1 use rustc_data_structures::fx::FxHashMap;
2 use rustc_index::bit_set::BitSet;
3 use rustc_middle::mir::{self, BasicBlock, Body, Location, Place};
4 use rustc_middle::ty::RegionVid;
5 use rustc_middle::ty::TyCtxt;
6 use rustc_mir_dataflow::impls::{EverInitializedPlaces, MaybeUninitializedPlaces};
7 use rustc_mir_dataflow::ResultsVisitable;
8 use rustc_mir_dataflow::{self, fmt::DebugWithContext, CallReturnPlaces, GenKill};
9 use rustc_mir_dataflow::{Analysis, Direction, Results};
13 places_conflict, BorrowSet, PlaceConflictBias, PlaceExt, RegionInferenceContext, ToRegionVid,
16 /// A tuple with named fields that can hold either the results or the transient state of the
17 /// dataflow analyses used by the borrow checker.
19 pub struct BorrowckAnalyses<B, U, E> {
25 /// The results of the dataflow analyses used by the borrow checker.
26 pub type BorrowckResults<'mir, 'tcx> = BorrowckAnalyses<
27 Results<'tcx, Borrows<'mir, 'tcx>>,
28 Results<'tcx, MaybeUninitializedPlaces<'mir, 'tcx>>,
29 Results<'tcx, EverInitializedPlaces<'mir, 'tcx>>,
32 /// The transient state of the dataflow analyses used by the borrow checker.
33 pub type BorrowckFlowState<'mir, 'tcx> =
34 <BorrowckResults<'mir, 'tcx> as ResultsVisitable<'tcx>>::FlowState;
36 macro_rules! impl_visitable {
38 $T:ident { $( $field:ident : $A:ident ),* $(,)? }
40 impl<'tcx, $($A),*, D: Direction> ResultsVisitable<'tcx> for $T<$( Results<'tcx, $A> ),*>
42 $( $A: Analysis<'tcx, Direction = D>, )*
45 type FlowState = $T<$( $A::Domain ),*>;
47 fn new_flow_state(&self, body: &mir::Body<'tcx>) -> Self::FlowState {
49 $( $field: self.$field.analysis.bottom_value(body) ),*
53 fn reset_to_block_entry(
55 state: &mut Self::FlowState,
58 $( state.$field.clone_from(&self.$field.entry_set_for_block(block)); )*
61 fn reconstruct_before_statement_effect(
63 state: &mut Self::FlowState,
64 stmt: &mir::Statement<'tcx>,
67 $( self.$field.analysis
68 .apply_before_statement_effect(&mut state.$field, stmt, loc); )*
71 fn reconstruct_statement_effect(
73 state: &mut Self::FlowState,
74 stmt: &mir::Statement<'tcx>,
77 $( self.$field.analysis
78 .apply_statement_effect(&mut state.$field, stmt, loc); )*
81 fn reconstruct_before_terminator_effect(
83 state: &mut Self::FlowState,
84 term: &mir::Terminator<'tcx>,
87 $( self.$field.analysis
88 .apply_before_terminator_effect(&mut state.$field, term, loc); )*
91 fn reconstruct_terminator_effect(
93 state: &mut Self::FlowState,
94 term: &mir::Terminator<'tcx>,
97 $( self.$field.analysis
98 .apply_terminator_effect(&mut state.$field, term, loc); )*
105 BorrowckAnalyses { borrows: B, uninits: U, ever_inits: E }
108 rustc_index::newtype_index! {
109 pub struct BorrowIndex {
110 DEBUG_FORMAT = "bw{}"
114 /// `Borrows` stores the data used in the analyses that track the flow
117 /// It uniquely identifies every borrow (`Rvalue::Ref`) by a
118 /// `BorrowIndex`, and maps each such index to a `BorrowData`
119 /// describing the borrow. These indexes are used for representing the
120 /// borrows in compact bitvectors.
121 pub struct Borrows<'a, 'tcx> {
123 body: &'a Body<'tcx>,
125 borrow_set: &'a BorrowSet<'tcx>,
126 borrows_out_of_scope_at_location: FxHashMap<Location, Vec<BorrowIndex>>,
135 struct OutOfScopePrecomputer<'a, 'tcx> {
136 visited: BitSet<mir::BasicBlock>,
137 visit_stack: Vec<StackEntry>,
138 body: &'a Body<'tcx>,
139 regioncx: &'a RegionInferenceContext<'tcx>,
140 borrows_out_of_scope_at_location: FxHashMap<Location, Vec<BorrowIndex>>,
143 impl<'a, 'tcx> OutOfScopePrecomputer<'a, 'tcx> {
144 fn new(body: &'a Body<'tcx>, regioncx: &'a RegionInferenceContext<'tcx>) -> Self {
145 OutOfScopePrecomputer {
146 visited: BitSet::new_empty(body.basic_blocks().len()),
150 borrows_out_of_scope_at_location: FxHashMap::default(),
155 impl<'tcx> OutOfScopePrecomputer<'_, 'tcx> {
156 fn precompute_borrows_out_of_scope(
158 borrow_index: BorrowIndex,
159 borrow_region: RegionVid,
162 // We visit one BB at a time. The complication is that we may start in the
163 // middle of the first BB visited (the one containing `location`), in which
164 // case we may have to later on process the first part of that BB if there
165 // is a path back to its start.
167 // For visited BBs, we record the index of the first statement processed.
168 // (In fully processed BBs this index is 0.) Note also that we add BBs to
169 // `visited` once they are added to `stack`, before they are actually
170 // processed, because this avoids the need to look them up again on
172 self.visited.insert(location.block);
174 let mut first_lo = location.statement_index;
175 let first_hi = self.body[location.block].statements.len();
177 self.visit_stack.push(StackEntry { bb: location.block, lo: first_lo, hi: first_hi });
179 while let Some(StackEntry { bb, lo, hi }) = self.visit_stack.pop() {
180 // If we process the first part of the first basic block (i.e. we encounter that block
181 // for the second time), we no longer have to visit its successors again.
182 let mut finished_early = bb == location.block && hi != first_hi;
184 let location = Location { block: bb, statement_index: i };
185 // If region does not contain a point at the location, then add to list and skip
186 // successor locations.
187 if !self.regioncx.region_contains(borrow_region, location) {
188 debug!("borrow {:?} gets killed at {:?}", borrow_index, location);
189 self.borrows_out_of_scope_at_location
193 finished_early = true;
199 // Add successor BBs to the work list, if necessary.
200 let bb_data = &self.body[bb];
201 debug_assert!(hi == bb_data.statements.len());
202 for succ_bb in bb_data.terminator().successors() {
203 if !self.visited.insert(succ_bb) {
204 if succ_bb == location.block && first_lo > 0 {
205 // `succ_bb` has been seen before. If it wasn't
206 // fully processed, add its first part to `stack`
208 self.visit_stack.push(StackEntry {
214 // And update this entry with 0, to represent the
215 // whole BB being processed.
219 // succ_bb hasn't been seen before. Add it to
220 // `stack` for processing.
221 self.visit_stack.push(StackEntry {
224 hi: self.body[succ_bb].statements.len(),
231 self.visited.clear();
235 impl<'a, 'tcx> Borrows<'a, 'tcx> {
238 body: &'a Body<'tcx>,
239 nonlexical_regioncx: &'a RegionInferenceContext<'tcx>,
240 borrow_set: &'a BorrowSet<'tcx>,
242 let mut prec = OutOfScopePrecomputer::new(body, nonlexical_regioncx);
243 for (borrow_index, borrow_data) in borrow_set.iter_enumerated() {
244 let borrow_region = borrow_data.region.to_region_vid();
245 let location = borrow_data.reserve_location;
247 prec.precompute_borrows_out_of_scope(borrow_index, borrow_region, location);
254 borrows_out_of_scope_at_location: prec.borrows_out_of_scope_at_location,
258 pub fn location(&self, idx: BorrowIndex) -> &Location {
259 &self.borrow_set[idx].reserve_location
262 /// Add all borrows to the kill set, if those borrows are out of scope at `location`.
263 /// That means they went out of a nonlexical scope
264 fn kill_loans_out_of_scope_at_location(
266 trans: &mut impl GenKill<BorrowIndex>,
269 // NOTE: The state associated with a given `location`
270 // reflects the dataflow on entry to the statement.
271 // Iterate over each of the borrows that we've precomputed
272 // to have went out of scope at this location and kill them.
274 // We are careful always to call this function *before* we
275 // set up the gen-bits for the statement or
276 // terminator. That way, if the effect of the statement or
277 // terminator *does* introduce a new loan of the same
278 // region, then setting that gen-bit will override any
279 // potential kill introduced here.
280 if let Some(indices) = self.borrows_out_of_scope_at_location.get(&location) {
281 trans.kill_all(indices.iter().copied());
285 /// Kill any borrows that conflict with `place`.
286 fn kill_borrows_on_place(&self, trans: &mut impl GenKill<BorrowIndex>, place: Place<'tcx>) {
287 debug!("kill_borrows_on_place: place={:?}", place);
289 let other_borrows_of_local = self
294 .flat_map(|bs| bs.iter())
297 // If the borrowed place is a local with no projections, all other borrows of this
298 // local must conflict. This is purely an optimization so we don't have to call
299 // `places_conflict` for every borrow.
300 if place.projection.is_empty() {
301 if !self.body.local_decls[place.local].is_ref_to_static() {
302 trans.kill_all(other_borrows_of_local);
307 // By passing `PlaceConflictBias::NoOverlap`, we conservatively assume that any given
308 // pair of array indices are unequal, so that when `places_conflict` returns true, we
309 // will be assured that two places being compared definitely denotes the same sets of
311 let definitely_conflicting_borrows = other_borrows_of_local.filter(|&i| {
315 self.borrow_set[i].borrowed_place,
317 PlaceConflictBias::NoOverlap,
321 trans.kill_all(definitely_conflicting_borrows);
325 impl<'tcx> rustc_mir_dataflow::AnalysisDomain<'tcx> for Borrows<'_, 'tcx> {
326 type Domain = BitSet<BorrowIndex>;
328 const NAME: &'static str = "borrows";
330 fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
331 // bottom = nothing is reserved or activated yet;
332 BitSet::new_empty(self.borrow_set.len() * 2)
335 fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {
336 // no borrows of code region_scopes have been taken prior to
337 // function execution, so this method has no effect.
341 impl<'tcx> rustc_mir_dataflow::GenKillAnalysis<'tcx> for Borrows<'_, 'tcx> {
342 type Idx = BorrowIndex;
344 fn before_statement_effect(
346 trans: &mut impl GenKill<Self::Idx>,
347 _statement: &mir::Statement<'tcx>,
350 self.kill_loans_out_of_scope_at_location(trans, location);
355 trans: &mut impl GenKill<Self::Idx>,
356 stmt: &mir::Statement<'tcx>,
360 mir::StatementKind::Assign(box (lhs, ref rhs)) => {
361 if let mir::Rvalue::Ref(_, _, place) = *rhs {
362 if place.ignore_borrow(
365 &self.borrow_set.locals_state_at_exit,
369 let index = self.borrow_set.get_index_of(&location).unwrap_or_else(|| {
370 panic!("could not find BorrowIndex for location {:?}", location);
376 // Make sure there are no remaining borrows for variables
377 // that are assigned over.
378 self.kill_borrows_on_place(trans, lhs);
381 mir::StatementKind::StorageDead(local) => {
382 // Make sure there are no remaining borrows for locals that
383 // are gone out of scope.
384 self.kill_borrows_on_place(trans, Place::from(local));
387 mir::StatementKind::FakeRead(..)
388 | mir::StatementKind::SetDiscriminant { .. }
389 | mir::StatementKind::Deinit(..)
390 | mir::StatementKind::StorageLive(..)
391 | mir::StatementKind::Retag { .. }
392 | mir::StatementKind::AscribeUserType(..)
393 | mir::StatementKind::Coverage(..)
394 | mir::StatementKind::CopyNonOverlapping(..)
395 | mir::StatementKind::Nop => {}
399 fn before_terminator_effect(
401 trans: &mut impl GenKill<Self::Idx>,
402 _terminator: &mir::Terminator<'tcx>,
405 self.kill_loans_out_of_scope_at_location(trans, location);
408 fn terminator_effect(
410 trans: &mut impl GenKill<Self::Idx>,
411 terminator: &mir::Terminator<'tcx>,
414 if let mir::TerminatorKind::InlineAsm { operands, .. } = &terminator.kind {
416 if let mir::InlineAsmOperand::Out { place: Some(place), .. }
417 | mir::InlineAsmOperand::InOut { out_place: Some(place), .. } = *op
419 self.kill_borrows_on_place(trans, place);
425 fn call_return_effect(
427 _trans: &mut impl GenKill<Self::Idx>,
428 _block: mir::BasicBlock,
429 _return_places: CallReturnPlaces<'_, 'tcx>,
434 impl DebugWithContext<Borrows<'_, '_>> for BorrowIndex {
435 fn fmt_with(&self, ctxt: &Borrows<'_, '_>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
436 write!(f, "{:?}", ctxt.location(*self))