diff options
Diffstat (limited to '')
| -rw-r--r-- | library/core/src/array/drain.rs | 76 | ||||
| -rw-r--r-- | library/core/src/array/equality.rs | 73 | ||||
| -rw-r--r-- | library/core/src/array/mod.rs | 273 |
3 files changed, 213 insertions, 209 deletions
diff --git a/library/core/src/array/drain.rs b/library/core/src/array/drain.rs new file mode 100644 index 000000000..5fadf907b --- /dev/null +++ b/library/core/src/array/drain.rs @@ -0,0 +1,76 @@ +use crate::iter::{TrustedLen, UncheckedIterator}; +use crate::mem::ManuallyDrop; +use crate::ptr::drop_in_place; +use crate::slice; + +/// A situationally-optimized version of `array.into_iter().for_each(func)`. +/// +/// [`crate::array::IntoIter`]s are great when you need an owned iterator, but +/// storing the entire array *inside* the iterator like that can sometimes +/// pessimize code. Notable, it can be more bytes than you really want to move +/// around, and because the array accesses index into it SRoA has a harder time +/// optimizing away the type than it does iterators that just hold a couple pointers. +/// +/// Thus this function exists, which gives a way to get *moved* access to the +/// elements of an array using a small iterator -- no bigger than a slice iterator. +/// +/// The function-taking-a-closure structure makes it safe, as it keeps callers +/// from looking at already-dropped elements. +pub(crate) fn drain_array_with<T, R, const N: usize>( + array: [T; N], + func: impl for<'a> FnOnce(Drain<'a, T>) -> R, +) -> R { + let mut array = ManuallyDrop::new(array); + // SAFETY: Now that the local won't drop it, it's ok to construct the `Drain` which will. + let drain = Drain(array.iter_mut()); + func(drain) +} + +/// See [`drain_array_with`] -- this is `pub(crate)` only so it's allowed to be +/// mentioned in the signature of that method. (Otherwise it hits `E0446`.) +// INVARIANT: It's ok to drop the remainder of the inner iterator. +pub(crate) struct Drain<'a, T>(slice::IterMut<'a, T>); + +impl<T> Drop for Drain<'_, T> { + fn drop(&mut self) { + // SAFETY: By the type invariant, we're allowed to drop all these. + unsafe { drop_in_place(self.0.as_mut_slice()) } + } +} + +impl<T> Iterator for Drain<'_, T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + let p: *const T = self.0.next()?; + // SAFETY: The iterator was already advanced, so we won't drop this later. + Some(unsafe { p.read() }) + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + let n = self.len(); + (n, Some(n)) + } +} + +impl<T> ExactSizeIterator for Drain<'_, T> { + #[inline] + fn len(&self) -> usize { + self.0.len() + } +} + +// SAFETY: This is a 1:1 wrapper for a slice iterator, which is also `TrustedLen`. +unsafe impl<T> TrustedLen for Drain<'_, T> {} + +impl<T> UncheckedIterator for Drain<'_, T> { + unsafe fn next_unchecked(&mut self) -> T { + // SAFETY: `Drain` is 1:1 with the inner iterator, so if the caller promised + // that there's an element left, the inner iterator has one too. + let p: *const T = unsafe { self.0.next_unchecked() }; + // SAFETY: The iterator was already advanced, so we won't drop this later. + unsafe { p.read() } + } +} diff --git a/library/core/src/array/equality.rs b/library/core/src/array/equality.rs index b2c895f88..d749865f7 100644 --- a/library/core/src/array/equality.rs +++ b/library/core/src/array/equality.rs @@ -1,6 +1,5 @@ +use crate::cmp::BytewiseEq; use crate::convert::TryInto; -use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize}; -use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize}; #[stable(feature = "rust1", since = "1.0.0")] impl<A, B, const N: usize> PartialEq<[B; N]> for [A; N] @@ -144,74 +143,14 @@ impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T { } } -impl<T: IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T { +impl<T: BytewiseEq<U>, U, const N: usize> SpecArrayEq<U, N> for T { fn spec_eq(a: &[T; N], b: &[U; N]) -> bool { - // SAFETY: This is why `IsRawEqComparable` is an `unsafe trait`. - unsafe { - let b = &*b.as_ptr().cast::<[T; N]>(); - crate::intrinsics::raw_eq(a, b) - } + // SAFETY: Arrays are compared element-wise, and don't add any padding + // between elements, so when the elements are `BytewiseEq`, we can + // compare the entire array at once. + unsafe { crate::intrinsics::raw_eq(a, crate::mem::transmute(b)) } } fn spec_ne(a: &[T; N], b: &[U; N]) -> bool { !Self::spec_eq(a, b) } } - -/// `U` exists on here mostly because `min_specialization` didn't let me -/// repeat the `T` type parameter in the above specialization, so instead -/// the `T == U` constraint comes from the impls on this. -/// # Safety -/// - Neither `Self` nor `U` has any padding. -/// - `Self` and `U` have the same layout. -/// - `Self: PartialEq<U>` is byte-wise (this means no floats, among other things) -#[rustc_specialization_trait] -unsafe trait IsRawEqComparable<U>: PartialEq<U> {} - -macro_rules! is_raw_eq_comparable { - ($($t:ty),+ $(,)?) => {$( - unsafe impl IsRawEqComparable<$t> for $t {} - )+}; -} - -// SAFETY: All the ordinary integer types have no padding, and are not pointers. -is_raw_eq_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize); - -// SAFETY: bool and char have *niches*, but no *padding* (and these are not pointer types), so this -// is sound -is_raw_eq_comparable!(bool, char); - -// SAFETY: Similarly, the non-zero types have a niche, but no undef and no pointers, -// and they compare like their underlying numeric type. -is_raw_eq_comparable!( - NonZeroU8, - NonZeroU16, - NonZeroU32, - NonZeroU64, - NonZeroU128, - NonZeroUsize, - NonZeroI8, - NonZeroI16, - NonZeroI32, - NonZeroI64, - NonZeroI128, - NonZeroIsize, -); - -// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus -// are also safe to equality-compare bitwise inside an `Option`. -// The way `PartialOrd` is defined for `Option` means that this wouldn't work -// for `<` or `>` on the signed types, but since we only do `==` it's fine. -is_raw_eq_comparable!( - Option<NonZeroU8>, - Option<NonZeroU16>, - Option<NonZeroU32>, - Option<NonZeroU64>, - Option<NonZeroU128>, - Option<NonZeroUsize>, - Option<NonZeroI8>, - Option<NonZeroI16>, - Option<NonZeroI32>, - Option<NonZeroI64>, - Option<NonZeroI128>, - Option<NonZeroIsize>, -); diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs index 2825e0bbb..1643842d6 100644 --- a/library/core/src/array/mod.rs +++ b/library/core/src/array/mod.rs @@ -10,16 +10,19 @@ use crate::convert::{Infallible, TryFrom}; use crate::error::Error; use crate::fmt; use crate::hash::{self, Hash}; -use crate::iter::TrustedLen; +use crate::iter::UncheckedIterator; use crate::mem::{self, MaybeUninit}; use crate::ops::{ ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try, }; use crate::slice::{Iter, IterMut}; +mod drain; mod equality; mod iter; +pub(crate) use drain::drain_array_with; + #[stable(feature = "array_value_iter", since = "1.51.0")] pub use iter::IntoIter; @@ -52,16 +55,11 @@ pub use iter::IntoIter; /// ``` #[inline] #[stable(feature = "array_from_fn", since = "1.63.0")] -pub fn from_fn<T, const N: usize, F>(mut cb: F) -> [T; N] +pub fn from_fn<T, const N: usize, F>(cb: F) -> [T; N] where F: FnMut(usize) -> T, { - let mut idx = 0; - [(); N].map(|_| { - let res = cb(idx); - idx += 1; - res - }) + try_from_fn(NeverShortCircuit::wrap_mut_1(cb)).0 } /// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call. @@ -101,9 +99,14 @@ where R: Try, R::Residual: Residual<[R::Output; N]>, { - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { try_collect_into_array_unchecked(&mut (0..N).map(cb)) } + let mut array = MaybeUninit::uninit_array::<N>(); + match try_from_fn_erased(&mut array, cb) { + ControlFlow::Break(r) => FromResidual::from_residual(r), + ControlFlow::Continue(()) => { + // SAFETY: All elements of the array were populated. + try { unsafe { MaybeUninit::array_assume_init(array) } } + } + } } /// Converts a reference to `T` into a reference to an array of length 1 (without copying). @@ -131,7 +134,8 @@ pub struct TryFromSliceError(()); impl fmt::Display for TryFromSliceError { #[inline] fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - fmt::Display::fmt(self.__description(), f) + #[allow(deprecated)] + self.description().fmt(f) } } @@ -139,20 +143,6 @@ impl fmt::Display for TryFromSliceError { impl Error for TryFromSliceError { #[allow(deprecated)] fn description(&self) -> &str { - self.__description() - } -} - -impl TryFromSliceError { - #[unstable( - feature = "array_error_internals", - reason = "available through Error trait and this method should not \ - be exposed publicly", - issue = "none" - )] - #[inline] - #[doc(hidden)] - pub fn __description(&self) -> &str { "could not convert slice to array" } } @@ -427,9 +417,7 @@ trait SpecArrayClone: Clone { impl<T: Clone> SpecArrayClone for T { #[inline] default fn clone<const N: usize>(array: &[T; N]) -> [T; N] { - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { collect_into_array_unchecked(&mut array.iter().cloned()) } + from_trusted_iterator(array.iter().cloned()) } } @@ -513,9 +501,7 @@ impl<T, const N: usize> [T; N] { where F: FnMut(T) -> U, { - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) } + self.try_map(NeverShortCircuit::wrap_mut_1(f)).0 } /// A fallible function `f` applied to each element on array `self` in order to @@ -552,9 +538,7 @@ impl<T, const N: usize> [T; N] { R: Try, R::Residual: Residual<[R::Output; N]>, { - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { try_collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) } + drain_array_with(self, |iter| try_from_trusted_iterator(iter.map(f))) } /// 'Zips up' two arrays into a single array of pairs. @@ -575,11 +559,9 @@ impl<T, const N: usize> [T; N] { /// ``` #[unstable(feature = "array_zip", issue = "80094")] pub fn zip<U>(self, rhs: [U; N]) -> [(T, U); N] { - let mut iter = IntoIterator::into_iter(self).zip(rhs); - - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { collect_into_array_unchecked(&mut iter) } + drain_array_with(self, |lhs| { + drain_array_with(rhs, |rhs| from_trusted_iterator(crate::iter::zip(lhs, rhs))) + }) } /// Returns a slice containing the entire array. Equivalent to `&s[..]`. @@ -626,9 +608,7 @@ impl<T, const N: usize> [T; N] { /// ``` #[unstable(feature = "array_methods", issue = "76118")] pub fn each_ref(&self) -> [&T; N] { - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { collect_into_array_unchecked(&mut self.iter()) } + from_trusted_iterator(self.iter()) } /// Borrows each element mutably and returns an array of mutable references @@ -648,9 +628,7 @@ impl<T, const N: usize> [T; N] { /// ``` #[unstable(feature = "array_methods", issue = "76118")] pub fn each_mut(&mut self) -> [&mut T; N] { - // SAFETY: we know for certain that this iterator will yield exactly `N` - // items. - unsafe { collect_into_array_unchecked(&mut self.iter_mut()) } + from_trusted_iterator(self.iter_mut()) } /// Divides one array reference into two at an index. @@ -810,105 +788,71 @@ impl<T, const N: usize> [T; N] { } } -/// Pulls `N` items from `iter` and returns them as an array. If the iterator -/// yields fewer than `N` items, this function exhibits undefined behavior. +/// Populate an array from the first `N` elements of `iter` /// -/// See [`try_collect_into_array`] for more information. +/// # Panics /// +/// If the iterator doesn't actually have enough items. /// -/// # Safety -/// -/// It is up to the caller to guarantee that `iter` yields at least `N` items. -/// Violating this condition causes undefined behavior. -unsafe fn try_collect_into_array_unchecked<I, T, R, const N: usize>(iter: &mut I) -> R::TryType -where - // Note: `TrustedLen` here is somewhat of an experiment. This is just an - // internal function, so feel free to remove if this bound turns out to be a - // bad idea. In that case, remember to also remove the lower bound - // `debug_assert!` below! - I: Iterator + TrustedLen, - I::Item: Try<Output = T, Residual = R>, - R: Residual<[T; N]>, -{ - debug_assert!(N <= iter.size_hint().1.unwrap_or(usize::MAX)); - debug_assert!(N <= iter.size_hint().0); - - // SAFETY: covered by the function contract. - unsafe { try_collect_into_array(iter).unwrap_unchecked() } +/// By depending on `TrustedLen`, however, we can do that check up-front (where +/// it easily optimizes away) so it doesn't impact the loop that fills the array. +#[inline] +fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] { + try_from_trusted_iterator(iter.map(NeverShortCircuit)).0 } -// Infallible version of `try_collect_into_array_unchecked`. -unsafe fn collect_into_array_unchecked<I, const N: usize>(iter: &mut I) -> [I::Item; N] +#[inline] +fn try_from_trusted_iterator<T, R, const N: usize>( + iter: impl UncheckedIterator<Item = R>, +) -> ChangeOutputType<R, [T; N]> where - I: Iterator + TrustedLen, + R: Try<Output = T>, + R::Residual: Residual<[T; N]>, { - let mut map = iter.map(NeverShortCircuit); - - // SAFETY: The same safety considerations w.r.t. the iterator length - // apply for `try_collect_into_array_unchecked` as for - // `collect_into_array_unchecked` - match unsafe { try_collect_into_array_unchecked(&mut map) } { - NeverShortCircuit(array) => array, + assert!(iter.size_hint().0 >= N); + fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T { + move |_| { + // SAFETY: We know that `from_fn` will call this at most N times, + // and we checked to ensure that we have at least that many items. + unsafe { iter.next_unchecked() } + } } + + try_from_fn(next(iter)) } -/// Pulls `N` items from `iter` and returns them as an array. If the iterator -/// yields fewer than `N` items, `Err` is returned containing an iterator over -/// the already yielded items. +/// Version of [`try_from_fn`] using a passed-in slice in order to avoid +/// needing to monomorphize for every array length. /// -/// Since the iterator is passed as a mutable reference and this function calls -/// `next` at most `N` times, the iterator can still be used afterwards to -/// retrieve the remaining items. +/// This takes a generator rather than an iterator so that *at the type level* +/// it never needs to worry about running out of items. When combined with +/// an infallible `Try` type, that means the loop canonicalizes easily, allowing +/// it to optimize well. /// -/// If `iter.next()` panicks, all items already yielded by the iterator are -/// dropped. +/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one +/// function that does the union of both things, but last time it was that way +/// it resulted in poor codegen from the "are there enough source items?" checks +/// not optimizing away. So if you give it a shot, make sure to watch what +/// happens in the codegen tests. #[inline] -fn try_collect_into_array<I, T, R, const N: usize>( - iter: &mut I, -) -> Result<R::TryType, IntoIter<T, N>> +fn try_from_fn_erased<T, R>( + buffer: &mut [MaybeUninit<T>], + mut generator: impl FnMut(usize) -> R, +) -> ControlFlow<R::Residual> where - I: Iterator, - I::Item: Try<Output = T, Residual = R>, - R: Residual<[T; N]>, + R: Try<Output = T>, { - if N == 0 { - // SAFETY: An empty array is always inhabited and has no validity invariants. - return Ok(Try::from_output(unsafe { mem::zeroed() })); - } + let mut guard = Guard { array_mut: buffer, initialized: 0 }; - let mut array = MaybeUninit::uninit_array::<N>(); - let mut guard = Guard { array_mut: &mut array, initialized: 0 }; - - for _ in 0..N { - match iter.next() { - Some(item_rslt) => { - let item = match item_rslt.branch() { - ControlFlow::Break(r) => { - return Ok(FromResidual::from_residual(r)); - } - ControlFlow::Continue(elem) => elem, - }; - - // SAFETY: `guard.initialized` starts at 0, which means push can be called - // at most N times, which this loop does. - unsafe { - guard.push_unchecked(item); - } - } - None => { - let alive = 0..guard.initialized; - mem::forget(guard); - // SAFETY: `array` was initialized with exactly `initialized` - // number of elements. - return Err(unsafe { IntoIter::new_unchecked(array, alive) }); - } - } + while guard.initialized < guard.array_mut.len() { + let item = generator(guard.initialized).branch()?; + + // SAFETY: The loop condition ensures we have space to push the item + unsafe { guard.push_unchecked(item) }; } mem::forget(guard); - // SAFETY: All elements of the array were populated in the loop above. - let output = unsafe { array.transpose().assume_init() }; - Ok(Try::from_output(output)) + ControlFlow::Continue(()) } /// Panic guard for incremental initialization of arrays. @@ -922,14 +866,14 @@ where /// /// To minimize indirection fields are still pub but callers should at least use /// `push_unchecked` to signal that something unsafe is going on. -pub(crate) struct Guard<'a, T, const N: usize> { +struct Guard<'a, T> { /// The array to be initialized. - pub array_mut: &'a mut [MaybeUninit<T>; N], + pub array_mut: &'a mut [MaybeUninit<T>], /// The number of items that have been initialized so far. pub initialized: usize, } -impl<T, const N: usize> Guard<'_, T, N> { +impl<T> Guard<'_, T> { /// Adds an item to the array and updates the initialized item counter. /// /// # Safety @@ -947,28 +891,73 @@ impl<T, const N: usize> Guard<'_, T, N> { } } -impl<T, const N: usize> Drop for Guard<'_, T, N> { +impl<T> Drop for Guard<'_, T> { fn drop(&mut self) { - debug_assert!(self.initialized <= N); + debug_assert!(self.initialized <= self.array_mut.len()); // SAFETY: this slice will contain only initialized objects. unsafe { crate::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut( - &mut self.array_mut.get_unchecked_mut(..self.initialized), + self.array_mut.get_unchecked_mut(..self.initialized), )); } } } -/// Returns the next chunk of `N` items from the iterator or errors with an -/// iterator over the remainder. Used for `Iterator::next_chunk`. +/// Pulls `N` items from `iter` and returns them as an array. If the iterator +/// yields fewer than `N` items, `Err` is returned containing an iterator over +/// the already yielded items. +/// +/// Since the iterator is passed as a mutable reference and this function calls +/// `next` at most `N` times, the iterator can still be used afterwards to +/// retrieve the remaining items. +/// +/// If `iter.next()` panicks, all items already yielded by the iterator are +/// dropped. +/// +/// Used for [`Iterator::next_chunk`]. +#[inline] +pub(crate) fn iter_next_chunk<T, const N: usize>( + iter: &mut impl Iterator<Item = T>, +) -> Result<[T; N], IntoIter<T, N>> { + let mut array = MaybeUninit::uninit_array::<N>(); + let r = iter_next_chunk_erased(&mut array, iter); + match r { + Ok(()) => { + // SAFETY: All elements of `array` were populated. + Ok(unsafe { MaybeUninit::array_assume_init(array) }) + } + Err(initialized) => { + // SAFETY: Only the first `initialized` elements were populated + Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) }) + } + } +} + +/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid +/// needing to monomorphize for every array length. +/// +/// Unfortunately this loop has two exit conditions, the buffer filling up +/// or the iterator running out of items, making it tend to optimize poorly. #[inline] -pub(crate) fn iter_next_chunk<I, const N: usize>( - iter: &mut I, -) -> Result<[I::Item; N], IntoIter<I::Item, N>> -where - I: Iterator, -{ - let mut map = iter.map(NeverShortCircuit); - try_collect_into_array(&mut map).map(|NeverShortCircuit(arr)| arr) +fn iter_next_chunk_erased<T>( + buffer: &mut [MaybeUninit<T>], + iter: &mut impl Iterator<Item = T>, +) -> Result<(), usize> { + let mut guard = Guard { array_mut: buffer, initialized: 0 }; + while guard.initialized < guard.array_mut.len() { + let Some(item) = iter.next() else { + // Unlike `try_from_fn_erased`, we want to keep the partial results, + // so we need to defuse the guard instead of using `?`. + let initialized = guard.initialized; + mem::forget(guard); + return Err(initialized) + }; + + // SAFETY: The loop condition ensures we have space to push the item + unsafe { guard.push_unchecked(item) }; + } + + mem::forget(guard); + Ok(()) } |