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Use `usize::repeat_u8` instead of implementing `repeat_byte` in `memchr.rs`
It's simpler that way and the tricks don't actually make a difference: https://godbolt.org/z/zrvYY1dGx
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also add is_empty to const raw slices
We have this on mutable raw slices but not const raw slices, which makes little sense.
Cc https://github.com/rust-lang/rust/issues/71146
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remove the memcpy-on-equal-ptrs assumption
One of the libc we support, musl, [defines `memcpy` with `restrict` pointers](https://git.musl-libc.org/cgit/musl/tree/src/string/memcpy.c#n5). This in fact matches the definition in the C standard. Calling that `memcpy` with overlapping pointers is clearly UB, who knows what the compiler did when optimizing this `memcpy` -- it certainly assumed source and destination to be disjoint.
Lucky enough, it does not seem like we actually need this assumption that `memcpy(p, p, n)` is always allowed. clang and GCC need it since they use `memcpy` to compile C assignments, but [we use memmove for similar code](https://godbolt.org/z/bcW85WYcM). There are no known cases where LLVM introduces calls to memcpy on equal pointers itself. (And if there were, that would be a soundness bug in rustc due to the musl issue mentioned above.)
This does mean we must make sure to never call the LLVM `memcpy` builtin on equal ranges even though the LangRef says that is allowed. Currently that is the case so we just need to make sure it remains the case. :) Cc `@rust-lang/opsem` `@rust-lang/wg-llvm`
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add track_caller for arith ops
Fixes #114814
`#[track_caller]` is works, r? `@scottmcm`
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Expand in-place iteration specialization to Flatten, FlatMap and ArrayChunks
This enables the following cases to collect in-place:
```rust
let v = vec![[0u8; 4]; 1024]
let v: Vec<_> = v.into_iter().flatten().collect();
let v: Vec<Option<NonZeroUsize>> = vec![NonZeroUsize::new(0); 1024];
let v: Vec<_> = v.into_iter().flatten().collect();
let v = vec![u8; 4096];
let v: Vec<_> = v.into_iter().array_chunks::<4>().collect();
```
Especially the nicheful-option-flattening should be useful in real code.
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Fix comments for unsigned non-zero `checked_add`, `saturating_add`
While looking at #118313, I happened to notice that two of the expanded comments appear to be slightly inaccurate.
For these two methods, `other` is an ordinary unsigned integer, so it can be zero.
Since the sum of non-zero and zero is always non-zero, the safety argument holds even when `other` is zero.
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Update mod comment
The comment of `ASCII_CASE_MASK` on line 477 is `If 6th bit is set ascii is lower case.` but the original comment of `*self ^ ((self.is_ascii_lowercase() as u8) * ASCII_CASE_MASK)` was `Toggle the fifth bit if this is a lowercase letter`
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optimize str::iter::Chars::advance_by
```
OLD:
str::iter::chars_advance_by_0001 0.00ns/iter +/- 0.00ns
str::iter::chars_advance_by_0010 13.00ns/iter +/- 1.00ns
str::iter::chars_advance_by_1000 1.20µs/iter +/- 15.00ns
NEW:
str::iter::chars_advance_by_0001 0.00ns/iter +/- 0.00ns
str::iter::chars_advance_by_0010 6.00ns/iter +/- 0.00ns
str::iter::chars_advance_by_1000 75.00ns/iter +/- 1.00ns
```
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For these two methods, `other` is an ordinary unsigned integer, so it can be zero.
Since the sum of non-zero and zero is always non-zero, the safety argument
holds even when `other` is zero.
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this avoids part of the char decoding work by not looking at utf8 continuation bytes
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panic_immediate_abort)
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r=notriddle
rustdoc: Remove space from fake-variadic fn ptr impls
before: `for fn (T₁, T₂, …, Tₙ) -> Ret`
after: `for fn(T₁, T₂, …, Tₙ) -> Ret`
I don't think we usually have spaces there, so it looks weird.
cc `@notriddle` since you added the space in https://github.com/rust-lang/rust/pull/98180 (or rather, added the feature with a space included).
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r=thomcc
Improve some comments for non-zero ops
This makes them a bit more explicit/correct.
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before: `for fn (T₁, T₂, …, Tₙ) -> Ret`
after: `for fn(T₁, T₂, …, Tₙ) -> Ret`
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Add `debug_assert_nounwind` and convert `assert_unsafe_precondition`
`assert_unsafe_precondition` checks non-CTFE-evaluable conditions in runtime and performs no-op in compile time, while many of its current usage can be checked during const eval.
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Stabilize `ptr::addr_eq`
This PR stabilize the `ptr_addr_eq` library feature, representing:
```rust
// core::ptr
pub fn addr_eq<T: ?Sized, U: ?Sized>(p: *const T, q: *const U) -> bool;
```
FCP has already started [on the tracking issue](https://github.com/rust-lang/rust/issues/116324#issuecomment-1813008697) and is waiting on the final period comment.
Note: stabilizing this feature is somewhat of requirement for a new T-lang lint, cf. https://github.com/rust-lang/rust/pull/117758#issuecomment-1813183686.
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Fixes error count display is different when there's only one error left
Supersedes #114759
### What did I do?
I did the small change in `rustc_errors` by hand. Then I did the other changes in `/compiler` by hand, those were just find replace on `*.rs` in the workspace. The changes in run-make are find replace for `run-make` in the workspace.
All other changes are blessed using `x test TEST --bless`. I blessed the tests that were blessed in #114759.
### how to review this nightmare
ping bors with an `r+`. You should check that my logic is sound and maybe quickly scroll through the diff, but fully verifying it seems fairly hard to impossible. I did my best to do this correctly.
Thank you `@adrianEffe` for bringing this up and your initial implementation.
cc `@flip1995,` you said you want to do a subtree sync asap
cc `@RalfJung` maybe you want to do a quick subtree sync afterwards as well for Miri
r? `@WaffleLapkin`
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Co-authored-by: Adrian <adrian.iosdev@gmail.com>
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memcpy assumptions: update GCC link
GCC now has this documented on an official website, not just in the bugtracker.
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Indicate that multiplication in Layout::array cannot overflow
Since https://github.com/rust-lang/rust/pull/113113, we have added a check that skips calling into the allocator at all if `capacity == 0`. The global, default allocator will not actually try to allocate though; it returns a dangling pointer explicitly. However, these two checks are not merged/deduplicated by LLVM and so we're comparing to zero twice whenever vectors are allocated/grown. Probably cheap, but also potentially expensive in code size and seems like an unfortunate miss.
This removes that extra check by telling LLVM that the multiplication as part of Layout::array can't overflow, turning the original non-zero value into a zero value afterwards. In my checks locally this successfully drops the duplicate comparisons.
See https://rust.godbolt.org/z/b6nPP9dcK for a code example.
```rust
pub fn foo(elements: usize) -> Vec<u32> {
Vec::with_capacity(elements)
}
```
r? `@scottmcm` since you touched this in a32305a80fd1409b054e97836321bd0621b142fd - curious if you have thoughts on doing this / can confirm my model of this being correct.
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Rollup of 6 pull requests
Successful merges:
- #116807 (Improve rewind documentation)
- #117656 (Update windows-bindgen and define `INVALID_HANDLE_VALUE` ourselves)
- #117940 (chore: remove unnecessary drop)
- #118028 (Document behavior of `<dyn Any as Any>::type_id()`)
- #118060 (Use an absolute path to the NUL device)
- #118224 (Sort unstable items last in rustdoc, instead of first)
r? `@ghost`
`@rustbot` modify labels: rollup
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Document behavior of `<dyn Any as Any>::type_id()`
See also #57893
`@rustbot` label A-docs T-libs
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