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Rollup merge of rust-lang#110950 - JohnBobbo96:rustc_arena_unsafe_fn,…
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… r=Nilstrieb

Deny the `unsafe_op_in_unsafe_fn` lint in `rustc_arena`.

r? `@Nilstrieb`
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GuillaumeGomez authored Apr 29, 2023
2 parents 7736e83 + 47fb8e6 commit 4a702c0
Showing 1 changed file with 31 additions and 11 deletions.
42 changes: 31 additions & 11 deletions compiler/rustc_arena/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
#![feature(rustc_attrs)]
#![cfg_attr(test, feature(test))]
#![feature(strict_provenance)]
#![deny(unsafe_op_in_unsafe_fn)]
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
#![allow(clippy::mut_from_ref)] // Arena allocators are one of the places where this pattern is fine.
Expand Down Expand Up @@ -74,19 +75,27 @@ impl<T> ArenaChunk<T> {
#[inline]
unsafe fn new(capacity: usize) -> ArenaChunk<T> {
ArenaChunk {
storage: NonNull::new_unchecked(Box::into_raw(Box::new_uninit_slice(capacity))),
storage: NonNull::from(Box::leak(Box::new_uninit_slice(capacity))),
entries: 0,
}
}

/// Destroys this arena chunk.
///
/// # Safety
///
/// The caller must ensure that `len` elements of this chunk have been initialized.
#[inline]
unsafe fn destroy(&mut self, len: usize) {
// The branch on needs_drop() is an -O1 performance optimization.
// Without the branch, dropping TypedArena<u8> takes linear time.
// Without the branch, dropping TypedArena<T> takes linear time.
if mem::needs_drop::<T>() {
let slice = self.storage.as_mut();
ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(&mut slice[..len]));
// SAFETY: The caller must ensure that `len` elements of this chunk have
// been initialized.
unsafe {
let slice = self.storage.as_mut();
ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(&mut slice[..len]));
}
}
}

Expand Down Expand Up @@ -255,7 +264,9 @@ impl<T> TypedArena<T> {
self.ensure_capacity(len);

let start_ptr = self.ptr.get();
self.ptr.set(start_ptr.add(len));
// SAFETY: `self.ensure_capacity` makes sure that there is enough space
// for `len` elements.
unsafe { self.ptr.set(start_ptr.add(len)) };
start_ptr
}

Expand Down Expand Up @@ -483,6 +494,10 @@ impl DroplessArena {
}
}

/// # Safety
///
/// The caller must ensure that `mem` is valid for writes up to
/// `size_of::<T>() * len`.
#[inline]
unsafe fn write_from_iter<T, I: Iterator<Item = T>>(
&self,
Expand All @@ -494,13 +509,18 @@ impl DroplessArena {
// Use a manual loop since LLVM manages to optimize it better for
// slice iterators
loop {
let value = iter.next();
if i >= len || value.is_none() {
// We only return as many items as the iterator gave us, even
// though it was supposed to give us `len`
return slice::from_raw_parts_mut(mem, i);
// SAFETY: The caller must ensure that `mem` is valid for writes up to
// `size_of::<T>() * len`.
unsafe {
match iter.next() {
Some(value) if i < len => mem.add(i).write(value),
Some(_) | None => {
// We only return as many items as the iterator gave us, even
// though it was supposed to give us `len`
return slice::from_raw_parts_mut(mem, i);
}
}
}
ptr::write(mem.add(i), value.unwrap());
i += 1;
}
}
Expand Down

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