Auto merge of #117880 - lqd:liveness-values, r=cjgillot

Refactor borrowck liveness values

This PR starts cleaning up `rustc_borrowck`, in particular around liveness values:
- refactors simple names that make no sense anymore: either referring to older structures using region elements, or to bitset containers and values.
- improves comments and fixes others
- removes unused return values and unneeded generic arguments

r? `@matthewjasper`

compiler/rustc_borrowck/src/constraint_generation.rs

@@ -9,7 +9,7 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::GenericArgsRef;
-use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 
 use crate::{
     borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, places_conflict,
@@ -18,7 +18,7 @@ use crate::{
 
 pub(super) fn generate_constraints<'tcx>(
     infcx: &InferCtxt<'tcx>,
-    liveness_constraints: &mut LivenessValues<RegionVid>,
+    liveness_constraints: &mut LivenessValues,
     all_facts: &mut Option<AllFacts>,
     location_table: &LocationTable,
     body: &Body<'tcx>,
@@ -43,7 +43,7 @@ struct ConstraintGeneration<'cg, 'tcx> {
     infcx: &'cg InferCtxt<'tcx>,
     all_facts: &'cg mut Option<AllFacts>,
     location_table: &'cg LocationTable,
-    liveness_constraints: &'cg mut LivenessValues<RegionVid>,
+    liveness_constraints: &'cg mut LivenessValues,
     borrow_set: &'cg BorrowSet<'tcx>,
     body: &'cg Body<'tcx>,
 }
@@ -167,7 +167,7 @@ impl<'cx, 'tcx> ConstraintGeneration<'cx, 'tcx> {
 
         self.infcx.tcx.for_each_free_region(&live_ty, |live_region| {
             let vid = live_region.as_var();
-            self.liveness_constraints.add_element(vid, location);
+            self.liveness_constraints.add_location(vid, location);
         });
     }
 

compiler/rustc_borrowck/src/region_infer/dump_mir.rs

@@ -67,7 +67,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
     ) -> io::Result<()> {
         for region in self.definitions.indices() {
-            let value = self.liveness_constraints.region_value_str(region);
+            let value = self.liveness_constraints.pretty_print_live_points(region);
             if value != "{}" {
                 with_msg(&format!("{region:?} live at {value}"))?;
             }

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -59,7 +59,7 @@ pub struct RegionInferenceContext<'tcx> {
     /// regions, these start out empty and steadily grow, though for
     /// each universally quantified region R they start out containing
     /// the entire CFG and `end(R)`.
-    liveness_constraints: LivenessValues<RegionVid>,
+    liveness_constraints: LivenessValues,
 
     /// The outlives constraints computed by the type-check.
     constraints: Frozen<OutlivesConstraintSet<'tcx>>,
@@ -333,7 +333,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         member_constraints_in: MemberConstraintSet<'tcx, RegionVid>,
         universe_causes: FxIndexMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
         type_tests: Vec<TypeTest<'tcx>>,
-        liveness_constraints: LivenessValues<RegionVid>,
+        liveness_constraints: LivenessValues,
         elements: &Rc<RegionValueElements>,
         live_loans: SparseBitMatrix<PointIndex, BorrowIndex>,
     ) -> Self {
@@ -360,7 +360,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let mut scc_values =
             RegionValues::new(elements, universal_regions.len(), &placeholder_indices);
 
-        for region in liveness_constraints.rows() {
+        for region in liveness_constraints.regions() {
             let scc = constraint_sccs.scc(region);
             scc_values.merge_liveness(scc, region, &liveness_constraints);
         }
@@ -1972,15 +1972,15 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         None
     }
 
-    /// Finds some region R such that `fr1: R` and `R` is live at `elem`.
+    /// Finds some region R such that `fr1: R` and `R` is live at `location`.
     #[instrument(skip(self), level = "trace", ret)]
-    pub(crate) fn find_sub_region_live_at(&self, fr1: RegionVid, elem: Location) -> RegionVid {
+    pub(crate) fn find_sub_region_live_at(&self, fr1: RegionVid, location: Location) -> RegionVid {
         trace!(scc = ?self.constraint_sccs.scc(fr1));
         trace!(universe = ?self.scc_universes[self.constraint_sccs.scc(fr1)]);
         self.find_constraint_paths_between_regions(fr1, |r| {
-            // First look for some `r` such that `fr1: r` and `r` is live at `elem`
-            trace!(?r, liveness_constraints=?self.liveness_constraints.region_value_str(r));
-            self.liveness_constraints.contains(r, elem)
+            // First look for some `r` such that `fr1: r` and `r` is live at `location`
+            trace!(?r, liveness_constraints=?self.liveness_constraints.pretty_print_live_points(r));
+            self.liveness_constraints.is_live_at(r, location)
         })
         .or_else(|| {
             // If we fail to find that, we may find some `r` such that

compiler/rustc_borrowck/src/region_infer/values.rs

@@ -117,65 +117,68 @@ pub(crate) enum RegionElement {
     PlaceholderRegion(ty::PlaceholderRegion),
 }
 
-/// When we initially compute liveness, we use an interval matrix storing
-/// liveness ranges for each region-vid.
-pub(crate) struct LivenessValues<N: Idx> {
+/// Records the CFG locations where each region is live. When we initially compute liveness, we use
+/// an interval matrix storing liveness ranges for each region-vid.
+pub(crate) struct LivenessValues {
     elements: Rc<RegionValueElements>,
-    points: SparseIntervalMatrix<N, PointIndex>,
+    points: SparseIntervalMatrix<RegionVid, PointIndex>,
 }
 
-impl<N: Idx> LivenessValues<N> {
-    /// Creates a new set of "region values" that tracks causal information.
-    /// Each of the regions in num_region_variables will be initialized with an
-    /// empty set of points and no causal information.
+impl LivenessValues {
+    /// Create an empty map of regions to locations where they're live.
     pub(crate) fn new(elements: Rc<RegionValueElements>) -> Self {
         Self { points: SparseIntervalMatrix::new(elements.num_points), elements }
     }
 
     /// Iterate through each region that has a value in this set.
-    pub(crate) fn rows(&self) -> impl Iterator<Item = N> {
+    pub(crate) fn regions(&self) -> impl Iterator<Item = RegionVid> {
         self.points.rows()
     }
 
-    /// Adds the given element to the value for the given region. Returns whether
-    /// the element is newly added (i.e., was not already present).
-    pub(crate) fn add_element(&mut self, row: N, location: Location) -> bool {
-        debug!("LivenessValues::add(r={:?}, location={:?})", row, location);
-        let index = self.elements.point_from_location(location);
-        self.points.insert(row, index)
+    /// Records `region` as being live at the given `location`.
+    pub(crate) fn add_location(&mut self, region: RegionVid, location: Location) {
+        debug!("LivenessValues::add_location(region={:?}, location={:?})", region, location);
+        let point = self.elements.point_from_location(location);
+        self.points.insert(region, point);
     }
 
-    /// Adds all the elements in the given bit array into the given
-    /// region. Returns whether any of them are newly added.
-    pub(crate) fn add_elements(&mut self, row: N, locations: &IntervalSet<PointIndex>) -> bool {
-        debug!("LivenessValues::add_elements(row={:?}, locations={:?})", row, locations);
-        self.points.union_row(row, locations)
+    /// Records `region` as being live at all the given `points`.
+    pub(crate) fn add_points(&mut self, region: RegionVid, points: &IntervalSet<PointIndex>) {
+        debug!("LivenessValues::add_points(region={:?}, points={:?})", region, points);
+        self.points.union_row(region, points);
     }
 
-    /// Adds all the control-flow points to the values for `r`.
-    pub(crate) fn add_all_points(&mut self, row: N) {
-        self.points.insert_all_into_row(row);
+    /// Records `region` as being live at all the control-flow points.
+    pub(crate) fn add_all_points(&mut self, region: RegionVid) {
+        self.points.insert_all_into_row(region);
     }
 
-    /// Returns `true` if the region `r` contains the given element.
-    pub(crate) fn contains(&self, row: N, location: Location) -> bool {
-        let index = self.elements.point_from_location(location);
-        self.points.row(row).is_some_and(|r| r.contains(index))
+    /// Returns whether `region` is marked live at the given `location`.
+    pub(crate) fn is_live_at(&self, region: RegionVid, location: Location) -> bool {
+        let point = self.elements.point_from_location(location);
+        self.points.row(region).is_some_and(|r| r.contains(point))
+    }
+
+    /// Returns whether `region` is marked live at any location.
+    pub(crate) fn is_live_anywhere(&self, region: RegionVid) -> bool {
+        self.live_points(region).next().is_some()
     }
 
-    /// Returns an iterator of all the elements contained by the region `r`
-    pub(crate) fn get_elements(&self, row: N) -> impl Iterator<Item = Location> + '_ {
+    /// Returns an iterator of all the points where `region` is live.
+    fn live_points(&self, region: RegionVid) -> impl Iterator<Item = PointIndex> + '_ {
         self.points
-            .row(row)
+            .row(region)
             .into_iter()
             .flat_map(|set| set.iter())
-            .take_while(move |&p| self.elements.point_in_range(p))
-            .map(move |p| self.elements.to_location(p))
+            .take_while(|&p| self.elements.point_in_range(p))
     }
 
-    /// Returns a "pretty" string value of the region. Meant for debugging.
-    pub(crate) fn region_value_str(&self, r: N) -> String {
-        region_value_str(self.get_elements(r).map(RegionElement::Location))
+    /// For debugging purposes, returns a pretty-printed string of the points where the `region` is
+    /// live.
+    pub(crate) fn pretty_print_live_points(&self, region: RegionVid) -> String {
+        pretty_print_region_elements(
+            self.live_points(region).map(|p| RegionElement::Location(self.elements.to_location(p))),
+        )
     }
 
     #[inline]
@@ -308,7 +311,7 @@ impl<N: Idx> RegionValues<N> {
     /// `self[to] |= values[from]`, essentially: that is, take all the
     /// elements for the region `from` from `values` and add them to
     /// the region `to` in `self`.
-    pub(crate) fn merge_liveness<M: Idx>(&mut self, to: N, from: M, values: &LivenessValues<M>) {
+    pub(crate) fn merge_liveness(&mut self, to: N, from: RegionVid, values: &LivenessValues) {
         if let Some(set) = values.points.row(from) {
             self.points.union_row(to, set);
         }
@@ -377,7 +380,7 @@ impl<N: Idx> RegionValues<N> {
 
     /// Returns a "pretty" string value of the region. Meant for debugging.
     pub(crate) fn region_value_str(&self, r: N) -> String {
-        region_value_str(self.elements_contained_in(r))
+        pretty_print_region_elements(self.elements_contained_in(r))
     }
 }
 
@@ -421,11 +424,12 @@ impl ToElementIndex for ty::PlaceholderRegion {
     }
 }
 
-pub(crate) fn location_set_str(
+/// For debugging purposes, returns a pretty-printed string of the given points.
+pub(crate) fn pretty_print_points(
     elements: &RegionValueElements,
     points: impl IntoIterator<Item = PointIndex>,
 ) -> String {
-    region_value_str(
+    pretty_print_region_elements(
         points
             .into_iter()
             .take_while(|&p| elements.point_in_range(p))
@@ -434,7 +438,8 @@ pub(crate) fn location_set_str(
     )
 }
 
-fn region_value_str(elements: impl IntoIterator<Item = RegionElement>) -> String {
+/// For debugging purposes, returns a pretty-printed string of the given region elements.
+fn pretty_print_region_elements(elements: impl IntoIterator<Item = RegionElement>) -> String {
     let mut result = String::new();
     result.push('{');
 

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -550,7 +550,7 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
             dropped_local,
             dropped_ty,
             drop_locations,
-            values::location_set_str(self.elements, live_at.iter()),
+            values::pretty_print_points(self.elements, live_at.iter()),
         );
 
         let drop_data = self.drop_data.entry(dropped_ty).or_insert_with({
@@ -599,7 +599,7 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
         debug!("make_all_regions_live(value={:?})", value);
         debug!(
             "make_all_regions_live: live_at={}",
-            values::location_set_str(elements, live_at.iter()),
+            values::pretty_print_points(elements, live_at.iter()),
         );
 
         // When using `-Zpolonius=next`, we want to record the loans that flow into this value's
@@ -618,7 +618,7 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
                     .borrowck_context
                     .constraints
                     .liveness_constraints
-                    .add_elements(live_region_vid, live_at);
+                    .add_points(live_region_vid, live_at);
 
                 // There can only be inflowing loans for this region when we are using
                 // `-Zpolonius=next`.

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -318,7 +318,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
                 .borrowck_context
                 .constraints
                 .liveness_constraints
-                .add_element(live_region_vid, location);
+                .add_location(live_region_vid, location);
         });
 
         // HACK(compiler-errors): Constants that are gathered into Body.required_consts
@@ -592,16 +592,16 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
             }
             self.cx.borrowck_context.constraints.outlives_constraints.push(constraint)
         }
-        for region in liveness_constraints.rows() {
+        for region in liveness_constraints.regions() {
             // If the region is live at at least one location in the promoted MIR,
             // then add a liveness constraint to the main MIR for this region
             // at the location provided as an argument to this method
-            if liveness_constraints.get_elements(region).next().is_some() {
+            if liveness_constraints.is_live_anywhere(region) {
                 self.cx
                     .borrowck_context
                     .constraints
                     .liveness_constraints
-                    .add_element(region, location);
+                    .add_location(region, location);
             }
         }
     }
@@ -899,7 +899,7 @@ pub(crate) struct MirTypeckRegionConstraints<'tcx> {
     /// not otherwise appear in the MIR -- in particular, the
     /// late-bound regions that it instantiates at call-sites -- and
     /// hence it must report on their liveness constraints.
-    pub(crate) liveness_constraints: LivenessValues<RegionVid>,
+    pub(crate) liveness_constraints: LivenessValues,
 
     pub(crate) outlives_constraints: OutlivesConstraintSet<'tcx>,
 
@@ -1443,7 +1443,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     self.borrowck_context
                         .constraints
                         .liveness_constraints
-                        .add_element(region_vid, term_location);
+                        .add_location(region_vid, term_location);
                 }
 
                 self.check_call_inputs(body, term, func, &sig, args, term_location, *call_source);