rust-lang/rust — pull request #15465 by SimonSapin (2014-07-06 00:12:49+00:00)
Title: Optimize String::push_byte()

`Vec::push_all` with a length 1 slice seems to have significant overhead compared to `Vec::push`.

```
test new_push_byte ... bench: 6985 ns/iter (+/- 487) = 17 MB/s
test old_push_byte ... bench: 19335 ns/iter (+/- 1368) = 6 MB/s
```

```rust
extern crate test;
use test::Bencher;

static TEXT: &'static str = "\
Unicode est un standard informatique qui permet des échanges \
de textes dans différentes langues, à un niveau mondial.";

#[bench]
fn old_push_byte(bencher: &mut Bencher) {
bencher.bytes = TEXT.len() as u64;
bencher.iter(|| {
let mut new = String::new();
for b in TEXT.bytes() {
unsafe { new.as_mut_vec().push_all([b]) }
}
})
}

#[bench]
fn new_push_byte(bencher: &mut Bencher) {
bencher.bytes = TEXT.len() as u64;
bencher.iter(|| {
let mut new = String::new();
for b in TEXT.bytes() {
unsafe { new.as_mut_vec().push(b) }
}
})
}
```