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 bb28622edf931..7c10047e9dc83 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 +1,5 @@
 use rustc_data_structures::frozen::Frozen;
-use rustc_data_structures::transitive_relation::TransitiveRelation;
+use rustc_data_structures::transitive_relation::{TransitiveRelation, TransitiveRelationBuilder};
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_infer::infer::outlives;
 use rustc_infer::infer::outlives::env::RegionBoundPairs;
@@ -61,25 +61,13 @@ pub(crate) fn create<'tcx>(
         constraints,
         universal_regions: universal_regions.clone(),
         region_bound_pairs: Default::default(),
-        relations: UniversalRegionRelations {
-            universal_regions: universal_regions.clone(),
-            outlives: Default::default(),
-            inverse_outlives: Default::default(),
-        },
+        outlives: Default::default(),
+        inverse_outlives: Default::default(),
     }
     .create()
 }
 
 impl UniversalRegionRelations<'_> {
-    /// Records in the `outlives_relation` (and
-    /// `inverse_outlives_relation`) that `fr_a: fr_b`. Invoked by the
-    /// builder below.
-    fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
-        debug!("relate_universal_regions: fr_a={:?} outlives fr_b={:?}", fr_a, fr_b);
-        self.outlives.add(fr_a, fr_b);
-        self.inverse_outlives.add(fr_b, fr_a);
-    }
-
     /// Given two universal regions, returns the postdominating
     /// upper-bound (effectively the least upper bound).
     ///
@@ -216,11 +204,20 @@ struct UniversalRegionRelationsBuilder<'this, 'tcx> {
     constraints: &'this mut MirTypeckRegionConstraints<'tcx>,
 
     // outputs:
-    relations: UniversalRegionRelations<'tcx>,
+    outlives: TransitiveRelationBuilder<RegionVid>,
+    inverse_outlives: TransitiveRelationBuilder<RegionVid>,
     region_bound_pairs: RegionBoundPairs<'tcx>,
 }
 
 impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
+    /// Records in the `outlives_relation` (and
+    /// `inverse_outlives_relation`) that `fr_a: fr_b`.
+    fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
+        debug!("relate_universal_regions: fr_a={:?} outlives fr_b={:?}", fr_a, fr_b);
+        self.outlives.add(fr_a, fr_b);
+        self.inverse_outlives.add(fr_b, fr_a);
+    }
+
     pub(crate) fn create(mut self) -> CreateResult<'tcx> {
         let unnormalized_input_output_tys = self
             .universal_regions
@@ -292,9 +289,9 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
         let fr_fn_body = self.universal_regions.fr_fn_body;
         for fr in self.universal_regions.universal_regions() {
             debug!("build: relating free region {:?} to itself and to 'static", fr);
-            self.relations.relate_universal_regions(fr, fr);
-            self.relations.relate_universal_regions(fr_static, fr);
-            self.relations.relate_universal_regions(fr, fr_fn_body);
+            self.relate_universal_regions(fr, fr);
+            self.relate_universal_regions(fr_static, fr);
+            self.relate_universal_regions(fr, fr_fn_body);
         }
 
         for data in &constraint_sets {
@@ -313,7 +310,11 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
         }
 
         CreateResult {
-            universal_region_relations: Frozen::freeze(self.relations),
+            universal_region_relations: Frozen::freeze(UniversalRegionRelations {
+                universal_regions: self.universal_regions,
+                outlives: self.outlives.freeze(),
+                inverse_outlives: self.inverse_outlives.freeze(),
+            }),
             region_bound_pairs: self.region_bound_pairs,
             normalized_inputs_and_output,
         }
@@ -356,7 +357,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
                     // The bound says that `r1 <= r2`; we store `r2: r1`.
                     let r1 = self.universal_regions.to_region_vid(r1);
                     let r2 = self.universal_regions.to_region_vid(r2);
-                    self.relations.relate_universal_regions(r2, r1);
+                    self.relate_universal_regions(r2, r1);
                 }
 
                 OutlivesBound::RegionSubParam(r_a, param_b) => {
diff --git a/compiler/rustc_data_structures/src/transitive_relation.rs b/compiler/rustc_data_structures/src/transitive_relation.rs
index 0ff64969b071c..f016c391fe777 100644
--- a/compiler/rustc_data_structures/src/transitive_relation.rs
+++ b/compiler/rustc_data_structures/src/transitive_relation.rs
@@ -1,45 +1,57 @@
+use crate::frozen::Frozen;
 use crate::fx::FxIndexSet;
-use crate::sync::Lock;
 use rustc_index::bit_set::BitMatrix;
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::mem;
+use std::ops::Deref;
 
 #[cfg(test)]
 mod tests;
 
 #[derive(Clone, Debug)]
-pub struct TransitiveRelation<T> {
+pub struct TransitiveRelationBuilder<T> {
     // List of elements. This is used to map from a T to a usize.
     elements: FxIndexSet<T>,
 
     // List of base edges in the graph. Require to compute transitive
     // closure.
     edges: Vec<Edge>,
+}
+
+#[derive(Debug)]
+pub struct TransitiveRelation<T> {
+    // Frozen transitive relation elements and edges.
+    builder: Frozen<TransitiveRelationBuilder<T>>,
 
-    // This is a cached transitive closure derived from the edges.
-    // Currently, we build it lazily and just throw out any existing
-    // copy whenever a new edge is added. (The Lock is to permit
-    // the lazy computation.) This is kind of silly, except for the
-    // fact its size is tied to `self.elements.len()`, so I wanted to
-    // wait before building it up to avoid reallocating as new edges
-    // are added with new elements. Perhaps better would be to ask the
-    // user for a batch of edges to minimize this effect, but I
-    // already wrote the code this way. :P -nmatsakis
-    closure: Lock<Option<BitMatrix<usize, usize>>>,
+    // Cached transitive closure derived from the edges.
+    closure: Frozen<BitMatrix<usize, usize>>,
 }
 
-// HACK(eddyb) manual impl avoids `Default` bound on `T`.
-impl<T: Eq + Hash> Default for TransitiveRelation<T> {
-    fn default() -> Self {
+impl<T> Deref for TransitiveRelation<T> {
+    type Target = Frozen<TransitiveRelationBuilder<T>>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.builder
+    }
+}
+
+impl<T: Clone> Clone for TransitiveRelation<T> {
+    fn clone(&self) -> Self {
         TransitiveRelation {
-            elements: Default::default(),
-            edges: Default::default(),
-            closure: Default::default(),
+            builder: Frozen::freeze(self.builder.deref().clone()),
+            closure: Frozen::freeze(self.closure.deref().clone()),
         }
     }
 }
 
+// HACK(eddyb) manual impl avoids `Default` bound on `T`.
+impl<T: Eq + Hash> Default for TransitiveRelationBuilder<T> {
+    fn default() -> Self {
+        TransitiveRelationBuilder { elements: Default::default(), edges: Default::default() }
+    }
+}
+
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Debug)]
 struct Index(usize);
 
@@ -49,7 +61,7 @@ struct Edge {
     target: Index,
 }
 
-impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
+impl<T: Eq + Hash + Copy> TransitiveRelationBuilder<T> {
     pub fn is_empty(&self) -> bool {
         self.edges.is_empty()
     }
@@ -63,23 +75,19 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
     }
 
     fn add_index(&mut self, a: T) -> Index {
-        let (index, added) = self.elements.insert_full(a);
-        if added {
-            // if we changed the dimensions, clear the cache
-            *self.closure.get_mut() = None;
-        }
+        let (index, _added) = self.elements.insert_full(a);
         Index(index)
     }
 
     /// Applies the (partial) function to each edge and returns a new
-    /// relation. If `f` returns `None` for any end-point, returns
-    /// `None`.
-    pub fn maybe_map<F, U>(&self, mut f: F) -> Option<TransitiveRelation<U>>
+    /// relation builder. If `f` returns `None` for any end-point,
+    /// returns `None`.
+    pub fn maybe_map<F, U>(&self, mut f: F) -> Option<TransitiveRelationBuilder<U>>
     where
         F: FnMut(T) -> Option<U>,
         U: Clone + Debug + Eq + Hash + Copy,
     {
-        let mut result = TransitiveRelation::default();
+        let mut result = TransitiveRelationBuilder::default();
         for edge in &self.edges {
             result.add(f(self.elements[edge.source.0])?, f(self.elements[edge.target.0])?);
         }
@@ -93,10 +101,38 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
         let edge = Edge { source: a, target: b };
         if !self.edges.contains(&edge) {
             self.edges.push(edge);
+        }
+    }
+
+    /// Compute the transitive closure derived from the edges, and converted to
+    /// the final result. After this, all elements will be immutable to maintain
+    /// the correctness of the result.
+    pub fn freeze(self) -> TransitiveRelation<T> {
+        let mut matrix = BitMatrix::new(self.elements.len(), self.elements.len());
+        let mut changed = true;
+        while changed {
+            changed = false;
+            for edge in &self.edges {
+                // add an edge from S -> T
+                changed |= matrix.insert(edge.source.0, edge.target.0);
 
-            // added an edge, clear the cache
-            *self.closure.get_mut() = None;
+                // add all outgoing edges from T into S
+                changed |= matrix.union_rows(edge.target.0, edge.source.0);
+            }
         }
+        TransitiveRelation { builder: Frozen::freeze(self), closure: Frozen::freeze(matrix) }
+    }
+}
+
+impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
+    /// Applies the (partial) function to each edge and returns a new
+    /// relation including transitive closures.
+    pub fn maybe_map<F, U>(&self, f: F) -> Option<TransitiveRelation<U>>
+    where
+        F: FnMut(T) -> Option<U>,
+        U: Clone + Debug + Eq + Hash + Copy,
+    {
+        Some(self.builder.maybe_map(f)?.freeze())
     }
 
     /// Checks whether `a < target` (transitively)
@@ -322,30 +358,7 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
     where
         OP: FnOnce(&BitMatrix<usize, usize>) -> R,
     {
-        let mut closure_cell = self.closure.borrow_mut();
-        let mut closure = closure_cell.take();
-        if closure.is_none() {
-            closure = Some(self.compute_closure());
-        }
-        let result = op(closure.as_ref().unwrap());
-        *closure_cell = closure;
-        result
-    }
-
-    fn compute_closure(&self) -> BitMatrix<usize, usize> {
-        let mut matrix = BitMatrix::new(self.elements.len(), self.elements.len());
-        let mut changed = true;
-        while changed {
-            changed = false;
-            for edge in &self.edges {
-                // add an edge from S -> T
-                changed |= matrix.insert(edge.source.0, edge.target.0);
-
-                // add all outgoing edges from T into S
-                changed |= matrix.union_rows(edge.target.0, edge.source.0);
-            }
-        }
-        matrix
+        op(&self.closure)
     }
 
     /// Lists all the base edges in the graph: the initial _non-transitive_ set of element
diff --git a/compiler/rustc_data_structures/src/transitive_relation/tests.rs b/compiler/rustc_data_structures/src/transitive_relation/tests.rs
index e1f4c7ee07315..e756c546e41ba 100644
--- a/compiler/rustc_data_structures/src/transitive_relation/tests.rs
+++ b/compiler/rustc_data_structures/src/transitive_relation/tests.rs
@@ -10,9 +10,10 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
 
 #[test]
 fn test_one_step() {
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "b");
     relation.add("a", "c");
+    let relation = relation.freeze();
     assert!(relation.contains("a", "c"));
     assert!(relation.contains("a", "b"));
     assert!(!relation.contains("b", "a"));
@@ -21,7 +22,7 @@ fn test_one_step() {
 
 #[test]
 fn test_many_steps() {
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "b");
     relation.add("a", "c");
     relation.add("a", "f");
@@ -31,6 +32,7 @@ fn test_many_steps() {
     relation.add("b", "e");
 
     relation.add("e", "g");
+    let relation = relation.freeze();
 
     assert!(relation.contains("a", "b"));
     assert!(relation.contains("a", "c"));
@@ -51,9 +53,10 @@ fn mubs_triangle() {
     //      ^
     //      |
     //      b
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "tcx");
     relation.add("b", "tcx");
+    let relation = relation.freeze();
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["tcx"]);
     assert_eq!(relation.parents("a"), vec!["tcx"]);
     assert_eq!(relation.parents("b"), vec!["tcx"]);
@@ -72,7 +75,7 @@ fn mubs_best_choice1() {
     // need the second pare down call to get the right result (after
     // intersection, we have [1, 2], but 2 -> 1).
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("0", "1");
     relation.add("0", "2");
 
@@ -80,6 +83,7 @@ fn mubs_best_choice1() {
 
     relation.add("3", "1");
     relation.add("3", "2");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("0", "3"), vec!["2"]);
     assert_eq!(relation.parents("0"), vec!["2"]);
@@ -99,7 +103,7 @@ fn mubs_best_choice2() {
     // Like the preceding test, but in this case intersection is [2,
     // 1], and hence we rely on the first pare down call.
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("0", "1");
     relation.add("0", "2");
 
@@ -107,6 +111,7 @@ fn mubs_best_choice2() {
 
     relation.add("3", "1");
     relation.add("3", "2");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("0", "3"), vec!["1"]);
     assert_eq!(relation.parents("0"), vec!["1"]);
@@ -118,12 +123,13 @@ fn mubs_best_choice2() {
 fn mubs_no_best_choice() {
     // in this case, the intersection yields [1, 2], and the "pare
     // down" calls find nothing to remove.
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("0", "1");
     relation.add("0", "2");
 
     relation.add("3", "1");
     relation.add("3", "2");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("0", "3"), vec!["1", "2"]);
     assert_eq!(relation.parents("0"), vec!["1", "2"]);
@@ -135,7 +141,7 @@ fn mubs_best_choice_scc() {
     // in this case, 1 and 2 form a cycle; we pick arbitrarily (but
     // consistently).
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("0", "1");
     relation.add("0", "2");
 
@@ -144,6 +150,7 @@ fn mubs_best_choice_scc() {
 
     relation.add("3", "1");
     relation.add("3", "2");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("0", "3"), vec!["1"]);
     assert_eq!(relation.parents("0"), vec!["1"]);
@@ -157,13 +164,14 @@ fn pdub_crisscross() {
     //   /\       |
     // b -> b1 ---+
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "a1");
     relation.add("a", "b1");
     relation.add("b", "a1");
     relation.add("b", "b1");
     relation.add("a1", "x");
     relation.add("b1", "x");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["a1", "b1"]);
     assert_eq!(relation.postdom_upper_bound("a", "b"), Some("x"));
@@ -179,7 +187,7 @@ fn pdub_crisscross_more() {
     //   /\    /\             |
     // b -> b1 -> b2 ---------+
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "a1");
     relation.add("a", "b1");
     relation.add("b", "a1");
@@ -194,6 +202,7 @@ fn pdub_crisscross_more() {
 
     relation.add("a3", "x");
     relation.add("b2", "x");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["a1", "b1"]);
     assert_eq!(relation.minimal_upper_bounds("a1", "b1"), vec!["a2", "b2"]);
@@ -210,11 +219,12 @@ fn pdub_lub() {
     //            |
     // b -> b1 ---+
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "a1");
     relation.add("b", "b1");
     relation.add("a1", "x");
     relation.add("b1", "x");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["x"]);
     assert_eq!(relation.postdom_upper_bound("a", "b"), Some("x"));
@@ -233,10 +243,11 @@ fn mubs_intermediate_node_on_one_side_only() {
     //           b
 
     // "digraph { a -> c -> d; b -> d; }",
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "c");
     relation.add("c", "d");
     relation.add("b", "d");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["d"]);
 }
@@ -252,12 +263,13 @@ fn mubs_scc_1() {
     //           b
 
     // "digraph { a -> c -> d; d -> c; a -> d; b -> d; }",
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "c");
     relation.add("c", "d");
     relation.add("d", "c");
     relation.add("a", "d");
     relation.add("b", "d");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["c"]);
 }
@@ -272,12 +284,13 @@ fn mubs_scc_2() {
     //      +--- b
 
     // "digraph { a -> c -> d; d -> c; b -> d; b -> c; }",
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "c");
     relation.add("c", "d");
     relation.add("d", "c");
     relation.add("b", "d");
     relation.add("b", "c");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["c"]);
 }
@@ -292,13 +305,14 @@ fn mubs_scc_3() {
     //           b ---+
 
     // "digraph { a -> c -> d -> e -> c; b -> d; b -> e; }",
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "c");
     relation.add("c", "d");
     relation.add("d", "e");
     relation.add("e", "c");
     relation.add("b", "d");
     relation.add("b", "e");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["c"]);
 }
@@ -314,13 +328,14 @@ fn mubs_scc_4() {
     //           b ---+
 
     // "digraph { a -> c -> d -> e -> c; a -> d; b -> e; }"
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     relation.add("a", "c");
     relation.add("c", "d");
     relation.add("d", "e");
     relation.add("e", "c");
     relation.add("a", "d");
     relation.add("b", "e");
+    let relation = relation.freeze();
 
     assert_eq!(relation.minimal_upper_bounds("a", "b"), vec!["c"]);
 }
@@ -352,10 +367,11 @@ fn parent() {
         (1, /*->*/ 3),
     ];
 
-    let mut relation = TransitiveRelation::default();
+    let mut relation = TransitiveRelationBuilder::default();
     for (a, b) in pairs {
         relation.add(a, b);
     }
+    let relation = relation.freeze();
 
     let p = relation.postdom_parent(3);
     assert_eq!(p, Some(0));
diff --git a/compiler/rustc_infer/src/infer/free_regions.rs b/compiler/rustc_infer/src/infer/free_regions.rs
index d566634a49203..728d691a2be7d 100644
--- a/compiler/rustc_infer/src/infer/free_regions.rs
+++ b/compiler/rustc_infer/src/infer/free_regions.rs
@@ -27,13 +27,13 @@ impl<'a, 'tcx> RegionRelations<'a, 'tcx> {
     }
 }
 
-#[derive(Clone, Debug, Default)]
+#[derive(Clone, Debug)]
 pub struct FreeRegionMap<'tcx> {
     // Stores the relation `a < b`, where `a` and `b` are regions.
     //
     // Invariant: only free regions like `'x` or `'static` are stored
     // in this relation, not scopes.
-    relation: TransitiveRelation<Region<'tcx>>,
+    pub(crate) relation: TransitiveRelation<Region<'tcx>>,
 }
 
 impl<'tcx> FreeRegionMap<'tcx> {
@@ -45,15 +45,6 @@ impl<'tcx> FreeRegionMap<'tcx> {
         self.relation.is_empty()
     }
 
-    // Record that `'sup:'sub`. Or, put another way, `'sub <= 'sup`.
-    // (with the exception that `'static: 'x` is not notable)
-    pub fn relate_regions(&mut self, sub: Region<'tcx>, sup: Region<'tcx>) {
-        debug!("relate_regions(sub={:?}, sup={:?})", sub, sup);
-        if sub.is_free_or_static() && sup.is_free() {
-            self.relation.add(sub, sup)
-        }
-    }
-
     /// Tests whether `r_a <= r_b`.
     ///
     /// Both regions must meet `is_free_or_static`.
diff --git a/compiler/rustc_infer/src/infer/outlives/env.rs b/compiler/rustc_infer/src/infer/outlives/env.rs
index b2decd64f0fd9..872886da36261 100644
--- a/compiler/rustc_infer/src/infer/outlives/env.rs
+++ b/compiler/rustc_infer/src/infer/outlives/env.rs
@@ -2,6 +2,7 @@ use crate::infer::free_regions::FreeRegionMap;
 use crate::infer::{GenericKind, InferCtxt};
 use crate::traits::query::OutlivesBound;
 use rustc_data_structures::fx::FxIndexSet;
+use rustc_data_structures::transitive_relation::TransitiveRelationBuilder;
 use rustc_middle::ty::{self, ReEarlyBound, ReFree, ReVar, Region};
 
 use super::explicit_outlives_bounds;
@@ -51,23 +52,48 @@ pub struct OutlivesEnvironment<'tcx> {
     region_bound_pairs: RegionBoundPairs<'tcx>,
 }
 
+/// Builder of OutlivesEnvironment.
+struct OutlivesEnvironmentBuilder<'tcx> {
+    param_env: ty::ParamEnv<'tcx>,
+    region_relation: TransitiveRelationBuilder<Region<'tcx>>,
+    region_bound_pairs: RegionBoundPairs<'tcx>,
+}
+
 /// "Region-bound pairs" tracks outlives relations that are known to
 /// be true, either because of explicit where-clauses like `T: 'a` or
 /// because of implied bounds.
 pub type RegionBoundPairs<'tcx> =
     FxIndexSet<ty::OutlivesPredicate<GenericKind<'tcx>, Region<'tcx>>>;
 
-impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
-    pub fn new(param_env: ty::ParamEnv<'tcx>) -> Self {
-        let mut env = OutlivesEnvironment {
+impl<'tcx> OutlivesEnvironment<'tcx> {
+    /// Create a builder using `ParamEnv` and add explicit outlives bounds into it.
+    fn builder(param_env: ty::ParamEnv<'tcx>) -> OutlivesEnvironmentBuilder<'tcx> {
+        let mut builder = OutlivesEnvironmentBuilder {
             param_env,
-            free_region_map: Default::default(),
+            region_relation: Default::default(),
             region_bound_pairs: Default::default(),
         };
 
-        env.add_outlives_bounds(None, explicit_outlives_bounds(param_env));
+        builder.add_outlives_bounds(None, explicit_outlives_bounds(param_env));
 
-        env
+        builder
+    }
+
+    #[inline]
+    /// Create a new `OutlivesEnvironment` without extra outlives bounds.
+    pub fn new(param_env: ty::ParamEnv<'tcx>) -> Self {
+        Self::builder(param_env).build()
+    }
+
+    /// Create a new `OutlivesEnvironment` with extra outlives bounds.
+    pub fn with_bounds<'a>(
+        param_env: ty::ParamEnv<'tcx>,
+        infcx: Option<&InferCtxt<'a, 'tcx>>,
+        extra_bounds: impl IntoIterator<Item = OutlivesBound<'tcx>>,
+    ) -> Self {
+        let mut builder = Self::builder(param_env);
+        builder.add_outlives_bounds(infcx, extra_bounds);
+        builder.build()
     }
 
     /// Borrows current value of the `free_region_map`.
@@ -79,6 +105,17 @@ impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
     pub fn region_bound_pairs(&self) -> &RegionBoundPairs<'tcx> {
         &self.region_bound_pairs
     }
+}
+
+impl<'a, 'tcx> OutlivesEnvironmentBuilder<'tcx> {
+    #[inline]
+    fn build(self) -> OutlivesEnvironment<'tcx> {
+        OutlivesEnvironment {
+            param_env: self.param_env,
+            free_region_map: FreeRegionMap { relation: self.region_relation.freeze() },
+            region_bound_pairs: self.region_bound_pairs,
+        }
+    }
 
     /// Processes outlives bounds that are known to hold, whether from implied or other sources.
     ///
@@ -86,11 +123,8 @@ impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
     /// contain inference variables, it must be supplied, in which
     /// case we will register "givens" on the inference context. (See
     /// `RegionConstraintData`.)
-    pub fn add_outlives_bounds<I>(
-        &mut self,
-        infcx: Option<&InferCtxt<'a, 'tcx>>,
-        outlives_bounds: I,
-    ) where
+    fn add_outlives_bounds<I>(&mut self, infcx: Option<&InferCtxt<'a, 'tcx>>, outlives_bounds: I)
+    where
         I: IntoIterator<Item = OutlivesBound<'tcx>>,
     {
         // Record relationships such as `T:'x` that don't go into the
@@ -122,7 +156,9 @@ impl<'a, 'tcx> OutlivesEnvironment<'tcx> {
                         // system to be more general and to make use
                         // of *every* relationship that arises here,
                         // but presently we do not.)
-                        self.free_region_map.relate_regions(r_a, r_b);
+                        if r_a.is_free_or_static() && r_b.is_free() {
+                            self.region_relation.add(r_a, r_b)
+                        }
                     }
                 }
             }
diff --git a/compiler/rustc_mir_dataflow/src/framework/mod.rs b/compiler/rustc_mir_dataflow/src/framework/mod.rs
index f9fd6c9c56b42..d9aff94fef2f9 100644
--- a/compiler/rustc_mir_dataflow/src/framework/mod.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/mod.rs
@@ -256,6 +256,7 @@ pub trait Analysis<'tcx>: AnalysisDomain<'tcx> {
     ///     .iterate_to_fixpoint()
     ///     .into_results_cursor(body);
     /// ```
+    #[inline]
     fn into_engine<'mir>(
         self,
         tcx: TyCtxt<'tcx>,
@@ -413,7 +414,7 @@ where
     }
 
     /* Extension methods */
-
+    #[inline]
     fn into_engine<'mir>(
         self,
         tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_typeck/src/check/compare_method.rs b/compiler/rustc_typeck/src/check/compare_method.rs
index db82be7a98fc6..dfef924f6993a 100644
--- a/compiler/rustc_typeck/src/check/compare_method.rs
+++ b/compiler/rustc_typeck/src/check/compare_method.rs
@@ -1,6 +1,6 @@
 use super::potentially_plural_count;
-use crate::check::regionck::OutlivesEnvironmentExt;
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
+use crate::outlives::outlives_bounds::InferCtxtExt as _;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
 use rustc_hir as hir;
@@ -401,8 +401,11 @@ fn compare_predicate_entailment<'tcx>(
 
         // Finally, resolve all regions. This catches wily misuses of
         // lifetime parameters.
-        let mut outlives_environment = OutlivesEnvironment::new(param_env);
-        outlives_environment.add_implied_bounds(infcx, wf_tys, impl_m_hir_id);
+        let outlives_environment = OutlivesEnvironment::with_bounds(
+            param_env,
+            Some(infcx),
+            infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
+        );
         infcx.check_region_obligations_and_report_errors(
             impl_m.def_id.expect_local(),
             &outlives_environment,
@@ -1513,8 +1516,10 @@ pub fn check_type_bounds<'tcx>(
 
         // Finally, resolve all regions. This catches wily misuses of
         // lifetime parameters.
-        let mut outlives_environment = OutlivesEnvironment::new(param_env);
-        outlives_environment.add_implied_bounds(&infcx, assumed_wf_types, impl_ty_hir_id);
+        let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_hir_id, assumed_wf_types);
+        let outlives_environment =
+            OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds);
+
         infcx.check_region_obligations_and_report_errors(
             impl_ty.def_id.expect_local(),
             &outlives_environment,
diff --git a/compiler/rustc_typeck/src/check/mod.rs b/compiler/rustc_typeck/src/check/mod.rs
index dfbef544b1d28..fb675212e3ffb 100644
--- a/compiler/rustc_typeck/src/check/mod.rs
+++ b/compiler/rustc_typeck/src/check/mod.rs
@@ -87,7 +87,6 @@ mod op;
 mod pat;
 mod place_op;
 mod region;
-pub mod regionck;
 pub mod rvalue_scopes;
 mod upvar;
 pub mod wfcheck;
diff --git a/compiler/rustc_typeck/src/check/regionck.rs b/compiler/rustc_typeck/src/check/regionck.rs
deleted file mode 100644
index d49a6138f7a02..0000000000000
--- a/compiler/rustc_typeck/src/check/regionck.rs
+++ /dev/null
@@ -1,47 +0,0 @@
-use crate::outlives::outlives_bounds::InferCtxtExt as _;
-use rustc_data_structures::fx::FxHashSet;
-use rustc_hir as hir;
-use rustc_infer::infer::outlives::env::OutlivesEnvironment;
-use rustc_infer::infer::InferCtxt;
-use rustc_middle::ty::Ty;
-
-pub(crate) trait OutlivesEnvironmentExt<'tcx> {
-    fn add_implied_bounds(
-        &mut self,
-        infcx: &InferCtxt<'_, 'tcx>,
-        fn_sig_tys: FxHashSet<Ty<'tcx>>,
-        body_id: hir::HirId,
-    );
-}
-
-impl<'tcx> OutlivesEnvironmentExt<'tcx> for OutlivesEnvironment<'tcx> {
-    /// This method adds "implied bounds" into the outlives environment.
-    /// Implied bounds are outlives relationships that we can deduce
-    /// on the basis that certain types must be well-formed -- these are
-    /// either the types that appear in the function signature or else
-    /// the input types to an impl. For example, if you have a function
-    /// like
-    ///
-    /// ```
-    /// fn foo<'a, 'b, T>(x: &'a &'b [T]) { }
-    /// ```
-    ///
-    /// we can assume in the caller's body that `'b: 'a` and that `T:
-    /// 'b` (and hence, transitively, that `T: 'a`). This method would
-    /// add those assumptions into the outlives-environment.
-    ///
-    /// Tests: `src/test/ui/regions/regions-free-region-ordering-*.rs`
-    #[instrument(level = "debug", skip(self, infcx))]
-    fn add_implied_bounds<'a>(
-        &mut self,
-        infcx: &InferCtxt<'a, 'tcx>,
-        fn_sig_tys: FxHashSet<Ty<'tcx>>,
-        body_id: hir::HirId,
-    ) {
-        for ty in fn_sig_tys {
-            let ty = infcx.resolve_vars_if_possible(ty);
-            let implied_bounds = infcx.implied_outlives_bounds(self.param_env, body_id, ty);
-            self.add_outlives_bounds(Some(infcx), implied_bounds)
-        }
-    }
-}
diff --git a/compiler/rustc_typeck/src/check/wfcheck.rs b/compiler/rustc_typeck/src/check/wfcheck.rs
index 4814aea7afb9e..b4b6fe8eeada3 100644
--- a/compiler/rustc_typeck/src/check/wfcheck.rs
+++ b/compiler/rustc_typeck/src/check/wfcheck.rs
@@ -1,5 +1,5 @@
-use crate::check::regionck::OutlivesEnvironmentExt;
 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
+use crate::outlives::outlives_bounds::InferCtxtExt as _;
 use rustc_ast as ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
@@ -104,8 +104,10 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
             return;
         }
 
-        let mut outlives_environment = OutlivesEnvironment::new(param_env);
-        outlives_environment.add_implied_bounds(infcx, assumed_wf_types, body_id);
+        let implied_bounds = infcx.implied_bounds_tys(param_env, body_id, assumed_wf_types);
+        let outlives_environment =
+            OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
+
         infcx.check_region_obligations_and_report_errors(body_def_id, &outlives_environment);
     })
 }
@@ -694,8 +696,11 @@ fn resolve_regions_with_wf_tys<'tcx>(
     // region constraints get added and solved there and we need to test each
     // call individually.
     tcx.infer_ctxt().enter(|infcx| {
-        let mut outlives_environment = OutlivesEnvironment::new(param_env);
-        outlives_environment.add_implied_bounds(&infcx, wf_tys.clone(), id);
+        let outlives_environment = OutlivesEnvironment::with_bounds(
+            param_env,
+            Some(&infcx),
+            infcx.implied_bounds_tys(param_env, id, wf_tys.clone()),
+        );
         let region_bound_pairs = outlives_environment.region_bound_pairs();
 
         add_constraints(&infcx, region_bound_pairs);
diff --git a/compiler/rustc_typeck/src/impl_wf_check/min_specialization.rs b/compiler/rustc_typeck/src/impl_wf_check/min_specialization.rs
index 97346f0f834c8..6240024d49c74 100644
--- a/compiler/rustc_typeck/src/impl_wf_check/min_specialization.rs
+++ b/compiler/rustc_typeck/src/impl_wf_check/min_specialization.rs
@@ -65,9 +65,9 @@
 //! cause use after frees with purely safe code in the same way as specializing
 //! on traits with methods can.
 
-use crate::check::regionck::OutlivesEnvironmentExt;
 use crate::constrained_generic_params as cgp;
 use crate::errors::SubstsOnOverriddenImpl;
+use crate::outlives::outlives_bounds::InferCtxtExt as _;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -157,8 +157,8 @@ fn get_impl_substs<'tcx>(
             return None;
         }
 
-        let mut outlives_env = OutlivesEnvironment::new(param_env);
-        outlives_env.add_implied_bounds(infcx, assumed_wf_types, impl1_hir_id);
+        let implied_bounds = infcx.implied_bounds_tys(param_env, impl1_hir_id, assumed_wf_types);
+        let outlives_env = OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
         infcx.check_region_obligations_and_report_errors(impl1_def_id, &outlives_env);
         let Ok(impl2_substs) = infcx.fully_resolve(impl2_substs) else {
             let span = tcx.def_span(impl1_def_id);
diff --git a/compiler/rustc_typeck/src/lib.rs b/compiler/rustc_typeck/src/lib.rs
index 8c6fb6a77181d..1ff9c6271316a 100644
--- a/compiler/rustc_typeck/src/lib.rs
+++ b/compiler/rustc_typeck/src/lib.rs
@@ -72,6 +72,7 @@ This API is completely unstable and subject to change.
 #![feature(slice_partition_dedup)]
 #![feature(try_blocks)]
 #![feature(is_some_with)]
+#![feature(type_alias_impl_trait)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_typeck/src/outlives/outlives_bounds.rs b/compiler/rustc_typeck/src/outlives/outlives_bounds.rs
index 229a64650848c..024e20d92234b 100644
--- a/compiler/rustc_typeck/src/outlives/outlives_bounds.rs
+++ b/compiler/rustc_typeck/src/outlives/outlives_bounds.rs
@@ -1,5 +1,7 @@
+use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
-use rustc_middle::ty::{self, Ty};
+use rustc_hir::HirId;
+use rustc_middle::ty::{self, ParamEnv, Ty};
 use rustc_trait_selection::infer::InferCtxt;
 use rustc_trait_selection::traits::query::type_op::{self, TypeOp, TypeOpOutput};
 use rustc_trait_selection::traits::query::NoSolution;
@@ -7,16 +9,24 @@ use rustc_trait_selection::traits::{ObligationCause, TraitEngine, TraitEngineExt
 
 pub use rustc_middle::traits::query::OutlivesBound;
 
-pub trait InferCtxtExt<'tcx> {
+type Bounds<'a, 'tcx: 'a> = impl Iterator<Item = OutlivesBound<'tcx>> + 'a;
+pub trait InferCtxtExt<'a, 'tcx> {
     fn implied_outlives_bounds(
         &self,
         param_env: ty::ParamEnv<'tcx>,
         body_id: hir::HirId,
         ty: Ty<'tcx>,
     ) -> Vec<OutlivesBound<'tcx>>;
+
+    fn implied_bounds_tys(
+        &'a self,
+        param_env: ty::ParamEnv<'tcx>,
+        body_id: hir::HirId,
+        tys: FxHashSet<Ty<'tcx>>,
+    ) -> Bounds<'a, 'tcx>;
 }
 
-impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
+impl<'a, 'cx, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'cx, 'tcx> {
     /// Implied bounds are region relationships that we deduce
     /// automatically. The idea is that (e.g.) a caller must check that a
     /// function's argument types are well-formed immediately before
@@ -87,4 +97,18 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
 
         output
     }
+
+    fn implied_bounds_tys(
+        &'a self,
+        param_env: ParamEnv<'tcx>,
+        body_id: HirId,
+        tys: FxHashSet<Ty<'tcx>>,
+    ) -> Bounds<'a, 'tcx> {
+        tys.into_iter()
+            .map(move |ty| {
+                let ty = self.resolve_vars_if_possible(ty);
+                self.implied_outlives_bounds(param_env, body_id, ty)
+            })
+            .flatten()
+    }
 }