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test into_boxed_slice with custom allocator in Miri
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RalfJung committed Mar 10, 2024
1 parent 81ebaf2 commit a7443f5
Showing 1 changed file with 14 additions and 4 deletions.
18 changes: 14 additions & 4 deletions src/tools/miri/tests/pass/box-custom-alloc-aliasing.rs
Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,8 @@ unsafe impl Allocator for MyAllocator {
}

unsafe fn deallocate(&self, ptr: NonNull<u8>, _layout: Layout) {
// Make sure accesses via `self` don't disturb anything.
let _val = self.bins[0].top.get();
// Since manually finding the corresponding bin of `ptr` is very expensive,
// doing pointer arithmetics is preferred.
// But this means we access `top` via `ptr` rather than `self`!
Expand All @@ -101,22 +103,30 @@ unsafe impl Allocator for MyAllocator {
if self.thread_id == thread_id {
unsafe { (*their_bin).push(ptr) };
} else {
todo!("Deallocating from another thread")
todo!("Deallocating from another thread");
}
// Make sure we can also still access this via `self` after the rest is done.
let _val = self.bins[0].top.get();
}
}

// Make sure to involve `Box` in allocating these,
// as that's where `noalias` may come from.
fn v<T, A: Allocator>(t: T, a: A) -> Vec<T, A> {
fn v1<T, A: Allocator>(t: T, a: A) -> Vec<T, A> {
(Box::new_in([t], a) as Box<[T], A>).into_vec()
}
fn v2<T, A: Allocator>(t: T, a: A) -> Vec<T, A> {
let v = v1(t, a);
// There was a bug in `into_boxed_slice` that caused aliasing issues,
// so round-trip through that as well.
v.into_boxed_slice().into_vec()
}

fn main() {
assert!(mem::size_of::<MyBin>() <= 128); // if it grows bigger, the trick to access the "header" no longer works
let my_alloc = MyAllocator::new();
let a = v(1usize, &my_alloc);
let b = v(2usize, &my_alloc);
let a = v1(1usize, &my_alloc);
let b = v2(2usize, &my_alloc);
assert_eq!(a[0] + 1, b[0]);
assert_eq!(addr_of!(a[0]).wrapping_add(1), addr_of!(b[0]));
drop((a, b));
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