) -> Self {
+        MaybeInitializedPlaces { tcx, body, mdpe, skip_unreachable_unwind: false }
+    }
+
+    pub fn skipping_unreachable_unwind(mut self) -> Self {
+        self.skip_unreachable_unwind = true;
+        self
+    }
+
+    pub fn is_unwind_dead(
+        &self,
+        place: mir::Place<'tcx>,
+        state: &MaybeReachable<ChunkedBitSet<MovePathIndex>>,
+    ) -> bool {
+        if let LookupResult::Exact(path) = self.move_data().rev_lookup.find(place.as_ref()) {
+            let mut maybe_live = false;
+            on_all_drop_children_bits(self.tcx, self.body, self.mdpe, path, |child| {
+                maybe_live |= state.contains(child);
+            });
+            !maybe_live
+        } else {
+            false
+        }
+    }
+}
+
+impl<'a, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'a, 'tcx> {
+    fn move_data(&self) -> &MoveData<'tcx> {
+        &self.mdpe.move_data
+    }
+}
+
+/// `MaybeUninitializedPlaces` tracks all places that might be
+/// uninitialized 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) {                        // maybe-uninit:
+///                                             // {a, b, c, d}
+///     let a = S; let mut b = S; let c; let d; // {      c, d}
+///
+///     if pred {
+///         drop(a);                            // {a,    c, d}
+///         b = S;                              // {a,    c, d}
+///
+///     } else {
+///         drop(b);                            // {   b, c, d}
+///         d = S;                              // {   b, c   }
+///
+///     }                                       // {a, b, c, d}
+///
+///     c = S;                                  // {a, b,    d}
+/// }
+/// ```
+///
+/// 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.
+///
+/// Similarly, at a given `drop` statement, the set-intersection
+/// between this data and `MaybeInitializedPlaces` yields the set of
+/// places that would require a dynamic drop-flag at that statement.
+pub struct MaybeUninitializedPlaces<'a, 'tcx> {
+    tcx: TyCtxt<'tcx>,
+    body: &'a Body<'tcx>,
+    mdpe: &'a MoveDataParamEnv<'tcx>,
+
+    mark_inactive_variants_as_uninit: bool,
+    skip_unreachable_unwind: BitSet<mir::BasicBlock>,
+}
+
+impl<'a, 'tcx> MaybeUninitializedPlaces<'a, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, mdpe: &'a MoveDataParamEnv<'tcx>) -> Self {
+        MaybeUninitializedPlaces {
+            tcx,
+            body,
+            mdpe,
+            mark_inactive_variants_as_uninit: false,
+            skip_unreachable_unwind: BitSet::new_empty(body.basic_blocks.len()),
+        }
+    }
+
+    /// Causes inactive enum variants to be marked as "maybe uninitialized" after a switch on an
+    /// enum discriminant.
+    ///
+    /// This is correct in a vacuum but is not the default because it causes problems in the borrow
+    /// checker, where this information gets propagated along `FakeEdge`s.
+    pub fn mark_inactive_variants_as_uninit(mut self) -> Self {
+        self.mark_inactive_variants_as_uninit = true;
+        self
+    }
+
+    pub fn skipping_unreachable_unwind(
+        mut self,
+        unreachable_unwind: BitSet<mir::BasicBlock>,
+    ) -> Self {
+        self.skip_unreachable_unwind = unreachable_unwind;
+        self
+    }
+}
+
+impl<'a, 'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'a, 'tcx> {
+    fn move_data(&self) -> &MoveData<'tcx> {
+        &self.mdpe.move_data
+    }
+}
+
+/// `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> {
+    tcx: TyCtxt<'tcx>,
+    body: &'a Body<'tcx>,
+    mdpe: &'a MoveDataParamEnv<'tcx>,
+}
+
+impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, mdpe: &'a MoveDataParamEnv<'tcx>) -> Self {
+        DefinitelyInitializedPlaces { tcx, body, mdpe }
+    }
+}
+
+impl<'a, 'tcx> HasMoveData<'tcx> for DefinitelyInitializedPlaces<'a, 'tcx> {
+    fn move_data(&self) -> &MoveData<'tcx> {
+        &self.mdpe.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`.
+///
+/// This dataflow is used to determine if an immutable local variable may
+/// be assigned to.
+///
+/// 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) {                        // ever-init:
+///                                             // {          }
+///     let a = S; let mut b = S; let c; let d; // {a, b      }
+///
+///     if pred {
+///         drop(a);                            // {a, b,     }
+///         b = S;                              // {a, b,     }
+///
+///     } else {
+///         drop(b);                            // {a, b,      }
+///         d = S;                              // {a, b,    d }
+///
+///     }                                       // {a, b,    d }
+///
+///     c = S;                                  // {a, b, c, d }
+/// }
+/// ```
+pub struct EverInitializedPlaces<'a, 'tcx> {
+    #[allow(dead_code)]
+    tcx: TyCtxt<'tcx>,
+    body: &'a Body<'tcx>,
+    mdpe: &'a MoveDataParamEnv<'tcx>,
+}
+
+impl<'a, 'tcx> EverInitializedPlaces<'a, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, mdpe: &'a MoveDataParamEnv<'tcx>) -> Self {
+        EverInitializedPlaces { tcx, body, mdpe }
+    }
+}
+
+impl<'a, 'tcx> HasMoveData<'tcx> for EverInitializedPlaces<'a, 'tcx> {
+    fn move_data(&self) -> &MoveData<'tcx> {
+        &self.mdpe.move_data
+    }
+}
+
+impl<'a, 'tcx> MaybeInitializedPlaces<'a, 'tcx> {
+    fn update_bits(
+        trans: &mut impl GenKill<MovePathIndex>,
+        path: MovePathIndex,
+        state: DropFlagState,
+    ) {
+        match state {
+            DropFlagState::Absent => trans.kill(path),
+            DropFlagState::Present => trans.gen(path),
+        }
+    }
+}
+
+impl<'a, 'tcx> MaybeUninitializedPlaces<'a, 'tcx> {
+    fn update_bits(
+        trans: &mut impl GenKill<MovePathIndex>,
+        path: MovePathIndex,
+        state: DropFlagState,
+    ) {
+        match state {
+            DropFlagState::Absent => trans.gen(path),
+            DropFlagState::Present => trans.kill(path),
+        }
+    }
+}
+
+impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
+    fn update_bits(
+        trans: &mut impl GenKill<MovePathIndex>,
+        path: MovePathIndex,
+        state: DropFlagState,
+    ) {
+        match state {
+            DropFlagState::Absent => trans.kill(path),
+            DropFlagState::Present => trans.gen(path),
+        }
+    }
+}
+
+impl<'tcx> AnalysisDomain<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
+    type Domain = MaybeReachable<ChunkedBitSet<MovePathIndex>>;
+    const NAME: &'static str = "maybe_init";
+
+    fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
+        // bottom = uninitialized
+        MaybeReachable::Unreachable
+    }
+
+    fn initialize_start_block(&self, _: &mir::Body<'tcx>, state: &mut Self::Domain) {
+        *state =
+            MaybeReachable::Reachable(ChunkedBitSet::new_empty(self.move_data().move_paths.len()));
+        drop_flag_effects_for_function_entry(self.tcx, self.body, self.mdpe, |path, s| {
+            assert!(s == DropFlagState::Present);
+            state.gen(path);
+        });
+    }
+}
+
+impl<'tcx> GenKillAnalysis<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
+    type Idx = MovePathIndex;
+
+    fn domain_size(&self, _: &Body<'tcx>) -> usize {
+        self.move_data().move_paths.len()
+    }
+
+    fn statement_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        statement: &mir::Statement<'tcx>,
+        location: Location,
+    ) {
+        drop_flag_effects_for_location(self.tcx, self.body, self.mdpe, location, |path, s| {
+            Self::update_bits(trans, path, s)
+        });
+
+        // Mark all places as "maybe init" if they are mutably borrowed. See #90752.
+        if self.tcx.sess.opts.unstable_opts.precise_enum_drop_elaboration
+            && let Some((_, rvalue)) = statement.kind.as_assign()
+            && let mir::Rvalue::Ref(_, mir::BorrowKind::Mut { .. }, place)
+                // FIXME: Does `&raw const foo` allow mutation? See #90413.
+                | mir::Rvalue::AddressOf(_, place) = rvalue
+            && let LookupResult::Exact(mpi) = self.move_data().rev_lookup.find(place.as_ref())
+        {
+            on_all_children_bits(self.tcx, self.body, self.move_data(), mpi, |child| {
+                trans.gen(child);
+            })
+        }
+    }
+
+    fn terminator_effect<'mir>(
+        &mut self,
+        state: &mut Self::Domain,
+        terminator: &'mir mir::Terminator<'tcx>,
+        location: Location,
+    ) -> TerminatorEdges<'mir, 'tcx> {
+        let mut edges = terminator.edges();
+        if self.skip_unreachable_unwind
+            && let mir::TerminatorKind::Drop { target, unwind, place, replace: _ } = terminator.kind
+            && matches!(unwind, mir::UnwindAction::Cleanup(_))
+            && self.is_unwind_dead(place, state)
+        {
+            edges = TerminatorEdges::Single(target);
+        }
+        drop_flag_effects_for_location(self.tcx, self.body, self.mdpe, location, |path, s| {
+            Self::update_bits(state, path, s)
+        });
+        edges
+    }
+
+    fn call_return_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        _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.tcx,
+                self.body,
+                self.move_data(),
+                self.move_data().rev_lookup.find(place.as_ref()),
+                |mpi| {
+                    trans.gen(mpi);
+                },
+            );
+        });
+    }
+
+    fn switch_int_edge_effects<G: GenKill<Self::Idx>>(
+        &mut self,
+        block: mir::BasicBlock,
+        discr: &mir::Operand<'tcx>,
+        edge_effects: &mut impl SwitchIntEdgeEffects<G>,
+    ) {
+        if !self.tcx.sess.opts.unstable_opts.precise_enum_drop_elaboration {
+            return;
+        }
+
+        let enum_ = discr.place().and_then(|discr| {
+            switch_on_enum_discriminant(self.tcx, &self.body, &self.body[block], discr)
+        });
+
+        let Some((enum_place, enum_def)) = enum_ else {
+            return;
+        };
+
+        let mut discriminants = enum_def.discriminants(self.tcx);
+        edge_effects.apply(|trans, edge| {
+            let Some(value) = edge.value else {
+                return;
+            };
+
+            // MIR building adds discriminants to the `values` array in the same order as they
+            // are yielded by `AdtDef::discriminants`. We rely on this to match each
+            // discriminant in `values` to its corresponding variant in linear time.
+            let (variant, _) = discriminants
+                .find(|&(_, discr)| discr.val == value)
+                .expect("Order of `AdtDef::discriminants` differed from `SwitchInt::values`");
+
+            // Kill all move paths that correspond to variants we know to be inactive along this
+            // particular outgoing edge of a `SwitchInt`.
+            drop_flag_effects::on_all_inactive_variants(
+                self.tcx,
+                self.body,
+                self.move_data(),
+                enum_place,
+                variant,
+                |mpi| trans.kill(mpi),
+            );
+        });
+    }
+}
+
+impl<'tcx> AnalysisDomain<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
+    type Domain = ChunkedBitSet<MovePathIndex>;
+
+    const NAME: &'static str = "maybe_uninit";
+
+    fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
+        // bottom = initialized (start_block_effect counters this at outset)
+        ChunkedBitSet::new_empty(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) {
+        // set all bits to 1 (uninit) before gathering counter-evidence
+        state.insert_all();
+
+        drop_flag_effects_for_function_entry(self.tcx, self.body, self.mdpe, |path, s| {
+            assert!(s == DropFlagState::Present);
+            state.remove(path);
+        });
+    }
+}
+
+impl<'tcx> GenKillAnalysis<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
+    type Idx = MovePathIndex;
+
+    fn domain_size(&self, _: &Body<'tcx>) -> usize {
+        self.move_data().move_paths.len()
+    }
+
+    fn statement_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        _statement: &mir::Statement<'tcx>,
+        location: Location,
+    ) {
+        drop_flag_effects_for_location(self.tcx, self.body, self.mdpe, location, |path, s| {
+            Self::update_bits(trans, path, s)
+        });
+
+        // Unlike in `MaybeInitializedPlaces` above, we don't need to change the state when a
+        // mutable borrow occurs. Places cannot become uninitialized through a mutable reference.
+    }
+
+    fn 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.tcx, self.body, self.mdpe, location, |path, s| {
+            Self::update_bits(trans, path, s)
+        });
+        if self.skip_unreachable_unwind.contains(location.block) {
+            let mir::TerminatorKind::Drop { target, unwind, .. } = terminator.kind else { bug!() };
+            assert!(matches!(unwind, mir::UnwindAction::Cleanup(_)));
+            TerminatorEdges::Single(target)
+        } else {
+            terminator.edges()
+        }
+    }
+
+    fn call_return_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        _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 0 (initialized).
+            on_lookup_result_bits(
+                self.tcx,
+                self.body,
+                self.move_data(),
+                self.move_data().rev_lookup.find(place.as_ref()),
+                |mpi| {
+                    trans.kill(mpi);
+                },
+            );
+        });
+    }
+
+    fn switch_int_edge_effects<G: GenKill<Self::Idx>>(
+        &mut self,
+        block: mir::BasicBlock,
+        discr: &mir::Operand<'tcx>,
+        edge_effects: &mut impl SwitchIntEdgeEffects<G>,
+    ) {
+        if !self.tcx.sess.opts.unstable_opts.precise_enum_drop_elaboration {
+            return;
+        }
+
+        if !self.mark_inactive_variants_as_uninit {
+            return;
+        }
+
+        let enum_ = discr.place().and_then(|discr| {
+            switch_on_enum_discriminant(self.tcx, &self.body, &self.body[block], discr)
+        });
+
+        let Some((enum_place, enum_def)) = enum_ else {
+            return;
+        };
+
+        let mut discriminants = enum_def.discriminants(self.tcx);
+        edge_effects.apply(|trans, edge| {
+            let Some(value) = edge.value else {
+                return;
+            };
+
+            // MIR building adds discriminants to the `values` array in the same order as they
+            // are yielded by `AdtDef::discriminants`. We rely on this to match each
+            // discriminant in `values` to its corresponding variant in linear time.
+            let (variant, _) = discriminants
+                .find(|&(_, discr)| discr.val == value)
+                .expect("Order of `AdtDef::discriminants` differed from `SwitchInt::values`");
+
+            // Mark all move paths that correspond to variants other than this one as maybe
+            // uninitialized (in reality, they are *definitely* uninitialized).
+            drop_flag_effects::on_all_inactive_variants(
+                self.tcx,
+                self.body,
+                self.move_data(),
+                enum_place,
+                variant,
+                |mpi| trans.gen(mpi),
+            );
+        });
+    }
+}
+
+impl<'a, 'tcx> AnalysisDomain<'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.tcx, self.body, self.mdpe, |path, s| {
+            assert!(s == DropFlagState::Present);
+            state.0.insert(path);
+        });
+    }
+}
+
+impl<'tcx> GenKillAnalysis<'tcx> for DefinitelyInitializedPlaces<'_, 'tcx> {
+    type Idx = MovePathIndex;
+
+    fn domain_size(&self, _: &Body<'tcx>) -> usize {
+        self.move_data().move_paths.len()
+    }
+
+    fn statement_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        _statement: &mir::Statement<'tcx>,
+        location: Location,
+    ) {
+        drop_flag_effects_for_location(self.tcx, self.body, self.mdpe, location, |path, s| {
+            Self::update_bits(trans, path, s)
+        })
+    }
+
+    fn 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.tcx, self.body, self.mdpe, location, |path, s| {
+            Self::update_bits(trans, path, s)
+        });
+        terminator.edges()
+    }
+
+    fn call_return_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        _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.tcx,
+                self.body,
+                self.move_data(),
+                self.move_data().rev_lookup.find(place.as_ref()),
+                |mpi| {
+                    trans.gen(mpi);
+                },
+            );
+        });
+    }
+}
+
+impl<'tcx> AnalysisDomain<'tcx> for EverInitializedPlaces<'_, 'tcx> {
+    type Domain = ChunkedBitSet<InitIndex>;
+
+    const NAME: &'static str = "ever_init";
+
+    fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
+        // bottom = no initialized variables by default
+        ChunkedBitSet::new_empty(self.move_data().inits.len())
+    }
+
+    fn initialize_start_block(&self, body: &mir::Body<'tcx>, state: &mut Self::Domain) {
+        for arg_init in 0..body.arg_count {
+            state.insert(InitIndex::new(arg_init));
+        }
+    }
+}
+
+impl<'tcx> GenKillAnalysis<'tcx> for EverInitializedPlaces<'_, 'tcx> {
+    type Idx = InitIndex;
+
+    fn domain_size(&self, _: &Body<'tcx>) -> usize {
+        self.move_data().inits.len()
+    }
+
+    #[instrument(skip(self, trans), level = "debug")]
+    fn statement_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        stmt: &mir::Statement<'tcx>,
+        location: Location,
+    ) {
+        let move_data = self.move_data();
+        let init_path_map = &move_data.init_path_map;
+        let init_loc_map = &move_data.init_loc_map;
+        let rev_lookup = &move_data.rev_lookup;
+
+        debug!("initializes move_indexes {:?}", &init_loc_map[location]);
+        trans.gen_all(init_loc_map[location].iter().copied());
+
+        if let mir::StatementKind::StorageDead(local) = stmt.kind {
+            // End inits for StorageDead, so that an immutable variable can
+            // be reinitialized on the next iteration of the loop.
+            let move_path_index = rev_lookup.find_local(local);
+            debug!("clears the ever initialized status of {:?}", init_path_map[move_path_index]);
+            trans.kill_all(init_path_map[move_path_index].iter().copied());
+        }
+    }
+
+    #[instrument(skip(self, trans, terminator), level = "debug")]
+    fn terminator_effect<'mir>(
+        &mut self,
+        trans: &mut Self::Domain,
+        terminator: &'mir mir::Terminator<'tcx>,
+        location: Location,
+    ) -> TerminatorEdges<'mir, 'tcx> {
+        let (body, move_data) = (self.body, self.move_data());
+        let term = body[location.block].terminator();
+        let init_loc_map = &move_data.init_loc_map;
+        debug!(?term);
+        debug!("initializes move_indexes {:?}", init_loc_map[location]);
+        trans.gen_all(
+            init_loc_map[location]
+                .iter()
+                .filter(|init_index| {
+                    move_data.inits[**init_index].kind != InitKind::NonPanicPathOnly
+                })
+                .copied(),
+        );
+        terminator.edges()
+    }
+
+    fn call_return_effect(
+        &mut self,
+        trans: &mut impl GenKill<Self::Idx>,
+        block: mir::BasicBlock,
+        _return_places: CallReturnPlaces<'_, 'tcx>,
+    ) {
+        let move_data = self.move_data();
+        let init_loc_map = &move_data.init_loc_map;
+
+        let call_loc = self.body.terminator_loc(block);
+        for init_index in &init_loc_map[call_loc] {
+            trans.gen(*init_index);
+        }
+    }
+}
+
+/// Inspect a `SwitchInt`-terminated basic block to see if the condition of that `SwitchInt` is
+/// an enum discriminant.
+///
+/// We expect such blocks to have a call to `discriminant` as their last statement like so:
+///
+/// ```text
+/// ...
+/// _42 = discriminant(_1)
+/// SwitchInt(_42, ..)
+/// ```
+///
+/// If the basic block matches this pattern, this function returns the place corresponding to the
+/// enum (`_1` in the example above) as well as the `AdtDef` of that enum.
+fn switch_on_enum_discriminant<'mir, 'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &'mir mir::Body<'tcx>,
+    block: &'mir mir::BasicBlockData<'tcx>,
+    switch_on: mir::Place<'tcx>,
+) -> Option<(mir::Place<'tcx>, ty::AdtDef<'tcx>)> {
+    for statement in block.statements.iter().rev() {
+        match &statement.kind {
+            mir::StatementKind::Assign(box (lhs, mir::Rvalue::Discriminant(discriminated)))
+                if *lhs == switch_on =>
+            {
+                match discriminated.ty(body, tcx).ty.kind() {
+                    ty::Adt(def, _) => return Some((*discriminated, *def)),
+
+                    // `Rvalue::Discriminant` is also used to get the active yield point for a
+                    // generator, but we do not need edge-specific effects in that case. This may
+                    // change in the future.
+                    ty::Generator(..) => return None,
+
+                    t => bug!("`discriminant` called on unexpected type {:?}", t),
+                }
+            }
+            mir::StatementKind::Coverage(_) => continue,
+            _ => return None,
+        }
+    }
+    None
+}