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43 changes: 22 additions & 21 deletions compiler/rustc_borrowck/src/type_check/free_region_relations.rs
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use rustc_data_structures::frozen::Frozen;
use rustc_data_structures::transitive_relation::TransitiveRelation;
use rustc_data_structures::transitive_relation::{TransitiveRelation, TransitiveRelationBuilder};
use rustc_infer::infer::canonical::QueryRegionConstraints;
use rustc_infer::infer::outlives;
use rustc_infer::infer::outlives::env::RegionBoundPairs;
Expand Down Expand Up @@ -61,25 +61,13 @@ pub(crate) fn create<'tcx>(
constraints,
universal_regions: universal_regions.clone(),
region_bound_pairs: Default::default(),
relations: UniversalRegionRelations {
universal_regions: universal_regions.clone(),
outlives: Default::default(),
inverse_outlives: Default::default(),
},
outlives: Default::default(),
inverse_outlives: Default::default(),
}
.create()
}

impl UniversalRegionRelations<'_> {
/// Records in the `outlives_relation` (and
/// `inverse_outlives_relation`) that `fr_a: fr_b`. Invoked by the
/// builder below.
fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
debug!("relate_universal_regions: fr_a={:?} outlives fr_b={:?}", fr_a, fr_b);
self.outlives.add(fr_a, fr_b);
self.inverse_outlives.add(fr_b, fr_a);
}

/// Given two universal regions, returns the postdominating
/// upper-bound (effectively the least upper bound).
///
Expand Down Expand Up @@ -216,11 +204,20 @@ struct UniversalRegionRelationsBuilder<'this, 'tcx> {
constraints: &'this mut MirTypeckRegionConstraints<'tcx>,

// outputs:
relations: UniversalRegionRelations<'tcx>,
outlives: TransitiveRelationBuilder<RegionVid>,
inverse_outlives: TransitiveRelationBuilder<RegionVid>,
region_bound_pairs: RegionBoundPairs<'tcx>,
}

impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
/// Records in the `outlives_relation` (and
/// `inverse_outlives_relation`) that `fr_a: fr_b`.
fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
debug!("relate_universal_regions: fr_a={:?} outlives fr_b={:?}", fr_a, fr_b);
self.outlives.add(fr_a, fr_b);
self.inverse_outlives.add(fr_b, fr_a);
}

pub(crate) fn create(mut self) -> CreateResult<'tcx> {
let unnormalized_input_output_tys = self
.universal_regions
Expand Down Expand Up @@ -292,9 +289,9 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
let fr_fn_body = self.universal_regions.fr_fn_body;
for fr in self.universal_regions.universal_regions() {
debug!("build: relating free region {:?} to itself and to 'static", fr);
self.relations.relate_universal_regions(fr, fr);
self.relations.relate_universal_regions(fr_static, fr);
self.relations.relate_universal_regions(fr, fr_fn_body);
self.relate_universal_regions(fr, fr);
self.relate_universal_regions(fr_static, fr);
self.relate_universal_regions(fr, fr_fn_body);
}

for data in &constraint_sets {
Expand All @@ -313,7 +310,11 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
}

CreateResult {
universal_region_relations: Frozen::freeze(self.relations),
universal_region_relations: Frozen::freeze(UniversalRegionRelations {
universal_regions: self.universal_regions,
outlives: self.outlives.freeze(),
inverse_outlives: self.inverse_outlives.freeze(),
}),
region_bound_pairs: self.region_bound_pairs,
normalized_inputs_and_output,
}
Expand Down Expand Up @@ -356,7 +357,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
// The bound says that `r1 <= r2`; we store `r2: r1`.
let r1 = self.universal_regions.to_region_vid(r1);
let r2 = self.universal_regions.to_region_vid(r2);
self.relations.relate_universal_regions(r2, r1);
self.relate_universal_regions(r2, r1);
}

OutlivesBound::RegionSubParam(r_a, param_b) => {
Expand Down
121 changes: 67 additions & 54 deletions compiler/rustc_data_structures/src/transitive_relation.rs
Original file line number Diff line number Diff line change
@@ -1,45 +1,57 @@
use crate::frozen::Frozen;
use crate::fx::FxIndexSet;
use crate::sync::Lock;
use rustc_index::bit_set::BitMatrix;
use std::fmt::Debug;
use std::hash::Hash;
use std::mem;
use std::ops::Deref;

#[cfg(test)]
mod tests;

#[derive(Clone, Debug)]
pub struct TransitiveRelation<T> {
pub struct TransitiveRelationBuilder<T> {
// List of elements. This is used to map from a T to a usize.
elements: FxIndexSet<T>,

// List of base edges in the graph. Require to compute transitive
// closure.
edges: Vec<Edge>,
}

#[derive(Debug)]
pub struct TransitiveRelation<T> {
// Frozen transitive relation elements and edges.
builder: Frozen<TransitiveRelationBuilder<T>>,

// This is a cached transitive closure derived from the edges.
// Currently, we build it lazily and just throw out any existing
// copy whenever a new edge is added. (The Lock is to permit
// the lazy computation.) This is kind of silly, except for the
// fact its size is tied to `self.elements.len()`, so I wanted to
// wait before building it up to avoid reallocating as new edges
// are added with new elements. Perhaps better would be to ask the
// user for a batch of edges to minimize this effect, but I
// already wrote the code this way. :P -nmatsakis
closure: Lock<Option<BitMatrix<usize, usize>>>,
// Cached transitive closure derived from the edges.
closure: Frozen<BitMatrix<usize, usize>>,
}

// HACK(eddyb) manual impl avoids `Default` bound on `T`.
impl<T: Eq + Hash> Default for TransitiveRelation<T> {
fn default() -> Self {
impl<T> Deref for TransitiveRelation<T> {
type Target = Frozen<TransitiveRelationBuilder<T>>;

fn deref(&self) -> &Self::Target {
&self.builder
}
}

impl<T: Clone> Clone for TransitiveRelation<T> {
fn clone(&self) -> Self {
TransitiveRelation {
elements: Default::default(),
edges: Default::default(),
closure: Default::default(),
builder: Frozen::freeze(self.builder.deref().clone()),
closure: Frozen::freeze(self.closure.deref().clone()),
}
}
}

// HACK(eddyb) manual impl avoids `Default` bound on `T`.
impl<T: Eq + Hash> Default for TransitiveRelationBuilder<T> {
fn default() -> Self {
TransitiveRelationBuilder { elements: Default::default(), edges: Default::default() }
}
}

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Debug)]
struct Index(usize);

Expand All @@ -49,7 +61,7 @@ struct Edge {
target: Index,
}

impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
impl<T: Eq + Hash + Copy> TransitiveRelationBuilder<T> {
pub fn is_empty(&self) -> bool {
self.edges.is_empty()
}
Expand All @@ -63,23 +75,19 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
}

fn add_index(&mut self, a: T) -> Index {
let (index, added) = self.elements.insert_full(a);
if added {
// if we changed the dimensions, clear the cache
*self.closure.get_mut() = None;
}
let (index, _added) = self.elements.insert_full(a);
Index(index)
}

/// Applies the (partial) function to each edge and returns a new
/// relation. If `f` returns `None` for any end-point, returns
/// `None`.
pub fn maybe_map<F, U>(&self, mut f: F) -> Option<TransitiveRelation<U>>
/// relation builder. If `f` returns `None` for any end-point,
/// returns `None`.
pub fn maybe_map<F, U>(&self, mut f: F) -> Option<TransitiveRelationBuilder<U>>
where
F: FnMut(T) -> Option<U>,
U: Clone + Debug + Eq + Hash + Copy,
{
let mut result = TransitiveRelation::default();
let mut result = TransitiveRelationBuilder::default();
for edge in &self.edges {
result.add(f(self.elements[edge.source.0])?, f(self.elements[edge.target.0])?);
}
Expand All @@ -93,10 +101,38 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
let edge = Edge { source: a, target: b };
if !self.edges.contains(&edge) {
self.edges.push(edge);
}
}

/// Compute the transitive closure derived from the edges, and converted to
/// the final result. After this, all elements will be immutable to maintain
/// the correctness of the result.
pub fn freeze(self) -> TransitiveRelation<T> {
let mut matrix = BitMatrix::new(self.elements.len(), self.elements.len());
let mut changed = true;
while changed {
changed = false;
for edge in &self.edges {
// add an edge from S -> T
changed |= matrix.insert(edge.source.0, edge.target.0);

// added an edge, clear the cache
*self.closure.get_mut() = None;
// add all outgoing edges from T into S
changed |= matrix.union_rows(edge.target.0, edge.source.0);
}
}
TransitiveRelation { builder: Frozen::freeze(self), closure: Frozen::freeze(matrix) }
}
}

impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
/// Applies the (partial) function to each edge and returns a new
/// relation including transitive closures.
pub fn maybe_map<F, U>(&self, f: F) -> Option<TransitiveRelation<U>>
where
F: FnMut(T) -> Option<U>,
U: Clone + Debug + Eq + Hash + Copy,
{
Some(self.builder.maybe_map(f)?.freeze())
}

/// Checks whether `a < target` (transitively)
Expand Down Expand Up @@ -322,30 +358,7 @@ impl<T: Eq + Hash + Copy> TransitiveRelation<T> {
where
OP: FnOnce(&BitMatrix<usize, usize>) -> R,
{
let mut closure_cell = self.closure.borrow_mut();
let mut closure = closure_cell.take();
if closure.is_none() {
closure = Some(self.compute_closure());
}
let result = op(closure.as_ref().unwrap());
*closure_cell = closure;
result
}

fn compute_closure(&self) -> BitMatrix<usize, usize> {
let mut matrix = BitMatrix::new(self.elements.len(), self.elements.len());
let mut changed = true;
while changed {
changed = false;
for edge in &self.edges {
// add an edge from S -> T
changed |= matrix.insert(edge.source.0, edge.target.0);

// add all outgoing edges from T into S
changed |= matrix.union_rows(edge.target.0, edge.source.0);
}
}
matrix
op(&self.closure)
}

/// Lists all the base edges in the graph: the initial _non-transitive_ set of element
Expand Down
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