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::FxIndexSet;
 use rustc_index::bit_set::SparseBitMatrix;
 use rustc_index::interval::IntervalSet;
 use rustc_index::interval::SparseIntervalMatrix;
 use rustc_index::Idx;
 use rustc_index::IndexVec;
 use rustc_middle::mir::{BasicBlock, Body, Location};
 use rustc_middle::ty::{self, RegionVid};
 use std::fmt::Debug;
 use std::rc::Rc;

 /// Maps between a `Location` and a `PointIndex` (and vice versa).
 pub(crate) struct RegionValueElements {
     /// For each basic block, how many points are contained within?
     statements_before_block: IndexVec<BasicBlock, usize>,

     /// Map backward from each point to the basic block that it
     /// belongs to.
     basic_blocks: IndexVec<PointIndex, BasicBlock>,

     num_points: usize,
 }

 impl RegionValueElements {
     pub(crate) fn new(body: &Body<'_>) -> Self {
         let mut num_points = 0;
         let statements_before_block: IndexVec<BasicBlock, usize> = body
             .basic_blocks
             .iter()
             .map(|block_data| {
                 let v = num_points;
                 num_points += block_data.statements.len() + 1;
                 v
             })
             .collect();
         debug!("RegionValueElements: statements_before_block={:#?}", statements_before_block);
         debug!("RegionValueElements: num_points={:#?}", num_points);

         let mut basic_blocks = IndexVec::with_capacity(num_points);
         for (bb, bb_data) in body.basic_blocks.iter_enumerated() {
             basic_blocks.extend((0..=bb_data.statements.len()).map(|_| bb));
         }

         Self { statements_before_block, basic_blocks, num_points }
     }

     /// Total number of point indices
     pub(crate) fn num_points(&self) -> usize {
         self.num_points
     }

     /// Converts a `Location` into a `PointIndex`. O(1).
     pub(crate) fn point_from_location(&self, location: Location) -> PointIndex {
         let Location { block, statement_index } = location;
         let start_index = self.statements_before_block[block];
         PointIndex::new(start_index + statement_index)
     }

     /// Converts a `Location` into a `PointIndex`. O(1).
     pub(crate) fn entry_point(&self, block: BasicBlock) -> PointIndex {
         let start_index = self.statements_before_block[block];
         PointIndex::new(start_index)
     }

     /// Return the PointIndex for the block start of this index.
     pub(crate) fn to_block_start(&self, index: PointIndex) -> PointIndex {
         PointIndex::new(self.statements_before_block[self.basic_blocks[index]])
     }

     /// Converts a `PointIndex` back to a location. O(1).
     pub(crate) fn to_location(&self, index: PointIndex) -> Location {
         assert!(index.index() < self.num_points);
         let block = self.basic_blocks[index];
         let start_index = self.statements_before_block[block];
         let statement_index = index.index() - start_index;
         Location { block, statement_index }
     }

     /// Sometimes we get point-indices back from bitsets that may be
     /// out of range (because they round up to the nearest 2^N number
     /// of bits). Use this function to filter such points out if you
     /// like.
     pub(crate) fn point_in_range(&self, index: PointIndex) -> bool {
         index.index() < self.num_points
     }
 }

 rustc_index::newtype_index! {
     /// A single integer representing a `Location` in the MIR control-flow
     /// graph. Constructed efficiently from `RegionValueElements`.
     #[debug_format = "PointIndex({})"]
     pub struct PointIndex {}
 }

 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),
 }

 /// When we initially compute liveness, we use an interval matrix storing
 /// liveness ranges for each region-vid.
 pub(crate) struct LivenessValues<N: Idx> {
     elements: Rc<RegionValueElements>,
     points: SparseIntervalMatrix<N, PointIndex>,
 }

 impl<N: Idx> LivenessValues<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<RegionValueElements>) -> Self {
         Self { points: SparseIntervalMatrix::new(elements.num_points), elements }
     }

     /// Iterate through each region that has a value in this set.
     pub(crate) fn rows(&self) -> impl Iterator<Item = N> {
         self.points.rows()
     }

     /// 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, row: N, location: Location) -> bool {
         debug!("LivenessValues::add(r={:?}, location={:?})", row, location);
         let index = self.elements.point_from_location(location);
         self.points.insert(row, index)
     }

     /// Adds all the elements in the given bit array into the given
     /// region. Returns whether any of them are newly added.
     pub(crate) fn add_elements(&mut self, row: N, locations: &IntervalSet<PointIndex>) -> bool {
         debug!("LivenessValues::add_elements(row={:?}, locations={:?})", row, locations);
         self.points.union_row(row, locations)
     }

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

     /// Returns `true` if the region `r` contains the given element.
     pub(crate) fn contains(&self, row: N, location: Location) -> bool {
         let index = self.elements.point_from_location(location);
         self.points.row(row).is_some_and(|r| r.contains(index))
     }

     /// Returns an iterator of all the elements contained by the region `r`
     pub(crate) fn get_elements(&self, row: N) -> impl Iterator<Item = Location> + '_ {
         self.points
             .row(row)
             .into_iter()
             .flat_map(|set| set.iter())
             .take_while(move |&p| self.elements.point_in_range(p))
             .map(move |p| self.elements.to_location(p))
     }

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

 /// 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<RegionValueElements>,
     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<RegionValueElements>,
         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<M: Idx>(&mut self, to: N, from: M, values: &LivenessValues<M>) {
         if let Some(set) = values.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 {
         region_value_str(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)
     }
 }

 pub(crate) fn location_set_str(
     elements: &RegionValueElements,
     points: impl IntoIterator<Item = PointIndex>,
 ) -> String {
     region_value_str(
         points
             .into_iter()
             .take_while(|&p| elements.point_in_range(p))
             .map(|p| elements.to_location(p))
             .map(RegionElement::Location),
     )
 }

 fn region_value_str(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::FxIndexSet;
	use rustc_index::bit_set::SparseBitMatrix;
	use rustc_index::interval::IntervalSet;
	use rustc_index::interval::SparseIntervalMatrix;
	use rustc_index::Idx;
	use rustc_index::IndexVec;
	use rustc_middle::mir::{BasicBlock, Body, Location};
	use rustc_middle::ty::{self, RegionVid};
	use std::fmt::Debug;
	use std::rc::Rc;

	/// Maps between a `Location` and a `PointIndex` (and vice versa).
	pub(crate) struct RegionValueElements {
	/// For each basic block, how many points are contained within?
	statements_before_block: IndexVec<BasicBlock, usize>,

	/// Map backward from each point to the basic block that it
	/// belongs to.
	basic_blocks: IndexVec<PointIndex, BasicBlock>,

	num_points: usize,
	}

	impl RegionValueElements {
	pub(crate) fn new(body: &Body<'_>) -> Self {
	let mut num_points = 0;
	let statements_before_block: IndexVec<BasicBlock, usize> = body
	.basic_blocks
	.iter()
	.map(\|block_data\| {
	let v = num_points;
	num_points += block_data.statements.len() + 1;
	v
	})
	.collect();
	debug!("RegionValueElements: statements_before_block={:#?}", statements_before_block);
	debug!("RegionValueElements: num_points={:#?}", num_points);

	let mut basic_blocks = IndexVec::with_capacity(num_points);
	for (bb, bb_data) in body.basic_blocks.iter_enumerated() {
	basic_blocks.extend((0..=bb_data.statements.len()).map(\|_\| bb));
	}

	Self { statements_before_block, basic_blocks, num_points }
	}

	/// Total number of point indices
	pub(crate) fn num_points(&self) -> usize {
	self.num_points
	}

	/// Converts a `Location` into a `PointIndex`. O(1).
	pub(crate) fn point_from_location(&self, location: Location) -> PointIndex {
	let Location { block, statement_index } = location;
	let start_index = self.statements_before_block[block];
	PointIndex::new(start_index + statement_index)
	}

	/// Converts a `Location` into a `PointIndex`. O(1).
	pub(crate) fn entry_point(&self, block: BasicBlock) -> PointIndex {
	let start_index = self.statements_before_block[block];
	PointIndex::new(start_index)
	}

	/// Return the PointIndex for the block start of this index.
	pub(crate) fn to_block_start(&self, index: PointIndex) -> PointIndex {
	PointIndex::new(self.statements_before_block[self.basic_blocks[index]])
	}

	/// Converts a `PointIndex` back to a location. O(1).
	pub(crate) fn to_location(&self, index: PointIndex) -> Location {
	assert!(index.index() < self.num_points);
	let block = self.basic_blocks[index];
	let start_index = self.statements_before_block[block];
	let statement_index = index.index() - start_index;
	Location { block, statement_index }
	}

	/// Sometimes we get point-indices back from bitsets that may be
	/// out of range (because they round up to the nearest 2^N number
	/// of bits). Use this function to filter such points out if you
	/// like.
	pub(crate) fn point_in_range(&self, index: PointIndex) -> bool {
	index.index() < self.num_points
	}
	}

	rustc_index::newtype_index! {
	/// A single integer representing a `Location` in the MIR control-flow
	/// graph. Constructed efficiently from `RegionValueElements`.
	#[debug_format = "PointIndex({})"]
	pub struct PointIndex {}
	}

	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),
	}

	/// When we initially compute liveness, we use an interval matrix storing
	/// liveness ranges for each region-vid.
	pub(crate) struct LivenessValues<N: Idx> {
	elements: Rc<RegionValueElements>,
	points: SparseIntervalMatrix<N, PointIndex>,
	}

	impl<N: Idx> LivenessValues<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<RegionValueElements>) -> Self {
	Self { points: SparseIntervalMatrix::new(elements.num_points), elements }
	}

	/// Iterate through each region that has a value in this set.
	pub(crate) fn rows(&self) -> impl Iterator<Item = N> {
	self.points.rows()
	}

	/// 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, row: N, location: Location) -> bool {
	debug!("LivenessValues::add(r={:?}, location={:?})", row, location);
	let index = self.elements.point_from_location(location);
	self.points.insert(row, index)
	}

	/// Adds all the elements in the given bit array into the given
	/// region. Returns whether any of them are newly added.
	pub(crate) fn add_elements(&mut self, row: N, locations: &IntervalSet<PointIndex>) -> bool {
	debug!("LivenessValues::add_elements(row={:?}, locations={:?})", row, locations);
	self.points.union_row(row, locations)
	}

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

	/// Returns `true` if the region `r` contains the given element.
	pub(crate) fn contains(&self, row: N, location: Location) -> bool {
	let index = self.elements.point_from_location(location);
	self.points.row(row).is_some_and(\|r\| r.contains(index))
	}

	/// Returns an iterator of all the elements contained by the region `r`
	pub(crate) fn get_elements(&self, row: N) -> impl Iterator<Item = Location> + '_ {
	self.points
	.row(row)
	.into_iter()
	.flat_map(\|set\| set.iter())
	.take_while(move \|&p\| self.elements.point_in_range(p))
	.map(move \|p\| self.elements.to_location(p))
	}

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

	/// 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<RegionValueElements>,
	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<RegionValueElements>,
	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<M: Idx>(&mut self, to: N, from: M, values: &LivenessValues<M>) {
	if let Some(set) = values.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 {
	region_value_str(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)
	}
	}

	pub(crate) fn location_set_str(
	elements: &RegionValueElements,
	points: impl IntoIterator<Item = PointIndex>,
	) -> String {
	region_value_str(
	points
	.into_iter()
	.take_while(\|&p\| elements.point_in_range(p))
	.map(\|p\| elements.to_location(p))
	.map(RegionElement::Location),
	)
	}

	fn region_value_str(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
	));
	}
	}
	}