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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; |
add651ee FG |
7 | use rustc_middle::mir::{ |
8 | self, BasicBlock, CallReturnPlaces, Local, Location, Statement, StatementKind, TerminatorEdges, | |
9 | }; | |
3c0e092e XL |
10 | use rustc_mir_dataflow::fmt::DebugWithContext; |
11 | use rustc_mir_dataflow::JoinSemiLattice; | |
add651ee | 12 | use rustc_mir_dataflow::{Analysis, AnalysisDomain}; |
e74abb32 | 13 | |
3c0e092e | 14 | use std::fmt; |
e74abb32 XL |
15 | use std::marker::PhantomData; |
16 | ||
f9f354fc | 17 | use super::{qualifs, ConstCx, Qualif}; |
e74abb32 XL |
18 | |
19 | /// A `Visitor` that propagates qualifs between locals. This defines the transfer function of | |
20 | /// `FlowSensitiveAnalysis`. | |
21 | /// | |
3c0e092e XL |
22 | /// To account for indirect assignments, data flow conservatively assumes that local becomes |
23 | /// qualified immediately after it is borrowed or its address escapes. The borrow must allow for | |
24 | /// mutation, which includes shared borrows of places with interior mutability. The type of | |
25 | /// borrowed place must contain the qualif. | |
e74abb32 | 26 | struct TransferFunction<'a, 'mir, 'tcx, Q> { |
f9f354fc | 27 | ccx: &'a ConstCx<'mir, 'tcx>, |
3c0e092e | 28 | state: &'a mut State, |
e74abb32 XL |
29 | _qualif: PhantomData<Q>, |
30 | } | |
31 | ||
a2a8927a | 32 | impl<'a, 'mir, 'tcx, Q> TransferFunction<'a, 'mir, 'tcx, Q> |
e74abb32 XL |
33 | where |
34 | Q: Qualif, | |
35 | { | |
3c0e092e XL |
36 | fn new(ccx: &'a ConstCx<'mir, 'tcx>, state: &'a mut State) -> Self { |
37 | TransferFunction { ccx, state, _qualif: PhantomData } | |
e74abb32 XL |
38 | } |
39 | ||
40 | fn initialize_state(&mut self) { | |
3c0e092e XL |
41 | self.state.qualif.clear(); |
42 | self.state.borrow.clear(); | |
e74abb32 | 43 | |
f9f354fc XL |
44 | for arg in self.ccx.body.args_iter() { |
45 | let arg_ty = self.ccx.body.local_decls[arg].ty; | |
46 | if Q::in_any_value_of_ty(self.ccx, arg_ty) { | |
3c0e092e | 47 | self.state.qualif.insert(arg); |
e74abb32 XL |
48 | } |
49 | } | |
50 | } | |
51 | ||
3c0e092e | 52 | fn assign_qualif_direct(&mut self, place: &mir::Place<'tcx>, mut value: bool) { |
e74abb32 XL |
53 | debug_assert!(!place.is_indirect()); |
54 | ||
3c0e092e XL |
55 | if !value { |
56 | for (base, _elem) in place.iter_projections() { | |
57 | let base_ty = base.ty(self.ccx.body, self.ccx.tcx); | |
58 | if base_ty.ty.is_union() && Q::in_any_value_of_ty(self.ccx, base_ty.ty) { | |
59 | value = true; | |
60 | break; | |
61 | } | |
62 | } | |
63 | } | |
64 | ||
e74abb32 | 65 | match (value, place.as_ref()) { |
dfeec247 | 66 | (true, mir::PlaceRef { local, .. }) => { |
3c0e092e | 67 | self.state.qualif.insert(local); |
e74abb32 XL |
68 | } |
69 | ||
70 | // For now, we do not clear the qualif if a local is overwritten in full by | |
71 | // an unqualified rvalue (e.g. `y = 5`). This is to be consistent | |
72 | // with aggregates where we overwrite all fields with assignments, which would not | |
73 | // get this feature. | |
dfeec247 | 74 | (false, mir::PlaceRef { local: _, projection: &[] }) => { |
3c0e092e | 75 | // self.state.qualif.remove(*local); |
e74abb32 XL |
76 | } |
77 | ||
78 | _ => {} | |
79 | } | |
80 | } | |
81 | ||
82 | fn apply_call_return_effect( | |
83 | &mut self, | |
84 | _block: BasicBlock, | |
a2a8927a | 85 | return_places: CallReturnPlaces<'_, 'tcx>, |
e74abb32 | 86 | ) { |
a2a8927a XL |
87 | return_places.for_each(|place| { |
88 | // We cannot reason about another function's internals, so use conservative type-based | |
89 | // qualification for the result of a function call. | |
90 | let return_ty = place.ty(self.ccx.body, self.ccx.tcx).ty; | |
91 | let qualif = Q::in_any_value_of_ty(self.ccx, return_ty); | |
ba9703b0 | 92 | |
a2a8927a XL |
93 | if !place.is_indirect() { |
94 | self.assign_qualif_direct(&place, qualif); | |
95 | } | |
96 | }); | |
e74abb32 | 97 | } |
3c0e092e XL |
98 | |
99 | fn address_of_allows_mutation(&self, _mt: mir::Mutability, _place: mir::Place<'tcx>) -> bool { | |
100 | // Exact set of permissions granted by AddressOf is undecided. Conservatively assume that | |
101 | // it might allow mutation until resolution of #56604. | |
102 | true | |
103 | } | |
104 | ||
105 | fn ref_allows_mutation(&self, kind: mir::BorrowKind, place: mir::Place<'tcx>) -> bool { | |
106 | match kind { | |
107 | mir::BorrowKind::Mut { .. } => true, | |
781aab86 | 108 | mir::BorrowKind::Shared | mir::BorrowKind::Fake => { |
3c0e092e XL |
109 | self.shared_borrow_allows_mutation(place) |
110 | } | |
111 | } | |
112 | } | |
113 | ||
114 | /// `&` only allow mutation if the borrowed place is `!Freeze`. | |
115 | /// | |
116 | /// This assumes that it is UB to take the address of a struct field whose type is | |
117 | /// `Freeze`, then use pointer arithmetic to derive a pointer to a *different* field of | |
118 | /// that same struct whose type is `!Freeze`. If we decide that this is not UB, we will | |
119 | /// have to check the type of the borrowed **local** instead of the borrowed **place** | |
120 | /// below. See [rust-lang/unsafe-code-guidelines#134]. | |
121 | /// | |
122 | /// [rust-lang/unsafe-code-guidelines#134]: https://github.com/rust-lang/unsafe-code-guidelines/issues/134 | |
123 | fn shared_borrow_allows_mutation(&self, place: mir::Place<'tcx>) -> bool { | |
2b03887a | 124 | !place.ty(self.ccx.body, self.ccx.tcx).ty.is_freeze(self.ccx.tcx, self.ccx.param_env) |
3c0e092e | 125 | } |
e74abb32 XL |
126 | } |
127 | ||
a2a8927a | 128 | impl<'tcx, Q> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx, Q> |
e74abb32 XL |
129 | where |
130 | Q: Qualif, | |
131 | { | |
132 | fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) { | |
133 | self.super_operand(operand, location); | |
134 | ||
135 | if !Q::IS_CLEARED_ON_MOVE { | |
136 | return; | |
137 | } | |
138 | ||
139 | // If a local with no projections is moved from (e.g. `x` in `y = x`), record that | |
140 | // it no longer needs to be dropped. | |
141 | if let mir::Operand::Move(place) = operand { | |
142 | if let Some(local) = place.as_local() { | |
3c0e092e XL |
143 | // For backward compatibility with the MaybeMutBorrowedLocals used in an earlier |
144 | // implementation we retain qualif if a local had been borrowed before. This might | |
145 | // not be strictly necessary since the local is no longer initialized. | |
146 | if !self.state.borrow.contains(local) { | |
147 | self.state.qualif.remove(local); | |
148 | } | |
e74abb32 XL |
149 | } |
150 | } | |
151 | } | |
152 | ||
153 | fn visit_assign( | |
154 | &mut self, | |
155 | place: &mir::Place<'tcx>, | |
156 | rvalue: &mir::Rvalue<'tcx>, | |
157 | location: Location, | |
158 | ) { | |
3c0e092e XL |
159 | let qualif = |
160 | qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.state.qualif.contains(l), rvalue); | |
e74abb32 XL |
161 | if !place.is_indirect() { |
162 | self.assign_qualif_direct(place, qualif); | |
163 | } | |
164 | ||
165 | // We need to assign qualifs to the left-hand side before visiting `rvalue` since | |
166 | // qualifs can be cleared on move. | |
167 | self.super_assign(place, rvalue, location); | |
168 | } | |
169 | ||
3c0e092e XL |
170 | fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) { |
171 | self.super_rvalue(rvalue, location); | |
172 | ||
173 | match rvalue { | |
174 | mir::Rvalue::AddressOf(mt, borrowed_place) => { | |
175 | if !borrowed_place.is_indirect() | |
176 | && self.address_of_allows_mutation(*mt, *borrowed_place) | |
177 | { | |
178 | let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty; | |
179 | if Q::in_any_value_of_ty(self.ccx, place_ty) { | |
180 | self.state.qualif.insert(borrowed_place.local); | |
181 | self.state.borrow.insert(borrowed_place.local); | |
182 | } | |
183 | } | |
184 | } | |
185 | ||
186 | mir::Rvalue::Ref(_, kind, borrowed_place) => { | |
187 | if !borrowed_place.is_indirect() && self.ref_allows_mutation(*kind, *borrowed_place) | |
188 | { | |
189 | let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty; | |
190 | if Q::in_any_value_of_ty(self.ccx, place_ty) { | |
191 | self.state.qualif.insert(borrowed_place.local); | |
192 | self.state.borrow.insert(borrowed_place.local); | |
193 | } | |
194 | } | |
195 | } | |
196 | ||
197 | mir::Rvalue::Cast(..) | |
198 | | mir::Rvalue::ShallowInitBox(..) | |
199 | | mir::Rvalue::Use(..) | |
064997fb | 200 | | mir::Rvalue::CopyForDeref(..) |
3c0e092e XL |
201 | | mir::Rvalue::ThreadLocalRef(..) |
202 | | mir::Rvalue::Repeat(..) | |
203 | | mir::Rvalue::Len(..) | |
204 | | mir::Rvalue::BinaryOp(..) | |
205 | | mir::Rvalue::CheckedBinaryOp(..) | |
206 | | mir::Rvalue::NullaryOp(..) | |
207 | | mir::Rvalue::UnaryOp(..) | |
208 | | mir::Rvalue::Discriminant(..) | |
209 | | mir::Rvalue::Aggregate(..) => {} | |
210 | } | |
211 | } | |
212 | ||
213 | fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { | |
214 | match statement.kind { | |
215 | StatementKind::StorageDead(local) => { | |
216 | self.state.qualif.remove(local); | |
217 | self.state.borrow.remove(local); | |
218 | } | |
219 | _ => self.super_statement(statement, location), | |
220 | } | |
221 | } | |
222 | ||
f035d41b | 223 | fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) { |
e74abb32 XL |
224 | // The effect of assignment to the return place in `TerminatorKind::Call` is not applied |
225 | // here; that occurs in `apply_call_return_effect`. | |
226 | ||
3c0e092e XL |
227 | // We ignore borrow on drop because custom drop impls are not allowed in consts. |
228 | // FIXME: Reconsider if accounting for borrows in drops is necessary for const drop. | |
f035d41b | 229 | self.super_terminator(terminator, location); |
e74abb32 XL |
230 | } |
231 | } | |
232 | ||
233 | /// The dataflow analysis used to propagate qualifs on arbitrary CFGs. | |
234 | pub(super) struct FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> { | |
f9f354fc | 235 | ccx: &'a ConstCx<'mir, 'tcx>, |
e74abb32 XL |
236 | _qualif: PhantomData<Q>, |
237 | } | |
238 | ||
239 | impl<'a, 'mir, 'tcx, Q> FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> | |
240 | where | |
241 | Q: Qualif, | |
242 | { | |
f9f354fc XL |
243 | pub(super) fn new(_: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self { |
244 | FlowSensitiveAnalysis { ccx, _qualif: PhantomData } | |
e74abb32 XL |
245 | } |
246 | ||
3c0e092e | 247 | fn transfer_function(&self, state: &'a mut State) -> TransferFunction<'a, 'mir, 'tcx, Q> { |
f9f354fc | 248 | TransferFunction::<Q>::new(self.ccx, state) |
e74abb32 XL |
249 | } |
250 | } | |
251 | ||
3c0e092e XL |
252 | #[derive(Debug, PartialEq, Eq)] |
253 | pub(super) struct State { | |
254 | /// Describes whether a local contains qualif. | |
255 | pub qualif: BitSet<Local>, | |
256 | /// Describes whether a local's address escaped and it might become qualified as a result an | |
257 | /// indirect mutation. | |
258 | pub borrow: BitSet<Local>, | |
259 | } | |
260 | ||
261 | impl Clone for State { | |
262 | fn clone(&self) -> Self { | |
263 | State { qualif: self.qualif.clone(), borrow: self.borrow.clone() } | |
264 | } | |
265 | ||
266 | // Data flow engine when possible uses `clone_from` for domain values. | |
267 | // Providing an implementation will avoid some intermediate memory allocations. | |
268 | fn clone_from(&mut self, other: &Self) { | |
269 | self.qualif.clone_from(&other.qualif); | |
270 | self.borrow.clone_from(&other.borrow); | |
271 | } | |
272 | } | |
273 | ||
274 | impl State { | |
275 | #[inline] | |
276 | pub(super) fn contains(&self, local: Local) -> bool { | |
277 | self.qualif.contains(local) | |
278 | } | |
279 | } | |
280 | ||
281 | impl<C> DebugWithContext<C> for State { | |
282 | fn fmt_with(&self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
283 | f.write_str("qualif: ")?; | |
284 | self.qualif.fmt_with(ctxt, f)?; | |
285 | f.write_str(" borrow: ")?; | |
286 | self.borrow.fmt_with(ctxt, f)?; | |
287 | Ok(()) | |
288 | } | |
289 | ||
290 | fn fmt_diff_with(&self, old: &Self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
291 | if self == old { | |
292 | return Ok(()); | |
293 | } | |
294 | ||
295 | if self.qualif != old.qualif { | |
296 | f.write_str("qualif: ")?; | |
297 | self.qualif.fmt_diff_with(&old.qualif, ctxt, f)?; | |
298 | f.write_str("\n")?; | |
299 | } | |
300 | ||
301 | if self.borrow != old.borrow { | |
302 | f.write_str("borrow: ")?; | |
303 | self.qualif.fmt_diff_with(&old.borrow, ctxt, f)?; | |
304 | f.write_str("\n")?; | |
305 | } | |
306 | ||
307 | Ok(()) | |
308 | } | |
309 | } | |
310 | ||
311 | impl JoinSemiLattice for State { | |
312 | fn join(&mut self, other: &Self) -> bool { | |
313 | self.qualif.join(&other.qualif) || self.borrow.join(&other.borrow) | |
314 | } | |
315 | } | |
316 | ||
a2a8927a | 317 | impl<'tcx, Q> AnalysisDomain<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q> |
e74abb32 XL |
318 | where |
319 | Q: Qualif, | |
320 | { | |
3c0e092e | 321 | type Domain = State; |
e74abb32 XL |
322 | |
323 | const NAME: &'static str = Q::ANALYSIS_NAME; | |
324 | ||
1b1a35ee | 325 | fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain { |
3c0e092e XL |
326 | State { |
327 | qualif: BitSet::new_empty(body.local_decls.len()), | |
328 | borrow: BitSet::new_empty(body.local_decls.len()), | |
329 | } | |
e74abb32 XL |
330 | } |
331 | ||
1b1a35ee | 332 | fn initialize_start_block(&self, _body: &mir::Body<'tcx>, state: &mut Self::Domain) { |
e74abb32 XL |
333 | self.transfer_function(state).initialize_state(); |
334 | } | |
dfeec247 | 335 | } |
e74abb32 | 336 | |
a2a8927a | 337 | impl<'tcx, Q> Analysis<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q> |
dfeec247 XL |
338 | where |
339 | Q: Qualif, | |
340 | { | |
e74abb32 | 341 | fn apply_statement_effect( |
fe692bf9 | 342 | &mut self, |
1b1a35ee | 343 | state: &mut Self::Domain, |
e74abb32 XL |
344 | statement: &mir::Statement<'tcx>, |
345 | location: Location, | |
346 | ) { | |
347 | self.transfer_function(state).visit_statement(statement, location); | |
348 | } | |
349 | ||
add651ee | 350 | fn apply_terminator_effect<'mir>( |
fe692bf9 | 351 | &mut self, |
1b1a35ee | 352 | state: &mut Self::Domain, |
add651ee | 353 | terminator: &'mir mir::Terminator<'tcx>, |
e74abb32 | 354 | location: Location, |
add651ee | 355 | ) -> TerminatorEdges<'mir, 'tcx> { |
e74abb32 | 356 | self.transfer_function(state).visit_terminator(terminator, location); |
add651ee | 357 | terminator.edges() |
e74abb32 XL |
358 | } |
359 | ||
360 | fn apply_call_return_effect( | |
fe692bf9 | 361 | &mut self, |
1b1a35ee | 362 | state: &mut Self::Domain, |
e74abb32 | 363 | block: BasicBlock, |
a2a8927a | 364 | return_places: CallReturnPlaces<'_, 'tcx>, |
e74abb32 | 365 | ) { |
a2a8927a | 366 | self.transfer_function(state).apply_call_return_effect(block, return_places) |
e74abb32 XL |
367 | } |
368 | } |