bjoernager/rust
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Refactor tagged ptr packing into a function

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This commit is contained in:
Maybe Waffle 2023-04-11 21:40:39 +00:00
parent 3c6f4c1260
commit 12fd610e01
1 changed files with 21 additions and 22 deletions
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43
compiler/rustc_data_structures/src/tagged_ptr/copy.rs
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@ -50,6 +50,10 @@ where
P: Pointer,
T: Tag,
{
pub fn new(pointer: P, tag: T) -> Self {
Self { packed: Self::pack(P::into_ptr(pointer), tag), data: PhantomData }
}
const TAG_BIT_SHIFT: usize = usize::BITS as usize - T::BITS;
const ASSERTION: () = {
assert!(T::BITS <= P::BITS);
@ -58,28 +62,28 @@ where
assert!(std::mem::size_of::<&P::Target>() == std::mem::size_of::<usize>());
};
pub fn new(pointer: P, tag: T) -> Self {
/// Pack pointer `ptr` that comes from [`P::into_ptr`] with a `tag`.
///
/// [`P::into_ptr`]: Pointer::into_ptr
fn pack(ptr: NonNull<P::Target>, tag: T) -> NonNull<P::Target> {
// Trigger assert!
let () = Self::ASSERTION;
let packed_tag = tag.into_usize() << Self::TAG_BIT_SHIFT;
Self {
packed: P::into_ptr(pointer).map_addr(|addr| {
// SAFETY:
// - The pointer is `NonNull` => it's address is `NonZeroUsize`
// - `P::BITS` least significant bits are always zero (`Pointer` contract)
// - `T::BITS <= P::BITS` (from `Self::ASSERTION`)
//
// Thus `addr >> T::BITS` is guaranteed to be non-zero.
//
// `{non_zero} | packed_tag` can't make the value zero.
ptr.map_addr(|addr| {
// SAFETY:
// - The pointer is `NonNull` => it's address is `NonZeroUsize`
// - `P::BITS` least significant bits are always zero (`Pointer` contract)
// - `T::BITS <= P::BITS` (from `Self::ASSERTION`)
//
// Thus `addr >> T::BITS` is guaranteed to be non-zero.
//
// `{non_zero} | packed_tag` can't make the value zero.
let packed = (addr.get() >> T::BITS) | packed_tag;
unsafe { NonZeroUsize::new_unchecked(packed) }
}),
data: PhantomData,
}
let packed = (addr.get() >> T::BITS) | packed_tag;
unsafe { NonZeroUsize::new_unchecked(packed) }
})
}
pub(super) fn pointer_raw(&self) -> NonNull<P::Target> {
@ -117,12 +121,7 @@ where
#[inline]
pub fn set_tag(&mut self, tag: T) {
// TODO: refactor packing into a function and reuse it here
let new_tag = T::into_usize(tag) << Self::TAG_BIT_SHIFT;
let tag_mask = (1 << T::BITS) - 1;
self.packed = self.packed.map_addr(|addr| unsafe {
NonZeroUsize::new_unchecked(addr.get() & !(tag_mask << Self::TAG_BIT_SHIFT) | new_tag)
});
self.packed = Self::pack(self.pointer_raw(), tag);
}
}