1 use rustc_data_structures::fx::FxHashMap;
2 use rustc_index::vec::IndexVec;
3 use rustc_middle::infer::MemberConstraint;
4 use rustc_middle::ty::{self, Ty};
9 /// Compactly stores a set of `R0 member of [R1...Rn]` constraints,
10 /// indexed by the region `R0`.
11 crate struct MemberConstraintSet<'tcx, R>
15 /// Stores the first "member" constraint for a given `R0`. This is an
16 /// index into the `constraints` vector below.
17 first_constraints: FxHashMap<R, NllMemberConstraintIndex>,
19 /// Stores the data about each `R0 member of [R1..Rn]` constraint.
20 /// These are organized into a linked list, so each constraint
21 /// contains the index of the next constraint with the same `R0`.
22 constraints: IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'tcx>>,
24 /// Stores the `R1..Rn` regions for *all* sets. For any given
25 /// constraint, we keep two indices so that we can pull out a
27 choice_regions: Vec<ty::RegionVid>,
30 /// Represents a `R0 member of [R1..Rn]` constraint
31 crate struct NllMemberConstraint<'tcx> {
32 next_constraint: Option<NllMemberConstraintIndex>,
34 /// The span where the hidden type was instantiated.
35 crate definition_span: Span,
37 /// The hidden type in which `R0` appears. (Used in error reporting.)
38 crate hidden_ty: Ty<'tcx>,
41 crate member_region_vid: ty::RegionVid,
43 /// Index of `R1` in `choice_regions` vector from `MemberConstraintSet`.
46 /// Index of `Rn` in `choice_regions` vector from `MemberConstraintSet`.
50 rustc_index::newtype_index! {
51 crate struct NllMemberConstraintIndex {
52 DEBUG_FORMAT = "MemberConstraintIndex({})"
56 impl Default for MemberConstraintSet<'tcx, ty::RegionVid> {
57 fn default() -> Self {
59 first_constraints: Default::default(),
60 constraints: Default::default(),
61 choice_regions: Default::default(),
66 impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
67 /// Pushes a member constraint into the set.
69 /// The input member constraint `m_c` is in the form produced by
70 /// the `rustc_middle::infer` code.
72 /// The `to_region_vid` callback fn is used to convert the regions
73 /// within into `RegionVid` format -- it typically consults the
74 /// `UniversalRegions` data structure that is known to the caller
75 /// (but which this code is unaware of).
76 crate fn push_constraint(
78 m_c: &MemberConstraint<'tcx>,
79 mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
81 debug!("push_constraint(m_c={:?})", m_c);
82 let member_region_vid: ty::RegionVid = to_region_vid(m_c.member_region);
83 let next_constraint = self.first_constraints.get(&member_region_vid).cloned();
84 let start_index = self.choice_regions.len();
85 let end_index = start_index + m_c.choice_regions.len();
86 debug!("push_constraint: member_region_vid={:?}", member_region_vid);
87 let constraint_index = self.constraints.push(NllMemberConstraint {
90 definition_span: m_c.definition_span,
91 hidden_ty: m_c.hidden_ty,
95 self.first_constraints.insert(member_region_vid, constraint_index);
96 self.choice_regions.extend(m_c.choice_regions.iter().map(|&r| to_region_vid(r)));
100 impl<R1> MemberConstraintSet<'tcx, R1>
102 R1: Copy + Hash + Eq,
104 /// Remap the "member region" key using `map_fn`, producing a new
105 /// member constraint set. This is used in the NLL code to map from
106 /// the original `RegionVid` to an scc index. In some cases, we
107 /// may have multiple `R1` values mapping to the same `R2` key -- that
108 /// is ok, the two sets will be merged.
109 crate fn into_mapped<R2>(
111 mut map_fn: impl FnMut(R1) -> R2,
112 ) -> MemberConstraintSet<'tcx, R2>
114 R2: Copy + Hash + Eq,
116 // We can re-use most of the original data, just tweaking the
117 // linked list links a bit.
119 // For example if we had two keys `Ra` and `Rb` that both now
120 // wind up mapped to the same key `S`, we would append the
121 // linked list for `Ra` onto the end of the linked list for
122 // `Rb` (or vice versa) -- this basically just requires
123 // rewriting the final link from one list to point at the other
124 // other (see `append_list`).
126 let MemberConstraintSet { first_constraints, mut constraints, choice_regions } = self;
128 let mut first_constraints2 = FxHashMap::default();
129 first_constraints2.reserve(first_constraints.len());
131 for (r1, start1) in first_constraints {
133 if let Some(&start2) = first_constraints2.get(&r2) {
134 append_list(&mut constraints, start1, start2);
136 first_constraints2.insert(r2, start1);
139 MemberConstraintSet { first_constraints: first_constraints2, constraints, choice_regions }
143 impl<R> MemberConstraintSet<'tcx, R>
147 crate fn all_indices(&self) -> impl Iterator<Item = NllMemberConstraintIndex> + '_ {
148 self.constraints.indices()
151 /// Iterate down the constraint indices associated with a given
152 /// peek-region. You can then use `choice_regions` and other
153 /// methods to access data.
156 member_region_vid: R,
157 ) -> impl Iterator<Item = NllMemberConstraintIndex> + '_ {
158 let mut next = self.first_constraints.get(&member_region_vid).cloned();
159 std::iter::from_fn(move || -> Option<NllMemberConstraintIndex> {
160 if let Some(current) = next {
161 next = self.constraints[current].next_constraint;
169 /// Returns the "choice regions" for a given member
170 /// constraint. This is the `R1..Rn` from a constraint like:
173 /// R0 member of [R1..Rn]
175 crate fn choice_regions(&self, pci: NllMemberConstraintIndex) -> &[ty::RegionVid] {
176 let NllMemberConstraint { start_index, end_index, .. } = &self.constraints[pci];
177 &self.choice_regions[*start_index..*end_index]
181 impl<'tcx, R> Index<NllMemberConstraintIndex> for MemberConstraintSet<'tcx, R>
185 type Output = NllMemberConstraint<'tcx>;
187 fn index(&self, i: NllMemberConstraintIndex) -> &NllMemberConstraint<'tcx> {
192 /// Given a linked list starting at `source_list` and another linked
193 /// list starting at `target_list`, modify `target_list` so that it is
194 /// followed by `source_list`.
199 /// target_list: A -> B -> C -> (None)
200 /// source_list: D -> E -> F -> (None)
206 /// target_list: A -> B -> C -> D -> E -> F -> (None)
209 constraints: &mut IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'_>>,
210 target_list: NllMemberConstraintIndex,
211 source_list: NllMemberConstraintIndex,
213 let mut p = target_list;
215 let mut r = &mut constraints[p];
216 match r.next_constraint {
219 r.next_constraint = Some(source_list);