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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; | |
10 | use rustc_span::DUMMY_SP; | |
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 | ||
30 | impl<Q> TransferFunction<'a, 'mir, 'tcx, Q> | |
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, | |
ba9703b0 XL |
83 | _func: &mir::Operand<'tcx>, |
84 | _args: &[mir::Operand<'tcx>], | |
85 | return_place: mir::Place<'tcx>, | |
e74abb32 | 86 | ) { |
ba9703b0 XL |
87 | // We cannot reason about another function's internals, so use conservative type-based |
88 | // qualification for the result of a function call. | |
f9f354fc XL |
89 | let return_ty = return_place.ty(self.ccx.body, self.ccx.tcx).ty; |
90 | let qualif = Q::in_any_value_of_ty(self.ccx, return_ty); | |
ba9703b0 | 91 | |
e74abb32 | 92 | if !return_place.is_indirect() { |
ba9703b0 | 93 | self.assign_qualif_direct(&return_place, qualif); |
e74abb32 XL |
94 | } |
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 { | |
122 | !place | |
123 | .ty(self.ccx.body, self.ccx.tcx) | |
124 | .ty | |
125 | .is_freeze(self.ccx.tcx.at(DUMMY_SP), self.ccx.param_env) | |
126 | } | |
e74abb32 XL |
127 | } |
128 | ||
129 | impl<Q> Visitor<'tcx> for TransferFunction<'_, '_, 'tcx, Q> | |
130 | where | |
131 | Q: Qualif, | |
132 | { | |
133 | fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) { | |
134 | self.super_operand(operand, location); | |
135 | ||
136 | if !Q::IS_CLEARED_ON_MOVE { | |
137 | return; | |
138 | } | |
139 | ||
140 | // If a local with no projections is moved from (e.g. `x` in `y = x`), record that | |
141 | // it no longer needs to be dropped. | |
142 | if let mir::Operand::Move(place) = operand { | |
143 | if let Some(local) = place.as_local() { | |
3c0e092e XL |
144 | // For backward compatibility with the MaybeMutBorrowedLocals used in an earlier |
145 | // implementation we retain qualif if a local had been borrowed before. This might | |
146 | // not be strictly necessary since the local is no longer initialized. | |
147 | if !self.state.borrow.contains(local) { | |
148 | self.state.qualif.remove(local); | |
149 | } | |
e74abb32 XL |
150 | } |
151 | } | |
152 | } | |
153 | ||
154 | fn visit_assign( | |
155 | &mut self, | |
156 | place: &mir::Place<'tcx>, | |
157 | rvalue: &mir::Rvalue<'tcx>, | |
158 | location: Location, | |
159 | ) { | |
3c0e092e XL |
160 | let qualif = |
161 | qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.state.qualif.contains(l), rvalue); | |
e74abb32 XL |
162 | if !place.is_indirect() { |
163 | self.assign_qualif_direct(place, qualif); | |
164 | } | |
165 | ||
166 | // We need to assign qualifs to the left-hand side before visiting `rvalue` since | |
167 | // qualifs can be cleared on move. | |
168 | self.super_assign(place, rvalue, location); | |
169 | } | |
170 | ||
3c0e092e XL |
171 | fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) { |
172 | self.super_rvalue(rvalue, location); | |
173 | ||
174 | match rvalue { | |
175 | mir::Rvalue::AddressOf(mt, borrowed_place) => { | |
176 | if !borrowed_place.is_indirect() | |
177 | && self.address_of_allows_mutation(*mt, *borrowed_place) | |
178 | { | |
179 | let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty; | |
180 | if Q::in_any_value_of_ty(self.ccx, place_ty) { | |
181 | self.state.qualif.insert(borrowed_place.local); | |
182 | self.state.borrow.insert(borrowed_place.local); | |
183 | } | |
184 | } | |
185 | } | |
186 | ||
187 | mir::Rvalue::Ref(_, kind, borrowed_place) => { | |
188 | if !borrowed_place.is_indirect() && self.ref_allows_mutation(*kind, *borrowed_place) | |
189 | { | |
190 | let place_ty = borrowed_place.ty(self.ccx.body, self.ccx.tcx).ty; | |
191 | if Q::in_any_value_of_ty(self.ccx, place_ty) { | |
192 | self.state.qualif.insert(borrowed_place.local); | |
193 | self.state.borrow.insert(borrowed_place.local); | |
194 | } | |
195 | } | |
196 | } | |
197 | ||
198 | mir::Rvalue::Cast(..) | |
199 | | mir::Rvalue::ShallowInitBox(..) | |
200 | | mir::Rvalue::Use(..) | |
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 | ||
f035d41b | 227 | if let mir::TerminatorKind::DropAndReplace { value, place, .. } = &terminator.kind { |
ba9703b0 | 228 | let qualif = qualifs::in_operand::<Q, _>( |
f9f354fc | 229 | self.ccx, |
3c0e092e | 230 | &mut |l| self.state.qualif.contains(l), |
ba9703b0 XL |
231 | value, |
232 | ); | |
233 | ||
f035d41b XL |
234 | if !place.is_indirect() { |
235 | self.assign_qualif_direct(place, qualif); | |
e74abb32 XL |
236 | } |
237 | } | |
238 | ||
3c0e092e XL |
239 | // We ignore borrow on drop because custom drop impls are not allowed in consts. |
240 | // FIXME: Reconsider if accounting for borrows in drops is necessary for const drop. | |
241 | ||
e74abb32 XL |
242 | // We need to assign qualifs to the dropped location before visiting the operand that |
243 | // replaces it since qualifs can be cleared on move. | |
f035d41b | 244 | self.super_terminator(terminator, location); |
e74abb32 XL |
245 | } |
246 | } | |
247 | ||
248 | /// The dataflow analysis used to propagate qualifs on arbitrary CFGs. | |
249 | pub(super) struct FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> { | |
f9f354fc | 250 | ccx: &'a ConstCx<'mir, 'tcx>, |
e74abb32 XL |
251 | _qualif: PhantomData<Q>, |
252 | } | |
253 | ||
254 | impl<'a, 'mir, 'tcx, Q> FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q> | |
255 | where | |
256 | Q: Qualif, | |
257 | { | |
f9f354fc XL |
258 | pub(super) fn new(_: Q, ccx: &'a ConstCx<'mir, 'tcx>) -> Self { |
259 | FlowSensitiveAnalysis { ccx, _qualif: PhantomData } | |
e74abb32 XL |
260 | } |
261 | ||
3c0e092e | 262 | fn transfer_function(&self, state: &'a mut State) -> TransferFunction<'a, 'mir, 'tcx, Q> { |
f9f354fc | 263 | TransferFunction::<Q>::new(self.ccx, state) |
e74abb32 XL |
264 | } |
265 | } | |
266 | ||
3c0e092e XL |
267 | #[derive(Debug, PartialEq, Eq)] |
268 | pub(super) struct State { | |
269 | /// Describes whether a local contains qualif. | |
270 | pub qualif: BitSet<Local>, | |
271 | /// Describes whether a local's address escaped and it might become qualified as a result an | |
272 | /// indirect mutation. | |
273 | pub borrow: BitSet<Local>, | |
274 | } | |
275 | ||
276 | impl Clone for State { | |
277 | fn clone(&self) -> Self { | |
278 | State { qualif: self.qualif.clone(), borrow: self.borrow.clone() } | |
279 | } | |
280 | ||
281 | // Data flow engine when possible uses `clone_from` for domain values. | |
282 | // Providing an implementation will avoid some intermediate memory allocations. | |
283 | fn clone_from(&mut self, other: &Self) { | |
284 | self.qualif.clone_from(&other.qualif); | |
285 | self.borrow.clone_from(&other.borrow); | |
286 | } | |
287 | } | |
288 | ||
289 | impl State { | |
290 | #[inline] | |
291 | pub(super) fn contains(&self, local: Local) -> bool { | |
292 | self.qualif.contains(local) | |
293 | } | |
294 | } | |
295 | ||
296 | impl<C> DebugWithContext<C> for State { | |
297 | fn fmt_with(&self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
298 | f.write_str("qualif: ")?; | |
299 | self.qualif.fmt_with(ctxt, f)?; | |
300 | f.write_str(" borrow: ")?; | |
301 | self.borrow.fmt_with(ctxt, f)?; | |
302 | Ok(()) | |
303 | } | |
304 | ||
305 | fn fmt_diff_with(&self, old: &Self, ctxt: &C, f: &mut fmt::Formatter<'_>) -> fmt::Result { | |
306 | if self == old { | |
307 | return Ok(()); | |
308 | } | |
309 | ||
310 | if self.qualif != old.qualif { | |
311 | f.write_str("qualif: ")?; | |
312 | self.qualif.fmt_diff_with(&old.qualif, ctxt, f)?; | |
313 | f.write_str("\n")?; | |
314 | } | |
315 | ||
316 | if self.borrow != old.borrow { | |
317 | f.write_str("borrow: ")?; | |
318 | self.qualif.fmt_diff_with(&old.borrow, ctxt, f)?; | |
319 | f.write_str("\n")?; | |
320 | } | |
321 | ||
322 | Ok(()) | |
323 | } | |
324 | } | |
325 | ||
326 | impl JoinSemiLattice for State { | |
327 | fn join(&mut self, other: &Self) -> bool { | |
328 | self.qualif.join(&other.qualif) || self.borrow.join(&other.borrow) | |
329 | } | |
330 | } | |
331 | ||
c295e0f8 | 332 | impl<Q> rustc_mir_dataflow::AnalysisDomain<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q> |
e74abb32 XL |
333 | where |
334 | Q: Qualif, | |
335 | { | |
3c0e092e | 336 | type Domain = State; |
e74abb32 XL |
337 | |
338 | const NAME: &'static str = Q::ANALYSIS_NAME; | |
339 | ||
1b1a35ee | 340 | fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain { |
3c0e092e XL |
341 | State { |
342 | qualif: BitSet::new_empty(body.local_decls.len()), | |
343 | borrow: BitSet::new_empty(body.local_decls.len()), | |
344 | } | |
e74abb32 XL |
345 | } |
346 | ||
1b1a35ee | 347 | fn initialize_start_block(&self, _body: &mir::Body<'tcx>, state: &mut Self::Domain) { |
e74abb32 XL |
348 | self.transfer_function(state).initialize_state(); |
349 | } | |
dfeec247 | 350 | } |
e74abb32 | 351 | |
c295e0f8 | 352 | impl<Q> rustc_mir_dataflow::Analysis<'tcx> for FlowSensitiveAnalysis<'_, '_, 'tcx, Q> |
dfeec247 XL |
353 | where |
354 | Q: Qualif, | |
355 | { | |
e74abb32 XL |
356 | fn apply_statement_effect( |
357 | &self, | |
1b1a35ee | 358 | state: &mut Self::Domain, |
e74abb32 XL |
359 | statement: &mir::Statement<'tcx>, |
360 | location: Location, | |
361 | ) { | |
362 | self.transfer_function(state).visit_statement(statement, location); | |
363 | } | |
364 | ||
365 | fn apply_terminator_effect( | |
366 | &self, | |
1b1a35ee | 367 | state: &mut Self::Domain, |
e74abb32 XL |
368 | terminator: &mir::Terminator<'tcx>, |
369 | location: Location, | |
370 | ) { | |
371 | self.transfer_function(state).visit_terminator(terminator, location); | |
372 | } | |
373 | ||
374 | fn apply_call_return_effect( | |
375 | &self, | |
1b1a35ee | 376 | state: &mut Self::Domain, |
e74abb32 XL |
377 | block: BasicBlock, |
378 | func: &mir::Operand<'tcx>, | |
379 | args: &[mir::Operand<'tcx>], | |
ba9703b0 | 380 | return_place: mir::Place<'tcx>, |
e74abb32 XL |
381 | ) { |
382 | self.transfer_function(state).apply_call_return_effect(block, func, args, return_place) | |
383 | } | |
384 | } |