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Speed up SparseBitMatrix.
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Using a `BTreeMap` to represent rows in the bit matrix is really slow.
This patch changes things so that each row is represented by a
`BitVector`. This is a less sparse representation, but a much faster
one.

As a result, `SparseBitSet` and `SparseChunk` can be removed.

Other minor changes in this patch.

- It renames `BitVector::insert()` as `merge()`, which matches the
  terminology in the other classes in bitvec.rs.

- It removes `SparseBitMatrix::is_subset()`, which is unused.

- It reinstates `RegionValueElements::num_elements()`, which #52190 had
  removed.

- It removes a low-value `debug!` call in `SparseBitMatrix::add()`.
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@nnethercote
nnethercote committed Jul 20, 2018
1 parent 4f3c7a4 commit 798209e
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Showing 2 changed files with 37 additions and 212 deletions.
236 changes: 28 additions & 208 deletions src/librustc_data_structures/bitvec.rs
View file
Expand Up @@ -9,8 +9,6 @@
// except according to those terms.

use indexed_vec::{Idx, IndexVec};
use std::collections::btree_map::Entry;
use std::collections::BTreeMap;
use std::iter::FromIterator;
use std::marker::PhantomData;

Expand Down Expand Up @@ -72,7 +70,7 @@ impl BitVector {
}

#[inline]
pub fn insert_all(&mut self, all: &BitVector) -> bool {
pub fn merge(&mut self, all: &BitVector) -> bool {
assert!(self.data.len() == all.data.len());
let mut changed = false;
for (i, j) in self.data.iter_mut().zip(&all.data) {
Expand Down Expand Up @@ -271,20 +269,26 @@ impl BitMatrix {
}
}

/// A moderately sparse bit matrix: rows are appended lazily, but columns
/// within appended rows are instantiated fully upon creation.
#[derive(Clone, Debug)]
pub struct SparseBitMatrix<R, C>
where
R: Idx,
C: Idx,
{
vector: IndexVec<R, SparseBitSet<C>>,
columns: usize,
vector: IndexVec<R, BitVector>,
marker: PhantomData<C>,
}

impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
/// Create a new empty sparse bit matrix with no rows or columns.
pub fn new() -> Self {
pub fn new(columns: usize) -> Self {
Self {
columns,
vector: IndexVec::new(),
marker: PhantomData,
}
}

Expand All @@ -293,23 +297,18 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
///
/// Returns true if this changed the matrix, and false otherwise.
pub fn add(&mut self, row: R, column: C) -> bool {
debug!(
"add(row={:?}, column={:?}, current_len={})",
row,
column,
self.vector.len()
);
let columns = self.columns;
self.vector
.ensure_contains_elem(row, || SparseBitSet::new());
self.vector[row].insert(column)
.ensure_contains_elem(row, || BitVector::new(columns));
self.vector[row].insert(column.index())
}

/// Do the bits from `row` contain `column`? Put another way, is
/// the matrix cell at `(row, column)` true? Put yet another way,
/// if the matrix represents (transitive) reachability, can
/// `row` reach `column`?
pub fn contains(&self, row: R, column: C) -> bool {
self.vector.get(row).map_or(false, |r| r.contains(column))
self.vector.get(row).map_or(false, |r| r.contains(column.index()))
}

/// Add the bits from row `read` to the bits from row `write`,
Expand All @@ -320,39 +319,23 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
/// `write` can reach everything that `read` can (and
/// potentially more).
pub fn merge(&mut self, read: R, write: R) -> bool {
let mut changed = false;

if read != write {
if self.vector.get(read).is_some() {
self.vector
.ensure_contains_elem(write, || SparseBitSet::new());
let (bit_set_read, bit_set_write) = self.vector.pick2_mut(read, write);

for read_chunk in bit_set_read.chunks() {
changed = changed | bit_set_write.insert_chunk(read_chunk).any();
}
}
if read == write || self.vector.get(read).is_none() {
return false;
}

changed
let columns = self.columns;
self.vector
.ensure_contains_elem(write, || BitVector::new(columns));
let (bitvec_read, bitvec_write) = self.vector.pick2_mut(read, write);
bitvec_write.merge(bitvec_read)
}

/// Merge a row, `from`, into the `into` row.
pub fn merge_into(&mut self, into: R, from: &SparseBitSet<C>) -> bool {
pub fn merge_into(&mut self, into: R, from: &BitVector) -> bool {
let columns = self.columns;
self.vector
.ensure_contains_elem(into, || SparseBitSet::new());
self.vector[into].insert_from(from)
}

/// True if `sub` is a subset of `sup`
pub fn is_subset(&self, sub: R, sup: R) -> bool {
sub == sup || {
let bit_set_sub = &self.vector[sub];
let bit_set_sup = &self.vector[sup];
bit_set_sub
.chunks()
.all(|read_chunk| read_chunk.bits_eq(bit_set_sup.contains_chunk(read_chunk)))
}
.ensure_contains_elem(into, || BitVector::new(columns));
self.vector[into].merge(from)
}

/// Number of elements in the matrix.
Expand All @@ -363,178 +346,15 @@ impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
/// Iterates through all the columns set to true in a given row of
/// the matrix.
pub fn iter<'a>(&'a self, row: R) -> impl Iterator<Item = C> + 'a {
self.vector.get(row).into_iter().flat_map(|r| r.iter())
self.vector.get(row).into_iter().flat_map(|r| r.iter().map(|n| C::new(n)))
}

/// Iterates through each row and the accompanying bit set.
pub fn iter_enumerated<'a>(&'a self) -> impl Iterator<Item = (R, &'a SparseBitSet<C>)> + 'a {
pub fn iter_enumerated<'a>(&'a self) -> impl Iterator<Item = (R, &'a BitVector)> + 'a {
self.vector.iter_enumerated()
}
}

#[derive(Clone, Debug)]
pub struct SparseBitSet<I: Idx> {
chunk_bits: BTreeMap<u32, Word>,
_marker: PhantomData<I>,
}

#[derive(Copy, Clone)]
pub struct SparseChunk<I> {
key: u32,
bits: Word,
_marker: PhantomData<I>,
}

impl<I: Idx> SparseChunk<I> {
#[inline]
pub fn one(index: I) -> Self {
let index = index.index();
let key_usize = index / 128;
let key = key_usize as u32;
assert_eq!(key as usize, key_usize);
SparseChunk {
key,
bits: 1 << (index % 128),
_marker: PhantomData,
}
}

#[inline]
pub fn any(&self) -> bool {
self.bits != 0
}

#[inline]
pub fn bits_eq(&self, other: SparseChunk<I>) -> bool {
self.bits == other.bits
}

pub fn iter(&self) -> impl Iterator<Item = I> {
let base = self.key as usize * 128;
let mut bits = self.bits;
(0..128)
.map(move |i| {
let current_bits = bits;
bits >>= 1;
(i, current_bits)
})
.take_while(|&(_, bits)| bits != 0)
.filter_map(move |(i, bits)| {
if (bits & 1) != 0 {
Some(I::new(base + i))
} else {
None
}
})
}
}

impl<I: Idx> SparseBitSet<I> {
pub fn new() -> Self {
SparseBitSet {
chunk_bits: BTreeMap::new(),
_marker: PhantomData,
}
}

pub fn capacity(&self) -> usize {
self.chunk_bits.len() * 128
}

/// Returns a chunk containing only those bits that are already
/// present. You can test therefore if `self` contains all the
/// bits in chunk already by doing `chunk ==
/// self.contains_chunk(chunk)`.
pub fn contains_chunk(&self, chunk: SparseChunk<I>) -> SparseChunk<I> {
SparseChunk {
bits: self.chunk_bits
.get(&chunk.key)
.map_or(0, |bits| bits & chunk.bits),
..chunk
}
}

/// Modifies `self` to contain all the bits from `chunk` (in
/// addition to any pre-existing bits); returns a new chunk that
/// contains only those bits that were newly added. You can test
/// if anything was inserted by invoking `any()` on the returned
/// value.
pub fn insert_chunk(&mut self, chunk: SparseChunk<I>) -> SparseChunk<I> {
if chunk.bits == 0 {
return chunk;
}
let bits = self.chunk_bits.entry(chunk.key).or_insert(0);
let old_bits = *bits;
let new_bits = old_bits | chunk.bits;
*bits = new_bits;
let changed = new_bits ^ old_bits;
SparseChunk {
bits: changed,
..chunk
}
}

/// Insert into bit set from another bit set.
pub fn insert_from(&mut self, from: &SparseBitSet<I>) -> bool {
let mut changed = false;
for read_chunk in from.chunks() {
changed = changed | self.insert_chunk(read_chunk).any();
}
changed
}

pub fn remove_chunk(&mut self, chunk: SparseChunk<I>) -> SparseChunk<I> {
if chunk.bits == 0 {
return chunk;
}
let changed = match self.chunk_bits.entry(chunk.key) {
Entry::Occupied(mut bits) => {
let old_bits = *bits.get();
let new_bits = old_bits & !chunk.bits;
if new_bits == 0 {
bits.remove();
} else {
bits.insert(new_bits);
}
new_bits ^ old_bits
}
Entry::Vacant(_) => 0,
};
SparseChunk {
bits: changed,
..chunk
}
}

pub fn clear(&mut self) {
self.chunk_bits.clear();
}

pub fn chunks<'a>(&'a self) -> impl Iterator<Item = SparseChunk<I>> + 'a {
self.chunk_bits.iter().map(|(&key, &bits)| SparseChunk {
key,
bits,
_marker: PhantomData,
})
}

pub fn contains(&self, index: I) -> bool {
self.contains_chunk(SparseChunk::one(index)).any()
}

pub fn insert(&mut self, index: I) -> bool {
self.insert_chunk(SparseChunk::one(index)).any()
}

pub fn remove(&mut self, index: I) -> bool {
self.remove_chunk(SparseChunk::one(index)).any()
}

pub fn iter<'a>(&'a self) -> impl Iterator<Item = I> + 'a {
self.chunks().flat_map(|chunk| chunk.iter())
}
}

#[inline]
fn words(elements: usize) -> usize {
(elements + WORD_BITS - 1) / WORD_BITS
Expand Down Expand Up @@ -584,8 +404,8 @@ fn union_two_vecs() {
assert!(!vec1.insert(3));
assert!(vec2.insert(5));
assert!(vec2.insert(64));
assert!(vec1.insert_all(&vec2));
assert!(!vec1.insert_all(&vec2));
assert!(vec1.merge(&vec2));
assert!(!vec1.merge(&vec2));
assert!(vec1.contains(3));
assert!(!vec1.contains(4));
assert!(vec1.contains(5));
Expand Down
13 changes: 9 additions & 4 deletions src/librustc_mir/borrow_check/nll/region_infer/values.rs
View file
Expand Up @@ -10,7 +10,7 @@

use rustc::mir::{BasicBlock, Location, Mir};
use rustc::ty::RegionVid;
use rustc_data_structures::bitvec::{SparseBitMatrix, SparseBitSet};
use rustc_data_structures::bitvec::{BitVector, SparseBitMatrix};
use rustc_data_structures::indexed_vec::Idx;
use rustc_data_structures::indexed_vec::IndexVec;
use std::fmt::Debug;
Expand Down Expand Up @@ -55,6 +55,11 @@ impl RegionValueElements {
}
}

/// Total number of element indices that exist.
crate fn num_elements(&self) -> usize {
self.num_points + self.num_universal_regions
}

/// Converts an element of a region value into a `RegionElementIndex`.
crate fn index<T: ToElementIndex>(&self, elem: T) -> RegionElementIndex {
elem.to_element_index(self)
Expand Down Expand Up @@ -186,7 +191,7 @@ impl<N: Idx> RegionValues<N> {
crate fn new(elements: &Rc<RegionValueElements>) -> Self {
Self {
elements: elements.clone(),
matrix: SparseBitMatrix::new(),
matrix: SparseBitMatrix::new(elements.num_elements()),
}
}

Expand Down Expand Up @@ -217,12 +222,12 @@ impl<N: Idx> RegionValues<N> {
/// Iterates through each row and the accompanying bit set.
pub fn iter_enumerated<'a>(
&'a self
) -> impl Iterator<Item = (N, &'a SparseBitSet<RegionElementIndex>)> + 'a {
) -> impl Iterator<Item = (N, &'a BitVector)> + 'a {
self.matrix.iter_enumerated()
}

/// Merge a row, `from`, originating in another `RegionValues` into the `into` row.
pub fn merge_into(&mut self, into: N, from: &SparseBitSet<RegionElementIndex>) -> bool {
pub fn merge_into(&mut self, into: N, from: &BitVector) -> bool {
self.matrix.merge_into(into, from)
}

Expand Down

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