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bors-servo
88c32dfc0e
Add #[inline] attribute to all fns which return SmallVec When rustc fails to inline a `SmallVec` constructor, it can carry a significant performance cost: for example, if `SmallVec::<[i64; 128]>::from_iter(...)` fails to inline, it will perform an unnecessary 1kb memcpy. I've recently been bitten by this when using `SmallVec` in a context where rustc seemed to be reluctant to perform inlining (a large fn with nested closures). Switching from `SmallVec::from_iter` to `SmallVec::new` and `push`, with a buffer size of 256 bytes, saved over 20ns per call. For larger buffers, `from_iter` carried a proportionally higher cost, even when the actual capacity in use didn't change.
rust-smallvec
"Small vector" optimization for Rust: store up to a small number of items on the stack
Example
use smallvec::{SmallVec, smallvec};
// This SmallVec can hold up to 4 items on the stack:
let mut v: SmallVec<[i32; 4]> = smallvec![1, 2, 3, 4];
// It will automatically move its contents to the heap if
// contains more than four items:
v.push(5);
// SmallVec points to a slice, so you can use normal slice
// indexing and other methods to access its contents:
v[0] = v[1] + v[2];
v.sort();