Merge from rustc

author: The rustc-dev-guide Cronjob Bot <github-actions@github.com> 2025-04-19 13:53:12 +0000
committer: The rustc-dev-guide Cronjob Bot <github-actions@github.com> 2025-04-19 13:53:12 +0000
commit: 3b2302ec0d17cbc94ef68b15f0bb6524f8b67f3f (patch)
tree: 05635b943c977eba01cebf3ef78d8a479e555de5 /compiler
parent: a0c64dce0d70d1be54a6fd7b7aa9ed37665ad998 (diff)
parent: a7c39b68616668a45f0afd62849a1da7c8ad2516 (diff)
download: rust-3b2302ec0d17cbc94ef68b15f0bb6524f8b67f3f.tar.gz
rust-3b2302ec0d17cbc94ef68b15f0bb6524f8b67f3f.zip
514 files changed, 8671 insertions, 7539 deletions
diff --git a/compiler/rustc_abi/src/extern_abi.rs b/compiler/rustc_abi/src/extern_abi.rs
index 4d70afd4e0b..55f4845d216 100644
--- a/compiler/rustc_abi/src/extern_abi.rs
+++ b/compiler/rustc_abi/src/extern_abi.rs
@@ -60,7 +60,6 @@ pub enum ExternAbi {
     System {
         unwind: bool,
     },
-    RustIntrinsic,
     RustCall,
     /// *Not* a stable ABI, just directly use the Rust types to describe the ABI for LLVM. Even
     /// normally ABI-compatible Rust types can become ABI-incompatible with this ABI!
@@ -128,7 +127,6 @@ abi_impls! {
             RiscvInterruptS =><= "riscv-interrupt-s",
             RustCall =><= "rust-call",
             RustCold =><= "rust-cold",
-            RustIntrinsic =><= "rust-intrinsic",
             Stdcall { unwind: false } =><= "stdcall",
             Stdcall { unwind: true } =><= "stdcall-unwind",
             System { unwind: false } =><= "system",
@@ -199,7 +197,7 @@ impl ExternAbi {
     /// - are subject to change between compiler versions
     pub fn is_rustic_abi(self) -> bool {
         use ExternAbi::*;
-        matches!(self, Rust | RustCall | RustIntrinsic | RustCold)
+        matches!(self, Rust | RustCall | RustCold)
     }
 
     pub fn supports_varargs(self) -> bool {
diff --git a/compiler/rustc_abi/src/layout.rs b/compiler/rustc_abi/src/layout.rs
index 7bffeaf4cc9..42250aa173b 100644
--- a/compiler/rustc_abi/src/layout.rs
+++ b/compiler/rustc_abi/src/layout.rs
@@ -315,7 +315,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         repr: &ReprOptions,
         variants: &IndexSlice<VariantIdx, IndexVec<FieldIdx, F>>,
         is_enum: bool,
-        is_unsafe_cell: bool,
+        is_special_no_niche: bool,
         scalar_valid_range: (Bound<u128>, Bound<u128>),
         discr_range_of_repr: impl Fn(i128, i128) -> (Integer, bool),
         discriminants: impl Iterator<Item = (VariantIdx, i128)>,
@@ -348,7 +348,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                 repr,
                 variants,
                 is_enum,
-                is_unsafe_cell,
+                is_special_no_niche,
                 scalar_valid_range,
                 always_sized,
                 present_first,
@@ -505,7 +505,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         repr: &ReprOptions,
         variants: &IndexSlice<VariantIdx, IndexVec<FieldIdx, F>>,
         is_enum: bool,
-        is_unsafe_cell: bool,
+        is_special_no_niche: bool,
         scalar_valid_range: (Bound<u128>, Bound<u128>),
         always_sized: bool,
         present_first: VariantIdx,
@@ -524,7 +524,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         let mut st = self.univariant(&variants[v], repr, kind)?;
         st.variants = Variants::Single { index: v };
 
-        if is_unsafe_cell {
+        if is_special_no_niche {
             let hide_niches = |scalar: &mut _| match scalar {
                 Scalar::Initialized { value, valid_range } => {
                     *valid_range = WrappingRange::full(value.size(dl))
diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
index 843d5ca61dd..59b74d29221 100644
--- a/compiler/rustc_abi/src/lib.rs
+++ b/compiler/rustc_abi/src/lib.rs
@@ -1829,7 +1829,7 @@ pub struct PointeeInfo {
     pub safe: Option<PointerKind>,
     /// If `safe` is `Some`, then the pointer is either null or dereferenceable for this many bytes.
     /// On a function argument, "dereferenceable" here means "dereferenceable for the entire duration
-    /// of this function call", i.e. it is UB for the memory that this pointer points to to be freed
+    /// of this function call", i.e. it is UB for the memory that this pointer points to be freed
     /// while this function is still running.
     /// The size can be zero if the pointer is not dereferenceable.
     pub size: Size,
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 97e6879c33e..1532ca77f71 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -120,6 +120,17 @@ impl Path {
         Path { segments: thin_vec![PathSegment::from_ident(ident)], span: ident.span, tokens: None }
     }
 
+    pub fn is_ident(&self, name: Symbol) -> bool {
+        if let [segment] = self.segments.as_ref()
+            && segment.args.is_none()
+            && segment.ident.name == name
+        {
+            true
+        } else {
+            false
+        }
+    }
+
     pub fn is_global(&self) -> bool {
         self.segments.first().is_some_and(|segment| segment.ident.name == kw::PathRoot)
     }
@@ -563,6 +574,7 @@ impl Pat {
     /// This is intended for use by diagnostics.
     pub fn to_ty(&self) -> Option<P<Ty>> {
         let kind = match &self.kind {
+            PatKind::Missing => unreachable!(),
             // In a type expression `_` is an inference variable.
             PatKind::Wild => TyKind::Infer,
             // An IDENT pattern with no binding mode would be valid as path to a type. E.g. `u32`.
@@ -625,7 +637,8 @@ impl Pat {
             | PatKind::Guard(s, _) => s.walk(it),
 
             // These patterns do not contain subpatterns, skip.
-            PatKind::Wild
+            PatKind::Missing
+            | PatKind::Wild
             | PatKind::Rest
             | PatKind::Never
             | PatKind::Expr(_)
@@ -676,6 +689,7 @@ impl Pat {
     /// Return a name suitable for diagnostics.
     pub fn descr(&self) -> Option<String> {
         match &self.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => Some("_".to_string()),
             PatKind::Ident(BindingMode::NONE, ident, None) => Some(format!("{ident}")),
             PatKind::Ref(pat, mutbl) => pat.descr().map(|d| format!("&{}{d}", mutbl.prefix_str())),
@@ -769,6 +783,9 @@ pub enum RangeSyntax {
 // Adding a new variant? Please update `test_pat` in `tests/ui/macros/stringify.rs`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum PatKind {
+    /// A missing pattern, e.g. for an anonymous param in a bare fn like `fn f(u32)`.
+    Missing,
+
     /// Represents a wildcard pattern (`_`).
     Wild,
 
@@ -1169,6 +1186,7 @@ pub enum MacStmtStyle {
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct Local {
     pub id: NodeId,
+    pub super_: Option<Span>,
     pub pat: P<Pat>,
     pub ty: Option<P<Ty>>,
     pub kind: LocalKind,
@@ -3926,7 +3944,7 @@ mod size_asserts {
     static_assert_size!(Item, 144);
     static_assert_size!(ItemKind, 80);
     static_assert_size!(LitKind, 24);
-    static_assert_size!(Local, 80);
+    static_assert_size!(Local, 96);
     static_assert_size!(MetaItemLit, 40);
     static_assert_size!(Param, 40);
     static_assert_size!(Pat, 72);
diff --git a/compiler/rustc_ast/src/ast_traits.rs b/compiler/rustc_ast/src/ast_traits.rs
index c9e2e9911ef..7f98e7ba8a6 100644
--- a/compiler/rustc_ast/src/ast_traits.rs
+++ b/compiler/rustc_ast/src/ast_traits.rs
@@ -6,7 +6,6 @@ use std::fmt;
 use std::marker::PhantomData;
 
 use crate::ptr::P;
-use crate::token::Nonterminal;
 use crate::tokenstream::LazyAttrTokenStream;
 use crate::{
     Arm, AssocItem, AttrItem, AttrKind, AttrVec, Attribute, Block, Crate, Expr, ExprField,
@@ -206,19 +205,6 @@ impl HasTokens for Attribute {
     }
 }
 
-impl HasTokens for Nonterminal {
-    fn tokens(&self) -> Option<&LazyAttrTokenStream> {
-        match self {
-            Nonterminal::NtBlock(block) => block.tokens(),
-        }
-    }
-    fn tokens_mut(&mut self) -> Option<&mut Option<LazyAttrTokenStream>> {
-        match self {
-            Nonterminal::NtBlock(block) => block.tokens_mut(),
-        }
-    }
-}
-
 /// A trait for AST nodes having (or not having) attributes.
 pub trait HasAttrs {
     /// This is `true` if this `HasAttrs` might support 'custom' (proc-macro) inner
diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index 0b65246693d..f104400a572 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -305,8 +305,8 @@ impl MetaItem {
         if let [PathSegment { ident, .. }] = self.path.segments[..] { Some(ident) } else { None }
     }
 
-    pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or_else(Ident::empty).name
+    pub fn name(&self) -> Option<Symbol> {
+        self.ident().map(|ident| ident.name)
     }
 
     pub fn has_name(&self, name: Symbol) -> bool {
@@ -511,13 +511,14 @@ impl MetaItemInner {
         }
     }
 
-    /// For a single-segment meta item, returns its name; otherwise, returns `None`.
+    /// For a single-segment meta item, returns its identifier; otherwise, returns `None`.
     pub fn ident(&self) -> Option<Ident> {
         self.meta_item().and_then(|meta_item| meta_item.ident())
     }
 
-    pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or_else(Ident::empty).name
+    /// For a single-segment meta item, returns its name; otherwise, returns `None`.
+    pub fn name(&self) -> Option<Symbol> {
+        self.ident().map(|ident| ident.name)
     }
 
     /// Returns `true` if this list item is a MetaItem with a name of `name`.
@@ -627,7 +628,7 @@ pub fn mk_doc_comment(
     Attribute { kind: AttrKind::DocComment(comment_kind, data), id: g.mk_attr_id(), style, span }
 }
 
-pub fn mk_attr(
+fn mk_attr(
     g: &AttrIdGenerator,
     style: AttrStyle,
     unsafety: Safety,
@@ -738,9 +739,9 @@ pub trait AttributeExt: Debug {
     fn id(&self) -> AttrId;
 
     /// For a single-segment attribute (i.e., `#[attr]` and not `#[path::atrr]`),
-    /// return the name of the attribute, else return the empty identifier.
-    fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or_else(Ident::empty).name
+    /// return the name of the attribute; otherwise, returns `None`.
+    fn name(&self) -> Option<Symbol> {
+        self.ident().map(|ident| ident.name)
     }
 
     /// Get the meta item list, `#[attr(meta item list)]`
@@ -752,7 +753,7 @@ pub trait AttributeExt: Debug {
     /// Gets the span of the value literal, as string, when using `#[attr = value]`
     fn value_span(&self) -> Option<Span>;
 
-    /// For a single-segment attribute, returns its name; otherwise, returns `None`.
+    /// For a single-segment attribute, returns its ident; otherwise, returns `None`.
     fn ident(&self) -> Option<Ident>;
 
     /// Checks whether the path of this attribute matches the name.
@@ -770,6 +771,11 @@ pub trait AttributeExt: Debug {
         self.ident().map(|x| x.name == name).unwrap_or(false)
     }
 
+    #[inline]
+    fn has_any_name(&self, names: &[Symbol]) -> bool {
+        names.iter().any(|&name| self.has_name(name))
+    }
+
     /// get the span of the entire attribute
     fn span(&self) -> Span;
 
@@ -813,8 +819,8 @@ impl Attribute {
         AttributeExt::id(self)
     }
 
-    pub fn name_or_empty(&self) -> Symbol {
-        AttributeExt::name_or_empty(self)
+    pub fn name(&self) -> Option<Symbol> {
+        AttributeExt::name(self)
     }
 
     pub fn meta_item_list(&self) -> Option<ThinVec<MetaItemInner>> {
@@ -846,6 +852,11 @@ impl Attribute {
         AttributeExt::has_name(self, name)
     }
 
+    #[inline]
+    pub fn has_any_name(&self, names: &[Symbol]) -> bool {
+        AttributeExt::has_any_name(self, names)
+    }
+
     pub fn span(&self) -> Span {
         AttributeExt::span(self)
     }
diff --git a/compiler/rustc_ast/src/expand/autodiff_attrs.rs b/compiler/rustc_ast/src/expand/autodiff_attrs.rs
index f01c781f46c..2f918faaf75 100644
--- a/compiler/rustc_ast/src/expand/autodiff_attrs.rs
+++ b/compiler/rustc_ast/src/expand/autodiff_attrs.rs
@@ -50,8 +50,16 @@ pub enum DiffActivity {
     /// with it.
     Dual,
     /// Forward Mode, Compute derivatives for this input/output and *overwrite* the shadow argument
+    /// with it. It expects the shadow argument to be `width` times larger than the original
+    /// input/output.
+    Dualv,
+    /// Forward Mode, Compute derivatives for this input/output and *overwrite* the shadow argument
     /// with it. Drop the code which updates the original input/output for maximum performance.
     DualOnly,
+    /// Forward Mode, Compute derivatives for this input/output and *overwrite* the shadow argument
+    /// with it. Drop the code which updates the original input/output for maximum performance.
+    /// It expects the shadow argument to be `width` times larger than the original input/output.
+    DualvOnly,
     /// Reverse Mode, Compute derivatives for this &T or *T input and *add* it to the shadow argument.
     Duplicated,
     /// Reverse Mode, Compute derivatives for this &T or *T input and *add* it to the shadow argument.
@@ -59,7 +67,15 @@ pub enum DiffActivity {
     DuplicatedOnly,
     /// All Integers must be Const, but these are used to mark the integer which represents the
     /// length of a slice/vec. This is used for safety checks on slices.
-    FakeActivitySize,
+    /// The integer (if given) specifies the size of the slice element in bytes.
+    FakeActivitySize(Option<u32>),
+}
+
+impl DiffActivity {
+    pub fn is_dual_or_const(&self) -> bool {
+        use DiffActivity::*;
+        matches!(self, |Dual| DualOnly | Dualv | DualvOnly | Const)
+    }
 }
 /// We generate one of these structs for each `#[autodiff(...)]` attribute.
 #[derive(Clone, Eq, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
@@ -92,6 +108,12 @@ pub struct AutoDiffAttrs {
     pub input_activity: Vec<DiffActivity>,
 }
 
+impl AutoDiffAttrs {
+    pub fn has_primal_ret(&self) -> bool {
+        matches!(self.ret_activity, DiffActivity::Active | DiffActivity::Dual)
+    }
+}
+
 impl DiffMode {
     pub fn is_rev(&self) -> bool {
         matches!(self, DiffMode::Reverse)
@@ -125,11 +147,7 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
     match mode {
         DiffMode::Error => false,
         DiffMode::Source => false,
-        DiffMode::Forward => {
-            activity == DiffActivity::Dual
-                || activity == DiffActivity::DualOnly
-                || activity == DiffActivity::Const
-        }
+        DiffMode::Forward => activity.is_dual_or_const(),
         DiffMode::Reverse => {
             activity == DiffActivity::Const
                 || activity == DiffActivity::Active
@@ -147,10 +165,8 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
 pub fn valid_ty_for_activity(ty: &P<Ty>, activity: DiffActivity) -> bool {
     use DiffActivity::*;
     // It's always allowed to mark something as Const, since we won't compute derivatives wrt. it.
-    if matches!(activity, Const) {
-        return true;
-    }
-    if matches!(activity, Dual | DualOnly) {
+    // Dual variants also support all types.
+    if activity.is_dual_or_const() {
         return true;
     }
     // FIXME(ZuseZ4) We should make this more robust to also
@@ -166,9 +182,7 @@ pub fn valid_input_activity(mode: DiffMode, activity: DiffActivity) -> bool {
     return match mode {
         DiffMode::Error => false,
         DiffMode::Source => false,
-        DiffMode::Forward => {
-            matches!(activity, Dual | DualOnly | Const)
-        }
+        DiffMode::Forward => activity.is_dual_or_const(),
         DiffMode::Reverse => {
             matches!(activity, Active | ActiveOnly | Duplicated | DuplicatedOnly | Const)
         }
@@ -183,10 +197,12 @@ impl Display for DiffActivity {
             DiffActivity::Active => write!(f, "Active"),
             DiffActivity::ActiveOnly => write!(f, "ActiveOnly"),
             DiffActivity::Dual => write!(f, "Dual"),
+            DiffActivity::Dualv => write!(f, "Dualv"),
             DiffActivity::DualOnly => write!(f, "DualOnly"),
+            DiffActivity::DualvOnly => write!(f, "DualvOnly"),
             DiffActivity::Duplicated => write!(f, "Duplicated"),
             DiffActivity::DuplicatedOnly => write!(f, "DuplicatedOnly"),
-            DiffActivity::FakeActivitySize => write!(f, "FakeActivitySize"),
+            DiffActivity::FakeActivitySize(s) => write!(f, "FakeActivitySize({:?})", s),
         }
     }
 }
@@ -214,7 +230,9 @@ impl FromStr for DiffActivity {
             "ActiveOnly" => Ok(DiffActivity::ActiveOnly),
             "Const" => Ok(DiffActivity::Const),
             "Dual" => Ok(DiffActivity::Dual),
+            "Dualv" => Ok(DiffActivity::Dualv),
             "DualOnly" => Ok(DiffActivity::DualOnly),
+            "DualvOnly" => Ok(DiffActivity::DualvOnly),
             "Duplicated" => Ok(DiffActivity::Duplicated),
             "DuplicatedOnly" => Ok(DiffActivity::DuplicatedOnly),
             _ => Err(()),
diff --git a/compiler/rustc_ast/src/expand/mod.rs b/compiler/rustc_ast/src/expand/mod.rs
index 04c81629323..323a8fab6d5 100644
--- a/compiler/rustc_ast/src/expand/mod.rs
+++ b/compiler/rustc_ast/src/expand/mod.rs
@@ -13,12 +13,12 @@ pub mod typetree;
 #[derive(Debug, Clone, Encodable, Decodable, HashStable_Generic)]
 pub struct StrippedCfgItem<ModId = DefId> {
     pub parent_module: ModId,
-    pub name: Ident,
+    pub ident: Ident,
     pub cfg: MetaItem,
 }
 
 impl<ModId> StrippedCfgItem<ModId> {
     pub fn map_mod_id<New>(self, f: impl FnOnce(ModId) -> New) -> StrippedCfgItem<New> {
-        StrippedCfgItem { parent_module: f(self.parent_module), name: self.name, cfg: self.cfg }
+        StrippedCfgItem { parent_module: f(self.parent_module), ident: self.ident, cfg: self.cfg }
     }
 }
diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index da510e4967d..294c6c9ba7a 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -6,7 +6,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
     test(attr(deny(warnings)))
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index f7d13acdfc4..6aae2e481a5 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -704,7 +704,8 @@ fn walk_parenthesized_parameter_data<T: MutVisitor>(vis: &mut T, args: &mut Pare
 }
 
 fn walk_local<T: MutVisitor>(vis: &mut T, local: &mut P<Local>) {
-    let Local { id, pat, ty, kind, span, colon_sp, attrs, tokens } = local.deref_mut();
+    let Local { id, super_, pat, ty, kind, span, colon_sp, attrs, tokens } = local.deref_mut();
+    visit_opt(super_, |sp| vis.visit_span(sp));
     vis.visit_id(id);
     visit_attrs(vis, attrs);
     vis.visit_pat(pat);
@@ -843,9 +844,9 @@ fn visit_lazy_tts<T: MutVisitor>(vis: &mut T, lazy_tts: &mut Option<LazyAttrToke
     visit_lazy_tts_opt_mut(vis, lazy_tts.as_mut());
 }
 
-/// Applies ident visitor if it's an ident; applies other visits to interpolated nodes.
-/// In practice the ident part is not actually used by specific visitors right now,
-/// but there's a test below checking that it works.
+/// Applies ident visitor if it's an ident. In practice this is not actually
+/// used by specific visitors right now, but there's a test below checking that
+/// it works.
 // No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
 pub fn visit_token<T: MutVisitor>(vis: &mut T, t: &mut Token) {
     let Token { kind, span } = t;
@@ -863,46 +864,12 @@ pub fn visit_token<T: MutVisitor>(vis: &mut T, t: &mut Token) {
         token::NtLifetime(ident, _is_raw) => {
             vis.visit_ident(ident);
         }
-        token::Interpolated(nt) => {
-            let nt = Arc::make_mut(nt);
-            visit_nonterminal(vis, nt);
-        }
         _ => {}
     }
     vis.visit_span(span);
 }
 
 // No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
-/// Applies the visitor to elements of interpolated nodes.
-//
-// N.B., this can occur only when applying a visitor to partially expanded
-// code, where parsed pieces have gotten implanted ito *other* macro
-// invocations. This is relevant for macro hygiene, but possibly not elsewhere.
-//
-// One problem here occurs because the types for flat_map_item, flat_map_stmt,
-// etc., allow the visitor to return *multiple* items; this is a problem for the
-// nodes here, because they insist on having exactly one piece. One solution
-// would be to mangle the MutVisitor trait to include one-to-many and
-// one-to-one versions of these entry points, but that would probably confuse a
-// lot of people and help very few. Instead, I'm just going to put in dynamic
-// checks. I think the performance impact of this will be pretty much
-// nonexistent. The danger is that someone will apply a `MutVisitor` to a
-// partially expanded node, and will be confused by the fact that their
-// `flat_map_item` or `flat_map_stmt` isn't getting called on `NtItem` or `NtStmt`
-// nodes. Hopefully they'll wind up reading this comment, and doing something
-// appropriate.
-//
-// BTW, design choice: I considered just changing the type of, e.g., `NtItem` to
-// contain multiple items, but decided against it when I looked at
-// `parse_item_or_view_item` and tried to figure out what I would do with
-// multiple items there....
-fn visit_nonterminal<T: MutVisitor>(vis: &mut T, nt: &mut token::Nonterminal) {
-    match nt {
-        token::NtBlock(block) => vis.visit_block(block),
-    }
-}
-
-// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
 fn visit_defaultness<T: MutVisitor>(vis: &mut T, defaultness: &mut Defaultness) {
     match defaultness {
         Defaultness::Default(span) => vis.visit_span(span),
@@ -1587,7 +1554,7 @@ pub fn walk_pat<T: MutVisitor>(vis: &mut T, pat: &mut P<Pat>) {
     vis.visit_id(id);
     match kind {
         PatKind::Err(_guar) => {}
-        PatKind::Wild | PatKind::Rest | PatKind::Never => {}
+        PatKind::Missing | PatKind::Wild | PatKind::Rest | PatKind::Never => {}
         PatKind::Ident(_binding_mode, ident, sub) => {
             vis.visit_ident(ident);
             visit_opt(sub, |sub| vis.visit_pat(sub));
diff --git a/compiler/rustc_ast/src/token.rs b/compiler/rustc_ast/src/token.rs
index d57a369eebf..055481f5d87 100644
--- a/compiler/rustc_ast/src/token.rs
+++ b/compiler/rustc_ast/src/token.rs
@@ -1,13 +1,10 @@
 use std::borrow::Cow;
 use std::fmt;
-use std::sync::Arc;
 
 pub use LitKind::*;
-pub use Nonterminal::*;
 pub use NtExprKind::*;
 pub use NtPatKind::*;
 pub use TokenKind::*;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::edition::Edition;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, kw, sym};
@@ -16,7 +13,6 @@ use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, kw, sym};
 use rustc_span::{Ident, Symbol};
 
 use crate::ast;
-use crate::ptr::P;
 use crate::util::case::Case;
 
 #[derive(Clone, Copy, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
@@ -34,10 +30,6 @@ pub enum InvisibleOrigin {
     // Converted from `proc_macro::Delimiter` in
     // `proc_macro::Delimiter::to_internal`, i.e. returned by a proc macro.
     ProcMacro,
-
-    // Converted from `TokenKind::Interpolated` in
-    // `TokenStream::flatten_token`. Treated similarly to `ProcMacro`.
-    FlattenToken,
 }
 
 impl PartialEq for InvisibleOrigin {
@@ -134,9 +126,7 @@ impl Delimiter {
         match self {
             Delimiter::Parenthesis | Delimiter::Bracket | Delimiter::Brace => false,
             Delimiter::Invisible(InvisibleOrigin::MetaVar(_)) => false,
-            Delimiter::Invisible(InvisibleOrigin::FlattenToken | InvisibleOrigin::ProcMacro) => {
-                true
-            }
+            Delimiter::Invisible(InvisibleOrigin::ProcMacro) => true,
         }
     }
 
@@ -337,9 +327,7 @@ impl From<IdentIsRaw> for bool {
     }
 }
 
-// SAFETY: due to the `Clone` impl below, all fields of all variants other than
-// `Interpolated` must impl `Copy`.
-#[derive(PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
+#[derive(Clone, Copy, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub enum TokenKind {
     /* Expression-operator symbols. */
     /// `=`
@@ -468,21 +456,6 @@ pub enum TokenKind {
     /// the `lifetime` metavariable in the macro's RHS.
     NtLifetime(Ident, IdentIsRaw),
 
-    /// An embedded AST node, as produced by a macro. This only exists for
-    /// historical reasons. We'd like to get rid of it, for multiple reasons.
-    /// - It's conceptually very strange. Saying a token can contain an AST
-    ///   node is like saying, in natural language, that a word can contain a
-    ///   sentence.
-    /// - It requires special handling in a bunch of places in the parser.
-    /// - It prevents `Token` from implementing `Copy`.
-    /// It adds complexity and likely slows things down. Please don't add new
-    /// occurrences of this token kind!
-    ///
-    /// The span in the surrounding `Token` is that of the metavariable in the
-    /// macro's RHS. The span within the Nonterminal is that of the fragment
-    /// passed to the macro at the call site.
-    Interpolated(Arc<Nonterminal>),
-
     /// A doc comment token.
     /// `Symbol` is the doc comment's data excluding its "quotes" (`///`, `/**`, etc)
     /// similarly to symbols in string literal tokens.
@@ -492,20 +465,7 @@ pub enum TokenKind {
     Eof,
 }
 
-impl Clone for TokenKind {
-    fn clone(&self) -> Self {
-        // `TokenKind` would impl `Copy` if it weren't for `Interpolated`. So
-        // for all other variants, this implementation of `clone` is just like
-        // a copy. This is faster than the `derive(Clone)` version which has a
-        // separate path for every variant.
-        match self {
-            Interpolated(nt) => Interpolated(Arc::clone(nt)),
-            _ => unsafe { std::ptr::read(self) },
-        }
-    }
-}
-
-#[derive(Clone, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
+#[derive(Clone, Copy, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub struct Token {
     pub kind: TokenKind,
     pub span: Span,
@@ -600,7 +560,7 @@ impl Token {
             | FatArrow | Pound | Dollar | Question | SingleQuote => true,
 
             OpenDelim(..) | CloseDelim(..) | Literal(..) | DocComment(..) | Ident(..)
-            | NtIdent(..) | Lifetime(..) | NtLifetime(..) | Interpolated(..) | Eof => false,
+            | NtIdent(..) | Lifetime(..) | NtLifetime(..) | Eof => false,
         }
     }
 
@@ -631,7 +591,6 @@ impl Token {
             PathSep                           | // global path
             Lifetime(..)                      | // labeled loop
             Pound                             => true, // expression attributes
-            Interpolated(ref nt) => matches!(&**nt, NtBlock(..)),
             OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(
                 MetaVarKind::Block |
                 MetaVarKind::Expr { .. } |
@@ -703,7 +662,6 @@ impl Token {
         match self.kind {
             OpenDelim(Delimiter::Brace) | Literal(..) | Minus => true,
             Ident(name, IdentIsRaw::No) if name.is_bool_lit() => true,
-            Interpolated(ref nt) => matches!(&**nt, NtBlock(..)),
             OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(
                 MetaVarKind::Expr { .. } | MetaVarKind::Block | MetaVarKind::Literal,
             ))) => true,
@@ -831,31 +789,20 @@ impl Token {
     /// Is this a pre-parsed expression dropped into the token stream
     /// (which happens while parsing the result of macro expansion)?
     pub fn is_metavar_expr(&self) -> bool {
-        #[allow(irrefutable_let_patterns)] // FIXME: temporary
-        if let Interpolated(nt) = &self.kind
-            && let NtBlock(_) = &**nt
-        {
-            true
-        } else if matches!(
+        matches!(
             self.is_metavar_seq(),
-            Some(MetaVarKind::Expr { .. } | MetaVarKind::Literal | MetaVarKind::Path)
-        ) {
-            true
-        } else {
-            matches!(self.is_metavar_seq(), Some(MetaVarKind::Path))
-        }
+            Some(
+                MetaVarKind::Expr { .. }
+                    | MetaVarKind::Literal
+                    | MetaVarKind::Path
+                    | MetaVarKind::Block
+            )
+        )
     }
 
-    /// Is the token an interpolated block (`$b:block`)?
-    pub fn is_whole_block(&self) -> bool {
-        #[allow(irrefutable_let_patterns)] // FIXME: temporary
-        if let Interpolated(nt) = &self.kind
-            && let NtBlock(..) = &**nt
-        {
-            return true;
-        }
-
-        false
+    /// Are we at a block from a metavar (`$b:block`)?
+    pub fn is_metavar_block(&self) -> bool {
+        matches!(self.is_metavar_seq(), Some(MetaVarKind::Block))
     }
 
     /// Returns `true` if the token is either the `mut` or `const` keyword.
@@ -1024,7 +971,7 @@ impl Token {
                 | PercentEq | CaretEq | AndEq | OrEq | ShlEq | ShrEq | At | DotDotDot | DotDotEq
                 | Comma | Semi | PathSep | RArrow | LArrow | FatArrow | Pound | Dollar | Question
                 | OpenDelim(..) | CloseDelim(..) | Literal(..) | Ident(..) | NtIdent(..)
-                | Lifetime(..) | NtLifetime(..) | Interpolated(..) | DocComment(..) | Eof,
+                | Lifetime(..) | NtLifetime(..) | DocComment(..) | Eof,
                 _,
             ) => {
                 return None;
@@ -1063,12 +1010,6 @@ pub enum NtExprKind {
     Expr2021 { inferred: bool },
 }
 
-#[derive(Clone, Encodable, Decodable)]
-/// For interpolation during macro expansion.
-pub enum Nonterminal {
-    NtBlock(P<ast::Block>),
-}
-
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Encodable, Decodable, Hash, HashStable_Generic)]
 pub enum NonterminalKind {
     Item,
@@ -1152,47 +1093,6 @@ impl fmt::Display for NonterminalKind {
     }
 }
 
-impl Nonterminal {
-    pub fn use_span(&self) -> Span {
-        match self {
-            NtBlock(block) => block.span,
-        }
-    }
-
-    pub fn descr(&self) -> &'static str {
-        match self {
-            NtBlock(..) => "block",
-        }
-    }
-}
-
-impl PartialEq for Nonterminal {
-    fn eq(&self, _rhs: &Self) -> bool {
-        // FIXME: Assume that all nonterminals are not equal, we can't compare them
-        // correctly based on data from AST. This will prevent them from matching each other
-        // in macros. The comparison will become possible only when each nonterminal has an
-        // attached token stream from which it was parsed.
-        false
-    }
-}
-
-impl fmt::Debug for Nonterminal {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            NtBlock(..) => f.pad("NtBlock(..)"),
-        }
-    }
-}
-
-impl<CTX> HashStable<CTX> for Nonterminal
-where
-    CTX: crate::HashStableContext,
-{
-    fn hash_stable(&self, _hcx: &mut CTX, _hasher: &mut StableHasher) {
-        panic!("interpolated tokens should not be present in the HIR")
-    }
-}
-
 // Some types are used a lot. Make sure they don't unintentionally get bigger.
 #[cfg(target_pointer_width = "64")]
 mod size_asserts {
@@ -1202,7 +1102,6 @@ mod size_asserts {
     // tidy-alphabetical-start
     static_assert_size!(Lit, 12);
     static_assert_size!(LitKind, 2);
-    static_assert_size!(Nonterminal, 8);
     static_assert_size!(Token, 24);
     static_assert_size!(TokenKind, 16);
     // tidy-alphabetical-end
diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index fb331e74aeb..43d25d18075 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -25,7 +25,7 @@ use rustc_span::{DUMMY_SP, Span, SpanDecoder, SpanEncoder, Symbol, sym};
 
 use crate::ast::AttrStyle;
 use crate::ast_traits::{HasAttrs, HasTokens};
-use crate::token::{self, Delimiter, InvisibleOrigin, Nonterminal, Token, TokenKind};
+use crate::token::{self, Delimiter, Token, TokenKind};
 use crate::{AttrVec, Attribute};
 
 /// Part of a `TokenStream`.
@@ -305,11 +305,6 @@ pub struct AttrsTarget {
 }
 
 /// A `TokenStream` is an abstract sequence of tokens, organized into [`TokenTree`]s.
-///
-/// The goal is for procedural macros to work with `TokenStream`s and `TokenTree`s
-/// instead of a representation of the abstract syntax tree.
-/// Today's `TokenTree`s can still contain AST via `token::Interpolated` for
-/// backwards compatibility.
 #[derive(Clone, Debug, Default, Encodable, Decodable)]
 pub struct TokenStream(pub(crate) Arc<Vec<TokenTree>>);
 
@@ -476,61 +471,6 @@ impl TokenStream {
         TokenStream::new(tts)
     }
 
-    pub fn from_nonterminal_ast(nt: &Nonterminal) -> TokenStream {
-        match nt {
-            Nonterminal::NtBlock(block) => TokenStream::from_ast(block),
-        }
-    }
-
-    fn flatten_token(token: &Token, spacing: Spacing) -> TokenTree {
-        match token.kind {
-            token::NtIdent(ident, is_raw) => {
-                TokenTree::Token(Token::new(token::Ident(ident.name, is_raw), ident.span), spacing)
-            }
-            token::NtLifetime(ident, is_raw) => TokenTree::Delimited(
-                DelimSpan::from_single(token.span),
-                DelimSpacing::new(Spacing::JointHidden, spacing),
-                Delimiter::Invisible(InvisibleOrigin::FlattenToken),
-                TokenStream::token_alone(token::Lifetime(ident.name, is_raw), ident.span),
-            ),
-            token::Interpolated(ref nt) => TokenTree::Delimited(
-                DelimSpan::from_single(token.span),
-                DelimSpacing::new(Spacing::JointHidden, spacing),
-                Delimiter::Invisible(InvisibleOrigin::FlattenToken),
-                TokenStream::from_nonterminal_ast(&nt).flattened(),
-            ),
-            _ => TokenTree::Token(token.clone(), spacing),
-        }
-    }
-
-    fn flatten_token_tree(tree: &TokenTree) -> TokenTree {
-        match tree {
-            TokenTree::Token(token, spacing) => TokenStream::flatten_token(token, *spacing),
-            TokenTree::Delimited(span, spacing, delim, tts) => {
-                TokenTree::Delimited(*span, *spacing, *delim, tts.flattened())
-            }
-        }
-    }
-
-    #[must_use]
-    pub fn flattened(&self) -> TokenStream {
-        fn can_skip(stream: &TokenStream) -> bool {
-            stream.iter().all(|tree| match tree {
-                TokenTree::Token(token, _) => !matches!(
-                    token.kind,
-                    token::NtIdent(..) | token::NtLifetime(..) | token::Interpolated(..)
-                ),
-                TokenTree::Delimited(.., inner) => can_skip(inner),
-            })
-        }
-
-        if can_skip(self) {
-            return self.clone();
-        }
-
-        self.iter().map(|tree| TokenStream::flatten_token_tree(tree)).collect()
-    }
-
     // If `vec` is not empty, try to glue `tt` onto its last token. The return
     // value indicates if gluing took place.
     fn try_glue_to_last(vec: &mut Vec<TokenTree>, tt: &TokenTree) -> bool {
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 1ef92ff8898..79193fcec63 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -323,7 +323,7 @@ pub fn walk_crate<'a, V: Visitor<'a>>(visitor: &mut V, krate: &'a Crate) -> V::R
 }
 
 pub fn walk_local<'a, V: Visitor<'a>>(visitor: &mut V, local: &'a Local) -> V::Result {
-    let Local { id: _, pat, ty, kind, span: _, colon_sp: _, attrs, tokens: _ } = local;
+    let Local { id: _, super_: _, pat, ty, kind, span: _, colon_sp: _, attrs, tokens: _ } = local;
     walk_list!(visitor, visit_attribute, attrs);
     try_visit!(visitor.visit_pat(pat));
     visit_opt!(visitor, visit_ty, ty);
@@ -750,7 +750,7 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) -> V::Res
             try_visit!(visitor.visit_pat(subpattern));
             try_visit!(visitor.visit_expr(guard_condition));
         }
-        PatKind::Wild | PatKind::Rest | PatKind::Never => {}
+        PatKind::Missing | PatKind::Wild | PatKind::Rest | PatKind::Never => {}
         PatKind::Err(_guar) => {}
         PatKind::Tuple(elems) | PatKind::Slice(elems) | PatKind::Or(elems) => {
             walk_list!(visitor, visit_pat, elems);
diff --git a/compiler/rustc_ast_lowering/src/block.rs b/compiler/rustc_ast_lowering/src/block.rs
index 1d9ca6bb9c8..c3222b79e55 100644
--- a/compiler/rustc_ast_lowering/src/block.rs
+++ b/compiler/rustc_ast_lowering/src/block.rs
@@ -95,6 +95,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn lower_local(&mut self, l: &Local) -> &'hir hir::LetStmt<'hir> {
         // Let statements are allowed to have impl trait in bindings.
+        let super_ = l.super_;
         let ty = l.ty.as_ref().map(|t| {
             self.lower_ty(t, self.impl_trait_in_bindings_ctxt(ImplTraitPosition::Variable))
         });
@@ -109,7 +110,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let span = self.lower_span(l.span);
         let source = hir::LocalSource::Normal;
         self.lower_attrs(hir_id, &l.attrs, l.span);
-        self.arena.alloc(hir::LetStmt { hir_id, ty, pat, init, els, span, source })
+        self.arena.alloc(hir::LetStmt { hir_id, super_, ty, pat, init, els, span, source })
     }
 
     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
diff --git a/compiler/rustc_ast_lowering/src/delegation.rs b/compiler/rustc_ast_lowering/src/delegation.rs
index 9899ee03a51..93c627f64c9 100644
--- a/compiler/rustc_ast_lowering/src/delegation.rs
+++ b/compiler/rustc_ast_lowering/src/delegation.rs
@@ -47,7 +47,7 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def_id::DefId;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{Asyncness, ResolverAstLowering};
-use rustc_span::{Ident, Span};
+use rustc_span::{Ident, Span, Symbol};
 use {rustc_ast as ast, rustc_hir as hir};
 
 use super::{GenericArgsMode, ImplTraitContext, LoweringContext, ParamMode};
@@ -85,7 +85,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     .delegation_fn_sigs
                     .get(&local_def_id)
                     .is_some_and(|sig| sig.has_self),
-                None => self.tcx.associated_item(def_id).fn_has_self_parameter,
+                None => self.tcx.associated_item(def_id).is_method(),
             },
             _ => span_bug!(span, "unexpected DefKind for delegation item"),
         }
@@ -234,12 +234,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         hir::FnSig { decl, header, span }
     }
 
-    fn generate_param(&mut self, span: Span) -> (hir::Param<'hir>, NodeId) {
+    fn generate_param(&mut self, idx: usize, span: Span) -> (hir::Param<'hir>, NodeId) {
         let pat_node_id = self.next_node_id();
         let pat_id = self.lower_node_id(pat_node_id);
+        let ident = Ident::with_dummy_span(Symbol::intern(&format!("arg{idx}")));
         let pat = self.arena.alloc(hir::Pat {
             hir_id: pat_id,
-            kind: hir::PatKind::Binding(hir::BindingMode::NONE, pat_id, Ident::empty(), None),
+            kind: hir::PatKind::Binding(hir::BindingMode::NONE, pat_id, ident, None),
             span,
             default_binding_modes: false,
         });
@@ -247,9 +248,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
         (hir::Param { hir_id: self.next_id(), pat, ty_span: span, span }, pat_node_id)
     }
 
-    fn generate_arg(&mut self, param_id: HirId, span: Span) -> hir::Expr<'hir> {
+    fn generate_arg(&mut self, idx: usize, param_id: HirId, span: Span) -> hir::Expr<'hir> {
         let segments = self.arena.alloc_from_iter(iter::once(hir::PathSegment {
-            ident: Ident::empty(),
+            ident: Ident::with_dummy_span(Symbol::intern(&format!("arg{idx}"))),
             hir_id: self.next_id(),
             res: Res::Local(param_id),
             args: None,
@@ -273,7 +274,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let mut args: Vec<hir::Expr<'_>> = Vec::with_capacity(param_count);
 
             for idx in 0..param_count {
-                let (param, pat_node_id) = this.generate_param(span);
+                let (param, pat_node_id) = this.generate_param(idx, span);
                 parameters.push(param);
 
                 let arg = if let Some(block) = block
@@ -289,7 +290,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     this.ident_and_label_to_local_id.insert(pat_node_id, param.pat.hir_id.local_id);
                     this.lower_target_expr(&block)
                 } else {
-                    this.generate_arg(param.pat.hir_id, span)
+                    this.generate_arg(idx, param.pat.hir_id, span)
                 };
                 args.push(arg);
             }
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index df4fd2ef52f..8e1a3cd1435 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -399,12 +399,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         expr: &'hir hir::Expr<'hir>,
         span: Span,
-        check_ident: Ident,
-        check_hir_id: HirId,
+        cond_ident: Ident,
+        cond_hir_id: HirId,
     ) -> &'hir hir::Expr<'hir> {
-        let checker_fn = self.expr_ident(span, check_ident, check_hir_id);
-        let span = self.mark_span_with_reason(DesugaringKind::Contract, span, None);
-        self.expr_call(span, checker_fn, std::slice::from_ref(expr))
+        let cond_fn = self.expr_ident(span, cond_ident, cond_hir_id);
+        let call_expr = self.expr_call_lang_item_fn_mut(
+            span,
+            hir::LangItem::ContractCheckEnsures,
+            arena_vec![self; *cond_fn, *expr],
+        );
+        self.arena.alloc(call_expr)
     }
 
     pub(crate) fn lower_const_block(&mut self, c: &AnonConst) -> hir::ConstBlock {
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 958a6917dff..fc32c4efce5 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -645,7 +645,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         (
                             // Disallow `impl Trait` in foreign items.
                             this.lower_fn_decl(fdec, i.id, sig.span, FnDeclKind::ExternFn, None),
-                            this.lower_fn_params_to_names(fdec),
+                            this.lower_fn_params_to_idents(fdec),
                         )
                     });
 
@@ -833,7 +833,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }) => {
                 // FIXME(contracts): Deny contract here since it won't apply to
                 // any impl method or callees.
-                let names = self.lower_fn_params_to_names(&sig.decl);
+                let idents = self.lower_fn_params_to_idents(&sig.decl);
                 let (generics, sig) = self.lower_method_sig(
                     generics,
                     sig,
@@ -851,7 +851,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 (
                     *ident,
                     generics,
-                    hir::TraitItemKind::Fn(sig, hir::TraitFn::Required(names)),
+                    hir::TraitItemKind::Fn(sig, hir::TraitFn::Required(idents)),
                     false,
                 )
             }
@@ -1206,8 +1206,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let precond = if let Some(req) = &contract.requires {
                     // Lower the precondition check intrinsic.
                     let lowered_req = this.lower_expr_mut(&req);
+                    let req_span = this.mark_span_with_reason(
+                        DesugaringKind::Contract,
+                        lowered_req.span,
+                        None,
+                    );
                     let precond = this.expr_call_lang_item_fn_mut(
-                        req.span,
+                        req_span,
                         hir::LangItem::ContractCheckRequires,
                         &*arena_vec![this; lowered_req],
                     );
@@ -1217,6 +1222,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 };
                 let (postcond, body) = if let Some(ens) = &contract.ensures {
                     let ens_span = this.lower_span(ens.span);
+                    let ens_span =
+                        this.mark_span_with_reason(DesugaringKind::Contract, ens_span, None);
                     // Set up the postcondition `let` statement.
                     let check_ident: Ident =
                         Ident::from_str_and_span("__ensures_checker", ens_span);
@@ -1303,7 +1310,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             // create a fake body so that the entire rest of the compiler doesn't have to deal with
             // this as a special case.
             return self.lower_fn_body(decl, contract, |this| {
-                if attrs.iter().any(|a| a.name_or_empty() == sym::rustc_intrinsic) {
+                if attrs.iter().any(|a| a.has_name(sym::rustc_intrinsic)) {
                     let span = this.lower_span(span);
                     let empty_block = hir::Block {
                         hir_id: this.next_id(),
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index d5d6dcd8d63..c40987541f4 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -32,7 +32,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(rust_logo)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
@@ -917,7 +916,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_delim_args(&self, args: &DelimArgs) -> DelimArgs {
-        DelimArgs { dspan: args.dspan, delim: args.delim, tokens: args.tokens.flattened() }
+        DelimArgs { dspan: args.dspan, delim: args.delim, tokens: args.tokens.clone() }
     }
 
     /// Lower an associated item constraint.
@@ -1247,7 +1246,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     safety: self.lower_safety(f.safety, hir::Safety::Safe),
                     abi: self.lower_extern(f.ext),
                     decl: self.lower_fn_decl(&f.decl, t.id, t.span, FnDeclKind::Pointer, None),
-                    param_names: self.lower_fn_params_to_names(&f.decl),
+                    param_idents: self.lower_fn_params_to_idents(&f.decl),
                 }))
             }
             TyKind::UnsafeBinder(f) => {
@@ -1494,20 +1493,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         }))
     }
 
-    fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Option<Ident>] {
+    fn lower_fn_params_to_idents(&mut self, decl: &FnDecl) -> &'hir [Option<Ident>] {
         self.arena.alloc_from_iter(decl.inputs.iter().map(|param| match param.pat.kind {
-            PatKind::Ident(_, ident, _) => {
-                if ident.name != kw::Empty {
-                    Some(self.lower_ident(ident))
-                } else {
-                    None
-                }
-            }
+            PatKind::Missing => None,
+            PatKind::Ident(_, ident, _) => Some(self.lower_ident(ident)),
             PatKind::Wild => Some(Ident::new(kw::Underscore, self.lower_span(param.pat.span))),
             _ => {
                 self.dcx().span_delayed_bug(
                     param.pat.span,
-                    "non-ident/wild param pat must trigger an error",
+                    "non-missing/ident/wild param pat must trigger an error",
                 );
                 None
             }
@@ -1771,24 +1765,23 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         ident: Ident,
         is_anon_in_path: IsAnonInPath,
     ) -> &'hir hir::Lifetime {
-        debug_assert_ne!(ident.name, kw::Empty);
         let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
         let res = match res {
-            LifetimeRes::Param { param, .. } => hir::LifetimeName::Param(param),
+            LifetimeRes::Param { param, .. } => hir::LifetimeKind::Param(param),
             LifetimeRes::Fresh { param, .. } => {
                 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
                 let param = self.local_def_id(param);
-                hir::LifetimeName::Param(param)
+                hir::LifetimeKind::Param(param)
             }
             LifetimeRes::Infer => {
                 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
-                hir::LifetimeName::Infer
+                hir::LifetimeKind::Infer
             }
             LifetimeRes::Static { .. } => {
                 debug_assert!(matches!(ident.name, kw::StaticLifetime | kw::UnderscoreLifetime));
-                hir::LifetimeName::Static
+                hir::LifetimeKind::Static
             }
-            LifetimeRes::Error => hir::LifetimeName::Error,
+            LifetimeRes::Error => hir::LifetimeKind::Error,
             LifetimeRes::ElidedAnchor { .. } => {
                 panic!("Unexpected `ElidedAnchar` {:?} at {:?}", ident, ident.span);
             }
@@ -2039,7 +2032,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 
     fn lower_array_length_to_const_arg(&mut self, c: &AnonConst) -> &'hir hir::ConstArg<'hir> {
-        match c.value.kind {
+        // We cannot just match on `ExprKind::Underscore` as `(_)` is represented as
+        // `ExprKind::Paren(ExprKind::Underscore)` and should also be lowered to `GenericArg::Infer`
+        match c.value.peel_parens().kind {
             ExprKind::Underscore => {
                 if !self.tcx.features().generic_arg_infer() {
                     feature_err(
@@ -2223,6 +2218,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.attrs.insert(hir_id.local_id, a);
         }
         let local = hir::LetStmt {
+            super_: None,
             hir_id,
             init,
             pat,
@@ -2392,7 +2388,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let r = hir::Lifetime::new(
             self.next_id(),
             Ident::new(kw::UnderscoreLifetime, self.lower_span(span)),
-            hir::LifetimeName::ImplicitObjectLifetimeDefault,
+            hir::LifetimeKind::ImplicitObjectLifetimeDefault,
             IsAnonInPath::No,
         );
         debug!("elided_dyn_bound: r={:?}", r);
diff --git a/compiler/rustc_ast_lowering/src/pat.rs b/compiler/rustc_ast_lowering/src/pat.rs
index 07cc64a1358..f94d788a9b0 100644
--- a/compiler/rustc_ast_lowering/src/pat.rs
+++ b/compiler/rustc_ast_lowering/src/pat.rs
@@ -26,6 +26,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             let pat_hir_id = self.lower_node_id(pattern.id);
             let node = loop {
                 match &pattern.kind {
+                    PatKind::Missing => break hir::PatKind::Missing,
                     PatKind::Wild => break hir::PatKind::Wild,
                     PatKind::Never => break hir::PatKind::Never,
                     PatKind::Ident(binding_mode, ident, sub) => {
diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index c464c159c34..0bd65aec10f 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -448,8 +448,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         generic_args.args.insert_many(
             0,
-            (start.as_u32()..end.as_u32()).map(|i| {
-                let id = NodeId::from_u32(i);
+            (start..end).map(|id| {
                 let l = self.lower_lifetime_anon_in_path(id, elided_lifetime_span);
                 GenericArg::Lifetime(l)
             }),
diff --git a/compiler/rustc_ast_lowering/src/stability.rs b/compiler/rustc_ast_lowering/src/stability.rs
index a2004bbb39f..eb052ba1c6d 100644
--- a/compiler/rustc_ast_lowering/src/stability.rs
+++ b/compiler/rustc_ast_lowering/src/stability.rs
@@ -79,10 +79,6 @@ pub fn extern_abi_stability(abi: ExternAbi) -> Result<(), UnstableAbi> {
         | ExternAbi::SysV64 { .. }
         | ExternAbi::System { .. }
         | ExternAbi::EfiApi => Ok(()),
-        // implementation details
-        ExternAbi::RustIntrinsic => {
-            Err(UnstableAbi { abi, feature: sym::intrinsics, explain: GateReason::ImplDetail })
-        }
         ExternAbi::Unadjusted => {
             Err(UnstableAbi { abi, feature: sym::abi_unadjusted, explain: GateReason::ImplDetail })
         }
diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index 25944392a52..80754a8f65a 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -79,6 +79,10 @@ ast_passes_extern_types_cannot = `type`s inside `extern` blocks cannot have {$de
     .suggestion = remove the {$remove_descr}
     .label = `extern` block begins here
 
+ast_passes_extern_without_abi = `extern` declarations without an explicit ABI are disallowed
+    .suggestion = specify an ABI
+    .help = prior to Rust 2024, a default ABI was inferred
+
 ast_passes_feature_on_non_nightly = `#![feature]` may not be used on the {$channel} release channel
     .suggestion = remove the attribute
     .stable_since = the feature `{$name}` has been stable since `{$since}` and no longer requires an attribute to enable
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 9916de8b7b1..1feb3e9bf9b 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -244,7 +244,7 @@ impl<'a> AstValidator<'a> {
     fn check_decl_no_pat(decl: &FnDecl, mut report_err: impl FnMut(Span, Option<Ident>, bool)) {
         for Param { pat, .. } in &decl.inputs {
             match pat.kind {
-                PatKind::Ident(BindingMode::NONE, _, None) | PatKind::Wild => {}
+                PatKind::Missing | PatKind::Ident(BindingMode::NONE, _, None) | PatKind::Wild => {}
                 PatKind::Ident(BindingMode::MUT, ident, None) => {
                     report_err(pat.span, Some(ident), true)
                 }
@@ -347,7 +347,7 @@ impl<'a> AstValidator<'a> {
                     sym::forbid,
                     sym::warn,
                 ];
-                !arr.contains(&attr.name_or_empty()) && rustc_attr_parsing::is_builtin_attr(*attr)
+                !attr.has_any_name(&arr) && rustc_attr_parsing::is_builtin_attr(*attr)
             })
             .for_each(|attr| {
                 if attr.is_doc_comment() {
@@ -684,7 +684,7 @@ impl<'a> AstValidator<'a> {
                     self.dcx().emit_err(errors::PatternFnPointer { span });
                 });
                 if let Extern::Implicit(extern_span) = bfty.ext {
-                    self.maybe_lint_missing_abi(extern_span, ty.id);
+                    self.handle_missing_abi(extern_span, ty.id);
                 }
             }
             TyKind::TraitObject(bounds, ..) => {
@@ -717,10 +717,12 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId) {
+    fn handle_missing_abi(&mut self, span: Span, id: NodeId) {
         // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
         // call site which do not have a macro backtrace. See #61963.
-        if self
+        if span.edition().at_least_edition_future() && self.features.explicit_extern_abis() {
+            self.dcx().emit_err(errors::MissingAbi { span });
+        } else if self
             .sess
             .source_map()
             .span_to_snippet(span)
@@ -945,8 +947,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 self.visit_attrs_vis_ident(&item.attrs, &item.vis, ident);
                 self.check_defaultness(item.span, *defaultness);
 
-                let is_intrinsic =
-                    item.attrs.iter().any(|a| a.name_or_empty() == sym::rustc_intrinsic);
+                let is_intrinsic = item.attrs.iter().any(|a| a.has_name(sym::rustc_intrinsic));
                 if body.is_none() && !is_intrinsic {
                     self.dcx().emit_err(errors::FnWithoutBody {
                         span: item.span,
@@ -996,7 +997,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 }
 
                 if abi.is_none() {
-                    self.maybe_lint_missing_abi(*extern_span, item.id);
+                    self.handle_missing_abi(*extern_span, item.id);
                 }
                 self.with_in_extern_mod(*safety, |this| {
                     visit::walk_item(this, item);
@@ -1370,7 +1371,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             },
         ) = fk
         {
-            self.maybe_lint_missing_abi(*extern_span, id);
+            self.handle_missing_abi(*extern_span, id);
         }
 
         // Functions without bodies cannot have patterns.
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 8e53e600f7a..6f9737e0831 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -2,7 +2,7 @@
 
 use rustc_ast::ParamKindOrd;
 use rustc_errors::codes::*;
-use rustc_errors::{Applicability, Diag, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic};
+use rustc_errors::{Applicability, Diag, EmissionGuarantee, Subdiagnostic};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Ident, Span, Symbol};
 
@@ -394,11 +394,7 @@ pub(crate) struct EmptyLabelManySpans(pub Vec<Span>);
 
 // The derive for `Vec<Span>` does multiple calls to `span_label`, adding commas between each
 impl Subdiagnostic for EmptyLabelManySpans {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.span_labels(self.0, "");
     }
 }
@@ -749,11 +745,7 @@ pub(crate) struct StableFeature {
 }
 
 impl Subdiagnostic for StableFeature {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("name", self.name);
         diag.arg("since", self.since);
         diag.help(fluent::ast_passes_stable_since);
@@ -823,3 +815,12 @@ pub(crate) struct DuplicatePreciseCapturing {
     #[label]
     pub bound2: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(ast_passes_extern_without_abi)]
+#[help]
+pub(crate) struct MissingAbi {
+    #[primary_span]
+    #[suggestion(code = "extern \"<abi>\"", applicability = "has-placeholders")]
+    pub span: Span,
+}
diff --git a/compiler/rustc_ast_pretty/src/pprust/mod.rs b/compiler/rustc_ast_pretty/src/pprust/mod.rs
index 97cb6e52d56..551506f2aef 100644
--- a/compiler/rustc_ast_pretty/src/pprust/mod.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/mod.rs
@@ -5,14 +5,10 @@ pub mod state;
 use std::borrow::Cow;
 
 use rustc_ast as ast;
-use rustc_ast::token::{Nonterminal, Token, TokenKind};
+use rustc_ast::token::{Token, TokenKind};
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
 pub use state::{AnnNode, Comments, PpAnn, PrintState, State, print_crate};
 
-pub fn nonterminal_to_string(nt: &Nonterminal) -> String {
-    State::new().nonterminal_to_string(nt)
-}
-
 /// Print the token kind precisely, without converting `$crate` into its respective crate name.
 pub fn token_kind_to_string(tok: &TokenKind) -> Cow<'static, str> {
     State::new().token_kind_to_string(tok)
diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index 3dbfc191f8f..0985ebf945b 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -11,7 +11,7 @@ use std::sync::Arc;
 
 use rustc_ast::attr::AttrIdGenerator;
 use rustc_ast::ptr::P;
-use rustc_ast::token::{self, CommentKind, Delimiter, IdentIsRaw, Nonterminal, Token, TokenKind};
+use rustc_ast::token::{self, CommentKind, Delimiter, IdentIsRaw, Token, TokenKind};
 use rustc_ast::tokenstream::{Spacing, TokenStream, TokenTree};
 use rustc_ast::util::classify;
 use rustc_ast::util::comments::{Comment, CommentStyle};
@@ -876,14 +876,6 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         }
     }
 
-    fn nonterminal_to_string(&self, nt: &Nonterminal) -> String {
-        // We extract the token stream from the AST fragment and pretty print
-        // it, rather than using AST pretty printing, because `Nonterminal` is
-        // slated for removal in #124141. (This method will also then be
-        // removed.)
-        self.tts_to_string(&TokenStream::from_nonterminal_ast(nt))
-    }
-
     /// Print the token kind precisely, without converting `$crate` into its respective crate name.
     fn token_kind_to_string(&self, tok: &TokenKind) -> Cow<'static, str> {
         self.token_kind_to_string_ext(tok, None)
@@ -976,8 +968,6 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
                 doc_comment_to_string(comment_kind, attr_style, data).into()
             }
             token::Eof => "<eof>".into(),
-
-            token::Interpolated(ref nt) => self.nonterminal_to_string(&nt).into(),
         }
     }
 
@@ -1336,6 +1326,9 @@ impl<'a> State<'a> {
                 self.print_outer_attributes(&loc.attrs);
                 self.space_if_not_bol();
                 self.ibox(INDENT_UNIT);
+                if loc.super_.is_some() {
+                    self.word_nbsp("super");
+                }
                 self.word_nbsp("let");
 
                 self.ibox(INDENT_UNIT);
@@ -1622,9 +1615,9 @@ impl<'a> State<'a> {
     fn print_pat(&mut self, pat: &ast::Pat) {
         self.maybe_print_comment(pat.span.lo());
         self.ann.pre(self, AnnNode::Pat(pat));
-        /* Pat isn't normalized, but the beauty of it
-        is that it doesn't matter */
+        /* Pat isn't normalized, but the beauty of it is that it doesn't matter */
         match &pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => self.word("_"),
             PatKind::Never => self.word("!"),
             PatKind::Ident(BindingMode(by_ref, mutbl), ident, sub) => {
@@ -1946,12 +1939,7 @@ impl<'a> State<'a> {
                 if let Some(eself) = input.to_self() {
                     self.print_explicit_self(&eself);
                 } else {
-                    let invalid = if let PatKind::Ident(_, ident, _) = input.pat.kind {
-                        ident.name == kw::Empty
-                    } else {
-                        false
-                    };
-                    if !invalid {
+                    if !matches!(input.pat.kind, PatKind::Missing) {
                         self.print_pat(&input.pat);
                         self.word(":");
                         self.space();
diff --git a/compiler/rustc_ast_pretty/src/pprust/tests.rs b/compiler/rustc_ast_pretty/src/pprust/tests.rs
index 4c42dd1f202..bc7f22766a5 100644
--- a/compiler/rustc_ast_pretty/src/pprust/tests.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/tests.rs
@@ -7,12 +7,12 @@ use super::*;
 fn fun_to_string(
     decl: &ast::FnDecl,
     header: ast::FnHeader,
-    name: Ident,
+    ident: Ident,
     generics: &ast::Generics,
 ) -> String {
     to_string(|s| {
         s.head("");
-        s.print_fn(decl, header, Some(name), generics);
+        s.print_fn(decl, header, Some(ident), generics);
         s.end(); // Close the head box.
         s.end(); // Close the outer box.
     })
diff --git a/compiler/rustc_attr_parsing/src/attributes/cfg.rs b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
index 0d6d521b40c..7cb1fede174 100644
--- a/compiler/rustc_attr_parsing/src/attributes/cfg.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
@@ -7,7 +7,6 @@ use rustc_session::config::ExpectedValues;
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::UNEXPECTED_CFGS;
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::kw;
 use rustc_span::{Span, Symbol, sym};
 
 use crate::session_diagnostics::{self, UnsupportedLiteralReason};
@@ -89,20 +88,6 @@ pub fn eval_condition(
     let cfg = match cfg {
         MetaItemInner::MetaItem(meta_item) => meta_item,
         MetaItemInner::Lit(MetaItemLit { kind: LitKind::Bool(b), .. }) => {
-            if let Some(features) = features {
-                // we can't use `try_gate_cfg` as symbols don't differentiate between `r#true`
-                // and `true`, and we want to keep the former working without feature gate
-                gate_cfg(
-                    &(
-                        if *b { kw::True } else { kw::False },
-                        sym::cfg_boolean_literals,
-                        |features: &Features| features.cfg_boolean_literals(),
-                    ),
-                    cfg.span(),
-                    sess,
-                    features,
-                );
-            }
             return *b;
         }
         _ => {
@@ -117,7 +102,7 @@ pub fn eval_condition(
     };
 
     match &cfg.kind {
-        MetaItemKind::List(mis) if cfg.name_or_empty() == sym::version => {
+        MetaItemKind::List(mis) if cfg.has_name(sym::version) => {
             try_gate_cfg(sym::version, cfg.span, sess, features);
             let (min_version, span) = match &mis[..] {
                 [MetaItemInner::Lit(MetaItemLit { kind: LitKind::Str(sym, ..), span, .. })] => {
@@ -164,18 +149,18 @@ pub fn eval_condition(
 
             // The unwraps below may look dangerous, but we've already asserted
             // that they won't fail with the loop above.
-            match cfg.name_or_empty() {
-                sym::any => mis
+            match cfg.name() {
+                Some(sym::any) => mis
                     .iter()
                     // We don't use any() here, because we want to evaluate all cfg condition
                     // as eval_condition can (and does) extra checks
                     .fold(false, |res, mi| res | eval_condition(mi, sess, features, eval)),
-                sym::all => mis
+                Some(sym::all) => mis
                     .iter()
                     // We don't use all() here, because we want to evaluate all cfg condition
                     // as eval_condition can (and does) extra checks
                     .fold(true, |res, mi| res & eval_condition(mi, sess, features, eval)),
-                sym::not => {
+                Some(sym::not) => {
                     let [mi] = mis.as_slice() else {
                         dcx.emit_err(session_diagnostics::ExpectedOneCfgPattern { span: cfg.span });
                         return false;
@@ -183,7 +168,7 @@ pub fn eval_condition(
 
                     !eval_condition(mi, sess, features, eval)
                 }
-                sym::target => {
+                Some(sym::target) => {
                     if let Some(features) = features
                         && !features.cfg_target_compact()
                     {
diff --git a/compiler/rustc_attr_parsing/src/attributes/transparency.rs b/compiler/rustc_attr_parsing/src/attributes/transparency.rs
index ad83a1f7af8..ce42b0507ed 100644
--- a/compiler/rustc_attr_parsing/src/attributes/transparency.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/transparency.rs
@@ -20,7 +20,7 @@ impl SingleAttributeParser for TransparencyParser {
     fn convert(cx: &AcceptContext<'_>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         match args.name_value().and_then(|nv| nv.value_as_str()) {
             Some(sym::transparent) => Some(Transparency::Transparent),
-            Some(sym::semitransparent) => Some(Transparency::SemiTransparent),
+            Some(sym::semiopaque | sym::semitransparent) => Some(Transparency::SemiOpaque),
             Some(sym::opaque) => Some(Transparency::Opaque),
             Some(other) => {
                 cx.dcx().span_err(cx.attr_span, format!("unknown macro transparency: `{other}`"));
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index a68d4578b40..972614a3366 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -222,7 +222,7 @@ impl<'sess> AttributeParser<'sess> {
             // if we're only looking for a single attribute,
             // skip all the ones we don't care about
             if let Some(expected) = self.parse_only {
-                if attr.name_or_empty() != expected {
+                if !attr.has_name(expected) {
                     continue;
                 }
             }
@@ -232,7 +232,7 @@ impl<'sess> AttributeParser<'sess> {
             // that's expanded right? But no, sometimes, when parsing attributes on macros,
             // we already use the lowering logic and these are still there. So, when `omit_doc`
             // is set we *also* want to ignore these
-            if omit_doc == OmitDoc::Skip && attr.name_or_empty() == sym::doc {
+            if omit_doc == OmitDoc::Skip && attr.has_name(sym::doc) {
                 continue;
             }
 
@@ -250,7 +250,7 @@ impl<'sess> AttributeParser<'sess> {
                     }))
                 }
                 // // FIXME: make doc attributes go through a proper attribute parser
-                // ast::AttrKind::Normal(n) if n.name_or_empty() == sym::doc => {
+                // ast::AttrKind::Normal(n) if n.has_name(sym::doc) => {
                 //     let p = GenericMetaItemParser::from_attr(&n, self.dcx());
                 //
                 //     attributes.push(Attribute::Parsed(AttributeKind::DocComment {
@@ -320,7 +320,7 @@ impl<'sess> AttributeParser<'sess> {
             ast::AttrArgs::Delimited(args) => AttrArgs::Delimited(DelimArgs {
                 dspan: args.dspan,
                 delim: args.delim,
-                tokens: args.tokens.flattened(),
+                tokens: args.tokens.clone(),
             }),
             // This is an inert key-value attribute - it will never be visible to macros
             // after it gets lowered to HIR. Therefore, we can extract literals to handle
diff --git a/compiler/rustc_attr_parsing/src/lib.rs b/compiler/rustc_attr_parsing/src/lib.rs
index a7465847e18..249e71ef70d 100644
--- a/compiler/rustc_attr_parsing/src/lib.rs
+++ b/compiler/rustc_attr_parsing/src/lib.rs
@@ -77,7 +77,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(rust_logo)]
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]
diff --git a/compiler/rustc_attr_parsing/src/parser.rs b/compiler/rustc_attr_parsing/src/parser.rs
index a8a1460591c..384fae59873 100644
--- a/compiler/rustc_attr_parsing/src/parser.rs
+++ b/compiler/rustc_attr_parsing/src/parser.rs
@@ -485,25 +485,7 @@ impl<'a> MetaItemListParserContext<'a> {
         }
 
         // or a path.
-        let path =
-            if let Some(TokenTree::Token(Token { kind: token::Interpolated(_), span, .. }, _)) =
-                self.inside_delimiters.peek()
-            {
-                self.inside_delimiters.next();
-                // We go into this path if an expr ended up in an attribute that
-                // expansion did not turn into a literal. Say, `#[repr(align(macro!()))]`
-                // where the macro didn't expand to a literal. An error is already given
-                // for this at this point, and then we do continue. This makes this path
-                // reachable...
-                let e = self.dcx.span_delayed_bug(
-                    *span,
-                    "expr in place where literal is expected (builtin attr parsing)",
-                );
-
-                return Some(MetaItemOrLitParser::Err(*span, e));
-            } else {
-                self.next_path()?
-            };
+        let path = self.next_path()?;
 
         // Paths can be followed by:
         // - `(more meta items)` (another list)
diff --git a/compiler/rustc_borrowck/src/consumers.rs b/compiler/rustc_borrowck/src/consumers.rs
index 45cdd232564..1f087b09234 100644
--- a/compiler/rustc_borrowck/src/consumers.rs
+++ b/compiler/rustc_borrowck/src/consumers.rs
@@ -15,6 +15,7 @@ pub use super::polonius::legacy::{
     RichLocation, RustcFacts,
 };
 pub use super::region_infer::RegionInferenceContext;
+use crate::{BorrowCheckRootCtxt, do_mir_borrowck};
 
 /// Options determining the output behavior of [`get_body_with_borrowck_facts`].
 ///
@@ -97,8 +98,9 @@ pub struct BodyWithBorrowckFacts<'tcx> {
 /// *   Polonius is highly unstable, so expect regular changes in its signature or other details.
 pub fn get_body_with_borrowck_facts(
     tcx: TyCtxt<'_>,
-    def: LocalDefId,
+    def_id: LocalDefId,
     options: ConsumerOptions,
 ) -> BodyWithBorrowckFacts<'_> {
-    *super::do_mir_borrowck(tcx, def, Some(options)).1.unwrap()
+    let mut root_cx = BorrowCheckRootCtxt::new(tcx, def_id);
+    *do_mir_borrowck(&mut root_cx, def_id, Some(options)).1.unwrap()
 }
diff --git a/compiler/rustc_borrowck/src/def_use.rs b/compiler/rustc_borrowck/src/def_use.rs
index 263f68d6a3d..b9ced81c46c 100644
--- a/compiler/rustc_borrowck/src/def_use.rs
+++ b/compiler/rustc_borrowck/src/def_use.rs
@@ -77,6 +77,9 @@ pub(crate) fn categorize(context: PlaceContext) -> Option<DefUse> {
         // Debug info is neither def nor use.
         PlaceContext::NonUse(NonUseContext::VarDebugInfo) => None,
 
+        // Backwards incompatible drop hint is not a use, just a marker for linting.
+        PlaceContext::NonUse(NonUseContext::BackwardIncompatibleDropHint) => None,
+
         PlaceContext::MutatingUse(MutatingUseContext::Deinit | MutatingUseContext::SetDiscriminant) => {
             bug!("These statements are not allowed in this MIR phase")
         }
diff --git a/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
index aa968a1e40f..134f30ed6f5 100644
--- a/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
@@ -406,8 +406,8 @@ impl<'tcx> TypeOpInfo<'tcx> for crate::type_check::InstantiateOpaqueType<'tcx> {
             // started MIR borrowchecking with, so the region
             // constraints have already been taken. Use the data from
             // our `mbcx` instead.
-            |vid| mbcx.regioncx.var_infos[vid].origin,
-            |vid| mbcx.regioncx.var_infos[vid].universe,
+            |vid| RegionVariableOrigin::Nll(mbcx.regioncx.definitions[vid].origin),
+            |vid| mbcx.regioncx.definitions[vid].universe,
         )
     }
 }
@@ -487,7 +487,7 @@ fn try_extract_error_from_region_constraints<'a, 'tcx>(
     let (sub_region, cause) = info?;
 
     debug!(?sub_region, "cause = {:#?}", cause);
-    let error = match (error_region, *sub_region) {
+    let error = match (error_region, sub_region.kind()) {
         (Some(error_region), ty::ReVar(vid)) => RegionResolutionError::SubSupConflict(
             vid,
             region_var_origin(vid),
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 1f4eb0c449f..cf735815fd2 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -647,7 +647,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     && tc.polarity() == ty::PredicatePolarity::Positive
                     && supertrait_def_ids(tcx, tc.def_id())
                         .flat_map(|trait_did| tcx.associated_items(trait_did).in_definition_order())
-                        .any(|item| item.fn_has_self_parameter)
+                        .any(|item| item.is_method())
             })
         }) {
             return None;
@@ -2500,11 +2500,11 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         );
         let ty::Tuple(params) = tupled_params.kind() else { return };
 
-        // Find the first argument with a matching type, get its name
-        let Some(this_name) = params.iter().zip(tcx.hir_body_param_names(closure.body)).find_map(
-            |(param_ty, name)| {
+        // Find the first argument with a matching type and get its identifier.
+        let Some(this_name) = params.iter().zip(tcx.hir_body_param_idents(closure.body)).find_map(
+            |(param_ty, ident)| {
                 // FIXME: also support deref for stuff like `Rc` arguments
-                if param_ty.peel_refs() == local_ty { name } else { None }
+                if param_ty.peel_refs() == local_ty { ident } else { None }
             },
         ) else {
             return;
@@ -2959,21 +2959,27 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
         }
 
-        let mut err = self.path_does_not_live_long_enough(borrow_span, &format!("`{name}`"));
+        let name = if borrow_span.in_external_macro(self.infcx.tcx.sess.source_map()) {
+            // Don't name local variables in external macros.
+            "value".to_string()
+        } else {
+            format!("`{name}`")
+        };
+
+        let mut err = self.path_does_not_live_long_enough(borrow_span, &name);
 
         if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
             let region_name = annotation.emit(self, &mut err);
 
             err.span_label(
                 borrow_span,
-                format!("`{name}` would have to be valid for `{region_name}`..."),
+                format!("{name} would have to be valid for `{region_name}`..."),
             );
 
             err.span_label(
                 drop_span,
                 format!(
-                    "...but `{}` will be dropped here, when the {} returns",
-                    name,
+                    "...but {name} will be dropped here, when the {} returns",
                     self.infcx
                         .tcx
                         .opt_item_name(self.mir_def_id().to_def_id())
@@ -3011,7 +3017,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
         } else {
             err.span_label(borrow_span, "borrowed value does not live long enough");
-            err.span_label(drop_span, format!("`{name}` dropped here while still borrowed"));
+            err.span_label(drop_span, format!("{name} dropped here while still borrowed"));
 
             borrow_spans.args_subdiag(&mut err, |args_span| {
                 crate::session_diagnostics::CaptureArgLabel::Capture {
@@ -3376,10 +3382,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         let (sugg_span, suggestion) = match tcx.sess.source_map().span_to_snippet(args_span) {
             Ok(string) => {
-                let coro_prefix = if string.starts_with("async") {
-                    // `async` is 5 chars long. Not using `.len()` to avoid the cast from `usize`
-                    // to `u32`.
-                    Some(5)
+                let coro_prefix = if let Some(sub) = string.strip_prefix("async") {
+                    let trimmed_sub = sub.trim_end();
+                    if trimmed_sub.ends_with("gen") {
+                        // `async` is 5 chars long.
+                        Some((trimmed_sub.len() + 5) as _)
+                    } else {
+                        // `async` is 5 chars long.
+                        Some(5)
+                    }
                 } else if string.starts_with("gen") {
                     // `gen` is 3 chars long
                     Some(3)
@@ -3774,7 +3785,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 method_args,
                 *fn_span,
                 call_source.from_hir_call(),
-                self.infcx.tcx.fn_arg_names(method_did)[0],
+                self.infcx.tcx.fn_arg_idents(method_did)[0],
             )
         {
             err.note(format!("borrow occurs due to deref coercion to `{deref_target_ty}`"));
diff --git a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
index f77dda0d386..a845431faca 100644
--- a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
@@ -95,7 +95,9 @@ impl<'tcx> BorrowExplanation<'tcx> {
                         && let hir::def::Res::Local(hir_id) = p.res
                         && let hir::Node::Pat(pat) = tcx.hir_node(hir_id)
                     {
-                        err.span_label(pat.span, format!("binding `{ident}` declared here"));
+                        if !ident.span.in_external_macro(tcx.sess.source_map()) {
+                            err.span_label(pat.span, format!("binding `{ident}` declared here"));
+                        }
                     }
                 }
             }
diff --git a/compiler/rustc_borrowck/src/diagnostics/mod.rs b/compiler/rustc_borrowck/src/diagnostics/mod.rs
index 899e145c2c0..f9f63ae92a8 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mod.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mod.rs
@@ -8,9 +8,7 @@ use rustc_errors::{Applicability, Diag, EmissionGuarantee, MultiSpan, listify};
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::{self as hir, CoroutineKind, LangItem};
 use rustc_index::IndexSlice;
-use rustc_infer::infer::{
-    BoundRegionConversionTime, NllRegionVariableOrigin, RegionVariableOrigin,
-};
+use rustc_infer::infer::{BoundRegionConversionTime, NllRegionVariableOrigin};
 use rustc_infer::traits::SelectionError;
 use rustc_middle::bug;
 use rustc_middle::mir::{
@@ -587,7 +585,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         // this by hooking into the pretty printer and telling it to label the
         // lifetimes without names with the value `'0`.
         if let ty::Ref(region, ..) = ty.kind() {
-            match **region {
+            match region.kind() {
                 ty::ReBound(_, ty::BoundRegion { kind: br, .. })
                 | ty::RePlaceholder(ty::PlaceholderRegion {
                     bound: ty::BoundRegion { kind: br, .. },
@@ -607,7 +605,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 
         let region = if let ty::Ref(region, ..) = ty.kind() {
-            match **region {
+            match region.kind() {
                 ty::ReBound(_, ty::BoundRegion { kind: br, .. })
                 | ty::RePlaceholder(ty::PlaceholderRegion {
                     bound: ty::BoundRegion { kind: br, .. },
@@ -633,9 +631,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     ) {
         let predicate_span = path.iter().find_map(|constraint| {
             let outlived = constraint.sub;
-            if let Some(origin) = self.regioncx.var_infos.get(outlived)
-                && let RegionVariableOrigin::Nll(NllRegionVariableOrigin::Placeholder(_)) =
-                    origin.origin
+            if let Some(origin) = self.regioncx.definitions.get(outlived)
+                && let NllRegionVariableOrigin::Placeholder(_) = origin.origin
                 && let ConstraintCategory::Predicate(span) = constraint.category
             {
                 Some(span)
@@ -1029,7 +1026,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 method_args,
                 *fn_span,
                 call_source.from_hir_call(),
-                self.infcx.tcx.fn_arg_names(method_did)[0],
+                self.infcx.tcx.fn_arg_idents(method_did)[0],
             );
 
             return FnSelfUse {
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index d1d783c22e3..4423edb0605 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -190,7 +190,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        fold_regions(tcx, ty, |region, _| match *region {
+        fold_regions(tcx, ty, |region, _| match region.kind() {
             ty::ReVar(vid) => self.to_error_region(vid).unwrap_or(region),
             _ => region,
         })
@@ -198,7 +198,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
     /// Returns `true` if a closure is inferred to be an `FnMut` closure.
     fn is_closure_fn_mut(&self, fr: RegionVid) -> bool {
-        if let Some(ty::ReLateParam(late_param)) = self.to_error_region(fr).as_deref()
+        if let Some(r) = self.to_error_region(fr)
+            && let ty::ReLateParam(late_param) = r.kind()
             && let ty::LateParamRegionKind::ClosureEnv = late_param.kind
             && let DefiningTy::Closure(_, args) = self.regioncx.universal_regions().defining_ty
         {
@@ -832,7 +833,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         if let (Some(f), Some(outlived_f)) =
             (self.to_error_region(fr), self.to_error_region(outlived_fr))
         {
-            if *outlived_f != ty::ReStatic {
+            if outlived_f.kind() != ty::ReStatic {
                 return;
             }
             let suitable_region = self.infcx.tcx.is_suitable_region(self.mir_def_id(), f);
@@ -887,7 +888,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     // Skip `async` desugaring `impl Future`.
                 }
                 if let TyKind::TraitObject(_, lt) = alias_ty.kind {
-                    if lt.res == hir::LifetimeName::ImplicitObjectLifetimeDefault {
+                    if lt.kind == hir::LifetimeKind::ImplicitObjectLifetimeDefault {
                         spans_suggs.push((lt.ident.span.shrink_to_hi(), " + 'a".to_string()));
                     } else {
                         spans_suggs.push((lt.ident.span, "'a".to_string()));
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_name.rs b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
index 45f5eaa514b..b08c10983bb 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_name.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
@@ -288,7 +288,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
         let tcx = self.infcx.tcx;
 
         debug!("give_region_a_name: error_region = {:?}", error_region);
-        match *error_region {
+        match error_region.kind() {
             ty::ReEarlyParam(ebr) => ebr.has_name().then(|| {
                 let def_id = tcx.generics_of(self.mir_def_id()).region_param(ebr, tcx).def_id;
                 let span = tcx.hir_span_if_local(def_id).unwrap_or(DUMMY_SP);
@@ -896,7 +896,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
         &self,
         fr: RegionVid,
     ) -> Option<RegionName> {
-        let ty::ReEarlyParam(region) = *self.to_error_region(fr)? else {
+        let ty::ReEarlyParam(region) = self.to_error_region(fr)?.kind() else {
             return None;
         };
         if region.has_name() {
@@ -912,7 +912,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
 
         let found = tcx
             .any_free_region_meets(&tcx.type_of(region_parent).instantiate_identity(), |r| {
-                *r == ty::ReEarlyParam(region)
+                r.kind() == ty::ReEarlyParam(region)
             });
 
         Some(RegionName {
@@ -931,7 +931,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
         &self,
         fr: RegionVid,
     ) -> Option<RegionName> {
-        let ty::ReEarlyParam(region) = *self.to_error_region(fr)? else {
+        let ty::ReEarlyParam(region) = self.to_error_region(fr)?.kind() else {
             return None;
         };
         if region.has_name() {
@@ -1007,7 +1007,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
                             if data.projection_term.self_ty() == ty => {}
                         _ => return false,
                     }
-                    tcx.any_free_region_meets(pred, |r| *r == ty::ReEarlyParam(region))
+                    tcx.any_free_region_meets(pred, |r| r.kind() == ty::ReEarlyParam(region))
                 })
             } else {
                 false
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 240bd20053b..3b66142eb2c 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -2,13 +2,13 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(rust_logo)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
+#![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]
@@ -21,6 +21,8 @@ use std::cell::RefCell;
 use std::marker::PhantomData;
 use std::ops::{ControlFlow, Deref};
 
+use borrow_set::LocalsStateAtExit;
+use root_cx::BorrowCheckRootCtxt;
 use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::dominators::Dominators;
@@ -35,7 +37,9 @@ use rustc_infer::infer::{
 };
 use rustc_middle::mir::*;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, ParamEnv, RegionVid, TyCtxt, TypingMode};
+use rustc_middle::ty::{
+    self, ParamEnv, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitable, TypingMode, fold_regions,
+};
 use rustc_middle::{bug, span_bug};
 use rustc_mir_dataflow::impls::{
     EverInitializedPlaces, MaybeInitializedPlaces, MaybeUninitializedPlaces,
@@ -45,7 +49,7 @@ use rustc_mir_dataflow::move_paths::{
 };
 use rustc_mir_dataflow::{Analysis, EntryStates, Results, ResultsVisitor, visit_results};
 use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT};
-use rustc_span::{Span, Symbol};
+use rustc_span::{ErrorGuaranteed, Span, Symbol};
 use smallvec::SmallVec;
 use tracing::{debug, instrument};
 
@@ -73,7 +77,6 @@ mod def_use;
 mod diagnostics;
 mod member_constraints;
 mod nll;
-mod opaque_types;
 mod path_utils;
 mod place_ext;
 mod places_conflict;
@@ -81,6 +84,7 @@ mod polonius;
 mod prefixes;
 mod region_infer;
 mod renumber;
+mod root_cx;
 mod session_diagnostics;
 mod type_check;
 mod universal_regions;
@@ -102,64 +106,202 @@ pub fn provide(providers: &mut Providers) {
     *providers = Providers { mir_borrowck, ..*providers };
 }
 
-fn mir_borrowck(tcx: TyCtxt<'_>, def: LocalDefId) -> &BorrowCheckResult<'_> {
+/// Provider for `query mir_borrowck`. Similar to `typeck`, this must
+/// only be called for typeck roots which will then borrowck all
+/// nested bodies as well.
+fn mir_borrowck(
+    tcx: TyCtxt<'_>,
+    def: LocalDefId,
+) -> Result<&ConcreteOpaqueTypes<'_>, ErrorGuaranteed> {
+    assert!(!tcx.is_typeck_child(def.to_def_id()));
     let (input_body, _) = tcx.mir_promoted(def);
+    debug!("run query mir_borrowck: {}", tcx.def_path_str(def));
+
     let input_body: &Body<'_> = &input_body.borrow();
-    if input_body.should_skip() || input_body.tainted_by_errors.is_some() {
-        debug!("Skipping borrowck because of injected body or tainted body");
-        // Let's make up a borrowck result! Fun times!
-        let result = BorrowCheckResult {
-            concrete_opaque_types: FxIndexMap::default(),
-            closure_requirements: None,
-            used_mut_upvars: SmallVec::new(),
-            tainted_by_errors: input_body.tainted_by_errors,
-        };
-        return tcx.arena.alloc(result);
+    if let Some(guar) = input_body.tainted_by_errors {
+        debug!("Skipping borrowck because of tainted body");
+        Err(guar)
+    } else if input_body.should_skip() {
+        debug!("Skipping borrowck because of injected body");
+        let opaque_types = ConcreteOpaqueTypes(Default::default());
+        Ok(tcx.arena.alloc(opaque_types))
+    } else {
+        let mut root_cx = BorrowCheckRootCtxt::new(tcx, def);
+        let PropagatedBorrowCheckResults { closure_requirements, used_mut_upvars } =
+            do_mir_borrowck(&mut root_cx, def, None).0;
+        debug_assert!(closure_requirements.is_none());
+        debug_assert!(used_mut_upvars.is_empty());
+        root_cx.finalize()
     }
+}
+
+/// Data propagated to the typeck parent by nested items.
+/// This should always be empty for the typeck root.
+#[derive(Debug)]
+struct PropagatedBorrowCheckResults<'tcx> {
+    closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
+    used_mut_upvars: SmallVec<[FieldIdx; 8]>,
+}
+
+/// After we borrow check a closure, we are left with various
+/// requirements that we have inferred between the free regions that
+/// appear in the closure's signature or on its field types. These
+/// requirements are then verified and proved by the closure's
+/// creating function. This struct encodes those requirements.
+///
+/// The requirements are listed as being between various `RegionVid`. The 0th
+/// region refers to `'static`; subsequent region vids refer to the free
+/// regions that appear in the closure (or coroutine's) type, in order of
+/// appearance. (This numbering is actually defined by the `UniversalRegions`
+/// struct in the NLL region checker. See for example
+/// `UniversalRegions::closure_mapping`.) Note the free regions in the
+/// closure's signature and captures are erased.
+///
+/// Example: If type check produces a closure with the closure args:
+///
+/// ```text
+/// ClosureArgs = [
+///     'a,                                         // From the parent.
+///     'b,
+///     i8,                                         // the "closure kind"
+///     for<'x> fn(&'<erased> &'x u32) -> &'x u32,  // the "closure signature"
+///     &'<erased> String,                          // some upvar
+/// ]
+/// ```
+///
+/// We would "renumber" each free region to a unique vid, as follows:
+///
+/// ```text
+/// ClosureArgs = [
+///     '1,                                         // From the parent.
+///     '2,
+///     i8,                                         // the "closure kind"
+///     for<'x> fn(&'3 &'x u32) -> &'x u32,         // the "closure signature"
+///     &'4 String,                                 // some upvar
+/// ]
+/// ```
+///
+/// Now the code might impose a requirement like `'1: '2`. When an
+/// instance of the closure is created, the corresponding free regions
+/// can be extracted from its type and constrained to have the given
+/// outlives relationship.
+#[derive(Clone, Debug)]
+pub struct ClosureRegionRequirements<'tcx> {
+    /// The number of external regions defined on the closure. In our
+    /// example above, it would be 3 -- one for `'static`, then `'1`
+    /// and `'2`. This is just used for a sanity check later on, to
+    /// make sure that the number of regions we see at the callsite
+    /// matches.
+    pub num_external_vids: usize,
+
+    /// Requirements between the various free regions defined in
+    /// indices.
+    pub outlives_requirements: Vec<ClosureOutlivesRequirement<'tcx>>,
+}
 
-    let borrowck_result = do_mir_borrowck(tcx, def, None).0;
-    debug!("mir_borrowck done");
+/// Indicates an outlives-constraint between a type or between two
+/// free regions declared on the closure.
+#[derive(Copy, Clone, Debug)]
+pub struct ClosureOutlivesRequirement<'tcx> {
+    // This region or type ...
+    pub subject: ClosureOutlivesSubject<'tcx>,
+
+    // ... must outlive this one.
+    pub outlived_free_region: ty::RegionVid,
 
-    tcx.arena.alloc(borrowck_result)
+    // If not, report an error here ...
+    pub blame_span: Span,
+
+    // ... due to this reason.
+    pub category: ConstraintCategory<'tcx>,
+}
+
+// Make sure this enum doesn't unintentionally grow
+#[cfg(target_pointer_width = "64")]
+rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
+
+/// The subject of a `ClosureOutlivesRequirement` -- that is, the thing
+/// that must outlive some region.
+#[derive(Copy, Clone, Debug)]
+pub enum ClosureOutlivesSubject<'tcx> {
+    /// Subject is a type, typically a type parameter, but could also
+    /// be a projection. Indicates a requirement like `T: 'a` being
+    /// passed to the caller, where the type here is `T`.
+    Ty(ClosureOutlivesSubjectTy<'tcx>),
+
+    /// Subject is a free region from the closure. Indicates a requirement
+    /// like `'a: 'b` being passed to the caller; the region here is `'a`.
+    Region(ty::RegionVid),
+}
+
+/// Represents a `ty::Ty` for use in [`ClosureOutlivesSubject`].
+///
+/// This abstraction is necessary because the type may include `ReVar` regions,
+/// which is what we use internally within NLL code, and they can't be used in
+/// a query response.
+#[derive(Copy, Clone, Debug)]
+pub struct ClosureOutlivesSubjectTy<'tcx> {
+    inner: Ty<'tcx>,
+}
+// DO NOT implement `TypeVisitable` or `TypeFoldable` traits, because this
+// type is not recognized as a binder for late-bound region.
+impl<'tcx, I> !TypeVisitable<I> for ClosureOutlivesSubjectTy<'tcx> {}
+impl<'tcx, I> !TypeFoldable<I> for ClosureOutlivesSubjectTy<'tcx> {}
+
+impl<'tcx> ClosureOutlivesSubjectTy<'tcx> {
+    /// All regions of `ty` must be of kind `ReVar` and must represent
+    /// universal regions *external* to the closure.
+    pub fn bind(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
+        let inner = fold_regions(tcx, ty, |r, depth| match r.kind() {
+            ty::ReVar(vid) => {
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_usize(vid.index()),
+                    kind: ty::BoundRegionKind::Anon,
+                };
+                ty::Region::new_bound(tcx, depth, br)
+            }
+            _ => bug!("unexpected region in ClosureOutlivesSubjectTy: {r:?}"),
+        });
+
+        Self { inner }
+    }
+
+    pub fn instantiate(
+        self,
+        tcx: TyCtxt<'tcx>,
+        mut map: impl FnMut(ty::RegionVid) -> ty::Region<'tcx>,
+    ) -> Ty<'tcx> {
+        fold_regions(tcx, self.inner, |r, depth| match r.kind() {
+            ty::ReBound(debruijn, br) => {
+                debug_assert_eq!(debruijn, depth);
+                map(ty::RegionVid::from_usize(br.var.index()))
+            }
+            _ => bug!("unexpected region {r:?}"),
+        })
+    }
 }
 
 /// Perform the actual borrow checking.
 ///
 /// Use `consumer_options: None` for the default behavior of returning
-/// [`BorrowCheckResult`] only. Otherwise, return [`BodyWithBorrowckFacts`] according
-/// to the given [`ConsumerOptions`].
-#[instrument(skip(tcx), level = "debug")]
+/// [`PropagatedBorrowCheckResults`] only. Otherwise, return [`BodyWithBorrowckFacts`]
+/// according to the given [`ConsumerOptions`].
+///
+/// For nested bodies this should only be called through `root_cx.get_or_insert_nested`.
+#[instrument(skip(root_cx), level = "debug")]
 fn do_mir_borrowck<'tcx>(
-    tcx: TyCtxt<'tcx>,
+    root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     def: LocalDefId,
     consumer_options: Option<ConsumerOptions>,
-) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
+) -> (PropagatedBorrowCheckResults<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
+    let tcx = root_cx.tcx;
     let infcx = BorrowckInferCtxt::new(tcx, def);
     let (input_body, promoted) = tcx.mir_promoted(def);
     let input_body: &Body<'_> = &input_body.borrow();
     let input_promoted: &IndexSlice<_, _> = &promoted.borrow();
     if let Some(e) = input_body.tainted_by_errors {
         infcx.set_tainted_by_errors(e);
-    }
-
-    let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
-    for var_debug_info in &input_body.var_debug_info {
-        if let VarDebugInfoContents::Place(place) = var_debug_info.value {
-            if let Some(local) = place.as_local() {
-                if let Some(prev_name) = local_names[local]
-                    && var_debug_info.name != prev_name
-                {
-                    span_bug!(
-                        var_debug_info.source_info.span,
-                        "local {:?} has many names (`{}` vs `{}`)",
-                        local,
-                        prev_name,
-                        var_debug_info.name
-                    );
-                }
-                local_names[local] = Some(var_debug_info.name);
-            }
-        }
+        root_cx.set_tainted_by_errors(e);
     }
 
     // Replace all regions with fresh inference variables. This
@@ -168,7 +310,7 @@ fn do_mir_borrowck<'tcx>(
     // will have a lifetime tied to the inference context.
     let mut body_owned = input_body.clone();
     let mut promoted = input_promoted.to_owned();
-    let free_regions = nll::replace_regions_in_mir(&infcx, &mut body_owned, &mut promoted);
+    let universal_regions = nll::replace_regions_in_mir(&infcx, &mut body_owned, &mut promoted);
     let body = &body_owned; // no further changes
 
     let location_table = PoloniusLocationTable::new(body);
@@ -185,15 +327,15 @@ fn do_mir_borrowck<'tcx>(
     // Compute non-lexical lifetimes.
     let nll::NllOutput {
         regioncx,
-        concrete_opaque_types,
         polonius_input,
         polonius_output,
         opt_closure_req,
         nll_errors,
         polonius_diagnostics,
     } = nll::compute_regions(
+        root_cx,
         &infcx,
-        free_regions,
+        universal_regions,
         body,
         &promoted,
         &location_table,
@@ -206,31 +348,23 @@ fn do_mir_borrowck<'tcx>(
     // Dump MIR results into a file, if that is enabled. This lets us
     // write unit-tests, as well as helping with debugging.
     nll::dump_nll_mir(&infcx, body, &regioncx, &opt_closure_req, &borrow_set);
-
-    // We also have a `#[rustc_regions]` annotation that causes us to dump
-    // information.
-    let diags_buffer = &mut BorrowckDiagnosticsBuffer::default();
-    nll::dump_annotation(
+    polonius::dump_polonius_mir(
         &infcx,
         body,
         &regioncx,
         &opt_closure_req,
-        &concrete_opaque_types,
-        diags_buffer,
+        &borrow_set,
+        polonius_diagnostics.as_ref(),
     );
 
-    let movable_coroutine =
-        // The first argument is the coroutine type passed by value
-        if let Some(local) = body.local_decls.raw.get(1)
-        // Get the interior types and args which typeck computed
-        && let ty::Coroutine(def_id, _) = *local.ty.kind()
-        && tcx.coroutine_movability(def_id) == hir::Movability::Movable
-    {
-        true
-    } else {
-        false
-    };
+    // We also have a `#[rustc_regions]` annotation that causes us to dump
+    // information.
+    nll::dump_annotation(&infcx, body, &regioncx, &opt_closure_req);
 
+    let movable_coroutine = body.coroutine.is_some()
+        && tcx.coroutine_movability(def.to_def_id()) == hir::Movability::Movable;
+
+    let diags_buffer = &mut BorrowckDiagnosticsBuffer::default();
     // While promoteds should mostly be correct by construction, we need to check them for
     // invalid moves to detect moving out of arrays:`struct S; fn main() { &([S][0]); }`.
     for promoted_body in &promoted {
@@ -240,6 +374,7 @@ fn do_mir_borrowck<'tcx>(
         // this check out of `MirBorrowckCtxt`, actually doing so is far from trivial.
         let move_data = MoveData::gather_moves(promoted_body, tcx, |_| true);
         let mut promoted_mbcx = MirBorrowckCtxt {
+            root_cx,
             infcx: &infcx,
             body: promoted_body,
             move_data: &move_data,
@@ -247,7 +382,6 @@ fn do_mir_borrowck<'tcx>(
             location_table: &location_table,
             movable_coroutine,
             fn_self_span_reported: Default::default(),
-            locals_are_invalidated_at_exit,
             access_place_error_reported: Default::default(),
             reservation_error_reported: Default::default(),
             uninitialized_error_reported: Default::default(),
@@ -279,13 +413,33 @@ fn do_mir_borrowck<'tcx>(
         promoted_mbcx.report_move_errors();
     }
 
+    let mut local_names = IndexVec::from_elem(None, &body.local_decls);
+    for var_debug_info in &body.var_debug_info {
+        if let VarDebugInfoContents::Place(place) = var_debug_info.value {
+            if let Some(local) = place.as_local() {
+                if let Some(prev_name) = local_names[local]
+                    && var_debug_info.name != prev_name
+                {
+                    span_bug!(
+                        var_debug_info.source_info.span,
+                        "local {:?} has many names (`{}` vs `{}`)",
+                        local,
+                        prev_name,
+                        var_debug_info.name
+                    );
+                }
+                local_names[local] = Some(var_debug_info.name);
+            }
+        }
+    }
+
     let mut mbcx = MirBorrowckCtxt {
+        root_cx,
         infcx: &infcx,
         body,
         move_data: &move_data,
         location_table: &location_table,
         movable_coroutine,
-        locals_are_invalidated_at_exit,
         fn_self_span_reported: Default::default(),
         access_place_error_reported: Default::default(),
         reservation_error_reported: Default::default(),
@@ -298,9 +452,9 @@ fn do_mir_borrowck<'tcx>(
         local_names,
         region_names: RefCell::default(),
         next_region_name: RefCell::new(1),
-        polonius_output,
         move_errors: Vec::new(),
         diags_buffer,
+        polonius_output: polonius_output.as_deref(),
         polonius_diagnostics: polonius_diagnostics.as_ref(),
     };
 
@@ -317,16 +471,6 @@ fn do_mir_borrowck<'tcx>(
 
     mbcx.report_move_errors();
 
-    // If requested, dump polonius MIR.
-    polonius::dump_polonius_mir(
-        &infcx,
-        body,
-        &regioncx,
-        &borrow_set,
-        polonius_diagnostics.as_ref(),
-        &opt_closure_req,
-    );
-
     // For each non-user used mutable variable, check if it's been assigned from
     // a user-declared local. If so, then put that local into the used_mut set.
     // Note that this set is expected to be small - only upvars from closures
@@ -347,17 +491,16 @@ fn do_mir_borrowck<'tcx>(
 
     debug!("mbcx.used_mut: {:?}", mbcx.used_mut);
     mbcx.lint_unused_mut();
-    let tainted_by_errors = mbcx.emit_errors();
+    if let Some(guar) = mbcx.emit_errors() {
+        mbcx.root_cx.set_tainted_by_errors(guar);
+    }
 
-    let result = BorrowCheckResult {
-        concrete_opaque_types: concrete_opaque_types.into_inner(),
+    let result = PropagatedBorrowCheckResults {
         closure_requirements: opt_closure_req,
         used_mut_upvars: mbcx.used_mut_upvars,
-        tainted_by_errors,
     };
 
     let body_with_facts = if consumer_options.is_some() {
-        let output_facts = mbcx.polonius_output;
         Some(Box::new(BodyWithBorrowckFacts {
             body: body_owned,
             promoted,
@@ -365,7 +508,7 @@ fn do_mir_borrowck<'tcx>(
             region_inference_context: regioncx,
             location_table: polonius_input.as_ref().map(|_| location_table),
             input_facts: polonius_input,
-            output_facts,
+            output_facts: polonius_output,
         }))
     } else {
         None
@@ -488,6 +631,7 @@ impl<'tcx> Deref for BorrowckInferCtxt<'tcx> {
 }
 
 struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
+    root_cx: &'a mut BorrowCheckRootCtxt<'tcx>,
     infcx: &'infcx BorrowckInferCtxt<'tcx>,
     body: &'a Body<'tcx>,
     move_data: &'a MoveData<'tcx>,
@@ -497,13 +641,6 @@ struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
     location_table: &'a PoloniusLocationTable,
 
     movable_coroutine: bool,
-    /// This keeps track of whether local variables are free-ed when the function
-    /// exits even without a `StorageDead`, which appears to be the case for
-    /// constants.
-    ///
-    /// I'm not sure this is the right approach - @eddyb could you try and
-    /// figure this out?
-    locals_are_invalidated_at_exit: bool,
     /// This field keeps track of when borrow errors are reported in the access_place function
     /// so that there is no duplicate reporting. This field cannot also be used for the conflicting
     /// borrow errors that is handled by the `reservation_error_reported` field as the inclusion
@@ -551,12 +688,11 @@ struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
     /// The counter for generating new region names.
     next_region_name: RefCell<usize>,
 
-    /// Results of Polonius analysis.
-    polonius_output: Option<Box<PoloniusOutput>>,
-
     diags_buffer: &'a mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>,
     move_errors: Vec<MoveError<'tcx>>,
 
+    /// Results of Polonius analysis.
+    polonius_output: Option<&'a PoloniusOutput>,
     /// When using `-Zpolonius=next`: the data used to compute errors and diagnostics.
     polonius_diagnostics: Option<&'a PoloniusDiagnosticsContext>,
 }
@@ -780,13 +916,20 @@ impl<'a, 'tcx> ResultsVisitor<'a, 'tcx, Borrowck<'a, 'tcx>> for MirBorrowckCtxt<
             | TerminatorKind::Return
             | TerminatorKind::TailCall { .. }
             | TerminatorKind::CoroutineDrop => {
-                // Returning from the function implicitly kills storage for all locals and statics.
-                // Often, the storage will already have been killed by an explicit
-                // StorageDead, but we don't always emit those (notably on unwind paths),
-                // so this "extra check" serves as a kind of backup.
-                for i in state.borrows.iter() {
-                    let borrow = &self.borrow_set[i];
-                    self.check_for_invalidation_at_exit(loc, borrow, span);
+                match self.borrow_set.locals_state_at_exit() {
+                    LocalsStateAtExit::AllAreInvalidated => {
+                        // Returning from the function implicitly kills storage for all locals and statics.
+                        // Often, the storage will already have been killed by an explicit
+                        // StorageDead, but we don't always emit those (notably on unwind paths),
+                        // so this "extra check" serves as a kind of backup.
+                        for i in state.borrows.iter() {
+                            let borrow = &self.borrow_set[i];
+                            self.check_for_invalidation_at_exit(loc, borrow, span);
+                        }
+                    }
+                    // If we do not implicitly invalidate all locals on exit,
+                    // we check for conflicts when dropping or moving this local.
+                    LocalsStateAtExit::SomeAreInvalidated { has_storage_dead_or_moved: _ } => {}
                 }
             }
 
@@ -1143,7 +1286,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         error_reported
     }
 
-    /// Through #123739, backward incompatible drops (BIDs) are introduced.
+    /// Through #123739, `BackwardIncompatibleDropHint`s (BIDs) are introduced.
     /// We would like to emit lints whether borrow checking fails at these future drop locations.
     #[instrument(level = "debug", skip(self, state))]
     fn check_backward_incompatible_drop(
@@ -1361,11 +1504,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     | AggregateKind::CoroutineClosure(def_id, _)
                     | AggregateKind::Coroutine(def_id, _) => {
                         let def_id = def_id.expect_local();
-                        let BorrowCheckResult { used_mut_upvars, .. } =
-                            self.infcx.tcx.mir_borrowck(def_id);
+                        let used_mut_upvars = self.root_cx.used_mut_upvars(def_id);
                         debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
-                        for field in used_mut_upvars {
-                            self.propagate_closure_used_mut_upvar(&operands[*field]);
+                        // FIXME: We're cloning the `SmallVec` here to avoid borrowing `root_cx`
+                        // when calling `propagate_closure_used_mut_upvar`. This should ideally
+                        // be unnecessary.
+                        for field in used_mut_upvars.clone() {
+                            self.propagate_closure_used_mut_upvar(&operands[field]);
                         }
                     }
                     AggregateKind::Adt(..)
@@ -1556,22 +1701,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         // we'll have a memory leak) and assume that all statics have a destructor.
         //
         // FIXME: allow thread-locals to borrow other thread locals?
-
-        let (might_be_alive, will_be_dropped) =
-            if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
-                // Thread-locals might be dropped after the function exits
-                // We have to dereference the outer reference because
-                // borrows don't conflict behind shared references.
-                root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
-                (true, true)
-            } else {
-                (false, self.locals_are_invalidated_at_exit)
-            };
-
-        if !will_be_dropped {
-            debug!("place_is_invalidated_at_exit({:?}) - won't be dropped", place);
-            return;
-        }
+        let might_be_alive = if self.body.local_decls[root_place.local].is_ref_to_thread_local() {
+            // Thread-locals might be dropped after the function exits
+            // We have to dereference the outer reference because
+            // borrows don't conflict behind shared references.
+            root_place.projection = TyCtxtConsts::DEREF_PROJECTION;
+            true
+        } else {
+            false
+        };
 
         let sd = if might_be_alive { Deep } else { Shallow(None) };
 
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index 8e7b6f083ac..fe899bb054f 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -8,10 +8,7 @@ use std::str::FromStr;
 use polonius_engine::{Algorithm, Output};
 use rustc_index::IndexSlice;
 use rustc_middle::mir::pretty::{PrettyPrintMirOptions, dump_mir_with_options};
-use rustc_middle::mir::{
-    Body, ClosureOutlivesSubject, ClosureRegionRequirements, PassWhere, Promoted, create_dump_file,
-    dump_enabled, dump_mir,
-};
+use rustc_middle::mir::{Body, PassWhere, Promoted, create_dump_file, dump_enabled, dump_mir};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_mir_dataflow::ResultsCursor;
@@ -24,8 +21,7 @@ use tracing::{debug, instrument};
 
 use crate::borrow_set::BorrowSet;
 use crate::consumers::ConsumerOptions;
-use crate::diagnostics::{BorrowckDiagnosticsBuffer, RegionErrors};
-use crate::opaque_types::ConcreteOpaqueTypes;
+use crate::diagnostics::RegionErrors;
 use crate::polonius::PoloniusDiagnosticsContext;
 use crate::polonius::legacy::{
     PoloniusFacts, PoloniusFactsExt, PoloniusLocationTable, PoloniusOutput,
@@ -33,13 +29,15 @@ use crate::polonius::legacy::{
 use crate::region_infer::RegionInferenceContext;
 use crate::type_check::{self, MirTypeckResults};
 use crate::universal_regions::UniversalRegions;
-use crate::{BorrowckInferCtxt, polonius, renumber};
+use crate::{
+    BorrowCheckRootCtxt, BorrowckInferCtxt, ClosureOutlivesSubject, ClosureRegionRequirements,
+    polonius, renumber,
+};
 
 /// The output of `nll::compute_regions`. This includes the computed `RegionInferenceContext`, any
 /// closure requirements to propagate, and any generated errors.
 pub(crate) struct NllOutput<'tcx> {
     pub regioncx: RegionInferenceContext<'tcx>,
-    pub concrete_opaque_types: ConcreteOpaqueTypes<'tcx>,
     pub polonius_input: Option<Box<PoloniusFacts>>,
     pub polonius_output: Option<Box<PoloniusOutput>>,
     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
@@ -78,6 +76,7 @@ pub(crate) fn replace_regions_in_mir<'tcx>(
 ///
 /// This may result in errors being reported.
 pub(crate) fn compute_regions<'a, 'tcx>(
+    root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     infcx: &BorrowckInferCtxt<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
@@ -98,8 +97,6 @@ pub(crate) fn compute_regions<'a, 'tcx>(
 
     let location_map = Rc::new(DenseLocationMap::new(body));
 
-    let mut concrete_opaque_types = ConcreteOpaqueTypes::default();
-
     // Run the MIR type-checker.
     let MirTypeckResults {
         constraints,
@@ -107,6 +104,7 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         opaque_type_values,
         polonius_context,
     } = type_check::type_check(
+        root_cx,
         infcx,
         body,
         promoted,
@@ -117,14 +115,8 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         flow_inits,
         move_data,
         Rc::clone(&location_map),
-        &mut concrete_opaque_types,
     );
 
-    // Create the region inference context, taking ownership of the
-    // region inference data that was contained in `infcx`, and the
-    // base constraints generated by the type-check.
-    let var_infos = infcx.get_region_var_infos();
-
     // If requested, emit legacy polonius facts.
     polonius::legacy::emit_facts(
         &mut polonius_facts,
@@ -137,13 +129,8 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         &constraints,
     );
 
-    let mut regioncx = RegionInferenceContext::new(
-        infcx,
-        var_infos,
-        constraints,
-        universal_region_relations,
-        location_map,
-    );
+    let mut regioncx =
+        RegionInferenceContext::new(infcx, constraints, universal_region_relations, location_map);
 
     // If requested for `-Zpolonius=next`, convert NLL constraints to localized outlives constraints
     // and use them to compute loan liveness.
@@ -181,11 +168,10 @@ pub(crate) fn compute_regions<'a, 'tcx>(
         infcx.set_tainted_by_errors(guar);
     }
 
-    regioncx.infer_opaque_types(infcx, opaque_type_values, &mut concrete_opaque_types);
+    regioncx.infer_opaque_types(root_cx, infcx, opaque_type_values);
 
     NllOutput {
         regioncx,
-        concrete_opaque_types,
         polonius_input: polonius_facts.map(Box::new),
         polonius_output,
         opt_closure_req: closure_region_requirements,
@@ -301,8 +287,6 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
-    concrete_opaque_types: &ConcreteOpaqueTypes<'tcx>,
-    diagnostics_buffer: &mut BorrowckDiagnosticsBuffer<'infcx, 'tcx>,
 ) {
     let tcx = infcx.tcx;
     let base_def_id = tcx.typeck_root_def_id(body.source.def_id());
@@ -318,7 +302,7 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     // better.
 
     let def_span = tcx.def_span(body.source.def_id());
-    let mut err = if let Some(closure_region_requirements) = closure_region_requirements {
+    let err = if let Some(closure_region_requirements) = closure_region_requirements {
         let mut err = infcx.dcx().struct_span_note(def_span, "external requirements");
 
         regioncx.annotate(tcx, &mut err);
@@ -340,15 +324,11 @@ pub(super) fn dump_annotation<'tcx, 'infcx>(
     } else {
         let mut err = infcx.dcx().struct_span_note(def_span, "no external requirements");
         regioncx.annotate(tcx, &mut err);
-
         err
     };
 
-    if !concrete_opaque_types.is_empty() {
-        err.note(format!("Inferred opaque type values:\n{concrete_opaque_types:#?}"));
-    }
-
-    diagnostics_buffer.buffer_non_error(err);
+    // FIXME(@lcnr): We currently don't dump the inferred hidden types here.
+    err.emit();
 }
 
 fn for_each_region_constraint<'tcx>(
diff --git a/compiler/rustc_borrowck/src/opaque_types.rs b/compiler/rustc_borrowck/src/opaque_types.rs
deleted file mode 100644
index 5c78814abdd..00000000000
--- a/compiler/rustc_borrowck/src/opaque_types.rs
+++ /dev/null
@@ -1,55 +0,0 @@
-use rustc_data_structures::fx::FxIndexMap;
-use rustc_hir::def_id::LocalDefId;
-use rustc_middle::ty::{OpaqueHiddenType, Ty, TyCtxt};
-
-#[derive(Debug, Default)]
-pub(super) struct ConcreteOpaqueTypes<'tcx> {
-    concrete_opaque_types: FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>>,
-}
-
-impl<'tcx> ConcreteOpaqueTypes<'tcx> {
-    pub(super) fn is_empty(&self) -> bool {
-        self.concrete_opaque_types.is_empty()
-    }
-
-    pub(super) fn into_inner(self) -> FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>> {
-        self.concrete_opaque_types
-    }
-
-    /// Insert an opaque type into the list of opaque types defined by this function
-    /// after mapping the hidden type to the generic parameters of the opaque type
-    /// definition.
-    pub(super) fn insert(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        def_id: LocalDefId,
-        hidden_ty: OpaqueHiddenType<'tcx>,
-    ) {
-        // Sometimes two opaque types are the same only after we remap the generic parameters
-        // back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to
-        // `(X, Y)` and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we
-        // only know that once we convert the generic parameters to those of the opaque type.
-        if let Some(prev) = self.concrete_opaque_types.get_mut(&def_id) {
-            if prev.ty != hidden_ty.ty {
-                let (Ok(guar) | Err(guar)) =
-                    prev.build_mismatch_error(&hidden_ty, tcx).map(|d| d.emit());
-                prev.ty = Ty::new_error(tcx, guar);
-            }
-            // Pick a better span if there is one.
-            // FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
-            prev.span = prev.span.substitute_dummy(hidden_ty.span);
-        } else {
-            self.concrete_opaque_types.insert(def_id, hidden_ty);
-        }
-    }
-
-    pub(super) fn extend_from_nested_body(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        nested_body: &FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>>,
-    ) {
-        for (&def_id, &hidden_ty) in nested_body {
-            self.insert(tcx, def_id, hidden_ty);
-        }
-    }
-}
diff --git a/compiler/rustc_borrowck/src/polonius/dump.rs b/compiler/rustc_borrowck/src/polonius/dump.rs
index aa64a7c4e2a..6a943e19208 100644
--- a/compiler/rustc_borrowck/src/polonius/dump.rs
+++ b/compiler/rustc_borrowck/src/polonius/dump.rs
@@ -5,7 +5,7 @@ use rustc_index::IndexVec;
 use rustc_middle::mir::pretty::{
     PassWhere, PrettyPrintMirOptions, create_dump_file, dump_enabled, dump_mir_to_writer,
 };
-use rustc_middle::mir::{Body, ClosureRegionRequirements, Location};
+use rustc_middle::mir::{Body, Location};
 use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_mir_dataflow::points::PointIndex;
 use rustc_session::config::MirIncludeSpans;
@@ -17,16 +17,16 @@ use crate::polonius::{
 };
 use crate::region_infer::values::LivenessValues;
 use crate::type_check::Locations;
-use crate::{BorrowckInferCtxt, RegionInferenceContext};
+use crate::{BorrowckInferCtxt, ClosureRegionRequirements, RegionInferenceContext};
 
 /// `-Zdump-mir=polonius` dumps MIR annotated with NLL and polonius specific information.
 pub(crate) fn dump_polonius_mir<'tcx>(
     infcx: &BorrowckInferCtxt<'tcx>,
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
+    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
     borrow_set: &BorrowSet<'tcx>,
     polonius_diagnostics: Option<&PoloniusDiagnosticsContext>,
-    closure_region_requirements: &Option<ClosureRegionRequirements<'tcx>>,
 ) {
     let tcx = infcx.tcx;
     if !tcx.sess.opts.unstable_opts.polonius.is_next_enabled() {
@@ -334,7 +334,7 @@ fn emit_mermaid_nll_regions<'tcx>(
     writeln!(out, "flowchart TD")?;
 
     // Emit the region nodes.
-    for region in regioncx.var_infos.indices() {
+    for region in regioncx.definitions.indices() {
         write!(out, "{}[\"", region.as_usize())?;
         render_region(region, regioncx, out)?;
         writeln!(out, "\"]")?;
@@ -387,7 +387,7 @@ fn emit_mermaid_nll_sccs<'tcx>(
     // Gather and emit the SCC nodes.
     let mut nodes_per_scc: IndexVec<_, _> =
         regioncx.constraint_sccs().all_sccs().map(|_| Vec::new()).collect();
-    for region in regioncx.var_infos.indices() {
+    for region in regioncx.definitions.indices() {
         let scc = regioncx.constraint_sccs().scc(region);
         nodes_per_scc[scc].push(region);
     }
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index a80d74d9e37..f8af9e59f63 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -9,22 +9,20 @@ use rustc_errors::Diag;
 use rustc_hir::def_id::CRATE_DEF_ID;
 use rustc_index::IndexVec;
 use rustc_infer::infer::outlives::test_type_match;
-use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound, VerifyIfEq};
+use rustc_infer::infer::region_constraints::{GenericKind, VerifyBound, VerifyIfEq};
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
 use rustc_middle::bug;
 use rustc_middle::mir::{
-    AnnotationSource, BasicBlock, Body, ClosureOutlivesRequirement, ClosureOutlivesSubject,
-    ClosureOutlivesSubjectTy, ClosureRegionRequirements, ConstraintCategory, Local, Location,
-    ReturnConstraint, TerminatorKind,
+    AnnotationSource, BasicBlock, Body, ConstraintCategory, Local, Location, ReturnConstraint,
+    TerminatorKind,
 };
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, UniverseIndex, fold_regions};
 use rustc_mir_dataflow::points::DenseLocationMap;
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::{DUMMY_SP, Span};
-use tracing::{debug, instrument, trace};
+use tracing::{Level, debug, enabled, instrument, trace};
 
-use crate::BorrowckInferCtxt;
 use crate::constraints::graph::{self, NormalConstraintGraph, RegionGraph};
 use crate::constraints::{ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet};
 use crate::dataflow::BorrowIndex;
@@ -37,6 +35,10 @@ use crate::region_infer::values::{LivenessValues, RegionElement, RegionValues, T
 use crate::type_check::free_region_relations::UniversalRegionRelations;
 use crate::type_check::{Locations, MirTypeckRegionConstraints};
 use crate::universal_regions::UniversalRegions;
+use crate::{
+    BorrowckInferCtxt, ClosureOutlivesRequirement, ClosureOutlivesSubject,
+    ClosureOutlivesSubjectTy, ClosureRegionRequirements,
+};
 
 mod dump_mir;
 mod graphviz;
@@ -139,13 +141,11 @@ impl RegionTracker {
 }
 
 pub struct RegionInferenceContext<'tcx> {
-    pub var_infos: VarInfos,
-
     /// Contains the definition for every region variable. Region
     /// variables are identified by their index (`RegionVid`). The
     /// definition contains information about where the region came
     /// from as well as its final inferred value.
-    definitions: IndexVec<RegionVid, RegionDefinition<'tcx>>,
+    pub(crate) definitions: Frozen<IndexVec<RegionVid, RegionDefinition<'tcx>>>,
 
     /// The liveness constraints added to each region. For most
     /// regions, these start out empty and steadily grow, though for
@@ -327,31 +327,34 @@ fn sccs_info<'tcx>(infcx: &BorrowckInferCtxt<'tcx>, sccs: &ConstraintSccs) {
     let mut var_to_origin_sorted = var_to_origin.clone().into_iter().collect::<Vec<_>>();
     var_to_origin_sorted.sort_by_key(|vto| vto.0);
 
-    let mut reg_vars_to_origins_str = "region variables to origins:\n".to_string();
-    for (reg_var, origin) in var_to_origin_sorted.into_iter() {
-        reg_vars_to_origins_str.push_str(&format!("{reg_var:?}: {origin:?}\n"));
+    if enabled!(Level::DEBUG) {
+        let mut reg_vars_to_origins_str = "region variables to origins:\n".to_string();
+        for (reg_var, origin) in var_to_origin_sorted.into_iter() {
+            reg_vars_to_origins_str.push_str(&format!("{reg_var:?}: {origin:?}\n"));
+        }
+        debug!("{}", reg_vars_to_origins_str);
     }
-    debug!("{}", reg_vars_to_origins_str);
 
     let num_components = sccs.num_sccs();
     let mut components = vec![FxIndexSet::default(); num_components];
 
-    for (reg_var_idx, scc_idx) in sccs.scc_indices().iter().enumerate() {
-        let reg_var = ty::RegionVid::from_usize(reg_var_idx);
+    for (reg_var, scc_idx) in sccs.scc_indices().iter_enumerated() {
         let origin = var_to_origin.get(&reg_var).unwrap_or(&RegionCtxt::Unknown);
         components[scc_idx.as_usize()].insert((reg_var, *origin));
     }
 
-    let mut components_str = "strongly connected components:".to_string();
-    for (scc_idx, reg_vars_origins) in components.iter().enumerate() {
-        let regions_info = reg_vars_origins.clone().into_iter().collect::<Vec<_>>();
-        components_str.push_str(&format!(
-            "{:?}: {:?},\n)",
-            ConstraintSccIndex::from_usize(scc_idx),
-            regions_info,
-        ))
+    if enabled!(Level::DEBUG) {
+        let mut components_str = "strongly connected components:".to_string();
+        for (scc_idx, reg_vars_origins) in components.iter().enumerate() {
+            let regions_info = reg_vars_origins.clone().into_iter().collect::<Vec<_>>();
+            components_str.push_str(&format!(
+                "{:?}: {:?},\n)",
+                ConstraintSccIndex::from_usize(scc_idx),
+                regions_info,
+            ))
+        }
+        debug!("{}", components_str);
     }
-    debug!("{}", components_str);
 
     // calculate the best representative for each component
     let components_representatives = components
@@ -381,6 +384,26 @@ fn sccs_info<'tcx>(infcx: &BorrowckInferCtxt<'tcx>, sccs: &ConstraintSccs) {
     debug!("SCC edges {:#?}", scc_node_to_edges);
 }
 
+fn create_definitions<'tcx>(
+    infcx: &BorrowckInferCtxt<'tcx>,
+    universal_regions: &UniversalRegions<'tcx>,
+) -> Frozen<IndexVec<RegionVid, RegionDefinition<'tcx>>> {
+    // Create a RegionDefinition for each inference variable.
+    let mut definitions: IndexVec<_, _> = infcx
+        .get_region_var_infos()
+        .iter()
+        .map(|info| RegionDefinition::new(info.universe, info.origin))
+        .collect();
+
+    // Add the external name for all universal regions.
+    for (external_name, variable) in universal_regions.named_universal_regions_iter() {
+        debug!("region {variable:?} has external name {external_name:?}");
+        definitions[variable].external_name = Some(external_name);
+    }
+
+    Frozen::freeze(definitions)
+}
+
 impl<'tcx> RegionInferenceContext<'tcx> {
     /// Creates a new region inference context with a total of
     /// `num_region_variables` valid inference variables; the first N
@@ -391,7 +414,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// of constraints produced by the MIR type check.
     pub(crate) fn new(
         infcx: &BorrowckInferCtxt<'tcx>,
-        var_infos: VarInfos,
         constraints: MirTypeckRegionConstraints<'tcx>,
         universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
         location_map: Rc<DenseLocationMap>,
@@ -422,11 +444,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             infcx.set_tainted_by_errors(guar);
         }
 
-        // Create a RegionDefinition for each inference variable.
-        let definitions: IndexVec<_, _> = var_infos
-            .iter()
-            .map(|info| RegionDefinition::new(info.universe, info.origin))
-            .collect();
+        let definitions = create_definitions(infcx, &universal_regions);
 
         let constraint_sccs =
             outlives_constraints.add_outlives_static(&universal_regions, &definitions);
@@ -449,7 +467,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             Rc::new(member_constraints.into_mapped(|r| constraint_sccs.scc(r)));
 
         let mut result = Self {
-            var_infos,
             definitions,
             liveness_constraints,
             constraints,
@@ -523,18 +540,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// means that the `R1: !1` constraint here will cause
     /// `R1` to become `'static`.
     fn init_free_and_bound_regions(&mut self) {
-        // Update the names (if any)
-        // This iterator has unstable order but we collect it all into an IndexVec
-        for (external_name, variable) in
-            self.universal_region_relations.universal_regions.named_universal_regions_iter()
-        {
-            debug!(
-                "init_free_and_bound_regions: region {:?} has external name {:?}",
-                variable, external_name
-            );
-            self.definitions[variable].external_name = Some(external_name);
-        }
-
         for variable in self.definitions.indices() {
             let scc = self.constraint_sccs.scc(variable);
 
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index a098450352f..550c57338d3 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -10,7 +10,7 @@ use rustc_trait_selection::opaque_types::check_opaque_type_parameter_valid;
 use tracing::{debug, instrument};
 
 use super::RegionInferenceContext;
-use crate::opaque_types::ConcreteOpaqueTypes;
+use crate::BorrowCheckRootCtxt;
 use crate::session_diagnostics::LifetimeMismatchOpaqueParam;
 use crate::universal_regions::RegionClassification;
 
@@ -58,12 +58,12 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// [rustc-dev-guide chapter]:
     /// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
-    #[instrument(level = "debug", skip(self, infcx), ret)]
+    #[instrument(level = "debug", skip(self, root_cx, infcx), ret)]
     pub(crate) fn infer_opaque_types(
         &self,
+        root_cx: &mut BorrowCheckRootCtxt<'tcx>,
         infcx: &InferCtxt<'tcx>,
         opaque_ty_decls: FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
-        concrete_opaque_types: &mut ConcreteOpaqueTypes<'tcx>,
     ) {
         let mut decls_modulo_regions: FxIndexMap<OpaqueTypeKey<'tcx>, (OpaqueTypeKey<'tcx>, Span)> =
             FxIndexMap::default();
@@ -140,11 +140,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 }
             }
 
-            concrete_opaque_types.insert(
-                infcx.tcx,
+            root_cx.add_concrete_opaque_type(
                 opaque_type_key.def_id,
-                OpaqueHiddenType { ty, span: concrete_type.span },
+                OpaqueHiddenType { span: concrete_type.span, ty },
             );
+
             // Check that all opaque types have the same region parameters if they have the same
             // non-region parameters. This is necessary because within the new solver we perform
             // various query operations modulo regions, and thus could unsoundly select some impls
@@ -186,7 +186,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        fold_regions(tcx, ty, |region, _| match *region {
+        fold_regions(tcx, ty, |region, _| match region.kind() {
             ty::ReVar(vid) => {
                 let scc = self.constraint_sccs.scc(vid);
 
diff --git a/compiler/rustc_borrowck/src/root_cx.rs b/compiler/rustc_borrowck/src/root_cx.rs
new file mode 100644
index 00000000000..13daa5c7221
--- /dev/null
+++ b/compiler/rustc_borrowck/src/root_cx.rs
@@ -0,0 +1,101 @@
+use rustc_abi::FieldIdx;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_hir::def_id::LocalDefId;
+use rustc_middle::bug;
+use rustc_middle::ty::{OpaqueHiddenType, Ty, TyCtxt, TypeVisitableExt};
+use rustc_span::ErrorGuaranteed;
+use smallvec::SmallVec;
+
+use crate::{ClosureRegionRequirements, ConcreteOpaqueTypes, PropagatedBorrowCheckResults};
+
+/// The shared context used by both the root as well as all its nested
+/// items.
+pub(super) struct BorrowCheckRootCtxt<'tcx> {
+    pub tcx: TyCtxt<'tcx>,
+    root_def_id: LocalDefId,
+    concrete_opaque_types: ConcreteOpaqueTypes<'tcx>,
+    nested_bodies: FxHashMap<LocalDefId, PropagatedBorrowCheckResults<'tcx>>,
+    tainted_by_errors: Option<ErrorGuaranteed>,
+}
+
+impl<'tcx> BorrowCheckRootCtxt<'tcx> {
+    pub(super) fn new(tcx: TyCtxt<'tcx>, root_def_id: LocalDefId) -> BorrowCheckRootCtxt<'tcx> {
+        BorrowCheckRootCtxt {
+            tcx,
+            root_def_id,
+            concrete_opaque_types: Default::default(),
+            nested_bodies: Default::default(),
+            tainted_by_errors: None,
+        }
+    }
+
+    /// Collect all defining uses of opaque types inside of this typeck root. This
+    /// expects the hidden type to be mapped to the definition parameters of the opaque
+    /// and errors if we end up with distinct hidden types.
+    pub(super) fn add_concrete_opaque_type(
+        &mut self,
+        def_id: LocalDefId,
+        hidden_ty: OpaqueHiddenType<'tcx>,
+    ) {
+        // Sometimes two opaque types are the same only after we remap the generic parameters
+        // back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to
+        // `(X, Y)` and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we
+        // only know that once we convert the generic parameters to those of the opaque type.
+        if let Some(prev) = self.concrete_opaque_types.0.get_mut(&def_id) {
+            if prev.ty != hidden_ty.ty {
+                let guar = hidden_ty.ty.error_reported().err().unwrap_or_else(|| {
+                    let (Ok(e) | Err(e)) =
+                        prev.build_mismatch_error(&hidden_ty, self.tcx).map(|d| d.emit());
+                    e
+                });
+                prev.ty = Ty::new_error(self.tcx, guar);
+            }
+            // Pick a better span if there is one.
+            // FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
+            prev.span = prev.span.substitute_dummy(hidden_ty.span);
+        } else {
+            self.concrete_opaque_types.0.insert(def_id, hidden_ty);
+        }
+    }
+
+    pub(super) fn set_tainted_by_errors(&mut self, guar: ErrorGuaranteed) {
+        self.tainted_by_errors = Some(guar);
+    }
+
+    fn get_or_insert_nested(&mut self, def_id: LocalDefId) -> &PropagatedBorrowCheckResults<'tcx> {
+        debug_assert_eq!(
+            self.tcx.typeck_root_def_id(def_id.to_def_id()),
+            self.root_def_id.to_def_id()
+        );
+        if !self.nested_bodies.contains_key(&def_id) {
+            let result = super::do_mir_borrowck(self, def_id, None).0;
+            if let Some(prev) = self.nested_bodies.insert(def_id, result) {
+                bug!("unexpected previous nested body: {prev:?}");
+            }
+        }
+
+        self.nested_bodies.get(&def_id).unwrap()
+    }
+
+    pub(super) fn closure_requirements(
+        &mut self,
+        nested_body_def_id: LocalDefId,
+    ) -> &Option<ClosureRegionRequirements<'tcx>> {
+        &self.get_or_insert_nested(nested_body_def_id).closure_requirements
+    }
+
+    pub(super) fn used_mut_upvars(
+        &mut self,
+        nested_body_def_id: LocalDefId,
+    ) -> &SmallVec<[FieldIdx; 8]> {
+        &self.get_or_insert_nested(nested_body_def_id).used_mut_upvars
+    }
+
+    pub(super) fn finalize(self) -> Result<&'tcx ConcreteOpaqueTypes<'tcx>, ErrorGuaranteed> {
+        if let Some(guar) = self.tainted_by_errors {
+            Err(guar)
+        } else {
+            Ok(self.tcx.arena.alloc(self.concrete_opaque_types))
+        }
+    }
+}
diff --git a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
index 6fbe1db6330..57516565147 100644
--- a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
+++ b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
@@ -6,7 +6,6 @@ use rustc_infer::infer::region_constraints::{GenericKind, VerifyBound};
 use rustc_infer::infer::{self, InferCtxt, SubregionOrigin};
 use rustc_infer::traits::query::type_op::DeeplyNormalize;
 use rustc_middle::bug;
-use rustc_middle::mir::{ClosureOutlivesSubject, ClosureRegionRequirements, ConstraintCategory};
 use rustc_middle::ty::{
     self, GenericArgKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, fold_regions,
 };
@@ -18,10 +17,10 @@ use crate::constraints::OutlivesConstraint;
 use crate::region_infer::TypeTest;
 use crate::type_check::{Locations, MirTypeckRegionConstraints};
 use crate::universal_regions::UniversalRegions;
+use crate::{ClosureOutlivesSubject, ClosureRegionRequirements, ConstraintCategory};
 
 pub(crate) struct ConstraintConversion<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
-    tcx: TyCtxt<'tcx>,
     universal_regions: &'a UniversalRegions<'tcx>,
     /// Each RBP `GK: 'a` is assumed to be true. These encode
     /// relationships like `T: 'a` that are added via implicit bounds
@@ -34,7 +33,6 @@ pub(crate) struct ConstraintConversion<'a, 'tcx> {
     /// logic expecting to see (e.g.) `ReStatic`, and if we supplied
     /// our special inference variable there, we would mess that up.
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
-    implicit_region_bound: ty::Region<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     known_type_outlives_obligations: &'a [ty::PolyTypeOutlivesPredicate<'tcx>],
     locations: Locations,
@@ -49,7 +47,6 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         infcx: &'a InferCtxt<'tcx>,
         universal_regions: &'a UniversalRegions<'tcx>,
         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
-        implicit_region_bound: ty::Region<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         known_type_outlives_obligations: &'a [ty::PolyTypeOutlivesPredicate<'tcx>],
         locations: Locations,
@@ -59,10 +56,8 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     ) -> Self {
         Self {
             infcx,
-            tcx: infcx.tcx,
             universal_regions,
             region_bound_pairs,
-            implicit_region_bound,
             param_env,
             known_type_outlives_obligations,
             locations,
@@ -96,7 +91,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         // into a vector. These are the regions that we will be
         // relating to one another.
         let closure_mapping = &UniversalRegions::closure_mapping(
-            self.tcx,
+            self.infcx.tcx,
             closure_args,
             closure_requirements.num_external_vids,
             closure_def_id,
@@ -111,7 +106,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
             let subject = match outlives_requirement.subject {
                 ClosureOutlivesSubject::Region(re) => closure_mapping[re].into(),
                 ClosureOutlivesSubject::Ty(subject_ty) => {
-                    subject_ty.instantiate(self.tcx, |vid| closure_mapping[vid]).into()
+                    subject_ty.instantiate(self.infcx.tcx, |vid| closure_mapping[vid]).into()
                 }
             };
 
@@ -127,14 +122,14 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         predicate: ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
         constraint_category: ConstraintCategory<'tcx>,
     ) {
+        let tcx = self.infcx.tcx;
         debug!("generate: constraints at: {:#?}", self.locations);
 
         // Extract out various useful fields we'll need below.
         let ConstraintConversion {
-            tcx,
             infcx,
+            universal_regions,
             region_bound_pairs,
-            implicit_region_bound,
             known_type_outlives_obligations,
             ..
         } = *self;
@@ -145,7 +140,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                 break;
             }
 
-            if !self.tcx.recursion_limit().value_within_limit(iteration) {
+            if !tcx.recursion_limit().value_within_limit(iteration) {
                 bug!(
                     "FIXME(-Znext-solver): Overflowed when processing region obligations: {outlives_predicates:#?}"
                 );
@@ -170,10 +165,11 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                             );
                         }
 
+                        let implicit_region_bound =
+                            ty::Region::new_var(tcx, universal_regions.implicit_region_bound());
                         // we don't actually use this for anything, but
                         // the `TypeOutlives` code needs an origin.
                         let origin = infer::RelateParamBound(self.span, t1, None);
-
                         TypeOutlives::new(
                             &mut *self,
                             tcx,
@@ -205,7 +201,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     /// are dealt with during trait solving.
     fn replace_placeholders_with_nll<T: TypeFoldable<TyCtxt<'tcx>>>(&mut self, value: T) -> T {
         if value.has_placeholders() {
-            fold_regions(self.tcx, value, |r, _| match *r {
+            fold_regions(self.infcx.tcx, value, |r, _| match r.kind() {
                 ty::RePlaceholder(placeholder) => {
                     self.constraints.placeholder_region(self.infcx, placeholder)
                 }
@@ -227,7 +223,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     }
 
     fn to_region_vid(&mut self, r: ty::Region<'tcx>) -> ty::RegionVid {
-        if let ty::RePlaceholder(placeholder) = *r {
+        if let ty::RePlaceholder(placeholder) = r.kind() {
             self.constraints.placeholder_region(self.infcx, placeholder).as_var()
         } else {
             self.universal_regions.to_region_vid(r)
diff --git a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
index eaac633b512..536a27763d2 100644
--- a/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
+++ b/compiler/rustc_borrowck/src/type_check/free_region_relations.rs
@@ -49,14 +49,12 @@ pub(crate) struct CreateResult<'tcx> {
 pub(crate) fn create<'tcx>(
     infcx: &InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    implicit_region_bound: ty::Region<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     constraints: &mut MirTypeckRegionConstraints<'tcx>,
 ) -> CreateResult<'tcx> {
     UniversalRegionRelationsBuilder {
         infcx,
         param_env,
-        implicit_region_bound,
         constraints,
         universal_regions,
         region_bound_pairs: Default::default(),
@@ -181,7 +179,6 @@ struct UniversalRegionRelationsBuilder<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
-    implicit_region_bound: ty::Region<'tcx>,
     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 
     // outputs:
@@ -320,7 +317,6 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
                 self.infcx,
                 &self.universal_regions,
                 &self.region_bound_pairs,
-                self.implicit_region_bound,
                 param_env,
                 &known_type_outlives_obligations,
                 Locations::All(span),
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index f6144a25938..3c00b819a96 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -45,7 +45,6 @@ use crate::borrow_set::BorrowSet;
 use crate::constraints::{OutlivesConstraint, OutlivesConstraintSet};
 use crate::diagnostics::UniverseInfo;
 use crate::member_constraints::MemberConstraintSet;
-use crate::opaque_types::ConcreteOpaqueTypes;
 use crate::polonius::legacy::{PoloniusFacts, PoloniusLocationTable};
 use crate::polonius::{PoloniusContext, PoloniusLivenessContext};
 use crate::region_infer::TypeTest;
@@ -53,7 +52,7 @@ use crate::region_infer::values::{LivenessValues, PlaceholderIndex, PlaceholderI
 use crate::session_diagnostics::{MoveUnsized, SimdIntrinsicArgConst};
 use crate::type_check::free_region_relations::{CreateResult, UniversalRegionRelations};
 use crate::universal_regions::{DefiningTy, UniversalRegions};
-use crate::{BorrowckInferCtxt, path_utils};
+use crate::{BorrowCheckRootCtxt, BorrowckInferCtxt, path_utils};
 
 macro_rules! span_mirbug {
     ($context:expr, $elem:expr, $($message:tt)*) => ({
@@ -102,6 +101,7 @@ mod relate_tys;
 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysis
 /// - `location_map` -- map between MIR `Location` and `PointIndex`
 pub(crate) fn type_check<'a, 'tcx>(
+    root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     infcx: &BorrowckInferCtxt<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
@@ -112,9 +112,7 @@ pub(crate) fn type_check<'a, 'tcx>(
     flow_inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
     move_data: &MoveData<'tcx>,
     location_map: Rc<DenseLocationMap>,
-    concrete_opaque_types: &mut ConcreteOpaqueTypes<'tcx>,
 ) -> MirTypeckResults<'tcx> {
-    let implicit_region_bound = ty::Region::new_var(infcx.tcx, universal_regions.fr_fn_body);
     let mut constraints = MirTypeckRegionConstraints {
         placeholder_indices: PlaceholderIndices::default(),
         placeholder_index_to_region: IndexVec::default(),
@@ -130,13 +128,7 @@ pub(crate) fn type_check<'a, 'tcx>(
         region_bound_pairs,
         normalized_inputs_and_output,
         known_type_outlives_obligations,
-    } = free_region_relations::create(
-        infcx,
-        infcx.param_env,
-        implicit_region_bound,
-        universal_regions,
-        &mut constraints,
-    );
+    } = free_region_relations::create(infcx, infcx.param_env, universal_regions, &mut constraints);
 
     let pre_obligations = infcx.take_registered_region_obligations();
     assert!(
@@ -153,6 +145,7 @@ pub(crate) fn type_check<'a, 'tcx>(
     };
 
     let mut typeck = TypeChecker {
+        root_cx,
         infcx,
         last_span: body.span,
         body,
@@ -160,14 +153,12 @@ pub(crate) fn type_check<'a, 'tcx>(
         user_type_annotations: &body.user_type_annotations,
         region_bound_pairs,
         known_type_outlives_obligations,
-        implicit_region_bound,
         reported_errors: Default::default(),
         universal_regions: &universal_region_relations.universal_regions,
         location_table,
         polonius_facts,
         borrow_set,
         constraints: &mut constraints,
-        concrete_opaque_types,
         polonius_liveness,
     };
 
@@ -215,6 +206,7 @@ enum FieldAccessError {
 /// way, it accrues region constraints -- these can later be used by
 /// NLL region checking.
 struct TypeChecker<'a, 'tcx> {
+    root_cx: &'a mut BorrowCheckRootCtxt<'tcx>,
     infcx: &'a BorrowckInferCtxt<'tcx>,
     last_span: Span,
     body: &'a Body<'tcx>,
@@ -226,14 +218,12 @@ struct TypeChecker<'a, 'tcx> {
     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
     region_bound_pairs: RegionBoundPairs<'tcx>,
     known_type_outlives_obligations: Vec<ty::PolyTypeOutlivesPredicate<'tcx>>,
-    implicit_region_bound: ty::Region<'tcx>,
     reported_errors: FxIndexSet<(Ty<'tcx>, Span)>,
     universal_regions: &'a UniversalRegions<'tcx>,
     location_table: &'a PoloniusLocationTable,
     polonius_facts: &'a mut Option<PoloniusFacts>,
     borrow_set: &'a BorrowSet<'tcx>,
     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
-    concrete_opaque_types: &'a mut ConcreteOpaqueTypes<'tcx>,
     /// When using `-Zpolonius=next`, the liveness helper data used to create polonius constraints.
     polonius_liveness: Option<PoloniusLivenessContext>,
 }
@@ -423,7 +413,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             self.infcx,
             self.universal_regions,
             &self.region_bound_pairs,
-            self.implicit_region_bound,
             self.infcx.param_env,
             &self.known_type_outlives_obligations,
             locations,
@@ -1568,11 +1557,15 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                         }
                     }
                     CastKind::Transmute => {
-                        span_mirbug!(
-                            self,
-                            rvalue,
-                            "Unexpected CastKind::Transmute, which is not permitted in Analysis MIR",
-                        );
+                        let ty_from = op.ty(self.body, tcx);
+                        match ty_from.kind() {
+                            ty::Pat(base, _) if base == ty => {}
+                            _ => span_mirbug!(
+                                self,
+                                rvalue,
+                                "Unexpected CastKind::Transmute {ty_from:?} -> {ty:?}, which is not permitted in Analysis MIR",
+                            ),
+                        }
                     }
                 }
             }
@@ -2503,16 +2496,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         args: GenericArgsRef<'tcx>,
         locations: Locations,
     ) -> ty::InstantiatedPredicates<'tcx> {
-        let closure_borrowck_results = tcx.mir_borrowck(def_id);
-        self.concrete_opaque_types
-            .extend_from_nested_body(tcx, &closure_borrowck_results.concrete_opaque_types);
-
-        if let Some(closure_requirements) = &closure_borrowck_results.closure_requirements {
+        if let Some(closure_requirements) = &self.root_cx.closure_requirements(def_id) {
             constraint_conversion::ConstraintConversion::new(
                 self.infcx,
                 self.universal_regions,
                 &self.region_bound_pairs,
-                self.implicit_region_bound,
                 self.infcx.param_env,
                 &self.known_type_outlives_obligations,
                 locations,
diff --git a/compiler/rustc_borrowck/src/type_check/opaque_types.rs b/compiler/rustc_borrowck/src/type_check/opaque_types.rs
index 8bab979a724..d41cbf757d7 100644
--- a/compiler/rustc_borrowck/src/type_check/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/type_check/opaque_types.rs
@@ -271,7 +271,7 @@ where
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        match *r {
+        match r.kind() {
             // ignore bound regions, keep visiting
             ty::ReBound(_, _) => {}
             _ => (self.op)(r),
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 8f6b405fcef..c11e14d214c 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -438,6 +438,10 @@ impl<'tcx> UniversalRegions<'tcx> {
         }
     }
 
+    pub(crate) fn implicit_region_bound(&self) -> RegionVid {
+        self.fr_fn_body
+    }
+
     pub(crate) fn tainted_by_errors(&self) -> Option<ErrorGuaranteed> {
         self.indices.tainted_by_errors.get()
     }
@@ -909,19 +913,19 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
     /// if it is a placeholder. Handling placeholders requires access to the
     /// `MirTypeckRegionConstraints`.
     fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
-        if let ty::ReVar(..) = *r {
-            r.as_var()
-        } else if let ty::ReError(guar) = *r {
-            self.tainted_by_errors.set(Some(guar));
-            // We use the `'static` `RegionVid` because `ReError` doesn't actually exist in the
-            // `UniversalRegionIndices`. This is fine because 1) it is a fallback only used if
-            // errors are being emitted and 2) it leaves the happy path unaffected.
-            self.fr_static
-        } else {
-            *self
+        match r.kind() {
+            ty::ReVar(..) => r.as_var(),
+            ty::ReError(guar) => {
+                self.tainted_by_errors.set(Some(guar));
+                // We use the `'static` `RegionVid` because `ReError` doesn't actually exist in the
+                // `UniversalRegionIndices`. This is fine because 1) it is a fallback only used if
+                // errors are being emitted and 2) it leaves the happy path unaffected.
+                self.fr_static
+            }
+            _ => *self
                 .indices
                 .get(&r)
-                .unwrap_or_else(|| bug!("cannot convert `{:?}` to a region vid", r))
+                .unwrap_or_else(|| bug!("cannot convert `{:?}` to a region vid", r)),
         }
     }
 
diff --git a/compiler/rustc_builtin_macros/messages.ftl b/compiler/rustc_builtin_macros/messages.ftl
index 603dc90bafc..5316e90847a 100644
--- a/compiler/rustc_builtin_macros/messages.ftl
+++ b/compiler/rustc_builtin_macros/messages.ftl
@@ -231,8 +231,6 @@ builtin_macros_format_unused_args = multiple unused formatting arguments
 
 builtin_macros_format_use_positional = consider using a positional formatting argument instead
 
-builtin_macros_invalid_crate_attribute = invalid crate attribute
-
 builtin_macros_multiple_default_attrs = multiple `#[default]` attributes
     .note = only one `#[default]` attribute is needed
     .label = `#[default]` used here
diff --git a/compiler/rustc_builtin_macros/src/autodiff.rs b/compiler/rustc_builtin_macros/src/autodiff.rs
index 7f99f75b2b9..daebd516499 100644
--- a/compiler/rustc_builtin_macros/src/autodiff.rs
+++ b/compiler/rustc_builtin_macros/src/autodiff.rs
@@ -17,7 +17,7 @@ mod llvm_enzyme {
     use rustc_ast::visit::AssocCtxt::*;
     use rustc_ast::{
         self as ast, AssocItemKind, BindingMode, ExprKind, FnRetTy, FnSig, Generics, ItemKind,
-        MetaItemInner, PatKind, QSelf, TyKind,
+        MetaItemInner, PatKind, QSelf, TyKind, Visibility,
     };
     use rustc_expand::base::{Annotatable, ExtCtxt};
     use rustc_span::{Ident, Span, Symbol, kw, sym};
@@ -72,6 +72,16 @@ mod llvm_enzyme {
         }
     }
 
+    // Get information about the function the macro is applied to
+    fn extract_item_info(iitem: &P<ast::Item>) -> Option<(Visibility, FnSig, Ident)> {
+        match &iitem.kind {
+            ItemKind::Fn(box ast::Fn { sig, ident, .. }) => {
+                Some((iitem.vis.clone(), sig.clone(), ident.clone()))
+            }
+            _ => None,
+        }
+    }
+
     pub(crate) fn from_ast(
         ecx: &mut ExtCtxt<'_>,
         meta_item: &ThinVec<MetaItemInner>,
@@ -199,38 +209,32 @@ mod llvm_enzyme {
             return vec![item];
         }
         let dcx = ecx.sess.dcx();
-        // first get the annotable item:
-        let (primal, sig, is_impl): (Ident, FnSig, bool) = match &item {
-            Annotatable::Item(iitem) => {
-                let (ident, sig) = match &iitem.kind {
-                    ItemKind::Fn(box ast::Fn { ident, sig, .. }) => (ident, sig),
-                    _ => {
-                        dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                        return vec![item];
-                    }
-                };
-                (*ident, sig.clone(), false)
-            }
+
+        // first get information about the annotable item:
+        let Some((vis, sig, primal)) = (match &item {
+            Annotatable::Item(iitem) => extract_item_info(iitem),
+            Annotatable::Stmt(stmt) => match &stmt.kind {
+                ast::StmtKind::Item(iitem) => extract_item_info(iitem),
+                _ => None,
+            },
             Annotatable::AssocItem(assoc_item, Impl { of_trait: false }) => {
-                let (ident, sig) = match &assoc_item.kind {
-                    ast::AssocItemKind::Fn(box ast::Fn { ident, sig, .. }) => (ident, sig),
-                    _ => {
-                        dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                        return vec![item];
+                match &assoc_item.kind {
+                    ast::AssocItemKind::Fn(box ast::Fn { sig, ident, .. }) => {
+                        Some((assoc_item.vis.clone(), sig.clone(), ident.clone()))
                     }
-                };
-                (*ident, sig.clone(), true)
-            }
-            _ => {
-                dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                return vec![item];
+                    _ => None,
+                }
             }
+            _ => None,
+        }) else {
+            dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
+            return vec![item];
         };
 
         let meta_item_vec: ThinVec<MetaItemInner> = match meta_item.kind {
             ast::MetaItemKind::List(ref vec) => vec.clone(),
             _ => {
-                dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
+                dcx.emit_err(errors::AutoDiffMissingConfig { span: item.span() });
                 return vec![item];
             }
         };
@@ -238,15 +242,6 @@ mod llvm_enzyme {
         let has_ret = has_ret(&sig.decl.output);
         let sig_span = ecx.with_call_site_ctxt(sig.span);
 
-        let vis = match &item {
-            Annotatable::Item(iitem) => iitem.vis.clone(),
-            Annotatable::AssocItem(assoc_item, _) => assoc_item.vis.clone(),
-            _ => {
-                dcx.emit_err(errors::AutoDiffInvalidApplication { span: item.span() });
-                return vec![item];
-            }
-        };
-
         // create TokenStream from vec elemtents:
         // meta_item doesn't have a .tokens field
         let mut ts: Vec<TokenTree> = vec![];
@@ -379,6 +374,22 @@ mod llvm_enzyme {
                 }
                 Annotatable::AssocItem(assoc_item.clone(), i)
             }
+            Annotatable::Stmt(ref mut stmt) => {
+                match stmt.kind {
+                    ast::StmtKind::Item(ref mut iitem) => {
+                        if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
+                            iitem.attrs.push(attr);
+                        }
+                        if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind))
+                        {
+                            iitem.attrs.push(inline_never.clone());
+                        }
+                    }
+                    _ => unreachable!("stmt kind checked previously"),
+                };
+
+                Annotatable::Stmt(stmt.clone())
+            }
             _ => {
                 unreachable!("annotatable kind checked previously")
             }
@@ -389,22 +400,40 @@ mod llvm_enzyme {
             delim: rustc_ast::token::Delimiter::Parenthesis,
             tokens: ts,
         });
+
         let d_attr = outer_normal_attr(&rustc_ad_attr, new_id, span);
-        let d_annotatable = if is_impl {
-            let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(asdf);
-            let d_fn = P(ast::AssocItem {
-                attrs: thin_vec![d_attr, inline_never],
-                id: ast::DUMMY_NODE_ID,
-                span,
-                vis,
-                kind: assoc_item,
-                tokens: None,
-            });
-            Annotatable::AssocItem(d_fn, Impl { of_trait: false })
-        } else {
-            let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
-            d_fn.vis = vis;
-            Annotatable::Item(d_fn)
+        let d_annotatable = match &item {
+            Annotatable::AssocItem(_, _) => {
+                let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(asdf);
+                let d_fn = P(ast::AssocItem {
+                    attrs: thin_vec![d_attr, inline_never],
+                    id: ast::DUMMY_NODE_ID,
+                    span,
+                    vis,
+                    kind: assoc_item,
+                    tokens: None,
+                });
+                Annotatable::AssocItem(d_fn, Impl { of_trait: false })
+            }
+            Annotatable::Item(_) => {
+                let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
+                d_fn.vis = vis;
+
+                Annotatable::Item(d_fn)
+            }
+            Annotatable::Stmt(_) => {
+                let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
+                d_fn.vis = vis;
+
+                Annotatable::Stmt(P(ast::Stmt {
+                    id: ast::DUMMY_NODE_ID,
+                    kind: ast::StmtKind::Item(d_fn),
+                    span,
+                }))
+            }
+            _ => {
+                unreachable!("item kind checked previously")
+            }
         };
 
         return vec![orig_annotatable, d_annotatable];
@@ -770,8 +799,19 @@ mod llvm_enzyme {
                         d_inputs.push(shadow_arg.clone());
                     }
                 }
-                DiffActivity::Dual | DiffActivity::DualOnly => {
-                    for i in 0..x.width {
+                DiffActivity::Dual
+                | DiffActivity::DualOnly
+                | DiffActivity::Dualv
+                | DiffActivity::DualvOnly => {
+                    // the *v variants get lowered to enzyme_dupv and enzyme_dupnoneedv, which cause
+                    // Enzyme to not expect N arguments, but one argument (which is instead larger).
+                    let iterations =
+                        if matches!(activity, DiffActivity::Dualv | DiffActivity::DualvOnly) {
+                            1
+                        } else {
+                            x.width
+                        };
+                    for i in 0..iterations {
                         let mut shadow_arg = arg.clone();
                         let old_name = if let PatKind::Ident(_, ident, _) = arg.pat.kind {
                             ident.name
@@ -794,7 +834,7 @@ mod llvm_enzyme {
                 DiffActivity::Const => {
                     // Nothing to do here.
                 }
-                DiffActivity::None | DiffActivity::FakeActivitySize => {
+                DiffActivity::None | DiffActivity::FakeActivitySize(_) => {
                     panic!("Should not happen");
                 }
             }
@@ -858,8 +898,8 @@ mod llvm_enzyme {
                 }
             };
 
-            if let DiffActivity::Dual = x.ret_activity {
-                let kind = if x.width == 1 {
+            if matches!(x.ret_activity, DiffActivity::Dual | DiffActivity::Dualv) {
+                let kind = if x.width == 1 || matches!(x.ret_activity, DiffActivity::Dualv) {
                     // Dual can only be used for f32/f64 ret.
                     // In that case we return now a tuple with two floats.
                     TyKind::Tup(thin_vec![ty.clone(), ty.clone()])
@@ -874,7 +914,7 @@ mod llvm_enzyme {
                 let ty = P(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None });
                 d_decl.output = FnRetTy::Ty(ty);
             }
-            if let DiffActivity::DualOnly = x.ret_activity {
+            if matches!(x.ret_activity, DiffActivity::DualOnly | DiffActivity::DualvOnly) {
                 // No need to change the return type,
                 // we will just return the shadow in place of the primal return.
                 // However, if we have a width > 1, then we don't return -> T, but -> [T; width]
diff --git a/compiler/rustc_builtin_macros/src/cfg_eval.rs b/compiler/rustc_builtin_macros/src/cfg_eval.rs
index b3ba9073118..da01e3e9607 100644
--- a/compiler/rustc_builtin_macros/src/cfg_eval.rs
+++ b/compiler/rustc_builtin_macros/src/cfg_eval.rs
@@ -92,11 +92,7 @@ impl CfgEval<'_> {
         // the location of `#[cfg]` and `#[cfg_attr]` in the token stream. The tokenization
         // process is lossless, so this process is invisible to proc-macros.
 
-        // 'Flatten' all nonterminals (i.e. `TokenKind::Interpolated`)
-        // to `None`-delimited groups containing the corresponding tokens. This
-        // is normally delayed until the proc-macro server actually needs to
-        // provide a `TokenKind::Interpolated` to a proc-macro. We do this earlier,
-        // so that we can handle cases like:
+        // Interesting cases:
         //
         // ```rust
         // #[cfg_eval] #[cfg] $item
@@ -104,8 +100,8 @@ impl CfgEval<'_> {
         //
         // where `$item` is `#[cfg_attr] struct Foo {}`. We want to make
         // sure to evaluate *all* `#[cfg]` and `#[cfg_attr]` attributes - the simplest
-        // way to do this is to do a single parse of a stream without any nonterminals.
-        let orig_tokens = annotatable.to_tokens().flattened();
+        // way to do this is to do a single parse of the token stream.
+        let orig_tokens = annotatable.to_tokens();
 
         // Re-parse the tokens, setting the `capture_cfg` flag to save extra information
         // to the captured `AttrTokenStream` (specifically, we capture
diff --git a/compiler/rustc_builtin_macros/src/cmdline_attrs.rs b/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
index 6afd8c4b43b..423b6a15b64 100644
--- a/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
+++ b/compiler/rustc_builtin_macros/src/cmdline_attrs.rs
@@ -1,44 +1,37 @@
 //! Attributes injected into the crate root from command line using `-Z crate-attr`.
 
-use rustc_ast::attr::mk_attr;
-use rustc_ast::{self as ast, AttrItem, AttrStyle, token};
-use rustc_parse::parser::ForceCollect;
-use rustc_parse::{new_parser_from_source_str, unwrap_or_emit_fatal};
+use rustc_ast::{self as ast};
+use rustc_errors::Diag;
+use rustc_parse::parser::attr::InnerAttrPolicy;
+use rustc_parse::{parse_in, source_str_to_stream};
 use rustc_session::parse::ParseSess;
 use rustc_span::FileName;
 
-use crate::errors;
-
 pub fn inject(krate: &mut ast::Crate, psess: &ParseSess, attrs: &[String]) {
     for raw_attr in attrs {
-        let mut parser = unwrap_or_emit_fatal(new_parser_from_source_str(
-            psess,
-            FileName::cli_crate_attr_source_code(raw_attr),
-            raw_attr.clone(),
-        ));
-
-        let start_span = parser.token.span;
-        let AttrItem { unsafety, path, args, tokens: _ } =
-            match parser.parse_attr_item(ForceCollect::No) {
-                Ok(ai) => ai,
-                Err(err) => {
+        let source = format!("#![{raw_attr}]");
+        let parse = || -> Result<ast::Attribute, Vec<Diag<'_>>> {
+            let tokens = source_str_to_stream(
+                psess,
+                FileName::cli_crate_attr_source_code(raw_attr),
+                source,
+                None,
+            )?;
+            parse_in(psess, tokens, "<crate attribute>", |p| {
+                p.parse_attribute(InnerAttrPolicy::Permitted)
+            })
+            .map_err(|e| vec![e])
+        };
+        let meta = match parse() {
+            Ok(meta) => meta,
+            Err(errs) => {
+                for err in errs {
                     err.emit();
-                    continue;
                 }
-            };
-        let end_span = parser.token.span;
-        if parser.token != token::Eof {
-            psess.dcx().emit_err(errors::InvalidCrateAttr { span: start_span.to(end_span) });
-            continue;
-        }
+                continue;
+            }
+        };
 
-        krate.attrs.push(mk_attr(
-            &psess.attr_id_generator,
-            AttrStyle::Inner,
-            unsafety,
-            path,
-            args,
-            start_span.to(end_span),
-        ));
+        krate.attrs.push(meta);
     }
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index b9197be4442..d9aac54ee73 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -527,15 +527,14 @@ impl<'a> TraitDef<'a> {
                     item.attrs
                         .iter()
                         .filter(|a| {
-                            [
+                            a.has_any_name(&[
                                 sym::allow,
                                 sym::warn,
                                 sym::deny,
                                 sym::forbid,
                                 sym::stable,
                                 sym::unstable,
-                            ]
-                            .contains(&a.name_or_empty())
+                            ])
                         })
                         .cloned(),
                 );
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index 4bbe212f429..d14ad8f4014 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -1,7 +1,7 @@
 use rustc_errors::codes::*;
 use rustc_errors::{
     Diag, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level, MultiSpan, SingleLabelManySpans,
-    SubdiagMessageOp, Subdiagnostic,
+    Subdiagnostic,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Ident, Span, Symbol};
@@ -110,13 +110,6 @@ pub(crate) struct ProcMacro {
 }
 
 #[derive(Diagnostic)]
-#[diag(builtin_macros_invalid_crate_attribute)]
-pub(crate) struct InvalidCrateAttr {
-    #[primary_span]
-    pub(crate) span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(builtin_macros_non_abi)]
 pub(crate) struct NonABI {
     #[primary_span]
@@ -691,13 +684,9 @@ pub(crate) struct FormatUnusedArg {
 // Allow the singular form to be a subdiagnostic of the multiple-unused
 // form of diagnostic.
 impl Subdiagnostic for FormatUnusedArg {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("named", self.named);
-        let msg = f(diag, crate::fluent_generated::builtin_macros_format_unused_arg.into());
+        let msg = diag.eagerly_translate(crate::fluent_generated::builtin_macros_format_unused_arg);
         diag.span_label(self.span, msg);
     }
 }
diff --git a/compiler/rustc_builtin_macros/src/lib.rs b/compiler/rustc_builtin_macros/src/lib.rs
index 606e85577f7..bcd40f980e6 100644
--- a/compiler/rustc_builtin_macros/src/lib.rs
+++ b/compiler/rustc_builtin_macros/src/lib.rs
@@ -5,7 +5,6 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
index 8862965c053..a91f2d38a93 100644
--- a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -20,14 +20,14 @@ use crate::errors;
 struct ProcMacroDerive {
     id: NodeId,
     trait_name: Symbol,
-    function_name: Ident,
+    function_ident: Ident,
     span: Span,
     attrs: Vec<Symbol>,
 }
 
 struct ProcMacroDef {
     id: NodeId,
-    function_name: Ident,
+    function_ident: Ident,
     span: Span,
 }
 
@@ -95,7 +95,7 @@ impl<'a> CollectProcMacros<'a> {
     fn collect_custom_derive(
         &mut self,
         item: &'a ast::Item,
-        function_name: Ident,
+        function_ident: Ident,
         attr: &'a ast::Attribute,
     ) {
         let Some((trait_name, proc_attrs)) =
@@ -109,7 +109,7 @@ impl<'a> CollectProcMacros<'a> {
                 id: item.id,
                 span: item.span,
                 trait_name,
-                function_name,
+                function_ident,
                 attrs: proc_attrs,
             }));
         } else {
@@ -123,12 +123,12 @@ impl<'a> CollectProcMacros<'a> {
         }
     }
 
-    fn collect_attr_proc_macro(&mut self, item: &'a ast::Item, function_name: Ident) {
+    fn collect_attr_proc_macro(&mut self, item: &'a ast::Item, function_ident: Ident) {
         if self.in_root && item.vis.kind.is_pub() {
             self.macros.push(ProcMacro::Attr(ProcMacroDef {
                 id: item.id,
                 span: item.span,
-                function_name,
+                function_ident,
             }));
         } else {
             let msg = if !self.in_root {
@@ -141,12 +141,12 @@ impl<'a> CollectProcMacros<'a> {
         }
     }
 
-    fn collect_bang_proc_macro(&mut self, item: &'a ast::Item, function_name: Ident) {
+    fn collect_bang_proc_macro(&mut self, item: &'a ast::Item, function_ident: Ident) {
         if self.in_root && item.vis.kind.is_pub() {
             self.macros.push(ProcMacro::Bang(ProcMacroDef {
                 id: item.id,
                 span: item.span,
-                function_name,
+                function_ident,
             }));
         } else {
             let msg = if !self.in_root {
@@ -303,7 +303,7 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
                 ProcMacro::Derive(m) => m.span,
                 ProcMacro::Attr(m) | ProcMacro::Bang(m) => m.span,
             };
-            let local_path = |cx: &ExtCtxt<'_>, name| cx.expr_path(cx.path(span, vec![name]));
+            let local_path = |cx: &ExtCtxt<'_>, ident| cx.expr_path(cx.path(span, vec![ident]));
             let proc_macro_ty_method_path = |cx: &ExtCtxt<'_>, method| {
                 cx.expr_path(cx.path(
                     span.with_ctxt(harness_span.ctxt()),
@@ -327,7 +327,7 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
                                     .map(|&s| cx.expr_str(span, s))
                                     .collect::<ThinVec<_>>(),
                             ),
-                            local_path(cx, cd.function_name),
+                            local_path(cx, cd.function_ident),
                         ],
                     )
                 }
@@ -345,8 +345,8 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
                         harness_span,
                         proc_macro_ty_method_path(cx, ident),
                         thin_vec![
-                            cx.expr_str(span, ca.function_name.name),
-                            local_path(cx, ca.function_name),
+                            cx.expr_str(span, ca.function_ident.name),
+                            local_path(cx, ca.function_ident),
                         ],
                     )
                 }
diff --git a/compiler/rustc_codegen_cranelift/src/driver/aot.rs b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
index 444dc441286..00136ac4a57 100644
--- a/compiler/rustc_codegen_cranelift/src/driver/aot.rs
+++ b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
@@ -169,8 +169,11 @@ fn produce_final_output_artifacts(
         if codegen_results.modules.len() == 1 {
             // 1) Only one codegen unit. In this case it's no difficulty
             //    to copy `foo.0.x` to `foo.x`.
-            let module_name = Some(&codegen_results.modules[0].name[..]);
-            let path = crate_output.temp_path(output_type, module_name);
+            let path = crate_output.temp_path_for_cgu(
+                output_type,
+                &codegen_results.modules[0].name,
+                sess.invocation_temp.as_deref(),
+            );
             let output = crate_output.path(output_type);
             if !output_type.is_text_output() && output.is_tty() {
                 sess.dcx()
@@ -183,22 +186,16 @@ fn produce_final_output_artifacts(
                 ensure_removed(sess.dcx(), &path);
             }
         } else {
-            let extension = crate_output
-                .temp_path(output_type, None)
-                .extension()
-                .unwrap()
-                .to_str()
-                .unwrap()
-                .to_owned();
-
             if crate_output.outputs.contains_explicit_name(&output_type) {
                 // 2) Multiple codegen units, with `--emit foo=some_name`. We have
                 //    no good solution for this case, so warn the user.
-                sess.dcx().emit_warn(ssa_errors::IgnoringEmitPath { extension });
+                sess.dcx()
+                    .emit_warn(ssa_errors::IgnoringEmitPath { extension: output_type.extension() });
             } else if crate_output.single_output_file.is_some() {
                 // 3) Multiple codegen units, with `-o some_name`. We have
                 //    no good solution for this case, so warn the user.
-                sess.dcx().emit_warn(ssa_errors::IgnoringOutput { extension });
+                sess.dcx()
+                    .emit_warn(ssa_errors::IgnoringOutput { extension: output_type.extension() });
             } else {
                 // 4) Multiple codegen units, but no explicit name. We
                 //    just leave the `foo.0.x` files in place.
@@ -351,6 +348,7 @@ fn make_module(sess: &Session, name: String) -> UnwindModule<ObjectModule> {
 
 fn emit_cgu(
     output_filenames: &OutputFilenames,
+    invocation_temp: Option<&str>,
     prof: &SelfProfilerRef,
     name: String,
     module: UnwindModule<ObjectModule>,
@@ -366,6 +364,7 @@ fn emit_cgu(
 
     let module_regular = emit_module(
         output_filenames,
+        invocation_temp,
         prof,
         product.object,
         ModuleKind::Regular,
@@ -391,6 +390,7 @@ fn emit_cgu(
 
 fn emit_module(
     output_filenames: &OutputFilenames,
+    invocation_temp: Option<&str>,
     prof: &SelfProfilerRef,
     mut object: cranelift_object::object::write::Object<'_>,
     kind: ModuleKind,
@@ -409,7 +409,7 @@ fn emit_module(
         object.set_section_data(comment_section, producer, 1);
     }
 
-    let tmp_file = output_filenames.temp_path(OutputType::Object, Some(&name));
+    let tmp_file = output_filenames.temp_path_for_cgu(OutputType::Object, &name, invocation_temp);
     let file = match File::create(&tmp_file) {
         Ok(file) => file,
         Err(err) => return Err(format!("error creating object file: {}", err)),
@@ -449,8 +449,11 @@ fn reuse_workproduct_for_cgu(
     cgu: &CodegenUnit<'_>,
 ) -> Result<ModuleCodegenResult, String> {
     let work_product = cgu.previous_work_product(tcx);
-    let obj_out_regular =
-        tcx.output_filenames(()).temp_path(OutputType::Object, Some(cgu.name().as_str()));
+    let obj_out_regular = tcx.output_filenames(()).temp_path_for_cgu(
+        OutputType::Object,
+        cgu.name().as_str(),
+        tcx.sess.invocation_temp.as_deref(),
+    );
     let source_file_regular = rustc_incremental::in_incr_comp_dir_sess(
         &tcx.sess,
         &work_product.saved_files.get("o").expect("no saved object file in work product"),
@@ -595,13 +598,19 @@ fn module_codegen(
 
         let global_asm_object_file =
             profiler.generic_activity_with_arg("compile assembly", &*cgu_name).run(|| {
-                crate::global_asm::compile_global_asm(&global_asm_config, &cgu_name, &cx.global_asm)
+                crate::global_asm::compile_global_asm(
+                    &global_asm_config,
+                    &cgu_name,
+                    &cx.global_asm,
+                    cx.invocation_temp.as_deref(),
+                )
             })?;
 
         let codegen_result =
             profiler.generic_activity_with_arg("write object file", &*cgu_name).run(|| {
                 emit_cgu(
                     &global_asm_config.output_filenames,
+                    cx.invocation_temp.as_deref(),
                     &profiler,
                     cgu_name,
                     module,
@@ -626,8 +635,11 @@ fn emit_metadata_module(tcx: TyCtxt<'_>, metadata: &EncodedMetadata) -> Compiled
         .as_str()
         .to_string();
 
-    let tmp_file =
-        tcx.output_filenames(()).temp_path(OutputType::Metadata, Some(&metadata_cgu_name));
+    let tmp_file = tcx.output_filenames(()).temp_path_for_cgu(
+        OutputType::Metadata,
+        &metadata_cgu_name,
+        tcx.sess.invocation_temp.as_deref(),
+    );
 
     let symbol_name = rustc_middle::middle::exported_symbols::metadata_symbol_name(tcx);
     let obj = create_compressed_metadata_file(tcx.sess, metadata, &symbol_name);
@@ -657,6 +669,7 @@ fn emit_allocator_module(tcx: TyCtxt<'_>) -> Option<CompiledModule> {
 
         match emit_module(
             tcx.output_filenames(()),
+            tcx.sess.invocation_temp.as_deref(),
             &tcx.sess.prof,
             product.object,
             ModuleKind::Allocator,
@@ -728,26 +741,27 @@ pub(crate) fn run_aot(
 
     let concurrency_limiter = IntoDynSyncSend(ConcurrencyLimiter::new(todo_cgus.len()));
 
-    let modules = tcx.sess.time("codegen mono items", || {
-        let mut modules: Vec<_> = par_map(todo_cgus, |(_, cgu)| {
-            let dep_node = cgu.codegen_dep_node(tcx);
-            tcx.dep_graph
-                .with_task(
+    let modules: Vec<_> =
+        tcx.sess.time("codegen mono items", || {
+            let modules: Vec<_> = par_map(todo_cgus, |(_, cgu)| {
+                let dep_node = cgu.codegen_dep_node(tcx);
+                let (module, _) = tcx.dep_graph.with_task(
                     dep_node,
                     tcx,
                     (global_asm_config.clone(), cgu.name(), concurrency_limiter.acquire(tcx.dcx())),
                     module_codegen,
                     Some(rustc_middle::dep_graph::hash_result),
-                )
-                .0
-        });
-        modules.extend(
-            done_cgus
+                );
+                IntoDynSyncSend(module)
+            });
+            modules
                 .into_iter()
-                .map(|(_, cgu)| OngoingModuleCodegen::Sync(reuse_workproduct_for_cgu(tcx, cgu))),
-        );
-        modules
-    });
+                .map(|module| module.0)
+                .chain(done_cgus.into_iter().map(|(_, cgu)| {
+                    OngoingModuleCodegen::Sync(reuse_workproduct_for_cgu(tcx, cgu))
+                }))
+                .collect()
+        });
 
     let allocator_module = emit_allocator_module(tcx);
 
diff --git a/compiler/rustc_codegen_cranelift/src/global_asm.rs b/compiler/rustc_codegen_cranelift/src/global_asm.rs
index 9ea92c300f8..79cefb05de3 100644
--- a/compiler/rustc_codegen_cranelift/src/global_asm.rs
+++ b/compiler/rustc_codegen_cranelift/src/global_asm.rs
@@ -132,6 +132,7 @@ pub(crate) fn compile_global_asm(
     config: &GlobalAsmConfig,
     cgu_name: &str,
     global_asm: &str,
+    invocation_temp: Option<&str>,
 ) -> Result<Option<PathBuf>, String> {
     if global_asm.is_empty() {
         return Ok(None);
@@ -146,7 +147,7 @@ pub(crate) fn compile_global_asm(
     global_asm.push('\n');
 
     let global_asm_object_file = add_file_stem_postfix(
-        config.output_filenames.temp_path(OutputType::Object, Some(cgu_name)),
+        config.output_filenames.temp_path_for_cgu(OutputType::Object, cgu_name, invocation_temp),
         ".asm",
     );
 
diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
index 75f3a3c1972..d3f47ad7263 100644
--- a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
+++ b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
@@ -1,5 +1,4 @@
-//! Codegen of intrinsics. This includes `extern "rust-intrinsic"`,
-//! functions marked with the `#[rustc_intrinsic]` attribute
+//! Codegen of intrinsics. This includes functions marked with the `#[rustc_intrinsic]` attribute
 //! and LLVM intrinsics that have symbol names starting with `llvm.`.
 
 macro_rules! intrinsic_args {
diff --git a/compiler/rustc_codegen_cranelift/src/lib.rs b/compiler/rustc_codegen_cranelift/src/lib.rs
index e7afaff3b42..9d9e790289c 100644
--- a/compiler/rustc_codegen_cranelift/src/lib.rs
+++ b/compiler/rustc_codegen_cranelift/src/lib.rs
@@ -124,6 +124,7 @@ impl<F: Fn() -> String> Drop for PrintOnPanic<F> {
 /// inside a single codegen unit with the exception of the Cranelift [`Module`](cranelift_module::Module).
 struct CodegenCx {
     output_filenames: Arc<OutputFilenames>,
+    invocation_temp: Option<String>,
     should_write_ir: bool,
     global_asm: String,
     inline_asm_index: usize,
@@ -142,6 +143,7 @@ impl CodegenCx {
         };
         CodegenCx {
             output_filenames: tcx.output_filenames(()).clone(),
+            invocation_temp: tcx.sess.invocation_temp.clone(),
             should_write_ir: crate::pretty_clif::should_write_ir(tcx),
             global_asm: String::new(),
             inline_asm_index: 0,
diff --git a/compiler/rustc_codegen_cranelift/src/main_shim.rs b/compiler/rustc_codegen_cranelift/src/main_shim.rs
index 6d5df2b0043..6eef97c14dd 100644
--- a/compiler/rustc_codegen_cranelift/src/main_shim.rs
+++ b/compiler/rustc_codegen_cranelift/src/main_shim.rs
@@ -1,6 +1,6 @@
 use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use rustc_hir::LangItem;
-use rustc_middle::ty::{AssocKind, GenericArg};
+use rustc_middle::ty::{AssocTag, GenericArg};
 use rustc_session::config::EntryFnType;
 use rustc_span::{DUMMY_SP, Ident};
 
@@ -104,10 +104,10 @@ pub(crate) fn maybe_create_entry_wrapper(
                 let termination_trait = tcx.require_lang_item(LangItem::Termination, None);
                 let report = tcx
                     .associated_items(termination_trait)
-                    .find_by_name_and_kind(
+                    .find_by_ident_and_kind(
                         tcx,
                         Ident::from_str("report"),
-                        AssocKind::Fn,
+                        AssocTag::Fn,
                         termination_trait,
                     )
                     .unwrap();
diff --git a/compiler/rustc_codegen_gcc/.github/workflows/ci.yml b/compiler/rustc_codegen_gcc/.github/workflows/ci.yml
index f96912e6b7a..ef024258ffc 100644
--- a/compiler/rustc_codegen_gcc/.github/workflows/ci.yml
+++ b/compiler/rustc_codegen_gcc/.github/workflows/ci.yml
@@ -1,8 +1,10 @@
 name: CI
 
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 permissions:
   contents: read
@@ -121,3 +123,22 @@ jobs:
         run: |
           cd build_system
           cargo test
+
+  # Summary job for the merge queue.
+  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+  success:
+    needs: [build, duplicates, build_system]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/compiler/rustc_codegen_gcc/.github/workflows/failures.yml b/compiler/rustc_codegen_gcc/.github/workflows/failures.yml
index d080bbfe91f..bc42eb1468e 100644
--- a/compiler/rustc_codegen_gcc/.github/workflows/failures.yml
+++ b/compiler/rustc_codegen_gcc/.github/workflows/failures.yml
@@ -2,7 +2,10 @@
 name: Failures
 
 on:
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 permissions:
   contents: read
@@ -108,3 +111,22 @@ jobs:
           echo "Error: 'the compiler unexpectedly panicked' found in output logs. CI Error!!"
           exit 1
         fi
+
+  # Summary job for the merge queue.
+  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+  success_failures:
+    needs: [build]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/compiler/rustc_codegen_gcc/.github/workflows/gcc12.yml b/compiler/rustc_codegen_gcc/.github/workflows/gcc12.yml
index bb9e020dc6a..da9a1506855 100644
--- a/compiler/rustc_codegen_gcc/.github/workflows/gcc12.yml
+++ b/compiler/rustc_codegen_gcc/.github/workflows/gcc12.yml
@@ -1,8 +1,10 @@
 name: CI libgccjit 12
 
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 permissions:
   contents: read
@@ -85,3 +87,22 @@ jobs:
     #- name: Run tests
       #run: |
         #./y.sh test --release --clean --build-sysroot ${{ matrix.commands }} --no-default-features
+
+  # Summary job for the merge queue.
+  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+  success_gcc12:
+    needs: [build]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/compiler/rustc_codegen_gcc/.github/workflows/m68k.yml b/compiler/rustc_codegen_gcc/.github/workflows/m68k.yml
index ed1fc02bd91..21731f7087e 100644
--- a/compiler/rustc_codegen_gcc/.github/workflows/m68k.yml
+++ b/compiler/rustc_codegen_gcc/.github/workflows/m68k.yml
@@ -3,8 +3,10 @@
 name: m68k CI
 
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 permissions:
   contents: read
@@ -105,3 +107,22 @@ jobs:
     - name: Run tests
       run: |
         ./y.sh test --release --clean --build-sysroot --sysroot-features compiler_builtins/no-f16-f128 ${{ matrix.commands }}
+
+  # Summary job for the merge queue.
+  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+  success_m68k:
+    needs: [build]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/compiler/rustc_codegen_gcc/.github/workflows/release.yml b/compiler/rustc_codegen_gcc/.github/workflows/release.yml
index 886ce90b471..47a40286554 100644
--- a/compiler/rustc_codegen_gcc/.github/workflows/release.yml
+++ b/compiler/rustc_codegen_gcc/.github/workflows/release.yml
@@ -1,8 +1,10 @@
 name: CI with sysroot compiled in release mode
 
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 permissions:
   contents: read
@@ -82,3 +84,22 @@ jobs:
           echo "Test is done with LTO enabled, hence inlining should occur across crates"
           exit 1
         fi
+
+  # Summary job for the merge queue.
+  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+  success_release:
+    needs: [build]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/compiler/rustc_codegen_gcc/.github/workflows/stdarch.yml b/compiler/rustc_codegen_gcc/.github/workflows/stdarch.yml
index d5ae6144496..4b9f48e7b18 100644
--- a/compiler/rustc_codegen_gcc/.github/workflows/stdarch.yml
+++ b/compiler/rustc_codegen_gcc/.github/workflows/stdarch.yml
@@ -1,8 +1,10 @@
 name: stdarch tests with sysroot compiled in release mode
 
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 permissions:
   contents: read
@@ -102,3 +104,22 @@ jobs:
         # TODO: remove --skip test_mm512_stream_ps when stdarch is updated in rustc.
         # TODO: remove --skip test_tile_ when it's implemented.
         STDARCH_TEST_EVERYTHING=1 CHANNEL=release CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER="${{ matrix.cargo_runner }}" TARGET=x86_64-unknown-linux-gnu CG_RUSTFLAGS="-Ainternal_features --cfg stdarch_intel_sde" ./y.sh cargo test --manifest-path build/build_sysroot/sysroot_src/library/stdarch/Cargo.toml -- --skip rtm --skip tbm --skip sse4a --skip test_mm512_stream_ps --skip test_tile_
+
+  # Summary job for the merge queue.
+  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+  success_stdarch:
+    needs: [build]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
diff --git a/compiler/rustc_codegen_gcc/Cargo.lock b/compiler/rustc_codegen_gcc/Cargo.lock
index 636e75b94a3..832603aa792 100644
--- a/compiler/rustc_codegen_gcc/Cargo.lock
+++ b/compiler/rustc_codegen_gcc/Cargo.lock
@@ -56,18 +56,18 @@ dependencies = [
 
 [[package]]
 name = "gccjit"
-version = "2.4.0"
+version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72fd91f4adbf02b53cfc73c97bc33c5f253009043f30c56a5ec08dd5c8094dc8"
+checksum = "2895ddec764de7ac76fe6c056050c4801a80109c066f177a00a9cc8dee02b29b"
 dependencies = [
  "gccjit_sys",
 ]
 
 [[package]]
 name = "gccjit_sys"
-version = "0.5.0"
+version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0fb7b8f48a75e2cfe78c3d9a980b32771c34ffd12d196021ab3f98c49fbd2f0d"
+checksum = "ac133db68db8a6a8b2c51ef4b18d8ea16682d5814c4641272fe37bbbc223d5f3"
 dependencies = [
  "libc",
 ]
diff --git a/compiler/rustc_codegen_gcc/Cargo.toml b/compiler/rustc_codegen_gcc/Cargo.toml
index 63d37358561..b50f2a626d5 100644
--- a/compiler/rustc_codegen_gcc/Cargo.toml
+++ b/compiler/rustc_codegen_gcc/Cargo.toml
@@ -22,7 +22,7 @@ master = ["gccjit/master"]
 default = ["master"]
 
 [dependencies]
-gccjit = "2.4"
+gccjit = "2.5"
 #gccjit = { git = "https://github.com/rust-lang/gccjit.rs" }
 
 # Local copy.
diff --git a/compiler/rustc_codegen_gcc/Readme.md b/compiler/rustc_codegen_gcc/Readme.md
index e92c16ece2f..d0e4dbba6d3 100644
--- a/compiler/rustc_codegen_gcc/Readme.md
+++ b/compiler/rustc_codegen_gcc/Readme.md
@@ -23,7 +23,7 @@ A secondary goal is to check if using the gcc backend will provide any run-time
 ## Building
 
 **This requires a patched libgccjit in order to work.
-You need to use my [fork of gcc](https://github.com/antoyo/gcc) which already includes these patches.**
+You need to use my [fork of gcc](https://github.com/rust-lang/gcc) which already includes these patches.**
 
 ```bash
 $ cp config.example.toml config.toml
@@ -40,7 +40,7 @@ to do a few more things.
 To build it (most of these instructions come from [here](https://gcc.gnu.org/onlinedocs/jit/internals/index.html), so don't hesitate to take a look there if you encounter an issue):
 
 ```bash
-$ git clone https://github.com/antoyo/gcc
+$ git clone https://github.com/rust-lang/gcc
 $ sudo apt install flex libmpfr-dev libgmp-dev libmpc3 libmpc-dev
 $ mkdir gcc-build gcc-install
 $ cd gcc-build
diff --git a/compiler/rustc_codegen_gcc/build_system/src/clone_gcc.rs b/compiler/rustc_codegen_gcc/build_system/src/clone_gcc.rs
index e28ee873eb6..b49dd47f352 100644
--- a/compiler/rustc_codegen_gcc/build_system/src/clone_gcc.rs
+++ b/compiler/rustc_codegen_gcc/build_system/src/clone_gcc.rs
@@ -61,7 +61,7 @@ pub fn run() -> Result<(), String> {
         return Ok(());
     };
 
-    let result = git_clone("https://github.com/antoyo/gcc", Some(&args.out_path), false)?;
+    let result = git_clone("https://github.com/rust-lang/gcc", Some(&args.out_path), false)?;
     if result.ran_clone {
         let gcc_commit = args.config_info.get_gcc_commit()?;
         println!("Checking out GCC commit `{}`...", gcc_commit);
diff --git a/compiler/rustc_codegen_gcc/build_system/src/test.rs b/compiler/rustc_codegen_gcc/build_system/src/test.rs
index 6c29c7d1825..df4ac85233b 100644
--- a/compiler/rustc_codegen_gcc/build_system/src/test.rs
+++ b/compiler/rustc_codegen_gcc/build_system/src/test.rs
@@ -529,20 +529,21 @@ fn asm_tests(env: &Env, args: &TestArg) -> Result<(), String> {
 
     env.insert("COMPILETEST_FORCE_STAGE0".to_string(), "1".to_string());
 
-    let extra =
-        if args.is_using_gcc_master_branch() { "" } else { " -Csymbol-mangling-version=v0" };
-
-    let rustc_args = &format!(
-        r#"-Zpanic-abort-tests \
-            -Zcodegen-backend="{pwd}/target/{channel}/librustc_codegen_gcc.{dylib_ext}" \
-            --sysroot "{sysroot_dir}" -Cpanic=abort{extra}"#,
+    let codegen_backend_path = format!(
+        "{pwd}/target/{channel}/librustc_codegen_gcc.{dylib_ext}",
         pwd = std::env::current_dir()
             .map_err(|error| format!("`current_dir` failed: {:?}", error))?
             .display(),
         channel = args.config_info.channel.as_str(),
         dylib_ext = args.config_info.dylib_ext,
-        sysroot_dir = args.config_info.sysroot_path,
-        extra = extra,
+    );
+
+    let extra =
+        if args.is_using_gcc_master_branch() { "" } else { " -Csymbol-mangling-version=v0" };
+
+    let rustc_args = format!(
+        "-Zpanic-abort-tests -Zcodegen-backend={codegen_backend_path} --sysroot {} -Cpanic=abort{extra}",
+        args.config_info.sysroot_path
     );
 
     run_command_with_env(
@@ -677,7 +678,7 @@ fn test_projects(env: &Env, args: &TestArg) -> Result<(), String> {
 fn test_libcore(env: &Env, args: &TestArg) -> Result<(), String> {
     // FIXME: create a function "display_if_not_quiet" or something along the line.
     println!("[TEST] libcore");
-    let path = get_sysroot_dir().join("sysroot_src/library/core/tests");
+    let path = get_sysroot_dir().join("sysroot_src/library/coretests");
     let _ = remove_dir_all(path.join("target"));
     run_cargo_command(&[&"test"], Some(&path), env, args)?;
     Ok(())
diff --git a/compiler/rustc_codegen_gcc/doc/add-attribute.md b/compiler/rustc_codegen_gcc/doc/add-attribute.md
index ae3bcc5e2eb..267c1819525 100644
--- a/compiler/rustc_codegen_gcc/doc/add-attribute.md
+++ b/compiler/rustc_codegen_gcc/doc/add-attribute.md
@@ -14,4 +14,4 @@ Finally, you need to update this repository by calling the relevant API you adde
 
 To test it, build `gcc`, run `cargo update -p gccjit` and then you can test the generated output for a given Rust crate.
 
-[gccjit.rs]: https://github.com/antoyo/gccjit.rs
+[gccjit.rs]: https://github.com/rust-lang/gccjit.rs
diff --git a/compiler/rustc_codegen_gcc/example/mini_core.rs b/compiler/rustc_codegen_gcc/example/mini_core.rs
index 5544aee9eaf..c554a87b825 100644
--- a/compiler/rustc_codegen_gcc/example/mini_core.rs
+++ b/compiler/rustc_codegen_gcc/example/mini_core.rs
@@ -51,6 +51,10 @@ impl<T: ?Sized> LegacyReceiver for &T {}
 impl<T: ?Sized> LegacyReceiver for &mut T {}
 impl<T: ?Sized, A: Allocator> LegacyReceiver for Box<T, A> {}
 
+#[lang = "receiver"]
+trait Receiver {
+}
+
 #[lang = "copy"]
 pub trait Copy {}
 
@@ -134,6 +138,14 @@ impl Mul for u8 {
     }
 }
 
+impl Mul for i32 {
+    type Output = Self;
+
+    fn mul(self, rhs: Self) -> Self::Output {
+        self * rhs
+    }
+}
+
 impl Mul for usize {
     type Output = Self;
 
@@ -142,6 +154,14 @@ impl Mul for usize {
     }
 }
 
+impl Mul for isize {
+    type Output = Self;
+
+    fn mul(self, rhs: Self) -> Self::Output {
+        self * rhs
+    }
+}
+
 #[lang = "add"]
 pub trait Add<RHS = Self> {
     type Output;
@@ -165,6 +185,14 @@ impl Add for i8 {
     }
 }
 
+impl Add for i32 {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self {
+        self + rhs
+    }
+}
+
 impl Add for usize {
     type Output = Self;
 
@@ -196,6 +224,14 @@ impl Sub for usize {
     }
 }
 
+impl Sub for isize {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self {
+        self - rhs
+    }
+}
+
 impl Sub for u8 {
     type Output = Self;
 
@@ -220,6 +256,14 @@ impl Sub for i16 {
     }
 }
 
+impl Sub for i32 {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self {
+        self - rhs
+    }
+}
+
 #[lang = "rem"]
 pub trait Rem<RHS = Self> {
     type Output;
@@ -628,6 +672,10 @@ pub mod libc {
         pub fn memcpy(dst: *mut u8, src: *const u8, size: usize);
         pub fn memmove(dst: *mut u8, src: *const u8, size: usize);
         pub fn strncpy(dst: *mut u8, src: *const u8, size: usize);
+        pub fn fflush(stream: *mut i32) -> i32;
+        pub fn exit(status: i32);
+
+        pub static stdout: *mut i32;
     }
 }
 
diff --git a/compiler/rustc_codegen_gcc/libgccjit.version b/compiler/rustc_codegen_gcc/libgccjit.version
index 417fd5b0393..125b04004b0 100644
--- a/compiler/rustc_codegen_gcc/libgccjit.version
+++ b/compiler/rustc_codegen_gcc/libgccjit.version
@@ -1 +1 @@
-e607be166673a8de9fc07f6f02c60426e556c5f2
+0ea98a1365b81f7488073512c850e8ee951a4afd
diff --git a/compiler/rustc_codegen_gcc/patches/0022-core-Disable-not-compiling-tests.patch b/compiler/rustc_codegen_gcc/patches/0022-core-Disable-not-compiling-tests.patch
deleted file mode 100644
index 70e3e2ba7fe..00000000000
--- a/compiler/rustc_codegen_gcc/patches/0022-core-Disable-not-compiling-tests.patch
+++ /dev/null
@@ -1,44 +0,0 @@
-From af0e237f056fa838c77463381a19b0dc993c0a35 Mon Sep 17 00:00:00 2001
-From: None <none@example.com>
-Date: Sun, 1 Sep 2024 11:42:17 -0400
-Subject: [PATCH] Disable not compiling tests
-
----
- library/core/tests/Cargo.toml | 14 ++++++++++++++
- library/core/tests/lib.rs     |  1 +
- 2 files changed, 15 insertions(+)
- create mode 100644 library/core/tests/Cargo.toml
-
-diff --git a/library/core/tests/Cargo.toml b/library/core/tests/Cargo.toml
-new file mode 100644
-index 0000000..ca326ac
---- /dev/null
-+++ b/library/core/tests/Cargo.toml
-@@ -0,0 +1,14 @@
-+[workspace]
-+
-+[package]
-+name = "coretests"
-+version = "0.0.0"
-+edition = "2021"
-+
-+[lib]
-+name = "coretests"
-+path = "lib.rs"
-+
-+[dependencies]
-+rand = { version = "0.8.5", default-features = false }
-+rand_xorshift = { version = "0.3.0", default-features = false }
-diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
-index a4a7946..ecfe43f 100644
---- a/library/core/tests/lib.rs
-+++ b/library/core/tests/lib.rs
-@@ -1,4 +1,5 @@
- // tidy-alphabetical-start
-+#![cfg(test)]
- #![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
- #![cfg_attr(test, feature(cfg_match))]
- #![feature(alloc_layout_extra)]
--- 
-2.47.1
-
diff --git a/compiler/rustc_codegen_gcc/patches/0028-core-Disable-long-running-tests.patch b/compiler/rustc_codegen_gcc/patches/0028-core-Disable-long-running-tests.patch
index dc1beae6d2e..20df4245cfd 100644
--- a/compiler/rustc_codegen_gcc/patches/0028-core-Disable-long-running-tests.patch
+++ b/compiler/rustc_codegen_gcc/patches/0028-core-Disable-long-running-tests.patch
@@ -1,17 +1,17 @@
-From eb703e627e7a84f1cd8d0d87f0f69da1f0acf765 Mon Sep 17 00:00:00 2001
-From: bjorn3 <bjorn3@users.noreply.github.com>
-Date: Fri, 3 Dec 2021 12:16:30 +0100
+From ec2d0dc77fb484d926b45bb626b0db6a4bb0ab5c Mon Sep 17 00:00:00 2001
+From: None <none@example.com>
+Date: Thu, 27 Mar 2025 09:20:41 -0400
 Subject: [PATCH] Disable long running tests
 
 ---
- library/core/tests/slice.rs | 2 ++
+ library/coretests/tests/slice.rs | 2 ++
  1 file changed, 2 insertions(+)
 
-diff --git a/library/core/tests/slice.rs b/library/core/tests/slice.rs
-index 8402833..84592e0 100644
---- a/library/core/tests/slice.rs
-+++ b/library/core/tests/slice.rs
-@@ -2462,6 +2462,7 @@ take_tests! {
+diff --git a/library/coretests/tests/slice.rs b/library/coretests/tests/slice.rs
+index d17e681..fba5cd6 100644
+--- a/library/coretests/tests/slice.rs
++++ b/library/coretests/tests/slice.rs
+@@ -2486,6 +2486,7 @@ split_off_tests! {
  #[cfg(not(miri))] // unused in Miri
  const EMPTY_MAX: &'static [()] = &[(); usize::MAX];
  
@@ -19,14 +19,14 @@ index 8402833..84592e0 100644
  // can't be a constant due to const mutability rules
  #[cfg(not(miri))] // unused in Miri
  macro_rules! empty_max_mut {
-@@ -2485,6 +2486,7 @@ take_tests! {
-     (take_mut_oob_max_range_to_inclusive, (..=usize::MAX), None, empty_max_mut!()),
-     (take_mut_in_bounds_max_range_from, (usize::MAX..), Some(&mut [] as _), empty_max_mut!()),
+@@ -2509,6 +2510,7 @@ split_off_tests! {
+     (split_off_mut_oob_max_range_to_inclusive, (..=usize::MAX), None, empty_max_mut!()),
+     (split_off_mut_in_bounds_max_range_from, (usize::MAX..), Some(&mut [] as _), empty_max_mut!()),
  }
 +*/
  
  #[test]
  fn test_slice_from_ptr_range() {
 -- 
-2.26.2.7.g19db9cfb68
+2.49.0
 
diff --git a/compiler/rustc_codegen_gcc/patches/cross_patches/0001-Disable-libstd-and-libtest-dylib.patch b/compiler/rustc_codegen_gcc/patches/cross_patches/0001-Disable-libstd-and-libtest-dylib.patch
index c220f53040f..fa360fe9e74 100644
--- a/compiler/rustc_codegen_gcc/patches/cross_patches/0001-Disable-libstd-and-libtest-dylib.patch
+++ b/compiler/rustc_codegen_gcc/patches/cross_patches/0001-Disable-libstd-and-libtest-dylib.patch
@@ -1,19 +1,18 @@
-From 966beefe08be6045bfcca26079b76a7a80413080 Mon Sep 17 00:00:00 2001
+From b2911e732d1bf0e28872495c4c47af1dad3c7911 Mon Sep 17 00:00:00 2001
 From: None <none@example.com>
-Date: Thu, 28 Sep 2023 17:37:38 -0400
+Date: Thu, 27 Mar 2025 14:30:10 -0400
 Subject: [PATCH] Disable libstd and libtest dylib
 
 ---
- library/std/Cargo.toml  | 2 +-
- library/test/Cargo.toml | 2 +-
- 2 files changed, 2 insertions(+), 2 deletions(-)
+ library/std/Cargo.toml | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/library/std/Cargo.toml b/library/std/Cargo.toml
-index 5b21355..cb0c49b 100644
+index 176da60..c183cdb 100644
 --- a/library/std/Cargo.toml
 +++ b/library/std/Cargo.toml
-@@ -9,7 +9,7 @@ description = "The Rust Standard Library"
- edition = "2021"
+@@ -10,7 +10,7 @@ edition = "2024"
+ autobenches = false
  
  [lib]
 -crate-type = ["dylib", "rlib"]
@@ -21,3 +20,6 @@ index 5b21355..cb0c49b 100644
  
  [dependencies]
  alloc = { path = "../alloc", public = true }
+-- 
+2.49.0
+
diff --git a/compiler/rustc_codegen_gcc/patches/libgccjit12/0001-core-Disable-portable-simd-test.patch b/compiler/rustc_codegen_gcc/patches/libgccjit12/0001-core-Disable-portable-simd-test.patch
index 9ef5e0e4f46..9d5b2dc537d 100644
--- a/compiler/rustc_codegen_gcc/patches/libgccjit12/0001-core-Disable-portable-simd-test.patch
+++ b/compiler/rustc_codegen_gcc/patches/libgccjit12/0001-core-Disable-portable-simd-test.patch
@@ -1,25 +1,17 @@
-From 124a11ce086952a5794d5cfbaa45175809497b81 Mon Sep 17 00:00:00 2001
+From 1a8f6b8e39f343959d4d2e6b6957a6d780ac3fc0 Mon Sep 17 00:00:00 2001
 From: None <none@example.com>
-Date: Sat, 18 Nov 2023 10:50:36 -0500
-Subject: [PATCH] [core] Disable portable-simd test
+Date: Thu, 27 Mar 2025 14:32:14 -0400
+Subject: [PATCH] Disable portable-simd test
 
 ---
- library/core/tests/lib.rs | 2 --
- 1 file changed, 2 deletions(-)
+ library/coretests/tests/lib.rs | 1 -
+ 1 file changed, 1 deletion(-)
 
-diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
-index b71786c..cf484d5 100644
---- a/library/core/tests/lib.rs
-+++ b/library/core/tests/lib.rs
-@@ -87,7 +87,6 @@
- #![feature(numfmt)]
- #![feature(pattern)]
- #![feature(pointer_is_aligned_to)]
--#![feature(portable_simd)]
- #![feature(ptr_metadata)]
- #![feature(slice_from_ptr_range)]
- #![feature(slice_internals)]
-@@ -155,7 +154,6 @@ mod pin;
+diff --git a/library/coretests/tests/lib.rs b/library/coretests/tests/lib.rs
+index 79022fe..9223b2f 100644
+--- a/library/coretests/tests/lib.rs
++++ b/library/coretests/tests/lib.rs
+@@ -165,7 +165,6 @@ mod pin;
  mod pin_macro;
  mod ptr;
  mod result;
@@ -27,4 +19,6 @@ index b71786c..cf484d5 100644
  mod slice;
  mod str;
  mod str_lossy;
--- 2.45.2
+-- 
+2.49.0
+
diff --git a/compiler/rustc_codegen_gcc/rust-toolchain b/compiler/rustc_codegen_gcc/rust-toolchain
index 940b3de9f74..fd898c59707 100644
--- a/compiler/rustc_codegen_gcc/rust-toolchain
+++ b/compiler/rustc_codegen_gcc/rust-toolchain
@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2025-01-12"
+channel = "nightly-2025-04-17"
 components = ["rust-src", "rustc-dev", "llvm-tools-preview"]
diff --git a/compiler/rustc_codegen_gcc/src/abi.rs b/compiler/rustc_codegen_gcc/src/abi.rs
index 9fe6baa3d25..a96b18e01c0 100644
--- a/compiler/rustc_codegen_gcc/src/abi.rs
+++ b/compiler/rustc_codegen_gcc/src/abi.rs
@@ -9,6 +9,8 @@ use rustc_middle::ty::Ty;
 use rustc_middle::ty::layout::LayoutOf;
 #[cfg(feature = "master")]
 use rustc_session::config;
+#[cfg(feature = "master")]
+use rustc_target::callconv::Conv;
 use rustc_target::callconv::{ArgAttributes, CastTarget, FnAbi, PassMode};
 
 use crate::builder::Builder;
@@ -105,6 +107,8 @@ pub trait FnAbiGccExt<'gcc, 'tcx> {
     // TODO(antoyo): return a function pointer type instead?
     fn gcc_type(&self, cx: &CodegenCx<'gcc, 'tcx>) -> FnAbiGcc<'gcc>;
     fn ptr_to_gcc_type(&self, cx: &CodegenCx<'gcc, 'tcx>) -> Type<'gcc>;
+    #[cfg(feature = "master")]
+    fn gcc_cconv(&self, cx: &CodegenCx<'gcc, 'tcx>) -> Option<FnAttribute<'gcc>>;
 }
 
 impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
@@ -227,4 +231,47 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         );
         pointer_type
     }
+
+    #[cfg(feature = "master")]
+    fn gcc_cconv(&self, cx: &CodegenCx<'gcc, 'tcx>) -> Option<FnAttribute<'gcc>> {
+        conv_to_fn_attribute(self.conv, &cx.tcx.sess.target.arch)
+    }
+}
+
+#[cfg(feature = "master")]
+pub fn conv_to_fn_attribute<'gcc>(conv: Conv, arch: &str) -> Option<FnAttribute<'gcc>> {
+    // TODO: handle the calling conventions returning None.
+    let attribute = match conv {
+        Conv::C
+        | Conv::Rust
+        | Conv::CCmseNonSecureCall
+        | Conv::CCmseNonSecureEntry
+        | Conv::RiscvInterrupt { .. } => return None,
+        Conv::Cold => return None,
+        Conv::PreserveMost => return None,
+        Conv::PreserveAll => return None,
+        Conv::GpuKernel => {
+            // TODO(antoyo): remove clippy allow attribute when this is implemented.
+            #[allow(clippy::if_same_then_else)]
+            if arch == "amdgpu" {
+                return None;
+            } else if arch == "nvptx64" {
+                return None;
+            } else {
+                panic!("Architecture {} does not support GpuKernel calling convention", arch);
+            }
+        }
+        Conv::AvrInterrupt => return None,
+        Conv::AvrNonBlockingInterrupt => return None,
+        Conv::ArmAapcs => return None,
+        Conv::Msp430Intr => return None,
+        Conv::X86Fastcall => return None,
+        Conv::X86Intr => return None,
+        Conv::X86Stdcall => return None,
+        Conv::X86ThisCall => return None,
+        Conv::X86VectorCall => return None,
+        Conv::X86_64SysV => FnAttribute::SysvAbi,
+        Conv::X86_64Win64 => FnAttribute::MsAbi,
+    };
+    Some(attribute)
 }
diff --git a/compiler/rustc_codegen_gcc/src/asm.rs b/compiler/rustc_codegen_gcc/src/asm.rs
index 415f8affab9..dbdf37ee6c9 100644
--- a/compiler/rustc_codegen_gcc/src/asm.rs
+++ b/compiler/rustc_codegen_gcc/src/asm.rs
@@ -36,7 +36,8 @@ use crate::type_of::LayoutGccExt;
 //
 // 3. Clobbers. GCC has a separate list of clobbers, and clobbers don't have indexes.
 //    Contrary, Rust expresses clobbers through "out" operands that aren't tied to
-//    a variable (`_`),  and such "clobbers" do have index.
+//    a variable (`_`),  and such "clobbers" do have index. Input operands cannot also
+//    be clobbered.
 //
 // 4. Furthermore, GCC Extended Asm does not support explicit register constraints
 //    (like `out("eax")`) directly, offering so-called "local register variables"
@@ -161,6 +162,16 @@ impl<'a, 'gcc, 'tcx> AsmBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
         // Also, we don't emit any asm operands immediately; we save them to
         // the one of the buffers to be emitted later.
 
+        let mut input_registers = vec![];
+
+        for op in rust_operands {
+            if let InlineAsmOperandRef::In { reg, .. } = *op {
+                if let ConstraintOrRegister::Register(reg_name) = reg_to_gcc(reg) {
+                    input_registers.push(reg_name);
+                }
+            }
+        }
+
         // 1. Normal variables (and saving operands to buffers).
         for (rust_idx, op) in rust_operands.iter().enumerate() {
             match *op {
@@ -183,25 +194,39 @@ impl<'a, 'gcc, 'tcx> AsmBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                             continue;
                         }
                         (Register(reg_name), None) => {
-                            // `clobber_abi` can add lots of clobbers that are not supported by the target,
-                            // such as AVX-512 registers, so we just ignore unsupported registers
-                            let is_target_supported =
-                                reg.reg_class().supported_types(asm_arch, true).iter().any(
-                                    |&(_, feature)| {
-                                        if let Some(feature) = feature {
-                                            self.tcx
-                                                .asm_target_features(instance.def_id())
-                                                .contains(&feature)
-                                        } else {
-                                            true // Register class is unconditionally supported
-                                        }
-                                    },
-                                );
-
-                            if is_target_supported && !clobbers.contains(&reg_name) {
-                                clobbers.push(reg_name);
+                            if input_registers.contains(&reg_name) {
+                                // the `clobber_abi` operand is converted into a series of
+                                // `lateout("reg") _` operands. Of course, a user could also
+                                // explicitly define such an output operand.
+                                //
+                                // GCC does not allow input registers to be clobbered, so if this out register
+                                // is also used as an in register, do not add it to the clobbers list.
+                                // it will be treated as a lateout register with `out_place: None`
+                                if !late {
+                                    bug!("input registers can only be used as lateout regisers");
+                                }
+                                ("r", dummy_output_type(self.cx, reg.reg_class()))
+                            } else {
+                                // `clobber_abi` can add lots of clobbers that are not supported by the target,
+                                // such as AVX-512 registers, so we just ignore unsupported registers
+                                let is_target_supported =
+                                    reg.reg_class().supported_types(asm_arch, true).iter().any(
+                                        |&(_, feature)| {
+                                            if let Some(feature) = feature {
+                                                self.tcx
+                                                    .asm_target_features(instance.def_id())
+                                                    .contains(&feature)
+                                            } else {
+                                                true // Register class is unconditionally supported
+                                            }
+                                        },
+                                    );
+
+                                if is_target_supported && !clobbers.contains(&reg_name) {
+                                    clobbers.push(reg_name);
+                                }
+                                continue;
                             }
-                            continue;
                         }
                     };
 
@@ -230,13 +255,10 @@ impl<'a, 'gcc, 'tcx> AsmBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                 }
 
                 InlineAsmOperandRef::InOut { reg, late, in_value, out_place } => {
-                    let constraint =
-                        if let ConstraintOrRegister::Constraint(constraint) = reg_to_gcc(reg) {
-                            constraint
-                        } else {
-                            // left for the next pass
-                            continue;
-                        };
+                    let ConstraintOrRegister::Constraint(constraint) = reg_to_gcc(reg) else {
+                        // left for the next pass
+                        continue;
+                    };
 
                     // Rustc frontend guarantees that input and output types are "compatible",
                     // so we can just use input var's type for the output variable.
@@ -589,114 +611,127 @@ fn estimate_template_length(
 }
 
 /// Converts a register class to a GCC constraint code.
-fn reg_to_gcc(reg: InlineAsmRegOrRegClass) -> ConstraintOrRegister {
-    let constraint = match reg {
-        // For vector registers LLVM wants the register name to match the type size.
+fn reg_to_gcc(reg_or_reg_class: InlineAsmRegOrRegClass) -> ConstraintOrRegister {
+    match reg_or_reg_class {
         InlineAsmRegOrRegClass::Reg(reg) => {
-            match reg {
-                InlineAsmReg::X86(_) => {
-                    // TODO(antoyo): add support for vector register.
-                    //
-                    // // For explicit registers, we have to create a register variable: https://stackoverflow.com/a/31774784/389119
-                    return ConstraintOrRegister::Register(match reg.name() {
-                        // Some of registers' names does not map 1-1 from rust to gcc
-                        "st(0)" => "st",
+            ConstraintOrRegister::Register(explicit_reg_to_gcc(reg))
+        }
+        InlineAsmRegOrRegClass::RegClass(reg_class) => {
+            ConstraintOrRegister::Constraint(reg_class_to_gcc(reg_class))
+        }
+    }
+}
 
-                        name => name,
-                    });
+fn explicit_reg_to_gcc(reg: InlineAsmReg) -> &'static str {
+    // For explicit registers, we have to create a register variable: https://stackoverflow.com/a/31774784/389119
+    match reg {
+        InlineAsmReg::X86(reg) => {
+            // TODO(antoyo): add support for vector register.
+            match reg.reg_class() {
+                X86InlineAsmRegClass::reg_byte => {
+                    // GCC does not support the `b` suffix, so we just strip it
+                    // see https://github.com/rust-lang/rustc_codegen_gcc/issues/485
+                    reg.name().trim_end_matches('b')
                 }
+                _ => match reg.name() {
+                    // Some of registers' names does not map 1-1 from rust to gcc
+                    "st(0)" => "st",
 
-                _ => unimplemented!(),
+                    name => name,
+                },
             }
         }
-        // They can be retrieved from https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html
-        InlineAsmRegOrRegClass::RegClass(reg) => match reg {
-            InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::vreg) => "w",
-            InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::vreg_low16) => "x",
-            InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::preg) => {
-                unreachable!("clobber-only")
-            }
-            InlineAsmRegClass::Arm(ArmInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::Arm(ArmInlineAsmRegClass::sreg)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::dreg_low16)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::qreg_low8)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::sreg_low16)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::dreg_low8)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::qreg_low4)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::dreg)
-            | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::qreg) => "t",
-            InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_upper) => "d",
-            InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_pair) => "r",
-            InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_iw) => "w",
-            InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_ptr) => "e",
-            InlineAsmRegClass::Bpf(BpfInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::Bpf(BpfInlineAsmRegClass::wreg) => "w",
-            InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::preg) => {
-                unreachable!("clobber-only")
-            }
-            InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::freg) => "f",
-            InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg_addr) => "a",
-            InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg_data) => "d",
-            InlineAsmRegClass::CSKY(CSKYInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::CSKY(CSKYInlineAsmRegClass::freg) => "f",
-            InlineAsmRegClass::Mips(MipsInlineAsmRegClass::reg) => "d", // more specific than "r"
-            InlineAsmRegClass::Mips(MipsInlineAsmRegClass::freg) => "f",
-            InlineAsmRegClass::Msp430(Msp430InlineAsmRegClass::reg) => "r",
-            // https://github.com/gcc-mirror/gcc/blob/master/gcc/config/nvptx/nvptx.md -> look for
-            // "define_constraint".
-            InlineAsmRegClass::Nvptx(NvptxInlineAsmRegClass::reg16) => "h",
-            InlineAsmRegClass::Nvptx(NvptxInlineAsmRegClass::reg32) => "r",
-            InlineAsmRegClass::Nvptx(NvptxInlineAsmRegClass::reg64) => "l",
-
-            InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::reg_nonzero) => "b",
-            InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::freg) => "f",
-            InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::vreg) => "v",
-            InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::cr)
-            | InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::xer) => {
-                unreachable!("clobber-only")
-            }
-            InlineAsmRegClass::RiscV(RiscVInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::RiscV(RiscVInlineAsmRegClass::freg) => "f",
-            InlineAsmRegClass::RiscV(RiscVInlineAsmRegClass::vreg) => {
-                unreachable!("clobber-only")
-            }
-            InlineAsmRegClass::X86(X86InlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::X86(X86InlineAsmRegClass::reg_abcd) => "Q",
-            InlineAsmRegClass::X86(X86InlineAsmRegClass::reg_byte) => "q",
-            InlineAsmRegClass::X86(X86InlineAsmRegClass::xmm_reg)
-            | InlineAsmRegClass::X86(X86InlineAsmRegClass::ymm_reg) => "x",
-            InlineAsmRegClass::X86(X86InlineAsmRegClass::zmm_reg) => "v",
-            InlineAsmRegClass::X86(X86InlineAsmRegClass::kreg) => "Yk",
-            InlineAsmRegClass::X86(
-                X86InlineAsmRegClass::kreg0
-                | X86InlineAsmRegClass::x87_reg
-                | X86InlineAsmRegClass::mmx_reg
-                | X86InlineAsmRegClass::tmm_reg,
-            ) => unreachable!("clobber-only"),
-            InlineAsmRegClass::SpirV(SpirVInlineAsmRegClass::reg) => {
-                bug!("GCC backend does not support SPIR-V")
-            }
-            InlineAsmRegClass::Wasm(WasmInlineAsmRegClass::local) => "r",
-            InlineAsmRegClass::S390x(S390xInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::S390x(S390xInlineAsmRegClass::reg_addr) => "a",
-            InlineAsmRegClass::S390x(S390xInlineAsmRegClass::freg) => "f",
-            InlineAsmRegClass::S390x(S390xInlineAsmRegClass::vreg) => "v",
-            InlineAsmRegClass::S390x(S390xInlineAsmRegClass::areg) => {
-                unreachable!("clobber-only")
-            }
-            InlineAsmRegClass::Sparc(SparcInlineAsmRegClass::reg) => "r",
-            InlineAsmRegClass::Sparc(SparcInlineAsmRegClass::yreg) => unreachable!("clobber-only"),
-            InlineAsmRegClass::Err => unreachable!(),
-        },
-    };
 
-    ConstraintOrRegister::Constraint(constraint)
+        _ => unimplemented!(),
+    }
+}
+
+/// They can be retrieved from https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html
+fn reg_class_to_gcc(reg_class: InlineAsmRegClass) -> &'static str {
+    match reg_class {
+        InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::vreg) => "w",
+        InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::vreg_low16) => "x",
+        InlineAsmRegClass::AArch64(AArch64InlineAsmRegClass::preg) => {
+            unreachable!("clobber-only")
+        }
+        InlineAsmRegClass::Arm(ArmInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::Arm(ArmInlineAsmRegClass::sreg)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::dreg_low16)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::qreg_low8)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::sreg_low16)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::dreg_low8)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::qreg_low4)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::dreg)
+        | InlineAsmRegClass::Arm(ArmInlineAsmRegClass::qreg) => "t",
+        InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_upper) => "d",
+        InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_pair) => "r",
+        InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_iw) => "w",
+        InlineAsmRegClass::Avr(AvrInlineAsmRegClass::reg_ptr) => "e",
+        InlineAsmRegClass::Bpf(BpfInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::Bpf(BpfInlineAsmRegClass::wreg) => "w",
+        InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::preg) => {
+            unreachable!("clobber-only")
+        }
+        InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::freg) => "f",
+        InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg_addr) => "a",
+        InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg_data) => "d",
+        InlineAsmRegClass::CSKY(CSKYInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::CSKY(CSKYInlineAsmRegClass::freg) => "f",
+        InlineAsmRegClass::Mips(MipsInlineAsmRegClass::reg) => "d", // more specific than "r"
+        InlineAsmRegClass::Mips(MipsInlineAsmRegClass::freg) => "f",
+        InlineAsmRegClass::Msp430(Msp430InlineAsmRegClass::reg) => "r",
+        // https://github.com/gcc-mirror/gcc/blob/master/gcc/config/nvptx/nvptx.md -> look for
+        // "define_constraint".
+        InlineAsmRegClass::Nvptx(NvptxInlineAsmRegClass::reg16) => "h",
+        InlineAsmRegClass::Nvptx(NvptxInlineAsmRegClass::reg32) => "r",
+        InlineAsmRegClass::Nvptx(NvptxInlineAsmRegClass::reg64) => "l",
+
+        InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::reg_nonzero) => "b",
+        InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::freg) => "f",
+        InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::vreg) => "v",
+        InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::cr)
+        | InlineAsmRegClass::PowerPC(PowerPCInlineAsmRegClass::xer) => {
+            unreachable!("clobber-only")
+        }
+        InlineAsmRegClass::RiscV(RiscVInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::RiscV(RiscVInlineAsmRegClass::freg) => "f",
+        InlineAsmRegClass::RiscV(RiscVInlineAsmRegClass::vreg) => {
+            unreachable!("clobber-only")
+        }
+        InlineAsmRegClass::X86(X86InlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::X86(X86InlineAsmRegClass::reg_abcd) => "Q",
+        InlineAsmRegClass::X86(X86InlineAsmRegClass::reg_byte) => "q",
+        InlineAsmRegClass::X86(X86InlineAsmRegClass::xmm_reg)
+        | InlineAsmRegClass::X86(X86InlineAsmRegClass::ymm_reg) => "x",
+        InlineAsmRegClass::X86(X86InlineAsmRegClass::zmm_reg) => "v",
+        InlineAsmRegClass::X86(X86InlineAsmRegClass::kreg) => "Yk",
+        InlineAsmRegClass::X86(
+            X86InlineAsmRegClass::kreg0
+            | X86InlineAsmRegClass::x87_reg
+            | X86InlineAsmRegClass::mmx_reg
+            | X86InlineAsmRegClass::tmm_reg,
+        ) => unreachable!("clobber-only"),
+        InlineAsmRegClass::SpirV(SpirVInlineAsmRegClass::reg) => {
+            bug!("GCC backend does not support SPIR-V")
+        }
+        InlineAsmRegClass::Wasm(WasmInlineAsmRegClass::local) => "r",
+        InlineAsmRegClass::S390x(S390xInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::S390x(S390xInlineAsmRegClass::reg_addr) => "a",
+        InlineAsmRegClass::S390x(S390xInlineAsmRegClass::freg) => "f",
+        InlineAsmRegClass::S390x(S390xInlineAsmRegClass::vreg) => "v",
+        InlineAsmRegClass::S390x(S390xInlineAsmRegClass::areg) => {
+            unreachable!("clobber-only")
+        }
+        InlineAsmRegClass::Sparc(SparcInlineAsmRegClass::reg) => "r",
+        InlineAsmRegClass::Sparc(SparcInlineAsmRegClass::yreg) => unreachable!("clobber-only"),
+        InlineAsmRegClass::Err => unreachable!(),
+    }
 }
 
 /// Type to use for outputs that are discarded. It doesn't really matter what
diff --git a/compiler/rustc_codegen_gcc/src/back/write.rs b/compiler/rustc_codegen_gcc/src/back/write.rs
index 51c5ba73e32..16c895322e8 100644
--- a/compiler/rustc_codegen_gcc/src/back/write.rs
+++ b/compiler/rustc_codegen_gcc/src/back/write.rs
@@ -24,19 +24,23 @@ pub(crate) unsafe fn codegen(
     {
         let context = &module.module_llvm.context;
 
-        let module_name = module.name.clone();
-
         let should_combine_object_files = module.module_llvm.should_combine_object_files;
 
-        let module_name = Some(&module_name[..]);
-
         // NOTE: Only generate object files with GIMPLE when this environment variable is set for
         // now because this requires a particular setup (same gcc/lto1/lto-wrapper commit as libgccjit).
         // TODO(antoyo): remove this environment variable.
         let fat_lto = env::var("EMBED_LTO_BITCODE").as_deref() == Ok("1");
 
-        let bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
-        let obj_out = cgcx.output_filenames.temp_path(OutputType::Object, module_name);
+        let bc_out = cgcx.output_filenames.temp_path_for_cgu(
+            OutputType::Bitcode,
+            &module.name,
+            cgcx.invocation_temp.as_deref(),
+        );
+        let obj_out = cgcx.output_filenames.temp_path_for_cgu(
+            OutputType::Object,
+            &module.name,
+            cgcx.invocation_temp.as_deref(),
+        );
 
         if config.bitcode_needed() {
             if fat_lto {
@@ -117,14 +121,22 @@ pub(crate) unsafe fn codegen(
         }
 
         if config.emit_ir {
-            let out = cgcx.output_filenames.temp_path(OutputType::LlvmAssembly, module_name);
+            let out = cgcx.output_filenames.temp_path_for_cgu(
+                OutputType::LlvmAssembly,
+                &module.name,
+                cgcx.invocation_temp.as_deref(),
+            );
             std::fs::write(out, "").expect("write file");
         }
 
         if config.emit_asm {
             let _timer =
                 cgcx.prof.generic_activity_with_arg("GCC_module_codegen_emit_asm", &*module.name);
-            let path = cgcx.output_filenames.temp_path(OutputType::Assembly, module_name);
+            let path = cgcx.output_filenames.temp_path_for_cgu(
+                OutputType::Assembly,
+                &module.name,
+                cgcx.invocation_temp.as_deref(),
+            );
             context.compile_to_file(OutputKind::Assembler, path.to_str().expect("path to str"));
         }
 
@@ -238,6 +250,7 @@ pub(crate) unsafe fn codegen(
         config.emit_asm,
         config.emit_ir,
         &cgcx.output_filenames,
+        cgcx.invocation_temp.as_deref(),
     ))
 }
 
diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs
index 6573b5b165e..5c70f4a7df9 100644
--- a/compiler/rustc_codegen_gcc/src/builder.rs
+++ b/compiler/rustc_codegen_gcc/src/builder.rs
@@ -368,16 +368,8 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
         let previous_arg_count = args.len();
         let orig_args = args;
         let args = {
-            let function_address_names = self.function_address_names.borrow();
-            let original_function_name = function_address_names.get(&func_ptr);
             func_ptr = llvm::adjust_function(self.context, &func_name, func_ptr, args);
-            llvm::adjust_intrinsic_arguments(
-                self,
-                gcc_func,
-                args.into(),
-                &func_name,
-                original_function_name,
-            )
+            llvm::adjust_intrinsic_arguments(self, gcc_func, args.into(), &func_name)
         };
         let args_adjusted = args.len() != previous_arg_count;
         let args = self.check_ptr_call("call", func_ptr, &args);
@@ -1271,7 +1263,50 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
     }
 
     fn fcmp(&mut self, op: RealPredicate, lhs: RValue<'gcc>, rhs: RValue<'gcc>) -> RValue<'gcc> {
-        self.context.new_comparison(self.location, op.to_gcc_comparison(), lhs, rhs)
+        // LLVM has a concept of "unordered compares", where eg ULT returns true if either the two
+        // arguments are unordered (i.e. either is NaN), or the lhs is less than the rhs. GCC does
+        // not natively have this concept, so in some cases we must manually handle NaNs
+        let must_handle_nan = match op {
+            RealPredicate::RealPredicateFalse => unreachable!(),
+            RealPredicate::RealOEQ => false,
+            RealPredicate::RealOGT => false,
+            RealPredicate::RealOGE => false,
+            RealPredicate::RealOLT => false,
+            RealPredicate::RealOLE => false,
+            RealPredicate::RealONE => false,
+            RealPredicate::RealORD => unreachable!(),
+            RealPredicate::RealUNO => unreachable!(),
+            RealPredicate::RealUEQ => false,
+            RealPredicate::RealUGT => true,
+            RealPredicate::RealUGE => true,
+            RealPredicate::RealULT => true,
+            RealPredicate::RealULE => true,
+            RealPredicate::RealUNE => false,
+            RealPredicate::RealPredicateTrue => unreachable!(),
+        };
+
+        let cmp = self.context.new_comparison(self.location, op.to_gcc_comparison(), lhs, rhs);
+
+        if must_handle_nan {
+            let is_nan = self.context.new_binary_op(
+                self.location,
+                BinaryOp::LogicalOr,
+                self.cx.bool_type,
+                // compare a value to itself to check whether it is NaN
+                self.context.new_comparison(self.location, ComparisonOp::NotEquals, lhs, lhs),
+                self.context.new_comparison(self.location, ComparisonOp::NotEquals, rhs, rhs),
+            );
+
+            self.context.new_binary_op(
+                self.location,
+                BinaryOp::LogicalOr,
+                self.cx.bool_type,
+                is_nan,
+                cmp,
+            )
+        } else {
+            cmp
+        }
     }
 
     /* Miscellaneous instructions */
diff --git a/compiler/rustc_codegen_gcc/src/context.rs b/compiler/rustc_codegen_gcc/src/context.rs
index 1e1f577bb3a..73718994e64 100644
--- a/compiler/rustc_codegen_gcc/src/context.rs
+++ b/compiler/rustc_codegen_gcc/src/context.rs
@@ -23,6 +23,8 @@ use rustc_target::spec::{
     HasTargetSpec, HasWasmCAbiOpt, HasX86AbiOpt, Target, TlsModel, WasmCAbi, X86Abi,
 };
 
+#[cfg(feature = "master")]
+use crate::abi::conv_to_fn_attribute;
 use crate::callee::get_fn;
 use crate::common::SignType;
 
@@ -213,33 +215,7 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
         let bool_type = context.new_type::<bool>();
 
         let mut functions = FxHashMap::default();
-        let builtins = [
-            "__builtin_unreachable",
-            "abort",
-            "__builtin_expect", /*"__builtin_expect_with_probability",*/
-            "__builtin_constant_p",
-            "__builtin_add_overflow",
-            "__builtin_mul_overflow",
-            "__builtin_saddll_overflow",
-            /*"__builtin_sadd_overflow",*/
-            "__builtin_smulll_overflow", /*"__builtin_smul_overflow",*/
-            "__builtin_ssubll_overflow",
-            /*"__builtin_ssub_overflow",*/ "__builtin_sub_overflow",
-            "__builtin_uaddll_overflow",
-            "__builtin_uadd_overflow",
-            "__builtin_umulll_overflow",
-            "__builtin_umul_overflow",
-            "__builtin_usubll_overflow",
-            "__builtin_usub_overflow",
-            "__builtin_powif",
-            "__builtin_powi",
-            "fabsf",
-            "fabs",
-            "copysignf",
-            "copysign",
-            "nearbyintf",
-            "nearbyint",
-        ];
+        let builtins = ["abort"];
 
         for builtin in builtins.iter() {
             functions.insert(builtin.to_string(), context.get_builtin_function(builtin));
@@ -509,7 +485,11 @@ impl<'gcc, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
     fn declare_c_main(&self, fn_type: Self::Type) -> Option<Self::Function> {
         let entry_name = self.sess().target.entry_name.as_ref();
         if !self.functions.borrow().contains_key(entry_name) {
-            Some(self.declare_entry_fn(entry_name, fn_type, ()))
+            #[cfg(feature = "master")]
+            let conv = conv_to_fn_attribute(self.sess().target.entry_abi, &self.sess().target.arch);
+            #[cfg(not(feature = "master"))]
+            let conv = None;
+            Some(self.declare_entry_fn(entry_name, fn_type, conv))
         } else {
             // If the symbol already exists, it is an error: for example, the user wrote
             // #[no_mangle] extern "C" fn main(..) {..}
@@ -605,7 +585,10 @@ impl<'b, 'tcx> CodegenCx<'b, 'tcx> {
         let mut name = String::with_capacity(prefix.len() + 6);
         name.push_str(prefix);
         name.push('.');
-        name.push_str(&(idx as u64).to_base(ALPHANUMERIC_ONLY));
+        // Offset the index by the base so that always at least two characters
+        // are generated. This avoids cases where the suffix is interpreted as
+        // size by the assembler (for m68k: .b, .w, .l).
+        name.push_str(&(idx as u64 + ALPHANUMERIC_ONLY as u64).to_base(ALPHANUMERIC_ONLY));
         name
     }
 }
diff --git a/compiler/rustc_codegen_gcc/src/declare.rs b/compiler/rustc_codegen_gcc/src/declare.rs
index 7cdbe3c0c62..c1ca3eb849e 100644
--- a/compiler/rustc_codegen_gcc/src/declare.rs
+++ b/compiler/rustc_codegen_gcc/src/declare.rs
@@ -58,7 +58,7 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
         variadic: bool,
     ) -> Function<'gcc> {
         self.linkage.set(FunctionType::Extern);
-        declare_raw_fn(self, name, () /*llvm::CCallConv*/, return_type, params, variadic)
+        declare_raw_fn(self, name, None, return_type, params, variadic)
     }
 
     pub fn declare_global(
@@ -92,7 +92,8 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
         &self,
         name: &str,
         _fn_type: Type<'gcc>,
-        callconv: (), /*llvm::CCallConv*/
+        #[cfg(feature = "master")] callconv: Option<FnAttribute<'gcc>>,
+        #[cfg(not(feature = "master"))] callconv: Option<()>,
     ) -> RValue<'gcc> {
         // TODO(antoyo): use the fn_type parameter.
         let const_string = self.context.new_type::<u8>().make_pointer().make_pointer();
@@ -123,14 +124,11 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
             #[cfg(feature = "master")]
             fn_attributes,
         } = fn_abi.gcc_type(self);
-        let func = declare_raw_fn(
-            self,
-            name,
-            (), /*fn_abi.llvm_cconv()*/
-            return_type,
-            &arguments_type,
-            is_c_variadic,
-        );
+        #[cfg(feature = "master")]
+        let conv = fn_abi.gcc_cconv(self);
+        #[cfg(not(feature = "master"))]
+        let conv = None;
+        let func = declare_raw_fn(self, name, conv, return_type, &arguments_type, is_c_variadic);
         self.on_stack_function_params.borrow_mut().insert(func, on_stack_param_indices);
         #[cfg(feature = "master")]
         for fn_attr in fn_attributes {
@@ -162,7 +160,8 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
 fn declare_raw_fn<'gcc>(
     cx: &CodegenCx<'gcc, '_>,
     name: &str,
-    _callconv: (), /*llvm::CallConv*/
+    #[cfg(feature = "master")] callconv: Option<FnAttribute<'gcc>>,
+    #[cfg(not(feature = "master"))] _callconv: Option<()>,
     return_type: Type<'gcc>,
     param_types: &[Type<'gcc>],
     variadic: bool,
@@ -192,6 +191,10 @@ fn declare_raw_fn<'gcc>(
         let name = &mangle_name(name);
         let func =
             cx.context.new_function(None, cx.linkage.get(), return_type, &params, name, variadic);
+        #[cfg(feature = "master")]
+        if let Some(attribute) = callconv {
+            func.add_attribute(attribute);
+        }
         cx.functions.borrow_mut().insert(name.to_string(), func);
 
         #[cfg(feature = "master")]
diff --git a/compiler/rustc_codegen_gcc/src/gcc_util.rs b/compiler/rustc_codegen_gcc/src/gcc_util.rs
index 6eae0c24f48..202764d5649 100644
--- a/compiler/rustc_codegen_gcc/src/gcc_util.rs
+++ b/compiler/rustc_codegen_gcc/src/gcc_util.rs
@@ -194,6 +194,7 @@ pub fn to_gcc_features<'a>(sess: &Session, s: &'a str) -> SmallVec<[&'a str; 2]>
 
 fn arch_to_gcc(name: &str) -> &str {
     match name {
+        "M68000" => "68000",
         "M68020" => "68020",
         _ => name,
     }
diff --git a/compiler/rustc_codegen_gcc/src/int.rs b/compiler/rustc_codegen_gcc/src/int.rs
index f3552d9b12f..9b5b0fde6e2 100644
--- a/compiler/rustc_codegen_gcc/src/int.rs
+++ b/compiler/rustc_codegen_gcc/src/int.rs
@@ -404,7 +404,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
 
         let ret_indirect = matches!(fn_abi.ret.mode, PassMode::Indirect { .. });
 
-        let result = if ret_indirect {
+        let call = if ret_indirect {
             let res_value = self.current_func().new_local(self.location, res_type, "result_value");
             let res_addr = res_value.get_address(self.location);
             let res_param_type = res_type.make_pointer();
@@ -432,8 +432,17 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
             );
             self.context.new_call(self.location, func, &[lhs, rhs, overflow_addr])
         };
-
-        (result, self.context.new_cast(self.location, overflow_value, self.bool_type).to_rvalue())
+        // NOTE: we must assign the result of the operation to a variable at this point to make
+        // sure it will be evaluated by libgccjit now.
+        // Otherwise, it will only be evaluated when the rvalue for the call is used somewhere else
+        // and overflow_value will not be initialized at the correct point in the program.
+        let result = self.current_func().new_local(self.location, res_type, "result");
+        self.block.add_assignment(self.location, result, call);
+
+        (
+            result.to_rvalue(),
+            self.context.new_cast(self.location, overflow_value, self.bool_type).to_rvalue(),
+        )
     }
 
     pub fn gcc_icmp(
@@ -865,6 +874,7 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
         let value_type = value.get_type();
         if self.is_native_int_type_or_bool(dest_typ) && self.is_native_int_type_or_bool(value_type)
         {
+            // TODO: use self.location.
             self.context.new_cast(None, value, dest_typ)
         } else if self.is_native_int_type_or_bool(dest_typ) {
             self.context.new_cast(None, self.low(value), dest_typ)
@@ -905,6 +915,7 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
         let name_suffix = match self.type_kind(dest_typ) {
             TypeKind::Float => "tisf",
             TypeKind::Double => "tidf",
+            TypeKind::FP128 => "tixf",
             kind => panic!("cannot cast a non-native integer to type {:?}", kind),
         };
         let sign = if signed { "" } else { "un" };
diff --git a/compiler/rustc_codegen_gcc/src/intrinsic/llvm.rs b/compiler/rustc_codegen_gcc/src/intrinsic/llvm.rs
index 2d731f88d7d..0eebd21001a 100644
--- a/compiler/rustc_codegen_gcc/src/intrinsic/llvm.rs
+++ b/compiler/rustc_codegen_gcc/src/intrinsic/llvm.rs
@@ -1,11 +1,90 @@
 use std::borrow::Cow;
 
-use gccjit::{CType, Context, Function, FunctionPtrType, RValue, ToRValue, UnaryOp};
+use gccjit::{CType, Context, Field, Function, FunctionPtrType, RValue, ToRValue, Type};
 use rustc_codegen_ssa::traits::BuilderMethods;
 
 use crate::builder::Builder;
 use crate::context::CodegenCx;
 
+fn encode_key_128_type<'a, 'gcc, 'tcx>(
+    builder: &Builder<'a, 'gcc, 'tcx>,
+) -> (Type<'gcc>, Field<'gcc>, Field<'gcc>) {
+    let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+    let field1 = builder.context.new_field(None, builder.u32_type, "field1");
+    let field2 = builder.context.new_field(None, m128i, "field2");
+    let field3 = builder.context.new_field(None, m128i, "field3");
+    let field4 = builder.context.new_field(None, m128i, "field4");
+    let field5 = builder.context.new_field(None, m128i, "field5");
+    let field6 = builder.context.new_field(None, m128i, "field6");
+    let field7 = builder.context.new_field(None, m128i, "field7");
+    let encode_type = builder.context.new_struct_type(
+        None,
+        "EncodeKey128Output",
+        &[field1, field2, field3, field4, field5, field6, field7],
+    );
+    #[cfg(feature = "master")]
+    encode_type.as_type().set_packed();
+    (encode_type.as_type(), field1, field2)
+}
+
+fn encode_key_256_type<'a, 'gcc, 'tcx>(
+    builder: &Builder<'a, 'gcc, 'tcx>,
+) -> (Type<'gcc>, Field<'gcc>, Field<'gcc>) {
+    let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+    let field1 = builder.context.new_field(None, builder.u32_type, "field1");
+    let field2 = builder.context.new_field(None, m128i, "field2");
+    let field3 = builder.context.new_field(None, m128i, "field3");
+    let field4 = builder.context.new_field(None, m128i, "field4");
+    let field5 = builder.context.new_field(None, m128i, "field5");
+    let field6 = builder.context.new_field(None, m128i, "field6");
+    let field7 = builder.context.new_field(None, m128i, "field7");
+    let field8 = builder.context.new_field(None, m128i, "field8");
+    let encode_type = builder.context.new_struct_type(
+        None,
+        "EncodeKey256Output",
+        &[field1, field2, field3, field4, field5, field6, field7, field8],
+    );
+    #[cfg(feature = "master")]
+    encode_type.as_type().set_packed();
+    (encode_type.as_type(), field1, field2)
+}
+
+fn aes_output_type<'a, 'gcc, 'tcx>(
+    builder: &Builder<'a, 'gcc, 'tcx>,
+) -> (Type<'gcc>, Field<'gcc>, Field<'gcc>) {
+    let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+    let field1 = builder.context.new_field(None, builder.u8_type, "field1");
+    let field2 = builder.context.new_field(None, m128i, "field2");
+    let aes_output_type = builder.context.new_struct_type(None, "AesOutput", &[field1, field2]);
+    let typ = aes_output_type.as_type();
+    #[cfg(feature = "master")]
+    typ.set_packed();
+    (typ, field1, field2)
+}
+
+fn wide_aes_output_type<'a, 'gcc, 'tcx>(
+    builder: &Builder<'a, 'gcc, 'tcx>,
+) -> (Type<'gcc>, Field<'gcc>, Field<'gcc>) {
+    let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+    let field1 = builder.context.new_field(None, builder.u8_type, "field1");
+    let field2 = builder.context.new_field(None, m128i, "field2");
+    let field3 = builder.context.new_field(None, m128i, "field3");
+    let field4 = builder.context.new_field(None, m128i, "field4");
+    let field5 = builder.context.new_field(None, m128i, "field5");
+    let field6 = builder.context.new_field(None, m128i, "field6");
+    let field7 = builder.context.new_field(None, m128i, "field7");
+    let field8 = builder.context.new_field(None, m128i, "field8");
+    let field9 = builder.context.new_field(None, m128i, "field9");
+    let aes_output_type = builder.context.new_struct_type(
+        None,
+        "WideAesOutput",
+        &[field1, field2, field3, field4, field5, field6, field7, field8, field9],
+    );
+    #[cfg(feature = "master")]
+    aes_output_type.as_type().set_packed();
+    (aes_output_type.as_type(), field1, field2)
+}
+
 #[cfg_attr(not(feature = "master"), allow(unused_variables))]
 pub fn adjust_function<'gcc>(
     context: &'gcc Context<'gcc>,
@@ -43,7 +122,6 @@ pub fn adjust_intrinsic_arguments<'a, 'b, 'gcc, 'tcx>(
     gcc_func: FunctionPtrType<'gcc>,
     mut args: Cow<'b, [RValue<'gcc>]>,
     func_name: &str,
-    original_function_name: Option<&String>,
 ) -> Cow<'b, [RValue<'gcc>]> {
     // TODO: this might not be a good way to workaround the missing tile builtins.
     if func_name == "__builtin_trap" {
@@ -504,6 +582,72 @@ pub fn adjust_intrinsic_arguments<'a, 'b, 'gcc, 'tcx>(
                 let arg4 = builder.context.new_rvalue_from_int(arg4_type, -1);
                 args = vec![a, b, c, arg4, new_args[3]].into();
             }
+            "__builtin_ia32_encodekey128_u32" => {
+                let mut new_args = args.to_vec();
+                let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+                let array_type = builder.context.new_array_type(None, m128i, 6);
+                let result = builder.current_func().new_local(None, array_type, "result");
+                new_args.push(result.get_address(None));
+                args = new_args.into();
+            }
+            "__builtin_ia32_encodekey256_u32" => {
+                let mut new_args = args.to_vec();
+                let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+                let array_type = builder.context.new_array_type(None, m128i, 7);
+                let result = builder.current_func().new_local(None, array_type, "result");
+                new_args.push(result.get_address(None));
+                args = new_args.into();
+            }
+            "__builtin_ia32_aesenc128kl_u8"
+            | "__builtin_ia32_aesdec128kl_u8"
+            | "__builtin_ia32_aesenc256kl_u8"
+            | "__builtin_ia32_aesdec256kl_u8" => {
+                let mut new_args = vec![];
+                let m128i = builder.context.new_vector_type(builder.i64_type, 2);
+                let result = builder.current_func().new_local(None, m128i, "result");
+                new_args.push(result.get_address(None));
+                new_args.extend(args.to_vec());
+                args = new_args.into();
+            }
+            "__builtin_ia32_aesencwide128kl_u8"
+            | "__builtin_ia32_aesdecwide128kl_u8"
+            | "__builtin_ia32_aesencwide256kl_u8"
+            | "__builtin_ia32_aesdecwide256kl_u8" => {
+                let mut new_args = vec![];
+
+                let mut old_args = args.to_vec();
+                let handle = old_args.swap_remove(0); // Called __P in GCC.
+                let first_value = old_args.swap_remove(0);
+
+                let element_type = first_value.get_type();
+                let array_type = builder.context.new_array_type(None, element_type, 8);
+                let result = builder.current_func().new_local(None, array_type, "result");
+                new_args.push(result.get_address(None));
+
+                let array = builder.current_func().new_local(None, array_type, "array");
+                let input = builder.context.new_array_constructor(
+                    None,
+                    array_type,
+                    &[
+                        first_value,
+                        old_args.swap_remove(0),
+                        old_args.swap_remove(0),
+                        old_args.swap_remove(0),
+                        old_args.swap_remove(0),
+                        old_args.swap_remove(0),
+                        old_args.swap_remove(0),
+                        old_args.swap_remove(0),
+                    ],
+                );
+                builder.llbb().add_assignment(None, array, input);
+                let input_ptr = array.get_address(None);
+                let arg2_type = gcc_func.get_param_type(1);
+                let input_ptr = builder.context.new_cast(None, input_ptr, arg2_type);
+                new_args.push(input_ptr);
+
+                new_args.push(handle);
+                args = new_args.into();
+            }
             _ => (),
         }
     } else {
@@ -541,33 +685,6 @@ pub fn adjust_intrinsic_arguments<'a, 'b, 'gcc, 'tcx>(
                 let c = builder.context.new_rvalue_from_vector(None, arg3_type, &[new_args[2]; 2]);
                 args = vec![a, b, c, new_args[3]].into();
             }
-            "__builtin_ia32_vfmaddsubpd256"
-            | "__builtin_ia32_vfmaddsubps"
-            | "__builtin_ia32_vfmaddsubps256"
-            | "__builtin_ia32_vfmaddsubpd" => {
-                if let Some(original_function_name) = original_function_name {
-                    match &**original_function_name {
-                        "llvm.x86.fma.vfmsubadd.pd.256"
-                        | "llvm.x86.fma.vfmsubadd.ps"
-                        | "llvm.x86.fma.vfmsubadd.ps.256"
-                        | "llvm.x86.fma.vfmsubadd.pd" => {
-                            // NOTE: since both llvm.x86.fma.vfmsubadd.ps and llvm.x86.fma.vfmaddsub.ps maps to
-                            // __builtin_ia32_vfmaddsubps, only add minus if this comes from a
-                            // subadd LLVM intrinsic, e.g. _mm256_fmsubadd_pd.
-                            let mut new_args = args.to_vec();
-                            let arg3 = &mut new_args[2];
-                            *arg3 = builder.context.new_unary_op(
-                                None,
-                                UnaryOp::Minus,
-                                arg3.get_type(),
-                                *arg3,
-                            );
-                            args = new_args.into();
-                        }
-                        _ => (),
-                    }
-                }
-            }
             "__builtin_ia32_ldmxcsr" => {
                 // The builtin __builtin_ia32_ldmxcsr takes an integer value while llvm.x86.sse.ldmxcsr takes a pointer,
                 // so dereference the pointer.
@@ -728,6 +845,96 @@ pub fn adjust_intrinsic_return_value<'a, 'gcc, 'tcx>(
             let f16_type = builder.context.new_c_type(CType::Float16);
             return_value = builder.context.new_cast(None, return_value, f16_type);
         }
+        "__builtin_ia32_encodekey128_u32" => {
+            // The builtin __builtin_ia32_encodekey128_u32 writes the result in its pointer argument while
+            // llvm.x86.encodekey128 returns a value.
+            // We added a result pointer argument and now need to assign its value to the return_value expected by
+            // the LLVM intrinsic.
+            let (encode_type, field1, field2) = encode_key_128_type(builder);
+            let result = builder.current_func().new_local(None, encode_type, "result");
+            let field1 = result.access_field(None, field1);
+            builder.llbb().add_assignment(None, field1, return_value);
+            let field2 = result.access_field(None, field2);
+            let field2_type = field2.to_rvalue().get_type();
+            let array_type = builder.context.new_array_type(None, field2_type, 6);
+            let ptr = builder.context.new_cast(None, args[2], array_type.make_pointer());
+            let field2_ptr =
+                builder.context.new_cast(None, field2.get_address(None), array_type.make_pointer());
+            builder.llbb().add_assignment(
+                None,
+                field2_ptr.dereference(None),
+                ptr.dereference(None),
+            );
+            return_value = result.to_rvalue();
+        }
+        "__builtin_ia32_encodekey256_u32" => {
+            // The builtin __builtin_ia32_encodekey256_u32 writes the result in its pointer argument while
+            // llvm.x86.encodekey256 returns a value.
+            // We added a result pointer argument and now need to assign its value to the return_value expected by
+            // the LLVM intrinsic.
+            let (encode_type, field1, field2) = encode_key_256_type(builder);
+            let result = builder.current_func().new_local(None, encode_type, "result");
+            let field1 = result.access_field(None, field1);
+            builder.llbb().add_assignment(None, field1, return_value);
+            let field2 = result.access_field(None, field2);
+            let field2_type = field2.to_rvalue().get_type();
+            let array_type = builder.context.new_array_type(None, field2_type, 7);
+            let ptr = builder.context.new_cast(None, args[3], array_type.make_pointer());
+            let field2_ptr =
+                builder.context.new_cast(None, field2.get_address(None), array_type.make_pointer());
+            builder.llbb().add_assignment(
+                None,
+                field2_ptr.dereference(None),
+                ptr.dereference(None),
+            );
+            return_value = result.to_rvalue();
+        }
+        "__builtin_ia32_aesdec128kl_u8"
+        | "__builtin_ia32_aesenc128kl_u8"
+        | "__builtin_ia32_aesdec256kl_u8"
+        | "__builtin_ia32_aesenc256kl_u8" => {
+            // The builtin for aesdec/aesenc writes the result in its pointer argument while
+            // llvm.x86.aesdec128kl returns a value.
+            // We added a result pointer argument and now need to assign its value to the return_value expected by
+            // the LLVM intrinsic.
+            let (aes_output_type, field1, field2) = aes_output_type(builder);
+            let result = builder.current_func().new_local(None, aes_output_type, "result");
+            let field1 = result.access_field(None, field1);
+            builder.llbb().add_assignment(None, field1, return_value);
+            let field2 = result.access_field(None, field2);
+            let ptr = builder.context.new_cast(
+                None,
+                args[0],
+                field2.to_rvalue().get_type().make_pointer(),
+            );
+            builder.llbb().add_assignment(None, field2, ptr.dereference(None));
+            return_value = result.to_rvalue();
+        }
+        "__builtin_ia32_aesencwide128kl_u8"
+        | "__builtin_ia32_aesdecwide128kl_u8"
+        | "__builtin_ia32_aesencwide256kl_u8"
+        | "__builtin_ia32_aesdecwide256kl_u8" => {
+            // The builtin for aesdecwide/aesencwide writes the result in its pointer argument while
+            // llvm.x86.aesencwide128kl returns a value.
+            // We added a result pointer argument and now need to assign its value to the return_value expected by
+            // the LLVM intrinsic.
+            let (aes_output_type, field1, field2) = wide_aes_output_type(builder);
+            let result = builder.current_func().new_local(None, aes_output_type, "result");
+            let field1 = result.access_field(None, field1);
+            builder.llbb().add_assignment(None, field1, return_value);
+            let field2 = result.access_field(None, field2);
+            let field2_type = field2.to_rvalue().get_type();
+            let array_type = builder.context.new_array_type(None, field2_type, 8);
+            let ptr = builder.context.new_cast(None, args[0], array_type.make_pointer());
+            let field2_ptr =
+                builder.context.new_cast(None, field2.get_address(None), array_type.make_pointer());
+            builder.llbb().add_assignment(
+                None,
+                field2_ptr.dereference(None),
+                ptr.dereference(None),
+            );
+            return_value = result.to_rvalue();
+        }
         _ => (),
     }
 
@@ -915,16 +1122,6 @@ pub fn intrinsic<'gcc, 'tcx>(name: &str, cx: &CodegenCx<'gcc, 'tcx>) -> Function
         "llvm.ctlz.v4i64" => "__builtin_ia32_vplzcntq_256_mask",
         "llvm.ctlz.v2i64" => "__builtin_ia32_vplzcntq_128_mask",
         "llvm.ctpop.v32i16" => "__builtin_ia32_vpopcountw_v32hi",
-        "llvm.x86.fma.vfmsub.sd" => "__builtin_ia32_vfmsubsd3",
-        "llvm.x86.fma.vfmsub.ss" => "__builtin_ia32_vfmsubss3",
-        "llvm.x86.fma.vfmsubadd.pd" => "__builtin_ia32_vfmaddsubpd",
-        "llvm.x86.fma.vfmsubadd.pd.256" => "__builtin_ia32_vfmaddsubpd256",
-        "llvm.x86.fma.vfmsubadd.ps" => "__builtin_ia32_vfmaddsubps",
-        "llvm.x86.fma.vfmsubadd.ps.256" => "__builtin_ia32_vfmaddsubps256",
-        "llvm.x86.fma.vfnmadd.sd" => "__builtin_ia32_vfnmaddsd3",
-        "llvm.x86.fma.vfnmadd.ss" => "__builtin_ia32_vfnmaddss3",
-        "llvm.x86.fma.vfnmsub.sd" => "__builtin_ia32_vfnmsubsd3",
-        "llvm.x86.fma.vfnmsub.ss" => "__builtin_ia32_vfnmsubss3",
         "llvm.x86.avx512.conflict.d.512" => "__builtin_ia32_vpconflictsi_512_mask",
         "llvm.x86.avx512.conflict.d.256" => "__builtin_ia32_vpconflictsi_256_mask",
         "llvm.x86.avx512.conflict.d.128" => "__builtin_ia32_vpconflictsi_128_mask",
@@ -1002,8 +1199,6 @@ pub fn intrinsic<'gcc, 'tcx>(name: &str, cx: &CodegenCx<'gcc, 'tcx>) -> Function
         "llvm.fshr.v32i16" => "__builtin_ia32_vpshrdv_v32hi",
         "llvm.fshr.v16i16" => "__builtin_ia32_vpshrdv_v16hi",
         "llvm.fshr.v8i16" => "__builtin_ia32_vpshrdv_v8hi",
-        "llvm.x86.fma.vfmadd.sd" => "__builtin_ia32_vfmaddsd3",
-        "llvm.x86.fma.vfmadd.ss" => "__builtin_ia32_vfmaddss3",
         "llvm.x86.rdrand.64" => "__builtin_ia32_rdrand64_step",
 
         // The above doc points to unknown builtins for the following, so override them:
@@ -1324,6 +1519,16 @@ pub fn intrinsic<'gcc, 'tcx>(name: &str, cx: &CodegenCx<'gcc, 'tcx>) -> Function
         "llvm.x86.avx512fp16.mask.vfmadd.cph.256" => "__builtin_ia32_vfmaddcph256_mask3",
         "llvm.x86.avx512fp16.mask.vfcmadd.cph.128" => "__builtin_ia32_vfcmaddcph128_mask3",
         "llvm.x86.avx512fp16.mask.vfmadd.cph.128" => "__builtin_ia32_vfmaddcph128_mask3",
+        "llvm.x86.encodekey128" => "__builtin_ia32_encodekey128_u32",
+        "llvm.x86.encodekey256" => "__builtin_ia32_encodekey256_u32",
+        "llvm.x86.aesenc128kl" => "__builtin_ia32_aesenc128kl_u8",
+        "llvm.x86.aesdec128kl" => "__builtin_ia32_aesdec128kl_u8",
+        "llvm.x86.aesenc256kl" => "__builtin_ia32_aesenc256kl_u8",
+        "llvm.x86.aesdec256kl" => "__builtin_ia32_aesdec256kl_u8",
+        "llvm.x86.aesencwide128kl" => "__builtin_ia32_aesencwide128kl_u8",
+        "llvm.x86.aesdecwide128kl" => "__builtin_ia32_aesdecwide128kl_u8",
+        "llvm.x86.aesencwide256kl" => "__builtin_ia32_aesencwide256kl_u8",
+        "llvm.x86.aesdecwide256kl" => "__builtin_ia32_aesdecwide256kl_u8",
 
         // TODO: support the tile builtins:
         "llvm.x86.ldtilecfg" => "__builtin_trap",
diff --git a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
index f38622074f1..d22f4229e23 100644
--- a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
+++ b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
@@ -78,6 +78,7 @@ fn get_simple_intrinsic<'gcc, 'tcx>(
         sym::maxnumf64 => "fmax",
         sym::copysignf32 => "copysignf",
         sym::copysignf64 => "copysign",
+        sym::copysignf128 => "copysignl",
         sym::floorf32 => "floorf",
         sym::floorf64 => "floor",
         sym::ceilf32 => "ceilf",
diff --git a/compiler/rustc_codegen_gcc/src/intrinsic/simd.rs b/compiler/rustc_codegen_gcc/src/intrinsic/simd.rs
index 8b454ab2a42..6d40d5297f1 100644
--- a/compiler/rustc_codegen_gcc/src/intrinsic/simd.rs
+++ b/compiler/rustc_codegen_gcc/src/intrinsic/simd.rs
@@ -399,7 +399,7 @@ pub fn generic_simd_intrinsic<'a, 'gcc, 'tcx>(
     }
 
     #[cfg(feature = "master")]
-    if name == sym::simd_insert {
+    if name == sym::simd_insert || name == sym::simd_insert_dyn {
         require!(
             in_elem == arg_tys[2],
             InvalidMonomorphization::InsertedType {
@@ -410,6 +410,8 @@ pub fn generic_simd_intrinsic<'a, 'gcc, 'tcx>(
                 out_ty: arg_tys[2]
             }
         );
+
+        // TODO(antoyo): For simd_insert, check if the index is a constant of the correct size.
         let vector = args[0].immediate();
         let index = args[1].immediate();
         let value = args[2].immediate();
@@ -422,13 +424,15 @@ pub fn generic_simd_intrinsic<'a, 'gcc, 'tcx>(
     }
 
     #[cfg(feature = "master")]
-    if name == sym::simd_extract {
+    if name == sym::simd_extract || name == sym::simd_extract_dyn {
         require!(
             ret_ty == in_elem,
             InvalidMonomorphization::ReturnType { span, name, in_elem, in_ty, ret_ty }
         );
+        // TODO(antoyo): For simd_extract, check if the index is a constant of the correct size.
         let vector = args[0].immediate();
-        return Ok(bx.context.new_vector_access(None, vector, args[1].immediate()).to_rvalue());
+        let index = args[1].immediate();
+        return Ok(bx.context.new_vector_access(None, vector, index).to_rvalue());
     }
 
     if name == sym::simd_select {
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
index bfa23174a19..624fdb4043c 100644
--- a/compiler/rustc_codegen_gcc/src/lib.rs
+++ b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -188,10 +188,10 @@ impl CodegenBackend for GccCodegenBackend {
         crate::DEFAULT_LOCALE_RESOURCE
     }
 
-    fn init(&self, sess: &Session) {
+    fn init(&self, _sess: &Session) {
         #[cfg(feature = "master")]
         {
-            let target_cpu = target_cpu(sess);
+            let target_cpu = target_cpu(_sess);
 
             // Get the second TargetInfo with the correct CPU features by setting the arch.
             let context = Context::default();
diff --git a/compiler/rustc_codegen_gcc/tests/failing-ui-tests.txt b/compiler/rustc_codegen_gcc/tests/failing-ui-tests.txt
index 082958bfe1f..499c1a96231 100644
--- a/compiler/rustc_codegen_gcc/tests/failing-ui-tests.txt
+++ b/compiler/rustc_codegen_gcc/tests/failing-ui-tests.txt
@@ -1,11 +1,9 @@
 tests/ui/allocator/no_std-alloc-error-handler-custom.rs
 tests/ui/allocator/no_std-alloc-error-handler-default.rs
 tests/ui/asm/may_unwind.rs
-tests/ui/asm/x86_64/multiple-clobber-abi.rs
 tests/ui/functions-closures/parallel-codegen-closures.rs
 tests/ui/linkage-attr/linkage1.rs
 tests/ui/lto/dylib-works.rs
-tests/ui/numbers-arithmetic/saturating-float-casts.rs
 tests/ui/sepcomp/sepcomp-cci.rs
 tests/ui/sepcomp/sepcomp-extern.rs
 tests/ui/sepcomp/sepcomp-fns-backwards.rs
@@ -33,7 +31,6 @@ tests/ui/unwind-no-uwtable.rs
 tests/ui/parser/unclosed-delimiter-in-dep.rs
 tests/ui/consts/missing_span_in_backtrace.rs
 tests/ui/drop/dynamic-drop.rs
-tests/ui/issues/issue-40883.rs
 tests/ui/issues/issue-43853.rs
 tests/ui/issues/issue-47364.rs
 tests/ui/macros/rfc-2011-nicer-assert-messages/assert-without-captures-does-not-create-unnecessary-code.rs
@@ -102,14 +99,12 @@ tests/ui/codegen/equal-pointers-unequal/as-cast/basic.rs
 tests/ui/codegen/equal-pointers-unequal/as-cast/inline1.rs
 tests/ui/codegen/equal-pointers-unequal/as-cast/print.rs
 tests/ui/codegen/equal-pointers-unequal/as-cast/inline2.rs
-tests/ui/codegen/equal-pointers-unequal/as-cast/print3.rs
 tests/ui/codegen/equal-pointers-unequal/as-cast/segfault.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/function.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/basic.rs
 tests/ui/codegen/equal-pointers-unequal/as-cast/zero.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/inline1.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/print.rs
-tests/ui/codegen/equal-pointers-unequal/exposed-provenance/print3.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/inline2.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/segfault.rs
 tests/ui/codegen/equal-pointers-unequal/exposed-provenance/zero.rs
@@ -117,8 +112,9 @@ tests/ui/codegen/equal-pointers-unequal/strict-provenance/basic.rs
 tests/ui/codegen/equal-pointers-unequal/strict-provenance/function.rs
 tests/ui/codegen/equal-pointers-unequal/strict-provenance/print.rs
 tests/ui/codegen/equal-pointers-unequal/strict-provenance/inline1.rs
-tests/ui/codegen/equal-pointers-unequal/strict-provenance/print3.rs
 tests/ui/codegen/equal-pointers-unequal/strict-provenance/inline2.rs
 tests/ui/codegen/equal-pointers-unequal/strict-provenance/segfault.rs
 tests/ui/codegen/equal-pointers-unequal/strict-provenance/zero.rs
 tests/ui/simd/simd-bitmask-notpow2.rs
+tests/ui/codegen/StackColoring-not-blowup-stack-issue-40883.rs
+tests/ui/uninhabited/uninhabited-transparent-return-abi.rs
diff --git a/compiler/rustc_codegen_gcc/tests/run/abort1.rs b/compiler/rustc_codegen_gcc/tests/run/abort1.rs
index fe46d9ae418..ff2bb75ece2 100644
--- a/compiler/rustc_codegen_gcc/tests/run/abort1.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/abort1.rs
@@ -3,45 +3,13 @@
 // Run-time:
 //   status: signal
 
-#![feature(auto_traits, lang_items, no_core, intrinsics, rustc_attrs)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-mod intrinsics {
-    use super::Sized;
-
-    #[rustc_nounwind]
-    #[rustc_intrinsic]
-    pub fn abort() -> !;
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 fn test_fail() -> ! {
     unsafe { intrinsics::abort() };
diff --git a/compiler/rustc_codegen_gcc/tests/run/abort2.rs b/compiler/rustc_codegen_gcc/tests/run/abort2.rs
index 4123f4f4bee..781f518e0b2 100644
--- a/compiler/rustc_codegen_gcc/tests/run/abort2.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/abort2.rs
@@ -3,45 +3,13 @@
 // Run-time:
 //   status: signal
 
-#![feature(auto_traits, lang_items, no_core, intrinsics, rustc_attrs)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-mod intrinsics {
-    use super::Sized;
-
-    #[rustc_nounwind]
-    #[rustc_intrinsic]
-    pub fn abort() -> !;
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 fn fail() -> i32 {
     unsafe { intrinsics::abort() };
diff --git a/compiler/rustc_codegen_gcc/tests/run/array.rs b/compiler/rustc_codegen_gcc/tests/run/array.rs
index e18a4ced6bc..3ab0c309fde 100644
--- a/compiler/rustc_codegen_gcc/tests/run/array.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/array.rs
@@ -8,20 +8,12 @@
 //     10
 
 #![feature(no_core)]
-
 #![no_std]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-        pub fn puts(s: *const u8) -> i32;
-    }
-}
+use mini_core::*;
 
 static mut ONE: usize = 1;
 
diff --git a/compiler/rustc_codegen_gcc/tests/run/asm.rs b/compiler/rustc_codegen_gcc/tests/run/asm.rs
index 4e05d026868..2dbf43be664 100644
--- a/compiler/rustc_codegen_gcc/tests/run/asm.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/asm.rs
@@ -174,6 +174,59 @@ fn asm() {
         mem_cpy(array2.as_mut_ptr(), array1.as_ptr(), 3);
     }
     assert_eq!(array1, array2);
+
+    // in and clobber registers cannot overlap. This tests that the lateout register without an
+    // output place (indicated by the `_`) is not added to the list of clobbered registers
+    let x = 8;
+    let y: i32;
+    unsafe {
+        asm!(
+            "mov rax, rdi",
+            in("rdi") x,
+            lateout("rdi") _,
+            out("rax") y,
+        );
+    }
+    assert_eq!((x, y), (8, 8));
+
+    // sysv64 is the default calling convention on unix systems. The rdi register is
+    // used to pass arguments in the sysv64 calling convention, so this register will be clobbered
+    #[cfg(unix)]
+    {
+        let x = 16;
+        let y: i32;
+        unsafe {
+            asm!(
+                "mov rax, rdi",
+                in("rdi") x,
+                out("rax") y,
+                clobber_abi("sysv64"),
+            );
+        }
+        assert_eq!((x, y), (16, 16));
+    }
+
+    // the `b` suffix for registers in the `reg_byte` register class is not supported in GCC
+    // and needs to be stripped in order to use these registers.
+    unsafe {
+        core::arch::asm!(
+            "",
+            out("al") _,
+            out("bl") _,
+            out("cl") _,
+            out("dl") _,
+            out("sil") _,
+            out("dil") _,
+            out("r8b") _,
+            out("r9b") _,
+            out("r10b") _,
+            out("r11b") _,
+            out("r12b") _,
+            out("r13b") _,
+            out("r14b") _,
+            out("r15b") _,
+        );
+    }
 }
 
 #[cfg(not(target_arch = "x86_64"))]
diff --git a/compiler/rustc_codegen_gcc/tests/run/assign.rs b/compiler/rustc_codegen_gcc/tests/run/assign.rs
index 286155852d5..4535ab5778e 100644
--- a/compiler/rustc_codegen_gcc/tests/run/assign.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/assign.rs
@@ -5,130 +5,13 @@
 //     7 8
 //     10
 
-#![allow(internal_features, unused_attributes)]
-#![feature(auto_traits, lang_items, no_core, intrinsics, rustc_attrs, track_caller)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-impl Copy for *mut i32 {}
-impl Copy for usize {}
-impl Copy for u8 {}
-impl Copy for i8 {}
-impl Copy for i32 {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-#[lang = "panic_location"]
-struct PanicLocation {
-    file: &'static str,
-    line: u32,
-    column: u32,
-}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn puts(s: *const u8) -> i32;
-        pub fn fflush(stream: *mut i32) -> i32;
-        pub fn printf(format: *const i8, ...) -> i32;
-
-        pub static stdout: *mut i32;
-    }
-}
-
-mod intrinsics {
-    #[rustc_nounwind]
-    #[rustc_intrinsic]
-    pub fn abort() -> !;
-}
-
-#[lang = "panic"]
-#[track_caller]
-#[no_mangle]
-pub fn panic(_msg: &'static str) -> ! {
-    unsafe {
-        libc::puts("Panicking\0" as *const str as *const u8);
-        libc::fflush(libc::stdout);
-        intrinsics::abort();
-    }
-}
-
-#[lang = "add"]
-trait Add<RHS = Self> {
-    type Output;
-
-    fn add(self, rhs: RHS) -> Self::Output;
-}
-
-impl Add for u8 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for i8 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for i32 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for usize {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for isize {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-#[track_caller]
-#[lang = "panic_const_add_overflow"]
-pub fn panic_const_add_overflow() -> ! {
-    panic("attempt to add with overflow");
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 fn inc_ref(num: &mut isize) -> isize {
     *num = *num + 5;
@@ -139,9 +22,8 @@ fn inc(num: isize) -> isize {
     num + 1
 }
 
-
 #[no_mangle]
-extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
+extern "C" fn main(mut argc: isize, _argv: *const *const u8) -> i32 {
     argc = inc(argc);
     unsafe {
         libc::printf(b"%ld\n\0" as *const u8 as *const i8, argc);
diff --git a/compiler/rustc_codegen_gcc/tests/run/closure.rs b/compiler/rustc_codegen_gcc/tests/run/closure.rs
index c7a236f74f9..a8a3fadfed4 100644
--- a/compiler/rustc_codegen_gcc/tests/run/closure.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/closure.rs
@@ -9,55 +9,38 @@
 //     Both args: 11
 
 #![feature(no_core)]
-
 #![no_std]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
+use mini_core::*;
 
 #[no_mangle]
-extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
+extern "C" fn main(argc: isize, _argv: *const *const u8) -> i32 {
     let string = "Arg: %d\n\0";
-    let mut closure = || {
-        unsafe {
-            libc::printf(string as *const str as *const i8, argc);
-        }
+    let mut closure = || unsafe {
+        libc::printf(string as *const str as *const i8, argc);
     };
     closure();
 
-    let mut closure = || {
-        unsafe {
-            libc::printf("Argument: %d\n\0" as *const str as *const i8, argc);
-        }
+    let mut closure = || unsafe {
+        libc::printf("Argument: %d\n\0" as *const str as *const i8, argc);
     };
     closure();
 
-    let mut closure = |string| {
-        unsafe {
-            libc::printf(string as *const str as *const i8, argc);
-        }
+    let mut closure = |string| unsafe {
+        libc::printf(string as *const str as *const i8, argc);
     };
     closure("String arg: %d\n\0");
 
-    let mut closure = |arg: isize| {
-        unsafe {
-            libc::printf("Int argument: %d\n\0" as *const str as *const i8, arg);
-        }
+    let mut closure = |arg: isize| unsafe {
+        libc::printf("Int argument: %d\n\0" as *const str as *const i8, arg);
     };
     closure(argc + 1);
 
-    let mut closure = |string, arg: isize| {
-        unsafe {
-            libc::printf(string as *const str as *const i8, arg);
-        }
+    let mut closure = |string, arg: isize| unsafe {
+        libc::printf(string as *const str as *const i8, arg);
     };
     closure("Both args: %d\n\0", argc + 10);
 
diff --git a/compiler/rustc_codegen_gcc/tests/run/condition.rs b/compiler/rustc_codegen_gcc/tests/run/condition.rs
index b02359702ed..bd3b6f7497f 100644
--- a/compiler/rustc_codegen_gcc/tests/run/condition.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/condition.rs
@@ -6,19 +6,12 @@
 //     1
 
 #![feature(no_core)]
-
 #![no_std]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
+use mini_core::*;
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
@@ -27,15 +20,14 @@ extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
             libc::printf(b"true\n\0" as *const u8 as *const i8);
         }
 
-        let string =
-            match argc {
-                1 => b"1\n\0",
-                2 => b"2\n\0",
-                3 => b"3\n\0",
-                4 => b"4\n\0",
-                5 => b"5\n\0",
-                _ => b"_\n\0",
-            };
+        let string = match argc {
+            1 => b"1\n\0",
+            2 => b"2\n\0",
+            3 => b"3\n\0",
+            4 => b"4\n\0",
+            5 => b"5\n\0",
+            _ => b"_\n\0",
+        };
         libc::printf(string as *const u8 as *const i8);
     }
     0
diff --git a/compiler/rustc_codegen_gcc/tests/run/empty_main.rs b/compiler/rustc_codegen_gcc/tests/run/empty_main.rs
index 042e44080c5..fe3df5a2389 100644
--- a/compiler/rustc_codegen_gcc/tests/run/empty_main.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/empty_main.rs
@@ -3,37 +3,13 @@
 // Run-time:
 //   status: 0
 
-#![feature(auto_traits, lang_items, no_core)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
diff --git a/compiler/rustc_codegen_gcc/tests/run/exit.rs b/compiler/rustc_codegen_gcc/tests/run/exit.rs
index 9a7c91c0adb..e0a59174bd3 100644
--- a/compiler/rustc_codegen_gcc/tests/run/exit.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/exit.rs
@@ -3,44 +3,13 @@
 // Run-time:
 //   status: 2
 
-#![feature(auto_traits, lang_items, no_core, intrinsics)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn exit(status: i32);
-    }
-}
-
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
diff --git a/compiler/rustc_codegen_gcc/tests/run/exit_code.rs b/compiler/rustc_codegen_gcc/tests/run/exit_code.rs
index c50d2b0d710..376824da845 100644
--- a/compiler/rustc_codegen_gcc/tests/run/exit_code.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/exit_code.rs
@@ -3,37 +3,13 @@
 // Run-time:
 //   status: 1
 
-#![feature(auto_traits, lang_items, no_core)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
diff --git a/compiler/rustc_codegen_gcc/tests/run/float.rs b/compiler/rustc_codegen_gcc/tests/run/float.rs
new file mode 100644
index 00000000000..424fa1cf4ad
--- /dev/null
+++ b/compiler/rustc_codegen_gcc/tests/run/float.rs
@@ -0,0 +1,28 @@
+// Compiler:
+//
+// Run-time:
+//   status: 0
+
+#![feature(const_black_box)]
+
+fn main() {
+    use std::hint::black_box;
+
+    macro_rules! check {
+        ($ty:ty, $expr:expr) => {{
+            const EXPECTED: $ty = $expr;
+            assert_eq!($expr, EXPECTED);
+        }};
+    }
+
+    check!(i32, (black_box(0.0f32) as i32));
+
+    check!(u64, (black_box(f32::NAN) as u64));
+    check!(u128, (black_box(f32::NAN) as u128));
+
+    check!(i64, (black_box(f64::NAN) as i64));
+    check!(u64, (black_box(f64::NAN) as u64));
+
+    check!(i16, (black_box(f32::MIN) as i16));
+    check!(i16, (black_box(f32::MAX) as i16));
+}
diff --git a/compiler/rustc_codegen_gcc/tests/run/fun_ptr.rs b/compiler/rustc_codegen_gcc/tests/run/fun_ptr.rs
index 98b351e5044..93b9baee1b2 100644
--- a/compiler/rustc_codegen_gcc/tests/run/fun_ptr.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/fun_ptr.rs
@@ -5,19 +5,12 @@
 //   stdout: 1
 
 #![feature(no_core)]
-
 #![no_std]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
+use mini_core::*;
 
 fn i16_as_i8(a: i16) -> i8 {
     a as i8
diff --git a/compiler/rustc_codegen_gcc/tests/run/int.rs b/compiler/rustc_codegen_gcc/tests/run/int.rs
index 58a26801b67..47b5dea46f8 100644
--- a/compiler/rustc_codegen_gcc/tests/run/int.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/int.rs
@@ -3,9 +3,7 @@
 // Run-time:
 //   status: 0
 
-/*
- * Code
- */
+#![feature(const_black_box)]
 
 fn main() {
     use std::hint::black_box;
diff --git a/compiler/rustc_codegen_gcc/tests/run/mut_ref.rs b/compiler/rustc_codegen_gcc/tests/run/mut_ref.rs
index b0215860406..fa50d5bc5d3 100644
--- a/compiler/rustc_codegen_gcc/tests/run/mut_ref.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/mut_ref.rs
@@ -1,4 +1,3 @@
-
 // Compiler:
 //
 // Run-time:
@@ -7,139 +6,20 @@
 //     6
 //     11
 
-#![allow(internal_features, unused_attributes)]
-#![feature(auto_traits, lang_items, no_core, intrinsics, rustc_attrs, track_caller)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-impl Copy for *mut i32 {}
-impl Copy for usize {}
-impl Copy for u8 {}
-impl Copy for i8 {}
-impl Copy for i32 {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-#[lang = "panic_location"]
-struct PanicLocation {
-    file: &'static str,
-    line: u32,
-    column: u32,
-}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn puts(s: *const u8) -> i32;
-        pub fn fflush(stream: *mut i32) -> i32;
-        pub fn printf(format: *const i8, ...) -> i32;
-
-        pub static stdout: *mut i32;
-    }
-}
-
-mod intrinsics {
-    #[rustc_nounwind]
-    #[rustc_intrinsic]
-    pub fn abort() -> !;
-}
-
-#[lang = "panic"]
-#[track_caller]
-#[no_mangle]
-pub fn panic(_msg: &'static str) -> ! {
-    unsafe {
-        libc::puts("Panicking\0" as *const str as *const u8);
-        libc::fflush(libc::stdout);
-        intrinsics::abort();
-    }
-}
-
-#[lang = "add"]
-trait Add<RHS = Self> {
-    type Output;
-
-    fn add(self, rhs: RHS) -> Self::Output;
-}
-
-impl Add for u8 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for i8 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for i32 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for usize {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for isize {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-#[track_caller]
-#[lang = "panic_const_add_overflow"]
-pub fn panic_const_add_overflow() -> ! {
-    panic("attempt to add with overflow");
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 struct Test {
     field: isize,
 }
 
 fn test(num: isize) -> Test {
-    Test {
-        field: num + 1,
-    }
+    Test { field: num + 1 }
 }
 
 fn update_num(num: &mut isize) {
@@ -147,7 +27,7 @@ fn update_num(num: &mut isize) {
 }
 
 #[no_mangle]
-extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
+extern "C" fn main(mut argc: isize, _argv: *const *const u8) -> i32 {
     let mut test = test(argc);
     unsafe {
         libc::printf(b"%ld\n\0" as *const u8 as *const i8, test.field);
diff --git a/compiler/rustc_codegen_gcc/tests/run/operations.rs b/compiler/rustc_codegen_gcc/tests/run/operations.rs
index 8ba7a4c5ed8..a1b0772f76b 100644
--- a/compiler/rustc_codegen_gcc/tests/run/operations.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/operations.rs
@@ -5,229 +5,13 @@
 //     39
 //     10
 
-#![allow(internal_features, unused_attributes)]
-#![feature(auto_traits, lang_items, no_core, intrinsics, arbitrary_self_types, rustc_attrs)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-impl Copy for *mut i32 {}
-impl Copy for usize {}
-impl Copy for u8 {}
-impl Copy for i8 {}
-impl Copy for i16 {}
-impl Copy for i32 {}
-
-#[lang = "deref"]
-pub trait Deref {
-    type Target: ?Sized;
-
-    fn deref(&self) -> &Self::Target;
-}
-
-#[lang = "legacy_receiver"]
-trait LegacyReceiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-#[lang = "panic_location"]
-struct PanicLocation {
-    file: &'static str,
-    line: u32,
-    column: u32,
-}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-        pub fn puts(s: *const u8) -> i32;
-        pub fn fflush(stream: *mut i32) -> i32;
-
-        pub static stdout: *mut i32;
-    }
-}
-
-mod intrinsics {
-    #[rustc_nounwind]
-    #[rustc_intrinsic]
-    pub fn abort() -> !;
-}
-
-#[lang = "panic"]
-#[track_caller]
-#[no_mangle]
-pub fn panic(_msg: &'static str) -> ! {
-    unsafe {
-        libc::puts("Panicking\0" as *const str as *const u8);
-        libc::fflush(libc::stdout);
-        intrinsics::abort();
-    }
-}
-
-#[lang = "add"]
-trait Add<RHS = Self> {
-    type Output;
-
-    fn add(self, rhs: RHS) -> Self::Output;
-}
-
-impl Add for u8 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for i8 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for i32 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for usize {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-impl Add for isize {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self {
-        self + rhs
-    }
-}
-
-#[lang = "sub"]
-pub trait Sub<RHS = Self> {
-    type Output;
-
-    fn sub(self, rhs: RHS) -> Self::Output;
-}
-
-impl Sub for usize {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self {
-        self - rhs
-    }
-}
-
-impl Sub for isize {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self {
-        self - rhs
-    }
-}
-
-impl Sub for u8 {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self {
-        self - rhs
-    }
-}
-
-impl Sub for i8 {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self {
-        self - rhs
-    }
-}
-
-impl Sub for i16 {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self {
-        self - rhs
-    }
-}
-
-#[lang = "mul"]
-pub trait Mul<RHS = Self> {
-    type Output;
-
-    #[must_use]
-    fn mul(self, rhs: RHS) -> Self::Output;
-}
-
-impl Mul for u8 {
-    type Output = Self;
-
-    fn mul(self, rhs: Self) -> Self::Output {
-        self * rhs
-    }
-}
-
-impl Mul for usize {
-    type Output = Self;
-
-    fn mul(self, rhs: Self) -> Self::Output {
-        self * rhs
-    }
-}
-
-impl Mul for isize {
-    type Output = Self;
-
-    fn mul(self, rhs: Self) -> Self::Output {
-        self * rhs
-    }
-}
-
-#[track_caller]
-#[lang = "panic_const_add_overflow"]
-pub fn panic_const_add_overflow() -> ! {
-    panic("attempt to add with overflow");
-}
-
-#[track_caller]
-#[lang = "panic_const_sub_overflow"]
-pub fn panic_const_sub_overflow() -> ! {
-    panic("attempt to subtract with overflow");
-}
-
-#[track_caller]
-#[lang = "panic_const_mul_overflow"]
-pub fn panic_const_mul_overflow() -> ! {
-    panic("attempt to multiply with overflow");
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
diff --git a/compiler/rustc_codegen_gcc/tests/run/ptr_cast.rs b/compiler/rustc_codegen_gcc/tests/run/ptr_cast.rs
index 0ba49e7187f..c1254c51ce9 100644
--- a/compiler/rustc_codegen_gcc/tests/run/ptr_cast.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/ptr_cast.rs
@@ -2,35 +2,32 @@
 //
 // Run-time:
 //   status: 0
-//   stdout: 1
+//   stdout: 10
+//     10
+//     42
 
 #![feature(no_core)]
-
 #![no_std]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
+use mini_core::*;
 
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
-
-static mut ONE: usize = 1;
-
-fn make_array() -> [u8; 3] {
-    [42, 10, 5]
+fn int_cast(a: u16, b: i16) -> (u8, u16, u32, usize, i8, i16, i32, isize, u8, u32) {
+    (
+        a as u8, a as u16, a as u32, a as usize, a as i8, a as i16, a as i32, a as isize, b as u8,
+        b as u32,
+    )
 }
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
+    let (a, b, c, d, e, f, g, h, i, j) = int_cast(10, 42);
     unsafe {
-        let ptr = ONE as *mut usize;
-        let value = ptr as usize;
-        libc::printf(b"%ld\n\0" as *const u8 as *const i8, value);
+        libc::printf(b"%d\n\0" as *const u8 as *const i8, c);
+        libc::printf(b"%ld\n\0" as *const u8 as *const i8, d);
+        libc::printf(b"%ld\n\0" as *const u8 as *const i8, j);
     }
     0
 }
diff --git a/compiler/rustc_codegen_gcc/tests/run/return-tuple.rs b/compiler/rustc_codegen_gcc/tests/run/return-tuple.rs
index 3cc1e274001..c1254c51ce9 100644
--- a/compiler/rustc_codegen_gcc/tests/run/return-tuple.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/return-tuple.rs
@@ -6,54 +6,13 @@
 //     10
 //     42
 
-#![feature(auto_traits, lang_items, no_core, intrinsics)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-#[lang = "copy"]
-pub unsafe trait Copy {}
-
-impl Copy for bool {}
-impl Copy for u8 {}
-impl Copy for u16 {}
-impl Copy for u32 {}
-impl Copy for u64 {}
-impl Copy for usize {}
-impl Copy for i8 {}
-impl Copy for i16 {}
-impl Copy for i32 {}
-impl Copy for isize {}
-impl Copy for f32 {}
-impl Copy for char {}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
-
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "legacy_receiver"]
-trait LegacyReceiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 fn int_cast(a: u16, b: i16) -> (u8, u16, u32, usize, i8, i16, i32, isize, u8, u32) {
     (
diff --git a/compiler/rustc_codegen_gcc/tests/run/slice.rs b/compiler/rustc_codegen_gcc/tests/run/slice.rs
index 825fcb8a081..449ccabef7f 100644
--- a/compiler/rustc_codegen_gcc/tests/run/slice.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/slice.rs
@@ -5,26 +5,17 @@
 //   stdout: 5
 
 #![feature(no_core)]
-
 #![no_std]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
+use mini_core::*;
 
 static mut TWO: usize = 2;
 
 fn index_slice(s: &[u32]) -> u32 {
-    unsafe {
-        s[TWO]
-    }
+    unsafe { s[TWO] }
 }
 
 #[no_mangle]
diff --git a/compiler/rustc_codegen_gcc/tests/run/static.rs b/compiler/rustc_codegen_gcc/tests/run/static.rs
index c3c8121b1e1..1e36cf4f3d3 100644
--- a/compiler/rustc_codegen_gcc/tests/run/static.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/static.rs
@@ -9,70 +9,13 @@
 //      12
 //      1
 
-#![feature(auto_traits, lang_items, no_core, intrinsics, rustc_attrs)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "destruct"]
-pub trait Destruct {}
-
-#[lang = "drop"]
-pub trait Drop {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-impl<T: ?Sized> Copy for *mut T {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-mod intrinsics {
-    use super::Sized;
-
-    #[rustc_nounwind]
-    #[rustc_intrinsic]
-    pub fn abort() -> !;
-}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
-
-#[lang = "structural_peq"]
-pub trait StructuralPartialEq {}
-
-#[lang = "drop_in_place"]
-#[allow(unconditional_recursion)]
-pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
-    // Code here does not matter - this is replaced by the
-    // real drop glue by the compiler.
-    drop_in_place(to_drop);
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 struct Test {
     field: isize,
@@ -84,20 +27,14 @@ struct WithRef {
 
 static mut CONSTANT: isize = 10;
 
-static mut TEST: Test = Test {
-    field: 12,
-};
+static mut TEST: Test = Test { field: 12 };
 
-static mut TEST2: Test = Test {
-    field: 14,
-};
+static mut TEST2: Test = Test { field: 14 };
 
-static mut WITH_REF: WithRef = WithRef {
-    refe: unsafe { &TEST },
-};
+static mut WITH_REF: WithRef = WithRef { refe: unsafe { &TEST } };
 
 #[no_mangle]
-extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
+extern "C" fn main(argc: isize, _argv: *const *const u8) -> i32 {
     unsafe {
         libc::printf(b"%ld\n\0" as *const u8 as *const i8, CONSTANT);
         libc::printf(b"%ld\n\0" as *const u8 as *const i8, TEST2.field);
diff --git a/compiler/rustc_codegen_gcc/tests/run/structs.rs b/compiler/rustc_codegen_gcc/tests/run/structs.rs
index 59b8f358863..da73cbed9ae 100644
--- a/compiler/rustc_codegen_gcc/tests/run/structs.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/structs.rs
@@ -5,44 +5,13 @@
 //   stdout: 1
 //     2
 
-#![feature(auto_traits, lang_items, no_core, intrinsics)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 struct Test {
     field: isize,
diff --git a/compiler/rustc_codegen_gcc/tests/run/tuple.rs b/compiler/rustc_codegen_gcc/tests/run/tuple.rs
index ed60a56a68c..e0f2e95f628 100644
--- a/compiler/rustc_codegen_gcc/tests/run/tuple.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/tuple.rs
@@ -4,44 +4,13 @@
 //   status: 0
 //   stdout: 3
 
-#![feature(auto_traits, lang_items, no_core, intrinsics)]
-#![allow(internal_features)]
-
+#![feature(no_core)]
 #![no_std]
 #![no_core]
 #![no_main]
 
-/*
- * Core
- */
-
-// Because we don't have core yet.
-#[lang = "sized"]
-pub trait Sized {}
-
-#[lang = "copy"]
-trait Copy {
-}
-
-impl Copy for isize {}
-
-#[lang = "receiver"]
-trait Receiver {
-}
-
-#[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
-
-mod libc {
-    #[link(name = "c")]
-    extern "C" {
-        pub fn printf(format: *const i8, ...) -> i32;
-    }
-}
-
-/*
- * Code
- */
+extern crate mini_core;
+use mini_core::*;
 
 #[no_mangle]
 extern "C" fn main(argc: i32, _argv: *const *const u8) -> i32 {
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index bf6138142b6..18d221d232e 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -119,14 +119,18 @@ pub(crate) fn create_target_machine(tcx: TyCtxt<'_>, mod_name: &str) -> OwnedTar
         tcx.output_filenames(()).split_dwarf_path(
             tcx.sess.split_debuginfo(),
             tcx.sess.opts.unstable_opts.split_dwarf_kind,
-            Some(mod_name),
+            mod_name,
+            tcx.sess.invocation_temp.as_deref(),
         )
     } else {
         None
     };
 
-    let output_obj_file =
-        Some(tcx.output_filenames(()).temp_path(OutputType::Object, Some(mod_name)));
+    let output_obj_file = Some(tcx.output_filenames(()).temp_path_for_cgu(
+        OutputType::Object,
+        mod_name,
+        tcx.sess.invocation_temp.as_deref(),
+    ));
     let config = TargetMachineFactoryConfig { split_dwarf_file, output_obj_file };
 
     target_machine_factory(
@@ -330,8 +334,11 @@ pub(crate) fn save_temp_bitcode(
         return;
     }
     let ext = format!("{name}.bc");
-    let cgu = Some(&module.name[..]);
-    let path = cgcx.output_filenames.temp_path_ext(&ext, cgu);
+    let path = cgcx.output_filenames.temp_path_ext_for_cgu(
+        &ext,
+        &module.name,
+        cgcx.invocation_temp.as_deref(),
+    );
     write_bitcode_to_file(module, &path)
 }
 
@@ -439,12 +446,9 @@ fn report_inline_asm(
     let span = if cookie == 0 || matches!(cgcx.lto, Lto::Fat | Lto::Thin) {
         SpanData::default()
     } else {
-        let lo = BytePos::from_u32(cookie as u32);
-        let hi = BytePos::from_u32((cookie >> 32) as u32);
         SpanData {
-            lo,
-            // LLVM version < 19 silently truncates the cookie to 32 bits in some situations.
-            hi: if hi.to_u32() != 0 { hi } else { lo },
+            lo: BytePos::from_u32(cookie as u32),
+            hi: BytePos::from_u32((cookie >> 32) as u32),
             ctxt: SyntaxContext::root(),
             parent: None,
         }
@@ -697,11 +701,12 @@ pub(crate) unsafe fn optimize(
     let llcx = &*module.module_llvm.llcx;
     let _handlers = DiagnosticHandlers::new(cgcx, dcx, llcx, module, CodegenDiagnosticsStage::Opt);
 
-    let module_name = module.name.clone();
-    let module_name = Some(&module_name[..]);
-
     if config.emit_no_opt_bc {
-        let out = cgcx.output_filenames.temp_path_ext("no-opt.bc", module_name);
+        let out = cgcx.output_filenames.temp_path_ext_for_cgu(
+            "no-opt.bc",
+            &module.name,
+            cgcx.invocation_temp.as_deref(),
+        );
         write_bitcode_to_file(module, &out)
     }
 
@@ -746,8 +751,11 @@ pub(crate) unsafe fn optimize(
         if let Some(thin_lto_buffer) = thin_lto_buffer {
             let thin_lto_buffer = unsafe { ThinBuffer::from_raw_ptr(thin_lto_buffer) };
             module.thin_lto_buffer = Some(thin_lto_buffer.data().to_vec());
-            let bc_summary_out =
-                cgcx.output_filenames.temp_path(OutputType::ThinLinkBitcode, module_name);
+            let bc_summary_out = cgcx.output_filenames.temp_path_for_cgu(
+                OutputType::ThinLinkBitcode,
+                &module.name,
+                cgcx.invocation_temp.as_deref(),
+            );
             if config.emit_thin_lto_summary
                 && let Some(thin_link_bitcode_filename) = bc_summary_out.file_name()
             {
@@ -804,8 +812,6 @@ pub(crate) unsafe fn codegen(
         let llmod = module.module_llvm.llmod();
         let llcx = &*module.module_llvm.llcx;
         let tm = &*module.module_llvm.tm;
-        let module_name = module.name.clone();
-        let module_name = Some(&module_name[..]);
         let _handlers =
             DiagnosticHandlers::new(cgcx, dcx, llcx, &module, CodegenDiagnosticsStage::Codegen);
 
@@ -817,8 +823,16 @@ pub(crate) unsafe fn codegen(
         // copy it to the .o file, and delete the bitcode if it wasn't
         // otherwise requested.
 
-        let bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
-        let obj_out = cgcx.output_filenames.temp_path(OutputType::Object, module_name);
+        let bc_out = cgcx.output_filenames.temp_path_for_cgu(
+            OutputType::Bitcode,
+            &module.name,
+            cgcx.invocation_temp.as_deref(),
+        );
+        let obj_out = cgcx.output_filenames.temp_path_for_cgu(
+            OutputType::Object,
+            &module.name,
+            cgcx.invocation_temp.as_deref(),
+        );
 
         if config.bitcode_needed() {
             if config.emit_bc || config.emit_obj == EmitObj::Bitcode {
@@ -860,7 +874,11 @@ pub(crate) unsafe fn codegen(
         if config.emit_ir {
             let _timer =
                 cgcx.prof.generic_activity_with_arg("LLVM_module_codegen_emit_ir", &*module.name);
-            let out = cgcx.output_filenames.temp_path(OutputType::LlvmAssembly, module_name);
+            let out = cgcx.output_filenames.temp_path_for_cgu(
+                OutputType::LlvmAssembly,
+                &module.name,
+                cgcx.invocation_temp.as_deref(),
+            );
             let out_c = path_to_c_string(&out);
 
             extern "C" fn demangle_callback(
@@ -902,7 +920,11 @@ pub(crate) unsafe fn codegen(
         if config.emit_asm {
             let _timer =
                 cgcx.prof.generic_activity_with_arg("LLVM_module_codegen_emit_asm", &*module.name);
-            let path = cgcx.output_filenames.temp_path(OutputType::Assembly, module_name);
+            let path = cgcx.output_filenames.temp_path_for_cgu(
+                OutputType::Assembly,
+                &module.name,
+                cgcx.invocation_temp.as_deref(),
+            );
 
             // We can't use the same module for asm and object code output,
             // because that triggers various errors like invalid IR or broken
@@ -932,7 +954,9 @@ pub(crate) unsafe fn codegen(
                     .prof
                     .generic_activity_with_arg("LLVM_module_codegen_emit_obj", &*module.name);
 
-                let dwo_out = cgcx.output_filenames.temp_path_dwo(module_name);
+                let dwo_out = cgcx
+                    .output_filenames
+                    .temp_path_dwo_for_cgu(&module.name, cgcx.invocation_temp.as_deref());
                 let dwo_out = match (cgcx.split_debuginfo, cgcx.split_dwarf_kind) {
                     // Don't change how DWARF is emitted when disabled.
                     (SplitDebuginfo::Off, _) => None,
@@ -997,6 +1021,7 @@ pub(crate) unsafe fn codegen(
         config.emit_asm,
         config.emit_ir,
         &cgcx.output_filenames,
+        cgcx.invocation_temp.as_deref(),
     ))
 }
 
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 35134e9f5a0..27f7f95f100 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -123,7 +123,7 @@ impl<'a, 'll, CX: Borrow<SCx<'ll>>> GenericBuilder<'a, 'll, CX> {
 /// Empty string, to be used where LLVM expects an instruction name, indicating
 /// that the instruction is to be left unnamed (i.e. numbered, in textual IR).
 // FIXME(eddyb) pass `&CStr` directly to FFI once it's a thin pointer.
-const UNNAMED: *const c_char = c"".as_ptr();
+pub(crate) const UNNAMED: *const c_char = c"".as_ptr();
 
 impl<'ll, CX: Borrow<SCx<'ll>>> BackendTypes for GenericBuilder<'_, 'll, CX> {
     type Value = <GenericCx<'ll, CX> as BackendTypes>::Value;
diff --git a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
index 7d264ba4d00..e7c071d05aa 100644
--- a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
+++ b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
@@ -10,7 +10,7 @@ use rustc_middle::bug;
 use tracing::{debug, trace};
 
 use crate::back::write::llvm_err;
-use crate::builder::SBuilder;
+use crate::builder::{SBuilder, UNNAMED};
 use crate::context::SimpleCx;
 use crate::declare::declare_simple_fn;
 use crate::errors::{AutoDiffWithoutEnable, LlvmError};
@@ -51,6 +51,7 @@ fn has_sret(fnc: &Value) -> bool {
 // using iterators and peek()?
 fn match_args_from_caller_to_enzyme<'ll>(
     cx: &SimpleCx<'ll>,
+    builder: &SBuilder<'ll, 'll>,
     width: u32,
     args: &mut Vec<&'ll llvm::Value>,
     inputs: &[DiffActivity],
@@ -78,7 +79,9 @@ fn match_args_from_caller_to_enzyme<'ll>(
     let enzyme_const = cx.create_metadata("enzyme_const".to_string()).unwrap();
     let enzyme_out = cx.create_metadata("enzyme_out".to_string()).unwrap();
     let enzyme_dup = cx.create_metadata("enzyme_dup".to_string()).unwrap();
+    let enzyme_dupv = cx.create_metadata("enzyme_dupv".to_string()).unwrap();
     let enzyme_dupnoneed = cx.create_metadata("enzyme_dupnoneed".to_string()).unwrap();
+    let enzyme_dupnoneedv = cx.create_metadata("enzyme_dupnoneedv".to_string()).unwrap();
 
     while activity_pos < inputs.len() {
         let diff_activity = inputs[activity_pos as usize];
@@ -90,13 +93,34 @@ fn match_args_from_caller_to_enzyme<'ll>(
             DiffActivity::Active => (enzyme_out, false),
             DiffActivity::ActiveOnly => (enzyme_out, false),
             DiffActivity::Dual => (enzyme_dup, true),
+            DiffActivity::Dualv => (enzyme_dupv, true),
             DiffActivity::DualOnly => (enzyme_dupnoneed, true),
+            DiffActivity::DualvOnly => (enzyme_dupnoneedv, true),
             DiffActivity::Duplicated => (enzyme_dup, true),
             DiffActivity::DuplicatedOnly => (enzyme_dupnoneed, true),
-            DiffActivity::FakeActivitySize => (enzyme_const, false),
+            DiffActivity::FakeActivitySize(_) => (enzyme_const, false),
         };
         let outer_arg = outer_args[outer_pos];
         args.push(cx.get_metadata_value(activity));
+        if matches!(diff_activity, DiffActivity::Dualv) {
+            let next_outer_arg = outer_args[outer_pos + 1];
+            let elem_bytes_size: u64 = match inputs[activity_pos + 1] {
+                DiffActivity::FakeActivitySize(Some(s)) => s.into(),
+                _ => bug!("incorrect Dualv handling recognized."),
+            };
+            // stride: sizeof(T) * n_elems.
+            // n_elems is the next integer.
+            // Now we multiply `4 * next_outer_arg` to get the stride.
+            let mul = unsafe {
+                llvm::LLVMBuildMul(
+                    builder.llbuilder,
+                    cx.get_const_i64(elem_bytes_size),
+                    next_outer_arg,
+                    UNNAMED,
+                )
+            };
+            args.push(mul);
+        }
         args.push(outer_arg);
         if duplicated {
             // We know that duplicated args by construction have a following argument,
@@ -114,7 +138,7 @@ fn match_args_from_caller_to_enzyme<'ll>(
                 } else {
                     let next_activity = inputs[activity_pos + 1];
                     // We analyze the MIR types and add this dummy activity if we visit a slice.
-                    next_activity == DiffActivity::FakeActivitySize
+                    matches!(next_activity, DiffActivity::FakeActivitySize(_))
                 }
             };
             if slice {
@@ -125,7 +149,10 @@ fn match_args_from_caller_to_enzyme<'ll>(
                 // int2 >= int1, which means the shadow vector is large enough to store the gradient.
                 assert_eq!(cx.type_kind(next_outer_ty), TypeKind::Integer);
 
-                for i in 0..(width as usize) {
+                let iterations =
+                    if matches!(diff_activity, DiffActivity::Dualv) { 1 } else { width as usize };
+
+                for i in 0..iterations {
                     let next_outer_arg2 = outer_args[outer_pos + 2 * (i + 1)];
                     let next_outer_ty2 = cx.val_ty(next_outer_arg2);
                     assert_eq!(cx.type_kind(next_outer_ty2), TypeKind::Pointer);
@@ -136,7 +163,7 @@ fn match_args_from_caller_to_enzyme<'ll>(
                 }
                 args.push(cx.get_metadata_value(enzyme_const));
                 args.push(next_outer_arg);
-                outer_pos += 2 + 2 * width as usize;
+                outer_pos += 2 + 2 * iterations;
                 activity_pos += 2;
             } else {
                 // A duplicated pointer will have the following two outer_fn arguments:
@@ -201,7 +228,23 @@ fn compute_enzyme_fn_ty<'ll>(
         }
 
         if attrs.width == 1 {
-            todo!("Handle sret for scalar ad");
+            // Enzyme returns a struct of style:
+            // `{ original_ret(if requested), float, float, ... }`
+            let mut struct_elements = vec![];
+            if attrs.has_primal_ret() {
+                struct_elements.push(inner_ret_ty);
+            }
+            // Next, we push the list of active floats, since they will be lowered to `enzyme_out`,
+            // and therefore part of the return struct.
+            let param_tys = cx.func_params_types(fn_ty);
+            for (act, param_ty) in attrs.input_activity.iter().zip(param_tys) {
+                if matches!(act, DiffActivity::Active) {
+                    // Now find the float type at position i based on the fn_ty,
+                    // to know what (f16/f32/f64/...) to add to the struct.
+                    struct_elements.push(param_ty);
+                }
+            }
+            ret_ty = cx.type_struct(&struct_elements, false);
         } else {
             // First we check if we also have to deal with the primal return.
             match attrs.mode {
@@ -344,6 +387,7 @@ fn generate_enzyme_call<'ll>(
         let outer_args: Vec<&llvm::Value> = get_params(outer_fn);
         match_args_from_caller_to_enzyme(
             &cx,
+            &builder,
             attrs.width,
             &mut args,
             &attrs.input_activity,
@@ -388,7 +432,11 @@ fn generate_enzyme_call<'ll>(
                 // now store the result of the enzyme call into the sret pointer.
                 let sret_ptr = outer_args[0];
                 let call_ty = cx.val_ty(call);
-                assert_eq!(cx.type_kind(call_ty), TypeKind::Array);
+                if attrs.width == 1 {
+                    assert_eq!(cx.type_kind(call_ty), TypeKind::Struct);
+                } else {
+                    assert_eq!(cx.type_kind(call_ty), TypeKind::Array);
+                }
                 llvm::LLVMBuildStore(&builder.llbuilder, call, sret_ptr);
             }
             builder.ret_void();
diff --git a/compiler/rustc_codegen_llvm/src/common.rs b/compiler/rustc_codegen_llvm/src/common.rs
index 457e5452ce9..a6f277e4455 100644
--- a/compiler/rustc_codegen_llvm/src/common.rs
+++ b/compiler/rustc_codegen_llvm/src/common.rs
@@ -4,8 +4,8 @@ use std::borrow::Borrow;
 
 use libc::{c_char, c_uint};
 use rustc_abi as abi;
+use rustc_abi::HasDataLayout;
 use rustc_abi::Primitive::Pointer;
-use rustc_abi::{AddressSpace, HasDataLayout};
 use rustc_ast::Mutability;
 use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::traits::*;
@@ -269,7 +269,8 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
             }
             Scalar::Ptr(ptr, _size) => {
                 let (prov, offset) = ptr.into_parts();
-                let (base_addr, base_addr_space) = match self.tcx.global_alloc(prov.alloc_id()) {
+                let global_alloc = self.tcx.global_alloc(prov.alloc_id());
+                let base_addr = match global_alloc {
                     GlobalAlloc::Memory(alloc) => {
                         // For ZSTs directly codegen an aligned pointer.
                         // This avoids generating a zero-sized constant value and actually needing a
@@ -301,12 +302,10 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
                                     format!("alloc_{hash:032x}").as_bytes(),
                                 );
                             }
-                            (value, AddressSpace::DATA)
+                            value
                         }
                     }
-                    GlobalAlloc::Function { instance, .. } => {
-                        (self.get_fn_addr(instance), self.data_layout().instruction_address_space)
-                    }
+                    GlobalAlloc::Function { instance, .. } => self.get_fn_addr(instance),
                     GlobalAlloc::VTable(ty, dyn_ty) => {
                         let alloc = self
                             .tcx
@@ -319,14 +318,15 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
                             .unwrap_memory();
                         let init = const_alloc_to_llvm(self, alloc, /*static*/ false);
                         let value = self.static_addr_of_impl(init, alloc.inner().align, None);
-                        (value, AddressSpace::DATA)
+                        value
                     }
                     GlobalAlloc::Static(def_id) => {
                         assert!(self.tcx.is_static(def_id));
                         assert!(!self.tcx.is_thread_local_static(def_id));
-                        (self.get_static(def_id), AddressSpace::DATA)
+                        self.get_static(def_id)
                     }
                 };
+                let base_addr_space = global_alloc.address_space(self);
                 let llval = unsafe {
                     llvm::LLVMConstInBoundsGEP2(
                         self.type_i8(),
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index 9a2473d6cf2..55b1e728b70 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -5,15 +5,11 @@ use rustc_abi::Align;
 use rustc_codegen_ssa::traits::{
     BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
 };
-use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
-use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_index::IndexVec;
-use rustc_middle::mir;
-use rustc_middle::mir::mono::MonoItemPartitions;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::TyCtxt;
 use rustc_session::RemapFileNameExt;
 use rustc_session::config::RemapPathScopeComponents;
-use rustc_span::def_id::DefIdSet;
 use rustc_span::{SourceFile, StableSourceFileId};
 use tracing::debug;
 
@@ -24,6 +20,7 @@ use crate::llvm;
 
 mod covfun;
 mod spans;
+mod unused;
 
 /// Generates and exports the coverage map, which is embedded in special
 /// linker sections in the final binary.
@@ -56,13 +53,6 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
         None => return,
     };
 
-    // The order of entries in this global file table needs to be deterministic,
-    // and ideally should also be independent of the details of stable-hashing,
-    // because coverage tests snapshots (`.cov-map`) can observe the order and
-    // would need to be re-blessed if it changes. As long as those requirements
-    // are satisfied, the order can be arbitrary.
-    let mut global_file_table = GlobalFileTable::new();
-
     let mut covfun_records = instances_used
         .iter()
         .copied()
@@ -70,18 +60,13 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
         // order that doesn't depend on the stable-hash-based order in which
         // instances were visited during codegen.
         .sorted_by_cached_key(|&instance| tcx.symbol_name(instance).name)
-        .filter_map(|instance| prepare_covfun_record(tcx, &mut global_file_table, instance, true))
+        .filter_map(|instance| prepare_covfun_record(tcx, instance, true))
         .collect::<Vec<_>>();
 
     // In a single designated CGU, also prepare covfun records for functions
     // in this crate that were instrumented for coverage, but are unused.
     if cx.codegen_unit.is_code_coverage_dead_code_cgu() {
-        let mut unused_instances = gather_unused_function_instances(cx);
-        // Sort the unused instances by symbol name, for the same reason as the used ones.
-        unused_instances.sort_by_cached_key(|&instance| tcx.symbol_name(instance).name);
-        covfun_records.extend(unused_instances.into_iter().filter_map(|instance| {
-            prepare_covfun_record(tcx, &mut global_file_table, instance, false)
-        }));
+        unused::prepare_covfun_records_for_unused_functions(cx, &mut covfun_records);
     }
 
     // If there are no covfun records for this CGU, don't generate a covmap record.
@@ -93,91 +78,88 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
         return;
     }
 
-    // Encode all filenames referenced by coverage mappings in this CGU.
-    let filenames_buffer = global_file_table.make_filenames_buffer(tcx);
-    // The `llvm-cov` tool uses this hash to associate each covfun record with
-    // its corresponding filenames table, since the final binary will typically
-    // contain multiple covmap records from different compilation units.
-    let filenames_hash = llvm_cov::hash_bytes(&filenames_buffer);
-
-    let mut unused_function_names = vec![];
+    // Prepare the global file table for this CGU, containing all paths needed
+    // by one or more covfun records.
+    let global_file_table =
+        GlobalFileTable::build(tcx, covfun_records.iter().flat_map(|c| c.all_source_files()));
 
     for covfun in &covfun_records {
-        unused_function_names.extend(covfun.mangled_function_name_if_unused());
-
-        covfun::generate_covfun_record(cx, filenames_hash, covfun)
-    }
-
-    // For unused functions, we need to take their mangled names and store them
-    // in a specially-named global array. LLVM's `InstrProfiling` pass will
-    // detect this global and include those names in its `__llvm_prf_names`
-    // section. (See `llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp`.)
-    if !unused_function_names.is_empty() {
-        assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
-
-        let name_globals = unused_function_names
-            .into_iter()
-            .map(|mangled_function_name| cx.const_str(mangled_function_name).0)
-            .collect::<Vec<_>>();
-        let initializer = cx.const_array(cx.type_ptr(), &name_globals);
-
-        let array = llvm::add_global(cx.llmod, cx.val_ty(initializer), c"__llvm_coverage_names");
-        llvm::set_global_constant(array, true);
-        llvm::set_linkage(array, llvm::Linkage::InternalLinkage);
-        llvm::set_initializer(array, initializer);
+        covfun::generate_covfun_record(cx, &global_file_table, covfun)
     }
 
     // Generate the coverage map header, which contains the filenames used by
     // this CGU's coverage mappings, and store it in a well-known global.
     // (This is skipped if we returned early due to having no covfun records.)
-    generate_covmap_record(cx, covmap_version, &filenames_buffer);
+    generate_covmap_record(cx, covmap_version, &global_file_table.filenames_buffer);
 }
 
-/// Maps "global" (per-CGU) file ID numbers to their underlying source files.
+/// Maps "global" (per-CGU) file ID numbers to their underlying source file paths.
+#[derive(Debug)]
 struct GlobalFileTable {
     /// This "raw" table doesn't include the working dir, so a file's
     /// global ID is its index in this set **plus one**.
-    raw_file_table: FxIndexMap<StableSourceFileId, Arc<SourceFile>>,
+    raw_file_table: FxIndexMap<StableSourceFileId, String>,
+
+    /// The file table in encoded form (possibly compressed), which can be
+    /// included directly in this CGU's `__llvm_covmap` record.
+    filenames_buffer: Vec<u8>,
+
+    /// Truncated hash of the bytes in `filenames_buffer`.
+    ///
+    /// The `llvm-cov` tool uses this hash to associate each covfun record with
+    /// its corresponding filenames table, since the final binary will typically
+    /// contain multiple covmap records from different compilation units.
+    filenames_hash: u64,
 }
 
 impl GlobalFileTable {
-    fn new() -> Self {
-        Self { raw_file_table: FxIndexMap::default() }
-    }
+    /// Builds a "global file table" for this CGU, mapping numeric IDs to
+    /// path strings.
+    fn build<'a>(tcx: TyCtxt<'_>, all_files: impl Iterator<Item = &'a SourceFile>) -> Self {
+        let mut raw_file_table = FxIndexMap::default();
+
+        for file in all_files {
+            raw_file_table.entry(file.stable_id).or_insert_with(|| {
+                file.name
+                    .for_scope(tcx.sess, RemapPathScopeComponents::MACRO)
+                    .to_string_lossy()
+                    .into_owned()
+            });
+        }
 
-    fn global_file_id_for_file(&mut self, file: &Arc<SourceFile>) -> GlobalFileId {
-        // Ensure the given file has a table entry, and get its index.
-        let entry = self.raw_file_table.entry(file.stable_id);
-        let raw_id = entry.index();
-        entry.or_insert_with(|| Arc::clone(file));
+        // FIXME(Zalathar): Consider sorting the file table here, but maybe
+        // only after adding filename support to coverage-dump, so that the
+        // table order isn't directly visible in `.coverage-map` snapshots.
 
-        // The raw file table doesn't include an entry for the working dir
-        // (which has ID 0), so add 1 to get the correct ID.
-        GlobalFileId::from_usize(raw_id + 1)
-    }
+        let mut table = Vec::with_capacity(raw_file_table.len() + 1);
 
-    fn make_filenames_buffer(&self, tcx: TyCtxt<'_>) -> Vec<u8> {
-        let mut table = Vec::with_capacity(self.raw_file_table.len() + 1);
-
-        // LLVM Coverage Mapping Format version 6 (zero-based encoded as 5)
-        // requires setting the first filename to the compilation directory.
-        // Since rustc generates coverage maps with relative paths, the
-        // compilation directory can be combined with the relative paths
-        // to get absolute paths, if needed.
-        table.push(
-            tcx.sess
-                .opts
-                .working_dir
-                .for_scope(tcx.sess, RemapPathScopeComponents::MACRO)
-                .to_string_lossy(),
-        );
+        // Since version 6 of the LLVM coverage mapping format, the first entry
+        // in the global file table is treated as a base directory, used to
+        // resolve any other entries that are stored as relative paths.
+        let base_dir = tcx
+            .sess
+            .opts
+            .working_dir
+            .for_scope(tcx.sess, RemapPathScopeComponents::MACRO)
+            .to_string_lossy();
+        table.push(base_dir.as_ref());
 
         // Add the regular entries after the base directory.
-        table.extend(self.raw_file_table.values().map(|file| {
-            file.name.for_scope(tcx.sess, RemapPathScopeComponents::MACRO).to_string_lossy()
-        }));
+        table.extend(raw_file_table.values().map(|name| name.as_str()));
 
-        llvm_cov::write_filenames_to_buffer(&table)
+        // Encode the file table into a buffer, and get the hash of its encoded
+        // bytes, so that we can embed that hash in `__llvm_covfun` records.
+        let filenames_buffer = llvm_cov::write_filenames_to_buffer(&table);
+        let filenames_hash = llvm_cov::hash_bytes(&filenames_buffer);
+
+        Self { raw_file_table, filenames_buffer, filenames_hash }
+    }
+
+    fn get_existing_id(&self, file: &SourceFile) -> Option<GlobalFileId> {
+        let raw_id = self.raw_file_table.get_index_of(&file.stable_id)?;
+        // The raw file table doesn't include an entry for the base dir
+        // (which has ID 0), so add 1 to get the correct ID.
+        Some(GlobalFileId::from_usize(raw_id + 1))
     }
 }
 
@@ -193,26 +175,31 @@ rustc_index::newtype_index! {
     struct LocalFileId {}
 }
 
-/// Holds a mapping from "local" (per-function) file IDs to "global" (per-CGU)
-/// file IDs.
+/// Holds a mapping from "local" (per-function) file IDs to their corresponding
+/// source files.
 #[derive(Debug, Default)]
 struct VirtualFileMapping {
-    local_to_global: IndexVec<LocalFileId, GlobalFileId>,
-    global_to_local: FxIndexMap<GlobalFileId, LocalFileId>,
+    local_file_table: IndexVec<LocalFileId, Arc<SourceFile>>,
 }
 
 impl VirtualFileMapping {
-    fn local_id_for_global(&mut self, global_file_id: GlobalFileId) -> LocalFileId {
-        *self
-            .global_to_local
-            .entry(global_file_id)
-            .or_insert_with(|| self.local_to_global.push(global_file_id))
+    fn push_file(&mut self, source_file: &Arc<SourceFile>) -> LocalFileId {
+        self.local_file_table.push(Arc::clone(source_file))
     }
 
-    fn to_vec(&self) -> Vec<u32> {
-        // This clone could be avoided by transmuting `&[GlobalFileId]` to `&[u32]`,
-        // but it isn't hot or expensive enough to justify the extra unsafety.
-        self.local_to_global.iter().map(|&global| GlobalFileId::as_u32(global)).collect()
+    /// Resolves all of the filenames in this local file mapping to a list of
+    /// global file IDs in its CGU, for inclusion in this function's
+    /// `__llvm_covfun` record.
+    ///
+    /// The global file IDs are returned as `u32` to make FFI easier.
+    fn resolve_all(&self, global_file_table: &GlobalFileTable) -> Option<Vec<u32>> {
+        self.local_file_table
+            .iter()
+            .map(|file| try {
+                let id = global_file_table.get_existing_id(file)?;
+                GlobalFileId::as_u32(id)
+            })
+            .collect::<Option<Vec<_>>>()
     }
 }
 
@@ -249,121 +236,3 @@ fn generate_covmap_record<'ll>(cx: &CodegenCx<'ll, '_>, version: u32, filenames_
 
     cx.add_used_global(covmap_global);
 }
-
-/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
-/// But since we don't want unused functions to disappear from coverage reports, we also scan for
-/// functions that were instrumented but are not participating in codegen.
-///
-/// These unused functions don't need to be codegenned, but we do need to add them to the function
-/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
-/// We also end up adding their symbol names to a special global array that LLVM will include in
-/// its embedded coverage data.
-fn gather_unused_function_instances<'tcx>(cx: &CodegenCx<'_, 'tcx>) -> Vec<ty::Instance<'tcx>> {
-    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
-
-    let tcx = cx.tcx;
-    let usage = prepare_usage_sets(tcx);
-
-    let is_unused_fn = |def_id: LocalDefId| -> bool {
-        // Usage sets expect `DefId`, so convert from `LocalDefId`.
-        let d: DefId = LocalDefId::to_def_id(def_id);
-        // To be potentially eligible for "unused function" mappings, a definition must:
-        // - Be eligible for coverage instrumentation
-        // - Not participate directly in codegen (or have lost all its coverage statements)
-        // - Not have any coverage statements inlined into codegenned functions
-        tcx.is_eligible_for_coverage(def_id)
-            && (!usage.all_mono_items.contains(&d) || usage.missing_own_coverage.contains(&d))
-            && !usage.used_via_inlining.contains(&d)
-    };
-
-    // FIXME(#79651): Consider trying to filter out dummy instantiations of
-    // unused generic functions from library crates, because they can produce
-    // "unused instantiation" in coverage reports even when they are actually
-    // used by some downstream crate in the same binary.
-
-    tcx.mir_keys(())
-        .iter()
-        .copied()
-        .filter(|&def_id| is_unused_fn(def_id))
-        .map(|def_id| make_dummy_instance(tcx, def_id))
-        .collect::<Vec<_>>()
-}
-
-struct UsageSets<'tcx> {
-    all_mono_items: &'tcx DefIdSet,
-    used_via_inlining: FxHashSet<DefId>,
-    missing_own_coverage: FxHashSet<DefId>,
-}
-
-/// Prepare sets of definitions that are relevant to deciding whether something
-/// is an "unused function" for coverage purposes.
-fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
-    let MonoItemPartitions { all_mono_items, codegen_units, .. } =
-        tcx.collect_and_partition_mono_items(());
-
-    // Obtain a MIR body for each function participating in codegen, via an
-    // arbitrary instance.
-    let mut def_ids_seen = FxHashSet::default();
-    let def_and_mir_for_all_mono_fns = codegen_units
-        .iter()
-        .flat_map(|cgu| cgu.items().keys())
-        .filter_map(|item| match item {
-            mir::mono::MonoItem::Fn(instance) => Some(instance),
-            mir::mono::MonoItem::Static(_) | mir::mono::MonoItem::GlobalAsm(_) => None,
-        })
-        // We only need one arbitrary instance per definition.
-        .filter(move |instance| def_ids_seen.insert(instance.def_id()))
-        .map(|instance| {
-            // We don't care about the instance, just its underlying MIR.
-            let body = tcx.instance_mir(instance.def);
-            (instance.def_id(), body)
-        });
-
-    // Functions whose coverage statements were found inlined into other functions.
-    let mut used_via_inlining = FxHashSet::default();
-    // Functions that were instrumented, but had all of their coverage statements
-    // removed by later MIR transforms (e.g. UnreachablePropagation).
-    let mut missing_own_coverage = FxHashSet::default();
-
-    for (def_id, body) in def_and_mir_for_all_mono_fns {
-        let mut saw_own_coverage = false;
-
-        // Inspect every coverage statement in the function's MIR.
-        for stmt in body
-            .basic_blocks
-            .iter()
-            .flat_map(|block| &block.statements)
-            .filter(|stmt| matches!(stmt.kind, mir::StatementKind::Coverage(_)))
-        {
-            if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
-                // This coverage statement was inlined from another function.
-                used_via_inlining.insert(inlined.def_id());
-            } else {
-                // Non-inlined coverage statements belong to the enclosing function.
-                saw_own_coverage = true;
-            }
-        }
-
-        if !saw_own_coverage && body.function_coverage_info.is_some() {
-            missing_own_coverage.insert(def_id);
-        }
-    }
-
-    UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
-}
-
-fn make_dummy_instance<'tcx>(tcx: TyCtxt<'tcx>, local_def_id: LocalDefId) -> ty::Instance<'tcx> {
-    let def_id = local_def_id.to_def_id();
-
-    // Make a dummy instance that fills in all generics with placeholders.
-    ty::Instance::new(
-        def_id,
-        ty::GenericArgs::for_item(tcx, def_id, |param, _| {
-            if let ty::GenericParamDefKind::Lifetime = param.kind {
-                tcx.lifetimes.re_erased.into()
-            } else {
-                tcx.mk_param_from_def(param)
-            }
-        }),
-    )
-}
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
index 048e1988c32..7bdbc685952 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
@@ -5,6 +5,7 @@
 //! [^win]: On Windows the section name is `.lcovfun`.
 
 use std::ffi::CString;
+use std::sync::Arc;
 
 use rustc_abi::Align;
 use rustc_codegen_ssa::traits::{
@@ -15,7 +16,7 @@ use rustc_middle::mir::coverage::{
     MappingKind, Op,
 };
 use rustc_middle::ty::{Instance, TyCtxt};
-use rustc_span::Span;
+use rustc_span::{SourceFile, Span};
 use rustc_target::spec::HasTargetSpec;
 use tracing::debug;
 
@@ -38,16 +39,15 @@ pub(crate) struct CovfunRecord<'tcx> {
 }
 
 impl<'tcx> CovfunRecord<'tcx> {
-    /// FIXME(Zalathar): Make this the responsibility of the code that determines
-    /// which functions are unused.
-    pub(crate) fn mangled_function_name_if_unused(&self) -> Option<&'tcx str> {
-        (!self.is_used).then_some(self.mangled_function_name)
+    /// Iterator that yields all source files referred to by this function's
+    /// coverage mappings. Used to build the global file table for the CGU.
+    pub(crate) fn all_source_files(&self) -> impl Iterator<Item = &SourceFile> {
+        self.virtual_file_mapping.local_file_table.iter().map(Arc::as_ref)
     }
 }
 
 pub(crate) fn prepare_covfun_record<'tcx>(
     tcx: TyCtxt<'tcx>,
-    global_file_table: &mut GlobalFileTable,
     instance: Instance<'tcx>,
     is_used: bool,
 ) -> Option<CovfunRecord<'tcx>> {
@@ -65,7 +65,7 @@ pub(crate) fn prepare_covfun_record<'tcx>(
         regions: ffi::Regions::default(),
     };
 
-    fill_region_tables(tcx, global_file_table, fn_cov_info, ids_info, &mut covfun);
+    fill_region_tables(tcx, fn_cov_info, ids_info, &mut covfun);
 
     if covfun.regions.has_no_regions() {
         debug!(?covfun, "function has no mappings to embed; skipping");
@@ -100,7 +100,6 @@ fn prepare_expressions(ids_info: &CoverageIdsInfo) -> Vec<ffi::CounterExpression
 /// Populates the mapping region tables in the current function's covfun record.
 fn fill_region_tables<'tcx>(
     tcx: TyCtxt<'tcx>,
-    global_file_table: &mut GlobalFileTable,
     fn_cov_info: &'tcx FunctionCoverageInfo,
     ids_info: &'tcx CoverageIdsInfo,
     covfun: &mut CovfunRecord<'tcx>,
@@ -114,11 +113,7 @@ fn fill_region_tables<'tcx>(
     };
     let source_file = source_map.lookup_source_file(first_span.lo());
 
-    // Look up the global file ID for that file.
-    let global_file_id = global_file_table.global_file_id_for_file(&source_file);
-
-    // Associate that global file ID with a local file ID for this function.
-    let local_file_id = covfun.virtual_file_mapping.local_id_for_global(global_file_id);
+    let local_file_id = covfun.virtual_file_mapping.push_file(&source_file);
 
     // In rare cases, _all_ of a function's spans are discarded, and coverage
     // codegen needs to handle that gracefully to avoid #133606.
@@ -187,7 +182,7 @@ fn fill_region_tables<'tcx>(
 /// as a global variable in the `__llvm_covfun` section.
 pub(crate) fn generate_covfun_record<'tcx>(
     cx: &CodegenCx<'_, 'tcx>,
-    filenames_hash: u64,
+    global_file_table: &GlobalFileTable,
     covfun: &CovfunRecord<'tcx>,
 ) {
     let &CovfunRecord {
@@ -199,12 +194,19 @@ pub(crate) fn generate_covfun_record<'tcx>(
         ref regions,
     } = covfun;
 
+    let Some(local_file_table) = virtual_file_mapping.resolve_all(global_file_table) else {
+        debug_assert!(
+            false,
+            "all local files should be present in the global file table: \
+                global_file_table = {global_file_table:?}, \
+                virtual_file_mapping = {virtual_file_mapping:?}"
+        );
+        return;
+    };
+
     // Encode the function's coverage mappings into a buffer.
-    let coverage_mapping_buffer = llvm_cov::write_function_mappings_to_buffer(
-        &virtual_file_mapping.to_vec(),
-        expressions,
-        regions,
-    );
+    let coverage_mapping_buffer =
+        llvm_cov::write_function_mappings_to_buffer(&local_file_table, expressions, regions);
 
     // A covfun record consists of four target-endian integers, followed by the
     // encoded mapping data in bytes. Note that the length field is 32 bits.
@@ -217,7 +219,7 @@ pub(crate) fn generate_covfun_record<'tcx>(
             cx.const_u64(func_name_hash),
             cx.const_u32(coverage_mapping_buffer.len() as u32),
             cx.const_u64(source_hash),
-            cx.const_u64(filenames_hash),
+            cx.const_u64(global_file_table.filenames_hash),
             cx.const_bytes(&coverage_mapping_buffer),
         ],
         // This struct needs to be packed, so that the 32-bit length field
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs
new file mode 100644
index 00000000000..68f60f169b5
--- /dev/null
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs
@@ -0,0 +1,170 @@
+use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, ConstCodegenMethods};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_middle::mir;
+use rustc_middle::mir::mono::MonoItemPartitions;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::def_id::DefIdSet;
+
+use crate::common::CodegenCx;
+use crate::coverageinfo::mapgen::covfun::{CovfunRecord, prepare_covfun_record};
+use crate::llvm;
+
+/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
+/// But since we don't want unused functions to disappear from coverage reports, we also scan for
+/// functions that were instrumented but are not participating in codegen.
+///
+/// These unused functions don't need to be codegenned, but we do need to add them to the function
+/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
+/// We also end up adding their symbol names to a special global array that LLVM will include in
+/// its embedded coverage data.
+pub(crate) fn prepare_covfun_records_for_unused_functions<'tcx>(
+    cx: &CodegenCx<'_, 'tcx>,
+    covfun_records: &mut Vec<CovfunRecord<'tcx>>,
+) {
+    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
+
+    let mut unused_instances = gather_unused_function_instances(cx);
+    // Sort the unused instances by symbol name, so that their order isn't hash-sensitive.
+    unused_instances.sort_by_key(|instance| instance.symbol_name);
+
+    // Try to create a covfun record for each unused function.
+    let mut name_globals = Vec::with_capacity(unused_instances.len());
+    covfun_records.extend(unused_instances.into_iter().filter_map(|unused| try {
+        let record = prepare_covfun_record(cx.tcx, unused.instance, false)?;
+        // If successful, also store its symbol name in a global constant.
+        name_globals.push(cx.const_str(unused.symbol_name.name).0);
+        record
+    }));
+
+    // Store the names of unused functions in a specially-named global array.
+    // LLVM's `InstrProfilling` pass will detect this array, and include the
+    // referenced names in its `__llvm_prf_names` section.
+    // (See `llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp`.)
+    if !name_globals.is_empty() {
+        let initializer = cx.const_array(cx.type_ptr(), &name_globals);
+
+        let array = llvm::add_global(cx.llmod, cx.val_ty(initializer), c"__llvm_coverage_names");
+        llvm::set_global_constant(array, true);
+        llvm::set_linkage(array, llvm::Linkage::InternalLinkage);
+        llvm::set_initializer(array, initializer);
+    }
+}
+
+/// Holds a dummy function instance along with its symbol name, to avoid having
+/// to repeatedly query for the name.
+struct UnusedInstance<'tcx> {
+    instance: ty::Instance<'tcx>,
+    symbol_name: ty::SymbolName<'tcx>,
+}
+
+fn gather_unused_function_instances<'tcx>(cx: &CodegenCx<'_, 'tcx>) -> Vec<UnusedInstance<'tcx>> {
+    assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
+
+    let tcx = cx.tcx;
+    let usage = prepare_usage_sets(tcx);
+
+    let is_unused_fn = |def_id: LocalDefId| -> bool {
+        // Usage sets expect `DefId`, so convert from `LocalDefId`.
+        let d: DefId = LocalDefId::to_def_id(def_id);
+        // To be potentially eligible for "unused function" mappings, a definition must:
+        // - Be eligible for coverage instrumentation
+        // - Not participate directly in codegen (or have lost all its coverage statements)
+        // - Not have any coverage statements inlined into codegenned functions
+        tcx.is_eligible_for_coverage(def_id)
+            && (!usage.all_mono_items.contains(&d) || usage.missing_own_coverage.contains(&d))
+            && !usage.used_via_inlining.contains(&d)
+    };
+
+    // FIXME(#79651): Consider trying to filter out dummy instantiations of
+    // unused generic functions from library crates, because they can produce
+    // "unused instantiation" in coverage reports even when they are actually
+    // used by some downstream crate in the same binary.
+
+    tcx.mir_keys(())
+        .iter()
+        .copied()
+        .filter(|&def_id| is_unused_fn(def_id))
+        .map(|def_id| make_dummy_instance(tcx, def_id))
+        .map(|instance| UnusedInstance { instance, symbol_name: tcx.symbol_name(instance) })
+        .collect::<Vec<_>>()
+}
+
+struct UsageSets<'tcx> {
+    all_mono_items: &'tcx DefIdSet,
+    used_via_inlining: FxHashSet<DefId>,
+    missing_own_coverage: FxHashSet<DefId>,
+}
+
+/// Prepare sets of definitions that are relevant to deciding whether something
+/// is an "unused function" for coverage purposes.
+fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
+    let MonoItemPartitions { all_mono_items, codegen_units, .. } =
+        tcx.collect_and_partition_mono_items(());
+
+    // Obtain a MIR body for each function participating in codegen, via an
+    // arbitrary instance.
+    let mut def_ids_seen = FxHashSet::default();
+    let def_and_mir_for_all_mono_fns = codegen_units
+        .iter()
+        .flat_map(|cgu| cgu.items().keys())
+        .filter_map(|item| match item {
+            mir::mono::MonoItem::Fn(instance) => Some(instance),
+            mir::mono::MonoItem::Static(_) | mir::mono::MonoItem::GlobalAsm(_) => None,
+        })
+        // We only need one arbitrary instance per definition.
+        .filter(move |instance| def_ids_seen.insert(instance.def_id()))
+        .map(|instance| {
+            // We don't care about the instance, just its underlying MIR.
+            let body = tcx.instance_mir(instance.def);
+            (instance.def_id(), body)
+        });
+
+    // Functions whose coverage statements were found inlined into other functions.
+    let mut used_via_inlining = FxHashSet::default();
+    // Functions that were instrumented, but had all of their coverage statements
+    // removed by later MIR transforms (e.g. UnreachablePropagation).
+    let mut missing_own_coverage = FxHashSet::default();
+
+    for (def_id, body) in def_and_mir_for_all_mono_fns {
+        let mut saw_own_coverage = false;
+
+        // Inspect every coverage statement in the function's MIR.
+        for stmt in body
+            .basic_blocks
+            .iter()
+            .flat_map(|block| &block.statements)
+            .filter(|stmt| matches!(stmt.kind, mir::StatementKind::Coverage(_)))
+        {
+            if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
+                // This coverage statement was inlined from another function.
+                used_via_inlining.insert(inlined.def_id());
+            } else {
+                // Non-inlined coverage statements belong to the enclosing function.
+                saw_own_coverage = true;
+            }
+        }
+
+        if !saw_own_coverage && body.function_coverage_info.is_some() {
+            missing_own_coverage.insert(def_id);
+        }
+    }
+
+    UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
+}
+
+fn make_dummy_instance<'tcx>(tcx: TyCtxt<'tcx>, local_def_id: LocalDefId) -> ty::Instance<'tcx> {
+    let def_id = local_def_id.to_def_id();
+
+    // Make a dummy instance that fills in all generics with placeholders.
+    ty::Instance::new(
+        def_id,
+        ty::GenericArgs::for_item(tcx, def_id, |param, _| {
+            if let ty::GenericParamDefKind::Lifetime = param.kind {
+                tcx.lifetimes.re_erased.into()
+            } else {
+                tcx.mk_param_from_def(param)
+            }
+        }),
+    )
+}
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs b/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs
index f52991b3697..d2591139d6e 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs
@@ -3,7 +3,6 @@ use std::collections::hash_map::Entry;
 use rustc_codegen_ssa::mir::debuginfo::{DebugScope, FunctionDebugContext};
 use rustc_codegen_ssa::traits::*;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_index::Idx;
 use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::mir::{Body, SourceScope};
 use rustc_middle::ty::layout::{FnAbiOf, HasTypingEnv};
@@ -43,8 +42,7 @@ pub(crate) fn compute_mir_scopes<'ll, 'tcx>(
     let mut instantiated = DenseBitSet::new_empty(mir.source_scopes.len());
     let mut discriminators = FxHashMap::default();
     // Instantiate all scopes.
-    for idx in 0..mir.source_scopes.len() {
-        let scope = SourceScope::new(idx);
+    for scope in mir.source_scopes.indices() {
         make_mir_scope(
             cx,
             instance,
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index 2eaaf127e41..7f3e486ca31 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -910,7 +910,8 @@ pub(crate) fn build_compile_unit_di_node<'ll, 'tcx>(
         && let Some(f) = output_filenames.split_dwarf_path(
             tcx.sess.split_debuginfo(),
             tcx.sess.opts.unstable_opts.split_dwarf_kind,
-            Some(codegen_unit_name),
+            codegen_unit_name,
+            tcx.sess.invocation_temp.as_deref(),
         ) {
         // We get a path relative to the working directory from split_dwarf_path
         Some(tcx.sess.source_map().path_mapping().to_real_filename(f))
@@ -1314,31 +1315,21 @@ fn build_generic_type_param_di_nodes<'ll, 'tcx>(
     ty: Ty<'tcx>,
 ) -> SmallVec<Option<&'ll DIType>> {
     if let ty::Adt(def, args) = *ty.kind() {
-        let generics = cx.tcx.generics_of(def.did());
-        return get_template_parameters(cx, generics, args);
-    }
-
-    return smallvec![];
-}
-
-pub(super) fn get_template_parameters<'ll, 'tcx>(
-    cx: &CodegenCx<'ll, 'tcx>,
-    generics: &ty::Generics,
-    args: ty::GenericArgsRef<'tcx>,
-) -> SmallVec<Option<&'ll DIType>> {
-    if args.types().next().is_some() {
-        let names = get_parameter_names(cx, generics);
-        let template_params: SmallVec<_> = iter::zip(args, names)
-            .filter_map(|(kind, name)| {
-                kind.as_type().map(|ty| {
-                    let actual_type = cx.tcx.normalize_erasing_regions(cx.typing_env(), ty);
-                    let actual_type_di_node = type_di_node(cx, actual_type);
-                    Some(cx.create_template_type_parameter(name.as_str(), actual_type_di_node))
+        if args.types().next().is_some() {
+            let generics = cx.tcx.generics_of(def.did());
+            let names = get_parameter_names(cx, generics);
+            let template_params: SmallVec<_> = iter::zip(args, names)
+                .filter_map(|(kind, name)| {
+                    kind.as_type().map(|ty| {
+                        let actual_type = cx.tcx.normalize_erasing_regions(cx.typing_env(), ty);
+                        let actual_type_di_node = type_di_node(cx, actual_type);
+                        Some(cx.create_template_type_parameter(name.as_str(), actual_type_di_node))
+                    })
                 })
-            })
-            .collect();
+                .collect();
 
-        return template_params;
+            return template_params;
+        }
     }
 
     return smallvec![];
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
index 6792c307fdc..7c701926d2c 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
@@ -363,7 +363,6 @@ fn build_coroutine_variant_struct_type_di_node<'ll, 'tcx>(
 
             state_specific_fields.into_iter().chain(common_fields).collect()
         },
-        // FIXME: this is a no-op. `build_generic_type_param_di_nodes` only works for Adts.
         |cx| build_generic_type_param_di_nodes(cx, coroutine_type_and_layout.ty),
     )
     .di_node
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata/type_map.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata/type_map.rs
index ae2ab32ef53..56fb12d3c22 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata/type_map.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata/type_map.rs
@@ -247,6 +247,16 @@ pub(super) fn stub<'ll, 'tcx>(
     StubInfo { metadata, unique_type_id }
 }
 
+struct AdtStackPopGuard<'ll, 'tcx, 'a> {
+    cx: &'a CodegenCx<'ll, 'tcx>,
+}
+
+impl<'ll, 'tcx, 'a> Drop for AdtStackPopGuard<'ll, 'tcx, 'a> {
+    fn drop(&mut self) {
+        debug_context(self.cx).adt_stack.borrow_mut().pop();
+    }
+}
+
 /// This function enables creating debuginfo nodes that can recursively refer to themselves.
 /// It will first insert the given stub into the type map and only then execute the `members`
 /// and `generics` closures passed in. These closures have access to the stub so they can
@@ -261,6 +271,44 @@ pub(super) fn build_type_with_children<'ll, 'tcx>(
 ) -> DINodeCreationResult<'ll> {
     assert_eq!(debug_context(cx).type_map.di_node_for_unique_id(stub_info.unique_type_id), None);
 
+    let mut _adt_stack_pop_guard = None;
+    if let UniqueTypeId::Ty(ty, ..) = stub_info.unique_type_id
+        && let ty::Adt(adt_def, args) = ty.kind()
+    {
+        let def_id = adt_def.did();
+        // If any sub type reference the original type definition and the sub type has a type
+        // parameter that strictly contains the original parameter, the original type is a recursive
+        // type that can expanding indefinitely. Example,
+        // ```
+        // enum Recursive<T> {
+        //     Recurse(*const Recursive<Wrap<T>>),
+        //     Item(T),
+        // }
+        // ```
+        let is_expanding_recursive =
+            debug_context(cx).adt_stack.borrow().iter().any(|(parent_def_id, parent_args)| {
+                if def_id == *parent_def_id {
+                    args.iter().zip(parent_args.iter()).any(|(arg, parent_arg)| {
+                        if let (Some(arg), Some(parent_arg)) = (arg.as_type(), parent_arg.as_type())
+                        {
+                            arg != parent_arg && arg.contains(parent_arg)
+                        } else {
+                            false
+                        }
+                    })
+                } else {
+                    false
+                }
+            });
+        if is_expanding_recursive {
+            // FIXME: indicate that this is an expanding recursive type in stub metadata?
+            return DINodeCreationResult::new(stub_info.metadata, false);
+        } else {
+            debug_context(cx).adt_stack.borrow_mut().push((def_id, args));
+            _adt_stack_pop_guard = Some(AdtStackPopGuard { cx });
+        }
+    }
+
     debug_context(cx).type_map.insert(stub_info.unique_type_id, stub_info.metadata);
 
     let members: SmallVec<_> =
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
index ae7d080db66..c5085927923 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
@@ -2,8 +2,8 @@
 
 use std::cell::{OnceCell, RefCell};
 use std::ops::Range;
-use std::ptr;
 use std::sync::Arc;
+use std::{iter, ptr};
 
 use libc::c_uint;
 use metadata::create_subroutine_type;
@@ -66,6 +66,7 @@ pub(crate) struct CodegenUnitDebugContext<'ll, 'tcx> {
     created_files: RefCell<UnordMap<Option<(StableSourceFileId, SourceFileHash)>, &'ll DIFile>>,
 
     type_map: metadata::TypeMap<'ll, 'tcx>,
+    adt_stack: RefCell<Vec<(DefId, GenericArgsRef<'tcx>)>>,
     namespace_map: RefCell<DefIdMap<&'ll DIScope>>,
     recursion_marker_type: OnceCell<&'ll DIType>,
 }
@@ -80,6 +81,7 @@ impl<'ll, 'tcx> CodegenUnitDebugContext<'ll, 'tcx> {
             builder,
             created_files: Default::default(),
             type_map: Default::default(),
+            adt_stack: Default::default(),
             namespace_map: RefCell::new(Default::default()),
             recursion_marker_type: OnceCell::new(),
         }
@@ -486,10 +488,40 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             generics: &ty::Generics,
             args: GenericArgsRef<'tcx>,
         ) -> &'ll DIArray {
-            let template_params = metadata::get_template_parameters(cx, generics, args);
+            if args.types().next().is_none() {
+                return create_DIArray(DIB(cx), &[]);
+            }
+
+            // Again, only create type information if full debuginfo is enabled
+            let template_params: Vec<_> = if cx.sess().opts.debuginfo == DebugInfo::Full {
+                let names = get_parameter_names(cx, generics);
+                iter::zip(args, names)
+                    .filter_map(|(kind, name)| {
+                        kind.as_type().map(|ty| {
+                            let actual_type = cx.tcx.normalize_erasing_regions(cx.typing_env(), ty);
+                            let actual_type_metadata = type_di_node(cx, actual_type);
+                            Some(cx.create_template_type_parameter(
+                                name.as_str(),
+                                actual_type_metadata,
+                            ))
+                        })
+                    })
+                    .collect()
+            } else {
+                vec![]
+            };
+
             create_DIArray(DIB(cx), &template_params)
         }
 
+        fn get_parameter_names(cx: &CodegenCx<'_, '_>, generics: &ty::Generics) -> Vec<Symbol> {
+            let mut names = generics.parent.map_or_else(Vec::new, |def_id| {
+                get_parameter_names(cx, cx.tcx.generics_of(def_id))
+            });
+            names.extend(generics.own_params.iter().map(|param| param.name));
+            names
+        }
+
         /// Returns a scope, plus `true` if that's a type scope for "class" methods,
         /// otherwise `false` for plain namespace scopes.
         fn get_containing_scope<'ll, 'tcx>(
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index 67135fcc308..d1d6bcebd33 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -1421,7 +1421,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
         return Ok(bx.shuffle_vector(args[0].immediate(), args[1].immediate(), indices));
     }
 
-    if name == sym::simd_insert {
+    if name == sym::simd_insert || name == sym::simd_insert_dyn {
         require!(
             in_elem == arg_tys[2],
             InvalidMonomorphization::InsertedType {
@@ -1432,40 +1432,49 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
                 out_ty: arg_tys[2]
             }
         );
-        let idx = bx
-            .const_to_opt_u128(args[1].immediate(), false)
-            .expect("typeck should have ensure that this is a const");
-        if idx >= in_len.into() {
-            return_error!(InvalidMonomorphization::SimdIndexOutOfBounds {
-                span,
-                name,
-                arg_idx: 1,
-                total_len: in_len.into(),
-            });
-        }
-        return Ok(bx.insert_element(
-            args[0].immediate(),
-            args[2].immediate(),
-            bx.const_i32(idx as i32),
-        ));
+
+        let index_imm = if name == sym::simd_insert {
+            let idx = bx
+                .const_to_opt_u128(args[1].immediate(), false)
+                .expect("typeck should have ensure that this is a const");
+            if idx >= in_len.into() {
+                return_error!(InvalidMonomorphization::SimdIndexOutOfBounds {
+                    span,
+                    name,
+                    arg_idx: 1,
+                    total_len: in_len.into(),
+                });
+            }
+            bx.const_i32(idx as i32)
+        } else {
+            args[1].immediate()
+        };
+
+        return Ok(bx.insert_element(args[0].immediate(), args[2].immediate(), index_imm));
     }
-    if name == sym::simd_extract {
+    if name == sym::simd_extract || name == sym::simd_extract_dyn {
         require!(
             ret_ty == in_elem,
             InvalidMonomorphization::ReturnType { span, name, in_elem, in_ty, ret_ty }
         );
-        let idx = bx
-            .const_to_opt_u128(args[1].immediate(), false)
-            .expect("typeck should have ensure that this is a const");
-        if idx >= in_len.into() {
-            return_error!(InvalidMonomorphization::SimdIndexOutOfBounds {
-                span,
-                name,
-                arg_idx: 1,
-                total_len: in_len.into(),
-            });
-        }
-        return Ok(bx.extract_element(args[0].immediate(), bx.const_i32(idx as i32)));
+        let index_imm = if name == sym::simd_extract {
+            let idx = bx
+                .const_to_opt_u128(args[1].immediate(), false)
+                .expect("typeck should have ensure that this is a const");
+            if idx >= in_len.into() {
+                return_error!(InvalidMonomorphization::SimdIndexOutOfBounds {
+                    span,
+                    name,
+                    arg_idx: 1,
+                    total_len: in_len.into(),
+                });
+            }
+            bx.const_i32(idx as i32)
+        } else {
+            args[1].immediate()
+        };
+
+        return Ok(bx.extract_element(args[0].immediate(), index_imm));
     }
 
     if name == sym::simd_select {
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 1d05c4eee4d..8de68925cab 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -112,8 +112,12 @@ pub fn link_binary(
                 codegen_results.crate_info.local_crate_name,
             );
             let crate_name = format!("{}", codegen_results.crate_info.local_crate_name);
-            let out_filename =
-                output.file_for_writing(outputs, OutputType::Exe, Some(crate_name.as_str()));
+            let out_filename = output.file_for_writing(
+                outputs,
+                OutputType::Exe,
+                &crate_name,
+                sess.invocation_temp.as_deref(),
+            );
             match crate_type {
                 CrateType::Rlib => {
                     let _timer = sess.timer("link_rlib");
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index e816e71379a..0fd4ed8475b 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -306,14 +306,18 @@ impl TargetMachineFactoryConfig {
             cgcx.output_filenames.split_dwarf_path(
                 cgcx.split_debuginfo,
                 cgcx.split_dwarf_kind,
-                Some(module_name),
+                module_name,
+                cgcx.invocation_temp.as_deref(),
             )
         } else {
             None
         };
 
-        let output_obj_file =
-            Some(cgcx.output_filenames.temp_path(OutputType::Object, Some(module_name)));
+        let output_obj_file = Some(cgcx.output_filenames.temp_path_for_cgu(
+            OutputType::Object,
+            module_name,
+            cgcx.invocation_temp.as_deref(),
+        ));
         TargetMachineFactoryConfig { split_dwarf_file, output_obj_file }
     }
 }
@@ -344,6 +348,7 @@ pub struct CodegenContext<B: WriteBackendMethods> {
     pub crate_types: Vec<CrateType>,
     pub each_linked_rlib_for_lto: Vec<(CrateNum, PathBuf)>,
     pub output_filenames: Arc<OutputFilenames>,
+    pub invocation_temp: Option<String>,
     pub regular_module_config: Arc<ModuleConfig>,
     pub metadata_module_config: Arc<ModuleConfig>,
     pub allocator_module_config: Arc<ModuleConfig>,
@@ -582,8 +587,11 @@ fn produce_final_output_artifacts(
         if let [module] = &compiled_modules.modules[..] {
             // 1) Only one codegen unit. In this case it's no difficulty
             //    to copy `foo.0.x` to `foo.x`.
-            let module_name = Some(&module.name[..]);
-            let path = crate_output.temp_path(output_type, module_name);
+            let path = crate_output.temp_path_for_cgu(
+                output_type,
+                &module.name,
+                sess.invocation_temp.as_deref(),
+            );
             let output = crate_output.path(output_type);
             if !output_type.is_text_output() && output.is_tty() {
                 sess.dcx()
@@ -596,22 +604,15 @@ fn produce_final_output_artifacts(
                 ensure_removed(sess.dcx(), &path);
             }
         } else {
-            let extension = crate_output
-                .temp_path(output_type, None)
-                .extension()
-                .unwrap()
-                .to_str()
-                .unwrap()
-                .to_owned();
-
             if crate_output.outputs.contains_explicit_name(&output_type) {
                 // 2) Multiple codegen units, with `--emit foo=some_name`. We have
                 //    no good solution for this case, so warn the user.
-                sess.dcx().emit_warn(errors::IgnoringEmitPath { extension });
+                sess.dcx()
+                    .emit_warn(errors::IgnoringEmitPath { extension: output_type.extension() });
             } else if crate_output.single_output_file.is_some() {
                 // 3) Multiple codegen units, with `-o some_name`. We have
                 //    no good solution for this case, so warn the user.
-                sess.dcx().emit_warn(errors::IgnoringOutput { extension });
+                sess.dcx().emit_warn(errors::IgnoringOutput { extension: output_type.extension() });
             } else {
                 // 4) Multiple codegen units, but no explicit name. We
                 //    just leave the `foo.0.x` files in place.
@@ -967,7 +968,12 @@ fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
         module.source.saved_files.get("dwo").as_ref().and_then(|saved_dwarf_object_file| {
             let dwarf_obj_out = cgcx
                 .output_filenames
-                .split_dwarf_path(cgcx.split_debuginfo, cgcx.split_dwarf_kind, Some(&module.name))
+                .split_dwarf_path(
+                    cgcx.split_debuginfo,
+                    cgcx.split_dwarf_kind,
+                    &module.name,
+                    cgcx.invocation_temp.as_deref(),
+                )
                 .expect(
                     "saved dwarf object in work product but `split_dwarf_path` returned `None`",
                 );
@@ -977,7 +983,11 @@ fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
     let mut load_from_incr_cache = |perform, output_type: OutputType| {
         if perform {
             let saved_file = module.source.saved_files.get(output_type.extension())?;
-            let output_path = cgcx.output_filenames.temp_path(output_type, Some(&module.name));
+            let output_path = cgcx.output_filenames.temp_path_for_cgu(
+                output_type,
+                &module.name,
+                cgcx.invocation_temp.as_deref(),
+            );
             load_from_incr_comp_dir(output_path, &saved_file)
         } else {
             None
@@ -1222,6 +1232,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
         split_dwarf_kind: tcx.sess.opts.unstable_opts.split_dwarf_kind,
         parallel: backend.supports_parallel() && !sess.opts.unstable_opts.no_parallel_backend,
         pointer_size: tcx.data_layout.pointer_size,
+        invocation_temp: sess.invocation_temp.clone(),
     };
 
     // This is the "main loop" of parallel work happening for parallel codegen.
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 1985b3b7170..12b7a487455 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -10,7 +10,7 @@ use rustc_ast::expand::allocator::{ALLOCATOR_METHODS, AllocatorKind, global_fn_n
 use rustc_attr_parsing::OptimizeAttr;
 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::profiling::{get_resident_set_size, print_time_passes_entry};
-use rustc_data_structures::sync::par_map;
+use rustc_data_structures::sync::{IntoDynSyncSend, par_map};
 use rustc_data_structures::unord::UnordMap;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::lang_items::LangItem;
@@ -640,8 +640,11 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         let metadata_cgu_name =
             cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("metadata")).to_string();
         tcx.sess.time("write_compressed_metadata", || {
-            let file_name =
-                tcx.output_filenames(()).temp_path(OutputType::Metadata, Some(&metadata_cgu_name));
+            let file_name = tcx.output_filenames(()).temp_path_for_cgu(
+                OutputType::Metadata,
+                &metadata_cgu_name,
+                tcx.sess.invocation_temp.as_deref(),
+            );
             let data = create_compressed_metadata_file(
                 tcx.sess,
                 &metadata,
@@ -757,7 +760,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
 
             let pre_compiled_cgus = par_map(cgus, |(i, _)| {
                 let module = backend.compile_codegen_unit(tcx, codegen_units[i].name());
-                (i, module)
+                (i, IntoDynSyncSend(module))
             });
 
             total_codegen_time += start_time.elapsed();
@@ -777,7 +780,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         match cgu_reuse {
             CguReuse::No => {
                 let (module, cost) = if let Some(cgu) = pre_compiled_cgus.remove(&i) {
-                    cgu
+                    cgu.0
                 } else {
                     let start_time = Instant::now();
                     let module = backend.compile_codegen_unit(tcx, cgu.name());
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index ddb61188983..b0c53ec93ce 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -114,7 +114,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                 AttributeKind::Repr(reprs) => {
                     codegen_fn_attrs.alignment = reprs
                         .iter()
-                        .find_map(|(r, _)| if let ReprAlign(x) = r { Some(*x) } else { None });
+                        .filter_map(|(r, _)| if let ReprAlign(x) = r { Some(*x) } else { None })
+                        .max();
                 }
 
                 _ => {}
@@ -345,20 +346,26 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                 no_sanitize_span = Some(attr.span());
                 if let Some(list) = attr.meta_item_list() {
                     for item in list.iter() {
-                        match item.name_or_empty() {
-                            sym::address => {
+                        match item.name() {
+                            Some(sym::address) => {
                                 codegen_fn_attrs.no_sanitize |=
                                     SanitizerSet::ADDRESS | SanitizerSet::KERNELADDRESS
                             }
-                            sym::cfi => codegen_fn_attrs.no_sanitize |= SanitizerSet::CFI,
-                            sym::kcfi => codegen_fn_attrs.no_sanitize |= SanitizerSet::KCFI,
-                            sym::memory => codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY,
-                            sym::memtag => codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMTAG,
-                            sym::shadow_call_stack => {
+                            Some(sym::cfi) => codegen_fn_attrs.no_sanitize |= SanitizerSet::CFI,
+                            Some(sym::kcfi) => codegen_fn_attrs.no_sanitize |= SanitizerSet::KCFI,
+                            Some(sym::memory) => {
+                                codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY
+                            }
+                            Some(sym::memtag) => {
+                                codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMTAG
+                            }
+                            Some(sym::shadow_call_stack) => {
                                 codegen_fn_attrs.no_sanitize |= SanitizerSet::SHADOWCALLSTACK
                             }
-                            sym::thread => codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD,
-                            sym::hwaddress => {
+                            Some(sym::thread) => {
+                                codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD
+                            }
+                            Some(sym::hwaddress) => {
                                 codegen_fn_attrs.no_sanitize |= SanitizerSet::HWADDRESS
                             }
                             _ => {
@@ -419,9 +426,9 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                             continue;
                         };
 
-                        let attrib_to_write = match meta_item.name_or_empty() {
-                            sym::prefix_nops => &mut prefix,
-                            sym::entry_nops => &mut entry,
+                        let attrib_to_write = match meta_item.name() {
+                            Some(sym::prefix_nops) => &mut prefix,
+                            Some(sym::entry_nops) => &mut entry,
                             _ => {
                                 tcx.dcx().emit_err(errors::UnexpectedParameterName {
                                     span: item.span(),
@@ -785,8 +792,7 @@ impl<'a> MixedExportNameAndNoMangleState<'a> {
 fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
     let attrs = tcx.get_attrs(id, sym::rustc_autodiff);
 
-    let attrs =
-        attrs.filter(|attr| attr.name_or_empty() == sym::rustc_autodiff).collect::<Vec<_>>();
+    let attrs = attrs.filter(|attr| attr.has_name(sym::rustc_autodiff)).collect::<Vec<_>>();
 
     // check for exactly one autodiff attribute on placeholder functions.
     // There should only be one, since we generate a new placeholder per ad macro.
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index b33de8802d8..42cea5c86d4 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -277,13 +277,13 @@ pub struct BinaryOutputToTty {
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_ignoring_emit_path)]
 pub struct IgnoringEmitPath {
-    pub extension: String,
+    pub extension: &'static str,
 }
 
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_ignoring_output)]
 pub struct IgnoringOutput {
-    pub extension: String,
+    pub extension: &'static str,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 67217927a87..5b2ed69535b 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -2,7 +2,6 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
@@ -105,13 +104,19 @@ impl<M> ModuleCodegen<M> {
         emit_asm: bool,
         emit_ir: bool,
         outputs: &OutputFilenames,
+        invocation_temp: Option<&str>,
     ) -> CompiledModule {
-        let object = emit_obj.then(|| outputs.temp_path(OutputType::Object, Some(&self.name)));
-        let dwarf_object = emit_dwarf_obj.then(|| outputs.temp_path_dwo(Some(&self.name)));
-        let bytecode = emit_bc.then(|| outputs.temp_path(OutputType::Bitcode, Some(&self.name)));
-        let assembly = emit_asm.then(|| outputs.temp_path(OutputType::Assembly, Some(&self.name)));
-        let llvm_ir =
-            emit_ir.then(|| outputs.temp_path(OutputType::LlvmAssembly, Some(&self.name)));
+        let object = emit_obj
+            .then(|| outputs.temp_path_for_cgu(OutputType::Object, &self.name, invocation_temp));
+        let dwarf_object =
+            emit_dwarf_obj.then(|| outputs.temp_path_dwo_for_cgu(&self.name, invocation_temp));
+        let bytecode = emit_bc
+            .then(|| outputs.temp_path_for_cgu(OutputType::Bitcode, &self.name, invocation_temp));
+        let assembly = emit_asm
+            .then(|| outputs.temp_path_for_cgu(OutputType::Assembly, &self.name, invocation_temp));
+        let llvm_ir = emit_ir.then(|| {
+            outputs.temp_path_for_cgu(OutputType::LlvmAssembly, &self.name, invocation_temp)
+        });
 
         CompiledModule {
             name: self.name.clone(),
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 0758e5d0456..6a37889217a 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -3,7 +3,7 @@ use std::iter;
 use rustc_index::IndexVec;
 use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
-use rustc_middle::mir::{Local, UnwindTerminateReason, traversal};
+use rustc_middle::mir::{Body, Local, UnwindTerminateReason, traversal};
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, HasTypingEnv, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_middle::{bug, mir, span_bug};
@@ -170,19 +170,29 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 ) {
     assert!(!instance.args.has_infer());
 
+    let tcx = cx.tcx();
     let llfn = cx.get_fn(instance);
 
-    let mir = cx.tcx().instance_mir(instance.def);
+    let mut mir = tcx.instance_mir(instance.def);
 
     let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty());
     debug!("fn_abi: {:?}", fn_abi);
 
-    if cx.tcx().codegen_fn_attrs(instance.def_id()).flags.contains(CodegenFnAttrFlags::NAKED) {
+    if tcx.codegen_fn_attrs(instance.def_id()).flags.contains(CodegenFnAttrFlags::NAKED) {
         crate::mir::naked_asm::codegen_naked_asm::<Bx>(cx, &mir, instance);
         return;
     }
 
-    let debug_context = cx.create_function_debug_context(instance, fn_abi, llfn, mir);
+    if tcx.features().ergonomic_clones() {
+        let monomorphized_mir = instance.instantiate_mir_and_normalize_erasing_regions(
+            tcx,
+            ty::TypingEnv::fully_monomorphized(),
+            ty::EarlyBinder::bind(mir.clone()),
+        );
+        mir = tcx.arena.alloc(optimize_use_clone::<Bx>(cx, monomorphized_mir));
+    }
+
+    let debug_context = cx.create_function_debug_context(instance, fn_abi, llfn, &mir);
 
     let start_llbb = Bx::append_block(cx, llfn, "start");
     let mut start_bx = Bx::build(cx, start_llbb);
@@ -194,7 +204,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     }
 
     let cleanup_kinds =
-        base::wants_new_eh_instructions(cx.tcx().sess).then(|| analyze::cleanup_kinds(mir));
+        base::wants_new_eh_instructions(tcx.sess).then(|| analyze::cleanup_kinds(&mir));
 
     let cached_llbbs: IndexVec<mir::BasicBlock, CachedLlbb<Bx::BasicBlock>> =
         mir.basic_blocks
@@ -217,7 +227,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         cleanup_kinds,
         landing_pads: IndexVec::from_elem(None, &mir.basic_blocks),
         funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks.len()),
-        cold_blocks: find_cold_blocks(cx.tcx(), mir),
+        cold_blocks: find_cold_blocks(tcx, mir),
         locals: locals::Locals::empty(),
         debug_context,
         per_local_var_debug_info: None,
@@ -233,7 +243,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         fx.compute_per_local_var_debug_info(&mut start_bx).unzip();
     fx.per_local_var_debug_info = per_local_var_debug_info;
 
-    let traversal_order = traversal::mono_reachable_reverse_postorder(mir, cx.tcx(), instance);
+    let traversal_order = traversal::mono_reachable_reverse_postorder(mir, tcx, instance);
     let memory_locals = analyze::non_ssa_locals(&fx, &traversal_order);
 
     // Allocate variable and temp allocas
@@ -310,6 +320,61 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     }
 }
 
+// FIXME: Move this function to mir::transform when post-mono MIR passes land.
+fn optimize_use_clone<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+    cx: &'a Bx::CodegenCx,
+    mut mir: Body<'tcx>,
+) -> Body<'tcx> {
+    let tcx = cx.tcx();
+
+    if tcx.features().ergonomic_clones() {
+        for bb in mir.basic_blocks.as_mut() {
+            let mir::TerminatorKind::Call {
+                args,
+                destination,
+                target,
+                call_source: mir::CallSource::Use,
+                ..
+            } = &bb.terminator().kind
+            else {
+                continue;
+            };
+
+            // CallSource::Use calls always use 1 argument.
+            assert_eq!(args.len(), 1);
+            let arg = &args[0];
+
+            // These types are easily available from locals, so check that before
+            // doing DefId lookups to figure out what we're actually calling.
+            let arg_ty = arg.node.ty(&mir.local_decls, tcx);
+
+            let ty::Ref(_region, inner_ty, mir::Mutability::Not) = *arg_ty.kind() else { continue };
+
+            if !tcx.type_is_copy_modulo_regions(cx.typing_env(), inner_ty) {
+                continue;
+            }
+
+            let Some(arg_place) = arg.node.place() else { continue };
+
+            let destination_block = target.unwrap();
+
+            bb.statements.push(mir::Statement {
+                source_info: bb.terminator().source_info,
+                kind: mir::StatementKind::Assign(Box::new((
+                    *destination,
+                    mir::Rvalue::Use(mir::Operand::Copy(
+                        arg_place.project_deeper(&[mir::ProjectionElem::Deref], tcx),
+                    )),
+                ))),
+            });
+
+            bb.terminator_mut().kind = mir::TerminatorKind::Goto { target: destination_block };
+        }
+    }
+
+    mir
+}
+
 /// Produces, for each argument, a `Value` pointing at the
 /// argument's value. As arguments are places, these are always
 /// indirect.
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 7e355b6406a..eade9e52de9 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -9,6 +9,7 @@ use rustc_middle::mir::{self, ConstValue};
 use rustc_middle::ty::Ty;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_middle::{bug, span_bug};
+use rustc_session::config::OptLevel;
 use tracing::{debug, instrument};
 
 use super::place::{PlaceRef, PlaceValue};
@@ -496,6 +497,18 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                     _ => (tag_imm, bx.cx().immediate_backend_type(tag_op.layout)),
                 };
 
+                // Layout ensures that we only get here for cases where the discriminant
+                // value and the variant index match, since that's all `Niche` can encode.
+                // But for emphasis and debugging, let's double-check one anyway.
+                debug_assert_eq!(
+                    self.layout
+                        .ty
+                        .discriminant_for_variant(bx.tcx(), untagged_variant)
+                        .unwrap()
+                        .val,
+                    u128::from(untagged_variant.as_u32()),
+                );
+
                 let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
 
                 // We have a subrange `niche_start..=niche_end` inside `range`.
@@ -537,6 +550,21 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                         relative_discr,
                         bx.cx().const_uint(tag_llty, relative_max as u64),
                     );
+
+                    // Thanks to parameter attributes and load metadata, LLVM already knows
+                    // the general valid range of the tag. It's possible, though, for there
+                    // to be an impossible value *in the middle*, which those ranges don't
+                    // communicate, so it's worth an `assume` to let the optimizer know.
+                    if niche_variants.contains(&untagged_variant)
+                        && bx.cx().sess().opts.optimize != OptLevel::No
+                    {
+                        let impossible =
+                            u64::from(untagged_variant.as_u32() - niche_variants.start().as_u32());
+                        let impossible = bx.cx().const_uint(tag_llty, impossible);
+                        let ne = bx.icmp(IntPredicate::IntNE, relative_discr, impossible);
+                        bx.assume(ne);
+                    }
+
                     (is_niche, cast_tag, niche_variants.start().as_u32() as u128)
                 };
 
@@ -553,7 +581,9 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                 );
 
                 // In principle we could insert assumes on the possible range of `discr`, but
-                // currently in LLVM this seems to be a pessimization.
+                // currently in LLVM this isn't worth it because the original `tag` will
+                // have either a `range` parameter attribute or `!range` metadata,
+                // or come from a `transmute` that already `assume`d it.
 
                 discr
             }
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 2b74c849f1a..b600b8918dd 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -34,7 +34,7 @@ use crate::check_consts::is_fn_or_trait_safe_to_expose_on_stable;
 use crate::errors;
 
 type QualifResults<'mir, 'tcx, Q> =
-    rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'mir, 'tcx, Q>>;
+    rustc_mir_dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'mir, 'tcx, Q>>;
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 enum ConstConditionsHold {
diff --git a/compiler/rustc_const_eval/src/check_consts/resolver.rs b/compiler/rustc_const_eval/src/check_consts/resolver.rs
index 8cee282311f..9f7fcc509a5 100644
--- a/compiler/rustc_const_eval/src/check_consts/resolver.rs
+++ b/compiler/rustc_const_eval/src/check_consts/resolver.rs
@@ -22,17 +22,17 @@ use super::{ConstCx, Qualif, qualifs};
 /// qualified immediately after it is borrowed or its address escapes. The borrow must allow for
 /// mutation, which includes shared borrows of places with interior mutability. The type of
 /// borrowed place must contain the qualif.
-struct TransferFunction<'a, 'mir, 'tcx, Q> {
-    ccx: &'a ConstCx<'mir, 'tcx>,
-    state: &'a mut State,
+struct TransferFunction<'mir, 'tcx, Q> {
+    ccx: &'mir ConstCx<'mir, 'tcx>,
+    state: &'mir mut State,
     _qualif: PhantomData<Q>,
 }
 
-impl<'a, 'mir, 'tcx, Q> TransferFunction<'a, 'mir, 'tcx, Q>
+impl<'mir, 'tcx, Q> TransferFunction<'mir, 'tcx, Q>
 where
     Q: Qualif,
 {
-    fn new(ccx: &'a ConstCx<'mir, 'tcx>, state: &'a mut State) -> Self {
+    fn new(ccx: &'mir ConstCx<'mir, 'tcx>, state: &'mir mut State) -> Self {
         TransferFunction { ccx, state, _qualif: PhantomData }
     }
 
@@ -124,7 +124,7 @@ where
     }
 }
 
-impl<'tcx, Q> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx, Q>
+impl<'tcx, Q> Visitor<'tcx> for TransferFunction<'_, 'tcx, Q>
 where
     Q: Qualif,
 {
@@ -228,20 +228,20 @@ where
 }
 
 /// The dataflow analysis used to propagate qualifs on arbitrary CFGs.
-pub(super) struct FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> {
-    ccx: &'a ConstCx<'mir, 'tcx>,
+pub(super) struct FlowSensitiveAnalysis<'mir, 'tcx, Q> {
+    ccx: &'mir ConstCx<'mir, 'tcx>,
     _qualif: PhantomData<Q>,
 }
 
-impl<'a, 'mir, 'tcx, Q> FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q>
+impl<'mir, 'tcx, Q> FlowSensitiveAnalysis<'mir, 'tcx, Q>
 where
     Q: Qualif,
 {
-    pub(super) fn new(_: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self {
+    pub(super) fn new(_: Q, ccx: &'mir ConstCx<'mir, 'tcx>) -> Self {
         FlowSensitiveAnalysis { ccx, _qualif: PhantomData }
     }
 
-    fn transfer_function(&self, state: &'a mut State) -> TransferFunction<'a, 'mir, 'tcx, Q> {
+    fn transfer_function(&self, state: &'mir mut State) -> TransferFunction<'mir, 'tcx, Q> {
         TransferFunction::<Q>::new(self.ccx, state)
     }
 }
@@ -313,7 +313,7 @@ impl JoinSemiLattice for State {
     }
 }
 
-impl<'tcx, Q> Analysis<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q>
+impl<'tcx, Q> Analysis<'tcx> for FlowSensitiveAnalysis<'_, 'tcx, Q>
 where
     Q: Qualif,
 {
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index e2675e2f4c9..6472aaa5758 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -6,7 +6,7 @@ use rustc_abi::WrappingRange;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Diag, DiagArgValue, DiagCtxtHandle, DiagMessage, Diagnostic, EmissionGuarantee, Level,
-    MultiSpan, SubdiagMessageOp, Subdiagnostic,
+    MultiSpan, Subdiagnostic,
 };
 use rustc_hir::ConstContext;
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -290,11 +290,7 @@ pub struct FrameNote {
 }
 
 impl Subdiagnostic for FrameNote {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("times", self.times);
         diag.arg("where_", self.where_);
         diag.arg("instance", self.instance);
@@ -302,7 +298,7 @@ impl Subdiagnostic for FrameNote {
         if self.has_label && !self.span.is_dummy() {
             span.push_span_label(self.span, fluent::const_eval_frame_note_last);
         }
-        let msg = f(diag, fluent::const_eval_frame_note.into());
+        let msg = diag.eagerly_translate(fluent::const_eval_frame_note);
         diag.span_note(span, msg);
     }
 }
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index c1948e9f31f..b69bc0918be 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -268,7 +268,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
     /// Call this on things you got out of the MIR (so it is as generic as the current
     /// stack frame), to bring it into the proper environment for this interpreter.
-    pub(super) fn instantiate_from_current_frame_and_normalize_erasing_regions<
+    pub fn instantiate_from_current_frame_and_normalize_erasing_regions<
         T: TypeFoldable<TyCtxt<'tcx>>,
     >(
         &self,
@@ -279,9 +279,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
     /// Call this on things you got out of the MIR (so it is as generic as the provided
     /// stack frame), to bring it into the proper environment for this interpreter.
-    pub(super) fn instantiate_from_frame_and_normalize_erasing_regions<
-        T: TypeFoldable<TyCtxt<'tcx>>,
-    >(
+    pub fn instantiate_from_frame_and_normalize_erasing_regions<T: TypeFoldable<TyCtxt<'tcx>>>(
         &self,
         frame: &Frame<'tcx, M::Provenance, M::FrameExtra>,
         value: T,
diff --git a/compiler/rustc_const_eval/src/interpret/intern.rs b/compiler/rustc_const_eval/src/interpret/intern.rs
index e4b2fe5d153..8f0cb197c44 100644
--- a/compiler/rustc_const_eval/src/interpret/intern.rs
+++ b/compiler/rustc_const_eval/src/interpret/intern.rs
@@ -30,6 +30,7 @@ use super::{
     AllocId, Allocation, InterpCx, MPlaceTy, Machine, MemoryKind, PlaceTy, err_ub, interp_ok,
 };
 use crate::const_eval;
+use crate::const_eval::DummyMachine;
 use crate::errors::NestedStaticInThreadLocal;
 
 pub trait CompileTimeMachine<'tcx, T> = Machine<
@@ -323,14 +324,17 @@ pub fn intern_const_alloc_for_constprop<'tcx, T, M: CompileTimeMachine<'tcx, T>>
     interp_ok(())
 }
 
-impl<'tcx, M: super::intern::CompileTimeMachine<'tcx, !>> InterpCx<'tcx, M> {
+impl<'tcx> InterpCx<'tcx, DummyMachine> {
     /// A helper function that allocates memory for the layout given and gives you access to mutate
     /// it. Once your own mutation code is done, the backing `Allocation` is removed from the
     /// current `Memory` and interned as read-only into the global memory.
     pub fn intern_with_temp_alloc(
         &mut self,
         layout: TyAndLayout<'tcx>,
-        f: impl FnOnce(&mut InterpCx<'tcx, M>, &PlaceTy<'tcx, M::Provenance>) -> InterpResult<'tcx, ()>,
+        f: impl FnOnce(
+            &mut InterpCx<'tcx, DummyMachine>,
+            &PlaceTy<'tcx, CtfeProvenance>,
+        ) -> InterpResult<'tcx, ()>,
     ) -> InterpResult<'tcx, AllocId> {
         // `allocate` picks a fresh AllocId that we will associate with its data below.
         let dest = self.allocate(layout, MemoryKind::Stack)?;
diff --git a/compiler/rustc_const_eval/src/lib.rs b/compiler/rustc_const_eval/src/lib.rs
index e03849c32f9..da52d60ae59 100644
--- a/compiler/rustc_const_eval/src/lib.rs
+++ b/compiler/rustc_const_eval/src/lib.rs
@@ -1,7 +1,6 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(rust_logo)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
diff --git a/compiler/rustc_data_structures/Cargo.toml b/compiler/rustc_data_structures/Cargo.toml
index fcaf2750507..f48c73b13b9 100644
--- a/compiler/rustc_data_structures/Cargo.toml
+++ b/compiler/rustc_data_structures/Cargo.toml
@@ -14,7 +14,7 @@ indexmap = "2.4.0"
 jobserver_crate = { version = "0.1.28", package = "jobserver" }
 measureme = "12.0.1"
 rustc-hash = "2.0.0"
-rustc-rayon = { version = "0.5.1", features = ["indexmap"] }
+rustc-rayon-core = { version = "0.5.0" }
 rustc-stable-hash = { version = "0.1.0", features = ["nightly"] }
 rustc_arena = { path = "../rustc_arena" }
 rustc_graphviz = { path = "../rustc_graphviz" }
diff --git a/compiler/rustc_data_structures/src/marker.rs b/compiler/rustc_data_structures/src/marker.rs
index 64c64bfa3c2..5f07cfef133 100644
--- a/compiler/rustc_data_structures/src/marker.rs
+++ b/compiler/rustc_data_structures/src/marker.rs
@@ -1,13 +1,13 @@
 use std::alloc::Allocator;
 
-#[rustc_on_unimplemented(message = "`{Self}` doesn't implement `DynSend`. \
+#[diagnostic::on_unimplemented(message = "`{Self}` doesn't implement `DynSend`. \
             Add it to `rustc_data_structures::marker` or use `IntoDynSyncSend` if it's already `Send`")]
 // This is an auto trait for types which can be sent across threads if `sync::is_dyn_thread_safe()`
 // is true. These types can be wrapped in a `FromDyn` to get a `Send` type. Wrapping a
 // `Send` type in `IntoDynSyncSend` will create a `DynSend` type.
 pub unsafe auto trait DynSend {}
 
-#[rustc_on_unimplemented(message = "`{Self}` doesn't implement `DynSync`. \
+#[diagnostic::on_unimplemented(message = "`{Self}` doesn't implement `DynSync`. \
             Add it to `rustc_data_structures::marker` or use `IntoDynSyncSend` if it's already `Sync`")]
 // This is an auto trait for types which can be shared across threads if `sync::is_dyn_thread_safe()`
 // is true. These types can be wrapped in a `FromDyn` to get a `Sync` type. Wrapping a
@@ -180,6 +180,12 @@ impl<T> FromDyn<T> {
     }
 
     #[inline(always)]
+    pub fn derive<O>(&self, val: O) -> FromDyn<O> {
+        // We already did the check for `sync::is_dyn_thread_safe()` when creating `Self`
+        FromDyn(val)
+    }
+
+    #[inline(always)]
     pub fn into_inner(self) -> T {
         self.0
     }
@@ -200,6 +206,13 @@ impl<T> std::ops::Deref for FromDyn<T> {
     }
 }
 
+impl<T> std::ops::DerefMut for FromDyn<T> {
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
 // A wrapper to convert a struct that is already a `Send` or `Sync` into
 // an instance of `DynSend` and `DynSync`, since the compiler cannot infer
 // it automatically in some cases. (e.g. Box<dyn Send / Sync>)
diff --git a/compiler/rustc_data_structures/src/obligation_forest/mod.rs b/compiler/rustc_data_structures/src/obligation_forest/mod.rs
index f63b201742d..2c62034c6e8 100644
--- a/compiler/rustc_data_structures/src/obligation_forest/mod.rs
+++ b/compiler/rustc_data_structures/src/obligation_forest/mod.rs
@@ -315,7 +315,7 @@ mod helper {
     use super::*;
     pub(super) type ObligationTreeIdGenerator = impl Iterator<Item = ObligationTreeId>;
     impl<O: ForestObligation> ObligationForest<O> {
-        #[cfg_attr(not(bootstrap), define_opaque(ObligationTreeIdGenerator))]
+        #[define_opaque(ObligationTreeIdGenerator)]
         pub fn new() -> ObligationForest<O> {
             ObligationForest {
                 nodes: vec![],
diff --git a/compiler/rustc_data_structures/src/sync/freeze.rs b/compiler/rustc_data_structures/src/sync/freeze.rs
index 9720b22ea7d..6338afb92c3 100644
--- a/compiler/rustc_data_structures/src/sync/freeze.rs
+++ b/compiler/rustc_data_structures/src/sync/freeze.rs
@@ -88,7 +88,7 @@ impl<T> FreezeLock<T> {
     #[inline]
     #[track_caller]
     pub fn write(&self) -> FreezeWriteGuard<'_, T> {
-        self.try_write().expect("still mutable")
+        self.try_write().expect("data should not be frozen if we're still attempting to mutate it")
     }
 
     #[inline]
diff --git a/compiler/rustc_data_structures/src/sync/parallel.rs b/compiler/rustc_data_structures/src/sync/parallel.rs
index 8ef8a3f3585..ba3c85ef5b1 100644
--- a/compiler/rustc_data_structures/src/sync/parallel.rs
+++ b/compiler/rustc_data_structures/src/sync/parallel.rs
@@ -7,7 +7,6 @@ use std::any::Any;
 use std::panic::{AssertUnwindSafe, catch_unwind, resume_unwind};
 
 use parking_lot::Mutex;
-use rayon::iter::{FromParallelIterator, IntoParallelIterator, ParallelIterator};
 
 use crate::FatalErrorMarker;
 use crate::sync::{DynSend, DynSync, FromDyn, IntoDynSyncSend, mode};
@@ -97,11 +96,11 @@ macro_rules! parallel {
 // This function only works when `mode::is_dyn_thread_safe()`.
 pub fn scope<'scope, OP, R>(op: OP) -> R
 where
-    OP: FnOnce(&rayon::Scope<'scope>) -> R + DynSend,
+    OP: FnOnce(&rayon_core::Scope<'scope>) -> R + DynSend,
     R: DynSend,
 {
     let op = FromDyn::from(op);
-    rayon::scope(|s| FromDyn::from(op.into_inner()(s))).into_inner()
+    rayon_core::scope(|s| FromDyn::from(op.into_inner()(s))).into_inner()
 }
 
 #[inline]
@@ -114,7 +113,7 @@ where
         let oper_a = FromDyn::from(oper_a);
         let oper_b = FromDyn::from(oper_b);
         let (a, b) = parallel_guard(|guard| {
-            rayon::join(
+            rayon_core::join(
                 move || guard.run(move || FromDyn::from(oper_a.into_inner()())),
                 move || guard.run(move || FromDyn::from(oper_b.into_inner()())),
             )
@@ -125,56 +124,103 @@ where
     }
 }
 
-pub fn par_for_each_in<I, T: IntoIterator<Item = I> + IntoParallelIterator<Item = I>>(
+fn par_slice<I: DynSend>(
+    items: &mut [I],
+    guard: &ParallelGuard,
+    for_each: impl Fn(&mut I) + DynSync + DynSend,
+) {
+    struct State<'a, F> {
+        for_each: FromDyn<F>,
+        guard: &'a ParallelGuard,
+        group: usize,
+    }
+
+    fn par_rec<I: DynSend, F: Fn(&mut I) + DynSync + DynSend>(
+        items: &mut [I],
+        state: &State<'_, F>,
+    ) {
+        if items.len() <= state.group {
+            for item in items {
+                state.guard.run(|| (state.for_each)(item));
+            }
+        } else {
+            let (left, right) = items.split_at_mut(items.len() / 2);
+            let mut left = state.for_each.derive(left);
+            let mut right = state.for_each.derive(right);
+            rayon_core::join(move || par_rec(*left, state), move || par_rec(*right, state));
+        }
+    }
+
+    let state = State {
+        for_each: FromDyn::from(for_each),
+        guard,
+        group: std::cmp::max(items.len() / 128, 1),
+    };
+    par_rec(items, &state)
+}
+
+pub fn par_for_each_in<I: DynSend, T: IntoIterator<Item = I>>(
     t: T,
-    for_each: impl Fn(I) + DynSync + DynSend,
+    for_each: impl Fn(&I) + DynSync + DynSend,
 ) {
     parallel_guard(|guard| {
         if mode::is_dyn_thread_safe() {
-            let for_each = FromDyn::from(for_each);
-            t.into_par_iter().for_each(|i| {
-                guard.run(|| for_each(i));
-            });
+            let mut items: Vec<_> = t.into_iter().collect();
+            par_slice(&mut items, guard, |i| for_each(&*i))
         } else {
             t.into_iter().for_each(|i| {
-                guard.run(|| for_each(i));
+                guard.run(|| for_each(&i));
             });
         }
     });
 }
 
-pub fn try_par_for_each_in<
-    T: IntoIterator + IntoParallelIterator<Item = <T as IntoIterator>::Item>,
-    E: Send,
->(
+/// This runs `for_each` in parallel for each iterator item. If one or more of the
+/// `for_each` calls returns `Err`, the function will also return `Err`. The error returned
+/// will be non-deterministic, but this is expected to be used with `ErrorGuaranteed` which
+/// are all equivalent.
+pub fn try_par_for_each_in<T: IntoIterator, E: DynSend>(
     t: T,
-    for_each: impl Fn(<T as IntoIterator>::Item) -> Result<(), E> + DynSync + DynSend,
-) -> Result<(), E> {
+    for_each: impl Fn(&<T as IntoIterator>::Item) -> Result<(), E> + DynSync + DynSend,
+) -> Result<(), E>
+where
+    <T as IntoIterator>::Item: DynSend,
+{
     parallel_guard(|guard| {
         if mode::is_dyn_thread_safe() {
-            let for_each = FromDyn::from(for_each);
-            t.into_par_iter()
-                .filter_map(|i| guard.run(|| for_each(i)))
-                .reduce(|| Ok(()), Result::and)
+            let mut items: Vec<_> = t.into_iter().collect();
+
+            let error = Mutex::new(None);
+
+            par_slice(&mut items, guard, |i| {
+                if let Err(err) = for_each(&*i) {
+                    *error.lock() = Some(err);
+                }
+            });
+
+            if let Some(err) = error.into_inner() { Err(err) } else { Ok(()) }
         } else {
-            t.into_iter().filter_map(|i| guard.run(|| for_each(i))).fold(Ok(()), Result::and)
+            t.into_iter().filter_map(|i| guard.run(|| for_each(&i))).fold(Ok(()), Result::and)
         }
     })
 }
 
-pub fn par_map<
-    I,
-    T: IntoIterator<Item = I> + IntoParallelIterator<Item = I>,
-    R: std::marker::Send,
-    C: FromIterator<R> + FromParallelIterator<R>,
->(
+pub fn par_map<I: DynSend, T: IntoIterator<Item = I>, R: DynSend, C: FromIterator<R>>(
     t: T,
     map: impl Fn(I) -> R + DynSync + DynSend,
 ) -> C {
     parallel_guard(|guard| {
         if mode::is_dyn_thread_safe() {
             let map = FromDyn::from(map);
-            t.into_par_iter().filter_map(|i| guard.run(|| map(i))).collect()
+
+            let mut items: Vec<(Option<I>, Option<R>)> =
+                t.into_iter().map(|i| (Some(i), None)).collect();
+
+            par_slice(&mut items, guard, |i| {
+                i.1 = Some(map(i.0.take().unwrap()));
+            });
+
+            items.into_iter().filter_map(|i| i.1).collect()
         } else {
             t.into_iter().filter_map(|i| guard.run(|| map(i))).collect()
         }
diff --git a/compiler/rustc_data_structures/src/unord.rs b/compiler/rustc_data_structures/src/unord.rs
index baa66cd7c85..3d44fb1fd48 100644
--- a/compiler/rustc_data_structures/src/unord.rs
+++ b/compiler/rustc_data_structures/src/unord.rs
@@ -109,6 +109,16 @@ impl<T, I: Iterator<Item = T>> UnordItems<T, I> {
     pub fn collect<C: From<UnordItems<T, I>>>(self) -> C {
         self.into()
     }
+
+    /// If the iterator has only one element, returns it, otherwise returns `None`.
+    #[track_caller]
+    pub fn get_only(mut self) -> Option<T> {
+        let item = self.0.next();
+        if self.0.next().is_some() {
+            return None;
+        }
+        item
+    }
 }
 
 impl<T> UnordItems<T, std::iter::Empty<T>> {
diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index 381309f83b2..a03834c519d 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -3,7 +3,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 // tidy-alphabetical-end
diff --git a/compiler/rustc_driver_impl/Cargo.toml b/compiler/rustc_driver_impl/Cargo.toml
index de643355f5f..c823d11126e 100644
--- a/compiler/rustc_driver_impl/Cargo.toml
+++ b/compiler/rustc_driver_impl/Cargo.toml
@@ -4,6 +4,7 @@ version = "0.0.0"
 edition = "2024"
 
 [dependencies]
+jiff = { version = "0.2.5", default-features = false, features = ["std"] }
 # tidy-alphabetical-start
 rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
@@ -50,7 +51,6 @@ rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_ty_utils = { path = "../rustc_ty_utils" }
 serde_json = "1.0.59"
 shlex = "1.0"
-time = { version = "0.3.36", default-features = false, features = ["alloc", "formatting", "macros"] }
 tracing = { version = "0.1.35" }
 # tidy-alphabetical-end
 
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 595ac1edd28..40cc82727a5 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -7,7 +7,6 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(decl_macro)]
@@ -30,7 +29,7 @@ use std::path::{Path, PathBuf};
 use std::process::{self, Command, Stdio};
 use std::sync::OnceLock;
 use std::sync::atomic::{AtomicBool, Ordering};
-use std::time::{Instant, SystemTime};
+use std::time::Instant;
 use std::{env, str};
 
 use rustc_ast as ast;
@@ -66,8 +65,6 @@ use rustc_span::FileName;
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_target::json::ToJson;
 use rustc_target::spec::{Target, TargetTuple};
-use time::OffsetDateTime;
-use time::macros::format_description;
 use tracing::trace;
 
 #[allow(unused_macros)]
@@ -264,6 +261,7 @@ pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send))
         hash_untracked_state: None,
         register_lints: None,
         override_queries: None,
+        extra_symbols: Vec::new(),
         make_codegen_backend: None,
         registry: diagnostics_registry(),
         using_internal_features: &USING_INTERNAL_FEATURES,
@@ -348,10 +346,6 @@ pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send))
             // Make sure name resolution and macro expansion is run.
             let _ = tcx.resolver_for_lowering();
 
-            if let Some(metrics_dir) = &sess.opts.unstable_opts.metrics_dir {
-                dump_feature_usage_metrics(tcx, metrics_dir);
-            }
-
             if callbacks.after_expansion(compiler, tcx) == Compilation::Stop {
                 return early_exit();
             }
@@ -370,6 +364,10 @@ pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send))
 
             tcx.ensure_ok().analysis(());
 
+            if let Some(metrics_dir) = &sess.opts.unstable_opts.metrics_dir {
+                dump_feature_usage_metrics(tcx, metrics_dir);
+            }
+
             if callbacks.after_analysis(compiler, tcx) == Compilation::Stop {
                 return early_exit();
             }
@@ -1300,13 +1298,8 @@ fn ice_path_with_config(config: Option<&UnstableOptions>) -> &'static Option<Pat
                 .or_else(|| std::env::current_dir().ok())
                 .unwrap_or_default(),
         };
-        let now: OffsetDateTime = SystemTime::now().into();
-        let file_now = now
-            .format(
-                // Don't use a standard datetime format because Windows doesn't support `:` in paths
-                &format_description!("[year]-[month]-[day]T[hour]_[minute]_[second]"),
-            )
-            .unwrap_or_default();
+        // Don't use a standard datetime format because Windows doesn't support `:` in paths
+        let file_now = jiff::Zoned::now().strftime("%Y-%m-%dT%H_%M_%S");
         let pid = std::process::id();
         path.push(format!("rustc-ice-{file_now}-{pid}.txt"));
         Some(path)
diff --git a/compiler/rustc_error_codes/src/error_codes/E0622.md b/compiler/rustc_error_codes/src/error_codes/E0622.md
index 4cb605b636d..9b8131a061e 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0622.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0622.md
@@ -1,13 +1,16 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 An intrinsic was declared without being a function.
 
 Erroneous code example:
 
-```compile_fail,E0622
+```no_run
 #![feature(intrinsics)]
 #![allow(internal_features)]
 
-extern "rust-intrinsic" {
-    pub static atomic_singlethreadfence_seqcst: fn();
+extern "C" {
+    #[rustc_intrinsic]
+    pub static atomic_singlethreadfence_seqcst: unsafe fn();
     // error: intrinsic must be a function
 }
 
@@ -22,9 +25,8 @@ error, just declare a function. Example:
 #![feature(intrinsics)]
 #![allow(internal_features)]
 
-extern "rust-intrinsic" {
-    pub fn atomic_singlethreadfence_seqcst(); // ok!
-}
+#[rustc_intrinsic]
+pub unsafe fn atomic_singlethreadfence_seqcst(); // ok!
 
 fn main() { unsafe { atomic_singlethreadfence_seqcst(); } }
 ```
diff --git a/compiler/rustc_error_codes/src/error_codes/E0755.md b/compiler/rustc_error_codes/src/error_codes/E0755.md
index 88b7f484969..b67f078c78e 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0755.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0755.md
@@ -5,7 +5,7 @@ Erroneous code example:
 ```compile_fail,E0755
 #![feature(ffi_pure)]
 
-#[ffi_pure] // error!
+#[unsafe(ffi_pure)] // error!
 pub fn foo() {}
 # fn main() {}
 ```
@@ -17,7 +17,7 @@ side effects or infinite loops:
 #![feature(ffi_pure)]
 
 extern "C" {
-    #[ffi_pure] // ok!
+    #[unsafe(ffi_pure)] // ok!
     pub fn strlen(s: *const i8) -> isize;
 }
 # fn main() {}
diff --git a/compiler/rustc_error_codes/src/error_codes/E0756.md b/compiler/rustc_error_codes/src/error_codes/E0756.md
index ffdc421aab5..aadde038d12 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0756.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0756.md
@@ -6,7 +6,7 @@ Erroneous code example:
 ```compile_fail,E0756
 #![feature(ffi_const)]
 
-#[ffi_const] // error!
+#[unsafe(ffi_const)] // error!
 pub fn foo() {}
 # fn main() {}
 ```
@@ -18,7 +18,7 @@ which have no side effects except for their return value:
 #![feature(ffi_const)]
 
 extern "C" {
-    #[ffi_const] // ok!
+    #[unsafe(ffi_const)] // ok!
     pub fn strlen(s: *const i8) -> i32;
 }
 # fn main() {}
diff --git a/compiler/rustc_error_codes/src/error_codes/E0757.md b/compiler/rustc_error_codes/src/error_codes/E0757.md
index 41b06b23c4f..fb75b028f45 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0757.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0757.md
@@ -6,8 +6,9 @@ Erroneous code example:
 #![feature(ffi_const, ffi_pure)]
 
 extern "C" {
-    #[ffi_const]
-    #[ffi_pure] // error: `#[ffi_const]` function cannot be `#[ffi_pure]`
+    #[unsafe(ffi_const)]
+    #[unsafe(ffi_pure)]
+    //~^ ERROR `#[ffi_const]` function cannot be `#[ffi_pure]`
     pub fn square(num: i32) -> i32;
 }
 ```
@@ -19,7 +20,7 @@ As `ffi_const` provides stronger guarantees than `ffi_pure`, remove the
 #![feature(ffi_const)]
 
 extern "C" {
-    #[ffi_const]
+    #[unsafe(ffi_const)]
     pub fn square(num: i32) -> i32;
 }
 ```
diff --git a/compiler/rustc_error_codes/src/lib.rs b/compiler/rustc_error_codes/src/lib.rs
index dfeef5a957d..2488d870899 100644
--- a/compiler/rustc_error_codes/src/lib.rs
+++ b/compiler/rustc_error_codes/src/lib.rs
@@ -397,7 +397,7 @@ E0618: 0618,
 E0619: 0619,
 E0620: 0620,
 E0621: 0621,
-E0622: 0622,
+E0622: 0622, // REMOVED: rustc-intrinsic ABI was removed
 E0623: 0623,
 E0624: 0624,
 E0625: 0625,
diff --git a/compiler/rustc_error_messages/src/lib.rs b/compiler/rustc_error_messages/src/lib.rs
index 39e78ae8841..3c6df147b1b 100644
--- a/compiler/rustc_error_messages/src/lib.rs
+++ b/compiler/rustc_error_messages/src/lib.rs
@@ -208,7 +208,7 @@ pub type LazyFallbackBundle = Arc<LazyLock<FluentBundle, impl FnOnce() -> Fluent
 
 /// Return the default `FluentBundle` with standard "en-US" diagnostic messages.
 #[instrument(level = "trace", skip(resources))]
-#[cfg_attr(not(bootstrap), define_opaque(LazyFallbackBundle))]
+#[define_opaque(LazyFallbackBundle)]
 pub fn fallback_fluent_bundle(
     resources: Vec<&'static str>,
     with_directionality_markers: bool,
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 794502d7aae..539ecfbb42e 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -181,22 +181,9 @@ where
     Self: Sized,
 {
     /// Add a subdiagnostic to an existing diagnostic.
-    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
-        self.add_to_diag_with(diag, &|_, m| m);
-    }
-
-    /// Add a subdiagnostic to an existing diagnostic where `f` is invoked on every message used
-    /// (to optionally perform eager translation).
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    );
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>);
 }
 
-pub trait SubdiagMessageOp<G: EmissionGuarantee> =
-    Fn(&mut Diag<'_, G>, SubdiagMessage) -> SubdiagMessage;
-
 /// Trait implemented by lint types. This should not be implemented manually. Instead, use
 /// `#[derive(LintDiagnostic)]` -- see [rustc_macros::LintDiagnostic].
 #[rustc_diagnostic_item = "LintDiagnostic"]
@@ -647,9 +634,9 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
     #[rustc_lint_diagnostics]
     pub fn note_expected_found(
         &mut self,
-        expected_label: &dyn fmt::Display,
+        expected_label: &str,
         expected: DiagStyledString,
-        found_label: &dyn fmt::Display,
+        found_label: &str,
         found: DiagStyledString,
     ) -> &mut Self {
         self.note_expected_found_extra(
@@ -665,9 +652,9 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
     #[rustc_lint_diagnostics]
     pub fn note_expected_found_extra(
         &mut self,
-        expected_label: &dyn fmt::Display,
+        expected_label: &str,
         expected: DiagStyledString,
-        found_label: &dyn fmt::Display,
+        found_label: &str,
         found: DiagStyledString,
         expected_extra: DiagStyledString,
         found_extra: DiagStyledString,
@@ -1227,15 +1214,21 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
     /// interpolated variables).
     #[rustc_lint_diagnostics]
     pub fn subdiagnostic(&mut self, subdiagnostic: impl Subdiagnostic) -> &mut Self {
-        let dcx = self.dcx;
-        subdiagnostic.add_to_diag_with(self, &|diag, msg| {
-            let args = diag.args.iter();
-            let msg = diag.subdiagnostic_message_to_diagnostic_message(msg);
-            dcx.eagerly_translate(msg, args)
-        });
+        subdiagnostic.add_to_diag(self);
         self
     }
 
+    /// Fluent variables are not namespaced from each other, so when
+    /// `Diagnostic`s and `Subdiagnostic`s use the same variable name,
+    /// one value will clobber the other. Eagerly translating the
+    /// diagnostic uses the variables defined right then, before the
+    /// clobbering occurs.
+    pub fn eagerly_translate(&self, msg: impl Into<SubdiagMessage>) -> SubdiagMessage {
+        let args = self.args.iter();
+        let msg = self.subdiagnostic_message_to_diagnostic_message(msg.into());
+        self.dcx.eagerly_translate(msg, args)
+    }
+
     with_fn! { with_span,
     /// Add a span.
     #[rustc_lint_diagnostics]
diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index cb2e1769fa1..8b59ba9984c 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -19,7 +19,7 @@ use {rustc_ast as ast, rustc_hir as hir};
 use crate::diagnostic::DiagLocation;
 use crate::{
     Diag, DiagArgValue, DiagCtxtHandle, Diagnostic, EmissionGuarantee, ErrCode, IntoDiagArg, Level,
-    SubdiagMessageOp, Subdiagnostic, fluent_generated as fluent,
+    Subdiagnostic, fluent_generated as fluent,
 };
 
 pub struct DiagArgFromDisplay<'a>(pub &'a dyn fmt::Display);
@@ -384,11 +384,7 @@ pub struct SingleLabelManySpans {
     pub label: &'static str,
 }
 impl Subdiagnostic for SingleLabelManySpans {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.span_labels(self.spans, self.label);
     }
 }
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index f5f7618285e..c0c5dba4677 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -47,7 +47,7 @@ pub use codes::*;
 pub use diagnostic::{
     BugAbort, Diag, DiagArg, DiagArgMap, DiagArgName, DiagArgValue, DiagInner, DiagStyledString,
     Diagnostic, EmissionGuarantee, FatalAbort, IntoDiagArg, LintDiagnostic, StringPart, Subdiag,
-    SubdiagMessageOp, Subdiagnostic,
+    Subdiagnostic,
 };
 pub use diagnostic_impls::{
     DiagArgFromDisplay, DiagSymbolList, ElidedLifetimeInPathSubdiag, ExpectedLifetimeParameter,
@@ -589,7 +589,8 @@ struct DiagCtxtInner {
     /// add more information). All stashed diagnostics must be emitted with
     /// `emit_stashed_diagnostics` by the time the `DiagCtxtInner` is dropped,
     /// otherwise an assertion failure will occur.
-    stashed_diagnostics: FxIndexMap<(Span, StashKey), (DiagInner, Option<ErrorGuaranteed>)>,
+    stashed_diagnostics:
+        FxIndexMap<StashKey, FxIndexMap<Span, (DiagInner, Option<ErrorGuaranteed>)>>,
 
     future_breakage_diagnostics: Vec<DiagInner>,
 
@@ -912,8 +913,12 @@ impl<'a> DiagCtxtHandle<'a> {
         // FIXME(Centril, #69537): Consider reintroducing panic on overwriting a stashed diagnostic
         // if/when we have a more robust macro-friendly replacement for `(span, key)` as a key.
         // See the PR for a discussion.
-        let key = (span.with_parent(None), key);
-        self.inner.borrow_mut().stashed_diagnostics.insert(key, (diag, guar));
+        self.inner
+            .borrow_mut()
+            .stashed_diagnostics
+            .entry(key)
+            .or_default()
+            .insert(span.with_parent(None), (diag, guar));
 
         guar
     }
@@ -922,9 +927,10 @@ impl<'a> DiagCtxtHandle<'a> {
     /// and [`StashKey`] as the key. Panics if the found diagnostic is an
     /// error.
     pub fn steal_non_err(self, span: Span, key: StashKey) -> Option<Diag<'a, ()>> {
-        let key = (span.with_parent(None), key);
         // FIXME(#120456) - is `swap_remove` correct?
-        let (diag, guar) = self.inner.borrow_mut().stashed_diagnostics.swap_remove(&key)?;
+        let (diag, guar) = self.inner.borrow_mut().stashed_diagnostics.get_mut(&key).and_then(
+            |stashed_diagnostics| stashed_diagnostics.swap_remove(&span.with_parent(None)),
+        )?;
         assert!(!diag.is_error());
         assert!(guar.is_none());
         Some(Diag::new_diagnostic(self, diag))
@@ -943,9 +949,10 @@ impl<'a> DiagCtxtHandle<'a> {
     where
         F: FnMut(&mut Diag<'_>),
     {
-        let key = (span.with_parent(None), key);
         // FIXME(#120456) - is `swap_remove` correct?
-        let err = self.inner.borrow_mut().stashed_diagnostics.swap_remove(&key);
+        let err = self.inner.borrow_mut().stashed_diagnostics.get_mut(&key).and_then(
+            |stashed_diagnostics| stashed_diagnostics.swap_remove(&span.with_parent(None)),
+        );
         err.map(|(err, guar)| {
             // The use of `::<ErrorGuaranteed>` is safe because level is `Level::Error`.
             assert_eq!(err.level, Error);
@@ -966,9 +973,10 @@ impl<'a> DiagCtxtHandle<'a> {
         key: StashKey,
         new_err: Diag<'_>,
     ) -> ErrorGuaranteed {
-        let key = (span.with_parent(None), key);
         // FIXME(#120456) - is `swap_remove` correct?
-        let old_err = self.inner.borrow_mut().stashed_diagnostics.swap_remove(&key);
+        let old_err = self.inner.borrow_mut().stashed_diagnostics.get_mut(&key).and_then(
+            |stashed_diagnostics| stashed_diagnostics.swap_remove(&span.with_parent(None)),
+        );
         match old_err {
             Some((old_err, guar)) => {
                 assert_eq!(old_err.level, Error);
@@ -983,7 +991,14 @@ impl<'a> DiagCtxtHandle<'a> {
     }
 
     pub fn has_stashed_diagnostic(&self, span: Span, key: StashKey) -> bool {
-        self.inner.borrow().stashed_diagnostics.get(&(span.with_parent(None), key)).is_some()
+        let inner = self.inner.borrow();
+        if let Some(stashed_diagnostics) = inner.stashed_diagnostics.get(&key)
+            && !stashed_diagnostics.is_empty()
+        {
+            stashed_diagnostics.contains_key(&span.with_parent(None))
+        } else {
+            false
+        }
     }
 
     /// Emit all stashed diagnostics.
@@ -997,7 +1012,11 @@ impl<'a> DiagCtxtHandle<'a> {
         let inner = self.inner.borrow();
         inner.err_guars.len()
             + inner.lint_err_guars.len()
-            + inner.stashed_diagnostics.values().filter(|(_diag, guar)| guar.is_some()).count()
+            + inner
+                .stashed_diagnostics
+                .values()
+                .map(|a| a.values().filter(|(_, guar)| guar.is_some()).count())
+                .sum::<usize>()
     }
 
     /// This excludes lint errors and delayed bugs. Unless absolutely
@@ -1486,16 +1505,18 @@ impl DiagCtxtInner {
     fn emit_stashed_diagnostics(&mut self) -> Option<ErrorGuaranteed> {
         let mut guar = None;
         let has_errors = !self.err_guars.is_empty();
-        for (_, (diag, _guar)) in std::mem::take(&mut self.stashed_diagnostics).into_iter() {
-            if !diag.is_error() {
-                // Unless they're forced, don't flush stashed warnings when
-                // there are errors, to avoid causing warning overload. The
-                // stash would've been stolen already if it were important.
-                if !diag.is_force_warn() && has_errors {
-                    continue;
+        for (_, stashed_diagnostics) in std::mem::take(&mut self.stashed_diagnostics).into_iter() {
+            for (_, (diag, _guar)) in stashed_diagnostics {
+                if !diag.is_error() {
+                    // Unless they're forced, don't flush stashed warnings when
+                    // there are errors, to avoid causing warning overload. The
+                    // stash would've been stolen already if it were important.
+                    if !diag.is_force_warn() && has_errors {
+                        continue;
+                    }
                 }
+                guar = guar.or(self.emit_diagnostic(diag, None));
             }
-            guar = guar.or(self.emit_diagnostic(diag, None));
         }
         guar
     }
@@ -1688,6 +1709,7 @@ impl DiagCtxtInner {
             if let Some((_diag, guar)) = self
                 .stashed_diagnostics
                 .values()
+                .flat_map(|stashed_diagnostics| stashed_diagnostics.values())
                 .find(|(diag, guar)| guar.is_some() && diag.is_lint.is_none())
             {
                 *guar
@@ -1700,13 +1722,9 @@ impl DiagCtxtInner {
     fn has_errors(&self) -> Option<ErrorGuaranteed> {
         self.err_guars.get(0).copied().or_else(|| self.lint_err_guars.get(0).copied()).or_else(
             || {
-                if let Some((_diag, guar)) =
-                    self.stashed_diagnostics.values().find(|(_diag, guar)| guar.is_some())
-                {
-                    *guar
-                } else {
-                    None
-                }
+                self.stashed_diagnostics.values().find_map(|stashed_diagnostics| {
+                    stashed_diagnostics.values().find_map(|(_, guar)| *guar)
+                })
             },
         )
     }
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index d14e476ba32..f5eaf7d616b 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -824,10 +824,10 @@ impl SyntaxExtension {
             return Err(item.span);
         }
 
-        match item.name_or_empty() {
-            sym::no => Ok(CollapseMacroDebuginfo::No),
-            sym::external => Ok(CollapseMacroDebuginfo::External),
-            sym::yes => Ok(CollapseMacroDebuginfo::Yes),
+        match item.name() {
+            Some(sym::no) => Ok(CollapseMacroDebuginfo::No),
+            Some(sym::external) => Ok(CollapseMacroDebuginfo::External),
+            Some(sym::yes) => Ok(CollapseMacroDebuginfo::Yes),
             _ => Err(item.path.span),
         }
     }
@@ -1102,7 +1102,7 @@ pub trait ResolverExpand {
     /// HIR proc macros items back to their harness items.
     fn declare_proc_macro(&mut self, id: NodeId);
 
-    fn append_stripped_cfg_item(&mut self, parent_node: NodeId, name: Ident, cfg: ast::MetaItem);
+    fn append_stripped_cfg_item(&mut self, parent_node: NodeId, ident: Ident, cfg: ast::MetaItem);
 
     /// Tools registered with `#![register_tool]` and used by tool attributes and lints.
     fn registered_tools(&self) -> &RegisteredTools;
diff --git a/compiler/rustc_expand/src/build.rs b/compiler/rustc_expand/src/build.rs
index f68172c1f67..6d616cf84bb 100644
--- a/compiler/rustc_expand/src/build.rs
+++ b/compiler/rustc_expand/src/build.rs
@@ -230,6 +230,7 @@ impl<'a> ExtCtxt<'a> {
             self.pat_ident(sp, ident)
         };
         let local = P(ast::Local {
+            super_: None,
             pat,
             ty,
             id: ast::DUMMY_NODE_ID,
@@ -245,6 +246,7 @@ impl<'a> ExtCtxt<'a> {
     /// Generates `let _: Type;`, which is usually used for type assertions.
     pub fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
         let local = P(ast::Local {
+            super_: None,
             pat: self.pat_wild(span),
             ty: Some(ty),
             id: ast::DUMMY_NODE_ID,
diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index bcc2703c39b..c70e259b2cd 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -238,18 +238,6 @@ impl<'a> StripUnconfigured<'a> {
                     Some(AttrTokenTree::Delimited(sp, spacing, delim, inner))
                 }
                 AttrTokenTree::Token(
-                    Token {
-                        kind:
-                            TokenKind::NtIdent(..)
-                            | TokenKind::NtLifetime(..)
-                            | TokenKind::Interpolated(..),
-                        ..
-                    },
-                    _,
-                ) => {
-                    panic!("Nonterminal should have been flattened: {:?}", tree);
-                }
-                AttrTokenTree::Token(
                     Token { kind: TokenKind::OpenDelim(_) | TokenKind::CloseDelim(_), .. },
                     _,
                 ) => {
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index bca846d2ec4..1e26d668194 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -1169,9 +1169,9 @@ trait InvocationCollectorNode: HasAttrs + HasNodeId + Sized {
         collector.cx.dcx().emit_err(RemoveNodeNotSupported { span, descr: Self::descr() });
     }
 
-    /// All of the names (items) declared by this node.
+    /// All of the identifiers (items) declared by this node.
     /// This is an approximation and should only be used for diagnostics.
-    fn declared_names(&self) -> Vec<Ident> {
+    fn declared_idents(&self) -> Vec<Ident> {
         vec![]
     }
 }
@@ -1306,7 +1306,7 @@ impl InvocationCollectorNode for P<ast::Item> {
         res
     }
 
-    fn declared_names(&self) -> Vec<Ident> {
+    fn declared_idents(&self) -> Vec<Ident> {
         if let ItemKind::Use(ut) = &self.kind {
             fn collect_use_tree_leaves(ut: &ast::UseTree, idents: &mut Vec<Ident>) {
                 match &ut.kind {
@@ -2053,25 +2053,25 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     ) -> Node::OutputTy {
         loop {
             return match self.take_first_attr(&mut node) {
-                Some((attr, pos, derives)) => match attr.name_or_empty() {
-                    sym::cfg => {
+                Some((attr, pos, derives)) => match attr.name() {
+                    Some(sym::cfg) => {
                         let (res, meta_item) = self.expand_cfg_true(&mut node, attr, pos);
                         if res {
                             continue;
                         }
 
                         if let Some(meta_item) = meta_item {
-                            for name in node.declared_names() {
+                            for ident in node.declared_idents() {
                                 self.cx.resolver.append_stripped_cfg_item(
                                     self.cx.current_expansion.lint_node_id,
-                                    name,
+                                    ident,
                                     meta_item.clone(),
                                 )
                             }
                         }
                         Default::default()
                     }
-                    sym::cfg_attr => {
+                    Some(sym::cfg_attr) => {
                         self.expand_cfg_attr(&mut node, &attr, pos);
                         continue;
                     }
@@ -2144,8 +2144,8 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     ) {
         loop {
             return match self.take_first_attr(node) {
-                Some((attr, pos, derives)) => match attr.name_or_empty() {
-                    sym::cfg => {
+                Some((attr, pos, derives)) => match attr.name() {
+                    Some(sym::cfg) => {
                         let span = attr.span;
                         if self.expand_cfg_true(node, attr, pos).0 {
                             continue;
@@ -2154,7 +2154,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         node.expand_cfg_false(self, pos, span);
                         continue;
                     }
-                    sym::cfg_attr => {
+                    Some(sym::cfg_attr) => {
                         self.expand_cfg_attr(node, &attr, pos);
                         continue;
                     }
diff --git a/compiler/rustc_expand/src/mbe/diagnostics.rs b/compiler/rustc_expand/src/mbe/diagnostics.rs
index e60a9e83184..b663e959744 100644
--- a/compiler/rustc_expand/src/mbe/diagnostics.rs
+++ b/compiler/rustc_expand/src/mbe/diagnostics.rs
@@ -66,9 +66,7 @@ pub(super) fn failed_to_match_macro(
     }
 
     if let MatcherLoc::Token { token: expected_token } = &remaining_matcher
-        && (matches!(expected_token.kind, TokenKind::Interpolated(_))
-            || matches!(token.kind, TokenKind::Interpolated(_))
-            || matches!(expected_token.kind, TokenKind::OpenDelim(Delimiter::Invisible(_)))
+        && (matches!(expected_token.kind, TokenKind::OpenDelim(Delimiter::Invisible(_)))
             || matches!(token.kind, TokenKind::OpenDelim(Delimiter::Invisible(_))))
     {
         err.note("captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens");
@@ -162,7 +160,7 @@ impl<'dcx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'dcx, 'match
                     .is_none_or(|failure| failure.is_better_position(*approx_position))
                 {
                     self.best_failure = Some(BestFailure {
-                        token: token.clone(),
+                        token: *token,
                         position_in_tokenstream: *approx_position,
                         msg,
                         remaining_matcher: self
diff --git a/compiler/rustc_expand/src/mbe/macro_parser.rs b/compiler/rustc_expand/src/mbe/macro_parser.rs
index d709fd79281..0065f83eb4e 100644
--- a/compiler/rustc_expand/src/mbe/macro_parser.rs
+++ b/compiler/rustc_expand/src/mbe/macro_parser.rs
@@ -179,7 +179,7 @@ pub(super) fn compute_locs(matcher: &[TokenTree]) -> Vec<MatcherLoc> {
         for tt in tts {
             match tt {
                 TokenTree::Token(token) => {
-                    locs.push(MatcherLoc::Token { token: token.clone() });
+                    locs.push(MatcherLoc::Token { token: *token });
                 }
                 TokenTree::Delimited(span, _, delimited) => {
                     let open_token = Token::new(token::OpenDelim(delimited.delim), span.open);
@@ -648,7 +648,7 @@ impl TtParser {
                     // There are no possible next positions AND we aren't waiting for the black-box
                     // parser: syntax error.
                     return Failure(T::build_failure(
-                        parser.token.clone(),
+                        parser.token,
                         parser.approx_token_stream_pos(),
                         "no rules expected this token in macro call",
                     ));
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index 77ec598e62a..c138b090877 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -12,7 +12,7 @@ use rustc_ast::{self as ast, DUMMY_NODE_ID, NodeId};
 use rustc_ast_pretty::pprust;
 use rustc_attr_parsing::{AttributeKind, find_attr};
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
-use rustc_errors::{Applicability, ErrorGuaranteed};
+use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
 use rustc_feature::Features;
 use rustc_hir as hir;
 use rustc_lint_defs::BuiltinLintDiag;
@@ -27,19 +27,18 @@ use rustc_span::hygiene::Transparency;
 use rustc_span::{Ident, MacroRulesNormalizedIdent, Span, kw, sym};
 use tracing::{debug, instrument, trace, trace_span};
 
-use super::diagnostics;
 use super::macro_parser::{NamedMatches, NamedParseResult};
+use super::{SequenceRepetition, diagnostics};
 use crate::base::{
     DummyResult, ExpandResult, ExtCtxt, MacResult, MacroExpanderResult, SyntaxExtension,
     SyntaxExtensionKind, TTMacroExpander,
 };
 use crate::expand::{AstFragment, AstFragmentKind, ensure_complete_parse, parse_ast_fragment};
-use crate::mbe;
 use crate::mbe::diagnostics::{annotate_doc_comment, parse_failure_msg};
-use crate::mbe::macro_check;
 use crate::mbe::macro_parser::NamedMatch::*;
 use crate::mbe::macro_parser::{Error, ErrorReported, Failure, MatcherLoc, Success, TtParser};
 use crate::mbe::transcribe::transcribe;
+use crate::mbe::{self, KleeneOp, macro_check};
 
 pub(crate) struct ParserAnyMacro<'a> {
     parser: Parser<'a>,
@@ -640,6 +639,37 @@ fn is_empty_token_tree(sess: &Session, seq: &mbe::SequenceRepetition) -> bool {
     }
 }
 
+/// Checks if a `vis` nonterminal fragment is unnecessarily wrapped in an optional repetition.
+///
+/// When a `vis` fragment (which can already be empty) is wrapped in `$(...)?`,
+/// this suggests removing the redundant repetition syntax since it provides no additional benefit.
+fn check_redundant_vis_repetition(
+    err: &mut Diag<'_>,
+    sess: &Session,
+    seq: &SequenceRepetition,
+    span: &DelimSpan,
+) {
+    let is_zero_or_one: bool = seq.kleene.op == KleeneOp::ZeroOrOne;
+    let is_vis = seq.tts.first().map_or(false, |tt| {
+        matches!(tt, mbe::TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)))
+    });
+
+    if is_vis && is_zero_or_one {
+        err.note("a `vis` fragment can already be empty");
+        err.multipart_suggestion(
+            "remove the `$(` and `)?`",
+            vec![
+                (
+                    sess.source_map().span_extend_to_prev_char_before(span.open, '$', true),
+                    "".to_string(),
+                ),
+                (span.close.with_hi(seq.kleene.span.hi()), "".to_string()),
+            ],
+            Applicability::MaybeIncorrect,
+        );
+    }
+}
+
 /// Checks that the lhs contains no repetition which could match an empty token
 /// tree, because then the matcher would hang indefinitely.
 fn check_lhs_no_empty_seq(sess: &Session, tts: &[mbe::TokenTree]) -> Result<(), ErrorGuaranteed> {
@@ -654,8 +684,10 @@ fn check_lhs_no_empty_seq(sess: &Session, tts: &[mbe::TokenTree]) -> Result<(),
             TokenTree::Sequence(span, seq) => {
                 if is_empty_token_tree(sess, seq) {
                     let sp = span.entire();
-                    let guar = sess.dcx().span_err(sp, "repetition matches empty token tree");
-                    return Err(guar);
+                    let mut err =
+                        sess.dcx().struct_span_err(sp, "repetition matches empty token tree");
+                    check_redundant_vis_repetition(&mut err, sess, seq, span);
+                    return Err(err.emit());
                 }
                 check_lhs_no_empty_seq(sess, &seq.tts)?
             }
@@ -778,7 +810,7 @@ impl<'tt> FirstSets<'tt> {
                         // token could be the separator token itself.
 
                         if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
-                            first.add_one_maybe(TtHandle::from_token(sep.clone()));
+                            first.add_one_maybe(TtHandle::from_token(*sep));
                         }
 
                         // Reverse scan: Sequence comes before `first`.
@@ -841,7 +873,7 @@ impl<'tt> FirstSets<'tt> {
                     // If the sequence contents can be empty, then the first
                     // token could be the separator token itself.
                     if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
-                        first.add_one_maybe(TtHandle::from_token(sep.clone()));
+                        first.add_one_maybe(TtHandle::from_token(*sep));
                     }
 
                     assert!(first.maybe_empty);
@@ -917,7 +949,7 @@ impl<'tt> Clone for TtHandle<'tt> {
             // This variant *must* contain a `mbe::TokenTree::Token`, and not
             // any other variant of `mbe::TokenTree`.
             TtHandle::Token(mbe::TokenTree::Token(tok)) => {
-                TtHandle::Token(mbe::TokenTree::Token(tok.clone()))
+                TtHandle::Token(mbe::TokenTree::Token(*tok))
             }
 
             _ => unreachable!(),
@@ -1093,7 +1125,7 @@ fn check_matcher_core<'tt>(
                 let mut new;
                 let my_suffix = if let Some(sep) = &seq_rep.separator {
                     new = suffix_first.clone();
-                    new.add_one_maybe(TtHandle::from_token(sep.clone()));
+                    new.add_one_maybe(TtHandle::from_token(*sep));
                     &new
                 } else {
                     &suffix_first
diff --git a/compiler/rustc_expand/src/mbe/quoted.rs b/compiler/rustc_expand/src/mbe/quoted.rs
index 0ea53627fe7..3f037259956 100644
--- a/compiler/rustc_expand/src/mbe/quoted.rs
+++ b/compiler/rustc_expand/src/mbe/quoted.rs
@@ -283,7 +283,7 @@ fn parse_tree<'a>(
         }
 
         // `tree` is an arbitrary token. Keep it.
-        tokenstream::TokenTree::Token(token, _) => TokenTree::Token(token.clone()),
+        tokenstream::TokenTree::Token(token, _) => TokenTree::Token(*token),
 
         // `tree` is the beginning of a delimited set of tokens (e.g., `(` or `{`). We need to
         // descend into the delimited set and further parse it.
@@ -321,7 +321,7 @@ fn parse_kleene_op(
     match iter.next() {
         Some(tokenstream::TokenTree::Token(token, _)) => match kleene_op(token) {
             Some(op) => Ok(Ok((op, token.span))),
-            None => Ok(Err(token.clone())),
+            None => Ok(Err(*token)),
         },
         tree => Err(tree.map_or(span, tokenstream::TokenTree::span)),
     }
diff --git a/compiler/rustc_expand/src/mbe/transcribe.rs b/compiler/rustc_expand/src/mbe/transcribe.rs
index 6e47ed6eb67..39186319b1c 100644
--- a/compiler/rustc_expand/src/mbe/transcribe.rs
+++ b/compiler/rustc_expand/src/mbe/transcribe.rs
@@ -1,5 +1,4 @@
 use std::mem;
-use std::sync::Arc;
 
 use rustc_ast::mut_visit::{self, MutVisitor};
 use rustc_ast::token::{
@@ -165,7 +164,7 @@ pub(super) fn transcribe<'a>(
                 if repeat_idx < repeat_len {
                     frame.idx = 0;
                     if let Some(sep) = sep {
-                        result.push(TokenTree::Token(sep.clone(), Spacing::Alone));
+                        result.push(TokenTree::Token(*sep, Spacing::Alone));
                     }
                     continue;
                 }
@@ -307,7 +306,9 @@ pub(super) fn transcribe<'a>(
                     let tt = match cur_matched {
                         MatchedSingle(ParseNtResult::Tt(tt)) => {
                             // `tt`s are emitted into the output stream directly as "raw tokens",
-                            // without wrapping them into groups.
+                            // without wrapping them into groups. Other variables are emitted into
+                            // the output stream as groups with `Delimiter::Invisible` to maintain
+                            // parsing priorities.
                             maybe_use_metavar_location(psess, &stack, sp, tt, &mut marker)
                         }
                         MatchedSingle(ParseNtResult::Ident(ident, is_raw)) => {
@@ -325,6 +326,11 @@ pub(super) fn transcribe<'a>(
                         MatchedSingle(ParseNtResult::Item(item)) => {
                             mk_delimited(item.span, MetaVarKind::Item, TokenStream::from_ast(item))
                         }
+                        MatchedSingle(ParseNtResult::Block(block)) => mk_delimited(
+                            block.span,
+                            MetaVarKind::Block,
+                            TokenStream::from_ast(block),
+                        ),
                         MatchedSingle(ParseNtResult::Stmt(stmt)) => {
                             let stream = if let StmtKind::Empty = stmt.kind {
                                 // FIXME: Properly collect tokens for empty statements.
@@ -385,15 +391,6 @@ pub(super) fn transcribe<'a>(
                         MatchedSingle(ParseNtResult::Vis(vis)) => {
                             mk_delimited(vis.span, MetaVarKind::Vis, TokenStream::from_ast(vis))
                         }
-                        MatchedSingle(ParseNtResult::Nt(nt)) => {
-                            // Other variables are emitted into the output stream as groups with
-                            // `Delimiter::Invisible` to maintain parsing priorities.
-                            // `Interpolated` is currently used for such groups in rustc parser.
-                            marker.visit_span(&mut sp);
-                            let use_span = nt.use_span();
-                            with_metavar_spans(|mspans| mspans.insert(use_span, sp));
-                            TokenTree::token_alone(token::Interpolated(Arc::clone(nt)), sp)
-                        }
                         MatchedSeq(..) => {
                             // We were unable to descend far enough. This is an error.
                             return Err(dcx.create_err(VarStillRepeating { span: sp, ident }));
@@ -441,7 +438,7 @@ pub(super) fn transcribe<'a>(
             // Nothing much to do here. Just push the token to the result, being careful to
             // preserve syntax context.
             mbe::TokenTree::Token(token) => {
-                let mut token = token.clone();
+                let mut token = *token;
                 mut_visit::visit_token(&mut marker, &mut token);
                 let tt = TokenTree::Token(token, Spacing::Alone);
                 result.push(tt);
diff --git a/compiler/rustc_expand/src/proc_macro_server.rs b/compiler/rustc_expand/src/proc_macro_server.rs
index ee6306e3961..4edaf68c89a 100644
--- a/compiler/rustc_expand/src/proc_macro_server.rs
+++ b/compiler/rustc_expand/src/proc_macro_server.rs
@@ -1,5 +1,4 @@
 use std::ops::{Bound, Range};
-use std::sync::Arc;
 
 use ast::token::IdentIsRaw;
 use pm::bridge::{
@@ -18,7 +17,7 @@ use rustc_parse::parser::Parser;
 use rustc_parse::{exp, new_parser_from_source_str, source_str_to_stream, unwrap_or_emit_fatal};
 use rustc_session::parse::ParseSess;
 use rustc_span::def_id::CrateNum;
-use rustc_span::{BytePos, FileName, Pos, SourceFile, Span, Symbol, sym};
+use rustc_span::{BytePos, FileName, Pos, Span, Symbol, sym};
 use smallvec::{SmallVec, smallvec};
 
 use crate::base::ExtCtxt;
@@ -309,15 +308,6 @@ impl FromInternal<(TokenStream, &mut Rustc<'_, '_>)> for Vec<TokenTree<TokenStre
                     }));
                 }
 
-                Interpolated(nt) => {
-                    let stream = TokenStream::from_nonterminal_ast(&nt);
-                    trees.push(TokenTree::Group(Group {
-                        delimiter: pm::Delimiter::None,
-                        stream: Some(stream),
-                        span: DelimSpan::from_single(span),
-                    }))
-                }
-
                 OpenDelim(..) | CloseDelim(..) => unreachable!(),
                 Eof => unreachable!(),
             }
@@ -467,7 +457,6 @@ impl<'a, 'b> Rustc<'a, 'b> {
 impl server::Types for Rustc<'_, '_> {
     type FreeFunctions = FreeFunctions;
     type TokenStream = TokenStream;
-    type SourceFile = Arc<SourceFile>;
     type Span = Span;
     type Symbol = Symbol;
 }
@@ -673,28 +662,6 @@ impl server::TokenStream for Rustc<'_, '_> {
     }
 }
 
-impl server::SourceFile for Rustc<'_, '_> {
-    fn eq(&mut self, file1: &Self::SourceFile, file2: &Self::SourceFile) -> bool {
-        Arc::ptr_eq(file1, file2)
-    }
-
-    fn path(&mut self, file: &Self::SourceFile) -> String {
-        match &file.name {
-            FileName::Real(name) => name
-                .local_path()
-                .expect("attempting to get a file path in an imported file in `proc_macro::SourceFile::path`")
-                .to_str()
-                .expect("non-UTF8 file path in `proc_macro::SourceFile::path`")
-                .to_string(),
-            _ => file.name.prefer_local().to_string(),
-        }
-    }
-
-    fn is_real(&mut self, file: &Self::SourceFile) -> bool {
-        file.is_real_file()
-    }
-}
-
 impl server::Span for Rustc<'_, '_> {
     fn debug(&mut self, span: Self::Span) -> String {
         if self.ecx.ecfg.span_debug {
@@ -704,8 +671,29 @@ impl server::Span for Rustc<'_, '_> {
         }
     }
 
-    fn source_file(&mut self, span: Self::Span) -> Self::SourceFile {
-        self.psess().source_map().lookup_char_pos(span.lo()).file
+    fn file(&mut self, span: Self::Span) -> String {
+        self.psess()
+            .source_map()
+            .lookup_char_pos(span.lo())
+            .file
+            .name
+            .prefer_remapped_unconditionaly()
+            .to_string()
+    }
+
+    fn local_file(&mut self, span: Self::Span) -> Option<String> {
+        self.psess()
+            .source_map()
+            .lookup_char_pos(span.lo())
+            .file
+            .name
+            .clone()
+            .into_local_path()
+            .map(|p| {
+                p.to_str()
+                    .expect("non-UTF8 file path in `proc_macro::SourceFile::path`")
+                    .to_string()
+            })
     }
 
     fn parent(&mut self, span: Self::Span) -> Option<Self::Span> {
diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 88e6593572b..fcc11dd3c1f 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -63,7 +63,7 @@ declare_features! (
     /// Allows using `const` operands in inline assembly.
     (accepted, asm_const, "1.82.0", Some(93332)),
     /// Allows using `label` operands in inline assembly.
-    (accepted, asm_goto, "CURRENT_RUSTC_VERSION", Some(119364)),
+    (accepted, asm_goto, "1.87.0", Some(119364)),
     /// Allows using `sym` operands in inline assembly.
     (accepted, asm_sym, "1.66.0", Some(93333)),
     /// Allows the definition of associated constants in `trait` or `impl` blocks.
@@ -95,6 +95,8 @@ declare_features! (
     (accepted, c_unwind, "1.81.0", Some(74990)),
     /// Allows `#[cfg_attr(predicate, multiple, attributes, here)]`.
     (accepted, cfg_attr_multi, "1.33.0", Some(54881)),
+    /// Allows the use of `#[cfg(<true/false>)]`.
+    (accepted, cfg_boolean_literals, "CURRENT_RUSTC_VERSION", Some(131204)),
     /// Allows the use of `#[cfg(doctest)]`, set when rustdoc is collecting doctests.
     (accepted, cfg_doctest, "1.40.0", Some(62210)),
     /// Enables `#[cfg(panic = "...")]` config key.
@@ -332,7 +334,7 @@ declare_features! (
     /// Allows `use<'a, 'b, A, B>` in `impl Trait + use<...>` for precise capture of generic args.
     (accepted, precise_capturing, "1.82.0", Some(123432)),
     /// Allows `use<..>` precise capturign on impl Trait in traits.
-    (accepted, precise_capturing_in_traits, "CURRENT_RUSTC_VERSION", Some(130044)),
+    (accepted, precise_capturing_in_traits, "1.87.0", Some(130044)),
     /// Allows procedural macros in `proc-macro` crates.
     (accepted, proc_macro, "1.29.0", Some(38356)),
     /// Allows multi-segment paths in attributes and derives.
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 1e33e2e9393..3b441729d75 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -6,6 +6,7 @@ use AttributeDuplicates::*;
 use AttributeGate::*;
 use AttributeType::*;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_span::edition::Edition;
 use rustc_span::{Symbol, sym};
 
 use crate::{Features, Stability};
@@ -65,9 +66,12 @@ pub enum AttributeSafety {
     /// Normal attribute that does not need `#[unsafe(...)]`
     Normal,
 
-    /// Unsafe attribute that requires safety obligations
-    /// to be discharged
-    Unsafe,
+    /// Unsafe attribute that requires safety obligations to be discharged.
+    ///
+    /// An error is emitted when `#[unsafe(...)]` is omitted, except when the attribute's edition
+    /// is less than the one stored in `unsafe_since`. This handles attributes that were safe in
+    /// earlier editions, but become unsafe in later ones.
+    Unsafe { unsafe_since: Option<Edition> },
 }
 
 #[derive(Clone, Copy)]
@@ -187,12 +191,23 @@ macro_rules! template {
 }
 
 macro_rules! ungated {
+    (unsafe($edition:ident) $attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $encode_cross_crate:expr $(,)?) => {
+        BuiltinAttribute {
+            name: sym::$attr,
+            encode_cross_crate: $encode_cross_crate,
+            type_: $typ,
+            safety: AttributeSafety::Unsafe { unsafe_since: Some(Edition::$edition) },
+            template: $tpl,
+            gate: Ungated,
+            duplicates: $duplicates,
+        }
+    };
     (unsafe $attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $encode_cross_crate:expr $(,)?) => {
         BuiltinAttribute {
             name: sym::$attr,
             encode_cross_crate: $encode_cross_crate,
             type_: $typ,
-            safety: AttributeSafety::Unsafe,
+            safety: AttributeSafety::Unsafe { unsafe_since: None },
             template: $tpl,
             gate: Ungated,
             duplicates: $duplicates,
@@ -217,7 +232,7 @@ macro_rules! gated {
             name: sym::$attr,
             encode_cross_crate: $encode_cross_crate,
             type_: $typ,
-            safety: AttributeSafety::Unsafe,
+            safety: AttributeSafety::Unsafe { unsafe_since: None },
             template: $tpl,
             duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::$gate, $msg, Features::$gate),
@@ -228,7 +243,7 @@ macro_rules! gated {
             name: sym::$attr,
             encode_cross_crate: $encode_cross_crate,
             type_: $typ,
-            safety: AttributeSafety::Unsafe,
+            safety: AttributeSafety::Unsafe { unsafe_since: None },
             template: $tpl,
             duplicates: $duplicates,
             gate: Gated(Stability::Unstable, sym::$attr, $msg, Features::$attr),
@@ -423,9 +438,9 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     ungated!(no_link, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(repr, Normal, template!(List: "C"), DuplicatesOk, EncodeCrossCrate::No),
-    ungated!(unsafe export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
-    ungated!(unsafe link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
-    ungated!(unsafe no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
+    ungated!(unsafe(Edition2024) export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
+    ungated!(unsafe(Edition2024) link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
+    ungated!(unsafe(Edition2024) no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing, EncodeCrossCrate::No),
     ungated!(link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding, EncodeCrossCrate::Yes),
 
@@ -752,7 +767,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     rustc_attr!(
         rustc_macro_transparency, Normal,
-        template!(NameValueStr: "transparent|semitransparent|opaque"), ErrorFollowing,
+        template!(NameValueStr: "transparent|semiopaque|opaque"), ErrorFollowing,
         EncodeCrossCrate::Yes, "used internally for testing macro hygiene",
     ),
     rustc_attr!(
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index 6ba7b22a0df..402e18c5d14 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -247,7 +247,7 @@ declare_features! (
     /// Allows unnamed fields of struct and union type
     (removed, unnamed_fields, "1.83.0", Some(49804), Some("feature needs redesign")),
     (removed, unsafe_no_drop_flag, "1.0.0", None, None),
-    (removed, unsized_tuple_coercion, "CURRENT_RUSTC_VERSION", Some(42877),
+    (removed, unsized_tuple_coercion, "1.87.0", Some(42877),
      Some("The feature restricts possible layouts for tuples, and this restriction is not worth it.")),
     /// Allows `union` fields that don't implement `Copy` as long as they don't have any drop glue.
     (removed, untagged_unions, "1.13.0", Some(55149),
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 710e129b609..e09ae3c1239 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -211,7 +211,7 @@ declare_features! (
     (internal, custom_mir, "1.65.0", None),
     /// Outputs useful `assert!` messages
     (unstable, generic_assert, "1.63.0", None),
-    /// Allows using the `rust-intrinsic`'s "ABI".
+    /// Allows using the #[rustc_intrinsic] attribute.
     (internal, intrinsics, "1.0.0", None),
     /// Allows using `#[lang = ".."]` attribute for linking items to special compiler logic.
     (internal, lang_items, "1.0.0", None),
@@ -391,8 +391,6 @@ declare_features! (
     (unstable, async_trait_bounds, "1.85.0", Some(62290)),
     /// Allows using C-variadics.
     (unstable, c_variadic, "1.34.0", Some(44930)),
-    /// Allows the use of `#[cfg(<true/false>)]`.
-    (unstable, cfg_boolean_literals, "1.83.0", Some(131204)),
     /// Allows the use of `#[cfg(contract_checks)` to check if contract checks are enabled.
     (unstable, cfg_contract_checks, "1.86.0", Some(128044)),
     /// Allows the use of `#[cfg(overflow_checks)` to check if integer overflow behaviour.
@@ -474,9 +472,11 @@ declare_features! (
     /// Allows `dyn* Trait` objects.
     (incomplete, dyn_star, "1.65.0", Some(102425)),
     /// Allows the .use postfix syntax `x.use` and use closures `use |x| { ... }`
-    (incomplete, ergonomic_clones, "CURRENT_RUSTC_VERSION", Some(132290)),
+    (incomplete, ergonomic_clones, "1.87.0", Some(132290)),
     /// Allows exhaustive pattern matching on types that contain uninhabited types.
     (unstable, exhaustive_patterns, "1.13.0", Some(51085)),
+    /// Disallows `extern` without an explicit ABI.
+    (unstable, explicit_extern_abis, "CURRENT_RUSTC_VERSION", Some(134986)),
     /// Allows explicit tail calls via `become` expression.
     (incomplete, explicit_tail_calls, "1.72.0", Some(112788)),
     /// Allows using `aapcs`, `efiapi`, `sysv64` and `win64` as calling conventions
@@ -511,7 +511,7 @@ declare_features! (
     /// Allows generic parameters and where-clauses on free & associated const items.
     (incomplete, generic_const_items, "1.73.0", Some(113521)),
     /// Allows the type of const generics to depend on generic parameters
-    (incomplete, generic_const_parameter_types, "CURRENT_RUSTC_VERSION", Some(137626)),
+    (incomplete, generic_const_parameter_types, "1.87.0", Some(137626)),
     /// Allows any generic constants being used as pattern type range ends
     (incomplete, generic_pattern_types, "1.86.0", Some(136574)),
     /// Allows registering static items globally, possibly across crates, to iterate over at runtime.
@@ -565,6 +565,8 @@ declare_features! (
     (incomplete, mut_ref, "1.79.0", Some(123076)),
     /// Allows using `#[naked]` on functions.
     (unstable, naked_functions, "1.9.0", Some(90957)),
+    /// Allows using `#[naked]` on `extern "Rust"` functions.
+    (unstable, naked_functions_rustic_abi, "CURRENT_RUSTC_VERSION", Some(138997)),
     /// Allows using `#[target_feature(enable = "...")]` on `#[naked]` on functions.
     (unstable, naked_functions_target_feature, "1.86.0", Some(138568)),
     /// Allows specifying the as-needed link modifier
@@ -602,7 +604,7 @@ declare_features! (
     /// Allows macro attributes on expressions, statements and non-inline modules.
     (unstable, proc_macro_hygiene, "1.30.0", Some(54727)),
     /// Allows the use of raw-dylibs on ELF platforms
-    (incomplete, raw_dylib_elf, "CURRENT_RUSTC_VERSION", Some(135694)),
+    (incomplete, raw_dylib_elf, "1.87.0", Some(135694)),
     /// Makes `&` and `&mut` patterns eat only one layer of references in Rust 2024.
     (incomplete, ref_pat_eat_one_layer_2024, "1.79.0", Some(123076)),
     /// Makes `&` and `&mut` patterns eat only one layer of references in Rust 2024—structural variant
@@ -630,7 +632,7 @@ declare_features! (
     /// Allows string patterns to dereference values to match them.
     (unstable, string_deref_patterns, "1.67.0", Some(87121)),
     /// Allows `super let` statements.
-    (incomplete, super_let, "CURRENT_RUSTC_VERSION", Some(139076)),
+    (unstable, super_let, "CURRENT_RUSTC_VERSION", Some(139076)),
     /// Allows subtrait items to shadow supertrait items.
     (unstable, supertrait_item_shadowing, "1.86.0", Some(89151)),
     /// Allows using `#[thread_local]` on `static` items.
@@ -664,14 +666,14 @@ declare_features! (
     /// Allows using the `#[used(linker)]` (or `#[used(compiler)]`) attribute.
     (unstable, used_with_arg, "1.60.0", Some(93798)),
     /// Allows use of attributes in `where` clauses.
-    (unstable, where_clause_attrs, "CURRENT_RUSTC_VERSION", Some(115590)),
+    (unstable, where_clause_attrs, "1.87.0", Some(115590)),
     /// Allows use of x86 `AMX` target-feature attributes and intrinsics
     (unstable, x86_amx_intrinsics, "1.81.0", Some(126622)),
     /// Allows use of the `xop` target-feature
     (unstable, xop_target_feature, "1.81.0", Some(127208)),
     /// Allows `do yeet` expressions
     (unstable, yeet_expr, "1.62.0", Some(96373)),
-    (unstable, yield_expr, "CURRENT_RUSTC_VERSION", Some(43122)),
+    (unstable, yield_expr, "1.87.0", Some(43122)),
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!
     // Features are listed in alphabetical order. Tidy will fail if you don't keep it this way.
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!
diff --git a/compiler/rustc_fluent_macro/src/fluent.rs b/compiler/rustc_fluent_macro/src/fluent.rs
index b04fd1b48f7..c96bb48a036 100644
--- a/compiler/rustc_fluent_macro/src/fluent.rs
+++ b/compiler/rustc_fluent_macro/src/fluent.rs
@@ -25,7 +25,10 @@ fn invocation_relative_path_to_absolute(span: Span, path: &str) -> PathBuf {
         path.to_path_buf()
     } else {
         // `/a/b/c/foo/bar.rs` contains the current macro invocation
+        #[cfg(bootstrap)]
         let mut source_file_path = span.source_file().path();
+        #[cfg(not(bootstrap))]
+        let mut source_file_path = span.local_file().unwrap();
         // `/a/b/c/foo/`
         source_file_path.pop();
         // `/a/b/c/foo/../locales/en-US/example.ftl`
diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index dc00b52a593..9372ab532bf 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -267,11 +267,16 @@ impl DefKind {
             | DefKind::ForeignTy
             | DefKind::TraitAlias
             | DefKind::TyParam
-            | DefKind::ExternCrate => DefPathData::TypeNs(Some(name.unwrap())),
-
-            // An associated type names will be missing for an RPITIT. It will
-            // later be given a name with `synthetic` in it, if necessary.
-            DefKind::AssocTy => DefPathData::TypeNs(name),
+            | DefKind::ExternCrate => DefPathData::TypeNs(name.unwrap()),
+
+            // An associated type name will be missing for an RPITIT.
+            DefKind::AssocTy => {
+                if let Some(name) = name {
+                    DefPathData::TypeNs(name)
+                } else {
+                    DefPathData::AnonAssocTy
+                }
+            }
 
             // It's not exactly an anon const, but wrt DefPathData, there
             // is no difference.
diff --git a/compiler/rustc_hir/src/definitions.rs b/compiler/rustc_hir/src/definitions.rs
index c52954aa96f..bf7b1eefcf6 100644
--- a/compiler/rustc_hir/src/definitions.rs
+++ b/compiler/rustc_hir/src/definitions.rs
@@ -47,12 +47,9 @@ impl DefPathTable {
         debug_assert_eq!(self.stable_crate_id, def_path_hash.stable_crate_id());
         let local_hash = def_path_hash.local_hash();
 
-        let index = {
-            let index = DefIndex::from(self.index_to_key.len());
-            debug!("DefPathTable::insert() - {:?} <-> {:?}", key, index);
-            self.index_to_key.push(key);
-            index
-        };
+        let index = self.index_to_key.push(key);
+        debug!("DefPathTable::insert() - {key:?} <-> {index:?}");
+
         self.def_path_hashes.push(local_hash);
         debug_assert!(self.def_path_hashes.len() == self.index_to_key.len());
 
@@ -271,9 +268,8 @@ pub enum DefPathData {
     Use,
     /// A global asm item.
     GlobalAsm,
-    /// Something in the type namespace. Will be empty for RPITIT associated
-    /// types, which are given a synthetic name later, if necessary.
-    TypeNs(Option<Symbol>),
+    /// Something in the type namespace.
+    TypeNs(Symbol),
     /// Something in the value namespace.
     ValueNs(Symbol),
     /// Something in the macro namespace.
@@ -291,6 +287,8 @@ pub enum DefPathData {
     /// An existential `impl Trait` type node.
     /// Argument position `impl Trait` have a `TypeNs` with their pretty-printed name.
     OpaqueTy,
+    /// An anonymous associated type from an RPITIT.
+    AnonAssocTy,
     /// A synthetic body for a coroutine's by-move body.
     SyntheticCoroutineBody,
 }
@@ -413,9 +411,7 @@ impl DefPathData {
     pub fn get_opt_name(&self) -> Option<Symbol> {
         use self::DefPathData::*;
         match *self {
-            TypeNs(name) => name,
-
-            ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
+            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
 
             Impl
             | ForeignMod
@@ -426,6 +422,7 @@ impl DefPathData {
             | Ctor
             | AnonConst
             | OpaqueTy
+            | AnonAssocTy
             | SyntheticCoroutineBody => None,
         }
     }
@@ -433,14 +430,9 @@ impl DefPathData {
     pub fn name(&self) -> DefPathDataName {
         use self::DefPathData::*;
         match *self {
-            TypeNs(name) => {
-                if let Some(name) = name {
-                    DefPathDataName::Named(name)
-                } else {
-                    DefPathDataName::Anon { namespace: sym::synthetic }
-                }
+            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => {
+                DefPathDataName::Named(name)
             }
-            ValueNs(name) | MacroNs(name) | LifetimeNs(name) => DefPathDataName::Named(name),
             // Note that this does not show up in user print-outs.
             CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
             Impl => DefPathDataName::Anon { namespace: kw::Impl },
@@ -451,6 +443,7 @@ impl DefPathData {
             Ctor => DefPathDataName::Anon { namespace: sym::constructor },
             AnonConst => DefPathDataName::Anon { namespace: sym::constant },
             OpaqueTy => DefPathDataName::Anon { namespace: sym::opaque },
+            AnonAssocTy => DefPathDataName::Anon { namespace: sym::anon_assoc },
             SyntheticCoroutineBody => DefPathDataName::Anon { namespace: sym::synthetic },
         }
     }
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 1a6c15b66a4..d02c767ea67 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -42,7 +42,7 @@ pub enum IsAnonInPath {
 }
 
 /// A lifetime. The valid field combinations are non-obvious. The following
-/// example shows some of them. See also the comments on `LifetimeName`.
+/// example shows some of them. See also the comments on `LifetimeKind`.
 /// ```
 /// #[repr(C)]
 /// struct S<'a>(&'a u32);       // res=Param, name='a, IsAnonInPath::No
@@ -84,7 +84,7 @@ pub struct Lifetime {
     pub ident: Ident,
 
     /// Semantics of this lifetime.
-    pub res: LifetimeName,
+    pub kind: LifetimeKind,
 
     /// Is the lifetime anonymous and in a path? Used only for error
     /// suggestions. See `Lifetime::suggestion` for example use.
@@ -130,7 +130,7 @@ impl ParamName {
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable_Generic)]
-pub enum LifetimeName {
+pub enum LifetimeKind {
     /// User-given names or fresh (synthetic) names.
     Param(LocalDefId),
 
@@ -160,16 +160,16 @@ pub enum LifetimeName {
     Static,
 }
 
-impl LifetimeName {
+impl LifetimeKind {
     fn is_elided(&self) -> bool {
         match self {
-            LifetimeName::ImplicitObjectLifetimeDefault | LifetimeName::Infer => true,
+            LifetimeKind::ImplicitObjectLifetimeDefault | LifetimeKind::Infer => true,
 
             // It might seem surprising that `Fresh` counts as not *elided*
             // -- but this is because, as far as the code in the compiler is
             // concerned -- `Fresh` variants act equivalently to "some fresh name".
             // They correspond to early-bound regions on an impl, in other words.
-            LifetimeName::Error | LifetimeName::Param(..) | LifetimeName::Static => false,
+            LifetimeKind::Error | LifetimeKind::Param(..) | LifetimeKind::Static => false,
         }
     }
 }
@@ -184,10 +184,10 @@ impl Lifetime {
     pub fn new(
         hir_id: HirId,
         ident: Ident,
-        res: LifetimeName,
+        kind: LifetimeKind,
         is_anon_in_path: IsAnonInPath,
     ) -> Lifetime {
-        let lifetime = Lifetime { hir_id, ident, res, is_anon_in_path };
+        let lifetime = Lifetime { hir_id, ident, kind, is_anon_in_path };
 
         // Sanity check: elided lifetimes form a strict subset of anonymous lifetimes.
         #[cfg(debug_assertions)]
@@ -202,7 +202,7 @@ impl Lifetime {
     }
 
     pub fn is_elided(&self) -> bool {
-        self.res.is_elided()
+        self.kind.is_elided()
     }
 
     pub fn is_anonymous(&self) -> bool {
@@ -1014,7 +1014,7 @@ pub struct WhereRegionPredicate<'hir> {
 impl<'hir> WhereRegionPredicate<'hir> {
     /// Returns `true` if `param_def_id` matches the `lifetime` of this predicate.
     fn is_param_bound(&self, param_def_id: LocalDefId) -> bool {
-        self.lifetime.res == LifetimeName::Param(param_def_id)
+        self.lifetime.kind == LifetimeKind::Param(param_def_id)
     }
 }
 
@@ -1237,7 +1237,7 @@ impl AttributeExt for Attribute {
             Attribute::Parsed(AttributeKind::DocComment { kind, comment, .. }) => {
                 Some((*comment, *kind))
             }
-            Attribute::Unparsed(_) if self.name_or_empty() == sym::doc => {
+            Attribute::Unparsed(_) if self.has_name(sym::doc) => {
                 self.value_str().map(|s| (s, CommentKind::Line))
             }
             _ => None,
@@ -1262,8 +1262,8 @@ impl Attribute {
     }
 
     #[inline]
-    pub fn name_or_empty(&self) -> Symbol {
-        AttributeExt::name_or_empty(self)
+    pub fn name(&self) -> Option<Symbol> {
+        AttributeExt::name(self)
     }
 
     #[inline]
@@ -1302,6 +1302,11 @@ impl Attribute {
     }
 
     #[inline]
+    pub fn has_any_name(&self, names: &[Symbol]) -> bool {
+        AttributeExt::has_any_name(self, names)
+    }
+
+    #[inline]
     pub fn span(&self) -> Span {
         AttributeExt::span(self)
     }
@@ -1555,6 +1560,7 @@ impl<'hir> Pat<'hir> {
 
         use PatKind::*;
         match self.kind {
+            Missing => unreachable!(),
             Wild | Never | Expr(_) | Range(..) | Binding(.., None) | Err(_) => true,
             Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) | Guard(s, _) => s.walk_short_(it),
             Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk_short_(it)),
@@ -1582,7 +1588,7 @@ impl<'hir> Pat<'hir> {
 
         use PatKind::*;
         match self.kind {
-            Wild | Never | Expr(_) | Range(..) | Binding(.., None) | Err(_) => {}
+            Missing | Wild | Never | Expr(_) | Range(..) | Binding(.., None) | Err(_) => {}
             Box(s) | Deref(s) | Ref(s, _) | Binding(.., Some(s)) | Guard(s, _) => s.walk_(it),
             Struct(_, fields, _) => fields.iter().for_each(|field| field.pat.walk_(it)),
             TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().for_each(|p| p.walk_(it)),
@@ -1720,6 +1726,9 @@ pub enum TyPatKind<'hir> {
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum PatKind<'hir> {
+    /// A missing pattern, e.g. for an anonymous param in a bare fn like `fn f(u32)`.
+    Missing,
+
     /// Represents a wildcard pattern (i.e., `_`).
     Wild,
 
@@ -1752,7 +1761,7 @@ pub enum PatKind<'hir> {
     Never,
 
     /// A tuple pattern (e.g., `(a, b)`).
-    /// If the `..` pattern fragment is present, then `Option<usize>` denotes its position.
+    /// If the `..` pattern fragment is present, then `DotDotPos` denotes its position.
     /// `0 <= position <= subpats.len()`
     Tuple(&'hir [Pat<'hir>], DotDotPos),
 
@@ -1817,6 +1826,8 @@ pub enum StmtKind<'hir> {
 /// Represents a `let` statement (i.e., `let <pat>:<ty> = <init>;`).
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub struct LetStmt<'hir> {
+    /// Span of `super` in `super let`.
+    pub super_: Option<Span>,
     pub pat: &'hir Pat<'hir>,
     /// Type annotation, if any (otherwise the type will be inferred).
     pub ty: Option<&'hir Ty<'hir>>,
@@ -3393,9 +3404,9 @@ pub struct BareFnTy<'hir> {
     pub abi: ExternAbi,
     pub generic_params: &'hir [GenericParam<'hir>],
     pub decl: &'hir FnDecl<'hir>,
-    // `Option` because bare fn parameter names are optional. We also end up
+    // `Option` because bare fn parameter identifiers are optional. We also end up
     // with `None` in some error cases, e.g. invalid parameter patterns.
-    pub param_names: &'hir [Option<Ident>],
+    pub param_idents: &'hir [Option<Ident>],
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
@@ -4850,7 +4861,7 @@ mod size_asserts {
     static_assert_size!(ImplItemKind<'_>, 40);
     static_assert_size!(Item<'_>, 88);
     static_assert_size!(ItemKind<'_>, 64);
-    static_assert_size!(LetStmt<'_>, 64);
+    static_assert_size!(LetStmt<'_>, 72);
     static_assert_size!(Param<'_>, 32);
     static_assert_size!(Pat<'_>, 72);
     static_assert_size!(Path<'_>, 40);
diff --git a/compiler/rustc_hir/src/hir/tests.rs b/compiler/rustc_hir/src/hir/tests.rs
index 62ef02d2f50..fcd0eafa461 100644
--- a/compiler/rustc_hir/src/hir/tests.rs
+++ b/compiler/rustc_hir/src/hir/tests.rs
@@ -57,7 +57,7 @@ fn trait_object_roundtrips_impl(syntax: TraitObjectSyntax) {
                 Lifetime {
                     hir_id: HirId::INVALID,
                     ident: Ident::new(sym::name, DUMMY_SP),
-                    res: LifetimeName::Static,
+                    kind: LifetimeKind::Static,
                     is_anon_in_path: IsAnonInPath::No,
                 }
             },
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 506358341b5..3c2897ef1d9 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -6,7 +6,7 @@
 //! 1. **Shallow visit**: Get a simple callback for every item (or item-like thing) in the HIR.
 //!    - Example: find all items with a `#[foo]` attribute on them.
 //!    - How: Use the `hir_crate_items` or `hir_module_items` query to traverse over item-like ids
-//!       (ItemId, TraitItemId, etc.) and use tcx.def_kind and `tcx.hir().item*(id)` to filter and
+//!       (ItemId, TraitItemId, etc.) and use tcx.def_kind and `tcx.hir_item*(id)` to filter and
 //!       access actual item-like thing, respectively.
 //!    - Pro: Efficient; just walks the lists of item ids and gives users control whether to access
 //!       the hir_owners themselves or not.
@@ -652,10 +652,10 @@ pub fn walk_foreign_item<'v, V: Visitor<'v>>(
     try_visit!(visitor.visit_ident(foreign_item.ident));
 
     match foreign_item.kind {
-        ForeignItemKind::Fn(ref sig, param_names, ref generics) => {
+        ForeignItemKind::Fn(ref sig, param_idents, ref generics) => {
             try_visit!(visitor.visit_generics(generics));
             try_visit!(visitor.visit_fn_decl(sig.decl));
-            for ident in param_names.iter().copied() {
+            for ident in param_idents.iter().copied() {
                 visit_opt!(visitor, visit_ident, ident);
             }
         }
@@ -744,7 +744,7 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat<'v>) -> V:
             visit_opt!(visitor, visit_pat_expr, lower_bound);
             visit_opt!(visitor, visit_pat_expr, upper_bound);
         }
-        PatKind::Never | PatKind::Wild | PatKind::Err(_) => (),
+        PatKind::Missing | PatKind::Never | PatKind::Wild | PatKind::Err(_) => (),
         PatKind::Slice(prepatterns, ref slice_pattern, postpatterns) => {
             walk_list!(visitor, visit_pat, prepatterns);
             visit_opt!(visitor, visit_pat, slice_pattern);
@@ -1169,9 +1169,9 @@ pub fn walk_trait_item<'v, V: Visitor<'v>>(
             try_visit!(visitor.visit_ty_unambig(ty));
             visit_opt!(visitor, visit_nested_body, default);
         }
-        TraitItemKind::Fn(ref sig, TraitFn::Required(param_names)) => {
+        TraitItemKind::Fn(ref sig, TraitFn::Required(param_idents)) => {
             try_visit!(visitor.visit_fn_decl(sig.decl));
-            for ident in param_names.iter().copied() {
+            for ident in param_idents.iter().copied() {
                 visit_opt!(visitor, visit_ident, ident);
             }
         }
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index 90fab01ba2d..b9f4a8cd165 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -182,6 +182,7 @@ language_item_table! {
     DynMetadata,             sym::dyn_metadata,        dyn_metadata,               Target::Struct,         GenericRequirement::None;
 
     Freeze,                  sym::freeze,              freeze_trait,               Target::Trait,          GenericRequirement::Exact(0);
+    UnsafeUnpin,             sym::unsafe_unpin,        unsafe_unpin_trait,         Target::Trait,          GenericRequirement::Exact(0);
 
     FnPtrTrait,              sym::fn_ptr_trait,        fn_ptr_trait,               Target::Trait,          GenericRequirement::Exact(0);
     FnPtrAddr,               sym::fn_ptr_addr,         fn_ptr_addr,                Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
@@ -235,6 +236,8 @@ language_item_table! {
     IndexMut,                sym::index_mut,           index_mut_trait,            Target::Trait,          GenericRequirement::Exact(1);
 
     UnsafeCell,              sym::unsafe_cell,         unsafe_cell_type,           Target::Struct,         GenericRequirement::None;
+    UnsafePinned,            sym::unsafe_pinned,       unsafe_pinned_type,         Target::Struct,         GenericRequirement::None;
+
     VaList,                  sym::va_list,             va_list,                    Target::Struct,         GenericRequirement::None;
 
     Deref,                   sym::deref,               deref_trait,                Target::Trait,          GenericRequirement::Exact(0);
@@ -439,6 +442,8 @@ language_item_table! {
     DefaultTrait3,           sym::default_trait3,      default_trait3_trait,       Target::Trait,          GenericRequirement::None;
     DefaultTrait2,           sym::default_trait2,      default_trait2_trait,       Target::Trait,          GenericRequirement::None;
     DefaultTrait1,           sym::default_trait1,      default_trait1_trait,       Target::Trait,          GenericRequirement::None;
+
+    ContractCheckEnsures,     sym::contract_check_ensures,      contract_check_ensures_fn,      Target::Fn, GenericRequirement::None;
 }
 
 /// The requirement imposed on the generics of a lang item
diff --git a/compiler/rustc_hir/src/lib.rs b/compiler/rustc_hir/src/lib.rs
index 6bc0f797cca..a84857e3597 100644
--- a/compiler/rustc_hir/src/lib.rs
+++ b/compiler/rustc_hir/src/lib.rs
@@ -4,7 +4,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(closure_track_caller)]
diff --git a/compiler/rustc_hir/src/tests.rs b/compiler/rustc_hir/src/tests.rs
index 0837444ffdb..18c2bfdac8c 100644
--- a/compiler/rustc_hir/src/tests.rs
+++ b/compiler/rustc_hir/src/tests.rs
@@ -17,7 +17,7 @@ fn def_path_hash_depends_on_crate_id() {
     // the crate by changing the crate disambiguator (e.g. via bumping the
     // crate's version number).
 
-    create_session_globals_then(Edition::Edition2024, None, || {
+    create_session_globals_then(Edition::Edition2024, &[], None, || {
         let id0 = StableCrateId::new(Symbol::intern("foo"), false, vec!["1".to_string()], "");
         let id1 = StableCrateId::new(Symbol::intern("foo"), false, vec!["2".to_string()], "");
 
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 194f2cd04e4..92701e3328e 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -1,5 +1,5 @@
-hir_analysis_ambiguous_assoc_item = ambiguous associated {$assoc_kind} `{$assoc_name}` in bounds of `{$qself}`
-    .label = ambiguous associated {$assoc_kind} `{$assoc_name}`
+hir_analysis_ambiguous_assoc_item = ambiguous associated {$assoc_kind} `{$assoc_ident}` in bounds of `{$qself}`
+    .label = ambiguous associated {$assoc_kind} `{$assoc_ident}`
 
 hir_analysis_ambiguous_lifetime_bound =
     ambiguous lifetime bound, explicit lifetime bound required
@@ -12,13 +12,13 @@ hir_analysis_assoc_item_is_private = {$kind} `{$name}` is private
     .label = private {$kind}
     .defined_here_label = the {$kind} is defined here
 
-hir_analysis_assoc_item_not_found = associated {$assoc_kind} `{$assoc_name}` not found for `{$qself}`
+hir_analysis_assoc_item_not_found = associated {$assoc_kind} `{$assoc_ident}` not found for `{$qself}`
 
 hir_analysis_assoc_item_not_found_found_in_other_trait_label = there is {$identically_named ->
         [true] an
         *[false] a similarly named
     } associated {$assoc_kind} `{$suggested_name}` in the trait `{$trait_name}`
-hir_analysis_assoc_item_not_found_label = associated {$assoc_kind} `{$assoc_name}` not found
+hir_analysis_assoc_item_not_found_label = associated {$assoc_kind} `{$assoc_ident}` not found
 hir_analysis_assoc_item_not_found_other_sugg = `{$qself}` has the following associated {$assoc_kind}
 hir_analysis_assoc_item_not_found_similar_in_other_trait_qpath_sugg =
     consider fully qualifying{$identically_named ->
@@ -486,6 +486,9 @@ hir_analysis_self_in_impl_self =
     `Self` is not valid in the self type of an impl block
     .note = replace `Self` with a different type
 
+hir_analysis_self_in_type_alias = `Self` is not allowed in type aliases
+    .label = `Self` is only available in impls, traits, and concrete type definitions
+
 hir_analysis_self_ty_not_captured = `impl Trait` must mention the `Self` type of the trait in `use<...>`
     .label = `Self` type parameter is implicitly captured by this `impl Trait`
     .note = currently, all type parameters are required to be mentioned in the precise captures list
diff --git a/compiler/rustc_hir_analysis/src/autoderef.rs b/compiler/rustc_hir_analysis/src/autoderef.rs
index b3eade8c8ae..99e495d9266 100644
--- a/compiler/rustc_hir_analysis/src/autoderef.rs
+++ b/compiler/rustc_hir_analysis/src/autoderef.rs
@@ -2,8 +2,8 @@ use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::PredicateObligations;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
 use rustc_session::Limit;
-use rustc_span::Span;
 use rustc_span::def_id::{LOCAL_CRATE, LocalDefId};
+use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits::ObligationCtxt;
 use tracing::{debug, instrument};
 
@@ -259,7 +259,11 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
     }
 }
 
-pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
+pub fn report_autoderef_recursion_limit_error<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    span: Span,
+    ty: Ty<'tcx>,
+) -> ErrorGuaranteed {
     // We've reached the recursion limit, error gracefully.
     let suggested_limit = match tcx.recursion_limit() {
         Limit(0) => Limit(2),
@@ -270,5 +274,5 @@ pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Spa
         ty,
         suggested_limit,
         crate_name: tcx.crate_name(LOCAL_CRATE),
-    });
+    })
 }
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index a0798656763..4f338c6a19e 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -397,8 +397,11 @@ fn best_definition_site_of_opaque<'tcx>(
                 return ControlFlow::Continue(());
             }
 
-            if let Some(hidden_ty) =
-                self.tcx.mir_borrowck(item_def_id).concrete_opaque_types.get(&self.opaque_def_id)
+            if let Some(hidden_ty) = self
+                .tcx
+                .mir_borrowck(item_def_id)
+                .ok()
+                .and_then(|opaque_types| opaque_types.0.get(&self.opaque_def_id))
             {
                 ControlFlow::Break((hidden_ty.span, item_def_id))
             } else {
@@ -413,9 +416,6 @@ fn best_definition_site_of_opaque<'tcx>(
             self.tcx
         }
         fn visit_expr(&mut self, ex: &'tcx hir::Expr<'tcx>) -> Self::Result {
-            if let hir::ExprKind::Closure(closure) = ex.kind {
-                self.check(closure.def_id)?;
-            }
             intravisit::walk_expr(self, ex)
         }
         fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) -> Self::Result {
@@ -443,13 +443,13 @@ fn best_definition_site_of_opaque<'tcx>(
             let impl_def_id = tcx.local_parent(parent);
             for assoc in tcx.associated_items(impl_def_id).in_definition_order() {
                 match assoc.kind {
-                    ty::AssocKind::Const | ty::AssocKind::Fn => {
+                    ty::AssocKind::Const { .. } | ty::AssocKind::Fn { .. } => {
                         if let ControlFlow::Break(span) = locator.check(assoc.def_id.expect_local())
                         {
                             return Some(span);
                         }
                     }
-                    ty::AssocKind::Type => {}
+                    ty::AssocKind::Type { .. } => {}
                 }
             }
 
@@ -719,7 +719,6 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
                     def_id,
                     tcx.def_ident_span(def_id).unwrap(),
                     i.name,
-                    ExternAbi::Rust,
                 )
             }
         }
@@ -741,11 +740,7 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 
             for &assoc_item in assoc_items.in_definition_order() {
                 match assoc_item.kind {
-                    ty::AssocKind::Fn => {
-                        let abi = tcx.fn_sig(assoc_item.def_id).skip_binder().abi();
-                        forbid_intrinsic_abi(tcx, assoc_item.ident(tcx).span, abi);
-                    }
-                    ty::AssocKind::Type if assoc_item.defaultness(tcx).has_value() => {
+                    ty::AssocKind::Type { .. } if assoc_item.defaultness(tcx).has_value() => {
                         let trait_args = GenericArgs::identity_for_item(tcx, def_id);
                         let _: Result<_, rustc_errors::ErrorGuaranteed> = check_type_bounds(
                             tcx,
@@ -788,65 +783,49 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
             };
             check_abi(tcx, it.span, abi);
 
-            match abi {
-                ExternAbi::RustIntrinsic => {
-                    for item in items {
-                        intrinsic::check_intrinsic_type(
-                            tcx,
-                            item.id.owner_id.def_id,
-                            item.span,
-                            item.ident.name,
-                            abi,
-                        );
-                    }
+            for item in items {
+                let def_id = item.id.owner_id.def_id;
+
+                let generics = tcx.generics_of(def_id);
+                let own_counts = generics.own_counts();
+                if generics.own_params.len() - own_counts.lifetimes != 0 {
+                    let (kinds, kinds_pl, egs) = match (own_counts.types, own_counts.consts) {
+                        (_, 0) => ("type", "types", Some("u32")),
+                        // We don't specify an example value, because we can't generate
+                        // a valid value for any type.
+                        (0, _) => ("const", "consts", None),
+                        _ => ("type or const", "types or consts", None),
+                    };
+                    struct_span_code_err!(
+                        tcx.dcx(),
+                        item.span,
+                        E0044,
+                        "foreign items may not have {kinds} parameters",
+                    )
+                    .with_span_label(item.span, format!("can't have {kinds} parameters"))
+                    .with_help(
+                        // FIXME: once we start storing spans for type arguments, turn this
+                        // into a suggestion.
+                        format!(
+                            "replace the {} parameters with concrete {}{}",
+                            kinds,
+                            kinds_pl,
+                            egs.map(|egs| format!(" like `{egs}`")).unwrap_or_default(),
+                        ),
+                    )
+                    .emit();
                 }
 
-                _ => {
-                    for item in items {
-                        let def_id = item.id.owner_id.def_id;
-                        let generics = tcx.generics_of(def_id);
-                        let own_counts = generics.own_counts();
-                        if generics.own_params.len() - own_counts.lifetimes != 0 {
-                            let (kinds, kinds_pl, egs) = match (own_counts.types, own_counts.consts)
-                            {
-                                (_, 0) => ("type", "types", Some("u32")),
-                                // We don't specify an example value, because we can't generate
-                                // a valid value for any type.
-                                (0, _) => ("const", "consts", None),
-                                _ => ("type or const", "types or consts", None),
-                            };
-                            struct_span_code_err!(
-                                tcx.dcx(),
-                                item.span,
-                                E0044,
-                                "foreign items may not have {kinds} parameters",
-                            )
-                            .with_span_label(item.span, format!("can't have {kinds} parameters"))
-                            .with_help(
-                                // FIXME: once we start storing spans for type arguments, turn this
-                                // into a suggestion.
-                                format!(
-                                    "replace the {} parameters with concrete {}{}",
-                                    kinds,
-                                    kinds_pl,
-                                    egs.map(|egs| format!(" like `{egs}`")).unwrap_or_default(),
-                                ),
-                            )
-                            .emit();
-                        }
-
-                        let item = tcx.hir_foreign_item(item.id);
-                        match &item.kind {
-                            hir::ForeignItemKind::Fn(sig, _, _) => {
-                                require_c_abi_if_c_variadic(tcx, sig.decl, abi, item.span);
-                            }
-                            hir::ForeignItemKind::Static(..) => {
-                                check_static_inhabited(tcx, def_id);
-                                check_static_linkage(tcx, def_id);
-                            }
-                            _ => {}
-                        }
+                let item = tcx.hir_foreign_item(item.id);
+                match &item.kind {
+                    hir::ForeignItemKind::Fn(sig, _, _) => {
+                        require_c_abi_if_c_variadic(tcx, sig.decl, abi, item.span);
+                    }
+                    hir::ForeignItemKind::Static(..) => {
+                        check_static_inhabited(tcx, def_id);
+                        check_static_linkage(tcx, def_id);
                     }
+                    _ => {}
                 }
             }
         }
@@ -947,31 +926,7 @@ fn check_impl_items_against_trait<'tcx>(
 
     let trait_def = tcx.trait_def(trait_ref.def_id);
 
-    let infcx = tcx.infer_ctxt().ignoring_regions().build(TypingMode::non_body_analysis());
-
-    let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
-    let cause = ObligationCause::misc(tcx.def_span(impl_id), impl_id);
-    let param_env = tcx.param_env(impl_id);
-
-    let self_is_guaranteed_unsized = match tcx
-        .struct_tail_raw(
-            trait_ref.self_ty(),
-            |ty| {
-                ocx.structurally_normalize_ty(&cause, param_env, ty).unwrap_or_else(|_| {
-                    Ty::new_error_with_message(
-                        tcx,
-                        tcx.def_span(impl_id),
-                        "struct tail should be computable",
-                    )
-                })
-            },
-            || (),
-        )
-        .kind()
-    {
-        ty::Dynamic(_, _, ty::DynKind::Dyn) | ty::Slice(_) | ty::Str => true,
-        _ => false,
-    };
+    let self_is_guaranteed_unsize_self = tcx.impl_self_is_guaranteed_unsized(impl_id);
 
     for &impl_item in impl_item_refs {
         let ty_impl_item = tcx.associated_item(impl_item);
@@ -987,7 +942,7 @@ fn check_impl_items_against_trait<'tcx>(
 
         if res.is_ok() {
             match ty_impl_item.kind {
-                ty::AssocKind::Fn => {
+                ty::AssocKind::Fn { .. } => {
                     compare_impl_item::refine::check_refining_return_position_impl_trait_in_trait(
                         tcx,
                         ty_impl_item,
@@ -997,12 +952,12 @@ fn check_impl_items_against_trait<'tcx>(
                             .instantiate_identity(),
                     );
                 }
-                ty::AssocKind::Const => {}
-                ty::AssocKind::Type => {}
+                ty::AssocKind::Const { .. } => {}
+                ty::AssocKind::Type { .. } => {}
             }
         }
 
-        if self_is_guaranteed_unsized && tcx.generics_require_sized_self(ty_trait_item.def_id) {
+        if self_is_guaranteed_unsize_self && tcx.generics_require_sized_self(ty_trait_item.def_id) {
             tcx.emit_node_span_lint(
                 rustc_lint_defs::builtin::DEAD_CODE,
                 tcx.local_def_id_to_hir_id(ty_impl_item.def_id.expect_local()),
@@ -1037,7 +992,7 @@ fn check_impl_items_against_trait<'tcx>(
             if !is_implemented
                 && tcx.defaultness(impl_id).is_final()
                 // unsized types don't need to implement methods that have `Self: Sized` bounds.
-                && !(self_is_guaranteed_unsized && tcx.generics_require_sized_self(trait_item_id))
+                && !(self_is_guaranteed_unsize_self && tcx.generics_require_sized_self(trait_item_id))
             {
                 missing_items.push(tcx.associated_item(trait_item_id));
             }
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 5e68bb31001..06a7b1f6c29 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -43,9 +43,11 @@ pub(super) fn compare_impl_item(
     debug!(?impl_trait_ref);
 
     match impl_item.kind {
-        ty::AssocKind::Fn => compare_impl_method(tcx, impl_item, trait_item, impl_trait_ref),
-        ty::AssocKind::Type => compare_impl_ty(tcx, impl_item, trait_item, impl_trait_ref),
-        ty::AssocKind::Const => compare_impl_const(tcx, impl_item, trait_item, impl_trait_ref),
+        ty::AssocKind::Fn { .. } => compare_impl_method(tcx, impl_item, trait_item, impl_trait_ref),
+        ty::AssocKind::Type { .. } => compare_impl_ty(tcx, impl_item, trait_item, impl_trait_ref),
+        ty::AssocKind::Const { .. } => {
+            compare_impl_const(tcx, impl_item, trait_item, impl_trait_ref)
+        }
     }
 }
 
@@ -442,7 +444,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for RemapLateParam<'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        if let ty::ReLateParam(fr) = *r {
+        if let ty::ReLateParam(fr) = r.kind() {
             ty::Region::new_late_param(
                 self.tcx,
                 fr.scope,
@@ -606,7 +608,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     // with placeholders, which imply nothing about outlives bounds, and then
     // prove below that the hidden types are well formed.
     let universe = infcx.create_next_universe();
-    let mut idx = 0;
+    let mut idx = ty::BoundVar::ZERO;
     let mapping: FxIndexMap<_, _> = collector
         .types
         .iter()
@@ -623,10 +625,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                     tcx,
                     ty::Placeholder {
                         universe,
-                        bound: ty::BoundTy {
-                            var: ty::BoundVar::from_usize(idx),
-                            kind: ty::BoundTyKind::Anon,
-                        },
+                        bound: ty::BoundTy { var: idx, kind: ty::BoundTyKind::Anon },
                     },
                 ),
             )
@@ -654,7 +653,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                 cause.span,
                 E0053,
                 "method `{}` has an incompatible return type for trait",
-                trait_m.name
+                trait_m.name()
             );
             infcx.err_ctxt().note_type_err(
                 &mut diag,
@@ -1032,11 +1031,11 @@ fn report_trait_method_mismatch<'tcx>(
         impl_err_span,
         E0053,
         "method `{}` has an incompatible type for trait",
-        trait_m.name
+        trait_m.name()
     );
     match &terr {
         TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
-            if trait_m.fn_has_self_parameter =>
+            if trait_m.is_method() =>
         {
             let ty = trait_sig.inputs()[0];
             let sugg = get_self_string(ty, |ty| ty == impl_trait_ref.self_ty());
@@ -1046,11 +1045,11 @@ fn report_trait_method_mismatch<'tcx>(
             // argument pattern and type.
             let (sig, body) = tcx.hir_expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
             let span = tcx
-                .hir_body_param_names(body)
+                .hir_body_param_idents(body)
                 .zip(sig.decl.inputs.iter())
-                .map(|(param_name, ty)| {
-                    if let Some(param_name) = param_name {
-                        param_name.span.to(ty.span)
+                .map(|(param_ident, ty)| {
+                    if let Some(param_ident) = param_ident {
+                        param_ident.span.to(ty.span)
                     } else {
                         ty.span
                     }
@@ -1255,7 +1254,7 @@ fn compare_self_type<'tcx>(
         get_self_string(self_arg_ty, can_eq_self)
     };
 
-    match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
+    match (trait_m.is_method(), impl_m.is_method()) {
         (false, false) | (true, true) => {}
 
         (false, true) => {
@@ -1266,14 +1265,14 @@ fn compare_self_type<'tcx>(
                 impl_m_span,
                 E0185,
                 "method `{}` has a `{}` declaration in the impl, but not in the trait",
-                trait_m.name,
+                trait_m.name(),
                 self_descr
             );
             err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
             if let Some(span) = tcx.hir_span_if_local(trait_m.def_id) {
                 err.span_label(span, format!("trait method declared without `{self_descr}`"));
             } else {
-                err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
+                err.note_trait_signature(trait_m.name(), trait_m.signature(tcx));
             }
             return Err(err.emit_unless(delay));
         }
@@ -1286,14 +1285,14 @@ fn compare_self_type<'tcx>(
                 impl_m_span,
                 E0186,
                 "method `{}` has a `{}` declaration in the trait, but not in the impl",
-                trait_m.name,
+                trait_m.name(),
                 self_descr
             );
             err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
             if let Some(span) = tcx.hir_span_if_local(trait_m.def_id) {
                 err.span_label(span, format!("`{self_descr}` used in trait"));
             } else {
-                err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
+                err.note_trait_signature(trait_m.name(), trait_m.signature(tcx));
             }
 
             return Err(err.emit_unless(delay));
@@ -1363,7 +1362,7 @@ fn compare_number_of_generics<'tcx>(
     let mut err_occurred = None;
     for (kind, trait_count, impl_count) in matchings {
         if impl_count != trait_count {
-            let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
+            let arg_spans = |item: &ty::AssocItem, generics: &hir::Generics<'_>| {
                 let mut spans = generics
                     .params
                     .iter()
@@ -1373,7 +1372,7 @@ fn compare_number_of_generics<'tcx>(
                         } => {
                             // A fn can have an arbitrary number of extra elided lifetimes for the
                             // same signature.
-                            !matches!(kind, ty::AssocKind::Fn)
+                            !item.is_fn()
                         }
                         _ => true,
                     })
@@ -1386,7 +1385,7 @@ fn compare_number_of_generics<'tcx>(
             };
             let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
                 let trait_item = tcx.hir_expect_trait_item(def_id);
-                let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
+                let arg_spans: Vec<Span> = arg_spans(&trait_, trait_item.generics);
                 let impl_trait_spans: Vec<Span> = trait_item
                     .generics
                     .params
@@ -1412,7 +1411,7 @@ fn compare_number_of_generics<'tcx>(
                     _ => None,
                 })
                 .collect();
-            let spans = arg_spans(impl_.kind, impl_item.generics);
+            let spans = arg_spans(&impl_, impl_item.generics);
             let span = spans.first().copied();
 
             let mut err = tcx.dcx().struct_span_err(
@@ -1421,7 +1420,7 @@ fn compare_number_of_generics<'tcx>(
                     "{} `{}` has {} {kind} parameter{} but its trait \
                      declaration has {} {kind} parameter{}",
                     item_kind,
-                    trait_.name,
+                    trait_.name(),
                     impl_count,
                     pluralize!(impl_count),
                     trait_count,
@@ -1512,7 +1511,7 @@ fn compare_number_of_method_arguments<'tcx>(
             impl_span,
             E0050,
             "method `{}` has {} but the declaration in trait `{}` has {}",
-            trait_m.name,
+            trait_m.name(),
             potentially_plural_count(impl_number_args, "parameter"),
             tcx.def_path_str(trait_m.def_id),
             trait_number_args
@@ -1527,7 +1526,7 @@ fn compare_number_of_method_arguments<'tcx>(
                 ),
             );
         } else {
-            err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
+            err.note_trait_signature(trait_m.name(), trait_m.signature(tcx));
         }
 
         err.span_label(
@@ -1581,7 +1580,7 @@ fn compare_synthetic_generics<'tcx>(
                 impl_span,
                 E0643,
                 "method `{}` has incompatible signature for trait",
-                trait_m.name
+                trait_m.name()
             );
             err.span_label(trait_span, "declaration in trait here");
             if impl_synthetic {
@@ -1703,7 +1702,7 @@ fn compare_generic_param_kinds<'tcx>(
     trait_item: ty::AssocItem,
     delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
-    assert_eq!(impl_item.kind, trait_item.kind);
+    assert_eq!(impl_item.as_tag(), trait_item.as_tag());
 
     let ty_const_params_of = |def_id| {
         tcx.generics_of(def_id).own_params.iter().filter(|param| {
@@ -1741,7 +1740,7 @@ fn compare_generic_param_kinds<'tcx>(
                 E0053,
                 "{} `{}` has an incompatible generic parameter for trait `{}`",
                 impl_item.descr(),
-                trait_item.name,
+                trait_item.name(),
                 &tcx.def_path_str(tcx.parent(trait_item.def_id))
             );
 
@@ -1877,7 +1876,7 @@ fn compare_const_predicate_entailment<'tcx>(
             cause.span,
             E0326,
             "implemented const `{}` has an incompatible type for trait",
-            trait_ct.name
+            trait_ct.name()
         );
 
         let trait_c_span = trait_ct.def_id.as_local().map(|trait_ct_def_id| {
@@ -2235,16 +2234,19 @@ fn param_env_with_gat_bounds<'tcx>(
     // of the RPITITs associated with the same body. This is because checking
     // the item bounds of RPITITs often involves nested RPITITs having to prove
     // bounds about themselves.
-    let impl_tys_to_install = match impl_ty.opt_rpitit_info {
-        None => vec![impl_ty],
-        Some(
-            ty::ImplTraitInTraitData::Impl { fn_def_id }
-            | ty::ImplTraitInTraitData::Trait { fn_def_id, .. },
-        ) => tcx
+    let impl_tys_to_install = match impl_ty.kind {
+        ty::AssocKind::Type {
+            data:
+                ty::AssocTypeData::Rpitit(
+                    ty::ImplTraitInTraitData::Impl { fn_def_id }
+                    | ty::ImplTraitInTraitData::Trait { fn_def_id, .. },
+                ),
+        } => tcx
             .associated_types_for_impl_traits_in_associated_fn(fn_def_id)
             .iter()
             .map(|def_id| tcx.associated_item(*def_id))
             .collect(),
+        _ => vec![impl_ty],
     };
 
     for impl_ty in impl_tys_to_install {
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index 42d785c8dd0..89fb35154b7 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -1,9 +1,8 @@
-//! Type-checking for the rust-intrinsic intrinsics that the compiler exposes.
+//! Type-checking for the `#[rustc_intrinsic]` intrinsics that the compiler exposes.
 
 use rustc_abi::ExternAbi;
-use rustc_errors::codes::*;
-use rustc_errors::{DiagMessage, struct_span_code_err};
-use rustc_hir::{self as hir, Safety};
+use rustc_errors::DiagMessage;
+use rustc_hir::{self as hir};
 use rustc_middle::bug;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -26,17 +25,10 @@ fn equate_intrinsic_type<'tcx>(
     sig: ty::PolyFnSig<'tcx>,
 ) {
     let (generics, span) = match tcx.hir_node_by_def_id(def_id) {
-        hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn { generics, .. }, .. })
-        | hir::Node::ForeignItem(hir::ForeignItem {
-            kind: hir::ForeignItemKind::Fn(_, _, generics),
-            ..
-        }) => (tcx.generics_of(def_id), generics.span),
-        _ => {
-            struct_span_code_err!(tcx.dcx(), span, E0622, "intrinsic must be a function")
-                .with_span_label(span, "expected a function")
-                .emit();
-            return;
+        hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn { generics, .. }, .. }) => {
+            (tcx.generics_of(def_id), generics.span)
         }
+        _ => tcx.dcx().span_bug(span, "intrinsic must be a function"),
     };
     let own_counts = generics.own_counts();
 
@@ -70,13 +62,7 @@ fn equate_intrinsic_type<'tcx>(
 }
 
 /// Returns the unsafety of the given intrinsic.
-pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hir::Safety {
-    let has_safe_attr = if tcx.has_attr(intrinsic_id, sym::rustc_intrinsic) {
-        tcx.fn_sig(intrinsic_id).skip_binder().safety()
-    } else {
-        // Old-style intrinsics are never safe
-        Safety::Unsafe
-    };
+fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hir::Safety {
     let is_in_list = match tcx.item_name(intrinsic_id.into()) {
         // When adding a new intrinsic to this list,
         // it's usually worth updating that intrinsic's documentation
@@ -148,7 +134,7 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -
         _ => hir::Safety::Unsafe,
     };
 
-    if has_safe_attr != is_in_list {
+    if tcx.fn_sig(intrinsic_id).skip_binder().safety() != is_in_list {
         tcx.dcx().struct_span_err(
             tcx.def_span(intrinsic_id),
             DiagMessage::from(format!(
@@ -163,12 +149,11 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -
 
 /// Remember to add all intrinsics here, in `compiler/rustc_codegen_llvm/src/intrinsic.rs`,
 /// and in `library/core/src/intrinsics.rs`.
-pub fn check_intrinsic_type(
+pub(crate) fn check_intrinsic_type(
     tcx: TyCtxt<'_>,
     intrinsic_id: LocalDefId,
     span: Span,
     intrinsic_name: Symbol,
-    abi: ExternAbi,
 ) {
     let generics = tcx.generics_of(intrinsic_id);
     let param = |n| {
@@ -232,15 +217,11 @@ pub fn check_intrinsic_type(
         };
         (n_tps, 0, 0, inputs, output, hir::Safety::Unsafe)
     } else if intrinsic_name == sym::contract_check_ensures {
-        // contract_check_ensures::<'a, Ret, C>(&'a Ret, C)
-        // where C: impl Fn(&'a Ret) -> bool,
+        // contract_check_ensures::<Ret, C>(Ret, C) -> Ret
+        // where C: for<'a> Fn(&'a Ret) -> bool,
         //
-        // so: two type params, one lifetime param, 0 const params, two inputs, no return
-
-        let p = generics.param_at(0, tcx);
-        let r = ty::Region::new_early_param(tcx, p.to_early_bound_region_data());
-        let ref_ret = Ty::new_imm_ref(tcx, r, param(1));
-        (2, 1, 0, vec![ref_ret, param(2)], tcx.types.unit, hir::Safety::Safe)
+        // so: two type params, 0 lifetime param, 0 const params, two inputs, no return
+        (2, 0, 0, vec![param(0), param(1)], param(1), hir::Safety::Safe)
     } else {
         let safety = intrinsic_operation_unsafety(tcx, intrinsic_id);
         let (n_tps, n_cts, inputs, output) = match intrinsic_name {
@@ -674,8 +655,12 @@ pub fn check_intrinsic_type(
             sym::simd_masked_load => (3, 0, vec![param(0), param(1), param(2)], param(2)),
             sym::simd_masked_store => (3, 0, vec![param(0), param(1), param(2)], tcx.types.unit),
             sym::simd_scatter => (3, 0, vec![param(0), param(1), param(2)], tcx.types.unit),
-            sym::simd_insert => (2, 0, vec![param(0), tcx.types.u32, param(1)], param(0)),
-            sym::simd_extract => (2, 0, vec![param(0), tcx.types.u32], param(1)),
+            sym::simd_insert | sym::simd_insert_dyn => {
+                (2, 0, vec![param(0), tcx.types.u32, param(1)], param(0))
+            }
+            sym::simd_extract | sym::simd_extract_dyn => {
+                (2, 0, vec![param(0), tcx.types.u32], param(1))
+            }
             sym::simd_cast
             | sym::simd_as
             | sym::simd_cast_ptr
@@ -706,7 +691,7 @@ pub fn check_intrinsic_type(
         };
         (n_tps, 0, n_cts, inputs, output, safety)
     };
-    let sig = tcx.mk_fn_sig(inputs, output, false, safety, abi);
+    let sig = tcx.mk_fn_sig(inputs, output, false, safety, ExternAbi::Rust);
     let sig = ty::Binder::bind_with_vars(sig, bound_vars);
     equate_intrinsic_type(tcx, span, intrinsic_id, n_tps, n_lts, n_cts, sig)
 }
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 7c5d7b33a34..5fbd771976b 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -137,15 +137,6 @@ fn get_owner_return_paths(
     })
 }
 
-/// Forbid defining intrinsics in Rust code,
-/// as they must always be defined by the compiler.
-// FIXME: Move this to a more appropriate place.
-pub fn forbid_intrinsic_abi(tcx: TyCtxt<'_>, sp: Span, abi: ExternAbi) {
-    if let ExternAbi::RustIntrinsic = abi {
-        tcx.dcx().span_err(sp, "intrinsic must be in `extern \"rust-intrinsic\" { ... }` block");
-    }
-}
-
 pub(super) fn maybe_check_static_with_link_section(tcx: TyCtxt<'_>, id: LocalDefId) {
     // Only restricted on wasm target for now
     if !tcx.sess.target.is_like_wasm {
@@ -214,7 +205,7 @@ fn missing_items_err(
 
     let missing_items_msg = missing_items
         .clone()
-        .map(|trait_item| trait_item.name.to_string())
+        .map(|trait_item| trait_item.name().to_string())
         .collect::<Vec<_>>()
         .join("`, `");
 
@@ -245,7 +236,7 @@ fn missing_items_err(
         let code = format!("{padding}{snippet}\n{padding}");
         if let Some(span) = tcx.hir_span_if_local(trait_item.def_id) {
             missing_trait_item_label
-                .push(errors::MissingTraitItemLabel { span, item: trait_item.name });
+                .push(errors::MissingTraitItemLabel { span, item: trait_item.name() });
             missing_trait_item.push(errors::MissingTraitItemSuggestion {
                 span: sugg_sp,
                 code,
@@ -416,14 +407,14 @@ fn fn_sig_suggestion<'tcx>(
         .enumerate()
         .map(|(i, ty)| {
             Some(match ty.kind() {
-                ty::Param(_) if assoc.fn_has_self_parameter && i == 0 => "self".to_string(),
+                ty::Param(_) if assoc.is_method() && i == 0 => "self".to_string(),
                 ty::Ref(reg, ref_ty, mutability) if i == 0 => {
                     let reg = format!("{reg} ");
                     let reg = match &reg[..] {
                         "'_ " | " " => "",
                         reg => reg,
                     };
-                    if assoc.fn_has_self_parameter {
+                    if assoc.is_method() {
                         match ref_ty.kind() {
                             ty::Param(param) if param.name == kw::SelfUpper => {
                                 format!("&{}{}self", reg, mutability.prefix_str())
@@ -436,7 +427,7 @@ fn fn_sig_suggestion<'tcx>(
                     }
                 }
                 _ => {
-                    if assoc.fn_has_self_parameter && i == 0 {
+                    if assoc.is_method() && i == 0 {
                         format!("self: {ty}")
                     } else {
                         format!("_: {ty}")
@@ -498,7 +489,7 @@ fn suggestion_signature<'tcx>(
     );
 
     match assoc.kind {
-        ty::AssocKind::Fn => fn_sig_suggestion(
+        ty::AssocKind::Fn { .. } => fn_sig_suggestion(
             tcx,
             tcx.liberate_late_bound_regions(
                 assoc.def_id,
@@ -508,14 +499,14 @@ fn suggestion_signature<'tcx>(
             tcx.predicates_of(assoc.def_id).instantiate_own(tcx, args),
             assoc,
         ),
-        ty::AssocKind::Type => {
+        ty::AssocKind::Type { .. } => {
             let (generics, where_clauses) = bounds_from_generic_predicates(
                 tcx,
                 tcx.predicates_of(assoc.def_id).instantiate_own(tcx, args),
             );
-            format!("type {}{generics} = /* Type */{where_clauses};", assoc.name)
+            format!("type {}{generics} = /* Type */{where_clauses};", assoc.name())
         }
-        ty::AssocKind::Const => {
+        ty::AssocKind::Const { name } => {
             let ty = tcx.type_of(assoc.def_id).instantiate_identity();
             let val = tcx
                 .infer_ctxt()
@@ -523,7 +514,7 @@ fn suggestion_signature<'tcx>(
                 .err_ctxt()
                 .ty_kind_suggestion(tcx.param_env(assoc.def_id), ty)
                 .unwrap_or_else(|| "value".to_string());
-            format!("const {}: {} = {};", assoc.name, ty, val)
+            format!("const {}: {} = {};", name, ty, val)
         }
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
index cf66ab708bb..7cb31a64e13 100644
--- a/compiler/rustc_hir_analysis/src/check/region.rs
+++ b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -8,6 +8,7 @@
 
 use std::mem;
 
+use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{self, Visitor};
@@ -44,6 +45,8 @@ struct ScopeResolutionVisitor<'tcx> {
     scope_tree: ScopeTree,
 
     cx: Context,
+
+    extended_super_lets: FxHashMap<hir::ItemLocalId, Option<Scope>>,
 }
 
 /// Records the lifetime of a local variable as `cx.var_parent`
@@ -214,18 +217,29 @@ fn resolve_stmt<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, stmt: &'tcx hi
     let stmt_id = stmt.hir_id.local_id;
     debug!("resolve_stmt(stmt.id={:?})", stmt_id);
 
-    // Every statement will clean up the temporaries created during
-    // execution of that statement. Therefore each statement has an
-    // associated destruction scope that represents the scope of the
-    // statement plus its destructors, and thus the scope for which
-    // regions referenced by the destructors need to survive.
+    if let hir::StmtKind::Let(LetStmt { super_: Some(_), .. }) = stmt.kind {
+        // `super let` statement does not start a new scope, such that
+        //
+        //     { super let x = identity(&temp()); &x }.method();
+        //
+        // behaves exactly as
+        //
+        //     (&identity(&temp()).method();
+        intravisit::walk_stmt(visitor, stmt);
+    } else {
+        // Every statement will clean up the temporaries created during
+        // execution of that statement. Therefore each statement has an
+        // associated destruction scope that represents the scope of the
+        // statement plus its destructors, and thus the scope for which
+        // regions referenced by the destructors need to survive.
 
-    let prev_parent = visitor.cx.parent;
-    visitor.enter_node_scope_with_dtor(stmt_id, true);
+        let prev_parent = visitor.cx.parent;
+        visitor.enter_node_scope_with_dtor(stmt_id, true);
 
-    intravisit::walk_stmt(visitor, stmt);
+        intravisit::walk_stmt(visitor, stmt);
 
-    visitor.cx.parent = prev_parent;
+        visitor.cx.parent = prev_parent;
+    }
 }
 
 fn resolve_expr<'tcx>(
@@ -446,14 +460,11 @@ fn resolve_expr<'tcx>(
         // Mark this expr's scope and all parent scopes as containing `yield`.
         let mut scope = Scope { local_id: expr.hir_id.local_id, data: ScopeData::Node };
         loop {
-            let span = match expr.kind {
-                hir::ExprKind::Yield(expr, hir::YieldSource::Await { .. }) => {
-                    expr.span.shrink_to_hi().to(expr.span)
-                }
-                _ => expr.span,
+            let data = YieldData {
+                span: expr.span,
+                expr_and_pat_count: visitor.expr_and_pat_count,
+                source: *source,
             };
-            let data =
-                YieldData { span, expr_and_pat_count: visitor.expr_and_pat_count, source: *source };
             match visitor.scope_tree.yield_in_scope.get_mut(&scope) {
                 Some(yields) => yields.push(data),
                 None => {
@@ -481,14 +492,19 @@ fn resolve_expr<'tcx>(
     visitor.cx = prev_cx;
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+enum LetKind {
+    Regular,
+    Super,
+}
+
 fn resolve_local<'tcx>(
     visitor: &mut ScopeResolutionVisitor<'tcx>,
     pat: Option<&'tcx hir::Pat<'tcx>>,
     init: Option<&'tcx hir::Expr<'tcx>>,
+    let_kind: LetKind,
 ) {
-    debug!("resolve_local(pat={:?}, init={:?})", pat, init);
-
-    let blk_scope = visitor.cx.var_parent;
+    debug!("resolve_local(pat={:?}, init={:?}, let_kind={:?})", pat, init, let_kind);
 
     // As an exception to the normal rules governing temporary
     // lifetimes, initializers in a let have a temporary lifetime
@@ -546,14 +562,50 @@ fn resolve_local<'tcx>(
     // A, but the inner rvalues `a()` and `b()` have an extended lifetime
     // due to rule C.
 
+    if let_kind == LetKind::Super {
+        if let Some(scope) = visitor.extended_super_lets.remove(&pat.unwrap().hir_id.local_id) {
+            // This expression was lifetime-extended by a parent let binding. E.g.
+            //
+            //     let a = {
+            //         super let b = temp();
+            //         &b
+            //     };
+            //
+            // (Which needs to behave exactly as: let a = &temp();)
+            //
+            // Processing of `let a` will have already decided to extend the lifetime of this
+            // `super let` to its own var_scope. We use that scope.
+            visitor.cx.var_parent = scope;
+        } else {
+            // This `super let` is not subject to lifetime extension from a parent let binding. E.g.
+            //
+            //     identity({ super let x = temp(); &x }).method();
+            //
+            // (Which needs to behave exactly as: identity(&temp()).method();)
+            //
+            // Iterate up to the enclosing destruction scope to find the same scope that will also
+            // be used for the result of the block itself.
+            while let Some(s) = visitor.cx.var_parent {
+                let parent = visitor.scope_tree.parent_map.get(&s).cloned();
+                if let Some(Scope { data: ScopeData::Destruction, .. }) = parent {
+                    break;
+                }
+                visitor.cx.var_parent = parent;
+            }
+        }
+    }
+
     if let Some(expr) = init {
-        record_rvalue_scope_if_borrow_expr(visitor, expr, blk_scope);
+        record_rvalue_scope_if_borrow_expr(visitor, expr, visitor.cx.var_parent);
 
         if let Some(pat) = pat {
             if is_binding_pat(pat) {
                 visitor.scope_tree.record_rvalue_candidate(
                     expr.hir_id,
-                    RvalueCandidate { target: expr.hir_id.local_id, lifetime: blk_scope },
+                    RvalueCandidate {
+                        target: expr.hir_id.local_id,
+                        lifetime: visitor.cx.var_parent,
+                    },
                 );
             }
         }
@@ -565,6 +617,7 @@ fn resolve_local<'tcx>(
     if let Some(expr) = init {
         visitor.visit_expr(expr);
     }
+
     if let Some(pat) = pat {
         visitor.visit_pat(pat);
     }
@@ -626,6 +679,7 @@ fn resolve_local<'tcx>(
 
             PatKind::Ref(_, _)
             | PatKind::Binding(hir::BindingMode(hir::ByRef::No, _), ..)
+            | PatKind::Missing
             | PatKind::Wild
             | PatKind::Never
             | PatKind::Expr(_)
@@ -642,6 +696,7 @@ fn resolve_local<'tcx>(
     ///        | [ ..., E&, ... ]
     ///        | ( ..., E&, ... )
     ///        | {...; E&}
+    ///        | { super let ... = E&; ... }
     ///        | if _ { ...; E& } else { ...; E& }
     ///        | match _ { ..., _ => E&, ... }
     ///        | box E&
@@ -678,6 +733,13 @@ fn resolve_local<'tcx>(
                 if let Some(subexpr) = block.expr {
                     record_rvalue_scope_if_borrow_expr(visitor, subexpr, blk_id);
                 }
+                for stmt in block.stmts {
+                    if let hir::StmtKind::Let(local) = stmt.kind
+                        && let Some(_) = local.super_
+                    {
+                        visitor.extended_super_lets.insert(local.pat.hir_id.local_id, blk_id);
+                    }
+                }
             }
             hir::ExprKind::If(_, then_block, else_block) => {
                 record_rvalue_scope_if_borrow_expr(visitor, then_block, blk_id);
@@ -803,7 +865,7 @@ impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> {
                     local_id: body.value.hir_id.local_id,
                     data: ScopeData::Destruction,
                 });
-                resolve_local(this, None, Some(body.value));
+                resolve_local(this, None, Some(body.value), LetKind::Regular);
             }
         })
     }
@@ -821,7 +883,11 @@ impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> {
         resolve_expr(self, ex, false);
     }
     fn visit_local(&mut self, l: &'tcx LetStmt<'tcx>) {
-        resolve_local(self, Some(l.pat), l.init)
+        let let_kind = match l.super_ {
+            Some(_) => LetKind::Super,
+            None => LetKind::Regular,
+        };
+        resolve_local(self, Some(l.pat), l.init, let_kind);
     }
     fn visit_inline_const(&mut self, c: &'tcx hir::ConstBlock) {
         let body = self.tcx.hir_body(c.body);
@@ -850,6 +916,7 @@ pub(crate) fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
             cx: Context { parent: None, var_parent: None },
             pessimistic_yield: false,
             fixup_scopes: vec![],
+            extended_super_lets: Default::default(),
         };
 
         visitor.scope_tree.root_body = Some(body.value.hir_id);
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 83d095ab72e..33d5a86beb3 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -408,7 +408,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
             let gat_def_id = gat_item.def_id.expect_local();
             let gat_item = tcx.associated_item(gat_def_id);
             // If this item is not an assoc ty, or has no args, then it's not a GAT
-            if gat_item.kind != ty::AssocKind::Type {
+            if !gat_item.is_type() {
                 continue;
             }
             let gat_generics = tcx.generics_of(gat_def_id);
@@ -432,7 +432,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
 
                 let item_required_bounds = match tcx.associated_item(item_def_id).kind {
                     // In our example, this corresponds to `into_iter` method
-                    ty::AssocKind::Fn => {
+                    ty::AssocKind::Fn { .. } => {
                         // For methods, we check the function signature's return type for any GATs
                         // to constrain. In the `into_iter` case, we see that the return type
                         // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
@@ -453,7 +453,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
                         )
                     }
                     // In our example, this corresponds to the `Iter` and `Item` associated types
-                    ty::AssocKind::Type => {
+                    ty::AssocKind::Type { .. } => {
                         // If our associated item is a GAT with missing bounds, add them to
                         // the param-env here. This allows this GAT to propagate missing bounds
                         // to other GATs.
@@ -474,7 +474,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
                             gat_generics,
                         )
                     }
-                    ty::AssocKind::Const => None,
+                    ty::AssocKind::Const { .. } => None,
                 };
 
                 if let Some(item_required_bounds) = item_required_bounds {
@@ -631,7 +631,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
         // Ignore `'static` lifetimes for the purpose of this lint: it's
         // because we know it outlives everything and so doesn't give meaningful
         // clues. Also ignore `ReError`, to avoid knock-down errors.
-        if let ty::ReStatic | ty::ReError(_) = **region_a {
+        if let ty::ReStatic | ty::ReError(_) = region_a.kind() {
             continue;
         }
         // For each region argument (e.g., `'a` in our example), check for a
@@ -672,7 +672,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
             // Again, skip `'static` because it outlives everything. Also, we trivially
             // know that a region outlives itself. Also ignore `ReError`, to avoid
             // knock-down errors.
-            if matches!(**region_b, ty::ReStatic | ty::ReError(_)) || region_a == region_b {
+            if matches!(region_b.kind(), ty::ReStatic | ty::ReError(_)) || region_a == region_b {
                 continue;
             }
             if region_known_to_outlive(tcx, item_def_id, param_env, wf_tys, *region_a, *region_b) {
@@ -1076,7 +1076,7 @@ fn check_associated_item(
         };
 
         match item.kind {
-            ty::AssocKind::Const => {
+            ty::AssocKind::Const { .. } => {
                 let ty = tcx.type_of(item.def_id).instantiate_identity();
                 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
                 wfcx.register_wf_obligation(span, loc, ty.into());
@@ -1089,7 +1089,7 @@ fn check_associated_item(
                 );
                 Ok(())
             }
-            ty::AssocKind::Fn => {
+            ty::AssocKind::Fn { .. } => {
                 let sig = tcx.fn_sig(item.def_id).instantiate_identity();
                 let hir_sig = sig_if_method.expect("bad signature for method");
                 check_fn_or_method(
@@ -1101,7 +1101,7 @@ fn check_associated_item(
                 );
                 check_method_receiver(wfcx, hir_sig, item, self_ty)
             }
-            ty::AssocKind::Type => {
+            ty::AssocKind::Type { .. } => {
                 if let ty::AssocItemContainer::Trait = item.container {
                     check_associated_type_bounds(wfcx, item, span)
                 }
@@ -1716,7 +1716,7 @@ fn check_method_receiver<'tcx>(
 ) -> Result<(), ErrorGuaranteed> {
     let tcx = wfcx.tcx();
 
-    if !method.fn_has_self_parameter {
+    if !method.is_method() {
         return Ok(());
     }
 
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 1f3f0b754bb..8ad9d80c6b5 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -656,7 +656,7 @@ fn infringing_fields_error<'tcx>(
                                 .entry((ty.clone(), predicate.clone()))
                                 .or_default()
                                 .push(origin.span());
-                            if let ty::RegionKind::ReEarlyParam(ebr) = *b
+                            if let ty::RegionKind::ReEarlyParam(ebr) = b.kind()
                                 && ebr.has_name()
                             {
                                 bounds.push((b.to_string(), a.to_string(), None));
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
index dc616576c9c..242639125b1 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
@@ -51,7 +51,7 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
 
         for &item1 in impl_items1.in_definition_order() {
             let collision = impl_items2
-                .filter_by_name_unhygienic(item1.name)
+                .filter_by_name_unhygienic(item1.name())
                 .any(|&item2| self.compare_hygienically(item1, item2));
 
             if collision {
@@ -64,7 +64,7 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
 
     fn compare_hygienically(&self, item1: ty::AssocItem, item2: ty::AssocItem) -> bool {
         // Symbols and namespace match, compare hygienically.
-        item1.kind.namespace() == item2.kind.namespace()
+        item1.namespace() == item2.namespace()
             && item1.ident(self.tcx).normalize_to_macros_2_0()
                 == item2.ident(self.tcx).normalize_to_macros_2_0()
     }
@@ -113,7 +113,7 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
         let mut res = Ok(());
         for &item1 in impl_items1.in_definition_order() {
             let collision = impl_items2
-                .filter_by_name_unhygienic(item1.name)
+                .filter_by_name_unhygienic(item1.name())
                 .find(|&&item2| self.compare_hygienically(item1, item2));
 
             if let Some(item2) = collision {
@@ -230,11 +230,11 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
                 let mut ids = impl_items
                     .in_definition_order()
                     .filter_map(|item| {
-                        let entry = connected_region_ids.entry(item.name);
+                        let entry = connected_region_ids.entry(item.name());
                         if let IndexEntry::Occupied(e) = &entry {
                             Some(*e.get())
                         } else {
-                            idents_to_add.push(item.name);
+                            idents_to_add.push(item.name());
                             None
                         }
                     })
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 625f51dd29e..4520fbe352c 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -14,6 +14,7 @@
 //! At present, however, we do run collection across all items in the
 //! crate as a kind of pass. This should eventually be factored away.
 
+use std::assert_matches::assert_matches;
 use std::cell::Cell;
 use std::iter;
 use std::ops::Bound;
@@ -42,9 +43,8 @@ use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::ObligationCtxt;
 use tracing::{debug, instrument};
 
-use crate::check::intrinsic::intrinsic_operation_unsafety;
 use crate::errors;
-use crate::hir_ty_lowering::errors::assoc_kind_str;
+use crate::hir_ty_lowering::errors::assoc_tag_str;
 use crate::hir_ty_lowering::{FeedConstTy, HirTyLowerer, RegionInferReason};
 
 pub(crate) mod dump;
@@ -439,9 +439,9 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
         &self,
         span: Span,
         def_id: LocalDefId,
-        assoc_name: Ident,
+        assoc_ident: Ident,
     ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
-        self.tcx.at(span).type_param_predicates((self.item_def_id, def_id, assoc_name))
+        self.tcx.at(span).type_param_predicates((self.item_def_id, def_id, assoc_ident))
     }
 
     fn lower_assoc_shared(
@@ -450,7 +450,7 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
         item_def_id: DefId,
         item_segment: &rustc_hir::PathSegment<'tcx>,
         poly_trait_ref: ty::PolyTraitRef<'tcx>,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> Result<(DefId, ty::GenericArgsRef<'tcx>), ErrorGuaranteed> {
         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
             let item_args = self.lowerer().lower_generic_args_of_assoc_item(
@@ -525,7 +525,7 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
                 inferred_sugg,
                 bound,
                 mpart_sugg,
-                what: assoc_kind_str(kind),
+                what: assoc_tag_str(assoc_tag),
             }))
         }
     }
@@ -1345,7 +1345,8 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
             compute_sig_of_foreign_fn_decl(tcx, def_id, sig.decl, abi, sig.header.safety())
         }
 
-        Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor().is_some() => {
+        Ctor(data) => {
+            assert_matches!(data.ctor(), Some(_));
             let adt_def_id = tcx.hir_get_parent_item(hir_id).def_id.to_def_id();
             let ty = tcx.type_of(adt_def_id).instantiate_identity();
             let inputs = data.fields().iter().map(|f| tcx.type_of(f.def_id).instantiate_identity());
@@ -1417,7 +1418,7 @@ fn recover_infer_ret_ty<'tcx>(
         GenericParamKind::Lifetime { .. } => true,
         _ => false,
     });
-    let fn_sig = fold_regions(tcx, fn_sig, |r, _| match *r {
+    let fn_sig = fold_regions(tcx, fn_sig, |r, _| match r.kind() {
         ty::ReErased => {
             if has_region_params {
                 ty::Region::new_error_with_message(
@@ -1704,18 +1705,13 @@ fn compute_sig_of_foreign_fn_decl<'tcx>(
     abi: ExternAbi,
     safety: hir::Safety,
 ) -> ty::PolyFnSig<'tcx> {
-    let safety = if abi == ExternAbi::RustIntrinsic {
-        intrinsic_operation_unsafety(tcx, def_id)
-    } else {
-        safety
-    };
     let hir_id = tcx.local_def_id_to_hir_id(def_id);
     let fty =
         ItemCtxt::new(tcx, def_id).lowerer().lower_fn_ty(hir_id, safety, abi, decl, None, None);
 
     // Feature gate SIMD types in FFI, since I am not sure that the
     // ABIs are handled at all correctly. -huonw
-    if abi != ExternAbi::RustIntrinsic && !tcx.features().simd_ffi() {
+    if !tcx.features().simd_ffi() {
         let check = |hir_ty: &hir::Ty<'_>, ty: Ty<'_>| {
             if ty.is_simd() {
                 let snip = tcx
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index 776b23bea8e..ce0f83d0ec2 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -172,33 +172,9 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     };
 
     if let Node::TraitItem(item) = node {
-        let parent = tcx.local_parent(item.hir_id().owner.def_id);
-        let Node::Item(parent_trait) = tcx.hir_node_by_def_id(parent) else {
-            unreachable!();
-        };
-
-        let (trait_generics, trait_bounds) = match parent_trait.kind {
-            hir::ItemKind::Trait(_, _, _, generics, supertraits, _) => (generics, supertraits),
-            hir::ItemKind::TraitAlias(_, generics, supertraits) => (generics, supertraits),
-            _ => unreachable!(),
-        };
-
-        // Implicitly add `Self: DefaultAutoTrait` clauses on trait associated items if
-        // they are not added as super trait bounds to the trait itself. See comment on
-        // `requires_default_supertraits` for more details.
-        if !icx.lowerer().requires_default_supertraits(trait_bounds, trait_generics) {
-            let mut bounds = Vec::new();
-            let self_ty_where_predicates = (parent, item.generics.predicates);
-            icx.lowerer().add_default_traits_with_filter(
-                &mut bounds,
-                tcx.types.self_param,
-                &[],
-                Some(self_ty_where_predicates),
-                item.span,
-                |tr| tr != hir::LangItem::Sized,
-            );
-            predicates.extend(bounds);
-        }
+        let mut bounds = Vec::new();
+        icx.lowerer().add_default_trait_item_bounds(item, &mut bounds);
+        predicates.extend(bounds);
     }
 
     let generics = tcx.generics_of(def_id);
@@ -383,7 +359,7 @@ fn compute_bidirectional_outlives_predicates<'tcx>(
 ) {
     for param in opaque_own_params {
         let orig_lifetime = tcx.map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local());
-        if let ty::ReEarlyParam(..) = *orig_lifetime {
+        if let ty::ReEarlyParam(..) = orig_lifetime.kind() {
             let dup_lifetime = ty::Region::new_early_param(
                 tcx,
                 ty::EarlyParamRegion { index: param.index, name: param.name },
@@ -608,12 +584,12 @@ pub(super) fn explicit_super_predicates_of<'tcx>(
 
 pub(super) fn explicit_supertraits_containing_assoc_item<'tcx>(
     tcx: TyCtxt<'tcx>,
-    (trait_def_id, assoc_name): (DefId, Ident),
+    (trait_def_id, assoc_ident): (DefId, Ident),
 ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     implied_predicates_with_filter(
         tcx,
         trait_def_id,
-        PredicateFilter::SelfTraitThatDefines(assoc_name),
+        PredicateFilter::SelfTraitThatDefines(assoc_ident),
     )
 }
 
@@ -641,7 +617,7 @@ pub(super) fn implied_predicates_with_filter<'tcx>(
     filter: PredicateFilter,
 ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     let Some(trait_def_id) = trait_def_id.as_local() else {
-        // if `assoc_name` is None, then the query should've been redirected to an
+        // if `assoc_ident` is None, then the query should've been redirected to an
         // external provider
         assert_matches!(filter, PredicateFilter::SelfTraitThatDefines(_));
         return tcx.explicit_super_predicates_of(trait_def_id);
@@ -858,11 +834,11 @@ pub(super) fn assert_only_contains_predicates_from<'tcx>(
 #[instrument(level = "trace", skip(tcx))]
 pub(super) fn type_param_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    (item_def_id, def_id, assoc_name): (LocalDefId, LocalDefId, Ident),
+    (item_def_id, def_id, assoc_ident): (LocalDefId, LocalDefId, Ident),
 ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
     match tcx.opt_rpitit_info(item_def_id.to_def_id()) {
         Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
-            return tcx.type_param_predicates((opaque_def_id.expect_local(), def_id, assoc_name));
+            return tcx.type_param_predicates((opaque_def_id.expect_local(), def_id, assoc_ident));
         }
         Some(ty::ImplTraitInTraitData::Impl { .. }) => {
             unreachable!("should not be lowering bounds on RPITIT in impl")
@@ -887,7 +863,7 @@ pub(super) fn type_param_predicates<'tcx>(
 
     let result = if let Some(parent) = parent {
         let icx = ItemCtxt::new(tcx, parent);
-        icx.probe_ty_param_bounds(DUMMY_SP, def_id, assoc_name)
+        icx.probe_ty_param_bounds(DUMMY_SP, def_id, assoc_ident)
     } else {
         ty::EarlyBinder::bind(&[] as &[_])
     };
@@ -913,7 +889,7 @@ pub(super) fn type_param_predicates<'tcx>(
     let extra_predicates = extend.into_iter().chain(icx.probe_ty_param_bounds_in_generics(
         hir_generics,
         def_id,
-        PredicateFilter::SelfTraitThatDefines(assoc_name),
+        PredicateFilter::SelfTraitThatDefines(assoc_ident),
     ));
 
     let bounds =
@@ -932,7 +908,7 @@ pub(super) fn type_param_predicates<'tcx>(
         _ => unreachable!(),
     };
     assert_only_contains_predicates_from(
-        PredicateFilter::SelfTraitThatDefines(assoc_name),
+        PredicateFilter::SelfTraitThatDefines(assoc_ident),
         bounds,
         self_ty,
     );
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 404753875ee..59ab36d98fd 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -16,7 +16,7 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::{self, InferKind, Visitor, VisitorExt};
 use rustc_hir::{
-    self as hir, AmbigArg, GenericArg, GenericParam, GenericParamKind, HirId, LifetimeName, Node,
+    self as hir, AmbigArg, GenericArg, GenericParam, GenericParamKind, HirId, LifetimeKind, Node,
 };
 use rustc_macros::extension;
 use rustc_middle::hir::nested_filter;
@@ -646,14 +646,14 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
         arg: &'tcx hir::PreciseCapturingArg<'tcx>,
     ) -> Self::Result {
         match *arg {
-            hir::PreciseCapturingArg::Lifetime(lt) => match lt.res {
-                LifetimeName::Param(def_id) => {
+            hir::PreciseCapturingArg::Lifetime(lt) => match lt.kind {
+                LifetimeKind::Param(def_id) => {
                     self.resolve_lifetime_ref(def_id, lt);
                 }
-                LifetimeName::Error => {}
-                LifetimeName::ImplicitObjectLifetimeDefault
-                | LifetimeName::Infer
-                | LifetimeName::Static => {
+                LifetimeKind::Error => {}
+                LifetimeKind::ImplicitObjectLifetimeDefault
+                | LifetimeKind::Infer
+                | LifetimeKind::Static => {
                     self.tcx.dcx().emit_err(errors::BadPreciseCapture {
                         span: lt.ident.span,
                         kind: "lifetime",
@@ -774,26 +774,26 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                         );
                     }
                 });
-                match lifetime.res {
-                    LifetimeName::ImplicitObjectLifetimeDefault => {
+                match lifetime.kind {
+                    LifetimeKind::ImplicitObjectLifetimeDefault => {
                         // If the user does not write *anything*, we
                         // use the object lifetime defaulting
                         // rules. So e.g., `Box<dyn Debug>` becomes
                         // `Box<dyn Debug + 'static>`.
                         self.resolve_object_lifetime_default(&*lifetime)
                     }
-                    LifetimeName::Infer => {
+                    LifetimeKind::Infer => {
                         // If the user writes `'_`, we use the *ordinary* elision
                         // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
                         // resolved the same as the `'_` in `&'_ Foo`.
                         //
                         // cc #48468
                     }
-                    LifetimeName::Param(..) | LifetimeName::Static => {
+                    LifetimeKind::Param(..) | LifetimeKind::Static => {
                         // If the user wrote an explicit name, use that.
                         self.visit_lifetime(&*lifetime);
                     }
-                    LifetimeName::Error => {}
+                    LifetimeKind::Error => {}
                 }
             }
             hir::TyKind::Ref(lifetime_ref, ref mt) => {
@@ -873,17 +873,17 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
 
     #[instrument(level = "debug", skip(self))]
     fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
-        match lifetime_ref.res {
-            hir::LifetimeName::Static => {
+        match lifetime_ref.kind {
+            hir::LifetimeKind::Static => {
                 self.insert_lifetime(lifetime_ref, ResolvedArg::StaticLifetime)
             }
-            hir::LifetimeName::Param(param_def_id) => {
+            hir::LifetimeKind::Param(param_def_id) => {
                 self.resolve_lifetime_ref(param_def_id, lifetime_ref)
             }
             // If we've already reported an error, just ignore `lifetime_ref`.
-            hir::LifetimeName::Error => {}
+            hir::LifetimeKind::Error => {}
             // Those will be resolved by typechecking.
-            hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Infer => {}
+            hir::LifetimeKind::ImplicitObjectLifetimeDefault | hir::LifetimeKind::Infer => {}
         }
     }
 
@@ -1063,15 +1063,15 @@ fn object_lifetime_default(tcx: TyCtxt<'_>, param_def_id: LocalDefId) -> ObjectL
 
                         for bound in bound.bounds {
                             if let hir::GenericBound::Outlives(lifetime) = bound {
-                                set.insert(lifetime.res);
+                                set.insert(lifetime.kind);
                             }
                         }
                     }
 
                     match set {
                         Set1::Empty => ObjectLifetimeDefault::Empty,
-                        Set1::One(hir::LifetimeName::Static) => ObjectLifetimeDefault::Static,
-                        Set1::One(hir::LifetimeName::Param(param_def_id)) => {
+                        Set1::One(hir::LifetimeKind::Static) => ObjectLifetimeDefault::Static,
+                        Set1::One(hir::LifetimeKind::Param(param_def_id)) => {
                             ObjectLifetimeDefault::Param(param_def_id.to_def_id())
                         }
                         _ => ObjectLifetimeDefault::Ambiguous,
@@ -1241,7 +1241,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     // Fresh lifetimes in APIT used to be allowed in async fns and forbidden in
                     // regular fns.
                     if let Some(hir::PredicateOrigin::ImplTrait) = where_bound_origin
-                        && let hir::LifetimeName::Param(param_id) = lifetime_ref.res
+                        && let hir::LifetimeKind::Param(param_id) = lifetime_ref.kind
                         && let Some(generics) =
                             self.tcx.hir_get_generics(self.tcx.local_parent(param_id))
                         && let Some(param) = generics.params.iter().find(|p| p.def_id == param_id)
@@ -1811,7 +1811,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                         self.tcx,
                         type_def_id,
                         constraint.ident,
-                        ty::AssocKind::Fn,
+                        ty::AssocTag::Fn,
                     ) {
                     bound_vars.extend(
                         self.tcx
@@ -1843,7 +1843,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     self.tcx,
                     type_def_id,
                     constraint.ident,
-                    ty::AssocKind::Type,
+                    ty::AssocTag::Type,
                 )
                 .map(|(bound_vars, _)| bound_vars);
                 self.with(scope, |this| {
@@ -1874,14 +1874,14 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
     fn supertrait_hrtb_vars(
         tcx: TyCtxt<'tcx>,
         def_id: DefId,
-        assoc_name: Ident,
-        assoc_kind: ty::AssocKind,
+        assoc_ident: Ident,
+        assoc_tag: ty::AssocTag,
     ) -> Option<(Vec<ty::BoundVariableKind>, &'tcx ty::AssocItem)> {
         let trait_defines_associated_item_named = |trait_def_id: DefId| {
-            tcx.associated_items(trait_def_id).find_by_name_and_kind(
+            tcx.associated_items(trait_def_id).find_by_ident_and_kind(
                 tcx,
-                assoc_name,
-                assoc_kind,
+                assoc_ident,
+                assoc_tag,
                 trait_def_id,
             )
         };
@@ -1894,8 +1894,8 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             let Some((def_id, bound_vars)) = stack.pop() else {
                 break None;
             };
-            // See issue #83753. If someone writes an associated type on a non-trait, just treat it as
-            // there being no supertrait HRTBs.
+            // See issue #83753. If someone writes an associated type on a non-trait, just treat it
+            // as there being no supertrait HRTBs.
             match tcx.def_kind(def_id) {
                 DefKind::Trait | DefKind::TraitAlias | DefKind::Impl { .. } => {}
                 _ => break None,
@@ -1904,7 +1904,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             if let Some(assoc_item) = trait_defines_associated_item_named(def_id) {
                 break Some((bound_vars.into_iter().collect(), assoc_item));
             }
-            let predicates = tcx.explicit_supertraits_containing_assoc_item((def_id, assoc_name));
+            let predicates = tcx.explicit_supertraits_containing_assoc_item((def_id, assoc_ident));
             let obligations = predicates.iter_identity_copied().filter_map(|(pred, _)| {
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {
@@ -2067,7 +2067,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                                     self.tcx,
                                     trait_def_id,
                                     item_segment.ident,
-                                    ty::AssocKind::Fn,
+                                    ty::AssocTag::Fn,
                                 )
                             });
 
@@ -2112,7 +2112,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                             self.tcx,
                             trait_def_id,
                             item_segment.ident,
-                            ty::AssocKind::Fn,
+                            ty::AssocTag::Fn,
                         ) else {
                             return;
                         };
@@ -2440,7 +2440,7 @@ fn is_late_bound_map(
         }
 
         fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
-            if let hir::LifetimeName::Param(def_id) = lifetime_ref.res {
+            if let hir::LifetimeKind::Param(def_id) = lifetime_ref.kind {
                 self.regions.insert(def_id);
             }
         }
@@ -2453,7 +2453,7 @@ fn is_late_bound_map(
 
     impl<'tcx> Visitor<'tcx> for AllCollector {
         fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
-            if let hir::LifetimeName::Param(def_id) = lifetime_ref.res {
+            if let hir::LifetimeKind::Param(def_id) = lifetime_ref.kind {
                 self.regions.insert(def_id);
             }
         }
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
index 3fe3d71b32d..50e20a19eda 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
@@ -32,9 +32,11 @@ pub(super) fn find_opaque_ty_constraints_for_impl_trait_in_assoc_type(
     for &assoc_id in tcx.associated_item_def_ids(impl_def_id) {
         let assoc = tcx.associated_item(assoc_id);
         match assoc.kind {
-            ty::AssocKind::Const | ty::AssocKind::Fn => locator.check(assoc_id.expect_local()),
+            ty::AssocKind::Const { .. } | ty::AssocKind::Fn { .. } => {
+                locator.check(assoc_id.expect_local())
+            }
             // Associated types don't have bodies, so they can't constrain hidden types
-            ty::AssocKind::Type => {}
+            ty::AssocKind::Type { .. } => {}
         }
     }
 
@@ -183,25 +185,23 @@ impl<'tcx> TaitConstraintLocator<'tcx> {
                     self.non_defining_use_in_defining_scope(item_def_id);
                 }
             }
-            DefiningScopeKind::MirBorrowck => {
-                let borrowck_result = tcx.mir_borrowck(item_def_id);
-                if let Some(guar) = borrowck_result.tainted_by_errors {
-                    self.insert_found(ty::OpaqueHiddenType::new_error(tcx, guar));
-                } else if let Some(&hidden_type) =
-                    borrowck_result.concrete_opaque_types.get(&self.def_id)
-                {
-                    debug!(?hidden_type, "found constraint");
-                    self.insert_found(hidden_type);
-                } else if let Err(guar) = tcx
-                    .type_of_opaque_hir_typeck(self.def_id)
-                    .instantiate_identity()
-                    .error_reported()
-                {
-                    self.insert_found(ty::OpaqueHiddenType::new_error(tcx, guar));
-                } else {
-                    self.non_defining_use_in_defining_scope(item_def_id);
+            DefiningScopeKind::MirBorrowck => match tcx.mir_borrowck(item_def_id) {
+                Err(guar) => self.insert_found(ty::OpaqueHiddenType::new_error(tcx, guar)),
+                Ok(concrete_opaque_types) => {
+                    if let Some(&hidden_type) = concrete_opaque_types.0.get(&self.def_id) {
+                        debug!(?hidden_type, "found constraint");
+                        self.insert_found(hidden_type);
+                    } else if let Err(guar) = tcx
+                        .type_of_opaque_hir_typeck(self.def_id)
+                        .instantiate_identity()
+                        .error_reported()
+                    {
+                        self.insert_found(ty::OpaqueHiddenType::new_error(tcx, guar));
+                    } else {
+                        self.non_defining_use_in_defining_scope(item_def_id);
+                    }
                 }
-            }
+            },
         }
     }
 }
@@ -264,20 +264,20 @@ pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(
                 Ty::new_diverging_default(tcx)
             }
         }
-        DefiningScopeKind::MirBorrowck => {
-            let borrowck_result = tcx.mir_borrowck(owner_def_id);
-            if let Some(guar) = borrowck_result.tainted_by_errors {
-                Ty::new_error(tcx, guar)
-            } else if let Some(hidden_ty) = borrowck_result.concrete_opaque_types.get(&def_id) {
-                hidden_ty.ty
-            } else {
-                let hir_ty = tcx.type_of_opaque_hir_typeck(def_id).instantiate_identity();
-                if let Err(guar) = hir_ty.error_reported() {
-                    Ty::new_error(tcx, guar)
+        DefiningScopeKind::MirBorrowck => match tcx.mir_borrowck(owner_def_id) {
+            Ok(concrete_opaque_types) => {
+                if let Some(hidden_ty) = concrete_opaque_types.0.get(&def_id) {
+                    hidden_ty.ty
                 } else {
-                    hir_ty
+                    let hir_ty = tcx.type_of_opaque_hir_typeck(def_id).instantiate_identity();
+                    if let Err(guar) = hir_ty.error_reported() {
+                        Ty::new_error(tcx, guar)
+                    } else {
+                        hir_ty
+                    }
                 }
             }
-        }
+            Err(guar) => Ty::new_error(tcx, guar),
+        },
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/constrained_generic_params.rs b/compiler/rustc_hir_analysis/src/constrained_generic_params.rs
index 53866aa27b1..951eda72ffe 100644
--- a/compiler/rustc_hir_analysis/src/constrained_generic_params.rs
+++ b/compiler/rustc_hir_analysis/src/constrained_generic_params.rs
@@ -80,7 +80,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ParameterCollector {
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        if let ty::ReEarlyParam(data) = *r {
+        if let ty::ReEarlyParam(data) = r.kind() {
             self.parameters.push(Parameter::from(data));
         }
     }
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index f2560f22874..508970cf255 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -23,7 +23,7 @@ pub(crate) struct AmbiguousAssocItem<'a> {
     #[label]
     pub span: Span,
     pub assoc_kind: &'static str,
-    pub assoc_name: Ident,
+    pub assoc_ident: Ident,
     pub qself: &'a str,
 }
 
@@ -75,7 +75,7 @@ pub(crate) struct AssocItemIsPrivate {
 pub(crate) struct AssocItemNotFound<'a> {
     #[primary_span]
     pub span: Span,
-    pub assoc_name: Ident,
+    pub assoc_ident: Ident,
     pub assoc_kind: &'static str,
     pub qself: &'a str,
     #[subdiagnostic]
@@ -1707,3 +1707,11 @@ pub(crate) enum SupertraitItemShadowee {
         traits: DiagSymbolList,
     },
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_self_in_type_alias, code = E0411)]
+pub(crate) struct SelfInTypeAlias {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
diff --git a/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs b/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
index 610b293a114..526ee30209c 100644
--- a/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
+++ b/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
@@ -4,7 +4,7 @@ use GenericArgsInfo::*;
 use rustc_errors::codes::*;
 use rustc_errors::{Applicability, Diag, Diagnostic, EmissionGuarantee, MultiSpan, pluralize};
 use rustc_hir as hir;
-use rustc_middle::ty::{self as ty, AssocItems, AssocKind, TyCtxt};
+use rustc_middle::ty::{self as ty, AssocItems, TyCtxt};
 use rustc_span::def_id::DefId;
 use tracing::debug;
 
@@ -486,13 +486,13 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
             let items: &AssocItems = self.tcx.associated_items(self.def_id);
             items
                 .in_definition_order()
-                .filter(|item| item.kind == AssocKind::Type)
+                .filter(|item| item.is_type())
                 .filter(|item| {
                     !self
                         .gen_args
                         .constraints
                         .iter()
-                        .any(|constraint| constraint.ident.name == item.name)
+                        .any(|constraint| constraint.ident.name == item.name())
                 })
                 .filter(|item| !item.is_impl_trait_in_trait())
                 .map(|item| self.tcx.item_ident(item.def_id).to_string())
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index c3bb860538e..bf91eb1b8fd 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -43,12 +43,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     }
 
     /// Checks whether `Self: DefaultAutoTrait` bounds should be added on trait super bounds
-    /// or associative items.
+    /// or associated items.
     ///
     /// To keep backward compatibility with existing code, `experimental_default_bounds` bounds
     /// should be added everywhere, including super bounds. However this causes a huge performance
     /// costs. For optimization purposes instead of adding default supertraits, bounds
-    /// are added to the associative items:
+    /// are added to the associated items:
     ///
     /// ```ignore(illustrative)
     /// // Default bounds are generated in the following way:
@@ -81,7 +81,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     ///
     /// Therefore, `experimental_default_bounds` are still being added to supertraits if
     /// the `SelfTyParam` or `AssocItemConstraint` were found in a trait header.
-    pub(crate) fn requires_default_supertraits(
+    fn requires_default_supertraits(
         &self,
         hir_bounds: &'tcx [hir::GenericBound<'tcx>],
         hir_generics: &'tcx hir::Generics<'tcx>,
@@ -120,6 +120,43 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         found
     }
 
+    /// Implicitly add `Self: DefaultAutoTrait` clauses on trait associated items if
+    /// they are not added as super trait bounds to the trait itself. See
+    /// `requires_default_supertraits` for more information.
+    pub(crate) fn add_default_trait_item_bounds(
+        &self,
+        trait_item: &hir::TraitItem<'tcx>,
+        bounds: &mut Vec<(ty::Clause<'tcx>, Span)>,
+    ) {
+        let tcx = self.tcx();
+        if !tcx.sess.opts.unstable_opts.experimental_default_bounds {
+            return;
+        }
+
+        let parent = tcx.local_parent(trait_item.hir_id().owner.def_id);
+        let hir::Node::Item(parent_trait) = tcx.hir_node_by_def_id(parent) else {
+            unreachable!();
+        };
+
+        let (trait_generics, trait_bounds) = match parent_trait.kind {
+            hir::ItemKind::Trait(_, _, _, generics, supertraits, _) => (generics, supertraits),
+            hir::ItemKind::TraitAlias(_, generics, supertraits) => (generics, supertraits),
+            _ => unreachable!(),
+        };
+
+        if !self.requires_default_supertraits(trait_bounds, trait_generics) {
+            let self_ty_where_predicates = (parent, trait_item.generics.predicates);
+            self.add_default_traits_with_filter(
+                bounds,
+                tcx.types.self_param,
+                &[],
+                Some(self_ty_where_predicates),
+                trait_item.span,
+                |tr| tr != hir::LangItem::Sized,
+            );
+        }
+    }
+
     /// Lazily sets `experimental_default_bounds` to true on trait super bounds.
     /// See `requires_default_supertraits` for more information.
     pub(crate) fn add_default_super_traits(
@@ -130,6 +167,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         hir_generics: &'tcx hir::Generics<'tcx>,
         span: Span,
     ) {
+        if !self.tcx().sess.opts.unstable_opts.experimental_default_bounds {
+            return;
+        }
+
         assert!(matches!(self.tcx().def_kind(trait_def_id), DefKind::Trait | DefKind::TraitAlias));
         if self.requires_default_supertraits(hir_bounds, hir_generics) {
             let self_ty_where_predicates = (trait_def_id, hir_generics.predicates);
@@ -263,11 +304,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 seen_unbound = true;
             }
             let emit_relax_err = || {
-                let unbound_traits =
-                    match self.tcx().sess.opts.unstable_opts.experimental_default_bounds {
-                        true => "`?Sized` and `experimental_default_bounds`",
-                        false => "`?Sized`",
-                    };
+                let unbound_traits = match tcx.sess.opts.unstable_opts.experimental_default_bounds {
+                    true => "`?Sized` and `experimental_default_bounds`",
+                    false => "`?Sized`",
+                };
                 // There was a `?Trait` bound, but it was neither `?Sized` nor `experimental_default_bounds`.
                 tcx.dcx().span_err(
                     unbound.span,
@@ -323,10 +363,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         for hir_bound in hir_bounds {
             // In order to avoid cycles, when we're lowering `SelfTraitThatDefines`,
             // we skip over any traits that don't define the given associated type.
-            if let PredicateFilter::SelfTraitThatDefines(assoc_name) = predicate_filter {
+            if let PredicateFilter::SelfTraitThatDefines(assoc_ident) = predicate_filter {
                 if let Some(trait_ref) = hir_bound.trait_ref()
                     && let Some(trait_did) = trait_ref.trait_def_id()
-                    && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
+                    && self.tcx().trait_may_define_assoc_item(trait_did, assoc_ident)
                 {
                     // Okay
                 } else {
@@ -391,16 +431,16 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     ) -> Result<(), ErrorGuaranteed> {
         let tcx = self.tcx();
 
-        let assoc_kind = if constraint.gen_args.parenthesized
+        let assoc_tag = if constraint.gen_args.parenthesized
             == hir::GenericArgsParentheses::ReturnTypeNotation
         {
-            ty::AssocKind::Fn
+            ty::AssocTag::Fn
         } else if let hir::AssocItemConstraintKind::Equality { term: hir::Term::Const(_) } =
             constraint.kind
         {
-            ty::AssocKind::Const
+            ty::AssocTag::Const
         } else {
-            ty::AssocKind::Type
+            ty::AssocTag::Type
         };
 
         // Given something like `U: Trait<T = X>`, we want to produce a predicate like
@@ -413,7 +453,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         //     trait SuperTrait<A> { type T; }
         let candidate = if self.probe_trait_that_defines_assoc_item(
             trait_ref.def_id(),
-            assoc_kind,
+            assoc_tag,
             constraint.ident,
         ) {
             // Simple case: The assoc item is defined in the current trait.
@@ -424,7 +464,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             self.probe_single_bound_for_assoc_item(
                 || traits::supertraits(tcx, trait_ref),
                 AssocItemQSelf::Trait(trait_ref.def_id()),
-                assoc_kind,
+                assoc_tag,
                 constraint.ident,
                 path_span,
                 Some(constraint),
@@ -434,7 +474,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let assoc_item = self
             .probe_assoc_item(
                 constraint.ident,
-                assoc_kind,
+                assoc_tag,
                 hir_ref_id,
                 constraint.span,
                 candidate.def_id(),
@@ -453,7 +493,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             })
             .or_insert(constraint.span);
 
-        let projection_term = if let ty::AssocKind::Fn = assoc_kind {
+        let projection_term = if let ty::AssocTag::Fn = assoc_tag {
             let bound_vars = tcx.late_bound_vars(constraint.hir_id);
             ty::Binder::bind_with_vars(
                 self.lower_return_type_notation_ty(candidate, assoc_item.def_id, path_span)?.into(),
@@ -502,7 +542,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         };
 
         match constraint.kind {
-            hir::AssocItemConstraintKind::Equality { .. } if let ty::AssocKind::Fn = assoc_kind => {
+            hir::AssocItemConstraintKind::Equality { .. } if let ty::AssocTag::Fn = assoc_tag => {
                 return Err(self.dcx().emit_err(crate::errors::ReturnTypeNotationEqualityBound {
                     span: constraint.span,
                 }));
@@ -639,7 +679,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         trait_def_id,
                         hir_ty.span,
                         item_segment,
-                        ty::AssocKind::Type,
+                        ty::AssocTag::Type,
                     );
                     return Ty::new_error(tcx, guar);
                 };
@@ -731,7 +771,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         )
                     },
                     AssocItemQSelf::SelfTyAlias,
-                    ty::AssocKind::Fn,
+                    ty::AssocTag::Fn,
                     assoc_ident,
                     span,
                     None,
@@ -743,7 +783,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             ) => self.probe_single_ty_param_bound_for_assoc_item(
                 param_did.expect_local(),
                 qself.span,
-                ty::AssocKind::Fn,
+                ty::AssocTag::Fn,
                 assoc_ident,
                 span,
             )?,
@@ -783,7 +823,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         let trait_def_id = bound.def_id();
         let assoc_ty = self
-            .probe_assoc_item(assoc_ident, ty::AssocKind::Fn, qpath_hir_id, span, trait_def_id)
+            .probe_assoc_item(assoc_ident, ty::AssocTag::Fn, qpath_hir_id, span, trait_def_id)
             .expect("failed to find associated type");
 
         Ok((bound, assoc_ty.def_id))
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs
index ecb453bced0..d1ee5a5494c 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs
@@ -49,13 +49,13 @@ pub(crate) fn validate_cmse_abi<'tcx>(
                 Ok(Err(index)) => {
                     // fn(x: u32, u32, u32, u16, y: u16) -> u32,
                     //                           ^^^^^^
-                    let span = if let Some(ident) = bare_fn_ty.param_names[index] {
+                    let span = if let Some(ident) = bare_fn_ty.param_idents[index] {
                         ident.span.to(bare_fn_ty.decl.inputs[index].span)
                     } else {
                         bare_fn_ty.decl.inputs[index].span
                     }
                     .to(bare_fn_ty.decl.inputs.last().unwrap().span);
-                    let plural = bare_fn_ty.param_names.len() - index != 1;
+                    let plural = bare_fn_ty.param_idents.len() - index != 1;
                     dcx.emit_err(errors::CmseInputsStackSpill { span, plural, abi });
                 }
                 Err(layout_err) => {
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
index aeebe45f881..88f74589204 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs
@@ -16,6 +16,7 @@ use smallvec::{SmallVec, smallvec};
 use tracing::{debug, instrument};
 
 use super::HirTyLowerer;
+use crate::errors::SelfInTypeAlias;
 use crate::hir_ty_lowering::{
     GenericArgCountMismatch, GenericArgCountResult, PredicateFilter, RegionInferReason,
 };
@@ -125,6 +126,19 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // ```
         let mut projection_bounds = FxIndexMap::default();
         for (proj, proj_span) in elaborated_projection_bounds {
+            let proj = proj.map_bound(|mut b| {
+                if let Some(term_ty) = &b.term.as_type() {
+                    let references_self = term_ty.walk().any(|arg| arg == dummy_self.into());
+                    if references_self {
+                        // With trait alias and type alias combined, type resolver
+                        // may not be able to catch all illegal `Self` usages (issue 139082)
+                        let guar = tcx.dcx().emit_err(SelfInTypeAlias { span });
+                        b.term = replace_dummy_self_with_error(tcx, b.term, guar);
+                    }
+                }
+                b
+            });
+
             let key = (
                 proj.skip_binder().projection_term.def_id,
                 tcx.anonymize_bound_vars(
@@ -187,7 +201,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                             tcx.associated_items(pred.trait_ref.def_id)
                                 .in_definition_order()
                                 // We only care about associated types.
-                                .filter(|item| item.kind == ty::AssocKind::Type)
+                                .filter(|item| item.is_type())
                                 // No RPITITs -- they're not dyn-compatible for now.
                                 .filter(|item| !item.is_impl_trait_in_trait())
                                 // If the associated type has a `where Self: Sized` bound,
@@ -401,7 +415,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     self.lower_lifetime(lifetime, RegionInferReason::ExplicitObjectLifetime)
                 } else {
                     let reason =
-                        if let hir::LifetimeName::ImplicitObjectLifetimeDefault = lifetime.res {
+                        if let hir::LifetimeKind::ImplicitObjectLifetimeDefault = lifetime.kind {
                             if let hir::Node::Ty(hir::Ty {
                                 kind: hir::TyKind::Ref(parent_lifetime, _),
                                 ..
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
index 6e9c178d33a..3759a224ff7 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
@@ -116,8 +116,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         &self,
         all_candidates: impl Fn() -> I,
         qself: AssocItemQSelf,
-        assoc_kind: ty::AssocKind,
-        assoc_name: Ident,
+        assoc_tag: ty::AssocTag,
+        assoc_ident: Ident,
         span: Span,
         constraint: Option<&hir::AssocItemConstraint<'tcx>>,
     ) -> ErrorGuaranteed
@@ -129,31 +129,35 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // First and foremost, provide a more user-friendly & “intuitive” error on kind mismatches.
         if let Some(assoc_item) = all_candidates().find_map(|r| {
             tcx.associated_items(r.def_id())
-                .filter_by_name_unhygienic(assoc_name.name)
-                .find(|item| tcx.hygienic_eq(assoc_name, item.ident(tcx), r.def_id()))
+                .filter_by_name_unhygienic(assoc_ident.name)
+                .find(|item| tcx.hygienic_eq(assoc_ident, item.ident(tcx), r.def_id()))
         }) {
             return self.complain_about_assoc_kind_mismatch(
-                assoc_item, assoc_kind, assoc_name, span, constraint,
+                assoc_item,
+                assoc_tag,
+                assoc_ident,
+                span,
+                constraint,
             );
         }
 
-        let assoc_kind_str = assoc_kind_str(assoc_kind);
+        let assoc_kind_str = assoc_tag_str(assoc_tag);
         let qself_str = qself.to_string(tcx);
 
         // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
         // valid span, so we point at the whole path segment instead.
-        let is_dummy = assoc_name.span == DUMMY_SP;
+        let is_dummy = assoc_ident.span == DUMMY_SP;
 
         let mut err = errors::AssocItemNotFound {
-            span: if is_dummy { span } else { assoc_name.span },
-            assoc_name,
+            span: if is_dummy { span } else { assoc_ident.span },
+            assoc_ident,
             assoc_kind: assoc_kind_str,
             qself: &qself_str,
             label: None,
             sugg: None,
             // Try to get the span of the identifier within the path's syntax context
             // (if that's different).
-            within_macro_span: assoc_name.span.within_macro(span, tcx.sess.source_map()),
+            within_macro_span: assoc_ident.span.within_macro(span, tcx.sess.source_map()),
         };
 
         if is_dummy {
@@ -164,15 +168,19 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let all_candidate_names: Vec<_> = all_candidates()
             .flat_map(|r| tcx.associated_items(r.def_id()).in_definition_order())
             .filter_map(|item| {
-                (!item.is_impl_trait_in_trait() && item.kind == assoc_kind).then_some(item.name)
+                if !item.is_impl_trait_in_trait() && item.as_tag() == assoc_tag {
+                    item.opt_name()
+                } else {
+                    None
+                }
             })
             .collect();
 
         if let Some(suggested_name) =
-            find_best_match_for_name(&all_candidate_names, assoc_name.name, None)
+            find_best_match_for_name(&all_candidate_names, assoc_ident.name, None)
         {
             err.sugg = Some(errors::AssocItemNotFoundSugg::Similar {
-                span: assoc_name.span,
+                span: assoc_ident.span,
                 assoc_kind: assoc_kind_str,
                 suggested_name,
             });
@@ -196,12 +204,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             .iter()
             .flat_map(|trait_def_id| tcx.associated_items(*trait_def_id).in_definition_order())
             .filter_map(|item| {
-                (!item.is_impl_trait_in_trait() && item.kind == assoc_kind).then_some(item.name)
+                (!item.is_impl_trait_in_trait() && item.as_tag() == assoc_tag).then(|| item.name())
             })
             .collect();
 
         if let Some(suggested_name) =
-            find_best_match_for_name(&wider_candidate_names, assoc_name.name, None)
+            find_best_match_for_name(&wider_candidate_names, assoc_ident.name, None)
         {
             if let [best_trait] = visible_traits
                 .iter()
@@ -209,17 +217,17 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 .filter(|trait_def_id| {
                     tcx.associated_items(trait_def_id)
                         .filter_by_name_unhygienic(suggested_name)
-                        .any(|item| item.kind == assoc_kind)
+                        .any(|item| item.as_tag() == assoc_tag)
                 })
                 .collect::<Vec<_>>()[..]
             {
                 let trait_name = tcx.def_path_str(best_trait);
                 err.label = Some(errors::AssocItemNotFoundLabel::FoundInOtherTrait {
-                    span: assoc_name.span,
+                    span: assoc_ident.span,
                     assoc_kind: assoc_kind_str,
                     trait_name: &trait_name,
                     suggested_name,
-                    identically_named: suggested_name == assoc_name.name,
+                    identically_named: suggested_name == assoc_ident.name,
                 });
                 if let AssocItemQSelf::TyParam(ty_param_def_id, ty_param_span) = qself
                     // Not using `self.item_def_id()` here as that would yield the opaque type itself if we're
@@ -246,7 +254,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         // The type param already has a bound for `trait_name`, we just need to
                         // change the associated item.
                         err.sugg = Some(errors::AssocItemNotFoundSugg::SimilarInOtherTrait {
-                            span: assoc_name.span,
+                            span: assoc_ident.span,
                             assoc_kind: assoc_kind_str,
                             suggested_name,
                         });
@@ -265,7 +273,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         Applicability::MaybeIncorrect
                     };
 
-                    let identically_named = suggested_name == assoc_name.name;
+                    let identically_named = suggested_name == assoc_ident.name;
 
                     if let DefKind::TyAlias = tcx.def_kind(item_def_id)
                         && !tcx.type_alias_is_lazy(item_def_id)
@@ -273,7 +281,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         err.sugg = Some(errors::AssocItemNotFoundSugg::SimilarInOtherTraitQPath {
                             lo: ty_param_span.shrink_to_lo(),
                             mi: ty_param_span.shrink_to_hi(),
-                            hi: (!identically_named).then_some(assoc_name.span),
+                            hi: (!identically_named).then_some(assoc_ident.span),
                             trait_ref,
                             identically_named,
                             suggested_name,
@@ -294,7 +302,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                             // We suggested constraining a type parameter, but the associated item on it
                             // was also not an exact match, so we also suggest changing it.
                             err.span_suggestion_verbose(
-                                assoc_name.span,
+                                assoc_ident.span,
                                 fluent::hir_analysis_assoc_item_not_found_similar_in_other_trait_with_bound_sugg,
                                 suggested_name,
                                 Applicability::MaybeIncorrect,
@@ -311,13 +319,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // suggest using it.
         if let [candidate_name] = all_candidate_names.as_slice() {
             err.sugg = Some(errors::AssocItemNotFoundSugg::Other {
-                span: assoc_name.span,
+                span: assoc_ident.span,
                 qself: &qself_str,
                 assoc_kind: assoc_kind_str,
                 suggested_name: *candidate_name,
             });
         } else {
-            err.label = Some(errors::AssocItemNotFoundLabel::NotFound { span: assoc_name.span });
+            err.label = Some(errors::AssocItemNotFoundLabel::NotFound { span: assoc_ident.span });
         }
 
         self.dcx().emit_err(err)
@@ -326,14 +334,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     fn complain_about_assoc_kind_mismatch(
         &self,
         assoc_item: &ty::AssocItem,
-        assoc_kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
         ident: Ident,
         span: Span,
         constraint: Option<&hir::AssocItemConstraint<'tcx>>,
     ) -> ErrorGuaranteed {
         let tcx = self.tcx();
 
-        let bound_on_assoc_const_label = if let ty::AssocKind::Const = assoc_item.kind
+        let bound_on_assoc_const_label = if let ty::AssocKind::Const { .. } = assoc_item.kind
             && let Some(constraint) = constraint
             && let hir::AssocItemConstraintKind::Bound { .. } = constraint.kind
         {
@@ -371,17 +379,17 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 hir::Term::Ty(ty) => ty.span,
                 hir::Term::Const(ct) => ct.span(),
             };
-            (span, Some(ident.span), assoc_item.kind, assoc_kind)
+            (span, Some(ident.span), assoc_item.as_tag(), assoc_tag)
         } else {
-            (ident.span, None, assoc_kind, assoc_item.kind)
+            (ident.span, None, assoc_tag, assoc_item.as_tag())
         };
 
         self.dcx().emit_err(errors::AssocKindMismatch {
             span,
-            expected: assoc_kind_str(expected),
-            got: assoc_kind_str(got),
+            expected: assoc_tag_str(expected),
+            got: assoc_tag_str(got),
             expected_because_label,
-            assoc_kind: assoc_kind_str(assoc_item.kind),
+            assoc_kind: assoc_tag_str(assoc_item.as_tag()),
             def_span: tcx.def_span(assoc_item.def_id),
             bound_on_assoc_const_label,
             wrap_in_braces_sugg,
@@ -394,9 +402,9 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         types: &[String],
         traits: &[String],
         name: Symbol,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> ErrorGuaranteed {
-        let kind_str = assoc_kind_str(kind);
+        let kind_str = assoc_tag_str(assoc_tag);
         let mut err =
             struct_span_code_err!(self.dcx(), span, E0223, "ambiguous associated {kind_str}");
         if self
@@ -565,7 +573,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         candidates: Vec<(DefId, (DefId, DefId))>,
         fulfillment_errors: Vec<FulfillmentError<'tcx>>,
         span: Span,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> ErrorGuaranteed {
         // FIXME(fmease): This was copied in parts from an old version of `rustc_hir_typeck::method::suggest`.
         // Either
@@ -575,14 +583,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         let tcx = self.tcx();
 
-        let kind_str = assoc_kind_str(kind);
+        let assoc_tag_str = assoc_tag_str(assoc_tag);
         let adt_did = self_ty.ty_adt_def().map(|def| def.did());
         let add_def_label = |err: &mut Diag<'_>| {
             if let Some(did) = adt_did {
                 err.span_label(
                     tcx.def_span(did),
                     format!(
-                        "associated {kind_str} `{name}` not found for this {}",
+                        "associated {assoc_tag_str} `{name}` not found for this {}",
                         tcx.def_descr(did)
                     ),
                 );
@@ -611,11 +619,11 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 self.dcx(),
                 name.span,
                 E0220,
-                "associated {kind_str} `{name}` not found for `{self_ty}` in the current scope"
+                "associated {assoc_tag_str} `{name}` not found for `{self_ty}` in the current scope"
             );
             err.span_label(name.span, format!("associated item not found in `{self_ty}`"));
             err.note(format!(
-                "the associated {kind_str} was found for\n{type_candidates}{additional_types}",
+                "the associated {assoc_tag_str} was found for\n{type_candidates}{additional_types}",
             ));
             add_def_label(&mut err);
             return err.emit();
@@ -696,7 +704,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         let mut err = self.dcx().struct_span_err(
             name.span,
-            format!("the associated {kind_str} `{name}` exists for `{self_ty}`, but its trait bounds were not satisfied")
+            format!("the associated {assoc_tag_str} `{name}` exists for `{self_ty}`, but its trait bounds were not satisfied")
         );
         if !bounds.is_empty() {
             err.note(format!(
@@ -706,7 +714,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }
         err.span_label(
             name.span,
-            format!("associated {kind_str} cannot be referenced on `{self_ty}` due to unsatisfied trait bounds")
+            format!("associated {assoc_tag_str} cannot be referenced on `{self_ty}` due to unsatisfied trait bounds")
         );
 
         for (span, mut bounds) in bound_spans {
@@ -757,7 +765,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // `issue-22560.rs`.
         let mut dyn_compatibility_violations = Ok(());
         for (assoc_item, trait_ref) in &missing_assoc_types {
-            names.entry(trait_ref).or_default().push(assoc_item.name);
+            names.entry(trait_ref).or_default().push(assoc_item.name());
             names_len += 1;
 
             let violations =
@@ -805,10 +813,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         return None;
                     };
 
-                    let assoc_item = tcx.associated_items(trait_def).find_by_name_and_kind(
+                    let assoc_item = tcx.associated_items(trait_def).find_by_ident_and_kind(
                         tcx,
                         ident,
-                        ty::AssocKind::Type,
+                        ty::AssocTag::Type,
                         trait_def,
                     );
 
@@ -848,16 +856,17 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let mut names: UnordMap<_, usize> = Default::default();
         for (item, _) in &missing_assoc_types {
             types_count += 1;
-            *names.entry(item.name).or_insert(0) += 1;
+            *names.entry(item.name()).or_insert(0) += 1;
         }
         let mut dupes = false;
         let mut shadows = false;
         for (item, trait_ref) in &missing_assoc_types {
-            let prefix = if names[&item.name] > 1 {
+            let name = item.name();
+            let prefix = if names[&name] > 1 {
                 let trait_def_id = trait_ref.def_id();
                 dupes = true;
                 format!("{}::", tcx.def_path_str(trait_def_id))
-            } else if bound_names.get(&item.name).is_some_and(|x| *x != item) {
+            } else if bound_names.get(&name).is_some_and(|x| *x != item) {
                 let trait_def_id = trait_ref.def_id();
                 shadows = true;
                 format!("{}::", tcx.def_path_str(trait_def_id))
@@ -867,7 +876,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
             let mut is_shadowed = false;
 
-            if let Some(assoc_item) = bound_names.get(&item.name)
+            if let Some(assoc_item) = bound_names.get(&name)
                 && *assoc_item != item
             {
                 is_shadowed = true;
@@ -876,17 +885,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     if assoc_item.def_id.is_local() { ", consider renaming it" } else { "" };
                 err.span_label(
                     tcx.def_span(assoc_item.def_id),
-                    format!("`{}{}` shadowed here{}", prefix, item.name, rename_message),
+                    format!("`{}{}` shadowed here{}", prefix, name, rename_message),
                 );
             }
 
             let rename_message = if is_shadowed { ", consider renaming it" } else { "" };
 
             if let Some(sp) = tcx.hir_span_if_local(item.def_id) {
-                err.span_label(
-                    sp,
-                    format!("`{}{}` defined here{}", prefix, item.name, rename_message),
-                );
+                err.span_label(sp, format!("`{}{}` defined here{}", prefix, name, rename_message));
             }
         }
         if potential_assoc_types.len() == missing_assoc_types.len() {
@@ -899,7 +905,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         {
             let types: Vec<_> = missing_assoc_types
                 .iter()
-                .map(|(item, _)| format!("{} = Type", item.name))
+                .map(|(item, _)| format!("{} = Type", item.name()))
                 .collect();
             let code = if let Some(snippet) = snippet.strip_suffix('>') {
                 // The user wrote `Trait<'a>` or similar and we don't have a type we can
@@ -934,16 +940,17 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             let mut names: FxIndexMap<_, usize> = FxIndexMap::default();
             for (item, _) in &missing_assoc_types {
                 types_count += 1;
-                *names.entry(item.name).or_insert(0) += 1;
+                *names.entry(item.name()).or_insert(0) += 1;
             }
             let mut label = vec![];
             for (item, trait_ref) in &missing_assoc_types {
-                let postfix = if names[&item.name] > 1 {
+                let name = item.name();
+                let postfix = if names[&name] > 1 {
                     format!(" (from trait `{}`)", trait_ref.print_trait_sugared())
                 } else {
                     String::new()
                 };
-                label.push(format!("`{}`{}", item.name, postfix));
+                label.push(format!("`{}`{}", name, postfix));
             }
             if !label.is_empty() {
                 err.span_label(
@@ -1018,12 +1025,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         .map(|simple_ty| tcx.incoherent_impls(simple_ty))
                 })
             && let name = Symbol::intern(&format!("{ident2}_{ident3}"))
-            && let Some(ty::AssocItem { kind: ty::AssocKind::Fn, .. }) = inherent_impls
+            && let Some(item) = inherent_impls
                 .iter()
                 .flat_map(|inherent_impl| {
                     tcx.associated_items(inherent_impl).filter_by_name_unhygienic(name)
                 })
                 .next()
+            && item.is_fn()
         {
             Err(struct_span_code_err!(self.dcx(), span, E0223, "ambiguous associated type")
                 .with_span_suggestion_verbose(
@@ -1625,10 +1633,10 @@ fn generics_args_err_extend<'a>(
     }
 }
 
-pub(crate) fn assoc_kind_str(kind: ty::AssocKind) -> &'static str {
-    match kind {
-        ty::AssocKind::Fn => "function",
-        ty::AssocKind::Const => "constant",
-        ty::AssocKind::Type => "type",
+pub(crate) fn assoc_tag_str(assoc_tag: ty::AssocTag) -> &'static str {
+    match assoc_tag {
+        ty::AssocTag::Fn => "function",
+        ty::AssocTag::Const => "constant",
+        ty::AssocTag::Type => "type",
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
index 8e62dce2191..483b61add33 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
@@ -501,8 +501,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let names: Vec<_> = tcx
             .associated_items(trait_def_id)
             .in_definition_order()
-            .filter(|assoc| assoc.kind.namespace() == Namespace::ValueNS)
-            .map(|cand| cand.name)
+            .filter(|assoc| assoc.namespace() == Namespace::ValueNS)
+            .map(|cand| cand.name())
             .collect();
         if let Some(typo) = find_best_match_for_name(&names, segment.ident.name, None) {
             diag.span_suggestion_verbose(
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index b4a71edc118..7605c6c6a42 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -38,8 +38,8 @@ use rustc_middle::middle::stability::AllowUnstable;
 use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::ty::print::PrintPolyTraitRefExt as _;
 use rustc_middle::ty::{
-    self, Const, GenericArgKind, GenericArgsRef, GenericParamDefKind, ParamEnv, Ty, TyCtxt,
-    TypeVisitableExt, TypingMode, Upcast, fold_regions,
+    self, AssocTag, Const, GenericArgKind, GenericArgsRef, GenericParamDefKind, ParamEnv, Ty,
+    TyCtxt, TypeVisitableExt, TypingMode, Upcast, fold_regions,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
@@ -51,7 +51,7 @@ use rustc_trait_selection::traits::wf::object_region_bounds;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 use tracing::{debug, instrument};
 
-use self::errors::assoc_kind_str;
+use self::errors::assoc_tag_str;
 use crate::check::check_abi_fn_ptr;
 use crate::errors::{AmbiguousLifetimeBound, BadReturnTypeNotation, NoVariantNamed};
 use crate::hir_ty_lowering::errors::{GenericsArgsErrExtend, prohibit_assoc_item_constraint};
@@ -147,7 +147,7 @@ pub trait HirTyLowerer<'tcx> {
         &self,
         span: Span,
         def_id: LocalDefId,
-        assoc_name: Ident,
+        assoc_ident: Ident,
     ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]>;
 
     /// Lower an associated type/const (from a trait) to a projection.
@@ -168,7 +168,7 @@ pub trait HirTyLowerer<'tcx> {
         item_def_id: DefId,
         item_segment: &hir::PathSegment<'tcx>,
         poly_trait_ref: ty::PolyTraitRef<'tcx>,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> Result<(DefId, GenericArgsRef<'tcx>), ErrorGuaranteed>;
 
     fn lower_fn_sig(
@@ -251,10 +251,10 @@ enum LowerAssocMode {
 }
 
 impl LowerAssocMode {
-    fn kind(self) -> ty::AssocKind {
+    fn assoc_tag(self) -> ty::AssocTag {
         match self {
-            LowerAssocMode::Type { .. } => ty::AssocKind::Type,
-            LowerAssocMode::Const => ty::AssocKind::Const,
+            LowerAssocMode::Type { .. } => ty::AssocTag::Type,
+            LowerAssocMode::Const => ty::AssocTag::Const,
         }
     }
 
@@ -268,7 +268,8 @@ impl LowerAssocMode {
     fn permit_variants(self) -> bool {
         match self {
             LowerAssocMode::Type { permit_variants } => permit_variants,
-            // FIXME(mgca): Support paths like `Option::<T>::None` or `Option::<T>::Some` which resolve to const ctors/fn items respectively
+            // FIXME(mgca): Support paths like `Option::<T>::None` or `Option::<T>::Some` which
+            // resolve to const ctors/fn items respectively.
             LowerAssocMode::Const => false,
         }
     }
@@ -932,12 +933,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     fn probe_trait_that_defines_assoc_item(
         &self,
         trait_def_id: DefId,
-        assoc_kind: ty::AssocKind,
-        assoc_name: Ident,
+        assoc_tag: AssocTag,
+        assoc_ident: Ident,
     ) -> bool {
         self.tcx()
             .associated_items(trait_def_id)
-            .find_by_name_and_kind(self.tcx(), assoc_name, assoc_kind, trait_def_id)
+            .find_by_ident_and_kind(self.tcx(), assoc_ident, assoc_tag, trait_def_id)
             .is_some()
     }
 
@@ -964,7 +965,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     }
 
     /// Search for a trait bound on a type parameter whose trait defines the associated item
-    /// given by `assoc_name` and `kind`.
+    /// given by `assoc_ident` and `kind`.
     ///
     /// This fails if there is no such bound in the list of candidates or if there are multiple
     /// candidates in which case it reports ambiguity.
@@ -975,14 +976,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         &self,
         ty_param_def_id: LocalDefId,
         ty_param_span: Span,
-        kind: ty::AssocKind,
-        assoc_name: Ident,
+        assoc_tag: AssocTag,
+        assoc_ident: Ident,
         span: Span,
     ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
-        debug!(?ty_param_def_id, ?assoc_name, ?span);
+        debug!(?ty_param_def_id, ?assoc_ident, ?span);
         let tcx = self.tcx();
 
-        let predicates = &self.probe_ty_param_bounds(span, ty_param_def_id, assoc_name);
+        let predicates = &self.probe_ty_param_bounds(span, ty_param_def_id, assoc_ident);
         debug!("predicates={:#?}", predicates);
 
         self.probe_single_bound_for_assoc_item(
@@ -990,17 +991,18 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 let trait_refs = predicates
                     .iter_identity_copied()
                     .filter_map(|(p, _)| Some(p.as_trait_clause()?.map_bound(|t| t.trait_ref)));
-                traits::transitive_bounds_that_define_assoc_item(tcx, trait_refs, assoc_name)
+                traits::transitive_bounds_that_define_assoc_item(tcx, trait_refs, assoc_ident)
             },
             AssocItemQSelf::TyParam(ty_param_def_id, ty_param_span),
-            kind,
-            assoc_name,
+            assoc_tag,
+            assoc_ident,
             span,
             None,
         )
     }
 
-    /// Search for a single trait bound whose trait defines the associated item given by `assoc_name`.
+    /// Search for a single trait bound whose trait defines the associated item given by
+    /// `assoc_ident`.
     ///
     /// This fails if there is no such bound in the list of candidates or if there are multiple
     /// candidates in which case it reports ambiguity.
@@ -1009,8 +1011,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         &self,
         all_candidates: impl Fn() -> I,
         qself: AssocItemQSelf,
-        assoc_kind: ty::AssocKind,
-        assoc_name: Ident,
+        assoc_tag: AssocTag,
+        assoc_ident: Ident,
         span: Span,
         constraint: Option<&hir::AssocItemConstraint<'tcx>>,
     ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
@@ -1020,15 +1022,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let tcx = self.tcx();
 
         let mut matching_candidates = all_candidates().filter(|r| {
-            self.probe_trait_that_defines_assoc_item(r.def_id(), assoc_kind, assoc_name)
+            self.probe_trait_that_defines_assoc_item(r.def_id(), assoc_tag, assoc_ident)
         });
 
         let Some(bound) = matching_candidates.next() else {
             let reported = self.complain_about_assoc_item_not_found(
                 all_candidates,
                 qself,
-                assoc_kind,
-                assoc_name,
+                assoc_tag,
+                assoc_ident,
                 span,
                 constraint,
             );
@@ -1039,12 +1041,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         if let Some(bound2) = matching_candidates.next() {
             debug!(?bound2);
 
-            let assoc_kind_str = errors::assoc_kind_str(assoc_kind);
+            let assoc_kind_str = errors::assoc_tag_str(assoc_tag);
             let qself_str = qself.to_string(tcx);
             let mut err = self.dcx().create_err(crate::errors::AmbiguousAssocItem {
                 span,
                 assoc_kind: assoc_kind_str,
-                assoc_name,
+                assoc_ident,
                 qself: &qself_str,
             });
             // Provide a more specific error code index entry for equality bindings.
@@ -1058,20 +1060,21 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 },
             );
 
-            // FIXME(#97583): Print associated item bindings properly (i.e., not as equality predicates!).
+            // FIXME(#97583): Print associated item bindings properly (i.e., not as equality
+            // predicates!).
             // FIXME: Turn this into a structured, translateable & more actionable suggestion.
             let mut where_bounds = vec![];
             for bound in [bound, bound2].into_iter().chain(matching_candidates) {
                 let bound_id = bound.def_id();
                 let bound_span = tcx
                     .associated_items(bound_id)
-                    .find_by_name_and_kind(tcx, assoc_name, assoc_kind, bound_id)
+                    .find_by_ident_and_kind(tcx, assoc_ident, assoc_tag, bound_id)
                     .and_then(|item| tcx.hir_span_if_local(item.def_id));
 
                 if let Some(bound_span) = bound_span {
                     err.span_label(
                         bound_span,
-                        format!("ambiguous `{assoc_name}` from `{}`", bound.print_trait_sugared(),),
+                        format!("ambiguous `{assoc_ident}` from `{}`", bound.print_trait_sugared(),),
                     );
                     if let Some(constraint) = constraint {
                         match constraint.kind {
@@ -1087,7 +1090,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                                 }
                                 // FIXME(#97583): This isn't syntactically well-formed!
                                 where_bounds.push(format!(
-                                    "        T: {trait}::{assoc_name} = {term}",
+                                    "        T: {trait}::{assoc_ident} = {term}",
                                     trait = bound.print_only_trait_path(),
                                 ));
                             }
@@ -1096,7 +1099,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         }
                     } else {
                         err.span_suggestion_verbose(
-                            span.with_hi(assoc_name.span.lo()),
+                            span.with_hi(assoc_ident.span.lo()),
                             "use fully-qualified syntax to disambiguate",
                             format!("<{qself_str} as {}>::", bound.print_only_trait_path()),
                             Applicability::MaybeIncorrect,
@@ -1104,7 +1107,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     }
                 } else {
                     err.note(format!(
-                        "associated {assoc_kind_str} `{assoc_name}` could derive from `{}`",
+                        "associated {assoc_kind_str} `{assoc_ident}` could derive from `{}`",
                         bound.print_only_trait_path(),
                     ));
                 }
@@ -1264,7 +1267,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 qself_ty,
                 hir_ref_id,
                 span,
-                mode.kind(),
+                mode.assoc_tag(),
             )? {
                 return Ok(LoweredAssoc::Term(did, args));
             }
@@ -1295,7 +1298,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         )
                     },
                     AssocItemQSelf::SelfTyAlias,
-                    mode.kind(),
+                    mode.assoc_tag(),
                     assoc_ident,
                     span,
                     None,
@@ -1307,12 +1310,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             ) => self.probe_single_ty_param_bound_for_assoc_item(
                 param_did.expect_local(),
                 qself.span,
-                mode.kind(),
+                mode.assoc_tag(),
                 assoc_ident,
                 span,
             )?,
             _ => {
-                let kind_str = assoc_kind_str(mode.kind());
+                let kind_str = assoc_tag_str(mode.assoc_tag());
                 let reported = if variant_resolution.is_some() {
                     // Variant in type position
                     let msg = format!("expected {kind_str}, found variant `{assoc_ident}`");
@@ -1419,7 +1422,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         &[qself_ty.to_string()],
                         &traits,
                         assoc_ident.name,
-                        mode.kind(),
+                        mode.assoc_tag(),
                     )
                 };
                 return Err(reported);
@@ -1428,10 +1431,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         let trait_did = bound.def_id();
         let assoc_item = self
-            .probe_assoc_item(assoc_ident, mode.kind(), hir_ref_id, span, trait_did)
+            .probe_assoc_item(assoc_ident, mode.assoc_tag(), hir_ref_id, span, trait_did)
             .expect("failed to find associated item");
-        let (def_id, args) =
-            self.lower_assoc_shared(span, assoc_item.def_id, assoc_segment, bound, mode.kind())?;
+        let (def_id, args) = self.lower_assoc_shared(
+            span,
+            assoc_item.def_id,
+            assoc_segment,
+            bound,
+            mode.assoc_tag(),
+        )?;
         let result = LoweredAssoc::Term(def_id, args);
 
         if let Some(variant_def_id) = variant_resolution {
@@ -1468,20 +1476,21 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         self_ty: Ty<'tcx>,
         block: HirId,
         span: Span,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> Result<Option<(DefId, GenericArgsRef<'tcx>)>, ErrorGuaranteed> {
         let tcx = self.tcx();
 
         if !tcx.features().inherent_associated_types() {
-            match kind {
-                // Don't attempt to look up inherent associated types when the feature is not enabled.
-                // Theoretically it'd be fine to do so since we feature-gate their definition site.
-                // However, due to current limitations of the implementation (caused by us performing
-                // selection during HIR ty lowering instead of in the trait solver), IATs can lead to cycle
-                // errors (#108491) which mask the feature-gate error, needlessly confusing users
-                // who use IATs by accident (#113265).
-                ty::AssocKind::Type => return Ok(None),
-                ty::AssocKind::Const => {
+            match assoc_tag {
+                // Don't attempt to look up inherent associated types when the feature is not
+                // enabled. Theoretically it'd be fine to do so since we feature-gate their
+                // definition site. However, due to current limitations of the implementation
+                // (caused by us performing selection during HIR ty lowering instead of in the
+                // trait solver), IATs can lead to cycle errors (#108491) which mask the
+                // feature-gate error, needlessly confusing users who use IATs by accident
+                // (#113265).
+                ty::AssocTag::Type => return Ok(None),
+                ty::AssocTag::Const => {
                     // We also gate the mgca codepath for type-level uses of inherent consts
                     // with the inherent_associated_types feature gate since it relies on the
                     // same machinery and has similar rough edges.
@@ -1493,7 +1502,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     )
                     .emit());
                 }
-                ty::AssocKind::Fn => unreachable!(),
+                ty::AssocTag::Fn => unreachable!(),
             }
         }
 
@@ -1502,7 +1511,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             .inherent_impls(adt_did)
             .iter()
             .filter_map(|&impl_| {
-                let (item, scope) = self.probe_assoc_item_unchecked(name, kind, block, impl_)?;
+                let (item, scope) =
+                    self.probe_assoc_item_unchecked(name, assoc_tag, block, impl_)?;
                 Some((impl_, (item.def_id, scope)))
             })
             .collect();
@@ -1541,7 +1551,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             self_ty,
             |self_ty| {
                 self.select_inherent_assoc_candidates(
-                    infcx, name, span, self_ty, param_env, candidates, kind,
+                    infcx, name, span, self_ty, param_env, candidates, assoc_tag,
                 )
             },
         )?;
@@ -1569,7 +1579,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         self_ty: Ty<'tcx>,
         param_env: ParamEnv<'tcx>,
         candidates: Vec<(DefId, (DefId, DefId))>,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> Result<(DefId, (DefId, DefId)), ErrorGuaranteed> {
         let tcx = self.tcx();
         let mut fulfillment_errors = Vec::new();
@@ -1620,7 +1630,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 candidates,
                 fulfillment_errors,
                 span,
-                kind,
+                assoc_tag,
             )),
 
             &[applicable_candidate] => Ok(applicable_candidate),
@@ -1639,12 +1649,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     fn probe_assoc_item(
         &self,
         ident: Ident,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
         block: HirId,
         span: Span,
         scope: DefId,
     ) -> Option<ty::AssocItem> {
-        let (item, scope) = self.probe_assoc_item_unchecked(ident, kind, block, scope)?;
+        let (item, scope) = self.probe_assoc_item_unchecked(ident, assoc_tag, block, scope)?;
         self.check_assoc_item(item.def_id, ident, scope, block, span);
         Some(item)
     }
@@ -1656,7 +1666,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     fn probe_assoc_item_unchecked(
         &self,
         ident: Ident,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
         block: HirId,
         scope: DefId,
     ) -> Option<(ty::AssocItem, /*scope*/ DefId)> {
@@ -1669,7 +1679,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let item = tcx
             .associated_items(scope)
             .filter_by_name_unhygienic(ident.name)
-            .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == ident)?;
+            .find(|i| i.as_tag() == assoc_tag && i.ident(tcx).normalize_to_macros_2_0() == ident)?;
 
         Some((*item, def_scope))
     }
@@ -1721,9 +1731,9 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 tcx.associated_items(*trait_def_id)
                         .in_definition_order()
                         .any(|i| {
-                            i.kind.namespace() == Namespace::TypeNS
+                            i.namespace() == Namespace::TypeNS
                                 && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
-                                && matches!(i.kind, ty::AssocKind::Type)
+                                && i.is_type()
                         })
                     // Consider only accessible traits
                     && tcx.visibility(*trait_def_id)
@@ -1769,7 +1779,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             item_def_id,
             trait_segment,
             item_segment,
-            ty::AssocKind::Type,
+            ty::AssocTag::Type,
         ) {
             Ok((item_def_id, item_args)) => {
                 Ty::new_projection_from_args(self.tcx(), item_def_id, item_args)
@@ -1794,7 +1804,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             item_def_id,
             trait_segment,
             item_segment,
-            ty::AssocKind::Const,
+            ty::AssocTag::Const,
         ) {
             Ok((item_def_id, item_args)) => {
                 let uv = ty::UnevaluatedConst::new(item_def_id, item_args);
@@ -1812,7 +1822,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         item_def_id: DefId,
         trait_segment: &hir::PathSegment<'tcx>,
         item_segment: &hir::PathSegment<'tcx>,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> Result<(DefId, GenericArgsRef<'tcx>), ErrorGuaranteed> {
         let tcx = self.tcx();
 
@@ -1820,7 +1830,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         debug!(?trait_def_id);
 
         let Some(self_ty) = opt_self_ty else {
-            return Err(self.error_missing_qpath_self_ty(trait_def_id, span, item_segment, kind));
+            return Err(self.error_missing_qpath_self_ty(
+                trait_def_id,
+                span,
+                item_segment,
+                assoc_tag,
+            ));
         };
         debug!(?self_ty);
 
@@ -1839,7 +1854,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         trait_def_id: DefId,
         span: Span,
         item_segment: &hir::PathSegment<'tcx>,
-        kind: ty::AssocKind,
+        assoc_tag: ty::AssocTag,
     ) -> ErrorGuaranteed {
         let tcx = self.tcx();
         let path_str = tcx.def_path_str(trait_def_id);
@@ -1876,7 +1891,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // FIXME: also look at `tcx.generics_of(self.item_def_id()).params` any that
         // references the trait. Relevant for the first case in
         // `src/test/ui/associated-types/associated-types-in-ambiguous-context.rs`
-        self.report_ambiguous_assoc(span, &type_names, &[path_str], item_segment.ident.name, kind)
+        self.report_ambiguous_assoc(
+            span,
+            &type_names,
+            &[path_str],
+            item_segment.ident.name,
+            assoc_tag,
+        )
     }
 
     pub fn prohibit_generic_args<'a>(
@@ -2858,10 +2879,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         let trait_ref = self.lower_impl_trait_ref(i.of_trait.as_ref()?, self.lower_ty(i.self_ty));
 
-        let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
+        let assoc = tcx.associated_items(trait_ref.def_id).find_by_ident_and_kind(
             tcx,
             *ident,
-            ty::AssocKind::Fn,
+            ty::AssocTag::Fn,
             trait_ref.def_id,
         )?;
 
diff --git a/compiler/rustc_hir_analysis/src/hir_wf_check.rs b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
index c01b81563dc..64c1a78bd1c 100644
--- a/compiler/rustc_hir_analysis/src/hir_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
@@ -4,7 +4,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::{ObligationCause, WellFormedLoc};
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self, TyCtxt, TypingMode, fold_regions};
+use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt, TypingMode, fold_regions};
 use rustc_span::def_id::LocalDefId;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 use tracing::debug;
@@ -77,6 +77,15 @@ fn diagnostic_hir_wf_check<'tcx>(
             let tcx_ty = fold_regions(self.tcx, tcx_ty, |r, _| {
                 if r.is_bound() { self.tcx.lifetimes.re_erased } else { r }
             });
+
+            // We may be checking the WFness of a type in an opaque with a non-lifetime bound.
+            // Perhaps we could rebind all the escaping bound vars, but they're coming from
+            // arbitrary debruijn indices and aren't particularly important anyways, since they
+            // are only coming from `feature(non_lifetime_binders)` anyways.
+            if tcx_ty.has_escaping_bound_vars() {
+                return;
+            }
+
             let cause = traits::ObligationCause::new(
                 ty.span,
                 self.def_id,
diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check.rs b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
index c30b39dfe76..cbdc501291b 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
@@ -112,14 +112,14 @@ pub(crate) fn enforce_impl_lifetime_params_are_constrained(
         .flat_map(|def_id| {
             let item = tcx.associated_item(def_id);
             match item.kind {
-                ty::AssocKind::Type => {
+                ty::AssocKind::Type { .. } => {
                     if item.defaultness(tcx).has_value() {
                         cgp::parameters_for(tcx, tcx.type_of(def_id).instantiate_identity(), true)
                     } else {
                         vec![]
                     }
                 }
-                ty::AssocKind::Fn | ty::AssocKind::Const => vec![],
+                ty::AssocKind::Fn { .. } | ty::AssocKind::Const { .. } => vec![],
             }
         })
         .collect();
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index e7ecd727a85..e1ad8124aea 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -59,7 +59,6 @@ This API is completely unstable and subject to change.
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
diff --git a/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs b/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs
index a0faa5e8429..780c27d4595 100644
--- a/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs
@@ -24,8 +24,8 @@ pub(super) fn infer_predicates(
 
     // If new predicates were added then we need to re-calculate
     // all crates since there could be new implied predicates.
-    loop {
-        let mut predicates_added = false;
+    for i in 0.. {
+        let mut predicates_added = vec![];
 
         // Visit all the crates and infer predicates
         for id in tcx.hir_free_items() {
@@ -83,14 +83,27 @@ pub(super) fn infer_predicates(
                 .get(&item_did.to_def_id())
                 .map_or(0, |p| p.as_ref().skip_binder().len());
             if item_required_predicates.len() > item_predicates_len {
-                predicates_added = true;
+                predicates_added.push(item_did);
                 global_inferred_outlives
                     .insert(item_did.to_def_id(), ty::EarlyBinder::bind(item_required_predicates));
             }
         }
 
-        if !predicates_added {
+        if predicates_added.is_empty() {
+            // We've reached a fixed point.
             break;
+        } else if !tcx.recursion_limit().value_within_limit(i) {
+            let msg = if let &[id] = &predicates_added[..] {
+                format!("overflow computing implied lifetime bounds for `{}`", tcx.def_path_str(id),)
+            } else {
+                "overflow computing implied lifetime bounds".to_string()
+            };
+            tcx.dcx()
+                .struct_span_fatal(
+                    predicates_added.iter().map(|id| tcx.def_span(*id)).collect::<Vec<_>>(),
+                    msg,
+                )
+                .emit();
         }
     }
 
diff --git a/compiler/rustc_hir_analysis/src/outlives/utils.rs b/compiler/rustc_hir_analysis/src/outlives/utils.rs
index d0a2a2230ab..044fb64ca82 100644
--- a/compiler/rustc_hir_analysis/src/outlives/utils.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/utils.rs
@@ -146,7 +146,7 @@ pub(crate) fn insert_outlives_predicate<'tcx>(
 
 fn is_free_region(region: Region<'_>) -> bool {
     // First, screen for regions that might appear in a type header.
-    match *region {
+    match region.kind() {
         // These correspond to `T: 'a` relationships:
         //
         //     struct Foo<'a, T> {
diff --git a/compiler/rustc_hir_analysis/src/variance/constraints.rs b/compiler/rustc_hir_analysis/src/variance/constraints.rs
index 8475903c68f..23223de918c 100644
--- a/compiler/rustc_hir_analysis/src/variance/constraints.rs
+++ b/compiler/rustc_hir_analysis/src/variance/constraints.rs
@@ -428,7 +428,7 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
         region: ty::Region<'tcx>,
         variance: VarianceTermPtr<'a>,
     ) {
-        match *region {
+        match region.kind() {
             ty::ReEarlyParam(ref data) => {
                 self.add_constraint(current, data.index, variance);
             }
diff --git a/compiler/rustc_hir_analysis/src/variance/mod.rs b/compiler/rustc_hir_analysis/src/variance/mod.rs
index 0800d99e945..dbba45dc7bb 100644
--- a/compiler/rustc_hir_analysis/src/variance/mod.rs
+++ b/compiler/rustc_hir_analysis/src/variance/mod.rs
@@ -44,13 +44,13 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
         return &[];
     }
 
-    match tcx.def_kind(item_def_id) {
+    let kind = tcx.def_kind(item_def_id);
+    match kind {
         DefKind::Fn
         | DefKind::AssocFn
         | DefKind::Enum
         | DefKind::Struct
         | DefKind::Union
-        | DefKind::Variant
         | DefKind::Ctor(..) => {
             // These are inferred.
             let crate_map = tcx.crate_variances(());
@@ -89,7 +89,11 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
     }
 
     // Variance not relevant.
-    span_bug!(tcx.def_span(item_def_id), "asked to compute variance for wrong kind of item");
+    span_bug!(
+        tcx.def_span(item_def_id),
+        "asked to compute variance for {}",
+        kind.descr(item_def_id.to_def_id())
+    );
 }
 
 #[derive(Debug, Copy, Clone)]
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 8c0c17f7a7d..ff4385c3bcc 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -397,7 +397,7 @@ impl<'a> State<'a> {
                 self.pclose();
             }
             hir::TyKind::BareFn(f) => {
-                self.print_ty_fn(f.abi, f.safety, f.decl, None, f.generic_params, f.param_names);
+                self.print_ty_fn(f.abi, f.safety, f.decl, None, f.generic_params, f.param_idents);
             }
             hir::TyKind::UnsafeBinder(unsafe_binder) => {
                 self.print_unsafe_binder(unsafe_binder);
@@ -473,14 +473,14 @@ impl<'a> State<'a> {
         self.maybe_print_comment(item.span.lo());
         self.print_attrs_as_outer(self.attrs(item.hir_id()));
         match item.kind {
-            hir::ForeignItemKind::Fn(sig, arg_names, generics) => {
+            hir::ForeignItemKind::Fn(sig, arg_idents, generics) => {
                 self.head("");
                 self.print_fn(
                     sig.decl,
                     sig.header,
                     Some(item.ident.name),
                     generics,
-                    arg_names,
+                    arg_idents,
                     None,
                 );
                 self.end(); // end head-ibox
@@ -899,10 +899,10 @@ impl<'a> State<'a> {
         ident: Ident,
         m: &hir::FnSig<'_>,
         generics: &hir::Generics<'_>,
-        arg_names: &[Option<Ident>],
+        arg_idents: &[Option<Ident>],
         body_id: Option<hir::BodyId>,
     ) {
-        self.print_fn(m.decl, m.header, Some(ident.name), generics, arg_names, body_id);
+        self.print_fn(m.decl, m.header, Some(ident.name), generics, arg_idents, body_id);
     }
 
     fn print_trait_item(&mut self, ti: &hir::TraitItem<'_>) {
@@ -914,8 +914,8 @@ impl<'a> State<'a> {
             hir::TraitItemKind::Const(ty, default) => {
                 self.print_associated_const(ti.ident, ti.generics, ty, default);
             }
-            hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(arg_names)) => {
-                self.print_method_sig(ti.ident, sig, ti.generics, arg_names, None);
+            hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Required(arg_idents)) => {
+                self.print_method_sig(ti.ident, sig, ti.generics, arg_idents, None);
                 self.word(";");
             }
             hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Provided(body)) => {
@@ -960,12 +960,16 @@ impl<'a> State<'a> {
 
     fn print_local(
         &mut self,
+        super_: bool,
         init: Option<&hir::Expr<'_>>,
         els: Option<&hir::Block<'_>>,
         decl: impl Fn(&mut Self),
     ) {
         self.space_if_not_bol();
         self.ibox(INDENT_UNIT);
+        if super_ {
+            self.word_nbsp("super");
+        }
         self.word_nbsp("let");
 
         self.ibox(INDENT_UNIT);
@@ -995,7 +999,9 @@ impl<'a> State<'a> {
         self.maybe_print_comment(st.span.lo());
         match st.kind {
             hir::StmtKind::Let(loc) => {
-                self.print_local(loc.init, loc.els, |this| this.print_local_decl(loc));
+                self.print_local(loc.super_.is_some(), loc.init, loc.els, |this| {
+                    this.print_local_decl(loc)
+                });
             }
             hir::StmtKind::Item(item) => self.ann.nested(self, Nested::Item(item)),
             hir::StmtKind::Expr(expr) => {
@@ -1488,7 +1494,7 @@ impl<'a> State<'a> {
 
                 // Print `let _t = $init;`:
                 let temp = Ident::from_str("_t");
-                self.print_local(Some(init), None, |this| this.print_ident(temp));
+                self.print_local(false, Some(init), None, |this| this.print_ident(temp));
                 self.word(";");
 
                 // Print `_t`:
@@ -1865,9 +1871,11 @@ impl<'a> State<'a> {
     fn print_pat(&mut self, pat: &hir::Pat<'_>) {
         self.maybe_print_comment(pat.span.lo());
         self.ann.pre(self, AnnNode::Pat(pat));
-        // Pat isn't normalized, but the beauty of it
-        // is that it doesn't matter
+        // Pat isn't normalized, but the beauty of it is that it doesn't matter.
         match pat.kind {
+            // Printing `_` isn't ideal for a missing pattern, but it's easy and good enough.
+            // E.g. `fn(u32)` gets printed as `fn(_: u32)`.
+            PatKind::Missing => self.word("_"),
             PatKind::Wild => self.word("_"),
             PatKind::Never => self.word("!"),
             PatKind::Binding(BindingMode(by_ref, mutbl), _, ident, sub) => {
@@ -2115,7 +2123,7 @@ impl<'a> State<'a> {
         header: hir::FnHeader,
         name: Option<Symbol>,
         generics: &hir::Generics<'_>,
-        arg_names: &[Option<Ident>],
+        arg_idents: &[Option<Ident>],
         body_id: Option<hir::BodyId>,
     ) {
         self.print_fn_header_info(header);
@@ -2127,16 +2135,16 @@ impl<'a> State<'a> {
         self.print_generic_params(generics.params);
 
         self.popen();
-        // Make sure we aren't supplied *both* `arg_names` and `body_id`.
-        assert!(arg_names.is_empty() || body_id.is_none());
+        // Make sure we aren't supplied *both* `arg_idents` and `body_id`.
+        assert!(arg_idents.is_empty() || body_id.is_none());
         let mut i = 0;
         let mut print_arg = |s: &mut Self, ty: Option<&hir::Ty<'_>>| {
             if i == 0 && decl.implicit_self.has_implicit_self() {
                 s.print_implicit_self(&decl.implicit_self);
             } else {
-                if let Some(arg_name) = arg_names.get(i) {
-                    if let Some(arg_name) = arg_name {
-                        s.word(arg_name.to_string());
+                if let Some(arg_ident) = arg_idents.get(i) {
+                    if let Some(arg_ident) = arg_ident {
+                        s.word(arg_ident.to_string());
                         s.word(":");
                         s.space();
                     }
@@ -2157,7 +2165,9 @@ impl<'a> State<'a> {
             s.end();
         });
         if decl.c_variadic {
-            self.word(", ");
+            if !decl.inputs.is_empty() {
+                self.word(", ");
+            }
             print_arg(self, None);
             self.word("...");
         }
@@ -2445,7 +2455,7 @@ impl<'a> State<'a> {
         decl: &hir::FnDecl<'_>,
         name: Option<Symbol>,
         generic_params: &[hir::GenericParam<'_>],
-        arg_names: &[Option<Ident>],
+        arg_idents: &[Option<Ident>],
     ) {
         self.ibox(INDENT_UNIT);
         self.print_formal_generic_params(generic_params);
@@ -2460,7 +2470,7 @@ impl<'a> State<'a> {
             },
             name,
             generics,
-            arg_names,
+            arg_idents,
             None,
         );
         self.end();
diff --git a/compiler/rustc_hir_typeck/messages.ftl b/compiler/rustc_hir_typeck/messages.ftl
index 872861d6289..9e1b70f5767 100644
--- a/compiler/rustc_hir_typeck/messages.ftl
+++ b/compiler/rustc_hir_typeck/messages.ftl
@@ -148,7 +148,7 @@ hir_typeck_never_type_fallback_flowing_into_unsafe_path = never type fallback af
 hir_typeck_never_type_fallback_flowing_into_unsafe_union_field = never type fallback affects this union access
     .help = specify the type explicitly
 
-hir_typeck_no_associated_item = no {$item_kind} named `{$item_name}` found for {$ty_prefix} `{$ty_str}`{$trait_missing_method ->
+hir_typeck_no_associated_item = no {$item_kind} named `{$item_ident}` found for {$ty_prefix} `{$ty_str}`{$trait_missing_method ->
     [true] {""}
     *[other] {" "}in the current scope
 }
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index 8f5fddd19d7..b19d9efe2c6 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -1042,30 +1042,31 @@ impl<'a, 'tcx> CastCheck<'tcx> {
         m_cast: ty::TypeAndMut<'tcx>,
     ) -> Result<CastKind, CastError<'tcx>> {
         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
-        if m_expr.mutbl >= m_cast.mutbl {
-            if let ty::Array(ety, _) = m_expr.ty.kind() {
-                // Due to the limitations of LLVM global constants,
-                // region pointers end up pointing at copies of
-                // vector elements instead of the original values.
-                // To allow raw pointers to work correctly, we
-                // need to special-case obtaining a raw pointer
-                // from a region pointer to a vector.
-
-                // Coerce to a raw pointer so that we generate RawPtr in MIR.
-                let array_ptr_type = Ty::new_ptr(fcx.tcx, m_expr.ty, m_expr.mutbl);
-                fcx.coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
-                    .unwrap_or_else(|_| {
-                        bug!(
+        if m_expr.mutbl >= m_cast.mutbl
+            && let ty::Array(ety, _) = m_expr.ty.kind()
+            && fcx.can_eq(fcx.param_env, *ety, m_cast.ty)
+        {
+            // Due to the limitations of LLVM global constants,
+            // region pointers end up pointing at copies of
+            // vector elements instead of the original values.
+            // To allow raw pointers to work correctly, we
+            // need to special-case obtaining a raw pointer
+            // from a region pointer to a vector.
+
+            // Coerce to a raw pointer so that we generate RawPtr in MIR.
+            let array_ptr_type = Ty::new_ptr(fcx.tcx, m_expr.ty, m_expr.mutbl);
+            fcx.coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
+                .unwrap_or_else(|_| {
+                    bug!(
                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
                         self.expr_ty,
                         array_ptr_type,
                     )
-                    });
+                });
 
-                // this will report a type mismatch if needed
-                fcx.demand_eqtype(self.span, *ety, m_cast.ty);
-                return Ok(CastKind::ArrayPtrCast);
-            }
+            // this will report a type mismatch if needed
+            fcx.demand_eqtype(self.span, *ety, m_cast.ty);
+            return Ok(CastKind::ArrayPtrCast);
         }
 
         Err(CastError::IllegalCast)
diff --git a/compiler/rustc_hir_typeck/src/check.rs b/compiler/rustc_hir_typeck/src/check.rs
index dabae7b1d09..2189fdf0f34 100644
--- a/compiler/rustc_hir_typeck/src/check.rs
+++ b/compiler/rustc_hir_typeck/src/check.rs
@@ -5,7 +5,7 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
-use rustc_hir_analysis::check::{check_function_signature, forbid_intrinsic_abi};
+use rustc_hir_analysis::check::check_function_signature;
 use rustc_infer::infer::RegionVariableOrigin;
 use rustc_infer::traits::WellFormedLoc;
 use rustc_middle::ty::{self, Binder, Ty, TyCtxt};
@@ -50,8 +50,6 @@ pub(super) fn check_fn<'a, 'tcx>(
 
     let span = body.value.span;
 
-    forbid_intrinsic_abi(tcx, span, fn_sig.abi);
-
     GatherLocalsVisitor::new(fcx).visit_body(body);
 
     // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index 467ca26e7ea..b8968b58769 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -970,7 +970,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.typeck_results.borrow_mut().user_provided_sigs.insert(expr_def_id, c_result);
 
         // Normalize only after registering in `user_provided_sigs`.
-        self.normalize(self.tcx.hir_span(hir_id), result)
+        self.normalize(self.tcx.def_span(expr_def_id), result)
     }
 
     /// Invoked when we are translating the coroutine that results
diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs
index f42ca3af2b3..fd899425f62 100644
--- a/compiler/rustc_hir_typeck/src/coercion.rs
+++ b/compiler/rustc_hir_typeck/src/coercion.rs
@@ -37,7 +37,6 @@
 
 use std::ops::Deref;
 
-use rustc_abi::ExternAbi;
 use rustc_attr_parsing::InlineAttr;
 use rustc_errors::codes::*;
 use rustc_errors::{Applicability, Diag, struct_span_code_err};
@@ -104,15 +103,6 @@ fn coerce_mutbls<'tcx>(
     if from_mutbl >= to_mutbl { Ok(()) } else { Err(TypeError::Mutability) }
 }
 
-/// Do not require any adjustments, i.e. coerce `x -> x`.
-fn identity(_: Ty<'_>) -> Vec<Adjustment<'_>> {
-    vec![]
-}
-
-fn simple<'tcx>(kind: Adjust) -> impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> {
-    move |target| vec![Adjustment { kind, target }]
-}
-
 /// This always returns `Ok(...)`.
 fn success<'tcx>(
     adj: Vec<Adjustment<'tcx>>,
@@ -132,7 +122,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         Coerce { fcx, cause, allow_two_phase, use_lub: false, coerce_never }
     }
 
-    fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
+    fn unify_raw(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
         debug!("unify(a: {:?}, b: {:?}, use_lub: {})", a, b, self.use_lub);
         self.commit_if_ok(|_| {
             let at = self.at(&self.cause, self.fcx.param_env);
@@ -162,13 +152,30 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         })
     }
 
+    /// Unify two types (using sub or lub).
+    fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
+        self.unify_raw(a, b)
+            .and_then(|InferOk { value: ty, obligations }| success(vec![], ty, obligations))
+    }
+
     /// Unify two types (using sub or lub) and produce a specific coercion.
-    fn unify_and<F>(&self, a: Ty<'tcx>, b: Ty<'tcx>, f: F) -> CoerceResult<'tcx>
-    where
-        F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
-    {
-        self.unify(a, b)
-            .and_then(|InferOk { value: ty, obligations }| success(f(ty), ty, obligations))
+    fn unify_and(
+        &self,
+        a: Ty<'tcx>,
+        b: Ty<'tcx>,
+        adjustments: impl IntoIterator<Item = Adjustment<'tcx>>,
+        final_adjustment: Adjust,
+    ) -> CoerceResult<'tcx> {
+        self.unify_raw(a, b).and_then(|InferOk { value: ty, obligations }| {
+            success(
+                adjustments
+                    .into_iter()
+                    .chain(std::iter::once(Adjustment { target: ty, kind: final_adjustment }))
+                    .collect(),
+                ty,
+                obligations,
+            )
+        })
     }
 
     #[instrument(skip(self))]
@@ -181,10 +188,14 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         // Coercing from `!` to any type is allowed:
         if a.is_never() {
             if self.coerce_never {
-                return success(simple(Adjust::NeverToAny)(b), b, PredicateObligations::new());
+                return success(
+                    vec![Adjustment { kind: Adjust::NeverToAny, target: b }],
+                    b,
+                    PredicateObligations::new(),
+                );
             } else {
                 // Otherwise the only coercion we can do is unification.
-                return self.unify_and(a, b, identity);
+                return self.unify(a, b);
             }
         }
 
@@ -192,7 +203,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         // we have no information about the source type. This will always
         // ultimately fall back to some form of subtyping.
         if a.is_ty_var() {
-            return self.coerce_from_inference_variable(a, b, identity);
+            return self.coerce_from_inference_variable(a, b);
         }
 
         // Consider coercing the subtype to a DST
@@ -248,7 +259,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             ty::FnPtr(a_sig_tys, a_hdr) => {
                 // We permit coercion of fn pointers to drop the
                 // unsafe qualifier.
-                self.coerce_from_fn_pointer(a, a_sig_tys.with(a_hdr), b)
+                self.coerce_from_fn_pointer(a_sig_tys.with(a_hdr), b)
             }
             ty::Closure(closure_def_id_a, args_a) => {
                 // Non-capturing closures are coercible to
@@ -258,7 +269,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             }
             _ => {
                 // Otherwise, just use unification rules.
-                self.unify_and(a, b, identity)
+                self.unify(a, b)
             }
         }
     }
@@ -266,12 +277,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
     /// Coercing *from* an inference variable. In this case, we have no information
     /// about the source type, so we can't really do a true coercion and we always
     /// fall back to subtyping (`unify_and`).
-    fn coerce_from_inference_variable(
-        &self,
-        a: Ty<'tcx>,
-        b: Ty<'tcx>,
-        make_adjustments: impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
-    ) -> CoerceResult<'tcx> {
+    fn coerce_from_inference_variable(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
         debug!("coerce_from_inference_variable(a={:?}, b={:?})", a, b);
         assert!(a.is_ty_var() && self.shallow_resolve(a) == a);
         assert!(self.shallow_resolve(b) == b);
@@ -299,12 +305,11 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 "coerce_from_inference_variable: two inference variables, target_ty={:?}, obligations={:?}",
                 target_ty, obligations
             );
-            let adjustments = make_adjustments(target_ty);
-            InferResult::Ok(InferOk { value: (adjustments, target_ty), obligations })
+            success(vec![], target_ty, obligations)
         } else {
             // One unresolved type variable: just apply subtyping, we may be able
             // to do something useful.
-            self.unify_and(a, b, make_adjustments)
+            self.unify(a, b)
         }
     }
 
@@ -332,7 +337,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 coerce_mutbls(mt_a.mutbl, mutbl_b)?;
                 (r_a, mt_a)
             }
-            _ => return self.unify_and(a, b, identity),
+            _ => return self.unify(a, b),
         };
 
         let span = self.cause.span;
@@ -438,7 +443,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 referent_ty,
                 mutbl_b, // [1] above
             );
-            match self.unify(derefd_ty_a, b) {
+            match self.unify_raw(derefd_ty_a, b) {
                 Ok(ok) => {
                     found = Some(ok);
                     break;
@@ -580,13 +585,13 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         // We only have the latter, so we use an inference variable
         // for the former and let type inference do the rest.
         let coerce_target = self.next_ty_var(self.cause.span);
-        let mut coercion = self.unify_and(coerce_target, target, |target| {
-            let unsize = Adjustment { kind: Adjust::Pointer(PointerCoercion::Unsize), target };
-            match reborrow {
-                None => vec![unsize],
-                Some((ref deref, ref autoref)) => vec![deref.clone(), autoref.clone(), unsize],
-            }
-        })?;
+
+        let mut coercion = self.unify_and(
+            coerce_target,
+            target,
+            reborrow.into_iter().flat_map(|(deref, autoref)| [deref, autoref]),
+            Adjust::Pointer(PointerCoercion::Unsize),
+        )?;
 
         let mut selcx = traits::SelectionContext::new(self);
 
@@ -709,7 +714,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             && let ty::Dynamic(b_data, _, ty::DynStar) = b.kind()
             && a_data.principal_def_id() == b_data.principal_def_id()
         {
-            return self.unify_and(a, b, |_| vec![]);
+            return self.unify(a, b);
         }
 
         // Check the obligations of the cast -- for example, when casting
@@ -809,23 +814,15 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
         // To complete the reborrow, we need to make sure we can unify the inner types, and if so we
         // add the adjustments.
-        self.unify_and(a, b, |_inner_ty| {
-            vec![Adjustment { kind: Adjust::ReborrowPin(mut_b), target: b }]
-        })
+        self.unify_and(a, b, [], Adjust::ReborrowPin(mut_b))
     }
 
-    fn coerce_from_safe_fn<F, G>(
+    fn coerce_from_safe_fn(
         &self,
-        a: Ty<'tcx>,
         fn_ty_a: ty::PolyFnSig<'tcx>,
         b: Ty<'tcx>,
-        to_unsafe: F,
-        normal: G,
-    ) -> CoerceResult<'tcx>
-    where
-        F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
-        G: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
-    {
+        adjustment: Option<Adjust>,
+    ) -> CoerceResult<'tcx> {
         self.commit_if_ok(|snapshot| {
             let outer_universe = self.infcx.universe();
 
@@ -834,9 +831,19 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 && hdr_b.safety.is_unsafe()
             {
                 let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
-                self.unify_and(unsafe_a, b, to_unsafe)
+                self.unify_and(
+                    unsafe_a,
+                    b,
+                    adjustment
+                        .map(|kind| Adjustment { kind, target: Ty::new_fn_ptr(self.tcx, fn_ty_a) }),
+                    Adjust::Pointer(PointerCoercion::UnsafeFnPointer),
+                )
             } else {
-                self.unify_and(a, b, normal)
+                let a = Ty::new_fn_ptr(self.tcx, fn_ty_a);
+                match adjustment {
+                    Some(adjust) => self.unify_and(a, b, [], adjust),
+                    None => self.unify(a, b),
+                }
             };
 
             // FIXME(#73154): This is a hack. Currently LUB can generate
@@ -853,7 +860,6 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
     fn coerce_from_fn_pointer(
         &self,
-        a: Ty<'tcx>,
         fn_ty_a: ty::PolyFnSig<'tcx>,
         b: Ty<'tcx>,
     ) -> CoerceResult<'tcx> {
@@ -862,15 +868,9 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         //!
 
         let b = self.shallow_resolve(b);
-        debug!("coerce_from_fn_pointer(a={:?}, b={:?})", a, b);
-
-        self.coerce_from_safe_fn(
-            a,
-            fn_ty_a,
-            b,
-            simple(Adjust::Pointer(PointerCoercion::UnsafeFnPointer)),
-            identity,
-        )
+        debug!(?fn_ty_a, ?b, "coerce_from_fn_pointer");
+
+        self.coerce_from_safe_fn(fn_ty_a, b, None)
     }
 
     fn coerce_from_fn_item(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
@@ -917,30 +917,16 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                     self.at(&self.cause, self.param_env).normalize(a_sig);
                 obligations.extend(o1);
 
-                let a_fn_pointer = Ty::new_fn_ptr(self.tcx, a_sig);
                 let InferOk { value, obligations: o2 } = self.coerce_from_safe_fn(
-                    a_fn_pointer,
                     a_sig,
                     b,
-                    |unsafe_ty| {
-                        vec![
-                            Adjustment {
-                                kind: Adjust::Pointer(PointerCoercion::ReifyFnPointer),
-                                target: a_fn_pointer,
-                            },
-                            Adjustment {
-                                kind: Adjust::Pointer(PointerCoercion::UnsafeFnPointer),
-                                target: unsafe_ty,
-                            },
-                        ]
-                    },
-                    simple(Adjust::Pointer(PointerCoercion::ReifyFnPointer)),
+                    Some(Adjust::Pointer(PointerCoercion::ReifyFnPointer)),
                 )?;
 
                 obligations.extend(o2);
                 Ok(InferOk { value, obligations })
             }
-            _ => self.unify_and(a, b, identity),
+            _ => self.unify(a, b),
         }
     }
 
@@ -984,10 +970,11 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 self.unify_and(
                     pointer_ty,
                     b,
-                    simple(Adjust::Pointer(PointerCoercion::ClosureFnPointer(safety))),
+                    [],
+                    Adjust::Pointer(PointerCoercion::ClosureFnPointer(safety)),
                 )
             }
-            _ => self.unify_and(a, b, identity),
+            _ => self.unify(a, b),
         }
     }
 
@@ -1002,7 +989,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         let (is_ref, mt_a) = match *a.kind() {
             ty::Ref(_, ty, mutbl) => (true, ty::TypeAndMut { ty, mutbl }),
             ty::RawPtr(ty, mutbl) => (false, ty::TypeAndMut { ty, mutbl }),
-            _ => return self.unify_and(a, b, identity),
+            _ => return self.unify(a, b),
         };
         coerce_mutbls(mt_a.mutbl, mutbl_b)?;
 
@@ -1012,16 +999,16 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         // representation, we still register an Adjust::DerefRef so that
         // regionck knows that the region for `a` must be valid here.
         if is_ref {
-            self.unify_and(a_raw, b, |target| {
-                vec![
-                    Adjustment { kind: Adjust::Deref(None), target: mt_a.ty },
-                    Adjustment { kind: Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)), target },
-                ]
-            })
+            self.unify_and(
+                a_raw,
+                b,
+                [Adjustment { kind: Adjust::Deref(None), target: mt_a.ty }],
+                Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)),
+            )
         } else if mt_a.mutbl != mutbl_b {
-            self.unify_and(a_raw, b, simple(Adjust::Pointer(PointerCoercion::MutToConstPointer)))
+            self.unify_and(a_raw, b, [], Adjust::Pointer(PointerCoercion::MutToConstPointer))
         } else {
-            self.unify_and(a_raw, b, identity)
+            self.unify(a_raw, b)
         }
     }
 }
@@ -1119,9 +1106,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let cause = self.cause(DUMMY_SP, ObligationCauseCode::ExprAssignable);
         // We don't ever need two-phase here since we throw out the result of the coercion.
         let coerce = Coerce::new(self, cause, AllowTwoPhase::No, true);
-        coerce
-            .autoderef(DUMMY_SP, expr_ty)
-            .find_map(|(ty, steps)| self.probe(|_| coerce.unify(ty, target)).ok().map(|_| steps))
+        coerce.autoderef(DUMMY_SP, expr_ty).find_map(|(ty, steps)| {
+            self.probe(|_| coerce.unify_raw(ty, target)).ok().map(|_| steps)
+        })
     }
 
     /// Given a type, this function will calculate and return the type given
@@ -1240,10 +1227,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
         };
         if let (Some(a_sig), Some(b_sig)) = (a_sig, b_sig) {
-            // Intrinsics are not coercible to function pointers.
-            if a_sig.abi() == ExternAbi::RustIntrinsic || b_sig.abi() == ExternAbi::RustIntrinsic {
-                return Err(TypeError::IntrinsicCast);
-            }
             // The signature must match.
             let (a_sig, b_sig) = self.normalize(new.span, (a_sig, b_sig));
             let sig = self
diff --git a/compiler/rustc_hir_typeck/src/demand.rs b/compiler/rustc_hir_typeck/src/demand.rs
index b845e2190ef..d1bc54ed73e 100644
--- a/compiler/rustc_hir_typeck/src/demand.rs
+++ b/compiler/rustc_hir_typeck/src/demand.rs
@@ -865,10 +865,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // `&'name Ty` -> `&'name mut Ty` or `&Ty` -> `&mut Ty`
                 vec![(
                     ty_ref.1.ty.span.shrink_to_lo(),
-                    format!(
-                        "{}mut ",
-                        if ty_ref.0.ident.span.lo() == ty_ref.0.ident.span.hi() { "" } else { " " },
-                    ),
+                    format!("{}mut ", if ty_ref.0.ident.span.is_empty() { "" } else { " " },),
                 )]
             };
             sugg.extend([
@@ -1092,14 +1089,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     /// This function checks whether the method is not static and does not accept other parameters than `self`.
     fn has_only_self_parameter(&self, method: &AssocItem) -> bool {
-        match method.kind {
-            ty::AssocKind::Fn => {
-                method.fn_has_self_parameter
-                    && self.tcx.fn_sig(method.def_id).skip_binder().inputs().skip_binder().len()
-                        == 1
-            }
-            _ => false,
-        }
+        method.is_method()
+            && self.tcx.fn_sig(method.def_id).skip_binder().inputs().skip_binder().len() == 1
     }
 
     /// If the given `HirId` corresponds to a block with a trailing expression, return that expression
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index b73cd26927a..9e7305430e5 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -5,7 +5,7 @@ use std::borrow::Cow;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagArgValue, DiagSymbolList, EmissionGuarantee, IntoDiagArg, MultiSpan,
-    SubdiagMessageOp, Subdiagnostic,
+    Subdiagnostic,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{self, Ty};
@@ -270,11 +270,7 @@ pub(crate) struct SuggestAnnotations {
     pub suggestions: Vec<SuggestAnnotation>,
 }
 impl Subdiagnostic for SuggestAnnotations {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         if self.suggestions.is_empty() {
             return;
         }
@@ -337,11 +333,7 @@ pub(crate) struct TypeMismatchFruTypo {
 }
 
 impl Subdiagnostic for TypeMismatchFruTypo {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("expr", self.expr.as_deref().unwrap_or("NONE"));
 
         // Only explain that `a ..b` is a range if it's split up
@@ -599,11 +591,7 @@ pub(crate) struct RemoveSemiForCoerce {
 }
 
 impl Subdiagnostic for RemoveSemiForCoerce {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut multispan: MultiSpan = self.semi.into();
         multispan.push_span_label(self.expr, fluent::hir_typeck_remove_semi_for_coerce_expr);
         multispan.push_span_label(self.ret, fluent::hir_typeck_remove_semi_for_coerce_ret);
@@ -727,7 +715,7 @@ pub(crate) struct NoAssociatedItem {
     #[primary_span]
     pub span: Span,
     pub item_kind: &'static str,
-    pub item_name: Ident,
+    pub item_ident: Ident,
     pub ty_prefix: Cow<'static, str>,
     pub ty_str: String,
     pub trait_missing_method: bool,
@@ -778,20 +766,16 @@ pub(crate) enum CastUnknownPointerSub {
 }
 
 impl rustc_errors::Subdiagnostic for CastUnknownPointerSub {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             CastUnknownPointerSub::To(span) => {
-                let msg = f(diag, crate::fluent_generated::hir_typeck_label_to);
+                let msg = diag.eagerly_translate(fluent::hir_typeck_label_to);
                 diag.span_label(span, msg);
-                let msg = f(diag, crate::fluent_generated::hir_typeck_note);
+                let msg = diag.eagerly_translate(fluent::hir_typeck_note);
                 diag.note(msg);
             }
             CastUnknownPointerSub::From(span) => {
-                let msg = f(diag, crate::fluent_generated::hir_typeck_label_from);
+                let msg = diag.eagerly_translate(fluent::hir_typeck_label_from);
                 diag.span_label(span, msg);
             }
         }
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 45ab8e03db5..d6a7bfc446a 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -482,7 +482,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             // All of these constitute a read, or match on something that isn't `!`,
             // which would require a `NeverToAny` coercion.
-            hir::PatKind::Binding(_, _, _, _)
+            hir::PatKind::Missing
+            | hir::PatKind::Binding(_, _, _, _)
             | hir::PatKind::Struct(_, _, _)
             | hir::PatKind::TupleStruct(_, _, _)
             | hir::PatKind::Tuple(_, _)
@@ -1599,11 +1600,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Ok(method)
             }
             Err(error) => {
-                if segment.ident.name == kw::Empty {
-                    span_bug!(rcvr.span, "empty method name")
-                } else {
-                    Err(self.report_method_error(expr.hir_id, rcvr_t, error, expected, false))
-                }
+                Err(self.report_method_error(expr.hir_id, rcvr_t, error, expected, false))
             }
         };
 
@@ -2204,8 +2201,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let fields = listify(&missing_mandatory_fields, |f| format!("`{f}`")).unwrap();
                 self.dcx()
                     .struct_span_err(
-                        span.shrink_to_hi(),
-                        format!("missing mandatory field{s} {fields}"),
+                        span.shrink_to_lo(),
+                        format!("missing field{s} {fields} in initializer"),
+                    )
+                    .with_span_label(
+                        span.shrink_to_lo(),
+                        "fields that do not have a defaulted value must be provided explicitly",
                     )
                     .emit();
                 return;
@@ -2583,9 +2584,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .into_iter()
                 .flat_map(|i| self.tcx.associated_items(i).in_definition_order())
                 // Only assoc fn with no receivers.
-                .filter(|item| {
-                    matches!(item.kind, ty::AssocKind::Fn) && !item.fn_has_self_parameter
-                })
+                .filter(|item| item.is_fn() && !item.is_method())
                 .filter_map(|item| {
                     // Only assoc fns that return `Self`
                     let fn_sig = self.tcx.fn_sig(item.def_id).skip_binder();
@@ -2598,8 +2597,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         return None;
                     }
                     let input_len = fn_sig.inputs().skip_binder().len();
-                    let order = !item.name.as_str().starts_with("new");
-                    Some((order, item.name, input_len))
+                    let name = item.name();
+                    let order = !name.as_str().starts_with("new");
+                    Some((order, name, input_len))
                 })
                 .collect::<Vec<_>>();
             items.sort_by_key(|(order, _, _)| *order);
@@ -2915,8 +2915,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
         // We failed to check the expression, report an error.
 
-        // Emits an error if we deref an infer variable, like calling `.field` on a base type of &_.
-        self.structurally_resolve_type(autoderef.span(), autoderef.final_ty(false));
+        // Emits an error if we deref an infer variable, like calling `.field` on a base type
+        // of `&_`. We can also use this to suppress unnecessary "missing field" errors that
+        // will follow ambiguity errors.
+        let final_ty = self.structurally_resolve_type(autoderef.span(), autoderef.final_ty(false));
+        if let ty::Error(_) = final_ty.kind() {
+            return final_ty;
+        }
 
         if let Some((adjustments, did)) = private_candidate {
             // (#90483) apply adjustments to avoid ExprUseVisitor from
@@ -2932,9 +2937,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             return Ty::new_error(self.tcx(), guar);
         }
 
-        let guar = if field.name == kw::Empty {
-            self.dcx().span_bug(field.span, "field name with no name")
-        } else if self.method_exists_for_diagnostic(
+        let guar = if self.method_exists_for_diagnostic(
             field,
             base_ty,
             expr.hir_id,
diff --git a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
index 64176dacb73..f5e0f01e4c5 100644
--- a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
+++ b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
@@ -611,6 +611,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         for pat in pats {
             self.cat_pattern(discr_place.clone(), pat, &mut |place, pat| {
                 match &pat.kind {
+                    PatKind::Missing => unreachable!(),
                     PatKind::Binding(.., opt_sub_pat) => {
                         // If the opt_sub_pat is None, then the binding does not count as
                         // a wildcard for the purpose of borrowing discr.
@@ -999,6 +1000,8 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     // determines whether to borrow *at the level of the deref pattern* rather than
                     // borrowing the bound place (since that inner place is inside the temporary that
                     // stores the result of calling `deref()`/`deref_mut()` so can't be captured).
+                    // HACK: this could be a fake pattern corresponding to a deref inserted by match
+                    // ergonomics, in which case `pat.hir_id` will be the id of the subpattern.
                     let mutable = self.cx.typeck_results().pat_has_ref_mut_binding(subpattern);
                     let mutability =
                         if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
@@ -1226,9 +1229,9 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         // actually this is somewhat "disjoint" from the code below
         // that aims to account for `ref x`.
         if let Some(vec) = self.cx.typeck_results().pat_adjustments().get(pat.hir_id) {
-            if let Some(first_ty) = vec.first() {
-                debug!("pat_ty(pat={:?}) found adjusted ty `{:?}`", pat, first_ty);
-                return Ok(*first_ty);
+            if let Some(first_adjust) = vec.first() {
+                debug!("pat_ty(pat={:?}) found adjustment `{:?}`", pat, first_adjust);
+                return Ok(first_adjust.source);
             }
         } else if let PatKind::Ref(subpat, _) = pat.kind
             && self.cx.typeck_results().skipped_ref_pats().contains(pat.hir_id)
@@ -1501,16 +1504,21 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         let mut projections = base_place.place.projections;
 
         let node_ty = self.cx.typeck_results().node_type(node);
-        // Opaque types can't have field projections, but we can instead convert
-        // the current place in-place (heh) to the hidden type, and then apply all
-        // follow up projections on that.
-        if node_ty != place_ty
-            && self
-                .cx
-                .try_structurally_resolve_type(self.cx.tcx().hir_span(base_place.hir_id), place_ty)
-                .is_impl_trait()
-        {
-            projections.push(Projection { kind: ProjectionKind::OpaqueCast, ty: node_ty });
+        if !self.cx.tcx().next_trait_solver_globally() {
+            // Opaque types can't have field projections, but we can instead convert
+            // the current place in-place (heh) to the hidden type, and then apply all
+            // follow up projections on that.
+            if node_ty != place_ty
+                && self
+                    .cx
+                    .try_structurally_resolve_type(
+                        self.cx.tcx().hir_span(base_place.hir_id),
+                        place_ty,
+                    )
+                    .is_impl_trait()
+            {
+                projections.push(Projection { kind: ProjectionKind::OpaqueCast, ty: node_ty });
+            }
         }
         projections.push(Projection { kind, ty });
         PlaceWithHirId::new(node, base_place.place.base_ty, base_place.place.base, projections)
@@ -1674,12 +1682,31 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         // Then we see that to get the same result, we must start with
         // `deref { deref { place_foo }}` instead of `place_foo` since the pattern is now `Some(x,)`
         // and not `&&Some(x,)`, even though its assigned type is that of `&&Some(x,)`.
-        for _ in
-            0..self.cx.typeck_results().pat_adjustments().get(pat.hir_id).map_or(0, |v| v.len())
-        {
+        let typeck_results = self.cx.typeck_results();
+        let adjustments: &[adjustment::PatAdjustment<'tcx>] =
+            typeck_results.pat_adjustments().get(pat.hir_id).map_or(&[], |v| &**v);
+        let mut adjusts = adjustments.iter().peekable();
+        while let Some(adjust) = adjusts.next() {
             debug!("applying adjustment to place_with_id={:?}", place_with_id);
-            place_with_id = self.cat_deref(pat.hir_id, place_with_id)?;
+            place_with_id = match adjust.kind {
+                adjustment::PatAdjust::BuiltinDeref => self.cat_deref(pat.hir_id, place_with_id)?,
+                adjustment::PatAdjust::OverloadedDeref => {
+                    // This adjustment corresponds to an overloaded deref; it borrows the scrutinee to
+                    // call `Deref::deref` or `DerefMut::deref_mut`. Invoke the callback before setting
+                    // `place_with_id` to the temporary storing the result of the deref.
+                    // HACK(dianne): giving the callback a fake deref pattern makes sure it behaves the
+                    // same as it would if this were an explicit deref pattern.
+                    op(&place_with_id, &hir::Pat { kind: PatKind::Deref(pat), ..*pat })?;
+                    let target_ty = match adjusts.peek() {
+                        Some(&&next_adjust) => next_adjust.source,
+                        // At the end of the deref chain, we get `pat`'s scrutinee.
+                        None => self.pat_ty_unadjusted(pat)?,
+                    };
+                    self.pat_deref_temp(pat.hir_id, pat, target_ty)?
+                }
+            };
         }
+        drop(typeck_results); // explicitly release borrow of typeck results, just in case.
         let place_with_id = place_with_id; // lose mutability
         debug!("applied adjustment derefs to get place_with_id={:?}", place_with_id);
 
@@ -1782,14 +1809,8 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 self.cat_pattern(subplace, subpat, op)?;
             }
             PatKind::Deref(subpat) => {
-                let mutable = self.cx.typeck_results().pat_has_ref_mut_binding(subpat);
-                let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
-                let re_erased = self.cx.tcx().lifetimes.re_erased;
                 let ty = self.pat_ty_adjusted(subpat)?;
-                let ty = Ty::new_ref(self.cx.tcx(), re_erased, ty, mutability);
-                // A deref pattern generates a temporary.
-                let base = self.cat_rvalue(pat.hir_id, ty);
-                let place = self.cat_deref(pat.hir_id, base)?;
+                let place = self.pat_deref_temp(pat.hir_id, subpat, ty)?;
                 self.cat_pattern(place, subpat, op)?;
             }
 
@@ -1832,6 +1853,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
             | PatKind::Expr(..)
             | PatKind::Range(..)
             | PatKind::Never
+            | PatKind::Missing
             | PatKind::Wild
             | PatKind::Err(_) => {
                 // always ok
@@ -1841,6 +1863,23 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         Ok(())
     }
 
+    /// Represents the place of the temp that stores the scrutinee of a deref pattern's interior.
+    fn pat_deref_temp(
+        &self,
+        hir_id: HirId,
+        inner: &hir::Pat<'_>,
+        target_ty: Ty<'tcx>,
+    ) -> Result<PlaceWithHirId<'tcx>, Cx::Error> {
+        let mutable = self.cx.typeck_results().pat_has_ref_mut_binding(inner);
+        let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
+        let re_erased = self.cx.tcx().lifetimes.re_erased;
+        let ty = Ty::new_ref(self.cx.tcx(), re_erased, target_ty, mutability);
+        // A deref pattern stores the result of `Deref::deref` or `DerefMut::deref_mut` ...
+        let base = self.cat_rvalue(hir_id, ty);
+        // ... and the inner pattern matches on the place behind that reference.
+        self.cat_deref(hir_id, base)
+    }
+
     fn is_multivariant_adt(&self, ty: Ty<'tcx>, span: Span) -> bool {
         if let ty::Adt(def, _) = self.cx.try_structurally_resolve_type(span, ty).kind() {
             // Note that if a non-exhaustive SingleVariant is defined in another crate, we need
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index 91190a32ff5..87d92b3fbde 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -27,9 +27,9 @@ use rustc_middle::ty::{
 };
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
+use rustc_span::Span;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;
-use rustc_span::{Span, kw};
 use rustc_trait_selection::error_reporting::infer::need_type_info::TypeAnnotationNeeded;
 use rustc_trait_selection::traits::{
     self, NormalizeExt, ObligationCauseCode, StructurallyNormalizeExt,
@@ -833,7 +833,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                 let trait_missing_method =
                     matches!(error, method::MethodError::NoMatch(_)) && ty.normalized.is_trait();
-                assert_ne!(item_name.name, kw::Empty);
                 self.report_method_error(
                     hir_id,
                     ty.normalized,
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index f4bd7ec701f..da0e8e362d6 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -616,7 +616,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 if let Some((DefKind::AssocFn, def_id)) =
                     self.typeck_results.borrow().type_dependent_def(call_expr.hir_id)
                     && let Some(assoc) = tcx.opt_associated_item(def_id)
-                    && assoc.fn_has_self_parameter
+                    && assoc.is_method()
                 {
                     Some(*receiver)
                 } else {
@@ -642,8 +642,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     TraitsInScope,
                     |mut ctxt| ctxt.probe_for_similar_candidate(),
                 )
-                && let ty::AssocKind::Fn = assoc.kind
-                && assoc.fn_has_self_parameter
+                && assoc.is_method()
             {
                 let args = self.infcx.fresh_args_for_item(call_name.span, assoc.def_id);
                 let fn_sig = tcx.fn_sig(assoc.def_id).instantiate(tcx, args);
@@ -684,10 +683,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .all(|(expected, found)| self.may_coerce(*expected, *found))
                 && fn_sig.inputs()[1..].len() == input_types.len()
             {
+                let assoc_name = assoc.name();
                 err.span_suggestion_verbose(
                     call_name.span,
-                    format!("you might have meant to use `{}`", assoc.name),
-                    assoc.name,
+                    format!("you might have meant to use `{}`", assoc_name),
+                    assoc_name,
                     Applicability::MaybeIncorrect,
                 );
                 return;
@@ -707,7 +707,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     tcx.def_span(assoc.def_id),
                     format!(
                         "there's is a method with similar name `{}`, but the arguments don't match",
-                        assoc.name,
+                        assoc.name(),
                     ),
                 );
                 return;
@@ -719,7 +719,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     format!(
                         "there's is a method with similar name `{}`, but their argument count \
                          doesn't match",
-                        assoc.name,
+                        assoc.name(),
                     ),
                 );
                 return;
@@ -1136,7 +1136,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 && let self_implicit =
                     matches!(call_expr.kind, hir::ExprKind::MethodCall(..)) as usize
                 && let Some(Some(arg)) =
-                    self.tcx.fn_arg_names(fn_def_id).get(expected_idx.as_usize() + self_implicit)
+                    self.tcx.fn_arg_idents(fn_def_id).get(expected_idx.as_usize() + self_implicit)
                 && arg.name != kw::SelfLower
             {
                 format!("/* {} */", arg.name)
@@ -2619,7 +2619,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         is_method: bool,
     ) -> Option<(IndexVec<ExpectedIdx, (Option<GenericIdx>, FnParam<'_>)>, &hir::Generics<'_>)>
     {
-        let (sig, generics, body_id, param_names) = match self.tcx.hir_get_if_local(def_id)? {
+        let (sig, generics, body_id, params) = match self.tcx.hir_get_if_local(def_id)? {
             hir::Node::TraitItem(&hir::TraitItem {
                 generics,
                 kind: hir::TraitItemKind::Fn(sig, trait_fn),
@@ -2661,7 +2661,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 None
             }
         });
-        match (body_id, param_names) {
+        match (body_id, params) {
             (Some(_), Some(_)) | (None, None) => unreachable!(),
             (Some(body), None) => {
                 let params = self.tcx.hir_body(body).params;
@@ -2678,7 +2678,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     params.get(is_method as usize..params.len() - sig.decl.c_variadic as usize)?;
                 debug_assert_eq!(params.len(), fn_inputs.len());
                 Some((
-                    fn_inputs.zip(params.iter().map(|&ident| FnParam::Name(ident))).collect(),
+                    fn_inputs.zip(params.iter().map(|&ident| FnParam::Ident(ident))).collect(),
                     generics,
                 ))
             }
@@ -2709,14 +2709,14 @@ impl<'tcx> Visitor<'tcx> for FindClosureArg<'tcx> {
 #[derive(Clone, Copy)]
 enum FnParam<'hir> {
     Param(&'hir hir::Param<'hir>),
-    Name(Option<Ident>),
+    Ident(Option<Ident>),
 }
 
 impl FnParam<'_> {
     fn span(&self) -> Span {
         match self {
             Self::Param(param) => param.span,
-            Self::Name(ident) => {
+            Self::Ident(ident) => {
                 if let Some(ident) = ident {
                     ident.span
                 } else {
@@ -2738,7 +2738,7 @@ impl FnParam<'_> {
                     {
                         Some(ident.name)
                     }
-                    FnParam::Name(ident)
+                    FnParam::Ident(ident)
                         if let Some(ident) = ident
                             && ident.name != kw::Underscore =>
                     {
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
index e14f1528d2c..934820eb4da 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
@@ -314,7 +314,7 @@ impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
         item_def_id: DefId,
         item_segment: &rustc_hir::PathSegment<'tcx>,
         poly_trait_ref: ty::PolyTraitRef<'tcx>,
-        _kind: ty::AssocKind,
+        _assoc_tag: ty::AssocTag,
     ) -> Result<(DefId, ty::GenericArgsRef<'tcx>), ErrorGuaranteed> {
         let trait_ref = self.instantiate_binder_with_fresh_vars(
             span,
@@ -488,7 +488,7 @@ fn parse_never_type_options_attr(
             item.span(),
             format!(
                 "unknown or duplicate never type option: `{}` (supported: `fallback`, `diverging_block_default`)",
-                item.name_or_empty()
+                item.name().unwrap()
             ),
         );
     }
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 912098c4e2d..91eb1989864 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -381,9 +381,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let mut suggestions = methods
                 .iter()
                 .filter_map(|conversion_method| {
+                    let conversion_method_name = conversion_method.name();
                     let receiver_method_ident = expr.method_ident();
                     if let Some(method_ident) = receiver_method_ident
-                        && method_ident.name == conversion_method.name
+                        && method_ident.name == conversion_method_name
                     {
                         return None; // do not suggest code that is already there (#53348)
                     }
@@ -391,20 +392,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let method_call_list = [sym::to_vec, sym::to_string];
                     let mut sugg = if let ExprKind::MethodCall(receiver_method, ..) = expr.kind
                         && receiver_method.ident.name == sym::clone
-                        && method_call_list.contains(&conversion_method.name)
+                        && method_call_list.contains(&conversion_method_name)
                     // If receiver is `.clone()` and found type has one of those methods,
                     // we guess that the user wants to convert from a slice type (`&[]` or `&str`)
                     // to an owned type (`Vec` or `String`). These conversions clone internally,
                     // so we remove the user's `clone` call.
                     {
-                        vec![(receiver_method.ident.span, conversion_method.name.to_string())]
+                        vec![(receiver_method.ident.span, conversion_method_name.to_string())]
                     } else if expr.precedence() < ExprPrecedence::Unambiguous {
                         vec![
                             (expr.span.shrink_to_lo(), "(".to_string()),
-                            (expr.span.shrink_to_hi(), format!(").{}()", conversion_method.name)),
+                            (expr.span.shrink_to_hi(), format!(").{}()", conversion_method_name)),
                         ]
                     } else {
-                        vec![(expr.span.shrink_to_hi(), format!(".{}()", conversion_method.name))]
+                        vec![(expr.span.shrink_to_hi(), format!(".{}()", conversion_method_name))]
                     };
                     let struct_pat_shorthand_field =
                         self.tcx.hir_maybe_get_struct_pattern_shorthand_field(expr);
diff --git a/compiler/rustc_hir_typeck/src/gather_locals.rs b/compiler/rustc_hir_typeck/src/gather_locals.rs
index 48fd5f1f982..5d87e800096 100644
--- a/compiler/rustc_hir_typeck/src/gather_locals.rs
+++ b/compiler/rustc_hir_typeck/src/gather_locals.rs
@@ -43,7 +43,7 @@ pub(super) struct Declaration<'a> {
 
 impl<'a> From<&'a hir::LetStmt<'a>> for Declaration<'a> {
     fn from(local: &'a hir::LetStmt<'a>) -> Self {
-        let hir::LetStmt { hir_id, pat, ty, span, init, els, source: _ } = *local;
+        let hir::LetStmt { hir_id, super_: _, pat, ty, span, init, els, source: _ } = *local;
         Declaration { hir_id, pat, ty, span, init, origin: DeclOrigin::LocalDecl { els } }
     }
 }
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index 46389668de7..af8ec373934 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -1,7 +1,6 @@
 // tidy-alphabetical-start
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(array_windows)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
@@ -117,7 +116,7 @@ fn typeck_with_inspect<'tcx>(
 
     let id = tcx.local_def_id_to_hir_id(def_id);
     let node = tcx.hir_node(id);
-    let span = tcx.hir_span(id);
+    let span = tcx.def_span(def_id);
 
     // Figure out what primary body this item has.
     let body_id = node.body_id().unwrap_or_else(|| {
@@ -266,7 +265,7 @@ fn infer_type_if_missing<'tcx>(fcx: &FnCtxt<'_, 'tcx>, node: Node<'tcx>) -> Opti
     let expected_type = if let Some(&hir::Ty { kind: hir::TyKind::Infer(()), span, .. }) = node.ty()
     {
         if let Some(item) = tcx.opt_associated_item(def_id.into())
-            && let ty::AssocKind::Const = item.kind
+            && let ty::AssocKind::Const { .. } = item.kind
             && let ty::AssocItemContainer::Impl = item.container
             && let Some(trait_item_def_id) = item.trait_item_def_id
         {
diff --git a/compiler/rustc_hir_typeck/src/method/mod.rs b/compiler/rustc_hir_typeck/src/method/mod.rs
index 4008021c3a8..1b67e2306aa 100644
--- a/compiler/rustc_hir_typeck/src/method/mod.rs
+++ b/compiler/rustc_hir_typeck/src/method/mod.rs
@@ -379,7 +379,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
 
         let def_id = method_item.def_id;
-        if method_item.kind != ty::AssocKind::Fn {
+        if !method_item.is_fn() {
             span_bug!(tcx.def_span(def_id), "expected `{m_name}` to be an associated function");
         }
 
@@ -529,17 +529,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
         }
 
-        let def_kind = pick.item.kind.as_def_kind();
+        let def_kind = pick.item.as_def_kind();
         tcx.check_stability(pick.item.def_id, Some(expr_id), span, Some(method_name.span));
         Ok((def_kind, pick.item.def_id))
     }
 
-    /// Finds item with name `item_name` defined in impl/trait `def_id`
+    /// Finds item with name `item_ident` defined in impl/trait `def_id`
     /// and return it, or `None`, if no such item was defined there.
-    fn associated_value(&self, def_id: DefId, item_name: Ident) -> Option<ty::AssocItem> {
+    fn associated_value(&self, def_id: DefId, item_ident: Ident) -> Option<ty::AssocItem> {
         self.tcx
             .associated_items(def_id)
-            .find_by_name_and_namespace(self.tcx, item_name, Namespace::ValueNS, def_id)
+            .find_by_ident_and_namespace(self.tcx, item_ident, Namespace::ValueNS, def_id)
             .copied()
     }
 }
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 0a01ec89a32..1d3a081cbb8 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -992,7 +992,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
 
     fn matches_return_type(&self, method: ty::AssocItem, expected: Ty<'tcx>) -> bool {
         match method.kind {
-            ty::AssocKind::Fn => self.probe(|_| {
+            ty::AssocKind::Fn { .. } => self.probe(|_| {
                 let args = self.fresh_args_for_item(self.span, method.def_id);
                 let fty = self.tcx.fn_sig(method.def_id).instantiate(self.tcx, args);
                 let fty = self.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, fty);
@@ -1583,7 +1583,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 },
                 None,
             ) {
-                self.private_candidate.set(Some((pick.item.kind.as_def_kind(), pick.item.def_id)));
+                self.private_candidate.set(Some((pick.item.as_def_kind(), pick.item.def_id)));
             }
         }
         None
@@ -1671,16 +1671,7 @@ impl<'tcx> Pick<'tcx> {
     /// Do not use for type checking.
     pub(crate) fn differs_from(&self, other: &Self) -> bool {
         let Self {
-            item:
-                AssocItem {
-                    def_id,
-                    name: _,
-                    kind: _,
-                    container: _,
-                    trait_item_def_id: _,
-                    fn_has_self_parameter: _,
-                    opt_rpitit_info: _,
-                },
+            item: AssocItem { def_id, kind: _, container: _, trait_item_def_id: _ },
             kind: _,
             import_ids: _,
             autoderefs: _,
@@ -1703,7 +1694,7 @@ impl<'tcx> Pick<'tcx> {
         if self.unstable_candidates.is_empty() {
             return;
         }
-        let def_kind = self.item.kind.as_def_kind();
+        let def_kind = self.item.as_def_kind();
         tcx.node_span_lint(lint::builtin::UNSTABLE_NAME_COLLISIONS, scope_expr_id, span, |lint| {
             lint.primary_message(format!(
                 "{} {} with this name may be added to the standard library in the future",
@@ -1712,7 +1703,7 @@ impl<'tcx> Pick<'tcx> {
             ));
 
             match (self.item.kind, self.item.container) {
-                (ty::AssocKind::Fn, _) => {
+                (ty::AssocKind::Fn { .. }, _) => {
                     // FIXME: This should be a `span_suggestion` instead of `help`
                     // However `self.span` only
                     // highlights the method name, so we can't use it. Also consider reusing
@@ -1723,17 +1714,12 @@ impl<'tcx> Pick<'tcx> {
                         tcx.def_path_str(self.item.def_id),
                     ));
                 }
-                (ty::AssocKind::Const, ty::AssocItemContainer::Trait) => {
+                (ty::AssocKind::Const { name }, ty::AssocItemContainer::Trait) => {
                     let def_id = self.item.container_id(tcx);
                     lint.span_suggestion(
                         span,
                         "use the fully qualified path to the associated const",
-                        format!(
-                            "<{} as {}>::{}",
-                            self.self_ty,
-                            tcx.def_path_str(def_id),
-                            self.item.name
-                        ),
+                        format!("<{} as {}>::{}", self.self_ty, tcx.def_path_str(def_id), name),
                         Applicability::MachineApplicable,
                     );
                 }
@@ -2222,7 +2208,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 let best_name = {
                     let names = applicable_close_candidates
                         .iter()
-                        .map(|cand| cand.name)
+                        .map(|cand| cand.name())
                         .collect::<Vec<Symbol>>();
                     find_best_match_for_name_with_substrings(
                         &names,
@@ -2234,10 +2220,12 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     applicable_close_candidates
                         .iter()
                         .find(|cand| self.matches_by_doc_alias(cand.def_id))
-                        .map(|cand| cand.name)
+                        .map(|cand| cand.name())
                 });
                 Ok(best_name.and_then(|best_name| {
-                    applicable_close_candidates.into_iter().find(|method| method.name == best_name)
+                    applicable_close_candidates
+                        .into_iter()
+                        .find(|method| method.name() == best_name)
                 }))
             }
         })
@@ -2252,10 +2240,10 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         // In Path mode (i.e., resolving a value like `T::next`), consider any
         // associated value (i.e., methods, constants) but not types.
         match self.mode {
-            Mode::MethodCall => item.fn_has_self_parameter,
+            Mode::MethodCall => item.is_method(),
             Mode::Path => match item.kind {
-                ty::AssocKind::Type => false,
-                ty::AssocKind::Fn | ty::AssocKind::Const => true,
+                ty::AssocKind::Type { .. } => false,
+                ty::AssocKind::Fn { .. } | ty::AssocKind::Const { .. } => true,
             },
         }
         // FIXME -- check for types that deref to `Self`,
@@ -2277,7 +2265,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         impl_ty: Ty<'tcx>,
         args: GenericArgsRef<'tcx>,
     ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
-        if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall {
+        if item.is_fn() && self.mode == Mode::MethodCall {
             let sig = self.xform_method_sig(item.def_id, args);
             (sig.inputs()[0], Some(sig.output()))
         } else {
@@ -2328,8 +2316,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     /// Determine if the given associated item type is relevant in the current context.
     fn is_relevant_kind_for_mode(&self, kind: ty::AssocKind) -> bool {
         match (self.mode, kind) {
-            (Mode::MethodCall, ty::AssocKind::Fn) => true,
-            (Mode::Path, ty::AssocKind::Const | ty::AssocKind::Fn) => true,
+            (Mode::MethodCall, ty::AssocKind::Fn { .. }) => true,
+            (Mode::Path, ty::AssocKind::Const { .. } | ty::AssocKind::Fn { .. }) => true,
             _ => false,
         }
     }
@@ -2346,8 +2334,9 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         let hir_id = self.fcx.tcx.local_def_id_to_hir_id(local_def_id);
         let attrs = self.fcx.tcx.hir_attrs(hir_id);
         for attr in attrs {
-            if sym::doc == attr.name_or_empty() {
-            } else if sym::rustc_confusables == attr.name_or_empty() {
+            if attr.has_name(sym::doc) {
+                // do nothing
+            } else if attr.has_name(sym::rustc_confusables) {
                 let Some(confusables) = attr.meta_item_list() else {
                     continue;
                 };
@@ -2367,7 +2356,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 continue;
             };
             for v in values {
-                if v.name_or_empty() != sym::alias {
+                if !v.has_name(sym::alias) {
                     continue;
                 }
                 if let Some(nested) = v.meta_item_list() {
@@ -2411,7 +2400,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         }
                         match edit_distance_with_substrings(
                             name.as_str(),
-                            x.name.as_str(),
+                            x.name().as_str(),
                             max_dist,
                         ) {
                             Some(d) => d > 0,
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 246b23f11b6..6a9fd7cdd48 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -25,6 +25,7 @@ use rustc_middle::bug;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, simplify_type};
 use rustc_middle::ty::print::{
     PrintTraitRefExt as _, with_crate_prefix, with_forced_trimmed_paths,
+    with_no_visible_paths_if_doc_hidden,
 };
 use rustc_middle::ty::{self, GenericArgKind, IsSuggestable, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::def_id::DefIdSet;
@@ -584,7 +585,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         mut span: Span,
         rcvr_ty: Ty<'tcx>,
-        item_name: Ident,
+        item_ident: Ident,
         expr_id: hir::HirId,
         source: SelfSource<'tcx>,
         args: Option<&'tcx [hir::Expr<'tcx>]>,
@@ -615,7 +616,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         } else if rcvr_ty.is_enum() {
             "variant or associated item"
         } else {
-            match (item_name.as_str().chars().next(), rcvr_ty.is_fresh_ty()) {
+            match (item_ident.as_str().chars().next(), rcvr_ty.is_fresh_ty()) {
                 (Some(name), false) if name.is_lowercase() => "function or associated item",
                 (Some(_), false) => "associated item",
                 (Some(_), true) | (None, false) => "variant or associated item",
@@ -630,7 +631,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             rcvr_ty,
             source,
             span,
-            item_name,
+            item_ident,
             &short_ty_str,
             &mut ty_file,
         ) {
@@ -642,13 +643,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             source,
             span,
             item_kind,
-            item_name,
+            item_ident,
             &short_ty_str,
             &mut ty_file,
         ) {
             return guar;
         }
-        span = item_name.span;
+        span = item_ident.span;
 
         // Don't show generic arguments when the method can't be found in any implementation (#81576).
         let mut ty_str_reported = ty_str.clone();
@@ -660,7 +661,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.tcx
                             .inherent_impls(adt_def.did())
                             .into_iter()
-                            .any(|def_id| self.associated_value(*def_id, item_name).is_some())
+                            .any(|def_id| self.associated_value(*def_id, item_ident).is_some())
                     } else {
                         false
                     }
@@ -677,14 +678,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let is_write = sugg_span.ctxt().outer_expn_data().macro_def_id.is_some_and(|def_id| {
             tcx.is_diagnostic_item(sym::write_macro, def_id)
                 || tcx.is_diagnostic_item(sym::writeln_macro, def_id)
-        }) && item_name.name == sym::write_fmt;
+        }) && item_ident.name == sym::write_fmt;
         let mut err = if is_write && let SelfSource::MethodCall(rcvr_expr) = source {
             self.suggest_missing_writer(rcvr_ty, rcvr_expr)
         } else {
             let mut err = self.dcx().create_err(NoAssociatedItem {
                 span,
                 item_kind,
-                item_name,
+                item_ident,
                 ty_prefix: if trait_missing_method {
                     // FIXME(mu001999) E0599 maybe not suitable here because it is for types
                     Cow::from("trait")
@@ -698,7 +699,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if is_method {
                 self.suggest_use_shadowed_binding_with_method(
                     source,
-                    item_name,
+                    item_ident,
                     &ty_str_reported,
                     &mut err,
                 );
@@ -709,10 +710,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 && let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = ty.kind
                 && let Res::SelfTyAlias { alias_to: impl_def_id, .. } = path.res
                 && let DefKind::Impl { .. } = self.tcx.def_kind(impl_def_id)
-                && let Some(candidate) = tcx.associated_items(impl_def_id).find_by_name_and_kind(
+                && let Some(candidate) = tcx.associated_items(impl_def_id).find_by_ident_and_kind(
                     self.tcx,
-                    item_name,
-                    ty::AssocKind::Type,
+                    item_ident,
+                    ty::AssocTag::Type,
                     impl_def_id,
                 )
                 && let Some(adt_def) = tcx.type_of(candidate.def_id).skip_binder().ty_adt_def()
@@ -721,7 +722,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             {
                 let def_path = tcx.def_path_str(adt_def.did());
                 err.span_suggestion(
-                    ty.span.to(item_name.span),
+                    ty.span.to(item_ident.span),
                     format!("to construct a value of type `{}`, use the explicit path", def_path),
                     def_path,
                     Applicability::MachineApplicable,
@@ -749,7 +750,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.find_builder_fn(&mut err, rcvr_ty, expr_id);
         }
 
-        if tcx.ty_is_opaque_future(rcvr_ty) && item_name.name == sym::poll {
+        if tcx.ty_is_opaque_future(rcvr_ty) && item_ident.name == sym::poll {
             err.help(format!(
                 "method `poll` found on `Pin<&mut {ty_str}>`, \
                 see documentation for `std::pin::Pin`"
@@ -764,7 +765,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         {
             self.suggest_await_before_method(
                 &mut err,
-                item_name,
+                item_ident,
                 rcvr_ty,
                 cal,
                 span,
@@ -786,7 +787,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if let SelfSource::MethodCall(rcvr_expr) = source
             && let ty::RawPtr(ty, ptr_mutbl) = *rcvr_ty.kind()
             && let Ok(pick) = self.lookup_probe_for_diagnostic(
-                item_name,
+                item_ident,
                 Ty::new_ref(tcx, ty::Region::new_error_misc(tcx), ty, ptr_mutbl),
                 self.tcx.hir_expect_expr(self.tcx.parent_hir_id(rcvr_expr.hir_id)),
                 ProbeScope::TraitsInScope,
@@ -807,7 +808,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             };
             err.span_note(
                 tcx.def_span(pick.item.def_id),
-                format!("the method `{item_name}` exists on the type `{ty}`", ty = pick.self_ty),
+                format!("the method `{item_ident}` exists on the type `{ty}`", ty = pick.self_ty),
             );
             let mut_str = ptr_mutbl.ptr_str();
             err.note(format!(
@@ -833,7 +834,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.suggest_fn_call(&mut err, rcvr_expr, rcvr_ty, |output_ty| {
                 let call_expr = self.tcx.hir_expect_expr(self.tcx.parent_hir_id(rcvr_expr.hir_id));
                 let probe = self.lookup_probe_for_diagnostic(
-                    item_name,
+                    item_ident,
                     output_ty,
                     call_expr,
                     ProbeScope::AllTraits,
@@ -872,13 +873,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 static_candidates,
                 rcvr_ty,
                 source,
-                item_name,
+                item_ident,
                 args,
                 sugg_span,
             );
             self.note_candidates_on_method_error(
                 rcvr_ty,
-                item_name,
+                item_ident,
                 source,
                 args,
                 span,
@@ -889,7 +890,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         } else if static_candidates.len() > 1 {
             self.note_candidates_on_method_error(
                 rcvr_ty,
-                item_name,
+                item_ident,
                 source,
                 args,
                 span,
@@ -903,7 +904,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut restrict_type_params = false;
         let mut suggested_derive = false;
         let mut unsatisfied_bounds = false;
-        if item_name.name == sym::count && self.is_slice_ty(rcvr_ty, span) {
+        if item_ident.name == sym::count && self.is_slice_ty(rcvr_ty, span) {
             let msg = "consider using `len` instead";
             if let SelfSource::MethodCall(_expr) = source {
                 err.span_suggestion_short(span, msg, "len", Applicability::MachineApplicable);
@@ -1348,7 +1349,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 };
                 let primary_message = primary_message.unwrap_or_else(|| {
                     format!(
-                        "the {item_kind} `{item_name}` exists for {actual_prefix} `{ty_str}`, \
+                        "the {item_kind} `{item_ident}` exists for {actual_prefix} `{ty_str}`, \
                          but its trait bounds were not satisfied"
                     )
                 });
@@ -1378,7 +1379,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // `Pin<&Self>`.
             if targs.len() == 1 {
                 let mut item_segment = hir::PathSegment::invalid();
-                item_segment.ident = item_name;
+                item_segment.ident = item_ident;
                 for t in [Ty::new_mut_ref, Ty::new_imm_ref, |_, _, t| t] {
                     let new_args =
                         tcx.mk_args_from_iter(targs.iter().map(|arg| match arg.as_type() {
@@ -1422,9 +1423,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     ty::Adt(adt, _) => self.tcx.is_lang_item(adt.did(), LangItem::String),
                     _ => false,
                 };
-                if is_string_or_ref_str && item_name.name == sym::iter {
+                if is_string_or_ref_str && item_ident.name == sym::iter {
                     err.span_suggestion_verbose(
-                        item_name.span,
+                        item_ident.span,
                         "because of the in-memory representation of `&str`, to obtain \
                          an `Iterator` over each of its codepoint use method `chars`",
                         "chars",
@@ -1438,10 +1439,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         .into_iter()
                         .copied()
                         .filter(|def_id| {
-                            if let Some(assoc) = self.associated_value(*def_id, item_name) {
+                            if let Some(assoc) = self.associated_value(*def_id, item_ident) {
                                 // Check for both mode is the same so we avoid suggesting
                                 // incorrect associated item.
-                                match (mode, assoc.fn_has_self_parameter, source) {
+                                match (mode, assoc.is_method(), source) {
                                     (Mode::MethodCall, true, SelfSource::MethodCall(_)) => {
                                         // We check that the suggest type is actually
                                         // different from the received one
@@ -1499,7 +1500,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // If the method name is the name of a field with a function or closure type,
         // give a helping note that it has to be called as `(x.f)(...)`.
         if let SelfSource::MethodCall(expr) = source {
-            if !self.suggest_calling_field_as_fn(span, rcvr_ty, expr, item_name, &mut err)
+            if !self.suggest_calling_field_as_fn(span, rcvr_ty, expr, item_ident, &mut err)
                 && similar_candidate.is_none()
                 && !custom_span_label
             {
@@ -1512,7 +1513,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let confusable_suggested = self.confusable_method_name(
             &mut err,
             rcvr_ty,
-            item_name,
+            item_ident,
             args.map(|args| {
                 args.iter()
                     .map(|expr| {
@@ -1530,12 +1531,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 source,
                 span,
                 rcvr_ty,
-                item_name,
+                item_ident,
                 expected.only_has_type(self),
             );
         }
 
-        self.suggest_unwrapping_inner_self(&mut err, source, rcvr_ty, item_name);
+        self.suggest_unwrapping_inner_self(&mut err, source, rcvr_ty, item_ident);
 
         for (span, mut bounds) in bound_spans {
             if !tcx.sess.source_map().is_span_accessible(span) {
@@ -1546,7 +1547,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let pre = if Some(span) == ty_span {
                 ty_span.take();
                 format!(
-                    "{item_kind} `{item_name}` not found for this {} because it ",
+                    "{item_kind} `{item_ident}` not found for this {} because it ",
                     rcvr_ty.prefix_string(self.tcx)
                 )
             } else {
@@ -1566,7 +1567,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             err.span_label(
                 span,
                 format!(
-                    "{item_kind} `{item_name}` not found for this {}",
+                    "{item_kind} `{item_ident}` not found for this {}",
                     rcvr_ty.prefix_string(self.tcx)
                 ),
             );
@@ -1578,7 +1579,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 &mut err,
                 span,
                 rcvr_ty,
-                item_name,
+                item_ident,
                 args.map(|args| args.len() + 1),
                 source,
                 no_match_data.out_of_scope_traits.clone(),
@@ -1595,7 +1596,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let adt_def = rcvr_ty.ty_adt_def().expect("enum is not an ADT");
             if let Some(var_name) = edit_distance::find_best_match_for_name(
                 &adt_def.variants().iter().map(|s| s.name).collect::<Vec<_>>(),
-                item_name.name,
+                item_ident.name,
                 None,
             ) && let Some(variant) = adt_def.variants().iter().find(|s| s.name == var_name)
             {
@@ -1721,7 +1722,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // that had unsatisfied trait bounds
             if unsatisfied_predicates.is_empty()
                 // ...or if we already suggested that name because of `rustc_confusable` annotation.
-                && Some(similar_candidate.name) != confusable_suggested
+                && Some(similar_candidate.name()) != confusable_suggested
             {
                 self.find_likely_intended_associated_item(
                     &mut err,
@@ -1736,14 +1737,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if !find_candidate_for_method {
             self.lookup_segments_chain_for_no_match_method(
                 &mut err,
-                item_name,
+                item_ident,
                 item_kind,
                 source,
                 no_match_data,
             );
         }
 
-        self.note_derefed_ty_has_method(&mut err, source, rcvr_ty, item_name, expected);
+        self.note_derefed_ty_has_method(&mut err, source, rcvr_ty, item_ident, expected);
         err.emit()
     }
 
@@ -1818,12 +1819,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         mode: Mode,
     ) {
         let tcx = self.tcx;
-        let def_kind = similar_candidate.kind.as_def_kind();
+        let def_kind = similar_candidate.as_def_kind();
         let an = self.tcx.def_kind_descr_article(def_kind, similar_candidate.def_id);
+        let similar_candidate_name = similar_candidate.name();
         let msg = format!(
             "there is {an} {} `{}` with a similar name",
             self.tcx.def_kind_descr(def_kind, similar_candidate.def_id),
-            similar_candidate.name,
+            similar_candidate_name,
         );
         // Methods are defined within the context of a struct and their first parameter
         // is always `self`, which represents the instance of the struct the method is
@@ -1833,7 +1835,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let ty_args = self.infcx.fresh_args_for_item(span, similar_candidate.def_id);
             let fn_sig = tcx.fn_sig(similar_candidate.def_id).instantiate(tcx, ty_args);
             let fn_sig = self.instantiate_binder_with_fresh_vars(span, infer::FnCall, fn_sig);
-            if similar_candidate.fn_has_self_parameter {
+            if similar_candidate.is_method() {
                 if let Some(args) = args
                     && fn_sig.inputs()[1..].len() == args.len()
                 {
@@ -1842,7 +1844,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     err.span_suggestion_verbose(
                         span,
                         msg,
-                        similar_candidate.name,
+                        similar_candidate_name,
                         Applicability::MaybeIncorrect,
                     );
                 } else {
@@ -1864,7 +1866,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 err.span_suggestion_verbose(
                     span,
                     msg,
-                    similar_candidate.name,
+                    similar_candidate_name,
                     Applicability::MaybeIncorrect,
                 );
             } else {
@@ -1877,7 +1879,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             err.span_suggestion_verbose(
                 span,
                 msg,
-                similar_candidate.name,
+                similar_candidate_name,
                 Applicability::MaybeIncorrect,
             );
         } else {
@@ -1901,7 +1903,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 {
                     if let Some(candidates) = find_attr!(self.tcx.get_all_attrs(inherent_method.def_id), AttributeKind::Confusables{symbols, ..} => symbols)
                         && candidates.contains(&item_name.name)
-                        && let ty::AssocKind::Fn = inherent_method.kind
+                        && inherent_method.is_fn()
                     {
                         let args =
                             ty::GenericArgs::identity_for_item(self.tcx, inherent_method.def_id)
@@ -1917,6 +1919,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             infer::FnCall,
                             fn_sig,
                         );
+                        let name = inherent_method.name();
                         if let Some(ref args) = call_args
                             && fn_sig.inputs()[1..]
                                 .iter()
@@ -1926,20 +1929,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         {
                             err.span_suggestion_verbose(
                                 item_name.span,
-                                format!("you might have meant to use `{}`", inherent_method.name),
-                                inherent_method.name,
+                                format!("you might have meant to use `{}`", name),
+                                name,
                                 Applicability::MaybeIncorrect,
                             );
-                            return Some(inherent_method.name);
+                            return Some(name);
                         } else if let None = call_args {
                             err.span_note(
                                 self.tcx.def_span(inherent_method.def_id),
-                                format!(
-                                    "you might have meant to use method `{}`",
-                                    inherent_method.name,
-                                ),
+                                format!("you might have meant to use method `{}`", name),
                             );
-                            return Some(inherent_method.name);
+                            return Some(name);
                         }
                     }
                 }
@@ -2115,8 +2115,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Only assoc fn with no receivers and only if
             // they are resolvable
             .filter(|item| {
-                matches!(item.kind, ty::AssocKind::Fn)
-                    && !item.fn_has_self_parameter
+                matches!(item.kind, ty::AssocKind::Fn { has_self: false, .. })
                     && self
                         .probe_for_name(
                             Mode::Path,
@@ -2260,7 +2259,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 };
 
                 let assoc = self.associated_value(assoc_did, item_name)?;
-                if assoc.kind != ty::AssocKind::Fn {
+                if !assoc.is_fn() {
                     return None;
                 }
 
@@ -3207,7 +3206,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // If this method receives `&self`, then the provided
                     // argument _should_ coerce, so it's valid to suggest
                     // just changing the path.
-                    && pick.item.fn_has_self_parameter
+                    && pick.item.is_method()
                     && let Some(self_ty) =
                         self.tcx.fn_sig(pick.item.def_id).instantiate_identity().inputs().skip_binder().get(0)
                     && self_ty.is_ref()
@@ -3328,7 +3327,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let path_strings = candidates.iter().map(|trait_did| {
                 format!(
                     "{prefix}{}{postfix}\n",
-                    with_crate_prefix!(self.tcx.def_path_str(*trait_did)),
+                    with_no_visible_paths_if_doc_hidden!(with_crate_prefix!(
+                        self.tcx.def_path_str(*trait_did)
+                    )),
                 )
             });
 
@@ -3336,7 +3337,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let parent_did = parent_map.get(trait_did).unwrap();
                 format!(
                     "{prefix}{}::*{postfix} // trait {}\n",
-                    with_crate_prefix!(self.tcx.def_path_str(*parent_did)),
+                    with_no_visible_paths_if_doc_hidden!(with_crate_prefix!(
+                        self.tcx.def_path_str(*parent_did)
+                    )),
                     self.tcx.item_name(*trait_did),
                 )
             });
@@ -3555,7 +3558,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             || (("Pin::new" == *pre)
                                 && ((sym::as_ref == item_name.name) || !unpin))
                             || inputs_len.is_some_and(|inputs_len| {
-                                pick.item.kind == ty::AssocKind::Fn
+                                pick.item.is_fn()
                                     && self
                                         .tcx
                                         .fn_sig(pick.item.def_id)
@@ -3613,7 +3616,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     && pick.autoderefs == 0
                     // Check that the method of the same name that was found on the new `Pin<T>`
                     // receiver has the same number of arguments that appear in the user's code.
-                    && inputs_len.is_some_and(|inputs_len| pick.item.kind == ty::AssocKind::Fn && self.tcx.fn_sig(pick.item.def_id).skip_binder().skip_binder().inputs().len() == inputs_len)
+                    && inputs_len.is_some_and(|inputs_len| pick.item.is_fn() && self.tcx.fn_sig(pick.item.def_id).skip_binder().skip_binder().inputs().len() == inputs_len)
                 {
                     let indent = self
                         .tcx
@@ -3751,7 +3754,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     && self
                         .associated_value(info.def_id, item_name)
                         .filter(|item| {
-                            if let ty::AssocKind::Fn = item.kind {
+                            if item.is_fn() {
                                 let id = item
                                     .def_id
                                     .as_local()
@@ -4274,17 +4277,17 @@ fn print_disambiguation_help<'tcx>(
     item: ty::AssocItem,
 ) -> Option<String> {
     let trait_impl_type = trait_ref.self_ty().peel_refs();
-    let trait_ref = if item.fn_has_self_parameter {
+    let trait_ref = if item.is_method() {
         trait_ref.print_only_trait_name().to_string()
     } else {
         format!("<{} as {}>", trait_ref.args[0], trait_ref.print_only_trait_name())
     };
     Some(
-        if matches!(item.kind, ty::AssocKind::Fn)
+        if item.is_fn()
             && let SelfSource::MethodCall(receiver) = source
             && let Some(args) = args
         {
-            let def_kind_descr = tcx.def_kind_descr(item.kind.as_def_kind(), item.def_id);
+            let def_kind_descr = tcx.def_kind_descr(item.as_def_kind(), item.def_id);
             let item_name = item.ident(tcx);
             let first_input =
                 tcx.fn_sig(item.def_id).instantiate_identity().skip_binder().inputs().get(0);
@@ -4299,7 +4302,7 @@ fn print_disambiguation_help<'tcx>(
             let args = if let Some(first_arg_type) = first_arg_type
                 && (first_arg_type == tcx.types.self_param
                     || first_arg_type == trait_impl_type
-                    || item.fn_has_self_parameter)
+                    || item.is_method())
             {
                 Some(receiver)
             } else {
diff --git a/compiler/rustc_hir_typeck/src/op.rs b/compiler/rustc_hir_typeck/src/op.rs
index 93f77b8409f..0e42a84ca32 100644
--- a/compiler/rustc_hir_typeck/src/op.rs
+++ b/compiler/rustc_hir_typeck/src/op.rs
@@ -372,7 +372,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 .associated_item_def_ids(def_id)
                                 .iter()
                                 .find(|item_def_id| {
-                                    self.tcx.associated_item(*item_def_id).name == sym::Output
+                                    self.tcx.associated_item(*item_def_id).name() == sym::Output
                                 })
                                 .cloned()
                         });
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index 9766ceda569..e5e4fc7f8b7 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -9,11 +9,13 @@ use rustc_errors::{
     Applicability, Diag, ErrorGuaranteed, MultiSpan, pluralize, struct_span_code_err,
 };
 use rustc_hir::def::{CtorKind, DefKind, Res};
+use rustc_hir::def_id::DefId;
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::{
     self as hir, BindingMode, ByRef, ExprKind, HirId, LangItem, Mutability, Pat, PatExpr,
     PatExprKind, PatKind, expr_needs_parens,
 };
+use rustc_hir_analysis::autoderef::report_autoderef_recursion_limit_error;
 use rustc_infer::infer;
 use rustc_middle::traits::PatternOriginExpr;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
@@ -29,11 +31,12 @@ use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
 use tracing::{debug, instrument, trace};
 use ty::VariantDef;
+use ty::adjustment::{PatAdjust, PatAdjustment};
 
 use super::report_unexpected_variant_res;
 use crate::expectation::Expectation;
 use crate::gather_locals::DeclOrigin;
-use crate::{FnCtxt, LoweredTy, errors};
+use crate::{FnCtxt, errors};
 
 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
@@ -161,15 +164,35 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 /// Mode for adjusting the expected type and binding mode.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 enum AdjustMode {
-    /// Peel off all immediate reference types.
-    Peel,
-    /// Reset binding mode to the initial mode.
-    /// Used for destructuring assignment, where we don't want any match ergonomics.
-    Reset,
+    /// Peel off all immediate reference types. If the `deref_patterns` feature is enabled, this
+    /// also peels smart pointer ADTs.
+    Peel { kind: PeelKind },
     /// Pass on the input binding mode and expected type.
     Pass,
 }
 
+/// Restrictions on what types to peel when adjusting the expected type and binding mode.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum PeelKind {
+    /// Only peel reference types. This is used for explicit `deref!(_)` patterns, which dereference
+    /// any number of `&`/`&mut` references, plus a single smart pointer.
+    ExplicitDerefPat,
+    /// Implicitly peel any number of references, and if `deref_patterns` is enabled, smart pointer
+    /// ADTs. In order to peel only as much as necessary for the pattern to match, the `until_adt`
+    /// field contains the ADT def that the pattern is a constructor for, if applicable, so that we
+    /// don't peel it. See [`ResolvedPat`] for more information.
+    Implicit { until_adt: Option<DefId> },
+}
+
+impl AdjustMode {
+    const fn peel_until_adt(opt_adt_def: Option<DefId>) -> AdjustMode {
+        AdjustMode::Peel { kind: PeelKind::Implicit { until_adt: opt_adt_def } }
+    }
+    const fn peel_all() -> AdjustMode {
+        AdjustMode::peel_until_adt(None)
+    }
+}
+
 /// `ref mut` bindings (explicit or match-ergonomics) are not allowed behind an `&` reference.
 /// Normally, the borrow checker enforces this, but for (currently experimental) match ergonomics,
 /// we track this when typing patterns for two purposes:
@@ -245,6 +268,47 @@ enum InheritedRefMatchRule {
     },
 }
 
+/// When checking patterns containing paths, we need to know the path's resolution to determine
+/// whether to apply match ergonomics and implicitly dereference the scrutinee. For instance, when
+/// the `deref_patterns` feature is enabled and we're matching against a scrutinee of type
+/// `Cow<'a, Option<u8>>`, we insert an implicit dereference to allow the pattern `Some(_)` to type,
+/// but we must not dereference it when checking the pattern `Cow::Borrowed(_)`.
+///
+/// `ResolvedPat` contains the information from resolution needed to determine match ergonomics
+/// adjustments, and to finish checking the pattern once we know its adjusted type.
+#[derive(Clone, Copy, Debug)]
+struct ResolvedPat<'tcx> {
+    /// The type of the pattern, to be checked against the type of the scrutinee after peeling. This
+    /// is also used to avoid peeling the scrutinee's constructors (see the `Cow` example above).
+    ty: Ty<'tcx>,
+    kind: ResolvedPatKind<'tcx>,
+}
+
+#[derive(Clone, Copy, Debug)]
+enum ResolvedPatKind<'tcx> {
+    Path { res: Res, pat_res: Res, segments: &'tcx [hir::PathSegment<'tcx>] },
+    Struct { variant: &'tcx VariantDef },
+    TupleStruct { res: Res, variant: &'tcx VariantDef },
+}
+
+impl<'tcx> ResolvedPat<'tcx> {
+    fn adjust_mode(&self) -> AdjustMode {
+        if let ResolvedPatKind::Path { res, .. } = self.kind
+            && matches!(res, Res::Def(DefKind::Const | DefKind::AssocConst, _))
+        {
+            // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
+            // Peeling the reference types too early will cause type checking failures.
+            // Although it would be possible to *also* peel the types of the constants too.
+            AdjustMode::Pass
+        } else {
+            // The remaining possible resolutions for path, struct, and tuple struct patterns are
+            // ADT constructors. As such, we may peel references freely, but we must not peel the
+            // ADT itself from the scrutinee if it's a smart pointer.
+            AdjustMode::peel_until_adt(self.ty.ty_adt_def().map(|adt| adt.did()))
+        }
+    }
+}
+
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Experimental pattern feature: after matching against a shared reference, do we limit the
     /// default binding mode in subpatterns to be `ref` when it would otherwise be `ref mut`?
@@ -321,79 +385,35 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Conversely, inside this module, `check_pat_top` should never be used.
     #[instrument(level = "debug", skip(self, pat_info))]
     fn check_pat(&self, pat: &'tcx Pat<'tcx>, expected: Ty<'tcx>, pat_info: PatInfo<'tcx>) {
-        let PatInfo { binding_mode, max_ref_mutbl, top_info: ti, current_depth, .. } = pat_info;
-
-        let path_res = match pat.kind {
+        // For patterns containing paths, we need the path's resolution to determine whether to
+        // implicitly dereference the scrutinee before matching.
+        let opt_path_res = match pat.kind {
             PatKind::Expr(PatExpr { kind: PatExprKind::Path(qpath), hir_id, span }) => {
-                Some(self.resolve_ty_and_res_fully_qualified_call(qpath, *hir_id, *span))
+                Some(self.resolve_pat_path(*hir_id, *span, qpath))
             }
+            PatKind::Struct(ref qpath, ..) => Some(self.resolve_pat_struct(pat, qpath)),
+            PatKind::TupleStruct(ref qpath, ..) => Some(self.resolve_pat_tuple_struct(pat, qpath)),
             _ => None,
         };
-        let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
-        let (expected, binding_mode, max_ref_mutbl) =
-            self.calc_default_binding_mode(pat, expected, binding_mode, adjust_mode, max_ref_mutbl);
-        let pat_info = PatInfo {
-            binding_mode,
-            max_ref_mutbl,
-            top_info: ti,
-            decl_origin: pat_info.decl_origin,
-            current_depth: current_depth + 1,
-        };
-
-        let ty = match pat.kind {
-            PatKind::Wild | PatKind::Err(_) => expected,
-            // We allow any type here; we ensure that the type is uninhabited during match checking.
-            PatKind::Never => expected,
-            PatKind::Expr(PatExpr { kind: PatExprKind::Path(qpath), hir_id, span }) => {
-                let ty = self.check_pat_path(
-                    *hir_id,
-                    pat.hir_id,
-                    *span,
-                    qpath,
-                    path_res.unwrap(),
-                    expected,
-                    &pat_info.top_info,
-                );
-                self.write_ty(*hir_id, ty);
-                ty
-            }
-            PatKind::Expr(lt) => self.check_pat_lit(pat.span, lt, expected, &pat_info.top_info),
-            PatKind::Range(lhs, rhs, _) => {
-                self.check_pat_range(pat.span, lhs, rhs, expected, &pat_info.top_info)
-            }
-            PatKind::Binding(ba, var_id, ident, sub) => {
-                self.check_pat_ident(pat, ba, var_id, ident, sub, expected, pat_info)
-            }
-            PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
-                self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, pat_info)
-            }
-            PatKind::Struct(ref qpath, fields, has_rest_pat) => {
-                self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, pat_info)
-            }
-            PatKind::Guard(pat, cond) => {
-                self.check_pat(pat, expected, pat_info);
-                self.check_expr_has_type_or_error(cond, self.tcx.types.bool, |_| {});
-                expected
-            }
-            PatKind::Or(pats) => {
-                for pat in pats {
-                    self.check_pat(pat, expected, pat_info);
-                }
-                expected
-            }
-            PatKind::Tuple(elements, ddpos) => {
-                self.check_pat_tuple(pat.span, elements, ddpos, expected, pat_info)
-            }
-            PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, pat_info),
-            PatKind::Deref(inner) => self.check_pat_deref(pat.span, inner, expected, pat_info),
-            PatKind::Ref(inner, mutbl) => self.check_pat_ref(pat, inner, mutbl, expected, pat_info),
-            PatKind::Slice(before, slice, after) => {
-                self.check_pat_slice(pat.span, before, slice, after, expected, pat_info)
-            }
-        };
-
+        let adjust_mode = self.calc_adjust_mode(pat, opt_path_res);
+        let ty = self.check_pat_inner(pat, opt_path_res, adjust_mode, expected, pat_info);
         self.write_ty(pat.hir_id, ty);
 
+        // If we implicitly inserted overloaded dereferences before matching, check the pattern to
+        // see if the dereferenced types need `DerefMut` bounds.
+        if let Some(derefed_tys) = self.typeck_results.borrow().pat_adjustments().get(pat.hir_id)
+            && derefed_tys.iter().any(|adjust| adjust.kind == PatAdjust::OverloadedDeref)
+        {
+            self.register_deref_mut_bounds_if_needed(
+                pat.span,
+                pat,
+                derefed_tys.iter().filter_map(|adjust| match adjust.kind {
+                    PatAdjust::OverloadedDeref => Some(adjust.source),
+                    PatAdjust::BuiltinDeref => None,
+                }),
+            );
+        }
+
         // (note_1): In most of the cases where (note_1) is referenced
         // (literals and constants being the exception), we relate types
         // using strict equality, even though subtyping would be sufficient.
@@ -437,62 +457,226 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
     }
 
-    /// Compute the new expected type and default binding mode from the old ones
-    /// as well as the pattern form we are currently checking.
-    fn calc_default_binding_mode(
+    // Helper to avoid resolving the same path pattern several times.
+    fn check_pat_inner(
         &self,
         pat: &'tcx Pat<'tcx>,
-        expected: Ty<'tcx>,
-        def_br: ByRef,
+        opt_path_res: Option<Result<ResolvedPat<'tcx>, ErrorGuaranteed>>,
         adjust_mode: AdjustMode,
-        max_ref_mutbl: MutblCap,
-    ) -> (Ty<'tcx>, ByRef, MutblCap) {
+        expected: Ty<'tcx>,
+        pat_info: PatInfo<'tcx>,
+    ) -> Ty<'tcx> {
         #[cfg(debug_assertions)]
-        if def_br == ByRef::Yes(Mutability::Mut)
-            && max_ref_mutbl != MutblCap::Mut
+        if pat_info.binding_mode == ByRef::Yes(Mutability::Mut)
+            && pat_info.max_ref_mutbl != MutblCap::Mut
             && self.downgrade_mut_inside_shared()
         {
             span_bug!(pat.span, "Pattern mutability cap violated!");
         }
-        match adjust_mode {
-            AdjustMode::Pass => (expected, def_br, max_ref_mutbl),
-            AdjustMode::Reset => (expected, ByRef::No, MutblCap::Mut),
-            AdjustMode::Peel => self.peel_off_references(pat, expected, def_br, max_ref_mutbl),
+
+        // Resolve type if needed.
+        let expected = if let AdjustMode::Peel { .. } = adjust_mode
+            && pat.default_binding_modes
+        {
+            self.try_structurally_resolve_type(pat.span, expected)
+        } else {
+            expected
+        };
+        let old_pat_info = pat_info;
+        let pat_info = PatInfo { current_depth: old_pat_info.current_depth + 1, ..old_pat_info };
+
+        match pat.kind {
+            // Peel off a `&` or `&mut` from the scrutinee type. See the examples in
+            // `tests/ui/rfcs/rfc-2005-default-binding-mode`.
+            _ if let AdjustMode::Peel { .. } = adjust_mode
+                && pat.default_binding_modes
+                && let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() =>
+            {
+                debug!("inspecting {:?}", expected);
+
+                debug!("current discriminant is Ref, inserting implicit deref");
+                // Preserve the reference type. We'll need it later during THIR lowering.
+                self.typeck_results
+                    .borrow_mut()
+                    .pat_adjustments_mut()
+                    .entry(pat.hir_id)
+                    .or_default()
+                    .push(PatAdjustment { kind: PatAdjust::BuiltinDeref, source: expected });
+
+                let mut binding_mode = ByRef::Yes(match pat_info.binding_mode {
+                    // If default binding mode is by value, make it `ref` or `ref mut`
+                    // (depending on whether we observe `&` or `&mut`).
+                    ByRef::No |
+                    // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
+                    ByRef::Yes(Mutability::Mut) => inner_mutability,
+                    // Once a `ref`, always a `ref`.
+                    // This is because a `& &mut` cannot mutate the underlying value.
+                    ByRef::Yes(Mutability::Not) => Mutability::Not,
+                });
+
+                let mut max_ref_mutbl = pat_info.max_ref_mutbl;
+                if self.downgrade_mut_inside_shared() {
+                    binding_mode = binding_mode.cap_ref_mutability(max_ref_mutbl.as_mutbl());
+                }
+                if binding_mode == ByRef::Yes(Mutability::Not) {
+                    max_ref_mutbl = MutblCap::Not;
+                }
+                debug!("default binding mode is now {:?}", binding_mode);
+
+                // Use the old pat info to keep `current_depth` to its old value.
+                let new_pat_info = PatInfo { binding_mode, max_ref_mutbl, ..old_pat_info };
+                // Recurse with the new expected type.
+                self.check_pat_inner(pat, opt_path_res, adjust_mode, inner_ty, new_pat_info)
+            }
+            // If `deref_patterns` is enabled, peel a smart pointer from the scrutinee type. See the
+            // examples in `tests/ui/pattern/deref_patterns/`.
+            _ if self.tcx.features().deref_patterns()
+                && let AdjustMode::Peel { kind: PeelKind::Implicit { until_adt } } = adjust_mode
+                && pat.default_binding_modes
+                // For simplicity, only apply overloaded derefs if `expected` is a known ADT.
+                // FIXME(deref_patterns): we'll get better diagnostics for users trying to
+                // implicitly deref generics if we allow them here, but primitives, tuples, and
+                // inference vars definitely should be stopped. Figure out what makes most sense.
+                && let ty::Adt(scrutinee_adt, _) = *expected.kind()
+                // Don't peel if the pattern type already matches the scrutinee. E.g., stop here if
+                // matching on a `Cow<'a, T>` scrutinee with a `Cow::Owned(_)` pattern.
+                && until_adt != Some(scrutinee_adt.did())
+                // At this point, the pattern isn't able to match `expected` without peeling. Check
+                // that it implements `Deref` before assuming it's a smart pointer, to get a normal
+                // type error instead of a missing impl error if not. This only checks for `Deref`,
+                // not `DerefPure`: we require that too, but we want a trait error if it's missing.
+                && let Some(deref_trait) = self.tcx.lang_items().deref_trait()
+                && self
+                    .type_implements_trait(deref_trait, [expected], self.param_env)
+                    .may_apply() =>
+            {
+                debug!("scrutinee ty {expected:?} is a smart pointer, inserting overloaded deref");
+                // The scrutinee is a smart pointer; implicitly dereference it. This adds a
+                // requirement that `expected: DerefPure`.
+                let mut inner_ty = self.deref_pat_target(pat.span, expected);
+                // Once we've checked `pat`, we'll add a `DerefMut` bound if it contains any
+                // `ref mut` bindings. See `Self::register_deref_mut_bounds_if_needed`.
+
+                let mut typeck_results = self.typeck_results.borrow_mut();
+                let mut pat_adjustments_table = typeck_results.pat_adjustments_mut();
+                let pat_adjustments = pat_adjustments_table.entry(pat.hir_id).or_default();
+                // We may reach the recursion limit if a user matches on a type `T` satisfying
+                // `T: Deref<Target = T>`; error gracefully in this case.
+                // FIXME(deref_patterns): If `deref_patterns` stabilizes, it may make sense to move
+                // this check out of this branch. Alternatively, this loop could be implemented with
+                // autoderef and this check removed. For now though, don't break code compiling on
+                // stable with lots of `&`s and a low recursion limit, if anyone's done that.
+                if self.tcx.recursion_limit().value_within_limit(pat_adjustments.len()) {
+                    // Preserve the smart pointer type for THIR lowering and closure upvar analysis.
+                    pat_adjustments
+                        .push(PatAdjustment { kind: PatAdjust::OverloadedDeref, source: expected });
+                } else {
+                    let guar = report_autoderef_recursion_limit_error(self.tcx, pat.span, expected);
+                    inner_ty = Ty::new_error(self.tcx, guar);
+                }
+                drop(typeck_results);
+
+                // Recurse, using the old pat info to keep `current_depth` to its old value.
+                // Peeling smart pointers does not update the default binding mode.
+                self.check_pat_inner(pat, opt_path_res, adjust_mode, inner_ty, old_pat_info)
+            }
+            PatKind::Missing | PatKind::Wild | PatKind::Err(_) => expected,
+            // We allow any type here; we ensure that the type is uninhabited during match checking.
+            PatKind::Never => expected,
+            PatKind::Expr(PatExpr { kind: PatExprKind::Path(_), hir_id, .. }) => {
+                let ty = match opt_path_res.unwrap() {
+                    Ok(ref pr) => {
+                        self.check_pat_path(pat.hir_id, pat.span, pr, expected, &pat_info.top_info)
+                    }
+                    Err(guar) => Ty::new_error(self.tcx, guar),
+                };
+                self.write_ty(*hir_id, ty);
+                ty
+            }
+            PatKind::Expr(lt) => self.check_pat_lit(pat.span, lt, expected, &pat_info.top_info),
+            PatKind::Range(lhs, rhs, _) => {
+                self.check_pat_range(pat.span, lhs, rhs, expected, &pat_info.top_info)
+            }
+            PatKind::Binding(ba, var_id, ident, sub) => {
+                self.check_pat_ident(pat, ba, var_id, ident, sub, expected, pat_info)
+            }
+            PatKind::TupleStruct(ref qpath, subpats, ddpos) => match opt_path_res.unwrap() {
+                Ok(ResolvedPat { ty, kind: ResolvedPatKind::TupleStruct { res, variant } }) => self
+                    .check_pat_tuple_struct(
+                        pat, qpath, subpats, ddpos, res, ty, variant, expected, pat_info,
+                    ),
+                Err(guar) => {
+                    let ty_err = Ty::new_error(self.tcx, guar);
+                    for subpat in subpats {
+                        self.check_pat(subpat, ty_err, pat_info);
+                    }
+                    ty_err
+                }
+                Ok(pr) => span_bug!(pat.span, "tuple struct pattern resolved to {pr:?}"),
+            },
+            PatKind::Struct(_, fields, has_rest_pat) => match opt_path_res.unwrap() {
+                Ok(ResolvedPat { ty, kind: ResolvedPatKind::Struct { variant } }) => self
+                    .check_pat_struct(pat, fields, has_rest_pat, ty, variant, expected, pat_info),
+                Err(guar) => {
+                    let ty_err = Ty::new_error(self.tcx, guar);
+                    for field in fields {
+                        self.check_pat(field.pat, ty_err, pat_info);
+                    }
+                    ty_err
+                }
+                Ok(pr) => span_bug!(pat.span, "struct pattern resolved to {pr:?}"),
+            },
+            PatKind::Guard(pat, cond) => {
+                self.check_pat(pat, expected, pat_info);
+                self.check_expr_has_type_or_error(cond, self.tcx.types.bool, |_| {});
+                expected
+            }
+            PatKind::Or(pats) => {
+                for pat in pats {
+                    self.check_pat(pat, expected, pat_info);
+                }
+                expected
+            }
+            PatKind::Tuple(elements, ddpos) => {
+                self.check_pat_tuple(pat.span, elements, ddpos, expected, pat_info)
+            }
+            PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, pat_info),
+            PatKind::Deref(inner) => self.check_pat_deref(pat.span, inner, expected, pat_info),
+            PatKind::Ref(inner, mutbl) => self.check_pat_ref(pat, inner, mutbl, expected, pat_info),
+            PatKind::Slice(before, slice, after) => {
+                self.check_pat_slice(pat.span, before, slice, after, expected, pat_info)
+            }
         }
     }
 
     /// How should the binding mode and expected type be adjusted?
     ///
-    /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
-    fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
-        // When we perform destructuring assignment, we disable default match bindings, which are
-        // unintuitive in this context.
-        if !pat.default_binding_modes {
-            return AdjustMode::Reset;
-        }
+    /// When the pattern contains a path, `opt_path_res` must be `Some(path_res)`.
+    fn calc_adjust_mode(
+        &self,
+        pat: &'tcx Pat<'tcx>,
+        opt_path_res: Option<Result<ResolvedPat<'tcx>, ErrorGuaranteed>>,
+    ) -> AdjustMode {
         match &pat.kind {
             // Type checking these product-like types successfully always require
             // that the expected type be of those types and not reference types.
-            PatKind::Struct(..)
-            | PatKind::TupleStruct(..)
-            | PatKind::Tuple(..)
-            | PatKind::Box(_)
-            | PatKind::Deref(_)
+            PatKind::Tuple(..)
             | PatKind::Range(..)
-            | PatKind::Slice(..) => AdjustMode::Peel,
+            | PatKind::Slice(..) => AdjustMode::peel_all(),
+            // When checking an explicit deref pattern, only peel reference types.
+            // FIXME(deref_patterns): If box patterns and deref patterns need to coexist, box
+            // patterns may want `PeelKind::Implicit`, stopping on encountering a box.
+            | PatKind::Box(_)
+            | PatKind::Deref(_) => AdjustMode::Peel { kind: PeelKind::ExplicitDerefPat },
             // A never pattern behaves somewhat like a literal or unit variant.
-            PatKind::Never => AdjustMode::Peel,
-            PatKind::Expr(PatExpr { kind: PatExprKind::Path(_), .. }) => match opt_path_res.unwrap() {
-                // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
-                // Peeling the reference types too early will cause type checking failures.
-                // Although it would be possible to *also* peel the types of the constants too.
-                Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
-                // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
-                // could successfully compile. The former being `Self` requires a unit struct.
-                // In either case, and unlike constants, the pattern itself cannot be
-                // a reference type wherefore peeling doesn't give up any expressiveness.
-                _ => AdjustMode::Peel,
-            },
+            PatKind::Never => AdjustMode::peel_all(),
+            // For patterns with paths, how we peel the scrutinee depends on the path's resolution.
+            PatKind::Struct(..)
+            | PatKind::TupleStruct(..)
+            | PatKind::Expr(PatExpr { kind: PatExprKind::Path(_), .. }) => {
+                // If there was an error resolving the path, default to peeling everything.
+                opt_path_res.unwrap().map_or(AdjustMode::peel_all(), |pr| pr.adjust_mode())
+            }
 
             // String and byte-string literals result in types `&str` and `&[u8]` respectively.
             // All other literals result in non-reference types.
@@ -501,13 +685,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Call `resolve_vars_if_possible` here for inline const blocks.
             PatKind::Expr(lt) => match self.resolve_vars_if_possible(self.check_pat_expr_unadjusted(lt)).kind() {
                 ty::Ref(..) => AdjustMode::Pass,
-                _ => AdjustMode::Peel,
+                _ => {
+                    // Path patterns have already been handled, and inline const blocks currently
+                    // aren't possible to write, so any handling for them would be untested.
+                    if cfg!(debug_assertions)
+                        && self.tcx.features().deref_patterns()
+                        && !matches!(lt.kind, PatExprKind::Lit { .. })
+                    {
+                        span_bug!(lt.span, "FIXME(deref_patterns): adjust mode unimplemented for {:?}", lt.kind);
+                    }
+                    AdjustMode::peel_all()
+                }
             },
 
             // Ref patterns are complicated, we handle them in `check_pat_ref`.
-            PatKind::Ref(..) => AdjustMode::Pass,
+            PatKind::Ref(..)
+            // No need to do anything on a missing pattern.
+            | PatKind::Missing
             // A `_` pattern works with any expected type, so there's no need to do anything.
-            PatKind::Wild
+            | PatKind::Wild
             // A malformed pattern doesn't have an expected type, so let's just accept any type.
             | PatKind::Err(_)
             // Bindings also work with whatever the expected type is,
@@ -524,64 +720,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    /// Peel off as many immediately nested `& mut?` from the expected type as possible
-    /// and return the new expected type and binding default binding mode.
-    /// The adjustments vector, if non-empty is stored in a table.
-    fn peel_off_references(
-        &self,
-        pat: &'tcx Pat<'tcx>,
-        expected: Ty<'tcx>,
-        mut def_br: ByRef,
-        mut max_ref_mutbl: MutblCap,
-    ) -> (Ty<'tcx>, ByRef, MutblCap) {
-        let mut expected = self.try_structurally_resolve_type(pat.span, expected);
-        // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
-        // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
-        // the `Some(5)` which is not of type Ref.
-        //
-        // For each ampersand peeled off, update the binding mode and push the original
-        // type into the adjustments vector.
-        //
-        // See the examples in `ui/match-defbm*.rs`.
-        let mut pat_adjustments = vec![];
-        while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
-            debug!("inspecting {:?}", expected);
-
-            debug!("current discriminant is Ref, inserting implicit deref");
-            // Preserve the reference type. We'll need it later during THIR lowering.
-            pat_adjustments.push(expected);
-
-            expected = self.try_structurally_resolve_type(pat.span, inner_ty);
-            def_br = ByRef::Yes(match def_br {
-                // If default binding mode is by value, make it `ref` or `ref mut`
-                // (depending on whether we observe `&` or `&mut`).
-                ByRef::No |
-                // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
-                ByRef::Yes(Mutability::Mut) => inner_mutability,
-                // Once a `ref`, always a `ref`.
-                // This is because a `& &mut` cannot mutate the underlying value.
-                ByRef::Yes(Mutability::Not) => Mutability::Not,
-            });
-        }
-
-        if self.downgrade_mut_inside_shared() {
-            def_br = def_br.cap_ref_mutability(max_ref_mutbl.as_mutbl());
-        }
-        if def_br == ByRef::Yes(Mutability::Not) {
-            max_ref_mutbl = MutblCap::Not;
-        }
-
-        if !pat_adjustments.is_empty() {
-            debug!("default binding mode is now {:?}", def_br);
-            self.typeck_results
-                .borrow_mut()
-                .pat_adjustments_mut()
-                .insert(pat.hir_id, pat_adjustments);
-        }
-
-        (expected, def_br, max_ref_mutbl)
-    }
-
     fn check_pat_expr_unadjusted(&self, lt: &'tcx hir::PatExpr<'tcx>) -> Ty<'tcx> {
         let ty = match &lt.kind {
             rustc_hir::PatExprKind::Lit { lit, negated } => {
@@ -1032,7 +1170,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         | PatKind::Tuple(..)
                         | PatKind::Slice(..) => "binding",
 
-                        PatKind::Wild
+                        PatKind::Missing
+                        | PatKind::Wild
                         | PatKind::Never
                         | PatKind::Binding(..)
                         | PatKind::Box(..)
@@ -1139,27 +1278,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         Ok(())
     }
 
-    fn check_pat_struct(
+    fn resolve_pat_struct(
         &self,
         pat: &'tcx Pat<'tcx>,
         qpath: &hir::QPath<'tcx>,
+    ) -> Result<ResolvedPat<'tcx>, ErrorGuaranteed> {
+        // Resolve the path and check the definition for errors.
+        let (variant, pat_ty) = self.check_struct_path(qpath, pat.hir_id)?;
+        Ok(ResolvedPat { ty: pat_ty, kind: ResolvedPatKind::Struct { variant } })
+    }
+
+    fn check_pat_struct(
+        &self,
+        pat: &'tcx Pat<'tcx>,
         fields: &'tcx [hir::PatField<'tcx>],
         has_rest_pat: bool,
+        pat_ty: Ty<'tcx>,
+        variant: &'tcx VariantDef,
         expected: Ty<'tcx>,
         pat_info: PatInfo<'tcx>,
     ) -> Ty<'tcx> {
-        // Resolve the path and check the definition for errors.
-        let (variant, pat_ty) = match self.check_struct_path(qpath, pat.hir_id) {
-            Ok(data) => data,
-            Err(guar) => {
-                let err = Ty::new_error(self.tcx, guar);
-                for field in fields {
-                    self.check_pat(field.pat, err, pat_info);
-                }
-                return err;
-            }
-        };
-
         // Type-check the path.
         let _ = self.demand_eqtype_pat(pat.span, expected, pat_ty, &pat_info.top_info);
 
@@ -1170,31 +1308,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    fn check_pat_path(
+    fn resolve_pat_path(
         &self,
         path_id: HirId,
-        pat_id_for_diag: HirId,
         span: Span,
-        qpath: &hir::QPath<'_>,
-        path_resolution: (Res, Option<LoweredTy<'tcx>>, &'tcx [hir::PathSegment<'tcx>]),
-        expected: Ty<'tcx>,
-        ti: &TopInfo<'tcx>,
-    ) -> Ty<'tcx> {
+        qpath: &'tcx hir::QPath<'_>,
+    ) -> Result<ResolvedPat<'tcx>, ErrorGuaranteed> {
         let tcx = self.tcx;
 
-        // We have already resolved the path.
-        let (res, opt_ty, segments) = path_resolution;
+        let (res, opt_ty, segments) =
+            self.resolve_ty_and_res_fully_qualified_call(qpath, path_id, span);
         match res {
             Res::Err => {
                 let e =
                     self.dcx().span_delayed_bug(qpath.span(), "`Res::Err` but no error emitted");
                 self.set_tainted_by_errors(e);
-                return Ty::new_error(tcx, e);
+                return Err(e);
             }
             Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::Variant, _) => {
                 let expected = "unit struct, unit variant or constant";
                 let e = report_unexpected_variant_res(tcx, res, None, qpath, span, E0533, expected);
-                return Ty::new_error(tcx, e);
+                return Err(e);
             }
             Res::SelfCtor(def_id) => {
                 if let ty::Adt(adt_def, _) = *tcx.type_of(def_id).skip_binder().kind()
@@ -1212,7 +1346,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         E0533,
                         "unit struct",
                     );
-                    return Ty::new_error(tcx, e);
+                    return Err(e);
                 }
             }
             Res::Def(
@@ -1225,15 +1359,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ => bug!("unexpected pattern resolution: {:?}", res),
         }
 
-        // Type-check the path.
+        // Find the type of the path pattern, for later checking.
         let (pat_ty, pat_res) =
             self.instantiate_value_path(segments, opt_ty, res, span, span, path_id);
+        Ok(ResolvedPat { ty: pat_ty, kind: ResolvedPatKind::Path { res, pat_res, segments } })
+    }
+
+    fn check_pat_path(
+        &self,
+        pat_id_for_diag: HirId,
+        span: Span,
+        resolved: &ResolvedPat<'tcx>,
+        expected: Ty<'tcx>,
+        ti: &TopInfo<'tcx>,
+    ) -> Ty<'tcx> {
         if let Err(err) =
-            self.demand_suptype_with_origin(&self.pattern_cause(ti, span), expected, pat_ty)
+            self.demand_suptype_with_origin(&self.pattern_cause(ti, span), expected, resolved.ty)
         {
-            self.emit_bad_pat_path(err, pat_id_for_diag, span, res, pat_res, pat_ty, segments);
+            self.emit_bad_pat_path(err, pat_id_for_diag, span, resolved);
         }
-        pat_ty
+        resolved.ty
     }
 
     fn maybe_suggest_range_literal(
@@ -1276,11 +1421,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         mut e: Diag<'_>,
         hir_id: HirId,
         pat_span: Span,
-        res: Res,
-        pat_res: Res,
-        pat_ty: Ty<'tcx>,
-        segments: &'tcx [hir::PathSegment<'tcx>],
+        resolved_pat: &ResolvedPat<'tcx>,
     ) {
+        let ResolvedPatKind::Path { res, pat_res, segments } = resolved_pat.kind else {
+            span_bug!(pat_span, "unexpected resolution for path pattern: {resolved_pat:?}");
+        };
+
         if let Some(span) = self.tcx.hir_res_span(pat_res) {
             e.span_label(span, format!("{} defined here", res.descr()));
             if let [hir::PathSegment { ident, .. }] = &*segments {
@@ -1303,7 +1449,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         );
                     }
                     _ => {
-                        let (type_def_id, item_def_id) = match pat_ty.kind() {
+                        let (type_def_id, item_def_id) = match resolved_pat.ty.kind() {
                             ty::Adt(def, _) => match res {
                                 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
                                 _ => (None, None),
@@ -1343,26 +1489,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         e.emit();
     }
 
-    fn check_pat_tuple_struct(
+    fn resolve_pat_tuple_struct(
         &self,
         pat: &'tcx Pat<'tcx>,
         qpath: &'tcx hir::QPath<'tcx>,
-        subpats: &'tcx [Pat<'tcx>],
-        ddpos: hir::DotDotPos,
-        expected: Ty<'tcx>,
-        pat_info: PatInfo<'tcx>,
-    ) -> Ty<'tcx> {
+    ) -> Result<ResolvedPat<'tcx>, ErrorGuaranteed> {
         let tcx = self.tcx;
-        let on_error = |e| {
-            for pat in subpats {
-                self.check_pat(pat, Ty::new_error(tcx, e), pat_info);
-            }
-        };
         let report_unexpected_res = |res: Res| {
             let expected = "tuple struct or tuple variant";
             let e = report_unexpected_variant_res(tcx, res, None, qpath, pat.span, E0164, expected);
-            on_error(e);
-            e
+            Err(e)
         };
 
         // Resolve the path and check the definition for errors.
@@ -1371,16 +1507,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if res == Res::Err {
             let e = self.dcx().span_delayed_bug(pat.span, "`Res::Err` but no error emitted");
             self.set_tainted_by_errors(e);
-            on_error(e);
-            return Ty::new_error(tcx, e);
+            return Err(e);
         }
 
         // Type-check the path.
         let (pat_ty, res) =
             self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.span, pat.hir_id);
         if !pat_ty.is_fn() {
-            let e = report_unexpected_res(res);
-            return Ty::new_error(tcx, e);
+            return report_unexpected_res(res);
         }
 
         let variant = match res {
@@ -1388,8 +1522,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.dcx().span_bug(pat.span, "`Res::Err` but no error emitted");
             }
             Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
-                let e = report_unexpected_res(res);
-                return Ty::new_error(tcx, e);
+                return report_unexpected_res(res);
             }
             Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
             _ => bug!("unexpected pattern resolution: {:?}", res),
@@ -1399,6 +1532,28 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let pat_ty = pat_ty.fn_sig(tcx).output();
         let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
 
+        Ok(ResolvedPat { ty: pat_ty, kind: ResolvedPatKind::TupleStruct { res, variant } })
+    }
+
+    fn check_pat_tuple_struct(
+        &self,
+        pat: &'tcx Pat<'tcx>,
+        qpath: &'tcx hir::QPath<'tcx>,
+        subpats: &'tcx [Pat<'tcx>],
+        ddpos: hir::DotDotPos,
+        res: Res,
+        pat_ty: Ty<'tcx>,
+        variant: &'tcx VariantDef,
+        expected: Ty<'tcx>,
+        pat_info: PatInfo<'tcx>,
+    ) -> Ty<'tcx> {
+        let tcx = self.tcx;
+        let on_error = |e| {
+            for pat in subpats {
+                self.check_pat(pat, Ty::new_error(tcx, e), pat_info);
+            }
+        };
+
         // Type-check the tuple struct pattern against the expected type.
         let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, &pat_info.top_info);
         let had_err = diag.map_err(|diag| diag.emit());
@@ -2282,36 +2437,49 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected: Ty<'tcx>,
         pat_info: PatInfo<'tcx>,
     ) -> Ty<'tcx> {
-        let tcx = self.tcx;
+        let target_ty = self.deref_pat_target(span, expected);
+        self.check_pat(inner, target_ty, pat_info);
+        self.register_deref_mut_bounds_if_needed(span, inner, [expected]);
+        expected
+    }
+
+    fn deref_pat_target(&self, span: Span, source_ty: Ty<'tcx>) -> Ty<'tcx> {
         // Register a `DerefPure` bound, which is required by all `deref!()` pats.
+        let tcx = self.tcx;
         self.register_bound(
-            expected,
+            source_ty,
             tcx.require_lang_item(hir::LangItem::DerefPure, Some(span)),
             self.misc(span),
         );
-        // <expected as Deref>::Target
-        let ty = Ty::new_projection(
+        // The expected type for the deref pat's inner pattern is `<expected as Deref>::Target`.
+        let target_ty = Ty::new_projection(
             tcx,
             tcx.require_lang_item(hir::LangItem::DerefTarget, Some(span)),
-            [expected],
+            [source_ty],
         );
-        let ty = self.normalize(span, ty);
-        let ty = self.try_structurally_resolve_type(span, ty);
-        self.check_pat(inner, ty, pat_info);
-
-        // Check if the pattern has any `ref mut` bindings, which would require
-        // `DerefMut` to be emitted in MIR building instead of just `Deref`.
-        // We do this *after* checking the inner pattern, since we want to make
-        // sure to apply any match-ergonomics adjustments.
+        let target_ty = self.normalize(span, target_ty);
+        self.try_structurally_resolve_type(span, target_ty)
+    }
+
+    /// Check if the interior of a deref pattern (either explicit or implicit) has any `ref mut`
+    /// bindings, which would require `DerefMut` to be emitted in MIR building instead of just
+    /// `Deref`. We do this *after* checking the inner pattern, since we want to make sure to
+    /// account for `ref mut` binding modes inherited from implicitly dereferencing `&mut` refs.
+    fn register_deref_mut_bounds_if_needed(
+        &self,
+        span: Span,
+        inner: &'tcx Pat<'tcx>,
+        derefed_tys: impl IntoIterator<Item = Ty<'tcx>>,
+    ) {
         if self.typeck_results.borrow().pat_has_ref_mut_binding(inner) {
-            self.register_bound(
-                expected,
-                tcx.require_lang_item(hir::LangItem::DerefMut, Some(span)),
-                self.misc(span),
-            );
+            for mutably_derefed_ty in derefed_tys {
+                self.register_bound(
+                    mutably_derefed_ty,
+                    self.tcx.require_lang_item(hir::LangItem::DerefMut, Some(span)),
+                    self.misc(span),
+                );
+            }
         }
-
-        expected
     }
 
     // Precondition: Pat is Ref(inner)
diff --git a/compiler/rustc_incremental/messages.ftl b/compiler/rustc_incremental/messages.ftl
index 2a65101d360..bbc1fab05df 100644
--- a/compiler/rustc_incremental/messages.ftl
+++ b/compiler/rustc_incremental/messages.ftl
@@ -93,7 +93,7 @@ incremental_undefined_clean_dirty_assertions =
 incremental_undefined_clean_dirty_assertions_item =
     clean/dirty auto-assertions not yet defined for Node::Item.node={$kind}
 
-incremental_unknown_item = unknown item `{$name}`
+incremental_unknown_rustc_clean_argument = unknown `rustc_clean` argument
 
 incremental_unrecognized_depnode = unrecognized `DepNode` variant: {$name}
 
diff --git a/compiler/rustc_incremental/src/errors.rs b/compiler/rustc_incremental/src/errors.rs
index b4a207386dc..dbc72d085be 100644
--- a/compiler/rustc_incremental/src/errors.rs
+++ b/compiler/rustc_incremental/src/errors.rs
@@ -107,11 +107,10 @@ pub(crate) struct NotLoaded<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(incremental_unknown_item)]
-pub(crate) struct UnknownItem {
+#[diag(incremental_unknown_rustc_clean_argument)]
+pub(crate) struct UnknownRustcCleanArgument {
     #[primary_span]
     pub span: Span,
-    pub name: Symbol,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_incremental/src/lib.rs b/compiler/rustc_incremental/src/lib.rs
index dabfb6a90ca..299ee487638 100644
--- a/compiler/rustc_incremental/src/lib.rs
+++ b/compiler/rustc_incremental/src/lib.rs
@@ -2,7 +2,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![deny(missing_docs)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
diff --git a/compiler/rustc_incremental/src/persist/dirty_clean.rs b/compiler/rustc_incremental/src/persist/dirty_clean.rs
index d40a0d514f6..64166255fa4 100644
--- a/compiler/rustc_incremental/src/persist/dirty_clean.rs
+++ b/compiler/rustc_incremental/src/persist/dirty_clean.rs
@@ -405,8 +405,7 @@ fn check_config(tcx: TyCtxt<'_>, attr: &Attribute) -> bool {
             debug!("check_config: searching for cfg {:?}", value);
             cfg = Some(config.contains(&(value, None)));
         } else if !(item.has_name(EXCEPT) || item.has_name(LOADED_FROM_DISK)) {
-            tcx.dcx()
-                .emit_err(errors::UnknownItem { span: attr.span(), name: item.name_or_empty() });
+            tcx.dcx().emit_err(errors::UnknownRustcCleanArgument { span: item.span() });
         }
     }
 
diff --git a/compiler/rustc_incremental/src/persist/fs.rs b/compiler/rustc_incremental/src/persist/fs.rs
index 76a1ff3cf38..f0d24d27e85 100644
--- a/compiler/rustc_incremental/src/persist/fs.rs
+++ b/compiler/rustc_incremental/src/persist/fs.rs
@@ -290,7 +290,7 @@ pub(crate) fn prepare_session_directory(sess: &Session, crate_name: Symbol) {
 
             // Try to remove the session directory we just allocated. We don't
             // know if there's any garbage in it from the failed copy action.
-            if let Err(err) = safe_remove_dir_all(&session_dir) {
+            if let Err(err) = std_fs::remove_dir_all(&session_dir) {
                 sess.dcx().emit_warn(errors::DeletePartial { path: &session_dir, err });
             }
 
@@ -324,7 +324,7 @@ pub fn finalize_session_directory(sess: &Session, svh: Option<Svh>) {
             incr_comp_session_dir.display()
         );
 
-        if let Err(err) = safe_remove_dir_all(&*incr_comp_session_dir) {
+        if let Err(err) = std_fs::remove_dir_all(&*incr_comp_session_dir) {
             sess.dcx().emit_warn(errors::DeleteFull { path: &incr_comp_session_dir, err });
         }
 
@@ -715,7 +715,7 @@ pub(crate) fn garbage_collect_session_directories(sess: &Session) -> io::Result<
     for directory_name in session_directories {
         if !lock_file_to_session_dir.items().any(|(_, dir)| *dir == directory_name) {
             let path = crate_directory.join(directory_name);
-            if let Err(err) = safe_remove_dir_all(&path) {
+            if let Err(err) = std_fs::remove_dir_all(&path) {
                 sess.dcx().emit_warn(errors::InvalidGcFailed { path: &path, err });
             }
         }
@@ -821,7 +821,7 @@ pub(crate) fn garbage_collect_session_directories(sess: &Session) -> io::Result<
     all_except_most_recent(deletion_candidates).into_items().all(|(path, lock)| {
         debug!("garbage_collect_session_directories() - deleting `{}`", path.display());
 
-        if let Err(err) = safe_remove_dir_all(&path) {
+        if let Err(err) = std_fs::remove_dir_all(&path) {
             sess.dcx().emit_warn(errors::FinalizedGcFailed { path: &path, err });
         } else {
             delete_session_dir_lock_file(sess, &lock_file_path(&path));
@@ -839,7 +839,7 @@ pub(crate) fn garbage_collect_session_directories(sess: &Session) -> io::Result<
 fn delete_old(sess: &Session, path: &Path) {
     debug!("garbage_collect_session_directories() - deleting `{}`", path.display());
 
-    if let Err(err) = safe_remove_dir_all(path) {
+    if let Err(err) = std_fs::remove_dir_all(path) {
         sess.dcx().emit_warn(errors::SessionGcFailed { path, err });
     } else {
         delete_session_dir_lock_file(sess, &lock_file_path(path));
@@ -862,30 +862,8 @@ fn all_except_most_recent(
     }
 }
 
-/// Since paths of artifacts within session directories can get quite long, we
-/// need to support deleting files with very long paths. The regular
-/// WinApi functions only support paths up to 260 characters, however. In order
-/// to circumvent this limitation, we canonicalize the path of the directory
-/// before passing it to std::fs::remove_dir_all(). This will convert the path
-/// into the '\\?\' format, which supports much longer paths.
-fn safe_remove_dir_all(p: &Path) -> io::Result<()> {
-    let canonicalized = match try_canonicalize(p) {
-        Ok(canonicalized) => canonicalized,
-        Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(()),
-        Err(err) => return Err(err),
-    };
-
-    std_fs::remove_dir_all(canonicalized)
-}
-
 fn safe_remove_file(p: &Path) -> io::Result<()> {
-    let canonicalized = match try_canonicalize(p) {
-        Ok(canonicalized) => canonicalized,
-        Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(()),
-        Err(err) => return Err(err),
-    };
-
-    match std_fs::remove_file(canonicalized) {
+    match std_fs::remove_file(p) {
         Err(err) if err.kind() == io::ErrorKind::NotFound => Ok(()),
         result => result,
     }
diff --git a/compiler/rustc_index/src/slice.rs b/compiler/rustc_index/src/slice.rs
index 67ac805c2bf..d2702bdb057 100644
--- a/compiler/rustc_index/src/slice.rs
+++ b/compiler/rustc_index/src/slice.rs
@@ -1,6 +1,6 @@
 use std::fmt;
 use std::marker::PhantomData;
-use std::ops::{Index, IndexMut};
+use std::ops::{Index, IndexMut, RangeBounds};
 use std::slice::GetDisjointMutError::*;
 use std::slice::{self, SliceIndex};
 
@@ -105,6 +105,17 @@ impl<I: Idx, T> IndexSlice<I, T> {
     }
 
     #[inline]
+    pub fn copy_within(
+        &mut self,
+        src: impl IntoSliceIdx<I, [T], Output: RangeBounds<usize>>,
+        dest: I,
+    ) where
+        T: Copy,
+    {
+        self.raw.copy_within(src.into_slice_idx(), dest.index());
+    }
+
+    #[inline]
     pub fn get<R: IntoSliceIdx<I, [T]>>(
         &self,
         index: R,
diff --git a/compiler/rustc_index_macros/src/newtype.rs b/compiler/rustc_index_macros/src/newtype.rs
index f0b58eabbff..eedbe630cf2 100644
--- a/compiler/rustc_index_macros/src/newtype.rs
+++ b/compiler/rustc_index_macros/src/newtype.rs
@@ -257,6 +257,13 @@ impl Parse for Newtype {
                 }
             }
 
+            impl std::ops::AddAssign<usize> for #name {
+                #[inline]
+                fn add_assign(&mut self, other: usize) {
+                    *self = *self + other;
+                }
+            }
+
             impl rustc_index::Idx for #name {
                 #[inline]
                 fn new(value: usize) -> Self {
diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 307110d9fbc..a1a0926cd81 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -159,7 +159,7 @@ impl CanonicalizeMode for CanonicalizeQueryResponse {
     ) -> ty::Region<'tcx> {
         let infcx = canonicalizer.infcx.unwrap();
 
-        if let ty::ReVar(vid) = *r {
+        if let ty::ReVar(vid) = r.kind() {
             r = infcx
                 .inner
                 .borrow_mut()
@@ -171,7 +171,7 @@ impl CanonicalizeMode for CanonicalizeQueryResponse {
             );
         };
 
-        match *r {
+        match r.kind() {
             ty::ReLateParam(_) | ty::ReErased | ty::ReStatic | ty::ReEarlyParam(..) => r,
 
             ty::RePlaceholder(placeholder) => canonicalizer.canonical_var_for_region(
@@ -227,7 +227,7 @@ impl CanonicalizeMode for CanonicalizeUserTypeAnnotation {
         canonicalizer: &mut Canonicalizer<'_, 'tcx>,
         r: ty::Region<'tcx>,
     ) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             ty::ReEarlyParam(_)
             | ty::ReLateParam(_)
             | ty::ReErased
@@ -321,7 +321,7 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             ty::ReBound(index, ..) => {
                 if index >= self.binder_index {
                     bug!("escaping late-bound region during canonicalization");
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index d53f631cc07..5220071c500 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -432,7 +432,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 }
                 GenericArgKind::Lifetime(result_value) => {
                     // e.g., here `result_value` might be `'?1` in the example above...
-                    if let ty::ReBound(debruijn, br) = *result_value {
+                    if let ty::ReBound(debruijn, br) = result_value.kind() {
                         // ... in which case we would set `canonical_vars[0]` to `Some('static)`.
 
                         // We only allow a `ty::INNERMOST` index in generic parameters.
diff --git a/compiler/rustc_infer/src/infer/freshen.rs b/compiler/rustc_infer/src/infer/freshen.rs
index f2bb66ff736..cae674165f0 100644
--- a/compiler/rustc_infer/src/infer/freshen.rs
+++ b/compiler/rustc_infer/src/infer/freshen.rs
@@ -109,7 +109,7 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for TypeFreshener<'a, 'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             ty::ReBound(..) => {
                 // leave bound regions alone
                 r
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
index 91595de97f7..e3522137d83 100644
--- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
+++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -218,7 +218,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                                 true
                             }
                             VarValue::Value(cur_region) => {
-                                match *cur_region {
+                                match cur_region.kind() {
                                     // If this empty region is from a universe that can name the
                                     // placeholder universe, then the LUB is the Placeholder region
                                     // (which is the cur_region). Otherwise, the LUB is the Static
@@ -310,7 +310,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
 
         match *b_data {
             VarValue::Empty(empty_ui) => {
-                let lub = match *a_region {
+                let lub = match a_region.kind() {
                     RePlaceholder(placeholder) => {
                         // If this empty region is from a universe that can
                         // name the placeholder, then the placeholder is
@@ -350,7 +350,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 // tighter bound than `'static`.
                 //
                 // (This might e.g. arise from being asked to prove `for<'a> { 'b: 'a }`.)
-                if let ty::RePlaceholder(p) = *lub
+                if let ty::RePlaceholder(p) = lub.kind()
                     && b_universe.cannot_name(p.universe)
                 {
                     lub = self.tcx().lifetimes.re_static;
@@ -377,7 +377,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 a_ui.min(b_ui) == b_ui
             }
             (VarValue::Value(a), VarValue::Empty(_)) => {
-                match *a {
+                match a.kind() {
                     // this is always on an error path,
                     // so it doesn't really matter if it's shorter or longer than an empty region
                     ReError(_) => false,
@@ -410,7 +410,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 }
             }
             (VarValue::Empty(a_ui), VarValue::Value(b)) => {
-                match *b {
+                match b.kind() {
                     // this is always on an error path,
                     // so it doesn't really matter if it's shorter or longer than an empty region
                     ReError(_) => false,
@@ -479,7 +479,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
     /// term "concrete regions").
     #[instrument(level = "trace", skip(self), ret)]
     fn lub_concrete_regions(&self, a: Region<'tcx>, b: Region<'tcx>) -> Region<'tcx> {
-        match (*a, *b) {
+        match (a.kind(), b.kind()) {
             (ReBound(..), _) | (_, ReBound(..)) | (ReErased, _) | (_, ReErased) => {
                 bug!("cannot relate region: LUB({:?}, {:?})", a, b);
             }
@@ -725,7 +725,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         // SubSupConflict(ReLateParam, ReLateParam) when reporting error, and so
         // the user will more likely get a specific suggestion.
         fn region_order_key(x: &RegionAndOrigin<'_>) -> u8 {
-            match *x.region {
+            match x.region.kind() {
                 ReEarlyParam(_) => 0,
                 ReLateParam(_) => 1,
                 _ => 2,
@@ -737,7 +737,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         let node_universe = self.var_infos[node_idx].universe;
 
         for lower_bound in &lower_bounds {
-            let effective_lower_bound = if let ty::RePlaceholder(p) = *lower_bound.region {
+            let effective_lower_bound = if let ty::RePlaceholder(p) = lower_bound.region.kind() {
                 if node_universe.cannot_name(p.universe) {
                     self.tcx().lifetimes.re_static
                 } else {
@@ -785,7 +785,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
             .expect("lower_vid_bounds should at least include `node_idx`");
 
         for upper_bound in &upper_bounds {
-            if let ty::RePlaceholder(p) = *upper_bound.region {
+            if let ty::RePlaceholder(p) = upper_bound.region.kind() {
                 if min_universe.cannot_name(p.universe) {
                     let origin = self.var_infos[node_idx].origin;
                     errors.push(RegionResolutionError::UpperBoundUniverseConflict(
@@ -913,7 +913,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         generic_ty: Ty<'tcx>,
         min: ty::Region<'tcx>,
     ) -> bool {
-        if let ty::ReError(_) = *min {
+        if let ty::ReError(_) = min.kind() {
             return true;
         }
 
@@ -931,18 +931,18 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
             }
 
             VerifyBound::OutlivedBy(r) => {
-                let a = match *min {
+                let a = match min.kind() {
                     ty::ReVar(rid) => var_values.values[rid],
                     _ => VarValue::Value(min),
                 };
-                let b = match **r {
+                let b = match r.kind() {
                     ty::ReVar(rid) => var_values.values[rid],
                     _ => VarValue::Value(*r),
                 };
                 self.sub_region_values(a, b)
             }
 
-            VerifyBound::IsEmpty => match *min {
+            VerifyBound::IsEmpty => match min.kind() {
                 ty::ReVar(rid) => match var_values.values[rid] {
                     VarValue::ErrorValue => false,
                     VarValue::Empty(_) => true,
@@ -989,7 +989,7 @@ impl<'tcx> LexicalRegionResolutions<'tcx> {
         tcx: TyCtxt<'tcx>,
         r: ty::Region<'tcx>,
     ) -> ty::Region<'tcx> {
-        let result = match *r {
+        let result = match r.kind() {
             ty::ReVar(rid) => match self.values[rid] {
                 VarValue::Empty(_) => r,
                 VarValue::Value(r) => r,
diff --git a/compiler/rustc_infer/src/infer/outlives/env.rs b/compiler/rustc_infer/src/infer/outlives/env.rs
index e924c974a02..cb5a33c5c97 100644
--- a/compiler/rustc_infer/src/infer/outlives/env.rs
+++ b/compiler/rustc_infer/src/infer/outlives/env.rs
@@ -69,7 +69,7 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
                     region_bound_pairs
                         .insert(ty::OutlivesPredicate(GenericKind::Alias(alias_b), r_a));
                 }
-                OutlivesBound::RegionSubRegion(r_a, r_b) => match (*r_a, *r_b) {
+                OutlivesBound::RegionSubRegion(r_a, r_b) => match (r_a.kind(), r_b.kind()) {
                     (
                         ty::ReStatic | ty::ReEarlyParam(_) | ty::ReLateParam(_),
                         ty::ReStatic | ty::ReEarlyParam(_) | ty::ReLateParam(_),
diff --git a/compiler/rustc_infer/src/infer/outlives/for_liveness.rs b/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
index 379410641fe..c44d9723f29 100644
--- a/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
+++ b/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
@@ -29,7 +29,7 @@ where
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        match *r {
+        match r.kind() {
             // ignore bound regions, keep visiting
             ty::ReBound(_, _) => {}
             _ => (self.op)(r),
diff --git a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
index 3cfc58dea05..e332b6d0447 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/leak_check.rs
@@ -155,7 +155,7 @@ impl<'a, 'tcx> LeakCheck<'a, 'tcx> {
             self.scc_universes[scc].take_min(universe, *region);
 
             // Detect those SCCs that directly contain a placeholder
-            if let ty::RePlaceholder(placeholder) = **region {
+            if let ty::RePlaceholder(placeholder) = region.kind() {
                 if self.outer_universe.cannot_name(placeholder.universe) {
                     // Update `scc_placeholders` to account for the fact that `P: S` must hold.
                     match self.scc_placeholders[scc] {
diff --git a/compiler/rustc_infer/src/infer/region_constraints/mod.rs b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
index 57555db37ab..40e2e654b2e 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/mod.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
@@ -463,7 +463,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         // cannot add constraints once regions are resolved
         debug!("origin = {:#?}", origin);
 
-        match (*sub, *sup) {
+        match (sub.kind(), sup.kind()) {
             (ReBound(..), _) | (_, ReBound(..)) => {
                 span_bug!(origin.span(), "cannot relate bound region: {:?} <= {:?}", sub, sup);
             }
@@ -595,7 +595,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
     }
 
     pub fn universe(&mut self, region: Region<'tcx>) -> ty::UniverseIndex {
-        match *region {
+        match region.kind() {
             ty::ReStatic
             | ty::ReErased
             | ty::ReLateParam(..)
@@ -618,9 +618,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
             RegionVid::from(value_count)..RegionVid::from(self.storage.unification_table.len());
         (
             range.clone(),
-            (range.start.index()..range.end.index())
-                .map(|index| self.storage.var_infos[ty::RegionVid::from(index)].origin)
-                .collect(),
+            (range.start..range.end).map(|index| self.storage.var_infos[index].origin).collect(),
         )
     }
 
diff --git a/compiler/rustc_infer/src/infer/relate/generalize.rs b/compiler/rustc_infer/src/infer/relate/generalize.rs
index e16212955ff..b0ccd35e8f0 100644
--- a/compiler/rustc_infer/src/infer/relate/generalize.rs
+++ b/compiler/rustc_infer/src/infer/relate/generalize.rs
@@ -571,7 +571,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for Generalizer<'_, 'tcx> {
     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
         assert_eq!(r, r2); // we are misusing TypeRelation here; both LHS and RHS ought to be ==
 
-        match *r {
+        match r.kind() {
             // Never make variables for regions bound within the type itself,
             // nor for erased regions.
             ty::ReBound(..) | ty::ReErased => {
diff --git a/compiler/rustc_infer/src/infer/resolve.rs b/compiler/rustc_infer/src/infer/resolve.rs
index 4a99c220975..245f1a4ac5e 100644
--- a/compiler/rustc_infer/src/infer/resolve.rs
+++ b/compiler/rustc_infer/src/infer/resolve.rs
@@ -89,7 +89,7 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for OpportunisticRegionResolver<'a, 'tcx
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             ty::ReVar(vid) => self
                 .infcx
                 .inner
@@ -153,7 +153,7 @@ impl<'a, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for FullTypeResolver<'a, 'tcx> {
     }
 
     fn try_fold_region(&mut self, r: ty::Region<'tcx>) -> Result<ty::Region<'tcx>, Self::Error> {
-        match *r {
+        match r.kind() {
             ty::ReVar(_) => Ok(self
                 .infcx
                 .lexical_region_resolutions
diff --git a/compiler/rustc_infer/src/infer/snapshot/fudge.rs b/compiler/rustc_infer/src/infer/snapshot/fudge.rs
index b5d3c26b05e..39c8c40ea7d 100644
--- a/compiler/rustc_infer/src/infer/snapshot/fudge.rs
+++ b/compiler/rustc_infer/src/infer/snapshot/fudge.rs
@@ -30,11 +30,12 @@ fn const_vars_since_snapshot<'tcx>(
     snapshot_var_len: usize,
 ) -> (Range<ConstVid>, Vec<ConstVariableOrigin>) {
     let range = vars_since_snapshot(table, snapshot_var_len);
+    let range = range.start.vid..range.end.vid;
 
     (
-        range.start.vid..range.end.vid,
-        (range.start.index()..range.end.index())
-            .map(|index| match table.probe_value(ConstVid::from_u32(index)) {
+        range.clone(),
+        range
+            .map(|index| match table.probe_value(index) {
                 ConstVariableValue::Known { value: _ } => {
                     ConstVariableOrigin { param_def_id: None, span: rustc_span::DUMMY_SP }
                 }
diff --git a/compiler/rustc_infer/src/traits/mod.rs b/compiler/rustc_infer/src/traits/mod.rs
index b537750f1b5..6d5ad96e31c 100644
--- a/compiler/rustc_infer/src/traits/mod.rs
+++ b/compiler/rustc_infer/src/traits/mod.rs
@@ -12,6 +12,7 @@ use std::hash::{Hash, Hasher};
 
 use hir::def_id::LocalDefId;
 use rustc_hir as hir;
+use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::Certainty;
 pub use rustc_middle::traits::*;
@@ -35,9 +36,11 @@ use crate::infer::InferCtxt;
 /// either identifying an `impl` (e.g., `impl Eq for i32`) that
 /// satisfies the obligation, or else finding a bound that is in
 /// scope. The eventual result is usually a `Selection` (defined below).
-#[derive(Clone)]
+#[derive(Clone, TypeFoldable, TypeVisitable)]
 pub struct Obligation<'tcx, T> {
     /// The reason we have to prove this thing.
+    #[type_foldable(identity)]
+    #[type_visitable(ignore)]
     pub cause: ObligationCause<'tcx>,
 
     /// The environment in which we should prove this thing.
@@ -51,6 +54,8 @@ pub struct Obligation<'tcx, T> {
     /// If this goes over a certain threshold, we abort compilation --
     /// in such cases, we can not say whether or not the predicate
     /// holds for certain. Stupid halting problem; such a drag.
+    #[type_foldable(identity)]
+    #[type_visitable(ignore)]
     pub recursion_depth: usize,
 }
 
diff --git a/compiler/rustc_infer/src/traits/structural_impls.rs b/compiler/rustc_infer/src/traits/structural_impls.rs
index 4335073d9bc..03661ebf7ec 100644
--- a/compiler/rustc_infer/src/traits/structural_impls.rs
+++ b/compiler/rustc_infer/src/traits/structural_impls.rs
@@ -1,8 +1,6 @@
 use std::fmt;
 
-use rustc_middle::ty::{
-    self, FallibleTypeFolder, TyCtxt, TypeFoldable, TypeVisitable, TypeVisitor, try_visit,
-};
+use rustc_middle::ty;
 
 use crate::traits;
 use crate::traits::project::Normalized;
@@ -34,31 +32,3 @@ impl<'tcx> fmt::Debug for traits::MismatchedProjectionTypes<'tcx> {
         write!(f, "MismatchedProjectionTypes({:?})", self.err)
     }
 }
-
-///////////////////////////////////////////////////////////////////////////
-// TypeFoldable implementations.
-
-impl<'tcx, O: TypeFoldable<TyCtxt<'tcx>>> TypeFoldable<TyCtxt<'tcx>>
-    for traits::Obligation<'tcx, O>
-{
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(traits::Obligation {
-            cause: self.cause,
-            recursion_depth: self.recursion_depth,
-            predicate: self.predicate.try_fold_with(folder)?,
-            param_env: self.param_env.try_fold_with(folder)?,
-        })
-    }
-}
-
-impl<'tcx, O: TypeVisitable<TyCtxt<'tcx>>> TypeVisitable<TyCtxt<'tcx>>
-    for traits::Obligation<'tcx, O>
-{
-    fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(&self, visitor: &mut V) -> V::Result {
-        try_visit!(self.predicate.visit_with(visitor));
-        self.param_env.visit_with(visitor)
-    }
-}
diff --git a/compiler/rustc_interface/Cargo.toml b/compiler/rustc_interface/Cargo.toml
index e3673935664..ff28dbeaee6 100644
--- a/compiler/rustc_interface/Cargo.toml
+++ b/compiler/rustc_interface/Cargo.toml
@@ -5,7 +5,6 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-rustc-rayon = { version = "0.5.0" }
 rustc-rayon-core = { version = "0.5.0" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_lowering = { path = "../rustc_ast_lowering" }
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 33b4a48b28d..708fe23b791 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -348,6 +348,10 @@ pub struct Config {
     /// the list of queries.
     pub override_queries: Option<fn(&Session, &mut Providers)>,
 
+    /// An extra set of symbols to add to the symbol interner, the symbol indices
+    /// will start at [`PREDEFINED_SYMBOLS_COUNT`](rustc_span::symbol::PREDEFINED_SYMBOLS_COUNT)
+    pub extra_symbols: Vec<&'static str>,
+
     /// This is a callback from the driver that is called to create a codegen backend.
     ///
     /// Has no uses within this repository, but is used by bjorn3 for "the
@@ -409,6 +413,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
         &early_dcx,
         config.opts.edition,
         config.opts.unstable_opts.threads,
+        &config.extra_symbols,
         SourceMapInputs { file_loader, path_mapping, hash_kind, checksum_hash_kind },
         |current_gcx| {
             // The previous `early_dcx` can't be reused here because it doesn't
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 747e36b6a1a..fde1872fb39 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -800,6 +800,7 @@ pub fn create_and_enter_global_ctxt<T, F: for<'tcx> FnOnce(TyCtxt<'tcx>) -> T>(
         sess.opts.cg.metadata.clone(),
         sess.cfg_version,
     );
+
     let outputs = util::build_output_filenames(&pre_configured_attrs, sess);
 
     let dep_type = DepsType { dep_names: rustc_query_impl::dep_kind_names() };
@@ -955,7 +956,9 @@ fn run_required_analyses(tcx: TyCtxt<'_>) {
             // Run unsafety check because it's responsible for stealing and
             // deallocating THIR.
             tcx.ensure_ok().check_unsafety(def_id);
-            tcx.ensure_ok().mir_borrowck(def_id)
+            if !tcx.is_typeck_child(def_id.to_def_id()) {
+                tcx.ensure_ok().mir_borrowck(def_id)
+            }
         });
     });
     sess.time("MIR_effect_checking", || {
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index a8e55663257..d405d044cae 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -53,7 +53,7 @@ where
         checksum_hash_kind,
     });
 
-    rustc_span::create_session_globals_then(DEFAULT_EDITION, sm_inputs, || {
+    rustc_span::create_session_globals_then(DEFAULT_EDITION, &[], sm_inputs, || {
         let temps_dir = sessopts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
         let io = CompilerIO {
             input: Input::Str { name: FileName::Custom(String::new()), input: String::new() },
@@ -614,6 +614,7 @@ fn test_codegen_options_tracking_hash() {
     tracked!(control_flow_guard, CFGuard::Checks);
     tracked!(debug_assertions, Some(true));
     tracked!(debuginfo, DebugInfo::Limited);
+    tracked!(dwarf_version, Some(5));
     tracked!(embed_bitcode, false);
     tracked!(force_frame_pointers, FramePointer::Always);
     tracked!(force_unwind_tables, Some(true));
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 83d80938b4e..c3a939f1ab0 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -117,6 +117,7 @@ fn run_in_thread_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: Send>(
     thread_stack_size: usize,
     edition: Edition,
     sm_inputs: SourceMapInputs,
+    extra_symbols: &[&'static str],
     f: F,
 ) -> R {
     // The "thread pool" is a single spawned thread in the non-parallel
@@ -134,9 +135,12 @@ fn run_in_thread_with_globals<F: FnOnce(CurrentGcx) -> R + Send, R: Send>(
         // name contains null bytes.
         let r = builder
             .spawn_scoped(s, move || {
-                rustc_span::create_session_globals_then(edition, Some(sm_inputs), || {
-                    f(CurrentGcx::new())
-                })
+                rustc_span::create_session_globals_then(
+                    edition,
+                    extra_symbols,
+                    Some(sm_inputs),
+                    || f(CurrentGcx::new()),
+                )
             })
             .unwrap()
             .join();
@@ -152,6 +156,7 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send,
     thread_builder_diag: &EarlyDiagCtxt,
     edition: Edition,
     threads: usize,
+    extra_symbols: &[&'static str],
     sm_inputs: SourceMapInputs,
     f: F,
 ) -> R {
@@ -168,18 +173,24 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send,
     let registry = sync::Registry::new(std::num::NonZero::new(threads).unwrap());
 
     if !sync::is_dyn_thread_safe() {
-        return run_in_thread_with_globals(thread_stack_size, edition, sm_inputs, |current_gcx| {
-            // Register the thread for use with the `WorkerLocal` type.
-            registry.register();
-
-            f(current_gcx)
-        });
+        return run_in_thread_with_globals(
+            thread_stack_size,
+            edition,
+            sm_inputs,
+            extra_symbols,
+            |current_gcx| {
+                // Register the thread for use with the `WorkerLocal` type.
+                registry.register();
+
+                f(current_gcx)
+            },
+        );
     }
 
     let current_gcx = FromDyn::from(CurrentGcx::new());
     let current_gcx2 = current_gcx.clone();
 
-    let builder = rayon::ThreadPoolBuilder::new()
+    let builder = rayon_core::ThreadPoolBuilder::new()
         .thread_name(|_| "rustc".to_string())
         .acquire_thread_handler(jobserver::acquire_thread)
         .release_thread_handler(jobserver::release_thread)
@@ -230,13 +241,13 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send,
     // pool. Upon creation, each worker thread created gets a copy of the
     // session globals in TLS. This is possible because `SessionGlobals` impls
     // `Send` in the parallel compiler.
-    rustc_span::create_session_globals_then(edition, Some(sm_inputs), || {
+    rustc_span::create_session_globals_then(edition, extra_symbols, Some(sm_inputs), || {
         rustc_span::with_session_globals(|session_globals| {
             let session_globals = FromDyn::from(session_globals);
             builder
                 .build_scoped(
                     // Initialize each new worker thread when created.
-                    move |thread: rayon::ThreadBuilder| {
+                    move |thread: rayon_core::ThreadBuilder| {
                         // Register the thread for use with the `WorkerLocal` type.
                         registry.register();
 
@@ -245,7 +256,9 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce(CurrentGcx) -> R + Send,
                         })
                     },
                     // Run `f` on the first thread in the thread pool.
-                    move |pool: &rayon::ThreadPool| pool.install(|| f(current_gcx.into_inner())),
+                    move |pool: &rayon_core::ThreadPool| {
+                        pool.install(|| f(current_gcx.into_inner()))
+                    },
                 )
                 .unwrap()
         })
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index 782d328a951..60c183bd56b 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -271,7 +271,7 @@ lint_expectation = this lint expectation is unfulfilled
 lint_extern_crate_not_idiomatic = `extern crate` is not idiomatic in the new edition
     .suggestion = convert it to a `use`
 
-lint_extern_without_abi = extern declarations without an explicit ABI are deprecated
+lint_extern_without_abi = `extern` declarations without an explicit ABI are deprecated
     .label = ABI should be specified here
     .suggestion = explicitly specify the {$default_abi} ABI
 
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index dae0efcbbc4..e65f4beab24 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -779,21 +779,19 @@ impl EarlyLintPass for AnonymousParameters {
         }
         if let ast::AssocItemKind::Fn(box Fn { ref sig, .. }) = it.kind {
             for arg in sig.decl.inputs.iter() {
-                if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
-                    if ident.name == kw::Empty {
-                        let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
+                if let ast::PatKind::Missing = arg.pat.kind {
+                    let ty_snip = cx.sess().source_map().span_to_snippet(arg.ty.span);
 
-                        let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
-                            (snip.as_str(), Applicability::MachineApplicable)
-                        } else {
-                            ("<type>", Applicability::HasPlaceholders)
-                        };
-                        cx.emit_span_lint(
-                            ANONYMOUS_PARAMETERS,
-                            arg.pat.span,
-                            BuiltinAnonymousParams { suggestion: (arg.pat.span, appl), ty_snip },
-                        );
-                    }
+                    let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
+                        (snip.as_str(), Applicability::MachineApplicable)
+                    } else {
+                        ("<type>", Applicability::HasPlaceholders)
+                    };
+                    cx.emit_span_lint(
+                        ANONYMOUS_PARAMETERS,
+                        arg.pat.span,
+                        BuiltinAnonymousParams { suggestion: (arg.pat.span, appl), ty_snip },
+                    );
                 }
             }
         }
@@ -1990,7 +1988,7 @@ impl ExplicitOutlivesRequirements {
 
         inferred_outlives
             .filter_map(|(clause, _)| match clause.kind().skip_binder() {
-                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match *a {
+                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a.kind() {
                     ty::ReEarlyParam(ebr)
                         if item_generics.region_param(ebr, tcx).def_id == lifetime.to_def_id() =>
                     {
@@ -2040,7 +2038,7 @@ impl ExplicitOutlivesRequirements {
                 let is_inferred = match tcx.named_bound_var(lifetime.hir_id) {
                     Some(ResolvedArg::EarlyBound(def_id)) => inferred_outlives
                         .iter()
-                        .any(|r| matches!(**r, ty::ReEarlyParam(ebr) if { item_generics.region_param(ebr, tcx).def_id == def_id.to_def_id() })),
+                        .any(|r| matches!(r.kind(), ty::ReEarlyParam(ebr) if { item_generics.region_param(ebr, tcx).def_id == def_id.to_def_id() })),
                     _ => false,
                 };
 
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 885a7308bdc..3660bb3f780 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -83,11 +83,6 @@ enum TargetLint {
     Ignored,
 }
 
-pub enum FindLintError {
-    NotFound,
-    Removed,
-}
-
 struct LintAlias {
     name: &'static str,
     /// Whether deprecation warnings should be suppressed for this alias.
@@ -231,13 +226,24 @@ impl LintStore {
         }
     }
 
-    pub fn register_group_alias(&mut self, lint_name: &'static str, alias: &'static str) {
-        self.lint_groups.insert(
+    fn insert_group(&mut self, name: &'static str, group: LintGroup) {
+        let previous = self.lint_groups.insert(name, group);
+        if previous.is_some() {
+            bug!("group {name:?} already exists");
+        }
+    }
+
+    pub fn register_group_alias(&mut self, group_name: &'static str, alias: &'static str) {
+        let Some(LintGroup { lint_ids, .. }) = self.lint_groups.get(group_name) else {
+            bug!("group alias {alias:?} points to unregistered group {group_name:?}")
+        };
+
+        self.insert_group(
             alias,
             LintGroup {
-                lint_ids: vec![],
+                lint_ids: lint_ids.clone(),
                 is_externally_loaded: false,
-                depr: Some(LintAlias { name: lint_name, silent: true }),
+                depr: Some(LintAlias { name: group_name, silent: true }),
             },
         );
     }
@@ -249,24 +255,17 @@ impl LintStore {
         deprecated_name: Option<&'static str>,
         to: Vec<LintId>,
     ) {
-        let new = self
-            .lint_groups
-            .insert(name, LintGroup { lint_ids: to, is_externally_loaded, depr: None })
-            .is_none();
         if let Some(deprecated) = deprecated_name {
-            self.lint_groups.insert(
+            self.insert_group(
                 deprecated,
                 LintGroup {
-                    lint_ids: vec![],
+                    lint_ids: to.clone(),
                     is_externally_loaded,
                     depr: Some(LintAlias { name, silent: false }),
                 },
             );
         }
-
-        if !new {
-            bug!("duplicate specification of lint group {}", name);
-        }
+        self.insert_group(name, LintGroup { lint_ids: to, is_externally_loaded, depr: None });
     }
 
     /// This lint should give no warning and have no effect.
@@ -292,23 +291,15 @@ impl LintStore {
         self.by_name.insert(name.into(), Removed(reason.into()));
     }
 
-    pub fn find_lints(&self, mut lint_name: &str) -> Result<Vec<LintId>, FindLintError> {
+    pub fn find_lints(&self, lint_name: &str) -> Option<&[LintId]> {
         match self.by_name.get(lint_name) {
-            Some(&Id(lint_id)) => Ok(vec![lint_id]),
-            Some(&Renamed(_, lint_id)) => Ok(vec![lint_id]),
-            Some(&Removed(_)) => Err(FindLintError::Removed),
-            Some(&Ignored) => Ok(vec![]),
-            None => loop {
-                return match self.lint_groups.get(lint_name) {
-                    Some(LintGroup { lint_ids, depr, .. }) => {
-                        if let Some(LintAlias { name, .. }) = depr {
-                            lint_name = name;
-                            continue;
-                        }
-                        Ok(lint_ids.clone())
-                    }
-                    None => Err(FindLintError::Removed),
-                };
+            Some(Id(lint_id)) => Some(slice::from_ref(lint_id)),
+            Some(Renamed(_, lint_id)) => Some(slice::from_ref(lint_id)),
+            Some(Removed(_)) => None,
+            Some(Ignored) => Some(&[]),
+            None => match self.lint_groups.get(lint_name) {
+                Some(LintGroup { lint_ids, .. }) => Some(lint_ids),
+                None => None,
             },
         }
     }
@@ -374,8 +365,12 @@ impl LintStore {
                             CheckLintNameResult::MissingTool
                         };
                     }
-                    Some(LintGroup { lint_ids, .. }) => {
-                        return CheckLintNameResult::Tool(lint_ids, None);
+                    Some(LintGroup { lint_ids, depr, .. }) => {
+                        return if let &Some(LintAlias { name, silent: false }) = depr {
+                            CheckLintNameResult::Tool(lint_ids, Some(name.to_string()))
+                        } else {
+                            CheckLintNameResult::Tool(lint_ids, None)
+                        };
                     }
                 },
                 Some(Id(id)) => return CheckLintNameResult::Tool(slice::from_ref(id), None),
@@ -393,15 +388,11 @@ impl LintStore {
                 None => self.check_tool_name_for_backwards_compat(&complete_name, "clippy"),
                 Some(LintGroup { lint_ids, depr, .. }) => {
                     // Check if the lint group name is deprecated
-                    if let Some(LintAlias { name, silent }) = depr {
-                        let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
-                        return if *silent {
-                            CheckLintNameResult::Ok(lint_ids)
-                        } else {
-                            CheckLintNameResult::Tool(lint_ids, Some((*name).to_string()))
-                        };
+                    if let &Some(LintAlias { name, silent: false }) = depr {
+                        CheckLintNameResult::Tool(lint_ids, Some(name.to_string()))
+                    } else {
+                        CheckLintNameResult::Ok(lint_ids)
                     }
-                    CheckLintNameResult::Ok(lint_ids)
                 }
             },
             Some(Id(id)) => CheckLintNameResult::Ok(slice::from_ref(id)),
@@ -412,7 +403,7 @@ impl LintStore {
     fn no_lint_suggestion(&self, lint_name: &str, tool_name: &str) -> CheckLintNameResult<'_> {
         let name_lower = lint_name.to_lowercase();
 
-        if lint_name.chars().any(char::is_uppercase) && self.find_lints(&name_lower).is_ok() {
+        if lint_name.chars().any(char::is_uppercase) && self.find_lints(&name_lower).is_some() {
             // First check if the lint name is (partly) in upper case instead of lower case...
             return CheckLintNameResult::NoLint(Some((Symbol::intern(&name_lower), false)));
         }
@@ -455,18 +446,8 @@ impl LintStore {
             None => match self.lint_groups.get(&*complete_name) {
                 // Now we are sure, that this lint exists nowhere
                 None => self.no_lint_suggestion(lint_name, tool_name),
-                Some(LintGroup { lint_ids, depr, .. }) => {
-                    // Reaching this would be weird, but let's cover this case anyway
-                    if let Some(LintAlias { name, silent }) = depr {
-                        let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
-                        if *silent {
-                            CheckLintNameResult::Tool(lint_ids, Some(complete_name))
-                        } else {
-                            CheckLintNameResult::Tool(lint_ids, Some((*name).to_string()))
-                        }
-                    } else {
-                        CheckLintNameResult::Tool(lint_ids, Some(complete_name))
-                    }
+                Some(LintGroup { lint_ids, .. }) => {
+                    CheckLintNameResult::Tool(lint_ids, Some(complete_name))
                 }
             },
             Some(Id(id)) => CheckLintNameResult::Tool(slice::from_ref(id), Some(complete_name)),
@@ -855,11 +836,11 @@ impl<'tcx> LateContext<'tcx> {
         &self,
         self_ty: Ty<'tcx>,
         trait_id: DefId,
-        name: &str,
+        name: Symbol,
     ) -> Option<Ty<'tcx>> {
         let tcx = self.tcx;
         tcx.associated_items(trait_id)
-            .find_by_name_and_kind(tcx, Ident::from_str(name), ty::AssocKind::Type, trait_id)
+            .find_by_ident_and_kind(tcx, Ident::with_dummy_span(name), ty::AssocTag::Type, trait_id)
             .and_then(|assoc| {
                 let proj = Ty::new_projection(tcx, assoc.def_id, [self_ty]);
                 tcx.try_normalize_erasing_regions(self.typing_env(), proj).ok()
diff --git a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
index ec8f8441575..5989ef9519c 100644
--- a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
+++ b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
@@ -69,7 +69,7 @@ impl<'tcx> LateLintPass<'tcx> for DerefIntoDynSupertrait {
             && let ty::Dynamic(data, _, ty::Dyn) = self_ty.kind()
             && let Some(self_principal) = data.principal()
             // `<T as Deref>::Target` is `dyn target_principal`
-            && let Some(target) = cx.get_associated_type(self_ty, did, "Target")
+            && let Some(target) = cx.get_associated_type(self_ty, did, sym::Target)
             && let ty::Dynamic(data, _, ty::Dyn) = target.kind()
             && let Some(target_principal) = data.principal()
             // `target_principal` is a supertrait of `t_principal`
diff --git a/compiler/rustc_lint/src/errors.rs b/compiler/rustc_lint/src/errors.rs
index d109a5c9030..586e55c8055 100644
--- a/compiler/rustc_lint/src/errors.rs
+++ b/compiler/rustc_lint/src/errors.rs
@@ -1,5 +1,5 @@
 use rustc_errors::codes::*;
-use rustc_errors::{Diag, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic};
+use rustc_errors::{Diag, EmissionGuarantee, Subdiagnostic};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::lint::Level;
 use rustc_span::{Span, Symbol};
@@ -26,11 +26,7 @@ pub(crate) enum OverruledAttributeSub {
 }
 
 impl Subdiagnostic for OverruledAttributeSub {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             OverruledAttributeSub::DefaultSource { id } => {
                 diag.note(fluent::lint_default_source);
diff --git a/compiler/rustc_lint/src/if_let_rescope.rs b/compiler/rustc_lint/src/if_let_rescope.rs
index 39ea8d8e324..a9b04511c6b 100644
--- a/compiler/rustc_lint/src/if_let_rescope.rs
+++ b/compiler/rustc_lint/src/if_let_rescope.rs
@@ -3,9 +3,7 @@ use std::ops::ControlFlow;
 
 use hir::intravisit::{self, Visitor};
 use rustc_ast::Recovered;
-use rustc_errors::{
-    Applicability, Diag, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic, SuggestionStyle,
-};
+use rustc_errors::{Applicability, Diag, EmissionGuarantee, Subdiagnostic, SuggestionStyle};
 use rustc_hir::{self as hir, HirIdSet};
 use rustc_macros::{LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::adjustment::Adjust;
@@ -327,11 +325,7 @@ struct IfLetRescopeRewrite {
 }
 
 impl Subdiagnostic for IfLetRescopeRewrite {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut suggestions = vec![];
         for match_head in self.match_heads {
             match match_head {
@@ -360,7 +354,7 @@ impl Subdiagnostic for IfLetRescopeRewrite {
                 .chain(repeat('}').take(closing_brackets.count))
                 .collect(),
         ));
-        let msg = f(diag, crate::fluent_generated::lint_suggestion);
+        let msg = diag.eagerly_translate(crate::fluent_generated::lint_suggestion);
         diag.multipart_suggestion_with_style(
             msg,
             suggestions,
diff --git a/compiler/rustc_lint/src/impl_trait_overcaptures.rs b/compiler/rustc_lint/src/impl_trait_overcaptures.rs
index 26481b97076..f1dc420aa3c 100644
--- a/compiler/rustc_lint/src/impl_trait_overcaptures.rs
+++ b/compiler/rustc_lint/src/impl_trait_overcaptures.rs
@@ -461,7 +461,7 @@ fn extract_def_id_from_arg<'tcx>(
     arg: ty::GenericArg<'tcx>,
 ) -> DefId {
     match arg.unpack() {
-        ty::GenericArgKind::Lifetime(re) => match *re {
+        ty::GenericArgKind::Lifetime(re) => match re.kind() {
             ty::ReEarlyParam(ebr) => generics.region_param(ebr, tcx).def_id,
             ty::ReBound(
                 _,
@@ -530,7 +530,7 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> for FunctionalVariances<'tcx> {
         a: ty::Region<'tcx>,
         _: ty::Region<'tcx>,
     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
-        let def_id = match *a {
+        let def_id = match a.kind() {
             ty::ReEarlyParam(ebr) => self.generics.region_param(ebr, self.tcx).def_id,
             ty::ReBound(
                 _,
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index f1fe07cfcfa..00775647ac6 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -1,10 +1,11 @@
 use rustc_ast::attr::AttributeExt;
 use rustc_ast_pretty::pprust;
-use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
+use rustc_data_structures::unord::UnordSet;
 use rustc_errors::{Diag, LintDiagnostic, MultiSpan};
 use rustc_feature::{Features, GateIssue};
+use rustc_hir::HirId;
 use rustc_hir::intravisit::{self, Visitor};
-use rustc_hir::{CRATE_HIR_ID, HirId};
 use rustc_index::IndexVec;
 use rustc_middle::bug;
 use rustc_middle::hir::nested_filter;
@@ -115,12 +116,11 @@ impl LintLevelSets {
     }
 }
 
-fn lints_that_dont_need_to_run(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LintId> {
+fn lints_that_dont_need_to_run(tcx: TyCtxt<'_>, (): ()) -> UnordSet<LintId> {
     let store = unerased_lint_store(&tcx.sess);
+    let root_map = tcx.shallow_lint_levels_on(hir::CRATE_OWNER_ID);
 
-    let map = tcx.shallow_lint_levels_on(rustc_hir::CRATE_OWNER_ID);
-
-    let dont_need_to_run: FxIndexSet<LintId> = store
+    let mut dont_need_to_run: FxHashSet<LintId> = store
         .get_lints()
         .into_iter()
         .filter(|lint| {
@@ -129,24 +129,31 @@ fn lints_that_dont_need_to_run(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LintId> {
                 lint.future_incompatible.is_some_and(|fut| fut.reason.has_future_breakage());
             !has_future_breakage && !lint.eval_always
         })
-        .filter_map(|lint| {
-            let lint_level = map.lint_level_id_at_node(tcx, LintId::of(lint), CRATE_HIR_ID);
-            if matches!(lint_level.level, Level::Allow)
-                || (matches!(lint_level.src, LintLevelSource::Default))
-                    && lint.default_level(tcx.sess.edition()) == Level::Allow
-            {
-                Some(LintId::of(lint))
-            } else {
-                None
-            }
+        .filter(|lint| {
+            let lint_level =
+                root_map.lint_level_id_at_node(tcx, LintId::of(lint), hir::CRATE_HIR_ID);
+            // Only include lints that are allowed at crate root or by default.
+            matches!(lint_level.level, Level::Allow)
+                || (matches!(lint_level.src, LintLevelSource::Default)
+                    && lint.default_level(tcx.sess.edition()) == Level::Allow)
         })
+        .map(|lint| LintId::of(*lint))
         .collect();
 
-    let mut visitor = LintLevelMaximum { tcx, dont_need_to_run };
-    visitor.process_opts();
-    tcx.hir_walk_attributes(&mut visitor);
+    for owner in tcx.hir_crate_items(()).owners() {
+        let map = tcx.shallow_lint_levels_on(owner);
+
+        // All lints that appear with a non-allow level must be run.
+        for (_, specs) in map.specs.iter() {
+            for (lint, level_and_source) in specs.iter() {
+                if !matches!(level_and_source.level, Level::Allow) {
+                    dont_need_to_run.remove(lint);
+                }
+            }
+        }
+    }
 
-    visitor.dont_need_to_run
+    dont_need_to_run.into()
 }
 
 #[instrument(level = "trace", skip(tcx), ret)]
@@ -340,76 +347,6 @@ impl<'tcx> Visitor<'tcx> for LintLevelsBuilder<'_, LintLevelQueryMap<'tcx>> {
     }
 }
 
-/// Visitor with the only function of visiting every item-like in a crate and
-/// computing the highest level that every lint gets put to.
-///
-/// E.g., if a crate has a global #![allow(lint)] attribute, but a single item
-/// uses #[warn(lint)], this visitor will set that lint level as `Warn`
-struct LintLevelMaximum<'tcx> {
-    tcx: TyCtxt<'tcx>,
-    /// The actual list of detected lints.
-    dont_need_to_run: FxIndexSet<LintId>,
-}
-
-impl<'tcx> LintLevelMaximum<'tcx> {
-    fn process_opts(&mut self) {
-        let store = unerased_lint_store(self.tcx.sess);
-        for (lint_group, level) in &self.tcx.sess.opts.lint_opts {
-            if *level != Level::Allow {
-                let Ok(lints) = store.find_lints(lint_group) else {
-                    return;
-                };
-                for lint in lints {
-                    self.dont_need_to_run.swap_remove(&lint);
-                }
-            }
-        }
-    }
-}
-
-impl<'tcx> Visitor<'tcx> for LintLevelMaximum<'tcx> {
-    type NestedFilter = nested_filter::All;
-
-    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
-        self.tcx
-    }
-
-    /// FIXME(blyxyas): In a future revision, we should also graph #![allow]s,
-    /// but that is handled with more care
-    fn visit_attribute(&mut self, attribute: &'tcx hir::Attribute) {
-        if matches!(
-            Level::from_attr(attribute),
-            Some((Level::Warn | Level::Deny | Level::Forbid | Level::Expect | Level::ForceWarn, _))
-        ) {
-            let store = unerased_lint_store(self.tcx.sess);
-            // Lint attributes are always a metalist inside a
-            // metalist (even with just one lint).
-            let Some(meta_item_list) = attribute.meta_item_list() else { return };
-
-            for meta_list in meta_item_list {
-                // Convert Path to String
-                let Some(meta_item) = meta_list.meta_item() else { return };
-                let ident: &str = &meta_item
-                    .path
-                    .segments
-                    .iter()
-                    .map(|segment| segment.ident.as_str())
-                    .collect::<Vec<&str>>()
-                    .join("::");
-                let Ok(lints) = store.find_lints(
-                    // Lint attributes can only have literals
-                    ident,
-                ) else {
-                    return;
-                };
-                for lint in lints {
-                    self.dont_need_to_run.swap_remove(&lint);
-                }
-            }
-        }
-    }
-}
-
 pub struct LintLevelsBuilder<'s, P> {
     sess: &'s Session,
     features: &'s Features,
@@ -580,11 +517,11 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
 
             let lint_flag_val = Symbol::intern(lint_name);
 
-            let Ok(ids) = self.store.find_lints(lint_name) else {
+            let Some(ids) = self.store.find_lints(lint_name) else {
                 // errors already handled above
                 continue;
             };
-            for id in ids {
+            for &id in ids {
                 // ForceWarn and Forbid cannot be overridden
                 if let Some(LevelAndSource { level: Level::ForceWarn | Level::Forbid, .. }) =
                     self.current_specs().get(&id)
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 9b5c564d332..212368bea82 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -21,7 +21,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(array_windows)]
@@ -125,9 +124,7 @@ use unused::*;
 
 #[rustfmt::skip]
 pub use builtin::{MissingDoc, SoftLints};
-pub use context::{
-    CheckLintNameResult, EarlyContext, FindLintError, LateContext, LintContext, LintStore,
-};
+pub use context::{CheckLintNameResult, EarlyContext, LateContext, LintContext, LintStore};
 pub use early::{EarlyCheckNode, check_ast_node};
 pub use late::{check_crate, late_lint_mod, unerased_lint_store};
 pub use levels::LintLevelsBuilder;
@@ -606,6 +603,11 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, see issue #127323 \
          <https://github.com/rust-lang/rust/issues/127323> for more information",
     );
+    store.register_removed(
+        "undefined_naked_function_abi",
+        "converted into hard error, see PR #139001 \
+         <https://github.com/rust-lang/rust/issues/139001> for more information",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 55d010e6d34..8ab64fbd127 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -6,7 +6,7 @@ use rustc_abi::ExternAbi;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagArgValue, DiagMessage, DiagStyledString, ElidedLifetimeInPathSubdiag,
-    EmissionGuarantee, LintDiagnostic, MultiSpan, SubdiagMessageOp, Subdiagnostic, SuggestionStyle,
+    EmissionGuarantee, LintDiagnostic, MultiSpan, Subdiagnostic, SuggestionStyle,
 };
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::DefId;
@@ -449,11 +449,7 @@ pub(crate) struct BuiltinUnpermittedTypeInitSub {
 }
 
 impl Subdiagnostic for BuiltinUnpermittedTypeInitSub {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut err = self.err;
         loop {
             if let Some(span) = err.span {
@@ -504,16 +500,12 @@ pub(crate) struct BuiltinClashingExternSub<'a> {
 }
 
 impl Subdiagnostic for BuiltinClashingExternSub<'_> {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut expected_str = DiagStyledString::new();
         expected_str.push(self.expected.fn_sig(self.tcx).to_string(), false);
         let mut found_str = DiagStyledString::new();
         found_str.push(self.found.fn_sig(self.tcx).to_string(), true);
-        diag.note_expected_found(&"", expected_str, &"", found_str);
+        diag.note_expected_found("", expected_str, "", found_str);
     }
 }
 
@@ -824,11 +816,7 @@ pub(crate) struct HiddenUnicodeCodepointsDiagLabels {
 }
 
 impl Subdiagnostic for HiddenUnicodeCodepointsDiagLabels {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         for (c, span) in self.spans {
             diag.span_label(span, format!("{c:?}"));
         }
@@ -842,11 +830,7 @@ pub(crate) enum HiddenUnicodeCodepointsDiagSub {
 
 // Used because of multiple multipart_suggestion and note
 impl Subdiagnostic for HiddenUnicodeCodepointsDiagSub {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             HiddenUnicodeCodepointsDiagSub::Escape { spans } => {
                 diag.multipart_suggestion_with_style(
@@ -1015,11 +999,7 @@ pub(crate) struct NonBindingLetSub {
 }
 
 impl Subdiagnostic for NonBindingLetSub {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let can_suggest_binding = self.drop_fn_start_end.is_some() || !self.is_assign_desugar;
 
         if can_suggest_binding {
@@ -1303,11 +1283,7 @@ pub(crate) enum NonSnakeCaseDiagSub {
 }
 
 impl Subdiagnostic for NonSnakeCaseDiagSub {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             NonSnakeCaseDiagSub::Label { span } => {
                 diag.span_label(span, fluent::lint_label);
@@ -1629,11 +1605,7 @@ pub(crate) enum OverflowingBinHexSign {
 }
 
 impl Subdiagnostic for OverflowingBinHexSign {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             OverflowingBinHexSign::Positive => {
                 diag.note(fluent::lint_positive_note);
diff --git a/compiler/rustc_lint/src/nonstandard_style.rs b/compiler/rustc_lint/src/nonstandard_style.rs
index df567e80e55..a3e7c84584d 100644
--- a/compiler/rustc_lint/src/nonstandard_style.rs
+++ b/compiler/rustc_lint/src/nonstandard_style.rs
@@ -423,11 +423,11 @@ impl<'tcx> LateLintPass<'tcx> for NonSnakeCase {
     }
 
     fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &hir::TraitItem<'_>) {
-        if let hir::TraitItemKind::Fn(_, hir::TraitFn::Required(pnames)) = item.kind {
+        if let hir::TraitItemKind::Fn(_, hir::TraitFn::Required(param_idents)) = item.kind {
             self.check_snake_case(cx, "trait method", &item.ident);
-            for param_name in pnames {
-                if let Some(param_name) = param_name {
-                    self.check_snake_case(cx, "variable", param_name);
+            for param_ident in param_idents {
+                if let Some(param_ident) = param_ident {
+                    self.check_snake_case(cx, "variable", param_ident);
                 }
             }
         }
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index a6c82f574a1..a084dacfb5b 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -864,8 +864,8 @@ fn ty_is_known_nonnull<'tcx>(
                 return true;
             }
 
-            // `UnsafeCell` has its niche hidden.
-            if def.is_unsafe_cell() {
+            // `UnsafeCell` and `UnsafePinned` have their niche hidden.
+            if def.is_unsafe_cell() || def.is_unsafe_pinned() {
                 return false;
             }
 
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 7b43aac90c7..806bca78f78 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -1201,7 +1201,8 @@ impl EarlyLintPass for UnusedParens {
             // Do not lint on `(..)` as that will result in the other arms being useless.
             Paren(_)
             // The other cases do not contain sub-patterns.
-            | Wild | Never | Rest | Expr(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) | Err(_) => {},
+            | Missing | Wild | Never | Rest | Expr(..) | MacCall(..) | Range(..) | Ident(.., None)
+            | Path(..) | Err(_) => {},
             // These are list-like patterns; parens can always be removed.
             TupleStruct(_, _, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps {
                 self.check_unused_parens_pat(cx, p, false, false, keep_space);
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 8a761a0a096..b25d2a30681 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -110,7 +110,6 @@ declare_lint_pass! {
         UNCONDITIONAL_PANIC,
         UNCONDITIONAL_RECURSION,
         UNCOVERED_PARAM_IN_PROJECTION,
-        UNDEFINED_NAKED_FUNCTION_ABI,
         UNEXPECTED_CFGS,
         UNFULFILLED_LINT_EXPECTATIONS,
         UNINHABITED_STATIC,
@@ -2831,39 +2830,6 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `undefined_naked_function_abi` lint detects naked function definitions that
-    /// either do not specify an ABI or specify the Rust ABI.
-    ///
-    /// ### Example
-    ///
-    /// ```rust
-    /// #![feature(asm_experimental_arch, naked_functions)]
-    ///
-    /// use std::arch::naked_asm;
-    ///
-    /// #[naked]
-    /// pub fn default_abi() -> u32 {
-    ///     unsafe { naked_asm!(""); }
-    /// }
-    ///
-    /// #[naked]
-    /// pub extern "Rust" fn rust_abi() -> u32 {
-    ///     unsafe { naked_asm!(""); }
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// The Rust ABI is currently undefined. Therefore, naked functions should
-    /// specify a non-Rust ABI.
-    pub UNDEFINED_NAKED_FUNCTION_ABI,
-    Warn,
-    "undefined naked function ABI"
-}
-
-declare_lint! {
     /// The `ineffective_unstable_trait_impl` lint detects `#[unstable]` attributes which are not used.
     ///
     /// ### Example
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 7fdbae3a59d..b4069b317bf 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -249,7 +249,7 @@ impl Level {
 
     /// Converts an `Attribute` to a level.
     pub fn from_attr(attr: &impl AttributeExt) -> Option<(Self, Option<LintExpectationId>)> {
-        Self::from_symbol(attr.name_or_empty(), || Some(attr.id()))
+        attr.name().and_then(|name| Self::from_symbol(name, || Some(attr.id())))
     }
 
     /// Converts a `Symbol` to a level.
diff --git a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
index 909083d5e86..bc9516b2e0c 100644
--- a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
+++ b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
@@ -20,14 +20,12 @@ use crate::diagnostics::utils::{
 /// The central struct for constructing the `add_to_diag` method from an annotated struct.
 pub(crate) struct SubdiagnosticDerive {
     diag: syn::Ident,
-    f: syn::Ident,
 }
 
 impl SubdiagnosticDerive {
     pub(crate) fn new() -> Self {
         let diag = format_ident!("diag");
-        let f = format_ident!("f");
-        Self { diag, f }
+        Self { diag }
     }
 
     pub(crate) fn into_tokens(self, mut structure: Structure<'_>) -> TokenStream {
@@ -86,19 +84,16 @@ impl SubdiagnosticDerive {
         };
 
         let diag = &self.diag;
-        let f = &self.f;
 
         // FIXME(edition_2024): Fix the `keyword_idents_2024` lint to not trigger here?
         #[allow(keyword_idents_2024)]
         let ret = structure.gen_impl(quote! {
             gen impl rustc_errors::Subdiagnostic for @Self {
-                fn add_to_diag_with<__G, __F>(
+                fn add_to_diag<__G>(
                     self,
                     #diag: &mut rustc_errors::Diag<'_, __G>,
-                    #f: &__F
                 ) where
                     __G: rustc_errors::EmissionGuarantee,
-                    __F: rustc_errors::SubdiagMessageOp<__G>,
                 {
                     #implementation
                 }
@@ -384,11 +379,10 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
                 Ok(quote! {})
             }
             "subdiagnostic" => {
-                let f = &self.parent.f;
                 let diag = &self.parent.diag;
                 let binding = &info.binding;
                 self.has_subdiagnostic = true;
-                Ok(quote! { #binding.add_to_diag_with(#diag, #f); })
+                Ok(quote! { #binding.add_to_diag(#diag); })
             }
             _ => {
                 let mut span_attrs = vec![];
@@ -531,12 +525,11 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
         let span_field = self.span_field.value_ref();
 
         let diag = &self.parent.diag;
-        let f = &self.parent.f;
         let mut calls = TokenStream::new();
         for (kind, slug, no_span) in kind_slugs {
             let message = format_ident!("__message");
             calls.extend(
-                quote! { let #message = #f(#diag, crate::fluent_generated::#slug.into()); },
+                quote! { let #message = #diag.eagerly_translate(crate::fluent_generated::#slug); },
             );
 
             let name = format_ident!(
diff --git a/compiler/rustc_macros/src/symbols.rs b/compiler/rustc_macros/src/symbols.rs
index 37200f62eb5..0400de62274 100644
--- a/compiler/rustc_macros/src/symbols.rs
+++ b/compiler/rustc_macros/src/symbols.rs
@@ -142,13 +142,13 @@ pub(super) fn symbols(input: TokenStream) -> TokenStream {
     output
 }
 
-struct Preinterned {
+struct Predefined {
     idx: u32,
     span_of_name: Span,
 }
 
 struct Entries {
-    map: HashMap<String, Preinterned>,
+    map: HashMap<String, Predefined>,
 }
 
 impl Entries {
@@ -163,7 +163,7 @@ impl Entries {
             prev.idx
         } else {
             let idx = self.len();
-            self.map.insert(s.to_string(), Preinterned { idx, span_of_name: span });
+            self.map.insert(s.to_string(), Predefined { idx, span_of_name: span });
             idx
         }
     }
@@ -295,10 +295,14 @@ fn symbols_with_errors(input: TokenStream) -> (TokenStream, Vec<syn::Error>) {
     }
 
     let symbol_digits_base = entries.map["0"].idx;
-    let preinterned_symbols_count = entries.len();
+    let predefined_symbols_count = entries.len();
     let output = quote! {
         const SYMBOL_DIGITS_BASE: u32 = #symbol_digits_base;
-        const PREINTERNED_SYMBOLS_COUNT: u32 = #preinterned_symbols_count;
+
+        /// The number of predefined symbols; this is the the first index for
+        /// extra pre-interned symbols in an Interner created via
+        /// [`Interner::with_extra_symbols`].
+        pub const PREDEFINED_SYMBOLS_COUNT: u32 = #predefined_symbols_count;
 
         #[doc(hidden)]
         #[allow(non_upper_case_globals)]
@@ -315,10 +319,13 @@ fn symbols_with_errors(input: TokenStream) -> (TokenStream, Vec<syn::Error>) {
         }
 
         impl Interner {
-            pub(crate) fn fresh() -> Self {
-                Interner::prefill(&[
-                    #prefill_stream
-                ])
+            /// Creates an `Interner` with the predefined symbols from the `symbols!` macro and
+            /// any extra symbols provided by external drivers such as Clippy
+            pub(crate) fn with_extra_symbols(extra_symbols: &[&'static str]) -> Self {
+                Interner::prefill(
+                    &[#prefill_stream],
+                    extra_symbols,
+                )
             }
         }
     };
diff --git a/compiler/rustc_macros/src/type_foldable.rs b/compiler/rustc_macros/src/type_foldable.rs
index c4f584dca43..85051311bee 100644
--- a/compiler/rustc_macros/src/type_foldable.rs
+++ b/compiler/rustc_macros/src/type_foldable.rs
@@ -14,27 +14,13 @@ pub(super) fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_m
 
     s.add_bounds(synstructure::AddBounds::Generics);
     s.bind_with(|_| synstructure::BindStyle::Move);
-    let body_fold = s.each_variant(|vi| {
+    let try_body_fold = s.each_variant(|vi| {
         let bindings = vi.bindings();
         vi.construct(|_, index| {
             let bind = &bindings[index];
 
-            let mut fixed = false;
-
             // retain value of fields with #[type_foldable(identity)]
-            bind.ast().attrs.iter().for_each(|x| {
-                if !x.path().is_ident("type_foldable") {
-                    return;
-                }
-                let _ = x.parse_nested_meta(|nested| {
-                    if nested.path.is_ident("identity") {
-                        fixed = true;
-                    }
-                    Ok(())
-                });
-            });
-
-            if fixed {
+            if has_ignore_attr(&bind.ast().attrs, "type_foldable", "identity") {
                 bind.to_token_stream()
             } else {
                 quote! {
@@ -44,6 +30,22 @@ pub(super) fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_m
         })
     });
 
+    let body_fold = s.each_variant(|vi| {
+        let bindings = vi.bindings();
+        vi.construct(|_, index| {
+            let bind = &bindings[index];
+
+            // retain value of fields with #[type_foldable(identity)]
+            if has_ignore_attr(&bind.ast().attrs, "type_foldable", "identity") {
+                bind.to_token_stream()
+            } else {
+                quote! {
+                    ::rustc_middle::ty::TypeFoldable::fold_with(#bind, __folder)
+                }
+            }
+        })
+    });
+
     s.bound_impl(
         quote!(::rustc_middle::ty::TypeFoldable<::rustc_middle::ty::TyCtxt<'tcx>>),
         quote! {
@@ -51,8 +53,32 @@ pub(super) fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_m
                 self,
                 __folder: &mut __F
             ) -> Result<Self, __F::Error> {
-                Ok(match self { #body_fold })
+                Ok(match self { #try_body_fold })
+            }
+
+            fn fold_with<__F: ::rustc_middle::ty::TypeFolder<::rustc_middle::ty::TyCtxt<'tcx>>>(
+                self,
+                __folder: &mut __F
+            ) -> Self {
+                match self { #body_fold }
             }
         },
     )
 }
+
+fn has_ignore_attr(attrs: &[syn::Attribute], name: &'static str, meta: &'static str) -> bool {
+    let mut ignored = false;
+    attrs.iter().for_each(|attr| {
+        if !attr.path().is_ident(name) {
+            return;
+        }
+        let _ = attr.parse_nested_meta(|nested| {
+            if nested.path.is_ident(meta) {
+                ignored = true;
+            }
+            Ok(())
+        });
+    });
+
+    ignored
+}
diff --git a/compiler/rustc_metadata/src/lib.rs b/compiler/rustc_metadata/src/lib.rs
index 028d5c8b609..3b44c44fcb9 100644
--- a/compiler/rustc_metadata/src/lib.rs
+++ b/compiler/rustc_metadata/src/lib.rs
@@ -1,6 +1,5 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(coroutines)]
diff --git a/compiler/rustc_metadata/src/native_libs.rs b/compiler/rustc_metadata/src/native_libs.rs
index 130a425e9c7..cee9cff0775 100644
--- a/compiler/rustc_metadata/src/native_libs.rs
+++ b/compiler/rustc_metadata/src/native_libs.rs
@@ -207,7 +207,7 @@ impl<'tcx> Collector<'tcx> {
 
         let sess = self.tcx.sess;
 
-        if matches!(abi, ExternAbi::Rust | ExternAbi::RustIntrinsic) {
+        if matches!(abi, ExternAbi::Rust) {
             return;
         }
 
@@ -226,8 +226,8 @@ impl<'tcx> Collector<'tcx> {
             let mut wasm_import_module = None;
             let mut import_name_type = None;
             for item in items.iter() {
-                match item.name_or_empty() {
-                    sym::name => {
+                match item.name() {
+                    Some(sym::name) => {
                         if name.is_some() {
                             sess.dcx().emit_err(errors::MultipleNamesInLink { span: item.span() });
                             continue;
@@ -242,7 +242,7 @@ impl<'tcx> Collector<'tcx> {
                         }
                         name = Some((link_name, span));
                     }
-                    sym::kind => {
+                    Some(sym::kind) => {
                         if kind.is_some() {
                             sess.dcx().emit_err(errors::MultipleKindsInLink { span: item.span() });
                             continue;
@@ -304,7 +304,7 @@ impl<'tcx> Collector<'tcx> {
                         };
                         kind = Some(link_kind);
                     }
-                    sym::modifiers => {
+                    Some(sym::modifiers) => {
                         if modifiers.is_some() {
                             sess.dcx()
                                 .emit_err(errors::MultipleLinkModifiers { span: item.span() });
@@ -316,7 +316,7 @@ impl<'tcx> Collector<'tcx> {
                         };
                         modifiers = Some((link_modifiers, item.name_value_literal_span().unwrap()));
                     }
-                    sym::cfg => {
+                    Some(sym::cfg) => {
                         if cfg.is_some() {
                             sess.dcx().emit_err(errors::MultipleCfgs { span: item.span() });
                             continue;
@@ -346,7 +346,7 @@ impl<'tcx> Collector<'tcx> {
                         }
                         cfg = Some(link_cfg.clone());
                     }
-                    sym::wasm_import_module => {
+                    Some(sym::wasm_import_module) => {
                         if wasm_import_module.is_some() {
                             sess.dcx().emit_err(errors::MultipleWasmImport { span: item.span() });
                             continue;
@@ -357,7 +357,7 @@ impl<'tcx> Collector<'tcx> {
                         };
                         wasm_import_module = Some((link_wasm_import_module, item.span()));
                     }
-                    sym::import_name_type => {
+                    Some(sym::import_name_type) => {
                         if import_name_type.is_some() {
                             sess.dcx()
                                 .emit_err(errors::MultipleImportNameType { span: item.span() });
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 4610a571da0..3c2245347f9 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -562,9 +562,9 @@ impl<'a, 'tcx> SpanDecoder for DecodeContext<'a, 'tcx> {
                     Symbol::intern(s)
                 })
             }
-            SYMBOL_PREINTERNED => {
+            SYMBOL_PREDEFINED => {
                 let symbol_index = self.read_u32();
-                Symbol::new_from_decoded(symbol_index)
+                Symbol::new(symbol_index)
             }
             _ => unreachable!(),
         }
@@ -1313,7 +1313,7 @@ impl<'a> CrateMetadataRef<'a> {
     fn get_fn_has_self_parameter(self, id: DefIndex, sess: &'a Session) -> bool {
         self.root
             .tables
-            .fn_arg_names
+            .fn_arg_idents
             .get(self, id)
             .expect("argument names not encoded for a function")
             .decode((self, sess))
@@ -1332,29 +1332,30 @@ impl<'a> CrateMetadataRef<'a> {
     }
 
     fn get_associated_item(self, id: DefIndex, sess: &'a Session) -> ty::AssocItem {
-        let name = if self.root.tables.opt_rpitit_info.get(self, id).is_some() {
-            kw::Empty
-        } else {
-            self.item_name(id)
-        };
-        let (kind, has_self) = match self.def_kind(id) {
-            DefKind::AssocConst => (ty::AssocKind::Const, false),
-            DefKind::AssocFn => (ty::AssocKind::Fn, self.get_fn_has_self_parameter(id, sess)),
-            DefKind::AssocTy => (ty::AssocKind::Type, false),
+        let kind = match self.def_kind(id) {
+            DefKind::AssocConst => ty::AssocKind::Const { name: self.item_name(id) },
+            DefKind::AssocFn => ty::AssocKind::Fn {
+                name: self.item_name(id),
+                has_self: self.get_fn_has_self_parameter(id, sess),
+            },
+            DefKind::AssocTy => {
+                let data = if let Some(rpitit_info) = self.root.tables.opt_rpitit_info.get(self, id)
+                {
+                    ty::AssocTypeData::Rpitit(rpitit_info.decode(self))
+                } else {
+                    ty::AssocTypeData::Normal(self.item_name(id))
+                };
+                ty::AssocKind::Type { data }
+            }
             _ => bug!("cannot get associated-item of `{:?}`", self.def_key(id)),
         };
         let container = self.root.tables.assoc_container.get(self, id).unwrap();
-        let opt_rpitit_info =
-            self.root.tables.opt_rpitit_info.get(self, id).map(|d| d.decode(self));
 
         ty::AssocItem {
-            name,
             kind,
             def_id: self.local_def_id(id),
             trait_item_def_id: self.get_trait_item_def_id(id),
             container,
-            fn_has_self_parameter: has_self,
-            opt_rpitit_info,
         }
     }
 
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 3dc82ce9d18..ecc2dcc5318 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -286,7 +286,7 @@ provide! { tcx, def_id, other, cdata,
     rendered_const => { table }
     rendered_precise_capturing_args => { table }
     asyncness => { table_direct }
-    fn_arg_names => { table }
+    fn_arg_idents => { table }
     coroutine_kind => { table_direct }
     coroutine_for_closure => { table }
     coroutine_by_move_body_def_id => { table }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 167122a9793..3ea61d1b40a 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -201,9 +201,9 @@ impl<'a, 'tcx> SpanEncoder for EncodeContext<'a, 'tcx> {
     }
 
     fn encode_symbol(&mut self, symbol: Symbol) {
-        // if symbol preinterned, emit tag and symbol index
-        if symbol.is_preinterned() {
-            self.opaque.emit_u8(SYMBOL_PREINTERNED);
+        // if symbol predefined, emit tag and symbol index
+        if symbol.is_predefined() {
+            self.opaque.emit_u8(SYMBOL_PREDEFINED);
             self.opaque.emit_u32(symbol.as_u32());
         } else {
             // otherwise write it as string or as offset to it
@@ -821,7 +821,9 @@ struct AnalyzeAttrState<'a> {
 #[inline]
 fn analyze_attr(attr: &impl AttributeExt, state: &mut AnalyzeAttrState<'_>) -> bool {
     let mut should_encode = false;
-    if !rustc_feature::encode_cross_crate(attr.name_or_empty()) {
+    if let Some(name) = attr.name()
+        && !rustc_feature::encode_cross_crate(name)
+    {
         // Attributes not marked encode-cross-crate don't need to be encoded for downstream crates.
     } else if attr.doc_str().is_some() {
         // We keep all doc comments reachable to rustdoc because they might be "imported" into
@@ -1099,7 +1101,6 @@ fn should_encode_variances<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, def_kind: Def
         DefKind::Struct
         | DefKind::Union
         | DefKind::Enum
-        | DefKind::Variant
         | DefKind::OpaqueTy
         | DefKind::Fn
         | DefKind::Ctor(..)
@@ -1109,6 +1110,7 @@ fn should_encode_variances<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, def_kind: Def
             matches!(tcx.opt_rpitit_info(def_id), Some(ty::ImplTraitInTraitData::Trait { .. }))
         }
         DefKind::Mod
+        | DefKind::Variant
         | DefKind::Field
         | DefKind::AssocConst
         | DefKind::TyParam
@@ -1338,7 +1340,7 @@ fn should_encode_const(def_kind: DefKind) -> bool {
 fn should_encode_fn_impl_trait_in_trait<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
     if let Some(assoc_item) = tcx.opt_associated_item(def_id)
         && assoc_item.container == ty::AssocItemContainer::Trait
-        && assoc_item.kind == ty::AssocKind::Fn
+        && assoc_item.is_fn()
     {
         true
     } else {
@@ -1469,7 +1471,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             }
             if let DefKind::Fn | DefKind::AssocFn = def_kind {
                 self.tables.asyncness.set_some(def_id.index, tcx.asyncness(def_id));
-                record_array!(self.tables.fn_arg_names[def_id] <- tcx.fn_arg_names(def_id));
+                record_array!(self.tables.fn_arg_idents[def_id] <- tcx.fn_arg_idents(def_id));
             }
             if let Some(name) = tcx.intrinsic(def_id) {
                 record!(self.tables.intrinsic[def_id] <- name);
@@ -1691,7 +1693,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
         match item.container {
             AssocItemContainer::Trait => {
-                if let ty::AssocKind::Type = item.kind {
+                if item.is_type() {
                     self.encode_explicit_item_bounds(def_id);
                     self.encode_explicit_item_self_bounds(def_id);
                     if tcx.is_conditionally_const(def_id) {
@@ -1706,7 +1708,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 }
             }
         }
-        if let Some(rpitit_info) = item.opt_rpitit_info {
+        if let ty::AssocKind::Type { data: ty::AssocTypeData::Rpitit(rpitit_info) } = item.kind {
             record!(self.tables.opt_rpitit_info[def_id] <- rpitit_info);
             if matches!(rpitit_info, ty::ImplTraitInTraitData::Trait { .. }) {
                 record_array!(
@@ -2199,7 +2201,7 @@ fn prefetch_mir(tcx: TyCtxt<'_>) {
     }
 
     let reachable_set = tcx.reachable_set(());
-    par_for_each_in(tcx.mir_keys(()), |&def_id| {
+    par_for_each_in(tcx.mir_keys(()), |&&def_id| {
         let (encode_const, encode_opt) = should_encode_mir(tcx, reachable_set, def_id);
 
         if encode_const {
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 96a1f65eeb0..5aa81f41b7b 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -36,9 +36,7 @@ use rustc_serialize::opaque::FileEncoder;
 use rustc_session::config::{SymbolManglingVersion, TargetModifier};
 use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{
-    ExpnIndex, MacroKind, SyntaxContextDataNonRecursive as SyntaxContextData,
-};
+use rustc_span::hygiene::{ExpnIndex, MacroKind, SyntaxContextKey};
 use rustc_span::{self, ExpnData, ExpnHash, ExpnId, Ident, Span, Symbol};
 use rustc_target::spec::{PanicStrategy, TargetTuple};
 use table::TableBuilder;
@@ -195,7 +193,7 @@ enum LazyState {
     Previous(NonZero<usize>),
 }
 
-type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextData>>>;
+type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextKey>>>;
 type ExpnDataTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnData>>>;
 type ExpnHashTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnHash>>>;
 
@@ -451,7 +449,7 @@ define_tables! {
     rendered_const: Table<DefIndex, LazyValue<String>>,
     rendered_precise_capturing_args: Table<DefIndex, LazyArray<PreciseCapturingArgKind<Symbol, Symbol>>>,
     asyncness: Table<DefIndex, ty::Asyncness>,
-    fn_arg_names: Table<DefIndex, LazyArray<Option<Ident>>>,
+    fn_arg_idents: Table<DefIndex, LazyArray<Option<Ident>>>,
     coroutine_kind: Table<DefIndex, hir::CoroutineKind>,
     coroutine_for_closure: Table<DefIndex, RawDefId>,
     adt_destructor: Table<DefIndex, LazyValue<ty::Destructor>>,
@@ -586,7 +584,7 @@ impl SpanTag {
 // Tags for encoding Symbol's
 const SYMBOL_STR: u8 = 0;
 const SYMBOL_OFFSET: u8 = 1;
-const SYMBOL_PREINTERNED: u8 = 2;
+const SYMBOL_PREDEFINED: u8 = 2;
 
 pub fn provide(providers: &mut Providers) {
     encoder::provide(providers);
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index aef56ea46e9..d1bbb0598fe 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -28,7 +28,7 @@ macro_rules! arena_types {
                     rustc_middle::mir::Body<'tcx>
                 >,
             [decode] typeck_results: rustc_middle::ty::TypeckResults<'tcx>,
-            [decode] borrowck_result: rustc_middle::mir::BorrowCheckResult<'tcx>,
+            [decode] borrowck_result: rustc_middle::mir::ConcreteOpaqueTypes<'tcx>,
             [] resolver: rustc_data_structures::steal::Steal<(
                 rustc_middle::ty::ResolverAstLowering,
                 std::sync::Arc<rustc_ast::Crate>,
@@ -89,7 +89,6 @@ macro_rules! arena_types {
             [] name_set: rustc_data_structures::unord::UnordSet<rustc_span::Symbol>,
             [] autodiff_item: rustc_ast::expand::autodiff_attrs::AutoDiffItem,
             [] ordered_name_set: rustc_data_structures::fx::FxIndexSet<rustc_span::Symbol>,
-            [] pats: rustc_middle::ty::PatternKind<'tcx>,
             [] valtree: rustc_middle::ty::ValTreeKind<'tcx>,
 
             // Note that this deliberately duplicates items in the `rustc_hir::arena`,
diff --git a/compiler/rustc_middle/src/hir/map.rs b/compiler/rustc_middle/src/hir/map.rs
index 21ab06c98a7..fee707f7b4c 100644
--- a/compiler/rustc_middle/src/hir/map.rs
+++ b/compiler/rustc_middle/src/hir/map.rs
@@ -1,3 +1,7 @@
+//! This module used to contain a type called `Map`. That type has since been
+//! eliminated, and all its methods are now on `TyCtxt`. But the module name
+//! stays as `map` because there isn't an obviously better name for it.
+
 use rustc_abi::ExternAbi;
 use rustc_ast::visit::{VisitorResult, walk_list};
 use rustc_data_structures::fingerprint::Fingerprint;
@@ -18,16 +22,6 @@ use crate::middle::debugger_visualizer::DebuggerVisualizerFile;
 use crate::query::LocalCrate;
 use crate::ty::TyCtxt;
 
-// FIXME: the structure was necessary in the past but now it
-// only serves as "namespace" for HIR-related methods, and can be
-// removed if all the methods are reasonably renamed and moved to tcx
-// (https://github.com/rust-lang/rust/pull/118256#issuecomment-1826442834).
-#[allow(unused)] // FIXME: temporary
-#[derive(Copy, Clone)]
-pub struct Map<'hir> {
-    pub(super) tcx: TyCtxt<'hir>,
-}
-
 /// An iterator that walks up the ancestor tree of a given `HirId`.
 /// Constructed using `tcx.hir_parent_iter(hir_id)`.
 struct ParentHirIterator<'tcx> {
@@ -281,7 +275,7 @@ impl<'tcx> TyCtxt<'tcx> {
         })
     }
 
-    pub fn hir_body_param_names(self, id: BodyId) -> impl Iterator<Item = Option<Ident>> {
+    pub fn hir_body_param_idents(self, id: BodyId) -> impl Iterator<Item = Option<Ident>> {
         self.hir_body(id).params.iter().map(|param| match param.pat.kind {
             PatKind::Binding(_, _, ident, _) => Some(ident),
             PatKind::Wild => Some(Ident::new(kw::Underscore, param.pat.span)),
@@ -335,7 +329,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Returns an iterator of the `DefId`s for all body-owners in this
     /// crate. If you would prefer to iterate over the bodies
-    /// themselves, you can do `self.hir().krate().body_ids.iter()`.
+    /// themselves, you can do `self.hir_crate(()).body_ids.iter()`.
     #[inline]
     pub fn hir_body_owners(self) -> impl Iterator<Item = LocalDefId> {
         self.hir_crate_items(()).body_owners.iter().copied()
@@ -343,7 +337,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn par_hir_body_owners(self, f: impl Fn(LocalDefId) + DynSend + DynSync) {
-        par_for_each_in(&self.hir_crate_items(()).body_owners[..], |&def_id| f(def_id));
+        par_for_each_in(&self.hir_crate_items(()).body_owners[..], |&&def_id| f(def_id));
     }
 
     pub fn hir_ty_param_owner(self, def_id: LocalDefId) -> LocalDefId {
diff --git a/compiler/rustc_middle/src/hir/mod.rs b/compiler/rustc_middle/src/hir/mod.rs
index 74369b6636c..a28dcb0cb8e 100644
--- a/compiler/rustc_middle/src/hir/mod.rs
+++ b/compiler/rustc_middle/src/hir/mod.rs
@@ -83,44 +83,39 @@ impl ModuleItems {
         &self,
         f: impl Fn(ItemId) -> Result<(), ErrorGuaranteed> + DynSend + DynSync,
     ) -> Result<(), ErrorGuaranteed> {
-        try_par_for_each_in(&self.free_items[..], |&id| f(id))
+        try_par_for_each_in(&self.free_items[..], |&&id| f(id))
     }
 
     pub fn par_trait_items(
         &self,
         f: impl Fn(TraitItemId) -> Result<(), ErrorGuaranteed> + DynSend + DynSync,
     ) -> Result<(), ErrorGuaranteed> {
-        try_par_for_each_in(&self.trait_items[..], |&id| f(id))
+        try_par_for_each_in(&self.trait_items[..], |&&id| f(id))
     }
 
     pub fn par_impl_items(
         &self,
         f: impl Fn(ImplItemId) -> Result<(), ErrorGuaranteed> + DynSend + DynSync,
     ) -> Result<(), ErrorGuaranteed> {
-        try_par_for_each_in(&self.impl_items[..], |&id| f(id))
+        try_par_for_each_in(&self.impl_items[..], |&&id| f(id))
     }
 
     pub fn par_foreign_items(
         &self,
         f: impl Fn(ForeignItemId) -> Result<(), ErrorGuaranteed> + DynSend + DynSync,
     ) -> Result<(), ErrorGuaranteed> {
-        try_par_for_each_in(&self.foreign_items[..], |&id| f(id))
+        try_par_for_each_in(&self.foreign_items[..], |&&id| f(id))
     }
 
     pub fn par_opaques(
         &self,
         f: impl Fn(LocalDefId) -> Result<(), ErrorGuaranteed> + DynSend + DynSync,
     ) -> Result<(), ErrorGuaranteed> {
-        try_par_for_each_in(&self.opaques[..], |&id| f(id))
+        try_par_for_each_in(&self.opaques[..], |&&id| f(id))
     }
 }
 
 impl<'tcx> TyCtxt<'tcx> {
-    #[inline(always)]
-    pub fn hir(self) -> map::Map<'tcx> {
-        map::Map { tcx: self }
-    }
-
     pub fn parent_module(self, id: HirId) -> LocalModDefId {
         if !id.is_owner() && self.def_kind(id.owner) == DefKind::Mod {
             LocalModDefId::new_unchecked(id.owner.def_id)
@@ -215,9 +210,9 @@ pub fn provide(providers: &mut Providers) {
         let hir_id = tcx.local_def_id_to_hir_id(def_id);
         tcx.hir_opt_ident_span(hir_id)
     };
-    providers.fn_arg_names = |tcx, def_id| {
+    providers.fn_arg_idents = |tcx, def_id| {
         if let Some(body_id) = tcx.hir_node_by_def_id(def_id).body_id() {
-            tcx.arena.alloc_from_iter(tcx.hir_body_param_names(body_id))
+            tcx.arena.alloc_from_iter(tcx.hir_body_param_idents(body_id))
         } else if let Node::TraitItem(&TraitItem {
             kind: TraitItemKind::Fn(_, TraitFn::Required(idents)),
             ..
@@ -231,7 +226,7 @@ pub fn provide(providers: &mut Providers) {
         } else {
             span_bug!(
                 tcx.hir_span(tcx.local_def_id_to_hir_id(def_id)),
-                "fn_arg_names: unexpected item {:?}",
+                "fn_arg_idents: unexpected item {:?}",
                 def_id
             );
         }
diff --git a/compiler/rustc_middle/src/hir/place.rs b/compiler/rustc_middle/src/hir/place.rs
index 60ce8544aa0..c3d10615cf1 100644
--- a/compiler/rustc_middle/src/hir/place.rs
+++ b/compiler/rustc_middle/src/hir/place.rs
@@ -40,6 +40,8 @@ pub enum ProjectionKind {
 
     /// A conversion from an opaque type to its hidden type so we can
     /// do further projections on it.
+    ///
+    /// This is unused if `-Znext-solver` is enabled.
     OpaqueCast,
 }
 
diff --git a/compiler/rustc_middle/src/infer/canonical.rs b/compiler/rustc_middle/src/infer/canonical.rs
index 3cd148cd442..5b860374496 100644
--- a/compiler/rustc_middle/src/infer/canonical.rs
+++ b/compiler/rustc_middle/src/infer/canonical.rs
@@ -39,15 +39,6 @@ pub type CanonicalVarInfo<'tcx> = ir::CanonicalVarInfo<TyCtxt<'tcx>>;
 pub type CanonicalVarValues<'tcx> = ir::CanonicalVarValues<TyCtxt<'tcx>>;
 pub type CanonicalVarInfos<'tcx> = &'tcx List<CanonicalVarInfo<'tcx>>;
 
-impl<'tcx> ty::TypeFoldable<TyCtxt<'tcx>> for CanonicalVarInfos<'tcx> {
-    fn try_fold_with<F: ty::FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_canonical_var_infos(v))
-    }
-}
-
 /// When we canonicalize a value to form a query, we wind up replacing
 /// various parts of it with canonical variables. This struct stores
 /// those replaced bits to remember for when we process the query
diff --git a/compiler/rustc_middle/src/lib.rs b/compiler/rustc_middle/src/lib.rs
index 1e6178144c9..8fe2cc7101b 100644
--- a/compiler/rustc_middle/src/lib.rs
+++ b/compiler/rustc_middle/src/lib.rs
@@ -29,7 +29,6 @@
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::potential_query_instability)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(allocator_api)]
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 4dfb362f3a2..db19c858e7c 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1636,8 +1636,8 @@ pub fn find_self_call<'tcx>(
         &body[block].terminator
         && let Operand::Constant(box ConstOperand { const_, .. }) = func
         && let ty::FnDef(def_id, fn_args) = *const_.ty().kind()
-        && let Some(ty::AssocItem { fn_has_self_parameter: true, .. }) =
-            tcx.opt_associated_item(def_id)
+        && let Some(item) = tcx.opt_associated_item(def_id)
+        && item.is_method()
         && let [Spanned { node: Operand::Move(self_place) | Operand::Copy(self_place), .. }, ..] =
             **args
     {
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index 5a038b27337..d57019fee0f 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -531,12 +531,12 @@ fn write_mir_intro<'tcx>(
 
     // construct a scope tree and write it out
     let mut scope_tree: FxHashMap<SourceScope, Vec<SourceScope>> = Default::default();
-    for (index, scope_data) in body.source_scopes.iter().enumerate() {
+    for (index, scope_data) in body.source_scopes.iter_enumerated() {
         if let Some(parent) = scope_data.parent_scope {
-            scope_tree.entry(parent).or_default().push(SourceScope::new(index));
+            scope_tree.entry(parent).or_default().push(index);
         } else {
             // Only the argument scope has no parent, because it's the root.
-            assert_eq!(index, OUTERMOST_SOURCE_SCOPE.index());
+            assert_eq!(index, OUTERMOST_SOURCE_SCOPE);
         }
     }
 
@@ -859,7 +859,7 @@ impl Debug for Statement<'_> {
             BackwardIncompatibleDropHint { ref place, reason: _ } => {
                 // For now, we don't record the reason because there is only one use case,
                 // which is to report breaking change in drop order by Edition 2024
-                write!(fmt, "backward incompatible drop({place:?})")
+                write!(fmt, "BackwardIncompatibleDropHint({place:?})")
             }
         }
     }
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index 5a9fe10938a..3fc05f2caf2 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/compiler/rustc_middle/src/mir/query.rs
@@ -6,14 +6,13 @@ use rustc_abi::{FieldIdx, VariantIdx};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def_id::LocalDefId;
+use rustc_index::IndexVec;
 use rustc_index::bit_set::BitMatrix;
-use rustc_index::{Idx, IndexVec};
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
 use rustc_span::{Span, Symbol};
-use smallvec::SmallVec;
 
 use super::{ConstValue, SourceInfo};
-use crate::ty::{self, CoroutineArgsExt, OpaqueHiddenType, Ty, TyCtxt, fold_regions};
+use crate::ty::{self, CoroutineArgsExt, OpaqueHiddenType, Ty};
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
@@ -85,16 +84,11 @@ impl Debug for CoroutineLayout<'_> {
     }
 }
 
-#[derive(Debug, TyEncodable, TyDecodable, HashStable)]
-pub struct BorrowCheckResult<'tcx> {
-    /// All the opaque types that are restricted to concrete types
-    /// by this function. Unlike the value in `TypeckResults`, this has
-    /// unerased regions.
-    pub concrete_opaque_types: FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>>,
-    pub closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
-    pub used_mut_upvars: SmallVec<[FieldIdx; 8]>,
-    pub tainted_by_errors: Option<ErrorGuaranteed>,
-}
+/// All the opaque types that are restricted to concrete types
+/// by this function. Unlike the value in `TypeckResults`, this has
+/// unerased regions.
+#[derive(Default, Debug, TyEncodable, TyDecodable, HashStable)]
+pub struct ConcreteOpaqueTypes<'tcx>(pub FxIndexMap<LocalDefId, OpaqueHiddenType<'tcx>>);
 
 /// The result of the `mir_const_qualif` query.
 ///
@@ -108,84 +102,6 @@ pub struct ConstQualifs {
     pub needs_non_const_drop: bool,
     pub tainted_by_errors: Option<ErrorGuaranteed>,
 }
-
-/// After we borrow check a closure, we are left with various
-/// requirements that we have inferred between the free regions that
-/// appear in the closure's signature or on its field types. These
-/// requirements are then verified and proved by the closure's
-/// creating function. This struct encodes those requirements.
-///
-/// The requirements are listed as being between various `RegionVid`. The 0th
-/// region refers to `'static`; subsequent region vids refer to the free
-/// regions that appear in the closure (or coroutine's) type, in order of
-/// appearance. (This numbering is actually defined by the `UniversalRegions`
-/// struct in the NLL region checker. See for example
-/// `UniversalRegions::closure_mapping`.) Note the free regions in the
-/// closure's signature and captures are erased.
-///
-/// Example: If type check produces a closure with the closure args:
-///
-/// ```text
-/// ClosureArgs = [
-///     'a,                                         // From the parent.
-///     'b,
-///     i8,                                         // the "closure kind"
-///     for<'x> fn(&'<erased> &'x u32) -> &'x u32,  // the "closure signature"
-///     &'<erased> String,                          // some upvar
-/// ]
-/// ```
-///
-/// We would "renumber" each free region to a unique vid, as follows:
-///
-/// ```text
-/// ClosureArgs = [
-///     '1,                                         // From the parent.
-///     '2,
-///     i8,                                         // the "closure kind"
-///     for<'x> fn(&'3 &'x u32) -> &'x u32,         // the "closure signature"
-///     &'4 String,                                 // some upvar
-/// ]
-/// ```
-///
-/// Now the code might impose a requirement like `'1: '2`. When an
-/// instance of the closure is created, the corresponding free regions
-/// can be extracted from its type and constrained to have the given
-/// outlives relationship.
-#[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable)]
-pub struct ClosureRegionRequirements<'tcx> {
-    /// The number of external regions defined on the closure. In our
-    /// example above, it would be 3 -- one for `'static`, then `'1`
-    /// and `'2`. This is just used for a sanity check later on, to
-    /// make sure that the number of regions we see at the callsite
-    /// matches.
-    pub num_external_vids: usize,
-
-    /// Requirements between the various free regions defined in
-    /// indices.
-    pub outlives_requirements: Vec<ClosureOutlivesRequirement<'tcx>>,
-}
-
-/// Indicates an outlives-constraint between a type or between two
-/// free regions declared on the closure.
-#[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
-pub struct ClosureOutlivesRequirement<'tcx> {
-    // This region or type ...
-    pub subject: ClosureOutlivesSubject<'tcx>,
-
-    // ... must outlive this one.
-    pub outlived_free_region: ty::RegionVid,
-
-    // If not, report an error here ...
-    pub blame_span: Span,
-
-    // ... due to this reason.
-    pub category: ConstraintCategory<'tcx>,
-}
-
-// Make sure this enum doesn't unintentionally grow
-#[cfg(target_pointer_width = "64")]
-rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
-
 /// Outlives-constraints can be categorized to determine whether and why they
 /// are interesting (for error reporting). Order of variants indicates sort
 /// order of the category, thereby influencing diagnostic output.
@@ -253,66 +169,6 @@ pub enum AnnotationSource {
     GenericArg,
 }
 
-/// The subject of a `ClosureOutlivesRequirement` -- that is, the thing
-/// that must outlive some region.
-#[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
-pub enum ClosureOutlivesSubject<'tcx> {
-    /// Subject is a type, typically a type parameter, but could also
-    /// be a projection. Indicates a requirement like `T: 'a` being
-    /// passed to the caller, where the type here is `T`.
-    Ty(ClosureOutlivesSubjectTy<'tcx>),
-
-    /// Subject is a free region from the closure. Indicates a requirement
-    /// like `'a: 'b` being passed to the caller; the region here is `'a`.
-    Region(ty::RegionVid),
-}
-
-/// Represents a `ty::Ty` for use in [`ClosureOutlivesSubject`].
-///
-/// This abstraction is necessary because the type may include `ReVar` regions,
-/// which is what we use internally within NLL code, and they can't be used in
-/// a query response.
-///
-/// DO NOT implement `TypeVisitable` or `TypeFoldable` traits, because this
-/// type is not recognized as a binder for late-bound region.
-#[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
-pub struct ClosureOutlivesSubjectTy<'tcx> {
-    inner: Ty<'tcx>,
-}
-
-impl<'tcx> ClosureOutlivesSubjectTy<'tcx> {
-    /// All regions of `ty` must be of kind `ReVar` and must represent
-    /// universal regions *external* to the closure.
-    pub fn bind(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
-        let inner = fold_regions(tcx, ty, |r, depth| match r.kind() {
-            ty::ReVar(vid) => {
-                let br = ty::BoundRegion {
-                    var: ty::BoundVar::new(vid.index()),
-                    kind: ty::BoundRegionKind::Anon,
-                };
-                ty::Region::new_bound(tcx, depth, br)
-            }
-            _ => bug!("unexpected region in ClosureOutlivesSubjectTy: {r:?}"),
-        });
-
-        Self { inner }
-    }
-
-    pub fn instantiate(
-        self,
-        tcx: TyCtxt<'tcx>,
-        mut map: impl FnMut(ty::RegionVid) -> ty::Region<'tcx>,
-    ) -> Ty<'tcx> {
-        fold_regions(tcx, self.inner, |r, depth| match r.kind() {
-            ty::ReBound(debruijn, br) => {
-                debug_assert_eq!(debruijn, depth);
-                map(ty::RegionVid::new(br.var.index()))
-            }
-            _ => bug!("unexpected region {r:?}"),
-        })
-    }
-}
-
 /// The constituent parts of a mir constant of kind ADT or array.
 #[derive(Copy, Clone, Debug, HashStable)]
 pub struct DestructuredConstant<'tcx> {
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 707c8d04d55..304b3caa6e1 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -652,6 +652,8 @@ pub enum CallSource {
     /// Other types of desugaring that did not come from the HIR, but we don't care about
     /// for diagnostics (yet).
     Misc,
+    /// Use of value, generating a clone function call
+    Use,
     /// Normal function call, no special source
     Normal,
 }
@@ -929,6 +931,8 @@ pub enum TerminatorKind<'tcx> {
         asm_macro: InlineAsmMacro,
 
         /// The template for the inline assembly, with placeholders.
+        #[type_foldable(identity)]
+        #[type_visitable(ignore)]
         template: &'tcx [InlineAsmTemplatePiece],
 
         /// The operands for the inline assembly, as `Operand`s or `Place`s.
@@ -939,6 +943,8 @@ pub enum TerminatorKind<'tcx> {
 
         /// Source spans for each line of the inline assembly code. These are
         /// used to map assembler errors back to the line in the source code.
+        #[type_foldable(identity)]
+        #[type_visitable(ignore)]
         line_spans: &'tcx [Span],
 
         /// Valid targets for the inline assembly.
@@ -1236,6 +1242,8 @@ pub enum ProjectionElem<V, T> {
 
     /// Like an explicit cast from an opaque type to a concrete type, but without
     /// requiring an intermediate variable.
+    ///
+    /// This is unused with `-Znext-solver`.
     OpaqueCast(T),
 
     /// A transmute from an unsafe binder to the type that it wraps. This is a projection
diff --git a/compiler/rustc_middle/src/mir/terminator.rs b/compiler/rustc_middle/src/mir/terminator.rs
index b2c51ad8864..82e8422c52d 100644
--- a/compiler/rustc_middle/src/mir/terminator.rs
+++ b/compiler/rustc_middle/src/mir/terminator.rs
@@ -454,7 +454,7 @@ mod helper {
         /// Like [`SwitchTargets::target_for_value`], but returning the same type as
         /// [`Terminator::successors`].
         #[inline]
-        #[cfg_attr(not(bootstrap), define_opaque(Successors))]
+        #[define_opaque(Successors)]
         pub fn successors_for_value(&self, value: u128) -> Successors<'_> {
             let target = self.target_for_value(value);
             (&[]).into_iter().copied().chain(Some(target))
@@ -463,7 +463,7 @@ mod helper {
 
     impl<'tcx> TerminatorKind<'tcx> {
         #[inline]
-        #[cfg_attr(not(bootstrap), define_opaque(Successors))]
+        #[define_opaque(Successors)]
         pub fn successors(&self) -> Successors<'_> {
             use self::TerminatorKind::*;
             match *self {
@@ -502,7 +502,7 @@ mod helper {
         }
 
         #[inline]
-        #[cfg_attr(not(bootstrap), define_opaque(SuccessorsMut))]
+        #[define_opaque(SuccessorsMut)]
         pub fn successors_mut(&mut self) -> SuccessorsMut<'_> {
             use self::TerminatorKind::*;
             match *self {
diff --git a/compiler/rustc_middle/src/mir/visit.rs b/compiler/rustc_middle/src/mir/visit.rs
index 3c83d962900..de4d5140e85 100644
--- a/compiler/rustc_middle/src/mir/visit.rs
+++ b/compiler/rustc_middle/src/mir/visit.rs
@@ -457,9 +457,15 @@ macro_rules! make_mir_visitor {
                             }
                         }
                     }
+                    StatementKind::BackwardIncompatibleDropHint { place, .. } => {
+                        self.visit_place(
+                            place,
+                            PlaceContext::NonUse(NonUseContext::BackwardIncompatibleDropHint),
+                            location
+                        );
+                    }
                     StatementKind::ConstEvalCounter => {}
                     StatementKind::Nop => {}
-                    StatementKind::BackwardIncompatibleDropHint { .. } => {}
                 }
             }
 
@@ -1348,6 +1354,8 @@ pub enum NonUseContext {
     AscribeUserTy(ty::Variance),
     /// The data of a user variable, for debug info.
     VarDebugInfo,
+    /// A `BackwardIncompatibleDropHint` statement, meant for edition 2024 lints.
+    BackwardIncompatibleDropHint,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -1422,7 +1430,9 @@ impl PlaceContext {
         use NonUseContext::*;
         match self {
             PlaceContext::MutatingUse(_) => ty::Invariant,
-            PlaceContext::NonUse(StorageDead | StorageLive | VarDebugInfo) => ty::Invariant,
+            PlaceContext::NonUse(
+                StorageDead | StorageLive | VarDebugInfo | BackwardIncompatibleDropHint,
+            ) => ty::Invariant,
             PlaceContext::NonMutatingUse(
                 Inspect | Copy | Move | PlaceMention | SharedBorrow | FakeBorrow | RawBorrow
                 | Projection,
diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index 6c6b9a5510c..5bd111fa2f2 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -25,7 +25,7 @@ pub trait EraseType: Copy {
 pub type Erase<T: EraseType> = Erased<impl Copy>;
 
 #[inline(always)]
-#[cfg_attr(not(bootstrap), define_opaque(Erase))]
+#[define_opaque(Erase)]
 pub fn erase<T: EraseType>(src: T) -> Erase<T> {
     // Ensure the sizes match
     const {
@@ -49,7 +49,7 @@ pub fn erase<T: EraseType>(src: T) -> Erase<T> {
 
 /// Restores an erased value.
 #[inline(always)]
-#[cfg_attr(not(bootstrap), define_opaque(Erase))]
+#[define_opaque(Erase)]
 pub fn restore<T: EraseType>(value: Erase<T>) -> T {
     let value: Erased<<T as EraseType>::Result> = value;
     // See comment in `erase` for why we use `transmute_unchecked`.
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 0d5fba3cc69..e94f088304b 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -161,11 +161,11 @@ rustc_queries! {
 
     /// Represents crate as a whole (as distinct from the top-level crate module).
     ///
-    /// If you call `hir_crate` (e.g., indirectly by calling `tcx.hir_crate()`),
-    /// we will have to assume that any change means that you need to be recompiled.
-    /// This is because the `hir_crate` query gives you access to all other items.
-    /// To avoid this fate, do not call `tcx.hir_crate()`; instead,
-    /// prefer wrappers like [`TyCtxt::hir_visit_all_item_likes_in_crate`].
+    /// If you call `tcx.hir_crate(())` we will have to assume that any change
+    /// means that you need to be recompiled. This is because the `hir_crate`
+    /// query gives you access to all other items. To avoid this fate, do not
+    /// call `tcx.hir_crate(())`; instead, prefer wrappers like
+    /// [`TyCtxt::hir_visit_all_item_likes_in_crate`].
     query hir_crate(key: ()) -> &'tcx Crate<'tcx> {
         arena_cache
         eval_always
@@ -197,7 +197,7 @@ rustc_queries! {
 
     /// Gives access to the HIR node's parent for the HIR owner `key`.
     ///
-    /// This can be conveniently accessed by methods on `tcx.hir()`.
+    /// This can be conveniently accessed by `tcx.hir_*` methods.
     /// Avoid calling this query directly.
     query hir_owner_parent(key: hir::OwnerId) -> hir::HirId {
         desc { |tcx| "getting HIR parent of `{}`", tcx.def_path_str(key) }
@@ -205,7 +205,7 @@ rustc_queries! {
 
     /// Gives access to the HIR nodes and bodies inside `key` if it's a HIR owner.
     ///
-    /// This can be conveniently accessed by methods on `tcx.hir()`.
+    /// This can be conveniently accessed by `tcx.hir_*` methods.
     /// Avoid calling this query directly.
     query opt_hir_owner_nodes(key: LocalDefId) -> Option<&'tcx hir::OwnerNodes<'tcx>> {
         desc { |tcx| "getting HIR owner items in `{}`", tcx.def_path_str(key) }
@@ -214,7 +214,7 @@ rustc_queries! {
 
     /// Gives access to the HIR attributes inside the HIR owner `key`.
     ///
-    /// This can be conveniently accessed by methods on `tcx.hir()`.
+    /// This can be conveniently accessed by `tcx.hir_*` methods.
     /// Avoid calling this query directly.
     query hir_attr_map(key: hir::OwnerId) -> &'tcx hir::AttributeMap<'tcx> {
         desc { |tcx| "getting HIR owner attributes in `{}`", tcx.def_path_str(key) }
@@ -484,7 +484,7 @@ rustc_queries! {
         desc { "computing `#[expect]`ed lints in this crate" }
     }
 
-    query lints_that_dont_need_to_run(_: ()) -> &'tcx FxIndexSet<LintId> {
+    query lints_that_dont_need_to_run(_: ()) -> &'tcx UnordSet<LintId> {
         arena_cache
         desc { "Computing all lints that are explicitly enabled or with a default level greater than Allow" }
     }
@@ -1026,6 +1026,13 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// Given an `impl_def_id`, return true if the self type is guaranteed to be unsized due
+    /// to either being one of the built-in unsized types (str/slice/dyn) or to be a struct
+    /// whose tail is one of those types.
+    query impl_self_is_guaranteed_unsized(impl_def_id: DefId) -> bool {
+        desc { |tcx| "computing whether `{}` has a guaranteed unsized self type", tcx.def_path_str(impl_def_id) }
+    }
+
     /// Maps a `DefId` of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
     /// Methods in these implementations don't need to be exported.
@@ -1153,11 +1160,10 @@ rustc_queries! {
         return_result_from_ensure_ok
     }
 
-    /// Borrow-checks the function body. If this is a closure, returns
-    /// additional requirements that the closure's creator must verify.
-    query mir_borrowck(key: LocalDefId) -> &'tcx mir::BorrowCheckResult<'tcx> {
+    /// Borrow-checks the given typeck root, e.g. functions, const/static items,
+    /// and its children, e.g. closures, inline consts.
+    query mir_borrowck(key: LocalDefId) -> Result<&'tcx mir::ConcreteOpaqueTypes<'tcx>, ErrorGuaranteed> {
         desc { |tcx| "borrow-checking `{}`", tcx.def_path_str(key) }
-        cache_on_disk_if(tcx) { tcx.is_typeck_child(key.to_def_id()) }
     }
 
     /// Gets a complete map from all types to their inherent impls.
@@ -1436,8 +1442,8 @@ rustc_queries! {
         desc { |tcx| "computing target features for inline asm of `{}`", tcx.def_path_str(def_id) }
     }
 
-    query fn_arg_names(def_id: DefId) -> &'tcx [Option<rustc_span::Ident>] {
-        desc { |tcx| "looking up function parameter names for `{}`", tcx.def_path_str(def_id) }
+    query fn_arg_idents(def_id: DefId) -> &'tcx [Option<rustc_span::Ident>] {
+        desc { |tcx| "looking up function parameter identifiers for `{}`", tcx.def_path_str(def_id) }
         separate_provide_extern
     }
 
@@ -1894,6 +1900,11 @@ rustc_queries! {
 
     // The macro which defines `rustc_metadata::provide_extern` depends on this query's name.
     // Changing the name should cause a compiler error, but in case that changes, be aware.
+    //
+    // The hash should not be calculated before the `analysis` pass is complete, specifically
+    // until `tcx.untracked().definitions.freeze()` has been called, otherwise if incremental
+    // compilation is enabled calculating this hash can freeze this structure too early in
+    // compilation and cause subsequent crashes when attempting to write to `definitions`
     query crate_hash(_: CrateNum) -> Svh {
         eval_always
         desc { "looking up the hash a crate" }
diff --git a/compiler/rustc_middle/src/query/on_disk_cache.rs b/compiler/rustc_middle/src/query/on_disk_cache.rs
index c6ecc679b7b..5431097cb1d 100644
--- a/compiler/rustc_middle/src/query/on_disk_cache.rs
+++ b/compiler/rustc_middle/src/query/on_disk_cache.rs
@@ -16,8 +16,7 @@ use rustc_serialize::opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixed
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_session::Session;
 use rustc_span::hygiene::{
-    ExpnId, HygieneDecodeContext, HygieneEncodeContext, SyntaxContext,
-    SyntaxContextDataNonRecursive as SyntaxContextData,
+    ExpnId, HygieneDecodeContext, HygieneEncodeContext, SyntaxContext, SyntaxContextKey,
 };
 use rustc_span::source_map::Spanned;
 use rustc_span::{
@@ -46,7 +45,7 @@ const TAG_EXPN_DATA: u8 = 1;
 // Tags for encoding Symbol's
 const SYMBOL_STR: u8 = 0;
 const SYMBOL_OFFSET: u8 = 1;
-const SYMBOL_PREINTERNED: u8 = 2;
+const SYMBOL_PREDEFINED: u8 = 2;
 
 /// Provides an interface to incremental compilation data cached from the
 /// previous compilation session. This data will eventually include the results
@@ -567,7 +566,7 @@ impl<'a, 'tcx> SpanDecoder for CacheDecoder<'a, 'tcx> {
             // We look up the position of the associated `SyntaxData` and decode it.
             let pos = syntax_contexts.get(&id).unwrap();
             this.with_position(pos.to_usize(), |decoder| {
-                let data: SyntaxContextData = decode_tagged(decoder, TAG_SYNTAX_CONTEXT);
+                let data: SyntaxContextKey = decode_tagged(decoder, TAG_SYNTAX_CONTEXT);
                 data
             })
         })
@@ -674,9 +673,9 @@ impl<'a, 'tcx> SpanDecoder for CacheDecoder<'a, 'tcx> {
                     Symbol::intern(s)
                 })
             }
-            SYMBOL_PREINTERNED => {
+            SYMBOL_PREDEFINED => {
                 let symbol_index = self.read_u32();
-                Symbol::new_from_decoded(symbol_index)
+                Symbol::new(symbol_index)
             }
             _ => unreachable!(),
         }
@@ -892,9 +891,9 @@ impl<'a, 'tcx> SpanEncoder for CacheEncoder<'a, 'tcx> {
 
     // copy&paste impl from rustc_metadata
     fn encode_symbol(&mut self, symbol: Symbol) {
-        // if symbol preinterned, emit tag and symbol index
-        if symbol.is_preinterned() {
-            self.encoder.emit_u8(SYMBOL_PREINTERNED);
+        // if symbol predefined, emit tag and symbol index
+        if symbol.is_predefined() {
+            self.encoder.emit_u8(SYMBOL_PREDEFINED);
             self.encoder.emit_u32(symbol.as_u32());
         } else {
             // otherwise write it as string or as offset to it
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 8d373cb3b30..c168142fb1e 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -747,6 +747,9 @@ pub struct Ascription<'tcx> {
 
 #[derive(Clone, Debug, HashStable, TypeVisitable)]
 pub enum PatKind<'tcx> {
+    /// A missing pattern, e.g. for an anonymous param in a bare fn like `fn f(u32)`.
+    Missing,
+
     /// A wildcard pattern: `_`.
     Wild,
 
@@ -812,23 +815,17 @@ pub enum PatKind<'tcx> {
     },
 
     /// Pattern obtained by converting a constant (inline or named) to its pattern
-    /// representation using `const_to_pat`.
+    /// representation using `const_to_pat`. This is used for unsafety checking.
     ExpandedConstant {
-        /// [DefId] of the constant, we need this so that we have a
-        /// reference that can be used by unsafety checking to visit nested
-        /// unevaluated constants and for diagnostics. If the `DefId` doesn't
-        /// correspond to a local crate, it points at the `const` item.
+        /// [DefId] of the constant item.
         def_id: DefId,
-        /// If `false`, then `def_id` points at a `const` item, otherwise it
-        /// corresponds to a local inline const.
-        is_inline: bool,
-        /// If the inline constant is used in a range pattern, this subpattern
-        /// represents the range (if both ends are inline constants, there will
-        /// be multiple InlineConstant wrappers).
+        /// The pattern that the constant lowered to.
         ///
-        /// Otherwise, the actual pattern that the constant lowered to. As with
-        /// other constants, inline constants are matched structurally where
-        /// possible.
+        /// HACK: we need to keep the `DefId` of inline constants around for unsafety checking;
+        /// therefore when a range pattern contains inline constants, we re-wrap the range pattern
+        /// with the `ExpandedConstant` nodes that correspond to the range endpoints. Hence
+        /// `subpattern` may actually be a range pattern, and `def_id` be the constant for one of
+        /// its endpoints.
         subpattern: Box<Pat<'tcx>>,
     },
 
diff --git a/compiler/rustc_middle/src/thir/visit.rs b/compiler/rustc_middle/src/thir/visit.rs
index 7d62ab7970d..f3da2a5cc8e 100644
--- a/compiler/rustc_middle/src/thir/visit.rs
+++ b/compiler/rustc_middle/src/thir/visit.rs
@@ -250,7 +250,8 @@ pub(crate) fn for_each_immediate_subpat<'a, 'tcx>(
     mut callback: impl FnMut(&'a Pat<'tcx>),
 ) {
     match &pat.kind {
-        PatKind::Wild
+        PatKind::Missing
+        | PatKind::Wild
         | PatKind::Binding { subpattern: None, .. }
         | PatKind::Constant { value: _ }
         | PatKind::Range(_)
diff --git a/compiler/rustc_middle/src/ty/adjustment.rs b/compiler/rustc_middle/src/ty/adjustment.rs
index f8ab555305f..a61a6c571a2 100644
--- a/compiler/rustc_middle/src/ty/adjustment.rs
+++ b/compiler/rustc_middle/src/ty/adjustment.rs
@@ -5,7 +5,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
 use rustc_span::Span;
 
-use crate::ty::{self, Ty, TyCtxt};
+use crate::ty::{Ty, TyCtxt};
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
 pub enum PointerCoercion {
@@ -133,7 +133,7 @@ impl OverloadedDeref {
         };
         tcx.associated_items(trait_def_id)
             .in_definition_order()
-            .find(|m| m.kind == ty::AssocKind::Fn)
+            .find(|item| item.is_fn())
             .unwrap()
             .def_id
     }
@@ -214,3 +214,25 @@ pub enum CustomCoerceUnsized {
     /// Records the index of the field being coerced.
     Struct(FieldIdx),
 }
+
+/// Represents an implicit coercion applied to the scrutinee of a match before testing a pattern
+/// against it. Currently, this is used only for implicit dereferences.
+#[derive(Clone, Copy, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
+pub struct PatAdjustment<'tcx> {
+    pub kind: PatAdjust,
+    /// The type of the scrutinee before the adjustment is applied, or the "adjusted type" of the
+    /// pattern.
+    pub source: Ty<'tcx>,
+}
+
+/// Represents implicit coercions of patterns' types, rather than values' types.
+#[derive(Clone, Copy, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
+#[derive(TypeFoldable, TypeVisitable)]
+pub enum PatAdjust {
+    /// An implicit dereference before matching, such as when matching the pattern `0` against a
+    /// scrutinee of type `&u8` or `&mut u8`.
+    BuiltinDeref,
+    /// An implicit call to `Deref(Mut)::deref(_mut)` before matching, such as when matching the
+    /// pattern `[..]` against a scrutinee of type `Vec<T>`.
+    OverloadedDeref,
+}
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index 00fe5cb0c5d..66517c97a68 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -53,6 +53,10 @@ bitflags::bitflags! {
         const IS_VARIANT_LIST_NON_EXHAUSTIVE = 1 << 8;
         /// Indicates whether the type is `UnsafeCell`.
         const IS_UNSAFE_CELL              = 1 << 9;
+        /// Indicates whether the type is `UnsafePinned`.
+        const IS_UNSAFE_PINNED              = 1 << 10;
+        /// Indicates whether the type is anonymous.
+        const IS_ANONYMOUS                = 1 << 11;
     }
 }
 rustc_data_structures::external_bitflags_debug! { AdtFlags }
@@ -302,6 +306,9 @@ impl AdtDefData {
         if tcx.is_lang_item(did, LangItem::UnsafeCell) {
             flags |= AdtFlags::IS_UNSAFE_CELL;
         }
+        if tcx.is_lang_item(did, LangItem::UnsafePinned) {
+            flags |= AdtFlags::IS_UNSAFE_PINNED;
+        }
 
         AdtDefData { did, variants, flags, repr }
     }
@@ -405,6 +412,12 @@ impl<'tcx> AdtDef<'tcx> {
         self.flags().contains(AdtFlags::IS_UNSAFE_CELL)
     }
 
+    /// Returns `true` if this is `UnsafePinned<T>`.
+    #[inline]
+    pub fn is_unsafe_pinned(self) -> bool {
+        self.flags().contains(AdtFlags::IS_UNSAFE_PINNED)
+    }
+
     /// Returns `true` if this is `ManuallyDrop<T>`.
     #[inline]
     pub fn is_manually_drop(self) -> bool {
diff --git a/compiler/rustc_middle/src/ty/assoc.rs b/compiler/rustc_middle/src/ty/assoc.rs
index ce4c08aa485..0c44fd2758d 100644
--- a/compiler/rustc_middle/src/ty/assoc.rs
+++ b/compiler/rustc_middle/src/ty/assoc.rs
@@ -18,27 +18,33 @@ pub enum AssocItemContainer {
 #[derive(Copy, Clone, Debug, PartialEq, HashStable, Eq, Hash, Encodable, Decodable)]
 pub struct AssocItem {
     pub def_id: DefId,
-    pub name: Symbol,
     pub kind: AssocKind,
     pub container: AssocItemContainer,
 
     /// If this is an item in an impl of a trait then this is the `DefId` of
     /// the associated item on the trait that this implements.
     pub trait_item_def_id: Option<DefId>,
-
-    /// Whether this is a method with an explicit self
-    /// as its first parameter, allowing method calls.
-    pub fn_has_self_parameter: bool,
-
-    /// `Some` if the associated item (an associated type) comes from the
-    /// return-position `impl Trait` in trait desugaring. The `ImplTraitInTraitData`
-    /// provides additional information about its source.
-    pub opt_rpitit_info: Option<ty::ImplTraitInTraitData>,
 }
 
 impl AssocItem {
+    // Gets the identifier, if it has one.
+    pub fn opt_name(&self) -> Option<Symbol> {
+        match self.kind {
+            ty::AssocKind::Type { data: AssocTypeData::Normal(name) } => Some(name),
+            ty::AssocKind::Type { data: AssocTypeData::Rpitit(_) } => None,
+            ty::AssocKind::Const { name } => Some(name),
+            ty::AssocKind::Fn { name, .. } => Some(name),
+        }
+    }
+
+    // Gets the identifier name. Aborts if it lacks one, i.e. is an RPITIT
+    // associated type.
+    pub fn name(&self) -> Symbol {
+        self.opt_name().expect("name of non-Rpitit assoc item")
+    }
+
     pub fn ident(&self, tcx: TyCtxt<'_>) -> Ident {
-        Ident::new(self.name, tcx.def_ident_span(self.def_id).unwrap())
+        Ident::new(self.name(), tcx.def_ident_span(self.def_id).unwrap())
     }
 
     /// Gets the defaultness of the associated item.
@@ -78,35 +84,65 @@ impl AssocItem {
 
     pub fn signature(&self, tcx: TyCtxt<'_>) -> String {
         match self.kind {
-            ty::AssocKind::Fn => {
+            ty::AssocKind::Fn { .. } => {
                 // We skip the binder here because the binder would deanonymize all
                 // late-bound regions, and we don't want method signatures to show up
                 // `as for<'r> fn(&'r MyType)`. Pretty-printing handles late-bound
                 // regions just fine, showing `fn(&MyType)`.
                 tcx.fn_sig(self.def_id).instantiate_identity().skip_binder().to_string()
             }
-            ty::AssocKind::Type => format!("type {};", self.name),
-            ty::AssocKind::Const => {
-                format!(
-                    "const {}: {:?};",
-                    self.name,
-                    tcx.type_of(self.def_id).instantiate_identity()
-                )
+            ty::AssocKind::Type { .. } => format!("type {};", self.name()),
+            ty::AssocKind::Const { name } => {
+                format!("const {}: {:?};", name, tcx.type_of(self.def_id).instantiate_identity())
             }
         }
     }
 
     pub fn descr(&self) -> &'static str {
         match self.kind {
-            ty::AssocKind::Const => "const",
-            ty::AssocKind::Fn if self.fn_has_self_parameter => "method",
-            ty::AssocKind::Fn => "associated function",
-            ty::AssocKind::Type => "type",
+            ty::AssocKind::Const { .. } => "associated const",
+            ty::AssocKind::Fn { has_self: true, .. } => "method",
+            ty::AssocKind::Fn { has_self: false, .. } => "associated function",
+            ty::AssocKind::Type { .. } => "associated type",
+        }
+    }
+
+    pub fn namespace(&self) -> Namespace {
+        match self.kind {
+            ty::AssocKind::Type { .. } => Namespace::TypeNS,
+            ty::AssocKind::Const { .. } | ty::AssocKind::Fn { .. } => Namespace::ValueNS,
+        }
+    }
+
+    pub fn as_def_kind(&self) -> DefKind {
+        match self.kind {
+            AssocKind::Const { .. } => DefKind::AssocConst,
+            AssocKind::Fn { .. } => DefKind::AssocFn,
+            AssocKind::Type { .. } => DefKind::AssocTy,
+        }
+    }
+    pub fn is_type(&self) -> bool {
+        matches!(self.kind, ty::AssocKind::Type { .. })
+    }
+
+    pub fn is_fn(&self) -> bool {
+        matches!(self.kind, ty::AssocKind::Fn { .. })
+    }
+
+    pub fn is_method(&self) -> bool {
+        matches!(self.kind, ty::AssocKind::Fn { has_self: true, .. })
+    }
+
+    pub fn as_tag(&self) -> AssocTag {
+        match self.kind {
+            AssocKind::Const { .. } => AssocTag::Const,
+            AssocKind::Fn { .. } => AssocTag::Fn,
+            AssocKind::Type { .. } => AssocTag::Type,
         }
     }
 
     pub fn is_impl_trait_in_trait(&self) -> bool {
-        self.opt_rpitit_info.is_some()
+        matches!(self.kind, AssocKind::Type { data: AssocTypeData::Rpitit(_) })
     }
 
     /// Returns true if:
@@ -114,7 +150,7 @@ impl AssocItem {
     /// - If it is in a trait impl, the item from the original trait has this attribute, or
     /// - It is an inherent assoc const.
     pub fn is_type_const_capable(&self, tcx: TyCtxt<'_>) -> bool {
-        if self.kind != ty::AssocKind::Const {
+        if !matches!(self.kind, ty::AssocKind::Const { .. }) {
             return false;
         }
 
@@ -129,25 +165,34 @@ impl AssocItem {
 }
 
 #[derive(Copy, Clone, PartialEq, Debug, HashStable, Eq, Hash, Encodable, Decodable)]
+pub enum AssocTypeData {
+    Normal(Symbol),
+    /// The associated type comes from an RPITIT. It has no name, and the
+    /// `ImplTraitInTraitData` provides additional information about its
+    /// source.
+    Rpitit(ty::ImplTraitInTraitData),
+}
+
+#[derive(Copy, Clone, PartialEq, Debug, HashStable, Eq, Hash, Encodable, Decodable)]
 pub enum AssocKind {
-    Const,
-    Fn,
-    Type,
+    Const { name: Symbol },
+    Fn { name: Symbol, has_self: bool },
+    Type { data: AssocTypeData },
 }
 
 impl AssocKind {
     pub fn namespace(&self) -> Namespace {
         match *self {
-            ty::AssocKind::Type => Namespace::TypeNS,
-            ty::AssocKind::Const | ty::AssocKind::Fn => Namespace::ValueNS,
+            ty::AssocKind::Type { .. } => Namespace::TypeNS,
+            ty::AssocKind::Const { .. } | ty::AssocKind::Fn { .. } => Namespace::ValueNS,
         }
     }
 
     pub fn as_def_kind(&self) -> DefKind {
         match self {
-            AssocKind::Const => DefKind::AssocConst,
-            AssocKind::Fn => DefKind::AssocFn,
-            AssocKind::Type => DefKind::AssocTy,
+            AssocKind::Const { .. } => DefKind::AssocConst,
+            AssocKind::Fn { .. } => DefKind::AssocFn,
+            AssocKind::Type { .. } => DefKind::AssocTy,
         }
     }
 }
@@ -155,13 +200,22 @@ impl AssocKind {
 impl std::fmt::Display for AssocKind {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            AssocKind::Fn => write!(f, "method"),
-            AssocKind::Const => write!(f, "associated const"),
-            AssocKind::Type => write!(f, "associated type"),
+            AssocKind::Fn { has_self: true, .. } => write!(f, "method"),
+            AssocKind::Fn { has_self: false, .. } => write!(f, "associated function"),
+            AssocKind::Const { .. } => write!(f, "associated const"),
+            AssocKind::Type { .. } => write!(f, "associated type"),
         }
     }
 }
 
+// Like `AssocKind`, but just the tag, no fields. Used in various kinds of matching.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum AssocTag {
+    Const,
+    Fn,
+    Type,
+}
+
 /// A list of `ty::AssocItem`s in definition order that allows for efficient lookup by name.
 ///
 /// When doing lookup by name, we try to postpone hygienic comparison for as long as possible since
@@ -169,17 +223,17 @@ impl std::fmt::Display for AssocKind {
 /// done only on items with the same name.
 #[derive(Debug, Clone, PartialEq, HashStable)]
 pub struct AssocItems {
-    items: SortedIndexMultiMap<u32, Symbol, ty::AssocItem>,
+    items: SortedIndexMultiMap<u32, Option<Symbol>, ty::AssocItem>,
 }
 
 impl AssocItems {
     /// Constructs an `AssociatedItems` map from a series of `ty::AssocItem`s in definition order.
     pub fn new(items_in_def_order: impl IntoIterator<Item = ty::AssocItem>) -> Self {
-        let items = items_in_def_order.into_iter().map(|item| (item.name, item)).collect();
+        let items = items_in_def_order.into_iter().map(|item| (item.opt_name(), item)).collect();
         AssocItems { items }
     }
 
-    /// Returns a slice of associated items in the order they were defined.
+    /// Returns an iterator over associated items in the order they were defined.
     ///
     /// New code should avoid relying on definition order. If you need a particular associated item
     /// for a known trait, make that trait a lang item instead of indexing this array.
@@ -196,36 +250,27 @@ impl AssocItems {
         &self,
         name: Symbol,
     ) -> impl '_ + Iterator<Item = &ty::AssocItem> {
-        self.items.get_by_key(name)
+        assert!(!name.is_empty());
+        self.items.get_by_key(Some(name))
     }
 
-    /// Returns the associated item with the given name and `AssocKind`, if one exists.
-    pub fn find_by_name_and_kind(
+    /// Returns the associated item with the given identifier and `AssocKind`, if one exists.
+    /// The identifier is matched hygienically.
+    pub fn find_by_ident_and_kind(
         &self,
         tcx: TyCtxt<'_>,
         ident: Ident,
-        kind: AssocKind,
+        assoc_tag: AssocTag,
         parent_def_id: DefId,
     ) -> Option<&ty::AssocItem> {
         self.filter_by_name_unhygienic(ident.name)
-            .filter(|item| item.kind == kind)
+            .filter(|item| item.as_tag() == assoc_tag)
             .find(|item| tcx.hygienic_eq(ident, item.ident(tcx), parent_def_id))
     }
 
-    /// Returns the associated item with the given name and any of `AssocKind`, if one exists.
-    pub fn find_by_name_and_kinds(
-        &self,
-        tcx: TyCtxt<'_>,
-        ident: Ident,
-        // Sorted in order of what kinds to look at
-        kinds: &[AssocKind],
-        parent_def_id: DefId,
-    ) -> Option<&ty::AssocItem> {
-        kinds.iter().find_map(|kind| self.find_by_name_and_kind(tcx, ident, *kind, parent_def_id))
-    }
-
-    /// Returns the associated item with the given name in the given `Namespace`, if one exists.
-    pub fn find_by_name_and_namespace(
+    /// Returns the associated item with the given identifier in the given `Namespace`, if one
+    /// exists. The identifier is matched hygienically.
+    pub fn find_by_ident_and_namespace(
         &self,
         tcx: TyCtxt<'_>,
         ident: Ident,
@@ -233,7 +278,7 @@ impl AssocItems {
         parent_def_id: DefId,
     ) -> Option<&ty::AssocItem> {
         self.filter_by_name_unhygienic(ident.name)
-            .filter(|item| item.kind.namespace() == ns)
+            .filter(|item| item.namespace() == ns)
             .find(|item| tcx.hygienic_eq(ident, item.ident(tcx), parent_def_id))
     }
 }
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 74b34afe616..23927c112bc 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -501,7 +501,7 @@ impl_decodable_via_ref! {
     &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
     &'tcx traits::ImplSource<'tcx, ()>,
     &'tcx mir::Body<'tcx>,
-    &'tcx mir::BorrowCheckResult<'tcx>,
+    &'tcx mir::ConcreteOpaqueTypes<'tcx>,
     &'tcx ty::List<ty::BoundVariableKind>,
     &'tcx ty::ListWithCachedTypeInfo<ty::Clause<'tcx>>,
     &'tcx ty::List<FieldIdx>,
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index ae1c6c670cb..dc5fe2d8f8b 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -3,6 +3,7 @@ use std::borrow::Cow;
 use rustc_data_structures::intern::Interned;
 use rustc_error_messages::MultiSpan;
 use rustc_macros::HashStable;
+use rustc_type_ir::walk::TypeWalker;
 use rustc_type_ir::{self as ir, TypeFlags, WithCachedTypeInfo};
 
 use crate::ty::{self, Ty, TyCtxt};
@@ -243,4 +244,18 @@ impl<'tcx> Const<'tcx> {
     pub fn is_ct_infer(self) -> bool {
         matches!(self.kind(), ty::ConstKind::Infer(_))
     }
+
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<TyCtxt<'tcx>> {
+        TypeWalker::new(self.into())
+    }
 }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 162ca1f4af8..fa2f1cf1a1c 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -437,6 +437,10 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         )
     }
 
+    fn impl_self_is_guaranteed_unsized(self, impl_def_id: DefId) -> bool {
+        self.impl_self_is_guaranteed_unsized(impl_def_id)
+    }
+
     fn has_target_features(self, def_id: DefId) -> bool {
         !self.codegen_fn_attrs(def_id).target_features.is_empty()
     }
@@ -460,7 +464,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     fn associated_type_def_ids(self, def_id: DefId) -> impl IntoIterator<Item = DefId> {
         self.associated_items(def_id)
             .in_definition_order()
-            .filter(|assoc_item| matches!(assoc_item.kind, ty::AssocKind::Type))
+            .filter(|assoc_item| assoc_item.is_type())
             .map(|assoc_item| assoc_item.def_id)
     }
 
@@ -866,7 +870,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         Ty(Interned::new_unchecked(
             self.type_
                 .intern(kind, |kind| {
-                    let flags = super::flags::FlagComputation::for_kind(&kind);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_kind(&kind);
                     let stable_hash = self.stable_hash(&flags, sess, untracked, &kind);
 
                     InternedInSet(self.arena.alloc(WithCachedTypeInfo {
@@ -892,7 +896,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         Const(Interned::new_unchecked(
             self.const_
                 .intern(kind, |kind: ty::ConstKind<'_>| {
-                    let flags = super::flags::FlagComputation::for_const_kind(&kind);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_const_kind(&kind);
                     let stable_hash = self.stable_hash(&flags, sess, untracked, &kind);
 
                     InternedInSet(self.arena.alloc(WithCachedTypeInfo {
@@ -908,7 +912,7 @@ impl<'tcx> CtxtInterners<'tcx> {
 
     fn stable_hash<'a, T: HashStable<StableHashingContext<'a>>>(
         &self,
-        flags: &ty::flags::FlagComputation,
+        flags: &ty::FlagComputation<TyCtxt<'tcx>>,
         sess: &'a Session,
         untracked: &'a Untracked,
         val: &T,
@@ -936,7 +940,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         Predicate(Interned::new_unchecked(
             self.predicate
                 .intern(kind, |kind| {
-                    let flags = super::flags::FlagComputation::for_predicate(kind);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_predicate(kind);
 
                     let stable_hash = self.stable_hash(&flags, sess, untracked, &kind);
 
@@ -957,7 +961,7 @@ impl<'tcx> CtxtInterners<'tcx> {
         } else {
             self.clauses
                 .intern_ref(clauses, || {
-                    let flags = super::flags::FlagComputation::for_clauses(clauses);
+                    let flags = ty::FlagComputation::<TyCtxt<'tcx>>::for_clauses(clauses);
 
                     InternedInSet(ListWithCachedTypeInfo::from_arena(
                         &*self.arena,
@@ -2143,7 +2147,7 @@ impl<'tcx> TyCtxt<'tcx> {
             return vec![];
         };
 
-        let mut v = TraitObjectVisitor(vec![], self.hir());
+        let mut v = TraitObjectVisitor(vec![]);
         v.visit_ty_unambig(hir_output);
         v.0
     }
@@ -2156,7 +2160,7 @@ impl<'tcx> TyCtxt<'tcx> {
         scope_def_id: LocalDefId,
     ) -> Option<(Vec<&'tcx hir::Ty<'tcx>>, Span, Option<Span>)> {
         let hir_id = self.local_def_id_to_hir_id(scope_def_id);
-        let mut v = TraitObjectVisitor(vec![], self.hir());
+        let mut v = TraitObjectVisitor(vec![]);
         // when the return type is a type alias
         if let Some(hir::FnDecl { output: hir::FnRetTy::Return(hir_output), .. }) = self.hir_fn_decl_by_hir_id(hir_id)
             && let hir::TyKind::Path(hir::QPath::Resolved(
diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
index d3abb3d64b8..fbb57b8df6b 100644
--- a/compiler/rustc_middle/src/ty/diagnostics.rs
+++ b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -571,15 +571,15 @@ pub fn suggest_constraining_type_params<'a>(
 }
 
 /// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
-pub struct TraitObjectVisitor<'tcx>(pub Vec<&'tcx hir::Ty<'tcx>>, pub crate::hir::map::Map<'tcx>);
+pub(crate) struct TraitObjectVisitor<'tcx>(pub(crate) Vec<&'tcx hir::Ty<'tcx>>);
 
 impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
     fn visit_ty(&mut self, ty: &'v hir::Ty<'v, AmbigArg>) {
         match ty.kind {
             hir::TyKind::TraitObject(_, tagged_ptr)
                 if let hir::Lifetime {
-                    res:
-                        hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static,
+                    kind:
+                        hir::LifetimeKind::ImplicitObjectLifetimeDefault | hir::LifetimeKind::Static,
                     ..
                 } = tagged_ptr.pointer() =>
             {
@@ -592,18 +592,6 @@ impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
     }
 }
 
-/// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
-pub struct StaticLifetimeVisitor<'tcx>(pub Vec<Span>, pub crate::hir::map::Map<'tcx>);
-
-impl<'v> hir::intravisit::Visitor<'v> for StaticLifetimeVisitor<'v> {
-    fn visit_lifetime(&mut self, lt: &'v hir::Lifetime) {
-        if let hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static = lt.res
-        {
-            self.0.push(lt.ident.span);
-        }
-    }
-}
-
 pub struct IsSuggestableVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
     infer_suggestable: bool,
diff --git a/compiler/rustc_middle/src/ty/erase_regions.rs b/compiler/rustc_middle/src/ty/erase_regions.rs
index 8bddb5c0fd7..45a0b1288db 100644
--- a/compiler/rustc_middle/src/ty/erase_regions.rs
+++ b/compiler/rustc_middle/src/ty/erase_regions.rs
@@ -65,7 +65,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for RegionEraserVisitor<'tcx> {
         // We must not erase bound regions. `for<'a> fn(&'a ())` and
         // `fn(&'free ())` are different types: they may implement different
         // traits and have a different `TypeId`.
-        match *r {
+        match r.kind() {
             ty::ReBound(..) => r,
             _ => self.tcx.lifetimes.re_erased,
         }
diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index a0e67929c52..5ecf1174def 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/compiler/rustc_middle/src/ty/error.rs
@@ -279,7 +279,7 @@ impl<'tcx> TyCtxt<'tcx> {
         p.hash(&mut s);
         let hash = s.finish();
         *path = Some(path.take().unwrap_or_else(|| {
-            self.output_filenames(()).temp_path_ext(&format!("long-type-{hash}.txt"), None)
+            self.output_filenames(()).temp_path_for_diagnostic(&format!("long-type-{hash}.txt"))
         }));
         let Ok(mut file) =
             File::options().create(true).read(true).append(true).open(&path.as_ref().unwrap())
diff --git a/compiler/rustc_middle/src/ty/flags.rs b/compiler/rustc_middle/src/ty/flags.rs
deleted file mode 100644
index b0c442d28f0..00000000000
--- a/compiler/rustc_middle/src/ty/flags.rs
+++ /dev/null
@@ -1,359 +0,0 @@
-use std::slice;
-
-use crate::ty::{self, GenericArg, GenericArgKind, InferConst, Ty, TypeFlags};
-
-#[derive(Debug)]
-pub struct FlagComputation {
-    pub flags: TypeFlags,
-
-    /// see `Ty::outer_exclusive_binder` for details
-    pub outer_exclusive_binder: ty::DebruijnIndex,
-}
-
-impl FlagComputation {
-    fn new() -> FlagComputation {
-        FlagComputation { flags: TypeFlags::empty(), outer_exclusive_binder: ty::INNERMOST }
-    }
-
-    #[allow(rustc::usage_of_ty_tykind)]
-    pub fn for_kind(kind: &ty::TyKind<'_>) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        result.add_kind(kind);
-        result
-    }
-
-    pub fn for_predicate(binder: ty::Binder<'_, ty::PredicateKind<'_>>) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        result.add_predicate(binder);
-        result
-    }
-
-    pub fn for_const_kind(kind: &ty::ConstKind<'_>) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        result.add_const_kind(kind);
-        result
-    }
-
-    pub fn for_clauses(clauses: &[ty::Clause<'_>]) -> FlagComputation {
-        let mut result = FlagComputation::new();
-        for c in clauses {
-            result.add_flags(c.as_predicate().flags());
-            result.add_exclusive_binder(c.as_predicate().outer_exclusive_binder());
-        }
-        result
-    }
-
-    fn add_flags(&mut self, flags: TypeFlags) {
-        self.flags = self.flags | flags;
-    }
-
-    /// indicates that `self` refers to something at binding level `binder`
-    fn add_bound_var(&mut self, binder: ty::DebruijnIndex) {
-        let exclusive_binder = binder.shifted_in(1);
-        self.add_exclusive_binder(exclusive_binder);
-    }
-
-    /// indicates that `self` refers to something *inside* binding
-    /// level `binder` -- not bound by `binder`, but bound by the next
-    /// binder internal to it
-    fn add_exclusive_binder(&mut self, exclusive_binder: ty::DebruijnIndex) {
-        self.outer_exclusive_binder = self.outer_exclusive_binder.max(exclusive_binder);
-    }
-
-    /// Adds the flags/depth from a set of types that appear within the current type, but within a
-    /// region binder.
-    fn bound_computation<T, F>(&mut self, value: ty::Binder<'_, T>, f: F)
-    where
-        F: FnOnce(&mut Self, T),
-    {
-        let mut computation = FlagComputation::new();
-
-        if !value.bound_vars().is_empty() {
-            computation.add_flags(TypeFlags::HAS_BINDER_VARS);
-        }
-
-        f(&mut computation, value.skip_binder());
-
-        self.add_flags(computation.flags);
-
-        // The types that contributed to `computation` occurred within
-        // a region binder, so subtract one from the region depth
-        // within when adding the depth to `self`.
-        let outer_exclusive_binder = computation.outer_exclusive_binder;
-        if outer_exclusive_binder > ty::INNERMOST {
-            self.add_exclusive_binder(outer_exclusive_binder.shifted_out(1));
-        } // otherwise, this binder captures nothing
-    }
-
-    #[allow(rustc::usage_of_ty_tykind)]
-    fn add_kind(&mut self, kind: &ty::TyKind<'_>) {
-        match kind {
-            &ty::Bool
-            | &ty::Char
-            | &ty::Int(_)
-            | &ty::Float(_)
-            | &ty::Uint(_)
-            | &ty::Never
-            | &ty::Str
-            | &ty::Foreign(..) => {}
-
-            &ty::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
-
-            &ty::Param(_) => {
-                self.add_flags(TypeFlags::HAS_TY_PARAM);
-            }
-
-            &ty::Closure(_, args)
-            | &ty::Coroutine(_, args)
-            | &ty::CoroutineClosure(_, args)
-            | &ty::CoroutineWitness(_, args) => {
-                self.add_args(args);
-            }
-
-            &ty::Bound(debruijn, _) => {
-                self.add_bound_var(debruijn);
-                self.add_flags(TypeFlags::HAS_TY_BOUND);
-            }
-
-            &ty::Placeholder(..) => {
-                self.add_flags(TypeFlags::HAS_TY_PLACEHOLDER);
-            }
-
-            &ty::Infer(infer) => match infer {
-                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
-                    self.add_flags(TypeFlags::HAS_TY_FRESH)
-                }
-
-                ty::TyVar(_) | ty::IntVar(_) | ty::FloatVar(_) => {
-                    self.add_flags(TypeFlags::HAS_TY_INFER)
-                }
-            },
-
-            &ty::Adt(_, args) => {
-                self.add_args(args);
-            }
-
-            &ty::Alias(kind, data) => {
-                self.add_flags(match kind {
-                    ty::Projection => TypeFlags::HAS_TY_PROJECTION,
-                    ty::Weak => TypeFlags::HAS_TY_WEAK,
-                    ty::Opaque => TypeFlags::HAS_TY_OPAQUE,
-                    ty::Inherent => TypeFlags::HAS_TY_INHERENT,
-                });
-
-                self.add_alias_ty(data);
-            }
-
-            &ty::Dynamic(obj, r, _) => {
-                for predicate in obj.iter() {
-                    self.bound_computation(predicate, |computation, predicate| match predicate {
-                        ty::ExistentialPredicate::Trait(tr) => computation.add_args(tr.args),
-                        ty::ExistentialPredicate::Projection(p) => {
-                            computation.add_existential_projection(&p);
-                        }
-                        ty::ExistentialPredicate::AutoTrait(_) => {}
-                    });
-                }
-
-                self.add_region(r);
-            }
-
-            &ty::Array(tt, len) => {
-                self.add_ty(tt);
-                self.add_const(len);
-            }
-
-            &ty::Pat(ty, pat) => {
-                self.add_ty(ty);
-                match *pat {
-                    ty::PatternKind::Range { start, end } => {
-                        self.add_const(start);
-                        self.add_const(end);
-                    }
-                }
-            }
-
-            &ty::Slice(tt) => self.add_ty(tt),
-
-            &ty::RawPtr(ty, _) => {
-                self.add_ty(ty);
-            }
-
-            &ty::Ref(r, ty, _) => {
-                self.add_region(r);
-                self.add_ty(ty);
-            }
-
-            &ty::Tuple(types) => {
-                self.add_tys(types);
-            }
-
-            &ty::FnDef(_, args) => {
-                self.add_args(args);
-            }
-
-            &ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
-                computation.add_tys(sig_tys.inputs_and_output);
-            }),
-
-            &ty::UnsafeBinder(bound_ty) => {
-                self.bound_computation(bound_ty.into(), |computation, ty| {
-                    computation.add_ty(ty);
-                })
-            }
-        }
-    }
-
-    fn add_predicate(&mut self, binder: ty::Binder<'_, ty::PredicateKind<'_>>) {
-        self.bound_computation(binder, |computation, atom| computation.add_predicate_atom(atom));
-    }
-
-    fn add_predicate_atom(&mut self, atom: ty::PredicateKind<'_>) {
-        match atom {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) => {
-                self.add_args(trait_pred.trait_ref.args);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(ty::HostEffectPredicate {
-                trait_ref,
-                constness: _,
-            })) => {
-                self.add_args(trait_ref.args);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
-                a,
-                b,
-            ))) => {
-                self.add_region(a);
-                self.add_region(b);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
-                ty,
-                region,
-            ))) => {
-                self.add_ty(ty);
-                self.add_region(region);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
-                self.add_const(ct);
-                self.add_ty(ty);
-            }
-            ty::PredicateKind::Subtype(ty::SubtypePredicate { a_is_expected: _, a, b }) => {
-                self.add_ty(a);
-                self.add_ty(b);
-            }
-            ty::PredicateKind::Coerce(ty::CoercePredicate { a, b }) => {
-                self.add_ty(a);
-                self.add_ty(b);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(ty::ProjectionPredicate {
-                projection_term,
-                term,
-            })) => {
-                self.add_alias_term(projection_term);
-                self.add_term(term);
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
-                self.add_args(slice::from_ref(&arg));
-            }
-            ty::PredicateKind::DynCompatible(_def_id) => {}
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
-                self.add_const(uv);
-            }
-            ty::PredicateKind::ConstEquate(expected, found) => {
-                self.add_const(expected);
-                self.add_const(found);
-            }
-            ty::PredicateKind::Ambiguous => {}
-            ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term }) => {
-                self.add_alias_term(alias);
-                self.add_term(term);
-            }
-            ty::PredicateKind::AliasRelate(t1, t2, _) => {
-                self.add_term(t1);
-                self.add_term(t2);
-            }
-        }
-    }
-
-    fn add_ty(&mut self, ty: Ty<'_>) {
-        self.add_flags(ty.flags());
-        self.add_exclusive_binder(ty.outer_exclusive_binder());
-    }
-
-    fn add_tys(&mut self, tys: &[Ty<'_>]) {
-        for &ty in tys {
-            self.add_ty(ty);
-        }
-    }
-
-    fn add_region(&mut self, r: ty::Region<'_>) {
-        self.add_flags(r.type_flags());
-        if let ty::ReBound(debruijn, _) = *r {
-            self.add_bound_var(debruijn);
-        }
-    }
-
-    fn add_const(&mut self, c: ty::Const<'_>) {
-        self.add_flags(c.flags());
-        self.add_exclusive_binder(c.outer_exclusive_binder());
-    }
-
-    fn add_const_kind(&mut self, c: &ty::ConstKind<'_>) {
-        match *c {
-            ty::ConstKind::Unevaluated(uv) => {
-                self.add_args(uv.args);
-                self.add_flags(TypeFlags::HAS_CT_PROJECTION);
-            }
-            ty::ConstKind::Infer(infer) => match infer {
-                InferConst::Fresh(_) => self.add_flags(TypeFlags::HAS_CT_FRESH),
-                InferConst::Var(_) => self.add_flags(TypeFlags::HAS_CT_INFER),
-            },
-            ty::ConstKind::Bound(debruijn, _) => {
-                self.add_bound_var(debruijn);
-                self.add_flags(TypeFlags::HAS_CT_BOUND);
-            }
-            ty::ConstKind::Param(_) => {
-                self.add_flags(TypeFlags::HAS_CT_PARAM);
-            }
-            ty::ConstKind::Placeholder(_) => {
-                self.add_flags(TypeFlags::HAS_CT_PLACEHOLDER);
-            }
-            ty::ConstKind::Value(cv) => self.add_ty(cv.ty),
-            ty::ConstKind::Expr(e) => self.add_args(e.args()),
-            ty::ConstKind::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
-        }
-    }
-
-    fn add_existential_projection(&mut self, projection: &ty::ExistentialProjection<'_>) {
-        self.add_args(projection.args);
-        match projection.term.unpack() {
-            ty::TermKind::Ty(ty) => self.add_ty(ty),
-            ty::TermKind::Const(ct) => self.add_const(ct),
-        }
-    }
-
-    fn add_alias_ty(&mut self, alias_ty: ty::AliasTy<'_>) {
-        self.add_args(alias_ty.args);
-    }
-
-    fn add_alias_term(&mut self, alias_term: ty::AliasTerm<'_>) {
-        self.add_args(alias_term.args);
-    }
-
-    fn add_args(&mut self, args: &[GenericArg<'_>]) {
-        for kind in args {
-            match kind.unpack() {
-                GenericArgKind::Type(ty) => self.add_ty(ty),
-                GenericArgKind::Lifetime(lt) => self.add_region(lt),
-                GenericArgKind::Const(ct) => self.add_const(ct),
-            }
-        }
-    }
-
-    fn add_term(&mut self, term: ty::Term<'_>) {
-        match term.unpack() {
-            ty::TermKind::Ty(ty) => self.add_ty(ty),
-            ty::TermKind::Const(ct) => self.add_const(ct),
-        }
-    }
-}
diff --git a/compiler/rustc_middle/src/ty/fold.rs b/compiler/rustc_middle/src/ty/fold.rs
index dc2c9e3d9f1..8d6871d2f1f 100644
--- a/compiler/rustc_middle/src/ty/fold.rs
+++ b/compiler/rustc_middle/src/ty/fold.rs
@@ -145,10 +145,10 @@ where
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             ty::ReBound(debruijn, br) if debruijn == self.current_index => {
                 let region = self.delegate.replace_region(br);
-                if let ty::ReBound(debruijn1, br) = *region {
+                if let ty::ReBound(debruijn1, br) = region.kind() {
                     // If the callback returns a bound region,
                     // that region should always use the INNERMOST
                     // debruijn index. Then we adjust it to the
@@ -278,7 +278,7 @@ impl<'tcx> TyCtxt<'tcx> {
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        let shift_bv = |bv: ty::BoundVar| ty::BoundVar::from_usize(bv.as_usize() + bound_vars);
+        let shift_bv = |bv: ty::BoundVar| bv + bound_vars;
         self.replace_escaping_bound_vars_uncached(
             value,
             FnMutDelegate {
diff --git a/compiler/rustc_middle/src/ty/generic_args.rs b/compiler/rustc_middle/src/ty/generic_args.rs
index 9c1ff134f0f..8de64b3bfac 100644
--- a/compiler/rustc_middle/src/ty/generic_args.rs
+++ b/compiler/rustc_middle/src/ty/generic_args.rs
@@ -11,12 +11,13 @@ use rustc_hir::def_id::DefId;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, extension};
 use rustc_serialize::{Decodable, Encodable};
 use rustc_type_ir::WithCachedTypeInfo;
+use rustc_type_ir::walk::TypeWalker;
 use smallvec::SmallVec;
 
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::{
     self, ClosureArgs, CoroutineArgs, CoroutineClosureArgs, FallibleTypeFolder, InlineConstArgs,
-    Lift, List, Ty, TyCtxt, TypeFoldable, TypeVisitable, TypeVisitor, VisitorResult,
+    Lift, List, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor, VisitorResult,
     walk_visitable_list,
 };
 
@@ -297,6 +298,20 @@ impl<'tcx> GenericArg<'tcx> {
             GenericArgKind::Const(ct) => ct.is_ct_infer(),
         }
     }
+
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<TyCtxt<'tcx>> {
+        TypeWalker::new(self)
+    }
 }
 
 impl<'a, 'tcx> Lift<TyCtxt<'tcx>> for GenericArg<'a> {
@@ -322,6 +337,14 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for GenericArg<'tcx> {
             GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
         }
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        match self.unpack() {
+            GenericArgKind::Lifetime(lt) => lt.fold_with(folder).into(),
+            GenericArgKind::Type(ty) => ty.fold_with(folder).into(),
+            GenericArgKind::Const(ct) => ct.fold_with(folder).into(),
+        }
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for GenericArg<'tcx> {
@@ -591,6 +614,27 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for GenericArgsRef<'tcx> {
                 }
             }
             0 => Ok(self),
+            _ => ty::util::try_fold_list(self, folder, |tcx, v| tcx.mk_args(v)),
+        }
+    }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        // See justification for this behavior in `try_fold_with`.
+        match self.len() {
+            1 => {
+                let param0 = self[0].fold_with(folder);
+                if param0 == self[0] { self } else { folder.cx().mk_args(&[param0]) }
+            }
+            2 => {
+                let param0 = self[0].fold_with(folder);
+                let param1 = self[1].fold_with(folder);
+                if param0 == self[0] && param1 == self[1] {
+                    self
+                } else {
+                    folder.cx().mk_args(&[param0, param1])
+                }
+            }
+            0 => self,
             _ => ty::util::fold_list(self, folder, |tcx, v| tcx.mk_args(v)),
         }
     }
@@ -626,6 +670,22 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<Ty<'tcx>> {
                     Ok(folder.cx().mk_type_list(&[param0, param1]))
                 }
             }
+            _ => ty::util::try_fold_list(self, folder, |tcx, v| tcx.mk_type_list(v)),
+        }
+    }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        // See comment justifying behavior in `try_fold_with`.
+        match self.len() {
+            2 => {
+                let param0 = self[0].fold_with(folder);
+                let param1 = self[1].fold_with(folder);
+                if param0 == self[0] && param1 == self[1] {
+                    self
+                } else {
+                    folder.cx().mk_type_list(&[param0, param1])
+                }
+            }
             _ => ty::util::fold_list(self, folder, |tcx, v| tcx.mk_type_list(v)),
         }
     }
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index 55ebd15248c..faad0a82acb 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -71,7 +71,7 @@ pub enum InstanceKind<'tcx> {
     /// - coroutines
     Item(DefId),
 
-    /// An intrinsic `fn` item (with `"rust-intrinsic"` ABI).
+    /// An intrinsic `fn` item (with`#[rustc_instrinsic]`).
     ///
     /// Alongside `Virtual`, this is the only `InstanceKind` that does not have its own callable MIR.
     /// Instead, codegen and const eval "magically" evaluate calls to intrinsics purely in the
@@ -746,7 +746,7 @@ impl<'tcx> Instance<'tcx> {
         let call_once = tcx
             .associated_items(fn_once)
             .in_definition_order()
-            .find(|it| it.kind == ty::AssocKind::Fn)
+            .find(|it| it.is_fn())
             .unwrap()
             .def_id;
         let track_caller =
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index ebb6a8c08a5..7ebfebea44e 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -1265,9 +1265,7 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: ExternAbi)
         | CCmseNonSecureCall
         | CCmseNonSecureEntry
         | Unadjusted => false,
-        Rust | RustCall | RustCold | RustIntrinsic => {
-            tcx.sess.panic_strategy() == PanicStrategy::Unwind
-        }
+        Rust | RustCall | RustCold => tcx.sess.panic_strategy() == PanicStrategy::Unwind,
     }
 }
 
diff --git a/compiler/rustc_middle/src/ty/list.rs b/compiler/rustc_middle/src/ty/list.rs
index 0fd370a5619..0cf5820959e 100644
--- a/compiler/rustc_middle/src/ty/list.rs
+++ b/compiler/rustc_middle/src/ty/list.rs
@@ -7,9 +7,9 @@ use std::{fmt, iter, mem, ptr, slice};
 use rustc_data_structures::aligned::{Aligned, align_of};
 use rustc_data_structures::sync::DynSync;
 use rustc_serialize::{Encodable, Encoder};
+use rustc_type_ir::FlagComputation;
 
-use super::flags::FlagComputation;
-use super::{DebruijnIndex, TypeFlags};
+use super::{DebruijnIndex, TyCtxt, TypeFlags};
 use crate::arena::Arena;
 
 /// `List<T>` is a bit like `&[T]`, but with some critical differences.
@@ -299,8 +299,8 @@ impl TypeInfo {
     }
 }
 
-impl From<FlagComputation> for TypeInfo {
-    fn from(computation: FlagComputation) -> TypeInfo {
+impl<'tcx> From<FlagComputation<TyCtxt<'tcx>>> for TypeInfo {
+    fn from(computation: FlagComputation<TyCtxt<'tcx>>) -> TypeInfo {
         TypeInfo {
             flags: computation.flags,
             outer_exclusive_binder: computation.outer_exclusive_binder,
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 80f1bd7c6f4..3698cfb9870 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -117,7 +117,6 @@ pub mod cast;
 pub mod codec;
 pub mod error;
 pub mod fast_reject;
-pub mod flags;
 pub mod inhabitedness;
 pub mod layout;
 pub mod normalize_erasing_regions;
@@ -128,7 +127,6 @@ pub mod significant_drop_order;
 pub mod trait_def;
 pub mod util;
 pub mod vtable;
-pub mod walk;
 
 mod adt;
 mod assoc;
@@ -539,6 +537,13 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Term<'tcx> {
             ty::TermKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
         }
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        match self.unpack() {
+            ty::TermKind::Ty(ty) => ty.fold_with(folder).into(),
+            ty::TermKind::Const(ct) => ct.fold_with(folder).into(),
+        }
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Term<'tcx> {
@@ -1464,7 +1469,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn provided_trait_methods(self, id: DefId) -> impl 'tcx + Iterator<Item = &'tcx AssocItem> {
         self.associated_items(id)
             .in_definition_order()
-            .filter(move |item| item.kind == AssocKind::Fn && item.defaultness(self).has_value())
+            .filter(move |item| item.is_fn() && item.defaultness(self).has_value())
     }
 
     pub fn repr_options_of_def(self, did: LocalDefId) -> ReprOptions {
@@ -1610,8 +1615,11 @@ impl<'tcx> TyCtxt<'tcx> {
     /// return-position `impl Trait` from a trait, then provide the source info
     /// about where that RPITIT came from.
     pub fn opt_rpitit_info(self, def_id: DefId) -> Option<ImplTraitInTraitData> {
-        if let DefKind::AssocTy = self.def_kind(def_id) {
-            self.associated_item(def_id).opt_rpitit_info
+        if let DefKind::AssocTy = self.def_kind(def_id)
+            && let AssocKind::Type { data: AssocTypeData::Rpitit(rpitit_info) } =
+                self.associated_item(def_id).kind
+        {
+            Some(rpitit_info)
         } else {
             None
         }
@@ -1939,15 +1947,15 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Hygienically compares a use-site name (`use_name`) for a field or an associated item with
     /// its supposed definition name (`def_name`). The method also needs `DefId` of the supposed
     /// definition's parent/scope to perform comparison.
-    pub fn hygienic_eq(self, use_name: Ident, def_name: Ident, def_parent_def_id: DefId) -> bool {
-        // We could use `Ident::eq` here, but we deliberately don't. The name
+    pub fn hygienic_eq(self, use_ident: Ident, def_ident: Ident, def_parent_def_id: DefId) -> bool {
+        // We could use `Ident::eq` here, but we deliberately don't. The identifier
         // comparison fails frequently, and we want to avoid the expensive
         // `normalize_to_macros_2_0()` calls required for the span comparison whenever possible.
-        use_name.name == def_name.name
-            && use_name
+        use_ident.name == def_ident.name
+            && use_ident
                 .span
                 .ctxt()
-                .hygienic_eq(def_name.span.ctxt(), self.expn_that_defined(def_parent_def_id))
+                .hygienic_eq(def_ident.span.ctxt(), self.expn_that_defined(def_parent_def_id))
     }
 
     pub fn adjust_ident(self, mut ident: Ident, scope: DefId) -> Ident {
diff --git a/compiler/rustc_middle/src/ty/opaque_types.rs b/compiler/rustc_middle/src/ty/opaque_types.rs
index c72efde0994..9445a18ad76 100644
--- a/compiler/rustc_middle/src/ty/opaque_types.rs
+++ b/compiler/rustc_middle/src/ty/opaque_types.rs
@@ -95,7 +95,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReverseMapper<'tcx> {
 
     #[instrument(skip(self), level = "debug")]
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             // Ignore bound regions and `'static` regions that appear in the
             // type, we only need to remap regions that reference lifetimes
             // from the function declaration.
diff --git a/compiler/rustc_middle/src/ty/parameterized.rs b/compiler/rustc_middle/src/ty/parameterized.rs
index b56e0862692..ecd6132b3ef 100644
--- a/compiler/rustc_middle/src/ty/parameterized.rs
+++ b/compiler/rustc_middle/src/ty/parameterized.rs
@@ -113,7 +113,7 @@ trivially_parameterized_over_tcx! {
     rustc_span::Span,
     rustc_span::Symbol,
     rustc_span::def_id::DefPathHash,
-    rustc_span::hygiene::SyntaxContextDataNonRecursive,
+    rustc_span::hygiene::SyntaxContextKey,
     rustc_span::Ident,
     rustc_type_ir::Variance,
     rustc_hir::Attribute,
diff --git a/compiler/rustc_middle/src/ty/pattern.rs b/compiler/rustc_middle/src/ty/pattern.rs
index 4cad1ab2099..758adc42e3e 100644
--- a/compiler/rustc_middle/src/ty/pattern.rs
+++ b/compiler/rustc_middle/src/ty/pattern.rs
@@ -1,14 +1,40 @@
 use std::fmt;
 
 use rustc_data_structures::intern::Interned;
-use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
+use rustc_macros::HashStable;
+use rustc_type_ir::ir_print::IrPrint;
+use rustc_type_ir::{
+    FlagComputation, Flags, {self as ir},
+};
 
+use super::TyCtxt;
 use crate::ty;
 
+pub type PatternKind<'tcx> = ir::PatternKind<TyCtxt<'tcx>>;
+
 #[derive(Copy, Clone, PartialEq, Eq, Hash, HashStable)]
 #[rustc_pass_by_value]
 pub struct Pattern<'tcx>(pub Interned<'tcx, PatternKind<'tcx>>);
 
+impl<'tcx> Flags for Pattern<'tcx> {
+    fn flags(&self) -> rustc_type_ir::TypeFlags {
+        match &**self {
+            ty::PatternKind::Range { start, end } => {
+                FlagComputation::for_const_kind(&start.kind()).flags
+                    | FlagComputation::for_const_kind(&end.kind()).flags
+            }
+        }
+    }
+
+    fn outer_exclusive_binder(&self) -> rustc_type_ir::DebruijnIndex {
+        match &**self {
+            ty::PatternKind::Range { start, end } => {
+                start.outer_exclusive_binder().max(end.outer_exclusive_binder())
+            }
+        }
+    }
+}
+
 impl<'tcx> std::ops::Deref for Pattern<'tcx> {
     type Target = PatternKind<'tcx>;
 
@@ -23,9 +49,9 @@ impl<'tcx> fmt::Debug for Pattern<'tcx> {
     }
 }
 
-impl<'tcx> fmt::Debug for PatternKind<'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
+impl<'tcx> IrPrint<PatternKind<'tcx>> for TyCtxt<'tcx> {
+    fn print(t: &PatternKind<'tcx>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *t {
             PatternKind::Range { start, end } => {
                 write!(f, "{start}")?;
 
@@ -53,10 +79,15 @@ impl<'tcx> fmt::Debug for PatternKind<'tcx> {
             }
         }
     }
+
+    fn print_debug(t: &PatternKind<'tcx>, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Self::print(t, fmt)
+    }
 }
 
-#[derive(Clone, PartialEq, Eq, Hash)]
-#[derive(HashStable, TyEncodable, TyDecodable, TypeVisitable, TypeFoldable)]
-pub enum PatternKind<'tcx> {
-    Range { start: ty::Const<'tcx>, end: ty::Const<'tcx> },
+impl<'tcx> rustc_type_ir::inherent::IntoKind for Pattern<'tcx> {
+    type Kind = PatternKind<'tcx>;
+    fn kind(self) -> Self::Kind {
+        *self
+    }
 }
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index 5904deaaaad..9172c5d3ab7 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -382,7 +382,7 @@ pub fn shrunk_instance_name<'tcx>(
             return (s, None);
         }
 
-        let path = tcx.output_filenames(()).temp_path_ext("long-type.txt", None);
+        let path = tcx.output_filenames(()).temp_path_for_diagnostic("long-type.txt");
         let written_to_path = std::fs::write(&path, s).ok().map(|_| path);
 
         (shrunk, written_to_path)
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 3281cb4135a..d739218af5e 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -63,6 +63,7 @@ thread_local! {
     static FORCE_TRIMMED_PATH: Cell<bool> = const { Cell::new(false) };
     static REDUCED_QUERIES: Cell<bool> = const { Cell::new(false) };
     static NO_VISIBLE_PATH: Cell<bool> = const { Cell::new(false) };
+    static NO_VISIBLE_PATH_IF_DOC_HIDDEN: Cell<bool> = const { Cell::new(false) };
     static RTN_MODE: Cell<RtnMode> = const { Cell::new(RtnMode::ForDiagnostic) };
 }
 
@@ -134,6 +135,8 @@ define_helper!(
     /// Prevent selection of visible paths. `Display` impl of DefId will prefer
     /// visible (public) reexports of types as paths.
     fn with_no_visible_paths(NoVisibleGuard, NO_VISIBLE_PATH);
+    /// Prevent selection of visible paths if the paths are through a doc hidden path.
+    fn with_no_visible_paths_if_doc_hidden(NoVisibleIfDocHiddenGuard, NO_VISIBLE_PATH_IF_DOC_HIDDEN);
 );
 
 #[must_use]
@@ -569,6 +572,10 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             return Ok(false);
         };
 
+        if self.tcx().is_doc_hidden(visible_parent) && with_no_visible_paths_if_doc_hidden() {
+            return Ok(false);
+        }
+
         let actual_parent = self.tcx().opt_parent(def_id);
         debug!(
             "try_print_visible_def_path: visible_parent={:?} actual_parent={:?}",
@@ -613,7 +620,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             // the children of the visible parent (as was done when computing
             // `visible_parent_map`), looking for the specific child we currently have and then
             // have access to the re-exported name.
-            DefPathData::TypeNs(Some(ref mut name)) if Some(visible_parent) != actual_parent => {
+            DefPathData::TypeNs(ref mut name) if Some(visible_parent) != actual_parent => {
                 // Item might be re-exported several times, but filter for the one
                 // that's public and whose identifier isn't `_`.
                 let reexport = self
@@ -634,7 +641,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             }
             // Re-exported `extern crate` (#43189).
             DefPathData::CrateRoot => {
-                data = DefPathData::TypeNs(Some(self.tcx().crate_name(def_id.krate)));
+                data = DefPathData::TypeNs(self.tcx().crate_name(def_id.krate));
             }
             _ => {}
         }
@@ -1207,7 +1214,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                             && assoc
                                 .trait_container(tcx)
                                 .is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Coroutine))
-                            && assoc.name == rustc_span::sym::Return
+                            && assoc.opt_name() == Some(rustc_span::sym::Return)
                         {
                             if let ty::Coroutine(_, args) = args.type_at(0).kind() {
                                 let return_ty = args.as_coroutine().return_ty();
@@ -1230,7 +1237,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                             p!(", ");
                         }
 
-                        p!(write("{} = ", tcx.associated_item(assoc_item_def_id).name));
+                        p!(write("{} = ", tcx.associated_item(assoc_item_def_id).name()));
 
                         match term.unpack() {
                             TermKind::Ty(ty) => p!(print(ty)),
@@ -2520,7 +2527,7 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
 
         let identify_regions = self.tcx.sess.opts.unstable_opts.identify_regions;
 
-        match *region {
+        match region.kind() {
             ty::ReEarlyParam(ref data) => data.has_name(),
 
             ty::ReLateParam(ty::LateParamRegion { kind, .. }) => kind.is_named(),
@@ -2590,7 +2597,7 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
         // the user might want to diagnose an error, but there is basically no way
         // to fit that into a short string. Hence the recommendation to use
         // `explain_region()` or `note_and_explain_region()`.
-        match *region {
+        match region.kind() {
             ty::ReEarlyParam(data) => {
                 p!(write("{}", data.name));
                 return Ok(());
@@ -2680,7 +2687,7 @@ impl<'a, 'tcx> ty::TypeFolder<TyCtxt<'tcx>> for RegionFolder<'a, 'tcx> {
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         let name = &mut self.name;
-        let region = match *r {
+        let region = match r.kind() {
             ty::ReBound(db, br) if db >= self.current_index => {
                 *self.region_map.entry(br).or_insert_with(|| name(Some(db), self.current_index, br))
             }
@@ -2704,7 +2711,7 @@ impl<'a, 'tcx> ty::TypeFolder<TyCtxt<'tcx>> for RegionFolder<'a, 'tcx> {
             }
             _ => return r,
         };
-        if let ty::ReBound(debruijn1, br) = *region {
+        if let ty::ReBound(debruijn1, br) = region.kind() {
             assert_eq!(debruijn1, ty::INNERMOST);
             ty::Region::new_bound(self.tcx, self.current_index, br)
         } else {
@@ -3284,7 +3291,7 @@ define_print! {
     }
 
     ty::ExistentialProjection<'tcx> {
-        let name = cx.tcx().associated_item(self.def_id).name;
+        let name = cx.tcx().associated_item(self.def_id).name();
         // The args don't contain the self ty (as it has been erased) but the corresp.
         // generics do as the trait always has a self ty param. We need to offset.
         let args = &self.args[cx.tcx().generics_of(self.def_id).parent_count - 1..];
diff --git a/compiler/rustc_middle/src/ty/region.rs b/compiler/rustc_middle/src/ty/region.rs
index c78306f2ca3..3e4f7a79d53 100644
--- a/compiler/rustc_middle/src/ty/region.rs
+++ b/compiler/rustc_middle/src/ty/region.rs
@@ -1,5 +1,3 @@
-use std::ops::Deref;
-
 use rustc_data_structures::intern::Interned;
 use rustc_errors::MultiSpan;
 use rustc_hir::def_id::DefId;
@@ -22,7 +20,7 @@ impl<'tcx> rustc_type_ir::inherent::IntoKind for Region<'tcx> {
     type Kind = RegionKind<'tcx>;
 
     fn kind(self) -> RegionKind<'tcx> {
-        *self
+        *self.0.0
     }
 }
 
@@ -32,7 +30,7 @@ impl<'tcx> rustc_type_ir::Flags for Region<'tcx> {
     }
 
     fn outer_exclusive_binder(&self) -> ty::DebruijnIndex {
-        match **self {
+        match self.kind() {
             ty::ReBound(debruijn, _) => debruijn.shifted_in(1),
             _ => ty::INNERMOST,
         }
@@ -163,7 +161,7 @@ impl<'tcx> Region<'tcx> {
 
     pub fn get_name(self) -> Option<Symbol> {
         if self.has_name() {
-            match *self {
+            match self.kind() {
                 ty::ReEarlyParam(ebr) => Some(ebr.name),
                 ty::ReBound(_, br) => br.kind.get_name(),
                 ty::ReLateParam(fr) => fr.kind.get_name(),
@@ -185,7 +183,7 @@ impl<'tcx> Region<'tcx> {
 
     /// Is this region named by the user?
     pub fn has_name(self) -> bool {
-        match *self {
+        match self.kind() {
             ty::ReEarlyParam(ebr) => ebr.has_name(),
             ty::ReBound(_, br) => br.kind.is_named(),
             ty::ReLateParam(fr) => fr.kind.is_named(),
@@ -199,32 +197,32 @@ impl<'tcx> Region<'tcx> {
 
     #[inline]
     pub fn is_error(self) -> bool {
-        matches!(*self, ty::ReError(_))
+        matches!(self.kind(), ty::ReError(_))
     }
 
     #[inline]
     pub fn is_static(self) -> bool {
-        matches!(*self, ty::ReStatic)
+        matches!(self.kind(), ty::ReStatic)
     }
 
     #[inline]
     pub fn is_erased(self) -> bool {
-        matches!(*self, ty::ReErased)
+        matches!(self.kind(), ty::ReErased)
     }
 
     #[inline]
     pub fn is_bound(self) -> bool {
-        matches!(*self, ty::ReBound(..))
+        matches!(self.kind(), ty::ReBound(..))
     }
 
     #[inline]
     pub fn is_placeholder(self) -> bool {
-        matches!(*self, ty::RePlaceholder(..))
+        matches!(self.kind(), ty::RePlaceholder(..))
     }
 
     #[inline]
     pub fn bound_at_or_above_binder(self, index: ty::DebruijnIndex) -> bool {
-        match *self {
+        match self.kind() {
             ty::ReBound(debruijn, _) => debruijn >= index,
             _ => false,
         }
@@ -233,7 +231,7 @@ impl<'tcx> Region<'tcx> {
     pub fn type_flags(self) -> TypeFlags {
         let mut flags = TypeFlags::empty();
 
-        match *self {
+        match self.kind() {
             ty::ReVar(..) => {
                 flags = flags | TypeFlags::HAS_FREE_REGIONS;
                 flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
@@ -275,14 +273,14 @@ impl<'tcx> Region<'tcx> {
 
     /// True for free regions other than `'static`.
     pub fn is_param(self) -> bool {
-        matches!(*self, ty::ReEarlyParam(_) | ty::ReLateParam(_))
+        matches!(self.kind(), ty::ReEarlyParam(_) | ty::ReLateParam(_))
     }
 
     /// True for free region in the current context.
     ///
     /// This is the case for `'static` and param regions.
     pub fn is_free(self) -> bool {
-        match *self {
+        match self.kind() {
             ty::ReStatic | ty::ReEarlyParam(..) | ty::ReLateParam(..) => true,
             ty::ReVar(..)
             | ty::RePlaceholder(..)
@@ -319,15 +317,6 @@ impl<'tcx> Region<'tcx> {
     }
 }
 
-impl<'tcx> Deref for Region<'tcx> {
-    type Target = RegionKind<'tcx>;
-
-    #[inline]
-    fn deref(&self) -> &RegionKind<'tcx> {
-        self.0.0
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub struct EarlyParamRegion {
diff --git a/compiler/rustc_middle/src/ty/significant_drop_order.rs b/compiler/rustc_middle/src/ty/significant_drop_order.rs
index 4881d611c12..561f84192b4 100644
--- a/compiler/rustc_middle/src/ty/significant_drop_order.rs
+++ b/compiler/rustc_middle/src/ty/significant_drop_order.rs
@@ -26,7 +26,7 @@ fn true_significant_drop_ty<'tcx>(
                     name_rev.push(tcx.crate_name(did.krate));
                 }
                 rustc_hir::definitions::DefPathData::TypeNs(symbol) => {
-                    name_rev.push(symbol.unwrap());
+                    name_rev.push(symbol);
                 }
                 _ => return None,
             }
@@ -143,25 +143,11 @@ pub fn ty_dtor_span<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Span> {
         | ty::UnsafeBinder(_) => None,
 
         ty::Adt(adt_def, _) => {
-            let did = adt_def.did();
-            let try_local_did_span = |did: DefId| {
-                if let Some(local) = did.as_local() {
-                    tcx.source_span(local)
-                } else {
-                    tcx.def_span(did)
-                }
-            };
-            let dtor = if let Some(dtor) = tcx.adt_destructor(did) {
-                dtor.did
-            } else if let Some(dtor) = tcx.adt_async_destructor(did) {
-                return Some(tcx.source_span(dtor.impl_did));
+            if let Some(dtor) = tcx.adt_destructor(adt_def.did()) {
+                Some(tcx.def_span(tcx.parent(dtor.did)))
             } else {
-                return Some(try_local_did_span(did));
-            };
-            let def_key = tcx.def_key(dtor);
-            let Some(parent_index) = def_key.parent else { return Some(try_local_did_span(dtor)) };
-            let parent_did = DefId { index: parent_index, krate: dtor.krate };
-            Some(try_local_did_span(parent_did))
+                Some(tcx.def_span(adt_def.did()))
+            }
         }
         ty::Coroutine(did, _)
         | ty::CoroutineWitness(did, _)
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index 798ef352c40..26861666c1d 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -6,20 +6,19 @@
 use std::fmt::{self, Debug};
 
 use rustc_abi::TyAndLayout;
-use rustc_ast::InlineAsmTemplatePiece;
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::LocalDefId;
-use rustc_span::Span;
 use rustc_span::source_map::Spanned;
-use rustc_type_ir::{ConstKind, VisitorResult, try_visit};
+use rustc_type_ir::{ConstKind, TypeFolder, VisitorResult, try_visit};
 
 use super::print::PrettyPrinter;
 use super::{GenericArg, GenericArgKind, Pattern, Region};
+use crate::infer::canonical::CanonicalVarInfos;
 use crate::mir::PlaceElem;
 use crate::ty::print::{FmtPrinter, Printer, with_no_trimmed_paths};
 use crate::ty::{
-    self, FallibleTypeFolder, InferConst, Lift, Term, TermKind, Ty, TyCtxt, TypeFoldable,
-    TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitor,
+    self, FallibleTypeFolder, Lift, Term, TermKind, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
+    TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
 
 impl fmt::Debug for ty::TraitDef {
@@ -61,6 +60,12 @@ impl<'tcx> fmt::Debug for ty::adjustment::Adjustment<'tcx> {
     }
 }
 
+impl<'tcx> fmt::Debug for ty::adjustment::PatAdjustment<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} -> {:?}", self.source, self.kind)
+    }
+}
+
 impl fmt::Debug for ty::BoundRegionKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
@@ -271,6 +276,7 @@ TrivialTypeTraversalImpls! {
     crate::ty::AssocKind,
     crate::ty::BoundRegion,
     crate::ty::BoundVar,
+    crate::ty::InferConst,
     crate::ty::Placeholder<crate::ty::BoundRegion>,
     crate::ty::Placeholder<crate::ty::BoundTy>,
     crate::ty::Placeholder<ty::BoundVar>,
@@ -337,24 +343,6 @@ impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ty::AdtDef<'tcx> {
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_poly_existential_predicates(v))
-    }
-}
-
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<ty::Const<'tcx>> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_const_list(v))
-    }
-}
-
 impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Pattern<'tcx> {
     fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
         self,
@@ -363,6 +351,11 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Pattern<'tcx> {
         let pat = (*self).clone().try_fold_with(folder)?;
         Ok(if pat == *self { self } else { folder.cx().mk_pat(pat) })
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        let pat = (*self).clone().fold_with(folder);
+        if pat == *self { self } else { folder.cx().mk_pat(pat) }
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Pattern<'tcx> {
@@ -378,6 +371,10 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Ty<'tcx> {
     ) -> Result<Self, F::Error> {
         folder.try_fold_ty(self)
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        folder.fold_ty(self)
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Ty<'tcx> {
@@ -436,6 +433,45 @@ impl<'tcx> TypeSuperFoldable<TyCtxt<'tcx>> for Ty<'tcx> {
 
         Ok(if *self.kind() == kind { self } else { folder.cx().mk_ty_from_kind(kind) })
     }
+
+    fn super_fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        let kind = match *self.kind() {
+            ty::RawPtr(ty, mutbl) => ty::RawPtr(ty.fold_with(folder), mutbl),
+            ty::Array(typ, sz) => ty::Array(typ.fold_with(folder), sz.fold_with(folder)),
+            ty::Slice(typ) => ty::Slice(typ.fold_with(folder)),
+            ty::Adt(tid, args) => ty::Adt(tid, args.fold_with(folder)),
+            ty::Dynamic(trait_ty, region, representation) => {
+                ty::Dynamic(trait_ty.fold_with(folder), region.fold_with(folder), representation)
+            }
+            ty::Tuple(ts) => ty::Tuple(ts.fold_with(folder)),
+            ty::FnDef(def_id, args) => ty::FnDef(def_id, args.fold_with(folder)),
+            ty::FnPtr(sig_tys, hdr) => ty::FnPtr(sig_tys.fold_with(folder), hdr),
+            ty::UnsafeBinder(f) => ty::UnsafeBinder(f.fold_with(folder)),
+            ty::Ref(r, ty, mutbl) => ty::Ref(r.fold_with(folder), ty.fold_with(folder), mutbl),
+            ty::Coroutine(did, args) => ty::Coroutine(did, args.fold_with(folder)),
+            ty::CoroutineWitness(did, args) => ty::CoroutineWitness(did, args.fold_with(folder)),
+            ty::Closure(did, args) => ty::Closure(did, args.fold_with(folder)),
+            ty::CoroutineClosure(did, args) => ty::CoroutineClosure(did, args.fold_with(folder)),
+            ty::Alias(kind, data) => ty::Alias(kind, data.fold_with(folder)),
+            ty::Pat(ty, pat) => ty::Pat(ty.fold_with(folder), pat.fold_with(folder)),
+
+            ty::Bool
+            | ty::Char
+            | ty::Str
+            | ty::Int(_)
+            | ty::Uint(_)
+            | ty::Float(_)
+            | ty::Error(_)
+            | ty::Infer(_)
+            | ty::Param(..)
+            | ty::Bound(..)
+            | ty::Placeholder(..)
+            | ty::Never
+            | ty::Foreign(..) => return self,
+        };
+
+        if *self.kind() == kind { self } else { folder.cx().mk_ty_from_kind(kind) }
+    }
 }
 
 impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for Ty<'tcx> {
@@ -496,6 +532,10 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::Region<'tcx> {
     ) -> Result<Self, F::Error> {
         folder.try_fold_region(self)
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        folder.fold_region(self)
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ty::Region<'tcx> {
@@ -511,6 +551,10 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::Predicate<'tcx> {
     ) -> Result<Self, F::Error> {
         folder.try_fold_predicate(self)
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        folder.fold_predicate(self)
+    }
 }
 
 // FIXME(clause): This is wonky
@@ -521,6 +565,10 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::Clause<'tcx> {
     ) -> Result<Self, F::Error> {
         Ok(folder.try_fold_predicate(self.as_predicate())?.expect_clause())
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        folder.fold_predicate(self.as_predicate()).expect_clause()
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ty::Predicate<'tcx> {
@@ -543,6 +591,11 @@ impl<'tcx> TypeSuperFoldable<TyCtxt<'tcx>> for ty::Predicate<'tcx> {
         let new = self.kind().try_fold_with(folder)?;
         Ok(folder.cx().reuse_or_mk_predicate(self, new))
     }
+
+    fn super_fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        let new = self.kind().fold_with(folder);
+        folder.cx().reuse_or_mk_predicate(self, new)
+    }
 }
 
 impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for ty::Predicate<'tcx> {
@@ -563,15 +616,6 @@ impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for ty::Clauses<'tcx> {
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::Clauses<'tcx> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_clauses(v))
-    }
-}
-
 impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::Const<'tcx> {
     fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
         self,
@@ -579,6 +623,10 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ty::Const<'tcx> {
     ) -> Result<Self, F::Error> {
         folder.try_fold_const(self)
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        folder.fold_const(self)
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ty::Const<'tcx> {
@@ -606,6 +654,20 @@ impl<'tcx> TypeSuperFoldable<TyCtxt<'tcx>> for ty::Const<'tcx> {
         };
         if kind != self.kind() { Ok(folder.cx().mk_ct_from_kind(kind)) } else { Ok(self) }
     }
+
+    fn super_fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        let kind = match self.kind() {
+            ConstKind::Param(p) => ConstKind::Param(p.fold_with(folder)),
+            ConstKind::Infer(i) => ConstKind::Infer(i.fold_with(folder)),
+            ConstKind::Bound(d, b) => ConstKind::Bound(d.fold_with(folder), b.fold_with(folder)),
+            ConstKind::Placeholder(p) => ConstKind::Placeholder(p.fold_with(folder)),
+            ConstKind::Unevaluated(uv) => ConstKind::Unevaluated(uv.fold_with(folder)),
+            ConstKind::Value(v) => ConstKind::Value(v.fold_with(folder)),
+            ConstKind::Error(e) => ConstKind::Error(e.fold_with(folder)),
+            ConstKind::Expr(e) => ConstKind::Expr(e.fold_with(folder)),
+        };
+        if kind != self.kind() { folder.cx().mk_ct_from_kind(kind) } else { self }
+    }
 }
 
 impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for ty::Const<'tcx> {
@@ -639,20 +701,9 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for rustc_span::ErrorGuaranteed {
     ) -> Result<Self, F::Error> {
         Ok(self)
     }
-}
-
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for InferConst {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        _folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(self)
-    }
-}
 
-impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for InferConst {
-    fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(&self, _visitor: &mut V) -> V::Result {
-        V::Result::output()
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, _folder: &mut F) -> Self {
+        self
     }
 }
 
@@ -683,40 +734,50 @@ impl<'tcx, T: TypeFoldable<TyCtxt<'tcx>> + Debug + Clone> TypeFoldable<TyCtxt<'t
             span: self.span.try_fold_with(folder)?,
         })
     }
-}
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx [InlineAsmTemplatePiece] {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        _folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(self)
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        Spanned { node: self.node.fold_with(folder), span: self.span.fold_with(folder) }
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx [Span] {
+impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<LocalDefId> {
     fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
         self,
         _folder: &mut F,
     ) -> Result<Self, F::Error> {
         Ok(self)
     }
-}
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<LocalDefId> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        _folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(self)
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, _folder: &mut F) -> Self {
+        self
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<PlaceElem<'tcx>> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_place_elems(v))
+macro_rules! list_fold {
+    ($($ty:ty : $mk:ident),+ $(,)?) => {
+        $(
+            impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for $ty {
+                fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
+                    self,
+                    folder: &mut F,
+                ) -> Result<Self, F::Error> {
+                    ty::util::try_fold_list(self, folder, |tcx, v| tcx.$mk(v))
+                }
+
+                fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(
+                    self,
+                    folder: &mut F,
+                ) -> Self {
+                    ty::util::fold_list(self, folder, |tcx, v| tcx.$mk(v))
+                }
+            }
+        )*
     }
 }
+
+list_fold! {
+    ty::Clauses<'tcx> : mk_clauses,
+    &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> : mk_poly_existential_predicates,
+    &'tcx ty::List<PlaceElem<'tcx>> : mk_place_elems,
+    CanonicalVarInfos<'tcx> : mk_canonical_var_infos,
+}
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 27ee363f1c1..301ae604574 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -16,6 +16,7 @@ use rustc_hir::def_id::DefId;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, extension};
 use rustc_span::{DUMMY_SP, Span, Symbol, sym};
 use rustc_type_ir::TyKind::*;
+use rustc_type_ir::walk::TypeWalker;
 use rustc_type_ir::{self as ir, BoundVar, CollectAndApply, DynKind, TypeVisitableExt, elaborate};
 use tracing::instrument;
 use ty::util::{AsyncDropGlueMorphology, IntTypeExt};
@@ -734,7 +735,7 @@ impl<'tcx> Ty<'tcx> {
                     .map(|principal| {
                         tcx.associated_items(principal.def_id())
                             .in_definition_order()
-                            .filter(|item| item.kind == ty::AssocKind::Type)
+                            .filter(|item| item.is_type())
                             .filter(|item| !item.is_impl_trait_in_trait())
                             .filter(|item| !tcx.generics_require_sized_self(item.def_id))
                             .count()
@@ -1872,14 +1873,14 @@ impl<'tcx> Ty<'tcx> {
 
     /// Fast path helper for testing if a type is `Sized`.
     ///
-    /// Returning true means the type is known to be sized. Returning
-    /// `false` means nothing -- could be sized, might not be.
+    /// Returning true means the type is known to implement `Sized`. Returning `false` means
+    /// nothing -- could be sized, might not be.
     ///
-    /// Note that we could never rely on the fact that a type such as `[_]` is
-    /// trivially `!Sized` because we could be in a type environment with a
-    /// bound such as `[_]: Copy`. A function with such a bound obviously never
-    /// can be called, but that doesn't mean it shouldn't typecheck. This is why
-    /// this method doesn't return `Option<bool>`.
+    /// Note that we could never rely on the fact that a type such as `[_]` is trivially `!Sized`
+    /// because we could be in a type environment with a bound such as `[_]: Copy`. A function with
+    /// such a bound obviously never can be called, but that doesn't mean it shouldn't typecheck.
+    /// This is why this method doesn't return `Option<bool>`.
+    #[instrument(skip(tcx), level = "debug")]
     pub fn is_trivially_sized(self, tcx: TyCtxt<'tcx>) -> bool {
         match self.kind() {
             ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
@@ -2029,6 +2030,20 @@ impl<'tcx> Ty<'tcx> {
     pub fn is_known_rigid(self) -> bool {
         self.kind().is_known_rigid()
     }
+
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<TyCtxt<'tcx>> {
+        TypeWalker::new(self.into())
+    }
 }
 
 impl<'tcx> rustc_type_ir::inherent::Tys<TyCtxt<'tcx>> for &'tcx ty::List<Ty<'tcx>> {
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index 7c437abfe24..4c5c669771f 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -77,8 +77,8 @@ pub struct TypeckResults<'tcx> {
     /// to a form valid in all Editions, either as a lint diagnostic or hard error.
     rust_2024_migration_desugared_pats: ItemLocalMap<Rust2024IncompatiblePatInfo>,
 
-    /// Stores the types which were implicitly dereferenced in pattern binding modes
-    /// for later usage in THIR lowering. For example,
+    /// Stores the types which were implicitly dereferenced in pattern binding modes or deref
+    /// patterns for later usage in THIR lowering. For example,
     ///
     /// ```
     /// match &&Some(5i32) {
@@ -86,11 +86,20 @@ pub struct TypeckResults<'tcx> {
     ///     _ => {},
     /// }
     /// ```
-    /// leads to a `vec![&&Option<i32>, &Option<i32>]`. Empty vectors are not stored.
+    /// leads to a `vec![&&Option<i32>, &Option<i32>]` and
+    ///
+    /// ```
+    /// #![feature(deref_patterns)]
+    /// match &Box::new(Some(5i32)) {
+    ///     Some(n) => {},
+    ///     _ => {},
+    /// }
+    /// ```
+    /// leads to a `vec![&Box<Option<i32>>, Box<Option<i32>>]`. Empty vectors are not stored.
     ///
     /// See:
     /// <https://github.com/rust-lang/rfcs/blob/master/text/2005-match-ergonomics.md#definitions>
-    pat_adjustments: ItemLocalMap<Vec<Ty<'tcx>>>,
+    pat_adjustments: ItemLocalMap<Vec<ty::adjustment::PatAdjustment<'tcx>>>,
 
     /// Set of reference patterns that match against a match-ergonomics inserted reference
     /// (as opposed to against a reference in the scrutinee type).
@@ -403,11 +412,15 @@ impl<'tcx> TypeckResults<'tcx> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_binding_modes }
     }
 
-    pub fn pat_adjustments(&self) -> LocalTableInContext<'_, Vec<Ty<'tcx>>> {
+    pub fn pat_adjustments(
+        &self,
+    ) -> LocalTableInContext<'_, Vec<ty::adjustment::PatAdjustment<'tcx>>> {
         LocalTableInContext { hir_owner: self.hir_owner, data: &self.pat_adjustments }
     }
 
-    pub fn pat_adjustments_mut(&mut self) -> LocalTableInContextMut<'_, Vec<Ty<'tcx>>> {
+    pub fn pat_adjustments_mut(
+        &mut self,
+    ) -> LocalTableInContextMut<'_, Vec<ty::adjustment::PatAdjustment<'tcx>>> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_adjustments }
     }
 
@@ -758,7 +771,7 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
                             _ => false,
                         },
 
-                        GenericArgKind::Lifetime(r) => match *r {
+                        GenericArgKind::Lifetime(r) => match r.kind() {
                             ty::ReBound(debruijn, br) => {
                                 // We only allow a `ty::INNERMOST` index in generic parameters.
                                 assert_eq!(debruijn, ty::INNERMOST);
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index e4863896fc8..08cee1101d0 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -2,7 +2,7 @@
 
 use std::{fmt, iter};
 
-use rustc_abi::{ExternAbi, Float, Integer, IntegerType, Size};
+use rustc_abi::{Float, Integer, IntegerType, Size};
 use rustc_apfloat::Float as _;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
@@ -819,7 +819,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Get an English description for the item's kind.
     pub fn def_kind_descr(self, def_kind: DefKind, def_id: DefId) -> &'static str {
         match def_kind {
-            DefKind::AssocFn if self.associated_item(def_id).fn_has_self_parameter => "method",
+            DefKind::AssocFn if self.associated_item(def_id).is_method() => "method",
             DefKind::Closure if let Some(coroutine_kind) = self.coroutine_kind(def_id) => {
                 match coroutine_kind {
                     hir::CoroutineKind::Desugared(
@@ -873,7 +873,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Gets an English article for the [`TyCtxt::def_kind_descr`].
     pub fn def_kind_descr_article(self, def_kind: DefKind, def_id: DefId) -> &'static str {
         match def_kind {
-            DefKind::AssocFn if self.associated_item(def_id).fn_has_self_parameter => "a",
+            DefKind::AssocFn if self.associated_item(def_id).is_method() => "a",
             DefKind::Closure if let Some(coroutine_kind) = self.coroutine_kind(def_id) => {
                 match coroutine_kind {
                     hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, ..) => "an",
@@ -1647,6 +1647,42 @@ pub fn fold_list<'tcx, F, L, T>(
     list: L,
     folder: &mut F,
     intern: impl FnOnce(TyCtxt<'tcx>, &[T]) -> L,
+) -> L
+where
+    F: TypeFolder<TyCtxt<'tcx>>,
+    L: AsRef<[T]>,
+    T: TypeFoldable<TyCtxt<'tcx>> + PartialEq + Copy,
+{
+    let slice = list.as_ref();
+    let mut iter = slice.iter().copied();
+    // Look for the first element that changed
+    match iter.by_ref().enumerate().find_map(|(i, t)| {
+        let new_t = t.fold_with(folder);
+        if new_t != t { Some((i, new_t)) } else { None }
+    }) {
+        Some((i, new_t)) => {
+            // An element changed, prepare to intern the resulting list
+            let mut new_list = SmallVec::<[_; 8]>::with_capacity(slice.len());
+            new_list.extend_from_slice(&slice[..i]);
+            new_list.push(new_t);
+            for t in iter {
+                new_list.push(t.fold_with(folder))
+            }
+            intern(folder.cx(), &new_list)
+        }
+        None => list,
+    }
+}
+
+/// Does the equivalent of
+/// ```ignore (illustrative)
+/// let v = self.iter().map(|p| p.try_fold_with(folder)).collect::<SmallVec<[_; 8]>>();
+/// folder.tcx().intern_*(&v)
+/// ```
+pub fn try_fold_list<'tcx, F, L, T>(
+    list: L,
+    folder: &mut F,
+    intern: impl FnOnce(TyCtxt<'tcx>, &[T]) -> L,
 ) -> Result<L, F::Error>
 where
     F: FallibleTypeFolder<TyCtxt<'tcx>>,
@@ -1719,10 +1755,7 @@ pub fn is_doc_notable_trait(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 /// the compiler to make some assumptions about its shape; if the user doesn't use a feature gate, they may
 /// cause an ICE that we otherwise may want to prevent.
 pub fn intrinsic_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::IntrinsicDef> {
-    if tcx.features().intrinsics()
-        && (matches!(tcx.fn_sig(def_id).skip_binder().abi(), ExternAbi::RustIntrinsic)
-            || tcx.has_attr(def_id, sym::rustc_intrinsic))
-    {
+    if tcx.features().intrinsics() && tcx.has_attr(def_id, sym::rustc_intrinsic) {
         let must_be_overridden = match tcx.hir_node_by_def_id(def_id) {
             hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn { has_body, .. }, .. }) => {
                 !has_body
diff --git a/compiler/rustc_middle/src/ty/visit.rs b/compiler/rustc_middle/src/ty/visit.rs
index e3b7a258c39..44c7b6a7c9e 100644
--- a/compiler/rustc_middle/src/ty/visit.rs
+++ b/compiler/rustc_middle/src/ty/visit.rs
@@ -77,7 +77,7 @@ impl<'tcx> TyCtxt<'tcx> {
             }
 
             fn visit_region(&mut self, r: ty::Region<'tcx>) -> Self::Result {
-                match *r {
+                match r.kind() {
                     ty::ReBound(debruijn, _) if debruijn < self.outer_index => {
                         ControlFlow::Continue(())
                     }
@@ -205,7 +205,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for LateBoundRegionsCollector {
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        if let ty::ReBound(debruijn, br) = *r {
+        if let ty::ReBound(debruijn, br) = r.kind() {
             if debruijn == self.current_index {
                 self.regions.insert(br.kind);
             }
@@ -231,9 +231,7 @@ impl MaxUniverse {
 impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxUniverse {
     fn visit_ty(&mut self, t: Ty<'tcx>) {
         if let ty::Placeholder(placeholder) = t.kind() {
-            self.max_universe = ty::UniverseIndex::from_u32(
-                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
-            );
+            self.max_universe = self.max_universe.max(placeholder.universe);
         }
 
         t.super_visit_with(self)
@@ -241,19 +239,15 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxUniverse {
 
     fn visit_const(&mut self, c: ty::consts::Const<'tcx>) {
         if let ty::ConstKind::Placeholder(placeholder) = c.kind() {
-            self.max_universe = ty::UniverseIndex::from_u32(
-                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
-            );
+            self.max_universe = self.max_universe.max(placeholder.universe);
         }
 
         c.super_visit_with(self)
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        if let ty::RePlaceholder(placeholder) = *r {
-            self.max_universe = ty::UniverseIndex::from_u32(
-                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
-            );
+        if let ty::RePlaceholder(placeholder) = r.kind() {
+            self.max_universe = self.max_universe.max(placeholder.universe);
         }
     }
 }
diff --git a/compiler/rustc_mir_build/src/builder/custom/mod.rs b/compiler/rustc_mir_build/src/builder/custom/mod.rs
index bfc16816e2e..902a6e7f115 100644
--- a/compiler/rustc_mir_build/src/builder/custom/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/custom/mod.rs
@@ -103,8 +103,9 @@ fn parse_attribute(attr: &Attribute) -> MirPhase {
     let mut dialect: Option<String> = None;
     let mut phase: Option<String> = None;
 
+    // Not handling errors properly for this internal attribute; will just abort on errors.
     for nested in meta_items {
-        let name = nested.name_or_empty();
+        let name = nested.name().unwrap();
         let value = nested.value_str().unwrap().as_str().to_string();
         match name.as_str() {
             "dialect" => {
diff --git a/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs b/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs
index 19669021eef..5918498f239 100644
--- a/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs
+++ b/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs
@@ -145,7 +145,7 @@ impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
             let arm = &self.thir[*arm];
             let value = match arm.pattern.kind {
                 PatKind::Constant { value } => value,
-                PatKind::ExpandedConstant { ref subpattern, def_id: _, is_inline: false }
+                PatKind::ExpandedConstant { ref subpattern, def_id: _ }
                     if let PatKind::Constant { value } = subpattern.kind =>
                 {
                     value
diff --git a/compiler/rustc_mir_build/src/builder/expr/into.rs b/compiler/rustc_mir_build/src/builder/expr/into.rs
index 333e69475c5..a9a07997410 100644
--- a/compiler/rustc_mir_build/src/builder/expr/into.rs
+++ b/compiler/rustc_mir_build/src/builder/expr/into.rs
@@ -328,7 +328,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             destination,
                             target: Some(success),
                             unwind: UnwindAction::Unreachable,
-                            call_source: CallSource::Misc,
+                            call_source: CallSource::Use,
                             fn_span: expr_span,
                         },
                     );
diff --git a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
index 29d400a957b..d66b38c5b00 100644
--- a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
@@ -101,24 +101,27 @@ impl<'tcx> MatchPairTree<'tcx> {
             place_builder = resolved;
         }
 
-        // Only add the OpaqueCast projection if the given place is an opaque type and the
-        // expected type from the pattern is not.
-        let may_need_cast = match place_builder.base() {
-            PlaceBase::Local(local) => {
-                let ty =
-                    Place::ty_from(local, place_builder.projection(), &cx.local_decls, cx.tcx).ty;
-                ty != pattern.ty && ty.has_opaque_types()
+        if !cx.tcx.next_trait_solver_globally() {
+            // Only add the OpaqueCast projection if the given place is an opaque type and the
+            // expected type from the pattern is not.
+            let may_need_cast = match place_builder.base() {
+                PlaceBase::Local(local) => {
+                    let ty =
+                        Place::ty_from(local, place_builder.projection(), &cx.local_decls, cx.tcx)
+                            .ty;
+                    ty != pattern.ty && ty.has_opaque_types()
+                }
+                _ => true,
+            };
+            if may_need_cast {
+                place_builder = place_builder.project(ProjectionElem::OpaqueCast(pattern.ty));
             }
-            _ => true,
-        };
-        if may_need_cast {
-            place_builder = place_builder.project(ProjectionElem::OpaqueCast(pattern.ty));
         }
 
         let place = place_builder.try_to_place(cx);
         let mut subpairs = Vec::new();
         let test_case = match pattern.kind {
-            PatKind::Wild | PatKind::Error(_) => None,
+            PatKind::Missing | PatKind::Wild | PatKind::Error(_) => None,
 
             PatKind::Or { ref pats } => Some(TestCase::Or {
                 pats: pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect(),
@@ -201,37 +204,8 @@ impl<'tcx> MatchPairTree<'tcx> {
                 None
             }
 
-            PatKind::ExpandedConstant { subpattern: ref pattern, def_id: _, is_inline: false } => {
-                MatchPairTree::for_pattern(place_builder, pattern, cx, &mut subpairs, extra_data);
-                None
-            }
-            PatKind::ExpandedConstant { subpattern: ref pattern, def_id, is_inline: true } => {
+            PatKind::ExpandedConstant { subpattern: ref pattern, .. } => {
                 MatchPairTree::for_pattern(place_builder, pattern, cx, &mut subpairs, extra_data);
-
-                // Apply a type ascription for the inline constant to the value at `match_pair.place`
-                if let Some(source) = place {
-                    let span = pattern.span;
-                    let parent_id = cx.tcx.typeck_root_def_id(cx.def_id.to_def_id());
-                    let args = ty::InlineConstArgs::new(
-                        cx.tcx,
-                        ty::InlineConstArgsParts {
-                            parent_args: ty::GenericArgs::identity_for_item(cx.tcx, parent_id),
-                            ty: cx.infcx.next_ty_var(span),
-                        },
-                    )
-                    .args;
-                    let user_ty = cx.infcx.canonicalize_user_type_annotation(ty::UserType::new(
-                        ty::UserTypeKind::TypeOf(def_id, ty::UserArgs { args, user_self_ty: None }),
-                    ));
-                    let annotation = ty::CanonicalUserTypeAnnotation {
-                        inferred_ty: pattern.ty,
-                        span,
-                        user_ty: Box::new(user_ty),
-                    };
-                    let variance = ty::Contravariant;
-                    extra_data.ascriptions.push(super::Ascription { annotation, source, variance });
-                }
-
                 None
             }
 
diff --git a/compiler/rustc_mir_build/src/builder/matches/mod.rs b/compiler/rustc_mir_build/src/builder/matches/mod.rs
index 3acf2a6a2a6..977d4f3e931 100644
--- a/compiler/rustc_mir_build/src/builder/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/mod.rs
@@ -920,6 +920,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             PatKind::Constant { .. }
             | PatKind::Range { .. }
+            | PatKind::Missing
             | PatKind::Wild
             | PatKind::Never
             | PatKind::Error(_) => {}
diff --git a/compiler/rustc_mir_build/src/builder/matches/test.rs b/compiler/rustc_mir_build/src/builder/matches/test.rs
index d1f9d4c34fe..73cc3c86e22 100644
--- a/compiler/rustc_mir_build/src/builder/matches/test.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/test.rs
@@ -140,8 +140,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let success_block = target_block(TestBranch::Success);
                 let fail_block = target_block(TestBranch::Failure);
 
-                let expect_ty = value.ty();
-                let expect = self.literal_operand(test.span, value);
+                let mut expect_ty = value.ty();
+                let mut expect = self.literal_operand(test.span, value);
 
                 let mut place = place;
                 let mut block = block;
@@ -174,6 +174,31 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         place = ref_str;
                         ty = ref_str_ty;
                     }
+                    &ty::Pat(base, _) => {
+                        assert_eq!(ty, value.ty());
+                        assert!(base.is_trivially_pure_clone_copy());
+
+                        let transmuted_place = self.temp(base, test.span);
+                        self.cfg.push_assign(
+                            block,
+                            self.source_info(scrutinee_span),
+                            transmuted_place,
+                            Rvalue::Cast(CastKind::Transmute, Operand::Copy(place), base),
+                        );
+
+                        let transmuted_expect = self.temp(base, test.span);
+                        self.cfg.push_assign(
+                            block,
+                            self.source_info(test.span),
+                            transmuted_expect,
+                            Rvalue::Cast(CastKind::Transmute, expect, base),
+                        );
+
+                        place = transmuted_place;
+                        expect = Operand::Copy(transmuted_expect);
+                        ty = base;
+                        expect_ty = base;
+                    }
                     _ => {}
                 }
 
@@ -715,7 +740,7 @@ fn trait_method<'tcx>(
     let item = tcx
         .associated_items(trait_def_id)
         .filter_by_name_unhygienic(method_name)
-        .find(|item| item.kind == ty::AssocKind::Fn)
+        .find(|item| item.is_fn())
         .expect("trait method not found");
 
     let method_ty = Ty::new_fn_def(tcx, item.def_id, args);
diff --git a/compiler/rustc_mir_build/src/builder/mod.rs b/compiler/rustc_mir_build/src/builder/mod.rs
index 8ca9ab58e45..59a52ae67cb 100644
--- a/compiler/rustc_mir_build/src/builder/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/mod.rs
@@ -485,7 +485,7 @@ fn construct_fn<'tcx>(
     };
 
     if let Some(custom_mir_attr) =
-        tcx.hir_attrs(fn_id).iter().find(|attr| attr.name_or_empty() == sym::custom_mir)
+        tcx.hir_attrs(fn_id).iter().find(|attr| attr.has_name(sym::custom_mir))
     {
         return custom::build_custom_mir(
             tcx,
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index 6fb9974fc8e..b6a856a6eb4 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -315,6 +315,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
     fn visit_pat(&mut self, pat: &'a Pat<'tcx>) {
         if self.in_union_destructure {
             match pat.kind {
+                PatKind::Missing => unreachable!(),
                 // binding to a variable allows getting stuff out of variable
                 PatKind::Binding { .. }
                 // match is conditional on having this value
@@ -403,9 +404,9 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 visit::walk_pat(self, pat);
                 self.inside_adt = old_inside_adt;
             }
-            PatKind::ExpandedConstant { def_id, is_inline, .. } => {
+            PatKind::ExpandedConstant { def_id, .. } => {
                 if let Some(def) = def_id.as_local()
-                    && *is_inline
+                    && matches!(self.tcx.def_kind(def_id), DefKind::InlineConst)
                 {
                     self.visit_inner_body(def);
                 }
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index 0e16f871b16..ae09db50235 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -2,7 +2,7 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagArgValue, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level,
-    MultiSpan, SubdiagMessageOp, Subdiagnostic, pluralize,
+    MultiSpan, Subdiagnostic, pluralize,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{self, Ty};
@@ -546,11 +546,7 @@ pub(crate) struct UnsafeNotInheritedLintNote {
 }
 
 impl Subdiagnostic for UnsafeNotInheritedLintNote {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.span_note(self.signature_span, fluent::mir_build_unsafe_fn_safe_body);
         let body_start = self.body_span.shrink_to_lo();
         let body_end = self.body_span.shrink_to_hi();
@@ -1031,11 +1027,7 @@ pub(crate) struct Variant {
 }
 
 impl<'tcx> Subdiagnostic for AdtDefinedHere<'tcx> {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("ty", self.ty);
         let mut spans = MultiSpan::from(self.adt_def_span);
 
@@ -1117,11 +1109,7 @@ pub(crate) struct Rust2024IncompatiblePatSugg {
 }
 
 impl Subdiagnostic for Rust2024IncompatiblePatSugg {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         // Format and emit explanatory notes about default binding modes. Reversing the spans' order
         // means if we have nested spans, the innermost ones will be visited first.
         for (span, def_br_mutbl) in self.default_mode_labels.into_iter().rev() {
diff --git a/compiler/rustc_mir_build/src/lib.rs b/compiler/rustc_mir_build/src/lib.rs
index a25697ba086..8e96d46dac2 100644
--- a/compiler/rustc_mir_build/src/lib.rs
+++ b/compiler/rustc_mir_build/src/lib.rs
@@ -3,7 +3,6 @@
 // tidy-alphabetical-start
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
index 31e22e69111..fde23413972 100644
--- a/compiler/rustc_mir_build/src/thir/cx/expr.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -191,7 +191,7 @@ impl<'tcx> ThirBuildCx<'tcx> {
                 let pointer_target = ExprKind::Field {
                     lhs: self.thir.exprs.push(expr),
                     variant_index: FIRST_VARIANT,
-                    name: FieldIdx::from(0u32),
+                    name: FieldIdx::ZERO,
                 };
                 let arg = Expr { temp_lifetime, ty: pin_ty, span, kind: pointer_target };
                 let arg = self.thir.exprs.push(arg);
@@ -226,7 +226,7 @@ impl<'tcx> ThirBuildCx<'tcx> {
                     adt_def: self.tcx.adt_def(pin_did),
                     variant_index: FIRST_VARIANT,
                     args,
-                    fields: Box::new([FieldExpr { name: FieldIdx::from(0u32), expr }]),
+                    fields: Box::new([FieldExpr { name: FieldIdx::ZERO, expr }]),
                     user_ty: None,
                     base: AdtExprBase::None,
                 }));
diff --git a/compiler/rustc_mir_build/src/thir/cx/mod.rs b/compiler/rustc_mir_build/src/thir/cx/mod.rs
index b3daed8a7e0..2f593b9a0a7 100644
--- a/compiler/rustc_mir_build/src/thir/cx/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/mod.rs
@@ -113,7 +113,7 @@ impl<'tcx> ThirBuildCx<'tcx> {
             apply_adjustments: tcx
                 .hir_attrs(hir_id)
                 .iter()
-                .all(|attr| attr.name_or_empty() != rustc_span::sym::custom_mir),
+                .all(|attr| !attr.has_name(rustc_span::sym::custom_mir)),
         }
     }
 
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index 9f5e2c06b22..78583a402fe 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -676,7 +676,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             unpeeled_pat = subpattern;
         }
 
-        if let PatKind::ExpandedConstant { def_id, is_inline: false, .. } = unpeeled_pat.kind
+        if let PatKind::ExpandedConstant { def_id, .. } = unpeeled_pat.kind
             && let DefKind::Const = self.tcx.def_kind(def_id)
             && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(pat.span)
             // We filter out paths with multiple path::segments.
@@ -1296,7 +1296,8 @@ fn report_non_exhaustive_match<'p, 'tcx>(
 
     for &arm in arms {
         let arm = &thir.arms[arm];
-        if let PatKind::ExpandedConstant { def_id, is_inline: false, .. } = arm.pattern.kind
+        if let PatKind::ExpandedConstant { def_id, .. } = arm.pattern.kind
+            && !matches!(cx.tcx.def_kind(def_id), DefKind::InlineConst)
             && let Ok(snippet) = cx.tcx.sess.source_map().span_to_snippet(arm.pattern.span)
             // We filter out paths with multiple path::segments.
             && snippet.chars().all(|c| c.is_alphanumeric() || c == '_')
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
index 372453688d2..a40001bf745 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -182,7 +182,10 @@ impl<'tcx> ConstToPat<'tcx> {
             }
         }
 
-        inlined_const_as_pat
+        // Wrap the pattern in a marker node to indicate that it is the result of lowering a
+        // constant. This is used for diagnostics, and for unsafety checking of inline const blocks.
+        let kind = PatKind::ExpandedConstant { subpattern: inlined_const_as_pat, def_id: uv.def };
+        Box::new(Pat { kind, ty, span: self.span })
     }
 
     fn field_pats(
diff --git a/compiler/rustc_mir_build/src/thir/pattern/migration.rs b/compiler/rustc_mir_build/src/thir/pattern/migration.rs
index bd7787b643d..12c457f13fc 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/migration.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/migration.rs
@@ -4,8 +4,7 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::MultiSpan;
 use rustc_hir::{BindingMode, ByRef, HirId, Mutability};
 use rustc_lint as lint;
-use rustc_middle::span_bug;
-use rustc_middle::ty::{self, Rust2024IncompatiblePatInfo, Ty, TyCtxt};
+use rustc_middle::ty::{self, Rust2024IncompatiblePatInfo, TyCtxt};
 use rustc_span::{Ident, Span};
 
 use crate::errors::{Rust2024IncompatiblePat, Rust2024IncompatiblePatSugg};
@@ -87,19 +86,18 @@ impl<'a> PatMigration<'a> {
     }
 
     /// Tracks when we're lowering a pattern that implicitly dereferences the scrutinee.
-    /// This should only be called when the pattern type adjustments list `adjustments` is
-    /// non-empty. Returns the prior default binding mode; this should be followed by a call to
-    /// [`PatMigration::leave_ref`] to restore it when we leave the pattern.
+    /// This should only be called when the pattern type adjustments list `adjustments` contains an
+    /// implicit deref of a reference type. Returns the prior default binding mode; this should be
+    /// followed by a call to [`PatMigration::leave_ref`] to restore it when we leave the pattern.
     pub(super) fn visit_implicit_derefs<'tcx>(
         &mut self,
         pat_span: Span,
-        adjustments: &[Ty<'tcx>],
+        adjustments: &[ty::adjustment::PatAdjustment<'tcx>],
     ) -> Option<(Span, Mutability)> {
-        let implicit_deref_mutbls = adjustments.iter().map(|ref_ty| {
-            let &ty::Ref(_, _, mutbl) = ref_ty.kind() else {
-                span_bug!(pat_span, "pattern implicitly dereferences a non-ref type");
-            };
-            mutbl
+        // Implicitly dereferencing references changes the default binding mode, but implicit derefs
+        // of smart pointers do not. Thus, we only consider implicit derefs of reference types.
+        let implicit_deref_mutbls = adjustments.iter().filter_map(|adjust| {
+            if let &ty::Ref(_, _, mutbl) = adjust.source.kind() { Some(mutbl) } else { None }
         });
 
         if !self.info.suggest_eliding_modes {
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index d20e051548b..8f058efdfac 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -13,14 +13,16 @@ use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::{self as hir, LangItem, RangeEnd};
 use rustc_index::Idx;
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::thir::{
     Ascription, FieldPat, LocalVarId, Pat, PatKind, PatRange, PatRangeBoundary,
 };
+use rustc_middle::ty::adjustment::{PatAdjust, PatAdjustment};
 use rustc_middle::ty::layout::IntegerExt;
-use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
-use rustc_span::def_id::LocalDefId;
+use rustc_span::def_id::DefId;
 use rustc_span::{ErrorGuaranteed, Span};
 use tracing::{debug, instrument};
 
@@ -62,13 +64,15 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
 
 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
     fn lower_pattern(&mut self, pat: &'tcx hir::Pat<'tcx>) -> Box<Pat<'tcx>> {
-        let adjustments: &[Ty<'tcx>] =
+        let adjustments: &[PatAdjustment<'tcx>] =
             self.typeck_results.pat_adjustments().get(pat.hir_id).map_or(&[], |v| &**v);
 
         // Track the default binding mode for the Rust 2024 migration suggestion.
+        // Implicitly dereferencing references changes the default binding mode, but implicit deref
+        // patterns do not. Only track binding mode changes if a ref type is in the adjustments.
         let mut opt_old_mode_span = None;
         if let Some(s) = &mut self.rust_2024_migration
-            && !adjustments.is_empty()
+            && adjustments.iter().any(|adjust| adjust.kind == PatAdjust::BuiltinDeref)
         {
             opt_old_mode_span = s.visit_implicit_derefs(pat.span, adjustments);
         }
@@ -101,17 +105,23 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             _ => self.lower_pattern_unadjusted(pat),
         };
 
-        let adjusted_pat = adjustments.iter().rev().fold(unadjusted_pat, |thir_pat, ref_ty| {
-            debug!("{:?}: wrapping pattern with type {:?}", thir_pat, ref_ty);
-            Box::new(Pat {
-                span: thir_pat.span,
-                ty: *ref_ty,
-                kind: PatKind::Deref { subpattern: thir_pat },
-            })
+        let adjusted_pat = adjustments.iter().rev().fold(unadjusted_pat, |thir_pat, adjust| {
+            debug!("{:?}: wrapping pattern with adjustment {:?}", thir_pat, adjust);
+            let span = thir_pat.span;
+            let kind = match adjust.kind {
+                PatAdjust::BuiltinDeref => PatKind::Deref { subpattern: thir_pat },
+                PatAdjust::OverloadedDeref => {
+                    let mutable = self.typeck_results.pat_has_ref_mut_binding(pat);
+                    let mutability =
+                        if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
+                    PatKind::DerefPattern { subpattern: thir_pat, mutability }
+                }
+            };
+            Box::new(Pat { span, ty: adjust.source, kind })
         });
 
         if let Some(s) = &mut self.rust_2024_migration
-            && !adjustments.is_empty()
+            && adjustments.iter().any(|adjust| adjust.kind == PatAdjust::BuiltinDeref)
         {
             s.leave_ref(opt_old_mode_span);
         }
@@ -124,7 +134,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         expr: Option<&'tcx hir::PatExpr<'tcx>>,
         // Out-parameters collecting extra data to be reapplied by the caller
         ascriptions: &mut Vec<Ascription<'tcx>>,
-        inline_consts: &mut Vec<LocalDefId>,
+        expanded_consts: &mut Vec<DefId>,
     ) -> Result<Option<PatRangeBoundary<'tcx>>, ErrorGuaranteed> {
         let Some(expr) = expr else { return Ok(None) };
 
@@ -139,10 +149,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                     ascriptions.push(ascription);
                     kind = subpattern.kind;
                 }
-                PatKind::ExpandedConstant { is_inline, def_id, subpattern } => {
-                    if is_inline {
-                        inline_consts.extend(def_id.as_local());
-                    }
+                PatKind::ExpandedConstant { def_id, subpattern } => {
+                    expanded_consts.push(def_id);
                     kind = subpattern.kind;
                 }
                 _ => break,
@@ -221,10 +229,10 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         // Collect extra data while lowering the endpoints, to be reapplied later.
         let mut ascriptions = vec![];
-        let mut inline_consts = vec![];
+        let mut expanded_consts = vec![];
 
         let mut lower_endpoint =
-            |expr| self.lower_pattern_range_endpoint(expr, &mut ascriptions, &mut inline_consts);
+            |expr| self.lower_pattern_range_endpoint(expr, &mut ascriptions, &mut expanded_consts);
 
         let lo = lower_endpoint(lo_expr)?.unwrap_or(PatRangeBoundary::NegInfinity);
         let hi = lower_endpoint(hi_expr)?.unwrap_or(PatRangeBoundary::PosInfinity);
@@ -269,17 +277,12 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         // `Foo::<'a>::A..=Foo::B`), we need to put the ascriptions for the associated
         // constants somewhere. Have them on the range pattern.
         for ascription in ascriptions {
-            kind = PatKind::AscribeUserType {
-                ascription,
-                subpattern: Box::new(Pat { span, ty, kind }),
-            };
+            let subpattern = Box::new(Pat { span, ty, kind });
+            kind = PatKind::AscribeUserType { ascription, subpattern };
         }
-        for def in inline_consts {
-            kind = PatKind::ExpandedConstant {
-                def_id: def.to_def_id(),
-                is_inline: true,
-                subpattern: Box::new(Pat { span, ty, kind }),
-            };
+        for def_id in expanded_consts {
+            let subpattern = Box::new(Pat { span, ty, kind });
+            kind = PatKind::ExpandedConstant { def_id, subpattern };
         }
         Ok(kind)
     }
@@ -290,6 +293,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         let mut span = pat.span;
 
         let kind = match pat.kind {
+            hir::PatKind::Missing => PatKind::Missing,
+
             hir::PatKind::Wild => PatKind::Wild,
 
             hir::PatKind::Never => PatKind::Never,
@@ -567,15 +572,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         // Lower the named constant to a THIR pattern.
         let args = self.typeck_results.node_args(id);
         let c = ty::Const::new_unevaluated(self.tcx, ty::UnevaluatedConst { def: def_id, args });
-        let subpattern = self.const_to_pat(c, ty, id, span);
-
-        // Wrap the pattern in a marker node to indicate that it is the result
-        // of lowering a named constant. This marker is used for improved
-        // diagnostics in some situations, but has no effect at runtime.
-        let mut pattern = {
-            let kind = PatKind::ExpandedConstant { subpattern, def_id, is_inline: false };
-            Box::new(Pat { span, ty, kind })
-        };
+        let mut pattern = self.const_to_pat(c, ty, id, span);
 
         // If this is an associated constant with an explicit user-written
         // type, add an ascription node (e.g. `<Foo<'a> as MyTrait>::CONST`).
@@ -612,18 +609,37 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         let ty = tcx.typeck(def_id).node_type(block.hir_id);
 
         let typeck_root_def_id = tcx.typeck_root_def_id(def_id.to_def_id());
-        let parent_args =
-            tcx.erase_regions(ty::GenericArgs::identity_for_item(tcx, typeck_root_def_id));
+        let parent_args = ty::GenericArgs::identity_for_item(tcx, typeck_root_def_id);
         let args = ty::InlineConstArgs::new(tcx, ty::InlineConstArgsParts { parent_args, ty }).args;
 
-        debug_assert!(!args.has_free_regions());
-
         let ct = ty::UnevaluatedConst { def: def_id.to_def_id(), args };
-        let subpattern = self.const_to_pat(ty::Const::new_unevaluated(self.tcx, ct), ty, id, span);
-
-        // Wrap the pattern in a marker node to indicate that it is the result
-        // of lowering an inline const block.
-        PatKind::ExpandedConstant { subpattern, def_id: def_id.to_def_id(), is_inline: true }
+        let c = ty::Const::new_unevaluated(self.tcx, ct);
+        let pattern = self.const_to_pat(c, ty, id, span);
+
+        // Apply a type ascription for the inline constant.
+        let annotation = {
+            let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis());
+            let args = ty::InlineConstArgs::new(
+                tcx,
+                ty::InlineConstArgsParts { parent_args, ty: infcx.next_ty_var(span) },
+            )
+            .args;
+            infcx.canonicalize_user_type_annotation(ty::UserType::new(ty::UserTypeKind::TypeOf(
+                def_id.to_def_id(),
+                ty::UserArgs { args, user_self_ty: None },
+            )))
+        };
+        let annotation =
+            CanonicalUserTypeAnnotation { user_ty: Box::new(annotation), span, inferred_ty: ty };
+        PatKind::AscribeUserType {
+            subpattern: pattern,
+            ascription: Ascription {
+                annotation,
+                // Note that we use `Contravariant` here. See the `variance` field documentation
+                // for details.
+                variance: ty::Contravariant,
+            },
+        }
     }
 
     /// Lowers the kinds of "expression" that can appear in a HIR pattern:
@@ -635,43 +651,41 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         expr: &'tcx hir::PatExpr<'tcx>,
         pat_ty: Option<Ty<'tcx>>,
     ) -> PatKind<'tcx> {
-        let (lit, neg) = match &expr.kind {
-            hir::PatExprKind::Path(qpath) => {
-                return self.lower_path(qpath, expr.hir_id, expr.span).kind;
-            }
+        match &expr.kind {
+            hir::PatExprKind::Path(qpath) => self.lower_path(qpath, expr.hir_id, expr.span).kind,
             hir::PatExprKind::ConstBlock(anon_const) => {
-                return self.lower_inline_const(anon_const, expr.hir_id, expr.span);
+                self.lower_inline_const(anon_const, expr.hir_id, expr.span)
             }
-            hir::PatExprKind::Lit { lit, negated } => (lit, *negated),
-        };
-
-        // We handle byte string literal patterns by using the pattern's type instead of the
-        // literal's type in `const_to_pat`: if the literal `b"..."` matches on a slice reference,
-        // the pattern's type will be `&[u8]` whereas the literal's type is `&[u8; 3]`; using the
-        // pattern's type means we'll properly translate it to a slice reference pattern. This works
-        // because slices and arrays have the same valtree representation.
-        // HACK: As an exception, use the literal's type if `pat_ty` is `String`; this can happen if
-        // `string_deref_patterns` is enabled. There's a special case for that when lowering to MIR.
-        // FIXME(deref_patterns): This hack won't be necessary once `string_deref_patterns` is
-        // superseded by a more general implementation of deref patterns.
-        let ct_ty = match pat_ty {
-            Some(pat_ty)
-                if let ty::Adt(def, _) = *pat_ty.kind()
-                    && self.tcx.is_lang_item(def.did(), LangItem::String) =>
-            {
-                if !self.tcx.features().string_deref_patterns() {
-                    span_bug!(
-                        expr.span,
-                        "matching on `String` went through without enabling string_deref_patterns"
-                    );
-                }
-                self.typeck_results.node_type(expr.hir_id)
+            hir::PatExprKind::Lit { lit, negated } => {
+                // We handle byte string literal patterns by using the pattern's type instead of the
+                // literal's type in `const_to_pat`: if the literal `b"..."` matches on a slice reference,
+                // the pattern's type will be `&[u8]` whereas the literal's type is `&[u8; 3]`; using the
+                // pattern's type means we'll properly translate it to a slice reference pattern. This works
+                // because slices and arrays have the same valtree representation.
+                // HACK: As an exception, use the literal's type if `pat_ty` is `String`; this can happen if
+                // `string_deref_patterns` is enabled. There's a special case for that when lowering to MIR.
+                // FIXME(deref_patterns): This hack won't be necessary once `string_deref_patterns` is
+                // superseded by a more general implementation of deref patterns.
+                let ct_ty = match pat_ty {
+                    Some(pat_ty)
+                        if let ty::Adt(def, _) = *pat_ty.kind()
+                            && self.tcx.is_lang_item(def.did(), LangItem::String) =>
+                    {
+                        if !self.tcx.features().string_deref_patterns() {
+                            span_bug!(
+                                expr.span,
+                                "matching on `String` went through without enabling string_deref_patterns"
+                            );
+                        }
+                        self.typeck_results.node_type(expr.hir_id)
+                    }
+                    Some(pat_ty) => pat_ty,
+                    None => self.typeck_results.node_type(expr.hir_id),
+                };
+                let lit_input = LitToConstInput { lit: &lit.node, ty: ct_ty, neg: *negated };
+                let constant = self.tcx.at(expr.span).lit_to_const(lit_input);
+                self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind
             }
-            Some(pat_ty) => pat_ty,
-            None => self.typeck_results.node_type(expr.hir_id),
-        };
-        let lit_input = LitToConstInput { lit: &lit.node, ty: ct_ty, neg };
-        let constant = self.tcx.at(expr.span).lit_to_const(lit_input);
-        self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind
+        }
     }
 }
diff --git a/compiler/rustc_mir_build/src/thir/print.rs b/compiler/rustc_mir_build/src/thir/print.rs
index 16cef0ec3ac..37248941e2c 100644
--- a/compiler/rustc_mir_build/src/thir/print.rs
+++ b/compiler/rustc_mir_build/src/thir/print.rs
@@ -664,6 +664,7 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
         print_indented!(self, "kind: PatKind {", depth_lvl);
 
         match pat_kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => {
                 print_indented!(self, "Wild", depth_lvl + 1);
             }
@@ -740,10 +741,9 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
                 print_indented!(self, format!("value: {:?}", value), depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);
             }
-            PatKind::ExpandedConstant { def_id, is_inline, subpattern } => {
+            PatKind::ExpandedConstant { def_id, subpattern } => {
                 print_indented!(self, "ExpandedConstant {", depth_lvl + 1);
                 print_indented!(self, format!("def_id: {def_id:?}"), depth_lvl + 2);
-                print_indented!(self, format!("is_inline: {is_inline:?}"), depth_lvl + 2);
                 print_indented!(self, "subpattern:", depth_lvl + 2);
                 self.print_pat(subpattern, depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);
diff --git a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
index 448fad2dc3e..95f488a925b 100644
--- a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
@@ -109,27 +109,29 @@ impl RustcMirAttrs {
             .flat_map(|attr| attr.meta_item_list().into_iter().flat_map(|v| v.into_iter()));
 
         for attr in rustc_mir_attrs {
-            let attr_result = if attr.has_name(sym::borrowck_graphviz_postflow) {
-                Self::set_field(&mut ret.basename_and_suffix, tcx, &attr, |s| {
-                    let path = PathBuf::from(s.to_string());
-                    match path.file_name() {
-                        Some(_) => Ok(path),
-                        None => {
-                            tcx.dcx().emit_err(PathMustEndInFilename { span: attr.span() });
+            let attr_result = match attr.name() {
+                Some(name @ sym::borrowck_graphviz_postflow) => {
+                    Self::set_field(&mut ret.basename_and_suffix, tcx, name, &attr, |s| {
+                        let path = PathBuf::from(s.to_string());
+                        match path.file_name() {
+                            Some(_) => Ok(path),
+                            None => {
+                                tcx.dcx().emit_err(PathMustEndInFilename { span: attr.span() });
+                                Err(())
+                            }
+                        }
+                    })
+                }
+                Some(name @ sym::borrowck_graphviz_format) => {
+                    Self::set_field(&mut ret.formatter, tcx, name, &attr, |s| match s {
+                        sym::two_phase => Ok(s),
+                        _ => {
+                            tcx.dcx().emit_err(UnknownFormatter { span: attr.span() });
                             Err(())
                         }
-                    }
-                })
-            } else if attr.has_name(sym::borrowck_graphviz_format) {
-                Self::set_field(&mut ret.formatter, tcx, &attr, |s| match s {
-                    sym::gen_kill | sym::two_phase => Ok(s),
-                    _ => {
-                        tcx.dcx().emit_err(UnknownFormatter { span: attr.span() });
-                        Err(())
-                    }
-                })
-            } else {
-                Ok(())
+                    })
+                }
+                _ => Ok(()),
             };
 
             result = result.and(attr_result);
@@ -141,12 +143,12 @@ impl RustcMirAttrs {
     fn set_field<T>(
         field: &mut Option<T>,
         tcx: TyCtxt<'_>,
+        name: Symbol,
         attr: &ast::MetaItemInner,
         mapper: impl FnOnce(Symbol) -> Result<T, ()>,
     ) -> Result<(), ()> {
         if field.is_some() {
-            tcx.dcx()
-                .emit_err(DuplicateValuesFor { span: attr.span(), name: attr.name_or_empty() });
+            tcx.dcx().emit_err(DuplicateValuesFor { span: attr.span(), name });
 
             return Err(());
         }
@@ -156,7 +158,7 @@ impl RustcMirAttrs {
             Ok(())
         } else {
             tcx.dcx()
-                .emit_err(RequiresAnArgument { span: attr.span(), name: attr.name_or_empty() });
+                .emit_err(RequiresAnArgument { span: attr.span(), name: attr.name().unwrap() });
             Err(())
         }
     }
diff --git a/compiler/rustc_mir_dataflow/src/lib.rs b/compiler/rustc_mir_dataflow/src/lib.rs
index 82c57ef5678..a0efc623b8e 100644
--- a/compiler/rustc_mir_dataflow/src/lib.rs
+++ b/compiler/rustc_mir_dataflow/src/lib.rs
@@ -1,5 +1,4 @@
 // tidy-alphabetical-start
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(assert_matches)]
 #![feature(associated_type_defaults)]
 #![feature(box_patterns)]
diff --git a/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs b/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs
index ed3b1ae4f42..daddb5dedbc 100644
--- a/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs
+++ b/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs
@@ -42,7 +42,7 @@ impl<'a, 'tcx> UndefinedTransmutesChecker<'a, 'tcx> {
         if self.tcx.is_const_fn(def_id)
             || matches!(
                 self.tcx.opt_associated_item(def_id),
-                Some(AssocItem { kind: AssocKind::Const, .. })
+                Some(AssocItem { kind: AssocKind::Const { .. }, .. })
             )
         {
             let fn_sig = function.ty(self.body, self.tcx).fn_sig(self.tcx).skip_binder();
diff --git a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
index cb844019857..4be67b873f7 100644
--- a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
+++ b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
@@ -35,7 +35,8 @@ impl<'tcx> crate::MirPass<'tcx> for CleanupPostBorrowck {
                         // MIR building, and are not needed after InstrumentCoverage.
                         CoverageKind::BlockMarker { .. } | CoverageKind::SpanMarker { .. },
                     )
-                    | StatementKind::FakeRead(..) => statement.make_nop(),
+                    | StatementKind::FakeRead(..)
+                    | StatementKind::BackwardIncompatibleDropHint { .. } => statement.make_nop(),
                     StatementKind::Assign(box (
                         _,
                         Rvalue::Cast(
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index 04d96f11707..92d5e152f58 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -203,7 +203,7 @@ struct TransformVisitor<'tcx> {
 
 impl<'tcx> TransformVisitor<'tcx> {
     fn insert_none_ret_block(&self, body: &mut Body<'tcx>) -> BasicBlock {
-        let block = BasicBlock::new(body.basic_blocks.len());
+        let block = body.basic_blocks.next_index();
         let source_info = SourceInfo::outermost(body.span);
 
         let none_value = match self.coroutine_kind {
@@ -547,7 +547,7 @@ fn transform_async_context<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 
     let get_context_def_id = tcx.require_lang_item(LangItem::GetContext, None);
 
-    for bb in START_BLOCK..body.basic_blocks.next_index() {
+    for bb in body.basic_blocks.indices() {
         let bb_data = &body[bb];
         if bb_data.is_cleanup {
             continue;
@@ -556,11 +556,11 @@ fn transform_async_context<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         match &bb_data.terminator().kind {
             TerminatorKind::Call { func, .. } => {
                 let func_ty = func.ty(body, tcx);
-                if let ty::FnDef(def_id, _) = *func_ty.kind() {
-                    if def_id == get_context_def_id {
-                        let local = eliminate_get_context_call(&mut body[bb]);
-                        replace_resume_ty_local(tcx, body, local, context_mut_ref);
-                    }
+                if let ty::FnDef(def_id, _) = *func_ty.kind()
+                    && def_id == get_context_def_id
+                {
+                    let local = eliminate_get_context_call(&mut body[bb]);
+                    replace_resume_ty_local(tcx, body, local, context_mut_ref);
                 }
             }
             TerminatorKind::Yield { resume_arg, .. } => {
@@ -1057,7 +1057,7 @@ fn insert_switch<'tcx>(
     let blocks = body.basic_blocks_mut().iter_mut();
 
     for target in blocks.flat_map(|b| b.terminator_mut().successors_mut()) {
-        *target = BasicBlock::new(target.index() + 1);
+        *target += 1;
     }
 }
 
@@ -1169,6 +1169,13 @@ fn create_coroutine_drop_shim<'tcx>(
     dump_mir(tcx, false, "coroutine_drop", &0, &body, |_, _| Ok(()));
     body.source.instance = drop_instance;
 
+    // Creating a coroutine drop shim happens on `Analysis(PostCleanup) -> Runtime(Initial)`
+    // but the pass manager doesn't update the phase of the coroutine drop shim. Update the
+    // phase of the drop shim so that later on when we run the pass manager on the shim, in
+    // the `mir_shims` query, we don't ICE on the intra-pass validation before we've updated
+    // the phase of the body from analysis.
+    body.phase = MirPhase::Runtime(RuntimePhase::Initial);
+
     body
 }
 
@@ -1186,7 +1193,7 @@ fn insert_panic_block<'tcx>(
     body: &mut Body<'tcx>,
     message: AssertMessage<'tcx>,
 ) -> BasicBlock {
-    let assert_block = BasicBlock::new(body.basic_blocks.len());
+    let assert_block = body.basic_blocks.next_index();
     let kind = TerminatorKind::Assert {
         cond: Operand::Constant(Box::new(ConstOperand {
             span: body.span,
@@ -1209,14 +1216,8 @@ fn can_return<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, typing_env: ty::Typing
     }
 
     // If there's a return terminator the function may return.
-    for block in body.basic_blocks.iter() {
-        if let TerminatorKind::Return = block.terminator().kind {
-            return true;
-        }
-    }
-
+    body.basic_blocks.iter().any(|block| matches!(block.terminator().kind, TerminatorKind::Return))
     // Otherwise the function can't return.
-    false
 }
 
 fn can_unwind<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) -> bool {
@@ -1293,12 +1294,12 @@ fn create_coroutine_resume_function<'tcx>(
                         kind: TerminatorKind::Goto { target: poison_block },
                     };
                 }
-            } else if !block.is_cleanup {
+            } else if !block.is_cleanup
                 // Any terminators that *can* unwind but don't have an unwind target set are also
                 // pointed at our poisoning block (unless they're part of the cleanup path).
-                if let Some(unwind @ UnwindAction::Continue) = block.terminator_mut().unwind_mut() {
-                    *unwind = UnwindAction::Cleanup(poison_block);
-                }
+                && let Some(unwind @ UnwindAction::Continue) = block.terminator_mut().unwind_mut()
+            {
+                *unwind = UnwindAction::Cleanup(poison_block);
             }
         }
     }
@@ -1340,12 +1341,14 @@ fn create_coroutine_resume_function<'tcx>(
     make_coroutine_state_argument_indirect(tcx, body);
 
     match transform.coroutine_kind {
+        CoroutineKind::Coroutine(_)
+        | CoroutineKind::Desugared(CoroutineDesugaring::Async | CoroutineDesugaring::AsyncGen, _) =>
+        {
+            make_coroutine_state_argument_pinned(tcx, body);
+        }
         // Iterator::next doesn't accept a pinned argument,
         // unlike for all other coroutine kinds.
         CoroutineKind::Desugared(CoroutineDesugaring::Gen, _) => {}
-        _ => {
-            make_coroutine_state_argument_pinned(tcx, body);
-        }
     }
 
     // Make sure we remove dead blocks to remove
@@ -1408,8 +1411,7 @@ fn create_cases<'tcx>(
                 let mut statements = Vec::new();
 
                 // Create StorageLive instructions for locals with live storage
-                for i in 0..(body.local_decls.len()) {
-                    let l = Local::new(i);
+                for l in body.local_decls.indices() {
                     let needs_storage_live = point.storage_liveness.contains(l)
                         && !transform.remap.contains(l)
                         && !transform.always_live_locals.contains(l);
@@ -1535,15 +1537,10 @@ impl<'tcx> crate::MirPass<'tcx> for StateTransform {
         let coroutine_kind = body.coroutine_kind().unwrap();
 
         // Get the discriminant type and args which typeck computed
-        let (discr_ty, movable) = match *coroutine_ty.kind() {
-            ty::Coroutine(_, args) => {
-                let args = args.as_coroutine();
-                (args.discr_ty(tcx), coroutine_kind.movability() == hir::Movability::Movable)
-            }
-            _ => {
-                tcx.dcx().span_bug(body.span, format!("unexpected coroutine type {coroutine_ty}"));
-            }
+        let ty::Coroutine(_, args) = coroutine_ty.kind() else {
+            tcx.dcx().span_bug(body.span, format!("unexpected coroutine type {coroutine_ty}"));
         };
+        let discr_ty = args.as_coroutine().discr_ty(tcx);
 
         let new_ret_ty = match coroutine_kind {
             CoroutineKind::Desugared(CoroutineDesugaring::Async, _) => {
@@ -1610,6 +1607,7 @@ impl<'tcx> crate::MirPass<'tcx> for StateTransform {
 
         let always_live_locals = always_storage_live_locals(body);
 
+        let movable = coroutine_kind.movability() == hir::Movability::Movable;
         let liveness_info =
             locals_live_across_suspend_points(tcx, body, &always_live_locals, movable);
 
diff --git a/compiler/rustc_mir_transform/src/early_otherwise_branch.rs b/compiler/rustc_mir_transform/src/early_otherwise_branch.rs
index 57f7893be1b..d49f5d9f9c3 100644
--- a/compiler/rustc_mir_transform/src/early_otherwise_branch.rs
+++ b/compiler/rustc_mir_transform/src/early_otherwise_branch.rs
@@ -103,9 +103,8 @@ impl<'tcx> crate::MirPass<'tcx> for EarlyOtherwiseBranch {
         let mut should_cleanup = false;
 
         // Also consider newly generated bbs in the same pass
-        for i in 0..body.basic_blocks.len() {
+        for parent in body.basic_blocks.indices() {
             let bbs = &*body.basic_blocks;
-            let parent = BasicBlock::from_usize(i);
             let Some(opt_data) = evaluate_candidate(tcx, body, parent) else { continue };
 
             trace!("SUCCESS: found optimization possibility to apply: {opt_data:?}");
diff --git a/compiler/rustc_mir_transform/src/elaborate_drop.rs b/compiler/rustc_mir_transform/src/elaborate_drop.rs
index 0d8cf524661..e3057a2f648 100644
--- a/compiler/rustc_mir_transform/src/elaborate_drop.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_drop.rs
@@ -258,31 +258,27 @@ where
     ) -> Vec<(Place<'tcx>, Option<D::Path>)> {
         variant
             .fields
-            .iter()
-            .enumerate()
-            .map(|(i, f)| {
-                let field = FieldIdx::new(i);
-                let subpath = self.elaborator.field_subpath(variant_path, field);
+            .iter_enumerated()
+            .map(|(field_idx, field)| {
+                let subpath = self.elaborator.field_subpath(variant_path, field_idx);
                 let tcx = self.tcx();
 
                 assert_eq!(self.elaborator.typing_env().typing_mode, ty::TypingMode::PostAnalysis);
-                // The type error for normalization may have been in dropck: see
-                // `compute_drop_data` in rustc_borrowck, in which case we wouldn't have
-                // deleted the MIR body and could have an error here as well.
-                let field_ty = match tcx
-                    .try_normalize_erasing_regions(self.elaborator.typing_env(), f.ty(tcx, args))
-                {
+                let field_ty = match tcx.try_normalize_erasing_regions(
+                    self.elaborator.typing_env(),
+                    field.ty(tcx, args),
+                ) {
                     Ok(t) => t,
                     Err(_) => Ty::new_error(
                         self.tcx(),
-                        self.elaborator
-                            .body()
-                            .tainted_by_errors
-                            .expect("Error in drop elaboration not found by dropck."),
+                        self.tcx().dcx().span_delayed_bug(
+                            self.elaborator.body().span,
+                            "Error normalizing in drop elaboration.",
+                        ),
                     ),
                 };
 
-                (tcx.mk_place_field(base_place, field, field_ty), subpath)
+                (tcx.mk_place_field(base_place, field_idx, field_ty), subpath)
             })
             .collect()
     }
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 68bc0ffce6b..8b8d1efbbd2 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -980,27 +980,17 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             }
         }
 
-        let tcx = self.tcx;
-        let mut projection = SmallVec::<[PlaceElem<'tcx>; 1]>::new();
-        loop {
-            if let Some(local) = self.try_as_local(copy_from_local_value, location) {
-                projection.reverse();
-                let place = Place { local, projection: tcx.mk_place_elems(projection.as_slice()) };
-                if rvalue.ty(self.local_decls, tcx) == place.ty(self.local_decls, tcx).ty {
-                    self.reused_locals.insert(local);
-                    *rvalue = Rvalue::Use(Operand::Copy(place));
-                    return Some(copy_from_value);
-                }
-                return None;
-            } else if let Value::Projection(pointer, proj) = *self.get(copy_from_local_value)
-                && let Some(proj) = self.try_as_place_elem(proj, location)
-            {
-                projection.push(proj);
-                copy_from_local_value = pointer;
-            } else {
-                return None;
+        // Allow introducing places with non-constant offsets, as those are still better than
+        // reconstructing an aggregate.
+        if let Some(place) = self.try_as_place(copy_from_local_value, location, true) {
+            if rvalue.ty(self.local_decls, self.tcx) == place.ty(self.local_decls, self.tcx).ty {
+                self.reused_locals.insert(place.local);
+                *rvalue = Rvalue::Use(Operand::Copy(place));
+                return Some(copy_from_local_value);
             }
         }
+
+        None
     }
 
     fn simplify_aggregate(
@@ -1672,14 +1662,14 @@ fn op_to_prop_const<'tcx>(
 }
 
 impl<'tcx> VnState<'_, 'tcx> {
-    /// If either [`Self::try_as_constant`] as [`Self::try_as_local`] succeeds,
+    /// If either [`Self::try_as_constant`] as [`Self::try_as_place`] succeeds,
     /// returns that result as an [`Operand`].
     fn try_as_operand(&mut self, index: VnIndex, location: Location) -> Option<Operand<'tcx>> {
         if let Some(const_) = self.try_as_constant(index) {
             Some(Operand::Constant(Box::new(const_)))
-        } else if let Some(local) = self.try_as_local(index, location) {
-            self.reused_locals.insert(local);
-            Some(Operand::Copy(local.into()))
+        } else if let Some(place) = self.try_as_place(index, location, false) {
+            self.reused_locals.insert(place.local);
+            Some(Operand::Copy(place))
         } else {
             None
         }
@@ -1712,6 +1702,35 @@ impl<'tcx> VnState<'_, 'tcx> {
         Some(ConstOperand { span: DUMMY_SP, user_ty: None, const_ })
     }
 
+    /// Construct a place which holds the same value as `index` and for which all locals strictly
+    /// dominate `loc`. If you used this place, add its base local to `reused_locals` to remove
+    /// storage statements.
+    #[instrument(level = "trace", skip(self), ret)]
+    fn try_as_place(
+        &mut self,
+        mut index: VnIndex,
+        loc: Location,
+        allow_complex_projection: bool,
+    ) -> Option<Place<'tcx>> {
+        let mut projection = SmallVec::<[PlaceElem<'tcx>; 1]>::new();
+        loop {
+            if let Some(local) = self.try_as_local(index, loc) {
+                projection.reverse();
+                let place =
+                    Place { local, projection: self.tcx.mk_place_elems(projection.as_slice()) };
+                return Some(place);
+            } else if let Value::Projection(pointer, proj) = *self.get(index)
+                && (allow_complex_projection || proj.is_stable_offset())
+                && let Some(proj) = self.try_as_place_elem(proj, loc)
+            {
+                projection.push(proj);
+                index = pointer;
+            } else {
+                return None;
+            }
+        }
+    }
+
     /// If there is a local which is assigned `index`, and its assignment strictly dominates `loc`,
     /// return it. If you used this local, add it to `reused_locals` to remove storage statements.
     fn try_as_local(&mut self, index: VnIndex, loc: Location) -> Option<Local> {
@@ -1762,11 +1781,12 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
             if let Some(value) = value {
                 if let Some(const_) = self.try_as_constant(value) {
                     *rvalue = Rvalue::Use(Operand::Constant(Box::new(const_)));
-                } else if let Some(local) = self.try_as_local(value, location)
-                    && *rvalue != Rvalue::Use(Operand::Move(local.into()))
+                } else if let Some(place) = self.try_as_place(value, location, false)
+                    && *rvalue != Rvalue::Use(Operand::Move(place))
+                    && *rvalue != Rvalue::Use(Operand::Copy(place))
                 {
-                    *rvalue = Rvalue::Use(Operand::Copy(local.into()));
-                    self.reused_locals.insert(local);
+                    *rvalue = Rvalue::Use(Operand::Copy(place));
+                    self.reused_locals.insert(place.local);
                 }
             }
         }
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index 0ab24e48d44..69e80ed54ea 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -903,9 +903,9 @@ fn inline_call<'tcx, I: Inliner<'tcx>>(
 
     let mut integrator = Integrator {
         args: &args,
-        new_locals: Local::new(caller_body.local_decls.len())..,
-        new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
-        new_blocks: BasicBlock::new(caller_body.basic_blocks.len())..,
+        new_locals: caller_body.local_decls.next_index()..,
+        new_scopes: caller_body.source_scopes.next_index()..,
+        new_blocks: caller_body.basic_blocks.next_index()..,
         destination: destination_local,
         callsite_scope: caller_body.source_scopes[callsite.source_info.scope].clone(),
         callsite,
@@ -1169,7 +1169,7 @@ impl Integrator<'_, '_> {
             if idx < self.args.len() {
                 self.args[idx]
             } else {
-                Local::new(self.new_locals.start.index() + (idx - self.args.len()))
+                self.new_locals.start + (idx - self.args.len())
             }
         };
         trace!("mapping local `{:?}` to `{:?}`", local, new);
@@ -1177,13 +1177,13 @@ impl Integrator<'_, '_> {
     }
 
     fn map_scope(&self, scope: SourceScope) -> SourceScope {
-        let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
+        let new = self.new_scopes.start + scope.index();
         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
         new
     }
 
     fn map_block(&self, block: BasicBlock) -> BasicBlock {
-        let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
+        let new = self.new_blocks.start + block.index();
         trace!("mapping block `{:?}` to `{:?}`", block, new);
         new
     }
diff --git a/compiler/rustc_mir_transform/src/instsimplify.rs b/compiler/rustc_mir_transform/src/instsimplify.rs
index 2eff6b31372..5f0c55ddc09 100644
--- a/compiler/rustc_mir_transform/src/instsimplify.rs
+++ b/compiler/rustc_mir_transform/src/instsimplify.rs
@@ -10,7 +10,6 @@ use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, layout};
 use rustc_span::{DUMMY_SP, Symbol, sym};
 
 use crate::simplify::simplify_duplicate_switch_targets;
-use crate::take_array;
 
 pub(super) enum InstSimplify {
     BeforeInline,
@@ -39,26 +38,26 @@ impl<'tcx> crate::MirPass<'tcx> for InstSimplify {
             attr::contains_name(tcx.hir_krate_attrs(), sym::rustc_preserve_ub_checks);
         for block in body.basic_blocks.as_mut() {
             for statement in block.statements.iter_mut() {
-                match statement.kind {
-                    StatementKind::Assign(box (_place, ref mut rvalue)) => {
-                        if !preserve_ub_checks {
-                            ctx.simplify_ub_check(rvalue);
-                        }
-                        ctx.simplify_bool_cmp(rvalue);
-                        ctx.simplify_ref_deref(rvalue);
-                        ctx.simplify_ptr_aggregate(rvalue);
-                        ctx.simplify_cast(rvalue);
-                        ctx.simplify_repeated_aggregate(rvalue);
-                        ctx.simplify_repeat_once(rvalue);
-                    }
-                    _ => {}
+                let StatementKind::Assign(box (.., rvalue)) = &mut statement.kind else {
+                    continue;
+                };
+
+                if !preserve_ub_checks {
+                    ctx.simplify_ub_check(rvalue);
                 }
+                ctx.simplify_bool_cmp(rvalue);
+                ctx.simplify_ref_deref(rvalue);
+                ctx.simplify_ptr_aggregate(rvalue);
+                ctx.simplify_cast(rvalue);
+                ctx.simplify_repeated_aggregate(rvalue);
+                ctx.simplify_repeat_once(rvalue);
             }
 
-            ctx.simplify_primitive_clone(block.terminator.as_mut().unwrap(), &mut block.statements);
-            ctx.simplify_intrinsic_assert(block.terminator.as_mut().unwrap());
-            ctx.simplify_nounwind_call(block.terminator.as_mut().unwrap());
-            simplify_duplicate_switch_targets(block.terminator.as_mut().unwrap());
+            let terminator = block.terminator.as_mut().unwrap();
+            ctx.simplify_primitive_clone(terminator, &mut block.statements);
+            ctx.simplify_intrinsic_assert(terminator);
+            ctx.simplify_nounwind_call(terminator);
+            simplify_duplicate_switch_targets(terminator);
         }
     }
 
@@ -105,43 +104,34 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
 
     /// Transform boolean comparisons into logical operations.
     fn simplify_bool_cmp(&self, rvalue: &mut Rvalue<'tcx>) {
-        match rvalue {
-            Rvalue::BinaryOp(op @ (BinOp::Eq | BinOp::Ne), box (a, b)) => {
-                let new = match (op, self.try_eval_bool(a), self.try_eval_bool(b)) {
-                    // Transform "Eq(a, true)" ==> "a"
-                    (BinOp::Eq, _, Some(true)) => Some(Rvalue::Use(a.clone())),
+        let Rvalue::BinaryOp(op @ (BinOp::Eq | BinOp::Ne), box (a, b)) = &*rvalue else { return };
+        *rvalue = match (op, self.try_eval_bool(a), self.try_eval_bool(b)) {
+            // Transform "Eq(a, true)" ==> "a"
+            (BinOp::Eq, _, Some(true)) => Rvalue::Use(a.clone()),
 
-                    // Transform "Ne(a, false)" ==> "a"
-                    (BinOp::Ne, _, Some(false)) => Some(Rvalue::Use(a.clone())),
+            // Transform "Ne(a, false)" ==> "a"
+            (BinOp::Ne, _, Some(false)) => Rvalue::Use(a.clone()),
 
-                    // Transform "Eq(true, b)" ==> "b"
-                    (BinOp::Eq, Some(true), _) => Some(Rvalue::Use(b.clone())),
+            // Transform "Eq(true, b)" ==> "b"
+            (BinOp::Eq, Some(true), _) => Rvalue::Use(b.clone()),
 
-                    // Transform "Ne(false, b)" ==> "b"
-                    (BinOp::Ne, Some(false), _) => Some(Rvalue::Use(b.clone())),
+            // Transform "Ne(false, b)" ==> "b"
+            (BinOp::Ne, Some(false), _) => Rvalue::Use(b.clone()),
 
-                    // Transform "Eq(false, b)" ==> "Not(b)"
-                    (BinOp::Eq, Some(false), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())),
+            // Transform "Eq(false, b)" ==> "Not(b)"
+            (BinOp::Eq, Some(false), _) => Rvalue::UnaryOp(UnOp::Not, b.clone()),
 
-                    // Transform "Ne(true, b)" ==> "Not(b)"
-                    (BinOp::Ne, Some(true), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())),
+            // Transform "Ne(true, b)" ==> "Not(b)"
+            (BinOp::Ne, Some(true), _) => Rvalue::UnaryOp(UnOp::Not, b.clone()),
 
-                    // Transform "Eq(a, false)" ==> "Not(a)"
-                    (BinOp::Eq, _, Some(false)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())),
+            // Transform "Eq(a, false)" ==> "Not(a)"
+            (BinOp::Eq, _, Some(false)) => Rvalue::UnaryOp(UnOp::Not, a.clone()),
 
-                    // Transform "Ne(a, true)" ==> "Not(a)"
-                    (BinOp::Ne, _, Some(true)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())),
+            // Transform "Ne(a, true)" ==> "Not(a)"
+            (BinOp::Ne, _, Some(true)) => Rvalue::UnaryOp(UnOp::Not, a.clone()),
 
-                    _ => None,
-                };
-
-                if let Some(new) = new {
-                    *rvalue = new;
-                }
-            }
-
-            _ => {}
-        }
+            _ => return,
+        };
     }
 
     fn try_eval_bool(&self, a: &Operand<'_>) -> Option<bool> {
@@ -151,64 +141,58 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
 
     /// Transform `&(*a)` ==> `a`.
     fn simplify_ref_deref(&self, rvalue: &mut Rvalue<'tcx>) {
-        if let Rvalue::Ref(_, _, place) | Rvalue::RawPtr(_, place) = rvalue {
-            if let Some((base, ProjectionElem::Deref)) = place.as_ref().last_projection() {
-                if rvalue.ty(self.local_decls, self.tcx) != base.ty(self.local_decls, self.tcx).ty {
-                    return;
-                }
-
-                *rvalue = Rvalue::Use(Operand::Copy(Place {
-                    local: base.local,
-                    projection: self.tcx.mk_place_elems(base.projection),
-                }));
-            }
+        if let Rvalue::Ref(_, _, place) | Rvalue::RawPtr(_, place) = rvalue
+            && let Some((base, ProjectionElem::Deref)) = place.as_ref().last_projection()
+            && rvalue.ty(self.local_decls, self.tcx) == base.ty(self.local_decls, self.tcx).ty
+        {
+            *rvalue = Rvalue::Use(Operand::Copy(Place {
+                local: base.local,
+                projection: self.tcx.mk_place_elems(base.projection),
+            }));
         }
     }
 
     /// Transform `Aggregate(RawPtr, [p, ()])` ==> `Cast(PtrToPtr, p)`.
     fn simplify_ptr_aggregate(&self, rvalue: &mut Rvalue<'tcx>) {
         if let Rvalue::Aggregate(box AggregateKind::RawPtr(pointee_ty, mutability), fields) = rvalue
+            && let meta_ty = fields.raw[1].ty(self.local_decls, self.tcx)
+            && meta_ty.is_unit()
         {
-            let meta_ty = fields.raw[1].ty(self.local_decls, self.tcx);
-            if meta_ty.is_unit() {
-                // The mutable borrows we're holding prevent printing `rvalue` here
-                let mut fields = std::mem::take(fields);
-                let _meta = fields.pop().unwrap();
-                let data = fields.pop().unwrap();
-                let ptr_ty = Ty::new_ptr(self.tcx, *pointee_ty, *mutability);
-                *rvalue = Rvalue::Cast(CastKind::PtrToPtr, data, ptr_ty);
-            }
+            // The mutable borrows we're holding prevent printing `rvalue` here
+            let mut fields = std::mem::take(fields);
+            let _meta = fields.pop().unwrap();
+            let data = fields.pop().unwrap();
+            let ptr_ty = Ty::new_ptr(self.tcx, *pointee_ty, *mutability);
+            *rvalue = Rvalue::Cast(CastKind::PtrToPtr, data, ptr_ty);
         }
     }
 
     fn simplify_ub_check(&self, rvalue: &mut Rvalue<'tcx>) {
-        if let Rvalue::NullaryOp(NullOp::UbChecks, _) = *rvalue {
-            let const_ = Const::from_bool(self.tcx, self.tcx.sess.ub_checks());
-            let constant = ConstOperand { span: DUMMY_SP, const_, user_ty: None };
-            *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant)));
-        }
+        let Rvalue::NullaryOp(NullOp::UbChecks, _) = *rvalue else { return };
+
+        let const_ = Const::from_bool(self.tcx, self.tcx.sess.ub_checks());
+        let constant = ConstOperand { span: DUMMY_SP, const_, user_ty: None };
+        *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant)));
     }
 
     fn simplify_cast(&self, rvalue: &mut Rvalue<'tcx>) {
-        if let Rvalue::Cast(kind, operand, cast_ty) = rvalue {
-            let operand_ty = operand.ty(self.local_decls, self.tcx);
-            if operand_ty == *cast_ty {
-                *rvalue = Rvalue::Use(operand.clone());
-            } else if *kind == CastKind::Transmute {
-                // Transmuting an integer to another integer is just a signedness cast
-                if let (ty::Int(int), ty::Uint(uint)) | (ty::Uint(uint), ty::Int(int)) =
-                    (operand_ty.kind(), cast_ty.kind())
-                    && int.bit_width() == uint.bit_width()
-                {
-                    // The width check isn't strictly necessary, as different widths
-                    // are UB and thus we'd be allowed to turn it into a cast anyway.
-                    // But let's keep the UB around for codegen to exploit later.
-                    // (If `CastKind::Transmute` ever becomes *not* UB for mismatched sizes,
-                    // then the width check is necessary for big-endian correctness.)
-                    *kind = CastKind::IntToInt;
-                    return;
-                }
-            }
+        let Rvalue::Cast(kind, operand, cast_ty) = rvalue else { return };
+
+        let operand_ty = operand.ty(self.local_decls, self.tcx);
+        if operand_ty == *cast_ty {
+            *rvalue = Rvalue::Use(operand.clone());
+        } else if *kind == CastKind::Transmute
+            // Transmuting an integer to another integer is just a signedness cast
+            && let (ty::Int(int), ty::Uint(uint)) | (ty::Uint(uint), ty::Int(int)) =
+                (operand_ty.kind(), cast_ty.kind())
+            && int.bit_width() == uint.bit_width()
+        {
+            // The width check isn't strictly necessary, as different widths
+            // are UB and thus we'd be allowed to turn it into a cast anyway.
+            // But let's keep the UB around for codegen to exploit later.
+            // (If `CastKind::Transmute` ever becomes *not* UB for mismatched sizes,
+            // then the width check is necessary for big-endian correctness.)
+            *kind = CastKind::IntToInt;
         }
     }
 
@@ -229,7 +213,9 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
         terminator: &mut Terminator<'tcx>,
         statements: &mut Vec<Statement<'tcx>>,
     ) {
-        let TerminatorKind::Call { func, args, destination, target, .. } = &mut terminator.kind
+        let TerminatorKind::Call {
+            func, args, destination, target: Some(destination_block), ..
+        } = &terminator.kind
         else {
             return;
         };
@@ -237,15 +223,8 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
         // It's definitely not a clone if there are multiple arguments
         let [arg] = &args[..] else { return };
 
-        let Some(destination_block) = *target else { return };
-
         // Only bother looking more if it's easy to know what we're calling
-        let Some((fn_def_id, fn_args)) = func.const_fn_def() else { return };
-
-        // Clone needs one arg, so we can cheaply rule out other stuff
-        if fn_args.len() != 1 {
-            return;
-        }
+        let Some((fn_def_id, ..)) = func.const_fn_def() else { return };
 
         // These types are easily available from locals, so check that before
         // doing DefId lookups to figure out what we're actually calling.
@@ -253,15 +232,12 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
 
         let ty::Ref(_region, inner_ty, Mutability::Not) = *arg_ty.kind() else { return };
 
-        if !inner_ty.is_trivially_pure_clone_copy() {
-            return;
-        }
-
-        if !self.tcx.is_lang_item(fn_def_id, LangItem::CloneFn) {
+        if !self.tcx.is_lang_item(fn_def_id, LangItem::CloneFn)
+            || !inner_ty.is_trivially_pure_clone_copy()
+        {
             return;
         }
 
-        let Ok([arg]) = take_array(args) else { return };
         let Some(arg_place) = arg.node.place() else { return };
 
         statements.push(Statement {
@@ -273,11 +249,11 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
                 )),
             ))),
         });
-        terminator.kind = TerminatorKind::Goto { target: destination_block };
+        terminator.kind = TerminatorKind::Goto { target: *destination_block };
     }
 
     fn simplify_nounwind_call(&self, terminator: &mut Terminator<'tcx>) {
-        let TerminatorKind::Call { func, unwind, .. } = &mut terminator.kind else {
+        let TerminatorKind::Call { ref func, ref mut unwind, .. } = terminator.kind else {
             return;
         };
 
@@ -290,7 +266,7 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
             ty::FnDef(..) => body_ty.fn_sig(self.tcx).abi(),
             ty::Closure(..) => ExternAbi::RustCall,
             ty::Coroutine(..) => ExternAbi::Rust,
-            _ => bug!("unexpected body ty: {:?}", body_ty),
+            _ => bug!("unexpected body ty: {body_ty:?}"),
         };
 
         if !layout::fn_can_unwind(self.tcx, Some(def_id), body_abi) {
@@ -299,10 +275,9 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
     }
 
     fn simplify_intrinsic_assert(&self, terminator: &mut Terminator<'tcx>) {
-        let TerminatorKind::Call { func, target, .. } = &mut terminator.kind else {
-            return;
-        };
-        let Some(target_block) = target else {
+        let TerminatorKind::Call { ref func, target: ref mut target @ Some(target_block), .. } =
+            terminator.kind
+        else {
             return;
         };
         let func_ty = func.ty(self.local_decls, self.tcx);
@@ -310,12 +285,10 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
             return;
         };
         // The intrinsics we are interested in have one generic parameter
-        if args.is_empty() {
-            return;
-        }
+        let [arg, ..] = args[..] else { return };
 
         let known_is_valid =
-            intrinsic_assert_panics(self.tcx, self.typing_env, args[0], intrinsic_name);
+            intrinsic_assert_panics(self.tcx, self.typing_env, arg, intrinsic_name);
         match known_is_valid {
             // We don't know the layout or it's not validity assertion at all, don't touch it
             None => {}
@@ -325,7 +298,7 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
             }
             Some(false) => {
                 // If we know the assert does not panic, turn the call into a Goto
-                terminator.kind = TerminatorKind::Goto { target: *target_block };
+                terminator.kind = TerminatorKind::Goto { target: target_block };
             }
         }
     }
@@ -346,9 +319,7 @@ fn resolve_rust_intrinsic<'tcx>(
     tcx: TyCtxt<'tcx>,
     func_ty: Ty<'tcx>,
 ) -> Option<(Symbol, GenericArgsRef<'tcx>)> {
-    if let ty::FnDef(def_id, args) = *func_ty.kind() {
-        let intrinsic = tcx.intrinsic(def_id)?;
-        return Some((intrinsic.name, args));
-    }
-    None
+    let ty::FnDef(def_id, args) = *func_ty.kind() else { return None };
+    let intrinsic = tcx.intrinsic(def_id)?;
+    Some((intrinsic.name, args))
 }
diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs
index 0a72a9d669f..8b4b214a3d4 100644
--- a/compiler/rustc_mir_transform/src/jump_threading.rs
+++ b/compiler/rustc_mir_transform/src/jump_threading.rs
@@ -90,7 +90,11 @@ impl<'tcx> crate::MirPass<'tcx> for JumpThreading {
         };
 
         for bb in body.basic_blocks.indices() {
-            finder.start_from_switch(bb);
+            let old_len = finder.opportunities.len();
+            // If we have any const-eval errors discard any opportunities found
+            if finder.start_from_switch(bb).is_none() {
+                finder.opportunities.truncate(old_len);
+            }
         }
 
         let opportunities = finder.opportunities;
@@ -150,14 +154,6 @@ impl Condition {
     fn matches(&self, value: ScalarInt) -> bool {
         (self.value == value) == (self.polarity == Polarity::Eq)
     }
-
-    fn inv(mut self) -> Self {
-        self.polarity = match self.polarity {
-            Polarity::Eq => Polarity::Ne,
-            Polarity::Ne => Polarity::Eq,
-        };
-        self
-    }
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -180,8 +176,21 @@ impl<'a> ConditionSet<'a> {
         self.iter().filter(move |c| c.matches(value))
     }
 
-    fn map(self, arena: &'a DroplessArena, f: impl Fn(Condition) -> Condition) -> ConditionSet<'a> {
-        ConditionSet(arena.alloc_from_iter(self.iter().map(f)))
+    fn map(
+        self,
+        arena: &'a DroplessArena,
+        f: impl Fn(Condition) -> Option<Condition>,
+    ) -> Option<ConditionSet<'a>> {
+        let mut all_ok = true;
+        let set = arena.alloc_from_iter(self.iter().map_while(|c| {
+            if let Some(c) = f(c) {
+                Some(c)
+            } else {
+                all_ok = false;
+                None
+            }
+        }));
+        all_ok.then_some(ConditionSet(set))
     }
 }
 
@@ -192,28 +201,28 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
 
     /// Recursion entry point to find threading opportunities.
     #[instrument(level = "trace", skip(self))]
-    fn start_from_switch(&mut self, bb: BasicBlock) {
+    fn start_from_switch(&mut self, bb: BasicBlock) -> Option<()> {
         let bbdata = &self.body[bb];
         if bbdata.is_cleanup || self.loop_headers.contains(bb) {
-            return;
+            return Some(());
         }
-        let Some((discr, targets)) = bbdata.terminator().kind.as_switch() else { return };
-        let Some(discr) = discr.place() else { return };
+        let Some((discr, targets)) = bbdata.terminator().kind.as_switch() else { return Some(()) };
+        let Some(discr) = discr.place() else { return Some(()) };
         debug!(?discr, ?bb);
 
         let discr_ty = discr.ty(self.body, self.tcx).ty;
         let Ok(discr_layout) = self.ecx.layout_of(discr_ty) else {
-            return;
+            return Some(());
         };
 
-        let Some(discr) = self.map.find(discr.as_ref()) else { return };
+        let Some(discr) = self.map.find(discr.as_ref()) else { return Some(()) };
         debug!(?discr);
 
         let cost = CostChecker::new(self.tcx, self.typing_env, None, self.body);
         let mut state = State::new_reachable();
 
         let conds = if let Some((value, then, else_)) = targets.as_static_if() {
-            let Some(value) = ScalarInt::try_from_uint(value, discr_layout.size) else { return };
+            let value = ScalarInt::try_from_uint(value, discr_layout.size)?;
             self.arena.alloc_from_iter([
                 Condition { value, polarity: Polarity::Eq, target: then },
                 Condition { value, polarity: Polarity::Ne, target: else_ },
@@ -227,7 +236,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         let conds = ConditionSet(conds);
         state.insert_value_idx(discr, conds, &self.map);
 
-        self.find_opportunity(bb, state, cost, 0);
+        self.find_opportunity(bb, state, cost, 0)
     }
 
     /// Recursively walk statements backwards from this bb's terminator to find threading
@@ -239,10 +248,10 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         mut state: State<ConditionSet<'a>>,
         mut cost: CostChecker<'_, 'tcx>,
         depth: usize,
-    ) {
+    ) -> Option<()> {
         // Do not thread through loop headers.
         if self.loop_headers.contains(bb) {
-            return;
+            return Some(());
         }
 
         debug!(cost = ?cost.cost());
@@ -250,16 +259,16 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             self.body.basic_blocks[bb].statements.iter().enumerate().rev()
         {
             if self.is_empty(&state) {
-                return;
+                return Some(());
             }
 
             cost.visit_statement(stmt, Location { block: bb, statement_index });
             if cost.cost() > MAX_COST {
-                return;
+                return Some(());
             }
 
             // Attempt to turn the `current_condition` on `lhs` into a condition on another place.
-            self.process_statement(bb, stmt, &mut state);
+            self.process_statement(bb, stmt, &mut state)?;
 
             // When a statement mutates a place, assignments to that place that happen
             // above the mutation cannot fulfill a condition.
@@ -271,7 +280,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         }
 
         if self.is_empty(&state) || depth >= MAX_BACKTRACK {
-            return;
+            return Some(());
         }
 
         let last_non_rec = self.opportunities.len();
@@ -284,9 +293,9 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             match term.kind {
                 TerminatorKind::SwitchInt { ref discr, ref targets } => {
                     self.process_switch_int(discr, targets, bb, &mut state);
-                    self.find_opportunity(pred, state, cost, depth + 1);
+                    self.find_opportunity(pred, state, cost, depth + 1)?;
                 }
-                _ => self.recurse_through_terminator(pred, || state, &cost, depth),
+                _ => self.recurse_through_terminator(pred, || state, &cost, depth)?,
             }
         } else if let &[ref predecessors @ .., last_pred] = &predecessors[..] {
             for &pred in predecessors {
@@ -311,12 +320,13 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             let first = &mut new_tos[0];
             *first = ThreadingOpportunity { chain: vec![bb], target: first.target };
             self.opportunities.truncate(last_non_rec + 1);
-            return;
+            return Some(());
         }
 
         for op in self.opportunities[last_non_rec..].iter_mut() {
             op.chain.push(bb);
         }
+        Some(())
     }
 
     /// Extract the mutated place from a statement.
@@ -430,23 +440,23 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         lhs: PlaceIndex,
         rhs: &Operand<'tcx>,
         state: &mut State<ConditionSet<'a>>,
-    ) {
+    ) -> Option<()> {
         match rhs {
             // If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`.
             Operand::Constant(constant) => {
-                let Some(constant) =
-                    self.ecx.eval_mir_constant(&constant.const_, constant.span, None).discard_err()
-                else {
-                    return;
-                };
+                let constant = self
+                    .ecx
+                    .eval_mir_constant(&constant.const_, constant.span, None)
+                    .discard_err()?;
                 self.process_constant(bb, lhs, constant, state);
             }
             // Transfer the conditions on the copied rhs.
             Operand::Move(rhs) | Operand::Copy(rhs) => {
-                let Some(rhs) = self.map.find(rhs.as_ref()) else { return };
+                let Some(rhs) = self.map.find(rhs.as_ref()) else { return Some(()) };
                 state.insert_place_idx(rhs, lhs, &self.map);
             }
         }
+        Some(())
     }
 
     #[instrument(level = "trace", skip(self))]
@@ -456,14 +466,18 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         lhs_place: &Place<'tcx>,
         rhs: &Rvalue<'tcx>,
         state: &mut State<ConditionSet<'a>>,
-    ) {
-        let Some(lhs) = self.map.find(lhs_place.as_ref()) else { return };
+    ) -> Option<()> {
+        let Some(lhs) = self.map.find(lhs_place.as_ref()) else {
+            return Some(());
+        };
         match rhs {
-            Rvalue::Use(operand) => self.process_operand(bb, lhs, operand, state),
+            Rvalue::Use(operand) => self.process_operand(bb, lhs, operand, state)?,
             // Transfer the conditions on the copy rhs.
-            Rvalue::CopyForDeref(rhs) => self.process_operand(bb, lhs, &Operand::Copy(*rhs), state),
+            Rvalue::CopyForDeref(rhs) => {
+                self.process_operand(bb, lhs, &Operand::Copy(*rhs), state)?
+            }
             Rvalue::Discriminant(rhs) => {
-                let Some(rhs) = self.map.find_discr(rhs.as_ref()) else { return };
+                let Some(rhs) = self.map.find_discr(rhs.as_ref()) else { return Some(()) };
                 state.insert_place_idx(rhs, lhs, &self.map);
             }
             // If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`.
@@ -471,7 +485,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
                 let agg_ty = lhs_place.ty(self.body, self.tcx).ty;
                 let lhs = match kind {
                     // Do not support unions.
-                    AggregateKind::Adt(.., Some(_)) => return,
+                    AggregateKind::Adt(.., Some(_)) => return Some(()),
                     AggregateKind::Adt(_, variant_index, ..) if agg_ty.is_enum() => {
                         if let Some(discr_target) = self.map.apply(lhs, TrackElem::Discriminant)
                             && let Some(discr_value) = self
@@ -484,30 +498,31 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
                         if let Some(idx) = self.map.apply(lhs, TrackElem::Variant(*variant_index)) {
                             idx
                         } else {
-                            return;
+                            return Some(());
                         }
                     }
                     _ => lhs,
                 };
                 for (field_index, operand) in operands.iter_enumerated() {
                     if let Some(field) = self.map.apply(lhs, TrackElem::Field(field_index)) {
-                        self.process_operand(bb, field, operand, state);
+                        self.process_operand(bb, field, operand, state)?;
                     }
                 }
             }
-            // Transfer the conditions on the copy rhs, after inversing polarity.
+            // Transfer the conditions on the copy rhs, after inverting the value of the condition.
             Rvalue::UnaryOp(UnOp::Not, Operand::Move(place) | Operand::Copy(place)) => {
-                if !place.ty(self.body, self.tcx).ty.is_bool() {
-                    // Constructing the conditions by inverting the polarity
-                    // of equality is only correct for bools. That is to say,
-                    // `!a == b` is not `a != b` for integers greater than 1 bit.
-                    return;
-                }
-                let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return };
-                let Some(place) = self.map.find(place.as_ref()) else { return };
-                // FIXME: I think This could be generalized to not bool if we
-                // actually perform a logical not on the condition's value.
-                let conds = conditions.map(self.arena, Condition::inv);
+                let layout = self.ecx.layout_of(place.ty(self.body, self.tcx).ty).unwrap();
+                let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return Some(()) };
+                let Some(place) = self.map.find(place.as_ref()) else { return Some(()) };
+                let conds = conditions.map(self.arena, |mut cond| {
+                    cond.value = self
+                        .ecx
+                        .unary_op(UnOp::Not, &ImmTy::from_scalar_int(cond.value, layout))
+                        .discard_err()?
+                        .to_scalar_int()
+                        .discard_err()?;
+                    Some(cond)
+                })?;
                 state.insert_value_idx(place, conds, &self.map);
             }
             // We expect `lhs ?= A`. We found `lhs = Eq(rhs, B)`.
@@ -517,34 +532,34 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
                 box (Operand::Move(place) | Operand::Copy(place), Operand::Constant(value))
                 | box (Operand::Constant(value), Operand::Move(place) | Operand::Copy(place)),
             ) => {
-                let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return };
-                let Some(place) = self.map.find(place.as_ref()) else { return };
+                let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return Some(()) };
+                let Some(place) = self.map.find(place.as_ref()) else { return Some(()) };
                 let equals = match op {
                     BinOp::Eq => ScalarInt::TRUE,
                     BinOp::Ne => ScalarInt::FALSE,
-                    _ => return,
+                    _ => return Some(()),
                 };
                 if value.const_.ty().is_floating_point() {
                     // Floating point equality does not follow bit-patterns.
                     // -0.0 and NaN both have special rules for equality,
                     // and therefore we cannot use integer comparisons for them.
                     // Avoid handling them, though this could be extended in the future.
-                    return;
+                    return Some(());
                 }
-                let Some(value) = value.const_.try_eval_scalar_int(self.tcx, self.typing_env)
-                else {
-                    return;
-                };
-                let conds = conditions.map(self.arena, |c| Condition {
-                    value,
-                    polarity: if c.matches(equals) { Polarity::Eq } else { Polarity::Ne },
-                    ..c
-                });
+                let value = value.const_.try_eval_scalar_int(self.tcx, self.typing_env)?;
+                let conds = conditions.map(self.arena, |c| {
+                    Some(Condition {
+                        value,
+                        polarity: if c.matches(equals) { Polarity::Eq } else { Polarity::Ne },
+                        ..c
+                    })
+                })?;
                 state.insert_value_idx(place, conds, &self.map);
             }
 
             _ => {}
         }
+        Some(())
     }
 
     #[instrument(level = "trace", skip(self))]
@@ -553,7 +568,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         bb: BasicBlock,
         stmt: &Statement<'tcx>,
         state: &mut State<ConditionSet<'a>>,
-    ) {
+    ) -> Option<()> {
         let register_opportunity = |c: Condition| {
             debug!(?bb, ?c.target, "register");
             self.opportunities.push(ThreadingOpportunity { chain: vec![bb], target: c.target })
@@ -566,30 +581,32 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             // If we expect `discriminant(place) ?= A`,
             // we have an opportunity if `variant_index ?= A`.
             StatementKind::SetDiscriminant { box place, variant_index } => {
-                let Some(discr_target) = self.map.find_discr(place.as_ref()) else { return };
+                let Some(discr_target) = self.map.find_discr(place.as_ref()) else {
+                    return Some(());
+                };
                 let enum_ty = place.ty(self.body, self.tcx).ty;
                 // `SetDiscriminant` guarantees that the discriminant is now `variant_index`.
                 // Even if the discriminant write does nothing due to niches, it is UB to set the
                 // discriminant when the data does not encode the desired discriminant.
-                let Some(discr) =
-                    self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()
-                else {
-                    return;
-                };
+                let discr =
+                    self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()?;
                 self.process_immediate(bb, discr_target, discr, state);
             }
             // If we expect `lhs ?= true`, we have an opportunity if we assume `lhs == true`.
             StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume(
                 Operand::Copy(place) | Operand::Move(place),
             )) => {
-                let Some(conditions) = state.try_get(place.as_ref(), &self.map) else { return };
+                let Some(conditions) = state.try_get(place.as_ref(), &self.map) else {
+                    return Some(());
+                };
                 conditions.iter_matches(ScalarInt::TRUE).for_each(register_opportunity);
             }
             StatementKind::Assign(box (lhs_place, rhs)) => {
-                self.process_assign(bb, lhs_place, rhs, state);
+                self.process_assign(bb, lhs_place, rhs, state)?;
             }
             _ => {}
         }
+        Some(())
     }
 
     #[instrument(level = "trace", skip(self, state, cost))]
@@ -600,7 +617,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         state: impl FnOnce() -> State<ConditionSet<'a>>,
         cost: &CostChecker<'_, 'tcx>,
         depth: usize,
-    ) {
+    ) -> Option<()> {
         let term = self.body.basic_blocks[bb].terminator();
         let place_to_flood = match term.kind {
             // We come from a target, so those are not possible.
@@ -615,9 +632,9 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             | TerminatorKind::FalseUnwind { .. }
             | TerminatorKind::Yield { .. } => bug!("{term:?} invalid"),
             // Cannot reason about inline asm.
-            TerminatorKind::InlineAsm { .. } => return,
+            TerminatorKind::InlineAsm { .. } => return Some(()),
             // `SwitchInt` is handled specially.
-            TerminatorKind::SwitchInt { .. } => return,
+            TerminatorKind::SwitchInt { .. } => return Some(()),
             // We can recurse, no thing particular to do.
             TerminatorKind::Goto { .. } => None,
             // Flood the overwritten place, and progress through.
@@ -632,7 +649,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
         if let Some(place_to_flood) = place_to_flood {
             state.flood_with(place_to_flood.as_ref(), &self.map, ConditionSet::BOTTOM);
         }
-        self.find_opportunity(bb, state, cost.clone(), depth + 1);
+        self.find_opportunity(bb, state, cost.clone(), depth + 1)
     }
 
     #[instrument(level = "trace", skip(self))]
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 6429d3f67ec..4d74ecddfb0 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -1,5 +1,4 @@
 // tidy-alphabetical-start
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(array_windows)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
@@ -498,8 +497,11 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
     }
 
     // We only need to borrowck non-synthetic MIR.
-    let tainted_by_errors =
-        if !tcx.is_synthetic_mir(def) { tcx.mir_borrowck(def).tainted_by_errors } else { None };
+    let tainted_by_errors = if !tcx.is_synthetic_mir(def) {
+        tcx.mir_borrowck(tcx.typeck_root_def_id(def.to_def_id()).expect_local()).err()
+    } else {
+        None
+    };
 
     let is_fn_like = tcx.def_kind(def).is_fn_like();
     if is_fn_like {
@@ -795,7 +797,7 @@ fn promoted_mir(tcx: TyCtxt<'_>, def: LocalDefId) -> &IndexVec<Promoted, Body<'_
     }
 
     if !tcx.is_synthetic_mir(def) {
-        tcx.ensure_done().mir_borrowck(def);
+        tcx.ensure_done().mir_borrowck(tcx.typeck_root_def_id(def.to_def_id()).expect_local());
     }
     let mut promoted = tcx.mir_promoted(def).1.steal();
 
diff --git a/compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs b/compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs
index 29a9133abe9..537f152938e 100644
--- a/compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs
+++ b/compiler/rustc_mir_transform/src/lint_tail_expr_drop_order.rs
@@ -512,23 +512,17 @@ struct LocalLabel<'a> {
 
 /// A custom `Subdiagnostic` implementation so that the notes are delivered in a specific order
 impl Subdiagnostic for LocalLabel<'_> {
-    fn add_to_diag_with<
-        G: rustc_errors::EmissionGuarantee,
-        F: rustc_errors::SubdiagMessageOp<G>,
-    >(
-        self,
-        diag: &mut rustc_errors::Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: rustc_errors::EmissionGuarantee>(self, diag: &mut rustc_errors::Diag<'_, G>) {
         diag.arg("name", self.name);
         diag.arg("is_generated_name", self.is_generated_name);
         diag.arg("is_dropped_first_edition_2024", self.is_dropped_first_edition_2024);
-        let msg = f(diag, crate::fluent_generated::mir_transform_tail_expr_local.into());
+        let msg = diag.eagerly_translate(crate::fluent_generated::mir_transform_tail_expr_local);
         diag.span_label(self.span, msg);
         for dtor in self.destructors {
-            dtor.add_to_diag_with(diag, f);
+            dtor.add_to_diag(diag);
         }
-        let msg = f(diag, crate::fluent_generated::mir_transform_label_local_epilogue);
+        let msg =
+            diag.eagerly_translate(crate::fluent_generated::mir_transform_label_local_epilogue);
         diag.span_label(self.span, msg);
     }
 }
diff --git a/compiler/rustc_mir_transform/src/match_branches.rs b/compiler/rustc_mir_transform/src/match_branches.rs
index 0d9d0368d37..5059837328e 100644
--- a/compiler/rustc_mir_transform/src/match_branches.rs
+++ b/compiler/rustc_mir_transform/src/match_branches.rs
@@ -20,13 +20,11 @@ impl<'tcx> crate::MirPass<'tcx> for MatchBranchSimplification {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         let typing_env = body.typing_env(tcx);
         let mut should_cleanup = false;
-        for i in 0..body.basic_blocks.len() {
-            let bbs = &*body.basic_blocks;
-            let bb_idx = BasicBlock::from_usize(i);
-            match bbs[bb_idx].terminator().kind {
+        for bb_idx in body.basic_blocks.indices() {
+            match &body.basic_blocks[bb_idx].terminator().kind {
                 TerminatorKind::SwitchInt {
-                    discr: ref _discr @ (Operand::Copy(_) | Operand::Move(_)),
-                    ref targets,
+                    discr: Operand::Copy(_) | Operand::Move(_),
+                    targets,
                     ..
                     // We require that the possible target blocks don't contain this block.
                 } if !targets.all_targets().contains(&bb_idx) => {}
@@ -66,9 +64,10 @@ trait SimplifyMatch<'tcx> {
         typing_env: ty::TypingEnv<'tcx>,
     ) -> Option<()> {
         let bbs = &body.basic_blocks;
-        let (discr, targets) = match bbs[switch_bb_idx].terminator().kind {
-            TerminatorKind::SwitchInt { ref discr, ref targets, .. } => (discr, targets),
-            _ => unreachable!(),
+        let TerminatorKind::SwitchInt { discr, targets, .. } =
+            &bbs[switch_bb_idx].terminator().kind
+        else {
+            unreachable!();
         };
 
         let discr_ty = discr.ty(body.local_decls(), tcx);
diff --git a/compiler/rustc_mir_transform/src/multiple_return_terminators.rs b/compiler/rustc_mir_transform/src/multiple_return_terminators.rs
index c63bfdcee85..f59b849e85c 100644
--- a/compiler/rustc_mir_transform/src/multiple_return_terminators.rs
+++ b/compiler/rustc_mir_transform/src/multiple_return_terminators.rs
@@ -18,19 +18,17 @@ impl<'tcx> crate::MirPass<'tcx> for MultipleReturnTerminators {
         // find basic blocks with no statement and a return terminator
         let mut bbs_simple_returns = DenseBitSet::new_empty(body.basic_blocks.len());
         let bbs = body.basic_blocks_mut();
-        for idx in bbs.indices() {
-            if bbs[idx].statements.is_empty()
-                && bbs[idx].terminator().kind == TerminatorKind::Return
-            {
+        for (idx, bb) in bbs.iter_enumerated() {
+            if bb.statements.is_empty() && bb.terminator().kind == TerminatorKind::Return {
                 bbs_simple_returns.insert(idx);
             }
         }
 
         for bb in bbs {
-            if let TerminatorKind::Goto { target } = bb.terminator().kind {
-                if bbs_simple_returns.contains(target) {
-                    bb.terminator_mut().kind = TerminatorKind::Return;
-                }
+            if let TerminatorKind::Goto { target } = bb.terminator().kind
+                && bbs_simple_returns.contains(target)
+            {
+                bb.terminator_mut().kind = TerminatorKind::Return;
             }
         }
 
diff --git a/compiler/rustc_mir_transform/src/patch.rs b/compiler/rustc_mir_transform/src/patch.rs
index 6a177faeac8..12ace04c5e2 100644
--- a/compiler/rustc_mir_transform/src/patch.rs
+++ b/compiler/rustc_mir_transform/src/patch.rs
@@ -181,7 +181,7 @@ impl<'tcx> MirPatch<'tcx> {
 
     /// Queues the addition of a new basic block.
     pub(crate) fn new_block(&mut self, data: BasicBlockData<'tcx>) -> BasicBlock {
-        let block = BasicBlock::new(self.term_patch_map.len());
+        let block = self.term_patch_map.next_index();
         debug!("MirPatch: new_block: {:?}: {:?}", block, data);
         self.new_blocks.push(data);
         self.term_patch_map.push(None);
diff --git a/compiler/rustc_mir_transform/src/post_analysis_normalize.rs b/compiler/rustc_mir_transform/src/post_analysis_normalize.rs
index 76c2f082c0b..5599dee4cca 100644
--- a/compiler/rustc_mir_transform/src/post_analysis_normalize.rs
+++ b/compiler/rustc_mir_transform/src/post_analysis_normalize.rs
@@ -39,20 +39,22 @@ impl<'tcx> MutVisitor<'tcx> for PostAnalysisNormalizeVisitor<'tcx> {
         _context: PlaceContext,
         _location: Location,
     ) {
-        // Performance optimization: don't reintern if there is no `OpaqueCast` to remove.
-        if place.projection.iter().all(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_))) {
-            return;
+        if !self.tcx.next_trait_solver_globally() {
+            // `OpaqueCast` projections are only needed if there are opaque types on which projections
+            // are performed. After the `PostAnalysisNormalize` pass, all opaque types are replaced with their
+            // hidden types, so we don't need these projections anymore.
+            //
+            // Performance optimization: don't reintern if there is no `OpaqueCast` to remove.
+            if place.projection.iter().any(|elem| matches!(elem, ProjectionElem::OpaqueCast(_))) {
+                place.projection = self.tcx.mk_place_elems(
+                    &place
+                        .projection
+                        .into_iter()
+                        .filter(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_)))
+                        .collect::<Vec<_>>(),
+                );
+            };
         }
-        // `OpaqueCast` projections are only needed if there are opaque types on which projections
-        // are performed. After the `PostAnalysisNormalize` pass, all opaque types are replaced with their
-        // hidden types, so we don't need these projections anymore.
-        place.projection = self.tcx.mk_place_elems(
-            &place
-                .projection
-                .into_iter()
-                .filter(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_)))
-                .collect::<Vec<_>>(),
-        );
         self.super_place(place, _context, _location);
     }
 
diff --git a/compiler/rustc_mir_transform/src/promote_consts.rs b/compiler/rustc_mir_transform/src/promote_consts.rs
index c8d8dc147e9..47d43830970 100644
--- a/compiler/rustc_mir_transform/src/promote_consts.rs
+++ b/compiler/rustc_mir_transform/src/promote_consts.rs
@@ -18,7 +18,7 @@ use either::{Left, Right};
 use rustc_const_eval::check_consts::{ConstCx, qualifs};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
-use rustc_index::{Idx, IndexSlice, IndexVec};
+use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, GenericArgs, List, Ty, TyCtxt, TypeVisitableExt};
@@ -864,17 +864,21 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
         new_temp
     }
 
-    fn promote_candidate(mut self, candidate: Candidate, next_promoted_id: usize) -> Body<'tcx> {
+    fn promote_candidate(
+        mut self,
+        candidate: Candidate,
+        next_promoted_index: Promoted,
+    ) -> Body<'tcx> {
         let def = self.source.source.def_id();
         let (mut rvalue, promoted_op) = {
             let promoted = &mut self.promoted;
-            let promoted_id = Promoted::new(next_promoted_id);
             let tcx = self.tcx;
             let mut promoted_operand = |ty, span| {
                 promoted.span = span;
                 promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
                 let args = tcx.erase_regions(GenericArgs::identity_for_item(tcx, def));
-                let uneval = mir::UnevaluatedConst { def, args, promoted: Some(promoted_id) };
+                let uneval =
+                    mir::UnevaluatedConst { def, args, promoted: Some(next_promoted_index) };
 
                 ConstOperand { span, user_ty: None, const_: Const::Unevaluated(uneval, ty) }
             };
@@ -1034,7 +1038,7 @@ fn promote_candidates<'tcx>(
             required_consts: Vec::new(),
         };
 
-        let mut promoted = promoter.promote_candidate(candidate, promotions.len());
+        let mut promoted = promoter.promote_candidate(candidate, promotions.next_index());
         promoted.source.promoted = Some(promotions.next_index());
         promotions.push(promoted);
     }
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index c9771467e49..c13ffae3649 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -66,7 +66,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceKind<'tcx>) -> Body<
             let call_mut = tcx
                 .associated_items(fn_mut)
                 .in_definition_order()
-                .find(|it| it.kind == ty::AssocKind::Fn)
+                .find(|it| it.is_fn())
                 .unwrap()
                 .def_id;
 
diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs
index 84905f4a400..5947637cded 100644
--- a/compiler/rustc_mir_transform/src/simplify.rs
+++ b/compiler/rustc_mir_transform/src/simplify.rs
@@ -597,20 +597,6 @@ impl<'tcx> MutVisitor<'tcx> for LocalUpdater<'tcx> {
         self.tcx
     }
 
-    fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
-        if let StatementKind::BackwardIncompatibleDropHint { place, reason: _ } =
-            &mut statement.kind
-        {
-            self.visit_local(
-                &mut place.local,
-                PlaceContext::MutatingUse(MutatingUseContext::Store),
-                location,
-            );
-        } else {
-            self.super_statement(statement, location);
-        }
-    }
-
     fn visit_local(&mut self, l: &mut Local, _: PlaceContext, _: Location) {
         *l = self.map[*l].unwrap();
     }
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index e7930f0a1e3..66fe3ef4141 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -221,12 +221,11 @@ impl<'a, 'tcx> CfgChecker<'a, 'tcx> {
 
         // Check for cycles
         let mut stack = FxHashSet::default();
-        for i in 0..parent.len() {
-            let mut bb = BasicBlock::from_usize(i);
+        for (mut bb, parent) in parent.iter_enumerated_mut() {
             stack.clear();
             stack.insert(bb);
             loop {
-                let Some(parent) = parent[bb].take() else { break };
+                let Some(parent) = parent.take() else { break };
                 let no_cycle = stack.insert(parent);
                 if !no_cycle {
                     self.fail(
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 6e676ac6b8d..d1d0f7cacae 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -688,7 +688,7 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                 let target_ty = self.monomorphize(target_ty);
                 let source_ty = self.monomorphize(source_ty);
                 let (source_ty, target_ty) =
-                    find_vtable_types_for_unsizing(self.tcx.at(span), source_ty, target_ty);
+                    find_tails_for_unsizing(self.tcx.at(span), source_ty, target_ty);
                 // This could also be a different Unsize instruction, like
                 // from a fixed sized array to a slice. But we are only
                 // interested in things that produce a vtable.
@@ -1037,36 +1037,35 @@ fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) ->
 ///
 /// Finally, there is also the case of custom unsizing coercions, e.g., for
 /// smart pointers such as `Rc` and `Arc`.
-fn find_vtable_types_for_unsizing<'tcx>(
+fn find_tails_for_unsizing<'tcx>(
     tcx: TyCtxtAt<'tcx>,
     source_ty: Ty<'tcx>,
     target_ty: Ty<'tcx>,
 ) -> (Ty<'tcx>, Ty<'tcx>) {
-    let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
-        let typing_env = ty::TypingEnv::fully_monomorphized();
-        if tcx.type_has_metadata(inner_source, typing_env) {
-            (inner_source, inner_target)
-        } else {
-            tcx.struct_lockstep_tails_for_codegen(inner_source, inner_target, typing_env)
-        }
-    };
+    let typing_env = ty::TypingEnv::fully_monomorphized();
+    debug_assert!(!source_ty.has_param(), "{source_ty} should be fully monomorphic");
+    debug_assert!(!target_ty.has_param(), "{target_ty} should be fully monomorphic");
 
     match (source_ty.kind(), target_ty.kind()) {
-        (&ty::Ref(_, a, _), &ty::Ref(_, b, _) | &ty::RawPtr(b, _))
-        | (&ty::RawPtr(a, _), &ty::RawPtr(b, _)) => ptr_vtable(a, b),
+        (
+            &ty::Ref(_, source_pointee, _),
+            &ty::Ref(_, target_pointee, _) | &ty::RawPtr(target_pointee, _),
+        )
+        | (&ty::RawPtr(source_pointee, _), &ty::RawPtr(target_pointee, _)) => {
+            tcx.struct_lockstep_tails_for_codegen(source_pointee, target_pointee, typing_env)
+        }
+
+        // `Box<T>` could go through the ADT code below, b/c it'll unpeel to `Unique<T>`,
+        // and eventually bottom out in a raw ref, but we can micro-optimize it here.
         (_, _)
             if let Some(source_boxed) = source_ty.boxed_ty()
                 && let Some(target_boxed) = target_ty.boxed_ty() =>
         {
-            ptr_vtable(source_boxed, target_boxed)
+            tcx.struct_lockstep_tails_for_codegen(source_boxed, target_boxed, typing_env)
         }
 
-        // T as dyn* Trait
-        (_, &ty::Dynamic(_, _, ty::DynStar)) => ptr_vtable(source_ty, target_ty),
-
         (&ty::Adt(source_adt_def, source_args), &ty::Adt(target_adt_def, target_args)) => {
             assert_eq!(source_adt_def, target_adt_def);
-
             let CustomCoerceUnsized::Struct(coerce_index) =
                 match crate::custom_coerce_unsize_info(tcx, source_ty, target_ty) {
                     Ok(ccu) => ccu,
@@ -1075,21 +1074,23 @@ fn find_vtable_types_for_unsizing<'tcx>(
                         return (e, e);
                     }
                 };
+            let coerce_field = &source_adt_def.non_enum_variant().fields[coerce_index];
+            // We're getting a possibly unnormalized type, so normalize it.
+            let source_field =
+                tcx.normalize_erasing_regions(typing_env, coerce_field.ty(*tcx, source_args));
+            let target_field =
+                tcx.normalize_erasing_regions(typing_env, coerce_field.ty(*tcx, target_args));
+            find_tails_for_unsizing(tcx, source_field, target_field)
+        }
 
-            let source_fields = &source_adt_def.non_enum_variant().fields;
-            let target_fields = &target_adt_def.non_enum_variant().fields;
-
-            assert!(
-                coerce_index.index() < source_fields.len()
-                    && source_fields.len() == target_fields.len()
-            );
+        // `T` as `dyn* Trait` unsizes *directly*.
+        //
+        // FIXME(dyn_star): This case is a bit awkward, b/c we're not really computing
+        // a tail here. We probably should handle this separately in the *caller* of
+        // this function, rather than returning something that is semantically different
+        // than what we return above.
+        (_, &ty::Dynamic(_, _, ty::DynStar)) => (source_ty, target_ty),
 
-            find_vtable_types_for_unsizing(
-                tcx,
-                source_fields[coerce_index].ty(*tcx, source_args),
-                target_fields[coerce_index].ty(*tcx, target_args),
-            )
-        }
         _ => bug!(
             "find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
             source_ty,
@@ -1308,7 +1309,7 @@ fn visit_mentioned_item<'tcx>(
         }
         MentionedItem::UnsizeCast { source_ty, target_ty } => {
             let (source_ty, target_ty) =
-                find_vtable_types_for_unsizing(tcx.at(span), source_ty, target_ty);
+                find_tails_for_unsizing(tcx.at(span), source_ty, target_ty);
             // This could also be a different Unsize instruction, like
             // from a fixed sized array to a slice. But we are only
             // interested in things that produce a vtable.
@@ -1689,7 +1690,7 @@ pub(crate) fn collect_crate_mono_items<'tcx>(
             let mut recursion_depths = DefIdMap::default();
             collect_items_rec(
                 tcx,
-                dummy_spanned(root),
+                dummy_spanned(*root),
                 &state,
                 &mut recursion_depths,
                 recursion_limit,
diff --git a/compiler/rustc_monomorphize/src/lib.rs b/compiler/rustc_monomorphize/src/lib.rs
index 5dbae50c499..8f6914f3d72 100644
--- a/compiler/rustc_monomorphize/src/lib.rs
+++ b/compiler/rustc_monomorphize/src/lib.rs
@@ -1,5 +1,4 @@
 // tidy-alphabetical-start
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(array_windows)]
 #![feature(file_buffered)]
 #![feature(if_let_guard)]
diff --git a/compiler/rustc_monomorphize/src/mono_checks/abi_check.rs b/compiler/rustc_monomorphize/src/mono_checks/abi_check.rs
index 0f5bdc8d768..94ee34c8b7b 100644
--- a/compiler/rustc_monomorphize/src/mono_checks/abi_check.rs
+++ b/compiler/rustc_monomorphize/src/mono_checks/abi_check.rs
@@ -111,6 +111,11 @@ fn wasm_abi_safe<'tcx>(tcx: TyCtxt<'tcx>, arg: &ArgAbi<'tcx, Ty<'tcx>>) -> bool
         }
     }
 
+    // Zero-sized types are dropped in both ABIs, so they're safe
+    if arg.layout.is_zst() {
+        return true;
+    }
+
     false
 }
 
diff --git a/compiler/rustc_monomorphize/src/mono_checks/move_check.rs b/compiler/rustc_monomorphize/src/mono_checks/move_check.rs
index 838bfdab1ea..7251ef478c6 100644
--- a/compiler/rustc_monomorphize/src/mono_checks/move_check.rs
+++ b/compiler/rustc_monomorphize/src/mono_checks/move_check.rs
@@ -3,7 +3,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::visit::Visitor as MirVisitor;
 use rustc_middle::mir::{self, Location, traversal};
-use rustc_middle::ty::{self, AssocKind, Instance, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, AssocTag, Instance, Ty, TyCtxt, TypeFoldable};
 use rustc_session::Limit;
 use rustc_session::lint::builtin::LARGE_ASSIGNMENTS;
 use rustc_span::source_map::Spanned;
@@ -148,11 +148,7 @@ impl<'tcx> MoveCheckVisitor<'tcx> {
         span: Span,
     ) {
         let source_info = self.body.source_info(location);
-        for reported_span in &self.move_size_spans {
-            if reported_span.overlaps(span) {
-                return;
-            }
-        }
+
         let lint_root = source_info.scope.lint_root(&self.body.source_scopes);
         let Some(lint_root) = lint_root else {
             // This happens when the issue is in a function from a foreign crate that
@@ -162,22 +158,43 @@ impl<'tcx> MoveCheckVisitor<'tcx> {
             // but correct span? This would make the lint at least accept crate-level lint attributes.
             return;
         };
+
+        // If the source scope is inlined by the MIR inliner, report the lint on the call site.
+        let reported_span = self
+            .body
+            .source_scopes
+            .get(source_info.scope)
+            .and_then(|source_scope_data| source_scope_data.inlined)
+            .map(|(_, call_site)| call_site)
+            .unwrap_or(span);
+
+        for previously_reported_span in &self.move_size_spans {
+            if previously_reported_span.overlaps(reported_span) {
+                return;
+            }
+        }
+
         self.tcx.emit_node_span_lint(
             LARGE_ASSIGNMENTS,
             lint_root,
-            span,
-            LargeAssignmentsLint { span, size: too_large_size.bytes(), limit: limit as u64 },
+            reported_span,
+            LargeAssignmentsLint {
+                span: reported_span,
+                size: too_large_size.bytes(),
+                limit: limit as u64,
+            },
         );
-        self.move_size_spans.push(span);
+
+        self.move_size_spans.push(reported_span);
     }
 }
 
 fn assoc_fn_of_type<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, fn_ident: Ident) -> Option<DefId> {
     for impl_def_id in tcx.inherent_impls(def_id) {
-        if let Some(new) = tcx.associated_items(impl_def_id).find_by_name_and_kind(
+        if let Some(new) = tcx.associated_items(impl_def_id).find_by_ident_and_kind(
             tcx,
             fn_ident,
-            AssocKind::Fn,
+            AssocTag::Fn,
             def_id,
         ) {
             return Some(new.def_id);
diff --git a/compiler/rustc_monomorphize/src/partitioning/autodiff.rs b/compiler/rustc_monomorphize/src/partitioning/autodiff.rs
index ebe0b258c1b..22d593b80b8 100644
--- a/compiler/rustc_monomorphize/src/partitioning/autodiff.rs
+++ b/compiler/rustc_monomorphize/src/partitioning/autodiff.rs
@@ -2,7 +2,7 @@ use rustc_ast::expand::autodiff_attrs::{AutoDiffItem, DiffActivity};
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::bug;
 use rustc_middle::mir::mono::MonoItem;
-use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
+use rustc_middle::ty::{self, Instance, PseudoCanonicalInput, Ty, TyCtxt, TypingEnv};
 use rustc_symbol_mangling::symbol_name_for_instance_in_crate;
 use tracing::{debug, trace};
 
@@ -22,23 +22,51 @@ fn adjust_activity_to_abi<'tcx>(tcx: TyCtxt<'tcx>, fn_ty: Ty<'tcx>, da: &mut Vec
     for (i, ty) in sig.inputs().iter().enumerate() {
         if let Some(inner_ty) = ty.builtin_deref(true) {
             if inner_ty.is_slice() {
+                // Now we need to figure out the size of each slice element in memory to allow
+                // safety checks and usability improvements in the backend.
+                let sty = match inner_ty.builtin_index() {
+                    Some(sty) => sty,
+                    None => {
+                        panic!("slice element type unknown");
+                    }
+                };
+                let pci = PseudoCanonicalInput {
+                    typing_env: TypingEnv::fully_monomorphized(),
+                    value: sty,
+                };
+
+                let layout = tcx.layout_of(pci);
+                let elem_size = match layout {
+                    Ok(layout) => layout.size,
+                    Err(_) => {
+                        bug!("autodiff failed to compute slice element size");
+                    }
+                };
+                let elem_size: u32 = elem_size.bytes() as u32;
+
                 // We know that the length will be passed as extra arg.
                 if !da.is_empty() {
                     // We are looking at a slice. The length of that slice will become an
                     // extra integer on llvm level. Integers are always const.
                     // However, if the slice get's duplicated, we want to know to later check the
                     // size. So we mark the new size argument as FakeActivitySize.
+                    // There is one FakeActivitySize per slice, so for convenience we store the
+                    // slice element size in bytes in it. We will use the size in the backend.
                     let activity = match da[i] {
                         DiffActivity::DualOnly
                         | DiffActivity::Dual
+                        | DiffActivity::Dualv
                         | DiffActivity::DuplicatedOnly
-                        | DiffActivity::Duplicated => DiffActivity::FakeActivitySize,
+                        | DiffActivity::Duplicated => {
+                            DiffActivity::FakeActivitySize(Some(elem_size))
+                        }
                         DiffActivity::Const => DiffActivity::Const,
                         _ => bug!("unexpected activity for ptr/ref"),
                     };
                     new_activities.push(activity);
                     new_positions.push(i + 1);
                 }
+
                 continue;
             }
         }
diff --git a/compiler/rustc_next_trait_solver/src/lib.rs b/compiler/rustc_next_trait_solver/src/lib.rs
index f575fe03019..92cdc28a37b 100644
--- a/compiler/rustc_next_trait_solver/src/lib.rs
+++ b/compiler/rustc_next_trait_solver/src/lib.rs
@@ -6,7 +6,7 @@
 
 // tidy-alphabetical-start
 #![allow(rustc::usage_of_type_ir_inherent)]
-#![cfg_attr(not(bootstrap), allow(rustc::usage_of_type_ir_traits))]
+#![allow(rustc::usage_of_type_ir_traits)]
 // tidy-alphabetical-end
 
 pub mod canonicalizer;
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
index 384a304c4a9..83b2465d05a 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -92,16 +92,20 @@ where
             let ty::Dynamic(bounds, _, _) = goal.predicate.self_ty().kind() else {
                 panic!("expected object type in `probe_and_consider_object_bound_candidate`");
             };
-            ecx.add_goals(
-                GoalSource::ImplWhereBound,
-                structural_traits::predicates_for_object_candidate(
-                    ecx,
-                    goal.param_env,
-                    goal.predicate.trait_ref(cx),
-                    bounds,
-                ),
-            );
-            ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+            match structural_traits::predicates_for_object_candidate(
+                ecx,
+                goal.param_env,
+                goal.predicate.trait_ref(cx),
+                bounds,
+            ) {
+                Ok(requirements) => {
+                    ecx.add_goals(GoalSource::ImplWhereBound, requirements);
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                }
+                Err(_) => {
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
+                }
+            }
         })
     }
 
@@ -792,37 +796,46 @@ where
         };
 
         match proven_via {
-            // Even when a trait bound has been proven using a where-bound, we
-            // still need to consider alias-bounds for normalization, see
-            // tests/ui/next-solver/alias-bound-shadowed-by-env.rs.
-            //
-            // FIXME(const_trait_impl): should this behavior also be used by
-            // constness checking. Doing so is *at least theoretically* breaking,
-            // see github.com/rust-lang/rust/issues/133044#issuecomment-2500709754
             TraitGoalProvenVia::ParamEnv | TraitGoalProvenVia::AliasBound => {
-                let mut candidates_from_env_and_bounds: Vec<_> = candidates
-                    .iter()
-                    .filter(|c| {
-                        matches!(
-                            c.source,
-                            CandidateSource::AliasBound | CandidateSource::ParamEnv(_)
-                        )
-                    })
-                    .map(|c| c.result)
-                    .collect();
+                let mut considered_candidates = Vec::new();
+                considered_candidates.extend(
+                    candidates
+                        .iter()
+                        .filter(|c| matches!(c.source, CandidateSource::ParamEnv(_)))
+                        .map(|c| c.result),
+                );
+
+                // Even when a trait bound has been proven using a where-bound, we
+                // still need to consider alias-bounds for normalization, see
+                // tests/ui/next-solver/alias-bound-shadowed-by-env.rs.
+                //
+                // We still need to prefer where-bounds over alias-bounds however.
+                // See tests/ui/winnowing/norm-where-bound-gt-alias-bound.rs.
+                //
+                // FIXME(const_trait_impl): should this behavior also be used by
+                // constness checking. Doing so is *at least theoretically* breaking,
+                // see github.com/rust-lang/rust/issues/133044#issuecomment-2500709754
+                if considered_candidates.is_empty() {
+                    considered_candidates.extend(
+                        candidates
+                            .iter()
+                            .filter(|c| matches!(c.source, CandidateSource::AliasBound))
+                            .map(|c| c.result),
+                    );
+                }
 
                 // If the trait goal has been proven by using the environment, we want to treat
                 // aliases as rigid if there are no applicable projection bounds in the environment.
-                if candidates_from_env_and_bounds.is_empty() {
+                if considered_candidates.is_empty() {
                     if let Ok(response) = inject_normalize_to_rigid_candidate(self) {
-                        candidates_from_env_and_bounds.push(response);
+                        considered_candidates.push(response);
                     }
                 }
 
-                if let Some(response) = self.try_merge_responses(&candidates_from_env_and_bounds) {
+                if let Some(response) = self.try_merge_responses(&considered_candidates) {
                     Ok(response)
                 } else {
-                    self.flounder(&candidates_from_env_and_bounds)
+                    self.flounder(&considered_candidates)
                 }
             }
             TraitGoalProvenVia::Misc => {
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index c2fb592c3f3..1526049719e 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -5,9 +5,10 @@ use derive_where::derive_where;
 use rustc_type_ir::data_structures::HashMap;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{
-    self as ty, Interner, Movability, Mutability, TypeFoldable, TypeFolder, TypeSuperFoldable,
-    Upcast as _, elaborate,
+    self as ty, FallibleTypeFolder, Interner, Movability, Mutability, TypeFoldable,
+    TypeSuperFoldable, Upcast as _, elaborate,
 };
 use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
 use tracing::instrument;
@@ -822,22 +823,16 @@ pub(in crate::solve) fn const_conditions_for_destruct<I: Interner>(
 /// impl Baz for dyn Foo<Item = Ty> {}
 /// ```
 ///
-/// However, in order to make such impls well-formed, we need to do an
+/// However, in order to make such impls non-cyclical, we need to do an
 /// additional step of eagerly folding the associated types in the where
 /// clauses of the impl. In this example, that means replacing
 /// `<Self as Foo>::Bar` with `Ty` in the first impl.
-///
-// FIXME: This is only necessary as `<Self as Trait>::Assoc: ItemBound`
-// bounds in impls are trivially proven using the item bound candidates.
-// This is unsound in general and once that is fixed, we don't need to
-// normalize eagerly here. See https://github.com/lcnr/solver-woes/issues/9
-// for more details.
 pub(in crate::solve) fn predicates_for_object_candidate<D, I>(
-    ecx: &EvalCtxt<'_, D>,
+    ecx: &mut EvalCtxt<'_, D>,
     param_env: I::ParamEnv,
     trait_ref: ty::TraitRef<I>,
     object_bounds: I::BoundExistentialPredicates,
-) -> Vec<Goal<I, I::Predicate>>
+) -> Result<Vec<Goal<I, I::Predicate>>, Ambiguous>
 where
     D: SolverDelegate<Interner = I>,
     I: Interner,
@@ -871,72 +866,130 @@ where
             .extend(cx.item_bounds(associated_type_def_id).iter_instantiated(cx, trait_ref.args));
     }
 
-    let mut replace_projection_with = HashMap::default();
+    let mut replace_projection_with: HashMap<_, Vec<_>> = HashMap::default();
     for bound in object_bounds.iter() {
         if let ty::ExistentialPredicate::Projection(proj) = bound.skip_binder() {
+            // FIXME: We *probably* should replace this with a dummy placeholder,
+            // b/c don't want to replace literal instances of this dyn type that
+            // show up in the bounds, but just ones that come from substituting
+            // `Self` with the dyn type.
             let proj = proj.with_self_ty(cx, trait_ref.self_ty());
-            let old_ty = replace_projection_with.insert(proj.def_id(), bound.rebind(proj));
-            assert_eq!(
-                old_ty,
-                None,
-                "{:?} has two generic parameters: {:?} and {:?}",
-                proj.projection_term,
-                proj.term,
-                old_ty.unwrap()
-            );
+            replace_projection_with.entry(proj.def_id()).or_default().push(bound.rebind(proj));
         }
     }
 
-    let mut folder =
-        ReplaceProjectionWith { ecx, param_env, mapping: replace_projection_with, nested: vec![] };
-    let folded_requirements = requirements.fold_with(&mut folder);
+    let mut folder = ReplaceProjectionWith {
+        ecx,
+        param_env,
+        self_ty: trait_ref.self_ty(),
+        mapping: &replace_projection_with,
+        nested: vec![],
+    };
 
-    folder
+    let requirements = requirements.try_fold_with(&mut folder)?;
+    Ok(folder
         .nested
         .into_iter()
-        .chain(folded_requirements.into_iter().map(|clause| Goal::new(cx, param_env, clause)))
-        .collect()
+        .chain(requirements.into_iter().map(|clause| Goal::new(cx, param_env, clause)))
+        .collect())
 }
 
-struct ReplaceProjectionWith<'a, D: SolverDelegate<Interner = I>, I: Interner> {
-    ecx: &'a EvalCtxt<'a, D>,
+struct ReplaceProjectionWith<'a, 'b, I: Interner, D: SolverDelegate<Interner = I>> {
+    ecx: &'a mut EvalCtxt<'b, D>,
     param_env: I::ParamEnv,
-    mapping: HashMap<I::DefId, ty::Binder<I, ty::ProjectionPredicate<I>>>,
+    self_ty: I::Ty,
+    mapping: &'a HashMap<I::DefId, Vec<ty::Binder<I, ty::ProjectionPredicate<I>>>>,
     nested: Vec<Goal<I, I::Predicate>>,
 }
 
-impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I>
-    for ReplaceProjectionWith<'_, D, I>
+impl<D, I> ReplaceProjectionWith<'_, '_, I, D>
+where
+    D: SolverDelegate<Interner = I>,
+    I: Interner,
 {
+    fn projection_may_match(
+        &mut self,
+        source_projection: ty::Binder<I, ty::ProjectionPredicate<I>>,
+        target_projection: ty::AliasTerm<I>,
+    ) -> bool {
+        source_projection.item_def_id() == target_projection.def_id
+            && self
+                .ecx
+                .probe(|_| ProbeKind::ProjectionCompatibility)
+                .enter(|ecx| -> Result<_, NoSolution> {
+                    let source_projection = ecx.instantiate_binder_with_infer(source_projection);
+                    ecx.eq(self.param_env, source_projection.projection_term, target_projection)?;
+                    ecx.try_evaluate_added_goals()
+                })
+                .is_ok()
+    }
+
+    /// Try to replace an alias with the term present in the projection bounds of the self type.
+    /// Returns `Ok<None>` if this alias is not eligible to be replaced, or bail with
+    /// `Err(Ambiguous)` if it's uncertain which projection bound to replace the term with due
+    /// to multiple bounds applying.
+    fn try_eagerly_replace_alias(
+        &mut self,
+        alias_term: ty::AliasTerm<I>,
+    ) -> Result<Option<I::Term>, Ambiguous> {
+        if alias_term.self_ty() != self.self_ty {
+            return Ok(None);
+        }
+
+        let Some(replacements) = self.mapping.get(&alias_term.def_id) else {
+            return Ok(None);
+        };
+
+        // This is quite similar to the `projection_may_match` we use in unsizing,
+        // but here we want to unify a projection predicate against an alias term
+        // so we can replace it with the the projection predicate's term.
+        let mut matching_projections = replacements
+            .iter()
+            .filter(|source_projection| self.projection_may_match(**source_projection, alias_term));
+        let Some(replacement) = matching_projections.next() else {
+            // This shouldn't happen.
+            panic!("could not replace {alias_term:?} with term from from {:?}", self.self_ty);
+        };
+        // FIXME: This *may* have issues with duplicated projections.
+        if matching_projections.next().is_some() {
+            // If there's more than one projection that we can unify here, then we
+            // need to stall until inference constrains things so that there's only
+            // one choice.
+            return Err(Ambiguous);
+        }
+
+        let replacement = self.ecx.instantiate_binder_with_infer(*replacement);
+        self.nested.extend(
+            self.ecx
+                .eq_and_get_goals(self.param_env, alias_term, replacement.projection_term)
+                .expect("expected to be able to unify goal projection with dyn's projection"),
+        );
+
+        Ok(Some(replacement.term))
+    }
+}
+
+/// Marker for bailing with ambiguity.
+pub(crate) struct Ambiguous;
+
+impl<D, I> FallibleTypeFolder<I> for ReplaceProjectionWith<'_, '_, I, D>
+where
+    D: SolverDelegate<Interner = I>,
+    I: Interner,
+{
+    type Error = Ambiguous;
+
     fn cx(&self) -> I {
         self.ecx.cx()
     }
 
-    fn fold_ty(&mut self, ty: I::Ty) -> I::Ty {
+    fn try_fold_ty(&mut self, ty: I::Ty) -> Result<I::Ty, Ambiguous> {
         if let ty::Alias(ty::Projection, alias_ty) = ty.kind() {
-            if let Some(replacement) = self.mapping.get(&alias_ty.def_id) {
-                // We may have a case where our object type's projection bound is higher-ranked,
-                // but the where clauses we instantiated are not. We can solve this by instantiating
-                // the binder at the usage site.
-                let proj = self.ecx.instantiate_binder_with_infer(*replacement);
-                // FIXME: Technically this equate could be fallible...
-                self.nested.extend(
-                    self.ecx
-                        .eq_and_get_goals(
-                            self.param_env,
-                            alias_ty,
-                            proj.projection_term.expect_ty(self.ecx.cx()),
-                        )
-                        .expect(
-                            "expected to be able to unify goal projection with dyn's projection",
-                        ),
-                );
-                proj.term.expect_ty()
-            } else {
-                ty.super_fold_with(self)
+            if let Some(term) = self.try_eagerly_replace_alias(alias_ty.into())? {
+                return Ok(term.expect_ty());
             }
-        } else {
-            ty.super_fold_with(self)
         }
+
+        ty.try_super_fold_with(self)
     }
 }
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
index 4edc293ad80..d56b0e5847e 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
@@ -355,7 +355,7 @@ where
                     // exist at all (see the FIXME at the start of this method), we have to deal with
                     // them for now.
                     delegate.instantiate_canonical_var_with_infer(info, span, |idx| {
-                        ty::UniverseIndex::from(prev_universe.index() + idx.index())
+                        prev_universe + idx.index()
                     })
                 } else if info.is_existential() {
                     // As an optimization we sometimes avoid creating a new inference variable here.
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
index 148ba02252d..9994c85d0d0 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
@@ -286,18 +286,23 @@ where
             // fixing it may cause inference breakage or introduce ambiguity.
             GoalSource::Misc => PathKind::Unknown,
             GoalSource::NormalizeGoal(path_kind) => path_kind,
-            GoalSource::ImplWhereBound => {
+            GoalSource::ImplWhereBound => match self.current_goal_kind {
                 // We currently only consider a cycle coinductive if it steps
                 // into a where-clause of a coinductive trait.
+                CurrentGoalKind::CoinductiveTrait => PathKind::Coinductive,
+                // While normalizing via an impl does step into a where-clause of
+                // an impl, accessing the associated item immediately steps out of
+                // it again. This means cycles/recursive calls are not guarded
+                // by impls used for normalization.
                 //
+                // See tests/ui/traits/next-solver/cycles/normalizes-to-is-not-productive.rs
+                // for how this can go wrong.
+                CurrentGoalKind::NormalizesTo => PathKind::Inductive,
                 // We probably want to make all traits coinductive in the future,
-                // so we treat cycles involving their where-clauses as ambiguous.
-                if let CurrentGoalKind::CoinductiveTrait = self.current_goal_kind {
-                    PathKind::Coinductive
-                } else {
-                    PathKind::Unknown
-                }
-            }
+                // so we treat cycles involving where-clauses of not-yet coinductive
+                // traits as ambiguous for now.
+                CurrentGoalKind::Misc => PathKind::Unknown,
+            },
             // Relating types is always unproductive. If we were to map proof trees to
             // corecursive functions as explained in #136824, relating types never
             // introduces a constructor which could cause the recursion to be guarded.
diff --git a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
index de6d21da0f5..fdeb276a58e 100644
--- a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
@@ -45,7 +45,6 @@ where
                             goal,
                             goal.predicate.alias,
                         );
-                        this.add_goal(GoalSource::AliasWellFormed, goal.with(cx, trait_ref));
                         this.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
                     })
                 })
@@ -134,7 +133,7 @@ where
                     // Add GAT where clauses from the trait's definition
                     // FIXME: We don't need these, since these are the type's own WF obligations.
                     ecx.add_goals(
-                        GoalSource::Misc,
+                        GoalSource::AliasWellFormed,
                         cx.own_predicates_of(goal.predicate.def_id())
                             .iter_instantiated(cx, goal.predicate.alias.args)
                             .map(|pred| goal.with(cx, pred)),
@@ -199,7 +198,7 @@ where
             // Add GAT where clauses from the trait's definition.
             // FIXME: We don't need these, since these are the type's own WF obligations.
             ecx.add_goals(
-                GoalSource::Misc,
+                GoalSource::AliasWellFormed,
                 cx.own_predicates_of(goal.predicate.def_id())
                     .iter_instantiated(cx, goal.predicate.alias.args)
                     .map(|pred| goal.with(cx, pred)),
@@ -232,7 +231,33 @@ where
             };
 
             if !cx.has_item_definition(target_item_def_id) {
-                return error_response(ecx, cx.delay_bug("missing item"));
+                // If the impl is missing an item, it's either because the user forgot to
+                // provide it, or the user is not *obligated* to provide it (because it
+                // has a trivially false `Sized` predicate). If it's the latter, we cannot
+                // delay a bug because we can have trivially false where clauses, so we
+                // treat it as rigid.
+                if cx.impl_self_is_guaranteed_unsized(impl_def_id) {
+                    match ecx.typing_mode() {
+                        ty::TypingMode::Coherence => {
+                            return ecx.evaluate_added_goals_and_make_canonical_response(
+                                Certainty::AMBIGUOUS,
+                            );
+                        }
+                        ty::TypingMode::Analysis { .. }
+                        | ty::TypingMode::Borrowck { .. }
+                        | ty::TypingMode::PostBorrowckAnalysis { .. }
+                        | ty::TypingMode::PostAnalysis => {
+                            ecx.structurally_instantiate_normalizes_to_term(
+                                goal,
+                                goal.predicate.alias,
+                            );
+                            return ecx
+                                .evaluate_added_goals_and_make_canonical_response(Certainty::Yes);
+                        }
+                    }
+                } else {
+                    return error_response(ecx, cx.delay_bug("missing item"));
+                }
             }
 
             let target_container_def_id = cx.parent(target_item_def_id);
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index d42c9980f46..409af8568d7 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -164,6 +164,7 @@ where
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
     ) -> Result<Candidate<I>, NoSolution> {
+        let cx = ecx.cx();
         if goal.predicate.polarity != ty::PredicatePolarity::Positive {
             return Err(NoSolution);
         }
@@ -174,20 +175,37 @@ where
 
         // Only consider auto impls of unsafe traits when there are no unsafe
         // fields.
-        if ecx.cx().trait_is_unsafe(goal.predicate.def_id())
+        if cx.trait_is_unsafe(goal.predicate.def_id())
             && goal.predicate.self_ty().has_unsafe_fields()
         {
             return Err(NoSolution);
         }
 
-        // We only look into opaque types during analysis for opaque types
-        // outside of their defining scope. Doing so for opaques in the
-        // defining scope may require calling `typeck` on the same item we're
-        // currently type checking, which will result in a fatal cycle that
-        // ideally we want to avoid, since we can make progress on this goal
-        // via an alias bound or a locally-inferred hidden type instead.
+        // We leak the implemented auto traits of opaques outside of their defining scope.
+        // This depends on `typeck` of the defining scope of that opaque, which may result in
+        // fatal query cycles.
+        //
+        // We only get to this point if we're outside of the defining scope as we'd otherwise
+        // be able to normalize the opaque type. We may also cycle in case `typeck` of a defining
+        // scope relies on the current context, e.g. either because it also leaks auto trait
+        // bounds of opaques defined in the current context or by evaluating the current item.
+        //
+        // To avoid this we don't try to leak auto trait bounds if they can also be proven via
+        // item bounds of the opaque. These bounds are always applicable as auto traits must not
+        // have any generic parameters. They would also get preferred over the impl candidate
+        // when merging candidates anyways.
+        //
+        // See tests/ui/impl-trait/auto-trait-leakage/avoid-query-cycle-via-item-bound.rs.
         if let ty::Alias(ty::Opaque, opaque_ty) = goal.predicate.self_ty().kind() {
             debug_assert!(ecx.opaque_type_is_rigid(opaque_ty.def_id));
+            for item_bound in cx.item_self_bounds(opaque_ty.def_id).skip_binder() {
+                if item_bound
+                    .as_trait_clause()
+                    .is_some_and(|b| b.def_id() == goal.predicate.def_id())
+                {
+                    return Err(NoSolution);
+                }
+            }
         }
 
         ecx.probe_and_evaluate_goal_for_constituent_tys(
@@ -926,7 +944,7 @@ where
              target_projection: ty::Binder<I, ty::ExistentialProjection<I>>| {
                 source_projection.item_def_id() == target_projection.item_def_id()
                     && ecx
-                        .probe(|_| ProbeKind::UpcastProjectionCompatibility)
+                        .probe(|_| ProbeKind::ProjectionCompatibility)
                         .enter(|ecx| -> Result<_, NoSolution> {
                             ecx.enter_forall(target_projection, |ecx, target_projection| {
                                 let source_projection =
@@ -1238,10 +1256,11 @@ where
     D: SolverDelegate<Interner = I>,
     I: Interner,
 {
+    #[instrument(level = "debug", skip(self, goal), ret)]
     pub(super) fn merge_trait_candidates(
         &mut self,
         goal: Goal<I, TraitPredicate<I>>,
-        candidates: Vec<Candidate<I>>,
+        mut candidates: Vec<Candidate<I>>,
     ) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
         if let TypingMode::Coherence = self.typing_mode() {
             let all_candidates: Vec<_> = candidates.into_iter().map(|c| c.result).collect();
@@ -1323,13 +1342,16 @@ where
 
         // If there are *only* global where bounds, then make sure to return that this
         // is still reported as being proven-via the param-env so that rigid projections
-        // operate correctly.
+        // operate correctly. Otherwise, drop all global where-bounds before merging the
+        // remaining candidates.
         let proven_via =
             if candidates.iter().all(|c| matches!(c.source, CandidateSource::ParamEnv(_))) {
                 TraitGoalProvenVia::ParamEnv
             } else {
+                candidates.retain(|c| !matches!(c.source, CandidateSource::ParamEnv(_)));
                 TraitGoalProvenVia::Misc
             };
+
         let all_candidates: Vec<_> = candidates.into_iter().map(|c| c.result).collect();
         if let Some(response) = self.try_merge_responses(&all_candidates) {
             Ok((response, Some(proven_via)))
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index 93fa89b68b9..e7f17bb6f99 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -543,7 +543,7 @@ parse_maybe_recover_from_bad_qpath_stage_2 =
     .suggestion = types that don't start with an identifier need to be surrounded with angle brackets in qualified paths
 
 parse_maybe_recover_from_bad_type_plus =
-    expected a path on the left-hand side of `+`, not `{$ty}`
+    expected a path on the left-hand side of `+`
 
 parse_maybe_report_ambiguous_plus =
     ambiguous `+` in a type
@@ -642,7 +642,9 @@ parse_mut_on_nested_ident_pattern = `mut` must be attached to each individual bi
     .suggestion = add `mut` to each binding
 parse_mut_on_non_ident_pattern = `mut` must be followed by a named binding
     .suggestion = remove the `mut` prefix
-parse_need_plus_after_trait_object_lifetime = lifetime in trait object type must be followed by `+`
+
+parse_need_plus_after_trait_object_lifetime = lifetimes must be followed by `+` to form a trait object type
+    .suggestion = consider adding a trait bound after the potential lifetime bound
 
 parse_nested_adt = `{$kw_str}` definition cannot be nested inside `{$keyword}`
     .suggestion = consider creating a new `{$kw_str}` definition instead of nesting
@@ -806,9 +808,6 @@ parse_trait_alias_cannot_be_unsafe = trait aliases cannot be `unsafe`
 parse_transpose_dyn_or_impl = `for<...>` expected after `{$kw}`, not before
     .suggestion = move `{$kw}` before the `for<...>`
 
-parse_type_ascription_removed =
-    if you meant to annotate an expression with a type, the type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>
-
 parse_unclosed_unicode_escape = unterminated unicode escape
     .label = missing a closing `{"}"}`
     .terminate = terminate the unicode escape
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index dfdef018bc3..44b4e1a3e47 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -7,8 +7,7 @@ use rustc_ast::util::parser::ExprPrecedence;
 use rustc_ast::{Path, Visibility};
 use rustc_errors::codes::*;
 use rustc_errors::{
-    Applicability, Diag, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level, SubdiagMessageOp,
-    Subdiagnostic,
+    Applicability, Diag, DiagCtxtHandle, Diagnostic, EmissionGuarantee, Level, Subdiagnostic,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::errors::ExprParenthesesNeeded;
@@ -30,7 +29,6 @@ pub(crate) struct AmbiguousPlus {
 #[derive(Diagnostic)]
 #[diag(parse_maybe_recover_from_bad_type_plus, code = E0178)]
 pub(crate) struct BadTypePlus {
-    pub ty: String,
     #[primary_span]
     pub span: Span,
     #[subdiagnostic]
@@ -1551,11 +1549,7 @@ pub(crate) struct FnTraitMissingParen {
 }
 
 impl Subdiagnostic for FnTraitMissingParen {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.span_label(self.span, crate::fluent_generated::parse_fn_trait_missing_paren);
         diag.span_suggestion_short(
             self.span.shrink_to_hi(),
@@ -1598,9 +1592,6 @@ pub(crate) struct PathSingleColon {
 
     #[suggestion(applicability = "machine-applicable", code = ":", style = "verbose")]
     pub suggestion: Span,
-
-    #[note(parse_type_ascription_removed)]
-    pub type_ascription: bool,
 }
 
 #[derive(Diagnostic)]
@@ -1617,9 +1608,6 @@ pub(crate) struct ColonAsSemi {
     #[primary_span]
     #[suggestion(applicability = "machine-applicable", code = ";", style = "verbose")]
     pub span: Span,
-
-    #[note(parse_type_ascription_removed)]
-    pub type_ascription: bool,
 }
 
 #[derive(Diagnostic)]
@@ -2806,6 +2794,8 @@ pub(crate) struct ReturnTypesUseThinArrow {
 pub(crate) struct NeedPlusAfterTraitObjectLifetime {
     #[primary_span]
     pub span: Span,
+    #[suggestion(code = " + /* Trait */", applicability = "has-placeholders")]
+    pub suggestion: Span,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_parse/src/lexer/unicode_chars.rs b/compiler/rustc_parse/src/lexer/unicode_chars.rs
index ff03b42484b..2bfa1ea4e05 100644
--- a/compiler/rustc_parse/src/lexer/unicode_chars.rs
+++ b/compiler/rustc_parse/src/lexer/unicode_chars.rs
@@ -376,7 +376,7 @@ pub(super) fn check_for_substitution(
             ascii_name,
         })
     };
-    (token.clone(), sugg)
+    (*token, sugg)
 }
 
 /// Extract string if found at current position with given delimiters
diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
index 79939aab7fc..2edc8c83017 100644
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@@ -4,7 +4,6 @@
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(array_windows)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
index cff998fa137..f1bd6a22730 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -120,7 +120,7 @@ impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
         // produce an empty `TokenStream` if no calls were made, and omit the
         // final token otherwise.
         let mut cursor_snapshot = self.cursor_snapshot.clone();
-        let tokens = iter::once(FlatToken::Token(self.start_token.clone()))
+        let tokens = iter::once(FlatToken::Token(self.start_token))
             .chain(iter::repeat_with(|| FlatToken::Token(cursor_snapshot.next())))
             .take(self.num_calls as usize);
 
@@ -186,7 +186,7 @@ impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
 impl<'a> Parser<'a> {
     pub(super) fn collect_pos(&self) -> CollectPos {
         CollectPos {
-            start_token: (self.token.clone(), self.token_spacing),
+            start_token: (self.token, self.token_spacing),
             cursor_snapshot: self.token_cursor.clone(),
             start_pos: self.num_bump_calls,
         }
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index ef044fe9d63..7c8e0146c3d 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -322,7 +322,7 @@ impl<'a> Parser<'a> {
         let mut recovered_ident = None;
         // we take this here so that the correct original token is retained in
         // the diagnostic, regardless of eager recovery.
-        let bad_token = self.token.clone();
+        let bad_token = self.token;
 
         // suggest prepending a keyword in identifier position with `r#`
         let suggest_raw = if let Some((ident, IdentIsRaw::No)) = self.token.ident()
@@ -382,7 +382,7 @@ impl<'a> Parser<'a> {
             // if the previous token is a valid keyword
             // that might use a generic, then suggest a correct
             // generic placement (later on)
-            let maybe_keyword = self.prev_token.clone();
+            let maybe_keyword = self.prev_token;
             if valid_prev_keywords.into_iter().any(|x| maybe_keyword.is_keyword(x)) {
                 // if we have a valid keyword, attempt to parse generics
                 // also obtain the keywords symbol
@@ -530,7 +530,7 @@ impl<'a> Parser<'a> {
                 //   let y = 42;
                 let guar = self.dcx().emit_err(ExpectedSemi {
                     span: self.token.span,
-                    token: self.token.clone(),
+                    token: self.token,
                     unexpected_token_label: None,
                     sugg: ExpectedSemiSugg::ChangeToSemi(self.token.span),
                 });
@@ -555,7 +555,7 @@ impl<'a> Parser<'a> {
                 let span = self.prev_token.span.shrink_to_hi();
                 let guar = self.dcx().emit_err(ExpectedSemi {
                     span,
-                    token: self.token.clone(),
+                    token: self.token,
                     unexpected_token_label: Some(self.token.span),
                     sugg: ExpectedSemiSugg::AddSemi(span),
                 });
@@ -609,6 +609,8 @@ impl<'a> Parser<'a> {
         // FIXME: translation requires list formatting (for `expect`)
         let mut err = self.dcx().struct_span_err(self.token.span, msg_exp);
 
+        self.label_expected_raw_ref(&mut err);
+
         // Look for usages of '=>' where '>=' was probably intended
         if self.token == token::FatArrow
             && expected.iter().any(|tok| matches!(tok, TokenType::Operator | TokenType::Le))
@@ -750,6 +752,25 @@ impl<'a> Parser<'a> {
         Err(err)
     }
 
+    /// Adds a label when `&raw EXPR` was written instead of `&raw const EXPR`/`&raw mut EXPR`.
+    ///
+    /// Given that not all parser diagnostics flow through `expected_one_of_not_found`, this
+    /// label may need added to other diagnostics emission paths as needed.
+    pub(super) fn label_expected_raw_ref(&mut self, err: &mut Diag<'_>) {
+        if self.prev_token.is_keyword(kw::Raw)
+            && self.expected_token_types.contains(TokenType::KwMut)
+            && self.expected_token_types.contains(TokenType::KwConst)
+            && self.token.can_begin_expr()
+        {
+            err.span_suggestions(
+                self.prev_token.span.shrink_to_hi(),
+                "`&raw` must be followed by `const` or `mut` to be a raw reference expression",
+                [" const".to_string(), " mut".to_string()],
+                Applicability::MaybeIncorrect,
+            );
+        }
+    }
+
     /// Checks if the current token or the previous token are misspelled keywords
     /// and adds a helpful suggestion.
     fn check_for_misspelled_kw(&self, err: &mut Diag<'_>, expected: &[TokenType]) {
@@ -801,7 +822,7 @@ impl<'a> Parser<'a> {
         let span = self.prev_token.span.shrink_to_hi();
         let mut err = self.dcx().create_err(ExpectedSemi {
             span,
-            token: self.token.clone(),
+            token: self.token,
             unexpected_token_label: Some(self.token.span),
             sugg: ExpectedSemiSugg::AddSemi(span),
         });
@@ -1636,19 +1657,19 @@ impl<'a> Parser<'a> {
 
         self.bump(); // `+`
         let _bounds = self.parse_generic_bounds()?;
-        let sum_span = ty.span.to(self.prev_token.span);
-
         let sub = match &ty.kind {
             TyKind::Ref(_lifetime, mut_ty) => {
                 let lo = mut_ty.ty.span.shrink_to_lo();
                 let hi = self.prev_token.span.shrink_to_hi();
                 BadTypePlusSub::AddParen { suggestion: AddParen { lo, hi } }
             }
-            TyKind::Ptr(..) | TyKind::BareFn(..) => BadTypePlusSub::ForgotParen { span: sum_span },
-            _ => BadTypePlusSub::ExpectPath { span: sum_span },
+            TyKind::Ptr(..) | TyKind::BareFn(..) => {
+                BadTypePlusSub::ForgotParen { span: ty.span.to(self.prev_token.span) }
+            }
+            _ => BadTypePlusSub::ExpectPath { span: ty.span },
         };
 
-        self.dcx().emit_err(BadTypePlus { ty: pprust::ty_to_string(ty), span: sum_span, sub });
+        self.dcx().emit_err(BadTypePlus { span: ty.span, sub });
 
         Ok(())
     }
@@ -1922,10 +1943,7 @@ impl<'a> Parser<'a> {
             && self.token == token::Colon
             && self.look_ahead(1, |next| line_idx(self.token.span) < line_idx(next.span))
         {
-            self.dcx().emit_err(ColonAsSemi {
-                span: self.token.span,
-                type_ascription: self.psess.unstable_features.is_nightly_build(),
-            });
+            self.dcx().emit_err(ColonAsSemi { span: self.token.span });
             self.bump();
             return true;
         }
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 9c457f150a3..df44b3cc23c 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -344,7 +344,7 @@ impl<'a> Parser<'a> {
     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
         self.dcx().emit_err(errors::FoundExprWouldBeStmt {
             span: self.token.span,
-            token: self.token.clone(),
+            token: self.token,
             suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
         });
     }
@@ -417,7 +417,7 @@ impl<'a> Parser<'a> {
         cur_op_span: Span,
     ) -> PResult<'a, P<Expr>> {
         let rhs = if self.is_at_start_of_range_notation_rhs() {
-            let maybe_lt = self.token.clone();
+            let maybe_lt = self.token;
             let attrs = self.parse_outer_attributes()?;
             Some(
                 self.parse_expr_assoc_with(Bound::Excluded(prec), attrs)
@@ -611,7 +611,7 @@ impl<'a> Parser<'a> {
 
     /// Recover on `not expr` in favor of `!expr`.
     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
-        let negated_token = self.look_ahead(1, |t| t.clone());
+        let negated_token = self.look_ahead(1, |t| *t);
 
         let sub_diag = if negated_token.is_numeric_lit() {
             errors::NotAsNegationOperatorSub::SuggestNotBitwise
@@ -637,9 +637,7 @@ impl<'a> Parser<'a> {
     /// Returns the span of expr if it was not interpolated, or the span of the interpolated token.
     fn interpolated_or_expr_span(&self, expr: &Expr) -> Span {
         match self.prev_token.kind {
-            TokenKind::NtIdent(..) | TokenKind::NtLifetime(..) | TokenKind::Interpolated(..) => {
-                self.prev_token.span
-            }
+            TokenKind::NtIdent(..) | TokenKind::NtLifetime(..) => self.prev_token.span,
             TokenKind::CloseDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(_))) => {
                 // `expr.span` is the interpolated span, because invisible open
                 // and close delims both get marked with the same span, one
@@ -829,6 +827,18 @@ impl<'a> Parser<'a> {
         if let Some(lt) = lifetime {
             self.error_remove_borrow_lifetime(span, lt.ident.span.until(expr.span));
         }
+
+        // Add expected tokens if we parsed `&raw` as an expression.
+        // This will make sure we see "expected `const`, `mut`", and
+        // guides recovery in case we write `&raw expr`.
+        if borrow_kind == ast::BorrowKind::Ref
+            && mutbl == ast::Mutability::Not
+            && matches!(&expr.kind, ExprKind::Path(None, p) if p.is_ident(kw::Raw))
+        {
+            self.expected_token_types.insert(TokenType::KwMut);
+            self.expected_token_types.insert(TokenType::KwConst);
+        }
+
         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
     }
 
@@ -1386,15 +1396,7 @@ impl<'a> Parser<'a> {
         maybe_recover_from_interpolated_ty_qpath!(self, true);
 
         let span = self.token.span;
-        if let token::Interpolated(nt) = &self.token.kind {
-            match &**nt {
-                token::NtBlock(block) => {
-                    let block = block.clone();
-                    self.bump();
-                    return Ok(self.mk_expr(self.prev_token.span, ExprKind::Block(block, None)));
-                }
-            };
-        } else if let Some(expr) = self.eat_metavar_seq_with_matcher(
+        if let Some(expr) = self.eat_metavar_seq_with_matcher(
             |mv_kind| matches!(mv_kind, MetaVarKind::Expr { .. }),
             |this| {
                 // Force collection (as opposed to just `parse_expr`) is required to avoid the
@@ -1415,9 +1417,13 @@ impl<'a> Parser<'a> {
             self.eat_metavar_seq(MetaVarKind::Literal, |this| this.parse_literal_maybe_minus())
         {
             return Ok(lit);
-        } else if let Some(path) = self.eat_metavar_seq(MetaVarKind::Path, |this| {
-            this.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))
-        }) {
+        } else if let Some(block) =
+            self.eat_metavar_seq(MetaVarKind::Block, |this| this.parse_block())
+        {
+            return Ok(self.mk_expr(span, ExprKind::Block(block, None)));
+        } else if let Some(path) =
+            self.eat_metavar_seq(MetaVarKind::Path, |this| this.parse_path(PathStyle::Type))
+        {
             return Ok(self.mk_expr(span, ExprKind::Path(None, path)));
         }
 
@@ -1612,7 +1618,7 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_expr_path_start(&mut self) -> PResult<'a, P<Expr>> {
-        let maybe_eq_tok = self.prev_token.clone();
+        let maybe_eq_tok = self.prev_token;
         let (qself, path) = if self.eat_lt() {
             let lt_span = self.prev_token.span;
             let (qself, path) = self.parse_qpath(PathStyle::Expr).map_err(|mut err| {
@@ -1671,7 +1677,7 @@ impl<'a> Parser<'a> {
         } else if self.eat_keyword(exp!(Loop)) {
             self.parse_expr_loop(label, lo)
         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
-            || self.token.is_whole_block()
+            || self.token.is_metavar_block()
         {
             self.parse_expr_block(label, lo, BlockCheckMode::Default)
         } else if !ate_colon
@@ -2073,7 +2079,7 @@ impl<'a> Parser<'a> {
         &mut self,
         mk_lit_char: impl FnOnce(Symbol, Span) -> L,
     ) -> PResult<'a, L> {
-        let token = self.token.clone();
+        let token = self.token;
         let err = |self_: &Self| {
             let msg = format!("unexpected token: {}", super::token_descr(&token));
             self_.dcx().struct_span_err(token.span, msg)
@@ -2166,10 +2172,15 @@ impl<'a> Parser<'a> {
                 let expr = self
                     .eat_metavar_seq(mv_kind, |this| this.parse_expr())
                     .expect("metavar seq expr");
-                let ast::ExprKind::Lit(token_lit) = expr.kind else {
-                    panic!("didn't reparse an expr");
-                };
-                Some(token_lit)
+                if let ast::ExprKind::Lit(token_lit) = expr.kind {
+                    Some(token_lit)
+                } else if let ast::ExprKind::Unary(UnOp::Neg, inner) = &expr.kind
+                    && let ast::Expr { kind: ast::ExprKind::Lit(_), .. } = **inner
+                {
+                    None
+                } else {
+                    panic!("unexpected reparsed expr: {:?}", expr.kind);
+                }
             }
             _ => None,
         }
@@ -2349,7 +2360,7 @@ impl<'a> Parser<'a> {
             }
         }
 
-        if self.token.is_whole_block() {
+        if self.token.is_metavar_block() {
             self.dcx().emit_err(errors::InvalidBlockMacroSegment {
                 span: self.token.span,
                 context: lo.to(self.token.span),
@@ -2374,7 +2385,7 @@ impl<'a> Parser<'a> {
     fn parse_expr_closure(&mut self) -> PResult<'a, P<Expr>> {
         let lo = self.token.span;
 
-        let before = self.prev_token.clone();
+        let before = self.prev_token;
         let binder = if self.check_keyword(exp!(For)) {
             let lo = self.token.span;
             let (lifetime_defs, _) = self.parse_late_bound_lifetime_defs()?;
@@ -2406,8 +2417,8 @@ impl<'a> Parser<'a> {
             FnRetTy::Default(_) => {
                 let restrictions =
                     self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET;
-                let prev = self.prev_token.clone();
-                let token = self.token.clone();
+                let prev = self.prev_token;
+                let token = self.token;
                 let attrs = self.parse_outer_attributes()?;
                 match self.parse_expr_res(restrictions, attrs) {
                     Ok((expr, _)) => expr,
@@ -2472,7 +2483,7 @@ impl<'a> Parser<'a> {
         if self.may_recover()
             && self.token.can_begin_expr()
             && !matches!(self.token.kind, TokenKind::OpenDelim(Delimiter::Brace))
-            && !self.token.is_whole_block()
+            && !self.token.is_metavar_block()
         {
             let snapshot = self.create_snapshot_for_diagnostic();
             let restrictions =
@@ -2654,7 +2665,7 @@ impl<'a> Parser<'a> {
             }
         } else {
             let attrs = self.parse_outer_attributes()?; // For recovery.
-            let maybe_fatarrow = self.token.clone();
+            let maybe_fatarrow = self.token;
             let block = if self.check(exp!(OpenBrace)) {
                 self.parse_block()?
             } else if let Some(block) = recover_block_from_condition(self) {
@@ -3519,7 +3530,7 @@ impl<'a> Parser<'a> {
         self.token.is_keyword(kw::Do)
             && self.is_keyword_ahead(1, &[kw::Catch])
             && self
-                .look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
+                .look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_metavar_block())
             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
     }
 
@@ -3530,7 +3541,7 @@ impl<'a> Parser<'a> {
     fn is_try_block(&self) -> bool {
         self.token.is_keyword(kw::Try)
             && self
-                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
+                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_metavar_block())
             && self.token_uninterpolated_span().at_least_rust_2018()
     }
 
@@ -3564,12 +3575,12 @@ impl<'a> Parser<'a> {
                 // `async move {`
                 self.is_keyword_ahead(lookahead + 1, &[kw::Move, kw::Use])
                     && self.look_ahead(lookahead + 2, |t| {
-                        *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block()
+                        *t == token::OpenDelim(Delimiter::Brace) || t.is_metavar_block()
                     })
             ) || (
                 // `async {`
                 self.look_ahead(lookahead + 1, |t| {
-                    *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block()
+                    *t == token::OpenDelim(Delimiter::Brace) || t.is_metavar_block()
                 })
             ))
     }
@@ -3862,7 +3873,7 @@ impl<'a> Parser<'a> {
                 return Err(this.dcx().create_err(errors::ExpectedStructField {
                     span: this.look_ahead(1, |t| t.span),
                     ident_span: this.token.span,
-                    token: this.look_ahead(1, |t| t.clone()),
+                    token: this.look_ahead(1, |t| *t),
                 }));
             }
             let (ident, expr) = if is_shorthand {
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 9405b58ab3b..39a0291cb1e 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -602,21 +602,13 @@ impl<'a> Parser<'a> {
         let polarity = self.parse_polarity();
 
         // Parse both types and traits as a type, then reinterpret if necessary.
-        let err_path = |span| ast::Path::from_ident(Ident::new(kw::Empty, span));
         let ty_first = if self.token.is_keyword(kw::For) && self.look_ahead(1, |t| t != &token::Lt)
         {
             let span = self.prev_token.span.between(self.token.span);
-            self.dcx().emit_err(errors::MissingTraitInTraitImpl {
+            return Err(self.dcx().create_err(errors::MissingTraitInTraitImpl {
                 span,
                 for_span: span.to(self.token.span),
-            });
-
-            P(Ty {
-                kind: TyKind::Path(None, err_path(span)),
-                span,
-                id: DUMMY_NODE_ID,
-                tokens: None,
-            })
+            }));
         } else {
             self.parse_ty_with_generics_recovery(&generics)?
         };
@@ -657,6 +649,7 @@ impl<'a> Parser<'a> {
                     other => {
                         if let TyKind::ImplTrait(_, bounds) = other
                             && let [bound] = bounds.as_slice()
+                            && let GenericBound::Trait(poly_trait_ref) = bound
                         {
                             // Suggest removing extra `impl` keyword:
                             // `impl<T: Default> impl Default for Wrapper<T>`
@@ -666,12 +659,12 @@ impl<'a> Parser<'a> {
                                 extra_impl_kw,
                                 impl_trait_span: ty_first.span,
                             });
+                            poly_trait_ref.trait_ref.path.clone()
                         } else {
-                            self.dcx().emit_err(errors::ExpectedTraitInTraitImplFoundType {
-                                span: ty_first.span,
-                            });
+                            return Err(self.dcx().create_err(
+                                errors::ExpectedTraitInTraitImplFoundType { span: ty_first.span },
+                            ));
                         }
-                        err_path(ty_first.span)
                     }
                 };
                 let trait_ref = TraitRef { path, ref_id: ty_first.id };
@@ -1739,8 +1732,7 @@ impl<'a> Parser<'a> {
             self.expect_semi()?;
             body
         } else {
-            let err =
-                errors::UnexpectedTokenAfterStructName::new(self.token.span, self.token.clone());
+            let err = errors::UnexpectedTokenAfterStructName::new(self.token.span, self.token);
             return Err(self.dcx().create_err(err));
         };
 
@@ -2310,7 +2302,7 @@ impl<'a> Parser<'a> {
             || self.token.is_keyword(kw::Union))
             && self.look_ahead(1, |t| t.is_ident())
         {
-            let kw_token = self.token.clone();
+            let kw_token = self.token;
             let kw_str = pprust::token_to_string(&kw_token);
             let item = self.parse_item(ForceCollect::No)?;
             let mut item = item.unwrap().span;
@@ -2543,7 +2535,7 @@ impl<'a> Parser<'a> {
             self.expect_semi()?;
             *sig_hi = self.prev_token.span;
             (AttrVec::new(), None)
-        } else if self.check(exp!(OpenBrace)) || self.token.is_whole_block() {
+        } else if self.check(exp!(OpenBrace)) || self.token.is_metavar_block() {
             self.parse_block_common(self.token.span, BlockCheckMode::Default, None)
                 .map(|(attrs, body)| (attrs, Some(body)))?
         } else if self.token == token::Eq {
@@ -2987,9 +2979,7 @@ impl<'a> Parser<'a> {
                 }
                 match ty {
                     Ok(ty) => {
-                        let ident = Ident::new(kw::Empty, this.prev_token.span);
-                        let bm = BindingMode::NONE;
-                        let pat = this.mk_pat_ident(ty.span, bm, ident);
+                        let pat = this.mk_pat(ty.span, PatKind::Missing);
                         (pat, ty)
                     }
                     // If this is a C-variadic argument and we hit an error, return the error.
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 3b0861a9942..2221a261b4c 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -13,7 +13,6 @@ mod ty;
 
 use std::assert_matches::debug_assert_matches;
 use std::ops::Range;
-use std::sync::Arc;
 use std::{fmt, mem, slice};
 
 use attr_wrapper::{AttrWrapper, UsePreAttrPos};
@@ -24,8 +23,8 @@ pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
 use path::PathStyle;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{
-    self, Delimiter, IdentIsRaw, InvisibleOrigin, MetaVarKind, Nonterminal, NtExprKind, NtPatKind,
-    Token, TokenKind,
+    self, Delimiter, IdentIsRaw, InvisibleOrigin, MetaVarKind, NtExprKind, NtPatKind, Token,
+    TokenKind,
 };
 use rustc_ast::tokenstream::{AttrsTarget, Spacing, TokenStream, TokenTree};
 use rustc_ast::util::case::Case;
@@ -98,21 +97,6 @@ pub enum ForceCollect {
     No,
 }
 
-#[macro_export]
-macro_rules! maybe_whole {
-    ($p:expr, $constructor:ident, |$x:ident| $e:expr) => {
-        #[allow(irrefutable_let_patterns)] // FIXME: temporary
-        if let token::Interpolated(nt) = &$p.token.kind
-            && let token::$constructor(x) = &**nt
-        {
-            #[allow(unused_mut)]
-            let mut $x = x.clone();
-            $p.bump();
-            return Ok($e);
-        }
-    };
-}
-
 /// If the next tokens are ill-formed `$ty::` recover them as `<$ty>::`.
 #[macro_export]
 macro_rules! maybe_recover_from_interpolated_ty_qpath {
@@ -342,12 +326,12 @@ impl TokenCursor {
             // below can be removed.
             if let Some(tree) = self.curr.curr() {
                 match tree {
-                    &TokenTree::Token(ref token, spacing) => {
+                    &TokenTree::Token(token, spacing) => {
                         debug_assert!(!matches!(
                             token.kind,
                             token::OpenDelim(_) | token::CloseDelim(_)
                         ));
-                        let res = (token.clone(), spacing);
+                        let res = (token, spacing);
                         self.curr.bump();
                         return res;
                     }
@@ -459,7 +443,6 @@ pub fn token_descr(token: &Token) -> String {
         (Some(TokenDescription::MetaVar(kind)), _) => format!("`{kind}` metavariable"),
         (None, TokenKind::NtIdent(..)) => format!("identifier `{s}`"),
         (None, TokenKind::NtLifetime(..)) => format!("lifetime `{s}`"),
-        (None, TokenKind::Interpolated(node)) => format!("{} `{s}`", node.descr()),
         (None, _) => format!("`{s}`"),
     }
 }
@@ -782,9 +765,16 @@ impl<'a> Parser<'a> {
             // Recovery is disabled when parsing macro arguments, so it must
             // also be disabled when reparsing pasted macro arguments,
             // otherwise we get inconsistent results (e.g. #137874).
-            let res = self.with_recovery(Recovery::Forbidden, |this| {
-                f(this).expect("failed to reparse {mv_kind:?}")
-            });
+            let res = self.with_recovery(Recovery::Forbidden, |this| f(this));
+
+            let res = match res {
+                Ok(res) => res,
+                Err(err) => {
+                    // This can occur in unusual error cases, e.g. #139445.
+                    err.delay_as_bug();
+                    return None;
+                }
+            };
 
             if let token::CloseDelim(delim) = self.token.kind
                 && let Delimiter::Invisible(InvisibleOrigin::MetaVar(mv_kind)) = delim
@@ -793,7 +783,12 @@ impl<'a> Parser<'a> {
                 self.bump();
                 Some(res)
             } else {
-                panic!("no close delim when reparsing {mv_kind:?}");
+                // This can occur when invalid syntax is passed to a decl macro. E.g. see #139248,
+                // where the reparse attempt of an invalid expr consumed the trailing invisible
+                // delimiter.
+                self.dcx()
+                    .span_delayed_bug(self.token.span, "no close delim with reparsing {mv_kind:?}");
+                None
             }
         } else {
             None
@@ -843,8 +838,10 @@ impl<'a> Parser<'a> {
     fn check_inline_const(&self, dist: usize) -> bool {
         self.is_keyword_ahead(dist, &[kw::Const])
             && self.look_ahead(dist + 1, |t| match &t.kind {
-                token::Interpolated(nt) => matches!(&**nt, token::NtBlock(..)),
                 token::OpenDelim(Delimiter::Brace) => true,
+                token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(
+                    MetaVarKind::Block,
+                ))) => true,
                 _ => false,
             })
     }
@@ -1390,7 +1387,7 @@ impl<'a> Parser<'a> {
         // Avoid const blocks and const closures to be parsed as const items
         if (self.check_const_closure() == is_closure)
             && !self
-                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
+                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_metavar_block())
             && self.eat_keyword_case(exp!(Const), case)
         {
             Const::Yes(self.prev_token_uninterpolated_span())
@@ -1520,7 +1517,7 @@ impl<'a> Parser<'a> {
             _ => {
                 let prev_spacing = self.token_spacing;
                 self.bump();
-                TokenTree::Token(self.prev_token.clone(), prev_spacing)
+                TokenTree::Token(self.prev_token, prev_spacing)
             }
         }
     }
@@ -1706,7 +1703,7 @@ impl<'a> Parser<'a> {
             dbg_fmt.field("prev_token", &self.prev_token);
             let mut tokens = vec![];
             for i in 0..lookahead {
-                let tok = self.look_ahead(i, |tok| tok.kind.clone());
+                let tok = self.look_ahead(i, |tok| tok.kind);
                 let is_eof = tok == TokenKind::Eof;
                 tokens.push(tok);
                 if is_eof {
@@ -1747,7 +1744,6 @@ impl<'a> Parser<'a> {
     pub fn token_uninterpolated_span(&self) -> Span {
         match &self.token.kind {
             token::NtIdent(ident, _) | token::NtLifetime(ident, _) => ident.span,
-            token::Interpolated(nt) => nt.use_span(),
             token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(_))) => {
                 self.look_ahead(1, |t| t.span)
             }
@@ -1759,7 +1755,6 @@ impl<'a> Parser<'a> {
     pub fn prev_token_uninterpolated_span(&self) -> Span {
         match &self.prev_token.kind {
             token::NtIdent(ident, _) | token::NtLifetime(ident, _) => ident.span,
-            token::Interpolated(nt) => nt.use_span(),
             token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(_))) => {
                 self.look_ahead(0, |t| t.span)
             }
@@ -1816,6 +1811,7 @@ pub enum ParseNtResult {
     Ident(Ident, IdentIsRaw),
     Lifetime(Ident, IdentIsRaw),
     Item(P<ast::Item>),
+    Block(P<ast::Block>),
     Stmt(P<ast::Stmt>),
     Pat(P<ast::Pat>, NtPatKind),
     Expr(P<ast::Expr>, NtExprKind),
@@ -1824,7 +1820,4 @@ pub enum ParseNtResult {
     Meta(P<ast::AttrItem>),
     Path(P<ast::Path>),
     Vis(P<ast::Visibility>),
-
-    /// This variant will eventually be removed, along with `Token::Interpolate`.
-    Nt(Arc<Nonterminal>),
 }
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
index b4e540d670d..b6e89cd7fa4 100644
--- a/compiler/rustc_parse/src/parser/nonterminal.rs
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -1,14 +1,7 @@
-use std::sync::Arc;
-
-use rustc_ast::HasTokens;
 use rustc_ast::ptr::P;
-use rustc_ast::token::Nonterminal::*;
 use rustc_ast::token::NtExprKind::*;
 use rustc_ast::token::NtPatKind::*;
-use rustc_ast::token::{
-    self, Delimiter, InvisibleOrigin, MetaVarKind, Nonterminal, NonterminalKind, Token,
-};
-use rustc_ast_pretty::pprust;
+use rustc_ast::token::{self, Delimiter, InvisibleOrigin, MetaVarKind, NonterminalKind, Token};
 use rustc_errors::PResult;
 use rustc_span::{Ident, kw};
 
@@ -45,13 +38,6 @@ impl<'a> Parser<'a> {
             }
         }
 
-        /// Old variant of `may_be_ident`. Being phased out.
-        fn nt_may_be_ident(nt: &Nonterminal) -> bool {
-            match nt {
-                NtBlock(_) => false,
-            }
-        }
-
         match kind {
             // `expr_2021` and earlier
             NonterminalKind::Expr(Expr2021 { .. }) => {
@@ -83,16 +69,12 @@ impl<'a> Parser<'a> {
                 | token::Ident(..)
                 | token::NtIdent(..)
                 | token::NtLifetime(..)
-                | token::Interpolated(_)
                 | token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(_))) => true,
                 _ => token.can_begin_type(),
             },
             NonterminalKind::Block => match &token.kind {
                 token::OpenDelim(Delimiter::Brace) => true,
                 token::NtLifetime(..) => true,
-                token::Interpolated(nt) => match &**nt {
-                    NtBlock(_) => true,
-                },
                 token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(k))) => match k {
                     MetaVarKind::Block
                     | MetaVarKind::Stmt
@@ -112,7 +94,6 @@ impl<'a> Parser<'a> {
             },
             NonterminalKind::Path | NonterminalKind::Meta => match &token.kind {
                 token::PathSep | token::Ident(..) | token::NtIdent(..) => true,
-                token::Interpolated(nt) => nt_may_be_ident(nt),
                 token::OpenDelim(Delimiter::Invisible(InvisibleOrigin::MetaVar(kind))) => {
                     may_be_ident(*kind)
                 }
@@ -136,110 +117,85 @@ impl<'a> Parser<'a> {
         // A `macro_rules!` invocation may pass a captured item/expr to a proc-macro,
         // which requires having captured tokens available. Since we cannot determine
         // in advance whether or not a proc-macro will be (transitively) invoked,
-        // we always capture tokens for any `Nonterminal` which needs them.
-        let mut nt = match kind {
+        // we always capture tokens for any nonterminal that needs them.
+        match kind {
             // Note that TT is treated differently to all the others.
-            NonterminalKind::TT => return Ok(ParseNtResult::Tt(self.parse_token_tree())),
+            NonterminalKind::TT => Ok(ParseNtResult::Tt(self.parse_token_tree())),
             NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
-                Some(item) => return Ok(ParseNtResult::Item(item)),
-                None => {
-                    return Err(self
-                        .dcx()
-                        .create_err(UnexpectedNonterminal::Item(self.token.span)));
-                }
+                Some(item) => Ok(ParseNtResult::Item(item)),
+                None => Err(self.dcx().create_err(UnexpectedNonterminal::Item(self.token.span))),
             },
             NonterminalKind::Block => {
                 // While a block *expression* may have attributes (e.g. `#[my_attr] { ... }`),
                 // the ':block' matcher does not support them
-                NtBlock(self.collect_tokens_no_attrs(|this| this.parse_block())?)
+                Ok(ParseNtResult::Block(self.collect_tokens_no_attrs(|this| this.parse_block())?))
             }
             NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
-                Some(stmt) => return Ok(ParseNtResult::Stmt(P(stmt))),
+                Some(stmt) => Ok(ParseNtResult::Stmt(P(stmt))),
                 None => {
-                    return Err(self
-                        .dcx()
-                        .create_err(UnexpectedNonterminal::Statement(self.token.span)));
+                    Err(self.dcx().create_err(UnexpectedNonterminal::Statement(self.token.span)))
                 }
             },
-            NonterminalKind::Pat(pat_kind) => {
-                return Ok(ParseNtResult::Pat(
-                    self.collect_tokens_no_attrs(|this| match pat_kind {
-                        PatParam { .. } => this.parse_pat_no_top_alt(None, None),
-                        PatWithOr => this.parse_pat_no_top_guard(
-                            None,
-                            RecoverComma::No,
-                            RecoverColon::No,
-                            CommaRecoveryMode::EitherTupleOrPipe,
-                        ),
-                    })?,
-                    pat_kind,
-                ));
-            }
+            NonterminalKind::Pat(pat_kind) => Ok(ParseNtResult::Pat(
+                self.collect_tokens_no_attrs(|this| match pat_kind {
+                    PatParam { .. } => this.parse_pat_no_top_alt(None, None),
+                    PatWithOr => this.parse_pat_no_top_guard(
+                        None,
+                        RecoverComma::No,
+                        RecoverColon::No,
+                        CommaRecoveryMode::EitherTupleOrPipe,
+                    ),
+                })?,
+                pat_kind,
+            )),
             NonterminalKind::Expr(expr_kind) => {
-                return Ok(ParseNtResult::Expr(self.parse_expr_force_collect()?, expr_kind));
+                Ok(ParseNtResult::Expr(self.parse_expr_force_collect()?, expr_kind))
             }
             NonterminalKind::Literal => {
                 // The `:literal` matcher does not support attributes.
-                return Ok(ParseNtResult::Literal(
+                Ok(ParseNtResult::Literal(
                     self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?,
-                ));
-            }
-            NonterminalKind::Ty => {
-                return Ok(ParseNtResult::Ty(
-                    self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?,
-                ));
+                ))
             }
-            // this could be handled like a token, since it is one
+            NonterminalKind::Ty => Ok(ParseNtResult::Ty(
+                self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?,
+            )),
+            // This could be handled like a token, since it is one.
             NonterminalKind::Ident => {
-                return if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
+                if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
                     self.bump();
                     Ok(ParseNtResult::Ident(ident, is_raw))
                 } else {
                     Err(self.dcx().create_err(UnexpectedNonterminal::Ident {
                         span: self.token.span,
-                        token: self.token.clone(),
+                        token: self.token,
                     }))
-                };
-            }
-            NonterminalKind::Path => {
-                return Ok(ParseNtResult::Path(P(
-                    self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?
-                )));
+                }
             }
+            NonterminalKind::Path => Ok(ParseNtResult::Path(P(
+                self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?
+            ))),
             NonterminalKind::Meta => {
-                return Ok(ParseNtResult::Meta(P(self.parse_attr_item(ForceCollect::Yes)?)));
+                Ok(ParseNtResult::Meta(P(self.parse_attr_item(ForceCollect::Yes)?)))
             }
             NonterminalKind::Vis => {
-                return Ok(ParseNtResult::Vis(P(self.collect_tokens_no_attrs(|this| {
-                    this.parse_visibility(FollowedByType::Yes)
-                })?)));
+                Ok(ParseNtResult::Vis(P(self
+                    .collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?)))
             }
             NonterminalKind::Lifetime => {
                 // We want to keep `'keyword` parsing, just like `keyword` is still
                 // an ident for nonterminal purposes.
-                return if let Some((ident, is_raw)) = self.token.lifetime() {
+                if let Some((ident, is_raw)) = self.token.lifetime() {
                     self.bump();
                     Ok(ParseNtResult::Lifetime(ident, is_raw))
                 } else {
                     Err(self.dcx().create_err(UnexpectedNonterminal::Lifetime {
                         span: self.token.span,
-                        token: self.token.clone(),
+                        token: self.token,
                     }))
-                };
+                }
             }
-        };
-
-        // If tokens are supported at all, they should be collected.
-        if matches!(nt.tokens_mut(), Some(None)) {
-            panic!(
-                "Missing tokens for nt {:?} at {:?}: {:?}",
-                nt,
-                nt.use_span(),
-                pprust::nonterminal_to_string(&nt)
-            );
         }
-
-        Ok(ParseNtResult::Nt(Arc::new(nt)))
     }
 }
 
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 9612f71b2af..d5f469f9aa9 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -363,7 +363,7 @@ impl<'a> Parser<'a> {
                 self.dcx().emit_err(TrailingVertNotAllowed {
                     span: self.token.span,
                     start: lo,
-                    token: self.token.clone(),
+                    token: self.token,
                     note_double_vert: matches!(self.token.kind, token::OrOr),
                 });
                 self.bump();
@@ -1519,8 +1519,8 @@ impl<'a> Parser<'a> {
                 etc = PatFieldsRest::Rest;
                 let mut etc_sp = self.token.span;
                 if first_etc_and_maybe_comma_span.is_none() {
-                    if let Some(comma_tok) = self
-                        .look_ahead(1, |t| if *t == token::Comma { Some(t.clone()) } else { None })
+                    if let Some(comma_tok) =
+                        self.look_ahead(1, |&t| if t == token::Comma { Some(t) } else { None })
                     {
                         let nw_span = self
                             .psess
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 9c6830c3672..02883655662 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -273,7 +273,6 @@ impl<'a> Parser<'a> {
                         self.dcx().emit_err(PathSingleColon {
                             span: self.prev_token.span,
                             suggestion: self.prev_token.span.shrink_to_hi(),
-                            type_ascription: self.psess.unstable_features.is_nightly_build(),
                         });
                     }
                     continue;
@@ -348,7 +347,6 @@ impl<'a> Parser<'a> {
                             err = self.dcx().create_err(PathSingleColon {
                                 span: self.token.span,
                                 suggestion: self.prev_token.span.shrink_to_hi(),
-                                type_ascription: self.psess.unstable_features.is_nightly_build(),
                             });
                         }
                         // Attempt to find places where a missing `>` might belong.
@@ -393,8 +391,8 @@ impl<'a> Parser<'a> {
                 } else {
                     // `(T, U) -> R`
 
-                    let prev_token_before_parsing = self.prev_token.clone();
-                    let token_before_parsing = self.token.clone();
+                    let prev_token_before_parsing = self.prev_token;
+                    let token_before_parsing = self.token;
                     let mut snapshot = None;
                     if self.may_recover()
                         && prev_token_before_parsing == token::PathSep
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 2cd09aa8959..0cc8b605018 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -23,8 +23,8 @@ use super::{
     AttrWrapper, BlockMode, FnParseMode, ForceCollect, Parser, Restrictions, SemiColonMode,
     Trailing, UsePreAttrPos,
 };
-use crate::errors::MalformedLoopLabel;
-use crate::{errors, exp, maybe_whole};
+use crate::errors::{self, MalformedLoopLabel};
+use crate::exp;
 
 impl<'a> Parser<'a> {
     /// Parses a statement. This stops just before trailing semicolons on everything but items.
@@ -75,10 +75,11 @@ impl<'a> Parser<'a> {
 
         let stmt = if self.token.is_keyword(kw::Super) && self.is_keyword_ahead(1, &[kw::Let]) {
             self.collect_tokens(None, attrs, force_collect, |this, attrs| {
+                let super_span = this.token.span;
                 this.expect_keyword(exp!(Super))?;
-                this.psess.gated_spans.gate(sym::super_let, this.prev_token.span);
                 this.expect_keyword(exp!(Let))?;
-                let local = this.parse_local(attrs)?; // FIXME(mara): implement super let
+                this.psess.gated_spans.gate(sym::super_let, super_span);
+                let local = this.parse_local(Some(super_span), attrs)?;
                 let trailing = Trailing::from(capture_semi && this.token == token::Semi);
                 Ok((
                     this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)),
@@ -89,7 +90,7 @@ impl<'a> Parser<'a> {
         } else if self.token.is_keyword(kw::Let) {
             self.collect_tokens(None, attrs, force_collect, |this, attrs| {
                 this.expect_keyword(exp!(Let))?;
-                let local = this.parse_local(attrs)?;
+                let local = this.parse_local(None, attrs)?;
                 let trailing = Trailing::from(capture_semi && this.token == token::Semi);
                 Ok((
                     this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)),
@@ -294,7 +295,7 @@ impl<'a> Parser<'a> {
         force_collect: ForceCollect,
     ) -> PResult<'a, Stmt> {
         let stmt = self.collect_tokens(None, attrs, force_collect, |this, attrs| {
-            let local = this.parse_local(attrs)?;
+            let local = this.parse_local(None, attrs)?;
             // FIXME - maybe capture semicolon in recovery?
             Ok((
                 this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)),
@@ -308,8 +309,8 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a local variable declaration.
-    fn parse_local(&mut self, attrs: AttrVec) -> PResult<'a, P<Local>> {
-        let lo = self.prev_token.span;
+    fn parse_local(&mut self, super_: Option<Span>, attrs: AttrVec) -> PResult<'a, P<Local>> {
+        let lo = super_.unwrap_or(self.prev_token.span);
 
         if self.token.is_keyword(kw::Const) && self.look_ahead(1, |t| t.is_ident()) {
             self.dcx().emit_err(errors::ConstLetMutuallyExclusive { span: lo.to(self.token.span) });
@@ -411,6 +412,7 @@ impl<'a> Parser<'a> {
         };
         let hi = if self.token == token::Semi { self.token.span } else { self.prev_token.span };
         Ok(P(ast::Local {
+            super_,
             ty,
             pat,
             kind,
@@ -516,7 +518,11 @@ impl<'a> Parser<'a> {
         let prev = self.prev_token.span;
         let sp = self.token.span;
         let mut e = self.dcx().struct_span_err(sp, msg);
-        let do_not_suggest_help = self.token.is_keyword(kw::In) || self.token == token::Colon;
+        self.label_expected_raw_ref(&mut e);
+
+        let do_not_suggest_help = self.token.is_keyword(kw::In)
+            || self.token == token::Colon
+            || self.prev_token.is_keyword(kw::Raw);
 
         // Check to see if the user has written something like
         //
@@ -694,9 +700,11 @@ impl<'a> Parser<'a> {
         blk_mode: BlockCheckMode,
         loop_header: Option<Span>,
     ) -> PResult<'a, (AttrVec, P<Block>)> {
-        maybe_whole!(self, NtBlock, |block| (AttrVec::new(), block));
+        if let Some(block) = self.eat_metavar_seq(MetaVarKind::Block, |this| this.parse_block()) {
+            return Ok((AttrVec::new(), block));
+        }
 
-        let maybe_ident = self.prev_token.clone();
+        let maybe_ident = self.prev_token;
         self.maybe_recover_unexpected_block_label(loop_header);
         if !self.eat(exp!(OpenBrace)) {
             return self.error_block_no_opening_brace();
@@ -763,10 +771,6 @@ impl<'a> Parser<'a> {
                                     Applicability::MaybeIncorrect,
                                 );
                             }
-                            if self.psess.unstable_features.is_nightly_build() {
-                                // FIXME(Nilstrieb): Remove this again after a few months.
-                                err.note("type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>");
-                            }
                         }
                     }
 
@@ -909,7 +913,7 @@ impl<'a> Parser<'a> {
                                 {
                                     if self.token == token::Colon
                                         && self.look_ahead(1, |token| {
-                                            token.is_whole_block()
+                                            token.is_metavar_block()
                                                 || matches!(
                                                     token.kind,
                                                     token::Ident(
diff --git a/compiler/rustc_parse/src/parser/tests.rs b/compiler/rustc_parse/src/parser/tests.rs
index 49ae6cb9b72..2f958f4d492 100644
--- a/compiler/rustc_parse/src/parser/tests.rs
+++ b/compiler/rustc_parse/src/parser/tests.rs
@@ -2554,7 +2554,7 @@ fn look(p: &Parser<'_>, dist: usize, kind: rustc_ast::token::TokenKind) {
     // Do the `assert_eq` outside the closure so that `track_caller` works.
     // (`#![feature(closure_track_caller)]` + `#[track_caller]` on the closure
     // doesn't give the line number in the test below if the assertion fails.)
-    let tok = p.look_ahead(dist, |tok| tok.clone());
+    let tok = p.look_ahead(dist, |tok| *tok);
     assert_eq!(kind, tok.kind);
 }
 
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 93705da22c4..42ebf26784d 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -7,7 +7,7 @@ use rustc_ast::{
     Pinnedness, PolyTraitRef, PreciseCapturingArg, TraitBoundModifiers, TraitObjectSyntax, Ty,
     TyKind, UnsafeBinderTy,
 };
-use rustc_errors::{Applicability, PResult};
+use rustc_errors::{Applicability, Diag, PResult};
 use rustc_span::{ErrorGuaranteed, Ident, Span, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
@@ -411,6 +411,9 @@ impl<'a> Parser<'a> {
                 TyKind::Path(None, path) if maybe_bounds => {
                     self.parse_remaining_bounds_path(ThinVec::new(), path, lo, true)
                 }
+                // For `('a) + …`, we know that `'a` in type position already lead to an error being
+                // emitted. To reduce output, let's indirectly suppress E0178 (bad `+` in type) and
+                // other irrelevant consequential errors.
                 TyKind::TraitObject(bounds, TraitObjectSyntax::None)
                     if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
                 {
@@ -425,12 +428,60 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
-        let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
-        let bounds = self.parse_generic_bounds_common(allow_plus)?;
-        if lt_no_plus {
-            self.dcx().emit_err(NeedPlusAfterTraitObjectLifetime { span: lo });
+        // A lifetime only begins a bare trait object type if it is followed by `+`!
+        if self.token.is_lifetime() && !self.look_ahead(1, |t| t.is_like_plus()) {
+            // In Rust 2021 and beyond, we assume that the user didn't intend to write a bare trait
+            // object type with a leading lifetime bound since that seems very unlikely given the
+            // fact that `dyn`-less trait objects are *semantically* invalid.
+            if self.psess.edition.at_least_rust_2021() {
+                let lt = self.expect_lifetime();
+                let mut err = self.dcx().struct_span_err(lo, "expected type, found lifetime");
+                err.span_label(lo, "expected type");
+                return Ok(match self.maybe_recover_ref_ty_no_leading_ampersand(lt, lo, err) {
+                    Ok(ref_ty) => ref_ty,
+                    Err(err) => TyKind::Err(err.emit()),
+                });
+            }
+
+            self.dcx().emit_err(NeedPlusAfterTraitObjectLifetime {
+                span: lo,
+                suggestion: lo.shrink_to_hi(),
+            });
+        }
+        Ok(TyKind::TraitObject(
+            self.parse_generic_bounds_common(allow_plus)?,
+            TraitObjectSyntax::None,
+        ))
+    }
+
+    fn maybe_recover_ref_ty_no_leading_ampersand<'cx>(
+        &mut self,
+        lt: Lifetime,
+        lo: Span,
+        mut err: Diag<'cx>,
+    ) -> Result<TyKind, Diag<'cx>> {
+        if !self.may_recover() {
+            return Err(err);
+        }
+        let snapshot = self.create_snapshot_for_diagnostic();
+        let mutbl = self.parse_mutability();
+        match self.parse_ty_no_plus() {
+            Ok(ty) => {
+                err.span_suggestion_verbose(
+                    lo.shrink_to_lo(),
+                    "you might have meant to write a reference type here",
+                    "&",
+                    Applicability::MaybeIncorrect,
+                );
+                err.emit();
+                Ok(TyKind::Ref(Some(lt), MutTy { ty, mutbl }))
+            }
+            Err(diag) => {
+                diag.cancel();
+                self.restore_snapshot(snapshot);
+                Err(err)
+            }
         }
-        Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
     }
 
     fn parse_remaining_bounds_path(
@@ -547,7 +598,7 @@ impl<'a> Parser<'a> {
 
             // Recovery
             mutbl = Mutability::Mut;
-            let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
+            let (dyn_tok, dyn_tok_sp) = (self.token, self.token_spacing);
             self.bump();
             self.bump_with((dyn_tok, dyn_tok_sp));
         }
@@ -886,7 +937,7 @@ impl<'a> Parser<'a> {
     /// ```
     fn parse_generic_bound(&mut self) -> PResult<'a, GenericBound> {
         let lo = self.token.span;
-        let leading_token = self.prev_token.clone();
+        let leading_token = self.prev_token;
         let has_parens = self.eat(exp!(OpenParen));
 
         let bound = if self.token.is_lifetime() {
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 6bbd650dcdf..b518fca7a65 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -157,7 +157,7 @@ fn is_attr_template_compatible(template: &AttributeTemplate, meta: &ast::MetaIte
 pub fn check_attribute_safety(psess: &ParseSess, safety: AttributeSafety, attr: &Attribute) {
     let attr_item = attr.get_normal_item();
 
-    if safety == AttributeSafety::Unsafe {
+    if let AttributeSafety::Unsafe { unsafe_since } = safety {
         if let ast::Safety::Default = attr_item.unsafety {
             let path_span = attr_item.path.span;
 
@@ -167,7 +167,13 @@ pub fn check_attribute_safety(psess: &ParseSess, safety: AttributeSafety, attr:
             // square bracket respectively.
             let diag_span = attr_item.span();
 
-            if attr.span.at_least_rust_2024() {
+            // Attributes can be safe in earlier editions, and become unsafe in later ones.
+            let emit_error = match unsafe_since {
+                None => true,
+                Some(unsafe_since) => attr.span.edition() >= unsafe_since,
+            };
+
+            if emit_error {
                 psess.dcx().emit_err(errors::UnsafeAttrOutsideUnsafe {
                     span: path_span,
                     suggestion: errors::UnsafeAttrOutsideUnsafeSuggestion {
@@ -188,6 +194,12 @@ pub fn check_attribute_safety(psess: &ParseSess, safety: AttributeSafety, attr:
             }
         }
     } else if let Safety::Unsafe(unsafe_span) = attr_item.unsafety {
+        // Allow (but don't require) `#[unsafe(naked)]` so that compiler-builtins can upgrade to it.
+        // FIXME(#139797): remove this special case when compiler-builtins has upgraded.
+        if attr.has_name(sym::naked) {
+            return;
+        }
+
         psess.dcx().emit_err(errors::InvalidAttrUnsafe {
             span: unsafe_span,
             name: attr_item.path.clone(),
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index bea86801ed7..99789b74488 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -404,7 +404,7 @@ passes_invalid_attr_at_crate_level =
 passes_invalid_attr_at_crate_level_item =
     the inner attribute doesn't annotate this {$kind}
 
-passes_invalid_macro_export_arguments = `{$name}` isn't a valid `#[macro_export]` argument
+passes_invalid_macro_export_arguments = invalid `#[macro_export]` argument
 
 passes_invalid_macro_export_arguments_too_many_items = `#[macro_export]` can only take 1 or 0 arguments
 
@@ -742,9 +742,6 @@ passes_trait_impl_const_stable =
 passes_transparent_incompatible =
     transparent {$target} cannot have other repr hints
 
-passes_undefined_naked_function_abi =
-    Rust ABI is unsupported in naked functions
-
 passes_unknown_external_lang_item =
     unknown external lang item: `{$lang_item}`
 
@@ -774,8 +771,8 @@ passes_unreachable_due_to_uninhabited = unreachable {$descr}
     .label_orig = any code following this expression is unreachable
     .note = this expression has type `{$ty}`, which is uninhabited
 
-passes_unrecognized_field =
-    unrecognized field name `{$name}`
+passes_unrecognized_argument =
+    unrecognized argument
 
 passes_unstable_attr_for_already_stable_feature =
     can't mark as unstable using an already stable feature
diff --git a/compiler/rustc_passes/src/abi_test.rs b/compiler/rustc_passes/src/abi_test.rs
index 671b7d7ad76..b139ed6a66c 100644
--- a/compiler/rustc_passes/src/abi_test.rs
+++ b/compiler/rustc_passes/src/abi_test.rs
@@ -9,7 +9,7 @@ use rustc_span::sym;
 use rustc_target::callconv::FnAbi;
 
 use super::layout_test::ensure_wf;
-use crate::errors::{AbiInvalidAttribute, AbiNe, AbiOf, UnrecognizedField};
+use crate::errors::{AbiInvalidAttribute, AbiNe, AbiOf, UnrecognizedArgument};
 
 pub fn test_abi(tcx: TyCtxt<'_>) {
     if !tcx.features().rustc_attrs() {
@@ -77,8 +77,8 @@ fn dump_abi_of_fn_item(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
     // The `..` are the names of fields to dump.
     let meta_items = attr.meta_item_list().unwrap_or_default();
     for meta_item in meta_items {
-        match meta_item.name_or_empty() {
-            sym::debug => {
+        match meta_item.name() {
+            Some(sym::debug) => {
                 let fn_name = tcx.item_name(item_def_id.into());
                 tcx.dcx().emit_err(AbiOf {
                     span: tcx.def_span(item_def_id),
@@ -88,8 +88,8 @@ fn dump_abi_of_fn_item(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
                 });
             }
 
-            name => {
-                tcx.dcx().emit_err(UnrecognizedField { span: meta_item.span(), name });
+            _ => {
+                tcx.dcx().emit_err(UnrecognizedArgument { span: meta_item.span() });
             }
         }
     }
@@ -118,8 +118,8 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
     }
     let meta_items = attr.meta_item_list().unwrap_or_default();
     for meta_item in meta_items {
-        match meta_item.name_or_empty() {
-            sym::debug => {
+        match meta_item.name() {
+            Some(sym::debug) => {
                 let ty::FnPtr(sig_tys, hdr) = ty.kind() else {
                     span_bug!(
                         meta_item.span(),
@@ -138,7 +138,7 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
                 let fn_name = tcx.item_name(item_def_id.into());
                 tcx.dcx().emit_err(AbiOf { span, fn_name, fn_abi: format!("{:#?}", abi) });
             }
-            sym::assert_eq => {
+            Some(sym::assert_eq) => {
                 let ty::Tuple(fields) = ty.kind() else {
                     span_bug!(
                         meta_item.span(),
@@ -188,8 +188,8 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
                     });
                 }
             }
-            name => {
-                tcx.dcx().emit_err(UnrecognizedField { span: meta_item.span(), name });
+            _ => {
+                tcx.dcx().emit_err(UnrecognizedArgument { span: meta_item.span() });
             }
         }
     }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 669349f3380..cbe5058b551 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -523,9 +523,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     fn check_no_sanitize(&self, attr: &Attribute, span: Span, target: Target) {
         if let Some(list) = attr.meta_item_list() {
             for item in list.iter() {
-                let sym = item.name_or_empty();
+                let sym = item.name();
                 match sym {
-                    sym::address | sym::hwaddress => {
+                    Some(s @ sym::address | s @ sym::hwaddress) => {
                         let is_valid =
                             matches!(target, Target::Fn | Target::Method(..) | Target::Static);
                         if !is_valid {
@@ -533,7 +533,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                                 attr_span: item.span(),
                                 defn_span: span,
                                 accepted_kind: "a function or static",
-                                attr_str: sym.as_str(),
+                                attr_str: s.as_str(),
                             });
                         }
                     }
@@ -544,7 +544,10 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                                 attr_span: item.span(),
                                 defn_span: span,
                                 accepted_kind: "a function",
-                                attr_str: sym.as_str(),
+                                attr_str: &match sym {
+                                    Some(name) => name.to_string(),
+                                    None => "...".to_string(),
+                                },
                             });
                         }
                     }
@@ -561,12 +564,15 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         allowed_target: Target,
     ) {
         if target != allowed_target {
+            let path = attr.path();
+            let path: Vec<_> = path.iter().map(|s| s.as_str()).collect();
+            let attr_name = path.join("::");
             self.tcx.emit_node_span_lint(
                 UNUSED_ATTRIBUTES,
                 hir_id,
                 attr.span(),
                 errors::OnlyHasEffectOn {
-                    attr_name: attr.name_or_empty(),
+                    attr_name,
                     target_name: allowed_target.name().replace(' ', "_"),
                 },
             );
@@ -589,7 +595,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         // * `#[track_caller]`
         // * `#[test]`, `#[ignore]`, `#[should_panic]`
         //
-        // NOTE: when making changes to this list, check that `error_codes/E0736.md` remains accurate
+        // NOTE: when making changes to this list, check that `error_codes/E0736.md` remains
+        // accurate.
         const ALLOW_LIST: &[rustc_span::Symbol] = &[
             // conditional compilation
             sym::cfg_trace,
@@ -624,6 +631,21 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         match target {
             Target::Fn
             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {
+                let fn_sig = self.tcx.hir_node(hir_id).fn_sig().unwrap();
+                let abi = fn_sig.header.abi;
+                if abi.is_rustic_abi() && !self.tcx.features().naked_functions_rustic_abi() {
+                    feature_err(
+                        &self.tcx.sess,
+                        sym::naked_functions_rustic_abi,
+                        fn_sig.span,
+                        format!(
+                            "`#[naked]` is currently unstable on `extern \"{}\"` functions",
+                            abi.as_str()
+                        ),
+                    )
+                    .emit();
+                }
+
                 for other_attr in attrs {
                     // this covers "sugared doc comments" of the form `/// ...`
                     // it does not cover `#[doc = "..."]`, which is handled below
@@ -657,11 +679,11 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         }
                     }
 
-                    if !ALLOW_LIST.iter().any(|name| other_attr.has_name(*name)) {
+                    if !other_attr.has_any_name(ALLOW_LIST) {
                         self.dcx().emit_err(errors::NakedFunctionIncompatibleAttribute {
                             span: other_attr.span(),
                             naked_span: attr.span(),
-                            attr: other_attr.name_or_empty(),
+                            attr: other_attr.name().unwrap(),
                         });
 
                         return;
@@ -1109,6 +1131,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             ItemKind::Trait(_, _, _, generics, _, items)
                 if generics.params.len() != 0
                     || items.iter().any(|item| matches!(item.kind, AssocItemKind::Type)) => {}
+            ItemKind::TyAlias(_, _, generics) if generics.params.len() != 0 => {}
             _ => {
                 self.dcx().emit_err(errors::DocSearchUnboxInvalid { span: meta.span() });
             }
@@ -1134,7 +1157,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     ) {
         match target {
             Target::Use | Target::ExternCrate => {
-                let do_inline = meta.name_or_empty() == sym::inline;
+                let do_inline = meta.has_name(sym::inline);
                 if let Some((prev_inline, prev_span)) = *specified_inline {
                     if do_inline != prev_inline {
                         let mut spans = MultiSpan::from_spans(vec![prev_span, meta.span()]);
@@ -1244,8 +1267,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     fn check_test_attr(&self, meta: &MetaItemInner, hir_id: HirId) {
         if let Some(metas) = meta.meta_item_list() {
             for i_meta in metas {
-                match (i_meta.name_or_empty(), i_meta.meta_item()) {
-                    (sym::attr | sym::no_crate_inject, _) => {}
+                match (i_meta.name(), i_meta.meta_item()) {
+                    (Some(sym::attr | sym::no_crate_inject), _) => {}
                     (_, Some(m)) => {
                         self.tcx.emit_node_span_lint(
                             INVALID_DOC_ATTRIBUTES,
@@ -1306,61 +1329,63 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         if let Some(list) = attr.meta_item_list() {
             for meta in &list {
                 if let Some(i_meta) = meta.meta_item() {
-                    match i_meta.name_or_empty() {
-                        sym::alias => {
+                    match i_meta.name() {
+                        Some(sym::alias) => {
                             if self.check_attr_not_crate_level(meta, hir_id, "alias") {
                                 self.check_doc_alias(meta, hir_id, target, aliases);
                             }
                         }
 
-                        sym::keyword => {
+                        Some(sym::keyword) => {
                             if self.check_attr_not_crate_level(meta, hir_id, "keyword") {
                                 self.check_doc_keyword(meta, hir_id);
                             }
                         }
 
-                        sym::fake_variadic => {
+                        Some(sym::fake_variadic) => {
                             if self.check_attr_not_crate_level(meta, hir_id, "fake_variadic") {
                                 self.check_doc_fake_variadic(meta, hir_id);
                             }
                         }
 
-                        sym::search_unbox => {
+                        Some(sym::search_unbox) => {
                             if self.check_attr_not_crate_level(meta, hir_id, "fake_variadic") {
                                 self.check_doc_search_unbox(meta, hir_id);
                             }
                         }
 
-                        sym::test => {
+                        Some(sym::test) => {
                             if self.check_attr_crate_level(attr, meta, hir_id) {
                                 self.check_test_attr(meta, hir_id);
                             }
                         }
 
-                        sym::html_favicon_url
-                        | sym::html_logo_url
-                        | sym::html_playground_url
-                        | sym::issue_tracker_base_url
-                        | sym::html_root_url
-                        | sym::html_no_source => {
+                        Some(
+                            sym::html_favicon_url
+                            | sym::html_logo_url
+                            | sym::html_playground_url
+                            | sym::issue_tracker_base_url
+                            | sym::html_root_url
+                            | sym::html_no_source,
+                        ) => {
                             self.check_attr_crate_level(attr, meta, hir_id);
                         }
 
-                        sym::cfg_hide => {
+                        Some(sym::cfg_hide) => {
                             if self.check_attr_crate_level(attr, meta, hir_id) {
                                 self.check_doc_cfg_hide(meta, hir_id);
                             }
                         }
 
-                        sym::inline | sym::no_inline => {
+                        Some(sym::inline | sym::no_inline) => {
                             self.check_doc_inline(attr, meta, hir_id, target, specified_inline)
                         }
 
-                        sym::masked => self.check_doc_masked(attr, meta, hir_id, target),
+                        Some(sym::masked) => self.check_doc_masked(attr, meta, hir_id, target),
 
-                        sym::cfg | sym::hidden | sym::notable_trait => {}
+                        Some(sym::cfg | sym::hidden | sym::notable_trait) => {}
 
-                        sym::rust_logo => {
+                        Some(sym::rust_logo) => {
                             if self.check_attr_crate_level(attr, meta, hir_id)
                                 && !self.tcx.features().rustdoc_internals()
                             {
@@ -1598,7 +1623,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         if target == Target::ForeignMod
             && let hir::Node::Item(item) = self.tcx.hir_node(hir_id)
             && let Item { kind: ItemKind::ForeignMod { abi, .. }, .. } = item
-            && !matches!(abi, ExternAbi::Rust | ExternAbi::RustIntrinsic)
+            && !matches!(abi, ExternAbi::Rust)
         {
             return;
         }
@@ -2283,7 +2308,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     fn check_macro_use(&self, hir_id: HirId, attr: &Attribute, target: Target) {
-        let name = attr.name_or_empty();
+        let name = attr.name().unwrap();
         match target {
             Target::ExternCrate | Target::Mod => {}
             _ => {
@@ -2315,12 +2340,12 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     attr.span(),
                     errors::MacroExport::TooManyItems,
                 );
-            } else if meta_item_list[0].name_or_empty() != sym::local_inner_macros {
+            } else if !meta_item_list[0].has_name(sym::local_inner_macros) {
                 self.tcx.emit_node_span_lint(
                     INVALID_MACRO_EXPORT_ARGUMENTS,
                     hir_id,
                     meta_item_list[0].span(),
-                    errors::MacroExport::UnknownItem { name: meta_item_list[0].name_or_empty() },
+                    errors::MacroExport::InvalidArgument,
                 );
             }
         } else {
@@ -2365,33 +2390,28 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
 
         // Warn on useless empty attributes.
-        let note = if (matches!(
-            attr.name_or_empty(),
-            sym::macro_use
-                | sym::allow
-                | sym::expect
-                | sym::warn
-                | sym::deny
-                | sym::forbid
-                | sym::feature
-                | sym::target_feature
-        ) && attr.meta_item_list().is_some_and(|list| list.is_empty()))
+        let note = if attr.has_any_name(&[
+            sym::macro_use,
+            sym::allow,
+            sym::expect,
+            sym::warn,
+            sym::deny,
+            sym::forbid,
+            sym::feature,
+            sym::target_feature,
+        ]) && attr.meta_item_list().is_some_and(|list| list.is_empty())
         {
-            errors::UnusedNote::EmptyList { name: attr.name_or_empty() }
-        } else if matches!(
-            attr.name_or_empty(),
-            sym::allow | sym::warn | sym::deny | sym::forbid | sym::expect
-        ) && let Some(meta) = attr.meta_item_list()
+            errors::UnusedNote::EmptyList { name: attr.name().unwrap() }
+        } else if attr.has_any_name(&[sym::allow, sym::warn, sym::deny, sym::forbid, sym::expect])
+            && let Some(meta) = attr.meta_item_list()
             && let [meta] = meta.as_slice()
             && let Some(item) = meta.meta_item()
             && let MetaItemKind::NameValue(_) = &item.kind
             && item.path == sym::reason
         {
-            errors::UnusedNote::NoLints { name: attr.name_or_empty() }
-        } else if matches!(
-            attr.name_or_empty(),
-            sym::allow | sym::warn | sym::deny | sym::forbid | sym::expect
-        ) && let Some(meta) = attr.meta_item_list()
+            errors::UnusedNote::NoLints { name: attr.name().unwrap() }
+        } else if attr.has_any_name(&[sym::allow, sym::warn, sym::deny, sym::forbid, sym::expect])
+            && let Some(meta) = attr.meta_item_list()
             && meta.iter().any(|meta| {
                 meta.meta_item().map_or(false, |item| item.path == sym::linker_messages)
             })
@@ -2424,7 +2444,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     return;
                 }
             }
-        } else if attr.name_or_empty() == sym::default_method_body_is_const {
+        } else if attr.has_name(sym::default_method_body_is_const) {
             errors::UnusedNote::DefaultMethodBodyConst
         } else {
             return;
@@ -2881,10 +2901,11 @@ fn check_duplicates(
     if matches!(duplicates, WarnFollowingWordOnly) && !attr.is_word() {
         return;
     }
+    let attr_name = attr.name().unwrap();
     match duplicates {
         DuplicatesOk => {}
         WarnFollowing | FutureWarnFollowing | WarnFollowingWordOnly | FutureWarnPreceding => {
-            match seen.entry(attr.name_or_empty()) {
+            match seen.entry(attr_name) {
                 Entry::Occupied(mut entry) => {
                     let (this, other) = if matches!(duplicates, FutureWarnPreceding) {
                         let to_remove = entry.insert(attr.span());
@@ -2911,7 +2932,7 @@ fn check_duplicates(
                 }
             }
         }
-        ErrorFollowing | ErrorPreceding => match seen.entry(attr.name_or_empty()) {
+        ErrorFollowing | ErrorPreceding => match seen.entry(attr_name) {
             Entry::Occupied(mut entry) => {
                 let (this, other) = if matches!(duplicates, ErrorPreceding) {
                     let to_remove = entry.insert(attr.span());
@@ -2919,11 +2940,7 @@ fn check_duplicates(
                 } else {
                     (attr.span(), *entry.get())
                 };
-                tcx.dcx().emit_err(errors::UnusedMultiple {
-                    this,
-                    other,
-                    name: attr.name_or_empty(),
-                });
+                tcx.dcx().emit_err(errors::UnusedMultiple { this, other, name: attr_name });
             }
             Entry::Vacant(entry) => {
                 entry.insert(attr.span());
diff --git a/compiler/rustc_passes/src/debugger_visualizer.rs b/compiler/rustc_passes/src/debugger_visualizer.rs
index 062d56a79a0..7a7a8175e55 100644
--- a/compiler/rustc_passes/src/debugger_visualizer.rs
+++ b/compiler/rustc_passes/src/debugger_visualizer.rs
@@ -28,17 +28,17 @@ impl DebuggerVisualizerCollector<'_> {
                 return;
             };
 
-            let (visualizer_type, visualizer_path) =
-                match (meta_item.name_or_empty(), meta_item.value_str()) {
-                    (sym::natvis_file, Some(value)) => (DebuggerVisualizerType::Natvis, value),
-                    (sym::gdb_script_file, Some(value)) => {
-                        (DebuggerVisualizerType::GdbPrettyPrinter, value)
-                    }
-                    (_, _) => {
-                        self.sess.dcx().emit_err(DebugVisualizerInvalid { span: meta_item.span });
-                        return;
-                    }
-                };
+            let (visualizer_type, visualizer_path) = match (meta_item.name(), meta_item.value_str())
+            {
+                (Some(sym::natvis_file), Some(value)) => (DebuggerVisualizerType::Natvis, value),
+                (Some(sym::gdb_script_file), Some(value)) => {
+                    (DebuggerVisualizerType::GdbPrettyPrinter, value)
+                }
+                (_, _) => {
+                    self.sess.dcx().emit_err(DebugVisualizerInvalid { span: meta_item.span });
+                    return;
+                }
+            };
 
             let file = match resolve_path(&self.sess, visualizer_path.as_str(), attr.span) {
                 Ok(file) => file,
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index 4e3e0324205..4052264b051 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -5,7 +5,7 @@ use rustc_ast::Label;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagCtxtHandle, DiagSymbolList, Diagnostic, EmissionGuarantee, Level,
-    MultiSpan, SubdiagMessageOp, Subdiagnostic,
+    MultiSpan, Subdiagnostic,
 };
 use rustc_hir::{self as hir, ExprKind, Target};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -756,7 +756,7 @@ pub(crate) enum MacroExport {
     OnDeclMacro,
 
     #[diag(passes_invalid_macro_export_arguments)]
-    UnknownItem { name: Symbol },
+    InvalidArgument,
 
     #[diag(passes_invalid_macro_export_arguments_too_many_items)]
     TooManyItems,
@@ -1045,11 +1045,10 @@ pub(crate) struct AbiInvalidAttribute {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unrecognized_field)]
-pub(crate) struct UnrecognizedField {
+#[diag(passes_unrecognized_argument)]
+pub(crate) struct UnrecognizedArgument {
     #[primary_span]
     pub span: Span,
-    pub name: Symbol,
 }
 
 #[derive(Diagnostic)]
@@ -1197,10 +1196,6 @@ pub(crate) struct UnlabeledCfInWhileCondition<'a> {
     pub cf_type: &'a str,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_undefined_naked_function_abi)]
-pub(crate) struct UndefinedNakedFunctionAbi;
-
 #[derive(Diagnostic)]
 #[diag(passes_no_patterns)]
 pub(crate) struct NoPatterns {
@@ -1437,7 +1432,7 @@ pub(crate) struct UselessAssignment<'a> {
 #[derive(LintDiagnostic)]
 #[diag(passes_only_has_effect_on)]
 pub(crate) struct OnlyHasEffectOn {
-    pub attr_name: Symbol,
+    pub attr_name: String,
     pub target_name: String,
 }
 
@@ -1856,11 +1851,7 @@ pub(crate) struct UnusedVariableStringInterp {
 }
 
 impl Subdiagnostic for UnusedVariableStringInterp {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.span_label(self.lit, crate::fluent_generated::passes_maybe_string_interpolation);
         diag.multipart_suggestion(
             crate::fluent_generated::passes_string_interpolation_only_works,
diff --git a/compiler/rustc_passes/src/input_stats.rs b/compiler/rustc_passes/src/input_stats.rs
index 1278e98afcf..71815448172 100644
--- a/compiler/rustc_passes/src/input_stats.rs
+++ b/compiler/rustc_passes/src/input_stats.rs
@@ -295,6 +295,7 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
         record_variants!(
             (self, p, p.kind, Some(p.hir_id), hir, Pat, PatKind),
             [
+                Missing,
                 Wild,
                 Binding,
                 Struct,
@@ -597,6 +598,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
         record_variants!(
             (self, p, p.kind, None, ast, Pat, PatKind),
             [
+                Missing,
                 Wild,
                 Ident,
                 Struct,
diff --git a/compiler/rustc_passes/src/layout_test.rs b/compiler/rustc_passes/src/layout_test.rs
index d4512c9417e..a19faf0fa83 100644
--- a/compiler/rustc_passes/src/layout_test.rs
+++ b/compiler/rustc_passes/src/layout_test.rs
@@ -13,7 +13,7 @@ use rustc_trait_selection::traits;
 
 use crate::errors::{
     LayoutAbi, LayoutAlign, LayoutHomogeneousAggregate, LayoutInvalidAttribute, LayoutOf,
-    LayoutSize, UnrecognizedField,
+    LayoutSize, UnrecognizedArgument,
 };
 
 pub fn test_layout(tcx: TyCtxt<'_>) {
@@ -79,28 +79,28 @@ fn dump_layout_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribute) {
             // The `..` are the names of fields to dump.
             let meta_items = attr.meta_item_list().unwrap_or_default();
             for meta_item in meta_items {
-                match meta_item.name_or_empty() {
+                match meta_item.name() {
                     // FIXME: this never was about ABI and now this dump arg is confusing
-                    sym::abi => {
+                    Some(sym::abi) => {
                         tcx.dcx().emit_err(LayoutAbi {
                             span,
                             abi: format!("{:?}", ty_layout.backend_repr),
                         });
                     }
 
-                    sym::align => {
+                    Some(sym::align) => {
                         tcx.dcx().emit_err(LayoutAlign {
                             span,
                             align: format!("{:?}", ty_layout.align),
                         });
                     }
 
-                    sym::size => {
+                    Some(sym::size) => {
                         tcx.dcx()
                             .emit_err(LayoutSize { span, size: format!("{:?}", ty_layout.size) });
                     }
 
-                    sym::homogeneous_aggregate => {
+                    Some(sym::homogeneous_aggregate) => {
                         tcx.dcx().emit_err(LayoutHomogeneousAggregate {
                             span,
                             homogeneous_aggregate: format!(
@@ -111,15 +111,15 @@ fn dump_layout_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribute) {
                         });
                     }
 
-                    sym::debug => {
+                    Some(sym::debug) => {
                         let normalized_ty = tcx.normalize_erasing_regions(typing_env, ty);
                         // FIXME: using the `Debug` impl here isn't ideal.
                         let ty_layout = format!("{:#?}", *ty_layout);
                         tcx.dcx().emit_err(LayoutOf { span, normalized_ty, ty_layout });
                     }
 
-                    name => {
-                        tcx.dcx().emit_err(UnrecognizedField { span: meta_item.span(), name });
+                    _ => {
+                        tcx.dcx().emit_err(UnrecognizedArgument { span: meta_item.span() });
                     }
                 }
             }
diff --git a/compiler/rustc_passes/src/lib.rs b/compiler/rustc_passes/src/lib.rs
index 6f6115af96c..93ff0f66d69 100644
--- a/compiler/rustc_passes/src/lib.rs
+++ b/compiler/rustc_passes/src/lib.rs
@@ -6,7 +6,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(let_chains)]
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs
index ed70d9ee91f..4e9b7fd44d4 100644
--- a/compiler/rustc_passes/src/liveness.rs
+++ b/compiler/rustc_passes/src/liveness.rs
@@ -96,7 +96,7 @@ use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self, RootVariableMinCaptureList, Ty, TyCtxt};
 use rustc_session::lint;
-use rustc_span::{BytePos, Span, Symbol, kw, sym};
+use rustc_span::{BytePos, Span, Symbol, sym};
 use tracing::{debug, instrument};
 
 use self::LiveNodeKind::*;
@@ -578,8 +578,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
     where
         F: FnMut(Variable) -> bool,
     {
-        for var_idx in 0..self.ir.var_kinds.len() {
-            let var = Variable::from(var_idx);
+        for var in self.ir.var_kinds.indices() {
             if test(var) {
                 write!(wr, " {var:?}")?;
             }
@@ -609,8 +608,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         debug!(
             "^^ liveness computation results for body {} (entry={:?})",
             {
-                for ln_idx in 0..self.ir.lnks.len() {
-                    debug!("{:?}", self.ln_str(LiveNode::from(ln_idx)));
+                for ln_idx in self.ir.lnks.indices() {
+                    debug!("{:?}", self.ln_str(ln_idx));
                 }
                 hir_id
             },
@@ -1021,7 +1020,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             }
 
             hir::ExprKind::Call(ref f, args) => {
-                let succ = self.check_is_ty_uninhabited(expr, succ);
+                let is_ctor = |f: &Expr<'_>| matches!(f.kind, hir::ExprKind::Path(hir::QPath::Resolved(_, path)) if matches!(path.res, rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Ctor(_, _), _)));
+                let succ =
+                    if !is_ctor(f) { self.check_is_ty_uninhabited(expr, succ) } else { succ };
+
                 let succ = self.propagate_through_exprs(args, succ);
                 self.propagate_through_expr(f, succ)
             }
@@ -1481,9 +1483,6 @@ impl<'tcx> Liveness<'_, 'tcx> {
 
     fn should_warn(&self, var: Variable) -> Option<String> {
         let name = self.ir.variable_name(var);
-        if name == kw::Empty {
-            return None;
-        }
         let name = name.as_str();
         if name.as_bytes()[0] == b'_' {
             return None;
@@ -1655,7 +1654,7 @@ impl<'tcx> Liveness<'_, 'tcx> {
                 // `&'name Ty` -> `&'name mut Ty` or `&Ty` -> `&mut Ty`
                 Some(mut_ty.ty.span.shrink_to_lo())
             };
-            let pre = if lt.ident.span.lo() == lt.ident.span.hi() { "" } else { " " };
+            let pre = if lt.ident.span.is_empty() { "" } else { " " };
             Some(errors::UnusedAssignSuggestion {
                 ty_span,
                 pre,
diff --git a/compiler/rustc_passes/src/naked_functions.rs b/compiler/rustc_passes/src/naked_functions.rs
index d35aedf9a56..3c9f8b72c36 100644
--- a/compiler/rustc_passes/src/naked_functions.rs
+++ b/compiler/rustc_passes/src/naked_functions.rs
@@ -1,6 +1,5 @@
 //! Checks validity of naked functions.
 
-use rustc_abi::ExternAbi;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{LocalDefId, LocalModDefId};
@@ -10,12 +9,11 @@ use rustc_middle::hir::nested_filter::OnlyBodies;
 use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::lint::builtin::UNDEFINED_NAKED_FUNCTION_ABI;
 use rustc_span::{Span, sym};
 
 use crate::errors::{
     NakedAsmOutsideNakedFn, NakedFunctionsAsmBlock, NakedFunctionsMustNakedAsm, NoPatterns,
-    ParamsNotAllowed, UndefinedNakedFunctionAbi,
+    ParamsNotAllowed,
 };
 
 pub(crate) fn provide(providers: &mut Providers) {
@@ -29,26 +27,21 @@ fn check_mod_naked_functions(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) {
             continue;
         }
 
-        let (fn_header, body_id) = match tcx.hir_node_by_def_id(def_id) {
+        let body = match tcx.hir_node_by_def_id(def_id) {
             hir::Node::Item(hir::Item {
-                kind: hir::ItemKind::Fn { sig, body: body_id, .. },
-                ..
+                kind: hir::ItemKind::Fn { body: body_id, .. }, ..
             })
             | hir::Node::TraitItem(hir::TraitItem {
-                kind: hir::TraitItemKind::Fn(sig, hir::TraitFn::Provided(body_id)),
+                kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)),
                 ..
             })
             | hir::Node::ImplItem(hir::ImplItem {
-                kind: hir::ImplItemKind::Fn(sig, body_id),
-                ..
-            }) => (sig.header, *body_id),
+                kind: hir::ImplItemKind::Fn(_, body_id), ..
+            }) => tcx.hir_body(*body_id),
             _ => continue,
         };
 
-        let body = tcx.hir_body(body_id);
-
         if tcx.has_attr(def_id, sym::naked) {
-            check_abi(tcx, def_id, fn_header.abi);
             check_no_patterns(tcx, body.params);
             check_no_parameters_use(tcx, body);
             check_asm(tcx, def_id, body);
@@ -60,20 +53,6 @@ fn check_mod_naked_functions(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) {
     }
 }
 
-/// Checks that function uses non-Rust ABI.
-fn check_abi(tcx: TyCtxt<'_>, def_id: LocalDefId, abi: ExternAbi) {
-    if abi == ExternAbi::Rust {
-        let hir_id = tcx.local_def_id_to_hir_id(def_id);
-        let span = tcx.def_span(def_id);
-        tcx.emit_node_span_lint(
-            UNDEFINED_NAKED_FUNCTION_ABI,
-            hir_id,
-            span,
-            UndefinedNakedFunctionAbi,
-        );
-    }
-}
-
 /// Checks that parameters don't use patterns. Mirrors the checks for function declarations.
 fn check_no_patterns(tcx: TyCtxt<'_>, params: &[hir::Param<'_>]) {
     for param in params {
diff --git a/compiler/rustc_pattern_analysis/src/errors.rs b/compiler/rustc_pattern_analysis/src/errors.rs
index 1f7852e5190..e60930d6cd2 100644
--- a/compiler/rustc_pattern_analysis/src/errors.rs
+++ b/compiler/rustc_pattern_analysis/src/errors.rs
@@ -1,4 +1,4 @@
-use rustc_errors::{Diag, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic};
+use rustc_errors::{Diag, EmissionGuarantee, Subdiagnostic};
 use rustc_macros::{LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::Ty;
 use rustc_span::Span;
@@ -55,11 +55,7 @@ pub struct Overlap {
 }
 
 impl Subdiagnostic for Overlap {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let Overlap { span, range } = self;
 
         // FIXME(mejrs) unfortunately `#[derive(LintDiagnostic)]`
@@ -103,11 +99,7 @@ pub struct GappedRange {
 }
 
 impl Subdiagnostic for GappedRange {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let GappedRange { span, gap, first_range } = self;
 
         // FIXME(mejrs) unfortunately `#[derive(LintDiagnostic)]`
diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index 31c4ee0fa0b..7c12f69f14c 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -1,5 +1,6 @@
 use std::fmt;
 use std::iter::once;
+use std::ops::ControlFlow;
 
 use rustc_abi::{FIRST_VARIANT, FieldIdx, Integer, VariantIdx};
 use rustc_arena::DroplessArena;
@@ -11,7 +12,8 @@ use rustc_middle::mir::{self, Const};
 use rustc_middle::thir::{self, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{
-    self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeVisitableExt, VariantDef,
+    self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
+    TypeVisitableExt, TypeVisitor, VariantDef,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
@@ -135,11 +137,22 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
     /// Returns the hidden type corresponding to this key if the body under analysis is allowed to
     /// know it.
     fn reveal_opaque_key(&self, key: OpaqueTypeKey<'tcx>) -> Option<Ty<'tcx>> {
-        self.typeck_results
-            .concrete_opaque_types
-            .get(&key.def_id)
-            .map(|x| ty::EarlyBinder::bind(x.ty).instantiate(self.tcx, key.args))
+        if let Some(hidden_ty) = self.typeck_results.concrete_opaque_types.get(&key.def_id) {
+            let ty = ty::EarlyBinder::bind(hidden_ty.ty).instantiate(self.tcx, key.args);
+            if ty.visit_with(&mut RecursiveOpaque { def_id: key.def_id.into() }).is_continue() {
+                Some(ty)
+            } else {
+                // HACK: We skip revealing opaque types which recursively expand
+                // to themselves. This is because we may infer hidden types like
+                // `Opaque<T> = Opaque<Opaque<T>>` or `Opaque<T> = Opaque<(T,)>`
+                // in hir typeck.
+                None
+            }
+        } else {
+            None
+        }
     }
+
     // This can take a non-revealed `Ty` because it reveals opaques itself.
     pub fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool {
         !ty.inhabited_predicate(self.tcx).apply_revealing_opaque(
@@ -460,7 +473,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             PatKind::AscribeUserType { subpattern, .. }
             | PatKind::ExpandedConstant { subpattern, .. } => return self.lower_pat(subpattern),
             PatKind::Binding { subpattern: Some(subpat), .. } => return self.lower_pat(subpat),
-            PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
+            PatKind::Missing | PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
                 ctor = Wildcard;
                 fields = vec![];
                 arity = 0;
@@ -1105,3 +1118,20 @@ pub fn analyze_match<'p, 'tcx>(
 
     Ok(report)
 }
+
+struct RecursiveOpaque {
+    def_id: DefId,
+}
+impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for RecursiveOpaque {
+    type Result = ControlFlow<()>;
+
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
+        if let ty::Alias(ty::Opaque, alias_ty) = t.kind() {
+            if alias_ty.def_id == self.def_id {
+                return ControlFlow::Break(());
+            }
+        }
+
+        if t.has_opaque_types() { t.super_visit_with(self) } else { ControlFlow::Continue(()) }
+    }
+}
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 643b82f4753..c7bab828659 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -1,6 +1,5 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(associated_type_defaults)]
diff --git a/compiler/rustc_query_impl/src/lib.rs b/compiler/rustc_query_impl/src/lib.rs
index 30a9e718d23..3c329dd0a0e 100644
--- a/compiler/rustc_query_impl/src/lib.rs
+++ b/compiler/rustc_query_impl/src/lib.rs
@@ -3,7 +3,6 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![allow(unused_parens)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(min_specialization)]
diff --git a/compiler/rustc_query_system/src/dep_graph/graph.rs b/compiler/rustc_query_system/src/dep_graph/graph.rs
index 9f34417973e..0d56db16099 100644
--- a/compiler/rustc_query_system/src/dep_graph/graph.rs
+++ b/compiler/rustc_query_system/src/dep_graph/graph.rs
@@ -141,7 +141,7 @@ impl<D: Deps> DepGraph<D> {
         let colors = DepNodeColorMap::new(prev_graph_node_count);
 
         // Instantiate a node with zero dependencies only once for anonymous queries.
-        let _green_node_index = current.alloc_node(
+        let _green_node_index = current.alloc_new_node(
             DepNode { kind: D::DEP_KIND_ANON_ZERO_DEPS, hash: current.anon_id_seed.into() },
             EdgesVec::new(),
             Fingerprint::ZERO,
@@ -149,7 +149,7 @@ impl<D: Deps> DepGraph<D> {
         assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_ZERO_DEPS_ANON_NODE);
 
         // Instantiate a dependy-less red node only once for anonymous queries.
-        let red_node_index = current.alloc_node(
+        let red_node_index = current.alloc_new_node(
             DepNode { kind: D::DEP_KIND_RED, hash: Fingerprint::ZERO.into() },
             EdgesVec::new(),
             Fingerprint::ZERO,
@@ -438,7 +438,7 @@ impl<D: Deps> DepGraphData<D> {
                 // memory impact of this `anon_node_to_index` map remains tolerable, and helps
                 // us avoid useless growth of the graph with almost-equivalent nodes.
                 self.current.anon_node_to_index.get_or_insert_with(target_dep_node, || {
-                    self.current.alloc_node(target_dep_node, task_deps, Fingerprint::ZERO)
+                    self.current.alloc_new_node(target_dep_node, task_deps, Fingerprint::ZERO)
                 })
             }
         };
@@ -680,8 +680,8 @@ impl<D: Deps> DepGraphData<D> {
         qcx: Qcx,
         diagnostic: &DiagInner,
     ) -> DepNodeIndex {
-        // Use `send` so we get an unique index, even though the dep node is not.
-        let dep_node_index = self.current.encoder.send(
+        // Use `send_new` so we get an unique index, even though the dep node is not.
+        let dep_node_index = self.current.encoder.send_new(
             DepNode {
                 kind: D::DEP_KIND_SIDE_EFFECT,
                 hash: PackedFingerprint::from(Fingerprint::ZERO),
@@ -713,20 +713,22 @@ impl<D: Deps> DepGraphData<D> {
                 }
             }
 
-            // Manually recreate the node as `promote_node_and_deps_to_current` expects all
-            // green dependencies.
-            let dep_node_index = self.current.encoder.send(
+            // Use `send_and_color` as `promote_node_and_deps_to_current` expects all
+            // green dependencies. `send_and_color` will also prevent multiple nodes
+            // being encoded for concurrent calls.
+            let dep_node_index = self.current.encoder.send_and_color(
+                prev_index,
+                &self.colors,
                 DepNode {
                     kind: D::DEP_KIND_SIDE_EFFECT,
                     hash: PackedFingerprint::from(Fingerprint::ZERO),
                 },
                 Fingerprint::ZERO,
                 std::iter::once(DepNodeIndex::FOREVER_RED_NODE).collect(),
+                true,
             );
+            // This will just overwrite the same value for concurrent calls.
             qcx.store_side_effect(dep_node_index, side_effect);
-
-            // Mark the node as green.
-            self.colors.insert(prev_index, DepNodeColor::Green(dep_node_index));
         })
     }
 
@@ -736,38 +738,43 @@ impl<D: Deps> DepGraphData<D> {
         edges: EdgesVec,
         fingerprint: Option<Fingerprint>,
     ) -> DepNodeIndex {
-        let dep_node_index =
-            self.current.alloc_node(key, edges, fingerprint.unwrap_or(Fingerprint::ZERO));
-
         if let Some(prev_index) = self.previous.node_to_index_opt(&key) {
             // Determine the color and index of the new `DepNode`.
-            let color = if let Some(fingerprint) = fingerprint {
+            let is_green = if let Some(fingerprint) = fingerprint {
                 if fingerprint == self.previous.fingerprint_by_index(prev_index) {
                     // This is a green node: it existed in the previous compilation,
                     // its query was re-executed, and it has the same result as before.
-                    DepNodeColor::Green(dep_node_index)
+                    true
                 } else {
                     // This is a red node: it existed in the previous compilation, its query
                     // was re-executed, but it has a different result from before.
-                    DepNodeColor::Red
+                    false
                 }
             } else {
                 // This is a red node, effectively: it existed in the previous compilation
                 // session, its query was re-executed, but it doesn't compute a result hash
                 // (i.e. it represents a `no_hash` query), so we have no way of determining
                 // whether or not the result was the same as before.
-                DepNodeColor::Red
+                false
             };
 
-            debug_assert!(
-                self.colors.get(prev_index).is_none(),
-                "DepGraph::with_task() - Duplicate DepNodeColor insertion for {key:?}",
+            let fingerprint = fingerprint.unwrap_or(Fingerprint::ZERO);
+
+            let dep_node_index = self.current.encoder.send_and_color(
+                prev_index,
+                &self.colors,
+                key,
+                fingerprint,
+                edges,
+                is_green,
             );
 
-            self.colors.insert(prev_index, color);
-        }
+            self.current.record_node(dep_node_index, key, fingerprint);
 
-        dep_node_index
+            dep_node_index
+        } else {
+            self.current.alloc_new_node(key, edges, fingerprint.unwrap_or(Fingerprint::ZERO))
+        }
     }
 
     fn promote_node_and_deps_to_current(&self, prev_index: SerializedDepNodeIndex) -> DepNodeIndex {
@@ -1167,8 +1174,7 @@ pub(super) struct CurrentDepGraph<D: Deps> {
     /// ID from the previous session. In order to side-step this problem, we make
     /// sure that anonymous `NodeId`s allocated in different sessions don't overlap.
     /// This is implemented by mixing a session-key into the ID fingerprint of
-    /// each anon node. The session-key is just a random number generated when
-    /// the `DepGraph` is created.
+    /// each anon node. The session-key is a hash of the number of previous sessions.
     anon_id_seed: Fingerprint,
 
     /// These are simple counters that are for profiling and
@@ -1186,12 +1192,8 @@ impl<D: Deps> CurrentDepGraph<D> {
         record_stats: bool,
         previous: Arc<SerializedDepGraph>,
     ) -> Self {
-        use std::time::{SystemTime, UNIX_EPOCH};
-
-        let duration = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
-        let nanos = duration.as_nanos();
         let mut stable_hasher = StableHasher::new();
-        nanos.hash(&mut stable_hasher);
+        previous.session_count().hash(&mut stable_hasher);
         let anon_id_seed = stable_hasher.finish();
 
         #[cfg(debug_assertions)]
@@ -1246,19 +1248,15 @@ impl<D: Deps> CurrentDepGraph<D> {
         assert_eq!(previous, fingerprint, "Unstable fingerprints for {:?}", key);
     }
 
-    /// Writes the node to the current dep-graph and allocates a `DepNodeIndex` for it.
-    /// Assumes that this is a node that has no equivalent in the previous dep-graph.
     #[inline(always)]
-    fn alloc_node(
+    fn record_node(
         &self,
+        dep_node_index: DepNodeIndex,
         key: DepNode,
-        edges: EdgesVec,
-        current_fingerprint: Fingerprint,
-    ) -> DepNodeIndex {
-        let dep_node_index = self.encoder.send(key, current_fingerprint, edges);
-
+        _current_fingerprint: Fingerprint,
+    ) {
         #[cfg(debug_assertions)]
-        self.record_edge(dep_node_index, key, current_fingerprint);
+        self.record_edge(dep_node_index, key, _current_fingerprint);
 
         if let Some(ref nodes_in_current_session) = self.nodes_in_current_session {
             outline(|| {
@@ -1267,6 +1265,20 @@ impl<D: Deps> CurrentDepGraph<D> {
                 }
             });
         }
+    }
+
+    /// Writes the node to the current dep-graph and allocates a `DepNodeIndex` for it.
+    /// Assumes that this is a node that has no equivalent in the previous dep-graph.
+    #[inline(always)]
+    fn alloc_new_node(
+        &self,
+        key: DepNode,
+        edges: EdgesVec,
+        current_fingerprint: Fingerprint,
+    ) -> DepNodeIndex {
+        let dep_node_index = self.encoder.send_new(key, current_fingerprint, edges);
+
+        self.record_node(dep_node_index, key, current_fingerprint);
 
         dep_node_index
     }
diff --git a/compiler/rustc_query_system/src/dep_graph/serialized.rs b/compiler/rustc_query_system/src/dep_graph/serialized.rs
index 7750d6d1fef..ac24628447d 100644
--- a/compiler/rustc_query_system/src/dep_graph/serialized.rs
+++ b/compiler/rustc_query_system/src/dep_graph/serialized.rs
@@ -92,6 +92,9 @@ pub struct SerializedDepGraph {
     /// Stores a map from fingerprints to nodes per dep node kind.
     /// This is the reciprocal of `nodes`.
     index: Vec<UnhashMap<PackedFingerprint, SerializedDepNodeIndex>>,
+    /// The number of previous compilation sessions. This is used to generate
+    /// unique anon dep nodes per session.
+    session_count: u64,
 }
 
 impl SerializedDepGraph {
@@ -146,6 +149,11 @@ impl SerializedDepGraph {
     pub fn node_count(&self) -> usize {
         self.nodes.len()
     }
+
+    #[inline]
+    pub fn session_count(&self) -> u64 {
+        self.session_count
+    }
 }
 
 /// A packed representation of an edge's start index and byte width.
@@ -226,12 +234,12 @@ impl SerializedDepGraph {
 
             // If the length of this node's edge list is small, the length is stored in the header.
             // If it is not, we fall back to another decoder call.
-            let num_edges = node_header.len().unwrap_or_else(|| d.read_usize());
+            let num_edges = node_header.len().unwrap_or_else(|| d.read_u32());
 
             // The edges index list uses the same varint strategy as rmeta tables; we select the
             // number of byte elements per-array not per-element. This lets us read the whole edge
             // list for a node with one decoder call and also use the on-disk format in memory.
-            let edges_len_bytes = node_header.bytes_per_index() * num_edges;
+            let edges_len_bytes = node_header.bytes_per_index() * (num_edges as usize);
             // The in-memory structure for the edges list stores the byte width of the edges on
             // this node with the offset into the global edge data array.
             let edges_header = node_header.edges_header(&edge_list_data);
@@ -252,6 +260,8 @@ impl SerializedDepGraph {
             .map(|_| UnhashMap::with_capacity_and_hasher(d.read_u32() as usize, Default::default()))
             .collect();
 
+        let session_count = d.read_u64();
+
         for (idx, node) in nodes.iter_enumerated() {
             if index[node.kind.as_usize()].insert(node.hash, idx).is_some() {
                 // Side effect nodes can have duplicates
@@ -273,6 +283,7 @@ impl SerializedDepGraph {
             edge_list_indices,
             edge_list_data,
             index,
+            session_count,
         })
     }
 }
@@ -296,7 +307,7 @@ struct SerializedNodeHeader<D> {
 // The fields of a `SerializedNodeHeader`, this struct is an implementation detail and exists only
 // to make the implementation of `SerializedNodeHeader` simpler.
 struct Unpacked {
-    len: Option<usize>,
+    len: Option<u32>,
     bytes_per_index: usize,
     kind: DepKind,
     hash: PackedFingerprint,
@@ -352,7 +363,7 @@ impl<D: Deps> SerializedNodeHeader<D> {
             assert_eq!(fingerprint, res.fingerprint());
             assert_eq!(node, res.node());
             if let Some(len) = res.len() {
-                assert_eq!(edge_count, len);
+                assert_eq!(edge_count, len as usize);
             }
         }
         Self { bytes, _marker: PhantomData }
@@ -366,7 +377,7 @@ impl<D: Deps> SerializedNodeHeader<D> {
 
         let kind = head & mask(Self::KIND_BITS) as u16;
         let bytes_per_index = (head >> Self::KIND_BITS) & mask(Self::WIDTH_BITS) as u16;
-        let len = (head as usize) >> (Self::WIDTH_BITS + Self::KIND_BITS);
+        let len = (head as u32) >> (Self::WIDTH_BITS + Self::KIND_BITS);
 
         Unpacked {
             len: len.checked_sub(1),
@@ -378,7 +389,7 @@ impl<D: Deps> SerializedNodeHeader<D> {
     }
 
     #[inline]
-    fn len(&self) -> Option<usize> {
+    fn len(&self) -> Option<u32> {
         self.unpack().len
     }
 
@@ -421,7 +432,8 @@ impl NodeInfo {
         e.write_array(header.bytes);
 
         if header.len().is_none() {
-            e.emit_usize(edges.len());
+            // The edges are all unique and the number of unique indices is less than u32::MAX.
+            e.emit_u32(edges.len().try_into().unwrap());
         }
 
         let bytes_per_index = header.bytes_per_index();
@@ -456,7 +468,8 @@ impl NodeInfo {
         e.write_array(header.bytes);
 
         if header.len().is_none() {
-            e.emit_usize(edge_count);
+            // The edges are all unique and the number of unique indices is less than u32::MAX.
+            e.emit_u32(edge_count.try_into().unwrap());
         }
 
         let bytes_per_index = header.bytes_per_index();
@@ -601,7 +614,7 @@ impl<D: Deps> EncoderState<D> {
             stats: _,
             kind_stats,
             marker: _,
-            previous: _,
+            previous,
         } = self;
 
         let node_count = total_node_count.try_into().unwrap();
@@ -612,6 +625,8 @@ impl<D: Deps> EncoderState<D> {
             count.encode(&mut encoder);
         }
 
+        previous.session_count.checked_add(1).unwrap().encode(&mut encoder);
+
         debug!(?node_count, ?edge_count);
         debug!("position: {:?}", encoder.position());
         IntEncodedWithFixedSize(node_count).encode(&mut encoder);
@@ -707,7 +722,8 @@ impl<D: Deps> GraphEncoder<D> {
         }
     }
 
-    pub(crate) fn send(
+    /// Encodes a node that does not exists in the previous graph.
+    pub(crate) fn send_new(
         &self,
         node: DepNode,
         fingerprint: Fingerprint,
@@ -718,6 +734,40 @@ impl<D: Deps> GraphEncoder<D> {
         self.status.lock().as_mut().unwrap().encode_node(&node, &self.record_graph)
     }
 
+    /// Encodes a node that exists in the previous graph, but was re-executed.
+    ///
+    /// This will also ensure the dep node is colored either red or green.
+    pub(crate) fn send_and_color(
+        &self,
+        prev_index: SerializedDepNodeIndex,
+        colors: &DepNodeColorMap,
+        node: DepNode,
+        fingerprint: Fingerprint,
+        edges: EdgesVec,
+        is_green: bool,
+    ) -> DepNodeIndex {
+        let _prof_timer = self.profiler.generic_activity("incr_comp_encode_dep_graph");
+        let node = NodeInfo { node, fingerprint, edges };
+
+        let mut status = self.status.lock();
+        let status = status.as_mut().unwrap();
+
+        // Check colors inside the lock to avoid racing when `send_promoted` is called concurrently
+        // on the same index.
+        match colors.get(prev_index) {
+            None => {
+                let dep_node_index = status.encode_node(&node, &self.record_graph);
+                colors.insert(
+                    prev_index,
+                    if is_green { DepNodeColor::Green(dep_node_index) } else { DepNodeColor::Red },
+                );
+                dep_node_index
+            }
+            Some(DepNodeColor::Green(dep_node_index)) => dep_node_index,
+            Some(DepNodeColor::Red) => panic!(),
+        }
+    }
+
     /// Encodes a node that was promoted from the previous graph. It reads the information directly from
     /// the previous dep graph and expects all edges to already have a new dep node index assigned.
     ///
@@ -733,8 +783,8 @@ impl<D: Deps> GraphEncoder<D> {
         let mut status = self.status.lock();
         let status = status.as_mut().unwrap();
 
-        // Check colors inside the lock to avoid racing when `send_promoted` is called concurrently
-        // on the same index.
+        // Check colors inside the lock to avoid racing when `send_promoted` or `send_and_color`
+        // is called concurrently on the same index.
         match colors.get(prev_index) {
             None => {
                 let dep_node_index =
diff --git a/compiler/rustc_resolve/Cargo.toml b/compiler/rustc_resolve/Cargo.toml
index 9ea9c58cfd1..0fcc3d8f6b3 100644
--- a/compiler/rustc_resolve/Cargo.toml
+++ b/compiler/rustc_resolve/Cargo.toml
@@ -18,7 +18,6 @@ rustc_expand = { path = "../rustc_expand" }
 rustc_feature = { path = "../rustc_feature" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_hir = { path = "../rustc_hir" }
-rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_metadata = { path = "../rustc_metadata" }
 rustc_middle = { path = "../rustc_middle" }
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index 4368f7882ff..cb328022c76 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -1207,7 +1207,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             for (rule_i, rule_span) in &self.r.macro_map[&def_id.to_def_id()].rule_spans {
                 self.r
                     .unused_macro_rules
-                    .entry(def_id)
+                    .entry(node_id)
                     .or_default()
                     .insert(*rule_i, (ident, *rule_span));
             }
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 6dc854758da..363a75911ad 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -170,10 +170,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
     fn report_with_use_injections(&mut self, krate: &Crate) {
         for UseError { mut err, candidates, def_id, instead, suggestion, path, is_call } in
-            self.use_injections.drain(..)
+            std::mem::take(&mut self.use_injections)
         {
             let (span, found_use) = if let Some(def_id) = def_id.as_local() {
-                UsePlacementFinder::check(krate, self.def_id_to_node_id[def_id])
+                UsePlacementFinder::check(krate, self.def_id_to_node_id(def_id))
             } else {
                 (None, FoundUse::No)
             };
@@ -1435,7 +1435,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let import_suggestions =
             self.lookup_import_candidates(ident, Namespace::MacroNS, parent_scope, is_expected);
         let (span, found_use) = match parent_scope.module.nearest_parent_mod().as_local() {
-            Some(def_id) => UsePlacementFinder::check(krate, self.def_id_to_node_id[def_id]),
+            Some(def_id) => UsePlacementFinder::check(krate, self.def_id_to_node_id(def_id)),
             None => (None, FoundUse::No),
         };
         show_candidates(
@@ -2550,7 +2550,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 .iter()
                 .filter_map(|item| {
                     let parent_module = self.opt_local_def_id(item.parent_module)?.to_def_id();
-                    Some(StrippedCfgItem { parent_module, name: item.name, cfg: item.cfg.clone() })
+                    Some(StrippedCfgItem {
+                        parent_module,
+                        ident: item.ident,
+                        cfg: item.cfg.clone(),
+                    })
                 })
                 .collect::<Vec<_>>();
             local_items.as_slice()
@@ -2558,12 +2562,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             self.tcx.stripped_cfg_items(module.krate)
         };
 
-        for &StrippedCfgItem { parent_module, name, ref cfg } in symbols {
-            if parent_module != module || name.name != *segment {
+        for &StrippedCfgItem { parent_module, ident, ref cfg } in symbols {
+            if parent_module != module || ident.name != *segment {
                 continue;
             }
 
-            let note = errors::FoundItemConfigureOut { span: name.span };
+            let note = errors::FoundItemConfigureOut { span: ident.span };
             err.subdiagnostic(note);
 
             if let MetaItemKind::List(nested) = &cfg.kind
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 5f0a2a597e9..180d6af219d 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -296,9 +296,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) -> Option<LexicalScopeBinding<'ra>> {
         assert!(ns == TypeNS || ns == ValueNS);
         let orig_ident = ident;
-        if ident.name == kw::Empty {
-            return Some(LexicalScopeBinding::Res(Res::Err));
-        }
         let (general_span, normalized_span) = if ident.name == kw::SelfUpper {
             // FIXME(jseyfried) improve `Self` hygiene
             let empty_span = ident.span.with_ctxt(SyntaxContext::root());
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 0b3633a452c..762e08b2be5 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -639,38 +639,38 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
 
                 if let Some(glob_binding) = resolution.shadowed_glob {
-                    let binding_id = match binding.kind {
-                        NameBindingKind::Res(res) => {
-                            Some(self.def_id_to_node_id[res.def_id().expect_local()])
-                        }
-                        NameBindingKind::Module(module) => {
-                            Some(self.def_id_to_node_id[module.def_id().expect_local()])
-                        }
-                        NameBindingKind::Import { import, .. } => import.id(),
-                    };
-
                     if binding.res() != Res::Err
                         && glob_binding.res() != Res::Err
                         && let NameBindingKind::Import { import: glob_import, .. } =
                             glob_binding.kind
-                        && let Some(binding_id) = binding_id
                         && let Some(glob_import_id) = glob_import.id()
                         && let glob_import_def_id = self.local_def_id(glob_import_id)
                         && self.effective_visibilities.is_exported(glob_import_def_id)
                         && glob_binding.vis.is_public()
                         && !binding.vis.is_public()
                     {
-                        self.lint_buffer.buffer_lint(
-                            HIDDEN_GLOB_REEXPORTS,
-                            binding_id,
-                            binding.span,
-                            BuiltinLintDiag::HiddenGlobReexports {
-                                name: key.ident.name.to_string(),
-                                namespace: key.ns.descr().to_owned(),
-                                glob_reexport_span: glob_binding.span,
-                                private_item_span: binding.span,
-                            },
-                        );
+                        let binding_id = match binding.kind {
+                            NameBindingKind::Res(res) => {
+                                Some(self.def_id_to_node_id(res.def_id().expect_local()))
+                            }
+                            NameBindingKind::Module(module) => {
+                                Some(self.def_id_to_node_id(module.def_id().expect_local()))
+                            }
+                            NameBindingKind::Import { import, .. } => import.id(),
+                        };
+                        if let Some(binding_id) = binding_id {
+                            self.lint_buffer.buffer_lint(
+                                HIDDEN_GLOB_REEXPORTS,
+                                binding_id,
+                                binding.span,
+                                BuiltinLintDiag::HiddenGlobReexports {
+                                    name: key.ident.name.to_string(),
+                                    namespace: key.ns.descr().to_owned(),
+                                    glob_reexport_span: glob_binding.span,
+                                    private_item_span: binding.span,
+                                },
+                            );
+                        }
                     }
                 }
             }
@@ -1012,7 +1012,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
                         // 2 segments, so the `resolve_path` above won't trigger it.
                         let mut full_path = import.module_path.clone();
-                        full_path.push(Segment::from_ident(Ident::empty()));
+                        full_path.push(Segment::from_ident(Ident::dummy()));
                         self.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
                     }
 
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 20e19caf909..bae2fdeecaf 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1948,7 +1948,7 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
 
         self.record_lifetime_res(
             anchor_id,
-            LifetimeRes::ElidedAnchor { start: id, end: NodeId::from_u32(id.as_u32() + 1) },
+            LifetimeRes::ElidedAnchor { start: id, end: id + 1 },
             LifetimeElisionCandidate::Ignore,
         );
         self.resolve_anonymous_lifetime(&lt, anchor_id, true);
@@ -4009,22 +4009,17 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             self.report_error(ident.span, error(ident));
         }
 
-        // Record as bound if it's valid:
-        let ident_valid = ident.name != kw::Empty;
-        if ident_valid {
-            bindings.last_mut().unwrap().1.insert(ident);
-        }
+        // Record as bound.
+        bindings.last_mut().unwrap().1.insert(ident);
 
         if already_bound_or {
             // `Variant1(a) | Variant2(a)`, ok
             // Reuse definition from the first `a`.
             self.innermost_rib_bindings(ValueNS)[&ident]
         } else {
+            // A completely fresh binding is added to the set.
             let res = Res::Local(pat_id);
-            if ident_valid {
-                // A completely fresh binding add to the set if it's valid.
-                self.innermost_rib_bindings(ValueNS).insert(ident, res);
-            }
+            self.innermost_rib_bindings(ValueNS).insert(ident, res);
             res
         }
     }
@@ -4611,6 +4606,11 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                     }
                 };
 
+                // Fix up partial res of segment from `resolve_path` call.
+                if let Some(id) = path[0].id {
+                    self.r.partial_res_map.insert(id, PartialRes::new(Res::PrimTy(prim)));
+                }
+
                 PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
             }
             PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
@@ -5012,8 +5012,7 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             return false;
         }
         let Some(local_did) = did.as_local() else { return true };
-        let Some(node_id) = self.r.def_id_to_node_id.get(local_did) else { return true };
-        !self.r.proc_macros.contains(node_id)
+        !self.r.proc_macros.contains(&local_did)
     }
 
     fn resolve_doc_links(&mut self, attrs: &[Attribute], maybe_exported: MaybeExported<'_>) {
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index b62bc6c45e0..d4fe446cc9f 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -1994,7 +1994,7 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
             .iter()
             .flat_map(|i| self.r.tcx.associated_items(i).in_definition_order())
             // Only assoc fn with no receivers.
-            .filter(|item| matches!(item.kind, ty::AssocKind::Fn) && !item.fn_has_self_parameter)
+            .filter(|item| item.is_fn() && !item.is_method())
             .filter_map(|item| {
                 // Only assoc fns that return `Self`
                 let fn_sig = self.r.tcx.fn_sig(item.def_id).skip_binder();
@@ -2007,8 +2007,9 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 if def.did() != def_id {
                     return None;
                 }
-                let order = !item.name.as_str().starts_with("new");
-                Some((order, item.name, input_len))
+                let name = item.name();
+                let order = !name.as_str().starts_with("new");
+                Some((order, name, input_len))
             })
             .collect::<Vec<_>>();
         items.sort_by_key(|(order, _, _)| *order);
@@ -2238,7 +2239,7 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                                     .get(&def_id)
                                     .is_some_and(|sig| sig.has_self),
                                 None => {
-                                    self.r.tcx.fn_arg_names(def_id).first().is_some_and(|&ident| {
+                                    self.r.tcx.fn_arg_idents(def_id).first().is_some_and(|&ident| {
                                         matches!(ident, Some(Ident { name: kw::SelfLower, .. }))
                                     })
                                 }
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 3ac66840d87..b121755acd9 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -56,7 +56,6 @@ use rustc_hir::def::{
 };
 use rustc_hir::def_id::{CRATE_DEF_ID, CrateNum, DefId, LOCAL_CRATE, LocalDefId, LocalDefIdMap};
 use rustc_hir::{PrimTy, TraitCandidate};
-use rustc_index::IndexVec;
 use rustc_metadata::creader::{CStore, CrateLoader};
 use rustc_middle::metadata::ModChild;
 use rustc_middle::middle::privacy::EffectiveVisibilities;
@@ -1141,7 +1140,7 @@ pub struct Resolver<'ra, 'tcx> {
     ast_transform_scopes: FxHashMap<LocalExpnId, Module<'ra>>,
     unused_macros: FxIndexMap<LocalDefId, (NodeId, Ident)>,
     /// A map from the macro to all its potentially unused arms.
-    unused_macro_rules: FxIndexMap<LocalDefId, UnordMap<usize, (Ident, Span)>>,
+    unused_macro_rules: FxIndexMap<NodeId, UnordMap<usize, (Ident, Span)>>,
     proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
     single_segment_macro_resolutions:
@@ -1184,7 +1183,6 @@ pub struct Resolver<'ra, 'tcx> {
     next_node_id: NodeId,
 
     node_id_to_def_id: NodeMap<Feed<'tcx, LocalDefId>>,
-    def_id_to_node_id: IndexVec<LocalDefId, ast::NodeId>,
 
     /// Indices of unnamed struct or variant fields with unresolved attributes.
     placeholder_field_indices: FxHashMap<NodeId, usize>,
@@ -1202,7 +1200,7 @@ pub struct Resolver<'ra, 'tcx> {
     trait_impls: FxIndexMap<DefId, Vec<LocalDefId>>,
     /// A list of proc macro LocalDefIds, written out in the order in which
     /// they are declared in the static array generated by proc_macro_harness.
-    proc_macros: Vec<NodeId>,
+    proc_macros: Vec<LocalDefId>,
     confused_type_with_std_module: FxIndexMap<Span, Span>,
     /// Whether lifetime elision was successful.
     lifetime_elision_allowed: FxHashSet<NodeId>,
@@ -1339,12 +1337,12 @@ impl<'tcx> Resolver<'_, 'tcx> {
         expn_id: ExpnId,
         span: Span,
     ) -> TyCtxtFeed<'tcx, LocalDefId> {
-        let data = def_kind.def_path_data(name);
         assert!(
             !self.node_id_to_def_id.contains_key(&node_id),
-            "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
+            "adding a def for node-id {:?}, name {:?}, data {:?} but a previous def exists: {:?}",
             node_id,
-            data,
+            name,
+            def_kind,
             self.tcx.definitions_untracked().def_key(self.node_id_to_def_id[&node_id].key()),
         );
 
@@ -1369,7 +1367,6 @@ impl<'tcx> Resolver<'_, 'tcx> {
             debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
             self.node_id_to_def_id.insert(node_id, feed.downgrade());
         }
-        assert_eq!(self.def_id_to_node_id.push(node_id), def_id);
 
         feed
     }
@@ -1385,6 +1382,19 @@ impl<'tcx> Resolver<'_, 'tcx> {
     pub fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
+
+    /// This function is very slow, as it iterates over the entire
+    /// [Resolver::node_id_to_def_id] map just to find the [NodeId]
+    /// that corresponds to the given [LocalDefId]. Only use this in
+    /// diagnostics code paths.
+    fn def_id_to_node_id(&self, def_id: LocalDefId) -> NodeId {
+        self.node_id_to_def_id
+            .items()
+            .filter(|(_, v)| v.key() == def_id)
+            .map(|(k, _)| *k)
+            .get_only()
+            .unwrap()
+    }
 }
 
 impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
@@ -1417,8 +1427,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             &mut Default::default(),
         );
 
-        let mut def_id_to_node_id = IndexVec::default();
-        assert_eq!(def_id_to_node_id.push(CRATE_NODE_ID), CRATE_DEF_ID);
         let mut node_id_to_def_id = NodeMap::default();
         let crate_feed = tcx.create_local_crate_def_id(crate_span);
 
@@ -1553,7 +1561,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             lint_buffer: LintBuffer::default(),
             next_node_id: CRATE_NODE_ID,
             node_id_to_def_id,
-            def_id_to_node_id,
             placeholder_field_indices: Default::default(),
             invocation_parents,
             legacy_const_generic_args: Default::default(),
@@ -1633,7 +1640,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     pub fn into_outputs(self) -> ResolverOutputs {
-        let proc_macros = self.proc_macros.iter().map(|id| self.local_def_id(*id)).collect();
+        let proc_macros = self.proc_macros;
         let expn_that_defined = self.expn_that_defined;
         let extern_crate_map = self.extern_crate_map;
         let maybe_unused_trait_imports = self.maybe_unused_trait_imports;
@@ -1648,7 +1655,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 .filter_map(|item| {
                     let parent_module =
                         self.node_id_to_def_id.get(&item.parent_module)?.key().to_def_id();
-                    Some(StrippedCfgItem { parent_module, name: item.name, cfg: item.cfg })
+                    Some(StrippedCfgItem { parent_module, ident: item.ident, cfg: item.cfg })
                 })
                 .collect(),
         );
@@ -2000,16 +2007,16 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 result,
                 result.map(|r| r.expn_data())
             );
-            // Then find the last semi-transparent mark from the end if it exists.
+            // Then find the last semi-opaque mark from the end if it exists.
             for (mark, transparency) in iter {
-                if transparency == Transparency::SemiTransparent {
+                if transparency == Transparency::SemiOpaque {
                     result = Some(mark);
                 } else {
                     break;
                 }
             }
             debug!(
-                "resolve_crate_root: found semi-transparent mark {:?} {:?}",
+                "resolve_crate_root: found semi-opaque mark {:?} {:?}",
                 result,
                 result.map(|r| r.expn_data())
             );
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 9d6ae0aa9d1..749b7f24c50 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -323,8 +323,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
     }
 
     fn record_macro_rule_usage(&mut self, id: NodeId, rule_i: usize) {
-        let did = self.local_def_id(id);
-        if let Some(rules) = self.unused_macro_rules.get_mut(&did) {
+        if let Some(rules) = self.unused_macro_rules.get_mut(&id) {
             rules.remove(&rule_i);
         }
     }
@@ -337,15 +336,12 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
                 ident.span,
                 BuiltinLintDiag::UnusedMacroDefinition(ident.name),
             );
+            // Do not report unused individual rules if the entire macro is unused
+            self.unused_macro_rules.swap_remove(&node_id);
         }
 
-        for (&def_id, unused_arms) in self.unused_macro_rules.iter() {
+        for (&node_id, unused_arms) in self.unused_macro_rules.iter() {
             for (&arm_i, &(ident, rule_span)) in unused_arms.to_sorted_stable_ord() {
-                if self.unused_macros.contains_key(&def_id) {
-                    // We already lint the entire macro as unused
-                    continue;
-                }
-                let node_id = self.def_id_to_node_id[def_id];
                 self.lint_buffer.buffer_lint(
                     UNUSED_MACRO_RULES,
                     node_id,
@@ -466,11 +462,11 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
     }
 
     fn declare_proc_macro(&mut self, id: NodeId) {
-        self.proc_macros.push(id)
+        self.proc_macros.push(self.local_def_id(id))
     }
 
-    fn append_stripped_cfg_item(&mut self, parent_node: NodeId, name: Ident, cfg: ast::MetaItem) {
-        self.stripped_cfg_items.push(StrippedCfgItem { parent_module: parent_node, name, cfg });
+    fn append_stripped_cfg_item(&mut self, parent_node: NodeId, ident: Ident, cfg: ast::MetaItem) {
+        self.stripped_cfg_items.push(StrippedCfgItem { parent_module: parent_node, ident, cfg });
     }
 
     fn registered_tools(&self) -> &RegisteredTools {
@@ -932,7 +928,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             .invocation_parents
                             .get(&parent_scope.expansion)
                             .map_or(ast::CRATE_NODE_ID, |parent| {
-                                self.def_id_to_node_id[parent.parent_def]
+                                self.def_id_to_node_id(parent.parent_def)
                             });
                         self.lint_buffer.buffer_lint(
                             LEGACY_DERIVE_HELPERS,
diff --git a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs
index d56ca9c2453..4b1b3903e40 100644
--- a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs
+++ b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs
@@ -721,7 +721,8 @@ fn encode_ty_name(tcx: TyCtxt<'_>, def_id: DefId) -> String {
             | hir::definitions::DefPathData::Use
             | hir::definitions::DefPathData::GlobalAsm
             | hir::definitions::DefPathData::MacroNs(..)
-            | hir::definitions::DefPathData::LifetimeNs(..) => {
+            | hir::definitions::DefPathData::LifetimeNs(..)
+            | hir::definitions::DefPathData::AnonAssocTy => {
                 bug!("encode_ty_name: unexpected `{:?}`", disambiguated_data.data);
             }
         });
diff --git a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs
index 129a32c6edd..d2917478e4e 100644
--- a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs
+++ b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs
@@ -240,7 +240,7 @@ fn trait_object_ty<'tcx>(tcx: TyCtxt<'tcx>, poly_trait_ref: ty::PolyTraitRef<'tc
         .flat_map(|super_poly_trait_ref| {
             tcx.associated_items(super_poly_trait_ref.def_id())
                 .in_definition_order()
-                .filter(|item| item.kind == ty::AssocKind::Type)
+                .filter(|item| item.is_type())
                 .filter(|item| !tcx.generics_require_sized_self(item.def_id))
                 .map(move |assoc_ty| {
                     super_poly_trait_ref.map_bound(|super_trait_ref| {
@@ -446,7 +446,7 @@ pub(crate) fn transform_instance<'tcx>(
             let call = tcx
                 .associated_items(trait_id)
                 .in_definition_order()
-                .find(|it| it.kind == ty::AssocKind::Fn)
+                .find(|it| it.is_fn())
                 .expect("No call-family function on closure-like Fn trait?")
                 .def_id;
 
diff --git a/compiler/rustc_sanitizers/src/lib.rs b/compiler/rustc_sanitizers/src/lib.rs
index c4a9cab24d0..e4792563e71 100644
--- a/compiler/rustc_sanitizers/src/lib.rs
+++ b/compiler/rustc_sanitizers/src/lib.rs
@@ -4,7 +4,6 @@
 //! compiler.
 
 // tidy-alphabetical-start
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(let_chains)]
 // tidy-alphabetical-end
 
diff --git a/compiler/rustc_serialize/src/opaque.rs b/compiler/rustc_serialize/src/opaque.rs
index 81f6266f8d1..0a55504a556 100644
--- a/compiler/rustc_serialize/src/opaque.rs
+++ b/compiler/rustc_serialize/src/opaque.rs
@@ -19,7 +19,7 @@ pub type FileEncodeResult = Result<usize, (PathBuf, io::Error)>;
 pub const MAGIC_END_BYTES: &[u8] = b"rust-end-file";
 
 /// The size of the buffer in `FileEncoder`.
-const BUF_SIZE: usize = 8192;
+const BUF_SIZE: usize = 64 * 1024;
 
 /// `FileEncoder` encodes data to file via fixed-size buffer.
 ///
diff --git a/compiler/rustc_session/Cargo.toml b/compiler/rustc_session/Cargo.toml
index a087725d34d..63772a32222 100644
--- a/compiler/rustc_session/Cargo.toml
+++ b/compiler/rustc_session/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2024"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 getopts = "0.2"
+rand = "0.9.0"
 rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_data_structures = { path = "../rustc_data_structures" }
diff --git a/compiler/rustc_session/src/code_stats.rs b/compiler/rustc_session/src/code_stats.rs
index b4597ae2515..6b18d450e9e 100644
--- a/compiler/rustc_session/src/code_stats.rs
+++ b/compiler/rustc_session/src/code_stats.rs
@@ -72,7 +72,7 @@ pub struct TypeSizeInfo {
 
 #[derive(Default)]
 pub struct CodeStats {
-    type_sizes: Lock<FxHashSet<TypeSizeInfo>>,
+    pub type_sizes: Lock<FxHashSet<TypeSizeInfo>>,
 }
 
 impl CodeStats {
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 56b3fe2ab4c..ff7ea5bd718 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -14,6 +14,7 @@ use std::str::{self, FromStr};
 use std::sync::LazyLock;
 use std::{cmp, fmt, fs, iter};
 
+use externs::{ExternOpt, split_extern_opt};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::stable_hasher::{StableOrd, ToStableHashKey};
 use rustc_errors::emitter::HumanReadableErrorType;
@@ -39,6 +40,7 @@ use crate::utils::CanonicalizedPath;
 use crate::{EarlyDiagCtxt, HashStableContext, Session, filesearch, lint};
 
 mod cfg;
+mod externs;
 mod native_libs;
 pub mod sigpipe;
 
@@ -1015,11 +1017,14 @@ impl OutFileName {
         &self,
         outputs: &OutputFilenames,
         flavor: OutputType,
-        codegen_unit_name: Option<&str>,
+        codegen_unit_name: &str,
+        invocation_temp: Option<&str>,
     ) -> PathBuf {
         match *self {
             OutFileName::Real(ref path) => path.clone(),
-            OutFileName::Stdout => outputs.temp_path(flavor, codegen_unit_name),
+            OutFileName::Stdout => {
+                outputs.temp_path_for_cgu(flavor, codegen_unit_name, invocation_temp)
+            }
         }
     }
 
@@ -1094,40 +1099,59 @@ impl OutputFilenames {
     /// Gets the path where a compilation artifact of the given type for the
     /// given codegen unit should be placed on disk. If codegen_unit_name is
     /// None, a path distinct from those of any codegen unit will be generated.
-    pub fn temp_path(&self, flavor: OutputType, codegen_unit_name: Option<&str>) -> PathBuf {
+    pub fn temp_path_for_cgu(
+        &self,
+        flavor: OutputType,
+        codegen_unit_name: &str,
+        invocation_temp: Option<&str>,
+    ) -> PathBuf {
         let extension = flavor.extension();
-        self.temp_path_ext(extension, codegen_unit_name)
+        self.temp_path_ext_for_cgu(extension, codegen_unit_name, invocation_temp)
     }
 
     /// Like `temp_path`, but specifically for dwarf objects.
-    pub fn temp_path_dwo(&self, codegen_unit_name: Option<&str>) -> PathBuf {
-        self.temp_path_ext(DWARF_OBJECT_EXT, codegen_unit_name)
+    pub fn temp_path_dwo_for_cgu(
+        &self,
+        codegen_unit_name: &str,
+        invocation_temp: Option<&str>,
+    ) -> PathBuf {
+        self.temp_path_ext_for_cgu(DWARF_OBJECT_EXT, codegen_unit_name, invocation_temp)
     }
 
     /// Like `temp_path`, but also supports things where there is no corresponding
     /// OutputType, like noopt-bitcode or lto-bitcode.
-    pub fn temp_path_ext(&self, ext: &str, codegen_unit_name: Option<&str>) -> PathBuf {
-        let mut extension = String::new();
+    pub fn temp_path_ext_for_cgu(
+        &self,
+        ext: &str,
+        codegen_unit_name: &str,
+        invocation_temp: Option<&str>,
+    ) -> PathBuf {
+        let mut extension = codegen_unit_name.to_string();
 
-        if let Some(codegen_unit_name) = codegen_unit_name {
-            extension.push_str(codegen_unit_name);
+        // Append `.{invocation_temp}` to ensure temporary files are unique.
+        if let Some(rng) = invocation_temp {
+            extension.push('.');
+            extension.push_str(rng);
         }
 
+        // FIXME: This is sketchy that we're not appending `.rcgu` when the ext is empty.
+        // Append `.rcgu.{ext}`.
         if !ext.is_empty() {
-            if !extension.is_empty() {
-                extension.push('.');
-                extension.push_str(RUST_CGU_EXT);
-                extension.push('.');
-            }
-
+            extension.push('.');
+            extension.push_str(RUST_CGU_EXT);
+            extension.push('.');
             extension.push_str(ext);
         }
 
         let temps_directory = self.temps_directory.as_ref().unwrap_or(&self.out_directory);
-
         self.with_directory_and_extension(temps_directory, &extension)
     }
 
+    pub fn temp_path_for_diagnostic(&self, ext: &str) -> PathBuf {
+        let temps_directory = self.temps_directory.as_ref().unwrap_or(&self.out_directory);
+        self.with_directory_and_extension(temps_directory, &ext)
+    }
+
     pub fn with_extension(&self, extension: &str) -> PathBuf {
         self.with_directory_and_extension(&self.out_directory, extension)
     }
@@ -1144,10 +1168,11 @@ impl OutputFilenames {
         &self,
         split_debuginfo_kind: SplitDebuginfo,
         split_dwarf_kind: SplitDwarfKind,
-        cgu_name: Option<&str>,
+        cgu_name: &str,
+        invocation_temp: Option<&str>,
     ) -> Option<PathBuf> {
-        let obj_out = self.temp_path(OutputType::Object, cgu_name);
-        let dwo_out = self.temp_path_dwo(cgu_name);
+        let obj_out = self.temp_path_for_cgu(OutputType::Object, cgu_name, invocation_temp);
+        let dwo_out = self.temp_path_dwo_for_cgu(cgu_name, invocation_temp);
         match (split_debuginfo_kind, split_dwarf_kind) {
             (SplitDebuginfo::Off, SplitDwarfKind::Single | SplitDwarfKind::Split) => None,
             // Single mode doesn't change how DWARF is emitted, but does add Split DWARF attributes
@@ -1537,9 +1562,10 @@ The default is {DEFAULT_EDITION} and the latest stable edition is {LATEST_STABLE
     )
 });
 
-static PRINT_KINDS_STRING: LazyLock<String> = LazyLock::new(|| {
+static PRINT_HELP: LazyLock<String> = LazyLock::new(|| {
     format!(
-        "[{}]",
+        "Compiler information to print on stdout (or to a file)\n\
+        INFO may be one of ({}).",
         PRINT_KINDS.iter().map(|(name, _)| format!("{name}")).collect::<Vec<_>>().join("|")
     )
 });
@@ -1598,14 +1624,7 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
             "Comma separated list of types of output for the compiler to emit",
             "[asm|llvm-bc|llvm-ir|obj|metadata|link|dep-info|mir]",
         ),
-        opt(
-            Stable,
-            Multi,
-            "",
-            "print",
-            "Compiler information to print on stdout",
-            &PRINT_KINDS_STRING,
-        ),
+        opt(Stable, Multi, "", "print", &PRINT_HELP, "INFO[=FILE]"),
         opt(Stable, FlagMulti, "g", "", "Equivalent to -C debuginfo=2", ""),
         opt(Stable, FlagMulti, "O", "", "Equivalent to -C opt-level=3", ""),
         opt(Stable, Opt, "o", "", "Write output to <filename>", "FILENAME"),
@@ -2046,7 +2065,8 @@ fn collect_print_requests(
             check_print_request_stability(early_dcx, unstable_opts, (print_name, *print_kind));
             *print_kind
         } else {
-            emit_unknown_print_request_help(early_dcx, req)
+            let is_nightly = nightly_options::match_is_nightly_build(matches);
+            emit_unknown_print_request_help(early_dcx, req, is_nightly)
         };
 
         let out = out.unwrap_or(OutFileName::Stdout);
@@ -2070,25 +2090,37 @@ fn check_print_request_stability(
     unstable_opts: &UnstableOptions,
     (print_name, print_kind): (&str, PrintKind),
 ) {
+    if !is_print_request_stable(print_kind) && !unstable_opts.unstable_options {
+        early_dcx.early_fatal(format!(
+            "the `-Z unstable-options` flag must also be passed to enable the `{print_name}` \
+                print option"
+        ));
+    }
+}
+
+fn is_print_request_stable(print_kind: PrintKind) -> bool {
     match print_kind {
         PrintKind::AllTargetSpecsJson
         | PrintKind::CheckCfg
         | PrintKind::CrateRootLintLevels
         | PrintKind::SupportedCrateTypes
-        | PrintKind::TargetSpecJson
-            if !unstable_opts.unstable_options =>
-        {
-            early_dcx.early_fatal(format!(
-                "the `-Z unstable-options` flag must also be passed to enable the `{print_name}` \
-                print option"
-            ));
-        }
-        _ => {}
+        | PrintKind::TargetSpecJson => false,
+        _ => true,
     }
 }
 
-fn emit_unknown_print_request_help(early_dcx: &EarlyDiagCtxt, req: &str) -> ! {
-    let prints = PRINT_KINDS.iter().map(|(name, _)| format!("`{name}`")).collect::<Vec<_>>();
+fn emit_unknown_print_request_help(early_dcx: &EarlyDiagCtxt, req: &str, is_nightly: bool) -> ! {
+    let prints = PRINT_KINDS
+        .iter()
+        .filter_map(|(name, kind)| {
+            // If we're not on nightly, we don't want to print unstable options
+            if !is_nightly && !is_print_request_stable(*kind) {
+                None
+            } else {
+                Some(format!("`{name}`"))
+            }
+        })
+        .collect::<Vec<_>>();
     let prints = prints.join(", ");
 
     let mut diag = early_dcx.early_struct_fatal(format!("unknown print request: `{req}`"));
@@ -2188,44 +2220,13 @@ pub fn parse_externs(
     matches: &getopts::Matches,
     unstable_opts: &UnstableOptions,
 ) -> Externs {
-    fn is_ascii_ident(string: &str) -> bool {
-        let mut chars = string.chars();
-        if let Some(start) = chars.next()
-            && (start.is_ascii_alphabetic() || start == '_')
-        {
-            chars.all(|char| char.is_ascii_alphanumeric() || char == '_')
-        } else {
-            false
-        }
-    }
-
     let is_unstable_enabled = unstable_opts.unstable_options;
     let mut externs: BTreeMap<String, ExternEntry> = BTreeMap::new();
     for arg in matches.opt_strs("extern") {
-        let (name, path) = match arg.split_once('=') {
-            None => (arg, None),
-            Some((name, path)) => (name.to_string(), Some(Path::new(path))),
-        };
-        let (options, name) = match name.split_once(':') {
-            None => (None, name),
-            Some((opts, name)) => (Some(opts), name.to_string()),
-        };
-
-        if !is_ascii_ident(&name) {
-            let mut error = early_dcx.early_struct_fatal(format!(
-                "crate name `{name}` passed to `--extern` is not a valid ASCII identifier"
-            ));
-            let adjusted_name = name.replace('-', "_");
-            if is_ascii_ident(&adjusted_name) {
-                #[allow(rustc::diagnostic_outside_of_impl)] // FIXME
-                error.help(format!(
-                    "consider replacing the dashes with underscores: `{adjusted_name}`"
-                ));
-            }
-            error.emit();
-        }
+        let ExternOpt { crate_name: name, path, options } =
+            split_extern_opt(early_dcx, unstable_opts, &arg).unwrap_or_else(|e| e.emit());
 
-        let path = path.map(|p| CanonicalizedPath::new(p));
+        let path = path.map(|p| CanonicalizedPath::new(p.as_path()));
 
         let entry = externs.entry(name.to_owned());
 
diff --git a/compiler/rustc_session/src/config/externs.rs b/compiler/rustc_session/src/config/externs.rs
new file mode 100644
index 00000000000..1420ee38bf2
--- /dev/null
+++ b/compiler/rustc_session/src/config/externs.rs
@@ -0,0 +1,79 @@
+//! This module contains code to help parse and manipulate `--extern` arguments.
+
+use std::path::PathBuf;
+
+use rustc_errors::{Diag, FatalAbort};
+
+use super::UnstableOptions;
+use crate::EarlyDiagCtxt;
+
+#[cfg(test)]
+mod tests;
+
+/// Represents the pieces of an `--extern` argument.
+pub(crate) struct ExternOpt {
+    pub(crate) crate_name: String,
+    pub(crate) path: Option<PathBuf>,
+    pub(crate) options: Option<String>,
+}
+
+/// Breaks out the major components of an `--extern` argument.
+///
+/// The options field will be a string containing comma-separated options that will need further
+/// parsing and processing.
+pub(crate) fn split_extern_opt<'a>(
+    early_dcx: &'a EarlyDiagCtxt,
+    unstable_opts: &UnstableOptions,
+    extern_opt: &str,
+) -> Result<ExternOpt, Diag<'a, FatalAbort>> {
+    let (name, path) = match extern_opt.split_once('=') {
+        None => (extern_opt.to_string(), None),
+        Some((name, path)) => (name.to_string(), Some(PathBuf::from(path))),
+    };
+    let (options, crate_name) = match name.split_once(':') {
+        None => (None, name),
+        Some((opts, crate_name)) => {
+            if unstable_opts.namespaced_crates && crate_name.starts_with(':') {
+                // If the name starts with `:`, we know this was actually something like `foo::bar` and
+                // not a set of options. We can just use the original name as the crate name.
+                (None, name)
+            } else {
+                (Some(opts.to_string()), crate_name.to_string())
+            }
+        }
+    };
+
+    if !valid_crate_name(&crate_name, unstable_opts) {
+        let mut error = early_dcx.early_struct_fatal(format!(
+            "crate name `{crate_name}` passed to `--extern` is not a valid ASCII identifier"
+        ));
+        let adjusted_name = crate_name.replace('-', "_");
+        if is_ascii_ident(&adjusted_name) {
+            #[allow(rustc::diagnostic_outside_of_impl)] // FIXME
+            error
+                .help(format!("consider replacing the dashes with underscores: `{adjusted_name}`"));
+        }
+        return Err(error);
+    }
+
+    Ok(ExternOpt { crate_name, path, options })
+}
+
+fn valid_crate_name(name: &str, unstable_opts: &UnstableOptions) -> bool {
+    match name.split_once("::") {
+        Some((a, b)) if unstable_opts.namespaced_crates => is_ascii_ident(a) && is_ascii_ident(b),
+        Some(_) => false,
+        None => is_ascii_ident(name),
+    }
+}
+
+fn is_ascii_ident(string: &str) -> bool {
+    let mut chars = string.chars();
+    if let Some(start) = chars.next()
+        && (start.is_ascii_alphabetic() || start == '_')
+    {
+        chars.all(|char| char.is_ascii_alphanumeric() || char == '_')
+    } else {
+        false
+    }
+}
diff --git a/compiler/rustc_session/src/config/externs/tests.rs b/compiler/rustc_session/src/config/externs/tests.rs
new file mode 100644
index 00000000000..65448869515
--- /dev/null
+++ b/compiler/rustc_session/src/config/externs/tests.rs
@@ -0,0 +1,92 @@
+use std::path::PathBuf;
+
+use super::split_extern_opt;
+use crate::EarlyDiagCtxt;
+use crate::config::UnstableOptions;
+
+/// Verifies split_extern_opt handles the supported cases.
+#[test]
+fn test_split_extern_opt() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions::default();
+
+    let extern_opt =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, None);
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, None);
+}
+
+/// Tests some invalid cases for split_extern_opt.
+#[test]
+fn test_split_extern_opt_invalid() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions::default();
+
+    // too many `:`s
+    let result = split_extern_opt(&early_dcx, unstable_opts, "priv:noprelude:foo=libbar.rlib");
+    assert!(result.is_err());
+    let _ = result.map_err(|e| e.cancel());
+
+    // can't nest externs without the unstable flag
+    let result = split_extern_opt(&early_dcx, unstable_opts, "noprelude:foo::bar=libbar.rlib");
+    assert!(result.is_err());
+    let _ = result.map_err(|e| e.cancel());
+}
+
+/// Tests some cases for split_extern_opt with nested crates like `foo::bar`.
+#[test]
+fn test_split_extern_opt_nested() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions { namespaced_crates: true, ..Default::default() };
+
+    let extern_opt =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo::bar=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo::bar").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, Some("priv,noprelude".to_string()));
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo::bar=libbar.rlib").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, Some(PathBuf::from("libbar.rlib")));
+    assert_eq!(extern_opt.options, None);
+
+    let extern_opt = split_extern_opt(&early_dcx, unstable_opts, "foo::bar").unwrap();
+    assert_eq!(extern_opt.crate_name, "foo::bar");
+    assert_eq!(extern_opt.path, None);
+    assert_eq!(extern_opt.options, None);
+}
+
+/// Tests some invalid cases for split_extern_opt with nested crates like `foo::bar`.
+#[test]
+fn test_split_extern_opt_nested_invalid() {
+    let early_dcx = EarlyDiagCtxt::new(<_>::default());
+    let unstable_opts = &UnstableOptions { namespaced_crates: true, ..Default::default() };
+
+    // crates can only be nested one deep.
+    let result =
+        split_extern_opt(&early_dcx, unstable_opts, "priv,noprelude:foo::bar::baz=libbar.rlib");
+    assert!(result.is_err());
+    let _ = result.map_err(|e| e.cancel());
+}
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index c70f1500d39..1b0794f79d3 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1956,6 +1956,9 @@ options! {
         "allow the linker to link its default libraries (default: no)"),
     dlltool: Option<PathBuf> = (None, parse_opt_pathbuf, [UNTRACKED],
         "import library generation tool (ignored except when targeting windows-gnu)"),
+    #[rustc_lint_opt_deny_field_access("use `Session::dwarf_version` instead of this field")]
+    dwarf_version: Option<u32> = (None, parse_opt_number, [TRACKED],
+        "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
     embed_bitcode: bool = (true, parse_bool, [TRACKED],
         "emit bitcode in rlibs (default: yes)"),
     extra_filename: String = (String::new(), parse_string, [UNTRACKED],
@@ -2331,6 +2334,8 @@ options! {
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes)"),
+    namespaced_crates: bool = (false, parse_bool, [TRACKED],
+        "allow crates to be namespaced by other crates (default: no)"),
     next_solver: NextSolverConfig = (NextSolverConfig::default(), parse_next_solver_config, [TRACKED],
         "enable and configure the next generation trait solver used by rustc"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],
diff --git a/compiler/rustc_session/src/output.rs b/compiler/rustc_session/src/output.rs
index a24919e434c..46dae9144cd 100644
--- a/compiler/rustc_session/src/output.rs
+++ b/compiler/rustc_session/src/output.rs
@@ -177,6 +177,13 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<C
     // If we're generating a test executable, then ignore all other output
     // styles at all other locations
     if session.opts.test {
+        if !session.target.executables {
+            session.dcx().emit_warn(errors::UnsupportedCrateTypeForTarget {
+                crate_type: CrateType::Executable,
+                target_triple: &session.opts.target_triple,
+            });
+            return Vec::new();
+        }
         return vec![CrateType::Executable];
     }
 
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index fb4a437a487..010ae42c280 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -6,6 +6,8 @@ use std::sync::Arc;
 use std::sync::atomic::AtomicBool;
 use std::{env, fmt, io};
 
+use rand::{RngCore, rng};
+use rustc_data_structures::base_n::{CASE_INSENSITIVE, ToBaseN};
 use rustc_data_structures::flock;
 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::profiling::{SelfProfiler, SelfProfilerRef};
@@ -203,6 +205,14 @@ pub struct Session {
 
     target_filesearch: FileSearch,
     host_filesearch: FileSearch,
+
+    /// A random string generated per invocation of rustc.
+    ///
+    /// This is prepended to all temporary files so that they do not collide
+    /// during concurrent invocations of rustc, or past invocations that were
+    /// preserved with a flag like `-C save-temps`, since these files may be
+    /// hard linked.
+    pub invocation_temp: Option<String>,
 }
 
 #[derive(PartialEq, Eq, PartialOrd, Ord)]
@@ -754,7 +764,11 @@ impl Session {
 
     /// Returns the DWARF version passed on the CLI or the default for the target.
     pub fn dwarf_version(&self) -> u32 {
-        self.opts.unstable_opts.dwarf_version.unwrap_or(self.target.default_dwarf_version)
+        self.opts
+            .cg
+            .dwarf_version
+            .or(self.opts.unstable_opts.dwarf_version)
+            .unwrap_or(self.target.default_dwarf_version)
     }
 
     pub fn stack_protector(&self) -> StackProtector {
@@ -1117,6 +1131,12 @@ pub fn build_session(
     let target_filesearch =
         filesearch::FileSearch::new(&sopts.search_paths, &target_tlib_path, &target);
     let host_filesearch = filesearch::FileSearch::new(&sopts.search_paths, &host_tlib_path, &host);
+
+    let invocation_temp = sopts
+        .incremental
+        .as_ref()
+        .map(|_| rng().next_u32().to_base_fixed_len(CASE_INSENSITIVE).to_string());
+
     let sess = Session {
         target,
         host,
@@ -1140,6 +1160,7 @@ pub fn build_session(
         expanded_args,
         target_filesearch,
         host_filesearch,
+        invocation_temp,
     };
 
     validate_commandline_args_with_session_available(&sess);
@@ -1310,7 +1331,9 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         sess.dcx().emit_err(errors::BranchProtectionRequiresAArch64);
     }
 
-    if let Some(dwarf_version) = sess.opts.unstable_opts.dwarf_version {
+    if let Some(dwarf_version) =
+        sess.opts.cg.dwarf_version.or(sess.opts.unstable_opts.dwarf_version)
+    {
         // DWARF 1 is not supported by LLVM and DWARF 6 is not yet finalized.
         if dwarf_version < 2 || dwarf_version > 5 {
             sess.dcx().emit_err(errors::UnsupportedDwarfVersion { dwarf_version });
diff --git a/compiler/rustc_smir/src/lib.rs b/compiler/rustc_smir/src/lib.rs
index 5d465bca4ee..77e5f3423d1 100644
--- a/compiler/rustc_smir/src/lib.rs
+++ b/compiler/rustc_smir/src/lib.rs
@@ -9,7 +9,6 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![allow(rustc::usage_of_ty_tykind)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
     test(attr(allow(unused_variables), deny(warnings)))
diff --git a/compiler/rustc_smir/src/rustc_internal/internal.rs b/compiler/rustc_smir/src/rustc_internal/internal.rs
index 36b68cc1398..6e13b87c41d 100644
--- a/compiler/rustc_smir/src/rustc_internal/internal.rs
+++ b/compiler/rustc_smir/src/rustc_internal/internal.rs
@@ -491,7 +491,6 @@ impl RustcInternal for Abi {
             Abi::CCmseNonSecureCall => rustc_abi::ExternAbi::CCmseNonSecureCall,
             Abi::CCmseNonSecureEntry => rustc_abi::ExternAbi::CCmseNonSecureEntry,
             Abi::System { unwind } => rustc_abi::ExternAbi::System { unwind },
-            Abi::RustIntrinsic => rustc_abi::ExternAbi::RustIntrinsic,
             Abi::RustCall => rustc_abi::ExternAbi::RustCall,
             Abi::Unadjusted => rustc_abi::ExternAbi::Unadjusted,
             Abi::RustCold => rustc_abi::ExternAbi::RustCold,
diff --git a/compiler/rustc_smir/src/rustc_internal/mod.rs b/compiler/rustc_smir/src/rustc_internal/mod.rs
index a546a44c870..146ba17d14f 100644
--- a/compiler/rustc_smir/src/rustc_internal/mod.rs
+++ b/compiler/rustc_smir/src/rustc_internal/mod.rs
@@ -244,6 +244,7 @@ where
 /// ```ignore(needs-extern-crate)
 /// # extern crate rustc_driver;
 /// # extern crate rustc_interface;
+/// # extern crate rustc_middle;
 /// # #[macro_use]
 /// # extern crate rustc_smir;
 /// # extern crate stable_mir;
@@ -264,6 +265,7 @@ where
 /// ```ignore(needs-extern-crate)
 /// # extern crate rustc_driver;
 /// # extern crate rustc_interface;
+/// # extern crate rustc_middle;
 /// # #[macro_use]
 /// # extern crate rustc_smir;
 /// # extern crate stable_mir;
@@ -328,6 +330,7 @@ macro_rules! run_driver {
         use rustc_driver::{Callbacks, Compilation, run_compiler};
         use rustc_middle::ty::TyCtxt;
         use rustc_interface::interface;
+        use rustc_smir::rustc_internal;
         use stable_mir::CompilerError;
         use std::ops::ControlFlow;
 
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
index 1ba25aa0e97..a757329bcf2 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
@@ -871,7 +871,6 @@ impl<'tcx> Stable<'tcx> for rustc_abi::ExternAbi {
             ExternAbi::CCmseNonSecureCall => Abi::CCmseNonSecureCall,
             ExternAbi::CCmseNonSecureEntry => Abi::CCmseNonSecureEntry,
             ExternAbi::System { unwind } => Abi::System { unwind },
-            ExternAbi::RustIntrinsic => Abi::RustIntrinsic,
             ExternAbi::RustCall => Abi::RustCall,
             ExternAbi::Unadjusted => Abi::Unadjusted,
             ExternAbi::RustCold => Abi::RustCold,
@@ -895,12 +894,21 @@ impl<'tcx> Stable<'tcx> for rustc_session::cstore::ForeignModule {
 impl<'tcx> Stable<'tcx> for ty::AssocKind {
     type T = stable_mir::ty::AssocKind;
 
-    fn stable(&self, _tables: &mut Tables<'_>) -> Self::T {
-        use stable_mir::ty::AssocKind;
-        match self {
-            ty::AssocKind::Const => AssocKind::Const,
-            ty::AssocKind::Fn => AssocKind::Fn,
-            ty::AssocKind::Type => AssocKind::Type,
+    fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
+        use stable_mir::ty::{AssocKind, AssocTypeData};
+        match *self {
+            ty::AssocKind::Const { name } => AssocKind::Const { name: name.to_string() },
+            ty::AssocKind::Fn { name, has_self } => {
+                AssocKind::Fn { name: name.to_string(), has_self }
+            }
+            ty::AssocKind::Type { data } => AssocKind::Type {
+                data: match data {
+                    ty::AssocTypeData::Normal(name) => AssocTypeData::Normal(name.to_string()),
+                    ty::AssocTypeData::Rpitit(rpitit) => {
+                        AssocTypeData::Rpitit(rpitit.stable(tables))
+                    }
+                },
+            },
         }
     }
 }
@@ -923,12 +931,9 @@ impl<'tcx> Stable<'tcx> for ty::AssocItem {
     fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
         stable_mir::ty::AssocItem {
             def_id: tables.assoc_def(self.def_id),
-            name: self.name.to_string(),
             kind: self.kind.stable(tables),
             container: self.container.stable(tables),
             trait_item_def_id: self.trait_item_def_id.map(|did| tables.assoc_def(did)),
-            fn_has_self_parameter: self.fn_has_self_parameter,
-            opt_rpitit_info: self.opt_rpitit_info.map(|rpitit| rpitit.stable(tables)),
         }
     }
 }
diff --git a/compiler/rustc_smir/src/stable_mir/mir/pretty.rs b/compiler/rustc_smir/src/stable_mir/mir/pretty.rs
index 439ebe978e5..8a6be0cd37a 100644
--- a/compiler/rustc_smir/src/stable_mir/mir/pretty.rs
+++ b/compiler/rustc_smir/src/stable_mir/mir/pretty.rs
@@ -22,9 +22,10 @@ impl Display for Ty {
 impl Display for AssocKind {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
-            AssocKind::Fn => write!(f, "method"),
-            AssocKind::Const => write!(f, "associated const"),
-            AssocKind::Type => write!(f, "associated type"),
+            AssocKind::Fn { has_self: true, .. } => write!(f, "method"),
+            AssocKind::Fn { has_self: false, .. } => write!(f, "associated function"),
+            AssocKind::Const { .. } => write!(f, "associated const"),
+            AssocKind::Type { .. } => write!(f, "associated type"),
         }
     }
 }
diff --git a/compiler/rustc_smir/src/stable_mir/ty.rs b/compiler/rustc_smir/src/stable_mir/ty.rs
index 1efa2fe13c5..4b153007bd8 100644
--- a/compiler/rustc_smir/src/stable_mir/ty.rs
+++ b/compiler/rustc_smir/src/stable_mir/ty.rs
@@ -1093,7 +1093,6 @@ pub enum Abi {
     CCmseNonSecureCall,
     CCmseNonSecureEntry,
     System { unwind: bool },
-    RustIntrinsic,
     RustCall,
     Unadjusted,
     RustCold,
@@ -1579,29 +1578,28 @@ crate_def! {
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
 pub struct AssocItem {
     pub def_id: AssocDef,
-    pub name: Symbol,
     pub kind: AssocKind,
     pub container: AssocItemContainer,
 
     /// If this is an item in an impl of a trait then this is the `DefId` of
     /// the associated item on the trait that this implements.
     pub trait_item_def_id: Option<AssocDef>,
+}
 
-    /// Whether this is a method with an explicit self
-    /// as its first parameter, allowing method calls.
-    pub fn_has_self_parameter: bool,
-
-    /// `Some` if the associated item (an associated type) comes from the
-    /// return-position `impl Trait` in trait desugaring. The `ImplTraitInTraitData`
-    /// provides additional information about its source.
-    pub opt_rpitit_info: Option<ImplTraitInTraitData>,
+#[derive(Clone, PartialEq, Debug, Eq, Serialize)]
+pub enum AssocTypeData {
+    Normal(Symbol),
+    /// The associated type comes from an RPITIT. It has no name, and the
+    /// `ImplTraitInTraitData` provides additional information about its
+    /// source.
+    Rpitit(ImplTraitInTraitData),
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
 pub enum AssocKind {
-    Const,
-    Fn,
-    Type,
+    Const { name: Symbol },
+    Fn { name: Symbol, has_self: bool },
+    Type { data: AssocTypeData },
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
@@ -1618,6 +1616,6 @@ pub enum ImplTraitInTraitData {
 
 impl AssocItem {
     pub fn is_impl_trait_in_trait(&self) -> bool {
-        self.opt_rpitit_info.is_some()
+        matches!(self.kind, AssocKind::Type { data: AssocTypeData::Rpitit(_) })
     }
 }
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index 9be16f8ce0c..d1da68ec236 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -56,44 +56,33 @@ impl !PartialOrd for SyntaxContext {}
 
 /// If this part of two syntax contexts is equal, then the whole syntax contexts should be equal.
 /// The other fields are only for caching.
-type SyntaxContextKey = (SyntaxContext, ExpnId, Transparency);
+pub type SyntaxContextKey = (SyntaxContext, ExpnId, Transparency);
 
 #[derive(Clone, Copy, Debug)]
 struct SyntaxContextData {
     outer_expn: ExpnId,
     outer_transparency: Transparency,
     parent: SyntaxContext,
-    /// This context, but with all transparent and semi-transparent expansions filtered away.
+    /// This context, but with all transparent and semi-opaque expansions filtered away.
     opaque: SyntaxContext,
     /// This context, but with all transparent expansions filtered away.
-    opaque_and_semitransparent: SyntaxContext,
+    opaque_and_semiopaque: SyntaxContext,
     /// Name of the crate to which `$crate` with this context would resolve.
     dollar_crate_name: Symbol,
 }
 
-/// Same as `SyntaxContextData`, but `opaque(_and_semitransparent)` cannot be recursive
-/// and use `None` if they need to refer to self. Used for encoding and decoding metadata.
-#[derive(Encodable, Decodable)]
-pub struct SyntaxContextDataNonRecursive {
-    outer_expn: ExpnId,
-    outer_transparency: Transparency,
-    parent: SyntaxContext,
-    opaque: Option<SyntaxContext>,
-    opaque_and_semitransparent: Option<SyntaxContext>,
-}
-
 impl SyntaxContextData {
     fn new(
         (parent, outer_expn, outer_transparency): SyntaxContextKey,
         opaque: SyntaxContext,
-        opaque_and_semitransparent: SyntaxContext,
+        opaque_and_semiopaque: SyntaxContext,
     ) -> SyntaxContextData {
         SyntaxContextData {
             outer_expn,
             outer_transparency,
             parent,
             opaque,
-            opaque_and_semitransparent,
+            opaque_and_semiopaque,
             dollar_crate_name: kw::DollarCrate,
         }
     }
@@ -104,7 +93,7 @@ impl SyntaxContextData {
             outer_transparency: Transparency::Opaque,
             parent: SyntaxContext::root(),
             opaque: SyntaxContext::root(),
-            opaque_and_semitransparent: SyntaxContext::root(),
+            opaque_and_semiopaque: SyntaxContext::root(),
             dollar_crate_name: kw::DollarCrate,
         }
     }
@@ -122,19 +111,6 @@ impl SyntaxContextData {
     }
 }
 
-impl SyntaxContextDataNonRecursive {
-    fn recursive(&self, ctxt: SyntaxContext) -> SyntaxContextData {
-        SyntaxContextData {
-            outer_expn: self.outer_expn,
-            outer_transparency: self.outer_transparency,
-            parent: self.parent,
-            opaque: self.opaque.unwrap_or(ctxt),
-            opaque_and_semitransparent: self.opaque_and_semitransparent.unwrap_or(ctxt),
-            dollar_crate_name: kw::DollarCrate,
-        }
-    }
-}
-
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
     #[orderable]
@@ -228,13 +204,13 @@ pub enum Transparency {
     /// Identifier produced by a transparent expansion is always resolved at call-site.
     /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
     Transparent,
-    /// Identifier produced by a semi-transparent expansion may be resolved
+    /// Identifier produced by a semi-opaque expansion may be resolved
     /// either at call-site or at definition-site.
     /// If it's a local variable, label or `$crate` then it's resolved at def-site.
     /// Otherwise it's resolved at call-site.
     /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
     /// but that's an implementation detail.
-    SemiTransparent,
+    SemiOpaque,
     /// Identifier produced by an opaque expansion is always resolved at definition-site.
     /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
     Opaque,
@@ -242,7 +218,7 @@ pub enum Transparency {
 
 impl Transparency {
     pub fn fallback(macro_rules: bool) -> Self {
-        if macro_rules { Transparency::SemiTransparent } else { Transparency::Opaque }
+        if macro_rules { Transparency::SemiOpaque } else { Transparency::Opaque }
     }
 }
 
@@ -490,7 +466,7 @@ impl HygieneData {
 
     fn normalize_to_macro_rules(&self, ctxt: SyntaxContext) -> SyntaxContext {
         debug_assert!(!self.syntax_context_data[ctxt.0 as usize].is_decode_placeholder());
-        self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
+        self.syntax_context_data[ctxt.0 as usize].opaque_and_semiopaque
     }
 
     fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
@@ -583,7 +559,7 @@ impl HygieneData {
         }
 
         let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
-        let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
+        let mut call_site_ctxt = if transparency == Transparency::SemiOpaque {
             self.normalize_to_macros_2_0(call_site_ctxt)
         } else {
             self.normalize_to_macro_rules(call_site_ctxt)
@@ -629,48 +605,34 @@ impl HygieneData {
         self.syntax_context_data.push(SyntaxContextData::decode_placeholder());
         self.syntax_context_map.insert(key, ctxt);
 
-        // Opaque and semi-transparent versions of the parent. Note that they may be equal to the
+        // Opaque and semi-opaque versions of the parent. Note that they may be equal to the
         // parent itself. E.g. `parent_opaque` == `parent` if the expn chain contains only opaques,
-        // and `parent_opaque_and_semitransparent` == `parent` if the expn contains only opaques
-        // and semi-transparents.
+        // and `parent_opaque_and_semiopaque` == `parent` if the expn contains only (semi-)opaques.
         let parent_opaque = self.syntax_context_data[parent.0 as usize].opaque;
-        let parent_opaque_and_semitransparent =
-            self.syntax_context_data[parent.0 as usize].opaque_and_semitransparent;
+        let parent_opaque_and_semiopaque =
+            self.syntax_context_data[parent.0 as usize].opaque_and_semiopaque;
 
-        // Evaluate opaque and semi-transparent versions of the new syntax context.
-        let (opaque, opaque_and_semitransparent) = match transparency {
-            Transparency::Transparent => (parent_opaque, parent_opaque_and_semitransparent),
-            Transparency::SemiTransparent => (
+        // Evaluate opaque and semi-opaque versions of the new syntax context.
+        let (opaque, opaque_and_semiopaque) = match transparency {
+            Transparency::Transparent => (parent_opaque, parent_opaque_and_semiopaque),
+            Transparency::SemiOpaque => (
                 parent_opaque,
-                // Will be the same as `ctxt` if the expn chain contains only opaques and semi-transparents.
-                self.alloc_ctxt(parent_opaque_and_semitransparent, expn_id, transparency),
+                // Will be the same as `ctxt` if the expn chain contains only (semi-)opaques.
+                self.alloc_ctxt(parent_opaque_and_semiopaque, expn_id, transparency),
             ),
             Transparency::Opaque => (
                 // Will be the same as `ctxt` if the expn chain contains only opaques.
                 self.alloc_ctxt(parent_opaque, expn_id, transparency),
-                // Will be the same as `ctxt` if the expn chain contains only opaques and semi-transparents.
-                self.alloc_ctxt(parent_opaque_and_semitransparent, expn_id, transparency),
+                // Will be the same as `ctxt` if the expn chain contains only (semi-)opaques.
+                self.alloc_ctxt(parent_opaque_and_semiopaque, expn_id, transparency),
             ),
         };
 
         // Fill the full data, now that we have it.
         self.syntax_context_data[ctxt.as_u32() as usize] =
-            SyntaxContextData::new(key, opaque, opaque_and_semitransparent);
+            SyntaxContextData::new(key, opaque, opaque_and_semiopaque);
         ctxt
     }
-
-    fn non_recursive_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContextDataNonRecursive {
-        debug_assert!(!self.syntax_context_data[ctxt.0 as usize].is_decode_placeholder());
-        let data = &self.syntax_context_data[ctxt.0 as usize];
-        SyntaxContextDataNonRecursive {
-            outer_expn: data.outer_expn,
-            outer_transparency: data.outer_transparency,
-            parent: data.parent,
-            opaque: (data.opaque != ctxt).then_some(data.opaque),
-            opaque_and_semitransparent: (data.opaque_and_semitransparent != ctxt)
-                .then_some(data.opaque_and_semitransparent),
-        }
-    }
 }
 
 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
@@ -1300,7 +1262,7 @@ impl HygieneEncodeContext {
     pub fn encode<T>(
         &self,
         encoder: &mut T,
-        mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextDataNonRecursive),
+        mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextKey),
         mut encode_expn: impl FnMut(&mut T, ExpnId, &ExpnData, ExpnHash),
     ) {
         // When we serialize a `SyntaxContextData`, we may end up serializing
@@ -1425,10 +1387,7 @@ pub fn decode_expn_id(
 // to track which `SyntaxContext`s we have already decoded.
 // The provided closure will be invoked to deserialize a `SyntaxContextData`
 // if we haven't already seen the id of the `SyntaxContext` we are deserializing.
-pub fn decode_syntax_context<
-    D: Decoder,
-    F: FnOnce(&mut D, u32) -> SyntaxContextDataNonRecursive,
->(
+pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContextKey>(
     d: &mut D,
     context: &HygieneDecodeContext,
     decode_data: F,
@@ -1450,16 +1409,9 @@ pub fn decode_syntax_context<
 
     // Don't try to decode data while holding the lock, since we need to
     // be able to recursively decode a SyntaxContext
-    let ctxt_data = decode_data(d, raw_id);
-
-    let ctxt = HygieneData::with(|hygiene_data| {
-        let ctxt_key = (ctxt_data.parent, ctxt_data.outer_expn, ctxt_data.outer_transparency);
-        *hygiene_data.syntax_context_map.entry(ctxt_key).or_insert_with(|| {
-            let ctxt = SyntaxContext::from_usize(hygiene_data.syntax_context_data.len());
-            hygiene_data.syntax_context_data.push(ctxt_data.recursive(ctxt));
-            ctxt
-        })
-    });
+    let (parent, expn_id, transparency) = decode_data(d, raw_id);
+    let ctxt =
+        HygieneData::with(|hygiene_data| hygiene_data.alloc_ctxt(parent, expn_id, transparency));
 
     let mut inner = context.inner.lock();
     let new_len = raw_id as usize + 1;
@@ -1471,12 +1423,21 @@ pub fn decode_syntax_context<
     ctxt
 }
 
-fn for_all_ctxts_in<F: FnMut(u32, SyntaxContext, &SyntaxContextDataNonRecursive)>(
+fn for_all_ctxts_in<F: FnMut(u32, SyntaxContext, &SyntaxContextKey)>(
     ctxts: impl Iterator<Item = SyntaxContext>,
     mut f: F,
 ) {
-    let all_data: Vec<_> =
-        HygieneData::with(|data| ctxts.map(|ctxt| (ctxt, data.non_recursive_ctxt(ctxt))).collect());
+    let all_data: Vec<_> = HygieneData::with(|data| {
+        ctxts
+            .map(|ctxt| {
+                (ctxt, {
+                    let item = data.syntax_context_data[ctxt.0 as usize];
+                    debug_assert!(!item.is_decode_placeholder());
+                    item.key()
+                })
+            })
+            .collect()
+    });
     for (ctxt, data) in all_data.into_iter() {
         f(ctxt.0, ctxt, &data);
     }
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 9e6ba2e1b9c..f788fd48037 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -116,9 +116,13 @@ pub struct SessionGlobals {
 }
 
 impl SessionGlobals {
-    pub fn new(edition: Edition, sm_inputs: Option<SourceMapInputs>) -> SessionGlobals {
+    pub fn new(
+        edition: Edition,
+        extra_symbols: &[&'static str],
+        sm_inputs: Option<SourceMapInputs>,
+    ) -> SessionGlobals {
         SessionGlobals {
-            symbol_interner: symbol::Interner::fresh(),
+            symbol_interner: symbol::Interner::with_extra_symbols(extra_symbols),
             span_interner: Lock::new(span_encoding::SpanInterner::default()),
             metavar_spans: Default::default(),
             hygiene_data: Lock::new(hygiene::HygieneData::new(edition)),
@@ -129,6 +133,7 @@ impl SessionGlobals {
 
 pub fn create_session_globals_then<R>(
     edition: Edition,
+    extra_symbols: &[&'static str],
     sm_inputs: Option<SourceMapInputs>,
     f: impl FnOnce() -> R,
 ) -> R {
@@ -137,7 +142,7 @@ pub fn create_session_globals_then<R>(
         "SESSION_GLOBALS should never be overwritten! \
          Use another thread if you need another SessionGlobals"
     );
-    let session_globals = SessionGlobals::new(edition, sm_inputs);
+    let session_globals = SessionGlobals::new(edition, extra_symbols, sm_inputs);
     SESSION_GLOBALS.set(&session_globals, f)
 }
 
@@ -156,7 +161,7 @@ where
     F: FnOnce(&SessionGlobals) -> R,
 {
     if !SESSION_GLOBALS.is_set() {
-        let session_globals = SessionGlobals::new(edition, None);
+        let session_globals = SessionGlobals::new(edition, &[], None);
         SESSION_GLOBALS.set(&session_globals, || SESSION_GLOBALS.with(f))
     } else {
         SESSION_GLOBALS.with(f)
@@ -172,7 +177,7 @@ where
 
 /// Default edition, no source map.
 pub fn create_default_session_globals_then<R>(f: impl FnOnce() -> R) -> R {
-    create_session_globals_then(edition::DEFAULT_EDITION, None, f)
+    create_session_globals_then(edition::DEFAULT_EDITION, &[], None, f)
 }
 
 // If this ever becomes non thread-local, `decode_syntax_context`
@@ -1112,7 +1117,7 @@ impl Span {
     /// Equivalent of `Span::mixed_site` from the proc macro API,
     /// except that the location is taken from the `self` span.
     pub fn with_mixed_site_ctxt(self, expn_id: ExpnId) -> Span {
-        self.with_ctxt_from_mark(expn_id, Transparency::SemiTransparent)
+        self.with_ctxt_from_mark(expn_id, Transparency::SemiOpaque)
     }
 
     /// Produces a span with the same location as `self` and context produced by a macro with the
diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index 6fdf8e46fec..0273bb040f4 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -633,6 +633,24 @@ impl SourceMap {
         sp
     }
 
+    /// Extends the given `Span` to just before the previous occurrence of `c`. Return the same span
+    /// if an error occurred while retrieving the code snippet.
+    pub fn span_extend_to_prev_char_before(
+        &self,
+        sp: Span,
+        c: char,
+        accept_newlines: bool,
+    ) -> Span {
+        if let Ok(prev_source) = self.span_to_prev_source(sp) {
+            let prev_source = prev_source.rsplit(c).next().unwrap_or("");
+            if accept_newlines || !prev_source.contains('\n') {
+                return sp.with_lo(BytePos(sp.lo().0 - prev_source.len() as u32 - 1_u32));
+            }
+        }
+
+        sp
+    }
+
     /// Extends the given `Span` to just after the previous occurrence of `pat` when surrounded by
     /// whitespace. Returns None if the pattern could not be found or if an error occurred while
     /// retrieving the code snippet.
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 31847ae3b46..f7b10d3c529 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -454,6 +454,7 @@ symbols! {
         and_then,
         anon,
         anon_adt,
+        anon_assoc,
         anonymous_lifetime_in_impl_trait,
         any,
         append_const_msg,
@@ -915,6 +916,7 @@ symbols! {
         expf16,
         expf32,
         expf64,
+        explicit_extern_abis,
         explicit_generic_args_with_impl_trait,
         explicit_tail_calls,
         export_name,
@@ -1067,7 +1069,6 @@ symbols! {
         ge,
         gen_blocks,
         gen_future,
-        gen_kill,
         generator_clone,
         generators,
         generic_arg_infer,
@@ -1185,6 +1186,7 @@ symbols! {
         instruction_set,
         integer_: "integer", // underscore to avoid clashing with the function `sym::integer` below
         integral,
+        internal_features,
         into_async_iter_into_iter,
         into_future,
         into_iter,
@@ -1399,6 +1401,7 @@ symbols! {
         naked,
         naked_asm,
         naked_functions,
+        naked_functions_rustic_abi,
         naked_functions_target_feature,
         name,
         names,
@@ -1881,6 +1884,7 @@ symbols! {
         select_unpredictable,
         self_in_typedefs,
         self_struct_ctor,
+        semiopaque,
         semitransparent,
         sha2,
         sha3,
@@ -1913,6 +1917,7 @@ symbols! {
         simd_eq,
         simd_expose_provenance,
         simd_extract,
+        simd_extract_dyn,
         simd_fabs,
         simd_fcos,
         simd_fexp,
@@ -1931,6 +1936,7 @@ symbols! {
         simd_ge,
         simd_gt,
         simd_insert,
+        simd_insert_dyn,
         simd_le,
         simd_lt,
         simd_masked_load,
@@ -2211,7 +2217,8 @@ symbols! {
         unsafe_extern_blocks,
         unsafe_fields,
         unsafe_no_drop_flag,
-        unsafe_pin_internals,
+        unsafe_pinned,
+        unsafe_unpin,
         unsize,
         unsized_const_param_ty,
         unsized_const_params,
@@ -2538,15 +2545,10 @@ rustc_index::newtype_index! {
 }
 
 impl Symbol {
-    const fn new(n: u32) -> Self {
+    pub const fn new(n: u32) -> Self {
         Symbol(SymbolIndex::from_u32(n))
     }
 
-    /// for use in Decoder only
-    pub fn new_from_decoded(n: u32) -> Self {
-        Self::new(n)
-    }
-
     /// Maps a string to its interned representation.
     #[rustc_diagnostic_item = "SymbolIntern"]
     pub fn intern(string: &str) -> Self {
@@ -2632,11 +2634,14 @@ struct InternerInner {
 }
 
 impl Interner {
-    fn prefill(init: &[&'static str]) -> Self {
-        Interner(Lock::new(InternerInner {
-            arena: Default::default(),
-            strings: init.iter().copied().collect(),
-        }))
+    fn prefill(init: &[&'static str], extra: &[&'static str]) -> Self {
+        let strings = FxIndexSet::from_iter(init.iter().copied().chain(extra.iter().copied()));
+        assert_eq!(
+            strings.len(),
+            init.len() + extra.len(),
+            "`init` or `extra` contain duplicate symbols",
+        );
+        Interner(Lock::new(InternerInner { arena: Default::default(), strings }))
     }
 
     #[inline]
@@ -2760,9 +2765,9 @@ impl Symbol {
         self != kw::Empty && self != kw::Underscore && !self.is_path_segment_keyword()
     }
 
-    /// Is this symbol was interned in compiler's `symbols!` macro
-    pub fn is_preinterned(self) -> bool {
-        self.as_u32() < PREINTERNED_SYMBOLS_COUNT
+    /// Was this symbol predefined in the compiler's `symbols!` macro
+    pub fn is_predefined(self) -> bool {
+        self.as_u32() < PREDEFINED_SYMBOLS_COUNT
     }
 }
 
diff --git a/compiler/rustc_span/src/symbol/tests.rs b/compiler/rustc_span/src/symbol/tests.rs
index c6aa7627b2b..660d0d7179a 100644
--- a/compiler/rustc_span/src/symbol/tests.rs
+++ b/compiler/rustc_span/src/symbol/tests.rs
@@ -3,7 +3,7 @@ use crate::create_default_session_globals_then;
 
 #[test]
 fn interner_tests() {
-    let i = Interner::prefill(&[]);
+    let i = Interner::prefill(&[], &[]);
     // first one is zero:
     assert_eq!(i.intern("dog"), Symbol::new(0));
     // re-use gets the same entry:
diff --git a/compiler/rustc_symbol_mangling/src/lib.rs b/compiler/rustc_symbol_mangling/src/lib.rs
index c9b15151a2c..cc33974cc62 100644
--- a/compiler/rustc_symbol_mangling/src/lib.rs
+++ b/compiler/rustc_symbol_mangling/src/lib.rs
@@ -89,7 +89,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(let_chains)]
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index 99d44bcd7eb..f310aa65500 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -368,7 +368,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
     }
 
     fn print_region(&mut self, region: ty::Region<'_>) -> Result<(), PrintError> {
-        let i = match *region {
+        let i = match region.kind() {
             // Erased lifetimes use the index 0, for a
             // shorter mangling of `L_`.
             ty::ReErased => 0,
@@ -615,7 +615,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
                         cx.print_def_path(trait_ref.def_id, trait_ref.args)?;
                     }
                     ty::ExistentialPredicate::Projection(projection) => {
-                        let name = cx.tcx.associated_item(projection.def_id).name;
+                        let name = cx.tcx.associated_item(projection.def_id).name();
                         cx.push("p");
                         cx.push_ident(name.as_str());
                         match projection.term.unpack() {
@@ -776,7 +776,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
                                     self.push_disambiguator(
                                         disambiguated_field.disambiguator as u64,
                                     );
-                                    self.push_ident(field_name.unwrap_or(kw::Empty).as_str());
+                                    self.push_ident(field_name.unwrap().as_str());
 
                                     field.print(self)?;
                                 }
@@ -858,7 +858,8 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
             | DefPathData::GlobalAsm
             | DefPathData::Impl
             | DefPathData::MacroNs(_)
-            | DefPathData::LifetimeNs(_) => {
+            | DefPathData::LifetimeNs(_)
+            | DefPathData::AnonAssocTy => {
                 bug!("symbol_names: unexpected DefPathData: {:?}", disambiguated_data.data)
             }
         };
diff --git a/compiler/rustc_target/src/callconv/loongarch.rs b/compiler/rustc_target/src/callconv/loongarch.rs
index 209d7483e61..c779720f97b 100644
--- a/compiler/rustc_target/src/callconv/loongarch.rs
+++ b/compiler/rustc_target/src/callconv/loongarch.rs
@@ -1,6 +1,6 @@
 use rustc_abi::{
-    BackendRepr, ExternAbi, FieldsShape, HasDataLayout, Primitive, Reg, RegKind, Size,
-    TyAbiInterface, TyAndLayout, Variants,
+    BackendRepr, FieldsShape, HasDataLayout, Primitive, Reg, RegKind, Size, TyAbiInterface,
+    TyAndLayout, Variants,
 };
 
 use crate::callconv::{ArgAbi, ArgExtension, CastTarget, FnAbi, PassMode, Uniform};
@@ -364,15 +364,11 @@ where
     }
 }
 
-pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>, abi: ExternAbi)
+pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
 {
-    if abi == ExternAbi::RustIntrinsic {
-        return;
-    }
-
     let grlen = cx.data_layout().pointer_size.bits();
 
     for arg in fn_abi.args.iter_mut() {
diff --git a/compiler/rustc_target/src/callconv/mod.rs b/compiler/rustc_target/src/callconv/mod.rs
index 55e39d093e2..7ecc46cc69d 100644
--- a/compiler/rustc_target/src/callconv/mod.rs
+++ b/compiler/rustc_target/src/callconv/mod.rs
@@ -717,16 +717,16 @@ impl<'a, Ty> FnAbi<'a, Ty> {
         }
     }
 
-    pub fn adjust_for_rust_abi<C>(&mut self, cx: &C, abi: ExternAbi)
+    pub fn adjust_for_rust_abi<C>(&mut self, cx: &C)
     where
         Ty: TyAbiInterface<'a, C> + Copy,
         C: HasDataLayout + HasTargetSpec,
     {
         let spec = cx.target_spec();
         match &*spec.arch {
-            "x86" => x86::compute_rust_abi_info(cx, self, abi),
-            "riscv32" | "riscv64" => riscv::compute_rust_abi_info(cx, self, abi),
-            "loongarch64" => loongarch::compute_rust_abi_info(cx, self, abi),
+            "x86" => x86::compute_rust_abi_info(cx, self),
+            "riscv32" | "riscv64" => riscv::compute_rust_abi_info(cx, self),
+            "loongarch64" => loongarch::compute_rust_abi_info(cx, self),
             "aarch64" => aarch64::compute_rust_abi_info(cx, self),
             _ => {}
         };
@@ -850,10 +850,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
                     //
                     // Note that the intrinsic ABI is exempt here as those are not
                     // real functions anyway, and the backend expects very specific types.
-                    if abi != ExternAbi::RustIntrinsic
-                        && spec.simd_types_indirect
-                        && !can_pass_simd_directly(arg)
-                    {
+                    if spec.simd_types_indirect && !can_pass_simd_directly(arg) {
                         arg.make_indirect();
                     }
                 }
diff --git a/compiler/rustc_target/src/callconv/riscv.rs b/compiler/rustc_target/src/callconv/riscv.rs
index 7368e225efa..cd1d3cd1eee 100644
--- a/compiler/rustc_target/src/callconv/riscv.rs
+++ b/compiler/rustc_target/src/callconv/riscv.rs
@@ -5,8 +5,8 @@
 // https://github.com/llvm/llvm-project/blob/8e780252a7284be45cf1ba224cabd884847e8e92/clang/lib/CodeGen/TargetInfo.cpp#L9311-L9773
 
 use rustc_abi::{
-    BackendRepr, ExternAbi, FieldsShape, HasDataLayout, Primitive, Reg, RegKind, Size,
-    TyAbiInterface, TyAndLayout, Variants,
+    BackendRepr, FieldsShape, HasDataLayout, Primitive, Reg, RegKind, Size, TyAbiInterface,
+    TyAndLayout, Variants,
 };
 
 use crate::callconv::{ArgAbi, ArgExtension, CastTarget, FnAbi, PassMode, Uniform};
@@ -370,15 +370,11 @@ where
     }
 }
 
-pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>, abi: ExternAbi)
+pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
 {
-    if abi == ExternAbi::RustIntrinsic {
-        return;
-    }
-
     let xlen = cx.data_layout().pointer_size.bits();
 
     for arg in fn_abi.args.iter_mut() {
diff --git a/compiler/rustc_target/src/callconv/x86.rs b/compiler/rustc_target/src/callconv/x86.rs
index ba3c1406211..8328f818f9b 100644
--- a/compiler/rustc_target/src/callconv/x86.rs
+++ b/compiler/rustc_target/src/callconv/x86.rs
@@ -1,6 +1,6 @@
 use rustc_abi::{
-    AddressSpace, Align, BackendRepr, ExternAbi, HasDataLayout, Primitive, Reg, RegKind,
-    TyAbiInterface, TyAndLayout,
+    AddressSpace, Align, BackendRepr, HasDataLayout, Primitive, Reg, RegKind, TyAbiInterface,
+    TyAndLayout,
 };
 
 use crate::callconv::{ArgAttribute, FnAbi, PassMode};
@@ -193,7 +193,7 @@ pub(crate) fn fill_inregs<'a, Ty, C>(
     }
 }
 
-pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>, abi: ExternAbi)
+pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
@@ -201,10 +201,7 @@ where
     // Avoid returning floats in x87 registers on x86 as loading and storing from x87
     // registers will quiet signalling NaNs. Also avoid using SSE registers since they
     // are not always available (depending on target features).
-    if !fn_abi.ret.is_ignore()
-        // Intrinsics themselves are not "real" functions, so theres no need to change their ABIs.
-        && abi != ExternAbi::RustIntrinsic
-    {
+    if !fn_abi.ret.is_ignore() {
         let has_float = match fn_abi.ret.layout.backend_repr {
             BackendRepr::Scalar(s) => matches!(s.primitive(), Primitive::Float(_)),
             BackendRepr::ScalarPair(s1, s2) => {
diff --git a/compiler/rustc_target/src/spec/base/lynxos178.rs b/compiler/rustc_target/src/spec/base/lynxos178.rs
new file mode 100644
index 00000000000..b9434ff5faa
--- /dev/null
+++ b/compiler/rustc_target/src/spec/base/lynxos178.rs
@@ -0,0 +1,31 @@
+use std::borrow::Cow;
+
+use crate::spec::{
+    PanicStrategy, RelocModel, RelroLevel, SplitDebuginfo, StackProbeType, TargetOptions, cvs,
+};
+
+pub(crate) fn opts() -> TargetOptions {
+    TargetOptions {
+        os: "lynxos178".into(),
+        dynamic_linking: false,
+        families: cvs!["unix"],
+        position_independent_executables: false,
+        static_position_independent_executables: false,
+        relro_level: RelroLevel::Full,
+        has_thread_local: false,
+        crt_static_respected: true,
+        panic_strategy: PanicStrategy::Abort,
+        linker: Some(Cow::Borrowed("x86_64-lynx-lynxos178-gcc")),
+        no_default_libraries: false,
+        eh_frame_header: false, // GNU ld (GNU Binutils) 2.37.50 does not support --eh-frame-hdr
+        max_atomic_width: Some(64),
+        supported_split_debuginfo: Cow::Borrowed(&[
+            SplitDebuginfo::Packed,
+            SplitDebuginfo::Unpacked,
+            SplitDebuginfo::Off,
+        ]),
+        relocation_model: RelocModel::Static,
+        stack_probes: StackProbeType::Inline,
+        ..Default::default()
+    }
+}
diff --git a/compiler/rustc_target/src/spec/base/mod.rs b/compiler/rustc_target/src/spec/base/mod.rs
index 71b6528c2dd..b368d93f007 100644
--- a/compiler/rustc_target/src/spec/base/mod.rs
+++ b/compiler/rustc_target/src/spec/base/mod.rs
@@ -19,6 +19,7 @@ pub(crate) mod linux_musl;
 pub(crate) mod linux_ohos;
 pub(crate) mod linux_uclibc;
 pub(crate) mod linux_wasm;
+pub(crate) mod lynxos178;
 pub(crate) mod msvc;
 pub(crate) mod netbsd;
 pub(crate) mod nto_qnx;
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 79f73ef28b3..3c769dad630 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -2078,6 +2078,7 @@ supported_targets! {
     ("riscv32imafc-unknown-nuttx-elf", riscv32imafc_unknown_nuttx_elf),
     ("riscv64imac-unknown-nuttx-elf", riscv64imac_unknown_nuttx_elf),
     ("riscv64gc-unknown-nuttx-elf", riscv64gc_unknown_nuttx_elf),
+    ("x86_64-lynx-lynxos178", x86_64_lynx_lynxos178),
 
     ("x86_64-pc-cygwin", x86_64_pc_cygwin),
 }
@@ -2962,14 +2963,9 @@ impl Target {
     pub fn is_abi_supported(&self, abi: ExternAbi) -> bool {
         use ExternAbi::*;
         match abi {
-            Rust
-            | C { .. }
-            | System { .. }
-            | RustIntrinsic
-            | RustCall
-            | Unadjusted
-            | Cdecl { .. }
-            | RustCold => true,
+            Rust | C { .. } | System { .. } | RustCall | Unadjusted | Cdecl { .. } | RustCold => {
+                true
+            }
             EfiApi => {
                 ["arm", "aarch64", "riscv32", "riscv64", "x86", "x86_64"].contains(&&self.arch[..])
             }
diff --git a/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs b/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs
index 9f02ed4bcbe..b9176c939f8 100644
--- a/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs
+++ b/compiler/rustc_target/src/spec/targets/riscv64_linux_android.rs
@@ -19,7 +19,7 @@ pub(crate) fn target() -> Target {
         options: TargetOptions {
             code_model: Some(CodeModel::Medium),
             cpu: "generic-rv64".into(),
-            features: "+m,+a,+f,+d,+c,+zicsr,+zifencei,+zba,+zbb,+zbs,+v".into(),
+            features: "+m,+a,+f,+d,+c,+b,+v,+zicsr,+zifencei".into(),
             llvm_abiname: "lp64d".into(),
             supported_sanitizers: SanitizerSet::ADDRESS,
             max_atomic_width: Some(64),
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_lynx_lynxos178.rs b/compiler/rustc_target/src/spec/targets/x86_64_lynx_lynxos178.rs
new file mode 100644
index 00000000000..654ae7c9c5b
--- /dev/null
+++ b/compiler/rustc_target/src/spec/targets/x86_64_lynx_lynxos178.rs
@@ -0,0 +1,34 @@
+use crate::spec::{SanitizerSet, StackProbeType, Target, base};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::lynxos178::opts();
+    base.cpu = "x86-64".into();
+    base.plt_by_default = false;
+    base.max_atomic_width = Some(64);
+    base.stack_probes = StackProbeType::Inline;
+    base.static_position_independent_executables = false;
+    base.supported_sanitizers = SanitizerSet::ADDRESS
+        | SanitizerSet::CFI
+        | SanitizerSet::KCFI
+        | SanitizerSet::DATAFLOW
+        | SanitizerSet::LEAK
+        | SanitizerSet::MEMORY
+        | SanitizerSet::SAFESTACK
+        | SanitizerSet::THREAD;
+    base.supports_xray = true;
+
+    Target {
+        llvm_target: "x86_64-unknown-unknown-gnu".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: Some("LynxOS-178".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(false),
+        },
+        pointer_width: 64,
+        data_layout:
+            "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128".into(),
+        arch: "x86_64".into(),
+        options: base,
+    }
+}
diff --git a/compiler/rustc_target/src/target_features.rs b/compiler/rustc_target/src/target_features.rs
index b4ec1879fed..aeace6a40c7 100644
--- a/compiler/rustc_target/src/target_features.rs
+++ b/compiler/rustc_target/src/target_features.rs
@@ -491,7 +491,8 @@ const MIPS_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
 static RISCV_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-start
     ("a", Stable, &["zaamo", "zalrsc"]),
-    ("c", Stable, &[]),
+    ("b", Unstable(sym::riscv_target_feature), &["zba", "zbb", "zbs"]),
+    ("c", Stable, &["zca"]),
     ("d", Unstable(sym::riscv_target_feature), &["f"]),
     ("e", Unstable(sym::riscv_target_feature), &[]),
     ("f", Unstable(sym::riscv_target_feature), &["zicsr"]),
@@ -520,17 +521,25 @@ static RISCV_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("zbkc", Stable, &[]),
     ("zbkx", Stable, &[]),
     ("zbs", Stable, &[]),
+    ("zca", Unstable(sym::riscv_target_feature), &[]),
+    ("zcb", Unstable(sym::riscv_target_feature), &["zca"]),
+    ("zcmop", Unstable(sym::riscv_target_feature), &["zca"]),
     ("zdinx", Unstable(sym::riscv_target_feature), &["zfinx"]),
+    ("zfa", Unstable(sym::riscv_target_feature), &["f"]),
     ("zfh", Unstable(sym::riscv_target_feature), &["zfhmin"]),
     ("zfhmin", Unstable(sym::riscv_target_feature), &["f"]),
     ("zfinx", Unstable(sym::riscv_target_feature), &["zicsr"]),
     ("zhinx", Unstable(sym::riscv_target_feature), &["zhinxmin"]),
     ("zhinxmin", Unstable(sym::riscv_target_feature), &["zfinx"]),
+    ("zicboz", Unstable(sym::riscv_target_feature), &[]),
     ("zicntr", Unstable(sym::riscv_target_feature), &["zicsr"]),
+    ("zicond", Unstable(sym::riscv_target_feature), &[]),
     ("zicsr", Unstable(sym::riscv_target_feature), &[]),
     ("zifencei", Unstable(sym::riscv_target_feature), &[]),
+    ("zihintntl", Unstable(sym::riscv_target_feature), &[]),
     ("zihintpause", Unstable(sym::riscv_target_feature), &[]),
     ("zihpm", Unstable(sym::riscv_target_feature), &["zicsr"]),
+    ("zimop", Unstable(sym::riscv_target_feature), &[]),
     ("zk", Stable, &["zkn", "zkr", "zkt"]),
     ("zkn", Stable, &["zbkb", "zbkc", "zbkx", "zkne", "zknd", "zknh"]),
     ("zknd", Stable, &[]),
@@ -541,6 +550,7 @@ static RISCV_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("zksed", Stable, &[]),
     ("zksh", Stable, &[]),
     ("zkt", Stable, &[]),
+    ("ztso", Unstable(sym::riscv_target_feature), &[]),
     ("zvbb", Unstable(sym::riscv_target_feature), &["zvkb"]),
     ("zvbc", Unstable(sym::riscv_target_feature), &["zve64x"]),
     ("zve32f", Unstable(sym::riscv_target_feature), &["zve32x", "f"]),
diff --git a/compiler/rustc_trait_selection/messages.ftl b/compiler/rustc_trait_selection/messages.ftl
index 05bbb42fb7c..74e38f525c8 100644
--- a/compiler/rustc_trait_selection/messages.ftl
+++ b/compiler/rustc_trait_selection/messages.ftl
@@ -268,8 +268,8 @@ trait_selection_oc_type_compat = type not compatible with trait
 trait_selection_opaque_captures_lifetime = hidden type for `{$opaque_ty}` captures lifetime that does not appear in bounds
     .label = opaque type defined here
 trait_selection_opaque_type_non_generic_param =
-    expected generic {$kind} parameter, found `{$ty}`
-    .label = {STREQ($ty, "'static") ->
+    expected generic {$kind} parameter, found `{$arg}`
+    .label = {STREQ($arg, "'static") ->
         [true] cannot use static lifetime; use a bound lifetime instead or remove the lifetime parameter from the opaque type
         *[other] this generic parameter must be used with a generic {$kind} parameter
     }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
index 40f8af1f691..fdd547448f0 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
@@ -2334,13 +2334,13 @@ impl<'tcx> ObligationCause<'tcx> {
         subdiags: Vec<TypeErrorAdditionalDiags>,
     ) -> ObligationCauseFailureCode {
         match self.code() {
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Fn, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Fn { .. }, .. } => {
                 ObligationCauseFailureCode::MethodCompat { span, subdiags }
             }
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Type, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Type { .. }, .. } => {
                 ObligationCauseFailureCode::TypeCompat { span, subdiags }
             }
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Const, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Const { .. }, .. } => {
                 ObligationCauseFailureCode::ConstCompat { span, subdiags }
             }
             ObligationCauseCode::BlockTailExpression(.., hir::MatchSource::TryDesugar(_)) => {
@@ -2398,13 +2398,13 @@ impl<'tcx> ObligationCause<'tcx> {
 
     fn as_requirement_str(&self) -> &'static str {
         match self.code() {
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Fn, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Fn { .. }, .. } => {
                 "method type is compatible with trait"
             }
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Type, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Type { .. }, .. } => {
                 "associated type is compatible with trait"
             }
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Const, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Const { .. }, .. } => {
                 "const is compatible with trait"
             }
             ObligationCauseCode::MainFunctionType => "`main` function has the correct type",
@@ -2422,9 +2422,13 @@ pub struct ObligationCauseAsDiagArg<'tcx>(pub ObligationCause<'tcx>);
 impl IntoDiagArg for ObligationCauseAsDiagArg<'_> {
     fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> rustc_errors::DiagArgValue {
         let kind = match self.0.code() {
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Fn, .. } => "method_compat",
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Type, .. } => "type_compat",
-            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Const, .. } => {
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Fn { .. }, .. } => {
+                "method_compat"
+            }
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Type { .. }, .. } => {
+                "type_compat"
+            }
+            ObligationCauseCode::CompareImplItem { kind: ty::AssocKind::Const { .. }, .. } => {
                 "const_compat"
             }
             ObligationCauseCode::MainFunctionType => "fn_main_correct_type",
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs
index 3559c660ee2..eaa06d8e8b0 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs
@@ -6,7 +6,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{Visitor, VisitorExt, walk_ty};
 use rustc_hir::{
     self as hir, AmbigArg, GenericBound, GenericParam, GenericParamKind, Item, ItemKind, Lifetime,
-    LifetimeName, LifetimeParamKind, MissingLifetimeKind, Node, TyKind,
+    LifetimeKind, LifetimeParamKind, MissingLifetimeKind, Node, TyKind,
 };
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
 use rustc_span::def_id::LocalDefId;
@@ -165,7 +165,7 @@ pub fn suggest_new_region_bound(
 
                 if let Some(span) = opaque.bounds.iter().find_map(|arg| match arg {
                     GenericBound::Outlives(Lifetime {
-                        res: LifetimeName::Static, ident, ..
+                        kind: LifetimeKind::Static, ident, ..
                     }) => Some(ident.span),
                     _ => None,
                 }) {
@@ -253,7 +253,7 @@ pub fn suggest_new_region_bound(
                 }
             }
             TyKind::TraitObject(_, lt) => {
-                if let LifetimeName::ImplicitObjectLifetimeDefault = lt.res {
+                if let LifetimeKind::ImplicitObjectLifetimeDefault = lt.kind {
                     err.span_suggestion_verbose(
                         fn_return.span.shrink_to_hi(),
                         format!("{declare} the trait object {captures}, {explicit}",),
@@ -414,7 +414,7 @@ pub struct HirTraitObjectVisitor<'a>(pub &'a mut Vec<Span>, pub DefId);
 impl<'a, 'tcx> Visitor<'tcx> for HirTraitObjectVisitor<'a> {
     fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx, AmbigArg>) {
         if let TyKind::TraitObject(poly_trait_refs, lifetime_ptr) = t.kind
-            && let Lifetime { res: LifetimeName::ImplicitObjectLifetimeDefault, .. } =
+            && let Lifetime { kind: LifetimeKind::ImplicitObjectLifetimeDefault, .. } =
                 lifetime_ptr.pointer()
         {
             for ptr in poly_trait_refs {
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/trait_impl_difference.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/trait_impl_difference.rs
index 74205922851..b66bd2c6ab7 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/trait_impl_difference.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/trait_impl_difference.rs
@@ -98,7 +98,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let assoc_item = self.tcx().associated_item(trait_item_def_id);
         let mut visitor = TypeParamSpanVisitor { tcx: self.tcx(), types: vec![] };
         match assoc_item.kind {
-            ty::AssocKind::Fn => {
+            ty::AssocKind::Fn { .. } => {
                 if let Some(hir_id) =
                     assoc_item.def_id.as_local().map(|id| self.tcx().local_def_id_to_hir_id(id))
                 {
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/util.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/util.rs
index 683b5b528c6..4a71ab4e06a 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/util.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/util.rs
@@ -42,7 +42,7 @@ pub fn find_param_with_region<'tcx>(
     anon_region: Region<'tcx>,
     replace_region: Region<'tcx>,
 ) -> Option<AnonymousParamInfo<'tcx>> {
-    let (id, kind) = match *anon_region {
+    let (id, kind) = match anon_region.kind() {
         ty::ReLateParam(late_param) => (late_param.scope, late_param.kind),
         ty::ReEarlyParam(ebr) => {
             let region_def = tcx.generics_of(generic_param_scope).region_param(ebr, tcx).def_id;
@@ -158,6 +158,6 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             && self
                 .tcx()
                 .opt_associated_item(scope_def_id.to_def_id())
-                .is_some_and(|i| i.fn_has_self_parameter)
+                .is_some_and(|i| i.is_method())
     }
 }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
index 5583deda99a..be508c8cee1 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
@@ -782,8 +782,8 @@ fn foo(&self) -> Self::T { String::new() }
         let methods: Vec<(Span, String)> = items
             .in_definition_order()
             .filter(|item| {
-                ty::AssocKind::Fn == item.kind
-                    && Some(item.name) != current_method_ident
+                item.is_fn()
+                    && Some(item.name()) != current_method_ident
                     && !tcx.is_doc_hidden(item.def_id)
             })
             .filter_map(|item| {
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
index c7f0a88f951..1cf1ac5403f 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
@@ -299,7 +299,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     self.tcx.param_env(generic_param_scope),
                     terr,
                 );
-                match (*sub, *sup) {
+                match (sub.kind(), sup.kind()) {
                     (ty::RePlaceholder(_), ty::RePlaceholder(_)) => {}
                     (ty::RePlaceholder(_), _) => {
                         note_and_explain_region(
@@ -391,7 +391,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 })
             }
             infer::RelateParamBound(span, ty, opt_span) => {
-                let prefix = match *sub {
+                let prefix = match sub.kind() {
                     ty::ReStatic => note_and_explain::PrefixKind::TypeSatisfy,
                     _ => note_and_explain::PrefixKind::TypeOutlive,
                 };
@@ -850,14 +850,14 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         add_lt_suggs: &mut Vec<(Span, String)>,
     ) -> String {
         struct LifetimeReplaceVisitor<'a> {
-            needle: hir::LifetimeName,
+            needle: hir::LifetimeKind,
             new_lt: &'a str,
             add_lt_suggs: &'a mut Vec<(Span, String)>,
         }
 
         impl<'hir> hir::intravisit::Visitor<'hir> for LifetimeReplaceVisitor<'_> {
             fn visit_lifetime(&mut self, lt: &'hir hir::Lifetime) {
-                if lt.res == self.needle {
+                if lt.kind == self.needle {
                     self.add_lt_suggs.push(lt.suggestion(self.new_lt));
                 }
             }
@@ -894,7 +894,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         };
 
         let mut visitor = LifetimeReplaceVisitor {
-            needle: hir::LifetimeName::Param(lifetime_def_id),
+            needle: hir::LifetimeKind::Param(lifetime_def_id),
             add_lt_suggs,
             new_lt: &new_lt,
         };
@@ -967,7 +967,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 format!("...so that the {}", sup_trace.cause.as_requirement_str()),
             );
 
-            err.note_expected_found(&"", sup_expected, &"", sup_found);
+            err.note_expected_found("", sup_expected, "", sup_found);
             return if sub_region.is_error() | sup_region.is_error() {
                 err.delay_as_bug()
             } else {
@@ -1017,7 +1017,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             infer::BoundRegion(_, br, infer::AssocTypeProjection(def_id)) => format!(
                 " for lifetime parameter {}in trait containing associated type `{}`",
                 br_string(br),
-                self.tcx.associated_item(def_id).name
+                self.tcx.associated_item(def_id).name()
             ),
             infer::RegionParameterDefinition(_, name) => {
                 format!(" for lifetime parameter `{name}`")
@@ -1048,7 +1048,7 @@ pub(super) fn note_and_explain_region<'tcx>(
     suffix: &str,
     alt_span: Option<Span>,
 ) {
-    let (description, span) = match *region {
+    let (description, span) = match region.kind() {
         ty::ReEarlyParam(_) | ty::ReLateParam(_) | ty::RePlaceholder(_) | ty::ReStatic => {
             msg_span_from_named_region(tcx, generic_param_scope, region, alt_span)
         }
@@ -1085,7 +1085,7 @@ fn msg_span_from_named_region<'tcx>(
     region: ty::Region<'tcx>,
     alt_span: Option<Span>,
 ) -> (String, Option<Span>) {
-    match *region {
+    match region.kind() {
         ty::ReEarlyParam(br) => {
             let param_def_id = tcx.generics_of(generic_param_scope).region_param(br, tcx).def_id;
             let span = tcx.def_span(param_def_id);
@@ -1185,7 +1185,7 @@ pub fn unexpected_hidden_region_diagnostic<'a, 'tcx>(
     });
 
     // Explain the region we are capturing.
-    match *hidden_region {
+    match hidden_region.kind() {
         ty::ReEarlyParam(_) | ty::ReLateParam(_) | ty::ReStatic => {
             // Assuming regionck succeeded (*), we ought to always be
             // capturing *some* region from the fn header, and hence it
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
index 59c93db9c8f..54b50851b74 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
@@ -348,11 +348,11 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         && let None = self.tainted_by_errors()
                     {
                         let (verb, noun) = match self.tcx.associated_item(item_id).kind {
-                            ty::AssocKind::Const => ("refer to the", "constant"),
-                            ty::AssocKind::Fn => ("call", "function"),
+                            ty::AssocKind::Const { .. } => ("refer to the", "constant"),
+                            ty::AssocKind::Fn { .. } => ("call", "function"),
                             // This is already covered by E0223, but this following single match
                             // arm doesn't hurt here.
-                            ty::AssocKind::Type => ("refer to the", "type"),
+                            ty::AssocKind::Type { .. } => ("refer to the", "type"),
                         };
 
                         // Replace the more general E0283 with a more specific error
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index bc45fc11e9b..5648021f613 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -2,6 +2,7 @@ use core::ops::ControlFlow;
 use std::borrow::Cow;
 use std::path::PathBuf;
 
+use rustc_abi::ExternAbi;
 use rustc_ast::TraitObjectSyntax;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::unord::UnordSet;
@@ -2799,32 +2800,57 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         }
 
         // Note any argument mismatches
-        let given_ty = params.skip_binder();
+        let ty::Tuple(given) = *params.skip_binder().kind() else {
+            return;
+        };
+
         let expected_ty = trait_pred.skip_binder().trait_ref.args.type_at(1);
-        if let ty::Tuple(given) = given_ty.kind()
-            && let ty::Tuple(expected) = expected_ty.kind()
-        {
-            if expected.len() != given.len() {
-                // Note number of types that were expected and given
-                err.note(
-                    format!(
-                        "expected a closure taking {} argument{}, but one taking {} argument{} was given",
-                        given.len(),
-                        pluralize!(given.len()),
-                        expected.len(),
-                        pluralize!(expected.len()),
-                    )
-                );
-            } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
-                // Print type mismatch
-                let (expected_args, given_args) = self.cmp(given_ty, expected_ty);
-                err.note_expected_found(
-                    &"a closure with arguments",
-                    expected_args,
-                    &"a closure with arguments",
-                    given_args,
-                );
-            }
+        let ty::Tuple(expected) = *expected_ty.kind() else {
+            return;
+        };
+
+        if expected.len() != given.len() {
+            // Note number of types that were expected and given
+            err.note(format!(
+                "expected a closure taking {} argument{}, but one taking {} argument{} was given",
+                given.len(),
+                pluralize!(given.len()),
+                expected.len(),
+                pluralize!(expected.len()),
+            ));
+            return;
+        }
+
+        let given_ty = Ty::new_fn_ptr(
+            self.tcx,
+            params.rebind(self.tcx.mk_fn_sig(
+                given,
+                self.tcx.types.unit,
+                false,
+                hir::Safety::Safe,
+                ExternAbi::Rust,
+            )),
+        );
+        let expected_ty = Ty::new_fn_ptr(
+            self.tcx,
+            trait_pred.rebind(self.tcx.mk_fn_sig(
+                expected,
+                self.tcx.types.unit,
+                false,
+                hir::Safety::Safe,
+                ExternAbi::Rust,
+            )),
+        );
+
+        if !self.same_type_modulo_infer(given_ty, expected_ty) {
+            // Print type mismatch
+            let (expected_args, given_args) = self.cmp(expected_ty, given_ty);
+            err.note_expected_found(
+                "a closure with signature",
+                expected_args,
+                "a closure with signature",
+                given_args,
+            );
         }
     }
 
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
index 38fcba4ea62..7d95a7b3fed 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -1988,7 +1988,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         {
             let closure: Vec<_> = self
                 .tcx
-                .fn_arg_names(fn_def_id)
+                .fn_arg_idents(fn_def_id)
                 .iter()
                 .enumerate()
                 .map(|(i, ident)| {
@@ -2112,16 +2112,20 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         trait_ref: DefId,
     ) {
         if let Some(assoc_item) = self.tcx.opt_associated_item(item_def_id) {
-            if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind {
+            if let ty::AssocKind::Const { .. } | ty::AssocKind::Type { .. } = assoc_item.kind {
                 err.note(format!(
                     "{}s cannot be accessed directly on a `trait`, they can only be \
                         accessed through a specific `impl`",
-                    self.tcx.def_kind_descr(assoc_item.kind.as_def_kind(), item_def_id)
+                    self.tcx.def_kind_descr(assoc_item.as_def_kind(), item_def_id)
                 ));
                 err.span_suggestion(
                     span,
                     "use the fully qualified path to an implementation",
-                    format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.name),
+                    format!(
+                        "<Type as {}>::{}",
+                        self.tcx.def_path_str(trait_ref),
+                        assoc_item.name()
+                    ),
                     Applicability::HasPlaceholders,
                 );
             }
@@ -3018,12 +3022,23 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                 [] => span_bug!(ty.span, "trait object with no traits: {ty:?}"),
                             };
                             let needs_parens = traits.len() != 1;
-                            err.span_suggestion_verbose(
-                                span,
-                                "you can use `impl Trait` as the argument type",
-                                "impl ",
-                                Applicability::MaybeIncorrect,
-                            );
+                            // Don't recommend impl Trait as a closure argument
+                            if let Some(hir_id) = hir_id
+                                && matches!(
+                                    self.tcx.parent_hir_node(hir_id),
+                                    hir::Node::Item(hir::Item {
+                                        kind: hir::ItemKind::Fn { .. },
+                                        ..
+                                    })
+                                )
+                            {
+                                err.span_suggestion_verbose(
+                                    span,
+                                    "you can use `impl Trait` as the argument type",
+                                    "impl ",
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
                             let sugg = if !needs_parens {
                                 vec![(span.shrink_to_lo(), format!("&{kw}"))]
                             } else {
@@ -5397,10 +5412,10 @@ fn point_at_assoc_type_restriction<G: EmissionGuarantee>(
                 );
             }
             if let Some(new) =
-                tcx.associated_items(data.impl_or_alias_def_id).find_by_name_and_kind(
+                tcx.associated_items(data.impl_or_alias_def_id).find_by_ident_and_kind(
                     tcx,
                     Ident::with_dummy_span(name),
-                    ty::AssocKind::Type,
+                    ty::AssocTag::Type,
                     data.impl_or_alias_def_id,
                 )
             {
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index 9f7bfe5101a..756d9a57b93 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -4,7 +4,7 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagCtxtHandle, DiagMessage, DiagStyledString, Diagnostic,
-    EmissionGuarantee, IntoDiagArg, Level, MultiSpan, SubdiagMessageOp, Subdiagnostic,
+    EmissionGuarantee, IntoDiagArg, Level, MultiSpan, Subdiagnostic,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -107,11 +107,7 @@ pub enum AdjustSignatureBorrow {
 }
 
 impl Subdiagnostic for AdjustSignatureBorrow {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             AdjustSignatureBorrow::Borrow { to_borrow } => {
                 diag.arg("len", to_borrow.len());
@@ -381,11 +377,7 @@ pub enum RegionOriginNote<'a> {
 }
 
 impl Subdiagnostic for RegionOriginNote<'_> {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut label_or_note = |span, msg: DiagMessage| {
             let sub_count = diag.children.iter().filter(|d| d.span.is_dummy()).count();
             let expanded_sub_count = diag.children.iter().filter(|d| !d.span.is_dummy()).count();
@@ -415,7 +407,7 @@ impl Subdiagnostic for RegionOriginNote<'_> {
                 label_or_note(span, fluent::trait_selection_subtype);
                 diag.arg("requirement", requirement);
 
-                diag.note_expected_found(&"", expected, &"", found);
+                diag.note_expected_found("", expected, "", found);
             }
             RegionOriginNote::WithRequirement { span, requirement, expected_found: None } => {
                 // FIXME: this really should be handled at some earlier stage. Our
@@ -446,11 +438,7 @@ pub enum LifetimeMismatchLabels {
 }
 
 impl Subdiagnostic for LifetimeMismatchLabels {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         match self {
             LifetimeMismatchLabels::InRet { param_span, ret_span, span, label_var1 } => {
                 diag.span_label(param_span, fluent::trait_selection_declared_different);
@@ -495,11 +483,7 @@ pub struct AddLifetimeParamsSuggestion<'a> {
 }
 
 impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut mk_suggestion = || {
             let Some(anon_reg) = self.tcx.is_suitable_region(self.generic_param_scope, self.sub)
             else {
@@ -689,11 +673,7 @@ pub struct IntroducesStaticBecauseUnmetLifetimeReq {
 }
 
 impl Subdiagnostic for IntroducesStaticBecauseUnmetLifetimeReq {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        mut self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(mut self, diag: &mut Diag<'_, G>) {
         self.unmet_requirements
             .push_span_label(self.binding_span, fluent::trait_selection_msl_introduces_static);
         diag.span_note(self.unmet_requirements, fluent::trait_selection_msl_unmet_req);
@@ -1008,17 +988,13 @@ pub struct ConsiderBorrowingParamHelp {
 }
 
 impl Subdiagnostic for ConsiderBorrowingParamHelp {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut type_param_span: MultiSpan = self.spans.clone().into();
         for &span in &self.spans {
             // Seems like we can't call f() here as Into<DiagMessage> is required
             type_param_span.push_span_label(span, fluent::trait_selection_tid_consider_borrowing);
         }
-        let msg = f(diag, fluent::trait_selection_tid_param_help.into());
+        let msg = diag.eagerly_translate(fluent::trait_selection_tid_param_help);
         diag.span_help(type_param_span, msg);
     }
 }
@@ -1053,18 +1029,14 @@ pub struct DynTraitConstraintSuggestion {
 }
 
 impl Subdiagnostic for DynTraitConstraintSuggestion {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let mut multi_span: MultiSpan = vec![self.span].into();
         multi_span.push_span_label(self.span, fluent::trait_selection_dtcs_has_lifetime_req_label);
         multi_span
             .push_span_label(self.ident.span, fluent::trait_selection_dtcs_introduces_requirement);
-        let msg = f(diag, fluent::trait_selection_dtcs_has_req_note.into());
+        let msg = diag.eagerly_translate(fluent::trait_selection_dtcs_has_req_note);
         diag.span_note(multi_span, msg);
-        let msg = f(diag, fluent::trait_selection_dtcs_suggestion.into());
+        let msg = diag.eagerly_translate(fluent::trait_selection_dtcs_suggestion);
         diag.span_suggestion_verbose(
             self.span.shrink_to_hi(),
             msg,
@@ -1101,11 +1073,7 @@ pub struct ReqIntroducedLocations {
 }
 
 impl Subdiagnostic for ReqIntroducedLocations {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        mut self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(mut self, diag: &mut Diag<'_, G>) {
         for sp in self.spans {
             self.span.push_span_label(sp, fluent::trait_selection_ril_introduced_here);
         }
@@ -1114,7 +1082,7 @@ impl Subdiagnostic for ReqIntroducedLocations {
             self.span.push_span_label(self.fn_decl_span, fluent::trait_selection_ril_introduced_by);
         }
         self.span.push_span_label(self.cause_span, fluent::trait_selection_ril_because_of);
-        let msg = f(diag, fluent::trait_selection_ril_static_introduced_by.into());
+        let msg = diag.eagerly_translate(fluent::trait_selection_ril_static_introduced_by);
         diag.span_note(self.span, msg);
     }
 }
@@ -1513,13 +1481,9 @@ pub struct SuggestTuplePatternMany {
 }
 
 impl Subdiagnostic for SuggestTuplePatternMany {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("path", self.path);
-        let message = f(diag, crate::fluent_generated::trait_selection_stp_wrap_many.into());
+        let message = diag.eagerly_translate(fluent::trait_selection_stp_wrap_many);
         diag.multipart_suggestions(
             message,
             self.compatible_variants.into_iter().map(|variant| {
@@ -1752,11 +1716,7 @@ pub struct AddPreciseCapturingAndParams {
 }
 
 impl Subdiagnostic for AddPreciseCapturingAndParams {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("new_lifetime", self.new_lifetime);
         diag.multipart_suggestion_verbose(
             fluent::trait_selection_precise_capturing_new_but_apit,
@@ -1896,11 +1856,7 @@ pub struct AddPreciseCapturingForOvercapture {
 }
 
 impl Subdiagnostic for AddPreciseCapturingForOvercapture {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         let applicability = if self.apit_spans.is_empty() {
             Applicability::MachineApplicable
         } else {
@@ -1926,7 +1882,7 @@ impl Subdiagnostic for AddPreciseCapturingForOvercapture {
 #[derive(Diagnostic)]
 #[diag(trait_selection_opaque_type_non_generic_param, code = E0792)]
 pub(crate) struct NonGenericOpaqueTypeParam<'a, 'tcx> {
-    pub ty: GenericArg<'tcx>,
+    pub arg: GenericArg<'tcx>,
     pub kind: &'a str,
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_trait_selection/src/errors/note_and_explain.rs b/compiler/rustc_trait_selection/src/errors/note_and_explain.rs
index 46622246a17..84e7686fdd3 100644
--- a/compiler/rustc_trait_selection/src/errors/note_and_explain.rs
+++ b/compiler/rustc_trait_selection/src/errors/note_and_explain.rs
@@ -1,4 +1,4 @@
-use rustc_errors::{Diag, EmissionGuarantee, IntoDiagArg, SubdiagMessageOp, Subdiagnostic};
+use rustc_errors::{Diag, EmissionGuarantee, IntoDiagArg, Subdiagnostic};
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::bug;
 use rustc_middle::ty::{self, TyCtxt};
@@ -20,7 +20,7 @@ impl<'a> DescriptionCtx<'a> {
         region: ty::Region<'tcx>,
         alt_span: Option<Span>,
     ) -> Option<Self> {
-        let (span, kind, arg) = match *region {
+        let (span, kind, arg) = match region.kind() {
             ty::ReEarlyParam(br) => {
                 let scope = tcx
                     .parent(tcx.generics_of(generic_param_scope).region_param(br, tcx).def_id)
@@ -162,17 +162,13 @@ impl RegionExplanation<'_> {
 }
 
 impl Subdiagnostic for RegionExplanation<'_> {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        f: &F,
-    ) {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("pref_kind", self.prefix);
         diag.arg("suff_kind", self.suffix);
         diag.arg("desc_kind", self.desc.kind);
         diag.arg("desc_arg", self.desc.arg);
 
-        let msg = f(diag, fluent::trait_selection_region_explanation.into());
+        let msg = diag.eagerly_translate(fluent::trait_selection_region_explanation);
         if let Some(span) = self.desc.span {
             diag.span_note(span, msg);
         } else {
diff --git a/compiler/rustc_trait_selection/src/opaque_types.rs b/compiler/rustc_trait_selection/src/opaque_types.rs
index c7b8f063196..cce67b066dd 100644
--- a/compiler/rustc_trait_selection/src/opaque_types.rs
+++ b/compiler/rustc_trait_selection/src/opaque_types.rs
@@ -46,7 +46,7 @@ pub fn check_opaque_type_parameter_valid<'tcx>(
             GenericArgKind::Lifetime(lt) => match defining_scope_kind {
                 DefiningScopeKind::HirTypeck => continue,
                 DefiningScopeKind::MirBorrowck => {
-                    matches!(*lt, ty::ReEarlyParam(_) | ty::ReLateParam(_))
+                    matches!(lt.kind(), ty::ReEarlyParam(_) | ty::ReLateParam(_))
                         || (lt.is_static() && opaque_env.param_equal_static(i))
                 }
             },
@@ -70,7 +70,7 @@ pub fn check_opaque_type_parameter_valid<'tcx>(
             opaque_env.param_is_error(i)?;
 
             return Err(infcx.dcx().emit_err(NonGenericOpaqueTypeParam {
-                ty: arg,
+                arg,
                 kind,
                 span,
                 param_span: tcx.def_span(opaque_param.def_id),
diff --git a/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs b/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs
index 3a939df25e0..d8dcd12aecb 100644
--- a/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs
+++ b/compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs
@@ -13,9 +13,9 @@ use rustc_next_trait_solver::solve::{GenerateProofTree, SolverDelegateEvalExt as
 use rustc_type_ir::solve::NoSolution;
 use tracing::{instrument, trace};
 
-use crate::solve::Certainty;
 use crate::solve::delegate::SolverDelegate;
 use crate::solve::inspect::{self, ProofTreeInferCtxtExt, ProofTreeVisitor};
+use crate::solve::{Certainty, deeply_normalize_for_diagnostics};
 use crate::traits::{FulfillmentError, FulfillmentErrorCode, wf};
 
 pub(super) fn fulfillment_error_for_no_solution<'tcx>(
@@ -151,7 +151,7 @@ fn find_best_leaf_obligation<'tcx>(
     //
     // We should probably fix the visitor to not do so instead, as this also
     // means the leaf obligation may be incorrect.
-    infcx
+    let obligation = infcx
         .fudge_inference_if_ok(|| {
             infcx
                 .visit_proof_tree(
@@ -161,7 +161,8 @@ fn find_best_leaf_obligation<'tcx>(
                 .break_value()
                 .ok_or(())
         })
-        .unwrap_or(obligation)
+        .unwrap_or(obligation);
+    deeply_normalize_for_diagnostics(infcx, obligation.param_env, obligation)
 }
 
 struct BestObligation<'tcx> {
@@ -291,6 +292,40 @@ impl<'tcx> BestObligation<'tcx> {
         }
     }
 
+    /// When a higher-ranked projection goal fails, check that the corresponding
+    /// higher-ranked trait goal holds or not. This is because the process of
+    /// instantiating and then re-canonicalizing the binder of the projection goal
+    /// forces us to be unable to see that the leak check failed in the nested
+    /// `NormalizesTo` goal, so we don't fall back to the rigid projection check
+    /// that should catch when a projection goal fails due to an unsatisfied trait
+    /// goal.
+    fn detect_trait_error_in_higher_ranked_projection(
+        &mut self,
+        goal: &inspect::InspectGoal<'_, 'tcx>,
+    ) -> ControlFlow<PredicateObligation<'tcx>> {
+        let tcx = goal.infcx().tcx;
+        if let Some(projection_clause) = goal.goal().predicate.as_projection_clause()
+            && !projection_clause.bound_vars().is_empty()
+        {
+            let pred = projection_clause.map_bound(|proj| proj.projection_term.trait_ref(tcx));
+            let obligation = Obligation::new(
+                tcx,
+                self.obligation.cause.clone(),
+                goal.goal().param_env,
+                deeply_normalize_for_diagnostics(goal.infcx(), goal.goal().param_env, pred),
+            );
+            self.with_derived_obligation(obligation, |this| {
+                goal.infcx().visit_proof_tree_at_depth(
+                    goal.goal().with(tcx, pred),
+                    goal.depth() + 1,
+                    this,
+                )
+            })
+        } else {
+            ControlFlow::Continue(())
+        }
+    }
+
     /// It is likely that `NormalizesTo` failed without any applicable candidates
     /// because the alias is not well-formed.
     ///
@@ -360,7 +395,8 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
             (true, Ok(Certainty::Maybe(MaybeCause::Ambiguity))) | (false, Err(_)) => {}
             _ => return ControlFlow::Continue(()),
         }
-        let pred_kind = goal.goal().predicate.kind();
+
+        let pred = goal.goal().predicate;
 
         let candidates = self.non_trivial_candidates(goal);
         let candidate = match candidates.as_slice() {
@@ -374,7 +410,7 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
             source: CandidateSource::Impl(impl_def_id),
             result: _,
         } = candidate.kind()
-            && goal.infcx().tcx.do_not_recommend_impl(impl_def_id)
+            && tcx.do_not_recommend_impl(impl_def_id)
         {
             trace!("#[do_not_recommend] -> exit");
             return ControlFlow::Break(self.obligation.clone());
@@ -382,12 +418,12 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
 
         // FIXME: Also, what about considering >1 layer up the stack? May be necessary
         // for normalizes-to.
-        let child_mode = match pred_kind.skip_binder() {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
-                ChildMode::Trait(pred_kind.rebind(pred))
+        let child_mode = match pred.kind().skip_binder() {
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) => {
+                ChildMode::Trait(pred.kind().rebind(trait_pred))
             }
-            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(pred)) => {
-                ChildMode::Host(pred_kind.rebind(pred))
+            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(host_pred)) => {
+                ChildMode::Host(pred.kind().rebind(host_pred))
             }
             ty::PredicateKind::NormalizesTo(normalizes_to)
                 if matches!(
@@ -395,7 +431,7 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                     ty::AliasTermKind::ProjectionTy | ty::AliasTermKind::ProjectionConst
                 ) =>
             {
-                ChildMode::Trait(pred_kind.rebind(ty::TraitPredicate {
+                ChildMode::Trait(pred.kind().rebind(ty::TraitPredicate {
                     trait_ref: normalizes_to.alias.trait_ref(tcx),
                     polarity: ty::PredicatePolarity::Positive,
                 }))
@@ -429,10 +465,12 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
         for nested_goal in nested_goals {
             trace!(nested_goal = ?(nested_goal.goal(), nested_goal.source(), nested_goal.result()));
 
+            let nested_pred = nested_goal.goal().predicate;
+
             let make_obligation = |cause| Obligation {
                 cause,
                 param_env: nested_goal.goal().param_env,
-                predicate: nested_goal.goal().predicate,
+                predicate: nested_pred,
                 recursion_depth: self.obligation.recursion_depth + 1,
             };
 
@@ -482,30 +520,21 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
 
         // alias-relate may fail because the lhs or rhs can't be normalized,
         // and therefore is treated as rigid.
-        if let Some(ty::PredicateKind::AliasRelate(lhs, rhs, _)) = pred_kind.no_bound_vars() {
-            if let Some(obligation) = goal
-                .infcx()
-                .visit_proof_tree_at_depth(
-                    goal.goal().with(goal.infcx().tcx, ty::ClauseKind::WellFormed(lhs.into())),
-                    goal.depth() + 1,
-                    self,
-                )
-                .break_value()
-            {
-                return ControlFlow::Break(obligation);
-            } else if let Some(obligation) = goal
-                .infcx()
-                .visit_proof_tree_at_depth(
-                    goal.goal().with(goal.infcx().tcx, ty::ClauseKind::WellFormed(rhs.into())),
-                    goal.depth() + 1,
-                    self,
-                )
-                .break_value()
-            {
-                return ControlFlow::Break(obligation);
-            }
+        if let Some(ty::PredicateKind::AliasRelate(lhs, rhs, _)) = pred.kind().no_bound_vars() {
+            goal.infcx().visit_proof_tree_at_depth(
+                goal.goal().with(tcx, ty::ClauseKind::WellFormed(lhs.into())),
+                goal.depth() + 1,
+                self,
+            )?;
+            goal.infcx().visit_proof_tree_at_depth(
+                goal.goal().with(tcx, ty::ClauseKind::WellFormed(rhs.into())),
+                goal.depth() + 1,
+                self,
+            )?;
         }
 
+        self.detect_trait_error_in_higher_ranked_projection(goal)?;
+
         ControlFlow::Break(self.obligation.clone())
     }
 }
diff --git a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
index 48a05ad29fb..24b87000e32 100644
--- a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
+++ b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
@@ -292,7 +292,7 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
                 inspect::ProbeStep::NestedProbe(ref probe) => {
                     match probe.kind {
                         // These never assemble candidates for the goal we're trying to solve.
-                        inspect::ProbeKind::UpcastProjectionCompatibility
+                        inspect::ProbeKind::ProjectionCompatibility
                         | inspect::ProbeKind::ShadowedEnvProbing => continue,
 
                         inspect::ProbeKind::NormalizedSelfTyAssembly
@@ -314,8 +314,10 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
         }
 
         match probe.kind {
-            inspect::ProbeKind::UpcastProjectionCompatibility
-            | inspect::ProbeKind::ShadowedEnvProbing => bug!(),
+            inspect::ProbeKind::ProjectionCompatibility
+            | inspect::ProbeKind::ShadowedEnvProbing => {
+                bug!()
+            }
 
             inspect::ProbeKind::NormalizedSelfTyAssembly | inspect::ProbeKind::UnsizeAssembly => {}
 
diff --git a/compiler/rustc_trait_selection/src/solve/normalize.rs b/compiler/rustc_trait_selection/src/solve/normalize.rs
index 232357dc71a..79fb044a67f 100644
--- a/compiler/rustc_trait_selection/src/solve/normalize.rs
+++ b/compiler/rustc_trait_selection/src/solve/normalize.rs
@@ -253,20 +253,28 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for DeeplyNormalizeForDiagnosticsFolder<'_,
     }
 
     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        deeply_normalize_with_skipped_universes(
-            self.at,
-            ty,
-            vec![None; ty.outer_exclusive_binder().as_usize()],
-        )
-        .unwrap_or_else(|_: Vec<ScrubbedTraitError<'tcx>>| ty.super_fold_with(self))
+        let infcx = self.at.infcx;
+        infcx
+            .commit_if_ok(|_| {
+                deeply_normalize_with_skipped_universes(
+                    self.at,
+                    ty,
+                    vec![None; ty.outer_exclusive_binder().as_usize()],
+                )
+            })
+            .unwrap_or_else(|_: Vec<ScrubbedTraitError<'tcx>>| ty.super_fold_with(self))
     }
 
     fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
-        deeply_normalize_with_skipped_universes(
-            self.at,
-            ct,
-            vec![None; ct.outer_exclusive_binder().as_usize()],
-        )
-        .unwrap_or_else(|_: Vec<ScrubbedTraitError<'tcx>>| ct.super_fold_with(self))
+        let infcx = self.at.infcx;
+        infcx
+            .commit_if_ok(|_| {
+                deeply_normalize_with_skipped_universes(
+                    self.at,
+                    ct,
+                    vec![None; ct.outer_exclusive_binder().as_usize()],
+                )
+            })
+            .unwrap_or_else(|_: Vec<ScrubbedTraitError<'tcx>>| ct.super_fold_with(self))
     }
 }
diff --git a/compiler/rustc_trait_selection/src/solve/select.rs b/compiler/rustc_trait_selection/src/solve/select.rs
index 4437fc5b029..4fdaf740287 100644
--- a/compiler/rustc_trait_selection/src/solve/select.rs
+++ b/compiler/rustc_trait_selection/src/solve/select.rs
@@ -177,7 +177,7 @@ fn to_selection<'tcx>(
         },
         ProbeKind::NormalizedSelfTyAssembly
         | ProbeKind::UnsizeAssembly
-        | ProbeKind::UpcastProjectionCompatibility
+        | ProbeKind::ProjectionCompatibility
         | ProbeKind::OpaqueTypeStorageLookup { result: _ }
         | ProbeKind::Root { result: _ }
         | ProbeKind::ShadowedEnvProbing
diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
index 1fca2f4da7e..02521c9453d 100644
--- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs
+++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
@@ -382,7 +382,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                     for (new_region, old_region) in
                         iter::zip(new_args.regions(), old_args.regions())
                     {
-                        match (*new_region, *old_region) {
+                        match (new_region.kind(), old_region.kind()) {
                             // If both predicates have an `ReBound` (a HRTB) in the
                             // same spot, we do nothing.
                             (ty::ReBound(_, _), ty::ReBound(_, _)) => {}
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index bcc247ba53c..93c7dae9c5b 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -537,7 +537,7 @@ fn plug_infer_with_placeholders<'tcx>(
         }
 
         fn visit_region(&mut self, r: ty::Region<'tcx>) {
-            if let ty::ReVar(vid) = *r {
+            if let ty::ReVar(vid) = r.kind() {
                 let r = self
                     .infcx
                     .inner
diff --git a/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs b/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
index fa6bbf1d6e5..519394685a8 100644
--- a/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
+++ b/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
@@ -188,7 +188,7 @@ fn bounds_reference_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span
     tcx.associated_items(trait_def_id)
         .in_definition_order()
         // We're only looking at associated type bounds
-        .filter(|item| item.kind == ty::AssocKind::Type)
+        .filter(|item| item.is_type())
         // Ignore GATs with `Self: Sized`
         .filter(|item| !tcx.generics_require_sized_self(item.def_id))
         .flat_map(|item| tcx.explicit_item_bounds(item.def_id).iter_identity_copied())
@@ -298,31 +298,33 @@ pub fn dyn_compatibility_violations_for_assoc_item(
     match item.kind {
         // Associated consts are never dyn-compatible, as they can't have `where` bounds yet at all,
         // and associated const bounds in trait objects aren't a thing yet either.
-        ty::AssocKind::Const => {
-            vec![DynCompatibilityViolation::AssocConst(item.name, item.ident(tcx).span)]
+        ty::AssocKind::Const { name } => {
+            vec![DynCompatibilityViolation::AssocConst(name, item.ident(tcx).span)]
         }
-        ty::AssocKind::Fn => virtual_call_violations_for_method(tcx, trait_def_id, item)
-            .into_iter()
-            .map(|v| {
-                let node = tcx.hir_get_if_local(item.def_id);
-                // Get an accurate span depending on the violation.
-                let span = match (&v, node) {
-                    (MethodViolationCode::ReferencesSelfInput(Some(span)), _) => *span,
-                    (MethodViolationCode::UndispatchableReceiver(Some(span)), _) => *span,
-                    (MethodViolationCode::ReferencesImplTraitInTrait(span), _) => *span,
-                    (MethodViolationCode::ReferencesSelfOutput, Some(node)) => {
-                        node.fn_decl().map_or(item.ident(tcx).span, |decl| decl.output.span())
-                    }
-                    _ => item.ident(tcx).span,
-                };
+        ty::AssocKind::Fn { name, .. } => {
+            virtual_call_violations_for_method(tcx, trait_def_id, item)
+                .into_iter()
+                .map(|v| {
+                    let node = tcx.hir_get_if_local(item.def_id);
+                    // Get an accurate span depending on the violation.
+                    let span = match (&v, node) {
+                        (MethodViolationCode::ReferencesSelfInput(Some(span)), _) => *span,
+                        (MethodViolationCode::UndispatchableReceiver(Some(span)), _) => *span,
+                        (MethodViolationCode::ReferencesImplTraitInTrait(span), _) => *span,
+                        (MethodViolationCode::ReferencesSelfOutput, Some(node)) => {
+                            node.fn_decl().map_or(item.ident(tcx).span, |decl| decl.output.span())
+                        }
+                        _ => item.ident(tcx).span,
+                    };
 
-                DynCompatibilityViolation::Method(item.name, v, span)
-            })
-            .collect(),
+                    DynCompatibilityViolation::Method(name, v, span)
+                })
+                .collect()
+        }
         // Associated types can only be dyn-compatible if they have `Self: Sized` bounds.
-        ty::AssocKind::Type => {
+        ty::AssocKind::Type { .. } => {
             if !tcx.generics_of(item.def_id).is_own_empty() && !item.is_impl_trait_in_trait() {
-                vec![DynCompatibilityViolation::GAT(item.name, item.ident(tcx).span)]
+                vec![DynCompatibilityViolation::GAT(item.name(), item.ident(tcx).span)]
             } else {
                 // We will permit associated types if they are explicitly mentioned in the trait object.
                 // We can't check this here, as here we only check if it is guaranteed to not be possible.
@@ -344,7 +346,7 @@ fn virtual_call_violations_for_method<'tcx>(
     let sig = tcx.fn_sig(method.def_id).instantiate_identity();
 
     // The method's first parameter must be named `self`
-    if !method.fn_has_self_parameter {
+    if !method.is_method() {
         let sugg = if let Some(hir::Node::TraitItem(hir::TraitItem {
             generics,
             kind: hir::TraitItemKind::Fn(sig, _),
@@ -797,7 +799,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseEscapingBoundRegions<'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        if let ty::ReBound(debruijn, _) = *r
+        if let ty::ReBound(debruijn, _) = r.kind()
             && debruijn < self.binder
         {
             r
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index e98a240a53f..1b76d48e431 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -24,10 +24,10 @@ use super::{
 };
 use crate::error_reporting::InferCtxtErrorExt;
 use crate::infer::{InferCtxt, TyOrConstInferVar};
-use crate::traits::EvaluateConstErr;
 use crate::traits::normalize::normalize_with_depth_to;
 use crate::traits::project::{PolyProjectionObligation, ProjectionCacheKeyExt as _};
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
+use crate::traits::{EvaluateConstErr, sizedness_fast_path};
 
 pub(crate) type PendingPredicateObligations<'tcx> = ThinVec<PendingPredicateObligation<'tcx>>;
 
@@ -335,6 +335,10 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
         let infcx = self.selcx.infcx;
 
+        if sizedness_fast_path(infcx.tcx, obligation.predicate) {
+            return ProcessResult::Changed(thin_vec::thin_vec![]);
+        }
+
         if obligation.predicate.has_aliases() {
             let mut obligations = PredicateObligations::new();
             let predicate = normalize_with_depth_to(
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index de337710b5e..0987c5b42d8 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -65,8 +65,8 @@ pub use self::specialize::{
 pub use self::structural_normalize::StructurallyNormalizeExt;
 pub use self::util::{
     BoundVarReplacer, PlaceholderReplacer, elaborate, expand_trait_aliases, impl_item_is_final,
-    supertrait_def_ids, supertraits, transitive_bounds_that_define_assoc_item, upcast_choices,
-    with_replaced_escaping_bound_vars,
+    sizedness_fast_path, supertrait_def_ids, supertraits, transitive_bounds_that_define_assoc_item,
+    upcast_choices, with_replaced_escaping_bound_vars,
 };
 use crate::error_reporting::InferCtxtErrorExt;
 use crate::infer::outlives::env::OutlivesEnvironment;
@@ -643,7 +643,7 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
 ) -> GenericArgsRef<'tcx> {
     struct ReplaceParamAndInferWithPlaceholder<'tcx> {
         tcx: TyCtxt<'tcx>,
-        idx: u32,
+        idx: ty::BoundVar,
     }
 
     impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReplaceParamAndInferWithPlaceholder<'tcx> {
@@ -653,19 +653,13 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
 
         fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
             if let ty::Infer(_) = t.kind() {
-                let idx = {
-                    let idx = self.idx;
-                    self.idx += 1;
-                    idx
-                };
+                let idx = self.idx;
+                self.idx += 1;
                 Ty::new_placeholder(
                     self.tcx,
                     ty::PlaceholderType {
                         universe: ty::UniverseIndex::ROOT,
-                        bound: ty::BoundTy {
-                            var: ty::BoundVar::from_u32(idx),
-                            kind: ty::BoundTyKind::Anon,
-                        },
+                        bound: ty::BoundTy { var: idx, kind: ty::BoundTyKind::Anon },
                     },
                 )
             } else {
@@ -675,16 +669,11 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
 
         fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
             if let ty::ConstKind::Infer(_) = c.kind() {
+                let idx = self.idx;
+                self.idx += 1;
                 ty::Const::new_placeholder(
                     self.tcx,
-                    ty::PlaceholderConst {
-                        universe: ty::UniverseIndex::ROOT,
-                        bound: ty::BoundVar::from_u32({
-                            let idx = self.idx;
-                            self.idx += 1;
-                            idx
-                        }),
-                    },
+                    ty::PlaceholderConst { universe: ty::UniverseIndex::ROOT, bound: idx },
                 )
             } else {
                 c.super_fold_with(self)
@@ -692,7 +681,7 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
         }
     }
 
-    args.fold_with(&mut ReplaceParamAndInferWithPlaceholder { tcx, idx: 0 })
+    args.fold_with(&mut ReplaceParamAndInferWithPlaceholder { tcx, idx: ty::BoundVar::ZERO })
 }
 
 /// Normalizes the predicates and checks whether they hold in an empty environment. If this
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 349569d750e..0dce504903c 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -669,30 +669,11 @@ fn project<'cx, 'tcx>(
 
     match candidates {
         ProjectionCandidateSet::Single(candidate) => {
-            Ok(Projected::Progress(confirm_candidate(selcx, obligation, candidate)))
+            confirm_candidate(selcx, obligation, candidate)
         }
         ProjectionCandidateSet::None => {
             let tcx = selcx.tcx();
-            let term = match tcx.def_kind(obligation.predicate.def_id) {
-                DefKind::AssocTy => Ty::new_projection_from_args(
-                    tcx,
-                    obligation.predicate.def_id,
-                    obligation.predicate.args,
-                )
-                .into(),
-                DefKind::AssocConst => ty::Const::new_unevaluated(
-                    tcx,
-                    ty::UnevaluatedConst::new(
-                        obligation.predicate.def_id,
-                        obligation.predicate.args,
-                    ),
-                )
-                .into(),
-                kind => {
-                    bug!("unknown projection def-id: {}", kind.descr(obligation.predicate.def_id))
-                }
-            };
-
+            let term = obligation.predicate.to_term(tcx);
             Ok(Projected::NoProgress(term))
         }
         // Error occurred while trying to processing impls.
@@ -1244,18 +1225,16 @@ fn confirm_candidate<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTermObligation<'tcx>,
     candidate: ProjectionCandidate<'tcx>,
-) -> Progress<'tcx> {
+) -> Result<Projected<'tcx>, ProjectionError<'tcx>> {
     debug!(?obligation, ?candidate, "confirm_candidate");
-    let mut progress = match candidate {
+    let mut result = match candidate {
         ProjectionCandidate::ParamEnv(poly_projection)
-        | ProjectionCandidate::Object(poly_projection) => {
-            confirm_param_env_candidate(selcx, obligation, poly_projection, false)
-        }
-
-        ProjectionCandidate::TraitDef(poly_projection) => {
-            confirm_param_env_candidate(selcx, obligation, poly_projection, true)
-        }
-
+        | ProjectionCandidate::Object(poly_projection) => Ok(Projected::Progress(
+            confirm_param_env_candidate(selcx, obligation, poly_projection, false),
+        )),
+        ProjectionCandidate::TraitDef(poly_projection) => Ok(Projected::Progress(
+            confirm_param_env_candidate(selcx, obligation, poly_projection, true),
+        )),
         ProjectionCandidate::Select(impl_source) => {
             confirm_select_candidate(selcx, obligation, impl_source)
         }
@@ -1266,23 +1245,26 @@ fn confirm_candidate<'cx, 'tcx>(
     // with new region variables, we need to resolve them to existing variables
     // when possible for this to work. See `auto-trait-projection-recursion.rs`
     // for a case where this matters.
-    if progress.term.has_infer_regions() {
+    if let Ok(Projected::Progress(progress)) = &mut result
+        && progress.term.has_infer_regions()
+    {
         progress.term = progress.term.fold_with(&mut OpportunisticRegionResolver::new(selcx.infcx));
     }
-    progress
+
+    result
 }
 
 fn confirm_select_candidate<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTermObligation<'tcx>,
     impl_source: Selection<'tcx>,
-) -> Progress<'tcx> {
+) -> Result<Projected<'tcx>, ProjectionError<'tcx>> {
     match impl_source {
         ImplSource::UserDefined(data) => confirm_impl_candidate(selcx, obligation, data),
         ImplSource::Builtin(BuiltinImplSource::Misc | BuiltinImplSource::Trivial, data) => {
             let tcx = selcx.tcx();
             let trait_def_id = obligation.predicate.trait_def_id(tcx);
-            if tcx.is_lang_item(trait_def_id, LangItem::Coroutine) {
+            let progress = if tcx.is_lang_item(trait_def_id, LangItem::Coroutine) {
                 confirm_coroutine_candidate(selcx, obligation, data)
             } else if tcx.is_lang_item(trait_def_id, LangItem::Future) {
                 confirm_future_candidate(selcx, obligation, data)
@@ -1304,7 +1286,8 @@ fn confirm_select_candidate<'cx, 'tcx>(
                 confirm_async_fn_kind_helper_candidate(selcx, obligation, data)
             } else {
                 confirm_builtin_candidate(selcx, obligation, data)
-            }
+            };
+            Ok(Projected::Progress(progress))
         }
         ImplSource::Builtin(BuiltinImplSource::Object { .. }, _)
         | ImplSource::Param(..)
@@ -1410,7 +1393,7 @@ fn confirm_future_candidate<'cx, 'tcx>(
         coroutine_sig,
     );
 
-    debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name, sym::Output);
+    debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name(), sym::Output);
 
     let predicate = ty::ProjectionPredicate {
         projection_term: ty::AliasTerm::new_from_args(
@@ -1456,7 +1439,7 @@ fn confirm_iterator_candidate<'cx, 'tcx>(
         gen_sig,
     );
 
-    debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name, sym::Item);
+    debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name(), sym::Item);
 
     let predicate = ty::ProjectionPredicate {
         projection_term: ty::AliasTerm::new_from_args(
@@ -1502,7 +1485,7 @@ fn confirm_async_iterator_candidate<'cx, 'tcx>(
         gen_sig,
     );
 
-    debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name, sym::Item);
+    debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name(), sym::Item);
 
     let ty::Adt(_poll_adt, args) = *yield_ty.kind() else {
         bug!();
@@ -2000,7 +1983,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTermObligation<'tcx>,
     impl_impl_source: ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>,
-) -> Progress<'tcx> {
+) -> Result<Projected<'tcx>, ProjectionError<'tcx>> {
     let tcx = selcx.tcx();
 
     let ImplSourceUserDefinedData { impl_def_id, args, mut nested } = impl_impl_source;
@@ -2011,19 +1994,34 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     let param_env = obligation.param_env;
     let assoc_ty = match specialization_graph::assoc_def(tcx, impl_def_id, assoc_item_id) {
         Ok(assoc_ty) => assoc_ty,
-        Err(guar) => return Progress::error(tcx, guar),
+        Err(guar) => return Ok(Projected::Progress(Progress::error(tcx, guar))),
     };
+
+    // This means that the impl is missing a definition for the
+    // associated type. This is either because the associate item
+    // has impossible-to-satisfy predicates (since those were
+    // allowed in <https://github.com/rust-lang/rust/pull/135480>),
+    // or because the impl is literally missing the definition.
     if !assoc_ty.item.defaultness(tcx).has_value() {
-        // This means that the impl is missing a definition for the
-        // associated type. This error will be reported by the type
-        // checker method `check_impl_items_against_trait`, so here we
-        // just return Error.
         debug!(
             "confirm_impl_candidate: no associated type {:?} for {:?}",
-            assoc_ty.item.name, obligation.predicate
+            assoc_ty.item.name(),
+            obligation.predicate
         );
-        return Progress { term: Ty::new_misc_error(tcx).into(), obligations: nested };
+        if tcx.impl_self_is_guaranteed_unsized(impl_def_id) {
+            // We treat this projection as rigid here, which is represented via
+            // `Projected::NoProgress`. This will ensure that the projection is
+            // checked for well-formedness, and it's either satisfied by a trivial
+            // where clause in its env or it results in an error.
+            return Ok(Projected::NoProgress(obligation.predicate.to_term(tcx)));
+        } else {
+            return Ok(Projected::Progress(Progress {
+                term: Ty::new_misc_error(tcx).into(),
+                obligations: nested,
+            }));
+        }
     }
+
     // If we're trying to normalize `<Vec<u32> as X>::A<S>` using
     //`impl<T> X for Vec<T> { type A<Y> = Box<Y>; }`, then:
     //
@@ -2033,6 +2031,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     let args = obligation.predicate.args.rebase_onto(tcx, trait_def_id, args);
     let args = translate_args(selcx.infcx, param_env, impl_def_id, args, assoc_ty.defining_node);
     let is_const = matches!(tcx.def_kind(assoc_ty.item.def_id), DefKind::AssocConst);
+
     let term: ty::EarlyBinder<'tcx, ty::Term<'tcx>> = if is_const {
         let did = assoc_ty.item.def_id;
         let identity_args = crate::traits::GenericArgs::identity_for_item(tcx, did);
@@ -2041,7 +2040,8 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     } else {
         tcx.type_of(assoc_ty.item.def_id).map_bound(|ty| ty.into())
     };
-    if !tcx.check_args_compatible(assoc_ty.item.def_id, args) {
+
+    let progress = if !tcx.check_args_compatible(assoc_ty.item.def_id, args) {
         let err = Ty::new_error_with_message(
             tcx,
             obligation.cause.span,
@@ -2051,7 +2051,8 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     } else {
         assoc_ty_own_obligations(selcx, obligation, &mut nested);
         Progress { term: term.instantiate(tcx, args), obligations: nested }
-    }
+    };
+    Ok(Projected::Progress(progress))
 }
 
 // Get obligations corresponding to the predicates from the where-clause of the
diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
index 5dbb4382fd1..507932699c7 100644
--- a/compiler/rustc_trait_selection/src/traits/query/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -144,7 +144,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxEscapingBoundVarVisitor {
 
     #[inline]
     fn visit_region(&mut self, r: ty::Region<'tcx>) {
-        match *r {
+        match r.kind() {
             ty::ReBound(debruijn, _) if debruijn > self.outer_index => {
                 self.escaping =
                     self.escaping.max(debruijn.as_usize() - self.outer_index.as_usize());
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
index 4f9e2e79d62..87fc532adaf 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
@@ -1,4 +1,3 @@
-use rustc_hir::LangItem;
 use rustc_infer::traits::Obligation;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::traits::query::NoSolution;
@@ -7,7 +6,7 @@ use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt};
 use rustc_span::Span;
 
 use crate::infer::canonical::{CanonicalQueryInput, CanonicalQueryResponse};
-use crate::traits::ObligationCtxt;
+use crate::traits::{ObligationCtxt, sizedness_fast_path};
 
 impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
     type QueryResponse = ();
@@ -16,15 +15,7 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
         tcx: TyCtxt<'tcx>,
         key: &ParamEnvAnd<'tcx, Self>,
     ) -> Option<Self::QueryResponse> {
-        // Proving Sized, very often on "obviously sized" types like
-        // `&T`, accounts for about 60% percentage of the predicates
-        // we have to prove. No need to canonicalize and all that for
-        // such cases.
-        if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_ref)) =
-            key.value.predicate.kind().skip_binder()
-            && tcx.is_lang_item(trait_ref.def_id(), LangItem::Sized)
-            && trait_ref.self_ty().is_trivially_sized(tcx)
-        {
+        if sizedness_fast_path(tcx, key.value.predicate) {
             return Some(());
         }
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 2cb7d2d8931..d71d1e9ae0f 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -317,7 +317,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     obligation.cause.clone(),
                     obligation.recursion_depth + 1,
                     obligation.param_env,
-                    obligation.predicate.rebind(trait_ref),
+                    trait_ref,
                 )
             };
 
@@ -343,7 +343,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     obligation.cause.clone(),
                     obligation.recursion_depth + 1,
                     obligation.param_env,
-                    obligation.predicate.rebind(outlives),
+                    outlives,
                 )
             };
 
@@ -404,7 +404,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
         }
 
-        let predicate = obligation.predicate.skip_binder();
+        let predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
 
         let mut assume = predicate.trait_ref.args.const_at(2);
         // FIXME(mgca): We should shallowly normalize this.
@@ -594,9 +594,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // Associated types that require `Self: Sized` do not show up in the built-in
             // implementation of `Trait for dyn Trait`, and can be dropped here.
             .filter(|item| !tcx.generics_require_sized_self(item.def_id))
-            .filter_map(
-                |item| if item.kind == ty::AssocKind::Type { Some(item.def_id) } else { None },
-            )
+            .filter_map(|item| if item.is_type() { Some(item.def_id) } else { None })
             .collect();
 
         for assoc_type in assoc_types {
@@ -1090,26 +1088,36 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             {
                 // See `assemble_candidates_for_unsizing` for more info.
                 // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
-                let iter = data_a
-                    .principal()
-                    .filter(|_| {
-                        // optionally drop the principal, if we're unsizing to no principal
-                        data_b.principal().is_some()
-                    })
-                    .map(|b| b.map_bound(ty::ExistentialPredicate::Trait))
-                    .into_iter()
-                    .chain(
+                let existential_predicates = if data_b.principal().is_some() {
+                    tcx.mk_poly_existential_predicates_from_iter(
                         data_a
-                            .projection_bounds()
-                            .map(|b| b.map_bound(ty::ExistentialPredicate::Projection)),
+                            .principal()
+                            .map(|b| b.map_bound(ty::ExistentialPredicate::Trait))
+                            .into_iter()
+                            .chain(
+                                data_a
+                                    .projection_bounds()
+                                    .map(|b| b.map_bound(ty::ExistentialPredicate::Projection)),
+                            )
+                            .chain(
+                                data_b
+                                    .auto_traits()
+                                    .map(ty::ExistentialPredicate::AutoTrait)
+                                    .map(ty::Binder::dummy),
+                            ),
                     )
-                    .chain(
+                } else {
+                    // If we're unsizing to a dyn type that has no principal, then drop
+                    // the principal and projections from the type. We use the auto traits
+                    // from the RHS type since as we noted that we've checked for auto
+                    // trait compatibility during unsizing.
+                    tcx.mk_poly_existential_predicates_from_iter(
                         data_b
                             .auto_traits()
                             .map(ty::ExistentialPredicate::AutoTrait)
                             .map(ty::Binder::dummy),
-                    );
-                let existential_predicates = tcx.mk_poly_existential_predicates_from_iter(iter);
+                    )
+                };
                 let source_trait = Ty::new_dynamic(tcx, existential_predicates, r_b, dyn_a);
 
                 // Require that the traits involved in this upcast are **equal**;
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 56ff46e89e7..4d88a23250a 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -49,7 +49,9 @@ use crate::infer::{InferCtxt, InferOk, TypeFreshener};
 use crate::solve::InferCtxtSelectExt as _;
 use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to};
 use crate::traits::project::{ProjectAndUnifyResult, ProjectionCacheKeyExt};
-use crate::traits::{EvaluateConstErr, ProjectionCacheKey, Unimplemented, effects};
+use crate::traits::{
+    EvaluateConstErr, ProjectionCacheKey, Unimplemented, effects, sizedness_fast_path,
+};
 
 mod _match;
 mod candidate_assembly;
@@ -603,6 +605,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             None => self.check_recursion_limit(&obligation, &obligation)?,
         }
 
+        if sizedness_fast_path(self.tcx(), obligation.predicate) {
+            return Ok(EvaluatedToOk);
+        }
+
         ensure_sufficient_stack(|| {
             let bound_predicate = obligation.predicate.kind();
             match bound_predicate.skip_binder() {
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 15f5cf916a4..035fd38c48a 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -1,6 +1,7 @@
 use std::collections::{BTreeMap, VecDeque};
 
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
+use rustc_hir::LangItem;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
 pub use rustc_infer::traits::util::*;
@@ -289,7 +290,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for BoundVarReplacer<'_, 'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
+        match r.kind() {
             ty::ReBound(debruijn, _)
                 if debruijn.as_usize()
                     >= self.current_index.as_usize() + self.universe_indices.len() =>
@@ -407,7 +408,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
     }
 
     fn fold_region(&mut self, r0: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        let r1 = match *r0 {
+        let r1 = match r0.kind() {
             ty::ReVar(vid) => self
                 .infcx
                 .inner
@@ -417,7 +418,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
             _ => r0,
         };
 
-        let r2 = match *r1 {
+        let r2 = match r1.kind() {
             ty::RePlaceholder(p) => {
                 let replace_var = self.mapped_regions.get(&p);
                 match replace_var {
@@ -504,3 +505,21 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
         }
     }
 }
+
+pub fn sizedness_fast_path<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tcx>) -> bool {
+    // Proving `Sized` very often on "obviously sized" types like `&T`, accounts for about 60%
+    // percentage of the predicates we have to prove. No need to canonicalize and all that for
+    // such cases.
+    if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_ref)) =
+        predicate.kind().skip_binder()
+    {
+        if tcx.is_lang_item(trait_ref.def_id(), LangItem::Sized)
+            && trait_ref.self_ty().is_trivially_sized(tcx)
+        {
+            debug!("fast path -- trivial sizedness");
+            return true;
+        }
+    }
+
+    false
+}
diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
index 165174c0bcc..3565c11249a 100644
--- a/compiler/rustc_trait_selection/src/traits/vtable.rs
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -197,10 +197,8 @@ fn own_existential_vtable_entries_iter(
     tcx: TyCtxt<'_>,
     trait_def_id: DefId,
 ) -> impl Iterator<Item = DefId> {
-    let trait_methods = tcx
-        .associated_items(trait_def_id)
-        .in_definition_order()
-        .filter(|item| item.kind == ty::AssocKind::Fn);
+    let trait_methods =
+        tcx.associated_items(trait_def_id).in_definition_order().filter(|item| item.is_fn());
 
     // Now list each method's DefId (for within its trait).
     let own_entries = trait_methods.filter_map(move |&trait_method| {
diff --git a/compiler/rustc_traits/src/codegen.rs b/compiler/rustc_traits/src/codegen.rs
index 4a889abfc28..88f02d16c7d 100644
--- a/compiler/rustc_traits/src/codegen.rs
+++ b/compiler/rustc_traits/src/codegen.rs
@@ -6,11 +6,11 @@
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::bug;
 use rustc_middle::traits::CodegenObligationError;
-use rustc_middle::ty::{self, PseudoCanonicalInput, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, PseudoCanonicalInput, TyCtxt, TypeVisitableExt, Upcast};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::traits::{
     ImplSource, Obligation, ObligationCause, ObligationCtxt, ScrubbedTraitError, SelectionContext,
-    Unimplemented,
+    Unimplemented, sizedness_fast_path,
 };
 use tracing::debug;
 
@@ -34,6 +34,13 @@ pub(crate) fn codegen_select_candidate<'tcx>(
     let (infcx, param_env) = tcx.infer_ctxt().ignoring_regions().build_with_typing_env(typing_env);
     let mut selcx = SelectionContext::new(&infcx);
 
+    if sizedness_fast_path(tcx, trait_ref.upcast(tcx)) {
+        return Ok(&*tcx.arena.alloc(ImplSource::Builtin(
+            ty::solve::BuiltinImplSource::Trivial,
+            Default::default(),
+        )));
+    }
+
     let obligation_cause = ObligationCause::dummy();
     let obligation = Obligation::new(tcx, obligation_cause, param_env, trait_ref);
 
diff --git a/compiler/rustc_traits/src/evaluate_obligation.rs b/compiler/rustc_traits/src/evaluate_obligation.rs
index c9ad096c6e9..7771db855d7 100644
--- a/compiler/rustc_traits/src/evaluate_obligation.rs
+++ b/compiler/rustc_traits/src/evaluate_obligation.rs
@@ -5,6 +5,7 @@ use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::query::CanonicalPredicateGoal;
 use rustc_trait_selection::traits::{
     EvaluationResult, Obligation, ObligationCause, OverflowError, SelectionContext, TraitQueryMode,
+    sizedness_fast_path,
 };
 use tracing::debug;
 
@@ -23,6 +24,10 @@ fn evaluate_obligation<'tcx>(
     debug!("evaluate_obligation: goal={:#?}", goal);
     let ParamEnvAnd { param_env, value: predicate } = goal;
 
+    if sizedness_fast_path(tcx, predicate) {
+        return Ok(EvaluationResult::EvaluatedToOk);
+    }
+
     let mut selcx = SelectionContext::with_query_mode(infcx, TraitQueryMode::Canonical);
     let obligation = Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate);
 
diff --git a/compiler/rustc_transmute/src/lib.rs b/compiler/rustc_transmute/src/lib.rs
index 7d800e49ff4..00928137d29 100644
--- a/compiler/rustc_transmute/src/lib.rs
+++ b/compiler/rustc_transmute/src/lib.rs
@@ -1,5 +1,4 @@
 // tidy-alphabetical-start
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![feature(never_type)]
 // tidy-alphabetical-end
 
diff --git a/compiler/rustc_transmute/src/maybe_transmutable/tests.rs b/compiler/rustc_transmute/src/maybe_transmutable/tests.rs
index 4d81382eba0..69a6b1b77f4 100644
--- a/compiler/rustc_transmute/src/maybe_transmutable/tests.rs
+++ b/compiler/rustc_transmute/src/maybe_transmutable/tests.rs
@@ -1,93 +1,115 @@
 use itertools::Itertools;
 
 use super::query_context::test::{Def, UltraMinimal};
-use crate::maybe_transmutable::MaybeTransmutableQuery;
-use crate::{Reason, layout};
+use crate::{Answer, Assume, Reason, layout};
 
-mod safety {
-    use super::*;
-    use crate::Answer;
+type Tree = layout::Tree<Def, !>;
+type Dfa = layout::Dfa<!>;
 
-    type Tree = layout::Tree<Def, !>;
+trait Representation {
+    fn is_transmutable(src: Self, dst: Self, assume: Assume) -> Answer<!>;
+}
 
-    const DST_HAS_SAFETY_INVARIANTS: Answer<!> =
-        Answer::No(crate::Reason::DstMayHaveSafetyInvariants);
+impl Representation for Tree {
+    fn is_transmutable(src: Self, dst: Self, assume: Assume) -> Answer<!> {
+        crate::maybe_transmutable::MaybeTransmutableQuery::new(src, dst, assume, UltraMinimal)
+            .answer()
+    }
+}
 
-    fn is_transmutable(src: &Tree, dst: &Tree, assume_safety: bool) -> crate::Answer<!> {
-        let src = src.clone();
-        let dst = dst.clone();
-        // The only dimension of the transmutability analysis we want to test
-        // here is the safety analysis. To ensure this, we disable all other
-        // toggleable aspects of the transmutability analysis.
-        let assume = crate::Assume {
-            alignment: true,
-            lifetimes: true,
-            validity: true,
-            safety: assume_safety,
-        };
+impl Representation for Dfa {
+    fn is_transmutable(src: Self, dst: Self, assume: Assume) -> Answer<!> {
         crate::maybe_transmutable::MaybeTransmutableQuery::new(src, dst, assume, UltraMinimal)
             .answer()
     }
+}
+
+fn is_transmutable<R: Representation + Clone>(
+    src: &R,
+    dst: &R,
+    assume: Assume,
+) -> crate::Answer<!> {
+    let src = src.clone();
+    let dst = dst.clone();
+    // The only dimension of the transmutability analysis we want to test
+    // here is the safety analysis. To ensure this, we disable all other
+    // toggleable aspects of the transmutability analysis.
+    R::is_transmutable(src, dst, assume)
+}
+
+mod safety {
+    use super::*;
+    use crate::Answer;
+
+    const DST_HAS_SAFETY_INVARIANTS: Answer<!> =
+        Answer::No(crate::Reason::DstMayHaveSafetyInvariants);
 
     #[test]
     fn src_safe_dst_safe() {
         let src = Tree::Def(Def::NoSafetyInvariants).then(Tree::u8());
         let dst = Tree::Def(Def::NoSafetyInvariants).then(Tree::u8());
-        assert_eq!(is_transmutable(&src, &dst, false), Answer::Yes);
-        assert_eq!(is_transmutable(&src, &dst, true), Answer::Yes);
+        assert_eq!(is_transmutable(&src, &dst, Assume::default()), Answer::Yes);
+        assert_eq!(
+            is_transmutable(&src, &dst, Assume { safety: true, ..Assume::default() }),
+            Answer::Yes
+        );
     }
 
     #[test]
     fn src_safe_dst_unsafe() {
         let src = Tree::Def(Def::NoSafetyInvariants).then(Tree::u8());
         let dst = Tree::Def(Def::HasSafetyInvariants).then(Tree::u8());
-        assert_eq!(is_transmutable(&src, &dst, false), DST_HAS_SAFETY_INVARIANTS);
-        assert_eq!(is_transmutable(&src, &dst, true), Answer::Yes);
+        assert_eq!(is_transmutable(&src, &dst, Assume::default()), DST_HAS_SAFETY_INVARIANTS);
+        assert_eq!(
+            is_transmutable(&src, &dst, Assume { safety: true, ..Assume::default() }),
+            Answer::Yes
+        );
     }
 
     #[test]
     fn src_unsafe_dst_safe() {
         let src = Tree::Def(Def::HasSafetyInvariants).then(Tree::u8());
         let dst = Tree::Def(Def::NoSafetyInvariants).then(Tree::u8());
-        assert_eq!(is_transmutable(&src, &dst, false), Answer::Yes);
-        assert_eq!(is_transmutable(&src, &dst, true), Answer::Yes);
+        assert_eq!(is_transmutable(&src, &dst, Assume::default()), Answer::Yes);
+        assert_eq!(
+            is_transmutable(&src, &dst, Assume { safety: true, ..Assume::default() }),
+            Answer::Yes
+        );
     }
 
     #[test]
     fn src_unsafe_dst_unsafe() {
         let src = Tree::Def(Def::HasSafetyInvariants).then(Tree::u8());
         let dst = Tree::Def(Def::HasSafetyInvariants).then(Tree::u8());
-        assert_eq!(is_transmutable(&src, &dst, false), DST_HAS_SAFETY_INVARIANTS);
-        assert_eq!(is_transmutable(&src, &dst, true), Answer::Yes);
+        assert_eq!(is_transmutable(&src, &dst, Assume::default()), DST_HAS_SAFETY_INVARIANTS);
+        assert_eq!(
+            is_transmutable(&src, &dst, Assume { safety: true, ..Assume::default() }),
+            Answer::Yes
+        );
     }
 }
 
 mod bool {
     use super::*;
-    use crate::Answer;
 
     #[test]
     fn should_permit_identity_transmutation_tree() {
-        let answer = crate::maybe_transmutable::MaybeTransmutableQuery::new(
-            layout::Tree::<Def, !>::bool(),
-            layout::Tree::<Def, !>::bool(),
-            crate::Assume { alignment: false, lifetimes: false, validity: true, safety: false },
-            UltraMinimal,
-        )
-        .answer();
-        assert_eq!(answer, Answer::Yes);
+        let src = Tree::bool();
+        assert_eq!(is_transmutable(&src, &src, Assume::default()), Answer::Yes);
+        assert_eq!(
+            is_transmutable(&src, &src, Assume { validity: true, ..Assume::default() }),
+            Answer::Yes
+        );
     }
 
     #[test]
     fn should_permit_identity_transmutation_dfa() {
-        let answer = crate::maybe_transmutable::MaybeTransmutableQuery::new(
-            layout::Dfa::<!>::bool(),
-            layout::Dfa::<!>::bool(),
-            crate::Assume { alignment: false, lifetimes: false, validity: true, safety: false },
-            UltraMinimal,
-        )
-        .answer();
-        assert_eq!(answer, Answer::Yes);
+        let src = Dfa::bool();
+        assert_eq!(is_transmutable(&src, &src, Assume::default()), Answer::Yes);
+        assert_eq!(
+            is_transmutable(&src, &src, Assume { validity: true, ..Assume::default() }),
+            Answer::Yes
+        );
     }
 
     #[test]
@@ -122,13 +144,7 @@ mod bool {
                 if src_set.is_subset(&dst_set) {
                     assert_eq!(
                         Answer::Yes,
-                        MaybeTransmutableQuery::new(
-                            src_layout.clone(),
-                            dst_layout.clone(),
-                            crate::Assume { validity: false, ..crate::Assume::default() },
-                            UltraMinimal,
-                        )
-                        .answer(),
+                        is_transmutable(&src_layout, &dst_layout, Assume::default()),
                         "{:?} SHOULD be transmutable into {:?}",
                         src_layout,
                         dst_layout
@@ -136,13 +152,11 @@ mod bool {
                 } else if !src_set.is_disjoint(&dst_set) {
                     assert_eq!(
                         Answer::Yes,
-                        MaybeTransmutableQuery::new(
-                            src_layout.clone(),
-                            dst_layout.clone(),
-                            crate::Assume { validity: true, ..crate::Assume::default() },
-                            UltraMinimal,
-                        )
-                        .answer(),
+                        is_transmutable(
+                            &src_layout,
+                            &dst_layout,
+                            Assume { validity: true, ..Assume::default() }
+                        ),
                         "{:?} SHOULD be transmutable (assuming validity) into {:?}",
                         src_layout,
                         dst_layout
@@ -150,13 +164,7 @@ mod bool {
                 } else {
                     assert_eq!(
                         Answer::No(Reason::DstIsBitIncompatible),
-                        MaybeTransmutableQuery::new(
-                            src_layout.clone(),
-                            dst_layout.clone(),
-                            crate::Assume { validity: false, ..crate::Assume::default() },
-                            UltraMinimal,
-                        )
-                        .answer(),
+                        is_transmutable(&src_layout, &dst_layout, Assume::default()),
                         "{:?} should NOT be transmutable into {:?}",
                         src_layout,
                         dst_layout
diff --git a/compiler/rustc_ty_utils/src/abi.rs b/compiler/rustc_ty_utils/src/abi.rs
index 48d5a4a0fcb..3d4ab33240a 100644
--- a/compiler/rustc_ty_utils/src/abi.rs
+++ b/compiler/rustc_ty_utils/src/abi.rs
@@ -244,7 +244,7 @@ fn fn_sig_for_fn_abi<'tcx>(
 fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: ExternAbi, c_variadic: bool) -> Conv {
     use rustc_abi::ExternAbi::*;
     match tcx.sess.target.adjust_abi(abi, c_variadic) {
-        RustIntrinsic | Rust | RustCall => Conv::Rust,
+        Rust | RustCall => Conv::Rust,
 
         // This is intentionally not using `Conv::Cold`, as that has to preserve
         // even SIMD registers, which is generally not a good trade-off.
@@ -660,7 +660,7 @@ fn fn_abi_adjust_for_abi<'tcx>(
     let tcx = cx.tcx();
 
     if abi.is_rustic_abi() {
-        fn_abi.adjust_for_rust_abi(cx, abi);
+        fn_abi.adjust_for_rust_abi(cx);
 
         // Look up the deduced parameter attributes for this function, if we have its def ID and
         // we're optimizing in non-incremental mode. We'll tag its parameters with those attributes
diff --git a/compiler/rustc_ty_utils/src/assoc.rs b/compiler/rustc_ty_utils/src/assoc.rs
index b7684e85d41..6cb9fdc6f93 100644
--- a/compiler/rustc_ty_utils/src/assoc.rs
+++ b/compiler/rustc_ty_utils/src/assoc.rs
@@ -6,7 +6,6 @@ use rustc_hir::{self as hir, AmbigArg};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, ImplTraitInTraitData, TyCtxt};
 use rustc_middle::{bug, span_bug};
-use rustc_span::kw;
 
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers {
@@ -129,39 +128,35 @@ fn associated_item(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AssocItem {
 
 fn associated_item_from_trait_item_ref(trait_item_ref: &hir::TraitItemRef) -> ty::AssocItem {
     let owner_id = trait_item_ref.id.owner_id;
-    let (kind, has_self) = match trait_item_ref.kind {
-        hir::AssocItemKind::Const => (ty::AssocKind::Const, false),
-        hir::AssocItemKind::Fn { has_self } => (ty::AssocKind::Fn, has_self),
-        hir::AssocItemKind::Type => (ty::AssocKind::Type, false),
+    let name = trait_item_ref.ident.name;
+    let kind = match trait_item_ref.kind {
+        hir::AssocItemKind::Const => ty::AssocKind::Const { name },
+        hir::AssocItemKind::Fn { has_self } => ty::AssocKind::Fn { name, has_self },
+        hir::AssocItemKind::Type => ty::AssocKind::Type { data: ty::AssocTypeData::Normal(name) },
     };
 
     ty::AssocItem {
-        name: trait_item_ref.ident.name,
         kind,
         def_id: owner_id.to_def_id(),
         trait_item_def_id: Some(owner_id.to_def_id()),
         container: ty::AssocItemContainer::Trait,
-        fn_has_self_parameter: has_self,
-        opt_rpitit_info: None,
     }
 }
 
 fn associated_item_from_impl_item_ref(impl_item_ref: &hir::ImplItemRef) -> ty::AssocItem {
     let def_id = impl_item_ref.id.owner_id;
-    let (kind, has_self) = match impl_item_ref.kind {
-        hir::AssocItemKind::Const => (ty::AssocKind::Const, false),
-        hir::AssocItemKind::Fn { has_self } => (ty::AssocKind::Fn, has_self),
-        hir::AssocItemKind::Type => (ty::AssocKind::Type, false),
+    let name = impl_item_ref.ident.name;
+    let kind = match impl_item_ref.kind {
+        hir::AssocItemKind::Const => ty::AssocKind::Const { name },
+        hir::AssocItemKind::Fn { has_self } => ty::AssocKind::Fn { name, has_self },
+        hir::AssocItemKind::Type => ty::AssocKind::Type { data: ty::AssocTypeData::Normal(name) },
     };
 
     ty::AssocItem {
-        name: impl_item_ref.ident.name,
         kind,
         def_id: def_id.to_def_id(),
         trait_item_def_id: impl_item_ref.trait_item_def_id,
         container: ty::AssocItemContainer::Impl,
-        fn_has_self_parameter: has_self,
-        opt_rpitit_info: None,
     }
 }
 
@@ -252,7 +247,7 @@ fn associated_type_for_impl_trait_in_trait(
     assert_eq!(tcx.def_kind(trait_def_id), DefKind::Trait);
 
     let span = tcx.def_span(opaque_ty_def_id);
-    // No name because this is a synthetic associated type.
+    // No name because this is an anonymous associated type.
     let trait_assoc_ty = tcx.at(span).create_def(trait_def_id, None, DefKind::AssocTy);
 
     let local_def_id = trait_assoc_ty.def_id();
@@ -264,16 +259,15 @@ fn associated_type_for_impl_trait_in_trait(
     trait_assoc_ty.def_ident_span(Some(span));
 
     trait_assoc_ty.associated_item(ty::AssocItem {
-        name: kw::Empty,
-        kind: ty::AssocKind::Type,
+        kind: ty::AssocKind::Type {
+            data: ty::AssocTypeData::Rpitit(ImplTraitInTraitData::Trait {
+                fn_def_id: fn_def_id.to_def_id(),
+                opaque_def_id: opaque_ty_def_id.to_def_id(),
+            }),
+        },
         def_id,
         trait_item_def_id: None,
         container: ty::AssocItemContainer::Trait,
-        fn_has_self_parameter: false,
-        opt_rpitit_info: Some(ImplTraitInTraitData::Trait {
-            fn_def_id: fn_def_id.to_def_id(),
-            opaque_def_id: opaque_ty_def_id.to_def_id(),
-        }),
     });
 
     // Copy visility of the containing function.
@@ -305,7 +299,7 @@ fn associated_type_for_impl_trait_in_impl(
         hir::FnRetTy::DefaultReturn(_) => tcx.def_span(impl_fn_def_id),
         hir::FnRetTy::Return(ty) => ty.span,
     };
-    // No name because this is a synthetic associated type.
+    // No name because this is an anonymous associated type.
     let impl_assoc_ty = tcx.at(span).create_def(impl_local_def_id, None, DefKind::AssocTy);
 
     let local_def_id = impl_assoc_ty.def_id();
@@ -317,13 +311,14 @@ fn associated_type_for_impl_trait_in_impl(
     impl_assoc_ty.def_ident_span(Some(span));
 
     impl_assoc_ty.associated_item(ty::AssocItem {
-        name: kw::Empty,
-        kind: ty::AssocKind::Type,
+        kind: ty::AssocKind::Type {
+            data: ty::AssocTypeData::Rpitit(ImplTraitInTraitData::Impl {
+                fn_def_id: impl_fn_def_id.to_def_id(),
+            }),
+        },
         def_id,
         trait_item_def_id: Some(trait_assoc_def_id),
         container: ty::AssocItemContainer::Impl,
-        fn_has_self_parameter: false,
-        opt_rpitit_info: Some(ImplTraitInTraitData::Impl { fn_def_id: impl_fn_def_id.to_def_id() }),
     });
 
     // Copy visility of the containing function.
diff --git a/compiler/rustc_ty_utils/src/implied_bounds.rs b/compiler/rustc_ty_utils/src/implied_bounds.rs
index 088d5e76b86..6fa763f18ef 100644
--- a/compiler/rustc_ty_utils/src/implied_bounds.rs
+++ b/compiler/rustc_ty_utils/src/implied_bounds.rs
@@ -4,9 +4,9 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
-use rustc_middle::bug;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, Ty, TyCtxt, fold_regions};
+use rustc_middle::{bug, span_bug};
 use rustc_span::Span;
 
 pub(crate) fn provide(providers: &mut Providers) {
@@ -21,7 +21,8 @@ pub(crate) fn provide(providers: &mut Providers) {
 }
 
 fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx [(Ty<'tcx>, Span)] {
-    match tcx.def_kind(def_id) {
+    let kind = tcx.def_kind(def_id);
+    match kind {
         DefKind::Fn => {
             let sig = tcx.fn_sig(def_id).instantiate_identity();
             let liberated_sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
@@ -75,7 +76,7 @@ fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx [(Ty<'
                     {
                         let orig_lt =
                             tcx.map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local());
-                        if matches!(*orig_lt, ty::ReLateParam(..)) {
+                        if matches!(orig_lt.kind(), ty::ReLateParam(..)) {
                             mapping.insert(
                                 orig_lt,
                                 ty::Region::new_early_param(
@@ -121,32 +122,38 @@ fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx [(Ty<'
             }
         }
         DefKind::AssocConst | DefKind::AssocTy => tcx.assumed_wf_types(tcx.local_parent(def_id)),
-        DefKind::OpaqueTy => bug!("implied bounds are not defined for opaques"),
-        DefKind::Mod
+        DefKind::Static { .. }
+        | DefKind::Const
+        | DefKind::AnonConst
+        | DefKind::InlineConst
         | DefKind::Struct
         | DefKind::Union
         | DefKind::Enum
-        | DefKind::Variant
         | DefKind::Trait
-        | DefKind::TyAlias
-        | DefKind::ForeignTy
         | DefKind::TraitAlias
+        | DefKind::TyAlias => ty::List::empty(),
+        DefKind::OpaqueTy
+        | DefKind::Mod
+        | DefKind::Variant
+        | DefKind::ForeignTy
         | DefKind::TyParam
-        | DefKind::Const
         | DefKind::ConstParam
-        | DefKind::Static { .. }
         | DefKind::Ctor(_, _)
         | DefKind::Macro(_)
         | DefKind::ExternCrate
         | DefKind::Use
         | DefKind::ForeignMod
-        | DefKind::AnonConst
-        | DefKind::InlineConst
         | DefKind::Field
         | DefKind::LifetimeParam
         | DefKind::GlobalAsm
         | DefKind::Closure
-        | DefKind::SyntheticCoroutineBody => ty::List::empty(),
+        | DefKind::SyntheticCoroutineBody => {
+            span_bug!(
+                tcx.def_span(def_id),
+                "`assumed_wf_types` not defined for {} `{def_id:?}`",
+                kind.descr(def_id.to_def_id())
+            );
+        }
     }
 }
 
diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 0017186c1b0..1915ba623cb 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -514,6 +514,9 @@ fn layout_of_uncached<'tcx>(
                 return map_layout(cx.calc.layout_of_union(&def.repr(), &variants));
             }
 
+            // UnsafeCell and UnsafePinned both disable niche optimizations
+            let is_special_no_niche = def.is_unsafe_cell() || def.is_unsafe_pinned();
+
             let get_discriminant_type =
                 |min, max| abi::Integer::repr_discr(tcx, ty, &def.repr(), min, max);
 
@@ -542,7 +545,7 @@ fn layout_of_uncached<'tcx>(
                     &def.repr(),
                     &variants,
                     def.is_enum(),
-                    def.is_unsafe_cell(),
+                    is_special_no_niche,
                     tcx.layout_scalar_valid_range(def.did()),
                     get_discriminant_type,
                     discriminants_iter(),
@@ -568,7 +571,7 @@ fn layout_of_uncached<'tcx>(
                     &def.repr(),
                     &variants,
                     def.is_enum(),
-                    def.is_unsafe_cell(),
+                    is_special_no_niche,
                     tcx.layout_scalar_valid_range(def.did()),
                     get_discriminant_type,
                     discriminants_iter(),
diff --git a/compiler/rustc_ty_utils/src/lib.rs b/compiler/rustc_ty_utils/src/lib.rs
index 143b7d53880..35cc6f39856 100644
--- a/compiler/rustc_ty_utils/src/lib.rs
+++ b/compiler/rustc_ty_utils/src/lib.rs
@@ -6,7 +6,6 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![cfg_attr(doc, recursion_limit = "256")] // FIXME(nnethercote): will be removed by #124141
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
diff --git a/compiler/rustc_ty_utils/src/opaque_types.rs b/compiler/rustc_ty_utils/src/opaque_types.rs
index 3aad97d86cc..cd730aeeea9 100644
--- a/compiler/rustc_ty_utils/src/opaque_types.rs
+++ b/compiler/rustc_ty_utils/src/opaque_types.rs
@@ -3,10 +3,10 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit;
 use rustc_hir::intravisit::Visitor;
-use rustc_middle::bug;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::util::{CheckRegions, NotUniqueParam};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
+use rustc_middle::{bug, span_bug};
 use rustc_span::Span;
 use tracing::{instrument, trace};
 
@@ -320,9 +320,12 @@ fn opaque_types_defined_by<'tcx>(
         | DefKind::AnonConst => {
             collector.collect_taits_declared_in_body();
         }
+        // Closures and coroutines are type checked with their parent
+        DefKind::Closure | DefKind::InlineConst => {
+            collector.opaques.extend(tcx.opaque_types_defined_by(tcx.local_parent(item)));
+        }
+        DefKind::AssocTy | DefKind::TyAlias | DefKind::GlobalAsm => {}
         DefKind::OpaqueTy
-        | DefKind::TyAlias
-        | DefKind::AssocTy
         | DefKind::Mod
         | DefKind::Struct
         | DefKind::Union
@@ -340,12 +343,13 @@ fn opaque_types_defined_by<'tcx>(
         | DefKind::ForeignMod
         | DefKind::Field
         | DefKind::LifetimeParam
-        | DefKind::GlobalAsm
         | DefKind::Impl { .. }
-        | DefKind::SyntheticCoroutineBody => {}
-        // Closures and coroutines are type checked with their parent
-        DefKind::Closure | DefKind::InlineConst => {
-            collector.opaques.extend(tcx.opaque_types_defined_by(tcx.local_parent(item)));
+        | DefKind::SyntheticCoroutineBody => {
+            span_bug!(
+                tcx.def_span(item),
+                "`opaque_types_defined_by` not defined for {} `{item:?}`",
+                kind.descr(item.to_def_id())
+            );
         }
     }
     tcx.mk_local_def_ids(&collector.opaques)
diff --git a/compiler/rustc_ty_utils/src/sig_types.rs b/compiler/rustc_ty_utils/src/sig_types.rs
index 5bb96f90029..dc6009116ac 100644
--- a/compiler/rustc_ty_utils/src/sig_types.rs
+++ b/compiler/rustc_ty_utils/src/sig_types.rs
@@ -116,7 +116,7 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
                 "{kind:?} has not seen any uses of `walk_types` yet, ping oli-obk if you'd like any help"
             )
         }
-        // These don't have any types.
+        // These don't have any types, but are visited during privacy checking.
         | DefKind::ExternCrate
         | DefKind::ForeignMod
         | DefKind::ForeignTy
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 9dc4f11e456..31d69eef5ec 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -3,6 +3,7 @@ use rustc_hir as hir;
 use rustc_hir::LangItem;
 use rustc_hir::def::DefKind;
 use rustc_index::bit_set::DenseBitSet;
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{
@@ -312,6 +313,61 @@ fn unsizing_params_for_adt<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> DenseBitSe
     unsizing_params
 }
 
+fn impl_self_is_guaranteed_unsized<'tcx>(tcx: TyCtxt<'tcx>, impl_def_id: DefId) -> bool {
+    debug_assert_eq!(tcx.def_kind(impl_def_id), DefKind::Impl { of_trait: true });
+
+    let infcx = tcx.infer_ctxt().ignoring_regions().build(ty::TypingMode::non_body_analysis());
+
+    let ocx = traits::ObligationCtxt::new_with_diagnostics(&infcx);
+    let cause = traits::ObligationCause::dummy();
+    let param_env = tcx.param_env(impl_def_id);
+
+    let tail = tcx.struct_tail_raw(
+        tcx.type_of(impl_def_id).instantiate_identity(),
+        |ty| {
+            ocx.structurally_normalize_ty(&cause, param_env, ty).unwrap_or_else(|_| {
+                Ty::new_error_with_message(
+                    tcx,
+                    tcx.def_span(impl_def_id),
+                    "struct tail should be computable",
+                )
+            })
+        },
+        || (),
+    );
+
+    match tail.kind() {
+        ty::Dynamic(_, _, ty::Dyn) | ty::Slice(_) | ty::Str => true,
+        ty::Bool
+        | ty::Char
+        | ty::Int(_)
+        | ty::Uint(_)
+        | ty::Float(_)
+        | ty::Adt(_, _)
+        | ty::Foreign(_)
+        | ty::Array(_, _)
+        | ty::Pat(_, _)
+        | ty::RawPtr(_, _)
+        | ty::Ref(_, _, _)
+        | ty::FnDef(_, _)
+        | ty::FnPtr(_, _)
+        | ty::UnsafeBinder(_)
+        | ty::Closure(_, _)
+        | ty::CoroutineClosure(_, _)
+        | ty::Coroutine(_, _)
+        | ty::CoroutineWitness(_, _)
+        | ty::Never
+        | ty::Tuple(_)
+        | ty::Alias(_, _)
+        | ty::Param(_)
+        | ty::Bound(_, _)
+        | ty::Placeholder(_)
+        | ty::Infer(_)
+        | ty::Error(_)
+        | ty::Dynamic(_, _, ty::DynStar) => false,
+    }
+}
+
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers {
         asyncness,
@@ -320,6 +376,7 @@ pub(crate) fn provide(providers: &mut Providers) {
         param_env_normalized_for_post_analysis,
         defaultness,
         unsizing_params_for_adt,
+        impl_self_is_guaranteed_unsized,
         ..*providers
     };
 }
diff --git a/compiler/rustc_type_ir/Cargo.toml b/compiler/rustc_type_ir/Cargo.toml
index 4adf7157926..83d3d78298e 100644
--- a/compiler/rustc_type_ir/Cargo.toml
+++ b/compiler/rustc_type_ir/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2024"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 derive-where = "1.2.7"
+ena = "0.14.3"
 indexmap = "2.0.0"
 rustc-hash = "1.1.0"
 rustc_ast_ir = { path = "../rustc_ast_ir", default-features = false }
diff --git a/compiler/rustc_type_ir/src/binder.rs b/compiler/rustc_type_ir/src/binder.rs
index e9055940310..27ea4e211fe 100644
--- a/compiler/rustc_type_ir/src/binder.rs
+++ b/compiler/rustc_type_ir/src/binder.rs
@@ -122,6 +122,10 @@ impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Binder<I, T> {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         folder.try_fold_binder(self)
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        folder.fold_binder(self)
+    }
 }
 
 impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Binder<I, T> {
@@ -135,7 +139,11 @@ impl<I: Interner, T: TypeFoldable<I>> TypeSuperFoldable<I> for Binder<I, T> {
         self,
         folder: &mut F,
     ) -> Result<Self, F::Error> {
-        self.try_map_bound(|ty| ty.try_fold_with(folder))
+        self.try_map_bound(|t| t.try_fold_with(folder))
+    }
+
+    fn super_fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        self.map_bound(|t| t.fold_with(folder))
     }
 }
 
diff --git a/compiler/rustc_type_ir/src/data_structures/mod.rs b/compiler/rustc_type_ir/src/data_structures/mod.rs
index 30c67d10d0e..a72669cbd18 100644
--- a/compiler/rustc_type_ir/src/data_structures/mod.rs
+++ b/compiler/rustc_type_ir/src/data_structures/mod.rs
@@ -1,5 +1,6 @@
 use std::hash::BuildHasherDefault;
 
+pub use ena::unify::{NoError, UnifyKey, UnifyValue};
 use rustc_hash::FxHasher;
 pub use rustc_hash::{FxHashMap as HashMap, FxHashSet as HashSet};
 
diff --git a/compiler/rustc_type_ir/src/flags.rs b/compiler/rustc_type_ir/src/flags.rs
index 6a2498242fe..e9d3a149a73 100644
--- a/compiler/rustc_type_ir/src/flags.rs
+++ b/compiler/rustc_type_ir/src/flags.rs
@@ -1,3 +1,9 @@
+use std::slice;
+
+use crate::inherent::*;
+use crate::visit::Flags;
+use crate::{self as ty, Interner};
+
 bitflags::bitflags! {
     /// Flags that we track on types. These flags are propagated upwards
     /// through the type during type construction, so that we can quickly check
@@ -128,3 +134,362 @@ bitflags::bitflags! {
         const HAS_BINDER_VARS             = 1 << 23;
     }
 }
+
+#[derive(Debug)]
+pub struct FlagComputation<I> {
+    pub flags: TypeFlags,
+
+    /// see `Ty::outer_exclusive_binder` for details
+    pub outer_exclusive_binder: ty::DebruijnIndex,
+
+    interner: std::marker::PhantomData<I>,
+}
+
+impl<I: Interner> FlagComputation<I> {
+    fn new() -> FlagComputation<I> {
+        FlagComputation {
+            flags: TypeFlags::empty(),
+            outer_exclusive_binder: ty::INNERMOST,
+            interner: std::marker::PhantomData,
+        }
+    }
+
+    #[allow(rustc::usage_of_ty_tykind)]
+    pub fn for_kind(kind: &ty::TyKind<I>) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        result.add_kind(kind);
+        result
+    }
+
+    pub fn for_predicate(binder: ty::Binder<I, ty::PredicateKind<I>>) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        result.add_predicate(binder);
+        result
+    }
+
+    pub fn for_const_kind(kind: &ty::ConstKind<I>) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        result.add_const_kind(kind);
+        result
+    }
+
+    pub fn for_clauses(clauses: &[I::Clause]) -> FlagComputation<I> {
+        let mut result = FlagComputation::new();
+        for c in clauses {
+            result.add_flags(c.as_predicate().flags());
+            result.add_exclusive_binder(c.as_predicate().outer_exclusive_binder());
+        }
+        result
+    }
+
+    fn add_flags(&mut self, flags: TypeFlags) {
+        self.flags = self.flags | flags;
+    }
+
+    /// indicates that `self` refers to something at binding level `binder`
+    fn add_bound_var(&mut self, binder: ty::DebruijnIndex) {
+        let exclusive_binder = binder.shifted_in(1);
+        self.add_exclusive_binder(exclusive_binder);
+    }
+
+    /// indicates that `self` refers to something *inside* binding
+    /// level `binder` -- not bound by `binder`, but bound by the next
+    /// binder internal to it
+    fn add_exclusive_binder(&mut self, exclusive_binder: ty::DebruijnIndex) {
+        self.outer_exclusive_binder = self.outer_exclusive_binder.max(exclusive_binder);
+    }
+
+    /// Adds the flags/depth from a set of types that appear within the current type, but within a
+    /// region binder.
+    fn bound_computation<T, F>(&mut self, value: ty::Binder<I, T>, f: F)
+    where
+        F: FnOnce(&mut Self, T),
+    {
+        let mut computation = FlagComputation::new();
+
+        if !value.bound_vars().is_empty() {
+            computation.add_flags(TypeFlags::HAS_BINDER_VARS);
+        }
+
+        f(&mut computation, value.skip_binder());
+
+        self.add_flags(computation.flags);
+
+        // The types that contributed to `computation` occurred within
+        // a region binder, so subtract one from the region depth
+        // within when adding the depth to `self`.
+        let outer_exclusive_binder = computation.outer_exclusive_binder;
+        if outer_exclusive_binder > ty::INNERMOST {
+            self.add_exclusive_binder(outer_exclusive_binder.shifted_out(1));
+        } // otherwise, this binder captures nothing
+    }
+
+    #[allow(rustc::usage_of_ty_tykind)]
+    fn add_kind(&mut self, kind: &ty::TyKind<I>) {
+        match *kind {
+            ty::Bool
+            | ty::Char
+            | ty::Int(_)
+            | ty::Float(_)
+            | ty::Uint(_)
+            | ty::Never
+            | ty::Str
+            | ty::Foreign(..) => {}
+
+            ty::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
+
+            ty::Param(_) => {
+                self.add_flags(TypeFlags::HAS_TY_PARAM);
+            }
+
+            ty::Closure(_, args)
+            | ty::Coroutine(_, args)
+            | ty::CoroutineClosure(_, args)
+            | ty::CoroutineWitness(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::Bound(debruijn, _) => {
+                self.add_bound_var(debruijn);
+                self.add_flags(TypeFlags::HAS_TY_BOUND);
+            }
+
+            ty::Placeholder(..) => {
+                self.add_flags(TypeFlags::HAS_TY_PLACEHOLDER);
+            }
+
+            ty::Infer(infer) => match infer {
+                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
+                    self.add_flags(TypeFlags::HAS_TY_FRESH)
+                }
+
+                ty::TyVar(_) | ty::IntVar(_) | ty::FloatVar(_) => {
+                    self.add_flags(TypeFlags::HAS_TY_INFER)
+                }
+            },
+
+            ty::Adt(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::Alias(kind, data) => {
+                self.add_flags(match kind {
+                    ty::Projection => TypeFlags::HAS_TY_PROJECTION,
+                    ty::Weak => TypeFlags::HAS_TY_WEAK,
+                    ty::Opaque => TypeFlags::HAS_TY_OPAQUE,
+                    ty::Inherent => TypeFlags::HAS_TY_INHERENT,
+                });
+
+                self.add_alias_ty(data);
+            }
+
+            ty::Dynamic(obj, r, _) => {
+                for predicate in obj.iter() {
+                    self.bound_computation(predicate, |computation, predicate| match predicate {
+                        ty::ExistentialPredicate::Trait(tr) => {
+                            computation.add_args(tr.args.as_slice())
+                        }
+                        ty::ExistentialPredicate::Projection(p) => {
+                            computation.add_existential_projection(&p);
+                        }
+                        ty::ExistentialPredicate::AutoTrait(_) => {}
+                    });
+                }
+
+                self.add_region(r);
+            }
+
+            ty::Array(tt, len) => {
+                self.add_ty(tt);
+                self.add_const(len);
+            }
+
+            ty::Pat(ty, pat) => {
+                self.add_ty(ty);
+                self.add_flags(pat.flags());
+            }
+
+            ty::Slice(tt) => self.add_ty(tt),
+
+            ty::RawPtr(ty, _) => {
+                self.add_ty(ty);
+            }
+
+            ty::Ref(r, ty, _) => {
+                self.add_region(r);
+                self.add_ty(ty);
+            }
+
+            ty::Tuple(types) => {
+                self.add_tys(types);
+            }
+
+            ty::FnDef(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
+                computation.add_tys(sig_tys.inputs_and_output);
+            }),
+
+            ty::UnsafeBinder(bound_ty) => {
+                self.bound_computation(bound_ty.into(), |computation, ty| {
+                    computation.add_ty(ty);
+                })
+            }
+        }
+    }
+
+    fn add_predicate(&mut self, binder: ty::Binder<I, ty::PredicateKind<I>>) {
+        self.bound_computation(binder, |computation, atom| computation.add_predicate_atom(atom));
+    }
+
+    fn add_predicate_atom(&mut self, atom: ty::PredicateKind<I>) {
+        match atom {
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) => {
+                self.add_args(trait_pred.trait_ref.args.as_slice());
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(ty::HostEffectPredicate {
+                trait_ref,
+                constness: _,
+            })) => {
+                self.add_args(trait_ref.args.as_slice());
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
+                a,
+                b,
+            ))) => {
+                self.add_region(a);
+                self.add_region(b);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
+                ty,
+                region,
+            ))) => {
+                self.add_ty(ty);
+                self.add_region(region);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
+                self.add_const(ct);
+                self.add_ty(ty);
+            }
+            ty::PredicateKind::Subtype(ty::SubtypePredicate { a_is_expected: _, a, b }) => {
+                self.add_ty(a);
+                self.add_ty(b);
+            }
+            ty::PredicateKind::Coerce(ty::CoercePredicate { a, b }) => {
+                self.add_ty(a);
+                self.add_ty(b);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::Projection(ty::ProjectionPredicate {
+                projection_term,
+                term,
+            })) => {
+                self.add_alias_term(projection_term);
+                self.add_term(term);
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
+                self.add_args(slice::from_ref(&arg));
+            }
+            ty::PredicateKind::DynCompatible(_def_id) => {}
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
+                self.add_const(uv);
+            }
+            ty::PredicateKind::ConstEquate(expected, found) => {
+                self.add_const(expected);
+                self.add_const(found);
+            }
+            ty::PredicateKind::Ambiguous => {}
+            ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term }) => {
+                self.add_alias_term(alias);
+                self.add_term(term);
+            }
+            ty::PredicateKind::AliasRelate(t1, t2, _) => {
+                self.add_term(t1);
+                self.add_term(t2);
+            }
+        }
+    }
+
+    fn add_ty(&mut self, ty: I::Ty) {
+        self.add_flags(ty.flags());
+        self.add_exclusive_binder(ty.outer_exclusive_binder());
+    }
+
+    fn add_tys(&mut self, tys: I::Tys) {
+        for ty in tys.iter() {
+            self.add_ty(ty);
+        }
+    }
+
+    fn add_region(&mut self, r: I::Region) {
+        self.add_flags(r.flags());
+        if let ty::ReBound(debruijn, _) = r.kind() {
+            self.add_bound_var(debruijn);
+        }
+    }
+
+    fn add_const(&mut self, c: I::Const) {
+        self.add_flags(c.flags());
+        self.add_exclusive_binder(c.outer_exclusive_binder());
+    }
+
+    fn add_const_kind(&mut self, c: &ty::ConstKind<I>) {
+        match *c {
+            ty::ConstKind::Unevaluated(uv) => {
+                self.add_args(uv.args.as_slice());
+                self.add_flags(TypeFlags::HAS_CT_PROJECTION);
+            }
+            ty::ConstKind::Infer(infer) => match infer {
+                ty::InferConst::Fresh(_) => self.add_flags(TypeFlags::HAS_CT_FRESH),
+                ty::InferConst::Var(_) => self.add_flags(TypeFlags::HAS_CT_INFER),
+            },
+            ty::ConstKind::Bound(debruijn, _) => {
+                self.add_bound_var(debruijn);
+                self.add_flags(TypeFlags::HAS_CT_BOUND);
+            }
+            ty::ConstKind::Param(_) => {
+                self.add_flags(TypeFlags::HAS_CT_PARAM);
+            }
+            ty::ConstKind::Placeholder(_) => {
+                self.add_flags(TypeFlags::HAS_CT_PLACEHOLDER);
+            }
+            ty::ConstKind::Value(cv) => self.add_ty(cv.ty()),
+            ty::ConstKind::Expr(e) => self.add_args(e.args().as_slice()),
+            ty::ConstKind::Error(_) => self.add_flags(TypeFlags::HAS_ERROR),
+        }
+    }
+
+    fn add_existential_projection(&mut self, projection: &ty::ExistentialProjection<I>) {
+        self.add_args(projection.args.as_slice());
+        match projection.term.kind() {
+            ty::TermKind::Ty(ty) => self.add_ty(ty),
+            ty::TermKind::Const(ct) => self.add_const(ct),
+        }
+    }
+
+    fn add_alias_ty(&mut self, alias_ty: ty::AliasTy<I>) {
+        self.add_args(alias_ty.args.as_slice());
+    }
+
+    fn add_alias_term(&mut self, alias_term: ty::AliasTerm<I>) {
+        self.add_args(alias_term.args.as_slice());
+    }
+
+    fn add_args(&mut self, args: &[I::GenericArg]) {
+        for kind in args {
+            match kind.kind() {
+                ty::GenericArgKind::Type(ty) => self.add_ty(ty),
+                ty::GenericArgKind::Lifetime(lt) => self.add_region(lt),
+                ty::GenericArgKind::Const(ct) => self.add_const(ct),
+            }
+        }
+    }
+
+    fn add_term(&mut self, term: I::Term) {
+        match term.kind() {
+            ty::TermKind::Ty(ty) => self.add_ty(ty),
+            ty::TermKind::Const(ct) => self.add_const(ct),
+        }
+    }
+}
diff --git a/compiler/rustc_type_ir/src/fold.rs b/compiler/rustc_type_ir/src/fold.rs
index e58f25f4ce7..ce1188070ca 100644
--- a/compiler/rustc_type_ir/src/fold.rs
+++ b/compiler/rustc_type_ir/src/fold.rs
@@ -45,6 +45,7 @@
 //! - u.fold_with(folder)
 //! ```
 
+use std::convert::Infallible;
 use std::mem;
 use std::sync::Arc;
 
@@ -56,12 +57,6 @@ use crate::inherent::*;
 use crate::visit::{TypeVisitable, TypeVisitableExt as _};
 use crate::{self as ty, Interner, TypeFlags};
 
-#[cfg(feature = "nightly")]
-type Never = !;
-
-#[cfg(not(feature = "nightly"))]
-type Never = std::convert::Infallible;
-
 /// This trait is implemented for every type that can be folded,
 /// providing the skeleton of the traversal.
 ///
@@ -82,18 +77,24 @@ pub trait TypeFoldable<I: Interner>: TypeVisitable<I> + Clone {
     ///
     /// For types of interest (such as `Ty`), the implementation of this method
     /// calls a folder method specifically for that type (such as
-    /// `F::try_fold_ty`). This is where control transfers from `TypeFoldable`
-    /// to `TypeFolder`.
+    /// `F::try_fold_ty`). This is where control transfers from [`TypeFoldable`]
+    /// to [`FallibleTypeFolder`].
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error>;
 
-    /// A convenient alternative to `try_fold_with` for use with infallible
-    /// folders. Do not override this method, to ensure coherence with
-    /// `try_fold_with`.
-    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
-        match self.try_fold_with(folder) {
-            Ok(t) => t,
-        }
-    }
+    /// The entry point for folding. To fold a value `t` with a folder `f`
+    /// call: `t.fold_with(f)`.
+    ///
+    /// For most types, this just traverses the value, calling `fold_with`
+    /// on each field/element.
+    ///
+    /// For types of interest (such as `Ty`), the implementation of this method
+    /// calls a folder method specifically for that type (such as
+    /// `F::fold_ty`). This is where control transfers from `TypeFoldable`
+    /// to `TypeFolder`.
+    ///
+    /// Same as [`TypeFoldable::try_fold_with`], but not fallible. Make sure to keep
+    /// the behavior in sync across functions.
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self;
 }
 
 // This trait is implemented for types of interest.
@@ -112,11 +113,7 @@ pub trait TypeSuperFoldable<I: Interner>: TypeFoldable<I> {
     /// A convenient alternative to `try_super_fold_with` for use with
     /// infallible folders. Do not override this method, to ensure coherence
     /// with `try_super_fold_with`.
-    fn super_fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
-        match self.try_super_fold_with(folder) {
-            Ok(t) => t,
-        }
-    }
+    fn super_fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self;
 }
 
 /// This trait is implemented for every infallible folding traversal. There is
@@ -128,7 +125,7 @@ pub trait TypeSuperFoldable<I: Interner>: TypeFoldable<I> {
 /// A blanket implementation of [`FallibleTypeFolder`] will defer to
 /// the infallible methods of this trait to ensure that the two APIs
 /// are coherent.
-pub trait TypeFolder<I: Interner>: FallibleTypeFolder<I, Error = Never> {
+pub trait TypeFolder<I: Interner>: Sized {
     fn cx(&self) -> I;
 
     fn fold_binder<T>(&mut self, t: ty::Binder<I, T>) -> ty::Binder<I, T>
@@ -195,42 +192,6 @@ pub trait FallibleTypeFolder<I: Interner>: Sized {
     }
 }
 
-// This blanket implementation of the fallible trait for infallible folders
-// delegates to infallible methods to ensure coherence.
-impl<I: Interner, F> FallibleTypeFolder<I> for F
-where
-    F: TypeFolder<I>,
-{
-    type Error = Never;
-
-    fn cx(&self) -> I {
-        TypeFolder::cx(self)
-    }
-
-    fn try_fold_binder<T>(&mut self, t: ty::Binder<I, T>) -> Result<ty::Binder<I, T>, Never>
-    where
-        T: TypeFoldable<I>,
-    {
-        Ok(self.fold_binder(t))
-    }
-
-    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, Never> {
-        Ok(self.fold_ty(t))
-    }
-
-    fn try_fold_region(&mut self, r: I::Region) -> Result<I::Region, Never> {
-        Ok(self.fold_region(r))
-    }
-
-    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, Never> {
-        Ok(self.fold_const(c))
-    }
-
-    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, Never> {
-        Ok(self.fold_predicate(p))
-    }
-}
-
 ///////////////////////////////////////////////////////////////////////////
 // Traversal implementations.
 
@@ -238,6 +199,10 @@ impl<I: Interner, T: TypeFoldable<I>, U: TypeFoldable<I>> TypeFoldable<I> for (T
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<(T, U), F::Error> {
         Ok((self.0.try_fold_with(folder)?, self.1.try_fold_with(folder)?))
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        (self.0.fold_with(folder), self.1.fold_with(folder))
+    }
 }
 
 impl<I: Interner, A: TypeFoldable<I>, B: TypeFoldable<I>, C: TypeFoldable<I>> TypeFoldable<I>
@@ -253,6 +218,10 @@ impl<I: Interner, A: TypeFoldable<I>, B: TypeFoldable<I>, C: TypeFoldable<I>> Ty
             self.2.try_fold_with(folder)?,
         ))
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        (self.0.fold_with(folder), self.1.fold_with(folder), self.2.fold_with(folder))
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Option<T> {
@@ -262,6 +231,10 @@ impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Option<T> {
             None => None,
         })
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        Some(self?.fold_with(folder))
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>, E: TypeFoldable<I>> TypeFoldable<I> for Result<T, E> {
@@ -271,41 +244,61 @@ impl<I: Interner, T: TypeFoldable<I>, E: TypeFoldable<I>> TypeFoldable<I> for Re
             Err(e) => Err(e.try_fold_with(folder)?),
         })
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        match self {
+            Ok(v) => Ok(v.fold_with(folder)),
+            Err(e) => Err(e.fold_with(folder)),
+        }
+    }
+}
+
+fn fold_arc<T: Clone, E>(
+    mut arc: Arc<T>,
+    fold: impl FnOnce(T) -> Result<T, E>,
+) -> Result<Arc<T>, E> {
+    // We merely want to replace the contained `T`, if at all possible,
+    // so that we don't needlessly allocate a new `Arc` or indeed clone
+    // the contained type.
+    unsafe {
+        // First step is to ensure that we have a unique reference to
+        // the contained type, which `Arc::make_mut` will accomplish (by
+        // allocating a new `Arc` and cloning the `T` only if required).
+        // This is done *before* casting to `Arc<ManuallyDrop<T>>` so that
+        // panicking during `make_mut` does not leak the `T`.
+        Arc::make_mut(&mut arc);
+
+        // Casting to `Arc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
+        // is `repr(transparent)`.
+        let ptr = Arc::into_raw(arc).cast::<mem::ManuallyDrop<T>>();
+        let mut unique = Arc::from_raw(ptr);
+
+        // Call to `Arc::make_mut` above guarantees that `unique` is the
+        // sole reference to the contained value, so we can avoid doing
+        // a checked `get_mut` here.
+        let slot = Arc::get_mut(&mut unique).unwrap_unchecked();
+
+        // Semantically move the contained type out from `unique`, fold
+        // it, then move the folded value back into `unique`. Should
+        // folding fail, `ManuallyDrop` ensures that the "moved-out"
+        // value is not re-dropped.
+        let owned = mem::ManuallyDrop::take(slot);
+        let folded = fold(owned)?;
+        *slot = mem::ManuallyDrop::new(folded);
+
+        // Cast back to `Arc<T>`.
+        Ok(Arc::from_raw(Arc::into_raw(unique).cast()))
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Arc<T> {
-    fn try_fold_with<F: FallibleTypeFolder<I>>(mut self, folder: &mut F) -> Result<Self, F::Error> {
-        // We merely want to replace the contained `T`, if at all possible,
-        // so that we don't needlessly allocate a new `Arc` or indeed clone
-        // the contained type.
-        unsafe {
-            // First step is to ensure that we have a unique reference to
-            // the contained type, which `Arc::make_mut` will accomplish (by
-            // allocating a new `Arc` and cloning the `T` only if required).
-            // This is done *before* casting to `Arc<ManuallyDrop<T>>` so that
-            // panicking during `make_mut` does not leak the `T`.
-            Arc::make_mut(&mut self);
-
-            // Casting to `Arc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
-            // is `repr(transparent)`.
-            let ptr = Arc::into_raw(self).cast::<mem::ManuallyDrop<T>>();
-            let mut unique = Arc::from_raw(ptr);
-
-            // Call to `Arc::make_mut` above guarantees that `unique` is the
-            // sole reference to the contained value, so we can avoid doing
-            // a checked `get_mut` here.
-            let slot = Arc::get_mut(&mut unique).unwrap_unchecked();
-
-            // Semantically move the contained type out from `unique`, fold
-            // it, then move the folded value back into `unique`. Should
-            // folding fail, `ManuallyDrop` ensures that the "moved-out"
-            // value is not re-dropped.
-            let owned = mem::ManuallyDrop::take(slot);
-            let folded = owned.try_fold_with(folder)?;
-            *slot = mem::ManuallyDrop::new(folded);
-
-            // Cast back to `Arc<T>`.
-            Ok(Arc::from_raw(Arc::into_raw(unique).cast()))
+    fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
+        fold_arc(self, |t| t.try_fold_with(folder))
+    }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        match fold_arc::<T, Infallible>(self, |t| Ok(t.fold_with(folder))) {
+            Ok(t) => t,
         }
     }
 }
@@ -315,30 +308,51 @@ impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Box<T> {
         *self = (*self).try_fold_with(folder)?;
         Ok(self)
     }
+
+    fn fold_with<F: TypeFolder<I>>(mut self, folder: &mut F) -> Self {
+        *self = (*self).fold_with(folder);
+        self
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Vec<T> {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         self.into_iter().map(|t| t.try_fold_with(folder)).collect()
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        self.into_iter().map(|t| t.fold_with(folder)).collect()
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for ThinVec<T> {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         self.into_iter().map(|t| t.try_fold_with(folder)).collect()
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        self.into_iter().map(|t| t.fold_with(folder)).collect()
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Box<[T]> {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         Vec::from(self).try_fold_with(folder).map(Vec::into_boxed_slice)
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        Vec::into_boxed_slice(Vec::from(self).fold_with(folder))
+    }
 }
 
 impl<I: Interner, T: TypeFoldable<I>, Ix: Idx> TypeFoldable<I> for IndexVec<Ix, T> {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         self.raw.try_fold_with(folder).map(IndexVec::from_raw)
     }
+
+    fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
+        IndexVec::from_raw(self.raw.fold_with(folder))
+    }
 }
 
 ///////////////////////////////////////////////////////////////////////////
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 59c2d3c2fc8..417803e75ea 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -155,6 +155,39 @@ pub trait Ty<I: Interner<Ty = Self>>:
     fn is_known_rigid(self) -> bool {
         self.kind().is_known_rigid()
     }
+
+    fn is_guaranteed_unsized_raw(self) -> bool {
+        match self.kind() {
+            ty::Dynamic(_, _, ty::Dyn) | ty::Slice(_) | ty::Str => true,
+            ty::Bool
+            | ty::Char
+            | ty::Int(_)
+            | ty::Uint(_)
+            | ty::Float(_)
+            | ty::Adt(_, _)
+            | ty::Foreign(_)
+            | ty::Array(_, _)
+            | ty::Pat(_, _)
+            | ty::RawPtr(_, _)
+            | ty::Ref(_, _, _)
+            | ty::FnDef(_, _)
+            | ty::FnPtr(_, _)
+            | ty::UnsafeBinder(_)
+            | ty::Closure(_, _)
+            | ty::CoroutineClosure(_, _)
+            | ty::Coroutine(_, _)
+            | ty::CoroutineWitness(_, _)
+            | ty::Never
+            | ty::Tuple(_)
+            | ty::Alias(_, _)
+            | ty::Param(_)
+            | ty::Bound(_, _)
+            | ty::Placeholder(_)
+            | ty::Infer(_)
+            | ty::Error(_)
+            | ty::Dynamic(_, _, ty::DynStar) => false,
+        }
+    }
 }
 
 pub trait Tys<I: Interner<Tys = Self>>:
@@ -550,7 +583,7 @@ pub trait Span<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
 
 pub trait SliceLike: Sized + Copy {
     type Item: Copy;
-    type IntoIter: Iterator<Item = Self::Item>;
+    type IntoIter: Iterator<Item = Self::Item> + DoubleEndedIterator;
 
     fn iter(self) -> Self::IntoIter;
 
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index fce93b735d7..71bfeabfda8 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -31,6 +31,7 @@ pub trait Interner:
     + IrPrint<ty::SubtypePredicate<Self>>
     + IrPrint<ty::CoercePredicate<Self>>
     + IrPrint<ty::FnSig<Self>>
+    + IrPrint<ty::PatternKind<Self>>
 {
     type DefId: DefId<Self>;
     type LocalDefId: Copy + Debug + Hash + Eq + Into<Self::DefId> + TypeFoldable<Self>;
@@ -104,7 +105,14 @@ pub trait Interner:
     type ErrorGuaranteed: Copy + Debug + Hash + Eq;
     type BoundExistentialPredicates: BoundExistentialPredicates<Self>;
     type AllocId: Copy + Debug + Hash + Eq;
-    type Pat: Copy + Debug + Hash + Eq + Debug + Relate<Self>;
+    type Pat: Copy
+        + Debug
+        + Hash
+        + Eq
+        + Debug
+        + Relate<Self>
+        + Flags
+        + IntoKind<Kind = ty::PatternKind<Self>>;
     type Safety: Safety<Self>;
     type Abi: Abi<Self>;
 
@@ -255,6 +263,8 @@ pub trait Interner:
         def_id: Self::DefId,
     ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = ty::Binder<Self, ty::TraitRef<Self>>>>;
 
+    fn impl_self_is_guaranteed_unsized(self, def_id: Self::DefId) -> bool;
+
     fn has_target_features(self, def_id: Self::DefId) -> bool;
 
     fn require_lang_item(self, lang_item: TraitSolverLangItem) -> Self::DefId;
diff --git a/compiler/rustc_type_ir/src/ir_print.rs b/compiler/rustc_type_ir/src/ir_print.rs
index 0c71f3a3df2..388ad09cb20 100644
--- a/compiler/rustc_type_ir/src/ir_print.rs
+++ b/compiler/rustc_type_ir/src/ir_print.rs
@@ -2,8 +2,8 @@ use std::fmt;
 
 use crate::{
     AliasTerm, AliasTy, Binder, CoercePredicate, ExistentialProjection, ExistentialTraitRef, FnSig,
-    HostEffectPredicate, Interner, NormalizesTo, OutlivesPredicate, ProjectionPredicate,
-    SubtypePredicate, TraitPredicate, TraitRef,
+    HostEffectPredicate, Interner, NormalizesTo, OutlivesPredicate, PatternKind,
+    ProjectionPredicate, SubtypePredicate, TraitPredicate, TraitRef,
 };
 
 pub trait IrPrint<T> {
@@ -57,9 +57,10 @@ define_display_via_print!(
     AliasTy,
     AliasTerm,
     FnSig,
+    PatternKind,
 );
 
-define_debug_via_print!(TraitRef, ExistentialTraitRef, ExistentialProjection);
+define_debug_via_print!(TraitRef, ExistentialTraitRef, PatternKind);
 
 impl<I: Interner, T> fmt::Display for OutlivesPredicate<I, T>
 where
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index 4e2baca2785..792090effcf 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -1,12 +1,12 @@
 // tidy-alphabetical-start
 #![allow(rustc::usage_of_ty_tykind)]
 #![allow(rustc::usage_of_type_ir_inherent)]
+#![allow(rustc::usage_of_type_ir_traits)]
 #![cfg_attr(
     feature = "nightly",
     feature(associated_type_defaults, never_type, rustc_attrs, negative_impls)
 )]
 #![cfg_attr(feature = "nightly", allow(internal_features))]
-#![cfg_attr(not(bootstrap), allow(rustc::usage_of_type_ir_traits))]
 // tidy-alphabetical-end
 
 extern crate self as rustc_type_ir;
@@ -31,6 +31,7 @@ pub mod outlives;
 pub mod relate;
 pub mod search_graph;
 pub mod solve;
+pub mod walk;
 
 // These modules are not `pub` since they are glob-imported.
 #[macro_use]
@@ -44,6 +45,7 @@ mod generic_arg;
 mod infer_ctxt;
 mod interner;
 mod opaque_ty;
+mod pattern;
 mod predicate;
 mod predicate_kind;
 mod region_kind;
@@ -67,6 +69,7 @@ pub use generic_arg::*;
 pub use infer_ctxt::*;
 pub use interner::*;
 pub use opaque_ty::*;
+pub use pattern::*;
 pub use predicate::*;
 pub use predicate_kind::*;
 pub use region_kind::*;
diff --git a/compiler/rustc_type_ir/src/pattern.rs b/compiler/rustc_type_ir/src/pattern.rs
new file mode 100644
index 00000000000..d74a82da1f9
--- /dev/null
+++ b/compiler/rustc_type_ir/src/pattern.rs
@@ -0,0 +1,16 @@
+use derive_where::derive_where;
+#[cfg(feature = "nightly")]
+use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
+use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
+
+use crate::Interner;
+
+#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+#[cfg_attr(
+    feature = "nightly",
+    derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
+)]
+pub enum PatternKind<I: Interner> {
+    Range { start: I::Const, end: I::Const },
+}
diff --git a/compiler/rustc_type_ir/src/predicate.rs b/compiler/rustc_type_ir/src/predicate.rs
index 22d0fa23d0c..8e10636ff65 100644
--- a/compiler/rustc_type_ir/src/predicate.rs
+++ b/compiler/rustc_type_ir/src/predicate.rs
@@ -374,7 +374,7 @@ impl<I: Interner> ty::Binder<I, ExistentialTraitRef<I>> {
 }
 
 /// A `ProjectionPredicate` for an `ExistentialTraitRef`.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
diff --git a/compiler/rustc_type_ir/src/solve/inspect.rs b/compiler/rustc_type_ir/src/solve/inspect.rs
index 18fb71dd290..b10641b287d 100644
--- a/compiler/rustc_type_ir/src/solve/inspect.rs
+++ b/compiler/rustc_type_ir/src/solve/inspect.rs
@@ -118,10 +118,12 @@ pub enum ProbeKind<I: Interner> {
     /// Used in the probe that wraps normalizing the non-self type for the unsize
     /// trait, which is also structurally matched on.
     UnsizeAssembly,
-    /// During upcasting from some source object to target object type, used to
-    /// do a probe to find out what projection type(s) may be used to prove that
-    /// the source type upholds all of the target type's object bounds.
-    UpcastProjectionCompatibility,
+    /// Used to do a probe to find out what projection type(s) match a given
+    /// alias bound or projection predicate. For trait upcasting, this is used
+    /// to prove that the source type upholds all of the target type's object
+    /// bounds. For object type bounds, this is used when eagerly replacing
+    /// supertrait aliases.
+    ProjectionCompatibility,
     /// Looking for param-env candidates that satisfy the trait ref for a projection.
     ShadowedEnvProbing,
     /// Try to unify an opaque type with an existing key in the storage.
diff --git a/compiler/rustc_type_ir/src/solve/mod.rs b/compiler/rustc_type_ir/src/solve/mod.rs
index 3aec4804b27..4e9b87fdf74 100644
--- a/compiler/rustc_type_ir/src/solve/mod.rs
+++ b/compiler/rustc_type_ir/src/solve/mod.rs
@@ -83,8 +83,11 @@ pub enum GoalSource {
     /// Instantiating a higher-ranked goal and re-proving it.
     InstantiateHigherRanked,
     /// Predicate required for an alias projection to be well-formed.
-    /// This is used in two places: projecting to an opaque whose hidden type
-    /// is already registered in the opaque type storage, and for rigid projections.
+    /// This is used in three places:
+    /// 1. projecting to an opaque whose hidden type is already registered in
+    ///    the opaque type storage,
+    /// 2. for rigid projections's trait goal,
+    /// 3. for GAT where clauses.
     AliasWellFormed,
     /// In case normalizing aliases in nested goals cycles, eagerly normalizing these
     /// aliases in the context of the parent may incorrectly change the cycle kind.
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index d35b22d517c..753a72a051a 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -6,9 +6,8 @@ use rustc_ast_ir::Mutability;
 #[cfg(feature = "nightly")]
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 #[cfg(feature = "nightly")]
-use rustc_data_structures::unify::{NoError, UnifyKey, UnifyValue};
-#[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
+use rustc_type_ir::data_structures::{NoError, UnifyKey, UnifyValue};
 use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
 
 use self::TyKind::*;
@@ -796,7 +795,6 @@ pub enum InferTy {
 
 /// Raw `TyVid` are used as the unification key for `sub_relations`;
 /// they carry no values.
-#[cfg(feature = "nightly")]
 impl UnifyKey for TyVid {
     type Value = ();
     #[inline]
@@ -812,7 +810,6 @@ impl UnifyKey for TyVid {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyValue for IntVarValue {
     type Error = NoError;
 
@@ -832,7 +829,6 @@ impl UnifyValue for IntVarValue {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyKey for IntVid {
     type Value = IntVarValue;
     #[inline] // make this function eligible for inlining - it is quite hot.
@@ -848,7 +844,6 @@ impl UnifyKey for IntVid {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyValue for FloatVarValue {
     type Error = NoError;
 
@@ -866,7 +861,6 @@ impl UnifyValue for FloatVarValue {
     }
 }
 
-#[cfg(feature = "nightly")]
 impl UnifyKey for FloatVid {
     type Value = FloatVarValue;
     #[inline]
diff --git a/compiler/rustc_middle/src/ty/walk.rs b/compiler/rustc_type_ir/src/walk.rs
index a23316ae6fc..5683e1f1712 100644
--- a/compiler/rustc_middle/src/ty/walk.rs
+++ b/compiler/rustc_type_ir/src/walk.rs
@@ -1,20 +1,21 @@
 //! An iterator over the type substructure.
 //! WARNING: this does not keep track of the region depth.
 
-use rustc_data_structures::sso::SsoHashSet;
 use smallvec::{SmallVec, smallvec};
 use tracing::debug;
 
-use crate::ty::{self, GenericArg, GenericArgKind, Ty};
+use crate::data_structures::SsoHashSet;
+use crate::inherent::*;
+use crate::{self as ty, Interner};
 
 // The TypeWalker's stack is hot enough that it's worth going to some effort to
 // avoid heap allocations.
-type TypeWalkerStack<'tcx> = SmallVec<[GenericArg<'tcx>; 8]>;
+type TypeWalkerStack<I> = SmallVec<[<I as Interner>::GenericArg; 8]>;
 
-pub struct TypeWalker<'tcx> {
-    stack: TypeWalkerStack<'tcx>,
+pub struct TypeWalker<I: Interner> {
+    stack: TypeWalkerStack<I>,
     last_subtree: usize,
-    pub visited: SsoHashSet<GenericArg<'tcx>>,
+    pub visited: SsoHashSet<I::GenericArg>,
 }
 
 /// An iterator for walking the type tree.
@@ -25,8 +26,8 @@ pub struct TypeWalker<'tcx> {
 /// in this situation walker only visits each type once.
 /// It maintains a set of visited types and
 /// skips any types that are already there.
-impl<'tcx> TypeWalker<'tcx> {
-    pub fn new(root: GenericArg<'tcx>) -> Self {
+impl<I: Interner> TypeWalker<I> {
+    pub fn new(root: I::GenericArg) -> Self {
         Self { stack: smallvec![root], last_subtree: 1, visited: SsoHashSet::new() }
     }
 
@@ -47,16 +48,16 @@ impl<'tcx> TypeWalker<'tcx> {
     }
 }
 
-impl<'tcx> Iterator for TypeWalker<'tcx> {
-    type Item = GenericArg<'tcx>;
+impl<I: Interner> Iterator for TypeWalker<I> {
+    type Item = I::GenericArg;
 
-    fn next(&mut self) -> Option<GenericArg<'tcx>> {
+    fn next(&mut self) -> Option<I::GenericArg> {
         debug!("next(): stack={:?}", self.stack);
         loop {
             let next = self.stack.pop()?;
             self.last_subtree = self.stack.len();
             if self.visited.insert(next) {
-                push_inner(&mut self.stack, next);
+                push_inner::<I>(&mut self.stack, next);
                 debug!("next: stack={:?}", self.stack);
                 return Some(next);
             }
@@ -64,63 +65,15 @@ impl<'tcx> Iterator for TypeWalker<'tcx> {
     }
 }
 
-impl<'tcx> GenericArg<'tcx> {
-    /// Iterator that walks `self` and any types reachable from
-    /// `self`, in depth-first order. Note that just walks the types
-    /// that appear in `self`, it does not descend into the fields of
-    /// structs or variants. For example:
-    ///
-    /// ```text
-    /// isize => { isize }
-    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
-    /// [isize] => { [isize], isize }
-    /// ```
-    pub fn walk(self) -> TypeWalker<'tcx> {
-        TypeWalker::new(self)
-    }
-}
-
-impl<'tcx> Ty<'tcx> {
-    /// Iterator that walks `self` and any types reachable from
-    /// `self`, in depth-first order. Note that just walks the types
-    /// that appear in `self`, it does not descend into the fields of
-    /// structs or variants. For example:
-    ///
-    /// ```text
-    /// isize => { isize }
-    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
-    /// [isize] => { [isize], isize }
-    /// ```
-    pub fn walk(self) -> TypeWalker<'tcx> {
-        TypeWalker::new(self.into())
-    }
-}
-
-impl<'tcx> ty::Const<'tcx> {
-    /// Iterator that walks `self` and any types reachable from
-    /// `self`, in depth-first order. Note that just walks the types
-    /// that appear in `self`, it does not descend into the fields of
-    /// structs or variants. For example:
-    ///
-    /// ```text
-    /// isize => { isize }
-    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
-    /// [isize] => { [isize], isize }
-    /// ```
-    pub fn walk(self) -> TypeWalker<'tcx> {
-        TypeWalker::new(self.into())
-    }
-}
-
 /// We push `GenericArg`s on the stack in reverse order so as to
 /// maintain a pre-order traversal. As of the time of this
 /// writing, the fact that the traversal is pre-order is not
 /// known to be significant to any code, but it seems like the
 /// natural order one would expect (basically, the order of the
 /// types as they are written).
-fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>) {
-    match parent.unpack() {
-        GenericArgKind::Type(parent_ty) => match *parent_ty.kind() {
+fn push_inner<I: Interner>(stack: &mut TypeWalkerStack<I>, parent: I::GenericArg) {
+    match parent.kind() {
+        ty::GenericArgKind::Type(parent_ty) => match parent_ty.kind() {
             ty::Bool
             | ty::Char
             | ty::Int(_)
@@ -136,7 +89,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             | ty::Foreign(..) => {}
 
             ty::Pat(ty, pat) => {
-                match *pat {
+                match pat.kind() {
                     ty::PatternKind::Range { start, end } => {
                         stack.push(end.into());
                         stack.push(start.into());
@@ -163,22 +116,25 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             }
             ty::Dynamic(obj, lt, _) => {
                 stack.push(lt.into());
-                stack.extend(obj.iter().rev().flat_map(|predicate| {
-                    let (args, opt_ty) = match predicate.skip_binder() {
-                        ty::ExistentialPredicate::Trait(tr) => (tr.args, None),
-                        ty::ExistentialPredicate::Projection(p) => (p.args, Some(p.term)),
-                        ty::ExistentialPredicate::AutoTrait(_) =>
-                        // Empty iterator
-                        {
-                            (ty::GenericArgs::empty(), None)
-                        }
-                    };
-
-                    args.iter().rev().chain(opt_ty.map(|term| match term.unpack() {
-                        ty::TermKind::Ty(ty) => ty.into(),
-                        ty::TermKind::Const(ct) => ct.into(),
-                    }))
-                }));
+                stack.extend(
+                    obj.iter()
+                        .rev()
+                        .filter_map(|predicate| {
+                            let (args, opt_ty) = match predicate.skip_binder() {
+                                ty::ExistentialPredicate::Trait(tr) => (tr.args, None),
+                                ty::ExistentialPredicate::Projection(p) => (p.args, Some(p.term)),
+                                ty::ExistentialPredicate::AutoTrait(_) => {
+                                    return None;
+                                }
+                            };
+
+                            Some(args.iter().rev().chain(opt_ty.map(|term| match term.kind() {
+                                ty::TermKind::Ty(ty) => ty.into(),
+                                ty::TermKind::Const(ct) => ct.into(),
+                            })))
+                        })
+                        .flatten(),
+                );
             }
             ty::Adt(_, args)
             | ty::Closure(_, args)
@@ -188,7 +144,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             | ty::FnDef(_, args) => {
                 stack.extend(args.iter().rev());
             }
-            ty::Tuple(ts) => stack.extend(ts.iter().rev().map(GenericArg::from)),
+            ty::Tuple(ts) => stack.extend(ts.iter().rev().map(|ty| ty.into())),
             ty::FnPtr(sig_tys, _hdr) => {
                 stack.extend(
                     sig_tys.skip_binder().inputs_and_output.iter().rev().map(|ty| ty.into()),
@@ -198,15 +154,15 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
                 stack.push(bound_ty.skip_binder().into());
             }
         },
-        GenericArgKind::Lifetime(_) => {}
-        GenericArgKind::Const(parent_ct) => match parent_ct.kind() {
+        ty::GenericArgKind::Lifetime(_) => {}
+        ty::GenericArgKind::Const(parent_ct) => match parent_ct.kind() {
             ty::ConstKind::Infer(_)
             | ty::ConstKind::Param(_)
             | ty::ConstKind::Placeholder(_)
             | ty::ConstKind::Bound(..)
             | ty::ConstKind::Error(_) => {}
 
-            ty::ConstKind::Value(cv) => stack.push(cv.ty.into()),
+            ty::ConstKind::Value(cv) => stack.push(cv.ty().into()),
 
             ty::ConstKind::Expr(expr) => stack.extend(expr.args().iter().rev()),
             ty::ConstKind::Unevaluated(ct) => {
diff --git a/compiler/rustc_type_ir_macros/src/lib.rs b/compiler/rustc_type_ir_macros/src/lib.rs
index 8eefecdc980..3a10d0d41ef 100644
--- a/compiler/rustc_type_ir_macros/src/lib.rs
+++ b/compiler/rustc_type_ir_macros/src/lib.rs
@@ -83,7 +83,7 @@ fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::Toke
     s.add_where_predicate(parse_quote! { I: Interner });
     s.add_bounds(synstructure::AddBounds::Fields);
     s.bind_with(|_| synstructure::BindStyle::Move);
-    let body_fold = s.each_variant(|vi| {
+    let body_try_fold = s.each_variant(|vi| {
         let bindings = vi.bindings();
         vi.construct(|_, index| {
             let bind = &bindings[index];
@@ -99,6 +99,22 @@ fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::Toke
         })
     });
 
+    let body_fold = s.each_variant(|vi| {
+        let bindings = vi.bindings();
+        vi.construct(|_, index| {
+            let bind = &bindings[index];
+
+            // retain value of fields with #[type_foldable(identity)]
+            if has_ignore_attr(&bind.ast().attrs, "type_foldable", "identity") {
+                bind.to_token_stream()
+            } else {
+                quote! {
+                    ::rustc_type_ir::TypeFoldable::fold_with(#bind, __folder)
+                }
+            }
+        })
+    });
+
     // We filter fields which get ignored and don't require them to implement
     // `TypeFoldable`. We do so after generating `body_fold` as we still need
     // to generate code for them.
@@ -111,7 +127,14 @@ fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::Toke
                 self,
                 __folder: &mut __F
             ) -> Result<Self, __F::Error> {
-                Ok(match self { #body_fold })
+                Ok(match self { #body_try_fold })
+            }
+
+            fn fold_with<__F: ::rustc_type_ir::TypeFolder<I>>(
+                self,
+                __folder: &mut __F
+            ) -> Self {
+                match self { #body_fold }
             }
         },
     )
author	The rustc-dev-guide Cronjob Bot <github-actions@github.com>	2025-04-19 13:53:12 +0000
committer	The rustc-dev-guide Cronjob Bot <github-actions@github.com>	2025-04-19 13:53:12 +0000
commit	3b2302ec0d17cbc94ef68b15f0bb6524f8b67f3f (patch)
tree	05635b943c977eba01cebf3ef78d8a479e555de5 /compiler
parent	a0c64dce0d70d1be54a6fd7b7aa9ed37665ad998 (diff)
parent	a7c39b68616668a45f0afd62849a1da7c8ad2516 (diff)
download	rust-3b2302ec0d17cbc94ef68b15f0bb6524f8b67f3f.tar.gz rust-3b2302ec0d17cbc94ef68b15f0bb6524f8b67f3f.zip