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matthiaskrgrmatthiaskrgr
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Rollup merge of #108039 - eggyal:traverse_refcounts_via_functors, r=oli-obk
Refactor refcounted structural_impls via functors The mapping of values in refcounted types can be extracted as a functor, simplifying the implementations in the type library (whose structural folding impls now all use such functors). This functor could also prove more generally useful elsewhere.
2 parents edcdab0 + 26e3363 commit 207d6e1

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4 files changed

+55
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lines changed

‎compiler/rustc_data_structures/src/functor.rs

Lines changed: 50 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
use rustc_index::vec::{Idx, IndexVec};
2-
use std::mem;
2+
use std::{mem, rc::Rc, sync::Arc};
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pub trait IdFunctor: Sized {
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type Inner;
@@ -65,3 +65,52 @@ impl<I: Idx, T> IdFunctor for IndexVec<I, T> {
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self.raw.try_map_id(f).map(IndexVec::from_raw)
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}
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}
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macro_rules! rc {
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($($rc:ident),+) => {$(
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impl<T: Clone> IdFunctor for $rc<T> {
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type Inner = T;
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#[inline]
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fn try_map_id<F, E>(mut self, mut f: F) -> Result<Self, E>
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where
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F: FnMut(Self::Inner) -> Result<Self::Inner, E>,
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{
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// We merely want to replace the contained `T`, if at all possible,
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// so that we don't needlessly allocate a new `$rc` or indeed clone
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// the contained type.
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unsafe {
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// First step is to ensure that we have a unique reference to
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// the contained type, which `$rc::make_mut` will accomplish (by
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// allocating a new `$rc` and cloning the `T` only if required).
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// This is done *before* casting to `$rc<ManuallyDrop<T>>` so that
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// panicking during `make_mut` does not leak the `T`.
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$rc::make_mut(&mut self);
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// Casting to `$rc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
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// is `repr(transparent)`.
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let ptr = $rc::into_raw(self).cast::<mem::ManuallyDrop<T>>();
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let mut unique = $rc::from_raw(ptr);
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// Call to `$rc::make_mut` above guarantees that `unique` is the
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// sole reference to the contained value, so we can avoid doing
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// a checked `get_mut` here.
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let slot = $rc::get_mut_unchecked(&mut unique);
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// Semantically move the contained type out from `unique`, fold
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// it, then move the folded value back into `unique`. Should
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// folding fail, `ManuallyDrop` ensures that the "moved-out"
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// value is not re-dropped.
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let owned = mem::ManuallyDrop::take(slot);
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let folded = f(owned)?;
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*slot = mem::ManuallyDrop::new(folded);
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// Cast back to `$rc<T>`.
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Ok($rc::from_raw($rc::into_raw(unique).cast()))
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}
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}
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}
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)+};
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}
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rc! { Rc, Arc }

‎compiler/rustc_data_structures/src/lib.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,7 @@
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#![feature(test)]
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#![feature(thread_id_value)]
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#![feature(vec_into_raw_parts)]
29+
#![feature(get_mut_unchecked)]
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#![allow(rustc::default_hash_types)]
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#![allow(rustc::potential_query_instability)]
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#![deny(rustc::untranslatable_diagnostic)]

‎compiler/rustc_type_ir/src/lib.rs

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,5 @@
11
#![feature(associated_type_defaults)]
22
#![feature(fmt_helpers_for_derive)]
3-
#![feature(get_mut_unchecked)]
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#![feature(min_specialization)]
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#![feature(never_type)]
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#![feature(rustc_attrs)]

‎compiler/rustc_type_ir/src/structural_impls.rs

Lines changed: 4 additions & 67 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,6 @@ use crate::Interner;
88
use rustc_data_structures::functor::IdFunctor;
99
use rustc_index::vec::{Idx, IndexVec};
1010

11-
use std::mem::ManuallyDrop;
1211
use std::ops::ControlFlow;
1312
use std::rc::Rc;
1413
use std::sync::Arc;
@@ -98,39 +97,8 @@ EnumTypeTraversalImpl! {
9897
}
9998

10099
impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Rc<T> {
101-
fn try_fold_with<F: FallibleTypeFolder<I>>(mut self, folder: &mut F) -> Result<Self, F::Error> {
102-
// We merely want to replace the contained `T`, if at all possible,
103-
// so that we don't needlessly allocate a new `Rc` or indeed clone
104-
// the contained type.
105-
unsafe {
106-
// First step is to ensure that we have a unique reference to
107-
// the contained type, which `Rc::make_mut` will accomplish (by
108-
// allocating a new `Rc` and cloning the `T` only if required).
109-
// This is done *before* casting to `Rc<ManuallyDrop<T>>` so that
110-
// panicking during `make_mut` does not leak the `T`.
111-
Rc::make_mut(&mut self);
112-
113-
// Casting to `Rc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
114-
// is `repr(transparent)`.
115-
let ptr = Rc::into_raw(self).cast::<ManuallyDrop<T>>();
116-
let mut unique = Rc::from_raw(ptr);
117-
118-
// Call to `Rc::make_mut` above guarantees that `unique` is the
119-
// sole reference to the contained value, so we can avoid doing
120-
// a checked `get_mut` here.
121-
let slot = Rc::get_mut_unchecked(&mut unique);
122-
123-
// Semantically move the contained type out from `unique`, fold
124-
// it, then move the folded value back into `unique`. Should
125-
// folding fail, `ManuallyDrop` ensures that the "moved-out"
126-
// value is not re-dropped.
127-
let owned = ManuallyDrop::take(slot);
128-
let folded = owned.try_fold_with(folder)?;
129-
*slot = ManuallyDrop::new(folded);
130-
131-
// Cast back to `Rc<T>`.
132-
Ok(Rc::from_raw(Rc::into_raw(unique).cast()))
133-
}
100+
fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
101+
self.try_map_id(|value| value.try_fold_with(folder))
134102
}
135103
}
136104

@@ -141,39 +109,8 @@ impl<I: Interner, T: TypeVisitable<I>> TypeVisitable<I> for Rc<T> {
141109
}
142110

143111
impl<I: Interner, T: TypeFoldable<I>> TypeFoldable<I> for Arc<T> {
144-
fn try_fold_with<F: FallibleTypeFolder<I>>(mut self, folder: &mut F) -> Result<Self, F::Error> {
145-
// We merely want to replace the contained `T`, if at all possible,
146-
// so that we don't needlessly allocate a new `Arc` or indeed clone
147-
// the contained type.
148-
unsafe {
149-
// First step is to ensure that we have a unique reference to
150-
// the contained type, which `Arc::make_mut` will accomplish (by
151-
// allocating a new `Arc` and cloning the `T` only if required).
152-
// This is done *before* casting to `Arc<ManuallyDrop<T>>` so that
153-
// panicking during `make_mut` does not leak the `T`.
154-
Arc::make_mut(&mut self);
155-
156-
// Casting to `Arc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
157-
// is `repr(transparent)`.
158-
let ptr = Arc::into_raw(self).cast::<ManuallyDrop<T>>();
159-
let mut unique = Arc::from_raw(ptr);
160-
161-
// Call to `Arc::make_mut` above guarantees that `unique` is the
162-
// sole reference to the contained value, so we can avoid doing
163-
// a checked `get_mut` here.
164-
let slot = Arc::get_mut_unchecked(&mut unique);
165-
166-
// Semantically move the contained type out from `unique`, fold
167-
// it, then move the folded value back into `unique`. Should
168-
// folding fail, `ManuallyDrop` ensures that the "moved-out"
169-
// value is not re-dropped.
170-
let owned = ManuallyDrop::take(slot);
171-
let folded = owned.try_fold_with(folder)?;
172-
*slot = ManuallyDrop::new(folded);
173-
174-
// Cast back to `Arc<T>`.
175-
Ok(Arc::from_raw(Arc::into_raw(unique).cast()))
176-
}
112+
fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
113+
self.try_map_id(|value| value.try_fold_with(folder))
177114
}
178115
}
179116

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