compiler/rustc_borrowck/src/region_infer/values.rs - toolchain/rustc - Git at Google

 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_index::bit_set::SparseBitMatrix;
 use rustc_index::interval::IntervalSet;
 use rustc_index::interval::SparseIntervalMatrix;
 use rustc_index::Idx;
 use rustc_middle::mir::{BasicBlock, Location};
 use rustc_middle::ty::{self, RegionVid};
 use rustc_mir_dataflow::points::{DenseLocationMap, PointIndex};
 use std::fmt::Debug;
 use std::rc::Rc;

 use crate::BorrowIndex;

 rustc_index::newtype_index! {
     /// A single integer representing a `ty::Placeholder`.
     #[debug_format = "PlaceholderIndex({})"]
     pub struct PlaceholderIndex {}
 }

 /// An individual element in a region value -- the value of a
 /// particular region variable consists of a set of these elements.
 #[derive(Debug, Clone)]
 pub(crate) enum RegionElement {
     /// A point in the control-flow graph.
     Location(Location),

     /// A universally quantified region from the root universe (e.g.,
     /// a lifetime parameter).
     RootUniversalRegion(RegionVid),

     /// A placeholder (e.g., instantiated from a `for<'a> fn(&'a u32)`
     /// type).
     PlaceholderRegion(ty::PlaceholderRegion),
 }

 /// Records the CFG locations where each region is live. When we initially compute liveness, we use
 /// an interval matrix storing liveness ranges for each region-vid.
 pub(crate) struct LivenessValues {
     /// The map from locations to points.
     elements: Rc<DenseLocationMap>,

     /// Which regions are live. This is exclusive with the fine-grained tracking in `points`, and
     /// currently only used for validating promoteds (which don't care about more precise tracking).
     live_regions: Option<FxHashSet<RegionVid>>,

     /// For each region: the points where it is live.
     ///
     /// This is not initialized for promoteds, because we don't care *where* within a promoted a
     /// region is live, only that it is.
     points: Option<SparseIntervalMatrix<RegionVid, PointIndex>>,

     /// When using `-Zpolonius=next`, for each point: the loans flowing into the live regions at
     /// that point.
     pub(crate) loans: Option<LiveLoans>,
 }

 /// Data used to compute the loans that are live at a given point in the CFG, when using
 /// `-Zpolonius=next`.
 pub(crate) struct LiveLoans {
     /// The set of loans that flow into a given region. When individual regions are marked as live
     /// in the CFG, these inflowing loans are recorded as live.
     pub(crate) inflowing_loans: SparseBitMatrix<RegionVid, BorrowIndex>,

     /// The set of loans that are live at a given point in the CFG.
     pub(crate) live_loans: SparseBitMatrix<PointIndex, BorrowIndex>,
 }

 impl LiveLoans {
     pub(crate) fn new(num_loans: usize) -> Self {
         LiveLoans {
             live_loans: SparseBitMatrix::new(num_loans),
             inflowing_loans: SparseBitMatrix::new(num_loans),
         }
     }
 }

 impl LivenessValues {
     /// Create an empty map of regions to locations where they're live.
     pub(crate) fn with_specific_points(elements: Rc<DenseLocationMap>) -> Self {
         LivenessValues {
             live_regions: None,
             points: Some(SparseIntervalMatrix::new(elements.num_points())),
             elements,
             loans: None,
         }
     }

     /// Create an empty map of regions to locations where they're live.
     ///
     /// Unlike `with_specific_points`, does not track exact locations where something is live, only
     /// which regions are live.
     pub(crate) fn without_specific_points(elements: Rc<DenseLocationMap>) -> Self {
         LivenessValues {
             live_regions: Some(Default::default()),
             points: None,
             elements,
             loans: None,
         }
     }

     /// Iterate through each region that has a value in this set.
     pub(crate) fn regions(&self) -> impl Iterator<Item = RegionVid> + '_ {
         self.points.as_ref().expect("use with_specific_points").rows()
     }

     /// Iterate through each region that has a value in this set.
     // We are passing query instability implications to the caller.
     #[rustc_lint_query_instability]
     #[allow(rustc::potential_query_instability)]
     pub(crate) fn live_regions_unordered(&self) -> impl Iterator<Item = RegionVid> + '_ {
         self.live_regions.as_ref().unwrap().iter().copied()
     }

     /// Records `region` as being live at the given `location`.
     pub(crate) fn add_location(&mut self, region: RegionVid, location: Location) {
         let point = self.elements.point_from_location(location);
         debug!("LivenessValues::add_location(region={:?}, location={:?})", region, location);
         if let Some(points) = &mut self.points {
             points.insert(region, point);
         } else {
             if self.elements.point_in_range(point) {
                 self.live_regions.as_mut().unwrap().insert(region);
             }
         }

         // When available, record the loans flowing into this region as live at the given point.
         if let Some(loans) = self.loans.as_mut() {
             if let Some(inflowing) = loans.inflowing_loans.row(region) {
                 loans.live_loans.union_row(point, inflowing);
             }
         }
     }

     /// Records `region` as being live at all the given `points`.
     pub(crate) fn add_points(&mut self, region: RegionVid, points: &IntervalSet<PointIndex>) {
         debug!("LivenessValues::add_points(region={:?}, points={:?})", region, points);
         if let Some(this) = &mut self.points {
             this.union_row(region, points);
         } else {
             if points.iter().any(|point| self.elements.point_in_range(point)) {
                 self.live_regions.as_mut().unwrap().insert(region);
             }
         }

         // When available, record the loans flowing into this region as live at the given points.
         if let Some(loans) = self.loans.as_mut() {
             if let Some(inflowing) = loans.inflowing_loans.row(region) {
                 if !inflowing.is_empty() {
                     for point in points.iter() {
                         loans.live_loans.union_row(point, inflowing);
                     }
                 }
             }
         }
     }

     /// Records `region` as being live at all the control-flow points.
     pub(crate) fn add_all_points(&mut self, region: RegionVid) {
         if let Some(points) = &mut self.points {
             points.insert_all_into_row(region);
         } else {
             self.live_regions.as_mut().unwrap().insert(region);
         }
     }

     /// Returns whether `region` is marked live at the given `location`.
     pub(crate) fn is_live_at(&self, region: RegionVid, location: Location) -> bool {
         let point = self.elements.point_from_location(location);
         if let Some(points) = &self.points {
             points.row(region).is_some_and(|r| r.contains(point))
         } else {
             unreachable!(
                 "Should be using LivenessValues::with_specific_points to ask whether live at a location"
             )
         }
     }

     /// Returns an iterator of all the points where `region` is live.
     fn live_points(&self, region: RegionVid) -> impl Iterator<Item = PointIndex> + '_ {
         let Some(points) = &self.points else {
             unreachable!(
                 "Should be using LivenessValues::with_specific_points to ask whether live at a location"
             )
         };
         points
             .row(region)
             .into_iter()
             .flat_map(|set| set.iter())
             .take_while(|&p| self.elements.point_in_range(p))
     }

     /// For debugging purposes, returns a pretty-printed string of the points where the `region` is
     /// live.
     pub(crate) fn pretty_print_live_points(&self, region: RegionVid) -> String {
         pretty_print_region_elements(
             self.live_points(region).map(|p| RegionElement::Location(self.elements.to_location(p))),
         )
     }

     #[inline]
     pub(crate) fn point_from_location(&self, location: Location) -> PointIndex {
         self.elements.point_from_location(location)
     }

     /// When using `-Zpolonius=next`, returns whether the `loan_idx` is live at the given `point`.
     pub(crate) fn is_loan_live_at(&self, loan_idx: BorrowIndex, point: PointIndex) -> bool {
         self.loans
             .as_ref()
             .expect("Accessing live loans requires `-Zpolonius=next`")
             .live_loans
             .contains(point, loan_idx)
     }
 }

 /// Maps from `ty::PlaceholderRegion` values that are used in the rest of
 /// rustc to the internal `PlaceholderIndex` values that are used in
 /// NLL.
 #[derive(Debug, Default)]
 pub(crate) struct PlaceholderIndices {
     indices: FxIndexSet<ty::PlaceholderRegion>,
 }

 impl PlaceholderIndices {
     /// Returns the `PlaceholderIndex` for the inserted `PlaceholderRegion`
     pub(crate) fn insert(&mut self, placeholder: ty::PlaceholderRegion) -> PlaceholderIndex {
         let (index, _) = self.indices.insert_full(placeholder);
         index.into()
     }

     pub(crate) fn lookup_index(&self, placeholder: ty::PlaceholderRegion) -> PlaceholderIndex {
         self.indices.get_index_of(&placeholder).unwrap().into()
     }

     pub(crate) fn lookup_placeholder(
         &self,
         placeholder: PlaceholderIndex,
     ) -> ty::PlaceholderRegion {
         self.indices[placeholder.index()]
     }

     pub(crate) fn len(&self) -> usize {
         self.indices.len()
     }
 }

 /// Stores the full values for a set of regions (in contrast to
 /// `LivenessValues`, which only stores those points in the where a
 /// region is live). The full value for a region may contain points in
 /// the CFG, but also free regions as well as bound universe
 /// placeholders.
 ///
 /// Example:
 ///
 /// ```text
 /// fn foo(x: &'a u32) -> &'a u32 {
 ///    let y: &'0 u32 = x; // let's call this `'0`
 ///    y
 /// }
 /// ```
 ///
 /// Here, the variable `'0` would contain the free region `'a`,
 /// because (since it is returned) it must live for at least `'a`. But
 /// it would also contain various points from within the function.
 #[derive(Clone)]
 pub(crate) struct RegionValues<N: Idx> {
     elements: Rc<DenseLocationMap>,
     placeholder_indices: Rc<PlaceholderIndices>,
     points: SparseIntervalMatrix<N, PointIndex>,
     free_regions: SparseBitMatrix<N, RegionVid>,

     /// Placeholders represent bound regions -- so something like `'a`
     /// in `for<'a> fn(&'a u32)`.
     placeholders: SparseBitMatrix<N, PlaceholderIndex>,
 }

 impl<N: Idx> RegionValues<N> {
     /// Creates a new set of "region values" that tracks causal information.
     /// Each of the regions in num_region_variables will be initialized with an
     /// empty set of points and no causal information.
     pub(crate) fn new(
         elements: &Rc<DenseLocationMap>,
         num_universal_regions: usize,
         placeholder_indices: &Rc<PlaceholderIndices>,
     ) -> Self {
         let num_placeholders = placeholder_indices.len();
         Self {
             elements: elements.clone(),
             points: SparseIntervalMatrix::new(elements.num_points()),
             placeholder_indices: placeholder_indices.clone(),
             free_regions: SparseBitMatrix::new(num_universal_regions),
             placeholders: SparseBitMatrix::new(num_placeholders),
         }
     }

     /// Adds the given element to the value for the given region. Returns whether
     /// the element is newly added (i.e., was not already present).
     pub(crate) fn add_element(&mut self, r: N, elem: impl ToElementIndex) -> bool {
         debug!("add(r={:?}, elem={:?})", r, elem);
         elem.add_to_row(self, r)
     }

     /// Adds all the control-flow points to the values for `r`.
     pub(crate) fn add_all_points(&mut self, r: N) {
         self.points.insert_all_into_row(r);
     }

     /// Adds all elements in `r_from` to `r_to` (because e.g., `r_to:
     /// r_from`).
     pub(crate) fn add_region(&mut self, r_to: N, r_from: N) -> bool {
         self.points.union_rows(r_from, r_to)
             | self.free_regions.union_rows(r_from, r_to)
             | self.placeholders.union_rows(r_from, r_to)
     }

     /// Returns `true` if the region `r` contains the given element.
     pub(crate) fn contains(&self, r: N, elem: impl ToElementIndex) -> bool {
         elem.contained_in_row(self, r)
     }

     /// Returns the lowest statement index in `start..=end` which is not contained by `r`.
     pub(crate) fn first_non_contained_inclusive(
         &self,
         r: N,
         block: BasicBlock,
         start: usize,
         end: usize,
     ) -> Option<usize> {
         let row = self.points.row(r)?;
         let block = self.elements.entry_point(block);
         let start = block.plus(start);
         let end = block.plus(end);
         let first_unset = row.first_unset_in(start..=end)?;
         Some(first_unset.index() - block.index())
     }

     /// `self[to] |= values[from]`, essentially: that is, take all the
     /// elements for the region `from` from `values` and add them to
     /// the region `to` in `self`.
     pub(crate) fn merge_liveness(&mut self, to: N, from: RegionVid, values: &LivenessValues) {
         let Some(value_points) = &values.points else {
             panic!("LivenessValues must track specific points for use in merge_liveness");
         };
         if let Some(set) = value_points.row(from) {
             self.points.union_row(to, set);
         }
     }

     /// Returns `true` if `sup_region` contains all the CFG points that
     /// `sub_region` contains. Ignores universal regions.
     pub(crate) fn contains_points(&self, sup_region: N, sub_region: N) -> bool {
         if let Some(sub_row) = self.points.row(sub_region) {
             if let Some(sup_row) = self.points.row(sup_region) {
                 sup_row.superset(sub_row)
             } else {
                 // sup row is empty, so sub row must be empty
                 sub_row.is_empty()
             }
         } else {
             // sub row is empty, always true
             true
         }
     }

     /// Returns the locations contained within a given region `r`.
     pub(crate) fn locations_outlived_by<'a>(&'a self, r: N) -> impl Iterator<Item = Location> + 'a {
         self.points.row(r).into_iter().flat_map(move |set| {
             set.iter()
                 .take_while(move |&p| self.elements.point_in_range(p))
                 .map(move |p| self.elements.to_location(p))
         })
     }

     /// Returns just the universal regions that are contained in a given region's value.
     pub(crate) fn universal_regions_outlived_by<'a>(
         &'a self,
         r: N,
     ) -> impl Iterator<Item = RegionVid> + 'a {
         self.free_regions.row(r).into_iter().flat_map(|set| set.iter())
     }

     /// Returns all the elements contained in a given region's value.
     pub(crate) fn placeholders_contained_in<'a>(
         &'a self,
         r: N,
     ) -> impl Iterator<Item = ty::PlaceholderRegion> + 'a {
         self.placeholders
             .row(r)
             .into_iter()
             .flat_map(|set| set.iter())
             .map(move |p| self.placeholder_indices.lookup_placeholder(p))
     }

     /// Returns all the elements contained in a given region's value.
     pub(crate) fn elements_contained_in<'a>(
         &'a self,
         r: N,
     ) -> impl Iterator<Item = RegionElement> + 'a {
         let points_iter = self.locations_outlived_by(r).map(RegionElement::Location);

         let free_regions_iter =
             self.universal_regions_outlived_by(r).map(RegionElement::RootUniversalRegion);

         let placeholder_universes_iter =
             self.placeholders_contained_in(r).map(RegionElement::PlaceholderRegion);

         points_iter.chain(free_regions_iter).chain(placeholder_universes_iter)
     }

     /// Returns a "pretty" string value of the region. Meant for debugging.
     pub(crate) fn region_value_str(&self, r: N) -> String {
         pretty_print_region_elements(self.elements_contained_in(r))
     }
 }

 pub(crate) trait ToElementIndex: Debug + Copy {
     fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool;

     fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool;
 }

 impl ToElementIndex for Location {
     fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
         let index = values.elements.point_from_location(self);
         values.points.insert(row, index)
     }

     fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool {
         let index = values.elements.point_from_location(self);
         values.points.contains(row, index)
     }
 }

 impl ToElementIndex for RegionVid {
     fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
         values.free_regions.insert(row, self)
     }

     fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool {
         values.free_regions.contains(row, self)
     }
 }

 impl ToElementIndex for ty::PlaceholderRegion {
     fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
         let index = values.placeholder_indices.lookup_index(self);
         values.placeholders.insert(row, index)
     }

     fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool {
         let index = values.placeholder_indices.lookup_index(self);
         values.placeholders.contains(row, index)
     }
 }

 /// For debugging purposes, returns a pretty-printed string of the given points.
 pub(crate) fn pretty_print_points(
     elements: &DenseLocationMap,
     points: impl IntoIterator<Item = PointIndex>,
 ) -> String {
     pretty_print_region_elements(
         points
             .into_iter()
             .take_while(|&p| elements.point_in_range(p))
             .map(|p| elements.to_location(p))
             .map(RegionElement::Location),
     )
 }

 /// For debugging purposes, returns a pretty-printed string of the given region elements.
 fn pretty_print_region_elements(elements: impl IntoIterator<Item = RegionElement>) -> String {
     let mut result = String::new();
     result.push('{');

     // Set to Some(l1, l2) when we have observed all the locations
     // from l1..=l2 (inclusive) but not yet printed them. This
     // gets extended if we then see l3 where l3 is the successor
     // to l2.
     let mut open_location: Option<(Location, Location)> = None;

     let mut sep = "";
     let mut push_sep = |s: &mut String| {
         s.push_str(sep);
         sep = ", ";
     };

     for element in elements {
         match element {
             RegionElement::Location(l) => {
                 if let Some((location1, location2)) = open_location {
                     if location2.block == l.block
                         && location2.statement_index == l.statement_index - 1
                     {
                         open_location = Some((location1, l));
                         continue;
                     }

                     push_sep(&mut result);
                     push_location_range(&mut result, location1, location2);
                 }

                 open_location = Some((l, l));
             }

             RegionElement::RootUniversalRegion(fr) => {
                 if let Some((location1, location2)) = open_location {
                     push_sep(&mut result);
                     push_location_range(&mut result, location1, location2);
                     open_location = None;
                 }

                 push_sep(&mut result);
                 result.push_str(&format!("{fr:?}"));
             }

             RegionElement::PlaceholderRegion(placeholder) => {
                 if let Some((location1, location2)) = open_location {
                     push_sep(&mut result);
                     push_location_range(&mut result, location1, location2);
                     open_location = None;
                 }

                 push_sep(&mut result);
                 result.push_str(&format!("{placeholder:?}"));
             }
         }
     }

     if let Some((location1, location2)) = open_location {
         push_sep(&mut result);
         push_location_range(&mut result, location1, location2);
     }

     result.push('}');

     return result;

     fn push_location_range(str: &mut String, location1: Location, location2: Location) {
         if location1 == location2 {
             str.push_str(&format!("{location1:?}"));
         } else {
             assert_eq!(location1.block, location2.block);
             str.push_str(&format!(
                 "{:?}[{}..={}]",
                 location1.block, location1.statement_index, location2.statement_index
             ));
         }
     }
 }
	#![deny(rustc::untranslatable_diagnostic)]
	#![deny(rustc::diagnostic_outside_of_impl)]
	use rustc_data_structures::fx::FxHashSet;
	use rustc_data_structures::fx::FxIndexSet;
	use rustc_index::bit_set::SparseBitMatrix;
	use rustc_index::interval::IntervalSet;
	use rustc_index::interval::SparseIntervalMatrix;
	use rustc_index::Idx;
	use rustc_middle::mir::{BasicBlock, Location};
	use rustc_middle::ty::{self, RegionVid};
	use rustc_mir_dataflow::points::{DenseLocationMap, PointIndex};
	use std::fmt::Debug;
	use std::rc::Rc;

	use crate::BorrowIndex;

	rustc_index::newtype_index! {
	/// A single integer representing a `ty::Placeholder`.
	#[debug_format = "PlaceholderIndex({})"]
	pub struct PlaceholderIndex {}
	}

	/// An individual element in a region value -- the value of a
	/// particular region variable consists of a set of these elements.
	#[derive(Debug, Clone)]
	pub(crate) enum RegionElement {
	/// A point in the control-flow graph.
	Location(Location),

	/// A universally quantified region from the root universe (e.g.,
	/// a lifetime parameter).
	RootUniversalRegion(RegionVid),

	/// A placeholder (e.g., instantiated from a `for<'a> fn(&'a u32)`
	/// type).
	PlaceholderRegion(ty::PlaceholderRegion),
	}

	/// Records the CFG locations where each region is live. When we initially compute liveness, we use
	/// an interval matrix storing liveness ranges for each region-vid.
	pub(crate) struct LivenessValues {
	/// The map from locations to points.
	elements: Rc<DenseLocationMap>,

	/// Which regions are live. This is exclusive with the fine-grained tracking in `points`, and
	/// currently only used for validating promoteds (which don't care about more precise tracking).
	live_regions: Option<FxHashSet<RegionVid>>,

	/// For each region: the points where it is live.
	///
	/// This is not initialized for promoteds, because we don't care where within a promoted a
	/// region is live, only that it is.
	points: Option<SparseIntervalMatrix<RegionVid, PointIndex>>,

	/// When using `-Zpolonius=next`, for each point: the loans flowing into the live regions at
	/// that point.
	pub(crate) loans: Option<LiveLoans>,
	}

	/// Data used to compute the loans that are live at a given point in the CFG, when using
	/// `-Zpolonius=next`.
	pub(crate) struct LiveLoans {
	/// The set of loans that flow into a given region. When individual regions are marked as live
	/// in the CFG, these inflowing loans are recorded as live.
	pub(crate) inflowing_loans: SparseBitMatrix<RegionVid, BorrowIndex>,

	/// The set of loans that are live at a given point in the CFG.
	pub(crate) live_loans: SparseBitMatrix<PointIndex, BorrowIndex>,
	}

	impl LiveLoans {
	pub(crate) fn new(num_loans: usize) -> Self {
	LiveLoans {
	live_loans: SparseBitMatrix::new(num_loans),
	inflowing_loans: SparseBitMatrix::new(num_loans),
	}
	}
	}

	impl LivenessValues {
	/// Create an empty map of regions to locations where they're live.
	pub(crate) fn with_specific_points(elements: Rc<DenseLocationMap>) -> Self {
	LivenessValues {
	live_regions: None,
	points: Some(SparseIntervalMatrix::new(elements.num_points())),
	elements,
	loans: None,
	}
	}

	/// Create an empty map of regions to locations where they're live.
	///
	/// Unlike `with_specific_points`, does not track exact locations where something is live, only
	/// which regions are live.
	pub(crate) fn without_specific_points(elements: Rc<DenseLocationMap>) -> Self {
	LivenessValues {
	live_regions: Some(Default::default()),
	points: None,
	elements,
	loans: None,
	}
	}

	/// Iterate through each region that has a value in this set.
	pub(crate) fn regions(&self) -> impl Iterator<Item = RegionVid> + '_ {
	self.points.as_ref().expect("use with_specific_points").rows()
	}

	/// Iterate through each region that has a value in this set.
	// We are passing query instability implications to the caller.
	#[rustc_lint_query_instability]
	#[allow(rustc::potential_query_instability)]
	pub(crate) fn live_regions_unordered(&self) -> impl Iterator<Item = RegionVid> + '_ {
	self.live_regions.as_ref().unwrap().iter().copied()
	}

	/// Records `region` as being live at the given `location`.
	pub(crate) fn add_location(&mut self, region: RegionVid, location: Location) {
	let point = self.elements.point_from_location(location);
	debug!("LivenessValues::add_location(region={:?}, location={:?})", region, location);
	if let Some(points) = &mut self.points {
	points.insert(region, point);
	} else {
	if self.elements.point_in_range(point) {
	self.live_regions.as_mut().unwrap().insert(region);
	}
	}

	// When available, record the loans flowing into this region as live at the given point.
	if let Some(loans) = self.loans.as_mut() {
	if let Some(inflowing) = loans.inflowing_loans.row(region) {
	loans.live_loans.union_row(point, inflowing);
	}
	}
	}

	/// Records `region` as being live at all the given `points`.
	pub(crate) fn add_points(&mut self, region: RegionVid, points: &IntervalSet<PointIndex>) {
	debug!("LivenessValues::add_points(region={:?}, points={:?})", region, points);
	if let Some(this) = &mut self.points {
	this.union_row(region, points);
	} else {
	if points.iter().any(\|point\| self.elements.point_in_range(point)) {
	self.live_regions.as_mut().unwrap().insert(region);
	}
	}

	// When available, record the loans flowing into this region as live at the given points.
	if let Some(loans) = self.loans.as_mut() {
	if let Some(inflowing) = loans.inflowing_loans.row(region) {
	if !inflowing.is_empty() {
	for point in points.iter() {
	loans.live_loans.union_row(point, inflowing);
	}
	}
	}
	}
	}

	/// Records `region` as being live at all the control-flow points.
	pub(crate) fn add_all_points(&mut self, region: RegionVid) {
	if let Some(points) = &mut self.points {
	points.insert_all_into_row(region);
	} else {
	self.live_regions.as_mut().unwrap().insert(region);
	}
	}

	/// Returns whether `region` is marked live at the given `location`.
	pub(crate) fn is_live_at(&self, region: RegionVid, location: Location) -> bool {
	let point = self.elements.point_from_location(location);
	if let Some(points) = &self.points {
	points.row(region).is_some_and(\|r\| r.contains(point))
	} else {
	unreachable!(
	"Should be using LivenessValues::with_specific_points to ask whether live at a location"
	)
	}
	}

	/// Returns an iterator of all the points where `region` is live.
	fn live_points(&self, region: RegionVid) -> impl Iterator<Item = PointIndex> + '_ {
	let Some(points) = &self.points else {
	unreachable!(
	"Should be using LivenessValues::with_specific_points to ask whether live at a location"
	)
	};
	points
	.row(region)
	.into_iter()
	.flat_map(\|set\| set.iter())
	.take_while(\|&p\| self.elements.point_in_range(p))
	}

	/// For debugging purposes, returns a pretty-printed string of the points where the `region` is
	/// live.
	pub(crate) fn pretty_print_live_points(&self, region: RegionVid) -> String {
	pretty_print_region_elements(
	self.live_points(region).map(\|p\| RegionElement::Location(self.elements.to_location(p))),
	)
	}

	#[inline]
	pub(crate) fn point_from_location(&self, location: Location) -> PointIndex {
	self.elements.point_from_location(location)
	}

	/// When using `-Zpolonius=next`, returns whether the `loan_idx` is live at the given `point`.
	pub(crate) fn is_loan_live_at(&self, loan_idx: BorrowIndex, point: PointIndex) -> bool {
	self.loans
	.as_ref()
	.expect("Accessing live loans requires `-Zpolonius=next`")
	.live_loans
	.contains(point, loan_idx)
	}
	}

	/// Maps from `ty::PlaceholderRegion` values that are used in the rest of
	/// rustc to the internal `PlaceholderIndex` values that are used in
	/// NLL.
	#[derive(Debug, Default)]
	pub(crate) struct PlaceholderIndices {
	indices: FxIndexSet<ty::PlaceholderRegion>,
	}

	impl PlaceholderIndices {
	/// Returns the `PlaceholderIndex` for the inserted `PlaceholderRegion`
	pub(crate) fn insert(&mut self, placeholder: ty::PlaceholderRegion) -> PlaceholderIndex {
	let (index, _) = self.indices.insert_full(placeholder);
	index.into()
	}

	pub(crate) fn lookup_index(&self, placeholder: ty::PlaceholderRegion) -> PlaceholderIndex {
	self.indices.get_index_of(&placeholder).unwrap().into()
	}

	pub(crate) fn lookup_placeholder(
	&self,
	placeholder: PlaceholderIndex,
	) -> ty::PlaceholderRegion {
	self.indices[placeholder.index()]
	}

	pub(crate) fn len(&self) -> usize {
	self.indices.len()
	}
	}

	/// Stores the full values for a set of regions (in contrast to
	/// `LivenessValues`, which only stores those points in the where a
	/// region is live). The full value for a region may contain points in
	/// the CFG, but also free regions as well as bound universe
	/// placeholders.
	///
	/// Example:
	///
	/// ```text
	/// fn foo(x: &'a u32) -> &'a u32 {
	/// let y: &'0 u32 = x; // let's call this `'0`
	/// y
	/// }
	/// ```
	///
	/// Here, the variable `'0` would contain the free region `'a`,
	/// because (since it is returned) it must live for at least `'a`. But
	/// it would also contain various points from within the function.
	#[derive(Clone)]
	pub(crate) struct RegionValues<N: Idx> {
	elements: Rc<DenseLocationMap>,
	placeholder_indices: Rc<PlaceholderIndices>,
	points: SparseIntervalMatrix<N, PointIndex>,
	free_regions: SparseBitMatrix<N, RegionVid>,

	/// Placeholders represent bound regions -- so something like `'a`
	/// in `for<'a> fn(&'a u32)`.
	placeholders: SparseBitMatrix<N, PlaceholderIndex>,
	}

	impl<N: Idx> RegionValues<N> {
	/// Creates a new set of "region values" that tracks causal information.
	/// Each of the regions in num_region_variables will be initialized with an
	/// empty set of points and no causal information.
	pub(crate) fn new(
	elements: &Rc<DenseLocationMap>,
	num_universal_regions: usize,
	placeholder_indices: &Rc<PlaceholderIndices>,
	) -> Self {
	let num_placeholders = placeholder_indices.len();
	Self {
	elements: elements.clone(),
	points: SparseIntervalMatrix::new(elements.num_points()),
	placeholder_indices: placeholder_indices.clone(),
	free_regions: SparseBitMatrix::new(num_universal_regions),
	placeholders: SparseBitMatrix::new(num_placeholders),
	}
	}

	/// Adds the given element to the value for the given region. Returns whether
	/// the element is newly added (i.e., was not already present).
	pub(crate) fn add_element(&mut self, r: N, elem: impl ToElementIndex) -> bool {
	debug!("add(r={:?}, elem={:?})", r, elem);
	elem.add_to_row(self, r)
	}

	/// Adds all the control-flow points to the values for `r`.
	pub(crate) fn add_all_points(&mut self, r: N) {
	self.points.insert_all_into_row(r);
	}

	/// Adds all elements in `r_from` to `r_to` (because e.g., `r_to:
	/// r_from`).
	pub(crate) fn add_region(&mut self, r_to: N, r_from: N) -> bool {
	self.points.union_rows(r_from, r_to)
	\| self.free_regions.union_rows(r_from, r_to)
	\| self.placeholders.union_rows(r_from, r_to)
	}

	/// Returns `true` if the region `r` contains the given element.
	pub(crate) fn contains(&self, r: N, elem: impl ToElementIndex) -> bool {
	elem.contained_in_row(self, r)
	}

	/// Returns the lowest statement index in `start..=end` which is not contained by `r`.
	pub(crate) fn first_non_contained_inclusive(
	&self,
	r: N,
	block: BasicBlock,
	start: usize,
	end: usize,
	) -> Option<usize> {
	let row = self.points.row(r)?;
	let block = self.elements.entry_point(block);
	let start = block.plus(start);
	let end = block.plus(end);
	let first_unset = row.first_unset_in(start..=end)?;
	Some(first_unset.index() - block.index())
	}

	/// `self[to] \|= values[from]`, essentially: that is, take all the
	/// elements for the region `from` from `values` and add them to
	/// the region `to` in `self`.
	pub(crate) fn merge_liveness(&mut self, to: N, from: RegionVid, values: &LivenessValues) {
	let Some(value_points) = &values.points else {
	panic!("LivenessValues must track specific points for use in merge_liveness");
	};
	if let Some(set) = value_points.row(from) {
	self.points.union_row(to, set);
	}
	}

	/// Returns `true` if `sup_region` contains all the CFG points that
	/// `sub_region` contains. Ignores universal regions.
	pub(crate) fn contains_points(&self, sup_region: N, sub_region: N) -> bool {
	if let Some(sub_row) = self.points.row(sub_region) {
	if let Some(sup_row) = self.points.row(sup_region) {
	sup_row.superset(sub_row)
	} else {
	// sup row is empty, so sub row must be empty
	sub_row.is_empty()
	}
	} else {
	// sub row is empty, always true
	true
	}
	}

	/// Returns the locations contained within a given region `r`.
	pub(crate) fn locations_outlived_by<'a>(&'a self, r: N) -> impl Iterator<Item = Location> + 'a {
	self.points.row(r).into_iter().flat_map(move \|set\| {
	set.iter()
	.take_while(move \|&p\| self.elements.point_in_range(p))
	.map(move \|p\| self.elements.to_location(p))
	})
	}

	/// Returns just the universal regions that are contained in a given region's value.
	pub(crate) fn universal_regions_outlived_by<'a>(
	&'a self,
	r: N,
	) -> impl Iterator<Item = RegionVid> + 'a {
	self.free_regions.row(r).into_iter().flat_map(\|set\| set.iter())
	}

	/// Returns all the elements contained in a given region's value.
	pub(crate) fn placeholders_contained_in<'a>(
	&'a self,
	r: N,
	) -> impl Iterator<Item = ty::PlaceholderRegion> + 'a {
	self.placeholders
	.row(r)
	.into_iter()
	.flat_map(\|set\| set.iter())
	.map(move \|p\| self.placeholder_indices.lookup_placeholder(p))
	}

	/// Returns all the elements contained in a given region's value.
	pub(crate) fn elements_contained_in<'a>(
	&'a self,
	r: N,
	) -> impl Iterator<Item = RegionElement> + 'a {
	let points_iter = self.locations_outlived_by(r).map(RegionElement::Location);

	let free_regions_iter =
	self.universal_regions_outlived_by(r).map(RegionElement::RootUniversalRegion);

	let placeholder_universes_iter =
	self.placeholders_contained_in(r).map(RegionElement::PlaceholderRegion);

	points_iter.chain(free_regions_iter).chain(placeholder_universes_iter)
	}

	/// Returns a "pretty" string value of the region. Meant for debugging.
	pub(crate) fn region_value_str(&self, r: N) -> String {
	pretty_print_region_elements(self.elements_contained_in(r))
	}
	}

	pub(crate) trait ToElementIndex: Debug + Copy {
	fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool;

	fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool;
	}

	impl ToElementIndex for Location {
	fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
	let index = values.elements.point_from_location(self);
	values.points.insert(row, index)
	}

	fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool {
	let index = values.elements.point_from_location(self);
	values.points.contains(row, index)
	}
	}

	impl ToElementIndex for RegionVid {
	fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
	values.free_regions.insert(row, self)
	}

	fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool {
	values.free_regions.contains(row, self)
	}
	}

	impl ToElementIndex for ty::PlaceholderRegion {
	fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
	let index = values.placeholder_indices.lookup_index(self);
	values.placeholders.insert(row, index)
	}

	fn contained_in_row<N: Idx>(self, values: &RegionValues<N>, row: N) -> bool {
	let index = values.placeholder_indices.lookup_index(self);
	values.placeholders.contains(row, index)
	}
	}

	/// For debugging purposes, returns a pretty-printed string of the given points.
	pub(crate) fn pretty_print_points(
	elements: &DenseLocationMap,
	points: impl IntoIterator<Item = PointIndex>,
	) -> String {
	pretty_print_region_elements(
	points
	.into_iter()
	.take_while(\|&p\| elements.point_in_range(p))
	.map(\|p\| elements.to_location(p))
	.map(RegionElement::Location),
	)
	}

	/// For debugging purposes, returns a pretty-printed string of the given region elements.
	fn pretty_print_region_elements(elements: impl IntoIterator<Item = RegionElement>) -> String {
	let mut result = String::new();
	result.push('{');

	// Set to Some(l1, l2) when we have observed all the locations
	// from l1..=l2 (inclusive) but not yet printed them. This
	// gets extended if we then see l3 where l3 is the successor
	// to l2.
	let mut open_location: Option<(Location, Location)> = None;

	let mut sep = "";
	let mut push_sep = \|s: &mut String\| {
	s.push_str(sep);
	sep = ", ";
	};

	for element in elements {
	match element {
	RegionElement::Location(l) => {
	if let Some((location1, location2)) = open_location {
	if location2.block == l.block
	&& location2.statement_index == l.statement_index - 1
	{
	open_location = Some((location1, l));
	continue;
	}

	push_sep(&mut result);
	push_location_range(&mut result, location1, location2);
	}

	open_location = Some((l, l));
	}

	RegionElement::RootUniversalRegion(fr) => {
	if let Some((location1, location2)) = open_location {
	push_sep(&mut result);
	push_location_range(&mut result, location1, location2);
	open_location = None;
	}

	push_sep(&mut result);
	result.push_str(&format!("{fr:?}"));
	}

	RegionElement::PlaceholderRegion(placeholder) => {
	if let Some((location1, location2)) = open_location {
	push_sep(&mut result);
	push_location_range(&mut result, location1, location2);
	open_location = None;
	}

	push_sep(&mut result);
	result.push_str(&format!("{placeholder:?}"));
	}
	}
	}

	if let Some((location1, location2)) = open_location {
	push_sep(&mut result);
	push_location_range(&mut result, location1, location2);
	}

	result.push('}');

	return result;

	fn push_location_range(str: &mut String, location1: Location, location2: Location) {
	if location1 == location2 {
	str.push_str(&format!("{location1:?}"));
	} else {
	assert_eq!(location1.block, location2.block);
	str.push_str(&format!(
	"{:?}[{}..={}]",
	location1.block, location1.statement_index, location2.statement_index
	));
	}
	}
	}