Rollup of 7 pull requests

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -3140,8 +3140,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
             hir.get(fn_hir_id) else { return None };
-        let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
-                hir.get_parent(fn_hir_id) else { bug!("ImplItem should have Impl parent") };
+        let i = hir.get_parent(fn_hir_id).expect_item().expect_impl();
 
         let trait_ref = self.instantiate_mono_trait_ref(
             i.of_trait.as_ref()?,

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -8,7 +8,7 @@ use rustc_errors::{
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit;
-use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
+use rustc_hir::{GenericParamKind, ImplItemKind};
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
@@ -918,7 +918,7 @@ fn report_trait_method_mismatch<'tcx>(
             // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
             // span points only at the type `Box<Self`>, but we want to cover the whole
             // argument pattern and type.
-            let ImplItemKind::Fn(ref sig, body) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{impl_m:?} is not a method") };
+            let (sig, body) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
             let span = tcx
                 .hir()
                 .body_param_names(body)
@@ -1080,12 +1080,12 @@ fn extract_spans_for_error_reporting<'tcx>(
 ) -> (Span, Option<Span>) {
     let tcx = infcx.tcx;
     let mut impl_args = {
-        let ImplItemKind::Fn(sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{:?} is not a method", impl_m) };
+        let (sig, _) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
         sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
     };
 
     let trait_args = trait_m.def_id.as_local().map(|def_id| {
-        let TraitItemKind::Fn(sig, _) = &tcx.hir().expect_trait_item(def_id).kind else { bug!("{:?} is not a TraitItemKind::Fn", trait_m) };
+        let (sig, _) = tcx.hir().expect_trait_item(def_id).expect_fn();
         sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
     });
 
@@ -1358,7 +1358,7 @@ fn compare_number_of_method_arguments<'tcx>(
             .def_id
             .as_local()
             .and_then(|def_id| {
-                let TraitItemKind::Fn(trait_m_sig, _) = &tcx.hir().expect_trait_item(def_id).kind else { bug!("{:?} is not a method", impl_m) };
+                let (trait_m_sig, _) = &tcx.hir().expect_trait_item(def_id).expect_fn();
                 let pos = trait_number_args.saturating_sub(1);
                 trait_m_sig.decl.inputs.get(pos).map(|arg| {
                     if pos == 0 {
@@ -1370,7 +1370,7 @@ fn compare_number_of_method_arguments<'tcx>(
             })
             .or(trait_item_span);
 
-        let ImplItemKind::Fn(impl_m_sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{:?} is not a method", impl_m) };
+        let (impl_m_sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
         let pos = impl_number_args.saturating_sub(1);
         let impl_span = impl_m_sig
             .decl
@@ -1506,7 +1506,7 @@ fn compare_synthetic_generics<'tcx>(
                     let _: Option<_> = try {
                         let impl_m = impl_m.def_id.as_local()?;
                         let impl_m = tcx.hir().expect_impl_item(impl_m);
-                        let hir::ImplItemKind::Fn(sig, _) = &impl_m.kind else { unreachable!() };
+                        let (sig, _) = impl_m.expect_fn();
                         let input_tys = sig.decl.inputs;
 
                         struct Visitor(Option<Span>, hir::def_id::LocalDefId);
@@ -1704,7 +1704,7 @@ pub(super) fn compare_impl_const_raw(
         );
 
         // Locate the Span containing just the type of the offending impl
-        let ImplItemKind::Const(ty, _) = tcx.hir().expect_impl_item(impl_const_item_def).kind else { bug!("{impl_const_item:?} is not a impl const") };
+        let (ty, _) = tcx.hir().expect_impl_item(impl_const_item_def).expect_const();
         cause.span = ty.span;
 
         let mut diag = struct_span_err!(
@@ -1717,7 +1717,7 @@ pub(super) fn compare_impl_const_raw(
 
         let trait_c_span = trait_const_item_def.as_local().map(|trait_c_def_id| {
             // Add a label to the Span containing just the type of the const
-            let TraitItemKind::Const(ty, _) = tcx.hir().expect_trait_item(trait_c_def_id).kind else { bug!("{trait_const_item:?} is not a trait const") };
+            let (ty, _) = tcx.hir().expect_trait_item(trait_c_def_id).expect_const();
             ty.span
         });
 

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1072,8 +1072,8 @@ fn check_type_defn<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, all_sized: b
             // All field types must be well-formed.
             for field in &variant.fields {
                 let field_id = field.did.expect_local();
-                let hir::Node::Field(hir::FieldDef { ty: hir_ty, .. }) = tcx.hir().get_by_def_id(field_id)
-                else { bug!() };
+                let hir::FieldDef { ty: hir_ty, .. } =
+                    tcx.hir().get_by_def_id(field_id).expect_field();
                 let ty = wfcx.normalize(hir_ty.span, None, tcx.type_of(field.did));
                 wfcx.register_wf_obligation(
                     hir_ty.span,
@@ -1106,8 +1106,8 @@ fn check_type_defn<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, all_sized: b
             {
                 let last = idx == variant.fields.len() - 1;
                 let field_id = field.did.expect_local();
-                let hir::Node::Field(hir::FieldDef { ty: hir_ty, .. }) = tcx.hir().get_by_def_id(field_id)
-                else { bug!() };
+                let hir::FieldDef { ty: hir_ty, .. } =
+                    tcx.hir().get_by_def_id(field_id).expect_field();
                 let ty = wfcx.normalize(hir_ty.span, None, tcx.type_of(field.did));
                 wfcx.register_bound(
                     traits::ObligationCause::new(

compiler/rustc_hir_analysis/src/check_unused.rs

@@ -29,7 +29,7 @@ pub fn check_crate(tcx: TyCtxt<'_>) {
         if item.span.is_dummy() {
             continue;
         }
-        let hir::ItemKind::Use(path, _) = item.kind else { unreachable!() };
+        let (path, _) = item.expect_use();
         let msg = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(path.span) {
             format!("unused import: `{}`", snippet)
         } else {

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -56,7 +56,7 @@ fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
         _ => {}
     }
 
-    let ItemKind::Impl(impl_) = tcx.hir().expect_item(impl_did).kind else { bug!("expected Drop impl item") };
+    let impl_ = tcx.hir().expect_item(impl_did).expect_impl();
 
     tcx.sess.emit_err(DropImplOnWrongItem { span: impl_.self_ty.span });
 }

compiler/rustc_hir_analysis/src/coherence/unsafety.rs

@@ -3,15 +3,13 @@
 
 use rustc_errors::struct_span_err;
 use rustc_hir as hir;
-use rustc_hir::def::DefKind;
 use rustc_hir::Unsafety;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::LocalDefId;
 
 pub(super) fn check_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
-    debug_assert!(matches!(tcx.def_kind(def_id), DefKind::Impl));
     let item = tcx.hir().expect_item(def_id);
-    let hir::ItemKind::Impl(impl_) = item.kind else { bug!() };
+    let impl_ = item.expect_impl();
 
     if let Some(trait_ref) = tcx.impl_trait_ref(item.owner_id) {
         let trait_ref = trait_ref.subst_identity();

compiler/rustc_hir_analysis/src/collect.rs

@@ -1348,8 +1348,7 @@ fn suggest_impl_trait<'tcx>(
 
 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::EarlyBinder<ty::TraitRef<'_>>> {
     let icx = ItemCtxt::new(tcx, def_id);
-    let item = tcx.hir().expect_item(def_id.expect_local());
-    let hir::ItemKind::Impl(impl_) = item.kind else { bug!() };
+    let impl_ = tcx.hir().expect_item(def_id.expect_local()).expect_impl();
     impl_
         .of_trait
         .as_ref()

compiler/rustc_middle/src/mir/mono.rs

@@ -318,16 +318,19 @@ impl<'tcx> CodegenUnit<'tcx> {
         base_n::encode(hash, base_n::CASE_INSENSITIVE)
     }
 
-    pub fn estimate_size(&mut self, tcx: TyCtxt<'tcx>) {
+    pub fn create_size_estimate(&mut self, tcx: TyCtxt<'tcx>) {
         // Estimate the size of a codegen unit as (approximately) the number of MIR
         // statements it corresponds to.
         self.size_estimate = Some(self.items.keys().map(|mi| mi.size_estimate(tcx)).sum());
     }
 
     #[inline]
+    /// Should only be called if [`create_size_estimate`] has previously been called.
+    ///
+    /// [`create_size_estimate`]: Self::create_size_estimate
     pub fn size_estimate(&self) -> usize {
-        // Should only be called if `estimate_size` has previously been called.
-        self.size_estimate.expect("estimate_size must be called before getting a size_estimate")
+        self.size_estimate
+            .expect("create_size_estimate must be called before getting a size_estimate")
     }
 
     pub fn modify_size_estimate(&mut self, delta: usize) {

compiler/rustc_mir_transform/src/lib.rs

@@ -548,13 +548,13 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         &[
             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
             &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
-            &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
             &unreachable_prop::UnreachablePropagation,
             &uninhabited_enum_branching::UninhabitedEnumBranching,
             &o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
             &inline::Inline,
             &remove_storage_markers::RemoveStorageMarkers,
             &remove_zsts::RemoveZsts,
+            &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
             &const_goto::ConstGoto,
             &remove_unneeded_drops::RemoveUnneededDrops,
             &sroa::ScalarReplacementOfAggregates,

compiler/rustc_mir_transform/src/normalize_array_len.rs

@@ -1,288 +1,104 @@
 //! This pass eliminates casting of arrays into slices when their length
 //! is taken using `.len()` method. Handy to preserve information in MIR for const prop
 
+use crate::ssa::SsaLocals;
 use crate::MirPass;
-use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::intern::Interned;
-use rustc_index::bit_set::BitSet;
 use rustc_index::vec::IndexVec;
+use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
-use rustc_middle::ty::{self, ReErased, Region, TyCtxt};
-
-const MAX_NUM_BLOCKS: usize = 800;
-const MAX_NUM_LOCALS: usize = 3000;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_mir_dataflow::impls::borrowed_locals;
 
 pub struct NormalizeArrayLen;
 
 impl<'tcx> MirPass<'tcx> for NormalizeArrayLen {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        // See #105929
-        sess.mir_opt_level() >= 4 && sess.opts.unstable_opts.unsound_mir_opts
+        sess.mir_opt_level() >= 3
     }
 
+    #[instrument(level = "trace", skip(self, tcx, body))]
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        // early returns for edge cases of highly unrolled functions
-        if body.basic_blocks.len() > MAX_NUM_BLOCKS {
-            return;
-        }
-        if body.local_decls.len() > MAX_NUM_LOCALS {
-            return;
-        }
+        debug!(def_id = ?body.source.def_id());
         normalize_array_len_calls(tcx, body)
     }
 }
 
-pub fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    // We don't ever touch terminators, so no need to invalidate the CFG cache
-    let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
-    let local_decls = &mut body.local_decls;
+fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
+    let borrowed_locals = borrowed_locals(body);
+    let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
 
-    // do a preliminary analysis to see if we ever have locals of type `[T;N]` or `&[T;N]`
-    let mut interesting_locals = BitSet::new_empty(local_decls.len());
-    for (local, decl) in local_decls.iter_enumerated() {
-        match decl.ty.kind() {
-            ty::Array(..) => {
-                interesting_locals.insert(local);
-            }
-            ty::Ref(.., ty, Mutability::Not) => match ty.kind() {
-                ty::Array(..) => {
-                    interesting_locals.insert(local);
-                }
-                _ => {}
-            },
-            _ => {}
-        }
-    }
-    if interesting_locals.is_empty() {
-        // we have found nothing to analyze
-        return;
-    }
-    let num_intesting_locals = interesting_locals.count();
-    let mut state = FxIndexMap::with_capacity_and_hasher(num_intesting_locals, Default::default());
-    let mut patches_scratchpad =
-        FxIndexMap::with_capacity_and_hasher(num_intesting_locals, Default::default());
-    let mut replacements_scratchpad =
-        FxIndexMap::with_capacity_and_hasher(num_intesting_locals, Default::default());
-    for block in basic_blocks {
-        // make length calls for arrays [T; N] not to decay into length calls for &[T]
-        // that forbids constant propagation
-        normalize_array_len_call(
-            tcx,
-            block,
-            local_decls,
-            &interesting_locals,
-            &mut state,
-            &mut patches_scratchpad,
-            &mut replacements_scratchpad,
-        );
-        state.clear();
-        patches_scratchpad.clear();
-        replacements_scratchpad.clear();
-    }
-}
+    let slice_lengths = compute_slice_length(tcx, &ssa, body);
+    debug!(?slice_lengths);
 
-struct Patcher<'a, 'tcx> {
-    tcx: TyCtxt<'tcx>,
-    patches_scratchpad: &'a FxIndexMap<usize, usize>,
-    replacements_scratchpad: &'a mut FxIndexMap<usize, Local>,
-    local_decls: &'a mut IndexVec<Local, LocalDecl<'tcx>>,
-    statement_idx: usize,
+    Replacer { tcx, slice_lengths }.visit_body_preserves_cfg(body);
 }
 
-impl<'tcx> Patcher<'_, 'tcx> {
-    fn patch_expand_statement(
-        &mut self,
-        statement: &mut Statement<'tcx>,
-    ) -> Option<std::vec::IntoIter<Statement<'tcx>>> {
-        let idx = self.statement_idx;
-        if let Some(len_statemnt_idx) = self.patches_scratchpad.get(&idx).copied() {
-            let mut statements = Vec::with_capacity(2);
-
-            // we are at statement that performs a cast. The only sound way is
-            // to create another local that performs a similar copy without a cast and then
-            // use this copy in the Len operation
-
-            match &statement.kind {
-                StatementKind::Assign(box (
-                    ..,
-                    Rvalue::Cast(
-                        CastKind::Pointer(ty::adjustment::PointerCast::Unsize),
-                        operand,
-                        _,
-                    ),
-                )) => {
-                    match operand {
-                        Operand::Copy(place) | Operand::Move(place) => {
-                            // create new local
-                            let ty = operand.ty(self.local_decls, self.tcx);
-                            let local_decl = LocalDecl::with_source_info(ty, statement.source_info);
-                            let local = self.local_decls.push(local_decl);
-                            // make it live
-                            let mut make_live_statement = statement.clone();
-                            make_live_statement.kind = StatementKind::StorageLive(local);
-                            statements.push(make_live_statement);
-                            // copy into it
-
-                            let operand = Operand::Copy(*place);
-                            let mut make_copy_statement = statement.clone();
-                            let assign_to = Place::from(local);
-                            let rvalue = Rvalue::Use(operand);
-                            make_copy_statement.kind =
-                                StatementKind::Assign(Box::new((assign_to, rvalue)));
-                            statements.push(make_copy_statement);
-
-                            // to reorder we have to copy and make NOP
-                            statements.push(statement.clone());
-                            statement.make_nop();
-
-                            self.replacements_scratchpad.insert(len_statemnt_idx, local);
-                        }
-                        _ => {
-                            unreachable!("it's a bug in the implementation")
-                        }
-                    }
-                }
-                _ => {
-                    unreachable!("it's a bug in the implementation")
+fn compute_slice_length<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ssa: &SsaLocals,
+    body: &Body<'tcx>,
+) -> IndexVec<Local, Option<ty::Const<'tcx>>> {
+    let mut slice_lengths = IndexVec::from_elem(None, &body.local_decls);
+
+    for (local, rvalue) in ssa.assignments(body) {
+        match rvalue {
+            Rvalue::Cast(
+                CastKind::Pointer(ty::adjustment::PointerCast::Unsize),
+                operand,
+                cast_ty,
+            ) => {
+                let operand_ty = operand.ty(body, tcx);
+                debug!(?operand_ty);
+                if let Some(operand_ty) = operand_ty.builtin_deref(true)
+                    && let ty::Array(_, len) = operand_ty.ty.kind()
+                    && let Some(cast_ty) = cast_ty.builtin_deref(true)
+                    && let ty::Slice(..) = cast_ty.ty.kind()
+                {
+                    slice_lengths[local] = Some(*len);
                 }
             }
-
-            self.statement_idx += 1;
-
-            Some(statements.into_iter())
-        } else if let Some(local) = self.replacements_scratchpad.get(&idx).copied() {
-            let mut statements = Vec::with_capacity(2);
-
-            match &statement.kind {
-                StatementKind::Assign(box (into, Rvalue::Len(place))) => {
-                    let add_deref = if let Some(..) = place.as_local() {
-                        false
-                    } else if let Some(..) = place.local_or_deref_local() {
-                        true
-                    } else {
-                        unreachable!("it's a bug in the implementation")
-                    };
-                    // replace len statement
-                    let mut len_statement = statement.clone();
-                    let mut place = Place::from(local);
-                    if add_deref {
-                        place = self.tcx.mk_place_deref(place);
-                    }
-                    len_statement.kind =
-                        StatementKind::Assign(Box::new((*into, Rvalue::Len(place))));
-                    statements.push(len_statement);
-
-                    // make temporary dead
-                    let mut make_dead_statement = statement.clone();
-                    make_dead_statement.kind = StatementKind::StorageDead(local);
-                    statements.push(make_dead_statement);
-
-                    // make original statement NOP
-                    statement.make_nop();
+            // The length information is stored in the fat pointer, so we treat `operand` as a value.
+            Rvalue::Use(operand) => {
+                if let Some(rhs) = operand.place() && let Some(rhs) = rhs.as_local() {
+                    slice_lengths[local] = slice_lengths[rhs];
                 }
-                _ => {
-                    unreachable!("it's a bug in the implementation")
+            }
+            // The length information is stored in the fat pointer.
+            // Reborrowing copies length information from one pointer to the other.
+            Rvalue::Ref(_, _, rhs) | Rvalue::AddressOf(_, rhs) => {
+                if let [PlaceElem::Deref] = rhs.projection[..] {
+                    slice_lengths[local] = slice_lengths[rhs.local];
                 }
             }
-
-            self.statement_idx += 1;
-
-            Some(statements.into_iter())
-        } else {
-            self.statement_idx += 1;
-            None
+            _ => {}
         }
     }
+
+    slice_lengths
 }
 
-fn normalize_array_len_call<'tcx>(
+struct Replacer<'tcx> {
     tcx: TyCtxt<'tcx>,
-    block: &mut BasicBlockData<'tcx>,
-    local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
-    interesting_locals: &BitSet<Local>,
-    state: &mut FxIndexMap<Local, usize>,
-    patches_scratchpad: &mut FxIndexMap<usize, usize>,
-    replacements_scratchpad: &mut FxIndexMap<usize, Local>,
-) {
-    for (statement_idx, statement) in block.statements.iter_mut().enumerate() {
-        match &mut statement.kind {
-            StatementKind::Assign(box (place, rvalue)) => {
-                match rvalue {
-                    Rvalue::Cast(
-                        CastKind::Pointer(ty::adjustment::PointerCast::Unsize),
-                        operand,
-                        cast_ty,
-                    ) => {
-                        let Some(local) = place.as_local() else { return };
-                        match operand {
-                            Operand::Copy(place) | Operand::Move(place) => {
-                                let Some(operand_local) = place.local_or_deref_local() else { return; };
-                                if !interesting_locals.contains(operand_local) {
-                                    return;
-                                }
-                                let operand_ty = local_decls[operand_local].ty;
-                                match (operand_ty.kind(), cast_ty.kind()) {
-                                    (ty::Array(of_ty_src, ..), ty::Slice(of_ty_dst)) => {
-                                        if of_ty_src == of_ty_dst {
-                                            // this is a cast from [T; N] into [T], so we are good
-                                            state.insert(local, statement_idx);
-                                        }
-                                    }
-                                    // current way of patching doesn't allow to work with `mut`
-                                    (
-                                        ty::Ref(
-                                            Region(Interned(ReErased, _)),
-                                            operand_ty,
-                                            Mutability::Not,
-                                        ),
-                                        ty::Ref(
-                                            Region(Interned(ReErased, _)),
-                                            cast_ty,
-                                            Mutability::Not,
-                                        ),
-                                    ) => {
-                                        match (operand_ty.kind(), cast_ty.kind()) {
-                                            // current way of patching doesn't allow to work with `mut`
-                                            (ty::Array(of_ty_src, ..), ty::Slice(of_ty_dst)) => {
-                                                if of_ty_src == of_ty_dst {
-                                                    // this is a cast from [T; N] into [T], so we are good
-                                                    state.insert(local, statement_idx);
-                                                }
-                                            }
-                                            _ => {}
-                                        }
-                                    }
-                                    _ => {}
-                                }
-                            }
-                            _ => {}
-                        }
-                    }
-                    Rvalue::Len(place) => {
-                        let Some(local) = place.local_or_deref_local() else {
-                            return;
-                        };
-                        if let Some(cast_statement_idx) = state.get(&local).copied() {
-                            patches_scratchpad.insert(cast_statement_idx, statement_idx);
-                        }
-                    }
-                    _ => {
-                        // invalidate
-                        state.remove(&place.local);
-                    }
-                }
-            }
-            _ => {}
-        }
-    }
+    slice_lengths: IndexVec<Local, Option<ty::Const<'tcx>>>,
+}
 
-    let mut patcher = Patcher {
-        tcx,
-        patches_scratchpad: &*patches_scratchpad,
-        replacements_scratchpad,
-        local_decls,
-        statement_idx: 0,
-    };
+impl<'tcx> MutVisitor<'tcx> for Replacer<'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
 
-    block.expand_statements(|st| patcher.patch_expand_statement(st));
+    fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, loc: Location) {
+        if let Rvalue::Len(place) = rvalue
+            && let [PlaceElem::Deref] = &place.projection[..]
+            && let Some(len) = self.slice_lengths[place.local]
+        {
+            *rvalue = Rvalue::Use(Operand::Constant(Box::new(Constant {
+                span: rustc_span::DUMMY_SP,
+                user_ty: None,
+                literal: ConstantKind::from_const(len, self.tcx),
+            })));
+        }
+        self.super_rvalue(rvalue, loc);
+    }
 }

compiler/rustc_monomorphize/src/partitioning/mod.rs

@@ -180,7 +180,7 @@ pub fn partition<'tcx>(
         partitioner.place_root_mono_items(cx, mono_items)
     };
 
-    initial_partitioning.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
+    initial_partitioning.codegen_units.iter_mut().for_each(|cgu| cgu.create_size_estimate(tcx));
 
     debug_dump(tcx, "INITIAL PARTITIONING:", initial_partitioning.codegen_units.iter());
 
@@ -200,7 +200,7 @@ pub fn partition<'tcx>(
         partitioner.place_inlined_mono_items(cx, initial_partitioning)
     };
 
-    post_inlining.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
+    post_inlining.codegen_units.iter_mut().for_each(|cgu| cgu.create_size_estimate(tcx));
 
     debug_dump(tcx, "POST INLINING:", post_inlining.codegen_units.iter());
 

compiler/rustc_passes/src/dead.rs

@@ -459,30 +459,32 @@ impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
 }
 
 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
-    if tcx.has_attr(def_id.to_def_id(), sym::lang) {
-        return true;
+    fn has_lang_attr(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
+        tcx.has_attr(def_id.to_def_id(), sym::lang)
+            // Stable attribute for #[lang = "panic_impl"]
+            || tcx.has_attr(def_id.to_def_id(), sym::panic_handler)
     }
 
-    // Stable attribute for #[lang = "panic_impl"]
-    if tcx.has_attr(def_id.to_def_id(), sym::panic_handler) {
-        return true;
+    fn has_allow_dead_code(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
+        let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
+        tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0 == lint::Allow
     }
 
-    if tcx.def_kind(def_id).has_codegen_attrs() {
-        let cg_attrs = tcx.codegen_fn_attrs(def_id);
+    fn has_used_like_attr(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
+        tcx.def_kind(def_id).has_codegen_attrs() && {
+            let cg_attrs = tcx.codegen_fn_attrs(def_id);
 
-        // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
-        // forcefully, e.g., for placing it in a specific section.
-        if cg_attrs.contains_extern_indicator()
-            || cg_attrs.flags.contains(CodegenFnAttrFlags::USED)
-            || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
-        {
-            return true;
+            // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
+            // forcefully, e.g., for placing it in a specific section.
+            cg_attrs.contains_extern_indicator()
+                || cg_attrs.flags.contains(CodegenFnAttrFlags::USED)
+                || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
         }
     }
 
-    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
-    tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0 == lint::Allow
+    has_allow_dead_code(tcx, def_id)
+        || has_used_like_attr(tcx, def_id)
+        || has_lang_attr(tcx, def_id)
 }
 
 // These check_* functions seeds items that

library/alloc/src/slice.rs

@@ -782,6 +782,38 @@ impl<T, A: Allocator> BorrowMut<[T]> for Vec<T, A> {
     }
 }
 
+// Specializable trait for implementing ToOwned::clone_into. This is
+// public in the crate and has the Allocator parameter so that
+// vec::clone_from use it too.
+#[cfg(not(no_global_oom_handling))]
+pub(crate) trait SpecCloneIntoVec<T, A: Allocator> {
+    fn clone_into(&self, target: &mut Vec<T, A>);
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T: Clone, A: Allocator> SpecCloneIntoVec<T, A> for [T] {
+    default fn clone_into(&self, target: &mut Vec<T, A>) {
+        // drop anything in target that will not be overwritten
+        target.truncate(self.len());
+
+        // target.len <= self.len due to the truncate above, so the
+        // slices here are always in-bounds.
+        let (init, tail) = self.split_at(target.len());
+
+        // reuse the contained values' allocations/resources.
+        target.clone_from_slice(init);
+        target.extend_from_slice(tail);
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T: Copy, A: Allocator> SpecCloneIntoVec<T, A> for [T] {
+    fn clone_into(&self, target: &mut Vec<T, A>) {
+        target.clear();
+        target.extend_from_slice(self);
+    }
+}
+
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Clone> ToOwned for [T] {
@@ -797,16 +829,7 @@ impl<T: Clone> ToOwned for [T] {
     }
 
     fn clone_into(&self, target: &mut Vec<T>) {
-        // drop anything in target that will not be overwritten
-        target.truncate(self.len());
-
-        // target.len <= self.len due to the truncate above, so the
-        // slices here are always in-bounds.
-        let (init, tail) = self.split_at(target.len());
-
-        // reuse the contained values' allocations/resources.
-        target.clone_from_slice(init);
-        target.extend_from_slice(tail);
+        SpecCloneIntoVec::clone_into(self, target);
     }
 }
 

library/alloc/src/vec/mod.rs

@@ -2646,35 +2646,6 @@ impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
     }
 }
 
-#[cfg(not(no_global_oom_handling))]
-trait SpecCloneFrom {
-    fn clone_from(this: &mut Self, other: &Self);
-}
-
-#[cfg(not(no_global_oom_handling))]
-impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
-    default fn clone_from(this: &mut Self, other: &Self) {
-        // drop anything that will not be overwritten
-        this.truncate(other.len());
-
-        // self.len <= other.len due to the truncate above, so the
-        // slices here are always in-bounds.
-        let (init, tail) = other.split_at(this.len());
-
-        // reuse the contained values' allocations/resources.
-        this.clone_from_slice(init);
-        this.extend_from_slice(tail);
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
-impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
-    fn clone_from(this: &mut Self, other: &Self) {
-        this.clear();
-        this.extend_from_slice(other);
-    }
-}
-
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
@@ -2695,7 +2666,7 @@ impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
     }
 
     fn clone_from(&mut self, other: &Self) {
-        SpecCloneFrom::clone_from(self, other)
+        crate::slice::SpecCloneIntoVec::clone_into(other.as_slice(), self);
     }
 }
 

src/librustdoc/config.rs

@@ -509,7 +509,7 @@ impl Options {
                 // these values up both in `dataset` and in the storage API, so it needs to be able
                 // to convert the names back and forth.  Despite doing this kebab-case to
                 // StudlyCaps transformation automatically, the JS DOM API does not provide a
-                // mechanism for doing the just transformation on a string.  So we want to avoid
+                // mechanism for doing just the transformation on a string.  So we want to avoid
                 // the StudlyCaps representation in the `dataset` property.
                 //
                 // We solve this by replacing all the `-`s with `_`s.  We do that here, when we

src/librustdoc/html/static/js/settings.js

@@ -1,5 +1,5 @@
 // Local js definitions:
-/* global getSettingValue, getVirtualKey, updateLocalStorage, updateSystemTheme */
+/* global getSettingValue, getVirtualKey, updateLocalStorage, updateTheme */
 /* global addClass, removeClass, onEach, onEachLazy, blurHandler, elemIsInParent */
 /* global MAIN_ID, getVar, getSettingsButton */
 
@@ -19,7 +19,7 @@
             case "theme":
             case "preferred-dark-theme":
             case "preferred-light-theme":
-                updateSystemTheme();
+                updateTheme();
                 updateLightAndDark();
                 break;
             case "line-numbers":

src/librustdoc/html/static/js/storage.js

@@ -153,79 +153,74 @@ function switchTheme(styleElem, mainStyleElem, newThemeName, saveTheme) {
     }
 }
 
-// This function is called from "main.js".
-// eslint-disable-next-line no-unused-vars
-function useSystemTheme(value) {
-    if (value === undefined) {
-        value = true;
-    }
-
-    updateLocalStorage("use-system-theme", value);
-
-    // update the toggle if we're on the settings page
-    const toggle = document.getElementById("use-system-theme");
-    if (toggle && toggle instanceof HTMLInputElement) {
-        toggle.checked = value;
-    }
-}
-
-const updateSystemTheme = (function() {
-    if (!window.matchMedia) {
-        // fallback to the CSS computed value
-        return () => {
-            const cssTheme = getComputedStyle(document.documentElement)
-                .getPropertyValue("content");
-
-            switchTheme(
-                window.currentTheme,
-                window.mainTheme,
-                JSON.parse(cssTheme) || "light",
-                true
-            );
+const updateTheme = (function() {
+    /**
+     * Update the current theme to match whatever the current combination of
+     * * the preference for using the system theme
+     *   (if this is the case, the value of preferred-light-theme, if the
+     *   system theme is light, otherwise if dark, the value of
+     *   preferred-dark-theme.)
+     * * the preferred theme
+     * … dictates that it should be.
+     */
+    function updateTheme() {
+        const use = (theme, saveTheme) => {
+            switchTheme(window.currentTheme, window.mainTheme, theme, saveTheme);
         };
-    }
-
-    // only listen to (prefers-color-scheme: dark) because light is the default
-    const mql = window.matchMedia("(prefers-color-scheme: dark)");
 
-    function handlePreferenceChange(mql) {
-        const use = theme => {
-            switchTheme(window.currentTheme, window.mainTheme, theme, true);
-        };
         // maybe the user has disabled the setting in the meantime!
         if (getSettingValue("use-system-theme") !== "false") {
             const lightTheme = getSettingValue("preferred-light-theme") || "light";
             const darkTheme = getSettingValue("preferred-dark-theme") || "dark";
 
-            if (mql.matches) {
-                use(darkTheme);
+            if (isDarkMode()) {
+                use(darkTheme, true);
             } else {
                 // prefers a light theme, or has no preference
-                use(lightTheme);
+                use(lightTheme, true);
             }
             // note: we save the theme so that it doesn't suddenly change when
             // the user disables "use-system-theme" and reloads the page or
             // navigates to another page
         } else {
-            use(getSettingValue("theme"));
+            use(getSettingValue("theme"), false);
         }
     }
 
-    mql.addListener(handlePreferenceChange);
+    // This is always updated below to a function () => bool.
+    let isDarkMode;
 
-    return () => {
-        handlePreferenceChange(mql);
-    };
-})();
+    // Determine the function for isDarkMode, and if we have
+    // `window.matchMedia`, set up an event listener on the preferred color
+    // scheme.
+    //
+    // Otherwise, fall back to the prefers-color-scheme value CSS captured in
+    // the "content" property.
+    if (window.matchMedia) {
+        // only listen to (prefers-color-scheme: dark) because light is the default
+        const mql = window.matchMedia("(prefers-color-scheme: dark)");
 
-function switchToSavedTheme() {
-    switchTheme(
-        window.currentTheme,
-        window.mainTheme,
-        getSettingValue("theme") || "light",
-        false
-    );
-}
+        isDarkMode = () => mql.matches;
+
+        if (mql.addEventListener) {
+            mql.addEventListener("change", updateTheme);
+        } else {
+            // This is deprecated, see:
+            // https://developer.mozilla.org/en-US/docs/Web/API/MediaQueryList/addListener
+            mql.addListener(updateTheme);
+        }
+    } else {
+        // fallback to the CSS computed value
+        const cssContent = getComputedStyle(document.documentElement)
+            .getPropertyValue("content");
+        // (Note: the double-quotes come from that this is a CSS value, which
+        // might be a length, string, etc.)
+        const cssColorScheme = cssContent || "\"light\"";
+        isDarkMode = () => (cssColorScheme === "\"dark\"");
+    }
+
+    return updateTheme;
+})();
 
 if (getSettingValue("use-system-theme") !== "false" && window.matchMedia) {
     // update the preferred dark theme if the user is already using a dark theme
@@ -235,13 +230,10 @@ if (getSettingValue("use-system-theme") !== "false" && window.matchMedia) {
         && darkThemes.indexOf(localStoredTheme) >= 0) {
         updateLocalStorage("preferred-dark-theme", localStoredTheme);
     }
-
-    // call the function to initialize the theme at least once!
-    updateSystemTheme();
-} else {
-    switchToSavedTheme();
 }
 
+updateTheme();
+
 if (getSettingValue("source-sidebar-show") === "true") {
     // At this point in page load, `document.body` is not available yet.
     // Set a class on the `<html>` element instead.
@@ -259,6 +251,6 @@ if (getSettingValue("source-sidebar-show") === "true") {
 // specifically when talking to a remote website with no caching.
 window.addEventListener("pageshow", ev => {
     if (ev.persisted) {
-        setTimeout(switchToSavedTheme, 0);
+        setTimeout(updateTheme, 0);
     }
 });

tests/mir-opt/const_prop/bad_op_unsafe_oob_for_slices.main.ConstProp.32bit.diff

@@ -33,11 +33,11 @@
           StorageLive(_4);                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:13: +3:15
           StorageLive(_5);                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:23: +3:24
           _5 = const 3_usize;              // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:23: +3:24
-          _6 = Len((*_1));                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
+          _6 = const 3_usize;              // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
 -         _7 = Lt(_5, _6);                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
 -         assert(move _7, "index out of bounds: the length is {} but the index is {}", move _6, _5) -> bb1; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
-+         _7 = Lt(const 3_usize, _6);      // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
-+         assert(move _7, "index out of bounds: the length is {} but the index is {}", move _6, const 3_usize) -> bb1; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
++         _7 = const false;                // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
++         assert(const false, "index out of bounds: the length is {} but the index is {}", const 3_usize, const 3_usize) -> bb1; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
       }
 
       bb1: {

tests/mir-opt/const_prop/bad_op_unsafe_oob_for_slices.main.ConstProp.64bit.diff

@@ -33,11 +33,11 @@
           StorageLive(_4);                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:13: +3:15
           StorageLive(_5);                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:23: +3:24
           _5 = const 3_usize;              // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:23: +3:24
-          _6 = Len((*_1));                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
+          _6 = const 3_usize;              // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
 -         _7 = Lt(_5, _6);                 // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
 -         assert(move _7, "index out of bounds: the length is {} but the index is {}", move _6, _5) -> bb1; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
-+         _7 = Lt(const 3_usize, _6);      // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
-+         assert(move _7, "index out of bounds: the length is {} but the index is {}", move _6, const 3_usize) -> bb1; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
++         _7 = const false;                // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
++         assert(const false, "index out of bounds: the length is {} but the index is {}", const 3_usize, const 3_usize) -> bb1; // scope 2 at $DIR/bad_op_unsafe_oob_for_slices.rs:+3:18: +3:25
       }
 
       bb1: {

tests/mir-opt/issue_76432.rs

@@ -1,3 +1,4 @@
+// compile-flags: -Zmir-enable-passes=-NormalizeArrayLen
 // Check that we do not insert StorageDead at each target if StorageDead was never seen
 
 // EMIT_MIR issue_76432.test.SimplifyComparisonIntegral.diff

tests/mir-opt/lower_array_len.array_bound.NormalizeArrayLen.diff

@@ -13,7 +13,6 @@
       let _8: usize;                       // in scope 0 at $DIR/lower_array_len.rs:+2:15: +2:20
       let mut _9: usize;                   // in scope 0 at $DIR/lower_array_len.rs:+2:9: +2:21
       let mut _10: bool;                   // in scope 0 at $DIR/lower_array_len.rs:+2:9: +2:21
-+     let mut _11: &[u8; N];               // in scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
 
       bb0: {
           StorageLive(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:8: +1:27
@@ -23,13 +22,10 @@
           StorageLive(_6);                 // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           StorageLive(_7);                 // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           _7 = &(*_2);                     // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         StorageLive(_11);                // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         _11 = _7;                        // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           _6 = move _7 as &[u8] (Pointer(Unsize)); // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           StorageDead(_7);                 // scope 0 at $DIR/lower_array_len.rs:+1:20: +1:21
 -         _5 = Len((*_6));                 // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         _5 = Len((*_11));                // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         StorageDead(_11);                // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
++         _5 = const N;                    // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           goto -> bb1;                     // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
       }
 

tests/mir-opt/lower_array_len.array_bound_mut.NormalizeArrayLen.diff

@@ -16,7 +16,6 @@
       let _11: usize;                      // in scope 0 at $DIR/lower_array_len.rs:+4:15: +4:16
       let mut _12: usize;                  // in scope 0 at $DIR/lower_array_len.rs:+4:9: +4:17
       let mut _13: bool;                   // in scope 0 at $DIR/lower_array_len.rs:+4:9: +4:17
-+     let mut _14: &[u8; N];               // in scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
 
       bb0: {
           StorageLive(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:8: +1:27
@@ -26,13 +25,10 @@
           StorageLive(_6);                 // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           StorageLive(_7);                 // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           _7 = &(*_2);                     // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         StorageLive(_14);                // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         _14 = _7;                        // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           _6 = move _7 as &[u8] (Pointer(Unsize)); // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           StorageDead(_7);                 // scope 0 at $DIR/lower_array_len.rs:+1:20: +1:21
 -         _5 = Len((*_6));                 // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         _5 = Len((*_14));                // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
-+         StorageDead(_14);                // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
++         _5 = const N;                    // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
           goto -> bb1;                     // scope 0 at $DIR/lower_array_len.rs:+1:16: +1:27
       }
 

tests/mir-opt/lower_array_len.array_len.NormalizeArrayLen.diff

@@ -6,19 +6,15 @@
       let mut _0: usize;                   // return place in scope 0 at $DIR/lower_array_len.rs:+0:52: +0:57
       let mut _2: &[u8];                   // in scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
       let mut _3: &[u8; N];                // in scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+     let mut _4: &[u8; N];                // in scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
 
       bb0: {
           StorageLive(_2);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           StorageLive(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           _3 = &(*_1);                     // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         StorageLive(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         _4 = _3;                         // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           _2 = move _3 as &[u8] (Pointer(Unsize)); // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           StorageDead(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:7: +1:8
 -         _0 = Len((*_2));                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         _0 = Len((*_4));                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         StorageDead(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
++         _0 = const N;                    // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           goto -> bb1;                     // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
       }
 

tests/mir-opt/lower_array_len.array_len_by_value.NormalizeArrayLen.diff

@@ -6,19 +6,15 @@
       let mut _0: usize;                   // return place in scope 0 at $DIR/lower_array_len.rs:+0:60: +0:65
       let mut _2: &[u8];                   // in scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
       let mut _3: &[u8; N];                // in scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+     let mut _4: &[u8; N];                // in scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
 
       bb0: {
           StorageLive(_2);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           StorageLive(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           _3 = &_1;                        // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         StorageLive(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         _4 = _3;                         // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           _2 = move _3 as &[u8] (Pointer(Unsize)); // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           StorageDead(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:7: +1:8
 -         _0 = Len((*_2));                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         _0 = Len((*_4));                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
-+         StorageDead(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
++         _0 = const N;                    // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
           goto -> bb1;                     // scope 0 at $DIR/lower_array_len.rs:+1:5: +1:14
       }
 

tests/mir-opt/lower_array_len.array_len_raw.NormalizeArrayLen.diff

@@ -0,0 +1,50 @@
+- // MIR for `array_len_raw` before NormalizeArrayLen
++ // MIR for `array_len_raw` after NormalizeArrayLen
+
+  fn array_len_raw(_1: [u8; N]) -> usize {
+      debug arr => _1;                     // in scope 0 at $DIR/lower_array_len.rs:+0:38: +0:41
+      let mut _0: usize;                   // return place in scope 0 at $DIR/lower_array_len.rs:+0:55: +0:60
+      let _2: &[u8];                       // in scope 0 at $DIR/lower_array_len.rs:+1:9: +1:12
+      let mut _3: &[u8; N];                // in scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+      let _4: &[u8; N];                    // in scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+      let mut _6: &[u8];                   // in scope 0 at $DIR/lower_array_len.rs:+3:5: +3:27
+      let _7: &[u8];                       // in scope 0 at $DIR/lower_array_len.rs:+3:14: +3:19
+      scope 1 {
+          debug arr => _2;                 // in scope 1 at $DIR/lower_array_len.rs:+1:9: +1:12
+          let _5: *const [u8];             // in scope 1 at $DIR/lower_array_len.rs:+2:9: +2:12
+          scope 2 {
+              debug arr => _5;             // in scope 2 at $DIR/lower_array_len.rs:+2:9: +2:12
+              scope 3 {
+              }
+          }
+      }
+
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/lower_array_len.rs:+1:9: +1:12
+          StorageLive(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+          StorageLive(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+          _4 = &_1;                        // scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+          _3 = &(*_4);                     // scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+          _2 = move _3 as &[u8] (Pointer(Unsize)); // scope 0 at $DIR/lower_array_len.rs:+1:21: +1:25
+          StorageDead(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:24: +1:25
+          StorageDead(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:25: +1:26
+          StorageLive(_5);                 // scope 1 at $DIR/lower_array_len.rs:+2:9: +2:12
+          _5 = &raw const (*_2);           // scope 1 at $SRC_DIR/core/src/ptr/mod.rs:LL:COL
+          StorageLive(_6);                 // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:27
+          StorageLive(_7);                 // scope 2 at $DIR/lower_array_len.rs:+3:14: +3:19
+          _7 = &(*_5);                     // scope 3 at $DIR/lower_array_len.rs:+3:14: +3:19
+          _6 = &(*_7);                     // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:27
+-         _0 = Len((*_6));                 // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:27
++         _0 = const N;                    // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:27
+          goto -> bb1;                     // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:27
+      }
+
+      bb1: {
+          StorageDead(_6);                 // scope 2 at $DIR/lower_array_len.rs:+3:26: +3:27
+          StorageDead(_5);                 // scope 1 at $DIR/lower_array_len.rs:+4:1: +4:2
+          StorageDead(_2);                 // scope 0 at $DIR/lower_array_len.rs:+4:1: +4:2
+          StorageDead(_7);                 // scope 0 at $DIR/lower_array_len.rs:+4:1: +4:2
+          return;                          // scope 0 at $DIR/lower_array_len.rs:+4:2: +4:2
+      }
+  }
+

tests/mir-opt/lower_array_len.array_len_reborrow.NormalizeArrayLen.diff

@@ -0,0 +1,44 @@
+- // MIR for `array_len_reborrow` before NormalizeArrayLen
++ // MIR for `array_len_reborrow` after NormalizeArrayLen
+
+  fn array_len_reborrow(_1: [u8; N]) -> usize {
+      debug arr => _1;                     // in scope 0 at $DIR/lower_array_len.rs:+0:43: +0:50
+      let mut _0: usize;                   // return place in scope 0 at $DIR/lower_array_len.rs:+0:64: +0:69
+      let _2: &mut [u8];                   // in scope 0 at $DIR/lower_array_len.rs:+1:9: +1:12
+      let mut _3: &mut [u8; N];            // in scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+      let mut _4: &mut [u8; N];            // in scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+      let mut _6: &[u8];                   // in scope 0 at $DIR/lower_array_len.rs:+3:5: +3:14
+      scope 1 {
+          debug arr => _2;                 // in scope 1 at $DIR/lower_array_len.rs:+1:9: +1:12
+          let _5: &[u8];                   // in scope 1 at $DIR/lower_array_len.rs:+2:9: +2:12
+          scope 2 {
+              debug arr => _5;             // in scope 2 at $DIR/lower_array_len.rs:+2:9: +2:12
+          }
+      }
+
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/lower_array_len.rs:+1:9: +1:12
+          StorageLive(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+          StorageLive(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+          _4 = &mut _1;                    // scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+          _3 = &mut (*_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+          _2 = move _3 as &mut [u8] (Pointer(Unsize)); // scope 0 at $DIR/lower_array_len.rs:+1:25: +1:33
+          StorageDead(_3);                 // scope 0 at $DIR/lower_array_len.rs:+1:32: +1:33
+          StorageDead(_4);                 // scope 0 at $DIR/lower_array_len.rs:+1:33: +1:34
+          StorageLive(_5);                 // scope 1 at $DIR/lower_array_len.rs:+2:9: +2:12
+          _5 = &(*_2);                     // scope 1 at $DIR/lower_array_len.rs:+2:15: +2:20
+          StorageLive(_6);                 // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:14
+          _6 = &(*_5);                     // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:14
+-         _0 = Len((*_6));                 // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:14
++         _0 = const N;                    // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:14
+          goto -> bb1;                     // scope 2 at $DIR/lower_array_len.rs:+3:5: +3:14
+      }
+
+      bb1: {
+          StorageDead(_6);                 // scope 2 at $DIR/lower_array_len.rs:+3:13: +3:14
+          StorageDead(_5);                 // scope 1 at $DIR/lower_array_len.rs:+4:1: +4:2
+          StorageDead(_2);                 // scope 0 at $DIR/lower_array_len.rs:+4:1: +4:2
+          return;                          // scope 0 at $DIR/lower_array_len.rs:+4:2: +4:2
+      }
+  }
+

tests/mir-opt/lower_array_len.rs

@@ -31,10 +31,26 @@ pub fn array_len_by_value<const N: usize>(arr: [u8; N]) -> usize {
     arr.len()
 }
 
+// EMIT_MIR lower_array_len.array_len_reborrow.NormalizeArrayLen.diff
+pub fn array_len_reborrow<const N: usize>(mut arr: [u8; N]) -> usize {
+    let arr: &mut [_] = &mut arr;
+    let arr = &*arr;
+    arr.len()
+}
+
+// EMIT_MIR lower_array_len.array_len_raw.NormalizeArrayLen.diff
+pub fn array_len_raw<const N: usize>(arr: [u8; N]) -> usize {
+    let arr: &[_] = &arr;
+    let arr = std::ptr::addr_of!(*arr);
+    unsafe { &*arr }.len()
+}
+
 fn main() {
     let _ = array_bound(3, &[0, 1, 2, 3]);
     let mut tmp = [0, 1, 2, 3, 4];
     let _ = array_bound_mut(3, &mut [0, 1, 2, 3]);
     let _ = array_len(&[0]);
     let _ = array_len_by_value([0, 2]);
+    let _ = array_len_reborrow([0, 2]);
+    let _ = array_len_raw([0, 2]);
 }

tests/ui/parser/bastion-of-the-turbofish.rs

@@ -34,7 +34,7 @@
 
 // See https://github.com/rust-lang/rust/pull/53562
 // and https://github.com/rust-lang/rfcs/pull/2527
-// and https://twitter.com/garblefart/status/1393236602856611843
+// and https://web.archive.org/web/20211010063452/https://twitter.com/garblefart/status/1393236602856611843
 // for context.
 
 fn main() {