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Auto merge of rust-lang#123835 - saethlin:vec-from-nonnull, r=<try>
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Avoid more NonNull-raw-NonNull roundtrips in Vec

r? the8472

The standard library in general has a lot of these round-trips from niched types to their raw innards and back. Such round-trips have overhead in debug builds since rust-lang#120594. I removed some such round-trips in that initial PR and I've been meaning to come back and hunt down more such examples (this is the last item on rust-lang#120848).
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bors committed Apr 12, 2024
2 parents a07f3eb + e4c567e commit 7d882e6
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Showing 6 changed files with 37 additions and 15 deletions.
5 changes: 5 additions & 0 deletions library/alloc/src/raw_vec.rs
Original file line number Diff line number Diff line change
Expand Up @@ -259,6 +259,11 @@ impl<T, A: Allocator> RawVec<T, A> {
Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap, alloc }
}

pub(crate) unsafe fn from_nonnull_in(ptr: NonNull<T>, capacity: usize, alloc: A) -> Self {
let cap = if T::IS_ZST { Cap::ZERO } else { unsafe { Cap(capacity) } };
Self { ptr: Unique::from(ptr), cap, alloc }
}

/// Gets a raw pointer to the start of the allocation. Note that this is
/// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
/// be careful.
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21 changes: 11 additions & 10 deletions library/alloc/src/vec/in_place_collect.rs
Original file line number Diff line number Diff line change
Expand Up @@ -161,7 +161,7 @@ use core::iter::{InPlaceIterable, SourceIter, TrustedRandomAccessNoCoerce};
use core::marker::PhantomData;
use core::mem::{self, ManuallyDrop, SizedTypeProperties};
use core::num::NonZero;
use core::ptr::{self, NonNull};
use core::ptr;

use super::{InPlaceDrop, InPlaceDstDataSrcBufDrop, SpecFromIter, SpecFromIterNested, Vec};

Expand Down Expand Up @@ -254,28 +254,30 @@ where
let (src_buf, src_ptr, src_cap, mut dst_buf, dst_end, dst_cap) = unsafe {
let inner = iterator.as_inner().as_into_iter();
(
inner.buf.as_ptr(),
inner.buf,
inner.ptr,
inner.cap,
inner.buf.as_ptr() as *mut T,
inner.buf.cast::<T>(),
inner.end as *const T,
inner.cap * mem::size_of::<I::Src>() / mem::size_of::<T>(),
)
};

// SAFETY: `dst_buf` and `dst_end` are the start and end of the buffer.
let len = unsafe { SpecInPlaceCollect::collect_in_place(&mut iterator, dst_buf, dst_end) };
let len = unsafe {
SpecInPlaceCollect::collect_in_place(&mut iterator, dst_buf.as_ptr() as *mut T, dst_end)
};

let src = unsafe { iterator.as_inner().as_into_iter() };
// check if SourceIter contract was upheld
// caveat: if they weren't we might not even make it to this point
debug_assert_eq!(src_buf, src.buf.as_ptr());
debug_assert_eq!(src_buf, src.buf);
// check InPlaceIterable contract. This is only possible if the iterator advanced the
// source pointer at all. If it uses unchecked access via TrustedRandomAccess
// then the source pointer will stay in its initial position and we can't use it as reference
if src.ptr != src_ptr {
debug_assert!(
unsafe { dst_buf.add(len) as *const _ } <= src.ptr.as_ptr(),
unsafe { dst_buf.add(len).cast() } <= src.ptr,
"InPlaceIterable contract violation, write pointer advanced beyond read pointer"
);
}
Expand Down Expand Up @@ -315,18 +317,17 @@ where
let dst_size = mem::size_of::<T>().unchecked_mul(dst_cap);
let new_layout = Layout::from_size_align_unchecked(dst_size, dst_align);

let result =
alloc.shrink(NonNull::new_unchecked(dst_buf as *mut u8), old_layout, new_layout);
let result = alloc.shrink(dst_buf.cast(), old_layout, new_layout);
let Ok(reallocated) = result else { handle_alloc_error(new_layout) };
dst_buf = reallocated.as_ptr() as *mut T;
dst_buf = reallocated.cast();
}
} else {
debug_assert_eq!(src_cap * mem::size_of::<I::Src>(), dst_cap * mem::size_of::<T>());
}

mem::forget(dst_guard);

let vec = unsafe { Vec::from_raw_parts(dst_buf, len, dst_cap) };
let vec = unsafe { Vec::from_nonnull(dst_buf, len, dst_cap) };

vec
}
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7 changes: 4 additions & 3 deletions library/alloc/src/vec/in_place_drop.rs
Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
use core::marker::PhantomData;
use core::ptr::NonNull;
use core::ptr::{self, drop_in_place};
use core::slice::{self};

Expand Down Expand Up @@ -31,7 +32,7 @@ impl<T> Drop for InPlaceDrop<T> {
// the source allocation - i.e. before the reallocation happened - to avoid leaking them
// if some other destructor panics.
pub(super) struct InPlaceDstDataSrcBufDrop<Src, Dest> {
pub(super) ptr: *mut Dest,
pub(super) ptr: NonNull<Dest>,
pub(super) len: usize,
pub(super) src_cap: usize,
pub(super) src: PhantomData<Src>,
Expand All @@ -42,8 +43,8 @@ impl<Src, Dest> Drop for InPlaceDstDataSrcBufDrop<Src, Dest> {
fn drop(&mut self) {
unsafe {
let _drop_allocation =
RawVec::<Src>::from_raw_parts_in(self.ptr.cast::<Src>(), self.src_cap, Global);
drop_in_place(core::ptr::slice_from_raw_parts_mut::<Dest>(self.ptr, self.len));
RawVec::<Src>::from_nonnull_in(self.ptr.cast::<Src>(), self.src_cap, Global);
drop_in_place(core::ptr::slice_from_raw_parts_mut::<Dest>(self.ptr.as_ptr(), self.len));
};
}
}
2 changes: 1 addition & 1 deletion library/alloc/src/vec/into_iter.rs
Original file line number Diff line number Diff line change
Expand Up @@ -433,7 +433,7 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for IntoIter<T, A> {
// `IntoIter::alloc` is not used anymore after this and will be dropped by RawVec
let alloc = ManuallyDrop::take(&mut self.0.alloc);
// RawVec handles deallocation
let _ = RawVec::from_raw_parts_in(self.0.buf.as_ptr(), self.0.cap, alloc);
let _ = RawVec::from_nonnull_in(self.0.buf, self.0.cap, alloc);
}
}
}
Expand Down
15 changes: 15 additions & 0 deletions library/alloc/src/vec/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -603,6 +603,11 @@ impl<T> Vec<T> {
pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
}

#[inline]
pub(crate) unsafe fn from_nonnull(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
unsafe { Self::from_nonnull_in(ptr, length, capacity, Global) }
}
}

impl<T, A: Allocator> Vec<T, A> {
Expand Down Expand Up @@ -820,6 +825,16 @@ impl<T, A: Allocator> Vec<T, A> {
unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
}

#[inline]
pub(crate) unsafe fn from_nonnull_in(
ptr: NonNull<T>,
length: usize,
capacity: usize,
alloc: A,
) -> Self {
unsafe { Vec { buf: RawVec::from_nonnull_in(ptr, capacity, alloc), len: length } }
}

/// Decomposes a `Vec<T>` into its raw components: `(pointer, length, capacity)`.
///
/// Returns the raw pointer to the underlying data, the length of
Expand Down
2 changes: 1 addition & 1 deletion library/alloc/src/vec/spec_from_iter.rs
Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ impl<T> SpecFromIter<T, IntoIter<T>> for Vec<T> {
if has_advanced {
ptr::copy(it.ptr.as_ptr(), it.buf.as_ptr(), it.len());
}
return Vec::from_raw_parts(it.buf.as_ptr(), it.len(), it.cap);
return Vec::from_nonnull(it.buf, it.len(), it.cap);
}
}

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