Erase query result types

Cargo.lock

@@ -3983,6 +3983,10 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "rustc_erase"
+version = "0.0.0"
+
 [[package]]
 name = "rustc_error_codes"
 version = "0.0.0"
@@ -4373,6 +4377,7 @@ dependencies = [
  "rustc_ast",
  "rustc_attr",
  "rustc_data_structures",
+ "rustc_erase",
  "rustc_error_messages",
  "rustc_errors",
  "rustc_feature",
@@ -4571,6 +4576,7 @@ dependencies = [
  "rustc-rayon-core",
  "rustc_ast",
  "rustc_data_structures",
+ "rustc_erase",
  "rustc_errors",
  "rustc_hir",
  "rustc_index",

compiler/rustc_data_structures/src/lib.rs

@@ -72,6 +72,7 @@ pub mod stable_hasher;
 mod atomic_ref;
 pub mod fingerprint;
 pub mod profiling;
+pub mod remap;
 pub mod sharded;
 pub mod stack;
 pub mod sync;

compiler/rustc_data_structures/src/remap.rs

@@ -0,0 +1,28 @@
+/// Remaps the type with a different lifetime for 'tcx if applicable.
+pub trait Remap {
+    type Remap<'a>;
+}
+
+impl Remap for u32 {
+    type Remap<'a> = u32;
+}
+
+impl<T: Remap> Remap for Option<T> {
+    type Remap<'a> = Option<T::Remap<'a>>;
+}
+
+impl Remap for () {
+    type Remap<'a> = ();
+}
+
+impl<T0: Remap, T1: Remap> Remap for (T0, T1) {
+    type Remap<'a> = (T0::Remap<'a>, T1::Remap<'a>);
+}
+
+impl<T0: Remap, T1: Remap, T2: Remap> Remap for (T0, T1, T2) {
+    type Remap<'a> = (T0::Remap<'a>, T1::Remap<'a>, T2::Remap<'a>);
+}
+
+impl<T0: Remap, T1: Remap, T2: Remap, T3: Remap> Remap for (T0, T1, T2, T3) {
+    type Remap<'a> = (T0::Remap<'a>, T1::Remap<'a>, T2::Remap<'a>, T3::Remap<'a>);
+}

compiler/rustc_data_structures/src/sharded.rs

@@ -1,14 +1,10 @@
 use crate::fx::{FxHashMap, FxHasher};
-use crate::sync::{Lock, LockGuard};
+use crate::sync::{CacheAligned, Lock, LockGuard};
 use std::borrow::Borrow;
 use std::collections::hash_map::RawEntryMut;
 use std::hash::{Hash, Hasher};
 use std::mem;
 
-#[derive(Clone, Default)]
-#[cfg_attr(parallel_compiler, repr(align(64)))]
-struct CacheAligned<T>(T);
-
 #[cfg(parallel_compiler)]
 // 32 shards is sufficient to reduce contention on an 8-core Ryzen 7 1700,
 // but this should be tested on higher core count CPUs. How the `Sharded` type gets used

compiler/rustc_data_structures/src/sync.rs

@@ -23,6 +23,9 @@ use std::hash::{BuildHasher, Hash};
 use std::ops::{Deref, DerefMut};
 use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe};
 
+mod worker_local;
+pub use worker_local::{Registry, WorkerLocal};
+
 pub use std::sync::atomic::Ordering;
 pub use std::sync::atomic::Ordering::SeqCst;
 
@@ -178,33 +181,6 @@ cfg_if! {
 
         use std::cell::Cell;
 
-        #[derive(Debug)]
-        pub struct WorkerLocal<T>(OneThread<T>);
-
-        impl<T> WorkerLocal<T> {
-            /// Creates a new worker local where the `initial` closure computes the
-            /// value this worker local should take for each thread in the thread pool.
-            #[inline]
-            pub fn new<F: FnMut(usize) -> T>(mut f: F) -> WorkerLocal<T> {
-                WorkerLocal(OneThread::new(f(0)))
-            }
-
-            /// Returns the worker-local value for each thread
-            #[inline]
-            pub fn into_inner(self) -> Vec<T> {
-                vec![OneThread::into_inner(self.0)]
-            }
-        }
-
-        impl<T> Deref for WorkerLocal<T> {
-            type Target = T;
-
-            #[inline(always)]
-            fn deref(&self) -> &T {
-                &self.0
-            }
-        }
-
         pub type MTRef<'a, T> = &'a mut T;
 
         #[derive(Debug, Default)]
@@ -324,8 +300,6 @@ cfg_if! {
             };
         }
 
-        pub use rayon_core::WorkerLocal;
-
         pub use rayon::iter::ParallelIterator;
         use rayon::iter::IntoParallelIterator;
 
@@ -365,6 +339,10 @@ pub fn assert_send<T: ?Sized + Send>() {}
 pub fn assert_send_val<T: ?Sized + Send>(_t: &T) {}
 pub fn assert_send_sync_val<T: ?Sized + Sync + Send>(_t: &T) {}
 
+#[derive(Clone, Default)]
+#[cfg_attr(parallel_compiler, repr(align(64)))]
+pub struct CacheAligned<T>(pub T);
+
 pub trait HashMapExt<K, V> {
     /// Same as HashMap::insert, but it may panic if there's already an
     /// entry for `key` with a value not equal to `value`

compiler/rustc_data_structures/src/sync/worker_local.rs

@@ -0,0 +1,189 @@
+use crate::sync::Lock;
+use std::cell::Cell;
+use std::cell::OnceCell;
+use std::ops::Deref;
+use std::sync::Arc;
+
+#[cfg(parallel_compiler)]
+use {crate::cold_path, crate::sync::CacheAligned};
+
+/// A pointer to the `RegistryData` which uniquely identifies a registry.
+/// This identifier can be reused if the registry gets freed.
+#[derive(Clone, Copy, Eq, PartialEq)]
+struct RegistryId(usize);
+
+impl RegistryId {
+    #[inline(always)]
+    /// Verifies that the current thread is associated with the registry and returns its unique
+    /// index within the registry. This panics if the current thread is not associated with this
+    /// registry.
+    ///
+    /// Note that there's a race possible where the identifer in `THREAD_DATA` could be reused
+    /// so this can succeed from a different registry.
+    #[cfg(parallel_compiler)]
+    fn verify(self) -> usize {
+        let (id, index) = THREAD_DATA.with(|data| (data.registry_id.get(), data.index.get()));
+
+        if id == self {
+            index
+        } else {
+            cold_path(|| panic!("Unable to verify registry association"))
+        }
+    }
+}
+
+struct RegistryData {
+    thread_limit: usize,
+    threads: Lock<usize>,
+}
+
+/// Represents a list of threads which can access worker locals.
+#[derive(Clone)]
+pub struct Registry(Arc<RegistryData>);
+
+thread_local! {
+    /// The registry associated with the thread.
+    /// This allows the `WorkerLocal` type to clone the registry in its constructor.
+    static REGISTRY: OnceCell<Registry> = OnceCell::new();
+}
+
+struct ThreadData {
+    registry_id: Cell<RegistryId>,
+    index: Cell<usize>,
+}
+
+thread_local! {
+    /// A thread local which contains the identifer of `REGISTRY` but allows for faster access.
+    /// It also holds the index of the current thread.
+    static THREAD_DATA: ThreadData = const { ThreadData {
+        registry_id: Cell::new(RegistryId(0)),
+        index: Cell::new(0),
+    }};
+}
+
+impl Registry {
+    /// Creates a registry which can hold up to `thread_limit` threads.
+    pub fn new(thread_limit: usize) -> Self {
+        Registry(Arc::new(RegistryData { thread_limit, threads: Lock::new(0) }))
+    }
+
+    /// Gets the registry associated with the current thread. Panics if there's no such registry.
+    pub fn current() -> Self {
+        REGISTRY.with(|registry| registry.get().cloned().expect("No assocated registry"))
+    }
+
+    /// Registers the current thread with the registry so worker locals can be used on it.
+    /// Panics if the thread limit is hit or if the thread already has an associated registry.
+    pub fn register(&self) {
+        let mut threads = self.0.threads.lock();
+        if *threads < self.0.thread_limit {
+            REGISTRY.with(|registry| {
+                if registry.get().is_some() {
+                    drop(threads);
+                    panic!("Thread already has a registry");
+                }
+                registry.set(self.clone()).ok();
+                THREAD_DATA.with(|data| {
+                    data.registry_id.set(self.id());
+                    data.index.set(*threads);
+                });
+                *threads += 1;
+            });
+        } else {
+            drop(threads);
+            panic!("Thread limit reached");
+        }
+    }
+
+    /// Gets the identifer of this registry.
+    fn id(&self) -> RegistryId {
+        RegistryId(&*self.0 as *const RegistryData as usize)
+    }
+}
+
+/// Holds worker local values for each possible thread in a registry. You can only access the
+/// worker local value through the `Deref` impl on the registry associated with the thread it was
+/// created on. It will panic otherwise.
+pub struct WorkerLocal<T> {
+    #[cfg(not(parallel_compiler))]
+    local: T,
+    #[cfg(parallel_compiler)]
+    locals: Box<[CacheAligned<T>]>,
+    #[cfg(parallel_compiler)]
+    registry: Registry,
+}
+
+// This is safe because the `deref` call will return a reference to a `T` unique to each thread
+// or it will panic for threads without an associated local. So there isn't a need for `T` to do
+// it's own synchronization. The `verify` method on `RegistryId` has an issue where the the id
+// can be reused, but `WorkerLocal` has a reference to `Registry` which will prevent any reuse.
+#[cfg(parallel_compiler)]
+unsafe impl<T: Send> Sync for WorkerLocal<T> {}
+
+impl<T> WorkerLocal<T> {
+    /// Creates a new worker local where the `initial` closure computes the
+    /// value this worker local should take for each thread in the registry.
+    #[inline]
+    pub fn new<F: FnMut(usize) -> T>(mut initial: F) -> WorkerLocal<T> {
+        #[cfg(parallel_compiler)]
+        {
+            let registry = Registry::current();
+            WorkerLocal {
+                locals: {
+                    let locals: Vec<_> =
+                        (0..registry.0.thread_limit).map(|i| CacheAligned(initial(i))).collect();
+                    locals.into_boxed_slice()
+                },
+                registry,
+            }
+        }
+        #[cfg(not(parallel_compiler))]
+        {
+            WorkerLocal { local: initial(0) }
+        }
+    }
+
+    /// Returns the worker-local value for each thread
+    #[inline]
+    pub fn into_inner(self) -> Vec<T> {
+        #[cfg(parallel_compiler)]
+        {
+            self.locals.into_vec().into_iter().map(|local| local.0).collect()
+        }
+        #[cfg(not(parallel_compiler))]
+        {
+            vec![self.local]
+        }
+    }
+}
+
+impl<T> WorkerLocal<Vec<T>> {
+    /// Joins the elements of all the worker locals into one Vec
+    pub fn join(self) -> Vec<T> {
+        self.into_inner().into_iter().flat_map(|v| v).collect()
+    }
+}
+
+impl<T: Default> Default for WorkerLocal<T> {
+    fn default() -> Self {
+        WorkerLocal::new(|_| T::default())
+    }
+}
+
+impl<T> Deref for WorkerLocal<T> {
+    type Target = T;
+
+    #[inline(always)]
+    #[cfg(not(parallel_compiler))]
+    fn deref(&self) -> &T {
+        &self.local
+    }
+
+    #[inline(always)]
+    #[cfg(parallel_compiler)]
+    fn deref(&self) -> &T {
+        // This is safe because `verify` will only return values less than
+        // `self.registry.thread_limit` which is the size of the `self.locals` array.
+        unsafe { &self.locals.get_unchecked(self.registry.id().verify()).0 }
+    }
+}

compiler/rustc_erase/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "rustc_erase"
+version = "0.0.0"
+edition = "2021"
+
+[lib]

compiler/rustc_erase/src/lib.rs

@@ -0,0 +1,46 @@
+// This is a separate crate so that we can `allow(incomplete_features)` for just `generic_const_exprs`
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+#[cfg(debug_assertions)]
+use std::intrinsics::type_name;
+use std::{
+    fmt,
+    mem::{size_of, transmute_copy, MaybeUninit},
+};
+
+#[derive(Copy, Clone)]
+pub struct Erased<const N: usize> {
+    data: MaybeUninit<[u8; N]>,
+    #[cfg(debug_assertions)]
+    type_id: &'static str,
+}
+
+impl<const N: usize> fmt::Debug for Erased<N> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Erased<{}>", N)
+    }
+}
+
+pub type Erase<T> = Erased<{ size_of::<T>() }>;
+
+#[inline(always)]
+pub fn erase<T: Copy>(src: T) -> Erased<{ size_of::<T>() }> {
+    Erased {
+        // SAFETY:: Is it safe to transmute to MaybeUninit
+        data: unsafe { transmute_copy(&src) },
+        #[cfg(debug_assertions)]
+        type_id: type_name::<T>(),
+    }
+}
+
+/// Restores an erased value.
+///
+/// This is only safe if `value` is a valid instance of `T`.
+/// For example if `T` was erased with `erase` previously.
+#[inline(always)]
+pub unsafe fn restore<T: Copy>(value: Erased<{ size_of::<T>() }>) -> T {
+    #[cfg(debug_assertions)]
+    assert_eq!(value.type_id, type_name::<T>());
+    unsafe { transmute_copy(&value.data) }
+}