extract polonius "constraint generation"

to help review, this duplicates the existing NLL + polonius constraint
generation component, before splitting them up to only do what they
individually need.

Author: lqd

compiler/rustc_borrowck/src/nll.rs

@@ -157,6 +157,14 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
         body,
         borrow_set,
     );
+    polonius::emit_cfg_and_loan_kills_facts(
+        infcx,
+        &mut liveness_constraints,
+        &mut all_facts,
+        location_table,
+        body,
+        borrow_set,
+    );
 
     let mut regioncx = RegionInferenceContext::new(
         infcx,

compiler/rustc_borrowck/src/polonius/constraint_generation.rs

@@ -0,0 +1,248 @@
+#![deny(rustc::untranslatable_diagnostic)]
+#![deny(rustc::diagnostic_outside_of_impl)]
+use rustc_infer::infer::InferCtxt;
+use rustc_middle::mir::visit::TyContext;
+use rustc_middle::mir::visit::Visitor;
+use rustc_middle::mir::{
+    Body, Local, Location, Place, PlaceRef, ProjectionElem, Rvalue, SourceInfo, Statement,
+    StatementKind, Terminator, TerminatorKind, UserTypeProjection,
+};
+use rustc_middle::ty::visit::TypeVisitable;
+use rustc_middle::ty::GenericArgsRef;
+use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt};
+
+use crate::{
+    borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, places_conflict,
+    region_infer::values::LivenessValues,
+};
+
+pub(super) fn generate_constraints<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    liveness_constraints: &mut LivenessValues<RegionVid>,
+    all_facts: &mut Option<AllFacts>,
+    location_table: &LocationTable,
+    body: &Body<'tcx>,
+    borrow_set: &BorrowSet<'tcx>,
+) {
+    let mut cg = ConstraintGeneration {
+        borrow_set,
+        infcx,
+        liveness_constraints,
+        location_table,
+        all_facts,
+        body,
+    };
+
+    for (bb, data) in body.basic_blocks.iter_enumerated() {
+        cg.visit_basic_block_data(bb, data);
+    }
+}
+
+/// 'cg = the duration of the constraint generation process itself.
+struct ConstraintGeneration<'cg, 'tcx> {
+    infcx: &'cg InferCtxt<'tcx>,
+    all_facts: &'cg mut Option<AllFacts>,
+    location_table: &'cg LocationTable,
+    liveness_constraints: &'cg mut LivenessValues<RegionVid>,
+    borrow_set: &'cg BorrowSet<'tcx>,
+    body: &'cg Body<'tcx>,
+}
+
+impl<'cg, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'tcx> {
+    /// We sometimes have `args` within an rvalue, or within a
+    /// call. Make them live at the location where they appear.
+    fn visit_args(&mut self, args: &GenericArgsRef<'tcx>, location: Location) {
+        self.add_regular_live_constraint(*args, location);
+        self.super_args(args);
+    }
+
+    /// We sometimes have `region` within an rvalue, or within a
+    /// call. Make them live at the location where they appear.
+    fn visit_region(&mut self, region: ty::Region<'tcx>, location: Location) {
+        self.add_regular_live_constraint(region, location);
+        self.super_region(region);
+    }
+
+    /// We sometimes have `ty` within an rvalue, or within a
+    /// call. Make them live at the location where they appear.
+    fn visit_ty(&mut self, ty: Ty<'tcx>, ty_context: TyContext) {
+        match ty_context {
+            TyContext::ReturnTy(SourceInfo { span, .. })
+            | TyContext::YieldTy(SourceInfo { span, .. })
+            | TyContext::UserTy(span)
+            | TyContext::LocalDecl { source_info: SourceInfo { span, .. }, .. } => {
+                span_bug!(span, "should not be visiting outside of the CFG: {:?}", ty_context);
+            }
+            TyContext::Location(location) => {
+                self.add_regular_live_constraint(ty, location);
+            }
+        }
+
+        self.super_ty(ty);
+    }
+
+    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
+        if let Some(all_facts) = self.all_facts {
+            let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
+            all_facts.cfg_edge.push((
+                self.location_table.start_index(location),
+                self.location_table.mid_index(location),
+            ));
+
+            all_facts.cfg_edge.push((
+                self.location_table.mid_index(location),
+                self.location_table.start_index(location.successor_within_block()),
+            ));
+
+            // If there are borrows on this now dead local, we need to record them as `killed`.
+            if let StatementKind::StorageDead(local) = statement.kind {
+                record_killed_borrows_for_local(
+                    all_facts,
+                    self.borrow_set,
+                    self.location_table,
+                    local,
+                    location,
+                );
+            }
+        }
+
+        self.super_statement(statement, location);
+    }
+
+    fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
+        // When we see `X = ...`, then kill borrows of
+        // `(*X).foo` and so forth.
+        self.record_killed_borrows_for_place(*place, location);
+
+        self.super_assign(place, rvalue, location);
+    }
+
+    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
+        if let Some(all_facts) = self.all_facts {
+            let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
+            all_facts.cfg_edge.push((
+                self.location_table.start_index(location),
+                self.location_table.mid_index(location),
+            ));
+
+            let successor_blocks = terminator.successors();
+            all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
+            for successor_block in successor_blocks {
+                all_facts.cfg_edge.push((
+                    self.location_table.mid_index(location),
+                    self.location_table.start_index(successor_block.start_location()),
+                ));
+            }
+        }
+
+        // A `Call` terminator's return value can be a local which has borrows,
+        // so we need to record those as `killed` as well.
+        if let TerminatorKind::Call { destination, .. } = terminator.kind {
+            self.record_killed_borrows_for_place(destination, location);
+        }
+
+        self.super_terminator(terminator, location);
+    }
+
+    fn visit_ascribe_user_ty(
+        &mut self,
+        _place: &Place<'tcx>,
+        _variance: ty::Variance,
+        _user_ty: &UserTypeProjection,
+        _location: Location,
+    ) {
+    }
+}
+
+impl<'cx, 'tcx> ConstraintGeneration<'cx, 'tcx> {
+    /// Some variable with type `live_ty` is "regular live" at
+    /// `location` -- i.e., it may be used later. This means that all
+    /// regions appearing in the type `live_ty` must be live at
+    /// `location`.
+    fn add_regular_live_constraint<T>(&mut self, live_ty: T, location: Location)
+    where
+        T: TypeVisitable<TyCtxt<'tcx>>,
+    {
+        debug!("add_regular_live_constraint(live_ty={:?}, location={:?})", live_ty, location);
+
+        self.infcx.tcx.for_each_free_region(&live_ty, |live_region| {
+            let vid = live_region.as_var();
+            self.liveness_constraints.add_element(vid, location);
+        });
+    }
+
+    /// When recording facts for Polonius, records the borrows on the specified place
+    /// as `killed`. For example, when assigning to a local, or on a call's return destination.
+    fn record_killed_borrows_for_place(&mut self, place: Place<'tcx>, location: Location) {
+        if let Some(all_facts) = self.all_facts {
+            let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
+
+            // Depending on the `Place` we're killing:
+            // - if it's a local, or a single deref of a local,
+            //   we kill all the borrows on the local.
+            // - if it's a deeper projection, we have to filter which
+            //   of the borrows are killed: the ones whose `borrowed_place`
+            //   conflicts with the `place`.
+            match place.as_ref() {
+                PlaceRef { local, projection: &[] }
+                | PlaceRef { local, projection: &[ProjectionElem::Deref] } => {
+                    debug!(
+                        "Recording `killed` facts for borrows of local={:?} at location={:?}",
+                        local, location
+                    );
+
+                    record_killed_borrows_for_local(
+                        all_facts,
+                        self.borrow_set,
+                        self.location_table,
+                        local,
+                        location,
+                    );
+                }
+
+                PlaceRef { local, projection: &[.., _] } => {
+                    // Kill conflicting borrows of the innermost local.
+                    debug!(
+                        "Recording `killed` facts for borrows of \
+                            innermost projected local={:?} at location={:?}",
+                        local, location
+                    );
+
+                    if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
+                        for &borrow_index in borrow_indices {
+                            let places_conflict = places_conflict::places_conflict(
+                                self.infcx.tcx,
+                                self.body,
+                                self.borrow_set[borrow_index].borrowed_place,
+                                place,
+                                places_conflict::PlaceConflictBias::NoOverlap,
+                            );
+
+                            if places_conflict {
+                                let location_index = self.location_table.mid_index(location);
+                                all_facts.loan_killed_at.push((borrow_index, location_index));
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+/// When recording facts for Polonius, records the borrows on the specified local as `killed`.
+fn record_killed_borrows_for_local(
+    all_facts: &mut AllFacts,
+    borrow_set: &BorrowSet<'_>,
+    location_table: &LocationTable,
+    local: Local,
+    location: Location,
+) {
+    if let Some(borrow_indices) = borrow_set.local_map.get(&local) {
+        all_facts.loan_killed_at.reserve(borrow_indices.len());
+        for &borrow_index in borrow_indices {
+            let location_index = location_table.mid_index(location);
+            all_facts.loan_killed_at.push((borrow_index, location_index));
+        }
+    }
+}

compiler/rustc_borrowck/src/polonius/mod.rs

@@ -3,16 +3,19 @@
 //! Will be removed in the future, once the in-tree `-Zpolonius=next` implementation reaches feature
 //! parity.
 
+use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::{Body, LocalKind, Location, START_BLOCK};
-use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_mir_dataflow::move_paths::{InitKind, InitLocation, MoveData};
 
 use crate::borrow_set::BorrowSet;
 use crate::facts::AllFacts;
 use crate::location::LocationTable;
+use crate::region_infer::values::LivenessValues;
 use crate::type_check::free_region_relations::UniversalRegionRelations;
 use crate::universal_regions::UniversalRegions;
 
+mod constraint_generation;
 mod invalidation;
 
 /// Emit facts needed for move/init analysis: moves and assignments.
@@ -130,7 +133,7 @@ pub(crate) fn emit_universal_region_facts(
     }
 }
 
-/// Emit facts about loan invalidations
+/// Emit facts about loan invalidations.
 pub(crate) fn emit_loan_invalidations_facts<'tcx>(
     tcx: TyCtxt<'tcx>,
     all_facts: &mut Option<AllFacts>,
@@ -145,3 +148,22 @@ pub(crate) fn emit_loan_invalidations_facts<'tcx>(
 
     invalidation::emit_loan_invalidations(tcx, all_facts, location_table, body, borrow_set);
 }
+
+/// Emit facts about CFG points and edges, as well as locations where loans are killed.
+pub(crate) fn emit_cfg_and_loan_kills_facts<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    liveness_constraints: &mut LivenessValues<RegionVid>,
+    all_facts: &mut Option<AllFacts>,
+    location_table: &LocationTable,
+    body: &Body<'tcx>,
+    borrow_set: &BorrowSet<'tcx>,
+) {
+    constraint_generation::generate_constraints(
+        infcx,
+        liveness_constraints,
+        all_facts,
+        location_table,
+        body,
+        borrow_set,
+    );
+}