Clean up `UniversalRegions`.

There is an `Rc<UniversalRegions>` within `UniversalRegionRelations`,
and yet the two types get passed around in tandem a lot.

This commit makes `UniversalRegionRelations` own `UniversalRegions`,
removing the `Rc` (which wasn't truly needed) and the tandem-passing.
This requires adding a `universal_relations` method to
`UniversalRegionRelations`, and renaming a couple of existing methods
producing iterators to avoid a name clash.

10 files changed, 46 insertions, 60 deletions

diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index f76603d5679..2e5ca6959a8 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -96,8 +96,6 @@ pub(crate) fn compute_regions<'a, 'tcx>(
     let mut all_facts =
         (polonius_input || AllFacts::enabled(infcx.tcx)).then_some(AllFacts::default());
 
-    let universal_regions = Rc::new(universal_regions);
-
     let elements = Rc::new(DenseLocationMap::new(body));
 
     // Run the MIR type-checker.
@@ -107,7 +105,7 @@ pub(crate) fn compute_regions<'a, 'tcx>(
             param_env,
             body,
             promoted,
-            Rc::clone(&universal_regions),
+            universal_regions,
             location_table,
             borrow_set,
             &mut all_facts,
@@ -140,11 +138,10 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         body,
         borrow_set,
         move_data,
-        &universal_regions,
         &universal_region_relations,
     );
 
-    if let Some(guar) = universal_regions.tainted_by_errors() {
+    if let Some(guar) = universal_region_relations.universal_regions.tainted_by_errors() {
         // Suppress unhelpful extra errors in `infer_opaque_types` by clearing out all
         // outlives bounds that we may end up checking.
         outlives_constraints = Default::default();
@@ -157,7 +154,6 @@ pub(crate) fn compute_regions<'a, 'tcx>(
     let mut regioncx = RegionInferenceContext::new(
         infcx,
         var_origins,
-        universal_regions,
         placeholder_indices,
         universal_region_relations,
         outlives_constraints,
diff --git a/compiler/rustc_borrowck/src/polonius/mod.rs b/compiler/rustc_borrowck/src/polonius/mod.rs
index 6862eb13427..9fccc00bdaf 100644
--- a/compiler/rustc_borrowck/src/polonius/mod.rs
+++ b/compiler/rustc_borrowck/src/polonius/mod.rs
@@ -12,7 +12,6 @@ use crate::borrow_set::BorrowSet;
 use crate::facts::{AllFacts, PoloniusRegionVid};
 use crate::location::LocationTable;
 use crate::type_check::free_region_relations::UniversalRegionRelations;
-use crate::universal_regions::UniversalRegions;
 
 mod loan_invalidations;
 mod loan_kills;
@@ -32,7 +31,6 @@ pub(crate) fn emit_facts<'tcx>(
     body: &Body<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     move_data: &MoveData<'_>,
-    universal_regions: &UniversalRegions<'_>,
     universal_region_relations: &UniversalRegionRelations<'_>,
 ) {
     let Some(all_facts) = all_facts else {
@@ -41,12 +39,7 @@ pub(crate) fn emit_facts<'tcx>(
     };
     let _prof_timer = tcx.prof.generic_activity("polonius_fact_generation");
     emit_move_facts(all_facts, move_data, location_table, body);
-    emit_universal_region_facts(
-        all_facts,
-        borrow_set,
-        universal_regions,
-        universal_region_relations,
-    );
+    emit_universal_region_facts(all_facts, borrow_set, universal_region_relations);
     emit_cfg_and_loan_kills_facts(all_facts, tcx, location_table, body, borrow_set);
     emit_loan_invalidations_facts(all_facts, tcx, location_table, body, borrow_set);
 }
@@ -129,7 +122,6 @@ fn emit_move_facts(
 fn emit_universal_region_facts(
     all_facts: &mut AllFacts,
     borrow_set: &BorrowSet<'_>,
-    universal_regions: &UniversalRegions<'_>,
     universal_region_relations: &UniversalRegionRelations<'_>,
 ) {
     // 1: universal regions are modeled in Polonius as a pair:
@@ -138,9 +130,10 @@ fn emit_universal_region_facts(
     //   the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
     //   added to the existing number of loans, as if they succeeded them in the set.
     //
+    let universal_regions = &universal_region_relations.universal_regions;
     all_facts
         .universal_region
-        .extend(universal_regions.universal_regions().map(PoloniusRegionVid::from));
+        .extend(universal_regions.universal_regions_iter().map(PoloniusRegionVid::from));
     let borrow_count = borrow_set.len();
     debug!(
         "emit_universal_region_facts: polonius placeholders, num_universals={}, borrow_count={}",
@@ -148,7 +141,7 @@ fn emit_universal_region_facts(
         borrow_count
     );
 
-    for universal_region in universal_regions.universal_regions() {
+    for universal_region in universal_regions.universal_regions_iter() {
         let universal_region_idx = universal_region.index();
         let placeholder_loan_idx = borrow_count + universal_region_idx;
         all_facts.placeholder.push((universal_region.into(), placeholder_loan_idx.into()));
diff --git a/compiler/rustc_borrowck/src/region_infer/dump_mir.rs b/compiler/rustc_borrowck/src/region_infer/dump_mir.rs
index 6b8dd1a49e7..ef3d6309c19 100644
--- a/compiler/rustc_borrowck/src/region_infer/dump_mir.rs
+++ b/compiler/rustc_borrowck/src/region_infer/dump_mir.rs
@@ -23,7 +23,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
         for region in self.regions() {
             if let NllRegionVariableOrigin::FreeRegion = self.definitions[region].origin {
-                let classification = self.universal_regions.region_classification(region).unwrap();
+                let classification =
+                    self.universal_regions().region_classification(region).unwrap();
                 let outlived_by = self.universal_region_relations.regions_outlived_by(region);
                 writeln!(
                     out,
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index 7e317ea6554..01d259653b8 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -191,10 +191,6 @@ pub struct RegionInferenceContext<'tcx> {
     /// Type constraints that we check after solving.
     type_tests: Vec<TypeTest<'tcx>>,
 
-    /// Information about the universally quantified regions in scope
-    /// on this function.
-    universal_regions: Rc<UniversalRegions<'tcx>>,
-
     /// Information about how the universally quantified regions in
     /// scope on this function relate to one another.
     universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
@@ -399,7 +395,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     pub(crate) fn new(
         infcx: &BorrowckInferCtxt<'tcx>,
         var_infos: VarInfos,
-        universal_regions: Rc<UniversalRegions<'tcx>>,
         placeholder_indices: Rc<PlaceholderIndices>,
         universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
         mut outlives_constraints: OutlivesConstraintSet<'tcx>,
@@ -409,7 +404,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         liveness_constraints: LivenessValues,
         elements: Rc<DenseLocationMap>,
     ) -> Self {
-        debug!("universal_regions: {:#?}", universal_regions);
+        let universal_regions = &universal_region_relations.universal_regions;
+
+        debug!("universal_regions: {:#?}", universal_region_relations.universal_regions);
         debug!("outlives constraints: {:#?}", outlives_constraints);
         debug!("placeholder_indices: {:#?}", placeholder_indices);
         debug!("type tests: {:#?}", type_tests);
@@ -453,7 +450,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             universe_causes,
             scc_values,
             type_tests,
-            universal_regions,
             universal_region_relations,
         };
 
@@ -518,7 +514,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     fn init_free_and_bound_regions(&mut self) {
         // Update the names (if any)
         // This iterator has unstable order but we collect it all into an IndexVec
-        for (external_name, variable) in self.universal_regions.named_universal_regions() {
+        for (external_name, variable) in
+            self.universal_region_relations.universal_regions.named_universal_regions_iter()
+        {
             debug!(
                 "init_free_and_bound_regions: region {:?} has external name {:?}",
                 variable, external_name
@@ -562,7 +560,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// (Panics if `r` is not a registered universal region.)
     pub(crate) fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
-        self.universal_regions.to_region_vid(r)
+        self.universal_regions().to_region_vid(r)
     }
 
     /// Returns an iterator over all the outlives constraints.
@@ -574,7 +572,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
     /// Adds annotations for `#[rustc_regions]`; see `UniversalRegions::annotate`.
     pub(crate) fn annotate(&self, tcx: TyCtxt<'tcx>, err: &mut Diag<'_, ()>) {
-        self.universal_regions.annotate(tcx, err)
+        self.universal_regions().annotate(tcx, err)
     }
 
     /// Returns `true` if the region `r` contains the point `p`.
@@ -686,7 +684,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         if outlives_requirements.is_empty() {
             (None, errors_buffer)
         } else {
-            let num_external_vids = self.universal_regions.num_global_and_external_regions();
+            let num_external_vids = self.universal_regions().num_global_and_external_regions();
             (
                 Some(ClosureRegionRequirements { num_external_vids, outlives_requirements }),
                 errors_buffer,
@@ -989,7 +987,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // always be in the root universe.
         if let Some(p) = self.scc_values.placeholders_contained_in(r_scc).next() {
             debug!("encountered placeholder in higher universe: {:?}, requiring 'static", p);
-            let static_r = self.universal_regions.fr_static;
+            let static_r = self.universal_regions().fr_static;
             propagated_outlives_requirements.push(ClosureOutlivesRequirement {
                 subject,
                 outlived_free_region: static_r,
@@ -1032,8 +1030,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // avoid potential non-determinism we approximate this by requiring
             // T: '1 and T: '2.
             for upper_bound in non_local_ub {
-                debug_assert!(self.universal_regions.is_universal_region(upper_bound));
-                debug_assert!(!self.universal_regions.is_local_free_region(upper_bound));
+                debug_assert!(self.universal_regions().is_universal_region(upper_bound));
+                debug_assert!(!self.universal_regions().is_local_free_region(upper_bound));
 
                 let requirement = ClosureOutlivesRequirement {
                     subject,
@@ -1101,7 +1099,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // To do so, we simply check every candidate `u_r` for equality.
             self.scc_values
                 .universal_regions_outlived_by(r_scc)
-                .filter(|&u_r| !self.universal_regions.is_local_free_region(u_r))
+                .filter(|&u_r| !self.universal_regions().is_local_free_region(u_r))
                 .find(|&u_r| self.eval_equal(u_r, r_vid))
                 .map(|u_r| ty::Region::new_var(tcx, u_r))
                 // In case we could not find a named region to map to,
@@ -1139,9 +1137,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
         // Find the smallest universal region that contains all other
         // universal regions within `region`.
-        let mut lub = self.universal_regions.fr_fn_body;
+        let mut lub = self.universal_regions().fr_fn_body;
         let r_scc = self.constraint_sccs.scc(r);
-        let static_r = self.universal_regions.fr_static;
+        let static_r = self.universal_regions().fr_static;
         for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
             let new_lub = self.universal_region_relations.postdom_upper_bound(lub, ur);
             debug!(?ur, ?lub, ?new_lub);
@@ -1288,12 +1286,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         debug!(
             "sup_region's value = {:?} universal={:?}",
             self.region_value_str(sup_region),
-            self.universal_regions.is_universal_region(sup_region),
+            self.universal_regions().is_universal_region(sup_region),
         );
         debug!(
             "sub_region's value = {:?} universal={:?}",
             self.region_value_str(sub_region),
-            self.universal_regions.is_universal_region(sub_region),
+            self.universal_regions().is_universal_region(sub_region),
         );
 
         let sub_region_scc = self.constraint_sccs.scc(sub_region);
@@ -1308,7 +1306,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 by super `{sup_region_scc:?}`, promoting to static",
             );
 
-            return self.eval_outlives(sup_region, self.universal_regions.fr_static);
+            return self.eval_outlives(sup_region, self.universal_regions().fr_static);
         }
 
         // Both the `sub_region` and `sup_region` consist of the union
@@ -1332,7 +1330,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // Now we have to compare all the points in the sub region and make
         // sure they exist in the sup region.
 
-        if self.universal_regions.is_universal_region(sup_region) {
+        if self.universal_regions().is_universal_region(sup_region) {
             // Micro-opt: universal regions contain all points.
             debug!("super is universal and hence contains all points");
             return true;
@@ -1736,7 +1734,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         debug!("provides_universal_region(r={:?}, fr1={:?}, fr2={:?})", r, fr1, fr2);
         let result = {
             r == fr2 || {
-                fr2 == self.universal_regions.fr_static && self.cannot_name_placeholder(fr1, r)
+                fr2 == self.universal_regions().fr_static && self.cannot_name_placeholder(fr1, r)
             }
         };
         debug!("provides_universal_region: result = {:?}", result);
@@ -1837,7 +1835,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
             // A constraint like `'r: 'x` can come from our constraint
             // graph.
-            let fr_static = self.universal_regions.fr_static;
+            let fr_static = self.universal_regions().fr_static;
             let outgoing_edges_from_graph =
                 self.constraint_graph.outgoing_edges(r, &self.constraints, fr_static);
 
@@ -1952,7 +1950,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     }
 
     pub(crate) fn universal_regions(&self) -> &UniversalRegions<'tcx> {
-        self.universal_regions.as_ref()
+        &self.universal_region_relations.universal_regions
     }
 
     /// Tries to find the best constraint to blame for the fact that
@@ -2212,7 +2210,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
     /// 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)
+        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
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index d676ce59cfe..993d5d86333 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -74,7 +74,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             debug!(?opaque_type_key, ?concrete_type);
 
             let mut arg_regions: Vec<(ty::RegionVid, ty::Region<'_>)> =
-                vec![(self.universal_regions.fr_static, infcx.tcx.lifetimes.re_static)];
+                vec![(self.universal_regions().fr_static, infcx.tcx.lifetimes.re_static)];
 
             let opaque_type_key =
                 opaque_type_key.fold_captured_lifetime_args(infcx.tcx, |region| {
@@ -88,12 +88,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                         // the same name and simplifies subsequent handling.
                         // See [rustc-dev-guide chapter] § "Semantic lifetime equality".
                         NllRegionVariableOrigin::FreeRegion => self
-                            .universal_regions
                             .universal_regions()
+                            .universal_regions_iter()
                             .filter(|&ur| {
                                 // See [rustc-dev-guide chapter] § "Closure restrictions".
                                 !matches!(
-                                    self.universal_regions.region_classification(ur),
+                                    self.universal_regions().region_classification(ur),
                                     Some(RegionClassification::External)
                                 )
                             })
diff --git a/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs b/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs
index cfd5a92787e..d0cfe572d08 100644
--- a/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs
+++ b/compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs
@@ -45,8 +45,8 @@ impl RegionInferenceContext<'_> {
 
         let graph = self.constraint_sccs.reverse();
         let mut paired_scc_regions = self
-            .universal_regions
             .universal_regions()
+            .universal_regions_iter()
             .map(|region| (self.constraint_sccs.scc(region), region))
             .collect::<Vec<_>>();
         paired_scc_regions.sort();
diff --git a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
index 03b8020b373..9d36e841a95 100644
--- a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
+++ b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
@@ -1,5 +1,3 @@
-use std::rc::Rc;
-
 use rustc_data_structures::frozen::Frozen;
 use rustc_data_structures::transitive_relation::{TransitiveRelation, TransitiveRelationBuilder};
 use rustc_hir::def::DefKind;
@@ -23,7 +21,7 @@ use crate::universal_regions::UniversalRegions;
 
 #[derive(Debug)]
 pub(crate) struct UniversalRegionRelations<'tcx> {
-    universal_regions: Rc<UniversalRegions<'tcx>>,
+    pub(crate) universal_regions: UniversalRegions<'tcx>,
 
     /// Stores the outlives relations that are known to hold from the
     /// implied bounds, in-scope where-clauses, and that sort of
@@ -54,7 +52,7 @@ pub(crate) fn create<'tcx>(
     infcx: &InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     implicit_region_bound: ty::Region<'tcx>,
-    universal_regions: Rc<UniversalRegions<'tcx>>,
+    universal_regions: UniversalRegions<'tcx>,
     constraints: &mut MirTypeckRegionConstraints<'tcx>,
 ) -> CreateResult<'tcx> {
     UniversalRegionRelationsBuilder {
@@ -184,7 +182,7 @@ impl UniversalRegionRelations<'_> {
 struct UniversalRegionRelationsBuilder<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    universal_regions: Rc<UniversalRegions<'tcx>>,
+    universal_regions: UniversalRegions<'tcx>,
     implicit_region_bound: ty::Region<'tcx>,
     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 
@@ -220,7 +218,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
         //   region `'r`, all of which are provided by our caller
         let fr_static = self.universal_regions.fr_static;
         let fr_fn_body = self.universal_regions.fr_fn_body;
-        for fr in self.universal_regions.universal_regions() {
+        for fr in self.universal_regions.universal_regions_iter() {
             debug!("build: relating free region {:?} to itself and to 'static", fr);
             self.relate_universal_regions(fr, fr);
             self.relate_universal_regions(fr_static, fr);
diff --git a/compiler/rustc_borrowck/src/type_check/liveness/mod.rs b/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
index 84fb36dd32a..fd51cc94548 100644
--- a/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/liveness/mod.rs
@@ -39,7 +39,7 @@ pub(super) fn generate<'a, 'tcx>(
 
     let free_regions = regions_that_outlive_free_regions(
         typeck.infcx.num_region_vars(),
-        typeck.universal_regions,
+        &typeck.universal_regions,
         &typeck.constraints.outlives_constraints,
     );
     let (relevant_live_locals, boring_locals) =
@@ -107,7 +107,7 @@ fn regions_that_outlive_free_regions<'tcx>(
     let rev_region_graph = rev_constraint_graph.region_graph(constraint_set, fr_static);
 
     // Stack for the depth-first search. Start out with all the free regions.
-    let mut stack: Vec<_> = universal_regions.universal_regions().collect();
+    let mut stack: Vec<_> = universal_regions.universal_regions_iter().collect();
 
     // Set of all free regions, plus anything that outlives them. Initially
     // just contains the free regions.
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index bca57d645dd..01397898958 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -121,7 +121,7 @@ pub(crate) fn type_check<'a, 'tcx>(
     param_env: ty::ParamEnv<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
-    universal_regions: Rc<UniversalRegions<'tcx>>,
+    universal_regions: UniversalRegions<'tcx>,
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     all_facts: &mut Option<AllFacts>,
@@ -150,7 +150,7 @@ pub(crate) fn type_check<'a, 'tcx>(
         infcx,
         param_env,
         implicit_region_bound,
-        Rc::clone(&universal_regions),
+        universal_regions,
         &mut constraints,
     );
 
@@ -166,7 +166,7 @@ pub(crate) fn type_check<'a, 'tcx>(
         known_type_outlives_obligations,
         implicit_region_bound,
         reported_errors: Default::default(),
-        universal_regions: &universal_regions,
+        universal_regions: &universal_region_relations.universal_regions,
         location_table,
         all_facts,
         borrow_set,
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index b63144f560f..953c48706f3 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -312,7 +312,7 @@ impl<'tcx> UniversalRegions<'tcx> {
 
     /// Returns an iterator over all the RegionVids corresponding to
     /// universally quantified free regions.
-    pub(crate) fn universal_regions(&self) -> impl Iterator<Item = RegionVid> {
+    pub(crate) fn universal_regions_iter(&self) -> impl Iterator<Item = RegionVid> {
         (FIRST_GLOBAL_INDEX..self.num_universals).map(RegionVid::from_usize)
     }
 
@@ -336,7 +336,7 @@ impl<'tcx> UniversalRegions<'tcx> {
     }
 
     /// Gets an iterator over all the early-bound regions that have names.
-    pub(crate) fn named_universal_regions<'s>(
+    pub(crate) fn named_universal_regions_iter<'s>(
         &'s self,
     ) -> impl Iterator<Item = (ty::Region<'tcx>, ty::RegionVid)> + 's {
         self.indices.indices.iter().map(|(&r, &v)| (r, v))