Merge from rustc

21 files changed, 474 insertions, 76 deletions

diff --git a/compiler/rustc_mir_transform/src/check_alignment.rs b/compiler/rustc_mir_transform/src/check_alignment.rs
new file mode 100644
index 00000000000..5815887e5bb
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/check_alignment.rs
@@ -0,0 +1,227 @@
+use crate::MirPass;
+use rustc_hir::def_id::DefId;
+use rustc_index::vec::IndexVec;
+use rustc_middle::mir::*;
+use rustc_middle::mir::{
+    interpret::{ConstValue, Scalar},
+    visit::{PlaceContext, Visitor},
+};
+use rustc_middle::ty::{Ty, TyCtxt, TypeAndMut};
+use rustc_session::Session;
+
+pub struct CheckAlignment;
+
+impl<'tcx> MirPass<'tcx> for CheckAlignment {
+    fn is_enabled(&self, sess: &Session) -> bool {
+        sess.opts.debug_assertions
+    }
+
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        let basic_blocks = body.basic_blocks.as_mut();
+        let local_decls = &mut body.local_decls;
+
+        for block in (0..basic_blocks.len()).rev() {
+            let block = block.into();
+            for statement_index in (0..basic_blocks[block].statements.len()).rev() {
+                let location = Location { block, statement_index };
+                let statement = &basic_blocks[block].statements[statement_index];
+                let source_info = statement.source_info;
+
+                let mut finder = PointerFinder {
+                    local_decls,
+                    tcx,
+                    pointers: Vec::new(),
+                    def_id: body.source.def_id(),
+                };
+                for (pointer, pointee_ty) in finder.find_pointers(statement) {
+                    debug!("Inserting alignment check for {:?}", pointer.ty(&*local_decls, tcx).ty);
+
+                    let new_block = split_block(basic_blocks, location);
+                    insert_alignment_check(
+                        tcx,
+                        local_decls,
+                        &mut basic_blocks[block],
+                        pointer,
+                        pointee_ty,
+                        source_info,
+                        new_block,
+                    );
+                }
+            }
+        }
+    }
+}
+
+impl<'tcx, 'a> PointerFinder<'tcx, 'a> {
+    fn find_pointers(&mut self, statement: &Statement<'tcx>) -> Vec<(Place<'tcx>, Ty<'tcx>)> {
+        self.pointers.clear();
+        self.visit_statement(statement, Location::START);
+        core::mem::take(&mut self.pointers)
+    }
+}
+
+struct PointerFinder<'tcx, 'a> {
+    local_decls: &'a mut LocalDecls<'tcx>,
+    tcx: TyCtxt<'tcx>,
+    def_id: DefId,
+    pointers: Vec<(Place<'tcx>, Ty<'tcx>)>,
+}
+
+impl<'tcx, 'a> Visitor<'tcx> for PointerFinder<'tcx, 'a> {
+    fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
+        if let PlaceContext::NonUse(_) = context {
+            return;
+        }
+        if !place.is_indirect() {
+            return;
+        }
+
+        let pointer = Place::from(place.local);
+        let pointer_ty = pointer.ty(&*self.local_decls, self.tcx).ty;
+
+        // We only want to check unsafe pointers
+        if !pointer_ty.is_unsafe_ptr() {
+            trace!("Indirect, but not an unsafe ptr, not checking {:?}", pointer_ty);
+            return;
+        }
+
+        let Some(pointee) = pointer_ty.builtin_deref(true) else {
+            debug!("Indirect but no builtin deref: {:?}", pointer_ty);
+            return;
+        };
+        let mut pointee_ty = pointee.ty;
+        if pointee_ty.is_array() || pointee_ty.is_slice() || pointee_ty.is_str() {
+            pointee_ty = pointee_ty.sequence_element_type(self.tcx);
+        }
+
+        if !pointee_ty.is_sized(self.tcx, self.tcx.param_env_reveal_all_normalized(self.def_id)) {
+            debug!("Unsafe pointer, but unsized: {:?}", pointer_ty);
+            return;
+        }
+
+        if [self.tcx.types.bool, self.tcx.types.i8, self.tcx.types.u8, self.tcx.types.str_]
+            .contains(&pointee_ty)
+        {
+            debug!("Trivially aligned pointee type: {:?}", pointer_ty);
+            return;
+        }
+
+        self.pointers.push((pointer, pointee_ty))
+    }
+}
+
+fn split_block(
+    basic_blocks: &mut IndexVec<BasicBlock, BasicBlockData<'_>>,
+    location: Location,
+) -> BasicBlock {
+    let block_data = &mut basic_blocks[location.block];
+
+    // Drain every statement after this one and move the current terminator to a new basic block
+    let new_block = BasicBlockData {
+        statements: block_data.statements.split_off(location.statement_index),
+        terminator: block_data.terminator.take(),
+        is_cleanup: block_data.is_cleanup,
+    };
+
+    basic_blocks.push(new_block)
+}
+
+fn insert_alignment_check<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
+    block_data: &mut BasicBlockData<'tcx>,
+    pointer: Place<'tcx>,
+    pointee_ty: Ty<'tcx>,
+    source_info: SourceInfo,
+    new_block: BasicBlock,
+) {
+    // Cast the pointer to a *const ()
+    let const_raw_ptr = tcx.mk_ptr(TypeAndMut { ty: tcx.types.unit, mutbl: Mutability::Not });
+    let rvalue = Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(pointer), const_raw_ptr);
+    let thin_ptr = local_decls.push(LocalDecl::with_source_info(const_raw_ptr, source_info)).into();
+    block_data
+        .statements
+        .push(Statement { source_info, kind: StatementKind::Assign(Box::new((thin_ptr, rvalue))) });
+
+    // Transmute the pointer to a usize (equivalent to `ptr.addr()`)
+    let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Copy(thin_ptr), tcx.types.usize);
+    let addr = local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
+    block_data
+        .statements
+        .push(Statement { source_info, kind: StatementKind::Assign(Box::new((addr, rvalue))) });
+
+    // Get the alignment of the pointee
+    let alignment =
+        local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
+    let rvalue = Rvalue::NullaryOp(NullOp::AlignOf, pointee_ty);
+    block_data.statements.push(Statement {
+        source_info,
+        kind: StatementKind::Assign(Box::new((alignment, rvalue))),
+    });
+
+    // Subtract 1 from the alignment to get the alignment mask
+    let alignment_mask =
+        local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
+    let one = Operand::Constant(Box::new(Constant {
+        span: source_info.span,
+        user_ty: None,
+        literal: ConstantKind::Val(
+            ConstValue::Scalar(Scalar::from_target_usize(1, &tcx)),
+            tcx.types.usize,
+        ),
+    }));
+    block_data.statements.push(Statement {
+        source_info,
+        kind: StatementKind::Assign(Box::new((
+            alignment_mask,
+            Rvalue::BinaryOp(BinOp::Sub, Box::new((Operand::Copy(alignment), one))),
+        ))),
+    });
+
+    // BitAnd the alignment mask with the pointer
+    let alignment_bits =
+        local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
+    block_data.statements.push(Statement {
+        source_info,
+        kind: StatementKind::Assign(Box::new((
+            alignment_bits,
+            Rvalue::BinaryOp(
+                BinOp::BitAnd,
+                Box::new((Operand::Copy(addr), Operand::Copy(alignment_mask))),
+            ),
+        ))),
+    });
+
+    // Check if the alignment bits are all zero
+    let is_ok = local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
+    let zero = Operand::Constant(Box::new(Constant {
+        span: source_info.span,
+        user_ty: None,
+        literal: ConstantKind::Val(
+            ConstValue::Scalar(Scalar::from_target_usize(0, &tcx)),
+            tcx.types.usize,
+        ),
+    }));
+    block_data.statements.push(Statement {
+        source_info,
+        kind: StatementKind::Assign(Box::new((
+            is_ok,
+            Rvalue::BinaryOp(BinOp::Eq, Box::new((Operand::Copy(alignment_bits), zero.clone()))),
+        ))),
+    });
+
+    // Set this block's terminator to our assert, continuing to new_block if we pass
+    block_data.terminator = Some(Terminator {
+        source_info,
+        kind: TerminatorKind::Assert {
+            cond: Operand::Copy(is_ok),
+            expected: true,
+            target: new_block,
+            msg: AssertKind::MisalignedPointerDereference {
+                required: Operand::Copy(alignment),
+                found: Operand::Copy(addr),
+            },
+            cleanup: None,
+        },
+    });
+}
diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
index c1cf6ee0f9e..ac55948e61b 100644
--- a/compiler/rustc_mir_transform/src/const_prop.rs
+++ b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -7,7 +7,7 @@ use rustc_const_eval::const_eval::CheckAlignment;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def::DefKind;
 use rustc_index::bit_set::BitSet;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::mir::visit::{
     MutVisitor, MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor,
 };
@@ -117,7 +117,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
             .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
         if traits::impossible_predicates(
             tcx,
-            traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),
+            traits::elaborate_predicates(tcx, predicates).collect(),
         ) {
             trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", def_id);
             return;
@@ -127,7 +127,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
 
         let dummy_body = &Body::new(
             body.source,
-            (*body.basic_blocks).clone(),
+            (*body.basic_blocks).to_owned(),
             body.source_scopes.clone(),
             body.local_decls.clone(),
             Default::default(),
@@ -319,7 +319,7 @@ struct ConstPropagator<'mir, 'tcx> {
     ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
-    local_decls: &'mir IndexVec<Local, LocalDecl<'tcx>>,
+    local_decls: &'mir IndexSlice<Local, LocalDecl<'tcx>>,
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'_, 'tcx> {
diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs
index 45bd98f39d2..d7696a57000 100644
--- a/compiler/rustc_mir_transform/src/const_prop_lint.rs
+++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs
@@ -9,7 +9,7 @@ use rustc_const_eval::interpret::{
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::HirId;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
@@ -93,7 +93,7 @@ impl<'tcx> MirLint<'tcx> for ConstProp {
             .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
         if traits::impossible_predicates(
             tcx,
-            traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),
+            traits::elaborate_predicates(tcx, predicates).collect(),
         ) {
             trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", def_id);
             return;
@@ -103,7 +103,7 @@ impl<'tcx> MirLint<'tcx> for ConstProp {
 
         let dummy_body = &Body::new(
             body.source,
-            (*body.basic_blocks).clone(),
+            (*body.basic_blocks).to_owned(),
             body.source_scopes.clone(),
             body.local_decls.clone(),
             Default::default(),
@@ -130,8 +130,8 @@ struct ConstPropagator<'mir, 'tcx> {
     ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
-    source_scopes: &'mir IndexVec<SourceScope, SourceScopeData<'tcx>>,
-    local_decls: &'mir IndexVec<Local, LocalDecl<'tcx>>,
+    source_scopes: &'mir IndexSlice<SourceScope, SourceScopeData<'tcx>>,
+    local_decls: &'mir IndexSlice<Local, LocalDecl<'tcx>>,
     // Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
     // the last known `SourceInfo` here and just keep revisiting it.
     source_info: Option<SourceInfo>,
diff --git a/compiler/rustc_mir_transform/src/copy_prop.rs b/compiler/rustc_mir_transform/src/copy_prop.rs
index f27beb64a14..c155048c98b 100644
--- a/compiler/rustc_mir_transform/src/copy_prop.rs
+++ b/compiler/rustc_mir_transform/src/copy_prop.rs
@@ -1,5 +1,5 @@
 use rustc_index::bit_set::BitSet;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
@@ -102,7 +102,7 @@ struct Replacer<'a, 'tcx> {
     fully_moved: BitSet<Local>,
     storage_to_remove: BitSet<Local>,
     borrowed_locals: BitSet<Local>,
-    copy_classes: &'a IndexVec<Local, Local>,
+    copy_classes: &'a IndexSlice<Local, Local>,
 }
 
 impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index 49028ca4e5e..689d6c71361 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -5,7 +5,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph::dominators::{self, Dominators};
 use rustc_data_structures::graph::{self, GraphSuccessors, WithNumNodes, WithStartNode};
 use rustc_index::bit_set::BitSet;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::mir::coverage::*;
 use rustc_middle::mir::{self, BasicBlock, BasicBlockData, Terminator, TerminatorKind};
 
@@ -176,10 +176,10 @@ impl CoverageGraph {
 
     fn add_basic_coverage_block(
         bcbs: &mut IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
-        bb_to_bcb: &mut IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
+        bb_to_bcb: &mut IndexSlice<BasicBlock, Option<BasicCoverageBlock>>,
         basic_blocks: Vec<BasicBlock>,
     ) {
-        let bcb = BasicCoverageBlock::from_usize(bcbs.len());
+        let bcb = bcbs.next_index();
         for &bb in basic_blocks.iter() {
             bb_to_bcb[bb] = Some(bcb);
         }
diff --git a/compiler/rustc_mir_transform/src/coverage/tests.rs b/compiler/rustc_mir_transform/src/coverage/tests.rs
index aded8039dc3..59b506e7345 100644
--- a/compiler/rustc_mir_transform/src/coverage/tests.rs
+++ b/compiler/rustc_mir_transform/src/coverage/tests.rs
@@ -65,7 +65,7 @@ impl<'tcx> MockBlocks<'tcx> {
     }
 
     fn push(&mut self, kind: TerminatorKind<'tcx>) -> BasicBlock {
-        let next_lo = if let Some(last) = self.blocks.last() {
+        let next_lo = if let Some(last) = self.blocks.last_index() {
             self.blocks[last].terminator().source_info.span.hi()
         } else {
             BytePos(1)
diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
index a7218a4f250..15f5df41153 100644
--- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
+++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -13,8 +13,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_mir_dataflow::value_analysis::{Map, State, TrackElem, ValueAnalysis, ValueOrPlace};
 use rustc_mir_dataflow::{lattice::FlatSet, Analysis, ResultsVisitor, SwitchIntEdgeEffects};
 use rustc_span::DUMMY_SP;
-use rustc_target::abi::Align;
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::{Align, FieldIdx, VariantIdx};
 
 use crate::MirPass;
 
@@ -148,7 +147,7 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
                         for (field_index, operand) in operands.iter().enumerate() {
                             if let Some(field) = self.map().apply(
                                 variant_target_idx,
-                                TrackElem::Field(Field::from_usize(field_index)),
+                                TrackElem::Field(FieldIdx::from_usize(field_index)),
                             ) {
                                 let result = self.handle_operand(operand, state);
                                 state.insert_idx(field, result, self.map());
diff --git a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
index 954bb5aff8d..85623499439 100644
--- a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
@@ -9,6 +9,7 @@ use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{Ty, TyCtxt};
+use rustc_target::abi::FieldIdx;
 
 /// Constructs the types used when accessing a Box's pointer
 pub fn build_ptr_tys<'tcx>(
@@ -32,9 +33,9 @@ pub fn build_projection<'tcx>(
     ptr_ty: Ty<'tcx>,
 ) -> [PlaceElem<'tcx>; 3] {
     [
-        PlaceElem::Field(Field::new(0), unique_ty),
-        PlaceElem::Field(Field::new(0), nonnull_ty),
-        PlaceElem::Field(Field::new(0), ptr_ty),
+        PlaceElem::Field(FieldIdx::new(0), unique_ty),
+        PlaceElem::Field(FieldIdx::new(0), nonnull_ty),
+        PlaceElem::Field(FieldIdx::new(0), ptr_ty),
     ]
 }
 
@@ -91,13 +92,14 @@ pub struct ElaborateBoxDerefs;
 impl<'tcx> MirPass<'tcx> for ElaborateBoxDerefs {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         if let Some(def_id) = tcx.lang_items().owned_box() {
-            let unique_did = tcx.adt_def(def_id).non_enum_variant().fields[0].did;
+            let unique_did =
+                tcx.adt_def(def_id).non_enum_variant().fields[FieldIdx::from_u32(0)].did;
 
             let Some(nonnull_def) = tcx.type_of(unique_did).subst_identity().ty_adt_def() else {
                 span_bug!(tcx.def_span(unique_did), "expected Box to contain Unique")
             };
 
-            let nonnull_did = nonnull_def.non_enum_variant().fields[0].did;
+            let nonnull_did = nonnull_def.non_enum_variant().fields[FieldIdx::from_u32(0)].did;
 
             let patch = MirPatch::new(body);
 
diff --git a/compiler/rustc_mir_transform/src/elaborate_drops.rs b/compiler/rustc_mir_transform/src/elaborate_drops.rs
index 3faccca823a..a028d6356d5 100644
--- a/compiler/rustc_mir_transform/src/elaborate_drops.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_drops.rs
@@ -15,7 +15,7 @@ use rustc_mir_dataflow::MoveDataParamEnv;
 use rustc_mir_dataflow::{on_all_children_bits, on_all_drop_children_bits};
 use rustc_mir_dataflow::{Analysis, ResultsCursor};
 use rustc_span::{DesugaringKind, Span};
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::{FieldIdx, VariantIdx};
 use std::fmt;
 
 /// During MIR building, Drop terminators are inserted in every place where a drop may occur.
@@ -252,7 +252,7 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, '_, 'tcx> {
         }
     }
 
-    fn field_subpath(&self, path: Self::Path, field: Field) -> Option<Self::Path> {
+    fn field_subpath(&self, path: Self::Path, field: FieldIdx) -> Option<Self::Path> {
         rustc_mir_dataflow::move_path_children_matching(self.ctxt.move_data(), path, |e| match e {
             ProjectionElem::Field(idx, _) => idx == field,
             _ => false,
diff --git a/compiler/rustc_mir_transform/src/generator.rs b/compiler/rustc_mir_transform/src/generator.rs
index 8a6360114dc..af6422c7246 100644
--- a/compiler/rustc_mir_transform/src/generator.rs
+++ b/compiler/rustc_mir_transform/src/generator.rs
@@ -73,7 +73,7 @@ use rustc_mir_dataflow::{self, Analysis};
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::{FieldIdx, VariantIdx};
 use rustc_target::spec::PanicStrategy;
 use std::{iter, ops};
 
@@ -162,9 +162,10 @@ impl<'tcx> MutVisitor<'tcx> for PinArgVisitor<'tcx> {
                 place,
                 Place {
                     local: SELF_ARG,
-                    projection: self
-                        .tcx()
-                        .mk_place_elems(&[ProjectionElem::Field(Field::new(0), self.ref_gen_ty)]),
+                    projection: self.tcx().mk_place_elems(&[ProjectionElem::Field(
+                        FieldIdx::new(0),
+                        self.ref_gen_ty,
+                    )]),
                 },
                 self.tcx,
             );
@@ -273,7 +274,7 @@ impl<'tcx> TransformVisitor<'tcx> {
             statements.push(Statement {
                 kind: StatementKind::Assign(Box::new((
                     Place::return_place(),
-                    Rvalue::Aggregate(Box::new(kind), vec![]),
+                    Rvalue::Aggregate(Box::new(kind), IndexVec::new()),
                 ))),
                 source_info,
             });
@@ -286,7 +287,7 @@ impl<'tcx> TransformVisitor<'tcx> {
         statements.push(Statement {
             kind: StatementKind::Assign(Box::new((
                 Place::return_place(),
-                Rvalue::Aggregate(Box::new(kind), vec![val]),
+                Rvalue::Aggregate(Box::new(kind), IndexVec::from_iter([val])),
             ))),
             source_info,
         });
@@ -297,7 +298,7 @@ impl<'tcx> TransformVisitor<'tcx> {
         let self_place = Place::from(SELF_ARG);
         let base = self.tcx.mk_place_downcast_unnamed(self_place, variant_index);
         let mut projection = base.projection.to_vec();
-        projection.push(ProjectionElem::Field(Field::new(idx), ty));
+        projection.push(ProjectionElem::Field(FieldIdx::new(idx), ty));
 
         Place { local: base.local, projection: self.tcx.mk_place_elems(&projection) }
     }
@@ -967,7 +968,7 @@ fn compute_layout<'tcx>(
 
     // Build the generator variant field list.
     // Create a map from local indices to generator struct indices.
-    let mut variant_fields: IndexVec<VariantIdx, IndexVec<Field, GeneratorSavedLocal>> =
+    let mut variant_fields: IndexVec<VariantIdx, IndexVec<FieldIdx, GeneratorSavedLocal>> =
         iter::repeat(IndexVec::new()).take(RESERVED_VARIANTS).collect();
     let mut remap = FxHashMap::default();
     for (suspension_point_idx, live_locals) in live_locals_at_suspension_points.iter().enumerate() {
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index 9cba8870f23..15b31d38394 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -10,7 +10,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
 use rustc_session::config::OptLevel;
 use rustc_span::{hygiene::ExpnKind, ExpnData, LocalExpnId, Span};
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::{FieldIdx, FIRST_VARIANT};
 use rustc_target::spec::abi::Abi;
 
 use crate::simplify::{remove_dead_blocks, CfgSimplifier};
@@ -270,7 +270,9 @@ impl<'tcx> Inliner<'tcx> {
             | InstanceDef::FnPtrShim(..)
             | InstanceDef::ClosureOnceShim { .. }
             | InstanceDef::DropGlue(..)
-            | InstanceDef::CloneShim(..) => return Ok(()),
+            | InstanceDef::CloneShim(..)
+            | InstanceDef::ThreadLocalShim(..)
+            | InstanceDef::FnPtrAddrShim(..) => return Ok(()),
         }
 
         if self.tcx.is_constructor(callee_def_id) {
@@ -424,13 +426,6 @@ impl<'tcx> Inliner<'tcx> {
         debug!("    final inline threshold = {}", threshold);
 
         // FIXME: Give a bonus to functions with only a single caller
-        let diverges = matches!(
-            callee_body.basic_blocks[START_BLOCK].terminator().kind,
-            TerminatorKind::Unreachable | TerminatorKind::Call { target: None, .. }
-        );
-        if diverges && !matches!(callee_attrs.inline, InlineAttr::Always) {
-            return Err("callee diverges unconditionally");
-        }
 
         let mut checker = CostChecker {
             tcx: self.tcx,
@@ -706,7 +701,7 @@ impl<'tcx> Inliner<'tcx> {
             // The `tmp0`, `tmp1`, and `tmp2` in our example above.
             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
                 // This is e.g., `tuple_tmp.0` in our example above.
-                let tuple_field = Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty));
+                let tuple_field = Operand::Move(tcx.mk_place_field(tuple, FieldIdx::new(i), ty));
 
                 // Spill to a local to make e.g., `tmp0`.
                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
@@ -911,8 +906,8 @@ impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
                     check_equal(self, *f_ty);
                 }
                 ty::Adt(adt_def, substs) => {
-                    let var = parent_ty.variant_index.unwrap_or(VariantIdx::from_u32(0));
-                    let Some(field) = adt_def.variant(var).fields.get(f.as_usize()) else {
+                    let var = parent_ty.variant_index.unwrap_or(FIRST_VARIANT);
+                    let Some(field) = adt_def.variant(var).fields.get(f) else {
                         self.validation = Err("malformed MIR");
                         return;
                     };
diff --git a/compiler/rustc_mir_transform/src/inline/cycle.rs b/compiler/rustc_mir_transform/src/inline/cycle.rs
index 792457c80b0..8aa3c23d019 100644
--- a/compiler/rustc_mir_transform/src/inline/cycle.rs
+++ b/compiler/rustc_mir_transform/src/inline/cycle.rs
@@ -83,7 +83,11 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
                 | InstanceDef::ReifyShim(_)
                 | InstanceDef::FnPtrShim(..)
                 | InstanceDef::ClosureOnceShim { .. }
+                | InstanceDef::ThreadLocalShim { .. }
                 | InstanceDef::CloneShim(..) => {}
+
+                // This shim does not call any other functions, thus there can be no recursion.
+                InstanceDef::FnPtrAddrShim(..) => continue,
                 InstanceDef::DropGlue(..) => {
                     // FIXME: A not fully substituted drop shim can cause ICEs if one attempts to
                     // have its MIR built. Likely oli-obk just screwed up the `ParamEnv`s, so this
diff --git a/compiler/rustc_mir_transform/src/instcombine.rs b/compiler/rustc_mir_transform/src/instcombine.rs
index 4182da1957e..3d06a0a495f 100644
--- a/compiler/rustc_mir_transform/src/instcombine.rs
+++ b/compiler/rustc_mir_transform/src/instcombine.rs
@@ -3,12 +3,14 @@
 use crate::MirPass;
 use rustc_hir::Mutability;
 use rustc_middle::mir::{
-    BinOp, Body, Constant, ConstantKind, LocalDecls, Operand, Place, ProjectionElem, Rvalue,
-    SourceInfo, Statement, StatementKind, Terminator, TerminatorKind, UnOp,
+    BinOp, Body, CastKind, Constant, ConstantKind, LocalDecls, Operand, Place, ProjectionElem,
+    Rvalue, SourceInfo, Statement, StatementKind, SwitchTargets, Terminator, TerminatorKind, UnOp,
 };
 use rustc_middle::ty::layout::ValidityRequirement;
+use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, ParamEnv, SubstsRef, Ty, TyCtxt};
 use rustc_span::symbol::Symbol;
+use rustc_target::abi::FieldIdx;
 
 pub struct InstCombine;
 
@@ -44,6 +46,7 @@ impl<'tcx> MirPass<'tcx> for InstCombine {
                 &mut block.terminator.as_mut().unwrap(),
                 &mut block.statements,
             );
+            ctx.combine_duplicate_switch_targets(&mut block.terminator.as_mut().unwrap());
         }
     }
 }
@@ -144,9 +147,53 @@ impl<'tcx> InstCombineContext<'tcx, '_> {
     }
 
     fn combine_cast(&self, _source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
-        if let Rvalue::Cast(_kind, operand, ty) = rvalue {
-            if operand.ty(self.local_decls, self.tcx) == *ty {
+        if let Rvalue::Cast(kind, operand, cast_ty) = rvalue {
+            let operand_ty = operand.ty(self.local_decls, self.tcx);
+            if operand_ty == *cast_ty {
                 *rvalue = Rvalue::Use(operand.clone());
+            } else if *kind == CastKind::Transmute {
+                // Transmuting an integer to another integer is just a signedness cast
+                if let (ty::Int(int), ty::Uint(uint)) | (ty::Uint(uint), ty::Int(int)) = (operand_ty.kind(), cast_ty.kind())
+                    && int.bit_width() == uint.bit_width()
+                {
+                    // The width check isn't strictly necessary, as different widths
+                    // are UB and thus we'd be allowed to turn it into a cast anyway.
+                    // But let's keep the UB around for codegen to exploit later.
+                    // (If `CastKind::Transmute` ever becomes *not* UB for mismatched sizes,
+                    // then the width check is necessary for big-endian correctness.)
+                    *kind = CastKind::IntToInt;
+                    return;
+                }
+
+                // Transmuting a fieldless enum to its repr is a discriminant read
+                if let ty::Adt(adt_def, ..) = operand_ty.kind()
+                    && adt_def.is_enum()
+                    && adt_def.is_payloadfree()
+                    && let Some(place) = operand.place()
+                    && let Some(repr_int) = adt_def.repr().int
+                    && repr_int.to_ty(self.tcx) == *cast_ty
+                {
+                    *rvalue = Rvalue::Discriminant(place);
+                    return;
+                }
+
+                // Transmuting a transparent struct/union to a field's type is a projection
+                if let ty::Adt(adt_def, substs) = operand_ty.kind()
+                    && adt_def.repr().transparent()
+                    && (adt_def.is_struct() || adt_def.is_union())
+                    && let Some(place) = operand.place()
+                {
+                    let variant = adt_def.non_enum_variant();
+                    for (i, field) in variant.fields.iter().enumerate() {
+                        let field_ty = field.ty(self.tcx, substs);
+                        if field_ty == *cast_ty {
+                            let place = place.project_deeper(&[ProjectionElem::Field(FieldIdx::from_usize(i), *cast_ty)], self.tcx);
+                            let operand = if operand.is_move() { Operand::Move(place) } else { Operand::Copy(place) };
+                            *rvalue = Rvalue::Use(operand);
+                            return;
+                        }
+                    }
+                }
             }
         }
     }
@@ -217,6 +264,19 @@ impl<'tcx> InstCombineContext<'tcx, '_> {
         terminator.kind = TerminatorKind::Goto { target: destination_block };
     }
 
+    fn combine_duplicate_switch_targets(&self, terminator: &mut Terminator<'tcx>) {
+        let TerminatorKind::SwitchInt { targets, .. } = &mut terminator.kind
+        else { return };
+
+        let otherwise = targets.otherwise();
+        if targets.iter().any(|t| t.1 == otherwise) {
+            *targets = SwitchTargets::new(
+                targets.iter().filter(|t| t.1 != otherwise),
+                targets.otherwise(),
+            );
+        }
+    }
+
     fn combine_intrinsic_assert(
         &self,
         terminator: &mut Terminator<'tcx>,
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 3a515fe8323..b52de4b72c9 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -5,7 +5,6 @@
 #![feature(map_try_insert)]
 #![feature(min_specialization)]
 #![feature(never_type)]
-#![feature(once_cell)]
 #![feature(option_get_or_insert_default)]
 #![feature(trusted_step)]
 #![feature(try_blocks)]
@@ -91,6 +90,7 @@ mod separate_const_switch;
 mod shim;
 mod ssa;
 // This pass is public to allow external drivers to perform MIR cleanup
+mod check_alignment;
 pub mod simplify;
 mod simplify_branches;
 mod simplify_comparison_integral;
@@ -546,6 +546,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         tcx,
         body,
         &[
+            &check_alignment::CheckAlignment,
             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
             &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
             &unreachable_prop::UnreachablePropagation,
diff --git a/compiler/rustc_mir_transform/src/lower_intrinsics.rs b/compiler/rustc_mir_transform/src/lower_intrinsics.rs
index 6a7ceb8fef7..c136642dff2 100644
--- a/compiler/rustc_mir_transform/src/lower_intrinsics.rs
+++ b/compiler/rustc_mir_transform/src/lower_intrinsics.rs
@@ -6,7 +6,7 @@ use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::{FieldIdx, VariantIdx};
 
 pub struct LowerIntrinsics;
 
@@ -211,7 +211,7 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                                                     Some(sym::Some),
                                                     VariantIdx::from_u32(1),
                                                 ),
-                                                PlaceElem::Field(Field::from_u32(0), *dest_ty),
+                                                PlaceElem::Field(FieldIdx::from_u32(0), *dest_ty),
                                             ],
                                             tcx,
                                         ),
diff --git a/compiler/rustc_mir_transform/src/lower_slice_len.rs b/compiler/rustc_mir_transform/src/lower_slice_len.rs
index c6e7468aab4..101fae2f08c 100644
--- a/compiler/rustc_mir_transform/src/lower_slice_len.rs
+++ b/compiler/rustc_mir_transform/src/lower_slice_len.rs
@@ -3,7 +3,7 @@
 
 use crate::MirPass;
 use rustc_hir::def_id::DefId;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
 
@@ -42,7 +42,7 @@ struct SliceLenPatchInformation<'tcx> {
 fn lower_slice_len_call<'tcx>(
     tcx: TyCtxt<'tcx>,
     block: &mut BasicBlockData<'tcx>,
-    local_decls: &IndexVec<Local, LocalDecl<'tcx>>,
+    local_decls: &IndexSlice<Local, LocalDecl<'tcx>>,
     slice_len_fn_item_def_id: DefId,
 ) {
     let mut patch_found: Option<SliceLenPatchInformation<'_>> = None;
diff --git a/compiler/rustc_mir_transform/src/remove_uninit_drops.rs b/compiler/rustc_mir_transform/src/remove_uninit_drops.rs
index e72729b152e..1f9e521d315 100644
--- a/compiler/rustc_mir_transform/src/remove_uninit_drops.rs
+++ b/compiler/rustc_mir_transform/src/remove_uninit_drops.rs
@@ -1,10 +1,11 @@
 use rustc_index::bit_set::ChunkedBitSet;
-use rustc_middle::mir::{Body, Field, TerminatorKind};
+use rustc_middle::mir::{Body, TerminatorKind};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, VariantDef};
 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::{LookupResult, MoveData, MovePathIndex};
 use rustc_mir_dataflow::{self, move_path_children_matching, Analysis, MoveDataParamEnv};
+use rustc_target::abi::FieldIdx;
 
 use crate::MirPass;
 
@@ -130,7 +131,7 @@ fn is_needs_drop_and_init<'tcx>(
                     .fields
                     .iter()
                     .enumerate()
-                    .map(|(f, field)| (Field::from_usize(f), field.ty(tcx, substs), mpi))
+                    .map(|(f, field)| (FieldIdx::from_usize(f), field.ty(tcx, substs), mpi))
                     .any(field_needs_drop_and_init)
             })
         }
@@ -138,7 +139,7 @@ fn is_needs_drop_and_init<'tcx>(
         ty::Tuple(fields) => fields
             .iter()
             .enumerate()
-            .map(|(f, f_ty)| (Field::from_usize(f), f_ty, mpi))
+            .map(|(f, f_ty)| (FieldIdx::from_usize(f), f_ty, mpi))
             .any(field_needs_drop_and_init),
 
         _ => true,
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index ebe63d6cb7e..9e406eba0fc 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -5,7 +5,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::InternalSubsts;
 use rustc_middle::ty::{self, EarlyBinder, GeneratorSubsts, Ty, TyCtxt};
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::{FieldIdx, VariantIdx, FIRST_VARIANT};
 
 use rustc_index::vec::{Idx, IndexVec};
 
@@ -76,7 +76,9 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
 
             build_drop_shim(tcx, def_id, ty)
         }
+        ty::InstanceDef::ThreadLocalShim(..) => build_thread_local_shim(tcx, instance),
         ty::InstanceDef::CloneShim(def_id, ty) => build_clone_shim(tcx, def_id, ty),
+        ty::InstanceDef::FnPtrAddrShim(def_id, ty) => build_fn_ptr_addr_shim(tcx, def_id, ty),
         ty::InstanceDef::Virtual(..) => {
             bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
         }
@@ -307,7 +309,7 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
 
     fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {}
 
-    fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
+    fn field_subpath(&self, _path: Self::Path, _field: FieldIdx) -> Option<Self::Path> {
         None
     }
     fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
@@ -321,6 +323,34 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
     }
 }
 
+fn build_thread_local_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'tcx> {
+    let def_id = instance.def_id();
+
+    let span = tcx.def_span(def_id);
+    let source_info = SourceInfo::outermost(span);
+
+    let mut blocks = IndexVec::with_capacity(1);
+    blocks.push(BasicBlockData {
+        statements: vec![Statement {
+            source_info,
+            kind: StatementKind::Assign(Box::new((
+                Place::return_place(),
+                Rvalue::ThreadLocalRef(def_id),
+            ))),
+        }],
+        terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
+        is_cleanup: false,
+    });
+
+    new_body(
+        MirSource::from_instance(instance),
+        blocks,
+        IndexVec::from_raw(vec![LocalDecl::new(tcx.thread_local_ptr_ty(def_id), span)]),
+        0,
+        span,
+    )
+}
+
 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
     debug!("build_clone_shim(def_id={:?})", def_id);
@@ -500,7 +530,7 @@ impl<'tcx> CloneShimBuilder<'tcx> {
             // created by block 2*i. We store this block in `unwind` so that the next clone block
             // will unwind to it if cloning fails.
 
-            let field = Field::new(i);
+            let field = FieldIdx::new(i);
             let src_field = self.tcx.mk_place_field(src, field, ity);
 
             let dest_field = self.tcx.mk_place_field(dest, field, ity);
@@ -723,7 +753,7 @@ fn build_call_shim<'tcx>(
     if let Some(untuple_args) = untuple_args {
         let tuple_arg = Local::new(1 + (sig.inputs().len() - 1));
         args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
-            Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), Field::new(i), *ity))
+            Operand::Move(tcx.mk_place_field(Place::from(tuple_arg), FieldIdx::new(i), *ity))
         }));
     }
 
@@ -816,11 +846,8 @@ pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> Body<'_> {
 
     let source_info = SourceInfo::outermost(span);
 
-    let variant_index = if adt_def.is_enum() {
-        adt_def.variant_index_with_ctor_id(ctor_id)
-    } else {
-        VariantIdx::new(0)
-    };
+    let variant_index =
+        if adt_def.is_enum() { adt_def.variant_index_with_ctor_id(ctor_id) } else { FIRST_VARIANT };
 
     // Generate the following MIR:
     //
@@ -864,3 +891,39 @@ pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> Body<'_> {
 
     body
 }
+
+/// ```ignore (pseudo-impl)
+/// impl FnPtr for fn(u32) {
+///     fn addr(self) -> usize {
+///         self as usize
+///     }
+/// }
+/// ```
+fn build_fn_ptr_addr_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
+    assert!(matches!(self_ty.kind(), ty::FnPtr(..)), "expected fn ptr, found {self_ty}");
+    let span = tcx.def_span(def_id);
+    let Some(sig) = tcx.fn_sig(def_id).subst(tcx, &[self_ty.into()]).no_bound_vars() else {
+        span_bug!(span, "FnPtr::addr with bound vars for `{self_ty}`");
+    };
+    let locals = local_decls_for_sig(&sig, span);
+
+    let source_info = SourceInfo::outermost(span);
+    // FIXME: use `expose_addr` once we figure out whether function pointers have meaningful provenance.
+    let rvalue = Rvalue::Cast(
+        CastKind::FnPtrToPtr,
+        Operand::Move(Place::from(Local::new(1))),
+        tcx.mk_imm_ptr(tcx.types.unit),
+    );
+    let stmt = Statement {
+        source_info,
+        kind: StatementKind::Assign(Box::new((Place::return_place(), rvalue))),
+    };
+    let statements = vec![stmt];
+    let start_block = BasicBlockData {
+        statements,
+        terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
+        is_cleanup: false,
+    };
+    let source = MirSource::from_instance(ty::InstanceDef::FnPtrAddrShim(def_id, self_ty));
+    new_body(source, IndexVec::from_elem_n(start_block, 1), locals, sig.inputs().len(), span)
+}
diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs
index 929d229dcdf..c79e1cf0805 100644
--- a/compiler/rustc_mir_transform/src/simplify.rs
+++ b/compiler/rustc_mir_transform/src/simplify.rs
@@ -28,8 +28,8 @@
 //! return.
 
 use crate::MirPass;
-use rustc_data_structures::fx::FxHashSet;
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
+use rustc_index::vec::{Idx, IndexSlice, IndexVec};
 use rustc_middle::mir::coverage::*;
 use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
@@ -48,6 +48,7 @@ impl SimplifyCfg {
 
 pub fn simplify_cfg<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     CfgSimplifier::new(body).simplify();
+    remove_duplicate_unreachable_blocks(tcx, body);
     remove_dead_blocks(tcx, body);
 
     // FIXME: Should probably be moved into some kind of pass manager
@@ -66,7 +67,7 @@ impl<'tcx> MirPass<'tcx> for SimplifyCfg {
 }
 
 pub struct CfgSimplifier<'a, 'tcx> {
-    basic_blocks: &'a mut IndexVec<BasicBlock, BasicBlockData<'tcx>>,
+    basic_blocks: &'a mut IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
     pred_count: IndexVec<BasicBlock, u32>,
 }
 
@@ -259,6 +260,49 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
     }
 }
 
+pub fn remove_duplicate_unreachable_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    struct OptApplier<'tcx> {
+        tcx: TyCtxt<'tcx>,
+        duplicates: FxIndexSet<BasicBlock>,
+    }
+
+    impl<'tcx> MutVisitor<'tcx> for OptApplier<'tcx> {
+        fn tcx(&self) -> TyCtxt<'tcx> {
+            self.tcx
+        }
+
+        fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) {
+            for target in terminator.successors_mut() {
+                // We don't have to check whether `target` is a cleanup block, because have
+                // entirely excluded cleanup blocks in building the set of duplicates.
+                if self.duplicates.contains(target) {
+                    *target = self.duplicates[0];
+                }
+            }
+
+            self.super_terminator(terminator, location);
+        }
+    }
+
+    let unreachable_blocks = body
+        .basic_blocks
+        .iter_enumerated()
+        .filter(|(_, bb)| {
+            // CfgSimplifier::simplify leaves behind some unreachable basic blocks without a
+            // terminator. Those blocks will be deleted by remove_dead_blocks, but we run just
+            // before then so we need to handle missing terminators.
+            // We also need to prevent confusing cleanup and non-cleanup blocks. In practice we
+            // don't emit empty unreachable cleanup blocks, so this simple check suffices.
+            bb.terminator.is_some() && bb.is_empty_unreachable() && !bb.is_cleanup
+        })
+        .map(|(block, _)| block)
+        .collect::<FxIndexSet<_>>();
+
+    if unreachable_blocks.len() > 1 {
+        OptApplier { tcx, duplicates: unreachable_blocks }.visit_body(body);
+    }
+}
+
 pub fn remove_dead_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let reachable = traversal::reachable_as_bitset(body);
     let num_blocks = body.basic_blocks.len();
@@ -325,8 +369,8 @@ pub fn remove_dead_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 /// instances in a single body, so the strategy described above is applied to
 /// coverage counters from each instance individually.
 fn save_unreachable_coverage(
-    basic_blocks: &mut IndexVec<BasicBlock, BasicBlockData<'_>>,
-    source_scopes: &IndexVec<SourceScope, SourceScopeData<'_>>,
+    basic_blocks: &mut IndexSlice<BasicBlock, BasicBlockData<'_>>,
+    source_scopes: &IndexSlice<SourceScope, SourceScopeData<'_>>,
     first_dead_block: usize,
 ) {
     // Identify instances that still have some live coverage counters left.
@@ -445,7 +489,7 @@ fn make_local_map<V>(
     local_decls: &mut IndexVec<Local, V>,
     used_locals: &UsedLocals,
 ) -> IndexVec<Local, Option<Local>> {
-    let mut map: IndexVec<Local, Option<Local>> = IndexVec::from_elem(None, &*local_decls);
+    let mut map: IndexVec<Local, Option<Local>> = IndexVec::from_elem(None, local_decls);
     let mut used = Local::new(0);
 
     for alive_index in local_decls.indices() {
diff --git a/compiler/rustc_mir_transform/src/sroa.rs b/compiler/rustc_mir_transform/src/sroa.rs
index ca2221520c8..c798bd05345 100644
--- a/compiler/rustc_mir_transform/src/sroa.rs
+++ b/compiler/rustc_mir_transform/src/sroa.rs
@@ -6,6 +6,7 @@ use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_mir_dataflow::value_analysis::{excluded_locals, iter_fields};
+use rustc_target::abi::FieldIdx;
 
 pub struct ScalarReplacementOfAggregates;
 
@@ -115,7 +116,7 @@ fn escaping_locals(excluded: &BitSet<Local>, body: &Body<'_>) -> BitSet<Local> {
 struct ReplacementMap<'tcx> {
     /// Pre-computed list of all "new" locals for each "old" local. This is used to expand storage
     /// and deinit statement and debuginfo.
-    fragments: IndexVec<Local, Option<IndexVec<Field, Option<(Ty<'tcx>, Local)>>>>,
+    fragments: IndexVec<Local, Option<IndexVec<FieldIdx, Option<(Ty<'tcx>, Local)>>>>,
 }
 
 impl<'tcx> ReplacementMap<'tcx> {
@@ -129,7 +130,7 @@ impl<'tcx> ReplacementMap<'tcx> {
     fn place_fragments(
         &self,
         place: Place<'tcx>,
-    ) -> Option<impl Iterator<Item = (Field, Ty<'tcx>, Local)> + '_> {
+    ) -> Option<impl Iterator<Item = (FieldIdx, Ty<'tcx>, Local)> + '_> {
         let local = place.as_local()?;
         let fields = self.fragments[local].as_ref()?;
         Some(fields.iter_enumerated().filter_map(|(field, &opt_ty_local)| {
diff --git a/compiler/rustc_mir_transform/src/ssa.rs b/compiler/rustc_mir_transform/src/ssa.rs
index 73168652f8f..be026402dd5 100644
--- a/compiler/rustc_mir_transform/src/ssa.rs
+++ b/compiler/rustc_mir_transform/src/ssa.rs
@@ -1,7 +1,7 @@
 use either::Either;
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_index::bit_set::BitSet;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::middle::resolve_bound_vars::Set1;
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
@@ -135,7 +135,7 @@ impl SsaLocals {
     ///   _d => _a // transitively through _c
     ///
     /// Exception: we do not see through the return place, as it cannot be substituted.
-    pub fn copy_classes(&self) -> &IndexVec<Local, Local> {
+    pub fn copy_classes(&self) -> &IndexSlice<Local, Local> {
         &self.copy_classes
     }