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>,
42 pub(crate) member_region_vid: ty::RegionVid,
44 /// Index of `R1` in `choice_regions` vector from `MemberConstraintSet`.
47 /// Index of `Rn` in `choice_regions` vector from `MemberConstraintSet`.
51 rustc_index::newtype_index! {
52 pub(crate) struct NllMemberConstraintIndex {
53 DEBUG_FORMAT = "MemberConstraintIndex({})"
57 impl Default for MemberConstraintSet<'_, ty::RegionVid> {
58 fn default() -> Self {
60 first_constraints: Default::default(),
61 constraints: Default::default(),
62 choice_regions: Default::default(),
67 impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
68 /// Pushes a member constraint into the set.
70 /// The input member constraint `m_c` is in the form produced by
71 /// the `rustc_middle::infer` code.
73 /// The `to_region_vid` callback fn is used to convert the regions
74 /// within into `RegionVid` format -- it typically consults the
75 /// `UniversalRegions` data structure that is known to the caller
76 /// (but which this code is unaware of).
77 pub(crate) fn push_constraint(
79 m_c: &MemberConstraint<'tcx>,
80 mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
82 debug!("push_constraint(m_c={:?})", m_c);
83 let member_region_vid: ty::RegionVid = to_region_vid(m_c.member_region);
84 let next_constraint = self.first_constraints.get(&member_region_vid).cloned();
85 let start_index = self.choice_regions.len();
86 let end_index = start_index + m_c.choice_regions.len();
87 debug!("push_constraint: member_region_vid={:?}", member_region_vid);
88 let constraint_index = self.constraints.push(NllMemberConstraint {
91 definition_span: m_c.definition_span,
92 hidden_ty: m_c.hidden_ty,
96 self.first_constraints.insert(member_region_vid, constraint_index);
97 self.choice_regions.extend(m_c.choice_regions.iter().map(|&r| to_region_vid(r)));
101 impl<'tcx, R1> MemberConstraintSet<'tcx, R1>
103 R1: Copy + Hash + Eq,
105 /// Remap the "member region" key using `map_fn`, producing a new
106 /// member constraint set. This is used in the NLL code to map from
107 /// the original `RegionVid` to an scc index. In some cases, we
108 /// may have multiple `R1` values mapping to the same `R2` key -- that
109 /// is ok, the two sets will be merged.
110 pub(crate) fn into_mapped<R2>(
112 mut map_fn: impl FnMut(R1) -> R2,
113 ) -> MemberConstraintSet<'tcx, R2>
115 R2: Copy + Hash + Eq,
117 // We can re-use most of the original data, just tweaking the
118 // linked list links a bit.
120 // For example if we had two keys `Ra` and `Rb` that both now
121 // wind up mapped to the same key `S`, we would append the
122 // linked list for `Ra` onto the end of the linked list for
123 // `Rb` (or vice versa) -- this basically just requires
124 // rewriting the final link from one list to point at the other
125 // other (see `append_list`).
127 let MemberConstraintSet { first_constraints, mut constraints, choice_regions } = self;
129 let mut first_constraints2 = FxHashMap::default();
130 first_constraints2.reserve(first_constraints.len());
132 for (r1, start1) in first_constraints {
134 if let Some(&start2) = first_constraints2.get(&r2) {
135 append_list(&mut constraints, start1, start2);
137 first_constraints2.insert(r2, start1);
140 MemberConstraintSet { first_constraints: first_constraints2, constraints, choice_regions }
144 impl<'tcx, R> MemberConstraintSet<'tcx, R>
148 pub(crate) fn all_indices(
150 ) -> impl Iterator<Item = NllMemberConstraintIndex> + Captures<'tcx> + '_ {
151 self.constraints.indices()
154 /// Iterate down the constraint indices associated with a given
155 /// peek-region. You can then use `choice_regions` and other
156 /// methods to access data.
157 pub(crate) fn indices(
159 member_region_vid: R,
160 ) -> impl Iterator<Item = NllMemberConstraintIndex> + Captures<'tcx> + '_ {
161 let mut next = self.first_constraints.get(&member_region_vid).cloned();
162 std::iter::from_fn(move || -> Option<NllMemberConstraintIndex> {
163 if let Some(current) = next {
164 next = self.constraints[current].next_constraint;
172 /// Returns the "choice regions" for a given member
173 /// constraint. This is the `R1..Rn` from a constraint like:
176 /// R0 member of [R1..Rn]
178 pub(crate) fn choice_regions(&self, pci: NllMemberConstraintIndex) -> &[ty::RegionVid] {
179 let NllMemberConstraint { start_index, end_index, .. } = &self.constraints[pci];
180 &self.choice_regions[*start_index..*end_index]
184 impl<'tcx, R> Index<NllMemberConstraintIndex> for MemberConstraintSet<'tcx, R>
188 type Output = NllMemberConstraint<'tcx>;
190 fn index(&self, i: NllMemberConstraintIndex) -> &NllMemberConstraint<'tcx> {
195 /// Given a linked list starting at `source_list` and another linked
196 /// list starting at `target_list`, modify `target_list` so that it is
197 /// followed by `source_list`.
202 /// target_list: A -> B -> C -> (None)
203 /// source_list: D -> E -> F -> (None)
209 /// target_list: A -> B -> C -> D -> E -> F -> (None)
212 constraints: &mut IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'_>>,
213 target_list: NllMemberConstraintIndex,
214 source_list: NllMemberConstraintIndex,
216 let mut p = target_list;
218 let mut r = &mut constraints[p];
219 match r.next_constraint {
222 r.next_constraint = Some(source_list);