1 files changed, 51 insertions, 12 deletions

diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index 852935676..b1f91a056 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -7,6 +7,7 @@ use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::scc::Sccs;
 use rustc_errors::Diagnostic;
 use rustc_hir::def_id::CRATE_DEF_ID;
+use rustc_index::bit_set::SparseBitMatrix;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_infer::infer::outlives::test_type_match;
 use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound, VerifyIfEq};
@@ -21,17 +22,17 @@ use rustc_middle::traits::ObligationCauseCode;
 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_span::Span;
 
+use crate::constraints::graph::{self, NormalConstraintGraph, RegionGraph};
+use crate::dataflow::BorrowIndex;
 use crate::{
-    constraints::{
-        graph::NormalConstraintGraph, ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet,
-    },
+    constraints::{ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet},
     diagnostics::{RegionErrorKind, RegionErrors, UniverseInfo},
     member_constraints::{MemberConstraintSet, NllMemberConstraintIndex},
     nll::PoloniusOutput,
     region_infer::reverse_sccs::ReverseSccGraph,
     region_infer::values::{
-        LivenessValues, PlaceholderIndices, RegionElement, RegionValueElements, RegionValues,
-        ToElementIndex,
+        LivenessValues, PlaceholderIndices, PointIndex, RegionElement, RegionValueElements,
+        RegionValues, ToElementIndex,
     },
     type_check::{free_region_relations::UniversalRegionRelations, Locations},
     universal_regions::UniversalRegions,
@@ -119,6 +120,9 @@ pub struct RegionInferenceContext<'tcx> {
     /// Information about how the universally quantified regions in
     /// scope on this function relate to one another.
     universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
+
+    /// The set of loans that are live at a given point in the CFG, when using `-Zpolonius=next`.
+    live_loans: SparseBitMatrix<PointIndex, BorrowIndex>,
 }
 
 /// Each time that `apply_member_constraint` is successful, it appends
@@ -330,6 +334,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         type_tests: Vec<TypeTest<'tcx>>,
         liveness_constraints: LivenessValues<RegionVid>,
         elements: &Rc<RegionValueElements>,
+        live_loans: SparseBitMatrix<PointIndex, BorrowIndex>,
     ) -> Self {
         debug!("universal_regions: {:#?}", universal_regions);
         debug!("outlives constraints: {:#?}", outlives_constraints);
@@ -383,6 +388,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             type_tests,
             universal_regions,
             universal_region_relations,
+            live_loans,
         };
 
         result.init_free_and_bound_regions();
@@ -637,11 +643,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         self.scc_universes[scc]
     }
 
-    /// Once region solving has completed, this function will return
-    /// the member constraints that were applied to the value of a given
-    /// region `r`. See `AppliedMemberConstraint`.
-    pub(crate) fn applied_member_constraints(&self, r: RegionVid) -> &[AppliedMemberConstraint] {
-        let scc = self.constraint_sccs.scc(r);
+    /// Once region solving has completed, this function will return the member constraints that
+    /// were applied to the value of a given SCC `scc`. See `AppliedMemberConstraint`.
+    pub(crate) fn applied_member_constraints(
+        &self,
+        scc: ConstraintSccIndex,
+    ) -> &[AppliedMemberConstraint] {
         binary_search_util::binary_search_slice(
             &self.member_constraints_applied,
             |applied| applied.member_region_scc,
@@ -683,7 +690,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // In Polonius mode, the errors about missing universal region relations are in the output
         // and need to be emitted or propagated. Otherwise, we need to check whether the
         // constraints were too strong, and if so, emit or propagate those errors.
-        if infcx.tcx.sess.opts.unstable_opts.polonius {
+        if infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
             self.check_polonius_subset_errors(
                 outlives_requirements.as_mut(),
                 &mut errors_buffer,
@@ -1938,7 +1945,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // Member constraints can also give rise to `'r: 'x` edges that
             // were not part of the graph initially, so watch out for those.
             // (But they are extremely rare; this loop is very cold.)
-            for constraint in self.applied_member_constraints(r) {
+            for constraint in self.applied_member_constraints(self.constraint_sccs.scc(r)) {
                 let p_c = &self.member_constraints[constraint.member_constraint_index];
                 let constraint = OutlivesConstraint {
                     sup: r,
@@ -2279,6 +2286,38 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         }
         None
     }
+
+    /// Access to the SCC constraint graph.
+    pub(crate) fn constraint_sccs(&self) -> &Sccs<RegionVid, ConstraintSccIndex> {
+        self.constraint_sccs.as_ref()
+    }
+
+    /// Access to the region graph, built from the outlives constraints.
+    pub(crate) fn region_graph(&self) -> RegionGraph<'_, 'tcx, graph::Normal> {
+        self.constraint_graph.region_graph(&self.constraints, self.universal_regions.fr_static)
+    }
+
+    /// Returns whether the given region is considered live at all points: whether it is a
+    /// placeholder or a free region.
+    pub(crate) fn is_region_live_at_all_points(&self, region: RegionVid) -> bool {
+        // FIXME: there must be a cleaner way to find this information. At least, when
+        // higher-ranked subtyping is abstracted away from the borrowck main path, we'll only
+        // need to check whether this is a universal region.
+        let origin = self.region_definition(region).origin;
+        let live_at_all_points = matches!(
+            origin,
+            NllRegionVariableOrigin::Placeholder(_) | NllRegionVariableOrigin::FreeRegion
+        );
+        live_at_all_points
+    }
+
+    /// Returns whether the `loan_idx` is live at the given `location`: whether its issuing
+    /// region is contained within the type of a variable that is live at this point.
+    /// Note: for now, the sets of live loans is only available when using `-Zpolonius=next`.
+    pub(crate) fn is_loan_live_at(&self, loan_idx: BorrowIndex, location: Location) -> bool {
+        let point = self.liveness_constraints.point_from_location(location);
+        self.live_loans.contains(point, loan_idx)
+    }
 }
 
 impl<'tcx> RegionDefinition<'tcx> {