6 files changed, 55 insertions, 40 deletions
diff --git a/compiler/rustc_ty_utils/src/abi.rs b/compiler/rustc_ty_utils/src/abi.rs
index d644cbccea1..d1197774fe9 100644
--- a/compiler/rustc_ty_utils/src/abi.rs
+++ b/compiler/rustc_ty_utils/src/abi.rs
@@ -254,7 +254,12 @@ fn adjust_for_rust_scalar<'tcx>(
             // The aliasing rules for `Box<T>` are still not decided, but currently we emit
             // `noalias` for it. This can be turned off using an unstable flag.
             // See https://github.com/rust-lang/unsafe-code-guidelines/issues/326
-            let noalias_for_box = cx.tcx.sess.opts.unstable_opts.box_noalias.unwrap_or(true);
+            let noalias_for_box = cx.tcx.sess.opts.unstable_opts.box_noalias;
+
+            // LLVM prior to version 12 had known miscompiles in the presence of noalias attributes
+            // (see #54878), so it was conditionally disabled, but we don't support earlier
+            // versions at all anymore. We still support turning it off using -Zmutable-noalias.
+            let noalias_mut_ref = cx.tcx.sess.opts.unstable_opts.mutable_noalias;
 
             // `&mut` pointer parameters never alias other parameters,
             // or mutable global data
@@ -263,29 +268,21 @@ fn adjust_for_rust_scalar<'tcx>(
             // and can be marked as both `readonly` and `noalias`, as
             // LLVM's definition of `noalias` is based solely on memory
             // dependencies rather than pointer equality
-            //
-            // Due to past miscompiles in LLVM, we apply a separate NoAliasMutRef attribute
-            // for UniqueBorrowed arguments, so that the codegen backend can decide whether
-            // or not to actually emit the attribute. It can also be controlled with the
-            // `-Zmutable-noalias` debugging option.
             let no_alias = match kind {
-                PointerKind::SharedMutable
-                | PointerKind::UniqueBorrowed
-                | PointerKind::UniqueBorrowedPinned => false,
+                PointerKind::SharedMutable | PointerKind::UniqueBorrowedPinned => false,
+                PointerKind::UniqueBorrowed => noalias_mut_ref,
                 PointerKind::UniqueOwned => noalias_for_box,
-                PointerKind::Frozen => !is_return,
+                PointerKind::Frozen => true,
             };
-            if no_alias {
+            // We can never add `noalias` in return position; that LLVM attribute has some very surprising semantics
+            // (see <https://github.com/rust-lang/unsafe-code-guidelines/issues/385#issuecomment-1368055745>).
+            if no_alias && !is_return {
                 attrs.set(ArgAttribute::NoAlias);
             }
 
             if kind == PointerKind::Frozen && !is_return {
                 attrs.set(ArgAttribute::ReadOnly);
             }
-
-            if kind == PointerKind::UniqueBorrowed && !is_return {
-                attrs.set(ArgAttribute::NoAliasMutRef);
-            }
         }
     }
 }
diff --git a/compiler/rustc_ty_utils/src/consts.rs b/compiler/rustc_ty_utils/src/consts.rs
index f8ff31f971b..a9b4e1420ea 100644
--- a/compiler/rustc_ty_utils/src/consts.rs
+++ b/compiler/rustc_ty_utils/src/consts.rs
@@ -267,8 +267,8 @@ struct IsThirPolymorphic<'a, 'tcx> {
     thir: &'a thir::Thir<'tcx>,
 }
 
-fn error<'tcx>(
-    tcx: TyCtxt<'tcx>,
+fn error(
+    tcx: TyCtxt<'_>,
     sub: GenericConstantTooComplexSub,
     root_span: Span,
 ) -> Result<!, ErrorGuaranteed> {
@@ -281,8 +281,8 @@ fn error<'tcx>(
     Err(reported)
 }
 
-fn maybe_supported_error<'tcx>(
-    tcx: TyCtxt<'tcx>,
+fn maybe_supported_error(
+    tcx: TyCtxt<'_>,
     sub: GenericConstantTooComplexSub,
     root_span: Span,
 ) -> Result<!, ErrorGuaranteed> {
@@ -349,10 +349,10 @@ impl<'a, 'tcx> visit::Visitor<'a, 'tcx> for IsThirPolymorphic<'a, 'tcx> {
 }
 
 /// Builds an abstract const, do not use this directly, but use `AbstractConst::new` instead.
-pub fn thir_abstract_const<'tcx>(
-    tcx: TyCtxt<'tcx>,
+pub fn thir_abstract_const(
+    tcx: TyCtxt<'_>,
     def: ty::WithOptConstParam<LocalDefId>,
-) -> Result<Option<ty::Const<'tcx>>, ErrorGuaranteed> {
+) -> Result<Option<ty::Const<'_>>, ErrorGuaranteed> {
     if tcx.features().generic_const_exprs {
         match tcx.def_kind(def.did) {
             // FIXME(generic_const_exprs): We currently only do this for anonymous constants,
diff --git a/compiler/rustc_ty_utils/src/implied_bounds.rs b/compiler/rustc_ty_utils/src/implied_bounds.rs
index f0d8c240ea5..b7a24a22c53 100644
--- a/compiler/rustc_ty_utils/src/implied_bounds.rs
+++ b/compiler/rustc_ty_utils/src/implied_bounds.rs
@@ -6,7 +6,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers { assumed_wf_types, ..*providers };
 }
 
-fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx ty::List<Ty<'tcx>> {
+fn assumed_wf_types(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::List<Ty<'_>> {
     match tcx.def_kind(def_id) {
         DefKind::Fn => {
             let sig = tcx.fn_sig(def_id);
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 2da98d33429..8d46ba320fc 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -194,7 +194,7 @@ fn resolve_associated_item<'tcx>(
                 && trait_item_id != leaf_def.item.def_id
                 && let Some(leaf_def_item) = leaf_def.item.def_id.as_local()
             {
-                tcx.compare_assoc_const_impl_item_with_trait_item((
+                tcx.compare_impl_const((
                     leaf_def_item,
                     trait_item_id,
                 ))?;
diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index c761a4dbe45..6aa016133ca 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -155,17 +155,37 @@ fn layout_of_uncached<'tcx>(
             }
 
             let unsized_part = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
-            let metadata = match unsized_part.kind() {
-                ty::Foreign(..) => {
+
+            let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type() {
+                let metadata_ty = tcx.normalize_erasing_regions(
+                    param_env,
+                    tcx.mk_projection(metadata_def_id, [pointee]),
+                );
+                let metadata_layout = cx.layout_of(metadata_ty)?;
+                // If the metadata is a 1-zst, then the pointer is thin.
+                if metadata_layout.is_zst() && metadata_layout.align.abi.bytes() == 1 {
                     return Ok(tcx.intern_layout(LayoutS::scalar(cx, data_ptr)));
                 }
-                ty::Slice(_) | ty::Str => scalar_unit(Int(dl.ptr_sized_integer(), false)),
-                ty::Dynamic(..) => {
-                    let mut vtable = scalar_unit(Pointer);
-                    vtable.valid_range_mut().start = 1;
-                    vtable
+
+                let Abi::Scalar(metadata) = metadata_layout.abi else {
+                    return Err(LayoutError::Unknown(unsized_part));
+                };
+                metadata
+            } else {
+                match unsized_part.kind() {
+                    ty::Foreign(..) => {
+                        return Ok(tcx.intern_layout(LayoutS::scalar(cx, data_ptr)));
+                    }
+                    ty::Slice(_) | ty::Str => scalar_unit(Int(dl.ptr_sized_integer(), false)),
+                    ty::Dynamic(..) => {
+                        let mut vtable = scalar_unit(Pointer);
+                        vtable.valid_range_mut().start = 1;
+                        vtable
+                    }
+                    _ => {
+                        return Err(LayoutError::Unknown(unsized_part));
+                    }
                 }
-                _ => return Err(LayoutError::Unknown(unsized_part)),
             };
 
             // Effectively a (ptr, meta) tuple.
@@ -489,8 +509,8 @@ enum SavedLocalEligibility {
 // of any variant.
 
 /// Compute the eligibility and assignment of each local.
-fn generator_saved_local_eligibility<'tcx>(
-    info: &GeneratorLayout<'tcx>,
+fn generator_saved_local_eligibility(
+    info: &GeneratorLayout<'_>,
 ) -> (BitSet<GeneratorSavedLocal>, IndexVec<GeneratorSavedLocal, SavedLocalEligibility>) {
     use SavedLocalEligibility::*;
 
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 5279fc69a31..87923ebbe4b 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -2,6 +2,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
+use rustc_session::config::TraitSolver;
 use rustc_trait_selection::traits;
 
 fn sized_constraint_for_ty<'tcx>(
@@ -121,7 +122,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     // are any errors at that point, so outside of type inference you can be
     // sure that this will succeed without errors anyway.
 
-    if tcx.sess.opts.unstable_opts.chalk {
+    if tcx.sess.opts.unstable_opts.trait_solver == TraitSolver::Chalk {
         let environment = well_formed_types_in_env(tcx, def_id);
         predicates.extend(environment);
     }
@@ -161,7 +162,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
                 kind: hir::ImplItemKind::Type(..) | hir::ImplItemKind::Fn(..),
                 ..
             }) => {
-                let parent_hir_id = tcx.hir().get_parent_node(hir_id);
+                let parent_hir_id = tcx.hir().parent_id(hir_id);
                 match tcx.hir().get(parent_hir_id) {
                     hir::Node::Item(hir::Item {
                         kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
@@ -225,10 +226,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
 /// that are assumed to be well-formed (because they come from the environment).
 ///
 /// Used only in chalk mode.
-fn well_formed_types_in_env<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    def_id: DefId,
-) -> &'tcx ty::List<Predicate<'tcx>> {
+fn well_formed_types_in_env(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::List<Predicate<'_>> {
     use rustc_hir::{ForeignItemKind, ImplItemKind, ItemKind, Node, TraitItemKind};
     use rustc_middle::ty::subst::GenericArgKind;