5 files changed, 8 insertions, 17 deletions
diff --git a/compiler/rustc_public/src/mir/body.rs b/compiler/rustc_public/src/mir/body.rs
index 276adacd99e..7bd06fee721 100644
--- a/compiler/rustc_public/src/mir/body.rs
+++ b/compiler/rustc_public/src/mir/body.rs
@@ -836,14 +836,6 @@ pub enum ProjectionElem {
     /// Like an explicit cast from an opaque type to a concrete type, but without
     /// requiring an intermediate variable.
     OpaqueCast(Ty),
-
-    /// A `Subtype(T)` projection is applied to any `StatementKind::Assign` where
-    /// type of lvalue doesn't match the type of rvalue, the primary goal is making subtyping
-    /// explicit during optimizations and codegen.
-    ///
-    /// This projection doesn't impact the runtime behavior of the program except for potentially changing
-    /// some type metadata of the interpreter or codegen backend.
-    Subtype(Ty),
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
@@ -1028,6 +1020,7 @@ pub enum CastKind {
     PtrToPtr,
     FnPtrToPtr,
     Transmute,
+    Subtype,
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
@@ -1089,7 +1082,7 @@ impl ProjectionElem {
                 Self::subslice_ty(ty, *from, *to, *from_end)
             }
             ProjectionElem::Downcast(_) => Ok(ty),
-            ProjectionElem::OpaqueCast(ty) | ProjectionElem::Subtype(ty) => Ok(*ty),
+            ProjectionElem::OpaqueCast(ty) => Ok(*ty),
         }
     }
 
diff --git a/compiler/rustc_public/src/mir/visit.rs b/compiler/rustc_public/src/mir/visit.rs
index 04c4d4d2a82..7563c9ca008 100644
--- a/compiler/rustc_public/src/mir/visit.rs
+++ b/compiler/rustc_public/src/mir/visit.rs
@@ -471,7 +471,6 @@ macro_rules! visit_place_fns {
                 ProjectionElem::Subslice { from: _, to: _, from_end: _ } => {}
                 ProjectionElem::Downcast(_idx) => {}
                 ProjectionElem::OpaqueCast(ty) => self.visit_ty(ty, location),
-                ProjectionElem::Subtype(ty) => self.visit_ty(ty, location),
             }
         }
     };
@@ -512,7 +511,6 @@ macro_rules! visit_place_fns {
                 ProjectionElem::Subslice { from: _, to: _, from_end: _ } => {}
                 ProjectionElem::Downcast(_idx) => {}
                 ProjectionElem::OpaqueCast(ty) => self.visit_ty(ty, location),
-                ProjectionElem::Subtype(ty) => self.visit_ty(ty, location),
             }
         }
     };
diff --git a/compiler/rustc_public/src/unstable/convert/internal.rs b/compiler/rustc_public/src/unstable/convert/internal.rs
index dc9abd88614..064fb6c6803 100644
--- a/compiler/rustc_public/src/unstable/convert/internal.rs
+++ b/compiler/rustc_public/src/unstable/convert/internal.rs
@@ -703,9 +703,6 @@ impl RustcInternal for ProjectionElem {
             ProjectionElem::OpaqueCast(ty) => {
                 rustc_middle::mir::PlaceElem::OpaqueCast(ty.internal(tables, tcx))
             }
-            ProjectionElem::Subtype(ty) => {
-                rustc_middle::mir::PlaceElem::Subtype(ty.internal(tables, tcx))
-            }
         }
     }
 }
diff --git a/compiler/rustc_public/src/unstable/convert/stable/mir.rs b/compiler/rustc_public/src/unstable/convert/stable/mir.rs
index b10af6526ea..62ab91d17ba 100644
--- a/compiler/rustc_public/src/unstable/convert/stable/mir.rs
+++ b/compiler/rustc_public/src/unstable/convert/stable/mir.rs
@@ -356,6 +356,7 @@ impl<'tcx> Stable<'tcx> for mir::CastKind {
             PtrToPtr => crate::mir::CastKind::PtrToPtr,
             FnPtrToPtr => crate::mir::CastKind::FnPtrToPtr,
             Transmute => crate::mir::CastKind::Transmute,
+            Subtype => crate::mir::CastKind::Subtype,
         }
     }
 }
@@ -453,7 +454,6 @@ impl<'tcx> Stable<'tcx> for mir::PlaceElem<'tcx> {
             // found at https://github.com/rust-lang/rust/pull/117517#issuecomment-1811683486
             Downcast(_, idx) => crate::mir::ProjectionElem::Downcast(idx.stable(tables, cx)),
             OpaqueCast(ty) => crate::mir::ProjectionElem::OpaqueCast(ty.stable(tables, cx)),
-            Subtype(ty) => crate::mir::ProjectionElem::Subtype(ty.stable(tables, cx)),
             UnwrapUnsafeBinder(..) => todo!("FIXME(unsafe_binders):"),
         }
     }
diff --git a/compiler/rustc_public/src/unstable/convert/stable/ty.rs b/compiler/rustc_public/src/unstable/convert/stable/ty.rs
index 7f14f878d37..59440e5407f 100644
--- a/compiler/rustc_public/src/unstable/convert/stable/ty.rs
+++ b/compiler/rustc_public/src/unstable/convert/stable/ty.rs
@@ -453,7 +453,10 @@ impl<'tcx> Stable<'tcx> for ty::TyKind<'tcx> {
                 TyKind::Alias(alias_kind.stable(tables, cx), alias_ty.stable(tables, cx))
             }
             ty::Param(param_ty) => TyKind::Param(param_ty.stable(tables, cx)),
-            ty::Bound(debruijn_idx, bound_ty) => {
+            ty::Bound(ty::BoundVarIndexKind::Canonical, _) => {
+                unreachable!()
+            }
+            ty::Bound(ty::BoundVarIndexKind::Bound(debruijn_idx), bound_ty) => {
                 TyKind::Bound(debruijn_idx.as_usize(), bound_ty.stable(tables, cx))
             }
             ty::CoroutineWitness(def_id, args) => TyKind::RigidTy(RigidTy::CoroutineWitness(
@@ -907,7 +910,7 @@ impl<'tcx> Stable<'tcx> for ty::RegionKind<'tcx> {
                 index: early_reg.index,
                 name: early_reg.name.to_string(),
             }),
-            ty::ReBound(db_index, bound_reg) => RegionKind::ReBound(
+            ty::ReBound(ty::BoundVarIndexKind::Bound(db_index), bound_reg) => RegionKind::ReBound(
                 db_index.as_u32(),
                 BoundRegion {
                     var: bound_reg.var.as_u32(),