naga/arena/
mod.rs

1/*! The [`Arena`], [`UniqueArena`], and [`Handle`] types.
2
3To improve translator performance and reduce memory usage, most structures are
4stored in an [`Arena`]. An `Arena<T>` stores a series of `T` values, indexed by
5[`Handle<T>`] values, which are just wrappers around integer indexes.
6For example, a `Function`'s expressions are stored in an `Arena<Expression>`,
7and compound expressions refer to their sub-expressions via `Handle<Expression>`
8values.
9
10A [`UniqueArena`] is just like an `Arena`, except that it stores only a single
11instance of each value. The value type must implement `Eq` and `Hash`. Like an
12`Arena`, inserting a value into a `UniqueArena` returns a `Handle` which can be
13used to efficiently access the value, without a hash lookup. Inserting a value
14multiple times returns the same `Handle`.
15
16If the `span` feature is enabled, both `Arena` and `UniqueArena` can associate a
17source code span with each element.
18
19[`Handle<T>`]: Handle
20*/
21
22mod handle;
23mod handle_set;
24mod handlevec;
25mod range;
26mod unique_arena;
27
28pub use handle::{BadHandle, Handle};
29pub(crate) use handle_set::HandleSet;
30pub(crate) use handlevec::HandleVec;
31pub use range::{BadRangeError, Range};
32pub use unique_arena::UniqueArena;
33
34use alloc::vec::Vec;
35use core::{fmt, ops};
36
37use crate::Span;
38
39use handle::Index;
40
41/// An arena holding some kind of component (e.g., type, constant,
42/// instruction, etc.) that can be referenced.
43///
44/// Adding new items to the arena produces a strongly-typed [`Handle`].
45/// The arena can be indexed using the given handle to obtain
46/// a reference to the stored item.
47#[derive(Clone)]
48#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
49#[cfg_attr(feature = "serialize", serde(transparent))]
50#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
51#[cfg_attr(test, derive(PartialEq))]
52pub struct Arena<T> {
53    /// Values of this arena.
54    data: Vec<T>,
55    #[cfg_attr(feature = "serialize", serde(skip))]
56    span_info: Vec<Span>,
57}
58
59impl<T> Default for Arena<T> {
60    fn default() -> Self {
61        Self::new()
62    }
63}
64
65impl<T: fmt::Debug> fmt::Debug for Arena<T> {
66    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
67        f.debug_map().entries(self.iter()).finish()
68    }
69}
70
71impl<T> Arena<T> {
72    /// Create a new arena with no initial capacity allocated.
73    pub const fn new() -> Self {
74        Arena {
75            data: Vec::new(),
76            span_info: Vec::new(),
77        }
78    }
79
80    /// Extracts the inner vector.
81    #[allow(clippy::missing_const_for_fn)] // ignore due to requirement of #![feature(const_precise_live_drops)]
82    pub fn into_inner(self) -> Vec<T> {
83        self.data
84    }
85
86    /// Returns the current number of items stored in this arena.
87    pub fn len(&self) -> usize {
88        self.data.len()
89    }
90
91    /// Returns `true` if the arena contains no elements.
92    pub fn is_empty(&self) -> bool {
93        self.data.is_empty()
94    }
95
96    /// Returns an iterator over the items stored in this arena, returning both
97    /// the item's handle and a reference to it.
98    pub fn iter(&self) -> impl DoubleEndedIterator<Item = (Handle<T>, &T)> + ExactSizeIterator {
99        self.data
100            .iter()
101            .enumerate()
102            .map(|(i, v)| unsafe { (Handle::from_usize_unchecked(i), v) })
103    }
104
105    /// Returns an iterator over the items stored in this arena, returning both
106    /// the item's handle and a reference to it.
107    pub fn iter_mut_span(
108        &mut self,
109    ) -> impl DoubleEndedIterator<Item = (Handle<T>, &mut T, &Span)> + ExactSizeIterator {
110        self.data
111            .iter_mut()
112            .zip(self.span_info.iter())
113            .enumerate()
114            .map(|(i, (v, span))| unsafe { (Handle::from_usize_unchecked(i), v, span) })
115    }
116
117    /// Drains the arena, returning an iterator over the items stored.
118    pub fn drain(&mut self) -> impl DoubleEndedIterator<Item = (Handle<T>, T, Span)> {
119        let arena = core::mem::take(self);
120        arena
121            .data
122            .into_iter()
123            .zip(arena.span_info)
124            .enumerate()
125            .map(|(i, (v, span))| unsafe { (Handle::from_usize_unchecked(i), v, span) })
126    }
127
128    /// Returns a iterator over the items stored in this arena,
129    /// returning both the item's handle and a mutable reference to it.
130    pub fn iter_mut(&mut self) -> impl DoubleEndedIterator<Item = (Handle<T>, &mut T)> {
131        self.data
132            .iter_mut()
133            .enumerate()
134            .map(|(i, v)| unsafe { (Handle::from_usize_unchecked(i), v) })
135    }
136
137    /// Adds a new value to the arena, returning a typed handle.
138    pub fn append(&mut self, value: T, span: Span) -> Handle<T> {
139        let index = self.data.len();
140        self.data.push(value);
141        self.span_info.push(span);
142        Handle::from_usize(index)
143    }
144
145    /// Fetch a handle to an existing type.
146    pub fn fetch_if<F: Fn(&T) -> bool>(&self, fun: F) -> Option<Handle<T>> {
147        self.data
148            .iter()
149            .position(fun)
150            .map(|index| unsafe { Handle::from_usize_unchecked(index) })
151    }
152
153    /// Adds a value with a custom check for uniqueness:
154    /// returns a handle pointing to
155    /// an existing element if the check succeeds, or adds a new
156    /// element otherwise.
157    pub fn fetch_if_or_append<F: Fn(&T, &T) -> bool>(
158        &mut self,
159        value: T,
160        span: Span,
161        fun: F,
162    ) -> Handle<T> {
163        if let Some(index) = self.data.iter().position(|d| fun(d, &value)) {
164            unsafe { Handle::from_usize_unchecked(index) }
165        } else {
166            self.append(value, span)
167        }
168    }
169
170    /// Adds a value with a check for uniqueness, where the check is plain comparison.
171    pub fn fetch_or_append(&mut self, value: T, span: Span) -> Handle<T>
172    where
173        T: PartialEq,
174    {
175        self.fetch_if_or_append(value, span, T::eq)
176    }
177
178    pub fn try_get(&self, handle: Handle<T>) -> Result<&T, BadHandle> {
179        self.data
180            .get(handle.index())
181            .ok_or_else(|| BadHandle::new(handle))
182    }
183
184    /// Get a mutable reference to an element in the arena.
185    pub fn get_mut(&mut self, handle: Handle<T>) -> &mut T {
186        self.data.get_mut(handle.index()).unwrap()
187    }
188
189    /// Get the range of handles from a particular number of elements to the end.
190    pub fn range_from(&self, old_length: usize) -> Range<T> {
191        let range = old_length as u32..self.data.len() as u32;
192        Range::from_index_range(range, self)
193    }
194
195    /// Clears the arena keeping all allocations
196    pub fn clear(&mut self) {
197        self.data.clear()
198    }
199
200    pub fn get_span(&self, handle: Handle<T>) -> Span {
201        *self
202            .span_info
203            .get(handle.index())
204            .unwrap_or(&Span::default())
205    }
206
207    /// Assert that `handle` is valid for this arena.
208    pub fn check_contains_handle(&self, handle: Handle<T>) -> Result<(), BadHandle> {
209        if handle.index() < self.data.len() {
210            Ok(())
211        } else {
212            Err(BadHandle::new(handle))
213        }
214    }
215
216    /// Assert that `range` is valid for this arena.
217    pub fn check_contains_range(&self, range: &Range<T>) -> Result<(), BadRangeError> {
218        // Since `range.inner` is a `Range<u32>`, we only need to check that the
219        // start precedes the end, and that the end is in range.
220        if range.inner.start > range.inner.end {
221            return Err(BadRangeError::new(range.clone()));
222        }
223
224        // Empty ranges are tolerated: they can be produced by compaction.
225        if range.inner.start == range.inner.end {
226            return Ok(());
227        }
228
229        let last_handle = Handle::new(Index::new(range.inner.end - 1).unwrap());
230        if self.check_contains_handle(last_handle).is_err() {
231            return Err(BadRangeError::new(range.clone()));
232        }
233
234        Ok(())
235    }
236
237    #[cfg(feature = "compact")]
238    pub(crate) fn retain_mut<P>(&mut self, mut predicate: P)
239    where
240        P: FnMut(Handle<T>, &mut T) -> bool,
241    {
242        let mut index = 0;
243        let mut retained = 0;
244        self.data.retain_mut(|elt| {
245            let handle = Handle::from_usize(index);
246            let keep = predicate(handle, elt);
247
248            // Since `predicate` needs mutable access to each element,
249            // we can't feasibly call it twice, so we have to compact
250            // spans by hand in parallel as part of this iteration.
251            if keep {
252                self.span_info[retained] = self.span_info[index];
253                retained += 1;
254            }
255
256            index += 1;
257            keep
258        });
259
260        self.span_info.truncate(retained);
261    }
262}
263
264#[cfg(feature = "deserialize")]
265impl<'de, T> serde::Deserialize<'de> for Arena<T>
266where
267    T: serde::Deserialize<'de>,
268{
269    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
270    where
271        D: serde::Deserializer<'de>,
272    {
273        let data = Vec::deserialize(deserializer)?;
274        let span_info = core::iter::repeat_n(Span::default(), data.len()).collect();
275
276        Ok(Self { data, span_info })
277    }
278}
279
280impl<T> ops::Index<Handle<T>> for Arena<T> {
281    type Output = T;
282    fn index(&self, handle: Handle<T>) -> &T {
283        &self.data[handle.index()]
284    }
285}
286
287impl<T> ops::IndexMut<Handle<T>> for Arena<T> {
288    fn index_mut(&mut self, handle: Handle<T>) -> &mut T {
289        &mut self.data[handle.index()]
290    }
291}
292
293impl<T> ops::Index<Range<T>> for Arena<T> {
294    type Output = [T];
295    fn index(&self, range: Range<T>) -> &[T] {
296        &self.data[range.inner.start as usize..range.inner.end as usize]
297    }
298}
299
300#[cfg(test)]
301mod tests {
302    use super::*;
303
304    #[test]
305    fn append_non_unique() {
306        let mut arena: Arena<u8> = Arena::new();
307        let t1 = arena.append(0, Default::default());
308        let t2 = arena.append(0, Default::default());
309        assert!(t1 != t2);
310        assert!(arena[t1] == arena[t2]);
311    }
312
313    #[test]
314    fn append_unique() {
315        let mut arena: Arena<u8> = Arena::new();
316        let t1 = arena.append(0, Default::default());
317        let t2 = arena.append(1, Default::default());
318        assert!(t1 != t2);
319        assert!(arena[t1] != arena[t2]);
320    }
321
322    #[test]
323    fn fetch_or_append_non_unique() {
324        let mut arena: Arena<u8> = Arena::new();
325        let t1 = arena.fetch_or_append(0, Default::default());
326        let t2 = arena.fetch_or_append(0, Default::default());
327        assert!(t1 == t2);
328        assert!(arena[t1] == arena[t2])
329    }
330
331    #[test]
332    fn fetch_or_append_unique() {
333        let mut arena: Arena<u8> = Arena::new();
334        let t1 = arena.fetch_or_append(0, Default::default());
335        let t2 = arena.fetch_or_append(1, Default::default());
336        assert!(t1 != t2);
337        assert!(arena[t1] != arena[t2]);
338    }
339}
naga/arena/mod.rs

naga/arena/
mod.rs
