1 //! This is the implementation of the pass which transforms generators into state machines.
3 //! MIR generation for generators creates a function which has a self argument which
4 //! passes by value. This argument is effectively a generator type which only contains upvars and
5 //! is only used for this argument inside the MIR for the generator.
6 //! It is passed by value to enable upvars to be moved out of it. Drop elaboration runs on that
7 //! MIR before this pass and creates drop flags for MIR locals.
8 //! It will also drop the generator argument (which only consists of upvars) if any of the upvars
9 //! are moved out of. This pass elaborates the drops of upvars / generator argument in the case
10 //! that none of the upvars were moved out of. This is because we cannot have any drops of this
11 //! generator in the MIR, since it is used to create the drop glue for the generator. We'd get
12 //! infinite recursion otherwise.
14 //! This pass creates the implementation for the Generator::resume function and the drop shim
15 //! for the generator based on the MIR input. It converts the generator argument from Self to
16 //! &mut Self adding derefs in the MIR as needed. It computes the final layout of the generator
17 //! struct which looks like this:
18 //! First upvars are stored
19 //! It is followed by the generator state field.
20 //! Then finally the MIR locals which are live across a suspension point are stored.
21 //! ```ignore (illustrative)
22 //! struct Generator {
28 //! This pass computes the meaning of the state field and the MIR locals which are live
29 //! across a suspension point. There are however three hardcoded generator states:
30 //! 0 - Generator have not been resumed yet
31 //! 1 - Generator has returned / is completed
32 //! 2 - Generator has been poisoned
34 //! It also rewrites `return x` and `yield y` as setting a new generator state and returning
35 //! GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
36 //! MIR locals which are live across a suspension point are moved to the generator struct
37 //! with references to them being updated with references to the generator struct.
39 //! The pass creates two functions which have a switch on the generator state giving
40 //! the action to take.
42 //! One of them is the implementation of Generator::resume.
43 //! For generators with state 0 (unresumed) it starts the execution of the generator.
44 //! For generators with state 1 (returned) and state 2 (poisoned) it panics.
45 //! Otherwise it continues the execution from the last suspension point.
47 //! The other function is the drop glue for the generator.
48 //! For generators with state 0 (unresumed) it drops the upvars of the generator.
49 //! For generators with state 1 (returned) and state 2 (poisoned) it does nothing.
50 //! Otherwise it drops all the values in scope at the last suspension point.
52 use crate::deref_separator::deref_finder;
54 use crate::util::expand_aggregate;
56 use rustc_data_structures::fx::FxHashMap;
58 use rustc_hir::lang_items::LangItem;
59 use rustc_index::bit_set::{BitMatrix, BitSet, GrowableBitSet};
60 use rustc_index::vec::{Idx, IndexVec};
61 use rustc_middle::mir::dump_mir;
62 use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
63 use rustc_middle::mir::*;
64 use rustc_middle::ty::subst::{Subst, SubstsRef};
65 use rustc_middle::ty::GeneratorSubsts;
66 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
67 use rustc_mir_dataflow::impls::{
68 MaybeBorrowedLocals, MaybeLiveLocals, MaybeRequiresStorage, MaybeStorageLive,
70 use rustc_mir_dataflow::storage::always_storage_live_locals;
71 use rustc_mir_dataflow::{self, Analysis};
72 use rustc_target::abi::VariantIdx;
73 use rustc_target::spec::PanicStrategy;
76 pub struct StateTransform;
78 struct RenameLocalVisitor<'tcx> {
84 impl<'tcx> MutVisitor<'tcx> for RenameLocalVisitor<'tcx> {
85 fn tcx(&self) -> TyCtxt<'tcx> {
89 fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
90 if *local == self.from {
95 fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) {
96 match terminator.kind {
97 TerminatorKind::Return => {
98 // Do not replace the implicit `_0` access here, as that's not possible. The
99 // transform already handles `return` correctly.
101 _ => self.super_terminator(terminator, location),
106 struct DerefArgVisitor<'tcx> {
110 impl<'tcx> MutVisitor<'tcx> for DerefArgVisitor<'tcx> {
111 fn tcx(&self) -> TyCtxt<'tcx> {
115 fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
116 assert_ne!(*local, SELF_ARG);
119 fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
120 if place.local == SELF_ARG {
125 projection: self.tcx().intern_place_elems(&[ProjectionElem::Deref]),
130 self.visit_local(&mut place.local, context, location);
132 for elem in place.projection.iter() {
133 if let PlaceElem::Index(local) = elem {
134 assert_ne!(local, SELF_ARG);
141 struct PinArgVisitor<'tcx> {
142 ref_gen_ty: Ty<'tcx>,
146 impl<'tcx> MutVisitor<'tcx> for PinArgVisitor<'tcx> {
147 fn tcx(&self) -> TyCtxt<'tcx> {
151 fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
152 assert_ne!(*local, SELF_ARG);
155 fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
156 if place.local == SELF_ARG {
161 projection: self.tcx().intern_place_elems(&[ProjectionElem::Field(
169 self.visit_local(&mut place.local, context, location);
171 for elem in place.projection.iter() {
172 if let PlaceElem::Index(local) = elem {
173 assert_ne!(local, SELF_ARG);
180 fn replace_base<'tcx>(place: &mut Place<'tcx>, new_base: Place<'tcx>, tcx: TyCtxt<'tcx>) {
181 place.local = new_base.local;
183 let mut new_projection = new_base.projection.to_vec();
184 new_projection.append(&mut place.projection.to_vec());
186 place.projection = tcx.intern_place_elems(&new_projection);
189 const SELF_ARG: Local = Local::from_u32(1);
191 /// Generator has not been resumed yet.
192 const UNRESUMED: usize = GeneratorSubsts::UNRESUMED;
193 /// Generator has returned / is completed.
194 const RETURNED: usize = GeneratorSubsts::RETURNED;
195 /// Generator has panicked and is poisoned.
196 const POISONED: usize = GeneratorSubsts::POISONED;
198 /// Number of variants to reserve in generator state. Corresponds to
199 /// `UNRESUMED` (beginning of a generator) and `RETURNED`/`POISONED`
200 /// (end of a generator) states.
201 const RESERVED_VARIANTS: usize = 3;
203 /// A `yield` point in the generator.
204 struct SuspensionPoint<'tcx> {
205 /// State discriminant used when suspending or resuming at this point.
207 /// The block to jump to after resumption.
209 /// Where to move the resume argument after resumption.
210 resume_arg: Place<'tcx>,
211 /// Which block to jump to if the generator is dropped in this state.
212 drop: Option<BasicBlock>,
213 /// Set of locals that have live storage while at this suspension point.
214 storage_liveness: GrowableBitSet<Local>,
217 struct TransformVisitor<'tcx> {
219 state_adt_ref: AdtDef<'tcx>,
220 state_substs: SubstsRef<'tcx>,
222 // The type of the discriminant in the generator struct
225 // Mapping from Local to (type of local, generator struct index)
226 // FIXME(eddyb) This should use `IndexVec<Local, Option<_>>`.
227 remap: FxHashMap<Local, (Ty<'tcx>, VariantIdx, usize)>,
229 // A map from a suspension point in a block to the locals which have live storage at that point
230 storage_liveness: IndexVec<BasicBlock, Option<BitSet<Local>>>,
232 // A list of suspension points, generated during the transform
233 suspension_points: Vec<SuspensionPoint<'tcx>>,
235 // The set of locals that have no `StorageLive`/`StorageDead` annotations.
236 always_live_locals: BitSet<Local>,
238 // The original RETURN_PLACE local
239 new_ret_local: Local,
242 impl<'tcx> TransformVisitor<'tcx> {
243 // Make a GeneratorState variant assignment. `core::ops::GeneratorState` only has single
244 // element tuple variants, so we can just write to the downcasted first field and then set the
245 // discriminant to the appropriate variant.
250 source_info: SourceInfo,
251 ) -> impl Iterator<Item = Statement<'tcx>> {
252 let kind = AggregateKind::Adt(self.state_adt_ref.did(), idx, self.state_substs, None, None);
253 assert_eq!(self.state_adt_ref.variant(idx).fields.len(), 1);
256 .bound_type_of(self.state_adt_ref.variant(idx).fields[0].did)
257 .subst(self.tcx, self.state_substs);
259 Place::return_place(),
260 std::iter::once((val, ty)),
267 // Create a Place referencing a generator struct field
268 fn make_field(&self, variant_index: VariantIdx, idx: usize, ty: Ty<'tcx>) -> Place<'tcx> {
269 let self_place = Place::from(SELF_ARG);
270 let base = self.tcx.mk_place_downcast_unnamed(self_place, variant_index);
271 let mut projection = base.projection.to_vec();
272 projection.push(ProjectionElem::Field(Field::new(idx), ty));
274 Place { local: base.local, projection: self.tcx.intern_place_elems(&projection) }
277 // Create a statement which changes the discriminant
278 fn set_discr(&self, state_disc: VariantIdx, source_info: SourceInfo) -> Statement<'tcx> {
279 let self_place = Place::from(SELF_ARG);
282 kind: StatementKind::SetDiscriminant {
283 place: Box::new(self_place),
284 variant_index: state_disc,
289 // Create a statement which reads the discriminant into a temporary
290 fn get_discr(&self, body: &mut Body<'tcx>) -> (Statement<'tcx>, Place<'tcx>) {
291 let temp_decl = LocalDecl::new(self.discr_ty, body.span).internal();
292 let local_decls_len = body.local_decls.push(temp_decl);
293 let temp = Place::from(local_decls_len);
295 let self_place = Place::from(SELF_ARG);
296 let assign = Statement {
297 source_info: SourceInfo::outermost(body.span),
298 kind: StatementKind::Assign(Box::new((temp, Rvalue::Discriminant(self_place)))),
304 impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
305 fn tcx(&self) -> TyCtxt<'tcx> {
309 fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
310 assert_eq!(self.remap.get(local), None);
315 place: &mut Place<'tcx>,
316 _context: PlaceContext,
319 // Replace an Local in the remap with a generator struct access
320 if let Some(&(ty, variant_index, idx)) = self.remap.get(&place.local) {
321 replace_base(place, self.make_field(variant_index, idx, ty), self.tcx);
325 fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
326 // Remove StorageLive and StorageDead statements for remapped locals
327 data.retain_statements(|s| match s.kind {
328 StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
329 !self.remap.contains_key(&l)
334 let ret_val = match data.terminator().kind {
335 TerminatorKind::Return => Some((
338 Operand::Move(Place::from(self.new_ret_local)),
341 TerminatorKind::Yield { ref value, resume, resume_arg, drop } => {
342 Some((VariantIdx::new(0), Some((resume, resume_arg)), value.clone(), drop))
347 if let Some((state_idx, resume, v, drop)) = ret_val {
348 let source_info = data.terminator().source_info;
349 // We must assign the value first in case it gets declared dead below
350 data.statements.extend(self.make_state(state_idx, v, source_info));
351 let state = if let Some((resume, mut resume_arg)) = resume {
353 let state = RESERVED_VARIANTS + self.suspension_points.len();
355 // The resume arg target location might itself be remapped if its base local is
356 // live across a yield.
358 if let Some(&(ty, variant, idx)) = self.remap.get(&resume_arg.local) {
359 replace_base(&mut resume_arg, self.make_field(variant, idx, ty), self.tcx);
365 self.suspension_points.push(SuspensionPoint {
370 storage_liveness: self.storage_liveness[block].clone().unwrap().into(),
373 VariantIdx::new(state)
376 VariantIdx::new(RETURNED) // state for returned
378 data.statements.push(self.set_discr(state, source_info));
379 data.terminator_mut().kind = TerminatorKind::Return;
382 self.super_basic_block_data(block, data);
386 fn make_generator_state_argument_indirect<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
387 let gen_ty = body.local_decls.raw[1].ty;
390 tcx.mk_ref(tcx.lifetimes.re_erased, ty::TypeAndMut { ty: gen_ty, mutbl: Mutability::Mut });
392 // Replace the by value generator argument
393 body.local_decls.raw[1].ty = ref_gen_ty;
395 // Add a deref to accesses of the generator state
396 DerefArgVisitor { tcx }.visit_body(body);
399 fn make_generator_state_argument_pinned<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
400 let ref_gen_ty = body.local_decls.raw[1].ty;
402 let pin_did = tcx.require_lang_item(LangItem::Pin, Some(body.span));
403 let pin_adt_ref = tcx.adt_def(pin_did);
404 let substs = tcx.intern_substs(&[ref_gen_ty.into()]);
405 let pin_ref_gen_ty = tcx.mk_adt(pin_adt_ref, substs);
407 // Replace the by ref generator argument
408 body.local_decls.raw[1].ty = pin_ref_gen_ty;
410 // Add the Pin field access to accesses of the generator state
411 PinArgVisitor { ref_gen_ty, tcx }.visit_body(body);
414 /// Allocates a new local and replaces all references of `local` with it. Returns the new local.
416 /// `local` will be changed to a new local decl with type `ty`.
418 /// Note that the new local will be uninitialized. It is the caller's responsibility to assign some
419 /// valid value to it before its first use.
420 fn replace_local<'tcx>(
423 body: &mut Body<'tcx>,
426 let new_decl = LocalDecl::new(ty, body.span);
427 let new_local = body.local_decls.push(new_decl);
428 body.local_decls.swap(local, new_local);
430 RenameLocalVisitor { from: local, to: new_local, tcx }.visit_body(body);
435 struct LivenessInfo {
436 /// Which locals are live across any suspension point.
437 saved_locals: GeneratorSavedLocals,
439 /// The set of saved locals live at each suspension point.
440 live_locals_at_suspension_points: Vec<BitSet<GeneratorSavedLocal>>,
442 /// Parallel vec to the above with SourceInfo for each yield terminator.
443 source_info_at_suspension_points: Vec<SourceInfo>,
445 /// For every saved local, the set of other saved locals that are
446 /// storage-live at the same time as this local. We cannot overlap locals in
447 /// the layout which have conflicting storage.
448 storage_conflicts: BitMatrix<GeneratorSavedLocal, GeneratorSavedLocal>,
450 /// For every suspending block, the locals which are storage-live across
451 /// that suspension point.
452 storage_liveness: IndexVec<BasicBlock, Option<BitSet<Local>>>,
455 fn locals_live_across_suspend_points<'tcx>(
458 always_live_locals: &BitSet<Local>,
461 let body_ref: &Body<'_> = &body;
463 // Calculate when MIR locals have live storage. This gives us an upper bound of their
465 let mut storage_live = MaybeStorageLive::new(always_live_locals.clone())
466 .into_engine(tcx, body_ref)
467 .iterate_to_fixpoint()
468 .into_results_cursor(body_ref);
470 // Calculate the MIR locals which have been previously
471 // borrowed (even if they are still active).
472 let borrowed_locals_results =
473 MaybeBorrowedLocals.into_engine(tcx, body_ref).pass_name("generator").iterate_to_fixpoint();
475 let mut borrowed_locals_cursor =
476 rustc_mir_dataflow::ResultsCursor::new(body_ref, &borrowed_locals_results);
478 // Calculate the MIR locals that we actually need to keep storage around
480 let requires_storage_results = MaybeRequiresStorage::new(body, &borrowed_locals_results)
481 .into_engine(tcx, body_ref)
482 .iterate_to_fixpoint();
483 let mut requires_storage_cursor =
484 rustc_mir_dataflow::ResultsCursor::new(body_ref, &requires_storage_results);
486 // Calculate the liveness of MIR locals ignoring borrows.
487 let mut liveness = MaybeLiveLocals
488 .into_engine(tcx, body_ref)
489 .pass_name("generator")
490 .iterate_to_fixpoint()
491 .into_results_cursor(body_ref);
493 let mut storage_liveness_map = IndexVec::from_elem(None, &body.basic_blocks);
494 let mut live_locals_at_suspension_points = Vec::new();
495 let mut source_info_at_suspension_points = Vec::new();
496 let mut live_locals_at_any_suspension_point = BitSet::new_empty(body.local_decls.len());
498 for (block, data) in body.basic_blocks.iter_enumerated() {
499 if let TerminatorKind::Yield { .. } = data.terminator().kind {
500 let loc = Location { block, statement_index: data.statements.len() };
502 liveness.seek_to_block_end(block);
503 let mut live_locals: BitSet<_> = BitSet::new_empty(body.local_decls.len());
504 live_locals.union(liveness.get());
507 // The `liveness` variable contains the liveness of MIR locals ignoring borrows.
508 // This is correct for movable generators since borrows cannot live across
509 // suspension points. However for immovable generators we need to account for
510 // borrows, so we conservatively assume that all borrowed locals are live until
511 // we find a StorageDead statement referencing the locals.
512 // To do this we just union our `liveness` result with `borrowed_locals`, which
513 // contains all the locals which has been borrowed before this suspension point.
514 // If a borrow is converted to a raw reference, we must also assume that it lives
515 // forever. Note that the final liveness is still bounded by the storage liveness
516 // of the local, which happens using the `intersect` operation below.
517 borrowed_locals_cursor.seek_before_primary_effect(loc);
518 live_locals.union(borrowed_locals_cursor.get());
521 // Store the storage liveness for later use so we can restore the state
522 // after a suspension point
523 storage_live.seek_before_primary_effect(loc);
524 storage_liveness_map[block] = Some(storage_live.get().clone());
526 // Locals live are live at this point only if they are used across
527 // suspension points (the `liveness` variable)
528 // and their storage is required (the `storage_required` variable)
529 requires_storage_cursor.seek_before_primary_effect(loc);
530 live_locals.intersect(requires_storage_cursor.get());
532 // The generator argument is ignored.
533 live_locals.remove(SELF_ARG);
535 debug!("loc = {:?}, live_locals = {:?}", loc, live_locals);
537 // Add the locals live at this suspension point to the set of locals which live across
538 // any suspension points
539 live_locals_at_any_suspension_point.union(&live_locals);
541 live_locals_at_suspension_points.push(live_locals);
542 source_info_at_suspension_points.push(data.terminator().source_info);
546 debug!("live_locals_anywhere = {:?}", live_locals_at_any_suspension_point);
547 let saved_locals = GeneratorSavedLocals(live_locals_at_any_suspension_point);
549 // Renumber our liveness_map bitsets to include only the locals we are
551 let live_locals_at_suspension_points = live_locals_at_suspension_points
553 .map(|live_here| saved_locals.renumber_bitset(&live_here))
556 let storage_conflicts = compute_storage_conflicts(
559 always_live_locals.clone(),
560 requires_storage_results,
565 live_locals_at_suspension_points,
566 source_info_at_suspension_points,
568 storage_liveness: storage_liveness_map,
572 /// The set of `Local`s that must be saved across yield points.
574 /// `GeneratorSavedLocal` is indexed in terms of the elements in this set;
575 /// i.e. `GeneratorSavedLocal::new(1)` corresponds to the second local
576 /// included in this set.
577 struct GeneratorSavedLocals(BitSet<Local>);
579 impl GeneratorSavedLocals {
580 /// Returns an iterator over each `GeneratorSavedLocal` along with the `Local` it corresponds
582 fn iter_enumerated(&self) -> impl '_ + Iterator<Item = (GeneratorSavedLocal, Local)> {
583 self.iter().enumerate().map(|(i, l)| (GeneratorSavedLocal::from(i), l))
586 /// Transforms a `BitSet<Local>` that contains only locals saved across yield points to the
587 /// equivalent `BitSet<GeneratorSavedLocal>`.
588 fn renumber_bitset(&self, input: &BitSet<Local>) -> BitSet<GeneratorSavedLocal> {
589 assert!(self.superset(&input), "{:?} not a superset of {:?}", self.0, input);
590 let mut out = BitSet::new_empty(self.count());
591 for (saved_local, local) in self.iter_enumerated() {
592 if input.contains(local) {
593 out.insert(saved_local);
599 fn get(&self, local: Local) -> Option<GeneratorSavedLocal> {
600 if !self.contains(local) {
604 let idx = self.iter().take_while(|&l| l < local).count();
605 Some(GeneratorSavedLocal::new(idx))
609 impl ops::Deref for GeneratorSavedLocals {
610 type Target = BitSet<Local>;
612 fn deref(&self) -> &Self::Target {
617 /// For every saved local, looks for which locals are StorageLive at the same
618 /// time. Generates a bitset for every local of all the other locals that may be
619 /// StorageLive simultaneously with that local. This is used in the layout
620 /// computation; see `GeneratorLayout` for more.
621 fn compute_storage_conflicts<'mir, 'tcx>(
622 body: &'mir Body<'tcx>,
623 saved_locals: &GeneratorSavedLocals,
624 always_live_locals: BitSet<Local>,
625 requires_storage: rustc_mir_dataflow::Results<'tcx, MaybeRequiresStorage<'mir, 'tcx>>,
626 ) -> BitMatrix<GeneratorSavedLocal, GeneratorSavedLocal> {
627 assert_eq!(body.local_decls.len(), saved_locals.domain_size());
629 debug!("compute_storage_conflicts({:?})", body.span);
630 debug!("always_live = {:?}", always_live_locals);
632 // Locals that are always live or ones that need to be stored across
633 // suspension points are not eligible for overlap.
634 let mut ineligible_locals = always_live_locals;
635 ineligible_locals.intersect(&**saved_locals);
637 // Compute the storage conflicts for all eligible locals.
638 let mut visitor = StorageConflictVisitor {
640 saved_locals: &saved_locals,
641 local_conflicts: BitMatrix::from_row_n(&ineligible_locals, body.local_decls.len()),
644 requires_storage.visit_reachable_with(body, &mut visitor);
646 let local_conflicts = visitor.local_conflicts;
648 // Compress the matrix using only stored locals (Local -> GeneratorSavedLocal).
650 // NOTE: Today we store a full conflict bitset for every local. Technically
651 // this is twice as many bits as we need, since the relation is symmetric.
652 // However, in practice these bitsets are not usually large. The layout code
653 // also needs to keep track of how many conflicts each local has, so it's
654 // simpler to keep it this way for now.
655 let mut storage_conflicts = BitMatrix::new(saved_locals.count(), saved_locals.count());
656 for (saved_local_a, local_a) in saved_locals.iter_enumerated() {
657 if ineligible_locals.contains(local_a) {
658 // Conflicts with everything.
659 storage_conflicts.insert_all_into_row(saved_local_a);
661 // Keep overlap information only for stored locals.
662 for (saved_local_b, local_b) in saved_locals.iter_enumerated() {
663 if local_conflicts.contains(local_a, local_b) {
664 storage_conflicts.insert(saved_local_a, saved_local_b);
672 struct StorageConflictVisitor<'mir, 'tcx, 's> {
673 body: &'mir Body<'tcx>,
674 saved_locals: &'s GeneratorSavedLocals,
675 // FIXME(tmandry): Consider using sparse bitsets here once we have good
676 // benchmarks for generators.
677 local_conflicts: BitMatrix<Local, Local>,
680 impl<'mir, 'tcx> rustc_mir_dataflow::ResultsVisitor<'mir, 'tcx>
681 for StorageConflictVisitor<'mir, 'tcx, '_>
683 type FlowState = BitSet<Local>;
685 fn visit_statement_before_primary_effect(
687 state: &Self::FlowState,
688 _statement: &'mir Statement<'tcx>,
691 self.apply_state(state, loc);
694 fn visit_terminator_before_primary_effect(
696 state: &Self::FlowState,
697 _terminator: &'mir Terminator<'tcx>,
700 self.apply_state(state, loc);
704 impl StorageConflictVisitor<'_, '_, '_> {
705 fn apply_state(&mut self, flow_state: &BitSet<Local>, loc: Location) {
706 // Ignore unreachable blocks.
707 if self.body.basic_blocks[loc.block].terminator().kind == TerminatorKind::Unreachable {
711 let mut eligible_storage_live = flow_state.clone();
712 eligible_storage_live.intersect(&**self.saved_locals);
714 for local in eligible_storage_live.iter() {
715 self.local_conflicts.union_row_with(&eligible_storage_live, local);
718 if eligible_storage_live.count() > 1 {
719 trace!("at {:?}, eligible_storage_live={:?}", loc, eligible_storage_live);
724 /// Validates the typeck view of the generator against the actual set of types saved between
726 fn sanitize_witness<'tcx>(
730 upvars: Vec<Ty<'tcx>>,
731 saved_locals: &GeneratorSavedLocals,
733 let did = body.source.def_id();
734 let param_env = tcx.param_env(did);
736 let allowed_upvars = tcx.normalize_erasing_regions(param_env, upvars);
737 let allowed = match witness.kind() {
738 &ty::GeneratorWitness(interior_tys) => {
739 tcx.normalize_erasing_late_bound_regions(param_env, interior_tys)
742 tcx.sess.delay_span_bug(
744 &format!("unexpected generator witness type {:?}", witness.kind()),
750 for (local, decl) in body.local_decls.iter_enumerated() {
751 // Ignore locals which are internal or not saved between yields.
752 if !saved_locals.contains(local) || decl.internal {
755 let decl_ty = tcx.normalize_erasing_regions(param_env, decl.ty);
757 // Sanity check that typeck knows about the type of locals which are
758 // live across a suspension point
759 if !allowed.contains(&decl_ty) && !allowed_upvars.contains(&decl_ty) {
762 "Broken MIR: generator contains type {} in MIR, \
763 but typeck only knows about {} and {:?}",
772 fn compute_layout<'tcx>(
773 liveness: LivenessInfo,
774 body: &mut Body<'tcx>,
776 FxHashMap<Local, (Ty<'tcx>, VariantIdx, usize)>,
777 GeneratorLayout<'tcx>,
778 IndexVec<BasicBlock, Option<BitSet<Local>>>,
782 live_locals_at_suspension_points,
783 source_info_at_suspension_points,
788 // Gather live local types and their indices.
789 let mut locals = IndexVec::<GeneratorSavedLocal, _>::new();
790 let mut tys = IndexVec::<GeneratorSavedLocal, _>::new();
791 for (saved_local, local) in saved_locals.iter_enumerated() {
793 tys.push(body.local_decls[local].ty);
794 debug!("generator saved local {:?} => {:?}", saved_local, local);
797 // Leave empty variants for the UNRESUMED, RETURNED, and POISONED states.
798 // In debuginfo, these will correspond to the beginning (UNRESUMED) or end
799 // (RETURNED, POISONED) of the function.
800 let body_span = body.source_scopes[OUTERMOST_SOURCE_SCOPE].span;
801 let mut variant_source_info: IndexVec<VariantIdx, SourceInfo> = [
802 SourceInfo::outermost(body_span.shrink_to_lo()),
803 SourceInfo::outermost(body_span.shrink_to_hi()),
804 SourceInfo::outermost(body_span.shrink_to_hi()),
810 // Build the generator variant field list.
811 // Create a map from local indices to generator struct indices.
812 let mut variant_fields: IndexVec<VariantIdx, IndexVec<Field, GeneratorSavedLocal>> =
813 iter::repeat(IndexVec::new()).take(RESERVED_VARIANTS).collect();
814 let mut remap = FxHashMap::default();
815 for (suspension_point_idx, live_locals) in live_locals_at_suspension_points.iter().enumerate() {
816 let variant_index = VariantIdx::from(RESERVED_VARIANTS + suspension_point_idx);
817 let mut fields = IndexVec::new();
818 for (idx, saved_local) in live_locals.iter().enumerate() {
819 fields.push(saved_local);
820 // Note that if a field is included in multiple variants, we will
821 // just use the first one here. That's fine; fields do not move
822 // around inside generators, so it doesn't matter which variant
823 // index we access them by.
824 remap.entry(locals[saved_local]).or_insert((tys[saved_local], variant_index, idx));
826 variant_fields.push(fields);
827 variant_source_info.push(source_info_at_suspension_points[suspension_point_idx]);
829 debug!("generator variant_fields = {:?}", variant_fields);
830 debug!("generator storage_conflicts = {:#?}", storage_conflicts);
833 GeneratorLayout { field_tys: tys, variant_fields, variant_source_info, storage_conflicts };
835 (remap, layout, storage_liveness)
838 /// Replaces the entry point of `body` with a block that switches on the generator discriminant and
839 /// dispatches to blocks according to `cases`.
841 /// After this function, the former entry point of the function will be bb1.
842 fn insert_switch<'tcx>(
843 body: &mut Body<'tcx>,
844 cases: Vec<(usize, BasicBlock)>,
845 transform: &TransformVisitor<'tcx>,
846 default: TerminatorKind<'tcx>,
848 let default_block = insert_term_block(body, default);
849 let (assign, discr) = transform.get_discr(body);
851 SwitchTargets::new(cases.iter().map(|(i, bb)| ((*i) as u128, *bb)), default_block);
852 let switch = TerminatorKind::SwitchInt {
853 discr: Operand::Move(discr),
854 switch_ty: transform.discr_ty,
855 targets: switch_targets,
858 let source_info = SourceInfo::outermost(body.span);
859 body.basic_blocks_mut().raw.insert(
862 statements: vec![assign],
863 terminator: Some(Terminator { source_info, kind: switch }),
868 let blocks = body.basic_blocks_mut().iter_mut();
870 for target in blocks.flat_map(|b| b.terminator_mut().successors_mut()) {
871 *target = BasicBlock::new(target.index() + 1);
875 fn elaborate_generator_drops<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
876 use crate::shim::DropShimElaborator;
877 use rustc_middle::mir::patch::MirPatch;
878 use rustc_mir_dataflow::elaborate_drops::{elaborate_drop, Unwind};
880 // Note that `elaborate_drops` only drops the upvars of a generator, and
881 // this is ok because `open_drop` can only be reached within that own
882 // generator's resume function.
884 let def_id = body.source.def_id();
885 let param_env = tcx.param_env(def_id);
887 let mut elaborator = DropShimElaborator { body, patch: MirPatch::new(body), tcx, param_env };
889 for (block, block_data) in body.basic_blocks.iter_enumerated() {
890 let (target, unwind, source_info) = match block_data.terminator() {
891 Terminator { source_info, kind: TerminatorKind::Drop { place, target, unwind } } => {
892 if let Some(local) = place.as_local() {
893 if local == SELF_ARG {
894 (target, unwind, source_info)
904 let unwind = if block_data.is_cleanup {
907 Unwind::To(unwind.unwrap_or_else(|| elaborator.patch.resume_block()))
912 Place::from(SELF_ARG),
919 elaborator.patch.apply(body);
922 fn create_generator_drop_shim<'tcx>(
924 transform: &TransformVisitor<'tcx>,
926 body: &mut Body<'tcx>,
927 drop_clean: BasicBlock,
929 let mut body = body.clone();
930 body.arg_count = 1; // make sure the resume argument is not included here
932 let source_info = SourceInfo::outermost(body.span);
934 let mut cases = create_cases(&mut body, transform, Operation::Drop);
936 cases.insert(0, (UNRESUMED, drop_clean));
938 // The returned state and the poisoned state fall through to the default
939 // case which is just to return
941 insert_switch(&mut body, cases, &transform, TerminatorKind::Return);
943 for block in body.basic_blocks_mut() {
944 let kind = &mut block.terminator_mut().kind;
945 if let TerminatorKind::GeneratorDrop = *kind {
946 *kind = TerminatorKind::Return;
950 // Replace the return variable
951 body.local_decls[RETURN_PLACE] = LocalDecl::with_source_info(tcx.mk_unit(), source_info);
953 make_generator_state_argument_indirect(tcx, &mut body);
955 // Change the generator argument from &mut to *mut
956 body.local_decls[SELF_ARG] = LocalDecl::with_source_info(
957 tcx.mk_ptr(ty::TypeAndMut { ty: gen_ty, mutbl: hir::Mutability::Mut }),
960 if tcx.sess.opts.unstable_opts.mir_emit_retag {
961 // Alias tracking must know we changed the type
962 body.basic_blocks_mut()[START_BLOCK].statements.insert(
966 kind: StatementKind::Retag(RetagKind::Raw, Box::new(Place::from(SELF_ARG))),
971 // Make sure we remove dead blocks to remove
972 // unrelated code from the resume part of the function
973 simplify::remove_dead_blocks(tcx, &mut body);
975 dump_mir(tcx, None, "generator_drop", &0, &body, |_, _| Ok(()));
980 fn insert_term_block<'tcx>(body: &mut Body<'tcx>, kind: TerminatorKind<'tcx>) -> BasicBlock {
981 let source_info = SourceInfo::outermost(body.span);
982 body.basic_blocks_mut().push(BasicBlockData {
983 statements: Vec::new(),
984 terminator: Some(Terminator { source_info, kind }),
989 fn insert_panic_block<'tcx>(
991 body: &mut Body<'tcx>,
992 message: AssertMessage<'tcx>,
994 let assert_block = BasicBlock::new(body.basic_blocks.len());
995 let term = TerminatorKind::Assert {
996 cond: Operand::Constant(Box::new(Constant {
999 literal: ConstantKind::from_bool(tcx, false),
1003 target: assert_block,
1007 let source_info = SourceInfo::outermost(body.span);
1008 body.basic_blocks_mut().push(BasicBlockData {
1009 statements: Vec::new(),
1010 terminator: Some(Terminator { source_info, kind: term }),
1017 fn can_return<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, param_env: ty::ParamEnv<'tcx>) -> bool {
1018 // Returning from a function with an uninhabited return type is undefined behavior.
1019 if tcx.conservative_is_privately_uninhabited(param_env.and(body.return_ty())) {
1023 // If there's a return terminator the function may return.
1024 for block in body.basic_blocks.iter() {
1025 if let TerminatorKind::Return = block.terminator().kind {
1030 // Otherwise the function can't return.
1034 fn can_unwind<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) -> bool {
1035 // Nothing can unwind when landing pads are off.
1036 if tcx.sess.panic_strategy() == PanicStrategy::Abort {
1040 // Unwinds can only start at certain terminators.
1041 for block in body.basic_blocks.iter() {
1042 match block.terminator().kind {
1043 // These never unwind.
1044 TerminatorKind::Goto { .. }
1045 | TerminatorKind::SwitchInt { .. }
1046 | TerminatorKind::Abort
1047 | TerminatorKind::Return
1048 | TerminatorKind::Unreachable
1049 | TerminatorKind::GeneratorDrop
1050 | TerminatorKind::FalseEdge { .. }
1051 | TerminatorKind::FalseUnwind { .. } => {}
1053 // Resume will *continue* unwinding, but if there's no other unwinding terminator it
1054 // will never be reached.
1055 TerminatorKind::Resume => {}
1057 TerminatorKind::Yield { .. } => {
1058 unreachable!("`can_unwind` called before generator transform")
1061 // These may unwind.
1062 TerminatorKind::Drop { .. }
1063 | TerminatorKind::DropAndReplace { .. }
1064 | TerminatorKind::Call { .. }
1065 | TerminatorKind::InlineAsm { .. }
1066 | TerminatorKind::Assert { .. } => return true,
1070 // If we didn't find an unwinding terminator, the function cannot unwind.
1074 fn create_generator_resume_function<'tcx>(
1076 transform: TransformVisitor<'tcx>,
1077 body: &mut Body<'tcx>,
1080 let can_unwind = can_unwind(tcx, body);
1082 // Poison the generator when it unwinds
1084 let source_info = SourceInfo::outermost(body.span);
1085 let poison_block = body.basic_blocks_mut().push(BasicBlockData {
1086 statements: vec![transform.set_discr(VariantIdx::new(POISONED), source_info)],
1087 terminator: Some(Terminator { source_info, kind: TerminatorKind::Resume }),
1091 for (idx, block) in body.basic_blocks_mut().iter_enumerated_mut() {
1092 let source_info = block.terminator().source_info;
1094 if let TerminatorKind::Resume = block.terminator().kind {
1095 // An existing `Resume` terminator is redirected to jump to our dedicated
1096 // "poisoning block" above.
1097 if idx != poison_block {
1098 *block.terminator_mut() = Terminator {
1100 kind: TerminatorKind::Goto { target: poison_block },
1103 } else if !block.is_cleanup {
1104 // Any terminators that *can* unwind but don't have an unwind target set are also
1105 // pointed at our poisoning block (unless they're part of the cleanup path).
1106 if let Some(unwind @ None) = block.terminator_mut().unwind_mut() {
1107 *unwind = Some(poison_block);
1113 let mut cases = create_cases(body, &transform, Operation::Resume);
1115 use rustc_middle::mir::AssertKind::{ResumedAfterPanic, ResumedAfterReturn};
1117 // Jump to the entry point on the unresumed
1118 cases.insert(0, (UNRESUMED, BasicBlock::new(0)));
1120 // Panic when resumed on the returned or poisoned state
1121 let generator_kind = body.generator_kind().unwrap();
1126 (POISONED, insert_panic_block(tcx, body, ResumedAfterPanic(generator_kind))),
1133 (RETURNED, insert_panic_block(tcx, body, ResumedAfterReturn(generator_kind))),
1137 insert_switch(body, cases, &transform, TerminatorKind::Unreachable);
1139 make_generator_state_argument_indirect(tcx, body);
1140 make_generator_state_argument_pinned(tcx, body);
1142 // Make sure we remove dead blocks to remove
1143 // unrelated code from the drop part of the function
1144 simplify::remove_dead_blocks(tcx, body);
1146 dump_mir(tcx, None, "generator_resume", &0, body, |_, _| Ok(()));
1149 fn insert_clean_drop(body: &mut Body<'_>) -> BasicBlock {
1150 let return_block = insert_term_block(body, TerminatorKind::Return);
1153 TerminatorKind::Drop { place: Place::from(SELF_ARG), target: return_block, unwind: None };
1154 let source_info = SourceInfo::outermost(body.span);
1156 // Create a block to destroy an unresumed generators. This can only destroy upvars.
1157 body.basic_blocks_mut().push(BasicBlockData {
1158 statements: Vec::new(),
1159 terminator: Some(Terminator { source_info, kind: term }),
1164 /// An operation that can be performed on a generator.
1165 #[derive(PartialEq, Copy, Clone)]
1172 fn target_block(self, point: &SuspensionPoint<'_>) -> Option<BasicBlock> {
1174 Operation::Resume => Some(point.resume),
1175 Operation::Drop => point.drop,
1180 fn create_cases<'tcx>(
1181 body: &mut Body<'tcx>,
1182 transform: &TransformVisitor<'tcx>,
1183 operation: Operation,
1184 ) -> Vec<(usize, BasicBlock)> {
1185 let source_info = SourceInfo::outermost(body.span);
1190 .filter_map(|point| {
1191 // Find the target for this suspension point, if applicable
1192 operation.target_block(point).map(|target| {
1193 let mut statements = Vec::new();
1195 // Create StorageLive instructions for locals with live storage
1196 for i in 0..(body.local_decls.len()) {
1198 // The resume argument is live on function entry. Don't insert a
1199 // `StorageLive`, or the following `Assign` will read from uninitialized
1204 let l = Local::new(i);
1205 let needs_storage_live = point.storage_liveness.contains(l)
1206 && !transform.remap.contains_key(&l)
1207 && !transform.always_live_locals.contains(l);
1208 if needs_storage_live {
1210 .push(Statement { source_info, kind: StatementKind::StorageLive(l) });
1214 if operation == Operation::Resume {
1215 // Move the resume argument to the destination place of the `Yield` terminator
1216 let resume_arg = Local::new(2); // 0 = return, 1 = self
1217 statements.push(Statement {
1219 kind: StatementKind::Assign(Box::new((
1221 Rvalue::Use(Operand::Move(resume_arg.into())),
1226 // Then jump to the real target
1227 let block = body.basic_blocks_mut().push(BasicBlockData {
1229 terminator: Some(Terminator {
1231 kind: TerminatorKind::Goto { target },
1236 (point.state, block)
1242 impl<'tcx> MirPass<'tcx> for StateTransform {
1243 fn phase_change(&self) -> Option<MirPhase> {
1244 Some(MirPhase::GeneratorsLowered)
1247 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
1248 let Some(yield_ty) = body.yield_ty() else {
1249 // This only applies to generators
1253 assert!(body.generator_drop().is_none());
1255 // The first argument is the generator type passed by value
1256 let gen_ty = body.local_decls.raw[1].ty;
1258 // Get the interior types and substs which typeck computed
1259 let (upvars, interior, discr_ty, movable) = match *gen_ty.kind() {
1260 ty::Generator(_, substs, movability) => {
1261 let substs = substs.as_generator();
1263 substs.upvar_tys().collect(),
1265 substs.discr_ty(tcx),
1266 movability == hir::Movability::Movable,
1271 .delay_span_bug(body.span, &format!("unexpected generator type {}", gen_ty));
1276 // Compute GeneratorState<yield_ty, return_ty>
1277 let state_did = tcx.require_lang_item(LangItem::GeneratorState, None);
1278 let state_adt_ref = tcx.adt_def(state_did);
1279 let state_substs = tcx.intern_substs(&[yield_ty.into(), body.return_ty().into()]);
1280 let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
1282 // We rename RETURN_PLACE which has type mir.return_ty to new_ret_local
1283 // RETURN_PLACE then is a fresh unused local with type ret_ty.
1284 let new_ret_local = replace_local(RETURN_PLACE, ret_ty, body, tcx);
1286 // We also replace the resume argument and insert an `Assign`.
1287 // This is needed because the resume argument `_2` might be live across a `yield`, in which
1288 // case there is no `Assign` to it that the transform can turn into a store to the generator
1289 // state. After the yield the slot in the generator state would then be uninitialized.
1290 let resume_local = Local::new(2);
1291 let new_resume_local =
1292 replace_local(resume_local, body.local_decls[resume_local].ty, body, tcx);
1294 // When first entering the generator, move the resume argument into its new local.
1295 let source_info = SourceInfo::outermost(body.span);
1296 let stmts = &mut body.basic_blocks_mut()[BasicBlock::new(0)].statements;
1301 kind: StatementKind::Assign(Box::new((
1302 new_resume_local.into(),
1303 Rvalue::Use(Operand::Move(resume_local.into())),
1308 let always_live_locals = always_storage_live_locals(&body);
1311 locals_live_across_suspend_points(tcx, body, &always_live_locals, movable);
1313 sanitize_witness(tcx, body, interior, upvars, &liveness_info.saved_locals);
1315 if tcx.sess.opts.unstable_opts.validate_mir {
1316 let mut vis = EnsureGeneratorFieldAssignmentsNeverAlias {
1317 assigned_local: None,
1318 saved_locals: &liveness_info.saved_locals,
1319 storage_conflicts: &liveness_info.storage_conflicts,
1322 vis.visit_body(body);
1325 // Extract locals which are live across suspension point into `layout`
1326 // `remap` gives a mapping from local indices onto generator struct indices
1327 // `storage_liveness` tells us which locals have live storage at suspension points
1328 let (remap, layout, storage_liveness) = compute_layout(liveness_info, body);
1330 let can_return = can_return(tcx, body, tcx.param_env(body.source.def_id()));
1332 // Run the transformation which converts Places from Local to generator struct
1333 // accesses for locals in `remap`.
1334 // It also rewrites `return x` and `yield y` as writing a new generator state and returning
1335 // GeneratorState::Complete(x) and GeneratorState::Yielded(y) respectively.
1336 let mut transform = TransformVisitor {
1343 suspension_points: Vec::new(),
1347 transform.visit_body(body);
1349 // Update our MIR struct to reflect the changes we've made
1350 body.arg_count = 2; // self, resume arg
1351 body.spread_arg = None;
1353 body.generator.as_mut().unwrap().yield_ty = None;
1354 body.generator.as_mut().unwrap().generator_layout = Some(layout);
1356 // Insert `drop(generator_struct)` which is used to drop upvars for generators in
1357 // the unresumed state.
1358 // This is expanded to a drop ladder in `elaborate_generator_drops`.
1359 let drop_clean = insert_clean_drop(body);
1361 dump_mir(tcx, None, "generator_pre-elab", &0, body, |_, _| Ok(()));
1363 // Expand `drop(generator_struct)` to a drop ladder which destroys upvars.
1364 // If any upvars are moved out of, drop elaboration will handle upvar destruction.
1365 // However we need to also elaborate the code generated by `insert_clean_drop`.
1366 elaborate_generator_drops(tcx, body);
1368 dump_mir(tcx, None, "generator_post-transform", &0, body, |_, _| Ok(()));
1370 // Create a copy of our MIR and use it to create the drop shim for the generator
1371 let drop_shim = create_generator_drop_shim(tcx, &transform, gen_ty, body, drop_clean);
1373 body.generator.as_mut().unwrap().generator_drop = Some(drop_shim);
1375 // Create the Generator::resume function
1376 create_generator_resume_function(tcx, transform, body, can_return);
1378 // Run derefer to fix Derefs that are not in the first place
1379 deref_finder(tcx, body);
1383 /// Looks for any assignments between locals (e.g., `_4 = _5`) that will both be converted to fields
1384 /// in the generator state machine but whose storage is not marked as conflicting
1386 /// Validation needs to happen immediately *before* `TransformVisitor` is invoked, not after.
1388 /// This condition would arise when the assignment is the last use of `_5` but the initial
1389 /// definition of `_4` if we weren't extra careful to mark all locals used inside a statement as
1390 /// conflicting. Non-conflicting generator saved locals may be stored at the same location within
1391 /// the generator state machine, which would result in ill-formed MIR: the left-hand and right-hand
1392 /// sides of an assignment may not alias. This caused a miscompilation in [#73137].
1394 /// [#73137]: https://github.com/rust-lang/rust/issues/73137
1395 struct EnsureGeneratorFieldAssignmentsNeverAlias<'a> {
1396 saved_locals: &'a GeneratorSavedLocals,
1397 storage_conflicts: &'a BitMatrix<GeneratorSavedLocal, GeneratorSavedLocal>,
1398 assigned_local: Option<GeneratorSavedLocal>,
1401 impl EnsureGeneratorFieldAssignmentsNeverAlias<'_> {
1402 fn saved_local_for_direct_place(&self, place: Place<'_>) -> Option<GeneratorSavedLocal> {
1403 if place.is_indirect() {
1407 self.saved_locals.get(place.local)
1410 fn check_assigned_place(&mut self, place: Place<'_>, f: impl FnOnce(&mut Self)) {
1411 if let Some(assigned_local) = self.saved_local_for_direct_place(place) {
1412 assert!(self.assigned_local.is_none(), "`check_assigned_place` must not recurse");
1414 self.assigned_local = Some(assigned_local);
1416 self.assigned_local = None;
1421 impl<'tcx> Visitor<'tcx> for EnsureGeneratorFieldAssignmentsNeverAlias<'_> {
1422 fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
1423 let Some(lhs) = self.assigned_local else {
1424 // This visitor only invokes `visit_place` for the right-hand side of an assignment
1425 // and only after setting `self.assigned_local`. However, the default impl of
1426 // `Visitor::super_body` may call `visit_place` with a `NonUseContext` for places
1427 // with debuginfo. Ignore them here.
1428 assert!(!context.is_use());
1432 let Some(rhs) = self.saved_local_for_direct_place(*place) else { return };
1434 if !self.storage_conflicts.contains(lhs, rhs) {
1436 "Assignment between generator saved locals whose storage is not \
1437 marked as conflicting: {:?}: {:?} = {:?}",
1445 fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
1446 match &statement.kind {
1447 StatementKind::Assign(box (lhs, rhs)) => {
1448 self.check_assigned_place(*lhs, |this| this.visit_rvalue(rhs, location));
1451 StatementKind::FakeRead(..)
1452 | StatementKind::SetDiscriminant { .. }
1453 | StatementKind::Deinit(..)
1454 | StatementKind::StorageLive(_)
1455 | StatementKind::StorageDead(_)
1456 | StatementKind::Retag(..)
1457 | StatementKind::AscribeUserType(..)
1458 | StatementKind::Coverage(..)
1459 | StatementKind::CopyNonOverlapping(..)
1460 | StatementKind::Nop => {}
1464 fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
1465 // Checking for aliasing in terminators is probably overkill, but until we have actual
1466 // semantics, we should be conservative here.
1467 match &terminator.kind {
1468 TerminatorKind::Call {
1477 self.check_assigned_place(*destination, |this| {
1478 this.visit_operand(func, location);
1480 this.visit_operand(arg, location);
1485 TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
1486 self.check_assigned_place(*resume_arg, |this| this.visit_operand(value, location));
1489 // FIXME: Does `asm!` have any aliasing requirements?
1490 TerminatorKind::InlineAsm { .. } => {}
1492 TerminatorKind::Call { .. }
1493 | TerminatorKind::Goto { .. }
1494 | TerminatorKind::SwitchInt { .. }
1495 | TerminatorKind::Resume
1496 | TerminatorKind::Abort
1497 | TerminatorKind::Return
1498 | TerminatorKind::Unreachable
1499 | TerminatorKind::Drop { .. }
1500 | TerminatorKind::DropAndReplace { .. }
1501 | TerminatorKind::Assert { .. }
1502 | TerminatorKind::GeneratorDrop
1503 | TerminatorKind::FalseEdge { .. }
1504 | TerminatorKind::FalseUnwind { .. } => {}