1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
use crate::arena::{Arena, Handle, Range, UniqueArena};
type Index = std::num::NonZeroU32;
/// A set of `Handle<T>` values.
pub struct HandleSet<T> {
/// Bound on zero-based indexes of handles stored in this set.
len: usize,
/// `members[i]` is true if the handle with zero-based index `i`
/// is a member.
members: bit_set::BitSet,
/// This type is indexed by values of type `T`.
as_keys: std::marker::PhantomData<T>,
}
impl<T> HandleSet<T> {
pub fn for_arena(arena: &impl ArenaType<T>) -> Self {
let len = arena.len();
Self {
len,
members: bit_set::BitSet::with_capacity(len),
as_keys: std::marker::PhantomData,
}
}
/// Add `handle` to the set.
pub fn insert(&mut self, handle: Handle<T>) {
// Note that, oddly, `Handle::index` does not return a 1-based
// `Index`, but rather a zero-based `usize`.
self.members.insert(handle.index());
}
/// Add handles from `iter` to the set.
pub fn insert_iter(&mut self, iter: impl IntoIterator<Item = Handle<T>>) {
for handle in iter {
self.insert(handle);
}
}
pub fn contains(&self, handle: Handle<T>) -> bool {
// Note that, oddly, `Handle::index` does not return a 1-based
// `Index`, but rather a zero-based `usize`.
self.members.contains(handle.index())
}
}
pub trait ArenaType<T> {
fn len(&self) -> usize;
}
impl<T> ArenaType<T> for Arena<T> {
fn len(&self) -> usize {
self.len()
}
}
impl<T: std::hash::Hash + Eq> ArenaType<T> for UniqueArena<T> {
fn len(&self) -> usize {
self.len()
}
}
/// A map from old handle indices to new, compressed handle indices.
pub struct HandleMap<T> {
/// The indices assigned to handles in the compacted module.
///
/// If `new_index[i]` is `Some(n)`, then `n` is the 1-based
/// `Index` of the compacted `Handle` corresponding to the
/// pre-compacted `Handle` whose zero-based index is `i`. ("Clear
/// as mud.")
new_index: Vec<Option<Index>>,
/// This type is indexed by values of type `T`.
as_keys: std::marker::PhantomData<T>,
}
impl<T: 'static> HandleMap<T> {
pub fn from_set(set: HandleSet<T>) -> Self {
let mut next_index = Index::new(1).unwrap();
Self {
new_index: (0..set.len)
.map(|zero_based_index| {
if set.members.contains(zero_based_index) {
// This handle will be retained in the compacted version,
// so assign it a new index.
let this = next_index;
next_index = next_index.checked_add(1).unwrap();
Some(this)
} else {
// This handle will be omitted in the compacted version.
None
}
})
.collect(),
as_keys: std::marker::PhantomData,
}
}
/// Return true if `old` is used in the compacted module.
pub fn used(&self, old: Handle<T>) -> bool {
self.new_index[old.index()].is_some()
}
/// Return the counterpart to `old` in the compacted module.
///
/// If we thought `old` wouldn't be used in the compacted module, return
/// `None`.
pub fn try_adjust(&self, old: Handle<T>) -> Option<Handle<T>> {
log::trace!(
"adjusting {} handle [{}] -> [{:?}]",
std::any::type_name::<T>(),
old.index() + 1,
self.new_index[old.index()]
);
// Note that `Handle::index` returns a zero-based index,
// but `Handle::new` accepts a 1-based `Index`.
self.new_index[old.index()].map(Handle::new)
}
/// Return the counterpart to `old` in the compacted module.
///
/// If we thought `old` wouldn't be used in the compacted module, panic.
pub fn adjust(&self, handle: &mut Handle<T>) {
*handle = self.try_adjust(*handle).unwrap();
}
/// Like `adjust`, but for optional handles.
pub fn adjust_option(&self, handle: &mut Option<Handle<T>>) {
if let Some(ref mut handle) = *handle {
self.adjust(handle);
}
}
/// Shrink `range` to include only used handles.
///
/// Fortunately, compaction doesn't arbitrarily scramble the expressions
/// in the arena, but instead preserves the order of the elements while
/// squeezing out unused ones. That means that a contiguous range in the
/// pre-compacted arena always maps to a contiguous range in the
/// post-compacted arena. So we just need to adjust the endpoints.
///
/// Compaction may have eliminated the endpoints themselves.
///
/// Use `compacted_arena` to bounds-check the result.
pub fn adjust_range(&self, range: &mut Range<T>, compacted_arena: &Arena<T>) {
let mut index_range = range.zero_based_index_range();
let compacted;
// Remember that the indices we retrieve from `new_index` are 1-based
// compacted indices, but the index range we're computing is zero-based
// compacted indices.
if let Some(first1) = index_range.find_map(|i| self.new_index[i as usize]) {
// The first call to `find_map` mutated `index_range` to hold the
// remainder of original range, which is exactly the range we need
// to search for the new last handle.
if let Some(last1) = index_range.rev().find_map(|i| self.new_index[i as usize]) {
// Build a zero-based end-exclusive range, given one-based handle indices.
compacted = first1.get() - 1..last1.get();
} else {
// The range contains only a single live handle, which
// we identified with the first `find_map` call.
compacted = first1.get() - 1..first1.get();
}
} else {
compacted = 0..0;
};
*range = Range::from_zero_based_index_range(compacted, compacted_arena);
}
}