Merging upstream version 1.66.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

29 files changed, 543 insertions, 441 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/error.rs b/compiler/rustc_const_eval/src/const_eval/error.rs
index 09d53331b..4977a5d6b 100644
--- a/compiler/rustc_const_eval/src/const_eval/error.rs
+++ b/compiler/rustc_const_eval/src/const_eval/error.rs
@@ -2,7 +2,6 @@ use std::error::Error;
 use std::fmt;
 
 use rustc_errors::Diagnostic;
-use rustc_hir as hir;
 use rustc_middle::mir::AssertKind;
 use rustc_middle::ty::{layout::LayoutError, query::TyCtxtAt, ConstInt};
 use rustc_span::{Span, Symbol};
@@ -23,11 +22,7 @@ pub enum ConstEvalErrKind {
     Abort(String),
 }
 
-impl MachineStopType for ConstEvalErrKind {
-    fn is_hard_err(&self) -> bool {
-        matches!(self, Self::Panic { .. })
-    }
-}
+impl MachineStopType for ConstEvalErrKind {}
 
 // The errors become `MachineStop` with plain strings when being raised.
 // `ConstEvalErr` (in `librustc_middle/mir/interpret/error.rs`) knows to
@@ -69,7 +64,7 @@ pub struct ConstEvalErr<'tcx> {
 impl<'tcx> ConstEvalErr<'tcx> {
     /// Turn an interpreter error into something to report to the user.
     /// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
-    /// Should be called only if the error is actually going to to be reported!
+    /// Should be called only if the error is actually going to be reported!
     pub fn new<'mir, M: Machine<'mir, 'tcx>>(
         ecx: &InterpCx<'mir, 'tcx, M>,
         error: InterpErrorInfo<'tcx>,
@@ -87,48 +82,10 @@ impl<'tcx> ConstEvalErr<'tcx> {
         ConstEvalErr { error: error.into_kind(), stacktrace, span }
     }
 
-    pub fn struct_error(
-        &self,
-        tcx: TyCtxtAt<'tcx>,
-        message: &str,
-        decorate: impl FnOnce(&mut Diagnostic),
-    ) -> ErrorHandled {
-        self.struct_generic(tcx, message, decorate, None)
-    }
-
     pub fn report_as_error(&self, tcx: TyCtxtAt<'tcx>, message: &str) -> ErrorHandled {
         self.struct_error(tcx, message, |_| {})
     }
 
-    pub fn report_as_lint(
-        &self,
-        tcx: TyCtxtAt<'tcx>,
-        message: &str,
-        lint_root: hir::HirId,
-        span: Option<Span>,
-    ) -> ErrorHandled {
-        self.struct_generic(
-            tcx,
-            message,
-            |lint: &mut Diagnostic| {
-                // Apply the span.
-                if let Some(span) = span {
-                    let primary_spans = lint.span.primary_spans().to_vec();
-                    // point at the actual error as the primary span
-                    lint.replace_span_with(span);
-                    // point to the `const` statement as a secondary span
-                    // they don't have any label
-                    for sp in primary_spans {
-                        if sp != span {
-                            lint.span_label(sp, "");
-                        }
-                    }
-                }
-            },
-            Some(lint_root),
-        )
-    }
-
     /// Create a diagnostic for this const eval error.
     ///
     /// Sets the message passed in via `message` and adds span labels with detailed error
@@ -137,13 +94,12 @@ impl<'tcx> ConstEvalErr<'tcx> {
     ///
     /// If `lint_root.is_some()` report it as a lint, else report it as a hard error.
     /// (Except that for some errors, we ignore all that -- see `must_error` below.)
-    #[instrument(skip(self, tcx, decorate, lint_root), level = "debug")]
-    fn struct_generic(
+    #[instrument(skip(self, tcx, decorate), level = "debug")]
+    pub fn struct_error(
         &self,
         tcx: TyCtxtAt<'tcx>,
         message: &str,
         decorate: impl FnOnce(&mut Diagnostic),
-        lint_root: Option<hir::HirId>,
     ) -> ErrorHandled {
         let finish = |err: &mut Diagnostic, span_msg: Option<String>| {
             trace!("reporting const eval failure at {:?}", self.span);
@@ -224,27 +180,9 @@ impl<'tcx> ConstEvalErr<'tcx> {
 
         let err_msg = self.error.to_string();
 
-        // Regular case - emit a lint.
-        if let Some(lint_root) = lint_root {
-            // Report as lint.
-            let hir_id =
-                self.stacktrace.iter().rev().find_map(|frame| frame.lint_root).unwrap_or(lint_root);
-            tcx.struct_span_lint_hir(
-                rustc_session::lint::builtin::CONST_ERR,
-                hir_id,
-                tcx.span,
-                |lint| {
-                    let mut lint = lint.build(message);
-                    finish(&mut lint, Some(err_msg));
-                    lint.emit();
-                },
-            );
-            ErrorHandled::Linted
-        } else {
-            // Report as hard error.
-            let mut err = struct_error(tcx, message);
-            finish(&mut err, Some(err_msg));
-            ErrorHandled::Reported(err.emit())
-        }
+        // Report as hard error.
+        let mut err = struct_error(tcx, message);
+        finish(&mut err, Some(err_msg));
+        ErrorHandled::Reported(err.emit())
     }
 }
diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
index a2f14e753..1b1052fdf 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -13,7 +13,7 @@ use rustc_middle::mir::pretty::display_allocation;
 use rustc_middle::traits::Reveal;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, subst::Subst, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::source_map::Span;
 use rustc_target::abi::{self, Abi};
 use std::borrow::Cow;
@@ -317,45 +317,23 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
         Err(error) => {
             let err = ConstEvalErr::new(&ecx, error, None);
-            // Some CTFE errors raise just a lint, not a hard error; see
-            // <https://github.com/rust-lang/rust/issues/71800>.
-            let is_hard_err = if let Some(def) = def.as_local() {
-                // (Associated) consts only emit a lint, since they might be unused.
-                !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
-                    // check if the inner InterpError is hard
-                    || err.error.is_hard_err()
+            let msg = if is_static {
+                Cow::from("could not evaluate static initializer")
             } else {
-                // use of broken constant from other crate: always an error
-                true
-            };
-
-            if is_hard_err {
-                let msg = if is_static {
-                    Cow::from("could not evaluate static initializer")
+                // If the current item has generics, we'd like to enrich the message with the
+                // instance and its substs: to show the actual compile-time values, in addition to
+                // the expression, leading to the const eval error.
+                let instance = &key.value.instance;
+                if !instance.substs.is_empty() {
+                    let instance = with_no_trimmed_paths!(instance.to_string());
+                    let msg = format!("evaluation of `{}` failed", instance);
+                    Cow::from(msg)
                 } else {
-                    // If the current item has generics, we'd like to enrich the message with the
-                    // instance and its substs: to show the actual compile-time values, in addition to
-                    // the expression, leading to the const eval error.
-                    let instance = &key.value.instance;
-                    if !instance.substs.is_empty() {
-                        let instance = with_no_trimmed_paths!(instance.to_string());
-                        let msg = format!("evaluation of `{}` failed", instance);
-                        Cow::from(msg)
-                    } else {
-                        Cow::from("evaluation of constant value failed")
-                    }
-                };
+                    Cow::from("evaluation of constant value failed")
+                }
+            };
 
-                Err(err.report_as_error(ecx.tcx.at(err.span), &msg))
-            } else {
-                let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
-                Err(err.report_as_lint(
-                    tcx.at(tcx.def_span(def.did)),
-                    "any use of this value will cause an error",
-                    hir_id,
-                    Some(err.span),
-                ))
-            }
+            Err(err.report_as_error(ecx.tcx.at(err.span), &msg))
         }
         Ok(mplace) => {
             // Since evaluation had no errors, validate the resulting constant.
diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index e5acacd91..35d58d2f6 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -2,10 +2,10 @@ use rustc_hir::def::DefKind;
 use rustc_middle::mir;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use std::borrow::Borrow;
-use std::collections::hash_map::Entry;
 use std::hash::Hash;
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::fx::IndexEntry;
 use std::fmt;
 
 use rustc_ast::Mutability;
@@ -107,18 +107,18 @@ impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
     }
 }
 
-impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
+impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxIndexMap<K, V> {
     #[inline(always)]
     fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
     where
         K: Borrow<Q>,
     {
-        FxHashMap::contains_key(self, k)
+        FxIndexMap::contains_key(self, k)
     }
 
     #[inline(always)]
     fn insert(&mut self, k: K, v: V) -> Option<V> {
-        FxHashMap::insert(self, k, v)
+        FxIndexMap::insert(self, k, v)
     }
 
     #[inline(always)]
@@ -126,7 +126,7 @@ impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
     where
         K: Borrow<Q>,
     {
-        FxHashMap::remove(self, k)
+        FxIndexMap::remove(self, k)
     }
 
     #[inline(always)]
@@ -148,8 +148,8 @@ impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
     #[inline(always)]
     fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E> {
         match self.entry(k) {
-            Entry::Occupied(e) => Ok(e.into_mut()),
-            Entry::Vacant(e) => {
+            IndexEntry::Occupied(e) => Ok(e.into_mut()),
+            IndexEntry::Vacant(e) => {
                 let v = vacant()?;
                 Ok(e.insert(v))
             }
diff --git a/compiler/rustc_const_eval/src/const_eval/mod.rs b/compiler/rustc_const_eval/src/const_eval/mod.rs
index d9c4ae4d5..1c33e7845 100644
--- a/compiler/rustc_const_eval/src/const_eval/mod.rs
+++ b/compiler/rustc_const_eval/src/const_eval/mod.rs
@@ -100,10 +100,10 @@ pub(crate) fn try_destructure_mir_constant<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     val: mir::ConstantKind<'tcx>,
-) -> InterpResult<'tcx, mir::DestructuredMirConstant<'tcx>> {
+) -> InterpResult<'tcx, mir::DestructuredConstant<'tcx>> {
     trace!("destructure_mir_constant: {:?}", val);
     let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
-    let op = ecx.mir_const_to_op(&val, None)?;
+    let op = ecx.const_to_op(&val, None)?;
 
     // We go to `usize` as we cannot allocate anything bigger anyway.
     let (field_count, variant, down) = match val.ty().kind() {
@@ -129,7 +129,7 @@ pub(crate) fn try_destructure_mir_constant<'tcx>(
         .collect::<InterpResult<'tcx, Vec<_>>>()?;
     let fields = tcx.arena.alloc_from_iter(fields_iter);
 
-    Ok(mir::DestructuredMirConstant { variant, fields })
+    Ok(mir::DestructuredConstant { variant, fields })
 }
 
 #[instrument(skip(tcx), level = "debug")]
@@ -139,7 +139,7 @@ pub(crate) fn deref_mir_constant<'tcx>(
     val: mir::ConstantKind<'tcx>,
 ) -> mir::ConstantKind<'tcx> {
     let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
-    let op = ecx.mir_const_to_op(&val, None).unwrap();
+    let op = ecx.const_to_op(&val, None).unwrap();
     let mplace = ecx.deref_operand(&op).unwrap();
     if let Some(alloc_id) = mplace.ptr.provenance {
         assert_eq!(
diff --git a/compiler/rustc_const_eval/src/const_eval/valtrees.rs b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
index a964fe846..f4da11883 100644
--- a/compiler/rustc_const_eval/src/const_eval/valtrees.rs
+++ b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
@@ -212,7 +212,7 @@ fn create_pointee_place<'tcx>(
 ) -> MPlaceTy<'tcx> {
     let tcx = ecx.tcx.tcx;
 
-    if !ty.is_sized(ecx.tcx, ty::ParamEnv::empty()) {
+    if !ty.is_sized(*ecx.tcx, ty::ParamEnv::empty()) {
         // We need to create `Allocation`s for custom DSTs
 
         let (unsized_inner_ty, num_elems) = get_info_on_unsized_field(ty, valtree, tcx);
@@ -398,7 +398,7 @@ fn valtree_into_mplace<'tcx>(
 
                 let mut place_inner = match ty.kind() {
                     ty::Str | ty::Slice(_) => ecx.mplace_index(&place, i as u64).unwrap(),
-                    _ if !ty.is_sized(ecx.tcx, ty::ParamEnv::empty())
+                    _ if !ty.is_sized(*ecx.tcx, ty::ParamEnv::empty())
                         && i == branches.len() - 1 =>
                     {
                         // Note: For custom DSTs we need to manually process the last unsized field.
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index c3547cb3a..4b0550767 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -1,146 +1,146 @@
 use rustc_hir::ConstContext;
-use rustc_macros::SessionDiagnostic;
+use rustc_macros::Diagnostic;
 use rustc_span::Span;
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unstable_in_stable)]
+#[derive(Diagnostic)]
+#[diag(const_eval_unstable_in_stable)]
 pub(crate) struct UnstableInStable {
     pub gate: String,
     #[primary_span]
     pub span: Span,
     #[suggestion(
-        const_eval::unstable_sugg,
+        unstable_sugg,
         code = "#[rustc_const_unstable(feature = \"...\", issue = \"...\")]\n",
         applicability = "has-placeholders"
     )]
     #[suggestion(
-        const_eval::bypass_sugg,
+        bypass_sugg,
         code = "#[rustc_allow_const_fn_unstable({gate})]\n",
         applicability = "has-placeholders"
     )]
     pub attr_span: Span,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::thread_local_access, code = "E0625")]
+#[derive(Diagnostic)]
+#[diag(const_eval_thread_local_access, code = "E0625")]
 pub(crate) struct NonConstOpErr {
     #[primary_span]
     pub span: Span,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::static_access, code = "E0013")]
+#[derive(Diagnostic)]
+#[diag(const_eval_static_access, code = "E0013")]
 #[help]
 pub(crate) struct StaticAccessErr {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
-    #[note(const_eval::teach_note)]
-    #[help(const_eval::teach_help)]
+    #[note(teach_note)]
+    #[help(teach_help)]
     pub teach: Option<()>,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::raw_ptr_to_int)]
+#[derive(Diagnostic)]
+#[diag(const_eval_raw_ptr_to_int)]
 #[note]
-#[note(const_eval::note2)]
+#[note(note2)]
 pub(crate) struct RawPtrToIntErr {
     #[primary_span]
     pub span: Span,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::raw_ptr_comparison)]
+#[derive(Diagnostic)]
+#[diag(const_eval_raw_ptr_comparison)]
 #[note]
 pub(crate) struct RawPtrComparisonErr {
     #[primary_span]
     pub span: Span,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::panic_non_str)]
+#[derive(Diagnostic)]
+#[diag(const_eval_panic_non_str)]
 pub(crate) struct PanicNonStrErr {
     #[primary_span]
     pub span: Span,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::mut_deref, code = "E0658")]
+#[derive(Diagnostic)]
+#[diag(const_eval_mut_deref, code = "E0658")]
 pub(crate) struct MutDerefErr {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::transient_mut_borrow, code = "E0658")]
+#[derive(Diagnostic)]
+#[diag(const_eval_transient_mut_borrow, code = "E0658")]
 pub(crate) struct TransientMutBorrowErr {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::transient_mut_borrow_raw, code = "E0658")]
+#[derive(Diagnostic)]
+#[diag(const_eval_transient_mut_borrow_raw, code = "E0658")]
 pub(crate) struct TransientMutBorrowErrRaw {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::max_num_nodes_in_const)]
+#[derive(Diagnostic)]
+#[diag(const_eval_max_num_nodes_in_const)]
 pub(crate) struct MaxNumNodesInConstErr {
     #[primary_span]
     pub span: Span,
     pub global_const_id: String,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unallowed_fn_pointer_call)]
+#[derive(Diagnostic)]
+#[diag(const_eval_unallowed_fn_pointer_call)]
 pub(crate) struct UnallowedFnPointerCall {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unstable_const_fn)]
+#[derive(Diagnostic)]
+#[diag(const_eval_unstable_const_fn)]
 pub(crate) struct UnstableConstFn {
     #[primary_span]
     pub span: Span,
     pub def_path: String,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unallowed_mutable_refs, code = "E0764")]
+#[derive(Diagnostic)]
+#[diag(const_eval_unallowed_mutable_refs, code = "E0764")]
 pub(crate) struct UnallowedMutableRefs {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
-    #[note(const_eval::teach_note)]
+    #[note(teach_note)]
     pub teach: Option<()>,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unallowed_mutable_refs_raw, code = "E0764")]
+#[derive(Diagnostic)]
+#[diag(const_eval_unallowed_mutable_refs_raw, code = "E0764")]
 pub(crate) struct UnallowedMutableRefsRaw {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
-    #[note(const_eval::teach_note)]
+    #[note(teach_note)]
     pub teach: Option<()>,
 }
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::non_const_fmt_macro_call, code = "E0015")]
+#[derive(Diagnostic)]
+#[diag(const_eval_non_const_fmt_macro_call, code = "E0015")]
 pub(crate) struct NonConstFmtMacroCall {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::non_const_fn_call, code = "E0015")]
+#[derive(Diagnostic)]
+#[diag(const_eval_non_const_fn_call, code = "E0015")]
 pub(crate) struct NonConstFnCall {
     #[primary_span]
     pub span: Span,
@@ -148,35 +148,35 @@ pub(crate) struct NonConstFnCall {
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unallowed_op_in_const_context)]
+#[derive(Diagnostic)]
+#[diag(const_eval_unallowed_op_in_const_context)]
 pub(crate) struct UnallowedOpInConstContext {
     #[primary_span]
     pub span: Span,
     pub msg: String,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unallowed_heap_allocations, code = "E0010")]
+#[derive(Diagnostic)]
+#[diag(const_eval_unallowed_heap_allocations, code = "E0010")]
 pub(crate) struct UnallowedHeapAllocations {
     #[primary_span]
     #[label]
     pub span: Span,
     pub kind: ConstContext,
-    #[note(const_eval::teach_note)]
+    #[note(teach_note)]
     pub teach: Option<()>,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::unallowed_inline_asm, code = "E0015")]
+#[derive(Diagnostic)]
+#[diag(const_eval_unallowed_inline_asm, code = "E0015")]
 pub(crate) struct UnallowedInlineAsm {
     #[primary_span]
     pub span: Span,
     pub kind: ConstContext,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::interior_mutable_data_refer, code = "E0492")]
+#[derive(Diagnostic)]
+#[diag(const_eval_interior_mutable_data_refer, code = "E0492")]
 pub(crate) struct InteriorMutableDataRefer {
     #[primary_span]
     #[label]
@@ -184,12 +184,12 @@ pub(crate) struct InteriorMutableDataRefer {
     #[help]
     pub opt_help: Option<()>,
     pub kind: ConstContext,
-    #[note(const_eval::teach_note)]
+    #[note(teach_note)]
     pub teach: Option<()>,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(const_eval::interior_mutability_borrow)]
+#[derive(Diagnostic)]
+#[diag(const_eval_interior_mutability_borrow)]
 pub(crate) struct InteriorMutabilityBorrow {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
index cbe985480..269ae15d4 100644
--- a/compiler/rustc_const_eval/src/interpret/cast.rs
+++ b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -43,9 +43,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 self.write_immediate(res, dest)?;
             }
 
-            Misc => {
+            IntToInt | IntToFloat => {
                 let src = self.read_immediate(src)?;
-                let res = self.misc_cast(&src, cast_ty)?;
+                let res = self.int_to_int_or_float(&src, cast_ty)?;
+                self.write_immediate(res, dest)?;
+            }
+
+            FloatToFloat | FloatToInt => {
+                let src = self.read_immediate(src)?;
+                let res = self.float_to_float_or_int(&src, cast_ty)?;
+                self.write_immediate(res, dest)?;
+            }
+
+            FnPtrToPtr | PtrToPtr => {
+                let src = self.read_immediate(&src)?;
+                let res = self.ptr_to_ptr(&src, cast_ty)?;
                 self.write_immediate(res, dest)?;
             }
 
@@ -126,13 +138,25 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(())
     }
 
-    pub fn misc_cast(
-        &mut self,
+    /// Handles 'IntToInt' and 'IntToFloat' casts.
+    pub fn int_to_int_or_float(
+        &self,
+        src: &ImmTy<'tcx, M::Provenance>,
+        cast_ty: Ty<'tcx>,
+    ) -> InterpResult<'tcx, Immediate<M::Provenance>> {
+        assert!(src.layout.ty.is_integral() || src.layout.ty.is_char() || src.layout.ty.is_bool());
+        assert!(cast_ty.is_floating_point() || cast_ty.is_integral() || cast_ty.is_char());
+
+        Ok(self.cast_from_int_like(src.to_scalar(), src.layout, cast_ty)?.into())
+    }
+
+    /// Handles 'FloatToFloat' and 'FloatToInt' casts.
+    pub fn float_to_float_or_int(
+        &self,
         src: &ImmTy<'tcx, M::Provenance>,
         cast_ty: Ty<'tcx>,
     ) -> InterpResult<'tcx, Immediate<M::Provenance>> {
         use rustc_type_ir::sty::TyKind::*;
-        trace!("Casting {:?}: {:?} to {:?}", *src, src.layout.ty, cast_ty);
 
         match src.layout.ty.kind() {
             // Floating point
@@ -142,47 +166,42 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             Float(FloatTy::F64) => {
                 return Ok(self.cast_from_float(src.to_scalar().to_f64()?, cast_ty).into());
             }
-            // The rest is integer/pointer-"like", including fn ptr casts
-            _ => assert!(
-                src.layout.ty.is_bool()
-                    || src.layout.ty.is_char()
-                    || src.layout.ty.is_integral()
-                    || src.layout.ty.is_any_ptr(),
-                "Unexpected cast from type {:?}",
-                src.layout.ty
-            ),
+            _ => {
+                bug!("Can't cast 'Float' type into {:?}", cast_ty);
+            }
         }
+    }
 
-        // # First handle non-scalar source values.
-
+    /// Handles 'FnPtrToPtr' and 'PtrToPtr' casts.
+    pub fn ptr_to_ptr(
+        &self,
+        src: &ImmTy<'tcx, M::Provenance>,
+        cast_ty: Ty<'tcx>,
+    ) -> InterpResult<'tcx, Immediate<M::Provenance>> {
+        assert!(src.layout.ty.is_any_ptr());
+        assert!(cast_ty.is_unsafe_ptr());
         // Handle casting any ptr to raw ptr (might be a fat ptr).
-        if src.layout.ty.is_any_ptr() && cast_ty.is_unsafe_ptr() {
-            let dest_layout = self.layout_of(cast_ty)?;
-            if dest_layout.size == src.layout.size {
-                // Thin or fat pointer that just hast the ptr kind of target type changed.
-                return Ok(**src);
-            } else {
-                // Casting the metadata away from a fat ptr.
-                assert_eq!(src.layout.size, 2 * self.pointer_size());
-                assert_eq!(dest_layout.size, self.pointer_size());
-                assert!(src.layout.ty.is_unsafe_ptr());
-                return match **src {
-                    Immediate::ScalarPair(data, _) => Ok(data.into()),
-                    Immediate::Scalar(..) => span_bug!(
-                        self.cur_span(),
-                        "{:?} input to a fat-to-thin cast ({:?} -> {:?})",
-                        *src,
-                        src.layout.ty,
-                        cast_ty
-                    ),
-                    Immediate::Uninit => throw_ub!(InvalidUninitBytes(None)),
-                };
-            }
+        let dest_layout = self.layout_of(cast_ty)?;
+        if dest_layout.size == src.layout.size {
+            // Thin or fat pointer that just hast the ptr kind of target type changed.
+            return Ok(**src);
+        } else {
+            // Casting the metadata away from a fat ptr.
+            assert_eq!(src.layout.size, 2 * self.pointer_size());
+            assert_eq!(dest_layout.size, self.pointer_size());
+            assert!(src.layout.ty.is_unsafe_ptr());
+            return match **src {
+                Immediate::ScalarPair(data, _) => Ok(data.into()),
+                Immediate::Scalar(..) => span_bug!(
+                    self.cur_span(),
+                    "{:?} input to a fat-to-thin cast ({:?} -> {:?})",
+                    *src,
+                    src.layout.ty,
+                    cast_ty
+                ),
+                Immediate::Uninit => throw_ub!(InvalidUninitBytes(None)),
+            };
         }
-
-        // # The remaining source values are scalar and "int-like".
-        let scalar = src.to_scalar();
-        Ok(self.cast_from_int_like(scalar, src.layout, cast_ty)?.into())
     }
 
     pub fn pointer_expose_address_cast(
@@ -203,7 +222,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     pub fn pointer_from_exposed_address_cast(
-        &mut self,
+        &self,
         src: &ImmTy<'tcx, M::Provenance>,
         cast_ty: Ty<'tcx>,
     ) -> InterpResult<'tcx, Immediate<M::Provenance>> {
@@ -220,6 +239,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(Scalar::from_maybe_pointer(ptr, self).into())
     }
 
+    /// Low-level cast helper function. This works directly on scalars and can take 'int-like' input
+    /// type (basically everything with a scalar layout) to int/float/char types.
     pub fn cast_from_int_like(
         &self,
         scalar: Scalar<M::Provenance>, // input value (there is no ScalarTy so we separate data+layout)
@@ -259,6 +280,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         })
     }
 
+    /// Low-level cast helper function. Converts an apfloat `f` into int or float types.
     fn cast_from_float<F>(&self, f: F, dest_ty: Ty<'tcx>) -> Scalar<M::Provenance>
     where
         F: Float + Into<Scalar<M::Provenance>> + FloatConvert<Single> + FloatConvert<Double>,
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index d37eaeed0..a9063ad31 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -258,6 +258,9 @@ impl<'tcx> fmt::Display for FrameInfo<'tcx> {
             {
                 write!(f, "inside closure")?;
             } else {
+                // Note: this triggers a `good_path_bug` state, which means that if we ever get here
+                // we must emit a diagnostic. We should never display a `FrameInfo` unless we
+                // actually want to emit a warning or error to the user.
                 write!(f, "inside `{}`", self.instance)?;
             }
             if !self.span.is_dummy() {
@@ -465,7 +468,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     #[inline]
     pub fn type_is_freeze(&self, ty: Ty<'tcx>) -> bool {
-        ty.is_freeze(self.tcx, self.param_env)
+        ty.is_freeze(*self.tcx, self.param_env)
     }
 
     pub fn load_mir(
@@ -683,11 +686,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         self.stack_mut().push(frame);
 
         // Make sure all the constants required by this frame evaluate successfully (post-monomorphization check).
-        for const_ in &body.required_consts {
-            let span = const_.span;
-            let const_ =
-                self.subst_from_current_frame_and_normalize_erasing_regions(const_.literal)?;
-            self.mir_const_to_op(&const_, None).map_err(|err| {
+        for ct in &body.required_consts {
+            let span = ct.span;
+            let ct = self.subst_from_current_frame_and_normalize_erasing_regions(ct.literal)?;
+            self.const_to_op(&ct, None).map_err(|err| {
                 // If there was an error, set the span of the current frame to this constant.
                 // Avoiding doing this when evaluation succeeds.
                 self.frame_mut().loc = Err(span);
@@ -929,11 +931,13 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     #[must_use]
-    pub fn generate_stacktrace(&self) -> Vec<FrameInfo<'tcx>> {
+    pub fn generate_stacktrace_from_stack(
+        stack: &[Frame<'mir, 'tcx, M::Provenance, M::FrameExtra>],
+    ) -> Vec<FrameInfo<'tcx>> {
         let mut frames = Vec::new();
         // This deliberately does *not* honor `requires_caller_location` since it is used for much
         // more than just panics.
-        for frame in self.stack().iter().rev() {
+        for frame in stack.iter().rev() {
             let lint_root = frame.current_source_info().and_then(|source_info| {
                 match &frame.body.source_scopes[source_info.scope].local_data {
                     mir::ClearCrossCrate::Set(data) => Some(data.lint_root),
@@ -947,6 +951,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         trace!("generate stacktrace: {:#?}", frames);
         frames
     }
+
+    #[must_use]
+    pub fn generate_stacktrace(&self) -> Vec<FrameInfo<'tcx>> {
+        Self::generate_stacktrace_from_stack(self.stack())
+    }
 }
 
 #[doc(hidden)]
diff --git a/compiler/rustc_const_eval/src/interpret/intern.rs b/compiler/rustc_const_eval/src/interpret/intern.rs
index 24dbc7695..6809a42dc 100644
--- a/compiler/rustc_const_eval/src/interpret/intern.rs
+++ b/compiler/rustc_const_eval/src/interpret/intern.rs
@@ -15,7 +15,7 @@
 //! that contains allocations whose mutability we cannot identify.)
 
 use super::validity::RefTracking;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_middle::mir::interpret::InterpResult;
@@ -37,7 +37,7 @@ pub trait CompileTimeMachine<'mir, 'tcx, T> = Machine<
     ExtraFnVal = !,
     FrameExtra = (),
     AllocExtra = (),
-    MemoryMap = FxHashMap<AllocId, (MemoryKind<T>, Allocation)>,
+    MemoryMap = FxIndexMap<AllocId, (MemoryKind<T>, Allocation)>,
 >;
 
 struct InternVisitor<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx, const_eval::MemoryKind>> {
@@ -47,7 +47,7 @@ struct InternVisitor<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx, const_ev
     ref_tracking: &'rt mut RefTracking<(MPlaceTy<'tcx>, InternMode)>,
     /// A list of all encountered allocations. After type-based interning, we traverse this list to
     /// also intern allocations that are only referenced by a raw pointer or inside a union.
-    leftover_allocations: &'rt mut FxHashSet<AllocId>,
+    leftover_allocations: &'rt mut FxIndexSet<AllocId>,
     /// The root kind of the value that we're looking at. This field is never mutated for a
     /// particular allocation. It is primarily used to make as many allocations as possible
     /// read-only so LLVM can place them in const memory.
@@ -79,7 +79,7 @@ struct IsStaticOrFn;
 /// to account for (e.g. for vtables).
 fn intern_shallow<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx, const_eval::MemoryKind>>(
     ecx: &'rt mut InterpCx<'mir, 'tcx, M>,
-    leftover_allocations: &'rt mut FxHashSet<AllocId>,
+    leftover_allocations: &'rt mut FxIndexSet<AllocId>,
     alloc_id: AllocId,
     mode: InternMode,
     ty: Option<Ty<'tcx>>,
@@ -114,7 +114,7 @@ fn intern_shallow<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx, const_eval:
     if let InternMode::Static(mutability) = mode {
         // For this, we need to take into account `UnsafeCell`. When `ty` is `None`, we assume
         // no interior mutability.
-        let frozen = ty.map_or(true, |ty| ty.is_freeze(ecx.tcx, ecx.param_env));
+        let frozen = ty.map_or(true, |ty| ty.is_freeze(*ecx.tcx, ecx.param_env));
         // For statics, allocation mutability is the combination of place mutability and
         // type mutability.
         // The entire allocation needs to be mutable if it contains an `UnsafeCell` anywhere.
@@ -332,8 +332,6 @@ pub enum InternKind {
 ///
 /// This *cannot raise an interpreter error*.  Doing so is left to validation, which
 /// tracks where in the value we are and thus can show much better error messages.
-/// Any errors here would anyway be turned into `const_err` lints, whereas validation failures
-/// are hard errors.
 #[instrument(level = "debug", skip(ecx))]
 pub fn intern_const_alloc_recursive<
     'mir,
@@ -357,7 +355,7 @@ pub fn intern_const_alloc_recursive<
     // `leftover_allocations` collects *all* allocations we see, because some might not
     // be available in a typed way. They get interned at the end.
     let mut ref_tracking = RefTracking::empty();
-    let leftover_allocations = &mut FxHashSet::default();
+    let leftover_allocations = &mut FxIndexSet::default();
 
     // start with the outermost allocation
     intern_shallow(
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs b/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs
index 91f4f0425..0e3867557 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs
@@ -4,7 +4,6 @@ use rustc_ast::Mutability;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::TerminatorKind;
 use rustc_middle::ty::layout::LayoutOf;
-use rustc_middle::ty::subst::Subst;
 use rustc_span::{Span, Symbol};
 
 use crate::interpret::{
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics/type_name.rs b/compiler/rustc_const_eval/src/interpret/intrinsics/type_name.rs
index 7e4c5fcb0..ffdb8de5b 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics/type_name.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics/type_name.rs
@@ -4,7 +4,7 @@ use rustc_hir::definitions::DisambiguatedDefPathData;
 use rustc_middle::mir::interpret::{Allocation, ConstAllocation};
 use rustc_middle::ty::{
     self,
-    print::{PrettyPrinter, Print, Printer},
+    print::{with_no_verbose_constants, PrettyPrinter, Print, Printer},
     subst::{GenericArg, GenericArgKind},
     Ty, TyCtxt,
 };
@@ -190,7 +190,9 @@ impl Write for AbsolutePathPrinter<'_> {
 
 /// Directly returns an `Allocation` containing an absolute path representation of the given type.
 pub(crate) fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ConstAllocation<'tcx> {
-    let path = AbsolutePathPrinter { tcx, path: String::new() }.print_type(ty).unwrap().path;
+    let path = with_no_verbose_constants!(
+        AbsolutePathPrinter { tcx, path: String::new() }.print_type(ty).unwrap().path
+    );
     let alloc = Allocation::from_bytes_byte_aligned_immutable(path.into_bytes());
     tcx.intern_const_alloc(alloc)
 }
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index 530e252b7..351152eba 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -426,7 +426,7 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     type ExtraFnVal = !;
 
     type MemoryMap =
-        rustc_data_structures::fx::FxHashMap<AllocId, (MemoryKind<Self::MemoryKind>, Allocation)>;
+        rustc_data_structures::fx::FxIndexMap<AllocId, (MemoryKind<Self::MemoryKind>, Allocation)>;
     const GLOBAL_KIND: Option<Self::MemoryKind> = None; // no copying of globals from `tcx` to machine memory
 
     type AllocExtra = ();
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index ed155fbfe..e5e015c1e 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -794,7 +794,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             todo.extend(static_roots);
             while let Some(id) = todo.pop() {
                 if reachable.insert(id) {
-                    // This is a new allocation, add the allocation it points to to `todo`.
+                    // This is a new allocation, add the allocation it points to `todo`.
                     if let Some((_, alloc)) = self.memory.alloc_map.get(id) {
                         todo.extend(
                             alloc.provenance().values().filter_map(|prov| prov.get_alloc_id()),
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index 0e3959b61..0c212cf59 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -534,7 +534,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // * During ConstProp, with `TooGeneric` or since the `required_consts` were not all
                 //   checked yet.
                 // * During CTFE, since promoteds in `const`/`static` initializer bodies can fail.
-                self.mir_const_to_op(&val, layout)?
+                self.const_to_op(&val, layout)?
             }
         };
         trace!("{:?}: {:?}", mir_op, *op);
@@ -549,45 +549,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         ops.iter().map(|op| self.eval_operand(op, None)).collect()
     }
 
-    // Used when the miri-engine runs into a constant and for extracting information from constants
-    // in patterns via the `const_eval` module
-    /// The `val` and `layout` are assumed to already be in our interpreter
-    /// "universe" (param_env).
     pub fn const_to_op(
         &self,
-        c: ty::Const<'tcx>,
-        layout: Option<TyAndLayout<'tcx>>,
-    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
-        match c.kind() {
-            ty::ConstKind::Param(_) | ty::ConstKind::Placeholder(..) => throw_inval!(TooGeneric),
-            ty::ConstKind::Error(DelaySpanBugEmitted { reported, .. }) => {
-                throw_inval!(AlreadyReported(reported))
-            }
-            ty::ConstKind::Unevaluated(uv) => {
-                // NOTE: We evaluate to a `ValTree` here as a check to ensure
-                // we're working with valid constants, even though we never need it.
-                let instance = self.resolve(uv.def, uv.substs)?;
-                let cid = GlobalId { instance, promoted: None };
-                let _valtree = self
-                    .tcx
-                    .eval_to_valtree(self.param_env.and(cid))?
-                    .unwrap_or_else(|| bug!("unable to create ValTree for {:?}", uv));
-
-                Ok(self.eval_to_allocation(cid)?.into())
-            }
-            ty::ConstKind::Bound(..) | ty::ConstKind::Infer(..) => {
-                span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", c)
-            }
-            ty::ConstKind::Value(valtree) => {
-                let ty = c.ty();
-                let const_val = self.tcx.valtree_to_const_val((ty, valtree));
-                self.const_val_to_op(const_val, ty, layout)
-            }
-        }
-    }
-
-    pub fn mir_const_to_op(
-        &self,
         val: &mir::ConstantKind<'tcx>,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
@@ -599,7 +562,36 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // manually normalized.
         let val = self.tcx.normalize_erasing_regions(self.param_env, *val);
         match val {
-            mir::ConstantKind::Ty(ct) => self.const_to_op(ct, layout),
+            mir::ConstantKind::Ty(ct) => {
+                match ct.kind() {
+                    ty::ConstKind::Param(_) | ty::ConstKind::Placeholder(..) => {
+                        throw_inval!(TooGeneric)
+                    }
+                    ty::ConstKind::Error(DelaySpanBugEmitted { reported, .. }) => {
+                        throw_inval!(AlreadyReported(reported))
+                    }
+                    ty::ConstKind::Unevaluated(uv) => {
+                        // NOTE: We evaluate to a `ValTree` here as a check to ensure
+                        // we're working with valid constants, even though we never need it.
+                        let instance = self.resolve(uv.def, uv.substs)?;
+                        let cid = GlobalId { instance, promoted: None };
+                        let _valtree = self
+                            .tcx
+                            .eval_to_valtree(self.param_env.and(cid))?
+                            .unwrap_or_else(|| bug!("unable to create ValTree for {uv:?}"));
+
+                        Ok(self.eval_to_allocation(cid)?.into())
+                    }
+                    ty::ConstKind::Bound(..) | ty::ConstKind::Infer(..) => {
+                        span_bug!(self.cur_span(), "unexpected ConstKind in ctfe: {ct:?}")
+                    }
+                    ty::ConstKind::Value(valtree) => {
+                        let ty = ct.ty();
+                        let const_val = self.tcx.valtree_to_const_val((ty, valtree));
+                        self.const_val_to_op(const_val, ty, layout)
+                    }
+                }
+            }
             mir::ConstantKind::Val(val, ty) => self.const_val_to_op(val, ty, layout),
             mir::ConstantKind::Unevaluated(uv, _) => {
                 let instance = self.resolve(uv.def, uv.substs)?;
@@ -799,13 +791,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 }
 
 // Some nodes are used a lot. Make sure they don't unintentionally get bigger.
-#[cfg(all(target_arch = "x86_64", target_pointer_width = "64", not(bootstrap)))]
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 mod size_asserts {
     use super::*;
     use rustc_data_structures::static_assert_size;
-    // These are in alphabetical order, which is easy to maintain.
+    // tidy-alphabetical-start
     static_assert_size!(Immediate, 48);
     static_assert_size!(ImmTy<'_>, 64);
     static_assert_size!(Operand, 56);
     static_assert_size!(OpTy<'_>, 80);
+    // tidy-alphabetical-end
 }
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index b32889290..b0625b5f4 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -280,7 +280,7 @@ impl<'tcx, Prov: Provenance> PlaceTy<'tcx, Prov> {
 
     #[inline(always)]
     #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980)
-    pub fn assert_mem_place(self) -> MPlaceTy<'tcx, Prov> {
+    pub fn assert_mem_place(&self) -> MPlaceTy<'tcx, Prov> {
         self.try_as_mplace().unwrap()
     }
 }
@@ -640,11 +640,17 @@ where
         // avoid force_allocation.
         let src = match self.read_immediate_raw(src)? {
             Ok(src_val) => {
-                assert!(!src.layout.is_unsized(), "cannot copy unsized immediates");
-                assert!(
-                    !dest.layout.is_unsized(),
-                    "the src is sized, so the dest must also be sized"
-                );
+                // FIXME(const_prop): Const-prop can possibly evaluate an
+                // unsized copy operation when it thinks that the type is
+                // actually sized, due to a trivially false where-clause
+                // predicate like `where Self: Sized` with `Self = dyn Trait`.
+                // See #102553 for an example of such a predicate.
+                if src.layout.is_unsized() {
+                    throw_inval!(SizeOfUnsizedType(src.layout.ty));
+                }
+                if dest.layout.is_unsized() {
+                    throw_inval!(SizeOfUnsizedType(dest.layout.ty));
+                }
                 assert_eq!(src.layout.size, dest.layout.size);
                 // Yay, we got a value that we can write directly.
                 return if layout_compat {
@@ -886,12 +892,11 @@ where
 mod size_asserts {
     use super::*;
     use rustc_data_structures::static_assert_size;
-    // These are in alphabetical order, which is easy to maintain.
-    static_assert_size!(MemPlaceMeta, 24);
+    // tidy-alphabetical-start
     static_assert_size!(MemPlace, 40);
+    static_assert_size!(MemPlaceMeta, 24);
     static_assert_size!(MPlaceTy<'_>, 64);
-    #[cfg(not(bootstrap))]
     static_assert_size!(Place, 40);
-    #[cfg(not(bootstrap))]
     static_assert_size!(PlaceTy<'_>, 64);
+    // tidy-alphabetical-end
 }
diff --git a/compiler/rustc_const_eval/src/interpret/projection.rs b/compiler/rustc_const_eval/src/interpret/projection.rs
index 77da8f104..6b2e2bb8a 100644
--- a/compiler/rustc_const_eval/src/interpret/projection.rs
+++ b/compiler/rustc_const_eval/src/interpret/projection.rs
@@ -350,6 +350,11 @@ where
     ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> {
         use rustc_middle::mir::ProjectionElem::*;
         Ok(match proj_elem {
+            OpaqueCast(ty) => {
+                let mut place = base.clone();
+                place.layout = self.layout_of(ty)?;
+                place
+            }
             Field(field, _) => self.place_field(base, field.index())?,
             Downcast(_, variant) => self.place_downcast(base, variant)?,
             Deref => self.deref_operand(&self.place_to_op(base)?)?.into(),
@@ -374,6 +379,11 @@ where
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
         use rustc_middle::mir::ProjectionElem::*;
         Ok(match proj_elem {
+            OpaqueCast(ty) => {
+                let mut op = base.clone();
+                op.layout = self.layout_of(ty)?;
+                op
+            }
             Field(field, _) => self.operand_field(base, field.index())?,
             Downcast(_, variant) => self.operand_downcast(base, variant)?,
             Deref => self.deref_operand(base)?.into(),
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs
index 50a82aa0e..57e40e168 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -35,7 +35,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 assert_eq!(discr.layout.ty, switch_ty);
 
                 // Branch to the `otherwise` case by default, if no match is found.
-                assert!(!targets.iter().is_empty());
                 let mut target_block = targets.otherwise();
 
                 for (const_int, target) in targets.iter() {
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index 14aaee6ac..8aa56c275 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -15,7 +15,6 @@ use rustc_middle::mir::interpret::InterpError;
 use rustc_middle::ty;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_span::symbol::{sym, Symbol};
-use rustc_span::DUMMY_SP;
 use rustc_target::abi::{Abi, Scalar as ScalarAbi, Size, VariantIdx, Variants, WrappingRange};
 
 use std::hash::Hash;
@@ -56,7 +55,7 @@ macro_rules! throw_validation_failure {
 /// This lets you use the patterns as a kind of validation list, asserting which errors
 /// can possibly happen:
 ///
-/// ```
+/// ```ignore(illustrative)
 /// let v = try_validation!(some_fn(), some_path, {
 ///     Foo | Bar | Baz => { "some failure" },
 /// });
@@ -65,7 +64,7 @@ macro_rules! throw_validation_failure {
 /// The patterns must be of type `UndefinedBehaviorInfo`.
 /// An additional expected parameter can also be added to the failure message:
 ///
-/// ```
+/// ```ignore(illustrative)
 /// let v = try_validation!(some_fn(), some_path, {
 ///     Foo | Bar | Baz => { "some failure" } expected { "something that wasn't a failure" },
 /// });
@@ -74,7 +73,7 @@ macro_rules! throw_validation_failure {
 /// An additional nicety is that both parameters actually take format args, so you can just write
 /// the format string in directly:
 ///
-/// ```
+/// ```ignore(illustrative)
 /// let v = try_validation!(some_fn(), some_path, {
 ///     Foo | Bar | Baz => { "{:?}", some_failure } expected { "{}", expected_value },
 /// });
@@ -726,7 +725,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
     ) -> InterpResult<'tcx> {
         // Special check preventing `UnsafeCell` inside unions in the inner part of constants.
         if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { inner: true, .. })) {
-            if !op.layout.ty.is_freeze(self.ecx.tcx.at(DUMMY_SP), self.ecx.param_env) {
+            if !op.layout.ty.is_freeze(*self.ecx.tcx, self.ecx.param_env) {
                 throw_validation_failure!(self.path, { "`UnsafeCell` in a `const`" });
             }
         }
diff --git a/compiler/rustc_const_eval/src/lib.rs b/compiler/rustc_const_eval/src/lib.rs
index 9f47d302a..443c01fdb 100644
--- a/compiler/rustc_const_eval/src/lib.rs
+++ b/compiler/rustc_const_eval/src/lib.rs
@@ -10,7 +10,6 @@ Rust MIR: a lowered representation of Rust.
 #![feature(decl_macro)]
 #![feature(exact_size_is_empty)]
 #![feature(let_chains)]
-#![cfg_attr(bootstrap, feature(let_else))]
 #![feature(map_try_insert)]
 #![feature(min_specialization)]
 #![feature(slice_ptr_get)]
@@ -21,9 +20,8 @@ Rust MIR: a lowered representation of Rust.
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
-#![feature(is_some_with)]
+#![feature(is_some_and)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 
 #[macro_use]
 extern crate tracing;
@@ -33,7 +31,6 @@ extern crate rustc_middle;
 pub mod const_eval;
 mod errors;
 pub mod interpret;
-mod might_permit_raw_init;
 pub mod transform;
 pub mod util;
 
@@ -62,7 +59,6 @@ pub fn provide(providers: &mut Providers) {
         const_eval::deref_mir_constant(tcx, param_env, value)
     };
     providers.permits_uninit_init =
-        |tcx, ty| might_permit_raw_init::might_permit_raw_init(tcx, ty, InitKind::Uninit);
-    providers.permits_zero_init =
-        |tcx, ty| might_permit_raw_init::might_permit_raw_init(tcx, ty, InitKind::Zero);
+        |tcx, ty| util::might_permit_raw_init(tcx, ty, InitKind::UninitMitigated0x01Fill);
+    providers.permits_zero_init = |tcx, ty| util::might_permit_raw_init(tcx, ty, InitKind::Zero);
 }
diff --git a/compiler/rustc_const_eval/src/might_permit_raw_init.rs b/compiler/rustc_const_eval/src/might_permit_raw_init.rs
deleted file mode 100644
index 37ffa19cc..000000000
--- a/compiler/rustc_const_eval/src/might_permit_raw_init.rs
+++ /dev/null
@@ -1,44 +0,0 @@
-use crate::const_eval::CompileTimeInterpreter;
-use crate::interpret::{InterpCx, MemoryKind, OpTy};
-use rustc_middle::ty::layout::LayoutCx;
-use rustc_middle::ty::{layout::TyAndLayout, ParamEnv, TyCtxt};
-use rustc_session::Limit;
-use rustc_target::abi::InitKind;
-
-pub fn might_permit_raw_init<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    ty: TyAndLayout<'tcx>,
-    kind: InitKind,
-) -> bool {
-    let strict = tcx.sess.opts.unstable_opts.strict_init_checks;
-
-    if strict {
-        let machine = CompileTimeInterpreter::new(
-            Limit::new(0),
-            /*can_access_statics:*/ false,
-            /*check_alignment:*/ true,
-        );
-
-        let mut cx = InterpCx::new(tcx, rustc_span::DUMMY_SP, ParamEnv::reveal_all(), machine);
-
-        let allocated = cx
-            .allocate(ty, MemoryKind::Machine(crate::const_eval::MemoryKind::Heap))
-            .expect("OOM: failed to allocate for uninit check");
-
-        if kind == InitKind::Zero {
-            cx.write_bytes_ptr(
-                allocated.ptr,
-                std::iter::repeat(0_u8).take(ty.layout.size().bytes_usize()),
-            )
-            .expect("failed to write bytes for zero valid check");
-        }
-
-        let ot: OpTy<'_, _> = allocated.into();
-
-        // Assume that if it failed, it's a validation failure.
-        cx.validate_operand(&ot).is_ok()
-    } else {
-        let layout_cx = LayoutCx { tcx, param_env: ParamEnv::reveal_all() };
-        ty.might_permit_raw_init(&layout_cx, kind)
-    }
-}
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index 7e15858c8..22a61774e 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -13,8 +13,11 @@ use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty,
 use rustc_middle::ty::{Binder, TraitPredicate, TraitRef, TypeVisitable};
 use rustc_mir_dataflow::{self, Analysis};
 use rustc_span::{sym, Span, Symbol};
-use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
-use rustc_trait_selection::traits::SelectionContext;
+use rustc_trait_selection::infer::InferCtxtExt;
+use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
+use rustc_trait_selection::traits::{
+    self, ObligationCauseCode, SelectionContext, TraitEngine, TraitEngineExt,
+};
 
 use std::mem;
 use std::ops::Deref;
@@ -550,7 +553,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 unimplemented!()
             }
 
-            Rvalue::Cast(CastKind::Misc, _, _) => {}
+            Rvalue::Cast(_, _, _) => {}
 
             Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {}
             Rvalue::ShallowInitBox(_, _) => {}
@@ -656,6 +659,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
             ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Downcast(..)
+            | ProjectionElem::OpaqueCast(..)
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Field(..)
             | ProjectionElem::Index(_) => {}
@@ -733,10 +737,49 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     let obligation =
                         Obligation::new(ObligationCause::dummy(), param_env, poly_trait_pred);
 
-                    let implsrc = tcx.infer_ctxt().enter(|infcx| {
+                    let implsrc = {
+                        let infcx = tcx.infer_ctxt().build();
                         let mut selcx = SelectionContext::new(&infcx);
                         selcx.select(&obligation)
-                    });
+                    };
+
+                    // do a well-formedness check on the trait method being called. This is because typeck only does a
+                    // "non-const" check. This is required for correctness here.
+                    {
+                        let infcx = tcx.infer_ctxt().build();
+                        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
+                        let predicates = tcx.predicates_of(callee).instantiate(tcx, substs);
+                        let hir_id = tcx
+                            .hir()
+                            .local_def_id_to_hir_id(self.body.source.def_id().expect_local());
+                        let cause = || {
+                            ObligationCause::new(
+                                terminator.source_info.span,
+                                hir_id,
+                                ObligationCauseCode::ItemObligation(callee),
+                            )
+                        };
+                        let normalized = infcx.partially_normalize_associated_types_in(
+                            cause(),
+                            param_env,
+                            predicates,
+                        );
+
+                        for p in normalized.obligations {
+                            fulfill_cx.register_predicate_obligation(&infcx, p);
+                        }
+                        for obligation in traits::predicates_for_generics(
+                            |_, _| cause(),
+                            self.param_env,
+                            normalized.value,
+                        ) {
+                            fulfill_cx.register_predicate_obligation(&infcx, obligation);
+                        }
+                        let errors = fulfill_cx.select_all_or_error(&infcx);
+                        if !errors.is_empty() {
+                            infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
+                        }
+                    }
 
                     match implsrc {
                         Ok(Some(ImplSource::Param(_, ty::BoundConstness::ConstIfConst))) => {
@@ -794,16 +837,15 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
                                 // improve diagnostics by showing what failed. Our requirements are stricter this time
                                 // as we are going to error again anyways.
-                                tcx.infer_ctxt().enter(|infcx| {
-                                    if let Err(e) = implsrc {
-                                        infcx.report_selection_error(
-                                            obligation.clone(),
-                                            &obligation,
-                                            &e,
-                                            false,
-                                        );
-                                    }
-                                });
+                                let infcx = tcx.infer_ctxt().build();
+                                if let Err(e) = implsrc {
+                                    infcx.err_ctxt().report_selection_error(
+                                        obligation.clone(),
+                                        &obligation,
+                                        &e,
+                                        false,
+                                    );
+                                }
 
                                 self.check_op(ops::FnCallNonConst {
                                     caller,
@@ -867,8 +909,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     return;
                 }
 
-                let is_intrinsic = tcx.is_intrinsic(callee);
-
                 if !tcx.is_const_fn_raw(callee) {
                     if !tcx.is_const_default_method(callee) {
                         // To get to here we must have already found a const impl for the
@@ -928,7 +968,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     // We do not use `const` modifiers for intrinsic "functions", as intrinsics are
                     // `extern` functions, and these have no way to get marked `const`. So instead we
                     // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
-                    if self.ccx.is_const_stable_const_fn() || is_intrinsic {
+                    if self.ccx.is_const_stable_const_fn() || tcx.is_intrinsic(callee) {
                         self.check_op(ops::FnCallUnstable(callee, None));
                         return;
                     }
@@ -968,7 +1008,10 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
                 if needs_non_const_drop {
                     self.check_op_spanned(
-                        ops::LiveDrop { dropped_at: Some(terminator.source_info.span) },
+                        ops::LiveDrop {
+                            dropped_at: Some(terminator.source_info.span),
+                            dropped_ty: ty_of_dropped_place,
+                        },
                         err_span,
                     );
                 }
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
index 5fb4bf638..b28d70194 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
@@ -156,10 +156,9 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
                         }),
                     );
 
-                    let implsrc = tcx.infer_ctxt().enter(|infcx| {
-                        let mut selcx = SelectionContext::new(&infcx);
-                        selcx.select(&obligation)
-                    });
+                    let infcx = tcx.infer_ctxt().build();
+                    let mut selcx = SelectionContext::new(&infcx);
+                    let implsrc = selcx.select(&obligation);
 
                     if let Ok(Some(ImplSource::UserDefined(data))) = implsrc {
                         let span = tcx.def_span(data.impl_def_id);
@@ -422,10 +421,11 @@ impl<'tcx> NonConstOp<'tcx> for InlineAsm {
 }
 
 #[derive(Debug)]
-pub struct LiveDrop {
+pub struct LiveDrop<'tcx> {
     pub dropped_at: Option<Span>,
+    pub dropped_ty: Ty<'tcx>,
 }
-impl<'tcx> NonConstOp<'tcx> for LiveDrop {
+impl<'tcx> NonConstOp<'tcx> for LiveDrop<'tcx> {
     fn build_error(
         &self,
         ccx: &ConstCx<'_, 'tcx>,
@@ -435,9 +435,13 @@ impl<'tcx> NonConstOp<'tcx> for LiveDrop {
             ccx.tcx.sess,
             span,
             E0493,
-            "destructors cannot be evaluated at compile-time"
+            "destructor of `{}` cannot be evaluated at compile-time",
+            self.dropped_ty,
+        );
+        err.span_label(
+            span,
+            format!("the destructor for this type cannot be evaluated in {}s", ccx.const_kind()),
         );
-        err.span_label(span, format!("{}s cannot evaluate destructors", ccx.const_kind()));
         if let Some(span) = self.dropped_at {
             err.span_label(span, "value is dropped here");
         }
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs b/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
index 4e210f663..d4570c598 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
@@ -1,6 +1,6 @@
 use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::{self, BasicBlock, Location};
-use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::{Ty, TyCtxt};
 use rustc_span::{symbol::sym, Span};
 
 use super::check::Qualifs;
@@ -58,9 +58,9 @@ impl<'mir, 'tcx> std::ops::Deref for CheckLiveDrops<'mir, 'tcx> {
     }
 }
 
-impl CheckLiveDrops<'_, '_> {
-    fn check_live_drop(&self, span: Span) {
-        ops::LiveDrop { dropped_at: None }.build_error(self.ccx, span).emit();
+impl<'tcx> CheckLiveDrops<'_, 'tcx> {
+    fn check_live_drop(&self, span: Span, dropped_ty: Ty<'tcx>) {
+        ops::LiveDrop { dropped_at: None, dropped_ty }.build_error(self.ccx, span).emit();
     }
 }
 
@@ -90,7 +90,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
                 }
 
                 if dropped_place.is_indirect() {
-                    self.check_live_drop(terminator.source_info.span);
+                    self.check_live_drop(terminator.source_info.span, dropped_ty);
                     return;
                 }
 
@@ -101,7 +101,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
                 if self.qualifs.needs_non_const_drop(self.ccx, dropped_place.local, location) {
                     // Use the span where the dropped local was declared for the error.
                     let span = self.body.local_decls[dropped_place.local].source_info.span;
-                    self.check_live_drop(span);
+                    self.check_live_drop(span, dropped_ty);
                 }
             }
 
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
index 6c73ef5a8..335992342 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -5,9 +5,9 @@
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::LangItem;
 use rustc_infer::infer::TyCtxtInferExt;
+use rustc_middle::mir;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, subst::SubstsRef, AdtDef, Ty};
-use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::{
     self, ImplSource, Obligation, ObligationCause, SelectionContext,
 };
@@ -91,7 +91,7 @@ impl Qualif for HasMutInterior {
     }
 
     fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, ty: Ty<'tcx>) -> bool {
-        !ty.is_freeze(cx.tcx.at(DUMMY_SP), cx.param_env)
+        !ty.is_freeze(cx.tcx, cx.param_env)
     }
 
     fn in_adt_inherently<'tcx>(
@@ -167,30 +167,28 @@ impl Qualif for NeedsNonConstDrop {
             }),
         );
 
-        cx.tcx.infer_ctxt().enter(|infcx| {
-            let mut selcx = SelectionContext::new(&infcx);
-            let Some(impl_src) = selcx.select(&obligation).ok().flatten() else {
-                // If we couldn't select a const destruct candidate, then it's bad
-                return true;
-            };
-
-            if !matches!(
-                impl_src,
-                ImplSource::ConstDestruct(_)
-                    | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
-            ) {
-                // If our const destruct candidate is not ConstDestruct or implied by the param env,
-                // then it's bad
-                return true;
-            }
+        let infcx = cx.tcx.infer_ctxt().build();
+        let mut selcx = SelectionContext::new(&infcx);
+        let Some(impl_src) = selcx.select(&obligation).ok().flatten() else {
+            // If we couldn't select a const destruct candidate, then it's bad
+            return true;
+        };
+
+        if !matches!(
+            impl_src,
+            ImplSource::ConstDestruct(_) | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
+        ) {
+            // If our const destruct candidate is not ConstDestruct or implied by the param env,
+            // then it's bad
+            return true;
+        }
 
-            if impl_src.borrow_nested_obligations().is_empty() {
-                return false;
-            }
+        if impl_src.borrow_nested_obligations().is_empty() {
+            return false;
+        }
 
-            // If we had any errors, then it's bad
-            !traits::fully_solve_obligations(&infcx, impl_src.nested_obligations()).is_empty()
-        })
+        // If we had any errors, then it's bad
+        !traits::fully_solve_obligations(&infcx, impl_src.nested_obligations()).is_empty()
     }
 
     fn in_adt_inherently<'tcx>(
@@ -308,6 +306,7 @@ where
 
             ProjectionElem::Deref
             | ProjectionElem::Field(_, _)
+            | ProjectionElem::OpaqueCast(_)
             | ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Downcast(_, _)
@@ -349,17 +348,13 @@ where
     // FIXME(valtrees): check whether const qualifs should behave the same
     // way for type and mir constants.
     let uneval = match constant.literal {
-        ConstantKind::Ty(ct) if matches!(ct.kind(), ty::ConstKind::Unevaluated(_)) => {
-            let ty::ConstKind::Unevaluated(uv) = ct.kind() else { unreachable!() };
-
-            Some(uv.expand())
-        }
-        ConstantKind::Ty(_) => None,
+        ConstantKind::Ty(ct) if matches!(ct.kind(), ty::ConstKind::Param(_)) => None,
+        ConstantKind::Ty(c) => bug!("expected ConstKind::Param here, found {:?}", c),
         ConstantKind::Unevaluated(uv, _) => Some(uv),
         ConstantKind::Val(..) => None,
     };
 
-    if let Some(ty::Unevaluated { def, substs: _, promoted }) = uneval {
+    if let Some(mir::UnevaluatedConst { def, substs: _, promoted }) = uneval {
         // Use qualifs of the type for the promoted. Promoteds in MIR body should be possible
         // only for `NeedsNonConstDrop` with precise drop checking. This is the only const
         // check performed after the promotion. Verify that with an assertion.
@@ -367,11 +362,8 @@ where
 
         // Don't peek inside trait associated constants.
         if promoted.is_none() && cx.tcx.trait_of_item(def.did).is_none() {
-            let qualifs = if let Some((did, param_did)) = def.as_const_arg() {
-                cx.tcx.at(constant.span).mir_const_qualif_const_arg((did, param_did))
-            } else {
-                cx.tcx.at(constant.span).mir_const_qualif(def.did)
-            };
+            assert_eq!(def.const_param_did, None, "expected associated const: {def:?}");
+            let qualifs = cx.tcx.at(constant.span).mir_const_qualif(def.did);
 
             if !Q::in_qualifs(&qualifs) {
                 return false;
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/resolver.rs b/compiler/rustc_const_eval/src/transform/check_consts/resolver.rs
index 60c1e4950..805e6096b 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/resolver.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/resolver.rs
@@ -8,7 +8,6 @@ use rustc_middle::mir::{self, BasicBlock, Local, Location, Statement, StatementK
 use rustc_mir_dataflow::fmt::DebugWithContext;
 use rustc_mir_dataflow::JoinSemiLattice;
 use rustc_mir_dataflow::{Analysis, AnalysisDomain, CallReturnPlaces};
-use rustc_span::DUMMY_SP;
 
 use std::fmt;
 use std::marker::PhantomData;
@@ -120,10 +119,7 @@ where
     ///
     /// [rust-lang/unsafe-code-guidelines#134]: https://github.com/rust-lang/unsafe-code-guidelines/issues/134
     fn shared_borrow_allows_mutation(&self, place: mir::Place<'tcx>) -> bool {
-        !place
-            .ty(self.ccx.body, self.ccx.tcx)
-            .ty
-            .is_freeze(self.ccx.tcx.at(DUMMY_SP), self.ccx.param_env)
+        !place.ty(self.ccx.body, self.ccx.tcx).ty.is_freeze(self.ccx.tcx, self.ccx.param_env)
     }
 }
 
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
index f7a7cc88a..f3ae16da4 100644
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ b/compiler/rustc_const_eval/src/transform/promote_consts.rs
@@ -13,6 +13,7 @@
 //! move analysis runs after promotion on broken MIR.
 
 use rustc_hir as hir;
+use rustc_middle::mir;
 use rustc_middle::mir::traversal::ReversePostorderIter;
 use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
@@ -40,10 +41,6 @@ pub struct PromoteTemps<'tcx> {
 }
 
 impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
-    fn phase_change(&self) -> Option<MirPhase> {
-        Some(MirPhase::Analysis(AnalysisPhase::Initial))
-    }
-
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // There's not really any point in promoting errorful MIR.
         //
@@ -361,7 +358,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                             return Err(Unpromotable);
                         }
                     }
-                    ProjectionElem::Downcast(..) => {
+                    ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
                         return Err(Unpromotable);
                     }
 
@@ -840,7 +837,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                 promoted.span = span;
                 promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
                 let substs = tcx.erase_regions(InternalSubsts::identity_for_item(tcx, def.did));
-                let uneval = ty::Unevaluated { def, substs, promoted: Some(promoted_id) };
+                let uneval = mir::UnevaluatedConst { def, substs, promoted: Some(promoted_id) };
 
                 Operand::Constant(Box::new(Constant {
                     span,
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 4aa98cb13..81b82a21f 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -13,7 +13,6 @@ use rustc_middle::mir::{
     TerminatorKind, UnOp, START_BLOCK,
 };
 use rustc_middle::ty::fold::BottomUpFolder;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeFoldable, TypeVisitable};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
@@ -106,7 +105,7 @@ pub fn equal_up_to_regions<'tcx>(
             },
         )
     };
-    tcx.infer_ctxt().enter(|infcx| infcx.can_eq(param_env, normalize(src), normalize(dest)).is_ok())
+    tcx.infer_ctxt().build().can_eq(param_env, normalize(src), normalize(dest)).is_ok()
 }
 
 struct TypeChecker<'a, 'tcx> {
@@ -236,9 +235,8 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
             // `Operand::Copy` is only supposed to be used with `Copy` types.
             if let Operand::Copy(place) = operand {
                 let ty = place.ty(&self.body.local_decls, self.tcx).ty;
-                let span = self.body.source_info(location).span;
 
-                if !ty.is_copy_modulo_regions(self.tcx.at(span), self.param_env) {
+                if !ty.is_copy_modulo_regions(self.tcx, self.param_env) {
                     self.fail(location, format!("`Operand::Copy` with non-`Copy` type {}", ty));
                 }
             }
@@ -285,7 +283,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                         this.fail(
                         location,
                         format!(
-                            "Field projection `{:?}.{:?}` specified type `{:?}`, but actual type is {:?}",
+                            "Field projection `{:?}.{:?}` specified type `{:?}`, but actual type is `{:?}`",
                             parent, f, ty, f_ty
                         )
                     )
@@ -557,25 +555,40 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 check_kinds!(a, "Cannot shallow init type {:?}", ty::RawPtr(..));
             }
             Rvalue::Cast(kind, operand, target_type) => {
+                let op_ty = operand.ty(self.body, self.tcx);
                 match kind {
-                    CastKind::Misc => {
-                        let op_ty = operand.ty(self.body, self.tcx);
-                        if op_ty.is_enum() {
+                    CastKind::DynStar => {
+                        // FIXME(dyn-star): make sure nothing needs to be done here.
+                    }
+                    // FIXME: Add Checks for these
+                    CastKind::PointerFromExposedAddress
+                    | CastKind::PointerExposeAddress
+                    | CastKind::Pointer(_) => {}
+                    CastKind::IntToInt | CastKind::IntToFloat => {
+                        let input_valid = op_ty.is_integral() || op_ty.is_char() || op_ty.is_bool();
+                        let target_valid = target_type.is_numeric() || target_type.is_char();
+                        if !input_valid || !target_valid {
+                            self.fail(
+                                location,
+                                format!("Wrong cast kind {kind:?} for the type {op_ty}",),
+                            );
+                        }
+                    }
+                    CastKind::FnPtrToPtr | CastKind::PtrToPtr => {
+                        if !(op_ty.is_any_ptr() && target_type.is_unsafe_ptr()) {
+                            self.fail(location, "Can't cast {op_ty} into 'Ptr'");
+                        }
+                    }
+                    CastKind::FloatToFloat | CastKind::FloatToInt => {
+                        if !op_ty.is_floating_point() || !target_type.is_numeric() {
                             self.fail(
                                 location,
                                 format!(
-                                    "enum -> int casts should go through `Rvalue::Discriminant`: {operand:?}:{op_ty} as {target_type}",
+                                    "Trying to cast non 'Float' as {kind:?} into {target_type:?}"
                                 ),
                             );
                         }
                     }
-                    CastKind::DynStar => {
-                        // FIXME(dyn-star): make sure nothing needs to be done here.
-                    }
-                    // Nothing to check here
-                    CastKind::PointerFromExposedAddress
-                    | CastKind::PointerExposeAddress
-                    | CastKind::Pointer(_) => {}
                 }
             }
             Rvalue::Repeat(_, _)
diff --git a/compiler/rustc_const_eval/src/util/might_permit_raw_init.rs b/compiler/rustc_const_eval/src/util/might_permit_raw_init.rs
new file mode 100644
index 000000000..6ca712233
--- /dev/null
+++ b/compiler/rustc_const_eval/src/util/might_permit_raw_init.rs
@@ -0,0 +1,151 @@
+use rustc_middle::ty::layout::{LayoutCx, LayoutOf, TyAndLayout};
+use rustc_middle::ty::{ParamEnv, TyCtxt};
+use rustc_session::Limit;
+use rustc_target::abi::{Abi, FieldsShape, InitKind, Scalar, Variants};
+
+use crate::const_eval::CompileTimeInterpreter;
+use crate::interpret::{InterpCx, MemoryKind, OpTy};
+
+/// Determines if this type permits "raw" initialization by just transmuting some memory into an
+/// instance of `T`.
+///
+/// `init_kind` indicates if the memory is zero-initialized or left uninitialized. We assume
+/// uninitialized memory is mitigated by filling it with 0x01, which reduces the chance of causing
+/// LLVM UB.
+///
+/// By default we check whether that operation would cause *LLVM UB*, i.e., whether the LLVM IR we
+/// generate has UB or not. This is a mitigation strategy, which is why we are okay with accepting
+/// Rust UB as long as there is no risk of miscompilations. The `strict_init_checks` can be set to
+/// do a full check against Rust UB instead (in which case we will also ignore the 0x01-filling and
+/// to the full uninit check).
+pub fn might_permit_raw_init<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ty: TyAndLayout<'tcx>,
+    kind: InitKind,
+) -> bool {
+    if tcx.sess.opts.unstable_opts.strict_init_checks {
+        might_permit_raw_init_strict(ty, tcx, kind)
+    } else {
+        let layout_cx = LayoutCx { tcx, param_env: ParamEnv::reveal_all() };
+        might_permit_raw_init_lax(ty, &layout_cx, kind)
+    }
+}
+
+/// Implements the 'strict' version of the `might_permit_raw_init` checks; see that function for
+/// details.
+fn might_permit_raw_init_strict<'tcx>(
+    ty: TyAndLayout<'tcx>,
+    tcx: TyCtxt<'tcx>,
+    kind: InitKind,
+) -> bool {
+    let machine = CompileTimeInterpreter::new(
+        Limit::new(0),
+        /*can_access_statics:*/ false,
+        /*check_alignment:*/ true,
+    );
+
+    let mut cx = InterpCx::new(tcx, rustc_span::DUMMY_SP, ParamEnv::reveal_all(), machine);
+
+    let allocated = cx
+        .allocate(ty, MemoryKind::Machine(crate::const_eval::MemoryKind::Heap))
+        .expect("OOM: failed to allocate for uninit check");
+
+    if kind == InitKind::Zero {
+        cx.write_bytes_ptr(
+            allocated.ptr,
+            std::iter::repeat(0_u8).take(ty.layout.size().bytes_usize()),
+        )
+        .expect("failed to write bytes for zero valid check");
+    }
+
+    let ot: OpTy<'_, _> = allocated.into();
+
+    // Assume that if it failed, it's a validation failure.
+    // This does *not* actually check that references are dereferenceable, but since all types that
+    // require dereferenceability also require non-null, we don't actually get any false negatives
+    // due to this.
+    cx.validate_operand(&ot).is_ok()
+}
+
+/// Implements the 'lax' (default) version of the `might_permit_raw_init` checks; see that function for
+/// details.
+fn might_permit_raw_init_lax<'tcx>(
+    this: TyAndLayout<'tcx>,
+    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
+    init_kind: InitKind,
+) -> bool {
+    let scalar_allows_raw_init = move |s: Scalar| -> bool {
+        match init_kind {
+            InitKind::Zero => {
+                // The range must contain 0.
+                s.valid_range(cx).contains(0)
+            }
+            InitKind::UninitMitigated0x01Fill => {
+                // The range must include an 0x01-filled buffer.
+                let mut val: u128 = 0x01;
+                for _ in 1..s.size(cx).bytes() {
+                    // For sizes >1, repeat the 0x01.
+                    val = (val << 8) | 0x01;
+                }
+                s.valid_range(cx).contains(val)
+            }
+        }
+    };
+
+    // Check the ABI.
+    let valid = match this.abi {
+        Abi::Uninhabited => false, // definitely UB
+        Abi::Scalar(s) => scalar_allows_raw_init(s),
+        Abi::ScalarPair(s1, s2) => scalar_allows_raw_init(s1) && scalar_allows_raw_init(s2),
+        Abi::Vector { element: s, count } => count == 0 || scalar_allows_raw_init(s),
+        Abi::Aggregate { .. } => true, // Fields are checked below.
+    };
+    if !valid {
+        // This is definitely not okay.
+        return false;
+    }
+
+    // Special magic check for references and boxes (i.e., special pointer types).
+    if let Some(pointee) = this.ty.builtin_deref(false) {
+        let pointee = cx.layout_of(pointee.ty).expect("need to be able to compute layouts");
+        // We need to ensure that the LLVM attributes `aligned` and `dereferenceable(size)` are satisfied.
+        if pointee.align.abi.bytes() > 1 {
+            // 0x01-filling is not aligned.
+            return false;
+        }
+        if pointee.size.bytes() > 0 {
+            // A 'fake' integer pointer is not sufficiently dereferenceable.
+            return false;
+        }
+    }
+
+    // If we have not found an error yet, we need to recursively descend into fields.
+    match &this.fields {
+        FieldsShape::Primitive | FieldsShape::Union { .. } => {}
+        FieldsShape::Array { .. } => {
+            // Arrays never have scalar layout in LLVM, so if the array is not actually
+            // accessed, there is no LLVM UB -- therefore we can skip this.
+        }
+        FieldsShape::Arbitrary { offsets, .. } => {
+            for idx in 0..offsets.len() {
+                if !might_permit_raw_init_lax(this.field(cx, idx), cx, init_kind) {
+                    // We found a field that is unhappy with this kind of initialization.
+                    return false;
+                }
+            }
+        }
+    }
+
+    match &this.variants {
+        Variants::Single { .. } => {
+            // All fields of this single variant have already been checked above, there is nothing
+            // else to do.
+        }
+        Variants::Multiple { .. } => {
+            // We cannot tell LLVM anything about the details of this multi-variant layout, so
+            // invalid values "hidden" inside the variant cannot cause LLVM trouble.
+        }
+    }
+
+    true
+}
diff --git a/compiler/rustc_const_eval/src/util/mod.rs b/compiler/rustc_const_eval/src/util/mod.rs
index a1876bed8..7a05cfd23 100644
--- a/compiler/rustc_const_eval/src/util/mod.rs
+++ b/compiler/rustc_const_eval/src/util/mod.rs
@@ -3,8 +3,10 @@ mod alignment;
 mod call_kind;
 pub mod collect_writes;
 mod find_self_call;
+mod might_permit_raw_init;
 
 pub use self::aggregate::expand_aggregate;
 pub use self::alignment::is_disaligned;
 pub use self::call_kind::{call_kind, CallDesugaringKind, CallKind};
 pub use self::find_self_call::find_self_call;
+pub use self::might_permit_raw_init::might_permit_raw_init;