simplify eat_digits
Simplify eat_digits by checking values in iterator, plus decrease function size, by returning unchecked slices.
https://godbolt.org/z/cxjav4
Add tests for Atomic*::fetch_{min,max}
This ensures that all atomic operations except for fences are tested. This has been useful to test my work on using atomic instructions for atomic operations in cg_clif instead of a global lock.
Ensure valid TraitRefs are created for GATs
This fixes `ProjectionTy::trait_ref` to use the correct substs. Places that need all of the substs have been updated to not use `trait_ref`.
r? ````@jackh726````
Implement RFC 2580: Pointer metadata & VTable
RFC: https://github.com/rust-lang/rfcs/pull/2580
~~Before merging this PR:~~
* [x] Wait for the end of the RFC’s [FCP to merge](https://github.com/rust-lang/rfcs/pull/2580#issuecomment-759145278).
* [x] Open a tracking issue: https://github.com/rust-lang/rust/issues/81513
* [x] Update `#[unstable]` attributes in the PR with the tracking issue number
----
This PR extends the language with a new lang item for the `Pointee` trait which is special-cased in trait resolution to implement it for all types. Even in generic contexts, parameters can be assumed to implement it without a corresponding bound.
For this I mostly imitated what the compiler was already doing for the `DiscriminantKind` trait. I’m very unfamiliar with compiler internals, so careful review is appreciated.
This PR also extends the standard library with new unstable APIs in `core::ptr` and `std::ptr`:
```rust
pub trait Pointee {
/// One of `()`, `usize`, or `DynMetadata<dyn SomeTrait>`
type Metadata: Copy + Send + Sync + Ord + Hash + Unpin;
}
pub trait Thin = Pointee<Metadata = ()>;
pub const fn metadata<T: ?Sized>(ptr: *const T) -> <T as Pointee>::Metadata {}
pub const fn from_raw_parts<T: ?Sized>(*const (), <T as Pointee>::Metadata) -> *const T {}
pub const fn from_raw_parts_mut<T: ?Sized>(*mut (),<T as Pointee>::Metadata) -> *mut T {}
impl<T: ?Sized> NonNull<T> {
pub const fn from_raw_parts(NonNull<()>, <T as Pointee>::Metadata) -> NonNull<T> {}
/// Convenience for `(ptr.cast(), metadata(ptr))`
pub const fn to_raw_parts(self) -> (NonNull<()>, <T as Pointee>::Metadata) {}
}
impl<T: ?Sized> *const T {
pub const fn to_raw_parts(self) -> (*const (), <T as Pointee>::Metadata) {}
}
impl<T: ?Sized> *mut T {
pub const fn to_raw_parts(self) -> (*mut (), <T as Pointee>::Metadata) {}
}
/// `<dyn SomeTrait as Pointee>::Metadata == DynMetadata<dyn SomeTrait>`
pub struct DynMetadata<Dyn: ?Sized> {
// Private pointer to vtable
}
impl<Dyn: ?Sized> DynMetadata<Dyn> {
pub fn size_of(self) -> usize {}
pub fn align_of(self) -> usize {}
pub fn layout(self) -> crate::alloc::Layout {}
}
unsafe impl<Dyn: ?Sized> Send for DynMetadata<Dyn> {}
unsafe impl<Dyn: ?Sized> Sync for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Debug for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Unpin for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Copy for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Clone for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Eq for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> PartialEq for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Ord for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> PartialOrd for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> Hash for DynMetadata<Dyn> {}
```
API differences from the RFC, in areas noted as unresolved questions in the RFC:
* Module-level functions instead of associated `from_raw_parts` functions on `*const T` and `*mut T`, following the precedent of `null`, `slice_from_raw_parts`, etc.
* Added `to_raw_parts`
Add a `Result::into_ok_or_err` method to extract a `T` from `Result<T, T>`
When updating code to handle the semi-recent deprecation of `compare_and_swap` in favor of `compare_exchange`, which returns `Result<T, T>`, I wanted this. I've also wanted it with code using `slice::binary_search` before.
The name (and perhaps the documentation) is the hardest part here, but this name seems consistent with the other Result methods, and equivalently memorable.
Document that `assert!` format arguments are evaluated lazily
It can be useful to do some computation in `assert!` format arguments, in order to get better error messages. For example:
```rust
assert!(
some_condition,
"The state is invalid. Details: {}",
expensive_call_to_get_debugging_info(),
);
```
It seems like `assert!` only evaluates the format arguments if the assertion fails, which is useful but doesn't appear to be documented anywhere. This PR documents the behavior and adds some tests.
To digit simplification
I found out the other day that all the ascii digits have the first four bits as one would hope them to. (Eg. char `2` ends `0b0010`). There are two bits to indicate it's in the digit range ( `0b0011_0000`). If it is a true digit then all the higher bits aside from these two will be 0 (as ascii is the lowest part of the unicode u32 spectrum). So XORing with `0b11_0000` should mean we either get the number 0-9 or alternativly we get a larger number in the u32 space. If we get something that's not 0-9 then it will be discarded as it will be greater than the radix.
The code seems so fast though that there's quite a lot of noise in the benchmarks so it's not that easy to prove conclusively that it's faster as well as less instructions.
The non-fast path I was toying with as well wondering if we could do this as then we'd only have one return and less instructions still:
```
match self {
'a'..='z' => self as u32 - 'a' as u32 + 10,
'A'..='Z' => self as u32 - 'A' as u32 + 10,
_ => { radix = 10; self as u32 ^ ASCII_DIGIT_MASK},
}
```
Here's the [godbolt](https://godbolt.org/z/883c9n).
( H/T to ``@byteshadow`` for pointing out xor was what I needed)
It can be useful to do some computation in `assert!` format arguments, in order to get better error messages. For example:
```rust
assert!(
some_condition,
"The state is invalid. Details: {}",
expensive_call_to_get_debugging_info(),
);
```
It seems like `assert!` only evaluates the format arguments if the assertion fails, which is useful but doesn't appear to be documented anywhere. This PR documents the behavior and adds some tests.
The former `chain`+`chain`+`fold` implementation looked nice from a
functional-programming perspective, but it introduced unnecessary layers
of abstraction on every `flat_map`/`flatten` fold. It's straightforward
to just fold each part in turn, and this makes it look like a simplified
version of the existing `try_fold` implementation.
For the `iter::bench_flat_map*` benchmarks, I get a large improvement in
`bench_flat_map_chain_sum`, from 1,598,473 ns/iter to 499,889 ns/iter,
and the rest are unchanged.
This does not suggest adding such a function to the public API. This is
just for the purpose of avoiding duplicate code. Many array methods
already contained the same kind of code and there are still many array
related methods to come (e.g. `Iterator::{chunks, map_windows, next_n,
...}`) which all basically need this functionality. Writing custom
`unsafe` code for each of those seems not like a good idea.
The `may_have_side_effect` is an implementation detail of `TrustedRandomAccess`
trait. It describes if obtaining an iterator element may have side effects. It
is currently implemented as an associated function.
Turn `may_have_side_effect` into an associated constant. This makes the
value immediately available to the optimizer.
The use of module-level functions instead of associated functions
on `<*const T>` or `<*mut T>` follows the precedent of
`ptr::slice_from_raw_parts` and `ptr::slice_from_raw_parts_mut`.
