Remove a few Rcs from RegionInferenceCtxt

src/librustc_mir/borrow_check/mod.rs

@@ -73,6 +73,24 @@ crate use place_ext::PlaceExt;
 crate use places_conflict::{places_conflict, PlaceConflictBias};
 crate use region_infer::RegionInferenceContext;
 
+/// An owned immutable value.
+#[derive(Debug)]
+struct Frozen<T>(T);
+
+impl<T> Frozen<T> {
+    pub fn freeze(val: T) -> Self {
+        Frozen(val)
+    }
+}
+
+impl<T> std::ops::Deref for Frozen<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
 // FIXME(eddyb) perhaps move this somewhere more centrally.
 #[derive(Debug)]
 crate struct Upvar {
@@ -1577,11 +1595,11 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 mpi,
             );
         } // Only query longest prefix with a MovePath, not further
-        // ancestors; dataflow recurs on children when parents
-        // move (to support partial (re)inits).
-        //
-        // (I.e., querying parents breaks scenario 7; but may want
-        // to do such a query based on partial-init feature-gate.)
+          // ancestors; dataflow recurs on children when parents
+          // move (to support partial (re)inits).
+          //
+          // (I.e., querying parents breaks scenario 7; but may want
+          // to do such a query based on partial-init feature-gate.)
     }
 
     /// Subslices correspond to multiple move paths, so we iterate through the

src/librustc_mir/borrow_check/region_infer/mod.rs

@@ -31,6 +31,7 @@ use crate::borrow_check::{
     },
     type_check::{free_region_relations::UniversalRegionRelations, Locations},
     universal_regions::UniversalRegions,
+    Frozen,
 };
 
 mod dump_mir;
@@ -54,12 +55,12 @@ pub struct RegionInferenceContext<'tcx> {
     liveness_constraints: LivenessValues<RegionVid>,
 
     /// The outlives constraints computed by the type-check.
-    constraints: Rc<OutlivesConstraintSet>,
+    constraints: Frozen<OutlivesConstraintSet>,
 
     /// The constraint-set, but in graph form, making it easy to traverse
     /// the constraints adjacent to a particular region. Used to construct
     /// the SCC (see `constraint_sccs`) and for error reporting.
-    constraint_graph: Rc<NormalConstraintGraph>,
+    constraint_graph: Frozen<NormalConstraintGraph>,
 
     /// The SCC computed from `constraints` and the constraint
     /// graph. We have an edge from SCC A to SCC B if `A: B`. Used to
@@ -112,7 +113,7 @@ pub struct RegionInferenceContext<'tcx> {
 
     /// Information about how the universally quantified regions in
     /// scope on this function relate to one another.
-    universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
+    universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
 }
 
 /// Each time that `apply_member_constraint` is successful, it appends
@@ -242,11 +243,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// The `outlives_constraints` and `type_tests` are an initial set
     /// of constraints produced by the MIR type check.
-    pub(crate) fn new(
+    pub(in crate::borrow_check) fn new(
         var_infos: VarInfos,
         universal_regions: Rc<UniversalRegions<'tcx>>,
         placeholder_indices: Rc<PlaceholderIndices>,
-        universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
+        universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
         outlives_constraints: OutlivesConstraintSet,
         member_constraints_in: MemberConstraintSet<'tcx, RegionVid>,
         closure_bounds_mapping: FxHashMap<
@@ -263,8 +264,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             .map(|info| RegionDefinition::new(info.universe, info.origin))
             .collect();
 
-        let constraints = Rc::new(outlives_constraints); // freeze constraints
-        let constraint_graph = Rc::new(constraints.graph(definitions.len()));
+        let constraints = Frozen::freeze(outlives_constraints);
+        let constraint_graph = Frozen::freeze(constraints.graph(definitions.len()));
         let fr_static = universal_regions.fr_static;
         let constraint_sccs = Rc::new(constraints.compute_sccs(&constraint_graph, fr_static));
 

src/librustc_mir/borrow_check/type_check/free_region_relations.rs

@@ -15,6 +15,7 @@ use crate::borrow_check::{
     type_check::constraint_conversion,
     type_check::{Locations, MirTypeckRegionConstraints},
     universal_regions::UniversalRegions,
+    Frozen,
 };
 
 #[derive(Debug)]
@@ -52,7 +53,7 @@ type RegionBoundPairs<'tcx> = Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>;
 type NormalizedInputsAndOutput<'tcx> = Vec<Ty<'tcx>>;
 
 crate struct CreateResult<'tcx> {
-    crate universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
+    pub(in crate::borrow_check) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
     crate region_bound_pairs: RegionBoundPairs<'tcx>,
     crate normalized_inputs_and_output: NormalizedInputsAndOutput<'tcx>,
 }
@@ -297,7 +298,7 @@ impl UniversalRegionRelationsBuilder<'cx, 'tcx> {
         }
 
         CreateResult {
-            universal_region_relations: Rc::new(self.relations),
+            universal_region_relations: Frozen::freeze(self.relations),
             region_bound_pairs: self.region_bound_pairs,
             normalized_inputs_and_output,
         }

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -55,6 +55,7 @@ use crate::borrow_check::{
     renumber,
     type_check::free_region_relations::{CreateResult, UniversalRegionRelations},
     universal_regions::{DefiningTy, UniversalRegions},
+    Frozen,
 };
 
 macro_rules! span_mirbug {
@@ -828,7 +829,7 @@ struct BorrowCheckContext<'a, 'tcx> {
 
 crate struct MirTypeckResults<'tcx> {
     crate constraints: MirTypeckRegionConstraints<'tcx>,
-    crate universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
+    pub(in crate::borrow_check) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
     crate opaque_type_values: FxHashMap<DefId, ty::ResolvedOpaqueTy<'tcx>>,
 }