1 files changed, 27 insertions, 21 deletions

diff --git a/compiler/rustc_infer/src/infer/sub.rs b/compiler/rustc_infer/src/infer/sub.rs
index b27571275..97354ba5d 100644
--- a/compiler/rustc_infer/src/infer/sub.rs
+++ b/compiler/rustc_infer/src/infer/sub.rs
@@ -2,7 +2,6 @@ use super::combine::{CombineFields, RelationDir};
 use super::SubregionOrigin;
 
 use crate::infer::combine::ConstEquateRelation;
-use crate::infer::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::traits::Obligation;
 use rustc_middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::visit::TypeVisitable;
@@ -11,8 +10,8 @@ use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use std::mem;
 
 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
-pub struct Sub<'combine, 'infcx, 'tcx> {
-    fields: &'combine mut CombineFields<'infcx, 'tcx>,
+pub struct Sub<'combine, 'a, 'tcx> {
+    fields: &'combine mut CombineFields<'a, 'tcx>,
     a_is_expected: bool,
 }
 
@@ -129,30 +128,37 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
             (&ty::Opaque(did, ..), _) | (_, &ty::Opaque(did, ..))
                 if self.fields.define_opaque_types && did.is_local() =>
             {
-                let mut generalize = |ty, ty_is_expected| {
-                    let var = infcx.next_ty_var_id_in_universe(
-                        TypeVariableOrigin {
-                            kind: TypeVariableOriginKind::MiscVariable,
-                            span: self.fields.trace.cause.span,
-                        },
-                        ty::UniverseIndex::ROOT,
-                    );
-                    self.fields.instantiate(ty, RelationDir::SubtypeOf, var, ty_is_expected)?;
-                    Ok(infcx.tcx.mk_ty_var(var))
-                };
-                let (a, b) = if self.a_is_expected { (a, b) } else { (b, a) };
-                let (a, b) = match (a.kind(), b.kind()) {
-                    (&ty::Opaque(..), _) => (a, generalize(b, true)?),
-                    (_, &ty::Opaque(..)) => (generalize(a, false)?, b),
-                    _ => unreachable!(),
-                };
                 self.fields.obligations.extend(
                     infcx
-                        .handle_opaque_type(a, b, true, &self.fields.trace.cause, self.param_env())?
+                        .handle_opaque_type(
+                            a,
+                            b,
+                            self.a_is_expected,
+                            &self.fields.trace.cause,
+                            self.param_env(),
+                        )?
                         .obligations,
                 );
                 Ok(a)
             }
+            // Optimization of GeneratorWitness relation since we know that all
+            // free regions are replaced with bound regions during construction.
+            // This greatly speeds up subtyping of GeneratorWitness.
+            (&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
+                let a_types = infcx.tcx.anonymize_bound_vars(a_types);
+                let b_types = infcx.tcx.anonymize_bound_vars(b_types);
+                if a_types.bound_vars() == b_types.bound_vars() {
+                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                        a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
+                    );
+                    for (a, b) in std::iter::zip(a_types, b_types) {
+                        self.relate(a, b)?;
+                    }
+                    Ok(a)
+                } else {
+                    Err(ty::error::TypeError::Sorts(ty::relate::expected_found(self, a, b)))
+                }
+            }
 
             _ => {
                 self.fields.infcx.super_combine_tys(self, a, b)?;