1 //! Implements a map from integer indices to data.
2 //! Rather than storing data for every index, internally, this maps entire ranges to the data.
3 //! To this end, the APIs all work on ranges, not on individual integers. Ranges are split as
4 //! necessary (e.g., when [0,5) is first associated with X, and then [1,2) is mutated).
5 //! Users must not depend on whether a range is coalesced or not, even though this is observable
6 //! via the iteration APIs.
10 use rustc_middle::ty::layout::Size;
12 #[derive(Clone, Debug)]
14 /// The range covered by this element; never empty.
15 range: ops::Range<u64>,
16 /// The data stored for this element.
19 #[derive(Clone, Debug)]
20 pub struct RangeMap<T> {
25 /// Creates a new `RangeMap` for the given size, and with the given initial value used for
28 pub fn new(size: Size, init: T) -> RangeMap<T> {
29 let size = size.bytes();
30 let mut map = RangeMap { v: Vec::new() };
32 map.v.push(Elem { range: 0..size, data: init });
37 /// Finds the index containing the given offset.
38 fn find_offset(&self, offset: u64) -> usize {
39 // We do a binary search.
40 let mut left = 0usize; // inclusive
41 let mut right = self.v.len(); // exclusive
43 debug_assert!(left < right, "find_offset: offset {} is out-of-bounds", offset);
44 let candidate = left.checked_add(right).unwrap() / 2;
45 let elem = &self.v[candidate];
46 if offset < elem.range.start {
47 // We are too far right (offset is further left).
48 debug_assert!(candidate < right); // we are making progress
50 } else if offset >= elem.range.end {
51 // We are too far left (offset is further right).
52 debug_assert!(candidate >= left); // we are making progress
61 /// Provides read-only iteration over everything in the given range. This does
62 /// *not* split items if they overlap with the edges. Do not use this to mutate
63 /// through interior mutability.
64 pub fn iter<'a>(&'a self, offset: Size, len: Size) -> impl Iterator<Item = &'a T> + 'a {
65 let offset = offset.bytes();
66 let len = len.bytes();
67 // Compute a slice starting with the elements we care about.
68 let slice: &[Elem<T>] = if len == 0 {
69 // We just need any empty iterator. We don't even want to
70 // yield the element that surrounds this position.
73 let first_idx = self.find_offset(offset);
76 // The first offset that is not included any more.
77 let end = offset + len;
78 slice.iter().take_while(move |elem| elem.range.start < end).map(|elem| &elem.data)
81 pub fn iter_mut_all<'a>(&'a mut self) -> impl Iterator<Item = &'a mut T> + 'a {
82 self.v.iter_mut().map(|elem| &mut elem.data)
85 // Splits the element situated at the given `index`, such that the 2nd one starts at offset
86 // `split_offset`. Do nothing if the element already starts there.
87 // Returns whether a split was necessary.
88 fn split_index(&mut self, index: usize, split_offset: u64) -> bool
92 let elem = &mut self.v[index];
93 if split_offset == elem.range.start || split_offset == elem.range.end {
98 elem.range.contains(&split_offset),
99 "the `split_offset` is not in the element to be split"
102 // Now we really have to split. Reduce length of first element.
103 let second_range = split_offset..elem.range.end;
104 elem.range.end = split_offset;
105 // Copy the data, and insert second element.
106 let second = Elem { range: second_range, data: elem.data.clone() };
107 self.v.insert(index + 1, second);
111 /// Provides mutable iteration over everything in the given range. As a side-effect,
112 /// this will split entries in the map that are only partially hit by the given range,
113 /// to make sure that when they are mutated, the effect is constrained to the given range.
114 /// Moreover, this will opportunistically merge neighbouring equal blocks.
119 ) -> impl Iterator<Item = &'a mut T> + 'a
121 T: Clone + PartialEq,
123 let offset = offset.bytes();
124 let len = len.bytes();
125 // Compute a slice containing exactly the elements we care about
126 let slice: &mut [Elem<T>] = if len == 0 {
127 // We just need any empty iterator. We don't even want to
128 // yield the element that surrounds this position, nor do
132 // Make sure we got a clear beginning
133 let mut first_idx = self.find_offset(offset);
134 if self.split_index(first_idx, offset) {
135 // The newly created 2nd element is ours
139 let first_idx = first_idx;
140 // Find our end. Linear scan, but that's ok because the iteration
141 // is doing the same linear scan anyway -- no increase in complexity.
142 // We combine this scan with a scan for duplicates that we can merge, to reduce
143 // the number of elements.
144 // We stop searching after the first "block" of size 1, to avoid spending excessive
145 // amounts of time on the merging.
146 let mut equal_since_idx = first_idx;
147 // Once we see too many non-mergeable blocks, we stop.
148 // The initial value is chosen via... magic. Benchmarking and magic.
149 let mut successful_merge_count = 3usize;
150 // When the loop is done, this is the first excluded element.
151 let mut end_idx = first_idx;
153 // Compute if `end` is the last element we need to look at.
154 let done = self.v[end_idx].range.end >= offset + len;
155 // We definitely need to include `end`, so move the index.
158 done || end_idx < self.v.len(),
159 "iter_mut: end-offset {} is out-of-bounds",
162 // see if we want to merge everything in `equal_since..end` (exclusive at the end!)
163 if successful_merge_count > 0 {
164 if done || self.v[end_idx].data != self.v[equal_since_idx].data {
165 // Everything in `equal_since..end` was equal. Make them just one element covering
167 let removed_elems = end_idx - equal_since_idx - 1; // number of elements that we would remove
168 if removed_elems > 0 {
169 // Adjust the range of the first element to cover all of them.
170 let equal_until = self.v[end_idx - 1].range.end; // end of range of last of the equal elements
171 self.v[equal_since_idx].range.end = equal_until;
172 // Delete the rest of them.
173 self.v.splice(equal_since_idx + 1..end_idx, std::iter::empty());
174 // Adjust `end_idx` because we made the list shorter.
175 end_idx -= removed_elems;
176 // Adjust the count for the cutoff.
177 successful_merge_count += removed_elems;
179 // Adjust the count for the cutoff.
180 successful_merge_count -= 1;
182 // Go on scanning for the next block starting here.
183 equal_since_idx = end_idx;
186 // Leave loop if this is the last element.
191 // Move to last included instead of first excluded index.
192 let end_idx = end_idx - 1;
193 // We need to split the end as well. Even if this performs a
194 // split, we don't have to adjust our index as we only care about
195 // the first part of the split.
196 self.split_index(end_idx, offset + len);
197 // Now we yield the slice. `end` is inclusive.
198 &mut self.v[first_idx..=end_idx]
200 slice.iter_mut().map(|elem| &mut elem.data)
208 /// Query the map at every offset in the range and collect the results.
209 fn to_vec<T: Copy>(map: &RangeMap<T>, offset: u64, len: u64) -> Vec<T> {
210 (offset..offset + len)
212 .map(|i| map.iter(Size::from_bytes(i), Size::from_bytes(1)).next().map(|&t| t).unwrap())
218 let mut map = RangeMap::<i32>::new(Size::from_bytes(20), -1);
220 for x in map.iter_mut(Size::from_bytes(10), Size::from_bytes(1)) {
224 assert_eq!(to_vec(&map, 10, 1), vec![42]);
225 assert_eq!(map.v.len(), 3);
227 // Insert with size 0.
228 for x in map.iter_mut(Size::from_bytes(10), Size::from_bytes(0)) {
231 for x in map.iter_mut(Size::from_bytes(11), Size::from_bytes(0)) {
234 assert_eq!(to_vec(&map, 10, 2), vec![42, -1]);
235 assert_eq!(map.v.len(), 3);
240 let mut map = RangeMap::<i32>::new(Size::from_bytes(20), -1);
241 for x in map.iter_mut(Size::from_bytes(11), Size::from_bytes(1)) {
244 for x in map.iter_mut(Size::from_bytes(15), Size::from_bytes(1)) {
247 assert_eq!(map.v.len(), 5);
248 assert_eq!(to_vec(&map, 10, 10), vec![-1, 42, -1, -1, -1, 43, -1, -1, -1, -1]);
250 for x in map.iter_mut(Size::from_bytes(10), Size::from_bytes(10)) {
255 assert_eq!(map.v.len(), 6);
256 assert_eq!(to_vec(&map, 10, 10), vec![23, 42, 23, 23, 23, 43, 23, 23, 23, 23]);
257 assert_eq!(to_vec(&map, 13, 5), vec![23, 23, 43, 23, 23]);
259 for x in map.iter_mut(Size::from_bytes(15), Size::from_bytes(5)) {
262 assert_eq!(map.v.len(), 6);
263 assert_eq!(to_vec(&map, 10, 10), vec![23, 42, 23, 23, 23, 19, 19, 19, 19, 19]);
264 // Should be seeing two blocks with 19.
266 map.iter(Size::from_bytes(15), Size::from_bytes(2)).map(|&t| t).collect::<Vec<_>>(),
270 // A NOP `iter_mut` should trigger merging.
271 for _ in map.iter_mut(Size::from_bytes(15), Size::from_bytes(5)) {}
272 assert_eq!(map.v.len(), 5);
273 assert_eq!(to_vec(&map, 10, 10), vec![23, 42, 23, 23, 23, 19, 19, 19, 19, 19]);