1 #![deny(rustc::untranslatable_diagnostic)]
2 #![deny(rustc::diagnostic_outside_of_impl)]
3 use rustc_data_structures::fx::FxHashMap;
4 use rustc_index::bit_set::BitSet;
5 use rustc_middle::mir::{self, BasicBlock, Body, Location, Place};
6 use rustc_middle::ty::RegionVid;
7 use rustc_middle::ty::TyCtxt;
8 use rustc_mir_dataflow::impls::{EverInitializedPlaces, MaybeUninitializedPlaces};
9 use rustc_mir_dataflow::ResultsVisitable;
10 use rustc_mir_dataflow::{self, fmt::DebugWithContext, CallReturnPlaces, GenKill};
11 use rustc_mir_dataflow::{Analysis, Direction, Results};
15 places_conflict, BorrowSet, PlaceConflictBias, PlaceExt, RegionInferenceContext, ToRegionVid,
18 /// A tuple with named fields that can hold either the results or the transient state of the
19 /// dataflow analyses used by the borrow checker.
21 pub struct BorrowckAnalyses<B, U, E> {
27 /// The results of the dataflow analyses used by the borrow checker.
28 pub type BorrowckResults<'mir, 'tcx> = BorrowckAnalyses<
29 Results<'tcx, Borrows<'mir, 'tcx>>,
30 Results<'tcx, MaybeUninitializedPlaces<'mir, 'tcx>>,
31 Results<'tcx, EverInitializedPlaces<'mir, 'tcx>>,
34 /// The transient state of the dataflow analyses used by the borrow checker.
35 pub type BorrowckFlowState<'mir, 'tcx> =
36 <BorrowckResults<'mir, 'tcx> as ResultsVisitable<'tcx>>::FlowState;
38 macro_rules! impl_visitable {
40 $T:ident { $( $field:ident : $A:ident ),* $(,)? }
42 impl<'tcx, $($A),*, D: Direction> ResultsVisitable<'tcx> for $T<$( Results<'tcx, $A> ),*>
44 $( $A: Analysis<'tcx, Direction = D>, )*
47 type FlowState = $T<$( $A::Domain ),*>;
49 fn new_flow_state(&self, body: &mir::Body<'tcx>) -> Self::FlowState {
51 $( $field: self.$field.analysis.bottom_value(body) ),*
55 fn reset_to_block_entry(
57 state: &mut Self::FlowState,
60 $( state.$field.clone_from(&self.$field.entry_set_for_block(block)); )*
63 fn reconstruct_before_statement_effect(
65 state: &mut Self::FlowState,
66 stmt: &mir::Statement<'tcx>,
69 $( self.$field.analysis
70 .apply_before_statement_effect(&mut state.$field, stmt, loc); )*
73 fn reconstruct_statement_effect(
75 state: &mut Self::FlowState,
76 stmt: &mir::Statement<'tcx>,
79 $( self.$field.analysis
80 .apply_statement_effect(&mut state.$field, stmt, loc); )*
83 fn reconstruct_before_terminator_effect(
85 state: &mut Self::FlowState,
86 term: &mir::Terminator<'tcx>,
89 $( self.$field.analysis
90 .apply_before_terminator_effect(&mut state.$field, term, loc); )*
93 fn reconstruct_terminator_effect(
95 state: &mut Self::FlowState,
96 term: &mir::Terminator<'tcx>,
99 $( self.$field.analysis
100 .apply_terminator_effect(&mut state.$field, term, loc); )*
107 BorrowckAnalyses { borrows: B, uninits: U, ever_inits: E }
110 rustc_index::newtype_index! {
111 pub struct BorrowIndex {
112 DEBUG_FORMAT = "bw{}"
116 /// `Borrows` stores the data used in the analyses that track the flow
119 /// It uniquely identifies every borrow (`Rvalue::Ref`) by a
120 /// `BorrowIndex`, and maps each such index to a `BorrowData`
121 /// describing the borrow. These indexes are used for representing the
122 /// borrows in compact bitvectors.
123 pub struct Borrows<'a, 'tcx> {
125 body: &'a Body<'tcx>,
127 borrow_set: &'a BorrowSet<'tcx>,
128 borrows_out_of_scope_at_location: FxHashMap<Location, Vec<BorrowIndex>>,
137 struct OutOfScopePrecomputer<'a, 'tcx> {
138 visited: BitSet<mir::BasicBlock>,
139 visit_stack: Vec<StackEntry>,
140 body: &'a Body<'tcx>,
141 regioncx: &'a RegionInferenceContext<'tcx>,
142 borrows_out_of_scope_at_location: FxHashMap<Location, Vec<BorrowIndex>>,
145 impl<'a, 'tcx> OutOfScopePrecomputer<'a, 'tcx> {
146 fn new(body: &'a Body<'tcx>, regioncx: &'a RegionInferenceContext<'tcx>) -> Self {
147 OutOfScopePrecomputer {
148 visited: BitSet::new_empty(body.basic_blocks.len()),
152 borrows_out_of_scope_at_location: FxHashMap::default(),
157 impl<'tcx> OutOfScopePrecomputer<'_, 'tcx> {
158 fn precompute_borrows_out_of_scope(
160 borrow_index: BorrowIndex,
161 borrow_region: RegionVid,
164 // We visit one BB at a time. The complication is that we may start in the
165 // middle of the first BB visited (the one containing `location`), in which
166 // case we may have to later on process the first part of that BB if there
167 // is a path back to its start.
169 // For visited BBs, we record the index of the first statement processed.
170 // (In fully processed BBs this index is 0.) Note also that we add BBs to
171 // `visited` once they are added to `stack`, before they are actually
172 // processed, because this avoids the need to look them up again on
174 self.visited.insert(location.block);
176 let mut first_lo = location.statement_index;
177 let first_hi = self.body[location.block].statements.len();
179 self.visit_stack.push(StackEntry { bb: location.block, lo: first_lo, hi: first_hi });
181 while let Some(StackEntry { bb, lo, hi }) = self.visit_stack.pop() {
182 // If we process the first part of the first basic block (i.e. we encounter that block
183 // for the second time), we no longer have to visit its successors again.
184 let mut finished_early = bb == location.block && hi != first_hi;
186 let location = Location { block: bb, statement_index: i };
187 // If region does not contain a point at the location, then add to list and skip
188 // successor locations.
189 if !self.regioncx.region_contains(borrow_region, location) {
190 debug!("borrow {:?} gets killed at {:?}", borrow_index, location);
191 self.borrows_out_of_scope_at_location
195 finished_early = true;
201 // Add successor BBs to the work list, if necessary.
202 let bb_data = &self.body[bb];
203 debug_assert!(hi == bb_data.statements.len());
204 for succ_bb in bb_data.terminator().successors() {
205 if !self.visited.insert(succ_bb) {
206 if succ_bb == location.block && first_lo > 0 {
207 // `succ_bb` has been seen before. If it wasn't
208 // fully processed, add its first part to `stack`
210 self.visit_stack.push(StackEntry {
216 // And update this entry with 0, to represent the
217 // whole BB being processed.
221 // succ_bb hasn't been seen before. Add it to
222 // `stack` for processing.
223 self.visit_stack.push(StackEntry {
226 hi: self.body[succ_bb].statements.len(),
233 self.visited.clear();
237 impl<'a, 'tcx> Borrows<'a, 'tcx> {
240 body: &'a Body<'tcx>,
241 nonlexical_regioncx: &'a RegionInferenceContext<'tcx>,
242 borrow_set: &'a BorrowSet<'tcx>,
244 let mut prec = OutOfScopePrecomputer::new(body, nonlexical_regioncx);
245 for (borrow_index, borrow_data) in borrow_set.iter_enumerated() {
246 let borrow_region = borrow_data.region.to_region_vid();
247 let location = borrow_data.reserve_location;
249 prec.precompute_borrows_out_of_scope(borrow_index, borrow_region, location);
256 borrows_out_of_scope_at_location: prec.borrows_out_of_scope_at_location,
260 pub fn location(&self, idx: BorrowIndex) -> &Location {
261 &self.borrow_set[idx].reserve_location
264 /// Add all borrows to the kill set, if those borrows are out of scope at `location`.
265 /// That means they went out of a nonlexical scope
266 fn kill_loans_out_of_scope_at_location(
268 trans: &mut impl GenKill<BorrowIndex>,
271 // NOTE: The state associated with a given `location`
272 // reflects the dataflow on entry to the statement.
273 // Iterate over each of the borrows that we've precomputed
274 // to have went out of scope at this location and kill them.
276 // We are careful always to call this function *before* we
277 // set up the gen-bits for the statement or
278 // terminator. That way, if the effect of the statement or
279 // terminator *does* introduce a new loan of the same
280 // region, then setting that gen-bit will override any
281 // potential kill introduced here.
282 if let Some(indices) = self.borrows_out_of_scope_at_location.get(&location) {
283 trans.kill_all(indices.iter().copied());
287 /// Kill any borrows that conflict with `place`.
288 fn kill_borrows_on_place(&self, trans: &mut impl GenKill<BorrowIndex>, place: Place<'tcx>) {
289 debug!("kill_borrows_on_place: place={:?}", place);
291 let other_borrows_of_local = self
296 .flat_map(|bs| bs.iter())
299 // If the borrowed place is a local with no projections, all other borrows of this
300 // local must conflict. This is purely an optimization so we don't have to call
301 // `places_conflict` for every borrow.
302 if place.projection.is_empty() {
303 if !self.body.local_decls[place.local].is_ref_to_static() {
304 trans.kill_all(other_borrows_of_local);
309 // By passing `PlaceConflictBias::NoOverlap`, we conservatively assume that any given
310 // pair of array indices are unequal, so that when `places_conflict` returns true, we
311 // will be assured that two places being compared definitely denotes the same sets of
313 let definitely_conflicting_borrows = other_borrows_of_local.filter(|&i| {
317 self.borrow_set[i].borrowed_place,
319 PlaceConflictBias::NoOverlap,
323 trans.kill_all(definitely_conflicting_borrows);
327 impl<'tcx> rustc_mir_dataflow::AnalysisDomain<'tcx> for Borrows<'_, 'tcx> {
328 type Domain = BitSet<BorrowIndex>;
330 const NAME: &'static str = "borrows";
332 fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
333 // bottom = nothing is reserved or activated yet;
334 BitSet::new_empty(self.borrow_set.len() * 2)
337 fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {
338 // no borrows of code region_scopes have been taken prior to
339 // function execution, so this method has no effect.
343 impl<'tcx> rustc_mir_dataflow::GenKillAnalysis<'tcx> for Borrows<'_, 'tcx> {
344 type Idx = BorrowIndex;
346 fn before_statement_effect(
348 trans: &mut impl GenKill<Self::Idx>,
349 _statement: &mir::Statement<'tcx>,
352 self.kill_loans_out_of_scope_at_location(trans, location);
357 trans: &mut impl GenKill<Self::Idx>,
358 stmt: &mir::Statement<'tcx>,
362 mir::StatementKind::Assign(box (lhs, ref rhs)) => {
363 if let mir::Rvalue::Ref(_, _, place) = *rhs {
364 if place.ignore_borrow(
367 &self.borrow_set.locals_state_at_exit,
371 let index = self.borrow_set.get_index_of(&location).unwrap_or_else(|| {
372 panic!("could not find BorrowIndex for location {:?}", location);
378 // Make sure there are no remaining borrows for variables
379 // that are assigned over.
380 self.kill_borrows_on_place(trans, lhs);
383 mir::StatementKind::StorageDead(local) => {
384 // Make sure there are no remaining borrows for locals that
385 // are gone out of scope.
386 self.kill_borrows_on_place(trans, Place::from(local));
389 mir::StatementKind::FakeRead(..)
390 | mir::StatementKind::SetDiscriminant { .. }
391 | mir::StatementKind::Deinit(..)
392 | mir::StatementKind::StorageLive(..)
393 | mir::StatementKind::Retag { .. }
394 | mir::StatementKind::AscribeUserType(..)
395 | mir::StatementKind::Coverage(..)
396 | mir::StatementKind::Intrinsic(..)
397 | mir::StatementKind::Nop => {}
401 fn before_terminator_effect(
403 trans: &mut impl GenKill<Self::Idx>,
404 _terminator: &mir::Terminator<'tcx>,
407 self.kill_loans_out_of_scope_at_location(trans, location);
410 fn terminator_effect(
412 trans: &mut impl GenKill<Self::Idx>,
413 terminator: &mir::Terminator<'tcx>,
416 if let mir::TerminatorKind::InlineAsm { operands, .. } = &terminator.kind {
418 if let mir::InlineAsmOperand::Out { place: Some(place), .. }
419 | mir::InlineAsmOperand::InOut { out_place: Some(place), .. } = *op
421 self.kill_borrows_on_place(trans, place);
427 fn call_return_effect(
429 _trans: &mut impl GenKill<Self::Idx>,
430 _block: mir::BasicBlock,
431 _return_places: CallReturnPlaces<'_, 'tcx>,
436 impl DebugWithContext<Borrows<'_, '_>> for BorrowIndex {
437 fn fmt_with(&self, ctxt: &Borrows<'_, '_>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
438 write!(f, "{:?}", ctxt.location(*self))