Repository: rust
Issue: Tracking Issue for arithmetic and certain bitwise ops on `AtomicPtr`
Labels: T-libs-api,C-tracking-issue

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Feature gate: `#![feature(strict_provenance_atomic_ptr)]`

This is a tracking issue for arithmetic and certain bitwise operations on `AtomicPtr`.
As part of the strict provenance experiment  #95228.

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This feature adds arithmetic (`add`, `sub`) and bitwise (`or`, `end`, `xor`) atomic operations for `AtomicPtr` in order to replace uses of `AtomicUsize`-but-actually-a-pointer to preserve provenance information for the compiler and remove `usize`->`ptr` casts from existing code.

Arithmetic ops behave as the their non-atomic **wrapping** versions. Bitwise ops behave as `.map_addr(|x| x op val)`.
### Public API

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```rust
// core::sync::atomic

impl<T> AtomicPtr<T> {
    pub fn fetch_ptr_add(&self, val: usize, order: Ordering) -> *mut T;
    pub fn fetch_ptr_sub(&self, val: usize, order: Ordering) -> *mut T;

    pub fn fetch_byte_add(&self, val: usize, order: Ordering) -> *mut T;
    pub fn fetch_byte_sub(&self, val: usize, order: Ordering) -> *mut T;

    pub fn fetch_or(&self, val: usize, order: Ordering) -> *mut T;
    pub fn fetch_and(&self, val: usize, order: Ordering) -> *mut T;
    pub fn fetch_xor(&self, val: usize, order: Ordering) -> *mut T;
}
```

### Steps / History

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- [x] Implementation: #96935
- [ ] Final comment period (FCP)[^1]
- [ ] Stabilization PR

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### Unresolved Questions

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- Naming (some discussion at https://github.com/rust-lang/libs-team/issues/126)


[^1]: https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html