rustc_middle/ty/list.rs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311
use std::alloc::Layout;
use std::cmp::Ordering;
use std::hash::{Hash, Hasher};
use std::ops::Deref;
use std::{fmt, iter, mem, ptr, slice};
use rustc_data_structures::aligned::{Aligned, align_of};
#[cfg(parallel_compiler)]
use rustc_data_structures::sync::DynSync;
use rustc_serialize::{Encodable, Encoder};
use super::flags::FlagComputation;
use super::{DebruijnIndex, TypeFlags};
use crate::arena::Arena;
/// `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.
pub type List<T> = RawList<(), T>;
/// A generic type that can be used to prepend a [`List`] with some header.
///
/// The header will be ignored for value-based operations like [`PartialEq`],
/// [`Hash`] and [`Encodable`].
#[repr(C)]
pub struct RawList<H, T> {
skel: ListSkeleton<H, T>,
opaque: OpaqueListContents,
}
/// A [`RawList`] without the unsized tail. This type is used for layout computation
/// and constructing empty lists.
#[repr(C)]
struct ListSkeleton<H, T> {
header: H,
len: usize,
/// Although this claims to be a zero-length array, in practice `len`
/// elements are actually present.
data: [T; 0],
}
impl<T> Default for &List<T> {
fn default() -> Self {
List::empty()
}
}
unsafe extern "C" {
/// A dummy type used to force `List` to be unsized while not requiring
/// references to it be wide pointers.
type OpaqueListContents;
}
impl<H, T> RawList<H, T> {
#[inline(always)]
pub fn len(&self) -> usize {
self.skel.len
}
#[inline(always)]
pub fn as_slice(&self) -> &[T] {
self
}
/// 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>,
header: H,
slice: &[T],
) -> &'tcx RawList<H, T>
where
T: Copy,
{
assert!(!mem::needs_drop::<T>());
assert!(mem::size_of::<T>() != 0);
assert!(!slice.is_empty());
let (layout, _offset) =
Layout::new::<ListSkeleton<H, T>>().extend(Layout::for_value::<[T]>(slice)).unwrap();
let mem = arena.dropless.alloc_raw(layout) as *mut RawList<H, T>;
unsafe {
// Write the header
(&raw mut (*mem).skel.header).write(header);
// Write the length
(&raw mut (*mem).skel.len).write(slice.len());
// Write the elements
(&raw mut (*mem).skel.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) -> <&'_ RawList<H, T> as IntoIterator>::IntoIter
where
T: Copy,
{
self.into_iter()
}
}
impl<'a, H, T: Copy> rustc_type_ir::inherent::SliceLike for &'a RawList<H, T> {
type Item = T;
type IntoIter = iter::Copied<<&'a [T] as IntoIterator>::IntoIter>;
fn iter(self) -> Self::IntoIter {
(*self).iter()
}
fn as_slice(&self) -> &[Self::Item] {
(*self).as_slice()
}
}
macro_rules! impl_list_empty {
($header_ty:ty, $header_init:expr) => {
impl<T> RawList<$header_ty, T> {
/// Returns a reference to the (per header unique, static) empty list.
#[inline(always)]
pub fn empty<'a>() -> &'a RawList<$header_ty, T> {
#[repr(align(64))]
struct MaxAlign;
static EMPTY: ListSkeleton<$header_ty, MaxAlign> =
ListSkeleton { header: $header_init, len: 0, data: [] };
assert!(mem::align_of::<T>() <= mem::align_of::<MaxAlign>());
// SAFETY: `EMPTY` is sufficiently aligned to be an empty list for all
// types with `align_of(T) <= align_of(MaxAlign)`, which we checked above.
unsafe { &*((&raw const EMPTY) as *const RawList<$header_ty, T>) }
}
}
};
}
impl_list_empty!((), ());
impl<H, T: fmt::Debug> fmt::Debug for RawList<H, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(**self).fmt(f)
}
}
impl<H, S: Encoder, T: Encodable<S>> Encodable<S> for RawList<H, T> {
#[inline]
fn encode(&self, s: &mut S) {
(**self).encode(s);
}
}
impl<H, T: PartialEq> PartialEq for RawList<H, T> {
#[inline]
fn eq(&self, other: &RawList<H, T>) -> bool {
// Pointer equality implies list equality (due to the unique contents
// assumption).
ptr::eq(self, other)
}
}
impl<H, T: Eq> Eq for RawList<H, T> {}
impl<H, T> Ord for RawList<H, T>
where
T: Ord,
{
fn cmp(&self, other: &RawList<H, 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<H, T> PartialOrd for RawList<H, T>
where
T: PartialOrd,
{
fn partial_cmp(&self, other: &RawList<H, 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<Hdr, T> Hash for RawList<Hdr, T> {
#[inline]
fn hash<H: Hasher>(&self, s: &mut H) {
// Pointer hashing is sufficient (due to the unique contents
// assumption).
ptr::from_ref(self).hash(s)
}
}
impl<H, T> Deref for RawList<H, T> {
type Target = [T];
#[inline(always)]
fn deref(&self) -> &[T] {
self.as_ref()
}
}
impl<H, T> AsRef<[T]> for RawList<H, T> {
#[inline(always)]
fn as_ref(&self) -> &[T] {
let data_ptr = (&raw const self.skel.data).cast::<T>();
// SAFETY: `data_ptr` has the same provenance as `self` and can therefore
// access the `self.skel.len` elements stored at `self.skel.data`.
// Note that we specifically don't reborrow `&self.skel.data`, because that
// would give us a pointer with provenance over 0 bytes.
unsafe { slice::from_raw_parts(data_ptr, self.skel.len) }
}
}
impl<'a, H, T: Copy> IntoIterator for &'a RawList<H, 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<H: Sync, T: Sync> Sync for RawList<H, T> {}
// We need this since `List` uses extern type `OpaqueListContents`.
#[cfg(parallel_compiler)]
unsafe impl<H: DynSync, T: DynSync> DynSync for RawList<H, T> {}
// Safety:
// Layouts of `ListSkeleton<H, T>` and `RawList<H, T>` are the same, modulo opaque tail,
// thus aligns of `ListSkeleton<H, T>` and `RawList<H, T>` must be the same.
unsafe impl<H, T> Aligned for RawList<H, T> {
const ALIGN: ptr::Alignment = align_of::<ListSkeleton<H, T>>();
}
/// A [`List`] that additionally stores type information inline to speed up
/// [`TypeVisitableExt`](super::TypeVisitableExt) operations.
pub type ListWithCachedTypeInfo<T> = RawList<TypeInfo, T>;
impl<T> ListWithCachedTypeInfo<T> {
#[inline(always)]
pub fn flags(&self) -> TypeFlags {
self.skel.header.flags
}
#[inline(always)]
pub fn outer_exclusive_binder(&self) -> DebruijnIndex {
self.skel.header.outer_exclusive_binder
}
}
impl_list_empty!(TypeInfo, TypeInfo::empty());
/// The additional info that is stored in [`ListWithCachedTypeInfo`].
#[repr(C)]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct TypeInfo {
flags: TypeFlags,
outer_exclusive_binder: DebruijnIndex,
}
impl TypeInfo {
const fn empty() -> Self {
Self { flags: TypeFlags::empty(), outer_exclusive_binder: super::INNERMOST }
}
}
impl From<FlagComputation> for TypeInfo {
fn from(computation: FlagComputation) -> TypeInfo {
TypeInfo {
flags: computation.flags,
outer_exclusive_binder: computation.outer_exclusive_binder,
}
}
}