Do not treat vtable supertraits as distinct when bound with different bound vars

18 files changed, 146 insertions, 115 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/constant.rs b/compiler/rustc_codegen_cranelift/src/constant.rs
index 3e7b81a96b6..05ba53430a8 100644
--- a/compiler/rustc_codegen_cranelift/src/constant.rs
+++ b/compiler/rustc_codegen_cranelift/src/constant.rs
@@ -245,7 +245,10 @@ pub(crate) fn data_id_for_vtable<'tcx>(
     ty: Ty<'tcx>,
     trait_ref: Option<Binder<'tcx, ExistentialTraitRef<'tcx>>>,
 ) -> DataId {
-    let alloc_id = tcx.vtable_allocation((ty, trait_ref));
+    let alloc_id = tcx.vtable_allocation((
+        ty,
+        trait_ref.map(|principal| tcx.instantiate_bound_regions_with_erased(principal)),
+    ));
     data_id_for_alloc_id(cx, module, alloc_id, Mutability::Not)
 }
 
diff --git a/compiler/rustc_codegen_gcc/src/common.rs b/compiler/rustc_codegen_gcc/src/common.rs
index bd5d6ba387c..20a3482aaa2 100644
--- a/compiler/rustc_codegen_gcc/src/common.rs
+++ b/compiler/rustc_codegen_gcc/src/common.rs
@@ -234,7 +234,12 @@ impl<'gcc, 'tcx> ConstCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
                     GlobalAlloc::VTable(ty, dyn_ty) => {
                         let alloc = self
                             .tcx
-                            .global_alloc(self.tcx.vtable_allocation((ty, dyn_ty.principal())))
+                            .global_alloc(self.tcx.vtable_allocation((
+                                ty,
+                                dyn_ty.principal().map(|principal| {
+                                    self.tcx.instantiate_bound_regions_with_erased(principal)
+                                }),
+                            )))
                             .unwrap_memory();
                         let init = const_alloc_to_gcc(self, alloc);
                         self.static_addr_of(init, alloc.inner().align, None)
diff --git a/compiler/rustc_codegen_llvm/src/common.rs b/compiler/rustc_codegen_llvm/src/common.rs
index b4e9b9f44f4..8908ae314b8 100644
--- a/compiler/rustc_codegen_llvm/src/common.rs
+++ b/compiler/rustc_codegen_llvm/src/common.rs
@@ -312,7 +312,12 @@ impl<'ll, 'tcx> ConstCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                     GlobalAlloc::VTable(ty, dyn_ty) => {
                         let alloc = self
                             .tcx
-                            .global_alloc(self.tcx.vtable_allocation((ty, dyn_ty.principal())))
+                            .global_alloc(self.tcx.vtable_allocation((
+                                ty,
+                                dyn_ty.principal().map(|principal| {
+                                    self.tcx.instantiate_bound_regions_with_erased(principal)
+                                }),
+                            )))
                             .unwrap_memory();
                         let init = const_alloc_to_llvm(self, alloc, /*static*/ false);
                         let value = self.static_addr_of(init, alloc.inner().align, None);
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index 8d782a618fc..587cb1bef2b 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -1406,7 +1406,7 @@ fn build_vtable_type_di_node<'ll, 'tcx>(
 
     let vtable_entries = if let Some(poly_trait_ref) = poly_trait_ref {
         let trait_ref = poly_trait_ref.with_self_ty(tcx, ty);
-        let trait_ref = tcx.erase_regions(trait_ref);
+        let trait_ref = tcx.erase_regions(tcx.instantiate_bound_regions_with_erased(trait_ref));
 
         tcx.vtable_entries(trait_ref)
     } else {
diff --git a/compiler/rustc_codegen_ssa/src/meth.rs b/compiler/rustc_codegen_ssa/src/meth.rs
index 64cd4c38937..c51a57be71c 100644
--- a/compiler/rustc_codegen_ssa/src/meth.rs
+++ b/compiler/rustc_codegen_ssa/src/meth.rs
@@ -96,24 +96,28 @@ fn dyn_trait_in_self(ty: Ty<'_>) -> Option<ty::PolyExistentialTraitRef<'_>> {
 pub(crate) fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
     cx: &Cx,
     ty: Ty<'tcx>,
-    trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+    poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
 ) -> Cx::Value {
     let tcx = cx.tcx();
 
     // Check the cache.
-    if let Some(&val) = cx.vtables().borrow().get(&(ty, trait_ref)) {
+    if let Some(&val) = cx.vtables().borrow().get(&(ty, poly_trait_ref)) {
         return val;
     }
 
+    // FIXME(trait_upcasting): Take a non-higher-ranked vtable as arg.
+    let trait_ref =
+        poly_trait_ref.map(|trait_ref| tcx.instantiate_bound_regions_with_erased(trait_ref));
+
     let vtable_alloc_id = tcx.vtable_allocation((ty, trait_ref));
     let vtable_allocation = tcx.global_alloc(vtable_alloc_id).unwrap_memory();
     let vtable_const = cx.const_data_from_alloc(vtable_allocation);
     let align = cx.data_layout().pointer_align.abi;
     let vtable = cx.static_addr_of(vtable_const, align, Some("vtable"));
 
-    cx.apply_vcall_visibility_metadata(ty, trait_ref, vtable);
-    cx.create_vtable_debuginfo(ty, trait_ref, vtable);
-    cx.vtables().borrow_mut().insert((ty, trait_ref), vtable);
+    cx.apply_vcall_visibility_metadata(ty, poly_trait_ref, vtable);
+    cx.create_vtable_debuginfo(ty, poly_trait_ref, vtable);
+    cx.vtables().borrow_mut().insert((ty, poly_trait_ref), vtable);
     vtable
 }
 
diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
index ef3e96784ce..b05efd10e66 100644
--- a/compiler/rustc_const_eval/src/interpret/cast.rs
+++ b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -419,8 +419,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                         self.tcx.supertrait_vtable_slot((src_pointee_ty, dest_pointee_ty));
                     let vtable_entries = self.vtable_entries(data_a.principal(), ty);
                     if let Some(entry_idx) = vptr_entry_idx {
-                        let Some(&ty::VtblEntry::TraitVPtr(upcast_trait_ref)) =
-                            vtable_entries.get(entry_idx)
+                        let Some(&ty::VtblEntry::TraitVPtr(_)) = vtable_entries.get(entry_idx)
                         else {
                             span_bug!(
                                 self.cur_span(),
@@ -429,13 +428,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                                 dest_pointee_ty
                             );
                         };
-                        let erased_trait_ref = upcast_trait_ref
-                            .map_bound(|r| ty::ExistentialTraitRef::erase_self_ty(*self.tcx, r));
-                        assert!(
-                            data_b
-                                .principal()
-                                .is_some_and(|b| self.eq_in_param_env(erased_trait_ref, b))
-                        );
                     } else {
                         // In this case codegen would keep using the old vtable. We don't want to do
                         // that as it has the wrong trait. The reason codegen can do this is that
diff --git a/compiler/rustc_const_eval/src/interpret/traits.rs b/compiler/rustc_const_eval/src/interpret/traits.rs
index af8d618b6b5..4cfaacebfcd 100644
--- a/compiler/rustc_const_eval/src/interpret/traits.rs
+++ b/compiler/rustc_const_eval/src/interpret/traits.rs
@@ -54,7 +54,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     ) -> &'tcx [VtblEntry<'tcx>] {
         if let Some(trait_) = trait_ {
             let trait_ref = trait_.with_self_ty(*self.tcx, dyn_ty);
-            let trait_ref = self.tcx.erase_regions(trait_ref);
+            let trait_ref =
+                self.tcx.erase_regions(self.tcx.instantiate_bound_regions_with_erased(trait_ref));
             self.tcx.vtable_entries(trait_ref)
         } else {
             TyCtxt::COMMON_VTABLE_ENTRIES
diff --git a/compiler/rustc_hir_analysis/src/collect/dump.rs b/compiler/rustc_hir_analysis/src/collect/dump.rs
index d990d824200..4a508fc0cf6 100644
--- a/compiler/rustc_hir_analysis/src/collect/dump.rs
+++ b/compiler/rustc_hir_analysis/src/collect/dump.rs
@@ -123,7 +123,7 @@ pub(crate) fn vtables<'tcx>(tcx: TyCtxt<'tcx>) {
                     );
                     continue;
                 };
-                tcx.vtable_entries(ty::Binder::dummy(trait_ref))
+                tcx.vtable_entries(trait_ref)
             }
             hir::ItemKind::TyAlias(_, _) => {
                 let ty = tcx.type_of(def_id).instantiate_identity();
@@ -149,7 +149,7 @@ pub(crate) fn vtables<'tcx>(tcx: TyCtxt<'tcx>) {
                 };
                 if let Some(principal) = data.principal() {
                     tcx.vtable_entries(
-                        principal.map_bound(|principal| principal.with_self_ty(tcx, ty)),
+                        tcx.instantiate_bound_regions_with_erased(principal).with_self_ty(tcx, ty),
                     )
                 } else {
                     TyCtxt::COMMON_VTABLE_ENTRIES
diff --git a/compiler/rustc_middle/src/query/keys.rs b/compiler/rustc_middle/src/query/keys.rs
index e243425c0b7..03fe0a300c0 100644
--- a/compiler/rustc_middle/src/query/keys.rs
+++ b/compiler/rustc_middle/src/query/keys.rs
@@ -95,7 +95,7 @@ impl<'tcx> Key for mir::interpret::GlobalId<'tcx> {
     }
 }
 
-impl<'tcx> Key for (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>) {
+impl<'tcx> Key for (Ty<'tcx>, Option<ty::ExistentialTraitRef<'tcx>>) {
     type Cache<V> = DefaultCache<Self, V>;
 
     fn default_span(&self, _: TyCtxt<'_>) -> Span {
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index d83bc19a6a2..6b6b4648764 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1437,9 +1437,9 @@ rustc_queries! {
         desc { |tcx| "finding all existential vtable entries for trait `{}`", tcx.def_path_str(key) }
     }
 
-    query vtable_entries(key: ty::PolyTraitRef<'tcx>)
+    query vtable_entries(key: ty::TraitRef<'tcx>)
                         -> &'tcx [ty::VtblEntry<'tcx>] {
-        desc { |tcx| "finding all vtable entries for trait `{}`", tcx.def_path_str(key.def_id()) }
+        desc { |tcx| "finding all vtable entries for trait `{}`", tcx.def_path_str(key.def_id) }
     }
 
     query first_method_vtable_slot(key: ty::TraitRef<'tcx>) -> usize {
@@ -1451,7 +1451,7 @@ rustc_queries! {
             key.1, key.0 }
     }
 
-    query vtable_allocation(key: (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>)) -> mir::interpret::AllocId {
+    query vtable_allocation(key: (Ty<'tcx>, Option<ty::ExistentialTraitRef<'tcx>>)) -> mir::interpret::AllocId {
         desc { |tcx| "vtable const allocation for <{} as {}>",
             key.0,
             key.1.map(|trait_ref| format!("{trait_ref}")).unwrap_or("_".to_owned())
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 0d41a1d7dbf..d0b78a89062 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -855,7 +855,12 @@ where
                     }
 
                     let mk_dyn_vtable = |principal: Option<ty::PolyExistentialTraitRef<'tcx>>| {
-                        let min_count = ty::vtable_min_entries(tcx, principal);
+                        let min_count = ty::vtable_min_entries(
+                            tcx,
+                            principal.map(|principal| {
+                                tcx.instantiate_bound_regions_with_erased(principal)
+                            }),
+                        );
                         Ty::new_imm_ref(
                             tcx,
                             tcx.lifetimes.re_static,
diff --git a/compiler/rustc_middle/src/ty/vtable.rs b/compiler/rustc_middle/src/ty/vtable.rs
index 455bd16ff8c..6c9e0e7c0eb 100644
--- a/compiler/rustc_middle/src/ty/vtable.rs
+++ b/compiler/rustc_middle/src/ty/vtable.rs
@@ -7,7 +7,7 @@ use rustc_type_ir::elaborate;
 use crate::mir::interpret::{
     AllocId, AllocInit, Allocation, CTFE_ALLOC_SALT, Pointer, Scalar, alloc_range,
 };
-use crate::ty::{self, Instance, PolyTraitRef, Ty, TyCtxt};
+use crate::ty::{self, Instance, TraitRef, Ty, TyCtxt};
 
 #[derive(Clone, Copy, PartialEq, HashStable)]
 pub enum VtblEntry<'tcx> {
@@ -22,7 +22,7 @@ pub enum VtblEntry<'tcx> {
     /// dispatchable associated function
     Method(Instance<'tcx>),
     /// pointer to a separate supertrait vtable, can be used by trait upcasting coercion
-    TraitVPtr(PolyTraitRef<'tcx>),
+    TraitVPtr(TraitRef<'tcx>),
 }
 
 impl<'tcx> fmt::Debug for VtblEntry<'tcx> {
@@ -59,7 +59,7 @@ pub const COMMON_VTABLE_ENTRIES_ALIGN: usize = 2;
 // function is an accurate approximation. We verify this when actually computing the vtable below.
 pub(crate) fn vtable_min_entries<'tcx>(
     tcx: TyCtxt<'tcx>,
-    trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+    trait_ref: Option<ty::ExistentialTraitRef<'tcx>>,
 ) -> usize {
     let mut count = TyCtxt::COMMON_VTABLE_ENTRIES.len();
     let Some(trait_ref) = trait_ref else {
@@ -67,7 +67,7 @@ pub(crate) fn vtable_min_entries<'tcx>(
     };
 
     // This includes self in supertraits.
-    for def_id in elaborate::supertrait_def_ids(tcx, trait_ref.def_id()) {
+    for def_id in elaborate::supertrait_def_ids(tcx, trait_ref.def_id) {
         count += tcx.own_existential_vtable_entries(def_id).len();
     }
 
@@ -83,7 +83,7 @@ pub(crate) fn vtable_min_entries<'tcx>(
 /// initial contents.)
 pub(super) fn vtable_allocation_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
-    key: (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
+    key: (Ty<'tcx>, Option<ty::ExistentialTraitRef<'tcx>>),
 ) -> AllocId {
     let (ty, poly_trait_ref) = key;
 
@@ -118,7 +118,7 @@ pub(super) fn vtable_allocation_provider<'tcx>(
 
     for (idx, entry) in vtable_entries.iter().enumerate() {
         let idx: u64 = u64::try_from(idx).unwrap();
-        let scalar = match entry {
+        let scalar = match *entry {
             VtblEntry::MetadataDropInPlace => {
                 if ty.needs_drop(tcx, ty::TypingEnv::fully_monomorphized()) {
                     let instance = ty::Instance::resolve_drop_in_place(tcx, ty);
@@ -134,13 +134,12 @@ pub(super) fn vtable_allocation_provider<'tcx>(
             VtblEntry::Vacant => continue,
             VtblEntry::Method(instance) => {
                 // Prepare the fn ptr we write into the vtable.
-                let fn_alloc_id = tcx.reserve_and_set_fn_alloc(*instance, CTFE_ALLOC_SALT);
+                let fn_alloc_id = tcx.reserve_and_set_fn_alloc(instance, CTFE_ALLOC_SALT);
                 let fn_ptr = Pointer::from(fn_alloc_id);
                 Scalar::from_pointer(fn_ptr, &tcx)
             }
             VtblEntry::TraitVPtr(trait_ref) => {
-                let super_trait_ref = trait_ref
-                    .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
+                let super_trait_ref = ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref);
                 let supertrait_alloc_id = tcx.vtable_allocation((ty, Some(super_trait_ref)));
                 let vptr = Pointer::from(supertrait_alloc_id);
                 Scalar::from_pointer(vptr, &tcx)
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index d53848f7461..150594ab94d 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -1138,11 +1138,12 @@ fn create_mono_items_for_vtable_methods<'tcx>(
         bug!("create_mono_items_for_vtable_methods: {trait_ty:?} not a trait type");
     };
     if let Some(principal) = trait_ty.principal() {
-        let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
-        assert!(!poly_trait_ref.has_escaping_bound_vars());
+        let trait_ref =
+            tcx.instantiate_bound_regions_with_erased(principal.with_self_ty(tcx, impl_ty));
+        assert!(!trait_ref.has_escaping_bound_vars());
 
         // Walk all methods of the trait, including those of its supertraits
-        let entries = tcx.vtable_entries(poly_trait_ref);
+        let entries = tcx.vtable_entries(trait_ref);
         debug!(?entries);
         let methods = entries
             .iter()
@@ -1197,7 +1198,12 @@ fn collect_alloc<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut MonoIt
             }
         }
         GlobalAlloc::VTable(ty, dyn_ty) => {
-            let alloc_id = tcx.vtable_allocation((ty, dyn_ty.principal()));
+            let alloc_id = tcx.vtable_allocation((
+                ty,
+                dyn_ty
+                    .principal()
+                    .map(|principal| tcx.instantiate_bound_regions_with_erased(principal)),
+            ));
             collect_alloc(tcx, alloc_id, output)
         }
     }
diff --git a/compiler/rustc_smir/src/rustc_smir/context.rs b/compiler/rustc_smir/src/rustc_smir/context.rs
index 31c7e6c3eb4..6313fac5aea 100644
--- a/compiler/rustc_smir/src/rustc_smir/context.rs
+++ b/compiler/rustc_smir/src/rustc_smir/context.rs
@@ -746,7 +746,9 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         let tcx = tables.tcx;
         let alloc_id = tables.tcx.vtable_allocation((
             ty.internal(&mut *tables, tcx),
-            trait_ref.internal(&mut *tables, tcx),
+            trait_ref
+                .internal(&mut *tables, tcx)
+                .map(|principal| tcx.instantiate_bound_regions_with_erased(principal)),
         ));
         Some(alloc_id.stable(&mut *tables))
     }
diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
index 72ddf01c791..b23d1da1608 100644
--- a/compiler/rustc_trait_selection/src/traits/vtable.rs
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -2,8 +2,8 @@ use std::fmt::Debug;
 use std::ops::ControlFlow;
 
 use rustc_hir::def_id::DefId;
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::infer::at::ToTrace;
-use rustc_infer::infer::{BoundRegionConversionTime, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
 use rustc_infer::traits::util::PredicateSet;
 use rustc_middle::bug;
@@ -20,7 +20,7 @@ use crate::traits::{ObligationCtxt, impossible_predicates, is_vtable_safe_method
 #[derive(Clone, Debug)]
 pub enum VtblSegment<'tcx> {
     MetadataDSA,
-    TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
+    TraitOwnEntries { trait_ref: ty::TraitRef<'tcx>, emit_vptr: bool },
 }
 
 /// Prepare the segments for a vtable
@@ -28,7 +28,7 @@ pub enum VtblSegment<'tcx> {
 // about our `Self` type here.
 pub fn prepare_vtable_segments<'tcx, T>(
     tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
+    trait_ref: ty::TraitRef<'tcx>,
     segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
 ) -> Option<T> {
     prepare_vtable_segments_inner(tcx, trait_ref, segment_visitor).break_value()
@@ -38,7 +38,7 @@ pub fn prepare_vtable_segments<'tcx, T>(
 /// such that we can use `?` in the body.
 fn prepare_vtable_segments_inner<'tcx, T>(
     tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
+    trait_ref: ty::TraitRef<'tcx>,
     mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
 ) -> ControlFlow<T> {
     // The following constraints holds for the final arrangement.
@@ -91,7 +91,7 @@ fn prepare_vtable_segments_inner<'tcx, T>(
     let mut emit_vptr_on_new_entry = false;
     let mut visited = PredicateSet::new(tcx);
     let predicate = trait_ref.upcast(tcx);
-    let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
+    let mut stack: SmallVec<[(ty::TraitRef<'tcx>, _, _); 5]> =
         smallvec![(trait_ref, emit_vptr_on_new_entry, maybe_iter(None))];
     visited.insert(predicate);
 
@@ -124,10 +124,19 @@ fn prepare_vtable_segments_inner<'tcx, T>(
             let &(inner_most_trait_ref, _, _) = stack.last().unwrap();
 
             let mut direct_super_traits_iter = tcx
-                .explicit_super_predicates_of(inner_most_trait_ref.def_id())
+                .explicit_super_predicates_of(inner_most_trait_ref.def_id)
                 .iter_identity_copied()
                 .filter_map(move |(pred, _)| {
-                    pred.instantiate_supertrait(tcx, inner_most_trait_ref).as_trait_clause()
+                    Some(
+                        tcx.instantiate_bound_regions_with_erased(
+                            pred.instantiate_supertrait(
+                                tcx,
+                                ty::Binder::dummy(inner_most_trait_ref),
+                            )
+                            .as_trait_clause()?,
+                        )
+                        .trait_ref,
+                    )
                 });
 
             // Find an unvisited supertrait
@@ -135,16 +144,11 @@ fn prepare_vtable_segments_inner<'tcx, T>(
                 .find(|&super_trait| visited.insert(super_trait.upcast(tcx)))
             {
                 // Push it to the stack for the next iteration of 'diving_in to pick up
-                Some(unvisited_super_trait) => {
-                    // We're throwing away potential constness of super traits here.
-                    // FIXME: handle ~const super traits
-                    let next_super_trait = unvisited_super_trait.map_bound(|t| t.trait_ref);
-                    stack.push((
-                        next_super_trait,
-                        emit_vptr_on_new_entry,
-                        maybe_iter(Some(direct_super_traits_iter)),
-                    ))
-                }
+                Some(next_super_trait) => stack.push((
+                    next_super_trait,
+                    emit_vptr_on_new_entry,
+                    maybe_iter(Some(direct_super_traits_iter)),
+                )),
 
                 // There are no more unvisited direct super traits, dive-in finished
                 None => break 'diving_in,
@@ -153,8 +157,7 @@ fn prepare_vtable_segments_inner<'tcx, T>(
 
         // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
         while let Some((inner_most_trait_ref, emit_vptr, mut siblings)) = stack.pop() {
-            let has_entries =
-                has_own_existential_vtable_entries(tcx, inner_most_trait_ref.def_id());
+            let has_entries = has_own_existential_vtable_entries(tcx, inner_most_trait_ref.def_id);
 
             segment_visitor(VtblSegment::TraitOwnEntries {
                 trait_ref: inner_most_trait_ref,
@@ -168,11 +171,6 @@ fn prepare_vtable_segments_inner<'tcx, T>(
             if let Some(next_inner_most_trait_ref) =
                 siblings.find(|&sibling| visited.insert(sibling.upcast(tcx)))
             {
-                // We're throwing away potential constness of super traits here.
-                // FIXME: handle ~const super traits
-                let next_inner_most_trait_ref =
-                    next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
-
                 stack.push((next_inner_most_trait_ref, emit_vptr_on_new_entry, siblings));
 
                 // just pushed a new trait onto the stack, so we need to go through its super traits
@@ -229,7 +227,7 @@ fn own_existential_vtable_entries_iter(
 /// that come from `trait_ref`, including its supertraits.
 fn vtable_entries<'tcx>(
     tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
+    trait_ref: ty::TraitRef<'tcx>,
 ) -> &'tcx [VtblEntry<'tcx>] {
     debug!("vtable_entries({:?})", trait_ref);
 
@@ -241,33 +239,26 @@ fn vtable_entries<'tcx>(
                 entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
             }
             VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                let existential_trait_ref = trait_ref
-                    .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
+                let existential_trait_ref = ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref);
 
                 // Lookup the shape of vtable for the trait.
                 let own_existential_entries =
-                    tcx.own_existential_vtable_entries(existential_trait_ref.def_id());
+                    tcx.own_existential_vtable_entries(existential_trait_ref.def_id);
 
                 let own_entries = own_existential_entries.iter().copied().map(|def_id| {
                     debug!("vtable_entries: trait_method={:?}", def_id);
 
                     // The method may have some early-bound lifetimes; add regions for those.
-                    let args = trait_ref.map_bound(|trait_ref| {
+                    // FIXME: Is this normalize needed?
+                    let args = tcx.normalize_erasing_regions(
+                        ty::TypingEnv::fully_monomorphized(),
                         GenericArgs::for_item(tcx, def_id, |param, _| match param.kind {
                             GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
                             GenericParamDefKind::Type { .. }
                             | GenericParamDefKind::Const { .. } => {
                                 trait_ref.args[param.index as usize]
                             }
-                        })
-                    });
-
-                    // The trait type may have higher-ranked lifetimes in it;
-                    // erase them if they appear, so that we get the type
-                    // at some particular call site.
-                    let args = tcx.normalize_erasing_late_bound_regions(
-                        ty::TypingEnv::fully_monomorphized(),
-                        args,
+                        }),
                     );
 
                     // It's possible that the method relies on where-clauses that
@@ -318,10 +309,11 @@ pub(crate) fn first_method_vtable_slot<'tcx>(tcx: TyCtxt<'tcx>, key: ty::TraitRe
     let ty::Dynamic(source, _, _) = *key.self_ty().kind() else {
         bug!();
     };
-    let source_principal =
-        source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self);
+    let source_principal = tcx.instantiate_bound_regions_with_erased(
+        source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self),
+    );
 
-    let target_principal = ty::Binder::dummy(ty::ExistentialTraitRef::erase_self_ty(tcx, key));
+    let target_principal = ty::ExistentialTraitRef::erase_self_ty(tcx, key);
 
     let vtable_segment_callback = {
         let mut vptr_offset = 0;
@@ -333,15 +325,14 @@ pub(crate) fn first_method_vtable_slot<'tcx>(tcx: TyCtxt<'tcx>, key: ty::TraitRe
                 VtblSegment::TraitOwnEntries { trait_ref: vtable_principal, emit_vptr } => {
                     if trait_refs_are_compatible(
                         tcx,
-                        vtable_principal
-                            .map_bound(|t| ty::ExistentialTraitRef::erase_self_ty(tcx, t)),
+                        ty::ExistentialTraitRef::erase_self_ty(tcx, vtable_principal),
                         target_principal,
                     ) {
                         return ControlFlow::Break(vptr_offset);
                     }
 
                     vptr_offset +=
-                        tcx.own_existential_vtable_entries(vtable_principal.def_id()).len();
+                        tcx.own_existential_vtable_entries(vtable_principal.def_id).len();
 
                     if emit_vptr {
                         vptr_offset += 1;
@@ -373,14 +364,15 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
     let ty::Dynamic(target, _, _) = *target.kind() else {
         bug!();
     };
-    let target_principal = target.principal()?;
+    let target_principal = tcx.instantiate_bound_regions_with_erased(target.principal()?);
 
     // Given that we have a target principal, it is a bug for there not to be a source principal.
     let ty::Dynamic(source, _, _) = *source.kind() else {
         bug!();
     };
-    let source_principal =
-        source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self);
+    let source_principal = tcx.instantiate_bound_regions_with_erased(
+        source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self),
+    );
 
     let vtable_segment_callback = {
         let mut vptr_offset = 0;
@@ -391,11 +383,10 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
                 }
                 VtblSegment::TraitOwnEntries { trait_ref: vtable_principal, emit_vptr } => {
                     vptr_offset +=
-                        tcx.own_existential_vtable_entries(vtable_principal.def_id()).len();
+                        tcx.own_existential_vtable_entries(vtable_principal.def_id).len();
                     if trait_refs_are_compatible(
                         tcx,
-                        vtable_principal
-                            .map_bound(|t| ty::ExistentialTraitRef::erase_self_ty(tcx, t)),
+                        ty::ExistentialTraitRef::erase_self_ty(tcx, vtable_principal),
                         target_principal,
                     ) {
                         if emit_vptr {
@@ -419,37 +410,32 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
 
 fn trait_refs_are_compatible<'tcx>(
     tcx: TyCtxt<'tcx>,
-    hr_vtable_principal: ty::PolyExistentialTraitRef<'tcx>,
-    hr_target_principal: ty::PolyExistentialTraitRef<'tcx>,
+    vtable_principal: ty::ExistentialTraitRef<'tcx>,
+    target_principal: ty::ExistentialTraitRef<'tcx>,
 ) -> bool {
-    if hr_vtable_principal.def_id() != hr_target_principal.def_id() {
+    if vtable_principal.def_id != target_principal.def_id {
         return false;
     }
 
     let (infcx, param_env) =
         tcx.infer_ctxt().build_with_typing_env(ty::TypingEnv::fully_monomorphized());
     let ocx = ObligationCtxt::new(&infcx);
-    let hr_source_principal =
-        ocx.normalize(&ObligationCause::dummy(), param_env, hr_vtable_principal);
-    let hr_target_principal =
-        ocx.normalize(&ObligationCause::dummy(), param_env, hr_target_principal);
-    infcx.enter_forall(hr_target_principal, |target_principal| {
-        let source_principal = infcx.instantiate_binder_with_fresh_vars(
-            DUMMY_SP,
-            BoundRegionConversionTime::HigherRankedType,
-            hr_source_principal,
-        );
-        let Ok(()) = ocx.eq_trace(
+    let source_principal = ocx.normalize(&ObligationCause::dummy(), param_env, vtable_principal);
+    let target_principal = ocx.normalize(&ObligationCause::dummy(), param_env, target_principal);
+    let Ok(()) = ocx.eq_trace(
+        &ObligationCause::dummy(),
+        param_env,
+        ToTrace::to_trace(
             &ObligationCause::dummy(),
-            param_env,
-            ToTrace::to_trace(&ObligationCause::dummy(), hr_target_principal, hr_source_principal),
-            target_principal,
-            source_principal,
-        ) else {
-            return false;
-        };
-        ocx.select_all_or_error().is_empty()
-    })
+            ty::Binder::dummy(target_principal),
+            ty::Binder::dummy(source_principal),
+        ),
+        target_principal,
+        source_principal,
+    ) else {
+        return false;
+    };
+    ocx.select_all_or_error().is_empty()
 }
 
 pub(super) fn provide(providers: &mut Providers) {
diff --git a/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder-vtable.stderr b/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder-vtable.stderr
index 1b99be4ab88..4bb7e1bdb6a 100644
--- a/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder-vtable.stderr
+++ b/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder-vtable.stderr
@@ -3,8 +3,6 @@ error: vtable entries: [
            MetadataSize,
            MetadataAlign,
            Method(<dyn for<'a> Trait<&(), &'a ()> as Supertrait<&()>>::_print_numbers - shim(reify)),
-           Method(<dyn for<'a> Trait<&(), &'a ()> as Supertrait<&()>>::_print_numbers - shim(reify)),
-           TraitVPtr(for<'a> <dyn for<'a> Trait<&(), &'a ()> as Supertrait<&'a ()>>),
            Method(<dyn for<'a> Trait<&(), &'a ()> as Trait<&(), &()>>::say_hello - shim(reify)),
        ]
   --> $DIR/multiple-supertraits-modulo-binder-vtable.rs:18:1
diff --git a/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.rs b/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.rs
new file mode 100644
index 00000000000..7bc069f4f44
--- /dev/null
+++ b/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.rs
@@ -0,0 +1,24 @@
+//@ run-pass
+//@ check-run-results
+
+#![feature(trait_upcasting)]
+
+trait Supertrait<T> {
+    fn _print_numbers(&self, mem: &[usize; 100]) {
+        println!("{mem:?}");
+    }
+}
+impl<T> Supertrait<T> for () {}
+
+trait Trait<T, U>: Supertrait<T> + Supertrait<U> {
+    fn say_hello(&self, _: &usize) {
+        println!("Hello!");
+    }
+}
+impl<T, U> Trait<T, U> for () {}
+
+fn main() {
+    (&() as &'static dyn for<'a> Trait<&'static (), &'a ()>
+        as &'static dyn Trait<&'static (), &'static ()>)
+        .say_hello(&0);
+}
diff --git a/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.run.stdout b/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.run.stdout
new file mode 100644
index 00000000000..10ddd6d257e
--- /dev/null
+++ b/tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.run.stdout
@@ -0,0 +1 @@
+Hello!