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Use Vec::extend in SmallVec::extend when applicable #52859

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Aug 1, 2018
Merged

Use Vec::extend in SmallVec::extend when applicable #52859

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9169934
Use Vec::extend in SmallVec::extend when applicable
ljedrz Jul 30, 2018
ca52648
Benchmarks for SmallVec
ljedrz Jul 31, 2018
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132 changes: 128 additions & 4 deletions src/librustc_data_structures/small_vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -169,10 +169,18 @@ impl<A: Array> FromIterator<A::Element> for SmallVec<A> {

impl<A: Array> Extend<A::Element> for SmallVec<A> {
fn extend<I: IntoIterator<Item=A::Element>>(&mut self, iter: I) {
let iter = iter.into_iter();
self.reserve(iter.size_hint().0);
for el in iter {
self.push(el);
if self.is_array() {
let iter = iter.into_iter();
self.reserve(iter.size_hint().0);

for el in iter {
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Arguably we should match on self here and either extend or push based on that, but maybe it's not worth it. Benchmarks would be good, but that's quite a bit of work.

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You mean instead of is_array? I wanted to do that, but I ran into issues with the borrow checker. I'm going to think about some possible benchmarks.

self.push(el);
}
} else {
match self.0 {
AccumulateVec::Heap(ref mut vec) => vec.extend(iter),
_ => unreachable!()
}
}
}
}
Expand Down Expand Up @@ -217,3 +225,119 @@ impl<A> Decodable for SmallVec<A>
})
}
}

#[cfg(test)]
mod tests {
extern crate test;
use self::test::Bencher;

use super::*;

#[bench]
fn fill_small_vec_1_10_with_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 1]> = SmallVec::with_capacity(10);

sv.extend(0..10);
})
}

#[bench]
fn fill_small_vec_1_10_wo_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 1]> = SmallVec::new();

sv.extend(0..10);
})
}

#[bench]
fn fill_small_vec_8_10_with_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 8]> = SmallVec::with_capacity(10);

sv.extend(0..10);
})
}

#[bench]
fn fill_small_vec_8_10_wo_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 8]> = SmallVec::new();

sv.extend(0..10);
})
}

#[bench]
fn fill_small_vec_32_10_with_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 32]> = SmallVec::with_capacity(10);

sv.extend(0..10);
})
}

#[bench]
fn fill_small_vec_32_10_wo_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 32]> = SmallVec::new();

sv.extend(0..10);
})
}

#[bench]
fn fill_small_vec_1_50_with_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 1]> = SmallVec::with_capacity(50);

sv.extend(0..50);
})
}

#[bench]
fn fill_small_vec_1_50_wo_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 1]> = SmallVec::new();

sv.extend(0..50);
})
}

#[bench]
fn fill_small_vec_8_50_with_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 8]> = SmallVec::with_capacity(50);

sv.extend(0..50);
})
}

#[bench]
fn fill_small_vec_8_50_wo_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 8]> = SmallVec::new();

sv.extend(0..50);
})
}

#[bench]
fn fill_small_vec_32_50_with_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 32]> = SmallVec::with_capacity(50);

sv.extend(0..50);
})
}

#[bench]
fn fill_small_vec_32_50_wo_cap(b: &mut Bencher) {
b.iter(|| {
let mut sv: SmallVec<[usize; 32]> = SmallVec::new();

sv.extend(0..50);
})
}
}