Lift `T: Sized` bounds from some `strict_provenance` pointer methods
This PR removes requirement for `T` (pointee type) to be `Sized` to call `pointer::{addr, expose_addr, with_addr, map_addr}`. These functions don't use `T`'s size, so there is no reason for them to require this. Updated public API:
cc ``@Gankra,`` #95228
r? libs-api
add ptr::from_{ref,mut}
We have methods to avoid almost all `as` casts around raw pointer handling, except for the initial cast from reference to raw pointer. These new methods close that gap.
(I also moved `null_mut` next to `null` to keep the file consistently organized.)
r? libs-api
Tracking issue: https://github.com/rust-lang/rust/issues/106116
Constify remaining `Layout` methods
Makes the methods on `Layout` that aren't yet unstably const, under the same feature and issue, #67521. Most of them required no changes, only non-trivial change is probably constifying `ValidAlignment` which may affect #102072
* Fix doc examples for Platforms with underaligned integer primitives.
* Mutable pointer doc examples use mutable pointers.
* Fill out tracking issue.
* Minor formatting changes.
Simplify some pointer method implementations
- Make `pointer::with_metadata_of` const (+simplify implementation) (cc #75091)
- Simplify implementation of various pointer methods
r? ```@scottmcm```
----
`from_raw_parts::<T>(this, metadata(self))` was annoying me for a while and I've finally figured out how it should _actually_ be done.
Fix mod_inv termination for the last iteration
On usize=u64 platforms, the 4th iteration would overflow the `mod_gate` back to 0. Similarly for usize=u32 platforms, the 3rd iteration would overflow much the same way.
I tested various approaches to resolving this, including approaches with `saturating_mul` and `widening_mul` to a double usize. Turns out LLVM likes `mul_with_overflow` the best. In fact now, that LLVM can see the iteration count is limited, it will happily unroll the loop into a nice linear sequence.
You will also notice that the code around the loop got simplified somewhat. Now that LLVM is handling the loop nicely, there isn’t any more reasons to manually unroll the first iteration out of the loop (though looking at the code today I’m not sure all that complexity was necessary in the first place).
Fixes#103361
Make `pointer::byte_offset_from` more generic
As suggested by https://github.com/rust-lang/rust/issues/96283#issuecomment-1288792955 (cc ````@scottmcm),```` make `pointer::byte_offset_from` work on pointers of different types. `byte_offset_from` really doesn't care about pointer types, so this is totally fine and, for example, allows patterns like this:
```rust
ptr::addr_of!(x.b).byte_offset_from(ptr::addr_of!(x))
```
The only possible downside is that this removes the `T` == `U` hint to inference, but I don't think this matter much. I don't think there are a lot of cases where you'd want to use `byte_offset_from` with a pointer of unbounded type (and in such cases you can just specify the type).
````@rustbot```` label +T-libs-api
interpret: support for per-byte provenance
Also factors the provenance map into its own module.
The third commit does the same for the init mask. I can move it in a separate PR if you prefer.
Fixes https://github.com/rust-lang/miri/issues/2181
r? `@oli-obk`
Add `rustc_deny_explicit_impl`
Also adjust `E0322` error message to be more general, since it's used for `DiscriminantKind` and `Pointee` as well.
Also add `rustc_deny_explicit_impl` on the `Tuple` and `Destruct` marker traits.
Add small clarification around using pointers derived from references
r? `@RalfJung`
One question about your example from https://github.com/rust-lang/libs-team/issues/122: at what point does UB arise? If writing 0 does not cause UB and the reference `x` is never read or written to (explicitly or implicitly by being wrapped in another data structure) after the call to `foo`, does UB only arise when dropping the value? I don't really get that since I thought references were always supposed to point to valid data?
```rust
fn foo(x: &mut NonZeroI32) {
let ptr = x as *mut NonZeroI32;
unsafe { ptr.cast::<i32>().write(0); } // no UB here
// What now? x is considered garbage when?
}
```
