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//! Implements a map from allocation ranges to data. This is somewhat similar to RangeMap, but the
//! ranges and data are discrete and non-splittable -- they represent distinct "objects". An
//! allocation in the map will always have the same range until explicitly removed
use rustc_target::abi::Size;
use std::ops::{Index, IndexMut, Range};
use rustc_const_eval::interpret::AllocRange;
#[derive(Clone, Debug)]
struct Elem<T> {
/// The range covered by this element; never empty.
range: AllocRange,
/// The data stored for this element.
data: T,
}
/// Index of an allocation within the map
type Position = usize;
#[derive(Clone, Debug)]
pub struct RangeObjectMap<T> {
v: Vec<Elem<T>>,
}
#[derive(Clone, Debug, PartialEq)]
pub enum AccessType {
/// The access perfectly overlaps (same offset and range) with the existing allocation
PerfectlyOverlapping(Position),
/// The access does not touch any existing allocation
Empty(Position),
/// The access overlaps with one or more existing allocations
ImperfectlyOverlapping(Range<Position>),
}
impl<T> RangeObjectMap<T> {
pub fn new() -> Self {
Self { v: Vec::new() }
}
/// Finds the position of the allocation containing the given offset. If the offset is not
/// in an existing allocation, then returns Err containing the position
/// where such allocation should be inserted
fn find_offset(&self, offset: Size) -> Result<Position, Position> {
self.v.binary_search_by(|elem| -> std::cmp::Ordering {
if offset < elem.range.start {
// We are too far right (offset is further left).
// (`Greater` means that `elem` is greater than the desired target.)
std::cmp::Ordering::Greater
} else if offset >= elem.range.end() {
// We are too far left (offset is further right).
std::cmp::Ordering::Less
} else {
// This is it!
std::cmp::Ordering::Equal
}
})
}
/// Determines whether a given access on `range` overlaps with
/// an existing allocation
pub fn access_type(&self, range: AllocRange) -> AccessType {
match self.find_offset(range.start) {
Ok(pos) => {
// Start of the range belongs to an existing object, now let's check the overlapping situation
let elem = &self.v[pos];
// FIXME: derive Eq for AllocRange in rustc
if elem.range.start == range.start && elem.range.size == range.size {
// Happy case: perfectly overlapping access
AccessType::PerfectlyOverlapping(pos)
} else {
// FIXME: add a last() method to AllocRange that returns the last inclusive offset (end() is exclusive)
let end_pos = match self.find_offset(range.end() - Size::from_bytes(1)) {
// If the end lands in an existing object, add one to get the exclusive position
Ok(inclusive_pos) => inclusive_pos + 1,
Err(exclusive_pos) => exclusive_pos,
};
AccessType::ImperfectlyOverlapping(pos..end_pos)
}
}
Err(pos) => {
// Start of the range doesn't belong to an existing object
match self.find_offset(range.end() - Size::from_bytes(1)) {
// Neither does the end
Err(end_pos) =>
if pos == end_pos {
// There's nothing between the start and the end, so the range thing is empty
AccessType::Empty(pos)
} else {
// Otherwise we have entirely covered an existing object
AccessType::ImperfectlyOverlapping(pos..end_pos)
},
// Otherwise at least part of it overlaps with something else
Ok(end_pos) => AccessType::ImperfectlyOverlapping(pos..end_pos + 1),
}
}
}
}
/// Inserts an object and its occupied range at given position
// The Position can be calculated from AllocRange, but the only user of AllocationMap
// always calls access_type before calling insert/index/index_mut, and we don't
// want to repeat the binary search on each time, so we ask the caller to supply Position
pub fn insert_at_pos(&mut self, pos: Position, range: AllocRange, data: T) {
self.v.insert(pos, Elem { range, data });
// If we aren't the first element, then our start must be greater than the previous element's end
if pos > 0 {
assert!(self.v[pos - 1].range.end() <= range.start);
}
// If we aren't the last element, then our end must be smaller than next element's start
if pos < self.v.len() - 1 {
assert!(range.end() <= self.v[pos + 1].range.start);
}
}
pub fn remove_pos_range(&mut self, pos_range: Range<Position>) {
self.v.drain(pos_range);
}
pub fn remove_from_pos(&mut self, pos: Position) {
self.v.remove(pos);
}
pub fn iter(&self) -> impl Iterator<Item = &T> {
self.v.iter().map(|e| &e.data)
}
}
impl<T> Index<Position> for RangeObjectMap<T> {
type Output = T;
fn index(&self, pos: Position) -> &Self::Output {
&self.v[pos].data
}
}
impl<T> IndexMut<Position> for RangeObjectMap<T> {
fn index_mut(&mut self, pos: Position) -> &mut Self::Output {
&mut self.v[pos].data
}
}
#[cfg(test)]
mod tests {
use rustc_const_eval::interpret::alloc_range;
use super::*;
#[test]
fn empty_map() {
// FIXME: make Size::from_bytes const
let four = Size::from_bytes(4);
let map = RangeObjectMap::<()>::new();
// Correctly tells where we should insert the first element (at position 0)
assert_eq!(map.find_offset(Size::from_bytes(3)), Err(0));
// Correctly tells the access type along with the supposed position
assert_eq!(map.access_type(alloc_range(Size::ZERO, four)), AccessType::Empty(0));
}
#[test]
#[should_panic]
fn no_overlapping_inserts() {
let four = Size::from_bytes(4);
let mut map = RangeObjectMap::<&str>::new();
// |_|_|_|_|#|#|#|#|_|_|_|_|...
// 0 1 2 3 4 5 6 7 8 9 a b c d
map.insert_at_pos(0, alloc_range(four, four), "#");
// |_|_|_|_|#|#|#|#|_|_|_|_|...
// 0 ^ ^ ^ ^ 5 6 7 8 9 a b c d
map.insert_at_pos(0, alloc_range(Size::from_bytes(1), four), "@");
}
#[test]
fn boundaries() {
let four = Size::from_bytes(4);
let mut map = RangeObjectMap::<&str>::new();
// |#|#|#|#|_|_|...
// 0 1 2 3 4 5
map.insert_at_pos(0, alloc_range(Size::ZERO, four), "#");
// |#|#|#|#|_|_|...
// 0 1 2 3 ^ 5
assert_eq!(map.find_offset(four), Err(1));
// |#|#|#|#|_|_|_|_|_|...
// 0 1 2 3 ^ ^ ^ ^ 8
assert_eq!(map.access_type(alloc_range(four, four)), AccessType::Empty(1));
let eight = Size::from_bytes(8);
// |#|#|#|#|_|_|_|_|@|@|@|@|_|_|...
// 0 1 2 3 4 5 6 7 8 9 a b c d
map.insert_at_pos(1, alloc_range(eight, four), "@");
// |#|#|#|#|_|_|_|_|@|@|@|@|_|_|...
// 0 1 2 3 4 5 6 ^ 8 9 a b c d
assert_eq!(map.find_offset(Size::from_bytes(7)), Err(1));
// |#|#|#|#|_|_|_|_|@|@|@|@|_|_|...
// 0 1 2 3 ^ ^ ^ ^ 8 9 a b c d
assert_eq!(map.access_type(alloc_range(four, four)), AccessType::Empty(1));
}
#[test]
fn perfectly_overlapping() {
let four = Size::from_bytes(4);
let mut map = RangeObjectMap::<&str>::new();
// |#|#|#|#|_|_|...
// 0 1 2 3 4 5
map.insert_at_pos(0, alloc_range(Size::ZERO, four), "#");
// |#|#|#|#|_|_|...
// ^ ^ ^ ^ 4 5
assert_eq!(map.find_offset(Size::ZERO), Ok(0));
assert_eq!(
map.access_type(alloc_range(Size::ZERO, four)),
AccessType::PerfectlyOverlapping(0)
);
// |#|#|#|#|@|@|@|@|_|...
// 0 1 2 3 4 5 6 7 8
map.insert_at_pos(1, alloc_range(four, four), "@");
// |#|#|#|#|@|@|@|@|_|...
// 0 1 2 3 ^ ^ ^ ^ 8
assert_eq!(map.find_offset(four), Ok(1));
assert_eq!(map.access_type(alloc_range(four, four)), AccessType::PerfectlyOverlapping(1));
}
#[test]
fn straddling() {
let four = Size::from_bytes(4);
let mut map = RangeObjectMap::<&str>::new();
// |_|_|_|_|#|#|#|#|_|_|_|_|...
// 0 1 2 3 4 5 6 7 8 9 a b c d
map.insert_at_pos(0, alloc_range(four, four), "#");
// |_|_|_|_|#|#|#|#|_|_|_|_|...
// 0 1 ^ ^ ^ ^ 6 7 8 9 a b c d
assert_eq!(
map.access_type(alloc_range(Size::from_bytes(2), four)),
AccessType::ImperfectlyOverlapping(0..1)
);
// |_|_|_|_|#|#|#|#|_|_|_|_|...
// 0 1 2 3 4 5 ^ ^ ^ ^ a b c d
assert_eq!(
map.access_type(alloc_range(Size::from_bytes(6), four)),
AccessType::ImperfectlyOverlapping(0..1)
);
// |_|_|_|_|#|#|#|#|_|_|_|_|...
// 0 1 ^ ^ ^ ^ ^ ^ ^ ^ a b c d
assert_eq!(
map.access_type(alloc_range(Size::from_bytes(2), Size::from_bytes(8))),
AccessType::ImperfectlyOverlapping(0..1)
);
// |_|_|_|_|#|#|#|#|_|_|@|@|_|_|...
// 0 1 2 3 4 5 6 7 8 9 a b c d
map.insert_at_pos(1, alloc_range(Size::from_bytes(10), Size::from_bytes(2)), "@");
// |_|_|_|_|#|#|#|#|_|_|@|@|_|_|...
// 0 1 2 3 4 5 ^ ^ ^ ^ ^ ^ ^ ^
assert_eq!(
map.access_type(alloc_range(Size::from_bytes(6), Size::from_bytes(8))),
AccessType::ImperfectlyOverlapping(0..2)
);
}
}