Merge from rust-lang/rust

17 files changed, 215 insertions, 346 deletions

diff --git a/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs b/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs
deleted file mode 100644
index daddb5dedbc..00000000000
--- a/compiler/rustc_mir_transform/src/check_undefined_transmutes.rs
+++ /dev/null
@@ -1,77 +0,0 @@
-use rustc_middle::mir::visit::Visitor;
-use rustc_middle::mir::{Body, Location, Operand, Terminator, TerminatorKind};
-use rustc_middle::ty::{AssocItem, AssocKind, TyCtxt};
-use rustc_session::lint::builtin::PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS;
-use rustc_span::sym;
-
-use crate::errors;
-
-/// Check for transmutes that exhibit undefined behavior.
-/// For example, transmuting pointers to integers in a const context.
-pub(super) struct CheckUndefinedTransmutes;
-
-impl<'tcx> crate::MirLint<'tcx> for CheckUndefinedTransmutes {
-    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
-        let mut checker = UndefinedTransmutesChecker { body, tcx };
-        checker.visit_body(body);
-    }
-}
-
-struct UndefinedTransmutesChecker<'a, 'tcx> {
-    body: &'a Body<'tcx>,
-    tcx: TyCtxt<'tcx>,
-}
-
-impl<'a, 'tcx> UndefinedTransmutesChecker<'a, 'tcx> {
-    // This functions checks two things:
-    // 1. `function` takes a raw pointer as input and returns an integer as output.
-    // 2. `function` is called from a const function or an associated constant.
-    //
-    // Why do we consider const functions and associated constants only?
-    //
-    // Generally, undefined behavior in const items are handled by the evaluator.
-    // But, const functions and associated constants are evaluated only when referenced.
-    // This can result in undefined behavior in a library going unnoticed until
-    // the function or constant is actually used.
-    //
-    // Therefore, we only consider const functions and associated constants here and leave
-    // other const items to be handled by the evaluator.
-    fn is_ptr_to_int_in_const(&self, function: &Operand<'tcx>) -> bool {
-        let def_id = self.body.source.def_id();
-
-        if self.tcx.is_const_fn(def_id)
-            || matches!(
-                self.tcx.opt_associated_item(def_id),
-                Some(AssocItem { kind: AssocKind::Const { .. }, .. })
-            )
-        {
-            let fn_sig = function.ty(self.body, self.tcx).fn_sig(self.tcx).skip_binder();
-            if let [input] = fn_sig.inputs() {
-                return input.is_raw_ptr() && fn_sig.output().is_integral();
-            }
-        }
-        false
-    }
-}
-
-impl<'tcx> Visitor<'tcx> for UndefinedTransmutesChecker<'_, 'tcx> {
-    // Check each block's terminator for calls to pointer to integer transmutes
-    // in const functions or associated constants and emit a lint.
-    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
-        if let TerminatorKind::Call { func, .. } = &terminator.kind
-            && let Some((func_def_id, _)) = func.const_fn_def()
-            && self.tcx.is_intrinsic(func_def_id, sym::transmute)
-            && self.is_ptr_to_int_in_const(func)
-            && let Some(call_id) = self.body.source.def_id().as_local()
-        {
-            let hir_id = self.tcx.local_def_id_to_hir_id(call_id);
-            let span = self.body.source_info(location).span;
-            self.tcx.emit_node_span_lint(
-                PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS,
-                hir_id,
-                span,
-                errors::UndefinedTransmute,
-            );
-        }
-    }
-}
diff --git a/compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs b/compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs
deleted file mode 100644
index 8da17a056e3..00000000000
--- a/compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs
+++ /dev/null
@@ -1,124 +0,0 @@
-use rustc_middle::mir::visit::Visitor;
-use rustc_middle::mir::{Body, Location, Operand, Terminator, TerminatorKind};
-use rustc_middle::ty::*;
-use rustc_session::lint::builtin::UNNECESSARY_TRANSMUTES;
-use rustc_span::source_map::Spanned;
-use rustc_span::{Span, sym};
-
-use crate::errors::UnnecessaryTransmute as Error;
-
-/// Check for transmutes that overlap with stdlib methods.
-/// For example, transmuting `[u8; 4]` to `u32`.
-pub(super) struct CheckUnnecessaryTransmutes;
-
-impl<'tcx> crate::MirLint<'tcx> for CheckUnnecessaryTransmutes {
-    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
-        let mut checker = UnnecessaryTransmuteChecker { body, tcx };
-        checker.visit_body(body);
-    }
-}
-
-struct UnnecessaryTransmuteChecker<'a, 'tcx> {
-    body: &'a Body<'tcx>,
-    tcx: TyCtxt<'tcx>,
-}
-
-impl<'a, 'tcx> UnnecessaryTransmuteChecker<'a, 'tcx> {
-    fn is_unnecessary_transmute(
-        &self,
-        function: &Operand<'tcx>,
-        arg: String,
-        span: Span,
-    ) -> Option<Error> {
-        let fn_sig = function.ty(self.body, self.tcx).fn_sig(self.tcx).skip_binder();
-        let [input] = fn_sig.inputs() else { return None };
-
-        let err = |sugg| Error { span, sugg, help: None };
-
-        Some(match (input.kind(), fn_sig.output().kind()) {
-            // dont check the length; transmute does that for us.
-            // [u8; _] => primitive
-            (Array(t, _), Uint(_) | Float(_) | Int(_)) if *t.kind() == Uint(UintTy::U8) => Error {
-                sugg: format!("{}::from_ne_bytes({arg})", fn_sig.output()),
-                help: Some(
-                    "there's also `from_le_bytes` and `from_be_bytes` if you expect a particular byte order",
-                ),
-                span,
-            },
-            // primitive => [u8; _]
-            (Uint(_) | Float(_) | Int(_), Array(t, _)) if *t.kind() == Uint(UintTy::U8) => Error {
-                sugg: format!("{input}::to_ne_bytes({arg})"),
-                help: Some(
-                    "there's also `to_le_bytes` and `to_be_bytes` if you expect a particular byte order",
-                ),
-                span,
-            },
-            // char → u32
-            (Char, Uint(UintTy::U32)) => err(format!("u32::from({arg})")),
-            // char (→ u32) → i32
-            (Char, Int(IntTy::I32)) => err(format!("u32::from({arg}).cast_signed()")),
-            // u32 → char
-            (Uint(UintTy::U32), Char) => Error {
-                sugg: format!("char::from_u32_unchecked({arg})"),
-                help: Some("consider `char::from_u32(…).unwrap()`"),
-                span,
-            },
-            // i32 → char
-            (Int(IntTy::I32), Char) => Error {
-                sugg: format!("char::from_u32_unchecked(i32::cast_unsigned({arg}))"),
-                help: Some("consider `char::from_u32(i32::cast_unsigned(…)).unwrap()`"),
-                span,
-            },
-            // uNN → iNN
-            (Uint(ty), Int(_)) => err(format!("{}::cast_signed({arg})", ty.name_str())),
-            // iNN → uNN
-            (Int(ty), Uint(_)) => err(format!("{}::cast_unsigned({arg})", ty.name_str())),
-            // fNN → xsize
-            (Float(ty), Uint(UintTy::Usize)) => {
-                err(format!("{}::to_bits({arg}) as usize", ty.name_str()))
-            }
-            (Float(ty), Int(IntTy::Isize)) => {
-                err(format!("{}::to_bits({arg}) as isize", ty.name_str()))
-            }
-            // fNN (→ uNN) → iNN
-            (Float(ty), Int(..)) => err(format!("{}::to_bits({arg}).cast_signed()", ty.name_str())),
-            // fNN → uNN
-            (Float(ty), Uint(..)) => err(format!("{}::to_bits({arg})", ty.name_str())),
-            // xsize → fNN
-            (Uint(UintTy::Usize) | Int(IntTy::Isize), Float(ty)) => {
-                err(format!("{}::from_bits({arg} as _)", ty.name_str(),))
-            }
-            // iNN (→ uNN) → fNN
-            (Int(int_ty), Float(ty)) => err(format!(
-                "{}::from_bits({}::cast_unsigned({arg}))",
-                ty.name_str(),
-                int_ty.name_str()
-            )),
-            // uNN → fNN
-            (Uint(_), Float(ty)) => err(format!("{}::from_bits({arg})", ty.name_str())),
-            // bool → { x8 }
-            (Bool, Int(..) | Uint(..)) => err(format!("({arg}) as {}", fn_sig.output())),
-            // u8 → bool
-            (Uint(_), Bool) => err(format!("({arg} == 1)")),
-            _ => return None,
-        })
-    }
-}
-
-impl<'tcx> Visitor<'tcx> for UnnecessaryTransmuteChecker<'_, 'tcx> {
-    // Check each block's terminator for calls to pointer to integer transmutes
-    // in const functions or associated constants and emit a lint.
-    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
-        if let TerminatorKind::Call { func, args, .. } = &terminator.kind
-            && let [Spanned { span: arg, .. }] = **args
-            && let Some((func_def_id, _)) = func.const_fn_def()
-            && self.tcx.is_intrinsic(func_def_id, sym::transmute)
-            && let span = self.body.source_info(location).span
-            && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(arg)
-            && let Some(lint) = self.is_unnecessary_transmute(func, snippet, span)
-            && let Some(hir_id) = terminator.source_info.scope.lint_root(&self.body.source_scopes)
-        {
-            self.tcx.emit_node_span_lint(UNNECESSARY_TRANSMUTES, hir_id, span, lint);
-        }
-    }
-}
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index cddb2f84778..d5d0d56f528 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -225,7 +225,7 @@ impl<'tcx> TransformVisitor<'tcx> {
             CoroutineKind::Coroutine(_) => span_bug!(body.span, "`Coroutine`s cannot be fused"),
             // `gen` continues return `None`
             CoroutineKind::Desugared(CoroutineDesugaring::Gen, _) => {
-                let option_def_id = self.tcx.require_lang_item(LangItem::Option, None);
+                let option_def_id = self.tcx.require_lang_item(LangItem::Option, body.span);
                 make_aggregate_adt(
                     option_def_id,
                     VariantIdx::ZERO,
@@ -242,7 +242,7 @@ impl<'tcx> TransformVisitor<'tcx> {
                     span: source_info.span,
                     const_: Const::Unevaluated(
                         UnevaluatedConst::new(
-                            self.tcx.require_lang_item(LangItem::AsyncGenFinished, None),
+                            self.tcx.require_lang_item(LangItem::AsyncGenFinished, body.span),
                             self.tcx.mk_args(&[yield_ty.into()]),
                         ),
                         self.old_yield_ty,
@@ -282,7 +282,7 @@ impl<'tcx> TransformVisitor<'tcx> {
         const ONE: VariantIdx = VariantIdx::from_usize(1);
         let rvalue = match self.coroutine_kind {
             CoroutineKind::Desugared(CoroutineDesugaring::Async, _) => {
-                let poll_def_id = self.tcx.require_lang_item(LangItem::Poll, None);
+                let poll_def_id = self.tcx.require_lang_item(LangItem::Poll, source_info.span);
                 let args = self.tcx.mk_args(&[self.old_ret_ty.into()]);
                 let (variant_idx, operands) = if is_return {
                     (ZERO, IndexVec::from_raw(vec![val])) // Poll::Ready(val)
@@ -292,7 +292,7 @@ impl<'tcx> TransformVisitor<'tcx> {
                 make_aggregate_adt(poll_def_id, variant_idx, args, operands)
             }
             CoroutineKind::Desugared(CoroutineDesugaring::Gen, _) => {
-                let option_def_id = self.tcx.require_lang_item(LangItem::Option, None);
+                let option_def_id = self.tcx.require_lang_item(LangItem::Option, source_info.span);
                 let args = self.tcx.mk_args(&[self.old_yield_ty.into()]);
                 let (variant_idx, operands) = if is_return {
                     (ZERO, IndexVec::new()) // None
@@ -310,7 +310,10 @@ impl<'tcx> TransformVisitor<'tcx> {
                         span: source_info.span,
                         const_: Const::Unevaluated(
                             UnevaluatedConst::new(
-                                self.tcx.require_lang_item(LangItem::AsyncGenFinished, None),
+                                self.tcx.require_lang_item(
+                                    LangItem::AsyncGenFinished,
+                                    source_info.span,
+                                ),
                                 self.tcx.mk_args(&[yield_ty.into()]),
                             ),
                             self.old_yield_ty,
@@ -323,7 +326,7 @@ impl<'tcx> TransformVisitor<'tcx> {
             }
             CoroutineKind::Coroutine(_) => {
                 let coroutine_state_def_id =
-                    self.tcx.require_lang_item(LangItem::CoroutineState, None);
+                    self.tcx.require_lang_item(LangItem::CoroutineState, source_info.span);
                 let args = self.tcx.mk_args(&[self.old_yield_ty.into(), self.old_ret_ty.into()]);
                 let variant_idx = if is_return {
                     ONE // CoroutineState::Complete(val)
@@ -496,7 +499,7 @@ fn make_coroutine_state_argument_indirect<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Bo
 fn make_coroutine_state_argument_pinned<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let ref_coroutine_ty = body.local_decls.raw[1].ty;
 
-    let pin_did = tcx.require_lang_item(LangItem::Pin, Some(body.span));
+    let pin_did = tcx.require_lang_item(LangItem::Pin, body.span);
     let pin_adt_ref = tcx.adt_def(pin_did);
     let args = tcx.mk_args(&[ref_coroutine_ty.into()]);
     let pin_ref_coroutine_ty = Ty::new_adt(tcx, pin_adt_ref, args);
@@ -557,7 +560,7 @@ fn transform_async_context<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> Ty
     // replace the type of the `resume` argument
     replace_resume_ty_local(tcx, body, CTX_ARG, context_mut_ref);
 
-    let get_context_def_id = tcx.require_lang_item(LangItem::GetContext, None);
+    let get_context_def_id = tcx.require_lang_item(LangItem::GetContext, body.span);
 
     for bb in body.basic_blocks.indices() {
         let bb_data = &body[bb];
@@ -618,7 +621,7 @@ fn replace_resume_ty_local<'tcx>(
     #[cfg(debug_assertions)]
     {
         if let ty::Adt(resume_ty_adt, _) = local_ty.kind() {
-            let expected_adt = tcx.adt_def(tcx.require_lang_item(LangItem::ResumeTy, None));
+            let expected_adt = tcx.adt_def(tcx.require_lang_item(LangItem::ResumeTy, body.span));
             assert_eq!(*resume_ty_adt, expected_adt);
         } else {
             panic!("expected `ResumeTy`, found `{:?}`", local_ty);
@@ -1095,7 +1098,7 @@ fn insert_term_block<'tcx>(body: &mut Body<'tcx>, kind: TerminatorKind<'tcx>) ->
 
 fn return_poll_ready_assign<'tcx>(tcx: TyCtxt<'tcx>, source_info: SourceInfo) -> Statement<'tcx> {
     // Poll::Ready(())
-    let poll_def_id = tcx.require_lang_item(LangItem::Poll, None);
+    let poll_def_id = tcx.require_lang_item(LangItem::Poll, source_info.span);
     let args = tcx.mk_args(&[tcx.types.unit.into()]);
     let val = Operand::Constant(Box::new(ConstOperand {
         span: source_info.span,
@@ -1437,7 +1440,7 @@ fn check_field_tys_sized<'tcx>(
             ),
             param_env,
             field_ty.ty,
-            tcx.require_lang_item(hir::LangItem::Sized, Some(field_ty.source_info.span)),
+            tcx.require_lang_item(hir::LangItem::Sized, field_ty.source_info.span),
         );
     }
 
@@ -1473,14 +1476,14 @@ impl<'tcx> crate::MirPass<'tcx> for StateTransform {
         let new_ret_ty = match coroutine_kind {
             CoroutineKind::Desugared(CoroutineDesugaring::Async, _) => {
                 // Compute Poll<return_ty>
-                let poll_did = tcx.require_lang_item(LangItem::Poll, None);
+                let poll_did = tcx.require_lang_item(LangItem::Poll, body.span);
                 let poll_adt_ref = tcx.adt_def(poll_did);
                 let poll_args = tcx.mk_args(&[old_ret_ty.into()]);
                 Ty::new_adt(tcx, poll_adt_ref, poll_args)
             }
             CoroutineKind::Desugared(CoroutineDesugaring::Gen, _) => {
                 // Compute Option<yield_ty>
-                let option_did = tcx.require_lang_item(LangItem::Option, None);
+                let option_did = tcx.require_lang_item(LangItem::Option, body.span);
                 let option_adt_ref = tcx.adt_def(option_did);
                 let option_args = tcx.mk_args(&[old_yield_ty.into()]);
                 Ty::new_adt(tcx, option_adt_ref, option_args)
@@ -1491,7 +1494,7 @@ impl<'tcx> crate::MirPass<'tcx> for StateTransform {
             }
             CoroutineKind::Coroutine(_) => {
                 // Compute CoroutineState<yield_ty, return_ty>
-                let state_did = tcx.require_lang_item(LangItem::CoroutineState, None);
+                let state_did = tcx.require_lang_item(LangItem::CoroutineState, body.span);
                 let state_adt_ref = tcx.adt_def(state_did);
                 let state_args = tcx.mk_args(&[old_yield_ty.into(), old_ret_ty.into()]);
                 Ty::new_adt(tcx, state_adt_ref, state_args)
diff --git a/compiler/rustc_mir_transform/src/coroutine/drop.rs b/compiler/rustc_mir_transform/src/coroutine/drop.rs
index 6b266da5a69..6021e795d21 100644
--- a/compiler/rustc_mir_transform/src/coroutine/drop.rs
+++ b/compiler/rustc_mir_transform/src/coroutine/drop.rs
@@ -42,7 +42,7 @@ fn build_poll_call<'tcx>(
     context_ref_place: &Place<'tcx>,
     unwind: UnwindAction,
 ) -> BasicBlock {
-    let poll_fn = tcx.require_lang_item(LangItem::FuturePoll, None);
+    let poll_fn = tcx.require_lang_item(LangItem::FuturePoll, DUMMY_SP);
     let poll_fn = Ty::new_fn_def(tcx, poll_fn, [fut_ty]);
     let poll_fn = Operand::Constant(Box::new(ConstOperand {
         span: DUMMY_SP,
@@ -77,11 +77,8 @@ fn build_pin_fut<'tcx>(
     let fut_ty = fut_place.ty(&body.local_decls, tcx).ty;
     let fut_ref_ty = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, fut_ty);
     let fut_ref_place = Place::from(body.local_decls.push(LocalDecl::new(fut_ref_ty, span)));
-    let pin_fut_new_unchecked_fn = Ty::new_fn_def(
-        tcx,
-        tcx.require_lang_item(LangItem::PinNewUnchecked, Some(span)),
-        [fut_ref_ty],
-    );
+    let pin_fut_new_unchecked_fn =
+        Ty::new_fn_def(tcx, tcx.require_lang_item(LangItem::PinNewUnchecked, span), [fut_ref_ty]);
     let fut_pin_ty = pin_fut_new_unchecked_fn.fn_sig(tcx).output().skip_binder();
     let fut_pin_place = Place::from(body.local_decls.push(LocalDecl::new(fut_pin_ty, span)));
     let pin_fut_new_unchecked_fn = Operand::Constant(Box::new(ConstOperand {
@@ -143,13 +140,15 @@ fn build_poll_switch<'tcx>(
     let Discr { val: poll_ready_discr, ty: poll_discr_ty } = poll_enum
         .discriminant_for_variant(
             tcx,
-            poll_enum_adt.variant_index_with_id(tcx.require_lang_item(LangItem::PollReady, None)),
+            poll_enum_adt
+                .variant_index_with_id(tcx.require_lang_item(LangItem::PollReady, DUMMY_SP)),
         )
         .unwrap();
     let poll_pending_discr = poll_enum
         .discriminant_for_variant(
             tcx,
-            poll_enum_adt.variant_index_with_id(tcx.require_lang_item(LangItem::PollPending, None)),
+            poll_enum_adt
+                .variant_index_with_id(tcx.require_lang_item(LangItem::PollPending, DUMMY_SP)),
         )
         .unwrap()
         .val;
@@ -316,16 +315,17 @@ pub(super) fn expand_async_drops<'tcx>(
         //  pending => return rv (yield)
         //  ready => *continue_bb|drop_bb*
 
+        let source_info = body[bb].terminator.as_ref().unwrap().source_info;
+
         // Compute Poll<> (aka Poll with void return)
-        let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, None));
+        let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, source_info.span));
         let poll_enum = Ty::new_adt(tcx, poll_adt_ref, tcx.mk_args(&[tcx.types.unit.into()]));
-        let poll_decl = LocalDecl::new(poll_enum, body.span);
+        let poll_decl = LocalDecl::new(poll_enum, source_info.span);
         let poll_unit_place = Place::from(body.local_decls.push(poll_decl));
 
         // First state-loop yield for mainline
         let context_ref_place =
-            Place::from(body.local_decls.push(LocalDecl::new(context_mut_ref, body.span)));
-        let source_info = body[bb].terminator.as_ref().unwrap().source_info;
+            Place::from(body.local_decls.push(LocalDecl::new(context_mut_ref, source_info.span)));
         let arg = Rvalue::Use(Operand::Move(Place::from(CTX_ARG)));
         body[bb].statements.push(Statement {
             source_info,
@@ -353,8 +353,9 @@ pub(super) fn expand_async_drops<'tcx>(
         let mut dropline_context_ref: Option<Place<'_>> = None;
         let mut dropline_call_bb: Option<BasicBlock> = None;
         if !is_dropline_bb {
-            let context_ref_place2: Place<'_> =
-                Place::from(body.local_decls.push(LocalDecl::new(context_mut_ref, body.span)));
+            let context_ref_place2: Place<'_> = Place::from(
+                body.local_decls.push(LocalDecl::new(context_mut_ref, source_info.span)),
+            );
             let drop_yield_block = insert_term_block(body, TerminatorKind::Unreachable); // `kind` replaced later to yield
             let drop_switch_block = build_poll_switch(
                 tcx,
@@ -382,12 +383,34 @@ pub(super) fn expand_async_drops<'tcx>(
             dropline_call_bb = Some(drop_call_bb);
         }
 
-        // value needed only for return-yields or gen-coroutines, so just const here
-        let value = Operand::Constant(Box::new(ConstOperand {
-            span: body.span,
-            user_ty: None,
-            const_: Const::from_bool(tcx, false),
-        }));
+        let value =
+            if matches!(coroutine_kind, CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _))
+            {
+                // For AsyncGen we need `yield Poll<OptRet>::Pending`
+                let full_yield_ty = body.yield_ty().unwrap();
+                let ty::Adt(_poll_adt, args) = *full_yield_ty.kind() else { bug!() };
+                let ty::Adt(_option_adt, args) = *args.type_at(0).kind() else { bug!() };
+                let yield_ty = args.type_at(0);
+                Operand::Constant(Box::new(ConstOperand {
+                    span: source_info.span,
+                    const_: Const::Unevaluated(
+                        UnevaluatedConst::new(
+                            tcx.require_lang_item(LangItem::AsyncGenPending, source_info.span),
+                            tcx.mk_args(&[yield_ty.into()]),
+                        ),
+                        full_yield_ty,
+                    ),
+                    user_ty: None,
+                }))
+            } else {
+                // value needed only for return-yields or gen-coroutines, so just const here
+                Operand::Constant(Box::new(ConstOperand {
+                    span: source_info.span,
+                    user_ty: None,
+                    const_: Const::from_bool(tcx, false),
+                }))
+            };
+
         use rustc_middle::mir::AssertKind::ResumedAfterDrop;
         let panic_bb = insert_panic_block(tcx, body, ResumedAfterDrop(coroutine_kind));
 
@@ -573,7 +596,7 @@ pub(super) fn create_coroutine_drop_shim<'tcx>(
 
     // Update the body's def to become the drop glue.
     let coroutine_instance = body.source.instance;
-    let drop_in_place = tcx.require_lang_item(LangItem::DropInPlace, None);
+    let drop_in_place = tcx.require_lang_item(LangItem::DropInPlace, body.span);
     let drop_instance = InstanceKind::DropGlue(drop_in_place, Some(coroutine_ty));
 
     // Temporary change MirSource to coroutine's instance so that dump_mir produces more sensible
@@ -644,7 +667,7 @@ pub(super) fn create_coroutine_drop_shim_async<'tcx>(
     }
 
     // Replace the return variable: Poll<RetT> to Poll<()>
-    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, None));
+    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, body.span));
     let poll_enum = Ty::new_adt(tcx, poll_adt_ref, tcx.mk_args(&[tcx.types.unit.into()]));
     body.local_decls[RETURN_PLACE] = LocalDecl::with_source_info(poll_enum, source_info);
 
@@ -695,7 +718,7 @@ pub(super) fn create_coroutine_drop_shim_proxy_async<'tcx>(
     let source_info = SourceInfo::outermost(body.span);
 
     // Replace the return variable: Poll<RetT> to Poll<()>
-    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, None));
+    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, body.span));
     let poll_enum = Ty::new_adt(tcx, poll_adt_ref, tcx.mk_args(&[tcx.types.unit.into()]));
     body.local_decls[RETURN_PLACE] = LocalDecl::with_source_info(poll_enum, source_info);
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index ddeae093df5..ec76076020e 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -1,8 +1,7 @@
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::mir;
 use rustc_middle::ty::TyCtxt;
-use rustc_span::source_map::SourceMap;
-use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span};
+use rustc_span::{DesugaringKind, ExpnKind, MacroKind, Span};
 use tracing::instrument;
 
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
@@ -84,18 +83,8 @@ pub(super) fn extract_refined_covspans<'tcx>(
     // Discard any span that overlaps with a hole.
     discard_spans_overlapping_holes(&mut covspans, &holes);
 
-    // Discard spans that overlap in unwanted ways.
+    // Perform more refinement steps after holes have been dealt with.
     let mut covspans = remove_unwanted_overlapping_spans(covspans);
-
-    // For all empty spans, either enlarge them to be non-empty, or discard them.
-    let source_map = tcx.sess.source_map();
-    covspans.retain_mut(|covspan| {
-        let Some(span) = ensure_non_empty_span(source_map, covspan.span) else { return false };
-        covspan.span = span;
-        true
-    });
-
-    // Merge covspans that can be merged.
     covspans.dedup_by(|b, a| a.merge_if_eligible(b));
 
     code_mappings.extend(covspans.into_iter().map(|Covspan { span, bcb }| {
@@ -241,26 +230,3 @@ fn compare_spans(a: Span, b: Span) -> std::cmp::Ordering {
         // - Both have the same start and span A extends further right
         .then_with(|| Ord::cmp(&a.hi(), &b.hi()).reverse())
 }
-
-fn ensure_non_empty_span(source_map: &SourceMap, span: Span) -> Option<Span> {
-    if !span.is_empty() {
-        return Some(span);
-    }
-
-    // The span is empty, so try to enlarge it to cover an adjacent '{' or '}'.
-    source_map
-        .span_to_source(span, |src, start, end| try {
-            // Adjusting span endpoints by `BytePos(1)` is normally a bug,
-            // but in this case we have specifically checked that the character
-            // we're skipping over is one of two specific ASCII characters, so
-            // adjusting by exactly 1 byte is correct.
-            if src.as_bytes().get(end).copied() == Some(b'{') {
-                Some(span.with_hi(span.hi() + BytePos(1)))
-            } else if start > 0 && src.as_bytes()[start - 1] == b'}' {
-                Some(span.with_lo(span.lo() - BytePos(1)))
-            } else {
-                None
-            }
-        })
-        .ok()?
-}
diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
index 99b95e7312b..0cf8142a560 100644
--- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
+++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -616,7 +616,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
             place,
             operand,
             &mut |elem, op| match elem {
-                TrackElem::Field(idx) => self.ecx.project_field(op, idx.as_usize()).discard_err(),
+                TrackElem::Field(idx) => self.ecx.project_field(op, idx).discard_err(),
                 TrackElem::Variant(idx) => self.ecx.project_downcast(op, idx).discard_err(),
                 TrackElem::Discriminant => {
                     let variant = self.ecx.read_discriminant(op).discard_err()?;
@@ -890,7 +890,8 @@ fn try_write_constant<'tcx>(
 
         ty::Tuple(elem_tys) => {
             for (i, elem) in elem_tys.iter().enumerate() {
-                let Some(field) = map.apply(place, TrackElem::Field(FieldIdx::from_usize(i))) else {
+                let i = FieldIdx::from_usize(i);
+                let Some(field) = map.apply(place, TrackElem::Field(i)) else {
                     throw_machine_stop_str!("missing field in tuple")
                 };
                 let field_dest = ecx.project_field(dest, i)?;
@@ -928,7 +929,7 @@ fn try_write_constant<'tcx>(
                 let Some(field) = map.apply(variant_place, TrackElem::Field(i)) else {
                     throw_machine_stop_str!("missing field in ADT")
                 };
-                let field_dest = ecx.project_field(&variant_dest, i.as_usize())?;
+                let field_dest = ecx.project_field(&variant_dest, i)?;
                 try_write_constant(ecx, &field_dest, field, ty, state, map)?;
             }
             ecx.write_discriminant(variant_idx, dest)?;
diff --git a/compiler/rustc_mir_transform/src/elaborate_drop.rs b/compiler/rustc_mir_transform/src/elaborate_drop.rs
index 73a58160a6a..3a5e2620b14 100644
--- a/compiler/rustc_mir_transform/src/elaborate_drop.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_drop.rs
@@ -1,6 +1,7 @@
 use std::{fmt, iter, mem};
 
 use rustc_abi::{FIRST_VARIANT, FieldIdx, VariantIdx};
+use rustc_hir::def::DefKind;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::Idx;
 use rustc_middle::mir::*;
@@ -234,11 +235,8 @@ where
 
         let (fut_ty, drop_fn_def_id, trait_args) = if call_destructor_only {
             // Resolving obj.<AsyncDrop::drop>()
-            let trait_ref = ty::TraitRef::new(
-                tcx,
-                tcx.require_lang_item(LangItem::AsyncDrop, Some(span)),
-                [drop_ty],
-            );
+            let trait_ref =
+                ty::TraitRef::new(tcx, tcx.require_lang_item(LangItem::AsyncDrop, span), [drop_ty]);
             let (drop_trait, trait_args) = match tcx.codegen_select_candidate(
                 ty::TypingEnv::fully_monomorphized().as_query_input(trait_ref),
             ) {
@@ -251,14 +249,47 @@ where
                     span_bug!(span, "invalid `AsyncDrop` impl_source: {:?}", impl_source);
                 }
             };
-            let drop_fn_def_id = tcx.associated_item_def_ids(drop_trait)[0];
+            // impl_item_refs may be empty if drop fn is not implemented in 'impl AsyncDrop for ...'
+            // (#140974).
+            // Such code will report error, so just generate sync drop here and return
+            let Some(drop_fn_def_id) = tcx
+                .associated_item_def_ids(drop_trait)
+                .first()
+                .and_then(|def_id| {
+                    if tcx.def_kind(def_id) == DefKind::AssocFn
+                        && tcx.check_args_compatible(*def_id, trait_args)
+                    {
+                        Some(def_id)
+                    } else {
+                        None
+                    }
+                })
+                .copied()
+            else {
+                tcx.dcx().span_delayed_bug(
+                    self.elaborator.body().span,
+                    "AsyncDrop type without correct `async fn drop(...)`.",
+                );
+                self.elaborator.patch().patch_terminator(
+                    pin_obj_bb,
+                    TerminatorKind::Drop {
+                        place,
+                        target: succ,
+                        unwind: unwind.into_action(),
+                        replace: false,
+                        drop: None,
+                        async_fut: None,
+                    },
+                );
+                return pin_obj_bb;
+            };
             let drop_fn = Ty::new_fn_def(tcx, drop_fn_def_id, trait_args);
             let sig = drop_fn.fn_sig(tcx);
             let sig = tcx.instantiate_bound_regions_with_erased(sig);
             (sig.output(), drop_fn_def_id, trait_args)
         } else {
             // Resolving async_drop_in_place<T> function for drop_ty
-            let drop_fn_def_id = tcx.require_lang_item(LangItem::AsyncDropInPlace, Some(span));
+            let drop_fn_def_id = tcx.require_lang_item(LangItem::AsyncDropInPlace, span);
             let trait_args = tcx.mk_args(&[drop_ty.into()]);
             let sig = tcx.fn_sig(drop_fn_def_id).instantiate(tcx, trait_args);
             let sig = tcx.instantiate_bound_regions_with_erased(sig);
@@ -285,7 +316,7 @@ where
         // pin_obj_place preparation
         let pin_obj_new_unchecked_fn = Ty::new_fn_def(
             tcx,
-            tcx.require_lang_item(LangItem::PinNewUnchecked, Some(span)),
+            tcx.require_lang_item(LangItem::PinNewUnchecked, span),
             [GenericArg::from(obj_ref_ty)],
         );
         let pin_obj_ty = pin_obj_new_unchecked_fn.fn_sig(tcx).output().no_bound_vars().unwrap();
@@ -318,15 +349,20 @@ where
                 bug!();
             };
             let obj_ptr_ty = Ty::new_mut_ptr(tcx, drop_ty);
-            let obj_ptr_place = Place::from(self.new_temp(obj_ptr_ty));
             let unwrap_ty = adt_def.non_enum_variant().fields[FieldIdx::ZERO].ty(tcx, adt_args);
-            let addr = Rvalue::RawPtr(
-                RawPtrKind::Mut,
-                pin_obj_place.project_deeper(
-                    &[ProjectionElem::Field(FieldIdx::ZERO, unwrap_ty), ProjectionElem::Deref],
-                    tcx,
-                ),
-            );
+            let obj_ref_place = Place::from(self.new_temp(unwrap_ty));
+            call_statements.push(self.assign(
+                obj_ref_place,
+                Rvalue::Use(Operand::Copy(tcx.mk_place_field(
+                    pin_obj_place,
+                    FieldIdx::ZERO,
+                    unwrap_ty,
+                ))),
+            ));
+
+            let obj_ptr_place = Place::from(self.new_temp(obj_ptr_ty));
+
+            let addr = Rvalue::RawPtr(RawPtrKind::Mut, tcx.mk_place_deref(obj_ref_place));
             call_statements.push(self.assign(obj_ptr_place, addr));
             obj_ptr_place
         };
@@ -898,7 +934,7 @@ where
     fn destructor_call_block_sync(&mut self, (succ, unwind): (BasicBlock, Unwind)) -> BasicBlock {
         debug!("destructor_call_block_sync({:?}, {:?})", self, succ);
         let tcx = self.tcx();
-        let drop_trait = tcx.require_lang_item(LangItem::Drop, None);
+        let drop_trait = tcx.require_lang_item(LangItem::Drop, DUMMY_SP);
         let drop_fn = tcx.associated_item_def_ids(drop_trait)[0];
         let ty = self.place_ty(self.place);
 
@@ -1251,6 +1287,23 @@ where
             }
             ty::Slice(ety) => self.drop_loop_trio_for_slice(*ety),
 
+            ty::UnsafeBinder(_) => {
+                // Unsafe binders may elaborate drops if their inner type isn't copy.
+                // This is enforced in typeck, so this should never happen.
+                self.tcx().dcx().span_delayed_bug(
+                    self.source_info.span,
+                    "open drop for unsafe binder shouldn't be encountered",
+                );
+                self.elaborator.patch().new_block(BasicBlockData {
+                    statements: vec![],
+                    terminator: Some(Terminator {
+                        source_info: self.source_info,
+                        kind: TerminatorKind::Unreachable,
+                    }),
+                    is_cleanup: self.unwind.is_cleanup(),
+                })
+            }
+
             _ => span_bug!(self.source_info.span, "open drop from non-ADT `{:?}`", ty),
         }
     }
diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index 5b03a4987ed..cffa0183fa7 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -158,33 +158,6 @@ pub(crate) struct MustNotSuspendReason {
     pub reason: String,
 }
 
-pub(crate) struct UnnecessaryTransmute {
-    pub span: Span,
-    pub sugg: String,
-    pub help: Option<&'static str>,
-}
-
-// Needed for def_path_str
-impl<'a> LintDiagnostic<'a, ()> for UnnecessaryTransmute {
-    fn decorate_lint<'b>(self, diag: &'b mut rustc_errors::Diag<'a, ()>) {
-        diag.primary_message(fluent::mir_transform_unnecessary_transmute);
-        diag.span_suggestion(
-            self.span,
-            "replace this with",
-            self.sugg,
-            lint::Applicability::MachineApplicable,
-        );
-        self.help.map(|help| diag.help(help));
-    }
-}
-
-#[derive(LintDiagnostic)]
-#[diag(mir_transform_undefined_transmute)]
-#[note]
-#[note(mir_transform_note2)]
-#[help]
-pub(crate) struct UndefinedTransmute;
-
 #[derive(Diagnostic)]
 #[diag(mir_transform_force_inline)]
 #[note]
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 209e818e9e3..92c30d239b5 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -438,8 +438,10 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                         dest.clone()
                     };
                     for (field_index, op) in fields.into_iter().enumerate() {
-                        let field_dest =
-                            self.ecx.project_field(&variant_dest, field_index).discard_err()?;
+                        let field_dest = self
+                            .ecx
+                            .project_field(&variant_dest, FieldIdx::from_usize(field_index))
+                            .discard_err()?;
                         self.ecx.copy_op(op, &field_dest).discard_err()?;
                     }
                     self.ecx
@@ -638,6 +640,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         place: PlaceRef<'tcx>,
         value: VnIndex,
         proj: PlaceElem<'tcx>,
+        from_non_ssa_index: &mut bool,
     ) -> Option<VnIndex> {
         let proj = match proj {
             ProjectionElem::Deref => {
@@ -682,6 +685,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             }
             ProjectionElem::Index(idx) => {
                 if let Value::Repeat(inner, _) = self.get(value) {
+                    *from_non_ssa_index |= self.locals[idx].is_none();
                     return Some(*inner);
                 }
                 let idx = self.locals[idx]?;
@@ -774,6 +778,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
 
         // Invariant: `value` holds the value up-to the `index`th projection excluded.
         let mut value = self.locals[place.local]?;
+        let mut from_non_ssa_index = false;
         for (index, proj) in place.projection.iter().enumerate() {
             if let Value::Projection(pointer, ProjectionElem::Deref) = *self.get(value)
                 && let Value::Address { place: mut pointee, kind, .. } = *self.get(pointer)
@@ -791,7 +796,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             }
 
             let base = PlaceRef { local: place.local, projection: &place.projection[..index] };
-            value = self.project(base, value, proj)?;
+            value = self.project(base, value, proj, &mut from_non_ssa_index)?;
         }
 
         if let Value::Projection(pointer, ProjectionElem::Deref) = *self.get(value)
@@ -804,6 +809,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         }
         if let Some(new_local) = self.try_as_local(value, location) {
             place_ref = PlaceRef { local: new_local, projection: &[] };
+        } else if from_non_ssa_index {
+            // If access to non-SSA locals is unavoidable, bail out.
+            return None;
         }
 
         if place_ref.local != place.local || place_ref.projection.len() < place.projection.len() {
@@ -1577,7 +1585,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             // We needed to check the variant to avoid trying to read the tag
             // field from an enum where no fields have variants, since that tag
             // field isn't in the `Aggregate` from which we're getting values.
-            Some((FieldIdx::from_usize(field_idx), field_layout.ty))
+            Some((field_idx, field_layout.ty))
         } else if let ty::Adt(adt, args) = ty.kind()
             && adt.is_struct()
             && adt.repr().transparent()
diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs
index 31b361ec1a9..48db536c122 100644
--- a/compiler/rustc_mir_transform/src/jump_threading.rs
+++ b/compiler/rustc_mir_transform/src/jump_threading.rs
@@ -388,7 +388,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
             lhs,
             constant,
             &mut |elem, op| match elem {
-                TrackElem::Field(idx) => self.ecx.project_field(op, idx.as_usize()).discard_err(),
+                TrackElem::Field(idx) => self.ecx.project_field(op, idx).discard_err(),
                 TrackElem::Variant(idx) => self.ecx.project_downcast(op, idx).discard_err(),
                 TrackElem::Discriminant => {
                     let variant = self.ecx.read_discriminant(op).discard_err()?;
diff --git a/compiler/rustc_mir_transform/src/large_enums.rs b/compiler/rustc_mir_transform/src/large_enums.rs
index 47cb478fe33..1a91d6bd7da 100644
--- a/compiler/rustc_mir_transform/src/large_enums.rs
+++ b/compiler/rustc_mir_transform/src/large_enums.rs
@@ -241,6 +241,7 @@ impl EnumSizeOpt {
             data,
             tcx.data_layout.ptr_sized_integer().align(&tcx.data_layout).abi,
             Mutability::Not,
+            (),
         );
         let alloc = tcx.reserve_and_set_memory_alloc(tcx.mk_const_alloc(alloc));
         Some((*adt_def, num_discrs, *alloc_cache.entry(ty).or_insert(alloc)))
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 10dbb3437dc..572ad585c8c 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -7,10 +7,7 @@
 #![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(impl_trait_in_assoc_type)]
-#![feature(map_try_insert)]
-#![feature(never_type)]
 #![feature(try_blocks)]
-#![feature(vec_deque_pop_if)]
 #![feature(yeet_expr)]
 // tidy-alphabetical-end
 
@@ -123,8 +120,6 @@ declare_passes! {
     mod check_const_item_mutation : CheckConstItemMutation;
     mod check_null : CheckNull;
     mod check_packed_ref : CheckPackedRef;
-    mod check_undefined_transmutes : CheckUndefinedTransmutes;
-    mod check_unnecessary_transmutes: CheckUnnecessaryTransmutes;
     // This pass is public to allow external drivers to perform MIR cleanup
     pub mod cleanup_post_borrowck : CleanupPostBorrowck;
 
@@ -390,8 +385,6 @@ fn mir_built(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
             &Lint(check_packed_ref::CheckPackedRef),
             &Lint(check_const_item_mutation::CheckConstItemMutation),
             &Lint(function_item_references::FunctionItemReferences),
-            &Lint(check_undefined_transmutes::CheckUndefinedTransmutes),
-            &Lint(check_unnecessary_transmutes::CheckUnnecessaryTransmutes),
             // What we need to do constant evaluation.
             &simplify::SimplifyCfg::Initial,
             &Lint(sanity_check::SanityCheck),
diff --git a/compiler/rustc_mir_transform/src/lower_intrinsics.rs b/compiler/rustc_mir_transform/src/lower_intrinsics.rs
index 9c21bcfc0d2..52f4c39c09b 100644
--- a/compiler/rustc_mir_transform/src/lower_intrinsics.rs
+++ b/compiler/rustc_mir_transform/src/lower_intrinsics.rs
@@ -262,6 +262,52 @@ impl<'tcx> crate::MirPass<'tcx> for LowerIntrinsics {
                         });
                         terminator.kind = TerminatorKind::Goto { target };
                     }
+                    sym::slice_get_unchecked => {
+                        let target = target.unwrap();
+                        let Ok([ptrish, index]) = take_array(args) else {
+                            span_bug!(
+                                terminator.source_info.span,
+                                "Wrong number of arguments for {intrinsic:?}",
+                            );
+                        };
+
+                        let place = ptrish.node.place().unwrap();
+                        assert!(!place.is_indirect());
+                        let updated_place = place.project_deeper(
+                            &[
+                                ProjectionElem::Deref,
+                                ProjectionElem::Index(
+                                    index.node.place().unwrap().as_local().unwrap(),
+                                ),
+                            ],
+                            tcx,
+                        );
+
+                        let ret_ty = generic_args.type_at(0);
+                        let rvalue = match *ret_ty.kind() {
+                            ty::RawPtr(_, Mutability::Not) => {
+                                Rvalue::RawPtr(RawPtrKind::Const, updated_place)
+                            }
+                            ty::RawPtr(_, Mutability::Mut) => {
+                                Rvalue::RawPtr(RawPtrKind::Mut, updated_place)
+                            }
+                            ty::Ref(region, _, Mutability::Not) => {
+                                Rvalue::Ref(region, BorrowKind::Shared, updated_place)
+                            }
+                            ty::Ref(region, _, Mutability::Mut) => Rvalue::Ref(
+                                region,
+                                BorrowKind::Mut { kind: MutBorrowKind::Default },
+                                updated_place,
+                            ),
+                            _ => bug!("Unknown return type {ret_ty:?}"),
+                        };
+
+                        block.statements.push(Statement {
+                            source_info: terminator.source_info,
+                            kind: StatementKind::Assign(Box::new((*destination, rvalue))),
+                        });
+                        terminator.kind = TerminatorKind::Goto { target };
+                    }
                     sym::transmute | sym::transmute_unchecked => {
                         let dst_ty = destination.ty(local_decls, tcx).ty;
                         let Ok([arg]) = take_array(args) else {
diff --git a/compiler/rustc_mir_transform/src/match_branches.rs b/compiler/rustc_mir_transform/src/match_branches.rs
index 8c0c3096899..5e511f1a418 100644
--- a/compiler/rustc_mir_transform/src/match_branches.rs
+++ b/compiler/rustc_mir_transform/src/match_branches.rs
@@ -284,12 +284,14 @@ fn can_cast(
     let v = match src_layout.ty.kind() {
         ty::Uint(_) => from_scalar.to_uint(src_layout.size),
         ty::Int(_) => from_scalar.to_int(src_layout.size) as u128,
-        _ => unreachable!("invalid int"),
+        // We can also transform the values of other integer representations (such as char),
+        // although this may not be practical in real-world scenarios.
+        _ => return false,
     };
     let size = match *cast_ty.kind() {
         ty::Int(t) => Integer::from_int_ty(&tcx, t).size(),
         ty::Uint(t) => Integer::from_uint_ty(&tcx, t).size(),
-        _ => unreachable!("invalid int"),
+        _ => return false,
     };
     let v = size.truncate(v);
     let cast_scalar = ScalarInt::try_from_uint(v, size).unwrap();
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index 9688ac8ed2e..6d45bbc6e16 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -98,7 +98,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceKind<'tcx>) -> Body<
             build_call_shim(tcx, instance, None, CallKind::Direct(def_id))
         }
         ty::InstanceKind::ClosureOnceShim { call_once: _, track_caller: _ } => {
-            let fn_mut = tcx.require_lang_item(LangItem::FnMut, None);
+            let fn_mut = tcx.require_lang_item(LangItem::FnMut, DUMMY_SP);
             let call_mut = tcx
                 .associated_items(fn_mut)
                 .in_definition_order()
diff --git a/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs b/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
index 7976b65aae7..fd7b7362cd9 100644
--- a/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
+++ b/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
@@ -6,7 +6,7 @@ use rustc_middle::mir::{
     BasicBlock, BasicBlockData, Body, Local, LocalDecl, MirSource, Operand, Place, Rvalue,
     SourceInfo, Statement, StatementKind, Terminator, TerminatorKind,
 };
-use rustc_middle::ty::{self, EarlyBinder, Ty, TyCtxt};
+use rustc_middle::ty::{self, EarlyBinder, Ty, TyCtxt, TypeVisitableExt};
 
 use super::*;
 use crate::patch::MirPatch;
@@ -64,7 +64,7 @@ pub(super) fn build_async_drop_shim<'tcx>(
     let needs_async_drop = drop_ty.needs_async_drop(tcx, typing_env);
     let needs_sync_drop = !needs_async_drop && drop_ty.needs_drop(tcx, typing_env);
 
-    let resume_adt = tcx.adt_def(tcx.require_lang_item(LangItem::ResumeTy, None));
+    let resume_adt = tcx.adt_def(tcx.require_lang_item(LangItem::ResumeTy, DUMMY_SP));
     let resume_ty = Ty::new_adt(tcx, resume_adt, ty::List::empty());
 
     let fn_sig = ty::Binder::dummy(tcx.mk_fn_sig(
@@ -121,9 +121,10 @@ pub(super) fn build_async_drop_shim<'tcx>(
         parent_args.as_coroutine().resume_ty(),
     )));
     body.phase = MirPhase::Runtime(RuntimePhase::Initial);
-    if !needs_async_drop {
+    if !needs_async_drop || drop_ty.references_error() {
         // Returning noop body for types without `need async drop`
-        // (or sync Drop in case of !`need async drop` && `need drop`)
+        // (or sync Drop in case of !`need async drop` && `need drop`).
+        // And also for error types.
         return body;
     }
 
@@ -219,7 +220,7 @@ fn build_adrop_for_coroutine_shim<'tcx>(
     body.source.instance = instance;
     body.phase = MirPhase::Runtime(RuntimePhase::Initial);
     body.var_debug_info.clear();
-    let pin_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, Some(span)));
+    let pin_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, span));
     let args = tcx.mk_args(&[proxy_ref.into()]);
     let pin_proxy_ref = Ty::new_adt(tcx, pin_adt_ref, args);
 
@@ -307,10 +308,10 @@ fn build_adrop_for_adrop_shim<'tcx>(
     let cor_ref = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, impl_ty);
 
     // ret_ty = `Poll<()>`
-    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, None));
+    let poll_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Poll, span));
     let ret_ty = Ty::new_adt(tcx, poll_adt_ref, tcx.mk_args(&[tcx.types.unit.into()]));
     // env_ty = `Pin<&mut proxy_ty>`
-    let pin_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, None));
+    let pin_adt_ref = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, span));
     let env_ty = Ty::new_adt(tcx, pin_adt_ref, tcx.mk_args(&[proxy_ref.into()]));
     // sig = `fn (Pin<&mut proxy_ty>, &mut Context) -> Poll<()>`
     let sig = tcx.mk_fn_sig(
@@ -375,7 +376,7 @@ fn build_adrop_for_adrop_shim<'tcx>(
     let cor_pin_ty = Ty::new_adt(tcx, pin_adt_ref, tcx.mk_args(&[cor_ref.into()]));
     let cor_pin_place = Place::from(locals.push(LocalDecl::new(cor_pin_ty, span)));
 
-    let pin_fn = tcx.require_lang_item(LangItem::PinNewUnchecked, Some(span));
+    let pin_fn = tcx.require_lang_item(LangItem::PinNewUnchecked, span);
     // call Pin<FutTy>::new_unchecked(&mut impl_cor)
     blocks.push(BasicBlockData {
         statements,
@@ -395,7 +396,7 @@ fn build_adrop_for_adrop_shim<'tcx>(
     });
     // When dropping async drop coroutine, we continue its execution:
     // we call impl::poll (impl_layout, ctx)
-    let poll_fn = tcx.require_lang_item(LangItem::FuturePoll, None);
+    let poll_fn = tcx.require_lang_item(LangItem::FuturePoll, span);
     let resume_ctx = Place::from(Local::new(2));
     blocks.push(BasicBlockData {
         statements: vec![],
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index c8aa7588d03..fd91508cc11 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -1253,7 +1253,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                             self.tcx,
                             self.tcx.require_lang_item(
                                 LangItem::CoerceUnsized,
-                                Some(self.body.source_info(location).span),
+                                self.body.source_info(location).span,
                             ),
                             [op_ty, *target_type],
                         )) {