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Rollup merge of #74762 - ssomers:btree_no_root_in_remove_kv_tracking,…
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… r=Mark-Simulacrum

BTreeMap::drain_filter should not touch the root during iteration

Although Miri doesn't point it out, I believe there is undefined behaviour using `drain_filter` when draining the 11th-last element from a tree that was larger. When this happens, the last remaining child nodes are merged, the root becomes empty and is popped from the tree. That last step establishes a mutable reference to the node elected root and writes a pointer in `node::Root`, while iteration continues to visit the same node.

This is mostly code from #74437, slightly adapted.
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@JohnTitor
JohnTitor authored Aug 2, 2020
2 parents 8c331ee + 99398dd commit 814b31e
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302 changes: 302 additions & 0 deletions library/alloc/benches/btree/map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -282,3 +282,305 @@ pub fn iter_10k(b: &mut Bencher) {
pub fn iter_1m(b: &mut Bencher) {
bench_iter(b, 1_000, 1_000_000);
}

const FAT: usize = 256;

// The returned map has small keys and values.
// Benchmarks on it have a counterpart in set.rs with the same keys and no values at all.
fn slim_map(n: usize) -> BTreeMap<usize, usize> {
(0..n).map(|i| (i, i)).collect::<BTreeMap<_, _>>()
}

// The returned map has small keys and large values.
fn fat_val_map(n: usize) -> BTreeMap<usize, [usize; FAT]> {
(0..n).map(|i| (i, [i; FAT])).collect::<BTreeMap<_, _>>()
}

// The returned map has large keys and values.
fn fat_map(n: usize) -> BTreeMap<[usize; FAT], [usize; FAT]> {
(0..n).map(|i| ([i; FAT], [i; FAT])).collect::<BTreeMap<_, _>>()
}

#[bench]
pub fn clone_slim_100(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| src.clone())
}

#[bench]
pub fn clone_slim_100_and_clear(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| src.clone().clear())
}

#[bench]
pub fn clone_slim_100_and_drain_all(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| src.clone().drain_filter(|_, _| true).count())
}

#[bench]
pub fn clone_slim_100_and_drain_half(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| {
let mut map = src.clone();
assert_eq!(map.drain_filter(|i, _| i % 2 == 0).count(), 100 / 2);
assert_eq!(map.len(), 100 / 2);
})
}

#[bench]
pub fn clone_slim_100_and_into_iter(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| src.clone().into_iter().count())
}

#[bench]
pub fn clone_slim_100_and_pop_all(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| {
let mut map = src.clone();
while map.pop_first().is_some() {}
map
});
}

#[bench]
pub fn clone_slim_100_and_remove_all(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| {
let mut map = src.clone();
while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
let v = map.remove(&elt);
debug_assert!(v.is_some());
}
map
});
}

#[bench]
pub fn clone_slim_100_and_remove_half(b: &mut Bencher) {
let src = slim_map(100);
b.iter(|| {
let mut map = src.clone();
for i in (0..100).step_by(2) {
let v = map.remove(&i);
debug_assert!(v.is_some());
}
assert_eq!(map.len(), 100 / 2);
map
})
}

#[bench]
pub fn clone_slim_10k(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| src.clone())
}

#[bench]
pub fn clone_slim_10k_and_clear(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| src.clone().clear())
}

#[bench]
pub fn clone_slim_10k_and_drain_all(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| src.clone().drain_filter(|_, _| true).count())
}

#[bench]
pub fn clone_slim_10k_and_drain_half(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| {
let mut map = src.clone();
assert_eq!(map.drain_filter(|i, _| i % 2 == 0).count(), 10_000 / 2);
assert_eq!(map.len(), 10_000 / 2);
})
}

#[bench]
pub fn clone_slim_10k_and_into_iter(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| src.clone().into_iter().count())
}

#[bench]
pub fn clone_slim_10k_and_pop_all(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| {
let mut map = src.clone();
while map.pop_first().is_some() {}
map
});
}

#[bench]
pub fn clone_slim_10k_and_remove_all(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| {
let mut map = src.clone();
while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
let v = map.remove(&elt);
debug_assert!(v.is_some());
}
map
});
}

#[bench]
pub fn clone_slim_10k_and_remove_half(b: &mut Bencher) {
let src = slim_map(10_000);
b.iter(|| {
let mut map = src.clone();
for i in (0..10_000).step_by(2) {
let v = map.remove(&i);
debug_assert!(v.is_some());
}
assert_eq!(map.len(), 10_000 / 2);
map
})
}

#[bench]
pub fn clone_fat_val_100(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| src.clone())
}

#[bench]
pub fn clone_fat_val_100_and_clear(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| src.clone().clear())
}

#[bench]
pub fn clone_fat_val_100_and_drain_all(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| src.clone().drain_filter(|_, _| true).count())
}

#[bench]
pub fn clone_fat_val_100_and_drain_half(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| {
let mut map = src.clone();
assert_eq!(map.drain_filter(|i, _| i % 2 == 0).count(), 100 / 2);
assert_eq!(map.len(), 100 / 2);
})
}

#[bench]
pub fn clone_fat_val_100_and_into_iter(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| src.clone().into_iter().count())
}

#[bench]
pub fn clone_fat_val_100_and_pop_all(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| {
let mut map = src.clone();
while map.pop_first().is_some() {}
map
});
}

#[bench]
pub fn clone_fat_val_100_and_remove_all(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| {
let mut map = src.clone();
while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
let v = map.remove(&elt);
debug_assert!(v.is_some());
}
map
});
}

#[bench]
pub fn clone_fat_val_100_and_remove_half(b: &mut Bencher) {
let src = fat_val_map(100);
b.iter(|| {
let mut map = src.clone();
for i in (0..100).step_by(2) {
let v = map.remove(&i);
debug_assert!(v.is_some());
}
assert_eq!(map.len(), 100 / 2);
map
})
}

#[bench]
pub fn clone_fat_100(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| src.clone())
}

#[bench]
pub fn clone_fat_100_and_clear(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| src.clone().clear())
}

#[bench]
pub fn clone_fat_100_and_drain_all(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| src.clone().drain_filter(|_, _| true).count())
}

#[bench]
pub fn clone_fat_100_and_drain_half(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| {
let mut map = src.clone();
assert_eq!(map.drain_filter(|i, _| i[0] % 2 == 0).count(), 100 / 2);
assert_eq!(map.len(), 100 / 2);
})
}

#[bench]
pub fn clone_fat_100_and_into_iter(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| src.clone().into_iter().count())
}

#[bench]
pub fn clone_fat_100_and_pop_all(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| {
let mut map = src.clone();
while map.pop_first().is_some() {}
map
});
}

#[bench]
pub fn clone_fat_100_and_remove_all(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| {
let mut map = src.clone();
while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
let v = map.remove(&elt);
debug_assert!(v.is_some());
}
map
});
}

#[bench]
pub fn clone_fat_100_and_remove_half(b: &mut Bencher) {
let src = fat_map(100);
b.iter(|| {
let mut map = src.clone();
for i in (0..100).step_by(2) {
let v = map.remove(&[i; FAT]);
debug_assert!(v.is_some());
}
assert_eq!(map.len(), 100 / 2);
map
})
}
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