1 use rustc_data_structures::captures::Captures;
2 use rustc_data_structures::fx::FxHashMap;
3 use rustc_index::vec::IndexVec;
4 use rustc_middle::infer::MemberConstraint;
5 use rustc_middle::ty::{self, Ty};
10 /// Compactly stores a set of `R0 member of [R1...Rn]` constraints,
11 /// indexed by the region `R0`.
12 pub(crate) struct MemberConstraintSet<'tcx, R>
16 /// Stores the first "member" constraint for a given `R0`. This is an
17 /// index into the `constraints` vector below.
18 first_constraints: FxHashMap<R, NllMemberConstraintIndex>,
20 /// Stores the data about each `R0 member of [R1..Rn]` constraint.
21 /// These are organized into a linked list, so each constraint
22 /// contains the index of the next constraint with the same `R0`.
23 constraints: IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'tcx>>,
25 /// Stores the `R1..Rn` regions for *all* sets. For any given
26 /// constraint, we keep two indices so that we can pull out a
28 choice_regions: Vec<ty::RegionVid>,
31 /// Represents a `R0 member of [R1..Rn]` constraint
32 pub(crate) struct NllMemberConstraint<'tcx> {
33 next_constraint: Option<NllMemberConstraintIndex>,
35 /// The span where the hidden type was instantiated.
36 pub(crate) definition_span: Span,
38 /// The hidden type in which `R0` appears. (Used in error reporting.)
39 pub(crate) hidden_ty: Ty<'tcx>,
41 pub(crate) key: ty::OpaqueTypeKey<'tcx>,
44 pub(crate) member_region_vid: ty::RegionVid,
46 /// Index of `R1` in `choice_regions` vector from `MemberConstraintSet`.
49 /// Index of `Rn` in `choice_regions` vector from `MemberConstraintSet`.
53 rustc_index::newtype_index! {
54 pub(crate) struct NllMemberConstraintIndex {
55 DEBUG_FORMAT = "MemberConstraintIndex({})"
59 impl Default for MemberConstraintSet<'_, ty::RegionVid> {
60 fn default() -> Self {
62 first_constraints: Default::default(),
63 constraints: Default::default(),
64 choice_regions: Default::default(),
69 impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
70 /// Pushes a member constraint into the set.
72 /// The input member constraint `m_c` is in the form produced by
73 /// the `rustc_middle::infer` code.
75 /// The `to_region_vid` callback fn is used to convert the regions
76 /// within into `RegionVid` format -- it typically consults the
77 /// `UniversalRegions` data structure that is known to the caller
78 /// (but which this code is unaware of).
79 pub(crate) fn push_constraint(
81 m_c: &MemberConstraint<'tcx>,
82 mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
84 debug!("push_constraint(m_c={:?})", m_c);
85 let member_region_vid: ty::RegionVid = to_region_vid(m_c.member_region);
86 let next_constraint = self.first_constraints.get(&member_region_vid).cloned();
87 let start_index = self.choice_regions.len();
88 let end_index = start_index + m_c.choice_regions.len();
89 debug!("push_constraint: member_region_vid={:?}", member_region_vid);
90 let constraint_index = self.constraints.push(NllMemberConstraint {
93 definition_span: m_c.definition_span,
94 hidden_ty: m_c.hidden_ty,
99 self.first_constraints.insert(member_region_vid, constraint_index);
100 self.choice_regions.extend(m_c.choice_regions.iter().map(|&r| to_region_vid(r)));
104 impl<'tcx, R1> MemberConstraintSet<'tcx, R1>
106 R1: Copy + Hash + Eq,
108 /// Remap the "member region" key using `map_fn`, producing a new
109 /// member constraint set. This is used in the NLL code to map from
110 /// the original `RegionVid` to an scc index. In some cases, we
111 /// may have multiple `R1` values mapping to the same `R2` key -- that
112 /// is ok, the two sets will be merged.
113 pub(crate) fn into_mapped<R2>(
115 mut map_fn: impl FnMut(R1) -> R2,
116 ) -> MemberConstraintSet<'tcx, R2>
118 R2: Copy + Hash + Eq,
120 // We can re-use most of the original data, just tweaking the
121 // linked list links a bit.
123 // For example if we had two keys `Ra` and `Rb` that both now
124 // wind up mapped to the same key `S`, we would append the
125 // linked list for `Ra` onto the end of the linked list for
126 // `Rb` (or vice versa) -- this basically just requires
127 // rewriting the final link from one list to point at the other
128 // other (see `append_list`).
130 let MemberConstraintSet { first_constraints, mut constraints, choice_regions } = self;
132 let mut first_constraints2 = FxHashMap::default();
133 first_constraints2.reserve(first_constraints.len());
135 for (r1, start1) in first_constraints {
137 if let Some(&start2) = first_constraints2.get(&r2) {
138 append_list(&mut constraints, start1, start2);
140 first_constraints2.insert(r2, start1);
143 MemberConstraintSet { first_constraints: first_constraints2, constraints, choice_regions }
147 impl<'tcx, R> MemberConstraintSet<'tcx, R>
151 pub(crate) fn all_indices(
153 ) -> impl Iterator<Item = NllMemberConstraintIndex> + Captures<'tcx> + '_ {
154 self.constraints.indices()
157 /// Iterate down the constraint indices associated with a given
158 /// peek-region. You can then use `choice_regions` and other
159 /// methods to access data.
160 pub(crate) fn indices(
162 member_region_vid: R,
163 ) -> impl Iterator<Item = NllMemberConstraintIndex> + Captures<'tcx> + '_ {
164 let mut next = self.first_constraints.get(&member_region_vid).cloned();
165 std::iter::from_fn(move || -> Option<NllMemberConstraintIndex> {
166 if let Some(current) = next {
167 next = self.constraints[current].next_constraint;
175 /// Returns the "choice regions" for a given member
176 /// constraint. This is the `R1..Rn` from a constraint like:
179 /// R0 member of [R1..Rn]
181 pub(crate) fn choice_regions(&self, pci: NllMemberConstraintIndex) -> &[ty::RegionVid] {
182 let NllMemberConstraint { start_index, end_index, .. } = &self.constraints[pci];
183 &self.choice_regions[*start_index..*end_index]
187 impl<'tcx, R> Index<NllMemberConstraintIndex> for MemberConstraintSet<'tcx, R>
191 type Output = NllMemberConstraint<'tcx>;
193 fn index(&self, i: NllMemberConstraintIndex) -> &NllMemberConstraint<'tcx> {
198 /// Given a linked list starting at `source_list` and another linked
199 /// list starting at `target_list`, modify `target_list` so that it is
200 /// followed by `source_list`.
205 /// target_list: A -> B -> C -> (None)
206 /// source_list: D -> E -> F -> (None)
212 /// target_list: A -> B -> C -> D -> E -> F -> (None)
215 constraints: &mut IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'_>>,
216 target_list: NllMemberConstraintIndex,
217 source_list: NllMemberConstraintIndex,
219 let mut p = target_list;
221 let mut r = &mut constraints[p];
222 match r.next_constraint {
225 r.next_constraint = Some(source_list);