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Use strict_provenance

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This commit is contained in:
Lukas Wirth 2025-01-10 15:17:07 +01:00
parent b7a3d606ea
commit 090a145d44
4 changed files with 8 additions and 39 deletions
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37
crates/intern/src/symbol.rs
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@ -13,7 +13,6 @@ use std::{
use dashmap::{DashMap, SharedValue};
use hashbrown::{hash_map::RawEntryMut, HashMap};
use rustc_hash::FxHasher;
use sptr::Strict;
use triomphe::Arc;
pub mod symbols;
@ -84,7 +83,7 @@ impl TaggedArcPtr {
#[inline]
pub(crate) unsafe fn try_as_arc_owned(self) -> Option<ManuallyDrop<Arc<Box<str>>>> {
// Unpack the tag from the alignment niche
let tag = Strict::addr(self.packed.as_ptr()) & Self::BOOL_BITS;
let tag = self.packed.as_ptr().addr() & Self::BOOL_BITS;
if tag != 0 {
// Safety: We checked that the tag is non-zero -> true, so we are pointing to the data offset of an `Arc`
Some(ManuallyDrop::new(unsafe {
@ -99,40 +98,18 @@ impl TaggedArcPtr {
fn pack_arc(ptr: NonNull<*const str>) -> NonNull<*const str> {
let packed_tag = true as usize;
// can't use this strict provenance stuff here due to trait methods not being const
// unsafe {
// // Safety: The pointer is derived from a non-null
// NonNull::new_unchecked(Strict::map_addr(ptr.as_ptr(), |addr| {
// // Safety:
// // - The pointer is `NonNull` => it's address is `NonZero<usize>`
// // - `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.
// (addr >> Self::BOOL_BITS) | packed_tag
// }))
// }
// so what follows is roughly what the above looks like but inlined
let self_addr = ptr.as_ptr() as *const *const str as usize;
let addr = self_addr | packed_tag;
let dest_addr = addr as isize;
let offset = dest_addr.wrapping_sub(self_addr as isize);
// SAFETY: The resulting pointer is guaranteed to be NonNull as we only modify the niche bytes
unsafe { NonNull::new_unchecked(ptr.as_ptr().cast::<u8>().wrapping_offset(offset).cast()) }
unsafe {
// Safety: The pointer is derived from a non-null and bit-oring it with true (1) will
// not make it null.
NonNull::new_unchecked(ptr.as_ptr().map_addr(|addr| addr | packed_tag))
}
}
#[inline]
pub(crate) fn pointer(self) -> NonNull<*const str> {
// SAFETY: The resulting pointer is guaranteed to be NonNull as we only modify the niche bytes
unsafe {
NonNull::new_unchecked(Strict::map_addr(self.packed.as_ptr(), |addr| {
addr & !Self::BOOL_BITS
}))
NonNull::new_unchecked(self.packed.as_ptr().map_addr(|addr| addr & !Self::BOOL_BITS))
}
}