Partially revert #9701

clippy_lints/src/dereference.rs

@@ -1282,10 +1282,10 @@ fn referent_used_exactly_once<'tcx>(
             possible_borrowers.push((body_owner_local_def_id, PossibleBorrowerMap::new(cx, mir)));
         }
         let possible_borrower = &mut possible_borrowers.last_mut().unwrap().1;
-        // If `place.local` were not included here, the `copyable_iterator::warn` test would fail. The
-        // reason is that `PossibleBorrowerVisitor::visit_terminator` considers `place.local` a possible
-        // borrower of itself. See the comment in that method for an explanation as to why.
-        possible_borrower.at_most_borrowers(cx, &[local, place.local], place.local, location)
+        // If `only_borrowers` were used here, the `copyable_iterator::warn` test would fail. The reason is
+        // that `PossibleBorrowerVisitor::visit_terminator` considers `place.local` a possible borrower of
+        // itself. See the comment in that method for an explanation as to why.
+        possible_borrower.bounded_borrowers(&[local], &[local, place.local], place.local, location)
             && used_exactly_once(mir, place.local).unwrap_or(false)
     } else {
         false

clippy_lints/src/redundant_clone.rs

@@ -131,7 +131,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
                 // `res = clone(arg)` can be turned into `res = move arg;`
                 // if `arg` is the only borrow of `cloned` at this point.
 
-                if cannot_move_out || !possible_borrower.at_most_borrowers(cx, &[arg], cloned, loc) {
+                if cannot_move_out || !possible_borrower.only_borrowers(&[arg], cloned, loc) {
                     continue;
                 }
 
@@ -178,7 +178,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
                 // StorageDead(pred_arg);
                 // res = to_path_buf(cloned);
                 // ```
-                if cannot_move_out || !possible_borrower.at_most_borrowers(cx, &[arg, cloned], local, loc) {
+                if cannot_move_out || !possible_borrower.only_borrowers(&[arg, cloned], local, loc) {
                     continue;
                 }
 

clippy_utils/src/mir/possible_borrower.rs

@@ -1,137 +1,90 @@
-use super::possible_origin::PossibleOriginVisitor;
+use super::{possible_origin::PossibleOriginVisitor, transitive_relation::TransitiveRelation};
 use crate::ty::is_copy;
-use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
+use rustc_data_structures::fx::FxHashMap;
 use rustc_index::bit_set::{BitSet, HybridBitSet};
 use rustc_lint::LateContext;
-use rustc_middle::mir::{
-    self, visit::Visitor as _, BasicBlock, Local, Location, Mutability, Statement, StatementKind, Terminator,
-};
-use rustc_middle::ty::{self, visit::TypeVisitor, TyCtxt};
-use rustc_mir_dataflow::{
-    fmt::DebugWithContext, impls::MaybeStorageLive, lattice::JoinSemiLattice, Analysis, AnalysisDomain,
-    CallReturnPlaces, ResultsCursor,
-};
+use rustc_middle::mir::{self, visit::Visitor as _, Mutability};
+use rustc_middle::ty::{self, visit::TypeVisitor};
+use rustc_mir_dataflow::{impls::MaybeStorageLive, Analysis, ResultsCursor};
 use std::borrow::Cow;
 use std::ops::ControlFlow;
 
 /// Collects the possible borrowers of each local.
 /// For example, `b = &a; c = &a;` will make `b` and (transitively) `c`
 /// possible borrowers of `a`.
 #[allow(clippy::module_name_repetitions)]
-struct PossibleBorrowerAnalysis<'b, 'tcx> {
-    tcx: TyCtxt<'tcx>,
+struct PossibleBorrowerVisitor<'a, 'b, 'tcx> {
+    possible_borrower: TransitiveRelation,
     body: &'b mir::Body<'tcx>,
+    cx: &'a LateContext<'tcx>,
     possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-struct PossibleBorrowerState {
-    map: FxIndexMap<Local, BitSet<Local>>,
-    domain_size: usize,
-}
-
-impl PossibleBorrowerState {
-    fn new(domain_size: usize) -> Self {
+impl<'a, 'b, 'tcx> PossibleBorrowerVisitor<'a, 'b, 'tcx> {
+    fn new(
+        cx: &'a LateContext<'tcx>,
+        body: &'b mir::Body<'tcx>,
+        possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
+    ) -> Self {
         Self {
-            map: FxIndexMap::default(),
-            domain_size,
+            possible_borrower: TransitiveRelation::default(),
+            cx,
+            body,
+            possible_origin,
         }
     }
 
-    #[allow(clippy::similar_names)]
-    fn add(&mut self, borrowed: Local, borrower: Local) {
-        self.map
-            .entry(borrowed)
-            .or_insert(BitSet::new_empty(self.domain_size))
-            .insert(borrower);
-    }
-}
-
-impl<C> DebugWithContext<C> for PossibleBorrowerState {
-    fn fmt_with(&self, _ctxt: &C, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        <_ as std::fmt::Debug>::fmt(self, f)
-    }
-    fn fmt_diff_with(&self, _old: &Self, _ctxt: &C, _f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        unimplemented!()
-    }
-}
+    fn into_map(
+        self,
+        cx: &'a LateContext<'tcx>,
+        maybe_live: ResultsCursor<'b, 'tcx, MaybeStorageLive<'tcx>>,
+    ) -> PossibleBorrowerMap<'b, 'tcx> {
+        let mut map = FxHashMap::default();
+        for row in (1..self.body.local_decls.len()).map(mir::Local::from_usize) {
+            if is_copy(cx, self.body.local_decls[row].ty) {
+                continue;
+            }
 
-impl JoinSemiLattice for PossibleBorrowerState {
-    fn join(&mut self, other: &Self) -> bool {
-        let mut changed = false;
-        for (&borrowed, borrowers) in other.map.iter() {
+            let mut borrowers = self.possible_borrower.reachable_from(row, self.body.local_decls.len());
+            borrowers.remove(mir::Local::from_usize(0));
             if !borrowers.is_empty() {
-                changed |= self
-                    .map
-                    .entry(borrowed)
-                    .or_insert(BitSet::new_empty(self.domain_size))
-                    .union(borrowers);
+                map.insert(row, borrowers);
             }
         }
-        changed
-    }
-}
-
-impl<'b, 'tcx> AnalysisDomain<'tcx> for PossibleBorrowerAnalysis<'b, 'tcx> {
-    type Domain = PossibleBorrowerState;
-
-    const NAME: &'static str = "possible_borrower";
-
-    fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
-        PossibleBorrowerState::new(body.local_decls.len())
-    }
-
-    fn initialize_start_block(&self, _body: &mir::Body<'tcx>, _entry_set: &mut Self::Domain) {}
-}
 
-impl<'b, 'tcx> PossibleBorrowerAnalysis<'b, 'tcx> {
-    fn new(
-        tcx: TyCtxt<'tcx>,
-        body: &'b mir::Body<'tcx>,
-        possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
-    ) -> Self {
-        Self {
-            tcx,
-            body,
-            possible_origin,
+        let bs = BitSet::new_empty(self.body.local_decls.len());
+        PossibleBorrowerMap {
+            map,
+            maybe_live,
+            bitset: (bs.clone(), bs),
         }
     }
 }
 
-impl<'b, 'tcx> Analysis<'tcx> for PossibleBorrowerAnalysis<'b, 'tcx> {
-    fn apply_call_return_effect(
-        &self,
-        _state: &mut Self::Domain,
-        _block: BasicBlock,
-        _return_places: CallReturnPlaces<'_, 'tcx>,
-    ) {
-    }
-
-    fn apply_statement_effect(&self, state: &mut Self::Domain, statement: &Statement<'tcx>, _location: Location) {
-        if let StatementKind::Assign(box (place, rvalue)) = &statement.kind {
-            let lhs = place.local;
-            match rvalue {
-                mir::Rvalue::Ref(_, _, borrowed) => {
-                    state.add(borrowed.local, lhs);
-                },
-                other => {
-                    if ContainsRegion
-                        .visit_ty(place.ty(&self.body.local_decls, self.tcx).ty)
-                        .is_continue()
-                    {
-                        return;
+impl<'a, 'b, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'b, 'tcx> {
+    fn visit_assign(&mut self, place: &mir::Place<'tcx>, rvalue: &mir::Rvalue<'_>, _location: mir::Location) {
+        let lhs = place.local;
+        match rvalue {
+            mir::Rvalue::Ref(_, _, borrowed) => {
+                self.possible_borrower.add(borrowed.local, lhs);
+            },
+            other => {
+                if ContainsRegion
+                    .visit_ty(place.ty(&self.body.local_decls, self.cx.tcx).ty)
+                    .is_continue()
+                {
+                    return;
+                }
+                rvalue_locals(other, |rhs| {
+                    if lhs != rhs {
+                        self.possible_borrower.add(rhs, lhs);
                     }
-                    rvalue_locals(other, |rhs| {
-                        if lhs != rhs {
-                            state.add(rhs, lhs);
-                        }
-                    });
-                },
-            }
+                });
+            },
         }
     }
 
-    fn apply_terminator_effect(&self, state: &mut Self::Domain, terminator: &Terminator<'tcx>, _location: Location) {
+    fn visit_terminator(&mut self, terminator: &mir::Terminator<'_>, _loc: mir::Location) {
         if let mir::TerminatorKind::Call {
             args,
             destination: mir::Place { local: dest, .. },
@@ -171,10 +124,10 @@ impl<'b, 'tcx> Analysis<'tcx> for PossibleBorrowerAnalysis<'b, 'tcx> {
 
             for y in mutable_variables {
                 for x in &immutable_borrowers {
-                    state.add(*x, y);
+                    self.possible_borrower.add(*x, y);
                 }
                 for x in &mutable_borrowers {
-                    state.add(*x, y);
+                    self.possible_borrower.add(*x, y);
                 }
             }
         }
@@ -210,98 +163,73 @@ fn rvalue_locals(rvalue: &mir::Rvalue<'_>, mut visit: impl FnMut(mir::Local)) {
     }
 }
 
-/// Result of `PossibleBorrowerAnalysis`.
+/// Result of `PossibleBorrowerVisitor`.
 #[allow(clippy::module_name_repetitions)]
 pub struct PossibleBorrowerMap<'b, 'tcx> {
-    body: &'b mir::Body<'tcx>,
-    possible_borrower: ResultsCursor<'b, 'tcx, PossibleBorrowerAnalysis<'b, 'tcx>>,
-    maybe_live: ResultsCursor<'b, 'tcx, MaybeStorageLive<'b>>,
-    pushed: BitSet<Local>,
-    stack: Vec<Local>,
+    /// Mapping `Local -> its possible borrowers`
+    pub map: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
+    maybe_live: ResultsCursor<'b, 'tcx, MaybeStorageLive<'tcx>>,
+    // Caches to avoid allocation of `BitSet` on every query
+    pub bitset: (BitSet<mir::Local>, BitSet<mir::Local>),
 }
 
-impl<'b, 'tcx> PossibleBorrowerMap<'b, 'tcx> {
-    pub fn new(cx: &LateContext<'tcx>, mir: &'b mir::Body<'tcx>) -> Self {
+impl<'a, 'b, 'tcx> PossibleBorrowerMap<'b, 'tcx> {
+    pub fn new(cx: &'a LateContext<'tcx>, mir: &'b mir::Body<'tcx>) -> Self {
         let possible_origin = {
             let mut vis = PossibleOriginVisitor::new(mir);
             vis.visit_body(mir);
             vis.into_map(cx)
         };
-        let possible_borrower = PossibleBorrowerAnalysis::new(cx.tcx, mir, possible_origin)
+        let maybe_storage_live_result = MaybeStorageLive::new(Cow::Owned(BitSet::new_empty(mir.local_decls.len())))
             .into_engine(cx.tcx, mir)
-            .pass_name("possible_borrower")
+            .pass_name("redundant_clone")
             .iterate_to_fixpoint()
             .into_results_cursor(mir);
-        let maybe_live = MaybeStorageLive::new(Cow::Owned(BitSet::new_empty(mir.local_decls.len())))
-            .into_engine(cx.tcx, mir)
-            .pass_name("possible_borrower")
-            .iterate_to_fixpoint()
-            .into_results_cursor(mir);
-        PossibleBorrowerMap {
-            body: mir,
-            possible_borrower,
-            maybe_live,
-            pushed: BitSet::new_empty(mir.local_decls.len()),
-            stack: Vec::with_capacity(mir.local_decls.len()),
-        }
+        let mut vis = PossibleBorrowerVisitor::new(cx, mir, possible_origin);
+        vis.visit_body(mir);
+        vis.into_map(cx, maybe_storage_live_result)
     }
 
-    /// Returns true if the set of borrowers of `borrowed` living at `at` includes no more than
-    /// `borrowers`.
-    /// Notes:
-    /// 1. It would be nice if `PossibleBorrowerMap` could store `cx` so that `at_most_borrowers`
-    /// would not require it to be passed in. But a `PossibleBorrowerMap` is stored in `LintPass`
-    /// `Dereferencing`, which outlives any `LateContext`.
-    /// 2. In all current uses of `at_most_borrowers`, `borrowers` is a slice of at most two
-    /// elements. Thus, `borrowers.contains(...)` is effectively a constant-time operation. If
-    /// `at_most_borrowers`'s uses were to expand beyond this, its implementation might have to be
-    /// adjusted.
-    pub fn at_most_borrowers(
+    /// Returns true if the set of borrowers of `borrowed` living at `at` matches with `borrowers`.
+    pub fn only_borrowers(&mut self, borrowers: &[mir::Local], borrowed: mir::Local, at: mir::Location) -> bool {
+        self.bounded_borrowers(borrowers, borrowers, borrowed, at)
+    }
+
+    /// Returns true if the set of borrowers of `borrowed` living at `at` includes at least `below`
+    /// but no more than `above`.
+    pub fn bounded_borrowers(
         &mut self,
-        cx: &LateContext<'tcx>,
-        borrowers: &[mir::Local],
+        below: &[mir::Local],
+        above: &[mir::Local],
         borrowed: mir::Local,
         at: mir::Location,
     ) -> bool {
-        if is_copy(cx, self.body.local_decls[borrowed].ty) {
-            return true;
-        }
-
-        self.possible_borrower.seek_before_primary_effect(at);
-        self.maybe_live.seek_before_primary_effect(at);
-
-        let possible_borrower = &self.possible_borrower.get().map;
-        let maybe_live = &self.maybe_live;
-
-        self.pushed.clear();
-        self.stack.clear();
+        self.maybe_live.seek_after_primary_effect(at);
 
-        if let Some(borrowers) = possible_borrower.get(&borrowed) {
-            for b in borrowers.iter() {
-                if self.pushed.insert(b) {
-                    self.stack.push(b);
-                }
+        self.bitset.0.clear();
+        let maybe_live = &mut self.maybe_live;
+        if let Some(bitset) = self.map.get(&borrowed) {
+            for b in bitset.iter().filter(move |b| maybe_live.contains(*b)) {
+                self.bitset.0.insert(b);
             }
         } else {
-            // Nothing borrows `borrowed` at `at`.
-            return true;
+            return false;
         }
 
-        while let Some(borrower) = self.stack.pop() {
-            if maybe_live.contains(borrower) && !borrowers.contains(&borrower) {
-                return false;
-            }
+        self.bitset.1.clear();
+        for b in below {
+            self.bitset.1.insert(*b);
+        }
 
-            if let Some(borrowers) = possible_borrower.get(&borrower) {
-                for b in borrowers.iter() {
-                    if self.pushed.insert(b) {
-                        self.stack.push(b);
-                    }
-                }
-            }
+        if !self.bitset.0.superset(&self.bitset.1) {
+            return false;
+        }
+
+        for b in above {
+            self.bitset.0.remove(*b);
         }
 
-        true
+        self.bitset.0.is_empty()
     }
 
     pub fn local_is_alive_at(&mut self, local: mir::Local, at: mir::Location) -> bool {