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Vec::dedup optimization - finishing polishes

This commit is contained in:
Soveu 2021-03-15 20:36:29 +01:00
parent 2abab1f688
commit afdbc9ece1
1 changed files with 7 additions and 11 deletions
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18
library/alloc/src/vec/mod.rs
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@ -1538,13 +1538,9 @@ impl<T, A: Allocator> Vec<T, A> {
impl<'a, T, A: core::alloc::Allocator> Drop for FillGapOnDrop<'a, T, A> {
fn drop(&mut self) {
/* This code gets executed either at the end of `dedup_by` or
* when `same_bucket` panics */
/* This code gets executed when `same_bucket` panics */
/* SAFETY (if finishing successfully): self.read == len, so
* no data is copied and length is set correctly */
/* SAFETY (if panicing): invariant guarantees that `read - write`
/* SAFETY: invariant guarantees that `read - write`
* and `len - read` never overflow and that the copy is always
* in-bounds. */
unsafe {
@ -1553,7 +1549,7 @@ impl<T, A: Allocator> Vec<T, A> {
/* How many items were left when `same_bucket` paniced.
* Basically vec[read..].len() */
let items_left = len - self.read;
let items_left = len.wrapping_sub(self.read);
/* Pointer to first item in vec[write..write+items_left] slice */
let dropped_ptr = ptr.add(self.write);
@ -1566,7 +1562,7 @@ impl<T, A: Allocator> Vec<T, A> {
/* How many items have been already dropped
* Basically vec[read..write].len() */
let dropped = self.read - self.write;
let dropped = self.read.wrapping_sub(self.write);
self.vec.set_len(len - dropped);
}
@ -1574,7 +1570,6 @@ impl<T, A: Allocator> Vec<T, A> {
}
let mut gap = FillGapOnDrop { read: 1, write: 1, vec: self };
let ptr = gap.vec.as_mut_ptr();
/* Drop items while going through Vec, it should be more efficient than
@ -1593,8 +1588,9 @@ impl<T, A: Allocator> Vec<T, A> {
} else {
let write_ptr = ptr.add(gap.write);
/* Looks like doing just `copy` can be faster than
* conditional `copy_nonoverlapping` */
/* Because `read_ptr` can be equal to `write_ptr`, we either
* have to use `copy` or conditional `copy_nonoverlapping`.
* Looks like the first option is faster. */
ptr::copy(read_ptr, write_ptr, 1);
/* We have filled that place, so go further */