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Commit | Line | Data |
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e74abb32 XL |
1 | //! Propagate `Qualif`s between locals and query the results. |
2 | //! | |
3 | //! This contains the dataflow analysis used to track `Qualif`s on complex control-flow graphs. | |
4 | ||
e74abb32 | 5 | use rustc_index::bit_set::BitSet; |
ba9703b0 | 6 | use rustc_middle::mir::visit::Visitor; |
3c0e092e XL |
7 | use rustc_middle::mir::{self, BasicBlock, Local, Location, Statement, StatementKind}; |
8 | use rustc_mir_dataflow::fmt::DebugWithContext; | |
9 | use rustc_mir_dataflow::JoinSemiLattice; | |
a2a8927a | 10 | use rustc_mir_dataflow::{Analysis, AnalysisDomain, CallReturnPlaces}; |
e74abb32 | 11 | |
3c0e092e | 12 | use std::fmt; |
e74abb32 XL |
13 | use std::marker::PhantomData; |
14 | ||
f9f354fc | 15 | use super::{qualifs, ConstCx, Qualif}; |
e74abb32 XL |
16 | |
17 | /// A `Visitor` that propagates qualifs between locals. This defines the transfer function of | |
18 | /// `FlowSensitiveAnalysis`. | |
19 | /// | |
3c0e092e XL |
20 | /// To account for indirect assignments, data flow conservatively assumes that local becomes |
21 | /// qualified immediately after it is borrowed or its address escapes. The borrow must allow for | |
22 | /// mutation, which includes shared borrows of places with interior mutability. The type of | |
23 | /// borrowed place must contain the qualif. | |
e74abb32 | 24 | struct TransferFunction<'a, 'mir, 'tcx, Q> { |
f9f354fc | 25 | ccx: &'a ConstCx<'mir, 'tcx>, |
3c0e092e | 26 | state: &'a mut State, |
e74abb32 XL |
27 | _qualif: PhantomData<Q>, |
28 | } | |
29 | ||
a2a8927a | 30 | impl<'a, 'mir, 'tcx, Q> TransferFunction<'a, 'mir, 'tcx, Q> |
e74abb32 XL |
31 | where |
32 | Q: Qualif, | |
33 | { | |
3c0e092e XL |
34 | fn new(ccx: &'a ConstCx<'mir, 'tcx>, state: &'a mut State) -> Self { |
35 | TransferFunction { ccx, state, _qualif: PhantomData } | |
e74abb32 XL |
36 | } |
37 | ||
38 | fn initialize_state(&mut self) { | |
3c0e092e XL |
39 | self.state.qualif.clear(); |
40 | self.state.borrow.clear(); | |
e74abb32 | 41 | |
f9f354fc XL |
42 | for arg in self.ccx.body.args_iter() { |
43 | let arg_ty = self.ccx.body.local_decls[arg].ty; | |
44 | if Q::in_any_value_of_ty(self.ccx, arg_ty) { | |
3c0e092e | 45 | self.state.qualif.insert(arg); |
e74abb32 XL |
46 | } |
47 | } | |
48 | } | |
49 | ||
3c0e092e | 50 | fn assign_qualif_direct(&mut self, place: &mir::Place<'tcx>, mut value: bool) { |
e74abb32 XL |
51 | debug_assert!(!place.is_indirect()); |
52 | ||
3c0e092e XL |
53 | if !value { |
54 | for (base, _elem) in place.iter_projections() { | |
55 | let base_ty = base.ty(self.ccx.body, self.ccx.tcx); | |
56 | if base_ty.ty.is_union() && Q::in_any_value_of_ty(self.ccx, base_ty.ty) { | |
57 | value = true; | |
58 | break; | |
59 | } | |
60 | } | |
61 | } | |
62 | ||
e74abb32 | 63 | match (value, place.as_ref()) { |
dfeec247 | 64 | (true, mir::PlaceRef { local, .. }) => { |
3c0e092e | 65 | self.state.qualif.insert(local); |
e74abb32 XL |
66 | } |
67 | ||
68 | // For now, we do not clear the qualif if a local is overwritten in full by | |
69 | // an unqualified rvalue (e.g. `y = 5`). This is to be consistent | |
70 | // with aggregates where we overwrite all fields with assignments, which would not | |
71 | // get this feature. | |
dfeec247 | 72 | (false, mir::PlaceRef { local: _, projection: &[] }) => { |
3c0e092e | 73 | // self.state.qualif.remove(*local); |
e74abb32 XL |
74 | } |
75 | ||
76 | _ => {} | |
77 | } | |
78 | } | |
79 | ||
80 | fn apply_call_return_effect( | |
81 | &mut self, | |
82 | _block: BasicBlock, | |
a2a8927a | 83 | return_places: CallReturnPlaces<'_, 'tcx>, |
e74abb32 | 84 | ) { |
a2a8927a XL |
85 | return_places.for_each(|place| { |
86 | // We cannot reason about another function's internals, so use conservative type-based | |
87 | // qualification for the result of a function call. | |
88 | let return_ty = place.ty(self.ccx.body, self.ccx.tcx).ty; | |
89 | let qualif = Q::in_any_value_of_ty(self.ccx, return_ty); | |
ba9703b0 | 90 | |
a2a8927a XL |
91 | if !place.is_indirect() { |
92 | self.assign_qualif_direct(&place, qualif); | |
93 | } | |
94 | }); | |
e74abb32 | 95 | } |
3c0e092e XL |
96 | |
97 | fn address_of_allows_mutation(&self, _mt: mir::Mutability, _place: mir::Place<'tcx>) -> bool { | |
98 | // Exact set of permissions granted by AddressOf is undecided. Conservatively assume that | |
99 | // it might allow mutation until resolution of #56604. | |
100 | true | |
101 | } | |
102 | ||
103 | fn ref_allows_mutation(&self, kind: mir::BorrowKind, place: mir::Place<'tcx>) -> bool { | |
104 | match kind { | |
105 | mir::BorrowKind::Mut { .. } => true, | |
106 | mir::BorrowKind::Shared | mir::BorrowKind::Shallow | mir::BorrowKind::Unique => { | |
107 | self.shared_borrow_allows_mutation(place) | |
108 | } | |
109 | } | |
110 | } | |
111 | ||
112 | /// `&` only allow mutation if the borrowed place is `!Freeze`. | |
113 | /// | |
114 | /// This assumes that it is UB to take the address of a struct field whose type is | |
115 | /// `Freeze`, then use pointer arithmetic to derive a pointer to a *different* field of | |
116 | /// that same struct whose type is `!Freeze`. If we decide that this is not UB, we will | |
117 | /// have to check the type of the borrowed **local** instead of the borrowed **place** | |
118 | /// below. See [rust-lang/unsafe-code-guidelines#134]. | |
119 | /// | |
120 | /// [rust-lang/unsafe-code-guidelines#134]: https://github.com/rust-lang/unsafe-code-guidelines/issues/134 | |
121 | fn shared_borrow_allows_mutation(&self, place: mir::Place<'tcx>) -> bool { | |
2b03887a | 122 | !place.ty(self.ccx.body, self.ccx.tcx).ty.is_freeze(self.ccx.tcx, self.ccx.param_env) |
3c0e092e | 123 | } |
e74abb32 XL |
124 | } |
125 | ||
a2a8927a | 126 | impl<'tcx, Q> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx, Q> |
e74abb32 XL |
127 | where |
128 | Q: Qualif, | |
129 | { | |
130 | fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) { | |
131 | self.super_operand(operand, location); | |
132 | ||
133 | if !Q::IS_CLEARED_ON_MOVE { | |
134 | return; | |
135 | } | |
136 | ||
137 | // If a local with no projections is moved from (e.g. `x` in `y = x`), record that | |
138 | // it no longer needs to be dropped. | |
139 | if let mir::Operand::Move(place) = operand { | |
140 | if let Some(local) = place.as_local() { | |
3c0e092e XL |
141 | // For backward compatibility with the MaybeMutBorrowedLocals used in an earlier |
142 | // implementation we retain qualif if a local had been borrowed before. This might | |
143 | // not be strictly necessary since the local is no longer initialized. | |
144 | if !self.state.borrow.contains(local) { | |
145 | self.state.qualif.remove(local); | |
146 | } | |
e74abb32 XL |
147 | } |
148 | } | |
149 | } | |
150 | ||
151 | fn visit_assign( | |
152 | &mut self, | |
153 | place: &mir::Place<'tcx>, | |
154 | rvalue: &mir::Rvalue<'tcx>, | |
155 | location: Location, | |
156 | ) { | |
3c0e092e XL |
157 | let qualif = |
158 | qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.state.qualif.contains(l), rvalue); | |
e74abb32 XL |
159 | if !place.is_indirect() { |
160 | self.assign_qualif_direct(place, qualif); | |
161 | } | |
162 | ||
163 | // We need to assign qualifs to the left-hand side before visiting `rvalue` since | |
164 | // qualifs can be cleared on move. | |
165 | self.super_assign(place, rvalue, location); | |
166 | } | |
167 | ||
3c0e092e XL |
168 | fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) { |
169 | self.super_rvalue(rvalue, location); | |
170 | ||
171 | match rvalue { | |
172 | mir::Rvalue::AddressOf(mt, borrowed_place) => { | |
173 | if !borrowed_place.is_indirect() | |
174 | && self.address_of_allows_mutation(*mt, *borrowed_place) | |
175 | { | |
176 | let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty; | |
177 | if Q::in_any_value_of_ty(self.ccx, place_ty) { | |
178 | self.state.qualif.insert(borrowed_place.local); | |
179 | self.state.borrow.insert(borrowed_place.local); | |
180 | } | |
181 | } | |
182 | } | |
183 | ||
184 | mir::Rvalue::Ref(_, kind, borrowed_place) => { | |
185 | if !borrowed_place.is_indirect() && self.ref_allows_mutation(*kind, *borrowed_place) | |
186 | { | |
187 | let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty; | |
188 | if Q::in_any_value_of_ty(self.ccx, place_ty) { | |
189 | self.state.qualif.insert(borrowed_place.local); | |
190 | self.state.borrow.insert(borrowed_place.local); | |
191 | } | |
192 | } | |
193 | } | |
194 | ||
195 | mir::Rvalue::Cast(..) | |
196 | | mir::Rvalue::ShallowInitBox(..) | |
197 | | mir::Rvalue::Use(..) | |
064997fb | 198 | | mir::Rvalue::CopyForDeref(..) |
3c0e092e XL |
199 | | mir::Rvalue::ThreadLocalRef(..) |
200 | | mir::Rvalue::Repeat(..) | |
201 | | mir::Rvalue::Len(..) | |
202 | | mir::Rvalue::BinaryOp(..) | |
203 | | mir::Rvalue::CheckedBinaryOp(..) | |
204 | | mir::Rvalue::NullaryOp(..) | |
205 | | mir::Rvalue::UnaryOp(..) | |
206 | | mir::Rvalue::Discriminant(..) | |
207 | | mir::Rvalue::Aggregate(..) => {} | |
208 | } | |
209 | } | |
210 | ||
211 | fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { | |
212 | match statement.kind { | |
213 | StatementKind::StorageDead(local) => { | |
214 | self.state.qualif.remove(local); | |
215 | self.state.borrow.remove(local); | |
216 | } | |
217 | _ => self.super_statement(statement, location), | |
218 | } | |
219 | } | |
220 | ||
f035d41b | 221 | fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) { |
e74abb32 XL |
222 | // The effect of assignment to the return place in `TerminatorKind::Call` is not applied |
223 | // here; that occurs in `apply_call_return_effect`. | |
224 | ||
3c0e092e XL |
225 | // We ignore borrow on drop because custom drop impls are not allowed in consts. |
226 | // FIXME: Reconsider if accounting for borrows in drops is necessary for const drop. | |
f035d41b | 227 | self.super_terminator(terminator, location); |
e74abb32 XL |
228 | } |
229 | } | |
230 | ||
231 | /// The dataflow analysis used to propagate qualifs on arbitrary CFGs. | |
232 | pub(super) struct FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> { | |
f9f354fc | 233 | ccx: &'a ConstCx<'mir, 'tcx>, |
e74abb32 XL |
234 | _qualif: PhantomData<Q>, |
235 | } | |
236 | ||
237 | impl<'a, 'mir, 'tcx, Q> FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> | |
238 | where | |
239 | Q: Qualif, | |
240 | { | |
f9f354fc XL |
241 | pub(super) fn new(_: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self { |
242 | FlowSensitiveAnalysis { ccx, _qualif: PhantomData } | |
e74abb32 XL |
243 | } |
244 | ||
3c0e092e | 245 | fn transfer_function(&self, state: &'a mut State) -> TransferFunction<'a, 'mir, 'tcx, Q> { |
f9f354fc | 246 | TransferFunction::<Q>::new(self.ccx, state) |
e74abb32 XL |
247 | } |
248 | } | |
249 | ||
3c0e092e XL |
250 | #[derive(Debug, PartialEq, Eq)] |
251 | pub(super) struct State { | |
252 | /// Describes whether a local contains qualif. | |
253 | pub qualif: BitSet<Local>, | |
254 | /// Describes whether a local's address escaped and it might become qualified as a result an | |
255 | /// indirect mutation. | |
256 | pub borrow: BitSet<Local>, | |
257 | } | |
258 | ||
259 | impl Clone for State { | |
260 | fn clone(&self) -> Self { | |
261 | State { qualif: self.qualif.clone(), borrow: self.borrow.clone() } | |
262 | } | |
263 | ||
264 | // Data flow engine when possible uses `clone_from` for domain values. | |
265 | // Providing an implementation will avoid some intermediate memory allocations. | |
266 | fn clone_from(&mut self, other: &Self) { | |
267 | self.qualif.clone_from(&other.qualif); | |
268 | self.borrow.clone_from(&other.borrow); | |
269 | } | |
270 | } | |
271 | ||
272 | impl State { | |
273 | #[inline] | |
274 | pub(super) fn contains(&self, local: Local) -> bool { | |
275 | self.qualif.contains(local) | |
276 | } | |
277 | } | |
278 | ||
279 | impl<C> DebugWithContext<C> for State { | |
280 | fn fmt_with(&self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
281 | f.write_str("qualif: ")?; | |
282 | self.qualif.fmt_with(ctxt, f)?; | |
283 | f.write_str(" borrow: ")?; | |
284 | self.borrow.fmt_with(ctxt, f)?; | |
285 | Ok(()) | |
286 | } | |
287 | ||
288 | fn fmt_diff_with(&self, old: &Self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
289 | if self == old { | |
290 | return Ok(()); | |
291 | } | |
292 | ||
293 | if self.qualif != old.qualif { | |
294 | f.write_str("qualif: ")?; | |
295 | self.qualif.fmt_diff_with(&old.qualif, ctxt, f)?; | |
296 | f.write_str("\n")?; | |
297 | } | |
298 | ||
299 | if self.borrow != old.borrow { | |
300 | f.write_str("borrow: ")?; | |
301 | self.qualif.fmt_diff_with(&old.borrow, ctxt, f)?; | |
302 | f.write_str("\n")?; | |
303 | } | |
304 | ||
305 | Ok(()) | |
306 | } | |
307 | } | |
308 | ||
309 | impl JoinSemiLattice for State { | |
310 | fn join(&mut self, other: &Self) -> bool { | |
311 | self.qualif.join(&other.qualif) || self.borrow.join(&other.borrow) | |
312 | } | |
313 | } | |
314 | ||
a2a8927a | 315 | impl<'tcx, Q> AnalysisDomain<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q> |
e74abb32 XL |
316 | where |
317 | Q: Qualif, | |
318 | { | |
3c0e092e | 319 | type Domain = State; |
e74abb32 XL |
320 | |
321 | const NAME: &'static str = Q::ANALYSIS_NAME; | |
322 | ||
1b1a35ee | 323 | fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain { |
3c0e092e XL |
324 | State { |
325 | qualif: BitSet::new_empty(body.local_decls.len()), | |
326 | borrow: BitSet::new_empty(body.local_decls.len()), | |
327 | } | |
e74abb32 XL |
328 | } |
329 | ||
1b1a35ee | 330 | fn initialize_start_block(&self, _body: &mir::Body<'tcx>, state: &mut Self::Domain) { |
e74abb32 XL |
331 | self.transfer_function(state).initialize_state(); |
332 | } | |
dfeec247 | 333 | } |
e74abb32 | 334 | |
a2a8927a | 335 | impl<'tcx, Q> Analysis<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q> |
dfeec247 XL |
336 | where |
337 | Q: Qualif, | |
338 | { | |
e74abb32 XL |
339 | fn apply_statement_effect( |
340 | &self, | |
1b1a35ee | 341 | state: &mut Self::Domain, |
e74abb32 XL |
342 | statement: &mir::Statement<'tcx>, |
343 | location: Location, | |
344 | ) { | |
345 | self.transfer_function(state).visit_statement(statement, location); | |
346 | } | |
347 | ||
348 | fn apply_terminator_effect( | |
349 | &self, | |
1b1a35ee | 350 | state: &mut Self::Domain, |
e74abb32 XL |
351 | terminator: &mir::Terminator<'tcx>, |
352 | location: Location, | |
353 | ) { | |
354 | self.transfer_function(state).visit_terminator(terminator, location); | |
355 | } | |
356 | ||
357 | fn apply_call_return_effect( | |
358 | &self, | |
1b1a35ee | 359 | state: &mut Self::Domain, |
e74abb32 | 360 | block: BasicBlock, |
a2a8927a | 361 | return_places: CallReturnPlaces<'_, 'tcx>, |
e74abb32 | 362 | ) { |
a2a8927a | 363 | self.transfer_function(state).apply_call_return_effect(block, return_places) |
e74abb32 XL |
364 | } |
365 | } |