1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
use rustc_infer::infer::InferCtxt;
use rustc_middle::mir::visit::TyContext;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{
    BasicBlock, BasicBlockData, Body, Local, Location, Place, PlaceRef, ProjectionElem, Rvalue,
    SourceInfo, Statement, StatementKind, Terminator, TerminatorKind, UserTypeProjection,
};
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::visit::TypeVisitable;
use rustc_middle::ty::{self, RegionVid, Ty};

use crate::{
    borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, nll::ToRegionVid,
    places_conflict, region_infer::values::LivenessValues,
};

pub(super) fn generate_constraints<'cx, 'tcx>(
    infcx: &InferCtxt<'cx, 'tcx>,
    liveness_constraints: &mut LivenessValues<RegionVid>,
    all_facts: &mut Option<AllFacts>,
    location_table: &LocationTable,
    body: &Body<'tcx>,
    borrow_set: &BorrowSet<'tcx>,
) {
    let mut cg = ConstraintGeneration {
        borrow_set,
        infcx,
        liveness_constraints,
        location_table,
        all_facts,
        body,
    };

    for (bb, data) in body.basic_blocks.iter_enumerated() {
        cg.visit_basic_block_data(bb, data);
    }
}

/// 'cg = the duration of the constraint generation process itself.
struct ConstraintGeneration<'cg, 'cx, 'tcx> {
    infcx: &'cg InferCtxt<'cx, 'tcx>,
    all_facts: &'cg mut Option<AllFacts>,
    location_table: &'cg LocationTable,
    liveness_constraints: &'cg mut LivenessValues<RegionVid>,
    borrow_set: &'cg BorrowSet<'tcx>,
    body: &'cg Body<'tcx>,
}

impl<'cg, 'cx, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'cx, 'tcx> {
    fn visit_basic_block_data(&mut self, bb: BasicBlock, data: &BasicBlockData<'tcx>) {
        self.super_basic_block_data(bb, data);
    }

    /// We sometimes have `substs` within an rvalue, or within a
    /// call. Make them live at the location where they appear.
    fn visit_substs(&mut self, substs: &SubstsRef<'tcx>, location: Location) {
        self.add_regular_live_constraint(*substs, location);
        self.super_substs(substs);
    }

    /// We sometimes have `region` within an rvalue, or within a
    /// call. Make them live at the location where they appear.
    fn visit_region(&mut self, region: ty::Region<'tcx>, location: Location) {
        self.add_regular_live_constraint(region, location);
        self.super_region(region);
    }

    /// We sometimes have `ty` within an rvalue, or within a
    /// call. Make them live at the location where they appear.
    fn visit_ty(&mut self, ty: Ty<'tcx>, ty_context: TyContext) {
        match ty_context {
            TyContext::ReturnTy(SourceInfo { span, .. })
            | TyContext::YieldTy(SourceInfo { span, .. })
            | TyContext::UserTy(span)
            | TyContext::LocalDecl { source_info: SourceInfo { span, .. }, .. } => {
                span_bug!(span, "should not be visiting outside of the CFG: {:?}", ty_context);
            }
            TyContext::Location(location) => {
                self.add_regular_live_constraint(ty, location);
            }
        }

        self.super_ty(ty);
    }

    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
        if let Some(all_facts) = self.all_facts {
            let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
            all_facts.cfg_edge.push((
                self.location_table.start_index(location),
                self.location_table.mid_index(location),
            ));

            all_facts.cfg_edge.push((
                self.location_table.mid_index(location),
                self.location_table.start_index(location.successor_within_block()),
            ));

            // If there are borrows on this now dead local, we need to record them as `killed`.
            if let StatementKind::StorageDead(local) = statement.kind {
                record_killed_borrows_for_local(
                    all_facts,
                    self.borrow_set,
                    self.location_table,
                    local,
                    location,
                );
            }
        }

        self.super_statement(statement, location);
    }

    fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
        // When we see `X = ...`, then kill borrows of
        // `(*X).foo` and so forth.
        self.record_killed_borrows_for_place(*place, location);

        self.super_assign(place, rvalue, location);
    }

    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
        if let Some(all_facts) = self.all_facts {
            let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
            all_facts.cfg_edge.push((
                self.location_table.start_index(location),
                self.location_table.mid_index(location),
            ));

            let successor_blocks = terminator.successors();
            all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
            for successor_block in successor_blocks {
                all_facts.cfg_edge.push((
                    self.location_table.mid_index(location),
                    self.location_table.start_index(successor_block.start_location()),
                ));
            }
        }

        // A `Call` terminator's return value can be a local which has borrows,
        // so we need to record those as `killed` as well.
        if let TerminatorKind::Call { destination, .. } = terminator.kind {
            self.record_killed_borrows_for_place(destination, location);
        }

        self.super_terminator(terminator, location);
    }

    fn visit_ascribe_user_ty(
        &mut self,
        _place: &Place<'tcx>,
        _variance: ty::Variance,
        _user_ty: &UserTypeProjection,
        _location: Location,
    ) {
    }
}

impl<'cx, 'cg, 'tcx> ConstraintGeneration<'cx, 'cg, 'tcx> {
    /// Some variable with type `live_ty` is "regular live" at
    /// `location` -- i.e., it may be used later. This means that all
    /// regions appearing in the type `live_ty` must be live at
    /// `location`.
    fn add_regular_live_constraint<T>(&mut self, live_ty: T, location: Location)
    where
        T: TypeVisitable<'tcx>,
    {
        debug!("add_regular_live_constraint(live_ty={:?}, location={:?})", live_ty, location);

        self.infcx.tcx.for_each_free_region(&live_ty, |live_region| {
            let vid = live_region.to_region_vid();
            self.liveness_constraints.add_element(vid, location);
        });
    }

    /// When recording facts for Polonius, records the borrows on the specified place
    /// as `killed`. For example, when assigning to a local, or on a call's return destination.
    fn record_killed_borrows_for_place(&mut self, place: Place<'tcx>, location: Location) {
        if let Some(all_facts) = self.all_facts {
            let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");

            // Depending on the `Place` we're killing:
            // - if it's a local, or a single deref of a local,
            //   we kill all the borrows on the local.
            // - if it's a deeper projection, we have to filter which
            //   of the borrows are killed: the ones whose `borrowed_place`
            //   conflicts with the `place`.
            match place.as_ref() {
                PlaceRef { local, projection: &[] }
                | PlaceRef { local, projection: &[ProjectionElem::Deref] } => {
                    debug!(
                        "Recording `killed` facts for borrows of local={:?} at location={:?}",
                        local, location
                    );

                    record_killed_borrows_for_local(
                        all_facts,
                        self.borrow_set,
                        self.location_table,
                        local,
                        location,
                    );
                }

                PlaceRef { local, projection: &[.., _] } => {
                    // Kill conflicting borrows of the innermost local.
                    debug!(
                        "Recording `killed` facts for borrows of \
                            innermost projected local={:?} at location={:?}",
                        local, location
                    );

                    if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
                        for &borrow_index in borrow_indices {
                            let places_conflict = places_conflict::places_conflict(
                                self.infcx.tcx,
                                self.body,
                                self.borrow_set[borrow_index].borrowed_place,
                                place,
                                places_conflict::PlaceConflictBias::NoOverlap,
                            );

                            if places_conflict {
                                let location_index = self.location_table.mid_index(location);
                                all_facts.loan_killed_at.push((borrow_index, location_index));
                            }
                        }
                    }
                }
            }
        }
    }
}

/// When recording facts for Polonius, records the borrows on the specified local as `killed`.
fn record_killed_borrows_for_local(
    all_facts: &mut AllFacts,
    borrow_set: &BorrowSet<'_>,
    location_table: &LocationTable,
    local: Local,
    location: Location,
) {
    if let Some(borrow_indices) = borrow_set.local_map.get(&local) {
        all_facts.loan_killed_at.reserve(borrow_indices.len());
        for &borrow_index in borrow_indices {
            let location_index = location_table.mid_index(location);
            all_facts.loan_killed_at.push((borrow_index, location_index));
        }
    }
}