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use crate::arena::Arena;
use rustc_data_structures::aligned::{align_of, Aligned};
use rustc_serialize::{Encodable, Encoder};
use rustc_type_ir::{InferCtxtLike, OptWithInfcx};
use std::alloc::Layout;
use std::cmp::Ordering;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::iter;
use std::mem;
use std::ops::Deref;
use std::ptr;
use std::slice;
/// `List<T>` is a bit like `&[T]`, but with some critical differences.
/// - IMPORTANT: Every `List<T>` is *required* to have unique contents. The
/// type's correctness relies on this, *but it does not enforce it*.
/// Therefore, any code that creates a `List<T>` must ensure uniqueness
/// itself. In practice this is achieved by interning.
/// - The length is stored within the `List<T>`, so `&List<Ty>` is a thin
/// pointer.
/// - Because of this, you cannot get a `List<T>` that is a sub-list of another
/// `List<T>`. You can get a sub-slice `&[T]`, however.
/// - `List<T>` can be used with `CopyTaggedPtr`, which is useful within
/// structs whose size must be minimized.
/// - Because of the uniqueness assumption, we can use the address of a
/// `List<T>` for faster equality comparisons and hashing.
/// - `T` must be `Copy`. This lets `List<T>` be stored in a dropless arena and
/// iterators return a `T` rather than a `&T`.
/// - `T` must not be zero-sized.
#[repr(C)]
pub struct List<T> {
len: usize,
/// Although this claims to be a zero-length array, in practice `len`
/// elements are actually present.
data: [T; 0],
opaque: OpaqueListContents,
}
extern "C" {
/// A dummy type used to force `List` to be unsized while not requiring
/// references to it be wide pointers.
type OpaqueListContents;
}
impl<T> List<T> {
/// Returns a reference to the (unique, static) empty list.
#[inline(always)]
pub fn empty<'a>() -> &'a List<T> {
#[repr(align(64))]
struct MaxAlign;
assert!(mem::align_of::<T>() <= mem::align_of::<MaxAlign>());
#[repr(C)]
struct InOrder<T, U>(T, U);
// The empty slice is static and contains a single `0` usize (for the
// length) that is 64-byte aligned, thus featuring the necessary
// trailing padding for elements with up to 64-byte alignment.
static EMPTY_SLICE: InOrder<usize, MaxAlign> = InOrder(0, MaxAlign);
unsafe { &*(&EMPTY_SLICE as *const _ as *const List<T>) }
}
pub fn len(&self) -> usize {
self.len
}
pub fn as_slice(&self) -> &[T] {
self
}
}
impl<T: Copy> List<T> {
/// Allocates a list from `arena` and copies the contents of `slice` into it.
///
/// WARNING: the contents *must be unique*, such that no list with these
/// contents has been previously created. If not, operations such as `eq`
/// and `hash` might give incorrect results.
///
/// Panics if `T` is `Drop`, or `T` is zero-sized, or the slice is empty
/// (because the empty list exists statically, and is available via
/// `empty()`).
#[inline]
pub(super) fn from_arena<'tcx>(arena: &'tcx Arena<'tcx>, slice: &[T]) -> &'tcx List<T> {
assert!(!mem::needs_drop::<T>());
assert!(mem::size_of::<T>() != 0);
assert!(!slice.is_empty());
let (layout, _offset) =
Layout::new::<usize>().extend(Layout::for_value::<[T]>(slice)).unwrap();
let mem = arena.dropless.alloc_raw(layout) as *mut List<T>;
unsafe {
// Write the length
ptr::addr_of_mut!((*mem).len).write(slice.len());
// Write the elements
ptr::addr_of_mut!((*mem).data)
.cast::<T>()
.copy_from_nonoverlapping(slice.as_ptr(), slice.len());
&*mem
}
}
// If this method didn't exist, we would use `slice.iter` due to
// deref coercion.
//
// This would be weird, as `self.into_iter` iterates over `T` directly.
#[inline(always)]
pub fn iter(&self) -> <&'_ List<T> as IntoIterator>::IntoIter {
self.into_iter()
}
}
impl<T: fmt::Debug> fmt::Debug for List<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(**self).fmt(f)
}
}
impl<'tcx, T: super::DebugWithInfcx<TyCtxt<'tcx>>> super::DebugWithInfcx<TyCtxt<'tcx>> for List<T> {
fn fmt<InfCtx: InferCtxtLike<TyCtxt<'tcx>>>(
this: OptWithInfcx<'_, TyCtxt<'tcx>, InfCtx, &Self>,
f: &mut core::fmt::Formatter<'_>,
) -> core::fmt::Result {
fmt::Debug::fmt(&this.map(|this| this.as_slice()), f)
}
}
impl<S: Encoder, T: Encodable<S>> Encodable<S> for List<T> {
#[inline]
fn encode(&self, s: &mut S) {
(**self).encode(s);
}
}
impl<T: PartialEq> PartialEq for List<T> {
#[inline]
fn eq(&self, other: &List<T>) -> bool {
// Pointer equality implies list equality (due to the unique contents
// assumption).
ptr::eq(self, other)
}
}
impl<T: Eq> Eq for List<T> {}
impl<T> Ord for List<T>
where
T: Ord,
{
fn cmp(&self, other: &List<T>) -> Ordering {
// Pointer equality implies list equality (due to the unique contents
// assumption), but the contents must be compared otherwise.
if self == other { Ordering::Equal } else { <[T] as Ord>::cmp(&**self, &**other) }
}
}
impl<T> PartialOrd for List<T>
where
T: PartialOrd,
{
fn partial_cmp(&self, other: &List<T>) -> Option<Ordering> {
// Pointer equality implies list equality (due to the unique contents
// assumption), but the contents must be compared otherwise.
if self == other {
Some(Ordering::Equal)
} else {
<[T] as PartialOrd>::partial_cmp(&**self, &**other)
}
}
}
impl<T> Hash for List<T> {
#[inline]
fn hash<H: Hasher>(&self, s: &mut H) {
// Pointer hashing is sufficient (due to the unique contents
// assumption).
(self as *const List<T>).hash(s)
}
}
impl<T> Deref for List<T> {
type Target = [T];
#[inline(always)]
fn deref(&self) -> &[T] {
self.as_ref()
}
}
impl<T> AsRef<[T]> for List<T> {
#[inline(always)]
fn as_ref(&self) -> &[T] {
unsafe { slice::from_raw_parts(self.data.as_ptr(), self.len) }
}
}
impl<'a, T: Copy> IntoIterator for &'a List<T> {
type Item = T;
type IntoIter = iter::Copied<<&'a [T] as IntoIterator>::IntoIter>;
#[inline(always)]
fn into_iter(self) -> Self::IntoIter {
self[..].iter().copied()
}
}
unsafe impl<T: Sync> Sync for List<T> {}
// We need this since `List` uses extern type `OpaqueListContents`.
#[cfg(parallel_compiler)]
use rustc_data_structures::sync::DynSync;
use super::TyCtxt;
#[cfg(parallel_compiler)]
unsafe impl<T: DynSync> DynSync for List<T> {}
// Safety:
// Layouts of `Equivalent<T>` and `List<T>` are the same, modulo opaque tail,
// thus aligns of `Equivalent<T>` and `List<T>` must be the same.
unsafe impl<T> Aligned for List<T> {
const ALIGN: ptr::Alignment = {
#[repr(C)]
struct Equivalent<T> {
_len: usize,
_data: [T; 0],
}
align_of::<Equivalent<T>>()
};
}