1 use rustc_data_structures::frozen::Frozen;
2 use rustc_data_structures::transitive_relation::TransitiveRelation;
3 use rustc_infer::infer::canonical::QueryRegionConstraints;
4 use rustc_infer::infer::outlives;
5 use rustc_infer::infer::region_constraints::GenericKind;
6 use rustc_infer::infer::InferCtxt;
7 use rustc_middle::mir::ConstraintCategory;
8 use rustc_middle::traits::query::OutlivesBound;
9 use rustc_middle::ty::{self, RegionVid, Ty};
10 use rustc_span::DUMMY_SP;
11 use rustc_trait_selection::traits::query::type_op::{self, TypeOp};
13 use type_op::TypeOpOutput;
16 type_check::constraint_conversion,
17 type_check::{Locations, MirTypeckRegionConstraints},
18 universal_regions::UniversalRegions,
22 crate struct UniversalRegionRelations<'tcx> {
23 universal_regions: Rc<UniversalRegions<'tcx>>,
25 /// Stores the outlives relations that are known to hold from the
26 /// implied bounds, in-scope where-clauses, and that sort of
28 outlives: TransitiveRelation<RegionVid>,
30 /// This is the `<=` relation; that is, if `a: b`, then `b <= a`,
31 /// and we store that here. This is useful when figuring out how
32 /// to express some local region in terms of external regions our
33 /// caller will understand.
34 inverse_outlives: TransitiveRelation<RegionVid>,
37 /// Each RBP `('a, GK)` indicates that `GK: 'a` can be assumed to
38 /// be true. These encode relationships like `T: 'a` that are
39 /// added via implicit bounds.
41 /// Each region here is guaranteed to be a key in the `indices`
42 /// map. We use the "original" regions (i.e., the keys from the
43 /// map, and not the values) because the code in
44 /// `process_registered_region_obligations` has some special-cased
45 /// logic expecting to see (e.g.) `ReStatic`, and if we supplied
46 /// our special inference variable there, we would mess that up.
47 type RegionBoundPairs<'tcx> = Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>;
49 /// As part of computing the free region relations, we also have to
50 /// normalize the input-output types, which we then need later. So we
51 /// return those. This vector consists of first the input types and
52 /// then the output type as the last element.
53 type NormalizedInputsAndOutput<'tcx> = Vec<Ty<'tcx>>;
55 crate struct CreateResult<'tcx> {
56 crate universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
57 crate region_bound_pairs: RegionBoundPairs<'tcx>,
58 crate normalized_inputs_and_output: NormalizedInputsAndOutput<'tcx>,
61 crate fn create<'tcx>(
62 infcx: &InferCtxt<'_, 'tcx>,
63 param_env: ty::ParamEnv<'tcx>,
64 implicit_region_bound: Option<ty::Region<'tcx>>,
65 universal_regions: &Rc<UniversalRegions<'tcx>>,
66 constraints: &mut MirTypeckRegionConstraints<'tcx>,
67 ) -> CreateResult<'tcx> {
68 UniversalRegionRelationsBuilder {
71 implicit_region_bound,
73 universal_regions: universal_regions.clone(),
74 region_bound_pairs: Vec::new(),
75 relations: UniversalRegionRelations {
76 universal_regions: universal_regions.clone(),
77 outlives: Default::default(),
78 inverse_outlives: Default::default(),
84 impl UniversalRegionRelations<'_> {
85 /// Records in the `outlives_relation` (and
86 /// `inverse_outlives_relation`) that `fr_a: fr_b`. Invoked by the
88 fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
89 debug!("relate_universal_regions: fr_a={:?} outlives fr_b={:?}", fr_a, fr_b);
90 self.outlives.add(fr_a, fr_b);
91 self.inverse_outlives.add(fr_b, fr_a);
94 /// Given two universal regions, returns the postdominating
95 /// upper-bound (effectively the least upper bound).
97 /// (See `TransitiveRelation::postdom_upper_bound` for details on
98 /// the postdominating upper bound in general.)
99 crate fn postdom_upper_bound(&self, fr1: RegionVid, fr2: RegionVid) -> RegionVid {
100 assert!(self.universal_regions.is_universal_region(fr1));
101 assert!(self.universal_regions.is_universal_region(fr2));
102 self.inverse_outlives
103 .postdom_upper_bound(fr1, fr2)
104 .unwrap_or(self.universal_regions.fr_static)
107 /// Finds an "upper bound" for `fr` that is not local. In other
108 /// words, returns the smallest (*) known region `fr1` that (a)
109 /// outlives `fr` and (b) is not local.
111 /// (*) If there are multiple competing choices, we return all of them.
112 crate fn non_local_upper_bounds<'a>(&'a self, fr: RegionVid) -> Vec<RegionVid> {
113 debug!("non_local_upper_bound(fr={:?})", fr);
114 let res = self.non_local_bounds(&self.inverse_outlives, fr);
115 assert!(!res.is_empty(), "can't find an upper bound!?");
119 /// Returns the "postdominating" bound of the set of
120 /// `non_local_upper_bounds` for the given region.
121 crate fn non_local_upper_bound(&self, fr: RegionVid) -> RegionVid {
122 let upper_bounds = self.non_local_upper_bounds(fr);
124 // In case we find more than one, reduce to one for
125 // convenience. This is to prevent us from generating more
126 // complex constraints, but it will cause spurious errors.
127 let post_dom = self.inverse_outlives.mutual_immediate_postdominator(upper_bounds);
129 debug!("non_local_bound: post_dom={:?}", post_dom);
132 .and_then(|post_dom| {
133 // If the mutual immediate postdom is not local, then
134 // there is no non-local result we can return.
135 if !self.universal_regions.is_local_free_region(post_dom) {
141 .unwrap_or(self.universal_regions.fr_static)
144 /// Finds a "lower bound" for `fr` that is not local. In other
145 /// words, returns the largest (*) known region `fr1` that (a) is
146 /// outlived by `fr` and (b) is not local.
148 /// (*) If there are multiple competing choices, we pick the "postdominating"
149 /// one. See `TransitiveRelation::postdom_upper_bound` for details.
150 crate fn non_local_lower_bound(&self, fr: RegionVid) -> Option<RegionVid> {
151 debug!("non_local_lower_bound(fr={:?})", fr);
152 let lower_bounds = self.non_local_bounds(&self.outlives, fr);
154 // In case we find more than one, reduce to one for
155 // convenience. This is to prevent us from generating more
156 // complex constraints, but it will cause spurious errors.
157 let post_dom = self.outlives.mutual_immediate_postdominator(lower_bounds);
159 debug!("non_local_bound: post_dom={:?}", post_dom);
161 post_dom.and_then(|post_dom| {
162 // If the mutual immediate postdom is not local, then
163 // there is no non-local result we can return.
164 if !self.universal_regions.is_local_free_region(post_dom) {
172 /// Helper for `non_local_upper_bounds` and `non_local_lower_bounds`.
173 /// Repeatedly invokes `postdom_parent` until we find something that is not
174 /// local. Returns `None` if we never do so.
175 fn non_local_bounds<'a>(
177 relation: &'a TransitiveRelation<RegionVid>,
179 ) -> Vec<RegionVid> {
180 // This method assumes that `fr0` is one of the universally
181 // quantified region variables.
182 assert!(self.universal_regions.is_universal_region(fr0));
184 let mut external_parents = vec![];
185 let mut queue = vec![fr0];
187 // Keep expanding `fr` into its parents until we reach
188 // non-local regions.
189 while let Some(fr) = queue.pop() {
190 if !self.universal_regions.is_local_free_region(fr) {
191 external_parents.push(fr);
195 queue.extend(relation.parents(fr));
198 debug!("non_local_bound: external_parents={:?}", external_parents);
203 /// Returns `true` if fr1 is known to outlive fr2.
205 /// This will only ever be true for universally quantified regions.
206 crate fn outlives(&self, fr1: RegionVid, fr2: RegionVid) -> bool {
207 self.outlives.contains(fr1, fr2)
210 /// Returns a vector of free regions `x` such that `fr1: x` is
212 crate fn regions_outlived_by(&self, fr1: RegionVid) -> Vec<RegionVid> {
213 self.outlives.reachable_from(fr1)
216 /// Returns the _non-transitive_ set of known `outlives` constraints between free regions.
217 crate fn known_outlives(&self) -> impl Iterator<Item = (RegionVid, RegionVid)> + '_ {
218 self.outlives.base_edges()
222 struct UniversalRegionRelationsBuilder<'this, 'tcx> {
223 infcx: &'this InferCtxt<'this, 'tcx>,
224 param_env: ty::ParamEnv<'tcx>,
225 universal_regions: Rc<UniversalRegions<'tcx>>,
226 implicit_region_bound: Option<ty::Region<'tcx>>,
227 constraints: &'this mut MirTypeckRegionConstraints<'tcx>,
230 relations: UniversalRegionRelations<'tcx>,
231 region_bound_pairs: RegionBoundPairs<'tcx>,
234 impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
235 crate fn create(mut self) -> CreateResult<'tcx> {
236 let unnormalized_input_output_tys = self
238 .unnormalized_input_tys
241 .chain(Some(self.universal_regions.unnormalized_output_ty));
243 // For each of the input/output types:
244 // - Normalize the type. This will create some region
245 // constraints, which we buffer up because we are
246 // not ready to process them yet.
247 // - Then compute the implied bounds. This will adjust
248 // the `region_bound_pairs` and so forth.
249 // - After this is done, we'll process the constraints, once
250 // the `relations` is built.
251 let mut normalized_inputs_and_output =
252 Vec::with_capacity(self.universal_regions.unnormalized_input_tys.len() + 1);
253 let constraint_sets: Vec<_> = unnormalized_input_output_tys
255 debug!("build: input_or_output={:?}", ty);
256 // We add implied bounds from both the unnormalized and normalized ty
258 let TypeOpOutput { output: norm_ty, constraints: constraints1, .. } = self
260 .and(type_op::normalize::Normalize::new(ty))
261 .fully_perform(self.infcx)
262 .unwrap_or_else(|_| {
266 .delay_span_bug(DUMMY_SP, &format!("failed to normalize {:?}", ty));
268 output: self.infcx.tcx.ty_error(),
273 // Note: we need this in examples like
277 // fn foo(&self) -> &Self::Bar;
281 // fn foo(&self) ->&() {}
284 // Both &Self::Bar and &() are WF
285 let constraints_implied = self.add_implied_bounds(norm_ty);
286 normalized_inputs_and_output.push(norm_ty);
287 constraints1.into_iter().chain(constraints_implied)
291 // Insert the facts we know from the predicates. Why? Why not.
292 let param_env = self.param_env;
293 self.add_outlives_bounds(outlives::explicit_outlives_bounds(param_env));
296 // - outlives is reflexive, so `'r: 'r` for every region `'r`
297 // - `'static: 'r` for every region `'r`
298 // - `'r: 'fn_body` for every (other) universally quantified
299 // region `'r`, all of which are provided by our caller
300 let fr_static = self.universal_regions.fr_static;
301 let fr_fn_body = self.universal_regions.fr_fn_body;
302 for fr in self.universal_regions.universal_regions() {
303 debug!("build: relating free region {:?} to itself and to 'static", fr);
304 self.relations.relate_universal_regions(fr, fr);
305 self.relations.relate_universal_regions(fr_static, fr);
306 self.relations.relate_universal_regions(fr, fr_fn_body);
309 for data in &constraint_sets {
310 constraint_conversion::ConstraintConversion::new(
312 &self.universal_regions,
313 &self.region_bound_pairs,
314 self.implicit_region_bound,
316 Locations::All(DUMMY_SP),
317 ConstraintCategory::Internal,
318 &mut self.constraints,
324 universal_region_relations: Frozen::freeze(self.relations),
325 region_bound_pairs: self.region_bound_pairs,
326 normalized_inputs_and_output,
330 /// Update the type of a single local, which should represent
331 /// either the return type of the MIR or one of its arguments. At
332 /// the same time, compute and add any implied bounds that come
334 fn add_implied_bounds(&mut self, ty: Ty<'tcx>) -> Option<Rc<QueryRegionConstraints<'tcx>>> {
335 debug!("add_implied_bounds(ty={:?})", ty);
336 let TypeOpOutput { output: bounds, constraints, .. } = self
338 .and(type_op::implied_outlives_bounds::ImpliedOutlivesBounds { ty })
339 .fully_perform(self.infcx)
340 .unwrap_or_else(|_| bug!("failed to compute implied bounds {:?}", ty));
341 self.add_outlives_bounds(bounds);
345 /// Registers the `OutlivesBound` items from `outlives_bounds` in
346 /// the outlives relation as well as the region-bound pairs
348 fn add_outlives_bounds<I>(&mut self, outlives_bounds: I)
350 I: IntoIterator<Item = OutlivesBound<'tcx>>,
352 for outlives_bound in outlives_bounds {
353 debug!("add_outlives_bounds(bound={:?})", outlives_bound);
355 match outlives_bound {
356 OutlivesBound::RegionSubRegion(r1, r2) => {
357 // `where Type:` is lowered to `where Type: 'empty` so that
358 // we check `Type` is well formed, but there's no use for
364 // The bound says that `r1 <= r2`; we store `r2: r1`.
365 let r1 = self.universal_regions.to_region_vid(r1);
366 let r2 = self.universal_regions.to_region_vid(r2);
367 self.relations.relate_universal_regions(r2, r1);
370 OutlivesBound::RegionSubParam(r_a, param_b) => {
371 self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
374 OutlivesBound::RegionSubProjection(r_a, projection_b) => {
375 self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));