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outline large copies

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This commit is contained in:
Lukas Markeffsky 2023-11-23 23:31:19 +01:00
parent 1e3849aed0
commit b6702939f7
1 changed files with 20 additions and 7 deletions
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27
library/alloc/src/collections/vec_deque/drain.rs
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@ -121,7 +121,27 @@ fn drop(&mut self) {
let head_len = source_deque.len();
let tail_len = new_len - head_len;
// When draining at the front (`.drain(..n)`) or at the back (`.drain(n..)`),
// we don't need to copy any data.
// Outlining this function helps LLVM to eliminate the copies in these cases.
if head_len != 0 && tail_len != 0 {
copy_data(source_deque, drain_len, head_len, tail_len);
}
if new_len == 0 {
source_deque.head = 0;
} else if head_len < tail_len {
source_deque.head = source_deque.to_physical_idx(drain_len);
}
source_deque.len = new_len;
#[cold]
fn copy_data<T, A: Allocator>(
source_deque: &mut VecDeque<T, A>,
drain_len: usize,
head_len: usize,
tail_len: usize,
) {
let (src, dst, len);
if head_len < tail_len {
src = source_deque.head;
@ -137,13 +157,6 @@ fn drop(&mut self) {
source_deque.wrap_copy(src, dst, len);
}
}
if new_len == 0 {
source_deque.head = 0;
} else if head_len < tail_len {
source_deque.head = source_deque.to_physical_idx(drain_len);
}
source_deque.len = new_len;
}
}