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Optimize alloc_from_iter

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This commit is contained in:
John Kåre Alsaker 2019-04-24 01:45:50 +02:00
parent 28482db247
commit ba5d9c094d
1 changed files with 24 additions and 5 deletions
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29
src/libarena/lib.rs
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@ -486,9 +486,31 @@ impl DroplessArena {
}
}
#[inline]
unsafe fn write_from_iter<T, I: Iterator<Item = T>>(
&self,
mut iter: I,
len: usize,
mem: *mut T,
) -> &mut [T] {
let mut i = 0;
// Use a manual loop since LLVM manages to optimize it better for
// slice iterators
loop {
let value = iter.next();
if i >= len || value.is_none() {
// We only return as many items as the iterator gave us, even
// though it was supposed to give us `len`
return slice::from_raw_parts_mut(mem, i);
}
ptr::write(mem.offset(i as isize), value.unwrap());
i += 1;
}
}
#[inline]
pub fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
let mut iter = iter.into_iter();
let iter = iter.into_iter();
assert!(mem::size_of::<T>() != 0);
assert!(!mem::needs_drop::<T>());
@ -505,10 +527,7 @@ impl DroplessArena {
let size = len.checked_mul(mem::size_of::<T>()).unwrap();
let mem = self.alloc_raw(size, mem::align_of::<T>()) as *mut _ as *mut T;
unsafe {
for i in 0..len {
ptr::write(mem.offset(i as isize), iter.next().unwrap())
}
slice::from_raw_parts_mut(mem, len)
self.write_from_iter(iter, len, mem)
}
}
(_, _) => {