Use more explicit and reliable ptr select in sort impls
Using `if ...` with the intent to avoid branches can be surprising to readers and carries the risk of turning into jumps/branches generated by some future compiler version, breaking crucial optimizations.
This commit replaces their usage with the explicit and IR annotated `bool::select_unpredictable`.
`transmute` should also assume non-null pointers
Previously it only did integer-ABI things, but this way it does data pointers too. That gives more information in general to the backend, and allows slightly simplifying one of the helpers in slice iterators.
Previously it only did integer-ABI things, but this way it does data pointers too. That gives more information in general to the backend, and allows slightly simplifying one of the helpers in slice iterators.
Using if ... with the intent to avoid branches can be surprising to readers and
carries the risk of turning into jumps/branches generated by some future
compiler version, breaking crucial optimizations.
This commit replaces their usage with the explicit and IR annotated
`bool::select_unpredictable`.
optimize slice::ptr_rotate for small rotates
r? `@scottmcm`
This swaps the positions and numberings of algorithms 1 and 2 in `slice::ptr_rotate`, and pulls the entire outer loop into algorithm 3 since it was redundant for the first two. Effectively, `ptr_rotate` now always does the `memcpy`+`memmove`+`memcpy` sequence if the shifts fit into the stack buffer.
With this change, an `IndexMap`-style `move_index` function is optimized correctly.
Assembly comparisons:
- `move_index`, before: https://godbolt.org/z/Kr616KnYM
- `move_index`, after: https://godbolt.org/z/1aoov6j8h
- the code from `#89714`, before: https://godbolt.org/z/Y4zaPxEG6
- the code from `#89714`, after: https://godbolt.org/z/1dPx83axc
related to #89714
some relevant discussion in https://internals.rust-lang.org/t/idea-shift-move-to-efficiently-move-elements-in-a-vec/22184
Behavior tests pass locally. I can't get any consistent microbenchmark results on my machine, but the assembly diffs look promising.
* Renames the methods:
* `get_many_mut` -> `get_disjoint_mut`
* `get_many_unchecked_mut` -> `get_disjoint_unchecked_mut`
* Does not rename the feature flag: `get_many_mut`
* Marks the feature as stable
* Renames some helper stuff:
* `GetManyMutError` -> `GetDisjointMutError`
* `GetManyMutIndex` -> `GetDisjointMutIndex`
* `get_many_mut_helpers` -> `get_disjoint_mut_helpers`
* `get_many_check_valid` -> `get_disjoint_check_valid`
This only touches slice methods.
HashMap's methods and feature gates are not renamed here
(nor are they stabilized).
Improve `select_nth_unstable` documentation clarity
* Instead uses `before` and `after` variable names in the example
where `greater` and `lesser` are flipped.
* Uses `<=` and `>=` instead of "less than or equal to" and "greater
than or equal to" to make the docs more concise.
* General attempt to remove unnecessary words and be more precise. For
example it seems slightly wrong to say "its final sorted position",
since this implies there is only one sorted position for this element.
Improve prose around `as_slice` example of IterMut
I've removed the cryptic message about not being able to call `&mut self` methods while retaining a shared borrow of the iterator, such as `as_slice` produces. This is just normal borrowing rules and does not seem especially relevant here. I can whip up a replacement if someone thinks it has value.
* Instead uses `before` and `after` variable names in the example
where `greater` and `lesser` are flipped.
* Uses `<=` and `>=` instead of "less than or equal to" and "greater
than or equal to" to make the docs more concise.
* General attempt to remove unnecessary words and be more precise. For
example it seems slightly wrong to say "its final sorted position",
since this implies there is only one sorted position for this element.
I've removed the cryptic message about not being able to call `&mut self` methods while retaining a shared borrow of the iterator, such as `as_slice` produces. This is just normal borrowing rules and does not seem especially relevant here. I can whip up a replacement if someone thinks it has value.
