1 use crate::nll::ToRegionVid;
2 use crate::path_utils::allow_two_phase_borrow;
3 use crate::place_ext::PlaceExt;
4 use crate::BorrowIndex;
5 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
6 use rustc_index::bit_set::BitSet;
7 use rustc_middle::mir::traversal;
8 use rustc_middle::mir::visit::{MutatingUseContext, NonUseContext, PlaceContext, Visitor};
9 use rustc_middle::mir::{self, Body, Local, Location};
10 use rustc_middle::ty::{RegionVid, TyCtxt};
11 use rustc_mir_dataflow::move_paths::MoveData;
15 pub struct BorrowSet<'tcx> {
16 /// The fundamental map relating bitvector indexes to the borrows
17 /// in the MIR. Each borrow is also uniquely identified in the MIR
18 /// by the `Location` of the assignment statement in which it
19 /// appears on the right hand side. Thus the location is the map
20 /// key, and its position in the map corresponds to `BorrowIndex`.
21 pub location_map: FxIndexMap<Location, BorrowData<'tcx>>,
23 /// Locations which activate borrows.
24 /// NOTE: a given location may activate more than one borrow in the future
25 /// when more general two-phase borrow support is introduced, but for now we
26 /// only need to store one borrow index.
27 pub activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
29 /// Map from local to all the borrows on that local.
30 pub local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
32 pub(crate) locals_state_at_exit: LocalsStateAtExit,
35 impl<'tcx> Index<BorrowIndex> for BorrowSet<'tcx> {
36 type Output = BorrowData<'tcx>;
38 fn index(&self, index: BorrowIndex) -> &BorrowData<'tcx> {
39 &self.location_map[index.as_usize()]
43 /// Location where a two-phase borrow is activated, if a borrow
44 /// is in fact a two-phase borrow.
45 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
46 pub enum TwoPhaseActivation {
49 ActivatedAt(Location),
52 #[derive(Debug, Clone)]
53 pub struct BorrowData<'tcx> {
54 /// Location where the borrow reservation starts.
55 /// In many cases, this will be equal to the activation location but not always.
56 pub reserve_location: Location,
57 /// Location where the borrow is activated.
58 pub activation_location: TwoPhaseActivation,
59 /// What kind of borrow this is
60 pub kind: mir::BorrowKind,
61 /// The region for which this borrow is live
62 pub region: RegionVid,
63 /// Place from which we are borrowing
64 pub borrowed_place: mir::Place<'tcx>,
65 /// Place to which the borrow was stored
66 pub assigned_place: mir::Place<'tcx>,
69 impl<'tcx> fmt::Display for BorrowData<'tcx> {
70 fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
71 let kind = match self.kind {
72 mir::BorrowKind::Shared => "",
73 mir::BorrowKind::Shallow => "shallow ",
74 mir::BorrowKind::Unique => "uniq ",
75 mir::BorrowKind::Mut { .. } => "mut ",
77 write!(w, "&{:?} {}{:?}", self.region, kind, self.borrowed_place)
81 pub enum LocalsStateAtExit {
83 SomeAreInvalidated { has_storage_dead_or_moved: BitSet<Local> },
86 impl LocalsStateAtExit {
88 locals_are_invalidated_at_exit: bool,
90 move_data: &MoveData<'tcx>,
92 struct HasStorageDead(BitSet<Local>);
94 impl<'tcx> Visitor<'tcx> for HasStorageDead {
95 fn visit_local(&mut self, local: Local, ctx: PlaceContext, _: Location) {
96 if ctx == PlaceContext::NonUse(NonUseContext::StorageDead) {
102 if locals_are_invalidated_at_exit {
103 LocalsStateAtExit::AllAreInvalidated
105 let mut has_storage_dead = HasStorageDead(BitSet::new_empty(body.local_decls.len()));
106 has_storage_dead.visit_body(&body);
107 let mut has_storage_dead_or_moved = has_storage_dead.0;
108 for move_out in &move_data.moves {
109 if let Some(index) = move_data.base_local(move_out.path) {
110 has_storage_dead_or_moved.insert(index);
113 LocalsStateAtExit::SomeAreInvalidated { has_storage_dead_or_moved }
118 impl<'tcx> BorrowSet<'tcx> {
122 locals_are_invalidated_at_exit: bool,
123 move_data: &MoveData<'tcx>,
125 let mut visitor = GatherBorrows {
128 location_map: Default::default(),
129 activation_map: Default::default(),
130 local_map: Default::default(),
131 pending_activations: Default::default(),
132 locals_state_at_exit: LocalsStateAtExit::build(
133 locals_are_invalidated_at_exit,
139 for (block, block_data) in traversal::preorder(&body) {
140 visitor.visit_basic_block_data(block, block_data);
144 location_map: visitor.location_map,
145 activation_map: visitor.activation_map,
146 local_map: visitor.local_map,
147 locals_state_at_exit: visitor.locals_state_at_exit,
151 pub(crate) fn activations_at_location(&self, location: Location) -> &[BorrowIndex] {
152 self.activation_map.get(&location).map_or(&[], |activations| &activations[..])
155 pub(crate) fn len(&self) -> usize {
156 self.location_map.len()
159 pub(crate) fn indices(&self) -> impl Iterator<Item = BorrowIndex> {
160 BorrowIndex::from_usize(0)..BorrowIndex::from_usize(self.len())
163 pub(crate) fn iter_enumerated(&self) -> impl Iterator<Item = (BorrowIndex, &BorrowData<'tcx>)> {
164 self.indices().zip(self.location_map.values())
167 pub(crate) fn get_index_of(&self, location: &Location) -> Option<BorrowIndex> {
168 self.location_map.get_index_of(location).map(BorrowIndex::from)
172 struct GatherBorrows<'a, 'tcx> {
174 body: &'a Body<'tcx>,
175 location_map: FxIndexMap<Location, BorrowData<'tcx>>,
176 activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
177 local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
179 /// When we encounter a 2-phase borrow statement, it will always
180 /// be assigning into a temporary TEMP:
184 /// We add TEMP into this map with `b`, where `b` is the index of
185 /// the borrow. When we find a later use of this activation, we
186 /// remove from the map (and add to the "tombstone" set below).
187 pending_activations: FxHashMap<mir::Local, BorrowIndex>,
189 locals_state_at_exit: LocalsStateAtExit,
192 impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
195 assigned_place: &mir::Place<'tcx>,
196 rvalue: &mir::Rvalue<'tcx>,
197 location: mir::Location,
199 if let mir::Rvalue::Ref(region, kind, ref borrowed_place) = *rvalue {
200 if borrowed_place.ignore_borrow(self.tcx, self.body, &self.locals_state_at_exit) {
201 debug!("ignoring_borrow of {:?}", borrowed_place);
205 let region = region.to_region_vid();
207 let borrow = BorrowData {
210 reserve_location: location,
211 activation_location: TwoPhaseActivation::NotTwoPhase,
212 borrowed_place: *borrowed_place,
213 assigned_place: *assigned_place,
215 let (idx, _) = self.location_map.insert_full(location, borrow);
216 let idx = BorrowIndex::from(idx);
218 self.insert_as_pending_if_two_phase(location, assigned_place, kind, idx);
220 self.local_map.entry(borrowed_place.local).or_default().insert(idx);
223 self.super_assign(assigned_place, rvalue, location)
226 fn visit_local(&mut self, temp: Local, context: PlaceContext, location: Location) {
227 if !context.is_use() {
231 // We found a use of some temporary TMP
232 // check whether we (earlier) saw a 2-phase borrow like
235 if let Some(&borrow_index) = self.pending_activations.get(&temp) {
236 let borrow_data = &mut self.location_map[borrow_index.as_usize()];
238 // Watch out: the use of TMP in the borrow itself
239 // doesn't count as an activation. =)
240 if borrow_data.reserve_location == location
241 && context == PlaceContext::MutatingUse(MutatingUseContext::Store)
246 if let TwoPhaseActivation::ActivatedAt(other_location) = borrow_data.activation_location
249 self.body.source_info(location).span,
250 "found two uses for 2-phase borrow temporary {:?}: \
258 // Otherwise, this is the unique later use that we expect.
259 // Double check: This borrow is indeed a two-phase borrow (that is,
260 // we are 'transitioning' from `NotActivated` to `ActivatedAt`) and
261 // we've not found any other activations (checked above).
263 borrow_data.activation_location,
264 TwoPhaseActivation::NotActivated,
265 "never found an activation for this borrow!",
267 self.activation_map.entry(location).or_default().push(borrow_index);
269 borrow_data.activation_location = TwoPhaseActivation::ActivatedAt(location);
273 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: mir::Location) {
274 if let mir::Rvalue::Ref(region, kind, ref place) = *rvalue {
275 // double-check that we already registered a BorrowData for this
277 let borrow_data = &self.location_map[&location];
278 assert_eq!(borrow_data.reserve_location, location);
279 assert_eq!(borrow_data.kind, kind);
280 assert_eq!(borrow_data.region, region.to_region_vid());
281 assert_eq!(borrow_data.borrowed_place, *place);
284 self.super_rvalue(rvalue, location)
288 impl<'a, 'tcx> GatherBorrows<'a, 'tcx> {
289 /// If this is a two-phase borrow, then we will record it
290 /// as "pending" until we find the activating use.
291 fn insert_as_pending_if_two_phase(
293 start_location: Location,
294 assigned_place: &mir::Place<'tcx>,
295 kind: mir::BorrowKind,
296 borrow_index: BorrowIndex,
299 "Borrows::insert_as_pending_if_two_phase({:?}, {:?}, {:?})",
300 start_location, assigned_place, borrow_index,
303 if !allow_two_phase_borrow(kind) {
304 debug!(" -> {:?}", start_location);
308 // When we encounter a 2-phase borrow statement, it will always
309 // be assigning into a temporary TEMP:
313 // so extract `temp`.
314 let Some(temp) = assigned_place.as_local() else {
316 self.body.source_info(start_location).span,
317 "expected 2-phase borrow to assign to a local, not `{:?}`",
322 // Consider the borrow not activated to start. When we find an activation, we'll update
325 let borrow_data = &mut self.location_map[borrow_index.as_usize()];
326 borrow_data.activation_location = TwoPhaseActivation::NotActivated;
329 // Insert `temp` into the list of pending activations. From
330 // now on, we'll be on the lookout for a use of it. Note that
331 // we are guaranteed that this use will come after the
333 let old_value = self.pending_activations.insert(temp, borrow_index);
334 if let Some(old_index) = old_value {
336 self.body.source_info(start_location).span,
337 "found already pending activation for temp: {:?} \
338 at borrow_index: {:?} with associated data {:?}",
341 self.location_map[old_index.as_usize()]