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Use a specialized varint + bitpacking scheme for DepGraph encoding

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This commit is contained in:
Ben Kimock 2023-04-29 21:51:32 -04:00
parent bf1e3f31f9
commit 94fe18f84b
8 changed files with 358 additions and 46 deletions
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2
compiler/rustc_middle/src/dep_graph/dep_node.rs
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@ -97,7 +97,7 @@ impl DepKind {
// discriminants of the variants have been assigned consecutively from 0
// so that just the one comparison suffices to check that the u16 can be
// transmuted to a DepKind.
const VARIANTS: u16 = {
pub const VARIANTS: u16 = {
let deps: &[DepKind] = &[$(DepKind::$variant,)*];
let mut i = 0;
while i < deps.len() {

16
compiler/rustc_middle/src/dep_graph/mod.rs
View File

@ -26,6 +26,7 @@
impl rustc_query_system::dep_graph::DepKind for DepKind {
const NULL: Self = DepKind::Null;
const RED: Self = DepKind::Red;
const MAX: u16 = DepKind::VARIANTS - 1;
fn debug_node(node: &DepNode, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "{:?}(", node.kind)?;
@ -68,6 +69,21 @@ fn read_deps<OP>(op: OP)
op(icx.task_deps)
})
}
#[track_caller]
#[inline]
fn from_u16(u: u16) -> Self {
if u > Self::MAX {
panic!("Invalid DepKind {u}");
}
// SAFETY: See comment on DepKind::VARIANTS
unsafe { std::mem::transmute(u) }
}
#[inline]
fn to_u16(self) -> u16 {
self as u16
}
}
impl<'tcx> DepContext for TyCtxt<'tcx> {

60
compiler/rustc_query_system/src/dep_graph/edges.rs Normal file
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@ -0,0 +1,60 @@
use crate::dep_graph::DepNodeIndex;
use smallvec::SmallVec;
use std::hash::{Hash, Hasher};
use std::ops::Deref;
#[derive(Default, Debug)]
pub struct EdgesVec {
max: u32,
edges: SmallVec<[DepNodeIndex; EdgesVec::INLINE_CAPACITY]>,
}
impl Hash for EdgesVec {
#[inline]
fn hash<H: Hasher>(&self, hasher: &mut H) {
Hash::hash(&self.edges, hasher)
}
}
impl EdgesVec {
pub const INLINE_CAPACITY: usize = 8;
#[inline]
pub fn new() -> Self {
Self::default()
}
#[inline]
pub fn push(&mut self, edge: DepNodeIndex) {
self.max = self.max.max(edge.as_u32());
self.edges.push(edge);
}
#[inline]
pub fn max_index(&self) -> u32 {
self.max
}
}
impl Deref for EdgesVec {
type Target = [DepNodeIndex];
#[inline]
fn deref(&self) -> &Self::Target {
self.edges.as_slice()
}
}
impl FromIterator<DepNodeIndex> for EdgesVec {
#[inline]
fn from_iter<T>(iter: T) -> Self
where
T: IntoIterator<Item = DepNodeIndex>,
{
let mut vec = EdgesVec::new();
for index in iter {
vec.push(index)
}
vec
}
}

31
compiler/rustc_query_system/src/dep_graph/graph.rs
View File

@ -8,7 +8,6 @@
use rustc_data_structures::unord::UnordMap;
use rustc_index::IndexVec;
use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
use smallvec::{smallvec, SmallVec};
use std::assert_matches::assert_matches;
use std::collections::hash_map::Entry;
use std::fmt::Debug;
@ -19,6 +18,7 @@
use super::query::DepGraphQuery;
use super::serialized::{GraphEncoder, SerializedDepGraph, SerializedDepNodeIndex};
use super::{DepContext, DepKind, DepNode, HasDepContext, WorkProductId};
use crate::dep_graph::EdgesVec;
use crate::ich::StableHashingContext;
use crate::query::{QueryContext, QuerySideEffects};
@ -137,7 +137,7 @@ pub fn new(
let _green_node_index = current.intern_new_node(
profiler,
DepNode { kind: DepKind::NULL, hash: current.anon_id_seed.into() },
smallvec![],
EdgesVec::new(),
Fingerprint::ZERO,
);
assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE);
@ -147,7 +147,7 @@ pub fn new(
profiler,
&prev_graph,
DepNode { kind: DepKind::RED, hash: Fingerprint::ZERO.into() },
smallvec![],
EdgesVec::new(),
None,
false,
);
@ -356,12 +356,12 @@ pub fn with_task<Ctxt: HasDepContext<DepKind = K>, A: Debug, R>(
let with_deps = |task_deps| K::with_deps(task_deps, || task(cx, arg));
let (result, edges) = if cx.dep_context().is_eval_always(key.kind) {
(with_deps(TaskDepsRef::EvalAlways), smallvec![])
(with_deps(TaskDepsRef::EvalAlways), EdgesVec::new())
} else {
let task_deps = Lock::new(TaskDeps {
#[cfg(debug_assertions)]
node: Some(key),
reads: SmallVec::new(),
reads: EdgesVec::new(),
read_set: Default::default(),
phantom_data: PhantomData,
});
@ -486,14 +486,14 @@ pub fn read_index(&self, dep_node_index: DepNodeIndex) {
// As long as we only have a low number of reads we can avoid doing a hash
// insert and potentially allocating/reallocating the hashmap
let new_read = if task_deps.reads.len() < TASK_DEPS_READS_CAP {
let new_read = if task_deps.reads.len() < EdgesVec::INLINE_CAPACITY {
task_deps.reads.iter().all(|other| *other != dep_node_index)
} else {
task_deps.read_set.insert(dep_node_index)
};
if new_read {
task_deps.reads.push(dep_node_index);
if task_deps.reads.len() == TASK_DEPS_READS_CAP {
if task_deps.reads.len() == EdgesVec::INLINE_CAPACITY {
// Fill `read_set` with what we have so far so we can use the hashset
// next time
task_deps.read_set.extend(task_deps.reads.iter().copied());
@ -572,9 +572,13 @@ pub fn with_feed_task<Ctxt: DepContext<DepKind = K>, A: Debug, R: Debug>(
}
}
let mut edges = SmallVec::new();
let mut edges = EdgesVec::new();
K::read_deps(|task_deps| match task_deps {
TaskDepsRef::Allow(deps) => edges.extend(deps.lock().reads.iter().copied()),
TaskDepsRef::Allow(deps) => {
for index in deps.lock().reads.iter().copied() {
edges.push(index);
}
}
TaskDepsRef::EvalAlways => {
edges.push(DepNodeIndex::FOREVER_RED_NODE);
}
@ -872,7 +876,7 @@ fn try_mark_previous_green<Qcx: QueryContext<DepKind = K>>(
let prev_deps = self.previous.edge_targets_from(prev_dep_node_index);
for &dep_dep_node_index in prev_deps {
for dep_dep_node_index in prev_deps {
self.try_mark_parent_green(qcx, dep_dep_node_index, dep_node, Some(&frame))?;
}
@ -1308,8 +1312,7 @@ fn promote_node_and_deps_to_current(
let key = prev_graph.index_to_node(prev_index);
let edges = prev_graph
.edge_targets_from(prev_index)
.iter()
.map(|i| prev_index_to_index[*i].unwrap())
.map(|i| prev_index_to_index[i].unwrap())
.collect();
let fingerprint = prev_graph.fingerprint_by_index(prev_index);
let dep_node_index = self.encoder.borrow().send(profiler, key, fingerprint, edges);
@ -1335,10 +1338,6 @@ fn debug_assert_not_in_new_nodes(
}
}
/// The capacity of the `reads` field `SmallVec`
const TASK_DEPS_READS_CAP: usize = 8;
type EdgesVec = SmallVec<[DepNodeIndex; TASK_DEPS_READS_CAP]>;
#[derive(Debug, Clone, Copy)]
pub enum TaskDepsRef<'a, K: DepKind> {
/// New dependencies can be added to the

8
compiler/rustc_query_system/src/dep_graph/mod.rs
View File

@ -1,10 +1,12 @@
pub mod debug;
mod dep_node;
mod edges;
mod graph;
mod query;
mod serialized;
pub use dep_node::{DepKindStruct, DepNode, DepNodeParams, WorkProductId};
pub use edges::EdgesVec;
pub use graph::{
hash_result, DepGraph, DepGraphData, DepNodeColor, DepNodeIndex, TaskDeps, TaskDepsRef,
WorkProduct, WorkProductMap,
@ -157,4 +159,10 @@ fn with_deps<OP, R>(deps: TaskDepsRef<'_, Self>, op: OP) -> R
fn read_deps<OP>(op: OP)
where
OP: for<'a> FnOnce(TaskDepsRef<'a, Self>);
fn from_u16(u: u16) -> Self;
fn to_u16(self) -> u16;
const MAX: u16;
}

284
compiler/rustc_query_system/src/dep_graph/serialized.rs
View File

@ -1,6 +1,6 @@
//! The data that we will serialize and deserialize.
//!
//! The dep-graph is serialized as a sequence of NodeInfo, with the dependencies
//! Notionally, the dep-graph is a sequence of NodeInfo with the dependencies
//! specified inline. The total number of nodes and edges are stored as the last
//! 16 bytes of the file, so we can find them easily at decoding time.
//!
@ -14,14 +14,16 @@
use super::query::DepGraphQuery;
use super::{DepKind, DepNode, DepNodeIndex};
use crate::dep_graph::EdgesVec;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fingerprint::PackedFingerprint;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::profiling::SelfProfilerRef;
use rustc_data_structures::sync::Lock;
use rustc_index::{Idx, IndexVec};
use rustc_serialize::opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixedSize, MemDecoder};
use rustc_serialize::{Decodable, Decoder, Encodable};
use smallvec::SmallVec;
use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
use std::marker::PhantomData;
// The maximum value of `SerializedDepNodeIndex` leaves the upper two bits
// unused so that we can store multiple index types in `CompressedHybridIndex`,
@ -31,6 +33,16 @@
pub struct SerializedDepNodeIndex {}
}
const DEP_NODE_SIZE: usize = std::mem::size_of::<SerializedDepNodeIndex>();
/// Amount of padding we need to add to the edge list data so that we can retrieve every
/// SerializedDepNodeIndex with a fixed-size read then mask.
const DEP_NODE_PAD: usize = DEP_NODE_SIZE - 1;
/// Amount of bits we need to store the number of used bytes in a SerializedDepNodeIndex.
/// Note that wherever we encode byte widths like this we actually store the number of bytes used
/// minus 1; for a 4-byte value we technically would have 5 widths to store, but using one byte to
/// store zeroes (which are relatively rare) is a decent tradeoff to save a bit in our bitfields.
const DEP_NODE_WIDTH_BITS: usize = DEP_NODE_SIZE / 2;
/// Data for use when recompiling the **current crate**.
#[derive(Debug)]
pub struct SerializedDepGraph<K: DepKind> {
@ -42,10 +54,10 @@ pub struct SerializedDepGraph<K: DepKind> {
/// For each DepNode, stores the list of edges originating from that
/// DepNode. Encoded as a [start, end) pair indexing into edge_list_data,
/// which holds the actual DepNodeIndices of the target nodes.
edge_list_indices: IndexVec<SerializedDepNodeIndex, (u32, u32)>,
/// A flattened list of all edge targets in the graph. Edge sources are
/// implicit in edge_list_indices.
edge_list_data: Vec<SerializedDepNodeIndex>,
edge_list_indices: IndexVec<SerializedDepNodeIndex, EdgeHeader>,
/// A flattened list of all edge targets in the graph, stored in the same
/// varint encoding that we use on disk. Edge sources are implicit in edge_list_indices.
edge_list_data: Vec<u8>,
/// Reciprocal map to `nodes`.
index: FxHashMap<DepNode<K>, SerializedDepNodeIndex>,
}
@ -64,9 +76,35 @@ fn default() -> Self {
impl<K: DepKind> SerializedDepGraph<K> {
#[inline]
pub fn edge_targets_from(&self, source: SerializedDepNodeIndex) -> &[SerializedDepNodeIndex] {
let targets = self.edge_list_indices[source];
&self.edge_list_data[targets.0 as usize..targets.1 as usize]
pub fn edge_targets_from(
&self,
source: SerializedDepNodeIndex,
) -> impl Iterator<Item = SerializedDepNodeIndex> + '_ {
let header = self.edge_list_indices[source];
let mut raw = &self.edge_list_data[header.start()..];
// Figure out where the edge list for `source` ends by getting the start index of the next
// edge list, or the end of the array if this is the last edge.
let end = self
.edge_list_indices
.get(source + 1)
.map(|h| h.start())
.unwrap_or_else(|| self.edge_list_data.len() - DEP_NODE_PAD);
// The number of edges for this node is implicitly stored in the combination of the byte
// width and the length.
let bytes_per_index = header.bytes_per_index();
let len = (end - header.start()) / bytes_per_index;
// LLVM doesn't hoist EdgeHeader::mask so we do it ourselves.
let mask = header.mask();
(0..len).map(move |_| {
// Doing this slicing in this order ensures that the first bounds check suffices for
// all the others.
let index = &raw[..DEP_NODE_SIZE];
raw = &raw[bytes_per_index..];
let index = u32::from_le_bytes(index.try_into().unwrap()) & mask;
SerializedDepNodeIndex::from_u32(index)
})
}
#[inline]
@ -84,11 +122,42 @@ pub fn fingerprint_by_index(&self, dep_node_index: SerializedDepNodeIndex) -> Fi
self.fingerprints[dep_node_index]
}
#[inline]
pub fn node_count(&self) -> usize {
self.index.len()
}
}
/// A packed representation of an edge's start index and byte width.
///
/// This is packed by stealing 2 bits from the start index, which means we only accomodate edge
/// data arrays up to a quarter of our address space. Which seems fine.
#[derive(Debug, Clone, Copy)]
struct EdgeHeader {
repr: usize,
}
impl EdgeHeader {
#[inline]
fn start(self) -> usize {
self.repr >> DEP_NODE_WIDTH_BITS
}
#[inline]
fn bytes_per_index(self) -> usize {
(self.repr & mask(DEP_NODE_WIDTH_BITS)) + 1
}
#[inline]
fn mask(self) -> u32 {
mask(self.bytes_per_index() * 8) as u32
}
}
fn mask(bits: usize) -> usize {
usize::MAX >> ((std::mem::size_of::<usize>() * 8) - bits)
}
impl<'a, K: DepKind + Decodable<MemDecoder<'a>>> Decodable<MemDecoder<'a>>
for SerializedDepGraph<K>
{
@ -107,32 +176,51 @@ fn decode(d: &mut MemDecoder<'a>) -> SerializedDepGraph<K> {
debug!(?node_count, ?edge_count);
let graph_bytes = d.len() - (2 * IntEncodedWithFixedSize::ENCODED_SIZE) - d.position();
let mut nodes = IndexVec::with_capacity(node_count);
let mut fingerprints = IndexVec::with_capacity(node_count);
let mut edge_list_indices = IndexVec::with_capacity(node_count);
let mut edge_list_data = Vec::with_capacity(edge_count);
// This slightly over-estimates the amount of bytes used for all the edge data but never by
// more than ~6%, because over-estimation only occurs for large nodes.
let mut edge_list_data = Vec::with_capacity(
graph_bytes - node_count * std::mem::size_of::<SerializedNodeHeader<K>>(),
);
for _index in 0..node_count {
let dep_node: DepNode<K> = Decodable::decode(d);
let _i: SerializedDepNodeIndex = nodes.push(dep_node);
// Decode the header for this edge; the header packs together as many of the fixed-size
// fields as possible to limit the number of times we update decoder state.
let node_header = SerializedNodeHeader { bytes: d.read_array(), _marker: PhantomData };
let _i: SerializedDepNodeIndex = nodes.push(node_header.node());
debug_assert_eq!(_i.index(), _index);
let fingerprint: Fingerprint = Decodable::decode(d);
let _i: SerializedDepNodeIndex = fingerprints.push(fingerprint);
let _i: SerializedDepNodeIndex = fingerprints.push(node_header.fingerprint());
debug_assert_eq!(_i.index(), _index);
// Deserialize edges -- sequence of DepNodeIndex
let len = d.read_usize();
let start = edge_list_data.len().try_into().unwrap();
for _ in 0..len {
let edge = Decodable::decode(d);
edge_list_data.push(edge);
}
let end = edge_list_data.len().try_into().unwrap();
let _i: SerializedDepNodeIndex = edge_list_indices.push((start, end));
// If the length of this node's edge list is small, the length is stored in the header.
// If it is not, we fall back to another decoder call.
let num_edges = node_header.len().unwrap_or_else(|| d.read_usize());
// The edges index list uses the same varint strategy as rmeta tables; we select the
// number of byte elements per-array not per-element. This lets us read the whole edge
// list for a node with one decoder call and also use the on-disk format in memory.
let edges_len_bytes = node_header.bytes_per_index() * num_edges;
// The in-memory structure for the edges list stores the byte width of the edges on
// this node with the offset into the global edge data array.
let edges_header = node_header.edges_header(&edge_list_data);
edge_list_data.extend(d.read_raw_bytes(edges_len_bytes));
let _i: SerializedDepNodeIndex = edge_list_indices.push(edges_header);
debug_assert_eq!(_i.index(), _index);
}
// When we access the edge list data, we do a fixed-size read from the edge list data then
// mask off the bytes that aren't for that edge index, so the last read may dangle off the
// end of the array. This padding ensure it doesn't.
edge_list_data.extend(&[0u8; DEP_NODE_PAD]);
let index: FxHashMap<_, _> =
nodes.iter_enumerated().map(|(idx, &dep_node)| (dep_node, idx)).collect();
@ -140,11 +228,151 @@ fn decode(d: &mut MemDecoder<'a>) -> SerializedDepGraph<K> {
}
}
#[derive(Debug, Encodable, Decodable)]
pub struct NodeInfo<K: DepKind> {
/// A packed representation of all the fixed-size fields in a `NodeInfo`.
///
/// This stores in one byte array:
/// * The `Fingerprint` in the `NodeInfo`
/// * The `Fingerprint` in `DepNode` that is in this `NodeInfo`
/// * The `DepKind`'s discriminant (a u16, but not all bits are used...)
/// * The byte width of the encoded edges for this node
/// * In whatever bits remain, the length of the edge list for this node, if it fits
struct SerializedNodeHeader<K> {
// 2 bytes for the DepNode
// 16 for Fingerprint in DepNode
// 16 for Fingerprint in NodeInfo
bytes: [u8; 34],
_marker: PhantomData<K>,
}
// The fields of a `SerializedNodeHeader`, this struct is an implementation detail and exists only
// to make the implementation of `SerializedNodeHeader` simpler.
struct Unpacked<K> {
len: Option<usize>,
bytes_per_index: usize,
kind: K,
hash: PackedFingerprint,
fingerprint: Fingerprint,
}
// Bit fields are
// 0..? length of the edge
// ?..?+2 bytes per index
// ?+2..16 kind
impl<K: DepKind> SerializedNodeHeader<K> {
const TOTAL_BITS: usize = std::mem::size_of::<K>() * 8;
const LEN_BITS: usize = Self::TOTAL_BITS - Self::KIND_BITS - Self::WIDTH_BITS;
const WIDTH_BITS: usize = DEP_NODE_WIDTH_BITS;
const KIND_BITS: usize = Self::TOTAL_BITS - K::MAX.leading_zeros() as usize;
const MAX_INLINE_LEN: usize = (u16::MAX as usize >> (Self::TOTAL_BITS - Self::LEN_BITS)) - 1;
#[inline]
fn new(node_info: &NodeInfo<K>) -> Self {
debug_assert_eq!(Self::TOTAL_BITS, Self::LEN_BITS + Self::WIDTH_BITS + Self::KIND_BITS);
let NodeInfo { node, fingerprint, edges } = node_info;
let mut head = node.kind.to_u16();
let free_bytes = edges.max_index().leading_zeros() as usize / 8;
let bytes_per_index = (DEP_NODE_SIZE - free_bytes).saturating_sub(1);
head |= (bytes_per_index as u16) << Self::KIND_BITS;
// Encode number of edges + 1 so that we can reserve 0 to indicate that the len doesn't fit
// in this bitfield.
if edges.len() <= Self::MAX_INLINE_LEN {
head |= (edges.len() as u16 + 1) << (Self::KIND_BITS + Self::WIDTH_BITS);
}
let hash: Fingerprint = node.hash.into();
// Using half-open ranges ensures an unconditional panic if we get the magic numbers wrong.
let mut bytes = [0u8; 34];
bytes[..2].copy_from_slice(&head.to_le_bytes());
bytes[2..18].copy_from_slice(&hash.to_le_bytes());
bytes[18..].copy_from_slice(&fingerprint.to_le_bytes());
#[cfg(debug_assertions)]
{
let res = Self { bytes, _marker: PhantomData };
assert_eq!(node_info.fingerprint, res.fingerprint());
assert_eq!(node_info.node, res.node());
if let Some(len) = res.len() {
assert_eq!(node_info.edges.len(), len);
}
}
Self { bytes, _marker: PhantomData }
}
#[inline]
fn unpack(&self) -> Unpacked<K> {
let head = u16::from_le_bytes(self.bytes[..2].try_into().unwrap());
let hash = self.bytes[2..18].try_into().unwrap();
let fingerprint = self.bytes[18..].try_into().unwrap();
let kind = head & mask(Self::KIND_BITS) as u16;
let bytes_per_index = (head >> Self::KIND_BITS) & mask(Self::WIDTH_BITS) as u16;
let len = (head as usize) >> (Self::WIDTH_BITS + Self::KIND_BITS);
Unpacked {
len: len.checked_sub(1),
bytes_per_index: bytes_per_index as usize + 1,
kind: DepKind::from_u16(kind),
hash: Fingerprint::from_le_bytes(hash).into(),
fingerprint: Fingerprint::from_le_bytes(fingerprint),
}
}
#[inline]
fn len(&self) -> Option<usize> {
self.unpack().len
}
#[inline]
fn bytes_per_index(&self) -> usize {
self.unpack().bytes_per_index
}
#[inline]
fn fingerprint(&self) -> Fingerprint {
self.unpack().fingerprint
}
#[inline]
fn node(&self) -> DepNode<K> {
let Unpacked { kind, hash, .. } = self.unpack();
DepNode { kind, hash }
}
#[inline]
fn edges_header(&self, edge_list_data: &[u8]) -> EdgeHeader {
EdgeHeader {
repr: (edge_list_data.len() << DEP_NODE_WIDTH_BITS) | (self.bytes_per_index() - 1),
}
}
}
#[derive(Debug)]
struct NodeInfo<K: DepKind> {
node: DepNode<K>,
fingerprint: Fingerprint,
edges: SmallVec<[DepNodeIndex; 8]>,
edges: EdgesVec,
}
impl<K: DepKind> Encodable<FileEncoder> for NodeInfo<K> {
fn encode(&self, e: &mut FileEncoder) {
let header = SerializedNodeHeader::new(self);
e.emit_raw_bytes(&header.bytes);
if header.len().is_none() {
e.emit_usize(self.edges.len());
}
let bytes_per_index = header.bytes_per_index();
for node_index in self.edges.iter() {
let bytes = node_index.as_u32().to_le_bytes();
e.emit_raw_bytes(&bytes[..bytes_per_index]);
}
}
}
struct Stat<K: DepKind> {
@ -303,7 +531,7 @@ pub(crate) fn send(
profiler: &SelfProfilerRef,
node: DepNode<K>,
fingerprint: Fingerprint,
edges: SmallVec<[DepNodeIndex; 8]>,
edges: EdgesVec,
) -> DepNodeIndex {
let _prof_timer = profiler.generic_activity("incr_comp_encode_dep_graph");
let node = NodeInfo { node, fingerprint, edges };

1
compiler/rustc_query_system/src/lib.rs
View File

@ -4,6 +4,7 @@
#![feature(min_specialization)]
#![feature(extern_types)]
#![feature(let_chains)]
#![feature(inline_const)]
#![allow(rustc::potential_query_instability)]
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]

2
compiler/rustc_serialize/src/opaque.rs
View File

@ -353,7 +353,7 @@ fn decoder_exhausted() -> ! {
}
#[inline]
fn read_array<const N: usize>(&mut self) -> [u8; N] {
pub fn read_array<const N: usize>(&mut self) -> [u8; N] {
self.read_raw_bytes(N).try_into().unwrap()
}