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Use NonNull::new_unchecked and NonNull::len in rustc_arena. #110921

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merged 1 commit into from
Apr 29, 2023
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Use NonNull::new_unchecked and NonNull::len in rustc_arena. #110921

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10 changes: 5 additions & 5 deletions compiler/rustc_arena/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ impl<T> ArenaChunk<T> {
#[inline]
unsafe fn new(capacity: usize) -> ArenaChunk<T> {
ArenaChunk {
storage: NonNull::new(Box::into_raw(Box::new_uninit_slice(capacity))).unwrap(),
storage: NonNull::new_unchecked(Box::into_raw(Box::new_uninit_slice(capacity))),
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This is a very nice example of why unsafe_op_in_unsafe_fn not being on by default is a big mistake. The safety condition of the function (which I actually don't know because it's not documented :/) has nothing to do with the safety condition of new_umchecked.

I'd love to take a PR denying that lint on rustc_arena if you want to.

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i have created a PR for this here #110950.

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Suggested change
storage: NonNull::new_unchecked(Box::into_raw(Box::new_uninit_slice(capacity))),
storage: NonNull::from(Box::leak(Box::new_uninit_slice(capacity))),

entries: 0,
}
}
Expand All @@ -85,7 +85,7 @@ impl<T> ArenaChunk<T> {
// The branch on needs_drop() is an -O1 performance optimization.
// Without the branch, dropping TypedArena<u8> takes linear time.
if mem::needs_drop::<T>() {
let slice = &mut *(self.storage.as_mut());
let slice = self.storage.as_mut();
ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(&mut slice[..len]));
}
}
Expand All @@ -104,7 +104,7 @@ impl<T> ArenaChunk<T> {
// A pointer as large as possible for zero-sized elements.
ptr::invalid_mut(!0)
} else {
self.start().add((*self.storage.as_ptr()).len())
self.start().add(self.storage.len())
}
}
}
Expand Down Expand Up @@ -288,7 +288,7 @@ impl<T> TypedArena<T> {
// If the previous chunk's len is less than HUGE_PAGE
// bytes, then this chunk will be least double the previous
// chunk's size.
new_cap = (*last_chunk.storage.as_ptr()).len().min(HUGE_PAGE / elem_size / 2);
new_cap = last_chunk.storage.len().min(HUGE_PAGE / elem_size / 2);
new_cap *= 2;
} else {
new_cap = PAGE / elem_size;
Expand Down Expand Up @@ -396,7 +396,7 @@ impl DroplessArena {
// If the previous chunk's len is less than HUGE_PAGE
// bytes, then this chunk will be least double the previous
// chunk's size.
new_cap = (*last_chunk.storage.as_ptr()).len().min(HUGE_PAGE / 2);
new_cap = last_chunk.storage.len().min(HUGE_PAGE / 2);
new_cap *= 2;
} else {
new_cap = PAGE;
Expand Down