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1 use crate::borrow_check::nll::ToRegionVid;
2 use crate::borrow_check::path_utils::allow_two_phase_borrow;
3 use crate::borrow_check::place_ext::PlaceExt;
4 use crate::dataflow::indexes::BorrowIndex;
5 use crate::dataflow::move_paths::MoveData;
6 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
7 use rustc_index::bit_set::BitSet;
8 use rustc_middle::mir::traversal;
9 use rustc_middle::mir::visit::{MutatingUseContext, NonUseContext, PlaceContext, Visitor};
10 use rustc_middle::mir::{self, Body, Local, Location};
11 use rustc_middle::ty::{RegionVid, TyCtxt};
12 use std::fmt;
13 use std::ops::Index;
14
15 crate 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 crate location_map: FxIndexMap<Location, BorrowData<'tcx>>,
22
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 crate activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
28
29 /// Map from local to all the borrows on that local.
30 crate local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
31
32 crate locals_state_at_exit: LocalsStateAtExit,
33 }
34
35 impl<'tcx> Index<BorrowIndex> for BorrowSet<'tcx> {
36 type Output = BorrowData<'tcx>;
37
38 fn index(&self, index: BorrowIndex) -> &BorrowData<'tcx> {
39 &self.location_map[index.as_usize()]
40 }
41 }
42
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 crate enum TwoPhaseActivation {
47 NotTwoPhase,
48 NotActivated,
49 ActivatedAt(Location),
50 }
51
52 #[derive(Debug, Clone)]
53 crate 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 crate reserve_location: Location,
57 /// Location where the borrow is activated.
58 crate activation_location: TwoPhaseActivation,
59 /// What kind of borrow this is
60 crate kind: mir::BorrowKind,
61 /// The region for which this borrow is live
62 crate region: RegionVid,
63 /// Place from which we are borrowing
64 crate borrowed_place: mir::Place<'tcx>,
65 /// Place to which the borrow was stored
66 crate assigned_place: mir::Place<'tcx>,
67 }
68
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 ",
76 };
77 write!(w, "&{:?} {}{:?}", self.region, kind, self.borrowed_place)
78 }
79 }
80
81 crate enum LocalsStateAtExit {
82 AllAreInvalidated,
83 SomeAreInvalidated { has_storage_dead_or_moved: BitSet<Local> },
84 }
85
86 impl LocalsStateAtExit {
87 fn build(
88 locals_are_invalidated_at_exit: bool,
89 body: &Body<'tcx>,
90 move_data: &MoveData<'tcx>,
91 ) -> Self {
92 struct HasStorageDead(BitSet<Local>);
93
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) {
97 self.0.insert(*local);
98 }
99 }
100 }
101
102 if locals_are_invalidated_at_exit {
103 LocalsStateAtExit::AllAreInvalidated
104 } else {
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);
111 }
112 }
113 LocalsStateAtExit::SomeAreInvalidated { has_storage_dead_or_moved }
114 }
115 }
116 }
117
118 impl<'tcx> BorrowSet<'tcx> {
119 pub fn build(
120 tcx: TyCtxt<'tcx>,
121 body: &Body<'tcx>,
122 locals_are_invalidated_at_exit: bool,
123 move_data: &MoveData<'tcx>,
124 ) -> Self {
125 let mut visitor = GatherBorrows {
126 tcx,
127 body: &body,
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,
134 body,
135 move_data,
136 ),
137 };
138
139 for (block, block_data) in traversal::preorder(&body) {
140 visitor.visit_basic_block_data(block, block_data);
141 }
142
143 BorrowSet {
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,
148 }
149 }
150
151 crate fn activations_at_location(&self, location: Location) -> &[BorrowIndex] {
152 self.activation_map.get(&location).map_or(&[], |activations| &activations[..])
153 }
154
155 crate fn len(&self) -> usize {
156 self.location_map.len()
157 }
158
159 crate fn indices(&self) -> impl Iterator<Item = BorrowIndex> {
160 BorrowIndex::from_usize(0)..BorrowIndex::from_usize(self.len())
161 }
162
163 crate fn iter_enumerated(&self) -> impl Iterator<Item = (BorrowIndex, &BorrowData<'tcx>)> {
164 self.indices().zip(self.location_map.values())
165 }
166
167 crate fn get_index_of(&self, location: &Location) -> Option<BorrowIndex> {
168 self.location_map.get_index_of(location).map(BorrowIndex::from)
169 }
170
171 crate fn contains(&self, location: &Location) -> bool {
172 self.location_map.contains_key(location)
173 }
174 }
175
176 struct GatherBorrows<'a, 'tcx> {
177 tcx: TyCtxt<'tcx>,
178 body: &'a Body<'tcx>,
179 location_map: FxIndexMap<Location, BorrowData<'tcx>>,
180 activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
181 local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
182
183 /// When we encounter a 2-phase borrow statement, it will always
184 /// be assigning into a temporary TEMP:
185 ///
186 /// TEMP = &foo
187 ///
188 /// We add TEMP into this map with `b`, where `b` is the index of
189 /// the borrow. When we find a later use of this activation, we
190 /// remove from the map (and add to the "tombstone" set below).
191 pending_activations: FxHashMap<mir::Local, BorrowIndex>,
192
193 locals_state_at_exit: LocalsStateAtExit,
194 }
195
196 impl<'a, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'tcx> {
197 fn visit_assign(
198 &mut self,
199 assigned_place: &mir::Place<'tcx>,
200 rvalue: &mir::Rvalue<'tcx>,
201 location: mir::Location,
202 ) {
203 if let mir::Rvalue::Ref(region, kind, ref borrowed_place) = *rvalue {
204 if borrowed_place.ignore_borrow(self.tcx, self.body, &self.locals_state_at_exit) {
205 debug!("ignoring_borrow of {:?}", borrowed_place);
206 return;
207 }
208
209 let region = region.to_region_vid();
210
211 let borrow = BorrowData {
212 kind,
213 region,
214 reserve_location: location,
215 activation_location: TwoPhaseActivation::NotTwoPhase,
216 borrowed_place: *borrowed_place,
217 assigned_place: *assigned_place,
218 };
219 let (idx, _) = self.location_map.insert_full(location, borrow);
220 let idx = BorrowIndex::from(idx);
221
222 self.insert_as_pending_if_two_phase(location, assigned_place, kind, idx);
223
224 self.local_map.entry(borrowed_place.local).or_default().insert(idx);
225 }
226
227 self.super_assign(assigned_place, rvalue, location)
228 }
229
230 fn visit_local(&mut self, temp: &Local, context: PlaceContext, location: Location) {
231 if !context.is_use() {
232 return;
233 }
234
235 // We found a use of some temporary TMP
236 // check whether we (earlier) saw a 2-phase borrow like
237 //
238 // TMP = &mut place
239 if let Some(&borrow_index) = self.pending_activations.get(temp) {
240 let borrow_data = &mut self.location_map[borrow_index.as_usize()];
241
242 // Watch out: the use of TMP in the borrow itself
243 // doesn't count as an activation. =)
244 if borrow_data.reserve_location == location
245 && context == PlaceContext::MutatingUse(MutatingUseContext::Store)
246 {
247 return;
248 }
249
250 if let TwoPhaseActivation::ActivatedAt(other_location) = borrow_data.activation_location
251 {
252 span_bug!(
253 self.body.source_info(location).span,
254 "found two uses for 2-phase borrow temporary {:?}: \
255 {:?} and {:?}",
256 temp,
257 location,
258 other_location,
259 );
260 }
261
262 // Otherwise, this is the unique later use that we expect.
263 // Double check: This borrow is indeed a two-phase borrow (that is,
264 // we are 'transitioning' from `NotActivated` to `ActivatedAt`) and
265 // we've not found any other activations (checked above).
266 assert_eq!(
267 borrow_data.activation_location,
268 TwoPhaseActivation::NotActivated,
269 "never found an activation for this borrow!",
270 );
271 self.activation_map.entry(location).or_default().push(borrow_index);
272
273 borrow_data.activation_location = TwoPhaseActivation::ActivatedAt(location);
274 }
275 }
276
277 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: mir::Location) {
278 if let mir::Rvalue::Ref(region, kind, ref place) = *rvalue {
279 // double-check that we already registered a BorrowData for this
280
281 let borrow_data = &self.location_map[&location];
282 assert_eq!(borrow_data.reserve_location, location);
283 assert_eq!(borrow_data.kind, kind);
284 assert_eq!(borrow_data.region, region.to_region_vid());
285 assert_eq!(borrow_data.borrowed_place, *place);
286 }
287
288 self.super_rvalue(rvalue, location)
289 }
290 }
291
292 impl<'a, 'tcx> GatherBorrows<'a, 'tcx> {
293 /// If this is a two-phase borrow, then we will record it
294 /// as "pending" until we find the activating use.
295 fn insert_as_pending_if_two_phase(
296 &mut self,
297 start_location: Location,
298 assigned_place: &mir::Place<'tcx>,
299 kind: mir::BorrowKind,
300 borrow_index: BorrowIndex,
301 ) {
302 debug!(
303 "Borrows::insert_as_pending_if_two_phase({:?}, {:?}, {:?})",
304 start_location, assigned_place, borrow_index,
305 );
306
307 if !allow_two_phase_borrow(kind) {
308 debug!(" -> {:?}", start_location);
309 return;
310 }
311
312 // When we encounter a 2-phase borrow statement, it will always
313 // be assigning into a temporary TEMP:
314 //
315 // TEMP = &foo
316 //
317 // so extract `temp`.
318 let temp = if let Some(temp) = assigned_place.as_local() {
319 temp
320 } else {
321 span_bug!(
322 self.body.source_info(start_location).span,
323 "expected 2-phase borrow to assign to a local, not `{:?}`",
324 assigned_place,
325 );
326 };
327
328 // Consider the borrow not activated to start. When we find an activation, we'll update
329 // this field.
330 {
331 let borrow_data = &mut self.location_map[borrow_index.as_usize()];
332 borrow_data.activation_location = TwoPhaseActivation::NotActivated;
333 }
334
335 // Insert `temp` into the list of pending activations. From
336 // now on, we'll be on the lookout for a use of it. Note that
337 // we are guaranteed that this use will come after the
338 // assignment.
339 let old_value = self.pending_activations.insert(temp, borrow_index);
340 if let Some(old_index) = old_value {
341 span_bug!(
342 self.body.source_info(start_location).span,
343 "found already pending activation for temp: {:?} \
344 at borrow_index: {:?} with associated data {:?}",
345 temp,
346 old_index,
347 self.location_map[old_index.as_usize()]
348 );
349 }
350 }
351 }