Overhaul `Constraint`.

This commit changes it to store a `Region` instead of a `RegionVid` for the `Var` cases:
- We avoid having to call `Region::new_var` to re-create `Region`s from
  `RegionVid`s in a few places, avoiding the interning process, giving a
  small perf win. (At the cost of the type allowing some invalid
  combinations of values.)
- All the cases now store two `Region`s, so the commit also separates
  the `ConstraintKind` (a new type) from the `sub` and `sup` arguments
  in `Constraint`.

1 files changed, 0 insertions, 1 deletions

diff --git a/compiler/rustc_traits/src/coroutine_witnesses.rs b/compiler/rustc_traits/src/coroutine_witnesses.rs
index 87d17f3e131..8a2a0832ddb 100644
--- a/compiler/rustc_traits/src/coroutine_witnesses.rs
+++ b/compiler/rustc_traits/src/coroutine_witnesses.rs
@@ -70,7 +70,6 @@ fn compute_assumptions<'tcx>(
         let region_constraints = infcx.take_and_reset_region_constraints();
 
         let outlives = make_query_region_constraints(
-            tcx,
             region_obligations,
             &region_constraints,
             region_assumptions,