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-rw-r--r--compiler/rustc_mir_transform/src/add_retag.rs3
-rw-r--r--compiler/rustc_mir_transform/src/coroutine.rs4
-rw-r--r--compiler/rustc_mir_transform/src/coroutine/by_move_body.rs6
-rw-r--r--compiler/rustc_mir_transform/src/coverage/counters.rs5
-rw-r--r--compiler/rustc_mir_transform/src/coverage/graph.rs89
-rw-r--r--compiler/rustc_mir_transform/src/coverage/query.rs2
-rw-r--r--compiler/rustc_mir_transform/src/coverage/spans.rs244
-rw-r--r--compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs192
-rw-r--r--compiler/rustc_mir_transform/src/coverage/tests.rs106
-rw-r--r--compiler/rustc_mir_transform/src/inline.rs65
-rw-r--r--compiler/rustc_mir_transform/src/inline/cycle.rs32
-rw-r--r--compiler/rustc_mir_transform/src/known_panics_lint.rs6
-rw-r--r--compiler/rustc_mir_transform/src/lib.rs2
-rw-r--r--compiler/rustc_mir_transform/src/promote_consts.rs2
-rw-r--r--compiler/rustc_mir_transform/src/required_consts.rs2
-rw-r--r--compiler/rustc_mir_transform/src/reveal_all.rs4
-rw-r--r--compiler/rustc_mir_transform/src/shim.rs55
-rw-r--r--compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs4
-rw-r--r--compiler/rustc_mir_transform/src/sroa.rs3
-rw-r--r--compiler/rustc_mir_transform/src/validate.rs9
20 files changed, 373 insertions, 462 deletions
diff --git a/compiler/rustc_mir_transform/src/add_retag.rs b/compiler/rustc_mir_transform/src/add_retag.rs
index f880476cec2..16977a63c59 100644
--- a/compiler/rustc_mir_transform/src/add_retag.rs
+++ b/compiler/rustc_mir_transform/src/add_retag.rs
@@ -4,6 +4,7 @@
 //! of MIR building, and only after this pass we think of the program has having the
 //! normal MIR semantics.
 
+use rustc_hir::LangItem;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 
@@ -27,7 +28,7 @@ fn may_contain_reference<'tcx>(ty: Ty<'tcx>, depth: u32, tcx: TyCtxt<'tcx>) -> b
         // References and Boxes (`noalias` sources)
         ty::Ref(..) => true,
         ty::Adt(..) if ty.is_box() => true,
-        ty::Adt(adt, _) if Some(adt.did()) == tcx.lang_items().ptr_unique() => true,
+        ty::Adt(adt, _) if tcx.is_lang_item(adt.did(), LangItem::PtrUnique) => true,
         // Compound types: recurse
         ty::Array(ty, _) | ty::Slice(ty) => {
             // This does not branch so we keep the depth the same.
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index 84512e81637..bf79b4e133a 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -68,7 +68,7 @@ use rustc_index::{Idx, IndexVec};
 use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::CoroutineArgs;
-use rustc_middle::ty::InstanceDef;
+use rustc_middle::ty::InstanceKind;
 use rustc_middle::ty::{self, CoroutineArgsExt, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_mir_dataflow::impls::{
@@ -1276,7 +1276,7 @@ fn create_coroutine_drop_shim<'tcx>(
     // Update the body's def to become the drop glue.
     let coroutine_instance = body.source.instance;
     let drop_in_place = tcx.require_lang_item(LangItem::DropInPlace, None);
-    let drop_instance = InstanceDef::DropGlue(drop_in_place, Some(coroutine_ty));
+    let drop_instance = InstanceKind::DropGlue(drop_in_place, Some(coroutine_ty));
 
     // Temporary change MirSource to coroutine's instance so that dump_mir produces more sensible
     // filename.
diff --git a/compiler/rustc_mir_transform/src/coroutine/by_move_body.rs b/compiler/rustc_mir_transform/src/coroutine/by_move_body.rs
index 10c0567eb4b..69d21a63f55 100644
--- a/compiler/rustc_mir_transform/src/coroutine/by_move_body.rs
+++ b/compiler/rustc_mir_transform/src/coroutine/by_move_body.rs
@@ -75,7 +75,7 @@ use rustc_middle::bug;
 use rustc_middle::hir::place::{Projection, ProjectionKind};
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::{self, dump_mir, MirPass};
-use rustc_middle::ty::{self, InstanceDef, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, InstanceKind, Ty, TyCtxt, TypeVisitableExt};
 use rustc_target::abi::{FieldIdx, VariantIdx};
 
 pub struct ByMoveBody;
@@ -102,7 +102,7 @@ impl<'tcx> MirPass<'tcx> for ByMoveBody {
 
         // We don't need to generate a by-move coroutine if the coroutine body was
         // produced by the `CoroutineKindShim`, since it's already by-move.
-        if matches!(body.source.instance, ty::InstanceDef::CoroutineKindShim { .. }) {
+        if matches!(body.source.instance, ty::InstanceKind::CoroutineKindShim { .. }) {
             return;
         }
 
@@ -193,7 +193,7 @@ impl<'tcx> MirPass<'tcx> for ByMoveBody {
         MakeByMoveBody { tcx, field_remapping, by_move_coroutine_ty }.visit_body(&mut by_move_body);
         dump_mir(tcx, false, "coroutine_by_move", &0, &by_move_body, |_, _| Ok(()));
         // FIXME: use query feeding to generate the body right here and then only store the `DefId` of the new body.
-        by_move_body.source = mir::MirSource::from_instance(InstanceDef::CoroutineKindShim {
+        by_move_body.source = mir::MirSource::from_instance(InstanceKind::CoroutineKindShim {
             coroutine_def_id: coroutine_def_id.to_def_id(),
         });
         body.coroutine.as_mut().unwrap().by_move_body = Some(by_move_body);
diff --git a/compiler/rustc_mir_transform/src/coverage/counters.rs b/compiler/rustc_mir_transform/src/coverage/counters.rs
index b5968517d77..a8b0f4a8d6d 100644
--- a/compiler/rustc_mir_transform/src/coverage/counters.rs
+++ b/compiler/rustc_mir_transform/src/coverage/counters.rs
@@ -168,11 +168,6 @@ impl CoverageCounters {
         self.counter_increment_sites.len()
     }
 
-    #[cfg(test)]
-    pub(super) fn num_expressions(&self) -> usize {
-        self.expressions.len()
-    }
-
     fn set_bcb_counter(&mut self, bcb: BasicCoverageBlock, counter_kind: BcbCounter) -> BcbCounter {
         if let Some(replaced) = self.bcb_counters[bcb].replace(counter_kind) {
             bug!(
diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index fd74a2a97e2..360dccb240d 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -14,16 +14,16 @@ use std::ops::{Index, IndexMut};
 /// A coverage-specific simplification of the MIR control flow graph (CFG). The `CoverageGraph`s
 /// nodes are `BasicCoverageBlock`s, which encompass one or more MIR `BasicBlock`s.
 #[derive(Debug)]
-pub(super) struct CoverageGraph {
+pub(crate) struct CoverageGraph {
     bcbs: IndexVec<BasicCoverageBlock, BasicCoverageBlockData>,
     bb_to_bcb: IndexVec<BasicBlock, Option<BasicCoverageBlock>>,
-    pub successors: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
-    pub predecessors: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
+    pub(crate) successors: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
+    pub(crate) predecessors: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
     dominators: Option<Dominators<BasicCoverageBlock>>,
 }
 
 impl CoverageGraph {
-    pub fn from_mir(mir_body: &mir::Body<'_>) -> Self {
+    pub(crate) fn from_mir(mir_body: &mir::Body<'_>) -> Self {
         let (bcbs, bb_to_bcb) = Self::compute_basic_coverage_blocks(mir_body);
 
         // Pre-transform MIR `BasicBlock` successors and predecessors into the BasicCoverageBlock
@@ -135,24 +135,28 @@ impl CoverageGraph {
     }
 
     #[inline(always)]
-    pub fn iter_enumerated(
+    pub(crate) fn iter_enumerated(
         &self,
     ) -> impl Iterator<Item = (BasicCoverageBlock, &BasicCoverageBlockData)> {
         self.bcbs.iter_enumerated()
     }
 
     #[inline(always)]
-    pub fn bcb_from_bb(&self, bb: BasicBlock) -> Option<BasicCoverageBlock> {
+    pub(crate) fn bcb_from_bb(&self, bb: BasicBlock) -> Option<BasicCoverageBlock> {
         if bb.index() < self.bb_to_bcb.len() { self.bb_to_bcb[bb] } else { None }
     }
 
     #[inline(always)]
-    pub fn dominates(&self, dom: BasicCoverageBlock, node: BasicCoverageBlock) -> bool {
+    pub(crate) fn dominates(&self, dom: BasicCoverageBlock, node: BasicCoverageBlock) -> bool {
         self.dominators.as_ref().unwrap().dominates(dom, node)
     }
 
     #[inline(always)]
-    pub fn cmp_in_dominator_order(&self, a: BasicCoverageBlock, b: BasicCoverageBlock) -> Ordering {
+    pub(crate) fn cmp_in_dominator_order(
+        &self,
+        a: BasicCoverageBlock,
+        b: BasicCoverageBlock,
+    ) -> Ordering {
         self.dominators.as_ref().unwrap().cmp_in_dominator_order(a, b)
     }
 
@@ -166,7 +170,7 @@ impl CoverageGraph {
     ///
     /// FIXME: That assumption might not be true for [`TerminatorKind::Yield`]?
     #[inline(always)]
-    pub(super) fn bcb_has_multiple_in_edges(&self, bcb: BasicCoverageBlock) -> bool {
+    pub(crate) fn bcb_has_multiple_in_edges(&self, bcb: BasicCoverageBlock) -> bool {
         // Even though bcb0 conceptually has an extra virtual in-edge due to
         // being the entry point, we've already asserted that it has no _other_
         // in-edges, so there's no possibility of it having _multiple_ in-edges.
@@ -212,7 +216,7 @@ impl graph::StartNode for CoverageGraph {
 impl graph::Successors for CoverageGraph {
     #[inline]
     fn successors(&self, node: Self::Node) -> impl Iterator<Item = Self::Node> {
-        self.successors[node].iter().cloned()
+        self.successors[node].iter().copied()
     }
 }
 
@@ -227,7 +231,7 @@ rustc_index::newtype_index! {
     /// A node in the control-flow graph of CoverageGraph.
     #[orderable]
     #[debug_format = "bcb{}"]
-    pub(super) struct BasicCoverageBlock {
+    pub(crate) struct BasicCoverageBlock {
         const START_BCB = 0;
     }
 }
@@ -259,23 +263,23 @@ rustc_index::newtype_index! {
 /// queries (`dominates()`, `predecessors`, `successors`, etc.) have branch (control flow)
 /// significance.
 #[derive(Debug, Clone)]
-pub(super) struct BasicCoverageBlockData {
-    pub basic_blocks: Vec<BasicBlock>,
+pub(crate) struct BasicCoverageBlockData {
+    pub(crate) basic_blocks: Vec<BasicBlock>,
 }
 
 impl BasicCoverageBlockData {
-    pub fn from(basic_blocks: Vec<BasicBlock>) -> Self {
+    fn from(basic_blocks: Vec<BasicBlock>) -> Self {
         assert!(basic_blocks.len() > 0);
         Self { basic_blocks }
     }
 
     #[inline(always)]
-    pub fn leader_bb(&self) -> BasicBlock {
+    pub(crate) fn leader_bb(&self) -> BasicBlock {
         self.basic_blocks[0]
     }
 
     #[inline(always)]
-    pub fn last_bb(&self) -> BasicBlock {
+    pub(crate) fn last_bb(&self) -> BasicBlock {
         *self.basic_blocks.last().unwrap()
     }
 }
@@ -364,7 +368,7 @@ fn bcb_filtered_successors<'a, 'tcx>(terminator: &'a Terminator<'tcx>) -> Covera
 /// CoverageGraph outside all loops. This supports traversing the BCB CFG in a way that
 /// ensures a loop is completely traversed before processing Blocks after the end of the loop.
 #[derive(Debug)]
-pub(super) struct TraversalContext {
+struct TraversalContext {
     /// BCB with one or more incoming loop backedges, indicating which loop
     /// this context is for.
     ///
@@ -375,7 +379,7 @@ pub(super) struct TraversalContext {
     worklist: VecDeque<BasicCoverageBlock>,
 }
 
-pub(super) struct TraverseCoverageGraphWithLoops<'a> {
+pub(crate) struct TraverseCoverageGraphWithLoops<'a> {
     basic_coverage_blocks: &'a CoverageGraph,
 
     backedges: IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>>,
@@ -384,7 +388,7 @@ pub(super) struct TraverseCoverageGraphWithLoops<'a> {
 }
 
 impl<'a> TraverseCoverageGraphWithLoops<'a> {
-    pub(super) fn new(basic_coverage_blocks: &'a CoverageGraph) -> Self {
+    pub(crate) fn new(basic_coverage_blocks: &'a CoverageGraph) -> Self {
         let backedges = find_loop_backedges(basic_coverage_blocks);
 
         let worklist = VecDeque::from([basic_coverage_blocks.start_node()]);
@@ -400,7 +404,7 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
 
     /// For each loop on the loop context stack (top-down), yields a list of BCBs
     /// within that loop that have an outgoing edge back to the loop header.
-    pub(super) fn reloop_bcbs_per_loop(&self) -> impl Iterator<Item = &[BasicCoverageBlock]> {
+    pub(crate) fn reloop_bcbs_per_loop(&self) -> impl Iterator<Item = &[BasicCoverageBlock]> {
         self.context_stack
             .iter()
             .rev()
@@ -408,39 +412,38 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
             .map(|header_bcb| self.backedges[header_bcb].as_slice())
     }
 
-    pub(super) fn next(&mut self) -> Option<BasicCoverageBlock> {
+    pub(crate) fn next(&mut self) -> Option<BasicCoverageBlock> {
         debug!(
             "TraverseCoverageGraphWithLoops::next - context_stack: {:?}",
             self.context_stack.iter().rev().collect::<Vec<_>>()
         );
 
         while let Some(context) = self.context_stack.last_mut() {
-            if let Some(bcb) = context.worklist.pop_front() {
-                if !self.visited.insert(bcb) {
-                    debug!("Already visited: {bcb:?}");
-                    continue;
-                }
-                debug!("Visiting {bcb:?}");
-
-                if self.backedges[bcb].len() > 0 {
-                    debug!("{bcb:?} is a loop header! Start a new TraversalContext...");
-                    self.context_stack.push(TraversalContext {
-                        loop_header: Some(bcb),
-                        worklist: VecDeque::new(),
-                    });
-                }
-                self.add_successors_to_worklists(bcb);
-                return Some(bcb);
-            } else {
-                // Strip contexts with empty worklists from the top of the stack
+            let Some(bcb) = context.worklist.pop_front() else {
+                // This stack level is exhausted; pop it and try the next one.
                 self.context_stack.pop();
+                continue;
+            };
+
+            if !self.visited.insert(bcb) {
+                debug!("Already visited: {bcb:?}");
+                continue;
+            }
+            debug!("Visiting {bcb:?}");
+
+            if self.backedges[bcb].len() > 0 {
+                debug!("{bcb:?} is a loop header! Start a new TraversalContext...");
+                self.context_stack
+                    .push(TraversalContext { loop_header: Some(bcb), worklist: VecDeque::new() });
             }
+            self.add_successors_to_worklists(bcb);
+            return Some(bcb);
         }
 
         None
     }
 
-    pub fn add_successors_to_worklists(&mut self, bcb: BasicCoverageBlock) {
+    fn add_successors_to_worklists(&mut self, bcb: BasicCoverageBlock) {
         let successors = &self.basic_coverage_blocks.successors[bcb];
         debug!("{:?} has {} successors:", bcb, successors.len());
 
@@ -494,11 +497,11 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
         }
     }
 
-    pub fn is_complete(&self) -> bool {
+    pub(crate) fn is_complete(&self) -> bool {
         self.visited.count() == self.visited.domain_size()
     }
 
-    pub fn unvisited(&self) -> Vec<BasicCoverageBlock> {
+    pub(crate) fn unvisited(&self) -> Vec<BasicCoverageBlock> {
         let mut unvisited_set: BitSet<BasicCoverageBlock> =
             BitSet::new_filled(self.visited.domain_size());
         unvisited_set.subtract(&self.visited);
@@ -506,7 +509,7 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
     }
 }
 
-pub(super) fn find_loop_backedges(
+fn find_loop_backedges(
     basic_coverage_blocks: &CoverageGraph,
 ) -> IndexVec<BasicCoverageBlock, Vec<BasicCoverageBlock>> {
     let num_bcbs = basic_coverage_blocks.num_nodes();
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index 65715253647..25744009be8 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -49,7 +49,7 @@ fn is_eligible_for_coverage(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
 /// Query implementation for `coverage_ids_info`.
 fn coverage_ids_info<'tcx>(
     tcx: TyCtxt<'tcx>,
-    instance_def: ty::InstanceDef<'tcx>,
+    instance_def: ty::InstanceKind<'tcx>,
 ) -> CoverageIdsInfo {
     let mir_body = tcx.instance_mir(instance_def);
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index bb6a666ff73..84a70d1f02d 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -1,9 +1,15 @@
+use std::collections::VecDeque;
+
+use rustc_data_structures::captures::Captures;
+use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::mir;
 use rustc_span::Span;
 
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
 use crate::coverage::mappings;
-use crate::coverage::spans::from_mir::SpanFromMir;
+use crate::coverage::spans::from_mir::{
+    extract_covspans_and_holes_from_mir, ExtractedCovspans, Hole, SpanFromMir,
+};
 use crate::coverage::ExtractedHirInfo;
 
 mod from_mir;
@@ -19,50 +25,181 @@ pub(super) fn extract_refined_covspans(
     basic_coverage_blocks: &CoverageGraph,
     code_mappings: &mut impl Extend<mappings::CodeMapping>,
 ) {
-    let sorted_span_buckets =
-        from_mir::mir_to_initial_sorted_coverage_spans(mir_body, hir_info, basic_coverage_blocks);
-    for bucket in sorted_span_buckets {
-        let refined_spans = refine_sorted_spans(bucket);
-        code_mappings.extend(refined_spans.into_iter().map(|RefinedCovspan { span, bcb }| {
+    let ExtractedCovspans { mut covspans, mut holes } =
+        extract_covspans_and_holes_from_mir(mir_body, hir_info, basic_coverage_blocks);
+
+    // First, perform the passes that need macro information.
+    covspans.sort_by(|a, b| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb));
+    remove_unwanted_macro_spans(&mut covspans);
+    split_visible_macro_spans(&mut covspans);
+
+    // We no longer need the extra information in `SpanFromMir`, so convert to `Covspan`.
+    let mut covspans = covspans.into_iter().map(SpanFromMir::into_covspan).collect::<Vec<_>>();
+
+    let compare_covspans = |a: &Covspan, b: &Covspan| {
+        compare_spans(a.span, b.span)
+            // After deduplication, we want to keep only the most-dominated BCB.
+            .then_with(|| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb).reverse())
+    };
+    covspans.sort_by(compare_covspans);
+
+    // Among covspans with the same span, keep only one,
+    // preferring the one with the most-dominated BCB.
+    // (Ideally we should try to preserve _all_ non-dominating BCBs, but that
+    // requires a lot more complexity in the span refiner, for little benefit.)
+    covspans.dedup_by(|b, a| a.span.source_equal(b.span));
+
+    // Sort the holes, and merge overlapping/adjacent holes.
+    holes.sort_by(|a, b| compare_spans(a.span, b.span));
+    holes.dedup_by(|b, a| a.merge_if_overlapping_or_adjacent(b));
+
+    // Split the covspans into separate buckets that don't overlap any holes.
+    let buckets = divide_spans_into_buckets(covspans, &holes);
+
+    for mut covspans in buckets {
+        // Make sure each individual bucket is internally sorted.
+        covspans.sort_by(compare_covspans);
+        let _span = debug_span!("processing bucket", ?covspans).entered();
+
+        let mut covspans = remove_unwanted_overlapping_spans(covspans);
+        debug!(?covspans, "after removing overlaps");
+
+        // Do one last merge pass, to simplify the output.
+        covspans.dedup_by(|b, a| a.merge_if_eligible(b));
+        debug!(?covspans, "after merge");
+
+        code_mappings.extend(covspans.into_iter().map(|Covspan { span, bcb }| {
             // Each span produced by the refiner represents an ordinary code region.
             mappings::CodeMapping { span, bcb }
         }));
     }
 }
 
-#[derive(Debug)]
-struct RefinedCovspan {
-    span: Span,
-    bcb: BasicCoverageBlock,
+/// Macros that expand into branches (e.g. `assert!`, `trace!`) tend to generate
+/// multiple condition/consequent blocks that have the span of the whole macro
+/// invocation, which is unhelpful. Keeping only the first such span seems to
+/// give better mappings, so remove the others.
+///
+/// (The input spans should be sorted in BCB dominator order, so that the
+/// retained "first" span is likely to dominate the others.)
+fn remove_unwanted_macro_spans(covspans: &mut Vec<SpanFromMir>) {
+    let mut seen_macro_spans = FxHashSet::default();
+    covspans.retain(|covspan| {
+        // Ignore (retain) non-macro-expansion spans.
+        if covspan.visible_macro.is_none() {
+            return true;
+        }
+
+        // Retain only the first macro-expanded covspan with this span.
+        seen_macro_spans.insert(covspan.span)
+    });
 }
 
-impl RefinedCovspan {
-    fn is_mergeable(&self, other: &Self) -> bool {
-        self.bcb == other.bcb
-    }
+/// When a span corresponds to a macro invocation that is visible from the
+/// function body, split it into two parts. The first part covers just the
+/// macro name plus `!`, and the second part covers the rest of the macro
+/// invocation. This seems to give better results for code that uses macros.
+fn split_visible_macro_spans(covspans: &mut Vec<SpanFromMir>) {
+    let mut extra_spans = vec![];
 
-    fn merge_from(&mut self, other: &Self) {
-        debug_assert!(self.is_mergeable(other));
-        self.span = self.span.to(other.span);
+    covspans.retain(|covspan| {
+        let Some(visible_macro) = covspan.visible_macro else { return true };
+
+        let split_len = visible_macro.as_str().len() as u32 + 1;
+        let (before, after) = covspan.span.split_at(split_len);
+        if !covspan.span.contains(before) || !covspan.span.contains(after) {
+            // Something is unexpectedly wrong with the split point.
+            // The debug assertion in `split_at` will have already caught this,
+            // but in release builds it's safer to do nothing and maybe get a
+            // bug report for unexpected coverage, rather than risk an ICE.
+            return true;
+        }
+
+        extra_spans.push(SpanFromMir::new(before, covspan.visible_macro, covspan.bcb));
+        extra_spans.push(SpanFromMir::new(after, covspan.visible_macro, covspan.bcb));
+        false // Discard the original covspan that we just split.
+    });
+
+    // The newly-split spans are added at the end, so any previous sorting
+    // is not preserved.
+    covspans.extend(extra_spans);
+}
+
+/// Uses the holes to divide the given covspans into buckets, such that:
+/// - No span in any hole overlaps a bucket (truncating the spans if necessary).
+/// - The spans in each bucket are strictly after all spans in previous buckets,
+///   and strictly before all spans in subsequent buckets.
+///
+/// The resulting buckets are sorted relative to each other, but might not be
+/// internally sorted.
+#[instrument(level = "debug")]
+fn divide_spans_into_buckets(input_covspans: Vec<Covspan>, holes: &[Hole]) -> Vec<Vec<Covspan>> {
+    debug_assert!(input_covspans.is_sorted_by(|a, b| compare_spans(a.span, b.span).is_le()));
+    debug_assert!(holes.is_sorted_by(|a, b| compare_spans(a.span, b.span).is_le()));
+
+    // Now we're ready to start carving holes out of the initial coverage spans,
+    // and grouping them in buckets separated by the holes.
+
+    let mut input_covspans = VecDeque::from(input_covspans);
+    let mut fragments = vec![];
+
+    // For each hole:
+    // - Identify the spans that are entirely or partly before the hole.
+    // - Put those spans in a corresponding bucket, truncated to the start of the hole.
+    // - If one of those spans also extends after the hole, put the rest of it
+    //   in a "fragments" vector that is processed by the next hole.
+    let mut buckets = (0..holes.len()).map(|_| vec![]).collect::<Vec<_>>();
+    for (hole, bucket) in holes.iter().zip(&mut buckets) {
+        let fragments_from_prev = std::mem::take(&mut fragments);
+
+        // Only inspect spans that precede or overlap this hole,
+        // leaving the rest to be inspected by later holes.
+        // (This relies on the spans and holes both being sorted.)
+        let relevant_input_covspans =
+            drain_front_while(&mut input_covspans, |c| c.span.lo() < hole.span.hi());
+
+        for covspan in fragments_from_prev.into_iter().chain(relevant_input_covspans) {
+            let (before, after) = covspan.split_around_hole_span(hole.span);
+            bucket.extend(before);
+            fragments.extend(after);
+        }
     }
+
+    // After finding the spans before each hole, any remaining fragments/spans
+    // form their own final bucket, after the final hole.
+    // (If there were no holes, this will just be all of the initial spans.)
+    fragments.extend(input_covspans);
+    buckets.push(fragments);
+
+    buckets
+}
+
+/// Similar to `.drain(..)`, but stops just before it would remove an item not
+/// satisfying the predicate.
+fn drain_front_while<'a, T>(
+    queue: &'a mut VecDeque<T>,
+    mut pred_fn: impl FnMut(&T) -> bool,
+) -> impl Iterator<Item = T> + Captures<'a> {
+    std::iter::from_fn(move || if pred_fn(queue.front()?) { queue.pop_front() } else { None })
 }
 
 /// Takes one of the buckets of (sorted) spans extracted from MIR, and "refines"
-/// those spans by removing spans that overlap in unwanted ways, and by merging
-/// compatible adjacent spans.
+/// those spans by removing spans that overlap in unwanted ways.
 #[instrument(level = "debug")]
-fn refine_sorted_spans(sorted_spans: Vec<SpanFromMir>) -> Vec<RefinedCovspan> {
+fn remove_unwanted_overlapping_spans(sorted_spans: Vec<Covspan>) -> Vec<Covspan> {
+    debug_assert!(sorted_spans.is_sorted_by(|a, b| compare_spans(a.span, b.span).is_le()));
+
     // Holds spans that have been read from the input vector, but haven't yet
     // been committed to the output vector.
     let mut pending = vec![];
     let mut refined = vec![];
 
     for curr in sorted_spans {
-        pending.retain(|prev: &SpanFromMir| {
+        pending.retain(|prev: &Covspan| {
             if prev.span.hi() <= curr.span.lo() {
                 // There's no overlap between the previous/current covspans,
                 // so move the previous one into the refined list.
-                refined.push(RefinedCovspan { span: prev.span, bcb: prev.bcb });
+                refined.push(prev.clone());
                 false
             } else {
                 // Otherwise, retain the previous covspan only if it has the
@@ -75,22 +212,57 @@ fn refine_sorted_spans(sorted_spans: Vec<SpanFromMir>) -> Vec<RefinedCovspan> {
     }
 
     // Drain the rest of the pending list into the refined list.
-    for prev in pending {
-        refined.push(RefinedCovspan { span: prev.span, bcb: prev.bcb });
+    refined.extend(pending);
+    refined
+}
+
+#[derive(Clone, Debug)]
+struct Covspan {
+    span: Span,
+    bcb: BasicCoverageBlock,
+}
+
+impl Covspan {
+    /// Splits this covspan into 0-2 parts:
+    /// - The part that is strictly before the hole span, if any.
+    /// - The part that is strictly after the hole span, if any.
+    fn split_around_hole_span(&self, hole_span: Span) -> (Option<Self>, Option<Self>) {
+        let before = try {
+            let span = self.span.trim_end(hole_span)?;
+            Self { span, ..*self }
+        };
+        let after = try {
+            let span = self.span.trim_start(hole_span)?;
+            Self { span, ..*self }
+        };
+
+        (before, after)
     }
 
-    // Do one last merge pass, to simplify the output.
-    debug!(?refined, "before merge");
-    refined.dedup_by(|b, a| {
-        if a.is_mergeable(b) {
-            debug!(?a, ?b, "merging list-adjacent refined spans");
-            a.merge_from(b);
-            true
-        } else {
-            false
+    /// If `self` and `other` can be merged (i.e. they have the same BCB),
+    /// mutates `self.span` to also include `other.span` and returns true.
+    ///
+    /// Note that compatible covspans can be merged even if their underlying
+    /// spans are not overlapping/adjacent; any space between them will also be
+    /// part of the merged covspan.
+    fn merge_if_eligible(&mut self, other: &Self) -> bool {
+        if self.bcb != other.bcb {
+            return false;
         }
-    });
-    debug!(?refined, "after merge");
 
-    refined
+        self.span = self.span.to(other.span);
+        true
+    }
+}
+
+/// Compares two spans in (lo ascending, hi descending) order.
+fn compare_spans(a: Span, b: Span) -> std::cmp::Ordering {
+    // First sort by span start.
+    Ord::cmp(&a.lo(), &b.lo())
+        // If span starts are the same, sort by span end in reverse order.
+        // This ensures that if spans A and B are adjacent in the list,
+        // and they overlap but are not equal, then either:
+        // - Span A extends further left, or
+        // - Both have the same start and span A extends further right
+        .then_with(|| Ord::cmp(&a.hi(), &b.hi()).reverse())
 }
diff --git a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
index b1f71035dde..09deb7534bf 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
@@ -1,7 +1,3 @@
-use std::collections::VecDeque;
-
-use rustc_data_structures::captures::Captures;
-use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::bug;
 use rustc_middle::mir::coverage::CoverageKind;
 use rustc_middle::mir::{
@@ -13,25 +9,25 @@ use rustc_span::{ExpnKind, MacroKind, Span, Symbol};
 use crate::coverage::graph::{
     BasicCoverageBlock, BasicCoverageBlockData, CoverageGraph, START_BCB,
 };
+use crate::coverage::spans::Covspan;
 use crate::coverage::ExtractedHirInfo;
 
+pub(crate) struct ExtractedCovspans {
+    pub(crate) covspans: Vec<SpanFromMir>,
+    pub(crate) holes: Vec<Hole>,
+}
+
 /// Traverses the MIR body to produce an initial collection of coverage-relevant
 /// spans, each associated with a node in the coverage graph (BCB) and possibly
 /// other metadata.
-///
-/// The returned spans are divided into one or more buckets, such that:
-/// - The spans in each bucket are strictly after all spans in previous buckets,
-///   and strictly before all spans in subsequent buckets.
-/// - The contents of each bucket are also sorted, in a specific order that is
-///   expected by the subsequent span-refinement step.
-pub(super) fn mir_to_initial_sorted_coverage_spans(
+pub(crate) fn extract_covspans_and_holes_from_mir(
     mir_body: &mir::Body<'_>,
     hir_info: &ExtractedHirInfo,
     basic_coverage_blocks: &CoverageGraph,
-) -> Vec<Vec<SpanFromMir>> {
+) -> ExtractedCovspans {
     let &ExtractedHirInfo { body_span, .. } = hir_info;
 
-    let mut initial_spans = vec![];
+    let mut covspans = vec![];
     let mut holes = vec![];
 
     for (bcb, bcb_data) in basic_coverage_blocks.iter_enumerated() {
@@ -40,150 +36,21 @@ pub(super) fn mir_to_initial_sorted_coverage_spans(
             body_span,
             bcb,
             bcb_data,
-            &mut initial_spans,
+            &mut covspans,
             &mut holes,
         );
     }
 
     // Only add the signature span if we found at least one span in the body.
-    if !initial_spans.is_empty() || !holes.is_empty() {
+    if !covspans.is_empty() || !holes.is_empty() {
         // If there is no usable signature span, add a fake one (before refinement)
         // to avoid an ugly gap between the body start and the first real span.
         // FIXME: Find a more principled way to solve this problem.
         let fn_sig_span = hir_info.fn_sig_span_extended.unwrap_or_else(|| body_span.shrink_to_lo());
-        initial_spans.push(SpanFromMir::for_fn_sig(fn_sig_span));
-    }
-
-    initial_spans.sort_by(|a, b| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb));
-    remove_unwanted_macro_spans(&mut initial_spans);
-    split_visible_macro_spans(&mut initial_spans);
-
-    let compare_covspans = |a: &SpanFromMir, b: &SpanFromMir| {
-        compare_spans(a.span, b.span)
-            // After deduplication, we want to keep only the most-dominated BCB.
-            .then_with(|| basic_coverage_blocks.cmp_in_dominator_order(a.bcb, b.bcb).reverse())
-    };
-    initial_spans.sort_by(compare_covspans);
-
-    // Among covspans with the same span, keep only one,
-    // preferring the one with the most-dominated BCB.
-    // (Ideally we should try to preserve _all_ non-dominating BCBs, but that
-    // requires a lot more complexity in the span refiner, for little benefit.)
-    initial_spans.dedup_by(|b, a| a.span.source_equal(b.span));
-
-    // Sort the holes, and merge overlapping/adjacent holes.
-    holes.sort_by(|a, b| compare_spans(a.span, b.span));
-    holes.dedup_by(|b, a| a.merge_if_overlapping_or_adjacent(b));
-
-    // Now we're ready to start carving holes out of the initial coverage spans,
-    // and grouping them in buckets separated by the holes.
-
-    let mut initial_spans = VecDeque::from(initial_spans);
-    let mut fragments: Vec<SpanFromMir> = vec![];
-
-    // For each hole:
-    // - Identify the spans that are entirely or partly before the hole.
-    // - Put those spans in a corresponding bucket, truncated to the start of the hole.
-    // - If one of those spans also extends after the hole, put the rest of it
-    //   in a "fragments" vector that is processed by the next hole.
-    let mut buckets = (0..holes.len()).map(|_| vec![]).collect::<Vec<_>>();
-    for (hole, bucket) in holes.iter().zip(&mut buckets) {
-        let fragments_from_prev = std::mem::take(&mut fragments);
-
-        // Only inspect spans that precede or overlap this hole,
-        // leaving the rest to be inspected by later holes.
-        // (This relies on the spans and holes both being sorted.)
-        let relevant_initial_spans =
-            drain_front_while(&mut initial_spans, |c| c.span.lo() < hole.span.hi());
-
-        for covspan in fragments_from_prev.into_iter().chain(relevant_initial_spans) {
-            let (before, after) = covspan.split_around_hole_span(hole.span);
-            bucket.extend(before);
-            fragments.extend(after);
-        }
+        covspans.push(SpanFromMir::for_fn_sig(fn_sig_span));
     }
 
-    // After finding the spans before each hole, any remaining fragments/spans
-    // form their own final bucket, after the final hole.
-    // (If there were no holes, this will just be all of the initial spans.)
-    fragments.extend(initial_spans);
-    buckets.push(fragments);
-
-    // Make sure each individual bucket is still internally sorted.
-    for bucket in &mut buckets {
-        bucket.sort_by(compare_covspans);
-    }
-    buckets
-}
-
-fn compare_spans(a: Span, b: Span) -> std::cmp::Ordering {
-    // First sort by span start.
-    Ord::cmp(&a.lo(), &b.lo())
-        // If span starts are the same, sort by span end in reverse order.
-        // This ensures that if spans A and B are adjacent in the list,
-        // and they overlap but are not equal, then either:
-        // - Span A extends further left, or
-        // - Both have the same start and span A extends further right
-        .then_with(|| Ord::cmp(&a.hi(), &b.hi()).reverse())
-}
-
-/// Similar to `.drain(..)`, but stops just before it would remove an item not
-/// satisfying the predicate.
-fn drain_front_while<'a, T>(
-    queue: &'a mut VecDeque<T>,
-    mut pred_fn: impl FnMut(&T) -> bool,
-) -> impl Iterator<Item = T> + Captures<'a> {
-    std::iter::from_fn(move || if pred_fn(queue.front()?) { queue.pop_front() } else { None })
-}
-
-/// Macros that expand into branches (e.g. `assert!`, `trace!`) tend to generate
-/// multiple condition/consequent blocks that have the span of the whole macro
-/// invocation, which is unhelpful. Keeping only the first such span seems to
-/// give better mappings, so remove the others.
-///
-/// (The input spans should be sorted in BCB dominator order, so that the
-/// retained "first" span is likely to dominate the others.)
-fn remove_unwanted_macro_spans(initial_spans: &mut Vec<SpanFromMir>) {
-    let mut seen_macro_spans = FxHashSet::default();
-    initial_spans.retain(|covspan| {
-        // Ignore (retain) non-macro-expansion spans.
-        if covspan.visible_macro.is_none() {
-            return true;
-        }
-
-        // Retain only the first macro-expanded covspan with this span.
-        seen_macro_spans.insert(covspan.span)
-    });
-}
-
-/// When a span corresponds to a macro invocation that is visible from the
-/// function body, split it into two parts. The first part covers just the
-/// macro name plus `!`, and the second part covers the rest of the macro
-/// invocation. This seems to give better results for code that uses macros.
-fn split_visible_macro_spans(initial_spans: &mut Vec<SpanFromMir>) {
-    let mut extra_spans = vec![];
-
-    initial_spans.retain(|covspan| {
-        let Some(visible_macro) = covspan.visible_macro else { return true };
-
-        let split_len = visible_macro.as_str().len() as u32 + 1;
-        let (before, after) = covspan.span.split_at(split_len);
-        if !covspan.span.contains(before) || !covspan.span.contains(after) {
-            // Something is unexpectedly wrong with the split point.
-            // The debug assertion in `split_at` will have already caught this,
-            // but in release builds it's safer to do nothing and maybe get a
-            // bug report for unexpected coverage, rather than risk an ICE.
-            return true;
-        }
-
-        extra_spans.push(SpanFromMir::new(before, covspan.visible_macro, covspan.bcb));
-        extra_spans.push(SpanFromMir::new(after, covspan.visible_macro, covspan.bcb));
-        false // Discard the original covspan that we just split.
-    });
-
-    // The newly-split spans are added at the end, so any previous sorting
-    // is not preserved.
-    initial_spans.extend(extra_spans);
+    ExtractedCovspans { covspans, holes }
 }
 
 // Generate a set of coverage spans from the filtered set of `Statement`s and `Terminator`s of
@@ -402,12 +269,12 @@ fn unexpand_into_body_span_with_prev(
 }
 
 #[derive(Debug)]
-struct Hole {
-    span: Span,
+pub(crate) struct Hole {
+    pub(crate) span: Span,
 }
 
 impl Hole {
-    fn merge_if_overlapping_or_adjacent(&mut self, other: &mut Self) -> bool {
+    pub(crate) fn merge_if_overlapping_or_adjacent(&mut self, other: &mut Self) -> bool {
         if !self.span.overlaps_or_adjacent(other.span) {
             return false;
         }
@@ -418,7 +285,7 @@ impl Hole {
 }
 
 #[derive(Debug)]
-pub(super) struct SpanFromMir {
+pub(crate) struct SpanFromMir {
     /// A span that has been extracted from MIR and then "un-expanded" back to
     /// within the current function's `body_span`. After various intermediate
     /// processing steps, this span is emitted as part of the final coverage
@@ -426,9 +293,9 @@ pub(super) struct SpanFromMir {
     ///
     /// With the exception of `fn_sig_span`, this should always be contained
     /// within `body_span`.
-    pub(super) span: Span,
-    visible_macro: Option<Symbol>,
-    pub(super) bcb: BasicCoverageBlock,
+    pub(crate) span: Span,
+    pub(crate) visible_macro: Option<Symbol>,
+    pub(crate) bcb: BasicCoverageBlock,
 }
 
 impl SpanFromMir {
@@ -436,23 +303,12 @@ impl SpanFromMir {
         Self::new(fn_sig_span, None, START_BCB)
     }
 
-    fn new(span: Span, visible_macro: Option<Symbol>, bcb: BasicCoverageBlock) -> Self {
+    pub(crate) fn new(span: Span, visible_macro: Option<Symbol>, bcb: BasicCoverageBlock) -> Self {
         Self { span, visible_macro, bcb }
     }
 
-    /// Splits this span into 0-2 parts:
-    /// - The part that is strictly before the hole span, if any.
-    /// - The part that is strictly after the hole span, if any.
-    fn split_around_hole_span(&self, hole_span: Span) -> (Option<Self>, Option<Self>) {
-        let before = try {
-            let span = self.span.trim_end(hole_span)?;
-            Self { span, ..*self }
-        };
-        let after = try {
-            let span = self.span.trim_start(hole_span)?;
-            Self { span, ..*self }
-        };
-
-        (before, after)
+    pub(crate) fn into_covspan(self) -> Covspan {
+        let Self { span, visible_macro: _, bcb } = self;
+        Covspan { span, bcb }
     }
 }
diff --git a/compiler/rustc_mir_transform/src/coverage/tests.rs b/compiler/rustc_mir_transform/src/coverage/tests.rs
index ca64688e6b8..048547dc9f5 100644
--- a/compiler/rustc_mir_transform/src/coverage/tests.rs
+++ b/compiler/rustc_mir_transform/src/coverage/tests.rs
@@ -24,7 +24,6 @@
 //! globals is comparatively simpler. The easiest way is to wrap the test in a closure argument
 //! to: `rustc_span::create_default_session_globals_then(|| { test_here(); })`.
 
-use super::counters;
 use super::graph::{self, BasicCoverageBlock};
 
 use itertools::Itertools;
@@ -551,108 +550,3 @@ fn test_covgraph_switchint_loop_then_inner_loop_else_break() {
     assert_successors(&basic_coverage_blocks, bcb(5), &[bcb(1)]);
     assert_successors(&basic_coverage_blocks, bcb(6), &[bcb(4)]);
 }
-
-#[test]
-fn test_find_loop_backedges_none() {
-    let mir_body = goto_switchint();
-    let basic_coverage_blocks = graph::CoverageGraph::from_mir(&mir_body);
-    if false {
-        eprintln!(
-            "basic_coverage_blocks = {:?}",
-            basic_coverage_blocks.iter_enumerated().collect::<Vec<_>>()
-        );
-        eprintln!("successors = {:?}", basic_coverage_blocks.successors);
-    }
-    let backedges = graph::find_loop_backedges(&basic_coverage_blocks);
-    assert_eq!(
-        backedges.iter_enumerated().map(|(_bcb, backedges)| backedges.len()).sum::<usize>(),
-        0,
-        "backedges: {:?}",
-        backedges
-    );
-}
-
-#[test]
-fn test_find_loop_backedges_one() {
-    let mir_body = switchint_then_loop_else_return();
-    let basic_coverage_blocks = graph::CoverageGraph::from_mir(&mir_body);
-    let backedges = graph::find_loop_backedges(&basic_coverage_blocks);
-    assert_eq!(
-        backedges.iter_enumerated().map(|(_bcb, backedges)| backedges.len()).sum::<usize>(),
-        1,
-        "backedges: {:?}",
-        backedges
-    );
-
-    assert_eq!(backedges[bcb(1)], &[bcb(3)]);
-}
-
-#[test]
-fn test_find_loop_backedges_two() {
-    let mir_body = switchint_loop_then_inner_loop_else_break();
-    let basic_coverage_blocks = graph::CoverageGraph::from_mir(&mir_body);
-    let backedges = graph::find_loop_backedges(&basic_coverage_blocks);
-    assert_eq!(
-        backedges.iter_enumerated().map(|(_bcb, backedges)| backedges.len()).sum::<usize>(),
-        2,
-        "backedges: {:?}",
-        backedges
-    );
-
-    assert_eq!(backedges[bcb(1)], &[bcb(5)]);
-    assert_eq!(backedges[bcb(4)], &[bcb(6)]);
-}
-
-#[test]
-fn test_traverse_coverage_with_loops() {
-    let mir_body = switchint_loop_then_inner_loop_else_break();
-    let basic_coverage_blocks = graph::CoverageGraph::from_mir(&mir_body);
-    let mut traversed_in_order = Vec::new();
-    let mut traversal = graph::TraverseCoverageGraphWithLoops::new(&basic_coverage_blocks);
-    while let Some(bcb) = traversal.next() {
-        traversed_in_order.push(bcb);
-    }
-
-    // bcb0 is visited first. Then bcb1 starts the first loop, and all remaining nodes, *except*
-    // bcb6 are inside the first loop.
-    assert_eq!(
-        *traversed_in_order.last().expect("should have elements"),
-        bcb(6),
-        "bcb6 should not be visited until all nodes inside the first loop have been visited"
-    );
-}
-
-#[test]
-fn test_make_bcb_counters() {
-    rustc_span::create_default_session_globals_then(|| {
-        let mir_body = goto_switchint();
-        let basic_coverage_blocks = graph::CoverageGraph::from_mir(&mir_body);
-        // Historically this test would use `spans` internals to set up fake
-        // coverage spans for BCBs 1 and 2. Now we skip that step and just tell
-        // BCB counter construction that those BCBs have spans.
-        let bcb_has_coverage_spans = |bcb: BasicCoverageBlock| (1..=2).contains(&bcb.as_usize());
-        let coverage_counters = counters::CoverageCounters::make_bcb_counters(
-            &basic_coverage_blocks,
-            bcb_has_coverage_spans,
-        );
-        assert_eq!(coverage_counters.num_expressions(), 0);
-
-        assert_eq!(
-            0, // bcb1 has a `Counter` with id = 0
-            match coverage_counters.bcb_counter(bcb(1)).expect("should have a counter") {
-                counters::BcbCounter::Counter { id, .. } => id,
-                _ => panic!("expected a Counter"),
-            }
-            .as_u32()
-        );
-
-        assert_eq!(
-            1, // bcb2 has a `Counter` with id = 1
-            match coverage_counters.bcb_counter(bcb(2)).expect("should have a counter") {
-                counters::BcbCounter::Counter { id, .. } => id,
-                _ => panic!("expected a Counter"),
-            }
-            .as_u32()
-        );
-    });
-}
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index fe2237dd2e9..d04bb8d302e 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -10,7 +10,7 @@ use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs}
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TypeVisitableExt;
-use rustc_middle::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
+use rustc_middle::ty::{self, Instance, InstanceKind, ParamEnv, Ty, TyCtxt};
 use rustc_session::config::{DebugInfo, OptLevel};
 use rustc_span::source_map::Spanned;
 use rustc_span::sym;
@@ -225,13 +225,8 @@ impl<'tcx> Inliner<'tcx> {
         // Normally, this shouldn't be required, but trait normalization failure can create a
         // validation ICE.
         let output_type = callee_body.return_ty();
-        if !util::relate_types(
-            self.tcx,
-            self.param_env,
-            ty::Variance::Covariant,
-            output_type,
-            destination_ty,
-        ) {
+        if !util::relate_types(self.tcx, self.param_env, ty::Covariant, output_type, destination_ty)
+        {
             trace!(?output_type, ?destination_ty);
             return Err("failed to normalize return type");
         }
@@ -261,13 +256,8 @@ impl<'tcx> Inliner<'tcx> {
                 self_arg_ty.into_iter().chain(arg_tuple_tys).zip(callee_body.args_iter())
             {
                 let input_type = callee_body.local_decls[input].ty;
-                if !util::relate_types(
-                    self.tcx,
-                    self.param_env,
-                    ty::Variance::Covariant,
-                    input_type,
-                    arg_ty,
-                ) {
+                if !util::relate_types(self.tcx, self.param_env, ty::Covariant, input_type, arg_ty)
+                {
                     trace!(?arg_ty, ?input_type);
                     return Err("failed to normalize tuple argument type");
                 }
@@ -276,13 +266,8 @@ impl<'tcx> Inliner<'tcx> {
             for (arg, input) in args.iter().zip(callee_body.args_iter()) {
                 let input_type = callee_body.local_decls[input].ty;
                 let arg_ty = arg.node.ty(&caller_body.local_decls, self.tcx);
-                if !util::relate_types(
-                    self.tcx,
-                    self.param_env,
-                    ty::Variance::Covariant,
-                    input_type,
-                    arg_ty,
-                ) {
+                if !util::relate_types(self.tcx, self.param_env, ty::Covariant, input_type, arg_ty)
+                {
                     trace!(?arg_ty, ?input_type);
                     return Err("failed to normalize argument type");
                 }
@@ -308,7 +293,7 @@ impl<'tcx> Inliner<'tcx> {
         }
 
         match callee.def {
-            InstanceDef::Item(_) => {
+            InstanceKind::Item(_) => {
                 // If there is no MIR available (either because it was not in metadata or
                 // because it has no MIR because it's an extern function), then the inliner
                 // won't cause cycles on this.
@@ -317,24 +302,24 @@ impl<'tcx> Inliner<'tcx> {
                 }
             }
             // These have no own callable MIR.
-            InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
+            InstanceKind::Intrinsic(_) | InstanceKind::Virtual(..) => {
                 return Err("instance without MIR (intrinsic / virtual)");
             }
             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
             // do not need to catch this here, we can wait until the inliner decides to continue
             // inlining a second time.
-            InstanceDef::VTableShim(_)
-            | InstanceDef::ReifyShim(..)
-            | InstanceDef::FnPtrShim(..)
-            | InstanceDef::ClosureOnceShim { .. }
-            | InstanceDef::ConstructCoroutineInClosureShim { .. }
-            | InstanceDef::CoroutineKindShim { .. }
-            | InstanceDef::DropGlue(..)
-            | InstanceDef::CloneShim(..)
-            | InstanceDef::ThreadLocalShim(..)
-            | InstanceDef::FnPtrAddrShim(..)
-            | InstanceDef::AsyncDropGlueCtorShim(..) => return Ok(()),
+            InstanceKind::VTableShim(_)
+            | InstanceKind::ReifyShim(..)
+            | InstanceKind::FnPtrShim(..)
+            | InstanceKind::ClosureOnceShim { .. }
+            | InstanceKind::ConstructCoroutineInClosureShim { .. }
+            | InstanceKind::CoroutineKindShim { .. }
+            | InstanceKind::DropGlue(..)
+            | InstanceKind::CloneShim(..)
+            | InstanceKind::ThreadLocalShim(..)
+            | InstanceKind::FnPtrAddrShim(..)
+            | InstanceKind::AsyncDropGlueCtorShim(..) => return Ok(()),
         }
 
         if self.tcx.is_constructor(callee_def_id) {
@@ -387,7 +372,7 @@ impl<'tcx> Inliner<'tcx> {
                 let callee =
                     Instance::resolve(self.tcx, self.param_env, def_id, args).ok().flatten()?;
 
-                if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
+                if let InstanceKind::Virtual(..) | InstanceKind::Intrinsic(_) = callee.def {
                     return None;
                 }
 
@@ -399,7 +384,7 @@ impl<'tcx> Inliner<'tcx> {
 
                 // Additionally, check that the body that we're inlining actually agrees
                 // with the ABI of the trait that the item comes from.
-                if let InstanceDef::Item(instance_def_id) = callee.def
+                if let InstanceKind::Item(instance_def_id) = callee.def
                     && self.tcx.def_kind(instance_def_id) == DefKind::AssocFn
                     && let instance_fn_sig = self.tcx.fn_sig(instance_def_id).skip_binder()
                     && instance_fn_sig.abi() != fn_sig.abi()
@@ -1078,10 +1063,10 @@ impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
 #[instrument(skip(tcx), level = "debug")]
 fn try_instance_mir<'tcx>(
     tcx: TyCtxt<'tcx>,
-    instance: InstanceDef<'tcx>,
+    instance: InstanceKind<'tcx>,
 ) -> Result<&'tcx Body<'tcx>, &'static str> {
-    if let ty::InstanceDef::DropGlue(_, Some(ty))
-    | ty::InstanceDef::AsyncDropGlueCtorShim(_, Some(ty)) = instance
+    if let ty::InstanceKind::DropGlue(_, Some(ty))
+    | ty::InstanceKind::AsyncDropGlueCtorShim(_, Some(ty)) = instance
         && let ty::Adt(def, args) = ty.kind()
     {
         let fields = def.all_fields();
diff --git a/compiler/rustc_mir_transform/src/inline/cycle.rs b/compiler/rustc_mir_transform/src/inline/cycle.rs
index 8c5f965108b..35bcd24ce95 100644
--- a/compiler/rustc_mir_transform/src/inline/cycle.rs
+++ b/compiler/rustc_mir_transform/src/inline/cycle.rs
@@ -3,7 +3,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::mir::TerminatorKind;
 use rustc_middle::ty::TypeVisitableExt;
-use rustc_middle::ty::{self, GenericArgsRef, InstanceDef, TyCtxt};
+use rustc_middle::ty::{self, GenericArgsRef, InstanceKind, TyCtxt};
 use rustc_session::Limit;
 use rustc_span::sym;
 
@@ -22,7 +22,7 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
         "you should not call `mir_callgraph_reachable` on immediate self recursion"
     );
     assert!(
-        matches!(root.def, InstanceDef::Item(_)),
+        matches!(root.def, InstanceKind::Item(_)),
         "you should not call `mir_callgraph_reachable` on shims"
     );
     assert!(
@@ -70,7 +70,7 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
             }
 
             match callee.def {
-                InstanceDef::Item(_) => {
+                InstanceKind::Item(_) => {
                     // If there is no MIR available (either because it was not in metadata or
                     // because it has no MIR because it's an extern function), then the inliner
                     // won't cause cycles on this.
@@ -80,24 +80,24 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
                     }
                 }
                 // These have no own callable MIR.
-                InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => continue,
+                InstanceKind::Intrinsic(_) | InstanceKind::Virtual(..) => continue,
                 // These have MIR and if that MIR is inlined, instantiated and then inlining is run
                 // again, a function item can end up getting inlined. Thus we'll be able to cause
                 // a cycle that way
-                InstanceDef::VTableShim(_)
-                | InstanceDef::ReifyShim(..)
-                | InstanceDef::FnPtrShim(..)
-                | InstanceDef::ClosureOnceShim { .. }
-                | InstanceDef::ConstructCoroutineInClosureShim { .. }
-                | InstanceDef::CoroutineKindShim { .. }
-                | InstanceDef::ThreadLocalShim { .. }
-                | InstanceDef::CloneShim(..) => {}
+                InstanceKind::VTableShim(_)
+                | InstanceKind::ReifyShim(..)
+                | InstanceKind::FnPtrShim(..)
+                | InstanceKind::ClosureOnceShim { .. }
+                | InstanceKind::ConstructCoroutineInClosureShim { .. }
+                | InstanceKind::CoroutineKindShim { .. }
+                | InstanceKind::ThreadLocalShim { .. }
+                | InstanceKind::CloneShim(..) => {}
 
                 // This shim does not call any other functions, thus there can be no recursion.
-                InstanceDef::FnPtrAddrShim(..) => {
+                InstanceKind::FnPtrAddrShim(..) => {
                     continue;
                 }
-                InstanceDef::DropGlue(..) | InstanceDef::AsyncDropGlueCtorShim(..) => {
+                InstanceKind::DropGlue(..) | InstanceKind::AsyncDropGlueCtorShim(..) => {
                     // FIXME: A not fully instantiated drop shim can cause ICEs if one attempts to
                     // have its MIR built. Likely oli-obk just screwed up the `ParamEnv`s, so this
                     // needs some more analysis.
@@ -151,12 +151,12 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
 
 pub(crate) fn mir_inliner_callees<'tcx>(
     tcx: TyCtxt<'tcx>,
-    instance: ty::InstanceDef<'tcx>,
+    instance: ty::InstanceKind<'tcx>,
 ) -> &'tcx [(DefId, GenericArgsRef<'tcx>)] {
     let steal;
     let guard;
     let body = match (instance, instance.def_id().as_local()) {
-        (InstanceDef::Item(_), Some(def_id)) => {
+        (InstanceKind::Item(_), Some(def_id)) => {
             steal = tcx.mir_promoted(def_id).0;
             guard = steal.borrow();
             &*guard
diff --git a/compiler/rustc_mir_transform/src/known_panics_lint.rs b/compiler/rustc_mir_transform/src/known_panics_lint.rs
index 6a20b46e7f9..8d6c00bbedb 100644
--- a/compiler/rustc_mir_transform/src/known_panics_lint.rs
+++ b/compiler/rustc_mir_transform/src/known_panics_lint.rs
@@ -706,9 +706,9 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
         self.super_operand(operand, location);
     }
 
-    fn visit_constant(&mut self, constant: &ConstOperand<'tcx>, location: Location) {
-        trace!("visit_constant: {:?}", constant);
-        self.super_constant(constant, location);
+    fn visit_const_operand(&mut self, constant: &ConstOperand<'tcx>, location: Location) {
+        trace!("visit_const_operand: {:?}", constant);
+        self.super_const_operand(constant, location);
         self.eval_constant(constant);
     }
 
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 3c0f4e9142b..afba6781a70 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -398,7 +398,7 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
     if is_fn_like {
         // Do not compute the mir call graph without said call graph actually being used.
         if pm::should_run_pass(tcx, &inline::Inline) {
-            tcx.ensure_with_value().mir_inliner_callees(ty::InstanceDef::Item(def.to_def_id()));
+            tcx.ensure_with_value().mir_inliner_callees(ty::InstanceKind::Item(def.to_def_id()));
         }
     }
 
diff --git a/compiler/rustc_mir_transform/src/promote_consts.rs b/compiler/rustc_mir_transform/src/promote_consts.rs
index ecd1179ca99..ecdca8292b4 100644
--- a/compiler/rustc_mir_transform/src/promote_consts.rs
+++ b/compiler/rustc_mir_transform/src/promote_consts.rs
@@ -956,7 +956,7 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Promoter<'a, 'tcx> {
         }
     }
 
-    fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, _location: Location) {
+    fn visit_const_operand(&mut self, constant: &mut ConstOperand<'tcx>, _location: Location) {
         if constant.const_.is_required_const() {
             self.promoted.required_consts.push(*constant);
         }
diff --git a/compiler/rustc_mir_transform/src/required_consts.rs b/compiler/rustc_mir_transform/src/required_consts.rs
index 71ac929d35e..00bfb5e6600 100644
--- a/compiler/rustc_mir_transform/src/required_consts.rs
+++ b/compiler/rustc_mir_transform/src/required_consts.rs
@@ -12,7 +12,7 @@ impl<'a, 'tcx> RequiredConstsVisitor<'a, 'tcx> {
 }
 
 impl<'tcx> Visitor<'tcx> for RequiredConstsVisitor<'_, 'tcx> {
-    fn visit_constant(&mut self, constant: &ConstOperand<'tcx>, _: Location) {
+    fn visit_const_operand(&mut self, constant: &ConstOperand<'tcx>, _: Location) {
         if constant.const_.is_required_const() {
             self.required_consts.push(*constant);
         }
diff --git a/compiler/rustc_mir_transform/src/reveal_all.rs b/compiler/rustc_mir_transform/src/reveal_all.rs
index 4d2eca57840..5eaa024f846 100644
--- a/compiler/rustc_mir_transform/src/reveal_all.rs
+++ b/compiler/rustc_mir_transform/src/reveal_all.rs
@@ -49,14 +49,14 @@ impl<'tcx> MutVisitor<'tcx> for RevealAllVisitor<'tcx> {
     }
 
     #[inline]
-    fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, location: Location) {
+    fn visit_const_operand(&mut self, constant: &mut ConstOperand<'tcx>, location: Location) {
         // We have to use `try_normalize_erasing_regions` here, since it's
         // possible that we visit impossible-to-satisfy where clauses here,
         // see #91745
         if let Ok(c) = self.tcx.try_normalize_erasing_regions(self.param_env, constant.const_) {
             constant.const_ = c;
         }
-        self.super_constant(constant, location);
+        self.super_const_operand(constant, location);
     }
 
     #[inline]
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index d03c2d18c0c..825f8957187 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -29,16 +29,16 @@ pub fn provide(providers: &mut Providers) {
     providers.mir_shims = make_shim;
 }
 
-fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'tcx> {
+fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceKind<'tcx>) -> Body<'tcx> {
     debug!("make_shim({:?})", instance);
 
     let mut result = match instance {
-        ty::InstanceDef::Item(..) => bug!("item {:?} passed to make_shim", instance),
-        ty::InstanceDef::VTableShim(def_id) => {
+        ty::InstanceKind::Item(..) => bug!("item {:?} passed to make_shim", instance),
+        ty::InstanceKind::VTableShim(def_id) => {
             let adjustment = Adjustment::Deref { source: DerefSource::MutPtr };
             build_call_shim(tcx, instance, Some(adjustment), CallKind::Direct(def_id))
         }
-        ty::InstanceDef::FnPtrShim(def_id, ty) => {
+        ty::InstanceKind::FnPtrShim(def_id, ty) => {
             let trait_ = tcx.trait_of_item(def_id).unwrap();
             // Supports `Fn` or `async Fn` traits.
             let adjustment = match tcx
@@ -58,10 +58,10 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
         // a virtual call, or a direct call to a function for which
         // indirect calls must be codegen'd differently than direct ones
         // (such as `#[track_caller]`).
-        ty::InstanceDef::ReifyShim(def_id, _) => {
+        ty::InstanceKind::ReifyShim(def_id, _) => {
             build_call_shim(tcx, instance, None, CallKind::Direct(def_id))
         }
-        ty::InstanceDef::ClosureOnceShim { call_once: _, track_caller: _ } => {
+        ty::InstanceKind::ClosureOnceShim { call_once: _, track_caller: _ } => {
             let fn_mut = tcx.require_lang_item(LangItem::FnMut, None);
             let call_mut = tcx
                 .associated_items(fn_mut)
@@ -73,16 +73,16 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
             build_call_shim(tcx, instance, Some(Adjustment::RefMut), CallKind::Direct(call_mut))
         }
 
-        ty::InstanceDef::ConstructCoroutineInClosureShim {
+        ty::InstanceKind::ConstructCoroutineInClosureShim {
             coroutine_closure_def_id,
             receiver_by_ref,
         } => build_construct_coroutine_by_move_shim(tcx, coroutine_closure_def_id, receiver_by_ref),
 
-        ty::InstanceDef::CoroutineKindShim { coroutine_def_id } => {
+        ty::InstanceKind::CoroutineKindShim { coroutine_def_id } => {
             return tcx.optimized_mir(coroutine_def_id).coroutine_by_move_body().unwrap().clone();
         }
 
-        ty::InstanceDef::DropGlue(def_id, ty) => {
+        ty::InstanceKind::DropGlue(def_id, ty) => {
             // FIXME(#91576): Drop shims for coroutines aren't subject to the MIR passes at the end
             // of this function. Is this intentional?
             if let Some(ty::Coroutine(coroutine_def_id, args)) = ty.map(Ty::kind) {
@@ -127,16 +127,16 @@ 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::AsyncDropGlueCtorShim(def_id, ty) => {
+        ty::InstanceKind::ThreadLocalShim(..) => build_thread_local_shim(tcx, instance),
+        ty::InstanceKind::CloneShim(def_id, ty) => build_clone_shim(tcx, def_id, ty),
+        ty::InstanceKind::FnPtrAddrShim(def_id, ty) => build_fn_ptr_addr_shim(tcx, def_id, ty),
+        ty::InstanceKind::AsyncDropGlueCtorShim(def_id, ty) => {
             async_destructor_ctor::build_async_destructor_ctor_shim(tcx, def_id, ty)
         }
-        ty::InstanceDef::Virtual(..) => {
-            bug!("InstanceDef::Virtual ({:?}) is for direct calls only", instance)
+        ty::InstanceKind::Virtual(..) => {
+            bug!("InstanceKind::Virtual ({:?}) is for direct calls only", instance)
         }
-        ty::InstanceDef::Intrinsic(_) => {
+        ty::InstanceKind::Intrinsic(_) => {
             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
         }
     };
@@ -240,7 +240,7 @@ fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>)
     block(&mut blocks, TerminatorKind::Goto { target: return_block });
     block(&mut blocks, TerminatorKind::Return);
 
-    let source = MirSource::from_instance(ty::InstanceDef::DropGlue(def_id, ty));
+    let source = MirSource::from_instance(ty::InstanceKind::DropGlue(def_id, ty));
     let mut body =
         new_body(source, blocks, local_decls_for_sig(&sig, span), sig.inputs().len(), span);
 
@@ -392,7 +392,10 @@ 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> {
+fn build_thread_local_shim<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    instance: ty::InstanceKind<'tcx>,
+) -> Body<'tcx> {
     let def_id = instance.def_id();
 
     let span = tcx.def_span(def_id);
@@ -472,7 +475,7 @@ impl<'tcx> CloneShimBuilder<'tcx> {
     }
 
     fn into_mir(self) -> Body<'tcx> {
-        let source = MirSource::from_instance(ty::InstanceDef::CloneShim(
+        let source = MirSource::from_instance(ty::InstanceKind::CloneShim(
             self.def_id,
             self.sig.inputs_and_output[0],
         ));
@@ -682,14 +685,14 @@ impl<'tcx> CloneShimBuilder<'tcx> {
 #[instrument(level = "debug", skip(tcx), ret)]
 fn build_call_shim<'tcx>(
     tcx: TyCtxt<'tcx>,
-    instance: ty::InstanceDef<'tcx>,
+    instance: ty::InstanceKind<'tcx>,
     rcvr_adjustment: Option<Adjustment>,
     call_kind: CallKind<'tcx>,
 ) -> Body<'tcx> {
     // `FnPtrShim` contains the fn pointer type that a call shim is being built for - this is used
     // to instantiate into the signature of the shim. It is not necessary for users of this
-    // MIR body to perform further instantiations (see `InstanceDef::has_polymorphic_mir_body`).
-    let (sig_args, untuple_args) = if let ty::InstanceDef::FnPtrShim(_, ty) = instance {
+    // MIR body to perform further instantiations (see `InstanceKind::has_polymorphic_mir_body`).
+    let (sig_args, untuple_args) = if let ty::InstanceKind::FnPtrShim(_, ty) = instance {
         let sig = tcx.instantiate_bound_regions_with_erased(ty.fn_sig(tcx));
 
         let untuple_args = sig.inputs();
@@ -741,8 +744,8 @@ fn build_call_shim<'tcx>(
     }
 
     // FIXME(eddyb) avoid having this snippet both here and in
-    // `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
-    if let ty::InstanceDef::VTableShim(..) = instance {
+    // `Instance::fn_sig` (introduce `InstanceKind::fn_sig`?).
+    if let ty::InstanceKind::VTableShim(..) = instance {
         // Modify fn(self, ...) to fn(self: *mut Self, ...)
         let mut inputs_and_output = sig.inputs_and_output.to_vec();
         let self_arg = &mut inputs_and_output[0];
@@ -1007,7 +1010,7 @@ fn build_fn_ptr_addr_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'t
         terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
         is_cleanup: false,
     };
-    let source = MirSource::from_instance(ty::InstanceDef::FnPtrAddrShim(def_id, self_ty));
+    let source = MirSource::from_instance(ty::InstanceKind::FnPtrAddrShim(def_id, self_ty));
     new_body(source, IndexVec::from_elem_n(start_block, 1), locals, sig.inputs().len(), span)
 }
 
@@ -1087,7 +1090,7 @@ fn build_construct_coroutine_by_move_shim<'tcx>(
         is_cleanup: false,
     };
 
-    let source = MirSource::from_instance(ty::InstanceDef::ConstructCoroutineInClosureShim {
+    let source = MirSource::from_instance(ty::InstanceKind::ConstructCoroutineInClosureShim {
         coroutine_closure_def_id,
         receiver_by_ref,
     });
diff --git a/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs b/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
index aa9c87d8f80..ea4f5fca59e 100644
--- a/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
+++ b/compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
@@ -529,7 +529,7 @@ impl<'tcx> AsyncDestructorCtorShimBuilder<'tcx> {
 
         last_bb.terminator = Some(Terminator { source_info, kind: TerminatorKind::Return });
 
-        let source = MirSource::from_instance(ty::InstanceDef::AsyncDropGlueCtorShim(
+        let source = MirSource::from_instance(ty::InstanceKind::AsyncDropGlueCtorShim(
             self.def_id,
             self.self_ty,
         ));
@@ -561,7 +561,7 @@ impl<'tcx> AsyncDestructorCtorShimBuilder<'tcx> {
 
             // If projection of Discriminant then compare with `Ty::discriminant_ty`
             if let ty::Alias(ty::Projection, ty::AliasTy { args, def_id, .. }) = expected_ty.kind()
-                && Some(*def_id) == self.tcx.lang_items().discriminant_type()
+                && self.tcx.is_lang_item(*def_id, LangItem::Discriminant)
                 && args.first().unwrap().as_type().unwrap().discriminant_ty(self.tcx) == operand_ty
             {
                 return;
diff --git a/compiler/rustc_mir_transform/src/sroa.rs b/compiler/rustc_mir_transform/src/sroa.rs
index f19c34cae7a..c2108795372 100644
--- a/compiler/rustc_mir_transform/src/sroa.rs
+++ b/compiler/rustc_mir_transform/src/sroa.rs
@@ -1,4 +1,5 @@
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
+use rustc_hir::LangItem;
 use rustc_index::bit_set::{BitSet, GrowableBitSet};
 use rustc_index::IndexVec;
 use rustc_middle::bug;
@@ -70,7 +71,7 @@ fn escaping_locals<'tcx>(
                 // Exclude #[repr(simd)] types so that they are not de-optimized into an array
                 return true;
             }
-            if Some(def.did()) == tcx.lang_items().dyn_metadata() {
+            if tcx.is_lang_item(def.did(), LangItem::DynMetadata) {
                 // codegen wants to see the `DynMetadata<T>`,
                 // not the inner reference-to-opaque-type.
                 return true;
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index 586c1254995..2cca1a6f507 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -1,6 +1,7 @@
 //! Validates the MIR to ensure that invariants are upheld.
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir::LangItem;
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
 use rustc_infer::traits::Reveal;
@@ -9,7 +10,7 @@ use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::{
-    self, CoroutineArgsExt, InstanceDef, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitableExt,
+    self, CoroutineArgsExt, InstanceKind, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitableExt,
     Variance,
 };
 use rustc_middle::{bug, span_bug};
@@ -43,7 +44,7 @@ impl<'tcx> MirPass<'tcx> for Validator {
         // terribly important that they pass the validator. However, I think other passes might
         // still see them, in which case they might be surprised. It would probably be better if we
         // didn't put this through the MIR pipeline at all.
-        if matches!(body.source.instance, InstanceDef::Intrinsic(..) | InstanceDef::Virtual(..)) {
+        if matches!(body.source.instance, InstanceKind::Intrinsic(..) | InstanceKind::Virtual(..)) {
             return;
         }
         let def_id = body.source.def_id();
@@ -94,7 +95,7 @@ impl<'tcx> MirPass<'tcx> for Validator {
         }
 
         if let MirPhase::Runtime(_) = body.phase {
-            if let ty::InstanceDef::Item(_) = body.source.instance {
+            if let ty::InstanceKind::Item(_) = body.source.instance {
                 if body.has_free_regions() {
                     cfg_checker.fail(
                         Location::START,
@@ -689,7 +690,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     }
                     ty::Adt(adt_def, args) => {
                         // see <https://github.com/rust-lang/rust/blob/7601adcc764d42c9f2984082b49948af652df986/compiler/rustc_middle/src/ty/layout.rs#L861-L864>
-                        if Some(adt_def.did()) == self.tcx.lang_items().dyn_metadata() {
+                        if self.tcx.is_lang_item(adt_def.did(), LangItem::DynMetadata) {
                             self.fail(
                                 location,
                                 format!(