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specialize Iterator::fold for vec::IntoIter

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LLVM currently adds a redundant check for the returned option, in addition
to the `self.ptr != self.end` check when using the default
`Iterator::fold` method that calls `vec::IntoIter::next` in a loop.
This commit is contained in:
Joshua Wong 2024-05-12 19:56:03 -05:00
parent 6165dca6db
commit 9d6b93c3e6
1 changed files with 27 additions and 2 deletions
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29
library/alloc/src/vec/into_iter.rs
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@ -289,13 +289,38 @@ fn count(self) -> usize {
};
}
fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
fn fold<B, F>(mut self, mut accum: B, mut f: F) -> B
where
F: FnMut(B, Self::Item) -> B,
{
if T::IS_ZST {
while self.ptr.as_ptr() != self.end.cast_mut() {
// SAFETY: we just checked that `self.ptr` is in bounds.
let tmp = unsafe { self.ptr.read() };
// See `next` for why we subtract from `end` here.
self.end = self.end.wrapping_byte_sub(1);
accum = f(accum, tmp);
}
} else {
// SAFETY: `self.end` can only be null if `T` is a ZST.
while self.ptr != non_null!(self.end, T) {
// SAFETY: we just checked that `self.ptr` is in bounds.
let tmp = unsafe { self.ptr.read() };
// SAFETY: the maximum this can be is `self.end`.
// Increment `self.ptr` first to avoid double dropping in the event of a panic.
self.ptr = unsafe { self.ptr.add(1) };
accum = f(accum, tmp);
}
}
accum
}
fn try_fold<B, F, R>(&mut self, mut accum: B, mut f: F) -> R
where
Self: Sized,
F: FnMut(B, Self::Item) -> R,
R: core::ops::Try<Output = B>,
{
let mut accum = init;
if T::IS_ZST {
while self.ptr.as_ptr() != self.end.cast_mut() {
// SAFETY: we just checked that `self.ptr` is in bounds.