225 lines
7.5 KiB
Rust
225 lines
7.5 KiB
Rust
use rustc_data_structures::fx::FxHashMap;
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use rustc_index::vec::IndexVec;
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use rustc_middle::infer::MemberConstraint;
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use rustc_middle::ty::{self, Ty};
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use rustc_span::Span;
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use std::hash::Hash;
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use std::ops::Index;
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/// Compactly stores a set of `R0 member of [R1...Rn]` constraints,
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/// indexed by the region `R0`.
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crate struct MemberConstraintSet<'tcx, R>
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where
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R: Copy + Eq,
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{
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/// Stores the first "member" constraint for a given `R0`. This is an
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/// index into the `constraints` vector below.
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first_constraints: FxHashMap<R, NllMemberConstraintIndex>,
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/// Stores the data about each `R0 member of [R1..Rn]` constraint.
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/// These are organized into a linked list, so each constraint
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/// contains the index of the next constraint with the same `R0`.
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constraints: IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'tcx>>,
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/// Stores the `R1..Rn` regions for *all* sets. For any given
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/// constraint, we keep two indices so that we can pull out a
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/// slice.
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choice_regions: Vec<ty::RegionVid>,
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}
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/// Represents a `R0 member of [R1..Rn]` constraint
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crate struct NllMemberConstraint<'tcx> {
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next_constraint: Option<NllMemberConstraintIndex>,
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/// The span where the hidden type was instantiated.
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crate definition_span: Span,
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/// The hidden type in which `R0` appears. (Used in error reporting.)
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crate hidden_ty: Ty<'tcx>,
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/// The region `R0`.
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crate member_region_vid: ty::RegionVid,
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/// Index of `R1` in `choice_regions` vector from `MemberConstraintSet`.
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start_index: usize,
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/// Index of `Rn` in `choice_regions` vector from `MemberConstraintSet`.
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end_index: usize,
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}
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rustc_index::newtype_index! {
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crate struct NllMemberConstraintIndex {
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DEBUG_FORMAT = "MemberConstraintIndex({})"
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}
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}
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impl Default for MemberConstraintSet<'tcx, ty::RegionVid> {
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fn default() -> Self {
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Self {
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first_constraints: Default::default(),
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constraints: Default::default(),
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choice_regions: Default::default(),
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}
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}
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}
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impl<'tcx> MemberConstraintSet<'tcx, ty::RegionVid> {
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/// Pushes a member constraint into the set.
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///
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/// The input member constraint `m_c` is in the form produced by
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/// the `rustc_middle::infer` code.
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///
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/// The `to_region_vid` callback fn is used to convert the regions
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/// within into `RegionVid` format -- it typically consults the
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/// `UniversalRegions` data structure that is known to the caller
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/// (but which this code is unaware of).
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crate fn push_constraint(
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&mut self,
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m_c: &MemberConstraint<'tcx>,
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mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
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) {
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debug!("push_constraint(m_c={:?})", m_c);
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let member_region_vid: ty::RegionVid = to_region_vid(m_c.member_region);
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let next_constraint = self.first_constraints.get(&member_region_vid).cloned();
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let start_index = self.choice_regions.len();
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let end_index = start_index + m_c.choice_regions.len();
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debug!("push_constraint: member_region_vid={:?}", member_region_vid);
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let constraint_index = self.constraints.push(NllMemberConstraint {
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next_constraint,
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member_region_vid,
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definition_span: m_c.definition_span,
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hidden_ty: m_c.hidden_ty,
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start_index,
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end_index,
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});
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self.first_constraints.insert(member_region_vid, constraint_index);
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self.choice_regions.extend(m_c.choice_regions.iter().map(|&r| to_region_vid(r)));
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}
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}
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impl<R1> MemberConstraintSet<'tcx, R1>
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where
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R1: Copy + Hash + Eq,
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{
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/// Remap the "member region" key using `map_fn`, producing a new
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/// member constraint set. This is used in the NLL code to map from
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/// the original `RegionVid` to an scc index. In some cases, we
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/// may have multiple `R1` values mapping to the same `R2` key -- that
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/// is ok, the two sets will be merged.
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crate fn into_mapped<R2>(
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self,
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mut map_fn: impl FnMut(R1) -> R2,
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) -> MemberConstraintSet<'tcx, R2>
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where
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R2: Copy + Hash + Eq,
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{
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// We can re-use most of the original data, just tweaking the
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// linked list links a bit.
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//
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// For example if we had two keys `Ra` and `Rb` that both now
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// wind up mapped to the same key `S`, we would append the
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// linked list for `Ra` onto the end of the linked list for
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// `Rb` (or vice versa) -- this basically just requires
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// rewriting the final link from one list to point at the other
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// other (see `append_list`).
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let MemberConstraintSet { first_constraints, mut constraints, choice_regions } = self;
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let mut first_constraints2 = FxHashMap::default();
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first_constraints2.reserve(first_constraints.len());
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for (r1, start1) in first_constraints {
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let r2 = map_fn(r1);
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if let Some(&start2) = first_constraints2.get(&r2) {
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append_list(&mut constraints, start1, start2);
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}
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first_constraints2.insert(r2, start1);
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}
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MemberConstraintSet { first_constraints: first_constraints2, constraints, choice_regions }
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}
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}
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impl<R> MemberConstraintSet<'tcx, R>
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where
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R: Copy + Hash + Eq,
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{
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crate fn all_indices(&self) -> impl Iterator<Item = NllMemberConstraintIndex> + '_ {
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self.constraints.indices()
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}
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/// Iterate down the constraint indices associated with a given
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/// peek-region. You can then use `choice_regions` and other
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/// methods to access data.
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crate fn indices(
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&self,
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member_region_vid: R,
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) -> impl Iterator<Item = NllMemberConstraintIndex> + '_ {
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let mut next = self.first_constraints.get(&member_region_vid).cloned();
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std::iter::from_fn(move || -> Option<NllMemberConstraintIndex> {
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if let Some(current) = next {
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next = self.constraints[current].next_constraint;
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Some(current)
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} else {
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None
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}
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})
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}
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/// Returns the "choice regions" for a given member
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/// constraint. This is the `R1..Rn` from a constraint like:
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///
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/// ```
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/// R0 member of [R1..Rn]
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/// ```
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crate fn choice_regions(&self, pci: NllMemberConstraintIndex) -> &[ty::RegionVid] {
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let NllMemberConstraint { start_index, end_index, .. } = &self.constraints[pci];
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&self.choice_regions[*start_index..*end_index]
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}
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}
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impl<'tcx, R> Index<NllMemberConstraintIndex> for MemberConstraintSet<'tcx, R>
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where
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R: Copy + Eq,
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{
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type Output = NllMemberConstraint<'tcx>;
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fn index(&self, i: NllMemberConstraintIndex) -> &NllMemberConstraint<'tcx> {
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&self.constraints[i]
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}
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}
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/// Given a linked list starting at `source_list` and another linked
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/// list starting at `target_list`, modify `target_list` so that it is
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/// followed by `source_list`.
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///
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/// Before:
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///
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/// ```
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/// target_list: A -> B -> C -> (None)
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/// source_list: D -> E -> F -> (None)
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/// ```
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///
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/// After:
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///
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/// ```
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/// target_list: A -> B -> C -> D -> E -> F -> (None)
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/// ```
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fn append_list(
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constraints: &mut IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'_>>,
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target_list: NllMemberConstraintIndex,
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source_list: NllMemberConstraintIndex,
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) {
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let mut p = target_list;
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loop {
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let mut r = &mut constraints[p];
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match r.next_constraint {
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Some(q) => p = q,
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None => {
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r.next_constraint = Some(source_list);
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return;
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}
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}
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}
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}
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