Auto merge of #3097 - RalfJung:rustup, r=RalfJung

Rustup

64 files changed, 971 insertions, 847 deletions

diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index 2ea399789b9..27072a60f65 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -245,7 +245,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             let Trait(PolyTraitRef { trait_ref, span: trait_span, .. }, _) = bound else { return; };
             diag.span_note(
                 *trait_span,
-                format!("due to current limitations in the borrow checker, this implies a `'static` lifetime")
+                "due to current limitations in the borrow checker, this implies a `'static` lifetime"
             );
             let Some(generics_fn) = hir.get_generics(self.body.source.def_id().expect_local()) else { return; };
             let Def(_, trait_res_defid) = trait_ref.path.res else { return; };
@@ -277,7 +277,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         if suggestions.len() > 0 {
             suggestions.dedup();
             diag.multipart_suggestion_verbose(
-                format!("consider restricting the type parameter to the `'static` lifetime"),
+                "consider restricting the type parameter to the `'static` lifetime",
                 suggestions,
                 Applicability::MaybeIncorrect,
             );
diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
index 9b5a6b89191..6d55fdc3074 100644
--- a/compiler/rustc_codegen_cranelift/src/base.rs
+++ b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -875,7 +875,7 @@ pub(crate) fn codegen_place<'tcx>(
             PlaceElem::Deref => {
                 cplace = cplace.place_deref(fx);
             }
-            PlaceElem::OpaqueCast(ty) => cplace = cplace.place_opaque_cast(fx, ty),
+            PlaceElem::OpaqueCast(ty) => bug!("encountered OpaqueCast({ty}) in codegen"),
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }
diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/simd.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/simd.rs
index c64a4008996..6efbe149863 100644
--- a/compiler/rustc_codegen_cranelift/src/intrinsics/simd.rs
+++ b/compiler/rustc_codegen_cranelift/src/intrinsics/simd.rs
@@ -21,7 +21,7 @@ fn report_simd_type_validation_error(
 pub(super) fn codegen_simd_intrinsic_call<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     intrinsic: Symbol,
-    _args: GenericArgsRef<'tcx>,
+    generic_args: GenericArgsRef<'tcx>,
     args: &[mir::Operand<'tcx>],
     ret: CPlace<'tcx>,
     target: BasicBlock,
@@ -117,6 +117,54 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
             });
         }
 
+        // simd_shuffle_generic<T, U, const I: &[u32]>(x: T, y: T) -> U
+        sym::simd_shuffle_generic => {
+            let [x, y] = args else {
+                bug!("wrong number of args for intrinsic {intrinsic}");
+            };
+            let x = codegen_operand(fx, x);
+            let y = codegen_operand(fx, y);
+
+            if !x.layout().ty.is_simd() {
+                report_simd_type_validation_error(fx, intrinsic, span, x.layout().ty);
+                return;
+            }
+
+            let idx = generic_args[2]
+                .expect_const()
+                .eval(fx.tcx, ty::ParamEnv::reveal_all(), Some(span))
+                .unwrap()
+                .unwrap_branch();
+
+            assert_eq!(x.layout(), y.layout());
+            let layout = x.layout();
+
+            let (lane_count, lane_ty) = layout.ty.simd_size_and_type(fx.tcx);
+            let (ret_lane_count, ret_lane_ty) = ret.layout().ty.simd_size_and_type(fx.tcx);
+
+            assert_eq!(lane_ty, ret_lane_ty);
+            assert_eq!(idx.len() as u64, ret_lane_count);
+
+            let total_len = lane_count * 2;
+
+            let indexes =
+                idx.iter().map(|idx| idx.unwrap_leaf().try_to_u16().unwrap()).collect::<Vec<u16>>();
+
+            for &idx in &indexes {
+                assert!(u64::from(idx) < total_len, "idx {} out of range 0..{}", idx, total_len);
+            }
+
+            for (out_idx, in_idx) in indexes.into_iter().enumerate() {
+                let in_lane = if u64::from(in_idx) < lane_count {
+                    x.value_lane(fx, in_idx.into())
+                } else {
+                    y.value_lane(fx, u64::from(in_idx) - lane_count)
+                };
+                let out_lane = ret.place_lane(fx, u64::try_from(out_idx).unwrap());
+                out_lane.write_cvalue(fx, in_lane);
+            }
+        }
+
         // simd_shuffle<T, I, U>(x: T, y: T, idx: I) -> U
         sym::simd_shuffle => {
             let (x, y, idx) = match args {
diff --git a/compiler/rustc_codegen_cranelift/src/value_and_place.rs b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
index ff95141ce90..d4273c0b593 100644
--- a/compiler/rustc_codegen_cranelift/src/value_and_place.rs
+++ b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
@@ -674,14 +674,6 @@ impl<'tcx> CPlace<'tcx> {
         }
     }
 
-    pub(crate) fn place_opaque_cast(
-        self,
-        fx: &mut FunctionCx<'_, '_, 'tcx>,
-        ty: Ty<'tcx>,
-    ) -> CPlace<'tcx> {
-        CPlace { inner: self.inner, layout: fx.layout_of(ty) }
-    }
-
     pub(crate) fn place_field(
         self,
         fx: &mut FunctionCx<'_, '_, 'tcx>,
diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index ddaff36f24b..c0cfe39f1e0 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -37,6 +37,8 @@ codegen_llvm_lto_disallowed = lto can only be run for executables, cdylibs and s
 
 codegen_llvm_lto_dylib = lto cannot be used for `dylib` crate type without `-Zdylib-lto`
 
+codegen_llvm_lto_proc_macro = lto cannot be used for `proc-macro` crate type without `-Zdylib-lto`
+
 codegen_llvm_missing_features =
     add the missing features in a `target_feature` attribute
 
diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index ba263296bb4..cb5acf79135 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -2,7 +2,7 @@ use crate::back::write::{
     self, bitcode_section_name, save_temp_bitcode, CodegenDiagnosticsStage, DiagnosticHandlers,
 };
 use crate::errors::{
-    DynamicLinkingWithLTO, LlvmError, LtoBitcodeFromRlib, LtoDisallowed, LtoDylib,
+    DynamicLinkingWithLTO, LlvmError, LtoBitcodeFromRlib, LtoDisallowed, LtoDylib, LtoProcMacro,
 };
 use crate::llvm::{self, build_string};
 use crate::{LlvmCodegenBackend, ModuleLlvm};
@@ -36,8 +36,12 @@ pub const THIN_LTO_KEYS_INCR_COMP_FILE_NAME: &str = "thin-lto-past-keys.bin";
 
 pub fn crate_type_allows_lto(crate_type: CrateType) -> bool {
     match crate_type {
-        CrateType::Executable | CrateType::Dylib | CrateType::Staticlib | CrateType::Cdylib => true,
-        CrateType::Rlib | CrateType::ProcMacro => false,
+        CrateType::Executable
+        | CrateType::Dylib
+        | CrateType::Staticlib
+        | CrateType::Cdylib
+        | CrateType::ProcMacro => true,
+        CrateType::Rlib => false,
     }
 }
 
@@ -87,6 +91,11 @@ fn prepare_lto(
                     diag_handler.emit_err(LtoDylib);
                     return Err(FatalError);
                 }
+            } else if *crate_type == CrateType::ProcMacro {
+                if !cgcx.opts.unstable_opts.dylib_lto {
+                    diag_handler.emit_err(LtoProcMacro);
+                    return Err(FatalError);
+                }
             }
         }
 
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 264c273ba30..665d195790c 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -139,6 +139,10 @@ pub(crate) struct LtoDisallowed;
 pub(crate) struct LtoDylib;
 
 #[derive(Diagnostic)]
+#[diag(codegen_llvm_lto_proc_macro)]
+pub(crate) struct LtoProcMacro;
+
+#[derive(Diagnostic)]
 #[diag(codegen_llvm_lto_bitcode_from_rlib)]
 pub(crate) struct LtoBitcodeFromRlib {
     pub llvm_err: String,
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index 9289c37d763..a97b803fc64 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -15,7 +15,7 @@ use rustc_codegen_ssa::mir::place::PlaceRef;
 use rustc_codegen_ssa::traits::*;
 use rustc_hir as hir;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, LayoutOf};
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, GenericArgsRef, Ty};
 use rustc_middle::{bug, span_bug};
 use rustc_span::{sym, symbol::kw, Span, Symbol};
 use rustc_target::abi::{self, Align, HasDataLayout, Primitive};
@@ -376,7 +376,9 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
             }
 
             _ if name.as_str().starts_with("simd_") => {
-                match generic_simd_intrinsic(self, name, callee_ty, args, ret_ty, llret_ty, span) {
+                match generic_simd_intrinsic(
+                    self, name, callee_ty, fn_args, args, ret_ty, llret_ty, span,
+                ) {
                     Ok(llval) => llval,
                     Err(()) => return,
                 }
@@ -911,6 +913,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
     bx: &mut Builder<'_, 'll, 'tcx>,
     name: Symbol,
     callee_ty: Ty<'tcx>,
+    fn_args: GenericArgsRef<'tcx>,
     args: &[OperandRef<'tcx, &'ll Value>],
     ret_ty: Ty<'tcx>,
     llret_ty: &'ll Type,
@@ -1030,6 +1033,56 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
         ));
     }
 
+    if name == sym::simd_shuffle_generic {
+        let idx = fn_args[2]
+            .expect_const()
+            .eval(tcx, ty::ParamEnv::reveal_all(), Some(span))
+            .unwrap()
+            .unwrap_branch();
+        let n = idx.len() as u64;
+
+        require_simd!(ret_ty, InvalidMonomorphization::SimdReturn { span, name, ty: ret_ty });
+        let (out_len, out_ty) = ret_ty.simd_size_and_type(bx.tcx());
+        require!(
+            out_len == n,
+            InvalidMonomorphization::ReturnLength { span, name, in_len: n, ret_ty, out_len }
+        );
+        require!(
+            in_elem == out_ty,
+            InvalidMonomorphization::ReturnElement { span, name, in_elem, in_ty, ret_ty, out_ty }
+        );
+
+        let total_len = in_len * 2;
+
+        let indices: Option<Vec<_>> = idx
+            .iter()
+            .enumerate()
+            .map(|(arg_idx, val)| {
+                let idx = val.unwrap_leaf().try_to_i32().unwrap();
+                if idx >= i32::try_from(total_len).unwrap() {
+                    bx.sess().emit_err(InvalidMonomorphization::ShuffleIndexOutOfBounds {
+                        span,
+                        name,
+                        arg_idx: arg_idx as u64,
+                        total_len: total_len.into(),
+                    });
+                    None
+                } else {
+                    Some(bx.const_i32(idx))
+                }
+            })
+            .collect();
+        let Some(indices) = indices else {
+            return Ok(bx.const_null(llret_ty));
+        };
+
+        return Ok(bx.shuffle_vector(
+            args[0].immediate(),
+            args[1].immediate(),
+            bx.const_vector(&indices),
+        ));
+    }
+
     if name == sym::simd_shuffle {
         // Make sure this is actually an array, since typeck only checks the length-suffixed
         // version of this intrinsic.
diff --git a/compiler/rustc_codegen_ssa/messages.ftl b/compiler/rustc_codegen_ssa/messages.ftl
index d0a078505d2..6f7d7482aea 100644
--- a/compiler/rustc_codegen_ssa/messages.ftl
+++ b/compiler/rustc_codegen_ssa/messages.ftl
@@ -46,8 +46,6 @@ codegen_ssa_ignoring_output = ignoring -o because multiple .{$extension} files w
 codegen_ssa_illegal_link_ordinal_format = illegal ordinal format in `link_ordinal`
     .note = an unsuffixed integer value, e.g., `1`, is expected
 
-codegen_ssa_incompatible_linking_modifiers = link modifiers combination `+bundle,+whole-archive` is unstable when generating rlibs
-
 codegen_ssa_insufficient_vs_code_product = VS Code is a different product, and is not sufficient.
 
 codegen_ssa_invalid_link_ordinal_nargs = incorrect number of arguments to `#[link_ordinal]`
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index a7ac728c59b..c4a0f6291e7 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -365,15 +365,9 @@ fn link_rlib<'a>(
     // loaded from the libraries found here and then encode that into the
     // metadata of the rlib we're generating somehow.
     for lib in codegen_results.crate_info.used_libraries.iter() {
-        let NativeLibKind::Static { bundle: None | Some(true), whole_archive } = lib.kind else {
+        let NativeLibKind::Static { bundle: None | Some(true), .. } = lib.kind else {
             continue;
         };
-        if whole_archive == Some(true)
-            && flavor == RlibFlavor::Normal
-            && !codegen_results.crate_info.feature_packed_bundled_libs
-        {
-            sess.emit_err(errors::IncompatibleLinkingModifiers);
-        }
         if flavor == RlibFlavor::Normal && let Some(filename) = lib.filename {
             let path = find_native_static_library(filename.as_str(), true, &lib_search_paths, sess);
             let src = read(path).map_err(|e| sess.emit_fatal(errors::ReadFileError {message: e }))?;
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 6c51dffedbf..1e4ea73a172 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -181,7 +181,7 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 old_info
             }
         }
-        (_, &ty::Dynamic(ref data, _, _)) => meth::get_vtable(cx, source, data.principal()),
+        (_, ty::Dynamic(data, _, _)) => meth::get_vtable(cx, source, data.principal()),
         _ => bug!("unsized_info: invalid unsizing {:?} -> {:?}", source, target),
     }
 }
@@ -857,7 +857,6 @@ impl CrateInfo {
             dependency_formats: tcx.dependency_formats(()).clone(),
             windows_subsystem,
             natvis_debugger_visualizers: Default::default(),
-            feature_packed_bundled_libs: tcx.features().packed_bundled_libs,
         };
         let crates = tcx.crates(());
 
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index bfd572a2eea..14311ec08fd 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -108,10 +108,6 @@ pub struct CreateTempDir {
 }
 
 #[derive(Diagnostic)]
-#[diag(codegen_ssa_incompatible_linking_modifiers)]
-pub struct IncompatibleLinkingModifiers;
-
-#[derive(Diagnostic)]
 #[diag(codegen_ssa_add_native_library)]
 pub struct AddNativeLibrary {
     pub library_path: PathBuf,
diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 7ebaca9b0bc..f6186a290f8 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -164,7 +164,6 @@ pub struct CrateInfo {
     pub dependency_formats: Lrc<Dependencies>,
     pub windows_subsystem: Option<String>,
     pub natvis_debugger_visualizers: BTreeSet<DebuggerVisualizerFile>,
-    pub feature_packed_bundled_libs: bool, // unstable feature flag.
 }
 
 #[derive(Encodable, Decodable)]
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
index a9ecbdc5f35..f775711f870 100644
--- a/compiler/rustc_codegen_ssa/src/mir/place.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/place.rs
@@ -463,7 +463,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 mir::ProjectionElem::Field(ref field, _) => {
                     cg_base.project_field(bx, field.index())
                 }
-                mir::ProjectionElem::OpaqueCast(ty) => cg_base.project_type(bx, ty),
+                mir::ProjectionElem::OpaqueCast(ty) => {
+                    bug!("encountered OpaqueCast({ty}) in codegen")
+                }
                 mir::ProjectionElem::Index(index) => {
                     let index = &mir::Operand::Copy(mir::Place::from(index));
                     let index = self.codegen_operand(bx, index);
diff --git a/compiler/rustc_const_eval/src/interpret/projection.rs b/compiler/rustc_const_eval/src/interpret/projection.rs
index 6c720ac4a57..f462c13816e 100644
--- a/compiler/rustc_const_eval/src/interpret/projection.rs
+++ b/compiler/rustc_const_eval/src/interpret/projection.rs
@@ -316,7 +316,9 @@ where
     {
         use rustc_middle::mir::ProjectionElem::*;
         Ok(match proj_elem {
-            OpaqueCast(ty) => base.transmute(self.layout_of(ty)?, self)?,
+            OpaqueCast(ty) => {
+                span_bug!(self.cur_span(), "OpaqueCast({ty}) encountered after borrowck")
+            }
             Field(field, _) => self.project_field(base, field.index())?,
             Downcast(_, variant) => self.project_downcast(base, variant)?,
             Deref => self.deref_pointer(&base.to_op(self)?)?.into(),
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 0d8733070a4..18b22882e7d 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -633,6 +633,14 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
         location: Location,
     ) {
         match elem {
+            ProjectionElem::OpaqueCast(ty)
+                if self.mir_phase >= MirPhase::Runtime(RuntimePhase::Initial) =>
+            {
+                self.fail(
+                    location,
+                    format!("explicit opaque type cast to `{ty}` after `RevealAll`"),
+                )
+            }
             ProjectionElem::Index(index) => {
                 let index_ty = self.body.local_decls[index].ty;
                 if index_ty != self.tcx.types.usize {
diff --git a/compiler/rustc_error_codes/src/error_codes/E0760.md b/compiler/rustc_error_codes/src/error_codes/E0760.md
index 85e5faada22..9c4739f0df0 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0760.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0760.md
@@ -5,7 +5,7 @@ or `Self` that references lifetimes from a parent scope.
 
 Erroneous code example:
 
-```compile_fail,edition2018
+```ignore,edition2018
 struct S<'a>(&'a i32);
 
 impl<'a> S<'a> {
diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index afcf30d0b29..32d8380abd3 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -197,6 +197,8 @@ declare_features! (
     /// + `impl<I:Iterator> Iterator for &mut Iterator`
     /// + `impl Debug for Foo<'_>`
     (accepted, impl_header_lifetime_elision, "1.31.0", Some(15872), None),
+    /// Allows referencing `Self` and projections in impl-trait.
+    (accepted, impl_trait_projections, "CURRENT_RUSTC_VERSION", Some(103532), None),
     /// Allows using `a..=b` and `..=b` as inclusive range syntaxes.
     (accepted, inclusive_range_syntax, "1.26.0", Some(28237), None),
     /// Allows inferring outlives requirements (RFC 2093).
@@ -267,6 +269,8 @@ declare_features! (
     (accepted, non_modrs_mods, "1.30.0", Some(44660), None),
     /// Allows the use of or-patterns (e.g., `0 | 1`).
     (accepted, or_patterns, "1.53.0", Some(54883), None),
+    /// Allows using `+bundle,+whole-archive` link modifiers with native libs.
+    (accepted, packed_bundled_libs, "CURRENT_RUSTC_VERSION", Some(108081), None),
     /// Allows annotating functions conforming to `fn(&PanicInfo) -> !` with `#[panic_handler]`.
     /// This defines the behavior of panics.
     (accepted, panic_handler, "1.30.0", Some(44489), None),
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 94afb6edcf6..a02c04ecd3e 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -241,8 +241,6 @@ declare_features! (
     (active, linkage, "1.0.0", Some(29603), None),
     /// Allows declaring with `#![needs_panic_runtime]` that a panic runtime is needed.
     (internal, needs_panic_runtime, "1.10.0", Some(32837), None),
-    /// Allows using `+bundled,+whole-archive` native libs.
-    (active, packed_bundled_libs, "1.69.0", Some(108081), None),
     /// Allows using the `#![panic_runtime]` attribute.
     (internal, panic_runtime, "1.10.0", Some(32837), None),
     /// Allows `extern "platform-intrinsic" { ... }`.
@@ -472,8 +470,6 @@ declare_features! (
     (active, impl_trait_in_assoc_type, "1.70.0", Some(63063), None),
     /// Allows `impl Trait` as output type in `Fn` traits in return position of functions.
     (active, impl_trait_in_fn_trait_return, "1.64.0", Some(99697), None),
-    /// Allows referencing `Self` and projections in impl-trait.
-    (active, impl_trait_projections, "1.67.0", Some(103532), None),
     /// Allows using imported `main` function
     (active, imported_main, "1.53.0", Some(28937), None),
     /// Allows associated types in inherent impls.
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 2a68d745c76..1c926533a27 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -38,6 +38,17 @@ hir_analysis_cast_thin_pointer_to_fat_pointer = cannot cast thin pointer `{$expr
 hir_analysis_closure_implicit_hrtb = implicit types in closure signatures are forbidden when `for<...>` is present
     .label = `for<...>` is here
 
+hir_analysis_coerce_unsized_may = the trait `{$trait_name}` may only be implemented for a coercion between structures
+
+hir_analysis_coerce_unsized_multi = implementing the trait `CoerceUnsized` requires multiple coercions
+    .note = `CoerceUnsized` may only be implemented for a coercion between structures with one field being coerced
+    .coercions_note = currently, {$number} fields need coercions: {$coercions}
+    .label = requires multiple coercions
+
+hir_analysis_coercion_between_struct_same_note = expected coercion between the same definition; expected `{$source_path}`, found `{$target_path}`
+
+hir_analysis_coercion_between_struct_single_note = expected a single field to be coerced, none found
+
 hir_analysis_const_bound_for_non_const_trait =
     ~const can only be applied to `#[const_trait]` traits
 
@@ -61,6 +72,15 @@ hir_analysis_copy_impl_on_type_with_dtor =
     the trait `Copy` cannot be implemented for this type; the type has a destructor
     .label = `Copy` not allowed on types with destructors
 
+hir_analysis_dispatch_from_dyn_multi = implementing the `DispatchFromDyn` trait requires multiple coercions
+    .note = the trait `DispatchFromDyn` may only be implemented for a coercion between structures with a single field being coerced
+    .coercions_note = currently, {$number} fields need coercions: {$coercions}
+
+hir_analysis_dispatch_from_dyn_repr = structs implementing `DispatchFromDyn` may not have `#[repr(packed)]` or `#[repr(C)]`
+
+hir_analysis_dispatch_from_dyn_zst = the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields with 1 byte alignment, and nothing else
+    .note = extra field `{$name}` of type `{$ty}` is not allowed
+
 hir_analysis_drop_impl_negative = negative `Drop` impls are not supported
 
 hir_analysis_drop_impl_on_wrong_item =
@@ -232,6 +252,8 @@ hir_analysis_pass_to_variadic_function = can't pass `{$ty}` to variadic function
 hir_analysis_placeholder_not_allowed_item_signatures = the placeholder `_` is not allowed within types on item signatures for {$kind}
     .label = not allowed in type signatures
 
+hir_analysis_requires_note = the `{$trait_name}` impl for `{$ty}` requires that `{$error_predicate}`
+
 hir_analysis_return_type_notation_conflicting_bound =
     ambiguous associated function `{$assoc_name}` for `{$ty_name}`
     .note = `{$assoc_name}` is declared in two supertraits: `{$first_bound}` and `{$second_bound}`
@@ -299,6 +321,9 @@ hir_analysis_too_large_static = extern static is too large for the current archi
 hir_analysis_track_caller_on_main = `main` function is not allowed to be `#[track_caller]`
     .suggestion = remove this annotation
 
+hir_analysis_trait_cannot_impl_for_ty = the trait `{$trait_name}` cannot be implemented for this type
+    .label = this field does not implement `{$trait_name}`
+
 hir_analysis_trait_object_declared_with_no_traits =
     at least one trait is required for an object type
     .alias_span = this alias does not contain a trait
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index eb1f48d23ff..44e1bdb8370 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -5,18 +5,15 @@ use super::compare_impl_item::check_type_bounds;
 use super::compare_impl_item::{compare_impl_method, compare_impl_ty};
 use super::*;
 use rustc_attr as attr;
-use rustc_errors::{Applicability, ErrorGuaranteed, MultiSpan};
+use rustc_errors::{ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
-use rustc_hir::def::{CtorKind, DefKind, Res};
+use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
-use rustc_hir::intravisit::Visitor;
-use rustc_hir::{ItemKind, Node, PathSegment};
-use rustc_infer::infer::opaque_types::ConstrainOpaqueTypeRegionVisitor;
+use rustc_hir::Node;
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
 use rustc_infer::traits::{Obligation, TraitEngineExt as _};
 use rustc_lint_defs::builtin::REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS;
-use rustc_middle::hir::nested_filter;
 use rustc_middle::middle::stability::EvalResult;
 use rustc_middle::traits::{DefiningAnchor, ObligationCauseCode};
 use rustc_middle::ty::fold::BottomUpFolder;
@@ -218,9 +215,6 @@ fn check_opaque(tcx: TyCtxt<'_>, id: hir::ItemId) {
     let args = GenericArgs::identity_for_item(tcx, item.owner_id);
     let span = tcx.def_span(item.owner_id.def_id);
 
-    if !tcx.features().impl_trait_projections {
-        check_opaque_for_inheriting_lifetimes(tcx, item.owner_id.def_id, span);
-    }
     if tcx.type_of(item.owner_id.def_id).instantiate_identity().references_error() {
         return;
     }
@@ -231,129 +225,6 @@ fn check_opaque(tcx: TyCtxt<'_>, id: hir::ItemId) {
     let _ = check_opaque_meets_bounds(tcx, item.owner_id.def_id, span, &origin);
 }
 
-/// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
-/// in "inheriting lifetimes".
-#[instrument(level = "debug", skip(tcx, span))]
-pub(super) fn check_opaque_for_inheriting_lifetimes(
-    tcx: TyCtxt<'_>,
-    def_id: LocalDefId,
-    span: Span,
-) {
-    let item = tcx.hir().expect_item(def_id);
-    debug!(?item, ?span);
-
-    struct ProhibitOpaqueVisitor<'tcx> {
-        tcx: TyCtxt<'tcx>,
-        opaque_identity_ty: Ty<'tcx>,
-        parent_count: u32,
-        references_parent_regions: bool,
-        selftys: Vec<(Span, Option<String>)>,
-    }
-
-    impl<'tcx> ty::visit::TypeVisitor<TyCtxt<'tcx>> for ProhibitOpaqueVisitor<'tcx> {
-        type BreakTy = Ty<'tcx>;
-
-        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-            debug!(?t, "root_visit_ty");
-            if t == self.opaque_identity_ty {
-                ControlFlow::Continue(())
-            } else {
-                t.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
-                    tcx: self.tcx,
-                    op: |region| {
-                        if let ty::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = *region
-                            && index < self.parent_count
-                        {
-                            self.references_parent_regions= true;
-                        }
-                    },
-                });
-                if self.references_parent_regions {
-                    ControlFlow::Break(t)
-                } else {
-                    ControlFlow::Continue(())
-                }
-            }
-        }
-    }
-
-    impl<'tcx> Visitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
-        type NestedFilter = nested_filter::OnlyBodies;
-
-        fn nested_visit_map(&mut self) -> Self::Map {
-            self.tcx.hir()
-        }
-
-        fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
-            match arg.kind {
-                hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
-                    [PathSegment { res: Res::SelfTyParam { .. }, .. }] => {
-                        let impl_ty_name = None;
-                        self.selftys.push((path.span, impl_ty_name));
-                    }
-                    [PathSegment { res: Res::SelfTyAlias { alias_to: def_id, .. }, .. }] => {
-                        let impl_ty_name = Some(self.tcx.def_path_str(*def_id));
-                        self.selftys.push((path.span, impl_ty_name));
-                    }
-                    _ => {}
-                },
-                _ => {}
-            }
-            hir::intravisit::walk_ty(self, arg);
-        }
-    }
-
-    if let ItemKind::OpaqueTy(&hir::OpaqueTy {
-        origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
-        ..
-    }) = item.kind
-    {
-        let args = GenericArgs::identity_for_item(tcx, def_id);
-        let opaque_identity_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-        let mut visitor = ProhibitOpaqueVisitor {
-            opaque_identity_ty,
-            parent_count: tcx.generics_of(def_id).parent_count as u32,
-            references_parent_regions: false,
-            tcx,
-            selftys: vec![],
-        };
-        let prohibit_opaque = tcx
-            .explicit_item_bounds(def_id)
-            .instantiate_identity_iter_copied()
-            .try_for_each(|(predicate, _)| predicate.visit_with(&mut visitor));
-
-        if let Some(ty) = prohibit_opaque.break_value() {
-            visitor.visit_item(&item);
-            let is_async = match item.kind {
-                ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
-                    matches!(origin, hir::OpaqueTyOrigin::AsyncFn(..))
-                }
-                _ => unreachable!(),
-            };
-
-            let mut err = feature_err(
-                &tcx.sess.parse_sess,
-                sym::impl_trait_projections,
-                span,
-                format!(
-                    "`{}` return type cannot contain a projection or `Self` that references \
-                    lifetimes from a parent scope",
-                    if is_async { "async fn" } else { "impl Trait" },
-                ),
-            );
-            for (span, name) in visitor.selftys {
-                err.span_suggestion(
-                    span,
-                    "consider spelling out the type instead",
-                    name.unwrap_or_else(|| format!("{ty:?}")),
-                    Applicability::MaybeIncorrect,
-                );
-            }
-            err.emit();
-        }
-    }
-}
-
 /// Checks that an opaque type does not contain cycles.
 pub(super) fn check_opaque_for_cycles<'tcx>(
     tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index 3c0d977917f..c61719c1fd2 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -20,6 +20,7 @@ fn equate_intrinsic_type<'tcx>(
     it: &hir::ForeignItem<'_>,
     n_tps: usize,
     n_lts: usize,
+    n_cts: usize,
     sig: ty::PolyFnSig<'tcx>,
 ) {
     let (own_counts, span) = match &it.kind {
@@ -51,7 +52,7 @@ fn equate_intrinsic_type<'tcx>(
 
     if gen_count_ok(own_counts.lifetimes, n_lts, "lifetime")
         && gen_count_ok(own_counts.types, n_tps, "type")
-        && gen_count_ok(own_counts.consts, 0, "const")
+        && gen_count_ok(own_counts.consts, n_cts, "const")
     {
         let it_def_id = it.owner_id.def_id;
         check_function_signature(
@@ -489,7 +490,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
     };
     let sig = tcx.mk_fn_sig(inputs, output, false, unsafety, Abi::RustIntrinsic);
     let sig = ty::Binder::bind_with_vars(sig, bound_vars);
-    equate_intrinsic_type(tcx, it, n_tps, n_lts, sig)
+    equate_intrinsic_type(tcx, it, n_tps, n_lts, 0, sig)
 }
 
 /// Type-check `extern "platform-intrinsic" { ... }` functions.
@@ -501,9 +502,9 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
 
     let name = it.ident.name;
 
-    let (n_tps, inputs, output) = match name {
+    let (n_tps, n_cts, inputs, output) = match name {
         sym::simd_eq | sym::simd_ne | sym::simd_lt | sym::simd_le | sym::simd_gt | sym::simd_ge => {
-            (2, vec![param(0), param(0)], param(1))
+            (2, 0, vec![param(0), param(0)], param(1))
         }
         sym::simd_add
         | sym::simd_sub
@@ -519,8 +520,8 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         | sym::simd_fmax
         | sym::simd_fpow
         | sym::simd_saturating_add
-        | sym::simd_saturating_sub => (1, vec![param(0), param(0)], param(0)),
-        sym::simd_arith_offset => (2, vec![param(0), param(1)], param(0)),
+        | sym::simd_saturating_sub => (1, 0, vec![param(0), param(0)], param(0)),
+        sym::simd_arith_offset => (2, 0, vec![param(0), param(1)], param(0)),
         sym::simd_neg
         | sym::simd_bswap
         | sym::simd_bitreverse
@@ -538,25 +539,25 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         | sym::simd_ceil
         | sym::simd_floor
         | sym::simd_round
-        | sym::simd_trunc => (1, vec![param(0)], param(0)),
-        sym::simd_fpowi => (1, vec![param(0), tcx.types.i32], param(0)),
-        sym::simd_fma => (1, vec![param(0), param(0), param(0)], param(0)),
-        sym::simd_gather => (3, vec![param(0), param(1), param(2)], param(0)),
-        sym::simd_scatter => (3, vec![param(0), param(1), param(2)], Ty::new_unit(tcx)),
-        sym::simd_insert => (2, vec![param(0), tcx.types.u32, param(1)], param(0)),
-        sym::simd_extract => (2, vec![param(0), tcx.types.u32], param(1)),
+        | sym::simd_trunc => (1, 0, vec![param(0)], param(0)),
+        sym::simd_fpowi => (1, 0, vec![param(0), tcx.types.i32], param(0)),
+        sym::simd_fma => (1, 0, vec![param(0), param(0), param(0)], param(0)),
+        sym::simd_gather => (3, 0, vec![param(0), param(1), param(2)], param(0)),
+        sym::simd_scatter => (3, 0, vec![param(0), param(1), param(2)], Ty::new_unit(tcx)),
+        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_cast
         | sym::simd_as
         | sym::simd_cast_ptr
         | sym::simd_expose_addr
-        | sym::simd_from_exposed_addr => (2, vec![param(0)], param(1)),
-        sym::simd_bitmask => (2, vec![param(0)], param(1)),
+        | sym::simd_from_exposed_addr => (2, 0, vec![param(0)], param(1)),
+        sym::simd_bitmask => (2, 0, vec![param(0)], param(1)),
         sym::simd_select | sym::simd_select_bitmask => {
-            (2, vec![param(0), param(1), param(1)], param(1))
+            (2, 0, vec![param(0), param(1), param(1)], param(1))
         }
-        sym::simd_reduce_all | sym::simd_reduce_any => (1, vec![param(0)], tcx.types.bool),
+        sym::simd_reduce_all | sym::simd_reduce_any => (1, 0, vec![param(0)], tcx.types.bool),
         sym::simd_reduce_add_ordered | sym::simd_reduce_mul_ordered => {
-            (2, vec![param(0), param(1)], param(1))
+            (2, 0, vec![param(0), param(1)], param(1))
         }
         sym::simd_reduce_add_unordered
         | sym::simd_reduce_mul_unordered
@@ -566,8 +567,9 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         | sym::simd_reduce_min
         | sym::simd_reduce_max
         | sym::simd_reduce_min_nanless
-        | sym::simd_reduce_max_nanless => (2, vec![param(0)], param(1)),
-        sym::simd_shuffle => (3, vec![param(0), param(0), param(1)], param(2)),
+        | sym::simd_reduce_max_nanless => (2, 0, vec![param(0)], param(1)),
+        sym::simd_shuffle => (3, 0, vec![param(0), param(0), param(1)], param(2)),
+        sym::simd_shuffle_generic => (2, 1, vec![param(0), param(0)], param(1)),
         _ => {
             let msg = format!("unrecognized platform-specific intrinsic function: `{name}`");
             tcx.sess.struct_span_err(it.span, msg).emit();
@@ -577,5 +579,5 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
 
     let sig = tcx.mk_fn_sig(inputs, output, false, hir::Unsafety::Unsafe, Abi::PlatformIntrinsic);
     let sig = ty::Binder::dummy(sig);
-    equate_intrinsic_type(tcx, it, n_tps, 0, sig)
+    equate_intrinsic_type(tcx, it, n_tps, 0, n_cts, sig)
 }
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 88c98fa979e..5fa65f33c76 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -329,41 +329,52 @@ fn bounds_from_generic_predicates<'tcx>(
             _ => {}
         }
     }
-    let generics = if types.is_empty() {
-        "".to_string()
-    } else {
-        format!(
-            "<{}>",
-            types
-                .keys()
-                .filter_map(|t| match t.kind() {
-                    ty::Param(_) => Some(t.to_string()),
-                    // Avoid suggesting the following:
-                    // fn foo<T, <T as Trait>::Bar>(_: T) where T: Trait, <T as Trait>::Bar: Other {}
-                    _ => None,
-                })
-                .collect::<Vec<_>>()
-                .join(", ")
-        )
-    };
+
     let mut where_clauses = vec![];
+    let mut types_str = vec![];
     for (ty, bounds) in types {
-        where_clauses
-            .extend(bounds.into_iter().map(|bound| format!("{}: {}", ty, tcx.def_path_str(bound))));
-    }
-    for projection in &projections {
-        let p = projection.skip_binder();
-        // FIXME: this is not currently supported syntax, we should be looking at the `types` and
-        // insert the associated types where they correspond, but for now let's be "lazy" and
-        // propose this instead of the following valid resugaring:
-        // `T: Trait, Trait::Assoc = K` → `T: Trait<Assoc = K>`
-        where_clauses.push(format!("{} = {}", tcx.def_path_str(p.projection_ty.def_id), p.term));
+        if let ty::Param(_) = ty.kind() {
+            let mut bounds_str = vec![];
+            for bound in bounds {
+                let mut projections_str = vec![];
+                for projection in &projections {
+                    let p = projection.skip_binder();
+                    let alias_ty = p.projection_ty;
+                    if bound == tcx.parent(alias_ty.def_id) && alias_ty.self_ty() == ty {
+                        let name = tcx.item_name(alias_ty.def_id);
+                        projections_str.push(format!("{} = {}", name, p.term));
+                    }
+                }
+                let bound_def_path = tcx.def_path_str(bound);
+                if projections_str.is_empty() {
+                    where_clauses.push(format!("{}: {}", ty, bound_def_path));
+                } else {
+                    bounds_str.push(format!("{}<{}>", bound_def_path, projections_str.join(", ")));
+                }
+            }
+            if bounds_str.is_empty() {
+                types_str.push(ty.to_string());
+            } else {
+                types_str.push(format!("{}: {}", ty, bounds_str.join(" + ")));
+            }
+        } else {
+            // Avoid suggesting the following:
+            // fn foo<T, <T as Trait>::Bar>(_: T) where T: Trait, <T as Trait>::Bar: Other {}
+            where_clauses.extend(
+                bounds.into_iter().map(|bound| format!("{}: {}", ty, tcx.def_path_str(bound))),
+            );
+        }
     }
+
+    let generics =
+        if types_str.is_empty() { "".to_string() } else { format!("<{}>", types_str.join(", ")) };
+
     let where_clauses = if where_clauses.is_empty() {
-        String::new()
+        "".to_string()
     } else {
         format!(" where {}", where_clauses.join(", "))
     };
+
     (generics, where_clauses)
 }
 
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index b7b162ce27b..c4fdffb0261 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -24,6 +24,9 @@ use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
+use rustc_trait_selection::traits::misc::{
+    type_allowed_to_implement_const_param_ty, ConstParamTyImplementationError,
+};
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
 use rustc_trait_selection::traits::{
@@ -865,43 +868,65 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
                     );
                 });
             } else {
-                let err_ty_str;
-                let mut is_ptr = true;
-
-                let err = match ty.kind() {
+                let diag = match ty.kind() {
                     ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
-                    ty::FnPtr(_) => Some("function pointers"),
-                    ty::RawPtr(_) => Some("raw pointers"),
-                    _ => {
-                        is_ptr = false;
-                        err_ty_str = format!("`{ty}`");
-                        Some(err_ty_str.as_str())
-                    }
+                    ty::FnPtr(_) => Some(tcx.sess.struct_span_err(
+                        hir_ty.span,
+                        "using function pointers as const generic parameters is forbidden",
+                    )),
+                    ty::RawPtr(_) => Some(tcx.sess.struct_span_err(
+                        hir_ty.span,
+                        "using raw pointers as const generic parameters is forbidden",
+                    )),
+                    _ => Some(tcx.sess.struct_span_err(
+                        hir_ty.span,
+                        format!("`{}` is forbidden as the type of a const generic parameter", ty),
+                    )),
                 };
 
-                if let Some(unsupported_type) = err {
-                    if is_ptr {
-                        tcx.sess.span_err(
-                            hir_ty.span,
-                            format!(
-                                "using {unsupported_type} as const generic parameters is forbidden",
-                            ),
-                        );
-                    } else {
-                        let mut err = tcx.sess.struct_span_err(
-                            hir_ty.span,
-                            format!(
-                                "{unsupported_type} is forbidden as the type of a const generic parameter",
-                            ),
-                        );
-                        err.note("the only supported types are integers, `bool` and `char`");
-                        if tcx.sess.is_nightly_build() {
-                            err.help(
-                            "more complex types are supported with `#![feature(adt_const_params)]`",
-                        );
+                if let Some(mut diag) = diag {
+                    diag.note("the only supported types are integers, `bool` and `char`");
+
+                    let cause = ObligationCause::misc(hir_ty.span, param.def_id);
+                    let may_suggest_feature = match type_allowed_to_implement_const_param_ty(
+                        tcx,
+                        tcx.param_env(param.def_id),
+                        ty,
+                        cause,
+                    ) {
+                        // Can never implement `ConstParamTy`, don't suggest anything.
+                        Err(ConstParamTyImplementationError::NotAnAdtOrBuiltinAllowed) => false,
+                        // May be able to implement `ConstParamTy`. Only emit the feature help
+                        // if the type is local, since the user may be able to fix the local type.
+                        Err(ConstParamTyImplementationError::InfrigingFields(..)) => {
+                            fn ty_is_local(ty: Ty<'_>) -> bool {
+                                match ty.kind() {
+                                    ty::Adt(adt_def, ..) => adt_def.did().is_local(),
+                                    // Arrays and slices use the inner type's `ConstParamTy`.
+                                    ty::Array(ty, ..) => ty_is_local(*ty),
+                                    ty::Slice(ty) => ty_is_local(*ty),
+                                    // `&` references use the inner type's `ConstParamTy`.
+                                    // `&mut` are not supported.
+                                    ty::Ref(_, ty, ast::Mutability::Not) => ty_is_local(*ty),
+                                    // Say that a tuple is local if any of its components are local.
+                                    // This is not strictly correct, but it's likely that the user can fix the local component.
+                                    ty::Tuple(tys) => tys.iter().any(|ty| ty_is_local(ty)),
+                                    _ => false,
+                                }
+                            }
+
+                            ty_is_local(ty)
                         }
-                        err.emit();
+                        // Implments `ConstParamTy`, suggest adding the feature to enable.
+                        Ok(..) => true,
+                    };
+                    if may_suggest_feature && tcx.sess.is_nightly_build() {
+                        diag.help(
+                            "add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types",
+                        );
                     }
+
+                    diag.emit();
                 }
             }
         }
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 94f3e8706fc..be70acfc35d 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -1,11 +1,10 @@
 //! Check properties that are required by built-in traits and set
 //! up data structures required by type-checking/codegen.
 
-use crate::errors::{
-    ConstParamTyImplOnNonAdt, CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem,
-};
+use crate::errors;
+
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{struct_span_err, ErrorGuaranteed, MultiSpan};
+use rustc_errors::{ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
@@ -65,7 +64,7 @@ fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
 
     let impl_ = tcx.hir().expect_item(impl_did).expect_impl();
 
-    tcx.sess.emit_err(DropImplOnWrongItem { span: impl_.self_ty.span });
+    tcx.sess.emit_err(errors::DropImplOnWrongItem { span: impl_.self_ty.span });
 }
 
 fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
@@ -91,10 +90,10 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
             infringing_fields_error(tcx, fields, LangItem::Copy, impl_did, span);
         }
         Err(CopyImplementationError::NotAnAdt) => {
-            tcx.sess.emit_err(CopyImplOnNonAdt { span });
+            tcx.sess.emit_err(errors::CopyImplOnNonAdt { span });
         }
         Err(CopyImplementationError::HasDestructor) => {
-            tcx.sess.emit_err(CopyImplOnTypeWithDtor { span });
+            tcx.sess.emit_err(errors::CopyImplOnTypeWithDtor { span });
         }
     }
 }
@@ -117,7 +116,7 @@ fn visit_implementation_of_const_param_ty(tcx: TyCtxt<'_>, impl_did: LocalDefId)
             infringing_fields_error(tcx, fields, LangItem::ConstParamTy, impl_did, span);
         }
         Err(ConstParamTyImplementationError::NotAnAdtOrBuiltinAllowed) => {
-            tcx.sess.emit_err(ConstParamTyImplOnNonAdt { span });
+            tcx.sess.emit_err(errors::ConstParamTyImplOnNonAdt { span });
         }
     }
 }
@@ -152,8 +151,6 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
 
     let param_env = tcx.param_env(impl_did);
 
-    let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg);
-
     let infcx = tcx.infer_ctxt().build();
     let cause = ObligationCause::misc(span, impl_did);
 
@@ -176,22 +173,19 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
                 let source_path = tcx.def_path_str(def_a.did());
                 let target_path = tcx.def_path_str(def_b.did());
 
-                create_err(&format!(
-                    "the trait `DispatchFromDyn` may only be implemented \
-                            for a coercion between structures with the same \
-                            definition; expected `{source_path}`, found `{target_path}`",
-                ))
-                .emit();
+                tcx.sess.emit_err(errors::DispatchFromDynCoercion {
+                    span,
+                    trait_name: "DispatchFromDyn",
+                    note: true,
+                    source_path,
+                    target_path,
+                });
 
                 return;
             }
 
             if def_a.repr().c() || def_a.repr().packed() {
-                create_err(
-                    "structs implementing `DispatchFromDyn` may not have \
-                         `#[repr(packed)]` or `#[repr(C)]`",
-                )
-                .emit();
+                tcx.sess.emit_err(errors::DispatchFromDynRepr { span });
             }
 
             let fields = &def_a.non_enum_variant().fields;
@@ -213,16 +207,11 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
                         infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, ty_a, ty_b)
                     {
                         if ok.obligations.is_empty() {
-                            create_err(
-                                "the trait `DispatchFromDyn` may only be implemented \
-                                 for structs containing the field being coerced, \
-                                 ZST fields with 1 byte alignment, and nothing else",
-                            )
-                            .note(format!(
-                                "extra field `{}` of type `{}` is not allowed",
-                                field.name, ty_a,
-                            ))
-                            .emit();
+                            tcx.sess.emit_err(errors::DispatchFromDynZST {
+                                span,
+                                name: field.name,
+                                ty: ty_a,
+                            });
 
                             return false;
                         }
@@ -233,36 +222,29 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
                 .collect::<Vec<_>>();
 
             if coerced_fields.is_empty() {
-                create_err(
-                    "the trait `DispatchFromDyn` may only be implemented \
-                        for a coercion between structures with a single field \
-                        being coerced, none found",
-                )
-                .emit();
+                tcx.sess.emit_err(errors::DispatchFromDynSingle {
+                    span,
+                    trait_name: "DispatchFromDyn",
+                    note: true,
+                });
             } else if coerced_fields.len() > 1 {
-                create_err("implementing the `DispatchFromDyn` trait requires multiple coercions")
-                    .note(
-                        "the trait `DispatchFromDyn` may only be implemented \
-                            for a coercion between structures with a single field \
-                            being coerced",
-                    )
-                    .note(format!(
-                        "currently, {} fields need coercions: {}",
-                        coerced_fields.len(),
-                        coerced_fields
-                            .iter()
-                            .map(|field| {
-                                format!(
-                                    "`{}` (`{}` to `{}`)",
-                                    field.name,
-                                    field.ty(tcx, args_a),
-                                    field.ty(tcx, args_b),
-                                )
-                            })
-                            .collect::<Vec<_>>()
-                            .join(", ")
-                    ))
-                    .emit();
+                tcx.sess.emit_err(errors::DispatchFromDynMulti {
+                    span,
+                    coercions_note: true,
+                    number: coerced_fields.len(),
+                    coercions: coerced_fields
+                        .iter()
+                        .map(|field| {
+                            format!(
+                                "`{}` (`{}` to `{}`)",
+                                field.name,
+                                field.ty(tcx, args_a),
+                                field.ty(tcx, args_b),
+                            )
+                        })
+                        .collect::<Vec<_>>()
+                        .join(", "),
+                });
             } else {
                 let ocx = ObligationCtxt::new(&infcx);
                 for field in coerced_fields {
@@ -288,11 +270,7 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
             }
         }
         _ => {
-            create_err(
-                "the trait `DispatchFromDyn` may only be implemented \
-                    for a coercion between structures",
-            )
-            .emit();
+            tcx.sess.emit_err(errors::CoerceUnsizedMay { span, trait_name: "DispatchFromDyn" });
         }
     }
 }
@@ -359,17 +337,13 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
             if def_a != def_b {
                 let source_path = tcx.def_path_str(def_a.did());
                 let target_path = tcx.def_path_str(def_b.did());
-                struct_span_err!(
-                    tcx.sess,
+                tcx.sess.emit_err(errors::DispatchFromDynSame {
                     span,
-                    E0377,
-                    "the trait `CoerceUnsized` may only be implemented \
-                           for a coercion between structures with the same \
-                           definition; expected `{}`, found `{}`",
+                    trait_name: "CoerceUnsized",
+                    note: true,
                     source_path,
-                    target_path
-                )
-                .emit();
+                    target_path,
+                });
                 return err_info;
             }
 
@@ -445,15 +419,11 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
                 .collect::<Vec<_>>();
 
             if diff_fields.is_empty() {
-                struct_span_err!(
-                    tcx.sess,
+                tcx.sess.emit_err(errors::CoerceUnsizedOneField {
                     span,
-                    E0374,
-                    "the trait `CoerceUnsized` may only be implemented \
-                           for a coercion between structures with one field \
-                           being coerced, none found"
-                )
-                .emit();
+                    trait_name: "CoerceUnsized",
+                    note: true,
+                });
                 return err_info;
             } else if diff_fields.len() > 1 {
                 let item = tcx.hir().expect_item(impl_did);
@@ -463,29 +433,17 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
                     tcx.def_span(impl_did)
                 };
 
-                struct_span_err!(
-                    tcx.sess,
+                tcx.sess.emit_err(errors::CoerceUnsizedMulti {
                     span,
-                    E0375,
-                    "implementing the trait \
-                                                `CoerceUnsized` requires multiple \
-                                                coercions"
-                )
-                .note(
-                    "`CoerceUnsized` may only be implemented for \
-                          a coercion between structures with one field being coerced",
-                )
-                .note(format!(
-                    "currently, {} fields need coercions: {}",
-                    diff_fields.len(),
-                    diff_fields
+                    coercions_note: true,
+                    number: diff_fields.len(),
+                    coercions: diff_fields
                         .iter()
-                        .map(|&(i, a, b)| { format!("`{}` (`{}` to `{}`)", fields[i].name, a, b) })
+                        .map(|&(i, a, b)| format!("`{}` (`{}` to `{}`)", fields[i].name, a, b))
                         .collect::<Vec<_>>()
-                        .join(", ")
-                ))
-                .span_label(span, "requires multiple coercions")
-                .emit();
+                        .join(", "),
+                });
+
                 return err_info;
             }
 
@@ -495,14 +453,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
         }
 
         _ => {
-            struct_span_err!(
-                tcx.sess,
-                span,
-                E0376,
-                "the trait `CoerceUnsized` may only be implemented \
-                       for a coercion between structures"
-            )
-            .emit();
+            tcx.sess.emit_err(errors::DispatchFromDynStruct { span, trait_name: "CoerceUnsized" });
             return err_info;
         }
     };
@@ -540,13 +491,6 @@ fn infringing_fields_error(
 
     let trait_name = tcx.def_path_str(trait_did);
 
-    let mut err = struct_span_err!(
-        tcx.sess,
-        impl_span,
-        E0204,
-        "the trait `{trait_name}` cannot be implemented for this type"
-    );
-
     // We'll try to suggest constraining type parameters to fulfill the requirements of
     // their `Copy` implementation.
     let mut errors: BTreeMap<_, Vec<_>> = Default::default();
@@ -554,14 +498,15 @@ fn infringing_fields_error(
 
     let mut seen_tys = FxHashSet::default();
 
+    let mut label_spans = Vec::new();
+
     for (field, ty, reason) in fields {
         // Only report an error once per type.
         if !seen_tys.insert(ty) {
             continue;
         }
 
-        let field_span = tcx.def_span(field.did);
-        err.span_label(field_span, format!("this field does not implement `{trait_name}`"));
+        label_spans.push(tcx.def_span(field.did));
 
         match reason {
             InfringingFieldsReason::Fulfill(fulfillment_errors) => {
@@ -625,13 +570,24 @@ fn infringing_fields_error(
             }
         }
     }
+    let mut notes = Vec::new();
     for ((ty, error_predicate), spans) in errors {
         let span: MultiSpan = spans.into();
-        err.span_note(
+        notes.push(errors::ImplForTyRequires {
             span,
-            format!("the `{trait_name}` impl for `{ty}` requires that `{error_predicate}`"),
-        );
+            error_predicate,
+            trait_name: trait_name.clone(),
+            ty,
+        });
     }
+
+    let mut err = tcx.sess.create_err(errors::TraitCannotImplForTy {
+        span: impl_span,
+        trait_name,
+        label_spans,
+        notes,
+    });
+
     suggest_constraining_type_params(
         tcx,
         tcx.hir().get_generics(impl_did).expect("impls always have generics"),
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index cd37221ae6f..221df4e36b2 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -1374,7 +1374,7 @@ fn impl_trait_ref(
                 // make astconv happy.
                 let mut path_segments = ast_trait_ref.path.segments.to_vec();
                 let last_segment = path_segments.len() - 1;
-                let mut args = path_segments[last_segment].args().clone();
+                let mut args = *path_segments[last_segment].args();
                 let last_arg = args.args.len() - 1;
                 assert!(matches!(args.args[last_arg], hir::GenericArg::Const(anon_const) if tcx.has_attr(anon_const.value.def_id, sym::rustc_host)));
                 args.args = &args.args[..args.args.len() - 1];
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 4705e40988b..0efe82b20ee 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -964,6 +964,25 @@ pub struct InherentTyOutside {
 }
 
 #[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_may, code = "E0378")]
+pub struct DispatchFromDynCoercion<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'a str,
+    #[note(hir_analysis_coercion_between_struct_same_note)]
+    pub note: bool,
+    pub source_path: String,
+    pub target_path: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_dispatch_from_dyn_repr, code = "E0378")]
+pub struct DispatchFromDynRepr {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(hir_analysis_inherent_ty_outside_relevant, code = "E0390")]
 #[help]
 pub struct InherentTyOutsideRelevant {
@@ -1025,3 +1044,108 @@ pub struct InherentNominal {
     #[label]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_dispatch_from_dyn_zst, code = "E0378")]
+#[note]
+pub struct DispatchFromDynZST<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub name: Symbol,
+    pub ty: Ty<'a>,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_may, code = "E0378")]
+pub struct DispatchFromDynSingle<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'a str,
+    #[note(hir_analysis_coercion_between_struct_single_note)]
+    pub note: bool,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_dispatch_from_dyn_multi, code = "E0378")]
+#[note]
+pub struct DispatchFromDynMulti {
+    #[primary_span]
+    pub span: Span,
+    #[note(hir_analysis_coercions_note)]
+    pub coercions_note: bool,
+    pub number: usize,
+    pub coercions: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_may, code = "E0376")]
+pub struct DispatchFromDynStruct<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_may, code = "E0377")]
+pub struct DispatchFromDynSame<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'a str,
+    #[note(hir_analysis_coercion_between_struct_same_note)]
+    pub note: bool,
+    pub source_path: String,
+    pub target_path: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_may, code = "E0374")]
+pub struct CoerceUnsizedOneField<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'a str,
+    #[note(hir_analysis_coercion_between_struct_single_note)]
+    pub note: bool,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_multi, code = "E0375")]
+#[note]
+pub struct CoerceUnsizedMulti {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[note(hir_analysis_coercions_note)]
+    pub coercions_note: bool,
+    pub number: usize,
+    pub coercions: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_coerce_unsized_may, code = "E0378")]
+pub struct CoerceUnsizedMay<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_trait_cannot_impl_for_ty, code = "E0204")]
+pub struct TraitCannotImplForTy {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: String,
+    #[label]
+    pub label_spans: Vec<Span>,
+    #[subdiagnostic]
+    pub notes: Vec<ImplForTyRequires>,
+}
+
+#[derive(Subdiagnostic)]
+#[note(hir_analysis_requires_note)]
+pub struct ImplForTyRequires {
+    #[primary_span]
+    pub span: MultiSpan,
+    pub error_predicate: String,
+    pub trait_name: String,
+    pub ty: String,
+}
diff --git a/compiler/rustc_hir_typeck/src/demand.rs b/compiler/rustc_hir_typeck/src/demand.rs
index 256a4bf9449..d97691369c9 100644
--- a/compiler/rustc_hir_typeck/src/demand.rs
+++ b/compiler/rustc_hir_typeck/src/demand.rs
@@ -644,7 +644,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             if self.can_eq(self.param_env, ty, expected) {
                                 err.span_label(
                                     ex.span,
-                                    format!("expected because of this `break`"),
+                                    "expected because of this `break`",
                                 );
                                 exit = true;
                             }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
index b34900da83b..5c3beee284f 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
@@ -621,7 +621,7 @@ fn foo(&self) -> Self::T { String::new() }
                         {
                             diag.span_label(
                                 item.span,
-                                format!("associated type is `default` and may be overridden"),
+                                "associated type is `default` and may be overridden",
                             );
                             return true;
                         }
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 460d54739a2..3c5cde4309b 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -1317,6 +1317,40 @@ impl<'tcx> LateContext<'tcx> {
     }
 
     /// If the given expression is a local binding, find the initializer expression.
+    /// If that initializer expression is another local binding, find its initializer again.
+    ///
+    /// This process repeats as long as possible (but usually no more than once).
+    /// Type-check adjustments are not taken in account in this function.
+    ///
+    /// Examples:
+    /// ```
+    /// let abc = 1;
+    /// let def = abc + 2;
+    /// //        ^^^^^^^ output
+    /// let def = def;
+    /// dbg!(def);
+    /// //   ^^^ input
+    /// ```
+    pub fn expr_or_init<'a>(&self, mut expr: &'a hir::Expr<'tcx>) -> &'a hir::Expr<'tcx> {
+        expr = expr.peel_blocks();
+
+        while let hir::ExprKind::Path(ref qpath) = expr.kind
+            && let Some(parent_node) = match self.qpath_res(qpath, expr.hir_id) {
+                Res::Local(hir_id) => self.tcx.hir().find_parent(hir_id),
+                _ => None,
+            }
+            && let Some(init) = match parent_node {
+                hir::Node::Expr(expr) => Some(expr),
+                hir::Node::Local(hir::Local { init, .. }) => *init,
+                _ => None
+            }
+        {
+            expr = init.peel_blocks();
+        }
+        expr
+    }
+
+    /// If the given expression is a local binding, find the initializer expression.
     /// If that initializer expression is another local or **outside** (`const`/`static`)
     /// binding, find its initializer again.
     ///
@@ -1338,7 +1372,10 @@ impl<'tcx> LateContext<'tcx> {
     /// dbg!(def);
     /// //   ^^^ input
     /// ```
-    pub fn expr_or_init<'a>(&self, mut expr: &'a hir::Expr<'tcx>) -> &'a hir::Expr<'tcx> {
+    pub fn expr_or_init_with_outside_body<'a>(
+        &self,
+        mut expr: &'a hir::Expr<'tcx>,
+    ) -> &'a hir::Expr<'tcx> {
         expr = expr.peel_blocks();
 
         while let hir::ExprKind::Path(ref qpath) = expr.kind
diff --git a/compiler/rustc_lint/src/foreign_modules.rs b/compiler/rustc_lint/src/foreign_modules.rs
index 7b291d558e0..e1df69bdaf2 100644
--- a/compiler/rustc_lint/src/foreign_modules.rs
+++ b/compiler/rustc_lint/src/foreign_modules.rs
@@ -5,19 +5,18 @@ use rustc_hir::def::DefKind;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::layout::LayoutError;
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
-use rustc_session::lint::{lint_array, LintArray};
 use rustc_span::{sym, Span, Symbol};
 use rustc_target::abi::FIRST_VARIANT;
 
 use crate::lints::{BuiltinClashingExtern, BuiltinClashingExternSub};
-use crate::types;
+use crate::{types, LintVec};
 
 pub(crate) fn provide(providers: &mut Providers) {
     *providers = Providers { clashing_extern_declarations, ..*providers };
 }
 
-pub(crate) fn get_lints() -> LintArray {
-    lint_array!(CLASHING_EXTERN_DECLARATIONS)
+pub(crate) fn get_lints() -> LintVec {
+    vec![CLASHING_EXTERN_DECLARATIONS]
 }
 
 fn clashing_extern_declarations(tcx: TyCtxt<'_>, (): ()) {
diff --git a/compiler/rustc_lint/src/invalid_from_utf8.rs b/compiler/rustc_lint/src/invalid_from_utf8.rs
index 1841e7c85a8..e398059ade9 100644
--- a/compiler/rustc_lint/src/invalid_from_utf8.rs
+++ b/compiler/rustc_lint/src/invalid_from_utf8.rs
@@ -84,9 +84,9 @@ impl<'tcx> LateLintPass<'tcx> for InvalidFromUtf8 {
                 )
             };
 
-            let mut init = cx.expr_or_init(arg);
+            let mut init = cx.expr_or_init_with_outside_body(arg);
             while let ExprKind::AddrOf(.., inner) = init.kind {
-                init = cx.expr_or_init(inner);
+                init = cx.expr_or_init_with_outside_body(inner);
             }
             match init.kind {
                 ExprKind::Lit(Spanned { node: lit, .. }) => {
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 284560465d6..72c103f2d4a 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -130,7 +130,7 @@ pub use late::{check_crate, late_lint_mod, unerased_lint_store};
 pub use passes::{EarlyLintPass, LateLintPass};
 pub use rustc_session::lint::Level::{self, *};
 pub use rustc_session::lint::{BufferedEarlyLint, FutureIncompatibleInfo, Lint, LintId};
-pub use rustc_session::lint::{LintArray, LintPass};
+pub use rustc_session::lint::{LintPass, LintVec};
 
 fluent_messages! { "../messages.ftl" }
 
@@ -196,7 +196,7 @@ late_lint_methods!(
             BoxPointers: BoxPointers,
             PathStatements: PathStatements,
             LetUnderscore: LetUnderscore,
-            InvalidReferenceCasting: InvalidReferenceCasting::default(),
+            InvalidReferenceCasting: InvalidReferenceCasting,
             // Depends on referenced function signatures in expressions
             UnusedResults: UnusedResults,
             NonUpperCaseGlobals: NonUpperCaseGlobals,
diff --git a/compiler/rustc_lint/src/noop_method_call.rs b/compiler/rustc_lint/src/noop_method_call.rs
index bc0b9d6d818..cfbca6efbfa 100644
--- a/compiler/rustc_lint/src/noop_method_call.rs
+++ b/compiler/rustc_lint/src/noop_method_call.rs
@@ -98,6 +98,12 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
         let Ok(Some(i)) = ty::Instance::resolve(cx.tcx, cx.param_env, did, args) else { return };
         // (Re)check that it implements the noop diagnostic.
         let Some(name) = cx.tcx.get_diagnostic_name(i.def_id()) else { return };
+        if !matches!(
+            name,
+            sym::noop_method_borrow | sym::noop_method_clone | sym::noop_method_deref
+        ) {
+            return;
+        }
 
         let receiver_ty = cx.typeck_results().expr_ty(receiver);
         let expr_ty = cx.typeck_results().expr_ty_adjusted(expr);
diff --git a/compiler/rustc_lint/src/passes.rs b/compiler/rustc_lint/src/passes.rs
index 7d2a9102640..508f3e1ec31 100644
--- a/compiler/rustc_lint/src/passes.rs
+++ b/compiler/rustc_lint/src/passes.rs
@@ -111,7 +111,7 @@ macro_rules! declare_combined_late_lint_pass {
                 }
             }
 
-            $v fn get_lints() -> $crate::LintArray {
+            $v fn get_lints() -> $crate::LintVec {
                 let mut lints = Vec::new();
                 $(lints.extend_from_slice(&$pass::get_lints());)*
                 lints
@@ -226,7 +226,7 @@ macro_rules! declare_combined_early_lint_pass {
                 }
             }
 
-            $v fn get_lints() -> $crate::LintArray {
+            $v fn get_lints() -> $crate::LintVec {
                 let mut lints = Vec::new();
                 $(lints.extend_from_slice(&$pass::get_lints());)*
                 lints
diff --git a/compiler/rustc_lint/src/reference_casting.rs b/compiler/rustc_lint/src/reference_casting.rs
index d540f473ae8..39def599be8 100644
--- a/compiler/rustc_lint/src/reference_casting.rs
+++ b/compiler/rustc_lint/src/reference_casting.rs
@@ -1,8 +1,7 @@
 use rustc_ast::Mutability;
-use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::{def::Res, Expr, ExprKind, HirId, Local, QPath, StmtKind, UnOp};
+use rustc_hir::{Expr, ExprKind, UnOp};
 use rustc_middle::ty::{self, TypeAndMut};
-use rustc_span::{sym, Span};
+use rustc_span::sym;
 
 use crate::{lints::InvalidReferenceCastingDiag, LateContext, LateLintPass, LintContext};
 
@@ -34,38 +33,18 @@ declare_lint! {
     "casts of `&T` to `&mut T` without interior mutability"
 }
 
-#[derive(Default)]
-pub struct InvalidReferenceCasting {
-    casted: FxHashMap<HirId, Span>,
-}
-
-impl_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
+declare_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
 
 impl<'tcx> LateLintPass<'tcx> for InvalidReferenceCasting {
-    fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx rustc_hir::Stmt<'tcx>) {
-        let StmtKind::Local(local) = stmt.kind else {
-            return;
-        };
-        let Local { init: Some(init), els: None, .. } = local else {
-            return;
-        };
-
-        if is_cast_from_const_to_mut(cx, init) {
-            self.casted.insert(local.pat.hir_id, init.span);
-        }
-    }
-
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
         let Some((is_assignment, e)) = is_operation_we_care_about(cx, expr) else {
             return;
         };
 
-        let orig_cast = if is_cast_from_const_to_mut(cx, e) {
-            None
-        } else if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind
-            && let Res::Local(hir_id) = &path.res
-            && let Some(orig_cast) = self.casted.get(hir_id) {
-            Some(*orig_cast)
+        let init = cx.expr_or_init(e);
+
+        let orig_cast = if is_cast_from_const_to_mut(cx, init) {
+            if init.span != e.span { Some(init.span) } else { None }
         } else {
             return;
         };
@@ -125,99 +104,51 @@ fn is_operation_we_care_about<'tcx>(
     deref_assign_or_addr_of(e).or_else(|| ptr_write(cx, e))
 }
 
-fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
-    let e = e.peel_blocks();
+fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, orig_expr: &'tcx Expr<'tcx>) -> bool {
+    let mut need_check_freeze = false;
+    let mut e = orig_expr;
 
-    fn from_casts<'tcx>(
-        cx: &LateContext<'tcx>,
-        e: &'tcx Expr<'tcx>,
-        need_check_freeze: &mut bool,
-    ) -> Option<&'tcx Expr<'tcx>> {
-        // <expr> as *mut ...
-        let mut e = if let ExprKind::Cast(e, t) = e.kind
-            && let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(t.hir_id).kind() {
-            e
-        // <expr>.cast_mut()
+    let end_ty = cx.typeck_results().node_type(orig_expr.hir_id);
+
+    // Bail out early if the end type is **not** a mutable pointer.
+    if !matches!(end_ty.kind(), ty::RawPtr(TypeAndMut { ty: _, mutbl: Mutability::Mut })) {
+        return false;
+    }
+
+    loop {
+        e = e.peel_blocks();
+        // <expr> as ...
+        e = if let ExprKind::Cast(expr, _) = e.kind {
+            expr
+        // <expr>.cast(), <expr>.cast_mut() or <expr>.cast_const()
         } else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
             && let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
-            && cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
+            && matches!(
+                cx.tcx.get_diagnostic_name(def_id),
+                Some(sym::ptr_cast | sym::const_ptr_cast | sym::ptr_cast_mut | sym::ptr_cast_const)
+            )
+        {
             expr
-        // UnsafeCell::raw_get(<expr>)
+        // ptr::from_ref(<expr>), UnsafeCell::raw_get(<expr>) or mem::transmute<_, _>(<expr>)
         } else if let ExprKind::Call(path, [arg]) = e.kind
             && let ExprKind::Path(ref qpath) = path.kind
             && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
-            && cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id)
+            && matches!(
+                cx.tcx.get_diagnostic_name(def_id),
+                Some(sym::ptr_from_ref | sym::unsafe_cell_raw_get | sym::transmute)
+            )
         {
-            *need_check_freeze = true;
+            if cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id) {
+                need_check_freeze = true;
+            }
             arg
         } else {
-            return None;
+            break;
         };
-
-        let mut had_at_least_one_cast = false;
-        loop {
-            e = e.peel_blocks();
-            // <expr> as *mut/const ... or <expr> as <uint>
-            e = if let ExprKind::Cast(expr, t) = e.kind
-                && matches!(cx.typeck_results().node_type(t.hir_id).kind(), ty::RawPtr(_) | ty::Uint(_))  {
-                had_at_least_one_cast = true;
-                expr
-            // <expr>.cast(), <expr>.cast_mut() or <expr>.cast_const()
-            } else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
-                && let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
-                && matches!(
-                    cx.tcx.get_diagnostic_name(def_id),
-                    Some(sym::ptr_cast | sym::const_ptr_cast | sym::ptr_cast_mut | sym::ptr_cast_const)
-                )
-            {
-                had_at_least_one_cast = true;
-                expr
-            // ptr::from_ref(<expr>) or UnsafeCell::raw_get(<expr>)
-            } else if let ExprKind::Call(path, [arg]) = e.kind
-                && let ExprKind::Path(ref qpath) = path.kind
-                && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
-                && matches!(
-                    cx.tcx.get_diagnostic_name(def_id),
-                    Some(sym::ptr_from_ref | sym::unsafe_cell_raw_get)
-                )
-            {
-                if cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id) {
-                    *need_check_freeze = true;
-                }
-                return Some(arg);
-            } else if had_at_least_one_cast {
-                return Some(e);
-            } else {
-                return None;
-            };
-        }
-    }
-
-    fn from_transmute<'tcx>(
-        cx: &LateContext<'tcx>,
-        e: &'tcx Expr<'tcx>,
-    ) -> Option<&'tcx Expr<'tcx>> {
-        // mem::transmute::<_, *mut _>(<expr>)
-        if let ExprKind::Call(path, [arg]) = e.kind
-            && let ExprKind::Path(ref qpath) = path.kind
-            && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
-            && cx.tcx.is_diagnostic_item(sym::transmute, def_id)
-            && let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(e.hir_id).kind() {
-            Some(arg)
-        } else {
-            None
-        }
     }
 
-    let mut need_check_freeze = false;
-    let Some(e) = from_casts(cx, e, &mut need_check_freeze).or_else(|| from_transmute(cx, e))
-    else {
-        return false;
-    };
-
-    let e = e.peel_blocks();
-    let node_type = cx.typeck_results().node_type(e.hir_id);
-    if let ty::Ref(_, inner_ty, Mutability::Not) = node_type.kind() {
+    let start_ty = cx.typeck_results().node_type(e.hir_id);
+    if let ty::Ref(_, inner_ty, Mutability::Not) = start_ty.kind() {
         // If an UnsafeCell method is involved we need to additionaly check the
         // inner type for the presence of the Freeze trait (ie does NOT contain
         // an UnsafeCell), since in that case we would incorrectly lint on valid casts.
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 84e7ecb0b88..7ba589c3b5a 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -785,16 +785,7 @@ macro_rules! declare_tool_lint {
     );
 }
 
-/// Declares a static `LintArray` and return it as an expression.
-#[macro_export]
-macro_rules! lint_array {
-    ($( $lint:expr ),* ,) => { lint_array!( $($lint),* ) };
-    ($( $lint:expr ),*) => {{
-        vec![$($lint),*]
-    }}
-}
-
-pub type LintArray = Vec<&'static Lint>;
+pub type LintVec = Vec<&'static Lint>;
 
 pub trait LintPass {
     fn name(&self) -> &'static str;
@@ -808,7 +799,7 @@ macro_rules! impl_lint_pass {
             fn name(&self) -> &'static str { stringify!($ty) }
         }
         impl $ty {
-            pub fn get_lints() -> $crate::LintArray { $crate::lint_array!($($lint),*) }
+            pub fn get_lints() -> $crate::LintVec { vec![$($lint),*] }
         }
     };
 }
diff --git a/compiler/rustc_middle/src/mir/basic_blocks.rs b/compiler/rustc_middle/src/mir/basic_blocks.rs
index cd770c395e4..3ecd5b9cd34 100644
--- a/compiler/rustc_middle/src/mir/basic_blocks.rs
+++ b/compiler/rustc_middle/src/mir/basic_blocks.rs
@@ -63,11 +63,14 @@ impl<'tcx> BasicBlocks<'tcx> {
     }
 
     /// Returns basic blocks in a reverse postorder.
+    ///
+    /// See [`traversal::reverse_postorder`]'s docs to learn what is preorder traversal.
+    ///
+    /// [`traversal::reverse_postorder`]: crate::mir::traversal::reverse_postorder
     #[inline]
     pub fn reverse_postorder(&self) -> &[BasicBlock] {
         self.cache.reverse_postorder.get_or_init(|| {
-            let mut rpo: Vec<_> =
-                Postorder::new(&self.basic_blocks, START_BLOCK).map(|(bb, _)| bb).collect();
+            let mut rpo: Vec<_> = Postorder::new(&self.basic_blocks, START_BLOCK).collect();
             rpo.reverse();
             rpo
         })
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index 349b32c10fb..76567c3f6b0 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -1146,10 +1146,10 @@ fn post_fmt_projection(projection: &[PlaceElem<'_>], fmt: &mut Formatter<'_>) ->
             ProjectionElem::ConstantIndex { offset, min_length, from_end: true } => {
                 write!(fmt, "[-{offset:?} of {min_length:?}]")?;
             }
-            ProjectionElem::Subslice { from, to, from_end: true } if to == 0 => {
+            ProjectionElem::Subslice { from, to: 0, from_end: true } => {
                 write!(fmt, "[{from:?}:]")?;
             }
-            ProjectionElem::Subslice { from, to, from_end: true } if from == 0 => {
+            ProjectionElem::Subslice { from: 0, to, from_end: true } => {
                 write!(fmt, "[:-{to:?}]")?;
             }
             ProjectionElem::Subslice { from, to, from_end: true } => {
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 201926fee3e..55f895f73b4 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -139,6 +139,7 @@ pub enum RuntimePhase {
     /// * [`TerminatorKind::Yield`]
     /// * [`TerminatorKind::GeneratorDrop`]
     /// * [`Rvalue::Aggregate`] for any `AggregateKind` except `Array`
+    /// * [`PlaceElem::OpaqueCast`]
     ///
     /// And the following variants are allowed:
     /// * [`StatementKind::Retag`]
diff --git a/compiler/rustc_middle/src/mir/traversal.rs b/compiler/rustc_middle/src/mir/traversal.rs
index ec16a8470c4..a1ff8410eac 100644
--- a/compiler/rustc_middle/src/mir/traversal.rs
+++ b/compiler/rustc_middle/src/mir/traversal.rs
@@ -41,6 +41,12 @@ impl<'a, 'tcx> Preorder<'a, 'tcx> {
     }
 }
 
+/// Preorder traversal of a graph.
+///
+/// This function creates an iterator over the `Body`'s basic blocks, that
+/// returns basic blocks in a preorder.
+///
+/// See [`Preorder`]'s docs to learn what is preorder traversal.
 pub fn preorder<'a, 'tcx>(body: &'a Body<'tcx>) -> Preorder<'a, 'tcx> {
     Preorder::new(body, START_BLOCK)
 }
@@ -178,7 +184,7 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
         // When we yield `C` and call `traverse_successor`, we push `B` to the stack, but
         // since we've already visited `E`, that child isn't added to the stack. The last
         // two iterations yield `B` and finally `A` for a final traversal of [E, D, C, B, A]
-        while let Some(&mut (_, ref mut iter)) = self.visit_stack.last_mut() && let Some(bb) = iter.next_back() {
+        while let Some(bb) = self.visit_stack.last_mut().and_then(|(_, iter)| iter.next_back()) {
             if self.visited.insert(bb) {
                 if let Some(term) = &self.basic_blocks[bb].terminator {
                     self.visit_stack.push((bb, term.successors()));
@@ -188,16 +194,14 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Iterator for Postorder<'a, 'tcx> {
-    type Item = (BasicBlock, &'a BasicBlockData<'tcx>);
+impl<'tcx> Iterator for Postorder<'_, 'tcx> {
+    type Item = BasicBlock;
 
-    fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
-        let next = self.visit_stack.pop();
-        if next.is_some() {
-            self.traverse_successor();
-        }
+    fn next(&mut self) -> Option<BasicBlock> {
+        let (bb, _) = self.visit_stack.pop()?;
+        self.traverse_successor();
 
-        next.map(|(bb, _)| (bb, &self.basic_blocks[bb]))
+        Some(bb)
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
@@ -215,10 +219,14 @@ impl<'a, 'tcx> Iterator for Postorder<'a, 'tcx> {
     }
 }
 
-/// Creates an iterator over the `Body`'s basic blocks, that:
+/// Postorder traversal of a graph.
+///
+/// This function creates an iterator over the `Body`'s basic blocks, that:
 /// - returns basic blocks in a postorder,
 /// - traverses the `BasicBlocks` CFG cache's reverse postorder backwards, and does not cache the
 ///   postorder itself.
+///
+/// See [`Postorder`]'s docs to learn what is postorder traversal.
 pub fn postorder<'a, 'tcx>(
     body: &'a Body<'tcx>,
 ) -> impl Iterator<Item = (BasicBlock, &'a BasicBlockData<'tcx>)> + ExactSizeIterator + DoubleEndedIterator
@@ -226,7 +234,28 @@ pub fn postorder<'a, 'tcx>(
     reverse_postorder(body).rev()
 }
 
-/// Reverse postorder traversal of a graph
+/// Returns an iterator over all basic blocks reachable from the `START_BLOCK` in no particular
+/// order.
+///
+/// This is clearer than writing `preorder` in cases where the order doesn't matter.
+pub fn reachable<'a, 'tcx>(
+    body: &'a Body<'tcx>,
+) -> impl 'a + Iterator<Item = (BasicBlock, &'a BasicBlockData<'tcx>)> {
+    preorder(body)
+}
+
+/// Returns a `BitSet` containing all basic blocks reachable from the `START_BLOCK`.
+pub fn reachable_as_bitset(body: &Body<'_>) -> BitSet<BasicBlock> {
+    let mut iter = preorder(body);
+    iter.by_ref().for_each(drop);
+    iter.visited
+}
+
+/// Reverse postorder traversal of a graph.
+///
+/// This function creates an iterator over the `Body`'s basic blocks, that:
+/// - returns basic blocks in a reverse postorder,
+/// - makes use of the `BasicBlocks` CFG cache's reverse postorder.
 ///
 /// Reverse postorder is the reverse order of a postorder traversal.
 /// This is different to a preorder traversal and represents a natural
@@ -246,65 +275,6 @@ pub fn postorder<'a, 'tcx>(
 /// A reverse postorder traversal of this graph is either `A B C D` or `A C B D`
 /// Note that for a graph containing no loops (i.e., A DAG), this is equivalent to
 /// a topological sort.
-///
-/// Construction of a `ReversePostorder` traversal requires doing a full
-/// postorder traversal of the graph, therefore this traversal should be
-/// constructed as few times as possible. Use the `reset` method to be able
-/// to re-use the traversal
-#[derive(Clone)]
-pub struct ReversePostorder<'a, 'tcx> {
-    body: &'a Body<'tcx>,
-    blocks: Vec<BasicBlock>,
-    idx: usize,
-}
-
-impl<'a, 'tcx> ReversePostorder<'a, 'tcx> {
-    pub fn new(body: &'a Body<'tcx>, root: BasicBlock) -> ReversePostorder<'a, 'tcx> {
-        let blocks: Vec<_> = Postorder::new(&body.basic_blocks, root).map(|(bb, _)| bb).collect();
-        let len = blocks.len();
-        ReversePostorder { body, blocks, idx: len }
-    }
-}
-
-impl<'a, 'tcx> Iterator for ReversePostorder<'a, 'tcx> {
-    type Item = (BasicBlock, &'a BasicBlockData<'tcx>);
-
-    fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
-        if self.idx == 0 {
-            return None;
-        }
-        self.idx -= 1;
-
-        self.blocks.get(self.idx).map(|&bb| (bb, &self.body[bb]))
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        (self.idx, Some(self.idx))
-    }
-}
-
-impl<'a, 'tcx> ExactSizeIterator for ReversePostorder<'a, 'tcx> {}
-
-/// Returns an iterator over all basic blocks reachable from the `START_BLOCK` in no particular
-/// order.
-///
-/// This is clearer than writing `preorder` in cases where the order doesn't matter.
-pub fn reachable<'a, 'tcx>(
-    body: &'a Body<'tcx>,
-) -> impl 'a + Iterator<Item = (BasicBlock, &'a BasicBlockData<'tcx>)> {
-    preorder(body)
-}
-
-/// Returns a `BitSet` containing all basic blocks reachable from the `START_BLOCK`.
-pub fn reachable_as_bitset(body: &Body<'_>) -> BitSet<BasicBlock> {
-    let mut iter = preorder(body);
-    (&mut iter).for_each(drop);
-    iter.visited
-}
-
-/// Creates an iterator over the `Body`'s basic blocks, that:
-/// - returns basic blocks in a reverse postorder,
-/// - makes use of the `BasicBlocks` CFG cache's reverse postorder.
 pub fn reverse_postorder<'a, 'tcx>(
     body: &'a Body<'tcx>,
 ) -> impl Iterator<Item = (BasicBlock, &'a BasicBlockData<'tcx>)> + ExactSizeIterator + DoubleEndedIterator
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 95dced644e1..d440ca31926 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -740,9 +740,7 @@ fn non_exhaustive_match<'p, 'tcx>(
                         ));
                 }
             } else if ty == cx.tcx.types.str_ {
-                err.note(format!(
-                    "`&str` cannot be matched exhaustively, so a wildcard `_` is necessary",
-                ));
+                err.note("`&str` cannot be matched exhaustively, so a wildcard `_` is necessary");
             } else if cx.is_foreign_non_exhaustive_enum(ty) {
                 err.note(format!("`{ty}` is marked as non-exhaustive, so a wildcard `_` is necessary to match exhaustively"));
             }
diff --git a/compiler/rustc_mir_dataflow/src/elaborate_drops.rs b/compiler/rustc_mir_dataflow/src/elaborate_drops.rs
index e24685cb90f..c9991e499b3 100644
--- a/compiler/rustc_mir_dataflow/src/elaborate_drops.rs
+++ b/compiler/rustc_mir_dataflow/src/elaborate_drops.rs
@@ -194,6 +194,7 @@ where
     D: DropElaborator<'b, 'tcx>,
     'tcx: 'b,
 {
+    #[instrument(level = "trace", skip(self), ret)]
     fn place_ty(&self, place: Place<'tcx>) -> Ty<'tcx> {
         place.ty(self.elaborator.body(), self.tcx()).ty
     }
@@ -220,11 +221,9 @@ where
     //
     // FIXME: I think we should just control the flags externally,
     // and then we do not need this machinery.
+    #[instrument(level = "debug")]
     pub fn elaborate_drop(&mut self, bb: BasicBlock) {
-        debug!("elaborate_drop({:?}, {:?})", bb, self);
-        let style = self.elaborator.drop_style(self.path, DropFlagMode::Deep);
-        debug!("elaborate_drop({:?}, {:?}): live - {:?}", bb, self, style);
-        match style {
+        match self.elaborator.drop_style(self.path, DropFlagMode::Deep) {
             DropStyle::Dead => {
                 self.elaborator
                     .patch()
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 5b24fa10bea..767f8e9f4fa 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -763,7 +763,7 @@ pub(super) fn filtered_statement_span(statement: &Statement<'_>) -> Option<Span>
         // and `_1` is the `Place` for `somenum`.
         //
         // If and when the Issue is resolved, remove this special case match pattern:
-        StatementKind::FakeRead(box (cause, _)) if cause == FakeReadCause::ForGuardBinding => None,
+        StatementKind::FakeRead(box (FakeReadCause::ForGuardBinding, _)) => None,
 
         // Retain spans from all other statements
         StatementKind::FakeRead(box (_, _)) // Not including `ForGuardBinding`
diff --git a/compiler/rustc_mir_transform/src/elaborate_drops.rs b/compiler/rustc_mir_transform/src/elaborate_drops.rs
index 6a89d067275..b62d7da2a4c 100644
--- a/compiler/rustc_mir_transform/src/elaborate_drops.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_drops.rs
@@ -170,6 +170,7 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, '_, 'tcx> {
         self.ctxt.param_env()
     }
 
+    #[instrument(level = "debug", skip(self), ret)]
     fn drop_style(&self, path: Self::Path, mode: DropFlagMode) -> DropStyle {
         let ((maybe_live, maybe_dead), multipart) = match mode {
             DropFlagMode::Shallow => (self.ctxt.init_data.maybe_live_dead(path), false),
diff --git a/compiler/rustc_mir_transform/src/large_enums.rs b/compiler/rustc_mir_transform/src/large_enums.rs
index 4eee45f8d00..886ff760481 100644
--- a/compiler/rustc_mir_transform/src/large_enums.rs
+++ b/compiler/rustc_mir_transform/src/large_enums.rs
@@ -54,11 +54,8 @@ impl EnumSizeOpt {
         let layout = tcx.layout_of(param_env.and(ty)).ok()?;
         let variants = match &layout.variants {
             Variants::Single { .. } => return None,
-            Variants::Multiple { tag_encoding, .. }
-                if matches!(tag_encoding, TagEncoding::Niche { .. }) =>
-            {
-                return None;
-            }
+            Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, .. } => return None,
+
             Variants::Multiple { variants, .. } if variants.len() <= 1 => return None,
             Variants::Multiple { variants, .. } => variants,
         };
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 9e4bc456d51..754f2ee8376 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -480,6 +480,7 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let passes: &[&dyn MirPass<'tcx>] = &[
         // These next passes must be executed together
         &add_call_guards::CriticalCallEdges,
+        &reveal_all::RevealAll, // has to be done before drop elaboration, since we need to drop opaque types, too.
         &elaborate_drops::ElaborateDrops,
         // This will remove extraneous landing pads which are no longer
         // necessary as well as well as forcing any call in a non-unwinding
@@ -526,7 +527,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         body,
         &[
             &check_alignment::CheckAlignment,
-            &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
             &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
             &unreachable_prop::UnreachablePropagation,
             &uninhabited_enum_branching::UninhabitedEnumBranching,
diff --git a/compiler/rustc_mir_transform/src/reveal_all.rs b/compiler/rustc_mir_transform/src/reveal_all.rs
index 065793348e4..55f1eac6f84 100644
--- a/compiler/rustc_mir_transform/src/reveal_all.rs
+++ b/compiler/rustc_mir_transform/src/reveal_all.rs
@@ -8,16 +8,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt};
 pub struct RevealAll;
 
 impl<'tcx> MirPass<'tcx> for RevealAll {
-    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 3 || super::inline::Inline.is_enabled(sess)
-    }
-
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        // Do not apply this transformation to generators.
-        if body.generator.is_some() {
-            return;
-        }
-
         let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
         RevealAllVisitor { tcx, param_env }.visit_body_preserves_cfg(body);
     }
@@ -35,6 +26,29 @@ impl<'tcx> MutVisitor<'tcx> for RevealAllVisitor<'tcx> {
     }
 
     #[inline]
+    fn visit_place(
+        &mut self,
+        place: &mut Place<'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;
+        }
+        // `OpaqueCast` projections are only needed if there are opaque types on which projections are performed.
+        // After the `RevealAll` 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<_>>(),
+        );
+    }
+
+    #[inline]
     fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, _: Location) {
         // We have to use `try_normalize_erasing_regions` here, since it's
         // possible that we visit impossible-to-satisfy where clauses here,
diff --git a/compiler/rustc_mir_transform/src/ssa.rs b/compiler/rustc_mir_transform/src/ssa.rs
index 3a675752fba..af9514ed6bb 100644
--- a/compiler/rustc_mir_transform/src/ssa.rs
+++ b/compiler/rustc_mir_transform/src/ssa.rs
@@ -78,14 +78,10 @@ impl SsaLocals {
             visitor.assignments[local] = Set1::One(LocationExtended::Arg);
         }
 
-        if body.basic_blocks.len() > 2 {
-            for (bb, data) in traversal::reverse_postorder(body) {
-                visitor.visit_basic_block_data(bb, data);
-            }
-        } else {
-            for (bb, data) in body.basic_blocks.iter_enumerated() {
-                visitor.visit_basic_block_data(bb, data);
-            }
+        // For SSA assignments, a RPO visit will see the assignment before it sees any use.
+        // We only visit reachable nodes: computing `dominates` on an unreachable node ICEs.
+        for (bb, data) in traversal::reverse_postorder(body) {
+            visitor.visit_basic_block_data(bb, data);
         }
 
         for var_debug_info in &body.var_debug_info {
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index 2c4bc7bb568..05b6c406206 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -509,7 +509,7 @@ parse_maybe_fn_typo_with_impl = you might have meant to write `impl` instead of
 
 parse_maybe_recover_from_bad_qpath_stage_2 =
     missing angle brackets in associated item path
-    .suggestion = try: `{$ty}`
+    .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}`
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 5d3ec683552..7c75e440aaa 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -59,9 +59,18 @@ pub(crate) enum BadTypePlusSub {
 #[diag(parse_maybe_recover_from_bad_qpath_stage_2)]
 pub(crate) struct BadQPathStage2 {
     #[primary_span]
-    #[suggestion(code = "", applicability = "maybe-incorrect")]
     pub span: Span,
-    pub ty: String,
+    #[subdiagnostic]
+    pub wrap: WrapType,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
+pub(crate) struct WrapType {
+    #[suggestion_part(code = "<")]
+    pub lo: Span,
+    #[suggestion_part(code = ">")]
+    pub hi: Span,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 6c8ef34063f..06b1b1523ed 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -16,7 +16,7 @@ use crate::errors::{
     StructLiteralBodyWithoutPath, StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens,
     StructLiteralNeedingParensSugg, SuggAddMissingLetStmt, SuggEscapeIdentifier, SuggRemoveComma,
     TernaryOperator, UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
-    UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead,
+    UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead, WrapType,
 };
 
 use crate::fluent_generated as fluent;
@@ -1589,10 +1589,9 @@ impl<'a> Parser<'a> {
         self.parse_path_segments(&mut path.segments, T::PATH_STYLE, None)?;
         path.span = ty_span.to(self.prev_token.span);
 
-        let ty_str = self.span_to_snippet(ty_span).unwrap_or_else(|_| pprust::ty_to_string(&ty));
         self.sess.emit_err(BadQPathStage2 {
-            span: path.span,
-            ty: format!("<{}>::{}", ty_str, pprust::path_to_string(&path)),
+            span: ty_span,
+            wrap: WrapType { lo: ty_span.shrink_to_lo(), hi: ty_span.shrink_to_hi() },
         });
 
         let path_span = ty_span.shrink_to_hi(); // Use an empty path since `position == 0`.
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index c3c43346ed8..15ec727e4c9 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -4140,6 +4140,12 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
         });
     }
 
+    fn resolve_expr_field(&mut self, f: &'ast ExprField, e: &'ast Expr) {
+        self.resolve_expr(&f.expr, Some(e));
+        self.visit_ident(f.ident);
+        walk_list!(self, visit_attribute, f.attrs.iter());
+    }
+
     fn resolve_expr(&mut self, expr: &'ast Expr, parent: Option<&'ast Expr>) {
         // First, record candidate traits for this expression if it could
         // result in the invocation of a method call.
@@ -4155,7 +4161,19 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
 
             ExprKind::Struct(ref se) => {
                 self.smart_resolve_path(expr.id, &se.qself, &se.path, PathSource::Struct);
-                visit::walk_expr(self, expr);
+                // This is the same as `visit::walk_expr(self, expr);`, but we want to pass the
+                // parent in for accurate suggestions when encountering `Foo { bar }` that should
+                // have been `Foo { bar: self.bar }`.
+                if let Some(qself) = &se.qself {
+                    self.visit_ty(&qself.ty);
+                }
+                self.visit_path(&se.path, expr.id);
+                walk_list!(self, resolve_expr_field, &se.fields, expr);
+                match &se.rest {
+                    StructRest::Base(expr) => self.visit_expr(expr),
+                    StructRest::Rest(_span) => {}
+                    StructRest::None => {}
+                }
             }
 
             ExprKind::Break(Some(label), _) | ExprKind::Continue(Some(label)) => {
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index 64440a6c04e..bc5f8a37b0f 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -41,7 +41,7 @@ type Res = def::Res<ast::NodeId>;
 
 /// A field or associated item from self type suggested in case of resolution failure.
 enum AssocSuggestion {
-    Field,
+    Field(Span),
     MethodWithSelf { called: bool },
     AssocFn { called: bool },
     AssocType,
@@ -51,7 +51,7 @@ enum AssocSuggestion {
 impl AssocSuggestion {
     fn action(&self) -> &'static str {
         match self {
-            AssocSuggestion::Field => "use the available field",
+            AssocSuggestion::Field(_) => "use the available field",
             AssocSuggestion::MethodWithSelf { called: true } => {
                 "call the method with the fully-qualified path"
             }
@@ -186,7 +186,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 fallback_label: format!("not a {expected}"),
                 span,
                 span_label: match res {
-                    Res::Def(kind, def_id) if kind == DefKind::TyParam => {
+                    Res::Def(DefKind::TyParam, def_id) => {
                         Some((self.r.def_span(def_id), "found this type parameter"))
                     }
                     _ => None,
@@ -215,7 +215,8 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
             }
         } else {
             let mut span_label = None;
-            let item_span = path.last().unwrap().ident.span;
+            let item_ident = path.last().unwrap().ident;
+            let item_span = item_ident.span;
             let (mod_prefix, mod_str, module, suggestion) = if path.len() == 1 {
                 debug!(?self.diagnostic_metadata.current_impl_items);
                 debug!(?self.diagnostic_metadata.current_function);
@@ -231,9 +232,35 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                     })
                 {
                     let sp = item_span.shrink_to_lo();
+
+                    // Account for `Foo { field }` when suggesting `self.field` so we result on
+                    // `Foo { field: self.field }`.
+                    let field = match source {
+                        PathSource::Expr(Some(Expr { kind: ExprKind::Struct(expr), .. })) => {
+                            expr.fields.iter().find(|f| f.ident == item_ident)
+                        }
+                        _ => None,
+                    };
+                    let pre = if let Some(field) = field && field.is_shorthand {
+                        format!("{item_ident}: ")
+                    } else {
+                        String::new()
+                    };
+                    // Ensure we provide a structured suggestion for an assoc fn only for
+                    // expressions that are actually a fn call.
+                    let is_call = match field {
+                        Some(ast::ExprField { expr, .. }) => {
+                            matches!(expr.kind, ExprKind::Call(..))
+                        }
+                        _ => matches!(
+                            source,
+                            PathSource::Expr(Some(Expr { kind: ExprKind::Call(..), ..})),
+                        ),
+                    };
+
                     match &item.kind {
                         AssocItemKind::Fn(fn_)
-                        if !sig.decl.has_self() && fn_.sig.decl.has_self() => {
+                        if (!sig.decl.has_self() || !is_call) && fn_.sig.decl.has_self() => {
                             // Ensure that we only suggest `self.` if `self` is available,
                             // you can't call `fn foo(&self)` from `fn bar()` (#115992).
                             // We also want to mention that the method exists.
@@ -243,20 +270,28 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             ));
                             None
                         }
+                        AssocItemKind::Fn(fn_)
+                        if !fn_.sig.decl.has_self() && !is_call => {
+                            span_label = Some((
+                                item.ident.span,
+                                "an associated function by that name is available on `Self` here",
+                            ));
+                            None
+                        }
                         AssocItemKind::Fn(fn_) if fn_.sig.decl.has_self() => Some((
                             sp,
                             "consider using the method on `Self`",
-                            "self.".to_string(),
+                            format!("{pre}self."),
                         )),
                         AssocItemKind::Fn(_) => Some((
                             sp,
                             "consider using the associated function on `Self`",
-                            "Self::".to_string(),
+                            format!("{pre}Self::"),
                         )),
                         AssocItemKind::Const(..) => Some((
                             sp,
                             "consider using the associated constant on `Self`",
-                            "Self::".to_string(),
+                            format!("{pre}Self::"),
                         )),
                         _ => None
                     }
@@ -621,17 +656,30 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 self.lookup_assoc_candidate(ident, ns, is_expected, source.is_call())
             {
                 let self_is_available = self.self_value_is_available(path[0].ident.span);
+                // Account for `Foo { field }` when suggesting `self.field` so we result on
+                // `Foo { field: self.field }`.
+                let pre = match source {
+                    PathSource::Expr(Some(Expr { kind: ExprKind::Struct(expr), .. }))
+                        if expr
+                            .fields
+                            .iter()
+                            .any(|f| f.ident == path[0].ident && f.is_shorthand) =>
+                    {
+                        format!("{path_str}: ")
+                    }
+                    _ => String::new(),
+                };
                 match candidate {
-                    AssocSuggestion::Field => {
+                    AssocSuggestion::Field(field_span) => {
                         if self_is_available {
-                            err.span_suggestion(
-                                span,
+                            err.span_suggestion_verbose(
+                                span.shrink_to_lo(),
                                 "you might have meant to use the available field",
-                                format!("self.{path_str}"),
+                                format!("{pre}self."),
                                 Applicability::MachineApplicable,
                             );
                         } else {
-                            err.span_label(span, "a field by this name exists in `Self`");
+                            err.span_label(field_span, "a field by that name exists in `Self`");
                         }
                     }
                     AssocSuggestion::MethodWithSelf { called } if self_is_available => {
@@ -640,10 +688,10 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                         } else {
                             "you might have meant to refer to the method"
                         };
-                        err.span_suggestion(
-                            span,
+                        err.span_suggestion_verbose(
+                            span.shrink_to_lo(),
                             msg,
-                            format!("self.{path_str}"),
+                            "self.".to_string(),
                             Applicability::MachineApplicable,
                         );
                     }
@@ -651,10 +699,10 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                     | AssocSuggestion::AssocFn { .. }
                     | AssocSuggestion::AssocConst
                     | AssocSuggestion::AssocType => {
-                        err.span_suggestion(
-                            span,
+                        err.span_suggestion_verbose(
+                            span.shrink_to_lo(),
                             format!("you might have meant to {}", candidate.action()),
-                            format!("Self::{path_str}"),
+                            "Self::".to_string(),
                             Applicability::MachineApplicable,
                         );
                     }
@@ -1667,11 +1715,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                         resolution.full_res()
                     {
                         if let Some(field_ids) = self.r.field_def_ids(did) {
-                            if field_ids
+                            if let Some(field_id) = field_ids
                                 .iter()
-                                .any(|&field_id| ident.name == self.r.tcx.item_name(field_id))
+                                .find(|&&field_id| ident.name == self.r.tcx.item_name(field_id))
                             {
-                                return Some(AssocSuggestion::Field);
+                                return Some(AssocSuggestion::Field(self.r.def_span(*field_id)));
                             }
                         }
                     }
diff --git a/compiler/rustc_smir/src/rustc_internal/mod.rs b/compiler/rustc_smir/src/rustc_internal/mod.rs
index 441aafd1257..1a9dea99f64 100644
--- a/compiler/rustc_smir/src/rustc_internal/mod.rs
+++ b/compiler/rustc_smir/src/rustc_internal/mod.rs
@@ -86,6 +86,10 @@ impl<'tcx> Tables<'tcx> {
         stable_mir::ty::ImplDef(self.create_def_id(did))
     }
 
+    pub fn region_def(&mut self, did: DefId) -> stable_mir::ty::RegionDef {
+        stable_mir::ty::RegionDef(self.create_def_id(did))
+    }
+
     pub fn prov(&mut self, aid: AllocId) -> stable_mir::ty::Prov {
         stable_mir::ty::Prov(self.create_alloc_id(aid))
     }
diff --git a/compiler/rustc_smir/src/rustc_smir/mod.rs b/compiler/rustc_smir/src/rustc_smir/mod.rs
index 5ff17613b4e..c6c97ce35e8 100644
--- a/compiler/rustc_smir/src/rustc_smir/mod.rs
+++ b/compiler/rustc_smir/src/rustc_smir/mod.rs
@@ -7,7 +7,8 @@
 //!
 //! For now, we are developing everything inside `rustc`, thus, we keep this module private.
 
-use hir::def::DefKind;
+use crate::rustc_smir::hir::def::DefKind;
+use crate::rustc_smir::stable_mir::ty::{BoundRegion, EarlyBoundRegion, Region};
 use rustc_hir as hir;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{alloc_range, AllocId};
@@ -1500,9 +1501,39 @@ impl<'tcx> Stable<'tcx> for ty::ImplPolarity {
 impl<'tcx> Stable<'tcx> for ty::Region<'tcx> {
     type T = stable_mir::ty::Region;
 
-    fn stable(&self, _: &mut Tables<'tcx>) -> Self::T {
-        // FIXME: add a real implementation of stable regions
-        opaque(self)
+    fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
+        Region { kind: self.kind().stable(tables) }
+    }
+}
+
+impl<'tcx> Stable<'tcx> for ty::RegionKind<'tcx> {
+    type T = stable_mir::ty::RegionKind;
+
+    fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
+        use stable_mir::ty::RegionKind;
+        match self {
+            ty::ReEarlyBound(early_reg) => RegionKind::ReEarlyBound(EarlyBoundRegion {
+                def_id: tables.region_def(early_reg.def_id),
+                index: early_reg.index,
+                name: early_reg.name.to_string(),
+            }),
+            ty::ReLateBound(db_index, bound_reg) => RegionKind::ReLateBound(
+                db_index.as_u32(),
+                BoundRegion { var: bound_reg.var.as_u32(), kind: bound_reg.kind.stable(tables) },
+            ),
+            ty::ReStatic => RegionKind::ReStatic,
+            ty::RePlaceholder(place_holder) => {
+                RegionKind::RePlaceholder(stable_mir::ty::Placeholder {
+                    universe: place_holder.universe.as_u32(),
+                    bound: BoundRegion {
+                        var: place_holder.bound.var.as_u32(),
+                        kind: place_holder.bound.kind.stable(tables),
+                    },
+                })
+            }
+            ty::ReErased => RegionKind::ReErased,
+            _ => unreachable!("{self:?}"),
+        }
     }
 }
 
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index c58fdbcb5e1..772e09291a1 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -1753,7 +1753,7 @@ impl SourceFile {
         // is recorded.
         let diff = match self.normalized_pos.binary_search_by(|np| np.pos.cmp(&pos)) {
             Ok(i) => self.normalized_pos[i].diff,
-            Err(i) if i == 0 => 0,
+            Err(0) => 0,
             Err(i) => self.normalized_pos[i - 1].diff,
         };
 
@@ -1775,7 +1775,7 @@ impl SourceFile {
             .binary_search_by(|np| (np.pos.0 + np.diff).cmp(&(self.start_pos.0 + offset)))
         {
             Ok(i) => self.normalized_pos[i].diff,
-            Err(i) if i == 0 => 0,
+            Err(0) => 0,
             Err(i) => self.normalized_pos[i - 1].diff,
         };
 
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 382754be2ca..4f46256626f 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1465,6 +1465,7 @@ symbols! {
         simd_shl,
         simd_shr,
         simd_shuffle,
+        simd_shuffle_generic,
         simd_sub,
         simd_trunc,
         simd_xor,
diff --git a/compiler/rustc_trait_selection/src/solve/search_graph/cache.rs b/compiler/rustc_trait_selection/src/solve/search_graph/cache.rs
deleted file mode 100644
index be48447e27c..00000000000
--- a/compiler/rustc_trait_selection/src/solve/search_graph/cache.rs
+++ /dev/null
@@ -1,102 +0,0 @@
-//! This module both handles the global cache which stores "finished" goals,
-//! and the provisional cache which contains partially computed goals.
-//!
-//! The provisional cache is necessary when dealing with coinductive cycles.
-//!
-//! For more information about the provisional cache and coinduction in general,
-//! check out the relevant section of the rustc-dev-guide.
-//!
-//! FIXME(@lcnr): Write that section, feel free to ping me if you need help here
-//! before then or if I still haven't done that before January 2023.
-use super::StackDepth;
-use rustc_data_structures::fx::FxHashMap;
-use rustc_index::IndexVec;
-use rustc_middle::traits::solve::{CanonicalInput, QueryResult};
-
-rustc_index::newtype_index! {
-    pub struct EntryIndex {}
-}
-
-#[derive(Debug, Clone)]
-pub(super) struct ProvisionalEntry<'tcx> {
-    /// In case we have a coinductive cycle, this is the
-    /// the current provisional result of this goal.
-    ///
-    /// This starts out as `None` for all goals and gets to some
-    /// when the goal gets popped from the stack or we rerun evaluation
-    /// for this goal to reach a fixpoint.
-    pub(super) response: Option<QueryResult<'tcx>>,
-    /// In case of a cycle, the position of deepest stack entry involved
-    /// in that cycle. This is monotonically decreasing in the stack as all
-    /// elements between the current stack element in the deepest stack entry
-    /// involved have to also be involved in that cycle.
-    ///
-    /// We can only move entries to the global cache once we're complete done
-    /// with the cycle. If this entry has not been involved in a cycle,
-    /// this is just its own depth.
-    pub(super) depth: StackDepth,
-
-    /// The goal for this entry. Should always be equal to the corresponding goal
-    /// in the lookup table.
-    pub(super) input: CanonicalInput<'tcx>,
-}
-
-pub(super) struct ProvisionalCache<'tcx> {
-    pub(super) entries: IndexVec<EntryIndex, ProvisionalEntry<'tcx>>,
-    // FIXME: This is only used to quickly check whether a given goal
-    // is in the cache. We should experiment with using something like
-    // `SsoHashSet` here because in most cases there are only a few entries.
-    pub(super) lookup_table: FxHashMap<CanonicalInput<'tcx>, EntryIndex>,
-}
-
-impl<'tcx> ProvisionalCache<'tcx> {
-    pub(super) fn empty() -> ProvisionalCache<'tcx> {
-        ProvisionalCache { entries: Default::default(), lookup_table: Default::default() }
-    }
-
-    pub(super) fn is_empty(&self) -> bool {
-        self.entries.is_empty() && self.lookup_table.is_empty()
-    }
-
-    /// Adds a dependency from the current leaf to `target` in the cache
-    /// to prevent us from moving any goals which depend on the current leaf
-    /// to the global cache while we're still computing `target`.
-    ///
-    /// Its important to note that `target` may already be part of a different cycle.
-    /// In this case we have to ensure that we also depend on all other goals
-    /// in the existing cycle in addition to the potentially direct cycle with `target`.
-    pub(super) fn add_dependency_of_leaf_on(&mut self, target: EntryIndex) {
-        let depth = self.entries[target].depth;
-        for provisional_entry in &mut self.entries.raw[target.index()..] {
-            // The depth of `target` is the position of the deepest goal in the stack
-            // on which `target` depends. That goal is the `root` of this cycle.
-            //
-            // Any entry which was added after `target` is either on the stack itself
-            // at which point its depth is definitely at least as high as the depth of
-            // `root`. If it's not on the stack itself it has to depend on a goal
-            // between `root` and `leaf`. If it were to depend on a goal deeper in the
-            // stack than `root`, then `root` would also depend on that goal, at which
-            // point `root` wouldn't be the root anymore.
-            debug_assert!(provisional_entry.depth >= depth);
-            provisional_entry.depth = depth;
-        }
-
-        // We only update entries which were added after `target` as no other
-        // entry should have a higher depth.
-        //
-        // Any entry which previously had a higher depth than target has to
-        // be between `target` and `root`. Because of this we would have updated
-        // its depth when calling `add_dependency_of_leaf_on(root)` for `target`.
-        if cfg!(debug_assertions) {
-            self.entries.iter().all(|e| e.depth <= depth);
-        }
-    }
-
-    pub(super) fn depth(&self, entry_index: EntryIndex) -> StackDepth {
-        self.entries[entry_index].depth
-    }
-
-    pub(super) fn provisional_result(&self, entry_index: EntryIndex) -> Option<QueryResult<'tcx>> {
-        self.entries[entry_index].response
-    }
-}
diff --git a/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs b/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
index 728d0fc1ae7..33513f6bd43 100644
--- a/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
@@ -1,10 +1,7 @@
-mod cache;
-
-use self::cache::ProvisionalEntry;
 use super::inspect;
 use super::inspect::ProofTreeBuilder;
 use super::SolverMode;
-use cache::ProvisionalCache;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_index::Idx;
 use rustc_index::IndexVec;
@@ -27,8 +24,14 @@ struct StackEntry<'tcx> {
     // The maximum depth reached by this stack entry, only up-to date
     // for the top of the stack and lazily updated for the rest.
     reached_depth: StackDepth,
+    // In case of a cycle, the depth of the root.
+    cycle_root_depth: StackDepth,
+
     encountered_overflow: bool,
     has_been_used: bool,
+    /// Starts out as `None` and gets set when rerunning this
+    /// goal in case we encounter a cycle.
+    provisional_result: Option<QueryResult<'tcx>>,
 
     /// We put only the root goal of a coinductive cycle into the global cache.
     ///
@@ -47,7 +50,7 @@ pub(super) struct SearchGraph<'tcx> {
     ///
     /// An element is *deeper* in the stack if its index is *lower*.
     stack: IndexVec<StackDepth, StackEntry<'tcx>>,
-    provisional_cache: ProvisionalCache<'tcx>,
+    stack_entries: FxHashMap<CanonicalInput<'tcx>, StackDepth>,
 }
 
 impl<'tcx> SearchGraph<'tcx> {
@@ -56,7 +59,7 @@ impl<'tcx> SearchGraph<'tcx> {
             mode,
             local_overflow_limit: tcx.recursion_limit().0.checked_ilog2().unwrap_or(0) as usize,
             stack: Default::default(),
-            provisional_cache: ProvisionalCache::empty(),
+            stack_entries: Default::default(),
         }
     }
 
@@ -85,6 +88,7 @@ impl<'tcx> SearchGraph<'tcx> {
     /// would cause us to not track overflow and recursion depth correctly.
     fn pop_stack(&mut self) -> StackEntry<'tcx> {
         let elem = self.stack.pop().unwrap();
+        assert!(self.stack_entries.remove(&elem.input).is_some());
         if let Some(last) = self.stack.raw.last_mut() {
             last.reached_depth = last.reached_depth.max(elem.reached_depth);
             last.encountered_overflow |= elem.encountered_overflow;
@@ -104,22 +108,17 @@ impl<'tcx> SearchGraph<'tcx> {
     }
 
     pub(super) fn is_empty(&self) -> bool {
-        self.stack.is_empty() && self.provisional_cache.is_empty()
+        self.stack.is_empty()
     }
 
     /// Whether we're currently in a cycle. This should only be used
     /// for debug assertions.
     pub(super) fn in_cycle(&self) -> bool {
         if let Some(stack_depth) = self.stack.last_index() {
-            // Either the current goal on the stack is the root of a cycle...
-            if self.stack[stack_depth].has_been_used {
-                return true;
-            }
-
-            // ...or it depends on a goal with a lower depth.
-            let current_goal = self.stack[stack_depth].input;
-            let entry_index = self.provisional_cache.lookup_table[&current_goal];
-            self.provisional_cache.entries[entry_index].depth != stack_depth
+            // Either the current goal on the stack is the root of a cycle
+            // or it depends on a goal with a lower depth.
+            self.stack[stack_depth].has_been_used
+                || self.stack[stack_depth].cycle_root_depth != stack_depth
         } else {
             false
         }
@@ -211,9 +210,8 @@ impl<'tcx> SearchGraph<'tcx> {
             }
         }
 
-        // Look at the provisional cache to detect cycles.
-        let cache = &mut self.provisional_cache;
-        match cache.lookup_table.entry(input) {
+        // Check whether we're in a cycle.
+        match self.stack_entries.entry(input) {
             // No entry, we push this goal on the stack and try to prove it.
             Entry::Vacant(v) => {
                 let depth = self.stack.next_index();
@@ -221,14 +219,14 @@ impl<'tcx> SearchGraph<'tcx> {
                     input,
                     available_depth,
                     reached_depth: depth,
+                    cycle_root_depth: depth,
                     encountered_overflow: false,
                     has_been_used: false,
+                    provisional_result: None,
                     cycle_participants: Default::default(),
                 };
                 assert_eq!(self.stack.push(entry), depth);
-                let entry_index =
-                    cache.entries.push(ProvisionalEntry { response: None, depth, input });
-                v.insert(entry_index);
+                v.insert(depth);
             }
             // We have a nested goal which relies on a goal `root` deeper in the stack.
             //
@@ -239,41 +237,50 @@ impl<'tcx> SearchGraph<'tcx> {
             //
             // Finally we can return either the provisional response for that goal if we have a
             // coinductive cycle or an ambiguous result if the cycle is inductive.
-            Entry::Occupied(entry_index) => {
+            Entry::Occupied(entry) => {
                 inspect.goal_evaluation_kind(inspect::WipCanonicalGoalEvaluationKind::CacheHit(
                     CacheHit::Provisional,
                 ));
 
-                let entry_index = *entry_index.get();
-                let stack_depth = cache.depth(entry_index);
+                let stack_depth = *entry.get();
                 debug!("encountered cycle with depth {stack_depth:?}");
-
-                cache.add_dependency_of_leaf_on(entry_index);
-                let mut iter = self.stack.iter_mut();
-                let root = iter.nth(stack_depth.as_usize()).unwrap();
-                for e in iter {
-                    root.cycle_participants.insert(e.input);
+                // We start by updating the root depth of all cycle participants, and
+                // add all cycle participants to the root.
+                let root_depth = self.stack[stack_depth].cycle_root_depth;
+                let (prev, participants) = self.stack.raw.split_at_mut(stack_depth.as_usize() + 1);
+                let root = &mut prev[root_depth.as_usize()];
+                for entry in participants {
+                    debug_assert!(entry.cycle_root_depth >= root_depth);
+                    entry.cycle_root_depth = root_depth;
+                    root.cycle_participants.insert(entry.input);
+                    // FIXME(@lcnr): I believe that this line is needed as we could
+                    // otherwise access a cache entry for the root of a cycle while
+                    // computing the result for a cycle participant. This can result
+                    // in unstable results due to incompleteness.
+                    //
+                    // However, a test for this would be an even more complex version of
+                    // tests/ui/traits/new-solver/coinduction/incompleteness-unstable-result.rs.
+                    // I did not bother to write such a test and we have no regression test
+                    // for this. It would be good to have such a test :)
+                    #[allow(rustc::potential_query_instability)]
+                    root.cycle_participants.extend(entry.cycle_participants.drain());
                 }
 
-                // If we're in a cycle, we have to retry proving the current goal
-                // until we reach a fixpoint.
+                // If we're in a cycle, we have to retry proving the cycle head
+                // until we reach a fixpoint. It is not enough to simply retry the
+                // `root` goal of this cycle.
+                //
+                // See tests/ui/traits/new-solver/cycles/fixpoint-rerun-all-cycle-heads.rs
+                // for an example.
                 self.stack[stack_depth].has_been_used = true;
-                return if let Some(result) = cache.provisional_result(entry_index) {
+                return if let Some(result) = self.stack[stack_depth].provisional_result {
                     result
                 } else {
-                    // If we don't have a provisional result yet, the goal has to
-                    // still be on the stack.
-                    let mut goal_on_stack = false;
-                    let mut is_coinductive = true;
-                    for entry in self.stack.raw[stack_depth.index()..]
+                    // If we don't have a provisional result yet we're in the first iteration,
+                    // so we start with no constraints.
+                    let is_coinductive = self.stack.raw[stack_depth.index()..]
                         .iter()
-                        .skip_while(|entry| entry.input != input)
-                    {
-                        goal_on_stack = true;
-                        is_coinductive &= entry.input.value.goal.predicate.is_coinductive(tcx);
-                    }
-                    debug_assert!(goal_on_stack);
-
+                        .all(|entry| entry.input.value.goal.predicate.is_coinductive(tcx));
                     if is_coinductive {
                         Self::response_no_constraints(tcx, input, Certainty::Yes)
                     } else {
@@ -294,40 +301,25 @@ impl<'tcx> SearchGraph<'tcx> {
                 // of the previous iteration is equal to the final result, at which
                 // point we are done.
                 for _ in 0..self.local_overflow_limit() {
-                    let response = prove_goal(self, inspect);
+                    let result = prove_goal(self, inspect);
 
                     // Check whether the current goal is the root of a cycle and whether
                     // we have to rerun because its provisional result differed from the
                     // final result.
-                    //
-                    // Also update the response for this goal stored in the provisional
-                    // cache.
                     let stack_entry = self.pop_stack();
                     debug_assert_eq!(stack_entry.input, input);
-                    let cache = &mut self.provisional_cache;
-                    let provisional_entry_index =
-                        *cache.lookup_table.get(&stack_entry.input).unwrap();
-                    let provisional_entry = &mut cache.entries[provisional_entry_index];
                     if stack_entry.has_been_used
-                        && provisional_entry.response.map_or(true, |r| r != response)
+                        && stack_entry.provisional_result.map_or(true, |r| r != result)
                     {
-                        // If so, update the provisional result for this goal and remove
-                        // all entries whose result depends on this goal from the provisional
-                        // cache...
-                        //
-                        // That's not completely correct, as a nested goal can also only
-                        // depend on a goal which is lower in the stack so it doesn't
-                        // actually depend on the current goal. This should be fairly
-                        // rare and is hopefully not relevant for performance.
-                        provisional_entry.response = Some(response);
-                        #[allow(rustc::potential_query_instability)]
-                        cache.lookup_table.retain(|_key, index| *index <= provisional_entry_index);
-                        cache.entries.truncate(provisional_entry_index.index() + 1);
-
-                        // ...and finally push our goal back on the stack and reevaluate it.
-                        self.stack.push(StackEntry { has_been_used: false, ..stack_entry });
+                        // If so, update its provisional result and reevaluate it.
+                        let depth = self.stack.push(StackEntry {
+                            has_been_used: false,
+                            provisional_result: Some(result),
+                            ..stack_entry
+                        });
+                        assert_eq!(self.stack_entries.insert(input, depth), None);
                     } else {
-                        return (stack_entry, response);
+                        return (stack_entry, result);
                     }
                 }
 
@@ -343,17 +335,7 @@ impl<'tcx> SearchGraph<'tcx> {
         //
         // It is not possible for any nested goal to depend on something deeper on the
         // stack, as this would have also updated the depth of the current goal.
-        let cache = &mut self.provisional_cache;
-        let provisional_entry_index = *cache.lookup_table.get(&input).unwrap();
-        let provisional_entry = &mut cache.entries[provisional_entry_index];
-        let depth = provisional_entry.depth;
-        if depth == self.stack.next_index() {
-            for (i, entry) in cache.entries.drain_enumerated(provisional_entry_index.index()..) {
-                let actual_index = cache.lookup_table.remove(&entry.input);
-                debug_assert_eq!(Some(i), actual_index);
-                debug_assert!(entry.depth == depth);
-            }
-
+        if final_entry.cycle_root_depth == self.stack.next_index() {
             // When encountering a cycle, both inductive and coinductive, we only
             // move the root into the global cache. We also store all other cycle
             // participants involved.
@@ -371,8 +353,6 @@ impl<'tcx> SearchGraph<'tcx> {
                 dep_node,
                 result,
             )
-        } else {
-            provisional_entry.response = Some(result);
         }
 
         result
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 2a333a4f0e3..2a586f810d6 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -3211,7 +3211,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         let name = match self.tcx.opaque_type_origin(def_id.expect_local()) {
             hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_) => {
-                format!("opaque type")
+                "opaque type".to_string()
             }
             hir::OpaqueTyOrigin::TyAlias { .. } => {
                 format!("`{}`", self.tcx.def_path_debug_str(def_id))
diff --git a/compiler/stable_mir/src/fold.rs b/compiler/stable_mir/src/fold.rs
index 16ae62311aa..6471b2c2a3a 100644
--- a/compiler/stable_mir/src/fold.rs
+++ b/compiler/stable_mir/src/fold.rs
@@ -4,17 +4,20 @@ use crate::Opaque;
 
 use super::ty::{
     Allocation, Binder, Const, ConstDef, ConstantKind, ExistentialPredicate, FnSig, GenericArgKind,
-    GenericArgs, Promoted, RigidTy, TermKind, Ty, TyKind, UnevaluatedConst,
+    GenericArgs, Promoted, Region, RigidTy, TermKind, Ty, TyKind, UnevaluatedConst,
 };
 
 pub trait Folder: Sized {
     type Break;
-    fn visit_ty(&mut self, ty: &Ty) -> ControlFlow<Self::Break, Ty> {
+    fn fold_ty(&mut self, ty: &Ty) -> ControlFlow<Self::Break, Ty> {
         ty.super_fold(self)
     }
     fn fold_const(&mut self, c: &Const) -> ControlFlow<Self::Break, Const> {
         c.super_fold(self)
     }
+    fn fold_reg(&mut self, reg: &Region) -> ControlFlow<Self::Break, Region> {
+        reg.super_fold(self)
+    }
 }
 
 pub trait Foldable: Sized + Clone {
@@ -26,7 +29,7 @@ pub trait Foldable: Sized + Clone {
 
 impl Foldable for Ty {
     fn fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        folder.visit_ty(self)
+        folder.fold_ty(self)
     }
     fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
         let mut kind = self.kind();
@@ -81,7 +84,7 @@ impl Foldable for UnevaluatedConst {
 
 impl Foldable for ConstDef {
     fn super_fold<V: Folder>(&self, _folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(self.clone())
+        ControlFlow::Continue(*self)
     }
 }
 
@@ -96,7 +99,7 @@ impl<T: Foldable> Foldable for Option<T> {
 
 impl Foldable for Promoted {
     fn super_fold<V: Folder>(&self, _folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(self.clone())
+        ControlFlow::Continue(*self)
     }
 }
 
@@ -106,6 +109,15 @@ impl Foldable for GenericArgs {
     }
 }
 
+impl Foldable for Region {
+    fn fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
+        folder.fold_reg(self)
+    }
+    fn super_fold<V: Folder>(&self, _: &mut V) -> ControlFlow<V::Break, Self> {
+        ControlFlow::Continue(self.clone())
+    }
+}
+
 impl Foldable for GenericArgKind {
     fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
         let mut this = self.clone();
@@ -136,7 +148,10 @@ impl Foldable for RigidTy {
             }
             RigidTy::Slice(inner) => *inner = inner.fold(folder)?,
             RigidTy::RawPtr(ty, _) => *ty = ty.fold(folder)?,
-            RigidTy::Ref(_, ty, _) => *ty = ty.fold(folder)?,
+            RigidTy::Ref(reg, ty, _) => {
+                *reg = reg.fold(folder)?;
+                *ty = ty.fold(folder)?
+            }
             RigidTy::FnDef(_, args) => *args = args.fold(folder)?,
             RigidTy::FnPtr(sig) => *sig = sig.fold(folder)?,
             RigidTy::Closure(_, args) => *args = args.fold(folder)?,
@@ -214,7 +229,7 @@ pub enum Never {}
 impl Folder for GenericArgs {
     type Break = Never;
 
-    fn visit_ty(&mut self, ty: &Ty) -> ControlFlow<Self::Break, Ty> {
+    fn fold_ty(&mut self, ty: &Ty) -> ControlFlow<Self::Break, Ty> {
         ControlFlow::Continue(match ty.kind() {
             TyKind::Param(p) => self[p],
             _ => *ty,
diff --git a/compiler/stable_mir/src/ty.rs b/compiler/stable_mir/src/ty.rs
index 82007e30683..6029e3c11ad 100644
--- a/compiler/stable_mir/src/ty.rs
+++ b/compiler/stable_mir/src/ty.rs
@@ -1,7 +1,7 @@
 use super::{
     mir::Safety,
     mir::{Body, Mutability},
-    with, AllocId, DefId,
+    with, AllocId, DefId, Symbol,
 };
 use crate::Opaque;
 use std::fmt::{self, Debug, Formatter};
@@ -34,7 +34,46 @@ pub struct Const {
 }
 
 type Ident = Opaque;
-pub type Region = Opaque;
+
+#[derive(Debug, Clone)]
+pub struct Region {
+    pub kind: RegionKind,
+}
+
+#[derive(Debug, Clone)]
+pub enum RegionKind {
+    ReEarlyBound(EarlyBoundRegion),
+    ReLateBound(DebruijnIndex, BoundRegion),
+    ReStatic,
+    RePlaceholder(Placeholder<BoundRegion>),
+    ReErased,
+}
+
+pub(crate) type DebruijnIndex = u32;
+
+#[derive(Debug, Clone)]
+pub struct EarlyBoundRegion {
+    pub def_id: RegionDef,
+    pub index: u32,
+    pub name: Symbol,
+}
+
+pub(crate) type BoundVar = u32;
+
+#[derive(Debug, Clone)]
+pub struct BoundRegion {
+    pub var: BoundVar,
+    pub kind: BoundRegionKind,
+}
+
+pub(crate) type UniverseIndex = u32;
+
+#[derive(Debug, Clone)]
+pub struct Placeholder<T> {
+    pub universe: UniverseIndex,
+    pub bound: T,
+}
+
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub struct Span(pub usize);
 
@@ -152,6 +191,9 @@ pub struct ConstDef(pub DefId);
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct ImplDef(pub DefId);
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct RegionDef(pub DefId);
+
 #[derive(Clone, Debug)]
 pub struct GenericArgs(pub Vec<GenericArgKind>);
 
diff --git a/compiler/stable_mir/src/visitor.rs b/compiler/stable_mir/src/visitor.rs
index 9c3b4cd994a..96100958138 100644
--- a/compiler/stable_mir/src/visitor.rs
+++ b/compiler/stable_mir/src/visitor.rs
@@ -4,7 +4,7 @@ use crate::Opaque;
 
 use super::ty::{
     Allocation, Binder, Const, ConstDef, ExistentialPredicate, FnSig, GenericArgKind, GenericArgs,
-    Promoted, RigidTy, TermKind, Ty, UnevaluatedConst,
+    Promoted, Region, RigidTy, TermKind, Ty, UnevaluatedConst,
 };
 
 pub trait Visitor: Sized {
@@ -15,6 +15,9 @@ pub trait Visitor: Sized {
     fn visit_const(&mut self, c: &Const) -> ControlFlow<Self::Break> {
         c.super_visit(self)
     }
+    fn visit_reg(&mut self, reg: &Region) -> ControlFlow<Self::Break> {
+        reg.super_visit(self)
+    }
 }
 
 pub trait Visitable {
@@ -101,6 +104,16 @@ impl Visitable for GenericArgs {
     }
 }
 
+impl Visitable for Region {
+    fn visit<V: Visitor>(&self, visitor: &mut V) -> ControlFlow<V::Break> {
+        visitor.visit_reg(self)
+    }
+
+    fn super_visit<V: Visitor>(&self, _: &mut V) -> ControlFlow<V::Break> {
+        ControlFlow::Continue(())
+    }
+}
+
 impl Visitable for GenericArgKind {
     fn super_visit<V: Visitor>(&self, visitor: &mut V) -> ControlFlow<V::Break> {
         match self {
@@ -128,7 +141,10 @@ impl Visitable for RigidTy {
             }
             RigidTy::Slice(inner) => inner.visit(visitor),
             RigidTy::RawPtr(ty, _) => ty.visit(visitor),
-            RigidTy::Ref(_, ty, _) => ty.visit(visitor),
+            RigidTy::Ref(reg, ty, _) => {
+                reg.visit(visitor);
+                ty.visit(visitor)
+            }
             RigidTy::FnDef(_, args) => args.visit(visitor),
             RigidTy::FnPtr(sig) => sig.visit(visitor),
             RigidTy::Closure(_, args) => args.visit(visitor),