Create Horatio: A faster implementation of Polonius.

Author: Tage Johansson

compiler/rustc_borrowck/src/borrow_set.rs

@@ -1,3 +1,4 @@
+use std::cell::OnceCell;
 use std::fmt;
 use std::ops::Index;
 
@@ -84,6 +85,7 @@ pub struct BorrowData<'tcx> {
     pub(crate) borrowed_place: mir::Place<'tcx>,
     /// Place to which the borrow was stored
     pub(crate) assigned_place: mir::Place<'tcx>,
+    pub(crate) dependent_regions: OnceCell<DenseBitSet<RegionVid>>,
 }
 
 // These methods are public to support borrowck consumers.
@@ -261,6 +263,7 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
                 activation_location: TwoPhaseActivation::NotTwoPhase,
                 borrowed_place,
                 assigned_place: *assigned_place,
+                dependent_regions: OnceCell::new(),
             };
             let (idx, _) = self.location_map.insert_full(location, borrow);
             let idx = BorrowIndex::from(idx);

compiler/rustc_borrowck/src/dataflow.rs

@@ -301,6 +301,7 @@ struct PoloniusOutOfScopePrecomputer<'a, 'tcx> {
     loans_out_of_scope_at_location: FxIndexMap<Location, Vec<BorrowIndex>>,
 }
 
+#[expect(dead_code)]
 impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
     fn compute(
         body: &Body<'tcx>,
@@ -476,11 +477,18 @@ impl<'a, 'tcx> Borrows<'a, 'tcx> {
             if !tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
                 calculate_borrows_out_of_scope_at_location(body, regioncx, borrow_set)
             } else {
-                PoloniusOutOfScopePrecomputer::compute(body, regioncx, borrow_set)
+                unimplemented!() // This should probably be removed.
             };
         Borrows { tcx, body, borrow_set, borrows_out_of_scope_at_location }
     }
 
+    /// A dummy `Borrows` with no useful information.
+    ///
+    /// Used for Polonius which doesn't need this.
+    pub fn dummy(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, borrow_set: &'a BorrowSet<'tcx>) -> Self {
+        Borrows { tcx, body, borrow_set, borrows_out_of_scope_at_location: Default::default() }
+    }
+
     /// Add all borrows to the kill set, if those borrows are out of scope at `location`.
     /// That means they went out of a nonlexical scope
     fn kill_loans_out_of_scope_at_location(
@@ -563,6 +571,10 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
     const NAME: &'static str = "borrows";
 
     fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
+        if !self.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
+            return DenseBitSet::new_empty(0);
+        }
+
         // bottom = nothing is reserved or activated yet;
         DenseBitSet::new_empty(self.borrow_set.len())
     }
@@ -578,6 +590,10 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
         _statement: &mir::Statement<'tcx>,
         location: Location,
     ) {
+        if !self.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
+            return;
+        }
+
         self.kill_loans_out_of_scope_at_location(state, location);
     }
 
@@ -587,6 +603,10 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
         stmt: &mir::Statement<'tcx>,
         location: Location,
     ) {
+        if !self.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
+            return;
+        }
+
         match &stmt.kind {
             mir::StatementKind::Assign(box (lhs, rhs)) => {
                 if let mir::Rvalue::Ref(_, _, place) = rhs {
@@ -636,6 +656,10 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
         _terminator: &mir::Terminator<'tcx>,
         location: Location,
     ) {
+        if !self.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
+            return;
+        }
+
         self.kill_loans_out_of_scope_at_location(state, location);
     }
 
@@ -645,6 +669,10 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
         terminator: &'mir mir::Terminator<'tcx>,
         _location: Location,
     ) -> TerminatorEdges<'mir, 'tcx> {
+        if !self.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
+            return terminator.edges();
+        }
+
         if let mir::TerminatorKind::InlineAsm { operands, .. } = &terminator.kind {
             for op in operands {
                 if let mir::InlineAsmOperand::Out { place: Some(place), .. }

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -632,8 +632,8 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
         // We want to focus on relevant live locals in diagnostics, so when polonius is enabled, we
         // ensure that we don't emit live boring locals as explanations.
         let is_local_boring = |local| {
-            if let Some(polonius_diagnostics) = self.polonius_diagnostics {
-                polonius_diagnostics.boring_nll_locals.contains(&local)
+            if let Some(polonius) = &self.polonius {
+                polonius.pcx.is_boring_local(local)
             } else {
                 assert!(!tcx.sess.opts.unstable_opts.polonius.is_next_enabled());